The basal transcriptional activity of unliganded human constitutive androstane receptor (hCAR) was shown to be repressed by the potent liver X receptor (LXR) agonist, T0901317, in a concentration-dependent manner using a reporter assay in cultured cells. T0901317 also repressed the basal transcriptional activity of both mouse and rat CAR. The certified hCAR agonist, CITCO, partially reversed this repressive effect of T0901317 on hCAR basal activity. Unlike hCAR, a three alanine insertion mutant and the splice variant 2 of hCAR require agonists, such as CITCO, to become transcriptionally active and the CITCO-induced reporter activity was repressed by T0901317. As has been previously shown for the typical hCAR inverse agonist, PK11195, T0901317 blocked the interaction of hCAR with steroid receptor co-activator 1 (SRC1). In contrast, the interaction between hCAR and nuclear receptor corepressor 1 (NCoR1) was promoted by PK11195 and T0901317. Furthermore, the hCAR-mediated basal induction of endogenous cytochrome P450 2B6 (CYP2B6) mRNA was adversely affected by co-treatment with T0901317.
9,10-Phenanthraquinone (9,10-PQ) is abundant in diesel exhaust particles (DEP) and causes oxidative protein modification in cells. We previously reported that redox cycling of 9,10-PQ with dithiols leads to the generation of an excess of superoxide (O2•−). Cu,Zn-superoxide dismutase (Cu,Zn-SOD), which dismutates O2•− to hydrogen peroxide (H2O2), is sensitive to its own product, H2O2. In this study, incubating 9,10-PQ with dithiols, but not monothiols, for 24 hr, resulted in the conversion of native Cu,Zn-SOD to its charge isomers, some of which did not show enzyme activity. Exposing Cu,Zn-SOD to 9,10-PQ in the presence of dihydrolipoic acid (DHLA), a model for low molecular weight endogenous dithiols, caused a concentration-dependent decrease in the enzyme activity. Under these conditions, copper release from the active site and Cu,Zn-SOD oxidation were detected, the evidence for which was carbonyl formation. Experiments using agents that scavenge reactive oxygen species (ROS) indicated that the hydroxyl radical (•OH) derived from H2O2 plays a critical role in the fragmentation of the enzyme. The findings presented suggest that Cu,Zn-SOD readily undergoes oxidative modification associated with activity loss, caused by ROS generated by the redox cycling of 9,10-PQ with endogenous dithiols such as DHLA and, presumably, proximal protein thiols.
ortho-Phenylphenol has been employed in post-harvest treatment of citrus fruits. Although o-phenylphenol has been reported to cause carcinomas in the urinary tract in rats, toxicity to the immune organs is still unknown. Herein, we report that administration of o-phenylphenol induces thymic atrophy and loss of thymocytes in female BALB/c mice. The influence seems to result from inhibition of the thymocyte development, because increased and decreased populations of the CD4– CD8– double-negative and CD4+ CD8+ double-positive thymocytes were observed in the o-phenylphenol-administered mice, respectively. ortho-Phenylphenol is metabolized to phenylhydroquinone by cytochrome P450 monooxygenases. Phenylhydroquinone made cell cycle of thymocytes to be arrested through reduced expression of the genes associated with G2/M phase and through phosphorylation of p53 at Ser15. Phosphorylation of p53 at Ser15 was upregulated by activation of not only ATR but also Erk1/2 and p38, leading to increase of apoptosis. Gene expression of cytochrome P450 1A1 (CYP1A1) was promoted in thymocytes from the o-phenylphenol-administered mice. Overall, our results suggest that o-phenylphenol induces CYP1A1 expression and is metabolized into phenylhydroquinone by the expressed CYP1A1 in thymocytes. The produced phenylhydroquinone in turn induces inhibition of thymocyte development through cell cycle arrest and apoptosis in the p53-dependent pathway.
