Download Vitamins B, E, K

Vitamins B, E, K
Objectives
• Know the names, vitamer and cofactor forms of
vitamins B1, B2, B3, B5, B6, B7, B9, and B12.
Know major sources of each, USRDA.
• Know major cofactor reaction type for each of
the B vitamins and vitamin K.
• Know the sources for vitamin E and K.
• Understand uptake systems for B12 and folic
acid.
• Understand deficiency disorders and toxicity for
the B vitamins and K and E.
The B’s
Designation –vitamer form – cofactor form
• B1 – Thiamine - thiamine pyrophosphate
• B2 – Riboflavin – FMN, FAD
• B3 – Niacin – NAD+, NADP+.
• B5 – Pantothenic acid – Coenzyme A
• B6 – Pyridoxine, pyridoxal, pyridoxamine –
pyridoxal phosphate (PLP)
• B7 – Biotin - biotin
• B9 – Folic acid - tetrahydrofolate
• B12 – Cobalamin – (deoxyadenosyl cobalamin,
methyl cobalamin)
The B-Complex
• All water soluble.
• Form enzyme cofactors of central metabolism.
• Readily available from foods in amounts required by average
healthy adults.
• Deficiencies can result from poor diet (e.g. B12 - vegans, B9 –
too few veggies, B3 – historically, corn based diets)
• Deficiencies can result from defective uptake (e.g. B12, B9).
• Deficiencies can result from drug interactions (e.g. B6isoniazid).
• There is a complex interplay with alcoholism, producing
deficiencies (e.g. B1, B3).
• Most studies suggest supplementation neither necessary nor
useful for average adult; may be harmful.
B1 Thiamine
TDP
Vitamer: thiamine
Cofactor: thiamine diphosphate
Adults require about 1.2 mg/day*. There is no set Tolerable Upper Intake Level (seems
nontoxic at 50 mg/day). Body stores about 30 mg in tissues, including muscle.
TPP is used by pyruvate, alpha-ketoglutarate, and branched chain ketoacid dehydrogenases
(TLC For Nancy is mnemonic to recall that these enzymes need Thiamine, Lipoic acid,
Coenzyme A, FAD, and NAD). FYI: In these
dehydrogenases the TPP carbon between S
and N ionizes and acts as a nucleophile to
attack the ketone of the substrate.
B2 Riboflavin
Requirement about 1.2 mg/day for adults. Leaches out of body quite readily. Oral riboflavin
is not toxic, and oral doses of up to 400 mg/day have been administered in studies.
Riboflavin is used to make FMN and FAD,
which are redox cofactors required for
many enzymes, including glutathione
reductase, a few cytp450 complexes, the
electron transport system, several
enzymes that interconvert forms of
vitamin A, FH4, and niacin (from
Tryptophan). FAD is the “F” in TLC For
Nancy (see thiamine).
B3: Niacin
Niacin
NAD+
For adults: 16mg/day (men) 14 mg/day (women). 35 mg/day is considered a tolerable upper
intake limit*. Three ounces chicken or salmon has about 10 mg. One cup fortified cereal has
about 25 mg. One cup cooked lentils has about 2 mg. One cup roast peanuts 20 mg.
NOTE TO SELF: If you want to get niacin from veggies
on right, you have to eat them, it is not sufficient just to
buy them and put in produce drawer.**
Niacin Therapy Hypercholesterolemia
• Oral niacin in large doses (1-3 gram/day) has been
shown to lower LDL and increase HDL cholesterol
in otherwise untreated patients. Patients already
taking a statin (now cheap, usually well-tolerated)
do not seem to benefit.
• Oral niacin in large doses commonly causes a
visible “face flush” that can be uncomfortable, and
can reduce patient compliance.
B5 Pantothenic acid
Adults 5 mg/day, abundant in many foods. No Tolerable Upper Limit
established. Coenzyme A used to carry acyl chains in many parts of
metabolism, particularly acetyl, malonyl, methylmalonyl, succinyl
CoAs.
B6 Pyridoxine
Pyridoxine
Pyridoxal Phosphate
RDA about 1.5-2 mg/day. Tolerable Upper Limits vary between 25 (UK) and 100 (US) mg/day.
