Insulin resistance and bone: a biological partnership.

Despite a clear association between type 2 diabetes (T2D) and fracture risk, the pathogenesis of bone fragility in T2D has not been clearly elucidated. Insulin resistance is the primary defect in T2D. Insulin signalling regulates both bone formation and bone resorption, but whether insulin resistance can affect bone has not been established. On the other hand, evidence exists that bone might play a role in the regulation of glucose metabolism. This article reviews the available experimental and clinical evidence on the interplay between bone and insulin resistance. Interestingly, a bilateral relationship between bone and insulin resistance seems to exist that unites them in a biological partnership.

A Unified Pathophysiological Construct of Diabetes and its Complications.

Advances in understanding diabetes mellitus (DM) through basic and clinical research have helped clarify and reunify a disease state fragmented into numerous etiologies and subtypes. It is now understood that a common pathophysiology drives the diabetic state throughout its natural history and across its varied clinical presentations, a pathophysiology involving metabolic insults, oxidative damage, and vicious cycles that aggravate and intensify organ dysfunction and damage. This new understanding of the disease requires that we revisit existing diagnostics and treatment approaches, which were built upon outmoded assumptions. 'The Common Pathophysiologic Origins of Diabetes Mellitus and its Complications Construct' is presented as a more accurate, foundational, and translatable construct of DM that helps make sense of the hitherto ambiguous findings of long-term outcome studies.

Blocking FSH induces thermogenic adipose tissue and reduces body fat.

Menopause is associated with bone loss and enhanced visceral adiposity. A polyclonal antibody that targets the ß-subunit of the pituitary hormone follicle-stimulating hormone (Fsh) increases bone mass in mice. Here, we report that this antibody sharply reduces adipose tissue in wild-type mice, phenocopying genetic haploinsufficiency for the Fsh receptor gene Fshr. The antibody also causes profound beiging, increases cellular mitochondrial density, activates brown adipose tissue and enhances thermogenesis. These actions result from the specific binding of the antibody to the ß-subunit of Fsh to block its action. Our studies uncover opportunities for simultaneously treating obesity and osteoporosis.

The Time Is Right for a New Classification System for Diabetes: Rationale and Implications of the ß-Cell-Centric Classification Schema.

The current classification system presents challenges to the diagnosis and treatment of patients with diabetes mellitus (DM), in part due to its conflicting and confounding definitions of type 1 DM, type 2 DM, and latent autoimmune diabetes of adults (LADA). The current schema also lacks a foundation that readily incorporates advances in our understanding of the disease and its treatment. For appropriate and coherent therapy, we propose an alternate classification system. The ß-cell-centric classification of DM is a new approach that obviates the inherent and unintended confusions of the current system. The ß-cell-centric model presupposes that all DM originates from a final common denominator-the abnormal pancreatic ß-cell. It recognizes that interactions between genetically predisposed ß-cells with a number of factors, including insulin resistance (IR), susceptibility to environmental influences, and immune dysregulation/inflammation, lead to the range of hyperglycemic phenotypes within the spectrum of DM. Individually or in concert, and often self-perpetuating, these factors contribute to ß-cell stress, dysfunction, or loss through at least 11 distinct pathways. Available, yet underutilized, treatments provide rational choices for personalized therapies that target the individual mediating pathways of hyperglycemia at work in any given patient, without the risk of drug-related hypoglycemia or weight gain or imposing further burden on the ß-cells. This article issues an urgent call for the review of the current DM classification system toward the consensus on a new, more useful system.

Repurposing of bisphosphonates for the prevention and therapy of nonsmall cell lung and breast cancer.

