Characterization of Microsomal Cytochrome P450-Dependent Monooxygenases in the Rat Olfactory Mucosa

Abstract

ABSTRACT:Nasal administration of a drug ensures therapeutic action by rapid systemic absorption and/or the entry of some molecules into the brain through different routes. Many recent studies have pointed out the presence of xenobiotic-metabolizing enzymes in rat olfactory mucosa (OM). Nevertheless, very little is known about the precise identity of isoforms of cytochrome P450 (P450)-dependent monooxygenases (P450) and their metabolic function in this tissue. Therefore, we evaluated mRNA expression of 19 P450 isoforms by semiquantitative reverse transcriptase-polymerase chain reaction and measured their microsomal activity toward six model substrates. For purposes of comparison, studies were conducted on OM and the liver. Specific activities toward phenacetin, chlorzoxazone, and dextromethorphan are higher in OM than in the liver; those toward lauric acid and testosterone are similar in both tissues, and that toward tolbutamide is much lower in OM. There are considerable differences between the two tissues with regard to mRNA expression of P450 isoforms. Some isoforms are expressed in OM but not in the liver (CYP1A1, 2G1, 2B21, and 4B1), whereas mRNA of others (CYP2C6, 2C11, 2D2, 3A1, 3A2, and 4A1) is present only in hepatic tissue. Although expression of CYP1A2, 2A1, 2A3, 2B2, 2D1, 2D4, 2E1, 2J4, and 3A9 is noticed in both tissues, there are a number of quantitative differences. On the whole, our results strongly suggest that CYP1A1, 1A2, 2A3, 2E1, 2G1, and 3A9 are among the main functional isoforms present in OM, at least regarding activities toward the six tested substrates. The implication of olfactory P450-dependent monooxygenases in toxicology, pharmacology, and physiology should be further investigated.

Effects of Typical Inducers on Olfactory Xenobiotic-Metabolizing Enzyme, Transporter, and Transcription Factor Expression in Rats

“…Our results showed that the basal mRNA expression and the activity of several phase I and phase II enzymes were of the same order of magnitude or higher in the OM than in the liver. This result is in good agreement with previous observations (Longo et al, 1988;Ben-Arie et al, 1993;Minn et al, 2005). In the present study, we show, for the first time, a significant expression of SULT1C1 mRNA in rat OM.…”

“…Indeed, although the P450 induction capacities of EQ are well known, inhibitory effects of EQ on P450 activities have also been reported (Stohs and Wu, 1982). Because CZX and POD activities are sustained by several P450s, such as CYP2E1, CYP2G1, 2A3, 1A1, and 1A2 (Minn et al, 2005), it is difficult to determine which enzymes are affected by EQ.…”

“…Microsomes and cytosols were prepared by differential centrifugation as described previously (Haber et al, 1994;Minn et al, 2005) and stored in small aliquots at Ϫ80°C. In each group, four pools of four OM were set up to have enough material to perform all of the enzyme assays on the same samples.…”

Expression and inducibility of CYP1A1, 1A2, 1B1 by β-naphthoflavone and CYP2B22, 3A22, 3A29, 3A46 by rifampicin in the respiratory and olfactory mucosa of pig

“…Several genes have been identified in the CYP3A subfamily of mammals (for example, five in rat and four in human), but the expression of these genes in nasal tissues has been poorly investigated. A recent study revealed that olfactory tissue of rat expresses a substantial level of CYP3A9 but not CYP3A1 and 3A2 (Minn et al, 2005). Also in the olfactory microsomes of pig, a CYP3A protein band was immunodetected by anti-rat CYP3A1 but the identity of this protein has not been established (Marini et al, 1998).…”

Intranasal Delivery—Modification of Drug Metabolism and Brain Disposition

“…In metabolism studies of the CYP substrates by human respiratory mucosa, it was found that ethoxyresorufin was not metabolized, and the metabolisms of both testosterone and loteprednol-etabonate were limited and markedly lower than that in the liver (7). On the contrary, metabolic clearance of testosterone was higher in olfactory mucosa than liver in rat (8). For enzymes such as glutathione transferase, epoxide hydroxylase and rhodanese, Gervasi's study suggested that their activities were comparable or lower than that of human liver, while the nasal UDPglucuronyltransferase activity was undetectable (5).…”