L-theanine enhances the improvements of EGCG on glucose and lipid metabolism disorders in obese rats

Epigallocatechin gallate (EGCG) and L-theanine (LTA) are two key bioactive components of tea that modulate nutrient metabolism. However, whether the combination of EGCG and LTA will result in synergistic benefits for glucose and lipid metabolism disorders is still unclear. Here, we treated leptin receptor-knockout (Lepr-KO) rats with EGCG and EGCG combined with LTA to examine how combined EGCG and LTA affect glucose and lipid metabolism disorders. Our data suggested that EGCG or EGCG plus LTA all significantly reduced serum triglycerides, total cholesterol, random blood glucose, and increased glucose tolerance, as well as alleviated fatty liver formation in Lepr-KO rats. Moreover, compared with EGCG alone, EGCG plus LTA significantly reduced random blood glucose and plasma triacylglycerols (TG) levels, and alleviated hepatic steatosis. Mechanistic analysis revealed that EGCG plus LTA improved glucose metabolism disorders by activating hepatic glucokinase (GCK) and glycogen synthase 2 (GYS2) expression, and inhibited fatty acid synthase (FAS) and stearoyl-CoA desaturase 1 (SCD1) for lowering hepatic TG accumulation. This study demonstrated that LTA enhances the improvements of EGCG on glucose and lipid metabolism disorders in Lepr-KO rats, especially in glycometabolism.