A variety of human cancers, including nonsmall cell lung (NSCLC), breast, and colon cancers, are driven by the human epidermal growth factor receptor (HER) family of receptor tyrosine kinases. Having shown that bisphosphonates, a class of drugs used widely for the therapy of osteoporosis and metastatic bone disease, reduce cancer cell viability by targeting HER1, we explored their potential utility in the prevention and therapy of HER-driven cancers. We show that bisphosphonates inhibit colony formation by HER1(ΔE746-A750)-driven HCC827 NSCLCs and HER1(wt)-expressing MB231 triple negative breast cancers, but not by HER(low)-SW620 colon cancers. In parallel, oral gavage with bisphosphonates of mice xenografted with HCC827 or MB231 cells led to a significant reduction in tumor volume in both treatment and prevention protocols. This result was not seen with mice harboring HER(low) SW620 xenografts. We next explored whether bisphosphonates can serve as adjunctive therapies to tyrosine kinase inhibitors (TKIs), namely gefitinib and erlotinib, and whether the drugs can target TKI-resistant NSCLCs. In silico docking, together with molecular dynamics and anisotropic network modeling, showed that bisphosphonates bind to TKIs within the HER1 kinase domain. As predicted from this combinatorial binding, bisphosphonates enhanced the effects of TKIs in reducing cell viability and driving tumor regression in mice. Impressively, the drugs also overcame erlotinib resistance acquired through the gatekeeper mutation T790M, thus offering an option for TKI-resistant NSCLCs. We suggest that bisphosphonates can potentially be repurposed for the prevention and adjunctive therapy of HER1-driven cancers.

Bisphosphonates inactivate human EGFRs to exert antitumor actions.

Bisphosphonates are the most commonly prescribed medicines for osteoporosis and skeletal metastases. The drugs have also been shown to reduce cancer progression, but only in certain patient subgroups, suggesting that there is a molecular entity that mediates bisphosphonate action on tumor cells. Using connectivity mapping, we identified human epidermal growth factor receptors (human EGFR or HER) as a potential new molecular entity for bisphosphonate action. Protein thermal shift and cell-free kinase assays, together with computational modeling, demonstrated that N-containing bisphosphonates directly bind to the kinase domain of HER1/2 to cause a global reduction in downstream signaling. By doing so, the drugs kill lung, breast, and colon cancer cells that are driven by activating mutations or overexpression of HER1. Knocking down HER isoforms thus abrogates cell killing by bisphosphonates, establishing complete HER dependence and ruling out a significant role for other receptor tyrosine kinases or the enzyme farnesyl pyrophosphate synthase. Consistent with this finding, colon cancer cells expressing low levels of HER do not respond to bisphosphonates. The results suggest that bisphosphonates can potentially be repurposed for the prevention and therapy of HER family-driven cancers.

Bone loss or lost bone: rationale and recommendations for the diagnosis and treatment of early postmenopausal bone loss.

Recent reports suggest that bone loss begins during late perimenopause at a dramatic rate, even before estrogen levels plummet. During the ensuing 5 years, there is evidence of the beginnings of microarchitectural deterioration, which impacts bone strength and ultimately enhances its propensity to fracture. The diagnosis of osteoporosis based on T-scores alone, or through stratification for a high fracture risk by FRAX, excludes these women who are rapidly losing bone. Because all antiosteoporosis therapies, in particular bisphosphonates, reduce bone loss, we propose aggressive, likely short-term therapy with a goal to reduce bone loss, stabilize bone density, and prevent microarchitectural deterioration.

Evaluating the antifracture efficacy of bisphosphonates.

Oral bisphosphonate dosing schedules have evolved from the original daily regimens to weekly (alendronate and risedronate) and monthly (risedronate and ibandronate) regimens. Intravenous (i.v.) bisphosphonates are administered less frequently-quarterly ibandronate injection and yearly zoledronic acid i.v. infusion. Comparative fracture efficacy among BP options is increasingly a focus of debate. The approved daily oral BPs and annual zoledronic acid infusion demonstrated vertebral fracture prevention in clinical trials; however, nonvertebral fracture prevention results varied. Nondaily regimens of licensed agents (except for zoledronic acid) were approved via "bridging trials", which compared changes in bone mineral density and bone turnover markers with the approved daily regimen and generally collected fractures as adverse events. Head-to-head antifracture efficacy trials directly comparing available BPs are unlikely because the required sample sizes, durations and costs would be prohibitively large. Observational studies and the concept of annual cumulative exposure, used recently to evaluate the efficacy of nondaily ibandronate regimens, provide alternative methods to compare BP efficacy. At this time, the available trial and meta-analysis evidence supports effective reduction of vertebral fractures and NVFs with all approved BP regimens. This article presents a comprehensive review of the key efficacy data for currently available BPs, including their nondaily regimens, to assist clinicians in assessing treatment options for NVF prevention.

