title: Identification of bound nitro musk-protein adducts in fish liver by gas chromatography-mass spectrometry: biotransformation, dose-response and toxicokinetics of nitro musk metabolites protein adducts in trout liver as biomarkers of exposure.
abstract: Ubiquitous occurrences of synthetic nitro musks are evident in the literature. The in vivo analysis of musk xylene (MX) and musk ketone (MK)-protein adducts in trout liver has been performed by gas chromatography-mass spectrometry using selected ion monitoring (GC-SIM-MS). Biotransformation, dose-response and toxicokinetics studies of 2-amino-MX (2-AMX), 2-amino-MK (2-AMK) and 4-amino-MX (4-AMX) metabolites, covalently bound to cysteine amino acids in proteins in fish liver, formed by enzymatic nitro-reduction of MX and MK, have been described. Trouts were exposed to single exposures of 0.010, 0.030, 0.10, and 0.30 mg/g MX and/or MK. Forty-two fish liver samples were collected from exposed- and control-fish subsequent to exposure intervals of 1 day, 3 days, and 7 days and were composited as per exposure schedules and times. Alkaline hydrolysis released bound metabolites from exposed liver composites that were extracted into n-hexane and then concentrated and analyzed by GC-SIM-MS. The presence of the metabolites in liver extracts was confirmed based on agreement of similar mass spectral properties and retention times with standards. In the dose-response study, the maximum adduct formation was 492.0 ng/g for 2-AMX, 505.5 ng/g for 2-AMK and 12588.5 ng/g for 4-AMX in liver at 0.03 mg/g MX and MK fish in 1 day after exposure. For toxicokinetics investigation, the highest amount of the target metabolites was found to be the same concentration as observed in the dose-response study for 1 day after exposure with 0.03 mg/g MX and MK fish and the half-lives of the metabolites were estimated to be 2-9 days based on assumption of first-order kinetics. Average recoveries exceeded 95% with a relative standard deviation (RSD) around 9%, and the limit of detection (LOD) ranged from 0.91 to 3.8 ng/g based on a signal to noise ratio of 10 (S/N=10) could be achieved for the metabolites. No metabolites were detected in the controls and exposed non-hydrolyzed liver extracts. This is the first report on dose-response and toxicokinetics of nitro musk-cysteine-protein adducts in fish liver.
authors.affiliation: Department of Chemistry/Physics, Center for Innovation and Entrepreneurship, Northwest Missouri State University, 800 University Drive, Maryville, MO 64468, USA. mmottaleb@yahoo.com
authors.forename: M Abdul
authors.initials: MA
authors.lastname: Mottaleb
authors.forename: Lantis I
authors.initials: LI
authors.lastname: Osemwengie
authors.forename: M Rafiq
authors.initials: MR
authors.lastname: Islam
authors.forename: G Wayne
authors.initials: GW
authors.lastname: Sovocool
mesh_terms: D015415:Biomarkers / Q000378:metabolism; D001711:Biotransformation; D004305:Dose-Response Relationship, Drug; D004781:Environmental Exposure / Q000032:analysis*; D008401:Gas Chromatography-Mass Spectrometry; D057230:Limit of Detection; D008099:Liver / Q000378:metabolism*; D014874:Water Pollutants, Chemical / Q000737:chemistry / Q000378:metabolism / Q000633:toxicity*; D014992:Xylenes / Q000737:chemistry / Q000378:metabolism / Q000633:toxicity*
chemical_list: D015415:Biomarkers; D014874:Water Pollutants, Chemical; D014992:Xylenes; C031447:musk xylene; C031448:musk ketone