The calcimimetic compound NPS R-568 suppresses parathyroid cell proliferation in rats with renal insufficiency. Control of parathyroid cell growth via a calcium receptor

Development of Robust Heterogeneous Chiral Rhodium Catalysts Utilizing Acid-Base and Electrostatic Interactions for Efficient Continuous-Flow Asymmetric Hydrogenations

Heterogeneous chiral Rh catalysts based on acid-base and electrostatic interactions have been developed. The robust catalysts demonstrate high activity and selectivity in the continuous-flow asymmetric hydrogenation of a wide variety of enamides and dehydroamino acids, providing optically active amides without leaching of metal species. The chiral environments can be easily tuned by changing the chiral ligands, demonstrating the high versatility of the heterogeneous catalysts. By applying these efficient catalysts, continuous synthesis of several active pharmaceutical ingredient intermediates was achieved.

A new model for the HPA axis explains dysregulation of stress hormones on the timescale of weeks

Stress activates a complex network of hormones known as the hypothalamic-pituitary-adrenal (HPA) axis. The HPA axis is dysregulated in chronic stress and psychiatric disorders, but the origin of this dysregulation is unclear and cannot be explained by current HPA models. To address this, we developed a mathematical model for the HPA axis that incorporates changes in the total functional mass of the HPA hormone-secreting glands. The mass changes are caused by HPA hormones which act as growth factors for the glands in the axis. We find that the HPA axis shows the property of dynamical compensation, where gland masses adjust over weeks to buffer variation in physiological parameters. These mass changes explain the experimental findings on dysregulation of cortisol and ACTH dynamics in alcoholism, anorexia, and postpartum. Dysregulation occurs for a wide range of parameters and is exacerbated by impaired glucocorticoid receptor (GR) feedback, providing an explanation for the implication of GR in mood disorders. These findings suggest that gland-mass dynamics may play an important role in the pathophysiology of stress-related disorders.

Cinacalcet use in pediatric chronic kidney disease. A survey study

OBJECTIVES

To evaluate the practice and attitude of pediatrics nephrologists about cinacalcet use in children.

METHODS

An electronic structured questionnaire was answered by pediatric nephrologists practicing in the Kingdom of Saudi Arabia (KSA) and Gulf Council countries (GCC).

RESULTS

A total of 42  pediatric nephrologists responded, of them, 42% used cinacalcet for young children ≤5 years of age and 79% used for children. There were wide variations in the method of administration (examples: crushed, divided, whole tablets), monitoring, doses and response definition, and follow-up. No serious complications after starting cinacalcet was observed in 50%, while 40% reported various complications, mainly hypocalcemia (70%). Cinacalcet was stopped without achieving the target parathyroid hormone in more than half (55%) of children because of intractable adverse effects (40%), poor response (30%), non-adherence (25%), or high cost (5%).

CONCLUSION

Cinacalcet is used by the majority of pediatric nephrologists in KSA and GCC. A standard clinical guideline is needed to be followed by all users.

Evocalcet prevents ectopic calcification and parathyroid hyperplasia in rats with secondary hyperparathyroidism

Background

Elevated parathyroid hormone (PTH) levels in secondary hyperparathyroidism (SHPT) lead to vascular calcification, which is associated with cardiovascular events and mortality. Increased PTH production is caused by the excessive proliferation of parathyroid gland cells, which is accelerated by abnormal mineral homeostasis. Evocalcet, an oral calcimimetic agent, inhibits the secretion of PTH from parathyroid gland cells and has been used for the management of SHPT in dialysis patients. We observed the effects of evocalcet on ectopic calcification and parathyroid hyperplasia using chronic kidney disease (CKD) rats with SHPT.

Methods

CKD rats with SHPT induced by adenine received evocalcet orally for 5 weeks. The calcium and inorganic phosphorus content in the aorta, heart and kidney was measured. Ectopic calcified tissues were also assessed histologically. To observe the effects on the proliferation of parathyroid gland cells, parathyroid glands were histologically assessed in CKD rats with SHPT induced by 5/6 nephrectomy (Nx) after receiving evocalcet orally for 4 weeks.

Results

Evocalcet prevented the increase in calcium and inorganic phosphorus content in the ectopic tissues and suppressed calcification of the aorta, heart and kidney in CKD rats with SHPT by reducing the serum PTH and calcium levels. Evocalcet suppressed the parathyroid gland cell proliferation and reduced the sizes of parathyroid cells in CKD rats with SHPT.

Conclusions

These findings suggest that evocalcet would prevent ectopic calcification and suppress parathyroid hyperplasia in patients with SHPT.

Continuous-Flow Amide and Ester Reductions Using Neat Borane Dimethylsulfide Complex

Reductions of amides and esters are of critical importance in synthetic chemistry, and there are numerous protocols for executing these transformations employing traditional batch conditions. Notably, strategies based on flow chemistry, especially for amide reductions, are much less explored. Herein, a simple process was developed in which neat borane dimethylsulfide complex (BH₃ ⋅DMS) was used to reduce various esters and amides under continuous-flow conditions. Taking advantage of the solvent-free nature of the commercially available borane reagent, high substrate concentrations were realized, allowing outstanding productivity and a significant reduction in E-factors. In addition, with carefully optimized short residence times, the corresponding alcohols and amines were obtained in high selectivity and high yields. The synthetic utility of the inexpensive and easily implemented flow protocol was further corroborated by multigram-scale syntheses of pharmaceutically relevant products. Owing to its beneficial features, including low solvent and reducing agent consumption, high selectivity, simplicity, and inherent scalability, the present process demonstrates fewer environmental concerns than most typical batch reductions using metal hydrides as reducing agents.

Early response of the parathyroid gland to withdrawal of a calcimimetic compound in uremic rats

Little is known about changes in parathyroid cells when calcimimetics are withdrawn. We examined the response of parathyroid glands to cinacalcet (Cina) withdrawal in uremic Sprague-Dawley rats fed a high-phosphate diet to develop secondary hyperparathyroidism and divided into groups treated with vehicle (UC), Cina, and Cina and maxacalcitol (Maxa), a vitamin D receptor activator (CiNa + Maxa). After 2 wk of treatment, vehicle and Cina were withdrawn and Maxa was continued. Rats were analyzed immediately (day 0) and 7 days (day 7) after withdrawal. The Cina and CiNa + Maxa groups had significantly lower parathyroid hormone (PTH) than the UC group on day 0, although PTH in the Cina group reached UC levels on day 7. On day 0, there were significantly more proliferating cell nuclear antigen-positive cells in the UC group compared with normal controls, and this increase was significantly suppressed in the Cina and CiNa + Maxa groups. On day 7, the Cina group, but not the CiNa + Maxa group, showed a significant increase in proliferating cell nuclear antigen-positive cells compared with the UC group. This increase was related to parathyroid cell diameter regression to UC levels, whereas combination treatment maintained diameter suppression. These results indicate that parathyroid growth activity is stimulated by Cina withdrawal, although the PTH level was not further increased. Continuous administration of Cina may be required for optimal control of secondary hyperparathyroidism, and simultaneous use of a vitamin D receptor activator may be advisable during Cina withdrawal.