Efficacy and tolerability of once-monthly oral ibandronate (150 mg) and once-weekly oral alendronate (70 mg): additional results from the Monthly Oral Therapy With Ibandronate For Osteoporosis Intervention (MOTION) study.

BACKGROUND: The MOTION (Monthly Oral Therapy with Ibandronate for Osteoporosis Intervention) study reported that once-monthly ibandronate was noninferior to once-weekly alendronate in terms of increasing bone mineral density (BMD) at the lumbar spine and total hip over 12 months. On analysis of secondary and exploratory end points in MOTION, which included trochanter and femoral neck BMD, monthly ibandronate was found to be noninferior to weekly alendronate. The coprimary, secondary, and exploratory BMD end points from MOTION have been previously reported. OBJECTIVE: This report presents additional results from the MOTION study, including response rates in terms of lumbar spine and total hip BMD gains above baseline; findings from a comparison of serum concentrations of bone turnover markers; and tolerability analysis, including adverse events that led to withdrawal and gastrointestinal (GI) adverse events. METHODS: MOTION was a 12-month (with 15-day follow-up), randomized, multinational, multicenter, double-blind, double-dummy, parallel-group, noninferiority study in postmenopausal women aged 55 to <85 years with osteoporosis. Patients were randomly assigned to receive 150-mg-monthly oral ibandronate and weekly alendronate-matched placebo, or 70-mg-weekly oral alendronate and monthly ibandronate-matched placebo, for 12 months. At baseline, day 7 of treatment, 3 and 6 months, 6 months + 7 days, and 12 months, serum concentrations of markers of bone resorption (C-telopeptide of the a chain of type 1 collagen [sCTX]) and bone formation (serum N-terminal propeptides of type 1 collagen) were measured in a subset of the total trial population. At baseline and month 12, BMD was measured using dual-energy x-ray absorptiometry. Exploratory analyses of patients whose spine, total hip, and trochanter BMD at 12 months were above baseline (responders) were also performed. RESULTS: A total of 1760 women were enrolled (ibandronate, 887 patients; alendronate, 873). The median changes in the trough concentrations of sCTX were -75.5% with monthly ibandronate and -81.2% with weekly alendronate. The percentage of patients with mean lumbar spine and total hip BMD gains above baseline (responders) were 90% and 87%, respectively, for ibandronate and 92% and 90%, respectively, for alendronate. GI adverse events were reported in

Progression of efficacy with ibandronate: a paradigm for the development of new bisphosphonates.

While initial preclinical studies provide an important starting point for dose selection, they may not provide adequate information to identify the optimal dosage for an extended treatment regimen. Determining the best dose for use in an extended dosing regimen requires ongoing development, illustrated best with the bisphosphonate, ibandronate. As mandated for regulatory purposes, the daily oral regimen of ibandronate was proven effective in significantly reducing the rate of new vertebral fractures assessed prospectively, and nonvertebral fractures in a high-risk population, assessed retrospectively. Extended dosing regimens, namely monthly and quarterly intravenous formulations, were developed subsequently to improve the convenience and enhance persistence, while maintaining or increasing efficacy. The continuing and progressive evolution of data led to the understanding that extension of drug-free interval requires higher annual cumulative skeletal exposures (ACE), which were not simply numerical multipliers of the interval and daily dose. For ibandronate, this led to dose selection for the oral monthly 150 mg (ACE 10.8 mg) and intravenous quarterly 3 mg (ACE 12 mg) formulations that proved superior in increasing bone mineral density (BMD) compared with oral daily 2.5 mg (ACE 5.5 mg) ibandronate. Pooling data from clinical trials with high ACE regimens (monthly and quarterly) led to the evolution of statistical evidence for a reduction in clinical and nonvertebral fractures with ibandronate. The ibandronate story should serve as an important future paradigm for bisphosphonate development.

