The effect of switching from teriparatide to anti-RANKL antibody on cancellous and cortical bone in ovariectomized mice

Comparative study in estrogen-depleted mice identifies skeletal and osteocyte transcriptomic responses to abaloparatide and teriparatide

Osteocytes express parathyroid hormone (PTH)/PTH-related protein (PTHrP) receptors and respond to the PTHrP analog abaloparatide (ABL) and to the PTH 1-34 fragment teriparatide (TPTD), which are used to treat osteoporosis. Several studies indicate overlapping but distinct skeletal responses to ABL or TPTD, but their effects on cortical bone may differ. Little is known about their differential effects on osteocytes. We compared cortical osteocyte and skeletal responses to ABL and TPTD in sham-operated and ovariectomized mice. Administered 7 weeks after ovariectomy for 4 weeks at a dose of 40 μg/kg/d, TPTD and ABL had similar effects on trabecular bone, but ABL showed stronger effects in cortical bone. In cortical osteocytes, both treatments decreased lacunar area, reflecting altered peri-lacunar remodeling favoring matrix accumulation. Osteocyte RNA-Seq revealed that several genes and pathways were altered by ovariectomy and affected similarly by TPTD and ABL. Notwithstanding, several signaling pathways were uniquely regulated by ABL. Thus, in mice, TPTD and ABL induced a positive osteocyte peri-lacunar remodeling balance, but ABL induced stronger cortical responses and affected the osteocyte transcriptome differently. We concluded that ABL affected the cortical osteocyte transcriptome in a manner subtly different from TPTD, resulting in more beneficial remodeling/modeling changes and homeostasis of the cortex.

Discontinuation of PTH therapy amplifies bone loss by increasing oxidative stress: An event ameliorated by sequential IL-17 neutralizing antibody therapy

Osteoporosis leads to excessive bone resorption which is not accompanied by equal amount of bone formation. PTH (1-34) forms the mainstay of bone anabolic therapy. Intermittent PTH (iPTH) has the ability to reconstruct skeleton, a property not shared by other anti-resorptives. In initial phases of PTH treatment, bone formation exceeds bone resorption. However, gradually this phase is replaced by increased bone resorption. Thus, a replacement post PTH discontinuation is much needed. Studies with bisphosphonates and Denosumab post PTH withdrawal have yielded promising but variable results. Thus, there is scope for trying new combinations. Our previous studies have shown the superior skeletal effects of neutralizing IL17 antibody (NIL17) over anti-RANKL antibody. Thus, here we investigated if sequential treatment of NIL17 after PTH withdrawal (SHIFT) could serve as a promising therapeutic approach for osteoporosis treatment. Our results show that PTH withdrawal (PTH-W) led to mitigation of its anabolic effects as evidenced by reduced BMD, bone trabecular and cortical microarchitectural parameters. In the continuous PTH (PTH-C) and the Shift group, all these parameters were preserved as par with the sham group. Shift therapy also significantly increased PINP levels. Most importantly, serum CTX-I levels and osteoclast numbers, which were elevated in PTH groups were significantly suppressed in NIL17 monotherapy and shift group. Also, expression of FOXO1 and ATF-4, the main regulators of redox balance and function in osteoblasts, were found to be enhanced maximally in the sequential therapy group. Our study thus advocates use of NIL17 as a replacement therapeutic option post PTH discontinuation.

Parathyroid Hormone 1 Receptor Signaling in Dental Mesenchymal Stem Cells: Basic and Clinical Implications

Parathyroid hormone (PTH) and parathyroid hormone-related protein (PTHrP) are two peptides that regulate mineral ion homeostasis, skeletal development, and bone turnover by activating parathyroid hormone 1 receptor (PTH1R). PTH1R signaling is of profound clinical interest for its potential to stimulate bone formation and regeneration. Recent pre-clinical animal studies and clinical trials have investigated the effects of PTH and PTHrP analogs in the orofacial region. Dental mesenchymal stem cells (MSCs) are targets of PTH1R signaling and have long been known as major factors in tissue repair and regeneration. Previous studies have begun to reveal important roles for PTH1R signaling in modulating the proliferation and differentiation of MSCs in the orofacial region. A better understanding of the molecular networks and underlying mechanisms for modulating MSCs in dental diseases will pave the way for the therapeutic applications of PTH and PTHrP in the future. Here we review recent studies involving dental MSCs, focusing on relationships with PTH1R. We also summarize recent basic and clinical observations of PTH and PTHrP treatment to help understand their use in MSCs-based dental and bone regeneration.

