Teriparatide in bisphosphonate-resistant osteoporosis: microarchitectural changes and clinical results after 6 and 18 months

Exploring the efficacy of photodynamic antimicrobial chemotherapy on diabetic foot ulcers in rats

We investigate the efficacy of photodynamic antimicrobial chemotherapy (PACT) and its combination with an antibiotic in the treatment of diabetic foot ulcers (DFUs) in rats using a novel cationic amino acid porphyrin-based photosensitizer. The research findings demonstrate that the combination of novel cationic photosensitizer-mediated PACT and an antibiotic exhibits significant therapeutic efficacy in treating deep ulcers in a rat model of DFUs. Moreover, the PACT + Antibiotic group displays enhanced angiogenesis, improved tissue maturation, and superior wound healing effect. Micro-computed tomography examination showed that the periosteal reaction was most obvious in the PACT + Antibiotic group. The cortical bone volume ratio (BV/TV), the bone mineral density, and trabecular thickness were significantly higher in the PACT + Antibiotic group than in the model group (p < 0.05). The combination of PACT and antibiotic plays a sensitizing therapeutic role, which provides a new idea for the clinical treatment of DFUs.

A brief review and clinical evidences of teriparatide therapy for atypical femoral fractures associated with long-term bisphosphonate treatment

The risk of bisphosphonate (BP)-associated atypical femur fracture (AFF) has markedly increased over recent decades due to suppression of bone turnover, accumulation of structural micro-damage and reduction of bone remodeling consequent to long-term BP treatment. These medications further delay bone union and result in challenging clinical management. Teriparatide (TPTD), a synthetic human parathyroid hormone, exhibits unique anabolic effects and can increase bone remodeling and improve bone microarchitecture, further promoting fracture healing and reducing the rate of bone non-union. In this study, we briefly define AFF as well as the effects of BPs on AFFs, detailed the role of TPTD in AFF management and the latest clinical therapeutic findings. We have confirmed that TPTD positively promotes the healing of AFFs by reducing the time to bone union and likelihood of non-union. Thus, teriparatide therapy could be considered as an alternative treatment for AFFs, however, further research is required for the establishment of effective clinical guidelines of TPTD use in the management of AFF.

Guidelines for the assessment of bone density and microarchitecture in vivo using high-resolution peripheral quantitative computed tomography

INTRODUCTION

The application of high-resolution peripheral quantitative computed tomography (HR-pQCT) to assess bone microarchitecture has grown rapidly since its introduction in 2005. As the use of HR-pQCT for clinical research continues to grow, there is an urgent need to form a consensus on imaging and analysis methodologies so that studies can be appropriately compared. In addition, with the recent introduction of the second-generation HrpQCT, which differs from the first-generation HR-pQCT in scan region, resolution, and morphological measurement techniques, there is a need for guidelines on appropriate reporting of results and considerations as the field adopts newer systems.

METHODS

A joint working group between the International Osteoporosis Foundation, American Society of Bone and Mineral Research, and European Calcified Tissue Society convened in person and by teleconference over several years to produce the guidelines and recommendations presented in this document.

RESULTS

An overview and discussion is provided for (1) standardized protocol for imaging distal radius and tibia sites using HR-pQCT, with the importance of quality control and operator training discussed; (2) standardized terminology and recommendations on reporting results; (3) factors influencing accuracy and precision error, with considerations for longitudinal and multi-center study designs; and finally (4) comparison between scanner generations and other high-resolution CT systems.

CONCLUSION

This article addresses the need for standardization of HR-pQCT imaging techniques and terminology, provides guidance on interpretation and reporting of results, and discusses unresolved issues in the field.

