bluuebunny/crossref_metadata_2025 huggingface dataset:
Assessing the Effects of Deprenyl on Longevity and Antioxidant Defenses in Different Animal Models
Authors: KITANI KENICHI , KANAI SETSUKO , IVY GWEN O. , CARRILLO MARIA CRISTINA
Published: February 2006

ABSTRACT: Among many pharmaceuticals that have been tested for their effects on longevities of different animal rodents, deprenyl is unique in that its effects on longevity has been tested in at least four different animal species by independent research groups and that the effect has been postulated to be due to its effect of raising such antioxidant enzyme activities as superoxide dismutase (SOD) and catalase (CAT) in selective brain regions. Thus far, in all four species of animals examined (rats, mice, hamsters, and dogs), a positive effect was demonstrated, although the extent of its effect is quite variable. Our group has examined the effect on longevities in rats and mice and on antioxidant enzymes in rats, mice, and dogs. Although in rats of both sexes, we have obtained positive effects on longevity, two studies with different doses in mice did not reveal a significantly positive effect. We have observed, however, significantly positive effects on SOD (in Cu, Zn‐, and Mn‐) as well as CAT (but not glutathione peroxidase) activities in the brain dopaminergic system such as in the S. nigra and striatum (but not in hippocampus) in all rats, mice, and dogs, although the effects were quite variable, depending on the doses used. In mice, however, a long‐term administration (3 x/w, 3 months) caused a remarkable decrease in the magnitude of activity as well as a narrowing of the effective dose range, which may explain a relatively weak effect of the drug on mouse longevity. Further, a recent study on aging beagle dogs by Ruehl et al. showed a remarkable effect on longevity, which agrees with our SOD study in dogs. Although deprenyl has been claimed to have several other effects, such as a radical scavenging effect and a neuroprotective effect, past reports on its effects on longevities and antioxidant defenses are compatible with the notion that the drug prolongs the life span of animals by reducing the oxidative damage to the brain dopaminergic system during aging. Further, our studies on F‐344 rats as well as a dog study by Ruehl et al. suggest that the drug may at least partially prolong the life span of animals by enhancing immune system function and preventing tumor development in animals.
Age‐associated Memory Impairment: Assessing the Role of Nitric Oxide
Authors: MEYER ROBERT C. , SPANGLER EDWARD L. , KAMETANI HIDEKI , INGRAM DONALD K.
Published: February 2006

ABSTRACT: Several neurotransmitter systems have been investigated to assess hypothesized mechanisms underlying the decline in recent memory abilities in normal aging and in Alzheimer's disease. Examining the performance ot F344 rats in a 14‐unit T‐maze (Stone maze), we have focused on the muscarinic cholinergic (mACh) and the N‐methyl‐d‐aspartate (NMDA) glutamate (Glu) systems and their interactions. Maze learning is impaired by antagonists to mACh or NMDA receptors. We have also shown that stimulation of mACh receptors can overcome a maze learning deficit induced by NMDA blockade, and stimulation of the NMDA receptor can overcome a similar blockade of mACh receptors. No consistent evidence in rats has been produced from our laboratory to reveal significant age‐related declines in mACh or NMDA receptor binding in the hippocampus (HC), a brain region that is greatly involved in processing of recent memory. Thus, we have directed attention to the possibility of a common signal transduction pathway, the nitric oxide (NO) system. Activated by calcium influx through the NMDA receptor, NO is hypothesized to be a retrograde messenger that enhances presynaptic Glu release. Maze learning can be impaired by inhibiting the synthetic enzyme for NO, nitric oxide synthase (NOS), or enhanced by stimulating NO release. However, we have found no age‐related loss of NOS‐containing HC neurons or fibers in rats. Additionally, other laboratories have reported no evidence of an age‐related loss of HC NOS activity. In a microdialysis study we have found preliminary evidence of reduced NO production following NMDA stimulation. We are currently working to identify the parameters of this phenomenon as well as testing various strategies for safely stimulating the NO system to improve memory function in aged rats.
Telomeres: Influencing the Rate of Aging
Authors: VON ZGLINICKI THOMAS
Published: February 2006

ABSTRACT: Evidence is reviewed that suggests a central role for telomeres in one major model of biological aging, namely, proliferative senescence. Telomeric shortening with each cell division does not only act as a biological clock, but appears to trigger the ultimate loss of proliferative ability via activation of the p53‐dependent check point system.

Oxidative stress induces single‐stranded damage in telomeric DNA. It is not clear yet whether this damage occurs in the form of single‐stranded gaps or overhangs or as arbitrarily distributed single‐stranded breaks. However, in contradiction to the rest of the genome, this damage is not repaired in telomeres. It is, therefore, the major cause of telomere shortening even under standard in vitro cell culture conditions. Therefore, controlling the oxidative load onto DNA, in general, and, especially, onto telomeres might become a major factor to influence the rate of aging.

