Identification of immunoreactive pancreatic stone protein in pancreatic stone, pancreatic tissue, and pancreatic juice

Pancreatic stone protein/regenerating protein family in pancreatic and gastrointestinal diseases

Pancreatic stone protein (PSP; reported in 1979), pancreatitis-associated protein (PAP; 1984) and regenerating protein (Reg I; 1988) were discovered independently in the fields of the exocrine (pancreatitis) and endocrine (diabetes) pancreas. Subsequent analysis revealed that PSP and Reg I are identical and PAP belongs to the same protein family. PSP/Reg I and PAP share a selective and specific trypsin cleavage site and result in insoluble fibrils (PTP, PATP). Search for a functional role of PSP had led to the idea that it might serve as an inhibitor in pancreatic stone formation and PSP was renamed lithostathine. Inhibitory effects of lithostathine in stone formation have been questioned. Evidence so far obtained can support a lithogenic role rather than a lithostatic role of PSP. PAP and its isoforms have been investigated mainly regarding responses to inflammation and stress. Reg I and its isoforms have been examined on regeneration, growth and mitogenesis in gastrointestinal neoplastic diseases as well as diabetes. Evidence obtained can be applied in the prediction of prognosis and therapy for inflammatory and neoplastic diseases.

Composition of clogging material in pancreatic endoprostheses

BACKGROUND

Endoscopic management of chronic pancreatitis (CP), especially pancreatic stent placement, has made tremendous advances. However, good clinical results are hampered by rapid occlusion. The objective of this study was to understand mechanisms and materials that cause stent occlusion.

METHODS

The clogging material of 50 lyophilized pancreatic endoprostheses (length 8.5 cm, range 5-14 cm, diameter 7-11F) from patients with CP was completely removed and weighed. Protein solubilization was achieved at pH 8.0 by using sodium dodecyl sulfate (SDS) and 2-mercaptoethanol in the presence of proteasome inhibitors. Proteins were separated by using a SDS-polyacrylamide gel electrophoresis. Protein identification was performed by the Western blot technique, as well as by mass spectrometry. Insoluble components were examined by polarized light microscopy and after staining (periodic acid-Schiff [PAS]).

RESULTS

Clogging material was found in 49 prostheses, mainly at the duodenal flap (80%). More than a third of the prostheses contained visible calcium carbonate calculi. Light microscopy and PAS staining showed plant debris (80%), crystals (73.5%), and mucopolysaccharides (100%). The dry weight of clogging material (18 +/- 13 mg, range 3-72 mg) correlated significantly with the stent diameter ( p = 0.029) but not with any other stent- or patient-related criteria. Albumin, its degradation products, and lithostathine were identified as the main proteinaceous components.

CONCLUSIONS

Almost all pancreatic stents had clogging material, predominantly located at the duodenal flap, which contained plant material, mucopolysaccharides, and crystals, as well as visible calcium carbonate calculi. Albumin and lithostathine may play an important role in the development of stent occlusion.

Theories, mechanisms, and models of alcoholic chronic pancreatitis

Alcoholic chronic pancreatitis is a severe, disabling, chronic inflammatory condition of the pancreas that is seen in fewer than 5% of alcoholics. The severity and unpredictability of this condition has lead to several theories on the mechanism causing chronic pancreatitis based on careful clinical observation. Hypothetical mechanisms were applied to various animal models. Finally, following multiple lines of evidence, there is a convergence of thought and development of some new models that are quite instructive. Taken together, chronic alcohol consumption by rats results in multiple effects on the pancreas that increase the risk of acute pancreatitis, including ongoing acinar cell injury that lowers the threshold for hyperstimulation-induced acute pancreatitis, neurohormonal injury, and adaptation that results in acinar cell hyperstimulation, increased susceptibility to viral mediated acute pancreatitis, and possibly other factors. After acute pancreatitis initiates the inflammatory process, the chronic inflammation and fibrosis of alcoholic chronic pancreatitis are driven by diet, the acinar cell stress response to continued alcohol that may be potentiated by toxic alcohol metabolites, hypoxia, hyperstimulation, and partial duct obstruction; plus the effects of proinflammatory immunocytes and cytokines; and by stellate cell-mediated fibrosis driven by anti-inflammatory cytokines, alcohol, and alcohol metabolites. The factors determining which alcoholic will develop alcoholic chronic pancreatitis likely involve genetic factors, dietary factors, and susceptibility to pancreatic injury through several mechanisms ranging from trauma to gallstones to viruses.

