Epigallocatechin gallate attenuates free fatty acid-induced hepatocyte apoptosis by restoring endoplasmic reticulum homeostasis.

Dairy cows during the transition period frequently experience negative energy balance (NEB), leading to elevated circulating non-esterified fatty acids (NEFA), which is a major risk factor for fatty liver disease. This study aimed to investigate the protective effects of epigallocatechin gallate (EGCG) on hepatocellular injury induced by NEFA, with an emphasis on elucidating the molecular pathways through which EGCG mitigates hepatic lipotoxicity. We observed that cows with fatty liver exhibited elevated levels of aspartate aminotransferase (AST), alanine aminotransferase (ALT), triglyceride (TG), and gamma-glutamyl transferase (GGT). Proteomic and Western blot analyses further revealed that the levels of cell apoptosis and endoplasmic reticulum (ER) stress in fatty liver dairy cows were significantly increased. Meanwhile, in palmitic acid (PA)-treated AML12 cells, EGCG pretreatment significantly alleviated hepatocyte apoptosis, as evidenced by a decreased Bax/Bcl2 ratio and a reduced apoptosis rate. Moreover, EGCG also mitigated ER stress by downregulating GRP78, HSP70, ATF4, and CHOP, and inhibited activation of the unfolded protein response (UPR), as indicated by reduced expression of XBP1, ATF6, phosphorylated IREα and PERK. Besides, in the ER stress cell model induced by tunicamycin (TM), it was further verified that EGCG can effectively alleviate hepatocyte apoptosis. The results indicate that EGCG alleviates the hepatocyte damage induced by NEFA through regulating the ER stress and UPR signaling, highlighting its potential as a natural intervention method for fatty liver diseases in transition dairy cows.