Calcemic actions of vitamin D: effects on the intestine, kidney and bone

Calcium and vitamin D homoeostasis in male fertility

Calcium and vitamin D have well-established roles in maintaining calcium balance and bone health. Decades of research in human subjects and animals have revealed that calcium and vitamin D also have effects on many other organs including male reproductive organs. The presence of calcium-sensing receptor, vitamin D receptor, vitamin D activating and inactivating enzymes and calcium channels in the testes, male reproductive tract and human spermatozoa suggests that vitamin D and calcium may modify male reproductive function. Functional animal models have shown that vitamin D deficiency in male rodents leads to a decrease in successful mating and fewer pregnancies, often caused by impaired sperm motility and poor sperm morphology. Human studies have to a lesser extent validated these findings; however, newer studies suggest a positive effect of vitamin D supplementation on semen quality in cases with vitamin D deficiency, which highlights the need for initiatives to prevent vitamin D deficiency. Calcium channels in male reproductive organs and spermatozoa contribute to the regulation of sperm motility and capacitation, both essential for successful fertilisation, which supports a need to avoid calcium deficiency. Studies have demonstrated that vitamin D, as a regulator of calcium homoeostasis, influences calcium influx in the testis and spermatozoa. Emerging evidence suggests a potential link between vitamin D deficiency and male infertility, although further investigation is needed to establish a definitive causal relationship. Understanding the interplay between vitamin D, calcium and male reproductive health may open new avenues for improving fertility outcomes in men.

Gestational vitamin D and offspring fracture risk: do associations persist into mid adolescence?

BACKGROUND

Previous studies report that maternal vitamin D exposure during pregnancy is associated with offspring later-life bone health. A study in the Vitamin D in Pregnancy (VIP) cohort reported sexually dimorphic effects of maternal 25-hydroxyvitamin-D (25(OH)D) and offspring fracture profiles at 10 years of age. We, therefore, aimed to determine associations between maternal 25(OH)D status and offspring fracture risk at 16 years of age in this cohort.

METHODS

In total, 475 mother-child pairs were recruited to the VIP study in southeastern Australia. Maternal serum samples were obtained at recruitment (<16 weeks' gestation) and/or 28-32 weeks' gestation and analysed for 25(OH)D. Radiologically-confirmed incident fractures in children were ascertained from date of birth (2002-2004) until July 16, 2019. Cox proportional hazard models were used to determine associations between maternal 25(OH)D and childhood fracture risk, and final models included maternal age at recruitment, offspring sex, birth weight, gestation length and season of 25(OH)D sample.

RESULTS

Data were available for 400 children (mean age 16.1 years). There were 122 (30.5%) children who sustained at least one fracture. Higher maternal 25(OH)D (per 10 nmol/L) in early gestation was associated with a decreased fracture risk in boys (HR 0.87; 95% CI: 0.77, 0.99); the pattern was reversed in girls (HR 1.10; 95% CI 1.00, 1.22). At late gestation, higher maternal 25(OH)D was associated with an increased fracture risk in girls (HR 1.14; 95% CI: 1.04, 1.24).

CONCLUSIONS

While our findings must be interpreted within the constraints of our limitations, we report that the contradictory risk profiles observed at early childhood in this cohort remain in adolescence.

Dual x-ray absorptiometry monitoring in pediatric short bowel syndrome: an integrative review

OBJECTIVE

To analyze the bone health of pediatric patients with short bowel syndrome intestinal failure (SBS-IF).

DATA SOURCE

An integrative literature review was performed using the data published in the MEDLINE-PubMed and Scientific Electronic Library Online (SciELO) databases between January 2010 and April 2021, and through a manual search of the reference lists of relevant studies. Studies were included if they assessed bone mineral density by the Dual X-Ray Absorptiometry (DXA) technique, incorporated pediatric patients (up to 20 years of age) with SBS under parenteral nutrition (PN) and were written in English. Eleven primary sources met the inclusion criteria for this study.

DATA SYNTHESIS

Pediatric patients with SBS-IF under long-term parenteral nutrition experienced frequent changes in bone metabolism, leading to osteoporotic fractures and growth failure. These patients have deficiencies in multiple nutrients, such as calcium, magnesium, phosphorus, and vitamin D. Consequently, there are variations in the secretion and regulation of the parathyroid hormone. In addition, the pharmacotechnical limitations related to calcium and phosphorus in the PN solution, use of glucocorticoids, and difficulty performing physical activity are risk factors for the development of metabolic bone disease in pediatric patients with SBS-IF.

CONCLUSIONS

Low bone mineral density was associated with a high risk of developing osteoporosis, fractures, and growth deficiency in pediatric patients with SBS-IF on PN therapy in the long term.

Genomically anchored vitamin D receptor mediates an abundance of bioprotective actions elicited by its 1,25-dihydroxyvitamin D hormonal ligand

The nuclear vitamin D receptor (VDR) mediates the actions of its physiologic 1,25-dihydroxyvitamin D3 (1,25D) ligand produced in kidney and at extrarenal sites during times of physiologic and cellular stress. The ligand-receptor complex transcriptionally controls genes encoding factors that regulate calcium and phosphate sensing/transport, bone remodeling, immune function, and nervous system maintenance. With the aid of parathyroid hormone (PTH) and fibroblast growth factor 23 (FGF23), 1,25D/VDR primarily participates in an intricate network of feedback controls that govern extracellular calcium and phosphate concentrations, mainly influencing bone formation and mineralization, ectopic calcification, and indirectly supporting many fundamental roles of calcium. Beyond endocrine and intracrine effects, 1,25D/VDR signaling impacts multiple biochemical phenomena that potentially affect human health and disease, including autophagy, carcinogenesis, cell growth/differentiation, detoxification, metabolic homeostasis, and oxidative stress mitigation. Several health advantages conferred by 1,25D/VDR appear to be promulgated by induction of klotho, an anti-aging renal peptide hormone which functions as a co-receptor for FGF23 and, like 1,25D, regulates nrf2, foxo, mTOR and other cellular protective pathways. Among hundreds of genes for which expression is modulated by 1,25D/VDR either primarily or secondarily in a cell-specific manner, the resulting gene products (in addition to those expressed in the classic skeletal mineral regulatory tissues kidney, intestine, and bone), fall into multiple biochemical categories including apoptosis, cholesterol homeostasis, glycolysis, hypoxia, inflammation, p53 signaling, unfolded protein response and xenobiotic metabolism. Thus, 1,25D/VDR is a bone mineral control instrument that also signals the maintenance of multiple cellular processes in the face of environmental and genetic challenges.

Calcium complexes of oxicams: new dimensions in rheumatoid arthritis treatment

Various metals have been complexed with drugs to improve their cellular impact. Inflammatory diseases like rheumatoid arthritis (RA) are characterized by unbalanced production of proinflammatory cytokines (PICs) and prostaglandins with decreased levels of vitamin D and calcium. The inflammation can be suppressed through targeting the formation of PICs or related enzymes by various treatment strategies that involve the use of corticosteroids, disease-modifying antirheumatic drugs and NSAIDs. We present a detailed review on the impact of calcium complexes of oxicams as an advanced treatment strategy for RA. The calcium complexes demonstrate promising capabilities to cure the disease, improve the strength of bones and suppress PICs in RA.

Effects of feeding 25-hydroxyvitamin D3 with an acidogenic diet during the prepartum period in dairy cows: Mineral metabolism, energy balance, and lactation performance of Holstein dairy cows

Our objective was to determine the effects of feeding 25-hydroxyvitamin D₃ [25(OH)D₃], or vitamin D₃ (cholecalciferol) on plasma, mineral, and metabolite concentrations, mineral balance, mineral excretion, rumination, energy balance, and milk production of dairy cows. We hypothesized that supplementing 3 mg/d of 25(OH)D₃ during the prepartum period would be more effective than supplementing vitamin D₃ at the National Research Council (2001) levels to minimize calcium imbalance during the transition period and improve milk production of dairy cows. Forty multiparous, pregnant nonlactating-Holstein cows were enrolled in this study. Body weight, body condition score, parity, and milk yield in the previous lactation (mean ± standard deviation) were 661 ± 59.2, 3.46 ± 0.35, 1.79 ± 0.87, and 33.2 ± 6.43 kg/d, respectively. Cows were enrolled into the blocks (n = 20 for each treatment) at 30 d of the expected day of calving to receive an acidogenic diet (373 g/kg of neutral detergent fiber and 136 g/kg of crude protein, dry matter basis; -110 mEq/kg) associated with the treatments: (1) control (CTRL), vitamin D₃ at 0.625 mg/d (equivalent to 25,000 IU of vitamin D₃/d) or (2) 25(OH)D₃ at 3 mg/d (equivalent to 120,000 IU of vitamin D₃/d). All cows were fed with the base ration for 49 d after calving. Blood samples were taken on d 7, 0, 1, 2, 21, and 42, relative to calving. No effect of treatment was observed for prepartum dry matter intake or body condition score. A trend for increase of ionized Ca was observed for the cows fed 25(OH)D₃, compared with the CTRL, but no effect of treatment was detected for total Ca or total P. Feeding 25(OH)D₃ increased colostrum yield. The plasmatic concentration of 25-hydroxyvitamin D₃ was increased with 25(OH)D₃ supplementation. 25-Hydroxyvitamin D₃ supplementation increased plasma glucose concentration at parturition. The postpartum dry matter intake was not influenced by treatments. Feeding 25(OH)D₃ increases milk yield, 3.5% fat-corrected milk, and energy-corrected milk and improves milk yield components in early lactation. Overall, these findings suggest that 25(OH)D₃ at 3 mg/d can improve the energy metabolism and lactation performance, compared with the current-feeding practice of supplementing vitamin D₃ at 0.625 mg/d.

