Marc Isabelle

Crucial role of NO and endothelium-derived hyperpolarizing factor in human sustained conduit artery flow-mediated dilatation.

Whether NO is involved or not in sustained conduit artery flow-mediated dilatation in humans remains unclear. Moreover, the role of endothelium-derived hyperpolarizing factor (EDHF), synthesized by cytochrome epoxygenases and acting through calcium-activated potassium channels, and its relationship with NO during flow-mediated dilatation have never been investigated previously. In 12 healthy subjects we measured radial artery diameter (echotracking) and blood flow (Doppler) during flow-mediated dilatation induced by gradual distal hand skin heating (34 to 44°C), during the local infusion of saline and inhibitors of NO synthase (NG-monomethyl-l-arginine [l-NMMA]: 8 to 20 &mgr;mol/min per liter), calcium-activated potassium channels (tetraethylammonium chloride: 9 &mgr;mol/min per liter), and cytochrome epoxygenases (fluconazole: 0.4 to 1.6 &mgr;mol/min per liter), alone and in combination. Mean wall shear stress, the flow-mediated dilatation stimulus, was calculated at each level of flow, and the diameter–wall shear stress relationship was constructed. During heating, compared with saline, the diameter–shear stress relationship was shifted downward by l-NMMA, tetraethylammonium, fluconazole, and, in a more pronounced manner, by the combinations of l-NMMA with tetraethylammonium or with fluconazole. Therefore, maximal radial artery flow-mediated dilatation, compared with saline (0.62±0.03 mm), was decreased under our experimental conditions by l-NMMA (−39±4%), tetraethylammonium chloride (−14±4%), fluconazole (−18±6%), and to a greater extent, by the combinations of l-NMMA with tetraethylammonium (−64±4%) or with fluconazole (−71±3%). This study demonstrates that NO and a cytochrome-related EDHF are involved in peripheral conduit artery flow-mediated dilatation in humans during sustained flow conditions. Moreover, the synergistic effects of the inhibitors strongly suggest a functional interaction between NO and EDHF pathways.

Role of reactive oxygen species in cocaine-induced cardiac dysfunction.

OBJECTIVE Contractility alterations and LV hypertrophy after chronic cocaine administration have been shown to be accompanied by an increase in oxidative stress. This study was carried out to investigate whether the production of reactive oxygen species is an early event of primary importance in cocaine-induced myocardial injury or simply occurs as a consequence of the ventricular dysfunction itself. METHODS AND RESULTS After 2 days of cocaine administration to rats, no differences were observed in echocardiographic parameters between the cocaine-treated group and the control group. However, an increase in oxidative stress in the myocardium was indicated by an increase in lipid peroxidation (+35%, cocaine vs. control), an increase in antioxidant enzymes (catalase +110%, glutathione peroxidase +40% and superoxide dismutase +38%) and of NADPH-driven superoxide production (assessed by chemiluminescence). Furthermore, higher gp91phox and p22phox mRNA expression, measured by quantitative real-time RT-PCR, was found in the cocaine group. On day 8, cocaine administration induced a cardiac dysfunction, characterized by a decrease in cardiac index (-30%, cocaine vs. controls) and left ventricular (LV) fractional shortening (-23%, cocaine vs. controls). This LV dysfunction was prevented by antioxidant treatment (100 mg/kg/day vitamin C and 100 U/kg/day vitamin E). Moreover, in these animals, antioxidant treatment decreased lipid peroxides and decreased the activity of NADPH oxidase, associated with the downregulation of gp91phox. CONCLUSION These data indicate that cocaine administration induces early NADPH-driven O2-. release which may play an important role in the development and progression of the LV dysfunction observed after chronic cocaine abuse.

Chronic reduction of nitric oxide level in adult spontaneously hypertensive rats induces aortic stiffness similar to old spontaneously hypertensive rats.

Introduction: Age and hypertension are two major determinants of arterial stiffness, as well as endothelial dysfunction. The present study was designed to test whether a chronic reduction of endogenous nitric oxide (NO) produces arterial stiffening close to that observed in old spontaneously hypertensive rats (SHR), and also to study the effect of an acute or a chronic decrease in blood pressure (BP) on aortic distensibility. Methods: BP, aortic stiffness, endothelial dysfunction and remodelling were measured in male adult (20-week-old) SHR, in adult SHR treated with a nonspecific NO synthase inhibitor L-NAME (SHR/L-NAME) for 2 weeks, in adult SHR/L-NAME cotreated with perindopril (1 mg/kg/day) and in old SHR (55-week-old). Age-matched WKY were used as a normotensive group. Results: Aortic endothelial dysfunction, remodelling and stiffening appeared in old SHR. Reduction of NO production in adult SHR caused similar alterations. Acute decreases in BP in SHR/L-NAME did not improve isobaric aortic distensibility but a chronic reduction of BP prevented endothelial dysfunction, aortic remodelling and aortic wall stiffening. Conclusion: NO reduction in adult SHR induces aortic alterations similar to those observed during aging, which supports the major role of NO in the development of arterial stiffening. These aortic alterations can be prevented by angiotensin-converting enzyme inhibitor treatment.

