Molecular mechanisms of alcohol associated pancreatitis

Alcohol abuse is commonly associated with the development of both acute and chronic pancreatitis. Despite this close association, the fact that only a small percentage of human beings who abuse alcohol develop pancreatitis indicates that alcohol abuse alone is not sufficient to initiate clinical pancreatitis. This contention is further supported by the fact that administration of ethanol to experimental animals does not cause pancreatitis. Because of these findings, it is widely believed that ethanol sensitizes the pancreas to injury and additional factors trigger the development of overt pancreatitis. How ethanol sensitizes the pancreas to pancreatitis is not entirely known. Numerous studies have demonstrated that ethanol and its metabolites have a number of deleterious effects on acinar cells. Important acinar cells properties that are affected by ethanol include: calcium signaling, secretion of zymogens, autophagy, cellular regeneration, the unfolded protein response, and mitochondrial membrane integrity. In addition to the actions of ethanol on acinar cells, it is apparent that ethanol also affects pancreatic stellatecells. Pancreatic stellate cells have a critical role in normal tissue repair and the pathologic fibrotic response. Given that ethanol and its metabolites affect so many pancreatic functions, and that all of these effects occur simultaneously, it is likely that none of these effects is "THE" effect. Instead, it is most likely that the cumulative effect of ethanol on the pancreas predisposes the organ to pancreatitis. The focus of this article is to highlight some of the important mechanisms by which ethanol alters pancreatic functions and may predispose the pancreas to disease.     

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.     

Molecular mechanisms of pancreatitis: current opinion

Pancreatitis (necroinflammation of the pancreas) has both acute and chronic manifestations. Gallstones are the major cause of acute pancreatitis, whereas alcohol is associated with acute as well as chronic forms of the disease. Cases of true idiopathic pancreatitis are steadily diminishing as more genetic causes of the disease are discovered. The pathogenesis of acute pancreatitis has been extensively investigated over the past four decades; the general current consensus is that the injury is initiated within pancreatic acinar cells subsequent to premature intracellular activation of digestive enzymes. Repeated attacks of acute pancreatitis have the potential to evolve into chronic disease characterized by fibrosis and loss of pancreatic function. Our knowledge of the process of scarring has advanced considerably with the isolation and study of pancreatic stellate cells, now established as the key cells in pancreatic fibrogenesis. The present review summarizes recent developments in the field particularly with respect to the progress made in unraveling the molecular mechanisms of acute and chronic pancreatic injury secondary to gallstones, alcohol and genetic factors. It is anticipated that continued research in the area will lead to the identification and characterization of molecular pathways that may be therapeutically targeted to prevent/inhibit the initiation and progression of the disease.     

Molecular mechanisms of stem cell therapy in alcoholic liver disease

Alcoholic liver disease affects a great number of people worldwide. With limited therapeutic options, stem cell therapy offers significant potential for these patients. To date, a limited number of clinical trials have produced transient clinical responses to cell therapy in patients with alcoholic liver disease. Stem cell therapy to reorganize the postnatal liver is an important theme and mission for patients with chronic liver disorders including alcoholic liver injury. We therefore should redevelop the evidence of cell-based liver regeneration therapy, focusing on targets (disease, patient's status and hepatic function), materials (cells, cytokines and genes), and methodology (stem cell types and their derived microparticles, transplantation route, implantation technology and tissue engineering). In this review, we summarize the recent findings regarding the experimental and clinical use of mesenchymal and liver stem cells, focusing mainly on the treatment of alcoholic liver disorders and their relevance in the field of regenerative medicine, and advances on the role of microvesicles and exosomes in this process. We discuss new advances in stem cell therapy from liver regeneration to liver re-organization, which is involved in the recent progress of on-going clinical trials, basic research in stem cell therapy and liver regeneration, and updated exosomes/microvesicles recovery/repairing technology.     

