High fluoride intakes cause osteomalacia and diminished bone strength in rats with renal deficiency

Intrinsic properties of osteomalacia bone evaluated by nanoindentation and FTIRM analysis

Osteomalacia is a pathological bone condition consisting in a deficient primary mineralization of the matrix, leading to an accumulation of osteoid tissue and reduced bone mechanical strength. The amounts, properties and organization of bone constituents at tissue level, are known to influence its mechanical properties. It is then important to investigate the relationship between mechanical behavior and tissue composition at this scale in order to provide a better understanding of bone fragility mechanisms associates with this pathology. Our purpose was to analyze the links between ultra-structural properties and the mechanical behavior of this pathological bone tissue (osteomalacia) at tissue level (mineral and osteoid separately, or global). Four bone biopsies were taken from patients with osteomalacia, and subsequently embedded, sectioned, and polished. Then nanoindentation tests were performed to determine local elastic modulus E, contact hardness Hc and true hardness H for both mineralized and organic bone phases and for the global bone. The creep of the bone was also studied using a special indentation procedure in order to assess visco-elasto-plastic (creep) bone behavior. This allowed a detailed study of the rheological models adapted to the bone and to calculate the parameters associated to a Burgers model. Ultra-structural parameters were measured by Fourier Transform InfraRed Microspectroscopy (FTIRM) on the same position as the indents. The use of rheological models confirmed a significant contribution from the organic phase on the viscous character of bone tissue. The elastic E and the elasto-plastic H_c deformation were correlated to both collagen maturity and Mineral/Matrix. The pure plastic deformation H was only correlated to the mineral phase. Our data show that mineral phase greatly affects mechanical variables (moduli and viscosities) and that organic phase (as illustrated in osteoid tissue) may play an important role in the creep behavior of bone. In conclusion, this study brings mechanical and physicochemical values for osteoid and mineral phases.

Increasing fluoride content deteriorates rat bone mechanical properties

Elevation of bone fluoride levels due to drinking beverages with high fluoride content or other means such as inhalation can result in skeletal fluorosis and lead to increased joint pain, skeletal deformities, and fracture. Because skeletal fluorosis alters bone's mineral composition, it is likely to affect bone's tissue-level mechanical properties with consequent effects on whole bone mechanical behavior. To investigate this, we determined whether incubation with in vitro sodium fluoride (NaF) altered bone's mechanical behavior at both the tissue- and whole bone-levels using cyclic reference point indentation (cRPI) and traditional 3-point bending, respectively. Forty-two ulnas from female adult rats (5-6 months) were randomly divided into 5 groups (vehicle, 0.05 M NaF, 0.25 M NaF, 0.75 M NaF, and 1.5 M NaF). Bones were washed in a detergent solution to remove organic barriers to ion exchange and incubated in respective treatment solutions (12 h, 23 °C). Cortical tissue mineral density (TMD) and geometry at the mid-diaphysis were determined by microCT. cRPI was performed on the distal diaphysis (9 N, 2 Hz, 10 cycles), and then bones were tested in 3-point bending to assess whole bone mechanical properties. The incubations in vehicle (0 M) up to 1.5 M in vitro NaF concentrations achieved bone fluoride levels ranging from approximately 0.70 to 15.8 ppm. NaF-incubated bones had significantly greater indentation distances, higher displacement-to-maximum force, and lower estimated elastic modulus, ultimate stress, and bending rigidity with increasing NaF concentration compared to vehicle-incubated bones. cRPI variables were moderately correlated to whole bone mechanical properties such that higher indentation distances were associated with lower estimated elastic modulus, ultimate stress, and bending rigidity. In conclusion, in vitro NaF incubation mostly has a deleterious effect on bone mechanical behavior with increasing NaF levels that is independent of bone turnover and reflected, in part, by less resistance of the tissue to cRPI-based indentation.

Weaker bones and white skin as adaptions to improve anthropological "fitness" for northern environments

The vitamin D paradox relates to the lower risk of osteoporosis in people of sub-Saharan African ancestry (Blacks) compared with people of European ancestry (Whites). The paradox implies that for bone health, Blacks require less vitamin D and calcium than Whites do. Why should populations that migrated northward out of Africa have ended up needing more vitamin D than tropical Blacks? Human skin color became lighter away from the tropics to permit greater skin penetration of the UVB light that generates vitamin D. Lack of vitamin D impairs intestinal calcium absorption and limits the amount of calcium that can deposit into the protein matrix of bone, causing rickets or osteomalacia. These can cause cephalopelvic disproportion and death in childbirth. Whiter skin was more fit for reproduction in UV-light restricted environments, but natural selection was also driven by the phenotype of bone per se. Bone formation starts with the deposition of bone-matrix proteins. Mineralization of the matrix happens more slowly, and it stiffens bone. If vitamin D and/or calcium supplies are marginal, larger bones will not be as fully mineralized as smaller bones. For the same amount of mineral, unmineralized or partially mineralized bone is more easily deformed than fully mineralized bone. The evidence leads to the hypothesis that to minimize the soft bone that causes pelvic deformation, a decrease in amount of bone, along with more rapid mineralization of osteoid improved reproductive fitness in Whites. Adaptation of bone biology for reproductive fitness in response to the environmental stress of limited availability of vitamin D and calcium came at the cost of greater risk of osteoporosis later in life.

