Disparate effects of mild, moderate, and severe secondary hyperparathyroidism on cancellous and cortical bone in rats with chronic renal insufficiency

Increased PHOSPHO1 expression mediates cortical bone mineral density in renal osteodystrophy

Patients with advanced chronic kidney disease (CKD) often present with skeletal abnormalities, a condition known as renal osteodystrophy (ROD). While tissue non-specific alkaline phosphatase (TNAP) and PHOSPHO1 are critical for bone mineralization, their role in the etiology of ROD is unclear. To address this, ROD was induced in both WT and Phospho1 knockout (P1KO) mice through dietary adenine supplementation. The mice presented with hyperphosphatemia, hyperparathyroidism, and elevated levels of FGF23 and bone turnover markers. In particular, we noted that in CKD mice, bone mineral density (BMD) was increased in cortical bone (P < 0.05) but decreased in trabecular bone (P < 0.05). These changes were accompanied by decreased TNAP (P < 0.01) and increased PHOSPHO1 (P < 0.001) expression in WT CKD bones. In P1KO CKD mice, the cortical BMD phenotype was rescued, suggesting that the increased cortical BMD of CKD mice was driven by increased PHOSPHO1 expression. Other structural parameters were also improved in P1KO CKD mice. We further investigated the driver of the mineralization defects, by studying the effects of FGF23, PTH, and phosphate administration on PHOSPHO1 and TNAP expression by primary murine osteoblasts. We found both PHOSPHO1 and TNAP expressions to be downregulated in response to phosphate and PTH. The in vitro data suggest that the TNAP reduction in CKD-MBD is driven by the hyperphosphatemia and/or hyperparathyroidism noted in these mice, while the higher PHOSPHO1 expression may be a compensatory mechanism. Increased PHOSPHO1 expression in ROD may contribute to the disordered skeletal mineralization characteristic of this progressive disorder.

Cortical and trabecular bone are equally affected in rats with renal failure and secondary hyperparathyroidism

Background

Changes in mineral metabolism and bone structure develop early in the course of chronic kidney disease and at end-stage are associated with increased risk of fragility fractures. The disruption of phosphorus homeostasis leads to secondary hyperparathyroidism, a common complication of chronic kidney disease. However, the molecular pathways by which high phosphorus influences bone metabolism in the early stages of the disease are not completely understood. We investigated the effects of a high phosphorus diet on bone and mineral metabolism using a 5/6 nephrectomy model of chronic kidney disease.

Methods

Four-week old rats were randomly assigned into groups: 1) Control with standard diet, 2) Nephrectomy with standard rodent diet, and 3) Nephrectomy with high phosphorus diet. Rats underwent in vivo imaging at baseline, day 14, and day 28, followed by ex vivo imaging.

Results

Cortical bone density at the femoral mid-diaphysis was reduced in nephrectomy-control and nephrectomy-high phosphorus compared to control rats. In contrast, trabecular bone mass was reduced at both the lumbar vertebrae and the femoral secondary spongiosa in nephrectomy-high phosphorus but not in nephrectomy-control. Reduced trabecular bone volume adjusted for tissue volume was caused by changes in trabecular number and separation at day 35. Histomorphometry revealed increased bone resorption in tibial secondary spongiosa in nephrectomy-control. High phosphorus diet-induced changes in bone microstructure were accompanied by increased serum parathyroid hormone and fibroblast growth factor 23 levels.

Conclusion

Our study demonstrates that changes in mineral metabolism and hormonal dysfunction contribute to trabecular and cortical bone changes in this model of early chronic kidney disease.

Etelcalcetide (AMG 416), a peptide agonist of the calcium-sensing receptor, preserved cortical bone structure and bone strength in subtotal nephrectomized rats with established secondary hyperparathyroidism

Sustained elevation of parathyroid hormone (PTH) is catabolic to cortical bone, as evidenced by deterioration in bone structure (cortical porosity), and is a major factor for increased fracture risk in chronic kidney disease (CKD). Etelcalcetide (AMG 416), a novel peptide agonist of the calcium-sensing receptor, reduces PTH levels in subtotal nephrectomized (Nx) rats and in hemodialysis patients with secondary hyperparathyroidism (SHPT) in clinical studies; however, effects of etelcalcetide on bone have not been determined. In a rat model of established SHPT with renal osteodystrophy, etelcalcetide or vehicle was administered by subcutaneous (s.c.) injection to subtotal Nx rats with elevated PTH (>750pg/mL) once per day for 6weeks. Sham-operated rats receiving vehicle (s.c.) served as non-SHPT controls. Prior to treatment, significant increases in serum creatinine (2-fold), blood urea nitrogen (BUN, 3-fold), PTH (5-fold), fibroblast growth factor-23 (FGF23; 13-fold) and osteocalcin (12-fold) were observed in SHPT rats compared to non-SHPT controls. Elevations in serum creatinine and BUN were unaffected by treatment with vehicle or etelcalcetide. In contrast, etelcalcetide significantly decreased PTH, FGF23 and osteocalcin, whereas vehicle treatment did not. Cortical bone porosity increased and bone strength decreased in vehicle-treated SHPT rats compared to non-SHPT controls. Cortical bone structure improved and energy to failure was significantly greater in SHPT rats treated with etelcalcetide compared to vehicle. Mineralization lag time and marrow fibrosis were significantly reduced by etelcalcetide. In conclusion, etelcalcetide reduced bone turnover, attenuated mineralization defect and marrow fibrosis, and preserved cortical bone structure and bone strength by lowering PTH in subtotal Nx rats with established SHPT.

The Influence of Chronic Kidney Disease on the Structural and Mechanical Properties of Canine Bone

Background

Chronic kidney disease (CKD) is common in companion animals. Secondary hyperparathyroidism is an inevitable consequence of the disease and may have deleterious effect on the bone; however, the information regarding CKD‐associated bone abnormalities in companion animals is scarce.

Hypothesis/Objectives

Dogs with CKD have decreased bone quality compared to dogs without CKD.

Animals

Nine dogs diagnosed with naturally occurring CKD for at least 6 months and 9 age‐matched controls.

Methods

Dogs with CKD were enrolled and compared to 9 age‐, weight‐, and sex‐matched control dogs with no evidence of CKD. Samples were assessed using light microscopy, mechanical testing, and microcomputed tomography. Variables evaluated included microstructural features such as number, size, and density of Haversian canals, resorption cavities and osteocytic lacunae, bone mineral density, porosity and Young's modulus.

Results

Median lacunae size was significantly smaller in the CKD group compared to the control group (P = 0.001). Resorption cavity density was higher in the CKD compared to the control group (10 [8–14] vs. 7 [4–9]/mm², respectively, P = 0.001). Overall porosity was significantly (2.3‐fold) higher in the CKD compared to the control group. There was no difference in Young's moduli between groups.

Conclusions and Clinical Importance

Naturally occurring CKD affects bone quality in dogs, but these changes are relatively mild and likely not to be manifested clinically. The duration of the disease in dogs evaluated here is short compared to cats and human patients, likely accounting for the more subtle changes in dogs compared to other species.

Elevated Levels of Peripheral Kynurenine Decrease Bone Strength in Rats with Chronic Kidney Disease

The diagnosis and treatment of bone disorders in patients with chronic kidney disease (CKD) represent a clinical challenge. CKD leads to mineral and bone complications starting early in the course of renal failure. Recently, we have observed the positive relationship between intensified central kynurenine turnover and bone strength in rats with subtotal 5/6 nephrectomy (5/6 Nx)-induced CKD. The aim of the present study was to determine the association between peripheral kynurenine pathway metabolites and bone strength in rats with 5/6 Nx-induced CKD. The animals were sacrificed 1 and 3 months after 5/6 Nx or sham operation. Nephrectomized rats presented higher concentrations of serum creatinine, urea nitrogen, and parathyroid hormone both 1 and 3 months after nephrectomy. These animals revealed higher concentrations of kynurenine and 3-hydroxykynurenine in the serum and higher gene expression of aryl hydrocarbon receptor (AhR) as a physiological receptor for kynurenine and AhR-dependent cytochrome in the bone tissue. Furthermore, nephrectomy significantly increased the number of osteoclasts in the bone without affecting their resorptive activity measured in serum. These changes were particularly evident in rats 1 month after 5/6 Nx. The main bone biomechanical parameters of the tibia were unchanged between nephrectomized and sham-operated rats but were significantly increased in older compared to younger animals. A similar trend was observed for geometrical parameters measured with calipers, bone mineral density based on Archimedes' method and image of bone microarchitecture obtained from micro-computed tomography analyses of tibial cortical bone. In nephrectomized animals, peripheral kynurenine levels correlated negatively with the main parameters of bone biomechanics, bone geometry, and bone mineral density values. In conclusion, our data suggest that CKD-induced elevated levels of peripheral kynurenine cause pathological changes in bone structure via AhR pathway. This finding opens new opportunities for the treatment/prevention of osteoporosis in CKD.

