Role of cannabinoids and the endocannabinoid system in modulation of diabetic cardiomyopathy

Diabetic complications, chiefly seen in long-term situations, are persistently deleterious to a large extent, requiring multi-factorial risk reduction strategies beyond glycemic control. Diabetic cardiomyopathy is one of the most common deleterious diabetic complications, being the leading cause of mortality among diabetic patients. The mechanisms of diabetic cardiomyopathy are multi-factorial, involving increased oxidative stress, accumulation of advanced glycation end products (AGEs), activation of various pro-inflammatory and cell death signaling pathways, and changes in the composition of extracellular matrix with enhanced cardiac fibrosis. The novel lipid signaling system, the endocannabinoid system, has been implicated in the pathogenesis of diabetes and its complications through its two main receptors: Cannabinoid receptor type 1 and cannabinoid receptor type 2, alongside other components. However, the role of the endocannabinoid system in diabetic cardiomyopathy has not been fully investigated. This review aims to elucidate the possible mechanisms through which cannabinoids and the endocannabinoid system could interact with the pathogenesis and the development of diabetic cardiomyopathy. These mechanisms include oxidative/ nitrative stress, inflammation, accumulation of AGEs, cardiac remodeling, and autophagy. A better understanding of the role of cannabinoids and the endocannabinoid system in diabetic cardiomyopathy may provide novel strategies to manipulate such a serious diabetic complication.     

AGE, RAGE, and ROS in diabetic nephropathy

Diabetic nephropathy is a major cause of morbidity and mortality in diabetic patients. Two key mechanisms implicated in the development of diabetic nephropathy include advanced glycation and oxidative stress. Advanced glycation is the irreversible attachment of reducing sugars onto amino groups of proteins to form advanced glycation end products (AGEs). AGE modification of proteins may lead to alterations in normal function by inducing cross-linking of extracellular matrices. Intracellular formation of AGEs also can cause generalized cellular dysfunction. Furthermore, AGEs can mediate their effects via specific receptors, such as the receptor for AGE (RAGE), activating diverse signal transduction cascades and downstream pathways, including generation of reactive oxygen species (ROS). Oxidative stress occurs as a result of the imbalance between ROS production and antioxidant defenses. Sources of ROS include the mitochondria, auto-oxidation of glucose, and enzymatic pathways including nicotinamide adenine dinucleotide phosphate reduced (NAD[P]H) oxidase. Beyond the current treatments to treat diabetic complications such as the optimization of blood pressure and glycemic control, it is predicted that new therapies designed to target AGEs, including AGE formation inhibitors and cross-link breakers, as well as targeting ROS using novel highly specific antioxidants, will become part of the treatment regimen for diabetic renal disease.     

Alagebrium reduces glomerular fibrogenesis and inflammation beyond preventing RAGE activation in diabetic apolipoprotein E knockout mice

Advanced glycation end products (AGEs) are important mediators of diabetic nephropathy that act through the receptor for AGEs (RAGE), as well as other mechanisms, to promote renal inflammation and glomerulosclerosis. The relative contribution of RAGE-dependent and RAGE-independent signaling pathways has not been previously studied in vivo. In this study, diabetic RAGE apoE double-knockout (KO) mice with streptozotocin-induced diabetes were treated with the AGE inhibitor, alagebrium (1 mg/kg/day), or the ACE inhibitor, quinapril (30 mg/kg/day), for 20 weeks, and renal parameters were assessed. RAGE deletion attenuated mesangial expansion, glomerular matrix accumulation, and renal oxidative stress associated with 20 weeks of diabetes. By contrast, inflammation and AGE accumulation associated with diabetes was not prevented. However, treatment with alagebrium in diabetic RAGE apoE KO mice reduced renal AGE levels and further reduced glomerular matrix accumulation. In addition, even in the absence of RAGE expression, alagebrium attenuated cortical inflammation, as denoted by the reduced expression of monocyte chemoattractant protein-1, intracellular adhesion molecule-1, and the macrophage marker cluster of differentiation molecule 11b. These novel findings confirm the presence of important RAGE-independent as well as RAGE-dependent signaling pathways that may be activated in the kidney by AGEs. This has important implications for the design of optimal therapeutic strategies for the prevention of diabetic nephropathy.     

