Role of advanced glycation end products in diabetic neuropathy

Diabetic neuropathy is the commonest form of peripheral neuropathy in the developed countries of the world. In diabetic patients, the presence of peripheral neuropathy increases their risks for developing foot ulceration and subsequent necrosis that necessitates lower limb amputation. Although the precise mechanisms underlying diabetic neuropathy remain unclear, there is evidence that hyperglycemia-induced formation of advanced glycation end products (AGEs) is related to diabetic neuropathy; AGE-modified peripheral nerve myelin is susceptible to phagocytosis by macrophages and contributes to segmental demyelination; modification of major axonal cytoskeletal proteins such as tubulin, neurofilament, and actin by AGEs results in axonal atrophy/degeneration and impaired axonal transport; and glycation of extracellular matrix protein laminin leads to impaired regenerative activity in diabetic neuropathy. Recently, the receptor for AGEs (RAGE) has been found to colocalize with AGEs in diabetic peripheral nerves. This suggests that, in diabetic neuropathy, AGEs and AGE/RAGE interactions induce oxidative stress, result in upregulation of nuclear factor (NF)-kappaB and various NF-kappaB-mediated proinflammatory genes, and exaggerate neurological dysfunction, including altered pain sensation. Additionally, AGE/RAGE-induced oxidative stress further accelerates formation of glycoxidation products such as Nepsilon-(carboxymethyl)lysine and pentosidine. Although new drugs that inhibit the formation of AGEs and block the AGE-RAGE interaction are being studied, no effective treatment modalities against AGE-induced nerve injury are currently available clinically. A therapeutic strategy to prevent and ameliorate diabetic neuropathy using anti-AGE agents needs to be established. In this review, the current issues involved in the role of the glycation process and the potential treatment options for diabetic neuropathy are explored.     

Involvement of hypoxia-inducible factor-1α in the oxidative stress induced by advanced glycation end products in murine Leydig cells

Hyperglycemia increases the formation of advanced glycation end products (AGEs), triggers oxidative impairments and influences inducible factor (HIF)-1α protein levels and transactivation function. Compromised HIF-1α in testis leads to male infertility. The aim of the study was to investigate the role of HIF-1α in oxidative stress induced by AGEs in murine Leydig TM3 cells. TM3 cells were treated with 50 μg/ml of AGEs, or HIF-1α siRNA or 500 μM of DMOG (dimethyloxalylglycine) respectively. The cells were also pretreated with HIF-1α siRNA or 500 μM of DMOG and then were treated with 50 μg/ml of AGEs. The formation of reactive oxygen species (ROS) and cell apoptosis was evaluated. The expression of caspase-3, Heme oxygenase (HO)-1, steroidogenic acute regulatory protein (StAR) and cytochrome P450 17α polypeptide 1 (CYP17A1) was examined by Western blotting. AGEs increased ROS production, induced apoptosis and activated HIF-1α and HO-1 in TM3 cells. HIF-1α attenuated the AGE-induced ROS formation and promoted apoptosis via the upregulation of caspase-3. Knockdown of HIF-1α inhibited the expression of CYP17A1 and StAR, and enhanced the inhibition of StAR and CYP17A1 by AGEs. These findings indicate that attenuated HIF-1α exacerbates the oxidative stress injury by AGEs in murine Leydig cells, and contributes to diabetic male infertility.     

Advanced lipid peroxidation end products in oxidative damage to proteins. Potential role in diseases and therapeutic prospects for the inhibitors

Reactive carbonyl compounds (RCCs) formed during lipid peroxidation and sugar glycoxidation, namely Advanced lipid peroxidation end products (ALEs) and Advanced Glycation end products (AGEs), accumulate with ageing and oxidative stress-related diseases, such as atherosclerosis, diabetes or neurodegenerative diseases. RCCs induce the 'carbonyl stress' characterized by the formation of adducts and cross-links on proteins, which progressively leads to impaired protein function and damages in all tissues, and pathological consequences including cell dysfunction, inflammatory response and apoptosis. The prevention of carbonyl stress involves the use of free radical scavengers and antioxidants that prevent the generation of lipid peroxidation products, but are inefficient on pre-formed RCCs. Conversely, carbonyl scavengers prevent carbonyl stress by inhibiting the formation of protein cross-links. While a large variety of AGE inhibitors has been developed, only few carbonyl scavengers have been tested on ALE-mediated effects. This review summarizes the signalling properties of ALEs and ALE-precursors, their role in the pathogenesis of oxidative stress-associated diseases, and the different agents efficient in neutralizing ALEs effects in vitro and in vivo. The generation of drugs sharing both antioxidant and carbonyl scavenger properties represents a new therapeutic challenge in the treatment of carbonyl stress-associated diseases.     