Effects of Teriparatide and Sequential Minodronate on Lumbar Spine Bone Mineral Density and Microarchitecture in Osteoporosis

The trabecular bone score (TBS) is a new surrogate for trabecular bone microarchitecture assessment, independent of bone mineral density (BMD), calculated from pixel gray-level variations in the lumbar spine (LS) dual-energy X-ray absorptiometry (DXA) image. Although Teriparatide (TPTD) increased LS-BMD as well as TBS in 2 years, the precise time-course of these parameters was not well known. The aim of this study was to determine the changes in LS-BMD and the TBS in osteoporotic patients treated with TPTD, followed by minodronate (MINO). Primary osteoporotic patients with a low LS-BMD (T-score < -2.5) and/or at least one vertebral fracture were treated with TPTD subcutaneously at 20 µg/day for 12-24 months, followed by MINO (orally at 50 mg/once monthly) for 12 months. LS-BMD and the TBS were measured at 0, 3, 6, 12, and 24 months after the initiation of TPTD treatment, and 12 months after the initiation of MINO. The increments of LS-BMD, significant at 6 months, increased until 12 months, whereas the increments of TBS, significant at 3 months (0.035 ± 0.011; p = 0.045 vs. the baseline), stabilized until 12 months. TPTD treatment, followed by 12 months of MINO, maintained both BMD and the TBS. Comparing the increments of the TBS to those of LS-BMD, our results indicate that TPTD treatment improved trabecular microarchitecture faster than mineralization. TPTD treatment, followed by MINO, can maintain both BMD and the TBS.

Examining the Relationships Between Bone Tissue Composition, Compositional Heterogeneity, and Fragility Fracture: A Matched Case-Controlled FTIRI Study

Fourier transform infrared imaging (FTIRI) provides information on spatial distribution of the chemical composition of thin tissue specimens at ∼7 µm spatial resolution. This study of 120 age- and bone mineral density (BMD)-matched patients was designed to investigate the association of FTIRI variables, measured in iliac crest biopsies, with fragility fractures at any site. An earlier study of 54 women found hip BMD to be a significant explanatory variable of fracture risk for cortical bone but not for cancellous bone. In the current study, where age and BMD were controlled through matching, no such association was observed, validating the pairing scheme. Our first study of unmatched iliac crest biopsies found increases in collagen maturity (cancellous and cortical bone) and mineral crystal size (cortical bone only) to be a significant explanatory variable of fracture when combined with other covariates. The ratio for collagen maturity has been correlated to the amount of enzymatic collagen cross-links. To assess the impact of other FTIRI variables (acid phosphate substitution, carbonate-to-phosphate ratio, and the pixel distribution [heterogeneity] of all relevant FTIRI variables), we examined biopsies from a matched case-controlled study, in which 60 women with fractures were each paired with an age- and BMD-matched female control. With the matched data set of 120 women, conditional logistic regression analyses revealed that significant explanatory variables of fracture were decreased carbonate-to-phosphate ratio in both cancellous (odds ratio [OR] = 0.580, 95% confidence interval [CI] 0.37-0.909, p = 0.0176) and cortical bone (OR = 0.519, 95% CI 0.325-0.829, p = 0.0061), and increased heterogeneity (broadened pixel distribution) of collagen maturity for cancellous bone (OR = 1.549, 95% CI 1.002-2.396, p = 0.0491). The observation that collagen maturity was no longer linked to fracture in age- and BMD-matched samples suggests that age-dependent variation in collagen maturity may be a more important contributory factor to fragility fractures than previously thought. © 2015 American Society for Bone and Mineral Research.

PTH(1-84) Administration in Hypoparathyroidism Transiently Reduces Bone Matrix Mineralization

Patients with hypoparathyroidism have low circulating parathyroid (PTH) levels and higher cancellous bone volume and trabecular thickness. Treatment with PTH(1-84) was shown to increase abnormally low bone remodeling dynamics. In this work, we studied the effect of 1-year or 2-year PTH(1-84) treatment on cancellous and cortical bone mineralization density distribution (Cn.BMDD and Ct.BMDD) based on quantitative backscattered electron imaging (qBEI) in paired transiliac bone biopsy samples. The study cohort comprised 30 adult hypoparathyroid patients (14 treated for 1 year; 16 treated for 2 years). At baseline, Cn.BMDD was shifted to higher mineralization densities in both treatment groups (average degree of mineralization Cn.CaMean +3.9% and +2.7%, p < 0.001) compared to reference BMDD. After 1-year PTH(1-84), Cn.CaMean was significantly lower than that at baseline (-6.3%, p < 0.001), whereas in the 2-year PTH(1-84) group Cn.CaMean did not differ from baseline. Significant changes of Ct.BMDD were observed in the 1-year treatment group only. The change in histomorphometric bone formation (mineralizing surface) was predictive for Cn.BMDD outcomes in the 1-year PTH(1-84) group, but not in the 2-year PTH(1-84) group. Our findings suggest higher baseline bone matrix mineralization consistent with the decreased bone turnover in hypoparathyroidism. PTH(1-84) treatment caused differential effects dependent on treatment duration that were consistent with the histomorphometric bone formation outcomes. The greater increase in bone formation during the first year of treatment was associated with a decrease in bone matrix mineralization, suggesting that PTH(1-84) exposure to the hypoparathyroid skeleton has the greatest effects on BMDD early in treatment.

