Lecture 6: Clinical proteins and enzyme markers Flashcards
Most common reasons for release of plasma enzymes and proteins into blood plasma
Tissue damage or cell death (necrosis/apoptosis/autophagy), usually caused by toxins or induced by ischemia.
Increased cell turn over during active growth, tissue repair, or in tumour invasion of normal tissue (as in cancer).
Increased concentrations of enzymes/proteins within cells, because of induction by diseases or drugs.
Duct obstruction. For example, exocrine secretions may be released into the blood, if the normal route of flow is obstructed or damaged
What is a useful clinical marker assay?
should be specific and sensitive for a particular tissue or disease. Some of the marker enzymes are expressed as isoenzymes/isomers in different tissues.
Sensitive assay
detects the smallest amount of the marker.
Specific assay
highly distinguishes between the marker and other undesirable substances.
Precise assay
reproducibility of an assay.
Accuracy of assay
how close the result is to the “true value”.
Sensitivity vs specificity
Often, increasing sensitivity leads to decreased specificity (increased false positive)
What does lactate DH do?
involved in anaerobic process of glycolysis
Catalyzes conversion of lactate to pyruvate in glycolytic pathway
Reversible reaction
Isoenzymes of lactate DH
composed of five isoenzymes formed from two major subunits, designated as the H (heart) and M (muscle) specific subunits.
Distribution of Lactate DH in tissues
Widely distributed in most tissues
The isoenzyme patterns of the tissues depend on the relative amounts of the LDH subunits.
Reaction catalyzed by creatine kinase (CK)
Conversion of creatine + ATP to creatine phosphate
Reversible
Which organs is CK specific for?
Skeletal and cardiac muscle
Brain also has large amount of CK (uses a lot of energy)
Isoenzymes of CK
Muscle (M) and Brain (B) subunits
Cardiac muscle CK
MB subunits (CK-2)
Skeletal muscle CK
MM (CK-3)
Skeletal muscle specific
Brain CK
BB (CK-1)
What happens if you see BB CK in blood?
Serious problem
BB should not be in blood because of blood brain barrier
What are troponins?
Tn
components of the regulatory contractile protein complex of muscles (cardiac and skeletal muscles).
Three types of troponins
Troponin T - tropomyosin bindnig
Troponin I - inhibitory actin binding
Troponin C - calcium binding
Solubility of troponins
Insoluble
When there is damage, you will see the soluble form
Distribution of aspartate and alanine aminotransferases
Widely distributed
Abundant in liver
ALT is present in most tissues
AST is more abundant than ALT
Activity of ALT and AST in liver
Similar activity
Activity of alkaline phosphatase (ALP)
group of enzymes with maximum activity in the pH range 9.0 – 10.5.
Hydrolytic enzymes, remove phosphate
Distribution of ALP
liver
bone
placenta
intestine.
Tissue distribution of alpha amylase
present mostly in the pancreas and salivary glands and smaller amounts in other tissues.
Reaction of alpha amylase
breakdown of starch/carbohydrate polymers into sugar.
Excretion of alpha amylase
The salivary and pancreatic amylase isoenzymes are usually filtered at the glomeruli in the kidneys.
Distribution of gamma-glutamyl transferase (GGT)
found mainly in the kidney, liver biliary tract and pancreas.
Function of GGT
cell surface protein contributing to the extracellular catabolism of glutathione, an antioxidant
LDH levels in disease
Heart and bone barrow: H subunits
Skeletal muscle: M subunits
Lung, brain, kidney and pancreas: both
What is abnormal CK associated with?
Skeletal and cardiac muscle damage, muscular dystrophy, intramuscular injection
BB is hardly ever detected in plasma
BUT in the absence of MM (skeletal) or MB (cardiac) isotopes, brain damage will be considered
Detection of cardiac troponins (Tn)
Cardiac troponins are very sensitive and highly specific (97% sensitivity and specificity) for detecting even a minimal amount of myocardial damage.
Elevations of cardiac troponin can occur without elevation of total CK and CK-MB
What troponins are used in assays?
cTnI and cTnT are more used than cTnC
Interpretation of cTnI and cTNT are similar
What biochemical markers are best for detecting myocardial infarction?
Troponins
cardiac specific cTnI is best
What does increase in AST or ALT in blood indicate?
leakage from damaged hepatocytes.
Also present in cardiac and skeletal muscle
Where are AST and ALT mainly used?
investigations of patients with liver diseases and suspected myocardial infarction and muscular dystrophy.
What is ALP used for in diagnoses?
Diagnoses of liver and bone diseases.
Used in standard liver function tests
When will amylase be elevated?
Acute pancreatitis
Lipase will also be high
Used for differential diagnosis of severe abdominal pain of sudden onset.
What can GGT be used for?
Liver function testing
Associated with cell membranes
How to distinguish between LDH iso forms
LDH isoenzymes have different electrophoretic mobility, physical and chemical properties.
Heart specific enzymes are present for one or two days after a chest pain
Indications of muscle disease
CK, AST, LDH and ALT activities may be increased
Cardiac troponins in detection of MI
Best at detecting MI
More specific than CK-MB
After MI, cardiac troponins increase within four hours and remain increased for several days
Not good for continuous monitoring
Troponin I
Highly specific and sensitive for MI
When is AST measured?
Used in patients with liver disease, suspected MI and muscular dystrophy
When is ALT measured?
Measured for hepatocellular damage, since it is more liver specific than AST.
What does elevated ALP indicate?
ALP activity is usually increased when there is cholestasis and not when there is hepatocellular damage.
increased in bone disease, such as in Paget’s disease, rickets and osteomalacia, where there is increased osteoblastic activity,
It is also elevated in hyper parathyroidism.
It is also used as tumor markers.
When is amylase increased?
Intestinal infarction or perforation.
Peritonitis (inflammation of peritoneum)
When do GGT and ALP increase in parallel?
when there is cholestasis in liver disease (obstruction of bile flow) .
What is increase in GGT stimulated by?
Cholestasis in liver disease
Alcohol and drug use (ex: anti epileptic drugs)
How can GGT help identify tissue of origin for ALP in plasma?
GGT is not raised in bone diseases, but is raised in liver.
So if ALP is high, but GGT is not, it is probably bone disease
Release of markers in MI
See figure
Why do enzyme activities and protein levels vary?
Due to their rate of release
