Causal effects of circulating cathepsins on cholecystitis, cholelithiasis, primary biliary cholangitis, primary sclerosing cholangitis, acute pancreatitis, and chronic pancreatitis

Gallbladder, biliary, and pancreatic disorders are nonneoplastic diseases marked by inflammation, epithelial injury, and fibrosis. Cathepsins are lysosomal proteases involved in inflammatory activation, immune regulation, extracellular matrix turnover, and pancreatic enzyme activation. Observational links between dysregulated cathepsins and hepatopancreatobiliary pathology could reflect confounding or reverse causation. This study used Mendelian randomization (MR) to assess whether circulating cathepsins causally influence gallbladder, biliary, and pancreatic diseases. We conducted a 2-sample MR analysis using genetic variants associated with circulating cathepsin levels from the INTERVAL genome-wide association studies (3301 European participants). Summary statistics for cholecystitis, cholelithiasis, primary biliary cholangitis (PBC), primary sclerosing cholangitis, acute pancreatitis, and chronic pancreatitis were extracted from European-ancestry genome-wide association studies consortia. Instrumental variables were selected at P < 5 × 10-6 with linkage disequilibrium r2 < 0.001 to maximize instrument availability while retaining independence. The inverse-variance weighted estimator was the primary model, complemented by weighted median, MR-Egger, and mode-based methods. Instrument strength, pleiotropy, and heterogeneity were evaluated via F statistics, MR-Egger intercept, MR Pleiotropy RESidual Sum and Outlier, and Cochran Q. Benjamini-Hochberg false discovery rate (FDR) correction accounted for multiple testing, and sensitivity analyses included leave-one-out tests and PhenoScanner filtering. Two cathepsin B associations remained significant after FDR correction. Higher genetically predicted cathepsin B was linked to lower PBC risk (odds ratio [OR] = 0.784; 95% confidence interval [CI]: 0.664-0.925; P = .004; FDR = 0.022) and higher cholecystitis risk (OR = 1.080; 95% CI: 1.022-1.141; P = .006; FDR = 0.018). Other nominal associations did not survive correction and should be interpreted cautiously: cathepsin O with cholelithiasis (OR = 1.001; 95% CI: 1.000-1.003; P = .033; FDR = 0.199), cathepsin L2 with acute pancreatitis (OR = 1.156; 95% CI: 1.008-1.327; P = .038; FDR = 0.227), and cathepsin H with chronic pancreatitis (OR = 0.922; 95% CI: 0.853-0.997; P = .043; FDR = 0.255). No heterogeneity, horizontal pleiotropy, or reverse causation was detected. Genetically predicted cathepsin B appears protective for PBC but increases cholecystitis risk, supporting distinct causal roles among circulating cathepsins in hepatopancreatobiliary diseases. Associations involving cathepsin O, L2, and H were nominal, warranting cautious interpretation, replication, and further functional studies.