Polyunsaturated Fatty Acids and Cytokines: Their Relationship in Acute Lung Injury

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are inflammatory diseases whose clinical severity depends on the grade of inflammatory response. Inflammatory cytokines are key elements in the pathogenesis of ALI/ARDS, and the occurrence of an imbalance between pro- and anti-inflammatory cytokines leads to additional non-pulmonary organ dysfunction which contributes to excess mortality rates. Treatment of these patients includes nutrition support with lipids, usually soybean oil-based lipid emulsions, which are rich in omega (n)-6 polyunsaturated fatty acids (PUFAs) and deficient in n-3 PUFAs; however, too much n-6 PUFAs are detrimental due to their pro-inflammatory effects. Conversely, a large amount of experimental studies and some randomized clinical trials showed the benefits of the n-3 PUFA administration in the context of ALI because of their anti-inflammatory properties. Based on these data, several scientific societies recommended in their guidelines, with an A or B grade of recommendation, the use of n-3 PUFAs in ALI/ARDS patients. However, at present, the issue of lipid therapy in ALI/ARDS is still controversial due, at least in part, to inconclusive or contradicting results in several recent clinical trials using n-3 PUFAs.