Endocrine Abstracts

Introduction: The development of colorectal cancer is influenced by dietary as well as growth factors. Butyrate, (NaB) one of the metabolic by-products of bacterial fermentation of dietary fibre is a primary source of energy for colonic mucosa. It has growth-promoting effects on normal colonic epithelial cells, induces cell cycle arrest, differentiation and apoptosis in colorectal cancer cells. Since it has been suggested that the apoptotic effects of NaB may be due to its synergistic action with vitamin D (VitD), we hypothesized that NaB may be involve in the regulation of vitamin D axis locally.

Methods: Biopsies from patients undergoing colonoscopy for irregular bowel habit without colonic pathology were incubated with 5 mM NaB for up to 48 hours. HT29 cells were cultured for up to 72hrs in serum free media with 5 mM NaB. Assessment was made of proliferation by the colorimetric MTS assay and direct cell counting using trypan blue; apoptosis by FACS analysis using propidium iodide and annexin staining. mRNA expression levels to the Vitamin D axis genes (1αOHase, 24OHase and VDR) and c-Myc were quantified by real-time RT-PCR.

Results: In HT29 cell line, NaB induced apoptosis in HT29 CRC cells line. Colonic explants gene expression varies between patients in response to NAB. NaB up-regulates both 1αOHase and 24OHase mRNA expression and down-regulate c-Myc and VDR mRNA levels. Similarly, in HT29 cells exposed to NaB, 1αOHase mRNA expression levels increased steadily to more than 700% of control levels after 72 hours. 24OHase mRNA expression was rapidly induced in NaB treated cells, rising from 400% by 24 hr to more than 1000% of control by 72 hours. Exposure of cells to NaB progressively inhibited VDR mRNA levels (by 50%) and c-Myc mRNA copy number by more than 70%.

Conclusions: Our findings suggest that there is a local regulatory pathway for both activation and further metabolism of VitD by the colon.