Treatment options for hypercalcemia after cosmetic oil injections: Lessons from human tissue cultures and a pilot intervention study

OBJECTIVE

Granuloma formation following self-administered cosmetic oil injections can lead to severe hypercalcemia and renal calcifications due to extra-renal vitamin D activation. This translational study aims to identify Prednisolone sparing therapeutics for hypercalcemia after development of granulomatous disease secondary to paraffin oil injections.

MATERIALS AND METHODS

Granuloma tissue isolated from five men were cultured ex vivo and treated with selected drugs to block generation of activated vitamin D (1,25(OH)₂D₃). In a retrospective study, we included data before and during different treatments of 21 men with paraffin oil induced granulomatous hypercalcemia (46 treatment courses) where serum calcium, parathyroid hormone, vitamin D metabolites, creatinine and inflammatory markers were measured.

RESULTS

Addition of Ketoconazole or Ciclosporin to granuloma tissue ex vivo culture, significantly suppressed production of 1,25(OH)₂D₃ after 48 h (both p < 0.05). Prednisolone was the first treatment option in most men and lowered serum levels of ionized calcium after 1, 2, 3 and 6 months compared with baseline (p < 0.05). Ketoconazole or Hydroxychloroquine had no significant effect on serum calcium levels and were unable to reduce the concomitant daily Prednisolone doses (p > 0.05). Azathioprine did not reduce calcium levels. However, addition of Tacrolimus to Prednisolone treatment enabled a reduction in Prednisolone dose after 3 months (p = 0.014), but with no additional effect on calcium homeostasis.

CONCLUSION

This study verifies that Prednisolone is an effective treatment and suggests that calcineurin inhibitors may be used as Prednisolone sparing treatment for paraffin oil-induced granulomatous hypercalcemia. Randomized clinical trials are needed to determine clinical efficacy.

High sodium chloride affects BMP-7 and 1α-hydroxylase levels through NCC and CLC-5 in NRK-52E cells

A diet high in sodium chloride (NaCl) can affect renal function damage and increase urinary calcium excretion, leading to bone loss. in renal tubules, Na-Cl co-transporter (NCC) and chloride channel 5 (CLC-5) are involved in regulating urinary calcium excretion. In addition, some cytokines, such as Bone morphogenetic protein 7 (BMP-7) and 1α-hydroxylase, are synthesized by renal tubules, which target on bone and play important roles on bone metabolism. However, the specific mechanisms between NaCl and these ion channels or cytokines still need investigations from many aspects. This study, in culture normal rat renal tubular epithelial NRK-52E cells, showed that high concentrations of NaCl significantly inhibited the cell viability and increased the cell apoptosis. High concentration of NaCl reduce bone mineral density (BMD), as demonstrated by the significantly increased mRNA and protein levels of NCC and osteopontin (OPN), but decreased the levels of CLC-5, BMP-7, and 1α-hydroxylase. In addition, we found that ovariectomized (OVX) rats on a high-salt diet for 12 weeks had altered levels of these indices in the renal cortices. Moreover, the BMD in fourth and fifth lumbar vertebra (LV4 and 5) and femurs were significantly decreased and bone microstructure was destroyed of these rats. We also demonstrated that high concentration of NaCl enhanced the inhibition of these cytokines which is beneficial to increase BMD, induced by modulating ion channels NCC and CLC-5. In conclusion, our results indicate that high concentration of NaCl reduce BMD by regulating ion channels NCC and CLC-5.

Tertiary and Postrenal Transplantation Hyperparathyroidism

Patients who have undergone kidney transplantation (KTx) (KTxps) are a distinctive population characterized by the persistence of some metabolic anomalies present during end-stage renal disease. Mineral metabolism (MM) parameters are frequently altered after KTx. These alterations involve calcium, phosphorus, vitamin D, and parathormone (PTH) disarrangements. At present, there is little consensus about the correct monitoring and management of PTH disorders in KTxps. This article presents the prevalence and epidemiologic and clinical impact of post-KTx hyper-PTH. The principal biochemical and instrumental investigations and the therapeutic options for these conditions are also reported.

Maternal vitamin D and offspring fracture risk: the Vitamin D in Pregnancy study

Vitamin D is important for bone health and strength. Previous studies report 25-hydroxyvitamin D (25(OH)D) exposure during pregnancy may impact offspring bone health later in life. In this study, maternal 25(OH)D at recruitment was associated with a lower fracture risk in boys and an increased fracture risk in girls at 28-32 weeks gestation.

PURPOSE

Maternal 25-hydroxyvitamin D (25(OH)D) in pregnancy has been shown to be associated with offspring bone measures in some studies, but few have examined fracture risk. We aimed to determine associations between maternal vitamin D status and offspring fracture risk.

METHODS

In total, 475 mother-child pairs participating in the Vitamin D in Pregnancy study in southeastern Australia were recruited. Maternal serum samples were taken at recruitment (< 16 weeks gestation) and/or 28-32 weeks gestation and analysed for 25(OH)D. Incident fractures in children were ascertained from date of birth (2002-2004) until December 31, 2012. Cox proportional hazard models included maternal age at recruitment, offspring sex, birth weight, gestation length and season of vitamin D sample.

RESULTS

Complete follow-up data were available for 400 children (median age = 9.5 years). There were 68 (17.0%) children who sustained at least one fracture. Higher maternal 25(OH)D (per 10 nmol/L) in early gestation was weakly associated with a decreased fracture risk in boys (HR 0.82; 95% CI 0.68, 0.99; p = 0.048) but not girls (HR 1.10; 95% CI 0.98, 1.25; p = 0.11). At late gestation, higher maternal 25(OH)D was associated with increased fracture risk in girls (HR 1.11; 95% CI 1.01, 1.23; p = 0.038) but not boys (HR 0.94; 95% CI 0.80, 1.10; p = 0.42). No statistically significant relationships were detected in analyses investigating 25(OH)D as a categorical variable.

CONCLUSION

There is some evidence that higher maternal 25(OH)D at recruitment was associated with lower fracture risk in boys, while higher maternal 25(OH)D at 28-32 weeks gestation was associated with an increased fracture risk in girls.

Vitamin D Effects on Bone Homeostasis and Cardiovascular System in Patients with Chronic Kidney Disease and Renal Transplant Recipients

Poor vitamin D status is common in patients with impaired renal function and represents one main component of the complex scenario of chronic kidney disease-mineral and bone disorder (CKD-MBD). Therapeutic and dietary efforts to limit the consequences of uremia-associated vitamin D deficiency are a current hot topic for researchers and clinicians in the nephrology area. Evidence indicates that the low levels of vitamin D in patients with CKD stage above 4 (GFR < 15 mL/min) have a multifactorial origin, mainly related to uremic malnutrition, namely impaired gastrointestinal absorption, dietary restrictions (low-protein and low-phosphate diets), and proteinuria. This condition is further worsened by the compromised response of CKD patients to high-dose cholecalciferol supplementation due to the defective activation of renal hydroxylation of vitamin D. Currently, the literature lacks large and interventional studies on the so-called non-calcemic activities of vitamin D and, above all, the modulation of renal and cardiovascular functions and immune response. Here, we review the current state of the art of the benefits of supplementation with native vitamin D in various clinical settings of nephrological interest: CKD, dialysis, and renal transplant, with a special focus on the effects on bone homeostasis and cardiovascular outcomes.

