Carcinogenic potential of chemicals is currently evaluated using a two year bioassay in rodents. Numerous difficulties are known for this assay, most notably, the lack of information regarding detailed dose response and human relevance of any positive findings. A screen for carcinogenic activity has been proposed based on a 90 day screening assay. Chemicals are first evaluated for proliferative activity in various tissues. If negative, lack of carcinogenic activity can be concluded. If positive, additional evaluation for DNA reactivity, immunosuppression, and estrogenic activity are evaluated. If these are negative, additional efforts are made to determine specific modes of action in the animal model, with a detailed evaluation of the potential relevance to humans. Applications of this approach are presented for liver and urinary bladder. Toxicologic pathology is critical for all of these evaluations, including a detailed histopathologic evaluation of the 90 day assay, immunohistochemical analyses for labeling index, and involvement in a detailed mode of action analysis. Additionally, the toxicologic pathologist needs to be involved with molecular evaluations and evaluations of new molecularly developed animal models. The toxicologic pathologist is uniquely qualified to provide the expertise needed for these evaluations.

Although 3,3′-iminodipropionitrile (IDPN) is widely used as a neurotoxicant to cause axonopathy due to accumulation of neurofilaments in several rodent models, its mechanism of neurotoxicity has not been fully understood. In particular, no information regarding microRNA (miRNA) alteration associated with IDPN is available. This study was conducted to reveal miRNA alteration related to IDPN-induced neurotoxicity. Rats were administered IDPN (20, 50, or 125 mg/kg/day) orally for 3, 7, and 14 days. Histopathological features were investigated using immunohistochemistry for neurofilaments and glial cells, and miRNA alterations were analyzed by microarray and reverse transcription polymerase chain reaction. Nervous symptoms such as ataxic gait and head bobbing were observed from Day 9 at 125 mg/kg. Axonal swelling due to accumulation of neurofilaments was observed especially in the pons, medulla, and spinal cord on Day 7 at 125 mg/kg and on Day 14 at 50 and 125 mg/kg. Furthermore, significant upregulation of miR-547* was observed in the pons and medulla in treated animals only on Day 14 at 125 mg/kg. This is the first report indicating that miR-547* is associated with IDPN-induced neurotoxicity, especially in an advanced stage of axonopathy.

To examine the effects of 4-methylthio-3-butenyl isothiocyanate on esophageal carcinogenesis, male 6-week-old F344 rats were subcutaneously injected with 0.5 mg/kg body weight N-nitrosomethylbenzylamine three times per week for 5 weeks and fed a diet supplemented with 80 ppm 4-methylthio-3-butenyl isothiocyanate, equivalent to 6.05 mg/kg body weight/day for the initiation stage, 4.03 mg/kg body weight/day for the promotion stage, or 4.79 mg/kg body weight/day for all stages. Although the incidence of lesions was not affected by 4-methylthio-3-butenyl isothiocyanate treatment, the multiplicity of squamous cell papilloma in the esophagus was significantly decreased in rats in the 4-methylthio-3-butenyl isothiocyanate initiation stage group (1.13 ± 0.74), 4-methylthio-3-butenyl isothiocyanate promotion stage group (1.47 ± 0.99), and 4-methylthio-3-butenyl isothiocyanate all stage group (1.47 ± 1.13) as compared with rats treated with N-nitrosomethylbenzylamine alone (3.00 ± 1.46). Immunohistochemical analysis revealed that 4-methylthio-3-butenyl isothiocyanate induced apoptosis, suppressed cell proliferation, and increased p21 expression when administered in the promotion phase. These modifying effects were not observed in the rats treated with 4-methylthio-3-butenyl isothiocyanate alone. Our results indicated that 4-methylthio-3-butenyl isothiocyanate may exert chemopreventive effects against N-nitrosomethylbenzylamine-induced esophageal carcinogenesis in rats.

The objective of the current study was to explore the inhibitory effects of quercetin on cadmium-induced autophagy in mouse kidneys. Mice were intraperitoneally injected with cadmium and quercetin once daily for 3 days. The LC3-II/β-actin ratio was used as the autophagy marker, and autophagy was observed by transmission electron microscopy. Oxidative stress was investigated in terms of reactive oxygen species, total antioxidant capacity, and malondialdehyde. Cadmium significantly induced typical autophagosome formation, increased the LC3-II/β-actin ratio, reactive oxygen species level, and malondialdehyde content, and decreased total antioxidant capacity. Interestingly, quercetin markedly decreased the cadmium-induced LC3-II/β-actin ratio, reactive oxygen species levels, and malondialdehyde content, and simultaneously increased total antioxidant capacity. Cadmium can inhibit total antioxidant capacity, produce a large amount of reactive oxygen species, lead to oxidative stress, and promote lipid peroxidation, eventually inducing autophagy in mouse kidneys. Quercetin could inhibit cadmium-induced autophagy via inhibition of oxidative stress. This study may provide a theoretical basis for the treatment of cadmium injury.

