LABORATORY DIAGNOSTICS OF ENZYME METABOLISM DISORDERS

1. LABORATORY DIAGNOSTICS OF ENZYME METABOLISM DISORDERS

2.

Enzymes are proteins that are capable of
accelerating biochemical reactions (possessing
catalytic activity).

3. Classification of enzymes:

Oxidoreductases, which catalyze oxidation-reduction
reactions.
Transferases, which transfer groups of atoms other than
hydrogen.
Hydrolases, which break down organic compounds by
adding the elements of a water molecule at the site of
cleavage.
Lyases, which form double bonds by removing or adding
groups of atoms.
Isomerases, which facilitate the intramolecular transfer of
atomic groups and the formation of isomeric forms.
Ligases, which join two molecules to form C-C, C-O, C-S, C-N
bonds, accompanied by the cleavage of a pyrophosphate
bond in ATP.

4.

In clinical laboratory diagnostics, all the listed enzymes are
conventionally divided into two groups:
1 – plasma-specific enzymes
They function while located in the blood plasma. They are
primarily synthesized in the liver.
When the organ where they are synthesized is damaged, their
concentration in the blood decreases.
Example: blood clotting and fibrinolysis factors, cholinesterase.
2 – organ-specific enzymes
They function while located inside cells.
When the organ where they are localized is damaged, their
concentration in the blood increases.
Example: troponin in acute myocardial infarction.

5. PLASMA-SPECIFIC ENZYMES

6. 1. Lecithin-cholesterol acyltransferase (LCAT)

Function: it binds cholesterol, removes it from the
walls of blood vessels, and transports it to liver
cells (it is located on the surface of HDL).
Synthesized in the liver. Eliminated by the kidneys.
Enzyme activity decreases:
- in liver diseases (acute and chronic hepatitis,
liver cirrhosis, toxic liver damage)
- in renal failure
- in hereditary LCAT deficiency

7. 2. Cholinesterase (ChE)

Function - разрушает ацетилхолин и родственные ему вещества.
Causes of increased activity:
arterial hypertension
nephrosis
obesity
alcoholism
diabetes mellitus
tetanus
Causes of decreased activity:
liver diseases
poisoning with organophosphorus compounds
myocardial infarction
oncological diseases

8. 3. Lysozyme

Function: антибактериальная (гидролизует полисахариды
клеточной стенки грамположительных бактерий).
Вырабатывается макрофагами, моноцитами и
нейтрофилами.
Causes of increased serum lysozyme levels:
- monocytic and myelocytic leukemias
- polycythemia
- kidney diseases with impaired filtration
- tuberculosis
- sarcoidosis
Causes of decreased serum lysozyme levels:
- neutropenia

9. 4. Renin

Function: it converts angiotensinogen to angiotensin I, which is then
transformed into angiotensin II by the action of ACE (Angiotensin-Converting
Enzyme). This leads to vasoconstriction and increased aldosterone secretion
(which stimulates the retention of sodium and water).
The (RAAS) Renin-Angiotensin-Aldosterone System contributes to increased
blood pressure.
Causes of increased renin levels in the blood:
- renovascular hypertension
- renin-secreting tumors
- use of oral contraceptives
- liver pathology (hepatitis, cirrhosis)
- pheochromocytoma
- adrenal cortex insufficiency, use of diuretics
Causes of decreased renin levels in the blood:
- arterial hypertension not related to the kidneys
- primary hyperaldosteronism
- administration of potassium supplements, ß-blockers

10. ORGAN-SPECIFIC ENZYMES

11. 1. Lactate dehydrogenase (LDH)

Function: catalyzes the conversion of pyruvic acid to lactic acid, and vice versa.
Causes of increased LDH1/2 levels in the blood:
- acute myocardial infarction
- leukemias
- hemolytic anemias
Causes of increased LDH3 levels in the blood:
- pulmonary embolism (PE)
- pulmonary infarction
- acute pancreatitis
- kidney diseases
- cardiovascular dysfunction with predominant failure of the pulmonary
circulation
Causes of increased LDH4/5 levels in the blood:
- liver diseases
- skeletal muscle diseases
- blood congestion in the systemic circulation

12. 2. Aminotransferases

Function: They catalyze transamination processes (the transfer of an NH3
group from an amino acid to a ketoacid).
They are found in all cells of our body (non-specific enzymes).
Differences:
1. ALT is eliminated more slowly than AST.
2. ALT is located in the cell cytoplasm. AST is located in the cell cytoplasm
and mitochondria.
↑ ↑ ↑ ALT, ↑ AST – liver damage
↑ ALT, ↑ ↑ ↑ AST – heart damage or skeletal muscle damage
Minor ↑ALT and AST : intake of vitamin C, antibiotics, antiarrhythmic drugs
Minor ↓ALT and AST : Vitamin B6 deficiency, pregnancy, renal failure
during hemodialysis

13. 3. Creatine phosphokinase (CPK) or Creatine kinase

Function: catalyzes the reversible reaction of creatine:
creatine phosphate ⇄ creatinine + ATP.
Isoenzymes:
BB-CPK (brain-type) - ↑ in brain diseases
MM-CPK (muscle-type) - ↑ in skeletal muscle diseases and
pulmonary embolism (PE)
MB-CPK (heart-type) - ↑ in heart diseases
The activity of MM-CPK in blood serum constitutes 94-96% of
total CPK.
The activity of MB-CPK constitutes about 4-6%.
Under normal conditions, BB-CPK is not detected in
peripheral blood (it does not cross the blood-brain barrier).

