Biochem Report Eznymes

Enzymes in action: Myocardial

InfarctionLopez, Amier Dayle

Lucero, Celina RoxanneMacatangay, Neon

Mallillin, NikkoMarcelino, Jonhenryk

Objectives:

At the end of the discussion, the students must be able to:

1. Define enzymes and myocardial infarction.

2. Describe the biochemical events that lead to MI.

3. Enumerate the different diagnostic enzymes.

4. Define isoenzymes and their roles in the diagnosis of MI.

5. Describe the initial rise, peak and descent of enzyme serum levels in accordance with the duration of the disease, from onset onwards.

Objectives:

5. Discuss the importance of enzyme assays in the diagnosis of MI.

6. Enumerate the non-enzymatic proteins that are of diagnostic to MI.

7. Enumerate the different enzymes that have therapeutic value to MI and describe their mechanisms of action.

8. Enumerate the anti-thrombotic drugs that can be used for MI and describe their mechanisms of action.

9. Define reperfusion injury and its relation to thrombolytic therapy.

What are enzymes?

Enzymes are biological catalysts that enhance the rate of metabolic processes

taking place in living cells without altering any significant change to the cells involved.

MAIN FUNCTIONS:

Increase rate of chemical reactions

Regulate metabolic reactions

What is myocardial infarction?

It is a heart attack that is caused by a decrease in the heart’s blood flow

that results to ischemia of the myocardial tissue.

In most cases, patients suffer from myocardial infarction due to an occlusion

of a coronary blood vessel by a thrombus.

Causes and risk factors

- Atherosclerosis

- Obesity

- Smoking

- Carbon monoxide poisoning

- Age

- Diabetes Mellitus

- Illegal Drugs (Cocaine)

- Family history

- Male- High level of LDL- Hypertension

BIOCHEMICAL EVENTS OF MYOCARDIAL

INFARCTION

TISSUE DAMAGE IN MI

TISSUE DAMAGE IN MI

How do enzymes assist AMI?

CARDIAC MARKERS:

Aspartate Aminotransferase (AST)

Aspartate + α-ketoglutarate → Oxaloacetate + Glutamate

One of the enzyme used to diagnose MI It is not specific for heart damage.Proved less than ideal

DIAGNOSTIC WINDOW:Rise: 6-8 hoursPeak: 24 hoursNormal: 5 days

CARDIAC MARKERS

Lactate Dehydrogenase, LDH

Lactate + NAD+ ↔ Pyruvate + NADH + H+

Catalyst for the interconversion of lactate and pyruvate LDH-1 isoenzyme is normally in the heart muscle. Widely distributed in the body with highest activities in

the heart, liver, skeletal muscles, and red blood cells

DIAGNOSTIC WINDOW:Rise: 12-24 hoursPeak: 48-72 hours

Normal: 10-14 days

!! Not specific for MI. !!

CARDIAC MARKERS

Creatine Kinase, CK-MB

Creatine + ATP → Creatine Phosphate + ADPVery sensitive indicator of AMILevels increase within 3-12 hours of the onset

of chest pain.DIAGNOSTIC WINDOW:

Rise: 4-6 hours of an MIPeaks at 24 hoursNormal: after 48 – 72 hours

CARDIAC MARKERS

TroponinContractile protein, not found in serum.Released only when myocardial necrosis occurs.Most sensitive and specific for myocardial infarction.

DIAGNOSTIC WINDOW:

Levels rise for 2-6 hours after an MI, and remain elevated for 4-10 days.

Peak time: 12 hours

CARDIAC TROPONINS served as a marker of all heart muscle damage

CARDIAC MARKERS

Myoglobin, MbHigh when there is muscle tissue damage

but has a low specificity for MI.Responds very rapidly, rising and

normalizing earlier than Troponin or CK-MB.Urine myoglobin level rises within 1-4 hours

from the onset of chest pain.

What are isoenzymes?

One of a group of enzymes that catalyze the same reaction but are

differentiated by variations in physical properties.

Isoenzymes could either be tissue specific or species specific that are

present in serum and other biological fluids and tissues.

ISOENZYMES

CK has three isoenzymes:

CK-BB (CK-1), CK-MB (CK-2), CK-MM (CK-3)

CK-MB (CK-2, hybrid type)CK-MB is the most significant isoenzyme of CK

for MIFound in skeletal and cardiac musclesElevation is considered the most specific

indicator of myocardial damage, particularly AMI.

