While the major source of vitamin D is D<sub>3</sub> from ultraviolet exposure, some supplements supply D<sub>2</sub>. The relative potency of vitamin D<sub>2</sub> versus vitamin D<sub>3</sub> remains controversial. The aims of the current study were, 1. To optimize the in vitro model, including use of cell lines, vitamin D concentrations, and outcome biomarkers. 2. To compare the potency of vitamin D<sub>2</sub> and D<sub>3</sub> metabolites on mouse and human bone cellular activity. 3. To explore the expression of VDR in osteoarthritic (OA) bone tissues as well as cellular responses to vitamin D<sub>2</sub> and D<sub>3</sub> metabolites ex-vivo. In mouse 2T3 osteoblasts, at physiological doses, both vitamin D<sub>2</sub> and D<sub>3</sub> metabolites increased ALP activity and mineralisation and up-regulated osteoblastic signature genes and proteins. At supra-physiological doses D<sub>3</sub> metabolites were more potent inhibitors of 2T3 function than D<sub>2</sub> metabolites. Although hBMS cell proliferation was inhibited by both 25(OH)D<sub>2</sub> and D<sub>3</sub>, ALP activity was enhanced by both metabolites. However, 25(OH)D<sub>3</sub> was a more potent stimulator of ALP and mineralisation of hBMSCs. D<sub>2</sub> and D<sub>3</sub> equally stimulated expression of CX43 and PHEX markers in osteocytic cell lines. Immunohistochemistry of femoral heads showed much reduced VDR expression in OA osteocytes and osteoclasts, yet both 25(OH)D2 and D<sub>3</sub> increased OA-hBMSCs mineralisation more than non-OA-hBMSCs ex-vivo. While vitamin D<sub>2</sub> or D<sub>3</sub> increased mouse 2T3 osteoblastic activity at physiological doses, OA and non-OA hBMSCs differentiation was more responsive to 25(OH)D<sub>3</sub>. Key bone cells such as osteocyte and osteoclasts expressed less VDR in OA. For the first time vitamin D<sub>2</sub> metabolites have been thoroughly examined and emerged as a potent stimulator of bone cell differentiation, at least in vitro. Vitamin D<sub>3</sub> in contrast is confirmed as highly potent in bone cells, but with toxicity at much lower doses than D<sub>2</sub>.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:635313 |
| Date | January 2015 |
| Creators | Zarei, Allahdad |
| Contributors | Sabokbar, Afsie; Javaid, Kassim; Hulley, Philippa; Moravat, Reza |
| Publisher | University of Oxford |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://ora.ox.ac.uk/objects/uuid:8d363814-c1e5-4f16-929d-18ac9debde75 |
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