Bisphenol AF (BPAF) is used as a curing or crosslinking agent in the processing of fluorocarbon elastomers, rubber processing, and specialty polymers due to its material characteristics, including thermal stability, chemical resistance, and compression set resistance, which are useful in plastics manufacturing and other fabrication processes. BPAF was selected for evaluation based on a review of compounds that are potentially endocrine-active after concerns were raised about possible effects of bisphenol A (BPA) on the brain, behavior, and prostate gland of fetuses, infants, and children at current human exposure levels. The review assessed a number of agents that could have endocrine activity and are either persistent in the environment or have high human exposures, including chemicals that are structurally related to BPA. BPAF was selected because of its potential for endocrine activity, lack of adequate toxicity data, and potential environmental persistence due to the presence of fluorine atoms. The objective of the present study was to characterize the potential for BPAF to adversely affect any phase of rat development, maturation, and ability to reproduce. The potential for BPAF to induce subchronic toxicity in the F generation, adversely affect the ability of the F generation to reproduce viable F offspring, and adversely affect F embryo-fetal development was assessed in Sprague Dawley (Hsd:Sprague Dawley SD) rats administered BPAF in 5K96 feed, a diet low in phytoestrogens, using the National Toxicology Program (NTP) modified one-generation (MOG) study design. NTP conducted a dose range-finding study with exposure concentrations of 0, 937.5, 1,875, 3,750, 7,500, and 15,000 ppm and based on findings of maternal and pup toxicity (significantly decreased body weights) observed at ≥7,500 ppm, exposure concentrations of 338, 1,125, and 3,750 ppm were selected for the MOG study.
MODIFIED ONE-GENERATION STUDY: F dietary exposure began on gestation day (GD) 6 and continued throughout the study. Biological samples were collected on GD 18 (maternal and fetal), on lactation day (LD) 4 (maternal), and on postnatal day (PND) 4 (pup) to determine maternal transfer. At weaning on PND 28, offspring were randomly assigned to the reproductive performance (1/sex/litter), prenatal (1/sex/litter), subchronic (1/sex/litter from 10 litters), or biological sampling (6/sex for sample collection on PND 28 to determine internal concentrations of BPAF and up to 12 females for sample collection at vaginal opening) cohort. Upon sexual maturity, F mating and pregnancy indices were evaluated. In the prenatal cohort, F prenatal development (litter size, fetal weight, and morphology) was assessed on GD 21. In the reproductive performance cohort, littering indices and F viability and growth were assessed until PND 91. The likelihood of identifying potential BPAF-induced adverse effects and their similarity and magnitude—at any phase of growth or development—was increased by examining related endpoints in multiple pups within a litter throughout life, across cohorts, and across generations. In this study, dietary consumption of BPAF was associated with lower F, F, and F mean body weights. The lower F female mean body weights and body weight gains during gestation were associated with a significant decrease in PND 1 F pup weights (9% and 15% in the 1,125 and 3,750 ppm groups, respectively) that continued through PND 98. Significant decreases in F mean body weights were also observed for 1,125 ppm male and female pups (12% on PND 28 for both males and females) through weaning, but only female postweaning mean body weights were significantly decreased through PND 91 for both the 338 and 1,125 ppm groups. Several biochemical and hematological changes in the F generation subchronic cohort were noted. BPAF exposure related changes included significant decreases in serum cholesterol concentrations in both sexes and in serum bile acid concentrations in males, while significant increases in serum triglyceride concentrations were noted in females. Hematological changes were limited to females and included significant decreases in erythrocyte count, hemoglobin concentration, and total white blood cell count. BPAF-related changes in reproductive performance were observed at all exposure concentrations. For the 3,750 ppm group, a complete absence of pregnant females in the F generation resulted in only two concentration groups for evaluation in the F generation (338 and 1,125 ppm). The majority (89%) of females in the 3,750 ppm group were not cycling and were in persistent estrus. A slight but significant increase in gestation length for F females and a significant decrease in F pup survival (PND 1–4) were also attributed to BPAF exposure. Similar findings, although to a lesser extent, were observed at lower concentrations in the prenatal cohort