[Investigating erythrocyte hemolysis assay use for proinflammatory potential prediction of silica particles]

OBJECTIVES

Crystalline silica, which is a causative agent of silicosis (an occupational disease), is manufactured in a variety of products (particles) with different particle characteristics, such as size and surface properties. In Japan, the products are currently uniformly controlled as crystalline silica, which is a substance subject to labeling and notification requirements. However, since the toxicity of silica particles reportedly varies depending on its characteristics, businesses are encouraged to conduct appropriate risk assessments for each product to prevent silicosis. Recently, silica particles have been reported to induce lysosomal membrane damage, leading to the activation of proinflammatory factors. An indirect method to evaluate lysosomal membrane damage known as the erythrocyte hemolysis assay, in which the erythrocyte membrane is assumed to be the lysosomal membrane, was performed. This study aimed to examine the possibility of constructing a screening system for proinflammatory potential prediction of silica particles based on their erythrocyte hemolytic activity.

METHODS

Hemolysis assays were performed on the silica particles with different sizes, crystallinity, and surface functional groups using the erythrocytes from a healthy volunteer. Additionally, the hemolytic activity of other element particles was compared with that of the silica particles, and 27 types of commercially available crystalline silica particle products underwent screening trials.

RESULTS

The hemolytic activity of silica particles was higher in crystalline than that in amorphous and increased with the decreasing size. The hemolytic reaction was particular to silica particles and rarely occurred in particles of other elements. Moreover, the hemolytic activity was significantly suppressed if the silica particles surface was modified with metal ions (Fe³⁺, Al³⁺). The hemolytic activities of the crystalline silica products used industrially significantly differed.

CONCLUSIONS

This study revealed that particle properties, such as size, crystallinity, and surface functional groups, affect the hemolytic activity of silica particles. Particularly, the surface functional groups (silanol groups) that are unique to silica particles were considered to be strongly involved in hemolytic activities. Since grading the commercially available crystalline silica particle products based on the hemolytic rate was possible, hemolytic activity was suggested to be an evaluation index for predicting the proinflammatory potential of silica particles.

o-Toluidine metabolism and effects in the urinary bladder of humanized-liver mice

Occupational exposure to aromatic amines is one of the most important risk factors for urinary bladder cancer. When considering the carcinogenesis of aromatic amines, metabolism of aromatic amines in the liver is an important factor. In the present study, we administered ortho-toluidine (OTD) in the diet to mice for 4 weeks. We used NOG-TKm30 mice (control) and humanized-liver mice, established via human hepatocyte transplantation, to compare differences in OTD-induced expression of metabolic enzymes in human and mouse liver cells. We also investigated OTD-urinary metabolites and proliferative effects on the urinary bladder epithelium. RNA and immunohistochemical analyses revealed that expression of N-acetyltransferases mRNA in the liver tended to be lower than that of the P450 enzymes, and that OTD administration had little effect on N-acetyltransferase mRNA expression levels. However, expression of CYP3A4 was increased in the livers of humanized-liver mice, and expression of Cyp2c29 (human CYP2C9/19) was increased in the livers of NOG-TKm30 mice. OTD metabolites in the urine and cell proliferation activities in the bladder urothelium of NOG-TKm30 and humanized-liver mice were similar. However, the concentration of OTD in the urine of NOG-TKm30 mice was markedly higher than in the urine of humanized-liver mice. These data demonstrate differences in hepatic metabolic enzyme expression induced by OTD in human and mouse liver cells, and consequent differences in the metabolism of OTD by human and mouse liver cells. This type of difference could have a profound impact on the carcinogenicity of compounds that are metabolized by the liver, and consequently, would be important in the extrapolation of data from animals to humans.

Increased serum anti-CYP2E1 IgG autoantibody levels may be involved in the pathogenesis of occupational trichloroethylene hypersensitivity syndrome: a case-control study

Occupational exposure to trichloroethylene (TCE) causes a systemic skin disorder with hepatitis known as TCE hypersensitivity syndrome (TCE-HS). Human Leukocyte Antigen (HLA)-B*13:01 is its susceptibility factor; however, the immunological pathogenesis of TCE-HS remains unknown. We herein examined the hypothesis that autoantibodies to CYP2E1 are primarily involved in TCE-HS. A case–control study of 80 TCE-HS patients, 186 TCE-tolerant controls (TCE-TC), and 71 TCE-nonexposed controls (TCE-nonEC) was conducted to measure their serum anti-CYP2E1 antibody (IgG) levels. The effects of TCE exposure indices, such as 8-h time-weighted-average (TWA) airborne concentrations, urinary metabolite concentrations, and TCE usage duration; sex; smoking and drinking habits; and alanine aminotransferase (ALT) levels on the antibody levels were also analyzed in the two control groups. There were significant differences in anti-CYP2E1 antibody levels among the three groups: TCE-TC > TCE-HS patients > TCE-nonEC. Antibody levels were not different between HLA-B*13:01 carriers and noncarriers in TCE-HS patients and TCE-TC. The serum CYP2E1 measurement suggested increased immunocomplex levels only in patients with TCE-HS. Multiple regression analysis for the two control groups showed that the antibody levels were significantly higher by the TCE exposure. Women had higher antibody levels than men; however, smoking, drinking, and ALT levels did not affect the anti-CYP2E1 antibody levels. Anti-CYP2E1 antibodies were elevated at concentrations lower than the TWA concentration of 2.5 ppm for TCE exposure. Since HLA-B*13:01 polymorphism was not involved in the autoantibody levels, the possible mechanism underlying the pathogenesis of TCE-HS is that TCE exposure induces anti-CYP2E1 autoantibody production, and HLA-B*13:01 is involved in the development of TCE-HS.

