Fatty acid essential

The essential fatty acids are also converted in the btxly to the 22-carbon fatty addsdocosapenta erioic aci d (DPA) and d oco sahexaenoic acid (DH A), DFA is made from linoleic acid DHA is made from linoienic acid. The functions of these 22-carbon fatty acids are not clear, but they may be important for vision and for other functions of the nervous system. DPA and DHA can be further elongated, in the body, to the very-long-chain fatty acids. The very-long-chain fatty acids contain 24 to 34 carbons, and occur in the brain, rods of the retina, and in the testes (Suh et ai, 1996). Their functions arc not dear. 

The information presented so far is summarized in the following diagram, Arachidonic acid could be considered to be the most important metabolite in the diagram  

Mammalian desaturases can introduce double bonds into fatty acids bif-liveen airbon-l0 and the carltoxi/l carboti. In contrast, plants can produce linoldc add, which has double bonds betw een carbons 9 and lO, and between carbons 12 and ) 3. J lants also synthesize lirolenic acid, which has double bonds between carbons 9 ond 0, carbons 12 and 1,1, and carbons 15 and 16, 

Linolenic acid is abbreviated as or 18 3o)3. The number before the colon 

C CHgCHjC fjCHtCNjCHjCHjCHjCHfC CHjCHiCHjCHgCH CHjCOOH ( iMricAcid 16 0] A -D turH  

Polyunsaturated fatty acids not synthesized in the body but required for normal metabolism are essential fatty acids (EFAs). EFAs are linoleic acid, linolenic acids (a and y), and arachidonic acid. All contain at least one double bond located beyond C-9 or within the terminal seven carbon atoms (Table 18-3). 

Introduction of double bonds does not occur in humans 

A double bond within the terminal seven carbon atoms can be present at o -3 or co-6. y-Linolenic acid is an a -6 EFA and a-linolenic acid an rw-3 EFA. Other co-3 EFA are eicosapentaenoic acid (EPA) and docosahexaenoic acid (EX)HA), both abundant in edible fish tissues. Vegetable oils are rich in rw-6 EFA (Table 18-4). Plants contain a-linolenic acid, which can be converted in the body to EPA and DOHA, but it is found within chloroplast membranes and not in seed oils hence, it may not be available in significant quantities in the diet. The a -3 and o)-6 EFA have different metabolic effects (see below). Particularly rich sources of EPA are fishes (e.g., salmon, mackerel, blue fish, herring, menhaden) that live in deep, cold waters. These fishes have fat in their muscles and their skin. In contrast, codfish, which have a similar habitat, store fat in liver rather than muscle. Thus, cod liver oi I is a good source of EPA, but it also contains high amounts of vitamins A and D, which can be toxic in large quantities (Chapters 38 and 37, respectively). Shellfi.sh also contain EPA. Plankton are the ultimate source of EPA. 

Desaturation occurs in such a way as to maintain a methylene-interrupted distribution of double bonds (that is, -CH=CH.CH2.CH=CH.CH2-). 

Ruminant bacteria produce some trans -unsaturated fatty acids when long-chain fatty acids are synthesised in the bacteria. These are absorbed by the host so that trans-unsaturated fatty acids can be found in adipose tissue and muscle of ruminants. 

There are four facts about essential fatty acids that need to 

The enzymes catalyse desaturation in sequence for example, the A desaturase converts stearate to oleic acid, which is converted, by the A desaturase, to the di-unsaturated fatty acid (18 2n-9), which is elongated to form eicosadienoic acid, which can be converted by the A -desaturase to the tri-unsaturated fatty acid (20 3n-9) which is known as Mead acid (see below). 

Particularly in the metabolism of the polyunsaturated fatty acids, the process of elongation occurs in sequence with desaturation to produce the specific acids required by the tissues in the body. 

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EDTA Efhylenediamineletra-acetic acid. EFA Essential fatty acids. ... 

CifiHjjOi. A fatly acid which is easily oxidized in air.-It occurs widely, in the form of glycerides, in vegetable oils and in mammalian lipids. Cholesieryl linoleale is an important constituent of blood. The add also occurs in lecithins. Together with arachidonic acid it is the most important essential fatty acid of human diet. 

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... 

The word essential as applied to naturally occurring organic substances can have two different meanings For example as used m the previous section with respect to fatty acids essential means necessary Lmoleic acid is an essential fatty acid it must be included m the diet for animals to grow properly because they lack the ability to biosyn thesize it directly... 

Essential ammo acids (Section 27 1) Ammo acids that must be present in the diet for normal growth and good health Essential fatty acids (Section 26 6) Fatty acids that must be present in the diet for normal growth and good health... 

The unsaturated fatty acids, linoleic [60-33-3] and linolenic [463-40-17, contain two and three double bonds and are considered beneficial components of the diet. The double bond is an essential ingredient for human nutrition when it is in the correct position on the fat molecule. Humans are unable to insert the double bond at the omega-3 and -6 position. Therefore, fatty acids containing double bonds at these positions are essential in the diet, including linoleic and linolenic acids. They are accordingly described as essential fatty acids (EFA) (23). 

Although a tme requirement for fat per se has not been estabUshed, the minimum level was based on recognition of fat as a source of essential fatty acids. 

Essential fatty acids (Section 26.6) Fatty acids that must be present in the diet for normal growth and good health. 

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... 