The calcium-sensing receptor in physiology and in calcitropic and noncalcitropic diseases

The Ca2+-sensing receptor (CaSR) is a dimeric family C G protein-coupled receptor that is expressed in calcitropic tissues such as the parathyroid glands and the kidneys and signals via G proteins and β-arrestin. The CaSR has a pivotal role in bone and mineral metabolism, as it regulates parathyroid hormone secretion, urinary Ca2+ excretion, skeletal development and lactation. The importance of the CaSR for these calcitropic processes is highlighted by loss-of-function and gain-of-function CaSR mutations that cause familial hypocalciuric hypercalcaemia and autosomal dominant hypocalcaemia, respectively, and also by the fact that alterations in parathyroid CaSR expression contribute to the pathogenesis of primary and secondary hyperparathyroidism. Moreover, the CaSR is an established therapeutic target for hyperparathyroid disorders. The CaSR is also expressed in organs not involved in Ca2+ homeostasis: it has noncalcitropic roles in lung and neuronal development, vascular tone, gastrointestinal nutrient sensing, wound healing and secretion of insulin and enteroendocrine hormones. Furthermore, the abnormal expression or function of the CaSR is implicated in cardiovascular and neurological diseases, as well as in asthma, and the CaSR is reported to protect against colorectal cancer and neuroblastoma but increase the malignant potential of prostate and breast cancers.

Defining potential roles of Pb(2+) in neurotoxicity from a calciomics approach

Metal ions play crucial roles in numerous biological processes, facilitating biochemical reactions by binding to various proteins. An increasing body of evidence suggests that neurotoxicity associated with exposure to nonessential metals (e.g., Pb(2+)) involves disruption of synaptic activity, and these observed effects are associated with the ability of Pb(2+) to interfere with Zn(2+) and Ca(2+)-dependent functions. However, the molecular mechanism behind Pb(2+) toxicity remains a topic of debate. In this review, we first discuss potential neuronal Ca(2+) binding protein (CaBP) targets for Pb(2+) such as calmodulin (CaM), synaptotagmin, neuronal calcium sensor-1 (NCS-1), N-methyl-d-aspartate receptor (NMDAR) and family C of G-protein coupled receptors (cGPCRs), and their involvement in Ca(2+)-signalling pathways. We then compare metal binding properties between Ca(2+) and Pb(2+) to understand the structural implications of Pb(2+) binding to CaBPs. Statistical and biophysical studies (e.g., NMR and fluorescence spectroscopy) of Pb(2+) binding are discussed to investigate the molecular mechanism behind Pb(2+) toxicity. These studies identify an opportunistic, allosteric binding of Pb(2+) to CaM, which is distinct from ionic displacement. Together, these data suggest three potential modes of Pb(2+) activity related to molecular and/or neural toxicity: (i) Pb(2+) can occupy Ca(2+)-binding sites, inhibiting the activity of the protein by structural modulation, (ii) Pb(2+) can mimic Ca(2+) in the binding sites, falsely activating the protein and perturbing downstream activities, or (iii) Pb(2+) can bind outside of the Ca(2+)-binding sites, resulting in the allosteric modulation of the protein activity. Moreover, the data further suggest that even low concentrations of Pb(2+) can interfere at multiple points within the neuronal Ca(2+) signalling pathways to cause neurotoxicity.

Parathyroid Nodular Hyperplasia and Responsiveness to Drug Therapy in Renal Secondary Hyperparathyroidism: An Open Question

The goal of the pharmacological therapy in secondary hyperparathyroidism (SHPT) is to reduce serum levels of parathyroid hormone and phosphorus, to correct those of calcium and vitamin D, to arrest or reverse the parathyroid hyperplasia. However, when nodular hyperplasia or an autonomous adenoma develops, surgery may be indicated. We reviewed the literature with the aim of defining if the echographic criteria predictive of unresponsiveness of SHPT to calcitriol therapy are valid also in the cinacalcet era and if drug therapy may reverse nodular hyperplasia of parathyroid gland (PTG). The responsiveness to therapy and regression of the nodular hyperplasia of PTG remains an open question in the calcimimetic era as well as the cutoff between medical and surgical therapy. Prospective studies are needed in order to clarify if an earlier use of cinacalcet in moderate SHPT might arrest the progression of parathyroid growth and stabilize SHPT.

Long-term effects of etelcalcetide as intravenous calcimimetic therapy in hemodialysis patients with secondary hyperparathyroidism

BACKGROUND

Secondary hyperparathyroidism (SHPT) is a serious major complication in hemodialysis patients with chronic kidney disease. Long-term maintenance of serum phosphate, calcium, and parathyroid hormone (PTH) levels in appropriate ranges in these patients is a major challenge. We investigated the efficacy and safety of long-term treatment with etelcalcetide, a novel intravenous calcimimetic, in Japanese SHPT patients on long-term hemodialysis.

METHODS

This study was a multicenter open-label study. A total of 191 hemodialysis patients with serum intact PTH (iPTH) > 240 pg/mL were enrolled. Etelcalcetide was administered thrice weekly for 52 weeks, with an initial dose of 5 mg and flexibility to adjust the dose between 2.5 and 15 mg and to adjust the dosing of concomitant medications for SHPT. The efficacy endpoint was the proportion of patients with serum iPTH decreased to the target range (60-240 pg/mL).

RESULTS

Serum iPTH levels decreased immediately after etelcalcetide was started. At the end of the study, 87.5% (95% confidence interval 81.4-92.2; 140/160 patients) of patients achieved target serum iPTH levels, with control of serum calcium and phosphate levels. Adverse events, mostly mild to moderate, were reported by 96.8% of patients and led to study discontinuation in 7.4% of patients. Nausea, vomiting, and symptomatic hypocalcemia were found in 4.7, 9.5, and 1.1%, with 0.5, 1.1, and 1.1% considered treatment-related.

CONCLUSIONS

Etelcalcetide effectively maintained serum iPTH, calcium, and phosphate levels in appropriate ranges with concomitant medications for SHPT for 52 weeks in Japanese hemodialysis patients, and was safe and well tolerated.

REGISTRATION NUMBER

JapicCTI-142665.

Biphasic response as a mechanism against mutant takeover in tissue homeostasis circuits

Tissues use feedback circuits in which cells send signals to each other to control their growth and survival. We show that such feedback circuits are inherently unstable to mutants that misread the signal level: Mutants have a growth advantage to take over the tissue, and cannot be eliminated by known cell-intrinsic mechanisms. To resolve this, we propose that tissues have biphasic responses in and the signal is toxic at both high and low levels, such as glucotoxicity of beta cells, excitotoxicity in neurons, and toxicity of growth factors to T cells. This gives most of these mutants a frequency-dependent selective disadvantage, which leads to their elimination. However, the biphasic mechanisms create a new unstable fixed point in the feedback circuit beyond which runaway processes can occur, leading to risk of diseases such as diabetes and neurodegenerative disease. Hence, glucotoxicity, which is a dangerous cause of diabetes, may have a protective anti-mutant effect. Biphasic responses in tissues may provide an evolutionary stable strategy that avoids invasion by commonly occurring mutants, but at the same time cause vulnerability to disease.

Calcium-Sensing Receptor and Transient Receptor Ankyrin-1 Mediate Emesis Induction by Deoxynivalenol (Vomitoxin)

The common foodborne mycotoxin deoxynivalenol (DON, vomitoxin) can negatively impact animal and human health by causing food refusal and vomiting. Gut enteroendocrine cells (EECs) secrete hormones that mediate DON's anorectic and emetic effects. In prior work utilizing a cloned EEC model, our laboratory discovered that DON-induced activation of calcium-sensing receptor (CaSR), a G-coupled protein receptor (GPCR), and transient receptor ankyrin-1 (TRPA1), a transient receptor potential (TRP) channel, drives Ca2+-mediated hormone secretion. Consistent with these in vitro findings, CaSR and TRPA1 mediate DON-induced satiety hormone release and food refusal in the mouse, an animal model incapable of vomiting. However, the roles of this GPCR and TRP in DON's emetic effects remain to be determined. To address this, we tested the hypothesis that DON triggers emesis in mink by activating CaSR and TRPA1. Oral gavage with selective agonists for CaSR (R-568) or TRPA1 (allyl isothiocyanate; AITC) rapidly elicited emesis in the mink in dose-dependent fashion. Oral pretreatment of the animals with the CaSR antagonist NPS-2143 or the TRP antagonist ruthenium red (RR), respectively, inhibited these responses. Importantly, DON-induced emesis in mink was similarly inhibited by oral pretreatment with NPS-2143 or RR. In addition, these antagonists suppressed concurrent DON-induced elevations in plasma peptide YY3-36 and 5-hydroxytryptamine-hormones previously demonstrated to mediate the toxin's emetic effects in mink. Furthermore, antagonist co-treatment additively suppressed DON-induced emesis and peptide YY 3-36 release. To summarize, the observations here strongly suggest that activation of CaSR and TRPA1 might have critical roles in DON-induced emesis.