Increased risk of occupational trichloroethylene hypersensitivity syndrome at exposure levels higher than 15 mg/L of urinary trichloroacetic acid, regardless of whether the patients had the HLA-B*13:01 allele

Occupational trichloroethylene (TCE) exposure can cause hypersensitivity syndrome (TCE-HS). The human leukocyte antigen (HLA)-B*13:01 is reportedly an important allele involved in TCE-HS onset. However, the threshold exposure level causing TCE-HS in relation to HLA-B*13:01 remains unknown. We conducted a case-control study comprising 37 TCE-HS patients and 97 age- and sex-matched TCE-tolerant controls from the Han Chinese population. Urine and blood of patients were collected on the first day of hospitalization, and those of controls were collected at the end of their shifts. Urinary trichloroacetic acid (TCA) was measured as an exposure marker, and end-of-shift levels in the patients were estimated using the biological half-life of 83.7 h. HLA-B genotype was identified using DNA from blood. Crude odds ratios (ORs) for TCE-HS in the groups with urinary TCA concentration >15 mg/L to ≤50 mg/L and of >50 mg/L were 21.9 [95% confidence interval (CI) 4.2-114.1] and 27.6 (6.1-125.8), respectively, when the group with urinary TCA ≤15 mg/L was used as a reference. The frequency of HLA-B*13:01, the most common allele in the patients, was 62.2% (23/37), which was significantly higher than 17.5% (17/97) in the TCE-tolerant controls, with a crude OR of 8.4 (3.1-22.6). The mutually-adjusted ORs for urinary TCA >15 to ≤50 mg/L, >50 mg/L, and for HLA-B*13:01 were 33.4 (4.1-270.8), 34.0 (5.3-217.1), and 11.0 (2.4-50.7), respectively. In conclusion, reduction of TCE exposure to ≤15 mg/L is required for TCE-HS prevention because urinary TCA concentration >15 mg/L showed increased risk of TCE-HS, regardless of whether the patients had the HLA-B*13:01 allele.

Correction to: Genotoxicity assessment of titanium dioxide nanoparticle accumulation of 90 days in the liver of gpt delta transgenic mice

[This corrects the article DOI: 10.1186/s41021-020-0146-3.].

Aldehyde dehydrogenase 2 deficiency significantly exacerbates tert-butyl alcohol-induced toxicity in mice

Owing to the use of ethyl tert-butyl ether (ETBE) as a fuel additive, the possible adverse effects of ETBE exposure have become a public concern. Our previous study showed that ETBE-induced toxicity in aldehyde dehydrogenase 2 (Aldh2) gene knockout (KO) mice was caused by its primary metabolite acetaldehyde, which was toxic. However, it is unclear whether tert-butyl alcohol (TBA), another main metabolite of ETBE, plays a role in ETBE-induced toxicity. To investigate this relationship, we analyzed the changes of TBA concentrations in tissues after ETBE exposure, and then evaluated the toxicity after direct TBA treatment in both KO and wild-type (WT) mice. An exposure to 500 ppm ETBE via inhalation resulted in the formation of its three metabolites, TBA, 2-methyl-1,2-propanediol and ethanol, whose concentrations in the liver, brain, fat and testis of male KO mice were significantly higher than the corresponding concentrations observed in male WT mice. Direct treatment to TBA (20 mg/mL of drinking water) caused significant changes in relative organ weights and histopathology, and increased levels of genetic damages in both types of mice. These toxic effects were also seen in KO mice exposed to a lower concentration of TBA (5 mg/mL), which was associated with increased oxidative stress in serum (reduced glutathione and reduced glutathione/oxidized glutathione ratio decreased). Our findings indicate that ALDH2 is involved in the metabolism of ETBE and TBA, and ALDH2 deficiency could greatly increase the sensitivity to TBA-induced toxicity.

Genotoxicity assessment of titanium dioxide nanoparticle accumulation of 90 days in the liver of gpt delta transgenic mice

Backgound

A variety of in vivo and in vitro studies to assess the genotoxicity of titanium dioxide nanoparticles (TiO₂ NPs) have been reported, but the results are inconsistent. Recently, we reported that TiO₂ NPs exhibit no genotoxic effects in the liver and erythrocytes during a relatively brief period following intravenous injection into mice. However, there is no information about long-term genotoxicity due to TiO₂ NP accumulation in tissues. In this study, we investigated the long-term mutagenic effects of TiO₂ NPs and the localization of residual TiO₂ NPs in mouse liver after multiple intravenous injections.

Results

Male gpt delta C57BL/6 J mice were administered with various doses of TiO₂ NPs weekly for 4 consecutive weeks. The long-term mutagenic effects on the liver were analyzed using gpt and Spi⁻ mutation assays 90 days after the final injection. We also quantified the amount of titanium in the liver using inductively coupled plasma mass spectrometry and observed the localization of TiO₂ NPs in the liver using transmission electron microscopy. Although TiO₂ NPs were found in the liver cells, the gpt and Spi⁻ mutation frequencies in the liver were not significantly increased by the TiO₂ NP administration.

Conclusions

These results clearly show that TiO₂ NPs have no mutagenic effects on the liver, even though the particles remain in the liver long-term.

Inhalation exposure to low levels of ethyl tertiary butyl ether: Its genetic effects were significantly modified by ALDH2 activity

Previous experiments showed that high concentrations of ethyl tertiary butyl ether (ETBE) exposure (500-5,000 ppm) significantly resulted in DNA damages in aldehyde dehydrogenase 2 (Aldh2) knockout (KO) mice. This study was aimed to verify the genotoxic effects in three genetic types, Aldh2 KO, heterogeneous (HT), and wild type (WT), of mice exposed to lower concentrations of ETBE (50-500 ppm) by inhalation. Histopathology assessments in the livers, measurements of genotoxic biomarkers in blood and livers, and urinary 8-hydroxydeoxyguanosion (8-OH-dG) for the oxidative DNA damage of whole body were performed. Significant histopathological changes and DNA strand breaks both in hepatocytes and leukocytes were found in HT and KO male mice exposed to ≥200 ppm ETBE, but not in 50 ppm ETBE. 8-OH-dG levels either in liver or urine were higher in the HT and KO male mice exposed to ≥200 ppm ETBE. The pathological and genetic effects of ETBE were almost at the same extents for HT and KO mice. Thus, 50 ppm could be the no observed adverse effect level for ETBE in HT and KO male mice, which was far lower than the 500 ppm in WT mice. These results suggested that decrease and deficiency of ALDH2 activity would significantly increase the sensitivity to ETBE-induced genotoxicity as well as hepatotoxic effects after exposure even to low concentrations of ETBE. Environ. Mol. Mutagen. 60: 145-153, 2019. © 2018 Wiley Periodicals, Inc.

