1. Trao đổi trực tuyến tại:
http://www.mientayvn.com/Y_online.html
2. Reading material
• Principles of Biochemistry with a Human
Focus by Garrett and Grisham, First
Edition, 2002, pages 453-468
• Handbook of NonPrescriptions Drugs,
11th edition, Chapter entitled “Nutritional
Products” by Loyd V. Allen, Jr.
3. Vitamins
• a group of organic compounds needed in small
quantities in the diet for normal activity of
tissues
• between 14 – 20 substances have been identified
as vitamins
• many vitamins act as cofactors, coenzymes or
prosthetic groups for enzymes
• most vitamins are derived from diet
• no calories are derived from vitamins
4. Vitamins
• first vitamin discovered was thiamine or
B1
• the term vitamin is derived from the fact
that the substances are needed for life
(vita) and because thiamine happened to
be an amine the term was coined as such
• however, not all vitamins are amines or
nitrogen containing compounds
5. Vitamins
• vitamin requirements are usually
expressed as RDA’s (recommended
dietary allowances)
• guidelines are provided by 2
organizations:
• the Food and Nutrition Board of the National
Academy of Sciences- National Research Council
• the Food and Drug Administration (FDA)
6. RDAs
• applications of RDAs include:
• evaluating the adequacy of the national food
supply
• establishing standards for menu planning
• establishing nutritional policy for public
institutions/organizations and hospitals
• evaluating diets in food consumption studies
• establishing labeling regulations
• setting guidelines for food product formulation
• developing materials for nutritional education
7. RDAs
• RDAs have limitations:
• they are too complex for direct consumer use
• they do not state ideal or optimal levels of intake
• the allowances for some categories are based on
limited data
• the data on some nutrients in foods is limited
• they do not evaluate nutritional status
• they do not apply to seriously ill or malnourished
patients
10. Vitamin loss
Loss is seen mainly in storage or food preparation
• Vitamin A: sensitive to oxygen and light
• Vitamin D: usually little loss
• Vitamin E: sensitive to oxidation especially
when heated or with alkali
• Vitamin K: sensitive to acids, alkali, light and
oxidizing agents
• Vitamin C: very sensitive to oxidation,
especially when heated in contact with metals
• Vitamin B complex: water solubility results in
loss in cooking water
• Riboflavin is sensitive to light
11. Vitamins
• Vitamins are typically divided into 2
groups:
– The fat soluble vitamins
• A, D, E, and K
– The water soluble vitamins
• The B vitamins (B1, B2, B3, B6, B7, B12 and
pantothenic acid)
• Ascorbic acid (vitamin C)
13. Cofactors
• provide “chemical teeth” for enzymes
• sometimes referred to as coenzymes
• enzymes: proteins with catalytic activity
– simple enzymes: large protein (polypeptide) that
catalyzes a reaction. The enzyme gets all the “tools”
(chemical teeth) it needs from the amino acids.
However, there are only 20 different amino acids
– conjugated enzymes : apoenzyme + cofactor =
holoenzyme
14. EXAMPLE:Proteases: enzymes that cleave
peptide bonds
N
N
N
H
R
O
H
R'
O
H
N
OH
H
R
O
+ H2N
N
R'
O
H
H2O
protease
Enzymes perform catalytic reactions such as hydrolysis; the
side chains of amino acids participate in the reactions
15. CH2OH
CH2
N
H
N
CH2-COOH
all these tools come from amino acids
in the protein active site
Usually electron-rich
side chains are involved
in the catalysis
Aliphatic chains are
normally involved in
hydrophobic interactions
example of a simple enzyme
A serine protease enzyme such as chymotrypsin
16. COO- O
HN
N
H
ASP HIS SER
COOH O-
N
NH
ASP HIS SER
R N
H
O
R'
COOH O
N
NH
ASP HIS SER
HN O-
R
R'
COO- O
HN
N
ASP HIS SER
R
O
R' NH2
H2O
HYDROLYTIC CATALYSIS
17. Example of a conjugated enzyme
N
N
R
O
H
H
N
R'
O
Zn+2
OH
cofactor needed for reaction
PRODUCTS + ENZYME
Zinc protease such
as ACE
18. Cofactors
• all water-soluble vitamins with the exception of
vitamin C are converted/activated to cofactors
• only vitamin K of the fat-soluble vitamins is
converted to a cofactor
• not all vitamins are cofactors; i.e., lipoic acid is
not a vitamin
• cofactors may also act as carriers of specific
functional groups such as methyl groups and
acyl groups
20. Pantothenic acid (vitamin B5)
CH2HO C
CH3
CH3
CH
OH
C N
O
CH2
H
CH2 COOH
First recognized in 1933 as a growth factor for yeast (Roger
J. Williams)
21. Pantothenic acid
• a yellow viscous oil (free acid)
