Decaffeinated green tea extract improves hypertension and insulin resistance in a rat model of metabolic syndrome

BackgroundOxidative stress and endothelial dysfunction are closely associated with hypertension and insulin resistance (IR) in metabolic syndrome (MetS). It is still controversial whether green tea extract (GTE) may have blood pressure (BP) lowering effect. Decaffeinated GTE might be presumed to have strong antioxidative effect and BP-lowering effect as compared with catechins. Thus we investigated whether decaffeinated-GTE could attenuate hypertension and IR by improving endothelial dysfunction and reducing oxidative stress in a rat model of MetS.Methods and Results20 Otsuka Long-Evans Tokushima Fatty (OLETF) rats at 13 weeks old, MetS rats, were randomized into a saline treated group (OLETF; n = 10) and a group treated with decaffeinated-GTE (25 mg/kg/day) (GTE-OLETF; n = 10). Intraperitoneal glucose tolerance tests and BP measurements were performed at 13 and 25 weeks. Decaffeinated-GTE significantly reduced BP (OLETF vs. GTE-OLETF; 130 ± 7 vs. 121 ± 3 mmHg, p = 0.01), fasting/postprandial 2 h glucose (141 ± 18/159 ± 13 vs. 115 ± 7/132 ± 16 mg/dL, p = 0.009/0.002) and insulin levels (4.8 ± 2.3 vs. 2.4 ± 1.3 ng/mL, p < 0.001). Decaffeinated-GTE significantly reduced vascular reactive oxygen species (ROS) formation and NADPH oxidase activity, and improved endothelium dependent relaxation in the thoracic aorta of OLETF rats. Decaffeinated-GTE also suppressed the expression of p47 and p22phox (NADPH oxidase subunits) in the immunohistochemical staining, and stimulated phosphorylation of endothelial nitric oxide synthase (eNOS) and Akt in the immunoblotting of aortas.ConclusionsDecaffeinated-GTE reduced the formation of ROS and NADPH oxidase activity and stimulated phosphorylation of eNOS and Akt in the aorta of a rat model of MetS, which resulted in improved endothelial dysfunction and IR, and eventually lowered BP.

► We administrated decaffeinated-green tea extract (GTE) in a powdered form to OLETF rats (a rat model of metabolic syndrome). ► Decaffeinated GTE reduced blood pressure, plasma glucose and insulin levels. ► These effects are caused by improving endothelial dysfunction and oxidative stress. ► Decaffeinated-GTE reduced the formation of ROS and NADPH oxidase activity and stimulated phosphorylation of eNOS and Akt. ► Decaffeinated-GTE might be a potential therapeutic agent for the patients with hypertension and insulin resistance.