Urinary excretion of acrylonitrile and its metabolites in rats

Isotope-dilution method for the determination of 1-vinyl-2-pyrrolidone-mercapturic acid as a potential human biomarker for 1-vinyl-2-pyrrolidone via online SPE ESI-LC/MS/MS in negative ionization mode

We established and validated a specific and sensitive analytical method for the determination of 1-vinyl-2-pyrrolidone (VP) as 1-vinyl-2-pyrrolidone-mercapturic acid (VPMA) in urine using an electrospray liquid chromatography tandem mass spectrometry (ESI-LC/MS/MS) column switching method. An online solid phase extraction (SPE) for sample cleanup was performed by column switching to a restricted access material and back-flushing to the analytical column. A Phenomenex Luna C8 column was used for sample separation (150mm; ID 4,6mm; 3μm). D4-VPMA served as an isotope labeled internal standard and was detected in negative multiple-reaction monitoring (MRM) mode. The Limit of quantification (LOQ) for VPMA was 1.5μg/L, the intra-day precision of three concentrations (2μg/L, 75μg/L and 400μg/L) of spiked urine samples ranged from 2.7 to 7.3%, the inter-day precision from 3.4 to 14.4%. The accuracy ranged from 6.2 to 9.0%, for the intra-day experiments and from 0.3 to 6.9% for the inter-day experiments. The method was applied to urines of Sprague-Dawley rats exposed to VP as a proof of principle of VPMA as a potential biomarker.

Facing the key workplace challenge: assessing and preventing exposure to nanoparticles at source

Nanomaterials present new challenges to understanding, predicting, and managing potential health risks in occupational environments. In this study, we characterize the key physical processes related to formation and growth of nanoparticles. The main focus is on various occupational environments, as these are known to be major environments with nanoparticles in indoor air. The protection of people potentially to be exposed to nanoparticles is one of the key issues in terms of risk assessment and prevention. Two of the main protection techniques that are discussed and characterized are ventilation and filtration, which are widely used in practical applications.

Acrylonitrile-induced morphological transformation in Syrian hamster embryo cells

Acrylonitrile (ACN) is a monomer used in the synthesis of rubber, fibers and plastics. Previous studies demonstrated that ACN induces brain neoplasms (predominately astrocytomas) in rats following chronic treatment. While the mechanisms of ACN-induced glial cell carcinogenicity have not been completely elucidated, investigations by our group and others have suggested a role for the induction of oxidative stress and the resultant oxidative damage in this process. In vitro cell transformation models are useful for detecting and studying the mechanisms of chemical carcinogenesis. Cell transformation by chemical carcinogens in Syrian hamster embryo (SHE) cells exhibits a multistage process similar to that observed in vivo, for both non-genotoxic and genotoxic carcinogens. In the present study, the ability of ACN to induce morphological transformation and oxidative damage was examined in SHE cells. ACN induced an increase in morphological transformation at doses of 50, 62.5 and 75 microg/ml (maximum sub-toxic dose tested) following 7 days of continuous treatment. SHE cells exposed to ACN for 24 h failed to increase morphological transformation. Morphological transformation by ACN was inhibited by co-treatment with the antioxidants alpha-tocopherol and (-)-epigallocathechin-3 gallate (EGCG) for 7 days. Treatment of SHE cells with 75 microg/ml ACN produced a significant increase in 8-hydroxy-2'-deoxyguanosine that was also inhibited by co-treatment with alpha-tocopherol or EGCG. These results support the proposal that oxidative stress and the resulting oxidative damage is involved in ACN-induced carcinogenicity.

Mutagenicity, carcinogenicity, and teratogenicity of acrylonitrile

Acrylonitrile (AN) is an important intermediary for the synthesis of a variety of organic products, such as artificial fibres, household articles and resins. Although acute effects are the primary concern for an exposure to AN, potential genotoxic, carcinogenic and teratogenic risks of AN have to be taken seriously in view of the large number of workers employed in such industries and the world-wide population using products containing and possibly liberating AN. An understanding of the effect of acrylonitrile must be based on a characterization of its metabolism as well as of the resulting products and their genotoxic properties. Tests for mutagenicity in bacteria have in general been positive, those in plants and on unscheduled DNA synthesis doubtful, and those on chromosome aberrations in vivo negative. Wherever positive results had been obtained, metabolic activation of AN appeared to be a prerequisite. The extent to which such mutagenic effects are significant in man depends, however, also on the conditions of exposure. It appears from the limited data that the ultimate mutagenic factor(s), such as 2-cyanoethylene oxide, may have little opportunity to act under conditions where people are exposed because it is formed only in small amounts and is rapidly degraded. The carcinogenic action of AN has been evaluated by various agencies and ranged from 'reasonably be anticipated to be a human carcinogen' to 'cannot be excluded', the most recent evaluation being 'possibly carcinogenic to humans'. Animal data that confirm the carcinogenic potential of AN have certain limitations with respect to the choice of species, type of tumors and length of follow up. Epidemiological studies which sometimes, but not always, yielded positive results, encounter the usual difficulties of confounding factors in chemical industries. Exposure of workers to AN should continue to be carefully monitored, but AN would not have to be considered a cancer risk to the population provided limitations on releases from consumer products and guidelines on AN in water and air are enforced. AN is teratogenic in laboratory animals (rat, hamster) at high doses when foetal/embryonic (and maternal) toxicity already is manifest. Pregnant workers should not be exposed to AN. In view of the small concentrations generally encountered outside plants, women not professionally exposed would appear not to be at risk of teratogenic effects due to AN. Future research should concentrate on the elucidation of the different degradation pathways in man and on epidemiological studies in workers including pregnant women, assessing also, if possible, individual exposure by bio-monitoring.