Inhibition of GSK-3β increases trabecular bone volume but not cortical bone volume in adenine-induced uremic mice with severe hyperparathyroidism

Patients with chronic kidney disease (CKD) are at increased risk for bone fractures compared with the general population. Repression of the Wnt/β‐catenin signaling pathway is associated with bone abnormalities. Inhibition of glycogen synthase kinase (GSK)‐3β, a critical component of the Wnt/β‐catenin signaling pathway, increases bone volume through accumulation of β‐catenin. It remains unknown whether inhibition of GSK‐3β increases bone volume in CKD. The present in vivo study examined the effects of GSK‐3β inhibition on bone volume in CKD mice. Wild‐type mice were divided into three groups. One group was fed a control diet (CNT) and the other two groups were fed a diet containing 0.2% adenine and given water with or without lithium chloride (LiCl), a GSK‐3 inhibitor (CKD, CKD+LiCl, respectively). GSK‐3β heterozygous knockout mice were fed a diet containing 0.2% adenine (CKD‐GSK‐3β^+/−). After 6 weeks, trabecular and cortical bone volumes of the femur were analyzed using microcomputed tomography. CKD mice developed azotemia, hyperphosphatemia, and hyperparathyroidism, followed by a decrease in cortical bone volume without any change in trabecular bone volume. Serum levels of urea nitrogen, phosphate, and parathyroid hormone were comparable among the three groups of CKD mice. Trabecular bone volume increased in CKD‐GSK‐3β^+/− and CKD+LiCl mice compared with CNT and CKD mice. However, there were no significant differences in cortical bone volume among the three groups of CKD mice. The results suggest that inhibition of GSK‐3β increases trabecular bone volume but not cortical bone volume in adenine‐induced uremic mice with uncontrolled hyperparathyroidism.

An update on bone imaging and markers in chronic kidney disease

Bone disorders in chronic kidney disease (CKD) are associated with heightened risks of fractures, vascular calcification, poor quality of life and mortality compared to the general population. However, diagnosis and management of these disorders in CKD are complex and appreciably limited by current diagnostic modalities. Areas covered: Bone histomorphometry remains the gold standard for diagnosis but is not widely utilised and lacks feasibility as a monitoring tool. In practice, non-invasive imaging and biochemical markers are preferred to guide therapeutic decisions. Expert commentary: This review aims to summarize the risk factors for, and spectrum of bone disease in CKD, as well as appraise the clinical utility of dual energy X-ray densitometry, peripheral quantitative computed tomography, high-resolution peripheral quantitative computed tomography, and bone turnover markers.

The Association between Elevated Levels of Peripheral Serotonin and Its Metabolite - 5-Hydroxyindoleacetic Acid and Bone Strength and Metabolism in Growing Rats with Mild Experimental Chronic Kidney Disease

Chronic kidney disease (CKD) is associated with disturbances in bone strength and metabolism. The alterations of the serotonergic system are also observed in CKD. We used the 5/6 nephrectomy model of CKD to assess the impact of peripheral serotonin and its metabolite– 5-hydroxyindoleacetic acid on bone biomechanical properties and metabolism in growing rats. The animals were sacrificed one and three months after nephrectomy. Biomechanical properties were determined on two different bone types: the cortical bone of the femoral diaphysis using three-point bending test and the mixed cortico-trabecular bone by the bending test of the femoral neck. Biomechanical tests revealed preserved cortical bone strength, whereas work to fracture (W) and yield load (F_y) of mixed cortico-trabecular bone were significantly lower in CKD compared to controls. Serum activity of alkaline phosphatase (ALP), a bone formation marker, and tartrate-resistant acid phosphatase (TRACP 5b) reflecting bone resorption, were similar in CKD and controls. ALP was associated with lower femoral stiffness and strength, and higher displacements and W. TRACP 5b was inversely associated with cortical F_u and W. The elevated peripheral serotonergic system in CKD was: inversely associated with stiffness but positively related to the displacements and W; inversely associated with cortical F_y but positively correlated with this parameter in cortico-trabecular bone; inversely associated with ALP in controls but positively correlated with this biomarker in CKD animals. In conclusion, this study demonstrates the distinct effect of mild degree of CKD on bone strength in rapidly growing rats. The impaired renal function affects the peripheral serotonin metabolism, which in turn may influence the strength and metabolism of bones in these rats. This relationship seems to be beneficial on the biomechanical properties of the cortico-trabecular bone, whereas the cortical bone strength can be potentially reduced.

The pitfall of treating low bone turnover: Effects on cortical porosity

Although it is recognized that cortical bone contributes significantly to the mechanical strength of the skeleton, little is known about this compartment from bone biopsy studies, particularly in CKD patients. In addition, there is no prospective data on the effects of CKD-MBD therapy on cortical porosity (Ct.Po). This is a post hoc analysis on data from a randomized controlled trial on the effects of different phosphate binders on bone remodelling. Therapy was adjusted according to the first biopsy, and included sevelamer or calcium acetate, calcitriol and changes in calcium dialysate concentration. We measured Ct.Po at baseline and one year after. Fifty-two patients (46±13years old, 67% women and 60% white) were enrolled. Ct.Po was already high at baseline in 85% of patients [30% (17, 46)] and correlated with PTH (p=0.001). Low bone turnover was seen in 28 patients (54.9%). After one-year treatment, PTH increased in patients with low turnover, as intended. However, increased Ct.Po was seen in 49 patients (94%). This increase correlated with the delta of phosphate (p=0.015) and the delta of PTH (p=0.03); it was also higher among non-white patients than in white patients (p=0.039). The risk of increase in Ct.Po was 4.5 higher among non-white patients. Adjusted multiple regression analysis showed that the delta of Ct.Po was dependent on delta PTH and race (r(2)=0.193). We concluded that in an attempt to increase bone turnover, the increase in PTH levels might be associated with higher cortical porosity, particularly in non-white patients. Whether this finding leads to a high risk of fracture deserves further investigation.

Does Secondary Renal Osteopathy Exist in Companion Animals?

Secondary renal hyperparathyroidism is an inevitable consequence of chronic kidney disease. In human patients, the disease is associated with decreased bone quality and increased fracture risk. Recent evidence suggests that bone quality is also decreased in companion animals, more pronouncedly in cats compared with dogs, likely because of a longer disease course. The clinical significance of these findings is yet to be determined. However, clinicians should keep in mind that animals with chronic kidney disease have decreased bone quality and increased fracture risk.

The effects of intervertebral disc degeneration combined with osteoporosis on vascularization and microarchitecture of the endplate in rhesus monkeys

PURPOSE

To evaluate the influence of osteoporosis on the microarchitecture and vascularization of the endplate in rhesus monkeys with or without intervertebral disc (IVD) degeneration using micro-computerized tomography (micro-CT), and to further analyze the correlation between osteoporosis and IVD degeneration.

METHODS

Twelve rhesus monkeys were randomly divided into the ovariectomy (OVX, n = 6) and the sham group (n = 6). The subchondral bone adjacent to the lumbar IVDs (from L4/5 to L6/7) of each monkey was randomly injected with 4 ml pingyangmycin (PYM) solution (1.5 mg/ml, PYM), or 4 ml phosphate buffered saline (PBS) as vehicle treatment, or exteriorized but not injected anything as control (Cntrl). Degenerative and osteoporotic processes were evaluated at different time points. Micro-CT and histology were performed to analyze microarchitecture, calcification area and vascularization of the endplate.

