Alpha-1 antitrypsin in the blood

Alpha _1- antitrypsin is a glycoprotein synthesized by the liver and provides 90% of the activity that inhibits trypsin in the blood. This glycoprotein inhibits the action of not only trypsin, but also chymotrypsin, elastase, kallikrein, cathepsins and other tissue proteases, promoting their cleavage.

A number of isoforms of this enzyme, encoded by different alleles, are described. One person in the blood can detect one or two forms of alpha ₁ -antitrypsin. The most common M-form. The formation of the Z-form (called so because of its special electrophoretic mobility in the gel) is associated with a gene mutation leading to the replacement of one of the amino acids in the M protein. Z-protein is hardly released from liver cells and causes local damage, which can lead to hepatitis and cirrhosis. To determine the concentration of alpha ₁ -antitrypsin in the blood serum, the nephelometry method is used. Establishment of the form of alpha ₁ -antitrypsin (ZZ, MM, MZ, FZ) is carried out by means of electrophoresis or molecular genetic methods.

Reference values (norm) of concentration of alpha ₁ -antitrypsin in blood serum: in adults under 60, 0.78-2 g / l, over 60 years - 1.15-2 g / l.

Alpha ₁ -antitrypsin belongs to the proteins of the acute phase, therefore its content in the blood serum increases in inflammatory processes (acute, subacute and chronic infectious diseases, acute hepatitis and liver cirrhosis in the active phase, necrotic processes, postoperative conditions, reductive phase of thermal burns, vaccination). The content of alpha ₁ -antitrypsin in the serum increases with malignant neoplasms: cancer (especially the cervix) and metastases, lymphomas (especially lymphogranulomatosis).

Of particular interest are cases of a decrease in the concentration of alpha ₁ -antitrypsin in the blood serum. Patients homozygous for the Z allele develop severe liver damage - neonatal hepatitis, liver cirrhosis. The pronounced insufficiency of alpha ₁ -antitrypsin is often combined with juvenile basal emphysema of the lungs, early development of emphysema (aged 20-40 years). Quite often, there are erased forms of congenital deficiency of alpha ₁ -antitrypsin (MZ-phenotype). These children have various forms of liver damage, including early cholestasis. In 1-2% of patients, cirrhosis develops.

The prevalence of homozygosity for the Z-allele is approximately 1: 3,000. In such cases, the activity of alpha ₁ -antitrypsin in serum is reduced to 10-15% of normal values. Not all people homozygous for the Z-allele develop lung and liver diseases. The risk of developing emphysema is significantly increased in smokers, since cigarette smoke oxidizes the thiol group of the active site in the alpha ₁ -antitrypsin molecule, which reduces the activity of the enzyme present in small amounts. Despite the fact that α ₁ -antitrypsin belongs to acute phase proteins, its concentration in Z-alleles homozygotes never rises above 50% of the lower limit of the norm.

In individuals with the MZ form of alpha ₁ -antitrypsin, its serum activity is approximately 60% of the norm, so the risk of developing lung diseases is significantly lower in comparison with people homozygous for the Z-allele.

Acquired deficiency of alpha ₁ -antitrypsin is observed in nephrotic syndrome, gastroenteropathy with loss of protein, acute phase of thermal burns. Reduction in the concentration of alpha ₁ -antitrypsin in the blood is possible in patients with viral hepatitis due to a violation of its synthesis in the liver, as well as respiratory distress syndrome, acute pancreatitis, coagulopathies due to increased consumption of this glycoprotein.

[1], [2], [3], [4], [5]