Chemistry, physiology, and therapeutic applications of calcitonin

Tyrosine 12 of human calcitonin modulates its amyloid formation, membrane binding, and bioactivity

Irreversible aggregation greatly limits the bioavailability and therapeutic activity of peptide-based drugs, so preventing protein or peptide aggregation is a common issue in drug formulation. Human calcitonin (hCT), a peptide hormone secreted by thyroidal parafollicular cells, can regulate blood calcium levels and maintain bone structure. Hence, it can be used as a treatment for metabolic bone diseases, such as osteoporosis and Paget's disease. However, hCT has a relatively high propensity to form amyloid fibrils that hinder its biological function and limit its pharmaceutical potential. In previous studies, we demonstrated, along with other research groups, that modifying specific residues of hCT is sufficient to prevent hCT aggregation. We proceeded to find the key residues that regulate the aggregation of hCT for a better understanding of the mechanism of hCT aggregation. In this work, we used amyloid propensity prediction software and found that Tyr12 may play a key role in regulating hCT aggregation. Thus, we propose three human calcitonin variants (Y12E, Y12P, Y12R) for hCT non-amyloidogenic substituents and examined the aggregation characteristics of variants using multiple biophysical techniques. Y12E showed the best anti-aggregation propensity and can work as inhibitor of hCT aggregation. We also found this residue is crucial for membrane binding and receptor binding. The data presented herein provides an overview of Tyr12 that should be carefully considered in peptide design.

Effects of Drynaria Total Flavonoid on the Microstructure of the Mandible in Ovariectomized Rats

Background

The aim of this study is to investigate the effects of Drynaria total flavonoids (DTF) on mandible microarchitecture, serum estrogen (E2), osteoprotegerin (OPG), and receptor activator of nuclear factor kappa-B ligand (RANKL) levels in an ovariectomy-induced osteoporosis rat model.

Material/Methods

Thirty female Sprague-Dawley rats were divided into 5 groups (n=6 per group): sham surgery, ovariectomy (OVX), and low-dose, middle-dose, and high-dose DTF. Mandibular osteoporosis was induced by ovariectomy; an equal amount of ovary-sized fat tissue was removed from the sham group. The DTF-treated groups were given DTF gavage at different doses for 12 weeks; the sham and OVX groups were given saline. After the treatment phase, the effects of DTF on the microarchitecture of the mandible were evaluated by measuring bone density, maximum load, morphometric parameters, and histopathological alterations. Serum E2, OPG, and RANKL levels were measured.

Results

The OVX group showed obvious osteoporosis in the mandible and decreased serum E2 levels and OPG/RANKL ratio. The low-dose group did not show significant improvement in mandibular microstructure. The middle-dose group showed significantly ameliorated osteoporosis. The high-dose group had further improvement in bone microstructures and increase of OPG/RANKL over the middle-dose group. Furthermore, ovariectomy significantly decreased serum E2, but DTF treatment failed to restore serum E2 levels.

Conclusions

Ovariectomy can cause significant bone loss in the rat mandible and a decrease in serum E2 and OPG/RANKL. DTF significantly improved the mandibular microstructure and restored OPG/RANKL balance, but it did not restore the decreased serum E2 concentration following ovariectomy.

The calcitonin and glucocorticoids combination: mechanistic insights into their class-effect synergy in experimental arthritis

INTRODUCTION

Previous work reported the anti-arthritic synergy afforded by combining calcitonin (CT) and glucocorticoids (GC). Here we focus on the pairing of elcatonin (eCT) and dexamethasone (Dex), querying whether: i) this was a class-effect action; ii) mechanistic insights could be unveiled; iii) the synergy affected canonical GC adverse effects.

METHODS

Using the rat collagen-induced arthritis model, different combinations of eCT and Dex, were administered from disease onset to peak (day 11 to 18). Macroscopic disease score was monitored throughout, with biochemical and histological analyses conducted on plasma and tissues at day 18. The effect on acute hyperglycaemia and liver enzyme message were also assessed.

