Oxidative stress in acute pancreatitis

The present work critically reviews the evidence for an involvement of free radicals in the pathophysiology of acute pancreatitis and the potential of treatment with antioxidants and scavenger substances. Data originating from clinical trials, experimental pancreatitis studies and in vitro investigations are included. Enhanced free radical activities and increased concentrations of lipid peroxides in plasma and tissue have been found in both patients and experimental animals with acute pancreatitis. The individual contribution of possible sources of free radicals (e.g., invading inflammatory cells, xanthine oxidase, cytochromes P450, nitric oxide synthase) is not yet clear, however. Since prophylactic administration of antioxidants diminished, in particular, pancreatic edema formation, free radicals seem to play an important role in the genesis of edema in acute pancreatitis. An involvement of free radicals in the pathogenesis of pancreatic necrosis could not yet be proven. Thus, no antioxidant treatment has proven useful for therapy of fulminant pancreatitis in animals to date. However, in severe acute pancreatitis characterized by death occurring after 12-18 hours, the seleno-organic compound Ebselen, which has a glutathione peroxidase-like activity, and the membrane permeable ascorbic acid derivative CV-3611 have been demonstrated to be effective. To date, controlled clinical studies have failed to demonstrate the therapeutic efficacy of antioxidant selenium or glutathione precursor supplementation. Therefore, further controlled clinical trials are needed to determine whether supplements of antioxidants can alter the clinical course of acute pancreatitis. Since the nitric oxide radical may even protect the pancreas, a purely negative discussion of the role of free radicals on the pancreas is not justified. The actual role of free radicals in acute pancreatitis, i.e. serving the body's defense against infection, being an epiphenomenon of the inflammatory process without pathophysiological relevance, or having true pathogenic significance, is not yet clear. Lipid peroxidation may perhaps not be the cause but rather the sequel of pancreatic inflammation and may likely reflect the severity of the systemic inflammatory response rather than that of pancreatic parenchyma damage. In vitro, exposure of isolated pancreatic acinar cells to oxidative stress caused rapid cell damage and death. Such knowledge from cellular studies might help to plan therapeutical trials to evaluate potentially effective therapies in the experimental animal, as well as in patients suffering from pancreatitis. Thus, to further clarify the role of oxidative stress in acute pancreatitis, an integrated approach is needed, including investigations at various biological levels, from isolated cells or even organelles to laboratory animals and, finally, clinical studies in man.

The role of calcium in pancreatitis

BACKGROUND/AIMS

A large, sustained increase in acinar [Ca2+]i may play a key role in the pathogenesis of acute pancreatitis. Many mechanisms which lead to cell damage in vitro and pancreatitis in vivo, such as free radicals or supraphysiological cerulein concentrations, cause a rapid increase in [Ca2+]i in pancreatic acinar cells. Little is known about why [Ca2+]i increases in some instances stimulate secretion and in other instances initiate cell death. So far, [Ca2+]i increases were thought to represent physiological signals when they occurred as oscillations at the single cell level.

METHODOLOGY

This paper reviews recent literature and our own original research about the role of calcium in the function of pancreatic acinar cells and the development of pancreatitis.

RESULTS

Recent studies showed that exposure of acinar cells to free radicals not only caused a bulk increase in [Ca2+]i but also resulted in calcium oscillations which had a lower frequency than, but similar amplitude to oscillations occurring after physiological stimuli. The absolute increase in [Ca2+]i did not definitely determine the cellular response. Instead, the duration of [Ca2+]i increase may have been more important. In contrast to previous belief of a direct relationship between [Ca2+]i oscillations and exocytosis, recent results show that radicals can induce [Ca2+]i oscillations which do not exert exocytosis but inhibit the secretory response to physiological stimuli. Further experiments showed that the [Ca2+]i release caused by radicals originates from thapsigargin-insensitive, ryanodine-sensitive stores.

CONCLUSIONS

The origin and duration of [Ca2+]i increases rather than their extent or oscillatory nature, determine whether the cell will secrete or die. An abnormal [Ca2+]i increase can trigger trypsin activation, acinar cell damage and acute pancreatitis. This hypothesis is supported by studies which show that calcium chelators inhibit radical-induced trypsin activation as well as cell necrosis and apoptosis. Thus, an inhibition of pathological [Ca2+]i release may have a therapeutic potential.