The overall objective of this research project is to understand factors which influence the formation and toxicity of catechol metabolites from aromatic compounds. The chemicals employed in these studies are both important environmental chemicals and model compounds for more complex aromatic compounds, and are sufficiently diverse so that general conclusions about the role of catechols can be drawn. The chemicals to be studied are benzene, bromobenzene, naphthalene, biphenyl, 4-chlorobiphenyl, and phenytoin, a widely used anticonvulsant drug which is teratogenic. The approach used in this project is to: 1) Identify and characterize the specific enzymes involved in catechol formation; and 2) Study the mechanism of catechol formation and toxicity in isolated hepatocytes, in perfused liver, and in vivo. This project has shown that catechol formation in isolated rat liver cells occurs primarily via oxidation of dihydrodiols, rather than by hydroxylation of phenols. The proposed studies will extend these observations to include rabbits and mice, and will determine the mechanism of catechol formation in vivo for two model compounds, 4-chlorobiphenyl and bromobenzene, using mass spectrometric analysis of metabolites formed from substrates specifically labeled with deuterium. The enzymatic basis for the differences between species and between tissues will be investigated by isolating oxido-reductases which convert dihydrodiols to catechols from the livers of rats, rabbits, and mice, and determining the levels of these enzymes by immunochemical techniques in livers and other tissues, including developing animals. Experiments will also be conducted with purified isozymes of liver microsomal cytochrome P-450, to resolve which isozymes hydroxylate phenol metabolites to catechols. An understanding of catechol formation is important to toxicology because of the reactive metabolites which can be formed from catechols by further oxidation reactions, i.e. o-quinones and semiquinones. In the present research project, the role of naphthalene-1,2-catechol in the pulmonary toxicity of naphthalene, and its toxicity in isolated rat liver cells will be investigated. In addition, the significance of catechol formation in the generation of reactive metabolites of phenytoin will be determined. The significance of these mechanistic and enzymatic studies to understanding the toxicity of other environmentally important aromatic compounds will be apparent from the reactivity of the catechols/quinones formed, and the enzymology involved in their formation.
| Billings, R E; Miller, N E; Dabbs, J E et al. (1991) Comparison of the toxicity of naphthalene and naphthalene-1,2-dihydrodiol (DIOL). Adv Exp Med Biol 283:681-4 |