Vitamin D Receptor Mediates a Myriad of Biological Actions Dependent on Its 1,25-Dihydroxyvitamin D Ligand: Distinct Regulatory Themes Revealed by Induction of Klotho and Fibroblast Growth Factor-23

The hormonal vitamin D metabolite, 1,25‐dihydroxyvitamin D [1,25(OH)₂D], produced in kidney, acts in numerous end organs via the nuclear vitamin D receptor (VDR) to trigger molecular events that orchestrate bone mineral homeostasis. VDR is a ligand‐controlled transcription factor that obligatorily heterodimerizes with retinoid X receptor (RXR) to target vitamin D responsive elements (VDREs) in the vicinity of vitamin D‐regulated genes. Circulating 1,25(OH)₂D concentrations are governed by PTH, an inducer of renal D‐hormone biosynthesis catalyzed by CYP27B1 that functions as the key player in a calcemic endocrine circuit, and by fibroblast growth factor‐23 (FGF23), a repressor of the CYP27B1 renal enzyme, creating a hypophosphatemic endocrine loop. 1,25(OH)₂D/VDR–RXR acts in kidney to induce Klotho (a phosphaturic coreceptor for FGF23) to correct hyperphosphatemia, NPT2a/c to correct hypophosphatemia, and TRPV5 and CaBP28k to enhance calcium reabsorption. 1,25(OH)₂D‐liganded VDR–RXR functions in osteoblasts/osteocytes by augmenting RANK‐ligand expression to paracrine signal osteoclastic bone resorption, while simultaneously inducing FGF23, SPP1, BGLP, LRP5, ANK1, ENPP1, and TNAP, and conversely repressing RUNX2 and PHEX expression, effecting localized control of mineralization to sculpt the skeleton. Herein, we document the history of 1,25(OH)₂D/VDR and summarize recent advances in characterizing their physiology, biochemistry, and mechanism of action by highlighting two examples of 1,25(OH)₂D/VDR molecular function. The first is VDR‐mediated primary induction of Klotho mRNA by 1,25(OH)₂D in kidney via a mechanism initiated by the docking of liganded VDR–RXR on a VDRE at −35 kb in the mouse Klotho gene. In contrast, the secondary induction of FGF23 by 1,25(OH)₂D in bone is proposed to involve rapid nongenomic action of 1,25(OH)₂D/VDR to acutely activate PI3K, in turn signaling the induction of MZF1, a transcription factor that, in cooperation with c‐ets1‐P, binds to an enhancer element centered at −263 bp in the promoter‐proximal region of the mouse fgf23 gene. Chronically, 1,25(OH)₂D‐induced osteopontin apparently potentiates MZF1. © 2020 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Hypercalcemia After Cosmetic Oil Injections: Unraveling Etiology, Pathogenesis, and Severity

Intramuscular injections of paraffin oil can cause foreign body granuloma formation and hypercalcemia. Macrophages with the ability to produce high levels of 1,25(OH)₂ D₃ may induce the mineral disturbance, but no major series of patients have been published to date. Here, medical history, physical evaluation, biochemical, and urinary analysis for calcium homeostasis were obtained from 88 males, who 6 years previously had injected paraffin or synthol oil into skeletal muscle. Moreover, granuloma tissue from three men was cultured for 48 hours ex vivo to determine 1,25(OH)₂ D₃ production supported by qPCR and immunohistochemistry of vitamin D metabolism and immune cell populations after treatment with 14 different drugs. The 88 men were stratified into men with hypercalcemia (34%), whereas normocalcemic men were separated into men with either normal (42%) or suppressed parathyroid hormone (PTH) (24%). All men had high calcium excretion, and nephrolithiasis was found in 48% of hypercalcemic men, 22% of normocalcemic men with normal PTH, and 47% of normocalcemic men with suppressed PTH. Risk factors for developing hypercalcemia were oil volume injected, injection of heated oil, high serum interleukin-2 receptor levels, and high urine calcium. High 1,25(OH)₂ D₃ /25OHD ratio, calcium excretion, and low PTH was associated with nephrolithiasis. The vitamin D activating enzyme CYP27B1 was markedly expressed in granuloma tissue, and 1,25(OH)₂ D₃ was released in concentrations corresponding to 40% to 50% of the production by human kidney specimens. Dexamethasone, ketoconazole, and ciclosporin significantly suppressed granulomatous production of 1,25(OH)₂ D₃ . In conclusion, this study shows that injection of large oil volumes alters calcium homeostasis and increases the risk of nephrolithiasis. Hypercalciuria is an early sign of disease, and high granulomatous 1,25(OH)₂ D₃ production is part of the cause. Prospective clinical trials are needed to determine if ciclosporin, ketoconazole, or other drugs can be used as prednisolone-sparing treatment. © 2020 American Society for Bone and Mineral Research (ASBMR).

Analysis of 1,25-Dihydroxyvitamin D3 Genomic Action Reveals Calcium-Regulating and Calcium-Independent Effects in Mouse Intestine and Human Enteroids

Although vitamin D is critical for the function of the intestine, most studies have focused on the duodenum. We show that transgenic expression of the vitamin D receptor (VDR) only in the distal intestine of VDR null mice (KO/TG mice) results in the normalization of serum calcium and rescue of rickets. Although it had been suggested that calcium transport in the distal intestine involves a paracellular process, we found that the 1,25-dihydroxyvitamin D3 [1,25(OH)2D3]-activated genes in the proximal intestine associated with active calcium transport (Trpv6, S100g, and Atp2b1) are also induced by 1,25(OH)2D3 in the distal intestine of KO/TG mice. In addition, Slc30a10, encoding a manganese efflux transporter, was one of the genes most induced by 1,25(OH)2D3 in both proximal and distal intestine. Both villus and crypt were found to express Vdr and VDR target genes. RNA sequence (RNA-seq) analysis of human enteroids indicated that the effects of 1,25(OH)2D3 observed in mice are conserved in humans. Using Slc30a10-/- mice, a loss of cortical bone and a marked decrease in S100g and Trpv6 in the intestine was observed. Our findings suggest an interrelationship between vitamin D and intestinal Mn efflux and indicate the importance of distal intestinal segments to vitamin D action.

Impact of acidity regulator and excipient nutrients on digestive solubility and intestinal transport of calcium from calcium phosphate and carbonate

The aim of the current study was to investigate the effect of an acidity regulator (SPORIX®), lactose, and vitamin D₃ as excipient ingredients on digestive solubility and intestinal transport of calcium from four different calcium materials (tricalcium phosphate (TCP), fish bone (FB), nano-fish bone (NFB), and algae calcium (AC)) through an in vitro digestion model system combined with Caco-2 cells. The concentration of ionized calcium (Ca²⁺) in an aqueous fraction after in vitro digestion increased with the addition of SPORIX®, and it was further enhanced by adding SPORIX® + lactose + vitamin D₃ into TCP, FB, NFB, and AC, respectively. In particular, FB with SPORIX® + lactose + vitamin D₃ enhanced calcium ionization to 33.89 ± 0.69 mg g^-1, which was about 11.76 times higher than that of FB only. In the case of intestinal cellular uptake of calcium, there was no significant difference in all the tested calcium materials with SPORIX® + lactose + vitamin D₃. However, the absolute amount of intestinal transport of calcium in FB (43.95 ± 3.29 μg) was significantly higher than other calcium materials with the addition of SPORIX® + lactose + vitamin D₃ (p < 0.05). This study suggests that the co-consumption of SPORIX®, lactose, and vitamin D₃ with FB could enhance the calcium bioavailability by lowering pH as well as improving calcium intestinal transport by modulating the paracellular and transcellular uptake mechanism.

Vitamin D oral gel for prevention of radiation-induced oral mucositis: A randomized clinical trial

OBJECTIVES

The aim of this clinical trial is to evaluate the effectiveness of topical oral vitamin D gel in prevention of radiation-induced oral mucositis.

MATERIAL AND METHODS

A three-armed randomized controlled clinical trial on forty-five head and neck cancer patients was conducted. First group: conventional treatment. Second group: Topical oral vitamin D gel. Third group: topical oral vitamin D gel plus the conventional treatment. All the patients were examined clinically three and six weeks after the start of radiotherapy for pain and WHO mucositis score.

RESULTS

After 6 weeks of radiotherapy, (33.5%) the patients in control group developed high-grade severity of oral mucositis while the patients in the two-test groups "vitamin D group and combined therapy group" remained with low-grade severity or with complete remission. Mean pain scores showed a significant decrease in the combined therapy group and to a close degree in vitamin D group rather than the control group.

CONCLUSION

Topical oral vitamin D gel has a beneficial effect in lowering oral mucositis development and in reducing pain sensation during the radiation period especially when combined with conventional therapeutic agents.

Evaluation of the effect of vitamin D3 supplementation on quantitative and qualitative parameters of spermograms and hormones in infertile men: A Randomized controlled trial

BACKGROUND

25-Hydroxy Vitamin D3 is known to have an effect on reproductive system in both genders and may change the semen parameters in men.

OBJECTIVE

Our study aimed to evaluate the effect of oral vitamin D3 supplementation on spermogram quantitative and qualitative parameters in infertile men.

MATERIALS AND METHODS

This study was a triple-blind randomized controlled trial involving 62 infertile men with impaired spermatogonial tests. They were randomly divided into placebo and D3-supplemented groups. Spermograms and tests for LH (Luteinizing Hormone), FSH (Follicle Stimulating Hormone), TT (Total Testosterone), FT (Free Testosterone), SHBG (Sex Hormone Bonding Globulin), FAI (Free Androgen Index) and vitamin D3 levels were performed before and after the intervention.

RESULTS

There were no significant differences between the two groups in parameters of the spermograms or serum levels of LH, FSH, TT, and FAI. In the intervention group, SHBG was significantly decreased after intervention (p = 0.01) and there was a significant increase in FT in the placebo group (p = 0.03).