Acute inhalation co-exposure to 1,2-dichloropropane and dichloromethane cause liver damage by inhibiting mitochondrial respiration and defense ability in mice

1,2-Dichloropropane (1,2-DCP) is used as an industrial solvent, insecticide fumigant and household dry cleaning product. Carcinogenicity caused by long-term exposure to 1,2-DCP is well established. However, the possible liver damage and related toxic mechanisms associated with acute inhalation exposure to 1,2-DCP are rarely reported. In this study, we investigated the effects of individual and combined exposure to 1,2-DCP and dichloromethane (DCM) on mice liver. The results showed that 1,2-DCP significantly caused liver necrosis, possibly due to 1,2-DCP-induced inhibition of the mitochondrial respiratory chain complex I-IV activities, resulting in mitochondrial dysfunction and extreme ATP consumption. Moreover, 1,2-DCP also decreased mitochondrial defense ability by inhibiting the mitochondrial glutathione S-transferase 1 (MGST1) activity, further aggravating liver damage. Additionally, we found that DCM co-exposure potentially enhanced 1,2-DCP toxicity. Our findings suggest that inhibition of mitochondrial function and MGST1 activity play critical roles in modulating 1,2-DCP-induced liver damage. Furthermore, our results contribute to study the new mechanism of mitochondria-dominated signaling pathways underlying liver injury induced by 1,2-DCP and DCM.

Trichloroethylene exposure results in the phosphorylation of histone H2AX in a human hepatic cell line through cytochrome P450 2E1-mediated oxidative stress

Trichloroethylene (TCE), a chlorinated hydrocarbon, was recently reclassified as a human carcinogen by the International Agency for Research on Cancer. Genotoxic events are known to be crucial steps in the initiation of cancer. The genotoxic properties of TCE have been examined in many studies using a standard battery of genotoxicity tests both in vitro and in vivo. However, consistent results have not been obtained, and studies investigating the mechanism behind the genotoxicity of this compound are lacking. In the present study, we examined the genotoxicity of TCE by assessing phosphorylated histone H2AX (γ-H2AX), a new sensitive and reliable marker of DNA damage, in WRL-68 cells, cultured human hepatocytes and mouse livers. Our results showed that TCE exposure results in the generation of γ-H2AX, both in vitro and in vivo. By investigating the in vitro mechanism, we found that TCE increases the levels of intracellular reactive oxygen species (ROS) and that this increase in ROS levels is attenuated in the presence of disulfiram, a specific cytochrome P450 2E1 (CYP2E1) inhibitor. Furthermore, γ-H2AX induced by TCE was also attenuated by CYP2E1 inhibitors and the antioxidant N-acetylcysteine. These results suggested that ROS, produced via cytochrome P450 2E1-mediated metabolic processing, is a major causal factor for γ-H2AX generation upon exposure to TCE.

Nanoparticle-rich diesel exhaust-induced liver damage via inhibited transactivation of peroxisome proliferator-activated receptor alpha

Diesel exhaust emission contains a high amount of nano-sized particles and is considered to be systemically distributed in the body. However, few studies about the effects of nanoparticle rich-diesel exhaust (NR-DE) on liver have been reported. The present investigation focuses on the effects of NR-DE on livers in rats, especially concerning inflammation and lipid metabolism. Male F344 rats were exposed to fresh air or low (24 ± 7 µg/m³ ), medium (39 ± 4 µg/m³ ) and high (138 ± 20 µg/m³ ) concentrations of NR-DE for 1, 2, or 3 months (5 hours/day, 5 days/week). Exposure to both medium and high concentrations of NR-DE for one month increased plasma asparate aminotransferase and alanine aminotransferase activities, while only high concentrations increased plasma interleukin-6 and hepatic nuclear factor kappa B (NFκB), suggesting that activation of hepatic inflammatory signaling took place. Although these exposures elevated peroxisome proliferator-activated receptor (PPAR) α levels or its binding activity to the response element, neither activated PPARα-target genes such as β-oxidative enzymes nor inhibited NFκB elevation. Thus, NR-DE may contain some materials that inhibit PPARα activation in relation to lipid metabolism and inflammation. Taken together, NR-DE exposure at one month may cause inflammation; however, this finding may not be observed after a longer exposure period. © 2015 Wiley Periodicals, Inc. Environ Toxicol 31: 1985-1995, 2016.

Control banding assessment of exposure of offset printing workers to organic solvents

Objectives:

We aimed to assess the exposure of offset printing workers to hazardous substances in the rinsing processes of small-sized companies using a control banding method.

Methods:

We obtained half-year amounts of hazardous substances purchased through a questionnaire survey and the hazardous information from the safety data sheets (SDSs) and related literature.

Results:

The amount of petroleum kerosine and carbon hydride markedly increased in 2013 compared with that in 2010. In contrast, the amount of dichloromethane (DCM) decreased in 2013, and 1,2-dichloropropane (DCP) was not used in either 2010 or 2013. Mineral oil and xylene were allocated to Hazard Group D and judged to require Control Approach 3. In addition to DCM with Global Harmonization System's carcinogenic category 1, mildly treated mineral oil and solvent naphtha, allocated into Hazard Group E, are carcinogenic to humans and were judged to require Control Approach 4. There are two limitations of the control banding assessment: first, only limited and scarce hazard information could be obtained from SDSs, and second, safe-sided judgment for control technology for industrial hygiene.

