Ethyl pyruvate prevents methyglyoxal-induced retinal vascular injury in rats

MicroRNA-93-5p participates in type 2 diabetic retinopathy through targeting Sirt1

OBJECTIVE

To investigate the role of miR-93-5p in rats with type 2 diabetic retinopathy (DR) through targeting Sirt1.

METHODS

The targeting correlation between miR-93-5p and Sirt1 was validated by dual-luciferase reporter gene assay. Type 2 diabetes mellitus (T2DM) rat models were received intravitreal injection of antagomir NC (negative control), miR-93-5p antagomir, miR-93-5p agomir and/or recombinant Sirt1, followed by observation of pathological changes in retina via HE staining. Besides, retinal vascular permeability was determined by fluorescein isothiocyanate-bovine serum albumin (FITC-BSA), while the retinal vasculature was observed through retinal trypsin digestion. Expression of miR-93-5p and Sirt1 was measured by qRT-PCR and Western blotting, while the levels of VEGF, proinflammatory cytokines and anti-oxidative indicators were determined using corresponding kits.

RESULTS

MiR-93-5p could target Sirt1 as analyzed by the luciferase reporter gene assay. Rats in the T2DM group presented the up-regulation of miR-93-5p and down-regulation of Sirt1 in the retina, and miR-93-5p inhibition could up-regulate Sirt1 expression in the T2DM rats. Recombinant Sirt1 decreased retinal vascular permeability and acellular capillaries with improved pathological changes in retina from T2DM rats, which was abolished by miR-93-5p agomir. Moreover, miR-93-5p inhibition or Sirt1 overexpression decreased the levels of VEGF and proinflammatory cytokines while enhancing the activity of anti-oxidative indicators. However, indicators above had no significant differences between T2DM group and T2DM + agomir + Sirt1 group.

CONCLUSION

MiR-93-5p, via targeting Sirt1, could affect the vascular permeability and acellular capillaries and mitigate the inflammation and oxidative stress in the retinas, which may play a critical role in DR.

Does Hyperglycemia Cause Oxidative Stress in the Diabetic Rat Retina?

Diabetes, being a metabolic disease dysregulates a large number of metabolites and factors. However, among those altered metabolites, hyperglycemia is considered as the major factor to cause an increase in oxidative stress that initiates the pathophysiology of retinal damage leading to diabetic retinopathy. Diabetes-induced oxidative stress in the diabetic retina and its damaging effects are well known, but still, the exact source and the mechanism of hyperglycemia-induced reactive oxygen species (ROS) generation especially through mitochondria remains uncertain. In this study, we analyzed precisely the generation of ROS and the antioxidant capacity of enzymes in a real-time situation under ex vivo and in vivo conditions in the control and streptozotocin-induced diabetic rat retinas. We also measured the rate of flux through the citric acid cycle by determining the oxidation of glucose to CO2 and glutamate, under ex vivo conditions in the control and diabetic retinas. Measurements of H2O2 clearance from the ex vivo control and diabetic retinas indicated that activities of mitochondrial antioxidant enzymes are intact in the diabetic retina. Short-term hyperglycemia seems to influence a decrease in ROS generation in the diabetic retina compared to controls, which is also correlated with a decreased oxidation rate of glucose in the diabetic retina. However, an increase in the formation of ROS was observed in the diabetic retinas compared to controls under in vivo conditions. Thus, our results suggest of diabetes/hyperglycemia-induced non-mitochondrial sources may serve as major sources of ROS generation in the diabetic retina as opposed to widely believed hyperglycemia-induced mitochondrial sources of excess ROS. Therefore, hyperglycemia per se may not cause an increase in oxidative stress, especially through mitochondria to damage the retina as in the case of diabetic retinopathy.

miR-450a-5p Eliminates MGO-Induced Insulin Resistance via Targeting CREB

Background and Objectives

miR-450a-5p was involved in fat formation, however, its role in insulin resistance remains unclear. This study investigated the effects of miR-450a-5p on endothelial cells, with the aim of finding a potential target for diabetes mellitus.

Methods and Results

Human umbilical vein endothelial cells (HUVECs) were treated with low-glucose, high-glucose, methylglyoxal (MGO), and insulin alone or in combination with MGO. The expression of miR-450a-5p in treated cells was measured by quantitative real-time polymerase chain reaction (qRT-PCR) assays. The cell activity, migration and fat formation were determined by MTT experiments, Transwell assay and oil red O staining. The expressions of eNOS/AKT pathway-related proteins in cells were assessed by Western blot (WB) analysis. Furthermore, the target gene of miR-450a-5p was analyzed by double-luciferase reporter analysis, and its effects on eNOS/AKT pathway were estimated. We found that the expression of miR-450a-5p was decreased obviously in endothelial cells treated with high-glucose and MGO. In vitro cell experiments showed that MGO could not only promote the activity of endothelial cells, but also accelerate cell migration and fat accumulation, which, however, could be reversed by up-regulation of miR-450a-5p. Moreover, MGO inhibited eNOS/AKT pathway activation and NO release mediated by insulin, and such effects were reversed by up-regulation of miR-450a-5p. Furthermore, CREB was the target gene for miR-450a-5p, had an activation effect on the eNOS/AKT pathway.

