The Dutch multidisciplinary guideline osteoporosis and fracture prevention, taking a local guideline to the international arena

BACKGROUND

In 2018, a grant was provided for an evidence-based guideline on osteoporosis and fracture prevention based on 10 clinically relevant questions.

METHODS

A multidisciplinary working group was formed with delegates from Dutch scientific and professional societies, including representatives from the patient's organization and the Dutch Institute for Medical Knowledge. The purpose was to obtain a broad consensus among all participating societies to facilitate the implementation of the updated guideline.

RESULTS

Novel recommendations in our guideline are as follows: - In patients with an indication for DXA of the lumbar spine and hips, there is also an indication for VFA. - Directly starting with anabolic drugs (teriparatide or romosozumab) in patients with a very high fracture risk; - Directly starting with zoledronic acid in patients 75 years and over with a hip fracture (independent of DXA); - Directly starting with parenteral drugs (denosumab, teriparatide, zoledronic acid) in glucocorticoid-induced osteoporosis with very high fracture risk; - A lifelong fracture risk management, including lifestyle, is indicated from the start of the first treatment.

CONCLUSION

In our new multidisciplinary guideline osteoporosis and fracture prevention, we developed 5 "relatively new statements" that are all a crucial step forward in the optimization of diagnosis and treatment for fracture prevention. We also developed 5 flowcharts, and we suppose that this may be helpful for individual doctors and their patients in daily practice and may facilitate implementation.

Medication-related osteonecrosis of the jaw: evolving research for multimodality medical management

PURPOSE

Medication-related osteonecrosis of the jaw (MRONJ) is a debilitating side effect of antiresorptive and antiangiogenic agents that can lead to progressive bone destruction in the maxillofacial region. Dental surgery, including tooth extractions, commonly trigger the onset of MRONJ. While guidelines suggest avoiding extraction when possible, complete avoidance is not always feasible, as necrosis can develop from dental and periodontal disease without dental procedures. The goal of this article is to provide an update review of current preventive and therapeutic approaches for MRONJ.

METHODS

A comprehensive electronic search was conducted on PubMed/MEDLINE, Embase, and Scopus databases. All English articles encompassing randomized controlled trials, systematic reviews, observational studies, and case studies were reviewed. The current medical treatments and adjuvant therapies for managing MRONJ patients were critically assessed and summarized.

RESULTS

Pentoxifylline and alpha tocopherol (PENT-E), teriparatide, photobiomodulation (PBM), photodynamic therapy (PDT), and the use of growth factors have shown to enhance healing in MRONJ patients. Implementing these methods alone or in conjunction with surgical treatment has been linked to reduced discomfort and improved wound healing and increased new bone formation.

DISCUSSION

While several adjuvant treatment modalities exhibit promising results in facilitating the healing process, current clinical practice guidelines predominantly recommend antibiotic therapy as a non-surgical approach, primarily addressing secondary infections in necrotic areas. However, this mainly addresses the potential infectious complication of MRONJ. Medical approaches including PENT-E, teriparatide, PBM, and PDT can result in successful management and should be considered prior to taking a surgical approach. Combined medical management for both preventing and managing MRONJ holds potential for achieving optimal clinical outcomes and avoiding surgical intervention, requiring further validation through larger studies and controlled trials.

Impact of Teriparatide on Complications and Patient-Reported Outcomes of Patients Undergoing Long Spinal Fusion According to Bone Density

BACKGROUND

Surgery for adult spinal deformity (ASD) poses substantial risks, including the development of symptomatic pseudarthrosis, which is twice as prevalent among patients with osteoporosis compared with those with normal bone mineral density (BMD). Limited data exist on the impact of teriparatide, an osteoanabolic compound, in limiting the rates of reoperation and pseudarthrosis after treatment of spinal deformity in patients with osteoporosis.

METHODS

Osteoporotic patients on teriparatide (OP-T group) were compared with patients with osteopenia (OPE group) and those with normal BMD. OP-T patients were matched with OPE patients and patients with normal BMD at a 1:2:2 ratio. All patients had a minimum 2-year follow-up and underwent posterior spinal fusion (PSF) involving >7 instrumented levels. The primary outcome was the 2-year reoperation rate. Secondary outcomes included pseudarthrosis with or without implant failure, proximal junctional kyphosis (PJK), and changes in patient-reported outcomes (PROs). Clinical outcomes were analyzed using conditional logistic regression. Changes in PROs were analyzed using a mixed-effects model.

RESULTS

Five hundred and forty patients (52.6% normal BMD, 32.9% OPE, 14.4% OP-T) were included. In the unmatched cohort, 2-year reoperation rates (odds ratio [OR] = 0.45 [95% confidence interval (CI): 0.20 to 0.91]) and pseudarthrosis rates (OR = 0.25 [95% CI: 0.08 to 0.61]) were significantly lower in the OP-T group than the OPE group. Seventy-eight patients in the OP-T group were matched to 156 patients in the OPE group. Among these matched patients, at 2 years, 23.1% (36) in the OPE group versus 11.5% (9) in the OP-T group had a reoperation (OR = 0.45, p = 0.0188), 21.8% (34) versus 6.4% (5) had pseudarthrosis with or without implant failure (OR = 0.25, p = 0.0048), and 6.4% (10) versus 7.7% (6) had PJK (OR = 1.18, p = 0.7547), respectively. At 2 years postoperatively, PROs were better among OP-T patients than OPE patients. Subsequently, 78 patients in the OP-T group were matched to 156 patients in the normal BMD group. Among these matched patients, there was no significant difference in 2-year reoperation (OR = 0.85 [95% CI: 0.37 to 1.98]), pseudarthrosis (OR = 0.51 [95% CI: 0.181 to 1.44]), and PJK rates (OR = 0.77 [95% CI: 0.28 to 2.06).

CONCLUSIONS

Osteoporotic patients on teriparatide demonstrated lower reoperation and symptomatic pseudarthrosis rates 2 years postoperatively compared with osteopenic patients. Moreover, patient-reported and clinical outcomes for osteoporotic patients on teriparatide were not different from those for patients with normal BMD.

LEVEL OF EVIDENCE

Therapeutic Level III . See Instructions for Authors for a complete description of levels of evidence.

Primary hyperparathyroidism and sarcoma: A case report and literature review

ABSTRACT

The relationship between primary hyperparathyroidism (PHPT) and bone sarcoma is debatable, especially after wider use of teriparatide treatment, concerns have intensified on the issue. Extensive search in English literature revealed 10 cases reported having PHPT and sarcomas. Besides, three cases of bone sarcoma occurring after teriparatide treatment had been reported. Hereby, we report a 51-year-old woman with a prolonged history of PHPT. She was diagnosed with chondrosarcoma 9 years after refusal and lack of treatment for PHPT. She was cured surgically for both chondrosarcoma and parathyroid adenoma at 1-year interval. So far, large cohorts did not show an increase in the incidence of bone sarcomas in PHPT. Several case observations, including the current one, as well as data from in vitro and rat studies, pointed out prolonged parathormone exposure, may be a risk for bone sarcomas. Under these circumstances, a safer attitude on individual basis would be the prevention of prolonged parathormone exposures.

Baseline serum PINP level is associated with the increase in hip bone mineral density seen with Romosozumab treatment in previously untreated women with osteoporosis

Baseline serum PINP value was significantly and independently associated with the increased bone mineral density (≥ 3%) in both total hip and femoral necks by 12 months of romosozumab treatment in patients with treatment-naive postmenopausal osteoporosis.

