P-159 Adiponectin Administration Reduces the Severity of Intestinal Inflammation and Cancer

Background

Adiponectin (APN) is an adipocytokine secreted by adipocytes that has been found to play a protective role in chronic inflammation and colon cancer. Our published data has shown that APN knockout (KO) mice have greater pathology of chronic inflammation and colon cancer and were found to have significantly higher polyp count and tumor area as compared to C57BL/6 (WT) mice. APC^Min/+mice is a well-studied model for both colon and intestinal cancer. APN administration has been shown to decrease intestinal tumors in APC^Min/+ mice but there is a lack of mechanistic explanation for the observed protective effect. Mucus secreted by the goblet cells has been shown to provide protection from toxins and gut bacteria infiltration. Our published data also indicate a reduction in goblet to epithelial cell ratio in APN KO mice as compared to the WT mice with increased colonic mucosal erosion and reduced mucus thickness.

Purpose

The primary objective of this study is to determine the effect of APN administration on intestinal inflammation, tumor growth and deduce its mechanism of action.

Methods

APNKO and APC^Min/+ mice were bred to get APNKO/APC^Min/+ mice. Adiponectin (1.5 mg/kg) was administered intraperitoneally to 4 weeks old APC^Min/+ and APNKO/APC^Min/+ mice, once a week for 16 weeks and were divided into 6 different treatment groups: (1) C57BL/6 wild type or control mice (WT) (n = 10), (2) APNKO (n = 10), (3) APC^Min/+ (n = 10), (4) APNKO/APC^Min/+ (n = 10), (5) APC^Min/+ + APN (n = 6), (6) APNKO x APC^Min/+ + APN (n = 6). Mice were observed for diarrhea, stool hemoccult, and weight loss during the length of the study and were sacrificed on day 112. Tumor number and area was counted in both the colon and small intestine. Spleen size and weight was measured. Serum was collected to determine APN concentration. Tissues were collected from the tumor and non-tumor area of the colon and small intestine for genomic and proteomic studies including Western Blot, ELISA, immunohistochemistry, cytokine profiling, goblet cell staining and immunofluorescence.

Results

We found that mice that were administered APN had reduced clinical manifestation of symptoms including reduce weight loss, diarrhea and fecal hemoccult. Histopathological scoring including degree of inflammation, immune cell infiltration and degree of tumor were reduced significantly with APN administration along with tumor number and tumor area. Cytokine profiling, oxidative stress studies and proteomic studies for inflammatory markers indicate a reduced secretion and expression of pro-inflammatory and cancer marker expression with a concomitant increase in anti-inflammatory and anti-cancer markers. Goblet to epithelial cell ratio was also found be significantly higher in mice administered APN indicating the protective role of APN by indirectly aiding in mucus secretion through modulating the ratio of mucins.

Conclusions

APN acts as a tumor suppressor by reducing pro-inflammatory and pro-cancerous markers and maintaining and improving goblet cell number that increases mucus secretion, which provide protection from colon insult and gut bacterial invasion.