Altered expression of genes related to zinc homeostasis in early mouse embryos exposed to di-2-ethylhexyl phthalate.

Numerous studies have shown that di-2-ethylhexyl phthalate (DEHP) is teratogenic in animals but the mechanism of developmental toxicity is not well understood. One hypothesis is altered zinc homeostasis. The present study has investigated the effect of DEHP exposure on several key genes in zinc metabolism (MT-I, MT-II, ZnT-1) for early mouse embryos exposed in utero. Time- and dose-dependent effects were examined using expression polymerase chain reaction (PCR) (relative to ACTB) and Western blot analysis of the maternal liver, embryonic brain, and visceral yolk sac at 9 days post-coitus (d.p.c.). Maternal exposure to 800 mg/kg DEHP increased the abundance of MT-I and MT-II transcripts in maternal liver at 3.0, 4.5 and 6.0 h after administration. MT-I and MT-II protein induction was confirmed by Western blot analysis. On the other hand, this exposure down-regulated both transcripts (MT-I, MT-II), as well as transcripts for a zinc transporter (ZnT-1), in the embryonic brain, but not the visceral yolk sac. To examine dose-response relationships, the experiment was repeated for DEHP exposures of 50, 200 and 800 mg/kg. The effect to MT-I and MT-II expression in the maternal liver became significant at the 200 mg/kg dose level. The contrasting effect to MT-I, MT-II and ZnT-1 expression in the embryo was also dose-dependent, and a benchmark computation for the dose resulting in a 5% change in the mean (BMD5) was estimated as 11.6 mg/kg for MT-I, 8.9 mg/kg for MT-II, and 6.6 mg/kg for ZnT-1. We conclude that DEHP exposure to pregnant dams at reasonably low levels during organogenesis stages can alter the expression of several key genes in embryonic zinc homeostasis.