Two genes encode the two subunits of cottonseed catalase

The isolation and sequence of a cDNA encoding a developmentally distinct subunit of cottonseed catalase are presented. A 1.8-kb cDNA was selected from a cDNA library constructed with poly(A)+ RNA isolated from 3-day-old dark-grown cotyledons in which a second subunit (designated SU 2 in an earlier publication) of catalase was predominantly synthesized. The cDNA encodes a 492-amino acid peptide with a calculated Mr of 56,900. The nucleotide sequence is 76% identical to a cDNA encoding another subunit (SU 1) which was predominantly synthesized in 1-day-old-cotyledons. Most of the divergence occurs in the 5' and 3' non-coding regions, and at the third positions of the codons. The deduced amino acid sequence is 92% identical to that of SU 1. Denaturing isoelectric focusing and SDS-PAGE of products transcribed and translated in vitro from these cDNAs revealed that the cDNA selected from the "1-day" library encoded SU 1 and the cDNA selected from the "3-day" library (this paper) encoded SU 2 of catalase. These data and results from Southern blot analyses of genomic DNA indicate that there are two genes encoding catalase subunits in cotton cotyledons, with only one copy of SU 1 and at least two copies of SU 2 in the genome. A peroxisomal targeting signal, e.g., Ser-Lys-Leu, is not located at the C-terminus of either subunit, or within 25 residues of the C-terminus of SU 1, although it occurs at six residues upstream from the C-terminus of SU 2. A possible location of a targeting sequence for catalase and other peroxisomal proteins lacking the C-terminal tripeptide motif is proposed.     

Calcium Metabolism and a Mars Mission: New Problems

Results of ground-based and spaceflight experiments are analyzed using a mathematical model to predict long-term effects of the adaptation of human mineral metabolism that takes place during spaceflights of extended duration. The changes in calcium metabolism induced by spaceflight, both real and simulated, are summarized. These changes include a decline in the amount of calcium in the bone pool inexchangeable with free calcium and a decrease in the capacity of tissue and blood buffer systems to retain calcium. In the mathematical model of calcium metabolism, the rates of the main calcium fluxes were estimated for normal conditions and for stress conditions mimicking the 110th day of spaceflight according to the rate of calcium efflux from bone. This analysis showed that, under ordinary living conditions, a 1-h calcium load of 8 mmol/h would give rise to only a 20% transient increase in PCa⁺⁺, causing a 17-fold increase in the calcium binding by tissue and blood buffer systems and an 11-fold increase in binding of the ion by blood buffers. The calcium content in woven bone was predicted to increase by 10–11% in response to this calcium load. The activity of the regulatory mechanisms in the model was varied. When the blood level of the active metabolite of vitamin D₃ was set to one-tenth of its norm, the rate of compact bone resorption changed only slightly. As calculated in the model, the calcium input from woven bone can be normalized by raising the calcitonin level 20-fold or by completely blocking the secretion of parathyroid hormone, neither of which is realistically achievable, whether on land in experiments simulating weightlessness or during spaceflight. The results of experiments and the data of simulation using the model show that none of the active calcium regulators tested can offset a microgravity-induced decline in the ability of calcium stores to retain calcium.     

Spatio-temporal self-organization of bone mineral metabolism and trabecular structure of primary bone

A nonlinear two-variable reaction-diffusion model of bone mineral metabolism, built from an overall self-oscillatory compartmental model of calcium metabolism in vivo, has been studied for its ability to generate spatial and spatio-temporal self-organizations in a two-dimensional space. Analytical and numerical results confirm the theoretical properties previously described for this kind of model. In particular, it is shown that, for a given set of reactional parameter values and certain values of the ratio of the two diffusion coefficients, there exists a set of unstable wavenumbers leading spontaneously to the development, from the homogeneous steady state, of either different types of stationary spatial patterns (hexagonal, striped and re-entrant hexagonal patterns) or more or less complex spatio-temporal expressions. We discuss the relevance of analogies established between some spatial or spatio-temporal structures predicted by the model and some peculiar features of the primary bone trabecular architecture which appear during embryonic ossification.     