CONCLUSION

The intake of vitamin D3 did not change the quality and quantity of spermograms and serum levels of LH, FSH, TT, and FAI but affected FT and SHBG. Further studies are still needed to clarify the biological role of vitamin D3 on fertility particularly on male fertility. This study lays a foundation for more extensive studies on male infertility.

Visceral Fat Is a Negative Determinant of Bone Health in Obese Postmenopausal Women

The protective effect of obesity on bone health has been challenged by studies that link visceral adiposity to poor bone microarchitecture in young obese men and women. In postmenopausal women, the role of visceral adipose tissue (VAT) on bone turnover markers (BTMs) has not been investigated. The aim was to investigate the impact of VAT on BTMs, total bone mineral density (BMD), vitamin D metabolites and parathyroid levels (1-84 PTH) levels in postmenopausal women. A total of 76 lean and overweight women (without osteoporosis) underwent VAT measurements by dual-energy X-ray absorptiometry (iDXA). Blood samples were analyzed for serum C-terminal telopeptide of type 1 collagen (CTX-1), osteocalcin, bone-specific alkaline phosphatase (bone ALP), 1–84 PTH and vitamin D (25 hydroxyvitamin D, 25(OH)D) levels. VAT volumes ranged from 91 to 3392 cm³ and body mass index (BMI) ranged from 18.3 to 53.9 kg/m². Women in the highest VAT quartile had significantly lower CTX-1, 25(OH)D, osteocalcin and the highest BMD (p < 0.05, for all). While VAT positively associated with BMD, after controlling for BMI, VAT was a negative predictor of BMD (β = 0.368, p < 0.05). VAT was an independent negative predictor of CTX-1 (β = −0.263, p < 0.05) and osteocalcin levels (β = −0.277, p < 0.05). Among all measures of adiposity, VAT was the strongest independent determinant of BMD and BTMs. In clinical settings, VAT, and not BMI, may be a sensitive predictor of bone health in obese women.

Fracture risk factors among children living in New Zealand

Factures are common during childhood. There are limited data available regarding relationships between bone fracture history and calcium intake, sugar sweetened beverages (SSBs) intake, vitamin D status, physical activity (PA), ethnicity, and body composition in New Zealand (NZ) children. Identifying groups of NZ children at risk of fracture and associated predictors may help to improve bone quality during childhood and decrease the risk of fractures throughout life. The aim of this study was to investigate fracture history and associated risk factors in New Zealand children. Children aged 8-12 years were recruited. Capillary blood spots collected from a finger prick were as analyzed for 25(OH)D concentrations. Bioelectrical impedance analysis (InBody720, Seoul, Korea) was used to measure body fat percentage (%BF). Information about fracture history, siblings' history of fractures, family osteoporosis history, PA, ethnicity, and intake of calcium containing foods, and SSBs was collected using questionnaires. Children (n = 647, 354 girls), mean ± SD age 9.8 ± 0.7 years were recruited from six Auckland primary schools. NZ European (n = 252) (NZE) and South Asian (n = 68) children reported the lowest (20.2 %) and highest (44.1 %) fracture incidence, respectively. NZE compared to South Asian children, had higher 25(OH)D concentrations (74.6 ± 19.8 vs. 48.4 ± 19.3 nmol/L, P < 0.001), higher total calcium intake (764.0 ± 394.4 vs. 592.7 ± 266.3 mg/d, P < 0.018), and lower %BF (19.5 ± 6.6 vs. 23.4 ± 8.4, P < 0.003). Māori children had the next highest fracture rate (32.5 %). This group had adequate 25(OH)D (64.2 ± 18.9 nmol/L), but high %BF (23.9 %) and most participated in vigorous PA. After stratifying by sex, binary logistic regression analysis revealed the main determinants of fracture history for boys were high %BF, low 25(OH)D, low calcium intake, high SSBs consumption, siblings' fracture history, family osteoporosis history, and being South Asian; and in girls, high SSBs consumption, siblings' fracture history, and family osteoporosis history. We found South Asian ethnicity was a significant risk factor for boys. Some children were at high risk of vitamin D deficiency and for whom supplementation may be necessary in winter. Good nutrition (especially good sources of calcium and reducing SSBs intakes) should be recommended to children during growth and development to reduce their risk of fractures.

Serotonin regulates maternal calcium homeostasis during the perinatal period of sheep

The goal of this experiment was to demonstrate the ability of an infusion of serotonin (5-HT; 5-hydroxytryptamine) precursors to increase 5-HT production during the transition from pregnancy to lactation and its effects on gene expression related to calcium (Ca) transporters in the mammary gland and bone resorption markers in the femur. Thirty pregnant Bamei mutton sheep were randomly assigned to 3 experimental groups. All groups received a daily intravenous infusion of saline (control group; n = 10), saline containing 0.178 mg of L-tryptophan/kg body weight (BW) (TRP group, n = 10) or 0.178 mg of 5-hydroxytryptophan/kg BW (5-HTP group, n = 10), beginning on day 7 of prepartum and continuing until delivery. Serum (pre- and postpartum), milk (postpartum), and femur and mammary gland tissue (day 9) were collected. Sheep infused with 5-HTP had a larger total serum Ca concentration on days 3, 6, 15, and 30 of lactation and total milk Ca concentration on days 3, 6, 12, and 15 of lactation compared with that of the control group. Sheep infused with 5-HTP and TRP increased blood and milk concentrations of 5-HT on days 3, 6, 9, and 30 of lactation and parathyroid hormone-related protein (PTHrP) on day 3 of prepartum and on days 3, 6, and 15 of lactation (P < 0.05). In addition, compared to that of the control group, the TRP or 5-HTP infusion upregulated PTHrP, a sodium/calcium exchanger, plasma membrane Ca2+ ATPase 2, secretory pathway Ca2+ ATPase 1, and calcium sensing receptor mRNA expression in mammary gland and receptor-activated nuclear factor kappa-B ligand mRNA expression in the femur, but had no effect on receptor-activated nuclear factor kappa-B and osteoprotegerin mRNA expression in the femur (P < 0.05). This suggests that 5-HT and PTHrP may be involved in regulating maternal Ca homeostasis during the transition from pregnancy to lactation in the sheep.

Management of Post-transplant Hyperparathyroidism and Bone Disease

Significant advances in immunosuppressive therapies have been made in renal transplantation, leading to increased allograft and patient survival. Despite improvement in overall patient survival, patients continue to require management of persistent post-transplant hyperparathyroidism. Medications that treat persistent hyperparathyroidism include vitamin D, vitamin D analogues, and calcimimetics. Medication side effects such as hypocalcemia or hypercalcemia, and adynamic bone disease, may lead to a decrease in the drugs. When medical management fails to control persistent post-transplant hyperparathyroidism, treatment is a parathyroidectomy. Surgical techniques are not uniform between centers and surgeons. Undergoing the surgery may include a subtotal technique or a technique including total parathyroid gland resection with partial heterotopic gland reimplantation. In addition, there are possible post-surgical complications. The ideal treatment for persistent post-transplant hyperparathyroidism is the treatment and prevention of the condition while patients are being managed for their late-stage chronic kidney disease and end-stage renal disease.

Relationship between 1,25-Dihydroxyvitamin D and Body Composition in Middle-Aged Sedentary Adults: The FIT-AGEING Study

Vitamin D deficiency is a worldwide health problem that, in addition to its well-known negative effects on musculoskeletal health, has been related to a wide range of acute and chronic age-related diseases. However, little is known about the association of body composition with the active, hormonal form of vitamin D, 1,25-dihydroxyvitamin D plasma levels (1,25(OH)₂D). Therefore, the aim of this study was to investigate the association of 1,25(OH)₂D with body composition including lean and fat body mass as well as bone mineral density (BMD) in middle-aged sedentary adults. A total of 73 (39 women) middle-aged sedentary adults (53.7 ± 5.1 years old) participated in the current study. We measured weight and height, and we used dual energy X-ray absorptiometry to measure lean body mass, fat body mass and BMD. Body mass index (BMI), lean mass index (LMI), and fat mass index (FMI) were calculated. 1,25(OH)₂D was measured using a DiaSorin Liaison® immunochemiluminometric analyzer. The results showed a negative association of 1,25(OH)₂D with BMI, LMI and BMD (β = −0.274, R² = 0.075, p = 0.019; β = −0.268, R² = 0.072, p = 0.022; and β = −0.325, R² = 0.105, p = 0.005, respectively), which persisted after controlling for age and sex. No significant differences in 1,25(OH)₂D across body weight status were observed after controlling for the same covariates. In summary, our results suggest that 1,25(OH)₂D could be negatively associated with BMI, LMI and BMD whereas no association was found with FMI in middle-aged sedentary adults.