Mechanisms of alcoholic pancreatitis

Alcoholic pancreatitis is a major complication of alcohol abuse. The risk of developing pancreatitis increases with increasing doses of alcohol, suggesting that alcohol exerts dose-related toxic effects on the pancreas. However, it is also clear that only a minority of alcoholics develop the disease, indicating that an additional trigger may be required to initiate clinically evident pancreatic injury. It is now well established that alcohol is metabolized by the pancreas via both oxidative and non-oxidative metabolites. Alcohol and its metabolites produce changes in the acinar cells, which may promote premature intracellular digestive enzyme activation thereby predisposing the gland to autodigestive injury. Pancreatic stellate cells (PSCs) are activated directly by alcohol and its metabolites and also by cytokines and growth factors released during alcohol-induced pancreatic necroinflammation. Activated PSCs are the key cells responsible for producing the fibrosis of alcoholic chronic pancreatitis. Efforts to identify clinically relevant factors that may explain the susceptibility of some alcoholics to pancreatitis have been underway for several years. An unequivocal, functionally characterized, association is yet to be identified in clinical studies, although in the experimental setting, endotoxin has been shown to trigger overt pancreatic injury and to promote disease progression in alcohol-fed animals. Thus, while the molecular effects of alcohol on the pancreas have been increasingly clarified in recent years, identification of predisposing or triggering factors remains a challenge.     

Treatment of alcoholic pancreatitis

Chronic pancreatitis is characterized by progressive and irreversible loss of pancreatic exocrine and endocrine function. The majority of cases in the Western world are related to alcohol consumption. Treatment of alcoholic chronic pancreatitis has been difficult, since the mechanisms of disease progression and the causes of pain are poorly understood. The conservative management of chronic pancreatitis focuses on (a) avoidance of precipitating factors such as alcohol and smoking; (b) treatment of pain, and (c) replacement of exocrine and endocrine function. There is a lack of good controlled, randomized treatment trials in alcoholic pancreatitis. However, there is good evidence that lifestyle changes, such as alcohol cessation, hamper progression of the disease. Conservative treatment of pain should be based on a stepwise approach; however, underlying causes such as pseudocysts may require endoscopic or surgical therapy. Treatment of exocrine insufficiency requires pancreatic enzyme supplementation and adjustment to several smaller meals per day, while treatment of endocrine insufficiency requires insulin treatment.     

Pathobiology of alcoholic pancreatitis.

This paper provides a summary of the effects of alcohol abuse on the pathobiologic responses that occur during acute and chronic pancreatitis considering both the human disease and animal/tissue models. The effects are multiple and include ones on cell death leading to necrosis; on inflammation resulting in a sensitized response to pancreatic stress; and fibrosis through effects of ethanol on pancreatic stellate cells and the plasminogen system. Although the effects of alcohol are multiple and complex, it is likely that a combination of a few key effects on these pathobiologic responses drive the increased sensitivity of the pancreas to acute pancreatitis with pancreatic stress and the promotion of chronic pancreatitis with pancreatic injury occurring during acute pancreatitis.     

The pathophysiology of alcoholic pancreatitis

The causal relationship between alcohol abuse and pancreatitis is undisputed. However, why some alcoholics manifest pancreatitis whereas others do not remains unexplained. Epidemiological data increasingly point toward an adjuvant role for genetic, dietary, and environmental factors. Significant advances have taken place in the last several years in the characterization of the pathophysiology of both experimental and human alcoholic pancreatitis. However, the pathogenesis of alcoholic pancreatitis remains unsettled. Toxic effects of alcohol on pancreatic acinar cells, "plugging" of pancreatic ductules by proteinaceous material, and reflux of bilio-duodenal juice into the pancreatic ducts have been suggested as putative pathogenetic mechanisms. Whereas at the present time only hypotheses can be formulated, it seems likely that the genesis of alcohol-related pancreatitis follows one or several of these proposed mechanisms. Pain in alcoholic pancreatitis is common and yet unexplained. Understanding the mechanism of pain in such patients is the key to our ability to manage it successfully. In this review, I have attempted to summarize and critically analyze our current understanding of these challenging problems.     

