Stimulation of osteoclast formation and bone resorption by glucocorticoids: Synergistic interactions with the calcium regulating hormones parathyroid hormone and 1,25(OH)2-vitamin D3

Osteoporosis is a significant health problem, with skeletal fractures increasing morbidity and mortality. Excess glucocorticoids (GC) represents the leading cause of secondary osteoporosis. The first phase of glucocorticoid-induced osteoporosis is increased bone resorption. In this Chapter, in vitro studies of the direct glucocorticoid receptor (GR) mediated cellular effects of GC on osteoclasts to affect bone resorption and indirect effects on osteoblast lineage cells to increase the RANKL/OPG ratio and stimulate osteoclastogenesis and bone resorption are reviewed in detail, together with detailed descriptions of in vivo effects of GC in different portions of the skeleton in research animals and humans. Brief sections are devoted to contrasting functions of GC in osteonecrosis, vitamin D formation, in vitro and in vivo bone resorptive actions dependent on vitamin D receptor and vitamin D toxicity, as well as the molecular basis of GR action. Included are also more detailed assessments of the interactions of GC with the major calcium regulating hormones, 1,25(OH)₂-vitamin D3 and parathyroid hormone, describing the in vitro increases in RANKL/OPG ratios, osteoclastogenesis and synergistic bone resorption that occurs when GC is combined with either 1,25(OH)₂-vitamin D3 or parathyroid hormone. Additionally, a molecular basic for the synergistic interaction of GC with 1,25(OH)₂-vitamin D3 is provided along with a suggested molecular basic for the interaction between GC and parathyroid hormone.

Safety of calcitonin stimulation tests with calcium

INTRODUCTION

Medullary thyroid carcinoma (MTC) is an aggressive form of thyroid cancer. Early detection is essential because only complete resection of the thyroid tumor and any local metastases can cure MTC. Calcitonin (CT) is a marker used for diagnosis of MTC. In controversial cases of slightly elevated CT levels, stimulation tests have shown their utility, but their safety should also be taken into account.

OBJECTIVE

Our aim is to present our own experience regarding the safety of CT stimulating tests.

MATERIALS AND METHODS

We applied a specific protocol of calcium stimulation test in 176 patients after informed consent (115 women with a median age of 46 years, range 21-79; 61 men with a median age of 54 years, range 22-78). We recorded the side effects and a further analysis was performed.

RESULTS

The most frequent side effects noted were hot flashes in 159 out of 176 patients (90.34%), followed by dysgeusia (32/176) and bradycardia (10/176). Severe bradycardia was reported in only one patient (0.568%), which was rapidly reversible. There was no correlation between patients' age, weight, height, body mass index, basal CT or peak stimulated CT, and grade of severity, but men were more likely to develop cardiovascular side effects than women, namely, bradycardia, tachycardia, ventricular or atrial extrasystoles, hypertension, hypotension, or angina (p = 0.024), with an odds ratio of 2.94 (CI: 1.11-7.76). We recommend thyroid surgery in all women with sCT above 285 pg/ml.

CONCLUSION

The calcium stimulation test is well tolerated, with few adverse reactions. The test should be performed with appropriate precautions (i.e., ECG monitoring during and after the test) to minimize the possibility of a serious event.

Immunomodulatory effect of in vitro calcitriol in fit and frail elderly

INTRODUCTION

Effect of calcitriol on PBMCs of healthy adults have been well studied but not much is known about its effect on the PBMCs of elderly patients with various degree of frailty syndrome and immune senescence. This study was aimed to assess the effect of in vitro calcitriol immunomodulatory effect on IL-6, IL-10 and IFN-γ in elderly patients who were fit, pre-frail and frail to see which group of patients might get the most benefit of calcitriol.

METHODS

This study was an experimental study on the PBMCs of 24 elderly people, of which 8 subjects each were in fit, pre-frail and frail categories based on the Cardiovascular Health Study criteria. IL-6, IL-10, and IFN-γ were examined by ELISA, before and after administration of lipopolysaccharide and 100 pg/mL calcitriol into PBMC cultures in vitro.

