Emerging and potential therapies for osteoporosis

Recent development of drugs for osteoporosis and anti-cancer agents: a patent analysis

Osteoporosis and cancer are becoming a major public health problem. Some studies have shown that osteoporosis drugs may have anti-cancer effects. To better understand the relationship between drugs for osteoporosis and antineoplastic agents, and to better demonstrate recent developments for patents concerning drugs for osteoporosis, we conducted an analysis of US patents. The results indicated that there was a good correlation between agents for osteoporosis and antineoplastic agents, which indicated that numerous anti-osteoporosis agents displayed antineoplastic activities. Our study was the first one to provide new evidence, through comprehensive analysis, for a correlation between anti-osteoporosis agents and anticancer agents. The present study may open new avenues for developing anticancer drugs and expanding the application role of anti-osteoporosis agents.

The functional mechanism of simvastatin in experimental osteoporosis

Osteoporosis is a systemic and metabolic bone disease. New drugs with good curative effect, fewer side effects, and high safety need to be developed urgently. Recently, simvastatin has been used to treat osteoporosis more frequently; however, its clinical effect and treatment mechanism are still unknown. With the use of animal models, the treatment effectiveness of simvastatin on experimental osteoporosis was investigated and the functional mechanism was preliminarily explored. The results show that simvastatin significantly increased the mechanical parameters such as maximum load, stiffness, and energy-absorbing capacity, and improved the microarchitecture. They indicated that the antiosteoporosis activity of simvastatin may be due to the promotion of proliferation and differentiation of osteoblasts. Simvastatin was effective in treating experimental osteoporosis. This study provides necessary experimental evidence for the clinical application of simvastatin in osteoporosis treatment.

Effects of OsteoKing on osteoporotic rabbits

Heng-Gu-Gu-Shang-Yu-He-Ji, also known as OsteoKing, is used as a herbal Traditional Chinese Medicine for the treatment of bone disease, including femoral head necrosis and osteoarthritis. However, whether OsteoKing has anti-osteoporotic properties has remained to be elucidated. The purpose of the present study was therefore to investigate the effects of OsteoKing on ovariectomy-induced osteoporosis in rabbits. Female New Zealand white rabbits were randomly divided into an ovariectomized (OVX) group and a sham-surgery group. The rabbits in the OVX group were subjected to an ovariectomy, while the rabbits in the sham group were subjected to the removal of an area of fat near the two ovaries. Bone mineral density, mechanical properties, serum biochemical parameters and micro-architecture were examined at 150 days post-OVX to characterize the experimental animal model. Once the osteoporotic rabbit model had been established, the rabbits in the OVX group were divided into the following groups: Model group, nilestriol group and 300 and 600 mg/kg OsteoKing groups, containing 16 rabbits in each group. OsteoKing and nilestriol were administered orally. The bone mineral density, mechanical properties, serum biochemical parameters, histology and micro-architecture were examined using dual-energy X-ray absorptiometric analysis, mechanical assessments, enzyme-linked immunosorbent assays, histopathological evaluation and micro-computerized tomography examination following 60 days and 120 days of treatment, respectively. Treatment with OsteoKing led to an elevation in the bone mineral density of the vertebra and serum phosphorus levels, reduced serum concentrations of osteocalcin, procollagen type I N-terminal peptide, tartrate-resistant acid phosphatase 5b and cross-linked N-telopeptide of type I collagen, improved mechanical properties (maximum load, stiffness and energy absorption capacity), and micro-architecture of the lumbar vertebra in the OVX osteoporotic rabbit model following treatment for 120 days. In conclusion, it was demonstrated that OsteoKing is effective in the prevention of estrogen deficiency-associated bone loss and may be a promising drug for the treatment of post-menopausal osteoporosis.

