LDL STIMULATES CHEMOTAXIS OF HUMAN MONOCYTES THROUGH A CYCLOOXYGENASE-DEPENDENT PATHWAY

Monocyte migration into the vessel wall is an early step in atherogene sis. Even though a number of chemotactic factors have been identified, the regulation of the chemotactic response is not clearly understood. As the release of arachidonic acid has been implicated in monocyte ch emotaxis, we studied the influence of LDL, which can supply this fatty acid to cells, on the chemotactic mobility of monocytes. Migration of human monocytic U937 cells was abolished by a 30-hour incubation in m edium containing lipoprotein-depleted 10% fetal calf serum. Thereafter , human VLDL, LDL, acetyl LDL, methyl LDL, HDL, free cholesterol, lino leic acid, oleic acid, or arachidonic acid was added. At the end of va rying incubation periods (0.5 to 8 hours), chemotaxis, viability, and cellular cholesterol content were measured. In the same experimental s etting we also studied the effects of the pharmacological agents chlor oquine, indomethacin, and acetylsalicylic acid on LDL-mediated chemota xis. Chemotaxis was restored by LDL in a dose- and time-dependent mann er starting at concentrations as low as 5 mu g/mL and at incubations;a s brief as 30 minutes. The other lipoproteins tested (VLDL, HDL, acety l LDL, and methyl LDL) as well as free cholesterol had no comparable e ffect on chemotaxis. Viability and total cholesterol content did not d iffer among the groups. Simultaneous incubation of cells with chloroqu ine, indomethacin, and acetylsalicylic acid reduced restitution of che motaxis by LDL by 71%, 82%, and 68%, respectively. In contrast, the ag ents had only slight inhibitory effects on the chemotactic mobility of serum-fed control cells. Incubation with linoleic acid showed a 60% r estoration of chemotaxis, whereas arachidonic acid stimulated chemotax is by 140% compared with the positive control. Preincubation of LDL wi th the monoclonal antibody MB47 directed against LDL resulted in a sig nificantly reduced migratory response. The data suggest a novel cycloo xygenase-dependent regulatory mechanism of chemotaxis by LDL.