Cellular and molecular consequences of calcineurin A alpha gene deletion.

Here we briefly review our studies that have unraveled an important role for the calcium- and calmodulin-sensitive enzyme calcineurin (CN) in bone remodeling. We find that the genetic deletion of the calcineurin Aalpha isoform results in osteoporosis, which is recapitulated in humans following calcineurin inhibitor therapy widely used after solid organ transplantation. Mechanistically, however, while both calcineurin inhibitors cyclosporine and tacrolimus initially stimulate osteoclastic bone resorption in humans, the predominant feature in the CNAalpha null mouse is a profound reduction in bone formation. We speculate that the so-called "calcineurin inhibitors" may interact with molecules other than calcineurin. The clinical relevance of these observations is explored.

Evidence that calcineurin is required for the genesis of bone-resorbing osteoclasts.

Here, we demonstrate that the Ca(2+)/calmodulin-sensitive phosphatase calcineurin is a necessary downstream mediator for osteoclast differentiation. Using quantitative PCR, we detected the calcineurin isoforms Aalpha, Abeta, Agamma (catalytic), and B1 (regulatory) in osteoclast precursor RAW-C3 cells. We found that, although the expression of these isoforms remained relatively unchanged during osteoclast differentiation, there was a profound increase in the expression of their primary substrate for calcineurin, nuclear factor of activated T cells (NFAT)c1. For gain-of-function studies, we incubated osteoclast precursors for 10 min with a calcineurin fusion protein (TAT-calcineurin Aalpha); this resulted in its receptorless influx into >90% of the precursor cells. A marked increase in the expression of the osteoclast differentiation markers tartrate-resistant acid phosphatase (TRAP) and integrin beta(3) followed. In addition, the expression of NFATc1, as well as the alternative substrate for calcineurin, IkappaBalpha, was significantly enhanced. Likewise, transfection with constitutively active NFAT resulted in an increased expression of both TRAP and integrin beta(3). In parallel loss-of-function studies, transfection with dominant-negative NFAT not only inhibited osteoclast formation but also reversed the induction of NFATc1, TRAP, and integrin beta(3) by TAT-calcineurin Aalpha. The expression of these markers was also inhibited by calcineurin Aalpha U1 small nuclear RNA, which significantly reduced calcineurin Aalpha mRNA and protein expression. Consistent with these observations, we observed a reduction in osteoclastogenesis in calcineurin Aalpha(-/-) cells and in osteoclast precursors treated with the calcineurin inhibitors cyclosporin A and FK506. Together, the gain- and loss-of-function experiments establish that calcineurin Aalpha is necessary for osteoclast formation from its precursor and that this occurs via an NFATc1-dependent mechanism.

Long-term proton pump inhibitor therapy and risk of hip fracture.

