Download MBBS Vitamin C Lecture PPT

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