Chemistry of cholesterol
Chemistry of Cholesterol
• Lecture objectives:
• At the end of lecture you will understand:
• The structure of cholesterol.
• Dietary sources of cholesterol.
• Cholesterol distribution in body.
• Normal plasma cholesterol level & formation of
cholesterol esters.
• Functions of cholesterol.
• Excretion of cholesterol.
Cholesterol is derived lipid
• It is 27-C cyclic isoprene unit, derived from acetyl
CoA
• Phenenthrene nucleus
• Cyclopentane ring
• OH group at 3rd C
• Double bond at 5th position
• Aliphatic chain at C-17
• Methyl gp at C18,19.
CHOLESTEROL CONTENTS OF FOODS
• Food group cholesterol mg/100g
• Brain 2000
• Kidney 375
• Liver 300
• Egg yolk 1500
• Beef 60-70
• Butter 250
• Skimmed milk 11
Blood lipids
• Plasma lipids are usually measured after 12
hours fasting. The total plasma lipids ranges
from 400-700 mg/dl (mean value 470 mg/dl).
The different types of plasma lipids are as
follows:
Cholesterol Distribution
• A 70 kg man contains about 140 gms of
cholesterol in body.
• Cholesterol is most abundant in brain that
contains approx: 30 gms specially in
mylinated structures & in CNS.
• It is present in small amounts in inner
mitochondrial membrane.
Blood Cholesterol
Plasma cholesterol is 150 – 200 mgs/ .
Plasma cholesterol is in a dynamic state,
entering the blood complexed with
lipoproteins and leaving the blood as tissues
remove cholesterol from lipoproteins or
degrade them intracellularly.
Cholesterol occurs in plasma in 2 forms:
free cholesterol (30%) and esterified form with
long chain fatty acids (70%).
It is the free cholesterols that exchanges
between different lipoproteins and plasma
membranes of cells.
Total cholesterol in plasma is normally
between 150- 200 mg/dl. 2/3 of this is
esterified with long chain FA (linoleic).
Cholesterol esters are continually
hydrolyzed in liver and resynthesized in
plasma.
Cholesterol is present in all the lipoproteins
but in fasting more than 60% is carried in
lipoproteins (LDL).
Cholesterol pool inside cells
• Cells of extrahepatic tissues take up cholesterol
from LDL & free cholesterol released in, has
following fates:
• A) Incorporated in cell membranes.
• B) The enzyme ACAT utilizes MUFA for re-
esterification & deposits cholesterol esters in
cell.
• C) In contrast LCAT uses PUFA for esterification &
added to HDL for transport to liver for excretion.
Functions of Cholesterol
Cholesterol is membrane component of all
plasma membranes & I/C membranes.
It is precursor of various steroid hormones.
It is precursor of vitamin D.
It is precursor of bile salts.
Cholesterol in bile appears to protect the
membrane of gall bladder from potentially
irritating & harmful effects of bile salts.
Excretion of Cholesterol
• Average diet supplies about 300 mgs/ day .
• Body synthesizes about 700 mgs / day.
• About 500 mg of cholesterol is excreted
through bile. The unabsorbed portion is
acted by intestinal bacteria's to form
cholestanol & coprostanol & is excreted in
feces.
• Another 500 mgs is converted to bile acids &
excreted as bile salts.
Factors promoting blood cholesterol
1. Age : men >45 years of age; women > 55
years of age
2. family history of CAD
3. smoking
4. Diet rich in saturated fsts
5. low HDL cholesterol
6. Obesity >30% overweight
7. Diabetes mellitus
8 lack of exercise
9 Hypothyroidism
10 Nephrotic syndrome
Factors to decrease risk of CHD
. Low fat diet having 25-30% caloric supply.
. Low intake of saturated fats.
. Take that fats which contain balanced proportion
of mono & PUFA.
.Moderate intake of dietary cholesterol
(300mg/day).
.Intake of plant fiber diet.
. Increased intake of antioxidants to protect LDL
from oxidation.
. Change in life style i.e adequate exercise.
HYPER CHOLESTEROLEMIA
• Hypothyroidism , Obstructive Jaundice , Diabetes
mellitus, Nephrotic Syndrome.
• Diet rich in saturated fats
• Smoking-Nicotine causes vasoconstriction of
coronary & carotid artery & enhance lipolysis &
increase VLDL.
• Stress, excessive sucrose consumption, intake of
excessive calories, lack of exercise.
• Family history of CAD.
• Homocystinuria: cause altered endothelial cell
function leading to thermbosis a risk factor of
CAD.
HYPO CHOLESTEROLEMIA
• Thyrotoxicosis,
• Mal absorption
• Acute infections
• Niacin in large dozes inhibit adipose
tissues lipolysis & lowers blood
cholesterol
• Increase intake of dietary fiber &
estrogen lowers cholesterol in blood.
Low-Density Lipoproteins (LDLs)
• “Bad” cholesterol
• Delivers cholesterol to cells
• Can increase build-up of plaque
• High levels of LDL associated with increased
risk for cardiovascular disease
High-Density Lipoproteins (HDLs)
• “Good” cholesterol
• Made by liver
• Circulates in the blood to collect excess
cholesterol from cells
• Returns cholesterol to liver for excretion in
bile
• Highest protein content
