Preventive Effect of Salicylate and Pyridoxamine on Diabetic Nephropathy

AGE/RAGE in diabetic kidney disease and ageing kidney

Diabetic kidney disease (DKD) is the primary cause of chronic kidney disease that inevitably progress to end-stage kidney disease. Intervention strategies such as blood glucose control is effective for preventing DKD, but many patients with DKD still reach end-stage kidney disease. Although comprehensive mechanisms shed light on the progression of DKD, the most compelling evidence has highlighted that hyperglycemia-related advanced glycation end products (AGEs) formation plays a central role in the pathogenesis of DKD. Pathologically, accumulation of AGEs-mediated receptor for AGEs (RAGE) triggers oxidative stress and inflammation, which is the major deleterious effect of AGEs in host and intestinal microenvironment of diabetic and ageing conditions. The activation of AGEs-mediated RAGE could evoke nicotinamide adenine dinucleotide phosphate oxidase-induced reactive oxygen and nitrogen species production and subsequently give rise to oxidative stress in DKD and ageing kidney. Therefore, targeting RAGE with its ligands mediated oxidative stress and chronic inflammation is considered as an additional intervention strategy for DKD and ageing kidney. In this review, we summarize AGEs/RAGE-mediated oxidative stress and inflammation signaling pathways in DKD and ageing kidney, discussing opportunities and challenges of targeting at AGEs/RAGE-induced oxidative stress that could hold the promising potential approach for improving DKD and ageing kidney.

The Glyoxalase System in Age-Related Diseases: Nutritional Intervention as Anti-Ageing Strategy

The glyoxalase system is critical for the detoxification of advanced glycation end-products (AGEs). AGEs are toxic compounds resulting from the non-enzymatic modification of biomolecules by sugars or their metabolites through a process called glycation. AGEs have adverse effects on many tissues, playing a pathogenic role in the progression of molecular and cellular aging. Due to the age-related decline in different anti-AGE mechanisms, including detoxifying mechanisms and proteolytic capacities, glycated biomolecules are accumulated during normal aging in our body in a tissue-dependent manner. Viewed in this way, anti-AGE detoxifying systems are proposed as therapeutic targets to fight pathological dysfunction associated with AGE accumulation and cytotoxicity. Here, we summarize the current state of knowledge related to the protective mechanisms against glycative stress, with a special emphasis on the glyoxalase system as the primary mechanism for detoxifying the reactive intermediates of glycation. This review focuses on glyoxalase 1 (GLO1), the first enzyme of the glyoxalase system, and the rate-limiting enzyme of this catalytic process. Although GLO1 is ubiquitously expressed, protein levels and activities are regulated in a tissue-dependent manner. We provide a comparative analysis of GLO1 protein in different tissues. Our findings indicate a role for the glyoxalase system in homeostasis in the eye retina, a highly oxygenated tissue with rapid protein turnover. We also describe modulation of the glyoxalase system as a therapeutic target to delay the development of age-related diseases and summarize the literature that describes the current knowledge about nutritional compounds with properties to modulate the glyoxalase system.

Pyridoxamine alleviates mechanical allodynia by suppressing the spinal receptor for advanced glycation end product-nuclear factor-B/extracellular signal-regulated kinase signaling pathway in diabetic rats

Diabetic neuropathic pain is a common complication of diabetes mellitus and requires a substantial amount of societal resources. Pyridoxamine is an inhibitor of advanced glycation and lipoxidation end products. Several animal and clinical studies have confirmed that pyridoxamine can inhibit a range of pathological changes in diabetes-induced organ injury and alleviate certain kinds of neuropathic pain. However, no studies have attempted to explore the effects of pyridoxamine on diabetic neuropathic pain. We conducted animal experiments to examine whether pyridoxamine could alleviate diabetic neuropathic pain and to explore the mechanism underlying these effects. Adult male Sprague Dawley rats were randomly assigned to the normal + sterile water group, diabetic + sterile water group, diabetic + pyridoxamine₁₀₀ group, diabetic +pyridoxamine₂₀₀ group, diabetic + pyridoxamine₄₀₀ group, or normal + pyridoxamine group. The rats in the diabetic +pyridoxamine₁₀₀, diabetic + pyridoxamine₂₀₀, diabetic + pyridoxamine₄₀₀, and normal + pyridoxamine groups received pyridoxamine at dosages of 100 mg/kg/day, 200 mg/kg/day, 400 mg/kg/day, and 400 mg/kg/day, respectively, via intragastric administration. The rats in the other groups received water daily. Pyridoxamine alleviated diabetic neuropathic pain at least partially by suppressing the activity of the spinal receptor for advanced glycation end products-nuclear factor-κB/extracellular signal-regulated kinase signaling pathway; additionally, pyridoxamine decreased advanced glycation end product-modified low-density lipoprotein, oxidized low-density lipoprotein, and interleukin-1β levels in the serum. The immunofluorescence staining results revealed that most phosphorylated nuclear factor-κB was localized to neuronal cells and not to microglia or astrocytes; this pattern may be associated with the upregulated expression of pain-related proteins. The abovementioned results indicate that pyridoxamine is a promising choice for the clinical treatment of diabetic neuropathic pain. Further investigations need to be carried out to confirm the benefits of pyridoxamine.

