Biochemical responses to sequential human parathyroid hormone (1-38) and calcitonin in osteoporotic patients

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.

Teriparatide (recombinant human parathyroid hormone 1-34) in postmenopausal women with osteoporosis: systematic review

CONTEXT AND OBJECTIVE

Osteoporosis is defined as a disease characterized by low bone mass and deterioration of the bone tissue microarchitecture. Teriparatide stimulates the formation and action of osteoblasts, which are responsible for bone formation, thus promoting bone tissue increase. The aim was to assess the effectiveness and safety of teriparatide for treating postmenopausal osteoporosis.

METHODS

A systematic review was conducted using the Cochrane Collaboration methodology.

RESULTS

1) Teriparatide 20 microg or 40 microg versus placebo: there was a benefit from teriparatide, considering the following outcomes: reduction in the number of new vertebral and non-vertebral fractures, and increased whole-body, lumbar and femoral bone mineral density. 2) Teriparatide 40 microg versus alendronate 10 mg/day for 14 months: there was no statistical difference regarding the incidence of new vertebral or non-vertebral fractures, although in the group that received teriparatide there was greater bone mineral density increase in the whole body, lumbar column and femur. 3) Estrogen plus teriparatide 25 microg versus estrogen: there was a benefit, considering the following outcomes: reduction in the number of new vertebral fractures, and increased whole-body, lumbar and femoral bone mineral density after three years.

CONCLUSIONS

When teriparatide is intermittently administered in low doses, it reduces the incidence of vertebral fractures (67%) and non-vertebral fractures (38%) and increases bone mineral density in the lumbar column and femur. There is a need for studies with longer observation in order to allow conclusions regarding the safety and duration of the therapeutic effects.

HMG CoA reductase inhibitors and the skeleton: a comprehensive review

Recent studies suggest that the mevalonate pathway plays an important role in skeletal metabolism. HMG CoA reductase inhibitors ("statins"), which inhibit a key enzyme in the mevalonate pathway, are widely used for the treatment of hyperlipidemia. In vitro and animal studies demonstrate that statins stimulate the production of BMP-2, a potent regulator of osteoblast differentiation and activity, suggesting that statins may have an anabolic effect on bone. Statin use in most, but not all observational studies is associated with a reduced risk of fracture, particularly hip fracture, even after adjustment for the confounding effects of age, weight and other medication use. This beneficial effect has not been observed in clinical trials designed to assess cardiovascular endpoints. The effects of statins on bone mass and bone turnover are controversial, but increased bone mass and reduced bone turnover have been observed in controlled studies. Further studies of the skeletal effects of statins are needed, particularly their effects on surrogate markers such as bone mass, bone turnover, and microarchitecture, to determine the optimal formulation, dosing and route of administration. Clinical trials with fracture endpoints are needed before statins can be recommended as therapeutic agents for osteoporosis.

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.

Parathyroid Hormone, Its Fragments and Their Analogs for the Treatment of Osteoporosis

The susceptibility to traumatic fracturing of osteopenic bones, and the spontaneous fracturing of osteoporotic bones by normal body movements caused by the microstructural deterioration and loss of bone, are currently treated with antiresorptive drugs, such as the bisphosphonates, calcitonin, estrogens, and selective estrogen receptor modulators. These antiresorptive agents target osteoclasts and, as their name indicates, reduce or stop bone resorption. They cannot directly stimulate bone formation, increase bone mass above normal values in ovariectomized rat models, or improve microstructure. However, there is a family of agents - the parathyroid hormone (PTH) and some of its fragments and their analogs - which directly stimulate bone growth and improve microstructure independently from impairing osteoclasts. These drugs are about to make their clinical debut in treating patients with osteoporosis and, probably not too far in the future, for accelerating fracture healing. They stimulate osteoblast accumulation and bone formation in three ways via signals from the type 1 PTH/PTH-related protein (PTHR1) receptors on proliferatively inactive preosteoblasts, osteoblasts, osteocytes and bone-lining cells. The receptor signals shut down the proliferative machinery in preosteoblasts and push their maturation to osteoblasts, cause the osteoblastic cells to make and secrete several factors that stimulate the extensive proliferation of osteoprogenitors without PTHRI receptors, stimulate the reversion of bone-lining cells to osteoblasts, and extend osteoblast lifespan and productivity by preventing them from suicidally initiating apoptosis. The first of the PTHs to reach the clinic will be teriparatide [recombinant human (h)PTH-(1-34)], which was recommended for approval in 2001 by the US Food and Drug Administration Endocrinology and Metabolic Drugs Advisory Committee for the treatment of postmenopausal osteoporosis. Teriparatide has been shown to considerably increase cancellous and cortical bone mass, improve bone microstructure, prevent fractures and thus provide benefits that cannot be provided by current antiresorptive drugs, when administered subcutaneously at a daily dose of 20 microg for no longer than 2 years to patients with osteoporosis.