RESULTS

OVX resulted in significant decrease of bone mineral density (BMD). PYM injection induced progressively IVD degeneration, which was more progressive when combined with OVX. There was a negative correlation between BMD and Pfirrmann grade in the subgroups with PYM injection. The micro-CT analysis showed the combination of osteoporosis and IVD degeneration led to more calcification of endplate than any one thereof. The decrease of vascular volume percent in the endplate of the OVX-PYM subgroup was significantly greater than that in the Sham-PYM subgroup, both of which showed significant less vascularization compared to the other subgroups.

CONCLUSION

In conclusion the osteoporosis could accumulate the calcification and decrease the vascularization in the endplates adjacent to the degenerated IVDs, which subsequently exacerbated degeneration of the degenerated IVDs.

Changes in skeletal collagen cross-links and matrix hydration in high- and low-turnover chronic kidney disease

Chronic kidney disease (CKD) increases fracture risk. The results of this work point to changes in bone collagen and bone hydration as playing a role in bone fragility associated with CKD.

INTRODUCTION

Clinical data have documented a clear increase in fracture risk associated with chronic kidney disease (CKD). Preclinical studies have shown reductions in bone mechanical properties although the tissue-level mechanisms for these differences remain unclear. The goal of this study was to assess collagen cross-links and matrix hydration, two variables known to affect mechanical properties, in animals with either high- or low-turnover CKD.

METHODS

At 35 weeks of age (>75% reduction in kidney function), the femoral diaphysis of male Cy/+ rats with high or low bone turnover rates, along with normal littermate (NL) controls, were assessed for collagen cross-links (pyridinoline (Pyd), deoxypyridinoline (Dpd), and pentosidine (PE)) using a high-performance liquid chromatography (HPLC) assay as well as pore and bound water per volume (pw and bw) using a (1)H nuclear magnetic resonance (NMR) technique. Material-level biomechanical properties were calculated based on previously published whole bone mechanical tests.

RESULTS

Cortical bone from animals with high-turnover disease had lower Pyd and Dpd cross-link levels (-21% each), lower bw (-10%), higher PE (+71%), and higher pw (+46%) compared to NL. Animals with low turnover had higher Dpd, PE (+71%), and bw (+7%) along with lower pw (-60%) compared to NL. Both high- and low-turnover animals had reduced material-level bone toughness compared to NL animals as determined by three-point bending.

CONCLUSIONS

These data document an increase in skeletal PE with advanced CKD that is independent of bone turnover rate and inversely related to decline in kidney function. Although hydration changes occur in both high- and low-turnover disease, the data suggest that nonenzymatic collagen cross-links may be a key factor in compromised mechanical properties of CKD.

The effect of naturally occurring chronic kidney disease on the micro-structural and mechanical properties of bone

Chronic kidney disease (CKD) is a growing public health concern worldwide, and is associated with marked increase of bone fragility. Previous studies assessing the effect of CKD on bone quality were based on biopsies from human patients or on laboratory animal models. Such studies provide information of limited relevance due to the small size of the samples (biopsies) or the non-physiologic CKD syndrome studied (rodent models with artificially induced CKD). Furthermore, the type, architecture, structure and biology of the bone of rodents are remarkably different from human bones; therefore similar clinicopathologic circumstances may affect their bones differently. We describe the effects of naturally occurring CKD with features resembling human CKD on the skeleton of cats, whose bone biology, structure and composition are remarkably similar to those of humans. We show that CKD causes significant increase of resorption cavity density compared with healthy controls, as well as significantly lower cortical mineral density, cortical cross-sectional area and cortical cross-sectional thickness. Young's modulus, yield stress, and ultimate stress of the cortical bone material were all significantly decreased in the skeleton of CKD cats. Cancellous bone was also affected, having significantly lower trabecular thickness and bone volume over total volume in CKD cats compared with controls. This study shows that naturally occurring CKD has deleterious effects on bone quality and strength. Since many similarities exist between human and feline CKD patients, including the clinicopathologic features of the syndrome and bone microarchitecture and biology, these results contribute to better understanding of bone abnormalities associated with CKD.

Advanced glycation end products suppress lysyl oxidase and induce bone collagen degradation in a rat model of renal osteodystrophy

Renal osteodystrophy (ROD) is a major problem in patients with renal insufficiency. The present study was designed to elucidate the role of bone collagen changes and osteoblast differentiation in a rat model of ROD pathogenesis induced by adenine. Typical characteristics of renal failure, including increased serum urea nitrogen, creatinine, inorganic phosphorus, and intact parathyroid hormone levels, and decreased serum calcium and 1,25(OH)2D3 levels, were observed in adenine-induced rats. Micro-computed tomography analysis of the femur in adenine-induced rats showed decreased bone mineral density and osteoporotic changes, confirmed by the three-point bending test. The cancellous bone histomorphometric parameters of the tibia showed increased osteoblast number, decreased osteoclast surface with peritrabecular fibrosis, and increased osteoid tissue, indicating a severe mineralization disorder similar to clinical ROD. Scanning and transmission electron microscopy revealed irregular alignment and increased diameter of bone collagen fibrils in adenine-induced rats. Protein expression analysis showed greater accumulation of advanced glycation end products (AGEs) in peritrabecular osteoblasts of adenine-induced rats than in the controls. In contrast, suppressed expression of runt-related transcription factor 2, alkaline phosphatase, secreted phosphoprotein 1 (Spp1), and lysyl oxidase (Lox) mRNA levels, particularly the amount of active LOX protein, were observed. In in-vitro experiments, mineralizing MC3T3-E1 osteoblastic cells stimulated with AGE-modified bovine serum albumin had attenuated the expression of Spp1 mRNA levels and active LOX protein, with a decrease in extracellular nodules of mineralization. These observations provide clues to ROD pathogenesis, as they indicate that the suppression of osteoblast differentiation and decreased active LOX protein associated with accumulation of AGEs in osteoblasts caused structural abnormalities of bone collagen fibrils and a severe mineralization disorder, leading to bone fragility.

Alterations of bone microstructure and strength in end-stage renal failure

End-stage renal disease (ESRD) patients have a high risk of fractures. We evaluated bone microstructure and finite-element analysis-estimated strength and stiffness in patients with ESRD by high-resolution peripheral computed tomography. We observed an alteration of cortical and trabecular bone microstructure and of bone strength and stiffness in ESRD patients.

INTRODUCTION

Fragility fractures are common in ESRD patients on dialysis. Alterations of bone microstructure contribute to skeletal fragility, independently of areal bone mineral density.

METHODS

We compared microstructure and finite-element analysis estimates of strength and stiffness by high-resolution peripheral quantitative computed tomography (HR-pQCT) in 33 ESRD patients on dialysis (17 females and 16 males; mean age, 47.0 ± 12.6 years) and 33 age-matched healthy controls.

RESULTS

Dialyzed women had lower radius and tibia cortical density with higher radius cortical porosity and lower tibia cortical thickness, compared to controls. Radius trabecular number was lower with higher heterogeneity of the trabecular network. Male patients displayed only a lower radius cortical density. Radius and tibia cortical thickness correlated negatively with bone-specific alkaline phosphatase (BALP). Microstructure did not correlate with parathyroid hormone (PTH) levels. Cortical porosity correlated positively with "Kidney Disease: Improving Global Outcomes" working group PTH level categories (r = 0.36, p < 0.04). BMI correlated positively with trabecular number (r = 0.4, p < 0.02) and negatively with trabecular spacing (r = -0.37, p < 0.03) and trabecular network heterogeneity (r = -0.4, p < 0.02). Biomechanics positively correlated with BMI and negatively with BALP.

CONCLUSION

Cortical and trabecular bone microstructure and calculated bone strength are altered in ESRD patients, predominantly in women. Bone microstructure and biomechanical assessment by HR-pQCT may be of major clinical relevance in the evaluation of bone fragility in ESRD patients.

