Characterization of mandibular bone in a mouse model of chronic kidney disease

Chronic kidney disease compromises structural and mechanical properties of maxillary cortical bone in a rat model

PURPOSE

This study aimed to investigate the effects of chronic kidney disease (CKD) on the structural and mechanical properties of the maxillary and mandibular cortical bone.

METHODS

The maxillary and mandibular cortical bones from CKD model rats were used in this study. CKD-induced histological, structural, and micro-mechanical alterations were assessed using histological analyses, micro-computed tomography (CT), bone mineral density (BMD) measurements, and nanoindentation tests.

RESULTS

Histological analyses indicated that CKD caused an increase in the number of osteoclasts and a decrease in the number of osteocytes in the maxilla. Micro-CT analysis revealed that CKD induced a void volume/cortical volume (%) increase, which was more remarkable in the maxilla than in the mandible. CKD also significantly decreased the BMD in the maxilla. In the nanoindentation stress-strain curve, the elastic-plastic transition point and loss modulus were lower in the CKD group than that in the control group in the maxilla, suggesting that CKD increased micro fragility of the maxillary bone.

CONCLUSIONS

CKD affected bone turnover in the maxillary cortical bone. Furthermore, the maxillary histological and structural properties were compromised, and micro-mechanical properties, including the elastic-plastic transition point and loss modulus, were altered by CKD.

Biomechanical and histomorphological analysis of the mandible in rats with chronic kidney disease

The present study aimed to investigate the biomechanical and histomorphological features of mandibles in an adenine-induced chronic kidney disease-mineral and bone disorder (CKD-MBD) rat model of CKD. A total of 14 Sprague-Dawley rats were randomized into the following two groups: control group and CKD group. At the end of the sixth week, all rats were euthanized, and serum was collected for biochemical marker tests. Macroscopic bone growth and biomechanical parameters were measured in the right hemimandible, while the left hemimandible was used for bone histomorphometric analysis. Compared to the control group, the CKD group showed a significant increase in serum creatinine, blood urea nitrogen, and serum parathyroid hormone at the end of the sixth week. The biomechanical structural properties significantly decreased in the CKD group compared to the control group. Bone histomorphometric analysis indicated that the trabecular bone volume of rats in the CKD group was significantly lower than that of the control group. In the CKD groups, the bone formation parameters of the trabecular bone were significantly increased, while the bone mineralization apposition rates of both the trabecular bone and periosteal cortical bone were significantly increased. The rat CKD model showed deteriorated structural mechanics, low trabecular bone volume, high trabecular bone formation, increased trabecular bone mineralization apposition rate, and increased cortical bone mineralization apposition rate, which met the characteristics of osteitis fibrosa, indicating that this model is a useful tool for the study of mandible diseases in CKD patients.

Alveolar bone and tibia responses to hormonal and mineral abnormalities in rats with chronic kidney disease: A pilot study

OBJECTIVES

As the impact of chronic kidney disease (CKD) severity on different bone types remains unclear, we induced increasing levels of CKD severity in a rat model and investigated hormone and mineral levels as well as alveolar and tibia bone histomorphology.

METHODS

Rats were divided into sham operation (sham), 4/6 nephrectomy (4/6Nx), 5/6Nx, and 4/6Nx with hyperphosphorous (HP) diet (4/6NxHP). At week 20, BUN, FGF23, PTH, and P were estimated in plasma. Bone parameters were evaluated by microCT, and osteoclasts and osteoid areas were evaluated by TRAP and H&E stains, respectively.

RESULTS

The 4/6NxHP and 5/6Nx groups had elevated PTH, and the 4/6NxHP group alone had elevated P. Compared to the 4/6Nx group, the 4/6NxHP group demonstrated increased FGF23 and P. In the alveolar bone, the 4/6NxHP group had reduced bone volume and BMD compared to the sham and 4/6Nx groups. In the tibia cortical bone, bone surface density was higher in the 4/6NxHP group compared to the sham group. Tibia cortical bone volume was negatively correlated with FGF23 and P. Moreover, alveolar bone volume was negatively correlated with FGF23, PTH, and P.