Continuous parathyroid hormone and estrogen administration increases vertebral cancellous bone volume and cortical width in the estrogen-deficient rat

Generally, it is believed that intermittent administration of parathyroid hormone (PTH) has an anabolic effect on the skeleton, whereas continuous administration is catabolic. However, there is evidence that continuous exposure to PTH may have an anabolic effect, for example, in patients with mild primary hyperparathyroidism (PHPT). The possibility of delivering PTH continuously may have important implications for the treatment of osteoporosis. Furthermore, estrogen treatment may be useful in the medical management of PHPT. Therefore, we examined the skeletal effects of continuous administration of PTH, with or without estrogen, in the estrogen-deficient rat with established osteopenia. Forty 7-month-old SD rats were divided into four ovariectomy (OVX) groups and one sham-operated group. Eight weeks post-OVX, three groups received subcutaneous implants of Alzet mini pumps loaded with PTH(1-34) (30 microg/kg per day), 17beta-estradiol (10 microg/kg per day) pellet, or both PTH and 17beta-estradiol separately for 4 weeks. OVX and sham control groups were given the mini pumps loaded with vehicle. Two doses of calcein (10 mg/kg) were given subcutaneously to all rats 2 days and 8 days before death. Histomorphometry was performed on cancellous and cortical bone of the fourth lumbar vertebra. At 3 months, post-OVX rats displayed bone loss with high bone turnover. Estrogen reversed OVX-mediated high turnover without restoring cancellous bone volume (BV/TV). PTH infusion further increased bone turnover and partially restored BV/TV. However, PTH infusion increased cortical porosity. Estrogen inhibited PTH-mediated cancellous bone resorption and substantially increased BV/TV above sham control. The combined treatment was associated with a significant increase in peritrabecular fibrosis and woven bone formation. The combined treatment of PTH infusion and estrogen replacement enhanced cortical width but estrogen did not prevent the PTH-induced cortical tunneling. We conclude that continuous administration of PTH and estrogen increases cortical porosity but has substantial beneficial effects on vertebral cancellous bone volume and cortical width in OVX rats.

Direct measurement of hormone-induced acidification in intact bone

Previous findings have shown that osteoblasts respond to parathyroid hormone (PTH) with an increase in extracellular acidification rate (ECAR) in addition to the known effect of PTH to increase local acidification by osteoclasts. We, therefore, investigated use of the Cytosensor to measure the ECAR response of whole intact bone to PTH employing microphysiometry. The Cytosensor measures a generic metabolic increase of cells to various agents. Using neonatal mouse calvaria, we found that the area surrounding the sagittal suture was particularly responsive to PTH. In this bone, the increase in ECAR was slower to develop (6 minutes) and more persistent than in cultured human osteoblast-like SaOS-2 cells and was preceded by a brief decrease in ECAR. Salmon calcitonin also produced an increase in ECAR in this tissue but with a different pattern than that elicited by PTH. Because PTH stimulates osteoclastic bone resorption in mouse calvaria via a cyclic adenosine monophosphate (cAMP)-mediated mechanism, we showed that the adenylyl cyclase activator forskolin also stimulated ECAR in this tissue. When the protein kinase A (PKA) pathway was activated by maintaining a high intracellular concentration of cAMP using N6-2'-0-dibutyryladenosine-cAMP (db-cAMP), there was a reduction of PTH-induced acidification, while isobutylmethylxanthine pretreatment potentiated the PTH-induced acidification, consistent with a PKA-mediated pathway. Thapsigargin and the protein kinase C (PKC) activator phorbol myristate acetate had no effect on the PTH-induced increase in ECAR in calvaria, indicating that PKC does not play a major role in the ECAR response in intact bone. These results indicate the utility of using microphysiometry to study ECAR responses in intact tissue and should enable elucidation of the relative importance of extracellular acidification by osteoblasts and osteoclasts to the anabolic and catabolic activities of PTH, respectively.