Conclusions

Up-regulated miR-450a-5p eliminates MGO-induced insulin resistance via targeting CREB, and therefore could be used as a potential target to improve insulin resistance and treat patients with diabetes-related diseases.

Ethyl Pyruvate Prevents Renal Damage Induced by Methylglyoxal-Derived Advanced Glycation End Products

The renal accumulation of advanced glycation end products (AGEs) is a causative factor of various renal diseases, including chronic kidney disease and diabetic nephropathy. AGE inhibitors, such as aminoguanidine and pyridoxamine, have the therapeutic activities for reversing the increase in renal AGE burden. This study evaluated the inhibitory effects of ethyl pyruvate (EP) on methylglyoxal- (MGO-) modified AGE cross-links with proteins in vitro. We also determined the potential activity of EP in reducing the renal AGE burden in exogenously MGO-injected rats. EP inhibited MGO-modified AGE-bovine serum albumin (BSA) cross-links to collagen (IC₅₀ = 0.19 ± 0.03 mM) in a dose-dependent manner, and its activity was stronger than aminoguanidine (IC₅₀ = 35.97 ± 0.85 mM). In addition, EP directly trapped MGO (IC₅₀ = 4.41 ± 0.08 mM) in vitro. In exogenous MGO-injected rats, EP suppressed AGE burden and MGO-induced oxidative injury in renal tissues. These activities of EP on the MGO-mediated AGEs cross-links with protein in vitro and in vivo showed its pharmacological potential for inhibiting AGE-induced renal diseases.

The Role of Glyoxalase-I (Glo-I), Advanced Glycation Endproducts (AGEs), and Their Receptor (RAGE) in Chronic Liver Disease and Hepatocellular Carcinoma (HCC)

Glyoxalase-I (Glo-I) and glyoxalase-II (Glo-II) comprise the glyoxalase system and are responsible for the detoxification of methylglyoxal (MGO). MGO is formed non-enzymatically as a by-product, mainly in glycolysis, and leads to the formation of advanced glycation endproducts (AGEs). AGEs bind to their receptor, RAGE, and activate intracellular transcription factors, resulting in the production of pro-inflammatory cytokines, oxidative stress, and inflammation. This review will focus on the implication of the Glo-I/AGE/RAGE system in liver injury and hepatocellular carcinoma (HCC). AGEs and RAGE are upregulated in liver fibrosis, and the silencing of RAGE reduced collagen deposition and the tumor growth of HCC. Nevertheless, data relating to Glo-I in fibrosis and cirrhosis are preliminary. Glo-I expression was found to be reduced in early and advanced cirrhosis with a subsequent increase of MGO-levels. On the other hand, pharmacological modulation of Glo-I resulted in the reduced activation of hepatic stellate cells and therefore reduced fibrosis in the CCl₄-model of cirrhosis. Thus, current research highlighted the Glo-I/AGE/RAGE system as an interesting therapeutic target in chronic liver diseases. These findings need further elucidation in preclinical and clinical studies.

OSSC1E-K19, a novel phytochemical component of Osteomeles schwerinae, prevents glycated albumin-induced retinal vascular injury in rats

In the pathophysiology of diabetic retinopathy (DR), advanced glycation end products (AGEs) and vascular endothelial growth factor (VEGF) are thought to have important roles. It is known that VEGF causes a breakdown of the blood‑retinal barrier (BRB) and retinal neovascularization; however, how AGEs affect the retina has largely remained elusive. OSSC1E‑K19 is a novel phytochemical component of Osteomeles schwerinae. The objective of the present study was to evaluate the protective effects of OSSC1E‑K19 on retinal vascular injury in AGE‑modified rat serum albumin (AGE-RSA)-induced retinopathy. AGE-RSA-injected rat eyes were used investigate the protective effects of OSSC1E‑K19 on BRB breakdown. Intravitreal injection of OSSC1E-K19 prevented AGE-RSA-induced BRB breakdown and decreased retinal VEGF expression in retinal vessels. In addition, OSSC1E-K19 inhibited the loss of occludin, a significant tight junction protein. These results supported the potential therapeutic utility of OSSC1E-K19 for retinal vascular permeability diseases.