Relationship between aortic mineral elements and osteodystrophy in mice with chronic kidney disease

In chronic kidney disease (CKD), osteodystrophy and arterial calcification often coexist. However, arterial alterations have not been addressed in CKD unaccompanied by evidence of calcification. We investigated the association of phosphate (P) and calcium (Ca) accumulation in calcification-free aortas with CKD-induced osteodystrophy. Aortic accumulation of magnesium (Mg), an inhibitor of calcification, was also examined. Male mice aged 26 weeks with CKD characterized by hyperparathyroidism and hyperphosphatemia (Nx, n = 8) and age-matched healthy male mice (shams, n = 8) were sampled for blood, and thoracic vertebrae and aortas were harvested. Bone structure and chemicals were analyzed by microcomputed tomography and infrared microspectroscopy, respectively, and aortic accumulation of P, Ca, and Mg was evaluated by plasma-atomic emission spectrometry. Volume fractions of cortical and trabecular bones were smaller in Nx than in sham animals (P < 0.05), attributed to cortical thinning and reduction in trabecular number, respectively. Bone chemicals were not different between the groups. No calcification was found in either group, but P, Ca, and Mg contents were higher in Nx than in shams (P < 0.05). The mass ratio of Ca/P was lower in Nx than in shams (P < 0.05), but that of Mg/Ca and Mg/P was not different between the groups. Aortic P and Ca contents were inversely correlated with the volume fraction of cortical bone (P < 0.05). In conclusion, the relationship of osteodystrophy with aortic P and Ca accumulation suggests the existence of a bone-vascular axis, even in calcification-free arteries in CKD. The preservation of ratios of Mg/Ca and Mg/P despite CKD development might contribute to calcification resistance.

Over-expression of Adamts1 in mice alters bone mineral density

ADAMTS1, a secreted multifunctional metalloproteinase with disintegrin and thrombospondin motifs, is an early response gene of parathyroid hormone (PTH) in osteoblasts. Mice engineered to lack Adamts1 are smaller compared to wild-type (WT) mice and ADAMTS1 metalloproteinase activity has been shown to increase osteoblastic growth in collagen gels. However, there are no reports investigating the consequence of Adamts1 over-expression on bone tissue in vivo. Here, we analyze bones of female and male transgenic (TG) mice over-expressing mouse Adamts1 using peripheral quantitative computed tomography to evaluate its effect on bone shape and mineral density. Western blotting of protein extracts and immunohistochemistry of bone sections reveal increased presence of Adamts1 protein in TG bones compared to WT bones. Phenotypic analyses of femur show that female TG mice have reduced metaphyseal total density, trabecular bone mineral density and trabecular mineral content. In contrast, male TG mice which were without changes in the metaphysis showed increased total density and cortical density at the mid-diaphysis cortical site. Female TG mice showed no significant changes at the cortical site compared to WT mice. Furthermore, diaphyseal endosteal compartment was only affected in male TG mice. Along these lines, Adamts1 increased blood levels of PTH only in females whereas it reduced osteocalcin levels only in males. These results reveal that Adamts1 has an impact on bone mineral density and thus further confirm Adamts1 as a potent regulator of bone remodeling.

Bone turnover markers predict changes in bone mineral density after parathyroidectomy in patients with renal hyperparathyroidism

OBJECTIVE

Patients on long-term dialysis may develop secondary hyperparathyroidism (SHPT), which causes varying degrees of bone mass loss. This condition is treated with parathyroidectomy (PTX). We investigated whether serial serum bone turnover markers could predict changes in bone mineral density (BMD) after PTX.

DESIGN AND PATIENTS

Renal patients on maintenance haemodialysis who received PTX for refractory SHPT (n = 26, male/female: 13/13; mean age: 48·6 ± 10·7 year) and control subjects without SHPT (n = 25) were prospectively followed for 1 year at two tertiary hospitals in Taiwan.

MEASUREMENTS

Serum intact parathyroid hormone (iPTH), bone-specific alkaline phosphatase (BAP) and type 5b tartrate-resistant acid phosphatase (TRAP) were measured serially. Additionally, femoral neck (FN) and lumbar spine (LS) BMD were measured before and 1 year after PTX.

RESULTS

After PTX, iPTH levels decreased markedly and persistently. BMDs increased in both the FN and LS, but particularly in the LS. Serum BAP progressively increased to a peak at 2 weeks after PTX. Serum TRAP levels progressively decreased over 6 months after PTX. In univariate correlation analyses, baseline iPTH correlated positively with T-score changes in FN (r = 0·45, P = 0·021) and LS (r = 0·48, P = 0·013). In multivariate regression models, changes in FN T-scores were negatively predicted by baseline BAP levels (r = -0·615, P = 0·005) and baseline FN T-scores (r = -0·563, P = 0·012), and they were positively predicted by baseline TRAP(r = 0·6, P =  0·007). Changes in LS T-scores were positively predicted by baseline TRAP values (r = 0·528, P = 0·01) and negatively predicted by the percentage change in BAP after 2 weeks (r = -0·501, P = 0·015).

CONCLUSIONS

Parathyroidectomy provided marked, sustained improvements in BMD for up to 1 year. Furthermore, markers of bone turnover predicted 1-year changes in FN and LS BMDs after PTX.

Assessment of axial bone rigidity in rats with metabolic diseases using CT-based structural rigidity analysis

Objectives

This study aims to assess the correlation of CT-based structural rigidity analysis with mechanically determined axial rigidity in normal and metabolically diseased rat bone.

Methods

A total of 30 rats were divided equally into normal, ovariectomized, and partially nephrectomized groups. Cortical and trabecular bone segments from each animal underwent micro-CT to assess their average and minimum axial rigidities using structural rigidity analysis. Following imaging, all specimens were subjected to uniaxial compression and assessment of mechanically-derived axial rigidity.

Results

The average structural rigidity-based axial rigidity was well correlated with the average mechanically-derived axial rigidity results (R2 = 0.74). This correlation improved significantly (p < 0.0001) when the CT-based Structural Rigidity Analysis (CTRA) minimum axial rigidity was correlated to the mechanically-derived minimum axial rigidity results (R2 = 0.84). Tests of slopes in the mixed model regression analysis indicated a significantly steeper slope for the average axial rigidity compared with the minimum axial rigidity (p = 0.028) and a significant difference in the intercepts (p = 0.022). The CTRA average and minimum axial rigidities were correlated with the mechanically-derived average and minimum axial rigidities using paired t-test analysis (p = 0.37 and p = 0.18, respectively).

Conclusions

In summary, the results of this study suggest that structural rigidity analysis of micro-CT data can be used to accurately and quantitatively measure the axial rigidity of bones with metabolic pathologies in an experimental rat model. It appears that minimum axial rigidity is a better model for measuring bone rigidity than average axial rigidity.

Assessment of axial bone rigidity in rats with metabolic diseases using CT-based structural rigidity analysis

Objectives

This study aims to assess the correlation of CT-based structural rigidity analysis with mechanically determined axial rigidity in normal and metabolically diseased rat bone.

Methods

A total of 30 rats were divided equally into normal, ovariectomized, and partially nephrectomized groups. Cortical and trabecular bone segments from each animal underwent micro-CT to assess their average and minimum axial rigidities using structural rigidity analysis. Following imaging, all specimens were subjected to uniaxial compression and assessment of mechanically-derived axial rigidity.

Results

The average structural rigidity-based axial rigidity was well correlated with the average mechanically-derived axial rigidity results (R² = 0.74). This correlation improved significantly (p < 0.0001) when the CT-based Structural Rigidity Analysis (CTRA) minimum axial rigidity was correlated to the mechanically-derived minimum axial rigidity results (R² = 0.84). Tests of slopes in the mixed model regression analysis indicated a significantly steeper slope for the average axial rigidity compared with the minimum axial rigidity (p = 0.028) and a significant difference in the intercepts (p = 0.022). The CTRA average and minimum axial rigidities were correlated with the mechanically-derived average and minimum axial rigidities using paired t-test analysis (p = 0.37 and p = 0.18, respectively).

Conclusions

In summary, the results of this study suggest that structural rigidity analysis of micro-CT data can be used to accurately and quantitatively measure the axial rigidity of bones with metabolic pathologies in an experimental rat model. It appears that minimum axial rigidity is a better model for measuring bone rigidity than average axial rigidity.

