Experimental evidence for the effects of calcium and vitamin D on bone: a review

Dietary protein levels during 12 to 26 wk improve the growth performance, bone quality, and testosterone in Pearl Gray male guinea fowl (Numida meleagris)

Guinea fowl (Numida meleagris), although native to Africa and despite its many potentials, does not represent the dominant species on the continent because of its seasonal reproductive nature and high keets mortality. This study was conducted to assess the effect of crude protein levels on growth performance, bone characteristics and reproductive activity of Pearl Gray male breeder guinea fowl from 12 to 26 wk of age. A total of 120 twelve-wk-old guinea fowls were randomly allotted to 3 dietary treatments with 8 replicates each and 5 birds per replicate using a completely randomized design. The dietary treatments comprised low level (LL), normal level (NL), and high level (HL) with diets respectively containing 15, 17, and 19% crude protein (CP). The results showed that guinea fowl in the HL treatment had a significantly lower feed conversion ratio (P = 0.008) than those in the other treatments. The birds fed the HL diet had significantly higher concentrations of testosterone (P < 0.05) than in the other treatments. High levels of calcium and phosphorus were observed in the femur of the HL group relative to the LL group. The birds in the LL treatment had a significantly higher (P = 0.007) femur robusticity index than those in the HL treatment. In conclusion, feeding 19% crude protein to Pearl Gray male guinea fowl from 12 to 26 wk of age improves growth performance, the density and strength of the femur and tibia and the reproductive tract. The CP level for the best performance of male guinea fowl from 12 to 26 wk of age is 19%.

The Functional Roles of Methionine and Arginine in Intestinal and Bone Health of Poultry: Review

This review explores the roles of methionine and arginine in promoting the well-being of poultry, with a specific focus on their impacts on intestinal and bone health. The metabolic pathways of methionine and arginine are elucidated, highlighting their distinct routes within the avian system. Beyond their fundamental importance in protein synthesis, methionine and arginine also exert their functional roles through their antioxidant capacities, immunomodulating effects, and involvement in the synthesis of metabolically important molecules such as S-adenosylmethionine, nitric oxide, and polyamines. These multifaceted actions enable methionine and arginine to influence various aspects of intestinal health such as maintaining the integrity of the intestinal barrier, regulating immune responses, and even influencing the composition of the gut microbiota. Additionally, they could play a pivotal role in promoting bone development and regulating bone remodeling, ultimately fostering optimal bone health. In conclusion, this review provides a comprehensive understanding of the potential roles of methionine and arginine in intestinal and bone health in poultry, thereby contributing to advancing the nutrition, overall health, and productivity of poultry in a sustainable manner.

The potential mechanism of the microbiota-gut-bone axis in osteoporosis: a review

Osteoporosis is the prevalent metabolic bone disease characterized by a decrease in bone quantity and/or quality and an increase in skeletal fragility, which increases susceptibility to fractures. Osteoporotic fractures severely affect the patients' quality of life and mortality. A plethora of evidences have suggested that the alterations in gut microbiome are associated with the changes in bone mass and microstructure. We summarized pre-clinical and clinical studies to elucidate the underlying mechanism of gut microbiota in osteoporosis. Probiotics, prebiotics, and traditional Chinese medicine may reverse the gut microbiota dysbiosis and consequently improve bone metabolism. However, the causality of gut microbiota on bone metabolism need to be investigated more in depth. In the present review, we focused on the potential mechanism of the microbiota-gut-bone axis and the positive therapeutic effect of probiotics, prebiotics, and traditional Chinese medicine on osteoporosis. Overall, the current scientific literatures support that the gut microbiota may be a novel therapeutic target in treatment of osteoporosis and fracture prevention.

