The addition of a raloxifene analog (LY117018) allows for reduced PTH(1-34) dosing during reversal of osteopenia in ovariectomized rats

Risedronate did not block the maximal anabolic effect of PTH in aged rats

The study was designed to investigate if pre-treating rats with a therapeutic equivalent dose of risedronate blunted the anabolic effects of PTH, and whether a withdrawal period prior to PTH treatment would alter any effect of risedronate on PTH treatment. Skeletally mature rats were treated for 18 weeks with vehicle, risedronate, or risedronate for 8 weeks followed by vehicle for 10 weeks (withdrawal period). At the end of this period, animals were treated for a further 12 weeks with PTH or PTH vehicle. Trabecular and cortical bone mass were monitored by serial pQCT, or by DXA and microCT. Bone histomorphometry was performed on the proximal tibiae and tibial shafts for bone turnover parameters at week 40. Risedronate alone moderately increased while PTH alone markedly increased trabecular bone mass at the proximal tibial (35% and 200%, respectively) and lumbar vertebral body (14% and 36%, respectively). The maximum bone gains were similar with and without pretreatment with risedronate as compared to the PTH alone. Continuous administration of risedronate for 18 weeks prior to PTH treatment had lower percentage increases in proximal tibial BMD during the first 8 weeks of PTH treatments, and had lower active bone forming surface and bone formation rates after being treated with PTH 12 weeks as compared to the PTH alone group. However, with the 10-week withdrawal period, risedronate did not blunt the stimulatory effect of PTH on osteoblast activity as shown by similar bone formation rates as with PTH alone. Our findings suggest that while risedronate pretreatment may slow the bone anabolic response to PTH, a withdrawal period prior to PTH treatment allows osteoblastic activity to respond normally to PTH stimulation.

Infrequent delivery of a long-acting PTH-Fc fusion protein has potent anabolic effects on cortical and cancellous bone

Skeletal anabolism with PTH is achieved through daily injections that result in brief exposure to the peptide. We hypothesized that similar anabolic effects could be achieved with less frequent but more sustained exposures to PTH. A PTH-Fc fusion protein with a longer half-life than PTH(1-34) increased cortical and cancellous BMD and bone strength with once- or twice-weekly injections.

INTRODUCTION

The anabolic effects of PTH are currently achieved with, and thought to require, daily injections that result in brief exposure to the peptide. We hypothesized that less frequent but more sustained exposures to PTH could also be anabolic for bone, provided that serum levels of PTH were not constant.

MATERIALS AND METHODS

PTH(1-34) was fused to the Fc fragment of human IgG1 to increase the half-life of PTH. Skeletal anabolism was examined in mice and rats treated once or twice per week with this PTH-Fc fusion protein.

RESULTS

PTH-Fc and PTH(1-34) had similar effects on PTH/PTHrP receptor activation, internalization, and signaling in vitro. However, PTH-Fc had a 33-fold longer mean residence time in the circulation of rats compared with that of PTH(1-34). Subcutaneous injection of PTH-Fc once or twice per week resulted in significant increases in bone volume, density, and strength in osteopenic ovariectomized mice and rats. These anabolic effects occurred in association with hypercalcemia and were significantly greater than those achievable with high concentrations of daily PTH(1-34). PTH-Fc also significantly improved cortical bone volume and density under conditions where daily PTH(1-34) did not. Antiresorptive co-therapy with estrogen further enhanced the ability of PTH-Fc to increase bone mass and strength in ovariectomized rats.

CONCLUSIONS

These results challenge the notion that brief daily exposure to PTH is essential for its anabolic effects on cortical and cancellous bone. PTH-derived molecules with a sustained circulating half-life may represent a powerful and previously undefined anabolic regimen for cortical and cancellous bone.

