Plasma Enzymes PDF

By Assoc Prof Dr Gnanajothy Ponnudurai Learning outcomes List the sources of circulating enzymes Describe the tissue specificity of the enzymes Describe the enzymes of clinical importance Describe the serum enzymes in myocardial infarction Introduction on enzymes  Biological catalysts produ...

By Assoc Prof Dr Gnanajothy Ponnudurai Learning outcomes List the sources of circulating enzymes Describe the tissue specificity of the enzymes Describe the enzymes of clinical importance Describe the serum enzymes in myocardial infarction Introduction on enzymes  Biological catalysts produced by living cells.  Protein in nature  Specific – each enzyme can catalyse only I type of reaction  Required in small quantity  Intracellular enzymes – enzymes produced by cells of a particular tissue and function within that cell. Eg: enzymes of glycolysis, TCA cycle, fatty acid synthesis  Extracellular enzymes – Enzymes produced by cells of a particular tissue from where these are liberated for use in other tissue. Eg: proteolytic enzymes of GI tract (trypsin, chymotrypsin)  Introduction on enzymes Enzymes can be powerful diagnostic tool. The following knowledge are important. i. enzyme reactions ii. sources of enzymes in tissues (where certain enzymes are concentrated in the body) iii. how their levels in blood changes in disease Important diagnostic questions! How does plasma Has tissue enzyme activity Which tissues damage occured, change during have been if so, what is its the course of the damaged? extent? disease? Sources of circulating enzymes  Some enzymes are formed specifically for release into circulation.  Normally present in plasma and have specific function to perform.  Mostly synthesised in liver and enter blood. Eg : Lipoprotein lipase, clotting factors  Sources of circulating enzymes  Most enzymes are present in small quantity in blood compared to tissues.  Small amounts of intracellular enzymes present in blood due to normal cell turnover.  Damage to cells results in increased amounts of intracellular enzymes released into the blood. Other possible causes of increase include:  Increased cell turnover (eg during active growth, tissue repair)  Cellular proliferation (eg neoplasia)  Increased enzyme synthesis (enzyme induction by disease or drug)  Decreased clearance Enzyme units One international unit (One IU) is the amount of enzyme that will convert one micromole of the substrate per minute per liter of sample and is abbreviated as U/L. Enzyme level and tissue specificity Enzymes of high specificity - found predominantly in one type of tissue. Enzymes of moderate specificity - more widely distributed in the body. Enzymes of low specificity are found everywhere. Enzyme level and tissue specificity Enzyme Principle tissue(s) High specificity Acid phosphatase Erythrocytes, prostate Alanine aminotransferase Liver Amylase Pancreas, salivary gland Lipase Pancreas Moderate specificity Aspartate Liver, heart, skeletal aminotransferase muscle Creatine kinase Heart, skeletal muscle, brain Low specificity Alkaline phosphatase Liver, bone, kidney …. Lactate dehydrogenase All tissues Enzyme level and tissue specificity  A major disadvantage in the use of enzymes for diagnosis of tissue damage is their lack of specificity for a particular tissue.  Many enzymes common to more than one tissue. Increase in plasma level of one enzyme could reflect damage to any one of these tissues.  Enzyme level and tissue specificity  Overcome difficulty by the use of : i) Enzyme combinations  Many tissues contain (and thus release when they are damaged) 2 or more enzymes in different proportions.  Alanine and aspartate aminotransferases are both present in cardiac, skeletal muscle and hepatocytes, but there is only very little alanine aminotransferase in cardiac and skeletal muscle. ii) ii) Isoenzymes  Some enzymes exist in different forms (isoforms/isoenzymes).  Individual isoenzymes characteristic of particular tissue. Isoenzymes Different forms of the same enzyme catalysing the same reaction Differ in their structure, physical and chemical properties Eg electrophoretic mobility Eg of isoenzymes: Lactate dehydrogenase has 5 isoenzymes Creatine kinase has 3 isoenzymes Enzymes of clinical importance Creatine kinase (CK) Aspartate aminotransferase (AST) Alanine aminotransferase (ALT) Lactate dehydrogenase (LDH) Alkaline phosphatase (ALP) Acid phosphatase (ACP) Gamma – glutamyl transferase (GGT) Amylase Lipase  Creatine kinase (CK) CK Creatine  Creatine phosphate Creatine phosphate is a high energy compound and acts as a ready source of energy in the muscle. Is a dimer. Two monomers, M and B. Three isoenzymes: MM, BB and MB Isoenzyme Subunits Source CKBB BB Brain CKMB MB Heart muscle CKMM MM Heart and skeletal muscle  Creatine kinase (CK)  Skeletal muscle :Has very high total CK. Over 98% is CKMM, less than 2% CKMB  Cardiac muscle: Also has a high total CK. 70-80% is CKMM, 20-30% is CKMB  Brain: Contain less CK, ofter CKBB. CKBB rarely appears in plasma, not of diagnostic imp  CK present in normal plasma is MM isoenzyme.  