Effects of marine mixtures of persistent organic pollutants on steroidogenesis on LH-stimulated primary Leydig cells

Abstract

The ability of POPs (persistent organic pollutants) to act as endocrine disruptors and their potential role in negative trends in male reproductive health have caused increased concern over the last few decades. There has been an increased focus on the endocrine disrupting capacity of environmental mixtures of pollutants, compared to earlier focus on single compound exposure studies. While Norwegian health authorities strongly recommend a higher consumption of fish and fish liver oil dietary supplements because of their beneficial health effects, they have been put forward as considerable sources of human intake of POPs. Leydig cells are responsible for the biosynthesis of testosterone, which is essential for male developmental and reproductive function. The predominant steroid biosynthesis Δ5 pathway is similar in pig and human. Thus, the porcine Leydig cell provides a useful model for investigating human testicular steroidogenesis. The aim of this study was to investigate the effects of POPs in three marine mixtures (“Cod”, “Waste” and “Tran”), representing different steps in the refinement process of cod liver oil used as a dietary supplement, on steroidogenesis in LH-stimulated primary porcine Leydig cells. The investigation of effects was performed through a holistic approach, including exploration of hormone production and regulation of genes involved in steroidogenesis, epigenetic and anti-oxidative mechanisms. In addition to the aspect of achieving a better understanding of the effect of POPs in mixtures on steroidogenesis, we also compared effects of the three mixtures. The mixtures gave three different exposure scenarios; exposure to “Cod” mixture (POPs extracted from crude cod liver oil), “Waste” mixture (POPs extracted from waste from the refinement process, containing mainly non-dioxin-like POPs) and “Tran” mixture (POPs extracted from finished cod liver oil dietary supplement). Environmentally relevant doses of the marine mixtures of POPs had a disrupting effect on steroidogenesis in primary LH-stimulated porcine Leydig cells. The “Cod”, “Waste” and “Tran” mixtures had a generally inhibitory effect on testosterone and 17β-estradiol production. The expression pattern of genes involved in steroidogenesis was decreased expression after exposure to all three mixtures. The decrease in gene expression could explain 5 the altered hormone production in exposed cells. There was a trend towards decreased expression aof genes involved in epigenetics and anti-oxidative mechanisms after exposure to the “Tran” mixture. The fact that endocrine disrupting effects were observed also with the “Tran” mixture, representing pollutants extracted from purified cod liver oil for human consumption, gives reason for concern. The beneficial effects of fish consumption and intake of cod liver oil supplements should be balanced against the increased exposure to POPs and their potential ability to exert negative health effects. Further investigation should be carried out to elucidate wether the endocrine disruption after “Tran” mixture exposure also occurs in vivo.