Prenatal developmental toxicity study in the Rabbit/FeMn slag/OECD414/Oral/GLP

Summary

The purpose of this study was to assess the influence of FeMn Slag (ferromanganese slag), a by-product of the production of manganese alloys, on embryo-fetal survival and development when administered during the organogenesis and fetal growth phases of pregnancy in the New Zealand White rabbit.

The study was conducted in two phases (Preliminary phase and Main phase).  In total, three groups of 22 females received FeMn Slag at doses of 100, 300 or 800 mg/kg/day and at a dose volume of 2 ml/kg by oral gavage administration, from Day 6 to 28 after mating inclusive.  A similarly constituted Control group received the vehicle, corn oil, at the same volume dose and for the same duration as treated groups.  Animals were killed on Day 29 after mating for reproductive assessment and fetal examination.

Clinical observations, body weight and food consumption were recorded.  Adult females were examined macroscopically at necropsy on Day 29 after mating and the gravid uterus weight was recorded.  All fetuses were examined macroscopically at necropsy and subsequently by detailed internal visceral examination of the head or skeletal examination. 

Results

There were seven premature deaths during the course of the study (five Control females, one female receiving 100 mg/kg/day and one female receiving 800 mg/kg/day), none of which were attributable to FeMn Slag.

Treatment at dose levels up to and including 800 mg/kg/day was generally well tolerated, with no test item-related signs observed in relation to dose administration or changes in clinical condition; the incidences of reductions in faecal output and thin build were secondary to the reductions in food consumption observed in all groups, including Controls, and were not attributed to FeMn Slag administration.  Maternal body weight performance, gravid uterine weights and net body weight losses and food consumption were unaffected by FeMn Slag administration at all dose levels investigated and there were no test item-related macroscopic abnormalities detected at scheduled termination.

There was no effect of maternal treatment with FeMn Slag on the mean numbers of implantations, pre-implantation loss or sex ratio at any dose level investigated.  At
800 mg/kg/day, a consistent and reproducible increase in the percentage of post-implantation loss was evident in both phases of the study, with fewer litters with 0 or 1 resorption present compared to the other three study groups; a relationship with FeMn Slag could not be discounted.  Post implantation loss was considered unaffected by maternal treatment at 100 or 300 mg/kg/day, and mean placental, litter and fetal weights were essentially similar to Controls in all treated groups.

There was an increased incidence of major abnormalities in all treated groups compared with concurrent control.  Although the total number of fetuses with major abnormalities in the
100 mg/kg/day group (seven fetuses in four litters) was essentially similar to Control (six fetuses in four litters), the nature of the major abnormalities detected in the 100 mg/kg/day group was distinctly different to the Control group and the Historical Control Data range (HCD) but was similar to those detected in the 300 or 800 mg/kg/day groups.

The major abnormalities that were observed were diverse in nature, however several litters (Group 2 No’s 41and 42; Group 3 No 54; Group 4 No’s 74, 76 and 87) had one or more fetuses affected with abnormalities including anasarca, open eyelids, various heart and blood vessel abnormalities and bent long bones, and the majority of these abnormalities had not previously been recorded in the HCD population.  As a consequence, the major abnormalities detected in the treated groups were considered to be attributable to FeMn Slag.

In addition to the major abnormalities, at 800 mg/kg/day there was an increased incidence of unossified areas within the cranial bones and mandibles, thoracic vertebral defects, various sternebral/rib and costal cartilage abnormalities, delayed/incomplete ossification of fontanelles, cranial centres, sternebrae, vertebrae, pelvic bones, epiphyses and digit bones with the incidences exceeding the HCD range.  At 300 mg/kg/day there was an increased incidence of unossified areas within the cranial bones and mandibles, delayed/incomplete ossification of fontanelles, cranial centres, sternebrae, vertebrae (litter 54), epiphyses, digit bones, pectoral and pelvic girdle and long bones (litter 54) which exceeded the HCD range

Conclusion

Based on the results obtained in this main rabbit embryo-fetal development study, the No‑Observed-Adverse-Effect-Level (NOAEL) for maternal toxicity was concluded to be
800 mg/kg/day.  Due to the increased incidence of post implantation loss at 800 mg/kg/day, the dose level of 300 mg/kg/day was concluded to be the NOAEL for embryo-fetal survival.  In view of the nature and incidence of major fetal abnormalities detected in all treated groups, which exceeded the concurrent Control and Historical Control Data ranges, a NOAEL for embryo-fetal development was not established.  The aetiology of these fetal malformations remains unclear and will be further investigated outside of the scope of this study.

 

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