Abstract-This study was designed to test the hypothesis that stimulation of nicotinamide adenine dinucleotide/ nicotinamide adenine dinucleotide phosphate (NADH/NADPH) oxidase is involved in increased vascular superoxide anion (⅐O 2 Ϫ ) production in spontaneously hypertensive rats (SHR). The study was performed in 16-week-old and 30-week-old normotensive Wistar-Kyoto rats (WKY 16 and WKY 30 , respectively) and in 16-week-old and 30-week-old SHR (SHR 16 and SHR 30 , respectively). In addition, 16-week-old SHR were treated with oral irbesartan (average dose 20 mg/kg per day) for 14 weeks (SHR 30 -I). Aortic NADH/NADPH oxidase activity was determined by use of chemiluminescence with lucigenin. The expression of p22phox messenger RNA was assessed by competitive reverse transcription-polymerase chain reaction. Vascular responses to acetylcholine were determined by isometric tension studies. Aortic wall structure was studied, determining the media thickness and the cross-sectional area by morphometric analysis. Whereas systolic blood pressure was significantly increased in the 2 groups of hypertensive animals compared with their normotensive controls, no differences were observed in systolic blood pressure between SHR 30 and SHR 16 . No other differences in the parameters measured were found between WKY 16 and SHR 16 . In SHR 30 compared with WKY 30 , we found significantly greater p22phox mRNA level, NADH/NADPH-driven ⅐O 2 Ϫ production, media thickness, and cross-sectional area and an impaired vasodilation in response to acetylcholine. Treated SHR had similar NADH/NADPH oxidase activity and p22phox expression as the WKY 30 group. The vascular functional and morphological parameters were improved in SHR 30 -I. These findings suggest that an association exists between p22phox gene overexpression and NADH/NADPH overactivity in the aortas of adult SHR. Enhanced NADH/NADPH oxidase-dependent ⅐O 2 Ϫ production may contribute to endothelial dysfunction and vascular hypertrophy in this genetic model of hypertension.

Increased vascular reactive oxygen species production, especially superoxide anion, contributes significantly in the functional and structural alterations present in hypertension. An enhanced superoxide production causes a diminished NO bioavailability by an oxidative reaction that inactivates NO. Exaggerated superoxide levels and a low NO bioavailability lead to endothelial dysfunction and hypertrophy of vascular cells. It has been shown that the enzyme NAD(P)H oxidase plays a major role as the most important source of superoxide anion in vascular cells. Several experimental observations have shown an enhanced superoxide generation as a result of the activation of vascular NAD(P)H oxidase in hypertension. Although this enzyme responds to stimuli such as vasoactive factors, growth factors, and cytokines, some recent data suggest the existence of a genetic background modulating the expression of its different components. New polymorphisms have been identified in the promoter of the p22 phox gene, an essential subunit of NAD(P)H oxidase, influencing the activity of this enzyme. Genetic investigations of these polymorphisms will provide novel markers for determination of genetic susceptibility to oxidative stress in hypertension.

Pressure overload causes cardiac fibroblast activation and transdifferentiation, leading to increased interstitial fibrosis formation and subsequently myocardial stiffness, diastolic and systolic dysfunction, and eventually heart failure. A better understanding of the molecular mechanisms underlying pressure overload-induced cardiac remodeling and fibrosis will have implications for heart failure treatment strategies. The microRNA (miRNA)-221/222 family, consisting of miR-221-3p and miR-222-3p, is differentially regulated in mouse and human cardiac pathology and inversely associated with kidney and liver fibrosis. We investigated the role of this miRNA family during pressure overload-induced cardiac remodeling. In myocardial biopsies of patients with severe fibrosis and dilated cardiomyopathy or aortic stenosis, we found significantly lower miRNA-221/222 levels as compared to matched patients with nonsevere fibrosis. In addition, miRNA-221/222 levels in aortic stenosis patients correlated negatively with the extent of myocardial fibrosis and with left ventricular stiffness. Inhibition of both miRNAs during AngII (angiotensin II)-mediated pressure overload in mice led to increased fibrosis and aggravated left ventricular dilation and dysfunction. In rat cardiac fibroblasts, inhibition of miRNA-221/222 derepressed TGF-β (transforming growth factor-β)-mediated profibrotic SMAD2 (mothers against decapentaplegic homolog 2) signaling and downstream gene expression, whereas overexpression of both miRNAs blunted TGF-β-induced profibrotic signaling. We found that the miRNA-221/222 family may target several genes involved in TGF-β signaling, including JNK1 (c-Jun N-terminal kinase 1), TGF-β receptor 1 and TGF-β receptor 2, and ETS-1 (ETS proto-oncogene 1). Our findings show that heart failure-associated downregulation of the miRNA-221/222 family enables profibrotic signaling in the pressure-overloaded heart.

These findings suggest that a diminished availability of NO secondary to an enhanced NADH/NADPH oxidase-dependent O2(.-) production may play a critical role in endothelial dysfunction of adult SHR.

The combination of low serum CITP : MMP-1 ratio and high serum PICP identifies hypertensive patients with heart failure presenting with a phenotype of myocardial fibrosis characterized by the concurrence of excessive CCL and CD and associated with poor outcome.

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Abstract-An association of increased apoptosis with overexpression of the proapoptotic protein Bax-␣ has been reported in the left ventricle of adult spontaneously hypertensive rats (SHR). Both alterations were corrected in SHR that received long-term treatment with the AT 1 antagonist losartan. To gain insight into the regulation of cardiac Bax-␣ protein in genetic hypertension, we investigated the expression of the protein p53 (a BAX gene transcription factor) and BAX mRNA in the left ventricle of 30-week-old Wistar-Kyoto rats (WKY), SHR, and SHR treated with losartan (20 mg ⅐ kg) during 14 weeks before death. The expression of p53 and Bax proteins was assessed by Western blot analysis. The expression of BAX mRNA was assessed by Northern blot analysis. The density of apoptotic cells was assessed by direct immunoperoxidase detection of biotin-labeled deoxyuridine nucleotides. Compared with WKY, untreated SHR exhibited increased apoptosis (PϽ0.05), increased Bax-␣ protein (PϽ0.05), and similar levels of p53 protein and BAX mRNA. Losartan given long term was associated with the normalization of apoptosis and Bax-␣ protein expression. The expression of BAX mRNA was decreased (PϽ0.05) in treated SHR compared with untreated SHR. No changes in the expression of p53 protein were observed in losartan-treated SHR. These results suggest that overexpression of the Bax-␣ protein seen in the left ventricle of adult SHR with increased apoptosis is not related to a p53-mediated upregulation of BAX gene transcription. Our data also suggest that normalization of Bax-␣ protein observed in SHR after long-term blockade of angiotensin II type 1 receptors may be due to the inhibition of BAX gene transcription. (Hypertension. 1999;33:1348-1352.)