Association of circulating leptin concentration with the risk of Clostridium difficile colitis and exploration of their associated mediators: A mendelian randomisation study

• The study has uncovered the causal relationships of genetically predicted circulating leptin levels on Clostridium difficile colitis risk. • Mediation analysis identifies cholesterol in sdLDL, PTHrP, and TPST2 as partial mediators of leptin's effect on Clostridium difficile colitis. • Findings reveal novel molecular pathways linking leptin to gut inflammation and Clostridium difficile colitis susceptibility. Clostridioides difficile infection (CDI) is a leading cause of nosocomial diarrhea and colitis, imposing a significant burden. This study aims to elucidate the causal relationship between leptin and Clostridium difficile colitis and identify potential molecular mediators. Using genome-wide association study (GWAS) summary statistics from the MRC Integrative Epidemiology Unit (MRC-IEU), we performed univariable and multivariable Mendelian randomization (MR) analyses, with inverse variance weighted (IVW) as the primary estimator, supplemented by weighted median, MR-Egger, and maximum likelihood methods. We also conducted linkage disequilibrium score regression (LDSC) to assess genetic correlations and two-step mediation MR to explore potential mediators. Multiple sensitivity analyses and Steiger tests ensured result robustness. Genetically predicted circulating leptin levels were associated with an increased risk of Clostridium difficile colitis (OR 2.456; 95% CI 1.231–4.90; P = 0.011). This association persisted in multivariable MR analyses incorporating adiponectin and resistin (OR 2.146; 95% CI 1.551–2.740; P = 0.012), and LDSC analysis revealed a genetic correlation between them (Rg = -0.521, Rg_SE = 0.599). Our mediation analysis indicated that leptin indirectly influenced CDI through “cholesterol in small dense LDL” (mediation proportion −2.99), “PTHrP” (mediation proportion −16.1%), and “TPST2” (mediation proportion −25.44%). Our findings demonstrate an effect of genetically predicted circulating leptin levels on Clostridium difficile colitis risk. Furthermore, we identified cholesterol in small dense LDL, PTHrP, and TPST2 as potential molecular mediators, providing insights into the underlying pathophysiological mechanisms.