Oral Delivery of Teriparatide Using a Nanoemulsion System: Design, in Vitro and in Vivo Evaluation

PURPOSE

Investigate the possibility of delivering teriparatide orally using nanoemulsion.

METHOD

Teriparatide was allowed to interact with chitosan in the presence of HPβCD.The formed polyelectrolyte complex (PEC) was characterized by DSC, FTIR, DLS and for entrapment efficiency. PEC was the incorporated in an oil phase consisting of Oleic Acid, Labrasol and Plurol Oleique to form a nanoemulsion. This preparation was characterized for refractive index, viscosity, pH, conductivity, particle size, and morphology.Bioavailability of the preparation was evaluated using rabbits against SC injection. The efficacy of the formula was tested using ovariectomized rats (an osteoporosis animal model) and mechanical and histological tests were conducted on their bones. The stability of the preparation was evaluated by storing samples at 4^o C, 25^o C and 40^o C for three months.

RESULTS

PEC testing demonstrate a complex formation with particle size of 208 nm, zeta potential of +17 mV and entrapment efficiency of 49%. For the nanoemulsion, the results demonstrate the formation of a nano-sized dispersed system (108 nm) with a drug loading of 98% and a percent protection of 90% and 71% in SGF and SIF respectively. Bioavailability results showed a sustained release profile was achieved following the oral formulation administration. Efficacy studies showed improvement in the strength, thickness and connectivity of bones. Short-term stability study demostrated that the nanoemulsion is mostly stable at 4^o C.

CONCLUSION

These findings demonstrate the ability of delivering Teriparatide orally using oleic acid based dispersion in combination with chitosan PEC.

Postmenopausal osteoporosis: Assessment and management

Osteoporosis increases the risk of fractures, which are associated with increased mortality and lower quality of life. Patients with prevalent fracture are at high risk to of sustaining another one. Optimal protein and calcium intakes, and vitamin D supplies, together with regular weight bearing physical exercise are the corner stones of fracture prevention. Evidence for anti-fracture efficacy of pharmacological interventions relies on results from randomised controlled trials in postmenopausal women with fractures as the primary outcome. Treatments with bone resorption inhibitors, like bisphosphonates or denosumab, and bone formation stimulator like teriparatide, reduce vertebral and non-vertebral fracture risk. A reduction in vertebral fracture risk can already be detected within a year after starting therapy.

Acute development of cortical porosity and endosteal naïve bone formation from the daily but not weekly short-term administration of PTH in rabbit

Teriparatide [human parathyroid hormone (1–34)], which exerts an anabolic effect on bone, is used for the treatment of osteoporosis in patients who are at a high risk for fracture. That the once-daily administration of teriparatide causes an increase in cortical porosity in animal models and clinical studies has been a matter of concern. However, it is not well documented that the frequency of administration and/or the total dose of teriparatide affect the cortical porosity. The present study developed 4 teriparatide regimens [20 μg/kg/day (D20), 40 μg/kg/day (D40), 140 μg/kg/week (W140) and 280 μg/kg/week (W280)] in the rabbit as a model animal with a well-developed Haversian system and osteons. The total weekly doses were equivalent in the low-dose groups (D20 and W140) and in the high-dose groups (D40 and W280). After the short-term (1 month) administration of TPDT, micro-CT, histomorphometry and three-dimensional second harmonic generation (3D-SHG) imaging to visualize the bone collagen demonstrated that daily regimens but not weekly regimens were associated with the significant development of cortical porosity and endosteal naïve bone formation by marrow fibrosis. We concomitantly monitored the pharmacokinetics of the plasma teriparatide levels as well as the temporal changes in markers of bone formation and resorption. The analyses in the present study suggested that the daily repeated administration of teriparatide causes more deleterious changes in the cortical microarchitecture than the less frequent administration of higher doses. The findings of the present study may have some implications for use of teriparatide in clinical treatment.

