Vinyl Chloride Metabolites Potentiate Inflammatory Liver Injury Caused by LPS in Mice

Abstract

Vinyl chloride (VC) is a ubiquitous environmental contaminant for which human risk is incompletely understood. We have previously reported that high occupational exposure to VC directly caused liver damage in humans. However, whether VC may also potentiate liver injury from other causes is not known. C57Bl/6J mice were administered chloroethanol (CE), a major metabolite of VC, and lipopolysaccharide (LPS) 24 h after CE. Samples were harvested for determination of liver damage, inflammation, and changes in carbohydrate and lipid metabolism. In mice, CE exposure alone caused no detectable liver damage. LPS exposure caused inflammatory liver damage, oxidative stress, lipid accumulation, and glycogen depletion; the effect of all of these variables was potentiated by CE pre-exposure. In vitro experiments suggest that VC metabolite chloroacetaldehyde (CAA) directly damages mitochondria, which may explain the sensitization effect observed in vivo Moreover, co-exposure of cells to CAA and TNFα caused increased cell death, supporting the hypothesis of sensitization by VC metabolites. Taken together, these data demonstrate that exposure to VC/metabolites at levels that are not overtly hepatotoxic can potentiate liver injury caused by another hepatotoxicant. This serves as proof-of-concept that VC hepatotoxicity may be modified by an additional metabolic stress such as endotoxemia, which commonly occurs in acute (eg, sepsis) and chronic (eg, NAFLD) diseases.

Role of dietary fatty acids in liver injury caused by vinyl chloride metabolites in mice.

“…DAMPs, such as reactive oxygen species (ROS) or products of necrosis (e.g., ATP) may directly activate the inflammasome (39,40). Previously, we demonstrated that VCmetabolite induced cell death favors necrosis (11), which supports this mechanism of action.…”

Vinyl chloride-diet interactions in liver disease : potential roles of autophagy and energy management.

“…In ALD, steatosis can be caused directly by ethanol metabolites' disruption of the balance between NAD + and NADH, leading to inhibition of β-oxidation and an accumulation of free fatty acids (FFA) and triglycerides (25 that showed a decrease in ATP production and decreased oxygen consumption rate with increasing CAA concentrations (22).…”

“…On the eleventh day, the two diet groups were further separated into additional groups that either received a bolus gavage of chloroethanol (CE; 50 mg/kg) or vehicle (saline), modified from Bertola et al, (53). The concentration of CE was determined by others to not directly cause liver damage (54) and was validated (22); mice were ethanol fasted for 4 hours prior to oral gavage and were sacrificed 4, 9, or 24 hours later (Figure 2A).…”

“…In order to elucidate mechanisms by which CE acts as an enhancing factor in a multiple-hit model, a more robust model of liver injury was used with CE + LPS, as previously described by Anders et al, (22). To verify that rapamycin inhibited mTOR activation, mTOR phosphorylation was analyzed via Western Blot ( Figure 5).…”

“…Indeed, previously it has been shown that VC causes necrotic rather than apoptotic cell death (8,22). In order to determine the cell death pathway in this model of injury, TUNEL-positive cells were visualized as an index of apoptosis and TUNEL-positive hepatocytes and non-parenchymal cells were counted.…”