Vitamin K(2) improves renal function and increases femoral bone strength in rats with renal insufficiency

Renal insufficiency induces cortical bone loss in rats. The present study examined the influence of vitamin K(2) on renal function, cortical bone mass, and bone strength in rats with renal insufficiency. Thirty male Sprague-Dawley rats (8 weeks old) were randomized by the stratified weight method to the following three groups of 10 animals each: sham operation (control), 5/6 nephrectomy, and 5/6 nephrectomy + oral vitamin K(2) (menaquinone-4, menatetrenone, 30 mg/kg, 5 days/week). Treatment was initiated 10 days after surgery. After 6 weeks of treatment, samples of serum, urine, and bone (femur and tibia) were obtained. Renal function was evaluated, bone histomorphometric analysis was performed on the tibial diaphysis, and the bone mineral density (BMD) and mechanical strength of the femoral diaphysis were determined by peripheral quantitative computed tomography and a three-point bending test, respectively. Nephrectomy induced renal dysfunction, as indicated by increased levels of serum creatinine and urea nitrogen along with a decrease of creatinine clearance; and it also decreased BMD without significantly affecting bone strength at the femoral diaphysis. Vitamin K(2) improved renal function parameters but did not significantly influence BMD at the femoral diaphysis. However, vitamin K(2) decreased the bone marrow area of the tibial diaphysis and increased the stiffness of the femoral diaphysis. These findings suggest that administration of vitamin K(2) improves renal function and increases cortical bone strength without altering BMD in rats with renal insufficiency.

Long-term treatment with lanthanum carbonate reduces mineral and bone abnormalities in rats with chronic renal failure

Background. Lanthanum carbonate (FOSRENOL^®, Shire Pharmaceuticals) is an effective non-calcium, non-resin phosphate binder for the treatment of hyperphosphataemia in patients with chronic kidney disease (CKD). In this study, we used a rat model of chronic renal failure (CRF) to examine the long-term effects of controlling serum phosphorus with lanthanum carbonate treatment on the biochemical and bone abnormalities associated with CKD–mineral and bone disorder (CKD–MBD).

Methods. Rats were fed a normal diet (normal renal function, NRF), or a diet containing 0.75% adenine for 3 weeks to induce CRF. NRF rats continued to receive normal diet plus vehicle or normal diet supplemented with 2% (w/w) lanthanum carbonate for 22 weeks. CRF rats received a diet containing 0.1% adenine, with or without 2% (w/w) lanthanum carbonate. Blood and urine biochemistry were assessed, and bone histomorphometry was performed at study completion.

Results. Treatment with 0.75% adenine induced severe CRF, as demonstrated by elevated serum creatinine. Hyperphosphataemia, hypocalcaemia, elevated calcium × phosphorus product and secondary hyperparathyroidism were evident in CRF + vehicle animals. Treatment with lanthanum carbonate reduced hyperphosphataemia and secondary hyperparathyroidism in CRF animals (P < 0.05), and had little effect in NRF animals. Bone histomorphometry revealed a severe form of bone disease with fibrosis in CRF + vehicle animals; lanthanum carbonate treatment reduced the severity of the bone abnormalities observed, particularly woven bone formation and fibrosis.

Conclusions. Long-term treatment with lanthanum carbonate reduced the biochemical and bone abnormalities of CKD–MBD in a rat model of CRF.

Systemic disorders of calcium dynamics in rats with adenine-induced renal failure: implication for chronic kidney disease-related complications

AIM

Chronic kidney disease (CKD) causes the dysregulation of systemic mineral metabolism. A major issue in CKD patients is the emergence of ectopic calcification in soft tissues, presumably due to increased levels of calcium (Ca) or inorganic phosphorus (Pi); however, the precise mechanisms have not been fully elucidated. Therefore, this study aims to evaluate Ca dynamics in an animal model of CKD.

METHODS

Renal failure was produced in rats by feeding an adenine-containing diet for 4 weeks, and time-course changes in biochemical parameters, including Ca, Pi, creatinine (Cr), blood urea nitrogen (BUN), parathyroid hormone (PTH), 1,25-dihydroxyvitamin D(3), and N-telopeptide and cross-linked collagen type I (NTx), were monitored once a week during the feeding period. Intestinal absorption, tissue contents, and urinary excretion of Ca were monitored using radioisotope (RI) (45)Ca.

RESULTS

Adenine-fed rats exhibited renal failure, ectopic calcification and altered serum parameters, including elevated levels of serum Pi, Cr, PTH and BUN. Serum Ca levels were not increased in rats with renal failure. RI-based experiments revealed that abnormal Ca dynamics including attenuated intestinal absorption, increased incorporation into soft tissues, particularly aortic tissue, in which it was increased threefold, and enhanced urinary excretion occurred in renal failure rats.

CONCLUSION

Rats with renal failure induced by an adenine diet exhibited severe abnormality of Ca dynamics, including Ca shortage and ectopic accumulation of Ca. These findings would provide useful information to research CKD-related complications.

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.

Osteoprotegerin abrogated cortical porosity and bone marrow fibrosis in a mouse model of constitutive activation of the PTH/PTHrP receptor

Intracortical porosities and marrow fibrosis are hallmarks of hyperparathyroidism and are present in bones of transgenic mice expressing constitutively active parathyroid hormone/parathyroid hormone-related protein receptors (PPR*Tg). Cortical porosity is the result of osteoclast activity; however, the etiology of marrow fibrosis is poorly understood. While osteoclast numbers and activity are regulated by osteoprotegerin (OPG), bisphosphonates suppress osteoclast activity but not osteoclast numbers. We therefore used OPG and bisphosphonates to evaluate the extent to which osteoclasts, as opposed to bone resorption, regulate marrow fibrosis in PPR*Tg mice after treatment of animals with vehicle, OPG, alendronate, or zoledronate. All three agents similarly increased trabecular bone volume in both PPR*Tg and control mice, suggesting that trabecular bone resorption was comparably suppressed by these agents. However, the number of trabecular osteoclasts was greatly decreased by OPG but not by either alendronate or zoledronate. Furthermore, intracortical porosity and marrow fibrosis were virtually abolished by OPG treatment, whereas alendronate and zoledronate only partially reduced these two parameters. The greater reductions in cortical porosity and increments in cortical bone mineral density with OPG in PPR*Tg mice were associated with greater improvements in bone strength. The differential effect of OPG versus bisphosphonates on marrow fibrosis, despite similar effects on trabecular bone volume, suggests that marrow fibrosis was related not only to bone resorption but also to the presence of osteoclasts.

Effect of sevelamer hydrochloride on bone in experimental uremic rats

Hyperphosphatemia in dialysis patients is known to cause secondary hyperparathyroidism and high-turnover bone disease. Sevelamer hydrochloride (sevelamer) is a nonabsorbed, calcium-free phosphate-binder. We determined the effect of sevelamer on parathyroid hormone (PTH)-induced high bone turnover. Rats were sham-operated or 5/6-nephrectomized (Nx) and fed a phosphate loading diet for 16 weeks or 5/6-nephrectomized and fed a phosphate loading diet for 8 weeks and then fed the same diet containing 3% sevelamer for the subsequent 8 weeks (Nx-S). Sevelamer significantly reduced serum PTH. The relative osteoid volume (OV/BV), osteoid surface (OS/BS), eroded surface (ES/BS), mineral appositional rate (MAR), volume-referent bone formation rate (BFR/TV), and bone-referent bone formation rate (BFR/BV) were measured for vertebral bone histomorphometric analysis. All parameters were statistically higher in the Nx rats than in the sham-operated control rats. The administration of sevelamer attenuated increases in OV/BV, ES/BS, BFR/TV, and BFR/BV. For femur histomorphometric analysis, the porosity area (%) (PoAr/CtAr), osteoid surface on the periosteal surface, osteoid surface on the endocortical surface (OS/Es), mineral appositional rate on the periosteal surface, mineral appositional rate on the endocortical surface, bone formation rate on the periosteal surface, and bone formation rate on the endocortical surface (Es BFR) were calculated. All parameters were higher in the Nx group than in the control group. Sevelamer inhibited the elevation of PoAr/CtAr, OS/Es, and Es BFR. Our findings suggest that the decrease in PTH by sevelamer may be beneficial in the treatment of high PTH-induced bone disease.