Anti-Osteoporotic Therapy After Fragility Fracture Lowers Rate of Subsequent Fracture: Analysis of a Large Population Sample

BACKGROUND

This investigation assessed the effectiveness of initiating anti-osteoporotic therapy after a fragility fracture in preventing subsequent fractures.

METHODS

The Truven Health MarketScan databases, which contain de-identified, integrated, person-specific claim data, were queried from 2003 to 2012. The study population included individuals fifty years of age or older who sustained a fragility fracture, defined as any fracture of the wrist, proximal part of the humerus, hip, or vertebra, and had three years of continuous enrollment following fracture. Patients were stratified into either an anti-osteoporotic therapy group or a no-treatment group. Subsequent fracture was defined as a fragility fracture occurring more than ninety days following the index fracture. Subjects were followed for three years. Unadjusted and age and sex-adjusted odds ratios for subsequent fracture were calculated for both groups.

RESULTS

This investigation included 31,069 subjects, of whom 10.6% were treated with anti-osteoporotic therapy following the index fracture. The anti-osteoporotic therapy group was older and had a greater proportion of female patients compared with the no-treatment group. The three-year subsequent fracture rates were 7.5% in the anti-osteoporotic therapy group and 9.7% in the no-treatment group. Unadjusted odds ratios for subsequent fracture showed that the anti-osteoporotic therapy group experienced a risk reduction of 33% after an index wrist fracture, 48% after an index proximal humeral fracture, 28% after an index hip fracture, 20% after an index vertebral fracture, and 25% after all fractures combined. Age and sex-adjusted odds ratios showed that the anti-osteoporotic therapy group experienced a reduction in risk of 50% after an index wrist fracture, 52% after an index proximal humeral fracture, 34% after an index hip fracture, 43% after an index vertebral fracture, and 40% after all fractures combined. The number needed to treat to prevent a subsequent fragility fracture was twenty-eight after an index wrist fracture, twenty after an index proximal humeral fracture, twenty-six after an index hip fracture, twenty-five after an index vertebral fracture, and twenty-seven after all fractures combined.

CONCLUSIONS

Treatment with anti-osteoporotic therapy after a fragility fracture leads to a 40% decrease in the three-year risk of subsequent fracture, when adjusted for age and sex. Initiation of anti-osteoporotic therapy following a fragility fracture can prevent a subsequent fracture over the following three years in approximately one of every twenty-seven patients treated.

New insights into treatment of osteoporosis in postmenopausal women

For the prevention of fractures, antiresorptive drugs (bisphosphonates and denosumab) that decrease high bone resorption and, secondarily, also bone formation, are the mainstream of therapy. Osteoanabolic drugs, such as teriparatide, increase bone formation more than bone resorption, and are used in severe osteoporosis, including patients treated with antiresorptive drugs who still lose bone and have recurrent fractures. New potential drugs for fracture prevention that uncouple bone resorption from bone formation include odanacatib, a specific inhibitor of cathepsin-K, the enzyme that degrades bone collagen type I, that inhibits bone resorption and only temporarily bone formation, and monoclonal antibodies against sclerostin (romosozumab, blosozumab), that stimulate bone formation and decrease bone resorption.