Fluoride exposure and kidney and liver function among adolescents in the United States: NHANES, 2013-2016

BACKGROUND

Hepato- and nephrotoxicity of fluoride have been demonstrated in animals, but few studies have examined potential effects in humans. This population-based study examines the relationship between chronic low-level fluoride exposure and kidney and liver function among United States (U.S.) adolescents. This study aimed to evaluate whether greater fluoride exposure is associated with altered kidney and liver parameters among U.S. youth.

METHODS

This cross-sectional study utilized data from the National Health and Nutrition Examination Survey (2013-2016). We analyzed data from 1983 and 1742 adolescents who had plasma and water fluoride measures respectively and did not have kidney disease. Fluoride was measured in plasma and household tap water. Kidney parameters included estimated glomerular filtration rate (calculated by the original Schwartz formula), serum uric acid, and the urinary albumin to creatinine ratio. Liver parameters were assessed in serum and included alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, blood urea nitrogen, gamma-glutamyl transferase, and albumin. Survey-weighted linear regression examined relationships between fluoride exposure and kidney and liver parameters after covariate adjustment. A Holm-Bonferroni correction accounted for multiple comparisons.

RESULTS

The average age of adolescents was 15.4 years. Median water and plasma fluoride concentrations were 0.48 mg/L and 0.33 μmol/L respectively. A 1 μmol/L increase in plasma fluoride was associated with a 10.36 mL/min/1.73 m2 lower estimated glomerular filtration rate (95% CI: -17.50, -3.22; p = 0.05), a 0.29 mg/dL higher serum uric acid concentration (95% CI: 0.09, 0.50; p = 0.05), and a 1.29 mg/dL lower blood urea nitrogen concentration (95%CI: -1.87, -0.70; p < 0.001). A 1 mg/L increase in water fluoride was associated with a 0.93 mg/dL lower blood urea nitrogen concentration (95% CI: -1.44, -0.42; p = 0.007).

CONCLUSIONS

Fluoride exposure may contribute to complex changes in kidney and liver related parameters among U.S. adolescents. As the study is cross-sectional, reverse causality cannot be ruled out; therefore, altered kidney and/or liver function may impact bodily fluoride absorption and metabolic processes.

Calcium Alleviates Fluoride-Induced Bone Damage by Inhibiting Endoplasmic Reticulum Stress and Mitochondrial Dysfunction

Excessive fluoride mainly causes skeletal lesions. Recently, it has been reported that an appropriate level of calcium can alleviate fluorosis. However, the appropriate concentration and mechanism of calcium addition is unclear. Hence, we evaluated the histopathology and ultrastructure, DNA fragmentation, hormonal imbalances, biomechanical levels, and expression of apoptosis-related genes after treating the rats with 150 mg/L NaF and different concentrations of CaCO₃. Our results suggested that NaF induced the histopathological and ultrastructural injury, with a concomitant increase in the DNA fragmentation (P < 0.05) and serum OC (17.5 ± 0.89 pmoL/L) at 120 days. In addition, the qRT-PCR and western blotting results indicated that NaF exposure upregulated the mRNA and protein expression of Bax, Calpain, Caspase 12, Caspase 9, Caspase 7, Caspase 3, CAD, PARP, and AIF while downregulated Bcl-2 (P < 0.01) and decreased the bone ultimate load by 27.1%, the ultimate stress by 10.1%, and the ultimate deformity by 23.3% at 120 days. However, 1% CaCO₃ supplementation decreased the serum OC (14.7 ± 0.65 pmoL/L), bone F content (P < 0.01), and fracture and breakage of collagen fibers and changed the expression of endoplasmic reticulum pathway-related genes and proteins at 120 days. Further, 1% CaCO₃ supplementation increased the bone ultimate load by 20.9%, the ultimate stress by 4.89%, and the ultimate deformity by 21.6%. In summary, we conclude that 1% CaCO₃ supplementation alleviated fluoride-induced bone damage by inhibiting endoplasmic reticulum stress and mitochondrial dysfunction.

Effects of Fluoride on Bone in an Animal Model of Vitamin D Deficiency

We investigated the combined effect of fluoride exposure and Vitamin D deficiency in causing bone damage as a precursor to development of Fluorotoxic Metabolic Bone Disease. Thirty-six male Sprague-Dawley rats were divided into 6 groups of six; 3 groups received a Vitamin D deficient diet whereas the other 3 received a Vitamin D adequate diet. Serum total 25-hydroxyvitamin D (25OHD), calcium, phosphorus, creatinine, Alkaline phosphatase (ALP), albumin, Parathyroid hormone (PTH), Osteocalcin and C terminal telopeptide (CTx) were measured following exposure to varying levels of fluoride in drinking water (< 1.0, 15 and 50 ppm). Full body Dual-energy X-ray Absorptiometry (DXA) scans were used to examine changes in bone morphology pre and post exposure to fluoride. Renal tubular function was assessed using serum creatinine and urine Cystatin C. Histopathological examination of sections of bone and kidney tissues were also performed. Prior to fluoride exposure, DXA scans revealed a significant decrease in Bone Mineral Density (BMD) and Bone Mineral content (BMC) (p < 0.05) but a significant increase in fat mass (p < 0.05) and fat percentage (p < 0.01) among Vitamin D deficient rats, with no significant change in biochemical parameters. Following exposure to fluoride, BMD was significantly increased (p < 0.05) in both groups with a corresponding increase in serum ALP, bone fluoride content, Osteocalcin, CTx and urine fluoride with increasing levels of fluoride exposure. Serum creatinine calcium and phosphate and urinary cystatin C levels showed no significant changes. Light microscopy examination revealed mild thickening and increased osteoid in 80% of the Vitamin D deficient rats exposed to high levels of fluoride but renal tubular changes were found only in one experimental and one control animal. Fluoride deposited in rat bone affects both osteoblastic and osteoclastic activity. Also, these effects are accentuated in the presence of Vitamin D deficiency.