Effects of vitamin D supplementation on follicular development, gonadotropins and sex hormone concentrations, and insulin resistance in induced polycystic ovary syndrome

Objective:

Polycystic ovary syndrome (PCOS) as a reproductive disorder disturbs ovarian follicular development, vitamin D stimulated insulin activity, and sex hormone concentrations. This study aimed to examine the effects of vitamin D on ovarian follicular development, insulin resistance, and sex hormone changes in rats with induced PCOS.

Materials and Methods:

Forty female Wistar rats were randomly divided into four groups: (1) control, (2) induced PCOS, (3) vitamin D-treated non-PCOS (sham group), (4) vitamin D treated PCOS groups. All rats were then sacrificed under anesthesia and ovarian tissue samples were evaluated histomorphometrically. Blood samples were collected for analyzing the serum concentrations of sex hormones and insulin resistance.

Results:

The number of atretic follicles at different stages of development increased in the PCOS ovaries (p<0.001). Vitamin D treatment significantly increased the normality of follicles in rats with PCOS (p<0.001). The serum concentration of follicle stimulating hormone and the estradiol significantly increased in rats with PCOS, whereas the testosterone and luteinizing hormone concentrations, glucose, insulin, and insulin resistance concentrations significantly decreased during vitamin D treatment (p<0.001).

Conclusion:

This study indicated that vitamin D treatment may protect ovarian tissue from the negative effect of PCOS by improving insulin activity and gonadotropin concentrations.

Review: Endocrine pathways to regulate calcium homeostasis around parturition and the prevention of hypocalcemia in periparturient dairy cows

Calcium homeostasis is crucial for the normal function of the organism. Parathyroid hormone, calcitriol and calcitonin play critical roles in the homeostatic regulation of calcium. Serotonin and prolactin have also been shown to be involved in the regulation of calcium homeostasis. In modern dairy cows, the endocrine pathways controlling calcium homeostasis during non-lactating and non-pregnant physiological states are unable to fully support the increased demand of calcium required for milk synthesis at the onset of lactation. This review describes different endocrine systems associated with the regulation of calcium homeostasis in mammalian species around parturition with special focus on dairy cows. Additionally, classic and novel strategies to reduce the incidence of hypocalcemia in parturient dairy cows are discussed.

Vitamin D and Obesity: Two Interacting Players in the Field of Infertility

Obesity plays an important role in human fertility in both genders. The same is true for vitamin D, for which accumulating evidence from observational human studies suggests a key role for both male and female fertility. In the latter case, however, robust data from relevant interventional studies are currently lacking. It is also not clear whether obesity and vitamin D deficiency, besides their independent effect on human infertility, act in synergy. Several pathogenetic mechanisms may be proposed as a linkage between vitamin D deficiency and obesity, with respect to infertility. In any case, the independent contribution of vitamin D deficiency in obese infertile states needs to be proven in interventional studies focusing on either vitamin D supplementation in obese or weight loss strategies in vitamin D-deficient infertile patients.

Vitamin D in the Spectrum of Prediabetes and Cardiovascular Autonomic Dysfunction

Vitamin D is a fat-soluble secosteroid hormone with pleiotropic effects. 1,25-Dihydroxyvitamin D coordinates the biosynthesis of neurotransmitters in the central nervous system, which regulate cardiovascular autonomic function and may explain its putative role in the development of cardiovascular autonomic neuropathy (CAN). CAN is an independent risk factor for mortality in patients with diabetes and prediabetes and is associated with an increased risk of developing type 2 diabetes and cardiovascular disease. Accumulating data indicate the presence of peripheral nerve injury at these early stages of dysglycemia and its multifactorial pathogenesis. Prediabetes is associated with vitamin D insufficiency. Vitamin D is proposed to prevent the progression of glucose intolerance. The putative underlying mechanisms include maintenance of the intracellular calcium concentration, direct stimulation of insulin receptor expression, and enhancement of the insulin response to glucose transporters. Vitamin D exerts a protective effect on peripheral nerve fibers by decreasing the demyelination process and inducing axonal regeneration. The effects of vitamin D supplementation on glucose tolerance and related autonomic nerve dysfunction have been a recent focus of scientific interest. Although well-designed observational studies are available, the causative relation between vitamin D deficiency, glucose intolerance, and CAN is still debatable. One reason might be that interventional studies are unpersuasive with regard to the beneficial clinical effects of vitamin D supplementation. Because of its favorable side effect profile, vitamin D supplementation might represent an attractive therapeutic option for treating the pandemic prevalence of prediabetes and vitamin D deficiency. Vitamin D supplementation can improve glucose tolerance and cardiovascular autonomic function and can thus reduce cardiovascular mortality among subjects with different stages of glucose intolerance and autonomic dysfunction. However, more patient-centered trials on the use of vitamin D supplementation in different conditions are needed.

Serum total oxidant/anti-oxidant status, ischemia-modified albumin and oxidized-low density lipoprotein levels in patients with vitamin D deficiency

OBJECTIVE

Oxidative damage may be responsible for the pathogenesis and complications of many diseases. Vitamin D deficiency has been suggested as a potential mediator of various extra-skeletal pathologies. However, there are limited data on anti-oxidant properties of vitamin D.

MATERIALS AND METHODS

Forty-one subjects with vitamin D deficiency and 30 healthy controls were enrolled into the study. The levels of total anti-oxidant status (TAS), total oxidant status (TOS), ischemia-modified albumin (IMA), oxidized-low density lipoprotein (ox-LDL), high-sensitivity C-reactive protein (hs-CRP) and fibrinogen were measured in both groups. The measurements were repeated in 17 patients after the replacement of vitamin D.

RESULTS

Serum IMA and TOS levels were significantly higher (p < 0.001 and p = 0.035, respectively), while TAS levels were significantly lower in patients, compared to controls (p < 0.001). Additionally, fibrinogen was significantly higher in patients than controls (p = 0.003), while ox-LDL and hs-CRP levels were similar between two groups. After the replacement of vitamin D, TAS level significantly increased (p = 0.037), and TOS and fibrinogen levels significantly decreased (p = 0.043 and p = 0.010, respectively). Vitamin D levels were negatively correlated with IMA and fibrinogen levels (r = -0.500, p < 0.001 and r = -0.391, p = 0.002, respectively), although positively correlated with TAS levels (r = 0.430, p < 0.001). No correlation was found between vitamin D levels, and the TOS, ox-LDL and hs-CRP levels.

CONCLUSIONS

In this study, while serum IMA, TOS and fibrinogen levels were increased, TAS levels were seen to be decreased in patients with vitamin D deficiency. These results suggest that oxidative/anti-oxidative balance shifts in favours of oxidative status in vitamin D deficiency.

Serum 25-hydroxyvitamin D level is associated with myopia in the Korea national health and nutrition examination survey

The aim of this article was to assess the associations of serum 25-hydroxyvitamin D [25(OH)D] and daily sun exposure time with myopia in Korean adults.This study is based on the Korea National Health and Nutrition Examination Survey (KNHANES) of Korean adults in 2010-2012; multiple logistic regression analyses were performed to examine the associations of serum 25(OH)D levels and daily sun exposure time with myopia, defined as spherical equivalent ≤-0.5D, after adjustment for age, sex, household income, body mass index (BMI), exercise, intraocular pressure (IOP), and education level. Also, multiple linear regression analyses were performed to examine the relationship between serum 25(OH)D levels with spherical equivalent after adjustment for daily sun exposure time in addition to the confounding factors above.Between the nonmyopic and myopic groups, spherical equivalent, age, IOP, BMI, waist circumference, education level, household income, and area of residence differed significantly (all P < 0.05). Compared with subjects with daily sun exposure time <2 hour, subjects with sun exposure time ≥2 to <5 hour, and those with sun exposure time ≥5 hour had significantly less myopia (P < 0.001). In addition, compared with subjects were categorized into quartiles of serum 25(OH)D, the higher quartiles had gradually lower prevalences of myopia after adjustment for confounding factors (P < 0.001). In multiple linear regression analyses, spherical equivalent was significantly associated with serum 25(OH)D concentration after adjustment for confounding factors (P = 0.002).Low serum 25(OH)D levels and shorter daily sun exposure time may be independently associated with a high prevalence of myopia in Korean adults. These data suggest a direct role for vitamin D in the development of myopia.

Serum 25-hydroxyvitamin D status among Saudi children with and without a history of fracture

BACKGROUND

The significance of vitamin D deficiency in the incidence of bone fractures in children has been under investigated. Here, we aimed to associate serum 25-hydroxyvitamin D levels and fractures in Saudi children.

MATERIALS AND METHODS

This cross-sectional study was conducted in 1022 Saudi children without fracture history [476 boys (age 14.56 ± 1.81, BMI 22.38 ± 5.81) and 546 girls (age 13.57 ± 1.67, BMI 22.24 ± 4.94)] and 234 Saudi children with a history of fracture [148 boys (age 14.25 ± 1.39, BMI 22.66 ± 6.08) and 86 girls (age 13.76 ± 1.35, BMI 21.33 ± 1.35)]. Anthropometric and fasting serum biochemical data were collected. Serum 25-hydroxyvitamin D level was assessed using electrochemiluminescence.

