Download MBBS Vitamin C Lecture PPT

INTRODUCTION

? Vitamin C is a water soluble vitamin
? Chemical name Ascorbic acid

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? Also known as antiscorbutic factor
? Deficiency of vitamin C leads to scurvy (not

known at that time) was discovered during famous

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voyage of Vasco da Gama in 1498

? Antiscorbutic factor was isolated in 1930 and

named as hexauronic acid by Albert Szent Gyorgi

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((Nobel prize- 1937)

? In 1933, Howarth established the structure and

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named it as Ascorbic acid(Nobel prize ? 1937)
CHEMISTRY

? Ascorbic acid is a hexose derivative & closely

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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)

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L ? Dehydro ascorbic acid (oxidized form)
? Most animals and plants can synthesize ascorbic acid

from glucose.

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? Man, higher primates, guinea pigs and bats are the only

species which cannot synthesize ascorbic acid (block in

gulono lactone oxidase step)

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Glucose

gulono lactone

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oxidase

Ascorbic acid

Gulono lactone

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PROPERTIES

? Vitamin C is heat labile
? In the process of cooking about 50% of vitamin

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passes to water & 20% is oxidized

? Only L isomers of ascorbic acid and dehydroascorbic

acid have antiscorbutic activity.

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? D-ascorbic acid has no activity.
? Ascorbic acid is a strong reducing agent.
? The strong reducing property of vitamin C depends

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on the double bonded (enediol) carbons.

? L-ascorbic acid is the dominant form present in

plasma and tissues.

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METABOLIC ROLE

? Ascorbic acid and Dehydroascorbic acid form

a very good redox system.

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? Ascorbic acid has specific roles in the copper-

containing

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hydroxylases

and

the

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-

ketoglutarate-linked

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iron-containing

hydroxylases

? It has a number of nonenzymic effects as a

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result of its action as a reducing agent and
oxygen radical quencher
1. Hydroxylation of Proline and Lysine

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? Ascorbic acid is necessary for the post-translational

hydroxylation of proline and lysine residues in proteins such
as collagen.

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? Hydroxyproline and hydroxylysine are essential for the

formation of cross links in the collagen, which gives the
tensile strength to the fibers.

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? This process is absolutely necessary for the normal

production of supporting tissues such as osteoid, collagen
and intercellular cement substance of capillaries.

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? Ascorbic acid & ferrous iron are cofactors
? Ascorbic acid is essential to keep the iron in ferrous form


Hydroxylation of Proline

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? Proline

hydroxylase

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catalyzes

the

hydroxylation of proline

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on collagen.

? Ascorbic acid & ferrous

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iron are cofactors .

CO2

? Ascorbic acid is essential

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to keep the iron in ferrous

form.

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? It essential for maturation

&cross-linking

of

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collagen.


Hydroxylation of lysine

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? Hydroxylation occurs after

the peptide chain synthesis
(posttranslational

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modifications)

? Lysine

hydroxylase

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catalyzes

the

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hydroxylation of lysine
residues

present

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on

collagen.

? It helps in formation of

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osteocalcin and the C1q
component of complement
2. Absorption of iron

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? Ascorbic acid enhances the iron absorbtion

from the intestine

? Ascorbic acid reduces ferric iron to ferrous

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state, which is preferentially absorbed.


3. Tryptophan Metabolism

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? Ascorbic acid is necessary for the hydroxy

lation of tryptophan to 5-hydroxy tryptophan.

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? This is required for the formation of serotonin


4. Tyrosine Metabolism

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? Vitamin C helps in the

oxidation

of

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parahydroxyphenyl

Ascorbic acid (Cu ++)

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pyruvate

to

homogentisic acid

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Ascorbic acid (Cu ++)

? It also helps in the

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oxidation

of

homogentisic acid

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5. Synthesis of Bile acids

? In the biosynthesis of

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.

bile acids Cholesterol 7
?hydroxylase,

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catalyzes the formation
of

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7

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?

hydroxycholesterol from
cholesterol.

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? In this vitamin C is a

cofactor

? It is a rate limiting step

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in bile acid synthesis


6. Synthesis of Norepinephrine

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? Dopamine conversion

into norepinephrine
requires vitamin C as

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TYROSINE

HYDROXYLASE

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DOPA

the Co enzyme.

? This is essential for

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synthesis

of

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catecholamines

? Adrenal medulla is

Vitamin C

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rich in vitamin C

NOR EPINEPHRINE

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DOPAMINE

HYDROXYLASE
7. Synthesis and release of adreno

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-cortical steroid hormone

? Adrenal gland possesses high levels of ascorbic

acid

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? Ascorbic acid is necessary for hydroxylation

reactions in the synthesis of corticosteroid
hormones.

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8. Reduction of methemoglobin

? It is useful for re-conversion of met-hemoglobin

to hemoglobin.

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9. Folic Acid Metabolism
? Ascorbic acid is helping the enzyme folate

reductase to reduce folic acid to tetrahydrofolic

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acid

? Thus it helps in the maturation of RBC.

DHFR

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FOLIC ACID

DIHYDROFOLATE

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DHFR

TETRA
HYDROFOLATE

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Vit C

Vit C

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9. Antioxidant property

? It

acts

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as

a

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hydrophilic,

chain

breaking antioxidant

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like vitamin E.

? It

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also

form

a

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relatively

stable

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radical

form,

the

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semidehydroascorbate.

? This is reduced back

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to ascorbic acid by

reductase

enzyme

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using

reduced

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glutathione.
10. Synthesis of Carnitine.

