Investigations of putative reproductive toxicity of low-dose exposures to flutamide in Wistar rats

Abstract

The current investigation examines whether the model anti-androgenic substance flutamide is capable of disrupting endocrine homeostasis at very low doses. The data generated clarify whether a non-monotonic dose-response relationship exists to enhance the current debate about the regulation of endocrine disruptors. Moreover, it is part of a series of investigations assessing the dose-response relationship of single and combined administration of anti-androgenic substances. A pre-postnatal in vivo study design was chosen, which was compliant with regulatory testing protocols. The test design was improved by additional endpoints addressing hormone levels, morphology, and histopathological examinations. Doses were chosen to represent a clear effect level (2.5 mg/kg bw/d), a low endocrine effect level (LOAEL, 0.25 mg/kg bw/d), a NOAEL for endocrine effects (0.025 mg/kg bw/d), a further dose at 0.0025 mg/kg bw/d flutamide, as well as an "ADI" (0.00025 mg/kg bw/d or 100-fold below the NOAEL) for the detection of a possible non-monotonic dose-response curve. Anti-androgenic changes were observable at LOAEL and the clear effect dose level but not at lower exposures. Nipple retention appeared to be the most sensitive measure of anti-androgenic effects, followed by age at sexual maturation, anogenital distance/anogenital index and male sex organ weights, as well as gross and histopathological findings. The results of all five doses indicate the absence of evidence for effects at very low dose levels. A non-monotonic dose-response relationship was not evident for the anti-androgenic drug flutamide.

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

“…This is in line with more general evidence that thresholds do exist for endocrine-related effects (Borgert et al 2013;EFSA Scientific Opinion 2013;Borgert et al 2012;Caldwell et al 2012). The existence of threshold doses was recently also shown for the anti-androgenic drug flutamide in a pre-and postnatal in vivo study in Wistar rats (Fussell et al 2015). Underlying uncertainties in an appropriate hazard assessment of substances with an endocrine mode of action are probably more the result of inappropriate study designs and the omission of relevant parameter.…”

First-trimester determination of fetal gender by ultrasound: measurement of the ano-genital distance

“…In the rat model, various substances have been administered to pregnant females to evaluate the impact on reproductive organ development in the offspring. [23,24,25]. When the pregnant female rat received flutamide (androgen receptor antagonist) or dibutylphthalate [24,25] the AGD at birth was shorter in male offspring.…”

“…[23,24,25]. When the pregnant female rat received flutamide (androgen receptor antagonist) or dibutylphthalate [24,25] the AGD at birth was shorter in male offspring. Exposure to phthalates was also associated with a higher prevalence of cryptorchidism and hypospadias [24].…”

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

“…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.…”

“…This signaling is important for the development and maintenance of male sexual health (Fridmans et al 2005 ). Flutamide has been shown to cause reduced AGDs, increased nipple retention, pubertal delays, decreased sex organ weights, hypospadias and reduced penile length in male rat offspring (summarized in Fussell et al 2015 ) and prochloraz was found to increase transient nipple retentions and caused delayed entries into puberty (Christiansen et al 2009 ; Laier et al 2006 ).…”