Strontium causes osteomalacia in chronic renal failure rats

Microelement strontium and human health: comprehensive analysis of the role in inflammation and non-communicable diseases (NCDs)

Strontium (Sr), a trace element with a long history and a significant presence in the Earth's crust, plays a critical yet often overlooked role in various biological processes affecting human health. This comprehensive review explores the multifaceted implications of Sr, especially in the context of non-communicable diseases (NCDs) such as cardiovascular diseases, osteoporosis, hypertension, and diabetes mellitus. Sr is predominantly acquired through diet and water and has shown promise as a clinical marker for calcium absorption studies. It contributes to the mitigation of several NCDs by inhibiting oxidative stress, showcasing antioxidant properties, and suppressing inflammatory cytokines. The review delves deep into the mechanisms through which Sr interacts with human physiology, emphasizing its uptake, metabolism, and potential to prevent chronic conditions. Despite its apparent benefits in managing bone fractures, hypertension, and diabetes, current research on Sr's role in human health is not exhaustive. The review underscores the need for more comprehensive studies to solidify Sr's beneficial associations and address the gaps in understanding Sr intake and its optimal levels for human health.

Ionomic Variation Among Tissues in Fallow Deer (Dama dama) by Sex and Age

(1) In mammals, the mineral nutrient and trace elemental composition of the body - the ionome - differs among individuals. It has been hypothesized that these differences may be related to age and sex, both for ecotoxic and essential elements. (2) We investigated whether and how intraspecific ionomic variation is related to age and sex in Fallow deer (Dama dama). We tested the predictions that concentrations of ecotoxic elements increase with age, that ionomic variation is lower among young individuals than among older individuals, and that reproductive females (does) have the lowest concentrations of essential elements. (3) Culled animals of different sex and age were obtained from a single protected area. The animals were dissected to collect 13 tissues, and concentrations of 22 different elements were measured in a sample of each tissue. (4) We described substantial ionomic variation between individuals. Some of this variation was related to age and sex, as predicted. Based on the limited existing knowledge on chemical element allocation and metabolism in the body, sex-related differences were more difficult to interpret than age-related differences. Since reference values are absent, we could not judge about the consequences of the elemental values that we found. (5) More extensive ionomic surveys, based on a wide range of elements and tissues, are needed to enlarge the understanding of within-species ionomic variation and potential biological, ecological, and metabolic consequences.

The correlation of urinary strontium with the risk of chronic kidney disease among the general United States population

Background

This study sought to illustrate whether urinary strontium levels were related to developing chronic kidney disease (CKD) in the United States population.

Methods

A total of 5,005 subjects were identified from the National Health and Nutrition Examination Survey 2011-2016. Survey-weighted logistic regression analysis, multivariate linear regression analysis, restricted cubic spline (RCS) plots curve and stratified analyses were undertaken to explicate the correlation between urinary strontium and CKD.

Results

With the increase of urinary strontium, the incidence rate of CKD and urinary albumin to creatinine ratio (UACR) levels gradually decreased, and estimated glomerular filtration rate (eGFR) levels gradually increased. After controlling all confounders, only urinary strontium in the fourth quartile was correlated to a lower CKD prevalence (OR: 0.59; 95% CI, 0.44-0.79) compared to the lowest quartile. Multivariate linear regression analysis showed that urinary strontium was positively correlated with eGFR but negatively with UACR. RCS curve suggested a nonlinear relationship between urinary strontium and CKD (P for non-linearity <0.001). Stratified analyses indicated no significant difference in the correlation between urinary strontium and CKD among different subgroups.

Conclusion

Urinary strontium was strongly correlated with a low risk of CKD, and this association was non-linear among the US population.

A Review on the Recent Advancements on Therapeutic Effects of Ions in the Physiological Environments

This review focuses on the therapeutic effects of ions when released in physiological environments. Recent studies have shown that metallic ions like Ag+, Sr2+, Mg2+, Mn2+, Cu2+, Ca2+, P+5, etc., have shown promising results in drug delivery systems and regenerative medicine. These metallic ions can be loaded in nanoparticles, mesoporous bioactive glass nanoparticles (MBGNs), hydroxyapatite (HA), calcium phosphates, polymeric coatings, and salt solutions. The metallic ions can exhibit different functions in the physiological environment such as antibacterial, antiviral, anticancer, bioactive, biocompatible, and angiogenic effects. Furthermore, the metals/metalloid ions can be loaded into scaffolds to improve osteoblast proliferation, differentiation, bone development, fibroblast growth, and improved wound healing efficacy. Moreover, different ions possess different therapeutic limits. Therefore, further mechanisms need to be developed for the highly controlled and sustained release of these ions. This review paper summarizes the recent progress in the use of metallic/metalloid ions in regenerative medicine and encourages further study of ions as a solution to cure diseases.

End-Stage Tibiotalar Osteoarthritis and Chronic Strontium Toxicity

Metal toxicity due to environmental sources or orthopedic implants has been a primary focus in recent literature. Specifically, in orthopedics, total joint arthroplasty regarding metal-on-metal articulation with cobalt-chromium articulation has adverse local and systemic effects. In particular, strontium toxicity is less known metal toxicity that can cause many systemic effects such as severe osteoporosis. This is the first reported case of strontium toxicity and end-stage tibiotalar osteoarthritis. We present a case of a 68-year-old female with bilateral ankle pain and deformity that were refractory to conservative measures, including physical therapy and anti-inflammatory medications. She was diagnosed with bilateral osteoarthritis and osteoporosis secondary to strontium toxicity by exclusion after extensive workup with a multi-disciplinary approach. The patient pursued conservative measures with ankle-foot orthosis, physical therapy, and anti-inflammatory medications. After the failure of conservative measures with over two years of follow-up, we recommended operative intervention to improve function and pain with staged bilateral tibiotalocalcaneal fusions utilizing an intramedullary device. Since she is moving out of state, she chose to pursue operative intervention at a different institution in order to establish long-term follow-up. The patient was placed on teriparatide for her osteoporosis secondary to strontium toxicity. Clinicians should be aware of strontium toxicity and its systemic effects and take a multi-disciplinary approach to treatment for optimal management.

The Role of Bone Biopsy in the Management of CKD-MBD

A bone biopsy is still considered the gold standard for diagnosis of renal osteodystrophy. It allows to measure both static and dynamic parameters of bone remodeling and is the only method able to evaluate mineralization and allows analysis of both cortical and trabecular bone. Although bone volume can be measured indirectly by dual-energy X-ray absorptiometry, mineralization defects, bone metal deposits, cellular number/activity, and even turnover abnormalities are difficult to determine by techniques other than qualitative bone histomorphometry. In this review, we evaluate the role of bone biopsy in the clinical practice.

