lecture (1) Clinical Enzymology.pdf

The Strategy for Teaching and learning is extracted from the Egypt Vision 2030 which is aligned with the sustainable UN development goals of the united nations (UN SDGs) SDGs Universal healthcare system capable of improving healt...

The Strategy for Teaching and learning is extracted from the Egypt Vision 2030 which is aligned with the sustainable UN development goals of the united nations (UN SDGs) SDGs Universal healthcare system capable of improving health conditions A high-quality education and training system Clinical Biochemistry Lecture 1 Clinical Enzymology Dr. Hameis Sleem Learning Objectives ▪ By the end of the lecture, student will be able to: Determine what is an enzyme. Define clinical enzymology. Classify enzymes in plasma. Point out the criteria for selection of enzymes for testing. Outline the assessment of cell damage & proliferation. List factors affecting enzyme activity. Describe how can we improve enzyme analysis. Define isoenzymes. List factors causing changes in enzyme analysis. Illustrate different enzyme patterns in different diseases. What is an Enzyme? An enzyme is a protein that catalyzes one or more specific biochemical reactions. Changes in plasma enzyme activities help to detect and localize tissue cell damage or proliferation, or to monitor treatment and progress of disease.  Why is it Easier to Measure Enzyme Activity than Protein Concentration? ▪ Because enzyme activity in body fluids can be determined easily by changes in substrate or product concentrations.  What is meant by Clinical Enzymology ? ▪ Measurement of some selected enzymes in specimens (usually of blood especially plasma ) for detection and monitoring of diseases.  PLASMA ENZYMES Enzymes present in plasma can be classified into 2 types Functional Plasma enzymes Non-functional plasma enzymes Present in plasma at higher concentration than Present in tissues at higher concentration than tissues plasma They function in plasma Do not have any function in plasma Mostly synthesized by the liver Mostly synthesized by liver, skeletal muscle, heart, brain etc Usually decreased in disease conditions Usually increased in disease conditions Eg. Clotting enzymes, lipoprotein lipase Eg. Creatine kinase, Alanine transaminase etc Measurement of these enzymes in plasma can be used to assess cell damage and proliferation i.e. diagnosis of disease.  “Non-Functional” Plasma Enzymes ▪ Clinical chemists are principally concerned with changes in activity in serum enzymes that are intracellular and that are normally present in serum in low activities. These are termed “non-functional plasma enzymes”. ▪ By measuring changes in the activities of these enzymes in disease , it is possible to infer the location and nature of pathological changes in tissues. What are the Criteria for Selection of an Enzyme to Test for a Disease?  Selection of Enzyme Tests ▪ Depend on a number of factors, most important one is the distribution of enzymes among the various tissues. ▪ It is important to emphasize that not all intracellular enzymes are equally valuable as indicators of cellular damage. ▪ Isocitrate dehydrogenase although its activity is high in heart muscle , after a myocardial infarction, it is rapidly inactivated on entering the vascular compartment. ▪ Ornithine carbamyltransferase ▪ It is an enzyme of the urea cycle and is totally liver-specific. Liver: blood ratio of about 100,000:1;thus, even minor degrees of hepatocyte damage should create a readily detectable elevation in blood levels. ▪ Yet this enzyme has not used in clinical enzymology, possibly because of the inconvenience of the assay and a lack of clinical experience with its results. ▪ Factors, other than tissue distribution would also define the enzymes of clinical interest e.g.: rate of disappearance from blood, ease of assay, cost of assay, quantity in blood. Distribution of Diagnostically Important Enzymes Enzyme Principal Sources Principal Clinical Applications Acid phosphatase Prostate, RBCs Carcinoma of prostate Alanine Liver, skeletal muscle, heart Hepatic