Increased cytotoxicity of Pb2+ with co-exposures to a mitochondrial uncoupler and mitochondrial calcium uniporter inhibitor

• Published in: Environmental science--processes & impacts Vol. 25; no. 11; pp. 1743 - 1751
• Main Authors: Lalwani, Pooja, King, Dillon E, Morton, Katherine S, Rivera, Nelson A, Huayta, Javier, Hsu-Kim, Heileen, Meyer, Joel N
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 15.11.2023
• Subjects: Calcium; Calcium (mitochondrial); Calcium ions; Carbonyl compounds; Carbonyls; Cell death; Cell viability; Chemical damage; Contaminants; Cyanides; Cytotoxicity; Exposure; Hepatocytes; Hypotheses; Imports; Lead; Membrane potential; Membranes; Mitochondria; Mixtures; Prediction models; Ruthenium; Ruthenium red; Toxicants; Toxicity
• ISSN: 2050-7887; 2050-7895
• DOI: 10.1039/d3em00188a

Lead (Pb2+) is an important developmental toxicant. The mitochondrial calcium uniporter (MCU) imports calcium ions using the mitochondrial membrane potential (MMP), and also appears to mediate the influx of Pb2+ into the mitochondria. Since our environment contains mixtures of toxic agents, it is important to consider multi-chemical exposures. To begin to develop generalizable, predictive models of interactive toxicity, we developed mechanism-based hypotheses about interactive effects of Pb2+ with other chemicals. To test these hypotheses, we exposed HepG2 (human liver) cells to Pb2+ alone and in mixtures with other mitochondria-damaging chemicals: carbonyl cyanide-p-trifluoromethoxyphenylhydrazone (FCCP), a mitochondrial uncoupler that reduces MMP, and Ruthenium Red (RuRed), a dye that inhibits the MCU. After 24 hours, Pb2+ alone, the mixture of Pb2+ and RuRed, and the mixture of Pb2+ and FCCP caused no decrease in cell viability. However, the combination of all three exposures led to a significant decrease in cell viability at higher Pb2+ concentrations. After 48 hours, the co-exposure to elevated Pb2+ concentrations and FCCP caused a significant decrease in cell viability, and the mixture of all three showed a clear dose-response curve with significant decreases in cell viability across a range of Pb2+ concentrations. We performed ICP-MS analyses on isolated mitochondrial and cytosolic fractions and found no differences in Pb2+ uptake across exposure groups, ruling out altered cellular uptake as the mechanism for interactive toxicity. We assessed MMP following exposure and observed a decrease in membrane potential that corresponds to loss of cell viability but is likely not sufficient to be the causative mechanistic driver of cell death. This research provides a mechanistically-based framework for understanding Pb2+ toxicity in mixtures with mitochondrial toxicants.