NICOTINE RECEPTOR AGONISTS IN STEM CELL AND PROGENITOR CELL RECRUITMENT

Abstract: The present invention features methods for recruitment of bone marrow-derived stem cells (e.g., endothelial cell precursers, hematopoietic stem cells) by administration of nicotine or other nicotine receptor agonist. The methods of the invention can be used in, for example, treatment of conditions amenable to treatment by recruitment of bone marrow-derived stem cells (e.g., neutropenia). The figure is a graph showing the capillary density (capillaries/myocyte) and the percentage of new vessels incorporating endothelial progenitor cells for saline control animals and nicotine treated animals.

Description: NICOTINE RECEPTOR AGONISTS IN STEM CELL AND PROGENITOR CELL RECRUITMENT FIELD OF THE INVENTION The invention relates generally to the field of mobilization and recruitment of stem cells and progenitor cells. BACKGROUND OF THE INVENTION Recruitment of stem cells and/or progenitor cells are important in a variety of applications. Vasculogenesis, which involves the growth of vessels derived from endothelial progenitor cells, is an example of such a process. Vasculogenesis, as well as angiogenesis, the process by which new blood vessels are formed from extant capillaries, and the factors that regulate these processes, are important in embryonic development, inflammation, and wound healing, and also contribute to pathologic conditions such as tumor growth, diabetic retinopathy, rheumatoid arthritis, and chronic inflammatory diseases (see, e.g., USPN 5,318,957; Yancopoulos et al. (1998) Cell 93:661-4; Folkman et al. (1996) Cell 87;1153-5; and Hanahan et al. (1996) Cell 86:353-64). Both angiogenesis and vasculogenesis involve the proliferation of endothelial cells. Endothelial cells line the walls of blood vessels; capillaries are comprised almost entirely of endothelial cells. The angiogenic process involves not only increased endothelial cell proliferation, but also comprises a cascade of additional events, including protease secretion by endothelial cells, degradation of the basement membrane, migration through the surrounding matrix, proliferation, alignment, differentiation into tube-like structures, and synthesis of a new basement membrane. Vasculogenesis involves recruitment and differentiation of mesenchymal cells into angioblasts, which then differentiate into endothelial cells which then form de novo vessels (see, e.g. , Folkman et al. (1996) Cell 87:1153-5). Several angiogenic and/or vasculogenic agents with different properties and mechanisms of action are well known in the art. For example, acidic and basic fibroblast growth factor (FGF), transforming growth factor alpha (TGF-α) and beta (TGF-β), tumor necrosis factor (TNF), platelet-derived growth factor (PDGF), vascular endothelial cell growth factor (VEGF), and angiogenin are potent and well-characterized angiogenesis-promoting agents. In addition, both nitric oxide and prostaglandin (a prostacyclin agonist) have been shown to be mediators of various angiogenic growth factors, such as VEGF and bFGF. However, the therapeutic applicability of some of these compounds, especially as systemic agents, is limited by their potent pleiotropic effects on various cell types. Angiogenesis and vasculogenesis have been the focus of intense interest since these processes can be exploited to therapeutic advantage Stimulation of angiogenesis and/or vasculogenesis can aid m the healing of wounds, the vasculaπzing of skin grafts, and the enhancement of collateral circulation where there has been vascular occlusion or stenosis (e g , to develop a "biobypass" around an obstruction due to coronary, carotid, or peripheral arterial occlusion disease) In addition, identification of agents that can stimulate recruitment of stem cells and/or progenitor cells could be useful in the treatment of other conditions associated with cellular injury and/or depletion of cells (e g , acquired or genetic immune deficiencies) There is an intense interest in factors such agents that are well-tolerated by the subject, but that are of high potency in effecting stimulation of stem cell and/or progentior cell recruitment Related Art Villablanca ((1998) "Nicotine stimulates DNA synthesis and proliferation in vascular endothelial cells in vitro," J Appl Physiol 84 2089-98) studied the effects of nicotine on endothelial DNA synthesis, DNA repair, proliferation, and cytoxicity using cultures of bovine pulmonary artery endothelial cells in vitro The reference Carty et al ((1996) "Nicotine and cotinine stimulate secretion of basic fibroblast growth factor and affect expression of matrix metalloproteinases in cultured human smooth muscle cells," J Vase Surg 24 927-35) demonstrate that mcotme stimulates vascular smooth muscle cells to produce fibroblast growth factor, and also upregulates the expression of several matrix metalloproteinases The investigators propose that these data demonstrate mechanisms by which smoking may cause atherosclerosis and aneurysms The reference by Belluardo et al ((1998) Acute intermittent mcotme treatment produces regional increases of basic fibroblast growth factor messenger RNA and protem in the tel-and diencephalon of the rat," Neuroscience 83 723-40) reported that nicotine stimulates the expression of fibroblast growth factor-2 in rat brain, which the investigators propose may explain the neuroprotective effect of nicotine in the rat brain Moffett et al (("Increased tyrosine phosphorylation and novel c«-actin element mediate activation of the fibroblast growth factor-2 (FGF-2) gene by nicotinic acetylcholine receptor New mechanism for trans-synaptic regulation of cellular development and plasticity, " Mol Brain Res 55 293-305) report that nicotine stimulates the expression of fibroblast growth factor-2 in neural crest-deπved adrenal pheochromatocytes utilizing a unique transcnptional pathway that requires tyrosine phosphorylation The authors propose that these findings suggest that activation of nicotine receptors may be involved in neural development Cucina et al ((1999) "Nicotine regulates basic fibroblastic growth factor and transforming growth factor βj production in endothelial cells," Biochem Biophys Res Commun 257 302-12) report that nicotine mcreases the release of bFGF, decreases the release of TGFβ 1 from endothelial cells, and increases endothelial mitogenesis The authors conclude that these effects may have a key role in the development and progression of atherosclerosis Volm et al (1999) "Angiogenesis and cigarette smoking in squamous cell lung carcinomas an immunohistochemical study of 28 cases " Anticancer Res 19(1 A) 333-6 reports that angiogenesis in lung tumors is linked to a patient's smoking habits Macklin et al (1998) "Human vascular endothelial cells express functional nicotinic acetylchobne receptors," J Pharmacol Exper Therap 287 435-9 reports that endothehal cells express both functional nicotinic (neuronal type) and muscaπnic acetylcholine receptors U S Pat Nos 5,318,957, 5,866,561, and 5,869,037 descπbe use of various compounds (haptoglobin and estrogen) and methods (adenoviral-mediated gene therapy of adipocytes) to effect angiogenesis For recent reviews in the field of angiogenesis and vasculogenesis, see, e g , Yancopoulos et al (1998) Cell 93 661-4, Folkman et al (1996) Cell 87,1153-5, and Hanahan et al (1996) Cell 86 353-64 SUMMARY OF THE INVENTION The present invention features methods for recruitment of bone marrow-derived stem cells (e g , endothelial cell precursors, hematopoietic stem cells) by administration of mcotme or other nicotine receptor agonist The methods of the invention can be used m, for example, treatment of conditions amenable to treatment by recruitment of bone marrow-derived stem cells (e g , neutropema) One object of the present invention to provide a method of recruiting endothelial progemtor cells to enhance angiogenesis Another object of the present mvention is to provide a method of treating and preventing diseases and ailments involving tissue damage (e g , to facilitate cellular repair), such as in myocardial and cerebral infarctions, mesentenc or limb ischemia, wounds, and vascular occlusion or stenosis Another object of this invention is to provide a method of accelerating wound healing, vasculaπzation and incorporation of skin grafts, musculocutaneous flaps or other surgically transplanted tissues, or to enhance the healing of a surgically created anastomosis Another object of the invention is provide a method of treating conditions or diseases associated with depletion of cells that develop from bone marrow-derived stem cells (e.g. , immune cells, e.g., neutrophils, eosinophils, T cells, B cells, macrophages, natural killer cells, and the like). These and other objects, advantages, and features of the invention will become apparent to those persons skilled in the art upon reading the details of the methods of the invention and compositions used therein as more fully described below. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 provides the chemical structures for the nicotine receptor agonists nicotine, epibatidine, and ABT-154, and for the nicotine receptor antagonists hexamethonium and mecamylamine. Fig. 2 is a graph illustrating the effect of oral nicotine upon fibro vascular growth in an animal model. Fig. 3 is a graph illustrating the effect of locally administered nicotine upon fibrovascular growth in an animal model using the disc angiogenesis system Fig. 4 is a graph illustrating comparing the relative angiogenic potencies of the angiogenic factors Del-1 and bFGF with locally or systemically administered nicotine. Fig. 5 is a graph illustrating the relative capillary densities in non-ischemic (control; "non-ischemic") ischemic limbs in the hind limb ischemia model ("ischemic"). Fig. 6 is a graph illustrating the effect of intramuscularly administered nicotine upon capillary density in an animal model of ischemia Fig. 7 is a graph illustrating the effect of intramuscularly administered nicotine upon capillary density in an untreated, non-ischemic limb of an animal of Fig. 6. Fig. 8 is a schematic illustrating an experimental model of mouse parabiosis used in assays for tracking migration of circulating cells such as progenitor cells. Fig. 9 is a graph showing the capillary density (capillaries/myocyte) and the percentage of new vessels incorporating endothelial progenitor cells for saline control animals and nicotine treated animals. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Before the present invention is described, it is to be understood that this invention is not limited to particular methodologies (e.g., modes of administration) or specific compositions described, as such may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting, since the scope of the present invention will be limited only by the appended claims. Unless denned otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, the preferred methods and materials are now described. All publications mentioned herein are incorporated herein by reference to disclose and describe the methods and/or materials in connection with which the publications are cited. It must be noted that as used herein and in the appended claims, the singular forms "a", "and", and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "a nicotine receptor agonist" includes a plurality of such agonists and -reference to "the nicotine receptor" includes reference to one or more receptors and equivalents thereof known to those skilled in the art, and so forth. The publications discussed herein are provided solely for their disclosure prior to the filing date of the present application. Nothing herein is to be construed as an admission that the present invention is not entitled to antedate such publication by virtue of prior invention. Further, the dates of publication provided may be different from the actual publication dates which may need to be independently confirmed. Definitions The term "nicotine receptor agonist" is meant to encompass nicotine (which is understood to include nicotine derivatives and like compounds) and other compounds that substantially specifically bind a nicotine receptor and provide a pharmacological effect, e.g., recruitment of stem cells to a treatment site, as in induction of angiogenesis. "Nicotine receptor agonists" encompass naturally-occurring compounds (including, but not limited to, small molecules, polypeptides, peptides, etc., particularly naturally-occurring plant alkaloids, and the like), endogenous ligands (e.g. , purified from a natural source, recombinantly produced, or synthetic, and further including derivatives and variants of such endogenous ligands), and synthetically produced compounds (e.g. , small molecules, peptides, etc.). The term "nicotine" is intended to mean the naturally occurring alkaloid known as nicotine, having the chemical name S-3-(l-methyl-2-pyrrolidinyl)pyridine, which may be isolated and purified from nature or synthetically produced in any manner. This tennis also intended to encompass the commonly occurring salts containing pharmacologically acceptable anions, such as hydro chloride, hydrobromide, hydroiodide, nitrate, sulfate or bisulfate, phosphate or acid phosphate, acetate, lactate, citrate or acid citrate, tartrate or bitartrate, succinate, maleate, fumarate, gluconate, saccharate, benzoate, methanesulfonate, ethanesulfonate, benzenesulfonate, j-toluene sulfonate, camphorate and pamoate salts. Nicotine is a colorless to pale yellow, strongly alkaline, oily, volatile, hygroscopic liquid having a molecular weight of 162.23 and the formula shown in Fig. 1. Unless specifically indicated otherwise, the term "nicotine" further includes any pharmacologically acceptable derivative or metabolite of nicotine which exhibits phaπnacotherapeutic properties similar to nicotine. Such derivatives, metabolites, and derivatives of metabolites are known in the art, and include, but are not necessarily limited to, cotinine, norcotinine, nornicotine, nicotine N-oxide, cotinine N-oxide, 3-hydroxycotinine and 5- hydroxycotinine or pharmaceutically acceptable salts thereof. A number of useful derivatives of nicotine are disclosed within the Physician's Desk Reference (most recent edition) as well as Harrison's Principles of Internal Medicine. The term "nicotine receptor" as in "nicotine receptor agonist" is meant to encompass the classic pentameric protein of the nicotine receptor (formed by subunits which are symmetrically arranged around a central ion channel) as well as any protein comprising a nicotine binding site that stimulates recruitment of stem cells or progenitor cells (e.g. , as in angiogenesis) upon binding to nicotine or other nicotine receptor agonist (e.g., the muscarinic acetylcholine receptor). Use of the term "nicotine receptor" in the phrase "nicotine receptor agonist" is not meant to limit the present invention to a theorized mechanism through which nicotine or other nicotine receptor agonists stimulate stem/progenitor cell recruitment (e.g., by binding a nicotine receptor), but rather is a means of describing the types of compounds contemplated by the invention that can be used to facilitate stimulation of stem/progenitor cell recruitment. The terms "treatment", "treating" and the like are used herein to generally mean obtaining a desired pharmacologic and/or physiologic effect, e.g., stimulation of angiogenesis and/or vasculogenesis. The effect may be prophylactic in terms of completely or partially preventing a disease or symptom thereof and/or may be therapeutic in terms of a partial or complete cure for a disease and/or adverse effect attributable to the disease. "Treatment" as used herein covers any treatment of a disease in a mammal, particularly a human, and includes: (a) preventing a disease or condition (e.g. , preventing the loss of a skin graft or a re-attached limb due to inadequate vascularization) from occurring in a subject who may be predisposed to the disease but has not yet been diagnosed as having it; (b) inhibiting the disease, e.g. , arresting its development; or (c) relieving the disease (e.g., enhancing the development of a "bio-bypass" around an obstructed vessel to improve blood flow to an organ). For example, in the context of the present invention, stimulation of angiogenesis and/or vasculogenesis is employed for subject having a disease or condition amenable to treatment by increasing vascularity and increasing blood flow. By "therapeutically effective amount of a nicotine receptor agonist" is meant an amount of a nicotine receptor agonist effective to facilitate a desired therapeutic effect, e.g., a desired level of angiogenic and/or vasculogenic stimulation. The precise desired therapeutic effect will vary according to the condition to be treated. By "isolated" is meant that the compound is separated from all or some of the components that accompany it in nature. By "substantially pure nicotine receptor agonist" is meant that the nicotine receptor agonist has been separated from components that accompany it in nature. Typically, a nicotine receptor agonist is substantially pure when it is at least 50% to 60%, by weight, free from naturally-occurring organic molecules with which it is naturally associated. Generally, the preparation is at least 75%, more preferably at least 90%, and most preferably at least 99%, by weight, nicotine receptor agonist. A substantially pure nicotine receptor agonist can be obtained, for example, by extraction from a natural source (e.g., tobacco), by chemically synthesizing the compound, or by a combination of purification and chemical modification. A substantially pure nicotine receptor agonist can also be obtained by, for example, enriching a sample having nicotine receptor agonist activity for a factor or factors that provide such activity, e.g., by obtaining a fraction having increased nicotine receptor agonist activity. Purity can be measured by any appropriate method, e.g., chromatography, mass spectroscopy, HPLC analysis, etc. For example, a nicotine receptor agonist is substantially free of naturally associated components when it is separated from those contaminants which accompany it in its natural state. Thus, a nicotine receptor agonist which is chemically synthesized or produced in a cellular system different from the cell from which it naturally originates will be substantially free from its naturally associated components The term "stem cell" is used herein to refer to a mammalian cell that has the ability both to self-renew, and to generate differentiated progeny (see Morrison et αl. (1997) Cell 88:287-298). Generally, stem cells also have one or more of the following properties: an ability to undergo asynchronous, or symmetric replication, that is where the two daughter cells after division can have different phenotypes; extensive self-renewal capacity; capacity for existence in a mitotically quiescent form; and clonal regeneration of all the tissue in which they exist, for example the ability of hematopoietic stem cells to reconstitute all hematopoietic lineages. "Progenitor cells" differ from stem cells in that they typically do not have the extensive self-renewal capacity, and often can only regenerate a subset of the lineages in the tissue from which they derive, for example only lymphoid, or erythroid lineages