RESULTS

Whilst eCT alone was inactive, it synergised at 1 µg/kg with low doses of Dex (7.5 or 15 µg/kg) to yield an anti-arthritic efficacy equivalent to a 4- to 7-fold higher Dex dose. Mechanistically, the anti-arthritic synergy corresponded to a marked attenuation in RA-relevant analytes. CXCL5 expression, in both plasma and joint, was markedly inhibited by the co-therapy. Finally, co-administration of eCT did not exacerbate metrics of GC adverse effects, and rescued some of them.

CONCLUSIONS

We present evidence of a class-effect action for the anti-arthritic synergy of CT/GC combination, underpinned by the powerful inhibition of joint destruction markers. Furthermore, we identify CXCL5 as a marker for the combination therapy with potential diagnostic and prognostic utility. Substantial GC dose reduction, together with the absence of exacerbated adverse effects, indicated a significant clinical potential for this co-therapy in RA and beyond.

Calcitonin in bone-guided regeneration of mandibles in ovariectomized rats: densitometric, histologic and histomorphometric analysis

The aim of the present study was to investigate bone promotion in surgical defects created in the mandible of normal and ovariectomized female rats using calcitonin associated with a polytetrafluoroethylene barrier. The 100 female rats were divided into four groups: control (C), control treated with calcitonin (CM), ovariectomized control (OV) and ovariectomized treated with calcitonin (OVM). A circumscribed bone defect 4mm in diameter was created in the region of the mandibular angle, and covered with the barrier. Groups CM and OVM received 2 IU/kg of synthetic salmon calcitonin intramuscularly three times a week. The animals were killed 3, 7, 14, 21 and 28 days after surgery. The bone defects were submitted to densitometric, histologic and histomorphometric analysis. Groups C and CM showed higher levels of bone formation after 7 days compared to the OV and OVM groups. A significant difference was observed between groups C and OV at 3-14 days. The OV group presented slower bone regeneration of the surgical bone defect created in the mandibular angle than group C. Synthetic salmon calcitonin accelerated regeneration of the bone defect in the mandibles of OVM animals similarly to group C, and also increased the formation of new bone during the regeneration process in CM.

Human osteoblast-like cell proliferation induced by calcitonin-related peptides involves PKC activity

The calcitonin peptides [calcitonin (CT), calcitonin gene-related peptide (CGRP), amylin] share many biological actions, including activity on bone cells. In the present study, CT (10(-11) to 10(-9) M) stimulated [(3)H]thymidine incorporation in primary cultures of human osteoblasts (hOB), as already demonstrated for CGRP and amylin. RT-PCR analysis showed that the calcitonin receptor and the calcitonin receptor-like receptor are both expressed in hOB. In these cells, CT (10(-10) M) and amylin (10(-9) M), in contrast to CGRP (10(-8) M), did not increase cAMP production. All three peptides stimulated protein kinase C (PKC) activity. To evaluate PKC involvement in hOB proliferation, cells were incubated with phorbol 12,13-dibutyrate, a stimulator of PKC activity; cell proliferation was increased in a dose-dependent manner (EC(50) = 3.4 x 10(-8) M). Staurosporine (10(-9) M), a PKC inhibitor, blocked phorbol 12,13-dibutyrate-induced PKC activity and cell proliferation. Inhibition of PKC by staurosporine also counteracted the stimulatory effect of CT, CGRP, and amylin on hOB proliferation. From these data, it is deduced that the activation of PKC is important for hOB proliferation and that it is involved in the anabolic effect of CT peptides on bone.

A double-blind, multicentre, placebo-controlled study of tiludronate in Paget's disease of bone

A multicentre, randomised, placebo-controlled, dose-ranging study was conducted to investigate the therapeutic activity and sustained efficacy of tiludronate (200 mg, 400 mg and 600 mg once daily) taken orally for 12 weeks in patients with Paget's disease. Serum alkaline phosphatase concentrations were compared with baseline at weeks 12 and 24; treatment success was defined as a 50% reduction compared with baseline. Changes in the hydroxyproline: creatinine ratio were also measured. Pain was assessed using the Huskisson Visual Analogue Scale and by questionnaire. Patients completing at least 11 weeks of treatment were followed-up 18 months later by postal questionnaire. Significantly greater numbers of patients in the tiludronate groups successfully responded to treatment compared with the placebo group. A dose-response was observed; the percentage of patients responding to treatment being 31% (200 mg), 52% (400 mg) and 82% (600 mg) at week 12 and 45% (200 mg), 70% (400 mg) and 82% (600 mg) at week 24. Tiludronate treatment also significantly reduced hydroxyproline: creatinine ratios compared with placebo, again showing a dose response. Dose-related gastrointestinal symptoms were the commonest adverse events, occurring in 2.4%, 11.0%, 5.5% and 18.9% of patients receiving placebo and tiludronate 200, 400 and 600 mg daily, respectively. The response to oral tiludronate was sustained for more than 18 months in some patients and there was evidence of a reduction in the longer term complications of the disease. These results show that oral tiludronate is an effective, well-tolerated treatment for Paget's disease; the 400 mg once daily dose appears to offer the optimum balance of efficacy and tolerance.