CKMM increases in skeletal muscle injury/disease  CKMB increases in myocardial infarction and other heart diseases  CKBB increases in head injury and diseases of the brain. Aspartate aminotransferase & Alanine aminotransferase Two amino transferases are used in diagnosis: aspartate aminotransferase (AST) and alanine aminotransferase (ALT) T stands for transaminase, this term has been replaced by aminotransferase , abbreviation not changed. Both enzymes are widely distributed in body tissues Sources of AST: Heart, liver, skeletal muscle, RBC Sources of ALT: Liver is the major source. Aspartate aminotransferase & Alanine aminotransferase AST level increases in Heart muscle disease – myocardial infarction Liver disease Muscle diseases ALT increases in all types of hepatocellular diseases such as viral hepatitis, cirrhosis, liver cancer In liver diseases, serum level of both AST and ALT increases. ALT is specific for the liver because it is present only in the liver. Lactate dehydrogenase (LDH) LDH is present in almost all the tissues in the body High concentrations found in heart and liver. Significant amounts present in erythrocyes. Skeleal muscle and kidney alco contain considerable amounts. LDH exist as a tetramer. Two monomers, H and M gives 5 isoenzymes. Lactate dehydrogenase (LDH Isoenzyme Source LD1 Heart, RBC LD2 Heart, RBC LD3 Liver, lung, spleen LD4 Liver, lung, spleen LD5 Skeletal muscle Hemolysed serum samples should not be used because it affects the LDH level (it will be high due to release of LD1 and LD2 from RBC) Alkaline phosphatase (ALP) Present in all tissues in the body. Present in high concentration in liver, bone, placenta, kidney, intestinal epithelium. Specific isoenzyme of ALP present in each tissue. Precise biochemical role not known. In many tissues it is attached to cell membrane, suggesting association between ALP and membrane transport.  Alkaline phosphatase (ALP) Significant increase in plasma ALP for physiological reasons:  Pregnancy  Release of ALP from placenta causes plasma ALP to rise in 2nd and 3rd trimesters  Infancy and childhood  Plasma ALP high at birth.  Falls rapidly thereafter, but remains 2-3 times the normal adult level.  Rises again during puberty due to osteoblastic activity during growth spurt.(Osteoblast secrete ALP)  Falls to the adult level as bone growth stops. Alkaline phosphatase (ALP) Changes in ALP activity due to disease: ALP commonly used in investigation of liver and bone diseases. In liver disease, increase in ALP is most frequently seen in cholestasis (obstruction of bile duct). Hepatocellular damage causes relatively little increase. In bone disease, plasma ALP is increased in when there is increase in osteoblastic activity eg.rickets, osteomalacia. Acid phosphatase (ACP) Almost every body tissue contains some amount of acid phosphatase, usually located in lysosomes. The prostate gland is the riches source. Other sources are erythrocytes, platelets and bone. Seminal fluid also contain significant levels, a finding of importance in rape cases. Gamma –glutamyl transferase (GGT)  Present in high concentration in the liver and bile duct, kidney and pancreas, prostate gland  Greatest diagnostic importance is in liver disease.  In liver disease, plasma GGT increases parallel with ALP, ie. it rises most when there is cholestasis.  Plasma GGT is raised more that ALP in hepatocellular damage.  Hepatic synthesis of GGT is induced by several drugs and alcohol.  Plasma GGT is raised in the absence of liver disease in many patients taking the  anticonvulsant drugs phenytoin and phenobarbital  rifampicin, used in treatment of tuberculosis  The increased plasma GGT is not due to cell damage but to an increase in enzyme production within cells. Gamma –glutamyl transferase (GGT) Plasma GGT is frequently very high in patients with alcoholic liver disease. Plasma GGT can be elevated in heavy alcohol drinkers, in the absence liver damage, due to enzyme induction. Plasma GGT can remain elevated for up to 3-4 weeks following abstinence from alcohol, even in the absence of liver damage. Plasma GGT is not raised in bone disease. Plasma GGT can help identify tissue of origin of a raised plasma ALP. Amylase Cleaves starch into maltose Present in exocrine pancreas and salivary gland. Isoenzymes differentiated by electrophoresis. Pancreatic (P-isoamylase) Salivary gland (S-isoamylase) Plasma amylase level is usually increased in acute pancreatitis, pancreatic injury, carcinoma of pancreas, salivary lesions Amylase Amylase is a relatively small molecule and is rapidly excreted by the kidney. (increase serum level in renal failure) In mild pancreatitis, serum level may be normal due to rapid clearance but increased urinary amylase. Amylase Macroamylasaemia  rare disorder,  part of plasma amylase combines with other proteins (immunoglobulin) forming complex called macroamylase.  macroamylase has much higher molecular weight  renal clearance is reduced  serum amylase levels appears elevated.  can misleadingly suggest the presence of clinical cause Lipase  Highest concentration of lipase is in pancreatic tissue and secretions.  No lipase found in muscle, liver, kidney or lung.  Primary diagnostic role of lipase is in the assessment of acute pancreatitis.  After the initial attack, the lipase levels in serum gradually rise over a period of 2-4 days.  This frequently paralleles the change seen with amylase.  If chronic pancreatitis exist, lipase determination is of little value. Loss of pancreatic tissue results in decrease in ability to produce and release enzyme into the blood.  Serum enzymes in myocardial infarction Plasma enzymes that assist in diagnosis of myocardial infarction: CK, CKMB, AST, LDH Time course of enzyme changes: Initial lag phase of at least 3 hrs (enzyme activities normal) Plasma enzymes rise rapidly and peaks 18-36 hrs Activities return to normal Rapid rise and fall of CKMB Relatively prolonged rise of LDH Thank you