Non-monotonic dose effects of in utero exposure to di(2-ethylhexyl) phthalate (DEHP) on testicular and serum testosterone and anogenital distance in male mouse fetuses

Abstract

Di(2-ethylhexyl) phthalate (DEHP) is a ubiquitous environmental contaminant. Epidemiological studies suggest that DEHP decreases masculinization of male fetuses. Numerous rat studies report DEHP reduces fetal testosterone production at doses greatly exceeding human exposure. We fed pregnant CD-1 mice 0.5 - 500,000 μg/kg/day DEHP from gestation day (GD) 9 - 18 and examined mothers and male fetuses on GD 18. We assessed non-monotonic dose-response by adding a quadratic term to a simple linear regression model. Except at the 500,000-μg/kg/day dose, DEHP stimulated an increase in maternal and fetal serum testosterone and increased anogenital distance (AGD). Non-monotonic dose-response curves were noted for AGD and maternal, and testis testosterone (p values 0.013 to 0.021). Because data from our highest dose (500,000-μg/kg/day) did not differ significantly from controls, this dose could have been incorrectly assumed to be the NOAEL had we only tested very high doses, as is typical in studies for regulatory agencies.

Expressomal approach for comprehensive analysis and visualization of ligand sensitivities of xenoestrogen responsive genes

“…Because animal studies often demonstrate significant biological effects of EDCs at concentrations far lower than the safety limits set by regulatory agencies, appropriateness of the use of "no observable effects limit" for EDC risk assessment has been questioned (8,25). The nonmonotonic dose-response may result in paradoxical observations that a lower EDC dose can be more toxic than a higher dose of the same chemical (8,10). Accumulation of transcriptomewide data on EDC sensitivities of individual EDC responsive genes will be critical for the mechanistic understanding of these extraordinary phenomena.…”

“…In addition to such low-dose effects, an increasing number of studies also support the concept of the nonmonotonic EDC effects, whose dose-response curves show U shapes or inverted-U shapes (8)(9)(10). However, whereas nonmonotonic dose-responses are often observed in the endocrine system, this notion conflicts with one of the Bradford-Hill criteria for cause-and-effect relationships that requires stronger effects with greater degrees of exposure (11), leading to controversies when biological effects are observed most strongly with lower rather than higher doses of EDCs (12)(13)(14).…”

Di(2‐ethylhexyl) phthalate (DEHP) [MAK Value Documentation, 2016]

“…The anogenital distance initially increased up to 0.005 mg/kg body weight and day and then returned to the control value. A quadratic fit was determined because the values of the high dose group did not differ from those of the control group (Do et al 2012). The results are not regarded as relevant to the evaluation because of the unclear procedure of dosing with a micropipette placed into an animal's mouth and because of the questionable approach of considering changes in the dose-response relationship (quadratic trend), while the linear trend test did not produce significant findings.…”

Di‐(2‐ethylhexyl)phthalat (DEHP) [MAK Value Documentation in German language, 2016]

“…Der anogenitale Abstand nahm erst bis zu 0,005 mg/kg KG und Tag zu, danach fiel er auf den Kontrollwert zurück. Es wurde eine quadratische Anpassung ermittelt, da sich die Werte der höchsten Dosisgruppe nicht von denen der Kontrolle unterschieden (Do et al 2012). Die unklare Dosisgabe per Mikropipette in das Maul und das in Frage zu stellende Vorgehen, eine veränderte Dosis-Wirkungsbeziehung (quadratischer Trend) zu betrachten, wohingegen im linearen Trendtest keine Signifikanz erreicht wurde, führen dazu, die Ergebnisse als nicht bewertungsrelevant anzusehen.…”