Colorectal cancer (CRC) is a major health issue in the UK, with a significant portion of cases potentially preventable through dietary and lifestyle changes. Diets high in omega-6 fatty acids are associated with increased CRC risk, while those rich in omega-3 fatty acids from fish may offer protective effects. The Seafood Polyp Prevention Trial aims to investigate the effectiveness of eicosapentaenoic acid (EPA), both alone and in combination with aspirin, in preventing colorectal adenomas in high-risk patients.

1. Diet and colorectal cancer risk
Nina Bailey
BSc (hons) MSc PhD ANutr

2. Colorectal cancer is the third most common cancer in the UK after
breast and lung cancer, with approximately 40,000 new cases
registered each year
Colorectal cancer is the second most common cause of cancer
death in the UK
Occurrence is strongly related to age, with almost three-quarters
of cases of colorectal cancer occurring in people aged 65 or over
It is estimated 50% of CRC cases could be avoided by improving
diet and increasing physical activity (World Cancer Research Fund,
2009)

3. The adenoma-carcinoma sequence
Carcinogenesis is recognised as a multi-step process involving a
combination of events at the cellular, molecular and
morphological levels pertaining to:
initiation (stable genomic alterations)
promotion (proliferation of genetically altered cells)
progression (an increase in tumour size, its spreading and
acquisition of additional genetic changes)

4. The adenoma-carcinoma sequence
The genetic changes in the malignant transformation process of
the colorectal mucosa include deletions, rearrangements and
mutations leading to either the activation or inactivation of specific
target genes including oncogenes (k-ras); tumour suppressor
genes (APC, p53, DCC) and mismatch repair (MMR) genes
Thus colorectal carcinogenesis sees the normal colonic mucosa
converted into a hyperproliferative state, leading to clonal
expansion, formation of an adenoma eventually leading to
carcinoma

7. Screening should begin at age 50, unless there is a family history of
colon cancer, in which case it should begin earlier
Faecal occult blood test (FOBT)
Stool samples tested for presence of blood
Sigmoidoscopy
Views lower third of the colon
Colonoscopy
Views entire colon
Colonoscopy should be done every ten years, Sigmoidoscopy and FOBT
every five years

8. The gastrointestinal tract undergoes a constant and rapid renewal and
is exposed to a hostile environment from both the systemic circulation
and from direct contact with the toxic content of the gut lumen
Earliest lesions in the development
of adenomas are dysplastic
aberrant crypt foci
The morphogenesis of adenomas
is not clearly understood
"top-down" vs "bottom-up“
The progression from adenoma to carcinoma can take several decades

9. Proximal/ascending colon
Active site of
carbohydrate
fermentation
Rapid transit
Low pH (c.a. 5.5/6.0)
Distal/descending colon
Active site of protein
fermentation
Slow transit
Neutral pH ≥ 7.0
Transverse colon
Slower fermentation rate
Reduced substrate availability

10. Dietary fat and CRC
High fat diets have long been hypothesised to increase the risk of
developing colorectal cancer, in part by increasing the secretion of bile
acids, which have a nonspecific irritant effect on the colonic lumen and
the production of genotoxic secondary bile acids, the metabolic by-
products of intestinal bacteria linked to hyperproliferation of the
colorectal mucosa
Whilst high fat diets are generally associated with increased
proliferation in the large bowel, it is the role of individual fatty acids,
rather than of total fat intake, that appears to be significant when
addressing CRC risk

11. Dietary fat and CRC
Diets that are high in saturated fats, for example, are thought to increase
the risk of cancer, whereas diets high in polyunsaturated fats that are rich
in omega-3 fatty acids derived from fish and fish oil are thought to
decrease the risk of cancer
Several studies indicate that whilst diets high in lard, beef tallow or corn
oil increase the concentration of colonic luminal secondary bile acids,
dietary fish oil at high concentrations have no such enhancing
effect (Bartram et al., 1998)
Dietary omega-6-PUFAs can promote carcinogenesis and can increase
chemically induced colonic tumours in rats, whereas diets rich in omega-3
tend to have an anti-promotional effect

