Epigallocatechin-3-gallate protects bovine ruminal epithelial cells against lipopolysaccharide-induced inflammatory damage by activating autophagy

Abstract Background：In non-ruminants, epigallocatechin-3-gallate (EGCG), a major bioactive ingredient of green tea, is well-known to alleviate inflammation. Whether EGCG confers protection against subacute ruminal acidosis (SARA)-induced inflammation and the underlying mechanisms are unknown. Results：Eight ruminally cannulated Holstein cows in mid-lactation were randomly assigned to either a low-concentrate (40%) diet (CON) or a high-concentrate (60%) diet (HC) for 3 weeks to induce SARA. Cows with SARAhad greater concentrations of tumor necrosis factor (TNF)-α and interleukin-6, and epithelium showed histological signs of damage. Lipopolysacharide was used in vitro to simulate the inflammatory damage caused by SARA uisng immortalized bovine rumen epithelial cells (BREC). Increased phosphorylation of IκBα and nuclear factor kappa-B (NF-κB) p65 due to 10 µg/mL LPS for 6 h revealed a successful chronic inflammatory response in BREC. Pre-treatment of BREC with 50 µM EGCG for 6 h before LPS challenge promoted the degradation of NLR family pyrin domain containing 3 (NLRP3) inflammasome through activation of autophagy, which further repressed activation of NF-κB pathway targeting Toll-like receptor 4(TLR4). The ECGG also upregulated tight junction (TJ) protein expression upon incubation with LPS. Conclusions：Subacute ruminal acidosis causes ruminal epithelium injury and systemic inflammation in dairy cows. However, the anti-inflammatory effects of EGCG help preserve the integrity of the epithelial barrier through activating autophagy when BREC are exposed to LPS. Thus, EGCG could potentially serve as an effective therapeutic agent for SARA-associated inflammation.