Intraperitoneal Calcitriol for Treatment of Severe Hyperparathyroidism in Children with Chronic Kidney Disease: A Therapy Forgotten

Active Vitamin D sterols such as calcitriol and alfacalcidol are quite effective in the treatment of mineral bone disease secondary to chronic kidney disease. However, some children on peritoneal dialysis (PD) are resistant to oral formulations of active Vitamin D, and use of an intravenous formulation in such patients is inconvenient. In these children, intraperitoneal (IP) calcitriol has been shown to be effective in the treatment of secondary hyperparathyroidism. However, its use has declined. We report 2 children, aged 1 and 9.5 years, on chronic cycler PD with severe secondary hyperparathyroidism refractory to oral active Vitamin D who were successfully treated with IP calcitriol for a period of 12 and 4 months, respectively. We also discuss the published literature on the efficacy of IP calcitriol for treatment of secondary hyperparathyroidism and specific considerations for its use in PD patients.

Dynamical compensation in physiological circuits

Biological systems can maintain constant steady-state output despite variation in biochemical parameters, a property known as exact adaptation. Exact adaptation is achieved using integral feedback, an engineering strategy that ensures that the output of a system robustly tracks its desired value. However, it is unclear how physiological circuits also keep their output dynamics precise-including the amplitude and response time to a changing input. Such robustness is crucial for endocrine and neuronal homeostatic circuits because they need to provide a precise dynamic response in the face of wide variation in the physiological parameters of their target tissues; how such circuits compensate their dynamics for unavoidable natural fluctuations in parameters is unknown. Here, we present a design principle that provides the desired robustness, which we call dynamical compensation (DC). We present a class of circuits that show DC by means of a nonlinear feedback loop in which the regulated variable controls the functional mass of the controlling endocrine or neuronal tissue. This mechanism applies to the control of blood glucose by insulin and explains several experimental observations on insulin resistance. We provide evidence that this mechanism may also explain compensation and organ size control in other physiological circuits.

Potential roles for calcium-sensing receptor (CaSR) and transient receptor potential ankyrin-1 (TRPA1) in murine anorectic response to deoxynivalenol (vomitoxin)

Food contamination by the trichothecene mycotoxin deoxynivalenol (DON, vomitoxin) has the potential to adversely affect animal and human health by suppressing food intake and impairing growth. In mice, the DON-induced anorectic response results from aberrant satiety hormone secretion by enteroendocrine cells (EECs) of the gastrointestinal tract. Recent in vitro studies in the murine STC-1 EEC model have linked DON-induced satiety hormone secretion to activation of calcium-sensing receptor (CaSR), a G-coupled protein receptor, and transient receptor potential ankyrin-1 (TRPA1), a TRP channel. However, it is unknown whether similar mechanisms mediate DON's anorectic effects in vivo. Here, we tested the hypothesis that DON-induced food refusal and satiety hormone release in the mouse are linked to activation of CaSR and TRPA1. Oral treatment with selective agonists for CaSR (R-568) or TRPA1 (allyl isothiocyanate (AITC)) suppressed food intake in mice, and the agonist's effects were suppressed by pretreatment with corresponding antagonists NPS-2143 or ruthenium red (RR), respectively. Importantly, NPS-2143 or RR inhibited both DON-induced food refusal and plasma elevations of the satiety hormones cholecystokinin (CCK) and peptide YY_3-36 (PYY_3-36); cotreatment with both antagonists additively suppressed both anorectic and hormone responses to DON. Taken together, these in vivo data along with prior in vitro findings support the contention that activation of CaSR and TRPA1 contributes to DON-induced food refusal by mediating satiety hormone exocytosis from EEC.

Active vitamin D potentiates the anti-neoplastic effects of calcium in the colon: A cross talk through the calcium-sensing receptor

Epidemiological studies suggest an inverse correlation between dietary calcium (Ca(2+)) and vitamin D intake and the risk of colorectal cancer (CRC). It has been shown in vitro that the active vitamin D metabolite, 1,25-dihydroxyvitamin D3 (1,25-D3) can upregulate expression of the calcium-sensing receptor (CaSR). In the colon, CaSR has been suggested to regulate proliferation of colonocytes. However, during tumorigenesis colonic CaSR expression is downregulated and we hypothesized that the loss of CaSR could influence the anti-tumorigenic effects of Ca(2+) and vitamin D. Our aim was to assess the impact of CaSR expression and function on the anti-neoplastic effects of 1,25-D3 in colon cancer cell lines. We demonstrated that in the healthy colon of mice, high vitamin D diet (2500 IU/kg diet) increased expression of differentiation and apoptosis markers, decreased expression of proliferation markers and significantly upregulated CaSR mRNA expression, compared with low vitamin D diet (100 IU/kg diet). To determine the role of CaSR in this process, we transfected Caco2-15 and HT29 CRC cells with wild type CaSR (CaSR-WT) or a dominant negative CaSR mutant (CaSR-DN) and treated them with 1,25-D3 alone, or in combination with CaSR activators (Ca(2+) and NPS R-568). 1,25-D3 enhanced the anti-proliferative effects of Ca(2+) and induced differentiation and apoptosis only in cells with a functional CaSR, which were further enhanced in the presence of NPS R-568, a positive allosteric modulator of CaSR. The mutant CaSR inhibited the anti-tumorigenic effects of 1,25-D3 suggesting that the anti-neoplastic effects of 1,25-D3 are, at least in part, mediated by the CaSR. Taken together, our data provides molecular evidence to support the epidemiological observation that both, vitamin D and calcium are needed for protection against malignant transformation of the colon and that their effect is modulated by the presence of a functional CaSR. This article is part of a Special Issue entitled '17th Vitamin D Workshop'.

Calcium-sensing receptor activation in chronic kidney disease: effects beyond parathyroid hormone control

Secondary hyperparathyroidism (SHPT) is an important complication of advanced chronic kidney disease (CKD). Cinacalcet, an allosteric modulator of the calcium-sensing receptor (CaSR) expressed in parathyroid glands, is the only calcimimetic approved to treat SHPT in patients on dialysis. By enhancing CaSR sensitivity for plasma extracellular calcium (Ca(2+)0), cinacalcet reduces serum parathyroid hormone, Ca(2+)0, and serum inorganic phosphorous concentrations, allowing better control of SHPT and CKD-mineral and bone disorders. Of interest, the CaSR also is expressed in a variety of tissues where its activation regulates diverse cellular processes, including secretion, apoptosis, and proliferation. Thus, the existence of potential off-target effects of cinacalcet cannot be neglected. This review summarizes our current knowledge concerning the potential role(s) of the CaSR expressed in various tissues in CKD-related disorders, independently of parathyroid hormone control.