ISOENZYMES

NV: 15-160 U/L (Male), 15-130 U/L (Female), CK-MB =<6% of total CK

After the onset of MI,CK-MB begin to rise within 4-8 hours, peaks at 12-24 hours, and returns to normal in 48-72 hours, with CK-MB >6% of the total

CK.

ASSAYS

Oliver-RosalkiMost commonly used method

pH: 6.8; 340nm

Creatine Phosphate + ADP ↔ Creatine + ATP

ATP + Glucose ↔ ADP + Glucose-6-Phosphate

Glucose-6-phosphate + NADPH+ ↔ 6-phosphogluconate + NADPH

HK

CK

G-6-PD

ISOENZYMES

AST has two isoenzyme fraction:

Cytoplasmic AST (predominant) Mitochondrial AST

NV: 5-37 U/L

After the onset of MI, AST rises within 6-8 hours, peaks at 24 hours, and return

to normal in 5 days.

ASSAYS

Karmen MethodMost commonly used

Uses malate dehydrogenase (MD)

pH: 8.8

Aspartate + α-ketoglutarate ↔ oxaloacetate + glutamate

Oxaloacetate + NADH + H+ ↔ malate + NAD+

AST

MD

ISOENZYMES

LD has five isoenzymes: LD1, LD2, LD3, LD4, LD5

LD1 (HHHH) = 17-17%Found in heart, RBCs, and kidneysRelatively abundant in cardiac muscle

LD2 (HHHM) = 27-37%Found in heart, RBCs, and kidneysGreater than I1 and the major LD

isoenzyme in healthy individuals

ISOENZYMES

NV: 100-225 U/L

After the onset of MI, LD begin to rise within 10-24 hours, peaks at

48-72 hours, and remains elevated for 10 days.

ASSAYS

Wacker MethodCommonly used method

340nm

Lactate + NAD+ ↔ Pyruvate + NADH + H+

LDH

The Rise, Peak, and Descent of Serum

Levels

ENZYME RISE PEAK NORMALIZE

CK 4-6 hours 12-24 hours 48-72 hours

AST 6-8 hours 24 hours 5 days

LD 10-12 hours 48-72 hours 10 days

The Rise, Peak, and Descent of Serum

Levels Serum levels in the episode of

myocardial infarction from its onset.

The Rise, Peak, and Descent of Serum

Levels

Anti- thrombotic drugs for MI

AspirinAn essential element in the management of

patients with MI because of its ability to inhibit platelet thromboxane A2 synthesis.

It is rapidly absorbed in the stomach and upper small intestine, reaching appreciable

plasma levels in 20 min and platelet inhibition in approximately 60 min.

The anti-platelet effect lasts for the life of the platelet (9-10 days).

Anti- thrombotic drugs for MI

Depyridamol-A pyrimidopyrimidine compound with antithrombic and vasolidating properties.

It activates the enzyme adenylate cylase by a prostacyclin-mediated effect on the platelet membrane.

Anti- thrombotic drugs for MI

At a more physiological concentrations, dipyridamole increases plasma adenosine

levels by inhibiting its uptake from vascular endothelium and erythrocytes, thereby

enhancing platelet adenyl cyclase activity.

Anti- thrombotic drugs for MI

Bivalirudin inhibits thrombin. It is utilized for anticoagulation to patients

with unstable angina who are undergoing PTCA.

HeparinAmplifies the activity of antithrombin III Prevents the conversion of fibrinogen to fibrin. Prevents re-accumulation of a clot after

spontaneous fibrinolysis.

Anti- thrombotic drugs for MI

EnoxaparinEnhances the inhibition of

thrombin through elevating the antithrombin III activity.

What is reperfusion injury?

Reperfusion Injury

This condition occurs when blood supply on a particular tissue or area of a tissue has been cut

off causing damage to tissue.Damage may vary depends on the intensity

of the infarct.

WHAT IS THROMBOLYTIC THERAPY?

This method is the most successful way of reducing the severity of the

damage caused by the myocardial infarction.

It removes the dangerous clots in the blood vessels through an injection of

clot-dissolving medications.

THERAPEUTIC ENZYMES: THROMBOLYTIC DRUGS

These enzymes are considered treatment for acute MI.

