Our objective is elucidation of mechanisms of xenobiotic metabolism in the regulation of the biological fate of foreign chemicals. The work has primarily been on azo dye carcinogens, some of which are frequently found in human environment. Rat liver microsomes metabolize butter yellow (dimethylaminoazobenzene, DAB) by oxidative and reductive pathways. The focus will be primarily on azoreductase inasmuch as this represents detoxication for DAB and other toxic azo dyes, and the mechanisms for azoreduction are not well understood. There are four aspects of the proposed research. (1) The form of cytochrome P-450 which catalyzes DAB azoreduction will be purified from rat liver microsomes. The technique includes affinity and ion exchange chromatography and more recent methods with preparative FPLC. Starting material will be microsomes from rats treated with clofibrate or similar hypolipidemic drug which selectively induce DAB azoreductase activity. (2) Studies on the purified enzyme will include kinetics, effects of inhibitors and structure-activity relationships. (3) The question of azoreduction sensitivity and insensitivity to oxygen will be addressed since reduction of certain azo dyes is inhibited by oxygen. Appearance of free radicals will be measured by EPR to test the theory that oxygen sensitivity is associated with a readily oxidized one electron reduced free radical intermediate during azoreduction. (4) The role of cytochrome b5 in DAB azoreduction will be investigated. Purified cytochrome will be prepared and used in purified reconstituted cytochrome P-450 systems. Antibodies will be prepared to cytochrome b5 and their effect on microsomal DAB azoreductase activity determined. (5) Studies will be performed in the perfused liver to determine the role of azoreduction in the hepatic fate of DAB. Biliary and urinary metabolites of DAB will be measured after treatment to induce or suppress DAB azoreduction.

Agency
National Institute of Health (NIH)
Institute
National Cancer Institute (NCI)
Type
Research Project (R01)
Project #
5R01CA014231-14
Application #
3163896
Study Section
Chemical Pathology Study Section (CPA)
Project Start
1983-06-01
Project End
1991-06-30
Budget Start
1987-07-01
Budget End
1988-06-30
Support Year
14
Fiscal Year
1987
Total Cost
Indirect Cost
Name
Albert Einstein College of Medicine
Department
Type
Schools of Medicine
DUNS #
009095365
City
Bronx
State
NY
Country
United States
Zip Code
10461
Zbaida, S; Brewer, C F; Levine, W G (1994) Hepatic microsomal azoreductase activity. Reactivity of azo dye substrates is determined by their electron densities and redox potentials. Drug Metab Dispos 22:412-8
Zbaida, S; Levine, W G (1992) Role of electronic factors in binding and reduction of azo dyes by hepatic microsomes. J Pharmacol Exp Ther 260:554-61
Stoddart, A M; Levine, W G (1992) Azoreductase activity by purified rabbit liver aldehyde oxidase. Biochem Pharmacol 43:2227-35
Levine, W G; Stoddart, A; Zbaida, S (1992) Multiple mechanisms in hepatic microsomal azoreduction. Xenobiotica 22:1111-20
Levine, W G (1991) Metabolism of azo dyes: implication for detoxication and activation. Drug Metab Rev 23:253-309
Zbaida, S; Levine, W G (1991) A novel application of cyclic voltammetry for direct investigation of metabolic intermediates in microsomal azo reduction. Chem Res Toxicol 4:82-8
Zbaida, S; Levine, W G (1990) Characteristics of two classes of azo dye reductase activity associated with rat liver microsomal cytochrome P450. Biochem Pharmacol 40:2415-23
Stoddart, A M; Levine, W G (1990) Azoreduction of dimethylaminoazobenzene (DAB) in primary cultures of rat hepatocytes. Effect of hypolipidemic agents. Drug Metab Dispos 18:36-41
Zbaida, S; Stoddart, A M; Levine, W G (1989) Studies on the mechanism of reduction of azo dye carcinogens by rat liver microsomal cytochrome P-450. Chem Biol Interact 69:61-71
Levine, W G; Raza, H (1988) Mechanism of azoreduction of dimethylaminoazobenzene by rat liver NADPH-cytochrome P-450 reductase and partially purified cytochrome P-450. Oxygen and carbon monoxide sensitivity and stimulation by FAD and FMN. Drug Metab Dispos 16:441-8

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