Exogenous parathyroid hormone attenuates ovariectomy-induced skeletal muscle weakness in vivo

Osteoporosis commonly affects the elderly and is associated with significant morbidity and mortality. Loss of bone mineral density induces muscle atrophy and increases fracture risk. However, muscle lipid content and droplet size are increased by aging and mobility impairments, inversely correlated with muscle function, and a cause of reduced motor function. Teriparatide, the synthetic form of human parathyroid hormone (PTH) 1-34, has been widely used to treat osteoporosis. Although PTH positively affects muscle differentiation in vitro, the precise function and mechanisms of muscle mass and power preservation are still poorly understood, especially in vivo. In this study, we investigated the effect of PTH on skeletal muscle atrophy and dysfunction using an ovariectomized murine model. Eight-week-old female C57BL/6J mice were ovariectomized or sham-operated. Within each surgical group, the mice were divided into PTH injection or control subgroups. Motor function was evaluated based on grip strength, treadmill running, and lactic acid concentration. PTH receptor was expressed in skeletal muscle cells and myoblasts. PTH inhibited ovariectomy-induced bone loss but not uterine atrophy or increased body weight; PTH not only abolished ovariectomy-induced reduction in grip strength and maximum running speed, but also significantly reduced the ovariectomy-induced increase in lactic acid concentration (compared with that observed in the vehicle control). PTH also abrogated the ovariectomy-induced reduction in the oxidative capacity of muscle fibers, their cross-sectional area, and intramyocellular lipid content, and induced cell proliferation, cell migration, and muscle differentiation, while reducing lipid secretion by C2C12 myoblasts via the Wnt/β-catenin pathway. PTH significantly ameliorated muscle weakness and attenuated exercise-induced lactate levels in ovariectomized mice. Our in vitro study demonstrated that PTH/Wnt signaling regulated the proliferation, migration, and differentiation of myoblasts and also reduced lipid secretion in myoblasts. Thus, PTH could regulate several aspects of muscle function and physiology, and may represent a novel therapeutic strategy for patients with osteoporosis.

PTPN5 promotes follicle-stimulating hormone secretion through regulating intracellular calcium homeostasis

Protein tyrosine phosphatase non-receptor type 5 (PTPN5), also called striatal-enriched protein tyrosine phosphatase (STEP), is highly expressed in neurons of the basal ganglia, hippocampus, cortex, and related structures, also in the pituitary. Gonadotropins are the key regulator of the reproduction in mammals. In this study, PTPN5 is detected to express in murine pituitary in a developmental manner. Moreover, the expression of PTPN5 in the pituitary is heavily reduced after ovary removal. Follicle-stimulating hormone (FSH) secretion in gonadotropes is regulated by PTPN5 via binding GnRH to GnRH-R. Two parallel signaling pathways, Gs-protein kinase A (PKA)-PTPN5 and Gq-phospholipases C (PLC)-p38 MAPK-PTPN5, cooperatively regulate GnRH-induced FSH secretion. We also show that influx of Ca²⁺ activates the Ca²⁺ -dependent phosphatase calcineurin, leading to the phosphorylation and activation of PTPN5. The intracellular release of Ca²⁺ is reduced via TC2153. In conclusion, blocking or knocking out of PTPN5 reduces the release of FSH in whole pituitary. Mechanically, PTPN5 regulates gonadotropes' function through regulating intracellular calcium homeostasis.

