Increased superoxide leads to decreased flow-induced dilation in resistance arteries of Mn-SOD-deficient mice

Catalytic Antioxidants in the Kidney

Reactive oxygen species and reactive nitrogen species are highly implicated in kidney injuries that include acute kidney injury, chronic kidney disease, hypertensive nephropathy, and diabetic nephropathy. Therefore, antioxidant agents are promising therapeutic strategies for kidney diseases. Catalytic antioxidants are defined as small molecular mimics of antioxidant enzymes, such as superoxide dismutase, catalase, and glutathione peroxidase, and some of them function as potent detoxifiers of lipid peroxides and peroxynitrite. Several catalytic antioxidants have been demonstrated to be effective in a variety of in vitro and in vivo disease models that are associated with oxidative stress, including kidney diseases. This review summarizes the evidence for the role of antioxidant enzymes in kidney diseases, the classifications of catalytic antioxidants, and their current applications to kidney diseases.

Paradoxical Roles of Antioxidant Enzymes: Basic Mechanisms and Health Implications

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are generated from aerobic metabolism, as a result of accidental electron leakage as well as regulated enzymatic processes. Because ROS/RNS can induce oxidative injury and act in redox signaling, enzymes metabolizing them will inherently promote either health or disease, depending on the physiological context. It is thus misleading to consider conventionally called antioxidant enzymes to be largely, if not exclusively, health protective. Because such a notion is nonetheless common, we herein attempt to rationalize why this simplistic view should be avoided. First we give an updated summary of physiological phenotypes triggered in mouse models of overexpression or knockout of major antioxidant enzymes. Subsequently, we focus on a series of striking cases that demonstrate "paradoxical" outcomes, i.e., increased fitness upon deletion of antioxidant enzymes or disease triggered by their overexpression. We elaborate mechanisms by which these phenotypes are mediated via chemical, biological, and metabolic interactions of the antioxidant enzymes with their substrates, downstream events, and cellular context. Furthermore, we propose that novel treatments of antioxidant enzyme-related human diseases may be enabled by deliberate targeting of dual roles of the pertaining enzymes. We also discuss the potential of "antioxidant" nutrients and phytochemicals, via regulating the expression or function of antioxidant enzymes, in preventing, treating, or aggravating chronic diseases. We conclude that "paradoxical" roles of antioxidant enzymes in physiology, health, and disease derive from sophisticated molecular mechanisms of redox biology and metabolic homeostasis. Simply viewing antioxidant enzymes as always being beneficial is not only conceptually misleading but also clinically hazardous if such notions underpin medical treatment protocols based on modulation of redox pathways.

Vascular TRP channels: performing under pressure and going with the flow

Endothelial cells and smooth muscle cells of resistance arteries mediate opposing responses to mechanical forces acting on the vasculature, promoting dilation in response to flow and constriction in response to pressure, respectively. In this review, we explore the role of TRP channels, particularly endothelial TRPV4 and smooth muscle TRPC6 and TRPM4 channels, in vascular mechanosensing circuits, placing their putative mechanosensitivity in context with other proposed upstream and downstream signaling pathways.

Oxidative stress induces gastric submucosal arteriolar dysfunction in the elderly

AIM: To evaluate human gastric submucosal vascular dysfunction and its mechanism during the aging process.

METHODS: Twenty male patients undergoing subtotal gastrectomy were enrolled in this study. Young and elderly patient groups aged 25-40 years and 60-85 years, respectively, were included. Inclusion criteria were: no clinical evidence of cardiovascular, renal or diabetic diseases. Conventional clinical examinations were carried out. After surgery, gastric submucosal arteries were immediately dissected free of fat and connective tissue. Vascular responses to acetylcholine (ACh) and sodium nitroprusside (SNP) were measured by isolated vascular perfusion. Morphological changes in the gastric mucosal vessels were observed by hematoxylin and eosin (HE) staining and Verhoeff van Gieson (EVG) staining. The expression of xanthine oxidase (XO) and manganese-superoxide dismutase (Mn-SOD) was assessed by Western blotting analysis. The malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) content and the activities of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) were determined according to commercial kits.

RESULTS: The overall structure of vessel walls was shown by HE and EVG staining, respectively. Disruption of the internal elastic lamina or neointimal layers was not observed in vessels from young or elderly patients; however, cell layer number in the vessel wall increased significantly in the elderly group. Compared with submucosal arteries in young patients, the amount of vascular collagen fibers, lumen diameter and media cross-sectional area were significantly increased in elderly patients. Ach- and SNP-induced vasodilatation in elderly arterioles was significantly decreased compared with that of gastric submucosal arterioles from young patients. Compared with the young group, the expression of XO and the contents of MDA and H₂O₂ in gastric submucosal arterioles were increased in the elderly group. In addition, the expression of Mn-SOD and the activities of SOD and GSH-Px in the elderly group decreased significantly compared with those in the young group.

