It has been established previously that low density lipoprotein (LDL) incubated with cultured endothelial cells, smooth muscle cells, or macrophages undergo a free radical-catalyzed oxidative modification. This modification involves lipid peroxides and extensive structural changes in the LDL molecule. The oxidatively modified LDL inhibits the motility of the mouse resident peritoneal macrophages, yet lysophosphatidylcholine in oxidized LDL acts as a chemotactic factor for circulating human monocytes. The present study demonstrated that the stimulation of human mononuclear cells with phorbol myristate acetate (PMA) results in an increase of oxidized LDL, which was assayed by LPO-KIT (obtained from Kyowa Hakko Inc.) in the culture medium. The medium containing oxidized LDL did not exhibit a chemotactic for human monocytes, but inhibited the chemotactic responses of monocytes to the N-formyl peptide and aortic extract.
These findings suggest that circulating monocytes may play a role in the subendothelial space by some chemotactic factors and become trapped in the splace due to the inhibitory effects of oxidatively modified LDL.