Inhibitors of the Maillard reaction and AGE breakers as therapeutics for multiple diseases

The Maillard reaction is a complex series of reactions that involve reducing-sugars and proteins, giving a multitude of end-products that are known as advanced glycation end-products (AGEs). AGEs can contribute to the pathogenesis of diabetes and neurological diseases such as Alzheimer's disease. AGEs also play a major role in vascular stiffening, atherosclerosis, osteoarthritis, inflammatory arthritis and cataracts. Thus, AGE inhibitors and AGE breakers offer a potential strategy as therapeutics for diverse diseases. Various AGE inhibitors have been developed in recent years, and their underlying mechanism is based on the attenuation of glycoxidation and/or oxidative stress by the sequestration of metal ions, reactive 1,2-dicarbonyl compounds, and reactive oxygen and reactive nitrogen species.     

The clinical relevance of advanced glycation endproducts (AGE) and recent developments in pharmaceutics to reduce AGE accumulation

Advanced glycation endproducts (AGE) are a class of compounds resulting from glycation and oxidation of proteins, lipids or nucleic acids. Glycation is the non-enzymatic addition or insertion of saccharide derivatives to these molecules. This leads to the formation of intermediary Schiff bases and Amadori products and finally to irreversible AGE. This classical view has been modified in recent years with recognition of the importance of oxidative and carbonyl stress in endogenous AGE formation. AGE may also have exogenous sources, in certain foods and tobacco smoke. A whole class of specific and non-specific receptors binding AGE has been characterized. Apart from cross-linking of proteins by AGE, the effects of receptor stimulation contribute to the development of chronic complications of conditions like diabetes mellitus, renal failure, and atherosclerosis. Possible interventions to reduce the effects of AGE accumulation include AGE formation inhibitors or breakers, or receptor blockers, but possibly also dietary interventions. Some of the problems with current assay or diagnostic techniques, and several unresolved issues on the role of AGE in disease will be discussed. Our review will focus on the clinical and pharmaceutical implications of these developments.     

The role of AGEs in cardiovascular disease

Advanced glycation end-products (AGEs) are generated in the diabetic milieu, as a result of chronic hyperglycemia and enhanced oxidative stress. These AGEs, via direct and receptor dependent pathways promote the development and progression of cardiovascular disease. AGEs accumulate at many sites of the body including the heart and large blood vessels in diabetes. These modified proteins interact with receptors such as RAGE to induce oxidative stress, increase inflammation by promoting NFkappaB activation and enhance extracellular matrix accumulation. These biological effects translate to accelerated plaque formation in diabetes as well as increased cardiac fibrosis with consequent effects on cardiac function. Strategies to reduce the ligation of AGEs to their receptors such as agents which reduce AGE accumulation, soluble RAGE which acts as a competitive antagonist to the binding of AGEs to RAGE and genetic deletions of RAGE appear to attenuate diabetes associated atherosclerosis. Benefits on cardiac dysfunction with these inhibitors of the AGE/RAGE axis are not as well characterised. In conclusion, therapeutic strategies targeting AGEs appear to have significant clinical potential, often in combination with currently used agents such as inhibitors of the renin-angiotensin system, to reduce the major burden of diabetes, its associated cardiovascular complications.     

