5-Lipooxygenase Activity in the Human Vessel Wall

Abstract

5-lipooxygenase products have been identified from a variety of cells and may play a role in the progression of atherosclerosis and in its clinical manifestations (spasm, thrombosis). We investigated whether human vascular fragments, freshly obtained at surgery, are able to produce leukotriene (LT) B4, a definite end product of 5-lipooxygenase, provided with biological activity. Fragments obtained from human saphenous veins (n=21) or aorta (fibrous plaques, n=15, atheromas, n=16) were incubated in buffer at 37°C with mechanical agitation sequentially in the absence (15 min) and in the presence (15 min) of 10 jjM calcium ionophore A-23187. At the end of each incubation, the buffer was sampled to be assayed by a specific radioimmunassay (RIA) for LTB4 (sensitivity 4.3+0.9 pg). Validation of the assay was performed by comparison with a chemotactic bioassay in Boyden chambers, by interpolation of a standard curve evaluating the chemotactic response of neutrophils to a standard LTB4 preparation. RIA resulted the only practicable method to detect concentrations lower than 2.5 ng/ml, compared both to bioassay and to HPLC, all three performed in the incubation media from 8 vascular fragments. Incubations were also performed in a chamber with selective exposure of the endothelial surface in order to detect possible production of LTB4 on the luminal site of the vessel. Both unstimulated and ionophore-stimulated LTB4 were higher (P< 0.01) in atheromas (2.7±1.2 and 6.3±1.8) than in fibrous plaques (0.51±0.22 and 1.19±0.38) or saphenous veins (0.74±0.34 and 3.07±1.39) (ng/g wet weight, mean±SD). Detectable spontaneous and stimulated LTB4 productions were also found in the incubation media of the chamber with atheromas (40±14 and 324±85 pg/cm2 area, respectively). Histology of the fragments confirmed a higher cellularity (macrophages, atherocytes) in atheromas as compared to fibrous plaques and veins. The human vascular wall is a definite site of 5-lipooxygenase activity, possibly arising from white cell infiltration. LTB4 production, able to reach the inner vessel surface and the blood stream, is a possible factor in the progression of the lesion by increasing vascular permeability or recruiting white blood cells.

Prostacyclin and Thromboxane Production by Autogenous Femoral Veins Grafted into the Arterial Circulation of the Dog

“…There were significant statisti- cal differences between the pairs (p <0.01) in both conditions of incubation, n = 30. All the vessels produced TxB2, but there was no statistical difference between arteries and veins: 26 ± 5 pg TxB2/mm2 (10-30) vs 19 ± 7 (8-38) in basal and 41 ± 7 (26-51) vs 40 ± 5 (30)(31)(32)(33)(34)(35)(36)(37)(38)(39)(40)(41)(42)(43)(44)(45)(46)(47) in stimulated conditions (n = 20 pairs of biopsies). Each artery or vein produced more 6-keto PGFla than TxB2.…”

“…Several factors including smooth muscle cell mitogen from platelets (7, 8) and non platelet sources, such as IU1 (9, 25) and mitogens released by endothelial cells (26,27) and also pros tanoids (17,18,25,28,29) may be implicated in this complex process. In atheromatous arteries the production of TxA2 and other products derived from AA by the lipooxygenase pathway are highly increased (28)(29)(30) and can even exceed that of PGI2. As TxA2 is known to induce platelet aggregation, our observations in venous grafts suggest that, under certain conditions, the increased vascular production of TxA2 may contribute to thrombosis.…”

“…Several oxygenated products of AA and linoleic acid metabolism released by cyclooxygenase or lipooxygenase pathways by the vessel wall or the circulating cells have been reported to modulate PGI2 synthesis (32,35). Moreover, some of these products may be directly or indirectly implicated in the neointimal fibromuscular hyperplasia and atherosclerosis (26,(28)(29)(30).…”