CULTURED HUMAN MICROVASCULAR ENDOTHELIAL CELLS SYNTHESIZE CYCLOOXYGENASE METABOLITES FROM ARACHIDONIC ACID IN RESPONSE TO LEUKOTRIENES C₄ AND D₄

Several investigators have demonstrated that endothelial cells have heterogeneous intrinsic properties depending on their vascular origin. In this respect, very limited knowledge exists concerning the production of eicosanoids by human microvascular endothelial cells (HMEC). The aim of this study was to determine: 1) the pattern of the production of cyclooxygenase metabolites by cultured HMEC from omental adipose tissue as compared to the classical study of human umbilical vein endothelial cells (HUVEC); 2) the modification of this metabolism upon leukotrienes (LTs) stimulation. Cultured HMEC produced prostaglandin (PG) E₂, PGF₂ , 6-keto-PGF₁ , and PGD₂ (measured by enzymoimmunoassay). In basal conditions, PGD₂ was the main product released in the supernatant. Upon stimulation with thrombin, arachidonic acid and calcium ionophore A23187, a marked increase in the production of PGE₂, PGF₂ , and 6-keto-PGFj , was observed; these results were quite different from HUVEC. In contrast, PGD₂ remained unchanged under our experimental conditions and thromboxane B₂ was always undetectable. In all cases, the release of PGE2 and PGF₂ , was higher than that of 6-keto-PGFj . A considerable amount of the metabolites produced remained cell-associated. The total production (release + cell bound) of cyclooxygenase products was stimulated by LTC₄ and LTD₄ in a dose-dependent manner (10^-9 to 10^-6 M). The production of PGD₂ was unchanged. LTC₄ and LTD₄ were almost equally potent, but LTB₄ was unable to stimulate PG synthesis (n=4). The production of metabolites induced by 1 uM LTC₄ or LTD₄ was even higher than that obtained in the presence of high concentrations of thrombin (5 U/ml). This contrasted with the more pronounced stimulation of thrombin on HUVEC as compared to LTs. In the kinetic studies (n=2) we have observed a slow time-course of release of PGE₂ and 6-keto-PGF1 into the supernatant of LTs-stimulated HMEC (half-maximal formation at 14-15 min). The stimulatory activity of LTC₄ and LTD₄ on the production of vasoactive cyclooxygenase metabolites by HMEC could be relevant in inflammatory processes.