Abstract:
The nonenzymatic glycation and crosslinking of proteins is a part of the aging process with the glycation endproducts and crosslinking of long-lived proteins increasing with age. This process is increased at elevated concentrations of reducing sugars in the blood and in the intracellular environment such as occurs with diabetes. The structural and functional integrity of the affected molecules become disturbed by these modifications and can result in severe consequences. The compounds of the present invention can be used to inhibit this process of nonenzymatic glycation and therefore to inhibit some of the ill effects caused by diabetes or by aging. The compounds are also useful for preventing premature aging, spoilage of proteins in food and can prevent discoloration of teeth.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is a continuation-in-part of application Ser. No. 09/800,976, filed Mar. 8, 2001, which is a continuation-in-part of application Ser. No. 09/543,703, filed Apr. 5, 2000, now U.S. Pat. No. 6,337,350, which is related to provisional application Serial No. 60/127,835, filed Apr. 5, 1999, which are all incorporated herein by reference. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    The present invention relates generally to the modification and aging of proteins through reaction with glucose and other reducing sugars, such as fructose or ribose and more particularly to the inhibition of nonenzymatic glycation of proteins which often results in formation of advanced glycation endproducts and crosslinks.  
           [0003]    An elevated concentration of reducing sugars in the blood and in the intracellular environment results in the nonenzymatic formation of glycation and dehydration condensation complexes known as advanced glycation end-products (AGEs). Nonenzymatic glycation is a complex series of reactions between reducing sugars and amino groups of proteins, lipids, and DNA. These complex products form on free amino groups on proteins, on lipids and on DNA (Bucala and Cerami, 1992; Bucala et al., 1993; Bucala et al., 1984). This phenomenon is called “browning” or a “Maillard” reaction and was discovered early in this century by the food industry (Maillard, 1916). The reaction is initiated with the reversible formation of Schiff&#39;s base which undergoes rearrangement to form a stable Amadori product. Both Schiffs base and Amadori product further undergo a series of reactions through dicarbonyl intermediates to form AGEs. The significance of a similar process in biology became evident only after the discovery of the glycosylated hemoglobins and their increased presence in diabetic patients (Rahbar, 1968; Rahbar et al., 1969). In human diabetic patients and in animal models of diabetes, these nonenzymatic reactions are accelerated and cause increased AGE formation and increased glycation of long-lived proteins such as collagen, fibronectin, tubulin, lens crystallin, myelin, laminin and actin, in addition to hemoglobin and albumin, and also of LDL associated lipids and apoprotein. Moreover, brown pigments with spectral and fluorescent properties similar to those of late-stage Maillard products have also been found in vivo in association with several long-lived proteins such as lens crystallin proteins and collagen from aged individuals. An age-related linear increase in pigments was observed in human dura collagen between the ages of 20 to 90 years. AGE modified proteins increase slowly with aging and are thought to contribute to normal tissue remodeling. Their level increases markedly in diabetic patients as a result of sustained high blood sugar levels and lead to tissue damage through a variety of mechanisms including alteration of tissue protein structure and function, stimulation of cellular responses through AGE specific receptors or the generation of reactive oxygen species (ROS) (for a recent review see Boel et al., 1995). The structural and functional integrity of the affected molecules, which often have major roles in cellular functions, become disturbed by these modifications, with severe consequences on affected organs such as kidney, eye, nerve, and micro-vascular functions (Silbiger et al., 1993; Brownlee et al., 1985).  
           [0004]    Structural changes on macromolecules by AGEs are known to accumulate under normal circumstances with increasing age. This accumulation is severely accelerated by diabetes and is strongly associated with hyperglycemia. For example, formation of AGE on protein in the subendothelial basement membrane causes extensive cross-link formation which leads to severe structural and functional changes in protein/protein and protein/cell interaction in the vascular wall (Haitoglou et al., 1992; Airaksinen et al., 1993).  
           [0005]    Enhanced formation and accumulation of advanced glycation end products (AGEs) have been implicated as a major pathogenesis process leading to diabetic complications, normal aging, atherosclerosis and Alzheimer&#39;s disease. This process is accelerated by diabetes and has been postulated to contribute to the development of a range of diabetic complications including nephropathy (Nicholls and Mandel, 1989), retinopathy (Hammes et al., 1991) and neuropathy (Cameron et al., 1992). Particularly, tissue damage to the kidney by AGEs leads to progressive decline in renal function, end-stage renal disease (ESRD) (Makita et al., 1994), and accumulation of low-molecular-weight (LMW) AGE peptides (glycotoxins) (Koschinsky et al., 1997) in the serum of patients with ESRD (Makita et al., 1991). These low molecular weight (LMW)-AGEs can readily form new crosslinks with plasma or tissue components, e.g., low density lipoprotein (LDL) (Bucala et al., 1994) or collagen (Miyata et al., 1993) and accelerate the progression of tissue damage and morbidity in diabetics.  