PURPOSE

Some patients fail to obtain a sufficiently increased hip bone mineral density (BMD) by romosozumab (ROMO) treatment. This study aimed to investigate the prognostic factor for increased hip BMD with ROMO in patients with treatment-naive postmenopausal osteoporosis.

METHODS

This prospective, observational, and multicenter study included patients (n = 63: mean age, 72.6 years; T-scores of the lumbar spine [LS], - 3.3; total hip [TH], - 2.6; femoral neck [FN], - 3.3; serum type I procollagen N-terminal propeptide [PINP], 68.5 µg/L) treated by ROMO for 12 months. BMD and serum bone turnover markers were evaluated at each time point. A responder analysis was performed to assess the patient percentage, and both univariate and multivariate analyses were performed to investigate the factors associated with clinically significant increased BMD (≥ 3%) in both TH and FN.

RESULTS

Percentage changes of BMD from baseline in the LS, TH, and FN areas were 17.5%, 4.9%, and 4.3%, respectively. In LS, 96.8% of patients achieved ≥ 6% increased LS-BMD, although 57.1% could not achieve ≥ 3% increased BMD in either TH or FN. Multiple regression analysis revealed that only the baseline PINP value was significantly and independently associated with ≥ 3% increased BMD in both TH and FN (p = 0.019, 95% confidence interval = 1.006-1.054). The optimal cut-off PINP value was 53.7 µg/L with 54.3% sensitivity and 92.3% specificity (area under the curve = 0.752).

CONCLUSIONS

In a real-world setting, baseline PINP value was associated with the increased BMD of TH and FN by ROMO treatment in treatment-naive patients.

Comparison of the efficacy between sequential therapy with teriparatide and denosumab and denosumab monotherapy in suppressing fragility fracture risk

In this retrospective study, the effectiveness of short-term teriparatide with denosumab in reducing fragility fracture risk was determined in comparison with denosumab monotherapy. Administration of sequential teriparatide with denosumab showed excellent outcomes in suppressing the risk for fragility fractures compared with denosumab monotherapy.

INTRODUCTION

To determine the effectiveness of short-term teriparatide with denosumab in reducing the risk of fragility fractures in comparison to denosumab monotherapy.

METHODS

The data of postmenopausal patients treated with denosumab for > 2 years between August 2015 and October 2020 were retrospectively analyzed. One hundred sixty four postmenopausal women of a total 615 were excluded, since they did not undergo > 2 bone mineral density (BMD) tests, were lost to follow-up, or received long-term teriparatide therapy. Total 320 patients received denosumab monotherapy and 131 patients received teriparatide for ≥ 3 months followed by denosumab. The number of osteoporotic fractures, presence of back pain before and after treatment, and annual BMD during treatment were comparatively assessed using t-test, Chi-square test, and linear mixed model analysis.

RESULTS

Before treatment, the denosumab monotherapy group had fewer osteoporotic fractures (mean ± standard deviation; 0.459 ± 0.689) than the sequential therapy group had (1.037 ± 0.871; p < 0.001). After treatment, the sequential therapy group had fewer osteoporotic fractures than the denosumab monotherapy group had (0.119 ± 0.348 versus 0.144 ± 0.385; p < 0.001). At 1 and 2 years after treatment, the increase in lumbar spine BMD was greater in the sequential therapy group than in the denosumab monotherapy group (p = 0.08, group × time). The difference between post and pre-treatment back pain visual analog scale score was significantly lower in the sequential therapy group than in the monotherapy group (3.246 ± 3.426 versus 1.734 ± 3.049; p < 0.001).

CONCLUSION

Short-term teriparatide use before denosumab showed excellent outcomes in suppressing the risk of fragility fractures compared with denosumab monotherapy.

Interventions for managing medication-related osteonecrosis of the jaw

BACKGROUND

Medication-related osteonecrosis of the jaw (MRONJ) is a severe adverse reaction experienced by some individuals to certain medicines commonly used in the treatment of cancer and osteoporosis (e.g. bisphosphonates, denosumab, and antiangiogenic agents), and involves the progressive destruction of bone in the mandible or maxilla. Depending on the drug, its dosage, and the duration of exposure, this adverse drug reaction may occur rarely (e.g. following the oral administration of bisphosphonate or denosumab treatments for osteoporosis, or antiangiogenic agent-targeted cancer treatment), or commonly (e.g. following intravenous bisphosphonate for cancer treatment). MRONJ is associated with significant morbidity, adversely affects quality of life (QoL), and is challenging to treat. This is an update of our review first published in 2017.

OBJECTIVES

To assess the effects of interventions versus no treatment, placebo, or an active control for the prophylaxis of MRONJ in people exposed to antiresorptive or antiangiogenic drugs. To assess the effects of non-surgical or surgical interventions (either singly or in combination) versus no treatment, placebo, or an active control for the treatment of people with manifest MRONJ.

SEARCH METHODS

Cochrane Oral Health's Information Specialist searched four bibliographic databases up to 16 June 2021 and used additional search methods to identify published, unpublished, and ongoing studies.  SELECTION CRITERIA: We included randomised controlled trials (RCTs) comparing one modality of intervention with another for the prevention or treatment of MRONJ. For 'prophylaxis of MRONJ', the primary outcome of interest was the incidence of MRONJ; secondary outcomes were QoL, time-to-event, and rate of complications and side effects of the intervention. For 'treatment of established MRONJ', the primary outcome of interest was healing of MRONJ; secondary outcomes were QoL, recurrence, and rate of complications and side effects of the intervention.

DATA COLLECTION AND ANALYSIS

Two review authors independently screened the search results, extracted the data, and assessed the risk of bias in the included studies. For dichotomous outcomes, we reported the risk ratio (RR) (or rate ratio) and 95% confidence intervals (CIs).

MAIN RESULTS

We included 13 RCTs (1668 participants) in this updated review, of which eight were new additions. The studies were clinically diverse and examined very different interventions, so meta-analyses could not be performed. We have low or very low certainty about available evidence on interventions for the prophylaxis or treatment of MRONJ. Prophylaxis of MRONJ Five RCTs examined different interventions to prevent the occurrence of MRONJ. One RCT compared standard care with regular dental examinations at three-month intervals and preventive treatments (including antibiotics before dental extractions and the use of techniques for wound closure that avoid exposure and contamination of bone) in men with metastatic prostate cancer treated with zoledronic acid. The intervention seemed to lower the risk of MRONJ (RR 0.10, 95% CI 0.02 to 0.39, 253 participants). Secondary outcomes were not evaluated. Dentoalveolar surgery is considered a common predisposing event for developing MRONJ and five RCTs tested various preventive measures to reduce the risk of postoperative MRONJ. The studies evaluated plasma rich in growth factors inserted into the postextraction alveolus in addition to standardised medical and surgical care versus standardised medical and surgical care alone (RR 0.08, 95% CI 0.00 to 1.51, 176 participants); delicate surgery and closure by primary intention versus non-traumatic tooth avulsion and closure by secondary intention (no case of postoperative MRONJ in either group); primary closure of the extraction socket with a mucoperiosteal flap versus application of platelet-rich fibrin without primary wound closure (no case of postoperative MRONJ in either group); and subperiosteal wound closure versus epiperiosteal wound closure (RR 0.09, 95% CI 0.00 to 1.56, 132 participants).  Treatment of MRONJ Eight RCTs examined different interventions for the treatment of established MRONJ; that is, the effect on MRONJ cure rates.  One RCT analysed hyperbaric oxygen (HBO) treatment used in addition to standard care (antiseptic rinses, antibiotics, and surgery) compared with standard care alone (at last follow-up: RR 1.56, 95% CI 0.77 to 3.18, 46 participants).  Healing rates from MRONJ were not significantly different between autofluorescence-guided bone surgery and conventional bone surgery (RR 1.08, 95% CI 0.85 to 1.37, 30 participants). Another RCT that compared autofluorescence- with tetracycline fluorescence-guided sequestrectomy for the surgical treatment of MRONJ found no significant difference (at one-year follow-up: RR 1.05, 95% CI 0.86 to 1.30, 34 participants).  Three RCTs investigated the effect of growth factors and autologous platelet concentrates on healing rates of MRONJ: platelet-rich fibrin after bone surgery versus surgery alone (RR 1.05, 95% CI 0.90 to 1.22, 47 participants), bone morphogenetic protein-2 together with platelet-rich fibrin versus platelet-rich fibrin alone (RR 1.10, 95% CI 0.94 to 1.29, 55 participants), and concentrated growth factor and primary wound closure versus primary wound closure only (RR 1.38, 95% CI 0.81 to 2.34, 28 participants).   Two RCTs focused on pharmacological treatment with teriparatide: teriparatide 20 μg daily versus placebo in addition to standard care (RR 0.96, 95% CI 0.31 to 2.95, 33 participants) and teriparatide 56.5 μg weekly versus teriparatide 20 μg daily in addition to standard care (RR 1.60, 95% CI 0.25 to 1.44, 12 participants).

