A Defect of Neuronal Nitric Oxide Synthase Increases Xanthine Oxidase-Derived Superoxide Anion and Attenuates the Control of Myocardial Oxygen Consumption by Nitric Oxide Derived From Endothelial Nitric Oxide Synthase

Abstract

Abstract-Endothelial nitric oxide synthase (eNOS) plays an important role in the control of myocardial oxygen consumption (MVO 2 ) by nitric oxide (NO). A NOS isoform is present in cardiac mitochondria and it is derived from neuronal NOS (nNOS). However, the role of nNOS in the control of MVO 2 remains unknown. MVO 2 in left ventricular tissues from nNOS Ϫ/Ϫ mice was measured in vitro. Stimulation of NO production by bradykinin or carbachol induced a significant reduction in MVO 2 in wild-type (WT) mice. In contrast to WT, bradykinin-or carbachol-induced reduction in MVO 2 was attenuated in nNOS Ϫ/Ϫ . S-methyl-L-thiocitrulline, a potent isoform selective inhibitor of nNOS, had no effect on bradykinin-induced reduction in MVO 2 in WT. Bradykinin-induced reduction in MVO 2 in eNOS Ϫ/Ϫ mice, in which nNOS still exists, was also attenuated. The attenuated bradykinin-induced reduction in MVO 2 in nNOS Ϫ/Ϫ was restored by preincubation with Tiron, ascorbic acid, Tempol, oxypurinol, or SB203850, an inhibitor of p38 kinase, but not apocynin. There was an increase in lucigenin-detectable superoxide anion (O 2 Ϫ ) in cardiac tissues from nNOScompared with WT. Tempol, oxypurinol, or SB203850 decreased O 2 Ϫ in all groups to levels that were not different from each other. There was an increase in phosphorylated p38 kinase normalized by total p38 kinase protein level in nNOS Key Words: endothelial nitric oxide synthase Ⅲ neuronal nitric oxide synthase Ⅲ superoxide anion Ⅲ p38 Ⅲ oxygen consumption N itric oxide (NO) attenuates mitochondrial respiration by nitrosylating the iron-sulfur centers of aconitase, complexes I and II of the electron transport chain, and through a very potent reversible alteration in the activity of cytochrome c oxidase. [1][2][3] We and others have shown that NO can modulate mitochondrial respiration and tissue oxygen consumption in whole body, 4 heart, skeletal muscle, and kidney both in vivo 5-8 and in vitro. 8 -10 Furthermore, we have shown that NO derived from endothelial NO synthase (eNOS) plays an important role in these processes. 11 Immunohistochemical studies have shown that a NOS is present in the mitochondria. 12-14 Giulivi et al have provided evidence for the production of NO by intact, purified mitochondria using two spectroscopic techniques. [15][16][17][18] In other laboratories, the production of NO by mitochondria has been shown by formation of L-citrulline from radiolabeled L-arginine. 12,19,20 Furthermore, Giulivi et al 17 have reported that mitochondrial NOS was identified as neuronal NOS (nNOS) with two posttranslational modifications in isolated mitochondria from rat liver. Kanai et al 21 identified mitochondrial NOS as nNOS in the isolated cardiac mitochondria from nNOS wild-type (WT) and knockout (nNOS Ϫ/Ϫ ) mice. Thus, nNOS may provide a local source of NO, which can modulate mitochondrial respiration and myocardial oxygen consumption (MVO 2 ). The role of nNOS in the regulation of MVO 2 remains to be elucidated.French et al 22 showed that the local production of NO by mitoch...

Reduced neuronal nitric oxide synthase expression contributes to cardiac oxidative stress and nitroso-redox imbalance in ob/ob mice

“…Importantly, the increased level of XOR activity in ob/ob mice is independent of XOR abundance, since proteins levels are similar in WT and ob/ob mice. This phenomenon is in accordance with previous findings from our group [33] and others [34] that have shown higher XOR activity in NOS1 −/− mice resulting in higher ROS production despite unchanged levels of XOR protein abundance. The increase in oxidative stress in ob/ob mice was not related to NADPH oxidase, which is another important source of ROS in the heart [23], as the expression of its subunits was similar between ob/ob mice and controls.…”

Deficiency of Neuronal Nitric Oxide Synthase Increases Mortality and Cardiac Remodeling After Myocardial Infarction

“…1,2 In addition, NOS1 constrains the activity of cardiac xanthine oxidoreductase (XOR), a major source of O 2 ⅐Ϫ in the heart, with which it forms a protein-protein interaction. 3,4 This in turn contributes to maintaining tissue balance between the production of reactive nitrogen species (RNS) and reactive oxygen species (ROS), the nitroso-redox balance. [3][4][5][6] After myocardial infarction (MI) and in failing myocardium due to dilated cardiomyopathy, NOS1 alters its subcellular localization and translocates to the sarcolemma, 7,8 where it exerts an inhibitory effect on ␤-adrenergic activity.…”

“…3,4 This in turn contributes to maintaining tissue balance between the production of reactive nitrogen species (RNS) and reactive oxygen species (ROS), the nitroso-redox balance. [3][4][5][6] After myocardial infarction (MI) and in failing myocardium due to dilated cardiomyopathy, NOS1 alters its subcellular localization and translocates to the sarcolemma, 7,8 where it exerts an inhibitory effect on ␤-adrenergic activity. The latter has been theorized to be maladaptive and a contributor to left ventricular (LV) dysfunction.…”

Conditional Overexpression of Neuronal Nitric Oxide Synthase Is Cardioprotective in Ischemia/Reperfusion

“…nNOS suppresses the activity of the cardiac XOR, which is one of the major sources of O 2 Ϫ production in the heart. It has been shown that this targeted inhibition maintains the balance between the production of reactive nitrogen species and reactive oxygen species (ROS) 3,8,9 in cardiac tissues. nNOS, also found in mitochondria, 10,11 inhibits the mitochondrial respiratory chain, resulting in inhibition of ATP production.…”