Abstract
INTRODUCTION: Exposures to volatile organic compounds and metals have previously been associated with liver diseases including steatohepatitis, although more data are needed. Benzene, toluene, ethylbenzene, xylenes, styrene (BTEXS) and metals were measured in blood samples collected between May 2012-July 2013 from volunteers participating in home visits for the Gulf Long-term Follow-up (GuLF) Study. This cross-sectional analysis evaluates associations of exposure biomarkers with serum liver injury and adipocytokine biomarkers in a sample of 214 men. METHODS: Adult nonsmoking men without a history of liver disease or heavy alcohol consumption were included. The serologic disease biomarkers evaluated were the hepatocellular injury biomarker, cytokeratin 18 [whole (CK18 M65) and caspase-cleaved fragment (CK18 M30)]; and adipocytokines. Confounder-adjusted beta coefficients were determined using linear regression models for the overall sample (primary endpoints) and for obesity-classified sub-groups (secondary endpoints). A product interaction term between the exposure of interest and a dichotomized indicator of obesity was included to determine the disease modifying effects of obesity on the biomarker associations. RESULTS: The study sample was 57% white and 51% obese. In the overall sample, lead was positively associated with CK18 M30 (β = 21.7 ± 6.0 (SE), p = 0.0004); IL-1β (β = 32.8 ± 5.2, p < 0.0001); IL-6 (β = 72.8 ± 18.3, p = 0.0001); and IL-8 (β = 140.8 ± 42.2, p = 0.001). Cadmium exposures were associated with increased IL-1β (β = 77.8 ± 26.3, p = 0.003) and IL-8 (β = 419.5 ± 201.2, p = 0.04). There were multiple significant interactions between obesity and exposure to lead, cadmium, benzene and toluene in relation to outcome biomarkers. Among obese participants (n = 108), benzene, lead, and cadmium were each positively associated with CK18 M30, IL-1β, IL-6, and IL-8. In obese subjects, lead was also inversely associated with leptin, and toluene was positively associated with IL-1β. CONCLUSION: For the overall sample, heavy metal exposures were associated with liver injury (lead only) and/or systemic inflammation (lead and cadmium). Obesity modified the associations between BTEXS and heavy metal exposures on several of the outcome variables. In the obesity subgroup, liver injury was positively associated with lead, cadmium and benzene exposures; systemic inflammation was increased with lead, cadmium, benzene, and toluene exposures; and leptin was inversely associated with lead exposures. The cross-sectional design of this study makes it difficult to determine causality, and all results should be interpreted cautiously. Nonetheless, the potential impact of exposures to lead, cadmium, benzene and toluene in steatohepatitis, an obesity-associated inflammatory liver disease, warrants further investigation.