ARACHIDONIC-ACID METABOLITES ARE INVOLVED IN MEDIATING RED-BLOOD-CELLADHERENCE TO ENDOTHELIUM

As an initial investigation into the possible role of endothelial cell (EC] lipoxygenase and cyclooxygenase metabolites in the adherence of red blood cells (RBCs) to ECs, we evaluated the effect of nordihydrogu aiaretic acid, (NDGA; 10 mu mol/L), BW755c (30 mu mol/L), aspirin (100 mu mol/L), and Indomethacin (10 mu mol/L) on RBC-K: adherence using a static incubation system and Cr-51-labeled RBCs. NDGA and -amino-L-[3 '-(trifluoromethyl)phenyl]-2-pyrazoline inhibitors of both the lipoxyg enase and cyclooxygenase pathways, significantly decreased basal adhes ion of RBCs to fetal bovine aortic ECs, whereas aspirin and indomethac in, selective inhibitors of the cyclooxygenase pathway, stimulated the adherence process. The inhibitor effect appeared to be mediated via a n effect on EC functions, since preincubation of ECs with NDGA, in con trast to RBC-NDGA preincubation, inhibited the adherence process. Beca use bovine aortic ECs generate mainly prostacyclin and IB-HETE from ar achidonic acid (AA) via the cyclooxygenase and the lipoxygenase pathwa ys respectively, the role of these products (100 pmol/L to 1 mu mol/L) on the adhesive process was further assessed. 15-HETE potentiated bas al adhesion of RBCs to bovine aortic ECs in a concentration-dependent manner, with maximal responses of approximately 50% to 150% over basel ine noted at concentrations between 1 and 100 nmol/L. 12-HETE, a struc tural isomer of 15-HETE and the major platelet lipoxygenase product, a lso stimulated RBC adherence. In contrast, prostacyclin (assessed usin g carbacyclin, a stable synthetic analog of prostacyclin with similar biologic properties) had no significant effect on this process. In fur ther studies, we demonstrated that the 12-HETE-induced adherence of si ckle RBCs was mediated via an up-regulation of the vitronectin recepto r on bovine aortic endothelium. Because microvascular capillary endoth elium is the surface most likely to encounter erythrocytes in vivo, we extended our studies to human retinal capillary ECs to assess the inv olvement of eicosanoids in sickle RBC-microvessel adhesion. As with bo vine aortic ECs, aspirin stimulated and NDGA decreased the adherence o f sickle RBCs to human retinal capillary endothelium. These microvascu lar ECs generated prostacyclin, HHT, 15-HETE, and 15-HPETE from endoge nous Ak Although carbacyclin and HHT had no effect on the adherence pr ocess, both 15-HETE and 15-HPETE (10 pmol/L to 100 nmol/L) stimulated RBC adhesion to capillary endothelium. Our studies document a role for the lipoxygenase metabolites in modulating basal adhesion of RBCs to both macrovascular and microvascular endothelium; the major cyclooxyge nase metabolites appear to play no role in this process.