Effects of teriparatide, alendronate, or both on bone turnover in osteoporotic men

Bisphosphonates for postmenopausal osteoporosis

Bisphosphonates are effective in reducing bone turnover, increasing BMD and reducing fracture risk in postmenopausal women with osteoporosis. The licensed bisphosphonates exhibit some differences in potency and speed of onset and offset of action. These differences mean that different agents may be more advantageous in different situations. Uncertainties still exist around the optimum duration of treatment and treatment holidays, how best to use bisphosphonates with anabolic treatments, and the benefits of treatment in patients who do not have a BMD T-score below -2.5.

Early changes in biochemical markers of bone turnover and their relationship with bone mineral density changes after 24 months of treatment with teriparatide

We report the changes in biochemical markers of bone formation during the first 6 months of teriparatide therapy in postmenopausal women with osteoporosis according to previous antiresorptive treatment. Prior therapy does not adversely affect the response to teriparatide treatment. Similar bone markers levels are reached after 6 months of treatment.

INTRODUCTION

The response of biochemical markers of bone turnover with teriparatide therapy in subjects who have previously received osteoporosis drugs is not fully elucidated. We examined biochemical markers of bone formation in women with osteoporosis treated with teriparatide and determined: (1) whether the response is associated with prior osteoporosis therapy, (2) which marker shows the best performance for detecting a response to therapy, and (3) the correlations between early changes in bone markers and subsequent bone mineral density (BMD) changes after 24 months of teriparatide.

METHODS

We conducted a prospective, open-label, 24-month study at 95 centers in 10 countries in 758 postmenopausal women with established osteoporosis (n = 181 treatment-naïve) who had at least one post-baseline bone marker determination. Teriparatide (20 μg/day) was administered for up to 24 months. We measured procollagen type I N-terminal propeptide (PINP), bone-specific alkaline phosphatase (b-ALP), and total alkaline phosphatase (t-ALP) at baseline, 1 and 6 months, and change in BMD at the lumbar spine, total hip and femoral neck from baseline to 24 months.

RESULTS

Significant increases in formation markers occurred after 1 month of teriparatide regardless of prior osteoporosis therapy. The absolute increase at 1 month was lower in previously treated versus treatment-naïve patients, but after 6 months all groups reached similar levels. PINP showed the best signal-to-noise ratio. Baseline PINP correlated positively and significantly with BMD response at 24 months.

CONCLUSIONS

This study suggests that the long-term responsiveness of bone formation markers to teriparatide is not affected in subjects previously treated with antiresorptive drugs.

Short-term bone marker responses to teriparatide and strontium ranelate in patients with osteoporosis previously treated with bisphosphonates

OBJECTIVE

To evaluate the responses of serum beta-CTX and osteocalcin in patients who were undergoing treatment with teriparatide or strontium ranelate (SR).

SUBJECTS AND METHODS

We analyzed 14 patients (12 women and 2 men; mean age of 71 years) taking teriparatide, and 13 female patients (mean age of 70 years) taking SR; all the patients having previously been on bisphosphonates. Serum beta-CTX and osteocalcin levels were determined before and after the first and third months of teriparatide treatment and up to the fourth month of treatment with SR.

RESULTS

We observed an initial significant increase in osteocalcin levels during the first month (165%, p = 0.01) followed by a peak of beta-CTX (180%, p = 0.02) after the third month of treatment with teriparatide. An increase in these markers was also observed with SR: 49% in osteocalcin (p = 0.002) and 80% in beta-CTX (p = 0.008).

CONCLUSION

SR had a predominantly short-term bone-forming effect in postmenopausal women with osteoporosis previously treated with bisphosphonates in a lesser degree than with teriparatide.

Time-dependent changes in skeletal response to teriparatide: escalating vs. constant dose teriparatide (PTH 1-34) in osteoporotic women

Once-daily injections of teriparatide initially increase biochemical markers of bone formation and resorption, but markers peak after 6-12 months and then decline despite continued treatment. We sought to determine whether increasing teriparatide doses in a stepwise fashion could prolong skeletal responsiveness. We randomized 52 postmenopausal women with low spine and/or hip bone mineral density (BMD) to either a constant or an escalating subcutaneous teriparatide dose (30 μg daily for 18months or 20 μg daily for 6 months, then 30 μg daily for 6 months, and then 40 μg daily for 6 months). Serum procollagen I N-terminal propeptide, osteocalcin, and C-terminal telopeptide of type I collagen were assessed frequently. BMD of the spine, hip, radius, and total body was measured every 6 months. Acute changes in urinary cyclic AMP in response to teriparatide were examined in a subset of women in the constant dose group. All bone markers differed significantly between the two treatment groups. During the final six months, bone markers declined in the constant dose group but remained stable or increased in the escalating dose group (all markers, p<0.017). Nonetheless, mean area under the curve did not differ between treatments for any bone marker, and BMD increases were equivalent in both treatment groups. Acute renal response to teriparatide, as assessed by urinary cyclic AMP, did not change over 18 months of teriparatide administration. In conclusion, stepwise increases in teriparatide prevented the decline in bone turnover markers that is observed with chronic administration without altering BMD increases. The time-dependent waning of the response to teriparatide appears to be bone-specific.