Pancreatic stone protein (lithostathine), a physiologically relevant pancreatic calcium carbonate crystal inhibitor?

Apart from digestive enzymes, pancreatic juice contains several proteins that are not directly involved in digestion. One of these, lithostathine, has been reported to exhibit calcite crystal inhibitor activity in vitro. As pancreatic juice is supersaturated with respect to calcium carbonate, it was hypothesized that lithostathine stabilizes pancreatic juice. Lithostathine is cleaved by trace amounts of trypsin, resulting in a C-terminal polypeptide and an N-terminal undecapeptide, which has been identified as the active site of lithostathine regarding crystal inhibition. We produced rat lithostathine in a baculovirus expression system. In order to test its functional activity, the protein was purified using a nondenaturing multi-step procedure. In the low micromolar range, recombinant rat lithostathine in vitro exhibited calcite crystal inhibitor activity, confirming earlier reports. Limited tryptic proteolysis of recombinant lithostathine was performed, and the two cleavage products were separated; the C-terminal polypeptide was precipitated by centrifugation, and the N-terminal undecapeptide was purified by high performance liquid chromatography. Only the C-terminal peptide displayed measurable calcite crystal inhibitory activity. Furthermore, synthetic undecapeptides with identical sequence to the N-terminal undecapeptides of rat or human lithostathine were inactive. However, when tested in the same in vitro assays, other pancreatic or extra-pancreatic proteins show inhibitory activity in the same concentration range as lithostathine, and inorganic phosphate is active as well. Based on these findings it seems unlikely that lithostathine is a physiologically relevant calcite crystal inhibitor. The name "lithostathine" is therefore inappropriate, and the protein's key function remains to be elucidated.

Pancreatic Reg/pancreatic stone protein (PSP) gene expression does not correlate with beta-cell growth and regeneration in rats

The Reg/pancreatic stone protein (PSP) gene is postulated to be an important regulator of pancreatic beta-cell growth. To investigate this hypothesis, we analysed the expression of the Reg/PSP gene following a 90% pancreatectomy and after chronic glucose infusion, two well-defined models of pancreatic beta-cell growth. There was a rapid induction of the Reg/PSP gene in the remnant pancreas after a 90% pancreatectomy in rats during the period of marked growth of the exocrine and islet tissue. However, a similar rapid, but smaller, induction of the Reg/PSP gene was observed in sham-operated rats and in non-surgical control rats in which there was no enhanced pancreatic growth. Furthermore, there was no pancreatic Reg/PSP gene induction in a model of selective beta-cell growth, the chronic glucose-infused rat. Thus, it is unlikely that Reg/PSP is a beta-cell specific growth factor, even though the function of this important pancreatic gene is still unknown.

The immunohistochemical evaluation of PSP/reg-protein in normal and diseased human pancreatic tissues

In order to elucidate the characteristics of reg-protein, which is identical to pancreatic stone protein (PSP/reg-protein), and the relationship between the generation and evolution of chronic pancreatitis and the expression of PSP/reg-protein in the pancreas, we investigated the expression of PSP/reg-protein in normal and diseased human pancreatic tissues by immunohistochemistry. The PSP/reg-protein was expressed in all cases with normal pancreas or chronic pancreatitis, and in 70.6% of cases with pancreatic cancer. This protein was present in the cytoplasm of acinar cells and, in some cases, in the intraluminal contents of ductules in nonmalignant tissues. From the view of distribution and cellular localization, PSP/reg-protein was expressed more broadly and densely in chronic pancreatitis with mild to moderate injury than in the normal pancreas. However, the protein was less expressed in severely damaged chronic pancreatitis tissue, such as calcifying pancreatitis, than in the normal pancreas. These findings suggest that mild to moderate injury to pancreatic tissue may stimulate the synthesis of PSP/reg-protein, whereas more severe injury tends to depress it.