Acute Hyperglycemia Induces Nitrotyrosine Formation and Apoptosis in Perfused Heart From Rat

Abstract

This study investigated coronary perfusion pressure, nitric oxide (NO) and superoxide production, nitrotyrosine (NT) formation, and cardiac cell apoptosis in isolated hearts perfused with high glucose concentration. Coronary perfusion pressure; NO and superoxide anion generation; immunostaining for NT, inducible NO synthase (iNOS), and the constitutive type of NO synthase (NOS) eNOS; iNOS and eNOS mRNA expression by Western blot and RT-PCR; and apoptosis of cardiac cells were studied in hearts perfused for 2 h with solutions containing D-glucose at a concentration of 11.1 mmol/l (control), D-glucose at the concentration of 33.3 mmol/l (high glucose), or D-glucose (33.3 mmol/l) plus glutathione (0.3 mmol/l). Perfusion of isolated hearts in conditions of high glucose concentration caused a significant increase of coronary perfusion pressure (P < 0.001) and an increase of both NO and superoxide generation. However, superoxide production was 300% higher than baseline, whereas NO production was 40% higher (P < 0.001 for both). This effect was accompanied by the formation of NT, and an increase of iNOS expression. eNOS remained unchanged. At the end of the experiments, cardiac cell apoptosis was evident in hearts perfused with high glucose. The effects of high glucose were significantly prevented by glutathione. This study demonstrates that high glucose for 2 h is enough to increase iNOS gene expression and NO release in working rat hearts. Upregulation of iNOS and raised NO generation are accompanied by a marked concomitant increase of superoxide production, a condition favoring the production of peroxynitrite, a powerful pro-oxidant that can mediate the toxic effects of high glucose on heart by itself and/or via the formation of nitrotyrosine, as suggested by the detection of cell apoptosis.

Evidence for an Independent and Cumulative Effect of Postprandial Hypertriglyceridemia and Hyperglycemia on Endothelial Dysfunction and Oxidative Stress Generation

“…31 All these events may convincingly be involved in the pathogenesis of CVD complications. This hypothesis is strongly supported by the recent demonstration that increased apoptosis of myocytes, endothelial cells, and fibroblasts in heart biopsy specimens from diabetic patients 32 and in hearts from streptozotocin diabetic rats, 33 even during acute hyperglycemia, 34 is selectively associated with levels of NT found in those cells. Furthermore, evidence that NT may induce endothelial dysfunction by itself 35 and that it is present in atherosclerotic lesions in humans and in diabetic cynomolgus mokeys 36 -37 suggests that peroxynitrite production may be strongly involved in atherogenesis.…”

Reactive oxygen species mediate a cellular ‘memory’ of high glucose stress signalling

“…1), compared with exposure to continuous normal glucose or high glucose. The markers chosen were: (1) the basement membrane protein fibronectin, shown to be overexpressed in the vessels of diabetic patients [23]; (2) the signalling kinase PKC-β, stimulated by high glucose through a cofactor, diacylglycerol [24,25]; (3) the mitochondrial pro-apoptotic protein BCL-2 family member Bax, indicative of mitochondrial stress [26] and associated with vascular diabetic complications [27]; (4) the DNA damage protein PAR, a product of PARP, shown to be a critical factor in the development of vascular diabetic complications [7]; (5) p47phox, an inducible subunit of the enzyme NAD(P)H oxidase, shown to be a source of ROS in the endothelium of diabetic patients [28]; and (6) the protein adduct 3-NY, a marker of oxidative stress and vascular diabetic complications [29][30][31][32]. As has been shown previously, chronic high glucose resulted in significantly increased levels of: fibronectin [10]; phospho-(activated) PKC-α/βII [25]; p47phox [33]; and 3-NY [31], while the increase in Bax was not statistically significant [27] (Fig.…”

AT 1 Blockade Prevents Glucose-Induced Cardiac Dysfunction in Ventricular Myocytes

“…22,23 The AT 1 receptor is a G protein-coupled receptor that mediates most of the known biologic effects of Ang II. Both local production of Ang II and AT 1 receptor expression are significantly increased in cardiac myocytes and vessels in streptozotocin-induced diabetic rats 24 and in vascular smooth muscle cells exposed to high glucose levels, 25 which are consistent with our findings.…”