Teriparatide: Its Use in the Treatment of Osteoporosis

The prevalence of osteoporosis is likely to rise with the increase in life expectancy of an ageing population. Current first line therapies for the treatment of osteoporosis are predominantly anti-resorptive. Teriparatide is a first in class, anabolic agent with a unique mechanism that results in increased bone formation. Daily subcutaneous injection for 6–24 months was effective in reducing vertebral and non-vertebral fracture rates, in improving bone mineral density (BMD) and in increasing bone formation rates in postmenopausal osteoporosis, with effects persisting following treatment cessation. Similar benefits on bone mass and bone formation were seen in men with osteoporosis and glucocorticoid induced osteoporosis. Beneficial effects on bone mass have been demonstrated in treatment naive subjects treated with teriparatide alone, sequentially with anti-resorptive therapy and concomitantly with some, but not all, anti-resorptive treatments due to an early blunting of the anabolic effect. Teriparatide is generally well tolerated. However, the high treatment cost and inconvenient mode of administration has limited it's use to patients with osteoporosis who have experienced an unsatisfactory response, who are intolerant to other osteoporosis therapies, or to patients at very high risk of fracture. Teriparatide treatment is currently restricted to a total lifetime treatment dose of 18 months of daily subcutaneous therapy due to concerns from animal studies suggesting an increased risk of osteosarcoma. More safety data may permit a longer duration of treatment in the future but will necessitate prolonged human studies. Teriparatide may serve a more prominent role in the treatment of older patients who continue to fracture despite low bone turnover or sustain side effects with anti-resorptive therapy.

Therapy of osteoporosis in men with teriparatide

Osteoanabolic therapy is an attractive therapeutic option for men with osteoporosis because it directly stimulates bone formation, an action not shared by any antiresorptive drug. Teriparatide (recombinant human PTH(1-34)) and PTH(1-84) are available in many countries but PTH(1-84) is not available in the United States. Only teriparatide is approved for the treatment of osteoporosis in men. It is also indicated in glucocorticoid-induced osteoporosis. Teriparatide is associated with major gains in bone density at the lumbar spine and, to a lesser extent, in the hip regions. Vertebral and nonvertebral fractures are reduced in postmenopausal women treated with teriparatide. Fracture reduction data in men are less secure because the number of study subjects is small and the studies have not been powered to document this endpoint. Nevertheless, observational data in men suggest a reduction in vertebral fractures with teriparatide. Attempts to show further beneficial effects of teriparatide in combination with antiresorptive agents have not been demonstrated yet to be superior to monotherapy with teriparatide alone. The duration of therapy with teriparatide is limited to 2 years. Thereafter, it is necessary to treat with an antiresorptive drug to maintain, and perhaps increase, densitometric gains. Teriparatide is well tolerated with a good safety profile.

Are osteoclasts needed for the bone anabolic response to parathyroid hormone? A study of intermittent parathyroid hormone with denosumab or alendronate in knock-in mice expressing humanized RANKL

PTH stimulates osteoblastic cells to form new bone and to produce osteoblast-osteoclast coupling factors such as RANKL. Whether osteoclasts or their activity are needed for PTH anabolism remains uncertain. We treated ovariectomized huRANKL knock-in mice with a human RANKL inhibitor denosumab (DMAb), alendronate (Aln), or vehicle for 4 weeks, followed by co-treatment with intermittent PTH for 4 weeks. Loss of bone mass and microarchitecture was prevented by Aln and further significantly improved by DMAb. PTH improved bone mass, microstructure, and strength, and was additive to Aln but not to DMAb. Aln inhibited biochemical and histomorphometrical indices of bone turnover,--i.e. osteocalcin and bone formation rate (BFR) on cancellous bone surfaces-, and Dmab inhibited them further. However Aln increased whereas Dmab suppressed osteoclast number and surfaces. PTH significantly increased osteocalcin and bone formation indices, in the absence or presence of either antiresorptive, although BFR remained lower in presence of Dmab. To further evaluate PTH effects in the complete absence of osteoclasts, high dose PTH was administered to RANK(-/-) mice. PTH increased osteocalcin similarly in RANK(-/-) and WT mice. It also increased BMD in RANK(-/-) mice, although less than in WT. These results further indicate that osteoclasts are not strictly required for PTH anabolism, which presumably still occurs via stimulation of modeling-based bone formation. However the magnitude of PTH anabolic effects on the skeleton, in particular its additive effects with antiresorptives, depends on the extent of the remodeling space, as determined by the number and activity of osteoclasts on bone surfaces.

Long-term treatment with bisphosphonates and their safety in postmenopausal osteoporosis

Bisphosphonates are the leading drugs for the treatment of osteoporosis. In randomized controlled trials (RCTs), alendronate, risedronate, and zoledronate have shown to reduce the risk of vertebral, nonvertebral, and hip fractures, whereas RCTs with ibandronate show antifracture efficacy at vertebral sites. Bisphosphonates are generally well tolerated and safe. Nevertheless, adverse events have been noted, and it is important to consider the strength of the evidence for causal relationships. Effects on the gastrointestinal tract and kidney function are well recognized, as are transient acute-phase reactions. Atrial fibrillation was first identified as a potential adverse event in a zoledronate trial, but subsequent trials and analyses failed to substantiate an association with bisphosphonates. Case reports have suggested a relationship between oral bisphosphonates and esophageal cancer, but this has not been demonstrated in epidemiologic studies. A possible association between bisphosphonate use and osteonecrosis of the jaw (ONJ) has also been suggested. However, the risk of ONJ in patients with osteoporosis appears to be very low, with no evidence from prospective RCTs of a causal association. There are reports of occasional occurrence of subtrochanteric or diaphyseal fractures in osteoporotic patients, but an association with bisphosphonate therapy is not substantiated by epidemiologic studies or prospective RCTs.

Effects of teriparatide, alendronate, or both in women with postmenopausal osteoporosis

CONTEXT

Teriparatide increases both bone formation and bone resorption.

OBJECTIVE

We sought to determine whether combining teriparatide with an antiresorptive agent would alter its anabolic action.

DESIGN AND SETTING

This was a randomized controlled trial conducted in a single university hospital.

PATIENTS AND INTERVENTION

We randomized 93 postmenopausal women with low bone mineral density (BMD) to alendronate 10 mg daily (group 1), teriparatide 40 microg sc daily (group 2), or both (group 3) for 30 months. Teriparatide was begun at month 6.

