Potential clinical applications
Potential clinical applications of the Pancreatitis-Associated Protein (PAP)
In1984, Pr Keim reported (1) that a new protein was strongly overexpressed in the pancreas during pancreatic disease and called it the Pancreatitis-Associated Protein. Patients with pancreatitis had elevated serum levels of PAP, suggesting that it could be a new biological marker of the disease (2). Advantages of PAP over existing markers : Routine markers of pancreatitis are pancreatic enzymes such as amylase, lipase, and trypsin. They are very useful for diagnosis because they increase in blood during the early phase of pancreatitis. However, they have no prognostic value because their increase is transient. From day 2-3, levels in mild or severe pancreatitis are similar. In fact, the pancreas reacts to aggression by turning on a stress-response mechanism (3). Synthesis of enzymes is strongly repressed, explaining why enzyme levels decrease in blood. But synthesis of stress proteins, including PAP, is concomitantly over-expressed. Hence, contrary to enzymes, PAP level in blood will parallel the intensity of pancreatic stress. PAP is therefore a prognostic marker of pancreatitis.
Acute pancreatitisA multicenter study (4) actually demonstrated that serum PAP reflects pancreatitis severity. Increased serum PAP in successive assays indicates a worsening of the patient’s condition, whereas decrease predicts resolution of the acute phase. Besides pancreatitis per se, serum PAP assay proved useful in other situations where detection of pancreatic alteration is important (5,6).
Chronic alcoholismAlcoholism is the main etiology of pancreatitis. In alcoholics, there is progressive degradation of the pancreas without clinical symptoms, until acute, often severe pancreatitis occurs. Elevated PAP reveals pancreatic alteration in many chronic, asymptomatic drinkers (7). Patients with high serum PAP are particularly at risk of developing acute pancreatitis. Testing PAP in alcoholics provides the clinician with biological data that support a warning on the risks of pancreatitis.
Kidney-pancreas transplantationPatients with kidney failure are often diabetics. When kidney transplantation is required, the pancreas can also be grafted. Success of the double graft is directly conditioned by the behaviour of the pancreatic graft. If signs of rejection develop, biopsy of the pancreatic graft is the only way of getting reliable information, but the procedure is potentially harmful.
Because the compatibility of the graft is never complete, the pancreatic graft always shows inflammation leading to PAP overexpression. The intensity of inflammation can be monitored with serum PAP, which allows early and precise modulation of the immunosuppressive treatment (8).
PAP being overexpressed in animals upon induction of intestinal inflammation, experiments were conducted to test whether elevated serum PAP could be a marker of severity in coeliac disease. All children with coeliac disease had elevated serum PAP. When inflammation was controlled by a gluten-free diet, PAP decreased to normal values. PAP can therefore be used to monitor the efficacy of the treatment and as index of compliance (19).