leukotriene-b4 and Aortic-Aneurysm--Abdominal

Leukotriene B4 (LTB4) has been associated with the initiation and progression of atherosclerosis and abdominal aortic aneurysm (AAA) formation. However, associations of LTB4 levels with tissue characteristics and adverse clinical outcome of advanced atherosclerosis and AAA are scarcely studied. We hypothesized that LTB4 levels are associated with a vulnerable plaque phenotype and adverse clinical outcome. Furthermore, that LTB4 levels are associated with inflammatory AAA and adverse clinical outcome.. Atherosclerotic plaques and AAA specimens were selected from two independent databases for LTB4 measurements. Plaques were isolated during carotid endarterectomy from asymptomatic (n = 58) or symptomatic (n = 317) patients, classified prior to surgery. LTB4 levels were measured without prior lipid extraction and levels were corrected for protein content. LTB4 levels were related to plaque phenotype, baseline patient characteristics and clinical outcome within three years following surgery. Seven non-diseased mammary artery specimens served as controls. AAA specimens were isolated during open repair, classified as elective (n = 189), symptomatic (n = 29) or ruptured (n = 23). LTB4 levels were measured similar to the plaque measurements and were related to tissue characteristics, baseline patient characteristics and clinical outcome. Twenty-six non-diseased aortic specimens served as controls.. LTB4 levels corrected for protein content were not significantly associated with histological characteristics specific for vulnerable plaques or inflammatory AAA as well as clinical presentation. Moreover, it could not predict secondary manifestations independently investigated in both databases. However, LTB4 levels were significantly lower in controls compared to plaque (p = 0.025) or AAA (p = 0.017).. LTB4 levels were not associated with a vulnerable plaque phenotype or inflammatory AAA or clinical presentation. This study does not provide supportive evidence for a role of LTB4 in atherosclerotic plaque destabilization or AAA expansion. However, these data should be interpreted with care, since LTB4 measurements were performed without prior lipid extractions.

Topics: Analysis of Variance; Aortic Aneurysm, Abdominal; Case-Control Studies; Humans; Immunohistochemistry; Leukotriene B4; Plaque, Atherosclerotic

Leukotriene B(4) (LTB(4)) is a pro-inflammatory lipid mediator generated by the enzymes 5-lipoxygenase (5-LO) and LTA(4)-hydrolase. LTB(4) signals primarily through its G protein-coupled receptor BLT1, which is highly expressed on specific leukocyte subsets. Recent genetic studies in humans as well as knockout studies in mice have implicated the leukotriene synthesis pathway in several vascular pathologies. Here we tested the hypothesis that pharmacological inhibition of BLT1 diminishes abdominal aortic aneurysm (AAA) formation, a major complication associated with atherosclerotic vascular disease. Chow-fed Apoe(-/-) mice were treated with a 4-week infusion of Angiotensin II (AngII, 1000 ng/(kg min)) beginning at 10 weeks of age, in a well-established murine AAA model. Administration of the selective BLT1 antagonist CP-105,696 beginning simultaneously with AngII infusion reduced the incidence of AAA formation from 82% to 40% (p<0.05). There was a concordant reduction in maximal aortic diameter from 2.35 mm to 1.56 mm (p<0.05). While administration of the antagonist on day 14 after the onset of AngII infusion diminished lesional macrophage accumulation, it did not significantly alter the size of AAA by day 42. Thus, pharmacological inhibition of BLT1 may ultimately hold clinical promise, but early intervention may be critical.

Topics: Angiotensin II; Animals; Aorta; Aortic Aneurysm, Abdominal; Benzopyrans; Carboxylic Acids; Chemotaxis; Disease Progression; Immunohistochemistry; Leukotriene B4; Male; Mice; Ultrasonography

Development and progression of acquired abdominal aortic aneurysms (AAAs) have been associated with different inflammatory mediators. The aim of the present study was to elucidate the topology and the potential mechanisms linking the leukotriene pathway to human AAAs. Human aneurysmal lesions were obtained from 24 patients undergoing surgery, and the intraluminal thrombus was separated from the vascular wall. Histological examination revealed major expression of the leukotriene-producing enzymes 5-lipoxygenase and LTA(4) hydrolase, as well as the two receptors for leukotriene B(4) (BLT1R and BLT2R), corresponding to neutrophils in the luminal part of the thrombus. In contrast, in the vascular wall, the leukotriene pathway mainly localized in macrophage-rich adventitial areas. Furthermore, conditioned media of the intraluminal thrombus contained significantly higher concentrations of leukotriene B(4) than that derived from the vascular wall, which were significantly correlated to other neutrophil-derived mediators, such as elastase/alpha(1)-antitrypsin complexes, myeloperoxidase, and MMP9/NGAL complexes. Finally, the neutrophil-chemotactic activity of the conditioned media from the intraluminal thrombus exhibited major inhibition by antagonists of the leukotriene B(4) receptors. Taken together, these results indicate neutrophil-derived leukotriene B(4) as a major neutrophil chemotactic factor released from the intraluminal thrombus of human AAAs and suggest that targeting BLT receptors may represent a potential medical therapeutic strategy in the prevention of AAA progression in humans.