• stable to moist heat (not to dry heat) and
to oxidizing and reducing agents
• hydrolyzed in acid or alkaline medium
• sources (numerous): liver, kidney, eggs,
lean beef, milk, molasses, cabbage,
cauliflower, broccoli, peanuts, sweet
potatoes, kale (derive its name from
everywhere)
22. Pantothenic acid
• serves in its activated form as the cofactor for
coenzyme A (CoA) and the acyl carrier protein (ACP)
• first phosphorylated by ATP to 4’-
phosphopantothenate
• next is the formation of 4’-phosphopantetheine by
addition of cysteine and decarboxylation
• adenylation by ATP forms dephospho-CoA
• phosphorylation to the 3’-OH of the ribose generates
CoA (coenzyme A)
24. Coenzyme A
• performs a vital role by transporting acetyl
groups from one substrate to another
• the key to this action is the reactive thioester
bond in the acetyl form of CoA
• the thioester bond is stable enough that it can
survive inside the cell, but unstable enough that
acetyl-CoA can readily transfer the acetyl
group to another molecule
25. N
CH3
H3C
H3C
OH
N
CH3
H3C
H3C
O CH3
O
acetyl CoA CoA acetylcholinecholine
Example of an acetylation reaction
Acetylcholine is an important neurotransmitter in
the autonomic nervous system (cholinergic) and in the brain
26. Pantothenic acid
• Deficiency:
– rats
• graying of hair/fur in black rats
• dermatitis
• inflammation of nasal mucosa
• hemorrhage of adrenal cortex
– humans
• has not been encountered or extremely rare
• difficult to induce with either synthetic diets
and/or with antagonists (omega-
methylpantothenic acid
27. Pantothenic acid
• vague symptoms in human deficiency:
• numbness and tingling in feet “burning foot”
• fatigue
• GIT disturbances
• available pharmaceutically as calcium
pantothenate (d-isomer) and as racemic
mixture
• 5 - 7 mg/day appear to prevent signs of
deficiency
• appears to be non-toxic (up to 10-20 gm have
been tolerated)
29. Thiamine
• has the odor and flavor of yeast
• slowly destroyed by moist heat; more
rapidly destroyed in a basic medium than
in an acid one
• source: whole cereals and grains; yeast;
organ meat
• pharmaceutical products use the
hydrochloride or mononitrate salts
30. Thiamine
• active form is thiamine pyrophosphate (formed
by the action of thiamine
diphosphotransferase)
• involved in the oxidative decarboxylation of
pyruvic acid and α-ketoglutaric acid
• involved in the transketolase reactions of the
triose phosphate pathway
• also required for nerve function (unrelated to
coenzyme activity)
33. Reactions in which thiamine
pyrophosphate is a cofactor
• Pyruvate decarboxylase
• Alcohol fermentation – pyruvate to acetaldehyde
• Pyruvate dehydrogenase
• Synthesis of acetyl-CoA
• Alpha-ketoglutarate dehydrogenase
• Citric acid cycle
• Transketolase reaction
• Carbon-fixation reactions of photosynthesis
• Acetolactase synthetase
• Valine, leucine biosynthesis
34. Thiamine pyrophosphate
• the key portion of this cofactor is the
thiazolium ring with its acidic hydrogen
• the hydrogen is removed by the enzyme
forming an ylid (anion next to cation)
• the anion can then react with carbonyl groups
in such molecules as pyruvate
• the pyrophosphate functionality acts as a
chemical handle which holds the cofactor in
place within the enzyme
35. N
N
NH2
N
S
C
H3C
H
H2C
H2
C O P
H3C
O
O
O-
P O-
O
O-
thiazolium ring
thiamine pyrophosphate
N
N
NH2
N
S
C
H3C
C
H2C
H2
C O P
H3C
O
O
O-
P O-
O
O-
OH
H3C
H
Hydroxyethyl thiamine pyrophosphate
37. C
CH2OH
C
O
HO H
CH OH
CH2-OPO3H2
C
CH OH
CH OH
CH2-OPO3H2
C
OH
OHH
D-xylulose-5-phosphate D-ribose-5-phosphate
C
C OH
CH OH
CH2-OPO3H2
H OH
C
H
HHO
C
CH2OH
O
C
C OHH
OH
CH2-OPO3H2
+
septulose-7-phosphate
3-phosphoglyceraldehy
transketolase
TPP
Transketolase reaction
38. Transketolase reaction
C
CH2OH
C
O
HO H
CH OH
CH2-OPO3H2
D-xylulose-5-phosphate D-erythrose-4-phosphate
C
C OHH
OH
CH2-OPO3H2
+
3-phosphoglyceraldehyde
transketolase
TPP
C
CH OH
C
OH
OHH
CH2-OPO3H2
CH OH
C HHO
C
CH2OH
O
CH OH
CH2-OPO3H2
D-fructose-6-phosphate
These reactions provide a link between the pentose phosphate pathway and
glycolysis
Activity of erythrocyte transketolase is commonly used as an index of
thiamine deficiency
40. Thiamine deficiency (severe)
• beri-beri (once associated with white
polished rice diets and with highly milled
wheat diets)
• 2 clinical types
• dry beri beri or neuritic beriberi
– associated with polyneuropathy (depressed peripheral
nerve function, sensory disturbance, loss of reflexes
and motor control and muscle wasting