Since the largely abused worldwide used of marijuana, there have been many ongoing debates regarding the adverse health effects of marijuana smoking. Marijuana smoking was recently proved to cause pulmonary toxicity by inducing genotoxic effects or generating reactive oxygen species. Because p53, a tumor suppressor gene, has an important pathophysiologic role in the regulation of lung epithelial cell DNA damage responses, we hypothesized that p53 may be involved in the oxidative stress-mediated apoptosis induced by marijuana smoking. First, we confirmed that marijuana smoke condensate (MSC) induces oxidative stress in BEAS-2B cells. We observed that reactive oxygen species (ROS) generation was increased by MSC in the DCFH-DA assay. Also, antioxidant enzyme (superoxide dismutase, catalase) activity and their mRNA expressions were up-regulated by MSC. Second, we investigated p53 involvement in the MSC-induced apoptotic pathway in BEAS-2B cells. The results showed that MSC increased caspase-3 activation and DNA fragmentation as markers of apoptosis. In addition, the mRNA levels of apoptosis-related genes (p53 and Bax) were increased by MSC and phospho-p53, along with the increase of Bax protein expression by MSC. Apoptosis and apoptosis-related gene expression were partially blocked by an inhibitor of p53-dependent transcriptional activation (pifithrin-α). The results indicate that p53 plays a role in MSC-induced apoptosis. Taken together, the findings of the present study suggest that MSC partially induces p53-mediated apoptosis through ROS generation in human lung epithelial cells and this may have broader implications for our understanding of pulmonary diseases.
Effects of the CYP3A4 intron 6 C>T (CYP3A4*22) polymorphism, which has recently been reported to have a critical role in vivo, were investigated by measuring CYP3A4 protein expression levels and CYP3A4-dependent drug oxidation activities in individual human liver microsomes in vitro. Prior to protein analysis, analysis of DNA samples indicated that 36 Caucasian subjects were genotyped as CYP3A4*1/*1 and five subjects were CYP3A4*1/*22, with a CYP3A4*22 allelic frequency of 6.1%. No CYP3A4*22 alleles were found in the Japanese samples (106 alleles). Individual differences in CYP2D6-dependent dextromethorphan O-demethylation activities in liver microsomes from Caucasians were not affected by either the CYP3A4*1/*22 or CYP3A5*1/*3 genotype. Liver microsomes genotyped as CYP3A4*1/*22 (n = 4) showed significantly lower CYP3A-dependent dextromethorphan N-demethylation, midazolam 1′-hydroxylation, and testosterone 6β-hydroxylation activities, as well as lower expression levels of CYP3A protein (28% of control), compared with those of the CYP3A4*1/*1 group (n = 19). The other polymorphism, CYP3A5*1/*3, did not show these differences (n = 4). The CYP3A4*22 polymorphism was associated with reduced CYP3A4 protein expression levels and resulted in decreased CYP3A4-dependent activities in human livers. The present results suggest an important role of low expression of CYP3A4 protein associated with the CYP3A4*22 allele in the individual differences in drug clearance.
The risk factors for breast cancer, the most common female malignant cancer, include environmental factors such as radiation, tobacco, a high-fat diet, and xenoestrogens as well as hormones. In addition, BRCA1 and BRCA2 are the most well-known genetic factors that increase risk for breast cancer. Coincidence of those environmental and genetic factors might augment the risk of tumorigenesis of breast. To verify this hypothesis, we briefly evaluated the carcinogenic potency of various environmental factors in the absence or presence of BRCA1 as a genetic factor in a normal mammary epithelial cell line, MCF10A. Many environmental factors tested increased cellular ROS level in the absence of other insult. In addition, TCDD, DMBA, 3MC, and BPA enhanced the BaP-induced ROS production. BRCA1 knockdown (BRCA1-KD) cells by siRNA significantly induced cellular accumulation of ROS compared to control cells. In this setting, the addition of paraquat, TCDD, DMBA, 2OHE2 or 4OHE2 significantly augmented ROS generation in BRCA1-KD MCF10A cells. Measurements of BaP-DNA adduct formation as a marker of DNA damage also revealed that BRCA1 deficiency leads increased DNA damage. In addition, TCDD and DMBA significantly increased BaP-DNA adduct formation in the absence of BRCA1. These results imply that elevated level of ROS is correlated with increase of DNA damage in BRCA1 defective cells. Taken together, our study suggests that several environmental factors might increase the risk of tumorigenesis in BRCA1 defective breast epithelial cells.