Selective estrogen receptor modulators (SERMS)

Hormone receptors and, specifically, estrogen receptors were described about four decades ago. For estrogens, there are two receptors, estrogen receptor alpha (ERalpha) and estrogen receptor beta (ERbeta). The two receptors are coded by different genes and their tissue expression varies across organs. ERalpha is predominantly expressed in reproductive tissues (uterus, breast, ovaries) liver and central nervous system, whereas ERbeta is expressed in other tissues such as bone, endothelium, lungs, urogenital tract, ovaries, central nervous system and prostate. More than seventy molecules that belong to the SERMS class have been described. There are 5 chemical groups: triphenylethylenes, benzotiophenes, tetrahydronaphtylenes, indoles and benzopyrans. All of these non-hormonal compounds are capable of activating the ER, reduce bone turnover rate and, as an antiresorptive, clearly improve bone density. Estrogens reduce bone turnover rate and, as an antiresorptive, clearly improve bone density. They are also beneficial for the relief of menopausal symptoms. An ongoing debate that extends over the decades, relates to to overall benefit/risk profile of estrogen or estrogen-progestin therapy since these therapies can increase the risk of serious health disorders, such as breast cancer. SERMs have increased our understanding of hormone-receptor regulatory mechanisms. Their development has permitted a targeted efficacy profile avoiding some of the side effects of the hormone therapy. Their clinical utility relies today mostly on the effects on breast cancer and bone.

Selective estrogen receptor modulator inhibits osteocyte apoptosis during abrupt estrogen withdrawal: implications for bone quality maintenance

Estrogens exert positive effects on the quantity and quality of bone, including the maintenance of osteocytes through the inhibition of their apoptosis. Ideally, selective estrogen receptor modulators (SERMs) confer all of the positive bone-associated effects of estrogens without any adverse effects. In a similar way to estrogen, the raloxifene analog LY 117018 has been shown to prevent bone loss in ovariectomized (OVX) rats. In this study, we investigated whether the osteocyte-sparing effect of 17beta-estradiol can be mimicked by the SERM LY 117018 in a rat model of OVX. Twenty-four juvenile female rats were divided into four treatment groups: sham-operated (SHAM), OVX, OVX + 17beta-estradiol (OVX+E(2)), and OVX + LY 117018 (OVX+SERM). At 7 or 14 days following the start of treatment, the radius and ulna were removed. The percentage of apoptotic osteocytes, determined using an in situ nick-translation method, was increased (2.5-fold at 7 days and sixfold at 14 days) in the OVX group compared with SHAM in both the radius and ulna. Treatment of OVX animals with either 17beta-estradiol at a dose rate of 0.125 mg/kg/day or LY 117018 at a dose rate of 3 mg/kg/day prevented these increases in osteocyte apoptosis similarly. These observations demonstrate that LY 117018 exerts a powerful inhibitory effect upon osteocyte apoptosis directly after estrogen loss, in a similar way to the known effect of 17beta-estradiol replacement. These results point to the potential benefits of SERMs on both the quantity and quality of bone in E(2)-depleted rats.

Teriparatide [human PTH(1-34)]: 2.5 years of experience on the use and safety of the drug for the treatment of osteoporosis

Longer survival in cystic fibrosis has led to more bone complications. One hundred thirty-six young patients were studied for 12-24 months. Low BMD was found in 66%. Fat mass and lean mass were also reduced. Impaired pulmonary function and total steroid dose had the greatest negative influence on bone.

INTRODUCTION

Low BMD is reported as a frequent complication in adult patients affected by cystic fibrosis (CF), but the available data are less consistent for younger patients.

MATERIALS AND METHODS

This study was designed to evaluate BMD longitudinally over 12-24 months in a sample of 136 young patients (3-24 years of age) and to investigate its major determinants. BMC and body composition were also evaluated.

RESULTS

BMD (expressed as Z score) of spine and of total body was reduced in 66% of patients. The prevalence of low BMD was the same in children, adolescents, and young adults. The main determinants of BMD were forced expiratory volume in 1 s (FEV1; as an index of pulmonary function), puberty, platelet count (as an index of portal hypertension), and cumulative steroid dose. Changes of FEV1 over time influenced BMD changes. Bone mass, fat mass (FM) and fat-free (lean) mass (FFM) were reduced in CF patients at both total body and subregions (trunk, limbs). Lean mass influenced BMD of total body and lower limbs, whereas fat mass (and BMI) influenced spine BMD. FEV1 also influenced FFM.

CONCLUSIONS

Low BMD was present in a significant proportion of CF patients, independent of sex and age. BMD depended on pulmonary function, steroid dose, and presence of advanced liver disease. Pulmonary function and puberty were the main stimuli for the increase of BMD over time. CF also altered body composition, and FFM was influenced by pulmonary function.