Administration of whey protein complexed vitamin D3 to vitamin D3-deficient growing Sprague-Dawley rats

Vitamin D deficiency is a global health issue with consequences for bone health. Complexation of vitamin D₃ with specific whey proteins might increase the bioavailability and enhance the effect of dietary supplementation on health outcomes. The current rat study was set up to investigate if complexation of vitamin D₃ with whey protein isolate (WPI) or β-lactoglobulin (B-LG) increases bioavailability of the vitamin and how it impacts markers of bone turnover and bone structure. For 8 weeks, growing male Sprague Dawley rats (n = 48) were fed a vitamin D-deficient diet and during the final 4 weeks gavage dosing of vitamin D₃ either alone (VitD) or complexed with WPI (VitD + WPI) or β-LG (VitD + B-LG) was administered. A placebo treatment (placebo) was also included. After sacrifice, samples of bone were collected and analyzed using biomechanical testing and μCT scanning. The concentrations of vitamin D₃, vitamin D₃ metabolites and bone markers (P1NP and CTX) were measured in serum. The results showed that VitD + B-LG appeared to induce lower levels of 25-hydroxy vitamin D₃ in serum compared to VitD alone. Markers of bone turnover were generally higher in the VitD group compared to placebo and the VitD + WPI and VitD + B-LG treatments. No effects of treatments on bone strength or bone microstructure were detected. In conclusion, whey protein complexation of vitamin D₃ supplements appeared to have no beneficial effects on circulating vitamin D₃ metabolites but this did not impose changes in bone strength or trabecular bone microstructure.

Moderate/subclinical calcium deficiency attenuates trabecular mass, microarchitecture and bone growth in growing rats

Adequate dietary calcium (Ca) intake is essential for bone accretion, peak bone mass (PBM) attainment, bone quality and strength during the mammalian growth period. Severe Ca deficiency during growing age results in secondary hyperparathyroidism (SHPT) and poor bone quality and strength. However, the impact of moderate Ca deficiency during rats early growth period on bone health and the reversibility with supplementing calcium later in adult life remains unclear. Female Sprague-Dawley (SD) rats (postnatal 28th day, P28) were initiated either with a moderate calcium-deficient diet (MCD, 0.25% w/w Ca) or a control diet (0.8% w/w Ca, control group) till P70. Thereafter, MCD rats were continued either with MCD diet or supplemented with calcium diet (0.8% w/w Ca, calcium supplemented group, CaS) till P150. Another group (control rats) were fed 0.8% w/w Ca containing diet from P28 till P150. MCD group, as compared to the control group, had significantly reduced serum ionized Ca and procollagen type 1 N-terminal propeptide (P1NP) at P70 while no significant change was observed in serum corrected Ca, inorganic phosphate (P), alkaline phosphatase (ALP), 25-hydroxy vitamin D [25(OH)D], intact parathyroid hormone (iPTH), and urinary C-terminal telopeptide of collagen 1 (CTX-1), Ca, and P. Femoral and tibial metaphysis in MCD rats had significantly reduced linear growth, cortical and trabecular volumetric BMD (vBMD), trabecular microarchitecture (BV/TV%, trabecular thickness, separation and number, structural model index and connectivity density), cortical thickness, and bone stiffness despite the absence of secondary hyperparathyroidism (SHPT). Continued MCD at P70-P150 results in persistence of compromised bone strength while calcium supplementation (CaS group) improved all the parameters related to bone strength and microarchitecture. Our results indicate that uncorrected moderate/subclinical calcium deficiency in growing rats can result in poor bone quality and strength despite the absence of SHPT. This finding could have relevance in children with poor calcium intake in childhood and adolescence.

Molecular Signaling Pathways and Essential Metabolic Elements in Bone Remodeling: An Implication of Therapeutic Targets for Bone Diseases

Bone is one of the dynamic tissues in the human body that undergoes continuous remodelling through subsequent actions of bone cells, osteoclasts, and osteoblasts. Several signal transduction pathways are involved in the transition of mesenchymal stem cells into osteoblasts. These primarily include Runx2, ATF4, Wnt signaling and sympathetic signalling. The differentiation of osteoclasts is controlled by M-CSF, RANKL, and costimulatory signalling. It is well known that bone remodelling is regulated through receptor activator of nuclear factor-kappa B ligand followed by binding to RANK, which eventually induces the differentiation of osteoclasts. The resorbing osteoclasts secrete TRAP, cathepsin K, MMP-9 and gelatinase to digest the proteinaceous matrix of type I collagen and form a saucer-shaped lacuna along with resorption tunnels in the trabecular bone. Osteoblasts secrete a soluble decoy receptor, osteoprotegerin that prevents the binding of RANK/RANKL and thus moderating osteoclastogenesis. Moreover, bone homeostasis is also regulated by several growth factors like, cytokines, calciotropic hormones, parathyroid hormone and sex steroids. The current review presents a correlation of the probable molecular targets underlying the regulation of bone mass and the role of essential metabolic elements in bone remodelling. Targeting these signaling pathways may help to design newer therapies for treating bone diseases.