Zinc oxide (ZnO) nano-sized particles (NPs) are beneficial materials used for sunscreens and cosmetics. Although ZnO NPs are widely used for cosmetics, the health effects of exposure during pregnancy on offspring are largely unknown. Here we investigated the effects of prenatal exposure to ZnO NPs on the monoaminergic system of the mouse brain. Subcutaneous administration of ZnO NPs to the pregnant ICR mice (total 500 μg/mouse) were carried out and then measured the levels of dopamine (DA), serotonin (5-HT), and noradrenalin, and their metabolites in 9 regions of the brain of offspring (6-week-old) using high performance liquid chromatography (HPLC). HPLC analysis demonstrated that DA levels were increased in hippocampus in the ZnO NP exposure group. In the levels of DA metabolites, homovanillic acid was increased in the prefrontal cortex and hippocampus, and 3, 4-dihydroxyphenylacetic acid was increased in the prefrontal cortex by prenatal ZnO NP exposure. Furthermore, DA turnover levels were increased in the prefrontal cortex, neostriatum, nucleus accumbens, and amygdala in the ZnO NP exposure group. We also found changes of the levels of serotonin in the hypothalamus, and of the levels of 5-HIAA (5-HT metabolite) in the prefrontal cortex and hippocampus in the ZnO NP-exposed group. The levels of 5-HT turnover were increased in each of the regions except for the cerebellum by prenatal ZnO NP exposure. The present study indicated that prenatal exposure to ZnO NPs might disrupt the monoaminergic system, and suggested the possibility of detrimental effects on the mental health of offspring.
Nitric oxide (NO) is produced by three different isoforms of the enzyme NO synthase (NOS). NOS isoforms are expressed in many cell types, including human dental pulp cells (HDPC). NO acts as an intracellular messenger at physiological levels although it can be cytotoxic at higher concentrations. Epigallocatechin gallate (EGCG), a major green tea polyphenol, has diverse pharmacological activities in cell growth and death. This study is aimed to investigate the apoptotic mechanism by NO and effects of EGCG on NO-induced apoptosis in HDPC. Sodium nitroprusside (SNP), an NO donor, decreased the cell viability of HDPC in a dose- and time-dependent manner. EGCG was administered for 1 hr before the SNP treatment, resulting in increased cell viability and reactive oxygen species (ROS) production inhibition. Expression of Bax, a pro-apoptotic Bcl-2 family, was upregulated, whereas expression of Bcl-2, an anti-apoptotic Bcl-2 family, was downregulated in SNP-treated HDPC. SNP augmented the release of cytochrome c from mitochondria into cytosol and enhanced caspase-9, and -3 activities, a marker of the apoptotic executing stage. EGCG ameliorated caspase-9 and -3 activities and cytochrome c release increased by SNP. These results suggest that EGCG has a protective effect against NO-induced apoptosis in HDPC by scavenging ROS and modulating the Bcl-2 family.
The administration of a sodium cholate-supplemented high-fat (CAHF) diet in mice induced the predominant accumulation of cholesterol esters (CE) in the liver and biochemical and histological features of liver injury. Cholesteryl oleate was the most abundant CE found in the liver of the mice fed the CAHF diet. We examined the effect of ethyl eicosapentaenoate (EPA) on hepatic CE accumulation and liver injury in the mice fed the CAHF diet. The EPA supplementation suppressed the elevation in the level of cholesteryl oleate in the liver. The expression levels of sterol O-acyltransferase-2 and stearoyl-CoA desaturase-1 mRNA in the liver were elevated in the mice fed the CAHF diet, but they were normalized by the EPA supplementation. However, the elevation in serum transaminase activity, the sign of inflammatory cell exudation and inflammatory gene responses in the liver of the mice fed the EPA-supplemented diet were enhanced compared with those of the mice fed the CAHF diet. We demonstrated that EPA supplementation attenuated CE accumulation but aggravated liver injury and liver inflammation in the mice fed the CAHF diet.