A case of teriparatide-induced severe hypophosphatemia and hypercalcemia

PTH (teriparatide) is used in the treatment of osteoporosis, and can sometimes cause transient hypercalcemia, but to date there have been no reports of persistent hypercalcemia and hypophosphatemia resulting from its use. We describe a case with marked hypophosphatemia and hypercalcemia associated with the use of teriparatide. The patient was a 49-year-old woman who was followed up for acute intermittent porphyria and glucocorticoid-induced osteoporosis (following administration of prednisolone at 22.5 mg/day), and presented with unexplained fracture of the left tibia, for which treatment with teriparatide at 20 μg/day was started. Two weeks after treatment with teriparatide, the patient developed hypophosphatemia, hypercalcemia, hyperalkaline phosphatasemia, low TmP/GFR, FEca, BAP, and urinary NT×, with low intact PTH. These changes were considered to be related to teriparatide. Cessation of teriparatide treatment resulted in normalization of all parameters at 10 weeks (serum P 3.6 mg/dl, corrected Ca 8.8 mg/dl, ALP 273 IU/l, intact PTH 63 pg/ml). The observed abnormalities were considered to be in part related to acute intermittent porphyria, which is known to delay hepatic teriparatide clearance, with subsequent delay of PTH action despite its intermittent use, resulting in hypercalcemia and hypophosphatemia.

Profile of changes in bone turnover markers during once-weekly teriparatide administration for 24 weeks in postmenopausal women with osteoporosis

SUMMARY

Changes in bone turnover markers with weekly 56.5 μg teriparatide injections for 24 weeks were investigated in women with osteoporosis. Changes in bone turnover markers 24 h after each injection of teriparatide were constant. During the 24 week period, bone formation markers increased and baseline bone resorption marker levels were maintained.

INTRODUCTION

This study aimed to clarify the changes in bone turnover markers during 24 weeks of once-weekly teriparatide injections in postmenopausal women with osteoporosis.

METHODS

The 24 h changes in pharmacokinetics (PK), calcium metabolism, and bone turnover markers (serum osteocalcin, procollagen type I N-terminal propeptide (P1NP), urinary cross-linked N-telopeptide of type I collagen (NTX), deoxypiridinoline (DPD)) after each injection of 56.5 μg teriparatide at the data collection weeks (0, 4, 12, and 24 weeks) were investigated. The changes were evaluated by comparison with the data at 0 h in each data collection week.

RESULTS

Similar 24 h changes in each parameter after injection of teriparatide were observed in each data collection week. Serum calcium increased transiently, and intact PTH decreased 4-8 h after injection; serum calcium subsequently returned to baseline levels. Calcium and intact PTH levels decreased for 24 weeks. Although serum osteocalcin decreased at 24 h, it was significantly increased at 4 weeks. P1NP decreased transiently and then increased significantly at 24 h. P1NP was significantly increased at 4 weeks. Urinary NTX and DPD were significantly increased transiently and then decreased at 24 h. The urinary DPD level decreased significantly at 4 weeks.

CONCLUSIONS

Twenty-four hour changes in PK, calcium metabolism, and bone turnover markers showed the same direction and level after once-weekly teriparatide injections for 24 weeks, with no attenuation of the effect over time. After 24 weeks, the bone formation marker, serum osteocalcin, increased significantly, but the serum P1NP, did not. Bone resorption markers decreased or remained the same.

Effects of a single injection of teriparatide on bone turnover markers in postmenopausal women

This study investigated the effects of a single administration of teriparatide on bone turnover markers in postmenopausal women. Teriparatide caused a transient increase in bone resorption and inhibition of bone formation followed by a subsequent increase in bone formation and a decrease in resorption that lasted at least 1 week.

INTRODUCTION

This study aims to investigate the effects of a single subcutaneous administration of teriparatide on bone turnover markers to elucidate why once weekly intermittent administration of teriparatide is effective on osteoporosis.

METHODS

Pharmacokinetics and calcium metabolism and bone turnover parameters were measured in 30 postmenopausal women after two doses of teriparatide (28.2 or 56.5 μg injection) or placebo in a randomized, double-blind, placebo-controlled study.

RESULTS

Teriparatide plasma concentration increased in a dose-dependent manner, and the maximum concentration was achieved 1 h after injection. Serum levels of calcium and phosphorus were transiently increased and decreased after teriparatide injection, respectively. Calcium metabolism returned to baseline levels 24 h later. Two days after injection, the serum level of 1,25-dihydroxy vitamin D was increased by ~80 % from baseline for both doses of teriparatide. Serum levels of osteocalcin and procollagen type I N-terminal propeptide decreased during the first 24 h followed by a ~10 % increase for 14 days. The serum level of cross-linked N-telopeptide (NTX) of type I collagen increased during the first 24 h followed by a 10 to 12 % dose-dependent suppression from baseline for 14 days. Urinary cross-linked C-telopeptide of type I collagen changes occurred in the same direction as serum NTX, but not dose dependently.