Effect of serum vitamin D, calcium, and phosphorus on mandibular residual ridge resorption in completely edentulous participants: A clinical study

STATEMENT OF PROBLEM

Published data regarding association between edentulous mandibular residual ridge resorption and nutritional status of geriatric patients is limited.

PURPOSE

The purpose of this clinical study was to evaluate the degree of mandibular residual ridge resorption in completely edentulous participants and to investigate the role of dietary nutrients in the resorption process.

MATERIAL AND METHODS

Three hundred (55% men and 45% women; aged between 35 and 85 years) completely edentulous participants with specific inclusion and exclusion criteria were enrolled for the study. A standardized panoramic radiograph was made, measurements were made digitally, and the amount of resorption was calculated using the Wical and Swoope method. The blood plasma levels of vitamin D3 were analyzed by using the direct competitive chemiluminescence immunoassay (CLIA) method, whereas the total calcium and phosphorus were determined by using spectrophotometer method. Statistical data of serum nutrient levels (calcium, phosphorus, and vitamin D3), age, sex, and residual ridge resorption were subjected to the Mann-Whitney U test, the Spearman correlation test, and a stepwise multiple linear regression analysis (α=.05).

RESULTS

Calcium (P=.003) and phosphorus (P<.001) levels were significantly increased in the female participants as compared with the male participants. Vitamin D3 levels were similar in all the participants. Moreover, metabolic levels of calcium (rho=-0.09), phosphorus (rho=-0.10), and vitamin D3 (rho=-0.02) were found to be reduced with increasing age. However, male participants had increased mandibular residual ridge resorption (P<.001) with positive correlation (rho=0.06) when compared with female participants. Mandibular ridge resorption was increased with a decrease in levels of serum nutrients.

CONCLUSIONS

Increased levels of mandibular residual ridge resorption were observed in participants with decreased levels of systemic biochemical parameters, including calcium, phosphorus, and vitamin D3. Moreover, male participants showed increased residual ridge resorption when compared with female participants, who showed a significantly higher level of serum nutrient levels. Serum nutrient levels decreased, whereas mandibular residual ridge resorption increased with age.

Vitamin D and the athlete-patient: state of the art

Vitamin D deficiency is common in athletes. The conventional measurement of vitamin D levels provides a general indicator of body stores. However, there are nuances in its interpretation as values of 25(OH)D do not correlate absolutely with the amount of 'bioavailable' vitamin to the cells. Vitamin D should be regarded as a hormone and influences between 5% and 10% of our total genome. Determining the precise effect of the vitamin, isolated from the actions of other cofactors, is not straightforward and restricts our complete understanding of all of its actions. Deficiency has harmful effects on not only bone and muscle but also wider areas, including immunity and respiratory and neurological activities. More caution should be applied regarding the ability of supranormal vitamin D levels to elevate athletic performance. Hopefully, future research will shed more light on optimal levels of vitamin D and supplementation regimes, and improved understanding of its intracellular control of our genetic mechanisms and how extrinsic influences modify its activity.

