Recently, scientific evidence supports a connection between environmental chemical exposures, which includes insecticides, and development of type 2 diabetes. However, there is limited information about the link between influences of neonicotinoid insecticides and incidence of type 2 diabetes. Thus, the purpose of the study was to determine effects of imidacloprid, a neonicotinoid insecticide, on glucose metabolism. Three different cell models were used; adipocytes (3T3-L1), hepatocytes (HepG2), and myotubes (C2C12). These cells were treated with imidacloprid (0, 10, and 20 μM) for 4-6 days followed by treatment with insulin for 15 min to determine responses. Insulin stimulated glucose uptake was reduced by imidacloprid in all three cell culture models. Treatment with imidacloprid reduced phosphorylation of protein kinase B (AKT), one of the major regulators of insulin signaling, without changing overall AKT expression. Subsequently, imidacloprid reduced phosphorylation of ribosomal S6 kinase (S6K), which is a downstream target of AKT and also a feed-back inhibitor of insulin signaling. These results suggest that imidacloprid could induce insulin resistance by affecting the insulin signaling cascade, particularly up-stream of AKT, in adipocytes, liver, and muscle.
Microcystin-leucine arginine (MC-LR), a cyclic heptapeptide produced by cyanobacteria, has strong reproductive toxicity. The present study was designed to elucidate the mechanism of declines in sperm quality as a result of exposure to MC-LR by using spermatogenic cells as a model system. MC-LR was intraperitoneally administered to male rats daily at 0, 50 and 100 µg/kg body weight for one week. Results showed that changes occurred in the structural of testis, the tubular diameter and the relative weight of the testes was significantly decreased following treatment with 100 μg/kg. Major differences in apoptosis and proliferation of testicular cells were observed at the100 μg/kg MC-LR. The gene expression levels of testis-specific histone 2B (TH2B) and transition protein 2 (TP2) were both significantly decreased. Meanwhile, the stem cell factor receptor (c-kit) was increased after exposure to 50 or 100 μg/kg MC-LR. This study demonstrated that MC-LR can alter the apoptosis, proliferation and differentiation of spermatogenic cells in vivo.
Methamphetamine (METH) is a powerful and toxic psychostimulant that is abused worldwide. Although many studies of its toxic functions have been done on animals and humans, the mechanism is still poorly understood. In addition, the doses of METH examined have often been low. Here, we investigated the effects of intoxication due to administration of 20 mg/kg METH on neuronal activity. The mice showed hyperthermia and stereotyped behavior during 60 min after injection. We examined plasma stress hormone levels, which indicated that exposure to METH stimulated the hypothalamic-pituitary-adrenal (HPA) axis and caused release of stress hormones soon after injection. The maximum levels of adrenocorticotropic hormone and corticosterone occurred 10 and 60 min, respectively, after injection. We examined c-Fos protein in 16 different brain regions at 60 min post injection to identify potential brain regions subject to the stimulant effect. Nine regions, including the anterior hypothalamic area, medial preoptic area, lateral hypothalamic area, paraventricular thalamic nucleus, lateral anterior hypothalamic nucleus, lateral septum, striatum, nucleus accumbens, and amygdala, showed a significant increase in c-Fos expression, while the other seven regions did not. These results indicate that responsive neurons in the regions containing c-Fos immunoreactivity (Fos-IR) may undergo cellular reaction to high-dose METH administration. The present study provides support for a relationship among hyperthermia, the HPA axis and neuronal activities in limited brain regions on exposure to 20 mg/kg METH.
Phenobarbital (PB) is a cytochrome P450 (CYP) 2B inducer, and piperonyl butoxide (PBO) is a CYP1A/2B inducer. These inducers have liver tumor-promoting effects in rats. In this study, we performed a rat two-stage liver carcinogenesis bioassay to examine the tumor-promoting effect of PB and PBO co-administration. Male rats received an intraperitoneal injection of N-diethylnitrosamine (DEN) for initiation. Two weeks after DEN administration, rats were given PB (60 or 120 ppm in drinking water), PBO (1,250 or 2,500 ppm in diet) or 60 ppm PB+1,250 ppm PBO for 6 weeks. One week after the PB/PBO treatment, all rats were subjected to a two-thirds partial hepatectomy. To evaluate the effect of the combined administration, we used two statistical additive models. In the isoadditive model, the average values of the area of GST-P positive foci in the PB+PBO group were significantly lower than those in the High PB or High PBO groups. In the heteroadditive model, the net values of Cyp1a1 mRNA level and microsomal reactive oxygen species (ROS) production in the PB+PBO group were significantly lower than the sum of those in the Low PB or Low PBO groups. On the contrary, there was no interactive effect in the PCNA-positive hepatocyte ratio, mRNA levels of Cyp2b1/2, Gstm3, Gpx2 and Nqo1, and the level of thiobarbituric acid-reactive substances in the PB+PBO group. These results suggest that PB and PBO co-administration causes suppressive effects in liver tumor-promoting activity in rats resulting from inhibited microsomal ROS production because of suppression of CYP1A induction.
