BOSTON – Exposure to heavy metals from natural and man-made sources may contribute to development of autoimmune liver disease, according to a recent U.K. study involving more than 3,500 patients.
Coal mines were particularly implicated, as they accounted for 39% of the risk of developing primary biliary cholangitis (PBC), reported lead author, of Newcastle (England) University, and colleagues.
“We know that the etiology of autoimmune liver disease remains unclear, but we’re increasingly coming to understand that it’s likely to be a complex interplay between genetic and environmental factors,” Dr. Dyson said during a presentation at the annual meeting of the American Association for the Study of Liver Diseases. Showing a map of England, she pointed out how three autoimmune liver diseases – PBC, primary sclerosing cholangitis (PSC), and autoimmune hepatitis (AIH) – each have unique clusters of distribution. “This implies that environmental exposure may have a role in disease pathogenesis.”
To investigate this possibility, Dr. Dyson and colleagues used structural equation modeling to look for associations between the above three autoimmune liver diseases, socioeconomic status, and environmental factors. Specific environmental factors included soil concentrations of heavy metals (cadmium, arsenic, lead, manganese, and iron), coal mines, lead mines, quarries, urban areas, traffic, stream pH, and landfills.
The study was conducted in the northeast of England, where migration rates are low, Dr. Dyson said. From this region, the investigators identified patients with PBC (n = 2,150), AIH (n = 963), and PSC (n = 472). Conceptual models were used to examine relationships between covariates and prevalence of disease, with good models exhibiting a root-mean-square error of association less than 0.05 and a 95% covariate significance. After adjusting for population density, comparative fit was used to measure variation within each model.
The best model for PBC revealed the aforementioned link with coal mines, proximity to which accounted for 39% of the pathogenesis of PBC. High levels of cadmium in soil had an interactive role with coal mines, and itself directly contributed 22% of the risk of PBC; however, Dr. Dyson noted that, while many cadmium-rich areas had high rates of PBC, not all did.
“This demonstrates the complexity of causality of disease, and we certainly can’t say that cadmium, in its own right, is a direct cause and effect,” Dr. Dyson said. “But I think [cadmium] certainly potentially is one of the factors at play.”
For AIH, coal mines contributed less (6%), although cadmium still accounted for 22% of variation of disease, as did alkaline areas. Finally, a significant link was found between PSC and regions with high arsenic levels.
“To conclude, our data suggest that heavy metals may be risk factors for autoimmune liver disease,” Dr. Dyson said. “There are a number of exposure routes that may be pertinent to patients, from heavy metals occurring via natural sources, and also via virtue of human activity, such as burning of fossil fuels, heavy-metal production, and pesticides.” Dr. Dyson emphasized this latter route, as some rural areas, where pesticide use is common, had high prevalence rates of autoimmune liver disease.
Dr. Dyson went on to put her findings in context. “Heavy metals are a well-recognized cause of immune dysregulation and epithelial injury and are actually actively transported into the bile, and that may be particularly relevant in terms of cholangiopathies. And this leads us to the possibility of interventions to reduce toxic exposure that may modify risk of disease.”
Looking to the future, Dr. Dyson described plans to build on this research with measurements of heavy metals in tissues, serum, and urine.
The investigators reported no relevant disclosures.
SOURCE: Dyson J et al. The Liver Meeting 2019, .