Establishing a total allowable concentration of o-toluidine in drinking water incorporating early lifestage exposure and susceptibility

Tracking Aromatic Amines from Sources to Surface Waters

This review examines the environmental occurrence and fate of aromatic amines (AAs), a group of environmental contaminants with possible carcinogenic and mutagenic effects. AAs are known to be partially responsible for the genotoxic traits of industrial wastewater (WW), and AA antioxidants are acutely toxic to some aquatic organisms. Still, there are gaps in the available data on sources, occurrence, transport, and fate in domestic WW and indoor environments, which complicate the prevention of adverse effects in aquatic ecosystems. We review key domestic sources of these compounds, including cigarette smoke and grilled protein-rich foods, and their presence indoors and in aquatic matrices. This provides a basis to evaluate the importance of nonindustrial sources to the overall environmental burden of AAs. Appropriate sampling techniques for AAs are described, including copper-phthalocyanine trisulfonate materials, XAD resins in solid-phase extraction, and solid-phase microextraction methods, which can offer insights into AA sources, transport, and fate. Further discussion is provided on potential progress in the research of AAs and their behavior in an aim to support the development of a more comprehensive understanding of their effects and potential environmental risks.

Evaluation of the Mechanisms Involved in the Development of Bladder Toxicity following Exposure to Occupational Bladder Cancer Causative Chemicals Using DNA Adductome Analysis

Occupational exposure to aromatic amines (AAs) is an important risk factor for urinary bladder cancer. This study aimed to evaluate the toxicity of AAs and analyze the carcinogenic mechanisms in rat bladder by comprehensive analysis of DNA adducts (DNA adductome). DNA was extracted from the bladder epithelia of rats treated with AAs, including acetoacet-o-toluidine (AAOT) and o-toluidine (OTD), and adductome analysis was performed. Principal component analysis-discriminant analysis revealed that OTD and AAOT observed in urinary bladder hyperplasia could be clearly separated from the controls and other AAs. After confirming the intensity of each adduct, four adducts were screened as having characteristics of the OTD/AAOT treatment. Comparing with the in-house DNA adduct database, three of four candidates were identified as oxidative DNA adducts, including 8-OH-dG, based on mass fragmentation together with high-resolution accurate mass (HRAM) spectrometry data. Therefore, findings suggested that oxidative stress may be involved in the toxicity of rat bladder epithelium exposed to AAs. Consequently, the administration of apocynin, an inhibitor of nicotinamide adenine dinucleotide phosphate oxidase, in six-week-old rats fed with 0.6% OTD in their diet resulted in simple hyperplastic lesions in the bladder that were suppressed by apocynin. The labeling indices of Ki67, γ-H2AX, and 8-OHdG were significantly decreased in an apocynin concentration-dependent manner. These findings indicate that oxidative stress may have contributed to the development of urinary cancer induced by OTD.

Mucosal damage and γ-H2AX formation in the rat urinary bladder induced by aromatic amines with structures similar to o-toluidine and o-anisidine

Although aromatic amines are widely used as raw materials for dyes, some, such as o-toluidine and o-anisidine, have shown concerning results regarding carcinogenicity in the urinary bladder. We have recently developed a short-term detection method for bladder carcinogens using immunohistochemistry for γ-H2AX, a DNA damage marker. Here, using this method, we evaluated aromatic amines with structures similar to o-toluidine and o-anisidine for bladder mucosal damage and potential carcinogenicity. In total, 17 aromatic amines were orally administered to male F344 rats for 28 days, and histopathological examination and γ-H2AX immunostaining of the urinary bladder were performed. Histopathological analysis revealed that seven aromatic amines, including 4-chloro-o-toluidine (4-CT), o-aminoazotoluene, 2-aminobenzyl alcohol (ABA), o-acetotoluidine (o-AT), 3,3'-dimethoxybenzidine, 4-aminoazobenzene (AAB), and 4,4'-methylenedianiline (MDA), induced various bladder lesions, such as hemorrhage, necrosis, and urothelial hyperplasia. The morphological characteristics of mucosal damage induced by these substances were divided into two major types: those resembling o-toluidine and those resembling o-anisidine. Six of these aromatic amines, excluding MDA, also caused significant increases in γ-H2AX formation in the bladder urothelium. Interestingly, 4-CT did not cause mucosal damage or γ-H2AX formation at the lower dose applied in previous carcinogenicity studies. These results showed for the first time that o-AT and ABA, metabolites of o-toluidine, as well as AAB caused damage to the bladder mucosa and suggested that they may be bladder carcinogens. In addition, 4-CT, which was thought to be a noncarcinogen, was found to exhibit bladder toxicity upon exposure to high doses, indicating that this compound may contribute to bladder carcinogenesis.