CONTEXT: Proton pump inhibitors (PPIs) may interfere with calcium absorption through induction of hypochlorhydria but they also may reduce bone resorption through inhibition of osteoclastic vacuolar proton pumps. OBJECTIVE: To determine the association between PPI therapy and risk of hip fracture. DESIGN, SETTING, AND PATIENTS: A nested case-control study was conducted using the General Practice Research Database (1987-2003), which contains information on patients in the United Kingdom. The study cohort consisted of users of PPI therapy and nonusers of acid suppression drugs who were older than 50 years. Cases included all patients with an incident hip fracture. Controls were selected using incidence density sampling, matched for sex, index date, year of birth, and both calendar period and duration of up-to-standard follow-up before the index date. For comparison purposes, a similar nested case-control analysis for histamine 2 receptor antagonists was performed. MAIN OUTCOME MEASURE: The risk of hip fractures associated with PPI use. RESULTS: There were 13,556 hip fracture cases and 135,386 controls. The adjusted odds ratio (AOR) for hip fracture associated with more than 1 year of PPI therapy was 1.44 (95% confidence interval [CI], 1.30-1.59). The risk of hip fracture was significantly increased among patients prescribed long-term high-dose PPIs (AOR, 2.65; 95% CI, 1.80-3.90; P<.001). The strength of the association increased with increasing duration of PPI therapy (AOR for 1 year, 1.22 [95% CI, 1.15-1.30]; 2 years, 1.41 [95% CI, 1.28-1.56]; 3 years, 1.54 [95% CI, 1.37-1.73]; and 4 years, 1.59 [95% CI, 1.39-1.80]; P<.001 for all comparisons). CONCLUSION: Long-term PPI therapy, particularly at high doses, is associated with an increased risk of hip fracture.

Nonsteroid immune modulators and bone disease.

Glucocorticoids have been the main agents for preventing organ rejection,but unfortunately they possess serious side effects. Newer immunosuppressive agents have therefore been introduced to overcome these effects and have had a dramatic impact on reducing the incidence of organ rejection, enhancing donor organ acceptance, and hence patient survival posttransplantation. However, calcineurin inhibitors (CIs), such as cyclosporine and tacrolimus, also have serious effects causing rapid and severe bone loss in animal models and humans. The mechanism accounting for this action is unclear at present, but the role of T lymphocyte action via RANKL seems to be of essence in triggering bone loss. The mechanism is complex and in vitro studies often produce results that are opposite to those seen in vivo. In addition to acute, rapid, and severe bone loss (ARSBL), the clinical picture shows an extremely high incidence of fractures at all sites, and depends upon the organ transplanted, preexisting bone disease, interval before transplantation, and the dose and duration of multiple immunosuppressive drugs. Other immune-modifying drugs, such as azathioprine, mycophenolate mofetil, and sirolimus, which are used in conjunction with glucocorticoids and CIs have not been shown to promote bone loss experimentally or clinically. With the exception of glucocorticoids, all of the agents discussed here demand further investigation with regard to their effects on bone health in the clinical setting.

Modeling of serum C-telopeptide levels with daily and monthly oral ibandronate in humans.

A previously validated kinetic-pharmacodynamic model was applied to changes in a marker of bone resorption (serum C-telopeptide cross-links of type I collagen [sCTX]) using data from a large-scale clinical trial of ibandronate (Monthly Oral iBandronate In LadiEs [MOBILE]). The model showed rapid and significant suppression of sCTX compared to baseline with daily and monthly ibandronate, and gradual recovery of sCTX levels between monthly doses. This modeled, post-dose oscillatory pattern of sCTX paralleled significant increases in BMD and was associated with an acceptable safety profile for patients in MOBILE, suggesting that the between-dose recovery of sCTX does not negatively affect the efficacy of once-monthly ibandronate.

Update of current therapeutic options for the treatment of postmenopausal osteoporosis.

BACKGROUND: Osteoporosis is a common chronic condition in elderly women and is associated with decreased bone strength and an increased risk for fractures. As the incidence of osteoporotic fractures continues to rise, it is important to identify the most effective therapies for reducing patients' risk of fracture. OBJECTIVE: This article reviews the medication classes commonly used for treating osteoporosis and the efficacy, tolerability, and drug-interaction potential of specific medications. The evidence for the use of combination therapies is summarized, as are the agents under investigation. METHODS: Relevant articles were identified through a search of MEDLINE (August 1985-August 2005) using the terms osteoporosis, postmenopausal, fracture, and efficacy combined with drug therapy, calcium, vitamin D, estrogen, progesterone, selective estrogen modulators, calcitonin, strontium ranelate, bisphosphonates, alendronate, risedronate, ibandronate, pamidronate, parathyroid hormone, combination therapy, and zoledronic acid. The identified articles were reviewed for suitability, with priority given to meta-analyses. RESULTS: Among the therapeutic options for the treatment of osteoporosis, the bisphosphonates appear to provide the greatest antiresorptive efficacy, with some bisphosphonates providing 7% to 8% increases in bone mineral density and 60% to 70% decreases in markers of bone resorption. Bisphosphonates also may reduce the incidence of new vertebral fractures by 50% to 52%. CONCLUSIONS: Bisphosphonates are currently the first choice for the treatment of osteoporosis. Use of intermittent regimens of the newer bisphosphonates appears to be a promising alternative to administration of daily or weekly treatment.

