Essential fatty acids functions

Prostaglandins arise from unsaturated C20 carboxylic acids such as arachidonic acid (see Table 26 1) Mammals cannot biosynthesize arachidonic acid directly They obtain Imoleic acid (Table 26 1) from vegetable oils m their diet and extend the car bon chain of Imoleic acid from 18 to 20 carbons while introducing two more double bonds Lmoleic acid is said to be an essential fatty acid, forming part of the dietary requirement of mammals Animals fed on diets that are deficient m Imoleic acid grow poorly and suffer a number of other disorders some of which are reversed on feed mg them vegetable oils rich m Imoleic acid and other polyunsaturated fatty acids One function of these substances is to provide the raw materials for prostaglandin biosynthesis... 

Some fatty acids are not synthesized by mammals and yet are necessary for normal growth and life. These essential fatty aeids include llnoleic and y-linolenic acids. These must be obtained by mammals in their diet (specifically from plant sources). Arachidonic acid, which is not found in plants, can only be synthesized by mammals from linoleic acid. At least one function of the essential fatty acids is to serve as a precursor for the synthesis of eicosanoids, such as... 

Rats fed a purified nonlipid diet containing vitamins A and D exhibit a reduced growth rate and reproductive deficiency which may be cured by the addition of linoleic, a-linolenic, and arachidonic acids to the diet. These fatty acids are found in high concentrations in vegetable oils (Table 14-2) and in small amounts in animal carcasses. These essential fatty acids are required for prostaglandin, thromboxane, leukotriene, and lipoxin formation (see below), and they also have various other functions which are less well defined. Essential fatty acids are found in the stmctural lipids of the cell, often in the 2 position of phospholipids, and are concerned with the structural integrity of the mitochondrial membrane. 

Besides water, the diet must provide metabolic fuels (mainly carbohydrates and lipids), protein (for growth and turnover of tissue proteins), fiber (for roughage), minerals (elements with specific metabolic functions), and vitamins and essential fatty acids (organic compounds needed in small amounts for essential metabolic and physiologic functions). The polysaccharides, tri-acylglycerols, and proteins that make up the bulk of the diet must be hydrolyzed to their constituent monosaccharides, fatty acids, and amino acids, respectively, before absorption and utilization. Minerals and vitamins must be released from the complex matrix of food before they can be absorbed and utifized. 

Biochemical assessment of trace element, vitamin, and essential fatty acid deficiencies should be based on the nutrient s function, but few practical... 

A functional method for detection depends upon competition for the activity of the and desaturases between a non-essential fatty acid (e.g. oleic acid) and an essential fatty acid (see above). If the latter is deficient, oleic acid is readily converted, via the desaturases, to Mead acid, since there is little competition (Figure 11.14). Hence the amount of the latter can be used as a marker for deficiency of essential fatty acids, although it is better to use the ratio of double bonds only three are present in Mead acid (i.e. a triene) but four are present in arachidonic acid (i.e. a tetraene). A ratio in plasma, triene/tetraene >4.0 is an indication of a deficiency of essential fatty acids. This method has shown that a deficiency can occur in a number of conditions which can lead to disease (Table 11.5). 

The essential fatty acids have a number of vital functions. 

To date there are no true inborn errors associated with essential fatty acid metabolism. However, we do know that the final step of DHA formation is the peroxisomal beta-oxidation of a homologous C24 fatty acid [7]. Consequently, patients with a generalised defect of peroxisomal function, such as Zellweger syndrome, are prone to develop deficiencies of essential fatty acids including DHA [9]. 

The co-3 fatty acids have numerous important functions, especially in the brain. Accordingly, a deficiency of DHA and EPA may cause dysfunction of the central nervous system and probably also the retina, thereby resulting in impaired vision. In addition, there is a variety of neurological and psychiatric disorders that have been associated with decreased levels of especially DHA and AA, such as, for example, schizophrenia and depression [3], post-traumatic stress syndrome, autism and attention deficit hyperactivity disorder. Since no primary inherited defect of essential fatty acid interconversion has yet been described, no specific explanations for the essential fatty acid concentration changes are readily available. 

Hartop, P.J., C.F. Allenby, and C. Prottey, Comparison of barrier function and lipids in psoriasis and essential fatty acid-deficient rats. Clin, Exp. Dermatol., 1978, 3 259-67. 

Essential Fatty Acids Biological Functions and Potential Applications in the Skin... 

Burr and Burr reported in 1929 a new deficiency disease produced by the rigid exclusion of fat from the diet. 1 Rodents fed a fat-free diet showed reduced growth and reproductive failure, accompanied by two prominent changes in the skin, that is, increased scaliness and impaired barrier function.1,2 Reversal of the features of deficiency by administration of linoleic acid (LA), led to the concept of essential fatty acids (EFA) that cannot be synthesized by the higher animals.2 Similarities between the clinical features of EFA deficiency and atopic dermatitis led Hansen in 1937 to discover low blood levels of unsaturated fat in atopic children,3 and he later reported that EFA-deficient infants developed an eczematous rash, which responded to LA supplements.4 Several studies had previously examined a range of dietary oil supplements in atopic dermatitis,5-8 with generally reported benefit. 

Elias, P.M. and Brown, B.E., The mammalian cutaneous permeability barrier defective barrier function in essential fatty acid deficiency correlates with the abnormal intercellular lipid deposition, Lab. Invest., 39, 574, 1978. 

Skin diseases including essential fatty acid deficiency and ichthyosis may also affect the transdermal delivery of a compound. Studies have shown that the epidermal barrier function is altered by abnormal lipid composition in noneczematous atopic dry skin. Numerous other dermatologic conditions affect the anatomical structure and function of skin, which may impact on the nature of the toxic responses seen. 

The high concentration of polyunsaturated fatty acids in cellular and subcellular membranes makes them particularly susceptible to free radical damage. In addition, mitochondrial membranes contain flavins as a part of their basic structure, potentially contributing C>2 resulting in free radical damage. The process of uncontrolled lipid peroxidation can result in the loss of essential polyunsaturated fatty acids, and the formation of toxic hydroperoxides and other secondary products. The loss of essential fatty acids may then result in loss of membrane integrity and loss of function. Extensive oxidation can also lead to rupture of... 

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