Polyunsaturated fatty acids and eicosanoids

Linoleic and α-linolenic acids, obtained from plant material in the diet, are the precursors in tissues of two families with opposing effects which are referred to as essential fatty acids (EFA): arachidonic acid (AA) and pentaene (eicosapentaenoic acid: EPA) and hexaene (docosahexaenoic acid: DHA) acids. The role of EFA is crucial, without a source of AA or compounds which can be converted into AA, synthesis of prostaglandins (PGs) by a cyclooxygenase (COX) enzyme would be com-promised, and this would seriously affect many normal metabolic processes. COX, also known as prostaglandin endoperoxide synthase (PGHs) or as prostaglandin G/H synthase, is a key membrane bound enzyme responsible for the oxidation of AA to PGs. Two COX isoforms have been identified, COX-1 and COX-2 that form PGH₂, a common precursor for the biosynthesis of thromboxane A2 (TxA2), prostacyclin (PGI₂) and PGs (PGD₂, PGE₂, PGF_2α. COX-1 enzyme is expressed constitutively in most cells and tissues. Its expression remains constant under either physiological or pathological conditions controlling synthesis of those PGs primarily involved in the regulation of homeostatic functions. In contrast, COX-2 is an intermediate response gene that encodes a 71-kDa protein. COX-2 is normally absent from most cells but highly inducible in certain cells in response to inflammatory stimuli resulting in enhanced PG release. PGs formed by COX-2 primarily mediate pain and inflammation but have multiple effects that can favour tumorigenesis. Common sources of ω-3 fatty acids include fish oils, algal oil squid oil and some plant oils, such as flaxseed oil.