Antialbuminuric actions of calcilytics in the remnant kidney

Hyperphosphatemia accelerates the progression of chronic kidney diseases. In the present study, the effects of ronacaleret, a calcilytic agent, on renal injury were assessed in the following four groups of rats: 5/6-nephrectomized Wistar rats as a control (C group), rats treated with ronacaleret (3 mg·kg(-1)·day(-1); R group), rats treated with calcitriol (30 ng·kg(-1)·day(-1); V group), and rats treated with both ronacaleret and calcitriol (R + V group). Three months later, rats were euthanized under anesthesia, and the remnant kidneys were harvested for analysis. Albuminuria was lower in the R and V groups than in the C group (P < 0.05). Creatinine clearance was elevated in the R and V groups compared with the C group (P < 0.05). Serum Ca(2+) and renal ANG II were higher in the R + V group than in the C group (P < 0.05 for each), and serum phosphate was reduced in the R group compared with the C group (P < 0.05). Fibroblast growth factor-23 was lower in the R group and higher in the V and R + V groups than in the C group. However, parathyroid hormone did not differ significantly among the four groups. Renal klotho expression was elevated in the R and V groups compared with the C group (P < 0.05). The present data indicate that ronacaleret preserves klotho expression and renal function with reductions in serum phosphate and albuminuria in 5/6-nephrectomized rats. Our findings demonstrate that vitamin D prevents declines in klotho expression and renal function, suppressing albuminuria.

Two Years of Cinacalcet Hydrochloride Treatment Decreased Parathyroid Gland Volume and Serum Parathyroid Hormone Level in Hemodialysis Patients With Advanced Secondary Hyperparathyroidism

The long-term effect of cinacalcet hydrochloride treatment on parathyroid gland (PTG) volume has been scarcely investigated in patients with moderate to advanced secondary hyperparathyroidism (SHPT). The present study was a prospective observational study to determine the effect of cinacalcet treatment on PTG volume and serum biochemical parameters in 60 patients with renal SHPT, already treated with intravenous vitamin D receptor activator (VDRA). Measurement of biochemical parameters and PTG volumes were performed periodically, which were analyzed by stratification into tertiles across the baseline parathyroid hormone (PTH) level or PTG volume. We also determined the factors that can estimate the changes in PTG volume and the achievement of the target PTH range by multivariable analyses. Two years of cinacalcet treatment significantly decreased the serum levels of PTH, calcium, and phosphate, followed by the improvement of achieving the target ranges for these parameters recommended by the Japanese Society for Dialysis Therapy. Cinacalcet decreased the maximal and total PTG volume by about 30%, and also decreased the serum PTH level independent of the baseline serum PTH level and PTG volume. Ten out of 60 patients showed 30% increase in maximal PTG after 2 years. Multivariable analysis showed that patients with nodular PTG at baseline and patients with higher serum calcium and PTH levels at 1 year were likely to exceed the target range of PTH at two years. In conclusion, cinacalcet treatment with intravenous VDRA therapy decreased both PTG volume and serum intact PTH level, irrespective of the pretreatment PTG status and past treatment history.

Effect of cinacalcet cessation on hyperparathyroidism in kidney transcaplant patients after long-term dialysis therapy

BACKGROUND

Cinacalcet is a promising therapy widely used in dialysis patients with hyperparathyroidism resistant to conventional therapy. However, reports regarding the influence of cinacalcet cessation after long-term use on kidney transplantation patients are few.

METHODS

This retrospective observational study included 40 dialysis patients who underwent kidney transplantation. Creatinine, corrected calcium, phosphorus, alkaline phosphatase, and intact parathyroid hormone levels were assessed before and after kidney transplantation according to pretransplant treatment of chronic kidney disease-mineral and bone disorder.

RESULTS

Ultrasonography revealed enlargement of the parathyroid in all patients treated with cinacalcet. Although the data at the time of kidney transplantation were comparable, the serum levels of calcium, alkaline phosphatase, and intact parathyroid hormone after kidney transplantation were higher in patients treated with cinacalcet than in those treated without. However, serum phosphate levels in the cinacalcet group were slightly higher at the time of kidney transplantation and significantly lower 3 months later.

CONCLUSIONS

Mineral abnormalities persisted in kidney transplant patients with enlarged parathyroid glands after discontinuation of cinacalcet treatment. Parathyroidectomy should be considered in kidney transplant candidates with the risk of developing refractory hyperparathyroidism after transplantation.

Establishment and characterization of a human parathyroid carcinoma derived cell line

Parathyroid carcinoma is a rare neoplasia associated with PTH-dependent hypercalcaemia. It is infrequent in primary hyperparathyroidism (HPT) and very rarely associated with uremic HPT. A continuous cell line named Pt.Kich-1 from a parathyroid carcinoma diagnosed in a patient with secondary hyperparathyroidism (II° HPTH) was established and maintained in vitro for more than 60 passages. The cells were characterized for their immunophenotypic and endocrine characteristics as well as for their functional status after treatment by the extracellular [Ca(2+)]e, and the calcium homeostasis regulator 1α,25 (OH)2D3. The cytogenetic features were established by the R-banding. The Pt.Kich-1 cultures show an aspect of admixed epithelial/mesenchymal like cells with a doubling time between 96 and 112h. The cells are immunoreactive for cytokeratin (60%), EMA (26%), vimentin (46%), E-cadherin (32%), and synaptophysin (16%), while chromogranin A was not detected. Hypotetraploid karyotype containing large chromosomal markers and double minute chromosomes was identified in 30% of the metaphases. Treatment of Pt.Kich-1 cells with 1.0mM, 1.5mM, and 1.7mM of extracellular [Ca(2+)]e increased the DNA synthesis, while the calcium homeostasis regulator, the 1α,25 (OH)2D3, at 10(-9)-10(-7)M inhibited the cell growth. The levels of PTH measured in the medium of early cultures ranging between 547 and 610pg/μg of DNA declined during the passages to a level between 6 and 12pg/μg of DNA. No effect on the PTH release by the Pt.Kich-1 cells was observed after treatment with the all-trans (ATRA) and 9-cis retinoic acid differentiation inducers. The described in vitro cellular model can serve as a useful tool to study the pathogenesis of parathyroid carcinoma and to improve the knowledge of the molecular mechanisms involved in the control of gland sensitivity to [Ca(2+)]e leading to PTH synthesis and secretion.

Chronic kidney disease: mineral and bone disorder in children

Childhood and adolescence are crucial times for the development of a healthy skeletal and cardiovascular system. Disordered mineral and bone metabolism accompany chronic kidney disease (CKD) and present significant obstacles to optimal bone strength, final adult height, and cardiovascular health. Early increases in bone and plasma fibroblast growth factor 23 (FGF23) are associated with early defects in skeletal mineralization. Later in the course of CKD, secondary hyperparathyroidism--caused by a combination of declining calcitriol values and phosphate retention--results in high-turnover renal osteodystrophy whereas increased levels of both phosphate and FGF23 contribute to cardiovascular disease. Treatment of hyperphosphatemia and secondary hyperparathyroidism improves high-turnover bone disease but fails to correct defects in skeletal mineralization. Because overtreatment may result in adynamic bone disease, growth failure, hypercalcemia, and progression of cardiovascular calcifications, therapy therefore must be titrated carefully to maintain optimal serum biochemical parameters according to stage of CKD. Newer therapeutic agents and new treatment paradigms may suppress serum PTH levels effectively while limiting intestinal calcium absorption and skeletal FGF23 stimulation and may provide future therapeutic alternatives for children with CKD.

