Publications

Parathyroid hormone (PTH) analogs with improved actions in vivo could lead to optimized treatments for bone and mineral ion diseases. Rapid clearance from the circulation and short dwell times on the PTH receptor limit the efficacies of conventional PTH peptides currently in medical use. Here, we seek to enhance PTH peptide efficacy using two distinct peptide lipidation strategies. First, we append a lipid chain to the peptide's C-terminus in a fashion to promote binding to serum albumin and hence prolong the peptide's circulation half-life in vivo. Second, we append a lipid chain to a lysine side chain in a fashion designed to anchor the peptide to the cell membrane as the ligand is bound to the receptor and hence increase its dwell time on the receptor. We find that both strategies of lipidation can profoundly enhance the efficacy of PTH peptides in vitro and in mice. Our results could lead to the development of modified PTH analogs with optimized therapeutic utility.

Bariatric surgeries such as Roux-en-Y gastric bypass (RYGB) and adjustable gastric banding (AGB) lead to long-term deficits in bone density but are also accompanied by decreased weight, which may lower the impact force with falls. The aim of this study was to compare the long-term skeletal impact of RYGB and AGB using a biomechanical evaluation of load-to-strength ratio at the distal radius as a surrogate for wrist fracture risk. We conducted a cross-sectional study evaluating bone microarchitectural parameters and bone turnover in adults who received either RYGB or AGB surgery ≥10 yr ago (RYGB: n = 22; AGB: n = 23). Bone strength at the distal radius was estimated by microfinite element analysis from HR-pQCT. We used a single-spring biomechanical model to estimate impact force and then calculated load-to-strength ratio as a ratio of impact force to bone strength, with higher load-to-strength ratios representing a higher susceptibility to fracture. In multivariable analyses, the RYGB group had higher bone resorption marker C-telopeptide (CTX) levels, lower volumetric bone density, and worse cortical and trabecular microarchitectural parameters than the AGB group. Furthermore, estimated bone strength at the radius was lower in the RYGB group (3725 ± 139 N vs 4141 ± 157 N, p = .030), and the load-to-strength ratio was higher in RYGB group as compared with AGB (0.84 ± 0.04 vs 0.72 ± 0.05, p = .035), suggestive of higher propensity for wrist fracture. Taken together, these results indicate the long-term deleterious skeletal effects are more concerning with RYGB than AGB.

We have proposed to the Food and Drug Administration (FDA) that treatment-related increases in total hip BMD (TH BMD) at 2 yr could be a surrogate endpoint for fracture risk reduction in clinical trials. The qualification of a surrogate includes a strong association of the surrogate with the clinical outcome. We compiled a large database of individual patient data (IPD) through the Foundation for the National Institutes of Health-American Society for Bone and Mineral Research- A Study to Advance BMD as a Regulatory Endpoint (FNIH-ASBMR-SABRE) project, and this analysis aimed to assess the relationship between baseline BMD and fracture risk in the placebo groups. We estimated the association of baseline TH, femoral neck (FN), and lumbar spine (LS) BMD with fracture risk using IPD from the combined placebo groups, which included data from 46 666 placebo participants in 25 RCTs. We estimated the relative risk (RR) of fracture per SD decrease in baseline BMD using logistic regression models for radiographic vertebral fractures and proportional hazards models for hip, non-vertebral, "all," and "all clinical" fractures. Total person-years in the combined placebo groups was 250 662 (mean baseline age 70.2 ± 7.2 yr, mean TH BMD T-score -1.97 ± 0.90). We observed significant relationships between baseline TH BMD and vertebral (RR = 1.55/SD), hip (RR = 2.27), non-vertebral (RR = 1.31), all (RR = 1.43), and all clinical (RR = 1.35) fracture risk. Fracture risk estimates were similar for FN BMD and after adjustment for age, race, and study. Fracture incidence increased with decreasing TH BMD quintile, confirming the strong graded association between TH BMD and fracture risk. There was a strong relationship between LS BMD and vertebral fracture risk (RR = 1.56/SD), but only a weak association with non-vertebral (RR = 1.07) and no association with hip (RR = 1.01) fracture risk. These data support the very strong relationship between hip BMD and fracture risk and provide supporting rationale for change in TH BMD as a surrogate for fracture risk reduction in future RCTs.