• wet beri beri or cardiovacular beriberi
– edema, congestive heart failure
41. N
N
N
S
OH
H3C H3C
CH2-CH2-OH
OXYTHIAMINE
NH2
H3C
N
H3C
CH2-CH2-OH
NEOPYRITHIAMINE
These 2 compounds are potent antithiamine agents which may
be used to induce symptoms of vitamin B1 deficiency in selected
animals. Oxythiamine competitively inhibits thiamine pyrophosphate
and becomes active after phosphorylation; neopyrithiamine
prevents the conversion of thiamine to thiamine pyrophosphate
42. Other clinical applications
• Alcohol neuritis (peripheral neuropathy)
• Sharp burning pain in the feet
• Deep muscle tenderness with numbness
• Coarse tremors, foot drop
• Wernicke’s encephalopathy
• Results from degeneration of basal ganglia due to
chronic/heavy use of alcohol
• Rigidity of extremities
• Complete or partial ophthalmoplegia
• Sleep disturbances
• Nausea and vomiting
43. Other clinical applications
• Korsakoff’s syndrome or psychosis
• Also a complication of chronic/heavy use of alcohol
• Usually follows DT’s (delirium tremens)
• Memory loss
• Delusions
• Disorientation
• Ocular palsies
• Combined Wenicke-Korsakoff syndrome
• Pregnancy neuritis
• Certain gastrointestinal disorders
44. Requirement for thiamine
• Based on energy needs
– 0.3 – 0.6 mg/1000 calories
– Increased requirements:
• Pregnancy and lactation
• Eating large amounts of raw sea food (clams) –
contain thiaminase
• Stress situations (high level of exercise, fever,
hyperthyroidism)
• Drinking large quantities of tea (contains
antagonist)
45. Thiamine assay
• biologic assay – in animals – time consuming
and costly (curative or protective)
• microbiologic using bacteria which require
thiamine for growth
• chemical/fluorescent assay – conversion of
thiamine to thiochrome by alkaline ferricyanide
N
N
N
N SH3C
CH 2-CH 2-OH
CH 3
THIOCHROME
46. Lipoic acid
• lipoic acid is a co-factor found in pyruvate
dehydrogenase and α-ketoglutarate
dehydrogenase, two multienzymes involved in
α-keto acid oxidation
• lipoic acid functions to couple acyl group
transfer and electron transfer during oxidation
and decarboxylation of α-ketoacids
• no evidence exists of a dietary lipoic acid
requirement in humans; therefore it is not
considered a vitamin
47. S S
H2C
C
H2
CH
COOH
SH HS
H2C
C
H2
CH
COOH
S S
H2C
C
H2
CH
C
N
O
H
CH
NH
C O
lipoic acid, oxidized form lipoic acid, reduced form
lipoamide complex (lipoyl-lysine conjugate)
Lipoic acid exists in 2 forms: a closed-ring disulfide form and
an open-chain reduced form; oxidation-reduction cycles interconvert
these 2 species; lipoic acid exists covalently attached in an amide
linkage with lysine residues on enzymes
48. Riboflavin
• vitamin B2, lactoflavin (ovo, hepato, verdo),
vitamin G
• a heterocyclic flavin linked to ribose analogous
to the nucleosides in RNA
• orange-yellow fluorescent compound
• found in significant quantities in green leafy
vegetables, milk and meats
• heat stable, but easily destroyed by light
• recommended intake is related to energy intake
(kcal) – RDA 1 – 2 mg/day
50. N
N
N
NH3C
H3C
CH3
O
H
O
LUMIFLAVIN
(produced by photochemical cleavage
of riboflavin under alkaline conditions)
N
NH3C
H3C
CH3
O
COOH
+ UREA
NHCH3
NH2H3C
H3C
OH-
OH-
NH
N OO
O
O
H
alloxan
4-amino-1,2-dimethyl
5-methylaminobenzene
Decomposition of riboflavin
51. Riboflavin
• 2 cofactors are involved:
– riboflavin phosphate (flavin mononucleotide,
FMN)
– flavin adenine dinucleotide (FAD)
• involved in the metabolism of
carbohydrates, fats and proteins (flavin
dehydrogenases/flavoproteins)
• hydrogen carriers in the respiratory
chain
52. N
N
N
N O
O
H
H3C
H3C
H2C C C C C O
H
OH
H
OH
H
OH H
H
P O
OH
O
P O
O
OH
CH2
O
N
N
N
N
NH2
OH OH
H H
HH
FLAVINE ADENINE DINUCLEOTIDE
59. Amino acid oxidases
C
R
NH3+H
CO2-
H2O NH3
FMN FMNH2
R
C O
CO2-
most amino acids (except serine, threonine, basic, and dicarboxylic acids)
can be deaminated by L-amino acid oxidases
60. Xanthine oxidase
N
N N
N
OH
H
N
N N
N
OH
H
HO
N
N N
N
OH
H
HO
OH
hypoxanthine xanthine uric acid
xanthine oxidase
Xanthine oxidase is a flavoprotein which also contains Fe and Mo
61. Fatty acyl-CoA desaturase
H H
R
H
SCoA
O
R
H
SCoA
O
H
FAD FADH2
fatty acyl-CoA desaturase
Important step in the biosynthesis of unsaturated fats; this
reaction is actually more complex than shown here and
involves other cofactors, but FAD is a key cofactor for the
enzyme
62. Riboflavin deficiency
• seldom seen in industrialized societies
• deficiency when seen:
• cheilosis (vertical fissure in the lips)