parenchymal disease aminotransferase (ALT) Aldolase Skeletal muscle, heart Muscle diseases Amylase Salivary glands, pancreas, ovaries Pancreatic diseases Aspartate Liver, skeletal muscle, heart, kidney, Myocardial infarction, hepatic parenchymal disease, aminotransferase RBCs muscle disease (AST) Cholinesterase Liver Organophosphorus insecticide poisoning, hepatic parenchymal diseases Creatine kinase (CK) Skeletal muscle, brain, heart, smooth muscle Myocardial infarction, muscle diseases g-Glutmyltransferase (GGT) Liver, kidney Hepatobiliary disease, alcoholism Lactate Heart, liver, skeletal muscle, RBCs, platelets, Myocardial infarction, haemolysis, hepatic parenchymal dehydrogenase lymph nodes diseases (LDH)  How Can We Assess Cell Damage & Proliferation ? The rate of enzyme release from damaged cells determines the extent of cell damage. In the absence of cell damage, the rate of release depends on: 1. The rate of cell proliferation. 2. Degree of induction of enzyme synthesis. 3. The rate of enzyme clearance from the circulation. 4. Obstruction to ducts (eg. pancreatic duct and bilary ducts).  What Are The Factors Affecting Enzyme Activity? ▪ Factors that cause an increase in enzyme activity : 1. Proliferation of cells (an ↑ in the rate of cell turnover or damage). 2. Increase in enzyme synthesis. 3. Decrease clearance from plasma. This occurs also in the presence of Macromolecules for example in macroamylasaemia where amylase form complexes with large molecules like Ig, so cannot be excreted. Examples of other enzymes are; LDH, ALP or CK. 4. Moderate exercise, or a large I.M injection, may lead to a rise in plasma CK. 5. Some drugs, such as phenobarbitone, may induce synthesis of the microsomal enzyme, gamma glutamyltransferase (GGT) What Are The Factors Affecting Enzyme Activity? ▪ Factors that cause a decrease in enzyme activity : 1. Decrease synthesis of enzymes. 2. Congenital deficiency.(Congenital disorders can be inherited or caused by environmental factors). 3. Presence of inherited variants.  How Can We Improve Enzyme Analysis? 1. Estimation of more than one enzyme: Many enzymes are widely distributed, but their relative concentrations may vary in different tissues. Eg. ALT & AST are abundant in the liver, the concentration of AST is much greater than that of ALT in heart muscle 2. Serial enzyme estimations : The rate of change of plasma enzyme activity is related to a balance between the rate of entry and rate of removal from the circulation. A persistently raised plasma enzyme activity is suggestive of a chronic disorder or occasionally of impaired clearance. ▪ Eg. ALT and LDH are predominantly located in cytoplasm, whereas AST occurs in both mitochondria and cytoplasm. Different disease processes in the same tissue may affect the cell in different ways, causing alteration in the relative plasma enzyme activities. 3. Isoenzymes determination : Different isoenzymes in plasma may arise from different tissues and their detection may give clues to the site of pathology. Examples: Alkaline phosphatase isoenzymes may distinguish between bone and liver disease. A specific isoenzyme of creatine kinase (CK- MB) is useful in early detection of myocardial infarction. Isoenzymes  What are the Factors causing Variations in Plasma Enzyme Assays ? 1. Analytical factors. 2. Biological factors. ▪ Pregnancy ALP ↑ during the last trimester of pregnancy. Several enzymes, such as the transaminases and CK, ↑ moderately during and after labour. ▪ Age AST and bilirubin is ↑ during the neonates. ALP of bony origin is ↑ in children and elderly. ▪ Sex GGT is ↑ in men than in women.  Plasma Enzyme Patterns in Diseases Acute myocardial Liver Diseases Muscle Enzymes in Malignancy Hematological infarction (AMI) Disease Disorders CK (CK-MB) AST CK-MM ACP ↑ in prostate cancer. ↑of LDH may be in LDH (LDH1) megaloblastic ALT ↑ in LDH1 & AST. anemia and ALP transaminase activity leukemia and in GGT in any malignancy. other conditions in which bone LDH Transaminase and ALP are marrow activity is used to monitor treatment abnormal. of malignant disease.