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Liver enzyme induction and inhibition as a biological marker of occupational exposure to volatile anaesthetics and other volatile organic chemicals

Objective

- To determine the ability of volatile anaesthetics (VAs) and other volatile organic chemicals (VOCs) to induce/inhibit cytochrome P-4502E1 and 1A in exposed workers.
- To clarify the role of and the relationship between individual genetic make-up (genotype) and occupational or environmental factors in determining toxicity.
- To identify individuals with increased sensitivity to VAs/VOCs, by P-450 genotyping and phenotyping and to assess the toxicological significance of enzyme induction/inhibition in workers exposed to these compounds.

The participants' expertise in occupational medicine, industrial hygiene, molecular and biochemical toxicology, pharmacology, toxicokinetics, pharmacogenetics and molecular biology will be used in an integrated, multidisciplinary approach to investigate cytochrome P-450 enzymes induction and inhibition as an occupational risk factor. The interaction between occupational, environmental and genetic factors will be studied at different levels of biological complexity: in vitro models, experimental animals and humans. Identification of the specific P-450 isoforms responsible for activation/detoxication of VAs/VOCs (including halothane, isofluorane, hydrochlorofluorocarbons, perchloroethylene and dimethylformamide) will be carried out using purified enzymes in reconstituted systems, transfected human cells synthesising specific P-450s (Crespi cell line) and liver microsomal preparations from rats pre-treated with selective P-450 inducers (betanaphtoflavone, pyridine and phenobarbital). The effects of VAs/VOCs on the P-450 system will be studied at the molecular level. The modification of the prosthetic haem group will be investigated by spectrofluorimetric, spectrophotometric and chromatographic techniques and the formation of adducts to the apoprotein by immunological and radioisotopic methods. Metabolic rate constants determined in vitro and compared with values obtained in animals and in humans in vivo will be used to validate a physiologically based pharmacokinetic (PBPK) model capable of simulating and, possibly, predicting the disposition, biotransformation and tissue availability of VAs/VOCs. The levels of exposure of workers to VAs/VOCs will be assessed by measurements of both environmental levels and internal dose and compared with the concentrations and doses known to induce different P-450s in animals. This would allow realistic conditions of exposure to be set for the in vivo studies and for the PBPK models. Identification of the hypersusceptible workers, i. e. those subjects exposed to VAs/VOCs who are at a higher risk of developing a toxic response due to their enhanced or decreased metabolic profile, will be achieved by genotyping and phenotyping for P-4502E1 and P-4501A. This approach will also allow the detection of any effect of exposure on the P-450-dependent activities in the workers. Finally, any early, toxicologically relevant effects of VAs/VOCs in workers will be evaluated by epidemiological techniques (cross-sectional study) and compared with the P-450 genotype and phenotype. This should also permit the validation of the existing environmental and/or biological exposure indexes (BEI) or the development of new ones.

Funding Scheme

CON - Coordination of research actions

Coordinator

Università degli Studi di Padova
Address
71,Via Facciolati
35127 Padova
Italy