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Histopathological Laboratories
Published in Dag K. Brune, Christer Edling, Occupational Hazards in the Health Professions, 2020
A. O. Myking, E. Røynstrand, O. D. Laerum
Xylene (dimethylbenzene) — Xylene exists in three isomeric forms. The commercial product, a colorless liquid with a characteristic odor known as xylol, is a mixture of all three. Xylene is produced from crude oil and may in its commercial form contain small amounts of impurities, mainly benzene derivatives. In occupational exposure, xylene is mainly absorbed through the lungs. Absorption of the vapor is similar for all three isomers and constitutes about 60 to 70% of the inhaled amount. Xylene may also be absorbed through the intact skin. The rate is estimated to be 2.0 to 2.5 μg/cm2/min. In comparison, approximately 75 mg of xylene is absorbed per minute through the lungs at a resting state at 100 ppm. Xylene is rapidly metabolized and excreted in the urine, mainly in the form of methylhippuric acid. Only 3 to 6% is eliminated through the respiratory air.
Pharmacokinetic Interactions of Drinking Water Contaminants
Published in Rhoda G.M. Wang, Water Contamination and Health, 2020
Ronald Brown, Jerry N. Blancato, David Young
A majority of the metabolic interactions listed in Table 4 involve inhibition of phase I (mixed-function oxidase-mediated) enzyme reactions; however, inhibition of phase II (conjugative) reactions by drinking water contaminants is also known to occur, either through direct enzyme inhibition or by depletion of necessary cofactors. For example, various haloacetonitriles known to occur as by-products of the drinking water disinfection process (e.g., trichloroacetonitrile) are potent inhibitors of glutathione-S-transfer-ase in liver cytosolic fractions, albeit at relatively high concentrations (50). However, environmentally or occupationally relevant exposures can also inhibit phase II enzyme systems. Campbell et al. (51) reported that the metabolism of m-xylene to m-methylhippuric acid in human volunteers exposed to xylene at a level equivalent to the occupational exposure limit (100 ppm) was inhibited 50% by coadministration of a therapeutic dose (1500 mg over 4 h) of aspirin. The metabolism of aspirin to its glycine conjugate was also inhibited to a similar extent. According to Campbell et al. (51), the likely mechanism for this interaction is mutual inhibition of the enzymes acyl coenzyme A-synthetase or glycine A'-acylase.
Metabolism and Toxicity of Occupational Neurotoxicants: Genetic, Physiological, and Environmental Determinants
Published in Lucio G. Costa, Luigi Manzo, Occupatinal Neurotoxicology, 2020
Stefano M. Candura, Luigi Manzo, Anna F. Castoldi, Lucio G. Costa
The main mechanism involved in the acute effects of ethanol on metabolic processes appears to be competition for binding with cytochromes P450. In some cases, the NADH generated by ethanol oxidation may inhibit Krebs cycle activity, thus depleting intermediates required for the generation of NADPH (i.e., the coenzyme of the P450 system).81 Acute interactions have been described for a number of commonly prescribed drugs, general anesthetics and industrial solvents.81 For example, after ethanol intake, blood xylene levels were found to increase by about 1.5- to 2-fold, while urinary methylhippuric acid excretion fell by approximately 50%, suggesting that ethanol decreases the metabolic clearance of xylene by about one half during xylene inhalation.83 These changes may have important practical consequences. Indeed, a proportion of work-related accidents are associated with alcohol consumption. One may wonder to what extent these events may be caused not only by ethanol itself, but also by an interaction with occupational toxicants exerting a depressant action on the central nervous system.
DNA damage and inflammatory response in workers exposed to fuels and paints
Published in Archives of Environmental & Occupational Health, 2021
Evelyne da Silva Brum, Lílian Marquezini da Silva, Taiane Piccini Teixeira, Laís da Rosa Moreira, Helena Kober, Marinês Calegari Lavall, José Édson Paz da Silva, Mariana Piana, Luana Suéling Lenz, Ivana Beatrice Mânica da Cruz, Thiago Duarte, Marta Maria Medeiros Frescura Duarte, Ricardo Brandão
Quantification of biological indicators of exposure, such as xenobiotics and/or its metabolites has been used to assess the exposure and contribute to the diagnosis of occupational diseases.35 Benzene, toluene and xylene are some of the most frequently represented solvents in the composition of paints and fuel. The internal dose of these solvents can be estimated by evaluating their metabolites, trans,trans-muconic acid, hippuric acid and methylhippuric acid, in the urine.3,53 Due to methodological difficulties, we did not quantify the levels of these metabolites in the workers evaluated in this study. It is worth mentioning that the above-stated solvents are only some of the constituents of paints and fuels. The main focus of this study was to more broadly assess the occupational exposure of GSA and painters, giving greater importance to new markers that may be useful in the evaluation of workers’ health. Besides, the sensitivity and specificity of solvent metabolites have been questioned when exposures are at or below 1 ppm.8 This fact supports the inclusion of the evaluation of other markers to assist the biological monitoring of occupational exposure.
Low-level occupational exposure to BTEX and dyschromatopsia: a systematic review and meta-analysis
Published in International Journal of Occupational Safety and Ergonomics, 2023
Younes Sohrabi, Fatemeh Rahimian, Esmaeel Soleimani, Soheil Hassanipour
Studies used biomonitoring to assess workers’ exposure reported urinary concentrations of toluene, xylene, mandelic acid, hippuric acid and/or methylhippuric acid [15,17,19]. Only one study [19] adjusted the urinary concentration of the studied metabolite for the urinary creatinine concentration and reported it as a geometric mean (methylhippuric acid 0.13 g/g creatinine in the exposed group vs non-detected levels in a referent group). Cavalleri et al. [15] reported a urinary toluene concentration of 0.063 ± 27 mg/l. Gong et al. [17] reported 60 ± 60 mg/l for xylene, 40 ± 90 mg/l for mandelic acid, 360 ± 400 mg/l for hippuric acid and 40 ± 60 mg/l for methylhippuric acid.