CONCLUSION: Gastric vascular dysfunction and senescence may be associated with increased oxidative stress and decreased antioxidative defense in the aging process.

Molecular biology of atherosclerosis

At least 468 individual genes have been manipulated by molecular methods to study their effects on the initiation, promotion, and progression of atherosclerosis. Most clinicians and many investigators, even in related disciplines, find many of these genes and the related pathways entirely foreign. Medical schools generally do not attempt to incorporate the relevant molecular biology into their curriculum. A number of key signaling pathways are highly relevant to atherogenesis and are presented to provide a context for the gene manipulations summarized herein. The pathways include the following: the insulin receptor (and other receptor tyrosine kinases); Ras and MAPK activation; TNF-α and related family members leading to activation of NF-κB; effects of reactive oxygen species (ROS) on signaling; endothelial adaptations to flow including G protein-coupled receptor (GPCR) and integrin-related signaling; activation of endothelial and other cells by modified lipoproteins; purinergic signaling; control of leukocyte adhesion to endothelium, migration, and further activation; foam cell formation; and macrophage and vascular smooth muscle cell signaling related to proliferation, efferocytosis, and apoptosis. This review is intended primarily as an introduction to these key signaling pathways. They have become the focus of modern atherosclerosis research and will undoubtedly provide a rich resource for future innovation toward intervention and prevention of the number one cause of death in the modern world.

CYP2C29 produces superoxide in response to shear stress

OBJECTIVE

Activation of CYP2C29 releases superoxide during shear stress-induced dilation (SSID).

METHODS

Mesenteric arteries isolated from female eNOS-KO and WT mice were cannulated and pressurized. Vasodilation and superoxide production in response to shear stress were assessed.

RESULTS

Shear stress-induced dilation was significantly attenuated in vessels of eNOS-KO compared with WT mice, which was normalized by tempol and PEG-Catalase, in a PPOH (inhibitor of CYP2C29)-sensitive manner, but remained unaffected by VAS2870 and allopurinol, inhibitors of NADPH oxidase and xanthine oxidase, respectively. NaNO(2)-induced dilation was comparable in both strains of mice. Confocal microscopy shows that SS-stimulated superoxide was increased particularly in the endothelium of eNOS-KO mice. HPLC analysis of 2-EOH indicated an increase in SS-stimulated superoxide in vessels of eNOS-KO mice, a response that was sensitive to PPOH. Inhibition of soluble epoxide hydrolase significantly enhanced SSID without affecting SS-stimulated superoxide production. CYP2C29 and catalase were upregulated, and exogenous H(2)O(2) caused vasoconstriction in vessels of eNOS-KO mice.

CONCLUSIONS

CYP2C29 synthesizes EETs to mediate SSID, and simultaneously releases superoxide and sequential H(2)O(2), which in turn impair SSID.

Decreases in manganese superoxide dismutase expression and activity contribute to oxidative stress in persistent pulmonary hypertension of the newborn

A rapid increase in the synthesis and release of nitric oxide (NO) facilitates the pulmonary vasodilation that occurs during birth-related transition. Alteration of this transition in persistent pulmonary hypertension of the newborn (PPHN) is associated with impaired function of endothelial nitric oxide synthase (eNOS) and an increase in oxidative stress. We investigated the hypothesis that a decrease in expression and activity of mitochondrial localized manganese superoxide dismutase (MnSOD) in pulmonary artery endothelial cells (PAEC) increases oxidative stress and impairs eNOS function in PPHN. We isolated PAEC and pulmonary arteries from fetal lambs with PPHN induced by prenatal ductus arteriosus ligation or sham ligation (control). We investigated MnSOD expression and activity, tyrosine nitration of MnSOD, and mitochondrial O(2)(-) levels in PAEC from control and PPHN lambs. We introduced exogenous MnSOD via an adenoviral vector (ad-MnSOD) transduction into PAEC and pulmonary arteries of PPHN lambs. The effect of ad-MnSOD was investigated on: mitochondrial O(2)(-) levels, MnSOD and eNOS expression and activity, intracellular hydrogen peroxide (H(2)O(2)) levels, and catalase expression in PAEC. MnSOD mRNA and protein levels and activity were decreased and MnSOD tyrosine nitration was increased in PPHN-PAEC. ad-MnSOD transduction of PPHN-PAEC increased its activity two- to threefold, decreased mitochondrial O(2)(-) levels, and increased H(2)O(2) levels and catalase expression. ad-MnSOD transduction improved eNOS expression and function and the relaxation response of PPHN pulmonary arteries. Our observations suggest that decreased MnSOD expression and activity contribute to the endothelial dysfunction observed in PPHN.