Treatment with a potent cathepsin K inhibitor preserves cortical and trabecular bone mass in ovariectomized monkeys

The cysteine protease cathepsin K is involved in osteoclast-mediated bone resorption. We evaluated the effect of daily oral dosing of an inhibitor of human cathepsin K (SB-462795 [relacatib]) for 9 months on bone turnover, mass, and architecture in estrogen-deficient cynomolgus monkeys. Ovariectomized animals were treated orally with relacatib at 1, 3, or 10 mg/kg/day, or oral vehicle plus alendronate at 0.05 mg/kg by IV injection once every 2 weeks. The control groups, ovariectomized and sham-ovariectomized animals, received vehicle (all groups n = 20 animals). Samples for biomarker analysis were collected at various times, bone mass changes were evaluated at 6 and 9 months of treatment, and histomorphometric analysis was performed at 9 months. Relacatib significantly reduced urinary N-telopeptide excretion within 1 week of treatment at all dose levels, an effect that was maintained at the highest dose level. At some time points bone formation markers were elevated at the lowest dose of relacatib. Animals treated with relacatib had dose-dependent preservation of areal bone mineral density reaching statistical significance in distal femur. In femur neck there was significant preservation of total volumetric BMD (vBMD) by relacatib. By histomorphometry, relacatib reduced indices of bone resorption and formation at cancellous sites as did alendronate. In cortical bone, osteonal bone formation rate was reduced by alendronate but preserved at low and medium doses of relacatib. Thus, relacatib preserved cortical and cancellous bone mass in ovariectomized monkeys.

Orally administered lactoferrin preserves bone mass and microarchitecture in ovariectomized rats

Lactoferrin (LF) is reported to stimulate osteoblast proliferation and inhibit osteoclast activity in bone cell culture. However, the effect of oral LF on bone in osteoporosis needs to be explored. Three-month-old female Sprague-Dawley rats (n = 70) were assigned to the following groups: sham-operated, ovariectomized (OVX) untreated, OVX + bovine serum albumin (BSA; 85 mg/kg body weight), OVX + LF (0.85 mg/kg, 8.5 mg/kg, and 85 mg/kg body weight), and OVX + 17beta-estradiol (E(2); 10 microg/kg body weight). After 3 mo of treatment, E(2) completely prevented the OVX-induced bone loss. OVX rats treated with LF were protected against the OVX-induced reduction of bone volume, trabecular number, and thickness, and the elevation of trabecular separation was prevented. LF also increased bone mineral density and increased the parameters of mechanical strength at 8.5- and 85-mg/kg doses. Greater bone formation and reduced bone resorption, as assessed by biochemical markers of bone remodeling, occurred in rats administered LF. LF at 8.5- and 85-mg/kg concentrations caused a significant decrease in serum calcium, but this reduction did not occur in rats fed 0.85 mg/kg LF. In addition, serum tumor necrosis factor-alpha and interleukin-6 production were suppressed and serum calcitonin was elevated significantly in LF-fed rats at all 3 doses. These findings indicated that oral LF not only preserved bone mass but also improved bone microarchitecture. The absorption of LF peptides and their effects on bone cells could to some extent account for the osteogenic function of oral LF.

Molecular analysis of the vaginal response to estrogens in the ovariectomized rat and postmenopausal woman

Background

Vaginal atrophy (VA) is the thinning of the vaginal epithelial lining, typically the result of lowered estrogen levels during menopause. Some of the consequences of VA include increased susceptibility to bacterial infection, pain during sexual intercourse, and vaginal burning or itching. Although estrogen treatment is highly effective, alternative therapies are also desired for women who are not candidates for post-menopausal hormone therapy (HT). The ovariectomized (OVX) rat is widely accepted as an appropriate animal model for many estrogen-dependent responses in humans; however, since reproductive biology can vary significantly between mammalian systems, this study examined how well the OVX rat recapitulates human biology.

Methods

We analyzed 19 vaginal biopsies from human subjects pre and post 3-month 17β-estradiol treated by expression profiling. Data were compared to transcriptional profiling generated from vaginal samples obtained from ovariectomized rats treated with 17β-estradiol for 6 hrs, 3 days or 5 days. The level of differential expression between pre- vs. post- estrogen treatment was calculated for each of the human and OVX rat datasets. Probe sets corresponding to orthologous rat and human genes were mapped to each other using NCBI Homologene.

Results

A positive correlation was observed between the rat and human responses to estrogen. Genes belonging to several biological pathways and GO categories were similarly differentially expressed in rat and human. A large number of the coordinately regulated biological processes are already known to be involved in human VA, such as inflammation, epithelial development, and EGF pathway activation.

Conclusion

At the transcriptional level, there is evidence of significant overlap of the effects of estrogen treatment between the OVX rat and human VA samples.