Conclusion:

Small-sized enterprises are encouraged to implement control banding assessment for hazardous substances and to access expert advice available from Regional Industrial Health Centers. Easy access to appropriate expert advice is important to compensate for the limited and scarce hazard information and safe-sided judgment for control technology for Control Approaches 3 and 4.

Importance of detoxifying enzymes in differentiating fibrotic development between SHRSP5/Dmcr and SHRSP rats

OBJECTIVES

High-fat and -cholesterol diet (HFC) induced fibrotic steatohepatitis in stroke-prone spontaneously hypertensive rat (SHRSP) 5/Dmcr, the fifth substrain from SHRSP, by dysregulating bile acid (BA) kinetics. This study aimed to clarify the histopathological and BA kinetic differences in HFC-induced fibrosis between SHRSP5/Dmcr and SHRSP.

METHODS

Ten-week-old male SHRSP5/Dmcr and SHRSP were randomly allocated to groups and fed with either control diet or HFC for 2 and 8 weeks. The liver histopathology, biochemical features, and molecular signaling involved in BA kinetics were measured.

RESULTS

HFC caused more severe hepatocyte ballooning, macrovesicular steatosis and fibrosis in SHRSP5/Dmcr than in SHRSP. It was noted that fibrosis was disproportionately formed in retroperitoneal side of both strains. As for BA kinetics, HFC greatly increased the level of Cyp7a1 and Cyp7b1 to the same degree in both strains at 8 weeks, while multidrug resistance-associated protein 3 was greater in SHRSP5/Dmcr than SHRSP. The diet decreased the level of bile salt export pump by the same degree in both strains, while constitutive androstane receptor, pregnane X receptor, and UDP-glucuronosyltransferase activity more prominent in SHRSP5/Dmcr than SHRSP at 8 weeks. In the fibrosis-related genes, only expression of collagen, type I, alpha 1 mRNA was greater in SHRSP5/Dmcr than SHRSP.

CONCLUSIONS

The greater progression of fibrosis in SHRSP5/Dmcr induced by HFC may be due to greater suppression of UDP-glucuronosyltransferase activity detoxifying toxicants, such as hydrophobic BAs.

Cytochrome P450 2E1 is responsible for the initiation of 1,2-dichloropropane-induced liver damage

1,2-Dichloropropane (1,2-DCP), a solvent, which is the main component of the cleaner used in the offset printing companies in Japan, is suspected to be the causative agent of bile duct cancer, which has been recently reported at high incidence in those offset printing workplaces. While there are some reports about the acute toxicity of 1,2-DCP, no information about its metabolism related to toxicity in animals is available. As part of our efforts toward clarifying the role of 1,2-DCP in the development of cancer, we studied the metabolic pathways and the hepatotoxic effect of 1,2-DCP in mice with or without cytochrome P450 2E1 (CYP2E1) activity. In an in vitro reaction system containing liver homogenate, 1,2-DCP was only metabolized by liver tissue of wild-type mice but not by that of cyp2e1-null mice. Furthermore, the kinetics of the solvent in mice revealed a great difference between the two genotypes; 1,2-DCP administration resulted in dose-dependent hepatic damage, as shown biochemically and pathologically, but this effect was only observed in wild-type mice. The nuclear factor κB p52 pathway was involved in the liver response to 1,2-DCP. Our results clearly indicate that the oxidative metabolism of 1,2-DCP in mice is exclusively catalyzed by CYP2E1, and this step is indispensable for the manifestation of the hepatotoxic effect of the solvent.

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.

Assessment of the genotoxicity of 1,2-dichloropropane and dichloromethane after individual and co-exposure by inhalation in mice

OBJECTIVE

Occurrence of cholangiocarcinoma was recently reported at a high incidence rate among the employees working for an offset printing company in Osaka, Japan. 1,2-Dichloropropane (1,2-DCP) and dichloromethane (DCM) are suspected to be the causes of the cancer, as they had been used as ink cleaners in large amounts. However, it is not clear whether these chlorinated organic solvents played a role in the occurrence of cholangiocarcinoma or why the incidence rate is so high among the workers in this industry. To provide possible evidence for this severe occupational problem, we investigated the genotoxic effects of 1,2-DCP and DCM.

METHODS

Male B6C3F1 and gpt Delta C57BL/6J mice were exposed by inhalation to the individual solvents or both solvents at multiple concentrations including the levels that were possibly present in the workplaces. The genotoxicity was analyzed by Pig-a gene mutation and micronuclei assays in peripheral blood and gpt mutation and comet assays in the livers of mice after repeated inhalation of 1,2-DCP or/and DCM.

RESULTS

The Pig-a mutant frequencies and micronuclei incidences were not significantly increased by exposure of either 1,2-DCP or/and DCM at any concentration, suggesting there was no genotoxic potential in bone marrow for both solvents. In the liver, DNA damage, as measured by the comet assay, was dose dependently increased by 1,2-DCP but not by DCM. The gpt mutant frequency was 2.6-fold that of the controls in the co-exposure group.

CONCLUSIONS

These results indicate that 1,2-DCP showed stronger genotoxicity in the liver and that the genotoxic effects were greatly enhanced by simultaneous exposure to DCM.

Dysregulated bile acid synthesis, metabolism and excretion in a high fat-cholesterol diet-induced fibrotic steatohepatitis in rats

BACKGROUND AND AIMS

Cholesterol over-intake is involved in the onset of nonalcoholic steatohepatitis (NASH), and hepatocellular bile acid (BA) accumulation correlates with liver injuries. However, how dietary cholesterol influences cholesterol and BA kinetics in NASH liver remains ambiguous and needs to be clarified.

METHODS

Molecular markers involved in cholesterol and BA kinetics were investigated at protein and mRNA levels in an already-established stroke-prone spontaneously hypertensive 5/Dmcr rat model with fibrotic steatohepatitis, by feeding a high fat-cholesterol (HFC) diet.

