The following abstract presents results of a study conducted by a contract laboratory for the National Toxicology Program. The findings were not evaluated in accordance with the levels of evidence for reproductive or developmental criteria established by NTP in March 2009. The findings and conclusions for this study should not be construed to represent the views of NTP or the U.S. Government.
Isoeugenol was evaluated for potential reproductive toxicity using the multigenerational Continuous Breeding paradigm. A dose-range study (Task 1a) was conducted using dose levels of 0, 500, 3000, 5500, and 8000 ppm via the feed to adult male and female rats (N=8). Since there were no treatment-related effects seen in the first study, the dose-range study (Task 1b) was repeated using gavage as the route of administration at dose levels of 0, 30, 100, 400, and 800 mg/kg/day. Because of the decreased body weights, body weight gains, and feed consumption in the males at 400 and 800 mg/kg/day, the following dose levels were selected for the F0 Evaluation (Task 2): 0, 70, 230, 700 mg/kg/day.
Beginning on Study Day (SD) 1, isoeugenol was administered daily via oral gavage at dose levels 0, 70, 230, 700 mg/kg/day to adult male and female rats (N = 20). The F0 cohabitation period began on SD 8. Mating pairs were allowed to produce three litters (F1a, F1b, and F1c). Dosing of the F1 generation was initiated on post-natal day (PND) 21 of the F1c animals. On PND 81 ± 10, F1c animals were assigned to mating pairs and allowed to produce three litters (F2a, F2b, and F2c). Endpoints evaluated included body weight, feed consumption, clinical signs, number and weight of pups, anogenital distance (AGD), sperm parameters, vaginal cytology, organ weights, and gross and microscopic pathology.
Throughout the F0 and F1 generations, a dose-related decrease was seen in the mean body weights of mid and high dose males (3-18%) and high-dose females (4-12%). Periodic decreases were seen in the F0 mid-dose female body weights. Feed consumption values were decreased in the high dose males by 12 - 26 % during the F0 generation. During Week 1, mid and high-dose females had decreased feed consumption by 8% and 20%, respectively. Feed consumption of the males during the F1 generation was decreased by 12 - 23 %. The aggregate number of live male pups born during all litters to the F0 parents was decreased by 21 % in the high-dose group. During the F1 matings, there were significant decreases of 4 - 6% in overall male, female, and combined pup weights. There were no effects on any other reproductive parameters throughout both generations. Sperm parameters and vaginal cytology were unchanged in the F0 and F1 generations.
At the F0 and F1 necropsies, some decreases in absolute organ weights and increases in organ-to-body-weight ratios were seen in the high-dose males and females. These differences may be attributed to decreased terminal body weights. Treatment-related microscopic findings included hyperkeratosis and hyperplasia in the non-glandular stomach at all dose levels and in both sexes of the F0 and F1 animals.
An Outbreeding cohabitation period (Task 3) revealed a 42 % increase in the number of live females per litter and an increase (34%) in the number of implantation sites in the naive females mated with the high-dose males. All other reproductive parameters were comparable between dose groups when naive males were mated with control or 700 mg/kg/day females and when naive females were mated with control and 700 mg/kg/day males.
Under the conditions of this study, isoeugenol produced some non-reproductive toxicity at all dose levels as noted by hyperkeratosis and hyperplasia in the non-glandular stomachs and decreased body weights (230 and 700 mg/kg/day males; and 700 mg/kg/day females) and mild reproductive toxicity at 700 mg/kg/day as noted by a decreased number of male pups per litter during the F0 cohabitation, and decreased male and female pup weights during the F1 cohabitation.
NTIS # PB2003-100083