12. Changes in omega fatty acids within the mucosa of CRC patients
Patients with CRC have shown increased concentrations of AA and AA
derived prostaglandins within the tumoural mucosa (Bennett et al, 1987)
Phospholipase A2 and prostaglandin E2 (potent tumour promoter) have
been shown to be increased in human colorectal cancer tissue (Soydan et
al., 1996)
Patients with CRC have shown increased concentrations of AA and DHA
(Neoptolemos et al., 1991)
Unlike EPA, DHA may have detrimental effects on CRC by accelerating
dysplastic tissue transformation (Woodworth et al., 2010)

13. Changes of the mucosal omega-3 and omega-6 fatty acid status occur early in
the colorectal adenoma-carcinoma sequence (Fernandez-Banares et al., 1996)
Plasma fatty acids
No difference between controls and adenoma groups
Cancer patients had significantly increased values of SFA and lower EPA compared
with both controls and adenoma groups
Colonic mucosa
Stepwise reduction in EPA from benign adenoma to more advanced carcinoma
(Dukes’ B to Dukes’ C-D)
Corresponding increase in the AA to EPA ratio
Low UI (unsaturation index) increase in SFA and decrease in MUFA

14. The AA to EPA ratio, inflammation and CRC
Inflammation creates the ideal “tumour microenvironment” and is now widely
recognised as an enabling characteristic of cancer in regard to enhanced cell
proliferation, cell survival, cell migration and angiogenesis
Many inflammatory mediators derived from AA such as cytokines, chemokines, and
eicosanoids are capable of stimulating the proliferation of both untransformed and
tumour cell proliferation
EPA, a key omega-3 fatty acid found in fish and fish oils possesses both anti-
inflammatory and anticancer activities, giving rise to end products that directly
oppose the actions of AA
The ratio of AA to EPA within the colic mucosa has the potential to modify the
inflammatory processes which influence the development of cancer

15. Influence on transcription factor activity, gene expression, and signal
transduction
Omega-3 and their metabolites may exert some of their antitumour effects
by affecting gene expression or the activities of signal transduction
molecules involved in the control of cell growth, differentiation apoptosis,
angiogenesis and metastasis:
•Peroxisome proliferator-activated receptor (PPAR)
•Nuclear transcription factor B
•Ras and protein kinase C
•Ornithine decarboxylase
•(HMG-CoA) reductase
•Cyclooxygenase-2 and lipoxygenases
•Phospholipase A2

16. Increased or decreased production of free radicals and reactive oxygen
species
Free radicals and reactive oxygen species (ROS) produced in cells
may attack PUFAs to form lipid hydroperoxides, which leads to the
formation of more free radicals and reactive aldehydes such as trans-4-
hydroxy-2-nonenal and malondialdehyde
These metabolites potentially generate DNA adducts in human cells,
which, if not repaired, have the potential to lead to cancer
Although omega-6 fatty acids augment these events through the
overproduction of AA-derived proinflammatory eicosanoids, the omega-3
fatty acids suppress inflammation and thus the overproduction of free
radicals and carcinogenesis

17. Bruce WR, Giacca A, Medline A: Possible mechanisms relating diet and risk of colon cancer.
Cancer Epidemiol Biomarkers Prev 2000, 9(12):1271-1279.

18. Fish consumption and CRC risk
Oily fish is a primary source of omega-3 fatty acids and a 2012 meta-
analysis of 22 prospective cohort and 19 case-control studies showed a
12% decrease in the relative risk (RR) of colorectal cancer (RR: 0.88;
95% CI: 0.78, 1.00) in a comparison of high fish consumption with low
fish consumption (Wu et al., 2012)
Dietary omega-3 exposure may not be sufficient for consistent anti-CRC
activity in individuals consuming moderate amounts of fish (a portion of
oily fish 2–3 times per week only provides the equivalent of
approximately 500 mg per day of EPA and DHA combined)

19. Fish or supplements?
EPA has been shown in studies to be significantly more effective than
DHA in reducing tumourigenesis in animal models of colorectal
cancer,with some indication that DHA may actually accelerate dysplastic
tissue transformation (Petrick et al., 2000; Woodworth et al., 2010)
Increasing numbers of studies are focusing on pure EPA as a safe and
potentially viable chemopreventative agent for the treatment of CRC
EPA has been shown to reduce intestinal adenoma multiplicity by 79% in
animal models of familial adenomatous polyposis (FAP) (Fini et al., 2010)
In humans, the effects of EPA (2g daily for 6 months) on rectal polyp
growth in patients with FAP produced a 22.4% decrease in adenoma
numbers and a 29.8% reduction in adenoma size (West et al., 2010)

