Oxidative stress-related factors in Bartter's and Gitelman's syndromes: Relevance for angiotensin II signalling

Abstract

Background. Bartter's and Gitelman's syndromes (BS/GS) have a blunted Gq protein-mediated cell signalling despite high circulating angiotensin II (Ang II) levels. This is associated with reduced Gαq gene expression, intracellular inositol trisphosphate and Ca++ release, PKC activity and cell reactivity. Ang II is a powerful stimulator of vascular oxidases but BS/GS patients show reduced total volatile LDL oxidation products and reduced LDL susceptibility to oxidation suggesting low level of oxidative stress. Therefore, we evaluated oxidative stress-related proteins in plasma and monocytes of patients with BS/GS, at baseline and after Ang II stimulation. Methods. In two BS and seven GS patients, biochemically and genetically characterized, and in 10 age- and sex-matched control subjects, we measured total plasma antioxidant power (AOP), plasma peroxynitrite level and gene expression of the NADH/NADPH oxidase subunit p22phox, TGFβ and haeme oxygenase-1 (HO-1) in circulating monocytes in basal condition and after stimulation with Ang II. Furthermore, we investigated the C242 T polymorphism of p22phox, whose topography in a potential haeme-binding site suggests a role in the regulation of oxidative stress. Results. AOP was higher in BS/GS patients than in controls (3.27 ± 0.95 mmol/l vs 1.05 ± 0.16, P=0.002), together with higher plasma renin activity and aldosterone level (9.88 ± 4.64 vs 0.95 ± 0.08 nmol Ang I/h/ml, P < 0.0001; and 0.73 ± 0.13 vs 0.18 ± 0.01 nmol/l, P < 0.0001, respectively). The plasma peroxynitrite level was undetectable both in patients and controls. mRNA expression of p22phox and TGFβ was reduced in BS/GS patients compared to controls [0.35 ± 0.08 vs 0.53±0.05 densitometric units (d.u.), P=0.005, and 0.82 ± 0.07 vs 1.15 ± 0.25 d.u., P=0.006, respectively]. HO-1 mRNA was increased in BS/GS patients in comparison to controls (0.88 ± 0.07 vs 0.78 ± 0.11 d.u., P=0.037). After acute Ang II exposure, p22phox, TGFβ and HO-1 gene expression significantly increased only in controls (from 0.59 ± 0.12 to 0.96 ± 0.11, P < 0.001, from 0.97 ± 0.1 to 1.27 ± 0.22, P < 0.008, and from 0.62 ± 0.1 to 0.82 ± 0.09, P < 0.001, respectively). Finally, C242 T polymorphism of p22phox was undetectable. Conclusions. The intracellular responses to Ang II mediated by reactive oxygen species are reduced in BS/GS patients. This may contribute to their vascular hyporeactivity.