Diabetes mellitus is a metabolic disease characterized by long-term hyperglycaemia, which leads to microangiopathy and macroangiopathy and ultimately increases the mortality of diabetic patients. Endothelial dysfunction, which has been recognized as a key factor in the pathogenesis of diabetic microangiopathy and macroangiopathy, is characterized by a reduction in NO bioavailability. Oxidative stress, which is the main pathogenic factor in diabetes, is one of the major triggers of endothelial dysfunction through the reduction in NO. In this review, we summarize the four sources of ROS in the diabetic vasculature and the underlying molecular mechanisms by which the pathogenic factors hyperglycaemia, hyperlipidaemia, adipokines and insulin resistance induce oxidative stress in endothelial cells in the context of diabetes. In addition, we discuss oxidative stress-targeted interventions, including hypoglycaemic drugs, antioxidants and lifestyle interventions, and their effects on diabetes-induced endothelial dysfunction. In summary, our review provides comprehensive insight into the roles of oxidative stress in diabetes-induced endothelial dysfunction.

Diabetic nephropathy (DN) is a chronic low-grade inflammatory disease. Oxidative stress and nuclear factor kappa B (NF-κB) signaling play an important role in the pathogenesis of DN. Short-chain fatty acids (SCFAs) produced from carbohydrate fermentation in the gastrointestinal tract exert positive regulatory effects on inflammation and kidney injuries. However, it is unclear whether SCFAs can prevent and ameliorate DN. In the present study, we evaluated the role and mechanism of the three main SCFAs (acetate, propionate, and butyrate) in high-fat diet (HFD) and streptozotocin- (STZ-) induced type2 diabetes (T2D) and DN mouse models and in high glucose-induced mouse glomerular mesangial cells (GMCs), to explore novel therapeutic strategies and molecular targets for DN. We found that exogenous SCFAs, especially butyrate, improved hyperglycemia and insulin resistance; prevented the formation of proteinuria and an increase in serum creatinine, urea nitrogen, and cystatin C; inhibited mesangial matrix accumulation and renal fibrosis; and blocked NF-κB activation in mice. SCFAs also inhibited high glucose-induced oxidative stress and NF-κB activation and enhanced the interaction between β-arrestin-2 and I-κBα in GMCs. Specifically, the beneficial effects of SCFAs were significantly facilitated by the overexpression GPR43 or imitated by a GPR43 agonist but were inhibited by siRNA-GPR43 in GMCs. These results support the conclusion that SCFAs, especially butyrate, partially improve T2D-induced kidney injury via GPR43-mediated inhibition of oxidative stress and NF-κB signaling, suggesting SCFAs may be potential therapeutic agents in the prevention and treatment of DN.

Although emerging evidence suggests that low levels of vitamin D may contribute to the development of autoimmune disease, the relationship between vitamin D reduction and autoimmune thyroid disease (AITD), which includes Graves’ disease (GD) and Hashimoto thyroiditis (HT), is still controversial. The aim was to evaluate the association between vitamin D levels and AITD through systematic literature review. We identified all studies that assessed the association between vitamin D and AITD from PubMed, Embase, CENTRAL, and China National Knowledge Infrastructure (CNKI) databases. We included studies that compared vitamin D levels between AITD cases and controls as well as those that measured the odds of vitamin D deficiency by AITD status. We combined the standardized mean differences (SMD) or the odds ratios (OR) in a random effects model. Twenty case-control studies provided data for a quantitative meta-analysis. Compared to controls, AITD patients had lower levels of 25(OH)D (SMD: −0.99, 95% CI: −1.31, −0.66) and were more likely to be deficient in 25(OH)D (OR 2.99, 95% CI: 1.88, 4.74). Furthermore, subgroup analyses result showed that GD and HT patients also had lower 25(OH)D levels and were more likely to have a 25(OH)D deficiency, suggesting that low levels of serum 25(OH)D was related to AITD.

Diabetic cardiomyopathy (DCM) is characterized by lipid accumulation, mitochondrial dysfunction, and aseptic inflammatory activation. Mitochondria-derived cytosolic DNA has been reported to induce inflammation by activating cyclic GMP-AMP synthase (cGAS)/the stimulator of interferon genes (STING) pathway in the adipose, liver, and kidney tissues. However, the role of cytosolic mtDNA in the progression of DCM is unclear. In this study, with an obesity-related DCM mouse model established by feeding db/db mice with a high-fat diet (HFD), we observed increased mtDNA in the cytosol and activated cGAS-STING signaling pathway during DCM, as well as the downstream targets, IRF3, NF-κB, IL-18, and IL-1β. In a further study with a palmitic acid (PA)-induced lipotoxic cell model established in H9C2 cells, we revealed that the cytosolic mtDNA was the result of PA-induced overproduction of mitochondrial ROS, which also led to the activation of the cGAS/STING system and its downstream targets. Notably, treatment of extracted mtDNA alone was sufficient to activate the cGAS-STING signaling pathway in cultured H9C2 cells. Besides, both knockdown of STING in PA-induced H9C2 cells and inhibition of STING by C-176 injection in the DCM mouse model could remarkably block the inflammation and apoptosis of cardiomyocytes. In conclusion, our study elucidated the critical role of cytosolic mtDNA-induced cGAS-STING activation in the pathogenesis of obesity-related DCM and provided preclinical validation for using a STING inhibitor as a new potential therapeutic strategy for the treatment of DCM. Graphical abstract

Recently, an connection between Short-chain fatty acids (SCFAs) produced by intestinal microbiota and kidney has been revealed. The aim of this study was to explore whether SCFAs or their specific G protein-coupled receptors 43 (GPR43) agonist inhibit oxidative stress and inflammatory response in glomerular mesangial cells (GMCs) induced by high glucose and lipopolysaccharide (LPS). Our research showed that treatment with SCFAs, especially acetate and butyrate, or GPR43 agonist significantly inhibited GMCs proliferation induced by high glucose and LPS, and then reversed the production of reactive oxygen species (ROS) and malondialdehyde (MDA) but increased levels of antioxidant enzyme superoxide dismutase (SOD). Furthermore, SCFAs or GPR43 agonist obviously increased the protein expression of GPR43 induced by high glucose and LPS, but diminished the expression of adhesion molecule intercellular adhesion molecule-1 (ICAM-1), and then decreased the proinflammatory cytokine monocyte chemoattractant protein (MCP-1) and interleukin-1β (IL-1β) release from GMCs stimulated by the high glucose and LPS. These combined results support the hypothesis that SCFAs or GPR43 agonist can inhibit oxidative stress and inflammation of GMCs induced by high glucose and LPS, suggesting that SCFAs induced signaling pathway may act as new therapeutic targets of diabetic nephropathy (DN).