Novel therapeutics for diabetic micro- and macrovascular complications

Diabetic patients have a two- to four-fold increased risk for the development of microvascular (renal, neuronal and retinal) and macrovascular complications. Unfortunately, these complications may develop in both Type 1 and Type 2 diabetic patients even with careful glycaemic, blood pressure and lipid control. With the worldwide increase in the incidence diabetes, new strategies to prevent the complications are urgently needed. Mediators of vascular damage of diabetes include poor glycemic control, lipoprotein abnormalities, hypertension, oxidative stress, inflammation and advanced glycation end-products (AGEs), which are modified proteins formed by non-enzymatic glycation. AGEs are resistant to enzymatic degradation and therefore very stable, thus their accumulation continues throughout aging. AGE accumulation causes arterial stiffening in the vessel wall, glomerulosclerosis in the kidney, and vascular hyperpermeability in the retina. Through their interaction with their putative receptor the so-called receptor for AGEs (RAGE), AGEs activate endothelial cells and macrophages, generate reactive oxygen species (ROS), induce overexpression of vascular endothelial growth factor (VEGF) and vascular cell adhesion molecule-1 (VCAM-1), and quench nitric oxide (NO). The pharmacological treatment currently available for either Type 1 or Type 2 diabetic patients does not directly address the excess accumulation of AGEs. Novel compounds that inhibit AGE formation, cleave AGE cross-links or reverse their interaction with RAGE are now accessible and could prove useful in meeting this challenge. Other strategies such as inhibition of the hexosamine pathway, vitamin therapy to reduce oxidation and AGE accumulation, reduction of the ROS, or blocking the actions of growth factors or intracellular messengers of cell differentiation are also currently under research. This review will recount recent advances in the development of therapeutic approaches for inhibiting and treating the development of diabetic end-organ damage.     

Inhibitory effects of amlodipine and fluvastatin on the deposition of advanced glycation end products in aortic wall of cholesterol and fructose-fed rabbits

Recent studies suggest that advanced glycation end products (AGEs) can promote the development of atherosclerotic lesions in a similar manner to oxidatively modified low density lipoproteins. As oxidative stress accelerates the formation of AGEs, antioxidant drugs may exert atheroprotective effects via suppression of AGE formation. Although amlodipine, a calcium channel blocker, and fluvastatin, a 3-hydroxy-3-methylglutaryl CoA reductase inhibitor, show antioxidant and atheroprotective effects, the relation of AGEs to their effects is unknown. We immunohistochemically investigated the inhibitory effects of chronic treatment with amlodipine (5 mg/kg per day) or fluvastatin at a dose insufficient to reduce plasma cholesterol levels (2 mg/kg per day) on the accumulation of AGEs in atherosclerotic aortas of rabbits fed 1% cholesterol diet and 10% fructose containing water. After eight weeks of treatment, AGEs, namely argpyrimidine, carboxymethyllysine and pyrraline, markedly accumulated with intimal thickening in cholesterol and fructose-fed control rabbits, while the drugs inhibited those changes other than the pyrraline deposition without plasma lipid-lowering effects. Enhanced lipid peroxidation was observed in plasma from cholesterol and fructose-fed rabbits only, and lipid peroxidation was not suppressed by the drugs. These results suggest that the atheroprotective effects of the drugs are at least partly due to the suppression of AGE accumulation although the exact mechanism of AGE suppression is ambiguous.     

Curcumin inhibits gene expression of receptor for advanced glycation end-products (RAGE) in hepatic stellate cells in vitro by elevating PPARγ activity and attenuating oxidative stress

BACKGROUND AND PURPOSE

Diabetes is characterized by hyperglycaemia, which facilitates the formation of advanced glycation end-products (AGEs). Type 2 diabetes mellitus is commonly accompanied by non-alcoholic steatohepatitis, which could lead to hepatic fibrosis. Receptor for AGEs (RAGE) mediates effects of AGEs and is associated with increased oxidative stress, cell growth and inflammation. The phytochemical curcumin inhibits the activation of hepatic stellate cells (HSCs), the major effectors during hepatic fibrogenesis. The aim of this study was to explore the underlying mechanisms of curcumin in the elimination of the stimulating effects of AGEs on the activation of HSCs. We hypothesize that curcumin eliminates the effects of AGEs by suppressing gene expression of RAGE.