AUTHORS CONCLUSIONS

Prophylaxis of medication-related osteonecrosis of the jaw One open-label RCT provided some evidence that dental examinations at three-month intervals and preventive treatments may be more effective than standard care for reducing the incidence of medication-related osteonecrosis of the jaw (MRONJ) in individuals taking intravenous bisphosphonates for advanced cancer. We assessed the certainty of the evidence to be very low. There is insufficient evidence to either claim or refute a benefit of the interventions tested for prophylaxis of MRONJ in patients with antiresorptive therapy undergoing dentoalveolar surgery. Although some interventions suggested a potential large effect, the studies were underpowered to show statistical significance, and replication of the results in larger studies is pending. Treatment of medication-related osteonecrosis of the jaw The available evidence is insufficient to either claim or refute a benefit, in addition to standard care, of any of the interventions studied for the treatment of MRONJ.

Spine Volumetric BMD and Strength in Premenopausal Idiopathic Osteoporosis: Effect of Teriparatide Followed by Denosumab

CONTEXT

Premenopausal women with idiopathic osteoporosis (PreMenIOP) have marked deficits in bone density, microstructure, and strength.

OBJECTIVE

To define effects of treatment with teriparatide followed by denosumab on lumbar spine (LS) volumetric bone mineral density (vBMD) and stiffness by finite element analysis assessed on central quantitative computed tomography (cQCT) scans.

DESIGN, SETTINGS, AND PARTICIPANTS

Ancillary analysis of baseline, post-teriparatide, and post-denosumab cQCT scans from a randomized trial of 41 women allocated to teriparatide (20 mcg daily; n = 28) or placebo (n = 11). After 6 months, those on teriparatide continued for 18 months, and those on placebo switched to teriparatide for 24 months. After completing teriparatide, 33 enrolled in a Phase 2B extension with denosumab (60 mg every 6 months) for 12 months.

MAIN OUTCOME MEASURES

Primary outcomes were percentage change from baseline in LS trabecular vBMD and stiffness after teriparatide and between end of teriparatide and completing denosumab. Percentage change from baseline in LS trabecular vBMD and stiffness after sequential teriparatide and denosumab were secondary outcomes.

FINDINGS

There were large increases (all Ps < 0.001) in trabecular vBMD (25%), other vBMD parameters, and stiffness (21%) after teriparatide. Statistically significant increases in trabecular vBMD (10%; P < 0.001) and other vBMD parameters (P = 0.03-0.001) were seen after denosumab, while stiffness increased by 7% (P = 0.068). Sequential teriparatide and denosumab led to highly significant (all Ps < 0.001) increases LS trabecular vBMD (43%), other vBMD parameters (15-31%), and stiffness (21%).

CONCLUSIONS

The large and statistically significant increases in volumetric density and stiffness after sequential treatment with teriparatide followed by denosumab are encouraging and support use of this regimen in PreMenIOP.

"Pregnancy and Lactation Associated Osteoporosis"

Pregnancy-associated osteoporosis (PAO) is a rare condition of skeletal fragility affecting women in pregnancy or the postpartum period. During normal pregnancy and lactation, substantial changes in calcium metabolism and skeletal physiology occur in order to meet the demands of the developing foetus. Whilst these adaptations are reversible and generally of no clinical consequence for the mother, a small number of women will develop osteoporosis and suffer fragility fractures. Vertebral fractures occur most commonly in PAO and are often multiple. Due to the rarity of PAO, systematic study to date has been limited. Aetiology is poorly understood, but traditional osteoporosis risk factors and genetic factors are likely to play a role. A small number of cases may be due to an underlying metabolic bone disorder or monogenic condition. Management of PAO is challenging, due both to a poor evidence base and the fact that spontaneous improvement in BMD is known to occur once pregnancy and lactation are complete. Bisphosphonates, denosumab and teriparatide have all been used in individual patients, but the data supporting their use are currently limited.

Denosumab After Teriparatide in Premenopausal Women With Idiopathic Osteoporosis

CONTEXT

We have previously reported that teriparatide is associated with substantial increases in bone mineral density (BMD) at the lumbar spine (LS), total hip (TH), and femoral neck (FN) and small declines at the distal radius in 41 premenopausal women with idiopathic osteoporosis (IOP), all severely affected with low trauma fractures and/or very low BMD. Effects of teriparatide dissipate if not followed by antiresorptives.

OBJECTIVE

To assess the effects of 12 and 24 months of denosumab in premenopausal women with IOP completing 24 months of teriparatide.

METHODS

This was a preplanned phase 2B extension study. Premenopausal women with IOP who had completed a course of teriparatide received denosumab 60 mg every 6 months over 24 months. The main outcome measure was within-group change in BMD at the LS at 12 months. Secondary outcomes include change in 12-month BMD at other sites, 24-month BMD at all sites, trabecular bone score (TBS), and bone turnover markers (BTMs).

RESULTS

After completing teriparatide, 32 participants took denosumab for 12 months and 29 for 24 months, with statistically significant increases in BMD at the LS (5.2 ± 2.6% and 6.9 ± 2.6%), TH (2.9 ± 2.4% and 4.6 ± 2.8%), and FN (3.0 ± 3.8% and 4.7 ± 4.9%). Over the entire 24-month teriparatide and 24-month denosumab treatment period, BMD increased by 21.9 ± 7.8% at the LS, 9.8 ± 4.6% at the TH, and 9.5 ± 4.7% at the FN (all P < .0001). TBS increased by 5.8 ± 5.6% (P < .001). Serum BTM decreased by 75% to 85% by 3 months and remained suppressed through 12 months of denosumab. Denosumab was generally well tolerated.

CONCLUSION

These data support the use of sequential teriparatide and denosumab to increase BMD in premenopausal women with severe osteoporosis.

Which injected antiosteoporotic medication is worth paying for? A cost-effectiveness analysis of teriparatide, zoledronate, ibandronate, and denosumab for postmenopausal osteoporotic women in China

OBJECTIVE

The purpose of this study was to evaluate the cost-effectiveness of four injected antiosteoporotic medications including teriparatide, zoledronate, ibandronate, and denosumab for postmenopausal osteoporotic women in China.

METHODS

A Markov microsimulation model was used to compare the cost-effectiveness of the four drugs above in Chinese postmenopausal osteoporotic women with no fracture history of hip, vertebral, or wrist at various ages (65, 70, 75, and 80) of therapy initiation from the health care payer perspective.