CONCLUSION

A single administration of teriparatide caused an immediate, transient increase in bone resorption and inhibited bone formation followed by an increase in bone formation and decrease in resorption for ≥1 week. These findings may provide proof for the effect of a once-weekly regimen of teriparatide on bone turnover.

[Effects of parathyroid hormone on bone metabolism : differences between intermittent and continuous treatment]

Numerous animal experiments and human studies have shown that intermittent injection of parathyroid hormone (PTH) exerts anabolic effects by increasing bone mass, whereas continuous PTH treatment decreases the bone mass. Thus, PTH has diverse effects on bone metabolism depending on the mode of administration. Several reports suggested that the duration of the serum concentration of PTH above the baseline level of endogenous PTH is a critical factor in regulating such anabolic and catabolic actions on the bone mass. However, the molecular mechanism of different PTH actions is not fully understood yet.

Pharmacokinetics of teriparatide (rhPTH[1-34]) and calcium pharmacodynamics in postmenopausal women with osteoporosis

Teriparatide (rhPTH[1-34]) affects calcium metabolism in a pattern consistent with the known actions of endogenous parathyroid hormone (PTH). This report describes the pharmacokinetics and resulting serum calcium response to teriparatide in postmenopausal women with osteoporosis. Pharmacokinetic samples for this analysis were obtained from 360 women who participated in the Fracture Prevention Trial. Postmenopausal women with osteoporosis received daily subcutaneous injections of either teriparatide 20 μg (4.86 μmol) or placebo, median 21 months' treatment. Serum teriparatide and calcium concentrations were measured throughout the study. An indirect-response model was developed to describe the pharmacokinetic-pharmacodynamic relationship between teriparatide concentrations and serum calcium response. The pharmacokinetics of teriparatide were characterized by rapid absorption (maximum concentration achieved within 30 min) and rapid elimination (half-life of 1 h), resulting in a total duration of exposure to the peptide of approximately 4 h. Teriparatide transiently increased serum calcium, with the maximum effect observed at approximately 4.25 h (median increase 0.4 mg/dl [0.1 mmol/l]). Calcium concentrations returned to predose levels by 16-24 h after each dose. Persistent hypercalcemia was not observed; one teriparatide 20 μg-treated patient had a predose serum calcium value above the normal range but <11.0 mg/dl (2.75 mmol/l). Following once-daily subcutaneous administration, teriparatide produces a modest but transient increase in serum calcium, consistent with the known effects of endogenous PTH on mineral metabolism. The excursion in serum calcium is brief, due to the short length of time that teriparatide concentrations are elevated.

Effect of transdermal teriparatide administration on bone mineral density in postmenopausal women

CONTEXT

Treatment of osteoporosis with an anabolic agent, teriparatide [human PTH 1-34 (TPTD)], is effective in reducing incident fractures, but patient resistance to daily sc injections has limited its use. A novel transdermal patch, providing a rapid, pulse delivery of TPTD, may provide a desirable alternative.

OBJECTIVE

The aim of the study was to determine the safety and efficacy of a novel transdermal TPTD patch compared to placebo patch and sc TPTD 20-microg injection in postmenopausal women with osteoporosis.

DESIGN

Our study consisted of 6-month, randomized, placebo-controlled, positive control, multidose daily administration.

PATIENTS

We enrolled 165 postmenopausal women (mean age, 64 yr) with osteoporosis.

INTERVENTIONS

A TPTD patch with a 20-, 30-, or 40-microg dose or a placebo patch was self-administered daily for 30-min wear time, or 20 microg of TPTD was injected daily.

OUTCOMES

The primary efficacy measure was mean percentage change in lumbar spine bone mineral density (BMD) from baseline at 6 months.

RESULTS

TPTD delivered by transdermal patch significantly increased lumbar spine BMD vs. placebo patch in a dose-dependent manner at 6 months (P < 0.001). TPTD 40-microg patch increased total hip BMD compared to both placebo patch and TPTD injection (P < 0.05). Bone turnover markers (procollagen type I N-terminal propeptide and C-terminal cross-linked telopeptide of type I collagen) increased from baseline in a dose-dependent manner in all treatment groups and were all significantly different from placebo patch (P < 0.001). All treatments were well tolerated, and no prolonged hypercalcemia was observed.