Neuropeptide Y1 Receptor Antagonist Alters Gut Microbiota and Alleviates the Ovariectomy-Induced Osteoporosis in Rats

A plethora of evidence has suggested that gut microbiota is involved in the occurrence and development of postmenopausal osteoporosis (PMO). It has been suggested that neuropeptide Y (NPY) modulates the bone metabolism through Y1 receptor (Y1R), and might be associated with gut microbiota. The present study aims to evaluate the anti-osteoporotic effects of Y1R antagonist and to investigate the potential mechanism by which Y1R antagonist regulates gut microbiota. In this study, eighteen female rats were randomly divided into three groups: the sham surgery (SHAM) group, the ovariectomized (OVX) group, and OVX+BIBO3304 group. After 6 weeks following surgery, Y1R antagonist BIBO3304 was administered to the rats in OVX+BIBO3304 group for 7 days. The bone microstructure and serum biochemical parameters were measured at 12 weeks after operation. The differences in the gut microbiota were analyzed by 16S rDNA gene sequencing. Heat-map and Spearman's correlation analyses were constructed to investigate the correlations between microbiota and bone metabolism-related parameters. The results indicated that OVX+BIBO3304 group showed significantly higher BMD, BV/TV, Tb.Th, Tb.N, Conn.D, and serum Ca²⁺ level than those in OVX group. Additionally, Y1R antagonist changed the gut microbiota composition with lower Firmicutes/Bacteroidetes ratio and higher proportions of some probiotics, including Lactobacillus. The correlation analysis showed that the changes of gut microbiota were closely associated with bone microstructure and serum Ca²⁺ levels. Our results suggested that Y1R antagonist played an anti-osteoporotic effect and regulated gut microbiota in OVX rats, indicating the potential to utilize Y1R antagonist as a novel treatment for PMO.

Involvement of PI3K/Akt/β-catenin signaling in schisandrin B-mitigated bone deterioration in an experimental rat model of estrogen deficiency

Introduction

Schisandrin B (SchB) has been reported to perform a wide range of biological functions, including antioxidant activity, anti-inflammatory activity and stimulation of osteoblast proliferation. However, the function and mechanism of SchB in ovariectomy (OVX)-induced osteoporosis are still unknown. The present study was designed to investigate the anti-osteoporotic activity of SchB in an experimental rat model of estrogen deficiency, which is usually used to mimic human postmenopausal osteoporosis (PMO).

Material and methods

OVX rats were orally treated with low (10 mg/kg) or high (50 mg/kg) doses of SchB for 8 weeks. Bone metabolism-related markers were measured by ELISA. The levels of protein expression were determined by western blotting analysis. Hematoxylin and eosin (H&E) and safranin O staining were performed to analyze trabecular bone and cartilage degeneration. Tartrate-resistant acid phosphatase (TRAP) staining was used to evaluate osteoclast differentiation.

Results

SchB administration markedly increased serum Ca levels and bone Ca content and decreased urinary calcium excretion in OVX-operated rats. In addition, high-dosage SchB treatment blocked osteoclastogenesis and improved trabecular bone and cartilage degeneration in the tibia of OVX-operated rats. Furthermore, high-dosage SchB treatment dramatically elevated the protein expression of phospho-PI3K, phospho-Akt and β-catenin in OVX-operated rats.

Conclusions

SchB exerted anti-osteoporotic activity in OVX-operated rats by accelerating the phosphorylation of PI3K and Akt, subsequently upregulating the expression of β-catenin.

The role of microbiota in tissue repair and regeneration

A comprehensive understanding of the human body endogenous microbiota is essential for acquiring an insight into the involvement of microbiota in tissue healing and regeneration process in order to enable development of biomaterials with a better integration with human body environment. Biomaterials used for biomedical applications are normally germ-free, and the human body as the host of the biomaterials is not germ-free. The complexity and role of the body microbiota in tissue healing/regeneration have been underestimated historically. Traditionally, studies aiming at the development of novel biomaterials had focused on the effects of environment within the target tissue, neglecting the signals generated from the microbiota and their impact on tissue regeneration. The significance of the human body microbiota in relation to metabolism, immune system, and consequently tissue regeneration has been recently realised and is a growing research field. This review summarises recent findings on the role of microbiota and mechanisms involved in tissue healing and regeneration, in particular skin, liver, bone, and nervous system regrowth and regeneration highlighting the potential new roles of microbiota for development of a new generation of biomaterials.

