Diseases of the exocrine pancreas such as carcinoma and acute relapsing and chronic pancreatitis are common in our society and are treatable only by pancreatectomy, if at all. There is currently no medical pancreatectomy. It was the purpose of this work to investigate a selective pancreatotoxin, cyanohydroxybutene (CHB) to assess its potential as such an agent. CHB is present in many common foods such as canola and cruciferous vegetables. In high doses it has been shown to damage acinar cells of the pancreas (Wallig et al, 1988). In this work, the model was established in rats using synthetic S-enantiomer CHB, found to be equipotent to the natural and racemic CHB, and a maximal survivable dose level determined, fatalities being caused within hours by massive liver necrosis. The degree of pancreatic acinar cell apoptosis and atrophy was found to increase with dose and to be more severe with subcutaneous delivery than oral, the latter route causing an effect on liver at lower doses than the subcutaneous. A single dose of 150mg/kg subcutaneously caused the same degree of acinar cell damage at 120 hours as did the same dose given daily 4 times. The sequence of histological changes after a single large dose was examined, showing synchronous apoptosis of almost all acinar cells, a phenomenon rarely described in vivo, followed by a failure of recovery at 28 days and severe pancreatic atrophy causing malabsorption. Ductal cells were not damaged by CHB but in response to acinar cell loss were seen to undergo rapid proliferation to reconstitute lobules, followed during the subsequent 3 days by apoptosis. Islets were present throughout the 28 day time course. The few acini present at 28 days were peri-islet, suggesting a regenerative attempt by islet cells.
It was hypothesised that the mode of action was oxidative damage. This was explored by blocking cholecystokinin receptors, adding anti-oxidants and depleting glutathione, and detoxifying the nitrile group of CHB. The results confirmed the mechanism as oxidative, probably at the cell membrane. Protein separation by 2- dimensional electrophoresis and analysis showed the appearance 4 and 6 hours after CHB administration of two proteins similar to acyl-CoA synthetase 5 and human prolactin-induced protein, the roles of which are unknown in this setting.
A toxin that selectively damages normal cells of a particular type may also damage malignant cells derived there from, as does nitrogen mustard to bone marrow. The acinar cell carcinoma (AR4-2J line) was susceptible to CHB but only in vivo or when in vitro cells are already stressed by a low-grade infection. Cell lines of ductal cell carcinoma which comprises 95% of pancreatic carcinoma in our community were resistant to CHB as were normal duct cells. Ongoing work involves examination of the mechanisms surrounding apoptosis of ductal cells between 96 and 168 hours after CHB administration, in an attempt to find a molecular trigger for apoptosis of malignant cells derived from ducts.