Placental transfer of dibutylphthalate metabolites in pregnant rats

Abstract

Gestational and lactational exposure of rats to di(n-butyl)phthalate (DBP) results in malformations of the male reproductive tract. Since these effects are observed at high doses (250-750 mg/kg/day), saturation of metabolism may contribute to the generation of effects and should be an important consideration in risk assessment. This study was designed to evaluate the metabolism of DBP prior to conducting pharmacokinetic studies in pregnant rats late in gestation. A single dose of 100 mg [ring- 14C]DBP/kg in corn oil was administered by gavage to female Sprague-Dawley rats. Urine and feces were collected for 24 h to obtain metabolite standards. Urinary metabolites were separated and characterized by HPLC, NMR, and LC-MS/MS. For characterization of metabolites in maternal and fetal plasma, pregnant Sprague-Dawley rats received a single dose of 100 mg [ring-14C] DBP/kg in corn oil by gavage on gestation day 20. At 2 h following dosing, maternal blood, liver, fat, placentae, and carcass were obtained. Fetal blood and carcasses were also collected. Blood, plasma, tissues, and carcasses were analyzed for radioactivity. The predominant urinary metabolites of DBP, monobutylphthalate (MBP) and MBP glucuronide, were characterized by NMR and LC-MS. Minor metabolites identified by LC-MS/MS in urine were phthalic acid, monohydroxybutylphthalate (MHBP), MHBP glucuronide, monobutanoic phthalic acid (MBPA), and MBPA glucuronide. Similarly in maternal and fetal plasma, the major metabolites detected were MBP and MBP glucuronide. MHBP, MHBP glucuronide, and MBPA were detected by LC-MS/MS in fetal and maternal plasma. MBPA glucuronide was detected only in maternal plasma. This study indicates that a number of metabolites of DBP, in addition to MBP and MBP glucuronide, reach the fetus following administration to pregnant rats.