Insulin protects pancreatic acinar cells during pancreatitis

Acute pancreatitis is a serious and sometimes fatal inflammatory disease whereby the pancreas digests itself. This is because the major function of the exocrine pancreas is to secrete powerful digestive enzymes into the gut to aid the digestion of food. If this process goes wrong then the enzymes can be activated inside the cells and released into the surrounding tissue where they start to digest the pancreas. This causes extensive tissue damage, inflammation and in severe cases, enzymes can enter the blood stream and start to attack distant organs, such as the lungs. Changes in cellular calcium concentration inside pancreatic cells stimulate the release of these digestive enzymes into the gut in response to hormones and neurotransmitters in a very controlled manner. This is achieved by maintaining very low calcium concentration inside cells, which is primarily regulated by calcium pumps on the cell membrane. This calcium pump uses chemical energy, derived from nutrient metabolism, to pump calcium out of the cell to maintain this low calcium. Under normal situations hormones or neurotransmitters stimulate a very rapid leak of calcium into the cell interior to stimulate secretion of digestive enzymes. The calcium pump then rapidly restores low calcium because prolonged elevated calcium is toxic to cells. The major causes of acute pancreatitis include alcohol metabolites, from excessive alcohol consumption and bile acid reflux from gall stones. These can cause this process to go wrong by inhibiting the chemical energy factories of the cells, which in turn inhibit the calcium pumps. This eventually leads to "uncontrolled calcium overload" within the cell, which is toxic and can lead to activation of digestive enzymes and the spiral of tissue damage that leads to pancreatitis. Our previous study showed that insulin, which is normally released from endocrine cells in close proximity to the exocrine cells of the pancreas, protects the exocrine cells from cellular injury. The insulin restored the cellular energy balance and protected the calcium pump. Therefore, the overall aim of this project is to investigate the precise mechanism for this insulin protection in animals with experimental pancreatitis. This will be achieved using mice in which the insulin receptor has been genetically deleted specifically in the exocrine pancreas. The successful outcome of this project could therefore reveal insulin as a potential treatment for pancreatitis. In addition this project may also reveal novel and more specific drug targets for the treatment of acute pancreatitis

Acute pancreatitis is a serious and sometimes fatal inflammatory disease whereby the pancreas digests itself. This is caused by bile acids and ethanol/fatty acid metabolites. Recently, impaired metabolism and cytotoxic calcium overload have been suggested to be the cardinal events that trigger the disease regardless of the cause. There is strong clinical evidence linking diabetes (both type-1 and type-2) and the severity of pancreatitis. Moreover, using two distinct experimental animal models (caerulein and fatty acid/ethanol-induced), our pilot data show that pancreatitis is worse in type-1 diabetic and PACIRKO mice, in which the insulin receptor has been genetically deleted. Furthermore, we have shown that insulin directly protects pancreatic acinar cells from cellular injury induced by pancreatitis agents, including; ATP depletion, inhibition of the plasma membrane Ca2+ pump (PMCA), cytotoxic Ca2+ overload and necrosis. This was due to a metabolic switch towards glycolysis, sufficient to maintain ATP to fuel the PMCA and thus prevent Ca2+ overload, even in the face of impaired mitochondrial function. The over-arching aim of this project is to test the hypothesis that insulin directly protects pancreatic acinar cells during pancreatitis. This will be directly and unambiguously tested in PACIRKO mice using cellular and in vivo models of pancreatitis, in which exogenous insulin is administered using a hyperinsulinaemic-euglycaemic clamp. In addition, the molecular mechanism for this insulin protection will be determined by investigating the signalling pathways and metabolic phenotype induced by insulin. The successful outcome of this project will further corroborate insulin, and related agents, as possible treatments for acute pancreatitis, regardless of the precise causative factor. It is hoped that this multidisciplinary approach from molecular mechanism to whole organism disease state will have major clinical implications for the treatment of acute pancreatitis.

The major beneficiaries of the current project include the patients that suffer from acute pancreatitis, the consultant intensivists, surgeons and health care professionals that treat the disease and the pharmaceutical industry who are likely to invest in pipeline drug development and clinical trials should this project reach its successful conclusion. Acute pancreatitis is common with an incidence of 1 in 10,000 and mortality of 10%. One-third of these have severe disease, which increases survival to 30%, with median inpatient stays of up to 100 days, thus constituting a significant health care burden. There is no specific therapy for acute pancreatitis and current paradigms of understanding the disease are clearly inadequate. Despite major efforts in recent years, we are far from an imminent cure. However, the current project provides real and tangible promise for the treatment of severe acute pancreatitis in the short term, and all forms of pancreatitis in the long term. This will have a substantial impact on health care economics, especially when one considers that severe acute pancreatitis is the leading cause of hospitalization for all gastroenterological diseases in the USA with an estimated cost of $2.6 billion per year. In the short term, if insulin administration using the hyperinsulinaemic euglycaemic clamp proves to be effective in reducing pancreatitis in mice, then this can be immediately translated to treat patients with severe acute pancreatitis. This is because these patients require critical care and often receive parental nutrition via a central venous line, to prevent excessive stimulation of the pancreas, which makes the hyperinsulinaemic euglycaemic clamp highly amenable to clinical translation. Moreover, the safety record of insulin, and indeed the hyperinsulinaemic euglycaemic clamp, has been well-tested.
Concomitant to the current basic scientific study, we will pursue parallel clinical studies, initially in the form of a robust translational evaluation of the role of endogenous insulin and glucose in the modulation of disease severity. This will involve taking regular blood samples from patients with acute pancreatitis to assess whether there is any correlation between the concentration of insulin, glucose, fatty acids or incretins with severity of disease. In addition, we will also carry out a retrospective case-control clinical assessment of the benefits of insulin treatment, used to treat sepsis secondary to clinical pancreatitis, matched with those patients with acute pancreatitis but without sepsis and thus not receiving insulin. Therefore, it is hoped that these initial clinical studies combined with a successful outcome from the insulin-clamp/caerulein-pancreatitis experiments in mice (SpAim 3), will provide substantive support for conducting a randomised controlled clinical trial, comparing all forms of severe acute pancreatitis with insulin therapy using the hyperinsulinaemic euglycaemic clamp versus those without.
In the longer term, dissection of the specific signalling and metabolic pathways responsible for this insulin protection could lead to the realistic discovery of novel specific insulin-mimetics for the treatment of pancreatitis without the deleterious effects of systemic insulin or the logistical difficulties controlling blood glucose. Such drugs might also be expanded to treat patients with mild to moderate pancreatitis. Furthermore, the metabolism-PMCA axis may provide a novel locus for potential therapeutic intervention, for a variety of other diseases, in which impaired metabolism and cytosolic calcium overload are critical pathological events. These include ischaemic diseases and cancer. Such a spin-off project is already underway in our laboratory on pancreatic cancer funded by the Pancreatic Cancer Research Fund (PCRF). This provides tangible evidence that this project has the potential to generate important new knowledge with real clinical potential.