RESULT

The mean serum vitamin D level was 26.2 (2.4) ng/ml. Vitamin D level is decreasing along with worsening of frailty status. After LPS induction, calcitriol did not reduce IL-6 and IFN-γ in all the groups. Calcitriol increased IL-10 in all groups, with the most observed change in the pre-frail group.

CONCLUSION

In vitro administration of calcitriol showed anti-inflammatory potential by increasing IL-10 mainly in pre-frail subjects.

Exploring the effect of vitamin D3 supplementation on surrogate biomarkers of cholesterol absorption and endogenous synthesis in patients with type 2 diabetes-randomized controlled trial

BACKGROUND

Inverse associations have been reported between serum 25-hydroxyvitamin D [25(OH)D] and circulating cholesterol concentrations in observational studies. Postulated mechanisms include reduced bioavailability of intestinal cholesterol and alterations in endogenous cholesterol synthesis.

OBJECTIVE

To explore the effect of daily supplementation with 4000 IU/d vitamin D3 for 24 wk on surrogate biomarkers of cholesterol absorption (campesterol and β-sitosterol) and endogenous synthesis (lathosterol and desmosterol).

METHODS

Ancillary study of The Vitamin D for Established Type 2 Diabetes (DDM2) trial. Patients with established type 2 diabetes (N = 127, 25-75 y, BMI 23-42 kg/m2) were randomly assigned to receive either 4000 IU vitamin D3 or placebo daily for 24 wk. Of participants without changes in cholesterol-lowering medications (n = 114), plasma surrogate cholesterol absorption and endogenous synthesis biomarker concentrations were measured and merged with available measures of serum LDL cholesterol and HDL cholesterol concentrations.

RESULTS

At week 24, vitamin D3 supplementation significantly increased 25(OH)D concentrations (+21.5 ± 13.4 ng/mL) but not insulin secretion rates (primary outcome of the parent study) as reported previously. In this ancillary study there was no significant effect of vitamin D3 supplementation on serum cholesterol profile or surrogate biomarkers of cholesterol absorption and endogenous synthesis. Compared with participants not treated with cholesterol-lowering medications, those who were treated exhibited a greater reduction in plasma campesterol concentrations in the vitamin D3 but not placebo group (P-interaction = 0.011). Analyzing the data on the basis of cholesterol absorption status (hypo- versus hyperabsorbers) or cholesterol synthesis status (hypo- versus hypersynthesizers) did not alter these results.

CONCLUSIONS

Vitamin D3 supplementation for 24 wk had no significant effect on surrogate biomarkers of cholesterol absorption or endogenous synthesis, consistent with the lack of effect on serum cholesterol profile. Vitamin D3 supplementation resulted in greater reduction in campesterol concentrations in participants not using compared with those using cholesterol-lowering medications. Further studies are required.This trial was registered at clinicaltrials.gov as NCT01736865.

Modulating effect of vitamin D3 on the mutagenicity and carcinogenicity of doxorubicin in Drosophila melanogaster and in silico studies

Vitamin D3 (VD3) deficiency increases DNA damage, while supplementation may exert a pro-oxidant activity, prevent viral infections and formation of tumors. The aim of this study was to investigate the mutagenicity and carcinogenicity of VD3 alone or in combination with doxorubicin (DXR) using the Somatic Mutation and Recombination Test and the Epithelial Tumor Test, both in Drosophila melanogaster. For better understanding of the molecular interactions of VD3 and receptors, in silico analysis were performed with molecular docking associated with molecular dynamics. Findings revealed that VD3 alone did not increase the frequency of mutant spots, but reduced the frequency of mutant spots when co-administered with DXR. In addition, VD3 did not alter the recombinogenic effect of DXR in both ST and HB crosses. VD3 alone did not increase the total frequency of tumor, but significantly reduced the total frequency of tumor when co-administered with DXR. Molecular modeling and molecular dynamics between calcitriol and Ecdysone Receptor (EcR) showed a stable interaction, indicating the possibility of signal transduction between VD3 and EcR. In conclusion, under these experimental conditions, VD3 has modulatory effects on the mutagenicity and carcinogenicity induced by DXR in somatic cells of D. melanogaster and exhibited satisfactory interactions with the EcR.

