Innate immune mechanisms linking non-esterified fatty acids and respiratory disease

Local airway inflammation in chronic respiratory disease is well described. Recently it has been recognised that chronic obstructive respiratory disease, asthma and obstructive sleep apnoea, all involve a systemic inflammatory component. Overspill of airway inflammation, as well as direct metabolic effects, are potential contributors to systemic inflammation. This review will discuss the role of certain types of fatty acids in promoting systemic inflammation, via the innate immune response. Fatty acids are necessary as the key energy source in the body. However, they can be detrimental if present in excess. Various features of respiratory disease lead to altered lipid metabolism, and notably an increase in circulating levels of non-esterified fatty acids (NEFA). Dietary intake, obesity, hypoxia and smoking, will be discussed as factors promoting an increase in circulating NEFA. While n−3 polyunsaturated and monounsaturated fatty acids may be non-(or anti-)inflammatory, saturated and n−6 polyunsaturated fatty acids have been shown to stimulate the innate immune response. Thus, increased circulating NEFA may be directly contributing to systemic inflammation, thereby increasing susceptibility of individuals to chronic inflammatory diseases, including respiratory disease, cardiovascular disease and diabetes. Finally, the review will discuss how the recognition of NEFA as important inflammatory stimulants in respiratory disease, leads to the possibility that pathways involved in lipid metabolism may provide therapeutic targets.