A structural approach to skeletal fragility in chronic kidney disease

Renal osteodystrophy is a multifactorial disorder of bone metabolism in chronic kidney disease (CKD). As CKD progresses, ensuing abnormalities in mineral metabolism result in distortions in trabecular microarchitecture, thinning of the cortical shell, and increased cortical porosity. Recent studies have shown significantly increased hip fracture rates in CKD stages 3 and 4, in dialysis patients, and in transplant recipients. The majority of studies of bone loss in CKD relied on dual-energy x-ray absorptiometry (DXA) measures of bone mineral density. However, DXA summarizes the total bone mass within the projected bone area, concealing distinct structural alterations in trabecular and cortical bone. Recent data have confirmed that peripheral quantitative computed tomography (pQCT) measures of cortical density and thickness provide substantially better fracture discrimination in dialysis patients, compared with hip or spine DXA. This review summarizes the growing evidence for bone fragility in CKD stages 3 through 5, considers the effects of CKD on trabecular and cortical bone structure as it relates to fracture risk, and details the potential advantages and disadvantages of DXA and alternative measures of bone density, geometry, and microarchitecture, including pQCT, high-resolution pQCT, and micro-magnetic resonance imaging for fracture risk assessment in CKD.

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.

Differential effects of intermittent PTH(1-34) and PTH(7-34) on bone microarchitecture and aortic calcification in experimental renal failure

PTH(1-84) and PTH(7-84) are elevated in chronic kidney disease (CKD). These peptides, as their shorter analogs PTH(1-34) and PTH(7-34) both promote PTH receptor (PTH1R) internalization but only PTH(1-34) and PTH(1-84) activate the receptor. Here, we examined the effects of intermittent administration of PTH(1-34) and PTH(7-34) on mineral ion metabolism, bone architecture, and vascular calcification in rats with experimental CKD. CKD with or without parathyroidectomy (PTX) was established by 5/6 nephrectomy (NPX) in rats. Animals were divided into 4 groups: Sham PTX+ sham NPX (Sham); PTX+ sham NPX (PTX); Sham PTX+NPX (NPX); PTX+NPX (PTX/NPX). Rats were treated with single daily doses of 40 microg/kg PTH(1-34), PTH(7-34), or vehicle. Creatinine was higher in NPX and Ca lower in PTX and PTX/NPX groups than in Sham or NPX rats. Plasma phosphate was higher in PTX, NPX and PTX/NPX than in Sham rats. PTH(1-34) was more hypercalcemic than PTH(7-34) in PTX rats. Fractional bone volume in rats treated with PTH(1-34) increased significantly in all groups compared to that of vehicle treatment. In addition, trabecular number, thickness and volumetric bone density increased in rats treated with PTH(1-34). In contrast, PTH(1-34) diminished vascular calcification. Bone and renal PTH1R mRNA expression was reduced as much or more in PTX/NPX rats as in NPX alone, whereas PTH(7-34) had no effect on PTH1R expression. Renal but not bone PTH1R mRNA increased in response to PTH(1-34). These findings suggest that PTH(1-34) exerts greater hypercalcemic and anabolic effects in parathyroidectomized and/or nephrectomized rats than does PTH(7-34). There was no evidence for significant bone or vascular actions of PTH(7-34). We conclude that PTH(1-34) protects against vascular calcification and bone demineralization in experimental renal failure.

Effect of cinacalcet on hypercalcemia and bone mineral density in renal transplanted patients with secondary hyperparathyroidism

BACKGROUND

Persistent secondary hyperparathyroidism (SHP) is the most frequent cause of hypercalcemia observed in approximately 10% of renal transplanted (RT) patients 1 year after surgery. Persistent SHP with hypercalcemia is an important factor of bone loss after renal transplantation. This study prospectively evaluates the effects of cinacalcet therapy on serum calcium (SCa) and parathyroid hormone (PTH) blood levels, and basically on bone mineral density (BMD) in RT patients with persistent hyperparathyroidism.

METHODS

Nine RT patients (eight women, one man) with allograft function more than 6 months were included based on total SCa more than 10.5 mg/dL and intact parathyroid hormone (iPTH) concentration more than 65 pg/mL. After inclusion, patients started on a single daily oral dose of 30 mg of cinacalcet. At inclusion and every study visit blood levels of creatinine, Ca, P, alkaline phosphatase, iPTH 1,25- dihydroxyvitamin D3, and 25-hydroxyvitamin D3 were assessed. Baseline and at the end of study radial BMD were measured. Study follow-up was 12 months.

RESULTS

During the study period, SCa decreased from 11.72+/-0.39 to 10.03+/-0.54 mg/dL (P<0.001). iPTH decreased from 308.85+/-120.12 to 214.66+/-53.75 mg/dL (P<0.05). The mean serum creatinine decreased from 1.58+/-0.34 to 1.25+/-0.27 mg/dL (P=0.03) and the mean radial BMD increased from 0.881+/-0.155 to 0.965+/-0.123 gr/cm2 (P<0.05). There were no significant changes in the other parameters assessed. One patient was excluded for gastrointestinal intolerance.

CONCLUSIONS

In RT patients with hypercalcemia secondary to persistent SHP, cinacalcet corrects hypercalcemia and PTH, simultaneously improving BMD.

Treatment of experimental renal osteodystrophy with pamidronate

We evaluated the effects of the bisphosphonate pamidronate on bone histomorphometry, structure and strength in male rats with uninephrectomy or with chronic renal disease induced by 5/6 nephrectomy. In rats with chronic renal disease the plasma urea, phosphate and parathyroid hormone levels were significantly increased compared to rats with a uninephroctomy and none of these parameters was affected by pamidronate treatment. In the femoral midshaft, chronic renal disease reduced cortical bone mineral density and content. No difference was observed in the breaking load of the femoral midshaft. In the distal femur, a high-turnover renal osteodystrophy was found but pamidronate suppressed this bone turnover and increased bone mineral content. Treatment had no effect on chronic disease-induced augmentation of osteoid volume or fibroblast surface. These studies show that in this model of stage 3 renal disease, pamidronate increased mineral content in the femoral midshaft and distal metaphysis primarily by adding bone to endocortical and trabecular surfaces but did not reduce osteitis fibrosa.

A structural approach to the assessment of fracture risk in children and adolescents with chronic kidney disease

Children with chronic kidney disease (CKD) have multiple risk factors for impaired accretion of trabecular and cortical bone. CKD during childhood poses an immediate fracture risk and compromises adult bone mass, resulting in significantly greater skeletal fragility throughout life. High-turnover disease initially results in thickened trabeculae, with greater bone volume. As disease progresses, resorption cavities dissect trabeculae, connectivity degrades, and bone volume decreases. Increased bone turnover also results in increased cortical porosity and decreased cortical thickness. Dual-energy X-ray absorptiometry (DXA)-based measures of bone mineral density (BMD) are derived from the total bone mass within the projected bone area (g/cm(2)), concealing distinct disease effects in trabecular and cortical bone. In contrast, peripheral quantitative computed tomography (pQCT) estimates volumetric BMD (vBMD, g/cm(3)), distinguishes between cortical and trabecular bone, and provides accurate estimates of cortical dimensions. Recent data have confirmed that pQCT measures of cortical vBMD and thickness provide substantially greater fracture discrimination in adult dialysis patients compared with hip or spine DXA. The following review considers the structural effects of renal osteodystrophy as it relates to fracture risk and the potential advantages and disadvantages of DXA and alternative measures of bone density, geometry, and microarchitecture, such as pQCT, micro-CT (microCT), and micro magnetic resonance imaging (microMRI) for fracture risk assessment.