Further experiments demonstrate that G‐rich single‐stranded telomeric DNA fragments do activate the p53 check point control, leading to an inhibition of proliferation in wild‐type p53 cells. Not only the shortening of telomeres down to a “signal value,” but accumulation of telomeric single‐stranded DNA fragments, as well, could be relevant triggers for proliferative senescence.
Nutrition, Osteoporosis, and Aging
Authors: NORDIN B. E. CHRISTOPHER , NEED ALLAN G. , STEURER TRACY , MORRIS HOWARD A. , CHATTERTON BARRY E. , HOROWITZ MICHAEL
Published: February 2006

ABSTRACT: Loss of bone is an almost universal accompaniment of aging that proceeds at an average rate of 0.5‐1% per annum from midlife onwards. There are at least four nutrients involved in this process: calcium, salt, protein, and vitamin D, at least in women. The pathogenesis of osteoporosis in men is more obscure. Calcium is a positive risk factor because calcium requirement rises at the menopause due to an increase in obligatory calcium loss and a small reduction in calcium absorption that persist to the end of life. A metaanalysis of 20 calcium trials shows that this process can generally be arrested by calcium supplementation, although there is some doubt about its effectiveness in the first few years after menopause. Salt is a negative risk factor because it increases obligatory calcium loss; every 100 mmol of sodium takes 1 mmol of calcium out of the body. Restricting salt intake lowers the rate of bone resorption in postmenopausal women. Protein is another negative risk factor; increasing animal protein intake from 40 to 80 g daily increases urine calcium by about 1 mmol/day. Low protein intakes in third world countries may partially protect against osteoporosis. Vitamin D (sometimes called a nutrient and sometimes a hormone) is important because age‐related vitamin D deficiency leads to malabsorption of calcium, accelerated bone loss, and increased risk of hip fracture. Vitamin D supplementation has been shown to retard bone loss and reduce hip fracture incidence in elderly women.
The Effect of Long‐term Dietary Supplementation with Antioxidantsa
Authors: MEYDANI M. , LIPMAN R. D. , HAN S. N. , WU D. , BEHARKA A. , MARTIN K. R. , BRONSON R. , CAO G. , SMITH D. , MEYDANI S. N.
Published: February 2006

ABSTRACT: The impact of diet and specific food groups on aging and age‐associated degenerative diseases has been widely recognized in recent years. The modern concept of the free radical theory of aging takes as its basis a shift in the antioxidant/prooxidant balance that leads to increased oxidative stress, dysregulation of cellular function, and aging. In the context of this theory, antioxidants can influence the primary “intrinsic” aging process as well as several secondary age‐associated pathological processes. For the latter, several epidemiological and clinical studies have revealed potential roles for dietary antioxidants in the age‐associated decline of immune function and the reduction of risk of morbidity and mortality from cancer and heart disease. We reported that long‐term supplementation with vitamin E enhances immune function in aged animals and elderly subjects. We have also found that the beneficial effect of vitamin E in the reduction of risk of atherosclerosis is, in part, associated with molecular modulation of the interaction of immune and endothelial cells. Even though the effects of dietary antioxidants on aging have been mostly observed in relation to age‐associated diseases, the effects cannot be totally separated from those related to the intrinsic aging process. For modulation of the aging process by antioxidants, earlier reports have indicated that antioxidant feeding increased the median life span of mice to some extent. To further delineate the effect of dietary antioxidants on aging and longevity, middle‐aged (18 mo) C57BL\6NIA male mice were fed ad libitum semisynthetic AIN‐76 diets supplemented with different antioxidants (vitamin E, glutathione, melatonin, and strawberry extract). We found that dietary antioxidants had no effect on the pathological outcome or on mean and maximum life span of the mice, which was observed despite the reduced level of lipid peroxidation products, 4‐hydroxynonenol, in the liver of animals supplemented with vitamin E and strawberry extract (1.34 ± 0.4 and 1.6 ± 0.5 nmol/g, respectively) compared to animals fed the control diet (2.35 ± 1.4 nmol/g). However, vitamin E‐supplemented mice had significantly lower lung viral levels following influenza infection, a viral challenge associated with oxidative stress. These and other observations indicate that, at present, the effects of dietary antioxidants are mainly demonstrated in connection with age‐associated diseases in which oxidative stress appears to be intimately involved. Further studies are needed to determine the effect of antioxidant supplementation on longevity in the context of moderate caloric restriction.
B Vitamins and Homocysteine in Cardiovascular Disease and Aging
Authors: WILCKEN DAVID E. L. , WILCKEN BRIDGET
Published: February 2006

ABSTRACT: The sulfur‐containing amino acid, homocysteine, is formed from the essential amino acid methionine, and a number of B vitamins are involved in methionine metabolism. Pyridoxine, vitamin B6, is a cofactor for cystathionine β synthase, which mediates the transformation of homocysteine to cystathionine, the initial step in the transsulfuration pathway and the urinary excretion of sulfur. In a normal diet there is conservation of the carbon skeleton, and about 50% of the homocysteine formed is remethylated to methionine via steps that require folic acid and vitamin B12. A deficiency of any of these three vitamins leads to modest homocyst(e)ine elevation, as does diminished renal function, both of which are common in the elderly. It is also established that homocyst(e)ine elevation of this order is associated with increased cardiovascular risk but is also associated with most established risk factors, although it is thought to be an independent contributor.

In the inborn error of metabolism homocystinuria due to cystathionine β synthase deficiency there is greatly increased circulating homocyst(e)ine and a clear association with precocious vascular disease. In about 50% of these patients there is a vascular event before the age of 30 years. The homocysteine‐induced adverse vascular changes appear to result from endothelial and smooth muscle cell effects and increased thrombogenesis. We have documented a highly significant reduction in the occurrence of vascular events during 539 patient years of treatment in 32 patients with cystathionine β synthase deficiency (mean age 30 years, range 9‐66 years) by aggressive homocyst(e)ine lowering with pyridoxine, folic acid, and B12 (
p = 0.0001
). The 15 pyridoxine nonresponsive patients also received oral betaine.