14. 4. Phosphatases

Function: catalyzes the removal of a phosphoric acid residue from organic compounds.
Alkaline and acid phosphatases are distinguished.
Isoenzymes of alkaline phosphatase: bone, hepatic, renal, placental, intestinal,
undifferentiated
Causes of increased alkaline phosphatase (ALP) in serum:
- liver diseases (hepatitis, cirrhosis, cancer, toxic damage)
- biliary tract diseases (obstructive cholecystitis, cholangitis)
- bone lesions (rickets, fractures, osteomyelitis, osteomalacia)
- hyperparathyroidism
- leukemias, multiple myeloma
- infectious mononucleosis
Causes of decreased alkaline phosphatase (ALP) in serum:
- hypothyroidism
- hypovitaminosis C, hypervitaminosis D
- senile osteoporosis
- severe anemia
- pituitary dwarfism

15.

Acid phosphatase
Isoenzymes: hepatic, erythrocytic, platelet,
prostatic.
Causes of increased acid phosphatase (ACP) in
serum:
- prostate cancer, especially with metastasis to the
bones
- hepatobiliary system diseases
- Sphingolipidoses (Gaucher disease, Niemann-Pick
disease)
- hemolytic anemias

16. 5. α-Amylase

Function: breakdown of glycogen and starch.
Human blood plasma contains two isoenzymes:
- pancreatic (P-type), which is excreted by the kidneys. In urine, α-amylase is
called urine diastase.
- salivary (S-type), which is not filtered by the kidneys.
Causes of increased α-amylase activity in blood serum:
- acute pancreatitis during the first 3-4 days of the illness
- acute surgical diseases of the abdominal organs
- epidemic parotitis (mumps)
- renal failure
Decreased α-amylase activity is observed:
- in pancreatic necrosis
- in liver diseases
- in burn disease, hypothyroidism
- in diabetes mellitus
Urine diastase ncreases significantly in acute pancreatitis and remains
elevated for up to 2 weeks after an episode of acute pancreatitis.

17. 6. Gamma-glutamyltransferase (GGT) or Gamma-glutamyl transpeptidase

It is considered one of the markers of hepatocyte
cytolysis, as well as cholestasis syndrome.
Causes of increased GGT activity in plasma:
- intra- and extrahepatic cholestasis
- acute viral hepatitis
- toxic and radiation-induced liver damage
- myocardial infarction
- chronic alcohol intoxication
- intake of anticonvulsants, rifampicin

18. LABORATORY SYNDROMES IN DIFFUSE LIVER LESIONS

19. Cytolysis syndrome

Laboratory signs of cytolysis syndrome:
1) increased activity of indicator enzymes in blood
plasma - ALT, AST, LDH and its isoenzymes - LDH4 and
LDH5
2) appearance of specific liver enzymes in the
blood: fructose-1-phosphate aldolase, sorbitol
dehydrogenase
3) increased concentration of ferritin, serum iron,
vitamin B12
4) elevated bilirubin level, mainly due to an increase
in the direct fraction.

20. Cholestasis syndrome

Laboratory signs of cholestasis syndrome:
1) increase in marker enzymes - ALP, GGT,
leucine aminopeptidase, 5'-nucleotidase
2) increase in direct bilirubin
3) increase in bile components - cholesterol, bile
acids, phospholipids, β-lipoproteins

21. Hepatocellular insufficiency syndrome

The blood of patients shows an increase in
indirect bilirubin and a decrease in the levels of
the following indicators:
1) total protein and, especially, albumin
2) transferrin
3) cholesterol
4) coagulation factors (II, V, VII)
5) cholinesterase
6) HDL

22. Mesenchymal-inflammatory syndrome

1) increased ESR
2) increased CRP
3) positive thymol test
4) increased gamma globulins
5) increased sialic acids

23. LABORATORY DIAGNOSIS OF MYOCARDIAL INFARCTION

Marker
Initial rise
(hours/days)
Peak elevation
(hours/days)
Return to normal
(hours/days)
Myoglobin
1-3 h
6-10 h
28-36 h
MB-CK (CK-MB)
4-6 h
12-18 h
40-56 h
Total CK
4-8 h
1-2 d
3-4 d
AST
6-12 h
18-36 h
3-4 d
Total LDH
24-48 h
3-6 d
8-14 d
LDH1
8-24 h
3d
up to 1 month
Cardiac-specific
troponin T
3-4 h
3-4 d
10-18 d
Leukocytosis
2-3 h
2-4 d
7d
ESR
2-3 d
7-10 d
3-4 weeks
CRP
First day
13-18 d
28-56 d

24. Laboratory signs of an unfavorable prognosis in acute myocardial infarction:

- leukocytosis above 15x10⁹/L, neutrophilia with a pronounced left shift
- lack of decrease in ESR after 10 days
- progressive increase in the concentration of sialic acids
- persistently elevated levels of C-reactive protein and fibrinogen
- reappearance of C-reactive protein in the blood
- increased enzyme activity: AST for more than 7 days; LDH for more than 2 weeks;
LDH1,2 for over 1 month; total CK for more than 7 days, or exceeding the norm by 10
times on days 1-2; CK-MB for more than 5 days, or an increase of more than 20 times the
normal level in the first day; GGT for more than 1.5 months; repeated hyperenzymemia
- hypermyoglobinemia for more than 5 days, or a level above 900 mcg/L on the first
day
- repeated hypermyoglobinemia
- severe metabolic acidosis (BE < -10)
- presence of laboratory signs of developing DIC syndrome (disseminated intravascular
coagulation)
- A 3 to 4-fold increase in the concentration of malondialdehyde on days 1-2