MAIN OUTCOME MEASURES

BMD of the lumbar spine, proximal femur, proximal radius, and total body was measured by dual-energy x-ray absorptiometry (DXA) every 6 months. Lumbar spine trabecular BMD was measured at baseline and month 30 by quantitative computed tomography. Serum osteocalcin, N-terminal propeptide of type 1 collagen, and N-telopeptide levels were assessed frequently. Women who had at least one repeat DXA scan on therapy were included in the analyses (n = 69).

RESULTS

DXA spine BMD increased more in women treated with teriparatide alone than with alendronate alone (18 +/- 11 vs. 7 +/- 4%; P < 0.001) or both (18+/-11 vs. 12 +/- 9%; P = 0.045). Similarly, femoral neck BMD increased more in women treated with teriparatide alone than with alendronate alone (11 +/- 5 vs. 4 +/- 4%; P < 0.001) or both (11 +/- 5 vs. 3 +/- 5%; P < 0.001). Quantitative computed tomography spine BMD increased 1 +/- 7, 61 +/- 31, and 24 +/- 24% in groups 1, 2, and 3 (P < 0.001 for all comparisons). Serum osteocalcin, N-terminal propeptide of type 1 collagen, and cross-linked N-telopeptides of type I collagen increased more with teriparatide alone than with both (P < 0.001 for each marker).

CONCLUSION

Alendronate reduces the ability of teriparatide to increase BMD and bone turnover in women.

A perspective on male osteoporosis

Osteoporosis and fragility fracture become common with advancing age in men. The incidence of osteoporosis-related fracture is similar to myocardial infarction and exceeds that of lung and prostate carcinoma combined. These fractures cause substantial morbidity, and the mortality following hip fracture is greater in men than in women. A decline in sex steroids and glucocorticoid and alcohol use, among other factors, contribute to bone loss and fracture risk. Approaches to reduce fracture risk in men are very similar to that in women - recognising and addressing muscle weakness/falls risk and optimising nutrition, with emphasis on calcium and vitamin D and medications when appropriate. Despite the high prevalence, osteoporosis remains largely undiagnosed and undertreated. Hopefully, increased recognition of male osteoporosis by health-care providers and the men themselves, in combination with recent consensus recommendations for treatment based on fracture-risk estimation, will reduce the burden of fragility fracture in men.

Clinical applications of RANK-ligand inhibition

An enhanced rate of bone remodelling fuelled by osteoclastogenesis mediates diseases such as osteoporosis, arthritic bone destruction, Paget's disease and malignancy-induced bone loss. Thus, the control of osteoclastogenesis is of major clinical importance. The receptor activator of nuclear factor kappa B (RANK); its ligand, RANKL and decoy receptor, osteoprotegerin, are critical determinants of osteoclastogenesis, and increased RANK signalling is involved in several bone diseases, providing the rationale for RANKL inhibition. The effects of RANKL inhibition are being witnessed in clinical trials of neutralizing fully human monoclonal antibodies that target RANKL (e.g. denosumab) and which induce profound and sustained inhibition of bone resorption. The relative efficacy, cost-effectiveness and side-effects of targeted RANKL inhibition compared with conventional antiresorptive drugs (i.e. bisphosphonates) should be resolved by clinical trials in coming years.

Effects of teriparatide retreatment in osteoporotic men and women

CONTEXT

The stimulatory effect of teriparatide on bone mineral density (BMD) and bone turnover is initially exuberant, but then diminishes.

OBJECTIVE

Our objective was to determine whether retreating with teriparatide after a drug-free period can restore the initial exuberant response to teriparatide.

DESIGN AND SETTING

This was a planned extension of a randomized controlled trial conducted in a single university hospital.

PATIENTS AND INTERVENTION

Subjects previously participated in a 30-month randomized trial comparing the effects of alendronate (group 1), teriparatide (group 2), or both (group 3) on BMD and bone turnover in men and women with low BMD (phase 1). Subjects who completed phase 1 on their assigned therapy entered phase 2 (months 30-42), during which teriparatide was stopped in groups 2 and 3. Teriparatide was administered to all subjects during months 42 to 54 (phase 3).

MAIN OUTCOME MEASURES

We compared changes in BMD and markers of bone turnover (serum osteocalcin, N-terminal propeptide of type 1 collagen, and N-telopeptide) between phase 1 and 3 in subjects receiving teriparatide alone.

RESULTS

Posterior-anterior and lateral spine BMD increased 12.5 +/- 1.5 and 16.9 +/- 1.7%, respectively, during the first 12 months of teriparatide administration and 5.2 +/- 0.8 and 6.2 +/- 1.8%, respectively, during teriparatide retreatment (P < 0.001 and P = 0.001). Increases in osteocalcin (P < 0.001), N-terminal propeptide of type 1 collagen (P < 0.001), and N-telopeptide (P < 0.001) were greater during the first period of teriparatide administration.

CONCLUSION

The response to teriparatide is attenuated when readministered after a 12-month hiatus.

Management of osteoporosis in the aging male: focus on zoledronic acid

Osteoporosis in the aging male remains an important yet under-recognized and undertreated disease. Current US estimates indicate that over 14 million men have osteoporosis or low bone mass, and men suffer approximately 500,000 osteoporotic fractures each year. Men experience fewer osteoporotic fractures than women but have higher mortality after fracture. Bisphosphonates are potent antiresorptive agents that inhibit osteoclast activity, suppress in vivo markers of bone turnover, increase bone mineral density, decrease fractures, and improve survival in men with osteoporosis. Intravenous zoledronic acid may be a preferable alternative to oral bisphosphonate therapy in patients with cognitive dysfunction, the inability to sit upright, or significant gastrointestinal pathology. Zoledronic acid (Reclast) is approved in the US as an annual 5 mg intravenous infusion to treat osteoporosis in men. The zoledronic acid (Zometa) 4 mg intravenous dose has been studied in the prevention of bone loss associated with androgen deprivation therapy.

