Oxidative stress-related factors in Bartter's and Gitelman's syndromes: relevance for angiotensin II signalling.
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 Galphaq 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 p22(phox), TGFbeta and haeme oxygenase-1 (HO-1) in circulating monocytes in basal condition and after stimulation with Ang II. Furthermore, we investigated the C(242)T polymorphism of p22(phox), 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 p22(phox) and TGFbeta 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, p22(phox), TGFbeta 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, C(242)T polymorphism of p22(phox) 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.
Calò
Lorenzo A
LA
Department of Clinical and Experimental Medicine, Clinica Medica 4, University of Padova, Italy. renzcalo@unipd.it
Pagnin
Elisa
E
Davis
Paul A
PA
Sartori
Michelangelo
M
Semplicini
Andrea
A
D000328:Adult; D000804:Angiotensin II / Q000378:metabolism*; D001477:Bartter Syndrome / Q000503:physiopathology*; D005260:Female; D006801:Humans; D000072181:Inositol Polyphosphate 5-Phosphatases; D008297:Male; D026901:Membrane Transport Proteins; D008875:Middle Aged; D009252:NADPH Dehydrogenase / Q000378:metabolism; D019255:NADPH Oxidases; D018384:Oxidative Stress / Q000502:physiology*; D030421:Peroxynitrous Acid / Q000097:blood; D010750:Phosphoproteins / Q000378:metabolism; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism; D016133:Polymerase Chain Reaction; D017382:Reactive Oxygen Species / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D016212:Transforming Growth Factor beta / Q000378:metabolism
D026901:Membrane Transport Proteins; D010750:Phosphoproteins; D017382:Reactive Oxygen Species; D016212:Transforming Growth Factor beta; D000804:Angiotensin II; D030421:Peroxynitrous Acid; D019255:NADPH Oxidases; C086986:CYBA protein, human; D009252:NADPH Dehydrogenase; D010744:Phosphoric Monoester Hydrolases; D000072181:Inositol Polyphosphate 5-Phosphatases