Toxicity from supplemental B6 has been described. One of the vitamins sometimes used in
legitimate “megavitamin therapy” to reverse problems arising from inherited defects in
metabolic enzymes (see later). PLP is used in
many enzymes of amino acid metabolism, forming
an initial adduct with the amino nitrogen. Further
catalysis involves aminotransferase,
decarboxylation, (D/L)racemase, dehydration, or
other sidechain chemistry. Glutamate
decarboxylase (GABA) and kynureninase (Trp
metabolism) are two sites sensitive to lower PLP
Pyridoxal Reacts With Isoniazid
Because of the ability of aldehydes to react with amines and their derivatives, the
anti-tuberculosis drug isoniazid (dosage 300+ mg/day) can react with pyridoxal to
form a derivative which is excreted. The reaction effectively removes pyridoxine
from the body and causes a pyridoxine deficiency disorder in treated TB patients.
It is standard to administer 25 mg/day of pyridoxine as a co-therapy with isoniazid
to avoid this.
B7 Biotin
CO2 
Carboxybiotin attached to E-Lys-NH
Normally biotin is made by intestinal bacteria, and there is no RDA in USA. It can be tolerated
in very high doses. However, egg white contains avidin, a protein that binds biotin, and
consumption of raw egg white can result in a deficiency. Additionally, biotin needs to be
attached to carboxylases by another enzyme, and defects cause deficiency-like symptoms.
Biotin is the CO2-binding cofactor in many carboxylases, including acetyl CoA and pyruvate
carboxylases.
B9 Folic Acid
Folic acid has three parts: a pteridine ring system (left), a para-aminobenzoate (PABA*) ring
(middle), glutamate on right. The glutamate moiety is often polyglutamate: size of polyGlu
can affect behavior and transport.
Cofactor forms of FH4 (several) contain single carbon moieties (e.g. methyl, formyl,
methylene) at the pteridine-PABA nitrogens.
The Dietary reference Intake (DRI) for adults is 400 microgram/day, with upper limit of 1000
ug/day. There is little risk of toxicity. BUT: folate uptake is very complex and natural food
folates and suppplement folates are taken up differentially.
Folate = Foliage, Get it?
Normal Child 
Needs Therapy 
FYI: Folate Complexity
Folate Transport
• Folate transport and metabolism are linked, complex, and
still being actively studied. Rest of this is FYI
• “PCFT” (Proton-Coupled Folate Transporter) is a folateproton symporter located in apical membrane of brush
border cells in small intestine (along with lots of other
carriers like Na-glucose and Na-amino acid). PCFT grabs
folate in gut, taking up ONLY the monoglutamate form. A
specific peptidase trims the polyglutamylated folates of the
diet to monoglutamates.
• A second transport system(s) probably takes folate from
brush border cell across basolateral memebrane to blood.
The same and other transporters take folate into liver and
kidney for storage and use and other cells for use.
• Within cells, folates can become polyglutamylated. This
probably helps them stay within those cells. Kidney and liver
can also hydrolyze polyglutamates to form monoglutamate.
Folate Supplements and Chemotherapeutic Agents
• Just to add to complexity of folate metabolism, the
various folate transport systems have differing
ability to carry folate, folate derivatives (e.g.
methyl folate and formyl tetrahdrofolate) and
chemotherapeutic mimics (e.g. methotrexate).
• Effectively, this means that methotrexate may be
transported differentially from folate. So, folinic
acid (a monoglutamate form of formyl FH4) is often
co-administered with methotrexate in a complex
schedule. Methotrexate kills cancer cells, as folinic
acid helps rescue normal cells. Much research
remains to be done in this area!
B12 Cobalamin
B12 is used in two reactions in the
human body. Homcysteine
methylation requires methyl B12,
whereas the methylmalonyl CoA
mutase reaction requires the
deoxyadenosyl form. Vitamer forms
include hydroxy and cyano
complexes.
The US RDA is 2-3 micrograms/day. Daily losses are small, and large
(mg) amounts are stored in liver, so deficiency takes years to
materialize.
Vitamin B12
• Where is it from? We usually say only “animal derived” foods. In
fact B12 is not made by animals (or plants or yeast or other fungi)
but only by some bacteria. Ruminant animals have B12producing bacterial symbionts in their upper gut, most animals
have in lower gut. Feces contain B12 that is then ingested by the
same or other animals.
