Makoto Shibutani

Developmental toxicity of brominated flame retardants, tetrabromobisphenol A and 1,2,5,6,9,10-hexabromocyclododecane, in rat offspring after maternal exposure from mid-gestation through lactation.

To evaluate developmental exposure effects of two brominated flame retardants, tetrabromobisphenol A (TBBPA) and 1,2,5,6,9,10-hexabromocyclododecane (HBCD), pregnant Sprague-Dawley rats were administered either chemical at doses of 100, 1000 or 10,000 ppm in a soy-free diet from gestation day 10 until the day 20 after delivery. Offspring exposed to TBBPA showed dose-unrelated slight decreases of serum triiodothyronine (T(3)) concentration at postnatal day 20, and there was no evidence of hypothyroidism-related neuronal mismigration and impaired oligodendroglial development as judged by morphometric analyses of NeuN-immunoreactive neuronal distribution in the hippocampal CA1, and area of corpus callosum as well as density of 2,3-cyclic nucleotide 3-phosphodiesterase (CNPase)-immunoreactive oligodendrocytes in the cingulate deep cortex at the adult stage. On the other hand, HBCD exerted a weak hypothyroidism evident with increases in thyroid weight, thyroid follicular cell hypertrophy and serum concentrations of thyroid-stimulating hormone as well as decreases of serum T(3) concentrations in offspring at 10,000 ppm at weaning. Increased thyroid weights and decreased serum T(3) concentrations were also observed in the adult stage from 1000 ppm. With regard to the effect on brain development, HBCD reduced density of CNPase-positive oligodendrocytes at 10,000 ppm, suggesting an impaired oligodendroglial development. Results thus suggest that TBBPA did not exert developmental brain effects, while HBCD did, and 100 ppm was determined to be the no-observed-adverse-effect level of HBCD from changes in thyroid parameters at the adult stage by maternal exposure, translating into 8.1-21.3mg/kg-d.

Assessment of developmental effects of hypothyroidism in rats from in utero and lactation exposure to anti-thyroid agents

To clarify the developmental effects of hypothyroidism and to establish a detection system of resultant brain retardation, pregnant rats were administered 3 or 12 ppm of 6-propyl-2-thiouracil (PTU) or 200 ppm of methimazole (MMI) in the drinking water from gestation day 10 to postnatal day 20 and maintained after weaning until 11 weeks of age (adult stage). Offspring displayed evidence of growth retardation lasting into the adult stage, which was particularly prominent in males. Except for hypothyroidism-related thyroid follicular cell hypertrophy, most histopathological changes that appeared at the end of chemical exposure were related to growth retardation and reversed by the adult stage. A delayed onset of puberty and an adult stage gonadal enlargement occurred by exposure to anti-thyroid agents, both being especially evident in males, and this effect might be related to gonadal growth suppression during exposure. At the adult stage, the distribution variability of hippocampal CA1 pyramidal neurons reflecting mismigration could be detected in animals receiving both thyrotoxins, with a dose-dependent effect by PTU. Similarly, a reduction in the area of the corpus callosum and oligodendroglial cell numbers in the cerebral deep cortex, both reflecting impaired oligodendroglial development, were detected in rats administered both chemicals. Thus, all effects, except for impaired brain development, might be linked to systemic growth retardation, and the brain morphometric methods employed in this study may be useful to evaluate the potency of chemicals to induce hypothyroidism-related brain retardation.

Proliferative and Nonproliferative Lesions of the Rat and Mouse Central and Peripheral Nervous Systems

Harmonization of diagnostic nomenclature used in the pathology analysis of tissues from rodent toxicity studies will enhance the comparability and consistency of data sets from different laboratories worldwide. The INHAND Project (International Harmonization of Nomenclature and Diagnostic Criteria for Lesions in Rats and Mice) is a joint initiative of four major societies of toxicologic pathology to develop a globally recognized nomenclature for proliferative and nonproliferative lesions in rodents. This article recommends standardized terms for classifying changes observed in tissues of the mouse and rat central (CNS) and peripheral (PNS) nervous systems. Sources of material include academic, government, and industrial histopathology databases from around the world. Covered lesions include frequent, spontaneous, and aging-related changes as well as principal toxicant-induced findings. Common artifacts that might be confused with genuine lesions are also illustrated. The neural nomenclature presented in this document is also available electronically on the Internet at the goRENI website (http://www.goreni.org/).

