Abstract
IDENTIFICATION OF THE ENVIRONMENTAL POLLUTANTS AND METABOLIC PATHWAYS ASSOCIATED WITH NONALCOHOLIC FATTY LIVER DISEASE SEVERITY
Background: Environmental pollutants are associated with disrupted hepatic metabolism and NAFLD. A pilot study (n=140) presented at AASLD elucidated exposures and metabolic pathways associated with NAFLD severity. To confirm these findings, a larger cross-sectional multi-‘omics study was performed in subjects with NAFLD.
Methods: Exposomics and metabolomics (LC-MS2 using HILIC & C18 columns & GC-MS2) were performed in plasma samples from 341 prospectively enrolled NAFLD patients diagnosed by AASLD guidelines. Fibrosis severity was determined by liver stiffness measurement (LSM) and steatosis by controlled attenuation parameter (CAP). LSM >8.6kPa was considered to be clinically significant fibrosis (CSF). Exposome- and metabolome-wide association studies (EWAS & MWAS) were performed using the R package xMSPanda. Pathway enrichment analyses were performed using mummichog.
Results: The NAFLD cohort (mean age = 53±14 years, mean BMI = 35±7 kg/m2) was 60% female and 95% White. 48% had diabetes-2, 53% had dyslipidemia, and 60% had hypertension. Four environmental pollutants (ethyl-decanoate, ethyl-undecanoate, diethylthiophosphoric acid, and hydroxycitronellal) were significantly associated with CSF (p<0.05, FDR<0.20). At a less stringent threshold (p<0.05, FDR>0.20), 42 exposures were associated with CSF. These included environmental phenols confirming results from the pilot study. The MWAS of LSM revealed significant associations with 271 (HILIC) and 314 (C18) metabolic features (p<0.05, FDR<0.05). Thirty metabolic pathways were associated with fibrosis including: bile acids; glycosphingolipids; vitamin D3; hexose-phosphorylation; keratan-sulfate; N-glycan; pyrimidine, arginine-proline; and linoleate, confirming results from the pilot study. CAP was significantly associated with 35 (HILIC) and 17 (C18) metabolic features. Fifteen pathways were associated with hepatic steatosis, 8 of which were previously identified in the pilot study.
Conclusion: Multiple environmental pollutants were associated with CSF, with several previously identified in the pilot cohort. Bile acid metabolism was the most significantly enriched pathway associated with liver fibrosis, and seven pathways were perturbed by both steatosis and fibrosis recapitulating results from the pilot study in this larger cohort. Reverse causality cannot be excluded. These findings suggests that pollutants have a significant impact on liver fibrosis in NALFD and warrant additional investigation.