Effects of daily treatment with parathyroid hormone 1-84 for 16 months on density, architecture and biomechanical properties of cortical bone in adult ovariectomized rhesus monkeys

Treatment with parathyroid hormone 1-84 (PTH) or teriparatide increases osteonal remodeling and decreases bone mineral density (BMD) at cortical (Ct) bone sites but may also increase bone size. Decreases in BMD and increases in size exert opposing effects on bone strength. In adult ovariectomized (OVX) rhesus monkeys, we assessed the effects of daily PTH treatment (5, 10 or 25 microg/kg) for 16 months on BMD at the radial, tibial and femoral diaphyses, and on biomechanical properties (3-point bending) of radial cortical bone and the femoral diaphysis. PTH treatment did not affect areal BMD measured by dual-energy X-ray absorptiometry at the tibial diaphysis but caused a rapid, dose-related decrease at the distal radial diaphysis. Peripheral quantitative computed tomography at the radial and femoral diaphyses confirmed a significant PTH dose-related decrease in volumetric Ct.BMD caused primarily by increased cortical area. Significant increases in cortical thickness were the result of nonsignificant increases in periosteal length and decreases in endocortical length. Histomorphometry revealed increased endocortical bone formation at the tibial diaphysis and rib, higher Haversian remodeling at the rib and increased cortical porosity at the rib and tibia. Biomechanical testing at the femoral diaphysis showed that PTH treatment had no effect on peak load, but significantly decreased stiffness and increased work-to-failure (the energy required to break the bone). Similar changes occurred in radial cortical beams but only stiffness was changed significantly. Thus, PTH treatment of OVX rhesus monkeys decreased BMD and stiffness of cortical bone but did not affect peak load, likely because of increased bone size. However, PTH treatment increased the energy required to break the femur making it more resistant to fracture.

Effects of treatment of ovariectomized adult rhesus monkeys with parathyroid hormone 1-84 for 16 months on trabecular and cortical bone structure and biomechanical properties of the proximal femur

Treatment of monkeys and humans with parathyroid hormone (PTH) 1-84 stimulates skeletal remodeling, which increases trabecular (Tb) bone mineral density (BMD) but decreases cortical (Ct) BMD at locations where these bone types predominate. We report the effects of daily PTH treatment (5, 10, or 25 microg/kg) of ovariectomized (OVX) rhesus monkeys for 16 months on bone structure and biomechanical properties at the proximal femur, a mixed trabecular and cortical bone site. PTH reversed the OVX-induced decrease in BMD measured by dual-energy X-ray absorptiometry at the proximal femur, femoral neck, and distal femur. Peripheral quantitative computed tomography confirmed a significant decrease in Ct.BMD and an increase in Tb.BMD at the total proximal femur and at the proximal and distal femoral metaphyses. The decrease in Ct.BMD resulted primarily from increased area because cortical bone mineral content was unaffected by PTH. Histomorphometry revealed that PTH significantly increased the trabecular bone formation rate (BFR) as well as trabecular bone volume and number. PTH did not affect periosteal or haversian BFR at the femoral neck, but cortical porosity was increased slightly. PTH had no effects on stiffness or peak load measured using a shear test, whereas work-to-failure, the energy required to fracture, was increased significantly. Thus, PTH treatment induced changes in trabecular and cortical bone at the proximal femur that were similar to those occurring at sites where these bone types predominate. Together, the changes had no effect on stiffness or peak load but increased the energy required to break the proximal femur, thereby making it more resistant to fracture.

Treatment of skeletally mature ovariectomized rhesus monkeys with PTH(1-84) for 16 months increases bone formation and density and improves trabecular architecture and biomechanical properties at the lumbar spine

Histomorphometric studies of treatments for osteoporosis in humans are restricted to iliac crest biopsies. We studied the effects of PTH(1-84) treatment at the lumbar spine of skeletally mature ovariectomized rhesus monkeys. PTH increased bone turnover, rapidly normalized BMD, and increased vertebral compressive strength. PTH increased trabecular bone volume primarily by increasing trabecular number by markedly increasing intratrabecular tunneling.

INTRODUCTION

Histomorphometric studies of the anabolic properties of PTH(1-84) (PTH) and related peptides in human bone are restricted to iliac crest biopsies. The ovariectomized (OVX) monkey is an accepted model of human postmenopausal bone loss and was used to study the effects of PTH treatment at clinically relevant skeletal sites.

MATERIALS AND METHODS

Skeletally mature rhesus monkeys were OVX or sham-operated and, after a bone depletion period of 9 months, treated daily for 16 months with PTH (5, 10, or 25 microg/kg). Markers of bone formation (serum osteocalcin) and resorption (urine N-telopeptide [NTX]) and lumbar spine BMD were measured throughout the study. Trabecular architecture and vertebral biomechanical properties were quantified at 16 months.

RESULTS

PTH treatment induced dose-dependent increases in bone turnover but did not increase serum calcium. Osteocalcin was significantly increased above OVX controls by 1 month. NTX was significantly elevated at 1 month with the highest dose, but not until 12 months with the 5 and 10 microg/kg doses. Lumbar spine BMD was 5% lower in OVX than in sham animals when treatment was started. All PTH doses increased BMD rapidly, with sham levels restored by 3-7 months with 10 and 25 microg/kg and by 16 months with 5 microg/kg. PTH treatment increased trabecular bone volume (BV/TV), primarily by increasing trabecular number, and dose-dependently increased bone formation rate (BFR) solely by increasing mineralizing surface. The largest effects on BV/TV and yield load occurred with the 10 microg/kg dose. The highest dose reduced trabecular thickness by markedly increasing intratrabecular tunneling.

CONCLUSIONS

PTH treatment of OVX rhesus monkeys increased bone turnover and increased BV/TV, BMD, and strength at the lumbar spine. All PTH doses were safe, but the 10 microg/kg dose was generally optimal, possibly because the highest dose resulted in too marked a stimulation of bone remodeling.

Renal insufficiency-induced bone loss is associated with an increase in bone size and preservation of strength in rat proximal femur

Chronic renal insufficiency (CRI) results in phosphate retention and secondary hyperparathyroidism, the treatment of which is largely based on the use of calcium salts as phosphate binders. Advanced CRI causes bone fragility, but information about bone geometry and strength in moderate CRI is scarce. We assigned 39 8-week-old male Sprague-Dawley rats to sham-operation (Sham) or 5/6 nephrectomy (NTX). Four weeks later, the rats were randomized to 0.3% calcium (Sham, NTX) or 3.0% calcium diet (Sham + Calcium, NTX + Calcium). After 8 weeks, the animals were sacrificed, plasma samples collected, and femora excised for neck and midshaft analyses: dual-energy X-ray absorptiometry, peripheral quantitative computed tomography, and biomechanical testing. The NTX increased plasma urea and PTH 1.6-fold and 3.6-fold, respectively, whereas high calcium intake suppressed PTH to 30% of controls. Total femoral bone mineral content decreased (-6.3%) in the NTX group, while this deleterious effect was reversed by high calcium diet. In the site-specific analysis of the femoral neck, the volumetric bone density (-6.5%) was decreased in the NTX group but not NTX + Calcium group. However, in the nephrectomized rats, there was also a concomitant increase in the cross-sectional area (+15%), and, despite the decrease in bone density, the mechanical strength of the femoral neck was maintained. In the midshaft, NTX decreased cortical volumetric bone density (-1.2%), but similar to the femoral neck, no differences were found in the mechanical strength. In conclusion, a decrease in bone mass in moderate experimental CRI was associated with a concomitant increase in bone size, and maintenance of mechanical competence. Although high calcium diet suppressed plasma PTH to under normal physiological levels, it prevented the CRI-induced loss of bone mass without an adverse influence on bone strength.

The receptor activator of nuclear factor-kappaB ligand inhibitor osteoprotegerin is a bone-protective agent in a rat model of chronic renal insufficiency and hyperparathyroidism

Osteoprotegerin (OPG) acts by neutralizing the receptor activator of nuclear factor-kappaB ligand (RANKL), the primary mediator of osteoclast differentiation, function, and survival. We examined whether OPG could affect the bone loss associated with chronic kidney disease (CKD) in a rodent model of CKD and secondary hyperparathyroidism (SHPT). SHPT was induced in rats by 5/6 nephrectomy (5/6 Nx) and a 1.2% P/0.6% Ca(2+) diet. Starting 1 week after 5/6 Nx, rats were treated with vehicle (veh) or OPG-Fc (3 mg/kg, intravenously) every 2 weeks for 9 weeks. At baseline, 3, 6, and 9 weeks, blood was taken and bone mineral density (BMD) and bone mineral content (BMC) were assessed by dual-energy X-ray absorptiometry. Serum parathyroid hormone (sPTH) levels reached 912 pg/ml in 5/6 Nx rats vs. 97 pg/ml in shams at 9 weeks. OPG-Fc had no effect on sPTH or Ca(2+) levels throughout the 9-week study, indicating that SHPT was a renal effect independent of bone changes. At 3 weeks, 5/6 Nx-veh rats had osteopenia compared with sham-veh rats and 5/6 Nx-OPG-Fc rats had significantly higher percent changes in whole-body BMC, leg BMD, and lumbar BMD versus 5/6 Nx-veh rats. By 6-9 weeks, elevated sPTH was associated with reversal of bone loss and osteitis fibrosa in the proximal tibial metaphysis. OPG-Fc decreased this sPTH-driven high bone turnover, resulting in augmented thickness of proximal tibial trabeculae in 5/6 Nx rats. Thus, RANKL inhibition with OPG-Fc can block the deleterious effects of continuously elevated sPTH on bone, suggesting that RANKL may be an important therapeutic target for protecting bone in patients with CKD and SHPT.

