Samuel Rahbar

Previous studies have shown that LR-90, a new inhibitor of AGE formation, prevented the development of experimental type 1 diabetic nephropathy. In this study, we examined the effects of LR-90 in the Zucker diabetic fatty (ZDF) rat, a model of type 2 diabetes and metabolic syndrome, and investigated the mechanisms by which it may protect against renal injury.

Accelerated formation of advanced glycation/lipoxidation and endproducts (AGEs/ALEs) has been implicated in the pathogenesis of various diabetic complications. Several natural and synthetic compounds have been proposed and tested as inhibitors of AGE/ALE formation. We have previously reported the therapeutic effects of several new AGE/ALE inhibitors on the prevention of nephropathy and dyslipidemia in streptozotocin (STZ)-induced diabetic rats. In this study, we investigated the effects of various concentrations of a compound, LR-90, on the progression of renal disease and its effects on AGE and receptor for AGE (RAGE) protein expression on the kidneys of diabetic STZ-rats. Diabetic male Sprague–Dawley rats were treated with or without LR-90 (0, 5, 20, 25, and 50 mg/l of drinking water). After 32 weeks, body weight, glycemic status, renal function, and plasma lipids were measured. Kidney histopathology and AGE/ALE accumulation and RAGE protein expression in tissues were also determined. In vitro studies were also performed to determine the possible mechanism of action of LR-90 in inhibiting AGE formation and AGE-protein cross-linking. LR-90 protected the diabetic kidneys by inhibiting the increase in urinary albumin-to-creatinine ratio and ameliorated hyperlipidemia in diabetic rats in a concentration-dependent fashion without any effects on hyperglycemia. LR-90 treatment also reduced kidney AGE/ALE accumulation and RAGE protein expression in a concentration-dependent manner. In vitro, LR-90 exhibited general antioxidant properties by inhibiting metal-catalyzed reactions and reactive oxygen species (^·OH radical) and reactive carbonyl species (methlyglyoxal, glyoxal) generations without any effect on pyridoxal 5′ phosphate. The compound also prevents AGE-protein cross-linking reactions. These findings demonstrate the bioefficacy of LR-90 in treating nephropathy and hyperlipidemia in diabetic animals by inhibiting AGE accumulation, RAGE protein expression, and protein oxidation in the diabetic kidney. Additionally, our study suggests that LR-90 may be useful also to delay the onset and progression of diabetic atherosclerosis as the compound can inhibit the expression of RAGE and inflammation-related pathology, as well as prevent lipid peroxidation reactions.

Ligation of advanced glycation end products (AGEs) with their receptor (RAGE) plays an important role in the development of various diabetes complications, including atherosclerosis. Monocyte activation, adhesion, and migration are key events in the pathogenesis of atherosclerosis. Previous studies showed that AGEs and S100b, a specific RAGE ligand, could augment monocyte inflammatory responses via RAGE. In this study, we examined whether LR-90, a compound belonging to a new class of AGE inhibitor, could inhibit inflammatory responses in human monocytes. Human THP-1 cells were pretreated with LR-90 and then stimulated with S100b. LR-90 significantly inhibited S100b-induced expression of RAGE and other proinflammatory genes including monocyte chemoattractant protein-1, interferon-γ–inducible protein-10, and cyclooxygenase-2 in a dose-dependent manner. These inhibitory effects may be exerted via inhibition of nuclear factor-κB (NF-κB) activation, as LR-90 suppressed both S100b–and tumor necrosis factor-α–induced IκB-α degradation as well as NF-κB promoter transcriptional activity. LR-90 also prevented oxidative stress in activated monocytes, as demonstrated by its inhibitory effects on S100b-induced expression of NADPH oxidase and intracellular superoxide production. In addition, LR-90 blocked S100b-induced monocyte adhesion to human umbilical vein endothelial cell. These new data show that, in addition to its AGE inhibitory effects, LR-90 has novel anti-inflammatory properties and might therefore have additional protective effects against diabetic vascular complications.

