Methylenebisacrylamide (MBA), a crosslinker and congener of acrylamide, was evaluated for reproductive toxicity, neurotoxicity, and dominant lethal effects in Swiss CD-1 mice, using the RACB protocol. MBA was tested as one of a series of acrylamide congeners with varying degrees of reproductive and neural toxicities; MBA was found previously to have greater testicular effects than detectable neurotoxic effects in mice. A dose-range finding study was used to help identify doses for the main study. Main study doses were set relatively low to prevent debilitating neurotoxicity: concentrations in drinking water were set at 0, 10, 30, and 60 ppm. Exposure lasted up to 27 weeks. Water consumption was elevated at all three doses in the F0 group at 8 weeks but not at 16 weeks; this is thought to be due to the poor palatability, and the mice playing with the sipper-tubes. Using the week 16 consumption data, these concentrations produced calculated MBA consumption of nearly equal to 1.6, 4.7, and 9.3 mg/kg/d.
MBA at these concentrations was not neurotoxic, based on the lack of change in grip strength in either generation.
The F0 mice in the middle and top dose groups had 11 and 14% fewer pups per litter, and pup weight was lower by 8% in the top dose group. After the last litter was delivered and weaned, control and high-dose males were mated with untreated females, who were killed prior to delivery of the litter. In this dominant lethal test, MBA exposure increased early embryonic death and total postimplantation death by 50% in the 60 ppm males. In treated females during the Task 3 crossover mating to determine the affected sex, there was a 12% decrease in pup weight adjusted for litter size, but no other effects. At necropsy, there was a 12% and 15% reduction in testis weight in the middle and top dose groups, respectively.
In the second generation, at the week of mating, male body weights were reduced by 10%, 13% and 14% (low to high dose groups, respectively), and female body weights were reduced by 5%, 10%, and 13%. The number of live pups/litter was decreased by 33% at the top dose. Live pup weight adjusted for litter size was reduced by nearly equal to 8% in the middle dose group, and by 17% in the top dose group. At necropsy, testis weights were reduced by 22% and 35% in the upper two dose groups, with similar reductions in epididymal weight. The terminal body weight reductions are partly responsible for the increase in relative liver and kidney weights seen in this generation.
In summary, MBA showed dominant lethal reproductive toxicity in F0 males (fewer live pups/litter, more resorptions) and females (lowered F1 pup weight) at exposure levels that did not affect body weight and had no effect on grip strength or histopathologic measures of neurotoxicity.