A. Fortuño

Vascular oxidant stress: molecular mechanisms and pathophysiological implications.

The term oxidative stress refers to a situation in which cells are exposed to excessive levels of either molecular oxygen or chemical derivatives of oxygen (ie, reactive oxygen species). Three enzyme systems produce reactive oxygen species in the vascular wall: NADH/NADPH oxidase, xanthine oxidoreductase, and endothelial nitric oxide synthase. Among vascular reactive oxygen species superoxide anion plays a critical role in vascular biology because it is the source for many other reactive oxygen species and various vascular cell functions. It is currently thought that increases in oxidant stress, namely excessive production of superoxide anion, are involved in the pathophysiology of endothelial dysfunction that accompanies a number of cardiovascular risk factors including hypercholesterolemia, hypertension and cigarette smoking. On the other hand, vascular oxidant stress plays a pivotal role in the evolution of clinical conditions such as atherosclerosis, diabetes and heart failure.ResumenEl término estrés oxidativo hace referencia a una situación en la que las células están expuestas a elevadas concentraciones de oxígeno o de sus derivados (especies reactivas del oxígeno). Tres son los sistemas enzimáticos principales que producen especies reactivas del oxígeno en la pared vascular: La NADH/NADPH oxidasa, la xantino óxido-reductasa y la sintasa endotelial del óxido nítrico. La especie reactiva del oxígeno fundamental de la pared vascular es el anión superóxido, pues es la fuente de otras especies reactivas y modifica múltiples funciones de las células vasculares. Actualmente se piensa que un aumento del estrés oxidativo, relacionado sobre todo con una excesiva producción de anión superóxido, interviene en la fisiopatología de la disfunción endotelial asociada a factores de riesgo cardiovascular como la hipercolesterolemia, la hipertensión y el tabaquismo. Además, el estrés oxidativo vascular puede ser determinante de la evolución de enfermedades como la aterosclerosis y la diabetes y de cardiopatías con insuficiencia cardiaca.

Association of increased erythrocyte Na+/H+ exchanger with renal Na+ retention in patients with essential hypertension

The goal of this study was to investigate the activity of the Na+/H+ exchanger in erythrocytes of patients with essential hypertension and its relation with urinary Na+ excretion. The study was performed in cells from 27 untreated hypertensive patients and 30 normotensive controls with similar age and sex distribution. All subjects were studied after 4 days on a controlled Na+ diet (145 mmol/day). The activity of the Na+/H+ exchanger was determined by acidifying cell pH and measuring the initial rate of the net Na(+)-dependent H+ efflux. The activity of the Na+/H+ exchanger was higher in hypertensive patients than in controls (301 +/- 45 v 162 +/- 23 mmol/L cells/h, mean +/- SEM; P < .01). With the upper limit of the normotensive population as a cut-off point (385 mmol/L cells/h), a subgroup of 12 hypertensive patients had an abnormally high activity of Na+/H+ exchanger. Compared with controls and with patients with normal exchanger activity, patients with increased exchanger activity were characterized by lower net (P < .01) and fractional (P < .05) Na+ excretion. The accumulative Na+ balance was higher (P < .01) in hypertensive patients with increased activity of the exchanger (39.90 +/- 3.47 mmol) than in the remaining hypertensive patients (0.59 +/- 6.96 mmol) or in the normotensive population (-5.71 +/- 6.12 mmol). After analyzing the relationship of renin activity with Na+ excretion it was observed that renin activity was inappropriately low in 9 (75%) patients with increased exchanger, in 6 (40%) patients with normal exchanger, and in 6 (20%) normotensives, these differences being significant (P<.01).

Angiotensin Converting Enzyme Inhibition Corrects Na+/H+ Exchanger Overactivity in Essential Hypertension

In this study, we investigated whether antihypertensive treatment with the angiotensin converting enzyme inhibitor quinapril modifies Na+/H+ exchanger activity or NHE-1 (isoform of the exchanger) mRNA expression in lymphocytes from patients with essential hypertension. Thirty-three hypertensive patients and 27 normotensive subjects were studied. Maximal sodium-proton exchange activity was determined by acidifying cell pH and measuring the initial rate of the net sodium-dependent proton efflux driven by an outward proton gradient. The transcript level of NHE-1 was measured by reverse transcription-polymerase chain reaction in comparison with a constitutively expressed reference gene (beta-actin). With the 100% confidence (upper) limit of the normotensive population as a cutoff point, a subgroup of 11 hypertensive patients had an abnormally high lymphocyte Na+/H+ exchange activity (group A). The activity of the exchanger was within the normal range in the remaining patients (group B). After 6 months of quinapril treatment the activity of the exchanger decreased to normal values (P < .001) in patients from group A, but remained unchanged in patients from group B. The NHE-1 mRNA expression was not modified with treatment neither in patients from the group A, nor in patients from the group B. These results suggest that chronic angiotensin enzyme inhibition with quinapril abolishes Na+/H+ exchange overactivity present in lymphocytes from a subgroup of hypertensive patients. This effect appears to be independent of changes in the expression of the mRNA encoding for the NHE-1 isoform of the exchanger.

