Engineered probiotic-mediated palmitoylethanolamide biosynthesis protects against colitis-associated liver injury

Chronic colitis promotes secondary liver injury through disruption of the gut-liver axis, whereby intestinal barrier breakdown enables portal translocation of microbial products that activate hepatic inflammatory and fibrogenic pathways. Palmitoylethanolamide (PEA), an endogenous ALIAmide acting primarily via PPAR-α, exerts anti-inflammatory and barrier-protective effects, but its clinical use is limited by poor oral bioavailability. We investigated whether mucosa-targeted, probiotic-mediated, in situ PEA biosynthesis could attenuate liver injury associated with chronic colitis. Male C57BL/6J mice were subjected to chronic dextran sulfate sodium (DSS) colitis and treated with an engineered Lactobacillus paracasei F19 strain expressing human NAPE-PLD (pNAPE-LP) plus ultra-low-dose palmitate, a control strain (pLP), or pNAPE-LP combined with the PPAR-α antagonist MK886. pNAPE-LP significantly increased colonic PEA levels and elevated circulating and hepatic PEA, confirming effective local production with systemic distribution. Treatment ameliorated colitis severity, restored tight-junction protein expression, and reduced endotoxemia. Importantly, pNAPE-LP attenuated colitis-associated liver injury by decreasing histological damage and collagen deposition, lowering transaminase levels, and reducing hepatic neutrophil infiltration. These effects were accompanied by the suppression of the hepatic TLR4/NF-κB/NLRP3 inflammasome axis, reduced caspase-1 activation, decreased IL-1β, TNF-α, and IL-6 levels, restored PPAR-α expression, and reduced Bax expression. The control strain was ineffective, and PPAR-α inhibition abolished both intestinal and hepatic protection. Collectively, these findings demonstrate that engineered probiotics acting as "living drug factories" can target the gut-liver axis via localized PEA biosynthesis, restoring barrier integrity and limiting hepatic inflammatory and fibrogenic signaling in chronic colitis.