Prenatal Developmental Toxicity Study in the Han Wistar Rat/Mn3O4/OECD 414/Oral/GLP
Introduction: The purpose of this study was the assessment of the influence of Mn3O4 (an industrial chemical) on embryo-fetal survival and development when administered during the organogenesis and fetal growth phases of pregnancy in the rat. Three groups of 20 females received Mn3O4 at doses of 83, 250 or 750 mg/kg/day by oral gavage administration, from Day 6 to 19 after mating. A similarly constituted Control group received the vehicle, 1.0% w/v methylcellulose (MC) aqueous solution at the same volume dose as treated groups and for the same duration. Animals were killed on Day 20 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 20 after mating and the gravid uterus weight recorded. All fetuses were examined macroscopically at necropsy and subsequently by detailed internal visceral examination or skeletal examination.
Results: The mean concentrations of Mn3O4 in test formulations analyzed for the study were within ±15% of nominal concentrations confirming accurate formulation, this is with the exception of the first occasion Group 4. There were two deaths in the 250 mg/kg/day group but these were considered unrelated to treatment. There were no signs seen at physical examinations or at post-dose observation considered related to treatment with Mn3O4. Bodyweight and bodyweight gain throughout gestation were similar to that of the Control for females which received 83 or 250 mg/kg/day. Bodyweight and bodyweight gain up until Day 18 of gestation were similar to that of the Control for females which received 750 mg/kg/day. Bodyweight gain thereafter from Days 18-20 of gestation was lower than that of the Control for females which received 750 mg/kg/day. This is likely a consequence of the slightly low litter size and mean fetal weights in this group. Gravid uterine weights were marginally low for animals which received 750 mg/kg/day when compared to the control group. This is likely a consequence of the slightly low mean fetal weights in this group. Adjusted bodyweight values were unaffected by treatment. Food consumption of females receiving 83, 250 and 750 mg/kg/day was similar to that of Controls. There were no test-material related macroscopic abnormalities detected in the adult females at scheduled termination on Day 20 of gestation.
One female (Group 4 female 73) was found to be not pregnant at macroscopic examination. 20, 20, 18 and 19 females in Groups 1, 2, 3 and 4, respectively were found to be pregnant with live young on Day 20 of gestation. Embryo-fetal survival was considered to be unaffected by treatment. For females which received Mn3O4 at 750 mg/kg/day, litter weight and overall fetal weight was marginally lower than that of the control as well as if compared to those animals which received 83 and 250 mg/kg/day. There was no effect of treatment on litter or fetal weights in animals which received Mn3O4 at 83 or 250 mg/kg/day. There was no effect of treatment on placental weights in animals which received Mn3O4. Fetal pathology examination at 750 mg/kg/day revealed there were a number of fetuses with bent scapula(e); bent radius/ulna/fibula; short/bent/and thickened humerus with associated medially thickened/kinked/incompletely ossified ribs. These findings are outside of both concurrent and Historical Control Data (HCD). However, some of these findings have been reported in published literature to be reversible in quantity and severity post-natally but because these occurred in a high frequency in this group only, these findings are considered related to treatment with Mn3O4.
Conclusion: In this study, treatment with Mn3O4 at 83 or 250 mg/kg/day was generally well tolerated. At 750 mg/kg/day, maternal body weight performance was unaffected by treatment with Mn3O4 up until Day 18 of gestation, however, bodyweight gain between Days 18-20 of gestation was lower than that of the control, and the gravid uterine weight of females which received Mn3O4 at 750 mg/kg/day was lower than that of the control. Litter size and mean fetal weights were slightly reduced. Embryo-fetal survival was considered unaffected by treatment, but fetal development was adversely affected with bent scapula(e); bent radius/ulna/fibula; short/bent/and thickened humerus with associated medially thickened/kinked/incompletely ossified ribs. Therefore, the No-Observed- Effect-Level (NOEL) for maternal toxicity was 750 mg/kg/day and the No-Observed-Adverse-Effect-Level (NOAEL) for embryo-fetal toxicity was concluded to be 250 mg/kg/day