RESULTS

Denosumab was dominant (ie, lower costs and greater quality-adjusted life-years [QALYs]) compared with other strategies at all ages studied. The incremental cost-effectiveness ratios (ICERs) of zoledronate or ibandronate versus no treatment were $4,482.88/ QALYs or $11,378/QALYs, respectively, at age 65 years, and the results at other ages were similar. In contrast, the incremental cost-effectiveness ratio of teriparatide strategy compared with no treatment exceeded the pre-determined threshold of a willingness-to-pay of $31,512/QALY regardless of the adoption of the patient assistance program at all ages studied, and a threshold analysis showed that teriparatide without patient assistance program became cost-effective when the annual drug cost is decreased to $1,644.87 (current cost: $8,764.65). The cost-effectiveness decision did not change in most of the one-way sensitivity analyses. A scenario analysis considering no offset effect of denosumab showed that zoledronate had the potential to become the optimal option relative to denosumab. In probabilistic sensitivity analyses, the probabilities of denosumab being cost-effective compared with other strategies were 100% at a willingness-to-pay of $31,512/QALY.

CONCLUSIONS

Among postmenopausal osteoporotic women in China, denosumab therapy is cost-effective at all ages examined from the health care payer perspective, compared with teriparatide, zoledronate, or ibandronate. This study will help clinicians and policymakers make better decisions about the relative economic value of osteoporosis treatments in China.

Teriparatide Treatment in Patients with Pregnancy- and Lactation-Associated Osteoporosis

Pregnancy- and lactation-associated osteoporosis (PLO) is a rare disease, presenting in most cases with severe back pain due to low energy vertebral fractures (VFs). Our purpose was to assess the effect of teriparatide (TPTD) vs. conventional management on areal bone mineral density (aBMD) and trabecular bone score (TBS) in patients with PLO. A multicenter retrospective cohort study concerning premenopausal women with PLO. Nineteen women were treated with TPTD (20 μg/day) (group A) plus calcium and vitamin D and eight women with calcium and vitamin D only (group B) for up to 24 months. The primary end-point was between group differences in lumbar spine (LS) and total hip (TH) aBMD, and TBS at 12 and 24 months. Patients in group A had sustained a median of 4.0 VFs (3-9) vs. 2.5 VFs (1-10) in group B (p = 0.02). At 12 months, patients on TPTD vs. controls achieved a mean aBMD increase of 20.9  ±  11.9% vs. 6.2  ±  4.8% at the LS (p < 0.001), 10.0  ±  11.6% vs. 5.8  ±  2.8% at the TH (p = 0.43), and 6.7  ±  6.9% vs. 0.9  ±  3.7% in TBS (p = 0.09), respectively. At 24 months, seven patients on TPTD and six controls achieved a mean LS aBMD increase of 32.9  ±  13.4% vs. 12.2  ±  4.2% (p = 0.001). P1NP levels during the first month of TPTD treatment were positively correlated with the 1-year LS aBMD change (r = 0.68, p = 0.03). No new clinical fractures occurred while on-treatment. In patients with PLO, TPTD treatment resulted in significantly greater increases in LS aBMD compared with calcium and vitamin D supplementation at 12 and 24 months.

Anti-RANKL monoclonal antibody and bortezomib prevent mechanical unloading-induced bone loss

INTRODUCTION

Bone loss is a major health concern for astronauts during long-term spaceflight and for patients during prolonged bed rest or paralysis. It is essential to develop therapeutic strategies to combat the bone loss occurring in people afflicted with disuse atrophy on earth as well as in astronauts in space, especially during prolonged missions. Although several drugs have been demonstrated for treating postmenopausal osteoporosis or bone-related diseases, their effects on microgravity-induced bone loss are still unclear.

MATERIALS AND METHODS

Here, we employed the hindlimb-unloading (HLU) tail suspension model and compared the preventive efficiencies of five agents including alendronate (ALN), raloxifene (Rox), teriparatide (TPTD), anti-murine RANKL monoclonal antibody (anti-RANKL) and proteasome inhibitor bortezomib (Bzb) on mechanical unloading-induced bone loss. Bone mineral density (BMD) was measured by quantitative computed tomography. The osteoblastic and osteoclastic activity were measured by serum ELISA, histology analysis, and histomorphometric analysis.

RESULTS

Compared to the control, ALN and anti-RANKL antibody could restore bone mass close to sham levels by inhibiting bone resorption. Bzb could increase the whole bone mass and strength by inhibiting bone resorption and promoting bone formation simultaneously. Meanwhile, Rox did not affect bone loss caused by HLU. TPTD stimulated cortical bone formation but the total bone mass was not increased significantly.

CONCLUSIONS

We demonstrated for the first time that anti-RANKL antibody and Bzb had a positive effect on preventing mechanical unloading-induced bone loss. This finding puts forward the potential use of anti-RANKL and Bzb on bone loss therapies or prophylaxis of astronauts in spaceflight.

Diagnosis and Management of Osteoporosis During COVID-19: Systematic Review and Practical Guidance

It is acknowledged that the COVID-19 pandemic has caused profound disruption to the delivery of healthcare services globally. This has affected the management of many long-term conditions including osteoporosis as resources are diverted to cover urgent care. Osteoporosis is a public health concern worldwide and treatment is required for the prevention of further bone loss, deterioration of skeletal micro-architecture, and fragility fractures. This review provides information on how the COVID-19 pandemic has impacted the diagnosis and management of osteoporosis. We also provide clinical recommendations on the adaptation of care pathways based on experience from five referral centres to ensure that patients with osteoporosis are still treated and to reduce the risk of fractures both for the individual patient and on a societal basis. We address the use of the FRAX tool for risk stratification and initiation of osteoporosis treatment and discuss the potential adaptations to treatment pathways in view of limitations on the availability of DXA. We focus on the issues surrounding initiation and maintenance of treatment for patients on parenteral therapies such as zoledronate, denosumab, teriparatide, and romosozumab during the pandemic. The design of these innovative care pathways for the management of patients with osteoporosis may also provide a platform for future improvement to osteoporosis services when routine clinical care resumes.

Role of bone-forming agents in the management of osteoporosis

Recent evidence confirms the superiority of osteoanabolic therapy compared to anti-remodeling drugs for rapid improvement in bone density and fracture risk reduction, providing strong justification for the use of these anabolic agents as the initial therapy in high-risk patients, to be followed by anti-remodeling therapy. This review will highlight the results of recent studies and define the current status of osteoanabolic therapy for osteoporosis.

Effect of weekly teriparatide injections on osteoporotic fracture healing: protocol for a double-blind, randomised controlled trial

INTRODUCTION

Both animal studies and clinical trials have shown that daily parathyroid hormone administration promotes bone fracture healing. We previously found that weekly injections of the recombinant human parathyroid hormone teriparatide at a dosage of 20 μg/kg promoted tibial fracture healing to the same extent as daily injections of teriparatide at a dosage of 10 μg/kg in a rodent model. However, the effect of weekly teriparatide administration on human fracture healing is unreported. This protocol describes a randomised controlled clinical trial designed to evaluate whether weekly administration of teriparatide accelerates fracture repair in humans.

METHODS AND ANALYSIS

This single-centre, double-blind, randomised controlled trial will be conducted in Peking University Third Hospital. Eligible patients with Colles' fracture incurred within 48 hours will be randomly divided into two groups (n=40 per group) that will receive 14 weekly subcutaneous injections of either saline or teriparatide (40 μg/week). The primary outcome will be the time taken to achieve radiographic healing, as assessed using the modified radiographic union scale for tibial fractures. The secondary outcomes will be functional assessments, including the self-administered Patient-Rated Wrist Evaluation questionnaire, grip strength and rate of fracture non-union.

