Lec. 4 Clinical Enzymology PDF

Diagnostic Enzymology Lec : 4 Dr.Thulfiqar A. Mohammed  Introduction Enzymes{biocatalysts}: are substances which accelerate the chemical reactions in living organisms without itself being altered during the reactions. Enzymes acts on substrates and conv...

Diagnostic Enzymology Lec : 4 Dr.Thulfiqar A. Mohammed  Introduction Enzymes{biocatalysts}: are substances which accelerate the chemical reactions in living organisms without itself being altered during the reactions. Enzymes acts on substrates and convert them to products. Enzyme catalysis is very rapid; usually 1 molecule of an enzyme can act upon about 1000 molecules of the substrate per minute. ‘ Characteristics of the enzymes: 1-All enzymes are proteins and made of 16% of nitrogen. 2-They are precipitated by ammonium sulfate or trichloroacetic acid (protein-precipitating reagents). 3-They are water soluble. 4-They are sensitive to heat {optimum temperature is 10 °C}and strong acids{optimum pH 6-8}. ISO-Enzymes: they are physically distinct forms of the same enzyme activity.  Introduction Which are actively Functional secreted into plasma Enzymes Normally their levels are low and increasing Non-functional drastically during cell death and diseases Cofactors and coenzymes Some enzymes required an additional to non proteins component for its optimum activity. This group may be either metal ion so it is called cofactor or a complex organic so it is called coenzyme. Cofactors: metal ion (e.g. Mg2+,Fe, Zn …..etc.) that assists an enzyme in facilitating a chemical reaction Coenzymes: non-protein organic substance derived from a vitamin (e.g. NAD, TPP,FAD , FMN, pantothenic acids …..etc.) act as a transient carriers of specific functional groups that assists an enzyme in facilitating a chemical reaction Enzyme Inhibitors There are different chemicals have the ability to bind enzyme and alter their activity these chemicals called enzyme inhibitors. Inhibitors include drug , antibiotics ,toxin as well as many natural products of enzymes reaction. Two general class of these inhibitors are recognized according to weather the inhibitors binding is reversibly or irreversibly to enzyme molecule. 1.Reversible inhibtors: (Competitive inhibition, Noncompetitive inhibition Uncompetitive inhibition) 2.Irreversible inhibtors. The enzyme activity in plasma may be: The enzyme activity in plasma may be: 1.higher than normal, due to the proliferation of cells, an increase in the rate of cell turnover or damage or in enzyme synthesis (induction), or to reduced clearance from plasma, 2.lower than normal, due to reduced synthesis, congenital deficiency or the presence of inherited variants of relatively low biological activity – examples of the latter are the cholinesterase variants FACTORS AFFECTING RESULTS OF PLASMA ENZYME ASSAYS Analytical factors, including: 1. Substrate concentration. 2. Product concentration. 3. Enzyme concentration. 4. Reaction temperature. 5. Reaction pH. 6. Presence of activators or inhibitors. Non-disease factors Age Plasma AST activity is moderately higher during the neonatal period than in adults. Sex Plasma GGT activity is higher in men than in women. Plasma CK activity is also higher in males, probably in part due to their increased muscle bulk. Race/ethnicity Plasma CK activity is higher in black people and Afro- Caribbeans than in white people. Physiological conditions Plasma ALP activity rises during the last trimester of pregnancy because of the presence of the placental isoenzyme. Cardiac Biomarkers A biomarker is a clinical laboratory test which is useful in detecting dysfunction of an organ. They are used to : Early detection of myocardial infraction. Monitoring of the prognosis of the cardiac diseases. Prediction of the risk for cardiac diseases. These markers are used to diagnose acute myocardial infraction and congestive heart failure. The most common cardiac markers include : Creatine kinase {CKMB},cardiac troponin I{CTI},cardiac troponin T{CTT},and brain natriuretic peptide {BNP}. Other marks :lactate dehydrogenase {LDH},AST, high sensitive C reactive protein {hCRP}. CREATINE KINASE (CK) The