RESULTS

Mean circulating 25-hydroxyvitamin (25OH) D level in subjects with a history of fracture was significantly lower in both boys (p < 0.01) and girls (p < 0.01) than those without, however both groups had low mean 25(OH)D levels. Furthermore, age was positively associated with 25-hydroxyvitamin D in boys (p < 0.05) and negatively in girls (p < 0.05) with a history of fracture.

CONCLUSION

In conclusion, vitamin D levels were significantly lower in children with a history of bone fractures in both boys and girls than those without such a history; even in the absence of fracture history, vitamin D status correction is warranted in the general Saudi pediatric population.

The association between vitamin D and parathyroid hormone and bone mineral density: the Dong-gu Study

The primary objective of the present study was to investigate the relationship between 25-hydroxyvitamin D (25[OH]D) and areal bone mineral density (aBMD) in Korean subjects from the general population aged ≥50 years. This study included 8,857 individuals who completed the baseline survey of the Dong-gu study, which was conducted in Korea from 2007-2010. The participants who fulfilled the detailed inclusion criteria underwent assessment of the femoral neck and lumbar spine aBMD as well as measurement of serum 25(OH)D and parathyroid hormone (PTH) levels. After adjusting for other covariates and log-PTH values, the mean aBMD of the femoral neck exhibited a significant increase with increasing 25(OH)D levels in both males (p < 0.001) and females (p = 0.005). Additionally, the mean aBMD of the lumbar spine exhibited a significant increase with increasing 25(OH)D levels in males (p = 0.011) but not females (p = 0.252). After adjusting for covariates and log-25(OH)D values, the mean aBMD values of the femoral neck and lumbar spine showed significant decreases with increasing PTH levels in both males and females (p < 0.001). The present findings demonstrate that the aBMD of the femoral neck was significantly associated with 25(OH)D levels independent of PTH in both males and females and that the aBMD of the lumbar spine was significantly associated with 25(OH)D levels independent of PTH in males, but not females.

Vitamin D-binding protein and free vitamin D concentrations in acromegaly

Free 25-hydroxyvitamin D [25(OH)D] is suggested to be important in the determination of vitamin D deficiency, since vitamin D-binding protein (VDBP) may affect total 25(OH)D levels. There are no data about free 25(OH)D concentrations in acromegaly. We aimed to investigate serum VDBP and total and free 25(OH)D levels in patients with acromegaly in comparison with control subjects. We recruited 54 patients with acromegaly and 32 control subjects who were similar according to age, gender, and body mass index. Serum VDBP levels were found to be increased in patients with acromegaly compared to control subjects [90.35 (72.45-111.10) vs. 69.52 (63.89-80.13) mg/l, p = 0.001]. There was statistically no significant difference in serum total 25(OH)D levels between the patients with acromegaly and control subjects [18.63 (13.35-27.73) vs. 22.51 (19.20-28.96) ng/ml, p = 0.05]. Free 25(OH)D levels were significantly decreased in patients with acromegaly compared to control subjects [14.55 (10.45-21.45) vs. 17.75 (15.30-23.75) pg/ml, p = 0.03]. Free 25(OH)D levels correlated positively with total 25(OH)D (p = 0.0001) and HDL cholesterol (p = 0.04) and negatively with fasting blood glucose (p = 0.04). Our findings indicate that VDBP is increased and free 25(OH)D is decreased in acromegaly, while there is no significant alteration in total 25(OH)D.

Roles of the kidney in the formation, remodeling and repair of bone

The relationship between the kidney and bone is highly complex, and the kidney plays an important role in the regulation of bone development and metabolism. The kidney is the major organ involved in the regulation of calcium and phosphate homeostasis, which is essential for bone mineralization and development. Many substances synthesized by the kidney, such as 1,25(OH)2D3, Klotho, bone morphogenetic protein-7, and erythropoietin, are involved in different stages of bone formation, remodeling and repair. In addition, some cytokines which can be affected by the kidney, such as osteoprotegerin, sclerostin, fibroblast growth factor -23 and parathyroid hormone, also play important roles in bone metabolism. In this paper, we summarize the possible effects of these kidney-related cytokines on bone and their possible mechanisms. Most of these cytokines can interact with one another, constituting an intricate network between the kidney and bone. Therefore, kidney diseases should be considered among patients presenting with osteodystrophy and disturbances in bone and mineral metabolism, and treatment for renal dysfunction may accelerate their recovery.

Extra-intestinal calcium handling contributes to normal serum calcium levels when intestinal calcium absorption is suboptimal

The active form of vitamin D, 1,25(OH)2D, is a crucial regulator of calcium homeostasis, especially through stimulation of intestinal calcium transport. Lack of intestinal vitamin D receptor (VDR) signaling does however not result in hypocalcemia, because the increased 1,25(OH)2D levels stimulate calcium handling in extra-intestinal tissues. Systemic VDR deficiency, on the other hand, results in hypocalcemia because calcium handling is impaired not only in the intestine, but also in kidney and bone. It remains however unclear whether low intestinal VDR activity, as observed during aging, is sufficient for intestinal calcium transport and for mineral and bone homeostasis. To this end, we generated mice that expressed the Vdr exclusively in the gut, but at reduced levels. We found that ~15% of intestinal VDR expression greatly prevented the Vdr null phenotype in young-adult mice, including the severe hypocalcemia. Serum calcium levels were, however, in the low-normal range, which may be due to the suboptimal intestinal calcium absorption, renal calcium loss, insufficient increase in bone resorption and normal calcium incorporation in the bone matrix. In conclusion, our results indicate that low intestinal VDR levels improve intestinal calcium absorption compared to Vdr null mice, but also show that 1,25(OH)2D-mediated fine-tuning of renal calcium reabsorption and bone mineralization and resorption is required to maintain fully normal serum calcium levels.

1α,25-Dihydroxyvitamin D3 inhibits the differentiation and bone resorption by osteoclasts generated from Wistar rat bone marrow-derived macrophages

The steroid hormone 1α,25-dihydroxyvitamin D₃ [1α,25-(OH)₂D₃] plays an important role in maintaining a balance in calcium and bone metabolism. To study the effects of 1α,25-(OH)₂D₃ on osteoclast (OC) formation and bone resorption, OC differentiation was induced in bone marrow-derived mononuclear cells from Wistar rats with the addition of macrophage colony stimulating factor and receptor activator for nuclear factor-κB ligand in vitro. Cells were then treated with 1α,25-(OH)₂D₃ at 10^-9, 10^-8 or 10^-7 mol/l. OCs were identified using tartrate-resistant acid phosphatase staining and activity was monitored in the absorption lacunae by scanning electron microscopy. Expression levels of functional proteins associated with bone absorption, namely carbonic anhydrase II, cathepsin K and matrix metalloproteinase-9 were evaluated by western blot analysis. The results showed that 1α,25-(OH)₂D₃ inhibited the formation and activation of OCs in a dose-dependent manner and downregulated the expression levels of bone absorption-associated proteins.

Segmental transport of Ca²⁺ and Mg²⁺ along the gastrointestinal tract

Calcium (Ca(2+)) and magnesium (Mg(2+)) ions are involved in many vital physiological functions. Since dietary intake is the only source of minerals for the body, intestinal absorption is essential for normal homeostatic levels. The aim of this study was to characterize the absorption of Ca(2+) as well as Mg(2+) along the gastrointestinal tract at a molecular and functional level. In both humans and mice the Ca(2+) channel transient receptor potential vanilloid subtype 6 (TRPV6) is expressed in the proximal intestinal segments, whereas Mg(2+) channel transient receptor potential melastatin subtype 6 (TRPM6) is expressed in the distal parts of the intestine. A method was established to measure the rate of Mg(2+) absorption from the intestine in a time-dependent manner by use of (25)Mg(2+). In addition, local absorption of Ca(2+) and Mg(2+) in different segments of the intestine of mice was determined by using surgically implanted intestinal cannulas. By these methods, it was demonstrated that intestinal absorption of Mg(2+) is regulated by dietary needs in a vitamin D-independent manner. Also, it was shown that at low luminal concentrations, favoring transcellular absorption, Ca(2+) transport mainly takes place in the proximal segments of the intestine, whereas Mg(2+) absorption predominantly occurs in the distal part of the gastrointestinal tract. Vitamin D treatment of mice increased serum Mg(2+) levels and 24-h urinary Mg(2+) excretion, but not intestinal absorption of (25)Mg(2+). Segmental cannulation of the intestine and time-dependent absorption studies using (25)Mg(2+) provide new ways to study intestinal Mg(2+) absorption.