Fructan-Enriched Diet Increases Bone Quality in Female Growing Rats at Calcium Deficiency

This study was designed to determine the effect of feeding female rats with low-calcium diet containing one of three fructan sources (Jerusalem artichoke, yacon, Beneo Orafti Synergy1), on selected bone parameters. Growing Wistar rats were fed modified AIN-93 G diet enriched in fructan sources (8%), added alone or as a strawberry sorbet ingredient. Two of eight groups were a validation model, where the positive control group was fed with recommended calcium dose in the diet (RCD), and negative one - with low calcium diet (LCD). After 12 weeks, femoral Ca content, bone densitometry, architecture and hardness were examined. The positive effects on femoral Ca content and cortical thickness, area and content in distal part of bone was observed after feeding animals diet enriched in Jerusalem artichoke sorbet. Beneficial action on other bone tomographic parameters (particularly trabecular volumetric bone mineral density) in this part of femur were associated mainly with the consumption of the diet with sorbet containing yacon. Our results showed an important role of diet containing frozen strawberry desserts enriched in fructan sources in the maintenance of healthy bones of growing organism. It may suggest possible synergisms between fructans and bioactive substances of strawberry.

5α-dihydrotestosterone reduces renal Cyp24a1 expression via suppression of progesterone receptor

Androgens act in concert with vitamin D to influence reabsorption of calcium. However, it is unclear whether androgens directly regulate vitamin D homeostasis or control other cellular events that are related to vitamin D metabolism. To examine whether the expression of vitamin D-related genes in mouse kidney is driven by androgens or androgen-dependent effects, the androgen receptor and other sex steroid receptors were monitored in orchidectomized mice treated with 5α-dihydrotestosterone (DHT). Our results revealed that exposing orchidectomized mice to DHT inhibited the expression of progesterone receptor (Pgr) with or without estrogen receptor α expression, the latter was confirmed by ER-positive (MCF7 and T47D) or -negative (PCT) cells analysis. The loss of Pgr in turn decreased the expression of renal 24-hydroxylase via transcriptional regulation because Cyp24a1 gene has a progesterone receptor-binding site on promoter. When male kidneys preferentially hydroxylate 25-hydroxyvitamin D₃ using 24-hydroxylase rather than 25-hydroxyvitamin D₃-1-alpha hydroxylase, DHT suppressed the Pgr-mediated 24-hydroxylase expression, and it is important to note that DHT increased the blood 25-hydroxyvitamin D₃ levels. These findings uncover an important link between androgens and vitamin D homeostasis and suggest that therapeutic modulation of Pgr may be used to treat vitamin D deficiency and related disorders.

Intestinal microbiota: a potential target for the treatment of postmenopausal osteoporosis

Postmenopausal osteoporosis (PMO) is a prevalent metabolic bone disease characterized by bone loss and structural destruction, which increases the risk of fracture in postmenopausal women. Owing to the high morbidity and serious complications of PMO, many efforts have been devoted to its prophylaxis and treatment. The intestinal microbiota is the complex community of microorganisms colonizing the gastrointestinal tract. Probiotics, which are dietary or medical supplements consisting of beneficial intestinal bacteria, work in concert with endogenous intestinal microorganisms to maintain host health. Recent studies have revealed that bone loss in PMO is closely related to host immunity, which is influenced by the intestinal microbiota. The curative effects of probiotics on metabolic bone diseases have also been demonstrated. The effects of the intestinal microbiota on bone metabolism suggest a promising target for PMO management. This review seeks to summarize the critical effects of the intestinal microbiota and probiotics on PMO, with a focus on the molecular mechanisms underlying the pathogenic relationship between bacteria and host, and to define the possible treatment options.