Glycation, glycoxidation and diabetes mellitus

Advanced glycation end-products (AGEs) result from a reaction between carbohydrates and the free amino groups of proteins, lipids, and DNA. Non enzymatic glycation, glycoxidation with glucose auto-oxidation and the polyol pathway are involved in glycated protein formation. AGEs also named glycotoxins are found in excess in pathological situations such as diabetes mellitus, renal failure, and aging or after absorption of food containing glycated products. Three major pathophysiological mechanisms are described to explain AGE toxicity, first AGEs can accumulate in the vessel wall and in collagen of different tissues; second in situ glycation is possible; third, AGEs bind to cell receptors inducing deleterious consequences. AGE receptor RAGE is a multiligand member of the immunoglobulin superfamily of cell surface molecules. AGE-receptor interaction can alter, macrophage, endothelial cell, mesangial and mesothelial cell functions and can induce inflammation. Oxidant stress, vascular hyperpermeability, vascular cell adhesion molecule-1 (VCAM-1) overexpression and monocytes chemotactic Protein-1 (MCP-1) production have been observed after cell activation by AGEs. AGEs appear to be involved in the genesis of diabetic macro but also microangiopathy such as retinopathy and glomerulosclerosis. New drugs are tested to prevent or break the AGE-protein cross-linkage, or to control the AGE-receptor interaction and their consequences. Dietary treatment, strict glycemic control and preservation of renal function remain the best approach for preventing AGE formation and limiting their deleterious effects.     

Molecular mechanisms of AGE/RAGE-mediated fibrosis in the diabetic heart

Chronic hyperglycemia is one of the main characteristics of diabetes. Persistent exposure to elevated glucose levels has been recognized as one of the major causal factors of diabetic complications. In pathologies, like type 2 diabetes mellitus(T2DM), mechanical and biochemical stimuli activate profibrotic signaling cascades resulting in myocardial fibrosis and subsequent impaired cardiac performance due to ventricular stiffness. High levels of glucose nonenzymatically react with long-lived proteins, such as collagen, to form advanced glycation end products(AGEs). AGE-modified collagen increase matrix stiffness making it resistant to hydrolytic turnover, resulting in an accumulation of extracellular matrix(ECM) proteins. AGEs account for many of the diabetic cardiovascular complications through their engagement of the receptor for AGE(RAGE). AGE/RAGE activation stimulates the secretion of numerous profibrotic growth factors, promotes increased collagen deposition leading to tissue fibrosis, as well as increased RAGE expression. To date, the AGE/RAGE cascade is not fully understood. In this review, we willdiscuss one of the major fibrotic signaling pathways, the AGE/RAGE signaling cascade, as well as propose an alternate pathway via Rap1 a that may offer insight into cardiovascular ECM remodeling in T2 DM. In a series of studies, we demonstrate a role for Rap1 a in the regulation of fibrosis and myofibroblast differentiation in isolated diabetic and non-diabetic fibroblasts. While these studies are still in a preliminary stage, inhibiting Rap1 a protein expression appears to down-regulate the molecular switch used to activate the ζ isotype of protein kinase C thereby promote AGE/RAGE-mediated fibrosis.     

Effect of irbesartan on the antioxidant defence system and nitric oxide release in diabetic rat kidney

BACKGROUND/AIMS: Increased oxidative stress is involved in the aetiology of diabetic nephropathy, and angiotensin II is reported to play a considerable role in the development of renal damage in diabetic kidney. Angiotensin antagonism can slow the progression of renal impairment in diabetes. The present study was thus designed to examine the effect of an angiotensin II type 1 (AT1) receptor antagonist, irbesartan on renal function, oxidative stress and nitric oxide (NO) release in streptozotocin (STZ)-induced diabetic rats. METHODS: Diabetes was induced by a single intraperitoneal injection of streptozotocin (65 mg/kg) in rats. After 4 weeks of STZ injection, rats were divided into four groups: the control rats, diabetic rats and diabetic rats treated with irbesartan (25 and 50 mg/kg, orally) respectively till 8 weeks starting from 4 weeks after STZ injection. Renal function was assessed by creatinine, blood urea nitrogen, creatinine clearance and urea clearance. Oxidative stress was measured by renal malondialdehyde (MDA), reduced glutathione (GSH), superoxide dismutase (SOD) and catalase. We also measured renal nitrite levels. RESULTS: At the end of the 8th week, diabetic rats exhibited renal dysfunction as evidenced by reduced creatinine and urea clearance along with enhanced albumin excretion rate as compared with control rats. Biochemical analysis of kidneys revealed a marked increase in oxidative stress demonstrated by increased lipid peroxidation and decreased activities of key antioxidant enzymes, GSH, SOD and catalase in diabetic rats. NO release was also significantly higher in diabetic rats than controls. Chronic treatment with irbesartan in diabetic rats significantly attenuated both renal dysfunction and oxidative stress along with increased NO levels as compared with untreated diabetic rats. The kidneys of diabetic rats showed morphological changes such as hyaline casts, glomerular thickening and moderate interstitial fibrosis and arteriolopathy, whereas irbesartan administration markedly prevented diabetic-induced renal morphological alterations. CONCLUSIONS: The present study suggests that oxidative stress/nitrosative stress is increased in the diabetic kidney and AT1 receptor blockade can prevent these changes. The results also suggest that in STZ-induced diabetic rats, the protective action of irbesartan might be mediated, at least in part, by its effect on tissue oxidant/antioxidant status.     

