ABSTRACT
INTRODUCTION Biotransformation of xenobiotics can profoundly influence their toxicity. Enzymes of virtually all toxicant biotransformation pathways have been detected in the nose including phase I hydrolysis (esterase, peptidase, epoxide hydrolase), reduction (carbonyl reduction), and oxidation [alcohol dehydrogenase, aldehyde dehydrogenase, flavin-monooxygenase, and cytochrome P450 monooxygenase (CYP)] pathways. Biotransformation enzymes of phase II pathways (glucuronide conjugation, glutathione conjugation, etc.) are present as well. Substrates for phase II biotransformation, in particular glutathione, are present in nasal tissues in concentrations similar to that in the liver in rodents as well as in man (1). Since phase I and phase II enzymes often catalyze sequential biotransformations, it is the balance of their activities which is critical in influencing the toxic response.