Methylmercury (MeHg) and polychlorinated biphenyls (PCBs) are environmentally persistent neurodevelopmental toxicants. In Japan, the most common source of human exposure is the consumption of contaminated fish and seafood. We investigated the accumulation of MeHg and PCBs in the brains of dams and offspring mice maternally exposed to MeHg and/or PCBs. Pregnant mice (C57BL/6Cr) were assigned to one of four exposure groups: control, MeHg alone (MeHg in diet at 5 mg/kg as Hg), PCB alone (Aroclor1254 by gavage at the dose of 18 mg/kg body weight/3 days) and MeHg+PCB. Levels of MeHg and PCBs were measured in the whole brains of dams and offspring mice on postnatal day 21 (PND21) and at 9 weeks of age. Total mercury, MeHg and PCB congener concentrations were determined by CVAAS, GC-ECD and HRGC/HRMS, respectively. For the mercury concentrations, there were no significant differences between MeHg alone and MeHg+PCB except for pups at 9 weeks. The maternal PCB levels were not significantly different between MeHg+PCB and PCB alone. In pup brain on PND21, MeHg+PCB resulted in a significantly higher PCB level than PCB alone. Although the levels of lightly chlorinated (= 4CBs) homologues were lower for MeHg+PCB than for PCB alone, those of highly chlorinated (>= 5CBs) homologues were significantly higher on PND21 for MeHg+PCB. The PCB composition in dams and pups shifted to higher chlorinated homologues compared with the composition of administered Aroclor1254. For these reasons, further detailed studies are necessary to clarify the interactional effects of PCB metabolism after coexposure to MeHg and PCBs.
Sodium dodecyl sulfate (SDS) and sodium dodecyl benzenesulfonate (SDBS) are widely used anionic surfactants in household, industrial, and institutional cleaners. Although there are many reports of their toxic effects, few studies have focused on the pharmacological properties of these surfactants. Peroxisome proliferator-activated receptor (PPAR) γ is a transcriptional factor belonging to the nuclear receptor superfamily. The ligands of PPARγ regulate its transcriptional activity and modulate many biological functions, including adipocyte differentiation and lipid metabolism. In this study, we investigated the ligand activities of SDS and SDBS for nuclear receptors using time-resolved fluorescence resonance energy transfer-based coactivator recruitment assays. SDS and SDBS showed selective ligand activities for PPARγ and these ligand activities were eliminated by a PPARγ antagonist. SDS and SDBS also promoted adipocyte differentiation accompanied by upregulation of adipocyte-specific gene expression in 3T3-L1 preadipocytes. These findings reveal novel actions of anionic alkyl surfactants as PPARγ ligands.
Metabolomic analysis was performed using the cerebellum of methylmercury-treated mice to elucidate the molecular mechanisms underlying methylmercury-induced cerebellar dysfunction. Methylmercury administration led to significant increases in the levels of 11 low molecular weight metabolites and significant reductions in the levels of 29 others, including several metabolites produced by amino acid and purine metabolism. Non-significant decreases in metabolites involved in the TCA cycle and in glutathione metabolism were also observed.
We assessed the effects of D-penicillamine (D-PA) on cross-linkages in elastin and vaso-regulatory function in rats. After administration of D-PA at a dose of 100 mg/kg/day for 7 weeks to adult and young rats, the thoracic aortas were isolated. The elastic lamellae in the aorta were disrupted histopathologically in all the treated groups. The content of cross-linkages in elastin, i.e. desmosine and isodesmosine, which gives elasticity to the aortic wall, was significantly reduced in the D-PA treated groups versus the control groups. On the other hand, the content of pyridinoline as a marker of insoluble collagen was significantly reduced in the D-PA treated groups, even though the total collagen content was not changed. In addition, after 7 weeks of treatment with D-PA, the change between systolic blood pressure before and after sympathetic stimulation (Δ-SBP) by L-epinephrine was about 2.5-fold larger than that in the control group. Similar results were obtained using angiotensin II or ouabain instead of L-epinephrine. These findings demonstrated that D-PA disrupted elastic lamellae of the rat aorta by reduction of the cross-linkages in elastin and collagen, which caused dysfunction of vaso-regulation. Also, they suggested the possibility that long-term treatment with D-PA in patients could cause a decrease in vaso-regulatory function and could increase the risk of cardiovascular events.
