Exposure to butyl paraben during gestation and lactation in Hsd:Sprague dawley SD rats via dosed feed

Abstract

Butyl paraben (BPB) is an antimicrobial used in a variety of consumer products. Due to widespread human exposure and reported estrogenic activity, the National Toxicology Program quantified internal exposure during critical periods of development. Time-mated female Hsd:Sprague Dawley SD rats were administered 0, 1500, 5000 or 15,000 ppm BPB via NIH-07 feed, ad libitum, from gestation day (GD) 6 to postnatal day (PND) 28. Dam plasma, amniotic fluid and fetuses were collected on GD18 and pup and dam plasma were collected on PNDs 4, 10, 14, 21 and 28 and analyzed for free (unconjugated) and total (unconjugated and conjugated) BPB using liquid chromatography-tandem mass spectrometry. Free BPB was below the limit of quantitation in fetuses (LOQ 1.91 ng BPB/g fetus) and amniotic fluid (LOQ 0.17 ng BPB/mL amniotic fluid) at 1500 ppm. Analyte levels in amniotic fluid were less than 1% of maternal plasma, suggesting limited placental transfer. Total BPB in PND4 pup plasma was less than 5% of dam plasma in all exposure groups, suggesting low lactational transfer. However, at nearly all time points and exposure groups, there were higher levels of free BPB in pup versus dam plasma, suggesting limited conjugation in pups. Pup conjugation of BPB was age-dependent, not reaching the percent-conjugation in dams (>99%) until PNDs 21 to 28. These data illustrate low placental and lactational transfer of dietary BPB and that poor conjugation in pups during early lactation results in higher exposure to free BPB in pups compared to dams.

Keywords: Butyl paraben; Conjugation; Lactational transfer; Maternal transfer; Metabolism ontogeny; Placental transfer.

Fig. 1

Gestational and Lactational Body Weights. (A) dam body weight during gestation, (B) dam body weights during lactation, (C) male pup body weights during lactation and (D) female pup body weights during lactation. Data shown are averages (dams) and average of litter averages (pups) + SEM. Group sizes (n) vary from 4 to 27 due to biological sampling. Asterisks indicate statistical significance (ANOVA and post-hoc using Dunnett 2- sided test) between control group and 15,000 ppm group. * p-value < 0.05, ** p-value < 0.01 and *** p-value < 0.001.

Fig. 2

Levels of Percent-Free Butyl Paraben During Lactation. Ontogeny of BPB Conjugation in Pups. Data represent the average of the litter averages for percent free BPB + SEM (n = 2 to 6 pups per litter, 4–5 litters per group/time point) detected in pup plasma. Percent free BPB is calculated as [(free BPB (ng/ml)/Total BPB (ng/ml))*100]. Thin black horizontal line at 1% indicates the average percent free BPB in dams as a reference. White bars represent animals in the 1500 ppm exposure group, grey bars for the 5000 ppm group and black bars for the 15,000 ppm group. Statistical significance indicated by asterisks (*p < 0.05, ** p < 0.01, *** p < 0.001) are for the percent free BPB in pup plasma versus dam plasma in the same exposure group.

Fig. 3

Comparison of Dam and Pup Plasma Levels During Lactation. Dam and pup exposure to dietary butyl paraben (5000 ppm) during lactation. Data represent average (dam, n = 4 to 5) and average of the litter averages (pups, n = 2 to 7 pups per litter, 3 to 5 litters per group) + SEM. (A) represents the total butyl paraben and (B) represents the unconjugated BPB (ng/mL plasma). White bars represent dam plasma and black bars represent pup plasma. These data are for the 5000 ppm exposure group only, however they are representative of the 1500 ppm and 15,000 ppm groups. Data for all groups are available in Supplementary material.