function of this enzyme is converting the creatine to creatine phosphate. The iso-enzymes of the CK ,is CK-BB {CK1 } which is found in the brain and CK-MB{CK2} which is found in the cardiac and skeletal muscles ,CK-MM{CK3}which mostly found in the skeletal muscles. Normal serum value for CK is 15-100 U/L for males and 10-80 U/L for females. CK-MB is an important diagnostic tool for of AMl because of it highly specific for cardiac injury. The onset of raising of CK-MB is 3-6 hours ,peak levels reached within 12-24 hours and CK levels return to its baseline with 36-72 hours. CK-MB activity tests have been increasingly replaced by CK-MB mass assays that measure the protein concentration of CK-MB rather than its catalytic activity because serum CK-MB mass raises one hour earlier than CK-MB activity. CREATINE KINASE (CK) and troponins The ratio of CK-MB mass \CK-MB activity is more specific for cardiac injury ,if the ratio is ≥3 is an indication of AMI rather than muscle damage. They are used in monitoring of thrombolytic The CK is significantly high in muscular dystrophies {500-1500 U\L}. Additionally is also increased in crush injury ,fractures and cerebrovascular diseases. Cardiac troponins: They are not enzymes. They are found in the cardiac and skeletal muscles not in the smooth muscles. They are measured at the beginning of ischemia and monitor the patients. Troponins Troponin I is released into the blood within 4 hours after the onset of symptoms of myocardial ischemia; peaks at 14-24 hours and remains elevated for 3-5 days post- infarction. Troponin I (TnI) is only found in the myocardium making it extremely specific for cardiac disease and its concentration is much higher than CK-MB ,makes it sensitive to cardiac injuries. CTI is very useful as a marker at any time interval after the heart attack. It is not increased in muscle injury; whereas CK2 may be elevated in some muscle injury. Serum level of Troponin T (TnT) increases within 6 hours of myocardial infarction, peaks at 72 hours and then remains elevated up to 7-14 days. It specifically indicates the extent of the cardiac damage and estimates the size of cardiac infraction on 3-4 days after AMI. Lactate dehydrogenase{LDH} The function of the enzyme is catalyzation of pyruvate to lactate. Iso-enzymes of LDH include five and each have many subunits mainly H{heart }and M {muscles}. Isoenzyme Subunits Electrophoresis Activity at 60 for 30 minutes Location Percentage in the serum mobility LDH-1 H4 Fastest Heat stable Heart 30% LDH-2 H3M1 Faster Heat stable RBCs 35% LDH-3 H2M2 Fast Partially degradation Brain 20% LDH-4 H1M3 Slow Heat liable Liver 10% LDH-5 M4 Slowest Heat liable Skeletal 5% muscles LDH Normal value of LDH in serum is 100-200 U/L.  LDH level is 100 times more inside the RBC than in plasma, and therefore minor amount of hemolysis will result in a false positive test. Strenuous exercise will slightly increase the value. In myocardial infarction, total LDH activity is increased, while H4 iso-enzyme is increased 5-10 times more. Increase in total LDH level is seen in hemolytic anemias, hepatocellular damage, muscular dystrophy, carcinomas, leukemias, and any condition which causes necrosis of body cells.  Other marks for MIs Myoglobin: An oxygen-binding heme protein. It found in high concentration in cardiac and skeletal muscles and released in the plasma in result to the damage of these tissues. The serum myoglobin directly reflects the patient's muscle mass and, therefore, varies with gender, age, and physical activity. Myoglobin is not considered as long-term marker because it excreted in the urine due to its small size. Myoglobin is significantly more sensitive than CK and CK-MB activities during the first hours after chest pain onset: Onset :1-4 hours {if remains normal within 8 hours ,the MI is excluded }. Peak : 6-9 hours. Duration : 18-24 hours. If the patient admitted to hospital within 12-14 hours and patients with kidney disorders ,CK-MB is preferred to measured. Brain Natriuretic Peptide (BNP) The natriuretic peptide family consists of three peptides: atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), and C-type