enzyme in clinical diagnosis

1. Enzymes
1st Year MBBS (Biochemistry)
1st Module (Foundation)

2. Objective
• Application of enzyme in clinical diagnosis

3. Enzymes in Clinical Diagnosis
• Enzyme assays are performed in blood samples and other body fluids to
further the diagnosis of a wide range of clinical conditions. Cellular
enzymes are usually confined to the cells in which they are synthesized and
where they function.
• During normal cellular turnover they are released into plasma, from where
they are subsequently removed and eliminated from the body. In plasma
they do not perform a physiological function and their plasma levels in
healthy state are low to absent.
• Under pathological conditions, the serum levels of cellular enzymes can
increase, because disease process can increase the cell-membrane
permeability and release of intracellular enzymes into serum.
• Metabolic stress without necrosis can also lead to elevated enzyme levels,
apparently by a transient increase of the membrane permeability.

4. • Blood plasma is the fluid, non-cellular fraction of blood. Laboratory
assays of enzyme activity most often use serum, which is the fluid
obtained by centrifugation of whole blood after it has been allowed
to coagulate.
• Plasma is a physiologic fluid, whereas serum is a fluid prepared in the
laboratory from a patient’s whole blood sample
• The level of specific enzyme activity in the plasma frequently
correlates with the extent of tissue damage. Therefore, determining
the extent of elevation of a particular enzyme activity in the blood
plasma is often useful in evaluating the extent of tissue damage,
response to therapies, and the prognosis for the patient

5. Some Clinically Useful Enzymes

6. Plasma enzymes as diagnostic tools
• Some enzymes show relatively high activity in only one or a few
tissues. Therefore, the presence of increased levels of these enzymes
in blood plasma reflects damage to the corresponding tissue.
• For example, the enzyme alanine aminotransferase (ALT) is one of
many enzymes that are abundant in the liver.
• The appearance of elevated levels of ALT in plasma signals possible
damage to hepatic tissue. Measurement of ALT released into a
patient’s blood from dying cells is part of the liver function test panel

7. Isoenzymes
• Isoenzymes are variant forms of a particular enzyme that all catalyze the same
reaction but have slightly different physical properties because of genetically
determined differences in amino acid sequence.
• Different organs commonly contain characteristic proportions of different
isoenzymes.
• LDH is found in relatively high concentration in most tissues;
LD1 in myocardial muscle
 LD2 in red blood cells
LD5 in liver and skeletal muscle
• The pattern of isoenzymes found in the blood plasma may, therefore, serve as a
means of identifying the site of tissue damage. The plasma levels of various
isoenzyme forms of LDH and of creatine kinase (CK) vary under different disease
states.

12. Diagnostic Use of Troponins

15. Creatine Kinase (CK)
• It is an important enzyme in energy metabolism that catalyzes
transfer of the phosphate group of creatine phosphate to ADP to form
ATP, thereby serving as an immediate source of ATP in contracting
muscles.
• It is a reasonably specific muscle enzyme, found in heart and skeletal
muscle. Besides muscle tissue, only the brain contains appreciable
amounts of CK
• Its activity rises in Duchenne muscular dystrophy and several other
muscular afflictions.
• The most important diagnostic clue is given in myocardial infarction
as it is the first enzyme to be elevated following an episode of MI

16. Lactate Dehydrogenase
• It is an enzyme of anaerobic glycolysis that catalyzes the reversible
interconversion of lactate and pyruvate.

17. Transaminases’
• These are important enzymes of intermediary metabolism that
catalyze reversible transfer of an amino group from an α-amino acid
to a α-keto acid.
• Aspartate transaminase Serum glutamate oxaloacetate transaminase,
or SGOT) and alanine transaminase (Serum glutamate pyruvate
transaminase, SGPT)
• AST
• ALT

19. Enzymes as Therapeutic Agents

21. Additional Clinical Uses of Enzymes
• Enzymes are employed in clinical laboratory for measurement of cellular
metabolites
• glucose oxidase
• Enzymes also are employed with increasing frequency for the treatment of
injuries and disease.
• tissue plasminogen activator (tPA) or streptokinase for treatment of acute
MI
• Trypsin for treatment of cystic fibrosis
• Intravenous infusion of recombinantly produced glycosylases can be used
to treat lysosomal storage syndromes such as Gaucher disease (β-
glucosidase), Pompe disease (α-glucosidase), Fabry disease (α-
galactosidase A), and Sly disease (β-glucuronidase).