Stearidonic acid metabolism

James, M. J. Ursin, V. M. Cleland L.G. metabolism of stearidonic acid in human subjects comparison with the metabolism of other n-3 fatty acids. Am J Clin Nutr 2003, 77, 1140-1145. 

Reasons proposed for the relatively poor conversion efficiency of ALA to EPA and DHA are that a substantial proportion of the ALA is diverted to P-oxidation (discussed above), that ALA is found distributed throughout all major tissue lipid pools (adipose, carcass, skin), and that in animals ALA might be excreted onto the fur (as discussed above). In addition, LA is the major dietary PUFA and is a competitive inhibitor of the metabolism of ALA to 18 4n-3 (commonly known as stearidonic acid see Chapter 9), a precursor of long-chain n-3 PUFA (see Figure 1). Furthermore, diets rich in LA decrease expression of the hepatic A -desaturase compared with fat-free diets this presumably also reduces the possibility of conversion of ALA to 18 4n-3 and of 24 5n-3 to 24 6n-3 (Cho et al, 1999a). 

Many unsaturated fatty acids, including stearidonic acid, are claimed to have anti-cancer properties at concentrations not harmful to normal cells. This has been shown, for example, in APC and nude mice (Kabakibi et al., 2001). When the incorporation and metabolism of a-linolenic and stearidonic acids were compared in non-malignant NIH-3T3 cells, a-hnolenic acid slightly stimulated growth but stearidonic acid showed a clear inhibitory effect (Cantrill etal., 1993). 

Cantrill, RC, Huang, YS, EUs, GW and Horrohin, DF (1993) Comparison of the metabolism of a-linolenic acid and its A desaturation produce stearidonic acid, in cultured NIH-3T3 cells. Lipids, 28, 163-166. 

FIGURE 12.2 Metabolism of co-3 fatty acids. The major plant-derived co-3 PUFAs are ALA (linolenic acid, 18 3n-3) and SDA (stearidonic acid, 18 4n-3). ALA has important health benefits of its own however, metabolism to longer chain co-3 s is relatively poor in the human body. The A-6-desaturase enzyme limits uptake. Since conversion of SDA is much higher than ALA, about 30% versus 5%, SDA is a much more effective source for longer chain co-3 s such as EPA. 

James, M.J., Ursin, V.M. and Cleland, L.G. 2003. Metabolism of stearidonic add in human subjects Comparison with the metabolism of other n-3 fatty acids. ArtL J. Clin. Nutr. 11 1140-1145. 

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