Identification of endocrine disrupting chemical doses in rats to reproduce human urinary metabolite concentrations

摘要

We are investigating the effects of the exposure of female Sprague-Dawley rats to 3 endocrine disrupting (ED) chemicals, diethyl phthalate (DEP), methyl paraben (MPB), triclosan (TCS), and their mixture, on 6 mammary cancer susceptibility windows. The ideal animal experiment would utilize multiple chemical doses, but budgetary constraints required the choice of a single dose for each ED. Most animal studies have tested ED effects with doses that are orders of magnitude higher than common human exposure. We have conducted a dose calibration study to determine the oral dose of each ED that would result in rat urinary metabolite concentrations comparable to the concentrations reported in the general US population. We used five doses per chemical based on its NOEL (No Observed Effect Level in mg/Kg/day; MBP=1050; TCS=50; DEP=1735) plus one control group (vehicle only); 5 adult female rats per chemical/group were dosed by oral gavage for 5 days. Doses ranged from 0.0005-173 mg/kg/day. Urine and blood, collected on the last day of exposure, were analyzed for ED metabolites by solid phase extraction-high performance liquid chromatography-isotope dilution tandem mass spectrometry. We used linear regression to assess relationships between oral dose and metabolite concentration. For all chemicals, the urine concentrations at the three lowest doses plus control demonstrated a very strong linear relationship (R2＞0.82). NOEL/10,000 (MPB, DEP) or NOEL/1,000 (TCS) doses resulted in urinary concentrations that were within the US population concentration range. The serum concentrations did not show a clear dose response for MEP and MPB. The relationship between serum and urine concentration varied by metabolite (R2: MEP:0.085; MPB:0.58; TCS:0.93). This dose calibration study facilitated the selection of oral doses that closely mimic the exposures experience of the human population, thereby providing an opportunity to examine the effect of realistic ED exposures on genetic dysregulation in rodent mammary tissue. Supported by NIEHS/NCI: 5U01ES019459.