Effects of Doenjang on oxidative stress and inflammation in adipose tissue of mice fed a high fat diet

Abstract

Obesity, now regarded as chronic, low-grade inflammation, is associated with metabolic syndrome. Especially, adipose tissue is considered as a main organ leading to systemic inflammation in obesity via secretion of pro-inflammatory adipokines. Doenjang, a traditional Korean fermented soybean paste, has been reported to have the anti-obesity and anti-inflammatory effects in serum and liver. In spite of its importance in obesity-related inflammation, there is no study to investigate the anti-obesity and anti-inflammatory effects of Doenjang in adipose tissue. Therefore, the present study investigated the protective effect of Doenjang on the inflammation and oxidative stress in adipose tissue of diet-induced obesity mouse. At 6 weeks of age, male C57BL/6J mice were fed a low fat diet (LF), a high fat diet (HF: 45% fat and 1% cholesterol), an HF containing Doenjang diet (HFDJ: 14.4% freeze-dried Doenjang) or an HF containing steamed soybean diet (HFSS: 11.7% freeze-dried steamed soybean) for 11 weeks. At the end of experiments, body weight and adipose tissue weight of mice fed an HFDJ diet exhibited significantly 16% and 19% lower than the HF group, respectively. Although there were no significant differences in adipocyte size and number among the HF diet-fed groups, consumption of Doenjang alleviated the incidence of crown-like structures in adipose tissue. Consistently, we observed that mice fed an LF diet and an HFDJ diet significantly lower mRNA levels of oxidative stress markers (heme oxygenase-1 and p40phox), pro-inflammatory adipokines (tumor necrosis factor alpha and macrophage chemoattractant protein-1), macrophage markers (CD68 and CD11c), and a fibrosis marker (transforming growth factor beta 1) in adipose tissue than mice fed an HF diet. Gene expression of anti-inflammatory adipokine, adiponectin was significantly higher in the HFDJ and HFSS groups than the HF group. These results demonstrate that Doenjang may ameliorate systemic inflammation and oxidative stress in obesity via inhibiting inflammatory signals in adipose tissue. The anti-oxidative stress and anti-inflammatory effects observed in adipose tissue with an HFSS diet were not as significant as those with an HFDJ diet. It suggests that the bioactive compounds produced during fermentation and aging process may be involved in the observed health-beneficial effects of Doenjang.