Metabolism of α- Linolenic Acid (ALA) in Meat Animals

A key function of ALA (C18:3 n-3) is as substrate for the synthesis of longer-chain omega 3 fatty acid found in fish EPA (C20:5 n-3) and DHA (C22:6 n-3) which play an important role in the regulation of inflammatory immune reactions and blood pressure, brain development, cognitive function, etc. (Sirot et al., 2008). The American Heart Association (AHA) recommends to increase the consumption of n-3 fatty acids and to reach a low omega 6/omega 3 ratio for reach a healthy status (Russo, 2009). Fat is an important component of the human diet, but current levels of intake are considered too high and the overall fatty acid composition imbalanced. There is an excessive intake of saturated fatty acids (SFA) relative to polyunsaturated fatty acids (PUFA), expressed usually as the P/S ratio, and the consumption of n-6 PUFA is too high relative to n-3 PUFA. The ratio of n-6/n-3 PUFA is a risk factor in cancers and coronary heart disease, especially the formation of blood clots leading to a heart attack. More recently, nutritionists have focused on the type of PUFA and the balance in the diet between n-3 PUFA formed from C18:3 n-3 and the n-6 PUFA from C18:2 n-6 (Willians, 2001) ALA and LNA (C18:2 n-6) serve as the precursor molecules from which the rest of fatty acids belonging to the n-3 and n-6 fatty acid family can be synthesized through a series of elongation and desaturation reactions. All the reactions are catalyzed by an enzymatic system consisting in fatty acyl-CoA synthetases Δ-6 and Δ-5 desaturases and respective elongases. These two fatty acid families not only share these enzymes, but they also compete for the same enzymes (Brenner, 1989). There are two basic metabolic fates for ALA. First it is subjected to ┚-oxidation and extensive carbon recycling. Second, it is converted into longer fatty acids via elongation and desaturation. The predominant fate of ALA is catabolism (Demar et al. 2005) and carbon recycling to acetate (Cunnane et al., 1997, 2003). In rodents, only 16% of an ALA dose is found in rat tissues, mainly adipose, and 6% was elongated /desaturated (Kaduce et al., 2008). Increasing the ALA content of the maternal diet of sucking rats led to increased of ALA, EPA and DPA (C22:5 n-3) in the whole body, skin epididymal fat pads and but there was no effect on the DHA content of these tissues nor on the brain or muscles (Bordoni et