Evidence for superoxide anion generation in aortas of cholesterol-fed rabbits treated with l -arginine

In vivo Evidence of Arterial Dynamic Properties Alteration in Atherosclerotic Rabbit

OBJECTIVES

Atherosclerosis severely damages the arterial wall. The aim of this study was to assess in vivo, for the first time, arterial dynamic properties, reactivity, and stiffness in atherosclerotic (ATH) rabbits.

METHODS

The rabbits were fed with 0.3% cholesterol diet. Femoral artery (FA) or abdominal aorta (AA) diameter was recorded by echotracking, together with blood pressure. Arterial reactivity after local administration of agents and stiffness were measured as diameter or pulsatile diameter changes.

RESULTS

FA dilation induced by acetylcholine was reduced in the function of diet duration (9-65 weeks). With mid-term diet duration (35-45 weeks), the dilation to nitroprusside was greatly reduced; the constriction to norepinephrine was reduced but not that to serotonin, thromboxane agonist, or angiotensin II. After 17- and 28-week diet AA and FA stiffness were increased while distensibility was reduced. Arterial stiffness measured by regional pulse wave velocity was unaltered. We observed that after 28-week diet, FA exhibited a stiffened wall at the plaque level and higher distensibility at the upstream site.

DISCUSSION/CONCLUSION

Arterial reactivity and compliance were greatly modified by atherosclerosis, at various degrees dependent on diet duration. ATH rabbit is therefore a suitable model for in vivo investigations of treatments targeting dynamic properties of arterial wall.

Effect of chronic L-Arginine supplementation on aortic fatty streak formation and serum nitric oxide concentration in normal and high-cholesterol fed rabbits

Several reports indicated the beneficial effects of short-term L-Arginine (L-Arg) administration on atherosclerosis processes. The aim of this study was to evaluate the effect of chronic L-Arg supplementation on serum lipid profile, aortic Fatty Streak (FS) formation, and serum Nitric oxide (NO) concentration in Normal Diet (ND) and High-Cholesterol Diet (HCD) fed rabbits. 24 male rabbits were randomly divided into four groups (n=6 in each group) (i): ND for seven months; (ii): ND for 1 month plus ND + L-Arg for six months; (iii): HCD (1%) for 1 month plus HCD (0.5%) for six months; (iv): HCD (1%) for 1 month plus HCD (0.5%) + L-Arg for six months. At the end of the study, histological evaluation of aortic FS formation was performed. Blood samples were taken for serum lipid profile and NO concentrations. L-Arg did not change serum total cholesterol, triglyceride, LDL and LDL/HDL ratio in normal and hypercholesterolemic rabbits (p>0.05). Histological examination of thoracic aortae revealed that the HCD group had higher FS formation compared to the ND group (2.1 ± 0.16 vs. 0 ± 0; respectively; p<0.05) and L-Arg supplementation did not attenuate FS formation in the HCD group (1.93 ± 0.17 compare to 2.1 ± 0.16; p>0.05). Serum NO level in the HCD group was higher than ND groups (p<0.05). Chronic L-Arg supplementation did not alter serum NO concentration either in the hypercholesterolemic or in the ND group (p>0.05). It seems that chronic L-Arg supplementation does not have beneficial effects on aortic fatty streak formation, serum lipids and NO concentrations in this model of experimental hypercholesterolemia.

Effect of L-arginine and selenium added to a hypocaloric diet enriched with legumes on cardiovascular disease risk factors in women with central obesity: a randomized, double-blind, placebo-controlled trial

BACKGROUND/AIMS

We aimed to discover if L-arginine and selenium alone or together can increase the effect of a hypocaloric diet enriched in legumes (HDEL) on central obesity and cardiovascular risk factors in women with central obesity.

METHODS

This randomized, double-blind, placebo-controlled trial was undertaken in 84 premenopausal women with central obesity. After a 2-week run-in period on an isocaloric diet, participants were randomly assigned to a control diet (HDEL), L-arginine (5 g/day) and HDEL, selenium (200 μg/day) and HDEL or L-arginine, selenium and HDEL for 6 weeks. Cardiovascular risk factors were assessed before intervention and 3 and 6 weeks afterwards.

RESULTS

After 6 weeks, L-arginine had significantly reduced waist circumference (WC); selenium had significantly lowered fasting concentrations of serum insulin and the homeostasis model assessment of insulin resistance index; the interaction between L-arginine and selenium significantly reduced the fasting concentration of nitric oxides (NO(x)), and HDEL lowered triglycerides (TG) and WC and significantly increased the fasting concentration of NO(x). HDEL reduced high-sensitivity C-reactive protein levels in the first half of the study and returned them to basal levels in the second half.

CONCLUSION

These data indicate the beneficial effects of L-arginine on central obesity, selenium on insulin resistance and HDEL on serum concentrations of NO(x) and TG.

