Abstract-Several recent studies have shown that certain forms of genetic or acquired hypertension are associated with oxidative stress and that animals with those types of hypertension respond favorably to antioxidant therapy. We hypothesize that oxidative stress may cause hypertension via (among other mechanisms) enhanced oxidation and inactivation of nitric oxide (NO). To test this hypothesis, Sprague-Dawley rats were subjected to oxidative stress by glutathione (GSH) depletion by means of the GSH synthase inhibitor buthionine sulfoximine (BSO, 30 mmol/L in drinking water) for 2 weeks. The control group was given drug-free drinking water. In parallel experiments, subgroups of animals were provided vitamin E-fortified chow and vitamin C-supplemented drinking water. The BSO-treated group showed a 3-fold decrease in tissue GSH content, a marked elevation in blood pressure, and a significant reduction in the urinary excretion of the NO metabolite nitrate plus nitrite, which suggests depressed NO availability. These characteristics were associated with a significant accumulation in various tissues of nitrotyrosine, which is the footprint of NO inactivation by reactive oxygen species. Administration of vitamin E plus vitamin C ameliorated hypertension, improved urinary nitrate-plus-nitrite excretion, and mitigated nitrotyrosine accumulation (despite GSH depletion) in the BSO-treated animals but had no effect in the control group. In conclusion, GSH depletion resulted in perturbation of the NO system and severe hypertension in normal animals. The effects of BSO were mitigated by concomitant antioxidant therapy despite GSH depletion, which supports the notion that oxidative stress was involved in the pathogenesis of hypertension in this model. O xidative reactions yield high-energy compounds that fuel various biochemical, biophysical, and mechanical functions of aerobic organisms. These reactions are a continuous source of potentially cytotoxic reactive oxygen species (ROS). Under physiological conditions, ROS produced in the course of normal metabolism are fully inactivated by an elaborate cellular and extracellular antioxidant defense system. 1,2 However, in certain pathological conditions, increased generation of ROS and/or depletion of antioxidant capacity leads to enhanced ROS activity and oxidative stress. By promoting lipid peroxidation, DNA damage, and protein modification, oxidative stress can cause cellular injury and tissue damage. 1,3 These processes have been implicated in the pathogenesis of various lesions observed in patients with ischemia, inflammation, aging, degenerative diseases, and numerous other disorders. 4 -6 Several recent studies 7-10 have provided convincing evidence of enhanced ROS activity in patients with various hypertensive disorders. We have found increased ROS activity in rats with lead-induced hypertension and in rats with chronic renal failure. 11 In addition, oxidative stress has been demonstrated in rats with cyclosporine-induced hypertension, 12,13 spontaneously hypertensive r...

Abstract-We have recently demonstrated that long-term consumption of a high-fat, refined-carbohydrate (HFS) diet induces hypertension (HTN) in normal rats compared with a low-fat, complex-carbohydrate (LFCC) diet. Limited evidence suggests that high-fat or high-sugar diets cause enhanced generation of reactive oxygen species (ROS). We therefore hypothesized that by inducing oxidative stress, the HFS diet may promote nitric oxide (NO) inactivation and HTN. To test this hypothesis, female Fischer rats were placed on either the HFS or the LFCC diet starting at 2 months of age. Blood pressure, urinary NO metabolites (NO x ), and total renal NO synthase activity were monitored, and the tissue abundance of nitrotyrosine (NT), which is the stable "footprint" of NO oxidation by ROS, was determined. The HFS diet group exhibited a gradual rise in arterial blood pressure and were hypertensive by 18 months. This trend was accompanied by a marked accumulation of NT in all tested tissues, an initial rise and a subsequent fall in NO synthase activity, and a fall in urinary NO x excretion. The HFS diet-fed animals had a blunted blood pressure response to the NO synthase inhibitor N -nitro-L-arginine methyl ester (L-NAME) compared with the LFCC diet group, which showed a marked hypertensive response to L-NAME. L-NAME-induced HTN was reversible with L-arginine in the LFCC diet group; however, HTN was not corrected by L-arginine supplementation in the HFS diet group. These findings point to enhanced ROS-mediated inactivation and sequestration of NO, which may contribute to the reduction of bioactive NO and HTN in the HFS diet-fed animals. Key Words: arginine Ⅲ endothelial Ⅲ free radicals Ⅲ insulin resistance Ⅲ L-NAME Ⅲ nitric oxide H ypertension (HTN) is the most common cardiovascular disease in the United States and is a hallmark risk factor for myocardial infarction, stroke, and congestive heart failure. 1 It has been estimated that one quarter of all adults and one half of all individuals Ͼ65 years of age have HTN, and it is more common in men than women. 1 The vast majority of patients with HTN have essential HTN of unknown etiology.The vascular endothelium is responsible for the production of several vasoactive substances, 1 of the most vital of which is nitric oxide (NO), a potent vasodilator synthesized from L-arginine by the enzyme NO synthase (NOS). Several investigations have demonstrated that endotheliumdependent relaxation is impaired in patients with essential HTN. 2 This endothelial dysfunction could be the result of a decrease in biologically active NO, ultimately leading to a depressor/pressor imbalance stemming from tonic removal of NO-mediated vasodilation. 2,3 There is evidence that hyperlipidemia 4 and high-sugar diets, 5 high-fat diets, 6 or both induce oxidative stress. We have recently demonstrated increased lipid peroxidation 7 and subsequently found direct evidence of NO oxidation by reactive oxygen species (ROS) in a model of lead-induced HTN. 8 In addition, we recently reported that female and male rats ...

