Modelling inhibition of avian aromatase by azole pesticides

Abstract

The potential effects of pesticides and their metabolites on the endocrine system are of major concern to wildlife and human health. In this context, the azole pesticides have earned special attention due to their cytochrome P450 aromatase inhibition potential. Cytochrome P450 aromatase (CYP19) catalyses the conversion of androstenedione and testosterone into oestrone and oestradiol, respectively. Thus, aromatase modulates the oestrogenic balance essential not only for females, but also for male physiology, including gonadal function. Its inhibition affects reproductive organs, fertility and sexual behaviour in humans and wildlife species. Several studies have shown that azole pesticides are able to inhibit human and fish aromatases but the information on birds is lacking. Consequently, it appeared to be of interest to estimate the aromatase inhibition of azoles in three different avian species, namely Gallus gallus, Coturnix coturnix japonica and Taeniopygia guttata. In the absence of the crystal structure of the aromatase enzyme in these bird species, homology models for the individual avian species were constructed using the crystal structure of human aromatase (hAr) (pdb: 3EQM) that showed high sequence similarity for G. gallus (82.0%), T. guttata (81.9%) and C. japonica (81.2%). A homology model with Oncorhynchus mykiss (81.9%) was also designed for comparison purpose. The homology-modelled aromatase for each avian and fish species and crystal structure of human aromatase were selected for docking 46 structurally diverse azoles and related compounds. We showed that the docking behaviour of the chemicals on the different aromatases was broadly the same. We also demonstrated that there was an acceptable level of correlation between the binding score values and the available aromatase inhibition data. This means that the homology models derived on bird and fish species can be used to approximate the potential inhibitory effects of azoles on their aromatase.

Residues of plant protection products in grey partridge eggs in French cereal ecosystems

“…Some ASs detected in partridge eggs may influence, under certain exposure conditions, the fecundity, the fertility and the development of embryos of some bird species (Lopez-Antia et al 2013 ; Rivière et al 1985 ) or are suspected to have endocrine disrupting properties (e.g., EFSA 2010 , 2011 ; Saxena et al 2015 ). However, whether such effects actually occur in the field remains an open question.…”

Chronic exposures to fungicide pyrimethanil: multi-organ effects on Italian tree frog (Hyla intermedia)

“…The role of steroids in amphibian’s gonad differentiation has not definitely been clarified and available information on the steroid hormonal control of gonad differentiation is scarce and conflicting 42 , 48 . However, one may speculate that aromatase inhibition would be one of the mechanisms involved in gonadal impairment after exposure to pyrimidine fungicides 49 , 50 . The AhR-mediated action does not exclude other alternative physiological responses and in fact pyrimethanil also induce inflammation as demonstrated by the presence of macrophage and mononuclear cellular infiltrate.…”

Can the inhibition of cytochrome P450 in aquatic invertebrates due to azole fungicides be estimated with in silico and in vitro models and extrapolated between species?

“…Comparable inhibitory concentrations in the µM range have been previously reported towards rat liver CYP2B and CYP3A activities, 51 fungal growth 37 and human as well as fish aromatase (CYP19). 1 On the other hand, inhibition of microsomal cytochrome P450 activity of C. riparius and L. stagnalis due to azole fungicides is, to the best of our knowledge, not yet available. IC50 values for rat liver (0.0032 -26 µM) and C. riparius (0.074 -18 µM) are within the same range.…”

“…22 The method, although not free from limitations, 21,22 has been recently used to investigate inhibition of aromatase (cytochrome P450 CYP19 involved in steroidogenesis) by azole fungicides, obtaining good degrees of correlation between docking scores and experimentally measured inhibition strengths of azoles toward aromatase activity in human (r: -0.81), fish brain (r: -0.69) and fish ovaries (r: -0.85). 1 However, the use of this approach for ecotoxicologically relevant aquatic invertebrates presents additional limitations, since the specific types and roles of cytochrome P450 present in these organisms are generally unknown. Therefore, crystallized cytochrome P450 structures are currently not available and since gene sequencing of non-target invertebrates is only in its infancy, also the creation of cytochrome P450 structures from homology models is limited.…”