Histology and immunohistochemistry of the parathyroid glands in renal secondary hyperparathyroidism refractory to vitamin D or cinacalcet therapy

BACKGROUND

Cinacalcet is a new effective treatment of secondary hyperparathyroidism (SHPT) in hemodialysis patients (HP), but the alterations of parathyroid gland (PTG) hyperplasia determined by cinacalcet and vitamin D have not been extensively investigated in humans.

METHODS

We performed histological analyses of 94 PTGs removed from 25 HP who underwent parathyroidectomy (PTx) because of SHPT refractory to therapy with vitamin D alone (group A=13 HP and 46 PTGs) or associated with cinacalcet (group B=12 HP and 48 PTGs). The number, weight, the macroscopic cystic/hemorrhagic changes, and type of hyperplasia of PTG (nodular=NH, diffuse=DH) were assessed. In randomly selected HP of group A (4 HP and 14 PTGs) and group B (4 HP and 15 PTGs), the labeling index of cells positive to Ki-67 and TUNEL and the semiquantitative score of immunohistochemistry staining of vitamin D receptor, calcium-sensing receptor, and vascular endothelial growth factor-α (VEGF-α) were measured in the entire PTGs and in the areas with DH or NH.

RESULTS

The number and weight of single and total PTG of each HP were similar in the two groups as well as the number of PTG with macroscopic cystic/hemorrhagic areas. TUNEL, Ki-67, and VEGF-α scores were higher in NH than in DH areas.

CONCLUSION

This observational study of a highly selected population of HP, submitted to PTx because SHPT refractory to therapy, shows that the macroscopic, microscopic, and immunochemistry characteristics of PTG in HP who received or did not receive cinacalcet before PTx did not differ significantly.

Phosphate binders, vitamin D and calcimimetics in the management of chronic kidney disease-mineral bone disorders (CKD-MBD) in children

In order to minimize complications on the skeleton and to prevent extraskeletal calcifications, the specific aims of the management of chronic kidney disease mineral and bone disorder (CKD-MBD) are to maintain blood levels of serum calcium and phosphorus as close to the normal range as possible, thereby maintaining serum parathyroid hormone (PTH) at levels appropriate for CKD stage, preventing hyperplasia of the parathyroid glands, avoiding the development of extra-skeletal calcifications, and preventing or reversing the accumulation of toxic substances such as aluminum and β2-microglobulin. In order to limit cardiovascular calcification, daily intake of elemental calcium, including from dietary sources and from phosphate binders, should not exceed twice the daily recommended intake for age and should not exceed 2.5 g/day. Calcium-free phosphate binders, such as sevelamer hydrochloride and sevelamer carbonate, are safe and effective alternatives to calcium-based binders, and their use widens the margin of safety for active vitamin D sterol therapy. Vitamin D deficiency is highly prevalent across the spectrum of CKD, and replacement therapy is recommended in vitamin D-deficient and insufficient individuals. Therapy with active vitamin D sterols is recommended after correction of the vitamin D deficiency state and should be titrated based on target PTH levels across the spectrum of CKD. Although the use of calcimimetic drugs has been proven to effectively control the biochemical features of secondary hyperparathyroidism, there is very limited experience with the use of such agents in pediatric patients and especially during the first years of life. Studies are needed to further define the role of such agents in the treatment of pediatric CKD-MBD.

Animal models of hyperfunctioning parathyroid diseases for drug development

BACKGROUND

Disorders of mineral and bone metabolism have been implicated as a risk factor in the high mortality in patients with chronic kidney disease (CKD). Hyperphosphatemia, disorders of vitamin D metabolism and secondary hyperparathyroidism of uremia (SHPT) are therapeutic targets in these patients to improve the mortality. Animal models for CKD are indispensable and uremic rats produced by 5/6-nephrectomies are one of the most useful animal models for the development of new therapeutic agents. As there are limitations of uremic rats such as short lifespan and less severity of secondary hyperparathyroidism distinct from CKD patients on maintenance hemodialysis, the development of new model animals is expected.

OBJECTIVE

This review discusses the molecular pathogenesis of hyperfunctioning parathyroid diseases and the applications of animal models exhibiting hyperparathyroidisms in the aspect of the development of new therapeutics.

CONCLUSION

PTH-cyclin D1 transgenic mice, with parathyroid-targeted overexpression of cyclin D1 oncogene, not only developed abnormal parathyroid cell proliferation but, notably, also developed biochemical hyperparathyroidism with characteristic abnormalities in bone. The mice exhibit age-dependent development of biochemical hyperparathyroidism, which enables testing of the drug precisely. In addition, the mice develop parathyroid cell hyperplasia, followed by monoclonal expansion, which is observed in refractory SHPT patients.

Gastric acid, calcium absorption, and their impact on bone health

Calcium balance is essential for a multitude of physiological processes, ranging from cell signaling to maintenance of bone health. Adequate intestinal absorption of calcium is a major factor for maintaining systemic calcium homeostasis. Recent observations indicate that a reduction of gastric acidity may impair effective calcium uptake through the intestine. This article reviews the physiology of gastric acid secretion, intestinal calcium absorption, and their respective neuroendocrine regulation and explores the physiological basis of a potential link between these individual systems.

Effects and safety of calcimimetics in end stage renal disease patients with secondary hyperparathyroidism: a meta-analysis

Purpose

Secondary hyperparathyroidism (SHPT) is one of the most common abnormalities of mineral metabolism in patients with chronic kidney disease. We performed a meta-analysis to determine the effect and safety of cinacalcet in SHPT patients receiving dialysis.

Methods

The meta-analysis was performed to determine the effect and safety of cinacalcet in SHPT patients receiving dialysis by using the search terms ‘cinacalcet’ or ‘mimpara’ or ‘sensipar’ or ‘calcimimetic’ or ‘R586’ on MEDLINE and EMBASE (January 1990 to February 2012).

Results

Fifteen trials were included, all of which were performed between 2000 and 2011 enrolling a total of 3387 dialysis patients. Our study showed that calcimimetic agents effectively ameliorated iPTH levels(WMD, −294.36 pg/mL; 95% CI, −322.76 to −265.95, P<0.001) in SHPT patients and reduced serum calcium (WMD, −0.81 mg/dL; 95% CI, −0.89 to −0.72, P<0.001) and phosphorus disturbances(WMD, −0.29 mg/dL; 95% CI, −0.41 to −0.17, P<0.001). The percentage of patients in whom there was a 30% decrease in serum iPTH levels by the end of the dosing was higher in cinacalcet group than that in control group(OR = 10.75, 95% CI: 6.65–17.37, P<0.001). However, no significant difference was found in all-cause mortality and all adverse events between calcimimetics and control groups(OR = 0.86, 95% CI: 0.46–1.60, P = 0.630; OR = 1.30, 95% CI: 0.78–2.18, P = 0.320, respectively). Compared with the control therapy, there was a significant increase in the episodes of hypocalcemia (OR = 2.46, 95% CI: 1.58–3.82, P<0.001), nausea (OR = 2.45, 95% CI: 1.29–4.66, P = 0.006), vomiting(OR = 2.78, 95% CI: 2.14–3.62, P<0.001), diarrhea(OR = 1.51, 95% CI: 1.04–2.20, P = 0.030) and upper respiratory tract infection (OR = 1.79, 95% CI: 1.20–2.66, P = 0.004)in calcimimetics group.

Conclusions

Calcimimetic treatment effectively improved biochemical parameters of SHPT patients receiving dialysis without increasing all-cause mortality and all adverse events.

Cinacalcet: will it play a role in reducing cardiovascular events?

