Download MBBS (Bachelor of Medicine and Bachelor of Surgery) Latest Vitamin C Lecture PPT
INTRODUCTION
? Vitamin C is a water soluble vitamin
? Chemical name Ascorbic acid
? Also known as antiscorbutic factor
? Deficiency of vitamin C leads to scurvy (not
known at that time) was discovered during famous
voyage of Vasco da Gama in 1498
? Antiscorbutic factor was isolated in 1930 and
named as hexauronic acid by Albert Szent Gyorgi
((Nobel prize- 1937)
? In 1933, Howarth established the structure and
named it as Ascorbic acid(Nobel prize ? 1937)
CHEMISTRY
? Ascorbic acid is a hexose derivative & closely
resembles monosaccharide's in structure .
? It is formed as an oxidation product of L- gulunolactone
? Vitamin C exists in two forms:
L ? ascorbic acid (reduces form)
L ? Dehydro ascorbic acid (oxidized form)
? Most animals and plants can synthesize ascorbic acid
from glucose.
? Man, higher primates, guinea pigs and bats are the only
species which cannot synthesize ascorbic acid (block in
gulono lactone oxidase step)
Glucose
gulono lactone
oxidase
Ascorbic acid
Gulono lactone
PROPERTIES
? Vitamin C is heat labile
? In the process of cooking about 50% of vitamin
passes to water & 20% is oxidized
? Only L isomers of ascorbic acid and dehydroascorbic
acid have antiscorbutic activity.
? D-ascorbic acid has no activity.
? Ascorbic acid is a strong reducing agent.
? The strong reducing property of vitamin C depends
on the double bonded (enediol) carbons.
? L-ascorbic acid is the dominant form present in
plasma and tissues.
METABOLIC ROLE
? Ascorbic acid and Dehydroascorbic acid form
a very good redox system.
? Ascorbic acid has specific roles in the copper-
containing
hydroxylases
and
the
-
ketoglutarate-linked
iron-containing
hydroxylases
? It has a number of nonenzymic effects as a
result of its action as a reducing agent and
oxygen radical quencher
1. Hydroxylation of Proline and Lysine
? Ascorbic acid is necessary for the post-translational
hydroxylation of proline and lysine residues in proteins such
as collagen.
? Hydroxyproline and hydroxylysine are essential for the
formation of cross links in the collagen, which gives the
tensile strength to the fibers.
? This process is absolutely necessary for the normal
production of supporting tissues such as osteoid, collagen
and intercellular cement substance of capillaries.
? Ascorbic acid & ferrous iron are cofactors
? Ascorbic acid is essential to keep the iron in ferrous form
Hydroxylation of Proline
? Proline
hydroxylase
catalyzes
the
hydroxylation of proline
on collagen.
? Ascorbic acid & ferrous
iron are cofactors .
CO2
? Ascorbic acid is essential
to keep the iron in ferrous
form.
? It essential for maturation
&cross-linking
of
collagen.
Hydroxylation of lysine
? Hydroxylation occurs after
the peptide chain synthesis
(posttranslational
modifications)
? Lysine
hydroxylase
catalyzes
the
hydroxylation of lysine
residues
present
on
collagen.
? It helps in formation of
osteocalcin and the C1q
component of complement
2. Absorption of iron
? Ascorbic acid enhances the iron absorbtion
from the intestine
? Ascorbic acid reduces ferric iron to ferrous
state, which is preferentially absorbed.
3. Tryptophan Metabolism
? Ascorbic acid is necessary for the hydroxy
lation of tryptophan to 5-hydroxy tryptophan.
? This is required for the formation of serotonin
4. Tyrosine Metabolism
? Vitamin C helps in the
oxidation
of
parahydroxyphenyl
Ascorbic acid (Cu ++)
pyruvate
to
homogentisic acid
Ascorbic acid (Cu ++)
? It also helps in the
oxidation
of
homogentisic acid
5. Synthesis of Bile acids
? In the biosynthesis of
.
bile acids Cholesterol 7
?hydroxylase,
catalyzes the formation
of
7
?
hydroxycholesterol from
cholesterol.
? In this vitamin C is a
cofactor
? It is a rate limiting step
in bile acid synthesis
6. Synthesis of Norepinephrine
? Dopamine conversion
into norepinephrine
requires vitamin C as
TYROSINE
HYDROXYLASE
DOPA
the Co enzyme.
? This is essential for
synthesis
of
catecholamines
? Adrenal medulla is
Vitamin C
rich in vitamin C
NOR EPINEPHRINE
DOPAMINE
HYDROXYLASE
7. Synthesis and release of adreno
-cortical steroid hormone
? Adrenal gland possesses high levels of ascorbic
acid
? Ascorbic acid is necessary for hydroxylation
reactions in the synthesis of corticosteroid
hormones.
8. Reduction of methemoglobin
? It is useful for re-conversion of met-hemoglobin
to hemoglobin.
9. Folic Acid Metabolism
? Ascorbic acid is helping the enzyme folate
reductase to reduce folic acid to tetrahydrofolic
acid
? Thus it helps in the maturation of RBC.
DHFR
FOLIC ACID
DIHYDROFOLATE
DHFR
TETRA
HYDROFOLATE
Vit C
Vit C
9. Antioxidant property
? It
acts
as
a
hydrophilic,
chain
breaking antioxidant
like vitamin E.
? It
also
form
a
relatively
stable
radical
form,
the
semidehydroascorbate.
? This is reduced back
to ascorbic acid by
reductase
enzyme
using
reduced
glutathione.
10. Synthesis of Carnitine.
? Vitamin C needed for Trimethyllysine and -
butyrobetaine hydroxylases which are required
for the synthesis of carnitine
11. Peptide hormone synthesis
? A number of peptide hormones have a carboxy
terminal amide that is derived from a terminal
glycine residue.