We assessed the effects of rofecoxib on cross-linkage formation in elastin and vaso-regulatory function in rats. After administration of rofecoxib at a dose of 10 mg/kg for 7 weeks to young rats and for 7 and 10 weeks to adult rats, thoracic aortas were isolated. The elastic lamellae in the aortas were disrupted histopathologically in all the treated groups. However, the content of cross-linkages in elastin, i.e. desmosine and isodesmosine, which give elasticity to the aortic wall, was not significantly different between the rofecoxib treated and control groups. On the other hand, although the baseline blood pressure was not changed during the treatment period in both young and adult rats, after several weeks of treatment with rofecoxib the change between systolic blood pressure before and after sympathetic stimulation by L-epinephrine was 2 to 3-fold larger than that in the control group. Similar results were obtained using angiotensin II instead of L-epinephrine. The exposure to rofecoxib (area under the plasma concentration-time curve) of rats after single administration was a few times higher than that of humans in clinical use. These findings indicate that rofecoxib did not directly inhibit formation of cross-linkages in elastin of the aorta in rats. However, the treatment with rofecoxib for several weeks disrupted elastic lamellae and caused depression of vaso-regulatory function in rats, which could bring on an increased risk of cardiovascular events in human.
Nonylphenol (NP), a widely distributed, toxic, endocrine-disrupting chemical, has estrogenic properties. However, its cardiac effects remain unclear. In this study, the effects of NP on isolated guinea pig hearts were studied in three separate experiments. First, hearts were perfused with 10-7 M NP or 10-5 M NP to determine whether NP was toxic to isolated healthy hearts. Next, hearts were subjected to 50 min of ischemia and 60 min of reperfusion (I50R60) with 10-7 M NP or 10-5 M NP to determine whether NP could aggravate ischemia/reperfusion (I/R) injury. Finally, the interaction of the cardio-protective agent 17β-estradiol (E2) with NP was studied using 10-7 M E2, 10-7 M E2 plus 10-7 M NP, and 10-7 M E2 plus 10-5 M NP. Heart rate (HR) and coronary flow (CF) were significantly decreased and the leakage of lactate dehydrogenase (LDH) in effluent was increased in the 10-5 M NP group. However, there were no obvious changes in HR, CF, the leakage of LDH or creatine kinase (CK), or the activity of superoxide dismutase in either of the NP treatments in the I50R60 model. Treatment with 10-7 M E2 attenuated I/R injury by increasing HR, decreasing the leakage of LDH and CK, and decreasing infarct size. However, these effects were reversed by both concentrations of NP. These data demonstrate that NP had direct toxic effects on normal hearts and NP might disrupt the cardio-protective effects of E2 on I/R injury.
Nevirapine is a non-nucleoside reverse transcriptase (RT) inhibitor used for the treatment of AIDS and the prevention of mother-to-child transmission of HIV-1. Despite its therapeutic benefits, treatment with nevirapine has been associated with significant incidences of liver and dermal toxicity. The present study examined the effects of nevirapine on cell growth and death in human hepatocyte HepG2 cells and THLE2 cells and the possible pathways involved in these effects. The concentrations of nevirapine inhibiting 50% cell growth were similar for both cell lines. Nevirapine (0-250 µM) treatment caused a slight increase in the amount of lactate dehydrogenase released into the medium. Apoptotic cell death did not contribute to the decrease in viable cells. Exposing of HepG2 cells to nevirapine caused G2/M phase arrest, and the activity of senescence-associated β-galactosidase was not altered. In THLE2 cells, the percentage of cells in G1/G0 phase was increased and cellular senescence was induced in a concentration-dependent manner. Endogenous non-telomeric RT activity was not detected in either cell line. Western blot analysis indicated lower levels of p53 and phospho-p53 (ser15) in HepG2 cells as compared to THLE2 cells; no significant changes in p53 or phospho-p53 (ser15) were noted with nevirapine treatment. These data demonstrate that nevirapine inhibits cell growth, induces cell cycle arrest at different phases, and has different effects on cellular senescence in HepG2 cells and THLE2 cells. The differential responses appear to be related to differences in the basal levels of p53 in the HepG2 cells and THLE2 cells.