Health risk assessment of heavy metals and strontium in groundwater used for drinking and cooking in 58 villages of Prakasam district, Andhra Pradesh, India

Groundwater is one of the most important sources of water for drinking and cooking in rural India. A total of 382 groundwater samples were collected from 58 villages and analyzed for HMs and Sr by inductively coupled plasma mass spectrometer. The average concentrations of HMs and Sr in water was in the order of strontium (Sr) > arsenic (As) > chromium (Cr) > lead (Pb) > mercury (Hg) > cadmium (Cd). Out of 58 villages, 21, 37, 35, 35, 35 and 39 villages had Cr, As, Cd, Hg, Pb and Sr higher (WHO limit) than their respectively permissible levels. Health risk assessment of HMs and Sr for humans revealed that the non-carcinogenicity hazard quotients (HQ_i+d) for HMs and Sr were higher than unity for adult and children. The hazard index (HI) was 531.066 for adult and 902.926 for children. The HI > 1 was observed in 45 villages for adults and 56 villages for children. The lifetime cancer risk in adult for As_i, As_d, and Pb_i in 36, 25 and 23 villages, whereas in children was 42, 20 and 22 villages, respectively. In conclusion, the health risks arising from consumption of groundwater containing HMs and Sr indicated that there is a significant carcinogenic risks for adult and children. This is the first attempt to provide information on the health risks of Sr in drinking water in India. The present findings can be useful for the development of potential strategies for risk control and management.

Strontium Calcium Phosphate Nanotubes as Bioinspired Building Blocks for Bone Regeneration

Calcium phosphate (CaP)-based ceramics are the most investigated materials for bone repairing and regeneration. However, the clinical performance of commercial ceramics is still far from that of the native tissue, which remains as the gold standard. Thus, reproducing the structural architecture and composition of bone matrix should trigger biomimetic response in synthetic materials. Here, we propose an innovative strategy based on the use of track-etched membranes as physical confinement to produce collagen-free strontium-substituted CaP nanotubes that tend to mimic the building block of bone, i.e., the mineralized collagen fibrils. A combination of high-resolution microscopic and spectroscopic techniques revealed the underlying mechanisms driving the nanotube formation. Under confinement, poorly crystalline apatite platelets assembled into tubes that resembled the mineralized collagen fibrils in terms of diameter and structure of bioapatite. Furthermore, the synergetic effect of Sr²⁺ and confinement gave rise to the stabilization of amorphous strontium CaP nanotubes. The nanotubes were tested in long-term culture of osteoblasts, supporting their maturation and mineralization without eliciting any cytotoxicity. Sr²⁺ released from the particles reduced the differentiation and activity of osteoclasts in a Sr²⁺ concentration-dependent manner. Their bioactivity was evaluated in a serum-like solution, showing that the particles spatially guided the biomimetic remineralization. Further, these effects were achieved at strikingly low concentrations of Sr²⁺ that is crucial to avoid side effects. Overall, these results open simple and promising pathways to develop a new generation of CaP multifunctional ceramics that are active in tissue regeneration and able to simultaneously induce biomimetic remineralization and control the imbalanced osteoclast activity responsible for bone density loss.

Osseointegration effects of local release of strontium ranelate from implant surfaces in rats

BACKGROUND

Numerous studies have reported the beneficial effects of strontium on bone growth, particularly by stimulating osteoblast proliferation and differentiation. Thus, strontium release around implants has been suggested as one possible strategy to enhance implant osseointegration.

AIM

This study aimed to evaluate whether the local release of strontium ranelate (Sr-ranelate) from implants coated with mesoporous titania could improve bone formation around implants in an animal model.

MATERIALS AND METHODS

Mesoporous titania (MT) thin coatings were formed utilizing the evaporation induced self-assembly (EISA) method using Pluronic (P123) with or without the addition of poly propylene glycol (PPG) to create materials with two different pore sizes. The MT was deposited on disks and mini-screws, both made of cp Ti grade IV. Scanning electron microscopy (SEM) was performed to characterize the MT using a Leo Ultra55 FEG instrument (Zeiss, Oberkochen, Germany). The MT was loaded with Sr-ranelate using soaking and the drug uptake and release kinetics to and from the surfaces were evaluated using quartz crystal microbalance with dissipation monitoring (QCM-D) utilizing a Q-sense E4 instrument. For the in vivo experiment, 24 adult rats were analyzed at two time points of implant healing (2 and 6 weeks). Titanium implants shaped as mini screws were coated with MT films and divided into two groups; supplied with Sr-ranelate (test group) and without Sr-ranelate (control group). Four implants (both test and control) were inserted in the tibia of each rat. The in vivo study was evaluated using histomorphometric analyses of the implant/bone interphase using optical microscopy.

RESULTS

SEM images showed the successful formation of evenly distributed MT films covering the entire surface with pore sizes of 6 and 7.2 nm, respectively. The QCM-D analysis revealed an absorption of 3300 ng/cm² of Sr-ranelate on the 7.2 nm MT, which was about 3 times more than the observed amount on the 6 nm MT (1200 ng/cm²). Both groups showed sustained release of Sr-ranelate from MT coated disks. The histomorphometric analysis revealed no significant differences in bone implant contact (BIC) and bone area (BA) between the implants with Sr-ranelate and implants in the control groups after 2 and 6 weeks of healing (BIC with a p-value of 0.43 after 2 weeks and 0.172 after 6 weeks; BA with a p-value of 0.503 after 2 weeks, and 0.088 after 6 weeks). The mean BIC and BA values within the same group showed significant increase among all groups between 2 and 6 weeks.

CONCLUSION

This study could not confirm any positive effects of Sr-ranelate on implant osseointegration.

Formation of stable strontium-rich amorphous calcium phosphate: Possible effects on bone mineral

Bone, tooth enamel, and dentin accumulate Sr²⁺, a natural trace element in the human body. Sr²⁺ comes from dietary and environmental sources and is thought to play a key role in osteoporosis treatments. However, the underlying impacts of Sr²⁺on bone mineralization remain unclear and the use of synthetic apatites (which are structurally different from bone mineral) and non-physiological conditions have led to contradictory results. Here, we report on the formation of a new Sr²⁺-rich and stable amorphous calcium phosphate phase, Sr(ACP). Relying on a bioinspired pathway, a series of Sr²⁺ substituted hydroxyapatite (HA) that combines the major bone mineral features is depicted as model to investigate how this phase forms and Sr²⁺ affects bone. In addition, by means of a comprehensive investigation the biomineralization pathway of Sr²⁺ bearing HA is described showing that not more than 10 at% of Sr²⁺, i.e. a physiological limit incorporated in bone, can be incorporated into HA without phase segregation. A combination of ³¹P and ¹H solid state NMR, energy electron loss spectromicroscopy, transmission electron microscopy, electron diffraction, and Raman spectroscopy shows that Sr²⁺ introduces disorder in the HA culminating with the unexpected Sr(ACP), which co-exists with the HA under physiological conditions. These results suggest that heterogeneous Sr²⁺ distribution in bone is associated with regions of low structural organization. Going further, such observations give clues from the physicochemical standpoint to understand the defects in bone formation induced by high Sr²⁺ doses. STATEMENT OF SIGNIFICANCE: Understanding the role played by Sr²⁺ has a relevant impact in physiological biomineralization and provides insights for its use as osteoporosis treatments. Previous studies inspired by the bone remodelling pathway led to the formation of biomimetic HA in terms of composition, structures and properties in water. Herein, by investigating different atomic percentage of Sr²⁺ related to Ca²⁺ in the synthesis, we demonstrate that 10% of Sr²⁺ is the critical loads into the biomimetic HA phase; similarly to bone. Unexpectedly, using higher amount leads to the formation of a stable Sr²⁺-rich amorphous calcium phosphate phase that may high-dose related pathologies. Our results provide further understanding of the different ways Sr²⁺ impacts bone.

