enzymes 4

Reaction catalyzed: CK 𝐶𝑟𝑒𝑎𝑡𝑖𝑛𝑒+𝐴𝑇𝑃 ↔ 𝐶𝑟𝑒𝑎𝑡𝑖𝑛𝑒 𝑃ℎ𝑜𝑠𝑝ℎ𝑎𝑡𝑒+𝐴𝐷𝑃 Nomenclature: Transferase (class) Creatine Kinase (practical name) CK (abbreviation) Activators: Mg2+ ( same as ALP & ACP) Inhibitors: Mg2+( if in high concentrations) Main function is in muscle where it is involved in formation of high energy storage compound (creatine phosphate ) and generation of ATP. Slightly higher CK values in males due to an increased muscle mass.

Most common method: reverse rxn proceeds 2-3x faster than the forward rxn & theres less interferences from side rxns CK 𝐶𝑟𝑒𝑎𝑡𝑖𝑛𝑒 𝑝ℎ𝑜𝑠𝑝ℎ𝑎𝑡𝑒+𝐴𝐷𝑃 ↔ 𝐶𝑟𝑒𝑎𝑡𝑖𝑛𝑒+𝐴𝑇𝑃 ℎ𝑒𝑥𝑜𝑘𝑖𝑛𝑎𝑠𝑒 𝐴𝑇𝑃+𝐺𝑙𝑢𝑐𝑜𝑠𝑒 ↔ Glucose−6−phosphate+ADP 𝐺− 6−𝑃𝐷 𝐺𝑙𝑢𝑐𝑜𝑠𝑒− 6− 𝑝ℎ𝑜𝑠𝑝ℎ𝑎𝑡𝑒 +𝑁𝐴𝐷𝑃+ ↔ 6−𝑃ℎ𝑜𝑠𝑝ℎ𝑜𝑔𝑙𝑢𝑐𝑜𝑛𝑎𝑡𝑒+𝑁𝐴𝐷𝑃𝐻 G-6-PD = Glucose-6-Phosphate dehydrogenase measuring an Increase in absorbance @340 nm, which is directly proportional to CK activity. optimal pH 6.8

• Three isoenzymes each with dimers (subunits) • Dimers consist of the 2 subunits M and/or B Memory Aid for the highest concentration: CK-MM = Much More CK1 = CK-BB ◦ Fastest (most anodal) in electrophoresis ◦ Found in the brain ◦ Usually undetectable CK2 = CK-MB ◦ Found in heart and diaphragm ◦ Undetectable to trace amounts; <6% of total CK ◦ Increase in CK-MB is the most specific indicator of myocardial damage CK3 = CK-MM ◦ Slowest of the three in electrophoresis ◦ Found in skeletal muscle ◦ Major isoenzyme; 94 - 100% of total CK

Macro-CK ◦Unusual immunoglobulin-enzyme complex (usually IgG + CK-BB) ◦No clinical significance CK-MI ◦Mitochondrial CK released during extensive damage to cell walls ◦Indicator of severe illness ◦Not present in normal serum

• Electrophoresis - reference method • Ion exchange chromatography • Immunoassays: ◦Immuno-inhibition assay can be used to measure CK2 (MB) ◦Total CK measured then anti-M applied which inhibits all M activity in CK3 (MM) and ½ of CK2 (MB) – assumes no CK1 (BB) ◦Difference of two = amount of B chain ◦Multiply by 2 = CK-MB * just know there is anti-M that inhibits M subunit activity

Evaluation of cardiac and skeletal muscle disorders CK1 (CK-BB) increased in: ◦ CNS disorders - damage to the blood/brain barrier allows enzyme to be released ◦ Tumors ◦ Childbirth - placenta & uterine tissue have CK-BB CK2 (CK-MB) increased in: ◦ Cardiac injury (e.g. AMI) CK3 (CK-MM) increased in: ◦ Heart and skeletal muscle damage ◦ After physical activity (up to 48 hrs afterwards) ◦ After intramuscular injections (up to a week afterwards) Total CK increases in most muscle diseases ◦ Marked increase in muscular dystrophy Esp. Duchenne muscular dystrophy (50 - 100X normal

• Avoid hemolysis • RBCs contain adenylate kinase (AK) which produces ATP • This ATP can then take part in the reaction and cause falsely elevated CK results

• CK-MB is the first enzyme to rise after an AMI • Rise 4-8 hours after onset of pain • Peaks 12-24 hours • Normal 2-3 days • CK-MB > 6% of total CK (normally < 6%)Enzyme Elevation Peak Return to Normal CK 4 - 8 hours 24 hours 3 days AST 6 8 hours 24 hours 5 days LD 12 24 hours 72 hours 10 days

Anatomy of the Heart • The heart is enclosed in a sac called the pericardium. • Cardiac wall is composed of 3 layers: 1. Epicardium (outer layer) • Coronary arteries are on epicardium • Middle layer • Endocardium (inner layer) • Most susceptible to myocardial ischemia

• The heart has 4 chambers: • Left and right atria (upper chambers) • Left and right ventricles (lower chambers) • The heart pumps blood by contracting and relaxing striated muscle fibers. • Proteins in the muscle fibers regulate contractions: • Actin • Myosin • Troponins

• Acute coronary syndrome (ACS) is a sudden cardiac disorder that varies in severity. • Includes: - Angina (chest pain on exertion with reversible tissue injury) - Unstable angina (with minor myocardial injury) - Myocardial infarction (with extensive tissue necrosis -irreversible) • Most conditions are caused an acute event in the coronary artery that obstructs circulation to a region in the heart.