• angular stomatitis (craks in the corner of the mouth)
• glossitis
• photophobia
• seborrheic dermatitis
• normochromic normocytic anemia
• usually encountered along with pellagra (niacin deficiency)
• newborns treated for hyperbilirubinemia by phototherapy
(riboflavin is unstable to light)
64. Biotin
• an imidazole sulfur containing compound
• sometimes referred to as vitamin B7 or vitamin H
• widely distributed in foods (liver, kidney, milk,
molasses)
• a large portion of the daily need of biotin is met by
synthesis by intestinal bacteria
• deficiency is usually the result of a defect in
utilization rather than simple dietary deficiency
65. Biotin
• like lipoic acid, biotin is converted to its
coenzyme form (called biotinyllysine or
biocytin) by formation of a covalent
amide bond to the nitrogen of a lysine
residue
• like lipoic acid it performs a highly
specialized function : adds a carboxyl
group to substrates
66. Biotin
• biochemical role: carbon dioxide
fixation
• two step process:
1. Binding of CO2 to biotin – N-carboxybiotin
2. Transfer of CO2 to a substrate
– Activation of biotin requires enzyme,
CO2, ATP and Mg++
67. Biotin
Biotin-dependent enzymes:
• Pyruvate carboxylase (synthesis of oxaloacetate
for gluconeogenesis and replenishment of the
citric acid cycle)
• Acetyl CoA carboxylase (fatty acid biosynthesis)
• Propionyl-CoA carboxylase
β-methylcrotonyl-CoA carboxylase
• holocarboxylase synthase (multiple carboxylase)
68. Reactions involving biotin enzymes
CH3C
O
CO2- CCH2
O
CO2--O2C
pyruvate oxaloacetate
CH3C
O
SCoA CCH2
O
SCoA-O2C
acetyl CoA malonyl CoA
CCH2
O
SCoAH3C
propionyl CoA
CCH
O
CO2--O2C
CH3
methylmalonyl CoA
HCO3
- + NH4
+ + ATP CH2N
O
O P OH
OH
O
carbamyl phosphate
69. Biotin
• deficiency:
• quite uncommon
• can be induced by feeding raw egg white (avidin)
• avidin is a protein which binds tighly with biotin (MW
70,000)
• symptoms are: anorexia, nausea, muscle pain, fine scaly
desquamation of the skin
• requirements: 150 – 200 mcg/day
• therapeutic use: in babies with infantile
seborrhea (cradle cap) and Leiner’s disease
72. Pyridoxine
• vitamin B6, rat “acrodynia factor”,
antidermatitis factor
• widespread occurrence
• pyridoxine: mostly in vegetable products
• pyridoxal and pyridoxamine: mostly in animal
products
• pyridoxine is stable in acid solution, but
unstable in neutral or alkaline solutions
(destroyed by light)
74. Pyridoxal phosphate
• pyridoxine is converted to pyridoxal phophate
by phosphorylation and oxidation to the
aldehyde
• pyridoxal phosphate is then attached to the
holoenzyme via a covalent bond to a lysine
residue (a Schiff’s base)
• the Schiff’s base bond is readily broken and
reformed
• this reversibility is very important in the
biochemical action of this cofactor
82. Pyridoxine
• deficiency:
– difficult to produce in humans
– may be accomplished artificially with a
pyridoxine antagonist (deoxypyridoxine)
– symptoms include: nausea and vomiting,
seborrheic dermatitis, depression and
confusion, mucous membrane lesions,
peripheral neuritis, anemia
83. Pyridoxine antagonists
N
N
NH-NH 2
Hydralazine (antihypertensive)
N
C
O NH
NH2
isoniazid (antitubercular)
O
N
OH2N
H
cycloserine (antitubercular)
CC
CH3 H
COOHHS
CH3 NH2
penicillamine (antirheumatic; Wilson's disease)
84. Pyridoxine can antagonize the antiparkinsonian use of
L-DOPA
L-DOPA L-DOPA L-dopamine
L-dopamine
CO 2
Brain
B 6 stimulates
this reaction outside
of the brain
use carbidopa: an inhibitor of DOPA decarboxylase
in combination with DOPA: Sinemet 10/100 or Sinemet 25/250
85. Pyridoxine deficiency
• can be monitored by measuring the level of
xanthurenic acid in the urine
• this is related to a decrease in kynureninase
activity (pyridoxal phosphate is the coenzyme)
• kynurenine, a breakdown product of
tryptophan is normally converted to kynurenic
acid – but in B6 deficiency it is shunted to form
xanthurenic acid
87. Pyridoxine
• requirements:
• children: 0.5 – 1.2 mg
• adults: 2.0 mg
• pregnancy: 2.5 mg
– Requirement for B6 is proportional to the level of
protein consumption
• therapeutic uses:
• deficiency
• to counterract the effects of antagonists
• certain rare forms of anemia
• in women taking oral contraceptives (estrogen shifts
tryptophan metabolism
88. N
COOH
NICOTINIC ACID
N
CONH 2
NICOTINAMIDE
Discovered in 1913 from
yeast; also known as
vitamin B3
1915 – 1920: Irving Golberg
demonstrated that lack of niacin
causes pellagra
one of the simplest
vitamin; like B6 also
a pyridine derivative
89.
