Antioxidant resveratrol restores renal sodium transport regulation in SHR

Abstract

Previously we have shown that in spontaneously hypertensive rats (SHR) renal angiotensin (Ang) II receptor (AT1R) upregulation leads to overstimulation of Na/K-ATPase by Ang II. There are reports that antioxidants can reduce oxidative stress and blood pressure (BP) in SHR, however the effect of these compounds on AT1R function remains to be determined. Therefore, we hypothesized that polyphenol antioxidant resveratrol would mitigate oxidative stress, normalize renal AT1R signaling, and reduce BP in SHR. SHR and wistar-kyoto (WKY) rats were treated with resveratrol for 8 weeks. Untreated SHR exhibited oxidative stress and enhanced renal proximal tubular Ang II-induced G-protein activation and Na/K-ATPase stimulation. Treatment of SHR with resveratrol mitigated oxidative stress, reduced BP, and normalized renal AT1R signaling. In SHR, nuclear expression of transcription factor NF-κB was increased while expression of Nrf2 was reduced. SHR also exhibited a significant decrease in renal antioxidant capacity and activities of phase II antioxidant enzymes. Resveratrol treatment of SHR abolished renal NF-κB activation, restored Nrf2-phase II antioxidant signaling and Ang II-mediated Na/K-ATPase regulation. These data show that in SHR, oxidative stress via activation of NF-κB upregulates AT1R-G-protein signaling resulting in overstimulation Na/K-ATPase which contributes to hypertension. Resveratrol, via Nrf2, activates phase II antioxidant enzymes, mitigates oxidative stress, normalizes AT1R-G-protein signaling and Na/K-ATPase regulation, and decreases BP in SHR.

Keywords: G proteins; Na/K‐ATPase; hypertension; oxidative stress; transcription factors.

Figure 1

Mean arterial pressure in spontaneously hypertensive rats (SHR) and WKY. Conscious arterial pressure was continuously measured from week 7 to week 11 in all experimental groups by radiotelemetry. ^*P < 0.05 versus WKY-V, ^#P < 0.05 versus SHR-R, and ^**P < 0.05 versus WKY-V at respective time points, using two-way ANOVA followed by Newman–Keuls post hoc test.

Figure 2

Effect of resveratrol on Nrf2 and phase II antioxidant enzymes in renal proximal tubules from WKY rats and spontaneously hypertensive rats (SHR). (A) Nrf2 nuclear expression, bars are mean ± SE, n = 5–7 rats in each group, and the assay was performed in triplicate. (B, C) Activities of heme oxygenase (HO-1) and NAD(P):quinine oxidoreductase 1(NQO). Data are presented as mean ± SE, n = 5–7 rats in each group, and the assays were performed in triplicate. ^*P < 0.05 versus WKY-V and ^#P < 0.05 versus SHR-V, using two-way ANOVA followed by Newman–Keuls post hoc test.

Figure 3

Effect of resveratrol on Ang II-induced renal proximal tubular Na/K-ATPase stimulation in WKY rats and spontaneously hypertensive rats (SHR). (A) Na/K-ATPase activity was measured as ⁸⁶Rb⁺ uptake. Proximal tubules were incubated with low (0.1 nmol/L) or high (1 μmol/L) Ang II concentrations (B) for 10 min. Proximal tubules were incubated with low or high Ang II concentrations in the presence of AT1R antagonist candesartan (Can). Data are presented as mean ± SE, n = 5–7 rats in each group, and the assays were performed in triplicate. ^*P < 0.05 versus respective basal and ^#P < 0.05 versus SHR-Ang II, using two-way ANOVA followed by Newman–Keuls post hoc test.

Figure 4

Effect of resveratrol on renal proximal tubular G-protein expression and coupling in WKY rats and spontaneously hypertensive rats (SHR). Top panels are representative western blots for (A) Giα and (B) Gq/11 and bars represent mean ± SE of band densities, n = 6–8 rats. (C) Ang II-mediated [³⁵S]GTPγS membrane binding in the absence and presence of Giα inhibitor pertussis toxin (PTX). Data are presented as mean ± SE, n = 6–8 rats in each group, and [³⁵S]GTPγS membrane binding was performed in triplicate. ^*P < 0.05 versus WKY-V, ^#P < 0.05 versus SHR-V, ^$P < 0.05 versus basal, ^ϕP<0.05 versus SHR-V (with Ang II 10^-6 mol/L), and ^**P < 0.05 versus corresponding Ang II (10^-6 mol/L) group, using two-way ANOVA followed by Newman–Keuls post hoc test.

Figure 5

Effect of resveratrol on renal proximal tubular nuclear NF-κB (p65) expression in WKY rats and spontaneously hypertensive rats (SHR). Data are presented as mean ± SE, n = 5–7 rats, and the assays were performed in triplicate.^*P < 0.05 versus WKY-V and ^#P < 0.05 versus SHR-V, using two-way ANOVA followed by Newman–Keuls post hoc test.