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Covalent Binding of Rofecoxib, but Not Other Cyclooxygenase-2 Inhibitors, to Allysine Aldehyde in Elastin of Human Aorta

Drug Metabolism & Pharmacokinetics Research Laboratories (M.O., T.M., S.M., T.I.), and Global Project Management Department (T.H.), Daiichi Sankyo Co., Ltd., Tokyo, Japan

In rats, it has been reported that rofecoxib, a cyclooxygenase-2 (COX-2) inhibitor, reacts with the aldehyde group of allysine in elastin to give a condensation covalent adduct, thereby preventing the formation of cross-linkages in the elastin and causing degradation of the elastic fibers in aortas in vivo. Acid, organic solvent, and proteolytic enzyme treatments of human aortic homogenate after incubation with [¹⁴C]rofecoxib demonstrated that most of the radioactivity is covalently bound to elastin. The in vitro covalent binding was inhibited in the presence of ß-aminopropionitrile, D-penicillamine, and hydralazine, which suggested that the aldehyde group of allysine in human elastin was relevant to the covalent binding. The in vitro covalent binding of [¹⁴C]rofecoxib was significantly decreased by the addition of only nonradiolabeled rofecoxib but not the other COX-2 inhibitors, celecoxib, valdecoxib, etoricoxib, and CS-706 [2-(4-ethoxyphenyl)-4-methyl 1-(4-sulfamoylphenyl)-1H-pyrrole], a novel selective COX-2 inhibitor. All the above COX-2 inhibitors except for rofecoxib had no reactivity with the aldehyde group of benzaldehyde used as a model compound of allysine aldehyde under a physiological pH condition. On the other hand, no retention of the radioactivity of [¹⁴C]rofecoxib was observed in human aortic endothelial cells in vitro, suggesting that rofecoxib is not retained in aortic endothelial cells in vivo. These results suggest that rofecoxib, but not other COX-2 inhibitors, is capable of covalently binding to the aldehyde group of allysine in human elastin. This might be one of the main causes of cardiovascular events by rofecoxib in clinical situations.