Diet Significantly Influences the Interleukin‐6 Response to Mouse Models of Peritoneal Sepsis

Abstract

IntroductionSepsis remains to be a tremendous health burden in the United States, affecting 1.7 million Americans and causing over 250,000 deaths each year. Previous work has shown high‐calorie diets to significantly alter the immune response and outcomes in animal models of sepsis; however, the diets used model overt metabolic dysfunction and not dietary patterns observed in a “typical” American. We developed a novel Americanized diet (AD) that incorporates several of the nutritional inadequacies reported in Americans and set out to determine how consumption of the AD influences immunological outcomes of peritoneal sepsis in mice.MethodologyMale C57Bl/6 mice were used in accordance to protocols approved by the Institutional Animal Care and Use Committee at LUCOM and compliant with the Guide for the Care and Use of Laboratory Animals. Mice received ad libitum access to experimental diets [chow, AD, or a commercially available high‐calorie Western diet (WD)] for 8‐weeks and peritonitis was induced with cecal‐ligation and puncture (CLP) or intraperitoneal injection of a fecal slurry (fecal peritonitis, “FP”). For both CLP and FP, blood was collected 24‐hours later for quantification of circulating interleukin‐6 (IL6). Another group of mice were fed their assigned diets and the spleens cultured ex vivo in DMEM media with lipopolysaccharide (LPS, 10ug/mL) or saline for 3 hours. Tissue and supernatant were collected and frozen until assayed for IL6 and inflammatory gene expression using a commercially available PCR‐microarray. All data were analyzed using general linear model procedures in SPSS with Tukey’s post hoc test and group averages were considered statistically significant with a P‐value less than 0.05.ResultsMice consuming AD and WD had ~3‐fold greater circulating IL6 following CLP (P=0.04) and FP (P<0.05) as compared to mice consuming chow. LPS stimulation of splenic tissue ex vivo caused a significant increase in secreted IL6 protein (P<0.001). Mice fed WD had the greatest IL6 concentration (425 pg/mL), which was greater than mice fed chow (163 pg/mL, P=0.04) but not mice fed AD (360 pg/mL, P=0.9). PCR‐array analysis confirmed the upregulation of IL6, with mice fed WD having double (P=0.03) the mRNA expression of splenic IL6 after LPS as compared to mice fed AD and chow. CCL12 expression was similarly upregulated in mice fed WD as compared to mice fed AD and chow (P=0.005).ConclusionOur data support the hypothesis that diet significantly influences the severity of animal models of sepsis. Consumption of a nutritionally inadequate AD caused a similar increase in circulating IL6 as compared to mice consuming a high calorie WD. However, the source of the additional circulating IL6 is unknown, ex vivo spleen stimulation studies with LPS did not report an increase in IL6 production in mice fed the AD. Future studies will determine if and how diet influences IL6 production in other tissues.