Ca(2+) and extracellular acidification rate responses to parathyroid hormone fragments in rat ROS 17/2 and human SaOS-2 cells

To examine the importance of the N- or C-termini of PTH(1-34) the effects of truncated fragments of PTH on human receptors in osteoblast-like SaOS-2 cells and rat receptors in rats ROS 17/2 cells were examined. Fura-2-loaded cells were used to monitor cytosolic free Ca(2+) concentration ([Ca2+]i), and the Cytosensor microphysiometer was used to monitor extracellular acidification rate (ECAR). C-terminally truncated fragments (1-31) and (1-28) of hPTH(1-34)NH(2) stimulated an increase in [Ca(2+)](i) and ECAR in both cell lines. hPTH(3-34)NH(2) and other N-terminally truncated fragments did not stimulate [Ca(2+)](i) or ECAR in either cell type. The signal transduction pathway of PTH-induced ECAR in ROS 17/2 cells was investigated to compare with previous results in SaOS-2 cells. Potentiation by IBMX, attenuation by 8Br-cAMP and lack of effect of the PKC inhibitor chelerythrine chloride support a cAMP/PKA-mediated signal transduction pathway in ROS 17/2, while the protein kinase C pathway was predominant in SaOS-2 cells. We conclude that the intact N-terminus of PTH is essential in PTH signaling mediated via either the cAMP/PKA or inositol lipid/Ca(2+)/PKC pathways in osteoblast-like cells.

Advantages of concurrent use of anabolic and antiresorptive agents over single use of these agents in increasing trabecular bone volume, connectivity, and biomechanical competence of rat vertebrae

The purpose of this study was to evaluate the usefulness of a combination regimen of anabolic and antiresorptive agents in increasing skeletal quantity and quality in comparison to a single-drug regimen with these agents. We examined histomorphometrically and biomechanically the effects of separate and combined administration of intermittent parathyroid hormone (PTH) and estrogen or bisphosphonate on both axial and appendicular skeletons of male Wistar rats, which were 4 months old and weighed approximately 300 g at the beginning of the treatment. The animals were untreated or injected with vehicle, recombinant human PTH(1-84) (PTH; 100 microg/kg daily), 17beta-estradiol (E2, 500 microg/kg every other day), incadronate disodium (YM175, 80 microg/kg every other day), combined PTH and E2 (PTH + E2), or a combination of PTH and YM175 (PTH + YM175). After 1 month of treatment, the three groups in which PTH was administered (PTH, PTH + E2, and PTH + YM175) had significantly higher trabecular bone volume and connectivity in the proximal tibial metaphyses (PTMs) compared with the untreated and vehicle-treated groups, whereas only combination groups (PTH + E2 and PTH + YM175) showed significant increases in these indices in the lumbar vertebrae. This site-related discrepancy was attributed to the fact that PTH significantly elevated bone resorption not in the PTMs but in the vertebrae. This increased bone resorption in the vertebrae was suppressed by the addition of an antiresorptive agent. As a result, trabecular bone mass, connectivity, and mechanical strength of the vertebrae were significantly increased from control levels only in the concurrent treatment groups (PTH + E2 and PTH + YM175). The superior skeletal effects of PTH cotherapy over PTH monotherapy were not seen with regard to bone mass, but with increased connectivity and mechanical strength. The concurrent use of PTH and an antiresorptive agent has been shown to be superior to the single use of PTH for enhancing these properties of rat vertebrae, which encourages future research, especially in larger animals.

The role of parathyroid hormone in the pathogenesis, prevention and treatment of postmenopausal osteoporosis