Calcitonin promotes osteoclast survival in vitro

Inactivation of resorbing osteoclasts by calcitonin is associated with typical morphological changes and alteration of the specific organization of osteoclast cytoskeleton. Here we show that calcitonin also promotes the survival of rat osteoclasts in vitro, cultured either on glass or bone, by delaying the onset of apoptosis. Parathyroid hormone had no effect on osteoclasts cultured on glass but it slightly increased apoptosis index of osteoclasts cultured on bone. Calcitonin was also able to rescue osteoclasts in calvarial explant cultures. The survival effect of calcitonin was mimicked by dibutyryl cAMP and could not be blocked by various metabolic inhibitors known to affect the apoptotic pathway. However, clodronate-induced apoptosis of osteoclasts could not be reversed by calcitonin and neither could calcitonin rescue osteoclasts already committed to apoptosis. It did not alter the distribution of Bcl-2 in osteoclasts. Our results show that at least in vitro calcitonin protects osteoclasts from apoptosis and suggest that it regulates the onset of apoptosis.

Calcitonin acutely increases tyrosyl-phosphorylation of proteins in human osteosarcoma (SaOS-2) cells

In order to test the hypothesis that salmon calcitonin has direct effects to modulate tyrosyl-protein phosphorylation in human osteosarcoma cells, SaOS-2 cells (with very high steady-state levels of skeletal alkaline phosphatase) were exposed to calcitonin, in duplicate serum-free cultures, at concentrations ranging from 10(-13) to 10(-9) mol/liter, for 0-60 minutes at 37 degrees C. Phospho-tyrosyl proteins were identified by autoradiography of Western blots after incubation with 125I-labeled antiphosphotyrosine antibodies (or with unlabeled antibodies and 125I-labeled protein A) and quantitated by laser densitometry. The results of these studies revealed (1) time-dependent effects of salmon calcitonin (sCt) (at 3 x 10(-12) mol/liter) to increase the level of tyrosylphosphorylation of at least six proteins, with apparent molecular weights of 20, 25, 27, 41, 48, and 135 kD (P < 0.05 for each); and (2) dose-dependent effects of sCt (during 15 minutes of exposure) to increase the level of tyrosyl-phosphorylation of at least 10 proteins with apparent molecular weights of 19, 20, 27, 35, 41, 102, 135, 195, 220, and 244 kD (P < 0.05 for each). A supplementary study of calcitonin effects on tyrosyl-protein phosphorylation in a subpopulation of SaOS-2 cells with very low steady-state levels of skeletal alkaline activity revealed similar responses--time and dose-dependent increases in the tyrosyl-phosphorylation of at least seven proteins with apparent molecular weights of 44, 48, 57, 62, 101, 244, and 280 kD (P < 0.05 for each).(ABSTRACT TRUNCATED AT 250 WORDS)

Paget's disease of bone: current concepts in pathogenesis and treatment

Recent advances have been made in understanding the aetiology, diagnosis and treatment of Paget's disease of bone (osteitis deformans). The role of viruses in the pathogenesis of the disease has been extensively investigated, although no causative link has yet been demonstrated between infective agents and Paget's disease. Recent advances in the diagnosis of the disease have been made with increasing usage of radionucleotide imaging to determine the extent and distribution of the lesions. Treatment options have been extended with the emergence of the biphosphonates as potential main line therapeutic agents.