Strontium Promotes Transforming Growth Factors β1 and β2 Expression in Rat Chondrocytes Cultured In Vitro

The transforming growth factors β1 (TGF-β1) and TGF-β2, as two distinct homodimers of TGF-β superfamily, involve in chondrocyte growth and differentiation. Emerging evidence has implied that strontium (Sr) plays an important role in the bone formation and resorption, and has strong effects on stimulating human cartilage matrix formation in vitro. However, the direct effects of Sr on TGF-β1 and TGF-β2 expressions in chondrocytes are not entirely clear. The purpose of this study was to evaluate the influence of different Sr concentrations on the expression of TGF-β1 and TGF-β2 in rat chondrocytes in vitro. Chondrocytes were isolated from Wistar rat articular by enzymatic digestion. Strontium chloride hexahydrate (SrCl₂·6H₂O) was used as a Sr source in this study. Sr was added to the culture solution at final concentrations of 0, 0.5, 1.0, 2.0, 5.0, 20.0, and 100 μg/mL. After 72 h of continuous culture, TGF-β1 and TGF-β2 mRNA abundance and protein expression levels in the chondrocytes were determined by real-time polymerase chain reaction (real-time PCR) and Western blot, respectively. The results showed that TGF-β1 and TGF-β2 expressions in chondrocytes increased dose-dependently with Sr concentration. The mRNA abundance of TGF-β1 and TGF-β2 were markedly higher than those observed for control (P < 0.01) when the Sr-treated concentration exceeded 1.0 and 5.0 μg/mL, respectively. The TGF-β1 and TGF-β2 protein expression levels were extremely significantly higher than those in the control group (P < 0.01) at above 5.0 μg/mL Sr-treatment. These results indicated that Sr could involve in the chondrocytes metabolism via regulating TGF-β1 and TGF-β2 signalling.

Ion release in ceramic bearings for total hip replacement: Results from an in vitro and an in vivo study

INTRODUCTION

Literature on the potential release of trace elements following implantation of Zirconia-platelet toughened alumina (ZPTA) ceramic components is scant. The present study therefore analysed the in vitro and in vivo potential release of ions from ZPTA bearings.

MATERIAL AND METHODS

An in vitro and in vivo study was conducted. The in vitro study compared leaching in bovine serum from two groups: ZPTA ceramic heads and Co-28Cr-6Mo alloy heads, both 28-mm diameter. A third group without implant served as reference group. An in vivo clinical study compared trace elements in the whole blood of patients with 36-mm diameter ZPTA ceramic-on-ceramic articulation after three and 12 months. A cohort of subjects without any prosthesis was used as control group. The release of ions was determined by high resolution-inductively coupled plasma-mass spectrometry.

RESULTS

In the in vitro experiment, significant differences (p ≤ 0.01) in trace element release for chromium, cobalt and molybdenum were found, with increased levels of ion release in the Co-28Cr-6Mo metal group. The very low detection limit for yttrium allowed detection of a small yttrium release from the ZPTA heads, which was not confirmed by the in vivo study. No significant difference between the groups was found for strontium, aluminium, and zirconium. In the in vivo study, no relevant differences in ion levels between the reference group without any implant and the study group were found at the three and 12-month follow-up.

CONCLUSION

This study supports that ZPTA ceramic articulation components are safe in terms of ion release, and may be an excellent alternative to bearings based on Co-28Cr-6Mo alloys.

Synthesis, characterization and biological evaluation of strontium/magnesium-co-substituted hydroxyapatite

The present study aims to investigate the contribution of two biologically important cations, Mg2+ and Sr2+, when co-substituted into the structure of hydroxyapatite (Ca10(PO4)6(OH)2, HA). The substituted samples were synthesized by a hydrothermal method that involved the addition of Mg2+ and Sr2+ containing precursors to partially replace Ca2+ in the apatite structure. Four co-substituted HA samples with different concentrations of Mg2+ and Sr2+ ((Mg + Sr)/(Mg + Sr + Ca) = 30%) were investigated, and they were compared with pure HA. Experimental results showed that only a limited amount of Mg (Mg/(Mg + Ca + Sr) < 14%) could successfully substitute for Ca in HA. In addition, Mg substitution resulted in reduced crystallinity, thermal stability and lattice parameters of HA. In contrast, Sr could fully substitute for Ca. Furthermore, the addition of Sr increased the lattice parameters of HA. Here, we obtained the cation leach liquor by immersing the prepared samples in a culture medium for cell experiments. The in vitro study showed that 10Mg20Sr promoted better MG63 cell attachment, proliferation and differentiation than HA. Thus, the presence of an appropriate proportion of Mg and Sr could play a significant role in the increased biocompatibility of HA.

Evaluating vitamin D with graded levels of strontium supplementation on broiler chicken performance and mineral composition

In order to examine the interactive effects of strontium and cholecalciferol in broiler nutrition a total of 288 male broiler chickens were fed over 28 days, eight different diets with six replicates comprising of two levels of vitamin D (5000 and 10 000 IU/kg) and four levels of strontium (0, 400, 800 and 1200 mg/kg) provided as strontium carbonate. Vitamin D and strontium produced a significant interaction on growth and feed efficiency with the addition of higher levels of vitamin D ameliorating the negative effects of strontium at 1200 mg/kg. The higher level of vitamin D also improved bodyweight gain (P < 0.05), had no effect on tibia bone composition but reduced calcium, phosphorus, potassium and magnesium retention (P < 0.05). Strontium supplementation produced no advantage to chicken performance but changed tibia bone composition. It was found that calcium and sodium maintained a ratio of ~30 : 1 in tibia bone. Vitamin D and strontium produced a significant physiological interaction and further research is required to elucidate optimum levels of supplementation for commercial broiler chicken production.

Effects of thirty elements on bone metabolism

The human skeleton, made of 206 bones, plays vital roles including supporting the body, protecting organs, enabling movement, and storing minerals. Bones are made of organic structures, intimately connected with an inorganic matrix produced by bone cells. Many elements are ubiquitous in our environment, and many impact bone metabolism. Most elements have antagonistic actions depending on concentration. Indeed, some elements are essential, others are deleterious, and many can be both. Several pathways mediate effects of element deficiencies or excesses on bone metabolism. This paper aims to identify all elements that impact bone health and explore the mechanisms by which they act. To date, this is the first time that the effects of thirty minerals on bone metabolism have been summarized.

Strontium potently inhibits mineralisation in bone-forming primary rat osteoblast cultures and reduces numbers of osteoclasts in mouse marrow cultures

SUMMARY

The basic mechanisms by which strontium ranelate acts on bone are still unclear. We show that an important action of strontium salts is to block calcification in cultures of osteoblasts, the bone-forming cells. These results suggest that strontium treatment could have previously overlooked effects on bone.

INTRODUCTION

The basic mechanisms of action of strontium ranelate (SrR) on bone have remained unclear. We studied the direct actions of Sr(2+) salts in functional cultures of osteoblasts and osteoclasts.

METHODS

Cultures of primary osteoblasts from rat calvariae and osteoclast-forming mouse marrow cells were treated continuously with either SrR or strontium chloride (SrCl2).

RESULTS

Abundant, discretely mineralised 'trabecular' bone structures formed in control osteoblast cultures after 14 days. SrR at 0.01, 0.1 and 1 mM inhibited mineralisation to 59, 98 and 100 % (all p < 0.001) of control values, respectively. SrCl2 at the same concentrations caused similar inhibitions. Osteoblast cell numbers and alkaline phosphatase activity were unaltered. SrR dose-dependently reduced the formation of multinucleated osteoclasts from marrow mononuclear cells cultured on dentine for 8 days in the presence of macrophage colony-stimulating factor (M-CSF) and receptor activator of nuclear factor kappa B ligand (RANKL), with a 50 % inhibition occurring at 1 mM; SrCl2 was slightly less effective, eliciting a maximal 30 % inhibition. Corresponding decreases in total resorption pit formation were observed, suggesting Sr(2+) salts affect osteoclast formation rather than resorptive activity.