An increase in ROS activity upregulates NOS expression in vitro in HCAECs grown in culture, and also in vivo in animals. This effect appears to be, in part, mediated by limiting the availability of NO, thereby exerting a negative feedback influence on NOS expression through activation of NFkappaB.

SUMMARY:Chronic iron (Fe) overload is associated with a marked increase in renal tissue iron content and injury. It is estimated that 10% of the American population carry the gene for hemochromatosis and 1% actually suffer from iron overload. The mechanism of iron overload-associated renal damage has not been fully elucidated. Iron can accelerate lipid peroxidation leading to organelle membrane dysfunction and subsequent cell injury/death. Iron-catalyzed generation of reactive oxygen species (ROS) is responsible for initiating the peroxidatic reaction. We investigated the possible association of oxidative stress and its impact on nitric oxide (NO) metabolism in iron-overload-associated renal injury. Rats were randomized into Fe-loaded (given 0.5 g elemental iron/kg body weight as iron dextran; IV), Fe-depleted (given an iron-free diet for 20 weeks), and control groups. Renal histology, tissue expression of endothelial and inducible nitric oxide synthases (eNOS and iNOS), renal tissue expression of nitrotyrosine, plasma, and renal tissue lipid peroxidation product, malondialdehyde (MDA), and plasma and urinary NO metabolites (NOx) were examined. Iron overload was associated with mild proteinuria, tissue iron deposition together with significant glomerulosclerosis, tubular atrophy, and interstitial fibrosis. Rare focal glomerulosclerosis and tubulointerstitial changes were noted in normal controls. No renal lesions were observed in Fe-depleted rats. Iron deposits were seen in glomeruli, proximal tubules, and interstitium. The iron staining in the distal tubules was negligible. Both plasma and renal tissue MDA and renal tissue nitrotyrosine were increased significantly in Fe-loaded rats compared with control rats. In contrast, Fe-depleted animals showed a marked reduction in plasma and renal tissue MDA and nitrotyrosine together with significant elevation of urinary NOx excretion. In addition, iron-overload was associated with up-regulation of renal eNOS and iNOS expressions when compared with the control and Fe-depleted rats that showed comparable values. In conclusion, chronic iron overload resulted in iron deposition in the glomeruli and proximal tubules with various renal lesions and evidence of increased ROS activity, enhanced ROS-mediated inactivation, and sequestration of NO and compensatory up-regulation of renal eNOS and iNOS expressions. However, iron depletion was associated with reduced MDA and tissue nitrotyrosine abundance, increased urinary NOx excretion, normal nitric oxide synthase (NOS) expression, and absence of renal injury. These findings point to the possible role of ROS in chronic iron overload-induced renal injury. (Lab Invest 2000, 80:1905-1914.