RESULTS

Unlike the control diet, the HFC diet deposited cholesterol greatly in rat livers, where 3-hydroxy-3-methylglutaryl CoA reductase, low-density lipoprotein (LDL) receptor and LDL receptor-related protein-1 were expectedly downregulated, especially at 8 and 14 weeks, suggesting that cholesterol synthesis and uptake in response to cholesterol accumulation may not be disorganized. The HFC diet did not upregulate liver X receptor-α, conversely, it enhanced classic BA synthesis by upregulating cholesterol 7α-hydroxylase but downregulating sterol 12α-hydroxylase, and influenced alternative synthesis by downregulating sterol 27-hydroxylase but upregulating oxysterol 7α-hydroxylase, mainly at 8 and 14 weeks, indicating that there were different productions of primary BA species. Unexpectedly, no feedback inhibition of BA synthesis by farnesoid X receptor occurred. Additionally, the HFC diet impaired BA detoxification by UDP-glucuronosyltransferase and sulfotransferase 2A1, and decreased excretion by bile salt export pump at 8 and 14 weeks, although it induced compensatory export by multidrug resistance-associated protein-3. The disturbed BA detoxification may correlate with suppressed pregnane X receptor and constitutive androstane receptor.

CONCLUSIONS

The HFC diet may accumulate BA in rat livers, which influences fibrotic steatohepatitis progression.

Evidence for diazinon-mediated inhibition of cis-permethrin metabolism and its effects on reproductive toxicity in adult male mice

The potential toxicity resulting from combinatorial effects of organophosphorus and pyrethroid insecticides are not completely known. We evaluated male reproductive toxicity in mice co-exposed to diazinon and cis-permethrin. Nine-week-old male Sv/129 mice were exposed to diazinon (10 μmol/kg/day) or cis-permethrin (90 μmol/kg/day) alone or in combination (100 μmol/kg/day), or vehicle (corn oil), for 6 weeks. Diazinon and the diazinon-permethrin mixture inhibited plasma and liver carboxylesterase activities. In the mixture group, urinary excretion of cis-permethrin metabolite 3-phenoxybenzoic acid decreased along with increased plasma and testicular concentrations of cis-permethrin, while excretion of diazinon metabolites, diethylphosphate and diethylthiophosphate, did not change, versus mice exposed to each chemical alone, which suggested that inhibition of carboxylesterase decreased the metabolic capacity to cis-permethrin. Though the co-exposure decreased testosterone biosynthesis, increased degenerate germ cells in seminiferous tubule and sperm morphological abnormalities versus controls more clearly than exposure to cis-permethrin alone, the expected potentiation of toxicity was not evident.

Effect of nanoparticle-rich diesel exhaust on testicular and hippocampus steroidogenesis in male rats

BACKGROUND

Nanoparticle-rich diesel exhaust (NR-DE) has potentially adverse effects on testicular steroidogenesis. However, it is unclear whether NR-DE influences steroidogenic systems in the brain.

OBJECTIVE

To investigate the effect of NR-DE on hippocampal steroidogenesis of adult male rats in comparison with its effect on the testis.

METHODS

F344 male rats (8-week-old) were randomly divided into four groups (n = 8 or 9 per group) and exposed to clean air with 4.6 ± 3.2 μg/m(3) in mass concentration, NR-DE with 38 ± 3 μg/m(3) (a level nearly equivalent to the environmental standard in Japan (low NR-DE)), NR-DE with 149 ± 8 μg/m(3) (high NR-DE), or filtered diesel exhaust with 3.1 ± 1.9 μg/m(3) (F-DE), for 5 hours/day, 5 days/week, for 1, 2 or 3 months. F-DE was prepared by removing only particulate matters from high NR-DE with an HEPA filter.

RESULTS

Exposures to the high NR-DE for 1 month, and low NR-DE for 2 months, significantly increased or tended to increase plasma and testicular testosterone levels compared to clean air exposure, which might have resulted from the increased expression of mRNA of steroidogenic acute regulatory protein and its protein in the testes of rats. In the hippocampus, high NR-DE exposure for 1 month significantly increased the androstendione level compared to the clean air exposure, while no significant difference was observed in the steroidogenesis between fresh air exposure and any exposure to NR-DE or F-DE.

CONCLUSION

NR-DE may influence steroidogenic enzymes in the testis, but not those in the hippocampus.

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.

Simultaneous changes in high-fat and high-cholesterol diet-induced steatohepatitis and severe fibrosis and those underlying molecular mechanisms in novel SHRSP5/Dmcr rat

OBJECTIVES

The aim of this study was to identify the molecular mechanisms underlying high-fat and high-cholesterol (HFC) diet-induced steatohepatitis and associated liver fibrosis progression in a novel stroke-prone, spontaneously hypertensive 5/Dmcr (SHRSP5/Dmcr) rat model.

METHODS

SHRSP5/Dmcr rats were given the control or HFC-diet for 2, 8, and 16 weeks. Plasma and hepatic gene expression of key molecules involved in fatty acid oxidation, inflammation, oxidative stress, and fibrosis were subsequently analyzed.

RESULTS

Rats fed the HFC-diet showed increased plasma tumor necrosis factor-α (TNF-α) and hepatic p50/p65 signals, but reduced hepatic Cu(2+)/Zn(2+)-superoxide dismutase across the treatment period and reduced plasma total adiponectin at 8 weeks. In HFC-diet-fed rats, transforming growth factor-β1 (TGF-β1) was elevated prior to the appearance of obvious liver fibrosis pathology at 2 weeks, followed by elevations in platelet-derived growth factor-B (PDGF-B) and α-smooth muscle actin (α-SMA), corresponding to evident liver fibrosis, at 8 weeks and by α(1) type I collagen production at 16 weeks. The HFC-diet increased hepatic total cholesterol accumulation, although hepatic triglyceride declined by 0.3-fold from 2 to 16 weeks due to reduced hepatic triglyceride synthesis, as suggested by the diacylglycerol acyltransferase 1 and 2 measurements.