CONCLUSION

Our findings are consistent with the documented physicochemical inhibitory action of Sr(2+) on mineralisation but contrast with reports that Sr(2+) increases osteoblast activity and number in vitro. Our results suggest that rather than acting as an agent that 'uncouples' bone formation and resorption, Sr(2+) acts as a global inhibitor of bone cell function, with particularly marked effects on mineralisation. The potential effects of long-term Sr(2+) on secondary mineralisation in bone deserve investigation.

Effects of soil trace elements on longevity population in China

Based on background concentrations of elements in soils and the sixth population census data of China, this study discussed the distribution characteristics of soil elements and longevity population at province level in China. Percentages of the aging population are high in Southwest China and the eastern coastal region but low in western and northwestern regions. Provinces in South and Southwest China gain a high level of longevity, while the northern part of China has a low level of longevity. The background concentration of Se in soil has a significant positive correlation with longevity index, while Ba and Ni have a significant negative correlation with longevity indexes. By regression analysis, longevity index C/100,000 can be expressed as C/100,000 = 1.679-0.205 Ni + 0.413 Co + 0.006 Se (with R (2) = 0.402 and p < 0.01), C/65+ can be expressed as C/65+=3.425-0.262 Ni + 0.435 Co + 0.006 Se (with R (2) = 0.369 and p < 0.01).

An overview of boron, lithium, and strontium in human health and profiles of these elements in urine of Japanese

The biological, medical and environmental roles of trace elements have attracted considerable attention over the years. In spite of their relevance in nutritional, occupational and toxicological aspects, there is still a lack of consistent and reliable measurement techniques and reliable information on reference values. In this review our understandings of the urinary profilings of boron, lithium and strontium are summarized and fundamental results obtained in our laboratory are discussed.Over the past decade we have successfully used inductively coupled plasma emission spectrometry for the determination of reference values for urinary concentrations of boron, lithium and strontium. Taking into account the short biological half-life of these elements and the fact that their major excretion route is via the kidney, urine was considered to be a suitable material for monitoring of exposure to these elements. We confirmed that urinary concentrations of boron, lithium and strontium follow a lognormal distribution. The geometric mean reference values and 95% confidence intervals were 798 μg/l (398-1599 μg/l) for boron, 23.5 μg/l (11.0-50.5 μg/l) for lithium and 143.9 μg/l (40.9-505.8 μg/l) for strontium. There were no discrepancies between our values and those previously reported. Our reference values and confidential intervals can be used as guidelines for the health screening of Japanese individuals to evaluate environmental or occupational exposure to these elements.

Bioinorganics and biomaterials: bone repair

The field of bioinorganics is well established in the development of a variety of therapies. However, their application to bone regeneration, specifically by way of localized delivery from functional implants, is in its infancy and is the topic of this review. The toxicity of inorganics is species, dose and duration specific. Little is known about how inorganic ions are effective therapeutically since their use is often the result of serendipity, observations from nutritional deficiency or excess and genetic disorders. Many researchers point to early work demonstrating a role for their element of interest as a micronutrient critical to or able to alter bone growth, often during skeletal development, as a basis for localized delivery. While one can appreciate how a deficiency can cause disruption of healing, it is difficult to explain how a locally delivered excess in a preclinical model or patient, which is presumably of normal nutritional status, can evoke more bone or faster healing. The review illustrates that inorganics can positively affect bone healing but various factors make literature comparisons difficult. Bioinorganics have the potential to have just as big an impact on bone regeneration as recombinant proteins without some of the safety concerns and high costs.

Minerals and vitamins in bone health: the potential value of dietary enhancement

Nutrition is important to bone health, and a number of minerals and vitamins have been identified as playing a potential role in the prevention of bone diseases, particularly osteoporosis. Despite this, there is currently no consensus on maximum levels to allow in food or as dietary supplements. The benefits of supplementation of populations at risk of osteoporosis with Ca and vitamin D are well established. Prolonged supplementation of Ca and vitamin D in elderly has been shown to prevent bone loss, and in some intervention studies to prevent fragility fractures. Although P is essential to bone health, the average intake is considered to be more than sufficient and supplementation could raise intake to adverse levels. The role of vitamin K in bone health is less well defined, though it may enhance the actions of Ca and vitamin D. Sr administered in pharmacological doses as the ranelate salt was shown to prevent fragility fractures in postmenopausal osteoporosis. However, there is no hard evidence that supplementation with Sr salts would be beneficial in the general population. Mg is a nutrient implicated in bone quality, but the benefit of supplementation via foodstuffs remains to be established. A consensus on dietary supplementation for bone health should balance the risks, for example, exposure of vulnerable populations to values close to maximal tolerated doses, against evidence for benefits from randomised clinical trials, such as those for Ca and vitamin D. Feedback from community studies should direct further investigations and help formulate a consensus on dietary supplementation for bone health.

Role of dietary phosphorus and degree of uremia in the development of renal bone disease in rats

The remnant kidney rat model has been extensively used for the evaluation of bone changes due to uremia. The present study aimed to assess the effect of the dietary phosphorus availability and of the severity of renal failure on bone histomorphometric changes and various biochemical markers over time in this model. Chronic renal failure (CRF) was induced in male Wistar rats by 5/6th nephrectomy. Half of the number of animals received a standard rat diet (STD) (0.67% P, containing low bioavailable phosphorus of plant origin); the other animals were fed a high phosphorus diet (HPD) (0.93% P, containing inorganic phosphorus with high bioavailability). Every two weeks, blood and urine samples were collected. At sacrifice after 6 or 12 weeks, bone samples were taken for the measurement of histological and histodynamic parameters. Serum creatinine measurements indicated the development of mild to moderate renal failure in both diet groups. Phosphaturia was unexpectedly low in all animals that received the STD, indicating relative phosphorus depletion despite the normal dietary phosphorus content. In the HPD CRF group, a decrease in calcemia and a rise in phosphatemia were seen after 12 weeks of CRF, which were more pronounced in animals with higher serum creatinine. Serum iPTH levels were distinctly increased in CRF rats fed a HPD, especially those with more pronounced renal failure. Serum osteocalcin and to a lesser extend tartrate-resistant acid phosphatase and urinary pyridinoline and deoxypyridinoline crosslinks were higher in the CRF animals compared to the shams, particularly in the animals of the HPD group with more pronounced CRF. In both diet groups, the CRF animals had significantly higher amounts of osteoid compared to shams. Only the animals that received a HPD developed distinct histological signs of secondary hyperparathyroidism (sHPTH), that is, an increased bone formation rate, mineral apposition rate, osteoblast perimeter, and eroded perimeter. Again, this effect was most prominent in rats with more severe CRF. In conclusion, data of the present study indicate that in experimental studies using the remnant kidney rat model, both the dietary phosphorus bioavailability and the degree of renal failure in the development of hyperparathyroidism should be considered.

Strontium ranelate for preventing and treating postmenopausal osteoporosis

BACKGROUND

Strontium ranelate is a new treatment for osteoporosis therefore, its benefits and harms need to be known.