90. Oxidation of nicotine yields
nicotinic acid
N
N
H
N
COOH[OXIDATION]
HNO3
nicotine nicotinic acid
This reaction does not occur in vivo – strictly a laboratory
reaction
91. Nicotinic acid
• niacin, vitamin B3, niacinamide, antipellagra
vitamin
• both form are active: the free acid and the
amide
• sources: organ meat (largest source), fish,
yeast, dried fruit, nuts, cereal grains, some
vegetables
• pellagra-inducing diets: corn meal, corn starch,
sweet potatoes, rice, syrup, pork fat (once a
common diet in southern states among
sharecroppers)
92. H
H2C
H
OH OH
H H
O
N
NH2
O
H
O P O
O
O-
P
O
O-
O CH2
HH
OH OR
H H
O
N
N
N
N
NH2
NAD - OXIDATION REACTIONS R = H
NADPH - REDUCTION REACTIONS R = PO3
Coenzyme forms
Two cofactor forms of niacin: NAD and NADP; these cofactors
are not tightly held by the enzyme and may be reused for reaction
after reaction
95. Sparing action of tryptophan
TRYPTOPHAN FORMYLKYNURENINE KYNURENINE
3-HYDROXYKYNURENINE3-HYDROXYANTHRANILIC ACID
NICOTINIC ACID
B6-dependent reaction
Tryptophan can substitute for niacin: 60 mg of tryptophan
is equivalent to 1 mg of niacin; 60 gm of protein contains 600
mg of tryptophan which then represent 10 mg of niacin
96. CH
COOH
NH 2
N
H
CH 2
CH 2
O
CH
COOH
NH 2
N
H
C O
Htryptophan
N-formylkynurenine
CH 2
O
CH
COOH
NH 2
NH 2
CH 2
O
CH
COOH
NH 2
NH 2
OH
3-hydroxykynurenine kynurenine
alanine
COOH
NH 2
OH
CO 2
N
COOH
3-hydroxyanthranilic acid
blocked by deficiency of thiamine
blocked by deficiency
of riboflavin
blocked by deficiency
of pyridoxine
98. Clinical uses of nicotinic acid
• pellagra symptoms from:
• gastric ulcer or carcinoma
• diarrhea
• isoniazid therapy
• carcinoid syndrome
• Hartnup disease (impairment of tryptophan absorption)
• peripheral vasodilator (nicotinic acid or
nicotinyl alcohol)
• hypolipidemic agent (only nicotinic acid in
large doses – lowers both triglycerides and
cholesterol (Niaspan, Nicobid)
99. Carcinoid syndrome
• a slow growing neoplasm of enterochromaffin cells
(ileum, stomach, bronchus)
• tryptophan metabolism is altered resulting in excess
serotonin synthesis
• symptoms include:
• facial flushing
• edema of head and neck
• abdomina cramps and diarrhea
• asthmatic symptoms
• cardiac insufficiency
• urinary 5-HIAA (5-hydroxyindole acetic acid) is high (5-
HIAA is a metabolite of serotonin; serotonin is derived
from tryptophan)
100. Cautions concerning the use of
nicotinic acid in large doses
• as an acid, it can erode gastrointestinal mucosa
leading to ulceration
• it also causes a depletion of glycogen stores and
fat reserves in skeletal and cardiac muscle
• additionally, there is an elevation in blood
glucose and uric acid production
• for these reasons, nicotinic therapy is not
recommended for diabetics or persons who
suffer from gout
101. Ascorbic acid
• vitamin C; anti-scorbutic vitamin (scurvy)
• structure is reminiscent of glucose
• produced in plants from glucose via the uronic
pathway
• the enzyme gulonolactone oxidase converts
gulonolactone to ascorbic acid
• exists in the enolic and ketonic forms
• sources: citrus fruits, tomatoes, green peppers,
strawberries, cantaloupe, cabbage, turnips,
peas, lettuce and aspargus
103. Ascorbic acid
• Biochemical functions:
– Production and maintenance of collagen
• Proline --------hydroxyproline
• Lysine -------- hydroxylysine
– Mitochondrial electron-transport chain (cytochrome
C)
– Metabolism of tyrosine
• Tyrosine ----- p-hydroxyphenylpyruvic acid---- 2,5-
dihydroxyphenylacetic acid (homogentisic acid)
104. Proline hydoxylase: (collagen formation)
Dopamine-beta hydroxylase ( neurotransmitter formation)
N
O
N
O
HO
vitamin C; O2
proline hydroxylase
NH2HO
HO
NH2HO
HO
OH
dopamine norepinephrine
dopamine beta
hydroxylase
O2; Vitamin C
105. O
OHO
OH
OHHO
O
OHO
OH
OO
O
Anti-oxidant properties of vitamin C:
helps prevent damage to cellular proteins and DNA
Normal metabolic processes in the cell lead to the generation
of reactive oxidizing agents such as superoxide
Superoxide can react with and damage protein and DNA, leading
to cellular changes that can lead to premature aging and cancer