Fluvastatin suppresses oxidative stress and fibrosis in the interstitium of mouse kidneys with unilateral ureteral obstruction

BACKGROUND: Recently, we demonstrated increased oxidative stress in the interstitium of ureteral obstructed kidneys based on the increased expression of heme oxygenase-1 and immunohistochemical detection of advanced glycation end products (AGE) in the interstitium. Antioxidant therapy may have a therapeutic potential toward interstitial fibrosis of unilateral ureteral obstruction (UUO) kidneys. Fluvastatin is an HMG-CoA reductase inhibitor and has been demonstrated to have an antioxidant activity in vitro. METHODS: The effects of fluvastatin on UUO kidneys from the viewpoints of antioxidant action in vivo and antifibrosis action were studied. To investigate the antioxidant action and its therapeutic efficacy of fluvastatin in UUO kidneys, AGE accumulation and fibrosis in the obstructed kidneys was compared among vehicle-, pravastatin-, or fluvastatin-treated (10 or 40 mg/kg/day) groups. RESULTS: Tubulointerstitial fibrosis was significantly attenuated in fluvastatin-treated animals. Fluvastatin significantly suppressed the degree of immunostaining of AGE in UUO kidneys. CONCLUSIONS: These results provide evidence for the antioxidant action of fluvastatin in vivo. The decreased interstitial fibrosis along with a decreased oxidative stress marker in the interstitial lesion strongly suggests the existence of a causal relationship between them. Fluvastatin may have therapeutic value in slowing or preventing interstitial fibrosis in progressive renal disease.     

Contributions of inflammation and cardiac matrix metalloproteinase activity to cardiac failure in diabetic cardiomyopathy: the role of angiotensin type 1 receptor antagonism

We investigated the effect of the angiotensin type 1 (AT-1) receptor antagonist, irbesartan, on matrix metalloproteinase (MMP) activity and cardiac cytokines in an animal model of diabetic cardiomyopathy. Diabetes was induced in 20 C57/bl6 mice by injection of streptozotocin (STZ). These animals were treated with irbesartan or placebo and were compared with nondiabetic controls. Left ventricular (LV) function was measured by pressure-volume loops with parameters for systolic function (end systolic elastance [Ees]) and diastolic function (cardiac stiffness) 8 weeks after STZ treatment. The cardiac protein content of interleukin (IL)1beta and transforming growth factor (TGF)beta1 were measured by enzyme-linked immunosorbent assay. The total cardiac collagen content and collagen type 1 and 3 were measured by histochemistry, and MMP-2 activity was measured by gelatin zymography. LV dysfunction was documented by impaired Ees and diastolic stiffness in STZ mice compared with controls. This was accompanied by increased TGFbeta, IL1beta, and fibrosis and decreased MMP-2 activity. Treatment with irbesartan attenuated LV dysfunction, IL1beta, TGFbeta, and cardiac fibrosis compared with untreated diabetic animals and normalized MMP activity. These findings present evidence that AT-1 receptor antagonists attenuate cardiac failure by decreasing cardiac inflammation and normalizing MMP activity, leading to normalized cardiac fibrosis in STZ-induced diabetic cardiomyopathy.     