CONCLUSIONS

TNF-α and p50/p65 molecular signals appeared to be major factors for HFC-diet-induced hepatic inflammation and oxidative stress facilitating liver disease progression. While the up-regulation of TGF-β1 prior to the appearance of any evident liver fibrosis could be an early signal for progressive liver fibrosis, elevated PDGF-B and α-SMA levels signified evident liver fibrosis at 8 weeks, and subsequent increased α(1) type I collagen production and reduced triglyceride synthesis indicated extensive liver fibrosis at 16 weeks in this novel SHRSP5/Dmcr model.

[Exposure to nanoparticle-rich diesel exhaust may cause liver damage]

Diesel exhaust (DE) is one of the air pollutants in the world, and exposure to DE is an environmental health concern. Most studies amongst the limited number of studies on hepatotoxicity have focused on genotoxicity or mutagenicity. However, DE exposure may cause liver damage because one prospective study suggests that DE exposure is associated with increased mortality due to arteriosclerosis and cirrhosis of the liver. Peroxisome proliferator-activated receptor (PPAR) α plays a role in the regulation of lipid homeostasis and inflammation and thereby may be involved in the progression of atherosclerosis. We investigated whether nanoparticle-rich diesel exhaust (NR-DE) affects the liver and how PPARα is involved in the NR-DE induced effects. We report these results briefly in this minireview. Our results suggest NR-DE-induced hepatic inflammation and dyslipidemia. PPARα may be involved in the development of these disorders.

Ammonium perfluorooctanoate may cause testosterone reduction by adversely affecting testis in relation to PPARα

Perfluorooctanoate, a peroxisome proliferator-activated receptor alpha (PPARα) agonist, has the potential to lower testosterone levels as a result of testicular toxicity. To elucidate the mechanism and impact of PPARα on this reproductive toxicity, ammonium perfluorooctanoate (APFO) at doses of 0, 1.0 (low) mg/kg/day, or 5.0 (high) mg/kg/day was orally given daily to 129/sv wild-type (mPPARα), Pparα-null and PPARα-humanized (hPPARα) mice for 6 weeks. Both low- and high-dose APFO significantly reduced plasma testosterone concentrations in mPPARα and hPPARα mice, respectively. These decreases may, in part, be associated with decreased expression of mitochondrial cytochrome P450 side-chain cleavage enzyme, steroidogenic acute regulatory protein or peripheral benzodiazepine receptor as well as microsomal cytochrome P450(17α) involved in the steroidogenesis. Additionally, both doses increased abnormalities in sperm morphology and vacuolated cells in the seminiferous tubules of both mouse lines. In contrast, APFO caused only a marginal effect either on the testosterone synthesis system or sperm and testis morphology in Pparα-null mice. These results suggest that APFO may disrupt testosterone biosynthesis by lowering the delivery of cholesterol into the mitochondria and decreasing the conversion of cholesterol to pregnenolone and androstandione in the testis of mPPARα and hPPARα mice, which may, in part, be related to APFO-induced mitochondrial damage.

Modulation of ammonium perfluorooctanoate-induced hepatic damage by genetically different PPARα in mice

Perfluorooctanoic acid is a ligand for peroxisome proliferator-activated receptor (PPARα). Ammonium perfluorooctanoate (APFO) at 0.1 and 0.3 mg/kg doses activated mouse PPARα, but not human PPARα. This study aimed to clarify whether milligram-order APFO can activate human PPARα, and the receptor is involved in APFO-induced chronic hepatic damage. Male Sv/129 wild-type (mPPARα), Pparα-null, and humanized PPARα (hPPARα) mice (8 weeks old) were divided into three groups. The first was treated with water and the other two with 1.0 and 5.0 mg/kg APFO for 6 weeks, orally, respectively. Both doses activated mouse and human PPARα to a similar or lower degree in the latter. APFO dose dependently increased hepatic triglyceride levels in Pparα-null and hPPARα mice, but conversely decreased those in mPPARα ones. APFO-induced hepatic damage differed markedly among the three genotyped groups: single-cell necrosis was observed in all genotyped mice; inflammatory cells and macrovesicular steatosis only in Pparα-null mice; and microvesicular steatosis and hydropic degenerations in hPPARα and Pparα-null mice. The molecular mechanism underlying these differences may be attributable to those of gene expressions involved in lipid homeostasis (PPARα, β- and ω-oxidation enzymes, and diacylglycerol acyltransferases) and uncoupling protein 2. Thus, milligram-order APFO activated both mouse and human PPARα in a different manner, which may reflect histopathologically different types of hepatic damage.

Hepatic peroxisome proliferator-activated receptor α may have an important role in the toxic effects of di(2-ethylhexyl)phthalate on offspring of mice

Maternal exposure to di(2-ethylhexyl)phthalate (DEHP) is associated with adverse effects on offspring, and the metabolites are agonists of peroxisome proliferator-activated receptor (PPAR) α, which exhibits species differences in expression and function. This study aimed to clarify the mechanism of DEHP-induced adverse effects on offspring in relation to maternal mouse and human PPARα. Male and female Sv/129 wild-type (mPPARα), Pparα-null and humanized PPARα (hPPARα) mice were treated with diets containing 0%, 0.01%, 0.05% (medium) or 0.1% (high) DEHP. After 4 weeks, males and females were mated. Dams were killed on gestational day 18 and postnatal day (PND) 2. High-dose DEHP decreased the number of total and live fetuses, and increased resorptions in mPPARα mice. In hPPARα mice, resorptions were increased above the medium dose, and the number of births was decreased at the high dose. The number of live pups on PND2 was decreased over the medium dose in mPPARα and at the high dose in hPPARα mice. No such findings were observed in Pparα-null mice. High-dose DEHP decreased plasma triglyceride in pregnant mPPARα mice, but not in Pparα-null and hPPARα ones. Above the medium dose in mPPARα mice significantly reduced hepatic microsomal triglyceride transfer protein (MTP) expression. Medium- and/or high-dose DEHP increased the levels of maternal PPARα target genes in mPPARα and hPPARα mice. Taken together, PPARα expression is required for the toxicity of DEHP in fetuses and pups and altered plasma triglyceride levels, through regulation of MTP may be important in mPPARα mice and not in hPPARα mice.