INSULIN RESISTANCE DETERMINES TELOMERE SHORTENING IN PHAGOCYTIC CELLS FROM METABOLIC SYNDROME PATIENTS. INVOLVEMENT OF NADPH OXIDASE-MEDIATED OXIDATIVE STRESS: PP.34.404

Objective: Telomere attrition has been reported in blood cells from metabolic syndrome patients. Oxidative stress has been postulated as a potential mechanism that may favor telomere shortening. The aim of this study was to analyze the relationship of NADPH oxidase-mediated oxidative stress with telomere shortening in phagocytic cells from MetS patients. Design and Method: IR was defined by the homeostasis model assessment index. Telomere length was determined by PCR in genomic DNA isolated from blood samples. NADPH oxidase-dependent superoxide production was evaluated by luminescence in peripheral blood mononuclear cells obtained from patients with MetS. As an index of oxidative stress, plasma concentrations of thiobarbituric acid-reactive substances (TBARS) were measured. Intima-media thickness (IMT) was determined by ultrasonography in carotid arteries. To ascertain the mechanisms involved in vivo, we performed in vitro experiments in cultured macrophages. Results: Telomere length was lower (P < 0.05) in IR than in IS metabolic syndrome patients. NADPH oxidase-dependent superoxide production was augmented (P < 0.05) in IR patients with respect to IS patients. Finally, carotid IMT was higher (P < 0.05) in IR than in IS patients. After adjusting for age and sex, telomere length correlated (P < 0.05) inversely with glucose, with phagocytic NADPH oxidase activity and with TBARS values, and with carotid IMT. In vitro studies showed that a chronic activation of NADPH oxidase was associated with a relevant shortening of telomere length in cultured macrophages. Conclusions: Telomere shortening in phagocytic cells associates with CV risk in in MetS patients with IR. This process may be mediated by oxidative stress mechanisms, which involve, among others, the overactivity of NADPH oxidase in phagocytic cells.

ACTIVATION OF PHAGOCYTIC NADPH OXIDASE IN HYPERTENSIVE HEART DISEASE: A ROLE FOR CARDIOTROPHIN-1?: PP.22.399

Objective: Oxidative stress and inflammation are interconnected mechanisms which are potentially involved in the pathogenesis of heart disease. We examined whether phagocytic NADPH oxidase activation is related to hypertensive heart disease (HHD). Besides, we analyzed whether NADPH oxidase activation is mediated by cardiotrophin-1 (CT-1), a cytokine that has been recently involved in the development of hypertensive left ventricular hypertrophy (LVH). Design and Method: Normotensive individuals, hypertensives without cardiac abnormalities and hypertensives with LVH were studied. LVH was determined by two-dimensional echocardiography. NADPH oxidase-mediated superoxide production was measured in peripheral blood mononuclear cells by luminescence. Serum CT-1 was measured by ELISA in samples from the antecubital vein. Results: Phagocytic NADPH oxidase activity and serum CT-1 levels were increased in hypertensives with LVH compared with normotensives and hypertensives without LVH. Phagocytic NADPH oxidase was positively correlated with serum CT-1 levels in all individuals, this association being independent of age and sex. In vitro experiments demonstrated that CT-1 stimulated NADPH oxidase activity in phagocytic cells. Conclusions: This study shows that phagocytic NADPH oxidase overactivity is associated with HHD. In addition, our data support a relevant role of CT1 as an additional player that promotes the activation of NADPH oxidase in phagocytic cells.

PROTECTIVE EFFECT IN HYPERTENSIVE HEART DISEASE OF THE 1742GG GENOTYPE OF THE HUMAN CARDIOTROPHIN-1 GENE: 6D.03

Introduction: Both clinical and experimental evidence indicates that cardiotrophin-1 (CT-1) is a cytokine that is critically involved in the development of left ventricular hypertrophy (LVH). We have investigated the effect of the 1742(C/G) polymorphism of human CT-1 gene (CTF1) on CT-1 levels and LVH in human essential hypertension. Materials and Methods: We genotyped 514 normotensive subjects and 386 hypertensive patients for 1742(C/G) polymorphism. Serum levels of CT-1 were assessed in 681subjects by ELISA. LVH was assessed in 297 subjects by bidimensional echocardiography. Results: The prevalence of the GG genotype was significantly reduced in the hypertensive group (8.4% in normotensive subjects, 4.9% in hypertensive patients, P = 0.046) and further reduced in patients with LVH (11.5% in normotensive subjects without LVH, 12.2% in hypertensives patients without LVH, 2.6% in hypertensive patients with LVH, P = 0.008). In addition, subjects of GG genotype presented lower serum levels of CT-1 (GG: 147.1 ± 10.5 fmol/mL, CC/CG: 187.1 ± 4.8 fmol/mL, P = 0.036) and lower left ventricular mass index (LVMI) (GG: 91 ± 6 g/m2, CC/CG: 119 ± 3 g/m2, P = 0.002) than CC/CG genotype subjects. Multivariate analyses showed that the 1742(C/G) polymorphism was a significant determinant of CT-1 levels and also of LVMI, after adjusting for confounding factors such as age, sex, systolic blood pressure and antihypertensive treatment. Conclusions: Our data indicate that the 1742(C/G) polymorphism of human CT-1 is a novel genetic marker in LVH, as it is associated with the LVMI in essential hypertension. The GG genotype may be protective against LVH and the levels of CT-1 may be one of the mechanisms underlying the effect of the polymorphism.