Blood BTEXS and heavy metal levels are associated with liver injury and systemic inflammation in Gulf states residents
Introduction
Volatile organic compound (VOC) and metal exposures have previously been associated with liver disease and endocrine/metabolic disruption (Heindel et al., 2017). However, more data are required for a deeper understanding of these associations. The purpose of this cross-sectional study is to evaluate associations between blood biomarkers of exposure and serologic biomarkers of liver injury and adipocytokines in Gulf coast residents. Exposures to BTEXS (benzene, toluene, ethylbenzene, xylene, styrene) and metals (lead, cadmium and mercury) as well as exposure-obesity interactions are evaluated.
Liver diseases associated with occupational VOC exposures range from acute liver failure, to toxicant-associated fatty liver disease (TAFLD) with or without fibrosis, and liver cancer (Cave et al., 2011a, Cave et al., 2011b; EASL, 2019; Tolman and Dalpiaz, 2013; Wahlang et al., 2013; Wahlang et al., 2019). Despite significant knowledge gaps, clinical guidance in these areas has recently been published (EASL, 2019; Nerenz et al., 2015). VOC-related occupational hepatotoxicity and TAFLD have been of particular interest for the petrochemical industry (EASL, 2019). Abnormal liver enzymes and biopsy-proven nonalcoholic steatohepatitis (NASH) with fibrosis and cholestasis were reported in workers with BTXS and other VOC exposures at a petrochemical plant in Brazil (Barberino et al., 2005; Cotrim et al., 1999, 2004, 2005). The liver disease improved following removal from the workplace (Cotrim et al., 1999). BTXS-exposed petrol workers from Iran had higher mean alanine aminotransferase activity (ALT) than unexposed controls; and ALT correlated positively with workplace BTXS concentrations (Neghab et al., 2015; Salehpour et al., 2019). BTX-exposed petrochemical workers from Argentina had significantly increased odds for hypertransaminasemia compared to unexposed controls; and about half of affected workers had hepatic steatosis by ultrasound (Perez et al., 2006).
When compared to the occupational health literature, less is known about the liver health effects of environmental VOC exposures. Urinary VOC metabolites were not associated with ‘unexplained ALT elevation’, a surrogate composite NASH biomarker, in the adult National Health and Nutrition Examination Survey (NHANES) 2003–2004 (Cave et al., 2010a). However, positive associations were observed between specific liver biochemistries and BTEX/other VOC exposures measured by passive exposure monitors in NHANES 1999–2000 (Liu et al., 2009). Likewise in NHANES, metals (e.g., lead, cadmium, and mercury) were positively associated with ‘unexplained ALT elevation’, liver enzymes, hepatic steatosis and/or NASH (Cave et al., 2010a; Hyder et al., 2013). A urinary metabolite of vinyl chloride was associated with increased odds for nonalcoholic fatty liver disease (NAFLD) in children living near a petrochemical complex (Wang et al., 2019). Following a 2010 benzene release during a flaring incident at a Texas refinery, mean liver enzymes were increased in exposed community residents vs. unexposed controls (D'Andrea and Reddy, 2016a, b).
When compared to imaging or histologic biomarkers of TAFLD, routine liver biochemistries, such as ALT may be insensitive for the detection of this VOC-related liver disease (Anakwue et al., 2017; Cave et al., 2010b). Cytokeratin 18 (CK18) is a serologic biomarker of hepatocyte death. Both the whole protein (CK18 M65) and its caspase-cleaved fragment (CK18 M30) may be measured in serum by enzyme-linked immunosorbent assays (ELISA). CK18 M65 reflects total hepatocyte death, and CK18 M30 indicates hepatocyte apoptosis. CK18 correlated with the severity of both alcoholic and nonalcoholic steatohepatitis (Feldstein et al., 2009; Vatsalya et al., 2019). Likewise, this biomarker appeared more effective than ALT for VOC-induced liver toxicity and toxicant-associated steatohepatitis (TASH) (Cave et al., 2010b, 2011). More recently, serum CK18 and adipocytokines have been used to investigate environmental liver disease and endocrine/metabolic disruption related to polychlorinated biphenyl and perfluoroalkyl substance exposures (Bassler et al., 2019; Clair et al., 2018). In cohort studies, TASH has been associated with increased hepatocyte death, increased serum pro-inflammatory cytokines and abnormal adipokines (Cave et al., 2010b, 2011; Clair et al., 2018).