OBJECTIVES

To determine the efficacy and safety of strontium ranelate for the treatment and prevention of postmenopausal osteoporosis.

SEARCH STRATEGY

We searched MEDLINE (1996 to March 2005), EMBASE (1996 to week 9 2005), the Cochrane Library (1996 to Issue 1 2005), reference lists of relevant articles and conference proceedings from the last two years. Additional data was sought from authors.

SELECTION CRITERIA

We included randomized controlled trials (RCTs) of at least one year duration comparing strontium ranelate versus placebo reporting fracture incidence, bone mineral density (BMD), health related quality of life or safety in postmenopausal women. Treatment (versus prevention) population was defined as women with prevalent vertebral fractures and/or lumbar spine BMD T score < -2.5 SD.

DATA COLLECTION AND ANALYSIS

Two reviewers independently determined study eligibility, assessed trial quality and extracted the relevant data. Disagreements were resolved by consensus. RCTs were grouped by dose of strontium ranelate and treatment duration. Where possible, meta-analysis was conducted using the random effects model.

MAIN RESULTS

Four trials met the inclusion criteria. Three included a treatment population (0.5 to 2 g of strontium ranelate daily) and one a prevention population (0.125 g, 0.5 g and 1 g daily). A 37% reduction in vertebral fractures (RR 0.63, 95% CI 0.56, 0.71) and a 14% reduction in non-vertebral fractures (RR 0.86, 95% CI 0.75, 0.98) were demonstrated over three years with 2 g of strontium ranelate daily in a treatment population. An increase in BMD was shown at all BMD sites after two to three years in both populations. Lower doses of strontium ranelate were superior to placebo and the highest dose demonstrated the greatest reduction in vertebral fractures and increase in BMD. An increased risk of diarrhea with 2 g of strontium ranelate was found; however, adverse events did not affect the risk of discontinuing treatment nor did it increase the risk of serious side effects, gastritis or death. Additional data suggests that the risk of vascular and nervous system side-effects is slightly increased with taking 2 g of strontium ranelate daily over three to four years.

AUTHORS' CONCLUSIONS

There is silver level evidence (www.cochranemsk.org) to support the efficacy of strontium ranelate for the reduction of fractures (vertebral and to a lesser extent non-vertebral) in postmenopausal osteoporotic women and an increase in BMD in postmenopausal women with/without osteoporosis. Diarrhea may occur however, adverse events leading to study withdrawal were not significantly increased with taking 2 g of strontium ranelate daily. Potential vascular and neurological side-effects need to be further explored.

Structural studies of human alkaline phosphatase in complex with strontium: implication for its secondary effect in bones

Strontium is used in the treatment of osteoporosis as a ranelate compound, and in the treatment of painful scattered bone metastases as isotope. At very high doses and in certain conditions, it can lead to osteomalacia characterized by impairment of bone mineralization. The osteomalacia symptoms resemble those of hypophosphatasia, a rare inherited disorder associated with mutations in the gene encoding for tissue-nonspecific alkaline phosphatase (TNAP). Human alkaline phosphatases have four metal binding sites--two for zinc, one for magnesium, and one for calcium ion--that can be substituted by strontium. Here we present the crystal structure of strontium-substituted human placental alkaline phosphatase (PLAP), a related isozyme of TNAP, in which such replacement can have important physiological implications. The structure shows that strontium substitutes the calcium ion with concomitant modification of the metal coordination. The use of the flexible and polarizable force-field TCPEp (topological and classical polarization effects for proteins) predicts that calcium or strontium has similar interaction energies at the calcium-binding site of PLAP. Since calcium helps stabilize a large area that includes loops 210-228 and 250-297, its substitution by strontium could affect the stability of this region. Energy calculations suggest that only at high doses of strontium, comparable to those found for calcium, can strontium substitute for calcium. Since osteomalacia is observed after ingestion of high doses of strontium, alkaline phosphatase is likely to be one of the targets of strontium, and thus this enzyme might be involved in this disease.

Effect of lithium carbonate on subchondral bone in sexually mature Wistar rats

Clinical and experimental studies have shown that lithium carbonate causes a number of clinical manifestations such as hyperparathyroidism, hypothyroidism, renal toxicity, and diabetes insipidus. The effect of this drug on the bone biology of experimental animals has not been studied to date. Therefore, the aim of the present experimental work was to study the effect of lithium on bone tissue in healthy sexually mature Wistar rats. Ten female Wistar rats, aged 312-412 months, 210-220 g body weight, were assigned to one of the following groups: untreated control group and experimental group receiving 45 mg/kg body weight/day of lithium carbonate in their drinking water during 3 months. Prior to euthanasia, blood samples were obtained in order to determine plasma phosphorus, calcium alkaline phosphatase, and lithium. After sacrifice, the tibiae were resected, processed, and embedded in paraffin. The following histomorphometric parameters were determined on digital photographs of the histologic sections: BV/TV (%), bone volume; Tb.Th (microm), trabecular thickness; Tb.N (mm(-2)/mm), trabecular number; Tb.Sp (microm), trabecular separation; Ob.S/BS (%), osteoblast surface; ES/BS (%), total erosive surface; Lc.S (%), lining cells surface; and GPC.Th (microm), thickness of growth plate cartilage. The results showed that administration of lithium carbonate cause bone loss in healthy sexually mature Wistar rats. Although the mechanism involved in bone toxicity remains to be clarified, the results obtained in the present study suggest that patients under long-term lithium therapy should be thoroughly evaluated, particularly those presenting other risk factors of osteopenia, such as menopause, low calcium intake, alcohol consumption, and glucocorticoid therapy.

Metal microcrystal pollutants: the heat resistant, transmissible nucleating agents that initiate the pathogenesis of TSEs?

This paper exposes the flaws in the conventional consensus on the origins of transmissible spongiform encephalopathies (TSEs) which decrees that the protein-only misfolded 'prion' represents the primary aetiological transmissible agent, and then reviews/presents the emerging data which indicates that environmental exposure to metal microcrystal pollutants (sourced from munitions, etc.) represents the heat resistant, transmissible nucleating agents which seed the metal-prion protein (PrP)-ferritin fibril crystals that cause TSE. Fresh analytical data is presented on the levels of metals in ecosystems which support populations affected by clusters of variant Creutzfeldt-Jacob disease (vCJD), sporadic/familial CJD, and the scrapie types of TSE that have emerged in the UK, Sicily, Sardinia, Calabria and Japan. This data further substantiates the abnormal geochemical template (e.g., elevated strontium (Sr), barium (Ba) and silver (Ag)) which was observed as a common hallmark of the TSE cluster ecosystems across North America, thereby supporting the hypothesis that these microcrystals serve as the piezoelectrion nucleators which seed the growth/multireplication of the aberrant metal-PrP-ferritin fibril features which characterise the neuropathology of the TSE diseased brain. A secondary pathogenic mechanism entails the inactivation of the sulphated proteoglycans which normally regulate the mineralisation process. This can be induced by a rogue metal mediated chelation of free sulphur, or by contamination with organo-sulphur pollutants that substitute at natural sulphur bonds, or via a mutation to the S-proteoglycan cell line; thereby enabling the aberrant overgrowth of rogue fibril crystal formations that possess a piezoelectric capacity which compromises the ability of the contaminated individual to process incoming acoustic/tactile pressure waves in the normal way. The crystals transduce incoming sonic energy into electrical energy, which, in turn, generates magnetic fields on the crystal surfaces that initiate chain reactions of free radical mediated spongiform neurodegeneration. Metal microcrystal nucleating agents provide a group of plausible aetiological candidates that explain the unique properties of the TSE causal agent - such as heat resistance, transmissibility, etc. - which the protein-only prion model fails to fulfill. This paper also discusses the possible nutritional measures that could best be adopted by populations living in high risk TSE ecosystems; as a means of preventing the successful implantation of these rogue microcrystals and their consequent hypermineralisation of the soft tissues within the CNS.

