Comparative toxicity of oleic and linoleic acid on human lymphocytes Maria F. Cury-Boaventura a, * , Renata Gorja ˜o a , Thaı ´s Martins de Lima a , Philip Newsholme b , Rui Curi a a Department of Physiology and Biophysics, Institute of Biomedical Sciences, Av. Prof. Lineu Prestes, 1524, CEP 05508-900, University of Sa ˜o Paulo, SP, Brazil b Department of Biochemistry, Conway Institute of Biomolecular and Biomedical Research, University College Dublin, Belfield, Dublin 4, Ireland Received 4 April 2005; accepted 12 July 2005 Abstract Commercially available lipid emulsions for parenteral nutrition are mainly composed by long chain triacylglycerol containing a high proportion of linoleic acid (LA) or oleic acid (OA). The immunological impact of such therapy is particularly important because parenteral diets are often administered to critically ill patients as a mechanism to supply adequate nutrition during catabolic stress conditions. The comparative toxicity of OA and LA on human lymphocytes and the type of cell death induced by these fatty acids were determined in vitro. Parameters of cell death were investigated by flow cytometry – cell viability, DNA fragmentation, phosphatidylserine externalization, mitochondrial depolarization, neutral lipid accumulation and production of reactive oxygen species – and by fluorescence microscopy— chromatin condensation. Additionally a spectrofluorometric assay was employed to determine the activities of caspase—3, 6 and 8. Evidence is presented herein that OA is less toxic to human lymphocytes than LA. However, both fatty acids promoted apoptosis and necrosis of these cells. The mechanism of cell death induced by OA involved activation of caspase 3 while the mechanism of death induced by LA involved mitochondrial depolarization and ROS production. Importantly, neutral lipid accumulation may be a mechanism to protect lymphocytes against the toxicity induced by OA. OA may offer an immunological less problematic alternative to LA with respect to fatty acid composition of parenteral nutritional emulsions. D 2005 Elsevier Inc. All rights reserved. Keywords: Lymphocytes; Oleic acid; Linoleic acid; Apoptosis; Necrosis Introduction The incorporation of lipid emulsions in parenteral diets is necessary to provide energy requirement to critically ill patients. Lipid emulsions for parenteral nutrition that are commercially available are mainly composed of long chain triglycerides (LCT) containing a high proportion of N-6 polyunsaturated fatty acids (PUFA) (60%), usually derived from soybean or sunflower oil. However, lipid emulsions containing N-9 monounsaturated fatty acids (MUFA) as the main fatty acids are also now available (Allwood, 2000). The immunological impact of such therapy is particularly important because parenteral diets are often administered to critically ill patients who may be immuno-compromised (Lindgren et al., 2001; Lin et al., 2002). Severe trauma and sepsis are associated with depressed immune functions and increase levels of putative immunosuppressive agents such as PGE 2 , IL-4, and IL-10 (Ahmad et al., 1997; Lanza _ Jacoby et al., 2001). In fact, infection and injury activate the immune system and bring about widespread metabolic changes. A combination of enhanced lipolysis in adipose tissue and increased hepatic lipogenesis in infected and injured indivi- duals cause a rapid increase in plasma concentrations of free fatty acids (Grimble, 1998; Zuijdgeest _ Van _ Leeuwen et al., 2002). Studies on the effect of fatty acids on immune response date back over 30 years (Piette and Saugier, 1970). In vitro and in vivo studies have shown that fatty acids modulate a number of leukocyte functions (Arrington et al., 2001; Kelley, 2001), including proliferation (Otton et al., 1998; Granato et al., 2000; Furukawa et al., 2002; Cavaglieri et al., 2003), activation by antigens (Granato et al., 2000), natural killer cell activity 0024-3205/$ - see front matter D 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.lfs.2005.07.038 * Corresponding author. Tel.: +55 11 30917245; fax: +55 11 30917285. E-mail address: mafecury@icb.usp.br (M.F. Cury-Boaventura). Life Sciences 78 (2006) 1448 – 1456 www.elsevier.com/locate/lifescie