Parathyroid hormone (PTH) is the principal regulator of bone remodeling in the adult skeleton. The acute in vivo effect of PTH is to increase bone resorption, although sustained increases in its circulating levels accelerate both formation and resorption. These divergent effects have focused attention on PTH as a factor contributing to bone loss in some postmenopausal women, as well as interest in its role as therapy for the disease. Sustained increases in PTH are classically seen in primary hyperparathyroidism. While still controversial, increasing evidence suggests that primary hyperparathyroidism is associated with increased rates of bone loss, particularly from cortical sites in the skeleton. It is clear that the remodeling space is increased in primary hyperparathyroidism, and that surgical correction of the disease leads to substantial increases in bone mass in patients with osteoporosis. Recently, secondary hyperparathyroidism has emerged as an important contributor to increased rates of bone turnover and bone loss in postmenopausal women. The etiology of secondary hyperparathyroidism in postmenopausal women is complex, and is probably related to alterations in vitamin D metabolism and tissue responsiveness to 1,25(OH)2vitamin D. PTH has emerged at the forefront of anabolic therapies for the treatment of postmenopausal osteoporosis. When given as a single agent, intermittent daily subcutaneous administration of PTH induces consistent gains in trabecular bone mass with more varying effects on the cortical envelope. However, recent therapeutic trials employing a second agent, most notably estrogen, give hope that this approach may provide the first truly efficacious anabolic therapy for this devastating disease.

Truncation of the amino terminus of PTH alters its anabolic activity on bone in vivo

In vitro studies of parathyroid hormone (PTH) structure and function have suggested that the anabolic effect of PTH on bone requires the presence of amino acid residues 28-34 (domains for protein kinase C activation and mitogenic activity), but not amino acid residues 1-7 (adenylate cyclase activation domain). We have tested this hypothesis with in vivo studies of human PTH (hPTH) analogs. Serum biomarkers and selected histomorphometric parameters of bone formation and resorption were assessed in adult, female, Sprague-Dawley rats following 19 daily injections of vehicle, 10 micrograms/kg body weight (bw) of hPTH(1-38), or a dose range of 10, 40, and 100 micrograms/100 g bw of hPTH(2-38) or hPTH(3-38). Treatment with hPTH(1-38) increased serum osteocalcin, the percentage of osteoblast surface, percentage of osteoid surface, percentage of bone volume, trabecular thickness, and bone formation rate, while it decreased the percentage of osteoclast surface. The hPTH(2-38) fragment exhibited 10%-25% of the in vivo anabolic activity of hPTH(1-38), while it had no effect on the percentage of osteoclast surface. The hPTH(3-38) fragment exhibited no biological activity on bone. In contrast, serum INS-PTH (intact-N-terminal specific PTH) levels were similarly and significantly increased above control in rats treated with hPTH(1-38), hPTH(2-38), or hPTH(3-38) at the same dose. This preliminary finding suggests that the differential activity of these peptides on bone is not due to differences in the circulating level of immunoreactive PTH (intact and amino-terminal fragments of PTH from endogenous and exogenous sources) several hours after PTH injection. However, we can draw no conclusion regarding the relative clearance rates of these peptides. Last, because hPTH(3-38) was without any detectable biological activity on rat bone in vivo, its mitogenic activity was confirmed in two osteoblast-like cell lines. In summary, the anabolic effect of hPTH(1-38) on bone in vivo was (1) diminished by removal of amino acid residue 1, and (2) abolished by the removal of amino acid residues 1 and 2. Although these findings suggest that the therapeutic benefits of exogenous PTH administration may depend upon activation of not only protein kinase C, but also adenylate cyclase, they do not rule out a differential PTH response due to other causes, e.g., metabolic inactivation.

Effect of parathyroid hormone (hPTH[1-34]) infusion on serum 1,25-dihydroxyvitamin D and parathyroid hormone in normal women

Calcium absorption declines with age. Because 1,25-dihydroxyvitamin D (1,25(OH)2D) is the major hormone controlling calcium absorption, changes in vitamin D metabolism may account for the malabsorption of aging. Serum levels of 1,25(OH)2D have been reported to either decrease or remain unchanged with age. To assess the effect of aging on renal production of 1,25(OH)2D, we evaluated the response of renal 25OHD 1 alpha hydroxylase to human parathyroid hormone (hPTH(1-34) stimulation in 119 women ages 25-83 years. In this population, baseline serum 25OHD and 1,25(OH)2D values did not significantly change with age, but serum iPTH (r = 0.44; p < 0.001) and serum creatinine (r = 0.31; p < 0.01) increased with age. However, the stimulatory activity of hPTH(1-34) on the renal production of 1,25(OH)2D declined with age (r3 = -0.36; p < 0.001) and was most apparent after age 75, being 50% less than that of younger women. Besides age, the production of 1,25(OH)2D was found to be dependent on baseline serum iPTH (r = -0.31; p < 0.0001). Administration of hPTH(1-34) led to suppression of endogenous PTH, and suppressibility of endogenous PTH declined with age (r = 0.53; p < 0.0001). The increase in serum PTH and decreased suppressibility of PTH with age could be due to mild secondary hyperparathyroidism. The increase in PTH with age is probably responsible for maintaining normal serum 1,25(OH)2D levels in elderly subjects; however, decreased metabolism of 1,25(OH)2D in the elderly could also maintain normal serum 1,25(OH)2D levels.