Exposure to excess amounts of manganese causes toxic effects, including neurological symptoms such as Parkinsonism. However, endogenous factors involved in the protection against manganese toxicity remain unclear. Previously, we showed that rat basophilic leukemia RBL-2H3 cells are highly sensitive to MnCl2 compared with other rat cell lines. To identify the genes involved in resistance to manganese toxicity, two lines of Mn-resistant cells showing resistance to 300 µM MnCl2 (RBL-Mnr300) and 1200 µM MnCl2 (RBL-Mnr1200) were developed from RBL-2H3 cells by a stepwise increase in MnCl2 concentration in the medium. Microarray analyses were carried out to compare gene expression between parental RBL-2H3 cells and RBL-Mnr300 or RBL-Mnr1200 cells. Five genes exhibited more than 10-fold up-regulation in both RBL-Mnr300 and RBL-Mnr1200 cells, and 24 genes exhibited less than 0.1-fold down-regulation in both Mn-resistant cell lines. The S100a9 and S100a10 genes, encoding the calcium-binding S100A9 and S100A10 proteins, respectively, were found among the three most down-regulated genes in both Mn-resistant cell lines. The marked decreases in mRNA levels of S100a9 and S100a10 were confirmed by real-time RT-PCR analyses. Further characterization and comparison of these Mn-resistant cells may enable the identification of novel genes that play important roles in the modification of manganese toxicity.
The substance 3-amino-5-mercapto-1,2,4-triazole (AMT, CAS No. 16691-43-3) was daily administered by gavage to Crl:CD (SD)IGS rats at doses of 0 (control), 10, 50, and 250 mg/kg bw/day. Males (12/group) were treated for a total of 42 days beginning 14 days before mating. Females (12/group) were treated beginning 14 days before mating to day 4 of lactation throughout the mating and gestation periods. No deaths occurred in males but three females died on day 23 of gestation at 250 mg/kg/day. Only temporary decreases in body weight and food intake were found in both sexes at 250 mg/kg/day. There were no considerable changes in general appearance, the functional battery tests, biochemical analysis or urinalysis. Anemia was observed in both sexes at 250 mg/kg/day. The relative weight of thyroid glands was significantly increased in both sexes at 250 mg/kg/day and hypertrophy of thyroid follicular cells was observed in 50 and 250 mg/kg/day males and 250 mg/kg/day females. As this effect on thyroid glands was considered to be the major toxicity, the possible mechanism was discussed comparing with the toxicity of structural similar analogs. Other histopathological changes in males were hypertrophy of centrilobular hepatocytes at 250 mg/kg/day, and anterior pituitary glands at 50 mg/kg/day and more. Vacuolization in renal tubular epithelium of females was observed at 50 and 250 mg/kg/day. For reproduction, the gestation period was prolonged and the delivery index was decreased at 250 mg/kg/day. The number of pups born and the birth index were also reduced. It was thus concluded that the NOAEL for repeated-dose toxicity was 10 mg/kg/day based on the thyrotoxicity and renal toxicity, and that the NOAEL for reproductive/developmental toxicity was 50 mg/kg/day based on the reduced number of offspring, etc.
Emerging evidence suggests that chronic exposure to DDT and its derivatives is associated with a variety of human disorders such as anemia. The present study demonstrated that p,p′-DDT caused microcystic anemia in a dose-dependent manner (0, 5, 50, and 500 ppm) in the long-term study up to 2 years. To elucidate the mechanism(s) by which p,p′-DDT induces anemia, certain hematological parameters were assessed in rats fed specific doses of p,p′-DDT for 2 weeks, and the effect of lipopolysaccharide on anemia of inflammation was also examined in p,p′-DDT-treated rats. The parameters included the content of hemoglobin per reticulocyte, mean corpuscular volume of reticulocytes and mature erythrocytes, corpuscular hemoglobin concentration mean of mature erythrocytes, and saturation levels of transferrin and iron. During the 2-week treatment period, hypochromic microcytic reticulocytes and hypochromic normocytic mature erythrocytes were observed in p,p′-DDT-treated rats, with no evidence of alteration in plasma iron levels. p,p′-DDT enhanced microcytosis of reticulocytes, as well as mature erythrocytes, which occurred due to severe hypoferremia resulting from anemia of inflammation; however, plasma iron levels were attenuated probably through the inhibition of interleukin-6. Our data suggests that long-term treatment with p,p′-DDT induces microcytic anemia, possibly because of the impairment of iron utility in erythrocytes.
