Total knowledge about the Enzymatic action of Cholinesterase & its functions.

1. CHOLINESTE
RASE

2. CHOLINESTERASE
An enzyme of the hydrolase class that
catalyzes the cleavage of the acyl group from various esters
of choline, including acetylcholine, and some related
compounds.

3. INTRODUCTION
Two related enzymes have the ability to hydrolyze acetylcholine.
One is acetylcholinesterase, which is called true cholinesterase or
cholinesterase I.
True cholinesterase is found in
(1) erythrocytes
(2) the lungs and spleen
(3) nerve endings
(4) the gray matter of the brain
It is responsible for the prompt hydrolysis of acetylcholine released at the
nerve endings to mediate transmission of the neural impulse across the
synapse.
The degradation of acetylcholine is required for the depolarization of the
nerve so that it is repolarized in the next conduction event.

4. The second cholinesterase is acyl choline acyl hydrolase.
It is also called
(1) pseudo cholinesterase
(2) semi cholinesterase
(3) butyrylcholinesterase,
(4) choline esterase 11.
Although it is found in the
(1) liver
(2) pancreas
(3) heart
(4) white matter of the brain
(5) serum
its biological role is unknown.
The type of reaction catalyzed by both cholinesterases is

5. Choline
bromideAcetylcholine
bromide

6. BIOCHEMISTRY
The two cholinesterases differ in specificity toward some substrates
while behaving similarly toward others.
The serum enzyme acts on benzoylcholin but does not hydrolyze
acetyl-β-methylcholine.
This specificity is reversed with the red cell enzyme as it hydrolyzes
acetyl-β-methylcholine but not benzoyl choline.
Of clinical interest are the atypical (genetic) variants of CHE,
characterized by diminished activity against acetylcholine and other
substrates, which are found in the sera of a small fraction of
apparently healthy people.
The gene controlling the synthesis of CHE (symbol BCHE) exists in
many allelic forms.

7. GENETIC BASIC
Most common allelic forms of genes that control synthesis of
cholinesterase are Eu, Ea, Ef, Es which describes as below:
 Eu Normal phenotype
 Ea Weakly active towards most substrate for CHE Increased
resistance to inhibition of enzyme activity by dibucaine.
 Ef Increased resistance to fluoride inhibition
 Es Absence of enzyme or presence of protein with minimal or
no catalytic activity

8. CLINICAL SIGNIFICANCE
As liver function test
As an indicator of possible insecticide poisoning
For detection of patients with atypical forms of enzyme who are at
risk for prolonged responses to certain muscle relaxants

9. Serum
Cholinesterase
RBC
Cholinesterase
Labile more Less
Inactivation faster Slow
Regeneration faster Slow
Accuracy less More
Indication For acute
cases
For chronic
cases

10. Blood test measurements of both AChE and PChE can be used as
surrogate measures of nervous system AChE activity.
Because cholinesterase levels vary greatly between individuals (inter-
individual variability) it is necessary to establish a pre exposure
baseline functioning level for each individual in order to determine
meaningful change in cholinesterase levels.

11. If no baseline exists, and the initial test reading during the illness episode
is within the laboratory’s normal range, the possibility of poisoning cannot
be excluded.
Follow-up testing should be done at 1-2 week intervals until a stable value
is evident.
If the values show an increasing trend, but eventually reach a stable value
30% or more above the first AChE level or 40% or more above the first PChE
value, it is evidence that an overexposure did occur.

12. RBC Cholinesterase Serum Cholinesterase
Low level Antimalarial drugs
Oral contraceptives
Acute infections
Chronic debilitating disease
Cocaine
Codeine
Dermatomyositis
Genetic deficiency
Hepatic parenchymal d's
Malnutrition
Morphine
Pregnancy
Oral contraceptives
Organic mercury
Succinylcholine
Use of collection tubes
containing fluoride
High level Nephrotic syndrome

13. PRINCIPLE OF
S.CHOLINESTRASE
ESTIMATION
The principle of the method is the measurement of the rate of
production of thiocholine as acetylthiocholine is hydrolyzed.
This is accomplished by the continuous reaction of the thiol with
dithiobisnitrobenzoate Ion to produce the yellow anion of 5-
mercapto-2-nitro-benzoic acid.
The rate of color production is measured at 412 nm in a
spectrophotometer.
(enzyme)
Acetylthiocholine ----> thiocholine + acetate
Thiocholine + dithiobisnitrobenzoate(DTNB)-----> yellow color

14. CHOLINESTERASE MONITORING
GUIDELINES
ADAPTED FROM GUIDELINES
ADOPTED BY THE STATES
OF WASHINGTON AND
CALIFORNIA
Utilize cholinesterase monitoring for individuals who apply OP pesticides
occupationally on more than 3 consecutive days, or for 30 or more hours within
any 30-day period.
Measure both acetylcholinesterase (red blood cell cholinesterase) and butyryl
cholinesterase (plasma cholinesterase).
Use the same laboratory and the same methodology for all testing so that results
may be accurately compared.
Obtain a baseline reading of both measures during the non-exposed period, at
least 30 days since the last exposure to OP pesticides. Repeat testing every 3-4
weeks during intensive OP and carbamate application periods.
Test within 3 days of any 30-day period in which the individual has met or
exceeded the handling hours threshold.
Compare each reading to the individual’s baseline. Take action as specified in the
following table.

15. THRESHOLDS FOR
CHOLINESTERASE
DECISION-MAKING
Decrease from
baseline
20% decrease in AChE or
PChE
30% decrease in AchE or
40% decrease in PChE
Action
Evaluate work practices
Remove worker from exposure to
organophosphates and carbamates
until levels return to within 80% of
baseline

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