Secondary hyperparathyroidism is a common complication of chronic kidney disease and it is associated with high morbidity and mortality. It is characterized by high parathyroid hormone levels and bone turnover leading to bone pain, deformity and fragility. Furthermore, secondary hyperparathyroidism adversely affects the cardiovascular system and has been associated with cardiovascular calcification and cardiomyopathy. Cinacalcet, a type II calcimimetic, is an effective and well-tolerated oral therapy for the management of secondary hyperparathyroidism. It is an allosteric activator of the calcium-sensing receptor enhancing sensitivity of parathyroid cells to extracellular calcium, which leads to inhibition of parathyroid hormone secretion. The calcium-sensing receptor expression in cardiomyocytes, endothelial cells and vascular smooth muscle cells raises the possibility that this receptor may be implicated in the pathophysiology of cardiovascular disease and constitute a potential therapeutic target. This article reviews the role of the calcimimetic agent cinacalcet in the prevention and progression of cardiovascular calcification and uremic cardiomyopathy in the chronic kidney disease setting.

Cinacalcet HCl prevents development of parathyroid gland hyperplasia and reverses established parathyroid gland hyperplasia in a rodent model of CKD

BACKGROUND

Secondary hyperparathyroidism (sHPT) represents an adaptive response to progressively impaired control of calcium, phosphorus and vitamin D in chronic kidney disease (CKD). It is characterized by parathyroid hyperplasia and excessive synthesis and secretion of parathyroid hormone (PTH). Parathyroid hyperplasia in uremic rats can be prevented by calcium-sensing receptor (CaSR) activation with the calcimimetic cinacalcet (Sensipar®/Mimpara®); however, it is unknown, how long the effects of cinacalcet persist after withdrawal of treatment or if cinacalcet is efficacious in uremic rats with established sHPT.

METHODS

We sought to determine the effect of cinacalcet discontinuation in uremic rats and whether cinacalcet was capable of influencing parathyroid hyperplasia in animals with established sHPT.

RESULTS

Discontinuation of cinacalcet resulted in reversal of the beneficial effects on serum PTH and parathyroid hyperplasia. In rats with established sHPT, cinacalcet decreased serum PTH and mediated regression of parathyroid hyperplasia. The cinacalcet-mediated decrease in parathyroid gland size was accompanied by increased expression of the cyclin-dependent kinase inhibitor p21. Prevention of cellular proliferation with cinacalcet occurred despite increased serum phosphorus and decreased serum calcium.

CONCLUSIONS

The animal data provided suggest established parathyroid hyperplasia can be reversed by modulating CaSR activity with cinacalcet and that continued treatment may be necessary to maintain reductions in PTH.

Cinacalcet HCl suppresses Cyclin D1 oncogene-derived parathyroid cell proliferation in a murine model for primary hyperparathyroidism

Cinacalcet HCl (cinacalcet) is a calcimimetic compound, which suppresses parathyroid (PTH) hormone secretion from parathyroid glands in both primary hyperparathyroidism (PHPT) and secondary hyperparathyroidism (SHPT). We previously reported the suppressive effect of cinacalcet on PTH secretion in vivo in a PHPT model mouse, in which parathyroid-targeted overexpression of the cyclin D1 oncogene caused chronic biochemical hyperparathyroidism and parathyroid cell hyperplasia. Although cinacalcet suppressed parathyroid cell proliferation in SHPT in 5/6-nephrectomized uremic rats, its effect on PHPT has not yet been determined. In this study, the effect of cinacalcet on parathyroid cell proliferation was analyzed in PHPT mice. Cinacalcet (1 mg/g) was mixed into the rodent diet and orally administrated to 80-week-old PHPT mice for 10 days before death. 5-Bromo-2'-deoxyuridine (BrdU, 6 mg/day) was infused by an osmotic pump for 5 days before death, followed by immunostaining of the thyroid-parathyroid complex using an anti-BrdU antibody to estimate parathyroid cell proliferation. Compared to untreated PHPT mice, cinacalcet significantly suppressed both serum calcium and PTH. The proportion of BrdU-positive cells to the total cell number in the parathyroid glands increased considerably in untreated PHPT mice (9.5 ± 3.1%) compared to wild-type mice (0.7 ± 0.1%) and was significantly suppressed by cinacalcet (1.2 ± 0.2%). Cinacalcet did not affect apoptosis in the parathyroid cells of PHPT mice. These data suggest that cinacalcet suppressed both serum PTH levels and parathyroid cell proliferation in vivo in PHPT.

Stimulation of the calcium-sensing receptor stabilizes the podocyte cytoskeleton, improves cell survival, and reduces toxin-induced glomerulosclerosis

Calcimimetics increase the sensitivity of the parathyroid calcium-sensing receptor to extracellular calcium for efficient control of hyperparathyroidism. Recent studies suggest that there are beneficial effects of calcimimetics beyond the control of bone and mineral homeostasis. Here, we tested whether the calcium-sensing receptor is also expressed and functionally relevant in podocytes. Analysis of microarray data using Gene Set Enrichment Analysis found that the calcimimetic R-568 influenced various pathways related to oxidative stress, cytoskeletal regulation, cell proliferation, and survival in cultured podocytes. R-568 induced a dose- and time-dependent phosphorylation of the ERK1/2-P90RSK-CREB signaling cascade, and induced pro-survival phosphorylation of BAD and Bcl-xl, thus reducing puromycin aminonucleoside (PAN)-induced podocyte apoptosis by half. Moreover, R-568 preserved the actin cytoskeleton in podocytes exposed to PAN and improved recovery from exposure to cytochalasin D, a reversible inhibitor of actin polymerization. In rats, co-administration of R-568 prevented the proteinuria caused by a single dose of PAN and attenuated the glomerulosclerosis and loss of GFR caused by repetitive puromycin treatment. Hence, calcimimetics limit podocyte damage by antiapoptotic and cytoskeleton-stabilizing effects and may constitute a new approach in the prevention and treatment of glomerular disease.

The effect of cinacalcet on bone remodeling and renal function in transplant patients with persistent hyperparathyroidism

BACKGROUND

Parathyroidectomy is associated with renal functional losses in transplant patients; cinacalcet offers an attractive alternative.

METHODS

We performed a prospective observational study in 58 patients with persisting hyperparathyroidism after renal transplantation (Ca≥2.6 mmol/L) and impaired renal transplant function (estimated glomerular filtration rate [eGFR] <50 mL/min). The patients received 30 to 90 mg cinacalcet for 12 months with the target to normalize serum Ca. We measured parathyroid hormone (PTH), serum Ca, serum phosphorus, alkaline phosphatase, bone-specific alkaline phosphatase, osteocalcin, and telopeptide at 0, 1, 2, 3, 6, 9, and 12 months of cinacalcet treatment. Fractional excretion of calcium and phosphorus (n=24) were monitored at 0 and 1 month.

RESULTS

At inclusion, creatinine was 181±70 μmol/L, eGFR 43±19 mL/min, PTH 371±279 pg/mL, and Ca 2.73±0.22 mmol/L. We observed nephrocalcinosis in 58% of biopsied patients at enrollment. After cinacalcet, Ca decreased significantly and normalized at nearly any measurement. Phosphorus increased significantly at months 1, 9, and 12. PTH decreased significantly, but only at months 9 and 12 and did not normalize. Bone-specific alkaline phosphatase increased significantly (>normal) by month 12. eGFR decreased and serum creatinine increased at all time points. The Δ(creatinine) % increase correlated significantly with the Δ(PTH) % decrease at month 1 and 12. Telopeptide and alkaline phosphatase correlated with PTH and telopeptide also correlated with serum creatinine.

CONCLUSION

Calcium-phosphorus homeostasis in hypercalcemic renal transplant patients normalizes under cinacalcet and PTH decreases, albeit not to normal. The renal functional decline could be PTH mediated, analogous to the effects observed after parathyroidectomy.

