Altered sensitivity of aspirin-acetylated prostaglandin G/H synthase-2 to inhibition by nonsteroidal anti-inflammatory drugs.
Aspirin (ASA) acetylates Ser516 of prostaglandin G/H synthase-2 (PGHS-2) resulting in a modified enzyme that converts arachidonic acid to 15(R)-hydroxy-eicosatetraeroic acid [15(R)-HETE]. ASA has pharmacological benefits that may not all be limited to inhibition of prostaglandin synthesis, and this study was initiated to further investigate the properties of ASA-acetylated PGHS-2 and of the mutation of Ser516 to methionine, which mimics ASA acetylation. Both the S516M mutant and ASA-acetylated form of PGHS-2 (ASA-PGHS-2) synthesize 15(R)-HETE and have apparent K(m) values for arachidonic acid within 10-fold of the apparent K(m) value for untreated PGHS-2. The time courses of turnover-dependent inactivation were similar for reactions catalyzed by PGHS-2 and ASA-PGHS-2, whereas the PGHS-2(S516M) showed a decrease in both the initial rate of 15-HETE production and rate of enzyme inactivation. The production of 15-HETE by modified PGHS-2 was sensitive to inhibition by most nonsteroidal anti-inflammatory drugs (NSAIDs), including selective PGHS-2 inhibitors. As observed for the cyclooxygenase activity of PGHS-2, the inhibition of 15-HETE production by indomethacin was time-dependent for both ASA-PGHS-2 and PGHS-2(S516M). However, two potent, structurally related NSAIDs, diclofenac and meclofenamic acid, do not inhibit either ASA-PGHS-2 or the PGHS-2(S516M) mutant. These results demonstrate that the sensitivity to inhibition by NSAIDs of the 15-HETE production by ASA-treated PGHS-2 is different than that of prostaglandin production by PGHS-2 and that Ser516 plays an important role in the interaction with fenamate inhibitors. The results also indicate that the conversion of arachidonic acid to 15-HETE by ASA-PGHS-2 is an efficient process providing a unique mechanism among NSAIDs that will not lead to arachidonic acid accumulation or shunting to other biosynthetic pathways.
Mancini
J A
JA
Department of Biochemistry and Molecular Biology, Merck Frosst Centre for Therapeutic Research, Kirkland, Québec, Canada. mancini@merck.com
Vickers
P J
PJ
O'Neill
G P
GP
Boily
C
C
Falgueyret
J P
JP
Riendeau
D
D
D000107:Acetylation; D000818:Animals; D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000494:pharmacology*; D016718:Arachidonic Acid / Q000378:metabolism; D001241:Aspirin / Q000494:pharmacology*; D019556:COS Cells; D016861:Cyclooxygenase Inhibitors / Q000494:pharmacology*; D015232:Dinoprostone / Q000096:biosynthesis; D006893:Hydroxyeicosatetraenoic Acids / Q000096:biosynthesis; D011451:Prostaglandin-Endoperoxide Synthases / Q000378:metabolism*
D000894:Anti-Inflammatory Agents, Non-Steroidal; D016861:Cyclooxygenase Inhibitors; D006893:Hydroxyeicosatetraenoic Acids; D016718:Arachidonic Acid; C025984:15-hydroxy-5,8,11,13-eicosatetraenoic acid; D011451:Prostaglandin-Endoperoxide Synthases; D015232:Dinoprostone; D001241:Aspirin