           [0006]    Direct evidence indicating the contribution of AGEs in the progression of diabetic complications in different lesions of the kidneys, the rat lens and in atherosclerosis has been reported (Vlassara et al., 1994; Vlassara et al., 1995; Horie et al., 1997; Matsumoto et al., 1997; Soulis-Liparota et al., 1991; Bucala and Vlassara, 1997; Bucala and Rahbar, 1998; Park et al., 1998). Indeed, the infusion of pre-formed AGEs into healthy rats induces glomerular hypertrophy and mesangial sclerosis, gene expression of matrix proteins and production of growth factors (Brownlee et al., 1991; Vlassara et al., 1995). Several lines of evidence indicate that the increase in reactive carbonyl intermediates (methylglyoxal, glycolaldehyde, glyoxal, 3-deoxyglucosone, malondialdehyde and hydroxynonenal) is the consequence of hyperglycemia in diabetes. “Carbonyl stress” leads to increased modification of proteins and lipids, followed by oxidant stress and tissue damage (Baynes and Thorpe, 1999; Onorato et al., 1998; McLellan et al., 1994). Further studies have revealed that aminoguanidine (AG), an inhibitor of AGE formation, ameliorates tissue impairment of glomeruli and reduces albuminuria in induced diabetic rats (Soulis-Liparota et al., 1991; Itakura et al., 1991). In humans, decreased levels of hemoglobin (Hb)-AGE (Makita et al., 1992) concomitant with amelioration of kidney function as the result of aminoguanidine therapy in diabetic patients, provides more evidence for the importance of AGEs in the pathogenesis of diabetic complications (Bucala and Vlassara, 1997).  
           [0007]    The global prevalence of diabetes mellitus, in particular in the United States, afflicting millions of individuals with significant increases of morbidity and mortality, together with the great financial burden for the treatment of diabetic complications in this country, are major incentives to search for and develop drugs with a potential for preventing or treating complications of the disease. So far the mechanisms of hyperglycemia-induced tissue damage in diabetes are not well understood. However, four pathogenic mechanisms have been proposed, including increased polyol pathway activity, activation of specific protein kinase C (PKC) isoforms, formation and accumulation of advanced glycation endproducts, and increased generation of reactive oxygen species (ROS) (Kennedy and Lyons, 1997). Most recent immunohistochemical studies on different tissues from kidneys obtained from ESRD patients (Horie et al., 1997) and diabetic rat lenses (Matsumoto et al., 1997), by using specific antibodies against carboxymethyllysine (CML), pentosidine, the two known glycoxidation products and pyrraline, have localized these AGE components in different lesions of the kidneys and the rat lens, and have provided more evidence in favor of protein-AGE formation in close association with generation of ROS to be major factors in causing permanent and irreversible modification of tissue proteins. Therefore, inhibitors of AGE formation and antioxidants hold promise as effective means of prevention and treatment of diabetic complications.  
           [0008]    The Diabetic Control and Complications Trial (DCCT), has identified hyperglycemia as the main risk factor for the development of diabetic complications (The Diabetes Control and Complications Trial Research Group, 1993). Compelling evidence identifies the formation of advanced glycation endproducts as the major pathogenic link between hyperglycemia and the long-term complications of diabetes (Makita et al., 1994; Koschinsky et al., 1997; Makita et al., 1993; Bucala et al., 1994; Bailey et al., 1998).  
           [0009]    The reactions between reducing sugars and amino groups of proteins, lipids and DNA undergo a series of reactions through dicarbonyl intermediates to generate advanced glycation endproducts (Bucala and Cerami, 1992; Bucala et al., 1993; Bucala et al., 1984).  
           [0010]    In human diabetic patients and in animal models of diabetes, AGE formation and accumulation of long-lived structural proteins and lipoproteins have been reported. Most recent reports indicate that glycation inactivates metabolic enzymes (Yan and Harding, 1999; Kato et al., 2000; Verbeke et al., 2000; O&#39;Harte et al., 2000). The glycation-induced change of immunoglobin G is of particular interest. Reports of glycation of the Fab fragment of IgG in diabetic patients suggest that immune deficiency observed in these patients may be explained by this phenomenon (Lapolla et al., 2000). Furthermore, an association between IgM response to IgG damaged by glycation and disease activity in rheumatoid arthritis has been reported (Lucey et al., 2000). Also, impairment of high-density lipoprotein function by glycation has been described (Hedrick et al., 2000).  
           [0011]    Methylglyoxal (MG) has recently received considerable attention as a common mediator and the most reactive dicarbonyl to form AGEs (Phillips and Thomalley, 1993; Beisswenger et al., 1998). It is also a source of reactive oxygen species (ROS) (free radicals) generation in the course of glycation reactions (Yim et al., 1995).  