Ibandronate treatment for osteoporosis: rationale, preclinical, and clinical development of extended dosing regimens.

Ibandronate is a potent nitrogen-containing bisphosphonate available as a once-monthly oral formulation for the treatment and prevention of osteoporosis. Preclinical experiments with estrogen-depleted rats, dogs, and monkeys demonstrated the efficacy of daily and intermittent ibandronate dosing. Initial clinical trials explored the optimal dosing regimens for oral administration in humans. The Oral Ibandronate Osteoporosis Vertebral Fracture Trial in North America and Europe (BONE) and Monthly Oral Ibandronate in Ladies (MOBILE) trials demonstrated that long-term daily and intermittent administration of ibandronate was efficacious for increasing bone mineral density, reducing markers of bone turnover, and preventing fractures, while maintaining bone quality. These preclinical and clinical ibandronate trials provided progressive evidence that a simple, long interval dosing regimen could offer efficacy and safety comparable with currently available bisphosphonates. It is anticipated that once-monthly ibandronate may have a positive impact on patient adherence, and ultimately, on fracture protection in osteoporotic women.

Calcineurin regulates bone formation by the osteoblast.

Two of the most commonly used immunosuppressants, cyclosporine A and tacrolimus (FK506), inhibit the activity of a ubiquitously expressed Ca(2+)/calmodulin-sensitive phosphatase, calcineurin. Because both drugs also cause profound bone loss in humans and in animal models, we explored whether calcineurin played a role in regulating skeletal remodeling. We found that osteoblasts contained mRNA and protein for all isoforms of calcineurin A and B. TAT-assisted transduction of fusion protein TAT-calcineurin Aalpha into osteoblasts resulted in the enhanced expression of the osteoblast differentiation markers Runx-2, alkaline phosphatase, bone sialoprotein, and osteocalcin. This expression was associated with a dramatic enhancement of bone formation in intact calvarial cultures. Calcineurin Aalpha(-/-) mice displayed severe osteoporosis, markedly reduced mineral apposition rates, and attenuated colony formation in 10-day ex vivo stromal cell cultures. The latter was associated with significant reductions in Runx2, bone sialoprotein, and osteocalcin expression, paralleled by similar decreases in response to FK506. Together, the gain- and loss-of-function experiments indicate that calcineurin regulates bone formation through an effect on osteoblast differentiation.

Bone metabolism in renal transplant patients treated with cyclosporine or sirolimus.

Sirolimus is a new immunosuppressive agent used as treatment to prevent acute renal allograft rejection. One of the complications of renal transplantation and subsequent long-term immunosuppression is bone loss associated with osteoporosis and consequent fracture. Two open-label, randomized, phase 2 studies comparing sirolimus versus cyclosporine (CsA) included indices of bone metabolism as secondary end-points. Markers of bone turnover, serum osteocalcin and urinary N-telopeptides, were measured over a 1-year period in 115 patients receiving either CsA or sirolimus as a primary therapy in combination with azathioprine and glucocorticoids (study A) or mycophenolate mofetil (MMF) and glucocorticoids (study B). Urinary excretion of N-telopeptides and the concentrations of serum osteocalcin were consistently higher in the CsA-treated patients and significantly different at week 24 for N-telopeptides and at weeks 12, 24, and 52 for osteocalcin. In conclusion, future trials are warranted to test whether a sirolimus-based regimen conserves bone mineral density compared with a CsA-based regimen.