Pathogenesis of infection in pancreatitis: from sterile inflammation to sepsis

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PROJECT SUMMARY: Acute pancreatitis (AP) affects @ 275,000/ year in the USA. AP starts suddenly and unpredictably as sterile inflammation but in severe cases can get infected, resulting in sepsis, prolonged hospitalization and sometimes death. Sepsis itself affects 1.5 million people /year in the USA, costs > $20 billion, results in 12-18% mortality and has a lot in common with AP. While defined as an overwhelming response to infection, a large portion of sepsis starts in sterile diseases like AP. AP has modelled the progression of sterile diseases to infection and sepsis since sepsis was first defined in 1992. Both diseases are poorly understood, and neither has a specific targeted therapy. Both diseases, when severe have distant organ failure, which we have shown to be due to the excessive and unregulated lipolytic release of unsaturated fatty acids during AP. Unbound fatty acids (uFA) refers to the small pool (<1%) of free fatty acids that are not bound to their main carrier, i.e. albumin, which is frequently low in severe AP. Our preliminary data show that pancreatic lipases generate uFA which are increased in the sera of severely septic patients. Additionally, uFA can rapidly incorporate into the membranes of inflammatory cells, trigger injury and impair their function. Based on these we hypothesize that uFA generated by pancreatic lipases cause inflammatory cell injury, impair bacterial clearance and result in sepsis during AP. We propose to study the molecular mechanisms of how lipotoxic inflammatory cell injury causes infections by using cell, animal models (Aim 2), and test the relevance of this in human AP, thus providing evidence to support changes in clinical AP management (Aim 1).In Aim 1 we will determine the clinical significance of lipotoxic inflammatory cell injury in clinical AP by determining the prognostic value of serum uFA and inflammatory cell injury at admission for AP vs. at time of infection, along with studying the relationship between type of uFA, nature of inflammatory injury with the type of infection. In Aim 2, we go on to determine the mechanisms and consequences of lipotoxic inflammatory cell injury in AP using cell and animal models. To do so we will study the dependence of inflammatory cell injury on pancreatic lipases and the lipid environment, determine the role of impaired bacterial clearance, and explore the mechanisms by which lipotoxic inflammatory cell injury occurs. By doing so, we hope to provide a broadly relevant, mechanistically sound, therapeutically amenable, novel explanation for sepsis. This work would set a conceptual framework to understand the pathogenesis of infection in sterile diseases (i.e. via uFA mediated inflammatory cell injury), which is clinically relevant- i.e. explains why a drop in white counts may signal increased risk of infection such as nosocomial infections and thus may not be always favorable. It can also provide improved diagnostic tools based on flow-cytometry to interpret WBC counts, injury and risk of infection, and suggest therapeutic options like the early replacement of albumin, prudent prophylactic antibiotic use, and targeting pancreatic lipases as an approach to avert the progression of sterile AP to severe sepsis and death.