Gene expression profiles in the amygdala of juvenile rats were compared between the two autistic rat models for mechanistic insights into impaired social behavior and enhanced anxiety in autism. The rats exposed to VPA by intraperitoneal administration to their dams at embryonic day (E) 12 were used as a model for autism (E2IP), and those by subcutaneous administration at postnatal day (P) 14 (P14SC) were used as a model for regressive autism; both of the models show impaired social behavior and enhanced anxiety as symptoms. Gene expression profiles in the amygdala of the rats (E12IP and P14SC) were analyzed by microarray and compared to each other. Only two genes, Neu2 and Mt2a, showed significant changes in the same direction in both of the rat models, and there were little similarities in the overall gene expression profiles between them. It was considered that gene expression changes per se in the amygdala might be an important cause for impaired social behavior and enhanced anxiety, rather than expression changes of particular genes.
Orphenadrine (ORPH), an anticholinergic agent, is a cytochrome P450 (CYP) 2B inducer. CYP2B inducers are known to 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 ORPH and to clarify its possible mechanism of action. Male rats were given a single intraperitoneal injection of N-diethylnitrosamine (DEN) as an initiation treatment. Two weeks after DEN administration, rats were fed a diet containing ORPH (0, 750, or 1,500 ppm) for 6 weeks. One week after the ORPH-administration rats were subjected to two-thirds partial hepatectomy for the acceleration of hepatocellular proliferation. The number and area of glutathione S-transferase placental form-positive foci significantly increased in the DEN-ORPH groups. Real-time RT-PCR revealed increased mRNA expression levels of Cyp2b1/2,Mrp2 and Cyclin D1 in the DEN-ORPH groups and of Gpx2 and Gstm3 in the DEN-High ORPH group. Microsomal reactive oxygen species (ROS) production and oxidative stress markers such as thiobarbituric acid-reactive substances and 8-hydroxydeoxyguanosine were increased in the DEN-High ORPH group. Immunohistochemically, constitutively active/androstane receptor (CAR) were clearly localized in the nuclei of hepatocytes in the DEN-ORPH groups. These results suggest that ORPH causes nuclear translocation of CAR resulting in the induction of the liver tumor-promoting activity. Furthermore, oxidative stress resulting from ROS production is also involved in the liver tumor-promoting activity of ORPH.
Phenobarbital (PB) and orphenadrine (ORPH) are cytochrome P450 (CYP) 2B inducers and 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 ORPH co-administration. Twelve male rats per group were given an intraperitoneal injection of N-diethylnitrosamine (DEN) for initiation. Two-week after DEN administration, rats were given PB (60 or 120 ppm in drinking water), ORPH (750 or 1,500 ppm in diet) or 60 ppm PB+750 ppm ORPH for 6-week. One-week after the PB/ORPH treatment, all rats were subjected to two-thirds partial hepatectomy. To evaluate the effect of the combined administration, we used two statistical models: a heteroadditive model and an isoadditive model. In the heteroadditive model, the net values of the number and area of glutathione S-transferase placental form (GST-P) positive foci, Cyp2b1/2, Gstm3 and Gpx2 mRNA levels, microsomal reactive oxygen species (ROS) production and thiobarbituric acid-reactive substances level in the PB+ORPH group were significantly higher than the sum of the net values of those in the Low PB and Low ORPH groups. In the isoadditive model, the average values of the area of GST-P positive foci and PCNA positive hepatocyte ratio and Gstm3 mRNA level in the PB+ORPH group were significantly higher than the average values of those in the High PB and High ORPH groups. These results suggest that PB and ORPH co-administration causes synergistic effects in liver tumor-promoting activity in rats resulting from oxidative stress due to enhanced microsomal ROS production.