The effects of Cosmos caudatus (ulam raja) on dynamic and cellular bone histomorphometry in ovariectomized rats

Background

Cosmos caudatus is a local plant which has antioxidant properties and contains high calcium. It is also reported to be able to strengthen the bone. This report is an extension to previously published article in Evidence Based Complementary and Alternative Medicine (doi:10.1155/2012/817814). In this study, we determined the effectiveness of C. caudatus as an alternative treatment for osteoporosis due to post-menopause by looking at the dynamic and cellular paramaters of bone histomorphometry.

Methods

Forty female Wistar rats were divided into four groups i.e. sham operated, ovariectomized, ovariectomized treated with calcium 1% ad libitum and ovariectomized force-fed with 500 mg/kg C. caudatus extract. Treatment was given six days a week for eight weeks.

Results

Dynamic and cellular histomorphometry parameters were measured. C. caudatus increased double-labeled surface (dLS/BS), mineral appositional rate (MAR), osteoid volume (OV/BV) and osteoblast surface (Ob.S/BS). C. caudatus also gave better results compared to calcium 1% in the osteoid volume (OV/BV) parameter.

Conclusions

C. caudatus at the 500 mg/kg dose may be an alternative treatment in restoring bone damage that may occur in post-menopausal women.

Determination of reference concentrations of strontium in urine by inductively coupled plasma atomic emission spectrometry

OBJECTIVE

The aim of this study was to establish reference concentrations of urinary strontium by inductively coupled plasma atomic emission spectrometry (ICP-AES).

METHODS

For the determination of strontium, urine samples were collected from healthy Japanese (n=146; 115 males, 31 females; mean age, 33±9 years; age range, 18 to 58 years). The urine samples stored at or below -20°C were thawed with incubation at 40°C for 30 min and sediments were dissolved by vigorous shakings. Then, the samples were centrifuged at 3000 g for 5 min, and the supernatant was directly aspired into a P-5200-3600/1200 ICP-AES system from Hitachi Ltd., Tokyo, Japan.

RESULTS

A steeper increase in the S/N ratio and a good effective linearity of the calibration line was obtained at 407.771 nm in the range of 0-300 μg/L strontium standard solution. Urine samples having the same background signal as that of 18 MΩ cm ultrapure blank water, a good correspondence of the single peak pattern of the spectra, accuracy and precision of spike recovery were also confirmed. Urinary strontium concentrations showed a log-normal distribution and a geometric mean concentration of 143.9 μg/L, with 5-95% confidential interval of 40.9-505.8 μg/L.

CONCLUSION

The results of this study will be useful as guidelines for the biological monitoring of strontium in normal subjects and in individuals therapeutically or environmentally exposed to strontium.

Effect of fluoridated water on plasma insulin levels and glucose homeostasis in rats with renal deficiency

Glucose intolerance in fluorosis areas and when fluoride is administered for the treatment of osteoporosis has been reported. Controlled fluoridation of drinking water is regarded as a safe and effective measure to control dental caries. However, the effect on glucose homeostasis was not studied so far. The aim of this study was to evaluate the effect of the intake of fluoridated water supply on glucose metabolism in rats with normal and deficient renal function. Male Sprague-Dawley rats were divided into eight groups of four rats. Renal insufficiency was induced in four groups (NX) which received drinking water containing 0, 1, 5, and 15 ppm F (NaF) for 60 days. Four groups with simulated surgery acted as controls. There were no differences in plasma glucose concentration after a glucose tolerance test between controls and NX rats and among rats with different intakes of fluoride. However, plasma insulin level increased as a function of fluoride concentration in drinking water, both in controls and in NX rats. It is concluded that the consumption of fluoridated water from water supply did not affect plasma glucose levels even in cases of animals with renal disease. However, a resistance to insulin action was demonstrated.

Comparative proteomics analysis of midgut samples from Takifugu rubripes exposed to excessive fluoride: initial molecular response to fluorosis

Comparative proteomic analysis was performed to identify proteins in the midgut of Takifugu rubripes (Fugu) in response to excessive fluoride. Sixteen fish were randomly divided into a control group and an experimental group. The control group was raised in soft water alone (F⁻= 0.4 mg/L), whereas the experimental group was raised in the soft water with sodium fluoride at a high concentration of 35 mg/L. After 3 days, proteins were extracted from the fish midgut and then subjected to two-dimensional (2-D) PAGE analysis. The matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI TOF/TOF MS) was applied to identify the differential expressed proteins between the two groups. Among 377 and 528 proteins detected in the control and the treated groups, respectively, 17 proteins were up-regulated and 218 were down-regulated (P < 0.01) in the fluoride-treated group, compared with the control group. We further analyzed 17 up-regulated proteins by MALDI TOF/TOF MS and identified 12 of them by MASCOT, of which eight were known proteins. Consistent with their annotated functions, these proteins seem to be involved in apoptosis and other functions related to fluorosis. Our results provide initial insights into the effects of excessive fluoride exposure on physiological and biochemical functions of Fugu midgut as well as on the toxicological mechanism of fluoride in both fish and human.

