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The Mammary Gland is a Sensitive Pubertal Target in CD-1 and C57Bl/6 Mice Following Perinatal Perfluorooctanoic Acid (PFOA) Exposure

Tucker DK, Macon MB, Strynar MJ, Dagnino S, Andersen E, Fenton SE.
Reprod Toxicol (2015) DOI: https://doi.org/10.1016/j.reprotox.2014.12.002 PMID:30496566

Publication

Abstract

Perfluorooctanoic acid (PFOA) is a developmental toxicant in mice, with varied strain outcomes depending on dose and period of exposure. The impact of PFOA on female mouse pubertal development at low doses (≤1mg/kg) has yet to be determined. Therefore, female offspring from CD-1 and C57Bl/6 dams exposed to PFOA, creating serum concentrations similar to humans, were examined for pubertal onset, including mammary gland development. Pups demonstrated a shorter PFOA elimination half-life than that reported for adult mice. Prenatal exposure to PFOA caused significant mammary developmental delays in female offspring in both strains. Delays started during puberty and persisted into young adulthood; severity was dose-dependent. Also an evaluation of female serum hormone levels and pubertal timing onset revealed no effects of PFOA compared to controls in either strain. These data suggest that the mammary gland is more sensitive to early low level PFOA exposures compared to other pubertal endpoints, regardless of strain.

Figures

Figure 1. Effects of PFOA treatment on serum hormone levels

All animals were sacrificed during estrus, with the exception of PND21 when vaginal opening had not occurred. CD-1 litter/treatment group n = 12–15 (PND 21), n = 9–10 (PND 35) and n = 8–10 (PND 56). C57Bl/6 litter n = 3–4 (PND 21) andn = 3–9 (PND 61).

Figure 2. Mammary whole mount assessment of early and late pubertal glands in CD-1 offspring

Representative image of control: PND 21, PND 35, and PND 56; 0.01 mg/kg: PND 21, PND 35 and PND 56; 0.1 mg/kg: PND 21, PND 35 and PND 56; 0.3 mg/kg: PND 21, PND 35 and PND 56 and 1.0 mg/kg: PND 21, PND 35 and PND 56. CD-1 n = 4–11 litters/treatment group. Significant inverse trends were noted between developmental scores and PFOA dose, indicating higher PFOA exposure was related to lower (more severe) developmental scores (p < 0.05).

Figure 3. Mammary whole mount assessment of early and late pubertal glands in C57Bl/6 offspring

Representative image of control: PND 21 and PND 61; 0.01 mg/kg: PND 21 and PND 61; 0.1 mg/kg: PND 21 and PND 61; 0.3 mg/kg: PND 21 and PND 61 and 1.0 mg/kg: PND 21 and PND 61. C57Bl/6 n = 2–10 litters/treatment group. Significant inverse trends were noted between developmental scores and PFOA dose, indicating higher PFOA exposure was related to lower (more severe) developmental scores (p<0.05).

Tables

Table 1. PFOA serum concentrations in CD-1 and C57Bl/6 mice

Significance observed in comparison to control. The LOQ (limit of quantitation) for C57Bl/6 animals was <10 ng/ml. CD-1 LOQ: Control 5 ng/ml, 0.01 mg/kg = 10 ng/ml, 0.1, 0.3 and 1.0 mg/kg = 100 ng/ml. All controls at PND 21 and 61 and 0.01, 0.1 and 0.3 mg/kg at PND 61 were less than LOQ. (n) = # of animals per dose group; CD-1 n = 4–12; C57Bl/6 n = 2–6. *p ≤ 0.05. **p ≤ 0.01.

Table 2. Body and liver weights of female CD-1 mice

Significance observed in comparison to control. Net body weight = body weight (g) − liver weight (g); relative liver weight = body weight (g)/liver weight (g) (n) = # of animals per dose group. n = 8-22. * p ≤ 0.05.

Table 3. Body and liver weights of female C57Bl/6 mice

Net body weight = body weight (g) − liver weight (g); relative Liver weight = body weight (g)/liver weight (g). (n) = # of animals per dose group; n = 2–9.

Table 4. Assessment of female pubertal events following prenatal PFOA exposures in CD-1 and C57Bl/6

All animals evaluated within each block were assessed as close as possible to the same time of day to minimalize variability. (n) = # of animals per dose group; CD-1 n = 4–11; C57Bl/6 n = 3–7. Units for these measurements are as follows: vaginal opening and first estrus are postnatal age in days and body weight (BW) in grams.

Table 5. Mammary gland developmental scores

Significance observed in comparison to control. Mammary glands scored between 1 (poor development) and 4 (best development). Individual pup scores were averaged and are represented by the mean values for each treatment group. (n) = # of animals per dose group; CD-1 n = 8-19 and C57Bl/6 n = 2-10. * p ≤ 0.05. ** p ≤ 0.01. *** p ≤ 0.001. **** p ≤ 0.0001.