Interleukin-18 binding protein deficiency results in gut microbiota dysbiosis and aggravated diet-induced MASH in mice.

Background & Aims: Metabolic dysfunction-associated steatotic liver disease (MASLD)/metabolic dysfunction-associated steatohepatitis (MASH) are now the most prevalent hepatic disorders worldwide. Growing evidence implicates physiological alterations in the gut-liver axis and gut microbiota dysbiosis in this process. IL-18-binding protein (IL-18BP) forms high affinity complexes with IL-18, thus blocking its interaction with IL-18 receptors. Methods: We used high-fat diet (HFD) and methionine choline deficient (MCD) diet to model MASLD/MASH in wild-type (WT) male mice (n = 6-8 mice per group). We also studied antimicrobial peptides (AMPs) production, gut microbiota composition, and liver phenotype in Il18bp -/- male mice on both HFD and MCD diets (n = 5-7 mice per group). We manipulated gut microbiota of Il18bp -/- and WT male mice through administration of phages, antibiotics, and through co-housing experiments (n = 4-8 mice per group). Results: Feeding WT mice with a HFD or an MCD diet led to a decrease in ileal AMPs expressions (respectively, by 63% and 37% for Lyz1; by 47% and 84% for Ang4; by 86% and 46% for Pla2g2a) and an enrichment in gut proteobacteria (respectively, by 7- and 23-fold for α-proteobacteria; by 2.1- and 1.7-fold for δ-proteobacteria; by 14- and 20-fold for γ-proteobacteria) when compared with standard chow diet (p <0.05). These changes were associated with a reduction in the ileal Il18bp expression (respectively, by 77% and 46%) in HFD and MCD diet-fed WT mice vs. chow diet-fed WT mice (p <0.05). Il18bp -/- mice exhibited a decrease in gut AMPs expression and storage (AMP granules area/crypt respectively decreased by 57% and 62.5% in Il18bp -/- vs. WT mice on HFD and MCD diets). Moreover, Clostridium/Turicimonas/Escherichia bacteria were constitutively over-represented in gut microbiota of Il18bp -/- vs. WT mice in a diet-amplified manner. Compared with WT mice, Il18bp -/- mice exhibited increased diet-induced hepatic damage (circulating alanine aminotransferase 84 vs. 41 U/L on HFD; 1,218 vs. 738 U/L on MCD diet, p <0.05), inflammation (liver tumor necrosis factor-alpha content 72 vs. 35 pg/g protein on HFD; 441 vs. 169 pg/g protein on MCD diet, p <0.05), and fibrosis (Sirius red 1.45 vs. 0.36% on HFD; 1.64 vs. 0.65% on MCD diet, p <0.01). These changes occurred independently of steatosis modification. Phages, antibiotic, and co-housing experiments revealed that specific gut microbiota featuring Il18bp -/- mice is implicated in their exacerbated liver inflammation and fibrosis status. Conclusions: IL-18BP limits the progression of MASLD/MASH by maintaining normal intestinal production of AMPs and composition of the gut microbiota. Impact and implications: We presently highlight a previously unknown protective role of IL-18BP in the integrity of the gut-liver axis. Increasing IL-18-binding protein levels (a clinically validated option to treat rare systemic auto-inflammatory diseases) represents a novel therapeutic perspective, not only for patients with MASLD/MASH, but also for patients presenting gut microbiota dysbiosis.