Abstract 5256: Intracellular lipid droplet quantity as a biomarker for obesity associated resistance to omega-3 fatty acid colon cancer prevention
Authors: Aslam Muhammad N. , Sridhar Nithya , Nadeem Maheen , Simon Becky R. , Ren Jianwei , Sen Ananda , Varani James , Smith William L. , Djuric Zora , Brenner Dean E. 
Published: July 2017

Rationale: Obesity induces resistance to Omega-3 (ω-3) FA anticarcinogenesis effect. Obesity associated excessive fatty acid intracellular concentration results in excess triglycerides stored as intracellular lipid droplets, saturated acyl-co-A transport of FA to triglycerides resulting in excess substrate for cyclooxygenase metabolism with increased formation of PGE2 and other inflammatory eicosanoids.

Methods: Five weeks old male F344 rats were randomized equally into two diet groups. One cohort fed a western diet of ω-6 fatty acids (EPA:ω6 ratio of 0) and other fed an ω-3 fatty acid supplemented diet (EPA:ω6 ratio of 0.4). One half from each diet group were further treated with azoxymethane/dextran sulfate sodium (AOM/DSS) and then euthanized at 21 weeks after the carcinogen induction. Snap frozen colon tissue were assayed for Prostaglandins and fatty acids. OCT fixed colonic tissue stained with oil red O (ORO) to detect lipid droplets which were quantified using Aperio image analysis. From the second set, rat colons were opened longitudinally and fixed in 10% Formalin. Tumors were identified and enumerated using stereomicroscope to get tumor count, incidence and volume. These tissue were subjected to hematoxylin & eosin staining for histological evaluation of colonic tumors.

Results: The ω-3 FA diet significantly increased the percent of eicosapentaenoic acid (EPA) in total fatty acids in both untreated and AOM/DSS-treated rats. EPA in the colonic tissue was increased with ω-3 diet as compared to ω-6 from 1.4±0.8 to 2.6±1.0* in untreated rats and from 1.3±1.3 to 3.3±1.7* in AOM/DSS-treated rats (*p&lt;0.005). PGE2 increased with AOM/DSS treatment. The ω-3 diet decreased PGE2 in colonic mucosa of untreated rats from 132±64 in ω-6 to 78±17 in ω-3 and 150±74 in ω-6 to 92±43 in ω-3 with AOM/DSS treatment. Most tumors were found in the distal colon (DC) with ω-3 diet significantly reducing the number of tumors (p value=0.0011). The ω-3 diet significantly reduced colonic adenoma volume and multiplicity. When tumors were stratified by size and location, there was a significant effect of diet in the DC, with ω-3 diet reducing the number of tumors in the 1-3mm range (p value=0.0018), 3-5mm (p value=0.0041) and &gt;5mm (p value=0.0055). ω-3 also reduced the number of 3-5mm size tumors in the cecum (p value=0.0377). On preliminary quantification of lipid droplets, there was a reduction in the positive pixels divided by the total pixels of ORO stained colonic tissue of ω-3 rats (0.004 ±0.01 as compared to 0.013±0.07 in ω-6 rats; p value=0.0121)

Conclusions: Dietary ω-3 supplementation that increases the EPA:AA ratio in colonic tissue phospholipids reduces excess intracellular FA concentrations reflected by a reduction in size and number of lipid droplets. Lipid droplet number and size may be useful as a biomarker for effective reduction of obesity associated inflammation and carcinogenesis risk.

Citation Format: Muhammad N. Aslam, Nithya Sridhar, Maheen Nadeem, Becky R. Simon, Jianwei Ren, Ananda Sen, James Varani, William L. Smith, Zora Djuric, Dean E. Brenner. Intracellular lipid droplet quantity as a biomarker for obesity associated resistance to omega-3 fatty acid colon cancer prevention [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5256. doi:10.1158/1538-7445.AM2017-5256