UNLABELLED: Up to 40% of elite athletes experience bone stress injuries (BSIs), with 20-30% facing reinjury. Early identification of runners at high risk of subsequent BSI could improve prevention strategies. However, the complex etiology and multifactorial risk factors of BSIs makes identifying predictive risk factors challenging. In a study of 30 female recreational athletes with tibial BSIs, 10 experienced additional BSIs over a 1-year period, prompting investigation of systemic biomarkers of subsequent BSIs using aptamer-based proteomic technology. We hypothesized that early proteomic signatures could discriminate runners who experienced subsequent BSIs. 1,500 proteins related to metabolic, immune, and bone healing pathways were examined. Using supervised machine learning and genetic programming methods, we analyzed serum protein signatures over the 1-year monitoring period. Models were also created with clinical metrics, including standard-of-care blood analysis, bone density measures, and health histories. Protein signatures collected within three weeks of BSI diagnosis achieved the greatest separation by sparse partial least squares discriminant analysis (sPLS-DA), clustering single and recurrent BSI individuals with a mean accuracy of 96 ± 0.02%. Genetic programming models independently verified the presence of candidate biomarkers, including fumarylacetoacetase, osteopontin, and trypsin-2, which significantly outperformed clinical metrics. Time-course differential expression analysis highlighted 112 differentially expressed proteins in individuals with additional BSIs. Gene set enrichment analysis mapped these proteins to pathways indicating increased fibrin clot formation and decreased immune signaling in recurrent BSI individuals. These findings provide new insights into biomarkers and dysregulated protein pathways associated with recurrent BSI and may lead to new preventative or therapeutic intervention strategies.

ONE SENTENCE SUMMARY: Our study identified candidate serum biomarkers to predict subsequent bone stress injuries in female runners, offering new insights for clinical monitoring and interventions.

Type 1 diabetes (T1D) is associated with an increased risk of hip fracture beyond what can be explained by reduced bone mineral density, possibly due to changes in bone material from accumulation of advanced glycation end-products (AGEs) and altered matrix composition, though data from human cortical bone in T1D are limited. The objective of this study was to evaluate cortical bone material behavior in T1D by examining specimens from cadaveric femora from older adults with long-duration T1D (≥50 yr; n = 20) and age- and sex-matched nondiabetic controls (n = 14). Cortical bone was assessed by mechanical testing (4-point bending, cyclic reference point indentation, impact microindentation), AGE quantification [total fluorescent AGEs, pentosidine, carboxymethyl lysine (CML)], and matrix composition via Raman spectroscopy. Cortical bone from older adults with T1D had diminished postyield toughness to fracture (-30%, p = .036), elevated levels of AGEs (pentosidine, +17%, p = .039), lower mineral crystallinity (-1.4%, p = .010), greater proline hydroxylation (+1.9%, p = .009), and reduced glycosaminoglycan (GAG) content (-1.3%, p < .03) compared to nondiabetics. In multiple regression models to predict cortical bone toughness, cortical tissue mineral density, CML, and Raman spectroscopic measures of enzymatic collagen crosslinks and GAG content remained highly significant predictors of toughness, while diabetic status was no longer significant (adjusted R2 > 0.60, p < .001). Thus, the impairment of cortical bone to absorb energy following long-duration T1D is well explained by AGE accumulation and modifications to the bone matrix. These results provide novel insight into the pathogenesis of skeletal fragility in individuals with T1D.

Vertebral compression fractures (VFs) and spinal degeneration are both common causes of back pain, particularly in older adults. Previous cross-sectional studies have shown a potential association between these entities, but there is limited evidence on the role of VFs in spinal degeneration. In this longitudinal study, we evaluated the association between prevalent VFs and the subsequent progression of facet joint osteoarthritis (FJOA) and intervertebral disc height narrowing (DHN), using data from the Framingham Heart Study Offspring and Third Generation Multi-Detector Computed Tomography study. Summary indices representing the total burden of each spinal parameter (VFs, DHN and FJOA) were calculated for each individual. We hypothesized that prevalent VFs are associated with worsening spinal degeneration. 370 (31%) of 1197 participants, had a baseline (prevalent) VF. The change in summary index of DHN over the follow-up period was significantly higher in those with versus without prevalent VF (difference in change in DHN 0.38, 95% CI 0.18 to 0.59, P<.001), but the change in summary index of FJOA was similar between those with and without prevalent VF. However, once adjusted for age, sex, cohort, smoking status, body mass index, and baseline DHN, the change in summary index of DHN did not differ by prevalent VF status. There was a modestly higher change in the FJOA summary index in those with prevalent VFs compared to those without in the fully adjusted model (difference in change in FJOA 0.62, 95% CI -0.01 to 1.24, P=.054), driven primarily by those with severe (grade 3) VF (difference in change in FJOA 4.48, 95% CI 1.99 to 6.97). Moreover, there was greater change in the summary index of FJOA with increasing severity of prevalent VF (linear trend P=.005). Beyond the established morbidity and mortality associated with VFs, our study suggests that VFs may also lead to worsening spine osteoarthritis.

