Absence of Inducible Nitric Oxide Synthase Reduces Myocardial Damage During Ischemia Reperfusion in Streptozotocin-Induced Hyperglycemic Mice

Abstract

We investigated the role of inducible nitric oxide synthase (iNOS) on ischemic myocardial damage and angiogenic process in genetically deficient iNOS (iNOS ؊/؊ ) mice and wild-type littermates (iNOS ؉/؉ ), with and without streptozotocin-induced (70 mg/kg intravenously) diabetes. After ischemia (25 min) and reperfusion (120 min), both iNOS ؉/؉ and iNOS ؊/؊ diabetic mice (blood glucose 22 mmol/l) had myocardial infarct size greater than their respective nondiabetic littermates (P < 0.01). Myocardial infarct size (P < 0.05), apoptotic index (P < 0.005), and tissue levels of tumor necrosis factor (P < 0.01), interleukin-6 (P < 0.01), and interleukin-18 (P < 0.01) were higher in nondiabetic iNOS ؊/؊ mice compared with nondiabetic iNOS ؉/؉ mice. As compared with diabetic iNOS ؊/؊ mice, diabetic iNOS ؉/؉ mice showed a greater infarct size (P < 0.01) associated with the highest tissue levels of nitrotyrosine and proinflammatory cytokines, as well as apoptosis. The beneficial role of iNOS in modulating defensive responses against ischemia/reperfusion injury seems to be abolished in diabetic mice. Diabetes 53: 454 -462, 2004 H yperglycemia is a risk factor for adverse outcomes during acute illness in patients with and without diabetes (1). In patients who have just experienced myocardial infarction, glucose values in excess of 110 -144 mg/dl are associated with a threefold increase in mortality and a higher risk of heart failure (2). Consequently, hyperglycemia, at the time of myocardial infarction, may be an important and potentially modifiable risk factor for poor outcome. An effect of high glucose to enhance inducible nitric oxide synthase (iNOS) expression has recently been reported (3). iNOS is a calcium-independent enzyme often induced by cytokines and produces high levels of NO. Although increased NO production from iNOS may decrease vascular resistance and enhance early defensive inflammatory response against reperfusion injury (4), which are beneficial to the ischemic myocardium, high levels of NO may also depress myocardial contractility and, through formation of peroxynitrite, may cause myocardial damage (5).Using knockout mice with a targeted disruption of the iNOS gene and control mice with a functional iNOS gene, we investigated the role of iNOS in the development of tissue damage in ischemic hearts after reperfusion during diabetes. We determined the extent of myocardial injury, apoptosis, and the levels of proinflammatory cytokines such as interleukin (IL)-18, IL-6, and tumor necrosis factor-␣ (TNF-␣) in heart tissue. RESEARCH DESIGN AND METHODSIschemia-reperfusion study was carried out in mice genetically deficient in iNOS (iNOS Ϫ/Ϫ ) and their wild-type littermates (iNOS ϩ/ϩ ). The homozygous iNOS Ϫ/Ϫ and iNOS ϩ/ϩ (wild-type C57B1/6 ϫ 129/Sv) male mice (20 -25 g; supplied by Fons A.J. Van de Loo, Department of Rheumatology, University Hospital Nijmegen, Nijmegen, The Netherlands) were generated as previously described (6). A neo cassette using homologous recombination replaced the first four exons of...

RAGE and Modulation of Ischemic Injury in the Diabetic Myocardium

“…Our results are consistent with previous studies of acute ischemia and reperfusion in which administration of semi-selective inhibitors of iNOS or iNOS-null mice enhanced cardiac performance and/or reduced myocardial infarct size (34 -37). Previous studies showed that iNOS played critical roles in diabetes and I/R in the heart, because iNOS-null mice displayed protection from the adverse effect of this injury, especially in diabetes (38). Our findings definitively link RAGE and RAGE signaling in endothelial cells and mononuclear phagocyte to generation of NO and pathogenic oxidant stress species in the diabetic heart.…”

The Insulin Sensitizer Pioglitazone Improves the Deterioration of Ischemic Preconditioning in Type 2 Diabetes Mellitus Rats

“…48) The difference in the type of diabetes may be the reason for these differences. [49][50][51] Therefore, the effect of IP may be decreased in type 2 diabetes mellitus with hyperinsulinemia, although it has not yet been clarified in type 1 diabetes mellitus without hyperinsulinemia.…”

Ischaemic preconditioning does not protect the heart in obese and lean animal models of Type 2 diabetes

“…It has been reported that nitric oxide, protein kinase C and K ATPchannels are involved in IPC in non-diabetic subjects and that nitric oxide metabolism is impaired in diabetic subjects. However, in Type 1 diabetic animals the presence of a functional inducible nitric oxide synthase gene (producing high levels of nitric oxide) seems to aggravate ischaemic damage [21]. Hyperglycaemia is considered a major determinant of the extent of myocardial infarction in experimentally induced Type 1 diabetes and even in the absence of diabetes [22,23].…”