Developmental Exposure to Manganese Chloride Induces Sustained Aberration of Neurogenesis in the Hippocampal Dentate Gyrus of Mice

The effect of exogenously administered manganese (Mn) on developmental neurogenesis in the hippocampal dentate gyrus was examined in male mice after maternal exposure to MnCl(2) (0, 32, 160, or 800 ppm as Mn in diet) from gestational day 10 to day 21 after delivery on weaning. Immunohistochemistry was performed to monitor neurogenesis and interneuron subpopulations on postnatal days (PNDs) 21 and 77 (adult stage). Reelin-synthesizing γ-aminobutyric acid (GABA)ergic interneurons increased in the hilus with ≥ 160 ppm on weaning to sustain to PND 77 at 800 ppm. Apoptosis in the neuroblast-producing subgranular zone increased with 800 ppm and TUC4-expressing immature granule cells decreased with 800 ppm on weaning, whereas at the adult stage, immature granule cells increased. On PND 21, transcript levels increased with Reln and its receptor gene Lrp8 and decreased with Dpysl3 coding TUC4 in the dentate gyrus, confirming immunohistochemical results. Double immunohistochemistry revealed a sustained increase of reelin-expressing and NeuN-lacking or weakly positive immature interneurons and NeuN-expressing mature neurons in the hilus through to the adult stage as examined at 800 ppm. Brain Mn concentrations increased at both PNDs 21 and 77 in all MnCl(2)-exposed groups. These results suggest that Mn targets immature granule cells causing apoptosis and neuronal mismigration. Sustained increases in immature reelin-synthesizing GABAergic interneurons may represent continued aberration in neurogenesis and following migration to cause an excessive response for overproduction of immature granule cells through to the adult stage. Sustained high concentration of Mn in the brain may be responsible for these changes.

Sustained production of Reelin-expressing interneurons in the hippocampal dentate hilus after developmental exposure to anti-thyroid agents in rats.

To detect molecular evidence reflecting a permanent disruption of neuronal development due to hypothyroidism, distribution of Reelin-producing cells that function in neuronal migration and positioning was analyzed in the hippocampal dentate hilus using rats. From gestation day 10, maternal rats were administered either 6-propyl-2-thiouracil (PTU) at 3 or 12ppm (0.57 or 1.97mg/kg body weight/day) or methimazole (MMI) at 200ppm (27.2mg/kg body weight/day) in the drinking water and male offspring were immunohistochemically examined at the end of exposure on weaning (postnatal day 20) and at the adult stage (11-week-old). Offspring with MMI and 12ppm PTU displayed evidence of growth retardation lasting into the adult stage. On the other hand, all exposure groups showed a sustained increase in Reelin-expressing cells in the dentate hilus until the adult stage in parallel with Calbindin-D-28K-expressing cells at weaning and with glutamic acid decarboxylase 67-positive cells in the adult stage, confirming an increase in gamma-aminobutyric acid (GABA)ergic interneurons. At the adult stage, NeuN-positive postmitotic mature neurons were also increased in the hilus in all exposure groups, however, the increased population of Reelin-producing cells at this stage was either weakly positive or negative for NeuN, indicative of immature neurons. At weaning, neuroblast-producing subgranular zone of the dentate gyrus showed increased apoptosis and decreased cell proliferation suggestive of impaired neurogenesis. The results suggest that sustained increases of immature GABAergic interneurons synthesizing Reelin in the hilus could be a signature of compensatory regulation for impaired neurogenesis and mismigration during the neuronal development as a hypothyroidism-related brain effect rather than that secondary to systemic growth retardation.