CONCLUSIONS

Our results demonstrate that hormone and mineral levels vary with CKD severity, and alveolar bone loss strongly correlates with these hormone and mineral alterations.

Dentoalveolar Alterations in an Adenine-Induced Chronic Kidney Disease Mouse Model

Chronic kidney disease (CKD) is characterized by kidney damage and loss of renal function. CKD mineral and bone disorder (CKD-MBD) describes the dysregulation of mineral homeostasis, including hyperphosphatemia and elevated parathyroid hormone (PTH) secretion, skeletal abnormalities, and vascular calcification. CKD-MBD impacts the oral cavity, with effects including salivary gland dysfunction, enamel hypoplasia and damage, increased dentin formation, decreased pulp volume, pulp calcifications, and altered jaw bones, contributing to clinical manifestations of periodontal disease and tooth loss. Underlying mechanisms are not fully understood, and CKD mouse models commonly require invasive procedures with high rates of infection and mortality. We aimed to characterize the dentoalveolar effects of an adenine diet (AD)-induced CKD (AD-CKD) mouse model. Eight-week-old C57BL/6J mice were provided either a normal phosphorus diet control (CTR) or adenine and high-phosphorus diet CKD to induce kidney failure. Mice were euthanized at 15 weeks old, and mandibles were collected for micro-computed tomography and histology. CKD mice exhibited kidney failure, hyperphosphatemia, and hyperparathyroidism in association with porous cortical bone in femurs. CKD mice showed a 30% decrease in molar enamel volume compared to CTR mice. Enamel wear was associated with reduced ductal components, ectopic calcifications, and altered osteopontin (OPN) deposition in submandibular salivary glands of CKD mice. Molar cusps in CKD mice were flattened, exposing dentin. Molar dentin/cementum volume increased 7% in CKD mice and pulp volume decreased. Histology revealed excessive reactionary dentin and altered pulp-dentin extracellular matrix proteins, including increased OPN. Mandibular bone volume fraction decreased 12% and bone mineral density decreased 9% in CKD versus CTR mice. Alveolar bone in CKD mice exhibited increased tissue-nonspecific alkaline phosphatase localization, OPN deposition, and greater osteoclast numbers. AD-CKD recapitulated key aspects reported in CKD patients and revealed new insights into CKD-associated oral defects. This model has potential for studying mechanisms of dentoalveolar defects or therapeutic interventions. © 2023 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Mouse Models of Mineral Bone Disorders Associated with Chronic Kidney Disease

Patients with chronic kidney disease (CKD) inevitably develop mineral and bone disorders (CKD–MBD), which negatively impact their survival and quality of life. For a better understanding of underlying pathophysiology and identification of novel therapeutic approaches, mouse models are essential. CKD can be induced by surgical reduction of a functional kidney mass, by nephrotoxic compounds and by genetic engineering specifically interfering with kidney development. These models develop a large range of bone diseases, recapitulating different types of human CKD–MBD and associated sequelae, including vascular calcifications. Bones are usually studied by quantitative histomorphometry, immunohistochemistry and micro-CT, but alternative strategies have emerged, such as longitudinal in vivo osteoblast activity quantification by tracer scintigraphy. The results gained from the CKD–MBD mouse models are consistent with clinical observations and have provided significant knowledge on specific pathomechanisms, bone properties and potential novel therapeutic strategies. This review discusses available mouse models to study bone disease in CKD.

Ammonia promotes the proliferation of bone marrow-derived mesenchymal stem cells by regulating the Akt/mTOR/S6k pathway

Ammonia plays an important role in cellular metabolism. However, ammonia is considered a toxic product. In bone marrow-derived mesenchymal stem cells, multipotent stem cells with high expression of glutamine synthetase (GS) in bone marrow, ammonia and glutamate can be converted to glutamine via glutamine synthetase activity to support the proliferation of MSCs. As a major nutritional amino acid for biosynthesis, glutamine can activate the Akt/mTOR/S6k pathway to stimulate cell proliferation. The activation of mTOR can promote cell entry into S phase, thereby enhancing DNA synthesis and cell proliferation. Our studies demonstrated that mesenchymal stem cells can convert the toxic waste product ammonia into nutritional glutamine via GS activity. Then, the Akt/mTOR/S6k pathway is activated to promote bone marrow-derived mesenchymal stem cell proliferation. These results suggest a new therapeutic strategy and potential target for the treatment of diseases involving hyperammonemia.