Although a cause and effect relationship is postulated for the increased cardiovascular risk associated with mild homocysteine elevation, a common cause of this elevation is the methylenetetrahydrofolate reductase C677T mutation. Homozygotes occur in about 11% of Caucasian populations. However, the mutation is not associated with increased coronary risk. Since mild homocysteine elevation is easily normalized by B vitamin supplementation, usually with folic acid, it remains for controlled clinical trials of this inexpensive therapy to determine whether normalizing mild homocyst(e)ine elevation reduces cardiovascular risk.
Nutrition, Cancer, and Aging
Authors: DREOSTI IVOR E.
Published: February 2006

ABSTRACT:The parallel increase in cancer risk with advancing age is well recognized, and several pathophysiological mechanisms common to both conditions have been proposed to explain this interrelationship. The importance of nutrition, both in delaying the aging process and in protecting against cancer is also well recognized, and it is therefore of interest to compare the relative impact several of the more widely studied dietary manipulations may have on each of these conditions.

For example, caloric restriction, which putatively reduces oxidative stress and effectively increases life span in animals also seems to reduce the incidence of many cancers, possibly due to diminished mitogenesis. Likewise, oxidative damage to DNA appears to be common to both processes but may be more important in the mitochondria with respect to aging and in the nucleus in relation to cancer. Inadequate dietary folate and impaired DNA methylation status are closely associated with increased cancer risk, and recently defective somatic cell methylation and accumulated genetic instability have been proposed as key mechanisms contributing to senescence.

Several other well‐established anticancer dietary strategies, which include increased fiber intake and the consumption of more fruits and vegetables, have not been studied extensively in relation to aging, although many of the phytochemicals considered important as chemopreventive agents for cancer may well contribute to delaying the aging process.

Although not directly related to nutrition, but nevertheless highly relevant, is the question of physical activity, which has been strongly linked to a reduction in risk of some cancers. Although less is known with respect to exercise and biological markers of aging, physical activity does appear to retard the age‐related decline in the muscle strength and in the bone density.
The Biochemical, Pathophysiological, and Medical Aspects of Ubiquinone Function
Authors: NOHL HANS , GILLE LARS , STANIEK KATRIN
Published: February 2006

ABSTRACT: Ubiquinone (Q) shares its biological implication in membrane‐associated redox reactions with a variety of other redox carriers, such as dehydrogenases, non‐heme‐iron proteins, and cytochromes. Peculiarities arise from the lack of transition metals, which in contrast to the other electron carriers do not participate in redox‐shuttle activities of Q. Another peculiarity is the lipophilicity of Q, which allows free movement between reductants and oxidants of a membrane. The chemistry of Q reduction and ubiquinol oxidation requires the stepwise acceptance and transfer of two single electrons associated with the addition or release of two single H+. These special qualities are widely used in biological membranes for linear electron transfer and transmembranous H+ translocation. In mitochondria it was long reported that under certain conditions linear e− transfer from the semireduced form (SQ.) to native oxidants of the respiratory chain may run out of control, thereby establishing a permanent source of oxygen radical release. It should be mentioned that in mitochondria e− transfer to dioxygen out of sequence requires a particular treatment with inhibitors and uncouplers of the respiratory chain. Nevertheless, it is generally assumed that Q is mainly involved in mitochondrial O2•‐ generation and that mitochondria represent the major source of O2•‐ radicals under physiologicalandvarious pathophysiological conditions. The ever‐increasing application of coenzyme Q as an antioxidant for the prophylaxis and treatment of a great variety of functional disorders, including senescence, has considerably stimulated our interest in the potential prooxidative potency of this natural electron carrier. Experimental evidence will be presented that under physiological conditions Q implicated inmitochondrial e− transfer of the respiratory chain is not involved in cellular oxygen activation. It will also be shown that alterations of Q from an e− carrier to an active radical promotor is possible under various conditions. In addition, reaction products emerging from the antioxidant activity of ubiquinol were found to stimulate the formation of inorganic as well as organic oxygen radicals.
Reactive Oxygen Intermediates, Molecular Damage, and Aging: Relation to Melatonin
Authors: REITER RUSSELL J. , GUERRERO JUAN M. , GARCIA JOAQUIN J. , ACUÑA‐CASTROVIEJO DARIO
Published: February 2006

ABSTRACT: Melatonin, the chief secretory product of the pineal gland, is a direct free radical scavenger and indirect antioxidant. In terms of its scavenging activity, melatonin has been shown to quench the hydroxyl radical, superoxide anion radical, singlet oxygen, peroxyl radical, and the peroxynitrite anion. Additionally, melatonin's antioxidant actions probably derive from its stimulatory effect on superoxide dismutase, glutathione peroxidase, glutathione reductase, and glucose‐6‐phosphate dehydrogenase and its inhibitory action on nitric oxide synthase. Finally, melatonin acts to stabilize cell membranes, thereby making them more resistant to oxidative attack. Melatonin is devoid of prooxidant actions.

