B Vitamins B&B Flashcards
which B vitamin CAN be stored in the body?
B12 - stored mostly in liver, some in muscle
others (B1,2,3,5,6,7,9) wash out of body quickly (water soluble)
how do B vitamin deficiencies generally present?
B vitamins used in many metabolic pathways, deficiencies have greatest effect on rapidly growing tissues
—> dermatitis, glossitis, diarrhea, cheilitis (skin breakdown at corners of lips)
vitamin B1, aka _____, is a cofactor for which 4 enzymes?
vitamin B1 = thiamine, converted to thiamine pyrophosphate (TPP)
- pyruvate dehydrogenase
- Alpha ketoglutarate Dehydrogenase (TCA)
- Alpha ketoacid Dehydrogenase (branched amino acid chains)
- Transketolase (HMP shunt)
vitamin B2, aka _____, is required for…
vitamin B2 = riboflavin
added to adenosine to create FAD+ (required by dehydrogenases) used in and ETC (as FMN - flavin mononucleotide)
what are the classic symptoms of vitamin B2 deficiency?
vitamin B2 = riboflavin (used to make FAD+)
—> dermatitis, glossitis
—> cheilitis (lip inflammation, cracks at corner of mouth) - classic sign
—> corneal vascularization (rare)
[deficiency = ariboflavinosis]
Vitamin B3, aka _____ is used for…
vitamin B3 = niacin
used to synthesize NADH and NADPH - used in ETC, dehydrogenases require NAD+
niacin, aka vitamin ____, can be synthesized from which amino acid?
niacin = vitamin B3, used to generate NADH/NADPH
can be synthesized from tryptophan, conversion requires vitamin B6 (vit. B6 deficiencies will present with symptoms of niacin deficiency!)
patients with what type of diet will classically be deficient in niacin (vit. B3)?
corn-based diets - corn does not contain niacin
niacin (B3) found in grains, milk, meats, liver
can also be synthesized from tryptophan (requires B6)
how does vitamin B3 deficiency present?
vitamin B3 = niacin, used to make NADH/NADPH
niacin/B3 deficiency = Pellagra
—> Dermatitis
—> Diarrhea
—> Dementia
—> Death
—> rash on sun-exposed areas
Pellagra
niacin/B3 deficiency = Pellagra
—> Dermatitis
—> Diarrhea
—> Dementia
—> Death
—> rash on sun-exposed areas
vitamin B3 = niacin, used to make NADH/NADPH
what are 3 classic clinical scenarios in which niacin (B3) deficiency develops?
vitamin B3 = niacin, used to make NADH/NADPH
- INH (isoniazid, TB drug) - decreases B6 activity
- Hartnup disease - AR absence of AA transporter in proximal tubule, loss of tryptophan in urine
- Carcinoid syndrome - GI tumor secretes serotonin via altered tryptophan metabolism, tryptophan unavailable
[recall B3 can be made from tryptophan, and this conversion requires B6]
Pt with PMH of INH (isoniazid) therapy for TB is presenting with dermatitis, diarrhea, dementia, and a rash on sun-exposed areas. What is likely going on?
Niacin/B3 deficiency (Pallagra)
INH decreases B6 activity, and recall B3 can be made from tryptophan with the assistance of B6
Pt with Carcinoid syndrome is presenting with dermatitis, diarrhea, dementia, and a rash on sun-exposed areas. What is likely going on?
niacin/B3 deficiency (Pellagra)
Carcinoid syndrome: GI tumor secreting serotonin - alters tryptophan metabolism such that most of it is used to synthesize serotonin (when usually only 1%) —> tryptophan deficiency
recall B3 can be made from tryptophan (requires B6 for conversion)
for what is niacin/vitamin B3 used as a treatment, and what occurs if it is taken in excess?
niacin/B3 - used to treat hyperlipidemia (separate from its role in generated NADH/NADPH)
in excess —> facial flushing via prostaglandin stimulation (can blunt with aspirin, which inhibits prostaglandins)
vitamin B5, aka ______, is used for…
vitamin B5 = pantothenic acid, used to coenzyme A (therefore any reaction requiring CoA also requires B5)
what is a classic sign of vitamin B5 deficiency?
vitamin B5 = pantothenic acid, used to coenzyme A
deficiency rare, but may present with “burning feet” (numbness)
vitamin B6 is composed of 3 compounds, which are all converted to ______
pyridoxal phosphate, PLP (active form of Vitamin B6)
used in:
- aminotransferase reactions
- neurotransmitter synthesis
- methionine —> cysteine pathway
- histamine synthesis
- glycogen breakdown (glycogen phosphorylase)
- tryptophan —> niacin conversion
- heme synthesis (ALA synthesis)
which 5 neurotransmitters require vitamin B6 for their synthesis?
active form of vitamin B6 = pyridoxal phosphate
- dopamine
- norepinephrine
- epinephrine
- serotonin
- GABA
basically all the main ones !