Association between periodontitis and chronic kidney disease

Periodontitis and chronic kidney disease are chronic conditions with high community prevalence across the world. Patients with chronic kidney disease have been noted to have a high burden of periodontitis, and several shared risk factors have been associated with the prevalence and severity of both conditions. However, the precise relationship between the two conditions, and the extent to which each may contribute to the development of the other, remains a matter of debate. The goals of the present work were to: (a) provide the most current and relevant literature overview of the association between periodontitis and chronic kidney disease; (b) explore mechanisms underlying this association; and (c) determine if evidence exists for an independent association between these conditions. We also assessed whether improved oral hygiene and periodontal treatment could reduce the risk of developing chronic kidney disease and, if so, what protocols these strategies involve. Finally, we aimed to reveal gaps in our current knowledge to delineate the directions of future research. Although the exact relationship between these two conditions has not yet been defined, we highlight the importance of the interprofessional interaction between dental practitioners and the nephrology team and the importance of oral health assessment in the management of chronic kidney disease.

Guidelines for Micro-Computed Tomography Analysis of Rodent Dentoalveolar Tissues

Micro–computed tomography (μCT) has become essential for analysis of mineralized as well as nonmineralized tissues and is therefore widely applicable in the life sciences. However, lack of standardized approaches and protocols for scanning, analyzing, and reporting data often makes it difficult to understand exactly how analyses were performed, how to interpret results, and if findings can be broadly compared with other models and studies. This problem is compounded in analysis of the dentoalveolar complex by the presence of four distinct mineralized tissues: enamel, dentin, cementum, and alveolar bone. Furthermore, these hard tissues interface with adjacent soft tissues, the dental pulp and periodontal ligament (PDL), making for a complex organ. Drawing on others' and our own experience analyzing rodent dentoalveolar tissues by μCT, we introduce techniques to successfully analyze dentoalveolar tissues with similar or disparate compositions, densities, and morphological characteristics. Our goal is to provide practical guidelines for μCT analysis of rodent dentoalveolar tissues, including approaches to optimize scan parameters (filters, voltage, voxel size, and integration time), reproducibly orient samples, define regions and volumes of interest, segment and subdivide tissues, interpret findings, and report methods and results. We include illustrative examples of analyses performed on genetically engineered mouse models with phenotypes in enamel, dentin, cementum, and alveolar bone. The recommendations are designed to increase transparency and reproducibility, promote best practices, and provide a basic framework to apply μCT analysis to the dentoalveolar complex that can also be extrapolated to a variety of other tissues of the body. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC. on behalf of American Society for Bone and Mineral Research.

Noninflammatory Stress-Induced Remodeling of Mandibular Bone: Impact of Age and Pregnancy

PURPOSE

The impact of noninflammatory stress, such as aging and pregnancy, on human long bone remodeling is well-established, but little is known about the impact of these stressors on oral bones, including the mandibular bone. To begin to fill this gap in our knowledge, we utilized a mouse mandibular model to evaluate the impact of noninflammatory simple stressors, ie, aging and pregnancy, on bone mandibular architecture and bone density in the mandible using micro-CT.

MATERIALS AND METHODS

For the present study, mandibles were obtained from both aged and pregnant C57BL/6 mice and analyzed using micro-CT technology. Micro-CT metrics included bone volume fraction (BVF), total volume (TV), tissue density, and apparent density in the mandible on the mandibular area of compact and trabecular bone, in which the teeth are embedded. All bone-related metrics data from aged and pregnant mice were analyzed using ANOVA analysis and visualized in boxplots.

RESULTS

Age-dependent bone remodeling occurred over 4 to 18 weeks of age, ie, increases in BVF, TV, BV/TV, as well as tissue and bone density. Evaluation of bone remodeling in breeder mice (repeated pregnancy model) and virgin mice (age-matched controls) at 37 weeks of age demonstrated that breeder mice had a dramatic decline in all bone metrics measured.