Local communication on and within bone controls bone remodeling

Bone remodeling is required for healthy calcium homeostasis and for repair of damage occurring with stress and age. Osteoclasts resorb bone and osteoblasts form bone. These processes normally occur in a tightly regulated sequence of events, where the amount of formed bone equals the amount of resorbed bone, thereby restoring the removed bone completely. Osteocytes are the third cell type playing an essential role in bone turnover. They appear to regulate activation of bone remodeling, and they exert both positive and negative regulation on both osteoclasts and osteoblasts. In this review, we consider the intricate communication between these bone cells in relation to bone remodeling, reviewing novel data from patients with mutations rendering different cell populations inactive, which have shown that these interactions are more complex than originally thought. We highlight the high probability that a detailed understanding of these processes will aid in the development of novel treatments for bone metabolic disorders, i.e. we discuss the possibility that bone resorption can be attenuated pharmacologically without a secondary reduction in bone formation.

Marked reduction of bone turnover by alendronate attenuates the acute response of bone resorption marker to endogenous parathyroid hormone

The aim of this study was to assess the effects of the antiresorptive treatments of alendronate (ALN), risedronate (RIS) and raloxifene (RLX) on the response of bone to endogenous parathyroid hormone (PTH) induced by acute hypocalcemia. Forty women (age, 55-80 years) with postmenopausal osteoporosis (treated with ALN, RIS and RLX or untreated-control group) were given infusions of sodium ethylenediaminetetraacetic acid (EDTA; 10 mg/kg of body weight). Serum ionized calcium (iCa), plasma intact PTH and marker of bone resorption, serum beta C-terminal telopeptide of type I collagen (beta-CTX; beta CrossLaps) were followed for 180 min. In all women, decrease in serum iCa following the EDTA load resulted in an acute increase in serum PTH. Between 60 and 180 min, plasma PTH in the ALN and RIS treated women remained significantly higher than in the control group. The integrated beta-CTX responses (area under curves, AUCs) to peaks of PTH were significantly lower in the ALN treated women than in those treated with RIS, RLX or control group. There was no significant difference in beta-CTX AUC response to PTH between RIS, RLX and control women. Taken together, these findings suggest that in women with postmenopausal osteoporosis treated with ALN, a substantial reduction of bone turnover blunts the acute bone resorbing effect of endogenous PTH.

Teriparatide: a review of its use in osteoporosis

Recombinant teriparatide (Forteo; Forsteo) is an anabolic (bone forming) agent. Studies have shown that subcutaneous teriparatide 20 microg/day is effective in women with postmenopausal osteoporosis, men with idiopathic or hypogonadal osteoporosis and patients with glucocorticoid-induced osteoporosis. Teriparatide improves bone mineral density (BMD) and alters the levels of bone formation and resorption markers; histomorphometric studies showed teriparatide-induced effects on bone structure, strength and quality. Subcutaneous teriparatide 20 microg/day administered over a treatment period of 11-21 months was effective in reducing the risk of fractures in and in improving BMD in men with idiopathic or hypogonadal osteoporosis, women with postmenopausal osteoporosis and patients with glucocorticoid-induced osteoporosis. Furthermore, the beneficial effects of teriparatide on vertebral fracture prevention and BMD appear to persist following treatment cessation. Teriparatide is generally well tolerated and treatment compliance rates are favourable. However, current limitations on the length of treatment and the high acquisition cost mean that teriparatide is best reserved for the treatment of patients with osteoporosis at high risk of fracture, or for patients with osteoporosis who have unsatisfactory responses to or intolerance of other osteoporosis therapies.

Early responsiveness of women with osteoporosis to teriparatide after therapy with alendronate or risedronate

BACKGROUND

Anabolic responsiveness to teriparatide can be blunted or delayed in patients previously treated with alendronate. The extent of this effect is different for other antiresorptives. This study evaluated the early anabolic effects of teriparatide in postmenopausal women with osteoporosis previously treated with alendronate or risedronate.

METHODS

Patients treated for at least 24 months with alendronate or risedronate discontinued their bisphosphonate and received teriparatide for 12 months. The primary endpoint was a comparison of changes from baseline in N-terminal propeptide of type 1 collagen after 3 months between prior bisphosphonate groups. We also examined changes in other bone turnover markers, bone mineral density (BMD), and relationships between early changes in bone turnover markers and 12-month areal and volumetric BMD.

RESULTS

In the prior risedronate group, the N-terminal propeptide of type 1 collagen increase was significantly greater after 3 months of teriparatide than in the prior alendronate group (mean +/- se, 86.0 +/- 5.6 vs. 61.2 +/- 5.3 ng/ml, respectively; P < 0.001). Findings were similar for the other bone turnover markers. The changes in areal BMD and trabecular spine volumetric BMD were also greater in the prior risedronate group (P < 0.05). Early changes in bone turnover markers correlated with changes in trabecular spine volumetric BMD at 12 months (Spearman r = 0.45). Teriparatide was well tolerated.

CONCLUSION

This nonrandomized but prospective study suggests that there may be differences in anabolic responsiveness to teriparatide as a function of the type of prior bisphosphonate exposure.

Effects of two years of daily teriparatide treatment on BMD in postmenopausal women with severe osteoporosis with and without prior antiresorptive treatment

Previous antiresorptive (AR) treatment may influence the response to teriparatide. We examined BMD response and safety in a subgroup of 503 postmenopausal women with osteoporosis who received teriparatide for 24 mo. Patients were divided into three groups based on their prior AR treatment: treatment-naïve (n = 84); pretreated with no evidence of inadequate treatment response (n = 134); and pretreated showing an inadequate response to AR treatment (n = 285), which was predefined based on the occurrence of fractures, persistent low BMD, and/or significant BMD loss while on therapy. Changes in BMD from baseline were analyzed using mixed model repeated measures. Lumbar spine BMD increased significantly from baseline at 6, 12, 18, and 24 mo in all three groups. The mean gain in spine BMD over 24 mo was greater in the treatment-naïve group (0.095 g/cm(2); 13.1%) than in the AR pretreated (0.074 g/cm(2); 10.2%; p < 0.005) and inadequate AR responder (0.071 g/cm(2); 9.8%; p < 0.001) groups. The corresponding increases in total hip BMD were 3.8%, 2.3%, and 2.3%, respectively. Early decreases in hip BMD in the inadequate AR responder group were reversed by 18 mo of treatment. Increases in BMD between 18 and 24 mo were highly significant. Nausea (13.3%) and arthralgia (11.7%) were the most commonly reported adverse events. Asymptomatic hypercalcemia was reported in 5.0% of patients. Teriparatide treatment for 24 mo is associated with a significant increase in BMD in patients with and without previous AR use. Prior AR treatment modestly blunted the BMD response to teriparatide. Safety was consistent with current prescribing label information.