Vitamin C reacts with superoxide, thus preventing this damage
106. Ascorbic acid
– conversion of folic acid to THFA
– hydroxylation reactions of cholesterol to cholic acid
– hydroxylation of tryptophan to 5-
hydroxytryptophan
– regulation of cholesterol biosynthesis in the adrenal
gland
– aids in the absorption and utilization of iron
– antioxidant properties may inhibit formation of
nitrosamines during digestion of protein
107. Ascorbic acid
• defiency: scurvy
– hemorrhage from mucous membranes,
mouth and GIT, skin and muscles
– gingivitis: swelling, tenderness, redness and
ulceration of gums
– loosening or loss of teeth
– swelling of joints
– rarefaction of bones and dentine
112. Vitamin B12
• synthesized by bacteria only
• red in color, levorotatory and stable to heat
• commercially available either as cyano or
hydroxocobalamin
• stored in the liver as the coenzyme
• absorbed only in the presence of the intrinsic
factor (a glycoprotein released by parietal cells)
• transported to tissues via transcobalamin II
• present in foods such as liver, fish, eggs, milk
• absent in vegetables and fruits
113. Vitamin B12
• by far the most complex vitamin in structure
• made up of a planar corrin ring (4 pyrroles)
• the only vitamin that possesses a metal ion
(cobalt) as part of its structure
• the major cofactor form of B12 is
adenosylcobalamin or 5’-
deoxyadenosylcobalamin
• small amounts of methylcobalamin also occur
(intermediate in methyl transfer reactions)
114. Vitamin B12
• the corrin ring is similar to the porphyrin ring
system found in hemoglobin except that in
corrin 2 of the pyrroles are linked directly
(without methylene bridges)
• the cobalt is coordinated to the 4 pyrrole
nitrogens
• one of the axial cobalt ligands is a nitrogen of
the dimethylbenzimidazole group
• the other axial ligand may be CN, OH, CH3 or
the 5’-carbon of a 5’-deoxyadenosyl group
115. N N
NN
CH 3
CH 3
H2NCOCH 2CH 2
H3C
H2NCOCH 2
CH 2CONH 2
H2NCOCH 2
CH 3
H2C
CH 2CH 2CONH 2
CH 3
CH 3
CH 2
NH
O
CH 2CONH 2
O
H3C
P
O
O
O
OH
HO
N
N
CH 3
CH 3
Co
CN
CH 3
H3C
H
VITAMIN B 12
corin nucleus
benzylimidazole
cobalt coordinated
116.
117. Vitamin B12
• biochemical functions (mediated by
coenzymes)
• mutase reaction (rearrangement reaction
– methylmalonyl CoA to succinyl CoA (lipid metabolism)
• methylation reactions
– uracil to thymine
– homocysteine to methionine
– aminoethanol to choline
• activation of amino acids for protein synthesis
• ribonucleotides to deoxyribonucleotides for DNA
synthesis in certain bacteria
118. Causes of B12 deficiency
• Pernicious anemia (autoimmune gastritis
against parietal cells - loss of intrinsic factor)
• rarely due dietary deficiency
• N2O/oral contaceptive drugs
• intestinal parasite
• gastrectomy
• chronic gastritis
• Schilling test
119. Diagnosis of B12 deficiency
• Schilling test
• distinguishes deficiency caused by pernicious
anemia with that caused by malabsorption
• compares absorption in radiolabeled B12 with
intrinsic factor and radiolabeled B12 without
intrinsic factor
• in pernicious anemia the B12 with intrinsic factor
will be absorbed while the B12 by itself will not
• in malabsorption neither will be absorbed
120. Manifestation of B12 deficiency
• macrocytic megaloblastic anemia
• megaloblasts are abnormal erythroid precursors in
bone marrow (most cells die in the bone marrow)
• reticulocyte index is low
• hyperchromic macrocytes appear in blood
• anemia reflects impaired DNA synthesis
• other cells may be involved (leukopenia,
thrombocytopenia
• spinal cord degeneration (irreversible)
• swelling, demyelination, cell death
• neurological disease
• results from deficient methylmalonyl-CoA mutase
• this cannot be treated with folic acid!!
121. Treatment of B12 deficiency
• use IM cyanocobalamin or hydroxocobalamin
• administer daily for 2 - 3 weeks, then every 2 -
4 weeks for life
• monitor reticulocytosis early to assure
treatment is working (reticulocyte count should
go up)
• monitor potassium levels to ensure
hypokalemia does not occur due to excessive
RBC synthesis
122.