In models of oxidative stress, melatonin has been shown to resist lipid peroxidation induced by paraquat, lipopolysaccharide, ischemia‐reperfusion, l‐cysteine, potassium cyanide, cadmium chloride, glutathione depletion, alloxan, and alcohol ingestion. Likewise, free radical damage to DNA induced by ionizing radiation, the chemical carcinogen safrole, lipopolysaccharide, and kainic acid are inhibited by melatonin. These findings illustrate that melatonin, due to its high lipid solubility and modest aqueous solubility, is able to protect macromolecules in all parts of the cell from oxidative damage. Melatonin also prevents the inhibitory action of ruthenium red at the level of the mitochondria, thereby promoting ATP production. In humans, the total antioxidative capacity of serum is related to melatonin levels. Thus, the reduction in melatonin with age may be a factor in increased oxidative damage in the elderly.
Morphogenesis of the Retinal Pigment Epithelium: Toward Understanding Retinal Degenerative Diseasesa
Authors: MARMORSTEIN ALAN D. , FINNEMANN SILVIA C. , BONILHA VERA L. , RODRIGUEZ‐BOULAN ENRIQUE
Published: February 2006

ABSTRACT: The phenotype of an epithelial cell is defined by a unique combination of morphology, gene and protein expression, and protein localization. Results indicate that the terminal differentiation of the RPE cell can be described in part by changes in the polarity of its surface proteins ανβ5 integrin, Na,K‐ATPase, N‐CAM, and EMMPRIN. Changes in protein/gene expression and protein localization in late stages of RPE development indentify ανβ5 integrin as a key player in RPE phagocytosis, and N‐CAM and EMMPRIN as potentially important molecules in other RPE functions necessary for photoreceptor survival. By studying the trafficking of the later two proteins it is shown that entry into an apical or basolateral pathway in RPE cells cannot be predicted by the distribution of a given protein in other epithelial cells, and that this distribution may change through the course of RPE development. The mechanisms used by RPE and other epithelia to establish and maintain their specific polarity properties are fundamental to the formation and maintenance of their specific epithelial phenotype. The ability to therapeutically direct molecules incorporated into RPE by gene therapy into apical or basal surfaces requires an understanding of protein localization and expression. Furthermore, evidence is provided that assays capitalizing on changes in gene/protein expression and protein localization during the late stages of RPE development can prove a productive way of identifying proteins used by RPE for photoreceptor support. This approach can continue to be exploited to identify other proteins essential for the mission of the RPE cell, that may thus be likely candidates for participation in retinal degenerative disease.
Inhibitory Interactions in the Patterning of Trunk Neural Crest Migration
Authors: KRULL CATHERINE E.
Published: February 2006

ABSTRACT: In avian embryos, trunk neural crest migrate segmentally through the somites entering the rostral but not caudal somitic sclerotome. Inhibitory molecules in the caudal somite could prohibit entry of neural crest caudally, and thus restrict cell migration to rostral somite territories. Two sets of cues, peanut agglutinin (PNA) binding glycoproteins and members of the Eph family of receptor tyrosine kinases (RTKs) and their ligands appear to play this role in segmenting cell migration. Addition of exogenous PNA to neural crest migrating in trunk explants disrupts the normal segmental pattern of migration: neural crest travel in rostral and caudal regions of the somites. Members of the Eph family display the correct spatiotemporal localization to influence neural crest migration: the RTK EphB3 is expressed by neural crest, whereas the transmembrane ligand ephrin‐B1 is expressed by caudal sclerotomal cells. Exogenous ephrin‐B1 added to nerual crest migrating in trunk explants also specifically disrupts the segmental organization of neural crest migration. Isolated neural crest avoid lanes containing ephrin‐B1 in vitro; this avoidance is abolished by addition of soluble ligand. Time‐lapse imaging reveals that neural crest exhibit a typical collapse response followed by process retraction upon encountering ligand. The results of these studies implicate PNA‐binding glycoproteins and Eph family members in sculpting the migratory patterns of neural precursors in the peripheral nervous system.
Wnt Signaling Stabilizes the Dual‐Function Protein β‐Catenin in Diverse Cell Typesa
Authors: GIARRÉ MARIANNA , SEMËNOV MIKHAIL V. , BROWN ANTHONY M.C.
Published: February 2006

ABSTRACT: The Wnt proteins constitute a large family of secreted signaling factors that perform a wide variety of inductive and regulatory functions in embryonic and postnatal development. In mammals, these include crucial roles in morphogenesis of the central nervous system, kidneys, limbs, and mammary glands. In recent years, much progress has been made in identifying components of the intracellular Wnt‐1 signal transduction pathway through studies in Drosophila, C. elegans, Xenopus, and mammalian systems. Several features of this pathway are remarkably well conserved in evolution. A key component of the Wnt pathway is the cytoplasmic protein β‐catenin, whose stability is increased as a result of Wnt signaling. Although morphological effects of Wnt‐1 in cell culture are seen in only a limited number of cell lines, we show here that responsiveness to Wnt‐1 at the biochemical level is a common property of both epithelial and mesenchymal cells. The increased abundance of β‐catenin may have at least two functional consequences, depending on the subcellular localization of the protein. In some cell lines that respond to Wnt‐1, there is a significant increase in the β‐catenin fraction associated with the plasma membrane, where the protein acts as a component of cell‐cell adhesive junctions. In other cell types, the major effect of Wnt signaling is an increase in the cytosolic pool of β‐catenin. increased abundance of this pool has recently been correlated with entry of β‐catenin into the nucleus, where the protein forms complexes with Tcf transcription factors and is thought to modulate the expression of specific genes. The dual consequences of Wnt signaling on cell adhesion and/or gene expression provide at least two potential mechanisms by which this key pathway can function in the regulation of morphogenesis.
Molecular Cloning and Developmental Expression of the Xenopus Homolog of Integrin α4a
Authors: WHITTAKER CHARLES A. , DESIMONE DOUGLAS W.
Published: February 2006