Chronic L-arginine administration increases oxidative and nitrosative stress in rat hyperoxaluric kidneys and excessive crystal deposition

Hyperoxaluric kidneys show an impaired diuretic response to acute infusion of L-arginine. In this study, we examined the chronic effect of l-arginine supplementation on CaOx crystal formation in hyperoxaluric rat kidneys. Eight groups were tested: control (received drinking water), L group (received L-arginine, 0.6%), LN group [received NG-nitro-L-arginine methyl ester (L-NAME, 10 mg/kg)], L + LN group (received L-arginine + l-NAME), HP group [received hydroxyl-L-proline (HP, 5%) mixed with chow to induce hyperoxaluria], L + HP group (received HP + L-arginine), HP + LN group, and L + HP + LN group. The duration was 42 days, and each group had eight animals. Urinary biochemistry and renal CaOx amounts were measured, as well as renal expressions of nitric oxide synthase (NOS) isoforms and NAD(P)H oxidase. The distribution of inducible NOS (iNOS), NAD(P)H oxidase, ED1-positive cells, and nitrotyrosine was examined by immunohistochemical and immunofluorescence studies, whereas superoxide production from the kidneys was examined by fluorescence spectrometric assay. Compared with the HP group, the L + HP group had excessive CaOx crystal accumulation and enhanced endothelial NOS (eNOS), iNOS, and NAD(P)H oxidase protein expression in the kidney. Urinary excretion of nitrotyrosine was markedly increased. Increased superoxide formation in the L + HP kidney was derived from NAD(P)H oxidase and uncoupled eNOS, and increased nitrotyrosine formation might derive from iNOS and ED1-positive cells that gathered around the CaOx crystals. L-NAME cotreatment (L + HP + LN group) reduced renal oxidative nitrosative stress and tubular damage, which were induced by L + HP. The results showed that chronic l-arginine treatment to the hyperoxaluric kidney with massive CaOx crystal deposition may have a toxic effect by enhancing intrarenal oxidative and nitrosative stress.

Endothelial arginase: a new target in atherosclerosis

Decreased endothelial nitric oxide (NO) bioavailability as it relates to endothelial dysfunction plays an important role in various cardiovascular disorders, including athero-sclerosis. Recent research has provided evidence that endothelial dysfunction in atherosclerosis is not primarily caused by decreased endothelial NO synthase (eNOS) gene expression, but rather deregulation of eNOS enzymatic activity, which contributes to the increased oxidative stress in atherosclerosis. Among other mechanisms, the substrate L-arginine is an important limiting factor for NO production. Emerging evidence demonstrates that L-arginine is not only converted to NO via eNOS, but also metabolized to urea and l-ornithine via arginase in endothelial cells. Hence, arginase competes with eNOS for the substrate L-arginine, resulting in deceased NO production. There are an increasing number of studies showing that enhanced arginase gene expression and/or activity contribute to endothelial dysfunction in various cardiovascular disorders, including atherosclerosis. Thus, endothelial arginase may represent a new therapeutic target in atherosclerosis.

Recent advances in understanding endothelial dysfunction in atherosclerosis

Over the last two decades, it has become evident that decreased bioavailability of endothelial nitric oxide (NO) produced from endothelial NO synthase (eNOS), referred to as endothelial dysfunction, plays a crucial role in the development and progression of atherosclerosis. Much progress has been made in understanding the mechanisms of decreased endothelial NO bioavailability at the levels of regulation of eNOS gene expression, eNOS enzymatic activity and NO inactivation. Initial studies suggest that increasing eNOS gene expression would improve endothelial NO release in the hope of inhibiting the progression of atherosclerosis. Recent experimental studies, however, do not always support this therapeutic concept and show some evidence that overexpression of eNOS in atherosclerosis may be even harmful for the disease progression.Thus, recent research to improve endothelial function in atherosclerosis has focused on regulation of eNOS enzymatic activity and prevention of NO inactivation by oxidative stress. Since the role of oxidative stress in endothelial NO bioavailability has been reviewed in a large number of comprehensive articles, this article focuses on the relevant regulatory mechanisms of eNOS enzymatic activity that are emerging to play a role in endothelial dysfunction in atherosclerosis.

Selective iNOS inhibitor, ONO1714 successfully retards the development of high-cholesterol diet induced atherosclerosis by novel mechanism

OBJECTIVE

We have reported that inducible nitric oxide synthase (iNOS) is present only in deep areas of plaque in atherosclerosis. However, the role of iNOS in the development of atherosclerosis is not well known. We therefore investigated the relevance of iNOS inhibition.