CONCLUSION

Transdermal patch delivery of TPTD in postmenopausal women with osteoporosis for 6 months is safe and effective in increasing lumbar spine and total hip BMD.

Treatment of osteoporosis with parathyroid hormone and teriparatide

Nowadays osteoporosis treatment is based primarily on therapy with antiresorptive agents, like the bisphosphonates. Parathyroid hormone (Preotact) and human recombinant parathyroid hormone peptide 1-34 (Teriparatide) are relatively new for the treatment of osteoporosis and belong to the group of anabolic agents. Both agents demonstrated an increase in bone mineral density and a significant reduction in vertebral fractures in postmenopausal women with osteoporosis when given for 18-24 months. Data on nonvertebral fractures are, however, not clear-cut, and so far only bisphosphonates and strontium ranelate have been demonstrated to reduce all types of fractures and therefore remain the front-line option for treatment of osteoporosis. As the safety, tolerability, and cost of the therapy also influence the choice of therapy, Preotact and Teriparatide might be useful additions to the armamentarium for (second-line) treatment of osteoporosis.

[Therapeutic agents for disorders of bone and calcium metabolism. Development of nasal formulation of hPTH (1-34)]

Intermittent administration of parathyroid hormone (PTH) has been shown to have strong anabolic effects on bone. However, the disadvantages associated with daily subcutaneous injection therapy are factors influencing patient acceptance and compliance. We have developed a nasal spray formula of hPTH (1-34), and found that peak serum hPTH (1-34) concentrations after treatment with nasal hPTH (1-34) spray are similar to those obtained after administration sc injection of hPTH (1-34). In order to determine clinical efficacy as well as safety and tolerability of nasal hPTH (1-34) spray therapy, a clinical trial was conducted in subjects with osteoporosis. Daily nasal hPTH (1-34) spray for 3 months significantly increased lumbar bone mineral density (L-BMD) in a dose-dependent manner. In addition, it was observed that one part of the L-BMD increases was a result of stimulating bone formation by the bone formation marker monitoring. Interestingly, bone resorption markers did not increase but were suppressed after 3 months, suggesting that there may be a different mechanism involved when comparing nasal hPTH (1-34) therapy with hPTH (1-34) sc administration.

High phosphorus diet changes phosphorus metabolism regardless of PTH action in rats

In this study, we ascertained whether the parathyroid hormone (PTH) dominantly regulated the effects of high phosphorus (P) intakes on urinary excretion of P and bone metabolism in rats. To maintain serum PTH level equally, parathyroidectomy (PTX) and sham-operated rats were constantly exposed to rPTH(1-34) and fed both control (0.3% P) and high P (1.2% P) diet for 7 days, respectively. Urinary excretions of P and C-terminal telopeptides of type I collagen were significantly increased in both PTX and sham rats by the high P diet. These results suggest that high P diet increased urinary P excretion while promoting bone resorption regardless of PTH-dependent regulation.

Assessing the Site of Recurrence in Patients with Secondary Hyperparathyroidism by a Simplified Casanova Autograftectomy Test

Patients with recurrent secondary hyperparathyroidism (rSHPT) following total parathyroidectomy and autotransplantation were prospectively studied by a modified Casanova test to discriminate between the graft-bearing arm and the neck as the site of the recurrence. The test measures intact parathyroid hormone (PTH) in blood obtained from the non-graft-bearing arm before an ischemic period and from the arm bearing the parathyroid graft during an ischemic period caused by an Esmarch bandage. The aim of this study was to evaluate the time course of PTH levels during the test and to establish an abbreviated procedure. A series of 30 patients with rSHPT who were admitted for reoperative surgery between 1994 and 2002 were studied. Systemic PTH levels were determined prior to suprasystolic exclusion of the graft-bearing arm as well as 2, 4, 6, 8, 10, 20, and 30 minutes during it and at 10 minutes afterward. Results were interpreted with a simple algorithm that suggested graft-dependent recurrence (GDR) whenever PTH levels dropped by more than 50% and neck-dominated recurrence (NDR) whenever the PTH levels dropped to less than 20%. Patients were operated on accordingly. Biochemical normalization of calcium and PTH was defined as success. Altogether, 15 patients had GDR and were cured after graft explantation. All of these patients were identified within 4 minutes of starting the test. Another 12 patients had NDR and were cured by excising overlooked or supernumerary glands. PTH levels were indeterminate in three patients (10%). Clinically, NDR is likely in all of these cases, but the test results were firmly established with 100% accuracy 8 minutes after the start of the test procedure. This abbreviated form of the Casanova test is advantageous for accurately determining the site of recurrence in the presence of rSHPT. It is less time-consuming, satisfactory in an ambulatory setting, equally effective, and less invasive than the original Casanova procedure.