• Industrially, B12 is made in bacterial fermentation, which can be
done in non-animal-using fashion.
• No yeast makes B12. Some fungi and animals produce
“pseudovitamin B12” which can score as B12 in some bacterialgrowth tests, but is not nutritive to animals. Pseudovitamin B12
can inhibit use of real B12. SOME “nutritional yeast” products
contain supplemental B12, otherwise yeast DOES NOT contain
usable B12. People need B12: they can get through animal
products or a synthetic source.
• Urinary methylmalonate is easy screening assay for poor B12
nutrition
B12 Uptake: Complex!
Vitamin E Tocopherol
US Dietary Reference Intake for adults is 15 mg/day. An upper tolerable limit of 1000 mg/day.
Rich sources are wheat germ oil, other oils, nuts and oily fruit (avocados)
Vitamin E activity is shown by several compounds, including alpha-tocopherol (picture).
Unlike other vitamins, E exerts its effects directly, not as a cofactor. Vitamin E is a lipid
soluble membrane-incorporated scavenger of peroxyl radicals. It has other regulatory roles
through binding to enzymes (e.g. protein kinase C) or altering transcription.
Vitamin E deficiency from inadequate nutrition is rare, but can occur from fat malabsorption
and rare genetic defects. Symptoms are neurological and include retinopathy, and vibratory
sensation defects.
Vitamin E Deficiency: Google Images
So the guy peacefully sleeping is healthy and the woman has insomnia from vitamin E
deficiency? NO! Apparently it’s the guy who has the vitamin E deficiency! Go figure!
Attached text revealed that vitamin E deficiency could cause problems with the
“reproductive apparatus”. Further info: Blazing Saddles.
Vitamin K
Gammacarboyglutamic acid.
Side chain varies in length
Vitamin K RDA for adults is about 100 micrograms/day. Half a cup of cooked kale has 531
micrograms. There is no known toxicity.
The role of vitamin K is as a cofactor for a carboxylase that adds CO2 to certain glutamate
residues of blood clotting proteins, such as thrombin (“Factor II”) and several others. The
resultant residue (upper right) is gammacarboxyglutamate or Gla (in 3-letter code). Gla residues
can bind Ca2+, and that role is essential for clotting factor function. Carboxylation is cotranslational.
There are several drugs that interact with Vitamin K. Warfarin (Coumadin) is an anticlotting drug that inhibits vitamin K reactions, such that the prescribing physician and the
patient must constantly balance the Coumadin/vitamin K intake. Since vitamin K is a natural and
variable part of foods, this can be difficult. Additionally, vitamin K and Coumadin action are not
instantaneous, like other clotting drugs: the clotting factors produced last for many days, and
take days to replace, so there are delays between starting vitamin K therapy for Warfarin
overdose, and getting a rebalanced clotting system.
Deficiencies
• We can think about vitamin deficiencies in terms of
their incidence, in terms of the nature and severity
of the symptoms, and the mechanism though
which deficiency arises.
How to Measure Vitamin Status
• It is horrifying to realize that our ability to measure
vitamin status clinically is often very poor. One also
need to realize there are often both analytical
assays that are more accurate, but slow and
expensive, and screening assays that are quick but
have many false positives and negatives.
• Thiamine: there is a HPLC-based blood TDP assay.
A blood thiamin assay inadequate to rule out
WE/KS, activation of intracellular thiamine
dependent enzymes better.
• Niacin: measured as niacin metabolites in urine.
Thiamine Deficiency: Wernicke’s
Encephalopathy, Korsakoff Syndrome
• A deficiency in brain B1 levels causes irreversible
brain pathology (WE) and neurological deficits (KS).
Symptoms can be arrested by thiamine therapy,
usually by injection, but generally memory loss and
neurological deficits are irreversible.
• Usual cause is thiamine deprivation through
alcoholism*, although also with eating disorders
and occasionally bariatric surgery. There is only
about 2-3 weeks worth of body thiamine, so
deficiency can occur quickly.
Niacin Deficiency: Pellagra
• Pellagra is the term for pathological niacin deficiency. Historically, it
arose in populations in which maize or sorghum was the major food.