β-N-methylamino-L-alanine (L-BMAA) is a neurotoxic amino acid produced by most cyanobacteria, which are extensively distributed in different environments all over the world. L-BMAA has been linked to a variety of neurodegenerative diseases. This work aims to analyze the toxicological action of L-BMAA related to alterations observed in different neurodegenerative illness as Alzheimer disease and amyotrophic lateral sclerosis. Our results demonstrate that neuroblastoma cells treated with L-BMAA show an increase in glycogen synthase kinase 3 β (GSk3β) and induce accumulation of TAR DNA-binding protein 43 (TDP-43) truncated forms (C-terminal fragments), phosphorylated and high molecular weight forms of TDP-43, that appears frequently in some neurodegenerative diseases.
For molecular analysis in anatomically-specific brain regions for rodent studies, it is necessary to establish a fast and accurate procedure for tissue sampling to achieve high integrity and expression fidelity of extracted molecules. The present study was performed to examine suitability of whole brain fixation with methacarn and subsequent tissue sampling using punch-biopsy devices for gene expression analysis in rats. After fixation, each specific region, i.e., hippocampal dentate gyrus, corpus callosum, cingulate cortex or cerebellar vermis was collected, and the integrity and variability of expression data of extracted total RNAs and polypeptides were examined. Methacarn fixation, acetone fixation, and unfixed tissues were compared. Methacarn fixation resulted in high integrity of total RNAs sufficient for conducting global expression analysis and superior in terms of uniformity in the integrity among brain regions to that of acetone fixation. Extracted polypeptide after methacarn fixation revealed similar integrity to that without fixation or with acetone fixation. Methacarn fixation resulted in lower mRNA expression variability between samples than acetone fixation in microarray analysis. The fidelity of polypeptide expression was mostly equivalent between methacarn and acetone fixation in 2-dimensional differential in-gel electrophoresis, although the expression levels of a small number of polypeptides from acetone-fixed tissues were affected. These results suggest that whole brain fixation with methacarn retains advantages for global analyses of mRNAs and polypeptides in rodent studies.
One of the toxicities caused by 1-Methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP) is damage to dopaminergic neurons. When injected into C57BL/6J mice, MPTP penetrates into the brain and is converted to 1-methyl-4-phenylpyridinium (MPP+) by monoamine oxidase (MAO)-B in astrocytes. MPP+ has high affinity for the dopamine transporter (DAT) on dopaminergic neurons, and is taken up into the cell to cause cell death. There have been relatively few researches on the acute MPTP toxicity to embryonic or newborn mice. In the present study, we attempted to evaluate the influence of MPTP and MPP+ on embryonic and newborn mice by measuring sequential changes in major indexes of MPTP toxicity and MPTP metabolism; levels of Tyrosine Hydroxylase (TH), DAT, MAO-A and MAO-B. In addition, we measured the levels of dopamine and its metabolites, 3,4-dihydroxy-phenylacetic acid (DOPAC) and homovanillic acid (HVA), in the brain of newborn mice. A single injection of MPTP and MPP+ reduced the levels of dopamine and its metabolites, DOPAC and HVA, in the brain of newborn mice about 6-12 hr after the injection. Similarly the levels of mRNAs and proteins of DAT and TH were lowered in the brain of embryonic and newborn mice as well. The levels of these indexes were generally recovered at 24 hr after injection, indicating that the neurotoxicity induced by a single injection of MPTP or MPP+ is temporary and recoverable in embryonic and newborn mice. By contrast, no significant changes in the expression levels of MAO-A and MAO-B were observed in either MPTP- or MPP+-treated mice.
