Abstract 1635: Effect of dietary fish oil on rat colonic prostaglandin (PG) E2 metabolism

Abstract PGE2, an eicosanoid generated from arachidonic acid (AA) by the cyclooxygenase function of prostaglandin H synthases (PGHS)-1 and 2, has been linked to the risk of many cancers including colorectal carcinogenesis. Targeting colonic PGE2 homeostasis by utilizing nutritional products such as fish oil may reduce endogenous PGE2 that, in turn, may decrease subsequent inflammatory events that lead to carcinogenesis. Rats were fed high fat fish oil diets contained different ratios of eicosapentaenoic acid (EPA) and n-6 fatty acid. The colon was horizontally divided into three equal length transections, first (proximal end), second (transverse) and third (distal end). Enzymes involved in PGE2 metabolism (15-hydroxyprostaglandin dehydrogenase (15-PGDH) and PGE synthase (mPGES)) were measured using quantitative PCR and semi-quantitative Western Blotting. GC-MS analysis was performed to detect fatty acid levels in serum and colon. LC-MS/MS analysis was used to examine eicosanoid levels. Our results showed that the colonic epithelial mucosa contained less PGE2 per mg of protein than did the whole colon. Colonic PGE2 and several eicosanoids including 13-Hydroxyoctadecadienoic acid(13HODE), 5-Hydroxyeico-satetraenoic acid (5 HETE), 15-Hydroxyeicosatetraenoic acid (15 HETE) and 12-Hydroxyeicosatetraenoic acid (12 HETE) were distributed differentially in different part of the colon. Dietary fish oil intake increased tissue levels of EPA in the colon. PGHS-2 gene was affected the most by dietary fish oil among all the genes tested in normal colon. Fish oil dose-dependently decreased PGHS-2 mRNA expression in all three colon sections. mRNA expression of 15-PGDH was higher in the third colonic section than the first two sections; however it was not altered by dietary fish oil. In conclusion, different parts of the colon have different eicosanoid profiles. The decreases in PGE2 in normal colon observed with fish oil feeding do not appear to be related to expression of PGHS-1, mPGES and 15-PGDH but are most closely correlated with PGHS-2 despite that PGHS-2 levels are already low in the normal colon. These data support the concept of anatomic variability in colonic carcinogenesis. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1635. doi:1538-7445.AM2012-1635