Comparative proteomics of kidney samples from puffer fish Takifugu rubripes exposed to excessive fluoride: an insight into molecular response to fluorosis

To investigate comparative proteomics of the pufferfish kidney exposed to excessive fluoride, the authors randomly put 16 fish into the control and treated groups that were raised in softwater alone (F(-) = 0.4 mg/L) or with sodium fluoride of 35 mg/L for 3 days, respectively. Then proteins of the fish kidneys were profiled by two-dimensional electrophoresis, and the matrix assisted laser desorption ionization time of flight mass spectrometry (MALDI TOF MS) was applied to identify the spots on the gel with altered densities. On average, 547 and 516 protein spots were detected in the control and the treated groups, respectively. Among them, 32 protein spots showed significant alteration (p < 0.05) between the fluoride-treated and the control groups, and 22 differentially expressed protein spots were identified by MALDI TOF-TOF MS. Consistent with their previously annotated functions, these proteins appear to be involved in the biological functions associated with fluorosis. These results will greatly advance one's understanding of the effects of fluoride exposure on the physiological and biochemical functions of takifugu kidney as well as the toxicological mechanism of fluoride-causing fluorosis in both fish and humans.

Beneficial effects of vitamin E isomer supplementation on static and dynamic bone histomorphometry parameters in normal male rats

Bone is a specialized connective tissue that functions as the load-bearing structure of the body. Free radicals may affect bone remodeling by regulating osteoclast activity in either the physiological or pathological condition. Vitamin E, a lipid-soluble antioxidant, has been demonstrated to offer protection against osteoporosis and to improve the bone material and structure of animal models. The aim of this study was to observe and compare the effects of alpha-tocopherol (alpha-tocopherol), delta-tocotrienol (delta-tocotrienol), and gamma-tocotrienol (gamma-tocotrienol) on the static and dynamic bone histomorphometric parameters in normal male rats. Thirty-two normal Sprague-Dawley male rats aged 3 months and weighing 200-250 g were randomly divided into four groups. The control group was supplemented with oral gavages of olive oil (vehicle), whereas the alpha-tocopherol, delta-tocotrienol, and gamma-tocotrienol groups were given oral gavages of 60 mg/kg alpha-tocopherol, delta-tocotrienol, and gamma-tocotrienol, respectively. The rats were injected twice with calcein to fluorochrome-label the bones. After 4 months of treatment, the rats were killed, and the left femurs were dissected out and prepared for bone histomorphometry. Both the static and dynamic parameters of the vitamin E-treated groups were better than those of the normal control group. Among the vitamin E-treated groups, the tocotrienol groups showed better histomorphometry results compared to the α-tocopherol group, with the γ-tocotrienol group demonstrating the best effects on both sets of parameters. We concluded that vitamin E can promote bone formation in normal rats, with gamma-tocotrienol being the most potent form of vitamin E.

Sodium fluoride influences the expression of keratins in cultured keratinocytes

Epithelia in lung, skin, and kidney are often exposed to fluoride, and tissue damage in lung and kidney due to fluoride is well documented. Nevertheless, the biological effects of fluoride on epithelia are poorly investigated. In the present study, we report effects of sodium fluoride (NaF) on the differentiation of a human epithelial cell line, HaCaT. These cells may serve as a keratinocyte model, because they express a wide spectrum of keratins (Ks), and they associate into stratified tissue-like arrangements along with changes in their keratin pattern. NaF was added to the culture medium at concentrations of 0.5 and 5 mM. Cell proliferation remained intact, but cell functions were altered at high dose, and HSP70 was induced. Reverse transcription-polymerase chain reaction and Western blotting revealed that keratin (K) 15 mRNA and protein expression, associated with stratification of epithelia, were inhibited. Also, expression of keratins typical for terminal differentiation, K1 and K10, was decreased and so was the expression of the K1/10 regulating enhancer binding protein c/EBP alpha. Stratification of HaCaT cells was abolished at high fluoride dose, as assessed by electron microscopy. The changes in keratin expression were not reversed by withdrawal of fluoride. Taken together, NaF at high dose blocked terminal differentiation of HaCaT cells, visible by keratin expression and failing stratification. This effect may disturb tissue formation due to altered cell interactions.

Quantitative (31)P NMR spectroscopy and (1)H MRI measurements of bone mineral and matrix density differentiate metabolic bone diseases in rat models