20. The seAFOod Polyp Prevention Trial (Hull et al., 2013)
The seAFOod Polyp Prevention Trial is a randomised, double-blind,
placebo-controlled, 2×2 factorial ‘efficacy’ study, which will determine
whether EPA prevents colorectal adenomas, either alone (1 g twice
daily) or in combination with aspirin (300mg daily)
EPA and aspirin are both potent inhibitors of COX-1 but they alter COX-2
activity in ways leading to production of different bioactive lipid
mediators, including PGE3 (EPA) and 15R-HETE (aspirin)

21. Aspirin belongs to a group of drugs
called NSAIDs (Non Steroidal Anti
Inflammatory Drugs) that inhibit (COX)
enzymes resulting in decreased
prostaglandin synthesis.
There are two isoforms of COX, COX-1
which is constitutively expressed and
COX-2 which is inducible.
In colorectal carcinogenesis there is
over expression of COX-2 enzyme

22. The seAFOod Polyp Prevention Trial
Aspirin irreversibly acetylates the COX enzymes leading to conversion of
EPA to 18R-hydroxyeicosapentaenoic acid (18R-HEPE) and then
trihydroxy-EPA, also known as resolvin E1, which has potent anti-
inflammatory activity
Participants are 55–73 year-old patients, who have been identified as
‘high risk’ (detection of ≥5 small adenomas or ≥3 adenomas with at least
one being ≥10 mm in diameter) at screening colonoscopy in the English
Bowel Cancer Screening Programme (BCSP)

23. The primary aim of the seAFOod Polyp Prevention Trial is to determine
whether the naturally-occurring EPA, prevents colorectal adenomas, either
alone or in combination with aspirin
The primary end-point is the number of participants with one or more
adenomas detected at routine one-year colonoscopy
Secondary end-points include the number of adenomas (total and ‘advanced’)
per patient, the location (left versus right colon) of colorectal adenomas and
the number of participants re-classified as ‘intermediate risk’ for future
surveillance
Exploratory end-points include levels of bioactive lipid mediators such as
omega-3 resolvin E1 and PGE in plasma, urine, erythrocytes and rectal
mucosa in order to gain insights into the mechanism(s) of action of EPA and
aspirin, alone and in combination

24. Summary
Western dietary and lifestyle factors, particularly those that create an
inflammatory environment, contribute significantly to CRC risk
Diets that are high in omega-6 increase CRC risk, whilst diets that are rich in
long-chain omega-3 may reduce the risk of developing CRC
Specifically a high AA to EPA ratio and low EPA is found within the tumour
mucosa and may play a role in driving carcinogenesis
Modifying diet to reduce systemic inflammation by manipulating the AA to
EPA ratio has the potential to modify CRC risk
Pure EPA, because of its safety and known anti-cancer benefits is now
entering phase III human trials as a chemopreventive agent

25. ninab@igennus.com
www.igennus.com
drninabailey.co.uk
0044 1223 421434

26. References
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W, Vonk RJ, Mulder NH et al: Effects of oral calcium supplementation on intestinal bile acids and cytolytic
activity of fecal water in patients with adenomatous polyps of the colon. Eur J Clin Invest 1993, 23(1):63-68.
Wu S, Feng B, Li K, Zhu X, Liang S, Liu X, Han S, Wang B, Wu K, Miao D et al: Fish consumption and colorectal
cancer risk in humans: a systematic review and meta-analysis. Am J Med 2012, 125(6):551-559 e555.
Fodde R: The APC gene in colorectal cancer. Eur J Cancer 2002, 38(7):867-871.
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27. Alteration of oestrogen metabolism
Oestrogen has proliferative effects on oestrogen-sensitive tissues and high
oestrogen concentrations may increase the risk of breast cancer and of
some other hormone-dependent cancers
AA-derived eicosanoid PGE2 has been shown to stimulate the activity of
aromatase P450, which converts 19-carbon steroids to oestrogens
PGE3, a product of EPA metabolism, does not activate aromatase P450
Increasing EPA intake leads to increased PGE3 and a decrease in PGE2 from
AA, thereby decreasing oestrogen production and reducing oestrogen-
stimulated cell growth