Sequential effects of chronic human PTH (1-84) treatment of estrogen-deficiency osteopenia in the rat

Although daily injections of parathyroid hormone (PTH) can rapidly reverse estrogen-deficiency bone loss in rats, PTH treatment of osteoporotic humans has to date produced more modest increases in bone mass. To explore the reasons for this important difference, we evaluated the dose- and time-dependence of human PTH 1-84 treatment effects on bone mass and biochemical markers of bone metabolism in rats with estrogen-deficiency bone loss. The highest doses of PTH increased spinal, femoral, and total skeletal mass to supra-normal levels and stimulated cortical endosteal bone formation. Spine and whole skeleton mass and density increased rapidly at first, but then increased more slowly; the rate of change decreased significantly (p < 0.01) during continued treatment with the highest doses of PTH. The effects of PTH treatment on biochemical markers also were both dose-dependent and time-dependent. Serum osteocalcin, a marker of osteoblast function, increased with the highest doses of PTH (p < 0.001), but reached an early plateau and later returned toward baseline. Urinary excretion of pyridinolines, a marker of osteoclast function, increased in a time-dependent fashion throughout treatment (p < 0.001). Serum 1,25(OH)2 vitamin D levels increased in a dose-related fashion, but then decreased toward control levels despite continued treatment. We demonstrate that both osteoblast and osteoclast function are increased during daily PTH therapy in the rat. The pattern of response depends on both the dose of PTH and the duration of therapy. These dose- and time-related effects should be taken into account when designing experimental PTH treatments for osteoporosis, and they deserve intensive study.

Harry M. Vars Research Award. Increase in lumbar spine bone mineral content in patients on long-term parenteral nutrition without vitamin D supplementation

BACKGROUND

We had previously shown that short-term withdrawal of vitamin D in patients with metabolic bone disease complicating home parenteral nutrition (HPN) corrected osteomalacia. We therefore conducted a prospective study of the effect of long term withdrawal of vitamin D in patients on home parenteral nutrition.

METHODS

Baseline measurements of bone mineral content, serum levels of calcium, phosphorus, parathormone, 25-OH and 1,25 (OH)2D; urinary calcium; and bone mineral density were measured. Then all parenteral vitamin D was withdrawn and the above parameters were followed for a mean of 4.5 years.

RESULTS

Lumbar spine bone mineral content (LSBMC) was 0.79 +/- 0.06 g/cm2 at the start of the study, well below the reference value, 1.16 +/- 0.13 g/cm2. Parathyroid hormone (PTH) (0.48 +/- 0.24 pmol/L) and 1,25-(OH)2D levels (22.8 +/- 7.9 pmol/L) were low and 25-hydroxyvitaniin D levels were normal (33.3 +/- 5.5 nmol/L) before removing vitandn D from the HPN solutions. After withdrawal of vitamin D for 4.5 +/- 0.2 years LSBMC increased from 0.79 +/- 0.06 to 0.93 0.07 g/cm2 (p < 0.005). Calcium phosphorus, magnesium and 25-hydroxyvitamin D did not change significantly, 1,25(OH)2D, and PTH levels became normal after withdrawal of vitamin D.

CONCLUSIONS

In selected patients with depressed PTH levels, long-term withdrawal of vitamin D during HPN increases LSBMC and levels of PTH and 1,25(OH)2D. There is no reduction of the mean level of 25-hydroxyvitamin D.