A series of safety assessments were performed on hydrogenated resistant maltodextrin prepared by converting the reducing terminal glucose of resistant maltodextrin into sorbitol. The reverse mutation assay did not show mutagenicity. Acute and 90-day subchronic oral toxicity studies in rats showed no death was observed in any groups, including the group receiving the highest single dose of 10 g/kg body weight or the highest dose of 5 g/kg body weight per day for 90 days. Mucous or watery stools were observed in the hydrogenated resistant maltodextrin treatment group on the acute study, which were transient and were associated with the osmotic pressure caused by intake of the high concentrations. Subchronic study showed dose-dependent increases in the weights of cecum alone, cecal contents alone, and cecum with cecal contents as well as hypertrophy of the cecal mucosal epithelium, which are considered to be common physiological responses after intake of indigestible carbohydrates. These results indicated that the no observed adverse effect level (NOAEL) of hydrogenated resistant maltodextrin was 10 g/kg body weight or more on the acute oral toxicity study and 5.0 g/kg body weight/day or more on the 90-day subchronic repeated oral toxicity study in rats. Further study performed in healthy adult humans showed that the acute no-effect level of hydrogenated resistant maltodextrin for diarrhea was 0.8 g/kg body weight for men and more than 1.0 g/kg body weight for women. The results of the current safety assessment studies suggest that hydrogenated resistant maltodextrin is safe for human consumption.
Triclosan (TCS) is a chemical compound used in household products as biocide. However, their pulmonary toxicity has been unclear. Thus, the purpose of this study was to investigate the possibility of injury to the lung by inhalation of TCS. Rats were exposed to TCS by single intratracheal instillation of 10 µg/B.W. kg for the low-dose group and 1,000 µg/B.W. kg for the high-dose group, respectively. TCS induced increase in the level of total cell (TC) count, polymorphonuclear leukocytes (PMNs), total protein (TP), lactate acid dehydrogenase (LDH), tumor necrosis factor alpha (TNF-α) and interleukin-6 (IL-6) in bronchoalveolar lavage fluid (BALF) at 1 day after instillation. However, most pulmonary toxicity marker levels except TP in BALF were restored 14 days after instillation. In addition, TCS led to reduction of cell viability with morphological change in lung eptiehelial cells (L2 cell). Therefore, TCS may affect responses of acute inflammation and permeability in the lung.
Although covalent modification of protein thiols by electrophilic metals is implicated in disruption of protein functions associated with toxicity, there are limited methods available to detect such modifications. In the present study, we established a convenient method to assess modification of protein thiols by electrophiles, referred to as a biotin-PEAC5-maleimide (BPM)-labeling assay. In this assay, protein S-modification by electrophiles can be estimated by a decrease in protein modification by BPM, a thiol reactive probe. Using methylmercury (MeHg) as a model electrophilic metal, thiol modification of cellular proteins was detected by the BPM-labeling assay in SH-SY5Y cell lysates and primary mouse hepatocytes. The sensitivity and reliability of the assay was confirmed by atomic absorption spectrometry with recombinant Keap1 as a model thiol protein. This assay was applied to not only MeHg but also to other metals such as cadmium and lead. We also established a BPM-precipitation assay with avidin-agarose beads to separate BPM-modified cellular proteins followed by detection with the individual antibodies. This assay was available for detecting MeHg-induced S-modification of cellular Keap1 in SH-SY5Y cells. Taken together, we have developed reliable simple methods to estimate protein S-modification by electrophilic metals.
Recent studies have reported that bisphenol A (BPA) influences brain development in fetal exposure to mice. The X-chromosome codes many neurodevelopment-related genes leading to abnormal development, such as mental retardation and intellectual deficiency. For females, most of expressions of X-linked genes are regulated by X-chromosome inactivation (XCI), which occurs during fetal period, and this mechanism is regulated by Xist and its antisense, Tsix. To clarify the possibility of X-mediated effect as a mechanism of neurodevelopmental disorders by BPA, pregnant ICR mice were orally administered 0.02 or 50 mg/kg of BPA on gestational days 6 and 15. Postnatally at days 2, 4 and weeks 3 and 7, mRNA expression of XCI-regulating factors (Xist and Tsix), X-linked neurodevelopment-related genes (Fmr1, Gdi1, Nlgn3, Pak3 and Ophn1), and sexual differentiation-related genes (ERα, ERβ and AR) were examined in cerebrums of female pups. Anogenital distance (AGD) and serum estradiol were also examined.In the 50 mg/kg exposed-group, reduced Xist, Fmr1, Gdi1, Nlgn3, and Pak3 and increased Tsix were observed simultaneously. Moderately reduced Xist, Gdi1, Nlgn3 and Pak3 were observed at 0.02 mg/kg BPA. ERα, ERβ and AR expression changes, shortened AGDs and reduced estradiol levels were observed in each exposure group.Fetal exposure to BPA changed expression of XCI-regulating factors and may alter the expression levels of X-linked neurodevelopment-related genes disrupting the XCI mechanism and function. This X-mediated effect is considered one of the mechanisms of various BPA-induced neurodevelopmental disorders.