Determinants of remission of Paget's disease of bone

Bisphosphonates are a safe and effective treatment for Paget's disease of bone, but little information is available about the factors influencing the duration of remission so obtained. We assessed 60 patients with Paget's disease treated with disodium pamidronate (APD). The mean duration of remission was 9.5 months (range 3-25). The major influences were the initial pretreatment alkaline phosphatase (ALP; r = -4.6, p < 0.0001), minimum posttreatment ALP (r = -0.51, p < 0.0001), and the rate of response of bone turnover to the first dose of APD (r = 0.61, p < 0.0001). Multiple linear regression showed that the initial response to treatment was the most significant influence. Also, despite a minimum ALP within the normal range, the duration of remission varied considerably (4-25 months). This may be due to the difficulties in applying a population-based normal range to individuals.

Drugs used in the treatment of metabolic bone disease. Clinical pharmacology and therapeutic use

Osteoporosis is the most important metabolic bone disease and places an increasing burden on the healthcare system. The condition can be prevented by the early introduction of hormone replacement therapy. The role of bisphosphonates in achieving the same result is being actively explored. The attraction of preventing bone loss is that it preserves the micro-architecture of bone, and therefore its mechanical integrity. The great problem of treating the established condition is that substantial bone loss is accompanied by architectural disintegration. Replacing lost bone may not necessarily restore mechanical integrity and protect against fractures. The management of Paget's disease has been quite revolutionised by the introduction of the bisphosphonates. The condition is a result of a primary increase in osteoclastic bone resorption which can be corrected by bisphosphonates, with considerable symptomatic improvement. The increasing potency and safety margin of the newer agents has meant that the threshold for treatment has fallen. There is now potential for long term control of bone turnover with the hope of preventing late complications. Hypercalcaemia of malignancy is usually the result of both increased bone destruction and decreased urinary calcium excretion. These two components of hypercalcaemia demand different approaches to management. The general availability of an ever-expanding range of increasingly potent bisphosphonates has resulted in a dramatic improvement in the treatment of increased bone resorption associated with malignancy. Many types of tumour, either directly or indirectly, compromise the ability of the kidney to eliminate a calcium load derived from increased bone destruction. Calcitonin is the only agent which is currently available to counter this process.

Calcitonin acutely increases net 45Ca uptake and alters alkaline phosphatase specific activity in human osteosarcoma cells

Although the primary skeletal action of exogenous calcitonin is to inhibit bone resorption, calcitonin also has effects on bone formation. In-vitro data indicate that the latter may include direct effects on bone cells of osteoblastic lineage. In the current studies, we examined the effects of calcitonin on cyclic adenosine monophosphate (cAMP) and PGE2 synthesis and 45Ca uptake in human osteosarcoma cells, specifically, TE-85 cells and subpopulations of SaOS-2 cells with low-, intermediate-, and high-steady-state levels of skeletal alkaline phosphatase (ALP) activity. Since previous in-vivo studies had shown that calcitonin could acutely decrease skeletal ALP activity in rat periosteal osteoblasts, we also measured the effects of calcitonin treatment on ALP specific activity. Neither salmon nor human calcitonin altered the net synthesis of cAMP or PGE2 by SaOS-2 cells, but human calcitonin gene-related peptide increased both (P < .001 and P < .005, respectively). Both salmon and human calcitonin had short-term effects to alter ALP activity in TE-85 and SaOS-2 cells. The effects were different in SaOS-2 subpopulations with different pretreatment ALP levels. Four hours of exposure to salmon calcitonin had dose-dependent, biphasic effects on ALP levels in SaOS-2 cells with intermediate pretreatment ALP levels, increasing ALP at doses between 0.16 and 1.6 nmol/L (P < .005) and decreasing ALP at higher concentrations (P < .05). Both salmon and human calcitonin, but not human calcitonin gene-related peptide, also had short-term effects to increase net 45Ca uptake by SaOS-2 cells; these effects were dose-dependent and long-lasting.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of calcitonin on bone histomorphometry and bone metabolism in rheumatoid arthritis

Twenty-four women (mean age +/- SD 49 +/- 13 years) with classical or definite rheumatoid arthritis (disease duration 15 +/- 8 years) were treated with synthetic salmon calcitonin (SCT) nasal spray 200 IU three times a week for 3 months. Bone biopsies from the iliac crest were taken before and after SCT treatment. Histomorphometrical quantification of undecalcified bone sections was made using the manual point-counting method. SCT decreased the resorption surface of trabecular bone (ES/BS) significantly (P less than 0.001). There was also a significant increase (P less than 0.05) in trabecular bone volume (BV/TV) after 3 months of treatment, whereas no statistically significant changes were found in osteoid parameters. There were no significant changes in biochemical analyses of bone metabolism. We conclude that SCT might be useful in the prevention of bone loss in RA.

