Organic matrix of pancreatic stones associated with nutritional pancreatitis

In recent studies performed on pancreatic stones from patients with alcoholic pancreatitis, a novel secretory protein was identified: the pancreatic stone protein (PSP Mr 14,000). This protein suppresses CaCO3 precipitation, and could therefore stabilize normally supersaturated pancreatic juice. Crystallographic analysis of stones from patients with nutritional pancreatitis (NP), as well as alcoholic pancreatitis (AP), revealed that the main constituent was calcite (CaCO3). In the present study, we investigated the organic matrix of NP stones. In the 14 cases studied, the organic matrix was rendered soluble after mineral dissolution with EDTA + citrate. Analysis of the isolated matrix revealed the presence of one major protein (Mr 14,000), and of a minor protein (Mr 30,000), which is in fact an aggregate form of the 14,000 Mr protein. Using PSP antibodies, complete immunological identity was found between PSP, the immunoreactive form of PSP present in nonactivated pancreatic juice, and the protein matrix of NP stones. Moreover, protein matrix of NP stones also inhibited the nucleation of CaCO3 crystal, and decreased their growth rate in vitro. The presence of PSP in all AP and NP stones suggests that it plays a key role in stone formation during the course of chronic pancreatitis. These results also suggest the existence of some pathophysiological links between these two apparently different etiological forms of calcifying pancreatitis.