Sarah Parsons | ALES Graduate Seminar

Event details: A graduate exam seminar is a presentation of the student’s final research project for their degree. This is an ALES PhD Final Exam Seminar by Sarah Parsons. This seminar is open to the general public to attend.

PhD with Drs. Vera Mazurak and Tom Clandinin .       

Thesis Topic: Chemotherapy-induced intestinal disruptions and the effect of eicosapentaenoic acid and docosahexaenoic acid on signalling mediators 

Abstract:

Chemotherapy agents, irinotecan (CPT-11) and 5-fluorouracil (5-FU), treat advanced colorectal cancer but are also cytotoxic to rapidly dividing intestinal epithelial cells. Inflammatory mediators and intestinal pathogenic bacteria are factors in chemotherapy-induced intestinal toxicity. Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are n-3 fatty acids with known anti-inflammatory and pro-resolving properties through the action of bioactive lipid metabolites (oxylipins) in several inflammatory diseases. Content of EPA and DHA is very low in intestinal membrane phospholipid, and the effect of EPA and DHA on intestinal oxylipins after chemotherapy is unknown. The objectives of this thesis were to investigate the effect of dietary EPA and DHA on colonic membrane phospholipid and subsequent inflammatory mediators following CPT-11+5-FU treatment over time and to compare that with the effect on the ileum. This objective was explored using an animal feeding study.

Female Fischer 344 rats were fed a control diet or a diet containing EPA and DHA initiated on the same day as chemotherapy (day 0). Ward colon tumor was implanted and allowed to grow for ~2 weeks prior to giving a clinically relevant dose of CPT-11 and 5-FU, administered sequentially within 24 hours. Rats were euthanized on day 0 and following chemotherapy on days 2, 4, and 8. Ileum and colon tissues were assessed for phospholipid fatty acids, cytokines, oxygenase enzyme protein, and oxylipins. Fecal microbiota sequencing, histological inflammatory scoring on colon tissue, and colonic myeloperoxidase levels were also assessed.

Chemotherapy depleted total phospholipids and essential fatty acids in the colon while having no effect on ileal phospholipid, suggesting specific cellular toxicity in colonic tissue. Total and individual oxylipins derived from AA increased after chemotherapy treatment, including prostaglandin (PG) D2, PGE2, 6-keto-PGF1α, thromboxane (Tx) B2, 5-hydroxyeicosatetraenoic acid (HETE), and 11,12-DiHETE in colon tissue and 6-keto-PGF1α, 8-HETE, and leukotriene B4 in ileum tissue. Early AA-derived signals corresponded with chemotherapy-induced disruptions to intestinal microbial communities and reduced total branched-chain fatty acids and isovalerate. Overt ileal and colonic inflammation were undetected through cytokines, immunohistochemistry, and myeloperoxidase levels.

Feeding the EPA+DHA diet resulted in a 9- and 2-fold relative increase from baseline to day 8 in EPA and DHA content of colonic membrane phospholipid, respectively, and a 40-fold and 2-fold relative increase in EPA and DHA content in ileal membrane phospholipid, respectively. Dietary EPA and DHA also prevented restoration of AA in colonic membrane phospholipid by day 8 exceeding a 1:1 replacement of AA with EPA and DHA in phospholipid molecular species. Rapid incorporation of EPA and DHA into intestinal membrane attenuated colonic TXB2 and PGE2 by day 2 and ileal 6-keto-PGF1α and PGD2 by day 4 to levels below baseline while increasing the anti-inflammatory AA metabolite lipoxin A4. The increase in EPA and DHA in membrane phospholipid corresponded with higher levels of EPA- and DHA-derived oxylipins by day 8, many of which are precursors to several specialized pro-resolving lipid mediators. The reduction in AA metabolites and increase in EPA and DHA metabolites implicates a lower inflammatory milieu that is likely responsible for mitigating early depletion of differentiating taxa and the number of late differentiating taxa in response to chemotherapy.

This thesis research suggests that the beneficial effect of EPA and DHA on ileum and colon tissue after cytotoxic chemotherapy is likely related to inhibiting regulatory enzymes that increase AA content in intestinal membrane phospholipid and synthesis of proinflammatory AA metabolites. Provision of EPA and DHA increases the very low levels of EPA and DHA content in ileal and colonic membrane phospholipid yielding EPA and DHA metabolites while reducing AA metabolites. Dietary EPA and DHA may, therefore, provide an important adjunct therapy to lower the risk of adverse intestinal effects of chemotherapy in colorectal cancer patients over multiple cycles.