Preclinical safety and efficacy of 24R,25-dihydroxyvitamin D3 or lactosylceramide treatment to enhance fracture repair

Preclinical safety and efficacy of 24R,25-dihydroxyvitamin D3 or lactosylceramide treatment to enhance fracture repair

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Background/Objective: Cyp24a1-null mice deficient in 24,25(OH)2D3 display impaired callus formation during the endochondral phase of bone fracture repair.The 24,25(OH)2D3 metabolite acted by binding to the TLC domain containing 3B isoform 2 (TLCD3B2, previously named FAM57B2) effector protein, which then synthesizes lactosylceramide (LacCer).Treatment with 24,25(OH)2D3 or LacCer restored callus size and mechanical properties in Cyp24a1-null mice.Methods: To assess the safety of these molecules and test their efficacy for bone healing in wild-type, non-genetically modified mice, we treated 12-week-old, osteotomized C57BL/6 female mice with each compound for up to 21 days post-osteotomy.

Control cohorts were injected with Europe/USA/Japan vehicle.Results: Neither compound was found to exhibit any nephro- nor hepato-toxicity.Calcemia remained stable throughout the experiment and was unaffected by either treatment.Supplementation with 24,25(OH)2D3 increased circulating levels of this metabolite about 8-fold, decreased 1,25(OH)2D3 levels, and significantly increased circulating 1,24,25(OH)3D3 levels, suggesting 1?-hydroxylation of 24,25(OH)2D3.

TLCD3B2 was found to be expressed in fracture callus at the surface Black Seed of unmineralized or pre-mineralized cartilage on day 10 and day 12 post-osteotomy and to progressively recede to become undetectable by day 18.Treatment with 24,25(OH)2D3 or LacCer reduced the number of TLCD3B2-positive cells.Both treatments also significantly increased stiffness and elastic modulus of the healing bone callus.Conclusion: Exogenous administration of 24,25(OH)2D3 or LacCer improved the biomechanical properties of repaired bones in wild-type animals without affecting circulating calcium levels or other blood parameters, demonstrating preclinical safety and efficacy.

Translational potential: Our data suggest the use of 24R,25-dihydroxyvitamin D3 or lactosylceramide for ameliorating fracture healing in clinical practice.