Acceleration of atherogenesis by COX-1-dependent prostanoid formation in low density lipoprotein receptor knockout mice

Abstract

The cyclooxygenase (COX) product, prostacyclin (PGI(2)), inhibits platelet activation and vascular smooth-muscle cell migration and proliferation. Biochemically selective inhibition of COX-2 reduces PGI(2) biosynthesis substantially in humans. Because deletion of the PGI(2) receptor accelerates atherogenesis in the fat-fed low density lipoprotein receptor knockout mouse, we wished to determine whether selective inhibition of COX-2 would accelerate atherogenesis in this model. To address this hypothesis, we used dosing with nimesulide, which inhibited COX-2 ex vivo, depressed urinary 2,3 dinor 6-keto PGF(1alpha) by approximately 60% but had no effect on thromboxane formation by platelets, which only express COX-1. By contrast, the isoform nonspecific inhibitor, indomethacin, suppressed platelet function and thromboxane formation ex vivo and in vivo, coincident with effects on PGI(2) biosynthesis indistinguishable from nimesulide. Indomethacin reduced the extent of atherosclerosis by 55 +/- 4%, whereas nimesulide failed to increase the rate of atherogenesis. Despite their divergent effects on atherogenesis, both drugs depressed two indices of systemic inflammation, soluble intracellular adhesion molecule-1, and monocyte chemoattractant protein-1 to a similar but incomplete degree. Neither drug altered serum lipids and the marked increase in vascular expression of COX-2 during atherogenesis. Accelerated progression of atherosclerosis is unlikely during chronic intake of specific COX-2 inhibitors. Furthermore, evidence that COX-1-derived prostanoids contribute to atherogenesis suggests that controlled evaluation of the effects of nonsteroidal anti-inflammatory drugs and/or aspirin on plaque progression in humans is timely.

Figure 1

Increasing Tx biosynthesis during atherogenesis in LDLR-KO mice. Excretion of the major urinary metabolite of Tx, 2,3-dinor TxB₂, in LDLR-KO mice on a Western-type diet receiving placebo (open bars), indomethacin (hatched bars), or nimesulide (closed bars) at 8 weeks of age and after 18 weeks of treatment (26 weeks of age). (*, P < 0.001.)

Figure 2

Increasing PGI₂ biosynthesis during atherogenesis in LDLR-KO mice. Excretion of 2,3-dinor-6-keto PGF_1α in LDLR-KO mice on a Western-type diet receiving placebo (open bars), indomethacin (hatched bars), or nimesulide (closed bars) at 8 weeks of age and after 18 weeks of treatment (26 weeks of age). (*, P < 0.001.)

Figure 3

Murine atherosclerotic aortas express high levels of COX-2 mRNA. Ribonuclease-protection assay analysis of COX-1 and COX-2 mRNA expression in aortas from LDLR-KO mice at baseline (8 weeks of age; lane 1), and LDLR-KO mice on a Western-type diet receiving placebo (lane 2), indomethacin (lane 3), or nimesulide (lane 4) for 18 weeks of treatment. Blots shown are representative of four separate experiments.

Figure 4

Photomicrographs of representative Sudan IV-stained aortas of LDLR-KO mice on a Western-type diet receiving placebo, indomethacin, or nimesulide for 18 weeks.

Figure 5

Percentage of total aortic-lesion areas in LDLR-KO mice (26 weeks of age) on Western-type diet receiving placebo, indomethacin, or nimesulide for 18 weeks (*, P < 0.001 vs. placebo).