Cyclooxygenase-2 promotes early atherosclerotic lesion formation in LDL receptor-deficient mice.

BACKGROUND: Atherosclerosis has features of an inflammatory disease. Because cyclooxygenase (COX)-2 is expressed in atherosclerotic lesions and promotes inflammation, we tested the hypotheses that selective COX-2 inhibition would reduce early lesion formation in LDL receptor-deficient (LDLR-/-) mice and that macrophage COX-2 expression contributes to atherogenesis in LDLR-/- mice. METHODS AND RESULTS: Treatment of male LDLR-/- mice fed the Western diet with rofecoxib or indomethacin for 6 weeks resulted in significant reductions in atherosclerosis in the proximal aorta (25% and 37%) and in the aorta en face (58% and 57%), respectively. Rofecoxib treatment did not inhibit platelet thromboxane production, a COX-1-mediated process, but it significantly reduced the urinary prostacyclin metabolite 2,3-dinor-6-keto-PGF1alpha. Fetal liver cell transplantation was used to generate LDLR-/- mice null for expression of the COX-2 gene by macrophages. After 8 weeks on the Western diet, COX-2-/- --> LDLR-/- mice developed significantly less (33% to 39%) atherosclerosis than control COX-2+/+ --> LDLR-/- mice. In both the inhibitor studies and the transplant studies, serum lipids did not differ significantly between groups. CONCLUSIONS: The present studies provide strong pharmacological and genetic evidence that COX-2 promotes early atherosclerotic lesion formation in LDLR-/- mice in vivo. These results support the potential of anti-inflammatory approaches to the prevention of atherosclerosis.

Inhibition of cyclooxygenase with indomethacin phenethylamide reduces atherosclerosis in apoE-null mice.

Non-selective inhibition of cyclooxygenase (COX) has been reported to reduce atherosclerosis in both rabbit and murine models. In contrast, selective inhibition of COX-2 has been shown to suppress early atherosclerosis in LDL-receptor null mice but not more advanced lesions in apoE deficient (apoE(-/-)) mice. We investigated the efficacy of the novel COX inhibitor indomethacin phenethylamide (INDO-PA) on the development of different stages of atherosclerotic lesion formation in female apoE(-/-) mice. INDO-PA, which is highly selective for COX-2 in vitro, reduced platelet thromboxane production by 61% in vivo, indicating partial inhibition of COX-1 in vivo. Treatment of female apoE(-/-) mice with 5mg/kg INDO-PA significantly reduced early to intermediate aortic atherosclerotic lesion formation (44 and 53%, respectively) in both the aortic sinus and aorta en face compared to controls. Interestingly, there was no difference in the extent of atherosclerosis in the proximal aorta in apoE(-/-) mice treated from 11 to 21 weeks of age with INDO-PA, yet there was a striking (76%) reduction in lesion size by en face analysis in these mice. These studies demonstrate the ability of non-selective COX inhibition with INDO-PA to reduce early to intermediate atherosclerotic lesion formation in apoE(-/-) mice, supporting a role for anti-inflammatory approaches in the prevention of atherosclerosis.

Cyclooxygenase-2 promotes early atherosclerotic lesion formation in ApoE-deficient and C57BL/6 mice.

Cyclooxygenase (COX) 2 is expressed in atherosclerotic lesions. We have previously reported that selective inhibition of COX-2 reduces early atherosclerosis in LDLR deficient mice. To examine the role of COX-2 in atherosclerosis in other mouse models, we studied the effects of selective COX-2 inhibition (by rofecoxib and NS-398) and nonselective COX inhibition (by indomethacin) on early atherosclerotic lesion formation in apolipoprotein E-deficient (apoE(-/-)) mice. Selective COX-2 and nonselective COX inhibition reduced atherosclerosis in female apoE(-/-) mice by 35-38% and 38-51% in the proximal and en face aortas, respectively. Next we investigated the role of macrophage COX-2 by transplanting COX-2(-/-) fetal liver cells into C57BL/6 mice and challenging the mice with an atherogenic diet. Genetic deletion of COX-2 from hematopoietic cells reduced atherosclerosis by 51%. In addition, LPS activated COX-2(-/-) macrophages had decreased expression of monocyte chemoattractant protein-1 (MCP-1) and tumor necrosis factor-alpha (TNFalpha). The results demonstrate that selective inhibition of COX-2 and elimination of COX-2 from macrophages significantly reduces early atherosclerotic lesion formation in apoE-deficient and C57BL/6 mice. These results are compatible with COX-2 expression by macrophages having a proatherogenic role, and support the potential of anti-inflammatory therapeutic approaches for atherosclerosis.

Physiological expression of macrophage apoE in the artery wall reduces atherosclerosis in severely hyperlipidemic mice.

We have previously reported that the introduction of macrophage apoE into mice lacking both apoE and the LDL receptor (apoE(-)(/-)/LDLR(-)(/-)) through bone marrow transplantation (apoE(+)(/+)/LDLR(-)(/-)-->apoE(-)(/-)/LDLR(-)(/-)) produces progressive accumulation of apoE in plasma without affecting lipid levels. This model provides a tool to study the effects of physiologically regulated amounts of macrophage apoE on atherogenesis in hyperlipidemic animals. Ten-week-old male apoE(-)(/-)/LDLR(-)(/-) mice were transplanted with either apoE(+)(/+)/LDLR(-)(/-) (n = 11) or apoE(-)(/-)/LDLR(-)(/-) (n = 14) marrow. Although there were no differences between the two groups in lipid levels at baseline or at 5 and 9 weeks after transplantation, apoE levels in the apoE(+)(/+)LDLR(-)(/-)-->apoE(-)(/-)/LDLR(-)(/-) mice increased to 4 times the apoE levels of normal mice. This resulted in a 60% decrease in aortic atherosclerosis in the apoE(+)(/+)/LDLR(-)(/-)-->apoE(-)(/-)/LDLR(-)(/-) compared with the apoE(-)(/-)/LDLR(-)(/-)-->apoE(-)(/-)/LDLR(-)(/-) controls, (15957 +/- 1907 vs. 40115 +/- 8302 micro m(2) +/- SEM, respectively). In a separate experiment, apoE(+)(/+)/LDLR(-)(/-) mice were transplanted with either apoE(+)(/+)/LDLR(-)(/-) or apoE(-)(/-)/LDLR(-)(/-) marrow and placed on a high-fat diet for 8 weeks. In the absence of macrophage apoE, lesion area was increased by 75% in the aortic sinus and by 56% in the distal aorta. These data show that physiologic levels of macrophage apoE in the vessel wall are anti-atherogenic in conditions of severe hyperlipidemia and can affect later stages of plaque development.