A vitamin D receptor selectively activated by gemini analogs reveals ligand dependent and independent effects

The bioactive form of vitamin D [1,25(OH)2D3] regulates mineral and bone homeostasis and exerts potent anti-inflammatory and antiproliferative properties through binding to the vitamin D receptor (VDR). The 3D structures of the VDR ligand-binding domain with 1,25(OH)2D3 or gemini analogs unveiled the molecular mechanism underlying ligand recognition. On the basis of structure-function correlations, we generated a point-mutated VDR (VDR(gem)) that is unresponsive to 1,25(OH)2D3, but the activity of which is efficiently induced by the gemini ligands. Moreover, we show that many VDR target genes are repressed by unliganded VDR(gem) and that mineral ion and bone homeostasis are more impaired in VDR(gem) mice than in VDR null mice, demonstrating that mutations abolishing VDR ligand binding result in more severe skeletal defects than VDR null mutations. As gemini ligands induce VDR(gem) transcriptional activity in mice and normalize their serum calcium levels, VDR(gem) is a powerful tool to further unravel both liganded and unliganded VDR signaling.

Beneficial effects of vitamin D on falls and fractures: is cognition rather than bone or muscle behind these benefits?

The beneficial effect of vitamin D on bone tissue has long been attributed mainly to its positive effect on the intestinal absorption of calcium and on bone mineralization, which increases the bone mineral density (BMD) and thus decreases the risk of fracture. Recently, numerous extra osseous effects of vitamin D have been described, amongst them a positive effect on neuromuscular and cognitive functions. Several lines of evidence suggest that the beneficial effects of vitamin D on fall and fracture risk can be explained more by its action on the neuromuscular and cognitive functions than by its direct effect on bone metabolism. In this review, we first report on the relationships between vitamin D and osteoporotic fracture risk. Then, we present the data from the literature regarding the effects of vitamin D on risk factors such as fall risk and reduction in BMD, physical performance, and cognitive performance. Specific emphasis is put on the latter because there is evidence of a relationship between low concentration of serum 25-hydroxyvitamin D (the primary indicator of vitamin D status) and low cognitive abilities which have been shown to be a risk factor for falling. It can be further suggested that high risk of fracture in cognitively impaired adults could be explained by lower protective reaction when falling, which would result, for instance, from a lack of planning and foresight of the fall. Future studies are nonetheless needed to elucidate the associations between vitamin D and different risk factors, in particular the link between vitamin D and various cognitive functions.

Metabolic bone disease in pediatric intestinal failure patients: prevalence and risk factors

PURPOSE

Patients with intestinal failure (IF) are known to have impaired absorption of nutrients required for maintenance of skeletal mass. Rates and risk factors of low bone mineral density (BMD) are unknown in pediatric IF patients.

METHODS

Following IRB approval, patients with IF having undergone DXA scans were identified and laboratory, clinical, and nutritional intake variables were recorded. Low BMD was defined by a z-score of less than or equal to -2.0. Univariate followed by multivariable regression analysis was performed.

RESULTS

Sixty-five patients underwent a total of 99 routine DXA scans. Twenty-seven (41%) had vitamin D deficiency, 22 (34%) had low BMD, and nineteen (29%) had a history of fractures. Variables noted to be associated with low BMD (p<0.1) on univariate analysis were considered for multivariable regression. Multivariable regression identified WAZ and serum calcium levels (p<0.05) as independent predictors of low BMD z-score. None of the other evaluated factors were associated with the risk of low BMD. Low BMD was not associated with risk of fractures.

CONCLUSION

There is a significant incidence of low BMD in children with IF. WAZ and lower serum calcium levels are associated with risk of low BMD. Additional long term prospective studies are needed to further characterize the risk factors associated with low BMD.

[Disorders of calcium metabolism]

The majority of clinical complaints derive from disorders of calcium metabolism and are associated with a wide variety of clinical symptoms caused by numerous diseases with entirely different types of pathophysiology. The prognosis varies from favorable to fatal depending on the pathophysiology of the underlying disorder of calcium metabolism; therefore, the diagnostic work-up aims to quickly identify the underlying disease causing the disturbance in calcium homeostasis. Every clinical situation with a diminished state of calcium absorption is treated with calcium and vitamin D in varying doses whereas every disorder with an increased calcium absorptive or resorptive state is treated with improved diuresis in addition to antiresorptive drugs, such as bisphosphonates. In many situations the management of a disturbed calcium balance requires an interdisciplinary approach in order to treat the underlying disease in parallel with correction of the calcium homeostasis.

Vascular calcification and renal bone disorders

At the early stage of chronic kidney disease (CKD), the systemic mineral metabolism and bone composition start to change. This alteration is known as chronic kidney disease-mineral bone disorder (CKD-MBD). It is well known that the bone turnover disorder is the most common complication of CKD-MBD. Besides, CKD patients usually suffer from vascular calcification (VC), which is highly associated with mortality. Many factors regulate the VC mechanism, which include imbalances in serum calcium and phosphate, systemic inflammation, RANK/RANKL/OPG triad, aldosterone, microRNAs, osteogenic transdifferentiation, and effects of vitamins. These factors have roles in both promoting and inhibiting VC. Patients with CKD usually have bone turnover problems. Patients with high bone turnover have increase of calcium and phosphate release from the bone. By contrast, when bone turnover is low, serum calcium and phosphate levels are frequently maintained at high levels because the reservoir functions of bone decrease. Both of these conditions will increase the possibility of VC. In addition, the calcified vessel may secrete FGF23 and Wnt inhibitors such as sclerostin, DKK-1, and secreted frizzled-related protein to prevent further VC. However, all of them may fight back the inhibition of bone formation resulting in fragile bone. There are several ways to treat VC depending on the bone turnover status of the individual. The main goals of therapy are to maintain normal bone turnover and protect against VC.

Pharmacological effects of vitamin D and its analogs: recent developments

Calcitriol, the hormonally active form of vitamin D, is well known for its diverse pharmacological activities, including modulation of cell growth, neuromuscular and immune function and reduction of inflammation. Calcitriol and its analogs exert potent effects on cellular differentiation and proliferation, regulate apoptosis and produce immunomodulatory effects. The purpose of this review is to provide information on various physiological and pharmacological activities of calcitriol and its newly discovered analogs. Special emphasis is given to skin diseases, cancer, diabetes and multiple sclerosis. A discussion is raised on the mechanisms of action of calcitriol and its analogs in various diseases, as well as on possible methods of delivery and targeting.

Genomic determinants of gene regulation by 1,25-dihydroxyvitamin D3 during osteoblast-lineage cell differentiation

The biological effects of 1α,25-dihydroxyvitamin D3 (1,25 (OH)2D3) on osteoblast differentiation and function differ significantly depending upon the cellular state of maturation. To explore this phenomenon mechanistically, we examined the impact of 1,25(OH)2D3 on the transcriptomes of both pre-osteoblastic (POBs) and differentiated osteoblastic (OBs) MC3T3-E1 cells, and assessed localization of the vitamin D receptor (VDR) at sites of action on a genome-scale using ChIP sequence analysis. We observed that the 1,25(OH)2D3-induced transcriptomes of POBs and OBs were quantitatively and qualitatively different, supporting not only the altered biology observed but the potential for a change in VDR interaction at the genome as well. This idea was confirmed through discovery that VDR cistromes in POBs and OBs were also strikingly different. Depletion of VDR-binding sites in OBs, due in part to reduced VDR expression, was the likely cause of the loss of VDR-target gene interaction. Continued novel regulation by 1,25(OH)2D3, however, suggested that factors in addition to the VDR might also be involved. Accordingly, we show that transcriptomic modifications are also accompanied by changes in genome binding of the master osteoblast regulator RUNX2 and the chromatin remodeler CCAAT/enhancer-binding protein β. Importantly, genome occupancy was also highlighted by the presence of epigenetic enhancer signatures that were selectively changed in response to both differentiation and 1,25(OH)2D3. The impact of VDR, RUNX2, and C/EBPβ on osteoblast differentiation is exemplified by their actions at the Runx2 and Sp7 gene loci. We conclude that each of these mechanisms may contribute to the diverse actions of 1,25(OH)2D3 on differentiating osteoblasts.

Vitamin D: direct effects of vitamin D metabolites on bone: lessons from genetically modified mice

The vitamin D endocrine system has clear beneficial effects on bone as demonstrated by prevention of rickets in children and by reducing the risk of osteomalacia or osteoporosis in adults or elderly subjects. Depending on the design of the study of genetically modified animals, however, 1,25(OH)2D and the vitamin D receptor (VDR) may have no effect, beneficial or even deleterious direct effects on bone. We present here a comprehensive model of the direct effects of vitamin D on bone. In case of sufficient calcium supply, vitamin D and its metabolites can improve the calcium balance and facilitate mineral deposition in bone matrix largely without direct effects on bone cells, although some beneficial effects may occur via mature osteoblasts, as demonstrated in mice with osteoblast-specific overexpression of VDR or 1α-hydroxylase. In case of calcium deficiency, however, 1,25(OH)2D enhances bone resorption, whereas simultaneously inhibiting bone mineralization, so as to defend serum calcium homeostasis at the expense of bone mass. This dual role probably provides a survival benefit for land vertebrates living in a calcium-poor environment.