Background Increased formation of advanced glycation/lipoxidation endproducts (AGEs/ALEs) has been implicated in the pathogenesis of various diabetic complications. Several compounds have been developed as inhibitors of AGE/ALE formation. We examined the effects of two new AGE/ALE inhibitors, LR‐9 and LR‐74, on the development of early renal disease and lipid metabolism in streptozotocin (STZ)‐induced diabetic rats. Methods Diabetic Sprague–Dawley rats were treated with either of the LR compounds for 32 weeks. Progression of renal disease was evaluated by measurements of urinary albumin and plasma creatinine concentrations. AGE/ALE and nitrotyrosine levels in kidneys were determined by immunohistochemistry. AGE‐induced chemical modification of the tail tendon collagen and levels of N^ε‐(carboxymethyl) and (carboxyethyl)‐ lysines (CML and CEL) in skin collagen were measured. Plasma lipids and their lipid hydroperoxide concentrations were also determined. In vitro, both compounds were tested for inhibiting lipid peroxidation reactions. Results Treatment of either LR compounds significantly inhibited the increase in albuminuria, creatinaemia, hyperlipidaemia and lipid peroxidation in diabetic rats without any effect on hyperglycaemia. Both compounds also reduced CML‐AGE and nitrotyrosine accumulation in kidney glomeruli and tubules, AGE‐linked fluorescence and cross‐linking of tail collagen, and levels of CML and CEL in skin collagen. In vitro, LR compounds inhibited the oxidation of human low‐density lipoprotein (LDL). Conclusion Both compounds can inhibit the progression of renal disease and also prevent dyslipidaemia in type‐1 diabetic animals. These compounds may have an additional beneficial effect as an antioxidant against lipid peroxidation, and thus may provide alternative therapeutic options for the treatment of various diabetic macrovascular complications. Copyright © 2005 John Wiley & Sons, Ltd.

Abstract: The accelerated formation of advanced glycation/lipoxidation end products (AGEs/ALEs) has been implicated in the pathogenesis of various diabetic complications. Several natural and synthetic compounds have been proposed and advanced as inhibitors of AGE/ALE formation. We examined the effects of two new AGE/ALE inhibitors, LR‐9 and LR‐74, on the prevention of early renal disease and dyslipidemia in streptozotocin (STZ)‐induced diabetic rats. Diabetic rats were treated with either LR‐9 or LR‐74 for 32 weeks. Progression of renal disease was evaluated by measurements of urinary albumin and plasma creatinine concentrations. AGE‐induced chemical modification of the tail tendon collagen and levels of N^ε‐(carboxymethyl)‐ and (carboxyethyl)‐ lysines (CML and CEL) in skin collagen were measured. AGE/ALE levels in kidneys were determined by immunohistochemistry. Plasma lipids and their lipid hydroperoxide concentrations were also determined. Treatment of either LR‐9 or LR‐74 significantly inhibited the increase in albuminuria, plasma creatinine, hyperlipidemia, and plasma lipid peroxidation in diabetic rats without any effects on hyperglycemia. Both compounds also reduced CML‐AGE accumulation in kidney glomeruli and tubules, AGE‐linked fluorescence and cross‐linking of tail collagen, and levels of CML and CEL in skin collagen. These results suggest that both LR compounds can inhibit the progression of renal disease and also prevent dyslipidemia in experimental diabetes. These compounds may have an additional beneficial effect as an antioxidant against lipid peroxidation, and thus may provide alternative therapeutic options for the treatment of various diabetic macrovascular complications.

Abstract: Glycated hemoglobins are minor components of human hemoglobin (Hb). These are formed nonenzymatically by condensation of glucose or other reducing sugars with α‐ and β‐chains of hemoglobin A. The subfraction HbA_1c, a nonenzymatic glycation at the amino‐terminal valines of the β‐chain, was identified by the author in the 1960s as a minor “abnormal fast‐moving hemoglobin band” in diabetic patients during routine screening for hemoglobin variants. This finding later turned out to be an important biomolecular marker with clinical and pathological applications. Measurement of HbA_1c in diabetic patients is an established procedure for evaluating long‐term control of diabetes, and the introduction of this measurement represents an outstanding contribution to the quality of care of diabetic patients in this century. More importantly, HbA_1c is the first example of in vivo nonenzymatic glycation of proteins, and its discovery opened new and still‐growing avenues of research on Maillard reactions in biological systems, including the concept of advanced glycation/lipoxidation end products (AGEs/ALEs) and the development of diabetic complications and various diseases associated with aging. Although interest in the Maillard reaction is growing rapidly, much remains to be done in this field, including detection and characterization of all in vivo AGEs/ALEs, development and clinical applications of AGE inhibitors and breakers, as well as investigations into the possible roles of the Maillard reaction in regulatory biology and carcinogenesis.

Advanced glycation and lipoxidation endproducts have been implicated in the pathogenesis of diabetic complications, including diabetic nephropathy. LR-90, a new advanced glycation endproduct inhibitor, was investigated for its effects on the development of renal disease in diabetic rats.