Vanadium toxicity in mice: possible impairment of lipid metabolism and mucosal epithelial cell necrosis in the small intestine.

Because precise information as to the toxicity of vanadium is required for practical use of vanadium compounds as antidiabetic drugs, we examined vanadium toxicity in mice fed normal diet or high-fat diet (C57BL/6N, male, 7 weeks) by oral administration of ammonium metavanadate (AMV) with a maximum dose of 20 mgV/kg/day. Marked lipid accumulation in hepatocytes, renal epithelial cells, and mucosal epithelial cells of the small and large intestines and severe degeneration, necrosis, and loss of mucosal epithelial cells in the small intestine were observed. These pathological changes were more severe in mice fed high-fat diet than mice fed normal diet, and the intensity of the changes increased with increase in the administered dose of AMV. By electron microscopy, the number and size of lipid droplets in hepatocytes were increased. In the small intestine, a TUNEL assay showed a decreased number of positive cells, and positive cells for acrolein immunohistochemistry were observed specifically in the mucosal epithelial cells indicating degeneration and necrosis in the AMV-treated group, suggesting that a possible factor responsible for cell necrosis in the small intestine could be oxidative stress. In conclusion, AMV may impair cellular lipid metabolism, resulting in lipid accumulation, and induce mucosal epithelial cell necrosis in the small intestine.

Influence of injection timing on severity of cadmium-induced testicular toxicity in mice.

Cadmium (Cd) is one of the endocrine disrupter and is a well-known testicular toxicant. Recently, we reported that Cd-induced mortality was markedly different by injection timing. In this report, we investigated whether severity of testicular toxicity was affected by injection timing of Cd. C57BL/6J mice (male, 7 w) were received single intraperitoneal injection of CdCl(2) (4.5 mg/kg) at zeitgeber time 6 (ZT6) or ZT18; these injection timings showed highest (ZT6) or lowest (ZT18) mortality in our previous study (Miura, 2012). After one week of the injection, several parameters for testicular toxicity such as epididymal sperm motility and numbers of sperm head both in cauda epididymidis and testis were measured. At ZT6 injection group, all parameters examined were significantly reduced compared to the control group. However, very interestingly, no significant changes were observed at ZT18 injection group. We obtained similar results by another experiment in which mice were received single subcutaneous injection of CdCl(2) (4 or 6 mg/kg) followed by measuring the parameters ten days after the injection. This diurnal variation was not contradictory to the result of the lethal toxicity which we showed earlier. Therefore, our results indicate that the testicular toxicity of Cd is also influenced by the injection timing.

Ultrastructural changes in the air-blood barrier in mice after intratracheal instillations of Asian sand dust and gold nanoparticles.

The purpose of this study was to investigate a possible translocation pathway of intratracheally instilled gold nanoparticles after the induction of acute pulmonary injury by Asian sand dust. ICR mice were intratracheally instilled with 800µg Asian sand particles (CJ-2 particles) 24h before instillation of 50-nm gold nanoparticles. Lungs from mice treated with Asian sand particles and gold nanoparticles showed an acute focal inflammation with an increased expression of proinflammatory cytokines (IL-6 and TNF-α) and oxidative stress markers (Cu/Zn SOD and iNOS) in alveolar macrophages, type I alveolar epithelial cells, and endothelial cells at the alveolar walls. Electron microscopy revealed a destruction of the alveolar walls with an increased number of endocytic vesicles in the cytoplasm of both type I epithelial cells and endothelial cells; gold nanoparticles were demonstrated in these endocytic vesicles. These findings suggest that translocation of the exposed nanoparticles may be enhanced in the lung tissues with acute inflammatory changes.

Mechanisms of cadmium-induced chronotoxicity in mice.

Biological defense factors show diurnal variations in their expression levels or activities. These variations can induce the different sensitivity to external toxicants of a day. We reported earlier that mice showed clear diurnal variation of cadmium (Cd)-induced toxicity, i.e., chronotoxicity. In this report, we investigated additional new evidences for the cadmium (Cd)-induced chronotoxicity, and considered the mechanisms contributed to this chronotoxicity. Male C57BL/6J mice were injected with CdCl2 (6.4 mg/kg, one shot) intraperitoneally at 6 different time points of a day (zeitgeber time (ZT); ZT2, ZT6, ZT10, ZT14, ZT18 or ZT22) followed by monitoring the mortality until 14 days after the injection. We observed extreme difference in survival numbers: surprisingly, all mice died at ZT2 injection while all mice survived at ZT18 injection. Moreover, in non-lethal dose of Cd (4.5 mg/kg), the values of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) used as indexes of hepatotoxicity markedly increased at ZT6 injection while mostly unchanged at ZT18 injection. To consider the mechanisms of this extreme diurnal variation, we examined biochemical studies and concluded that the diurnal variation was not caused by the differences in hepatic Cd level, basal hepatic metallothionein (MT) level, and induction level or induction speed of hepatic MT. We suggested that one of the candidate determination factors was glutathione. We believe that the "chronotoxicology" for metal toxicity may be classic, yet new viewpoint in modern toxicology field.

Diurnal variation of cadmium-induced mortality in mice.

Circadian timing largely modifies efficacy of many medicinal drugs. This viewpoint has been applied in the clinical medicine, known as chronotherapy. We think this viewpoint should also be introduced into toxicology as "chronotoxicology", however, information about the diurnal variation in toxicant sensitivity is still very scarce. We present here a clear and reproducible diurnal variation of cadmium (Cd)-induced mortality in mice. Male ICR mice kept under standard condition (12 hr light/dark cycle, lights on at 08:00) were injected with CdCl(2) (7.2 mg/kg, one shot) intraperitoneally at different time points in the day (zeitgeber time (ZT) 0, 4, 8, 12, 16 or 20). Survival number was determined at 14 days after injection. Interestingly, mice were sensitive to Cd acute toxicity at ZT8, while tolerant at mid-dark to early-light phase (ZT16, ZT20 and ZT0). Hepatic GSH level showed small daily fluctuation, lowest at ZT8 and highest at ZT20, and this fluctuation was similar to the diurnal variation of Cd sensitivity. In contrast, hepatic metallothionein (MT) level was not significant in these time points, although their level also showed small daily fluctuation. Our results indicated that Cd-induced mortality had clear diurnal variation, and suggested that the hepatic GSH level was one of the important factors for determination of this Cd-induced diurnal mortality.