The Efficacy of PTH and Abaloparatide to Counteract Immobilization-Induced Osteopenia Is in General Similar

Immobilization results in a substantial bone loss and increased fracture risk. Powerful bone anabolic therapies are necessary to counteract the bone loss and reduce fracture risk during periods with immobilization. Intermittent parathyroid hormone 1-34 (PTH) (teriparatide) and PTH related peptide analog abaloparatide (ABL) are potent bone anabolic therapies acting through the same receptor, but induce different durations of signaling response. We investigated the efficacy of PTH or ABL in preventing immobilization-induced bone loss in rats in a direct mole-to-mole comparison. Immobilization was achieved by injecting botulinum toxin type A (BTX) into the right hindlimb musculature. Sixty 14-week-old female Wistar rats were allocated to the following groups: Baseline, Control, BTX, BTX + PTH (80 μg/kg/day), and BTX + ABL (77 μg/kg/day). Immobilization resulted in a substantial and significant reduction in bone mineral density (aBMD), metaphyseal and epiphyseal trabecular bone volume fraction (BV/TV) and trabecular thickness (Tb.Th), metaphyseal trabecular number (Tb.N), and femoral neck bone strength. Both PTH and ABL prevented the immobilization-induced decrease in aBMD, metaphyseal and epiphyseal Tb.Th, and metaphyseal Tb.N. In addition, PTH rescued the reduction in metaphyseal BV/TV and femoral neck strength, while ABL did not. However, the effect of PTH and ABL did not differ significantly for serum calcium, aBMD, metaphyseal, and epiphyseal BV/TV, Tb.Th, or Tb.N. In conclusion, in a mole-to-mole comparison the efficacy of PTH and ABL is similar in counteracting immobilization-induced reduction in bone mineral density, deterioration in trabecular microarchitecture, and decrease in bone strength.

Medical Treatment for Osteoporosis: From Molecular to Clinical Opinions

Osteoporosis is a major concern all over the world. With aging, a gradual loss of bone mass results in osteopenia and osteoporosis. Heritable factors account for 60–80% of optimal bone mineralization. Modifiable factors, such as weight-bearing exercise, nutrition, body mass, and hormonal milieu, play an important role in the development of osteopenia and osteoporosis in adulthood. Currently, anti-resorptive agents, including estrogen, bisphosphonates, and selective estrogen receptor modulators (SERMs), are the drugs of choice for osteoporosis. Other treatments include parathyroid hormone (PTH) as well as the nutritional support of calcium and vitamin D. New treatments such as tissue-selective estrogen receptor complexes (TSECs) are currently in use too. This review, which is based on a systematic appraisal of the current literature, provides current molecular and genetic opinions on osteoporosis and its medical treatment. It offers evidence-based information to help researchers and clinicians with osteoporosis assessment. However, many issues regarding osteoporosis and its treatment remain unknown or controversial and warrant future investigation.

The role of vitamin D in the pathogenesis and treatment of diabetes mellitus: a narrative review

