Calcidiol and prostate cancer.

Epidemiological studies suggest that serum calcidiol (25(OH)-Vitamin D3) seems to be associated with several cancers including prostate cancer. We have made several experimental studies in order to clarify the mechanism(s) involved in the association. Calcidiol has been regarded as an inactive prohormone for calcitriol, which possesses the highest biological activity of the Vitamin D metabolites, when it is evaluated on the basis of bioactivity/nmol.

The role of Vitamin D3 metabolism in prostate cancer.

Vitamin D deficiency increases risk of prostate cancer. According to our recent results, the key Vitamin D hormone involved in the regulation of cell proliferation in prostate is 25(OH) Vitamin D3. It is mainly acting directly through the Vitamin D receptor (VDR), but partially also through its 1alpha-hydroxylation in the prostate.

5alpha-dihydrotestosterone inhibits 1alpha,25-dihydroxyvitamin D3-induced expression of CYP24 in human prostate cancer cells.

Background: A cross-talk between 1alpha,25-dihydroxyvitamin D(3) [1alpha,25-(OH)(2)D(3)] and 5alpha-dihydrotestosterone (DHT) in the growth inhibition has been demonstrated, but the mechanism is unknown.

Methods: The expression of 25-hydroxyvitamin D(3) 24-hydroxylase (24-hydroxylase) was measured using a real-time quantitative RT-PCR assay and the catabolism of 1alpha,25-(OH)(2)D(3) was measured using a radioreceptor assay.

Results: Real-time RT-PCR showed that DHT at 1-100 nM significantly inhibited 1alpha,25-(OH)(2)D(3)-induced expression of 24-hydroxylase in LNCaP cells.