Water Soluble Vitamins Flashcards
Thiamine characteristics?
Active form: thiamine pyrophosphate (TPP)
TPP is involved in alpha-keto acids
What are the two types of thiamine transporter?
THTR 2 (low or normal concentrations, active transport)
THTR 1 (high concentration, passive)
Alcohol affects only the THTR 2 carrier mediated transport
Thiamine deficiency leads to…
Wet beri-beri (edema and CV problems)
Dry beri-beri (neurological problems)
Wernicke-Korsakoff syndrome: CNS lesions, associated with alcoholism
Riboflavin (Vitamin B2)
Is readily destroyed by sunlight
Active forms are FMN (can be reduced to FMNH2) and FAD (can be reduced to FADH2)
Riboflavin deficiency
Stomatitis (inflammation of mouth)
Cheilosis (painful cracking of corners of mouth)
Glossitis (inflammation of tongue)
Niacin
Active forms: NAD+, NADP+; serve as coenzymes in RedOx reactions
Tryptophan can make NAD, de novo
ADP ribose can help convert NAD to nicotinamide
How does niacin help lower LDL and increase HDL?
Decrease in LDL is due to noncompetitive inhibition by niacin on a liver enzyme involved in triglyceride synthesis
This decreased synthesis results in intracellular apo B degradation and decreased secretion of VLDL particles
Niacin deficiency characteristics
Pellagra: dermatitis, dementia, diarrhea (3 D’s); also caused by insufficient tryptophan
Hartnup’s dx: affects amino acid transport; an increased need for niacin may lead to its deficiency
Biotin
The enzyme biotinidase removes bound biotin from protein (a good thing!)
Deficiency of biotinidase results in increased fatty acid production; also, body becomes biotin deficient
Biotin deficiency
Caused by defects in reutilization (not diet); see biotinidase
Absence of holocarboxylase synthase enzyme causes multiple carboxylase deficiency
Panthothenic acid
Is a component of coenzyme A (CoA)
Folic acid
Consists of pteridine attached to PABA and a glutamic acid
Monoglutaminated folic acid is taken up by the reduced folate carrier (RFC) in the intestine
Formation of tetrahydrofolic acid (THF) is inhibited by…
Methotrexate, a treatment option which inhibits the dihydrofolate reductase
Also, anything affecting vit B12 production will also affect folate production
Megaloblastic anemia
Is caused by diminished synthesis of purines and thymidine, leading to the inability of cells to both divide and make DNA
Macrocytic RBCs are seen (no cell division, so the cells keep growing)
Transulfuration pathway needs vit B6
Spina Bifida
Is caused by a C -> T substitution (valine for alanine)
May account for neural tube defect
Histidine load test is used for?
Measuring FIGLU and seeing if there is a deficiency in folic acid
If FIGLU is high in the urine sample, THF is therefore low, because it would have converted the FIGLU into other things (if things were normal, FIGLU would not be high in the urine)
Dietary Vitamin B12 overview
B12 binds to transcobalamin I in the stomach which then travel to the intestine and are then destroyed by pancreatic proteases
The freed B12 then binds to intrinsic factor (IF), and then are absorbed by ileum and then carried by transcobalamins
Absorption and transport of Vit B12
B12 is bound by transcobalamin II when transported to the tissues
Dx and deficiencies associated with B12
Crohn’s Dx: affects ileum so that there is an impairment of bile acid and B12 absorption
Dx sx: megaloblasic anemia, pernicious anemia (if lacking IF), homocystinuria (homocysteine does not convert to methionine) and methylmalonic aciduria
Methylmalonic aciduria characteristics
Propionyl CoA —biotin—> methylmalonyl CoA –vit B12–> succinyl CoA -> citric acid cycle and gluconeogenesis
If vit B12 is deficient, MM CoA cannot convert to succinyl CoA; thus, MM CoA builds up (bad!)
Pyridoxine (Vit B6)
Pyridoxal phosphate (PLP) is the active form
PLP is essential for transaminase rxns and the synthesis of the NTs (serotonin, epi, norepi and GABA)
PLP also required for synthesis of alanine (precursor of heme)
Vitamin B6 deficiency
Causes hypoglycemia due to impairments of glycogenolysis and gluconeogenesis
May cause sideroblastic microcytic anemia
How to test for vit B6 defiency
Tryptophan load test
Trp usually ends up forming alanine, because PLP cleaves kynurenine. If PLP is deficienct, it, instead, leads to an increase in xanthurenic acid, a measurable quantity after a load test.
Ascorbic acid / Vitamin C
Important for collagen formation
Deficiencies lead to weak collagen, bleeding gums, poor wound healing and petechiae