Combination teriparatide and raloxifene therapy for postmenopausal osteoporosis: results from a 6-month double-blind placebo-controlled trial

We compared combination treatment with teriparatide plus raloxifene with teriparatide alone in women with postmenopausal osteoporosis in a 6-month double-blind, placebo-controlled trial that measured biochemical markers of bone turnover and BMD. Markers of bone formation and spine BMD increased similarly with teriparatide alone and combination therapy. However, combination therapy induced a significantly smaller increase in bone resorption versus teriparatide alone and significantly increased total hip BMD versus baseline.

INTRODUCTION

The effects of combining two approved treatments for osteoporosis with different modes of action were examined by comparing teriparatide [rhPTH(1-34)] monotherapy with combination teriparatide and raloxifene therapy.

MATERIALS AND METHODS

A 6-month randomized, double-blind trial comparing teriparatide plus raloxifene (n = 69) versus teriparatide plus placebo (n = 68) was conducted in postmenopausal women with osteoporosis.

RESULTS

Bone formation (N-terminal propeptide of type 1 collagen [PINP]) increased similarly in both treatment groups. However, the increase in bone resorption (serum C-terminal telopeptide of type I collagen [CTx]) in the combination group was significantly smaller than in the teriparatide-alone group (p = 0.015). Lumbar spine BMD significantly increased 5.19 +/- 0.67% from baseline in the teriparatide-alone group. In the combination group, lumbar spine (6.19 +/- 0.65%), femoral neck (2.23 +/- 0.64%), and total hip (2.31 +/- 0.56%) BMD significantly increased from baseline to study endpoint, and the increase in total hip BMD was significantly greater than in the teriparatide-alone group (p = 0.04). In the teriparatide-alone group, mean serum calcium levels increased from baseline to endpoint (0.30 +/- 0.06 mg/dl, p < 0.001), whereas mean serum phosphate remained unchanged. In the combination group, mean serum calcium was unchanged, and mean serum phosphate decreased (-0.20 +/- 0.06 mg/dl, p < 0.001) from baseline to endpoint. Changes in serum calcium (p < 0.001) and phosphate (p < 0.004) were significantly different between treatment groups. The safety profile of combination therapy was similar to teriparatide alone.

CONCLUSIONS

Combination therapy increased bone formation to a similar degree as teriparatide alone. However, the increase in bone resorption was significantly less and total hip BMD significantly increased for combination therapy compared with teriparatide alone. Combination treatment with raloxifene may thus enhance the bone forming effects of teriparatide. Further studies over longer treatment duration that include fracture endpoints are necessary to fully ascertain the clinical significance of combination raloxifene plus teriparatide therapy in postmenopausal osteoporosis.

Therapeutic potential of oestrogen receptor ligands in development for osteoporosis

Accelerated bone loss secondary to loss of ovarian function at menopause is well recognised as a major risk factor for osteoporotic fractures in postmenopausal women. Postmenopausal bone loss can be prevented or arrested by oestrogen replacement therapy (ERT). It has also been reported that ERT protects against cardiovascular disease by improving the serum lipid profile, however there are mixed reports concerning these benefits. Unopposed ERT causes an unacceptable increase in the risk of endometrial cancer and proliferative effects in mammary tissue resulting in an increased risk of breast cancer. While this can be counteracted by combining ERT with a low-dose of a progestin, withdrawal bleeding and the continuing uncertainty about the effect of oestrogen on the risk of breast cancer contribute to poor compliance for long-term use. Because of the known and suspected risks of oestrogen therapy it has been estimated that in the US < 40% of women on ERT will continue treatment beyond one year. An ideal therapy would retain the desirable skeletal and cardiovascular effects of oestrogen, lack oestrogenic activity on the endometrium and reduce the incidence of breast cancer. The concept of selective oestrogen receptor modulation (SERM) has been demonstrated for a number of compounds including tamoxifen, raloxifene, droloxifene, GW-5638 and levormeloxifene. However, the clinical utility of these agents will depend on the profile of tissue-specific effects and the extent to which they are translated into in vivo efficacy. A SERM is defined as a compound that has oestrogen agonism on one or more of the desired target tissues, such as bone or liver, and has antagonism and/or minimal agonism (i.e., clinically insignificant) in reproductive tissue, such as the breast or uterus. Although tamoxifen acts as a SERM, it is also associated with an increased incidence (4% gynaecological symptoms greater than placebo control) of endometrial cancer. Indeed, there have been a number of mechanistic-based studies to explain the increased incidence of endometrial carcinomas in tamoxifen treated patients, which provide an in vitro insight into the adverse clinical observations in vivo. Attempts to improve on the pharmacological profile of tamoxifen have resulted in compounds that differ in their oestrogen agonist/antagonist characteristics, including the pure oestrogen antagonists. This suggests that it may be possible to develop a molecule with a desired profile of tissue-specific agonist/antagonist activities by establishing bone and cardiovascular protective effects but having no effects (or even behaving as an antagonist) in the reproductive tissues.