钙、磷摄入对骨代谢及骨组织形态影响的研究进展

骨代谢始终贯穿于动物的生命过程之中,而机体摄入的钙、磷水平和钙、磷比例又是骨代谢的重要影响因素。钙、磷摄入水平和比例的改变会使甲状旁腺激素（PTH）、降钙素（CT）和1α,25-双羟维生素D3[1,25-（OH）2D3]的水平产生变化,影响RANK／RANKL／OPG系统对骨细胞功能的调控,进而对骨代谢及骨组织形态产生影响。骨唾液酸蛋白（Bone Sialoprotein,BSP）是目前评价成骨细胞分化和骨骼矿化情况的新指标,研究BSP表达水平的变化规律,可以从分子水平解释钙、磷摄入水平和比例对骨组织形态影响的机理。而骨组织形态计量学（Bone Histomorphometry）则是研究钙、磷摄入水平和比例对骨组织形态影响的重要方法。     

Individual and combined effects of calciotropic hormones and growth factors on mineral metabolism in embryonic chick tibiae

Summary We have investigated single and combined effects of calciotropic hormones and growth factors on the regulation of alkaline phosphatase (ALP) activity and calcium metabolism in an optimized serum-free bone organ culture system of embryonic chick tibiae. Parathyroid hormone PTH(1–34) alone mobilized calcium from bone tissue time- and dose-dependently and inhibited ALP activity. Both the bisphosphonate (BM 21.0955) and to a lesser extent salmon calcitonin alone slightly increased calcium uptake and inhibited the stimulation of bone resorption by PTH(1–34). 1,25(OH)₂D₃ mobilized calcium and inhibited ALP activity in contrast to 24,25(OH)₂D₃ which inhibited ALP activity but had no significant effect on calcium metabolism. Interestingly the combination of PTH(1–34) with 1,25(OH)₂D₃ but not 24,25(OH)₂D₃ reduced calcium mobilization. The combination of the midregional fragment PTH(28–48), which by itself has no effect on calcium metabolism, with 1,25(OH)₂D₃ reduced calcium mobilization more efficiently. Several PTH-regulated mediators have been assayed in this system. Of the tested growth factors, IGF-I at high concentrations caused bone resorption with no effect on ALP activity. TGF-β₁ (transforming growth factor β) and BMP-2 had no significant effect on calcium metabolism; however, ALP activity was inhibited by TGF-β₁ and induced dose dependently by BMP-2. Of the other factors known to be present in bone, platelet-derived growth factor (PDGF_A/B) and epidermal growth factor (EGF) had a small effect on calcium mobilization but had no effect on ALP activity. bFGF reduced ALP activity slightly without an effect on calcium metabolism. Our results show that this in vitro system can mimic some interactions of calciotropic hormones in vivo and allows the assaying of mediators in terms of regulation of ALP activity and of calcium metabolism.     

Kinetic analysis of binding interaction between the subgroup A Rous sarcoma virus glycoprotein SU and its cognate receptor Tva: calcium is not required for ligand binding

Tva is the receptor for subgroup A Rous sarcoma virus, and it contains a single LDL-A module which is the site of virus interaction. In this study, we expressed the entire extracellular region of Tva (referred to as Ecto-Tva) as a GST fusion protein and characterized its refolding properties. We demonstrated that the correct folding of the Ecto-Tva protein, like that of the Tva LDL-A module, is calcium dependent. We used the IAsys system to measure the kinetics of binding between the surface (SU) subunit of the viral glycoprotein and Tva in real time. We found that the Ecto-Tva protein and the Tva LDL-A module displayed similar affinities for SU, providing direct evidence that the LDL-A module of Tva is the only viral interaction domain of the receptor. Furthermore, misfolded Tva proteins displayed lower binding affinities to SU, largely due to a decrease in their association rates, suggesting that a high association rate between SU and Tva is crucial for efficient virus-host interaction. Furthermore, we found that calcium did not influence the overall binding affinity between Tva and SU. These results indicate that, although calcium is important in facilitating correct folding of the LDL-A module of Tva, it is not essential for ligand binding. Thus, these results may have broad implications for the mechanism of protein folding and ligand recognition of the LDL receptor and other members of the LDL receptor superfamily.     