CONCLUSIONS

This study underscores the need for more research on noninflammatory stress-related mandibular bone remodeling (eg, age and pregnancy), which compromises bone strength and tooth anchoring. The data also underscores loss of alveolar bone height, as in periodontitis, is an important metric for a more complete assessment of bone loss. This report on mice provides essential data that can be applied for oral-maxillofacial surgeons and periodontists when planning for dental implants in patients with such stressors. Periodontitis related bone loss occurs independent of skeletal homeostasis, although osteoporosis may adversely affect alveolar bone height in humans.

[A Meta-analysis of the effect of non-surgical periodontal therapy on inflammatory factors in patients with chronic kidney disease and periodontitis]

OBJECTIVE

A study was conducted to systematically evaluate the clinical efficacy of inflammatory factors in patients with chronic kidney disease and periodontitis after non-surgical periodontal therapy.

METHODS

We searched the databases of CNKI, Wanfang, CBM, PubMed, Embase, and Cochrane Library from inception to December 2019. Two reviewers independently collected all literature related to inflammatory factors in patients with chronic kidney disease and periodontitis after non-surgical periodontal therapy. These factors include C-reactive protein (CRP), interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α). The literature was screened according to the inclusion and exclusion criteria. The quality of the studies was strictly evaluated, and the data were extracted. The literature of randomized controlled trials in accordance with the standards was Meta-analyzed with Revman 5.3 software.

RESULTS

Six randomized controlled trials were included. Compared with the control groups, the results of meta-analysis showed that non-surgical periodontal therapy significantly reduced the levels of CRP [MD=-0.58, 95%CI (-1.13, -0.02), P=0.04] and IL-6 [MD=-2.76, 95%CI (-5.15, -0.37), P=0.02] in these patients but not that of TNF-α [MD=-3.87, 95%CI (-8.79, 1.05), P=0.12].

CONCLUSIONS

Simultaneous regular renal treatment and non-surgical periodontal therapy can help relieve the periodontal damage on patients with chronic kidney disease and periodontitis. Moreover, it can improve the status of some inflammatory factors. This finding is conducive to the control and treatment of chronic kidney disease and periodontitis and needs to be a focus of research and in clinical operation.

Nephrectomy Does not Exacerbate Cancellous Bone loss in Thalassemic Mice

Patients with β-thalassemia have an increased risk of developing chronic kidney disease which is associated with osteoporosis and periodontitis. The purpose of this study was to evaluate mandibular and femoral bone change in heterozygous β-globin knockout (BKO) mice following 5/6 nephrectomy (Nx). Female and male BKO mouse blood smears demonstrated microcytic hypochromic anemia. Serum urea nitrogen, creatinine, calcium, and phosphorus levels were not changed in BKO mice. Nx increased the serum levels of urea nitrogen in both wild type (WT) and BKO mice and the level was much higher in BKO males. Serum level of creatinine was increased in Nx WT but not BKO mice. However, serum calcium and phosphorus levels were not altered. Nx induced comparable renal fibrosis in BKO mice and WT controls. Bone loss was observed in mandibular cancellous bone but not cortical bone of both male and female BKO mice. Nx decreased cancellous bone volume and cortical thickness in WT. Interestingly, BKO mice were resistant to Nx-induced cancellous bone loss. However, cortical thickness and cortical bone mineral density were reduced in Nx male BKO mice. Nx increased mRNA levels of type I collagen, Osx and Trap in WT but not BKO mice. Similarly, Nx reduced cancellous bone volume in femurs and increased osteoblast number and osteoclast number in WT not BKO mice. Serum FGF23 and erythropoietin levels were markedly increased in BKO mice. Nx decreased serum erythropoietin but not FGF23 levels. Since WT treated with erythropoietin exhibited a significant reduction in cancellous bone volume, it was possible that lower level of erythropoietin in Nx BKO mice prevented the Nx-induced cancellous bone loss.

Growth differentiation factor 11 impairs titanium implant healing in the femur and leads to mandibular bone loss

BACKGROUND

Growth differentiation factor 11 (GDF11), a secreted member of the transforming growth factor-β superfamily, has recently been suggested as an anti-aging factor that declines with age in the bloodstream, and restoration of the youthful level by administration of its recombinant protein could reverse age-related dysfunctions. However, its effects on titanium implant osseointegration and mandibular bone during aging remain unknown.