ETHICS AND DISSEMINATION

Ethical approval has been obtained from the Peking University Third Hospital Medical Science Research Ethics Committee (M2020207). The findings will be disseminated in peer-reviewed publications.

TRIAL REGISTRATION NUMBER

NCT04473989: protocol version: 1.

Evaluation of factors affecting the occurrence of second atypical fracture after bone union of the first atypical fracture

PURPOSE

Teriparatide is sometimes used in the treatment of atypical femoral fracture (AFF). Even if bone union is achieved, orthopedic physicians must consider the risk of relapse. This study aimed to investigate the factors affecting AFF recurrence, and to determine the appropriate treatment for osteoporosis after bone union.

METHODS

One hundred thirty-one consecutive AFFs in 113 Japanese patients were included. Eleven patients had AFF in the unaffected limb (9 patients) after the first AFF or re-fracture at the original fracture site (2 patients) after bone union of the first AFF was confirmed. We divided all patients into two groups: the second fracture group (22 AFFs in 11 patients) and non-second fracture group (109 AFFs in 102 patients). We compared clinical information between the 2 groups and investigated the factors affecting AFF recurrence using the Student t-, Welch t-, and chi-square tests.

RESULTS

Although there was no significant difference in clinical characteristics between the 2 groups, multivariate analysis of factors associated with AFF recurrence identified short duration of treatment with teriparatide and active vitamin D₃ (p = 0.0408 and 0.0366, respectively) as risk factors. Even in the analysis excluding subtrochanteric AFF, short periods of teriparatide and active vitamin D₃ administration were observed as risk factors (p = 0.0484 and 0.0346, respectively).

CONCLUSION

The administration of teriparatide for as long as possible after occurrence first AFF and the use of active vitamin D₃ after completion of teriparatide therapy may be the most effective strategy to prevent the recurrence of AFF.

A probable atypical ulnar fracture in a man receiving denosumab

BACKGROUND

Atypical femur fractures are widely recognized and associated with anti-resorptive therapy, most commonly bisphosphonates. These fractures generally occur in the femoral shaft or subtrochanteric region. Cases of atypical fractures at non-femur sites, including the ulna, have been reported.

CASE REPORT

Here we report a probable atypical ulnar fracture in a man receiving denosumab, who had been using his upper extremities for transfers and ambulation. Radiographs demonstrated a non-comminuted, transverse fracture somewhat similar to findings of atypical femur fractures. He was deemed a poor surgical candidate and treated with teriparatide. To our knowledge, this is the first reported probable atypical ulnar fracture potentially associated with denosumab use.

CONCLUSION

We believe it important that clinicians be aware of the association of anti-resorptive therapy with atypical fractures not only of the femur, but also at other skeletal sites. In patients on long-term anti-resorptive therapy, it is appropriate to consider that persistent "prodromal" pain might indicate an impending atypical fracture at an atypical skeletal site.

Persistence and adherence to parenteral osteoporosis therapies: a systematic review

Osteoporosis is a chronic disease of low bone mass and fragility. Treatment is frequently compromised by suboptimal medication compliance causing increased morbidity. This review investigates adherence and persistence to parenteral osteoporosis therapies. Findings reveal parenteral medications requiring reduced dosing frequency have higher compliance than oral therapies. This systematic review examines real-world adherence to parenteral osteoporosis therapies. We searched PubMed, Medline, and EMBASE databases for English language observational studies that examined patient adherence and/or persistence to parenteral osteoporosis treatments (teriparatide sc, ibandronate iv, zoledronic acid iv, and denosumab sc) in adults with osteoporosis published up to September 2018. Studies with only self-reported adherence or persistence data and those with less than 20 patients were excluded. Quality assessment of included studies was completed using the Newcastle-Ottawa quality assessment scale (NOS). We identified 40 eligible studies. Teriparatide was examined in 29 studies, with persistence rates of 10-87% (median 55%) at 1 year and 10-69% (median 29.5%) at 2 years, and adherence rates of 21-89% (median 53%) at 1 year and 37-68% (median 40%) at 2 years. Ten studies of zoledronic acid reported persistence rates of 34-73% (median 42%) for second dose and 20-54% (median 35.8%) for third dose. Ten studies of ibandronate adherence reported and 2-year persistence rates of 31-58% (median 47.5%) in 1 year and 13-35% (median 25%) at 2 years, and adherence rates of 21-72% (median 47.3%) and 15-58% (median 36.5%) respectively. Denosumab was reported in 19 studies, with second (1 year) and fourth (2 year) dose persistence rates of 61-100% (median 81%) and 36-99% (median 45.5%). There is substantial heterogeneity in reports of persistence and adherence rates with parenteral osteoporosis therapies. Most of the published data are from short-term studies and evaluations of long-term adherence and persistence with parenteral therapies for osteoporosis are needed.

Treatment of postmenopausal osteoporosis with bone-forming and antiresorptive treatments: Combined and sequential approaches

Efficient therapies are available for the treatment of osteoporosis. Bisphosphonates and denosumab are the most commonly used antiresorptive therapies. Despite differences in the increase in bone mineral density seen with these drugs, the reductions in fracture risk are similar; 50-70%, 20%, and 40% for vertebral, non-vertebral and hip fractures, respectively. The bone-forming treatments; teriparatide and abaloparatide increase bone mineral density more than the antiresorptives and the reductions in fracture risk are 85% and 40-50% for vertebral and non-vertebral fractures, respectively, compared to placebo. The VERO study demonstrated a >50% reduction in vertebral and clinical fractures in women treated with teriparatide compared to risedronate. The dual-action treatment; romosozumab leads to more pronounced increases in BMD than other treatment modalities and reduces the risk of vertebral and clinical fractures by 73% and 36% compared to placebo after 12 months and the sequential treatment regime; romosozumab for 12 months followed by alendronate reduced the risk of vertebral, non-vertebral and hip fractures by 48%, 20% and 38%, respectively compared to alendronate after 2-3 years. The evidence for combination therapy targeting both resorption and formation is limited as only short-term studies with BMD as the endpoint have been performed. All bone-forming and dual-action treatments increase BMD and reduce the fracture risk, however, the effect wears off with time and treatment is therefore only temporary and should be followed by antiresorptive treatment with a bisphosphonate or denosumab. The sequence of treatment matters as the BMD response to teriparatide is reduced in patients previously treated with bisphosphonates; however, based on the findings of the VERO trial, the anti-fracture efficacy of bone-forming treatment in comparison with risedronate seems to be preserved after bisphosphonate therapy. The DATA study suggested that transitioning from denosumab to teriparatide is problematic due to the increase in bone resorption occurring after stopping denosumab. Studies have shown further improvements in BMD when transitioning from oral bisphosphonates to zoledronic acid or denosumab. Management of osteoporosis will in many patients include a long-term treatment plan. This will often include sequential therapy which in severe cases preferably should start with bone-forming followed by antiresorptive treatment. The severity of osteoporosis, reaching a treatment goal, and responding to treatment failure are important factors determining the treatment sequence in the individual patient.

Teriparatide improves microarchitectural characteristics of peri-implant bone in orchiectomized rats

This study evaluated the peri-implant bone repair in orchiectomized rats receiving intermittently PTH 1-34. The treatment returned the bone quality and quantity of the animals to normal in the computerized microtomography, laser confocal microscopy, and histological analysis. The PTH 1-34 promoted marked bone formation with increased volume, improved quality, and greater bone turnover.

