Polyunsaturated fatty acids INDEX

Oxidative damage to membrane polyunsaturated fatty acids leads to the formation of numerous lipid peroxidation products, some of which can be measured as index of oxidative stress, including hydrocarbons, aldehydes, alcohols, ketones, and short carboxylic acids. 

Pentane and ethane (end products of n-6 and n-3 polyunsaturated fatty acid peroxidation, respectively) in expired air are useful markers of in vivo lipid peroxidation. Nevertheless, when gas chromatography is used to measure hydrocarbons, some technical difficulties may be experienced because chromatographic resolution of pentane from isoprene and isopentane is extremely difficult to achieve. Another possible problem could be the presence of these gases as contaminants in atmosphere. Furthermore, the production of hydrocarbon gases depends on the presence of metal ions to decompose lipid peroxides. If such ions are only available in limited amounts, this index may be inaccurate. 

PTFE polytetrafluoroethylene PUFA polyunsaturated fatty acid PV peroxide value PVDF polyvinylidene difluoride PVP polyvinylpyrrolidone PVPP polyvinylpolypyrolidone RAS retronasal aroma stimulator RDA recommended dietary allowance RF radio frequency RFI relative fluorescence intensity RI retention index RNU relative nitrogen utilization ROESY rotational nuclear Overhauser enhancement spectroscopy RP-HPLC reversed-phase HPLC RPER relative protein efficiency ratio RS resistant starch RT retention time RVP relative vapor pressure S sieman (unit of conductance)... 

Fig. 10. Polyunsaturated fatty acids (PUFA) modulate the effects of the APOA-IG-A polymorphism on high density lipoprotein (HDL)-cholesterol concentrations in a gender-specific manner [data from Ordovas etal. (115), reproduced with permission]. In women carriers of the A allele, higher PUFA intakes were associated with higher HDL cholesterol concentrations, whereas the opposite effect was observed in G/G women. Adjusted for age, body mass index, alcohol, smoking, intake of energy, saturated fatty acids, monounsaturated fatty acids, and polyunsaturated fatty acids. Interaction of G x PUFA, P< 0.005.

A third study focused on the effect of CLA and vitamin A on the polyunsaturated fatty acid (PUFA) composition, chemiluminescence and peroxidizability index of microsomes and mitochondria isolated from rat liver (43). The PUFA composition of microsomes and mitochondria changed by CLA and vitamin A treatment. The simultaneous analysis of peroxidizability index, chemiluminescence and fatty acid composition demonstrated that CLA is more effective than vitamin A in protecting microsomes or mitochondria against peroxidative damage. 

One attempt to classify fish fats (Lambertsen, 1978) is exemplified in Table 10.5. The percentages of as few as eight fatty acids of marine oils and lipids add up to about 80% of those present at 2-3% or more. Nutritionists may request 18 0, 18 2, 18 3 and 20 4, so 12 fatty acids have also been employed. Compared to lard, beef or sheep fats (see above), fish oils are considered highly unsaturated. One of the common trading standards of fish oils is the iodine value (IV). The iodine values of the monoethylenic fatty acids are 90 for 18 1 and 420 for 20 5n-3. Because of the extreme differences in IV for the typical two types of acids in Table 10.5, it was possible (Ackman, 1966) to develop an empirical formula percent polyunsaturated fatty acids = 10.7 + 0.337 (iodine value of oil—100). Table 10.6 shows the applicability of this formula. Since one of the objectives of the preparation of encapsulated fish oil products is to deliver 20 5n-3 and 22 6n-3 (Ackman et al., 1989 Sagredos, 1992), the iodine value is an easily utilized index of the suitability of raw materials for this or other uses. 

From this discussion it will be apparent that while all EFA are polyunsaturated, not all polyunsaturated fatty acids are EFA. Nutritionists and biochemists have used the ratio of 5,8,11-20 3/5,8,11,14-20 4 (often called the triene tetraene ratio) as a biochemical index of essential fatty acid status (Figure 5.5). For many years, it was held that a ratio greater than 0.4 was diagnostic of EFA deficiency but recent work has suggested that it may be prudent to revise this figure downwards to nearer 0.2. 

Figure 7. Relationship of oxidation and degree of polyunsaturation. Polyunsaturation is measured as the methylene bridge index (MBI), which is a more precise measure of extent of unsaturation and oxidizability than the double bond index. It is the mean number of 6is-allylic methylene bridge positions per fatty acid (or fatty acyl chain) in a lipid ensemble. The rate of lipid radical formation measures formation of an oxidative product, while O2 consumption (% O2 lost per sec) is a measure of utilization of a reactant. (Drawn using our data abstracted from Wagner, B.A., Buettner, G.R., and Bums, C.P. 1994, Biochemistry 33 4449-4453).

Because methylene-interrupted polyunsaturates do not have strongly absorbing chromo-phores in the UV region, detection by refractive index or far-UV detection (205-214 nm) has been utilized in RP-HPLC separations of free fatty acids and their aliphatic esters. Refractive index detection is less sensitive than UV detection. However, with far-UV detection, solvents absorbing UV below 210 cannot be used. The RP-HPLC separations reported to date have generally involved derivatization designed to incorporate aromatic chromophores allowing detection by fluorescence or UV detection. 

Moreover, studies about lipidogenesis and lipid metabolism have focused on a nuclear receptor, peroxisome proliferation-activated receptor y (PPAR-y). PPAR-y gene is a good example for involvement in a gene-environment interaction. Activation of PPAR-y leads to peroxisome proliferation and increased oxidation of fatty acids. PPAR-y activation results in adipocyte differentiation as well as improved insulin signaling of mature adipocytes. PPAR-y is associated with insulin resistance and blood pressure [5]. In individuals with a specific polymorphism in the PPAR-y (Prol2Ala), a low polyunsaturated-to-saturated fat ratio has been demonstrated to be associated with an increase in body mass index and fasting insulin concentrations [88]. 

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