           [0012]    Nature has devised several humoral and cellular defense mechanisms to protect tissues from the deleterious effects of “carbonyl stress” and accumulation of AGEs, e.g., the glyoxylase systems (I and II) and aldose reductase catalyze the detoxification of MG to D-lactate (McLellan et al., 1994). Amadoriases are also a novel class of enzymes found inAspergillus which catalyze the deglycation of Amadori products (Takahashi et al., 1997). Furthermore, several AGE-receptors have been characterized on the surface membranes of monocytes and on macrophage, endothelial, mesangial and hepatic cells. One of these receptors, RAGE, a member of the immunoglobulin superfamily, has been found to have a wide tissue distribution (Schmidt et al., 1994; Yan et al., 1997). The discovery of various natural defense mechanisms against glycation and AGE formation suggests an important role of AGEs in the pathogenesis of vascular and peripheral nerve damage in diabetes. MG binds to and irreversibly modifies arginine and lysine residues in proteins. MG modified proteins have been shown to be ligands for the AGE receptor (Westwood et al., 1997) indicating that MG modified proteins are analogous (Schalkwijk et al., 1998) to those found in AGEs. Furthermore, glycolaldehyde, a reactive intermediate in AGE formation, generates an active ligand for macrophage scavenger receptor (Nagai et al., 2000). The effects of MG on LDL have been characterized in vivo and in vitro (Bucala et al., 1993).  
           [0013]    Lipid peroxidation of polyunsaturated fatty acids (PUFA), such as arachidonate, also yields carbonyl compounds; some are identical to those formed from carbohydrates (Al-Abed et al., 1996), such as MG and GO, and others are characteristic of lipids, such as malondialdehyde (MDA) and 4-hydroxynonenal (HNE) (Requena et al., 1997). The latter two carbonyl compounds produce lipoxidation products (Al-Abed et al., 1996; Requena et al., 1997). A recent report emphasizes the importance of lipid-derived MDA in the cross-linking of modified collagen and in diabetes mellitus (Slatter et al., 2000). A number of AGE compounds, both fluorophores and nonfluorescent, are involved in crosslinking proteins and have been characterized (Baynes and Thorpe, 1999). In addition to glucose derived AGE-protein crosslinks, AGE crosslinking also occurs between tissue proteins and AGE-containing peptide fragments formed from AGE-protein digestion and turnover. These reactive AGE-peptides, now called glycotoxins, are normally cleared by the kidneys. In diabetic patients, these glycotoxins react with the serum proteins and are a source for widespread tissue damage (He et al., 1999). However, detailed information on the chemical nature of the crosslink structures remain unknown. The crosslinking structures characterized to date, on the basis of chemical and spectroscopic analyses, constitute only a small fraction of the AGE crosslinks which occur in vivo, with the major crosslinking structure(s) still unknown. Most recently, a novel acid-labile AGE-structure, N-omega-carboxymethylarginine (CMA), has been identified by enzymatic hydrolysis of collagen. Its concentration was found to be 100 times greater than the concentration of pentosidine (Iijima et al., 2000) and it is assumed to be a major AGE crosslinking structure.  
           [0014]    In addition to aging and diabetes, the formation of AGEs has been linked with several other pathological conditions. IgM anti-IgG-AGE appears to be associated with clinical measurements of rheumatoid arthritis activity (Lucey et al., 2000). A correlation between AGEs and rheumatoid arthritis was also made in North American Indians (Newkirk et al., 1998). AGEs are present in brain plaques in Alzheimer&#39;s disease and the presence of AGEs may help promote the development of Alzheimer&#39;s disease (Durany et al., 1999; Munch et al., 1998; Munch et al., 1997). Uremic patients have elevated levels of serum AGEs compared to age-matched controls (Odani et al., 1999; Dawnay and Millar, 1998). AGEs have also been correlated with neurotoxicity (Kikuchi et al., 1999). AGE proteins have been associated with atherosclerosis in mice (Sano et al., 1999) and with atherosclerosis in persons undergoing hemodialysis (Takayama et al., 1998). A study in which aminoguanidine was fed to rabbits showed that increasing amounts of aminoguanidine led to reduced plaque formation in the aorta thus suggesting that advanced glycation may participate in atherogenesis and raising the possibility that inhibitors of advanced glycation may retard the process (Panagiotopoulos et al., 1998). Significant deposition of N(epsilon)-carboxymethyl lysine (CML), an advanced glycation endproduct, is seen in astrocytic hyaline inclusions in persons with familial amyotrophic lateral sclerosis but is not seen in normal control samples (Kato et al., 1999; Shibata et al., 1999). Cigarette smoking has also been linked to increased accumulation of AGEs on plasma low density lipoprotein, structural proteins in the vascular wall, and the lens proteins of the eye, with some of these effects possibly leading to pathogenesis of atherosclerosis and other diseases associated with tobacco usage (Nicholl and Bucala, 1998). Finally, a study in which aminoguanidine was fed to rats showed that the treatment protected against progressive cardiovascular and renal decline (Li et al., 1996).  
           [0015]    The mechanism of the inhibitory effects of aminoguanidine in the cascade of glycosylation events has been investigated. To date, the exact mechanism of AG-mediated inhibition of AGE formation is not completely known. Several lines of in vitro experiments resulted in contrasting conclusions. Briefly, elevated concentrations of reducing sugars cause reactions between carbohydrate carbonyl and protein amino groups leading to:  
           [0016]    1. Reversible formation of Schiff&#39;s bases followed by  
           [0017]    2. Amadori condensatioii/dehydration products such as 3-deoxyglucason (3-DG), a highly reactive dicarbonyl compound (Kato et al., 1990).  
