This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. ALI and the acute respiratory distress syndrome (ARDS) are common and severe complications of pulmonary or systemic injury, resulting in hypoxemic respiratory failure. The recent King County Lung Injury Project found the incidence to be 79 cases/100,000 person-years, exceeding most previous estimates.1 ALI is a major cause of morbidity and mortality and further research aimed at reducing these consequences is needed. The devastating clinical manifestations of ALI are thought to result from massive activation of the proinflammatory response.2, 3 Activated macrophages release cytokines such as IL-1, IL-6, IL-8, IL-10, and TNF-¿, which in turn activate neutrophils locally. The activated neutrophils then produce proteases, oxidants, and lipid-derived mediators including eicosanoids, which perpetuate the lung injury cycle.4 The eicosanoid inflammatory mediators are derived from arachidonic acid (AA), a common membrane phospholipids in the usual Western diet.5, 6 When the inflammatory cascade is activated, AA is metabolized by cyclooxygenase (COX) to the 2-series prostaglandins (PGs) and thromboxanes (TXs) and by 5-lipoxygenase (LOX) to the 4-series leukotrienes (LTs). These pro-inflammatory eicosanoids play a prominent role in fever, vascular permeability, vasodilatation, platelet aggregation, leukocyte adhesion, bronchoconstriction, and production of other cytokines.7-11 Eicosapentaenoic acid (EPA) and docosahexanoic acid (DHA) are two essential n-3 FAs found in fish oil. When consumed, n-3 FAs are incorporated into immune cell membranes,12, 13 replacing AA.6 By restricting the amount of substrate AA, the formation of eicosanoids is limited.9 EPA also acts to inhibit metabolism of AA by COX.14 Additionally, EPA is a substrate for COX and 5-LOX and is metabolized to the 3-series PGs and TXs and the 5-series LTs, which are significantly less active than those derived from AA.15, 16 EPA and DHA have been shown in animal studies to decrease production of AA-derived eicosanoids.17, 18 EPA and DHA improved survival in rats receiving an infectious challenge19 and in rodent models of endotoxin-induced shock20 and chronic sepsis.21 EPA attenuated pulmonary edema in a pig ALI model.22 EPA and DHA have been combined with ¿-linoleic acid (GLA) and antioxidants (vitamins E and C, ¿-carotene, taurine, and L-carnitine) into a commercial high-fat low-carbohydrate enteral formula called Oxepa¿ (Ross Products). GLA is an n-6 FA found in borage oil that is metabolized to dihomo-¿-linoleic acid that is then converted to AA. Oxepa¿ has been evaluated in several industry-sponsored animal studies. It has been shown to decrease AA concentration in inflammatory cell membranes;23-28 reduce alveolar concentrations of LTB4, PGE2, and TXB2;24, 25 decrease pulmonary capillary permeability;24 and reduce alveolar neutrophil accumulation25 in endotoxemic rats. The only studies of n-3 FAs in critically ill humans have used Oxepa¿. Three small phase II trials have been performed in patients with ALI and sepsis.29-31 The control groups in all 3 trials were given Pulmocare¿ (Ross Products), a high-fat low-carbohydrate enteral formula that is isonitrogenous with Oxepa¿ but does not contain fish oil. Each study found positive physiological, biochemical, and clinical outcomes in the Oxepa¿ group, including improved oxygenation, decreased BALF neutrophil count, reduced BALF IL-8 and LTB4, decreased duration of mechanical ventilation, decreased ICU length of stay, and fewer new organ failures. One study found a mortality benefit with Oxepa¿.31 Interpretation of these data is restricted by two important limitations: 1) the control groups were fed a formula containing high amounts of corn oil, which is largely composed of linoleic acid (n-6 FA) and may be proinflammatory since it could increase concentrations of AA and 2) the independent effects of n-3 FAs on inflammatory, physiologic, and clinical outcomes in ALI patients are impossible to assess. Furthermore, the investigational approach of combining several nutrients into a commercial enteral formula for critically ill patients leads to two important problems: 1) the scientific "proof of concept" for each nutrient is poor, with no phase I and II human trials being published on the individual agents and 2) patients may not receive adequate amounts of the nutrient since delivery is dependent upon enteral feeding (ICU patients commonly receive 60% of their prescribed caloric need).32 Even with these limitations, I believe the therapeutic benefits of Oxepa¿ most likely result from EPA+DHA rather than GLA or antioxidants, although a positive interaction between the nutrients cannot be ruled out. Antioxidants likely have only minimal, if any, contribution because the existing literature does not support a large clinical benefit with antioxidant supplementation.33 Additionally, two large RCTs of intravenous PGE1, which is increased by GLA,34, 35 in ALI patients have found no improvement in survival, duration of ventilation, or length of stay.36, 37 To answer the question of whether or not EPA and DHA have an independent therapeutic benefit in patients with ALI, we are conducting a phase II RCT of enteral fish oil versus placebo.