Is cytochrome P450 CYP2D activity present in pig liver?

Abstract

The presence of CYP2D in pig livers has been studied using different strains of pig, different CYP2D test substrates and monoclonal and polyclonal antibodies. The results of the studies lacked consistency, therefore the aim of this study was to identify the reasons for these inconsistencies. Liver microsomes isolated from conventional pigs and minipigs were tested in Western blotting using both monoclonal and polyclonal antibodies against human CYP2D6. The microsomes were also incubated with three different CYP2D tes t substrates.'The immunoblotting only gave a positive response when hybridised with polyclonal antibody. The pig microsomes did not metabolise debrisoquine, but metabolised two other test substrates, dextromethorphan and bufuralol. No correlation was found between the two enzyme assays and CYP2D apoprotein level. On the other hand positive correlations were found between dextromethorphan and bufuralol metabolism and the CYP2B immunochemical protein level, indicating that the CYP2B isoenzyme may be involved in the metabolism of these substrates. Further, assays using immunoinhibition and chemical inhibition of these reactions were performed. No response was obtained in the immunoinhibition assay. When using chemical inhibition, however, an average inhibition percentage of 83 were obtained with orphenadrine, a human CYP2B inhibitor. Average Ki values of 26.9 microM and 43.6 microM for orphenadrine indicate that it was a potent inhibitor. A rat and a mouse CYP2B inhibitor, resveratrol and pilocarpine, inhibited the reaction with an average of 40 and 70 percentage respectively. Orphenadrine did not inhibit CYPIA, CYP2A, CYP2E and CYP3A activities up to more than maximum 12 percentage, showing that it was almost selective for dextromethorphan metabolism. These results indicate that dextromethorphan and bufuralol metabolism may be catalysed by CYP2B and not CYP2D.