Diabetes mellitus, a metabolic disorder associated with chronic complications, is traditionally classified into two main subtypes. Type 1 diabetes mellitus (T1DM) results from gradual pancreatic islet β cell autoimmune destruction, extending over months or years. Type 2 diabetes mellitus (T2DM) is a heterogeneous disorder, with both insulin resistance and impairment in insulin secretion contributing to its pathogenesis. Vitamin D is a fat-soluble vitamin with an established role in calcium metabolism. Recently, several studies have provided evidence suggesting a role for it in various non-skeletal metabolic conditions, including both types of diabetes mellitus. Preclinical studies of vitamin D action on insulin secretion, insulin action, inflammatory processes, and immune regulation, along with evidence of an increase of hypovitaminosis D worldwide, have prompted several epidemiological, observational, and supplementation clinical studies investigating a potential biological interaction between hypovitaminosis D and diabetes. This narrative review aims to summarize current knowledge on the effect of vitamin D on T1DM and T2DM pathogenesis, prevention, and treatment, as well as on micro- and macrovascular complications of the disease. Furthermore, on the basis of current existing evidence, we aim to highlight areas for potential future research.

Mutation update and long-term outcome after treatment with active vitamin D3 in Chinese patients with pseudovitamin D-deficiency rickets (PDDR)

Pseudovitamin D-deficiency rickets is a rare disease which is caused by CYP27B1. In this study, we identified 9 mutations in 7 PDDR patients. In addition, we observed the response to long-term treatment of calcitriol in 15 Chinese patients with PDDR, which showed that the biochemical abnormalities had been corrected satisfactorily after 1-year treatment.

INTRODUCTION

Pseudovitamin D-deficiency rickets is a rare autosomal recessive disorder resulting from a defect in 25-hydroxyvitamin D 1α-hydroxylase, which is encoded by CYP27B1. The purpose of this study was to identify the CYP27B1 mutations and investigate the response to long-term treatment of calcitriol in Chinese patients with PDDR.

METHODS

We investigated CYP27B1 mutations in seven individuals from six separate families. To investigate the response to long-term (13 years) treatment with calcitriol in PDDR patients, we additionally collected clinical data of eight families from our previous report and analyzed their biochemical parameter and radiographic changes during the treatment.

RESULTS

Nine different mutations were identified: two novel missense mutations (G194R, R259L), three novel and one reported deletion mutations (c1442delA, c1504delA, c311-321del, and c. 48-60del), two novel nonsense mutations (c.85G>T, c.580G>T), and a reported insertion mutation (c1325-1332insCCCACCC). The statistical analysis revealed that parathyroid hormone (PTH) and ALP significantly decreased after 6-month and 1-year treatment with calcitriol respectively. Urine calcium was measured in all the patients without kidney stones being documented. After 6-year treatment, the radiographic abnormalities had also been improved. Two patients who had reached their final height are both with short stature (height Z-score below - 2.0).

CONCLUSIONS

We identified seven novel mutations of CYP27B1 gene in seven Chinese PDDR families. Our findings revealed after 1-year treatment of active vitamin D₃, PTH and ALP significantly decreased. The correction of the biochemical abnormalities had not improved the final height satisfactorily.

Desensitizing mouse cardiac troponin C to calcium converts slow muscle towards a fast muscle phenotype

KEY POINTS

The Ca2+ -desensitizing D73N mutation in slow skeletal/cardiac troponin C caused dilatated cardiomyopathy in mice, but the consequences of this mutation in skeletal muscle were not known. The D73N mutation led to a rightward shift in the force versus pCa (-log [Ca]) relationship in slow-twitch mouse fibres. The D73N mutation led to a rightward shift in the force-stimulation frequency relationship and reduced fatigue resistance of mouse soleus muscle. The D73N mutation led to reduced cross-sectional area of slow-twitch fibres in mouse soleus muscle without affecting fibre type composition of the muscle. The D73N mutation resulted in significantly shorter times to peak force and to relaxation during isometric twitches and tetani in mouse soleus muscle. The D73N mutation led to major changes in physiological properties of mouse soleus muscle, converting slow muscle toward a fast muscle phenotype.