? Vitamin C needed for Trimethyllysine and -

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butyrobetaine hydroxylases which are required
for the synthesis of carnitine

11. Peptide hormone synthesis

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? A number of peptide hormones have a carboxy

terminal amide that is derived from a terminal
glycine residue.

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? Hydroxylation of this glycine is carried out by

a copper-containing enzyme peptidyl glycine
hydroxylase, which requires vitamin C
12. Phagocytosis

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? Ascorbic acid stimulates phagocytic action of

leukocytes and helps in the formation of

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antibodies.

13. Sparing action of other vitamins:
? Ascorbic acid is a strong antioxidant
? It spares vitamin A, E and some B-complex

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vitamins from oxidation

14. Immunological function:
? Vitamin C increases the synthesis of

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immunoglobulins & increases the cell mediated

immunity.
15. Prevention of Cataract

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? Vitamin C is concentrated in the lens of eye.

Regular intake of ascorbic acid reduces the risk
of cataract formation.

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16. Activation of Protein C
? Vitamin C is required for postsynthetic

modification of the precursor of protein C, the

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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

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? It spares vitamin A, E and some B-complex

vitamins from oxidation.

18. Preventive role of vitamin C

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? Vitamin C helps in the prevention of cancer,

atherosclerosis and delays ageing process.
Metabolism

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? Ascorbic acid is readily absorbed from

gastrointestinal tract.

? The vitamin is excreted in urine.

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? Since vitamin C is a strong reducing agent, the

Benedict's test will be positive in the urine
sample after the vitamin administration.

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? Plasma ascorbic acid level - 0.7 to 1.2 mg/dl
.

? Oxidation of ascorbic acid yields dehydro ascorbic

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acid, which is oxidized further to oxalic acid through
diketo-L-gulonic acid

? Ascorbic acid is partly excreted unchanged and partly

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as oxalic acid.

? Most of the oxalates in urine are derived from

ascorbic acid, and the rest from glycine metabolism.

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2H H

Dehydro -

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2O

Diketo L ?Gulonic

L-Ascorbic acid

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Ascorbic acid

acid

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Oxalic acid
Dietary Sources of Vitamin C

? Rich sources are amla (Indian gooseberry),guava ,lime,

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lemon,Cabbage and green leafy vegetables.

? Germinating pulses contain large amount of vitamin C.
RDA
? Recommended daily allowance is 60 - 75 mg/day

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(equal to 40-50 mL orange juice).

? During pregnancy, lactation, and in aged people

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requirement may be 100 mg/day

? Smokers, chronic alcoholics and women on oral

contraceptives require up to125 mg/day.

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Deficiency

CAUSES
? Scurvy is caused by a dietary deficiency of

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vitamin C.

? The body's pool of vitamin C can be depleted

in 1-3 months.

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.

Risk factors include the following:

? Babies who are fed only cow's milk during the first

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year of life

? Alcoholism
? Cigarette smokers

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? Pregnant and lactating women
? Thyrotoxicosis
? Elderly individuals who eat a tea-and-toast diet
? Economically disadvantaged persons
? Refugees

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? People with disease of the small intestine
? Those on hemodialysis and peritoneal dialysis.


DEFICIENCY MANIFESTATION

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DEFICIENCY MANIFESTATION

1. Scurvy
? The deficiency of ascorbic

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acid results in scurvy

? It is due to impaired

collagen formation and

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poor blood vessel support.

? Swollen, spongy and

Bleeding gums are the

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characteristic feature
DEFICIENCY MANIFESTATION

2. Infantile Scurvy (Barlow's Disease)
? In infants between 6 to 12 months of age

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(period in which weaning from breast milk)

? Infants loose appetite and weight.
? Painful tenderness of the extremities.

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? Bleeding from gums and mucous membrane.
DEFICIENCY MANIFESTATION

3. Hemorrhagic Tendency
? Capillary fragility enhances hemorrhagic tendencies

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resulting in bleeding under the skin even on slight
pressure.

? Small dots like patches called petehiae and relatively

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large patches as ecchymoses

? Large accumulation of blood in subcutaneous tissues

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is called haematoma.

? In severe cases bleeding may occur from nose

(epistaxis), eye (retinal hemorrhage), urethra

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(hematuria), intestine (malena) etc.
DEFICIENCY MANIFESTATION

4. Bones
? Ground substance formed by osteoblasts is

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defective. So the bones become weak and
fracture easily with slightest of trauma or even
pressure.

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? Such bones are called Scorbutic bones.
? There may be bleeding into the joints leading

to hemarthrosis.
DEFICIENCY MANIFESTATION

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5. Anemia
? In vitamin C deficiency, microcytic, hypochromic

anemia is seen.

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? Poikilocytosis and anisocytosis are also common in

anemia due to deficiency of vitamin C.

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? 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.

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DEFICIENCY MANIFESTATION

6. Poor wound healing
? Vitamin C deficiency is associated with poor

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wound healing.

? Because of its power to heal wounds, vitamin

C has been recommended for treatment of

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ulcer, trauma, and burns.

7. Myalgia
? Myalgias may occur because of reduced

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carnitine production.

Therapeutic Use of Vitamin C

? The beneficial effect of vitamin C is used in the

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treatment of TB

? Clinical dose is 500 mg/day
? Vitamin C is recommended for treatment of ulcer,

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trauma and burns

? There is very little good evidence that high doses of

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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

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in the body

? More than 2000 mg may cause iron over load.