Bone Mineral Density, Mechanical, Microstructural Properties and Mineral Content of the Femur in Growing Rats Fed with Cactus Opuntia ficus indica (L.) Mill. (Cactaceae) Cladodes as Calcium Source in Diet

Mechanical, microstructural properties, mineral content and bone mineral density (BMD) of the femur were evaluated in growing rats fed with Opuntia ficus indica (L.) Mill. (Cactaceae) cladodes at different maturity stages as calcium source. Male weanling rats were fed with cladodes at early maturity stage (25 and 60 days of age, belonging to groups N-60 and N-200, respectively) and cladodes at late maturity stage (100 and 135 days of age, belonging to groups N-400 and N-600, respectively) for 6 weeks. Additionally, a control group fed with calcium carbonate as calcium source was included for comparative purposes. All diets were fitted to the same calcium content (5 g/kg diet). The failure load of femurs was significantly lower (p ≤ 0.05) in groups N-60 and N-200 in comparison to N-400, N-600 and control groups. The cortical width (Ct.Wi) and trabecular thickness (Tb.Th) of the femurs in control and N-600 groups were significantly higher (p ≤ 0.05) than Ct.Wi and Tb.Th of femurs in groups N-60 and N-200. Trabecular separation of the femurs in N-60 and N-200 groups showed the highest values compared with all experimental groups. The highest calcium content in the femurs were observed in control, N-600 and N-400 groups; whereas the lowest phosphorus content in the bones were detected in N-200, N-600 and N-400 groups. Finally, the BMD in all experimental groups increased with age; nevertheless, the highest values were observed in N-600 and control groups during pubertal and adolescence stages. The results derived from this research demonstrate, for the first time, that the calcium found in Opuntia ficus indica cladodes is actually bioavailable and capable of improving mineral density and mechanical and microstructural properties of the bones. These findings suggest that the consumption of cladodes at late maturity stage within the diet might have a beneficial impact on bone health.

Calcium Deficiency in Bangladesh: Burden and Proposed Solutions for the First 1000 Days

BACKGROUND

Bangladesh incurs among the highest prevalence of stunting and micronutrient deficiencies in the world, despite efforts against diarrheal disease, respiratory infections, and protein-energy malnutrition which have led to substantial and continuous reductions in child mortality over the past 35 years. Although programs have generally paid more attention to other micronutrients, the local importance of calcium to health has been less recognized.

OBJECTIVE

To synthesize available information on calcium deficiency in Bangladesh in order to inform the design of an effective national calcium program.

METHODS

We searched 3 online databases and a multitude of survey reports to conduct a narrative review of calcium epidemiology in Bangladesh, including population intake, determinants and consequences of deficiency, and tested interventions, with particular reference to young children and women of childbearing age. This was supplemented with secondary analysis of a national household survey in order to map the relative extent of calcium adequacy among different demographics.

RESULTS

Intake of calcium is low in the general population of Bangladesh, with potentially serious and persistent effects on public health. These effects are especially pertinent to young children and reproductive-age women, by virtue of increased physiologic needs, disproportionately poor access to dietary calcium sources, and a confluence of other local determinants of calcium status in these groups.

CONCLUSION

A tablet supplementation program for pregnant women is an appealing approach for the reduction in preeclampsia and preterm birth. Further research is warranted to address the comparative benefit of different promising approaches in children for the prevention of rickets.

Long-term vitamin D deficiency in older adult C57BL/6 mice does not affect bone structure, remodeling and mineralization

Animal models show that vitamin D deficiency may have severe consequences for skeletal health. However, most studies have been performed in young rodents for a relatively short period, while in older adult rodents the effects of long-term vitamin D deficiency on skeletal health have not been extensively studied. Therefore, the first aim of this study was to determine the effects of long-term vitamin D deficiency on bone structure, remodeling and mineralization in bones from older adult mice. The second aim was to determine the effects of long-term vitamin D deficiency on mRNA levels of genes involved in vitamin D metabolism in bones from older adult mice. Ten months old male C57BL/6 mice were fed a diet containing 0.5% calcium, 0.2% phosphate and 0 (n=8) or 1 (n=9) IU vitamin D₃/gram for 14 months. At an age of 24 months, mice were sacrificed for histomorphometric and micro-computed tomography (micro-CT) analysis of humeri as well as analysis of CYP27B1, CYP24 and VDR mRNA levels in tibiae and kidneys using RT-qPCR. Plasma samples, obtained at 17 and 24 months of age, were used for measurements of 25-hydroxyvitamin D (25(OH)D) (all samples), phosphate and parathyroid hormone (PTH) (terminal samples) concentrations. At the age of 17 and 24 months, mean plasma 25(OH)D concentrations were below the detection limit (<4nmol/L) in mice receiving vitamin D deficient diets. Plasma phosphate and PTH concentrations did not differ between both groups. Micro-CT and histomorphometric analysis of bone mineral density, structure and remodeling did not reveal differences between control and vitamin D deficient mice. Long-term vitamin D deficiency did also not affect CYP27B1 mRNA levels in tibiae, while CYP24 mRNA levels in tibiae were below the detection threshold in both groups. VDR mRNA levels in tibiae from vitamin D deficient mice were 0.7 fold lower than those in control mice. In conclusion, long-term vitamin D deficiency in older adult C57BL/6 mice, accompanied by normal plasma PTH and phosphate concentrations, does not affect bone structure, remodeling and mineralization. In bone, expression levels of CYP27B1 are also not affected by long-term vitamin D deficiency in older adult C57BL/6 mice. Our results suggest that mice at old age have a low or absent response to vitamin D deficiency probably due to factors such as a decreased bone formation rate or a reduced response of bone cells to 25(OH)D and 1,25(OH)₂D. Older adult mice may therefore be less useful for the study of the effects of vitamin D deficiency on bone health in older people.

