Flashcards in Biochem: Vitamins Deck (105)
mineral oil intake can cause ____ vitamin deficiencies.
mineral oil intake can cause fat-soluble vitamin deficiencies
Retinol (Vitamin A)
- where do you get it?
- Found in liver and leafy vegetables.
- constituent of visual pigments (retinal)
- essential for normal differentiation of epithelial cells into specialized tissue (pancreatic cells, mucus-secreting cells)
- prevents squamous metaplasia.
- Used to treat measles and AML subtype M3.
- Retinol is vitamin A, so think retin-A (used topically for wrinkles and Acne).
- oral isotretinoin used to treat severe cystic acne (teratogenic)
- Use all-trans retinoic acid to treat acute promyelocytic leukemia
Deficiency of Vitamin A (retinol) symptoms
- Night blindness (nyctalopia)
- dry, scaly skin (xerosis cutis)
- corneal degeneration (keratomalacia)
- Bitot spots on conjunctiva
Acute Vitamin A Toxicity
- Acute toxicity: nausea, vomiting, vertigo, and blurred vision
Chronic Vitamin A Toxicity
- Chronic toxicity: alopecia, dry skin (eg, scaliness), hepatic toxicity and enlargement, arthralgias, and pseudotumor cerebri.
- Teratogenic (cleft palate, cardiac abnormalities), therefore a negative pregnancy test and 2 forms of contraception are required before isotretinoin (vitamin A derivative) is prescribed
Vitamin B1 (thiamine)
- In thiamine pyrophosphate (TPP), a cofactor for several dehydrogenase enzyme reactions:
1. Pyruvate dehydrogenase (links glycolysis to
2. α-ketoglutarate dehydrogenase (TCA cycle)
3. Transketolase (HMP shunt)
4. Branched-chain ketoacid dehydrogenase
- Think (ATP):
A: α-ketoglutarate dehydrogenase
P: Pyruvate dehydrogenase.
- what's damaged
- confusion, ophthalmoplegia, ataxia (classic triad) +
- personality change
- memory loss (permanent).
- Damage to medial dorsal nucleus of thalamus, mammillary bodies.
beri beri Symptoms
1. Dry Beri Beri:
- symmetrical muscle wasting.
2. Wet beriberi:
- high-output cardiac failure (dilated cardiomyopathy), edema.
*Spell beri beri as Ber1Ber1 to remember vitamin B1
Vitamin B2 (riboflavin) function
- Component of flavins FAD and FMN
- used as cofactors in redox reactions
- ex) the succinate dehydrogenase reaction in the TCA cycle.
- "(F)AD and (F)MN are derived from ribo(F)lavin
- (B2 ≈ 2 ATP)
Vitamin B2 (riboflavin) deficiency
- The 2 C’s of B2:
- Cheilosis (inflammation of lips, scaling and fissures at the corners of the mouth)
- Corneal vascularization
Deficiency of Vitamin B1 (Thiamine)
- Impaired glucose breakdown leads to
- ATP depletion worsened by glucose infusion
- highly aerobic tissues (eg, brain, heart) are affected first.
- Wernicke-Korsakoff syndrome and beriberi.
- Seen in malnutrition and alcoholism (2° to malnutrition and malabsorption).
- Diagnosis made by increase in RBC transketolase activity following vitamin B1 administration
Vitamin B3 (niacin) Function
- Constituent of NAD+, NADP+ (used in redox reactions).
- Derived from tryptophan
- Synthesis requires vitamins B2 and B6
- Used to treat dyslipidemia
- lowers levels of VLDL and raises levels of HDL.