Role of local vitamin D signaling and cellular calcium transport system in bone homeostasis

Mouse genetic studies have demonstrated that the 1,25-dihydroxyvitamin D [1,25(OH)2D] endocrine system is required for calcium (Ca(2+)) and bone homeostasis. These studies reported severe hypocalcemia and impaired bone mineralization associated with rickets in mutant mice. Specific phenotypes of these mice with an engineered deletion of 1,25(OH)2D cell signaling resemble the features observed in humans with the same congenital disease or severe 1,25(OH)2D deficiency. Decreased active intestinal Ca(2+) absorption because of reduced expression of epithelial Ca(2+) channels is a crucial mechanism that contributes to the major phenotypes observed in the mutant mice. The importance of intestinal Ca(2+) absorption supported by 1,25(OH)2D-mediated transport was further emphasized by the observation that Ca(2+) supplementation rescues hypocalcemia and restores bone mineralization in both patients and mice lacking 1,25(OH)2D signaling. This observation questions the direct role of 1,25(OH)2D signaling in bone tissue. Studies regarding tissue-specific manipulation of 1,25(OH)2D function have provided a consensus on this issue by demonstrating a direct action of 1,25(OH)2D on cells in bone tissue through bone metabolism and mineral homeostasis. In addition, movement of Ca(2+) from the bone as a result of osteoclastic bone resorption also provides a large Ca(2+) supply in Ca(2+) homeostasis; however, the system controlling Ca(2+) homeostasis in osteoclasts has not been fully identified. Transient receptor potential vanilloid (TRPV) 4 mediates Ca(2+) influx during the late stage of osteoclast differentiation, thereby regulating the Ca(2+) signaling essential for cellular events during osteoclast differentiation; however, the system-modifying effect of TRPV4 activity should be determined. Furthermore, it remains unknown how local Ca(2+) metabolism participates in systemic Ca(2+) homeostasis through bone remodeling. New insights are therefore required to understand this issue.

Risk of metabolic bone disease is increased both during and after weaning off parenteral nutrition in pediatric intestinal failure

AIM

To assess bone health in pediatric intestinal failure (IF).

METHODS

A population-based cohort of 41 IF patients (age 9.9 years) underwent evaluation of bone mineral density (BMD), bone biochemistry, nutritional status and growth. Eleven patients remained on parenteral nutrition (PN) after 69 months. Thirty had weaned off PN 9.0 years earlier (mean), i.e. after 30 months on PN.

RESULTS

The majority of patients had lumbar spine or femoral BMD Z-score ≤-1.0 (70%), vitamin D deficiency (serum 25-hydroxyvitamin-D, S-25-OHD, <50 nmol/l, 41%) or secondary hyperparathyroidism (plasma parathyroid hormone >47 ng/l, 44%), equally during and after weaning off PN. Hyperparathyroidism was absent when S-25-OHD was >80 nmol/l. Until puberty, height (-1.4 to -0.8, age 1-12) and weight Z-scores (-1.3 to -0.5, age 1-16) were below the normal mean (p < 0.05). Small bowel length associated with S-25-OHD levels (r = 0.489, p = 0.013). In a multivariate model, time after weaning off PN (β = -0.597, p = 0.001), duration of PN (β = -0.466, p = 0.006) and calcium intake (β = -0.331, p = 0.035) predicted decreased lumbar spine BMD.

CONCLUSIONS

In pediatric IF, vitamin D insufficiency, secondary hyperparathyroidism and decreased BMD are common. BMD, vitamin D, calcium and nutritional status should be closely monitored during and after weaning off PN to ensure sufficient vitamin D and mineral substitution for normal growth and bone mass attainment.

Recovery versus persistence of disordered mineral metabolism in kidney transplant recipients

In patients with end-stage renal disease, successful renal transplantation improves the quality of life and increases survival, as compared with long-term dialysis treatment. Although it long has been believed that successful kidney transplantation to a large extent solves the problem of chronic kidney disease-mineral and bone disorders (CKD-MBD), increasing evidence indicates that it only changes the phenotype of CKD-MBD. Posttransplant CKD-MBD reflects the effects of immunosuppression, previous CKD-MBD persisting after transplantation, and de novo CKD-MBD. A major and often-underestimated problem after successful renal transplantation is persistent hyperparathyroidism. Besides contributing to posttransplant hypercalcemia and hypophosphatemia, persistent hyperparathyroidism may be involved in the pathogenesis of allograft dysfunction (nephrocalcinosis), progression of vascular calcification, and bone disease (uncoupling of bone formation and bone resorption and bone mineral density loss) in renal transplant recipients. Similar to nontransplanted patients, CKD-MBD has a detrimental impact on (cardiovascular) mortality and morbidity. Additional studies urgently are needed to get more insights into the pathophysiology of posttransplant CKD-MBD. These new insights will allow for a more targeted and causal therapeutic approach.

Vitamin D in thyroid tumorigenesis and development

Besides its classical role in bone and calcium homeostasis, 1,25-dihydroxyvitamin D3 (1,25(OH)2D3), the active form of vitamin D, has many non-classical effects; antiproliferative, anti-apoptotic and prodifferentiating effects of 1,25(OH)2D3 have been described in several tumour types in preclinical models. This review focuses on the insights gained in the elucidation of the role of 1,25(OH)2D3 in the normal thyroid and in the pathogenesis, progression and treatment of thyroid cancer, the most common endocrine malignancy. An increasing amount of observations points towards a role for impaired 1,25(OH)2D3-VDR signalling in the occurrence and progression of thyroid cancer, and a potential for structural analogues in the multimodal treatment of dedifferentiated iodine-resistant thyroid cancer. A role for vitamin D in thyroid-related autoimmunity is less convincing and needs further study. Altered 1,25(OH)2D3-VDR signalling does not influence normal thyroid development nor thyrocyte function, but does affect C-cell function, at least in rodents. If these findings also apply to humans deserves further study.

The delicate balance between vitamin D, calcium and bone homeostasis: lessons learned from intestinal- and osteocyte-specific VDR null mice

The serum calcium levels and the calcium content of the skeleton are highly interdependent. Indeed, bone requires calcium to preserve its strength, but it is at the same time also the predominant calcium storage from which calcium can be mobilized to supply the serum pool. The active form of vitamin D [1,25(OH)2D] plays a crucial role in regulating the transfer of calcium between blood and bone, evidenced by experimental data obtained from systemic, intestinal-specific and osteocyte-specific vitamin D receptor (Vdr) null mice. In fact, 1,25(OH)2D is required to maintain normocalcemia and bone health by enhancing intestinal calcium absorption when dietary calcium intake is normal/low. When, however, insufficient calcium is absorbed via the intestine, 1,25(OH)2D levels will increase and will act on mature osteoblasts and osteocytes to minimize calcium levels in bone tissue in favor of the blood calcium pool. Mechanistically, the high 1,25(OH)2D levels enhance bone remodeling which leads to osteopenia, and suppress bone matrix mineralization by increasing the levels of mineralization inhibitors, which causes hyperosteoidosis and hypomineralization. Thus, depending on the intestinal calcium acquisition, 1,25(OH)2D will target the intestine and/or the skeleton to maintain calcium levels in serum within a normal range.

Vitamin D signaling in osteocytes: effects on bone and mineral homeostasis

The active form of vitamin D [1,25(OH)2D] is an important regulator of calcium and bone homeostasis, as evidenced by the consequences of 1,25(OH)2D inactivity in man and mice, which include hypocalcemia, hypophosphatemia, secondary hyperparathyroidism and bone abnormalities. The recent generation of tissue-specific (intestine, osteoblast/osteocyte, chondrocyte) vitamin D receptor (Vdr) null mice has provided mechanistic insight in the cell-specific actions of 1,25(OH)2D and their contribution to the integrative physiology of VDR signaling that controls bone and mineral metabolism. These studies have demonstrated that even with normal dietary calcium intake, 1,25(OH)2D is crucial to maintain normal calcium and bone homeostasis and accomplishes this primarily through stimulation of intestinal calcium transport. When, moreover, insufficient calcium is acquired from the diet (severe dietary calcium restriction, lack of intestinal VDR activity), 1,25(OH)2D levels will increase and will directly act on osteoblasts and osteocytes to enhance bone resorption and to suppress bone matrix mineralization. Although this system is essential to maintain normal calcium levels in blood during a negative calcium balance, the consequences for bone are disastrous and generate an increased fracture risk. These findings evidently demonstrate that preservation of serum calcium levels has priority over skeletal integrity. Since vitamin D supplementation is an essential part of anti-osteoporotic therapy, mechanistic insight in vitamin D actions is required to define the optimal therapeutic regimen, taking into account the amount of dietary calcium supply, in order to maximize the targeted outcome and to avoid side-effects. We will review the current understanding concerning the functions of osteoblastic/osteocytic VDR signaling which not only include the regulation of bone metabolism, but also comprise the control of calcium and phosphate homeostasis via fibroblast growth factor (FGF) 23 secretion and the maintenance of the hematopoeitic stem cell (HSC) niche, with special focus on the experimental data obtained from systemic and osteoblast/osteocyte-specific Vdr null mice.