1 major enzymes of diagnostic interest dr. essam h. jiffri

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Major Enzymes of Diagnostic Interest

Dr. Essam H. Jiffri

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Phosphatases

Acid Phosphatase

- The richest source of acid phosphatase is the prostate, significant amounts are also found in erythrocytes, liver, spleen and platelets.

- Diagnostically, acid phosphatase measurements are used for monitoring metastatic carcinoma of the prostate serum levels .

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Acid Phosphatase

- Some acid phosphatase is released into the circulation when the prostate is examined per rectum (P.R) and blood should be taken before this examination.

- Serum acid phosphatase may be increased through nonprostatic causes, these include haemolysis, bone disease, particularly Paget's disease and metastatic carcinoma of the breast.

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Acid Phosphatase

Prostate-Specific Antigen

- Prostate-specific antigen (PSA) found in prostatic tissue and is raised in serum in a higher proportion in cases of metastatic carcinoma than acid phosphatase

- It is a more sensitive but less specific indicator of metastatic prostatic carcinoma.

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Alkaline Phosphatase

- Alkaline phosphatase is found in liver, bone, intestine, placenta and kidney, the main sources of serum enzyme are the hepatobiliary tree and osteoblasts.

- Physiologically increased levels are seen during periods of active bone growth, particularly in infants and at puberty.

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- Values increase during the second and third trimesters of pregnancy to about twice those normally seen in adults.

- Pathologically increases in serum alkaline phosphatase occur mainly in hepatobiliary disease and bone disease.

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-To identify the tissue of origin by determining alkaline phosphatase isoenzymes or by estimating the activity of another enzyme, usually Gamma-glutamyl transferase, which rises in parallel with biliary alkaline phosphatase.

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- Alkaline phosphatase activity in serum is usually estimated to detect increased levels, but markedly reduced levels are found in the inherited condition (hypophosphatasia), which is caused by defective bone calcification.

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Transaminases

Aspartate Aminotransferase

- Aspartate aminotranferase (AST) is widely distributed, the heart, liver, skeletal muscle and kidney being rich sources.

- Smaller amounts are found in erythrocytes and slight increases can occur in haemolysis.

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Transaminases

Aspartate Aminotransferase

- The major diagnostic applications are in the investigation of myocardial infarction, liver disease and muscle disease.

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Transaminases

Alanine Aminotransferase

- Alanine aminotransferase (ALT) is also widely distributed, the largest amounts occur in liver.

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Transaminases

Alanine Aminotransferase

- Smaller amounts occur in the heart and ALT usually remains normal following myocardial infarction unless congestive cardiac failure occurs, causing release from the liver.

- ALT is more specific for liver disease than AST.

Abnormalities of AST and ALT in various disease states

SkeletalMuscleInjury

AMICHFHepatitisCirrhosisBiliaryObstruction

AST↑ or ↑↑↑ or ↑↑↑ or ↑↑↑↑↑↑↑

ALT→→↑ or ↑↑↑↑↑↑↑

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Gamma-glutamyl Transferase

- Gamma-glutamyl transferase (GGT) is found in several tissues, the kidney being the richest source.

- Significant amounts are present in the liver and pancreas, the major diagnostic application of GGT measurements in the investigation of hepatobiliary disease.

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- Elevations in serum levels (70-80%) of patients who abuse alcohol, with more marked elevations occurring in the presence of alcoholic liver disease.

- Gamm-glutamyl transferase is a less sensitive indicator of hepatocellular disease than transaminases but high serum levels occur in cholestasis.

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- Serum GGT activity sometimes increases following myocardial infarction and in congestive cardiac failure, this is probably due to hepatic congestion.

Amylase

- Amylase is a digestive enzyme, hydrolyzes glycosidic bonds in polymers of glucose, such as starch and glycogen, to produce maltose and other polysaccharides and dextrins.

- Amylase is produced by the pancreas and salivary glands and its main diagnostic application is in the investigation of acute abdominal pain.

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Amylase

- The main source of elevated serum amylase activity is the pancreas.

- Conditions causing increased levels of amylase:o Pancreatitiso Renal insufficiencyo Ovarian malignancyo Ectopic pregnancyo Salpingitiso Lung carcinomao Cardiac surgeryo Mumps

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Amylase

- Serum amylase activities greater than 10 times the upper limit of normal are diagnostic of acute pancreatitis.

- Elevated amylase activity may also be due to macroamylasemia (amylase is bound to immuno-globulin typically IgG in serum).

- Patients with macroamylasemia evaluated using amylase:creatinine clearance ratio (ACCR).

- The ACCR is typically increased in acute pancreatitis.

Lipase

- Lipase is also a digestive enzyme secreted by the pancreas.

- Catalyzes the hydrolysis of ester bonds in triglycerides to produce fatty acids and 2-acylglycerol.