Neuropathy and the vascular-bone axis in diabetes: lessons from Charcot osteoarthropathy

Emerging evidence from the last two decades has shown that vascular calcification (VC) is a regulated, cell-mediated process orchestrated by vascular smooth muscle cells (VSMCs) and that this process bears many similarities to bone mineralization. While many of the mechanisms driving VSMC calcification have been well established, it remains unclear what factors in specific disease states act to promote vascular calcification and in parallel, bone loss. Diabetes is a condition most commonly associated with VC and bone abnormalities. In this review, we describe how factors associated with the diabetic milieu impact on VSMCs, focusing on the role of oxidative stress, inflammation, impairment of the advanced glycation end product (AGE)/receptor for AGE system and, importantly, diabetic neuropathy. We also explore the link between bone and VC in diabetes with a specific emphasis on the receptor activator of nuclear factor κβ ligand/osteoprotegerin system. Finally, we describe what insights can be gleaned from studying Charcot osteoarthropathy, a rare complication of diabetic neuropathy, in which the occurrence of VC is frequent and where bone lysis is extreme.     

Alterations in intervertebral disc composition,matrix homeostasis and biomechanical behavior in the UCD‐T2DM rat model of type 2 diabetes

Type 2 diabetes (T2D) adversely affects many tissues, and the greater incidence of discogenic low back pain among diabetic patients suggests that the intervertebral disc is affected too. Using a rat model of polygenic obese T2D, we demonstrate that diabetes compromises several aspects of disc composition, matrix homeostasis, and biomechanical behavior. Coccygeal motion segments were harvested from 6‐month‐old lean Sprague‐Dawley rats, obese Sprague‐Dawley rats, and diabetic obese UCD‐T2DM rats (diabetic for 69 ± 7 days). Findings indicated that diabetes but not obesity reduced disc glycosaminoglycan and water contents, and these degenerative changes correlated with increased vertebral endplate thickness and decreased endplate porosity, and with higher levels of the advanced glycation end‐product (AGE) pentosidine. Consistent with their diminished glycosaminoglycan and water contents and their higher AGE levels, discs from diabetic rats were stiffer and exhibited less creep when compressed. At the matrix level, elevated expression of hypoxia‐inducible genes and catabolic markers in the discs from diabetic rats coincided with increased oxidative stress and greater interactions between AGEs and one of their receptors (RAGE). Taken together, these findings indicate that endplate sclerosis, increased oxidative stress, and AGE/RAGE‐mediated interactions could be important factors for explaining the greater incidence of disc pathology in T2D. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 33:738–746, 2015.     

Highlights and Hotspots of Protein Glycation in End-Stage Renal Disease

Analysis of tissues, plasma, urine, other body fluids, and dialysate for glycation adducts has revealed the presence of two major forms: glycation adduct residues of proteins and related glycated amino acids—called glycation free adducts. The major effect on protein glycation in uremia is loss of clearance of glycation free adducts and their marked increase in plasma. Changes in glycation adduct residue content of plasma protein in uremia is, in contrast, relatively modest. There is now doubt as to whether the concept of interaction of advanced glycation endproduct (AGE)-modified proteins with putative AGE receptors can be sustained in vivo. A residual important feature of the receptor for AGEs may be decrease in expression of glyoxalase 1 of the antiglycation defence by S100A12 protein leaving the vasculature vulnerable to dicarbonyl stress and related AGE formation. The dicarbonyl proteome, proteins susceptible to dicarbonyl glycation at functional sites, is the likely mediator of glycation damage in uremia. Glycation of type IV collagen with shedding of endothelial cells and glycation of apolipoprotein B100 with increased atherogenicity of low density lipoprotein are two examples which may link protein glycation to increased risk of cardiovascular disease in end-stage renal disease.     

The next generation of diabetic nephropathy therapies: an update

Although treatments for diabetic kidney disease are available, many patients still have progressive disease. More effective therapies are urgently needed. Novel agents currently under evaluation in clinical trials are described in this review. Sulodexide, a mixture of three glycosaminoglycans, appears to prevent diabetic nephropathy in experimental models by ameliorating abnormalities in the glomerular basement membrane and mesangial matrix. Pyridoxamine is an inhibitor of advanced glycation end-product (AGE) formation derived from vitamin B(6). Alagebrium is an AGE cross-link breaker. AGEs injure the kidneys and other vascular targets by mechanisms such as oxidative stress, inflammation, and protein cross-linking, among others. By inhibiting AGE formation or breaking AGE cross-links, experimental models have demonstrated kidney protection. Ruboxistaurin is an inhibitor of protein kinase C beta (PKC-beta), a mediator of signal transduction that leads to cell growth, fibrosis, and tissue injury. In diabetes, PKC-beta is up-regulated and activated in the kidney. Ruboxistaurin prevents diabetic kidney disease in animal models. These agents have appeared promising (by reduction of albuminuria and preservation of kidney function) in phase II studies. To determine whether clinical outcomes (mortality, renal, and cardiovascular events) are improved beyond the current standard of care, phase III trials are planned.     