Osteoporosis primer for the vertebroplasty practitioner: expanding the focus beyond needles and cement

Osteoporosis is a common cause of vertebral compression fractures. Although vertebroplasty is used to treat the pain, the risk of additional compression fractures is very high in these patients. Adequate evaluation and management of the underlying osteoporosis is critical to reducing the risk of subsequent fractures. Such an evaluation involves understanding the underlying physiology of osteoporosis and the role of calcium, vitamin D, prescription medication, and lifestyle changes. This brief review is intended to familiarize neuroradiologists with these aspects so they can advise patients about optimizing fracture risk reduction.

Bisphosphonates: mechanism of action and role in clinical practice

Bisphosphonates are primary agents in the current pharmacological arsenal against osteoclast-mediated bone loss due to osteoporosis, Paget disease of bone, malignancies metastatic to bone, multiple myeloma, and hypercalcemia of malignancy. In addition to currently approved uses, bisphosphonates are commonly prescribed for prevention and treatment of a variety of other skeletal conditions, such as low bone density and osteogenesis imperfecta. However, the recent recognition that bisphosphonate use is associated with pathologic conditions including osteonecrosis of the jaw has sharpened the level of scrutiny of the current widespread use of bisphosphonate therapy. Using the key words bisphosphonate and clinical practice in a PubMed literature search from January 1, 1998, to May 1, 2008, we review current understanding of the mechanisms by which bisphosphonates exert their effects on osteoclasts, discuss the role of bisphosphonates in clinical practice, and highlight some areas of concern associated with bisphosphonate use.

Osteoporosis in men

With the aging of the population, there is a growing recognition that osteoporosis and fractures in men are a significant public health problem, and both hip and vertebral fractures are associated with increased morbidity and mortality in men. Osteoporosis in men is a heterogeneous clinical entity: whereas most men experience bone loss with aging, some men develop osteoporosis at a relatively young age, often for unexplained reasons (idiopathic osteoporosis). Declining sex steroid levels and other hormonal changes likely contribute to age-related bone loss, as do impairments in osteoblast number and/or activity. Secondary causes of osteoporosis also play a significant role in pathogenesis. Although there is ongoing controversy regarding whether osteoporosis in men should be diagnosed based on female- or male-specific reference ranges (because some evidence indicates that the risk of fracture is similar in women and men for a given level of bone mineral density), a diagnosis of osteoporosis in men is generally made based on male-specific reference ranges. Treatment consists both of nonpharmacological (lifestyle factors, calcium and vitamin D supplementation) and pharmacological (most commonly bisphosphonates or PTH) approaches, with efficacy similar to that seen in women. Increasing awareness of osteoporosis in men among physicians and the lay public is critical for the prevention of fractures in our aging male population.

Mechanisms of action of bisphosphonates: similarities and differences and their potential influence on clinical efficacy

Bisphosphonates (BPs) are well established as the leading drugs for the treatment of osteoporosis. There is new knowledge about how they work. The differences that exist among individual BPs in terms of mineral binding and biochemical actions may explain differences in their clinical behavior and effectiveness.

INTRODUCTION

The classical pharmacological effects of bisphosphonates (BPs) appear to be the result of two key properties: their affinity for bone mineral and their inhibitory effects on osteoclasts.

DISCUSSION

There is new information about both properties. Mineral binding affinities differ among the clinically used BPs and may influence their differential distribution within bone, their biological potency, and their duration of action. The antiresorptive effects of the nitrogen-containing BPs (including alendronate, risedronate, ibandronate, and zoledronate) appear to result from their inhibition of the enzyme farnesyl pyrophosphate synthase (FPPS) in osteoclasts. FPPS is a key enzyme in the mevalonate pathway, which generates isoprenoid lipids utilized for the post-translational modification of small GTP-binding proteins that are essential for osteoclast function. Effects on other cellular targets, such as osteocytes, may also be important. BPs share several common properties as a drug class. However, as with other families of drugs, there are obvious chemical, biochemical, and pharmacological differences among the individual BPs. Each BP has a unique profile that may help to explain potential clinical differences among them, in terms of their speed and duration of action, and effects on fracture reduction.

The osteoclast: friend or foe?

Bone is a dynamic organ constantly remodeled to support calcium homeostasis and structural needs. The osteoclast is the cell responsible for removing both the organic and inorganic components of bone. It is derived from hematopoietic progenitors in the macrophage lineage and differentiates in response to the tumor necrosis factor family cytokine receptor activator of NF kappa B ligand. alpha v beta 3 integrin mediates cell adhesion necessary for polarization and formation of an isolated, acidified resorptive microenvironment. Defects in osteoclast function, whether genetic or iatrogenic, may increase bone mass but lead to poor bone quality and a high fracture risk. Pathological stimulation of osteoclast formation and resorption occurs in postmenopausal osteoporosis, inflammatory arthritis, and metastasis of tumors to bone. In these diseases, osteoclast activity causes bone loss that leads to pain, deformity, and fracture. Thus, osteoclasts are critical for normal bone function, but their activity must be controlled.

