Biomarkers for MI

Question 1

What is a biomarker?

Answer 1

any molecule (lipid, enzyme, protein, etc) that can be used to diagnose a clinical condition, they are specific biological molecules whose concentration changes due to specific conditions

The most common ones are enzymes as they are normally not found in the blood

Question 2

What is an isozyme?

Answer 2

They are large proteins made of several subunits catalyzing specific reactions, isozymes might be different in their affinity to the substrate in different tissues

An isozyme (or isoenzyme) is like a twin version of a special helper in your body called an enzyme.

Now, just like there can be twins who look a little different but do the same things, isozymes are different versions of the same enzyme. They do the same job, but in slightly different ways or in different parts of your body.

For example, one isozyme might work in your heart, while another works in your liver, but both are doing similar jobs to keep you healthy!

Question 3

What are some examples of enzymes with different isozymes?

Answer 3

1) Dehydrogenases

2) Oxidases

3) Transaminases

4) Phosphatases

Question 4

What are the main types of biomarkers used for MI?

Answer 4

1) Enzymes (AST, LDH, CK-MB)

2) Proteins (myoglobin & troponin)

Question 5

What is the AST biomarker?

Answer 5

• It is an enzyme that transfers ammonia from aspartate to a-ketoglutarate
• Involved in the liver function test
• It was the first enzyme used as a cardiac biomarker

Question 6

Do we still use AST as a biomarker, and what is the reason for that?

Answer 6

No

1) Not specific

2) It elevates 12 hours post-MI, reaching the peak after 36 hours which is to much as the patients would come before that to the A&E, and reverts back to normal in 2-3 days

Question 7

What is lactate dehydrogenase?

Answer 7

• An tetra-subunit-enzyme that converts pyruvate to lactate under anaerobic conditions
• It is found in high concentrations in most tissues

Question 8

What are the different isozymes of LDH?

Answer 8

There are five different isozu=ymes:

• LD5 is prevalent in the liver and skeletal muscles
• LD2 in RBC
• LD1 IN Myocardial cells (contains four H subunits and sometimes 3H and one M)

Question 9

What is the time period for LDH?

Answer 9

• It raises after 24 hours of a MI
• Peaks at 72 hours
• detectable for 7-10 days

Question 10

When can we use the LDH biomarker for AMI?

Answer 10

• It is used to detect AMI in patients who have had the symptoms for more than 24 hours, so it is used in the monitoring stage after the patient comes complaining of symptoms and not the attack itself

Question 11

Is the LDH biomarker sufficient to be used alone as an indicator for MI

Answer 11

No, Because it is widespread in the body

Question 12

What is the function of creatine kinase?

Answer 12

• It is an enzyme that transfers phosphate to ADP making it an ATP
• It is found in all muscle tissues and brain

Question 13

What are the different isozymes of creatine kinase?

Answer 13

1) CK-MM mainly in the skeletal muscles

2) CK-MB mainly in the Heart

3) CK-BB mainly in the brain

Question 14

When will CK be used as a biomarker for AMI?

Answer 14

• Its activity in the blood increases 4-6 hours after MI and peaks at 24 hours, making it perfect for diagnosing acute cases
• But it regresses in 2-4 days and thus its not good for monitoring

Question 15

What is myoglobin?

Answer 15

• It is a type of heart that stores oxygen in the muscles

Question 16

When is myoglobin used as a biomarker for MI?

Answer 16

• Due to its low molecular weight it is released by the damaged myocardium in 2-4 hours making it good for diagnosing MI in the A&E along with CK and troponin, it peaks in the Bloodstream in about 12 hours and returns back to normal in 2-4 days

Question 17

What is the bad side of myoglobin when detecting MI?

Answer 17

It is not specific to the myocardium and can be caused by skeletal muscle injury

Question 18

What is troponin?

Answer 18

• It is a complex of 3 proteins (T, I & C)
• It binds and regulates the thin filaments of the cardiac muscle
• Cardiac troponin T and I are most specific for myocardial cell injury
• The most important MI marker

Question 19

How is troponin used as a biomarker for MI?

Answer 19

• Ordered immediately and after 6-12 hours
• Troponin I and T appear in the plasma 4-8 hours post MI and are best measured 12 hours after chest pain it stays elevated for 7-10 days which makes it good for both acute and monitoring stages of MI

Question 20

Why is troponin a better biomarker than CK-MB

Answer 20

Because unlike CK troponin has a higher level of elevation and does not increase due to IM injections, accidents, and exercise

Question 21

Which biomarkers are used for acute MI detection?

Answer 21

1) CK (4-6h)

2) Myoglobin (2-4h)

3) Troponin (4-6h)

Question 22

Which biomarkers are used for the monitoring of MI?

Answer 22

1) LDH (7-12 days “stays elevated”)

2) Troponin (7-10 days)

Question 23

What is the disadvantage of Troponin T when diagnosing MI?

Answer 23

• It is not that specific (Troponin (TnT) may be elevated in non–MI cardiac cases such as myocarditis, kidney disease, congestive heart failure, pulmonary embolism, ETC.