In this study, bone mineral density (BMD) of normal (CON), ovariectomized (OVX), and partially nephrectomized (NFR) rats was measured by (31)P NMR spectroscopy; bone matrix density was measured by (1)H water- and fat-suppressed projection imaging (WASPI); and the extent of bone mineralization (EBM) was obtained by the ratio of BMD/bone matrix density. The capability of these MR methods to distinguish the bone composition of the CON, OVX, and NFR groups was evaluated against chemical analysis (gravimetry). For cortical bone specimens, BMD of the CON and OVX groups was not significantly different; BMD of the NFR group was 22.1% (by (31)P NMR) and 17.5% (by gravimetry) lower than CON. For trabecular bone specimens, BMD of the OVX group was 40.5% (by (31)P NMR) and 24.6% (by gravimetry) lower than CON; BMD of the NFR group was 26.8% (by (31)P NMR) and 21.5% (by gravimetry) lower than CON. No significant change of cortical bone matrix density between CON and OVX was observed by WASPI or gravimetry; NFR cortical bone matrix density was 10.3% (by WASPI) and 13.9% (by gravimetry) lower than CON. OVX trabecular bone matrix density was 38.0% (by WASPI) and 30.8% (by gravimetry) lower than CON, while no significant change in NFR trabecular bone matrix density was observed by either method. The EBMs of OVX cortical and trabecular specimens were slightly higher than CON but not significantly different from CON. Importantly, EBMs of NFR cortical and trabecular specimens were 12.4% and 26.3% lower than CON by (31)P NMR/WASPI, respectively, and 4.0% and 11.9% lower by gravimetry. Histopathology showed evidence of osteoporosis in the OVX group and severe secondary hyperparathyroidism (renal osteodystrophy) in the NFR group. These results demonstrate that the combined (31)P NMR/WASPI method is capable of discerning the difference in EBM between animals with osteoporosis and those with impaired bone mineralization.

Compressive axial mechanical properties of rat bone as functions of bone volume fraction, apparent density and micro-ct based mineral density

Mechanical testing has been regarded as the gold standard to investigate the effects of pathologies on the structure-function properties of the skeleton. With recent advances in computing power of personal computers, virtual alternatives to mechanical testing are gaining acceptance and use. We have previously introduced such a technique called structural rigidity analysis to assess mechanical strength of skeletal tissue with defects. The application of this technique is predicated upon the use of relationships defining the strength of bone as a function of its density for a given loading mode. We are to apply this technique in rat models to assess their compressive skeletal response subjected to a host of biological and pharmaceutical stimulations. Therefore, the aim of this study is to derive a relationship expressing axial compressive mechanical properties of rat cortical and cancellous bone as a function of equivalent bone mineral density, bone volume fraction or apparent density over a range of normal and pathologic bones. We used bones from normal, ovariectomized and partially nephrectomized animals. All specimens underwent micro-computed tomographic imaging to assess bone morphometric and densitometric indices and uniaxial compression to failure. We obtained univariate relationships describing 71-78% of the mechanical properties of rat cortical and cancellous bone based on equivalent mineral density, bone volume fraction or apparent density over a wide range of density and common skeletal pathologies. The relationships reported in this study can be used in the structural rigidity analysis introduced by the authors to provide a non-invasive method to assess the compressive strength of bones affected by pathology and/or treatment options.

Comparison of failure mechanisms for cements used in skeletal luting applications

Glass Polyalkenoate Cements (GPCs) based on strontium calcium zinc silicate (Sr-Ca-Zn-SiO(2)) glasses and low molecular weight poly(acrylic acid) (PAA) have been shown to exhibit suitable compressive strength (65 MPa) and flexural strength (14 MPa) for orthopaedic luting applications. In this study, two such GPC formulations, alongside two commercial cements (Simplex P and Hydroset) were examined. Fracture toughness and tensile bond strength to sintered hydroxyapatite and a biomedical titanium alloy were examined. Fracture toughness of the commercial Poly(methyl methacrylate) cement, Simplex P, (3.02 MPa m(1/2)) was superior to that of the novel GPC (0.36 MPa m(1/2)) and the commercial calcium phosphate cement, Hydroset, for which no significant fracture toughness was obtained. However, tensile bond strengths of the novel GPCs (0.38 MPa), after a prolonged period (30 days), were observed to be superior to commercial controls (Simplex P: 0.07 MPa, Hydroset: 0.16 MPa).

Shortcomings of DXA to assess changes in bone tissue density and microstructure induced by metabolic bone diseases in rat models

The aim of this study is to demonstrate the deficiencies of dual-energy X-ray absorptiometry (DXA), compared with quantitative computed tomography, to reflect and differentiate between changes in bone mineral density and microstructure that contribute to a well-defined finding of altered skeletal state for both osteoporosis and renal osteodystrophy induced by chronic renal insufficiency.

INTRODUCTION

The aim of this study is to demonstrate the deficiencies of dual-energy X-ray absorptiometry (DXA), compared with quantitative CT, to reflect and differentiate between changes in bone mineral density and microstructure that contribute to a well-defined finding of altered skeletal state for both osteoporosis and renal osteodystrophy induced by chronic renal insufficiency.

METHODS

Forty-five female Sprague-Dawley rats were divided into three equal groups: control, ovariectomy, and nephrectomy. Following euthanasia, femurs were excised, divided into diaphyseal and distal metaphyseal sections, and subjected to DXA and micro-CT imaging and mechanical testing.

RESULTS

Ovariectomy does not affect the structural and mechanical properties of cortical bone material, but partial nephrectomy does adversely affect these properties. Both are verified by DXA and micro-CT imaging and mechanical testing. Meanwhile, nephrectomy does not affect trabecular bone microstructure or equivalent density, yet ovariectomy affects the trabecular microstructure. DXA is unable to detect changes in trabecular bone microstructure in relation to changes in their mechanical properties.