Quarterly intravenous ibandronate for postmenopausal osteoporosis

Osteoporosis is under-recognized and undertreated among postmenopausal women. Nitrogen-containing bisphosphonates are its first-line pharmacotherapy. Oral bisphosphonate treatment requires stringent dosing guidelines to minimize gastrointestinal irritation and enhance absorption. This paper reviews the efficacy, safety and tolerability of quarterly intravenous ibandronate 3 mg injection, approved in 2006 in the USA and Europe. Quarterly intravenous ibandronate injection has shown superior efficacy to daily oral ibandronate for bone mineral density increase and fracture prevention. No drug-related serious atrial fibrillation events have been reported with intravenous ibandronate. The regimen has a favorable renal safety profile. Quarterly intravenous ibandronate is administered as a simple 15-30-s intravenous injection in a physician's office and provides a beneficial option for patients who are unable to tolerate oral administration.

Valid treatment options for osteoporosis and osteopenia in HIV-infected persons

OBJECTIVE

To review clinical data on bone ossification agents that may be considered for use in the treatment of osteoporosis and osteopenia in HIV-infected patients.

DATA SOURCES

A literature search was performed using MEDLINE (1950-January 2008), EMBASE, PubMed, and abstracts from major HIV conferences (February 2001-October 2007). These searches were limited to human data published in English and used the key words bisphosphonates, calcitonin, raloxifene, teriparatide, HAART, osteopenia, osteoporosis, and HIV/AIDS. Additional articles were retrieved from citations of selected references.

STUDY SELECTION AND DATA EXTRACTION

Relevant information on the pharmacology, pharmacokinetics, safety, and efficacy of available treatment with hormonal and nonhormonal agents was selected. Greater emphasis was placed on randomized clinical trials than on retrospective studies.

DATA SYNTHESIS

Osteoporosis in HIV-infected persons is at least as prevalent as in postmenopausal women, yet this population is not listed in primary care guidelines as one that should be considered for screening. In addition to bisphosphonates, calcitonin, raloxifene, and teriparatide are used to treat bone disorders. Three clinical trials to date have evaluated the use of a bisphosphonate in HIV-infected persons. The trials showed a marked increase in bone mineral density in patients taking alendronate versus those in the control groups (with/without calcium, exercise, and/or vitamin D in 1 or both arms). Dosing restrictions complicate the use of these agents; diet, exercise, and calcium supplementation remain the foremost recommended strategies to prevent bone loss. The use of estrogen, testosterone, calcitonin, and teriparatide is less studied in HIV-positive patients, but may be considered in select cases. There are some investigational drugs and agents not available in the US; however, there are not enough data to support their use.

CONCLUSIONS

Alendronate appears to be a promising treatment option for HIV-infected patients with osteoporosis and osteopenia. Further research is required to determine the safety and efficacy of other available drugs. Until additional information is provided, and with available knowledge on the metabolism profiles of antiretroviral and bone ossification agents, alendronate appears to be the preferred agent to use in this population.

Effects of previous antiresorptive therapy on the bone mineral density response to two years of teriparatide treatment in postmenopausal women with osteoporosis

INTRODUCTION

EUROFORS was a 2-yr prospective, randomized trial of postmenopausal women with established osteoporosis, designed to investigate various sequential treatments after teriparatide 20 microg/d for 1 yr. The present secondary analysis examined the effects of 2 yr of open-label teriparatide in women previously treated with antiresorptive drugs for at least 1 yr.

METHODS

A subgroup of 245 women with osteoporosis who had 2 yr of teriparatide treatment were stratified by previous predominant antiresorptive treatment into four groups: alendronate (n=107), risedronate (n=59), etidronate (n=30), and non-bisphosphonate (n=49). Bone mineral density (BMD) at the lumbar spine and hip was determined after 6, 12, 18, and 24 months, and bone formation markers were measured after 1 and 6 months.

RESULTS

Significant increases in bone formation markers occurred in all groups after 1 month of teriparatide treatment. Lumbar spine BMD increased at all visits, whereas a transient decrease in hip BMD, which was subsequently reversed, was observed in all groups. BMD responses were similar in all previous antiresorptive groups. Previous etidronate users showed a higher increase at the spine but not at the hip BMD. Duration of previous antiresorptive therapy and lag time between stopping previous therapy and starting teriparatide did not affect the BMD response at any skeletal site. Treatment-emergent adverse events were similar to those reported in treatment-naive postmenopausal women with osteoporosis treated with teriparatide.

CONCLUSIONS

Teriparatide induces positive effects on BMD and markers of bone formation in postmenopausal women with established osteoporosis, regardless of previous long-term exposure to antiresorptive therapies.

Additive effects of PTH and bisphosphonates on the bone healing response to metaphyseal implants in rats

BACKGROUND

When PTH is used to increase the amount of bone in osteoporotic patients, combination with bisphosphonates is known to attenuate the response. This might be explained by the reduced number of remodeling sites after bisphosphonate treatment, which reduces the number of cells able to respond to PTH. However, in a repair situation after trauma, a large number of osteoblasts reside in the wound site. If their activity is no longer coupled to osteoclasts, decreased resorption by bisphosphonates and stimulation of osteoblastic activity by PTH should both (independently) increase bone formation. Thus, we hypothesized that in contrast to the case in osteoporosis treatment, PTH and bisphosphonates have an additive effect in situations involving bone regeneration.

MATERIAL AND METHODS

Stainless steel screws, either coated with biphosphonates or uncoated, were inserted in 46 rat tibias. This normally elicits a bone repair response, leading to a gradual increase in the strength of screw fixation. Half of the rats also received daily injections of teriparatide (PTH). Thus, there were 4 groups: control, bisphosphonate, PTH, and bisphosphonate plus PTH. Pull-out force and energy were measured after 2 weeks.

RESULTS

The combined treatment had the strongest effect. It doubled the pull-out force and tripled the pull-out energy, compared to untreated controls. Also, bisphosphonate or PTH alone increased the pull-out force and energy, although less. No treatment cross-dependency was observed.