           [0018]    3. Irreversible and highly reactive advanced glycosylation endproducts. Examples of early Amadori products are ketoamines which undergo further condensation reactions to form late AGEs. A number of AGE products have been purified and characterized recently, each one constituting only minor fractions of the in vivo generated AGEs. Examples are pyrraline, pentosidine, carboxymethyl-lysine (CML), carboxyethyl-lysine (CEL), crossline, pyrrolopyridinium, methylglyoxal lysine dimer (MOLD), Arg-Lys imidazole, arginine pyridinium, cypentodine, piperidinedinone enol and alkyl, formyl, diglycosyl-pyrrole (Vlassara, 1994).  
           [0019]    Analysis of glycation products formed in vitro on a synthetic peptide has demonstrated that aminoguanidine does not inhibit formation of early Amadori products (Edelstein and Brownlee, 1992). Similar conclusions were reached by analysis of glycation products formed on BSA (Requena et al., 1993). In both experiments AGE formation was strongly inhibited by AG as analyzed by fluorescence measurements and by mass spectral analysis. The mass spectral analysis did not detect peptide complexes with molecular mass corresponding to an incorporation of AG in the complex. Detailed mechanistic studies using NMR, mass spectroscopy and X-ray diffraction have shown that aminoguani dine reacts with AGE precursor 3-DG to form 3-amino-5- and 3-amino-6-substituted triazines (Hirsch et al., 1992). In contrast, other experiments using labeled  14 C-AG with lens proteins suggest that AG becomes bound to the proteins and also reacts with the active aldose form of free sugars (Harding, 1990).  
           [0020]    Several other potential drug candidates as AGE inhibitors have been reported. These studies evaluated the agent&#39;s ability to inhibit AGE formation and AGE-protein crosslinking compared to that of aminoguanidine (AG) through in vitro and in vivo evaluations (Nakamura et al., 1997; Kochakian et al., 1996). A recent breakthrough in this field is the discovery of a compound, N-phenacylthiazolium bromide (PTB), which selectively cleaves AGE-derived protein crosslinks in vitro and in vivo (Vasan et al., 1996; Ulrich and Zhang, 1997). The pharmacological ability to break irreversible AGE-mediated protein crosslinking offers potential therapeutic use.  
           [0021]    It is well documented that early pharmaceutical intervention against the long-term consequences of hyperglycemia-induced crosslinking prevent the development of severe late complications of diabetes. The development of nontoxic and highly effective drugs that completely stop glucose-mediated crosslinking in the tissues and body fluids is a highly desirable goal. The prototype of the pharmaceutical compounds investigated both in vitro and in vivo to intervene with the formation of AGEs on proteins is aminoguanidine (AG), a small hydrazine-like compound (Brownlee et al., 1986). However, a number of other compounds were found to have such an inhibitory effect on AGE formation. Examples are D-lysine. (Sensi et al., 1993), desferrioxamine (Takagi et al., 1995), D-penicillamine (McPherson et al., 1988), thiamine pyrophosphate and pyridoxamine (Booth et al., 1997) which have no structural similarities to aminoguanidme.  
           [0022]    Clinical trials of AG as the first drug candidate intended to inhibit AGE formation are in progress (Corbett et al., 1992). A number of hydrazine-like and non-hydrazine compounds have been investigated. So far AG has been found to be the most useful with fewer side effects than other tested compounds of the prior art. AG is also a well known selective inhibitor of nitric oxide (NO) and can also have antioxidant effects (Tilton et al., 1993).  
           [0023]    A number of other potential drug candidates to be used as AGE inhibitors have been discovered recently and evaluated both in vitro and in vivo (Nakamura et al., 1997; Soulis et al., 1997). While the success in studies with aminoguanidine and similar compounds is promising, the need to develop additional inhibitors of AGEs continues to exist in order to broaden the availability and the scope of this activity and therapeutic utility.  
         SUMMARY OF THE INVENTION  
         [0024]    Derivatives of phenoxyisobutyric acids and of benzoic acid, including aryl and heterocyclic ureido derivatives and aryl and heterocyclic carboxamido derivatives, have been found to inhibit the nonenzymatic glycation of proteins which often results in formation of advanced glycation endproducts and crosslinks. Many other phenoxyisobutyric acid derivatives as well as certain other compounds as set out below also have been found to inhibit the nonenzymatic glycation of proteins. The nonenzymatic glycation and crosslinking of proteins is a part of the aging process with the glycation endproducts and crosslinking of long-lived proteins increasing with age. This process is increased at elevated concentrations of reducing sugars in the blood and in the intracellular environment such as occurs with diabetes. The structural and functional integrity of the affected molecules become disturbed by these modifications and can result in severe consequences. The compounds of the present invention can be used to inhibit this process of nonenzymatic glycation and crosslinking and therefore to inhibit some of the ill effects caused by diabetes orby aging. The compounds are also useful for preventing premature aging, rheumatoid arthritis, Alzheimer&#39;s disease, uremia, neurotoxicity, atherosclerosis, and spoilage of proteins in food and can prevent discoloration of teeth. 
