Hydroxylation of CYP11A1-derived products of vitamin D3 metabolism by human and mouse CYP27B1.

Abstract

CYP11A1 can hydroxylate vitamin D3 at carbons 17, 20, 22, and 23, producing a range of secosteroids which are biologically active with respect to their ability to inhibit proliferation and stimulate differentiation of various cell types, including cancer cells. As 1α-hydroxylation of the primary metabolite of CYP11A1 action, 20S-hydroxyvitamin D3 [20(OH)D3], greatly influences its properties, we examined the ability of both human and mouse CYP27B1 to 1α-hydroxylate six secosteroids generated by CYP11A1. Based on their kcat/Km values, all CYP11A1-derived metabolites are poor substrates for CYP27B1 from both species compared with 25-hydroxyvitamin D3. No hydroxylation of metabolites with a 17α-hydroxyl group was observed. 17α,20-Dihydroxyvitamin D3 acted as an inhibitor on human CYP27B1 but not the mouse enzyme. We also tested CYP27B1 activity on 20,24-, 20,25-, and 20,26-dihydroxyvitamin D3, which are products of CYP24A1 or CYP27A1 activity on 20(OH)D3. All three compounds were metabolized with higher catalytic efficiency (kcat/Km) by both mouse and human CYP27B1 than 25-hydroxyvitamin D3. CYP27B1 action on these new dihydroxy derivatives was confirmed to be 1α-hydroxylation by mass spectrometry and nuclear magnetic resonance analyses. Both 1,20,25- and 1,20,26- trihydroxyvitamin D3 were tested for their ability to inhibit melanoma (SKMEL-188) colony formation, and were significantly more active than 20(OH)D3. This study shows that CYP11A1-derived secosteroids are 1α-hydroxylated by both human and mouse CYP27B1 with low catalytic efficiency, and that the presence of a 17α-hydroxyl group completely blocks 1α-hydroxylation. In contrast, the secondary metabolites produced by subsequent hydroxylation of 20(OH)D3 at C24, C25, or C26 are very good substrates for CYP27B1.

• Authors: Edith K Y Tang, Jianjun Chen, Zorica Janjetovic, Elaine W Tieu, Andrzej T Slominski, Wei Li, Robert C Tuckey
• Journal: Drug metabolism and disposition: the biological fate of chemicals (Drug Metab Dispos) Vol. 41 Issue 5 Pg. 1112-24 (May 2013) ISSN: 1521-009X [Electronic] United States
• PMID: 23454830 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, Non-U.S. Gov't)

Chemical References

• Enzyme Inhibitors
• Cholecalciferol
• 25-Hydroxyvitamin D3 1-alpha-Hydroxylase
• Cholesterol Side-Chain Cleavage Enzyme

Topics

• 25-Hydroxyvitamin D3 1-alpha-Hydroxylase (antagonists & inhibitors, metabolism)
• Animals
• Cholecalciferol (analogs & derivatives, metabolism)
• Cholesterol Side-Chain Cleavage Enzyme (metabolism)
• Enzyme Inhibitors (pharmacology)
• Humans
• Hydroxylation
• Magnetic Resonance Spectroscopy
• Mass Spectrometry
• Mice