Differential response to trichloroethylene-induced hepatosteatosis in wild-type and PPARalpha-humanized mice

BACKGROUND

Trichloroacetic acid, an oxidative metabolite of trichloroethylene (TRI), is a ligand of the peroxisome proliferator-activated receptor alpha (PPAR) alpha, which is involved in lipid homeostasis and anti-inflammation.

OBJECTIVE

We examined the role of mouse and human PPARalpha in TRI-induced hepatic steatosis and toxicity.

METHODS

Male wild-type (mPPARalpha), Pparalpha-null, and humanized PPARalpha (hPPARalpha) mice on an Sv/129 background were exposed via inhalation to 0, 1,000, and 2,000 ppm TRI for 8 hr/day for 7 days. We assessed TRI-induced steatosis or hepatic damage through biochemical and histopathological measurements.

RESULTS

Plasma alanine aminotransferase and aspartate aminotransferase activities increased in all mouse lines after exposure to 1,000 and 2,000 ppm TRI. Exposure induced hepatocyte necrosis and inflammatory cells in all mouse lines, but hepatic lipid accumulation was observed only in Pparalpha-null and hPPARalpha mice. No differences were observed in TRI-mediated induction of hepatic PPARalpha target genes except for a few genes that differed between mPPARalpha and hPPARalpha mice. However, TRI significantly increased expression of triglyceride (TG)-synthesizing enzymes, diacyl-glicerol acyltransferases, and PPARgamma in Pparalpha-null and hPPARalpha mice, which may account for the increased TG in their livers. TRI exposure elevated nuclear factor-kappa B (NFkappaB) p52 mRNA and protein in all mice regardless of PPARalpha genotype.

CONCLUSIONS

NFkappaB-p52 is a candidate molecular marker for inflammation caused by TRI, and PPARalpha may be involved in TRI-induced hepatosteatosis. However, human PPARalpha may afford only weak protection against TRI-mediated effects compared with mouse PPARalpha.

Bisphenol A may cause testosterone reduction by adversely affecting both testis and pituitary systems similar to estradiol

Bisphenol A (BPA) causes reproductive toxicities, but the mechanisms are still unclear. In the present study, we sought to clarify these mechanisms in comparison with those of 17beta-estradiol (E2). Prepubertal Wistar/ST male rats (4 weeks old) were subcutaneously administered BPA (0, 20, 100 and 200 mg/kg/day) or E2 (10 and 100 microg/kg/day) for 6 weeks. Both BPA and E2 treatments decreased plasma and testicular testosterone levels, and plasma luteinizing hormone (LH), but not E2 and follicle-stimulating hormone levels, though E2 treatment increased its plasma level. In relation to the decreased testosterone levels, BPA and E2 decreased expressions of steroidogenic enzymes and cholesterol carrier protein in Leydig cells. Thus, decreased testosterone levels in plasma might have resulted from decreased expressions of these enzymes and protein as well as from decreased plasma LH levels. Interestingly, the changes in steroidogenic enzymes and carrier protein were observed at lower levels of exposure to BPA or E2 than those inhibiting plasma LH levels. Microscopically, 200 mg/kg BPA and 100 microg/kg E2 significantly decreased Leydig cell numbers in the testis. In addition, BPA and E2 also decreased expression of estrogen receptor alpha-mRNA, which might be related to the decreased numbers of Leydig cells. Thus, BPA directly affects not only the Leydig cells but also the pituitary gland, but the former may be impaired at lower exposure concentrations than the latter.

Microgram-order ammonium perfluorooctanoate may activate mouse peroxisome proliferator-activated receptor alpha, but not human PPARalpha

Perfluorooctanoic acid (PFOA) is a ligand for peroxisome proliferator-activated receptor (PPAR) alpha, which exhibits marked species differences in expression and function, especially between rodents and humans. We investigated the functional difference in PFOA response between mice and humans, using a humanized PPARalpha transgenic mouse line. Three genotyped mice, 129/Sv wild-type (mPPARalpha), Pparalpha-null mice and humanized PPARalpha (hPPARalpha) mice (8-week-old males) were divided into three groups: the first was treated with water daily for 2 weeks by gavage (control group), and the remaining two groups were treated with 0.1 and 0.3mg/kg ammonium perflurooctanate (APFO), respectively, for 2 weeks by gavage. The APFO dosages used did not influence the plasma triglyceride or total cholesterol levels in any mouse line, but the high dose increased both hepatic lipid levels only in mPPARalpha mice. APFO increased mRNA and/or protein levels of PPARalpha target genes cytochrome P450 Cyp4a10, peroxisomal thiolase and bifunctional protein only in the liver of mPPARalpha mice, but not in Pparalpha-null or hPPARalpha mice. This chemical also increased expression of mitochondrial very long chain acyl-CoA dehydrogenase only in the liver of mPPARalpha mice. Taken together, human PPARalpha may be less responsive to PFOA than that of mice when a relatively low dose is applied. This information may be very valuable in considering whether PFOA influences the lipid metabolism in humans.

Nanoparticle-rich diesel exhaust may disrupt testosterone biosynthesis and metabolism via growth hormone

We previously reported that exposure to low (22.5+/-0.2 nm in diameter, 15.4+/-1.0 microg/m(3) in mass weight, 2.27x10(5)/cm(3) in mean number concentration), and medium (26.1+/-0.5 nm, 36.4+/-1.2 microg/m(3), 5.11x10(5)/cm(3)) concentrations of nanoparticle-rich diesel exhaust (NR-DE) for 1 and 2 months (5 h/day, 5 days/week) significantly increased plasma testosterone in male Fischer 344 rats, whereas exposure to a high concentration (27.1+/-0.5 nm, 168.8+/-2.7 microg/m(3), 1.36x10(6)/cm(3)) did not. The present study attempts to clarify the mechanism of this elevation. Low and medium exposures to NR-DE for 1 and 2 months significantly increased steroidogenic acute regulatory protein (StAR)- and cytochrome P450 side-chain cleavage (P450scc)-mRNA and their protein expressions in the testis of rats, in which the elevation pattern was very similar to that of plasma testosterone levels. Interestingly, both exposure levels for 1 month significantly increased growth hormone (GH) receptor expression in the testis, and low exposure also increased testicular insulin-like growth factor I-mRNA levels and hepatic microsomal cytochrome P450 2C11-mRNA and their protein levels in rats. These two factors are thought to be related to growth hormone secretion. Disruption of testosterone biosynthesis by NR-DE exposure may be a mode of action for reproductive toxicity, which may, in part, be regulated by increasing StAR and P450scc expressions via GH signalling.