DISCUSSION

Dual energy X-ray absorptiometry measures the average bone mineral content in a 2D projected area and cannot differentiate whether the changes occur in the bone microstructure or equivalent bone tissue density. In contrast, micro-CT provides an accurate measurement of the changes in both equivalent bone tissue mineral density and microstructure for cancellous and cortical bone.

High-frequency oscillatory motions enhance the simulated mechanical properties of non-weight bearing trabecular bone

Extremely low-level oscillatory accelerations, applied without constraint, can increase bone formation. Here, we tested the hypothesis that high-frequency oscillations, applied in the absence of functional weight bearing, can be sensed by trabecular bone to produce a structure that is more efficient in sustaining applied loads. The left leg of anesthetized adult female mice (n=18) was subjected to high-frequency oscillations at 45 Hz, 0.6g for 20 min/day, 5 days/week for 3 weeks, while the contralateral leg served as an internal control. To remove the potential interference of the habitual strain environment with the imposed physical signal, the hindlimbs of these mice were chronically unloaded. In vivo microCT scans of the proximal metaphyseal region of the tibia were transformed into finite element meshes to evaluate trabecular and cortical mechanical properties. Simulated longitudinal compression tests showed that the short applications of high-frequency oscillations were sensed primarily by trabecular bone. At the end of the experimental period, apparent trabecular stiffness of the oscillated bones was 38% (p<0.001) greater than that of non-weight bearing controls. Simulated uniaxial loads applied to trabecular bone induced 21%, 52%, and 131% greater (p<0.05) median, peak compressive, and peak tensile longitudinal stresses in control than in stimulated bones. Non-weight bearing control bones were also characterized by greater transverse normal and shear stresses (77% and 54%, respectively, p<0.001) as well as 35% greater (p=0.03) longitudinal shear stresses. Compared to normal age-matched controls (n=18), oscillations were able to attenuate, but not fully prevent, the decline in trabecular mechanical properties associated with the removal of weight bearing. These data indicate not only that bone cells can sense low-level, high-frequency oscillatory accelerations, but also that they can orchestrate a structural response that produces a stiffer trabecular structure that may be less prone to fracture.

Recommendations for an update of the current (2001) regulatory requirements for registration of drugs to be used in the treatment of osteoporosis in postmenopausal women and in men

Recent advances in the understanding of the epidemiology of osteoporosis suggest that certain parts of the current European guidelines for the registration of drugs in osteoporosis might be no longer substantiated. The object of this review is to provide the European regulatory authorities with an evidence-based working document providing suggestions for the revision of the "Note for guidance for the approval of drugs to be used in postmenopausal osteoporosis" (CPMP/EWP/552/95). Following an extensive review of the literature (1990-2004), the Group for the Respect of Ethics and Excellence in Science (GREES) organized a workshop including European regulators, academic scientists and representatives of the pharmaceutical industry. The outcomes of this meeting reflect the personal views of those who attended and should not, in any case, be seen as an official position paper of any regulatory agency. The group identified a certain number of points that deserve discussion. They mainly relate to the nature of the indication being granted to new chemical entities (treatment of osteoporosis in women at high risk of fracture instead of prevention and treatment of osteoporosis), the requirements of showing an anti-fracture efficacy on all or on major nonvertebral fractures (instead of the hip), the duration of pivotal trials (2 years instead of 3) and the possibility of considering bridging studies for new routes of administration, new doses or new regimens of previously approved drugs. The group also recommends that an indication could be granted for the treatment of osteoporosis in males on the basis of a placebo-controlled study, with bone mineral density changes after 1 year as the primary endpoint, for medications approved in the treatment of osteoporosis in women at high risk of fractures.

Effects of Vitamin K1 on fluoride-induced bone changes in growing rats: A histomorphometric and radiodensitometric study

The aim of this study was to investigate the potential effects of Vitamin K(1) supplementation on skeletal changes related to fluoride in growing rats. Forty male Wistar rats aged 4 weeks were assigned at random into three groups: high-dose fluoride (125 ppm) group; high-dose fluoride+Vitamin K(1) (0.2mg/(g day)) group; and a control group. The experimental period was 12 weeks. The L(3) vertebrae and the right tibiae were removed, and specimens were analysed by histologic and histomorphometric methods. Quantitative radiodensitometry was also employed to assess the differences in bone mineral density (BMD) between the groups. In the tibia, total tissue area was higher in the study groups than the control group (P<0.05). Cortical bone area was slightly higher in the fluoride+K(1) group than the fluoride group, and marrow cavity area was lower in the fluoride+K(1) group (P<0.05). In the L3 vertebral cancellous bone, bone volume, trabecular number and trabecular thickness were higher in the study groups than the control group (P<0.05). Trabecular separation was reduced in the study groups (P<0.05), and was lower in the fluoride+K(1) group than the fluoride group (P<0.05). The fluoride+K(1) group had a significantly higher BMD than the other groups (P<0.05), and the fluoride group had a significantly higher BMD than the control group (P<0.05). The present study found that fluoride administration increased bone mass in both vertebrae and tibiae in growing rats. Simultaneous administration of Vitamin K(1) and fluoride resulted in an additional increase in vertebral bone mass.

