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FSU HUN 3224 - Essential Fatty Acids

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Essential Fatty Acids-The two essential fatty acids are Linoleic acid (Omega 6) and alpha-Lenolenic acid (Omega 3). Why are those two the essential ones? Because our body cannot produce those, so we must obtain those through our diet. So whay can our body not produce them? Well last class we discussed our body lacking 2 desaturases; Delta-12 AND DELTA-15. They are responsible for inserting those double bonds in those two positions in a FA. Looking at the formulas, we see that Linoleic acid and alpha Linolenic acid are both 18 carbons long; however, Linoleic acid has only two double bonds with the first one being on carbon 6, starting from the methyl end. Alpha Linolenic acid has 3 double bonds,the first one is on carbon 3, starting form the methyl end. Through the delta nomenclature we can see that our Omega 6 has delta 9 and delta 12. So our body can insert the delta 9 but cannot insert the delta 12. Looking at the alpha Linolenic acid we have a delta 9, 12 and 15. Our body can insert the delta 9 (starts counting from carboxyl end) but cannot do it on carbon 12 or 15-We are going to take a closer look at Omega 6 FA. The parent compound it Linoleic acid so it is the most basic compound and it will have other compounds derive from this. Two examples are Arachidonic acid and Dihomo-gamma-Linolenic acid. We can find Linolenic acid from corn oil, safflower oil or sunflower oil.-Taking a closer look at its metabolism we can see that Linoleic acid is going to be de-saturated in order to form gamma-Linolenic acid. Then we will go through elongation to form Dihomo-gamma-Linolenic acid. Then another desaturation will happen to form Arachidonic acid, which is a 20 C long molecule with 4 double bonds. Since they are all derived form Linoleic acid, they all have their first double bond on carbon 6 (starting count at methyl end)-Now looking at Omega 3 (Alpha Linolenic acid). We will see that the sources are a little different: canola oil, soybean oil and fish oil. Fish do not produce Omega 3 however; fish consume seaweed and algae from the ocean, which is how they obtain that Omega 3. DHA and EPA are examples, will see later in metabolism.-Taking a closer look at Alpha Linolenic Acid metabolism, we see that Omega 3 will go through a desaturation first to form a double bond, followed by an elongation. Another desaturation is done to form EPA (now a 20 carbon long molecule with 5 double bonds). Another elongation and desaturation occur to form Docosahexaenoic acid (DHA) (a 22 carbon molecule with 6 double bonds)-So what are the functions of those essential FA? Well we know that the membrane contains PL and those PL contain unsaturated FA, which would be Linoleic acid, Linolenic acid, EPA and Arachidonic acid. The higher the degree of unsaturation among FA in a membrane, the greater the fluidity of that membrane. The membrane's fluidity is an important determinant for the hormone's receptor binding sites. If the membrane has more unsaturated FA, it will be more fluid and less rigid which is better for our body. Those essential FA are going to be precursors of Eicosanoids, which are going to have several physiological implications in our body. Essential FA are also going to beimportant for the formation of DHA which is needed for retina and brain development. Essential FA also provides energy.-The deficiency of essential FA is very rare but it may develop with fat mal-absorption syndromes such as cystic fibrosis, Celiac disease, Crone’s disease, Diverticulitis and even some cancers. They decrease absorption of fat. The symptoms of such deficiencies are retarded growth, Dermatitis (scaly skin), Loss of water through skin (leaky membranes) and Infertility if you are missing omega 6 (Linoleic acid). Symptoms for missing Omega 3 (alpha Linolenic acid) are neurological and visual abnormalities.-Lets now talk about the Eicosanoids. They are 20 carbon molecules that have hormone like activity. Hormones are secreted in a specific site and then go into the bloodstream and bind to receptors in different cells of tissues in our body. So Eicosanoids are said to have hormone like activity because they are going to be secreted and act in the same cell by which they were secreted (outtercrine) or act in neighboring cells (paracrine). So we have 4 types of eicosanoids: Prostaglandins (Prostanoids), Thromboxanes (Prostanoids), Prostacyclins (Prostanoids) and Leukotrienes.- Eicosanoids are synthesized mainly by Arachidonic acid, which is an Omega 6 derivative, or form EPA, which is an Omega 3 derivative. Arachidonic acid and EPA will be part of the PL in the membrane. Phospholipase A2 is the enzyme responsible for cleaving those two FA from the membrane and releasing it to the cytosol. Once those are in the cytosol they can follow two pathways: Cyclooxygenase (COX) or Lipooxygenase (LOX). COX forms Prostanoids. LOX forms Leukotrienes.-Looking at this diagram you see the membrane PL and that the Phospholipase A2 is responsible for releasing EPA/Arachidonic acid from the membrane. They can then follow those two pathways just mentioned.-Cyclooxygenase Pathway: We have two isoforms COX1 and COX2. They catalyze the same reaction but those two enzymes are regulated differently.-COX1: This carry out normal physiological function of prostaglandins in our body. It is present in most cells of the body. It plays a role in maintaining homeostasis, in protecting the lining of our stomach (cytoprotection) and also platelet aggregation. It also protects our kidneys and heart.-COX2: This is induced with inflammatory cells. For example, macrophages. This enzyme is induced when there is tissue disruption in our body, during exercise, growth factors, cytokine secretion, and tumor promoters. It mainly plays a role in inflammation ad triggering pain. So COX1 and 2 will be found in blood vessels, stomach and kidneys- Here we can see a picture of those two pathways. The COX pathway is cyclic while the LOX is linear. Those two enzymes are responsible for inserting oxygen into the FA structure. So if the FA enters the COX pathway we will be forming Prostaglandins, Prostacyclins and Thromboxanes; all of them have different functions in our body. The LOX pathway will insert an oxygen in the position of carbon 5, forming a 5hydroxyperoxyacosatetranoic acid. From that we can form the Leukotriene.-The biological actions of Eicosanoids: Prostaglandins are going to be produced by most nucleated cells of our body and will be acted upon


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