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Accelerated sub-lesional bone loss is common in the first 2-3 years after traumatic spinal cord injury (TSCI), particularly in the distal femur and proximal tibia. Few studies have explored efficacy of antiresorptives for acute bone loss prevention post-TSCI, with limited data for knee bone mineral density (BMD) or beyond two years follow-up. An open-label non-randomized study was performed at Royal North Shore Hospital and Royal Rehab Centre, Sydney between 2018 and 2023. An 'acute interventional cohort' (n = 11) with TSCI (duration ≤ 12-weeks) received a single infusion of 4 mg zoledronic acid (ZOL) at baseline. A 'chronic non-interventional cohort' (n = 9) with TSCI (duration 1-5-years) did not receive ZOL. All participants underwent baseline and 6-monthly blood tests (including CTx and P1NP) and 12-monthly DXA BMD scans (including distal femur and proximal tibia). Participants were predominantly Caucasian and male (mean age 38.4 years). At baseline, the 'acute' cohort had higher serum CTx, P1NP and sclerostin concentrations, while the 'chronic' cohort had lower left hip and knee BMD. Majority with acute TSCI experienced an acute phase reaction after ZOL (9/11; 82%). In the acute cohort, left hip BMD fell by mean ~ 15% by 48 months. Left distal femoral and proximal tibial BMD declined by mean ~ 6-13% at 12 months and ~ 20-23% at 48 months, with a tendency towards greater BMD loss in motor-complete TSCI. A single early ZOL infusion in acute TSCI could not attenuate rapidly declining hip and knee BMD. Prospective controlled studies are required to establish the optimal strategy for preventing early bone loss after acute TSCI., (© 2024. The Author(s).)

Vitamin D deficiency is associated with muscle weakness, pain, and atrophy. Serum vitamin D predicts muscle strength and age-related muscle changes. However, precise mechanisms by which vitamin D affects skeletal muscle are unclear. To address this question, this study characterizes the muscle phenotype and gene expression of mice with deletion of vitamin D receptor (VDRKO) or diet-induced vitamin D deficiency. VDRKO and vitamin D-deficient mice had significantly weaker grip strength than their controls. Weakness progressed with age and duration of vitamin D deficiency, respectively. Histological assessment showed that VDRKO mice had muscle fibers that were significantly smaller in size and displayed hyper-nuclearity. Real-time PCR also indicated muscle developmental changes in VDRKO mice with dysregulation of myogenic regulatory factors (MRFs) and increased myostatin in quadriceps muscle (>2-fold). Vitamin D-deficient mice also showed increases in myostatin and the atrophy marker E3-ubiqutin ligase MuRF1. As a potential explanation for grip strength weakness, both groups of mice had down-regulation of genes encoding calcium-handling and sarco-endoplasmic reticulum calcium transport ATPase (Serca) channels. This is the first report of reduced strength, morphological, and gene expression changes in VDRKO and vitamin D-deficient mice where confounding by calcium, magnesium, and phosphate have been excluded by direct testing. Although suggested in earlier in vitro work, this study is the first to report an in vivo association between vitamin D, myostatin, and the regulation of muscle mass. These findings support a direct role for vitamin D in muscle function and corroborate earlier work on the presence of VDR in this tissue.

CYP27B1 encodes mitochondrial 1α-hydroxylase, which converts 25-hydroxyvitamin D to its active 1,25-dihydroxylated metabolite. We tested the hypothesis that common variants in the CYP27B1 promoter are associated with fracture risk. The study was designed as a population-based genetic association study, which involved 153 men and 596 women aged 65-101 years, who had been followed for 2.2 years (range 0.1-5.5) between 1999 and 2006. During the follow-up period, the incidence of fragility fractures was ascertained. Bone ultrasound attenuation (BUA) was measured in all individuals, as were serum 25-hydroxyvitamin D and PTH concentrations; 86% subjects had vitamin D insufficiency. Genotypes were determined for the -1260C>A (rs10877012) and +2838T>C (rs4646536) CYP27B1 polymorphisms. A reporter gene assay was used to assess functional expression of the -1260C>A CYP27B1 variants. The association between genotypes and fracture risk was analyzed by Cox's proportional hazards model. We found that genotypic distribution of CYP27B1 -1260 and CYP27B1 +2838 polymorphisms was consistent with the Hardy-Weinberg equilibrium law. The two polymorphisms were in high linkage disequilibrium, with D' = 0.96 and r² = 0.94. Each C allele of the CYP27B1 -1260 polymorphism was associated with increased risk of fracture (hazard ratio = 1.34, 95% CI 1.03-1.73), after adjustment for age, sex, number of falls, and BUA. In transient transfection studies, a reporter gene downstream of the -1260(A)-containing promoter was more highly expressed than that containing the C allele. These data suggest that a common but functional variation within the CYP27B1 promoter gene is associated with fracture risk in the elderly.