Two generation reproduction study of ethylbenzene by inhalation in Crl‐CD rats

Abstract

BACKGROUND: This study was conducted to evaluate the potential adverse effects of ethylbenzene (EB) on reproductive capability from whole-body inhalation exposure of F 0 and F 1 parental animals. METHODS: Four groups of Crl:CD(SD)IGS BR rats (30/sex/group for F 0 and 25/sex/group for F 1 ) were exposed to 0, 25, 100, and 500 ppm EB for 6 hr/day for at least 70 consecutive days before mating. Inhalation exposure for the F 0 and F 1 females continued throughout mating, gestation through gestation day (GD) 20, and lactation days (LD) 5-21. On LD 1-4, females received EB in corn oil via oral gavage at dose levels of 26, 90, and 342 mg/kg/day (divided into three equal doses, approximately 2 hr apart), as calculated from a physiologically-based pharmacokinetic (PBPK) model to provide similar maternal blood area-under-concentration (AUC) as provided by inhalation. Pups were weaned on postnatal day (PND) 21 and exposure of the F 1 generation started on PND 22. Estimates of internal exposure were determined by measuring EB concentrations in blood collected from F 1 dams (4/group) and their culled pups 1 hr after the last gavage dose on PND 4. On PND 22, blood was collected from these same F 1 dams and their weanlings for EB analysis 1 hr after a 6-hr inhalation exposure. The remainder of the F 2 generation was not directly exposed. RESULTS: EB exposure did not affect survival or clinical observations. Male rats in the 500 ppm group in both generations gained weight more slowly than the controls. There were no indications of adverse effects on reproductive performance in either generation. Male and female mating and fertility indices, pre-coital intervals, spermatogenic endpoints, ovarian follicle counts, reproductive organ weights, lengths of estrous cycle and gestation, live litter size, pup weights, developmental landmarks, and postnatal survival were unaffected. No adverse exposure-related macroscopic pathology was noted at any level. CONCLUSIONS: Increased liver weights were found in the animals exposed to 500 ppm. F 1 maternal whole blood EB concentrations of 0.49, 3.51, or 18.28 mg/L were found 1 hr after administration of a composite oral dose of 26, 90, or 342 mg/kg/day, respectively, but no detectable EB was found in blood samples of their F 2 PND 4 culled pups. F 1 maternal mean whole blood EB levels 1 hr after a 6-hr inhalation exposure on postpartum day (PPD) 22 was 0.11 mg/L (25 ppm), 0.56 mg/L (100 ppm), and 11 mg/L (500 ppm). For the offspring exposed with their dams on PND 22, F 2 pup blood EB concentrations ranged from 0.017-0.039 mg/L (25 ppm), 0.165-0.465 mg/L (100 ppm), and 8.82-15.74 mg/L (500 ppm). Because decreased weight gain in the 500 ppm males was transient and no histopathological changes were associated with the increased liver weights in the 500 ppm male and female groups, these changes were not considered adverse. Therefore, for parental systemic toxicity, 100 ppm was considered a NOEL and 500 ppm a NOAEL in this study. The 500 ppm exposure concentration was considered a NOAEL for

Inhalation developmental neurotoxicity study of ethylbenzene in Crl‐CD rats

“…Several reproductive and developmental toxicity studies of ethylbenzene have been reported previously Hardin et al, 1981;Ungvary and Tatrai, 1985;Saillenfait et al, 2003;Faber et al, 2006). Narcotic effects from acute inhalation exposures have been reported in male rats exposed to 2180 ppm ethylbenzene (Molnár et al, 1986) and mice exposed to 2000 ppm ethylbenzene (Tegeris and Balster, 1994).…”

“…In addition to these standard assessments within the two-generation study, blood samples were collected on lactation day (LD) 4 and 22 from a subset of F 1 -generation dams as well as from culled F 2 offspring from those dams on postnatal day (PND) 4 and an additional pup/gender/litter (not selected to continue on study in the developmental neurotoxicity component) from those dams after weaning and a single day of direct exposure to ethylbenzene on PND 22. The results concerning the reproductive outcome of the ethylbenzene two-generation toxicity study as well as maternal and offspring blood levels of ethylbenzene have been reported previously (Faber et al, 2006). In most inhalation reproductive toxicity studies that do not include whole body exposures of entire litters, maternal inhalation exposures are stopped temporarily from gestation day (GD) 20 through LD 4.…”

“…The developmental neurotoxicity study component presented was an F 2 -generation assessment added on to a two-generation inhalation reproductive toxicity study (Faber et al, 2006). It was undertaken in support of the United States Environmental Protection Agency's Voluntary Children's Chemical Exposure Program (VCCEP) assessment of ethylbenzene (United States Environmental Protection Agency, 2000).…”

“…Before the two-generation study (Faber et al, 2006), a preliminary study was conducted to determine: the exposure levels of ethylbenzene that would generate minimal maternal and weanling toxicity but allow successful completion of gestation, parturition, and lactation processes; the feasibility of gavage dosing of dams during LD 1-4; and whether to begin inhalation exposures of F 1 weanlings on PND 22 or PND 29 in that study. Male and female rats were exposed daily to either clean filtered air or vapor atmospheres of 100, 500, or 1000 ppm (parts per million) ethylbenzene 6 hr/day.…”

“…Parental exposure levels were 0, 25, 100, and 500 ppm, and gavage dose levels on LD 1-4 were 0, 26, 90, and 342 mg/ kg/day (Faber et al, 2006) …”