Metab II Exam 3 Vitamins What are they Group of organic compounds that meet the following criteria o Present in small amounts in food such as natural components o Not synthesized by the host in the amount to meet normal physiological processes o Essential even if it is in minute amounts They are needed for normal physiological function such as Growth Development Reproduction Maintenance Their absence or deficiency or underutilization caused specific deficiencies syndromes that can be reversed by the addition of the vitamin o They are present in small amounts in food as natural components History They have been discovered over the years due to deficiencies for the most part o Scurvy vitamin C o Night blindness low vitamin A o Beriberi associated with polished rice which is thiamin and vitamin B o Pellagra associated with corn and Niacin o Rickets treated with liver low vitamin D The first discovered was Thiamin in 1897 o Called it a vitamine o 4 vital vitamine Antiberiberi Antiscurvy Antirickets And antipellagra o Then changed it to vitamin Fat soluble Vitamins Soluble in fat and fat solvents Require fats for absorption and transport o Transported via chylomicrons and other lipoproteins to target tissues Excess intake stored in body Small amounts excreted in bile Deficiency symptoms slow to develop Not absolutely necessary in diet every day Absorbed into lymphatic system and follow lipid transport o Follow lipids for entry and exit out of the intestinal cells Some have precursors or provitamins Needed only by higher organisms Stored in the body in appreciable amounts mostly adipose tissues and liver Deficiency except for Vit D is unlikely in US May be toxic and relatively low levels o 6 to 10 time RDA o More common in water soluble vitamins Water soluble Vitamins Soluble in water Minimal storage of dietary excess Excreted in urine Deficiency symptoms may develop rapidly Must be supplied in diet almost every day Absorbed into blood via portal vein Generally do not have precursors o Present in such in diet Needed by both simple and complex organisms Toxic only at mega dose o 10 times RDA Vitamin E Tocopherol Includes 8 different compounds vitamers o Two subgroups of 4 isomers alpha beta gamma delta Tocopherols Tocotrienols Saturated chain Alpha and beta have highest bioavailability Unsaturated side chain Much lower bioavailability and really don t do much o The structures of these 4 isomers is really differentiated by the number of methyl side groups then their saturated bones and of course their bioavailability All metabolites are synthesized in plants o Oils are the best source In food 75 of alpha tocopherol and 20 beta tocopherol and 5 tocotrienol o In animals it is found in fatty tissues Inferior source to plants o Especially rich in seeds bran and germ sections of plants Food sources of vitamin E o Found mainly in seeds and nuts Wheat germ 192mg 100g Corn 21mg 100g Peanut 13mg 100g Soybeans51mg 100g Vegetable 2mg 100g Eggs meat and fish 1mg 100g Functions of Vitamin E o As an antioxidant Maintains membrane permeability Not just cell membranes but also throughout cell in ER and mitochondria In the process vit E is oxidized into tocopherol radical and must be regretted Requires vit C glutathione and NADP Terminates chain propagation reactions involving lipid peroxyl radicals It provides Hydrogen from it C 6 hydroxyl group o Protective effects in atherogenesis besides preventions of lipid oxidations Inhibits platelets and other monocyte adhesions and aggregation o Maintenance of normal reproductive systems o May be anticarcinogenic Reactive oxygen species or ROS o SUPEROXIDE RADICAL O2 o PEROXYL RADICAL O2 2 o HYDROXY FREE RADICALS OH o HYDROPEROXYL RADICALS HO2 o LIPID CARBON CENTERED RADICALS L o LIPID PEROXYL RADICALS LOO HYDROGEN PEROXIDE H2O2 Lipid hydroperoxide LOOH Initiation of chain reactions caused by hydroxyl free radical attack on an unsaturated fatty acid o This is what will happen if vitamin E is not there to prevent radicals Explanation of this reaction L O2 LOO lipid peroxyl radical o Once formed can take H from other organic compounds e g PUFA to generate a chain reaction propagation with lipid carbon centered radical L to form LOO LH L LOOH lipid hydroperoxyde o Vit E in reduced state can break a chain of radical attack and prevent further uptake of H from fatty acids LOO EH LOOH E oxidized vitamin E or vit E radical o Lipid hydroperoxide o It also provides H to reduce L lipid carbon centered radical L H LH E o It is also necessary to remove LOOH created They can destroy normal cell architecture It could be accomplished by the action of glutathione peroxidase LPRadiency attacks fatty acid and Vitamin E donates hydrogen to stop this radical from producing 2LOOH 2GSH GPX Se 2LOH H2O GSSG hydroxy fatty acid o GSH glutathione tripeptide composed of glycine cysteine and glutamic acid present in reduced stage GSSG gluthione reductase 2GSH Also in the process vitamin E is oxidized tocopherol radical and must be regenerated o Requires vitamin C glutathione and NADP to copherol radical is left and it go to the regeneration cycles of vitamin E The regeneration of Vitamin E alpha tocopherol In the third circle GSSG production o This portion of the cycle could not continue without selenium reaction of glutathione It will be neutralized back into Vitamin E from ascorbic acid or Vit C but Vit C is oxidized and Vit E is reduced Now Vitamin C will need glutathione back into Vit C by using energy from NADPH Target Organs for Vit E Neuromuscular vascular and reproductive Deficiency is related to the lack of antioxidant leading to cell damage Vit E General Info DRI new revised in 2000 o 15 mg day as alpha tocopherol for all adults Requirements will increase with PUFA intake Vit C and Se may spare Vit E Absorption storage o Absorbed as free form and follows lipids in entry and exit out of intestine Transported as lipids o Stored mostly in adipose tissue and some in liver Population at risk o People with fat malabsorption Cystic fibrosis and other hepatobiliary disorders o premature low birth weight infants Limited transplacental movement Infants may be given supplements for it being so low Vitamin E toxicity o One of the least toxic o At high doses may antagonize the utilization of other fat soluble vitamins Assessing Vitamin E status o Serum tocopherol concentration Need to calculate ratio vit E total lipids 0 6 is adequate More lipids consumed higher the concentration o
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