? Hydroxylation of this glycine is carried out by
a copper-containing enzyme peptidyl glycine
hydroxylase, which requires vitamin C
12. Phagocytosis
? Ascorbic acid stimulates phagocytic action of
leukocytes and helps in the formation of
antibodies.
13. Sparing action of other vitamins:
? Ascorbic acid is a strong antioxidant
? It spares vitamin A, E and some B-complex
vitamins from oxidation
14. Immunological function:
? Vitamin C increases the synthesis of
immunoglobulins & increases the cell mediated
immunity.
15. Prevention of Cataract
? Vitamin C is concentrated in the lens of eye.
Regular intake of ascorbic acid reduces the risk
of cataract formation.
16. Activation of Protein C
? Vitamin C is required for postsynthetic
modification of the precursor of protein C, the
vitamin K-dependent protease that hydrolyzes
activated factor V in the blood-clotting cascade.
17.Sparing action of other vitamins
? Ascorbic acid is a strong antioxidant
? It spares vitamin A, E and some B-complex
vitamins from oxidation.
18. Preventive role of vitamin C
? Vitamin C helps in the prevention of cancer,
atherosclerosis and delays ageing process.
Metabolism
? Ascorbic acid is readily absorbed from
gastrointestinal tract.
? The vitamin is excreted in urine.
? Since vitamin C is a strong reducing agent, the
Benedict's test will be positive in the urine
sample after the vitamin administration.
? Plasma ascorbic acid level - 0.7 to 1.2 mg/dl
.
? Oxidation of ascorbic acid yields dehydro ascorbic
acid, which is oxidized further to oxalic acid through
diketo-L-gulonic acid
? Ascorbic acid is partly excreted unchanged and partly
as oxalic acid.
? Most of the oxalates in urine are derived from
ascorbic acid, and the rest from glycine metabolism.
2H H
Dehydro -
2O
Diketo L ?Gulonic
L-Ascorbic acid
Ascorbic acid
acid
Oxalic acid
Dietary Sources of Vitamin C
? Rich sources are amla (Indian gooseberry),guava ,lime,
lemon,Cabbage and green leafy vegetables.
? Germinating pulses contain large amount of vitamin C.
RDA
? Recommended daily allowance is 60 - 75 mg/day
(equal to 40-50 mL orange juice).
? During pregnancy, lactation, and in aged people
requirement may be 100 mg/day
? Smokers, chronic alcoholics and women on oral
contraceptives require up to125 mg/day.
Deficiency
CAUSES
? Scurvy is caused by a dietary deficiency of
vitamin C.
? The body's pool of vitamin C can be depleted
in 1-3 months.
.
Risk factors include the following:
? Babies who are fed only cow's milk during the first
year of life
? Alcoholism
? Cigarette smokers
? Pregnant and lactating women
? Thyrotoxicosis
? Elderly individuals who eat a tea-and-toast diet
? Economically disadvantaged persons
? Refugees
? People with disease of the small intestine
? Those on hemodialysis and peritoneal dialysis.
DEFICIENCY MANIFESTATION
DEFICIENCY MANIFESTATION
1. Scurvy
? The deficiency of ascorbic
acid results in scurvy
? It is due to impaired
collagen formation and
poor blood vessel support.
? Swollen, spongy and
Bleeding gums are the
characteristic feature
DEFICIENCY MANIFESTATION
2. Infantile Scurvy (Barlow's Disease)
? In infants between 6 to 12 months of age
(period in which weaning from breast milk)
? Infants loose appetite and weight.
? Painful tenderness of the extremities.
? Bleeding from gums and mucous membrane.
DEFICIENCY MANIFESTATION
3. Hemorrhagic Tendency
? Capillary fragility enhances hemorrhagic tendencies
resulting in bleeding under the skin even on slight
pressure.
? Small dots like patches called petehiae and relatively
large patches as ecchymoses
? Large accumulation of blood in subcutaneous tissues
is called haematoma.
? In severe cases bleeding may occur from nose
(epistaxis), eye (retinal hemorrhage), urethra
(hematuria), intestine (malena) etc.
DEFICIENCY MANIFESTATION
4. Bones
? Ground substance formed by osteoblasts is
defective. So the bones become weak and
fracture easily with slightest of trauma or even
pressure.
? Such bones are called Scorbutic bones.
? There may be bleeding into the joints leading
to hemarthrosis.
DEFICIENCY MANIFESTATION
5. Anemia
? In vitamin C deficiency, microcytic, hypochromic
anemia is seen.
? Poikilocytosis and anisocytosis are also common in
anemia due to deficiency of vitamin C.
? The reasons for anemia may be:
a. Loss of blood by hemorrhage
b. Decreased iron absorption
c. Decreased tetrahydrofolic acid
d. Accumulation of met-hemoglobin.
DEFICIENCY MANIFESTATION
6. Poor wound healing
? Vitamin C deficiency is associated with poor
wound healing.
? Because of its power to heal wounds, vitamin
C has been recommended for treatment of
ulcer, trauma, and burns.
7. Myalgia
? Myalgias may occur because of reduced
carnitine production.
Therapeutic Use of Vitamin C
? The beneficial effect of vitamin C is used in the
treatment of TB
? Clinical dose is 500 mg/day
? Vitamin C is recommended for treatment of ulcer,
trauma and burns
? There is very little good evidence that high doses of
vitamin C prevent the common cold, although they
may reduce the duration and severity of symptoms.
Toxicity of vitamin C
? Excess vitamin C is excreted, and is not accumulated
in the body
? More than 2000 mg may cause iron over load.
This post was last modified on 30 November 2021