Regulation of CYP27B1 mRNA Expression in Primary Human Osteoblasts

The enzyme 1α-hydroxylase (gene CYP27B1) catalyzes the synthesis of 1,25(OH)2D in both renal and bone cells. While renal 1α-hydroxylase is tightly regulated by hormones and 1,25(OH)2D itself, the regulation of 1α-hydroxylase in bone cells is poorly understood. The aim of this study was to investigate in a primary human osteoblast culture whether parathyroid hormone (PTH), fibroblast growth factor 23 (FGF23), calcitonin, calcium, phosphate, or MEPE affect mRNA levels of CYP27B1. Our results show that primary human osteoblasts in the presence of high calcium concentrations increase their CYP27B1 mRNA levels by 1.3-fold. CYP27B1 mRNA levels were not affected by PTH1-34, rhFGF23, calcitonin, phosphate, and rhMEPE. Our results suggest that the regulation of bone 1α-hydroxylase is different from renal 1α-hydroxylase. High calcium concentrations in bone may result in an increased local synthesis of 1,25(OH)2D leading to an enhanced matrix mineralization. In this way, the local synthesis of 1,25(OH)2D may contribute to the stimulatory effect of calcium on matrix mineralization.

The content of fluoride, calcium and magnesium in the hair of young men of the Bantu language group from Tanzania versus social conditioning

The present study aimed at analysing the content of fluorine (F), calcium (Ca) and magnesium (Mg) in the hair of young male students (n =52) of a secondary school in Mafinga in Tanzania (Africa) who participated in anthropological examinations. Ca and Mg concentrations were determined using atomic absorption spectrophotometer while F levels using a potentiometric method. F in the hair of boys from older group (≥16 years old; n =24) was significantly higher than in the younger group (<16 years old; n =28) versus Ca and Mg levels. High carbohydrate diet was predominant- mainly based on corn or bean and meat served once a week, with few fruit and raw vegetables. Collective catering in the dormitory reflected habits and culinary preferences at home. The lack of balanced diet, with majority of the nutritional energy supplied by easily accessible and cheap carbohydrates, was reflected in dietary deficiencies, characterised, among others, by visible skin conditions and tooth decay.