EXPERIMENTAL APPROACH

Gene promoter activities were evaluated by transient transfection assays. The expression of rage was silenced by short hairpin RNA. Gene expression was analysed by real-time PCR and Western blots. Oxidative stress was evaluated.

KEY RESULTS

AGEs induced rage expression in cultured HSCs, which played a critical role in the AGEs-induced activation of HSCs. Curcumin at 20 µM eliminated the AGE effects, which required the activation of PPARγ. In addition, curcumin attenuated AGEs-induced oxidative stress in HSCs by elevating the activity of glutamate-cysteine ligase and by stimulating de novo synthesis of glutathione, leading to the suppression of gene expression of RAGE.

CONCLUSION AND IMPLICATIONS

Curcumin suppressed gene expression of RAGE by elevating the activity of PPARγ and attenuating oxidative stress, leading to the elimination of the AGE effects on the activation of HSCs.

LINKED ARTICLE

This article is commented on by Stefanska, pp. 2209–2211 of this issue. To view this commentary visit http://dx.doi.org/10.1111/j.1476-5381.2012.01959.x     

Protection against advanced glycation end products and oxidative stress during the development of diabetic keratopathy by KIOM-79

Objectives KIOM‐79 is a mixture of 80% ethanol extracts of parched Puerariae radix, gingered Magnoliae cortex, Glycyrrhizae radix and Euphorbiae radix. The preventive effect of KIOM‐79 on the development of diabetic keratopathy has been investigated. Methods Seven‐week‐old male Zucker diabetic fatty (ZDF) rats were treated with KIOM‐79 (50 mg/kg body weight) once a day orally for 13 weeks. The thickness of the cornea was measured and the extent of corneal cell death was detected by a terminal deoxynucleotidyl transferase dUTP nick‐end labelling assay. The expression of advanced glycation end products (AGEs), 8‐hydroxydeoxyguanosine, nuclear factor‐kappaB (NF‐κB), Bax and Bcl‐2 were evaluated in corneal tissues. Key findings The administration of KIOM‐79 prevented corneal oedema and apoptotic cell death of corneal cells. The accumulation of AGE in corneal tissues was reduced in ZDF rats treated with KIOM‐79. Moreover, KIOM‐79 attenuated oxidative DNA damage, NF‐κB activation and Bax overexpression in the cornea. Conclusions The results suggested that KIOM‐79 exhibited corneal protective properties by not only reducing oxidative stress but inhibiting the AGEs/NF‐κB downstream signal pathway during the development of diabetic keratopathy.     

Agents that block advanced glycation end product (AGE)-RAGE (receptor for AGEs)-oxidative stress system: a novel therapeutic strategy for diabetic vascular complications

Background: Diabetic vascular complications are leading causes of acquired blindness, end-stage renal failure, a variety of neuropathies, and accelerated atherosclerosis, which together could account for disabilities and high mortality rates in patients with diabetes. Since there is accumulating evidence that the advanced glycation end product (AGE)–RAGE (receptor for AGEs)–oxidative stress axis is involved in diabetic vascular complications, inhibition of the AGE–RAGE system may be a promising target for therapeutic intervention in these devastating disorders. Objective: In this review, we discuss several types of agent that may be able to inhibit the AGE–RAGE–oxidative stress system, and their therapeutic implications in vascular complications in diabetes. Methods: We have analyzed currently available scientific literature in the field of AGE–RAGE to create a comprehensive review on novel therapeutic agents for vascular complications in diabetes. Results/conclusion: Inhibition of AGE formation, blockade of the AGE–RAGE interaction, and suppression of RAGE expression or its downstream pathways may be novel therapeutic strategies for the treatment of vascular complications in diabetes.     

