A critical assessment of the endocrine susceptibility of the human testis to phthalates from fetal life to adulthood.
CONTEXT Phthalates are ubiquitous environmental chemicals. Fetal exposure to certain phthalates [e.g. di-n-butyl phthalate (DBP)] causes masculinization disorders in rats, raising concern for similar effects in humans. We investigated whether DBP exposure impairs steroidogenesis by the human fetal testis. OBJECTIVE The aim of the study was to determine effects of DBP exposure on testosterone production by normally growing human fetal testis xenografts. DESIGN Human fetal testes (14-20 wk gestation; n=12) were xenografted into castrate male nude mice that were treated for 4-21 d with vehicle, or 500 mg/kg·d DBP, or monobutyl phthalate (active metabolite of DBP); all mice were treated with human chorionic gonadotropin to mimic normal human pregnancy. Rat fetal testis xenografts were exposed for 4 d to DBP as a positive control. MAIN OUTCOME MEASURES Testosterone production was assessed by measuring host serum testosterone and seminal vesicle (SV) weights at termination, plus testis gene expression (rats). RESULTS Human fetal testis xenografts showed similar survival (∼80%) and total graft weight (8.6 vs. 10.1 mg) in vehicle and DBP-exposed hosts, respectively. Serum testosterone (0.56 vs. 0.64 ng/ml; P>0.05) and SV weight (67.2 vs. 81.9 mg; P>0.05) also did not differ. Exposure to monobutyl phthalate gave similar results. In contrast, exposure of rat fetal xenografts to DBP significantly reduced SV weight and testis Cyp11a1/StAR mRNA expression and lowered testosterone levels, confirming that DBP exposure can inhibit steroidogenesis in xenografts, further validating the negative findings on testosterone production in the human. CONCLUSIONS Exposure of human fetal testes to DBP is unlikely to impair testosterone production as it does in rats. This has important safety and regulatory implications.