Human polymorphonuclear leukocytes (PMN) not only generate and respond to
leukotriene B4 (
LTB4), but also catabolize this mediator of
inflammation rapidly and specifically by omega-oxidation (probably due to the action of a
cytochrome P-450 enzyme). To develop pharmacologically useful inhibitors of the
LTB4 omega-hydroxylase in human PMN, we devised a general scheme for synthesizing terminal acetylenic
fatty acids based on the "acetylenic zipper" reaction. We found that the
LTB4 omega-hydroxylase in intact PMN and in PMN sonicates is inactivated in a concentration-dependent fashion by terminal acetylenic analogues of lauric, palmitic, and
stearic acids (i.e. 11-dodecynoic, 15-hexadecynoic, and 17-octadecynoic
acids). Consistent with a suicidal process, inactivation of the
LTB4 omega-hydroxylase requires molecular
oxygen and
NADPH, is time-dependent, and follows pseudo-first-order kinetics. Inactivation of the
omega-hydroxylase by acetylenic
fatty acids also is dependent on the terminal acetylenic moiety and the
carbon chain length.
Saturated fatty acids lacking a terminal acetylenic moiety do not inactivate the
omega-hydroxylase. In addition, the two long-chain (C16, C18) acetylenic
fatty acids inactivate the
omega-hydroxylase at much lower concentrations (less than 5.0 microM) than those required for inactivation by the short-chain (C12) terminal acetylenic
fatty acid (100 microM). Potent suicidal inhibitors of the
LTB4 omega-hydroxylase in human PMN will help elucidate the roles played by
LTB4 and its omega-oxidation products in regulating PMN function and in mediating
inflammation.