Amino acids injure mesangial cells by advanced glycation end products, oxidative stress, and protein kinase C

BACKGROUND: In diabetes, high intake of dietary protein exacerbates responses associated with kidney damage. Increased levels of amino acids could injure cells by providing free amino groups for glycation reactions leading to advanced glycation end products (AGEs). METHODS: Rat mesangial cells were cultured with increased amino acids designed to resemble protein feeding, high glucose (30.5 mmol/L), and, the combination, amino acids/high glucose. AGEs, reactive oxygen species (ROS), protein kinase C (PKC) activity and production, and mitogen-activated protein (MAP) kinase-extracellular signal regulated kinase (ERK) 1,2 activity were measured. Inhibitors were used to determine roles of these processes in fibrosis and/or AGE formation. RESULTS: AGE immunostaining increased when cells were cultured in amino acids and was comparable to that observed with high glucose. In amino acids/high glucose, AGE immunostaining appeared even greater. Amino acids, high glucose, and amino acids/high glucose induced ROS production. Aminoguanidine and vitamin E prevented AGE accumulation and induction of protein and mRNA for fibrosis markers [transforming growth factor-beta1 (TGF-beta1), fibronectin, and collagen IV]. PKC and ERK 1,2 activity increased with amino acids, high glucose, and amino acids/high glucose. PKC-beta inhibition prevented ERK 1,2 activation and fibrosis induction. ERK 1,2 inhibition also blocked the fibrosis response. CONCLUSION: A profibrotic injury response occurred in mesangial cells exposed to amino acids, with or without high glucose, by formation of AGE, oxidative stress, and activation of the PKC-beta and MAP kinase-ERK 1,2 signal pathway. These observations provide new insight into cellular mechanisms of kidney damage produced by excess dietary protein, particularly in diabetes.     

Candesartan reduced advanced glycation end-products accumulation and diminished nitro-oxidative stress in type 2 diabetic KK/Ta mice.

BACKGROUND: Angiotensin-II induces nitro-oxidative stress in patients with diabetic nephropathy. Peroxynitrite and reactive oxide species can accelerate formation of advanced glycation end-products (AGEs). We investigated the effects of candesartan, an angiotensin-II type 1 receptor blocker (ARB), on the formation of AGEs and nitro-oxidative stress in type 2 diabetic KK/Ta mouse kidneys. METHODS: KK/Ta mice were divided into three treatment groups: an early treatment group receiving 4 mg/kg/day candesartan from 6 to 28 weeks of age, a late treatment group receiving the same candesartan dose from 12 to 28 weeks of age and a group receiving the vehicle for candesartan. BALB/c mice treated with vehicle were used as controls. We evaluated at 28 weeks the renal expressions of carboxymethyllysine, the receptor for AGE (RAGE), the p47phox component of NADPH oxidase, endothelial nitric oxide synthase (eNOS), induced nitric oxide synthase (iNOS) and 8-OHdG and nitrotyrosine by immunohistochemistry and/or by competitive RT-PCR. RESULTS: Kidneys from KK/Ta mice showed increased formation of AGEs, nitro-oxidative stress and RAGE expression and these were attenuated by candesartan treatment. Protein and mRNA expressions of p47phox and iNOS were upregulated in KK/Ta kidneys, which also showed increased immunostaining intensities of 8-OHdG and nitrotyrosine. Treatment with candesartan attenuated all of these changes and prevented significant albuminuria. There were no significant differences in the expression of eNOS among the four groups. CONCLUSIONS: These findings suggest that candesartan, an ARB, reduces AGE accumulation and subsequent albuminuria by down-regulating the NADPH oxidase p47phox component and iNOS expression and by attenuating RAGE expression in type 2 diabetic KK/Ta mouse kidneys.     

