Lecture 3 - Clinical Enzymology and Biomarkers Flashcards
What are biomarkers, and how can they be utilized in clinical practice?
Biomarkers are substances in the blood whose concentrations change in response to disease. They can be used to monitor the onset or progression of disease and predict clinical outcomes. Biomarkers can include enzymes, proteins, hormones, and metabolic products.
How does tissue damage lead to the release of enzymes into the plasma, and what are the causes of enzyme release into circulation?
Tissue damage, such as necrosis or injury, can cause enzymes to be released into the plasma. Enzyme release can be due to various factors, including ischemia in the heart (leading to myocardial infarction), an increase in cell turnover (e.g., growth, tissue repair, or cancer), increased enzyme production (e.g., in liver cirrhosis), obstruction (e.g., gallstones blocking the bile duct), infection (e.g., hepatitis), and inflammation (e.g., pancreatitis).
How is enzyme activity measured in clinical samples, and what does one international unit represent?
Enzyme activity is measured by assessing the biochemical reaction that the enzyme catalyzes. One international unit represents the amount of enzyme that, under specific assay conditions, converts 1 μmol of substrate per minute.
Explain the two methods for measuring enzyme activity: kinetic fixed time and kinetic continuous monitoring.
In kinetic fixed time, the reaction is stopped after a defined period of time, while in kinetic continuous monitoring, the reaction rate is continuously monitored to determine enzyme activity.
Provide an example of an enzyme (Aspartate Amino Transferase) and describe the method used to measure its activity.
To measure AST activity, a kinetic continuous monitoring method is used. The reaction must be coupled because the reaction to form oxaloacetate can’t be seen spectrophotometrically. Instead, the rate of loss of NADH is measured.
What is immunoprecipitation, and how is it applied in clinical enzymology using Lactate Dehydrogenase (LDH1) as an example?
Immunoprecipitation involves binding antibodies to specific enzymes or proteins. For LDH1 measurement, a mixture of LDH 1-5 is present in the serum. Antibodies bind to LDH 2-5, and a secondary antibody bound to an insoluble particle is used. After centrifugation, LDH 1 activity is measured.
What are isoenzymes, and how can they be used in clinical diagnostics?
Isoenzymes are enzymes that catalyze the same reaction but arise from different genes, resulting in proteins with different amino acid compositions. They are often tissue-specific and can be used to locate the organ or tissue that has been damaged.
Provide an example of an isoenzyme (Lactate Dehydrogenase - LDH) and explain how it is utilized in clinical diagnosis.
LDH has five isoenzymes (1-5) with different tissue distributions. These isoenzymes can be used to diagnose conditions such as acute MI, haemolytic anaemia, hepatic disorders, and more based on their elevations in specific tissues.
Describe Creatine Kinase (CK) and its isoenzymes, and explain how CK is used as a cardiac biomarker.
CK consists of M (muscle) and B (brain) subunits, giving rise to three different isoenzymes. CK is used as a cardiac biomarker because the heart has a higher ratio of CK(MB) to CK(MM) compared to skeletal muscle, making it helpful in detecting cardiac-related conditions.
What are some cardiac biomarkers, and how do they differ in terms of sensitivity and duration of elevation after an acute myocardial infarction (MI)?
Cardiac biomarkers include Troponins I and T, and myoglobin. Troponins have increased sensitivity compared to cardiac enzymes, and they remain elevated for several days to weeks after an acute MI. Myoglobin is helpful for diagnosing AMIs within the first 0-4 hours.
