Submitted to: Archives Of Biochemistry and Biophysics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/16/2001
Publication Date: N/A
Citation: Interpretive Summary: One form of vitamin D, vitamin D3 (commonly found in animals), has part of its structure removed and modified to make the vitamin water-soluble. Dissolved in water, calcitroic acid can be excreted from the body. A second form of vitamin D, vitamin D2 (commonly found in plants), is used as a dietary supplement. Vitamin D2 can be added to oral vitamin supplements or dairy products, like milk. Although vitamin D2 is very similar to vitamin D3, slight differences make it appear different to the body when the body wants to excrete it. Scientists have assumed that both vitamins D2 and D3 are excreted as the same product. This paper is the first to show that vitamin D2 is broken down to calcitroic acid, the same excreted product as that of vitamin D3. This discovery assures the world that ingesting vitamin D2 will not cause the buildup of any toxic vitamin D products in the human body. This important discovery was illustrated when giving the activated form of vitamin D2 to human skin cells and to a rat kidney. This paper explains how the kidney and human skin cells modified the structure of vitamin D2, removed part of its structure, and created the same product as seen in vitamin D3, calcitroic acid. This paper opens the door for a new series of possible treatments for patients with cancer and some skin diseases. Pharmaceutical companies can work backwards from the end product, shown here, to develop these new treatments. Anyone from farmers, to vitamin companies, to the consumer can now use vitamin D2 as a supplement without fear of toxic building of metabolic products.
Technical Abstract: Calcitroic acid (1a-hydroxy-23 carboxy-24,25,26,27-tetranorvitamin D3) is known to be the major water-soluble metabolite produced during the deactivation of 1a,25-dihydroxyvitamin D3. This deactivation process involves a series of oxidation reactions at C24 and C23 leading to side- chain cleavage and, ultimately, formation of the calcitroic acid. Like 1a,25-dihydroxyvitamin D3, 1a,25-dihydroxyvitamin D2 is known to undergo side-chain oxidation; however, there has been no evidence suggesting that 1a,25-dihydroxyvitamin D2 undergoes side-chain cleavage. To investigate this possibility, we studied 1a,25-dihydroxyvitamin D2 metabolism in HPK1A-ras cells as well as the well characterized perfused rat kidney system. Lipid and aqueous soluble metabolites were prepared for characterization. Aqueous-soluble metabolites were subjected to reverse phase HPLC analysis. The major aqueous-soluble metabolite from both the kidney and cell incubations co-migrated with authentic calcitroic acid on 2 reverse-phase HPLC columns of different chemistry. The putative calcitroic acid from the cell and kidney incubations was methylated and found to co-migrate with methylated authentic standard on straight-phase and reverse-phase HPLC columns. The identity of the methylated metabolite from cell incubations was also confirmed by mass spectral analysis. These data show that calcitroic acid is a major terminal product for the deactivation of 1a,25-dihydroxyvitamin D2. Intermediates leading to the formation of the calcitroic acid in the 1a,25-dihydroxyvitamin D2 metabolism pathway are currently being studied.