Functional alterations of human neutrophils by medium-chain triglyceride emulsions: evaluation of phagocytosis, bacterial killing, and oxidative activity.

Medium-chain triglyceride (MCT) and long-chain triglyceride (LCT) emulsions currently used in nutritional therapy were evaluated for their in vitro effect on neutrophil oxidative metabolism, phagocytosis, and bacterial killing activities. Neutrophils from healthy adult male volunteers were assessed after blood incubation with commercially available fat emulsions containing LCT, MCT, or a mixture of 50% MCT and 50% LCT at a final triglyceride concentration of 20 mg/ml. It was observed that MCT-containing emulsions stimulated nitroblue tetrazolium (NBT) dye reduction by neutrophils as determined by a cytochemical NBT test performed directly on whole blood. This effect was dose dependent. However, after lipid removal by cell washing, the MCT-treated neutrophils showed decreased production of hydrogen peroxide (H2O2) and NBT reduction in response to bacterial lipopolysaccharide or phorbol myristate acetate stimuli as well as impaired phagocytosis and killing of Staphylococcus aureus. In contrast, the LCT emulsion did not alter any of the neutrophil functions evaluated. The present data suggest that MCTs elicit the oxidative metabolism of neutrophils, probably by phagocytosis of fat particles and, depending on the lipid concentration, this effect may not be reversible, leading to impairment of the cellular response to subsequent membrane stimuli.