Fluorescent risedronate analogues reveal bisphosphonate uptake by bone marrow monocytes and localization around osteocytes in vivo

Anke J Roelofs, Fraser Coxon, Frank H Ebetino, Mark W Lundy, Zachary J Henneman, George H Nancollas, Shuting Sun, Katarzyna M Blazewska, Joy Lynn F Bala, Boris A Kashemirov, Aysha B Khalid, Charles E McKenna, Michael J Rogers

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Abstract

Bisphosphonates are effective antiresorptive agents owing to their bone-targeting property and ability to inhibit osteoclasts. It remains unclear, however, whether any non-osteoclast cells are directly affected by these drugs in vivo. Two fluorescent risedronate analogues, carboxyfluorescein-labeled risedronate (FAM-RIS) and Alexa Fluor 647–labeled risedronate (AF647-RIS), were used to address this question. Twenty-four hours after injection into 3-month-old mice, fluorescent risedronate analogues were bound to bone surfaces. More detailed analysis revealed labeling of vascular channel walls within cortical bone. Furthermore, fluorescent risedronate analogues were present in osteocytic lacunae in close proximity to vascular channels and localized to the lacunae of newly embedded osteocytes close to the bone surface. Following injection into newborn rabbits, intracellular uptake of fluorescently labeled risedronate was detected in osteoclasts, and the active analogue FAM-RIS caused accumulation of unprenylated Rap1A in these cells. In addition, CD14high bone marrow monocytes showed relatively high levels of uptake of fluorescently labeled risedronate, which correlated with selective accumulation of unprenylated Rap1A in CD14+ cells, as well as osteoclasts, following treatment with risedronate in vivo. Similar results were obtained when either rabbit or human bone marrow cells were treated with fluorescent risedronate analogues in vitro. These findings suggest that the capacity of different cell types to endocytose bisphosphonate is a major determinant for the degree of cellular drug uptake in vitro as well as in vivo. In conclusion, this study shows that in addition to bone-resorbing osteoclasts, bisphosphonates may exert direct effects on bone marrow monocytes in vivo. © 2010 American Society for Bone and Mineral Research
Original languageEnglish
Pages (from-to)606-616
Number of pages11
JournalJournal of Bone and Mineral Research
Volume25
Issue number3
DOIs
Publication statusPublished - Mar 2010

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Keywords

  • bisphosphonates
  • fluorescent conjugates
  • cellular uptake
  • osteocytes
  • monocytes

Cite this

Roelofs, A. J., Coxon, F., Ebetino, F. H., Lundy, M. W., Henneman, Z. J., Nancollas, G. H., Sun, S., Blazewska, K. M., Lynn F Bala, J., Kashemirov, B. A., Khalid, A. B., McKenna, C. E., & Rogers, M. J. (2010). Fluorescent risedronate analogues reveal bisphosphonate uptake by bone marrow monocytes and localization around osteocytes in vivo. Journal of Bone and Mineral Research, 25(3), 606-616. https://doi.org/10.1359/jbmr.091009