in a hematopoietic setting. The term "stem/progenitor cell" used throughout is used for simplicity, is not meant to be limiting, and is meant to encompass stem cells, progemtor cells, and both stem and progenitor cells Stem cells may be characterized by both the presence of markers associated with specific epitopes identified by antibodies and the absence of certain markers as identified by the lack of binding of specific antibodies Stem cells may also be identified by functional assays both in vitro and in vivo, particularly assays relating to the ability of stem cells to give nse to multiple differentiated progeny "Stem cells" is meant to mclude, but is not necessarily limited to, hematopoietic stem cells and progenitor cells deπved therefrom (U S Pat No 5,061,620), neural crest stem cells (see Morrison et al (1999) Cell 96 737-749), embryonic stem cells, mesenchymal stem, mesodermal stem cells, etc Other hematopoietic "progenitor" cells of interest include cells dedicated to lymphoid lineages, e g immature T cell and B cell populations The methods of the present invention are useful in expanding selected populations of these cells "Mesenchymal progenitor cells" is meant to mclude, but is not necessarily limited to, endothehal progemtor cells and other cells dedicated to development mto cells of mesenchymal lineages, e g , connective tissue, cartilage, chondrocytes, bone (osteoblasts), fat cells (adipocytes), and the outer layers of blood vessels Overview of the Invention The present invention is based on the surprising discovery that nicotine mduces recruitment of endothehal progemtor cells to blood vessels and provides for induction of angiogenesis The inventors' initial inquiries were based on the clinical observation that smokers often have inadequate collateral development after coronary or peripheral arterial obstruction, i e , the inventors at first suspected that mcotme might play a role m inhibition of angiogenesis Accordingly, the inventors began by testmg the local effects of mcotme in the disc angiogenesis system (DAS) Unexpectedly, the inventors discovered that nicotine was as or more potent as an angiogenic agent than any growth factor tested m this system, including Dell (Penta et al (1999) JBiol Chem 274(16) 11101-9) and bFGF Additional studies revealed that the potent angiogenic effects of nicotine were mediated m part by products of the cyclooxygenase cascade, and in part by the NO synthase pathway Studies usmg the disc angiogenesis system suggested that mcotme may be useful for therapeutic angiogenesis However, because angiogenesis is such a complex process, to demonstrate proof of principle that an agent has utility for therapeutic angiogenesis, the agent was tested in an animal model of disease that requires angiogenesis for its treatment Accordingly, studies were performed in an animal model of arterial occlusion (the muπne hind limb ischemia model) Usmg this model of arterial occlusion, the inventors obtained compelling evidence that nicotine induces therapeutic angiogenesis. In addition, the inventors discovered that induction of angiogenesis by nicotine involves mobilization and recruitment of endothelial progenitor cells to the site of injury. This discovery suggests that nicotine can induce mobilization and recruitment of stem cells and progenitor cells, and thus can be used to treat conditions in which a cell population has been depleted due to, for example, infection, physical damage, autoimmunity, etc. Thus, the inventors have discovered that nicotine, a component of tobacco smoke, provides the basis of a new therapeutic approach to enhance angiogenesis in the treatment of coronary, peripheral, or other occlusive arterial diseases; for the enhancement of wound healing and the improved vascularization of surgically transplanted tissues or organs(e.g., skin grafts or reattached limbs); and for the recruitment and mobilization of stem cells and progenitor cells to provide for repopulation of a depleted or damaged mature cell population. In view of its similar or relatively enhanced potency relative to other, conventional angiogenic agents, nicotine has significant advantage over current candidates as the basis of therapeutic angiogenesis. Moreover, the pharmacology and pharmacokinetics of nicotine have already been well-characterized in the context of smoking (e.g., in an effort to facilitate smoking cessation) and methods for slow release and local delivery have already been intensively investigated. Processes for the manufacture of nicotine and nicotine agonists are also well characterized. Furthermore, these small molecules are more easily synthesized and stored than complex angiogenic peptides. Accordingly, the invention encompasses methods and compositions for mobilization and recruitment of stem cells and/or progenitor cells, by administration of a nicotine receptor agonist. Nicotine and Other Nicotine Receptor Agonists The methods of the invention are accomplished by administration of a nicotine receptor agonist, particularly nicotine, nicotine metabolite, or nicotine derivative. Methods for production of nicotine derivatives and analogues are well known in the art. See, e.g., U.S. Pat. No. 4,590,278; 4,321,387; 4,452,984; 4,442,292; and 4,332,945. Additional nicotine receptor agonists of interest include, but are not necessarily limited to, naturally occurring plant alkaloids (e.g., lobeline, lobeline derivatives, and the like), which plant- derived compounds can be provided in a herbal preparation (e.g. , in the form of dried tobacco leaves, in a poultice, in a botanical preparation, etc.), in isolated form (e.g. , separated or partially separated from the materials that naturally accompany it), or in a substantially purified form. Other nicotine receptor agonists include choline esterase inhibitors (e g , that increase local concentration of acetylcholme), deπvatives of epibatidme that specifically bmd the neuronal type of nicotinic receptors (with reduced binding to the muscaπnic receptor) and having reduced deleteπous side- effects (e g , Epidoxidme, ABT-154, ABT-418, ABT-594, Abbott Laboratones (Damaj et al (1998) J Pharmacol Exp Ther 284 1058-65, describing several analogs of epibatidme of equal potency but with high specificity to the neuronal type of nicotinic receptors) Further nicotine receptor agonists of mterest mclude, but are not necessaπly limited to, N-methylcarbamyl and N-methylthi-O- carbamyl esters of choline (e g , tπmethylaminoethanol) (Abood et al (1988) Pharmacol Biochem Behav 30 403-8), acetylchobne (an endogenous bgand for the mcotme receptor), and the like Nicotine receptor agomsts can also be readily identified usmg methods well known m the art For example, the ability of a candidate mcotme receptor agomst can be screened for bmdmg to a mcotme receptor in vitro, and the ability of the candidate agent to recruit stem cells and/or progemtor cells can be assessed in vivo (e g , usmg the disc angiogenesis system (DAS), m the hind hmb ischemia model, etc ) Pharmaceutical Compositions Upon reading the present specification, the ordinarily skilled artisan will appreciate that the pharmaceutical compositions compπsmg a mcotme receptor agomst descnbed herem can be provided m a wide variety of formulations More particularly, the mcotme receptor agomst can be formulated mto pharmaceutical compositions by combmation with appropπate, pharmaceutically acceptable earners or diluents, and may be formulated mto preparations in solid, semi-solid (e g , gel), hquid or gaseous forms, such as tablets, capsules, powders, granules, ointments, solutions, suppositones, injections, inhalants and aerosols Where the mcotme receptor agomst is a naturally- occurring compound, the pharmaceutical composition can also be provided as an herbal preparation (e g , m the form of tobacco leaves, as a poultice of plant matter, m a botamcal preparation, etc ) The mcotme receptor agomst formulation used will vary according to the condition or disease to be treated, the route of administration, the amount of mcotme receptor agomst to be administered, and other vanables that will be readily appreciated by the ordinarily skilled artisan In general, and as discussed m more detail below, administration of nicotine receptor agomsts can be either systemic or local, and can be achieved m vaπous ways, mcludmg, but not necessarily limited to, administration by a route that is parenteral, intravenous, mtra-arteπal, lnter-pencardial, intramuscular, intrapentoneal, transdermal, transcutaneous, subdermal, intradermal, lntrapulmonary, etc In pharmaceutical dosage forms, the nicotine receptor agomst may be administered in the form of their pharmaceutically acceptable salts, or they may also be used alone or in appropriate association, as well as in combination, with other pharmaceutically active compounds. The following methods and excipients are merely exemplary and are in no way limiting. The nicotine receptor agonist can be formulated into preparations for injection by dissolving, suspending or emulsifying them in an aqueous or nonaqueous solvent, such as vegetable or other similar oils, synthetic aliphatic acid glycerides, esters of higher aliphatic acids or propylene glycol; and if desired, with conventional additives such as solubilizers, isotonic agents, suspending agents, emulsifying agents, stabilizers and preservatives. Formulations suitable for topical, transcutaneous, and transdermal administration, e.g. , to aclminister the nicotine receptor agonist directly to a wound, may be similarly prepared through use of appropriate suspending agents, solubibzers, thickening agents, stabilizers, and preservatives. Topical formulations may be