METHODS

Two-month-old and 18-month-old C57BL male mice were given daily intraperitoneal injections of recombinant GDF11 (rGDF11) or vehicle for 6 weeks. Experimental titanium implants were inserted into femurs on the fourth week. Inhibition of GDF11 function was achieved by GDF11 antibody. Implant-bearing femurs were subjected to histomorphometric analysis and biomechanical evaluation. Mandibles were scanned with micro-CT and decalcified for histological measurements.

RESULTS

In both young adult and aged mice, supraphysiologic GDF11 leads to a significantly decreased bone-to-implant contact ratio (BIC) and peri-implant bone volume/total volume (BV/TV) at the histologic level and reduced resistance at the biomechanical level, indicating weakened implant fixation. Moreover, rGDF11 administration resulted in less trabecular bone volume and thinner cortical thickness in the mandible, which was further compromised in the old animals. In contrast, inhibition of GDF11 improved peri-implant bone healing in old mice.

CONCLUSIONS

Rather than functioning as a rejuvenating factor, exogenous GDF11 negatively affects not only titanium implant healing but also mandibular bone in both young and old mice. In contrast, neutralization of endogenous GDF11 has positive effects on implant fixation in aged mice.

Chronic Kidney Disease Impairs Bone Defect Healing in Rats

Chronic kidney disease (CKD) has been regarded as a risk for bone health. The aim of this study was to evaluate the effect of CKD on bone defect repair in rats. Uremia was induced by subtotal renal ablation, and serum levels of BUN and PTH were significantly elevated four weeks after the second renal surgery. Calvarial defects of 5-mm diameter were created and implanted with or without deproteinized bovine bone mineral (DBBM). Micro-CT and histological analyses consistently revealed a decreased newly regenerated bone volume for CKD rats after 4 and 8 weeks. In addition, 1.4-mm-diameter cortical bone defects were established in the distal end of femora and filled with gelatin sponge. CKD rats exhibited significantly lower values of regenerated bone and bone mineral density (BMD) within the cortical gap after 2 and 4 weeks. Moreover, histomorphometric analysis showed an increase in both osteoblast number (N.Ob/B.Pm) and osteoclast number (N.Oc/B.Pm) in CKD groups due to hyperparathyroidism. Notably, collagen maturation was delayed in CKD rats as verified by Masson’s Trichrome staining. These data indicate that declined renal function negatively affects bone regeneration in both calvarial and femoral defects.

Estrogen Deficiency Leads to Further Bone Loss in the Mandible of CKD Mice

Background

Chronic kidney disease (CKD) has been regarded as a grave public health problem. Estrogen is a critical factor for both renal protection and bone remodeling. Our previous study demonstrated that CKD impairs the healing of titanium implants. The aim of this study was to investigate the effects of estrogen deficiency on the mandibular bone in CKD mice.

Methods

Forty eleven-week-old female C57BL mice were used in this study. Uremia and estrogen deficiency were induced by 5/6 nephrectomy and ovariectomy (OVX), respectively. After 8 weeks, the mice were sacrificed, and their mandibles were collected for micro-CT analysis and histological examination.

Results

All the mice survived the experimental period. Serum measurements confirmed a significant increase in BUN in the CKD group that was further increased by OVX. OVX led to significant decreases in both the BV/TV and cortical thickness of the mandibular bone in CKD mice.

Conclusion

In summary, our findings indicate that estrogen deficiency leads to further mandibular bone loss in CKD mice.

High-fat diet-induced obesity triggers alveolar bone loss and spontaneous periodontal disease in growing mice

Background

The relationship between high-fat food consumption and obesity is well-established. However, it is as yet unclear whether high-fat diet (HFD)-induced obesity in childhood and adolescence determines age-related changes in jaw bone health. The aim of this study is to examine the age-related influence of HFD-induced obesity on mandibular bone architecture and the structure of the periodontium in growing mice.

