PHARMACOLOGICAL CONTROL OF HUMAN POLYMORPHONUCLEAR LEUKOCYTE DEGRANULATION BY FENAMATES AND INHIBITORS OF RECEPTOR-MEDIATED CALCIUM-ENTRY AND PROTEIN-KINASE-C

The present work was designed to study the mechanism of inhibitory act ion of flufenamic and tolfenamic acids on the degranulation response o f human polymorphonuclear leukocytes (PMNs). We have recently shown th at fenamates inhibit PMN degranulation as well as other PMN functions at micromolar drug concentrations. However, the mechanism of their act ion remains unknown. To clarify this mechanism, the degranulation resp onse was induced by agents known to activate different steps in the ac tivation cascade in PMNs: the receptor-mediated activator fMLP (N-form yl-L-methionyl-L-leucyl-L-phenylalanine); a calcium ionophore (A23187) ; an inhibitor of calcium-ATPase (thapsigargin); and an activator of p rotein kinase C (phorbol myristate acetate, PMA). For comparison, SK&F 96365 (an inhibitor of receptor-mediated calcium entry), Po 31-8220 ( an inhibitor of protein kinase C) and ketoprofen (another cyclooxygena se inhibitor) were used. Flufenamic and tolfenamic acids inhibited A23 187- and fMLP-induced degranulation in a dose-dependent manner. The th apsigargin-triggered response was reduced only slightly and that induc ed by PMA remained unaltered. The pattern of the inhibitory action of fenamates differed from those of Ro 31-8220 and ketoprofen. The action of fenamates resembled that of the inhibitor of receptor-mediated cal cium entry, SK&F 96365, especially when A23187, fMLP or PMA were used to stimulate the cells. This prompted us to measure the effects of flu fenamic and tolfenamic acids on receptor-mediated calcium entry. The t wo fenamates inhibited the fMLP-induced increase in intracellular free calcium in fura-2 loaded PMNs in the presence but not in the absence of extracellular calcium. The results suggest that the suppressive act ions of fenamates on PMN degranulation are neither related to the acti vity of cyclooxygenase nor PMA-activated protein kinase C. In contrast , fenamates resemble the antagonist of receptor-mediated calcium entry , SK&F 96365, in their antagonistic action on PMN degranulation.