Topics: Antigens, CD; Antigens, Differentiation, Myelomonocytic; Aortic Aneurysm, Abdominal; Arachidonate 5-Lipoxygenase; Chemotaxis, Leukocyte; Clot Retraction; Epoxide Hydrolases; Humans; Leukotriene B4; Neutrophils; Receptors, Leukotriene B4; Thrombosis

Leukotriene B(4) is a proinflammatory lipid mediator generated by the enzymes 5-lipoxygenase and leukotriene A(4) hydrolase. Leukotriene B(4) signals primarily through its high-affinity G protein-coupled receptor, BLT1, which is highly expressed on specific leukocyte subsets. Recent genetic studies in humans as well as knockout studies in mice have implicated the leukotriene synthesis pathway in several vascular pathologies. In this study, we tested the hypothesis that BLT1 is necessary for abdominal aortic aneurysm (AAA) formation, a major complication of atherosclerotic vascular disease. Chow-fed Apoe(-/-) and Apoe(-/-)/Blt1(-/-) mice were treated with a 4-wk infusion of angiotensin II (1000 ng/min/kg) beginning at 20 wk of age, in a well-established murine AAA model. We found a reduced incidence of AAA formation as well as concordant reductions in the maximum suprarenal/infrarenal diameter and total suprarenal/infrarenal area in the angiotensin II-treated Apoe(-/-)/Blt1(-/-) mice as compared with the Apoe(-/-) controls. Diminished AAA formation in BLT1-deficient mice was associated with significant reductions in mononuclear cell chemoattractants and leukocyte accumulation in the vessel wall, as well as striking reductions in the production of matrix metalloproteinases-2 and -9. Thus, we have shown that BLT1 contributes to the frequency and size of abdominal aortic aneurysms in mice and that BLT1 deletion in turn inhibits proinflammatory circuits and enzymes that modulate vessel wall integrity. These findings extend the role of BLT1 to a critical complication of vascular disease and underscore its potential as a target for intervention in modulating multiple pathologies related to atherosclerosis.

Topics: Animals; Aorta, Abdominal; Aortic Aneurysm, Abdominal; Apolipoproteins E; Cell Migration Inhibition; Disease Models, Animal; Humans; Leukotriene B4; Macrophages; Matrix Metalloproteinase 2; Matrix Metalloproteinase 9; Matrix Metalloproteinase Inhibitors; Mice; Mice, Inbred C57BL; Mice, Knockout; Monocytes; Receptors, Leukotriene B4; T-Lymphocytes

The purpose of this study was to assess the role of polymorphonuclear neutrophil (PMN)-generated leukotriene B4 (LTB4) as an etiologic agent in the pulmonary dysfunction seen after operation in patients undergoing abdominal aortic aneurysm repair.. Blood was analyzed in 10 consecutive patients undergoing elective infrarenal abdominal aortic aneurysm repair for plasma thromboxane B2, lactoferrin, C3a, and PMN-generated LTB4.. There was a close linear correlation (r = 0.88; p < 0.001) between aortic clamp time and PMN LTB4 production. Conversely, aortic clamp time and the ratio of arterial oxygen pressure to fraction of inspired oxygen, a measure of pulmonary function, were inversely related (r = -0.80; p < 0.008). PMNs from patients with long aortic cross-clamp times generated three times more LTB4 than those patients with short cross-clamp times (194 +/- 29.6 vs 64.9 +/- 9.7 ng per 5 x 10(6) PMN; p < 0.05). Similarly, the pressure/inspired oxygen ratio was significantly lower on admission to the intensive care unit in patients with long cross-clamp times as compared with patients with short cross-clamp times (237 +/- 14 vs 342 +/- 5; p < 0.005). In addition, patients with long cross-clamp times remained intubated longer than patients with short times (1.6 +/- 0.2 vs 0.6 +/- 0.4 days; p < 0.05).. These data suggest a causal role for LTB4 in the generation of pulmonary dysfunction in patients undergoing abdominal aortic aneurysm repair, similar to what has been shown in animal models.

Topics: Aged; Aorta; Aortic Aneurysm, Abdominal; Constriction; Humans; Leukotriene B4; Lung; Male; Middle Aged; Neutrophils; Oxygen Consumption; Reperfusion Injury; Time Factors

Aortic aneurysm repair produces inflammatory mediators, neutrophil activation, and remote organ injury. Reperfusion plasma from these patients produces microvascular injury in an ex vivo chemotactic model. This study investigates the mechanism of this injury. Vena caval blood was obtained before and 15 minutes after aortic clamp removal (n = 16) or at laparotomy (n = 10). Plasma or saline solution was introduced into unit dose chambers fixed atop dermabrasions on the back of depilated anesthetized rabbits. Animals were treated with intravenous saline solution (n = 4); made neutropenic with nitrogen mustard (n = 4); pretreated with the xanthine oxidase inhibitor allopurinol (n = 4); or cotreated intravenously with the free radical scavengers superoxide dismutase (SOD) and catalase (n = 4). Three hours later neutrophil counts (polymorphonuclear cells [PMN]/mm3) and activity (free radical production by flow cytometry), protein leakage, and inflammatory mediators (thromboxane [TX] and leukotriene B4 [LTB4]) were measured. In contrast to control plasma in untreated rabbits, reperfusion plasma produced TX and LTB4 generation (1090 +/- 105 and 794 +/- 91 pg/ml, respectively, p < 0.01), PMN accumulation (1636 +/- 210/mm3, p < 0.01) and activation (276 +/- 31 mean fluorescent units), and microvascular permeability (554 +/- 90 micrograms/ml, p < 0.01). Neutropenia (3 +/- 1 PMN/mm3) and cotreatment with SOD and catalase abolished these responses, whereas pretreatment with allopurinol did not. Human reperfusion plasma contains a soluble factor that stimulates free radical generation by rabbit neutrophils to produce a microvascular injury characterized by de novo TX production, neutrophil accumulation and activation, and increased microvascular permeability to protein.

Topics: Allopurinol; Animals; Aortic Aneurysm, Abdominal; Catalase; Cell Movement; Chemotaxis, Leukocyte; Dermabrasion; Humans; Inflammation; Leukocyte Count; Leukotriene B4; Male; Neutrophils; Proteins; Rabbits; Reperfusion Injury; Skin; Superoxide Dismutase; Thromboxane B2