Methods

Male C57BL/6 J mice (6-weeks-old) were divided into two groups (n = 6 each): the control group received a control diet and the experimental group a HFD. After treatment for 4, 8, or 12 weeks, trabecular and cortical bone architecture was assessed using micro-computed tomography. The periodontium and alveolar bone structure were evaluated by histopathology.

Results

In HFD mice, body weight, serum total cholesterol, and serum leptin levels were significantly higher than those in age-matched control mice (p < 0.05, all comparisons). Reductions in trabecular bone volume and in cortical bone growth (measured as the thickness and cross sectional area) in HFD mice were significant compared with the control mice after 4 weeks of treatment (p < 0.05, both comparisons). Significant decreases in cortical bone density in HFD-fed vs. age-matched control mice were determined after 12 weeks (p < 0.05). In the HFD mice, the periodontal ligament fibres were disrupted, having lost their orientation with respect to the bone surface, and constriction of the periodontal ligament space was inhibited.

Conclusions

These results suggest that HFD-induced obesity during growth not only triggers mandibular osteoporosis but also increases the risk of spontaneous periodontal disease.

Effect of estrogen deficiency on the fixation of titanium implants in chronic kidney disease mice

We established a chronic kidney disease (CKD) mouse model with estrogen deficiency and inserted titanium implants into the femur of such mice to investigate the fixation of the implants. Both the histomorphometry and implant resistance indicated that estrogen deficiency impaired the fixation of titanium implants inserted into such mice.

INTRODUCTION

CKD has been regarded as a worldwide public health problem. Estrogen is a critical factor for both renal protection and bone remodeling. A previous study demonstrated that CKD impairs the early healing of titanium implants. However, the combined effect of estrogen deficiency and CKD on the fixation of titanium implants is largely unknown.

METHODS

Forty 9-week-old female C57BL mice were randomly divided into sham, ovariectomy (OVX), CKD, and CKD + OVX groups. Uremia and estrogen deficiency were induced by 5/6 nephrectomy and OVX, respectively. Experimental titanium implants were inserted into the distal end of the femur. Bone-implant contact (BIC) ratio and bone volume (BV/TV) around the implants were histomorphometrically analyzed. The fixation strength of the implant was measured by a biomechanical push-in resistance test.

RESULTS

Serum measurement confirmed a significant increase in serum blood urea nitrogen (BUN) in the CKD group, which was further increased by OVX. Estrogen deficiency led to significant decreases in the BIC ratio, BV/TV, and the push-in resistance in CKD animals. There was a significant interaction between the effects of OVX and CKD, with OVX exacerbating the effects of CKD on BIC ratio and push-in resistance.

CONCLUSIONS

The results indicated that estrogen deficiency exerts a synergistic effect with CKD and further impairs the fixation of titanium implants in CKD mice.

Vitamin D supplementation enhances the fixation of titanium implants in chronic kidney disease mice

Vitamin D (Vit D) deficiency is a common condition in chronic kidney disease (CKD) patients that negatively affects bone regeneration and fracture healing. Previous study has shown that timely healing of titanium implants is impaired in CKD. This study aimed to investigate the effect of Vit D supplementation on implant osseointegration in CKD mice. Uremia was induced by 5/6 nephrectomy in C57BL mice. Eight weeks after the second renal surgery, animals were given 1,25(OH)2D3 three times a week intraperitoneally for four weeks. Experimental titanium implants were inserted into the distal end of femurs two weeks later. Serum measurements confirmed decreased 1,25(OH)2D levels in CKD mice, which could be successfully corrected by Vit D injections. Moreover, the hyperparathyroidism observed in CKD mice was also corrected. X-ray examination and histological sections showed successful osseointegration in these mice. Histomorphometrical analysis revealed that the bone-implant contact (BIC) ratio and bone volume (BV/TV) around the implant were significantly increased in the Vit D-supplementation group. In addition, resistance of the implant, as measured by a push-in method, was significantly improved compared to that in the vehicle group. These results demonstrate that Vit D supplementation is an effective approach to improve the fixation of titanium implants in CKD.