Two biochemical indices of mouse bone formation are increased, in vivo, in response to calcitonin

In a series of four studies, adult female Swiss-Webster mice were used to measure the effects of salmon calcitonin on two biochemical indices of local and systematic bone formation: (1) skeletal alkaline phosphatase activity--in serum and in extracts of calvaria and tibiae, and (2) calvarial collagenase-digestible protein synthesis--measured, acutely, in vitro. Subcutaneous calcitonin doses ranged from 50 to 400 mU/mouse/day (0.95-18.1 U/kg/day), and treatment schedules were continuous (daily) for 2-14 days, acute, or intermittent (2 days/week for 6 weeks). The effects of calcitonin on these bone formation indices (skeletal alkaline phosphatase and collagenase-digestible protein synthesis) were biphasic with respect to dose and treatment time, being increased in response to short-term, low-dose treatment, but not long-term, continuous treatment. The effects of long-term intermittent calcitonin treatment were dose-dependent increases in skeletal alkaline phosphatase in calvaria and serum (r = 0.948, P less than 0.02, and r = 0.960, P less than 0.01, respectively).

Calcitonin has direct effects on 3[H]-thymidine incorporation and alkaline phosphatase activity in human osteoblast-line cells

Calcitonin had direct and dose-dependent actions on human osteoblast-line cells (in serum-free monolayer culture) to increase cell proliferation and alkaline phosphatase activity/mg cell protein. Salmon calcitonin increased (human osteosarcoma) SaOS-2 cell proliferation, as evidenced by dose-dependent increases in 3[H]-thymidine incorporation into DNA (e.g., 153% of control after 20 h exposure at 0.1 nM, P less than 0.01), and MTT (thyzolyl blue) reduction/deposition (e.g., 161% of control after 72 h exposure at 0.03 nM). Continuous exposure was not required to elicit these proliferative responses. These effects were not unique to salmon calcitonin or to SaOS-2 cells. Similar effects were seen with human calcitonin (but not heat-inactivated human calcitonin) and with (human osteosarcoma) TE-85 cells and human osteoblast-line cells prepared from femoral heads. In addition to effects on cell proliferation, calcitonin also increased alkaline phosphatase-specific activity in SaOS-2 cells (e.g., 180% of control after 72 h of exposure to 0.1 nM salmon calcitonin, P less than .005).

Calcitonin (but not calcitonin gene-related peptide) increases mouse bone cell proliferation in a dose-dependent manner, and increases mouse bone formation, alone and in combination with fluoride

Previous in vitro studies have shown that salmon calcitonin had direct effects to increase parameters associated with embryonic chicken bone formation and to increase mouse and chicken osteoblast-line cell proliferation. The current studies demonstrate increased cell proliferation (i.e., [3H]-thymidine incorporation into DNA and tetrazolium salt reduction/deposition) in the osteoblastic murine cell line MC-3T3-E1 in response to salmon calcitonin (P less than 0.005) and to human calcitonin (P less than 0.005), but not to human calcitonin gene-related peptide. The current studies also show that salmon calcitonin increased several indices of murine bone formation. We found that 72 hours of exposure to salmon calcitonin [at 5 mU/ml-about 0.37 nM; mU/ml = milliunits of calcitonin activity/ml incubation medium (at 4,000 U/mg protein)] increased net 45Ca deposition (121% of control, P less than 0.05), net [3H]-proline incorporation 149% of control, P less than 0.001), and alkaline phosphatase activity (146% of control, P less than 0.01), in neonatal mouse half-calvaria. The calcitonin-dependent increase in alkaline phosphatase activity was not affected by co-incubation with 1 nM parathyroid hormone. Co-incubation with fluoride (which also increased net [3H]-proline incorporation and alkaline phosphatase activity in neonatal mouse half-calvaria, P less than 0.05, for each) enhanced the osteogenic response to low-dose calcitonin, (i.e., co-incubation with fluoride shifted the biphasic calcitonin dose-response curve to a range of lower calcitonin concentrations). The calcitonin-fluoride combinations had proportional effects on net [3H]-proline incorporation and alkaline phosphatase in the treated mouse calvaria (r = 0.78, P less than 0.005).

