ARTICLE I 151 I Inhibition of Human Neutrophil Leukotriene B4 Synthesis in Essential Fatty Acid Deficiency: Role of Leukotriene A Hydrolase Leslie G. Cleland a,*, Michael J. James a, Susanna M. Proudman a, Mark A. Neumann b and Robert A. Gibson b aRheumatology Unit, Royal Adelaide Hospital, Adelaide, South Australia and bDepartment of Paediatrics, Flinders Medical Centre, Bedford Park, South Australia, Australia A female subject dependent on long-term total par- enteral nutrition developed an aversion and noncompli- ance to a prescribed weekly lipid infusion designed to meet essential fatty acid (EFA) requirements. Fatty acids (FA) in the subject's plasma and isolated periph- eral blood neutrophils were analyzed in search of bio- chemical evidence of EFA deficiency. Neutrophil 5- lipoxygenase metabolism was examined to assess the possible effects of EFA deficiency on neutrophil eicosanoid metabolism. EFA deficiency was confirmed by marked depletion of linoleic acid (18:2n-6) and accu- mulation of eicosatrienoic acid (ETrA; 20:3n-9) in plasma and neutrophil phospholipids. In the neu- trophils, ETrA comprised 5.2% of phospholipid FA (nor- mal reference values <0.1%), and arachidonic acid (AA; 20:4n-6) comprised 8.6% of phospholipid FA (normal ref- erence range 10-16%). When stimulated by A23187 in vitro on three separate occasions, the subject's neu- trophils displayed impaired synthesis of leukotriene B 4 (LTB4) , but produced normal amounts of 5-hydroxy- eicosatetraenoic acid and all-trans isomers of LTB 4 formed nonenzymatically from leukotriene A 4 (LTA4). This pattern of synthesis suggested inhibition of LTA hydrolase and was also seen in neutrophils from healthy subjects by addition of exogenous ETrA in vitro. Com- parative studies of the effects of ETrA and eico-sapen- taenoic acid (20:5n-3) on neutrophils in vitro suggested that ETrA is the more potent inhibitor. Accumulation of ETrA, rather than depletion of AA, appears principally responsible for the observed impairment of neutrophil LTB 4 synthesis seen in this EFA-deficient subject. Lipids 29, 151-155 (1994). Eicosanoid mediators of inflammation, such as prosta- glandins, thromboxane and leukotrienes are typically derived from arachidonic acid (AA, 20:4n-6) as n-6 fatty acids (FA) are the prevalent essential fatty acids (EFA) in the Western diet, which contains relatively little n-3 FA. In the presence of severe dietary EFA deficiency, oleic acid (18:1n-9), which can be synthesized endoge- nously, becomes the predominant substrate for the he- patic desaturase/elongase enzymes that normally con- vert dietary linoleic acid (LA; 18:2n-6) to AA. As a result, plasma and cellular levels of eicosatrienoic acid (ETrA; *To whom correspondence should be addressed at Rheumatology Unit, Royal Adelaide Hospital, North Terrace, Adelaide, South Australia, Australia 5000. Abbreviations: AA, arachidonicacid (20:4n-6); EFA,essential fatty acids; EPA, eicosapentaenoic acid; ETrA, n-9 eicosatrienoic acid (20:3n-9); FA, fatty acid(s); HPLC, high-performanceliquid chro- matography;LA, linoleicacid (18:2n-6); LTA, leukotriene A; LTB 4, leukotriene B4; 5-HETE, 5-hydroxyeicosatetraenoic acid. 20:3n-9) increase, and the overall cellular content of 20 carbon highly unsaturated fatty acids is maintained, in spite of AA depletion (1,2). EFA deficiency has been associated with reduced in- flammatory responses in animals (3,4), including ame- lioration in models ofinfiammatory disease (5-8). Early studies demonstrated that EFA-deficient animals with experimentally-induced inflammation had reduced pro- duction of prostaglandins derived from AA via the cy- clooxygenase pathway (3). Prostaglandins can have am- bivalent effects on inflammation, including mediation of enhanced nociception (8) and tissue oedema (9,10), but decreased T lymphocyte responses (11). More recently, the potential importance of the alter- nate 5-1ipoxygenase pathway of AA metabolism has been recognized. This pathway is active in both mononu- clear phagocytes and neutrophils and, in the latter, is the principal pathway of AA metabolism (12). An impor- tant product of this pathway is leukotriene B 4 (LTB4), which is a very potent neutrophil chemotaxin and also stimulates neutrophil degranulation and oxidative burst activity (12). LTB 4 can have pro-inflammatory effects on mononuclear cells, including enhancement of production of the key inflammatory cytokines interleukin-1 (13,14), interleukin-2 (15) and interferon-gamma (15,16). LTB4 inhibits mitogen-induced proliferation of CD4 § T cells and enhances proliferation of CD8 § T cells (17,18) and, accordingly, may also modulate immunological re- sponses. EFA deficiency in rats is associated with marked inhibition of LTB4 production by neutrophils stimulated in vivo (19,20). The effect of EFA deficiency on LTB4 production in humans has not been reported. A woman receiving total parenteral nutrition with in- tolerance to intravenous lipid therapy and severe EFA deficiency has provided the opportunity to assess this issue in a human subject. In vitro studies, in which neu- trophils from healthy volunteers were treated with ETrA, were also undertaken to assess the possible rela- tionship between the observed ETrA accumulation and impaired LTB4 synthesis in the neutrophils of the EFA- deficient subject. MATERIALS AND METHODS Experimental subject. A 33-year-old female had been maintained on total parenteral nutrition via an in- dwelling subclavian catheter for 12 years, following subtotal resection of the small and large bowel for idio- pathic intestinal pseudo-obstruction. She also had three successful pregnancies during this period. Complica- tions included superior vena cava obstruction, recurrent septicaemia, proximal myopathy and an osteoporotic rib Copyright 9 1994 by AOCS Press LIPIDS, Vol. 29, no. 3 (1994)