Diet, inflammation, and chronic kidney disease: getting to the heart of the matter

Cardiovascular disease (CVD) remains a leading cause of death in patients with chronic kidney disease (CKD). CVD is now thought to result from the interplay of several factors including inflammation, oxidative stress and endothelial dysfunction. Advanced glycation end products (AGE) are known to be elevated in patients with CKD and these compounds possess these pro-oxidant, pro-inflammatory and anti-endothelial properties. There has been a great deal of literature linking diet and inflammation, and recent work has shown the diet to be a significant contributor to the body's AGE pool. We herein hypothesize that a diet high in AGE plays an important role in the initiation of chronic subclinical inflammation that seems to underlie the high prevalence of CVD in CKD patients. Herein we will briefly examine the evidence linking different components of diet with inflammation in CKD patients. We will then focus on the role of dietary AGEs in inflammation and potentially CVD in CKD, and in conclusion, we will propose dietary modifications as part of a multifactorial approach to ameliorate unhealthy lifestyles among CKD patients. The most important message is that simple changes in culinary technique rather than in the food nutrient composition may be the most important part of preventing CVD in this population.     

The effects of valsartan on the accumulation of circulating and renal advanced glycation end products in experimental diabetes

BACKGROUND: Blockade of the RAS with the ACE inhibitor ramipril prevents the accumulation of advanced glycation end products (AGEs) in experimental diabetes. Although AT1 receptor antagonists may inhibit AGE formation in vitro, their effect in normotensive animals with type 1 diabetes has not been established. METHODS: Streptozotocin-induced diabetic and control animals were randomized (N=10/group) to receive the AT1 antagonist valsartan at a dose of 30 mg/kg/day by oral gavage for 24 weeks, or no intervention. Renal and plasma AGE accumulation was correlated with renal functional parameters. RESULTS: Valsartan reduced the albumin excretion rate consistent with its renoprotective effects. Renal and skin collagen accumulation of the non-fluorescent AGE carboxymethyllysine (CML) were increased in animals with diabetes, but normalized following treatment with valsartan. Renal fluorescence and skin collagen pentosidine levels were also increased by diabetes. However, valsartan only provided a modest attenuation of these parameters. In addition, diabetes was associated with increased plasma fluorescence, which was unaffected by AT1 antagonism. CONCLUSION: Renoprotective doses of valsartan are associated with a significant reduction in the accumulation of tissue and plasma CML. These effects were not the same for all AGEs, suggesting combination approaches will be required to optimize renoprotection in diabetes.     

Pyridoxal phosphate prevents progression of diabetic nephropathy.

BACKGROUND: We have demonstrated that pyridoxal 5'-phosphate (PLP), an active form of vitamin B6, inhibits formation of advanced glycation end-products (AGEs) by trapping 3-deoxyglucosone. The present study aimed to clarify if PLP could exert beneficial effects on nephropathy in diabetic rats. METHODS: Streptozotocin (STZ)-induced diabetic rats were treated by oral administration of PLP or pyridoxamine (PM), another active form of vitamin B6, at a dose of 600 mg/kg/day for 16 weeks. AGEs [imidazolone, N(epsilon)-(carboxymethyl)lysine (CML) and N(2)-carboxyethyl-2'-deoxyguanosine (CEdG)], transforming growth factor-beta1 (TGF-beta1), type 1 collagen and fibronectin were detected in the kidneys using immunohistochemistry. Gene expression of TGF-beta1 and receptor for AGEs (RAGEs) in the kidneys was determined using real-time quantitative polymerase chain reaction. RESULTS: Administration of PLP significantly inhibited albuminuria, glomerular hypertrophy, mesangial expansion, and interstitial fibrosis as compared with diabetic rats. PLP markedly inhibited accumulation of AGEs such as imidazolone, CML and CEdG, a DNA-linked AGE, in glomeruli. PLP significantly inhibited expression of TGF-beta1, type 1 collagen, fibronectin and RAGE in the kidneys. PLP was superior to PM in inhibiting accumulation of AGEs, expression of TGF-beta1, type 1 collagen, and fibronectin, and the development of diabetic nephropathy. CONCLUSIONS: PLP prevented progression of nephropathy in STZ-induced diabetic rats by inhibiting formation of AGEs. PLP is considered a promising active form of vitamin B6 for the treatment of AGE-linked disorders such as diabetic nephropathy.