Lung inflammation associated with acute necrotizing pancreatitis in dogs and mice

Acute necrotizing pancreatitis (ANP) is a common gastrointestinal cause of emergency admissions in dogs and humans and can lead to a systemic inflammatory response syndrome resulting in multiple organ dysfunction syndrome. Among the various complications associated with ANP, acute lung injury (ALI) or its more severe form, acute respiratory distress syndrome (ARDS), are major contributors leading to high mortality rates associated with severe acute pancreatitis (AP) in human patients. The incidence of ALI/ARDS in ANP dogs is not well characterized. However, signs of respiratory complications have been reported clinically in dogs suffering from AP. The pathophysiology of ANP and its systemic complications in dogs and humans are not well understood. Most of the data related to AP comes from rodent models of AP, which may not always represent the true mechanisms occurring in the lungs of dogs or humans with ANP. I decided to undertake evaluation of pancreas and lungs from dogs (N=21) that died of ANP. The cases were selected through the search of the medical records of the Veterinary Medical Center of the Western College of Veterinary Medicine (WCVM). Six healthy SPCA dogs were used as controls. The histology of pancreas was first graded to record the range of ANP severities within dog cases included in this study. Then, characterization of lung inflammation was done with histological grading and qualitative analysis of immunohistochemical staining for von Willebrand Factor (vWF), Toll-Like Receptor-4 (TLR4), interleukin-6 (IL6), and inducible nitric oxide synthase (iNOS). Quantification of the recruitment of septal macrophages in the lungs, designated as pulmonary intravascular macrophages (PIMs), in ANP dogs was achieved by counting the number of positive cells in alveolar septa using a macrophage antibody (MAC387). The results revealed that dogs suffering from ANP have variable lung inflammation, which was characterized by a significant infiltration of mononuclear phagocyte cells in the alveolar septa of all ANP dogs (median, 138; range 31-935) compared to control dogs (median: 1.5; range 0-16; p < 0.001), which suggested that PIMs are induced in ANP. In addition, robust staining for vWF in alveolar septal capillaries in lungs of ANP dogs suggested a strong microvascular inflammatory response. Finally, TLR4, IL6, and iNOS expression was increased in lungs of ANP dogs compared to control dogs. The second study was to investigate whether PIMs are induced in a mouse model of L-arginine-induced ANP. Therefore, lungs of L-arginine treated mice (n=7 per time point) were evaluated at various time points (24 hours, 72 hours and 120 hours) using histology and immunohistochemical staining for CD68 cells and vWF. Nine control mice were used. Counting of CD68-positive cells in the lungs of mice treated with L-arginine showed increased numbers of mononuclear phagocytes in alveolar septa at every time point (p