Mitochondrial reactive oxygen species-mediated signaling in endothelial cells

Once thought of as toxic by-products of cellular metabolism, reactive oxygen species (ROS) have been implicated in a large variety of cell-signaling processes. Several enzymatic systems contribute to ROS production in vascular endothelial cells, including NA(D)PH oxidase, xanthine oxidase, uncoupled endothelial nitric oxide synthase, and the mitochondrial electron transport chain. The respiratory chain is the major source of ROS in most mammalian cells, but the role of mitochondria-derived ROS in vascular cell signaling has received little attention. A new paradigm has evolved in recent years postulating that, in addition to producing ATP, mitochondria also play a key role in cell signaling and regulate a variety of cellular functions. This review focuses on the emerging role of mitochondrial ROS as signaling molecules in vascular endothelial cells. Specifically, we discuss some recent findings that indicate that mitochondrial ROS regulate vascular endothelial function, focusing on major sites of ROS production in endothelial mitochondria, factors modulating mitochondrial ROS production, the physiological and clinical implications of endothelial mitochondrial ROS, and methodological considerations in the study of mitochondrial contribution to vascular ROS generation.

Nitric oxide and peroxynitrite in health and disease

The discovery that mammalian cells have the ability to synthesize the free radical nitric oxide (NO) has stimulated an extraordinary impetus for scientific research in all the fields of biology and medicine. Since its early description as an endothelial-derived relaxing factor, NO has emerged as a fundamental signaling device regulating virtually every critical cellular function, as well as a potent mediator of cellular damage in a wide range of conditions. Recent evidence indicates that most of the cytotoxicity attributed to NO is rather due to peroxynitrite, produced from the diffusion-controlled reaction between NO and another free radical, the superoxide anion. Peroxynitrite interacts with lipids, DNA, and proteins via direct oxidative reactions or via indirect, radical-mediated mechanisms. These reactions trigger cellular responses ranging from subtle modulations of cell signaling to overwhelming oxidative injury, committing cells to necrosis or apoptosis. In vivo, peroxynitrite generation represents a crucial pathogenic mechanism in conditions such as stroke, myocardial infarction, chronic heart failure, diabetes, circulatory shock, chronic inflammatory diseases, cancer, and neurodegenerative disorders. Hence, novel pharmacological strategies aimed at removing peroxynitrite might represent powerful therapeutic tools in the future. Evidence supporting these novel roles of NO and peroxynitrite is presented in detail in this review.

Rho-kinase contributes to hypoxia/reoxygenation-induced cerebral endothelial dysfunction

Hypoxia/reoxygenation (H/R) in vitro induced cerebral endothelial dysfunction is mediated by superoxide production. However, the intracellular pathways involved remain unclear. The present study was designed to investigate the involvement of Rho-kinase and its interaction with nitric oxide (NO) in cerebral endothelial dysfunction after H/R. Arterial diameter and intraluminal pressure were simultaneously measured in vitro on rat posterior cerebral arteries. Vascular NO production was determined by measuring stable NO metabolites nitrate/nitrite. H/R selectively inhibited cerebral vasodilation to the endothelium-dependent agonist acetylcholine (ACh, 0.01 to 10 micromol/L) and caused NO deficiency. H/R-impaired vasodilation to ACh was reversed by Y27632 (1 micromol/L), a specific inhibitor of Rho-kinase, but not by chelerythrine (1 micromol/L), a selective inhibitor of protein kinase C. Y27632 had no protective effect in the presence of N-nitro-L-arginine methyl ester (L-NAME; 100 micromol/L), a specific endothelial NO synthase inhibitor. L-NAME (100 micromol/L) alone failed to modulate H/R-impaired vasodilation, so did L-arginine (3 mmol/L), a substrate for NO synthase. However, a stable NO donor diethylenetetra amine-NONOate (5 micromol/L) normalized H/R-impaired dilation to ACh. In conclusion, H/R-induced endothelial dysfunction is associated with activation of Rho-kinase-dependent pathway and NO deficiency. Pretreatment with either Y27632 or the stable NO donor profoundly prevented H/R-mediated cerebral endothelial dysfunction.

