Background and Purpose: Metabolic disruption and obesity are ongoing public health problems that have been linked to chemical exposures. However, understanding causal pathways is difficult as real-world exposures do not occur in isolation but rather as complex chemical mixtures. To improve understanding of the toxic effects of chemical mixtures, we obtained a set of real-world exposure mixture profiles derived from chemical biomonitoring data collected from the Environmental Influences on Child Health Outcomes Fetal Growth Studies (ECHO-FGS) birth cohort. The mixture profiles characterized five distinct exposure scenarios that consisted of varying concentrations of p,p’-DDE, PCB153, BDE47, and PFOS. Using in vitro cell cultures, these mixtures were evaluated for their effects on PPARγ, PPARα, and mitochondrial metabolism.
Methods: Observed concentrations of each chemical mixture profile of p,p’-DDE, PCB153, BDE47, and PFOS were examined at 1X, 50X and 500X. We tested for mixture effects on metabolic disruption by examining whether the individual chemicals or chemical mixtures activate PPARα/γ and perturb mitochondrial metabolism. To test activation of PPARα/γ, transactivation assays were performed in human hepatoma HepG2 cells using a Dual-Glo luciferase kit. Mitochondrial metabolism was measured as Oxygen Consumption Rate (OCR) after 24-hour exposures in C2C12 murine myoblast cells, which have high mitochondria numbers, with the MitoStress Test on an Agilent Seahorse XF Pro Analyzer (Agilent Technologies, Santa Clara, CA).
Results: PPARα is activated by exposure to mixture Profile 3 at 500X, a profile that is dominated by BDE47. BDE47 and PCB153 also activated PPARα, individually. Surprisingly, Profile 4, that is dominated by PFOS, did not activate PPARα. None of the chemical profiles or individual chemicals activated PPARγ. However, PPARγ activation was enhanced by exposure to 500X Profile 1 or 4 combined with the known positive agonist, rosiglitazone, suggesting that some chemical mixtures may boost natural PPARγ activation. MitoStress assays performed in C2C12 myoblasts revealed that mixture profiles 1 and 3 perturbed mitochondrial metabolism more than the other mixture profiles with Profile 1 perturbing Basal Respiration, Maximal Respiration, Spare Respiratory Capacity, ATP-Coupled Respiration and Non-Mitochondrial Oxygen Consumption. Profile 3 perturbed Basal Respiration, Maximal Respiration, Spare Respiratory Capacity and ATP-Coupled Respiration. Mixture Profile 4 moderately perturbed Basal Respiration and ATP-Coupled Respiration.
Conclusions: These findings show agonistic effects of mixture Profile 3 on PPARα in conjunction with perturbed mitochondrial metabolism as measured by Oxygen Consumption Rate (OCR). Profiles 1 and 4 enhanced PPARγ activation and also perturbed mitochondrial metabolism with profile 1 showing stronger effects. These results suggest that disruption in PPAR activity may play a role in the association of these chemical mixture profiles with obesity.