Functional alterations of human neutrophils by medium-chain triglyceride emulsions: evaluation of phagocytosis, bacterial killing, and oxidative activity R. Bellinati-Pires, D.L. Waitzberg,t M.M. Salgado,* and M.M.S. Carneiro-Sampaio tDepartment of Surgery, Medical School, University of Sao Paulo, 404 Journal of Leukocyte Biology Volume 53, April 1993 *Laboratory of Immunology, Adolfo Lutz Institute and Sao Paulo, SI Brazil Abstract: 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 incuba- tion with commercially available fat emulsions contain- ing LCT, MCT, or a mixture ofSO% MCT and 50% LCT at a final triglyceride concentration of 20 mg/mi. It was observed that MCT-containing emulsions stimulated nitroblue tetrazolium (NBT) dye reduction by neutro- phils as determined by a cytochemical NBT test per- formed directly on whole blood. This effect was dose de- pendent. However, after lipid removal by cell washing, the MCT-treated neutrophils showed decreased produc- tion of hydrogen peroxide (H202) and NBT reduction in response to bacterial lipopolysaccharide or phorbol my- ristate acetate stimuli as well as impaired phagocytosis and killing of Staphylococcus aureus. In contrast, the LCT emulsion did not alter any of the neutrophil func- tions 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 mem- brane stimuli. J. Leukoc. Biol. 53: 404-410; 1993. Key Words: triglyceride emulsions . parente al nutrition . neu trophil functions INTRODUCTION There is evidence that changes in dietary fatty acid composi- tion have important implications for host defense mecha- nisms [i-3]. With the introduction oflipid emulsions in total parenteral nutrition (TPN) regimens, the influence of fatty acids on the phagocytic system has received a good deal of attention. The lipid emulsions currently used in TPN consist of long-chain triglyceride (LCT) from vegetable oil, which has a high content of w-6 polyunsaturated fatty acids. These emulsions are valuable as a source ofessential fatty acids and fuel calories; however, there are controversies about their effect on phagocytic cell functions. Depressed chemotaxis and chemiluminescence have been reported in human neu- trophils after intravenous (iv.) administration of LCT [4-6]. On the other hand, other in vivo studies have not confirmed impairment of these neutrophil functions or of the phago- cytic and bactericidal activities [7-10]. These discrepancies could not be explained by the infusion rate or the serum tn- glyceride concentrations observed after LCT administration. Controversial results have also been reported regarding the in vitro effect of LCT on neutrophil function. In this case, the neutrophil disorders seen after cell incubation with LCT [5, 11] could be attributed to the hypotonic condition of this fat emulsion, despite the presence ofglycerol at a theoretical- ly isosmolar concentration. This effect was not observed when the lipid emulsion was dialyzed against isotonic saline or when NaCl crystals were added at a final concentration of 0.85% [12]. Moreover, previous experiments performed with free fatty acids demonstrated that saturated, but not unsaturated, long-chain fatty acids may alter neutrophil functions in vitro [13]. Medium-chain triglycerides (MCTs) consisting of saturated fatty acids (6 to 12 carbons) have been found to play an im- portant role in nutritional therapy [14]. Because MCTs are readily metabolized and cleared from the blood [15], some nutritionists have introduced them in TPN. At present, a mixture of 50% MCT and 50% LCT (MCT/LCT) is avail- able for iv. administration to patients in hypercatabolic states caused by trauma or sepsis [14, 16, 17]. A previous study demonstrated that saturated medium-chain free fatty acids stimulate in vitro neutrophil oxidative metabolism and superoxide anion production [18]. It should be emphasized that the effect ofthese fatty acids on the microbicidal activity of neutrophils is not entirely clear. Furthermore, little is known about the effect of MCT-containing emulsions on hu- man blood phagocytes. Taking these facts into consideration, we investigated the effect of fat emulsions containing MCT, LCT, and the MCT/LCT mixture on human neutrophils, with emphasis on in vitro changes in oxidative metabolism, phagocytosis, and bacterial killing activity. MATERIAL AND METHODS Human blood Venous blood was collected from 20 healthy adult male volunteers aged 18-41 years and from a 7-year-old boy with chronic granulomatous disease (CGD). The patient was ad- Abbreviations: CGD, chronic granulomatous disease; HRPO, horse- radish peroxidase; lB/N, ingested bacterialneutrophil; iv. , intravenous; LCT, long-chain triglyceride; LPS, lipopolysaccharide; MCT, medium- chain triglyceride; NBT, nitroblue tetrazolium; PBS, phosphate-buffered saline; PMA. phorbol myristate acetate; TPN, total parenteral nutrition. Reprint requests: Raquel Bellinati-Pires, Secao de Imunologia, Instituto Adolfo Lutz, Av. Dr. Arnaldo 355, 119 andar, 01246-902, S#{227}o Paulo, SP, Brasil. Received October 17, 1992; accepted January 5, 1993.