Effect of cyclooxygenase inhibitors and protease inhibitors on phorbol-induced stimulation of oxygen consumption and superoxide production by rat pulmonary macrophages

Oxygen consumption and superoxide anion production by pulmonary macrophages are both increased by phorbol myristate acetate (PMA) but the two processes have been separated using protease inhibitors and cyclooxygenase inhibitors. Pretreatment with the protease inhibitors (L-1-tosylamido-2-phenylethylchloromethyl ketone (TPCK) and N-alpha-p-tosyl-L-lysine chloromethyl ketone (TLCK), as well as with the cyclooxygenase inhibitors acetylsalicylic acid (ASA) and ibuprofen (IBU), inhibited the stimulation of superoxide production and oxygen consumption by phorbol myristate acetate. However, whereas the order of potency for inhibition of stimulation of superoxide production was TPCK greater than TLCK greater than IBU greater than ASA, the order of potency for inhibition of stimulation of oxygen consumption was ASA greater than IBU greater than TPCK = TLCK. Although all four agents were effective inhibitors of PMA-stimulated superoxide production and oxygen consumption when added before PMA, in contrast to the cyclooxygenase inhibitors. TPCK was unable to inhibit oxygen consumption by more than 70-80% regardless of the concentration used, although superoxide generation could be inhibited completely. When added after PMA, ASA did not suppress either oxygen consumption or superoxide production and ibuprofen was only one-half as effective as an inhibitor. TPCK and TLCK, when added after PMA, accelerated the return to basal rates of both oxygen consumption and superoxide production. None of the four agents had any effect on basal superoxide production or oxygen consumption at the concentrations used. The data support the interpretation that both prostaglandin biosynthesis and protease activity may be associated with the activation of the superoxide-generating system of pulmonary macrophages. The consumption of molecular oxygen following stimulation of the cells with phorbol myristate acetate is not due solely to the generation of superoxide, however, since each process is inhibited with different potency by the same group of inhibitors. There appears to be a component of oxygen consumption which results from the activation of cyclooxygenase and, unlike superoxide production, cannot be completely inhibited by treatment with protease inhibitors.