Adverse mandibular bone effects associated with kidney disease are only partially corrected with bisphosphonate and/or calcium treatment

BACKGROUND/AIMS

Patients with chronic kidney disease (CKD) have a high prevalence of periodontal disease that may predispose to tooth loss and inflammation. The goal of this study was to test the hypotheses that a genetic rat model of progressive CKD would exhibit altered oral bone properties and that treatment with either bisphosphonates or calcium could attenuate these adverse changes.

METHODS

At 25 weeks of age, rats were treated with zoledronate (ZOL), calcium gluconate, or their combination for 5 or 10 weeks. Mandible bone properties were assessed using micro-computed tomography to determine bone volume (BV/TV) and cementum-enamel junction to alveolar crest distance (CEJ-AC).

RESULTS

Untreated CKD animals had significantly lower BV/TV at both 30 (-5%) and 35 (-14%) weeks of age and higher CEJ-AC (+27 and 29%) compared to normal animals. CKD animals had a significantly higher parathyroid hormone (PTH) compared to normal animals, yet similar levels of C-reactive protein (CRP). ZOL treatment normalized BV/TV over the first 5 weeks but this benefit was lost by 10 weeks. Calcium treatment, alone or in combination with ZOL, was effective in normalizing BV/TV at both time points. Neither ZOL nor calcium was able to correct the higher CEJ-AC caused by CKD. Calcium, but not ZOL, significantly reduced serum PTH, while neither treatment affected CRP.

CONCLUSIONS

(i) This progressive animal model of CKD shows a clear mandibular skeletal phenotype consistent with periodontitis, (ii) the periodontitis is not associated with systemic inflammation as measured by CRP, and (iii) reducing PTH has positive effects on the mandible phenotype.

Effect of chronic kidney disease on the healing of titanium implants

Chronic kidney disease (CKD) has become a worldwide public health problem. However, its effect on osseointegration of dental implants is largely unknown. The aim of this study is to investigate whether CKD impairs the quality of the osseointegration of titanium implants. Uremia was induced by 5/6 nephrectomy in mice, and serum levels of BUN, FGF23, PTH and ALP were significantly increased. For in vitro tests, bone marrow mesenchymal stem cells (BMMSCs) were obtained and cultured on titanium discs. There was no significant difference in term of expression of osteogenic marker genes including Osx, Col-1, Ocn, and Opn, as quantified by qPCR. Moreover, Alizarin Red S staining showed comparable mineralized nodules formation. Histomorphometrical analysis of experimental implants inserted in the femurs of CKD mice revealed a trend of decreased BIC ratio at 2-week healing. The strength of bone-implant integration, as measured by a push-in method, was significantly lower for the CKD group at 2 weeks, although a comparable level was reached at 4 weeks. These results demonstrated that CKD only negatively affects the osseointegration of titanium implants at the early stage.

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.

High phosphate feeding promotes mineral and bone abnormalities in mice with chronic kidney disease

BACKGROUND

Chronic kidney disease-mineral bone disorder (CKD-MBD) is a systemic syndrome characterized by imbalances in mineral homeostasis, renal osteodystrophy (ROD) and ectopic calcification. The mechanisms underlying this syndrome in individuals with chronic kidney disease (CKD) are not yet clear.

METHODS

We examined the effect of normal phosphate (NP) or high phosphate (HP) feeding in the setting of CKD on bone pathology, serum biochemistry and vascular calcification in calcification-prone dilute brown non-agouti (DBA/2) mice.

RESULTS

In both NP and HP-fed CKD mice, elevated serum parathyroid hormone and alkaline phosphatase (ALP) levels were observed, but serum phosphorus levels were equivalent compared with sham controls. CKD mice on NP diet showed trabecular alterations in the long bone consistent with high-turnover ROD, including increased trabecular number with abundant osteoblasts and osteoclasts. Despite trabecular bone and serum biochemical changes, CKD/NP mice did not develop vascular calcification. In contrast, CKD/HP mice developed arterial medial calcification (AMC), more severe trabecular bone alterations and cortical bone abnormalities that included decreased cortical thickness and density, and increased cortical porosity. Cortical bone porosity and trabecular number strongly correlated with the degree of aortic calcification.

CONCLUSIONS

HP feeding was required to induce the full spectrum of CKD-MBD symptoms in CKD mice.