Styrene trimer may increase thyroid hormone levels via down-regulation of the aryl hydrocarbon receptor (AhR) target gene UDP-glucuronosyltransferase

BACKGROUND

Styrene trimers (STs) are polystyrene-container-eluted materials that are sometimes detected in packaged foods. Although the possible endocrine-disrupting effects of STs, such as estrogenic activities, have been reported, their potential thyroid toxicity, such as that caused by the related endocrine disruptor 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), has not been studied in detail.

OBJECTIVE

Using wild-type and aryl hydrocarbon receptor (Ahr)-null mice, we investigated whether 2,4,6-triphenyl-1-hexene (ST-1), an isomer of STs, influences thyroxin (T(4)) levels in the same manner as TCDD, which induces UDP-glucuronosyltransferase (UGT) via the AhR, resulting in a decrease in T(4) levels in the plasma of mice.

METHODS

Both wild-type and Ahr-null mice (five mice per group) were treated for 4 days by gavage with ST-1 (0, 32, or 64 micromol/kg).

RESULTS

High-dose (64 micromol/kg) ST-1 decreased the expression of AhR, cytochrome P450 (CYP) 1A1/2, UGT1A1/A6, and CYP2B10 mRNAs and the enzyme activity for CYP1A and UGT1A only in the wild-type mice. This dose decreased AhR DNA binding, but paradoxically increased AhR translocation to the nucleus. In contrast, a high dose of ST-1 increased T(4) levels in the plasma in wild-type mice but did not influence T(4) levels in AhR-null mice.

CONCLUSIONS

Although ST-1 treatment might cause an increase in AhR levels in the nucleus by inhibiting AhR export, this chemical down-regulated AhR mRNA, thus leading to down-regulation of AhR target genes and an increase in plasma T(4) levels.

Permethrin may disrupt testosterone biosynthesis via mitochondrial membrane damage of Leydig cells in adult male mouse

Permethrin, a popular synthetic pyrethroid insecticide used to control noxious insects in agriculture, forestry, households, horticulture, and public health throughout the world, poses risks of environmental exposure. Here we evaluate the reproductive toxicity of cis-permethrin in adult male ICR mice that were orally administered cis-permethrin (0, 35, or 70 mg/kg d) for 6 wk. Caudal epididymal sperm count and sperm motility in the treated groups were statistically reduced in a dose-dependent manner. Testicular testosterone production and plasma testosterone concentration were significantly and dose-dependently decreased with an increase in LH, and a significant regression was observed between testosterone levels and cis-permethrin residues in individual mice testes after exposure. However, no significant changes were observed in body weight, reproductive organ absolute and relative weights, sperm morphology, and plasma FSH concentration after cis-permethrin treatment. Moreover, cis-permethrin exposure significantly diminished the testicular mitochondrial mRNA expression levels of peripheral benzodiazepine receptor (PBR), steroidogenic acute regulatory protein (StAR), and cytochrome P450 side-chain cleavage (P450scc) and enzyme and protein expression levels of StAR and P450scc. At the electron microscopic level, mitochondrial membrane damage was found in Leydig cells of the exposed mouse testis. Our results suggest that the insecticide permethrin may cause mitochondrial membrane impairment in Leydig cells and disrupt testosterone biosynthesis by diminishing the delivery of cholesterol into the mitochondria and decreasing the conversion of cholesterol to pregnenolone in the cells, thus reducing subsequent testosterone production.

Pyrene-induced CYP1A2 and SULT1A1 may be regulated by CAR and not by AhR

Aryl hydrocarbon receptor (AhR) plays important roles in the regulation and induction of xenobiotic-metabolizing enzymes including the cytochromes P450 1 family (CYP1) and UDP-glucuronosyltransferases 1A (UGT1As) by polycyclic aromatic hydrocarbons as well as chlorinated aromatic hydrocarbons. To determine whether pyrene-induced xenobiotic-metabolizing enzymes are regulated by AhR, male AhR (+/+) and (-/-) mice were used. Both genotyped mice were exposed to 0, 205, 300 or 410 mg/(kgday pyrene), once daily, for four consecutive days by gavage. Exposure to pyrene did not influence hepatic CYP1A1-mRNA in mice of both genotypes, whereas it induced hepatic CYP1A2 protein and mRNA expression and associated 7-ethoxyresorufin O-deethylase and pyrene 1-hydroxylation activities in both AhR (+/+) and (-/-) mice. Similar effects were also found with sulfotransferase 1A1 expression and the associated 1-hydroxypyrene sulfation activity. In contrast, pyrene exposure increased expression of the UGT1A1 and 1A6, and glucuronidation activities associated with 1-hydroxypyrene and 1-naphthol in the liver only in AhR (-/-) mice, although pyrene treatment dose-dependently decreased the latter activity. Pyrene exposure did not increase AhR-mRNA expression in AhR (+/+) mice. In contrast, pyrene-induced expression of the hepatic constitutive androstane receptor (CAR) and one of its target genes, CYP2B10, in both AhR (+/+) and (-/-) mice. These results strongly suggest that pyrene-induced CYP1A2 and SULT1A1 are regulated by CAR, not by AhR. However, the mechanisms of UGT1A1 and 1A6 induction by pyrene were not elucidated in this study.