Structure Model Index Does Not Measure Rods and Plates in Trabecular Bone

Structure model index (SMI) is widely used to measure rods and plates in trabecular bone. It exploits the change in surface curvature that occurs as a structure varies from spherical (SMI = 4), to cylindrical (SMI = 3) to planar (SMI = 0). The most important assumption underlying SMI is that the entire bone surface is convex and that the curvature differential is positive at all points on the surface. The intricate connections within the trabecular continuum suggest that a high proportion of the surface could be concave, violating the assumption of convexity and producing regions of negative differential. We implemented SMI in the BoneJ plugin and included the ability to measure the amounts of surface that increased or decreased in area after surface mesh dilation, and the ability to visualize concave and convex regions. We measured SMI and its positive (SMI(+)) and negative (SMI(-)) components, bone volume fraction (BV/TV), the fraction of the surface that is concave (CF), and mean ellipsoid factor (EF) in trabecular bone using 38 X-ray microtomography (XMT) images from a rat ovariectomy model of sex steroid rescue of bone loss, and 169 XMT images from a broad selection of 87 species' femora (mammals, birds, and a crocodile). We simulated bone resorption by eroding an image of elephant trabecule and recording SMI and BV/TV at each erosion step. Up to 70%, and rarely <20%, of the trabecular surface is concave (CF 0.155-0.700). SMI is unavoidably influenced by aberrations induced by SMI(-), which is strongly correlated with BV/TV and CF. The plate-to-rod transition in bone loss is an erroneous observation resulting from the close and artifactual relationship between SMI and BV/TV. SMI cannot discern between the distinctive trabecular geometries typical of mammalian and avian bone, whereas EF clearly detects birds' more plate-like trabecule. EF is free from confounding relationships with BV/TV and CF. SMI results reported in the literature should be treated with suspicion. We propose that EF should be used instead of SMI for measurements of rods and plates in trabecular bone.

Parathyroid hormone therapy for hypoparathyroidism

Hypoparathyroidism is a disease characterized by hypocalcemia and insufficient parathyroid hormone (PTH). It is a rare disorder that has been given an orphan disease designation in the United States and European Union. Hypoparathyroidism is the only endocrine deficiency disease for which the missing hormone, PTH, is not yet an approved therapy. Conventional therapy includes calcium and active vitamin D supplementation, often in large doses. Although serum calcium can be controlled with conventional therapy, it can be a challenge and, moreover, does not address other aspects of the disease, such as abnormal skeletal features and reduced quality of life. This review focuses on PTH replacement therapy in hypoparathyroidism, utilizing the full-length molecule PTH(1-84) as well as the fully active but truncated form PTH(1-34). PTH therapy addresses some aspects of the disease not ameliorated with conventional therapy.

Comparative effects of teriparatide and ibandronate on spine bone mineral density (BMD) and microarchitecture (TBS) in postmenopausal women with osteoporosis: a 2-year open-label study

Treatment effects over 2 years of teriparatide vs. ibandronate in postmenopausal women with osteoporosis were compared using lumbar spine bone mineral density (BMD) and trabecular bone score (TBS). Teriparatide induced larger increases in BMD and TBS compared to ibandronate, suggesting a more pronounced effect on bone microarchitecture of the bone anabolic drug.

INTRODUCTION

The trabecular bone score (TBS) is an index of bone microarchitecture, independent of bone mineral density (BMD), calculated from anteroposterior spine dual X-ray absorptiometry (DXA) scans. The potential role of TBS for monitoring treatment response with bone-active substances is not established. The aim of this study was to compare the effects of recombinant human 1-34 parathyroid hormone (teriparatide) and the bisphosphonate ibandronate (IBN), on lumbar spine (LS) BMD and TBS in postmenopausal women with osteoporosis.

METHODS

Two patient groups with matched age, body mass index (BMI), and baseline LS BMD, treated with either daily subcutaneous teriparatide (N = 65) or quarterly intravenous IBN (N = 122) during 2 years and with available LS BMD measurements at baseline and 2 years after treatment initiation were compared.

RESULTS

Baseline characteristics (overall mean ± SD) were similar between groups in terms of age 67.9 ± 7.4 years, body mass index 23.8 ± 3.8 kg/m(2), BMD L1-L4 0.741 ± 0.100 g/cm(2), and TBS 1.208 ± 0.100. Over 24 months, teriparatide induced a significantly larger increase in LS BMD and TBS than IBN (+7.6 % ± 6.3 vs. +2.9 % ± 3.3 and +4.3 % ± 6.6 vs. +0.3 % ± 4.1, respectively; P < 0.0001 for both). LS BMD and TBS were only weakly correlated at baseline (r (2) = 0.04) with no correlation between the changes in BMD and TBS over 24 months.