- Lipase along with amylase is utilized in the diagnosis of pancreatitis.

- In the past, amylase was the test of choice for the diagnosis of pancreatic disease.

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Lipase

- Lipase is now considered to be more sensitive and specific than amylase as a marker of pancreatitis.

- In patient with acute pancreatitis, lipase increased sooner and usually remains elevated for a longer period of time compared to amylase.

- Pancreatic lipase has at least three isoforms.- Lipase isoforms provide more accurate diagnostic

information than the measurement of total enzyme activity.

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Lipase

- Lipase in the peripheral circulation is removed via glomerular filtration and is completely reabsorbed by proximal tubule and not normally excreted in urine.

- In patient with acute pancreatitis, lipase value > 10 times the upper limit of the reference interval and characterized as being pathogenic for the disease.

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Cholinesterase

Two types of cholinesterase are found in man:

• Acetylcholinesterase (AChE) also referred to as:

true or RBC cholinesterase

• Serum cholinesterase (SChE) also referred to as:– Pseudocholinesterase or– Acylcholin acylhydrolase

Tissues Containing the Cholinesterases

AChE:o Nervous systemo Erythrocyteso Lungso Spleen

SChE:o Serumo Hearto Livero Pancrease

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Cholinesterase

Cholinesterase Deficiency

- Cholinesterase is synthesized in the liver and serum levels are often low in hepatic disease.

- Organophosphorus insecticides, which are used in sheep dips, inhibit both cholinesterases and serum cholinesterase can be used to screen for poisoning.

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Creatine Kinase

- CK catalyses the phosphorylation of creatine.

- The richest source of the enzyme is skeletal muscle while cardiac muscle and brain.

Tissues Containing Highest Levels of CK

o Skeletal muscleo Cardiac muscleo Braino Smooth muscle of the colono Small intestineo Uteruso Prostateo Lungso Kidneys

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Conditions Causing a Marked Elevation in Total CK Activity

o Acute myocardial infarctiono Muscular dystrophyo Intramuscular injectiono Pregnancyo Strenuous exerciseo Surgeryo Traumao Myopathieso Hypothyroidismo Neoplastic disorders of the prostate,gastrointestinal

tract,or bladder

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Creatine Kinase

- The main diagnostic application of CK is in the investigation of muscle disease, when the major circulating isoenzyme is CK-MM, and myocardial infarction, in which CK-MB predominates.

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Lactate Dehydrogenate

- Most tissues contain LDH and therefore measurements of the enzyme have low specificity.

- LD composed of combination of two subunits designated H (heart) amd M (muscle), this may be improved by determining isoenzymes; five forms occur, the proportions of which vary between tissues.

Tissue Specificities of the LD Isoenzymes

• Predominant isoenzymes in myocardium and erythrocytes- LD-1 (HHHH)

- LD-2 (HHHM)

• Predominant isoenzymes in lungs and spleen- LD-3 (HHMM)

- LD-4 (HMMM)

• Predominant isoenzymes in liver and skeletal muscle- LD-5 (MMMM)

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- Isoenzymes can be determined by electrophoresis which separates different forms on the basis of their electrical charge, heart having a high proportion of fast-moving enzyme, while the least mobile form predominates in liver.

- The main diagnostic application of LDH measurements is in the investigation of myocardial infarction.

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- LDH catalyses the reversible oxidation of L-lactate to pyruvate but also has activity against other hydroxy- and keto-acids, including hydroxybutyrate (2-oxobutyrate).

- The cardiac isoenzyme has a high affinity for this substrate, while liver LDH reacts with it very slowly; therefore, the cardiac isoenzyme may be determined by measuring hydroxybutyrate dehydrogenase (HBD) activity.

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EnzymeOriginMain applications

Acid phosphataseProstate, erythrocytesMetastatic carcinoma of prostate

Alanine aminotransferase (ALT, SGPT)

Hepatocytes

Kidney

Hepatocelluar disease

Alkaline phosphatase (ALP)Hepatobiliary tree

Bone

GI tract, placenta, kidney

Cholestatic disease

Bone disease

Lipase

Amylase

Pancrease

Pancrease, Salivary glands

Acute pancreatitis

Acute pancreatitis

Aspartate aminotransferase (AST, SGOT)

Hepatocytes

Cardiac muscle

Skeletal muscle

Hepatocelluar disease

Myocardial infarction

Muscle disease

CholinesteraseLiverOrganophosphorous poisoning

Creatine kinase (CK)Skeletal Muscle

Heart Muscle

Brain

Muscle disease


y-Glutamyl transferase (GGT)Liver

Pancrease

Kideny

Cholestasis

Alcohol abuse

Lactate dehydrogenase (LDH)Cardiac muscle

Skeletal muscle

Erythrocytes, liver


1 major enzymes of diagnostic interest dr. essam h. jiffri

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