Pyridoxamine Treatment of HK-2 Human Proximal Tubular Epithelial Cells Reduces Oxidative Stress and the Inhibition of Autophagy Induced by High Glucose Levels

Background

Diabetic nephropathy is a predominant cause of renal failure, which is an important chronic complication of diabetes. Pyridoxamine (PM) has been reported to protect renal tubular epithelial cells against oxidative damage and delay or inhibit the development and generation of glucose-induced renal insufficiency at the early stage of disease. In this study, we attempted to explore the protection mechanism of PM on human proximal tubular epithelial cells (HK-2 cells) induced by high glucose.

Material/Methods

HK-2 cells were cultivated by high glucose medium in the absence or presence of PM. Cell Counting Kit-8 was used to investigate the most appropriate drug concentration of PM by detecting the cell viability of HK-2 cells. The expression of autophagy-related protein Beclin-1, LC-3II, and p62 was measured by western blot analysis, reverse transcription-quantitative polymerase chain reaction (RT-qPCR), and immunofluorescence. The expression and localization of Beclin-1 and p62 were also detected via immunofluorescence. The intracellular reactive oxygen species generation was detected using the reactive oxygen species assay kit. The effects of PM on antioxidant defenses were evaluated with glutathione peroxidase (GPx), manganese superoxide dismutase (MnSOD) activity, and glutathione/glutathione disulfide (GSH/GSSG) ratio.

Results

High glucose levels were able to upregulate the expression of oxidative stress associated protein and inhibit autophagy-associated changes verified by western blotting, RT-qPCR and immunofluorescence. Administration of PM reversed the high glucose-induced low-expressed Beclin-1 and LC-3II, and overexpressed p62 and intracellular reactive oxygen species levels. Furthermore, non-enzymatic antioxidant defenses and enzymatic antioxidant defenses were turned on by the application of PM.

Conclusions

Treatment with PM could reverse high glucose-induced inhibition of autophagy and oxidative stress.

Targeting inflammation in diabetic nephropathy: a tale of hope

INTRODUCTION

Diabetic nephropathy (DN) is the leading cause of chronic kidney disease (CKD) and end-stage renal disease (ESRD). Beyond the new anti-diabetic drugs that possess markedly cardiovascular and renal protective effects, no novel direct therapies for DN have become available on the market in the last twenty years. Recently well-designed clinical trials for the treatment of DN, with attractive pathogenetic rationale, e.g. bardoxolone and atrasentan, were canceled or stopped because of safety concerns or lack of reaching the end points, respectively.

AREAS COVERED

In this review, we focus on the involvement of inflammation in the pathogenesis of DN. We update information from recent experimental and clinical studies that reported beneficial effects of several agents targeting chemokines, cytokines, transcription factors and kinases as well as several compounds with anti-inflammatory properties on DN.

EXPERT OPINION

Inflammation plays a key role in the DN progression. Preclinical studies have identified several anti-inflammatory molecules that effective decrease albuminuria and/or proteinuria. However, limited clinical trials in humans have been performed to confirm these results. Inhibitors of CCL2/CCR2, IL-1β and JAK/STAT pathways, and Nrf2 inducers are promising therapeutic options to improve the renal outcome of patients with DN, but appropriate clinical trials are necessary.

Red onion scales ameliorated streptozotocin-induced diabetes and diabetic nephropathy in Wistar rats in relation to their metabolite fingerprint

AIM

The present study was designed to investigate the effect of red onion scales extract (ROS) against diabetic nephropathy, in relation to its metabolic profiling.

METHODS

Four groups of male Wistar rats were assigned as follows; 1st untreated group, 2nd group (animals with diabetes) treated with streptozotocin (STZ, 50 mg/kg) IP, 3rd group co-treated with ROS (150 mg/kg + STZ, 50 mg/kg) and 4th group co-treated with ROS by a dose (300 mg/kg + STZ, 50 mg/kg) daily. After four weeks, random and fasting blood glucose (FBG) levels, serum insulin, advanced glycation end products (AGEs), urea, uric acid and inflammatory and fibrotic gene expression were evaluated. Moreover, histopathological examination of the renal tissues was performed. In addition, the metabolic profiling of ROS was performed via RP-HPLC-DAD-QTOF-MS and -MS/MS.

RESULTS

The metabolic profiling of ROS revealed that protocatechuic acid and cyanidin-3-O-glucoside were the predominant compounds among 32 metabolites identified in the extract. ROS treated groups showed improvement of FBG and AGEs levels, whereas serum insulin level showed significant elevation. In addition, down-regulation of inflammatory mRNA expression associated with the hyperglycemic condition and amelioration in histopathological alterations in kidney tissues were observed.