Severe hyperparathyroidism with bone abnormalities and metastatic calcification in rats with adenine-induced uraemia

BACKGROUND

Marked parathyroid hyperplasia with bone diseases and vascular calcification are unsolved issues in dialysis patients. In this study, we made azotemic model rats by adenine feeding and analyzed the development and progression of the abnormalities.

METHODS

Renal failure was induced in 8-week-old male Wistar rats by feeding 0.75% adenine-containing diet for 6 weeks. Serum parameters, parathyroid hyperplasia, bone changes and metastatic calcification were examined at 2, 4 and 6 weeks.

RESULTS

Progressive increase of serum creatinine and inorganic phosphate, and decreased levels of serum calcium and 1,25(OH)2D3 were confirmed. Markedly enlarged parathyroid glands and extremely high PTH levels were observed in all adenine-fed rats compared with the control (PTH: 199.3+/-58.0 vs 10.5+/-3.0 pmol/l, P<0.01, respectively, at 6 weeks). In cortical bone of the femur, the morphometric parameters showed increased bone resorption with increased fibrosis, whereas in the trabecular bone, bone resorption decreased and bone volume increased with a larger amount of osteoid compared with the control. Metastatic calcification in aorta, coronary artery and other soft tissues were also found in adenine-fed rats.

CONCLUSIONS

Uraemic rats made by adenine diet developed severe abnormalities of calcium metabolism in a relatively short period and therefore they may serve as a useful model for the analysis of parathyroid hyperplasia and vascular calcification in chronic renal failure.

Assessment of bone mass following renal transplantation in children

Throughout childhood and adolescence, skeletal growth results in site-specific increases in trabecular and cortical dimensions and density. Childhood osteoporosis can be defined as a skeletal disorder characterized by compromised bone strength predisposing to an increased risk of fracture. Pediatric renal transplant recipients have multiple risk factors for impaired bone density and bone strength, including pre-existing renal osteodystrophy, delayed growth and development, malnutrition, decreased weight-bearing activity, inflammation, and immunosuppressive therapies. Dual energy X-ray absorptiometry (DXA) is the most-common method for the assessment of skeletal status in children and adults. However, DXA has many important limitations that are unique to the assessment of bone health in children. Furthermore, DXA is limited in its ability to distinguish between the distinct, and sometimes opposing, effects of renal disease on cortical and trabecular bone. This review summarizes these limitations and the difficulties in assessing and interpreting bone measures in pediatric transplantation are highlighted in a review of select studies. Alternative strategies are presented for clinical and research applications.

Mechanotransduction in bone does not require a functional cyclooxygenase-2 (COX-2) gene

COX-2 is a key enzyme involved in the response of bone to loading. However, using mice with a null mutation of the COX-2 gene, we found that a functional COX-2 gene is not required for mechanotransduction. This paradoxical finding may have resulted, in part, from mechanically induced COX-1 activity.

INTRODUCTION

Cyclooxygenase-2 (COX-2) is an important mediator in the response of bone to mechanical loading, with pharmacological inhibition of COX-2 effectively eliminating or reducing mechanically induced bone formation. In this study, we further investigated the role of COX-2 in skeletal mechanotransduction using a genetic approach. The aim was to compare the skeletal responsiveness of COX-2 homozygous mutant (COX-2(-/-)) and wildtype control (COX-2(+/+)) mice to investigate whether a functional COX-2 gene is necessary for mechanotransduction.

MATERIALS AND METHODS

Adult female COX-2(+/+) and COX-2(-/-) mice on a C57BL/6x129/ola background were studied using the ulna axial loading model. The response to 2 days of loading for 120 cycles/day at 2 Hz was measured histomorphometrically. Phenotypic characterization of the femurs in these mice was also performed. In a separate group of animals, the expression of the remaining COX isozyme, COX-1, was assessed using real-time RT-PCR 4 h after one bout of 120 loading cycles.

RESULTS

Null mutation of the COX-2 gene resulted in a consistent femoral phenotype of reduced bone mass, altered architecture, and inferior mechanical properties. Many of these differences were nullified after adjustment for body weight. Nevertheless, body weight-corrected values showed a consistent trend of reduced mechanical properties in COX-2(-/-) mice. Genotype did not influence the response to mechanical loading, with no histomorphometric differences being found between COX-2(+/+) and COX-2(-/-) mice. Real-time RT-PCR showed COX-2(-/-) mice to express significantly greater COX-1 expression in loaded ulnas than in loaded ulnas in COX-2(+/+) mice. There were no differences in COX-1 expression in nonloaded ulnas.

CONCLUSIONS

A functional COX-2 gene was not found to be required for skeletal mechanotransduction. This is in contrast to previous pharmacological studies showing that COX-2 is critical to the response of bone to loading. Investigating a potential reason for the absence of a genotype difference in this study, we found that mice with a null mutation in the COX-2 gene possess inductive skeletal COX-1 expression.

Lifetime high calcium intake increases osteoporotic fracture risk in old age

Caloric restriction prolongs life span. Calcium restriction may preserve bone health. In osteoporosis, bone mineral density (BMD) has significantly decreased, due to a lack of osteoblast bone formation. Traditional osteoporosis prevention is aimed at maximizing BMD, but the lifetime effects of continuously maintaining a high BMD on eventual bone health in old age, have not been studied. Strikingly, in countries with a high mean BMD, fracture rates in the elderly are significantly higher than in countries with a low mean BMD. Studies show that this is not based on genetic differences. Also, in primary hyperparathyroidism, on the brink of osteoporosis, BMD levels may be significantly higher than normal. Maybe, BMD does not represent long term bone health, but merely momentary bone strength. And maybe, maintaining a high BMD might actually wear out bone health. Since osteoporosis particularly occurs in the elderly, and because in osteoporotic bone less osteoblasts are available, the underlying process may have to do with ageing of osteoblastic cells. In healthy subjects, osteoblastic bone cells respond to the influx of calcium by composing a matrix upon which calcium precipitates. In the process of creating this matrix, 50-70% of the involved osteoblasts die. The greater the influx of calcium, the greater osteoblast activity, and the greater osteoblast apoptosis rate. An increased osteoblast apoptosis rate leads to a decrease in the age-related osteoblast replicative capacity (ARORC). In comparison to healthy bone, in osteoporotic bone the decrease in the replicative capacity of osteoblastic cells is greater. Due to the eventual resulting lack of osteoblast activity, micro-fractures cannot be repaired. Continuously maintaining a high BMD comes with continuously high bone remodeling rates, which regionally exhaust the ARORC, eventually leading to irreparable microfractures. Regarding long time influences on bone health, adequate estrogen levels are known to be protective against osteoporosis. This is generally attributed to its inhibiting influence on osteoclast activity. Instead, its net effects on osteoblast metabolism may be the key to osteoporosis prevention. Adequate estrogen levels inhibit osteoblast activity, calcium apposition and osteoblast apoptosis rate, preserving the ARORC.

CONCLUSION

Regarding osteoporosis prevention, ARORC better than BMD represents bone health. Regarding ARORC, adequate estrogen levels are protective, opposing the similar effects of hyperparathyroidism and a high calcium diet. Tests need to be performed in mice to assess the lifetime effects of a high versus a low calcium diet, on eventual bone fracture toughness.