Cytochrome P450 Pig Liver Pie: Determination of Individual Cytochrome P450 Isoform Contents in Microsomes from Two Pig Livers Using Liquid Chromatography in Conjunction with Mass Spectrometry

The cytochrome P450 (P450) family of enzymes is a major player in the metabolism of therapeutic drugs available on the market, and the development of novel drugs has to take into account these enzymes in the fate of new drugs. Testing the pharmacokinetic behavior of new drugs in animals is a common part of the drug development process. Pigs are increasingly used for this purpose because of their similarity of enzymatic pattern to humans. In this study, adult Suffolk White pig liver microsomal samples were analyzed using mass-spectrometry-based techniques to identify and relatively quantify the porcine hepatic P450 enzymes. The total corrected microsomal protein content (milligrams of protein per gram of liver tissue) was estimated at 32.6 and 36.2 mg/g liver tissue in two samples, and the main identified liver P450 subfamilies were CYP1A, CYP2A, CYP2C, CYP2D, CYP2E, and CYP3A. Label-free quantification was performed using the exponentially modified protein abundance index, and the highest abundance enzymes were CYP2A19 at 34% and CYP2D25 at 26% of the total identified drug-metabolizing P450 enzymes. The highest abundance subfamilies were CYP2A (34%), CYP2C (16%), CYP2D (26%), and CYP3A (14%). Moreover, primary sequence alignment was used to identify human homologs of the identified porcine P450s. Porcine CYP1A2 and CYP2E1 were shown to be equivalent to human CYP1A2 and CYP2E1, respectively. Porcine CYP2A19 has the highest sequence homology to human CYP2A6 and CYP2A13, and pig CYP2C33v4 and CYP2C49 are the porcine equivalent of human CYP2C9 and CYP2C18, respectively. Both identified pig CYP3A enzymes (CYP3A29 and CYP39) were highly homologous to CYP3A4/5.