also utilized with a means to provide continuous administration of nicotine or other nicotine receptor agonist by, for example, incorporation into slow-release pellets or controlled-release patches. The nicotine receptor agonist can also be formulated in a biocompatible gel, which gel can be applied topically (e.g., to facilitate wound healing) or implanted (e.g., to provide for sustained release of nicotine receptor agonist at an internal treatment site). Suitable gels and methods for formulating a desired compound for dehvery using the gel are well known in the art (see, e.g. , US Pat. Nos. 5,801,033; 5,827,937; 5,700,848; and MATRIGEL™). For oral preparations, the nicotine receptor agonist can be used alone or in combination with appropriate additives to make tablets, powders, granules or capsules, for example, with conventional additives, such as lactose, mannitol, corn starch or potato starch; with binders, such as crystalline cellulose, cellulose derivatives, acacia, corn starch or gelatins; with disintegrators, such as corn starch, potato starch or sodium carboxymethylcellulose; with lubricants, such as talc or magnesium stearate; and if desired, with diluents, buffering agents, moistening agents, preservatives and flavoring agents. The nicotine receptor agonist can be utilized in aerosol formulation to be administered via inhalation. The compounds of the present invention can be formulated into pressurized acceptable propellants such as dichlorodifluoromethane, propane, nitrogen and the like. Furthermore, the nicotine receptor agonist can be made into suppositories by mixing with a variety of bases such as emulsifying bases or water-soluble bases. The compounds of the present invention can be administered rectalfy via a suppository. The suppository can include vehicles such as cocoa butter, carbowaxes and polyethylene glycols, which melt at body temperature, yet are solidified at room temperature. Unit dosage forms for oral or rectal administration such as syrups, elixirs, and suspensions may be provided wherein each dosage unit, for example, teaspoonful, tablespoonful, tablet or suppository, contains a predetermined amount of the composition containing one or more inhibitors. Similarly, unit dosage forms for injection or intravenous administration may comprise the inhibitor(s) in a composition as a solution in sterile water, normal saline or another pharmaceutically acceptable carrier. The term "unit dosage form," as used herein, refers to physically discrete units suitable as unitary dosages for human and/or animal subjects, each unit containing a predetermined quantity of nicotine receptor agonist calculated in an amount sufficient to produce the desired effect in association with a pharmaceutically acceptable diluent, carrier or vehicle. The specifications for the unit dosage forms of the present invention depend on the particular compound employed and the effect to be achieved, and the pharmaco dynamics associated with each compound in the host. The pharmaceutically acceptable excipients, such as vehicles, adjuvants, carriers or diluents, are readily available to the pubbc. Moreover, pharmaceutically acceptable auxibary substances, such as pH adjusting and buffering agents, tonicity adjusting agents, stabilizers, wetting agents and the like, are readily available to the public. In addition to one or more nicotine receptor agonists, the pharmaceutical formulations according to the invention can comprise or be administered in parallel with additional active agents. For example, where the pharmaceutical formulation is to be administered to promote angiogenesis and/or vasculogenesis, the formulation can comprise additional agents to further enhance angiogenesis by enhancing nitric oxide (NO) levels (e.g. , by enhancing activity of NO synthase, by enhancing release of NO, etc.) or prostacyclin levels (e.g. , by enhancing activity prostacyclin synthase, by enhancing release of prostacyclin, etc.) Exemplary NO level-enhancing agents include, but are not necessarily limited to, L-arginine, L-lysine, and peptides enriched with these arnino acids which can serve as substrates for NO; agents that preserve NO activity such as antioxidants (e.g., tocopherol, ascorbic acid, ubiquinone) or antioxidant enzymes (e.g., superoxide dismutase); and agents which can enhance NO synthase activity (e.g. , tetrahydrobiopterin, or precursors for tetrahydrobiopterin (e.g. , sepiapterin)); and the like. Exemplary prostacyclin level-enhancing agents include, but are not bmited to precursors for prostacyclin such as eicosopentanoic acid and docosohexanoic acid; and prostanoids such as prostaglandin El and its analogues; and the like. Alternatively or in addition, the pharmaceutical compositions according to the invention can comprise additional agents for stimulation of stem cell and/or endothehal cells recruitment that act through pathways other than the mcotme receptor (e g , m angiogenesis or vasculogenesis, VEGF, FGF (e g , aFGF, bFGF), Dell, etc ) Particularly where the mcotme receptor agomst is to be debvered for local application, e g , by an intramuscular route, it may be desirable to provide the mcotme receptor agomst in a gel or matrix The gel or matrix can, for example, provide at least the initial substrate upon which, for example, new tissue can form. For example, the gel or matrix can be extruded mto an ischemic region to form a path for new blood vessel formation so as to bypass an obstruction m the area Administration of Nicotine Receptor Agonists for Mobilization/Recruitment of Stem and Progenitor Cells in vivo In order to accompbsh mobilization or recruitment of stem cells and/or progemtor cells, mcotme or other mcotme receptor agomsts can be administered in any suitable manner, preferably with pharmaceutically acceptable earners One skilled m the art will readily appreciate that there are available a vanety of suitable methods of administering mcotme or other mcotme receptor agomst m the context of the present mvention , and, although more than one route can be used to administer a particular compound, a particular route can provide a more immediate, more effective, and/or associated with fewer side effects than another route In general, a mcotme receptor agomst can be administered according to the method of the mvention by, for example, a parenteral, mtravenous, intra-artenal, mter-pencardial, mtramuscular, mtrapeπtoneal, transdermal, transcutaneous, subdermal, intradermal, or mtrapulmonary route In order to avoid the side-effects associated with systemic mcotme, it may be preferable to administer mcotme locally (either alone or with additional active agents, e g , to enhance the activity of the NO synthase or prostacyclin synthase pathways m stimulation of angiogenesis, or to facilitate development of stem or progemtor cells mto the desired mature cells (e g , endothehal cells) Local administration can be accomphshed by, for example, direct mjection (e g , intramuscular mjection) at the desired treatment site, by mtroduction of the mcotme receptor agomst formulation intravenously at a site near a desired treatment site (e g , mto a vessel or capillary that feeds a treatment site), by intra-artenal or lntra-pencardial mtroduction, by mtroduction (e g , by mjection or other method of implantation) of a mcotme receptor agomst formulation m a biocompatible gel or capsule within or adjacent a treatment site, by mjection directly mto muscle or other tissue m which mcreased blood flow and/or mcreased vasculaπty is desired and/or to which recruitment of stem cells or progemtor cells is desired, by rectal mtroduction of the formulation (e g , m the form of a suppository to, for example, facilitate vasculaπzation of a surgically created anastomosis after resection of a piece of the bowel), etc In one particular application of interest, the mcot e receptor agomst formulation is employed m a "biobypass" method, wherem instead of performing a more mvasive procedure, such as a coronary bypass operation, a mcotme receptor agomst formulation is administered to mduce growth of new blood vessels around the blocked region In this embodiment, the mcotme receptor agomst formulation can be administered in the area of and/or proximate to the ischemic tissue to stimulate angiogenesis In some embodiments it may be desirable to debver the mcotme receptor agomst directly to the wall of a vessel One exemplary method of vessel wall admmistration mvolves the use of a drug dehvery catheter, particularly a drug delivery catheter compnsing an inflatable balloon that can facibtate delivery to a vessel wall Thus, m one embodiment the method of the mvention compπses dehvery of a mcotme receptor agomst to a vessel wall by inflating a balloon catheter, wherem the balloon compnses a mcotme receptor agonist formulation covering a substantial portion of the balloon The mcotme receptor agomst formulation is held m place against the vessel wall, promotmg adsorption through the vessel wall In one example, the catheter is a perfusion balloon catheter, which allows perfusion of blood through the catheter while holding the mcotme receptor agomst against the vessel walls for longer adsorption times Examples of catheters suitable for mcotme receptor agomst apphcation mclude drug delivery catheters disclosed m U S Pat Nos 5,558,642, U S Pat No 5,554,119, 5,591,129, and the like In another embodiment of mterest, the mcotme receptor agomst formulation is debvered m the form of a biocompatible gel, which can be implanted (e g , by mjection mto or adjacent a treatment site, by extrusion mto or adjacent a tissue to be treated, etc ) Gel formulations compnsmg a mcot e receptor agomst can be designed to