Parathyroid hormone restores bone mass and enhances osteoblast insulin-like growth factor I gene expression in ovariectomized rats

In the osteopenic rat model, estrogen deficiency results in increased bone turnover with net bone loss occurring during cancellous modeling. However, estrogen-deficient rats treated with parathyroid hormone (PTH) experience a net gain of bone tissue due to the anabolic effects of PTH. To evaluate the possibility that local insulinlike growth factor I (IGF-I) production modulates the in vivo balance of bone formation and resorption in ovariectomized (OVX) estrogen-deficient rats and in OVX rats treated with PTH, we have studied the expression of IGF-I mRNA in cancellous bone osteoblasts using in situ hybridization techniques. Three-month-old virgin rats were subjected to sham surgery or OVX. Two weeks later, half the OVX rats began treatment with hPTH(1-34), 5 micrograms/100 g body weight, 5 days/week for 4 weeks. All animals were killed at the same time, providing three groups: sham surgery alone; OVX alone; and OVX + PTH. Bone histomorphometry performed in undecalcified sections of tibial metaphysis confirmed that OVX rats had significantly (p < 0.05) increased bone surface formation rates (BFR/BS, micron 3/micron 2/year) with osteopenia while OVX + PTH rats had increased BFR/BS with increased bone volumes compared to sham animals (p < 0.05). Decalcified tissue from all three groups contained immunoreactive IGF-I. Similar tissue sections were hybridized with an 35S-labeled IGF-I antisense riboprobe. Evaluation of the specific signal over cancellous osteoblasts allowed a relative estimate of IGF-I mRNA transcript abundance in the three groups by counting silver grains per osteoblast, corrected for background activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Human parathyroid hormone-(1-38) restores cancellous bone to the immobilized, osteopenic proximal tibial metaphysis in rats

The purpose of this study was to determine if human parathyroid hormone-(1-38) (hPTH(1-38)) can restore cancellous bone mass to the established osteopenic, immobilized proximal tibial metaphyses of female rats. The right hindlimbs of 6-month-old female Sprague-Dawley rats were immobilized by bandaging the right hindlimbs to the abdomen. After 30 days of right hindlimb immobilization, the rats were subcutaneously injected with 200 micrograms hPTH(1-38)/kg/day for 15 days (short-term treatment) or 75 days (longer-term treatment). Static bone histomorphometry was performed on the primary spongiosa, and both static and dynamic histomorphometry were performed on the secondary spongiosa of the right proximal tibial metaphyses. Immobilization for 30 days without treatment decreased trabecular bone area, number, and thickness in both primary and secondary spongiosa, and induced an increase in eroded perimeter and a decrease in tissue referent-bone formation rate in the secondary spongiosa. These changes reached a new steady state thereafter. Treatment with 200 micrograms hPTH(1-38)/kg/day for 15 days, beginning 30 days after immobilization, significantly increased trabecular bone area, thickness, and number in both primary and secondary spongiosa despite continuous immobilization when compared with controls. The short-term PTH treatment (15 days) significantly increased labeling perimeter, mineral apposition rate, and tissue referent-bone formation rate in the secondary spongiosa and stimulated longitudinal bone growth as compared with the controls. Longer PTH treatment (75 days) further increased trabecular bone area, thickness, and number as compared with controls and groups given short-term PTH treatment (15 days). The bone formation indices in the secondary spongiosa of the longer-term treated rats were lower than those of the short-term treated group, but they were still higher than those of controls. Our findings indicate that PTH treatment stimulates cancellous bone formation, and restores and adds extra cancellous bone to the established, disuse-osteopenic proximal tibial metaphysis of female rats with continuously immobilized right hindlimbs. These results suggest that PTH may be useful in treating disuse-induced osteoporosis in humans.

Interpretation and clinical significance of alkaline phosphatase isoenzyme patterns

Alkaline phosphatase (ALP, EC 3.1.3.1) is a membrane-bound metalloenzyme that consists of a group of true isoenzymes, all glycoproteins, encoded for by at least four different gene loci: tissue-nonspecific, intestinal, placental, and germ-cell ALP. Through posttranslational modifications of the tissue-nonspecific gene, for example, through differences in carbohydrate composition, bone and liver ALP are formed. Nowadays, most commercially available methods for separating or measuring ALP isoenzymes are easy to perform and sensitive and allow for reproducible and quantitative results. As more isoenzymes and isoforms have been characterized, confusion has arisen due to the many different names they were given. For the sake of simplicity and because of structural analogies, we propose an alternative nomenclature for the ALP isoenzymes and isoforms based on their structural characteristics: soluble, dimeric (Sol), anchor-bearing (Anch), and membrane-bound (Mem) liver, bone, intestinal, and placental ALP. Together with lipoprotein-bound liver ALP and immunoglobulin-bound ALP, these names largely fit the many forms of ALP one can encounter in human serum and tissues. The clinically relevant isoenzymes are sol-liver, Mem-liver, lipoprotein-bound liver, and Sol-intestinal ALP in liver diseases, and Sol-bone and Anch-bone ALP in bone diseases. Many different isoenzyme patterns can be found in malignancies and renal diseases. This test provides the clinician with valuable information for diagnostic purposes as well as for follow-up of patients and monitoring of treatment. However, ALP isoenzyme determination will only provide clinically useful information if the patterns are correctly interpreted. In this respect, care should be taken to use the proper reference ranges, taking into account the age and sex of the patient. A normal total ALP activity does not rule out the presence of an abnormal isoenzyme pattern, particularly in children. Separating ALP into its isoenzymes adds considerable value to the mere assay of total ALP activity.