INTRODUCTION

Osteoporosis can be a problem in implant osseointegration. So this study aimed to evaluate the quantity and quality of peri-implant bone repair in orchiectomized Wistar rats receiving intermittently administered PTH 1-34.

METHODS

Animals (n = 24) were divided into 3 groups: healthy control (SHAM), orchiectomized (ORQ), and orchiectomized and treated with 0.5 μg/kg/day PTH 1-34 (TERI), and each received an implant in the right and left tibial metaphysis, which was allowed to repair for 60 days. The resultant bone formation was evaluated through computerized microtomography (micro-CT) to compare the percent bone volume (BV/TV), trabecular thickness (Tb.Th), trabecular number and separation (Tb.N, Tb.Sp), and bone implant contact (BIC) through the intersection surface (i.S) between groups. Laser confocal microscopy was used to evaluate fluorochrome areas for mineral apposition rate (MAR) and neoformed bone area (NBA). In addition, histological evaluation of calcified tissues with Stevenel blue and alizarin red staining was performed.

RESULTS

Treatment with PTH 1-34 returned the bone quality and quantity of the osteoporotic animal to normal, as the TERI group presented statistically significant higher values for BV/TV, Tb.Th, and BIC parameters compared with ORQ (p < 0.05), but when compared with SHAM (p > 0.05), no statistical difference was noted. In addition, in the bone turnover analysis (MAR, NBA) for TERI, the highest results are presented, followed by SHAM, and then ORQ (TERI × ORQ: p < 0.05).

CONCLUSIONS

Intermittent treatment with PTH 1-34 on orchiectomized animals promoted marked bone formation with increased volume, improved quality, and greater bone turnover in the peri-implant space, returning the bone quality and quantity to the present standard in healthy animals.

Which Drug Next? Sequential Therapy for Osteoporosis

The proliferation of drugs with unique modes of action for treating osteoporosis has been most welcome. Fear of complications, even though rare, associated with long-term bisphosphonates (BPs) changed prescribing patterns. The BPs are stored in bone for years. Drugs not stored in bone; for example, abaloparatide, teriparatide, denosumab, and romosozumab have expanded our armamentarium for treating osteoporosis but have brought new challenges. Bone accrued during treatment with the last 3 drugs, and perhaps abaloparatide, is lost rapidly after their withdrawal due to rebound increase in bone resorption. Treatment with these drugs must be followed by administration of an antiresorptive agent. The article by Kendler et al. (1) in this issue of JCEM reports alendronate preserves bone accrued during administration of denosumab.

Atypical femoral fracture, case report and literature review

INTRODUCTION

Bisphosphonates have been the gold standard in the management of osteoporosis. Its antiresorptive effect has reduced the incidence of fractures due to bone fragility, as well as its impact on public health. We present the clinical case of a patient in prolonged treatment with bisphosphonates and atypical bilateral femur fracture.

CASE REPORT

A 65-year-old female who presented a fall from her own height, on treatment with risedronate for seven years, and a history of systemic arterial hypertension and hypercholesterolemia, both with medical treatment. Diagnosed with bilateral atypical femoral fracture, treated with closed reduction internal fixation (CRIF) with intramedullary nailing, application of calcium citrate and teriparatide.

DISCUSSION

Multiple studies indicate that the benefit of using bisphosphonates for osteoporosis is higher than the risk of presenting atypical fractures.

[Secondary osteoporosis UPDATE. Drugs under development for metabolic bone disease]

For the treatment of osteoporosis, anti-resorptive agents including bisphosphonates and raloxifene are widely used. As new anti-resorptive drugs, anti-RANKL antibody and cathepsin K inhibitor are under development. Among bone anabolic agents, daily subcutaneous injection of teriparatide will soon become available in Japan. In addition, new anabolic agents such as calcilitycs and anti-sclerostin antibody are under clinical or preclinical development for the treatment of osteoporosis.

Cyclic AMP formation in rat bone and kidney cells is stimulated equally by parathyroid hormone-related protein (PTHrP) 1-34 and PTH 1-34

Parathyroid hormone-related protein (PTHrP) plays a major role in the pathogenesis of humoral hypercalcemia of malignancy. It interacts with the PTH receptor and has therefore a nearly identical effect on bone cells as PTH. However, PTHrP is thought to be less potent than PTH in stimulating adenylate cyclase in canine renal membranes, leading to the hypothesis of a differential efficiency in signal transduction by PTHrP with respect to bone vs kidney. In a homologous model with intact osteoblast-like cells (UMR 106) and primary kidney cells, both from the rat, we have tested N-terminal peptide fragments, based on the rat amino acid sequence 1-34, of PTH and PTHrP. Compared with PTHrP(1-34), rat PTH(1-34) had a similar relative potency in bone cells (85%) and in kidney cells (140%) in its ability to stimulate adenylate cyclase. Human PTH(1-34) was 5.6- to 6.5-fold less potent than rat PTH(1-34) in both cell types. In human osteoblast-like cells (SaOS-2), rat and human PTH were essentially equally potent compared to PTHrP(1-34) (identical sequence in rat and human) in stimulating cAMP accumulation. In conclusion, our study revealed the equipotency of rat PTH(1-34) and PTHrP(1-34) in stimulating intracellular cAMP formation in a homologous system of rat bone and kidney cells. There seemed to be no unique signal transduction mechanism of PTHrP to the adenylate cyclase in rat kidney cells compared with bone cells.

[Drugs under development for osteoporosis ]

Osteoporosis is a disease in which the density and quality of bone is reduced, leading to an increase in fragility fractures. Osteoporosis is a major health threat affecting more than 10 million people in Japan. Emerging evidence has shown that anti-resorptive drugs such as bisphosphonates and raloxifene efficiently increase bone mass and prevent osteoporotic fractures by maintaining bone homeostasis. In addition, anabolic drugs such as parathyroid hormone and novel anti-resorptive drugs such as anti-RANKL drugs and cathepsin K inhibitors, which directly target osteoclasts are under development. In this review, we would like to summarize the current status of the development of anti-osteoporotic drugs.

[Newly developed drugs for osteoporosis in overseas and their future roles for the therapy]

Bisphosphonates are widely used, though gastrointestinal tolerance is a problem on daily administration. Intermittent regimen, from once weekly to once yearly, is now available in overseas and can overcome GI adverse events. New generation of anti-resorptive agents (anti-RANKL antibody and a new SERM, bazedoxifene) are promising and will be soon available for the treatment of osteoporosis. Anabolic agents such as teriparatide and strontium ranelate have marked effects on BMD and reduction on fracture risk. While none of these options is suitable for everyone, the range of future available therapies does mean that most patients can find an intervention that is effective and acceptable.

