Phenotyping of cytochromes P-450 in human tissues with monoclonal antibodies
Abstract
Cytochrome P-450 (P-450)-dependent aryl hydrocarbon hydroxylase (AHHase) and 7-ethoxycoumarin deethylase (ECDEtase) in human tissues were differentially inhibited by monoclonal antibodies (MAbs) that were prepared to inhibit and completely inhibited the activity of 3-methylcholanthrene-induced rat liver P-450. The AHHase and ECDEtase of placentas from individual women who smoked were inhibited by the MAbs by 83-90% and by 34-74%, respectively. Benz[a]anthracene (BaA)-induced AHHase and ECDEtase in lymphocytes were inhibited 18-65% and 30-78%, respectively. The enzymes in both control and BaA-induced human cells in culture were inhibited to different extents. Both the AHHase and ECDEtase in control and BaA-induced monocytes and in normal liver were largely unaffected by the MAb. Thus, we have with the MAbs: (i) identified P-450s with a common antigenic site in placenta, lymphocytes, and human cells in culture; (ii) identified two forms of hydrocarbon-induced P-450s in lymphocytes, at least one of which is common with the induced P-450s of placenta and with a P-450 form present in uninduced lymphocytes; (iii) identified two forms of P-450 responsible for smoking-induced ECDEtase activity in placenta, one of which is also responsible for AHHase activity; (iv) shown that the P-450s of liver, basal, and BaA-induced monocytes are different from the MAb-sensitive P-450s of placenta and lymphocytes; (v) quantitated in several human tissues the percentages of control and inducible AHHase and ECDEtase that are dependent on the MAb-sensitive P-450; and (vi) defined by HPLC the contribution of the MAb-sensitive P-450 to the formation of specific benzo[a]-pyrene metabolites. The results demonstrate the value of MAbs for defining antigenic site relatedness for different enzymatic functions of P-450s and for identifying and quantifying the amount of a specific enzyme activity in a tissue dependent on specific P-450s. This study may be a prototype for the use of MAbs for phenotyping and mapping of P-450s responsible for specific metabolic reactions and, thus, may be useful in determining the relationship of P-450 phenotype to individual differences in drug metabolism and carcinogen susceptibility.
