Modulation of colonocyte proliferation and apoptosis by dietary fish oil in experimental colorectal carcinogenesis

Eicosapentaenoic acid (EPA) reduces crypt cell proliferation and increases apoptosis in normal colonic mucosa in subjects with a history of colorectal adenomas

BACKGROUND AND AIMS

Omega-3 fatty acids in fish oil exert a protective effect on the development of colorectal cancer in animal models. Patients with colorectal adenomas have been shown to have increased crypt cell proliferation and decreased apoptosis in macroscopically normal appearing colonic mucosa. We investigated whether dietary supplementation with eicosapentaenoic acid (EPA) could alter crypt cell proliferation and apoptosis in such patients.

PATIENTS/METHODS

Thirty subjects were randomised to either 3 months of highly purified EPA in free fatty acid form (2 g/day) or to no treatment. Colonic biopsies were taken at the initial colonoscopy and repeated 3 months later, and analysed for cell proliferation and apoptosis (immunohistochemistry) and mucosal fatty acid content.

RESULTS/FINDINGS

Crypt cell proliferation was significantly reduced whilst apoptosis was significantly increased after EPA supplementation. Neither crypt cell proliferation nor apoptosis were altered in the control group. EPA in the mucosa increased significantly after EPA supplementation, whereas there was no significant change in controls.

CONCLUSIONS

Dietary supplementation with EPA significantly increases levels of this fatty acid in colonic mucosa, associated with significantly reduced proliferation and increased mucosal apoptosis. Further studies are needed to assess the potential efficacy of EPA supplementation in preventing polyps in the chemoprevention of colorectal cancer.

ω-3 Polyunsaturated fatty acids and ionizing radiation: Combined cytotoxicity on human colorectal adenocarcinoma cells

OBJECTIVE

This study evaluated whether omega-3 polyunsaturated fatty acids (PUFAs) could enhance the radiosensitivity of three different human colorectal adenocarcinoma cell lines. To understand the underlying mechanisms, the effects of omega-3 PUFAs on the cell growth, survival, and apoptosis were evaluated alone or in combination with an antioxidant (vitamin E) and compared with the effects of omega-6 PUFAs.

METHODS

LS174T, CO112, and Caco-2 cell survival was assessed by clonogenic assay after a 3-d pretreatment with omega-3/omega-6 PUFAs and/or vitamin E before a single X-ray exposure to 4 Gy. Cell growth and viability were measured by double fluorescence-activated cell sorter analyses using propidium iodide and fluorescein isothiocyanate-conjugated annexin V. Student's t test or multivariable linear regression analyses were used for comparison.

RESULTS

Preincubation with 30 to 100 micromol/L of omega-3 PUFAs induced a dose-dependent additive decrease in cell survival after irradiation (P < 0.05). Evaluation of the underlying mechanisms indicated that omega-3 PUFAs mainly decreased the cell number via apoptosis induction. Moreover, formation of lipid peroxidation products and modulation of cyclooxygenase II activity seemed to be involved, because coincubation with 10 micromol/L vitamin E abolished the effect of 50 micromol/L of omega-3 PUFAs (P < 0.05), whereas omega-6 PUFAs could partly mimic omega-3 PUFA effects.

CONCLUSION

These observations suggest that omega-3 PUFAs may be potential candidates as nutritional adjuvants to enhance the efficacy of human colorectal cancer radiotherapy.

Omega-3 fatty acids: molecular approaches to optimal biological outcomes

PURPOSE OF REVIEW

This review discusses recent advances in delineating basic mechanisms underlying the beneficial effects of omega-3 fatty acids on health and on disease.

RECENT FINDINGS

While a substantial number of studies have delineated many differences between the biological effects of saturated versus polyunsaturated fatty acids, less is known about the long-chain omega-3 fatty acids commonly present in certain fish oils. In this review, we focus on recent studies relating to basic mechanisms whereby omega-3 fatty acids modulate cellular pathways to exert beneficial effects on promoting health and decreasing risks of certain diseases. We will use, as examples, conditions of the cardiovascular, neurological, and immunological systems as well as diabetes and cancer, and then discuss basic regulatory pathways.

SUMMARY

Omega-3 fatty acids are major regulators of multiple molecular pathways, altering many areas of cellular and organ function, metabolism and gene expression. Generally, these regulatory events lead to "positive" endpoints relating to health and disease.

n-3 Polyunsaturated fatty acids and colon cancer prevention

The incidence of colon cancer in industrialised countries has increased since the early 1970s. It is estimated that more than one-third of cases are associated with factors related to a Western diet. Both the type and amount of dietary fats consumed have been implicated in colon cancer aetiology. Recent studies have demonstrated that n-3 polyunsaturated fatty acids (PUFAs), commonly found in fish oil (FO), could prevent colon cancer development. Evidences show that n-3 PUFAs act at different stages of cancer development and through several mechanisms including the modulation of arachidonic acid-derived prostaglandin synthesis, and Ras protein and protein kinase C expression and activity. As a result, n-3 PUFAs limit tumour cell proliferation, increase apoptotic potential along the crypt axis, promote cell differentiation and possibly limit angiogenesis. The modulatory actions of n-3 PUFAs on the immune system and their anti-inflammatory effects might also play a role in reducing colon carcinogenesis. There remains, nevertheless, some ambiguity over the safety of n-3 PUFAs with respect to secondary tumour formation. However, it appears that n-3 PUFAs may be of use in colon cancer prevention.

Anticarcinogenic effects of diet-related apoptosis in the colorectal mucosa

The crypt is the fundamental unit of epithelial proliferation in the intestinal mucosa. The progeny of the pluripotent stem cells located near the base of the crypt migrate towards the crypt orifice, divide once or twice more, and then undergo differentiation, senescence and exfoliation. Programmed cell death (apoptosis) also occurs deep in the proliferative zone. Various lines of evidence suggest that apoptosis provides a protective mechanism against neoplasia by removing genetically damaged stem cells from the epithelium before they can undergo clonal expansion. Several different classes of food constituents, including certain polyunsaturated fatty acids, the short-chain fatty acid butyrate, and some phytochemicals including flavonoids and glucosinolates breakdown products, can modulate both cellular proliferation and programmed death. Each of these food components has also been shown to suppress the emergence of aberrant crypt foci in animal models of carcinogenesis. Further mechanistic and clinical studies are required to establish whether such dietary effects can be exploited to achieve preventive or therapeutic effects in humans.

New food components and gastrointestinal health

Apart from its main functions of digestion, absorption and faecal processing, the human gastrointestinal tract has a complex pattern of muscular activity regulated by a largely autonomous nervous system, and its various organs contain large concentrations of immune and endocrine tissues. Any failure of these closely-integrated systems can lead to diseases ranging from the mildly irritating to the life threatening. Food contains a huge variety of chemical species, many of which are biologically active, and the distal regions of the gut are colonised by a rich and metabolically-active commensal flora that depend on nutrients derived ultimately from the host's dietary residues. The present paper explores the evidence for significant effects of food ingredients on functional bowel disorders, intestinal infections, and aspects of epithelial cell physiology involved in the development of colo-rectal neoplasia. Various strategies, including the manipulation of the colo-rectal microflora with pre- and probiotics, and the development of new products and plant varieties containing biologically-active constituents, have the potential to underpin the development of novel functional food products. However, these products will need to be based on proven biological principles, and fully tested for efficacy and safety. The rapidly-developing fields of functional genomics and cell biology will open up new experimental strategies to explore these possibilities, and emerging processing technologies seem likely to provide novel methods for their exploitation.