ABSTRACT: Integrin receptors containing an α4 subunit mediate cell‐cell adhesion by binding to VCAM and MadCAM‐1 in addition to supporting cell‐extracellular matrix (ECM) adhesion by binding to the alternatively spliced V‐region of fibronectin (FN). Studies in chick and mouse embryos have implicated these integrins in neural crest migration, myotube formation, heart development, and placentation. Because integrin‐FN adhesive interactions have been shown to play essential roles in mammalian development, studies were initiated of integrin α4 in amphibian embryos, which are better suited to experimental analyses of the earliest stages of embryogenesis. Here, the cDNA cloning and pattern of expression of the Xenopus laevis homolog of integrin α4 is reported. Xenopusα4 is 55% identical at the amino‐acid level to both its human and mouse counterparts, including conservation of an α4‐specific protease cleavage site, 11 potential N‐linked glycosylation sites, and 24 cysteine residues. in situ hybridization analysis reveals that transcripts encoding α4 are expressed in epidermis and the branchial arches. Although α4 transcripts can be detected as early as gastrulation, the protein is observed only after tailbud stages of development and is spatially restricted to the epidermis and gills of tadpole stage embryos. From these data it is concluded that Xenopus integrin α4 has structural features in common with other vertebrate α4 homologs, but is detected in a more restricted tissue distribution during development than α4 in other species.
Endochondral Ossification Is Dependent on the Mechanical Properties of Cartilage Tissue and on Intracellular Signals in Chondrocytesa
Authors: TALTS JAN F. , PFEIFER ALEXANDER , HOFMANN FRANZ , HUNZIKER ERNST B. , ZHOU XIAO‐HONG , ASZÓDI ATTILA , FÄSSLER REINHARD
Published: February 2006

ABSTRACT: Skeletal elements are formed either by replacing a preformed cartilagenous matrix template in a process called endochondral ossification or directly from mesenchyme by a process known as membranous ossification. Longitudinal growth of bones is achieved by growth plates where calcified cartilage is converted into bone. To investigate the role of extracellular matrix as well as intracellular signaling pathways in the formation and growth of bone, the genes coding for type II collagen and cyclic guanosine 3′,5′‐monophosphate (cGMP)‐dependent protein kinase (cGK) II, were disrupted. It is demonstrated that loss of Col2a1 or cGKII led to abnormal endochondral ossification and skeletal development. In cGKII −/− mice, bones derived by membranous ossification developed normally while bones derived by endochondral ossification were shortened. This growth defect was not associated with a general metabolic disturbance. In Col2a1 knockout mice, endochondral ossification was completely absent, whereas membraneous ossification was not affected. Despite the defects in bone formation, invasion of blood vessels into bone cavities and formation of bone marrow occurred in Col2a1‐null mice. Taken together, the phenotypes of these two knockout mice show that chondrocytes need a well‐functioning extracellular matrix scaffold and a normal cGMP‐signaling system for endochondral ossification to form a normal skeleton.
β‐Catenin Directly Induces Expression of the Siamois Gene, and Can Initiate Signaling Indirectly via a Membrane‐Tethered Forma
Authors: NELSON RICHARD W. , GUMBINER BARRY M.
Published: February 2006

ABSTRACT: β‐catenin to directly induce the expression of siamois (a homeobox‐containing gene involved in axial patterning) in a cell‐autonomous, protein synthesis independent manner. Siamois can thus be considered a direct target of β‐catenin signaling in Xenopus. Expression of a portion of the armadillo repeat region of β‐catenin via a membrane‐tethered fusion protein is shown to give similar levels of siamois induction and axis duplication as a free, untethered form. Reduction of endogenous free β‐catenin levels by overexpression of C‐cadherin leads to complete inhibition of signaling by the membrane‐tethered repeat region. Since the membrane‐tethered repeat region is unlikely to be hound up by C‐cadherin, these results show that the membrane‐tethered β‐catenin relies on endogenous β‐catenin for signaling. We propose that the membrane‐tethered construct acts by titrating a cytoplasmic inhibitor of β‐catenin signaling.
The PS Integrins Are Required for a Regulatory Event during Drosophila Wing Morphogenesisa
Authors: BRABANT MARC C. , FRISTROM DIANNE , BUNCH THOMAS A. , BAKER SCOTT E. , BROWER DANNY L.
Published: February 2006

ABSTRACT: The PS1 and PS2 integrins are required for morphogenesis of the adult Drosophila wing. Clonal analysis experiments have shown that both integrins are necessary to maintain adhesion between the dorsal and ventral wing epithelia. We have found that early in wing morphogenesis, the integrins are also required for a regulatory event, and this may explain why PS1 and PS2 must be expressed on opposite surfaces of the wing at the onset of pupariation. Overexpression of integrin subunits during this early phase can lead to separation of dorsal and ventral surfaces, and we present evidence here that this dominant phenotype (the Blistermaker phenotype) results from a gain of integrin function, as opposed to negative interference from free integrin subunits. A possible model for an integrin signaling requirement in the wing is discussed.
Extracellular Matrix Remodeling during Morphogenesisa
Authors: WERB ZENA , CHIN JENNIE R.
Published: February 2006