Effect of raloxifene and its interaction with human PTH on bone formation

We studied the of effects raloxifene alone or in combination with human PTH (hPTH) 1-34 in mineralizing cultures of SaOS-2 cells. Raloxifene (10(-8)-10(-6) M) increased bone nodule formation in cultures of SaOS-2 cells when added intermittently from day 8 to day 17. A single 24-h treatment with 10(-8) M hPTH (1-34) at day 8 reduced the nodule area by 75.6% at day 17, and raloxifene added concomitantly with hPTH (1-34) reduced this inhibitory effect in a dose-dependent manner. Raloxifene also reduced the hPTH (1-34)-induced inhibition of alkaline phosphatase (ALP) activity. The 10-fold stimulation of c-fos mRNA expression by hPTH (1-34) was not influenced by raloxifene co-treatment. The protein kinase A (PKA) inhibitor 6-22 amide (1.7 nM) and the protein kinase C (PKC) inhibitor-bisindolylmaleimide 1 (10 nM) did not influence the separate effects of PTH and raloxifene on mineralized bone nodule formation. This is the first report on the interaction of PTH and raloxifene in an osteoblast culture system.

Bone growth stimulators. New tools for treating bone loss and mending fractures

In the new millennium, humans will be traveling to Mars and eventually beyond with skeletons that respond to microgravity by self-destructing. Meanwhile in Earth's aging populations growing numbers of men and many more women are suffering from crippling bone loss. During the first decade after menopause all women suffer an accelerating loss of bone, which in some of them is severe enough to result in "spontaneous" crushing of vertebrae and fracturing of hips by ordinary body movements. This is osteoporosis, which all too often requires prolonged and expensive care, the physical and mental stress of which may even kill the patient. Osteoporosis in postmenopausal women is caused by the loss of estrogen. The slower development of osteoporosis in aging men is also due at least in part to a loss of the estrogen made in ever smaller amounts in bone cells from the declining level of circulating testosterone and is needed for bone maintenance as it is in women. The loss of estrogen increases the generation, longevity, and activity of bone-resorbing osteoclasts. The destructive osteoclast surge can be blocked by estrogens and selective estrogen receptor modulators (SERMs) as well as antiosteoclast agents such as bisphosphonates and calcitonin. But these agents stimulate only a limited amount of bone growth as the unaffected osteoblasts fill in the holes that were dug by the now suppressed osteoclasts. They do not stimulate osteoblasts to make bone--they are antiresorptives not bone anabolic agents. (However, certain estrogen analogs and bisphosphates may stimulate bone growth to some extent by lengthening osteoblast working lives.) To grow new bone and restore bone strength lost in space and on Earth we must know what controls bone growth and destruction. Here we discuss the newest bone controllers and how they might operate. These include leptin from adipocytes and osteoblasts and the statins that are widely used to reduce blood cholesterol and cardiovascular damage. But the main focus of this article is necessarily the currently most promising of the anabolic agents, the potent parathyroid hormone (PTH) and certain of its 31- to 38-aminoacid fragments, which are either in or about to be in clinical trial or in the case of Lilly's Forteo [hPTH-(1-34)] tentatively approved by the Food and Drug Administration for treating osteoporosis and mending fractures.

Parathyroid hormone in the treatment of osteoporosis

Parathyroid hormone (PTH), especially intact human PTH [hPTH(1-84)] and its various fragments [hPTH(1-31), (1-34), (1-36), (1-38) and their modifications], has been used for the treatment of osteoporosis over the last 10 years. Although chronic continuous excess of PTH markedly increases bone resorption, as seen in the typical example of primary hyperparathyroidism and osteitis fibrosa generalisata, intermittent PTH administration has been found to stimulate bone formation in animals, providing a basis for the use of PTH as a therapeutic agent for osteoporosis. In addition to dramatically increasing trabecular bone density and also sustaining cortical bone density, PTH administration increases bone strength and reduces the fracture rate, despite occasional increases in cortical porosity. Administration of PTH in combination with antiresorptive agents such as estrogen, calcitonin, vitamin D and bisphosphonates augments its effect. Because of its bone anabolic action, PTH is expected to be effective for osteoporosis in those of advanced age with suppressed bone remodelling, which might not respond favourably to antiresorptive agents.

