Inhibition of cytochrome P450 mediated enzyme activity by alkylphosphocholines.
The inhibitory potency of four alkylphospholipids: rac-1-O-phosphocholine-2-hydroxy-octadecane (rac-2-OH), rac-1-O-phosphocholine-2-O-acetyl-octadecane (rac-2-O-acetyl), rac-1-O-phosphocholine-2-amino-octadecane (rac-2-NH2) and rac-1-O-phosphocholine-2-N-acetyloctadecane (rac-2-N-acetyl), on the cytochrome P450-dependent monooxygenase activity has been evaluated. The IC50 values of the alkylphosphocholines with 7-ethoxycoumarin as substrate in liver microsomal fractions of PB-treated rats and with a reconstituted CYP2B1: NADPH-P450-reductase system are in the range of 3.2-5.0 microM and 2.8-3.5 microM, respectively. Lineweaver-Burk plots with the inhibitors in concentrations that were found to cause roughly a 50% inhibition and with 7-ethoxycoumarin as substrate revealed for all four alkylphospholipids a competitive inhibition type. The degree of the competitive inhibition is quantified by the Ki values. With liver microsomal fractions of PB-treated rats, the Ki values of rac-2-OH (Ki = 1.36 microM) and rac-2-O-acetyl (Ki = 1.33 microM) differs slightly from those of rac-2-NH2 (Ki = 2.2 microM) and rac-2-N-acetyl (Ki = 2.2 microM), but with the reconstituted CYP2B1: NADPH-P450-reductase system all Ki values are in the small range of 1.8 - 2.6 microM, indicating that the short substituted group at the 2-position (OH; O-acetyl; NH2; N-acetyl) of the long chain octadecanol part of the phosphodiesters exhibit no essential role on the strong inhibitory potency of these alkylphosphocholines on the 7-ethoxycoumarin-O-deethylase activity.
Haehner
Thomas
T
Department of Physiological Chemistry, University Ulm, Albert-Einstein-Allee 11, D-89081 Ulm, Germany.
Massing
Ulrich
U
Diesinger
Torsten
T
Müller-Enoch
Dieter
D
D000818:Animals; D019362:Cytochrome P-450 CYP2B1 / Q000037:antagonists & inhibitors*; D065607:Cytochrome P-450 Enzyme Inhibitors; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007700:Kinetics; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology*; D010767:Phosphorylcholine / Q000031:analogs & derivatives* / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley
D065607:Cytochrome P-450 Enzyme Inhibitors; D004791:Enzyme Inhibitors; D010767:Phosphorylcholine; D019362:Cytochrome P-450 CYP2B1