METHODS AND RESULTS

Seven groups of male rabbits were fed a 0.5% high-cholesterol diet (HCD) for 8 weeks. Gp1-HCD was fed HCD only; Gp2-O17 was fed HCD with ONO1714, an iNOS inhibitor; Gp3-AG was fed HCD with amino-guanidine (AG), an iNOS inhibitor; Gp4-AR was fed HCD with l-arginine; Gp5-AR-O17 was fed HCD with l-arginine with ONO1714; Gp6-LNA was fed HCD with l-NAME (a NOS inhibitor); and Gp7-LN-O17 was fed HCD with l-NAME plus ONO1714. ONO1714 decreased atherosclerosis by about 70% (area occupied by lesions: 3.0+/-0.4% in Gp2-O17 versus 10.3+/-1.6% in Gp1-HCD) and also decreased atherosclerosis in Gp7-LN-O17. The ONO compound enhanced the atheroprotective effect of l-arginine. Amino-guanidine also showed an anti-atherosclerotic effect. Tone-related basal NO release and acetylcholine-induced NO-dependent relaxation were improved in Gp2-O17 and Gp5-AR-O17. O(2)(-) release was decreased in Gp2-O17 and Gp7-LN-O17.

CONCLUSION

ONO1714 retards the progression of atherosclerosis in rabbits. Although the up-regulation of endothelial nitric oxide synthase (eNOS) and the decrease of O(2)(-) may play roles in this retardation, the inhibition of iNOS may be the principal factor, alone was not sufficient.

Therapeutic potential of nitric oxide donors in the prevention and treatment of atherosclerosis

Well-known risk factors for atherosclerosis include hypercholesterolaemia, hypertension, diabetes, and smoking. These conditions are associated with endothelial dysfunction, which itself is associated with reduced endothelial generation of nitric oxide (NO). This is an overview of the implications of NO generation in atherosclerosis and of the potential therapeutic benefit of drugs which donate NO, such as organic nitrates, nicorandil, and sydnonimines, or those which increase the availability of endogenous NO, such as statins, angiotensin-converting enzyme inhibitors, L-arginine, and tetrahydrobiopterin.

Identification of cytochrome-b5 reductase as the enzyme responsible for NADH-dependent lucigenin chemiluminescence in human spermatozoa

Lucigenin-dependent chemiluminescence together with 2-[4-iodophenyl]-3-[4-nitrophenyl]-5-[2,4-disulfophenyl]-2H tetrazolium monosodium salt (WST-1) reduction can be detected following addition of NADH to many cell types, including human sperm suspensions. Although many reports suggest that such a phenomenon is due to reactive oxygen species production, other oxygen detecting metabolite probes, such as MCLA and luminol, do not produce a chemiluminescent signal in this model system. The enzyme responsible for NADH-dependent lucigenin chemiluminescence was purified and identified as cytochrome-b5 reductase. In support of this concept, COS-7 cells overexpressing cytochrome-b5 reductase displayed at least a 3-fold increase in the previously mentioned activity compared with mock-transfected cells. Fractions containing cytochrome-b5 reductase were capable of inducing both lucigenin-dependent chemiluminescence and WST-1 reduction. Oxygen radicals clearly did not mediate the cytochrome b5-mediated activation of these probes in vitro since neither luminol nor MCLA gave a chemiluminescence response in the presence of the enzyme and the cofactor NADH. These results emphasize the importance of the direct NADH-dependent reduction of these putative superoxide-sensitive probes by cytochrome-b5 reductase even though this enzyme does not, on its own accord, produce reactive oxygen species.

Do incremental increases in blood pressure elicit neointimal plaques through endothelial injury?

Fowl (males more than females) show maturation-dependent rises in blood pressure (BP) and formation of neointimal plaques (NPs), resembling balloon catheter injury-induced neointima, in the abdominal aorta (AbA) just above the bifurcation. The plaque comprises neointimal cells containing abundant endoplasmic reticulum and extracellular matrix. Hence, we investigated whether rapid incremental BP increases in male chicks trigger NP formation, possibly via endothelial injury in hemodynamically selective areas. In 6-wk-old chicks (n = 8) treated 4 wk with solvent (Sv; minipump) or arginine supplement (Arg; 0.3% in drinking water), BP increased from 140 +/- 5 to 159 +/- 4 (Sv) and from 138 +/- 4 to 157 +/- 3 (Arg) mmHg, whereas propranolol treatment (Prop, 8 mg.kg(-1).day(-1); minipump) prevented the rise. Arg and Prop groups had, respectively, 73% and 77% smaller (P < 0.05) NP areas and 19% and 25% less (P < 0.01) AbA medial thickness than Sv controls. In 16-wk-old cockerels, established BP remained high after Sv and Arg treatments. In the Prop group, BP decreased, but neither NP area nor medial thickness was lower than in the Sv group, whereas the Arg group showed greater NP area and medial thickness. Pulse pressure, determined by intravascular transducer, increased as the pulse wave descended the aorta. The results suggest that maturation-dependent rises in BP in chicks may trigger NP formation in the lower segment of the AbA, which was prevented by inhibition of BP increase, or via a possible increase in nitric oxide availability. BP reduction exerts no effect once BP reaches a plateau. Involvement of endothelial injury leading to NP formation and hemodynamic forces selective for the lesion-prone area remain to be determined.