Pancreatitis Trypsinogen

The trypsin family of proteases plays a role in acute and chronic pancreatitis, as well as leads to its ultimate destruction [4, 105]. In pancreatitis, active exocrine enzymes are prematurely released inside the pancreatic duct. Various factors can contribute to the development of acute pancreatitis. Trypsinogen, chymotrypsinogen, procarboxypeptidase, and proelastase are inactive proforms of proteolytic enzymes produced by the pancreatic acinar cells. Following secretion these enzymes are activated in a cascade that converts trypsinogen to trypsin in the duodenum and/or small intestine. 

Their mode of appearance in the lumen of the intestine is rather complicated and involves activation of trypsinogen secretion by enterokinase. Once trypsin is formed it activates chymotrypsinogen. Pancreatic lipase is also secreted into the lumen with the pancreatic fluid. The digestion process of fatty acids by their lipase-mediated hydrolysis is completed by bile salts, which are also secreted in the duodenum and are crucial for micellization of lipophilic compounds. The micelles formed in the duodenum enable the absorption of hydro-phobic drugs such as steroids. They pose, however, a serious constraint for the stability of drug delivery carriers such as liposomes and emulsions. 

Human pancreatic secretory trypsin inhibitor (hPSTI) can be potentially assayed as an indicator of necrotic complications in AP (Ol). This protein is an inhibitor of trypsinogen, which is produced in acinar cells in the quantity of approximately 2% of the potential content of trypsin in pancreas. Trypsin binds with its inhibitor hPSTI, then with AMG, and only this complex, trypsin-o 2-macroglobulin, is eliminated from plasma (B10). Pezzili (P3) suggests that early attempts to determine the severity of the AP process based on the measurement of hPSTI within 24 hr from the first sensations of pain show a sensitivity of 79%, whereas an increase in CRP concentration has a sensitivity of 29% only (Table 3). 

Trypsinogen-Activating Peptide (TAP). The most reliable way to assess trypsinogen activation is to measure trypsinogen-activation peptide (TAP) in serum, urine, pancreatic tissue, or ascitic fluid (H5, M4). Studies on TAP in... 

Gl. Gambino, R., Urinary trypsinogen-2. The investigation of apromising new test for pancreatitis— continues. Lab. Report 19,42-43 (1997). 

H4. Hedstrom, J., Korvuo, A., Kenkimaki, P., Tikanoja, S., Haapiainen, R., and Kivilaaks, E., Urinary trypsinogen-2 test strip for acute pancreatitis. Lancet 347,729—730 (1996). 

N3. Neoptolemos, J., Kemppainen, E., Mayer, J., Fitzpatric, J., Raraty, M., and Slavin, J., Early prediction of severity in acute pancreatitis by urinary trypsinogen activation peptide A multicentre study. Lancet 255, 1955-1960 (2000). 

T3. Tenner, S., Fernandez-del Castillo, C., Washaw, A., Steinberg, W., Hermon-Taylor, J., and Valenzuela, J. E., Urinary trypsinogen activation peptide (TAP) predicts severity in patients with acute pancreatitis. Int. J. Pancreatol. 21,105-110 (1997). 

Figure 26-2. The pancreatic enzyme cascade. Pancreatic proteases enter the intestinal lumen as inactive zymogens. Within the duodenum, a specific enzyme of the duodenal mucosa, enterokinase, activates trypsinogen by releasing the trypsinogen activation peptide (TAP). Subsequently, active trypsin activates the other zymogens and acts autocat-alytically.

Small quantities of pancreatic enzymes are released from the pancreas into the bloodstream even physiologically and are detectable as low serum activities and/or concentrations of lipase, amylase, trypsinogen, and chymotrypsino-gen, respectively. Since progressive destruction of the organ occurs in chronic pancreatitis, this should theoretically be reflected by decreased serum enzymes, but so far these tests are not clinically useful because of their low accuracy. 

In the duodenum, the pancreatic zymogens, trypsinogen, chymotrypsinogen, proelastase and procarboxypeptidase are converted into active enzymes by enteropeptidase and trypsin, as shown in Fig. 15-6. The activation of all the zymogens involves cleavage of peptide bonds and removal of peptides, enabling conformational changes and formation of a functional active site. 

Enterokinase, a brush-border enzyme, activates trypsinogen into trypsin, which in tnm converts a number of precursor pancreatic proteases into their active forms. 

Fig. 1. Chromatography of bovine pancreatic juice on DEAE-cellulose (anionic proteins) and Amberlite IRC-50 (cationic proteins) (1). RNAase, ribonuclease ChTg-a, chymotrypsinogen A Tg, trypsinogen ProCp-B and Cp-B, procarboxypeptidase B and carboxypeptidase B DNAase, deoxyribonuclease ProCp-A, procarboxypeptidase A.

Since the specific activities of pure porcine amylase (23), lipase (16), and trypsinogen (Section III, F) are known, approximate values for the percentage of the three enzymes in pig pancreatic juice can be estimated as stated above. These values are respectively 7.5, 2.5, and 24 % of the total proteins. By taking into account the specific activity of pure pig chymotrypsinogen A (Section III, D), a value of 14% is found for this class of precursors. However, the value is preliminary since the specific activity and the amount of the second chymotrypsinogen of pig are not yet known. 

Keller and Cohen (36) also subjected to chromatography acidic extracts of cattle pancreatic microsomes and ribosomes. In microsomes they found the expected amounts of all enzymes which are known to be stable in acid, viz., chymotrypsinogen A, trypsinogen, deoxyribonuclease, and ribonuclease. The amounts of chymotrypsinogen B were abnormally low and ribonuclease B was perhaps not present. The results concerning ribosomes were made somewhat uncertain by the ability of these particles to incorporate proteins from the medium. Nevertheless, a series of characteristic enzymes could be isolated from what appears to be the very site of their biosynthesis. 

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