The in vitro effects of 2 representative mycotoxins, T-2 toxin and deoxynivalenol (DON), of trichothecene group on the electron transport system (ETS) of mitochondria in rat cardiomyocytes were investigated by measuring oxygen consumption rates (OCR). The ATP-linked OCR and the reserve capacity (RC) of the mitochondria ETS were quantified by a “mitochondria stress test” which was estimated by the OCR responses to oligomycin and carbonyl cyanide-p-trifluoromethoxyphenylhydrazone, with an extracellular flux analyzer. The basal OCR was significantly inhibited by the application of T-2 toxin at concentrations of 6 × 10-1 to 6 × 10-5 μM and DON at concentrations of 0.78 to 100 μM for 24 hr. The threshold of cardiomyocyte toxicity was estimated to be between 6.0 × 10-6 and 6.0 × 10-5μM for T-2 toxicity on both ATP-linked OCR and RC and between 0.39 and 0.78 μM on ATP-linked OCR or between 1.56 and 3.13 μM on RC for DON. The decrease in OCR of cardiomyocytes exposed to T-2 toxin with a concentration of 6.0 × 10-3 and6.0 × 10-4 μM was significantly inhibited by antioxidants, catalase and vitamin C. In conclusion, the present study demonstrated, through the direct and real-time measurement of respiratory function in mitochondria, that a marked inhibition of mitochondrial ETS function in cardiomyocytes was induced by T-2 toxin and DON and that the mitochondrial dysfunction by T-2 toxin was largely associated with oxidative stress.
We examined the genotoxicity of magnetite nanoparticles (primary particle size: 10 nm) on human A549 and Chinese hamster ovary (CHO) AA8 cells. Six hours’ treatment with the particles dose-dependently increased the frequency of micronuclei (MN) in the A549 and CHO AA8 cells up to 5.2% and 5.0% at a dose of 200 µg/ml (34 µg/cm2), respectively. In A549 cells, treatment with the nanoparticles (2 µg/ml) for 1 hr induced H2AX phosphorylation, which is suggestive of DNA double strand breaks (DSB). Treating CHO AA8 cells with 2 µg/ml (0.34 µg/cm2) magnetite for 1 hour resulted in a five times higher frequency of sister chromatid exchange (SCE) than the control level. We detected reactive oxygen species (ROS) in CHO cells treated with the particles. These findings indicate that magnetite nanoparticles induce ROS in mammalian cells, leading to the direct or indirect induction of DSB, followed by clastogenic events including MN and SCE.
Lead is known to induce neurotoxicity, particularly in young children, and GluR2, an AMPA-type glutamate receptor subunit, plays an important role in neuronal cell survival. Therefore, we hypothesized that altered GluR2 expression plays a role in lead-induced neuronal cell death. To test this idea, we investigated the effect of exposure to 5 and 20 µM lead for 1-9 days on the viability and GluR2 expression of primary-cultured rat cortical neurons. The number of trypan-blue stained cells was increased by exposure to 5 µM lead for 9 days or 20 µM lead for 7-9 days, and LDH release was increased after exposure to 20 µM lead for 9 days. GluR2 expression was reduced by exposure to 5-100 µM lead, but not 0.1-1 µM lead, for 9 days. Immunocytochemistry also confirmed that GluR2 expression was decreased in the presence of lead. Application of 50 ng/ml brain-derived neurotrophic factor (BDNF) led to a recovery of lead-induced neuronal cell death, accompanied with increased GluR2 expression. Our results suggest that long-term exposure to lead induces neuronal cell death, in association with a decrease of GluR2 expression.