The role of proteinases in extracellular matrix remodeling during the developmental program of bone, cartilage, muscle, and epithelial differentiation in the mandibular arch during embryogenesis was investigated. ECM changes accompany morphogenesis during development. The most dramatic changes occur during development of bone and cartilage. The expression of matrix metalloproteinases (MMPs) was altered by regulating expression of MMPs by growth factors, by inhibiting MMP activity, and by genetic ablation of MMPs. The data point to critical roles for MMPs in cartilage development and endochondral bone formation. MMPs appear to regulate not only ECM degradation but also programmed cell death, cell migration, and invasion during these morphogenic processes. The data suggest that matrix metalloproteinases play a pivotal role in the morphogenesis of structures derived from epithelium (oral sulcus), somitic mesoderm (tongue), and cranial neural crest (Meckel's cartilage).
Fibronectin and Integrins in Cell Adhesion, Signaling, and Morphogenesis
Authors: MIYAMOTO SHINGO , KATHZ BEN‐ZION , LAFRENIE ROBERT M. , YAMADA KENNETH M.
Published: February 2006

ABSTRACT: Fibronectin and integrins play crucial roles in a variety of morphogenetic processes, in which they mediate cell adhesion, migration, and signal transduction. They induce hierarchical transmembrane organization of cytoskeletal and signaling molecules into multimolecular complexes of more than 30 proteins. Organization of these complexes is a synergistic process dependent on integrin aggregation and occupancy, as well as tyrosine phosphorylation. Integrins also cooperate with growth‐factor receptors to enhance signaling. Fibronectin and integrins induce a variety of downstream effects, including enhanced transcription factor activity, induction of over 30 genes (>half novel), and altered expression of over 100 proteins. Fibronectin and integrins therefore trigger a hierarchy of signaling responses involved in regulating processes crucial for normal morphogenesis, including cell adhesion, migration, and specific gene expression.
Morphogenesis of the First Blood Vessels
Authors: DRAKE CHRISTOPHER J. , HUNGERFORD JILL E. , LITTLE CHARLES D.
Published: February 2006

ABSTRACT: The initial phase of vessel formation is the establishment of nascent endothelial tubes from mesodermal precursor cells. Development of the vascular epithelium is examined using the transcription factor TAL1 as a marker of endothelial precursor cells (angioblasts), and a functional assay based on intact, whole‐mounted quail embryos. Experimental studies examining the role(s) of integrins and vascular endothelial growth factor (VEGF) establish that integrin‐mediated cell adhesion is necessary for normal endothelial tube formation and that stimulation of embryonic endothelial cells with exogenous VEGF results in a massive “fusion” of vessels and the obliteration of normally avascular zones.

The second phase of vessel morphogenesis is assembly of the vessel wall. To understand the process by which mesenchyme gives rise to vascular smooth muscle, a novel monoclonal antibody, 1E12, that recognizes smooth muscle precursor cells was used. Additionally, development of the vessel wall was examined using the expression of extracellular matrix proteins as markers. Comparison of labeling patterns of 1E12 and the extracelllar matrix molecles fibulin‐1 and fibrillin‐2 indicate vessel wall heterogeneity at the earliest stages of development; thus smooth muscle cell diversity is manifested during the differentiation and assembly of the vessel wall. From these studies it is postulated that the extracellular matrix composition of the vessel wall may prove to be the best marker of smooth muscle diversity.

The data are discussed in the context of recent work by others, especially provocative new studies suggesting an endothelial origin for vascular smooth muscle cells. Also discussed is recent work that provides clues to the mechanism of vascular smooth muscle induction and recruitment. Based on these findings, vascular smooth muscle cells can be thought of as existing along a continuum of phenotypes. This spectrum varies from mainly matrix‐producing cells to primarily contractile cells; thus no one cell type typifies vascular smooth muscle. This view of the smooth muscle cell is considered in terms of a contrasting opinion that views smooth muscle cell as existing in either a synthetic or proliferative state.
There Is Binding of Collagen IV to β1 Integrin during Early Skin Basement Membrane Assembly
Authors: FLEISCHMAJER RAUL , PERLISH JEROME S. , MACDONALD DOUGLAS E. , SCHECHTER ALAN , MURDOCH ALAN D. , IOZZO RENATO V. , YAMADA YOSHIHIKO
Published: February 2006

ABSTRACT: This study is concerned with the mechanism of basement membrane assembly in an in vitro 3‐dimensional skin‐culture system. Dermal fibroblasts alone can synthesize collagen IV, perlecan, and nidogen, but cannot assemble them into a basement membrane. When keratinocytes are added to the culture, however, linear assembly of collagen IV, perlecan, and nidogen is noted at the epidermo‐dermal interface. Northern blots and in situ hybridization showed that perlecan and nidogen mRNAs derive exclusively from fibroblasts, while the α2 (IV) collagen chain is expressed by both keratinocytes and fibroblasts, although the major source is in the mesenchyma (80%). Prior to the development of the lamina densa, collagen IV colocalizes with α1 integrins, most likely α1β1 and α2β1, which are known receptors for this collagen. Blocking experiments with the AIIB2 mAb (anti‐β1 integrin subunit) and by peptide inhibition with the CB3(IV) collagen fragment disrupted the assembly of collagen IV. This study suggests that the initiation of basement‐membrane formation involves binding of collagen IV molecules to keratinocyte cell‐matrix integrins. These complexes act as nucleation sites for further polymerization of collagen IV molecules mostly derived from fibroblasts, by a process of self‐assembly.
Blood Perfusion Measurements in the Canine Prostate During Transurethral Hyperthermia
Authors: XU LISA X. , ZHU LIANG , HOLMES KENNETH R.
Published: February 2006