ABSTRACT

The missense mutation, D73N, in mouse cardiac troponin C has a profound impact on cardiac function, mediated by a decreased myofilament Ca2+ sensitivity. Mammalian cardiac muscle and slow skeletal muscle normally share expression of the same troponin C isoform. Therefore, the objective of this study was to determine the consequences of the D73N mutation in skeletal muscle, as a potential mechanism that contributes to the morbidity associated with heart failure or other conditions in which Ca2+ sensitivity might be altered. Effects of the D73N mutation on physiological properties of mouse soleus muscle, in which slow-twitch fibres are prevalent, were examined. The mutation resulted in a rightward shift of the force-stimulation frequency relationship, and significantly faster kinetics of isometric twitches and tetani in isolated soleus muscle. Furthermore, soleus muscles from D73N mice underwent a significantly greater reduction in force during a fatigue test. The mutation significantly reduced slow fibre mean cross-sectional area without affecting soleus fibre type composition. The effects of the mutation on Ca2+ sensitivity of force development in soleus skinned slow and fast fibres were also examined. As expected, the D73N mutation did not affect the Ca2+ sensitivity of force development in fast fibres but resulted in substantially decreased Ca2+ sensitivity in slow fibres. The results demonstrate that a point mutation in a single constituent of myofilaments (slow/cardiac troponin C) led to major changes in physiological properties of skeletal muscle and converted slow muscle toward a fast muscle phenotype with reduced fatigue resistance and Ca2+ sensitivity of force generation.

The effects of high-dose calcitriol and individualized exercise on bone metabolism in breast cancer survivors on hormonal therapy: a phase II feasibility trial

INTRODUCTION

Cancer treatment-induced bone loss (CTIBL) is a long-term side effect of breast cancer therapy. Both calcitriol and weight-bearing exercise improve bone metabolism for osteoporotic patients, but are unproven in a breast cancer population. We used a novel high-dose calcitriol regimen with an individualized exercise intervention to improve bone metabolism in breast cancer survivors.

METHODS

We accrued 41 subjects to this open label, 2 × 2 factorial, randomized feasibility trial. Breast cancer survivors were randomized to receive the following: (1) calcitriol (45 micrograms/week), (2) individualized exercise with progressive walking and resistance training, (3) both, or (4) a daily multivitamin (control condition) for 12 weeks. Primary outcomes included changes in biomarkers of bone formation, bone resorption, and the bone remodeling index, a composite measure of bone formation and resorption. Safety measures included clinical and biochemical adverse events. A main effect analysis was used for these endpoints.

RESULTS

Hypercalcemia was limited to three grade I cases with no grade ≥ 2 cases. Among exercisers, 100% engaged in the prescribed aerobic training and 44.4% engaged in the prescribed resistance training. Calcitriol significantly improved bone formation (Cohen's d = 0.64; p < 0.01), resulting in a non-significant increase in the bone remodeling index (Cohen's d = 0.21; p = 31). Exercise failed to improve any of the bone biomarkers.

CONCLUSIONS

Both calcitriol and exercise were shown to be feasible and well tolerated. Calcitriol significantly improved bone formation, resulting in a net increase of bone metabolism. Compliance with the exercise intervention was sub-optimal, which may have led to a lack of effect of exercise on bone metabolism.

Treatment of osteoporosis with recombinant parathyroid hormone, utilisation of total body DXA to observe treatment effects on total body composition and factors determining response to therapy

PURPOSE

Recombinant parathyroid hormone (rPTH) increases bone mineral density (BMD). However, certain other potential effects of rPTH remain to be studied. The aim of this study is to identify whether bone turnover markers, relevant biochemical parameters or total body fat and muscle composition affect the response to rPTH and to establish if these parameters in particular change during treatment.

METHODS

One hundred seventy-two participants were treated with rPTH, and 128 subjects who fully complied with the therapy and completed their investigations including biochemical bone markers and total body composition at baseline, 6 months and 1 year of the treatment were divided into responder and non-responder groups. A total body dual-energy X-ray absorptiometry (DXA) scanner was used to assess the body muscle, fat and bone composition.