Effects of gonadal steroid suppression on skeletal sensitivity to parathyroid hormone in men

Hypogonadism is associated with osteoporosis in men. GnRH- agonist-induced hypogonadism increases bone turnover and bone loss in men, but the mechanism underlying these changes is unknown. To determine whether gonadal steroid deprivation increases the skeletal sensitivity to PTH or blunts the ability of PTH to promote 1,25-dihydroxyvitamin D formation, we infused human PTH-(1-34) at a dose of 0.55 U/kg.h for 24 h, in 11 men (ages, 50-82 yr) with locally advanced, node-positive, or biochemically recurrent prostate cancer but no evidence of bone metastases. PTH infusions were performed before initiation of GnRH agonist therapy (leuprolide acetate, 22.5 mg im, every 3 months) and again after 6 months of confirmed GnRH agonist-induced hypogonadism. Serum osteocalcin (OC), bone- specific alkaline phosphatase (BSAP), N-telopeptide (NTX), whole-blood ionized calcium, and 1,25-dihydroxyvitamin D were measured at baseline and every 6 h during each PTH infusion. Urinary NTX and free deoxypyridinoline (DPD) were assessed on spot morning samples before PTH infusion and on 24-h samples collected during the PTH infusions. Sex steroid levels were lowered to the castrate range in all subjects. Baseline serum NTX levels (drawn before PTH infusion) increased from 9.1 +/- 3.7 before leuprolide therapy to 13.9 +/- 5.0 nmol bone collagen equivalents (BCE)/L after leuprolide therapy (P = 0.003). Spot urine NTX collected before PTH infusion increased from 28 +/- 8 before leuprolide therapy to 49 +/- 17 nmol BCE/mmol creatinine after leuprolide therapy (P < 0.001), and urinary DPD increased from 4.7 +/- 1.1 to 7.4 +/- 1.8 nmol BCE/mmol creatinine (P < 0.001). Baseline serum OC and BSAP levels drawn before each PTH infusion did not change before vs. after leuprolide therapy. Serum NTX levels increased significantly during PTH infusion pre-GnRH agonist therapy (P < 0.001), and the rate of increase was greater after 6 months of GnRH agonist-induced hypogonadism (P < 0.01 for the difference in rates of change before and after GnRH agonist administration). Serum OC and BSAP levels decreased during PTH infusion (P < 0.001 for OC and P = 0.002 for BSAP), but the rates of decrease did not differ before or after leuprolide therapy (P = 0.45 for OC and P: = 0.19 for BSAP). Whole-blood ionized calcium levels increased during PTH infusion (P < 0.001), and the rate of increase was greater after GnRH agonist-induced hypogonadism (P = 0.068). Serum 1,25-dihydroxyvitamin D levels increased in response to PTH infusion before leuprolide therapy (P = 0.022), but there was no difference in the rate of increase before or after leuprolide therapy (P = 0.66). The incremental increase in urinary NTX excretion, but not DPD, during PTH infusion was greater after 6 months of leuprolide therapy (P = 0.029 for NTX, P = 0.578 for DPD). We conclude that suppression of sex steroids in elderly men increases the skeletal responsiveness to the bone resorbing effects of PTH infusion but does not affect the response of bone formation markers or 1,25-dihydroxyvitamin D to PTH. Changes in skeletal sensitivity to PTH may play an important role in the pathogenesis of hypogonadal bone loss in men.

Domain-specific gene activation by parathyroid hormone in osteoblastic ROS17/2.8 cells

Parathyroid hormone (PTH)-mediated gene activation was assessed in the osteoblast-like rat cell line ROS17/2.8 with two PTH fragments harboring distinct activating domains: PTH-(1-34) and PTH-(28-48). The PTH response of genes expressed immediate early in the cell cycle or in the osteoblast developmental sequence was investigated. In addition, subtractive cloning was used to identify genes in ROS17/2.8 cells that are activated by the two PTH domains. PTH-(1-34) immediately increased the transcript levels of c-fos and c-jun at a considerably higher rate than PTH-(28-48). A significant immediate PTH effect on osteoblastic marker genes could not be detected, with the exception of elevated ornithine decarboxylase transcript levels. However, continuous application of PTH-(1-34) increased transcript levels of the osteoblast-specific osteocalcin gene and reduced those of other osteoblastic marker genes including alkaline phosphatase and the PTH/PTH-related peptide receptor. By subtractive cloning, nine cDNAs were isolated corresponding to mRNAs directly up-regulated by PTH-(1-34) or PTH-(28-48). Among these were a cyclic phosphodiesterase, a (cytosine 5)-methyltransferase, an 80-kDa protein kinase C substrate, junB, and a novel GC-binding protein. Three cDNAs are unknown at present. Interestingly, in all cases, the efficiency of gene activation by PTH-(28-48) was substantially lower in comparison with PTH-(1-34). PTH-mediated protein kinase C signaling in ROS17/2.8 cells may therefore constitute a minor pathway in comparison with the dominant cAMP/protein kinase A cascade.

Pretreatment with 17 beta-estradiol attenuates basal- and PTH-stimulated membrane adenylyl cyclase activity in human osteoblast-like SAOS-2 cells

Parathyroid hormone (PTH)-stimulated production of cAMP by intact human osteoblast-like SaOS-2 cells is diminished by pretreatment with 17 beta-estradiol (E2). The goal of the present study was to determine whether E2, affected adenylyl cyclase activity in cell membranes. Cells were deprived of steroid hormones for 24 h and then incubated with E2 (1 nM) or vehicle for 12 h. Cell membranes were prepared and incubated with [alpha-32P]-ATP in the absence or presence of agonist, and the amount of [32P]-cAMP produced was measured to quantify adenylyl cyclase activity. There was less cAMP produced by membranes from E2-treated cells in response to PTH, GTP gamma S, forskolin, and Mn2+. E2 had no effect on the amounts of Gs or Gi. We propose that pretreatment of SaOS-2 cells with E2 reduced membrane cyclase activity, at least in part, by actions on the PTH-sensitive adenylyl cyclase and/or the G protein-adenylyl cyclase complex.

Regulation of Na-K-ATPase activity in the proximal tubule: role of the protein kinase C pathway and of eicosanoids

To evaluate further the signal transduction mechanisms involved in the short-term modulation of Na-K-ATPase activity in the mammalian kidney, we examined the role of phospholipase C-protein kinase C (PLC-PKC) pathway and of various eicosanoids in this process, using microdissected rat proximal convoluted tubules. Dopamine (DA) and parathyroid hormone (either synthetic PTH1-34 or PTH3-34) inhibited Na-K-ATPase activity in dose-dependent manner; this effect was reproduced by PKC530-558 fragment and blocked by the specific PKC inhibitor calphostin C, as well as by the PLC inhibitors neomycin and U-73122. Pump inhibition by DA, PTH, or arachidonic acid, and by PKC activators phorbol dibutyrate (PDBu) or dioctanoyl glycerol (DiC8) was abolished by ethoxyresorufin, an inhibitor of the cytochrome P450-dependent monooxygenase pathway, but was unaffected by indomethacin or nordihydroguaiaretic acid, inhibitors of the cyclooxygenase and lipoxygenase pathways of the arachidonic acid cascade, respectively. Furthermore, each of the three monooxygenase products tested (20-HETE, 12(R)-HETE, or 11,12-DHT) caused a dose-dependent inhibition of the pump. The effect of DA, PTH, PDBu or DiC8, as well as that of 20-HETE was not altered when sodium entry was blocked with the amiloride analog ethylisopropyl amiloride or increased with nystatin. We conclude that short-term regulation of proximal tubule Na-K-ATPase activity by dopamine and parathyroid hormone occurs via the PLC-PKC signal transduction pathway and is mediated by cytochrome P450-dependent monooxygenase products of arachidonic acid metabolism, which may interact with the pump rather than alter sodium access to it.

Abnormal calcaemic response to PTH in the uraemic rat without secondary hyperparathyroidism

BACKGROUND

Skeletal resistance to the calcaemic action of parathyroid hormone (PTH) is an important pathogenic factor in the development of secondary hyperparathyroidism. Since parathyroidectomy normalizes the calcaemic response to PTH in uraemic animals, the increase in PTH levels has been advanced as a cause of skeletal resistance to the calcaemic action of PTH. This study was designed to evaluate in uraemic rats the effect of normal PTH levels on the calcaemic response to PTH.