- NAD derived from Niacin
- (B3 ≈ 3 ATP)
Vitamin B3 (niacin) Deficiency
- Severe deficiency leads to pellagra, which can be caused by Hartnup disease, malignant carcinoid syndrome (increased tryptophan metabolism), and isoniazid (decreased vitamin B6)
- Symptoms of pellagra ("The 3 D's of B3"):
2. Dementia (also hallucinations)
- C3/C4 dermatome circumferential “broad collar” rash [Casal necklace]
- hyperpigmentation of sun-exposed limbs
Vitamin B3 (niacin) Excess
- Facial flushing (induced by prostaglandin, not histamine; can avoid by taking aspirin with niacin)
- autosomal recessive
- Deficiency of neutral amino acid (ex tryptophan) transporters in proximal renal tubular cells and on enterocytes
- causes neutral aminoaciduria
- and decreased absorption from the gut
- decreased tryptophan for conversion to niacin
- this causes pellagra-like symptoms.
- Treat with high- protein diet and nicotinic acid
Vitamin B5 (pantothenic acid) Function
- Essential component of coenzyme A (CoA, a cofactor for acyl transfers)
- and fatty acid synthase
- B5 is “pento”thenic acid
Vitamin B5 (pantothenic acid) Deficiency
- adrenal insufficiency
Vitamin B6 (pyridoxine) Function
- Converted to pyridoxal phosphate (PLP), a cofactor used in
1. transamination (eg, ALT and AST)
2. decarboxylation reactions
3. glycogen phosphorylase.
- Synthesis of cystathionine, heme, niacin, histamine, and neurotransmitters including serotonin, epinephrine, norepinephrine (NE), dopamine, and GABA
Vitamin B6 (pyridoxine) Deficiency
- peripheral neuropathy (deficiency inducible by isoniazid and oral contraceptives)
- sideroblastic anemias due to impai`red hemoglobin synthesis and iron excess
Vitamin B7 (biotin) function
- “Avidin in egg whites avidly binds biotin"
- Cofactor for carboxylation enzymes (which add a 1-carbon group):
1. Pyruvate carboxylase: converts pyruvate (3C) to oxaloacetate (4C)
2. Acetyl-CoA carboxylase: converts acetyl-CoA (2C) to malonyl-CoA (3C)
3. Propionyl-CoA carboxylase: converts propionyl-CoA
(3C) to methylmalonyl-CoA (4C)
Vitamin B7 (biotin) deficiency
- Relatively rare
- Caused by antibiotic use or excessive ingestion of raw egg whites
Vitamin B9 (folate) function
- Converted to tetrahydrofolic acid (THF)
- a coenzyme for 1-carbon transfer/methylation reactions
- Important for the synthesis of nitrogenous bases in DNA and RNA.
- Supplemental maternal folic acid in early pregnancy to decrease risk of neural tube defects
Causes of Vitamin B9 (folate) deficiency and Labs
- MC vitamin deficiency in the US.
- Seen in alcoholism and pregnancy.
- Deficiency can be caused by several drugs (eg, phenytoin, sulfonamides, methotrexate)
- elevated homocysteine
- normal methylmalonic acid levels
Vitamin B9 (folate)
- found where?
- absorbed where?
- stored where?
- Found in leafy green vegetables.
- (FOLate from FOLiage)
- Absorbed in jejunum
- Small reserve pool stored primarily in the liver
- Features of Vitamin B9 (folate) Deficiency
- Macrocytic, megaloblastic anemia
- hypersegmented polymorphonuclear cells (PMNs)
- no neurologic symptoms (as opposed to vitamin B12 deficiency)
- elevated homocysteine
- normal methylmalonic acid levels
- Mineral essential for the activity of 100+ enzymes.
- Important in the formation of zinc fingers (transcription factor motif)
- Delayed wound healing
- decreased adult hair (axillary, facial, pubic)
- dysgeusia (distortion of the sense of taste)
- acrodermatitis enteropathica
- May predispose to alcoholic cirrhosis
1. Protein malnutrition resulting in:
- skin lesions
- edema due to decreased plasma oncotic pressure
- liver malfunction (fatty change due to decreased apolipoprotein synthesis).
- Clinical picture is small child with swollen abdomen
- Kwashiorkor results from a protein-deficient MEAL:
- "Marasmus results in Muscle wasting"
- Total calorie malnutrition resulting in emaciation (tissue and muscle wasting, loss of subcutaneous fat)
* +/– edema