Effect of ultrastructural changes on the toughness of bone

The ultrastructure of bone can be considered as a conjunction between the biology and the biomechanics of the tissue. It is the result of cellular and molecular activities of bone formation, and its organization dominates the mechanical behavior of bone. Following this perspective, the objective of this review is to provide a current understanding of bone ultrastructure and its relationships with the toughness of the tissue. Therefore, we first provide a discussion on the organization of bone constituents, namely collagen, mineral, and water. Then, we present evidence on how the toughness of bone relates to its ultrastructure through the formation of micro damage. In addition, attention is given to how damage accumulation serves as a toughening mechanism. Finally, we describe how changes in the ultrastructure-caused by osteogenesis imperfecta, gamma irradiation, fluoride treatment, and aging affect the toughness and competence of bone.

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.

Strontium ranelate: a novel mode of action leading to renewed bone quality

Various bone resorption inhibitors and bone stimulators have been shown to decrease the risk of osteoporotic fractures. However, there is still a need for agents promoting bone formation by inducing positive uncoupling between bone formation and bone resorption. In vitro studies have suggested that strontium ranelate enhances osteoblast cell replication and activity. Simultaneously, strontium ranelate dose-dependently inhibits osteoclast activity. In vivo studies indicate that strontium ranelate stimulates bone formation and inhibits bone resorption and prevents bone loss and/or promotes bone gain. This positive uncoupling between bone formation and bone resorption results in bone gain and improvement in bone geometry and microarchitecture, without affecting the intrinsic bone tissue quality. Thus, all the determinants of bone strength are positively influenced. In conclusion, strontium ranelate, a new treatment of postmenopausal osteoporosis, acts through an innovative mode of action, both stimulating bone formation and inhibiting bone resorption, resulting in the rebalancing of bone turnover in favor of bone formation. Strontium ranelate increases bone mass while preserving the bone mineralization process, resulting in improvement in bone strength and bone quality.

Infrared imaging of calcified tissue in bone biopsies from adults with osteomalacia

Osteomalacia is a pathological bone condition in which there is deficient primary mineralization of the matrix, leading to an accumulation of osteoid tissue and reduced bone mechanical strength. The hypothesis that there are no qualitative or quantitative differences in osteomalacic bone mineral or matrix compared to disease-free bones was tested by examining unstained sections of polymethyl methacrylate (PMMA) embedded iliac crest biopsies using Fourier transform infrared imaging (FTIRI) at approximately 6-microm spatial resolution. Controls were seven female subjects, aged 36-57, without apparent bone disease. The experimental group consisted of 11 patients aged 22-72, diagnosed with osteomalacia. The spectroscopic parameters analyzed in each data set were previously established as sensitive to bone quality: phosphate/amide I band area ratio (mineral content), 1660/1690 cm(-1) peak ratio (collagen cross-links), and the 1030/1020 cm(-1) peak ratio (mineral crystallinity). The correspondence between spectroscopic mineral content (phosphate/amide I ratio) and ash weight was validated for apatite crystals of different composition and crystallite size. The FTIRI results from the biopsies expressed as color-coded images and pixel population means were compared with the nonparametric Mann-Whitney U test. There were no significant differences in the cortical parameters. Significant difference was found in the mineral content of the trabecular regions with a lower mean value in osteomalacia (P = 0.01) than in controls. Mineral crystallinity tended to be decreased in the trabecular bone (P = 0.09). This study supports the hypothesis that, in osteomalacia, the quality of the organic matrix and of mineral in the center of bone does not change, while less-than-optimal mineralization occurs at the bone surface. This study provides the first spectroscopic evaluation of whole bone mineral and matrix properties in osteomalacia, demonstrating that there are few differences in collagen cross-links between biopsies from patients with osteomalacia and from individuals without histological evidence of bone disease.

Association between fluoride, magnesium, aluminum and bone quality in renal osteodystrophy

INTRODUCTION

Trace elements are known to influence bone metabolism; however, their effects may be exacerbated in renal failure because dialysis patients are unable to excrete excess elements properly. Our study correlated bone quality in dialysis patients with levels of bone fluoride, magnesium, and aluminum. A number of studies have linked trace elements, including fluoride, magnesium, and aluminum, to the development of renal osteodystrophy (ROD). However, little is known about the relationship between trace elements and changes in bone quality in ROD patients. The purpose of this study was to examine bone quality in ROD patients, and correlate differences in bone quality to trace element concentrations in bone. Bone quality encompasses parameters that contribute to the mechanical integrity of the bone.

METHODS

One hundred fifty-three anterior iliac crest bone biopsies from patients with ROD were examined and subdivided into five groups based on the pathological features. Parameters contributing to bone quality, such as bone structure and remodeling, connectivity, mineralization, and microhardness, were assessed and correlated to bone chemical composition. In addition, clinical symptoms of ROD were assessed and correlated with bone composition.

RESULTS AND CONCLUSIONS

There were no differences in bone architecture between the different ROD bone groups; however, differences in bone mineralization and microhardness were observed. Increase in bone fluoride was associated with increased osteoid parameters and decreased bone microhardness. Bone mineralization and microhardness decreased with increasing bone magnesium content and intact parathyroid hormone (PTH) level. Moreover, bone magnesium increased with intact PTH levels. The relationship between PTH, bone magnesium, mineralization, and microhardness was primarily observed in aplastic bone disorder. Furthermore, bone magnesium and aluminum contents were positively associated with bone pain and proximal myopathy in these patients. Most importantly, fluoride, magnesium, and aluminum showed significant correlations with one another. These results suggested that in ROD, bone fluoride may diminish bone microhardness by interfering with mineralization. Magnesium may be involved in the suppression of PTH secretion, lowering bone turnover thus leading to an increase in bone mineralization profile and microhardness in aplastic bone disorder. The effects of fluoride and magnesium on bone quality may be exacerbated by their interaction with aluminum.