       
    
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0025]    [0025]FIGS. 1 and 2 show the results for compounds LR103-115 in the post-Amadori protein assay. FIG. 1 shows the inhibition of post-Amadori AGE formation by LR103-108 at concentrations of 0.05, 0.10, 0.50, 1.00 and 5.00 mM. FIG. 2 shows the inhibition of post-Amadori AGE formation by LR109-115 at concentrations of 0.05, 0.10, 0.50, 1.00 and 5.00 mM.  
         [0026]    [0026]FIGS. 3 and 4 show examples of copper-chelating activity of some of the novel compounds including LR103, LR104, LR105 and LR106. The IC 50  of LR103 is ˜75 μM and that of LR104˜100 μM, demonstrating these compounds to be strong chelators of copper.  
         [0027]    [0027]FIGS. 5 and 6 demonstrate dicarbonyl scavenging properties for compounds LR103-LR115. FIG. 5 shows data from MGO trapping and FIG. 6 shows data from glycolaldehyde trapping activities of the compounds. These classes of compounds have both transient-metal-chelating and dicarbonyl scavenging properties.  
         [0028]    [0028]FIG. 7 shows the structure of compound LR103.  
         [0029]    [0029]FIG. 8 shows the structure of compound LR104.  
         [0030]    [0030]FIG. 9 shows the structure of compound LR105.  
         [0031]    [0031]FIG. 10 shows the structure of compound LR106.  
         [0032]    [0032]FIG. 11 shows the structure of compound LR107.  
         [0033]    [0033]FIG. 12 shows the structure of compound LR108.  
         [0034]    [0034]FIG. 13 shows the structure of compound LR109.  
         [0035]    [0035]FIG. 14 shows the structure of compound LR110.  
         [0036]    [0036]FIG. 15 shows the structure of compound LR111.  
         [0037]    [0037]FIG. 16 shows the structure of compound LR112.  
         [0038]    [0038]FIG. 17 shows the structure of compound LR113.  
         [0039]    [0039]FIG. 18 shows the structure of compound LR114.  
         [0040]    [0040]FIG. 19 shows the structure of compound LR115. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0041]    We have previously reported new classes of compounds which are aryl (and heterocyclic) ureido and aryl (and heterocyclic) carboxamido phenoxyisobutyric acids and also benzoic acid derivatives and related compounds as inhibitors of glycation and AGE formation (Rahbar et al., 1999; Rahbar et al., 2000; Rahbar et al., 2002). In the course of screening different classes of organic compounds for investigation of their possible inhibitory effects on advanced glycation endproducts (AGEs), we found that most of the phenylureido substituted phenoxy propionic acid derivatives tested have inhibitory effects and several of these compounds were potent inhibitors of AGE-formation at concentrations much lower than an equally inhibiting concentration of aminoguanidine. The aim of the present study was to develop classes of novel inhibitors of glycation, AGE formation and AGE-crosslinking and to investigate their effects through in vitro chemical and immunochemical assays. A total of 115 compounds were designed and synthesized. The first 102 compounds have been reported elsewhere. The thirteen novel compounds reported here were designed and developed based upon the previously reported LR23 (4-(3,5-dichlorophenylureido)-phenoxyisobutyryl-1-amidocyclohexane-1-carboxylic acid)) which was one of the most powerful inhibitors reported previously (Rahbar et al., 1999; U.S. Pat. No. 6,337,350 B 1 which is incorporated herein by reference). These compounds are based upon LR3 (see FIG. 20), the synthesis of which is reported in Lalezari and Lalezari (1989) which is incorporated herein. Considerable increase in the inhibitory potencies, particularly on inhibition of AGE-protein-crosslinking, were found in the compounds as compared to the prototype LR23 and are 20 to 30 times more effective. (Khalifah et al., 1999).  
         [0042]    The mechanism by which this class of compounds inhibits glycation, AGE-formation, and crosslinking is yet to be known in full. Two major mechanisms, transient-metal-chelation such as copper and iron, and scavenging or trapping of reactive carboynyl intermediates have been proposed to be responsible for AGE-inhibitory function of known AGE-inhibitors. The present study indicates that these compounds are powerful inhibitors that act at multiple steps of glycation and AGE-formation, i.e., early stage, as evidenced by lowering Hb AlC  levels in the δ-Glu assay, a specific assay for the early stage of glycation (type A or B inhibitor). Most of these compounds strongly inhibit the post-Amadori glycation as demonstrated by the BSA-glucose and G.K.-Ribose assays (type D inhibitors), and a good number of them are powerful inhibitors of AGE protein crosslinking, as evidenced by a specific ELISA assay (type E inhibitors as described by Baynes Classification (Khalifah et al., 1999).  
