Long - chain polyenoic acids

In nature, fish apparently acquire polyunsaturated lipids in one of two ways. The first of them conforms with the concept of Saigent and Henderson (1980), Watanabe (1982) and Henderson et al. (1985), that some species of fish do not need to synthesize long-chain polyenoic acids, since they occur in phytoplankton, which are eaten by zooplankton which in turn are food for fish. Takahashi et al. (1985) described the situation as unsaturated fatty acids being transferred from plant organisms to phytoplankton-eating fish to predatory fish. 

We have examined the distribution of long-chain polyenoic acids in different animal species with the objective of establishing whether or not different food selection patterns were associated with differences in tissue fatty acids and in particular, brain fatty acids. 

Analysis of placental lipids showed consistently a far higher recovery of isotope from the long-chain polyenoic acids. More than 10% of the placental isotope was in the 22 5o)3 and 22 6o)3 fatty acids (Fig. 5). In the fetus the proportion of isotope in the long-chain polyenoic acids had further increased to over 25 % (Fig. 

The results demonstrate that the fetus is not simply dependent on maternal food intake, but that both placenta and fetus actively reprocess the essential fatty acids with the result that long-chain polyenoic acids are incorporated into the developing brain lipids. Although this process is clearly of great importance to brain development, the conversion of a —linolenic acid to docosahexaenoic acid is slow. A low desaturation rate of parent essential fatty acids is consistent with the Zn )iXKO studies reported by Professor Brenner and Dr. Sprecher earlier in this conference and with our iyi )AJ00 observations in the rat (Hassam, Sinclair Crawford, 1975 Hassam Crawford, 1976 Hassam, Rivers Crawford, 1976). In the cat the desaturase was not detected (Rivers, Sinclair Crawford, 1975) iyi )lvo. 

Our results suggest that the placental barrier, together with the remetabolism of the EFA, provides a powerful control mechanism to ensure the supply of predominantly long-chain polyenoic acids to the fetal brain. 

On the other hand, some fish are able to synthesize long-chain polyenoic fatty acids (Kayama et al., 1963) from shorter carbon chains. Docosohexaenoic acid is laid down in coho salmon in quantities related to the size of the fish, rather than to its availability in the diet (Tinsley et al., 1973). Rainbow trout fed on 18 2 and 18 3 fatty acids can produce 20 3, 22 5 and 22 6 fatty acids in substantial quantities (Owen et al., 1975), but these workers noticed that the capacity of marine flatfish to elongate or desaturate the carbon chains was more limited. They found that 70% of the radioactivity of labelled 18 3 appeared later in the 22 6 fatty acid of rainbow trout, but that turbot converted only 3-15% of labelled precursors into polyunsaturated fatty acids of longer chain length. It was suggested that turbot in the wild probably received adequate polyunsaturated acids in their diet, which the fish therefore did not need to modify. The elongation of the carbon chains and the creation of more double bonds is also only slight in Atlantic cod, another marine teleost, presumably for the same reason (Ross, 1977). 

These long-chain fatty acids have formulae similar to those described above but contain one or more double bonds. This group of fatty acids may be subdivided into monoenoic and polyenoic types. A general summary of the chemical nature of the unsaturated fatty acids follows. 

Aveldano ML A novel group of very long chain polyenoic fatty acids in dipolyunsaturated phosphatidylcholines from vertebrate retina.. 1 Biol Chem 1987 262 1172-1179. 

Zellweger s (cerebrohepatorenal) syndrome occurs in individuals with a rare inherited absence of peroxisomes in all tissues. Patients accumulate C26-C38 polyenoic acids in brain tissue owing to defective peroxisomal oxidation of the very-long-chain fatty acids synthesized in the brain for myelin formation. In liver, bile acid and ether lipid synthesis are affected, as is the oxidation of very-long-chain fatty acids. 

Brain accumulation of long-chain polyenoic, saturated and mono-unsaturated fatty acids. 

Pol)umsaturated (or polyenoic) fatty acids are those long-chain fatty acids which include two or more double bonds in the molecule. At least one of these, linoleic acid, 18 2(9,12), has been found in almost every higher protist, plant and animal, so far examined, and in most... 

Certain long-chain unsaturated fatty acids of metabolic significance in mammals are shown in Figure 23-1. Other C20, C22, and C24 polyenoic fatty acids may be derived from oleic, linoleic, and a-flnolenic acids by chain elongation. Palmitoleic and oleic acids are not essential in the diet because the tissues can introduce a double bond at the position of a saturated fatty acid. 

Normally, the method of choice for the analysis of complex mixtures of polyenoic fatty acids such as those derived from fish oils is capillary gas chromatography with prechromato-graphic derivatization and mass spectrometric detection. However, GC is impractical for the purification of the large amounts of polyenoic fatty acids required for biological and clinical studies. Moreover, the temperatures required in GC may cause degradation of oxidized long-chain polyunsaturated fatty acids that are present as minor components of the mixture. 

Suh M, Wierzbicki AA, Clandinin MT. Dietary fat alters membrane composition in rod outer segments in normal and diabetic rats impact on content of very-long-chain (C>24) polyenoic fatty acids. Biochim Biophys Acta 1994 1214 54-62. 

The developing brain accumulates long-chain (C20 and C22) polyenoic fatty acids, particularly during cell division (Crawford Sinclair, 1972 Sinclair Crawford, 1972). Vz novo synthesis of these acids does not occur in higher animals and they are derived either directly from food or by metabolism from the parent essential fatty acids, linoleate and a-linolenate. 

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