Fecal microbiota transplantation mitigates vaginal atrophy in ovariectomized mice

Vulvovaginal atrophy (VVA) is a common menopause-related symptom affecting more than 50% of midlife and older women and cancer patients whose ovarian function are lost or damaged. Regardless of estrogen deficiency, whether other factors such as the gut microbiota play role in VVA have not been thoroughly investigated. To this end, we performed ovariectomy on 12-weeks’ old mice and follow-up at 4 weeks after ovariectomy, and observed atrophied vagina and an altered gut microbiota in ovariectomized mice.. We further performed fecal microbiota transplantation with feces from another cohort of ovary-intact fecund female mice to the ovariectomized ones, and found that the vaginal epithelial atrophy was significantly alleviated as well as the gut microbiota was pointedly changed. All these results suggest that ovarian activity has some influence on the gut microbiota, and the latter from the ovary-intact female mice can somehow make the vagina of mice deficient in ovarian function healthier maybe by up-expressing ESR1 in vaginal cells and enhancing regeneration in vagina. This kind of association between gut microbiota and vaginal health need further exploration such that it may provide an alternative treatment by modulating gut microbiota in patients suffering from VVA but may be reluctant to hormone therapy.

Frequent administration of abaloparatide shows greater gains in bone anabolic window and bone mineral density in mice: A comparison with teriparatide

Abaloparatide (ABL) is a novel 34-amino acid peptide analog of parathyroid hormone-related protein. In clinical studies, although ABL showed a greater bone mineral density (BMD) increase than teriparatide (TPTD, human parathyroid hormone 1-34), the responses of ABL to bone formation and resorption markers were weaker, making it difficult to understand the relationship between the bone anabolic window (increase in bone formation versus resorption) and bone mass. In the present study, the effects of ABL and TPTD were compared in mice. Given that the rate of bone turnover is higher in rodents than in humans, the comparison was made with several administration regimens providing equivalent daily dosages: once daily (QD, 30 μg/kg every 24 h), twice daily (BID, 15 μg/kg every 12 h), or three times a day (TID, 10 μg/kg every 8 h). Frequent administration of ABL showed higher BMD with enhancement of trabecular and cortical bone mass and structures than that of TPTD, consistent with the clinical results seen with once daily administration. ABL increased bone formation marker levels more than TPTD with more frequent regimens, while bone resorption marker levels were not different between ABL and TPTD in all regimens. Analysis of bone histomorphometry and gene expression also suggested that ABL increased bone formation more than TPTD, while the effect on bone resorption was almost comparable between ABL and TPTD. The bone anabolic windows calculated from bone turnover markers indicated that ABL enhanced the anabolic windows more than TPTD, leading to a robust increase in BMD. The mechanism by which ABL showed a better balance of bone turnover was suggested to be partly due to the enhanced remodeling-based bone formation involved in Ephb4. Taken together, our findings would help elucidate the mechanism by which ABL shows excellent BMD gain and reduction of fractures in patients with osteoporosis.

Sustained anti-osteoporotic action of risedronate compared to anti-RANKL antibody following discontinuation in ovariectomized mice

Bisphosphonates and the anti-receptor activator of nuclear factor-kappa B ligand (RANKL) antibody denosumab are effective anti-resorptive drugs commonly prescribed for osteoporosis. Both drugs may, however, have intolerable side effects; so, it is critical to examine their residual efficacy such as maintenance of bone mass following cessation. Therefore, we compared the changes in bone histology following discontinuation of the aminobisphosphonate risedronate and anti-RANKL antibody in ovariectomized (OVX) mice. Twelve-week-old female C57BL/6 N mice were OVX or sham operated. Four weeks after surgery, mice were treated with vehicle, a single injection of anti-RANKL antibody (5 mg/kg), or risedronate (5 μg/kg/day, s.c.) for 4 weeks (the treatment period), followed by vehicle treatment for an additional 4 weeks (discontinuation period). The lumbar spine and proximal tibia were evaluated by micro-computed tomography. In addition, the lumbar spine, proximal tibia, and the femoral shaft were examined by bone histomorphometry. After 4 weeks of discontinuation, OVX mice initially treated with the anti-RANKL antibody exhibited a trend of bone loss associated with increased turnover in both trabecular and cortical bones, although the difference was not significant. By contrast, OVX mice treated with risedronate exhibited maintained or even increased bone mass and suppressed bone turnover. Patients discontinuing denosumab should be carefully monitored for recurrent osteoporosis symptoms, and a replacement drug should be considered.