Allosteric modulation of family C G-protein-coupled receptors: from molecular insights to therapeutic perspectives

Allosteric receptor modulation is an attractive concept in drug targeting because it offers important potential advantages over conventional orthosteric agonism or antagonism. Allosteric ligands modulate receptor function by binding to a site distinct from the recognition site for the endogenous agonist. They often have no effect on their own and therefore act only in conjunction with physiological receptor activation. This article reviews the current status of allosteric modulation at family C G-protein coupled receptors in the light of their specific structural features on the one hand and current concepts in receptor theory on the other hand. Family C G-protein-coupled receptors are characterized by a large extracellular domain containing the orthosteric agonist binding site known as the "venus flytrap module" because of its bilobal structure and the dynamics of its activation mechanism. Mutational analysis and chimeric constructs have revealed that allosteric modulators of the calcium-sensing, metabotropic glutamate and GABA(B) receptors bind to the seven transmembrane domain, through which they modify signal transduction after receptor activation. This is in contrast to taste-enhancing molecules, which bind to different parts of sweet and umami receptors. The complexity of interactions between orthosteric and allosteric ligands is revealed by a number of adequate biochemical and electrophysiological assay systems. Many allosteric family C GPCR modulators show in vivo efficacy in behavioral models for a variety of clinical indications. The positive allosteric calcium sensing receptor modulator cinacalcet is the first drug of this type to enter the market and therefore provides proof of principle in humans.

Effects of calcimimetic combined with an angiotensin-converting enzyme inhibitor on uremic cardiomyopathy progression

BACKGROUND/AIMS

Angiotensin-converting enzyme (ACE) inhibitors have cardioprotective properties and functional calcium-sensing receptors express in cardiac myocytes.

METHODS

Rats were made uremic by 5/6 nephrectomy and treated as follows: uremic rats were fed on a regular diet (UC), uremic + enalapril (E), uremic + calcimimetic agent R-568 (R-568), and uremic + enalapril + R-568 (E+R-568). A group of normal rats served as controls (NC).

RESULTS

Blood pressure (BP) and left ventricle mass were elevated significantly in the UC and R-568 groups compared with those in the NC group, but were indistinguishable from normal controls in the E and E+R-568 groups. Cardiac fibrosis was significantly increased in the UC group compared with that in the NC group. This increase was significantly attenuated in the R-568 and E groups, and the attenuation was further enhanced in the E+R-568 group. Factors associated with cardiac hypertrophy such as proliferating cell nuclear antigen, cyclin D1, and cyclin D2, as well as factors associated with cardiac fibrosis such as type I collagen, fibronectin, and transforming growth factor-β1 were significantly increased in the UC group compared with those in the NC group. Monotherapy with R-568 or E attenuated this increase and the combination further attenuated these measures.

CONCLUSIONS

Calcimimetics can suppress the progression of uremic cardiomyopathy and this effect is amplified when BP is controlled via renin-angiotensin system blockade.

Hyperparathyroidism and malnutrition with severe vitamin D deficiency

BACKGROUND

Vitamin D deficiency and its associated problems are common in developing Asian countries and countries of the Middle East. Various factors, including poor nutritional status and other compounding factors such as dietary, cultural, ethnic, and environmental factors, play a major role in contributing to the poor calcium and vitamin D homeostasis. Vitamin D deficiency is thought to exacerbate signs and symptoms of hyperparathyroidism (HPT). In this overview, we present evidence of the impact of vitamin D and calcium deficiency on primary HPT (PHPT).

METHODS

We performed an evidence-based review of articles published in the English language between January 1960 and June 2008.

RESULTS

Level IV evidence suggests widespread calcium and vitamin D deficiency in developing countries (issue 1). Limited level IV evidence suggests malnutrition as a primary cause of calcium and vitamin D deficiency (issue 2). Level IV evidence suggests that calcium and vitamin deficiencies cause secondary HPT and possibly PHPT as well (issues 3 and 4). A literature search revealed only six studies that correlated vitamin D levels with clinical, biochemical, and pathologic features of PHPT (issue 5). These studies provide level IV evidence suggesting that vitamin D deficiency causes some specific clinical features of PHPT as well as exacerbating other features of the disease.

CONCLUSIONS

In the developing countries, which have severe vitamin D and calcium deficient population, PHPT patients present with advanced disease and particularly severe bone symptoms. There is presently only level IV evidence of vitamin D status affecting the clinical severity of PHPT.

Effectiveness of cinacalcet in patients with recurrent/persistent secondary hyperparathyroidism following parathyroidectomy: results of the ECHO study

BACKGROUND

Progressive secondary hyperparathyroidism (sHPT) is characterized by parathyroid gland hyperplasia which may ultimately require parathyroidectomy (PTX). Although PTX is generally a successful treatment for those patients subjected to surgery, a significant proportion develops recurrent sHPT following PTX. ECHO was a pan-European observational study which evaluated the achievement of KDOQI(TM) treatment targets with cinacalcet use in patients on dialysis. Previously published results showed that cinacalcet plus flexible vitamin D therapy lowered serum PTH, phosphorus and calcium in the clinical practice with similar efficacy as seen in phase III trials.

METHODS

This subgroup analysis of ECHO describes the real-world cinacalcet treatment effect in patients with recurrent or persistent sHPT after PTX (n = 153) compared to sHPT patients without prior history of PTX (n = 1696).

RESULTS

Both groups of patients had substantially elevated serum PTH with comparable sHPT severity at baseline. After 12 months of cinacalcet treatment, 20.3% (26/128) of patients with prior PTX and 18.2% (253/1388) of patients without prior PTX achieved serum PTH and Ca × P values within the recommended KDOQI(TM) target ranges.

CONCLUSIONS

Our data support the successful use of cinacalcet in patients with recurrent/persistent sHPT after PTX.

Cinacalcet effectively reduces parathyroid hormone secretion and gland volume regardless of pretreatment gland size in patients with secondary hyperparathyroidism

BACKGROUND AND OBJECTIVES

Cinacalcet is effective in reducing serum parathyroid hormone (PTH) in patients with secondary hyperparathyroidism. However, it has not been proven whether parathyroid gland size predicts response to therapy and whether cinacalcet is capable of inducing a reduction in parathyroid volume.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

This 52-week, multicenter, open-label study enrolled hemodialysis patients with moderate to severe secondary hyperparathyroidism (intact PTH >300 pg/ml). Doses of cinacalcet were adjusted between 25 and 100 mg to achieve intact PTH <180 pg/ml. Ultrasonography was performed to measure the parathyroid gland size at baseline, week 26, and week 52. Findings were also compared with those of historical controls.

RESULTS

Of the 81 subjects enrolled, 56 had parathyroid glands smaller than 500 mm(3) (group S) and 25 had at least one enlarged gland larger than 500 mm(3) (group L). Treatment with cinacalcet effectively decreased intact PTH by 55% from baseline in group S and by 58% in group L. A slightly greater proportion of patients in group S versus group L achieved an intact PTH <180 pg/ml (46 versus 32%) and a >30% reduction from baseline (88 versus 78%), but this was not statistically significant. Cinacalcet therapy also resulted in a significant reduction in parathyroid gland volume regardless of pretreatment size, which was in sharp contrast to historical controls (n = 87) where parathyroid gland volume progressively increased with traditional therapy alone.

CONCLUSIONS

Cinacalcet effectively decreases serum PTH levels and concomitantly reduces parathyroid gland volume, even in patients with marked parathyroid hyperplasia.