Paget's disease of bone

Paget's disease is a relatively common bone disease. This review aims to present reasonable treatment recommendations with enough background to understand them. To accomplish this end, some aspects of basic bone cell biology, biochemistry, and pathology are presented, as are speculations about possible causes of this disease. Treatment of Paget's disease will be considered in three sections. The first two sections will review treatment with calcitonin and diphosphonates, respectively. These sections briefly will consider the mechanism of action of the drugs, review in detail clinical studies of drug effectiveness, and summarize the advantages and disadvantages of each drug. The third section details specific treatment recommendations for each of the six clinical settings in which treatment of Paget's disease is justified.

Paget's disease of bone: early and late responses to three different modes of treatment with aminohydroxypropylidene bisphosphonate (APD)

Early and late responses to treatment with either oral (600 mg/day) or intravenous (20 mg/day) (3-amino-1-hydroxypropylidene)-1,1-bisphosphonate (aminohydroxypropylidene bisphosphonate; APD) were studied in 142 patients with Paget's disease of bone who had not previously been treated with bisphosphonate. The efficacy of three therapeutic regimens was compared: (a) oral aminohydroxypropylidene bisphosphonate given continuously until six months after the serum alkaline phosphatase activity had returned to normal (long term); (b) oral aminohydroxypropylidene bisphosphonate given until urinary hydroxyproline excretion had returned to normal (short term); (c) intravenous aminohydroxypropylidene bisphosphonate for 10 days. With either oral or intravenous treatment the decrease in urinary hydroxyproline excretion was rapid and always preceded the fall in serum alkaline phosphatase activity. Normal urinary hydroxyproline excretion is essential for return of the serum alkaline phosphatase activity to normal. Complete biochemical remission, defined as return of the serum alkaline phosphatase activity to normal, was obtained in 129 patients (91%). The median duration of remission as assessed by actuarial analysis was 2.7 years. This study found no difference in the long term among the three modes of treatment, suggesting that for most patients with Paget's disease a short course of intravenous aminohydroxypropylidene bisphosphonate will produce longlasting, complete remission without need for maintenance treatment.

Quantitative bone scintigraphy in Paget's disease treated with APD

Half-yearly bone scintigrams of 27 patients with Paget's disease, who were treated with the bisphosphonate APD, were evaluated. Uptake of 99Tcm-Sn-EHDP was determined by computer analysis. All patients reached clinical and biochemical remission, usually within 6 months. The scintigraphic uptake dropped steeply during the first 6 months and only slightly during the second 6 months. The decrease in uptake was proportional to the original uptake and averaged 80% of this value. The residual 20% persisted, although clinical and biochemical remission were attained. The scintigraphic results obtained with APD agree with our earlier findings for patients in remission after treatment with a combination of calcitonin and EHDP. Eight patients suffered a recurrence after discontinuation of APD. In all cases scintigraphic deterioration also occurred, usually simultaneously or 6 months before the recurrence. In two patients with scintigraphic deterioration a recurrence could not be confirmed during this study. The scintigraphic deterioration presented as one of the three patterns seen after combination therapy.

Clinical experience with the use of two diphosphonates in the treatment of Paget's disease

The effects of EHDP (20 mg/kd/day) and APD (4.5 mg/kg/day) given for three months to patients with severe symptomatic Paget's disease have been compared in an open trial of 17 patients. Both drugs were equally effective in producing a prompt reduction in pair scores, urine hydroxyproline, and serum alkaline phosphatase levels. The remission was maintained for a variable period after stopping treatment. Both drugs were well tolerated, and a one-month course of either drug was not effective. Comparison with published responses from previous studies indicates that EHDP given at this dose as a relatively short course is more effective than a lower dose for a longer period of time; the present study does not suggest that APD has significant advantages.

