Enzymes in Body Fluids Lecture outline

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Enzymes in Body FluidsLecture outline

• Dr. Essam H. Jiffri

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Upon completion of this chapter, the following
will be covered

• - Introduction
• - Factors affecting serum enzyme
• Rate of entry of enzymes into blood
• Enzyme inhibitors
• Clearance of enzyme

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Specificity of serum enzyme measurements

• Test results and clinical features
• Test pattern recognition
• Isoenzymes

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Major enzymes of diagnostic interest

• Phosphatases
• Transaminases
• G-Glutamyl transferase
• Amylase and Lipase
• Cholinesterase
• Creatine kinase
• Lactate dehydrogenase

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Serum enzymes in disease

• Myocardial infarction
• Muscle disease
• Liver disease
• Bone disease
• Enzymes in urine
• Haematological disorders
• Tissue enzymes

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• - Methods for the determination in serum and
  urine
• - Case histories

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Introduction

• -Enzymes are protein catalysts which are found in
  small amounts, mainly within cells such as
  clotting factors.
• -Most enzymes with diagnostic applications
  function within the cells in which they are
  synthesized and since they have a large molecular
  mass, they do not cross cell membranes readily.

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Introduction

• -Normally only small quantities of intracellular
  enzymes leak from cells into blood or other body
  fluids.
• -The amounts are too low for enzyme mass to be
  measured, their activities can be monitored.

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Introduction

• -Most clinical enzyme measurements using serum,
  occasionally other fluids, such as urine and gut
  secretions, are investigated.
• -In general, increased rather than decreased
  activities of enzymes are of diagnostic interest
  in body.

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Factors Affecting Serum Enzyme Activities

• The activity of an enzyme in the circulation
  depends on a balance between
• 1- The rate of release from tissues (rate of
  entry
• of enzyme into blood),
• 2- The presence of inhibitors, and
• 3- The rate of removal

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1.Rate of entry of enzyme into blood

• The main factors affecting the rate of entry of
  enzyme into blood are
• The rate of synthesis
• The mass of enzyme producing cells, and
• Cell damage

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Enzyme Synthesis

• -The rate of enzyme synthesis is increased
  particularly in conditions affecting the liver.
• -Biliary obstruction causes increased synthesis
  of enzyme located in the hepatobiliary tree.
• -Some agents induce increased synthesis of enzyme
  by hepatocytes, example
• ( phenobarbitone and phenyrtoin).

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Mass of Enzyme Producing cells

• -Serum alkaline phosphatase originating from bone
  reflects osteoblastic activity, this is increased
  (leading to high serum alkaline phosphatase
  activity in children who are actively growing or
  where bone disease is present in which increased
  osteoblastic activity occurs, e.g. Pagets
  disease).

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Mass of Enzyme Producing cells

• -The placenta produces alkaline phosphatase,
  causing increased levels in the third trimester.
• -Metastatic carcinoma of the prostate produces
  increased acid phosphatase levels.

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Cell Damage

• -Increased amounts may leak from tissues that are
  inflamed, necrotic, or metabolically abnormal,
  leading to increased serum levels.
• -Examples include raised transaminase levels in
  hepatitis, creatine kinase (CK) following
  myocardial infarction and lactate dehydrogenase
  (LDH).

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2. Enzyme Inhibitors

• -Organophosphate poisoning which irreversibly
  inhibits cholinesterase.

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3. Clearance of Enzymes

• -Serum enzyme activity is also affected by the
  rate of removal of enzymes from the circulation,
  and understanding of these mechanisms is
  incomplete.
• -Possibilities include removal by
  reticuloendothelial system.
• -Renal excretion appears unimportant, except for
  amylase which is small enough to be cleared by
  the kidney.

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FACTORS AFFECTING SERUM ENZYME ACTIVITY

• Tissue damage Rate of synthesis
  Mass of enzyme
  producing tissue
• Rate of entry into blood
• Inhibition Serum enzyme
  activity
• Rate of removal
• Clearance Inactivation

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Specificity of Serum Enzyme Measurements

• - Many enzymes which are used diagnostically
  originate from more than one tissue which
  potentially limits their specificity.

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Main applications Origin Enzyme
Metastatic carcinoma of prostate Prostate, erythrocytes Acid phosphatase
Hepatocelluar disease Hepatocytes Kidney Alanine aminotransferase (ALT, SGPT)
Cholestatic disease Bone disease Hepatobiliary tree Bone GI tract, placenta, kidney Alkaline phosphatase (ALP)
Acute pancreatitis Acute pancreatitis Pancrease Pancrease, Salivary glands Lipase Amylase
Hepatocelluar disease Myocardial infarction Muscle disease Hepatocytes Cardiac muscle Skeletal muscle Aspartate aminotransferase (AST, SGOT)
Organophosphorous poisoning Liver Cholinesterase
Muscle disease Myocardial infarction Skeletal Muscle Heart Muscle Brain Creatine kinase (CK)
Cholestasis Alcohol abuse Liver Pancrease Kideny y-Glutamyl transferase (GGT)
Myocardial infarction Cardiac muscle Skeletal muscle Erythrocytes, liver Lactate dehydrogenase (LDH)
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Specificity of Serum Enzyme Measurements

• - Increased serum CK could be due to myocardial
  infarction or skeletal muscle disease, and
  increased LDH occurs through multiple causes.
• - This would limit the usefulness of enzyme
  measurements if their specificity was not
  increased.

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Specificity of Serum Enzyme Measurements

• - Greater specificity is achieved in three ways
• Interpreting investigations in the light of
  clinical features (test results and clinical
  features).
• Test pattern recognition,
• Isoenzyme determination.

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Test Results and Clinical Features

• Serum aspartate aminotransferase (AST) activity
  may be raised due to myocardial infarction or
  because of diseases affecting hepatocytes, such
  as viral hepatitis.
• - Occasionally, increased AST may originate from
  the liver because of complications of myocardial
  infarction, such as congestive cardiac failure.

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Test Pattern Recognition

• - Investigations are rarely done in isolation and
  recognition of test patterns may aid differential
  diagnosis.
• - Alkaline phosphatase is raised in cholestasis
  and bone disease, in cholestasis, there are often
  increases in bilirubin and transaminase levels,
  while these do not occur in bone disease.

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Test Pattern Recognition

• -If an isolated increase in alkaline phosphatase
  occurs, the estimation of gamma-glutamyl-
  tranferase may be helpful, as high serum
  activities of this enzyme occur in cholestasis
  while levels are normal in bone disease.

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Isoenzymes

• Multiple forms of enzymes (isoenzymes) occur
  which have similar catalytic activities but
  different structures.
• - Different isoenzymes are often organ-specific
  and their determination may improve the
  specificity of enzyme tests.

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Isoenzymes

• - The heterogeneity of some isoenzymes is due to
  different protein subunits which are coded for by
  separate genes.
• - Lactate dehydrogenase has four subunits of two
  different types (H and M), five isoenzymes occur,
  H4 originating from the heart and M4 from the
  liver.

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Isoenzymes

• Creatine kinase has two subunits, M and B three
  isoenzymes occur, BB from brain, MM from skeletal
  muscle and MB from the heart.

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Isoenzymes

• - Isoenzymes may be differentiated because of
  different physicochemical properties by
  techniques such as
• Electrophoresis
• Immunochemical properties (immunoassay) or
• Chemical properties (differential activity for
  some substrates or susceptibility to inhibitors).