Elevation of cell proliferation via generation of reactive oxygen species by piperonyl butoxide contributes to its liver tumor-promoting effects in mice

Piperonyl butoxide (PBO) is a pesticide synergist used with pyrethroids as a domestic insecticide, and it acts as a non-genotoxic hepatocarcinogen in rats and mice. To clarify whether oxidative stress is involved in the liver tumor-promoting effect of PBO in mice, male mice were subjected to two-thirds partial hepatectomy, followed by N-diethylnitrosamine (DEN) treatment, and given a diet containing 0.6% PBO for 25xa0weeks. The incidences of cytokeratin (CK) 8/18-positive foci, adenomas, and carcinomas significantly increased in the DENxa0+xa0PBO group compared with the DEN-alone group. The PCNA-positive ratio significantly increased in non-tumor hepatocytes, CK8/18-positive foci and adenomas in the DENxa0+xa0PBO group compared with the DEN-alone group. PBO increased reactive oxygen species (ROS) production in microsomes but did not change oxidative DNA damage as assessed by 8-hydroxydeoxyguanosine (8-OHdG). In real-time RT–PCR, PBO upregulated the expression of genes related to metabolism, such as Cytochrome P450 1a1, 2a5, and 2b10, and metabolic stress, such as Por and Nqo1, but downregulated Egfr and Ogg1. PBO also increased early response genes downstream of mitogen-activated protein kinase (MAPK), such as c-Myc that is induced by excessive ROS production, and G1/S transition-related genes, such as E2f1 and Ccnd1. Thus, PBO can generate ROS via the metabolic pathway without any induction of oxidative DNA damage, activate cell growth, increase c-Myc- and E2F1-related pathways, and act as a liver tumor promoter of DEN-induced hepatocarcinogenesis in mice.

Antioxidant enzymatically modified isoquercitrin or melatonin supplementation reduces oxidative stress-mediated hepatocellular tumor promotion of oxfendazole in rats.

To clarify whether enzymatically modified isoquercitrin (EMIQ) or melatonin (MLT) supplementation reduces oxidative stress-mediated hepatocellular tumor-promoting effect of oxfendazole (OX), a benzimidazole anthelmintic, male rats were administered a single intraperitoneal injection of N-diethylnitrosamine (DEN) and were fed a diet containing OX (500xa0ppm) for 10xa0weeks with or without EMIQ (2,000xa0ppm) or MLT (100xa0ppm) in the drinking water after DEN initiation. One week after the commencement of the administration of OX, rats were subjected to two-thirds of partial hepatectomy. The number of GST-P-positive foci promoted by OX was significantly inhibited by the combined antioxidant EMIQ or MLT administration, and the area of GST-P-positive foci was inhibited by the administration of MLT. Real-time RT–PCR analysis revealed decreases in mRNA expression levels of cytochrome P450, family 2, subfamily b, polypeptide 2 (Cyp2b2) and malic enzyme 1 (Me1) in the DEN-OX-EMIQ and DEN-OX-MLT groups and decreases in mRNA expression levels of Cyp1a1 and aldo–keto reductase family 7, member A3 (Akr7a3) in the DEN-OX-MLT group compared to those in the DEN-OX group. In in vitro ROS production assay, inhibited production of NADPH-dependent ROS was observed by the treatment with EMIQ or MLT. These results suggest that coadministration of EMIQ or MLT suppresses the hepatocellular tumor-promoting activity of OX in rats through the decrease in ROS production by the activation of CYPs.

Dual antitumor mechanisms of Notch signaling inhibitor in a T-cell acute lymphoblastic leukemia xenograft model

Constitutive activation of Notch signaling is required for the proliferation of a subgroup of human T‐cell acute lymphoblastic leukemias (T‐ALL). Previous in vitro studies have demonstrated the therapeutic potential of Notch signaling inhibitors for treating T‐ALL. To further examine this possibility, we applied a γ‐secretase inhibitor (GSI) to T‐ALL xenograft models. Treatment of established subcutaneous tumors with GSI resulted in partial or complete regression of tumors arising from four T‐ALL cell lines that were also sensitive to GSI in vitro. To elucidate the mechanism of action, we transduced DND‐41 cells with the active form of Notch1 (aN1), which conferred resistance to in vitro GSI treatment. Nevertheless, in vivo treatment with GSI induced a partial but significant regression of subcutaneous tumors that developed from aN1‐transduced DND‐41 cells, whereas it induced complete regression of tumors that developed from mock‐transduced DND‐41 cells. These findings indicate that the remarkable efficacy of GSI might be attributable to dual mechanisms, directly via apoptosis of DND‐41 cells through the inhibition of cell‐autonomous Notch signaling, and indirectly via disturbance of tumor angiogenesis through the inhibition of non‐cell‐autonomous Notch signaling. (Cancer Sci 2009; 100: 2444–2450)