         [0043]    The mechanism of the inhibitory activities of guanidino compound inhibitors such as two known inhibitors of glycation (aminoguanidine and metformin) is that they are postulated to trap MG and other α-dicarbonyl intermediates of glycation. A most recent study has documented the reaction of metformin with MG and glyoxal (GO), forming guanidino-dicarbonyl adducts further supporting this idea (Ruggiero-Lopez et al., 1999).  
         [0044]    Using new assay methods specific for the early (Amadori) and late (post-Amadori) stages of glycation revealed some inhibitors to have greater effects in the early stage and some in the late stage of glycation. However, most of the inhibitor compounds we have investigated are multistage inhibitors. The reaction of reducing sugars with α- and ε-amino groups of proteins is not a random process but rather a site specific reaction which depends on the nature and the vicinity of these chemical groups. The future task is to specifically define the site and/or sites of interaction of an inhibitor compound in the complex series of reactions and intermediate substrates, leading to AGE formation and cross-linking.  
         [0045]    The development of the novel inhibitors of glycation, AGE formation, and AGE-protein crosslinking expands the existing arsenals of inhibitors of glycation reaction that can find therapeutic applications for the prevention of diabetic complications, as well as the prevention of other diseases associated with increased glycation of proteins or lipids. Furthermore, the availability of these compounds may prove useful as tools to study the cascade of reactions and intermediate substrate in the process of AGE-formation and AGE-protein cross-linking.  
         [0046]    The compounds and their useful compositions utilized in the present invention contain agents capable of reacting with the highly active carbonyl intermediate of an early glycation product thereby preventing those early products from later forming the advanced glycation endproducts which lead to protein crosslinking and to protein aging.  
         [0047]    Other utilities envisioned for the present invention are: prevention of premature aging and of spoilage of the proteins in foodstuffs (U.S. Pat. No. 5,661,139). The present agents are also useful in the area of oral hygiene as they prevent discoloration of teeth.  
         [0048]    Compounds  
         [0049]    Compounds of the present invention are shown in FIGS.  7 - 19  as LR103-LR115, and were screened for inhibitory effects on protein glycation and AGE-formation. For purposes of disclosure, the names assigned to these structures are:  
         [0050]    LR103: 1-[(4-chlorobenzyl)-3-(3,4-dichlorophenylureido)]-4-phenoxyisobutyric acid.  
         [0051]    LR104: 4-(4-fluoro-3-chlorophenylurido) phenoxyisobutyrylamidophenyl-2-carboxylic acid.  
         [0052]    LR105: 1[(2-fluoro-6-chlorobenzyl)-3-(3,4-dichlorophenyureido)]-4-phenoxyisobutyric acid.  
         [0053]    LR106: 4-(4-chlorobenzylaminophenoxyisobutyric) acid.  
         [0054]    LR107: 2-chlorobenzene-1,4-bis(4-ureidophenoxyisobutyric acid).  
         [0055]    LR108: 1-[(4-chlorobenzyl)-3-(3,5-dichlorophenyureido)]-4-phenoxyisobutyric acid.  
         [0056]    LR109: 1-[(2-fluoro-6-chlorobenzyl)-3-(2-fluoro-6-chlorophenylureido)]-4-phenoxyisobutyric acid.  
         [0057]    LR110: 4-(1,2,3,4-tetrahydroacridine-9-carboxamidophenoxyisobutyric)acid.  
         [0058]    LR111: 8-quinolinoxy acetic acid  
         [0059]    LR112: 4,4′-bis [(methyleneoxyethyleneamino)phenoxy]isobutyric acid.  
         [0060]    LR113: L-8-quinolinolyl (acetylhistidine)  
         [0061]    LR114: 4-[(3,5-dichlorophenyureido) phenoxyisobutyrylamido]-2-hydroxybenzene-4-carboxylic acid.  
         [0062]    LR115: L, α-4-[(3,5-dichlorophenyureido) phenoxyisobutyrylamido]phenylalanine.  
         [0063]    The above compounds are capable of inhibiting the formation of advanced glycation end products on target proteins and the resulting protein crosslinking. In the present invention, thirteen new compounds, which are derivatives of previously reported inhibitors of glycation and AGE formation, were investigated and also found to be inhibitors of multistage glycation, AGE formation and AGE-protein-cross-linking. An ideal agent would prevent the formation of the chromophore and its associated crosslinks of proteins and trapping of proteins on the other proteins, such as occurs in arteries and in the kidneys. The compounds of the invention may be administered to mammals including humans to prevent or reduce protein glycation and crosslinking (protein aging). The compounds may be administered orally at variable dosage depending on the activity of each agent in a single or individual amounts. In addition the compounds may be administered parenterally or rectally. The compounds of the invention, the rationale behind the different assay methods of the present invention, and their use are illustrated by the following Examples.  