Mechanical and chemical characteristics of mineral produced by basic fibroblast growth factor-treated bone marrow stromal cells in vitro

It has been shown that various organ and cell cultures exhibit increased mineral formation with the addition of basic fibroblast growth factor (bFGF) and phosphate ions in the medium. However, to date there has been no attempt to relate the chemical composition of mineral formed in vitro to a measure of its mechanical properties. This information is important for understanding the in vivo mineralization process, the development of in vitro models, and the design of tissue-engineered bone substitutes. In this study we examined the reduced modulus; hardness; and mineral-to-matrix, crystallinity, carbonate-to-mineral, and calcium-to-phosphorus ratios of mineral formed by bFGF-treated rat-derived bone marrow stromal cells in vitro. The cells were treated with 1 or 3 mM beta-glycerophosphate for 3 and 4 weeks. Both mechanical parameters, reduced modulus and hardness, increased with increasing beta-glycerophosphate concentration. The only chemical measure of the mineral composition that exhibited the same dependency was the mineral-to-matrix ratio. The values of crystallinity and carbonate fraction were similar to those for intact cortical bone, but the calcium-to-phosphorus ratio was substantially lower than that of normal bone. These data indicate that the mineral formed by bFGF-treated bone cells is mechanically and chemically different from naturally formed lamellar bone tissue after 4 weeks in culture. These results can be used to improve in vitro models of mineral formation as well as enhance the design of tissue-engineered bone substitutes.

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.

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.

Hyperkalemia risks in hemodialysed patients consuming fluoride-rich water

In order to observe the consequences of chronic ingestion of high fluoride-rich water on plasma potassium levels of hemodialysed subjects, we have conducted a retrospective study on 25 patients with chronic renal failure, treated with a substitute method, six of whom (consumers group, group C) were drinkers of a bicarbonate (about 4500 mg/l) and fluoride-rich (9 mg/l) mineral water, the Vichy Saint-Yorre water. With respect to sodium polystyrene sulfonate consumption (n = 17), there was no significant difference between group C and NC (non-consumers group). A significant correlation between plasma fluoride and potassium levels was observed only before dialysis (P < 1 x 10(-7)) but not after dialysis. A group by group analysis revealed that this correlation was linked to group C (P < 5 x 10(-6)), in which kalemia before dialysis was higher than that observed in group NC (P < 0.005). Moreover, it appeared that the higher fluoride levels were, the higher the kalemia was inclined to be. Thus, the risks of hyperkalemia in dialysed patients, who also drink Vichy St-Yorre water or other fluoride-rich waters, are more important, while not forgetting the risk of fluorosis. The mechanisms by which chronically administered fluoride could increase kalemia are also discussed.

Chronic fluoride exposure does not cause detrimental, extraskeletal effects in nutritionally deficient rats

On the basis of observations that endemic fluorosis occurs more often in malnourished populations, a series of studies tested the hypothesis that deficient dietary intake of calcium, protein or energy affects fluoride metabolism so that the margin of safe fluoride exposure may be reduced. The objective of the investigation was to determine whether changes in fluoride metabolism in nutritionally deficient rats resulted in manifestation of any extraskeletal toxic fluoride effects not observed in healthy animals. This investigation included two studies, one that monitored the effect of calcium deficiency on the effects of chronic fluoride exposure, and a second study that observed fluoride effects in rats that were deficient either in protein or in energy and total nutrient intake. Control and experimental rats received drinking water containing 0, 0.26 (5), 0.79 (15) or 2.63 (50) mmol fluoride/L (mg/L) for 16 or 48 wk. Control rats were fed optimal diets and experimental rats were fed diets deficient in calcium (Study 1) or protein (Study 2). An additional group of experimental rats (Study 2) was provided with a restricted amount of diet; thus these rats were deficient in energy and total nutrient intake. The intake, excretion and retention of fluoride were monitored; after the rats were killed, tissue fluoride levels and biochemical markers of tissue function were analyzed. Bone marrow cells were harvested from some of the rats, after 48 wk of treatment, for determining the frequency of sister chromatid exchange, a marker of genetic damage. Although there were significant differences among fluoride treatment groups in fluoride excretion and retention that resulted in significantly greater fluoride levels in tissues of the experimental rats, we were unable to detect any harmful, extraskeletal biochemical, physiologic or genetic effects of fluoride in the nutritionally deficient rats.

Investigation of fluoride elimination during a dialysis session

We have conducted a study of the elimination kinetics of fluoride ions by a log linear regression analysis of plasma levels obtained during a bicarbonate hemodialysis session, with a dialyzer in polymercaprin for six patients with chronic renal failure. Using plasma fluoride levels of 35 patients studied for 20 months, we have validated these kinetics for hemodialysis with sodium bicarbonate, acetate-free biofiltration, hemodiafiltration with low flow rate and other dialyzers. Our results show that the decrease in plasma fluoride levels is statistically significant only after the first hour, and the fall reaches approximately 30% after a 4 h dialysis session. We propose that post-dialysis measurements of plasma fluoride are now not necessary if levels before dialysis are known.