New therapies for treatment of rheumatoid arthritis

Rheumatoid arthritis is characterised by pain, swelling, and destruction of joints, with resultant disability. Only disease-modifying antirheumatic drugs can interfere with the disease process. In the past few years, biological agents, especially inhibitors of tumour necrosis factor, have allowed for hitherto unseen therapeutic benefit, although even with these drugs the frequency and degree of responses are restricted. Therefore, new agents are needed, and three novel biological compounds for treatment of rheumatoid arthritis have already been used in practice or are on the horizon: rituximab (anti-CD20), abatacept (cytotoxic T-lymphocyte antigen 4 immunoglobulin), and tocilizumab (anti-interleukin 6 receptor). We discuss the targets of these drugs, the roles of these targets in the pathogenesis of rheumatoid arthritis, and the efficacy and adverse effects of these agents from clinical trial data. Novel therapeutic strategies in conjunction with optimised disease assessment for better treatment of rheumatoid arthritis and an outlook into potential future targets are also presented.

Identification of a novel pyrazolo[3,4-d]pyrimidine able to inhibit cell proliferation of a human osteogenic sarcoma in vitro and in a xenograft model in mice

New pyrazolo[3,4-d]pyrimidines were synthesized and found to inhibit Src phosphorylation in a cell-free assay. Some of them significantly reduced the growth of human osteogenic sarcoma (SaOS-2) cells. The best compound, in terms of inhibitory properties toward both Src and SaOS-2 cells, was further investigated and found to reduce bone resorption when used to treat mouse osteoclasts, without interfering with normal osteoblast growth. Moreover, its metabolic stability prompted its study on a human SaOS-2 xenograft tumor model in nude mice, where the compound reduced significantly both the volume and weight of the tumor. These experimental findings make the new compound an interesting hit in the field of bone-related diseases.

The anabolic and catabolic responses in bone repair

The literature on fracture repair has been reviewed. The traditional concepts of delayed and nonunion have been examined in terms of the phased and balanced anabolic and catabolic responses in bone repair. The role of medical manipulation of these inter-related responses in the fracture healing have been considered.

Cysteine cathepsins: cellular roadmap to different functions

Cysteine cathepsins belong to the papain-like family C1 of clan CA cysteine peptidases. These enzymes are ubiquitously expressed and exert their proteolytic activity mainly, but not exclusively within the compartments along the endocytic pathway. Moreover, cysteine cathepsins are active in pericellular environments as soluble enzymes or bound to cell surface receptors at the plasma membrane, and possibly even within secretory vesicles, the cytosol, mitochondria, and within the nuclei of eukaryotic cells. Proteolytic actions performed by cysteine cathepsins are essential in the maintenance of homeostasis and depend heavily upon their correct sorting and trafficking within cells. As a consequence, the numerous and diverse approaches to identification, qualitative and quantitative determination, and visualization of cysteine cathepsin functions in vitro, in situ, and in vivo cover the entire spectrum of biochemistry, molecular and cell biology. This review focuses upon the transport pathways directing cysteine cathepsins to their points of action and thus emphasizes the broader role and functionality of cysteine cathepsins in a number of specific cellular locales. Such understanding will provide a foundation for future research investigating the involvement of these peptidases with their substrates, inhibitors, and the intertwined proteolytic networks at the hubs of complex biological systems.

Loss-of-function mutations in the Nav1.7 gene underlie congenital indifference to pain in multiple human populations

Congenital indifference to pain (CIP) is a rare condition in which patients have severely impaired pain perception, but are otherwise essentially normal. We identified and collected DNA from individuals from nine families of seven different nationalities in which the affected individuals meet the diagnostic criteria for CIP. Using homozygosity mapping and haplotype sharing methods, we narrowed the CIP locus to chromosome 2q24-q31, a region known to contain a cluster of voltage-gated sodium channel genes. From these prioritized candidate sodium channels, we identified 10 mutations in the SCN9A gene encoding the sodium channel protein Nav1.7. The mutations completely co-segregated with the disease phenotype, and nine of these SCN9A mutations resulted in truncation and loss-of-function of the Nav1.7 channel. These genetic data further support the evidence that Nav1.7 plays an essential role in mediating pain in humans, and that SCN9A mutations identified in multiple different populations underlie CIP.

Mice lacking cathepsin K maintain bone remodeling but develop bone fragility despite high bone mass

Bone microstructural and biomechanical properties were analyzed in mice genetically lacking cathepsin K (CatK). CatK deficiency (CatK(-/-)) produced mild osteopetrosis, elevated numbers of osteoclasts, regions of disorganized bone microstructure, and increased bone fragility, showing how chronic alteration of enzyme activity during skeletal development dramatically affects bone organization and function.