Corn contains niacin, but it is bound to corn fiber. Mesoamericans
always ground corn with lime (CaCO3, “nixtamilization”), which
frees niacin. Europeans began to use corn culture, but did not
nixatamilize the corn, so it failed to provide niacin. The disorder was
rampant in earlt 20th century USA, and worldwide in prison camps
and other impoverished areas. Pellagra can arise among alcoholics
from poor niacin content of diet, and lessened uptake.
• Pellagra is characterized by the “4 Ds”: Dermatitis is striking and
aggravated by sun. Diarrhea contributes to potentially fatal
electrolyte imbalance and dehydration, Dementia arises through
buildup of NAD precursors and lack of NAD/NADP. Death is a final
outcome.
• Niacin can be made from tryptophan, but synthesis is weak and
inhibited by leucine. Poor B6 nutrition exacerbates the B6 effect.
Folate Deficiency: Macrocytic Anemia
• Active single carbon metabolism is required for
human dTMP and purine synthesis, so poor folate
nutrition results in a failure of red blood cell
precursors to mature, and causes an anemia (low
hematocrit) that is characterized by these large
precursor cells. Readily reversed by folate in diet.
• More insidiously, folate deficiency can cause failure
of neural tube closure (extreme is spina bifida). The
key period is in the early weeks of pregnancy, when
the mother may not be fully cognizant of
nutritional needs. Today USDA requires
supplemental folate in flour and baked goods.
B12 Deficiency: Irreversible Neurological Deficits
• In the absence of sufficient B12, methylmalonate builds
up and causes neurological problems, seen in gaiting
and in cognitive deficits. The damage is stopped by B12,
but is irreversible.
• BUT: low B12 also results in trapping FH4 in its methyl
form, causing a consequent folate deficiency anemia.
This anemia is far easier to spot than the subtle
neurological damage, and may result in misdiagnosis of
folate deficiency. Folate supplementation will fix the
anemia, but not the ongoing neurological issues.
• Because the body stores mg quantities of B12, and
sheds only ug quantities daily, B12 deficiency is very
slow to show symptoms, so quite insidious.
Who gets B12 Deficiency?
• Inadequate nutrition: vegan diets do not contain
B12. Synthetic B12 is a vegan product. It is a myth
that “nutritional yeast” naturally contains B12, but
some nutritional yeast is supplemented with B12:
the label must say so and be quantitative
• Inadequate uptake: older adults secrete far less
intrinsic factor and can have adequate B12 in diet,
but fail to take it up. These people will require
supplementation, often by intramuscular injection.
• For people with B12 deficiency, the initial injection
schedule is daily, then less frequently. Aim is to
build body stores, which goes slowly.
Supplements
• Americans use vitamin supplements! In general,
neither useful nor harmful.* BUT, in specific cases
can be valuable, and can definitely be toxic either
directly, or in form taken.
• B3 (niacin) – large doses in anti-cholesterol therapy
(1-3 grams/day!), drug test duplicity can cause face
flush, heart irregularities.
Vitamins and Food Preparation
• Some people are obsessive about vitamins. With a
normal diet they probably do not need to be. BUT,
these folks figure that while green veggies contain
folic acid, cooking will destroy the vitamin.
• Actual situation is more complex: for folate
(example) raw green veggies often fail to release
folate in digestive system. Cooking aids in release,
although destroying some of the vitamin.
• Key Point: cooked veggies are NOT devoid of B
vitamins.
What’s In Wheaties, Anyway?
And Total?
So idea here is to fill all your
vitamin requirements by 8
a.m.? Except for A and D
(note cautious content) most
items here not particularly
toxic. In cereal most of the
vitamin content comes from
added ingredients, not the
cereal grain itself.
Megavitamin Therapy
• “Megavitamin” is used to describe two different
things: a quackery approach to health, but also
specific prescribed therapy to remediate an
inherited or acquired inability of the cofactor to
work correctly. These megavitamin-responsive
disorders are rare, but there are many types.
• In “gyrate atrophy of choroid and retina” ornithine
aminotransferase has low activity, sometimes
through weak binding of PLP. In those particular
cases high oral B6 can cure this problem*.
• There is oldish review** that lists 50 such
disorders.