Association between 5-lipoxygenase expression and plaque instability in humans

Objective - The participation of 5- lipoxygenase ( 5- LO) in the development of atherosclerosis has been suggested by recent studies. However, a role for 5- LO as a modulator of atherosclerotic plaque instability has not been previously reported in humans. Thus, the aims of this study was to analyze the expression of 5- LO in human carotid plaques and to investigate the mechanism by which this enzyme could lead to plaque instability and rupture. Methods and Results - We obtained atherosclerotic plaques from 60 patients undergoing carotid endarterectomy. We divided the plaques into symptomatic and symptomatic according to clinical evidence of plaque instability. Clinical evidence of plaque instability was provided by the assessment of recent ischemic symptoms attributable to the stenosis and by the presence of ipsilateral cerebral lesion( s) determined by computed tomography. Plaques were analyzed for CD68 + macrophages, CD3 + T cells, alpha- actin + smooth muscle cells, 5- LO, cyclooxygenase 2, matrix metalloproteinase ( MMP)- 2, and MMP- 9 by immunohistochemical, immunoblotting, and densitometric analyses. MMP activity was assessed by zymography. Leukotriene ( LT) B-4 and collagen were quantified by ELISA and Sirius red polarization, respectively. The percentage of macrophage- rich and T- cell - rich areas was larger in symptomatic compared with asymptomatic patients ( 25 +/- 6% versus 8 +/- 4%, P < 0.0001, and 74 +/- 17 versus 18 +/- 4 cell/ mm(2), P < 0.003). 5- LO expression was higher in symptomatic compared with asymptomatic plaques ( 24 +/- 4% versus 6 +/- 3%, P < 0.0001) and was associated with increased MMP- 2 and MMP- 9 expression ( 27 +/- 4% versus 7 +/- 3%, P < 0.0001, and 29 +/- 5% versus 8 +/- 2%, P < 0.0001) and activity and with decreased collagen content ( 6.9 +/- 2.4% versus 17.8 +/- 3.1%, P < 0.01). Immunofluorescence showed that 5- LO and MMPs colocalize in activated macrophages. Notably, higher 5- LO in symptomatic plaques correlated with increased LTB4 production ( 18.15 +/- 3.56 versus 11.27 +/- 3.04 ng/ g tissue, P < 0.0001). Conclusions - The expression of 5- LO is elevated in symptomatic compared with asymptomatic plaques and is associated with acute ischemic syndromes, possibly through the generation of LTB4, subsequent MMP biosynthesis, and plaque rupture.