An evaluation of several biochemical markers for bone formation and resorption in a protocol utilizing cyclical parathyroid hormone and calcitonin therapy for osteoporosis

Female patients (n = 20) with osteoporosis, aged 66 +/- 5 yr were studied during a 24-h infusion of parathyroid hormone (PTH [1-34]) at a rate of 0.5 IU equivalents/kg.h, and then during a 28-d period of subcutaneous injections, at a dose of 800 IU equivalents per day. Thereafter half the patients received subcutaneous injections of calcitonin, 75 U/d for 42 d, and all patients were followed to the end of a 90-d cycle. Biochemical markers of bone formation (serum alkaline phosphatase, osteocalcin, and the carboxy-terminal extension peptide of pro-collagen 1) and bone resorption (fasting urine calcium, hydroxyproline, and deoxypyridinoline) were compared during treatment by the intravenous and subcutaneous route of PTH administration, and subsequently during calcitonin therapy. During intravenous PTH infusion there were significant reductions in all three bone formation markers, despite expected rises in urinary calcium and hydroxyproline. By contrast, the circulating markers of bone formation increased rapidly by > 100% of baseline values during daily PTH injections (P < 0.001). Significant increases in bone resorption markers were only seen at the end of the 28 d of injections, but were < 100% over baseline values, (P < 0.05). Quantitative bone histomorphometry from biopsies obtained after 28 d of PTH treatment confirmed that bone formation at both the cellular and tissue levels were two to five times higher than similar indices measured in a control group of biopsies from untreated osteoporotic women. Subsequent treatment of these patients with calcitonin showed no significant changes in the biochemical markers of bone formation and only a modest attenuation of bone resorption. Thus, PTH infusion may inhibit bone formation, as judged by circulating biochemical markers, whereas daily injections confirm the potent anabolic actions of the hormone. Sequential calcitonin therapy does not appear to act synergistically with PTH in cyclical therapeutic protocols.

Effects of a short course of oral phosphate treatment on serum parathyroid hormone(1-84) and biochemical markers of bone turnover: a dose-response study

To investigate the possible use of oral phosphate as an activator of bone remodeling in coherence treatment of osteoporosis, 82 postmenopausal females, aged 50-75 years, were randomized to treatment with oral phosphate (750, 1500, or 2550 mg/day) or placebo for 7 days and followed for 4 months thereafter. All patients had sustained at least one previous fracture of the distal forearm and had a bone mineral content of the contralateral forearm or bone mineral density of the lumbar spine lower than normal mean for age. Urinary phosphate/creatinine ratio increased in a dose-dependent fashion during treatment (P less than 0.001), whereas no significant changes were seen in serum phosphate or serum calcium. Serum parathyroid hormone (PTH) rose significantly (P less than 0.05) during treatment to a maximum of 36 and 33% in the groups receiving 1500 and 2250 mg/day, respectively, whereas serum 1,25-dihydroxycholecalciferol remained unchanged. In the group receiving 1500 mg/day, mean serum osteocalcin was increased in the period from day 1 to day 28 (P less than 0.05), but no significant changes were observed in urinary hydroxyproline/creatinine ratio, or serum bone alkaline phosphatase. We conclude that a short course of oral phosphate treatment increases serum PTH considerably. Furthermore, 1500 mg/day but not 2250 mg/day increases serum osteocalcin. No clear biochemical evidence, however, of increased activation of bone remodeling could be demonstrated in either group.

