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  • Title: Selective inhibition of prostaglandin endoperoxide synthase-1 (cyclooxygenase-1) by valerylsalicylic acid.
    Author: Bhattacharyya DK, Lecomte M, Dunn J, Morgans DJ, Smith WL.
    Journal: Arch Biochem Biophys; 1995 Feb 20; 317(1):19-24. PubMed ID: 7872783.
    Abstract:
    Aspirin causes a time-dependent inhibition of prostaglandin endoperoxide H synthases (PGHS)-1 and -2 by acetylating active site serines present in both isozymes. In the case of PGHS-1, aspirin acetylation blocks cyclooxygenase activity, apparently by preventing arachidonate binding to the cyclooxygenase active site. With PGHS-2, acetylation does not block substrate binding but rather alters the enzyme in such a way that the acetylated form of PGHS-2 produces 15R-hydroxyeicosatetraenoic acid (15R-HETE) instead of the usual prostaglandin endoperoxide product. Based on these differences between PGHS-1 and PGHS-2, we reasoned that a salicylate ester containing an acyl group somewhat larger than the acetyl group of aspirin might be a selective inhibitor of PGHS-2. Accordingly, we prepared and tested eight different acyl salicylates as inhibitors of human (h) PGHS-1 and -2 expressed transiently in cos-1 cells. Valeryl(pentanoyl)salicylate (VSA) was the only compound in this series which showed isozyme selectivity, and, surprisingly, VSA inhibited hPGHS-1 much more effectively than hPGHS-2. Inhibition of hPGHS-1 by VSA was time-dependent. VSA also inhibited ovine PGHS-1 but did not inhibit the S530A mutant of ovine PGHS-1. This latter mutant, which lacks the active site serine hydroxyl group, is also refractory to inhibition by acetylsalicylate. Thus, we conclude that VSA acylates the active site serine of PGHS-1. VSA inhibited prostanoid synthesis by serum-starved murine NIH 3T3 cells which express only PGHS-1; in contrast, VSA caused only partial inhibition of prostanoid synthesis by serum-stimulated 3T3 cells which express both PGHS isozymes. Our results establish that VSA can be used as a reasonably selective inhibitor of PGHS-1.
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