Lysophosphatidylcholine induces the production of IL-1beta by human monocytes

There is evidence for the presence of lysophosphatidylcholine (lysoPC) in oxidatively modified low density lipoprotein, human plasma and in atherosclerotic lesions. We studied the effect of lysoPC on the cytokine production by human monocytes. Among all the cytokines tested (IL-8, TNF alpha, MCP-1 and IL-1beta), we found that lysoPC most consistently stimulated human monocytes to produce IL-1beta in a dose and time dependent manner. Adherent monocytes were exposed to lysoPC in cell culture medium containing 0.5% bovine serum albumin. When exposed to lysoPC from 12.5 to 75 microM, the cellular content of IL-1beta increased 2-4 fold. Up to a concentration of 50 microM no cytotoxic effect could be seen. Over 50 microM there was evidence of toxicity. The level of IL-1beta reached its highest level at 24 h and then declined. At 48 h, the cell associated IL-1beta was low, but still the lysoPC stimulated cells produced 4.1 times more IL-1beta than controls. Also the IL-1beta mRNA was augmented by lysoPC in parallel with the IL-1beta protein levels. The stimulatory effect of lysoPC was dependent on its chain length. There was no effect on IL-1beta production when the acyl chain was shorter than 16. We also found that saturated lysoPC 18:0 stimulated IL-1beta production more than the monounsaturated lysoPC 18:1. Thus, the lysoPC in oxidatively modified LDL may stimulate the production of IL-1beta in macrophages, which may contribute to the inflammatory response in atherosclerotic tissue.