Thrombolytic Drugs are used to lyse (dissolve) blood clots (thrombi) thru tPA (Tissue

plasminogen activator) “streptokinase” by forming a cleaved product called plasmin.

THERAPEUTIC ENZYMES: THROMBOLYTIC DRUGS

Plasmin is a proteolytic enzymes that is capable of breaking the structural integrity of blood clots.

That is why thrombolytic drugs are also called “plasminogen activators

or “fibrinolytic drugs”.

THERAPEUTIC ENZYMES: THROMBOLYTIC DRUGS

There are three major classes of Fibrinolytic drugs:

Tissue plasminogen activator (tPA)

Streptokinase

Urokinase

While drugs in these three classes all have the ability to effectively dissolve blood clots, they

differ in their detailed mechanisms in ways that alter their selectivity for fibrin clots.

tPA

Tissue plasminogen activator produces clot lysis through the following sequence:

tPA binds to fibrin on the surface of the clot

Activates fibrin-bound plasminogen

Plasmin is cleaved from the plasminogen associated with the fibrin

Fibrin molecules are broken apart by the plasmin and the clot dissolves

Streptokinase

It is not a protease and has no enzymatic activity; however, it forms a complex with

plasminogen that releases plasmin.

Unlike tPA, it does not bind preferentially to clot-associated fibrin and therefore binds equally

to circulating and non-circulating plasminogen.

Therefore, SK produces significant fibrinogenolysis along with clot fibrinolysis

Urokinase

It is synthesized by the kidney that directly converts plasminogen

to active plasmin.

This therapeutic enzyme act as thrombolytic agent in the treatment of severe or massive deep venous thrombosis, pulmonary embolism,

myocardial infarction, and occluded intravenous or dialysis cannulas.

THERAPEUTIC ENZYMES: THROMBOLYTIC DRUGS

It is important to note that the efficacy of thrombolytic drugs depends on the age of

the clot.

Older clots have more fibrin cross-linking and are more compacted; therefore, older

clots are more difficult to dissolve.

THERAPEUTIC ENZYMES: THROMBOLYTIC DRUGS

For treating acute myocardial infarction, the thrombolytic drugs should ideally be given within the

first 2 hours.

Beyond that time, the efficacy diminishes and higher doses are

generally required to achieve desired lysis.

SUMMARY

Myocardial Infarction is the irreversible necrosis of heart muscle secondary to prolonged ischemia.

Atherosclerosis leads to myocardial infarction that forms large thrombus in the artery which will inhibit normal blood flow into the heart.

Diagnostic Enzymes: (CARDIAC MARKERS) Aspartate Aminotransferase (AST) Lactate Dehydrogenase (LDH) Creatine Kinase, CK-MB Troponin Myoglobin

SUMMARY

Isoenzymes are group of enzymes that catalyze the same reaction but with different variation in physical properties.

Order and Appearance: Myoglobin (1-4 hours) Troponin (2-6 hours) CK-MB (4-6 hours) AST (6-8 hours) LD (10-24 hours)

SUMMARY

Different assays are used for the measurement of enzyme levels in the serum.

Troponin and Myoglobin are proteins that are not enzymatic in nature but can still help in diagnosing MI.

Anti-thombotic drugs for myocardial infarction: Aspirin Depyridamol Bivalirudin Heparin Enoxaparin

SUMMARY

Reperfusion Injury occurs when the blood supply to an area of tissue is cut off.

Therapeutic enzymes (Thrombolytic/ Fibrinolytic drugs)Tissue plasminogen activation (tPA)StreptokinaseUrokinase

REFERENCES

Murray, R. K., Bender, D. A. et. al. 2009. Harper’s Illustrated Biochemistry. 28th ed. United States of America: McGraw-Hill Companies. 122-123, 126-128.

Harvey, R. A. 2010. Lippincott’s Illustrated Reviews: Biochemistry. 5th ed. Lippincott Williams and Wilkins.

Unknown. 1990. Acute Myocardial Infarction: Setting Priorities for Effectiveness Research. Washington DC: National Academy Press. 5-6.

Biswanger, H. 2011. Practical Enzymology. 2nd Ed. Wiley-VCH Verlag and Co.

REFERENCES

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Klabunde, R. 2009. Cardiovascular pharmacology concepts. Retrieved from:http://www.cvpharmacology.com/thrombolytic/thrombolytic.htm

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