Prompt inhibition of fMLP-induced Ca2+ mobilization by parenteral lipid emulsions in human neutrophils.

It remains unclear whether modulation of immune system functions by lipids contributes to the increased infection rate observed in patients treated with parenteral nutrition. We therefore evaluated the effects of lipid emulsions derived from fish oil [very long chain triglycerides (VLCT)], olive oil [long-chain triglycerides- mono-unsaturated fatty acid (LCT-MUFA)], soya oil [long-chain triglycerides (LCT)], or a physical mixture of coconut and soya oil [mixed long- and medium-chain triglycerides (LCT-MCT)] on neutrophil activation. N-formyl-methionyl-leucyl-phenylalanine (fMLP) evoked an immediate increase of the cytosolic Ca2+ concentration ([Ca2+](i,av)) in a suspension of neutrophils. When added 3 min before fMLP, however, all four lipid emulsions reduced the hormone-induced increase in [Ca2+](i,av) with the same efficacy but with different potency. Half-maximal inhibition was reached at emulsion concentrations of 0.24 mM VLCT, 0.32 mM LCT-MCT, 0.52 mM LCT, and 0.82 mM LCT-MUFA. Similarly to the lipids, the protein kinase C (PKC) activator PMA markedly reduced the fMLP-induced increase in [Ca2+](i,av). PMA inhibition was abolished by the PKC inhibitor staurosporine. In contrast, however, this drug did not interfere with the inhibitory lipid effect, indicating that the lipids act primarily in a PKC-independent manner. In summary, this study shows that nutritional lipids can evoke a prompt and significant attenuation of hormone-induced neutrophil stimulation and that the emulsions based on fish oil and a mixture of coconut oil and soya oil are among the most potent ones in this respect.