A microbial metabolite reduces alcohol-induced inflammation via dual modulation of NF-κB and Interferon pathway.

BACKGROUND AND AIMS: Alcohol-associated hepatitis (AH) is characterized by excessive inflammation and blunted antiviral interferon (IFN) responses. We hypothesized that specific gut microbiome-derived metabolites could selectively enhance interferon signaling while limiting NF-κB mediated inflammation, thereby restoring immune balance in AH. Our goal is to identify microbiome-derived metabolites that differentially regulate the NF-κB and IFN signaling pathways.

METHODS AND RESULTS: We used human monocytic THP1-Dual cells, which secrete reporters for NF-κB and IFN signaling, to model innate immune responses and screened a library of 152 gut microbiome-derived metabolites. From the metabolite screen, 4-hydroxyphenylacetic acid (4-HPAA) emerged as a unique immunomodulator: in LPS-challenged cells, 4-HPAA selectively increased IFN signaling with minimal NF-κB activation. 4-HPAA was evaluated in vivo using a NIAAA-model, with 4-HPAA supplementation (0.4mg/ml) added to the diet. In the NIAAA-model, dietary 4-HPAA did not induce liver injury and was associated with enhanced interferon-stimulated gene expression. Simultaneously, 4-HPAA reduced pro-inflammatory markers such as Il1β, Ly6g and F4/80 compared to the group exposed to ethanol alone. Metabolomic profiling of mouse cecal contents revealed 4-HPAA supplementation counteracted ethanol's metabolic effects, selectively reducing triglyceride-associated lipids that had accumulated with ethanol feeding.

CONCLUSIONS: 4-HPAA enhances interferon signaling and antiviral gene induction while dampening NF-κB-driven inflammation in the presence of LPS, both in vitro and in vivo. In an acute-on-chronic alcohol injury model, 4-HPAA attenuated hepatic inflammation, reduced immune cell recruitment, and activated antioxidant defenses, reflecting a shift toward a more hepatoprotective effect. 4-HPAA treatment was associated with reduced pro-inflammatory markers and modest attenuation of ethanol-induced liver injury. Additionally, 4-HPAA reversed ethanol-induced lipid-dysregulation, particularly triglyceride accumulation, highlighting its metabolic benefit in alcohol-fed mice. In conclusion, 4-HPAA rebalances immune and metabolic pathways by enhancing IFN signaling, suppressing NF-κB inflammation, and reversing alcohol-induced hepatic injury and lipid accumulation.