• Occurs when there is a sudden reduction in blood circulation to myocardial tissue. • This results in: - Ischemia - lack of blood supply/O2 - Necrosis - death of cells - Release of cellular contents - such as cardiac enzymes & proteins into the bloodstream • Symptoms of decreased blood flow • Pain • Clammy skin • Shortness of breath • Nausea

• Electrocardiograms (ECGs) can record variations in electrical potential caused by the excitation of the heart muscle. • In a healthy individual, each cardiac cycle’s electrical potential changes are similar to every other cycle and include three major components: -Atrial depolarization (P wave) -Ventricular depolarization (QRS complex) -Repolarization (ST segment and T wave)

• A patient with any type of myocardial infarction in which the ST segment is elevated in one or several leads of the ECG • ECG pattern seen in this case is as follows: Normal Hours after infarction, the ST segment becomes elevated Hours to days later, the T wave inverts and the Q wave becomes larger Days to weeks later, the ST segment returns to near normal Weeks to months later the T wave becomes upright again, but the large Q wave may remain

• A myocardial infarction in which the ST segment is not elevated in any leads of the ECG. • Magnitude of cell death is less than STEMI. • No elevation of the ST segment with increased troponin levels is considered NSTEMI

• Angina is a condition marked by severe pain in the chest, often also spreading to the shoulders, arms, and neck, caused by an inadequate supply of blood to the heart. • Unstable ischemia with no evidence of cardiac necrosis (no increase in troponins) is classified as unstable angina. • Unstable angina occurs unpredictably or suddenly increases in severity or frequency

• Atherosclerosis is the major cause of acute coronary syndrome. • Deposits of fatty material (plaques) form on the inner lining of the coronary arteries that feed the surface of the heart. • Plaques are composed of lipid, cell debris, smooth muscle cells, collagen, and sometimes calcium. • These plaques narrow the artery’s lumen • Atherosclerotic plaque (atheroma) can break open and form blood clots within the vessel which will further block or completely stop blood flow. • Leads to myocardial infarction and ischemic stroke • Irreversible cardiac injury occurs when the occlusion is complete for 15-20 minutes. • Restoring blood flow in first 60-90 minutes allows maximal salvage of tissue. • Patients with STEMI are given clot-dissolving agents (thrombolysis)

• Syndrome characterized by ineffective pumping of the heart which can lead to accumulation of fluid in the lungs. • Characterized by breathlessness and abnormal sodium and water retention, often leading to edema. • Because heart is not able to pump sufficient blood, organs and other tissues do not receive enough oxygen and nutrients to function properly. • Natriuretic peptides are biomarkers that will progressively increase with the severity of disease.

• Cardiac biomarkers are biological compounds whose measurement is useful in the diagnosis or detection of cardiac disease • Useful when patients have nondiagnostic ECGs. • Characteristics of a clinically useful cardiac marker for detecting AMI:- Must be rapidly released from heart into circulation. - Analytical assays must be rapid and able to measure low concentrations in blood samples. - Should persist in the circulation for several days to provide a late diagnostic time window.

• Cardiac biomarkers are used to: • Detect cardiac disorders - Detect risk of developing cardiac disorders - Monitor the disorder - Predict the response of a disorder to treatment

American Association of Clinical Chemistry (AACC) proposed elements for POC guidelines: • Members of emergency departments, primary care physicians, cardiologists, hospital admin, and clinical lab staff should work collectively to develop accelerated protocol for use of biomarkers in evaluation of patients with possible ACS. • Quality assurance measures should be used with monitoring to reduce medical errors and improve patient treatment. • Laboratory should perform biomarker testing with maximum TAT of 1 hour; optimally 30 minutes. • If 1-hour TAT is not possible, should consider implementing POC assays • Performance specifications and characteristics for central lab and POC assays should not differ. • POC assays should provide quantitative results

• CK, AST & LD used • Amount of increase roughly equal to size of infarct • CK and LD isoenzymes are most specific and sensitive for interpretation ◦↑ CK-MB ◦LD-1 > LD-2 (flipped pattern)

• CK-MB ≥ 6% of total CK, LD-1>LD-2 (flipped pattern)• Confirms AMI • Found in 80-85% AMI patients • CK-MB ≥ 6% of total, LD-2> LD-1 • Some form of myocardial damage • Not confirmatory • CK-MB < 6% of total • No myocardial infarct • CK-MB < 6% of total; LD-1>LD-2 • No myocardial damage • Seen in non-cardiac disorders (intravascular hemolysis, renal cortex infarct, megaloblastic anemia, hemolyzed sample)

• Other proteins (not enzymes) • Include: ◦Myoglobin ◦Troponins ◦Natriuretic peptides • These are used in the evaluation of AMI and CHF