Some Biotransformation Enzymes Responsible for Polycyclic Aromatic Hydrocarbon Metabolism in Rat Nasal Turbinâtes:Effects on Enzyme Activities of in Vitro Modifiers and Intraperitoneal and Inhalation Exposure of Rats to Inducing Agents1

Respiratory tract biotransformation of many xenobiotics found in inhaled environmental pollutants is generally considered es sential for the mutagenic, carcinogenic, and/or toxic response of lung tissue to these xenobiotics. Typical environmental pollutants contain known carcinogens adsorbed onto particles which can deposit in the nasal pharyngeal region of the respiratory tract. The purpose of this study was to characterize the metabolic capacity of rat nasal tissue. Both oxidative and nonoxidative enzyme activities were investigated which included aryl hydro carbon hydroxylase (AHH), epoxide hydrolase (EH), uridine 5'diphosphate-glucuronyltransferase (UDPGT), and glutathione transferase. Specific enzyme activities of AHH, EH, UDPGT, and glutathione transferase were 0.023, 6.4, 20.4, and 24.8 nmol product per mg protein per min, respectively. Benzo(a)pyrene was metabolized by AHH to dihydrodiols, quiñones,and phenols in quantities which were about 10 times greater than those reported for rat lung microsomes. Small, but detectable, quan tities of benzo(a)pyrene tetrols were also measured in reaction flasks in which rat nasal tissue was incubated with benzo(a)pyrene. Attempts to increase the microsomal enzyme activities of AHH, EH, and UDPGT by pretreating rats with various inducing agents by both i.p. injection (phénobarbital, 3-methylcholanthrene, Aroclor 1254, and 2,3,7,8-tetrachlorodibenzo-p-dioxine) and inhalation exposure (BaP) resulted in rat nasal monooxygenases only being induced (2-fold) after pretreatment with 2,3,7,8tetrachlorodibenzo-p-dioxine. Phénobarbital increased enzyme activities of EH and UDPGT by about 50%. These data suggest that rat nasal tissue may contain multiple forms of cytochrome P-450 and of EH and UDPGT. The results from this study support the notion that nasal tissue may be important in determining the metabolic fate of inhaled xenobiotics. 1Research supported in part by the Environmental Protection Agency via Interagency Agreement EPA-81-D-X0533 under United States Department of En ergy Contract DE-AC04-76EV01013 and in part by the Department of Energy under Contract No. DE-AC04-76EV01013 and conducted in facilities fully ac credited by the American Association for Accreditation of Laboratory Animal Care. Although the research described in this document has been funded in part by the Environmental Protection Agency through Interagency Agreement No. EPA-81-DX0533 to the Department of Energy, it has not been subjected to Environmental Protection Agency review and therefore does not necessarily reflect the views of the Environmental Protection Agency and no official endorsement should be inferred. Mention of trade names or commercial products does not constitute endorsement or recommendation for use. Portions of this work were presented at the Second Joint Meeting of the American Society for Pharmacology and Experi mental Therapeutics/Society of Toxicology in Louisville, Ky., August 1982 (4). 2To whom requests for reprints should be addressed, at Inhalation Toxicology Research Institute, Lovelace Biomédicaland Environmental Research Institute, P. O. Box 5890, Albuquerque, N. M. 87185. Received October 25, 1982; accepted June 10,1983. INTRODUCTION Respiratory tract tissue, which serves as a major site of deposition of inhaled xenobiotics, is a target for inhaled carcin ogens (1). Pulmonary biotransformation of many xenobiotics found in inhaled environmental pollutants (e.g., PAH3) is generally considered essential for the mutagenic, carcinogenic, and/or toxic effects of these xenobiotics on lung tissue (1). Studies to assess the relative activities in lung tissue of both activating and inactivating enzymes responsible for the overall biotransforma tion of inhaled xenobiotics in lung tissue have used such prepa rations as lung cell homogenates (20), cultured lung cells (12, 16), cultured tracheal-bronchial expiants (2, 12), and isolated perfused lung preparations (3,23,28). Until recently, nasal tissue has been neglected as a site of xenobiotic biotransformation, despite its potential role as a "first line of defense" to inhaled xenobiotics. Nasal tissue metabolism may be particularly impor tant because many environmental pollutants contain known car cinogens adsorbed onto particles of sizes (1to 100-/tm mass median aerodynamic diameter) which deposit in the nasopharyngeal region of the respiratory tract (32, 40). Cytochrome P-450-dependent monooxygenase activities have been measured in nasal tissue of both dogs (14) and rodents (9, 17) and found active toward a variety of substrates including aniline, aminopyrine, and p-nitroanisole. The importance of cy tochrome P-450 in the metabolic activation of a variety of promutagens is well understood (29, 45). For example, BaP, a prototypic PAH carcinogen, is metabolized to a wide variety of both organicand water-soluble metabolites which include epoxides, phenols, quiñones, frans-dihydrodiols, and GSH, sulfate, and glucuronide conjugates (19). The importance of further me tabolism of the dihydrodiols to highly carcinogenic diol-epoxides has been reviewed extensively (29, 45). The purpose of the present investigation was to characterize the metabolic capacity of rat nasal tissue. Both oxidative and nonoxidative (hydrolysis; conjugation) enzyme activities (includ ing AHH (EC 1.14.14.2), EH (EC 3.3.2.3), UDP-glucuronyltrans3The abbreviations used are: PAH, polycyclic aromatic hydrocarbons; BaP, benzo(a)pyrene; GSH, glutathione; AHH, aryl hydrocarbon hydroxylase; EH, epox ide hydrolase; TCDD, 2.3.7,8-tetrachlorodibenzo-p-dioxin: BSA, bovine serum al bumin; PB, sodium phénobarbital; 3-MC, 3-methylcholanthrene; SKF-525A, 2diethylaminoethyl-2,2-diphenylvalerate; [BaP-9,10-diol, trans-9,10-dihydrobenzo(a)pyrene-9,10-diol; BaP-4,5-diol, trans-4,5-dihydrobenzo(a)pyrene-4,5-diol; BaP-7,8-diol, trans-7,8-dihydrobenzo(a)pyrene-7,8-diol; BaP-4,5-oxide, 4,5-dihydrobenzo(a)pyrene-4,5-oxide; 3-OH-BaP, 3-hydroxybenzo(a)pyrene; 9-OH-BaP, 9-hydroxybenzo(a)pyrene; BaP-1,6-dione. 1,6-dihydrobenzo(a)pyrene-1,6-dione; BaP-3,6-dione, 3,6-dihydrobenzo(a)pyrene-3,6-dione; BaP-6,12-dione, 6,12-dihydrobenzo(a)pyrene-6,12-dione; BaP-tetrols, BaP-(+}-r-7,f-8,c-9,c-10-tetrahydroxy7,8,9,10-tetrahydrotetrol, BaP-(+)-r-7,f-8,r-9,c-10-tetrahydroxy-7,8,9,10-tetrahydrotetrol, BaP-<+)-r-7,f-8,c-9,r-10-tetrahydroxy-7,8,9,10-tetrahydrotetrol; BaP-<+)r-7,f-8,f-9,MO-tetrahydroxy-7,8.9,10-tetrahydrotetrol; DEM, diethyl maléate.