To investigate the neurotoxicity profile of glycidol and its effect on developmental hippocampal neurogenesis, pregnant Sprague Dawley rats were given drinking water containing 0, 100, 300, or 1000 ppm glycidol from gestational day 6 until weaning on day 21 after delivery. At 1000 ppm, dams showed progressively worsening gait abnormalities, and histopathological examination showed generation of neurofilament-L(+) spheroids in the cerebellar granule layer and dorsal funiculus of the medulla oblongata, central chromatolysis in the trigeminal nerve ganglion cells, and axonal degeneration in the sciatic nerves. Decreased dihydropyrimidinase-like 3(+) immature granule cells in the subgranular zone (SGZ) and increased immature reelin(+) or calbindin-2(+) γ-aminobutyric acid-ergic interneurons and neuron-specific nuclear protein (NeuN)(+) mature neurons were found in the dentate hilus of the offspring of the 1000 ppm group on weaning. Hilar changes remained until postnatal day 77, with the increases in reelin(+) and NeuN(+) cells being present at ≥ 300 ppm, although the SGZ change disappeared. Thus, glycidol caused axon injury in the central and peripheral nervous systems of adult rats, suggesting that glycidol targets the newly generating nerve terminals of immature granule cells, resulting in the suppression of late-stage hippocampal neurogenesis. The sustained hilar changes may be a sign of continued aberrations in neurogenesis and migration. The no-observed-adverse-effect level was determined to be 300 ppm (48.8mg/kg body weight/day) for dams and 100 ppm (18.5mg/kg body weight/day) for offspring. The sustained developmental exposure effect on offspring neurogenesis was more sensitive than the adult axonal injury.

Recent studies suggest that there is no reliable rapid means for evaluating the carcinogenic potential of chemicals considered to be carcinogens. Carcinogenic bioassays are typically time-consuming and expensive 1.5-or 2-year studies using mice and rats. Alternative animal models using transgenic or gene targeting technologies (Eastin, 1998) or two-stage carcinogenesis models (Tamano, 2010) are also expensive and time-consuming or have limited target organs. Toxicogenomic approaches for prediction of carcinogenic potential in each target organ appear promising. However, they are also expensive and require some integrative methodologies between ABSTRACT -We have previously reported that renal carcinogens examined in rats increase tubular cell proliferation and topoisomerase (Topo) IIα + cells. The present study was aimed at identifying early prediction markers of carcinogens after 28-day treatment in rats. Following gene expression screening by microarrays in renal tubules with renal carcinogens, immunohistochemical analysis and TUNELassay were performed with carcinogens targeting different organs. All renal carcinogens tested (ferric nitrilotriacetic acid, ochratoxin A (OTA), monuron, tris(2-chloroethyl) phosphate, and potassium bromate) increased tubular cells immunoreactive for minichromosome maintenance 3 (Mcm3) or ubiquitin D (Ubd) or those showing apoptosis, compared with untreated controls or non-carcinogenic renal toxicants. Carcinogens targeting the liver (thioacetamide (TAA), fenbendazole, piperonyl butoxide (PBO) and methyleugenol), thyroid (sulfadimethoxine), urinary bladder (phenylethyl isothiocyanate), forestomach (butylated hydroxyanisole), glandular stomach (catechol), and colon (chenodeoxycholic acid and 2-amino-1-methyl-6-phenylimidazo [4,5-b]pyridine) were examined for induction of Mcm3, Ubd, Topo IIα, Ki-67 and apoptosis using non-carcinogenic toxicants as negative controls. All carcinogens increased Mcm3 + , Ubd + , Topo IIα + , Ki-67 + or TUNEL + cells, except for hepatocarcinogen PBO and both colon carcinogens, which did not increase cell proliferation. Ubd + cells co-expressing Topo IIα was increased without changing phospho-Histone H3-co-expressing cell population as examined with OTA and TAA. Results revealed cooperative responses of Topo IIα, Ubd and apoptosis by carcinogens inducing high proliferation activity, irrespective of target organs, examined here after a 28-day administration. Aberrant expression of Ubd at G 2 phase and increased apoptosis reflecting aberrant cell cycle regulation may be the common feature of these carcinogens.

We have shown that maternal manganese (Mn) exposure caused sustained disruption of hippocampal neurogenesis of mouse offspring. To clarify the effects of maternal Mn exposure on epigenetic gene regulation contributing to the sustained disruption of hippocampal neurogenesis, we treated pregnant ICR mice with MnCl₂ in diet from gestational day 10 through day 21 after delivery on weaning and searched epigenetically downregulated genes by global promoter methylation analysis in the hippocampal dentate gyrus of male offspring on postnatal day (PND) 21 and PND 77. By CpG promoter microarray analysis on PND 21 following 800-ppm Mn exposure, sustained promoter hypermethylation and transcript downregulation through PND 77 were confirmed with Mid1, Atp1a3, and Nr2f1, whereas Pvalb showed a transient hypermethylation only on weaning. The numbers of Pvalb⁺ and ATP1a3⁺ neurons suggestive of γ-aminobutyric acid (GABA)ergic interneurons, Mid1⁺ cells suggestive of late-stage granule cell lineage and GABAergic interneurons, and COUP-TF1⁺ cells suggestive of early-stage granule cell lineage were all reduced on PND 21, and reductions were sustained on PND 77 except for no change in Pvalb⁺ cells. Mid1⁺ cells showed asymmetric distribution with right-side predominance, and Mn exposure abolished it by promoter hypermethylation of the right side. These findings indicate epigenetic mechanisms as mediators, through which Mn exposure modulates neurogenesis involving both granule cell lineage and GABAergic interneurons with long-lasting and stable repercussions. Disruption of asymmetric cellular distribution of Mid1 suggests that higher brain functions specialized in the left or right side of the brain were affected.