CONCLUSION

This study displayed the presence of 32 phenolic compounds in the ethanolic extract of ROS, a common by-product of the industrial production of onion in Egypt. This study proved the therapeutic potential of ROS as antidiabetic agent and its preventive effect against diabetic nephropathy. Therefore, this study represents a perspective of the utilization of food waste products.

Protective Effects of Pyridoxamine Supplementation in the Early Stages of Diet-Induced Kidney Dysfunction

Pyridoxamine, a structural analog of vitamin B6 that exerts antiglycative effects, has been proposed as supplementary approach in patients with initial diabetic nephropathy. However, the molecular mechanism(s) underlying its protective role has been so far slightly examined. C57Bl/6J mice were fed with a standard diet (SD) or a diet enriched in fat and fructose (HD) for 12 weeks. After 3 weeks, two subgroups of SD and HD mice started pyridoxamine supplementation (150 mg/kg/day) in the drinking water. HD fed mice showed increased body weight and impaired glucose tolerance, whereas pyridoxamine administration significantly improved insulin sensitivity, but not body weight, and reduced diet-induced increase in serum creatinine and urine albumin. Kidney morphology of HD fed mice showed strong vacuolar degeneration and loss of tubule brush border, associated with a drastic increase in both advanced glycation end products (AGEs) and AGEs receptor (RAGE). These effects were significantly counteracted by pyridoxamine, with consequent reduction of the diet-induced overactivation of NF-kB and Rho/ROCK pathways. Overall, the present study demonstrates for the first time that the administration of the antiglycative compound pyridoxamine can reduce the early stages of diet-dependent kidney injury and dysfunction by interfering at many levels with the profibrotic signaling and inflammatory cascades.

Quercetin nanoparticle complex attenuated diabetic nephropathy via regulating the expression level of ICAM-1 on endothelium

The purpose of the study was to reveal the therapeutic effect of quercetin (QUE) nanoparticle complex on diabetic nephropathy (DN) by regulating the expression of intercellular adhesion molecular-1 (ICAM-1) on endothelium as compared to free QUE. QUE 10 mg/kg as a single abdominal subcutaneous injection daily for 8 weeks continuously in diabetic rats and 10 mg/kg QUE nanoparticle complex as a single abdominal subcutaneous injection every 5 days, continuously administered for 8 weeks to diabetic rats. Blood and left kidneys were collected; pathological change of kidney, renal function, oxidative stress level, blood glucose level, serum lipid, urine protein, and albumin/creatinine ratio were measured; and neutrophil adhesion, ICAM-1 expression, and CD11b⁺ cells infiltration were observed. Both QUE and QUE nanoparticle complex preconditioning ameliorated the pathological damage of kidney and improved renal function, alleviated renal oxidative stress injury, restricted inflammatory cells infiltration, and downregulated the ICAM-1 expression as compared to DN group, while QUE nanoparticle complex significantly alleviated this effect.

Preparation of exenatide-loaded linear poly(ethylene glycol)-brush poly(l-lysine) block copolymer: potential implications on diabetic nephropathy

The poly(ethylene glycol)-b-brush poly(l-lysine) polymer (PEG-b-(PELG50-g-PLL3)) was synthesized and evaluated as a nanocarrier for prolonging delivery of exenatide through the abdominal subcutaneous injection route. The isoelectric point of exenatide was 4.86, and exenatide could combine with PEG-b-(PELG50-g-PLL3) polymers via electrostatic interactions at pH 7.4. This polymer was a good candidate for achieving prolonged drug delivery for exenatide, considering its high molecular weight. Besides the physicochemical characterization of the polymer, in vitro and in vivo applications were researched as a sustained exenatide delivery system. In the in vitro release research, 20.16%-76.88% of total exenatide was released from the PEG-b-(PELG50-g-PLL3) polymer within 7 days. The synthesized block-brush polymers and exenatide-block-brush polymers were analyzed by nuclear magnetic resonance spectroscopy, gel permeation chromatography, transmission electron microscopy, nanoparticle size instrument, and scanning electron microscopy. The best formulation was selected for in vivo experimentation to achieve blood glucose control in diabetic rat models using free exenatide as the control. The hypoglycemic action of the formulation following subcutaneous injection in diabetic rats lasted 7 days, and the results indicated that exenatide-block-brush polymers demonstrate enhanced long-acting hypoglycemic action. Besides the hypoglycemic action, exenatide-block-brush polymers significantly alleviated diabetic nephropathy via improving renal function, decreasing oxidative stress injury, decreasing urinary albumin excretion rate, mitigating albumin/creatinine ratio, reducing blood lipids, abating kidney index, weakening apoptosis, and downregulating expression of connective tissue growth factor. All of the results suggested that PEG-b-(PELG50-g-PLL3) polymers could be used as potential exenatide nanocarriers, with efficient encapsulation and sustained release.