CONCLUSIONS

In postmenopausal women with osteoporosis, a 2-year treatment with teriparatide led to a significantly larger increase in LS BMD and TBS than IBN, suggesting that teriparatide had more pronounced effects on bone microarchitecture than IBN.

Bisphosphonate-osteoclasts: changes in osteoclast morphology and function induced by antiresorptive nitrogen-containing bisphosphonate treatment in osteoporosis patients

Osteoclasts are unique cells capable of bone resorption and therefore have become a major target in osteoporosis treatment strategies. Bisphosphonates suppress bone turnover via interference with the internal enzymatic cell system of osteoclasts leading to cytoskeletal disruption. This mechanism found its clinical relevance in reducing bone resorption, stabilizing bone mass and reducing fracture risk in osteoporosis patients. However, knowledge about specific in vivo changes in osteoclast cell morphology and function is still insufficient. We examined osteoclasts in 23 paired bone biopsies from osteoporosis patients (18 males, 5 females; age: 52.6±11.5yrs) under nitrogen-containing bisphosphonate administration with a mean treatment duration of three years. Formalin-fixed, undecalcified sections were assessed by qualitative and quantitative bone histomorphometry, where the osteoclast morphology, nuclei, distribution, location as well as resorption parameters were investigated to obtain information about cell function and viability. After three years of treatment, resorption parameters decreased significantly while the number of osteoclasts remained unchanged. Out of 23 patients, nine developed previously termed "giant-osteoclasts" with increased size, numerous nuclei (>10 nuclei/Oc) and oftentimes detachment from the bone surface. These cells frequently had pycnotic nuclei and other morphological signs suggestive of osteoclast apoptosis. Characteristic large-sized osteoclasts were uniquely found in patients treated with nitrogen-containing bisphosphonates, thus being clearly distinguishable from giant-osteoclasts in other bone disorders such as Paget disease, secondary hyperparathyroidism or osteopetrosis. The resorption indices of large-sized osteoclasts, specifically the eroded perimeter and erosion depth, revealed significantly reduced values but not an entirely inhibited resorption capability. Bisphosphonate-osteoclasts' viability and affinity to bone seem significantly disturbed while the apoptotic process may be prolonged for a yet unknown period of time in favor of maintaining a low bone turnover.

PTH replacement therapy of hypoparathyroidism

Hypoparathyroidism is characterized by hypocalcemia with inappropriately low parathyroid hormone (PTH) levels. Bone turnover is abnormally low and bone mineral density (BMD) is typically increased. Plasma calcium levels can be normalized by treatment with calcium supplements and vitamin D analogs, but bone turnover remains low and patients complain of a reduced quality of life (QoL). During recent years, a number of studies have shown that PTH replacement therapy (PTH-RT) may maintain calcium levels within the normal range, while the need for calcium and vitamin D supplements is reduced. In the initial response to subcutaneous PTH injections once or twice daily, bone turnover is overstimulated. BMD increases in cancellous bone, but decreases in cortical bone due to an increased porosity. Microcomputed tomography scans and histomorphometric studies on bone biopsies have shown changes similar to the well-known bone anabolic effects of PTH treatment in osteoporosis rather than a normalization of bone remodeling balancing the anabolic and catabolic effects of PTH. Most recently, continuous PTH delivery by pump was shown to increase the levels of bone markers into the normal range (without overstimulation of bone turnover) and with a normalization of renal calcium excretion. As PTH has a short plasma half-life, these findings indicate that exposure to PTH once or twice daily is not sufficient to reestablish a calcium homeostasis and bone metabolism that resembles normal physiology. Further studies should assess the effects of continuous PTH exposure by pump delivery (or multiple daily injections) on BMD and bone histology, as well as the effects of PTH-RT on indices of QoL.