natriuretic peptide (CNP). ANP is produced primarily in the cardiac atria. BNP is present in human brain, but more in the cardiac ventricles. The active BNP is secreted by the ventricles of the heart in response to excessive stretching of heart muscle cells (cardiomyocytes). These natriuretic peptides defend against excess salt and water retention. Inactive form of BNP is pro-BNP which is converted to BNP in cardiac cells. In congestive heart failure ,ANP AND BNP are high and their concentrations are correlated to the extent of the ventricular dysfunction and pro-BNP is the best indicator. High BNP predict high mortality rates.  hs-CRP hs-CRP stands for high sensitivity for CRP. It measures the inflammation in the body. High levels of the hs-CRP is seen in the patients which have a future risk to the cardiovascular diseases. Concentration mg\L Risk < 1 mg\L Lowest risk 1-3 mg\L Intermediate risk 3 mg\L Highest risk Cholinesterase (ChE) Acetyl cholinesterase{true ChE}:It is found in the RBCs and nerve endings. Newly formed RBC will have high levels of ChE which is slowly reduced according to the age of the cell. Pseudo cholinesterase or type II ChE is nonspecific and can hydrolyze acyl esters. It is produced mainly by liver cells. Succinyl choline is a widely used muscle relaxant. It is a structural analogue of ACh, and so competitively fixes on post-synaptic receptors of ACh. Succinyl choline is hydrolyzed by the liver ChE within 2–4 minutes. If the enzyme is deficient ,the degradation will elongate for several hours and causes scolion apnea. Organophosphorus insecticides (Parathione) irreversibly inhibit ChE in RBCs.  Measurement of ChE level in RBCs is useful to determine the amount of exposure in persons working with these insecticides. Causes of decreased plasma cholinesterase activity - Hepatic parenchymal disease (reduced synthesis). - Ingestion, or absorption through the skin, of such anticholinesterases as organophosphates. -Inherited abnormal cholinesterase variants, with low biological activity. - Pregnancy. Causes of increased plasma cholinesterase activity - Recovery from liver damage (actively growing hepatocytes). - Nephrotic syndrome. Suxamethonium sensitivity The muscle relaxants suxamethonium (succinyl choline, ‘scoline’) and mivacurium are usually broken down by plasma cholinesterase, and this limits the duration of their action. Giving these agents to patients with a low cholinesterase activity (usually due to an enzyme variant) may result in a prolonged period of apnoea (‘scoline apnoea’); such patients may need prolonged ventilatory support after an operation. The abnormal cholinesterase variants may be classified by measuring the percentage inhibition of the enzyme activity by dibucaine (dibucaine number) or by fluoride (fluoride number). A low dibucaine number and/or fluoride number with or without low plasma activity is suggestive of a cholinesterase variant, for example A, K, J, F types. There is also a silent gene type. The identification of patients susceptible to suxamethonium, and of their affected relatives, is important. Close blood relatives should be traced and investigated to identify their genotype, and so to predict the chance of future anaesthetic risk. All affected individuals should carry a warning card or a ‘Medic Alert’ and should notify the anaesthetist if they require an anaesthetic Amylase Normal serum value is 50-120 IU/L. The main function is converting the polysaccharides to simpler sugars. They produce by pancreas and salivary glands. There are three forms of amylase enzyme include : α-amylase {which is found in the mammalians } and it works effectively at pH (6-7) β-amylase {which is found in the plants and micro-organism(yeasts ,molds ,and bacteria)}.Its activity is optimum at pH (4-5). γ-amylase {which is found in the animals and micro-organsmis},it cleaves glycosidic bonds in extremely acidic media pH is 3. Amylase Amylase concentration is increased about 1000 fold in acute pancreatitis reaching its highest values after 5-12 days of inset of disease and the values are returning to the baseline within 2-4 hours. Urinary concentration of the amylase is