Evaluation of possible genotoxic mechanisms for acrylonitrile tumorigenicity

Acrylonitrile (ACN) exposure is associated with tumors in rat brain, Zymbal gland, and mammary gland. Adducts affecting base pairing were formed in isolated DNA exposed in vitro to the ACN metabolite cyanoethylene oxide (CNEO). DNA from liver, which is not a cancer target organ in ACN-exposed rats, contained low levels of 7-(2-oxoethyl)guanine, and adduct believed not to interfere with base pairing. No adducts have been detected in brain DNA from ACN-exposed rats, suggesting that brain tumors may have arisen by mechanisms other than ACN-DNA reactivity. Genotoxicity assays of ACN have indicated no particular carcinogenic mechanism. Positive reverse mutagenesis in Salmonella typhimurium HisG46 base substitution tester strains by ACN is attributable to CNEO. Other in vitro genotoxicity test assays of ACN have yielded mixed results, without consistent effect of metabolic activation. Some positive genotoxicity data for ACN appear to result from artifacts or from non-DNA-reactive mechanisms. In vivo micronucleus, chromosome aberration, and autoradiographic unscheduled DNA synthesis assays were negative for ACN. The comparative genotoxicity of vinyl chloride and ACN indicates that despite other similarities, they cause rodent tumors by different mechanisms. Also, they absence of ACN-DNA adduct formation in the rat brain suggests the operation of epigenetic mechanisms.

Determination of mercapturic acid excretions in exposure control to toxicants

Toxicants can be converted in vivo by a variety of biotransformation reactions into substances that are more, equally, or less noxious than the parent compound. Although conjugation with glutathione is a process that usually results in less harmful products, these products might subsequently form new metabolites that exert more toxicity than the parent compound. These conjugation reactions are catalyzed by several classes of glutathione-S-transferase isoenzymes and thus result in the urinary or biliary excretion of N-acetyl-L-cysteine-S-conjugates (mercapturic acids). Inasmuch as GSH-S-transferase activity varies among different tissues, urinary excretion of mercapturic acids might reflect tissue-specific toxicity. Urinary mercapturic acids are biomarkers of internal and, in some cases, effective dose. The utility of these markers is, however, limited to times shortly after exposure. Studies on possible human deficiencies in some GSH-S-transferases might help us better understand interindividual variations in susceptibility to different toxicants and thus the differences in the pathway of mercapturic acid excretion pattern.

N-acetyl-S-(2-hydroxyethyl)-L-cysteine as a potential tool in biological monitoring studies? A critical evaluation of possibilities and limitations

In mammalian species, including man, N-acetyl-S-(2-hydroxyethyl)-L-cysteine (2-HEMA) is a common urinary metabolite of a large number of structurally different xenobiotic chemicals. It is a common urinary end product of glutathione pathway metabolism of a variety of chemicals possessing electrophilic properties and, in most cases, also a genotoxic potential. Five different chemically reactive intermediates, with different electrophilic properties, may be involved in the formation of 2-HEMA. An inventory of chemicals known to lead to the formation of 2-HEMA, or based on their chemical structure expected to do so, is presented. Furthermore, an attempt is made to evaluate the possibilities and limitations in terms of the potential use of urinary 2-HEMA as a tool in biomonitoring studies. Two other related, sulfur-containing urinary metabolites, i.e. N-acetyl-(S-carboxymethyl)-L-cysteine and thio-diacetic acid, are proposed as possible alternatives to urinary 2-HEMA. It is suggested that 2-HEMA might be seen as a potentially useful and sensitive signal parameter for the assessment of exposure of animals and man to a variety of electrophilic and therefore potentially toxic xenobiotic chemicals.

Effect of glutathione depletion on the irreversible association of acrylonitrile with tissue macromolecules after oral administration to rats

Binding of acrylonitrile and its reactive metabolites to tissue macromolecules, especially nucleic acids, may be responsible for its carcinogenicity in rats. Both acrylonitrile and its primary metabolite, 2-cyanoethylene oxide, also react with glutathione. To better understand the role of glutathione in the manifestation of acrylonitrile toxicity, the irreversible binding to tissue macromolecules was assessed in control and glutathione-depleted F-344 rats treated with a 4 mg/kg dose (po) of [2,3-14C]acrylonitrile. Glutathione was depleted in rat tissues by the administration of a combined intraperitoneal phorone/buthionine sulfoximine treatment (300 mg/kg and 2 mmol/kg, respectively) given 30 min prior to acrylonitrile administration. The amount of total radioactivity recovered from brain, stomach (target organs), liver, kidney, lung, and blood (nontarget organs) was similar between control and glutathione-depleted rats. However, stomach, lung, blood, and liver showed an increase in total radioactivity content after glutathione depletion by phorone/buthionine sulfoximine treatment. Glutathione depletion also caused an increase in acrylonitrile-derived non-dialysable radioactivity (MW greater than 3500 Da) in liver, lung, kidney, stomach, blood, and brain macromolecules between 6 and 24 hr after the dose. There was no organ-specific accumulation of radiolabel in RNA in control rats. However, an increase in the radiolabel associated with nucleic acids in the target organs but not in the nontarget organs was measured in glutathione-depleted rats. Urinary excretion of thiocyanate, a metabolite derived from the epoxide pathway, was also increased by 300% in glutathione-depleted rats. These results suggest that glutathione might play a role in the extent of 2-cyanoethylene oxide formation and in the distribution of the radiolabel among tissues.