facilitate local release of the mcotme receptor agomst and other active agents for a sustained penod (e g , over a peπod of hours, days, weeks, etc ) The gel can be mjected mto or near a treatment site, e g , usmg a needle or other debvery device In one embodiment, the gel is placed mto or on an instrument which is mserted mto the tissue and then slowly withdrawn to leave a track of gel, resulting m stimulation of stem cell and/or progemtor cell recruitment along the path made by the instrument This latter method of dehvery may be particularly desirable for, for example, directing course of a biobypass In other embodiments it may be desirable to deliver the mcot e receptor agomst formulation topically, e g , for localized dehvery, e g , to facibtate wound healmg Topical application can be accomphshed by use of a biocompatible gel, which may be provided m the form of a patch, or by use of a cream, foam, and the like Several gels, patches, creams, foams, and the like appropnate for apphcation to wounds can be modified for debvery of mcotme receptor agomst formulations according to the mvention (see, e g , U S Pat Nos 5,853,749, 5,844,013, 5,804,213, 5,770.229. and the like). In general, topical administration is accomphshed using a carrier such as a hydrophihc colloid or other material that provides a moist environment. Alternatively, for the purpose of wound healing the nicotine agonist could be supplied, with or without other agents in a gel or cream the could be applied to the wound. An example of such an application would be as a sodium carboxymethylcellulose-based topical gel with a low bioburden containing the nicotine agonist and other active ingredients together with preservatives and stabilizers. In other embodiments, the nicotine receptor agonist formulation is delivered locally or systemically, using a transdermal patch. Several transdermal patches are well known in the art for systemic delivery of nicotine to facibtate smoking cessation, and such patches may be modified to provide for debvery of an amount of nicotine receptor agonist effective to stimulate stem cell and/or progenitor cell recruitment according to the invention (see, e.g., U.S. Pat. Nos. 4,920,989; and 4,943,435, NICOTROL™ patch, and the like). In other methods of debvery, the nicotine receptor agomst can be administered using iontophoretic techniques. Methods and compositions for use in iontophoresis are well known in the art (see, e.g., U.S. Pat. Nos. 5,415,629; 5,899,876; 5,807,306; and the like). The desirable extent of stem/progenitor cell mobilization/recruitment will depend on the particular condition or disease being treated, as well as the stabihty of the patient and possible side- effects. In proper doses and with suitable administration, the present invention provides for a wide range of development of blood vessels (e.g., from little development to essentially full development), as well as for wide ranges of stem cell or progenitor cell mobilization and/or recruitment (e.g. , mobilization of a sufficient number of cells to provide for complete repopulation of a cell type (e.g., to provide for replenishment of immune cells in a host immunocompromised following infection, radiotherapy, chemotherapy, and the like; or to provide for localized recruitment of stem cells or progenitor cells to a site of local injury (e.g., as in wound healing, local ischemia, etc.)). The activity of nicotine receptor agonists in stem/progenitor cell mobmzation/recruitment can be controlled by administration of compounds that interfere with nicotine receptor agonist- mediated recruitment. In this sense, the invention also provides for a means of controlling or inhibiting activity of nicotine receptor agonists by interfering with its role in these processes. This may be accomplished, for example, administration of agents that inhibit the abibty of the nicotine receptor agonist to mediate its effects through the nicotine receptor (e.g. , by inhibiting binding to the nicotine receptor). Exemplary nicotinic receptor antagonists include hexamethonium and mecamylamine (formulas provided in Fig. 1). Alternatively, nicotine receptor agonist-mediated activity can be controlled or inhibited by administration of inhibitors of processes downstream of nicotine receptor signaling. For example, inhibitors of nitric oxide synthase and/or prostacyclin antagonists can be administered to inhibit activity of a nicotine receptor agonist in stimulating angiogenesis. The inhibitor may be administered in the same manner and dosages to mammals such as humans, as described with respect to the nicotine receptor agonist. Where the subject has had exposure, particularly chronic exposure, to a nicotine receptor agonist (e.g., as in a subject who is a smoker and who has had prior, particularly chronic, systemic exposure to nicotine), the nicotine receptor or other nicotine receptor agonist-binding receptor that mediates stimulation of stem/progenitor cell mobilization/recruitment may be present at lower levels than in subjects who have not had previous exposure or chronic exposure to a nicotine receptor agonist. In such subjects, it thus may be desirable to administer an initial course of a nicotine receptor antagonist to stimulate an increase in nicotine binding-receptors. Dose The dose of nicotine or other nicotine receptor agonist administered to a subject, particularly a human, in the context of the present invention should be sufficient to effect a desired therapeutic response (e.g., mobilization/recruitment of stem/progenitor cells in a therapeutically effective number, therapeutic angiogenic response, etc.) in the subject over a reasonable time frame. The dose will be determined by the potency of the particular nicotine receptor agonist employed and the condition of the subject, as well as the body weight of the subject to be treated. For example, the level or affinity or both of the nicotine receptor agonist for the nicotine receptor may play a role in regulating the compound's activity. The size of the dose also will be determined by the existence, nature, and extent of any adverse side-effects that might accompany the administration of a particular compound. In determining the effective amount of nicotine or nicotine receptor agonist in the stimulation of stem progenitor cell recruitment, the route of administration, the kinetics of the release system (e.g., pill, gel or other matrix), and the potency of the nicotine agonist is considered so as to achieve the desired effect with minimal adverse side effects. The nicotine receptor agonist will typically be administered to the subject being treated for a time period ranging from a day to a few weeks, consistent with the clinical condition of the treated subject. The following dosages assume that nicotine is being administered, or a nicotine receptor agonist with similar potency and efficacy as nicotine. As will be readily apparent to the ordinarily skilled artisan, the dosage is adjusted for nicotine receptor agonists according to their potency and/or efficacy relative to nicotine. If given orally or as an inhalant, the dose may be in the range of about 0.01 mg to 10 mg, given 1 to 20 times daily, and can be up to a total daily dose of about 0.1 mg to 100 mg. If applied topically, for the purpose of a systemic effect, the patch or cream would be designed to provide for systemic dehvery of a dose in the range of about 0.01 mg to 10 mg. If the purpose of the topical formulation (e.g., cream) is to provide a local effect, the dose would likely be in the range of about 0.001 mg to 1 mg. If injected for the purpose of a systemic effect, the matrix in which the nicotine agonist is administered is designed to provide for a systemic dehvery of a dose in the range of about 0.001 mg to 1 mg. If injected for the purpose of a local effect, the matrix is designed to release locally an amount of nicotine agonist in the range of about 0.003 mg to 1 mg. Regardless of the route of administration, the dose of nicotine receptor agonist can be administered over any appropriate time period, e.g., over the course of 1 to 24 hours, over one to several days, etc. Furthermore, multiple doses can be administered over a selected time period. A suitable dose can be administered in suitable subdoses per day, particularly in a prophylactic regimen. The precise treatment level will be dependent upon the response of the subject being treated. In the treatment of some individuals with nicotine receptor agonists, it may be desirable to utilize a "megadosing" regimen. In such a treatment, a large dose of the nicotine receptor agonist is administered to an individual, time is allowed for the compound to act, and then a suitable reagent, e.g., a nicotine receptor antagonist, is administered to the individual to render the active compound ineffective or to reduce its systemic side-effects. Conditions amenable to treatment by nicotine receptor agonist-mediated angiogenesis The methods and nicotine receptor agonist-comprising compositions of the invention can be used to treat a variety of conditions that would benefit from recruitment of stem/progenitor cells. In one embodiment, nicotine receptor agonists are used to stimulate recruitment of endothehal progenitor cells to provide for stimulation of angiogenesis, stimulation of vasculogenesis, increased blood flow, and/or increased vascularity. Use of nicotine receptor agonists in this embodiment are refened to generally herein as "therapeutic angiogenesis." Examples of conditions and diseases amenable to therapeutic angiogenesis according to the method of the invention include any condition associated with an obstruction of a blood vessel, e.g., obstruction