lecture 14.docx

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Biochem. and Medical Genetics
Course Code
BGEN 3020
Jason Leboe- Mcgowan

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Lecture 14 Water Soluble Vitamins Vitamin C: a) Classic example of Vitamin C deficiency: older person on tea and toast diet – indicating that they are malnourished; pt gets bleeding of the gums = scurvy, due to vit C def. Vit C is responsible for hydroxylation of proline and lysine, and this occurs in the Golgi apparatus b/c that’s where post-translational modification occurs. Pts have weak Type I collagen b/c cannot crossbridge it; therefore, BV’s are unstable and gums bleed. Get bleeding of the gums, inflammation, and may loose teeth. b) Associated question: what complication is associated with severe hemophilia A? Hemearthroses, and caused by Vit C deficiency (b/c the BV’s are unstable and they rupture). c) Physical diagnosis of Vitamin C deficiency: Along with the tea and toast diet, there is also perifollicular hemorrhage (hemorrhage around the hair follicles). See ring sideroblast (nucleated RBC, and has too much iron in the mitochondria), ring around the hair follicle and also see cork screw hairs due to vit C def. The tongue looks like it hurts and patients with vit C have a smooth tongue – glossitis, with kelosis around ankles, plus a hemorrhagic diathesis = scurvy. d) Excess vitamin C: very common b/c pts take way too much vit C (6-8gm), main complication is Renal stones (increased uric acid stones, and other kinds of stones). Vitamin C and D both have toxicity stones. e) Vitamin C is used in ancillary Rx for methemoglobinuria; it is a reducing agent and a great scavenger hunter for free radicals (knocks them off). f) Cofactor in biochemical pathway: Vit C is a cofactor for converting the catecholamine NE into Epi. Vitamin B 1Thiamine): a) Involved in many biochemical reactions: transketolase rxn’s in the pentose phosphate shunt; and pyruvate dehydrogenase; alpha keto glutarate dehydrogenase; and alpha keto acid dehydrogenase. All the dehydrogenase rxns require thiamine as a cofactor. Pyruvate dehydrogenase is the main rxn that converts pyruvate into acetyl CoA. Pyruvate can also be converted to OAA with a carboxylase enzyme. When you combine acetyl CoA with OAA, you make citrate, and you are in the TCA cycle. b) So, if thiamine def, b/c it is involved in the pyruvate dehydrogenase rxn (which converts pyruvate to acetyl CoA), you will not have a lot of acetyl CoA around, therefore, won’t have much citrate around, therefore, you won’t have the TCA cycle working efficiently, and LESS ATP. Therefore, the problem with thiamine def is ATP depletion. When you go from pyruvate to acetyl CoA, you generate 2 NADH’s and since this is in the mito, you get 6 ATP (so, just from going from pyruvate to acetyl-Coa, gives 6 ATP); and then with TCA, get 24 ATP’s. 6 + 24 = 30 ATP; the total you can get from completely metabolizing glucose is 38 ATP; so, if you are thiamine def, you are out 30 ATP’s; so, the main prob of thiamine def is ATP depletion. c) In thiamine def you’ll see foot drop (dry beriberi), and pitting edema (wet beriberi). How does this explain wet/dry beriberi? 1) Dry beriberi = peripheral neuropathy, and refers to Wernicke’s korsakoff psychosis (can’t remember old and new things – like an exam – ie “used to know that, but can’t remember now”; a memory problem). It takes a lot of ATP for synthesis of myelin; without myelin, you will get peripheral neuropathy and foot drop (due to common peroneal palsy), can get wrist drop (radial nerve palsy), and claw hand (ulnar nerve palsy). Wernicke’s encephalopathy is confusion, ataxia, and nystagmus. All of these are due to demyelization. 2) Wet beriberi = heart failure; MCC thiamine def = alcohol (not polished rice). Alcoholics are the MC people with thiamine def. Wet beriberi is referring to cardiomyopathy – cause: LHF went into RHF which lead to pitting edema. Heart needs ATP to function, therefore, the pt with have congestive cardiomyopathy; their heart will have biventricular enlargement (the whole chest will be heart), with left and right HF (pitting edema is a sign of right HF due to increased hydrostatic pressure behind the failed heart). If you give IV thiamine, can reverse; and in some cases it’s related to toxicity of alcohol, and cannot work. d) Example: pt in ER given IV of 5% dextrose and normal saline; all of sudden, pt develops confusion, nystagmus, and ataxia, and opthalmaplegia. Diagnosis: subclinical thiamine deficiency. As soon as the glucose was hung up, the pyruvate went to acetyl CoA and used the rest of thiamine...then went into acute Wernicke’s encephalopathy. Therefore, moral of the story: give IV thiamine before hanging up IV glucose, especially in ER. f) When people come in comatose or semicomatose, several things you always do: 1) 50% glucose if a hypoglycemia problem 2) naloxone (OD) 3) IV thiamine Vitamin B (3iacin): Slide: Rash in sun exposed area = pellagra (aka dermatitis), due to niacin def (also diarrhea, dermatitis, dementia); hyperpigmentation in sun-exposed areas = Cassel’s necklace (dermatitis/pellagra); NAD/NADP rxns (N stands for nicotinamide, and the nicotinamide was derived from niacin). Therefore, all the oxidation rxns rxn’s are niacin dependent. Example: pyruvate to acetyl CoA = went from NAD to NADH and niacin is involved here. Tryptophan can used in synthesizing niacin and serotonin (why it’s an essential aa); but it’s not the main source of niacin, but a good source. Nicotinic acid = least expensive lipid lowering drug; see the flushing assoc with it; supposed to take aspirin with it to remove the flushing related to nicotinic acid (used in treating familial hyperlipidemia), it is the DOC for elevated
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