Organisms differ with respect to formation, processing, and utilization of polyunsaturated fatty acids. E. coli, for example, does not have any polyunsaturated fatty acids. Eukaryotes do synthesize a variety of polyunsaturated fatty acids, certain organisms more than others. For example, plants manufacture double bonds between the A and the methyl end of the chain, but mammals cannot. Plants readily desaturate oleic acid at the 12-position (to give linoleic acid) or at both the 12- and 15-positions (producing linolenic acid). Mammals require polyunsaturated fatty acids, but must acquire them in their diet. As such, they are referred to as essential fatty acids. On the other hand, mammals can introduce double bonds between the double bond at the 8- or 9-posi-tion and the carboxyl group. Enzyme complexes in the endoplasmic reticulum desaturate the 5-position, provided a double bond exists at the 8-position, and form a double bond at the 6-position if one already exists at the 9-position. Thus, oleate can be unsaturated at the 6,7-position to give an 18 2 d5-A ,A fatty acid. 

Drugs of particularly complex structure are often prepared commercially by partial synthesis from some abundant, structurally related, natural product obtained from plants. The majority i)f steroid drugs are in fact prepared in just this way. Prostaglandins are unique in that no prostanoid compounds have yet been found in plants, a perhaps surprising finding in view of the wide distribution of essential fatty acids in plant materials. 

One of the most prominent problems confronting the modem food processor is the prevention of rancidity. Rancidity affects not only the palatability of the food but the nutritive value as well—for example, oxidative spoilage of fats has been shown to be responsible for the partial destruction of the essential fatty acids (6) and of other dietary nutrients such as vitamins A (12) and E (9), and perhaps D (26) and certain members of the B complex (5, 29, SO). When one considers that nearly every food contains some fat and that this fat is subject to oxidative spoilage, the magnitude of the problem of rancidity is at once obvious. 

The 20 carbon fatty acid, 5,8,11,14 - eicosatetranoic acid, an essential fatty acid that serves as a precursor for protaglandins. 

An IV fat emulsion contains soybean or safflower oil and a mixture of natural triglycerides, predominately unsaturated fatty acids. It is used in the prevention and treatment of essential fatty acid deficiency. It also provides nonprotein calories for those receiving TPN when calorie requirements cannot be met by glucose. Examples of intravenous fat emulsion include Intralipid 10% and 20%, Liposyn II 10% and 20%, and Liposyn III 10% and 20%. Fat emulsion is used as a source of calories and essential fatty acids for... 

Not only eukaryotic cells but also bacteria have successfully been targeted by PNA anhsense strategies. Thus it has been shown that PNA complementary to ribosomal RNA or mRNA encoding an essential fatty acid biosynthesis protein, effectively kills E. coli. Furthermore, it has been shown that PNA directed to the start codon of the y -lactamase gene re-sensitized otherwise resistant E. coli to the antibiohc ampiciUin [64—66]. Conjugating a simple transporter peptide to the PNA increased the potency significantly, and an even more potent antibacterial PNA... 

Linoleic and a-linolenic acids are the only fatty acids known to be essential for the complete nutrition of many species of animals, including humans, and are known as the nutritionally essential fatty acids. In most mammals, arachidonic acid can be formed from linoleic acid (Figure 23-4). Double bonds can be intro-... 

Figure 23-1. Structure of some unsaturated fatty acids. Although the carbon atoms in the molecules are conventionally numbered—ie, numbered from the carboxyl terminal—the co numbers (eg, co7 in palmitoleic acid) are calculated from the reverse end (the methyl terminal) of the molecules. The information in parentheses shows, for instance, that a-linolenic acid contains double bonds starting at the third carbon from the methyl terminal, has 18 carbons and 3 double bonds, and has these double bonds at the 9th, 12th, and 15th carbons from the carboxyl terminal. (Asterisks Classified as "essential fatty acids.")...

DEFICIENCY SYMPTOMS ARE PRODUCED WHEN THE ESSENTIAL FATTY ACIDS (EFA) ARE ABSENT FROM THE DIET... 

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. 

Small amounts of trans-unsamrated fatty acids are found in ruminant fat (eg, butter fat has 2-7%), where they arise from the action of microorganisms in the rumen, but the main source in the human diet is from partially hydrogenated vegetable oils (eg, margarine). Trans fatty acids compete with essential fatty acids and may exacerbate essential fatty acid deficiency. Moreover, they are strucmrally similar to samrated fatty acids (Chapter 14) and have comparable effects in the promotion of hypercholesterolemia and atherosclerosis (Chapter 26). 

There are three groups of eicosanoids that are synthesized from C20 eicosanoic acids derived from the essential fatty acids linoleate and a-linolenate, or directly from dietary arachidonate and eicosapentaenoate (Figure 23-5). Arachidonate, usually derived from the 2 position of phospholipids in the plasma membrane by the action of phospholipase Aj (Figure 24-6)—but also from the diet—is the substrate for the synthesis of the PG2, 1X2 series (prostanoids) by the cyclooxygenase pathway, or the LT4 and LX4 series by the lipoxygenase pathway, with the two pathways competing for the arachidonate substrate (Figure 23-5). 

Essential Fatty Acids Do Not Exert All Their Physiologic Effects Via Prostaglandin Synthesis... 

The role of essential fatty acids in membrane formation is unrelated to prostaglandin formation. Prostaglandins do not reheve symptoms of essential fatty acid deficiency, and an essential fatty acid deficiency is not caused by inhibition of prostaglandin synthesis. 

Symptoms of Essential Fatty Acid Deficiency in Humans Include Skin Lesions Impairment of Lipid Transport... 

In adults subsisting on ordinary diets, no signs of essential fatty acid deficiencies have been reported. How-... 

Highet animals have A, A, A, and desatutases but cannot insert new double bonds beyond the 9 position of fatty acids. Thus, the essential fatty acids hnoleic ((o6) and a-linolenic ((03) must be obtained from the diet. 

Eicosanoids are derived from Cjo (eicosanoic) fatty acids synthesized from the essential fatty acids and comprise important gtoups of physiologically and pharmacologically active compounds, including the prostaglandins, thromboxanes, leukotrienes, and lipoxins. 

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