Differential induction of BLT receptor expression on human endothelial cells by lipopolysacharide, cytokines, and leukotriene B(4)

Leukotriene (LT) B(4) is a powerful chemotactic and immune modulating agent that signals via two receptors denoted BLT(1) and BLT(2). Here we report that BLT(1) and BLT(2) are expressed at low levels in an apparently silent state in human umbilical vein endothelial cells (HUVEC). However, treatment with LPS leads to a >10 fold increase in the levels of BLT(1) mRNA without any significant effects on BLT(2) mRNA. In parallel, LPS also increases the amounts of BLT(1) protein. Tumor necrosis factor-α (TNF-α) increases the expression of BLT(2) mRNA ≈6 times above basal levels with only a modest increase in BLT(1) mRNA. Interleukin-1β causes variable and parallel increases of both BLT(1) and BLT(2) mRNA. The natural ligand LTB(4) also increases BLT(1), but not BLT(2), mRNA and protein expression. Along with the induction of BLT(1) and/or BLT(2), HUVEC acquire the capacity to respond to LTB(4) with increased levels of intracellular calcium and these signals can be blocked by isotype selective BLT antagonists, CP-105696 and LY-255283. In addition, treatment of HUVEC with LTB(4) causes increased release of both nitrite, presumably reflecting nitric oxide (NO), and monocyte chemoattractant protein-1. Our data indicate that expression of functional BLT receptors may occur at the surface of endothelial cells in response to LPS, cytokines, and ligand, which in turn may have functional consequences during the early vascular responses to inflammation. Moreover, the results point to BLT receptors as potential targets for pharmacological intervention in LT-dependent inflammatory diseases such as asthma, rheumatoid arthritis, and arteriosclerosis

Expanding expression of the 5-lipoxygenase pathway within the arterial wall during human atherogenesis

Oxidation products of low-density lipoproteins have been suggested to promote inflammation during atherogenesis, and reticulocyte-type 15-lipoxygenase has been implicated to mediate this oxidation. In addition, the 5-lipoxygenase cascade leads to formation of leukotrienes, which exhibit strong proinflammatory activities in cardiovascular tissues. Here, we studied both lipoxygenase pathways in human atherosclerosis. The 5-lipoxygenase pathway was abundantly expressed in arterial walls of patients afflicted with various lesion stages of atherosclerosis of the aorta and of coronary and carotid arteries. 5-lipoxygenase localized to macrophages, dendritic cells, foam cells, mast cells, and neutrophilic granulocytes, and the number of 5-lipoxygenase expressing cells markedly increased in advanced lesions. By contrast, reticulocyte-type 15-lipoxygenase was expressed at levels that were several orders of magnitude lower than 5-lipoxygenase in both normal and diseased arteries, and its expression could not be related to lesion pathology. Our data support a model of atherogenesis in which 5-lipoxygenase cascade-dependent inflammatory circuits consisting of several leukocyte lineages and arterial wall cells evolve within the blood vessel wall during critical stages of lesion development. They raise the possibility that antileukotriene drugs may be an effective treatment regimen in late-stage disease