Prevention of bone loss in ovariectomized rats by pulsatile transdermal iontophoretic administration of human PTH(1-34)

Serum human parathyroid hormone (1-34)[hPTH(1-34)] levels and the anabolic effect of hPTH(1-34) were compared after administration using multiple pulses of iontophoresis or subcutaneous (sc) intermittent injections to ovariectomized (OVX) Sprague Dawley rats. Triple-pulse iontophoretic administration of hPTH(1-34) (doses: 40-400 microg/patch), achieved by repeated 30-min applications of a 0.1 mA/cm(2) current separated by 45-min rest intervals, produced three sharp peaks in the serum hPTH(1-34) level in response to application of the current. Each peak appeared at the end of the 30-min current application period and was proportional to the hPTH(1-34) dose. Compared with once-daily sc injections (7 pulses/week), triple-pulses iontophoretic administered 3 times/week (9 pulses/week) for 4 weeks produced dose-related increases in the bone mineral density (BMD) of the distal 1/3 femur. For the sc administration, the relative BMD values using the vehicle injection as a reference standard for 1, 5, and 25 microg/kg/day were 104, 114, and 121%, respectively. For iontophoretic administration, the relative BMD values using the placebo patch as a reference standard for 40, 120, and 400 microg/patch were 104, 110, and 116%, respectively. The increase in the BMD plotted against the area under the hPTH(1-34) serum level-time curve (AUC) over 1 week resulted in similar straight lines in the 9 pulses/week iontophoretic administration and the 7 pulses/week sc administration groups. The estimated iontophoretic dose giving an equivalent BMD to once-daily sc administration at 5 microg/kg/day was 120 microg/patch. These findings strongly suggest that three iontophoretic pulses administered on alternate days will exert an anabolic effect equivalent to that of daily sc administration at doses giving the same weekly AUC. Furthermore, this method of administering hPTH(1-34) might enable self-medication, a useful advance in the treatment of osteoporosis.

Comparison of peripheral bone and body axis skeleton in a rat model of mild-to-moderate renal failure in the presence of physiological serum levels of calcitropic hormones

The skeleton is characterized by anatomic heterogeneity of metabolic turnover. Site-dependent differences in hormonal effects seem likely. Hyporesponsiveness of osteoclasts to parathyroid hormone (PTH) and probably calcitriol was recently demonstrated in the fifth lumbar vertebra of a rat model with moderate renal failure. We compared histomorphometric findings of the tibial head to these data. Histomorphometric measurements were carried out in sections of the right tibial head of pair-fed male Sprague-Dawley rats. Subtotally nephrectomized (SNx), parathyroidectomized (PTx), rats, which received either solvent or rat PTH(1-34) (100 ng/kg per hour) + calcitriol (5 pmol/kg per hour) via osmotic minipumps were compared with sham-operated controls. Results were compared with data from the fifth lumbar vertebra reported recently. Osteoclast numerical density and osteoclast surface density were lower in the tibial head and the lumbar vertebra of solvent-treated SNxPTx rats than in sham-operated controls (p < 0.05), and could not be returned to normal by the substitution of PTH + calcitriol (p < 0.05). On the other hand, there were differences between interventional effects on the tibial head and on the lumbar vertebra concerning parameters describing osteoblasts and trabecular bone volume. In the tibial head, osteoblast surface density was nearly unchanged in both interventions. Nevertheless, bone volume increased after SNxPTx without substitution of PTH + calcitriol (p < 0.05), and no further changes occurred after hormonal replacement. In contrast, osteoblast surface density in the lumbar vertebra was decreased slightly compared with values in sham-operated rats; a clear but nonsignificant increase occurred after the administration of calcitropic hormones. This was accompanied by unchanged trabecular bone volume after SNxPTx. Hormonal replacement, however, caused an increase in trabecular bone volume (p < 0.05), which represents an anabolic effect, which contrasts with findings from the tibial head. The different interventional effects on the lumbar spine and on peripheral bone, regarding the parameters reflecting the condition of osteoblasts, may be intrinsic to the uremic syndrome itself as well as to dissimilar growth manner, function, and mechanical requirements. The findings substantiate the site dependence of bone surface cell metabolism in renal failure and should be the subject of further study. Corresponding results with regard to bone resorption argue for a bone-site-independent, diminished response of osteoclasts to calcitropic hormones.