INTERPRETATION

Because bisphosphonates mainly influence osteoclasts, and intermittent administration of PTH mainly influences osteoblasts, our findings indicate that to a large extent these cells work without coupling in this model. It appears that bisphosphonates are unlikely to attenuate the response to PTH during the formation of new bone.

Short-term changes in serum PINP predict long-term changes in trabecular bone in the rat ovariectomy model

Serum procollagen I N-terminal propeptide (PINP) is a sensitive bone formation marker in humans. We have developed a nonradioactive immunoassay for rat PINP and studied PINP as a bone formation marker in the rat ovariectomy (OVX) model. Two OVX studies were performed with 3-month-old rats, both including measurement of PINP, C-terminal cross-linked telopeptide of type I collagen (CTX), and N-terminal mid-fragment of osteocalcin. A pilot 14-day study contained a sham-operated control group and an OVX group, and an extensive 8-week study contained a sham-operated control group and OVX groups receiving vehicle and 17 beta-estradiol (E2, 10 microg/kg/day s.c.). The bone markers were measured before the operation and at days 2, 4, 7, 10, and 14 in the pilot study and before the operations and at 2 and 8 weeks in the extensive study. Trabecular bone parameters were determined by peripheral quantitative computed tomography and histomorphometry from tibial metaphysis in the extensive study. The rat PINP immunoassay had the following characteristics: intra-assay coefficient of variation (CV) 2.8%, interassay CV 7.5%, dilution linearity 95%, and recovery 107%. PINP increased significantly during the first 2 weeks after OVX and returned to sham level at 8 weeks. E2 prevented the increase caused by OVX. Changes in PINP at 2 weeks correlated strongly with changes in CTX and osteocalcin at 2 weeks and with trabecular bone parameters at 8 weeks. As a conclusion, short-term changes in PINP predict long-term changes in trabecular bone parameters, suggesting that PINP is a reliable marker of bone formation in the rat OVX model.

[Metabolic bone diseases]

Osteomalacia is caused by impaired vitamin D receptor (VDR) signaling, calcium deficiency, and altered bone mineralization. This can be due to insufficient sunlight exposure, malabsorption, reduced D hormone activation in chronic kidney disease, and rare alterations of VDR signaling and phosphate metabolism. Leading symptoms are bone pain, muscular cramps, and increased incidence of falls in the elderly. The adequate respective countermeasures are to optimize the daily intake of calcium and vitamin D3 and to replace active D hormone and phosphate if deficient. Osteoporosis is characterized by bone fragility fractures upon minor physical impact. Indications for diagnosis and treatment can be established by estimating the absolute fracture risk, taking into account bone mineral density, age, gender, and individual risk factors. Exercise, intervention programs to avoid falls, and specific drugs are capable of substantially reducing fracture risk even in the elderly. Secondary osteoporosis primarily requires both bone-altering medications and effective treatment of underlying diseases.

Development of a low-dose anti-resorptive drug regimen reveals synergistic suppression of bone formation when coupled with disuse

Safe and effective countermeasures to spaceflight-induced osteoporosis are required to mitigate the potential for mission-critical fractures and ensure long-term bone health in astronauts. Two anti-resorptive drugs, the bisphosphonate zoledronic acid (ZOL) and the anti-receptor activator of NF-kappaB ligand protein osteoprotegerin (OPG), were investigated to find the minimum, comparable doses that yield a maximal increase in bone quality, while minimizing deleterious effects on turnover and mineralization. Through a series of five trials in normally loaded female mice (n = 56/trial), analysis of trabecular volume fraction and connectivity using microcomputed tomography, along with biomechanical testing, quantitative histomorphometry, and compositional analysis, was used to select 45 microg/kg ZOL and 500 microg/kg OPG as doses that satisfy these criteria. These doses were then examined for their ability to mitigate bone loss following short-term unloading through hindlimb suspension (HLS). Seventy-two mice were prophylactically administered ZOL, OPG, or PBS and assigned to loaded control or 2-wk HLS groups (n = 12 for each of 6 groups). Both anti-resorptives were able to preserve trabecular microarchitecture and femoral elastic and maximum force in HLS mice (+30-40% ZOL/OPG vs. PBS). In HLS mice, anti-resorptive dosing reduced resorption perimeter at the femoral endocortical surface by 30% vs. PBS. In loaded control mice, anti-resorptives produced no change in bone formation rate; however, reductions in bone formation rate brought about by HLS were exacerbated by anti-resorptive treatment, suggesting synergistic inhibition of osteoblasts during disuse. Refined anti-resorptive dosing will tend to target countermeasures to the period of disuse, resulting in faster recovery and less adverse effects for astronauts.

Osteoporosis in men: its pathophysiology and the role of teriparatide in its treatment

As the population ages, the burden of osteoporosis in men is expected to rise. Implementation of preventive measures such as falls prevention strategies, exercise and adequate calcium and vitamin D intake is recommended. However, when the diagnosis of osteoporosis is made, effective treatments need to be initiated to prevent fractures. As opposed to postmenopausal women, reduced bone formation is the predominant mechanism of age-related bone loss in men, making anabolic agents a logical treatment option for men with osteoporosis. Teriparatide is the only anabolic agent currently approved for treatment of osteoporosis in men. This paper summarizes the mechanism of action of teriparatide, as well as its tolerability and safety. Furthermore, the evidence supporting the efficacy of teriparatide treatment in men with osteoporosis is reviewed and its current role in the management of osteoporosis in men is discussed.

Biochemical assessment of bone turnover and bone fragility in men

Osteoporosis in men is less studied than in women. Few data concern biochemical bone turnover markers (BTM) in men and their potential use.

METHODOLOGY

We evaluated papers concerning BTM in men cited on Medline. Selection of studies were based on the number of subjects, age range, group homogeneity, follow-up duration, number of BTM.

