Enhanced catabolism of branched-chain amino acids uncouples anti-inflammatory and antioxidant functions in liver macrophages

Background Metabolic dysfunction–associated steatotic liver disease (MASLD) is marked by inflammation mediated by resident liver macrophages (RLMs). Branched-chain amino acids (BCAAs; leucine, isoleucine, valine) are elevated in early MASLD, yet their role in RLM biology is unclear. Aim We investigated whether BCAA exposure and impaired catabolism affect LPS-induced RLMs activation. Methods Primary rat RLMs were treated with high BCAA concentrations (15 mM) and/or LPS stimulation (100 ng/ml). BCAA metabolic enzymes, inflammatory markers, oxidative stress, and metabolic reprogramming were assessed. BCKDK inhibitor BT2 was used to enhance BCAA catabolism: Results RLMs expressed BCAT1, upregulated by LPS but downregulated by BCAAs. BCAAs exerted protective effects by selectively reversing LPS-induced CD11b, MCP-1, HIF-1α, and Arg1 expression, reducing ROS and attenuating NRF2. BCAAs promoted metabolic shift toward oxidative phosphorylation with increased ATP and reduced HK1 expression. BT2 enhanced catabolism restored BCAT1 and maintained anti-inflammatory effects but abolished antioxidant protection. Only leucine-BT2 suppressed NF-κB translocation. HIF-1α stabilization and HMGB1-mediated protection, restoring inflammatory gene expression and ROS levels. Conclusions BCAAs modulate RLM activation by regulating HIF-1α and HMGB1 signaling and redox homeostasis. Their protective effects depend on intact HIF-1α/HMGB1 pathways rather than catabolic flux, revealing a context-dependent role of BCAAs in hepatic inflammation.