123. Folic acid
• MOA
• deficiency
• use
• drug interactions with folic acid
124. N
N N
N
N
H
C
N
CH
H
OH
H2N
O COOH
COOH
FOLIC ACID
Chemically composed of pteroic acid (pteridine and PABA)
and glutamic acid
Also known as folacin, vitamin M and pteroylglutamic acid
Widely distributed in leaves (foliage) of plants
125. FOLIC ACID
• absorbed by both active and passive transport
• on the average we absorb 50 -200ug per day
(about 10 -25% of dietary intake)
• storage is in the form of 5-methyl THF (5 -20
mg)
• found in green vegetable, dietary yeasts, liver,
kidney
• bacteria synthesize their own folic acid
(dihydropteroate synthetase)
126. Folic acid
• Biochemical functions
– one carbon fragment transfer (formyl,
methyl, hydroxymethyl)
• conversion of homocysteine to methionine
• conversion of serine to glycine
• synthesis of thymidylic acid
• synthesis of purines (de novo)
• histdine metabolism
• synthesis of glycine
133. METHOTREXATE
– also known as amethopterin or MTX
– a potent inhibitor of dihydrofolate reductase which
catalyzes the conversion of folic acid to tetrahydrofolic
acid (THFA)
– THFA acts as an acceptor of a one-carbon unit from
either formate or formaldehyde
– 5-formyl THFA is also known as folinic acid or the
citrovorum factor (leucovorin)
– THFA one-carbon carriers are important in the synthesis
of purines, thymine, choline, and other important cellular
constituents
– MTX is used in treating acute lymphocytic leukemia in
children, choriocarcinoma, osteogenic sarcoma,
carcinomas of the head, neck, bladder and testis
– in lower doses: treatment of psoriasis and rheumatoid
arthritis
134. – diaminopyrimidines inhibitors of dihydrofolate reductase
– have activity in both bacterial and protozoal organisms
– more effective if used in combination with another drug
– pyrimethamine is more selective for protozoal enzyme than
trimethoprim
– used in treatment of malaria and PCP
N
N
NH 2
CH 2CH 3
H2N Cl
PYRIMETHAMINE
N
N
CH 2
OCH 3
OCH 3
OCH 3
H2N
NH 2
TRIMETHOPRIM
(DARAPRIM)
136. Fat soluble vitamins
• Vitamins A, D, K and E are the fat-
soluble vitamins
• excessive use of vitamins A and K can
lead to toxicities
• fat soluble vitamin tend to be stored in
fatty tissues of the body and in the liver
137. Vitamin A
• Exits in 3 forms:
• all trans-retinol
• long chain fatty acyl ester of retinol (main
storage form)
• retinal (the active form in the retina)
• retinoic acid is also considered to be
physiologically active
• provitamin A or carotene can be
converted to retinol in vivo
138. Vitamin A
• recommended intakes are expressed in
retinol equivalents (RE)
1 RE = 1 mcg of retinol
= 6 mcg of β-carorene
= 12 mcg other carotenes
• older usage expressed activity in USP
units or International units (IU). These
were based on biological activity in the
vitamin a-deficient rat (1 IU = 0.3 mcg of
retinol)
142. Vision and the role of vitamin A
• photoreception is the function of 2
specialized cell types: rods and cones
• both types of cells contain a
photosensitive compound called opsin
– in rod cells opsin is called scotopsin and the
receptor is called rhodopsin or visual purple
– rhodopsin is a serpentine receptor imbedded
in the membrane of the rod cell; it is a
complex between scotopsin and 11-cis retinal
143. Vision and the role of vitamin A
• intracellularly, rhodopsin is coupled to a G-
protein called transducin
• when rhodopsin is exposed to light, it is
bleached releasing the 11-cis-retinal from opsin
• absorption of photons by 11-cis-retinal triggers
the conversion to all-trans-retinal (one
important conformational intermediate is
metarhodopsin II); also there is a change in
conformation of the photoreceptor
144. Vision and the role of vitamin A
• these transformations activate a
phosphodiesterase (which hydrolyzes c-GMP to
GMP)
• c-GMP is necessary to maintain the Na+
channels in the rods in the open conformation
• with a decrease in c-GMP, there occurs a
closure of the Na+ channels, which leads to
hyperpolarization of the rod cells with
concomittant propagation of nerve impulses to
the brain
145.
