Protective effects of pu-erh tea on LDL oxidation and nitric oxide generation in macrophage cells

Effects of water extract of pu-erh tea (WEPT) on low density of lipoprotein (LDL) oxidation and their regulation of nitric oxide in macrophage RAW 264.7 cells were determined. The results showed that WEPT significantly scavenged H2O2 in a concentration-dependent manner. In the range of 0–0.1 mg/mL, the inhibitory action on LDL oxidation increased with increasing concentration of WEPT. In addition, WEPT scavenged O2− and inhibited the activity of xanthine oxidase, suggested that WEPT showed effectively inhibitory effect on oxidative stress. WEPT at 200 μg/mL not only increased the glutathione (GSH) content by 41.5-fold but also enhanced activity of glutathione peroxidase (GPX), glutathione reductase (GR), glutathione transferase (GST) and catalase (CAT) in 3T3 cells by 1.8-, 2.6-, 10.9- and 4.3-fold compared to the control, respectively, revealing that WEPT may positively modulate the GSH and antioxidant enzyme system. Moreover, WEPT scavenged NO generated by sodium nitroprusside (SNP). The expression of inducible nitric oxide synthase (iNOS) in lipopolysaccharide (LPS)-activated macrophage RAW 264.7 cells was inhibited by WEPT. Reverse transcription-polymerase chain reaction (RT-PCR) analysis indicated that the iNOS mRNA expression was suppressed by WEPT. Furthermore, the down-regulated degradation of IκB-α by WEPT was found, indicating that WEPT suppressed iNOS enzyme expression as a result of preventing nuclear factor-kappa B (NF-κB) activation. The HPLC analyses showed that gallic acid, epicatechin and caffeine, which are polyphenolics with bioactive action, were found in WEPT. Overall, these findings suggest that pu-erh tea may play a crucial role in preventing such oxidation-related diseases as atherosclerosis and other types of vascular diseases.