Steven D. Leach

Intracellular activation of digestive zymogens in rat pancreatic acini. Stimulation by high doses of cholecystokinin.

The mechanism by which digestive zymogens become activated during acute pancreatitis remains poorly understood. Given the ability for cholecystokinin (CCK) to induce pancreatitis in vivo, the effects of high dose CCK on preparations of isolated pancreatic acini were examined. Using an immunologic technique for the detection of zymogen activation, CCK was found to stimulate the conversion of procarboxypeptidase A1 to a 35-kD form having the same net charge and electrophoretic mobility as purified recombinant carboxypeptidase A1. This enhanced conversion was proportional to the dose of CCK (maximal at 100 nM), and time dependent. CCK also produced changes in the electrophoretic mobility of procarboxypeptidase B and chymotrypsinogen 2 immunoreactivity, consistent with activation of these zymogens. These events were detectable only within acinar cell pellets and not in the incubation medium, suggesting an intracellular site of conversion. The conversion of procarboxypeptidase A1 to its active form was inhibited by pretreatment with the weak base chloroquine (40 microM) and the protonophore monensin (10 microM). This conversion was also inhibited by pretreatment with the serine protease inhibitor benzamidine (10 mM) but not the cysteine protease inhibitor E64 (100 microM). The results suggest that high dose CCK stimulates the intracellular activation of digestive zymogens within isolated pancreatic acini. This event appears to require an acidic subcellular compartment and serine protease activity.

Experimental models of acute pancreatitis

Acute pancreatitis remains a disease of uncertain pathogenesis and nonspecific therapy. Because of the practical problems plaguing investigation of pancreatitis in man, investigators have developed various experimental animal models of pancreatitis in order to develop rationale concepts regarding pathogenesis and therapy. Despite numerous investigations over the past century, the events involved in the initiation and progression of pancreatitis remain obscure. Indeed, identification of the cellular mechanisms responsible for the initiation of this disease may allow for significant advances in therapy. Previous studies have largely focused on the mechanism of pancreatitis at the organ level. It is now apparent that the early initiating events in acute pancreatitis probably occur at a membrane or intracellular level. The resolution of the cellular events which underlie the development of pancreatitis in combination with the introduction of new therapeutic agents may enable a rational and safe protocol to be developed for the support of patients with pancreatitis. In this review different experimental models of acute pancreatitis are discussed. Emphasis is placed on the relevance of various models to clinical pancreatitis.

Characterization of cAMP-dependent protein kinase activation by CCK in rat pancreas.

This study reports on the use of a new sensitive assay of cAMP‐dependent protein kinase activity to examine the effect of cholecystokinin (CCK) on the cAMP second messenger cascade in rat pancreatic acini. Treatment of acini with both low (pM) and high (nM) concentrations of CCK was associated with an increase in cAMP‐dependent protein kinase activity. The increases in kinase activity were detected in the absence of phosphodiesterase inhibition, a condition required to detect a measurable increase in cellular cAMP in these cells. Furthermore, the cAMP cascade was dissociated from the secretory effects of CCK, since the CCK analogue, OPE, mediates enzyme secretion but does not increase cellular cAMP levels or kinase activity.

New Perspectives on Acute Pancreatitis

The past decade has witnessed considerable changes in the clinical management of acute pancreatitis. Simultaneously, significant advances have been made in understanding the cellular and biochemical events involved in the initiation of this disease. This review summarizes recent clinical and scientific progress regarding acute pancreatitis and suggests areas for future investigation.

Acute pancreatitis at its Centenary: The contribution of Reginald Fitz

1989 represents the 100th anniversary of Reginald Fitzs initial characterization of acute pancreatitis. Our current understanding of this disease has advanced little beyond Fitzs early description. While survival from pancreatitis has improved largely through advancements in critical care techniques, no medical or surgical therapy exists that can limit pancreatic autodigestion and inflammation. Recent investigations have suggested that pancreatitis may result from a disruption of normal stimulus-secretion coupling within the acinar cell. Future research based on these observations may ultimately result in successful therapy for this disease.

Influence of chloroquine on diet-induced pancreatitis.

Recent investigations have suggested that digestive zymogens may become activated within the acinar cell during acute pancreatitis. While the molecular events responsible for intracellular zymogen activation remain unknown, several potential enzymatic pathways require an acidic pH to optimally proceed. We therefore proposed that manipulation of subcellular pH might alter the course of experimental pancreatitis. Chloroquine, a weak base that raises the pH of acidic subcellular compartments, was administered to young female mice in which pancreatitis was induced by a choline-deficient, ethionine- supplemented (CDE) diet. Control animals were maintained on regular laboratory chow. Examination of isolated pancreatic acini using acridine orange cytofluorescence demonstrated expansion of acidic subcellular compartments in animals fed the CDE diet. These compartments were effectively neutralized in animals receiving chloroquine. Animals receiving continuous infusions of high-dose chloroquine demonstrated a significant (p <0.05) decrease in free pancreatic tryptic activity as well as improved survival. These changes were also associated with decreased trypsinogen content in animals treated with high-dose chloroquine, suggesting an additional potential effect of chloroquine on zymogen synthesis and accumulation. One explanation of these findings is that a low-pH compartment may be important in the pathogenesis of diet-induced pancreatitis.