Polyenoic acid

Polyunsaturated (polyethenoid, polyenoic) acids, containing two or more double bonds. 

Schnurr et al. [22] showed that rabbit 15-LOX oxidized beef heart submitochondrial particles to form phospholipid-bound hydroperoxy- and keto-polyenoic fatty acids and induced the oxidative modification of membrane proteins. It was also found that the total oxygen uptake significantly exceeded the formation of oxygenated polyenoic acids supposedly due to the formation of hydroxyl radicals by the reaction of ubiquinone with lipid 15-LOX-derived hydroperoxides. However, it is impossible to agree with this proposal because it is known for a long time [23] that quinones cannot catalyze the formation of hydroxyl radicals by the Fenton reaction. Oxidation of intracellular unsaturated acids (for example, linoleic and arachidonic acids) by lipoxygenases can be suppressed by fatty acid binding proteins [24]. 

Linoleic (C18 2) and linolenic (C18 3) acids cannot be synthesized by mammals and must be supplied in the diet, i.e. they are essential fatty acids (linoleic is the only true essential acid). These two polyenoic acids may then be elongated and/or further desaturated by mechanisms similar to stearic - oleic, to provide a full range of polyenoic acids. A summary of these reactions is given in Figure 3.12a, b. 

Polyenoic acids also give rise to malondialdehyde, a reactive mutagenic compound, which can be reduced... 

Prostaglandins are not stored by cells but are synthesized in response to external stimuli. Arachi-donic acid and other polyenoic acids are present in relatively small amounts (e.g., 1% of total plasma... 

As indicated above, there are many possible oxidation products of the different polyenoic acids. It is probably naive to ascribe the effects of dietary intervention reported thus far to such metabolites. Carefully controlled clinical studies will be needed before these questions can be satisfactorily answered. However, subjects on diets containing highly saturated fatty acids clearly show increased platelet aggregation when compared with other study groups. Such diets (eg, in Finland and the USA) are associated with higher rates of myocardial infarction than are more polyunsaturated diets (eg, in Italy). 

Within each of two Black Sea species, anchovy (warm water) and sprat (cold water), both the concentrations and absolute amounts of phospholipids fluctuate within similar limits, but do not change during the annual cycles in the same tissues. This contrasts with, for example, the considerable differences between the phospholipid contents of red and white muscle or between that of either of them and liver (Shchepkina, 1980a Shchepkin and Minyuk, 1987). The content of polyenoic acids in the phospholipids of anchovy is higher than that in the sprat (Yuneva, 1990) possible explanations will be given in Chapter 3. 

Studies by Johnston and Roots (1964), Roots (1968) and Kreps (1981) have revealed an increased ratio between the plasmalogenic and diacyl forms of phosphatidyl ethanolamine in oceanic fish from low-temperature waters. During cold adaptation, the ratios between the main phospholipid fractions alter the relative proportion of phosphatidyl choline decrease and phosphatidyl ethanolamine, phosphatidyl serine and sphingomyelin, all of which contain large amounts of polyenoic acids, increase (Caldwell and Vemberg, 1970 Miller etal, 1976 Wodke, 1978 Hazel, 1979 Brichon et al., 1980 van den Thillart and de Bruin, 1981 Zabelinsky and Shukolyukova, 1989). 

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. 

Rabinovich and Ripatti (1990) have shown that docosohexaenoic acid has conformational properties which keep its physico-chemical and, possibly, functional characteristics effective over a wide temperature range. This ensures the adaptation of cell membranes to changes of metabolic activity. Fluctuation in locomotory activity is one factor responsible for these changes. From their studies of the sea cucumber, Cucumaria frondatrix, Kostetsky et al. (1992) concluded that polyenoic acids of linolenic affinity did not exhibit a direct relatonship with temperature adaptation. In contrast to this, Zabelinsky et al. (1995) claim that C20 5o>3 (not C22 6a>3) and Cl8 1 are the fatty acids of key importance for temperature adaptation in marine fish. 

Figure 33 Seasonal dynamics of lipid unsaturation in anchovy. (After Shulman, 1978a Yuneva, 1990.) Continuous line, iodine value broken line, total polyenoic acids.

In the anchovy, the total saturated fatty acids content in the reserve and structural lipid fractions is maximal in the autumn and minimal during the rest of the year. However, the polyenoic acids in these two fractions are maximal in winter, spring and summer, but minimal in autumn. During spring and summer, a substantial reduction is observed in the quantity of 16 0,18 1 and 22 6 in the triacyl-glycerols, perhaps because of transfer to sexual products in which they accumulate as stored energy (saturated and monoenoic acids) or as structural elements (polyenoic acids). They are of similar importance in this context in capelin, horse-mackerel, cod, Pacific saury, eelpout and trout (Jeffries, 1972 Dobrusin, 1978 Ackman, 1983 Henderson etaL, 1984). 

Cw-polyenoic acids are present at low concentrations in milk fat, because of the biohydrogenation reactions that take place in the rumen. These acids are comprised almost exclusively of linoleic acid (9c, 12c-18 2), about 1.2 to 1.7% and a-linolenic acid (9c, 12c, 15c-18 3), about 0.9 to 1.2% (Table 1.2). These two fatty acids are essential fatty acids they cannot be synthesised within the body and must be supplied by the diet. In recent times, the usage of the term essential has been extended to include derivatives of these fatty acids, which are not synthesised in significant quantities (e.g., eicosapentaenoic acid, 20 5 and docosahexaenoic acid, 22 6). The proportion of a-linolenic acid appears to be affected by the cow s diet the concentration is higher in milk from pasture-fed cows than in milk from barn-fed cows (Hebeisen et al., 1993 Wolff et al., 1995). In the case of linoleic... 

Sodium amalgam serves to reduce selectively the double bond in an olefinic acid containing the thiophene or furan ring. " This reagent is also employed to prepare olefinic acids by partial reduction of certain polyenoic acids, e.g., 3-pentenoic acid (60%) from vinylacrylic acid. Among the dibasic acids prepared by this method are succinic acid from maleic acid (98%) by catalytic hydrogenation over Raney nickel catalyst and alkylsuccinic acids from alkenylsuccinic acids made by the Diels-Alder reaction of simple olefins and maleic anhydride. ... 

Rao GHR, KidmeNP, Peiler JD, White JG. Influence of polyenoic acids on arachidonic arid metdx>lism and platdd function. In Cardiovascular Disease, Gallo L ed. New York Plenum PuUicatioits 1988. 

Other polyenoic acids, e.g., eicosapentaenoic acid, docosahexaenoic acid. 

Yavin E, Menkes JH. Polyenoic acid metabohsm in cultured dissociated brain cells. J Lipid Res 1974 15 152-157. 

The rate of drying is a function of polyunsaturated or polyenoic acid content. This rate increases rather rapidly up to a polyenoic content of about 50%. Above that figure, a limiting value is gradually approached. 

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. 

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