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Bone mass and suppression of turnover were maintained after stopping bisphophonates.

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Bone turnover was rapidly increased after discontinuation of anti-RANKL antibody.

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Periosteal bone formation was maintained after administration of antiresorptive drugs.

The effects of different doses of teriparatide on bisphosphonate-related osteonecrosis of the jaw in mice

OBJECTIVES

This study aimed to investigate the therapeutic effect of different doses of teriparatide (TPTD) on bisphosphonate-related osteonecrosis of the jaw (BRONJ).

MATERIALS AND METHODS

To establish the BRONJ model, 20 mice were randomly divided into two groups: a group that received tail vein administration of zoledronic acid with dexamethasone (ZA-125 µg/kg, DEX 5 mg/kg) and a group that received saline weekly. The mice subsequently underwent bilateral maxillary first molar extraction. After 8 weeks of modelling administration, the maxilla samples were examined by micro-computed tomography and histological staining (haematoxylin and eosin, Masson's trichrome and tartrate-resistant acid phosphatase) and the cytokine level was measured (enzyme-linked immunosorbent assay and Western blot). To determine the role of TPTD in BRONJ, the same protocol as previously described was applied in 100 mice (80 received ZA + DEX, and 20 received saline). After 8 weeks of modelling administration, 80 ZA + DEX mice were randomly divided into four groups: three groups with subcutaneous administration of TPTD (i.e. T1-3, T2-10 and T3-30 µg kg^-1  day^-1 ) and one group with saline daily for the next 8 weeks. The other 20 saline mice continued to receive saline daily.

RESULTS

In Part 1, the level of receptor activator of nuclear factor-kappa Β ligand and the numbers of osteoclasts differed between the model and control groups. In Part 2, we found that TPTD had a positive effect on BRONJ in a mouse model based on clinical and histomorphological observations. Among the three treatment groups, the T1 and T2 groups significantly differed from the model group, whereas the T3 group showed no statistical differences.

CONCLUSION

Subcutaneous administration of TPTD has a beneficial effect on BRONJ in mice. Nevertheless, further studies are needed to determine whether the therapeutic effect on BRONJ is dose-dependent.

Molecular understanding of pharmacological treatment of osteoporosis

Osteoporosis is a serious health concern, particularly in aged societies. The burden of osteoporosis with its associated morbidity and mortality due to fracture has become a critical socioeconomic problem.

Skeletal integrity is maintained through a balance of bone resorption and bone formation. The bone turnover process, called bone remodelling.

Recently, a number of anti-osteoporosis drugs with excellent anti-osteoporosis and fracture effects have been developed. They are mainly classified into two groups according to their effects on bone remodelling: anti-resorptive agents and anabolic agents.

Cite this article: EFORT Open Rev 2019;4:158-164. DOI: 10.1302/2058-5241.4.180018

Cepharanthine Prevents Estrogen Deficiency-Induced Bone Loss by Inhibiting Bone Resorption

Osteoporosis is a common health problem worldwide caused by an imbalance of bone formation vs. bone resorption. However, current therapeutic approaches aimed at enhancing bone formation or suppressing bone resorption still have some limitations. In this study, we demonstrated for the first time that cepharanthine (CEP, derived from Stephania cepharantha Hayata) exerted a protective effect on estrogen deficiency-induced bone loss. This protective effect was confirmed to be achieved through inhibition of bone resorption in vivo, rather than through enhancement of bone formation in vivo. Furthermore, the in vitro study revealed that CEP attenuated receptor activator of nuclear factor κB ligand (RANKL)-induced osteoclast formation, and suppressed bone resorption by impairing the c-Jun N-terminal kinase (JNK) and phosphatidylinositol 3-kinase (PI3K)-AKT signaling pathways. The inhibitory effect of CEP could be partly reversed by treatment with anisomycin (a JNK and p38 agonist) and/or SC79 (an AKT agonist) in vitro. Our results thus indicated that CEP could prevent estrogen deficiency-induced bone loss by inhibiting osteoclastogenesis. Hence, CEP might be a novel therapeutic agent for anti-osteoporosis therapy.