Transcript Clinical Applications of Enzymes

Clinical Applications of Enzymes
Clinical examples and
case studies.
Hepatitis
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A 36-year old man was admitted to a hospital following
episodes of nausea, vomiting, and general malaise.
His urine was darker than usual.
Upon examination it was discovered that his liver was enlarged
and tender to palpation.
Liver function tests were abnormal; plasma ALT was 1500 IU/L
(Alanine aminotransferase 6.0 – 21 U/L); AST was 400 IU/L
(Aspartate aminotransferase 7.0 – 20 U/L).
During the next 24 hours the man developed jaundice, and his
plasma total bilirubin was 9.0 mg/dL (0.2 – 1 mg/dL).
A diagnosis of hepatitis was made.
Biochemical Questions:
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What reactions are catalyzed by AST and
ALT? What is the coenzyme?
What conditions are important to maintain
in performing the enzyme assays?
Which other enzymes might have been
elevated in the plasma?
How does “total” bilirubin relate to “direct”
and “indirect” bilirubin?
Case discussion:
Hepatitis is an inflammation of the liver.
Transaminases (amino acids metabolism)
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Catalyze the transfer of α-amino groups from amino acid
to a α-keto acid through the intermediary coenzyme
pyridoxal phosphate (derived from the B6 vitamin,
pyridoxine)
Amino acids enter into the Krebs cycle for oxidation to
CO2 and H2O
Amino acid1 + keto acid2 ↔ amino acid 2 + keto acid1
(pyridoxal phosphate ↔ pyridoxamine phosphate) slide 11
ALT and AST
2. Temperature and pH
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Excessive shaking and elevated temp
should be avoided
Anticoagulants shouldn't inhibit the assays
Hemolysis should be avoided in order not
to release enzymes of the blood cells
3. Other enzymes that could be
elevated:
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A number of proteins may leak from cell
into plasma, such as other transaminases
and LD can be elevated in liver diseases
AST and ALT high levels occurs before
jaundice is noted
There is poor correlation of enzyme activity
with severity of the disease
4. Bilirubin
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Biliribin is derived from the breaking down of the hemoglobin of
aging red blood cells
Bilirubin is insoluble in water; to be excreted it is converted to a
water-soluble bilirubin diglucuronide in the liver
The first formed “indirect” bilirubin is bound to albumin and rapidly
transported in plasma to the liver; albumin is not taken into the liver
cells
“Direct” bilirubin (water soluble) is secreted into the bile canaliculus,
together with other bile constituents and is collected in the
gallbladder
Some of the bile pigments are excreted in the feces and some water
soluble bilirubin (not free bilirubin) is excreted by the kidney into the
urine
Bilirubin continue:
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In hepatitis, the formation of water soluble bilirubin is
less efficient
The secretion of “direct” bilirubin (water soluble
bilirubin) into the bile canaliculi is impaired
The result is a backing-up of the bilirubin excretion
with a build-up of total bilirubin in the blood.
The initial increase is expressed as a darkened
urine, followed by jaundice