A high fat diet-induced impaired glucose metabolism in mice with targeted deletion of calpain in osteoblasts

The ubiquitously expressed Calpains 1 and 2 belong to a family of calcium-dependent intracellular cysteine proteases. Both calpains are heterodimers consisting of a large subunit and a small regulatory subunit encoded by the gene Capns1. To investigate a role for the calpain small subunit in cells of the osteoblast lineage in vivo, we previously generated osteoblast-specific Capns1 knockout mice and characterized their bone phenotype. In this study, we further examined effects of low calcium and high fat diets on their bone, fat, and glucose homeostasis.Osteoblast-specific Capns1 knockout mice showed significantly reduced serum levels of total and uncarboxylated osteocalcin, and this was presumably due to their impaired bone formation and bone resorption. The reduced bone resorptive function of the mutant mice was also significant under a low calcium diet. Thus, these results suggest that reduced uncarboxylated osteocalcin levels of mutant mice were, at least in part, due to their osteoporotic bone with impaired bone resorptive function. Interestingly, unlike osteocalcin knockout mice, mutant mice on a normal chow diet were leaner than control littermates; this was likely due to their reduced food intake and overall lower energy homeostasis. To test this hypothesis, we next provided mutant mice with a high fat diet and further examined an effect of their reduced uncarboxylated osteocalcin levels on body composition and glucose metabolism. The average mean body weight of mutant mice became indistinguishable with that of controls after 2 weeks on a high fat diet, and continued to show an upward trend, at least, up to 6 weeks. Moreover, mutant mice on a high fat diet exhibited a significant increase in serum levels of leptin and resistin, adipocyte-specific adipokines, and developed impaired glucose tolerance. Collectively, mice with osteoporosis and reduced bone resorptive function showed reduced serum uncarboxylated osteocalcin levels and were susceptible to increase body adiposity and develop impaired glucose tolerance under a high fat diet.     

Changes in urinary excretion of pyridinium cross-links during Spacelab-J.

In SLJ-1 we proposed to study three major objectives. They were; 1. hormonal changes associated with fluid and electrolyte metabolism, 2. the effect of space flight on the circadian rhythms of endocrine and metabolic systems, 3. the changes in the indices of the bone and muscle metabolism during space flight. In this report, the changes in the bone metabolism during Spacelab-J will be presented with a special emphasis on urinary excretion of pyridinium cross-links. Timed urine samples from three Japanese payload specialists were obtained for 3 days from May 19 to 21, 1991 (one year before the launch = L-1 year). Immediately before the launch (L-3 to L-0), urine samples were obtained from a payload specialist who was on board the Space Shuttle Endeavor (PS). During the inflight period (flight from September 3 to 10 in 1992), urine samples from the PS were collected by using Urine Monitoring System (UMS). After the landing, they were obtained from the PS for three days (R+0-R+2). Various parameters related to bone metabolism such as hydroxyproline, pyridinium cross-links and calcium were determined. It was noted that excretion of hydroxyproline decreased during the preflight periods when compared with that in the control L-1 year period. The average excretory rate during control period was 846.2 +/- 198.7 milligrams/hour (mean +/- SD), while those in the preflight 474.6 +/- 171.1 milligrams/hour, suggesting the diminished collagen intake during the preflight period. Average excretion rate of pyridinium cross-links during the first 4 mission days (MD0-MD3) was similar to that of preflight and control L-1 year period. However, it was significantly increased during the last 4 mission days (MD4-MD7). It returned to the preflight level during postflight days (R+0-R+2). Increased urinary excretion of calcium during the last 4 mission days were also observed. These results suggest that increase in bone resorption could occur during relatively short stay in microgravity.     

Comparison of histomorphometric values in iliac trabecular bone of beagle dogs raised under different breeding systems.

In order to clarify individual differences in bone metabolism among colony-raised beagle dogs, histomorphometric values of iliac trabecular bone and values of serum biochemical constituents related to bone were examined in 10 and 17 beagle dogs raised, respectively, under our two breeding systems in which differences in factors such as exercise, ultraviolet rays, and mineral content of the diet affect bone metabolism. At the age of 14 months, all dogs were injected with tetracycline hydrochloride and calcein twice for double bone labeling in order to measure dynamic as well as static parameters by bone histomorphometry and the ilium was later biopsied. The measurement on cancellous bone areas of undecalcified iliac sections was performed with a semiautomatic image analyser. Values of total calcium, phosphorus, alkalinephosphatase activity, parathyroid hormone and calcitonin in serum were also determined. The results showed that there were no significant differences between the two groups in histomorphometric values, except for the osteoid volume (p less than 0.05) and osteoid surface/trabecular surface ratio (p less than 0.01) in females, or in serum biochemical constituents, except for alkalinephosphatase activity (p less than 0.001) in males, indicating there were virtually no individual differences in bone metabolism in normal colony raised beagle dogs.     