OPG and PTH-(1-34) have additive effects on bone density and mechanical strength in osteopenic ovariectomized rats

PTH is a potent bone anabolic factor, and its combination with antiresorptive agents has been proposed as a therapy for osteoporosis. We tested the effects of PTH, alone and in combination with the novel antiresorptive agent OPG, in a rat model of severe osteopenia. Sprague Dawley rats were sham-operated or ovariectomized at 3 months of age. Rats were untreated for 15 months, at which time ovariectomy had caused significant decreases in bone mineral density in the lumbar vertebrae and femur. Rats were then treated for 5.5 months with vehicle (PBS), human PTH-(1-34) (80 microg/kg), rat OPG (10 mg/kg), or OPG plus PTH (all three times per wk, sc). Treatment of ovariectomized rats with OPG or PTH alone increased bone mineral density in the lumbar vertebrae and femur, whereas PTH plus OPG caused significantly greater and more rapid increases than either therapy alone (P < 0.05). OPG significantly reduced osteoclast surface in the lumbar vertebrae and femur (P < 0.05 vs. sham or ovariectomized), but had no effect on osteoblast surface at either site. Ovariectomy significantly decreased the mechanical strength of the lumbar vertebrae and femur. In the lumbar vertebrae, OPG plus PTH was significantly more effective than PTH alone at reversing ovariectomy-induced deficits in stiffness and elastic modulus. These data suggest that OPG plus PTH represent a potentially useful therapeutic option for patients with severe osteoporosis.

Osteocyte and osteoblast apoptosis and excessive bone deposition accompany failure of collagenase cleavage of collagen

Mice carrying a targeted mutation (r) in Col1a1, encoding a collagenase-resistant form of type I collagen, have altered skeletal remodeling. In hematoxylin and eosin-stained paraffin sections, we detect empty lacunae in osteocytes in calvariae from Col1a1(r/r) mice at age 2 weeks, increasing through age 10-12 months. Empty lacunae appear to result from osteocyte apoptosis, since staining of osteocytes/periosteal osteoblasts with terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling is increased in Col1a1(r/r) relative to wild-type bones. Osteocyte perilacunar matrices stained with Ab that recognizes collagenase collagen alpha1(I) chain cleavage ends in wild-type but not Col1a1(r/r) calvariae. Increased calvarial periosteal and tibial/femoral endosteal bone deposition was found in Col1a1(r/r) mice from ages 3-12 months. Calcein labeling of calvarial surfaces was increased in Col1a1(r/r) relative to wild-type mice. Daily injections of synthetic parathyroid hormone for 30 days increased calcein-surface labeling in wild-type but caused no further increase in the already high calcein staining of Col1a1(r/r) bones. Thus, failure of collagenase cleavage of type I collagen in Col1a1(r/r) mice is associated with osteocyte/osteoblast death but increases bone deposition in a manner that mimics the parathyroid hormone-induced bone surface activation seen in wild-type mice.

The parathyroid hormone, its fragments and analogues--potent bone-builders for treating osteoporosis

As populations age a rising number of men and women, but especially women during the first decade after menopause, become victims of a severe, accelerated loss of bone with crippling fractures known as osteoporosis. This often results in costly, prolonged hospitalisation and perhaps indirectly, death. Osteoporosis in women is caused by the menopausal oestrogen decline, which removes several key restraints on the generation, longevity and activity of bone-resorbing osteoclasts. Although there are many antiresorptive drugs on or coming onto the market (calcitonin, bisphosphonates, oestrogen and SERMS) that can slow or stop further bone loss, there are none that can restore lost bone mechanical strength by directly stimulating osteoblast activity and bone growth. However, there is a family of potent bone-building peptides, namely the 84 amino acid parathyroid hormone (PTH). Its 31 to 38 amino acid N-terminal fragments are currently in or about to enter clinical trials. We can predict that these peptides will be effective therapeutics for osteoporosis especially when supplemented with bisphosphonates or SERMs to protect the new bone from osteoclasts. These peptides should also accelerate the healing of fractures in persons of all ages and restore lost bone mass and mechanical strength to astronauts following their return to earth after long voyages in space.