Suppressive effect of enzymatically modified isoquercitrin on phenobarbital-induced liver tumor promotion in rats

To investigate the effect of enzymatically modified isoquercitrin (EMIQ) on hepatocellular tumor promotion induced by phenobarbital (PB), male rats were administered a single intraperitoneal injection of 200xa0mg/kgxa0N-diethylnitrosamine (DEN) and then fed with a diet containing PB (500xa0ppm) for 8xa0weeks, with or without EMIQ (2,000xa0ppm) in the drinking water. One week after PB administration, rats underwent a two-thirds partial hepatectomy. The PB-induced increase in the number and area of glutathione S-transferase placental form-positive foci and the proliferating cell nuclear antigen-positive ratio was significantly suppressed by EMIQ. Real-time reverse transcription–polymerase chain reaction analysis revealed increases in mRNA expression levels of Cyp2b2 and Mrp2 in the DEN-PB and DEN-PB-EMIQ groups compared with the DEN-alone group, while the level of Mrp2 decreased in the DEN-PB-EMIQ group compared with the DEN-PB group. There were no significant changes in microsomal reactive oxygen species (ROS) production and oxidative stress markers between the DEN-PB and DEN-PB-EMIQ groups. Immunohistochemically, the constitutive active/androstane receptor (CAR) in the DEN-PB group was clearly localized in the nuclei, but its immunoreactive intensity was decreased in the DEN-PB-EMIQ group. These results indicate that EMIQ suppressed the liver tumor-promoting activity of PB by inhibiting nuclear translocation of CAR, and not by suppression of oxidative stress.

Concomitant apoptosis and regeneration of liver cells as a mechanism of liver-tumor promotion by β-naphthoflavone involving TNFα-signaling due to oxidative cellular stress in rats

β-naphthoflavone (BNF) is a strong inducer of cytochrome P450 1A enzymes, and exerts liver tumor-promoting activity through enhancement of oxidative stress responses in rats. This study investigated the role of the tissue environment surrounding hepatocellular preneoplastic lesions in the early tumor-promotion stage by BNF, using enzymatically modified isoquercitrin (EMIQ) as an anti-oxidative chemopreventive agent. Male F344 rats were fed a diet containing BNF (0.5%) for 6 weeks, with or without EMIQ (0.2%) in the drinking water, 2 weeks after initiation with N-diethylnitrosamine, and were subjected to two-thirds partial hepatectomy 1 week after starting BNF-promotion. BNF-treatment increased concentrations of liver thiobarbituric acid-reactive substances, single liver cells expressing glutathione S-transferase placental form or heme oxygenase (HO)-1, and concomitant apoptosis and proliferation of liver cells. Transcript upregulation of anti-oxidative enzymes (Aldh1a1 and Nqo1), cell cycle-related molecules (Cdc20 and Cdkn2b) and inflammation-related molecules including proinflammatory cytokines (Ccl2, Col1a1, Il6, Nos2 and Serpine1) was also evident. Furthermore, BNF increased HO-1-expressing Kupffer cells and liver cells expressing tumor necrosis factor receptor 1 (TNFR1) and the TNFR1-associated death domain. Most of these BNF-induced fluctuations disappeared or were suppressed by EMIQ in conjunction with suppression of tumor-promotion. Tnf transcript levels with BNF were also suppressed by EMIQ. These results suggest that BNF-induced oxidative stress causes single liver cell toxicity, allowing subsequent concomitant apoptosis and regeneration involving inflammatory responses including TNFα-signaling, contributing to tumor promotion. Kupffer cells may act to protect against inflammatory stimuli induced as a result of oxidative cellular stress by BNF, causing proinflammatory cytokine level fluctuations.