KCa3.1 channels maintain endothelium-dependent vasodilatation in isolated perfused kidneys of spontaneously hypertensive rats after chronic inhibition of NOS

BACKGROUND AND PURPOSE The purpose of the study was to investigate renal endothelium‐dependent vasodilatation in a model of severe hypertension associated with kidney injury.

Selenium diet-supplementation improves cocaine-induced myocardial oxidative stress and prevents cardiac dysfunction in rats

Chronic cocaine abuse causes cardiac dysfunction and induces oxidative stress. The goal of this study was to evaluate whether an enhanced antioxidant pool, induced by the administration of selenium, may prevent the myocardial dysfunction induced by cocaine. Cocaine was administered for 7 days (15 mg/kg/day, i.p.) to rats pretreated for 4 weeks with selenium (1.16 mg/L/day, p.o.). Cardiac function was evaluated by cardiac index and left ventricular (LV) fractional shortening (FS) measured by echocardiography. The redox ratio and enzymatic activities of glutathione peroxidase (GPX) and superoxide dismutase (SOD) were measured in the LV myocardium. Cocaine administration induced a cardiac dysfunction, as evidenced by a decrease in cardiac index and LV FS as well as by an increase in LV diameters. Moreover, antioxidant markers and redox ratio were altered in rats after cocaine exposure. Selenite supplementation induced a significant limitation of cardiac index and FS alterations observed after cocaine administration. This improvement in cardiac function was associated with a redox ratio recovery while SOD and GPX activities remained unchanged. Thus, selenite reversed both the oxidative stress and the contractile dysfunction induced by cocaine administration. These results suggest a major role of oxidative stress in the cocaine‐induced cardiotoxicity.

The Efficacy of Cardiac Anti-miR-208a Therapy Is Stress Dependent

MicroRNAs (miRNAs) are important regulators of biology and disease. Recent animal efficacy studies validate the therapeutic benefit of miRNA modulation and underscore the therapeutic value of miRNA-targeting oligonucleotides. However, whether disease conditions (stress) influence the pharmacological effects of an anti-miR is currently unknown. To study the effect of disease on target regulation after anti-miR treatment, we injected animals with anti-miR-208a, a synthetic oligonucleotide that inhibits the cardiomyocyte-specific miR-208a. Our data indicate that the presence of stress increases the number of regulated miR-208a targets, and that higher stress levels correlate with stronger target derepression. Additionally, the type of stress also influences which targets are regulated upon miR-208a inhibition. Studies in a large animal model indicate a similar stress-dependent anti-miR effect. Subsequent in vitro studies suggest that the influence of stress on anti-miR efficacy depends at least in part on increased cellular anti-miR uptake. These data indicate that the pharmacological effect of anti-miRs is stronger under disease conditions, and that both the type and severity of disease determine the therapeutic outcome. These facts will be important for assessing the therapeutic dose and predicting the therapeutic outcome when applying anti-miRs in a clinical setting.

SBP, DBP, and pulse blood pressure variability are temporally associated with the increase in pulse wave velocity in a model of aortic stiffness.

Background: Enhanced aortic stiffness and blood pressure variability (BPV) are independent risk factors for cardiovascular disease and all-cause mortality in man. They are also correlated with increased blood pressure (BP) and/or arterial remodeling. However, the interplay between BP and BPV on the stiffening process is still unclear. Our objectives were to determine the temporal evolution of both BPV and pulse wave velocity (PWV), a surrogate measure of arterial stiffness, using an animal model of remodeling-dependent aortic stiffening. Method: We thus, developed a new telemetric technique allowing continuous measurement of PWV in conscious, unrestrained rats. Studies were performed in spontaneously hypertensive rats (SHR) treated for 2 weeks with N-nitro-L-arginine methyl ester, a nitric oxide synthase inhibitor (SHR-LN). BPV was evaluated conventionally or with a new device composed of two pressure transducers in two different sets of rats. This allowed a continuous monitoring of telemetered PWV, systolic (SPV), diastolic (DPV), and pulse pressure variability (PPV). Aortic structure was then characterized by immunohistochemical analysis. Results: SPV, DPV, and PPV were increased in SHR-LN, when calculated by 24-h SD or using average real variability a parameter used to assess short-term variability in man. We observed rapid and simultaneous increases in BP, SPV, and PWV. Interestingly, PPV was the most increased parameter resulting mainly from different time course of SPV and DPV. Structural alterations of the aortic wall were observed, with a eutrophic inward remodeling and accumulation of fibronectin and its two main receptors (&agr;5 and &agr;v integrins). Conclusion: This offers unequivocal evidence of a significant relationship between PWV, BPV, and arterial structure.