       EXAMPLE 1  
     Hemoglobin-δ-Gluconolactone (δ-Glu) Assay  
       [0064]    The δ-Glu assay is a specific method for investigation of inhibitors of the early stage ofglycation. Evaluation ofearly glycation products (Amadori) formation on hemoglobin (Hb Alc ) is performed by incubating red blood cells with an oxidized form of glucose in the presence and the absence of the inhibitor compound followed by determination of Hb Alc  in the test versus the control (Rahbar and Nadler., 1999). This test is based on a report by Lindsay et al. (1997). δ-Glu, an oxidized analogue of glucose, can react rapidly with hemoglobin within the red cells and significantly increases the Hb AlC  levels within hours after incubation. By contrast, glucose requires weeks for an equivalent reaction to occur. We have used this finding to devise an assay method to measure early stage glycation of hemoglobin (Amadori product) and an assay to evaluate the ability of an inhibitor to inhibit Hb AlC  formation. Briefly, fresh blood was drawn in potassium-EDTA and prepared for incubation within 30 minutes of collection by mixing 200 μL of blood with 40 μL of either phosphate buffered-saline (PBS), pH 7.4, alone, PBS containing 50 millimoles/L δ-Glu (Sigma), or PBS containing 50 millimoles/L δ-Glu plus 1 millimole/L inhibitor. After incubation for 16 hours at 37° C., the percentage of glycated hemoglobin present was determined. The percentage of glycated Hb (Hb AlC ) was determined using a dedicated ion-exchange HPLC system (BIORAD DIAMAT). Blood samples were analyzed in triplicate. The % inhibition of Hb AlC  formation by the compound was calculated according to the following formula:  
         ((B−C)/(B−A))×100  
         [0065]    where A is Hb AlC  concentration in the baseline control tube not treated with δ-Glu, B is the HbA lC  concentration in blood incubated with δ-Glu, C is the Hb Alc  content of the test tube treated both with δ-Glu and the inhibitor compound.  
         [0066]    The amount of (Hb AlC ) formation using δ-Glu treated whole blood from normal volunteers using 1 millimole/L of the compounds was calculated. The results, calculated as percent inhibition of Hb Alc  formation, are shown in Table 1. Various inhibitors (compounds LR103-LR115) show different levels of Hb AlC  depending on their inhibitory potencies. All 13 compounds show inhibitory activity as detected by in vitro assay methods, and 9 compounds demonstrated moderate to high percent inhibition (PI) in all tests, 20 to 30 times stronger than aminoguanidme.  
                                           TABLE 1                           Percent Inhibition by LR103-LR115 in the δ-Glu Assay                Compound   Percent Inhibition                            AG   12.1           LR103   43.2           LR104   47.7           LR105   38.6           LR106   40.9           LR107   43.2           LR108   2.0           LR109   56.8           LR110   38.6           LR111   38.6           LR112   43.2           LR113   36.3           LR114   45.4           LR115   47.7                      
 
         [0067]    The above experiment suggests that this type of drug therapy has benefits in reducing the pathology associated with the formation of early glycation products, a preliminary step in the advanced glycation end product formation.  
       EXAMPLE 2  
     BSA-Glucose Assay  
       [0068]    This test is used to evaluate the ability of the inhibitors to inhibit glucose-mediated development of fluorescence of BSA (Ikeda et al., 1996). Triplicate samples of BSA (fraction V, essentially fatty acid free, low endotoxin) from Sigma 50 mg/mL and 800 mM glucose (144 mg/mL) in 1.5 M phosphate buffer pH 7.4 containing NaN 3  0.2 g/L was incubated under aseptic conditions at 37° C. for 7 days in the presence or absence of various concentrations of the compounds. After 7 days of incubation each sample was examined for the development of specific fluorescence (excitation, 330 nm; emission, 410 nm). The % inhibition of AGE formation in the test sample versus control was calculated for each inhibitor compound. Aminoguanidine (50 mM) was used as a positive control. The results are shown in Table 2.  
         [0069]    This method assays for inhibitors of late glycation and AGE formation (post-Amadori). The results show that most of the thirteen compounds investigated strongly inhibit post-Amadori glycation, AGE formation and AGE crosslinking.  