Oxidative damage in the liver of rats treated with glycolaldehyde

Liver diseases are often associated with hyperglycemia, inflammation, and oxidative stress. These conditions, commonly associated with diabetes mellitus and obesity, facilitate the formation of advanced glycation end products (AGEs). These products are known to impair protein function and promote inflammation. Accumulation of AGEs such as N(ε)-(carboxymethyl)lysine (CML) is related to chronic liver diseases and their severity. Although several reports suggest a crucial role of AGEs in liver failure, there is little investigation on the direct effects of reducing sugars, precursors of AGEs, and on the onset and progression of liver failure. In this work, we investigate the effects of intravenously administrated glycolaldehyde (GA), a short-chain aldehyde, on oxidative parameters in the liver of Wistar rats. Animals received a single injection of GA (10, 50, or 100 mg/kg) and were sacrificed after 6, 12, or 24 hours. Levels of protein carbonyl, lipid peroxidation, and reduced thiol were quantified. The activities of catalase, superoxide dismutase, and glyoxalase I were also assessed. The amount of CML was quantified with specific antibody. There was an increase in oxidative stress markers in the liver of GA-treated rats. Glycolaldehyde induced a decrease in the activities of all enzymes assayed. Also, all tested doses led to an increase in CML content. Our data suggest that GA might play an important role in liver diseases through the impairment of antioxidant defenses and generation of AGEs.     

Advanced glycation endproducts in food and their effects on health

Advanced glycation endproducts (AGEs) form by Maillard-reactions after initial binding of aldehydes with amines or amides in heated foods or in living organisms. The mechanisms of formation may include ionic as well as oxidative and radical pathways. The reactions may proceed within proteins to form high-molecular weight (HMW) AGEs or among small molecules to form low-molecular weight (LMW) AGEs. All free amino acids form AGEs, but lysine or arginine side chains dominate AGE formation within proteins. The analysis of AGEs in foods and body fluids is most often performed by ELISA or LC-MS; however, none of the methodologies cover all HMW and LMW AGEs. Most research is, therefore, carried out using ’representative’ AGE compounds, most often N^ε-carboxymethyl-lysine (CML). Only LMW AGEs, including peptide-bound forms, and carbonyls may be absorbed from the gut and contribute to the body burden of AGEs. Some AGEs interact with specific pro- or anti-inflammatory receptors. Most studies on the biological effects of AGEs have been carried out by administering heated foods. The pro-inflammatory and deteriorating biological effects of AGEs in these studies, therefore, need further confirmation. The current review points out several research needs in order to address important questions on AGEs in foods and health.     

Regulation of advanced glycation end product (AGE)-receptor (RAGE) system by PPAR-gamma agonists and its implication in cardiovascular disease

Non-enzymatic modification of proteins by reducing sugars leads to the formation of advanced glycation end products (AGEs), whose process has been reported to progress under physiological aging, oxidative stress or diabetic conditions. There is a growing body of evidence that AGEs and their receptor (RAGE) axis is involved in the pathogenesis of cardiovascular disease (CVD). Indeed, engagement of RAGE with AGEs is shown to elicit oxidative stress generation and subsequently evoke inflammatory and thrombogenic responses in various types of cells, including endothelial cells, smooth muscle cells, macrophages and renal cells, thus playing an important role in the development and progression of vascular injury in both diabetes and non-diabetes. These observations suggest that the inhibition of AGE formation, down-regulation of RAGE expression or blockade of the RAGE downstream signaling may be a promising therapeutic target for preventing CVD. Recently, peroxisome proliferator-activated receptor-γ (PPARγ) is involved in not only adipocyte differentiation, but also vascular homeostasis. Therefore, in this study, we review effects of PPARγ agonists on the AGE–RAGE system and their implication in CVD.     

Polyphenols with antiglycation activity and mechanisms of action: A review of recent findings

Advanced glycation end products (AGEs) are substances composed of amino groups of proteins and reducing sugars. The initial and propagation phases of the glycation process are accompanied by the production of a large amount of free radicals, carbonyl species, and reactive dicarbonyl species, of which, methylglyoxal (MG) is the most reactive and can cause dicarbonyl stress, influencing normal physiological functions. In the advanced phase, the production of AGEs and the interaction between AGEs and their receptor, RAGE, are also considered to be among the causes of chronic diseases, oxidative stress, and inflammatory reaction. Till date, multiple physiological activities of polyphenols have been confirmed. Recently, there have been many studies discussing the ability of polyphenols to suppress the MG and AGEs formation, which was also confirmed in some in vivo studies. This review article collects recent literatures concerning the effects of polyphenols on the generation of MG and AGEs through different pathways and discusses the feasibility of the inhibition of glycative stress and dicarbonyl stress by polyphenols.     