ABSTRACT: Using a thermal pulse decay technique, blood perfusion rates were measured within different regions in the canine prostate under normal and hyperthermic conditions induced either by the microwave or the radio frequency heating. Results indicate that, under the normal condition, the periurethral region is most highly perfused with an average rate of 0.60±0.25ml/min/gm (n=4) while the perfusion rate is 0.34±0.22ml/min/gm (n=10) in parenchyma. An approximately 3.5 fold increase in perfusion from the respective baselines was observed in both regions when the local tissue temperature was raised to 41.5°C by the microwave heating. Another 0.5 fold increase was found in parenchyma after the tissue was further heated to 43.1°C at which oscillatory behaviors in tissue temperature have been observed. To further study the cause of these oscillatory behaviors, the instantaneous blood perfusion response to changes in local tissue temperature was investigated using the radio frequency heating. It has been revealed that blood flow acts as a feedback of local tissue temperature in a closed control system. The thermally stimulated blood perfusion increase appeared to be a function of tissue temperature and its temporal gradient. Results from this study have shown experimental evidences of local thermoregulation in the prostate during hyperthermia.
Optimization of Temperature Distributions for Regional Hyperthermia Based on a Nonlinear Heat Transfer Modela
Authors: ERDMANN BODO , LANG JENS , SEEBASS MARTIN
Published: February 2006

ABSTRACT: We describe an optimization process specially designed for regional hyperthermia of deep seated tumors in order to achieve desired steady‐state temperature distributions. A nonlinear three‐dimensional heat‐transfer model based on temperature‐dependent blood perfusion is applied to predict the temperature. Optimal heating is obtained by minimizing an integral object function which measures the distance between desired and model predicted temperatures. Sequential minima are calculated from successively improved constant‐rate perfusion models employing a damped Newton method in an inner iteration. Numerical results for a Sigma 60 applicator are presented.
3‐D Temperature Distribution in Ultrasound Hyperthermia with Interstitial Waveguide Applicatora
Authors: JAROSZ BOGUSLAW J.
Published: February 2006

ABSTRACT: Knowledge of temperature distribution in thermal treatment of cancerous tissue is of primary importance for the therapy success. We discuss here finite element analysis approach to obtain 3‐D temperature distribution in heating with a four‐applicator array. A comparison of phantom and simulation temperatures indicated that inclusion of shear component in heating with ultrasound interstitial applicators improves significantly the simulation quality factor. We included this component in simulations of 3‐D temperature pattern when heating brain tissue with the array. The simulations for the tissue show that the perfusion remains a primary factor in defining the pattern.
Fluid Filtration across the Arterial Wall under Flow Conditions: Is Wall Shear Rate Another Factor Affecting Filtration Rate?a
Authors: DENG XIAOYAN , MAROIS YVES , GUIDOIN ROBERT
Published: February 2006

ABSTRACT: The effect of flow on fluid filtration across an arterial wall was investigated in the canine common carotid artery. The arteries were cannulated in situ to maintain their in vivo length and endothelium intact. The excised vessels were pressurized at 120 mmHg through an overflow head‐tank system that provided a constant flow rate to the perfused vessels. Filtration rates across the walls of the carotid arteries tested were measured under 4 different experimental conditions: 1) albumin‐free Krebs solution under absent flow condition; 2) albumin‐free Krebs solution with flow (148 ± 8 ml/min); 3) Krebs solution containing 1.0 g/dl bovine serum albumin under absent flow condition; 4) Krebs solution containing 1.0 g/dl bovine serum albumin with flow (148 ± 8 ml/min). Under absent flow conditions, the addition of albumin to the Krebs solution (1.0 g/dl) led to an approximate 25% drop in filtration rate (p < 0.001). It was found that fluid flow affected the filtration rate of the albumin solution, yet failed to affect the filtration rate of albumin‐free solution across the arterial wall. The present study suggests that the change in filtration rate of the albumin solution under flow condition may indicate the change in the luminal surface concentration of albumin due to flow.
Mathematical model for controlled diffusional release of dispersed solute drugs from monolithic implants
Authors: Collins R. , Jinuntuya N. , Petpirom P. , Wasuwanich S.
Published: February 2006

ABSTRACT: New mathematical models are formulated and analytical solutions are presented for the diffusional release of a solute from both non‐erodible and biodegradable multi‐layered slab matrices in which the initial drug loading c0 is greater than the solubility limit cs. A Stefan problem with moving boundaries results from this formulation. An inward moving diffusional front separates the reservoir (unextracted region) containing the undissolved drug from the partially extracted region. The cumulative mass released is determined as a function of time. The ultimate goal of such an investigation is to provide a reliable design tool for the fabrication of specialized implantable capsule/drug combinations to deliver prespecified and reproducible dosages over a wide spectrum of conditions and required durations of therapeutic treatment. Such a mathematical/computational tool may also prove effective in the prediction of suitable dosages for other drugs of differing chemical or molecular properties without additional elaborate animal testing.
Response Of A Liver Tissue Slab To An Hyperosmotic Sucrose Boundary Condition: Microscale Cellular And Vascular Level Effectsa
Authors: BHOWMICK SANKHA , KHAMIS CHAOUKI A. , BISCHOF JOHN C.
Published: February 2006