钙敏感受体在骨代谢中的研究进展

钙敏感受体感受细胞外的钙离子水平,调控一系列激素的释放以维持机体的钙稳态。钙稳态的调节过程与骨代谢相偶联,钙敏感受体通过直接或间接对破骨和成骨细胞的调控,动员或者抑制骨钙入血。虽然钙敏感受体已被证实调控骨代谢,但是详尽的调控机制仍在不断探究中。目前认为细胞外的高钙水平会激活钙敏感受体,抑制甲状旁腺激素分泌并促进降钙素释放,进而破骨细胞被抑制,成骨细胞动员,增加了骨质合成。本文就近年来关于钙敏感受体调控骨代谢的研究进展作一综述,为促进钙敏感受体及相关作用因子治疗骨代谢疾病的研究提供参考。     

Ferredoxins from two sulfonylurea herbicide monooxygenase systems in Streptomyces griseolus.

We have purified and characterized two ferredoxins, designated Fd-1 and Fd-2, from the soluble protein fraction of sulfonylurea herbicide induced Streptomyces griseolus. These cells have previously been shown to contain two inducible cytochromes P-450, P-450SU1 (CYP105A1) and P-450SU2 (CYP105B1), responsible for herbicide metabolism [O'Keefe, D. P., Romesser, J. A., & Leto, K. J. (1988) Arch. Microbiol. 149, 406-412]. Although Fd-2 is more effective, either ferredoxin can restore sulfonylurea monooxygenase activity to an aerobic mixture of NADPH, spinach ferredoxin:NADP oxidoreductase, purified cytochrome P-450SU1, and herbicide substrate. The gene for Fd-1 is located in the genome just downstream of the gene for cytochrome P-450SU1; the gene for Fd-2 follows the gene for P-450SU2. The deduced amino acid sequences of the two ferredoxins show that, if monomeric, each has a molecular mass of approximately 7 kDa, and alignment of the two sequences demonstrates that they are approximately 52% positionally identical. The spectroscopic properties and iron and acid-labile sulfide contents of both ferredoxins suggest that, as isolated, each contains a single [3Fe-4S] cluster. The presence of only three cysteines in Fd-1 and comparisons with three [4Fe-4S] ferredoxins with high sequence similarity suggest that both Fd-1 and Fd-2 have an alanine in the position where these [4Fe-4S] proteins have a fourth cysteine ligand to the cluster. Transformation of Streptomyces lividans, a strain unable to metabolize sulfonylureas, with DNA encoding both P-450SU1 and Fd-1 results in cells capable of herbicide metabolism. S. lividans transformants encoding only cytochrome P-450SU1 do not metabolize herbicide.(ABSTRACT TRUNCATED AT 250 WORDS)     

Calcium metabolism and cardiovascular function after spaceflight.

To determine the influence of dietary calcium on spaceflight-induced alterations in calcium metabolism and blood pressure (BP), 9-wk-old spontaneously hypertensive rats, fed either high- (2%) or low-calcium (0.02%) diets, were flown on an 18-day shuttle flight. On landing, flight animals had increased ionized calcium (P < 0.001), elevated parathyroid hormone levels (P < 0.001), reduced calcitonin levels (P < 0.05), unchanged 1,25(OH)(2)D(3) levels, and elevated skull (P < 0.01) and reduced femur bone mineral density. Basal and thrombin-stimulated platelet free calcium (intracellular calcium concentration) were also reduced (P < 0.05). There was a tendency for indirect systolic BP to be reduced in conscious flight animals (P = 0.057). However, mean arterial pressure was elevated (P < 0.001) after anesthesia. Dietary calcium altered all aspects of calcium metabolism (P < 0.001), as well as BP (P < 0.001), but the only interaction with flight was a relatively greater increase in ionized calcium in flight animals fed low- compared with high-calcium diets (P < 0.05). The results indicate that 1) flight-induced disruptions of calcium metabolism are relatively impervious to dietary calcium in the short term, 2) increased ionized calcium did not normalize low-calcium-induced elevations of BP, and 3) parathyroid hormone was paradoxically increased in the high-calcium-fed flight animals after landing.     