Numerous pieces of evidence have revealed that oxaliplatin (OXA) evokes mechanical and cold hypersensitivity. However, the mechanism underlying these bothersome side effects needs to be further investigated. It is well known that cyclooxygenase-2 (COX-2) and extracellular signal-regulated kinases (ERK1/2) signaling play crucial roles in several pain states. Our previous data showed that Akt2 in the dorsal root ganglion (DRG) participated in the regulation of OXA-induced neuropathic pain. But it is still unclear whether spinal ERK1/2 signaling is involved in the regulation of OXA-induced hyperalgesia, and the linkage between COX-2 and ERK1/2 signaling in mediating OXA-induced hyperalgesia also remains unclear. In this research, we investigated the possible mechanism of celecoxib, a COX-2 inhibitor, in OXA-induced neuropathic pain. Our results show that single dose of OXA (12 mg/kg) significantly attenuated both the tail withdrawal latency (TWL) and mechanical withdrawal threshold (MWT) at days 4 after the OXA treatment. Administration of celecoxib (30 mg/kg/day) for 4 and 6 days inhibited the decrease in TWL and MWT, and each was significantly higher than that of the OXA+vehicle group and was equivalent to that of the vehicles group. OXA increased the expression of cyclooxygenase-2 (COX-2) mRNA and phosphorylated extracellular signal-regulated kinase1/2 (pERK1/2) protein in the lumbar 4-5 (L4-5) spinal cord dorsal horn neurons. Administration of celecoxib for 7 days suppressed the increase in expression of COX-2 and pERK1/2 induced by OXA. Our findings suggested that COX-2 and ERK1/2 signaling in spinal cord contributed to the OXA-induced neuropathic pain.

Alloxan had been recognized as having a direct nephrotoxic effect different from its diabetogenic action. We encountered previously unreported granulomatous tubulointerstitial nephritis with severe luminal and interstitial mineralization in one diabetic rat after one week of alloxan administration. Histopathologically, many dilated and occluded proximal and distal tubules were segmentally observed in the cortex and outer medulla. The tubular lumen contained minerals and cell debris. Tubular epithelial cells were degenerated and piled up, and they protruded into the lumen, where they enveloped minerals. Mineralization was observed mainly in the tubular lumen, and to some extent in the subepithelium and interstitium. The mineralization beneath the tubular epithelium was often continuous from the subepithelium to the interstitium. In these lesions, the tubular basement membrane was disrupted by mineralization, and a granuloma with multinuclear foreign-body giant cells was formed in the interstitial areas.

Mott cells are a variant form of plasma cells in humans and laboratory animals. This report describes the morphological characteristics of Mott cells observed in a 33-week-old female CB6F1-Tg rasH2 mouse. Microscopically, a large number of round cells with abundant eosinophilic globules, which were variable in size, were observed in the spleen and were densely distributed in the red pulp adjacent to the marginal zone. A few similar cells were present in the submandibular lymph node and bone marrow. Neither systemic nor local chronic inflammatory changes were seen in this animal. These cells were positive for mouse immunoglobulins. Ultrastructurally, the dilated rough endoplasmic reticulum had a homogenous substances with an intermediate electron density. On the basis of the above findings, these cells were identified as Mott cells. The present lesion is thought to be a spontaneous lesion, an unusual appearance of Mott cells without any associated pathological conditions.

Yolk sac carcinoma is an extremely rare tumor in rats and is usually found in the genital system of aged animals. We encountered a yolk sac carcinoma in the pulmonary artery of an 18-week-old female Sprague-Dawley rat. In a repeated dosing toxicity study (once weekly for 4 weeks, intraperitoneal), this rat was unexpectedly found dead on the 55th day after the final administration of the test article. At necropsy, grayish white nodules were found on the lung surface. Histopathologically, tumor emboli were observed in the trunk and branch of the pulmonary artery. Tumor cells with slightly basophilic vacuolated cytoplasm and large vesicular nuclei formed nests or clusters and were embedded in a homogenous eosinophilic and periodic acid-Schiff reaction positive matrix. The tumor cells and matrix were immunoreactive for laminin. The embolic tumor resembled yolk sac carcinoma showing a parietal pattern in rodents. Although the primary site was unknown, the tumor was considered to be a metastatic yolk sac carcinoma.

Extraskeletal osteosarcoma is a very rare tumor in humans and animals. This paper describes a case of extraskeletal osteosarcoma observed in the duodenum of a male ICR mouse. Grossly, a solid mass pushing up the tunica serosa was observed in the duodenal wall. Histologically, the tumor was located in the lamina propria mucosae and tela mucosa. Neoplastic cells densely proliferated in these areas, and replaced of the normal tissue components. A small amount of osteoid and a small clump of bone tissue were observed in the area of neoplastic cell proliferation, especially in the lamina propria mucosae. Neoplastic cells consisted of atypical polygonal cells and pleomorphic spindle-shaped cells, and the former were predominant. Mitotic figures were occasionally observed. Neither invasion of vessels in the duodenum nor metastasis to distant organs was observed. There were no skeletal tumors in the body. Immunohistochemically, the neoplastic cells were positive for anti-osteocalcin, osteonectin, vimentin, and S-100 protein. Judging from these results, the present tumor was diagnosed as extraskeletal osteosarcoma. This is the first report of spontaneous extraskeletal osteosarcoma arising from the duodenum of a mouse.

In order to clarify the histological localization of cadmium (Cd) in the placenta, we analyzed paraffin sections of placentas from rats with a single Cd exposure on gestation day 18 by the LA-ICP-MS imaging method compared with the histopathological changes. The placentas were sampled at 1 hour, 2 hours, 3 hours, 6 hours, and 24 hours after treatment. Histopathologically, the trophoblasts in the labyrinth zone of the Cd group showed swelling at 1 hour. At 2 and 3 hours, the trophoblasts showed swelling and vacuolar degeneration. At 6 and 24 hours, the syncytiotrophoblasts selectively underwent necrosis/apoptosis, resulting in a decrease in number. Remarkable metallothionein expression was observed in the trophoblastic septa, particularly cytotrophoblasts at 24 hours. The LA-ICP-MS analysis detected the localization of Cd in the fetal part of the placenta from 1 hour onwards. In particular, the intensity of Cd was prominent in the labyrinth zone and tended to increase with the progression of trophoblastic septa damages. The LA-ICP-MS analysis using the paraffin sections detected the localization of Cd in the fetal part of the placenta, and this methodology will be one of the valuable tools to detect heavy metals in toxicological pathology.