Exposure to ionizing radiation for oncological therapy increases the risk for late-onset fractures in survivors. However, the effects of total body irradiation (TBI) on adult bone are not well-characterized. The primary aim of this study was to quantify the long-term effects of TBI on bone microstructure, material composition, and mechanical behavior in skeletally mature rhesus macaque (Macaca mulatta) non-human primates. Femora were obtained post-mortem from animals exposed to an acute dose of TBI (6.0-6.75 Gy) nearly a decade earlier, age-matched non-irradiated controls, and non-irradiated young animals. The microstructure of femoral trabecular and cortical bone was assessed via micro-computed tomography. Material composition was evaluated by measuring total fluorescent advanced glycation end products (fAGEs). Cortical bone mechanical behavior was quantified via four-point bending and cyclic reference point indentation (cRPI). Animals exposed to TBI had slightly worse cortical microstructure, including lower cortical thickness (-11%, p = 0.037) and cortical area (-24%, p = 0.049), but similar fAGE content and mechanical properties as age-matched controls. Aging did not influence cortical microstructure, fAGE content, or cRPI measures but diminished femoral cortical post-yield properties, including toughness to fracture (-32%, p = 0.032). Because TBI was administered after the acquisition of peak bone mass, these results suggest that the skeletons of long-term survivors of adulthood TBI may be resilient, retaining or recovering their mechanical integrity during the post-treatment period, despite radiation-induced architectural deficits. Further investigation is necessary to better understand radiation-induced skeletal fragility in mature and immature bone to improve care for radiation patients of all ages.

Some osteoporosis drug trials have suggested that treatment is more effective in those with low BMD measured by DXA. This study used data from a large set of randomized controlled trials (RCTs) to determine whether the anti-fracture efficacy of treatments differs according to baseline BMD. We used individual patient data from 25 RCTs (103 086 subjects) of osteoporosis medications collected as part of the FNIH-ASBMR SABRE project. Participants were stratified into FN BMD T-score subgroups (≤-2.5, > -2.5). We used Cox proportional hazard regression to estimate treatment effect for clinical fracture outcomes and logistic regression for the radiographic vertebral fracture outcome. We also performed analyses based on BMD quintiles. Overall, 42% had a FN BMD T-score ≤ -2.5. Treatment with anti-osteoporosis drugs led to significant reductions in fractures in both T-score ≤ -2.5 and > -2.5 subgroups. Compared to those with FN BMD T-score > -2.5, the risk reduction for each fracture outcome was greater in those with T-score ≤ -2.5, but only the all-fracture outcome reached statistical significance (interaction P = .001). Results were similar when limited to bisphosphonate trials. In the quintile analysis, there was significant anti-fracture efficacy across all quintiles for vertebral fractures and with greater effects on fracture risk reduction for non-vertebral, all, and all clinical fractures in the lower BMD quintiles (all interaction P ≤ .03). In summary, anti-osteoporotic medications reduced the risk of fractures regardless of baseline BMD. Significant fracture risk reduction with treatment for 4 of the 5 fracture endpoints was seen in participants with T-scores above -2.5, though effects tended to be larger and more significant in those with baseline T-scores <-2.5.

UNLABELLED: To understand whether the bone loss which occurs after vertical sleeve gastrectomy increases the risk of fracture, we used an engineering model to estimate risk in participants before and after surgery. We found that estimated risk decreased 1 year after surgery and remained lower, though had rebounded, at year 2.

PURPOSE: Vertical sleeve gastrectomy (VSG) improves metabolic health in young people with obesity but is accompanied by substantial loss of bone mass and estimated bone strength. We thus estimated fracture risk following VSG using the load-to-strength ratio (LSR), which integrates bone strength estimates with the predicted force of a fall.

METHODS: Prospective 2-year study of youth ages 13-24 years with obesity undergoing VSG (n = 24) or lifestyle therapy (n = 34). We performed high-resolution peripheral quantitative computed tomography of the distal radius and microfinite element analysis to estimate bone strength and calculated LSR.

RESULTS: VSG participants lost 26.4 ± 8.1% weight at year 1 (p < 0.001), which was sustained at year 2, while control participants gained weight at year 2 (4.5 ± 8.3%, p = 0.009). The predicted impact force decreased at years 1 and 2 following VSG (p < 0.001) but increased at year 2 among controls (p = 0.011). Estimated bone strength was unchanged at year 1 but decreased (p < 0.001) at year 2 following VSG, while bone strength did not change in controls. At year 1, the LSR decreased among VSG participants (p < 0.001), implying a lower risk of fracture. At year 2, the LSR was lower than baseline (p < 0.001), but higher compared to year 1 (p = 0.001). LSR did not change in the control group.

CONCLUSIONS: Short-term estimated fracture risk at the radius following VSG decreases. However, ongoing bone loss despite stable weight between years 1 and 2 leads to a concerning rise in estimated fracture risk. Longer follow-up will be critical to evaluate the trajectory of fracture risk. (ClinicalTrials.gov NCT02557438, registered 9/23/2015).