Lipid Metabolic Disturbance Induced by Triphenyl Phosphate and Hydroxy Metabolite in HepG2 Cells Through Activation of the PPARs Pathway and Endoplasmic Reticulum Stress

Abstract

Triphenyl phosphate (TPHP) has been widely used as flame retardants and been detected with increasing frequency in environment. TPHP can transform into mono-hydroxylated phosphate (OH-TPHP) and diester diphenyl phosphate (DPHP) through biotransformation. So far, information on the toxicology effects of TPHP metabolites and molecular regulatory mechanisms is still limit. This study investigated the adverse effects of TPHP, OH-TPHP, and DPHP in HepG2 cells in terms of cell viability, lactate dehydrogenase release, reactive oxygen species generation, and mitochondrial membrane potential. The transcriptomic changes were measured using RNA sequencing, and bioinformatics characteristics including biological functions, signal pathways and protein-protein interaction were analyzed to explore the potential molecular mechanisms. Results displayed that the order of toxic effects was OH-TPHP> TPHP> DPHP. The prioritized biological functions changes induced by TPHP and OH-TPHP were correlated with lipid metabolism. Significant lipid accumulation was observed as confirmed by increased total cholesterol and triglycerides contents, and enhanced oil red O staining. Enrichment of PPARα/γ and down-stream genes indicated participation of the PPARs signal pathway in lipid metabolism disorder. In addition, TPHP and OH-TPHP induced endoplasmic reticulum stress (ERS), which was further confirmed by the ERS inhibitor experiment. In general, TPHP and OH-TPHP had obvious cytotoxic effects in HepG2 cells. The lipid metabolism disorder induced by TPHP and OH-TPHP was mediated through the PPARs signal pathway and endoplasmic reticulum stress.

Note:
Funding declaration: This work was supported by National Natural Science Foundation of China (No:42077388); Local Innovative and Research Teams Project of Guangdong Pearl River Talents Program (2017BT01Z134); Guangdong Foundation for Program of Science and Technology Research (Grant No:2020B1212060053)

Conflict of Interests: none

Keywords: Triphenyl phosphate (TPHP), OH-TPHP, DPHP, lipid metabolism, PPARs signal pathway, Endoplasmic reticulum stress