Time-evolution and reversibility of strontium-induced osteomalacia in chronic renal failure rats

BACKGROUND

Patients with impaired renal function can accumulate strontium in the bone, which has been associated with the development of osteomalacia. A causal role for strontium in the development of the disease was presented in chronic renal failure (CRF) rats. Strontium-ranelate has been put forward as a therapeutic agent in the treatment of osteoporosis. Since the target population for strontium treatment consists mainly in postmenopausal osteoporotic women, who may have a reduced renal function, the risk for osteomalacia should be considered.

METHODS

To determine the time evolution and reversibility of the strontium-induced mineralization defect, CRF rats were loaded with strontium (2 g/L) (+/- 200 mg/kg/day) during 2, 6, and 12 weeks, followed by a washout period of 0, 2, 4, or 8 weeks.

RESULTS

Histologic examination of the bone of the animals treated with strontium revealed signs of osteomalacia already after 2 weeks. Animals that received strontium during 6 and 12 weeks had a significantly higher osteoid perimeter, area and thickness as compared to CRF controls. After 12 weeks, the mineralization was significantly affected, as evidenced by a lower double-labeled surface, mineral apposition and bone formation rate in combination with an increased osteoid maturation time and mineralization lag time. The osteoblast perimeter was significantly lower in the strontium-treated animals. After the washout periods, these effects were reversed and the bone lesions evolved to the values of CRF controls. This went along with an 18% reduction of the bone strontium content. A significant rise in serum alkaline phosphatase (ALP) activity was apparent in the strontium-treated animals as compared to CRF controls. This was not only due to higher levels of the bone ALP but also to those of the liver and the intestinal isoenzymes. Serum parathyroid hormone (PTH) levels decreased during strontium treatment. After cessation of the treatment, the serum ALP activity and PTH concentration reversed to control levels.

CONCLUSION

In this study evidence is provided for the rapid development of a mineralization defect in strontium-loaded CRF rats, accompanied by a reduced osteoblast number, reduced PTH synthesis or secretion, and increased serum ALP levels. These effects can be rapidly reversed after withdrawal of the compound.

Dialysis water as a determinant of the adequacy of dialysis

Hemodialysis patients are exposed to large volumes of water in the form of dialysate. Contaminants from the dialysate may cross the dialyzer membrane into the blood and have the potential to compromise the adequacy of dialysis. Several chemicals found commonly in drinking water have long been known to be toxic to hemodialysis patients. More recently, it has become apparent that even low levels of bacterial products in dialysate may adversely impact dialysis adequacy through their ability to stimulate an inflammatory response. Minimum levels of water and dialysate quality have been recommended to protect patients from chemical and microbiologic contaminants. Complying with these recommendations requires an appropriately designed water purification and distribution system, combined with a surveillance program designed to maintain dialysate quality.

Effects of strontium on the physicochemical characteristics of hydroxyapatite

In a previous experimental study using a chronic renal failure rat model, a dose-related multiphasic effect of strontium (Sr) on bone formation was found that could be reproduced in an in vitro set-up using primary rat osteoblasts. The results from the latter study allowed us to distinguish between a reduced nodule formation in the presence of an intact mineralization at low Sr-doses (1 microg/ml) and an interference of the element with the hydroxyapatite (HA) formation at high doses (20-100 microg/ml). To further investigate the latter effect of Sr on physicochemical bone mineral properties, an in vitro study was set up in which the UMR-106 rat osteosarcoma cell line was exposed to Sr, added to the cell culture medium in a concentration range varying between 0-100 microg/ml. Temporal growth and functionality of the culture was investigated by measurement of the alkaline phosphatase activity and calcium (Ca) concentration in the culture medium (used as an index of Ca-incorporation, i.e., HA formation) at various time points. At the end of the culture period (14 days post-confluence), samples of the mineralized cultures were taken for further analysis using X-ray diffraction (XRD) and Fourier Transform Infra-Red Spectroscopy (FTIR). Synthetic HA doped with various Sr concentrations (based on the cell culture and previous experimental studies and yielding Sr/(Sr + Ca) ratios ranging from 0-60%), was prepared and examined for crystal growth and solubility. Crystal size was assessed using scanning electron microscopy (SEM). Ca incorporation indicated a reduced mineralization in the 20 and 100 microg/ml Sr groups vs. controls. Sr-doped synthetic HA showed a significant dose-dependent reduction in crystal growth, as assessed by SEM, and an increase in solubility, apparent from 12.7% Sr/(Sr + Ca) on. Moreover, in both mineralized cultures and synthetic HA, XRD and FTIR analysis showed a reduced crystallinity and altered crystal lattice at similar concentrations. These new data support our previous in vivo and in vitro findings and point to a potential physicochemical interference of Sr with HA formation and crystal properties in vivo.

The biological role of strontium

This review summarises old and more recent literature on the biological role of the bone-seeking trace metal strontium (Sr). It covers areas of chemistry, nutrition, toxicity, transport across biological membranes, homeostasis, general physiology, calcium-strontium interactions, and particularly the role of strontium in bone. The promoting action of strontium on calcium uptake into bone at moderate strontium supplementation, and the rachitogenic action of strontium at higher dietary strontium levels are emphasised. The literature is summarised of the novel antiosteoporotic drug strontium ranelate, which appears to act by a combination of reduced bone resorption and increased uptake of calcium into bone.

Normal matrix mineralization induced by strontium ranelate in MC3T3-E1 osteogenic cells

There is growing evidence that strontium ranelate (SR; S12911-2, PROTELOS; Institut de Recherches Internationales Servier, Courbevoie, France), a compound containing 2 atoms of stable strontium (Sr), influences bone cells and bone metabolism in vitro and in vivo. We previously reported that SR increases bone mass in rats and mice by stimulating bone formation and inhibiting bone resorption. We also showed that short-term treatment with SR enhances osteoblastic cell recruitment and function in short-term rat calvaria cultures. Because Sr incorporates into the bone matrix, it was of interest to determine whether SR may affect matrix mineralization in long-term culture. To this goal, osteogenic mouse calvaria-derived MC3T3-E1 osteoblastic cells were cultured for up to 14 days in the presence of ascorbic acid and phosphate to induce matrix formation and mineralization. Matrix formation was determined by incorporation of tritiated proline during collagen synthesis. Matrix mineralization was quantified by measuring the number and surface of mineralized nodules using a digital image analyzer. In this model, 1,25(OH)2 vitamin D (1 nmol/L) used as internal control, increased alkaline phosphatase (ALP) activity, an early osteoblast marker, on days 4, 10, and 14 of culture. Treatment with SR (1 mmol/L Sr(2+)) increased ALP activity at days 4 and 14 of culture. SR also increased collagen synthesis at days 4 and 10 of culture. In contrast, 1,25(OH)2 vitamin D (1 nmol/L) inhibited collagen synthesis at 4 to 14 days of culture. Long-term treatment with SR (0.1 to 1 mmol/L Sr(2+)) dose dependently increased Sr concentration into the calcified nodules, but did not alter matrix mineralization in long-term culture, as shown by the ratio of the surface of mineralized nodules to the number of mineralized nodules on day 14 of culture. These results show that long-term treatment with SR increases collagenous matrix formation by MC3T3-E1 osteoblasts without inducing deleterious effect on matrix mineralization.

