Epigallocatechin-3-Gallate Restores the Pulmonary Keap1-Nrf2-HO-1 Pathway and Attenuates Bile Acid-Associated Lung Injury in a Mouse Model of MASH

The crosstalk between the liver and the lung is complex and not yet fully understood; however, recent studies suggest that metabolic dysfunction, often originating in the liver, can influence lung injury and other lung diseases. The current study investigates the role of bile acids (BA) in mediating lung injury in a mouse model of metabolic dysfunction-associated steatohepatitis (MASH). Ob/Ob mice were fed a high-fat diet (HFD) for 4 weeks to establish a MASH model. Littermate mice were used as controls. Mice of each genotype were randomized to epigallocatechin-3-gallate (EGCG; 200 mg/kg/day, oral gavage) or vehicle. BA levels were assessed in serum and bronchoalveolar lavage fluid (BALF), and lung and liver tissues were obtained and evaluated for histological damage, epithelial apoptosis, and oxidative stress markers. MASH mice exhibited significant pulmonary injury, characterized by elevated pulmonary Sftpd mRNA expression (2.10 ± 0.68-fold) and sRAGE levels (986 ± 144 pg/mL), together with increased apoptosis of alveolar type I (30.0 ± 8.0%) and type II (32.4 ± 7.8%) epithelial cells, indicating impaired alveolar integrity. Pulmonary oxidative stress was evidenced by increased malondialdehyde (MDA) levels (0.67 ± 0.11 nmol/mg tissue) and a marked reduction in superoxide dismutase (SOD) protein levels (6.25 ± 3.30 ng/mg tissue). Serum bile acid concentrations were significantly elevated (14.99 ± 2.80 µM; 11.9-fold increase), accompanied by a 5.6-fold increase in BALF BA concentrations. EGCG treatment reduced serum bile acid concentrations to 9.68 ± 2.18 µM and BALF bile acid levels to 0.274 ± 0.125 µM, while decreasing Sftpd expression (1.29 ± 0.25-fold), sRAGE (392 ± 234 pg/mL), alveolar epithelial apoptosis (AT-1: 15.0 ± 3.8%; AT-2: 22.1 ± 7.0%), and MDA levels (0.36 ± 0.10 nmol/mg tissue). In parallel, EGCG significantly restored pulmonary SOD protein levels (17.80 ± 5.91 ng/mg tissue). Mechanistically, EGCG restored the transcriptional expression of the pulmonary Keap1-Nrf2-HO-1 antioxidant pathway by suppressing Keap1 while increasing Nfe2l2 and Hmox1 expression, consistent with improved endogenous antioxidant defenses and redox homeostasis. In conclusion, MASH is accompanied by pulmonary injury, alveolar epithelial apoptosis and oxidative stress, occurring in parallel with systemic and alveolar bile acid accumulation. EGCG attenuated these changes and was associated with recovery of pulmonary Keap1-Nrf2-HO-1 signaling.