Comparing effect levels of regulatory studies with endpoints derived in targeted anti-androgenic studies: example prochloraz

Abstract

Prochloraz is an imidazole fungicide, and its regulatory toxicological data package has been primarily generated in the 1990s. More recently, studies have been published demonstrating an interaction with hormone receptors/steroidogenesis and effects with an endocrine mode of action. In the present study, prochloraz has been investigated in a comprehensive in vivo study including relevant elements of current regulatory reproduction toxicity studies and additional mechanistic parameters. Prochloraz was administered per gavage in oil from GD 6 to PND 83 to pregnant and lactating Wistar rats and their respective offspring, at doses of 0.01 mg/kg bw/day (acceptable daily intake of prochloraz), 5 mg/kg bw/day [expected no-observed-effect-level (NOEL)] and 30 mg/kg bw/day. At 30 mg/kg bw/day maternal and offspring effects (decreased viability, lower number of live offspring) were seen including a delayed entry into male puberty (+1 day) accompanied by lower male offspring body weights, increased anogenital distance/index in females and transiently retained nipples in males at PND 12 (not seen at PND 20). The only finding at the "expected NOEL" was increased incidences of transiently retained nipples in males which are not considered adverse. No effects were seen in the low-dose group. There was no evidence for a non-monotonic dose-response curve or effects at low levels.

Anogenital distance as a toxicological or clinical marker for fetal androgen action and risk for reproductive disorders

“…Regarding reproductive effects, prochloraz exposure can induce nipple retention in male offspring (Christiansen et al 2009;Vinggaard et al 2005), whereas effects on AGD are conflicting between studies. If taking birth-weight into account, there were no significant effects on male AGD at doses similar to those causing nipple retention (25-150 mg/kg) (Christiansen et al 2009;Melching-Kollmuss et al 2017;Noriega et al 2005;Vinggaard et al 2005). Another study reported around 10% shorter male AGD after fetal exposure to high doses of prochloraz concomitant with nipple retention at the same doses (Laier et al 2006).…”

“…Female rats exposed to the azole fungicide prochloraz present with longer AGD at birth, concomitant with elevated progesterone levels (Laier et al 2006;Melching-Kollmuss et al 2017). Prochloraz can induce progesterone synthesis in vitro by CYP17 inhibition at concentrations above 10 nM (Dreisig et al 2013), a mechanism confirmed in vivo, where fetal plasma concentrations were measured at 24 nM following maternal exposure to 150 mg/kg bw/day of prochloraz (Laier et al 2006).…”

Assessment of occupational exposure to pesticide mixtures with endocrine-disrupting activity

“…A minor change in the concentration of an endocrine disrupting chemical can induce significant changes in biological endpoints even though the dose is small (Futran Fuhrman et al 2015). Currently, risk assessment methodologies do not sufficiently assess the hazard associated with low-dose exposure to endocrine active substances (Melching-Kollmuss et al 2017) and the lack of a universal definition for "low dose" is one obstacle to this.…”

Investigations on the dose–response relationship of combined exposure to low doses of three anti-androgens in Wistar rats

“…The mixtures data reported in this investigation were captured in the final of a series of three separate experiments of the same study design addressing the theme of single and mixed exposures to low dose levels of anti-androgens. Since we have previously published the effects of the single-substance exposures to the three test substances in prior reports (Fussell et al 2015 ; Melching-Kollmuss et al 2017 ; Flick et al 2016 ), these outcomes will not be discussed here in detail. Instead, the included single-substance exposure data are presented only for the purposes of comparison to the mixed exposures tested in this specific investigation and will be discussed only in this context.…”

“…The results of the single compound testing have been published previously, i.e. flutamide (Fussell et al 2015 ), prochloraz (Melching-Kollmuss et al 2017 ) and vinclozolin (Flick et al 2016 ). Here we report on the effects of combined exposure to all three anti-androgens.…”