Immunochemical analysis of Cytochrome P450 variability in human leukapheresed samples and its consequences for the risk assessment process

Abstract

Xenobiotic metabolizing Cytochrome P450 (P450) enzymes were investigated in leukapheresed samples from 50 human individuals. It was the aim of the study (a) to get insight into the extent of extrahepatic P450 variability, (b) to investigate whether and to which extent P450 expression and variability as it is seen in the liver corresponds to P450 expression at extrahepatic sites, and (c) to contribute to the replacement of traditionally used default factors (usually 10 for interindividual variability) by data-derived factors in the risk assessment process. P450 enzymes were determined by Western Blotting. Immunoquantification was performed for P450 1A, 1B1, 2C, 2D6, 2E1, and 3A which were—with the exception of the polymorphically expressed CYP2D6—detectable in all samples investigated. Amounts of P450 enzymes in leukapheresed samples were (except CYP1B1) lower compared to those reported for the liver. The P450 variabilities were expressed by the ratios between the 95th and the 5th percentiles. They displayed 7-(CYP1A), 4-(CYP1B1), 6-(CYP2C), 30-(CYP2D6), 3-(CYP2E1), and 4-(CYP3A) fold variability in specific protein content. The results show (a) qualitative and quantitative differences in the expression of P450 proteins in leukapheresed samples from 50 individuals compared to liver, (b) a different extent of variability depending on the P450 enzyme, and (c) in cases where polymorphically distributed P450 enzymes are involved, the traditionally used factor of 10 might be too low to account for interindividual variability in both toxicokinetics and toxicodynamics.