Pathophysiology of acute and infected pancreatitis

Two key pathologic acinar cell responses of acute pancreatitis are vacuole accumulation and trypsinogen activation. Degradation of long-lived proteins, a measure of autophagic efficiency, is markedly inhibited in pancreatitis. Further, processing of the lysosomal proteases cathepsin L (CatL) and CatB into their fully active, mature forms is reduced in pancreatitis, as are their activities in the lysosome-enriched subcellular fraction. These findings indicate that autophagy is retarded in pancreatitis due to deficient lysosomal degradation caused by impaired cathepsin processing. Trypsinogen activation occurred in pancreatitis and is prevented by inhibiting autophagy. A marker of trypsinogen activation partially localized to autophagic vacuoles, and pharmacologic inhibition of CatL increased the amount of active trypsin in acinar cells. The results suggest that retarded autophagy is associated with an imbalance between CatL, which degrades trypsinogen and trypsin, and CatB, which converts trypsinogen into trypsin, resulting in intra-acinar accumulation of active trypsin in pancreatitis. Thus, deficient lysosomal degradation may be a dominant mechanism for increased intra-acinar trypsin in pancreatitis. Proinflammatory cytokines and oxidative stress play a pivotal role in the early pathophysiological events of the disease. Cytokines such as interleukin 1beta and tumor necrosis factor alpha initiate and propagate almost all consequences of the systemic inflammatory response syndrome. On the other hand, depletion of pancreatic glutathione is an early hallmark of acute pancreatitis and reactive oxygen species are also associated with the inflammatory process. Changes in thiol homeostasis and redox signaling decisively contribute to amplification of the inflammatory cascade through mitogen activated protein kinase (MAP kinase) pathways.