C. N. Vanicek1, M. M. Aldajani1, N. Alhazzaa1, R. Agarwal1, J. P. Geibel1 1Yale University School Of Medicine,Surgery,New Haven, CT, USA
Introduction:
For colorectal cancer to grow and invade healthy tissues, it must maintain a higher (more alkali) intracellular pH and a lower (more acidic) extracellular pH, in the immediate environment around the metaplastic cell. For this reason, colorectal cancer remains as one of the leading causes of death in the United States and worldwide.
In a study presented at this meeting we provide evidence that acute Vitamin C exposure at high doses could down regulate Na-dependent acid efflux pathways in colonic crypt cells. In previous studies, Vitamin C was shown to increase nitric oxide production through stimulating nitric oxide synthase. The role of nitric oxide (NO) on cancer growth remains complex. Prolonged chronic exposure to NO ,which is typical during chronic inflammation, leads to gene mutations which were linked to cancer development. However, conversely it also has been shown that NO derived from macrophages, Kupffer cells, natural killer cells, and endothelial cells is a tumorcidal agent that results in cancer apoptosis and cessation of growth and metastasis. In this present study we examined the acute effects of Vitamin C exposure on nitric oxide
production and its effects on Na-dependent acid secretion.
Methods:
Following excision, rat colon was digested leaving single isolated crypts, which were then
incubated with the pH sensitive dye BCECF. The crypts were then imaged while being perfused
with solutions either containing or devoid of Vitamin C, L-NAME and L-Arginine. The ratio image
data was collected every 10 second. to allow a direct real time measurement of changes in pH All
data were then analyzed with GraphPad Prism.
Results:
By comparing rates of pH recovery under these various conditions we found that: 1) There was no difference in the Na-dependent H extrusion rate between Vitamin C and L-arginine. 2) Treatment of colonic crypts with L-NAME, a NO synthesis inhibitor, reversed the Vitamin C dependent NHE inhibition.
Conclusion:
We found that exposure to Vitamin C gives a similar inhibition in acid secretion as Arginine a known NO producer. This further shows a tight link to Vitamin C and NO production and the ability of NO to significantly inhibit hydrogen ion excretion. In separate studies where crypts were given L-NAME the level of acid secretion returned to normal control rates. Our data suggest a tight link between Vitamin C exposure and a reduction of acid secretion via NO synthesis. Therefor the anti-tumorigenic effect equated to Vitamin C may be synergistic with the tumorcidal effect of NO found in other tissues.