of an artery, vein, or of a capillary system Specific examples of such conditions or disease include, but are not necessarily limited to, coronary occlusive disease, carotid occlusive disease, arterial occlusive disease, peripheral arterial disease, atherosclerosis, myointimal hyperplasia (e.g. , due to vascular surgery or balloon angioplasty or vascular stenting), thromboangiitis obhterans, thrombotic disorders, vascuhtis, and the like. Examples of conditions or diseases that can be prevented usmg the methods of the invention include, but are not necessarily limited to, heart attack (myocardial infarction) or other vascular death, stroke, death or loss of limbs associated with decreased blood flow, and the like. Other forms of therapeutic angiogenesis mclude, but are not necessaπly limited to, the use of mcotme receptor agomsts to accelerate healing of wounds or ulcers, to improve the vasculaπzation of skin grafts or reattached bmbs so as to preserve their function and viability, to improve the healmg of surgical anastomoses(e g , as in re-connecting portions of the bowel after gastrointestinal surgery), and to improve the growth of skin or hair Conditions amenable to treatment by nicotine receptor agonist-mediated induction of stem cell and/or progenitor cell mobilization and/or recruitment In addition to stimulation of endothehal progemtor cells m angiogenesis and/or vasculogenesis, mcotme or other mcotme receptor agomsts can also be used to mobilize and/or recruit stem cells and/or progemtor cells to provide for replacement of a depleted mature cell or to supplement a population of mature cells By "mobilization" is meant the induction of movement of stem and/or progemtor cells from their site of ongin (e g , the bone marrow) and mto the systemic circulation. "Recruitment" refers to the movement of stem cells and/or progemtor ceUs from the systemic circulation and to a local site, e , to a wound or other site of physical damage, site of infection, an organ, etc In addition to or as part of the mobilization/recr tment processes, mcotme receptor agomsts can also mduce proliferation and maturation of stem cells and progemtor cells Conditions amenable to treatment by mobilization of stem cells and/or progemtor cells mclude, but are not necessaπly limited to, conditions amenable to treatment by mcreasmg the number of immune cells (e g , neutrophils, eosmophils, T cells, B cells, macrophages, natural killer cells), cells of mesenchymal oπgm (e g , cells of connective tissue, cells of cartilage, chondrocytes, bone (osteoblasts), fat cells (adipocytes), and cells of blood vessels, e g , endothehal cells) In one embodiment, the mobihzed/recruited cells are mesenchymal stem cells Mesenchymal stem cells are a population of progemtor cells in the bone marrow that are capable of differentiating mto bone, cartilage, muscle, tendon, and other connective tissues (Bruder et al (1998) Clin Orthop (355 Suppl S247-56) Human mesenchymal stem cells are positive for the markers SH2, SH3 and SH4 In another embodiment, the mobilized/recruited cells are hematopoietic stem cells Hematopoietic cells encompass HSCs, erythrocytes, neutrophils, monocytes, platelets, mast cells, eosmophils and basophils, B and T lymphocytes and NK cells as well as the respective lineage progemtor cells As used herem, a hematopoietic stem cell (HSC) refers to a primitive or pluπpotential hematopoietic stem cell that is capable of giving πse to progeny in all defined hematolymphoid lineages limiting numbers of stem cells are capable of fully reconstitutmg lethally irradiated mice, leading to their long-term survival In humans, the CD34 + Thy-1 + Lm hematopoietic stem cells are the equivalent of the murine c-kit + Thy-l.l l0 Lin "710 Sca-1 + (KTLS) hematopoietic stem cells and are a virtually pure population of multilineage hematopoietic stem cells. Human hematopoietic stem cells present on their surfaces the markers CD34, thy-1, SCAH-1 and SCAH-2; and are negative for lineage specific markers which may include glycophorin A, CD3, CD24, CD16, CD14, CD38, CD45RA, CD36, CD2, CD19, CD56, CD66a, and CD66b; T cell specific markers, tumor specific markers, etc. Markers useful for identification of mesodermal stem cells include FcγRII, FcγRIII, Thy-1 , CD44, VLA-4α, LFA-lβ, HSA, ICAM-1, CD45, Aa4.1, Sca-1, etc. See also U.S. Pat. Nos. 5,035,994; 5,061,620; 5,061,620; and Terstappen et al. (1992) Blood 79:666-677). In another embodiment, the mobilized/recruited stem cells are neural crest stem cells. Neural crest stem cells are positive for low-affinity nerve growth factor receptor (LNGFR), and negative for the markers sulfatide, gbal fibrillary acidic protein (GFAP), myelin protein P D , peripherin and neurofilament. In an embodiment of particular interest, the cells mobilized and recruited cells are endothehal progenitor cells. Exemplary conditions amenable to treatment by mobilization/recruitment of stem progenitor cells include, but are not necessarily hmited to ischemia, immune deficiency disorders (e.g., neutropenia, leukopenia, acquired immunodeficiencies, etc.), and hemophilia (e.g., acquired hemophilia). The methods of the invention can also be used in the treatment of damage that results from injury (e.g., mechanical, physical, chemical, radiation, nuclear, autoimmune, pathogen-mediated injury, and the bke). Conditions amenable to treatment by mobilization/recruitment of stem cells and/or progenitor cells can result from any of a variety of causes. For example, reduction of a mature cell population can be a direct or secondary effect of a disease or injury, can result from treatment of a disease or injury (e.g., as in chemotherapy for treatment of cancer), For example, neutropenia, a condition associated with depletion of neutrophils, can result from bone marrow damage from certain types of leukemia, lymphoma or metastatic cancer; adverse reactions to medication such as a diuretics or antibiotics; therapies that can cause depletion of immune cells, e.g., radiation treatment or chemotherapy; viral infections cause by, for example, EBV virus (e.g., infectious mononucleosis), HIV, and the like; bacterial infections (e.g., tuberculosis); or autoimmune diseases (e.g., systemic lupus erythromatosis). EXAMPLES The following examples are put forth so as to provide those of ordinary skill in the art with a complete disclosure and description of how to make and use the present invention, and are not intended to limit the scope of what the inventors regard as their invention nor are they intended to represent that the experiments below are all or the only experiments performed. Efforts have been made to ensure accuracy with respect to numbers used (e.g. amounts, temperature, etc.) but some experimental enors and deviations should be accounted for. Unless indicated otherwise, parts are parts by weight, molecular weight is weight average molecular weight, temperature is in degrees Centigrade, and pressure is at or near atmospheric. Methods and Materials The following is a description of the methods and materials used in the specific examples below. Animals. Eight to ten week old female wild type C57BL/6J mice were used. The mice weighed 20-25 grams (Jackson Laboratories, Bar Harbor, ME and Department of Comparative Medicine (DCM), Stanford, CA), and were maintained as previously described (Maxwell et al. (1998) Circulation 1998 98(4):369-374). Disc Angiogenesis System (DAS) To study whether nicotine induces angiogenesis in vivo, we employed the disc angiogenesis system (DAS) (Kowalski et al. (1992) Exp Mol Pathol 5_6_(1):1-19; Fajardo et al. (\998) Lab Invest 58:718-7244). Preparation of the disc. The DAS consisted of a disc (11 mm in diameter and 1 mm thickness) made of apolyvinyl alcohol sponge (Kanebo PVA, RippeyCo., Santa Clara, CA). Both sides were covered with nitrocellulose cell-impermeable filters (Milbpore filters, 0.45μm in pore diameter, Milbpore, SF, CA) of the same diameter as the sponge disc, fixed to the sponge using Millipore glue #1 (xx70000.00, Milbpore). As a result, cells(and thus vessels) could penetrate or exit only through the rim of the disc (Kowalski etal. (1992) Exp Mol Pathol 56(1):1-19; Fajardo et al. (1998) Lab Invest 58:718-7244). In order to study the local effect of nicotine on angiogenesis, nicotine was placed in a pellet which was added directly to the disc. Briefly, a 1.5-mm core (pellet) was cut from the disc center. Both the pellets and discs were sterilized prior to assembly in a laminar flow hood. The pellet was loaded with up to 20 mcl of the nicotine solution and subsequently air-dried. We placed in the disc pellets with either vehicle (PBS, Sigma, Chemical Co., St Louis, MO, n=5) or nicotine(10-6 M, Aldnch Chemical Company, Milwaukee, WI, n=5) to study the effects of locally administered mcotme For companson, m some cases basic fibroblast growth factor(bFGF, 20 meg) or Del-1 proteιn(0 2 M) was added to the peUet, rather than mcotme Both bFGF and Del-1 are known to mduce angiogenesis The pellet was then coated with ethylene- vinyl acetate co-polymer (Elvax, Dupont, Chemcentral Corp , Chicago, IL) which would permit slow release of the mcotme from the pellet mto the disc The pellet was then re-inserted mto the disc before sealing the disc with the milhpore filters To study the systemic effects of mcotme, in some cases the animals were administered mcotme m their drinking water (see below) Implantation of the disc The mice were anesthetized with 4% chloralhydrate [intrapentoneal administration (I p ), 0 1 cc/lOg body weight] The flanks and postenor surface of the thorax were shaved and cleaned with saturated 70% isopropyl alcohol A 2-cm incision was made m the skin of