Tetrahydroxystilbene glycoside improves endothelial dysfunction and hypertension in obese rats: The role of omentin-1

RATIONALE

Hypertension in obesity has become a major threat for public health. Omentin-1, a novel adipokine, is down-regulated in obesity. Tetrahydroxystilbene glycoside (TSG) is the main ingredient extracted from Polygonum multiflorum Thunb (PMT), a traditional Chinese medicinal herb safely used for protecting cardiovascular systems over bimillennium. This study aims to examine (i) the impact of omentin-1 downregulation on obesity-related hypertension in murine models and the underlying mechanisms; (ii) whether tetrahydroxystilbene glycoside (TSG) improved endothelial dysfunction and obesity-associated hypertension via the increase of omentin-1.

METHODS

(TSG-treated) male Zucker diabetic fatty (ZDF) rats and omentin-1 knockout (OMT^-/-) mice were used. In vitro, human umbilical vein endothelial cells (HUVECs) and mature adipocytes differentiated from human visceral preadipocyte (HPA-v) were maintained in a co-culture system.

RESULTS

TSG was the main active component of PMT reducing systolic blood pressure and improving endothelial vasodilation. Fortnight-TSG treatment (100 mg/kg/day) increased serum omentin-1 level, also activated Akt/eNOS signaling and enhanced NO bioactivity; decreased expression of NOX2 and p22^phox, suppressed production of superoxide and peroxynitrite anion. OMT^-/- mice showed elevated blood pressure and impaired endothelial vasorelaxation, whereas hypotensive effect of TSG was blunted. In co-culture system, TSG incubation promoted binding of peroxisome proliferator-activated receptor-γ (PPAR-γ) and Itln-1 promoter in adipocytes, activated Akt/eNOS/NO signaling and attenuated oxidative/nitrative stress in HUVECs. Suppression of Itln-1 with siRNA significantly blocked the protective effect of TSG in vitro.

CONCLUSIONS

Down-regulation of omentin-1 induces endothelial dysfunction and hypertension in obesity. TSG treatment (at least partially) increases omentin-1 via promoting binding of PPAR-γ and Itln-1 promoter in adipose tissues, subsequently exerts protective effects on endothelial function via activating Akt/eNOS/NO signaling and attenuating oxidative/nitrative stress. These results suggest that TSG could be developed as a promising anti-hypertension agent that protects against endothelial dysfunction and obesity-associated cardiovascular diseases.

Anti-amyloidgenic and neurotrophic effects of tetrahydroxystilbene glucoside on a chronic mitochondrial dysfunction rat model induced by sodium azide

Alzheimer's disease (AD) is an irreversible neurodegenerative brain disorder with complex pathogenesis. Emerging evidence indicates that there is a tight relationship between mitochondrial dysfunction and β-amyloid (Aβ) formation. 2,3,5,4'-Tetrahydroxystilbene-2-O-β-D-glucoside (TSG) is one of the main active components extracted from Polygonum multiflorum. The purpose of the present study was to investigate the effects of TSG on Aβ production and neurotrophins in the brains of rats by using a mitochondrial dysfunction rat model induced by sodium azide (NaN₃), an inhibitor of mitochondrial cytochrome c oxidase (COX). NaN₃ was administered to rats by continuous subcutaneous infusion for 28 days via implanted osmotic minipumps to establish the animal model. TSG was intragastrically administered starting 24 h after the operation. The activity of mitochondrial COX was measured by a biochemical method. The content of Aβ 1-42 was detected by ELISA. The expression of neurotrophic factors was determined by Western blot and immunohistochemistry. The results showed that NaN₃ infusion for 28 days induced a decrease in mitochondrial COX activity, an increase in Aβ 1-42 content and the expression of amyloidogenic β-amyloid precursor protein (APP), beta-site APP cleaving enzyme 1 (BACE1) and presenilin 1 (PS1), and a decline in the expression of neurotrophins in the hippocampus of rats. Intragastrical administration of TSG elevated mitochondrial COX activity, decreased Aβ 1-42 content and the expression of APP, BACE1 and PS1, and enhanced the expression of nerve growth factor, brain-derived neurotrophic factor (BDNF) and its receptor tropomyosin-related kinase B (TrkB) in the hippocampus of NaN₃-infused rats. These findings suggest that TSG may be beneficial in blocking or slowing the progression of AD by enhancing mitochondrial function, decreasing Aβ production and increasing neurotrophic factors at some extent.