TRPV5 and TRPV6 are expressed in placenta and bone tissues during pregnancy in mice

We investigated the dynamic expression of calcium transporters, TRPV5 and TRPV6, in placenta and bone to determine their role in maternal and fetal calcium balance during gestation. In placenta, TRPV5 was expressed predominantly in syncytiotrophoblasts of the labyrinthine zone, whereas TRPV6 was expressed in spongiotrophoblasts of the junction zone. In bone, the two transporters were found in osteoblasts, osteoclasts, cartilage and bone matrices. During the first half of gestation, TRPV5 and TRPV6 levels in bone were increased on pregnancy day (P) 0.5, then decreased on P3.5 followed by a slight increase on P6.5. During the second half of pregnancy, both the proteins and their mRNAs gradually increased from P9.5 to P15.5?P17.5 in both bone and placenta, followed at parturition by relatively high amounts in placenta, but markedly decreased amounts in bone. The expression pattern is likely related to the fetal and maternal calcium requirement during gestation, which may be regulated by estrogen and other hormones, because the fetal demand for calcium is greatest during the last few days of gestation for rats; maternal calcium metabolism is designed to meet the calcium needs of the fetus during this period. We found that TRPV5 and TRPV6 are involved in calcium transport in the placenta and bone, and therefore play a role in calcium homeostasis during embryonic and fetal development.     

Elements of the Polycomb Repressor SU(Z)12 Needed for Histone H3-K27 Methylation,the Interface with E(Z), and In Vivo Function

Polycomb repressive complex 2 (PRC2) is an essential chromatin-modifying enzyme that implements gene silencing. PRC2 methylates histone H3 on lysine-27 and is conserved from plants to flies to humans. In Drosophila melanogaster, PRC2 contains four core subunits: E(Z), SU(Z)12, ESC, and NURF55. E(Z) bears a SET domain that houses the enzyme active site. However, PRC2 activity depends upon critical inputs from SU(Z)12 and ESC. The stimulatory mechanisms are not understood. We present here functional dissection of the SU(Z)12 subunit. SU(Z)12 contains two highly conserved domains: an ∼140-amino-acid VEFS domain and a Cys₂-His₂ zinc finger (ZnF). Analysis of recombinant PRC2 bearing VEFS domain alterations, including some modeled after leukemia mutations, identifies distinct elements needed for SU(Z)12 assembly with E(Z) and stimulation of histone methyltransferase. The results define an extensive VEFS subdomain that organizes the SU(Z)12-E(Z) interface. Although the SU(Z)12 ZnF is not needed for methyltransferase in vitro, genetic rescue assays show that the ZnF is required in vivo. Chromatin immunoprecipitations reveal that this ZnF facilitates PRC2 binding to a genomic target. This study defines functionally critical SU(Z)12 elements, including key determinants of SU(Z)12-E(Z) communication. Together with recent findings, this illuminates PRC2 modulation by conserved inputs from its noncatalytic subunits.     

Effect of vitamin D-containing plant extracts on osteoporotic bone

Adequate supply of vitamin D₃ is not sufficient for the prevention of post-menopausal osteoporosis, because of a tightly regulated critical step in formation of the most active vitamin D metabolite 1,25-dihydroxyvitamin D₃. Direct application of 1,25(OH)₂D₃, however, was effective in reducing fracture rate and increasing bone mineral density as has been shown in large clinical studies.

Extracts from Solanum glaucophyllum and Trisetum flavescens plants containing 1,25(OH)₂D₃-glycosides were characterized by their vitamin D-activity in a quail eggshell bioassay and applied in an osteoporosis model in ovariectomized rats.

An extract from the grass T. flavescens and a purified extract from S. glaucophyllum were characterized by the absence of alkaloids and the analytically determined content of 1,25(OH)₂D₃. In the ovariectomized rat model after 6 months duration, the bone metabolism relevant markers serum calcium, 1,25(OH)₂D₃, urinary crosslinks and calcium were measured. At termination tibial mineral content was determined and as imaging procedure micro-computerized tomography was applied. The bisphosphonate alendronate was used as a positive standard.

While alendronate reduced bone resorption, as seen in a reduced urinary crosslink excretion, both vitamin D metabolite-containing extracts were able to improve bone mineral density by an enhanced calcium turnover.     

Properties of three isoforms of the 116-kDa subunit of vacuolar H+-ATPase from a single vertebrate species. Cloning, gene expression and protein characterization of functionally distinct isoforms in Gallus gallus.

