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Abstract
Various novel biochemical markers indicate pancreatic cellular injury more accurately than serum amylase or lipase. One of these is a non-enzymatic secretory protein called pancreatitis-associated protein (PAP). The main function of PAP is unclear at present but it may be an acute phase protein in the defence reactions of pancreatic cells. The protein was characterized in 1984 as a serum marker of pancreatitis. The serum PAP is expressed 6 hours after the induction of pancreatitis, and it increases to maximal levels within 2 4 days: PAP is not sufficiently sensitive for the diagnosis of acute pancreatitis in the emergency room. The sensitivity and specificity of PAP in the differentiation of severe from mild pancreatitis is between 60-70%. This is not superior to serum CRP assays or CT scans. PAP increases in pancreatic cellular injury without pancreatitis (subclinical cell damage, graft rejection) where PAP may have a diagnostic role.
Introduction
The exocrine pancreas provides water, sodium bicarbonate, electrolytes and various enzymes to aid digestion. More than 90% of the digestive proteins in pancreatic juice consists of enzymes and proenzymes. Pancreatic proteases, such as trypsin, phospholipases, lipase, amylase and ribonuclease account for the majority of these proteins. All these enzymes are synthesized in the acinar cells at very rapid rates; the time required from synthesis to secretion into the acinar lumen is in the order of 50 minutes.1 From clusters of acini, the pancreatic juice is drained by two ductular systems, the Ducts of Wirsung and Santorini, into the duodenum.
Virtually all enzymes synthesized by the pancreas have been incriminated in the pathogenesis of pancreatitis. Pancreatitis-associated protein (PAP) is a recently discovered exocrinic secretory protein without known enzymatic activity.2 PAP is not secreted in detectable concentrations under normal conditions, but its expression is strongly induced in experimental and clinical acute pancreatitis.3,4 PAP has been suggested as a stress protein or an acute phase protein induced upon cell insult. Very recent studies indicate that in addition to the pancreas, other organs are able to synthesize PAP. A protein immunoreactivity similar to PAP has been found in jejunum and ileum5 and liver.6 The biochemistry of this novel protein is reviewed here with special reference to the diagnosis of acute pancreatitis.
Biochemistry
PAP was identified in...