146. H3C CH3
CH3
CH3
H3C
N
H
N
N
O
H
H
11-cis
Schiff's base
lysine chain of opsin
CH3H3C
H3C
CH3
N
CH3
N
NO
H
H
H
1. light
2. isomerization of retinal
3. change in shape of rhodopsin
11-trans retinal
signal transduction nerve impulse
RHODOPSIN
(11-cis retinal + opsin)
147. Additional role of retinol
• retinol also functions in the synthesis of
certain glycoproteins and
mucopolysaccharides necessary for
mucous production and normal growth
regulation
• this is accomplished by phosphorylation
of retinol to retinyl phosphate which then
functions similarly to dolichol phosphate
148. CH3
CH3H3C
CH3
COOH
CH3
RETINOIC ACID (RETIN A)
Retinoic acid (Retin-A) is important for cellular differentiation;
It controls cellular growth – particularly cell growth
Used in the treatment of acne; also used as an anti-wrinkle agent
(Retin A, Retin A micro, Avita, Renova)
Also used orally to treat acute promyelocytic leukemia (APL)
Product used is Vesanoid (10 mg capsules)
150. CH3O CH3
H3C
CH3 CH3 CH3
COOH
ACITRETIN (SORIATANE)
An aromatic analog of retinoic acid; orally effective and
used in the management and treatment of psoriasis
151. Etretinate (Tegison)
CH3
H3C
CH3O CH3
CH3 CH3
O
OC2H5
Esterified form of acitretin; also used orally in the
treatment of recalcitrant psoriasis; 10 and 25 mg capsules
154. Bexarotene (Targretin)
• indicated for the treatment of cutaneous
manifestations of cutaneous T-cell
lymphoma
• usually the patients receiving this drug
have failed to respond to other treatment
protocols
• pregnancy (Category X drug)
156. Tazarotene (Tazorac)
N C C
S
H3C CH3
EtO2C
Topical treatment of patient with facial acne vulgaris of
mild to moderate severity; gel 0.05%, 0.1%
157. Vitamin A toxicity
• vitamin A is higly toxic when taken in
large amounts either acutely or
chronically
• may occur with 200 mg (666,000 IU) in
adults or half this amount in children
• signs include headache, nausea and
vomiting, increased cerebrospinal fluid
pressure, blurred vision and bulging of
the fontanelle in infants
158. Chemical name Abbreviation Generic name
Vitamin D2 D2 ergocalciferol
Vitamin D3 D3 Cholecalciferol
25-
hydroxyvitamin
D3
25(OH)D3 calciferol
1,25-dihydroxy
vitamin D3
1,25-(OH)3 Calcitriol
24,25-dihydroxy
vitamin D3
24,25(OH)2D3 Secalcifediol
159. Vitamin D
• There are 2 major precursor forms:
• 7-dehydrocholesterol
• ergosterol
• UV irradiation affords cholecalciferol (vitamin
D3) and ergocalciferol (vitamin D2)
• Discovery:
• 1890 – sunlight prevents rickets
• 1924 – Steanbock and Hess found that irradiating certain
foods produced vitamin D2
• 1970 – hormonally active form of vitamin D discovered
160. Vitamin D
• RDA – 20 μg (required in minute amounts)
• disease of deficiency: rickets
• Malformation of bones – due to improper bone
mineralization
• Hypervitaminosis
• Toxic dose only 10X higher than the RDA
• Causes hypercalcemia – can lead to cardiac arrest
• vitamin D is not a vitamin (or a cofactor) – it is
a steroid hormone
164. Biological functions
• Calcium homeostasis – it is critical for the body
to maintain the proper calcium level in the
blood stream
– Intestinal calcium absorption: acts as a signal to tell
intestinal cells to take up more calcium from the gut
– Bone calcium mobilization
• Signals osteoclast (bone cells) to release calcium into the
blood stream in response to low calcium levels
165. Biological functions
• Cellular differentiation – much less well understood –
signal to bone marrow cells to change into other cells
leukemia cell
1α,25(OH)2 vitamin D3
normal white blood cell
derived from bone marrow grows at the proper rate
high levels
Problem: 1α,25(OH)2-D3 causes hypercalcemia
166. Various analogs of vitamin D
OH
HO
synthetic analog of vitamin D
Potential use:
-anti-cancer agent
-immunosuppressive
169. Doxercalciferol (Hectorol)
• a synthetic vitamin D analog that undergoes in
vivo metabolic activation to 1-α,25-
dihydroxyvitamin D2
• Activation does not require involvement of the
kidneys
• Used in hyperparathyroidism in patients
undergoing chronic renal dialysis
• Initial dose 10 mcg orally 3 times per week
173. Calcipotriol (Dovonex)
H3C
CH2
HO OH
OH
a vitamin D derivative approved
for the treatment of psoriasis.
Mechanism of action is unknown.
Receptor affinity is similar to that
of calcitriol, but is less than 1% as
active in regulating calcium
metabolism
174. Calcipotriene
• An analog of vitamin D3 with a modified
side-chain containing a 24-OH group and
a cyclopropyl group
• binds strongly to the D3 receptor on
keratinocytes in skin and it suppresses
their proliferation (used in psoriasis)
• has only about 0.5% of the activity of D3
on calcium and phosphorus metabolism
176. Vitamin K
• the koagulation vitamin
• exists in 2 forms:
– plant origin: phylloquinone or vit K1
– bacterial origin: menaquinones or vit K2
• also certain synthetic quinones have
vitamin K activity
– menadione (vitamin K3)
– menadiol sodium phosphate (vitamin K4)
182. Vitamin E
• alpha (E1), beta (E2) and gamma(E3)
tocopherol
• sources: plant oils (corn, peanut, wheat
germ), green leafy vegetables, meat, eggs
• value resides in the antioxidant
properties of vitamin E (may prevent the
formation of peroxides)
184. Vitamin E
• Estimated requirements: 5 mg/day + 0.6
mg/day of unstaurated fat
• Biological function – antioxidant for fatty
acids
– Acts like vitamin C; prevents lipid
peroxidation and/or damage to cells by lipid
hydroperoxides
185. Uses for vitamin E
• hemolytic anemia in premature infants,
unresponsive to B12, Fe and folic acid
• macrocytic megaloblastic anemia seen in
children with severe protein-calorie
malnutrition
186. Other coenzymes
O
O
CH3
CH2CH3O
CH3O
CH C
CH3
CH2 H
10
Coenzyme Q (Ubiquinone)
N
N
N
NH2N
H
H OH
CHH CH
OH
CH3
OH
Tetrahydrobiopterin
Serves as entry into the electron-
transport chain
Involved in the conversion of
phenylalanine to tyrosine