                                           TABLE 2                           Percent Inhibition by LR103-LR115 in the BSA-Glucose Assay                Compound   Percent Inhibition                            AG   74.0           LR103   4           LR104   18.4           LR105   21.5           LR106   14.4           LR107   28.7           LR108   31.1           LR109   34.6           LR110   28.5           LR111   21.6           LR112   44.7           LR113   21.5           LR114   22.7           LR115   22.3                      
 
       EXAMPLE 3  
     N-Acetyl-Glycyl-Lysine Methyl Ester (G.K. Peptide)—Ribose Assay  
       [0070]    Evaluation of the late glycation products (AGEs), and AGE-inhibition by the new inhibitor compounds was tested by incubation of G.K. peptide in ribose in the presence or the absence of the agent, followed by determination of chromophores generated in the course of glycation and AGE formation through determination of their specific fluorescence. The Nagaraj et al. (1996) method used to evaluate the ability of the compounds of the present invention to inhibit the crosslinking of N-acetylglycyl-lysine methyl ester in the presence of ribose was as follows:  
         [0071]    Stock Solutions:  
         [0072]    0.5 M sodium phosphate buffer pH 7.4 containing NaN 3  0.2 g/L  
         [0073]    GK peptide (Sigma) 80 mg/mL in 0.5 M sodium phosphate buffer pH 7.4  
         [0074]    Ribose 800 mM (120 mg/mL) in 0.5 M phosphate buffer  
         [0075]    Triplicate samples of equal volumes (0.1 mL) of the 3 stock solutions were mixed together, filtered through a 0.2 micron filter (Coming) and incubated under aseptic conditions for 24 hours at 37° C. The inhibitor compounds were added to a final concentration of 1 millimole/L. At the end of the incubation period, samples were analyzed for their specific fluorescence (excitation, 330 nm; emission, 415 nm). The % inhibition by different concentrations of inhibitor was calculated as described above. Aminoguanidine was used at 50 mM as a positive control.  
         [0076]    Table 3 shows the inhibitory effects of the compounds to block specific fluorescence of protein-AGE in these separate determinations, using G.K. peptide-ribose assay. The results of this assay show that most of the thirteen compounds investigated have strong inhibitory effects.  
                                           TABLE 3                           Percent Inhibition by LR103-LR115 in the G.K.-Ribose Assay                Compound   Percent Inhibition                            AG   67           LR103   14           LR104   0           LR105   12           LR106   10.5           LR107   19.5           LR108   19.7           LR109   9.5           LR110   11           LR111   9.7           LR112   21           LR113   11           LR114   7.2           LR115   0                      
 
       EXAMPLE 4  
     Post-Amadori Protein Assay  
       [0077]    An elaborate approach to prepare AGE-free Amadori rich proteins using ribose as sugar has been recently reported (Khalifa et al., 1999). Protein is first incubated with 0.5 M ribose for 24 hours at 37° C., following which excess free ribose is removed and Schiff bases are discharged by dialysis at 4° C. Subsequently, conversion to AGE protein is initiated by warming to 37° C. in the presence and absence of a candidate post-Amadori inhibitor. This assay was used for evaluation of the inhibitory effects to putative compounds. Briefly, AGE-free, Amardori rich proteins using BSA as protein and ribose as glycating agents was prepared according to Khalifa et al., followed by extensive dialysis at 4° C. for 24 hours against phosphate buffer. Dialysed preparation was then diluted, warmed and incubated for 7 days at 37° C. in the presence and the absence of candidate inhibitor. ELISA detection of AGE products was performed as described by Khalifa et al., except that 0.5-1 (instead of 0.3) μg of protein was coated into each polystyrene well, and Superblot buffer was used for blocking the wells. A rabbit polyclonal anti-RNase-AGE was prepared using an established protocol (Makita et al., 1992) and used at 1:1000 dilution. The results using compounds LR103-LR115 are shown in FIGS. 1 and 2.  
       EXAMPLE 5  
     Inhibition of Copper-Catalyzed Autooxidation of Ascorbic Acid  
       [0078]    This assay was performed according to Price et al. (2001). The kinetics of oxidation of ascorbic acid (AA) at the rate of decrease in absorbance at 265 nm was measured. For studies with AGE inhibitors, the ascorbic acid was added to initiate the reaction. Aliquots were removed at 0, 15, 30, 45, and 60 minutes and transferred to autoinjector vials containing DPTA. Samples were analyzed by reverse phase HPLC, (Waters 2690 Millenium 32 Separator Module), equipped with an auto-injector using Xterra™ RP18 column (250×4.6 mm, 5 μm). Solvents and gradient were all used as described in Price et al. (2001). The concentration of each inhibitor compound that inhibited the rate of AA oxidation by 50% was calculated using Prism (Graph Pad-San Diego). Examples of copper-chelating activity of some of the novel compounds are demonstrated in FIGS. 3 and 4.  
       EXAMPLE 6  
     Scavenging of Carbonyl Intermediates of AGE Formation  
       [0079]    Experimental procedures, incubation conditions, ELISA detection of CML-BSA, determination of reactive-carbonyl and dicarbonyl groups were all performed according to Voziyan et al., (2002). FIGS. 5 and 6 demonstrate dicarbonyl scavenging properties of all the compounds. FIG. 5 shows data from methylglyoxal (MGO) trapping. FIG. 6 shows data for all the compounds from glycolaldehyde trapping. The data indicate that these classes of compounds have both transient-metal-chelating and dicarbonyl scavenging properties.  
         [0080]    While the invention has been disclosed in this patent application by reference to the details of preferred embodiments of the invention, it is to be understood that the disclosure is intended in an illustrative rather than in a limiting sense, as it is contemplated that modifications will readily occur to those skilled in the art, within the spirit of the invention and the scope of the appended claims.  
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         [0185]    Patents  
         [0186]    U.S. Pat. No. 5,661,139  
         [0187]    U.S. Pat. No. 6,337,350