glycogen phosphorylase requires which vitamin?
glycogen phosphorylase requires Vitamin B6 (pyridoxal phosphate)
what type of anemia occurs from vitamin B6 deficiency and why?
vitamin B6 = pyridoxal phosphate, required for a butt ton of reactions include heme synthesis
required for synthesis of ALA (gamma-aminolevulinic acid)
B6 deficiency —> sideroblastic anemia (iron cannot be incorporated into heme, and so it accumulates in RBC cytoplasms) - microcytic, hypochromic
patients taking isoniazid (INH) for TB take supplements of vitamin ____ because…
isoniazid (INH) has similar structure to B6 (pyridoxal phosphate) and can inactivate it —> relative B6 deficiency
therefore, patients on INH must take B6 supplements
what are the classic symptoms of vitamin B6 deficiency?
vitamin B6 = pyridoxal phosphate, used in lots of reactions
deficiency is very rare, but can cause CNS symptoms - seizures, confusion, neuropathy
also possible glossitis, oral ulcers
which B vitamin is the only one to pose a threat of potential toxicity, and how does this present?
B vitamins are water soluble, excess is usually washed out
exception is B6 (pyridoxal phosphate) - massive intake (via supplements) may cause sensory neuropathy —> pain/numbness in legs, difficulty walking
vitamin B7, aka _____, is required for which 3 important metabolic enzymes?
vitamin B7 = biotin, cofactor for carboxylation enzymes* (add 1 carbon group via CO2)
- pyruvate carboxylase (gluconeogenesis)
- acetyl CoA carboxylase (fatty acid synthesis)
- propionyl-CoA carboxylase (entry into TCA cycle)
*”ABC” enzymes - require ATP, Biotin, and CO2
vitamin B7/biotin deficiency is very rare, but is classically caused by…
massive consumption of raw egg whites - contain avidin, which binds B7 and prevents its absorption
which B vitamin is NOT absorbed in the jejunum?
B12 - absorbed in terminal ileum
which 2 B vitamin deficiencies cause megaloblastic anemia and what are the classic findings?
folate (B9) or B12 deficiencies - required for thymidine synthesis (for DNA synthesis)
—> high levels of homocysteine (cannot be converted to methionine)
—> hypersegmented neutrophils
—> large RBC (high MCV)
[recall B12 deficiency will also present with elevated methylmalonic acid, required for myelin synthesis]
vitamin B12, aka _____, comes from…
vitamin B12 = cobalamin (contains cobalt)
only synthesized by bacteria, found in meats
dietary deficiency very rare, liver can store years worth of B12
what is the unique role of vitamin B12 (cobalamin) from folate (B9) that helps distinguish a B12 deficiency from a folate deficiency?
both will present with elevated homocysteine (—> megaloblastic anemia)
but vitamin B12 is also required for odd chain fatty acid metabolism —> high levels of methylmalonic acid (MMA), defect in myelin synthesis —> peripheral neuropathy involving dorsal spinal columns (subacute combined degeneration (SCD)
bilateral, legs > arms, ataxia, loss of vibration and position sense
what is the cause of pernicious anemia?
autoimmune destruction of gastric parietal cells —> loss of secretion of intrinsic factor —> defect in B12 absorption in the terminal ileum
type II hypersensitivity, associated with HLA-DR antigens
what vitamin deficiency is associated with pernicious anemia?
autoimmune destruction of gastric parietal cells —> loss of secretion of intrinsic factor —> defect in B12 absorption in the terminal ileum
type II hypersensitivity, associated with HLA-DR antigens
how does pernicious anemia present?
autoimmune destruction of gastric parietal cells —> loss of secretion of intrinsic factor —> defect in B12 absorption in the terminal ileum
presents with chronic inflammation of the gastric body, more common among women, associated with gastric adenocarcinoma
what are the 4 forms of vitamin B1 deficiency?
B1 = thiamine, deficiency = Beriberi
dry: muscle wasting, peripheral neuropathy (feet)
wet: edema, enlarged heart
infantile: heart failure (babies breast-fed by thiamine deficient mothers)
cerebral (Wernicke-Korsakoff): ataxia, impaired mental status (alcoholism)
vitamin B9, aka _____, is important for…(3)
B9 = folate (folic acid)
- DNA/RNA synthesis
- methionine recycling (conversion of homocysteine to methionine)
- SAM (S-adenosylmethionine) synthesis, for methylation reactions
what occurs from vitamin B9 deficiency?
B9 = folate
—> DNA strand breaks (recall folate required for DNA/RNA synthesis)
—> hyperhomocysteinemia (recall folate is required to convert homocysteine to methionine)
—> megaloblastic anemia
—> neural tube defects (spinal bifida, anencephaly)
what will a peripheral smear show in a patient with vitamin B9 deficiency?
B9 = folate, deficiency —> megaloblastic anemia
peripheral smear shows macrocytic anemia + hypersegmented PMNs
