Toxicological mechanisms and potencies of organophosphate esters in KGN human ovarian granulosa cells as revealed by high-throughput transcriptomics

Despite the growing number of studies reporting potential risks associated with exposure to organophosphate esters (OPEs), their molecular mechanisms of action remain poorly defined. We used the high-throughput TempO-Seq platform to investigate the effects of frequently detected OPEs on the expression of similar to 3000 environmentally responsive genes in KGN human ovarian granulosa cells. Cells were exposed for 48 h to 1 of 5 OPEs (0.1-50 mu M): tris(methylphenyl) phosphate (TMPP), isopropylated triphenyl phosphate (IPPP), tert-butylphenyl diphenyl phosphate (BPDP), triphenyl phosphate (TPHP), or tris(2-butoxyethyl) phosphate (TBOEP). The sequencing data indicate that 4 OPEs induced transcriptional changes, whereas TBOEP had no effect within the concentration range tested. Multiple pathway databases were used to predict alterations in biological processes based on differentially expressed genes. At lower concentrations, inhibition of the cholesterol biosynthetic pathway was the predominant effect of OPEs; this was likely a consequence of intracellular cholesterol accumulation. At higher concentrations, BPDP and TPHP had distinct effects, primarily affecting pathways involved in cell cycle progression and other stress responses. Benchmark concentration modeling revealed that BPDP had the lowest transcriptomic point of departure. However, in vitro to in vivo extrapolation modeling indicated that TMPP was bioactive at lower concentrations than the other OPEs. We conclude that these new approach methodologies provide information on the mechanism(s) underlying the effects of data-poor compounds and assist in the derivation of protective points of departure for use in chemical read-across and decision-making.

Automated summary

Despite the increasing number of studies on the potential risks associated with exposure to organophosphate esters (OPEs), their molecular mechanisms of action are still poorly understood. In this study, the effects of commonly detected OPEs on gene expression in human ovarian granulosa cells were investigated using the high-throughput TempO-Seq platform. The results revealed that OPEs had different effects on various biological pathways, with inhibition of the cholesterol biosynthetic pathway being the predominant effect at lower concentrations. At higher concentrations, OPEs primarily affected pathways related to cell cycle progression and stress responses.