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Published online before print September 20, 2007

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(Journal of Leukocyte Biology. 2007;82:1501-1509.)
© 2007 by Society for Leukocyte Biology

Acyl chain-dependent effect of lysophosphatidylcholine on human neutrophils

P. J. Ojala^*, T. E. Hirvonen^*, M. Hermansson, P. Somerharju and J. Parkkinen^*,,1

^* Finnish Red Cross Blood Service, Helsinki, Finland;
Institute of Biomedicine, Department of Biochemistry, University of Helsinki, Helsinki, Finland; and
Department of Clinical Chemistry, Helsinki University Central Hospital, Helsinki, Finland

¹Correspondence: Department of Clinical Chemistry, Helsinki University Central Hospital, Biomedicum, FIN-00290 Helsinki, Finland. E-mail: jaakko.parkkinen{at}helsinki.fi

Lysophosphatidylcholine (LPC) is the most abundant lysophospholipid in plasma and tissues, and its level increases in ischemia and inflammation. LPC induces various proinflammatory actions in leukocytes, endothelial cells, and smooth muscle cells, but its effects may vary, depending on the acyl chain. In the present study, we identified the molecular species of LPC in human plasma and studied their effects on human neutrophils. Unsaturated LPC species over a wide concentration range (5–200 µM) induced long-lasting superoxide production in neutrophils. The response was preceded by a >10-min lag time and lasted for 60–90 min. Superoxide production was prevented when albumin was added together with LPC at a molar ratio of 1:2 or higher, and significant inhibition was observed even when albumin was added 4–8 min after LPC. Saturation of albumin by fivefold molar excess of stearic acid reduced the inhibitory effect significantly. Saturated LPCs, particularly the most abundant 16:0 species, induced significantly less superoxide production than the unsaturated species and only at 5–10 µM concentrations. Saturated LPC species elicited a several-fold higher increase in cytoplasmic calcium and at >20 µM, increased plasma membrane permeability. A mixture of LPCs mimicking the plasma LPC composition induced nearly similar superoxide production as the most active LPC18:1 alone. These results indicate remarkable acyl chain-dependent differences in the cellular effects of LPC. Elevation of LPC level may increase inflammation through activation of neutrophil NADPH oxidase, particularly when the simultaneous increase of free fatty acids diminishes the ability of albumin to scavenge LPCs.

Key Words: superoxide • NADPH oxidase • albumin • free fatty acids • ischemia