The purpose of this study was to investigate the effects of di-(2-ethylhexyl) phthalate (DEHP) treatment on MyoD and myogenin expression and myotube formation in the murine C2C12 cells. Myogenic differentiation is principally regulated by activities of myogenic regulatory factors, such as MyoD and myogenin, leading the elongation and fusion of mononucleated myoblasts into multinucleated myotubes. In the present study, myogenic differentiation of C2C12 cells was induced by serum deprivation with medium containing vehicle or DEHP (10, 100, 1,000 μg/ml) for 5 days. Using 3-(4,5-dimethylthiazol-2-yl) 2,5-diphenyltetrazolium bromide (MTT) assay clearly demonstrated cell viability was not affected by DEHP at any given dose. At the dose of 1,000 μg/ml DEHP, the elongation of multinucleated myotubes, and the percent of nuclei incorporated into myosin heavy chain (MyHC)-stained myotubes were markedly reduced. In addition, immunoblotting revealed expression of muscle specific marker MyHC, as well as myogenic regulatory factors MyoD and myogenin, were reduced in DEHP-treated myotubes during myogenic differentiation. Taken together, the results showed that DEHP may impair myogenic differentiation through repression of myogenic regulatory factors, such as MyoD and myogenin, resulting in a reduction of MyHC expression. This in vitro study suggests that DEHP may be an environmental risk factor for myogenesis.
1,2-Naphthoquinone (1,2-NQ) is found to be an electrophile contaminated in the atmosphere. Although we found that 1,2-NQ activates epidermal growth factor receptor (EGFR) coupled to inhibition of protein tyrosine phosphatase 1B (PTP1B) activity through covalent modification of Cys121 in human epithelial A431 cells, modulation of its downstream signal transduction pathway caused by 1,2-NQ remains to be elucidated. In the present study, we examined whether 1,2-NQ could affect such cellular signaling in human pulmonary A549 cells. Exposure of A549 cells to 1,2-NQ increased EGFR phosphorylation, resulting in activation of MEK/ERK signaling that was blocked by either PD15035 or PD98059. As a result, DNA binding activity of transcription factor AP-1 was enhanced during exposure to 1,2-NQ in the cells. These results suggest that the atmospheric electrophile phosphorylates EGFR, thereby activating the MEK/ERK/AP-1 signal transduction pathway in A549 cells.
Cadmium (Cd) is a toxic heavy metal and chronic exposure causes kidney injury. This study used DNA microarray analysis to examine gene expression in the kidney of mice chronically exposed to Cd. Female C57BL/6J mice were fed a 300 ppm Cd-containing diet or a control diet for 12 months. In comparison with control mice, the expression levels of 32 genes, including Hmox1 and Mt2, were elevated more than 2.0-fold, whereas 113 genes, including transport- and ubiquitination-related genes, were reduced less than 0.5-fold.
The central nervous system (CNS) is known to be sensitive to pollutants during its development. Uranium (U) is a heavy metal that occurs naturally in the environment as a component of the earth’s crust, and populations may therefore be chronically exposed to U through drinking water and food. Previous studies have shown that the CNS is a target of U in rats exposed in adulthood. We assessed the effects of U on behavior and cholinergic system of rats exposed from birth for 10 weeks at 10 mg.L-1 or 40 mg.L-1. For behavioral analysis, the sleep/wake cycle (recorded by telemetry), the object recognition memory and the spatial working memory (Y-maze) were evaluated. Acetylcholine (ACh) and acetylcholinesterase (AChE) levels were evaluated in the entorhinal cortex and hippocampus. At 40 mg.L-1, U exposure impaired object recognition memory (-20%), but neither spatial working memory nor the sleep/wake cycle was impaired. A significant decrease was observed in both the ACh concentration (-14%) and AChE activity (-14%) in the entorhinal cortex, but not in the hippocampus. Any significant effect on behaviour and cholinergic system was observed at 10 mg U.L-1. These results demonstrate that early exposure to U during postnatal life induces a structure cerebral-dependant cholinergic response and modifies such memory process in rats. This exposure to U early in life could have potential delayed effects in adulthood.
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