Mechanisms in the pathogenesis of diabetic cardiomyopathy

Molecular mechanisms of cardiotoxicity induced by acetamide and its chiral isomers

Acetamide (ACT) is used in a racemic form, and the considerable residues of this compound in the environment raise potential safety concerns for human health. We investigated the toxicity of ACT and its chiral isomers on human cardiomyocyte (AC16) cell line and zebrafish embryonic heart, and found that (+)-S-ACT was the main component causing cardiac toxicity. Our findings indicate that the IC50 of (±)-Rac-ACT on AC16 cells was 20.19 μg/mL. (-)-R-ACT, (±)-Rac-ACT, and (+)-S-ACT caused DNA damage and apoptosis in AC16 cells at this concentration. The underlying molecular mechanism may involve the induction of reactive oxygen species (ROS). The accumulation of ROS results in a decline in mitochondrial membrane potential (MMP) and prompts the release of cytochrome c (cyt c) from the mitochondria. This cascade of events ultimately activates the caspase-3 and caspase-9 signaling pathways, resulting in apoptosis. Furthermore, in vivo observations in zebrafish hearts demonstrated caspase-3 activation and the presence of the DNA damage marker (γH2AX), indicating that (+)-S-ACT is more toxic to cardiomyocytes than (-)-R-ACT and (±)-Rac-ACT. These findings suggest that (+)-S-ACT may be the primary component responsible for the toxicity of (±)-Rac-ACT in AC16 cells. Overall, these findings raise public awareness regarding the risks associated with chiral isomeric pesticides and provide a scientific foundation for their appropriate use.

Spiraeoside protects human cardiomyocytes against high glucose-induced injury, oxidative stress, and apoptosis by activation of PI3K/Akt/Nrf2 pathway

The present study aimed to explore the effect of spiraeoside, an active quercetin glucoside, on diabetic cardiomyopathy in vitro. Our results showed that spiraeoside attenuated high glucose (HG)-induced reduction of cell viability and increased myocardial enzymes lactate dehydrogenase and aspartate aminotransferase in AC16 cells. Spiraeoside exerted antioxidant activity in HG-induced AC16 cells as spiraeoside inhibited reactive oxygen species and malondialdehyde production and increased activities of superoxide dismutase, glutathione peroxidase, and catalase. Spiraeoside prevented HG-induced apoptosis of AC16 cells. HG stimulation-caused the decrease in the expression levels of p-Akt, nuclear Nrf2, and HO-1 was elevated after spiraeoside treatment in AC16 cells. However, the effects of spiraeoside were reversed by LY294002. In conclusion, spiraeoside protected AC16 cells against HG-induced oxidative stress, cell injury, and apoptosis. The protective effect of spiraeoside was regulated by the PI3K/Akt/Nrf2 signaling pathway.

Diabetic cardiomyopathy: effects of fenofibrate and metformin in an experimental model--the Zucker diabetic rat

Background

Diabetic cardiomyopathy (DCM) contributes to cardiac failure in diabetic patients. It is characterized by excessive lipids accumulation, with increased triacylglycerol (TAG) stores, and fibrosis in left ventricle (LV). The mechanisms responsible are incompletely known and no specific treatment is presently defined. We evaluated the possible usefulness of two molecules promoting lipid oxidation, fenofibrate and metformin, in an experimental model of DCM, the Zucker diabetic rat (ZDF).

Methods

ZDF and controls (C) rats were studied at 7, 14 and 21 weeks. After an initial study at 7 weeks, ZDF rats received no treatment, metformin or fenofibrate until final studies (at 14 or 21 weeks). C rats received no treatment. Each study comprised measurements of metabolic parameters (plasma glucose, TAG, insulin levels) and sampling of heart for histology and measurements of TAG content and relevant mRNA concentration.

Results

ZDF rats were insulin-resistant at 7 weeks, type 2 diabetic at 14 weeks and diabetic with insulin deficiency at 21 weeks. Their plasma TAG levels were increased. ZDF rats had at 7 weeks an increased LV TAG content with some fibrosis. LV TAG content increased in untreated ZDF rats at 14 and 21 weeks and was always higher than in C. Fibrosis increased also moderately in untreated ZDF rats. Metformin and fenofibrate decreased plasma TAG concentrations. LV TAG content was decreased by metformin (14 and 21 weeks) and by fenofibrate (14 weeks). Fibrosis was reduced by fenofibrate only and was increased by metformin. Among the mRNA measured, fenofibrate increased Acyl-CoA Oxidase mRNA level, metformin decreased Acyl-CoA Synthase and increased AdipoR1 and pro-inflammatory mRNA levels.

Conclusion

Fenofibrate had favourable actions on DCM. Metformin had beneficial effect on TAG content but not on fibrosis. PPARα agonists could be useful for the prevention and treatment of DCM.

Diabetic cardiomyopathy: recent evidence from mouse models of type 1 and type 2 diabetes

Diabetic cardiomyopathy is defined as ventricular dysfunction of the diabetic heart in the absence of coronary artery disease. With the use of both in vivo and ex vivo techniques to assess cardiac phenotype, reduced contractile performance can be observed in experiments with mouse models of both type 1 (insulin-deficient) and type 2 (insulin-resistant) diabetes. Both systolic dysfunction (reduced left ventricular pressures and decreased cardiac output) and diastolic dysfunction (impaired relaxation) is observed in diabetic hearts, along with enhanced susceptibility to ischemic injury. Metabolism is also altered in diabetic mouse hearts: glucose utilization is reduced and fatty acid utilization is increased. The use of geneticallyengineered mice has provided a powerful experimental approach to test mechanisms that may be responsible for the deleterious effects of diabetes on cardiac function.Key words: cardiac function, cardiac metabolism, cardiac phenotype.