Development of a highly sensitive and specific two-site enzyme immunoassay for parathyroid hormone (1-34): application to pharmacokinetic study on intranasal parathyroid hormone (1-34) in human

A highly sensitive and specific two-site enzyme immunoassay for parathyroid hormone (1-34) (PTH(1-34)) and its usability for the pharmacokinetic study are described. Plasma samples were incubated simultaneously with 2,4-dinitrophenylated anti-PTH(1-34) IgG and anti-PTH(1-34) Fab'-beta-D-galactosidase conjugate. The immune complex formed of the three components was trapped onto (anti-2,4-dinitrophenyl group) IgG-coated polystyrene balls. beta-D-Galactosidase activity bound to the polystyrene balls was assayed by fluorometry. The practical detection limit of PTH(1-34) was 50 fg (12 amol)/0.05 ml of sample and 1 pg/ml as the concentration and practically no interference occurred by PTH(1-84) and PTH-related protein (1-34) up to 300 pg/ml and 10 ng/ml, respectively. The application of this method has enabled us to directly estimate the bioavailability of PTH(1-34) dosed intranasally at the prescribed level (0.090 mg). The pharmacokinetic parameters of the intranasal PTH(1-34) (n = 4) thus estimated were as follows: the area under the plasma concentration-time curve (AUC) = 20,500+/-15,900(SD) pg.min/ml; the mean residence time (MRT) = 194+/-16.3(SD) min; and the maximal concentration (Cmax) = 98+/-51 (SD) pg/ml with the maximal time (Tmax) = 35.0+/-12.2(SD) min.

Validation and application of an immunoradiometric assay for the determination of human parathyroid hormone fragment 1-34 in dog plasma following subcutaneous and intravenous administration

A method for the measurement of human parathyroid hormone fragment 1-34 (PTH1-34) in dog plasma was developed by modification of a commercially available immunodiometric assay (IRMA) designed for the determination of rat PTH1-34 in serum. Major modifications were made to the assay in order to circumvent significant problems encountered during the validation of the IRMA. PTH1-34 was found to be highly unstable in both rat serum and dog serum and plasma at room temperature, in contrast to literature reports. The addition of a protease inhibitor cocktail to serum or plasma samples was necessary to prevent in-vitro proteolytic degradation of human PTH1-34 prior to analysis. Additionally, plasma was chosen over serum as the sample matrix to expedite the separation of samples from cells, minimizing proteolytic degradation prior to the addition of cocktail. Finally, the reported 100% cross-reactivity between rat and human PTH1-34 was found to be only 65%; therefore, a human PTH1-34 standard was substituted for the rat standard. These modifications allowed the accurate measurement of human PTH1-34 in plasma obtained from dogs dosed intravenously and subcutaneously with human PTH1-34 using a commercially available kit.

Secretion of parathyroid hormone-related peptide in patients with multiple myeloma

Stimulation of bone resorption by local factors, the cytokines, is key to the development of hypercalcemia in multiple myeloma patients. Parathyroid hormone-related peptide, the systemic factor found in humoral hypercalcemia, has rarely been incriminated in myeloma. We report a case of myeloma with hypercalcemia and elevated serum level of parathyroid hormone-related peptide. Bisphosphonate therapy was rapidly effective in correcting serum calcium levels despite persistent high levels of the peptide. Seven other cases of myeloma with hypercalcemia and high serum parathyroid hormone-related peptide levels have been reported. Expression by myeloma plasmocytes of the messenger RNA for this peptide has also been demonstrated. These data suggest that parathyroid hormone-related peptide may contribute to the development of hypercalcemia in some myeloma patients.