the flank contra-lateral to the implantation site Blunt dissection through the subcutaneous tissue produced a channel mto which the saline moistened disc was inserted The skin was closed with 5 0 silk suture (Kowalski et al (1992) Exp Mol Pathol 56(1) 1-19, Fajardo et al (1998) Lab Invest 58 718-7244) Disc removal and preparation Two weeks after disc implantation, the mice were sacrificed with an overdose of 4% chloral hydrate (l p ) and cervical dislocation A careful incision was made next to the skin overlying the implanted disc, and the disc was gently removed from the implantation site Attached tissue was carefully detached from the disc After removmg the disc, one filter was separated from the disc Discs were then fixed m 10% formalin and embedded flat m paraffin Subsequently, 5 μm sections were made in a plane through the center of the disc and parallel to the disc surface Quantitation of results The disc sections were stained with H&E for hght microscopy and histomorphometπc measurement of radial growth, and stained with toluidine blue for quantitative determination of total area of fibro vascular growth Usmg a video microscope and a computer assisted digital image analysis system (NIH Image 1 59b9), the entire area of fibro vascular growth in the toluidine blue stained disc was calculated and expressed m mm 2 As descnbed in a previous study, total fibro vascular growth area is directly proportional to the total area of the disc occupied by blood vessels (Kowalski et al (1992) Exp Mol Pathol 56(1) 1-19, Fajardo et al (1998) Lab Invest 58 718-7244) Therefore, the measurement of such total area is used as an mdex of angiogenesis (Kowalski et al (1992), supra, Fajardo et al (1998), supra) Vascular continuity assessment To visualize the microvessels m the disc sections and to estabhsh that there was continuity between the systemic and disc vasculatures, luconyl blue dye was injected into the left carotid artery prior to euthanizing the mice. Animals were anesthetized using 4% chloralhydrate (i.p., 0.1 cc/10 g body weight). An incision was made in the ventral midline of the neck. After the carotid sheath was exposed, the left carotid artery was separated from the neurovascular bundle and secured by two 4.0 silk sutures. An incision was made in the carotid and a 15-cm length of PE10 tubing (Beckton Dickinson, Sparks MD) was introduced into the carotid artery and advanced to the ascending aorta just distal to the aortic valve. About 1.0 ml of luconyl blue was then slowly injected from a 1 ml syringe through the tubing into the thoracic aorta. The presence of blue dye in the fibro vascular network in the disc was detected by bght microscopy. Microscopy revealed microvessels lined by a single layer of endothelium and erythrocytes contained within their lumen. Luconyl blue dye was observed throughout the vessels of the disc. Murine Ischemic Hind Limb Model of Peripheral Arterial Disease (PAD) Mice were anesthetized with 4% chloral hydrate [intraperitoneal administration (i.p.), 0.1 cc/10 g body weight). The medial surface of both hind limbs were shaved and then cleaned with betadine solution. A 1.5 -cm longitudinal incision was performed, extending from the knee to the inguinal ligament. Through this incision, the superficial femoral artery was dissected free along its length. After the distal ends of both the external iliac and superficial femoral arteries were ligated with 7.0 (Ethicon), complete excision of the femoral artery was performed. An additional set of mice underwent sham operation. The incisions were then closed with discontinuous stitches of 5.0 silk suture (Ethic on). Ampicillin (1 mg/10 gm body weight) intraperitoneal injection was administered after surgical procedure. Histological studies. Tissue Preparation. Three weeks after surgery, mice were euthanized with an overdose of 4% chloral hydrate (i.p) and cervical dislocation, and the adductor and semimembranous muscles were collected for capillary density assessment. Briefly, a longitudinal incision in the medial thigh was made to expose the entire hindlimb muscle. The adductor and semimembranous muscles were removed and immediately frozen in OCT. Subsequently, sections 5 μm were taken from the mid- region of each muscle in a transverse orientation. The sections were air dried and fixed in acetone. Capillary Densitometry. Immunohisto chemistry was performed using an alkaline phosphatase assay to identify the endothehal cells. An eosin counterstain was used to differentiate myocytes. Capillaries and myocytes were identified and counted using light microscopy (20X). For each section, four different fields were selected and the total number of capillaries and myocytes per field determined. These values were averaged to provide a determination of capillary density for each experimental limb. To ensure that value for capillary density was not overestimated due to muscle atrophy, or underestimated due to interstitial edema, capillary density was expressed as a ratio of capillanes to myocytes present m the same field Data Analysis All data are given as mean +/-SEM Statistical significance was tested usmg unpaired, two- tailed t-test for compaπsons between groups Statistical significance was accepted for p<0 05 Example 1 Systemic effect of mcotme upon angiogenesis in vivo To study the effects of mcotme m systemically treated mice, mcotme (60 mcg/ml, n=5) was diluted m the drinking water The mechamsm of mcotme-mduced angiogenesis was studied by giving oral supplementation of indomethacin (20 mcg/ml, Sigma, n=5) and or LNNA (6 mg/ml, Sigma, n=5) to mice having an implanted DAS both locally treated (nicotine inside the DAS) and systemically treated (mcotme diluted m drinking water) Concentrations of mcotme, mdomethacm, and LNNA were determined m accordance to studies usmg oral supplementation of these agents m murme models (Maxwell et al (1998) Circulation 1998 98(4) 369-374, Fulton et al (1980) Int J Cancer 26(5) 669-73, Rowell et al (1983) J Pharmacological Methods 9 249-261) Under basal conditions (untreated water, vehicle-treated disc), fibrovascular growth mto the disc occurred Vessels could be seen growmg mto the disc These vessels were in continuity with the systemic circulation as manifested by the influx of leuconyl dye mto the disc vasculature, after systemic administration of the dye The area of the fibrovascular growth mto the disc under basal conditions was somewhat greater than 10 mm 2 (Fig 2) With systemic admmistration of mcotme, there was a dramatic mcrease in fibrovascular growth with an area of 35 mm 2 (Fig 2) The effect of mcotme was blocked by the NO synthase inhibitor L, rutro-arginine (LNNA) as well as by mdomethacm, indicating that synthesis of both mtnc oxide and prostacyclin were required for the angiogenic effect of mcotme Example 2 Local effect of mcotme upon angiogenesis in vivo In order to determine if local administration of L-arginine could be effective at mducmg angiogenesis, m some animals, mcotme was placed within a pellet that was mserted mto the disc angiogenesis system (descπbed above) When mcotme was placed m the disc (rather than administered m the water of the animals as descnbed in Example 1) a similar effect was observed The fibrovascular growth under basal conditions (about 10 mm 2 ) was mcreased to about 20 mm (Fig 3) Again, mdomethacm or LNNA blocked the effects of mcotme These studies indicate that systemic or local administration of mcotme mduces angiogenesis Example 3: Comparison of effects of nicotine with other angiogenic agents The effects of nicotine were compared with the angiogenic agents bFGF and Dell . The comparison with bFGF is particularly important because this agent is already in clinical trials in humans for therapeutic angiogenesis. In comparison to vehicle, bFGF, Dell, and nicotine each increased angiogenesis to the same degree. Systemically administered nicotine enhanced angiogenesis to a much greater degree than locally administered bFGF and Del-1 (Fig 4). Paradoxically, the effect of systemic nicotine administration was greater than local nicotine administration, even though systemic nicotine administration undoubtedly produced lower local levels in the disc. This paradox led the investigators to consider that the systemic administration of nicotine was inducing vasculogenesis(recruitment of endothehal precursors from the bone marrow) as well as local angiogenesis (see Example 5 below). Intermediate doses of nicotine administered intramuscularly had the greatest effect. At higher intramuscular doses of nicotine, less angiogenesis is observed. Example 4: Induction of angiogenesis in the murine hindbmb ischemia model of peripheral arterial disease To provide more compelling evidence for the therapeutic angiogenic effects of nicotine, the angiogenic effects of nicotine were examined in a model of arterial occlusive disease, the murine ischemic hindbmb (described above). Daily intramuscular injections of nicotine solution or vehicle were administered (50μl) for a period of three weeks. Five groups of animals received 0, 3, 30, 300 or 3200 ng/kg of nicotine by intramuscular injection daily (represented in Figs. 6 and 7 as IX (0.0811 ng nicotine in 50 μl saline (= 0.003 μg/kg), 10X (0.811 ng nicotine in 50 μl saline (= 0.03 μg/kg), 100X (8.11 ng nicotine in 50 μl saline (= 0.3 μg/kg), and 1000X (81.1 ng nicotine in 50 μl saline (= 3.2 μg/kg)). As shown in Fig 5, 3 weeks after surgery, capillary density (capillaries/myocyte) was increased in operated bmbs (ischemic) in comparison to non-operated bmbs (non-ischemic) consistent with a basal angiogenic response to ischemia As shown in Figs. 6 and 7, nicotine enhanced the angiogenic response to