Response of Paget's disease to human calcitonin in patients resistant to porcine calcitonin

Eleven patients with Paget's disease of bone, treated intermittently for 2-4 years with porcine calcitonin (pCT) and clinically resistant to pCT [no modifications of serum alkaline phosphatase (ALP) and urinary hydroxyproline ( uHOP ) during pCT administration] were treated with 0.5-0.25 mg/day of human calcitonin (hCT) for 3-6 months. Nine of our patients showed biochemical improvement during the first 2 months of treatment, with reduction in ALP and uHOP . In one patient with slightly increased ALP and uHOP , and in another one during the second treatment course, hCT treatment did not modify the biochemical indices of bone disease. However all patients, including those with biochemical resistance, experienced a remarkable diminution of bone pain, which had not been observed during previous pCT treatment courses. Therefore, hCT appears to be indicated for therapeutic use in patients who are resistant to foreign calcitonins.

The origin of osteoclasts: evidence, clinical implications and investigative challenges of an extra-skeletal source

Recent evidence for an extraskeletal origin of osteoclasts and the historical record of the genesis of osteoclasts are examined critically. Reviews of the structure, function and development of osteoclasts from mononuclear precursors, the local regulation of bone resorption and the coupling of bone formation to preceding resorption are presented as a background for discussing the clinical implications for management of osteolytic bone diseases. The roles of osteoclasts and macrophages as phagocytes are compared and contrasted, and recent evidence for macrophage heterogeneity resulting from site-specific monoblastic precursors is reviewed. The implications of these recent developments in macrophage biology are extrapolated to osteoclasts and the existence of site-specific, extraskeletal osteoclast precursors is proposed. Finally, the investigative challenges inherent in these perspectives are discussed.

Regulation of calcitonin and parathyroid hormone secretion by oestrogens

Calcitonin is a peptide hormone secreted by C-cells which, in humans, are found mainly in the thyroid gland. It now seems that a major physiological function of this hormone in man is the long-term maintenance of the skeleton achieved by control of bone resorption. A marked sex difference in circulating calcitonin levels normally exists, with a relative deficiency in women as compared to men. It has now been found that oestrogens regulate calcitonin secretion and it appears likely that the loss of ovarian function at the menopause accelerates the natural decline in calcitonin secretion which occurs with age. Thus, post-menopausal women are more markedly calcitonin-deficient. Levels of the bone-resorbing hormones, parathyroid hormone (PTH) and 1,25 dihydroxyvitamin D are not elevated post-menopausally and it seems likely that the increased bone resorption which leads to post-menopausal bone loss is due mainly to the loss of oestrogen and calcitonin secretion.

The construction and partial characterization of plasmids containing complementary DNA sequences to human calcitonin precursor polyprotein

(1) Total poly(A)-containing RNA isolated from human thyroid medullary carcinoma tissue was shown to direct the synthesis in the wheat germ cell-free system of a major (Mr 21000) and several minor forms of human calcitonin precursor polyproteins. Evidence for processing of these precursor(s) by the wheat germ cell-free system is also presented. (2) A small complementary DNA (cDNA) plasmid library has been constructed in the PstI site of the plasmid pAT153, using total human thyroid medullary carcinoma poly(A)-containing RNA as the starting material. (3) Plasmids containing abundant cDNA sequences were selected by hybridization in situ, and two of these (ph T-B3 and phT-B6) were characterized by hybridization--translation and restriction analysis. Each was shown to contain human calcitonin precursor polyprotein cDNA sequences. (4) RNA blotting techniques demonstrate that the human calcitonin precursor polyprotein is encoded within a mRNA containing 1000 bases. (5) The results demonstrate that human calcitonin is synthesized as a precursor polyprotein.

Salmon calcitonin therapy for Paget's disease of bone. The problem of acquired clinical resistance

During the initial months of long-term treatment of Paget's disease of bone with salmon calcitonin, circulating alkaline phosphatase activity and urinary hydroxyproproline excretion usually decrease by about 50%. In 22 of 85 patients these parameters returned to pretreatment levels despite continuous therapy. Nineteen patients who were resistant to salmon calcitonin had salmon calcitonin antibodies in high titer. Human calcitonin has been effective in suppressing disease activity in these patients. The pathogenesis of calcitonin resistance in patients without antibodies is unknown.