COVALENT BINDING OF RADIOACTIVITY FROM [¹⁴C]ROFECOXIB, BUT NOT [¹⁴C]CELECOXIB OR [¹⁴C]CS-706, TO THE ARTERIAL ELASTIN OF RATS

Abstract

ABSTRACT:Rofecoxib is a cyclooxygenase-2 (COX-2) inhibitor that has been withdrawn from the market because of an increased risk of cardiovascular (CV) events. With a special focus on the arteries, the distribution profiles of radioactivity in rats orally administered Rofecoxib (VIOXX) is a potent and highly selective cyclooxygenase-2 (COX-2) inhibitor that has been widely used as a nonsteroidal anti-inflammatory drug (NSAID). However, this drug was withdrawn from the worldwide market because of an increased risk of cardiovascular (CV) events found in the Adenomatous Polyp Prevention on VIOXX (APPROVe) trial, which was conducted for the prevention of the recurrence of colorectal polyps and included 2600 patients with no history of CV disease before enrollment (Merck, 2004). The study had originally been intended to last for 3 years but was halted in midcourse because of the increased CV risks among patients in the group that was taking 25 mg of rofecoxib, in which the incidence of risk was more than twice that in the group taking the placebo.In the last few years, it has been reported that other selective COX-2 inhibitors (e.g., etoricoxib, parecoxib/valdecoxib, and celecoxib) and nonselective NSAIDs (e.g., naproxen) may also have a potential for increased CV risk (Bombardier et al., 2000;Ott et al., 2003; FDA, 2004; FDA Advisory Committee.com, 2004; NIH, 2004;Aldington et al., 2005;Krotz et al., 2005;Nussmeier et al., 2005). However, rofecoxib differs in the following ways: 1) a significantly greater frequency and higher odds of CV events (Mamdani et al., 2004;Solomon et al., 2004a;Graham et al., 2005;Kimmel et al., 2005); 2) a shorter period and a lower dose (even at the clinical dose) leading to the incidence of CV events; and 3) an earlier onset and a greater hypertensive effect correlating closely with CV risk (Brinker et al., 2004;Solomon et al., 2004b;Wolfe et al., 2004;Fredy et al., 2005). Therefore, it is suggested that rofecoxib could have distinctive mechanisms or more potent toxic activity leading to CV risks, in comparison with other selective COX-2 inhibitors or nonselective NSAIDs. Consequently, it is vital to investigate rofecoxib by comparing it with other selective COX-2 inhibitors to clarify its relevance to increased CV events.Several hypotheses have been proposed to explain the mechanism for the increased risk of CV events with rofecoxib. McAdam et al. (1999) suggested the endothelial prostacyclin (PGI 2 )/thromboxane A 2 (TxA 2 ) imbalance theory, whereby the CV complications caused by selective COX-2 inhibitors might be partially due to an imbalance of the concentration ratio of two prostanoids with major CV actions: PGI 2 , a vasodilator and inhibitor of platelet aggregation, and TxA 2 , a vasoconstrictor and promotor of platelet aggregation. That is, selective COX-2 inhibitors diminish the production of PGI 2 in the endothelium, but not TxA 2 in the platelets, so that the relative concentration of TxA 2 increases around the affected area, which might increase the risks. Walter et al. (200...

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

“…As shown in Table 1, the largest amount of the radioactivity from [ 14 C]rofecoxib that was covalently bound to the aorta was recovered in the elastolytic fraction, suggesting that rofecoxib is covalently bound to elastin in the human aorta. This result was consistent with that obtained in rat aorta (Oitate et al, 2006).…”

“…The binding of [ 14 C]celecoxib was significantly lower than that of [ 14 C]rofecoxib, supporting our previous result; that is, there was no retention of radioactivity in the aorta after oral administration of [ 14 C]celecoxib to rats in vivo, whereas the radioactivity from [ 14 C]rofecoxib was retained by and accumulated in the rat aorta (Oitate et al, 2006). The covalent binding of [ 14 C]rofecoxib to rat aortic homogenate in vitro was significantly decreased by the addition of only rofecoxib, whereas the other COX-2 inhibitors had no such effect.…”

“…14 C]rofecoxib in vivo (Oitate et al, 2006). However, it differed in one way: in the rat aorta almost all of the radioactivity (Ͼ90%) was recovered in the elastolytic fraction with a small percentage in the collagenolytic fraction, whereas in the human aorta approximately 41% of the total binding radioactivity was recovered in the collagenolytic fraction as well as in the elastolytic fraction.…”

“…The supernatant was discarded, and the precipitate was washed by resuspension and centrifugation successively with 0.6 M TCA, 80% (v/v) methanol, and 100% methanol until only background radioactivity was measured in each wash. According to a previous report (Oitate et al, 2006), the resulting precipitate was enzymatically treated successively with collagenase (25,000 units, from Clostridium histolyticum; Wako Pure Chemical Industries, Ltd., Osaka, Japan) in 0.1 M Tris-HCl buffer, pH 8.0, at 37°C for 16 h, elastase (4000 units, from porcine pancreas; Wako Pure Chemical Industries, Ltd.) in 0.1 M Tris-HCl buffer, pH 8.5, at 37°C for 16 h, and pronase (10,000 units, from Streptomyces griseus; Merck, Darmstadt, Germany) in 0.1 M sodium phosphate buffer, pH 7.5, at 37°C for 16 h, and then the radioactivity recovered in each proteolytic fraction was measured.…”

Investigation of Long-Term Retention of Unchanged (−)-N-{2-[(R)-3-(6,7-Dimethoxy-1,2,3,4-tetrahydroisoquinoline-2-carbonyl)piperidino]ethyl}-4-fluorobenzamide, A Novel “Funny” If Current Channel Inhibitor, and Its Metabolites in the Eyeball and Thoracic Aorta of Rats

“…The residue precipitated from the thoracic aorta described above was treated with enzymes according to a previously described method (Oitate et al, 2006) with minor modifications. The precipitate was resuspended in 5 ml of 0.1 mol/l Tris-HCl buffer (pH 8.0) containing collagenase (5000 units/ml; Amano Enzyme, Aichi, Japan) and incubated at 37°C for 16 h. After centrifugation (1800g, room temperature, 10 min), the supernatant containing the collagen digests was collected.…”