ABSTRACT: Transport of a non‐permeating CPA in liver tissue was studied by experimental and theoretical techniques. The system consisted of a 20 mm × 15 mm × 500 μm (thick) slab of liver tissue which was exposed to culture media and hyperosmotic sucrose (0.3 or 0.6 M) at the boundary. The volumetric changes of cell and vascular spaces within the tissue slab at 125μm from one of the symmetric boundaries was studied by slam freezing followed by freeze substitution microscopy. The experimental data was then theoretically investigated using two models; one based on an effective diffusion coefficient for sucrose, and another which incorporated the convective flux of water out of the cells (and the tissue) while sucrose diffuses in. We estimate the effective diffusion of sucrose as 16–33% of the actual diffusivity of sucrose in bulk water. The role of convection of water out of the tissue is against the flow of sucrose and appears to be important in reducing the effective diffusivity of the sucrose. The role of vascular compliance, porosity and tortuosity are also discussed with respect to our results.
Analysis of Mass Transport during Warming of Cryopreserved Cellsa
Authors: KASHARIN ALEXANDER V. , KARLSSON JENS O.M.
Published: February 2006

ABSTRACT: As a first step towards developing mechanistic models of damage to cryopreserved cells during the warming process, an analysis of water transport during warming was undertaken. With the aim of identifying regimes in which conventional twocompartment, membrane‐limited water transport models will be valid for predicting cell dehydration/rehydration during warming, the Peclet number was evaluated. Simulations showed that Pe » 1 during the early stages of warming, indicating that transport was rate‐limited by diffusion to and from the membrane. However, by comparing the time‐scale of transport to the time‐scale of the warming process, it was possible to identify conditions in which the membrane‐limited transport model would yield adequate predictions in diffusion‐dominated regimes. Simulations suggested that a membrane‐limited model would fail during slow warming of rapidly cooled cells, but that it would perform adequately if cooling was slow, or if warming was rapid.
Method of Designing Pre‐freezing Protocol in Cryopreservation of Biological Materials
Authors: SHIRAKASHI RYO , TANASAWA ICHIRO
Published: February 2006

ABSTRACT: Procedures of determing the pre‐freezing protocol in cryopreservation of biological materials are discussed. In order to cryopreserve biological materials, especially tissues with large sizes, the concentration of cryoprotective agents (CPAs) should be high enough after pre‐freezing process, because a high concentration CPA solution can be vitrified a rather low cooling rate. In the pre‐freezing process, the concentration of CPA is raised gradually to avoid osmotic stress. In this paper, a conventional method of designing the pre‐freezing protocol is proposed. The rate of increase of the concentration of CPA can be calculated on the basis of Kedem‐Katchalsky equations using the membrane permeabilities, Lp, w and s. Optimal protocol can be determined by calculating a process in which the normalized volume of the cell is kept constant whole through the process.
Network Thermodynamic Model of Coupled Transport in a Multicellular Tissue ‐ The Islet of Langerhansa
Authors: DE FREITAS ROBSON C. , DILLER KENNETH R. , LACHENBRUCH CHARLES A. , MERCHANT FATIMA A.
Published: February 2006

Abstract: Network thermodynamic modeling via bond graphs was used to describe the water and cryoprotectant additive (CPA) transport in a multicellular tissue. The model is presented as a tool to understand the osmotic behavior of the islets of Langerhans when exposed to ternary aqueous solutions containing an electrolyte and a CPA. It accounts for the effects of the location of cells within the tissue and an interstitial matrix, plus differential permeabilities to water and CPA. The interstitial matrix was assumed to be a porous medium able to store the chemical species being transported. Controlled osmotic stress experiments were conducted on isolated rat pancreas islets to measure the transient volumetric response to step‐wise changes in dimethyl sulfoxide, Me2SO, concentration. The model provides a tool for predicting the transient volumetric response of peripheral and interior cells and of interstitial tissue, as well as the build up of solute concentration, during addition and removal of CPAs and freezing and thawing protocols. Inverse solution methods were applied to determine values for standard cell memebrane permeability parameters Lp, ω and σ as well as for the interstitial flow conductivities Kw and Kp,.
Effects of Glycerol on Intracellular Ice Formation and Dehydration of Onion Epidermisa
Authors: TSURUTA TAKAHARU , ISHIMOTO YUKO , MASUOKA TAKASHI
Published: February 2006

ABSTRACT: Microscopic observations of freezing processes of onion epidermis have been carried out using a directional solidification stage. Effects of cryoprotectant on the intracellular ice formation and the dehydration were examined for several kinds of concentrations of glycerol in a wide range of cooling rate. With an increase of the glycerol concentration the ice formation due to the surface‐catalyzed nucleation (SCN) at the plasma membrane was suppressed and the freezing temperature decreased. Especially, under a rapid cooling condition, a large supercooling should be achieved and we observed a different type of freezing in the lower temperature conditions. At the slower cooling rate, on the other hand, the use of glycerol can not prevent the cell shrinkage caused by the dehydration. It is also found that the intracellular ice formation and the dehydration under the ordinary cooling condition can be estimated based on the SCN theory by Toner et al. and Mazuar's dehydration model.