Detection and clinical application of serum pepsinogen

As early as the early 19th century, researchers found a substance that can break down proteins in gastric juice and named it pepsin. Half a century later, it was found that pepsin is secreted in the form of an inactive zymogen to protect the stomach tissue from damage, which is called pepsinogen (PG). After a large number of long-term and in-depth research, people continue to generate new knowledge and develop various measurement methods for clinical application. Pepsinogen

Pepsinogen belongs to the family of aspartases, a single-chain polypeptide with a molecular weight of 42 kDa and 375 amino acids, and an isoelectric point of 3.7. It can be divided into 7 zones by agarose electrophoresis, and it is divided into PG 1~7 according to the speed of its movement to the anode. By detecting its immunogenicity, it was found that PG 1-5 immunogenicity is similarly called pepsinogen I (PC, I) or pepsinogen A (PG A), which is secreted by the main cells of the gastric gland and mucous cervical cells; PG 6-7 is called PGII or (PG C). In addition to the secretion of the above two cells, the Bnmner glands of the cardia gland, the pyloric gland, and the upper part of the duodenum are also secreted. There are some differences in gene loci, immunoreactivity and biochemical characteristics. The secretion of pepsinogen is associated with stimulation of cholinergic nerves, gastrin and histamine, and hypoglycemia caused by insulin injection. Drugs that inhibit gastric acid secretion can reduce their secretion. Pepsin is secreted and stored in the secretory granules at the top of the cells. When the cells are stimulated, they are released into the glandular cavity in the form of exocytosis. Only about 1% enter the blood circulation. In normal human blood, the source is single and stable. PGI is 6 times that of PGII. The optimum pH for activation is different, the former is 1.5-2.0, the latter is 3.2; the pH is >5, the activity is inactivated, and the irreversible denaturation occurs when the pH is 7.2 or the temperature is higher than 65 °C. PG I is more sensitive to alkaline degeneration than PGII.

The released inactive pepsinogen is converted to active pepsin by a self-catalyzed, amino-terminal hydrolysis of a peptide chain containing 42 amino acid residues under the action of gastric acid or under acidic conditions, and the molecular weight is reduced to 35kDa, the optimum pH is -3.5. Pepsin is an endonuclease that breaks down proteins into purines and mites, and very small amounts of peptides or amino acids. 2 detection of pepsinogen

In the 1980s, Japan first reported the establishment of PGI and PGII tests. The earliest methodologies used radioimmunoassay and enzyme immunoassay, and later time-resolved fluorescence immunoassays. These methods have good sensitivity and specificity, are suitable for the detection of large-scale specimens, and are mostly cumbersome manual operations. In addition, the isotope contamination and half-life limitations of radioimmunoassay and the need for specific counters, time-resolved fluorescence immunoassays also require specific detectors and other factors that limit their clinical application. The latex-enhanced immunoturbidimetric assay introduced in recent years has the same sensitivity and specificity as the above method, and can be detected on any biochemical analyzer, and the PG I and PGII contents can be quantitatively determined conveniently, quickly and stably. Calculate the ratio of PG I/PGII, high degree of automation, easy storage of reagents, and radioactive contamination. It is suitable for patients of all ages and physiques. It can be measured at any time and is suitable for large-scale census. 3 clinical application

Since the stomach is almost the only source of pepsinogen, the detection of serum pepsinogen content can reflect the secretion level of gastric mucosa, and the morphology and function of gastric mucosa at different sites are inferred.

3.1 Superficial gastritis Early superficial gastric mucosal inflammation stimulates the main cells to secrete pepsinogen, stomach acid and gastrin, while gastric acid and gastrin stimulate the secretion of pepsinogen; sustained inflammation and mucosal reaction can cause the main Cell damage and secretion are reduced. Erosive gastric mucosal hyperplasia and inflammatory infiltration increase gastric mucosal permeability, and the amount of PGII infiltration into the blood circulation increases. Therefore, serum pepsinogen levels in patients with superficial gastritis and erosive gastritis increase, but the increase in PG I is not as good as PGII, so the ratio of PG I/PGII decreases.

3.2 Helicobacter pylori infection (Helicobacter pylori, HP) has been listed by the World Health Organization as one of the main carcinogenic factors in human gastric cancer. In the process of chronic non-atrophic gastritis - atrophic gastritis - intestinal metaplasia - dysplasia - intestinal type of gastric cancer, HP plays an extremely important role. According to foreign reports, 80% of patients with moderate to severe atrophic gastritis are positive for HP, and patients with atrophic gastritis with gastric antrum are 18 times more likely to develop gastric cancer than normal people, while mucosa of gastric antrum and stomach have mucosa. Atrophic patients will be 90 times more dangerous than normal.

When HP is infected, it stimulates the increase of gastrin secretion in gastric antrum, which leads to the increase of pepsinogen secretion. The increase of PGII is more obvious than that of PG I, and the ratio of PG I / PGII is decreased. The degree of HP infection, the location of the lesion, and the extent of the lesion were different for PG I, PGII, and PG I/PG II. In the early stage of infection, PGI and PGII increased, and PG I/PGII decreased. If further serious lesions occurred in the gastric mucosa, PG I decreased, PGII was normal or elevated, and PG I/PGII ratio decreased. It can be seen that the detection of PG is superior to the advanced stage in the early stage of HP infection. When the drug treatment is effective. The PG II content decreases with the decrease of Helicobacter pylori, and the therapeutic effect can be observed accordingly.

3.3 Gastric cancer Gastric cancer is one of the common malignant tumors, and its mortality rate ranks second among common malignant tumors. X-ray examination of barium meal has radiation exposure damage, endoscopy is painful, and it is difficult for ordinary people to accept. Both of these examinations require large medical equipment and full-time personnel, which is time-consuming, labor-intensive, and expensive, and is not suitable for large-scale census. In gastric cancer, PGI decreased, PGII was normal or elevated, and PG I/PGII ratio decreased. When gastric cancer patients have a very low level of PG after total gastrectomy, gastric cancer cells with secretory function proliferate and PG levels increase, which can be used to detect postoperative conditions. 4 Summary

The traditional methods of diagnosis and treatment of stomach diseases such as barium meal and gastroscopy bring a lot of inconvenience to patients, and the various detection methods of PG bring convenience to clinical diagnosis and screening of various stomach diseases, and the suspicious people who are screened are diagnosed by endoscopy. It not only improves the positive rate of inspection of large medical equipment, especially patients reduce the pain and economic burden. In order to improve the specificity and sensitivity of the diagnosis, some scholars have suggested combining pepsinogen with gastrin and gastric cancer-associated antigens. However, due to the different methodologies, a large number of studies and comparisons with the gold standard are required in determining the Cut-off values ​​of various diseases.

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