Novel isoforms of NADPH-oxidase in cerebral vascular control

Reactive oxygen species (ROS) are thought to play an important role in the initiation and progression of a variety of vascular diseases. Furthermore, accumulating evidence indicates that ROS may also serve as important cell signalling molecules for the regulation of normal vascular function. Recently, a novel family of proteins (Nox1, 2 and 4) that act as the catalytic subunit of the superoxide (O2-) producing enzyme NADPH-oxidase has been discovered in vascular cells. There is now preliminary evidence suggesting that NADPH-oxidase-derived ROS may serve as a physiological vasodilator mechanism in the cerebral circulation. Moreover, the activity of NADPH-oxidase is profoundly greater in cerebral versus systemic arteries. Studies have shown that Nox1, Nox2 (also known as gp91phox) and Nox4 are all expressed in cerebral arteries, suggesting that multiple isoforms of NADPH-oxidase may be important for ROS production by cerebral arteries. Enhanced NADPH-oxidase activity is associated with several vascular-related diseases, including hypertension, stroke, subarachnoid haemorrhage and Alzheimer's dementia; however, the consequences of this for cerebral vascular function are controversial. For example, there is some evidence suggesting that NADPH-oxidase-derived O2- may play a role in endothelial dysfunction of cerebral arteries and a subsequent rise in cerebral vascular tone, associated with hypertension. However, activation of NADPH-oxidase elicits cerebral vasodilatation in vivo, and this mechanism is enhanced in chronic hypertension. While further supportive evidence is needed, it is an intriguing possibility that NADPH-oxidase-derived ROS may play a protective role in regulating cerebral vascular tone during disease.

A computational model for free radicals transport in the microcirculation

Nitric oxide (NO), superoxide (O(2)(-)), and peroxynitrite (ONOO(-)) interactions in pathophysiologic conditions such as cardiovascular disease, hypertension, and diabetes have been studied extensively in vivo and in vitro. A reduction in bioavailability of NO is a common event that is known as the endothelial dysfunction in these conditions. Despite intense investigation of NO biotransport and O(2)(-) and ONOO(-) biochemical interactions in vasculature, we have very little quantitative knowledge of distributions and concentrations of NO, O(2)(-), and ONOO(-) under normal physiologic and pathophysiologic conditions. Based on fundamental principles of mass balance, vessel geometry, and reaction kinetics, we developed a mathematical model of these free radicals transport in and around an arteriole during oxidative stress. We investigated the role of O(2)(-) and ONOO(-) in inactivating vasoactive NO. The model predictions include (a) NO interactions with oxygen, O(2)(-), and ONOO(-) have relatively little effect on the NO level in the vascular smooth muscle under physiologic conditions; (b) superoxide diffuses only a few microns from its source, whereas peroxynitrite diffuses over a larger distance; and (c) reduced superoxide dismutase levels significantly increase O(2)(-) and peroxynitrite concentrations and decrease NO concentration. Model results indicate that the reduced NO bioavailability and enhanced peroxynitrite formation may vary depending on the location of oxidative stress in the microcirculation, which occurs at diverse vascular cell locations in diabetes, aging, and cardiovascular diseases. The results will have significant implications for our understanding of these free radical interactions in physiologic and pathophysiologic conditions resulting from endothelial dysfunction.

Selective cerebral vascular dysfunction in Mn-SOD-deficient mice

We tested the hypothesis that the mitochondrial form of superoxide dismutase [manganese superoxide dismutase (Mn-SOD)] protects the cerebral vasculature. Basilar arteries (baseline diameter ∼140 μm) from mice were isolated, cannulated, and pressurized to measure vessel diameter. In arteries from C57BL/6 mice preconstricted with U-46619, acetylcholine (ACh; an endothelium-dependent vasodilator) produced dilation that was similar in male and female mice and abolished by an inhibitor of nitric oxide synthase. Vasodilation to ACh was not altered in heterozygous male or female Mn-SOD-deficient (Mn-SOD+/−) mice compared with wild-type littermate controls (Mn-SOD+/+). Constriction of the basilar artery to arginine vasopressin, but not KCl or U-46619, was increased in Mn-SOD+/− mice ( P < 0.05), and this effect was prevented by tempol, a scavenger of superoxide. We also examined responses of cerebral (pial) arterioles (branches of the middle cerebral artery, control diameter ∼30 μm) to ACh in anesthetized mice using a cranial window. Responses to ACh, but not nitroprusside (an endothelium-independent agonist), were reduced ( P < 0.05) in cerebral arterioles in Mn-SOD+/− mice, and this effect was prevented by tempol. Thus these are the first data on the role of Mn-SOD in cerebral circulation. In the basilar artery, ACh produced nitric oxide-mediated dilation that was similar in male and female mice. Under normal conditions in cerebral arteries, responses to ACh were not altered but constrictor responses were selectively enhanced in Mn-SOD+/− mice. In the cerebral microcirculation, there was superoxide-mediated impairment of responses to ACh.