Bone densitometric and histomorphometric responses to sequential human parathyroid hormone (1-38) and salmon calcitonin in osteoporotic patients

Cyclical treatments of osteoporosis utilizing a skeletal Activator of bone remodelling, and sequential therapy with a Depressor to selectively block the resulting phase of osteoclastic resorption have been dubbed 'ADFR' therapy; there is usually a treatment Free interval while the activated bone multicellular units complete the remodelling cycle before the protocol is Repeated. In this report an ADFR protocol was developed in which all patients received synthetic hPTH (1-38) for the first 14 days of a 100 day cycle. Half the patients received no other therapy (Group 1), but were followed closely with repeated vertebral bone mineral measurements over two full cycles. The remaining patients (Group 2) were randomly allocated to receive salmon calcitonin, at an average dose of 79 units per day for a 56 day depressor period immediately following each phase of activation. Detailed bone histomorphometry was performed on iliac biopsies obtained before treatment and at the end of the second cycle (Day 200). In Group 1, the serum alkaline phosphatase (Alk. P'ase) increased by 23 +/- 12% (P less than 0.01) and by 18 +/- 16% (P less than 0.03) of the baseline values following PTH treatment during the first and second cycles, respectively. The overall changes in serum Alk. P'ase across time were significantly less (P less than 0.04) in Group 2; however this parameter also increased by 15 +/- 15% during the first cycle and 8 +/- 6% during the second cycle. Vertebral BMC increased by 13% in Group I (P less than 0.01), but forearm BMC decreased by 11% (P less than 0.05) over the two cycles of therapy. There were no significant changes in bone mineral measurements in Group 2, but the differences between the two groups were not significant. Eighteen paired biopsies were available for histomorphometric analysis. There were no significant changes in static parameters measuring total bone tissue, osteoclastic function or osteoid formation after two cycles of treatment. Individual bone formation rates (surface referent) were not significantly different between the two groups; the pooled data for all biopsies showed a small but insignificant increase from 0.030 +/- 0.018 to 0.035 +/- 0.028 mm3/mm2/day. However there was a significant increase in the activation frequency (the probability of a remodelling event occurring on queiscent cancellous surface) from 13 +/- 7 to 27 +/- 26/day x 10(-4) (P less than 0.05) when calculated for the pooled data from both groups.(ABSTRACT TRUNCATED AT 400 WORDS)

hPTH 1-34 treatment of osteoporosis with added hormone replacement therapy: biochemical, kinetic and histological responses

Twelve patients with vertebral fracture osteoporosis were recruited into a trial of treatment with hPTH 1-34 by daily injection for 1 year combined (from the 5th month) with an anti-resorptive agent (oestrogen, n = 9; nandrolone, n = 3). Treatment outcomes were monitored by biochemical and radiotracer measurements together with histomorphometry of transiliac biopsies before and at the end of treatment following double in vivo pre-labelling with demethylchlortetracycline. Indices of whole body bone formation, obtained from the analysis of 85Sr data, showed substantial increases (P less than 0.005) for all three indices measured) while biochemical (hydroxyproline) and kinetic measurements of bone resorption showed modest and equivocal changes only. As a result calcium balance improved. Gastrointestinal calcium absorption showed a tendency to improve, while urine calcium decreased; but these changes were statistically not significant except for radiocalcium absorption in the oestrogen treated subgroup. Histomorphometry revealed substantial increases in cancellous bone volume as reported previously with hPTH 1-34 given alone. However, iliac (as distinct from whole body) indices related to bone formation and resorption appeared to have returned towards pre-treatment values by the time of the second biopsy under the influence of the anti-resorptive agent given with the hPTH 1-34. It is confirmed that hPTH 1-34 therapy can increase iliac cancellous bone mass (as well as spinal cancellous bone mass as reported earlier) without a long-term increment in whole body bone resorption, providing the hPTH is combined with an anti-resorptive agent.

A new direction for osteoporosis research: a review and proposal

This article suggests why drugs that only reduce the activity of existing osteoclasts or enhance the activity of existing osteoblasts probably cannot cure the osteopenias associated with most osteoporoses. Instead they should add only limited amounts of bone, which should begin to disappear after treatment stops. That behavior depends on these facts. Different threshold ranges of mechanical bone strains control gains and losses of bone mass. One threshold controls gains by modeling drifts, and a lower one controls losses by remodeling BMUs. A drug that does not change those thresholds should limit gains (or losses) of bone during indefinitely continued treatment. Success in curing those osteopenias should require learning how to change the thresholds.