Clinical Applications of Enzymes

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Clinical Applications of Enzymes

• Clinical examples and case studies.

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Hepatitis

• 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.

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Biochemical Questions

1. What reactions are catalyzed by AST and ALT? What
   is the coenzyme?
2. What conditions are important to maintain in
   performing the enzyme assays?
3. Which other enzymes might have been elevated in
   the plasma?
4. How does total bilirubin relate to direct and
   indirect bilirubin?

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Case discussion Hepatitis is an inflammation of
the liver.

• Transaminases (amino acids metabolism)
• Catalyze the transfer of a-amino groups from
  amino acid to a a-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

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2. Temperature and pH

• 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

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3. Other enzymes that could be elevated

1. A number of proteins may leak from cell into
   plasma, such as other transaminases and LD can be
   elevated in liver diseases
2. AST and ALT high levels occurs before jaundice is
   noted
3. There is poor correlation of enzyme activity with
   severity of the disease

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4. Bilirubin

1. Biliribin is derived from the breaking down of
   the hemoglobin of aging red blood cells
2. Bilirubin is insoluble in water to be excreted
   it is converted to a water-soluble bilirubin
   diglucuronide in the liver
3. 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
4. Direct bilirubin (water soluble) is secreted
   into the bile canaliculus, together with other
   bile constituents and is collected in the
   gallbladder
5. 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

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Bilirubin continue

• 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