Naringenin prevents ischaemic stroke damage via anti‐apoptotic and anti‐oxidant effects

Apoptosis and oxidative stress are considered to be the major factors associated with the development and progression of many ischaemic cerebrovascular diseases. Naringenin (NAR) is an abundant flavanone in citrus plants and has been found to exhibit anti‐oxidant, anti‐carcinogenic and anti‐apoptotic effects. This study aimed to investigate the anti‐apoptotic and anti‐oxidant effects of naringenin on ischaemic stroke. In vitro, cortical neuron cells isolated from the brains of neonatal Sprague–Dawley rats were randomly divided into control, oxygen and glucose deprivation/reperfusion (OGD/Rep), NAR‐L, NAR‐M and NAR‐H groups. MTT and RT‐PCR were used for cell proliferation and apoptosis‐related proteins analyses. The effects of NAR on the Nrf2 signalling pathway were investigated using transfection approaches. Differences in mitochondrial dysfunction were analyzed by flow cytometry. In vivo, middle cerebral artery occlusion (MCAO) model was prepared and neurological defects and the brain wet/dry (W/D) ratio were assessed and recorded; apoptosis was measured based on the TUNEL assay. Additionally, biochemical indices were detected both in vitro and in vivo. NAR promoted cortical neuron cell proliferation, inhibited apoptosis and oxidative stress, and regulated the localization of Nrf2 protein (P<.05). Furthermore, silencing and overexpression of Nrf2 affected cortical neuron cell proliferation and apoptosis (P<.05). In vivo, NAR could alleviate cerebral oedema, improve neurological defects, and reduce apoptosis and oxidative stress (P<.05). These findings demonstrated that NAR could reduce apoptosis and oxidative stress and that Nrf2 signalling pathway is involved in this regulatory process. NAR has health‐promoting properties because of its anti‐apoptotic and anti‐oxidant effects in cases of ischaemic stroke.     

Crocetin prevents AGEs-induced vascular endothelial cell apoptosis.

Advanced glycation end products (AGEs) are causally correlated with diabetic vascular complications. AGEs triggered oxidative reaction then accelerated endothelial cell apoptosis is a critical event in the process of vascular complications. Crocetin, a carotenoid has been previously shown to have strong antioxidant activates. Therefore, this study was designed to investigate the role of crocetin on the prevention of AGEs-mediated cell apoptosis in bovine aortic endothelial cells (BEC) and the mechanisms involved. Exposure of BEC to 200 microg/ml AGEs for 48 h results in a significant increase in apoptotic rate, compared with control. AGEs-induced DNA fragmentation preferentially occurred in the S phase cells. Crocetin prevented AGEs-induced BEC apoptosis, which correlates with crocetin attenuation of AGEs mediated increase of intracellular reactive oxygen species (ROS) formation and elevation of intracellular Ca2+ concentration ([Ca2+]i) level (P<0.01 versus AGEs group). These results demonstrate that crocetin prevents AGEs-induced BEC apoptosis through ROS inhibition and [Ca2+]i stabilization and suggest that crocetin may exert a beneficial effect in preventing diabetes-associated vascular complications.     

Proteomic identification of carbonylated proteins in F344 rat hippocampus after 1-bromopropane exposure

