The effect of vitamin D on gene expression in colorectal tumours and normal colon.
Munro, Francesca Maree
Background Colorectal cancer (CRC) is the third most frequently diagnosed malignancy and the fourth leading cause of death from cancer worldwide. In New Zealand, incidence rates of CRC are projected to decline in all age groups. The overall burden is projected to continue increasing as a result of population growth and an aging population. Epidemiological studies have reported an inverse association between vitamin D status and incidence of CRC. Higher serum vitamin D levels at the time of diagnosis or post-surgery have been associated with improved long-term outcome in CRC, but there is no proven causal link. It has been postulated that vitamin D levels should be maintained at >80 nmol/L for both bone and overall health. Vitamin D deficiency is common in NZ particularly in the winter months. The primary aim of this study was to examine whether a single large dose of vitamin D administered to CRC patients in the window between diagnosis and surgery could have a measurable effect on vitamin D responsive genes in the tumour and corresponding normal colon. Methods The study was a randomised, double-blind, placebo-controlled trial of vitamin D supplementation in patients undergoing elective surgery for CRC at Dunedin Hospital. For the primary outcome, RNA from resected normal and tumour tissue was profiled on microarray gene-chips. Array gene expression data were analysed using single gene analysis to identify differentially expressed individual genes and over-representation and gene-set analysis (GSA) to identify differences in pathway expression. Secondary outcomes including complication rate, length of hospitalisation, post-operative recovery and survival were measured. Results There were no baseline differences between the treatment and control groups. Pre-incision vitamin D concentrations were higher in the treatment than in the placebo group (mean 87 +/- 22 vs 49 +/- 19 nmol/L; p= >0.001). The complication rate and length of hospitalisation were within the expected range for this cohort. No differences in post-operative recovery, cancer recurrence or survival were observed. There were no significant differences in single gene expression between the treatment and control groups. There were also no significant differences in gene expression of vitamin D modulated genes between the groups. Differences in pathway expression were identified between the treatment arm and placebo arm. In the normal tissue, patients randomised to receive vitamin D had down-regulation of a number of pathways compared to those randomised to the placebo group including Fatty Acid Metabolism, Drug Metabolism - Cytochrome P450, Metabolism of Xenobiotics by Cytochrome P450, Vitamin Digestion and Absorption and Negative Regulation of Growth pathways. In the tumour tissue the treated group also had down-regulation of several pathways compared to the placebo group including the Fatty Acid Metabolism, Fatty Acid beta-Oxidation and Oxidative Phosphorylation pathways. In the paired analysis the expression of the Ribosome and Translational Termination pathways were enhanced by vitamin D in the tumour tissue of a subgroup of patients and reduced in another subgroup, compared to the normal tissue. Over-representation analyses identified a number of other pathways that may be different between the study groups. Conclusion In this randomised controlled trial potentially significant biological differences between the vitamin D and placebo groups were identified. The Fatty Acid Metabolism and Fatty Acid beta-Oxidation pathways were down-regulated in the tumour tissue of the treated patients compared with the untreated patients. Down-regulation of fatty acid metabolism in the tumour may lead to the slowing of tumour growth. Un-metabolised butyrate (short-chain fatty acid utilised by colon epithelia) may also precipitate reduced cell proliferation and enhanced differentiation and apoptosis. Further work is required to develop our understanding of the impact of vitamin D on the biology of colorectal cancer.
Advisor: McCall, John Lindsay; Black, Michael A
Degree Name: Master of Science
Degree Discipline: Biochemistry
Publisher: University of Otago
Keywords: Colorectal cancer; Vitamin D
Research Type: Thesis