L-theanine reduces muscle drip loss by regulating oxidative stress-mediated glycolysis disturbance and cytoskeletal protein degradation

This study investigated the effects of L-theanine on muscle drip loss, glycolysis, and cytoskeletal protein expression while elucidating its underlying mechanisms. Results demonstrated that diquat-induced oxidative stress exacerbated muscle drip loss by impairing cellular water balance. Diquat significantly increased reactive oxygen species (ROS), malondialdehyde (MDA) and corticosterone (CORT) content in serum, while suppressing serum antioxidant enzyme activities and nuclear factor erythroid 2-related factor 2 (Nrf2) and its downstream target genes expression in gastrocnemius (GAS) muscle of mice. Furthermore, diquat disrupted muscle structural integrity, upregulated glycolytic enzyme activities and glycolysis-related gene expression, while inhibiting calpain activity, desmin degradation and the expression of calpain 1 (CAPN1), CAPN2, and integrin β1. In addition, diquat significantly upregulated hypoxia-inducible factor 1α (HIF-1α) and glucocorticoid receptor α (GRα) expression. Dietary L-theanine supplementation effectively decreased muscle drip loss, increased antioxidant capacity and the expression of Nrf2-related signaling molecules, while decreasing muscle glycolysis. It also decreased the expression of desmin, HIF-1α and GRα, and increased calpain activity and the expression of CAPN1, CAPN2, and integrin β1 in GAS muscle of diquat-stressed mice. In conclusion, L-theanine alleviated diquat-induced oxidative stress, glycolytic dysregulation and abnormal cytoskeletal protein degradation, thereby reducing drip loss, and the effect might be related to the inhibition of HIF-1α and GRα expression.