Vacuolar H+-ATPases (V-ATPases) are involved in a wide variety of essential cellular processes. An unresolved question is how the cell regulates the activity of these proton pumps and their targeting to distinct cellular compartments. There is growing evidence for the presence of subunit diversity amongst V-pumps, particularly regarding the 116-kDa subunit (called the a subunit). We have cloned and characterized three isoforms (a1, a2 and a3) of this subunit from chicken. The amino-acid sequences of these homologues are approximately 50% similar and their nucleotide differences indicate that they are products of distinct genes. The levels of mRNA expression of these isoforms was quantified by ribonuclease protection analysis. The a1 and a2 isoforms have a similar tissue distribution, with the highest level of mRNA expression in brain, an intermediate level in kidney and relatively low levels in liver and bone. In contrast, the highest level of expression of the a3 isoform is in bone and liver, with a moderate level in kidney, and the lowest level in brain. An antibody against the a1 isoform reacted with a 116 kDa protein in a brain V-ATPase preparation that was not detected in bone or liver V-ATPase preparations, whereas an antibody against the a3 isoform reacted with a 116-kDa peptide in bone and liver, but not brain V-ATPases preparations. The bone and brain V-ATPases showed differential sensitivity to the inhibitors bafilomycin and (2Z,4E)-5-(5,6-dichloro-2-indolyl)-2-methoxy-N-[4-(2, 2,6,6-tetramethyl)piperidinyl]-2,4-pentadienamide. Thus, this work demonstrates the presence of structurally and functionally distinct V-ATPases in a single vertebrate species.     

Abnormal calcium metabolism in normocalcaemic sarcoidosis.

In studies of calcium metabolism in 13 unselected patients with untreated sarcoidosis all were normocalcaemic but five had hypercalcuria. All had normal renal function. Calcium absorption was indexed by a double isotope test. 45Ca hyperabsorption occurred in six patients. Ten kinetic studies were carried out with 47Ca and in six bone turnover was increased. 45Ca absorption correlated well with the calculated bone uptake rate of calcium, and with urine calcium excretion. These results suggest that in sarcoidosis abnormalities in calcium metabolism are fairly common although they rarely result in sustained hypercalcaemia.     

Involvement of cholecalciferol metabolism in birds in the adaptation of calcium absorption to the needs during reproduction.

1. The metabolism of calcium and cholecalciferol in quail (Coturnix coturnix japonica) and chicken (Gallus domesticus) during maturation was correlated to gonadal activity and plasma oestrogen levels. 2. Birds with undeveloped ovaries (immature), developed ovaries but not laying (mature), and after laying 3-8 eggs (laying), were used in the first series. 3. Birds in which egg production had been arrested by Nicarbazin, were used in the second series. 4. Plasma 17 beta-oestradiol and calcium were elevated in the mature bird, with no further change in the laying bird. Kidney 25-hydroxycholecalciferol-1-hydroxylase and intestinal calcium-binding protein increased slightly in the mature bird, whereas they were grossly elevated in the laying bird. 5. Calcium and phosphorus absorption were markedly elevated in the laying bird. 6. No changes were noted in plasma 25-hydroxycholecalciferol, at any stage of maturation. 7. During the arrest of egg production by Nicarbazin, 17 beta-oestradiol level, calcium concentration of plasma, and medullary bone were maintained. Kidney 25-hydroxy-cholecalciferol-1-hydroxylase, intestinal calcium-binding protein and absorption of calcium were strikingly reduced. 8. The results suggest that changes in calcium absorption and cholecalciferol metabolism during maturation in birds are not directly affected by gonadal hormones; they appear to represent an adaptation to the increased calcium needs due to medullary bone formation and, more importantly, to the large losses of calcium imposed by shell formation.     

Pivotal role of boron supplementation on bone health: A narrative review

BackgroundBoron is a trace element that plays an important role in numerous biological functions, including calcium metabolism, growth and maintenance of bone tissue. However, there are still no precise indications regarding a possible role of boron supplementation, and its amount of supplementation, to maintain bone health. So the aim of this narrative review was to consider the state of the art on the effectiveness of boron supplementation (alone or with other micronutrients) on growth and maintenance of bone in humans through control of calcium, vitamin D and sex steroid hormone metabolism in order to suggest a daily dosage of boron supplementation.Main findingsThis review included 11 eligible studies: 7 regarding the supplementation with boron alone and 4 regarding supplementation with boron and other nutrients. Despite the number of studies considered being low, the number of subjects studied is high (594) and the results are interesting.ConclusionsThe studies considered in this narrative review have evaluated the positive effectiveness on bone, in humans, through control of calcium, vitamin D and sex steroid hormone metabolism, considering a dietary supplementation of 3 mg/day of boron (alone or with other nutrients); this supplementation is demonstrably useful to support bone health (in order to prevent and maintain adequate bone mineral density), also considering the daily dose of 3 mg is much lower than the Upper Level indicated by EFSA in the daily dose of 10 mg.