Dose-dependent effects of strontium on osteoblast function and mineralization

BACKGROUND

Strontium-ranelate is now being used in the treatment of osteoporosis in elderly patients. As the majority of these patients already have a decreased renal function they are at an increased risk for accumulation of the element. Recent findings from epidemiologic studies in dialysis patients and experimental data obtained in a chronic renal failure (CRF) rat model established a dose-related multiphasic effect of strontium (Sr) on bone formation. To confirm these in vivo findings an in vitro set-up, consisting of primary rat osteoblast cultures, was applied. Sr was added to the culture medium at concentrations of 0, 0.5, 1.0, 2.0, 5.0, 20, and 100 microg/mL, respectively.

METHODS

Calcium incorporation (index of mineralization) and alkaline phosphatase activity were determined in the medium during the culture period, while at the end of the experiment, nodule formation (mineralized + unmineralized area) was quantified using a digital imaging system. mRNA synthesis of various osteoblast specific genes was assessed by means of reverse transcription polymerase chain reaction (RT-PCR).

RESULTS

Compared to the control group (0 microg/mL Sr), a significantly reduced nodule formation in the presence of an intact mineralization was found for the lowest 0.5 and 1 microg/mL Sr doses, suggesting an impaired in vitro osteoblast differentiation. Both nodule formation and mineralization were normal for the 2 and 5 microg/mL doses. For the highest Sr doses (20 and 100 microg/mL) a reduced mineralization was observed in the presence of an intact nodule formation indicating an inhibitory effect on the hydroxyapatite formation. The alkaline phosphatase activity reflected the multiphasic pattern of the nodule formation while the calcium incorporation corresponded with the pattern of nodular mineralization. No variations in cell proliferation were found. RT-PCR revealed that Sr interfered with the osteoblast at the level of the mRNA synthesis of several relevant genes.

CONCLUSION

Using the proposed in vitro model we confirmed the multiphasic effect of Sr on bone formation previously demonstrated in a CRF rat model. The data presented allow us to suggest that at low concentrations Sr interferes with the bone formation at the level of cell differentiation, whereas at high concentrations the disturbed mineralization in the presence of an intact nodule formation is indicative for a physicochemical interference of Sr with the hydroxyapatite formation.

Dose-dependent effects of strontium on bone of chronic renal failure rats

BACKGROUND

We previously reported on increased bone strontium (Sr) levels in dialysis patients with osteomalacia versus those presenting other types of renal osteodystrophy. A causal role of strontium in the development of osteomalacia was established in a chronic renal failure (CRF) rat model.

METHODS

In the present study we investigated whether the effect of Sr on bone was related to dosage. Four groups of CRF rats were studied: a control group (control-CFR; N=6) not receiving strontium and three groups of animals loaded orally with Sr during 18 weeks by adding the element as the SrCl2. H20 compound to the drinking water at concentrations of 0.03 g/100mL (Sr-30; N=6), 0.075 g/100mL (Sr-75; N=6), or 0.15 g/100mL (Sr-150; N=6) respectively. A fifth group consisting of seven animals with intact renal function (control-NRF), not receiving Sr served as controls for the effect of CRF on bone histology.

RESULTS

As compared to the control-NRF and control-CRF groups, Sr administration resulted in a dose-dependent increase in bone and serum Sr levels. No difference in body weight and biochemical serum and urinary parameters [i.e., calcium (Ca), phosphorus (P), and creatinine] was noted between the various CRF groups. At sacrifice, intact parathyroid hormone (iPTH) levels of CRF groups were significantly (P < 0.05) higher than the values measured in the control-NRF group indicating the development of hyperparathyroidism secondary to the installation of the CRF. This is further supported by the differences in bone histomorphometry between the control-CRF and control-NRF animals, which, respectively, showed an increased amount of osteoid (mean +/- SEM 3.4 +/- 1.2% vs. 0.37 +/- 0.14%, P < 0.05) in combination with a distinct osteoblastic activity (35 +/- 11% vs. <2%, P < 0.05) and an increased bone formation rate [(BFR), 677 +/- 177 microm 2/mm2/day vs. 130 +/- 50 microm 2/mm2/day, P < 0.05]. Bone surface area and erodic perimeter did not differ between the various study groups. In the Sr-30 group, Sr loading went along with a dramatic reduction of the BFR as indicated by the total absence of double tetracyclin labels and osteoblastic activity, which in the presence of a low to normal amount of osteoid (2.7 +/- 1.9%) points to the development of the adynamic type of renal osteodystrophy. Interestingly, compared to the control-CRF group, histodynamic and histologic parameters of the Sr-75 group did not differ significantly and a substantial osteoblastic activity (7.6 +/- 4.0%) was seen also. In the Sr-150 group, the various osteoid parameters were significantly (P < 0.05) increased vs. all other groups and were accompanied by a reduced BFR and mineral apposition rate (MAR) and an increased mineralization lag time (MLT), indicating a mineralization defect and the development of osteomalacia.

CONCLUSIONS

Our findings indicate that the role of Sr in the development of bone lesions in renal failure is complex and that, depending on the dose, the element may act via multiple pathways.

Fluoride and strontium accumulation in bone does not correlate with osteoid tissue in dialysis patients

BACKGROUND

Osteomalacia is now a rare disease in dialysis patients in developed countries since the withdrawal of aluminium overload. The involvement of fluoride and strontium in the pathogenesis of the disease has been suggested. The aim of this study was to investigate a possible association between osteomalacia in dialysis patients and the fluoride or strontium contents of bone.

METHODS

Of 271 bone biopsies from chronic haemodialysis patients referred to our centre, we studied the nine biopsies from patients with osteomalacia. They were compared with 23 biopsies from patients with hyperparathyroidism and 24 biopsies from patients with adynamic bone disease. Histomorphometric static and dynamic indices were measured. Bone fluoride and strontium contents were measured in biopsies from haemodialysis patients, and were compared with those of control patients.

RESULTS

In the nine patients with osteomalacia, we found an absence of double labelled surfaces and increased osteoid thickness. Mild aluminium overload was observed in two of the nine patients. The bone strontium content of the entire dialysis population studied was not significantly different from control values (0.023+/-0.001 vs 0.019+/-0.002% mol/mol, P=0.15). However, bone strontium level was slightly but significantly increased in patients with osteomalacia (0.030+/-0.005%), compared with both controls (0.019+/-0.002%, P<0.05) and the other bone diseases (0.021+/-0.002%, P<0.05). Bone fluoride content was significantly higher in the entire dialysis population than in the controls (0.33+/-0.04 vs 0.13+/-0.018% (g/g ash weight), P=0.04). It was increased in osteomalacic patients compared with controls and with patients having hyperparathyroidism or adynamic bone disease. There was no correlation between formation indices (OV/BV, OS/BS, Ob.S/BS) and bone fluoride or strontium content.

