Abundant endogenous metabolitesLipidsLipid metabolism, including uptake, transport, synthesis and degradation, is a complex process regulated by a number of signalling pathways. Lipids have important biological functions in energy storage, as structural components of cell membranes and as signalling molecules. The lipid components of biological membranes were originally considered to be merely structural, but considerable evidence now exists demonstrating the importance of lipid signalling via a variety of receptors11 (TABLE 1). Alteration of lipid metabolism leads to changes in membrane composition and permeability, gene expression and protein distribution and function, as well as in cellular functions such as cell growth, proliferation, differentiation, survival, apoptosis, inflammation and motility, causing the development and progression of many diseases.