Dietary Supplementation with (−)-Epigallocatechin-3-gallate Reduces Inflammatory Response in Adipose Tissue of Non-obese Type 2 Diabetic Goto-Kakizaki (GK) Rats

(-)-Epigallocatechin gallate (EGCG), a major catechin in green tea, is an antioxidant associated with the reduction of oxidative stress in vitro. However, the mechanisms underlying the effects of EGCG on adipose tissue-related metabolic disturbances in vivo are not understood. This study examined whether dietary supplementation of EGCG reduces the oxidative stress-associated inflammatory response in the mesenteric adipose tissue of non-obese type 2 diabetic Goto-Kakizaki (GK) rats. GK rats were fed a normal diet or diet containing 0.1, 0.2, or 0.5% EGCG (w/w) for 25 weeks. The mRNA levels of IL-1β were significantly reduced in GK rats given 0.1% EGCG (0.059 ± 0.008; means ± SEM in arbitrary unit) compared with those in GK rats given a control diet (0.135 ± 0.011), but not in those given 0.2% EGCG (0.123 ± 0.012) or 0.5% EGCG (0.112 ± 0.019). The mRNA and protein level of other genes for inflammatory responses such as IL-18, TNF-α, MCP-1, CD11s, CD18, and resistin were also significantly reduced in rats given 0.1% EGCG, but not in those given ≥ 0.2% EGCG. This suggests that supplementation with EGCG at relatively low concentrations (0.1%) in GK rats reduces expression of genes and proteins involved in inflammation in adipose tissue.