Lecture 6: Clinical proteins and enzyme markers

Question 1

Most common reasons for release of plasma enzymes and proteins into blood plasma

Answer 1

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

Question 2

What is a useful clinical marker assay?

Answer 2

should be specific and sensitive for a particular tissue or disease. Some of the marker enzymes are expressed as isoenzymes/isomers in different tissues.

Question 3

Sensitive assay

Answer 3

detects the smallest amount of the marker.

Question 4

Specific assay

Answer 4

highly distinguishes between the marker and other undesirable substances.

Question 5

Precise assay

Answer 5

reproducibility of an assay.

Question 6

Accuracy of assay

Answer 6

how close the result is to the “true value”.

Question 7

Sensitivity vs specificity

Answer 7

Often, increasing sensitivity leads to decreased specificity (increased false positive)

Question 8

What does lactate DH do?

Answer 8

involved in anaerobic process of glycolysis

Catalyzes conversion of lactate to pyruvate in glycolytic pathway

Reversible reaction

Question 9

Isoenzymes of lactate DH

Answer 9

composed of five isoenzymes formed from two major subunits, designated as the H (heart) and M (muscle) specific subunits.

Question 10

Distribution of Lactate DH in tissues

Answer 10

Widely distributed in most tissues

The isoenzyme patterns of the tissues depend on the relative amounts of the LDH subunits.

Question 11

Reaction catalyzed by creatine kinase (CK)

Answer 11

Conversion of creatine + ATP to creatine phosphate

Reversible

Question 12

Which organs is CK specific for?

Answer 12

Skeletal and cardiac muscle

Brain also has large amount of CK (uses a lot of energy)

Question 13

Isoenzymes of CK

Answer 13

Muscle (M) and Brain (B) subunits

Question 14

Cardiac muscle CK

Answer 14

MB subunits (CK-2)

Question 15

Skeletal muscle CK

Answer 15

MM (CK-3)

Skeletal muscle specific

Question 16

Brain CK

Answer 16

BB (CK-1)

Question 17

What happens if you see BB CK in blood?

Answer 17

Serious problem

BB should not be in blood because of blood brain barrier

Question 18

What are troponins?

Answer 18

Tn

components of the regulatory contractile protein complex of muscles (cardiac and skeletal muscles).

Question 19

Three types of troponins

Answer 19

Troponin T - tropomyosin bindnig

Troponin I - inhibitory actin binding

Troponin C - calcium binding

Question 20

Solubility of troponins

Answer 20

Insoluble

When there is damage, you will see the soluble form

Question 21

Distribution of aspartate and alanine aminotransferases

Answer 21

Widely distributed

Abundant in liver

ALT is present in most tissues

AST is more abundant than ALT

Question 22

Activity of ALT and AST in liver

Answer 22

Similar activity

Question 23

Activity of alkaline phosphatase (ALP)

Answer 23

group of enzymes with maximum activity in the pH range 9.0 – 10.5.

Hydrolytic enzymes, remove phosphate

Question 24

Distribution of ALP

Answer 24

liver

bone

placenta

intestine.

Question 25

Tissue distribution of alpha amylase

Answer 25

present mostly in the pancreas and salivary glands and smaller amounts in other tissues.

Question 26

Reaction of alpha amylase

Answer 26

breakdown of starch/carbohydrate polymers into sugar.

Question 27

Excretion of alpha amylase

Answer 27

The salivary and pancreatic amylase isoenzymes are usually filtered at the glomeruli in the kidneys.

Question 28

Distribution of gamma-glutamyl transferase (GGT)

Answer 28

found mainly in the kidney, liver biliary tract and pancreas.

Question 29

Function of GGT

Answer 29

cell surface protein contributing to the extracellular catabolism of glutathione, an antioxidant

Question 30

LDH levels in disease

Answer 30

Heart and bone barrow: H subunits Skeletal muscle: M subunits Lung, brain, kidney and pancreas: both

Question 31

What is abnormal CK associated with?

Answer 31

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

Question 32

Detection of cardiac troponins (Tn)

Answer 32

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

Question 33

What troponins are used in assays?

Answer 33

cTnI and cTnT are more used than cTnC Interpretation of cTnI and cTNT are similar

Question 34

What biochemical markers are best for detecting myocardial infarction?

Answer 34

Troponins cardiac specific cTnI is best

Question 35

What does increase in AST or ALT in blood indicate?

Answer 35

leakage from damaged hepatocytes. Also present in cardiac and skeletal muscle

Question 36

Where are AST and ALT mainly used?

Answer 36

investigations of patients with liver diseases and suspected myocardial infarction and muscular dystrophy.

Question 37

What is ALP used for in diagnoses?

Answer 37

Diagnoses of liver and bone diseases. Used in standard liver function tests

Question 38

When will amylase be elevated?

Answer 38

Acute pancreatitis Lipase will also be high Used for differential diagnosis of severe abdominal pain of sudden onset.

Question 39

What can GGT be used for?

Answer 39

Liver function testing Associated with cell membranes

Question 40

How to distinguish between LDH iso forms

Answer 40

LDH isoenzymes have different electrophoretic mobility, physical and chemical properties. Heart specific enzymes are present for one or two days after a chest pain

Question 41

Indications of muscle disease

Answer 41

CK, AST, LDH and ALT activities may be increased

Question 42

Cardiac troponins in detection of MI

Answer 42

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

Question 43

Troponin I

Answer 43

Highly specific and sensitive for MI

Question 44

When is AST measured?

Answer 44

Used in patients with liver disease, suspected MI and muscular dystrophy

Question 45

When is ALT measured?

Answer 45

Measured for hepatocellular damage, since it is more liver specific than AST.

Question 46

What does elevated ALP indicate?

Answer 46

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.

Question 47

When is amylase increased?

Answer 47

Intestinal infarction or perforation. Peritonitis (inflammation of peritoneum)

Question 48

When do GGT and ALP increase in parallel?

Answer 48

when there is cholestasis in liver disease (obstruction of bile flow) .

Question 49

What is increase in GGT stimulated by?

Answer 49

Cholestasis in liver disease Alcohol and drug use (ex: anti epileptic drugs)

Question 50

How can GGT help identify tissue of origin for ALP in plasma?

Answer 50

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

Question 51

Release of markers in MI

Answer 51

See figure

Question 52

Why do enzyme activities and protein levels vary?

Answer 52

Due to their rate of release