Diabetes in chronic alcoholic pancreatitis

Chronic alcoholic pancreatitis (CAP) is often complicated by the onset of diabetes mellitus. The aim of this study was to assess the residual beta cell function (evaluated by means of the glucagon test) and the mean disposal rate of insulin (with the insulin tolerance test) in 66 CAP patients with or without abnormalities of glucose metabolism and in 19 control subjects. On the basis of our data, we conclude that the glucose metabolism abnormalities in chronic pancreatitis occurs as a result not merely of impaired production of endogenous insulin, but also as result of a combination of the latter together with insulin resistance.     

Genetic polymorphisms in alcoholic pancreatitis

BACKGROUND: Chronic, excessive alcohol consumption is clearly associated with acute and chronic pancreatitis. However, both clinical and laboratory studies demonstrate that alcohol consumption alone does not directly cause alcoholic chronic pancreatitis. Growing evidence suggests that environmental and possibly genetic cofactors must also be present to overcome the redundant mechanisms protecting the pancreas from pancreatitis and facilitating complete recovery. METHODS: The SAPE hypothesis model was used to organize potential triggering factors, susceptibility factors and disease-modifying factors based on insights from animal studies. A systematic review of genetic studies on alcoholic pancreatitis was conducted and the results were analyzed in the context of animal studies. RESULTS: To date, no major genetic cofactors for susceptibility or progression have been identified in approximately 90% of cases of human alcoholic chronic pancreatitis. Mutations have been identified in the pancreatic secretory trypsin inhibitor gene (SPINK1) in about 8% of cases, and an excess in cystic fibrosis transmembrane conductance inhibitor (CFTR) gene variants have been reported, but the details of the complex genetics with CFTR have not been clarified. None of the polymorphisms in alcohol-metabolizing genes or detoxifying genes appear to explain pancreatic susceptibility. CONCLUSIONS: New, adequately powered genetic studies are needed. Several major genetic epidemiology studies are underway in both Europe and the United States to help determine why only a subset of alcoholics develop alcoholic chronic pancreatitis.     

Nasogastric suction in alcoholic pancreatitis

In order to assess the usefulness of nasogastric suction in acute alcoholic pancreatitis, 37 patients with alcoholic pancreatitis were prospectively investigated. The study failed to demonstrate efficacy of nasogastric suction in those patients with mild disease. Application of a system of prognostic signs proved useful in discriminating between mild and severe disease. Routine use of ultrasound examinations detected three pancreatic pseudocysts before they became clinically apparent. In instituting appropriate therapy in mild pancreatitis, factors such as patient comfort should be considered in the absence of proven significant value of nasogastric suction.     

Genetic polymorphisms in alcoholic pancreatitis

Chronic, excessive alcohol consumption is clearly associated with acute and chronic pancreatitis. However, both clinical and laboratory studies have demonstrated that alcohol consumption alone does not directly cause pancreatitis. Growing evidence suggests that environmental and possibly genetic cofactors must also be present before the mechanisms protecting the pancreas from pancreatitis are circumvented and pancreatitis develops. The discovery that mutations in the cationic trypsinogen gene (R122H, N29I) predisposed to acute and chronic pancreatitis focused attention on possible genetic predispositions. Mutations in the cationic trypsinogen gene, however, are rarely associated with alcoholic chronic pancreatitis. Mutations in the SPINK1 gene (e.g. N34S) provide a threefold increased risk, and cystic fibrosis transmembrane conductance regulator (CFTR) mutations continue to be investigated. However, the major cofactor associated with alcoholic chronic pancreatitis is yet to be identified.     

The pathogenesis of chronic alcoholic pancreatitis

The pathogenesis of chronic alcoholic pancreatitis has not been elucidated yet. There are many theories about this topic. The first regards the initial injuries in the ductal pancreatic system. The second considers that the primary lesion is located in the acinar cells. Three hypotheses are elaborated in this respect: the intervention of toxic metabolites, oxidative stress or neuroimmmune system. The third theory sustains that a severe initial attack of acute pancreatitis may induce lesions typical of chronic pancreatitis. Recently the intervention of genetic factors, responsible for the susceptibility chronic pancreatitis has been put forward.