Determining the Effect of Diet on a Novel Model of Fecal Peritonitis in Mice

Sepsis is a healthcare burden and has a mortality rate that exceeds many forms of cancer and AIDS combined. Previous research has shown obesity to exacerbate the severity of sepsis in both human and animal models, however the exact mechanisms involved remain unclear. We have recently created a novel Americanized rodent diet (AD) that is a significant improvement upon current disease-inducing rodent diets as it considers several dietary inadequacies present in the human diet. Previously we reported that mice consuming the AD had greater IL-6 expression in the murine cecal-ligation and puncture (CLP) model of polymicrobial sepsis as compared to mice consuming chow. However, it was unclear whether the reduced inflammatory response in chow-fed mice was due to diet or experimental complications associated with surgery in obese mice. Therefore, we set out to determine the effect of diet in a novel, standardized fecal peritonitis model in mice. All experiments were performed in accordance with protocols approved by the Liberty University IACUC and conform to the FASEB Statement of Principles for the use of animals in research and education. 3-week old male mice of the C57Bl/6 strain were purchased from The Jackson Laboratory and acclimated to the new environment and chow diet for 1-week. After one week, mice were given ad libitum access to chow (18% protein), our AD, or a commercially available “Western” diet (WD) for 6 weeks (n=6). The AD consists of a modified chow pellet and synthetic pellet formulated to match the reported 50th percentile of American intake for several nutrients. After 6 weeks, fecal peritonitis was induced by a single intraperitoneal injection (5 uL/gram of body weight) of the supernatant of a 40 mg/mL solution of mouse fecal pellets in saline. Mouse pain and distress was monitored over the following 18 hours and animals were then euthanized and blood was collected to quantify circulating IL-6 by ELISA. All statistical analyses were performed using general linear models in SPSS with “Diet” as the independent variable. Mice consuming the AD and WD had similar weight gain during the 6 week feeding study, which was significantly greater than mice consuming chow (P=0.004). All mice were exposed to the fecal peritonitis model and showed clear signs of pain and distress between 6 and 12 hours after injection (based on lack of movement, grooming, and obvious pyloerectus). Mice consuming chow displayed minimal signs of ailment at 18 hours whereas mice fed the WD still displayed obvious signs of illness at the same timepoint. Mice fed the AD appeared to recover at an intermediate rate, with more activity and grooming than mice fed the WD. Interestingly, both the AD and WD fed mice had a similar increase in circulating IL-6 as compared to mice fed chow (175 versus 60 ug/mL respectively, P=0.03). Taken together, our results suggest that the severity of sepsis in mice fed different diets is not solely dependent upon adiposity or the severity of inflammation (based on circulating IL-6 concentrations). Future studies will determine the source of IL-6 (tissue and cell type) and further delineate the immunological effects of diet in animal models of disease