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.

Occurrence of microplastics in commercial marine dried fish in Asian countries

The major risk of microplastics in marine environments is the bioaccumulation in marine organisms. Plastic ingestion by marine organisms has been investigated and recently more attention has been given to microplastics in seafood. However, it is seldom reported the occurrence of microplastics in marine commercial dried fish products available for human consumption. Here, we report the occurrence of microplastics in 14different marine dried fish products from seven Asian countries. Microplastics were observed in most dried fish, with fibers representing ~80% of the total-microplastics. The major plastic polymers, identified using Micro-Raman spectroscopy, included polyethylene (35%), polyethylene terephthalate (26%), polystyrene (18%), polyvinyl chloride (12%), and polypropylene (9%). The highest count, in either per individual (1.92 ± 0.12) or per gram of dried fish (0.56 ± 0.03), were found in Etrumeus micropus from Japan. Marine dried fish, which are typically eaten whole, may contribute to the ingestion of microplastics by humans, posing potential health risks especially in Asian countries. Further studies are needed to identify the occurrence of smaller sized microplastics and nanoplastics and their potential health impacts.

Recent advances in γH2AX biomarker-based genotoxicity assays: A marker of DNA damage and repair

The phosphorylation of histone variant H2AX and formation of γH2AX is a primary response to the DNA double-strand breaks (DSBs). Detection of γH2AX is a robust and sensitive tool for diagnosis of DNA damage and repair in pre-clinical drug discovery investigations. In addition, the replication stress also leads to the formation of γH2AX and cell death and so γH2AX can serve as a surrogate marker of drug-induced cytotoxicity. Recent advances in genomic research offer an opportunity to detect γH2AX as a specific biomarker for quantitative analysis of DNA damages and repair using high content screening technology and quantitative imaging analysis. The proposed approaches identify a wide range of genetic disorders and are applied in combination with other assays in drug discovery and also for the evaluation of the efficacy of various developmental drugs. In the current review, we provide recent insights into the potential of γH2AX biomarker as a powerful tool in genotoxicity analyses for the monitoring and managing of cancer diseases.

Simple, selective, and identifiable analysis of aromatic monoamines with a surrogate on sulfuric acid impregnated filters by derivatization with an acid chloride reagent and HPLC with fluorescence detection

A simple and selective derivatization and detection method for o-toluidine, o-anisidine, and 2,4-dimethylaniline was developed using a sulfuric acid impregnated filter, 4-(N-chloroformylmethyl-N-methylamino)-7-nitro-2,1,3-benzoxadiazole, and a surrogate (o-ethylaniline), which allowed simple, rapid, selective, and identifiable analysis by high-performance liquid chromatography with fluorescence detection. These amines were successfully derivatized in a pH 5 buffer solution containing acetonitrile at 35°C for 10 min (linear in the range 0-400 ng/mL, n = 5, aromatic amines: r > 0.9980, aromatic amines with surrogate correction: r > 0.9997, aromatic amines in the presence of phenol and aliphatic amines with surrogate correction: r > 0.9996). The retention times of these derivatized aromatic amines were <17 min using isocratic elution. No derivatives corresponding to phenol or the aliphatic amines (i.e., cyclohexylamine and hexylamine) were detected in the reaction solution. This method can therefore be considered applicable for the analysis of samples from occupational environments, as samples were successfully extracted, derivatized, and measured by high-performance liquid chromatography following spiking of a sulfuric acid impregnated filter with aromatic amines, phenols, and aliphatic amines. Indeed, only the aromatic amines were quantitatively detected without pretreatment, with no other spiked compounds being detected.