Identification of metabolites of carcinogens by 13C NMR spectroscopy

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.

Sodium thiosulfate protects against acrylonitrile-induced elevation of glial fibrillary acidic protein levels by replenishing glutathione

Acrylonitrile (ACN) like many organic solvents produce neurotoxicity by elevating brain glial fibrillary acidic protein (GFAP), a putative biomarker of astrogliosis. In this study we tested the hypothesis that sodium thiosulfate (STS) protective action against ACN-induced astrogliosis is glutathione (GSH) mediated. Male Sprague-Dawley rats were administered for 2 weeks intraperitoneal doses (50 mg/kg body weight) of the ACN, with or without STS as outline in the Methods section. Specific brain regions were tested for GFAP, GSH and glutathione-S-transferase (GST) enzyme activity. In the brain regions tested STS significantly (P</=0.05) maintained GFAP levels at the basal saline control levels, when compared to ACN-treated groups. STS also significantly (P</=0.05) increased GSH levels in these brain regions with a corresponding increased in GST enzyme activity. Although the data indicated that STS antidotal action against ACN-induced neurotoxicity is likely to involve GSH and GST activity, other complex series of mechanisms may be involved.

Biotransformation of [(12)C]- and [(13)C]-tert-amyl methyl ether and tert-amyl alcohol

tert-Amyl methyl ether (TAME) is intended for use as a gasoline additive to increase oxygen content. Increased oxygen content in gasoline reduces tailpipe emissions of hydrocarbons and carbon monoxide from cars. Due to possible widespread use of TAME, the toxicity of TAME is under investigation. We studied the biotransformation of TAME in rats and one human volunteer after inhalation of (12)C- or (13)C-labeled TAME. In addition, the biotransformation of [(13)C]-tert-amyl alcohol was studied in rats after gavage. Urinary metabolites were identified by GC/MS and (13)C NMR. Rats (two males and two females) were individually exposed to 2000 ppm [(12)C]- or [(13)C]TAME for 6 h, and urine was collected for 48 h. Free and glucuronidated 2-methyl-2,3-butanediol and a glucuronide of tert-amyl alcohol were identified by (13)C NMR, GC/MS, and LC/MS/MS as major urinary metabolites on the basis of the relative intensities of the (13)C NMR signals. The presence of several minor metabolites was also indicated by (13)C NMR; they were identified as tert-amyl alcohol, 2-hydroxy-2-methylbutyric acid, and 3-hydroxy-3-methylbutyric acid. One human volunteer was exposed to an initial concentration of 27 000 ppm [(13)C]TAME by inhalation for 4 min from a 2 L gas sampling bag, and metabolites of TAME excreted in urine were analyzed by (13)C NMR. All TAME metabolites identified in rats were also present in the human urine samples. To study tert-amyl alcohol biotransformation, male rats (n = 3) were treated with 250 mg/kg [(13)C]-tert-amyl alcohol dissolved in corn oil by gavage, and urine was collected for 48 h. (13)C NMR of the urine samples showed the presence of metabolites identical to those in the urine of [(13)C]TAME-treated rats. Our results suggest that TAME is extensively metabolized by rats and humans to tert-amyl alcohol which may be further oxidized to diols and carboxylic acids. These reactions are likely mediated by cytochrome P450-dependent oxidations.