The pleiotropic effects of vitamin D in bone

A current controversial question related to vitamin D supplementation is what level of serum 25-hydroxyvitamin D3 (25(OH)D3) is required to reduce the incidence of osteoporotic fractures. The reasoning behind vitamin D supplementation has been mostly derived from the role of vitamin D to promote intestinal calcium absorption and reduce bone resorption. While minimum 25(OH)D3 levels of 20nmol/L are required for sufficient intestinal calcium absorption to prevent osteomalacia, the mechanistic details of how higher 25(OH)D3 levels, well beyond that required for optimal calcium absorption, are able to prevent fractures and increase bone mineral density is unclear. Substantial evidence has arisen over the past decade that conversion of 25(OH)D3 to 1,25(OH)2D3via the 1-alpha hydroxylase (CYP27B1) enzyme in osteoblasts, osteocytes, chondrocytes and osteoclasts regulates processes such as cell proliferation, maturation and mineralization as well as bone resorption, which are all dependent on the presence the of the vitamin D receptor (VDR). We and others have also shown that increased vitamin D activity in mature osteoblasts by increasing levels of VDR or CYP27B1 leads to improved bone mineral volume using two separate transgenic mouse models. While questions remain regarding activities of vitamin D in bone to influence the anabolic and catabolic processes, the biological importance of vitamin D activity within the bone is unquestioned. However, a clearer understanding of the varied mechanisms by which vitamin D directly and indirectly influences mineral bone status are required to support evidence-based recommendations for vitamin D supplementation to reduce the risk of fractures. This article is part of a Special Issue entitled 'Vitamin D workshop'.

Vitamin D actions to regulate calcium and skeletal homeostasis

The endocrine action of plasma 1,25-dihydroxyvitamin D plays a key role in the regulation of plasma calcium and phosphate homeostasis with activities on the intestine, kidney and bone. A current, controversial question is whether vitamin D exerts direct actions on bone cells to regulate bone mineral homeostasis. Results from clinical, rodent model and in vitro studies on human bone cells provide an impressive body of data to support this proposal particularly at the level of serum 25-hydroxyvitamin D status. Each of the major bone cell types is capable of metabolising vitamin D to the active metabolite, 1,25-dihydroxyvitamin D. Thus under conditions when bone tissue synthesis of 1,25-dihydroxyvitamin D is optimal, vitamin D activity enhances bone mineral status. Dietary calcium and phosphate intakes are the critical environmental cues together with vitamin D status to determine whether 1,25-dihydroxyvitamin D exerts an anabolic or catabolic action on bone mineral status.

Vitamin D Status: Current Opinion on Critical Levels for Plasma Calcium and Bone Mineral Homeostasis

Currently there is an unprecedented level of interest regarding the purported wide-ranging beneficial effects of an adequate vitamin D status translating into marked increases in test requests for clinical laboratories. The well characterised endocrine pathway of vitamin D metabolism and action is solely responsible for vitamin D regulating plasma calcium and phosphate homeostasis. A large body of data confirm that vitamin D exerts activities within each of the major bone cells and that these same cells are capable of synthesising the active metabolite, 1,25-dihydroxyvitamin D from 25-hydroxyvitamin D. Such data arising from in vitro studies, animal models and clinical sources are consistent with a paradigm that local metabolism of vitamin D by bone cells to form 1,25-dihydroxyvitamin D and its consequent local actions within bone cells exerts an anabolic effect to increase bone mineral status. The data reviewed here provide plausible mechanisms for both catabolic and anabolic actions of vitamin D on bone depending on dietary calcium intake.

Autocrine and paracrine actions of vitamin d

Vitamin D deficiency continues to attract considerable attention because of claims that an adequate status can reduce the risk of a wide range of diseases. The facts are that this hormone modulates the expression of a very large number of genes, possibly some 5 to 10% of the genome; that it has been subject to very strong evolutionary pressures; and that its biological activities are exerted across a wide range of tissues, and these all contribute to the plausibility that such claims may eventually be found to be valid. While the endocrine action of the active metabolite, 1,25-dihydroxyvitamin D, has been well-characterised to contribute to maintaining plasma calcium and phosphate homeostasis through regulation of intestinal absorption, recent research has focused on its autocrine and/or paracrine activities. Such activities of vitamin D have been best characterised in skin tissues and the immune system where it regulates cell differentiation and maturation as well as the innate immune system. Recent data are now available to implicate autocrine/paracrine activities in each of the major bone cell types where it also regulates cell proliferation and differentiation. In rodent models, adequate levels of serum 25-hydroxyvitamin D have been found to be critical to optimise bone health and to protect against osteoporosis. These findings are consistent with clinical data that such activity is present in humans. The introduction of an autocrine/paracrine paradigm for vitamin D has significant implications for critical levels of serum 25-hydroxyvitamin D for optimal health.