METHODS

To maintain normal PTH levels, rats were parathyroidectomized (PTX) and rat 1-34 PTH was infused at a rate of 0.022 microg/100 g per hour via a subcutaneously implanted miniosmotic pump; this rate of infusion was considered to be the normal PTH replacement dose since it normalized serum calcium and phosphorus in PTX rats with normal renal function. Two separate studies were performed. In the first study, rats were maintained on a moderate-phosphorus (0.6%) diet and rats were divided into four groups: (I) normal; (II) uraemic; (III) PTX with normal PTH replacement; and (IV) uraemic with PTX and normal PTH replacement. In a second study, the groups were the same except that a high-phosphorus (1.2%) diet was given to increase the magnitude of hyperparathyroidism in rats with intact parathyroid glands; an additional group (V) identical to group IV except that rats received daily calcitriol was included. After 14 days, rats received a 48-h infusion of high-dose rat 1-34 PTH (0.11 microg/100 g per hour) to evaluate the calcaemic response to PTH. Results. The calcaemic response to PTH was similar in normal rats and PTX rats replacement on both a moderate and high-phosphorus diet. In uraemic rats, the calcaemic response to PTH was decreased and the maintenance of normal PTH levels by PTH replacement did not correct the decreased calcaemic response to PTH; moreover, calcitriol supplementation did not improve the calcaemic response to PTH. Finally, hypocalcaemia was observed in uraemic rats with PTH replacement and was more profound than in rats on a high-phosphorus diet.

CONCLUSIONS

This study demonstrates that the maintenance of a normal PTH level in uraemic rats did not correct the impaired calcaemic response to PTH, suggesting that factors intrinsic to uraemia, independent of phosphorus, calcitriol, and PTH participate in the decreased calcaemic response to PTH in uraemia.

The human PTH2 receptor: binding and signal transduction properties of the stably expressed recombinant receptor

We have generated a series of stably transfected HEK-293 cell lines expressing the newly identified alternate human PTH receptor (hPTH2 receptor). This receptor subtype is selectively activated by N-terminal PTH-(1-34) and not the corresponding N-terminal (1-34) region of the functionally and structurally related hormone, PTH-related protein (PTHrP). A total of 20 distinct clones displaying different levels of PTH-responsive cAMP production were analyzed. None responded to PTHrP-(1-34). One of these clones (BP-16), displaying maximal PTH responsiveness, was chosen for more detailed evaluation. The BP-16 clone (and the parental HEK-293 cell line lacking both the hPTH/PTHrP receptor and the hPTH2 receptor) were examined for PTH binding, PTH-stimulated cAMP accumulation, PTH-stimulated changes in intracellular calcium ([Ca2+]i) levels, and hPTH2 receptor messenger RNA expression. In addition, we studied the photomediated cross-linking of a potent PTH agonist, namely [Nle8,18,Lys13 (epsilon-pBz2), 2-L-Nal23,Tyr34]bPTH(1-34)NH2 (K13), to the hPTH2 receptor on BP-16 cells. Photoaffinity cross-linking identified an approximately 90-kDa cell membrane component that was specifically competed by PTH-(1-34) and other receptor-interacting ligands. PTH-(1-34) and K13 are potent stimulators of both cAMP accumulation and increases in (Ca2+]i levels, and both bind to the hPTH2 receptor with high affinity (apparent Kd, 2.8 +/- 0.9 x 10(-8) and 8.5 +/- 1.7 x 10(-8) M, respectively). There was no apparent binding, cAMP-stimulating activity, or [Ca 2+]i signaling observed, nor was specific competition vs. binding of a PTH-(1-34) radioligand ([125I]PTH) with PTHrP-(1-34)NH2 found. PTHrP-(1-34) failed to inhibit cross-linking of the hPTH2 receptor by radiolabeled K13 ([125I]K13). However, effective competition vs. [125I]PTH and [125I]K13 binding and [125I]K13 cross-linking were observed with the potent PTH/PTHrP receptor antagonists, PTHrP-(7-34)NH2 and PTH-(7-34)NH2. PTHrP-(7-34)NH2 was shown to be a partial agonist that weakly stimulates both cAMP accumulation and increases in [Ca 2+]i levels in BP-16 cells. These data suggest that the hPTH2 receptor is distinct from the hPTH/PTHrP receptor in the structural features it requires for ligand binding in the family of PTH and PTHrP peptides.

Estrogen blocks parathyroid hormone (PTH)-stimulated osteoclast-like cell formation by selectively affecting PTH-responsive cyclic adenosine monophosphate pathway

Several lines of evidence have previously indicated that estrogen inhibits PTH-induced bone resorption in vivo and in vitro. However, its mechanism remains unknown. Therefore, the present study was performed to investigate the effect of estrogen on PTH-stimulated osteoclast-like cell formation and clarify its mechanism. 17 beta-estradiol (17 beta-E2) significantly antagonized osteoclast-like cell formation stimulated by 10(-8) M human (h) PTH-(1-34) as well as 10(-8) M hPTH-related peptide (PTHrP)-(1-34)in osteoblast-containing mouse bone cell cultures. The conditioned medium derived from osteoblastic SaOS-2 cells or MC3T3-E1 cells pretreated with both PTH-(1-34) (10(-8)M) and 17 beta-E2(10(-8)M) stimulated osteoclast-like cell formation from hemopoietic blast cells more weakly than conditioned medium from cells pretreated with PTH-(1-34) alone. Moreover, 10(-8) M 17 beta-E2 significantly blocked the formation of osteoclast-like cells stimulated by 10(-8) M hPTH-(1-34) in spleen cell cultures derived from 5-fluorouracil-pretreated mice. On the other hand, 10(-8) M 17 beta-E2 significantly inhibited osteoclast-like cell formation stimulated by dbcAMP (10(-4)M) and Sp-cAMPS (10(-4)M), as well as forskolin (10(-5)M) in mouse bone cell cultures. In contrast, 10(-8)M 17 beta-E2 did not affect PMA (10(-7)M)-, A23187 (10(-7)M)-, or BAYK-8644 (5 x 10(-6) M)-stimulated osteoclast-like cell formation. In conclusion, the present study demonstrated that estrogen inhibits PTH-stimulated osteoclast-like cell formation by directly acting on hemopoietic blast cells as well as by indirectly acting on them via osteoblasts. The inhibitory effects of estrogen on PTH-stimulated osteoclast-like cell formation seemed to be mediated through blocking the cAMP-dependent protein kinase pathway but not by blocking calcium/protein kinase C.

Effects of a synthetic N-terminal fragment of stanniocalcin on the metabolism of mammalian bone in vitro

A synthetic peptide corresponding to the N-terminal amino acid residues of stanniocalcin (STC1-20) and including a region that is known to be an active site in teleosts was prepared and tested for its effects on the metabolism of mammalian bone in vitro. STC1-20 (10(-10)-10(-12) M) inhibited increases in the number of tartrate-resistant acid phosphatase-positive, multinucleated cells promoted by an N-terminal fragment of human parathyroid hormone (hPTH1-34) in cultures of murine hemopoietic cells. STC1-20 also slightly decreased the rate of loss of radioactivity from calvariae of fetal rats that had been prelabeled with 45Ca, both with and without stimulation by hPTH1-34. The accumulation of cAMP induced by hPTH1-34 in ROS 17/2.8-5 cells was suppressed by STC1-20 (10(-10)-10(-12) M). Treatment with STC1-20 (10(-11)-10(-13) M) caused increases of the rate of incorporation of [3H]proline into the collagenase-digestible protein of calvariae in newborn mice. From these results, it appears that STC1-20 has diverse effects on the metabolism of mammalian bone, causing a biphasic response. Such effects have not been observed with intact stanniocalcin or with materials from the corpuscles of Stannius and they are also different from the effects of hPTH1-34.