and included a significant decrease in the number of F females with live fetuses or live litters, number of corpora lutea, and number of implantation sites in the 1,125 ppm group, which were associated with a significant increase in pre- and postimplantation loss values. Significant decreases in the number of corpora lutea and implantation sites were also noted for the prenatal cohort females in the 338 ppm group. Changes in organ weights were also observed in the F generation. In the subchronic cohort, significant increases in the relative weights of the lungs, adrenal glands, and thyroid gland were noted in the 3,750 ppm F males. Significant decreases in relative weights for the liver and kidney (left) were also observed at 3,750 ppm for F males and microscopic findings were observed in the male kidney (mineral lesions along the junction of the cortex and medulla). In F males, lower absolute weights of the dorsolateral prostate, ventral prostate, and seminal vesicles with coagulating glands were observed in the 1,125 and 3,750 ppm groups and of the Cowper’s gland and levator ani/bulbocavernosus muscle (LABC) in the 3,750 ppm group. The organ weight changes in the 3,750 ppm group were more than the magnitude of the reductions in body weight and, along with histopathology observations of hypoplasia, indicated a potential direct BPAF-mediated suppression of maturation of these tissues. F males exhibited similar findings in the same reproductive tissues as F males in the 338 and 1,125 ppm groups. Changes in reproductive organ weights that appeared secondary to the effect of BPAF on body weight were limited to lower absolute weights of the testes, epididymides, and preputial glands in all three F exposed groups. The lower testes weights may also be due to direct (germinal epithelium degeneration and Leydig cell atrophy) effects of BPAF exposure. Changes in reproductive organ weights that appear to be secondary to the effect of BPAF on body weight for the F exposed males were limited to the testes and epididymides. Histopathology was not performed on the F generation. BPAF-related changes in andrology parameters were noted in both F and F males. In F females, reproductive toxicity associated with exposure to BPAF included significant decreases in absolute ovarian and uterus/cervix/vagina weights, with gross observations of reduced size and hypoplasia in the 3,750 ppm group. In the subchronic cohort, significant increases in the relative weights of the thyroid gland and liver were noted in the 3,750 ppm F females. Significant decreases in absolute ovarian weights were also observed in the 338 and 1,125 ppm F females. The magnitude of the reduction in weights of the ovaries in the 1,125 ppm group was more than the magnitude of the reduction in body weight, suggesting a direct BPAF-mediated suppression of maturation of this tissue. BPAF-related changes consistent with impaired development include lower mean body weights for all generations, including fetal or pup weights and reduced litter sizes, as well as impacts on fetal parameters and select developmental markers. Developmental landmarks impacted by BPAF exposure included time to vaginal opening (VO), testicular descent, and balanopreputial separation (BPS). No impacts on anogenital distance or areolae and nipple retention were observed in this study. The time to VO was significantly accelerated in all BPAF-exposed groups for both the F and F generations at all exposure concentrations. The mean day of testicular descent was not affected in the F generation, although one male in the 1,125 ppm group and 11 males in the 3,750 ppm group did not attain testicular descent by study termination; however, the mean day of testicular descent was significantly delayed by approximately 2 days for the F offspring in the 1,125 ppm group. In addition, 10 F males in the 3,750 ppm group did not attain BPS. The time to BPS was significantly delayed in both the F and F offspring in the 1,125 and 3,750 ppm groups for the F generation and the 1,125 ppm group for the F generation. BPAF exposure resulted in fetal malformations of the penis and vagina in two F males and three F females in the 3,750 ppm group. Additional findings were limited to an increase in the incidence of dilated and/or misshapen lateral ventricle (brain) in the 1,125 ppm group, which NTP has not recorded in its previous studies, and increases in the incidences of rudimentary and full lumbar I (L1) ribs in the 338 ppm group and rudimentary L1 ribs in the 1,125 ppm group for the prenatal cohort. These last findings were outside the NTP historical control ranges; however, the lack of an exposure-related response impedes a more thorough assessment to determine if they may have been related to BPAF exposure. (This is an abridged version of the abstract. Go to the Abstract page to see the full text and summary table.)