RESULTS

BTM levels are high in young men, then decrease with age. In elderly men, bone resorption increases with age more than bone formation. Variability of individual values is high and their significance is unclear. In elderly men, BTM levels correlate negatively with bone mineral density suggesting that accelerated bone turnover underlies age-related bone loss. Data on the prediction of accelerated bone loss and fractures by BTM in men are scant. Testosterone treatment induces a decrease in bone resorption followed by a decrease in bone formation. Bisphosphonates and calcitonin decrease BTM levels in osteoporotic men. Parathyroid hormone 1-34 and growth hormone induce a rapid increase in bone turnover followed by a progressive slowdown.

CONCLUSIONS

Few studies concern BTM in men. Currently available data are not sufficient to suggest guidelines for the practical use of BTM in the clinical management of the osteoporosis in elderly men.

The effects of combination of alendronate and human parathyroid hormone(1-34) on bone strength are synergistic in the lumbar vertebra and additive in the femur of C57BL/6J mice

A cyclic PTH regimen is as effective as a daily regimen on bone density gain in humans and in improving bone quality in mice. Our previous murine study evaluated the effects of a cyclic PTH regimen in the absence of a bisphosphonate, whereas our human study addressed the effects of a cyclic PTH regimen in the presence of ongoing alendronate (ALN) treatment. Accordingly, the current study examined the effects of cyclic or daily PTH regimens in combination with ALN on bone quality and bone density in mice. Twenty-week-old, female C57BL/6J mice were treated with the following sc injections (n = 10): 1) vehicle for 5 d/wk (control); 2) ALN (20 microg/kg x d) 3 d/wk (ALN); 3) human PTH(1-34) (40 microg/kg x d) 5 d/wk (daily PTH); 4) daily PTH in addition to ALN (daily PTH plus ALN); 5) PTH 5 d/wk and vehicle 5 d/wk alternating weekly (cyclic PTH); 6) cyclic PTH in addition to ALN (cyclic PTH plus ALN); and 7) PTH and ALN alternating weekly (alt PTH and ALN). Bone mineral density was measured weekly by dual-energy x-ray absorptiometry, and at 7 wk, bone markers, bone structure, and bone strength were evaluated by biochemical assays, peripheral quantitative computed tomography and mechanical testing, respectively. At 7 wk, all treatments significantly increased femoral and vertebral bone mineral density. ALN slightly decreased endosteal circumference, whereas PTH increased periosteal circumference, resulting in significant increases in femoral cortical thickness in all groups. PTH and ALN enhanced bone strength synergistically in the lumbar vertebrae and additively in the femur. Combined therapy, however, had no effects on bone markers. The results show that combinations of ALN and PTH, in both daily and cyclic regimens, produce more beneficial effects than treatment with either agent alone, suggesting that the mechanisms of actions of ALN and PTH on bone quality may be complementary.

Drug insight: the use of bisphosphonates for the prevention and treatment of osteoporosis in men

Osteoporosis has long been recognized as a disease affecting postmenopausal women but it has become increasingly clear that men are affected by low bone density and suffer the consequences of osteoporotic fractures. Men attending clinical urological practices might be at raised risk of bone loss due to hypogonadism, either identified during work-up of erectile dysfunction or induced by androgen deprivation therapy for treatment of prostate cancer. The availability of bisphosphonate drugs with proven efficacy in fracture reduction has revolutionized osteoporosis therapy in the past decade. The use of these agents has been traditionally based on data obtained predominantly from postmenopausal women and cases of glucocorticoid-induced osteoporosis, but data are becoming increasingly available to justify their use in men. Despite the availability and favorable safety profile of bisphosphonates, many patients are not receiving therapy. This article serves to review the data regarding bisphosphonate use in men, discussing particularly the pharmacology and mechanisms of action of these agents, and findings from clinical studies supporting their use for fracture prevention.

PINP: a serum biomarker of bone formation in the rat

Serum PINP has emerged as a reliable marker of bone turnover in humans and is routinely used to monitor bone formation. However, the effects of PTH (1-34) on bone turnover have not been evaluated following short-term treatment. We present data demonstrating that PINP is an early serum biomarker in the rat for assessing bone anabolic activity in response to treatment with PTH (1-38). Rat serum PINP levels were found to increase following as few as 6 days of treatment with PTH (1-38) and these increases paralleled expression of genes associated with bone formation, as well as, later increases in BMD. Additionally, PINP levels were unaffected by treatment with an antiresorptive bisphosphonate. PINP may be used to detect PTH-induced early bone formation in the rat and may be more generally applicable for preclinical testing of potential bone anabolic drugs.

Update in osteoporosis and metabolic bone disorders

Considerable progress has been made in the development and testing of agents to treat osteoporosis. Most impressive are reports on new antiresorptive agents--both bisphosphonates (ibandronate and zoledronic acid) and monoclonal antibodies (MAbs) (denosumab) directed against receptor activator of nuclear factor kappaB-ligand, a key molecule in the control of commitment and activation of osteoclasts. Bisphosphonates promise convenience and potency at slowing bone loss, whereas denosumab offers powerful suppression of resorption and rapid offset of action. Attention is also shifting from the osteoclast as a target for new therapies to the osteoblast and the osteocyte, with its complex network within the depths of bone. Wnt signaling through the frizzled receptor and its coreceptor, the low-density lipoprotein receptor related protein-5, appears from both molecular and in vivo evidence to be a pivotal pathway for modulating osteoblastic activity, bone formation, and bone strength. The recently identified product of the SOST gene or sclerostin has also been shown to block Wnt signaling. Sclerostin is produced by the osteocytes buried in the bone and is a new target to treat bone loss. Clinical trial reports indicate that the calcimimetic cinacalcet can effectively treat PTH hypersecretion due to primary and secondary hyperparathyroidism and parathyroid carcinoma. Lastly, it is now recognized that the matrix protein dentin matrix protein-1 enhances the release of the phosphate-regulating factor fibroblast growth factor 23 and that mutations in dentin matrix protein-1 play a causative role in a form of hypophosphatemic rickets.