Steroid levels, steroid metabolic pathways and their modulation by endocrine disruptors in invertebrates

Abstract

[EN] Ninety-five percent of all animal species are invertebrates, and like vertebrates, they are susceptible to endocrine disruption. Nevertheless, there are important gaps on the knowledge of the endocrine system of invertebrates that hinder the understanding of the endocrine disruption phenomena in those species. Steroid synthesis and metabolism is one of several possible targets of endocrine disruptors. This thesis aimed to characterize sex steroid metabolism in different invertebrate species, to test the in vitro effect of model endocrine disruptors in those species, and to test the in vivo effect of model endocrine disruptors on steroid levels and metabolism in species from a selected phyla (Mollusca). The species investigated (Mollusca: Marisa cornuarietis, Mytilus sp., and/or Crassostrea virginica; Crustacea: Hyalella azteca; and Echinoderma: Paracentrotus lividus) were able to form a series of phase I metabolites of testosterone that are also formed by vertebrates, with the exception of 4-androstene-3?,17?-diol, a metabolite formed by P. lividus and H. azteca. One of the major differences with vertebrate species was the lower contribution of hydroxylases in the metabolism of testosterone, and the metabolic fate of androstenedione in molluscs (5?-reduction instead of 17?-reduction). Regarding phase II metabolism of testosterone, sulfotransferases were found at high levels in P. lividus, but low or undetectable levels were present in H. azteca and the molluscan species investigated. In contrast, the conjugation of steroids with fatty acid moieties was present in all invertebrates investigated, showing that acyl-CoA:steroid acyltransferases are well-conserved through evolution. Steroid levels and the enzymatic activities for some metabolic pathways showed differences between males and females, among tissues, and between seasons in some invertebrate species, which adds further evidence for a physiological role of sex steroids in invertebrates. Some xenobiotics modulated steroid metabolic pathways in invertebrates in vitro. Among the pathways investigated, 5?-reductase and sulfotransferase showed the highest sensitivity to inhibition/activation by tributyltin (TBT), triphenyltin (TPT) and fenarimol. Finally, the effects of the exposure to estradiol, crude oil, and the mixture of crude oil and alkylphenolic compounds in Mytilus sp. and the exposure to methyltestosterone, TBT, TPT and fenarimol in the gastropod M. cornuarietis were investigated. The type of effects induced by estradiol depended greatly on the concentration. Some of the responses observed in mussels exposed to crude oil and the mixture of crude oil and alkylphenols were similar to those observed in mussels exposed to the highest concentrations of estradiol. Those experiments also showed that esterification seems to play a key role in the regulation of free steroid levels in bivalve molluscs. The exposure to the organotin compounds (TBT and TPT) caused imposex and decreased esterified steroid levels in females of M. cornuarietis, but not in males. Methyltestosterone and fenarimol induced imposex in females, but did not lead to alterations in esterified steroid levels. Therefore, the connection between a decrease of esterified steroids and the phenomena of imposex could not be proved. The exposure to TPT inhibited???-reductase in female M. cornuarietis. However, neither TPT nor TBT altered the sexual dimorphism in androstenedione metabolism that exists in the digestive gland/gonad complex of this snail species. Overall, this thesis contributes to the knowledge of androgen metabolism in invertebrate species and identifies possible targets of endocrine disruption.

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