INTRODUCTION

Mouse models of CatK deficiency recapitulate the osteopetrosis of human pyknodysostosis and allow study of clinically relevant issues: how inhibition of this enzyme activity affects bone integrity structurally and biomechanically. To address these questions, we generated CatK-deficient mice by targeted disruption of the Ctsk gene and compared their bone structural and mechanical properties with wildtype (WT) controls.

MATERIALS AND METHODS

Standard histomorphometric and biomechanical analyses were performed on femora from C57BL/6J male and female CatK(-/-), CatK(+/-), and WT mice.

RESULTS

CatK(-/-) femora exhibited the mild metaphyseal osteopetrosis, a greater cortical bone area and thickness, normal bone strength, but a high degree of brittleness (nearly 50-70% decrease in postyield displacement versus WT) and a 30-40% reduction in the work-to-failure. In cancellous bone, osteoclast numbers and resorption surface were increased markedly (approximately 150% and 50%, respectively), despite the overall decrease in net bone resorption for CatK-deficient mice. Bone formation indices were altered in CatK(-/-) mice as well, with significant increases in mineral appositional rate, but not in bone formation surface; these data suggest difference in osteoblast work but not in their recruitment in CatK deficiency. CatK-deficient cortical bones had large areas of woven bone and intracortical resorption spaces within the disorganized tissue. Bone phenotype in CatK(-/-) was similar in males and females.

CONCLUSIONS

Genetic CatK deficiency in mice results not only in the impairment of osteoclast function and osteopetrosis, but also altered osteoblast function, defective tissue organization, and very brittle bones. Whether this bone fragility in CatK deficiency results entirely from indirect effects of suppressed bone turnover because of impaired osteoclast function or perhaps represents a previously unappreciated more direct role for CatK in bone formation remains to be established.

Newer drug treatments: Their effects on fracture prevention

Drug treatment of osteoporosis is based on the knowledge of mechanisms of bone turnover and the manipulation of the cellular components of bone turnover in terms of recruitment, activation and apoptosis of the cells involved. Based on their mechanisms of action, drugs used in the treatment of osteoporosis can be divided into those that inhibit bone turnover (bisphosphonates, SERMs, calcitonin), those that stimulate bone turnover (parathyroid hormone), and those with mixed effects (strontium ranelate). In this chapter we discuss the anti-fracture effects of some newer drugs together with innovative aspects of intake (monthly oral intake for ibandronate) or mechanisms of action (parathyroid hormone and strontium ranelate). Some new drugs that are being studied for their potential anti-fracture effects are listed.

Lactoferrin--a novel bone growth factor

Lactoferrin is an iron-binding glycoprotein that belongs to the transferrin family. It is present in breast milk, in epithelial secretions, and in the secondary granules of neutrophils. In healthy subjects lactoferrin circulates at concentrations of 2-7 x 10(-6) g/ml. Lactoferrin is a pleiotropic factor with potent antimicrobial and immunomodulatory activities. Recently, we have shown that lactoferrin can also promote bone growth. At physiological concentrations, lactoferrin potently stimulates the proliferation and differentiation of primary osteoblasts and also acts as a survival factor inhibiting apoptosis induced by serum withdrawal. Lactoferrin also affects osteoclast formation and, in murine bone marrow culture, lactoferrin potently inhibits osteoclastogenesis. In vivo, local injection of lactoferrin above the hemicalvaria of adult mice results in substantial increases in the dynamic histomorphometric indices of bone formation and bone area. The mitogenic effect of lactoferrin in osteoblast-like cells is mediated mainly through LRP1, a member of the family of low-density lipoprotein receptor-related proteins that are primarily known as endocytic receptors. Using confocal laser scanning microscopy, we demonstrated that fluorescently labeled lactoferrin is endocytosed and can be visualized in the cytoplasm of primary osteoblastic cells. Lactoferrin also induces activation of p42/44 MAPK signaling in primary osteoblasts, but the two pathways seem to operate independently as activation of MAPK signaling, but not endocytosis, is necessary for the mitogenic effect of lactoferrin. We conclude that lactoferrin may have a physiological role in bone growth and healing, and a potential therapeutic role as an anabolic factor in osteoporosis.