1-Bromopropane (1-BP) is neurotoxic in both experimental animals and humans. Previous proteomic analysis of rat hippocampus implicated alteration of protein expression in oxidative stress, suggesting that oxidative stress plays a role in 1-BP-induced neurotoxicity. To understand this role at the protein level, we exposed male F344 rats to 1-BP at 0, 400, or 1000 ppm for 8 h/day for 1 week or 4 weeks by inhalation and quantitated changes in hippocampal protein carbonyl using a protein carbonyl assay, two-dimensional gel electrophoresis (2-DE), immunoblotting, and matrix-assisted laser-desorption ionization time-of-flight mass spectrometry (MALDI-TOF-TOF/MS). Hippocampal reactive oxygen species and protein carbonyl were significantly increased, demonstrating 1-BP-associated induction of oxidative stress and protein damage. MALDI-TOF-TOF/MS identified 10 individual proteins with increased carbonyl modification (p < 0.05; fold-change ≥ 1.5). The identified proteins were involved in diverse biological processes including glycolysis, ATP production, tyrosine catabolism, GTP binding, guanine degradation, and neuronal metabolism of dopamine. Hippocampal triosephosphate isomerase (TPI) activity was significantly reduced and negatively correlated with TPI carbonylation (p < 0.001; r = 0.83). Advanced glycation end-product (AGE) levels were significantly elevated both in the hippocampus and plasma, and hippocampal AGEs correlated negatively with TPI activity (p < 0.001; r = 0.71). In conclusion, 1-BP-induced neurotoxicity in the rat hippocampus seems to involve oxidative damage of cellular proteins, decreased TPI activity, and elevated AGEs.     

Nephroprotective effect of Paeonia emodi via inhibition of advanced glycation end products and oxidative stress in streptozotocin–nicotinamide induced diabetic nephropathy

The present study aimed to evaluate the effect of alcohol (PA) and hydroalcohol (PHA) extract of Paeonia emodi Royale roots in treatment of streptozotocin–nicotinamide induced diabetic nephropathy. Diabetes mellitus was induced in male Wistar rats by streptozotocin (65 mg/kg intraperitoneally) 15 minutes after nicotinamide (230 mg/kg, intraperitoneally) administration and diabetic nephropathy was assessed by measuring serum glucose, renal parameters (urea, uric acid, creatinine, and blood urea nitrogen level) and lipid profile. The rats were treated with different doses of extracts (100 mg/kg, 200 mg/kg, and 400 mg/kg) for 45 days. Oxidative stress was assessed by measuring tissue antioxidant enzymes level along with the formation of advanced glycation end-products (AGEs) in kidney. PA and PHA (400 mg/kg) produced significant attenuation in the serum glucose level (165.08 ± 3.353 mg/dL and 154.27 ± 2.209 mg/dL, respectively) as compared to control. Elevated renal parameters, lipid levels, tissue antioxidant enzymes and AGE formation were also restored in a dose-dependent manner. These findings suggest that by amelioration of oxidative stress and formation of AGEs, PA and PHA significantly inhibited the progression diabetic nephropathy in rats.     

Methylglyoxal promotes oxidative stress and endothelial dysfunction

Modern diets can cause modern diseases. Research has linked a metabolite of sugar, methylglyoxal (MG), to the development of diabetic complications, but the exact mechanism has not been fully elucidated. The present study was designed to investigate whether MG could directly influence endothelial function, oxidative stress and inflammation in Wistar and Goto-Kakizaki (GK) rats, an animal model of type 2 diabetes. Wistar and GK rats treated with MG in the drinking water for 3 months were compared with the respective control rats. The effects of MG were investigated on NO-dependent vasorelaxation in isolated rat aortic arteries from the different groups. Insulin resistance, NO bioavailability, glycation, a pro-inflammatory biomarker monocyte chemoattractant protein-1 (MCP-1) and vascular oxidative stress were also evaluated. Methylglyoxal treated Wistar rats significantly reduced the efficacy of NO-dependent vasorelaxation (p<0.001). This impairment was accompanied by a three fold increase in the oxidative stress marker nitrotyrosine. Advanced glycation endproducts (AGEs) formation was significantly increased as well as MCP-1 and the expression of the receptor for AGEs (RAGE). NO bioavailability was significantly attenuated and accompanied by an increase in superoxide anion immunofluorescence. Methylglyoxal treated GK rats significantly aggravated endothelial dysfunction, oxidative stress, AGEs accumulation and diminished NO bioavailability when compared with control GK rats. These results indicate that methylglyoxal induced endothelial dysfunction in normal Wistar rats and aggravated the endothelial dysfunction present in GK rats. The mechanism is at least in part by increasing oxidative stress and/or AGEs formation with a concomitant increment of inflammation and a decrement in NO bioavailability. The present study provides further evidence for methylglyoxal as one of the causative factors in the pathogenesis of atherosclerosis and development of macrovascular diabetic complication.