CONCLUSIONS

We found a prevalence of osteomalacia of 3.3% in our biopsy series for chronic dialysis patients. However, although bone strontium and fluoride contents were slightly increased, no causal relationship with these individual metals and osteomalacia could be firmly established in this small number of patients. The hypothesis of strontium- or fluoride-induced osteomalacia in renal patients merits further investigation.

Increased bone strontium levels in hemodialysis patients with osteomalacia

BACKGROUND

In this study, we report on the association between increased bone strontium levels and the presence of osteomalacia in end-stage renal failure patients treated by hemodialysis.

METHODS

We performed a histologic examination and determined the strontium content and strontium/calcium ratios in bone biopsies of 100 hemodialysis patients recruited from various centers all over the world. Aside from the bone strontium concentration, the bone aluminum content was assessed. The bone zinc concentration, a nonrelevant element for bone toxicity, was also measured.

RESULTS

Bone strontium levels and bone strontium/calcium ratios were increased in subjects with osteomalacia when compared with those with the other types of renal osteodystrophy. Bone strontium and bone calcium levels correlated with each other. The slope of the linear regression curve correlating these parameters was much steeper in the osteomalacic group (Y = 2.22X - 120) as compared with the other types of renal osteodystrophy (Y = 0.52X - 5.7). Within the group of patients with osteomalacia, bone strontium levels also significantly correlated with the bone aluminum content (r = 0.72, P = 0.018). No such correlation was found for the other types of renal osteodystrophy. The bone zinc concentration of subjects with normal renal function did not differ significantly from the values noted for the various types of renal osteodystrophy taken as separate groups, nor could increased bone zinc concentrations be associated with a particular bone lesion.

CONCLUSIONS

Our data demonstrate an association between osteomalacia and increased bone strontium concentrations in dialysis patients. Further studies are warranted to establish whether strontium plays either a primary, secondary, or contributive role in the development of the latter type of renal osteodystrophy.

Low bone turnover in patients with renal failure

Renal failure inevitably leads to metabolic bone disease. Low turnover disease or adynamic bone disease (ABD) is characterized by a low number of osteoblasts with normal or reduced numbers of osteoclasts. Mineralization proceeds at a normal rate, resulting in normal or decreased osteoid thickness. Recently, it became clear that the relative contribution of the various types of renal osteodystrophy (ROD) to the spectrum of the histologic picture in renal failure patients underwent profound changes during the last 25 years. At the moment, the exact physiopathological mechanisms behind ABD are not yet elucidated, and thus the reason(s) for its increasing prevalence remains poorly understood. A number of epidemiological and experimental data suggest a multifactorial pathophysiologic process, in which hypoparathyroidism and suppression of the osteoblast are the main actors. Compared to adynamic bone disease, osteomalacia has now become a much rarer disease (around 4%), at least in Western countries. On the other hand, recent studies indicate that this particular bone disease entity might still regularly occur in less developed countries. Osteomalacia originates from a direct effect on the mineralization process. With this type of renal bone disease, the effects of secondary hyperparathyroidism on bone are overridden by a number of metabolic abnormalities that finally result in a defective bone mineralization, as occurs, for instance, when the lag time between osteoid deposition and its mineralization is increased. The relationship between exogenous and endogenous vitamin D deficiency (mainly calcitriol) and the histologic finding of osteomalacia in uremic patients is well known. Recent data showed distinctly lowered 25-(OH) vitamin D3 levels in the presence of unaffected calcitriol concentrations in patients with osteomalacic lesions, as assessed radiologically by the presence of Looser's zones. Recently, we found that bone strontium levels were increased in patients with osteomalacia as compared to all other types of ROD. Strontium accumulation appeared to originate mainly from the use of strontium-contaminated dialysate, which resulted from the addition of strontium-containing acetate-based concentrates. Evidence for a causal role of the element in the development of a mineralization defect could be tested experimentally by adding strontium to drinking water in a chronic renal failure rat model.

Increased serum strontium levels in dialysis patients: an epidemiological survey

BACKGROUND

We previously reported on increased bone strontium levels in dialysis patients with osteomalacia versus those presenting other types of renal osteodystrophy. A causal role of strontium in the development of osteomalacia was established in a chronic renal failure rat model.

METHODS

To further elucidate the latter issue and to find out whether dialysis patients from particular centers/countries are at an increased risk for strontium accumulation, a worldwide multicenter study was established. In total, 834 patients from 34 dialysis centers in 23 countries were included. In each of the patients, a serum sample was taken for strontium determination, and water and dialysate samples were taken at the various steps of the water purification process. For each patient clinical data and for each center dialysis modalities were recorded.

RESULTS

Strontium levels in serum of dialysis patients showed major differences between the various centers, ranging from mean values of 25 +/- 8 microgram/liter in the center with the lowest level up to 466 +/- 90 microgram/liter in the center with the highest concentration. It is of interest that these high levels were mainly found in developing countries. Furthermore, our data point toward a role of the final dialysate in the accumulation of the element, as indicated by the strong correlation (r = 0.74, P < 0.001) between mean serum and dialysate strontium levels. As the high tap water concentration of strontium was adequately reduced during the water purification process, contamination of the final dialysis fluid occurred by the addition of concentrates contaminated with strontium. Besides the dialysate, other factors, such as duration of dialysis, vitamin D supplements, or types of phosphate binders, played a less important role in the accumulation of the element.

CONCLUSIONS

Data of this multicenter study indicate patients of particular dialysis centers to be at an increased risk for strontium accumulation, the clinical consequence of which is under current investigation.

Aluminum, Iron, Lead, Cadmium, Copper, Zinc, Chromium, Magnesium, Strontium, and Calcium Content in Bone of End-Stage Renal Failure Patients

Background: Little is known about trace metal alterations in the bones of dialysis patients or whether particular types of renal osteodystrophy are associated with either increased or decreased skeletal concentrations of trace elements. Because these patients are at risk for alterations of trace elements as well as for morbidity from skeletal disorders, we measured trace elements in bone of patients with end-stage renal disease.

Methods: We analyzed bone biopsies of 100 end-stage renal failure patients enrolled in a hemodialysis program. The trace metal contents of bone biopsies with histological features of either osteomalacia, adynamic bone disease, mixed lesion, normal histology, or hyperparathyroidism were compared with each other and with the trace metal contents of bone of subjects with normal renal function. Trace metals were measured by atomic absorption spectrometry.

Results: The concentrations of aluminum, chromium, and cadmium were increased in bone of end-stage renal failure patients. Comparing the trace metal/calcium ratio, significantly higher values were found for the bone chromium/calcium, aluminum/calcium, zinc/calcium, magnesium/calcium, and strontium/calcium ratios. Among types of renal osteodystrophy, increased bone aluminum, lead, and strontium concentrations and strontium/calcium and aluminum/calcium ratios were found in dialysis patients with osteomalacia vs the other types of renal osteodystrophy considered as one group. Moreover, the concentrations of several trace elements in bone were significantly correlated with each other. Bone aluminum was correlated with the time on dialysis, whereas bone iron, aluminum, magnesium, and strontium tended to be associated with patient age. Bone trace metal concentrations did not depend on vitamin D intake nor on the patients’ gender.

Conclusions: The concentration of several trace elements in bone of end-stage renal failure patients is disturbed, and some of the trace metals under study might share pathways of absorption, distribution, and accumulation. The clinical significance of the increased/decreased concentrations of several trace elements other than aluminum in bone of dialysis patients deserves further investigation.