The present cross-sectional pilot study investigates associations between blood exposure (BTEXS and metals) biomarkers and serum disease (CK18/adipocytokine) biomarkers using archived materials from a Deepwater Horizon (DWH) oil spill response subcohort. Because steatohepatitis is an obesity-associated inflammatory liver disease, interactions between exposures and obesity impacting on the disease biomarkers are also investigated. The tested hypothesis is that the exposures are significantly associated with CK18 and adipocytokine levels and interact with obesity.
Subjects for this pilot study were from a subset of the Gulf Long-term Follow-up Study (GuLF Study) participants enrolled in a Chemical Biomonitoring Study (CBS) carried out between 2012 and 2013. Blood BTEXS and metal (lead, cadmium and mercury) levels were previously determined in CBS participants. While the parent GuLF Study was focused on health effects associated with oil spill response and clean-up exposures, because the blood specimens for the CBS participants were obtained several years after the spill and VOCs have short half-lives, the measured BTEXS levels are unlikely to be related to oil spill hydrocarbon exposures (Ashley and Prah, 1997; Chambers et al., 2018). Indeed, despite living in a region with prolific petrochemical and industrial operations, blood BTEX levels in this population were shown to be comparable to population levels measured in NHANES (Werder et al., 2018). Thus, while these participants may have previously experienced short term high environmental and/or occupational BTEXS exposures related to the DWH oil spill and response, their exposures at the time of assessment were likely similar to the general U.S. residential population. Therefore, the data generated by this research is relevant to both occupational and environmental liver diseases.
Section snippets
Study design and participants
Data and archived serum samples were obtained from the GuLF Study, a prospective cohort of individuals (ages 21 and older) who participated in oil spill response activities and others who received safety training, but did not work on the spill, following the 2010 Deepwater Horizon disaster. Participants enrolled between 2011 and 2013. A detailed description of this study is available elsewhere (Kwok et al., 2017). Approximately 2–3 years after the disaster (May 2012–July 2013), a convenience
Results
In this sample of adult nonsmoking men, approximately half (53%) of participants are age 45 or younger and half (50%) are obese (Table 1). The study sample is predominantly white (57%), while 37% are black and 6% are classified as other race. All participants reported that they were not current smokers and over half (54%) had non-detectable levels of serum cotinine. The detectable cotinine levels in the remaining sample suggest that participants may have had recent, appreciable exposure to
Discussion
In this sample of 214 adult males living in the Gulf coast region, we examined cross-sectional associations between blood BTEXS and metals and serum liver injury biomarkers and adipocytokines. In the overall sample, positive associations were observed between lead exposure with hepatocyte apoptosis (CK18 M30) and pro-inflammatory cytokines (IL-1β, IL-6 and IL-8); and for cadmium exposures with IL-1β and IL-8. Thus, heavy metal exposures were associated with liver injury (lead only) and/or
Funding source
This work was funded, in part, by the National Institutes of Health (R35ES028373, P42ES023716, T32ES011564, P20GM113226, and P50AA024337) and National Institutes of Health Common Fund and the Intramural Research Program of the National Institutes of Health, National Institute of Environmental Health Sciences (Z01 ES 102945).
CRediT authorship contribution statement
Emily J. Werder: Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Project administration, Resources, Supervision, Validation, Visualization, Writing - original draft, Writing - review & editing. Juliane I. Beier: Conceptualization, Data curation, Formal analysis, Funding acquisition, Investigation, Methodology, Project administration, Resources, Supervision, Validation, Visualization, Writing - original draft, Writing - review & editing. Dale P. Sandler:
Declaration of competing interest
The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Dr. Cave previously received a contract from Lakeside Life Sciences related to the clinical development of the cytokeratin 18 biomarker for alcoholic hepatitis. That contract is not directly related to this work.
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