[Development of a Novel Male Reproductive Toxicity Assessment Method to Predict Male-mediated Effects on the Next Generation].

Less than 10% of the candidate drug compounds are associated with male reproductive toxicity. Genetic and/or epigenetic information on sperm may be crucial for fetal development. Therefore, developmental toxicity, such as paternally transmitted birth defects, is possible if genetic abnormalities in the male germ line persist and accumulate in the sperm during spermatogenesis. First, this study provides an overview of chemical and male reproductive toxicity, which may lead to developmental toxicity from the perspective of male reproduction. Second, we demonstrate methods for evaluating male reproductive toxicity to anticipate male-mediated developmental toxicity. We developed a novel staining technique for evaluating sperm quality, as well as a noninvasive imaging analysis of male reproductive toxicity. The former is a mammalian male germ cell-specific staining method using reactive blue 2 dye (RB2), as previously confirmed in human sperm, and a method for detecting the early-stage DNA fragmentation in a single nucleus from mouse spermatozoa using single-cell pulsed-field gel electrophoresis. The latter is a new, ready-to-use, and compact magnetic resonance imaging (MRI) platform utilizing a high-field permanent magnet to evaluate male reproductive toxicity. The histopathological analysis supported the suitability of the MRI platform. The present study, for the first time, revealed a rapid, noninvasive evaluation of male reproductive toxicity in vivo using compact MRI. These novel toxicity assessments can help predict male-mediated developmental toxicity, contributing to accelerated drug discovery and drug repositioning.