Differing effects of PTH 1-34, PTH 1-84, and zoledronic acid on bone microarchitecture and estimated strength in postmenopausal women with osteoporosis: an 18-month open-labeled observational study using HR-pQCT

Whereas the beneficial effects of intermittent treatment with parathyroid hormone (PTH) (intact PTH 1-84 or fragment PTH 1-34, teriparatide) on vertebral strength is well documented, treatment may not be equally effective in the peripheral skeleton. We used high-resolution peripheral quantitative computed tomography (HR-pQCT) to detail effects on compartmental geometry, density, and microarchitecture as well as finite element (FE) estimated integral strength at the distal radius and tibia in postmenopausal osteoporotic women treated with PTH 1-34 (20 µg sc daily, n = 18) or PTH 1-84 (100 µg sc daily, n = 20) for 18 months in an open-label, nonrandomized study. A group of postmenopausal osteoporotic women receiving zoledronic acid (5 mg infusion once yearly, n = 33) was also included. Anabolic therapy increased cortical porosity in radius (PTH 1-34 32 ± 37%, PTH 1-84 39 ± 32%, both p < 0.001) and tibia (PTH 1-34 13 ± 27%, PTH 1-84 15 ± 22%, both p < 0.001) with corresponding declines in cortical density. With PTH 1-34, increases in cortical thickness in radius (2.0 ± 3.8%, p < 0.05) and tibia (3.8 ± 10.4%, p < 0.01) were found. Trabecular number increased in tibia with both PTH 1-34 (4.2 ± 7.1%, p < 0.05) and PTH 1-84 (5.3 ± 8.3%, p < 0.01). Zoledronic acid did not impact cortical porosity at either site but increased cortical thickness (3.0 ± 3.5%, p < 0.01), total (2.7 ± 2.5%, p < 0.001) and cortical density (1.5 ± 2.0%, p < 0.01) in tibia as well as trabecular volume fraction in radius (2.5 ± 5.1%, p < 0.05) and tibia (2.2 ± 2.2%, p < 0.01). FE estimated bone strength was preserved, but not increased, with PTH 1-34 and zoledronic acid at both sites, whereas it decreased with PTH 1-84 in radius (-2.8 ± 5.8%, p < 0.05) and tibia (-3.9 ± 4.8%, p < 0.001). Conclusively, divergent treatment-specific effects in cortical and trabecular bone were observed with anabolic and zoledronic acid therapy. The finding of decreased estimated strength with PTH 1-84 treatment was surprising and warrants confirmation.

Teriparatide improves bone quality and healing of atypical femoral fractures associated with bisphosphonate therapy

Bone remodelling suppressants like the bisphosphonates reduce bone loss and slow progression of structural decay. As remodelling removes damaged bone, when remodelling suppression is protracted, bone quality may be compromised predisposing to microdamage accumulation and atypical femoral fractures. The aim of this study was to determine whether teriparatide therapy assists in fracture healing and improves bone quality in patients with bisphosphonate associated atypical femoral fractures. A prospective study was conducted involving 14 consecutive patients presenting during 2 years with atypical femoral fracture. All patients were offered teriparatide therapy unless contraindicated. Age and sex matched control subjects without fragility fractures or anti-resorptive treatment were recruited. High resolution peripheral micro-computed tomography (HRpQCT) scans of the distal radius and distal tibia were analysed for their cortical bone tissue mineralisation density using new software (StrAx1.0, StrAxCorp, Australia) at baseline and 6 months after teriparatide. Administration of 20 μg of teriparatide subcutaneously daily for 6 months to 5 of the 14 patients was associated with 2-3 fold increase in bone remodelling markers (p=0.01) and fracture healing. At the distal radius, the proportion of less densely mineralised bone increased by 29.5% (p=0.01), and the proportion of older, more densely mineralised bone decreased by 16.2% (p=0.03). Similar observations were made at the distal tibia. Of the nine patients managed conservatively or surgically, seven had poor fracture healing with ongoing pain, one sustained a contralateral atypical fracture and one had fracture union after 1 year. Teriparatide may assist in healing of atypical fractures and restoration of bone quality.

Treatment failure in osteoporosis

Guidelines concerning the definition of failure of therapies used to reduce the risk of fracture are provided.

INTRODUCTION

This study aims to provide guidelines concerning the definition of failure of therapies used to reduce the risk of fracture.

METHODS

A working group of the Committee of Scientific Advisors of the International Osteoporosis Foundation was convened to define outcome variables that may assist clinicians in decision making.

RESULTS

In the face of limited evidence, failure of treatment may be inferred when two or more incident fractures have occurred during treatment, when serial measurements of bone remodelling markers are not suppressed by anti-resorptive therapy and where bone mineral density continues to decrease.