Comparison of active vitamin D compounds and a calcimimetic in mineral homeostasis

The differential effects between cinacalcet and active vitamin D compounds on parathyroid function, mineral metabolism, and skeletal function are incompletely understood. Here, we studied cinacalcet and active vitamin D compounds in mice expressing the null mutation for Cyp27b1, which encodes 25-hydroxyvitamin D-1α-hydroxylase, thereby lacking endogenous 1,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)]. Vehicle-treated mice given high dietary calcium had hypocalcemia, hypophosphatemia, and marked secondary hyperparathyroidism. Doxercalciferol and 1,25(OH)(2)D(3) each normalized these parameters and corrected both the abnormal growth plate architecture and the diminished longitudinal bone growth observed in these mice. In contrast, cinacalcet suppressed serum parathyroid hormone (PTH) cyclically and did not correct the skeletal abnormalities and hypocalcemia persisted. Vehicle-treated mice given a "rescue diet" (high calcium and phosphorus, 20% lactose) had normal serum calcium and PTH levels; cinacalcet induced transient hypocalcemia and mild hypercalciuria. The active vitamin D compounds and cinacalcet normalized the increased osteoblast activity observed in mice with secondary hyperparathyroidism; cinacalcet, however, increased the number and activity of osteoclasts. In conclusion, cinacalcet reduces PTH in a cyclical manner, does not eliminate hypocalcemia, and does not correct abnormalities of the growth plate. Doxercalciferol and 1,25(OH)(2)D(3) reduce PTH in a sustained manner, normalize serum calcium, and improve skeletal abnormalities.

Primary hyperparathyroidism in patients with multiple endocrine neoplasia type 1

Primary hyperparathyroidism may occur as a part of an inherited syndrome in a combination with pancreatic endocrine tumours and/or pituitary adenoma, which is classified as Multiple Endocrine Neoplasia type 1 (MEN-1). This syndrome is caused by a germline mutation in MEN-1 gene encoding a tumour-suppressor protein, menin. Primary hyperparathyroidism is the most frequent clinical presentation of MEN-1, which usually appears in the second decade of life as an asymptomatic hypercalcemia and progresses through the next decades. The most frequent clinical presentation of MEN-1-associated primary hyperparathyroidism is bone demineralisation and recurrent kidney stones rarely followed by chronic kidney disease. The aim of this paper is to present the pathomechanism, screening procedures, diagnosis, and management of primary hyperparathyroidism in the MEN-1 syndrome. It also summarises the recent advances in the pharmacological therapy with a new group of drugs-calcimimetics.

Depressed expression of Klotho and FGF receptor 1 in hyperplastic parathyroid glands from uremic patients

Fibroblast growth factor 23 (FGF23) exerts its effect by binding to its cognate FGF receptor 1 (FGFR1) in the presence of its co-receptor Klotho. Parathyroid glands express both FGFR1 and Klotho, and FGF23 decreases parathyroid hormone gene expression and hormone secretion directly. In uremic patients with secondary hyperparathyroidism (SHPT), however, parathyroid hormone secretion remains elevated despite extremely high FGF23 levels. To determine the mechanism of this resistance, we measured the expression of Klotho, FGFR1, and the proliferative marker Ki67 in 7 normal and 80 hyperplastic parathyroid glands from uremic patients by immunohistochemistry. All uremic patients had severe SHPT along with markedly high FGF23 levels. Quantitative real-time reverse transcription PCR showed that the mRNA levels for Klotho and FGFR1correlated significantly with their semi-quantitative immunohistochemical intensity. Compared with normal tissue, the immunohistochemical expression of Klotho and FGFR1 decreased, but Ki67 expression increased significantly in hyperplastic parathyroid glands, particularly in glands with nodular hyperplasia. These results suggest that the depressed expression of the Klotho-FGFR1 complex in hyperplastic glands underlies the pathogenesis of SHPT and its resistance to extremely high FGF23 levels in uremic patients.

The calcium-sensing receptor (CaSR) defends against hypercalcemia independently of its regulation of parathyroid hormone secretion

The calcium-sensing receptor (CaSR) controls parathyroid hormone (PTH) secretion, which, in turn, via direct and indirect actions on kidney, bone, and intestine, maintains a normal extracellular ionized calcium concentration (Ca(2+)(o)). There is less understanding of the CaSR's homeostatic importance outside of the parathyroid gland. We have employed single and double knockout mouse models, namely mice lacking PTH alone (CaSR(+/+) PTH(-/-), referred to as C(+)P(-)), lacking both CaSR and PTH (CaSR(-/-) PTH(-/-), C(-)P(-)) or wild-type (CaSR(+/+) PTH(+/+), C(+)P(+)) mice to study CaSR-specific functions without confounding CaSR-mediated changes in PTH. The mice received three hypercalcemic challenges: an oral Ca(2+) load, injection or constant infusion of PTH via osmotic pump, or a phosphate-deficient diet. C(-)P(-) mice show increased susceptibility to developing hypercalcemia with all three challenges compared with the other two genotypes, whereas C(+)P(-) mice defend against hypercalcemia similarly to C(+)P(+) mice. Reduced renal Ca(2+) clearance contributes to the intolerance of the C(-)P(-) mice to Ca(2+) loads, as they excrete less Ca(2+) at any given Ca(2+)(o) than the other two genotypes, confirming the CaSR's direct role in regulating renal Ca(2+) handling. In addition, C(+)P(+) and C(+)P(-), but not C(-)P(-), mice showed increases in serum calcitonin (CT) levels during hypercalcemia. The level of 1,25(OH)(2)D(3) in C(-)P(-) mice, in contrast, was similar to those in C(+)P(-) and C(+)P(+) mice during an oral Ca(2+) load, indicating that increased 1,25(OH)(2)D(3) production cannot account for the oral Ca(2+)-induced hypercalcemia in the C(-)P(-) mice. Thus, CaSR-stimulated PTH release serves as a "floor" to defend against hypocalcemia. In contrast, high-Ca(2+)(o)-induced inhibition of PTH is not required for a robust defense against hypercalcemia, at least in mice, whereas high-Ca(2+)(o)-stimulated, CaSR-mediated CT secretion and renal Ca(2+) excretion, and perhaps other factors, serve as a "ceiling" to limit hypercalcemia resulting from various types of hypercalcemic challenges.

Calcimimetics in the chronic kidney disease-mineral and bone disorder

Mineral and bone disorders (MBD) are both an early and very common complication of chronic kidney disease (CKD). It is now accepted that they represent a significant risk factor, explaining the high cardiovascular morbidity and mortality in CKD patients. During the last decade, we have been witnessing many advances in the nomenclature, classification, pathophysiology, diagnosis, and treatment of CKD and some of its complications, such as CKD-MBD. The identification of the calcium-sensing receptor (CaSR) involvement in the pathogenesis of primary and secondary hyperparathyroidism (SHPT) and the availability of a new class of drugs called calcimimetics are two outstanding examples. Cinacalcet, the only available calcimimetic, has been shown to be a very effective therapeutic tool in CKD-MBD. Many clinical trials with cinacalcet in hemodialysis patients with SHPT have shown a reduction in parathyroid hormone, calcium (Ca), phosphate (P) and Ca x P product levels, allowing far greater success in reaching therapeutic goals as recommended by international guidelines. Additionally, some studies have shown that the use of cinacalcet may improve other aspects of CKD-MBD, reducing the risk of vascular calcification and parathyroidectomy, among others. Prospective studies on dialysis patients, with hard endpoint data, are currently underway. This review summarizes the most significant aspects of calcimimimetics based on both experimental and clinical results, underlining their possibilities not only for the treatment of isolated SHPT but also for other CKD-MBD related conditions.