ischemia relative to controls. With vehicle control, 0.35 capillaries/myocyte were detected in the ischemic limb. At an intermediate dose of 0.03 μg/kg, nicotine nearly doubled angiogenic response (to 0.67 capillaries/myocyte). At the highest dose of nicotine, angiogenesis was not increased; indeed at this dose some toxicity was observed, with evidence of interstitial edema and myocyte necrosis. The angiogenic effect remained local to the site of nicotine injection, since no angiogenic effect was detected in a non-ischemic hindhmbs (Fig 6) Thus, local intramuscular administration of these doses of mcotme did not result m a systemic angiogenic effect These studies mdicate that mcotme enhances angiogenesis in a murine model of human penpheral artenal disease, and that mcotme receptor agomsts are useful for therapeutic angiogenesis Example 5 Nicotme induces angiogenesis by recruitment of endothehal progemtor cells In order to further examine the role of mcotme m induction of angiogenesis, the recruitment of endothehal progemtor cells was studied The model of mouse parabiosis, m which cross- circulation is established between two individuals (Eichwald, et al (1963) JNatl Cancer Inst 30 783-94, Weissman et al (1984) Transplantation 37 3-6), is an ideal assay for trackmg the migration of circulating cells with endothehal potential to sites of angiogenesis m vivo Cells ansing from one partner can be differentiated from the other by virtue of stable genetic markers such as sex chromosomes or the presence of a reporter transgene such as LacZ (Fig 8) The goal is to eliminate biases inherent m models that require pre-selection of a given cell type, and to avoid mampulations (such as total body lnadiation) required to overcome lmmunological or physiological barners between the putative precursor cells and the expenmental hosts The use of highly mbred laboratory mice allows unparalleled versatility m the use of congemc and transgemc markers to perform lineage-tracking experiments The parabiotic mouse model is an excellent model for studying the biology and genetic program of endothehal progemtors, and m estabhshmg the role of circulatmg precursors m the development of penvascular supporting structures Parabiotic mouse pairs were created to investigate the mobilization and incorporation of precursors to vessel formation m normal and ischemic conditions usmg a hind bmb ischemia model of angiogenesis (as descnbed above), and the effect of nicotine The parabiotic partners were selected so that they shared all major histo compatibility antigens, and were therefore free of lmmunological barners to cell migration and angiogenesis Assaying for genetic markers unique to one animal of the pair (e g , the Y chromosome where the pair is made up of a female mouse and a male mouse) provides for unambiguous ceU trackmg between the mice The model is further optimized by the use of a second genetic marker to differential the individuals (e g , a transgene present m one partner and not the other), thus mcreasmg the sensitivity and the accuracy of the identification of the ongin of smgle cells Ten week old male mice (mouse A either a C57/B16 ROSA 26 mice (Jackson Laboratory, Bar Harbor, ME) or a tie-2-LacZ ("Sato") transgemc mouse (Schlager et al (1995) Development 121(4) 1089-98, Schlager et al (1997) Proc Natl Acad Sci USA 94(7) 3058-63) that has endothehal specific β-galactosidase expression), which constitutively express the LacZ transgene, were surgically jomed to a female age and strain-matched mice (mouse B either C57/B6 (LacZ ) mouse (to be jomed with the ROSA26 mouse) or a C57B16 mouse (to be jomed with the tie-2-LacZ mouse) by making a continuous unilateral skm mcision between the fore and hindhmb jomts of each mouse An anastomosis of the leg jomts and the skm with its adherent subcutaneous tissue of mouse A to mouse B was then made with nylon sutures, and the mice allowed to recover Previous studies usmg this model have shown that cross-circulation is rehably estabhshed within 2 weeks (Eichwald, et al (1963) J Natl Cancer Inst 30 783-94; Weissman et al (1984) Transplantation 37 3-6) Cross- circulation m these animals was confirmed by trackmg the flow of Evans blue dye from mouse A to mouse B followmg mtravenous mjection In addition, penpheral blood leukocytes (pbls) were tested for contnbutions from each partner by FACS-gal staining (Fieπng et al (1991) Cytometry Y2 291- 301 ) or Y-chromosome FISH to guarantee that both cells and plasma freely interchange Weissman et al have shown previously that parabiosis of syngeneic males to females does not result m a detectable anti H-Y immune response (Weissman et al (1984) Transplantation 37 3-6) The LacZ " females were exposed to hindbmb ischemia whereas the LacZ * males were not Test mice were treated with mcotme systemically by adding mcotme to the drinking water (0 1 g/L drinking water) Control mice did not receive mcotme m their drinking water Five pairs of parabiotic mice were mcluded m each of the test and control groups Ischemic and non-ischemic hindhmbs were removed from the female mice at 3 weeks after mduction of the ischemia and exammed for the presence of cells denved from their male partners The phenotype of the cells m the hindhmbs were evaluated usmg histology methods by confocal microscopy Double staining for CD 31 and β-galactosidase identified EPCs denved from the transgemc mouse EPC frequency was defined as the number of vessels containing transgemc endothehal cells divided by the total vessels exammed m representative sections Results Examination of ischemic hind bmbs from the legs of control and nicotine-treated female partners joined with a Sato/tie-2/LacZ transgemc male showed that EPCs from Sato mouse crossed over to the area of angiogenesis m the female mouse and incorporated into new vessels These EPCs were readily identified as they were double stained for CD 31 (endothehal marker) and β-galactosidase (which is under endothehal cell-specific tie-2 promoter control in the Sato mice) The results are illustrated graphically m Fig 9 The percentage of vessels that incorporated endothehal progemtor cells (EPCs) during angiogenesis m response to hind hmb ischemia was low in the saline group (1 6 %) However, stimulation of the native angiogenic response by mcotme resulted in a significant increase in the number of vessels and in the percentage of vessels that incorporated EPC (7.3 %; PO.001). While the present invention has been described with reference to the specific embodiments thereof, it should be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the true spirit and scope of the invention. In addition, many modifications may be made to adapt a particular situation, material, composition of matter, process, process step or steps, to the objective, spirit and scope of the present invention. All such modifications are intended to be within the scope of the claims appended hereto.

Claims: CLAIMS What is claimed is: 1. A method for mobilizing stem cells in a mammal, the method comprising administering to a mammal a nicotine receptor agonist in an amount effective to stimulate mobilization of a stem cell from bone marrow of the mammal to a treatment site in the mammal. 2. The method of claim 1, wherein the nicotine receptor agonist is nicotine. 3. The method of claim 1 , wherein said administering is at a local site. 4. The method of claim 1, wherein said administering is intramuscular. 5. The method of claim 1, wherein said administering is intravascular. 6. The method of claim 1, wherein the treatment site is in the bloodstream of the mammal. 7. The method of claim 1, wherein the treatment site is a wound or ulcer. 8. The method of claim 1, wherein the stem cell is of hematopoetic or mesenchymal lineage. 9. The method of claim 1, wherein the agonist is effective to stimulate incorporation of circulating stem cebs into the treatment site. 10. The method of claim 1 , wherein the agonist is effective to promote wound healing at the treatment site. 11. A method of mobilizing a progenitor cell in a mammal, the method comprising administering to a mammal a nicotine receptor agonist in an amount effective to stimulate mobibzation of a progenitor cell from bone marrow of the mammal to a treatment site in the mammal. 12. The method of claim 11, wherein the nicotine receptor agonist is nicotine. 13. The method of claim 11, wherein said administering is at alocal site. 14. The method of claim 11, wherein said administering is intramuscular. 15. The method of claim 11, wherein said administering is intravascular. 16. The method of claim 11, wherein the progenitor cell is of mesenchemymal or hematopoietic lineage. 17. The method of claim 11, wherein the agonist is effective to stimulate incorporation of circulating progenitor cells mto the treatment site. 18. A pharmaceutical composition comprising a pharmaceutically acceptable carrier and a nicotine receptor agonist in an amount effective to stimulate mobilization of stem cells. 19. The pharmaceutical composition of claim 18, wherein the nicotine receptor agonist is nicotine.

Inventors: COOKE JOHN, HEESCHEN CHRISTOPHER, JANG JAMES, JOHNSON FRANCES LAURI, PATHAK ANJALI, TSAO PHILLIP, COOKE, JOHN, HEESCHEN, CHRISTOPHER, JANG, JAMES, JOHNSON, FRANCES, LAURI, PATHAK, ANJALI, TSAO, PHILLIP
Applicants: COOKE JOHN, HEESCHEN CHRISTOPHER, JANG JAMES, JOHNSON FRANCES LAURI, PATHAK ANJALI, TSAO PHILLIP, UNIV LELAND STANFORD JUNIOR, COOKE, JOHN, HEESCHEN, CHRISTOPHER, JANG, JAMES, JOHNSON, FRANCES, LAURI, PATHAK, ANJALI, THE BOARD OF TRUSTEES OF THE LELAND STANFORD JUNIOR UNIVERSITY, TSAO, PHILLIP
Application year: 2000
Main classification: A61K31
IPC codes: A61K31, A61K45, A61P17