Effect of a potent cyclooxygenase inhibitor, 5-ethyl-4-methoxy-2-phenylquinoline (KTC-5), on human platelets

Abstract

Abstract Because the metabolites of arachidonic acid participate in many physiopathological responses, including inflammation and platelet aggregation, cyclooxygenase inhibitors are important in the treatment of associated diseases. A biologically active compound, 5-ethyl-4-methoxy-2-phenyl-quinoline (KTC-5), selectively and concentration dependently inhibited aggregation of platelets from man and ATP release caused by arachidonic acid (200 μM) and collagen (10 μ g mL−1) without affecting the aggregation caused by thrombin (0.1 U mL−1) and U46619 (2 μM). The IC50 value (drug concentration inhibiting maximum response by 50%) of KTC-5 for aggregation induced by arachidonic acid and collagen was 0.11 ± 0.04 μM and 0.20 ± 0.03 μM, respectively. This inhibitory effect of KTC-5 was reversible and time dependent. KTC-5 specifically inhibited intracellular calcium mobilization initiated by arachidonic acid or collagen without affecting that caused by thrombin or U46619 in human platelets. Furthermore, KTC-5 inhibited thromboxane B2 and prostaglandin D2 formation provoked by arachidonic acid. The IC50 value of KTC-5 for arachidonic-acid-induced thromboxane B2 formation was 0.07 ± 0.02 μM. Based on these observations, the data indicated that KTC-5 potently inhibited human platelet aggregation and ATP release mainly via the inhibition of the cyclooxygenase-1 activity. Moreover, KTC-5 inhibited lipopolysaccharide-induced prostaglandin E2 formation in RAW264.7 cells in the presence of external arachidonic acid with an IC50 value of 0.17 ± 0.06 μM. Immunoblot analysis showed that KTC-5 did not affect the cyclooxygenase-2 expression in the presence of lipopolysaccharide on RAW264.7 cells. This result indicated that KTC-5 affects the activity of cyclooxygenase-2. According to these data, we concluded that KTC-5 is a cyclooxygenase inhibitor for both subtypes.