RESULTS

rPTH significantly increased BMD spine at 1 year (p = 0.000). Twenty-four-hour urinary calcium was significantly increased at 6 months in the responder group (p = 0.00). There was a trend to an increase in the fat and muscle mass (p = 0.52 and 0.45, respectively), and it was not negatively affected by rPTH. Bone turnover markers (P1NP and OC) did not show statistically significant difference over time between responders and non-responders (p = 0.74 and p = 0.19, respectively).

CONCLUSIONS

Hypercalciuria which is a frequent feature in osteoporotic population may predict non-responders at 6 months of rPTH, and it may help to optimise individual patient's treatment. Unlike endogenous PTH in pathological conditions, rPTH is anabolic to bone and has no detrimental effects on the body fat and muscle composition.

Review of the guideline of the American College of Physicians on the treatment of osteoporosis

This review, endorsed by the International Osteoporosis Foundation and the European Society for Clinical and Economic Aspects of Osteoporosis, Osteoarthritis and Musculoskeletal Diseases, summarizes several failings of the recent guidelines of the American College of Physicians (ACP) on the treatment of low bone density or osteoporosis to prevent fractures.

INTRODUCTION

The ACP recently issued guidelines for the treatment of low bone density or osteoporosis to prevent fractures.

METHODS

Literature review and critical review of the ACP guidelines.

RESULTS

The guideline is lacking in scope due to the endorsement of treatment based on T-scores rather than fracture risk assessment and in failure to adequately consider anabolic therapies.

CONCLUSIONS

The ACP guideline appears outdated.

Regulation of TMEM16A/ANO1 and TMEM16F/ANO6 ion currents and phospholipid scrambling by Ca2+ and plasma membrane lipid

KEY POINTS

TMEM16 proteins can operate as Ca2+ -activated Cl- channels or scramble membrane phospholipids, which are both highly relevant mechanisms during disease. Overexpression of TMEM16A and TMEM16F were found to be partially active at 37°C and at resting intracellular Ca2+ concentrations. We show that TMEM16 Cl- currents and phospholipid scrambling can be activated by modification of plasma membrane phospholipids, through reactive oxygen species and phospholipase A2. While phospholipids and Cl- ions are likely to use the same pore within TMEM16F, TMEM16A only conducts Cl- ions. Lipid regulation of TMEM16 proteins is highly relevant during inflammation and regulated cell death such as apoptosis and ferroptosis.

ABSTRACT

TMEM16/anoctamin (ANO) proteins form Ca2+ -activated ion channels or phospholipid scramblases. We found that both TMEM16A/ANO1 and TMEM16F/ANO6 produced Cl- currents when activated by intracellular Ca2+ , but only TMEM16F was able to expose phosphatidylserine to the outer leaflet of the plasma membrane. Mutations within TMEM16F or TMEM16A/F chimeras similarly changed Cl- currents and phospholipid scrambling, suggesting the same intramolecular pathway for Cl- and phospholipids. When overexpressed, TMEM16A and TMEM16F produced spontaneous Cl- currents at 37°C even at resting intracellular Ca2+ levels, which was abolished by inhibition of phospholipase A2 (PLA2 ). Connversely, activation of PLA2 or application of active PLA2 , as well as lipid peroxidation induced by reactive oxygen species (ROS) using staurosporine or tert-butyl hydroperoxide, enhanced ion currents by TMEM16A/F and in addition activated phospholipid scrambling by TMEM16F. Thus, TMEM16 proteins are activated by an increase in intracellular Ca2+ , or independent of intracellular Ca2+ , by modifications occurring in plasma and intracellular membrane phospholipids. These results may help to explain why regions distant to the TMEM16 pore and the Ca2+ binding sites control Cl- currents and phospholipid scrambling. Regulation of TMEM16 proteins through modification of membrane phospholipids occurs during regulated cell death such as apoptosis and ferroptosis. It contributes to inflammatory and nerve injury-induced hypersensitivity and generation of pain and therefore provides a regulatory mechanism that is particularly relevant during disease.