Polyphenol-containing azuki bean (Vigna angularis) extract attenuates blood pressure elevation and modulates nitric oxide synthase and caveolin-1 expressions in rats with hypertension

Abstract 

Background and aims

Azuki beans (Vigna angularis) contain polyphenols such as proanthocyanidins that exhibit potential radical scavenging activities. We herein investigated the effects of polyphenol-containing azuki bean extract (ABE) on elevated blood pressure, nitric oxide (NO) production, and expressions of endothelial NO synthase (eNOS), inducible NOS (iNOS), and caveolin-1 proteins in the aorta and kidney of chronically hypertensive rats.

Methods and results

Spontaneously hypertensive rats (SHRs/Izm) with approximately 200mm Hg systolic blood pressure (SBP) were randomly divided into 2 groups fed either 0% or 0.9% ABE-containing diet. Age-matched normotensive Wistar–Kyoto rats were used as the control. The content of 24-h urinary nitrate/nitrite (NOx) excretion was measured to evaluate NO production. After 8 weeks of treatment, the eNOS, iNOS, and caveolin-1 protein expressions in the aorta and kidney were analyzed by western blotting. The SBP of the ABE-treated SHR was significantly lower than that of the untreated SHR. The level of 24-h urinary NOx excretion was significantly higher in the ABE-treated SHR than in the untreated SHR. The eNOS and iNOS expressions in the aorta and kidney were remarkably upregulated in the untreated SHR but suppressed in the ABE-treated SHR. The vascular and renal caveolin-1 expressions were upregulated in the ABE-treated SHR.

Conclusions

ABE reduced the elevated blood pressure and increased NO production in long-term treatment. It may be associated with the modulation of eNOS and iNOS protein expressions in the aorta and kidney during the development of hypertension.

Keywords: Nitric oxide, Nitric oxide synthase, Caveolin-1, Azuki bean (Vigna angularis), Polyphenols, Spontaneously hypertensive rats