CONCLUSION

The provision of pragmatic criteria to define failure to respond to treatment provides an unmet clinical need and may stimulate research into an important issue.

Daily parathyroid hormone 1-34 replacement therapy for hypoparathyroidism induces marked changes in bone turnover and structure

Parathyroid hormone (PTH) has variable actions on bone. Chronically increased PTH is catabolic and leads to osteoporosis; yet intermittent administration is anabolic and increases bone mass. PTH deficiency is associated with decreased bone remodeling and increased bone mass. However, the effects of PTH replacement therapy on bone in hypoparathyroidism are not well known. We discontinued calcitriol therapy and treated 5 hypoparathyroid subjects (2 adults and 3 adolescents) with synthetic human PTH 1-34 (hPTH 1-34), injected two to three times daily for 18 months, with doses individualized to maintain serum calcium at 1.9 to 2.25 mmol/L. Biochemical markers and bone mineral density (BMD) were assessed every 6 months; iliac-crest biopsies were performed before and after 1 year of treatment. hPTH 1-34 therapy significantly increased bone markers to supranormal levels. Histomorphometry revealed that treatment dramatically increased cancellous bone volume and trabecular number and decreased trabecular separation. Changes in trabecular width were variable, suggesting that the increase in trabecular number was due to the observed intratrabecular tunneling. Cortical width remained unchanged; however, hPTH 1-34 treatment increased cortical porosity. Cancellous bone remodeling was also stimulated, inducing significant changes in osteoid, mineralizing surface, and bone formation rate. Similar changes were seen in endocortical and intracortical remodeling. BMD Z-scores were unchanged at the spine and femoral neck. Total hip Z-scores increased; however, total body BMD Z-scores decreased during the first 6 months of treatment and then stabilized, remaining significantly decreased compared to baseline. Radial Z-scores also decreased with treatment; this was most pronounced in the growing adolescent. Daily hPTH 1-34 therapy for hypoparathyroidism stimulated bone turnover, increased bone volume, and altered bone structure in the iliac crest. These findings suggest that treatment with hPTH 1-34 in hypoparathyroid adults and adolescents has varying effects in the different skeletal compartments, leading to an increase in trabecular bone and an apparent trabecularization of cortical bone.

Trabecular reorganization in consecutive iliac crest biopsies when switching from bisphosphonate to strontium ranelate treatment

BACKGROUND

Several agents are available to treat osteoporosis while addressing patient-specific medical needs. Individuals' residual risk to severe fracture may require changes in treatment strategy. Data at osseous cellular and microstructural levels due to a therapy switch between agents with different modes of action are rare. Our study on a series of five consecutively taken bone biopsies from an osteoporotic individual over a six-year period analyzes changes in cellular characteristics, bone microstructure and mineralization caused by a therapy switch from an antiresorptive (bisphosphonate) to a dual action bone agent (strontium ranelate).

METHODOLOGY/PRINCIPAL FINDINGS

Biopsies were progressively taken from the iliac crest of a female patient. Four biopsies were taken during bisphosphonate therapy and one biopsy was taken after one year of strontium ranelate (SR) treatment. Furthermore, serum bone markers and dual x-ray absorptiometry measurements were acquired. Undecalcified histology was used to assess osteoid parameters and bone turnover. Structural indices and degree of mineralization were determined using microcomputed tomography, quantitative backscattered electron imaging, and combined energy dispersive x-ray/µ-x-ray-fluorescence microanalysis.

CONCLUSIONS/SIGNIFICANCE

Microstructural data revealed a notable increase in bone volume fraction after one year of SR treatment compared to the bisphosphonate treatment period. Indices of connectivity density, structure model index and trabecular bone pattern factor were predominantly enhanced indicating that the architectural transformation from trabecular rods to plates was responsible for the bone volume increase and less due to changes in trabecular thickness and number. Administration of SR following bisphosphonates led to a maintained mineralization profile with an uptake of strontium on the bone surface level. Reactivated osteoclasts designed tunneling, hook-like intratrabecular resorption sites. The appearance of tunneling resorption lacunae and the formation of both mini-modeling units and osteon-like structures within increased plate-like cancellous bone mass provides additional information on the mechanisms of strontium ranelate following bisphosphonate treatment, which may deserve special attention when monitoring a treatment switch.