Elsevier

Bone

Volume 81, December 2015, Pages 247-254
Bone

Original Full Length Article
Altered material properties are responsible for bone fragility in rats with chronic kidney injury

https://doi.org/10.1016/j.bone.2015.07.015Get rights and content

Highlights

  • The roles of uremia in the bone abnormalities were examined in uremic rats.

  • In uremic animals, bone viscoelastic mechanical properties were deteriorated.

  • Pentosidine-to-matrix ratio was increased.

  • The degree of orientation of the c-axis in biological apatite was decreased.

  • These abnormalities showed no relations to the parathyroid function.

Abstract

Chronic kidney disease (CKD) is associated with an increased risk of fragility fractures, but the underlying pathophysiological mechanism remains obscure. We performed an in vivo experimental study to examine the roles of uremia and abnormal mineral/parathyroid metabolism in the development of bone metabolic abnormalities in uremic rats. Male Sprague-Dawley rats were divided into four groups, comprising sham operation (high turnover bone control = HTB-Cont), 5/6-nephrectomy (high turnover bone nephrectomized = HTB-Nx), thyroparathyroidectomy (low turnover bone control = LTB-Cont), and thyroparathyroidectomy plus 5/6 nephrectomy (low turnover bone nephrectomized = LTB-Nx), and maintained for 16 weeks. Uremia was successfully created in the LTB-Nx and HTB-Nx groups, while hyperparathyroidism was only found in the HTB-Nx group. Cancellous bone histomorphometry revealed significantly higher bone turnover in the HTB-Nx group than in the LTB-Nx group. Storage modulus at 1 Hz and tan delta in cortical bone of the femur, which represent the viscoelastic mechanical properties, were significantly lower in both Nx groups than in the Cont groups regardless of bone metabolism. Pentosidine-to-matrix ratio was increased and crystallinity was decreased in both Nx groups regardless of bone turnover. Mineral-to-matrix ratio was significantly decreased in the HTB-Nx group, but increased in the LTB-Nx group. Enzymatic collagen crosslinks were decreased in the HTB-Nx group. The degree of orientation of the c-axis in carbonated hydroxyapatite (biological apatite = BAp) crystallites was decreased in both Nx groups regardless of bone metabolism. Stepwise multivariate regression revealed that pentosodine-to-matrix ratio and BAp preferential c-axis orientation were significantly associated with storage modulus and tan delta. In conclusion, bone elastic mechanical properties deteriorated regardless of bone metabolism or bone mass in rats with chronic kidney injury. Various changes in bone mineral properties were associated with CKD, including abnormal parathyroid function, impaired bone turnover, and uremia associated with the accumulation of uremic toxins, were responsible for these changes. Pentosidine-to-matrix ratio and BAp orientation at position 5 were the two meaningful determinants of elastic bone mechanical strength, and both factors were associated with the severity of uremia, but not parathyroid function or bone metabolism. These two factors may account for the increased bone fragility among CKD patients.

Introduction

Chronic kidney disease (CKD) is associated with abnormalities in systemic mineral metabolism, which is termed CKD-related mineral and bone disease (CKD-MBD) [1]. Abnormal bone metabolism is one of the major manifestations of CKD-MBD. In fact, abnormal bone turnover and/or bone mineralization derived from abnormal systemic mineral metabolism are commonly found among CKD patients [2], [3].

CKD is also associated with an increased risk of fragility fractures. Predialysis patients with an estimated glomerular filtration rate of < 45 ml/min/1.73 m2 have twice the risk of hip fractures compared with healthy individuals [4]. Moreover, dialysis patients have a several times higher risk of hip fractures than the general population [5], [6].

Bone mass is a partial predictor of fracture [7], even among CKD patients [8], [9]. The determinants of bone strength other than bone mass are collectively referred to as bone quality. Bone quality relies on many factors including bone turnover, mineralization, microarchitecture, collagen crosslinking, and matrix composition [7].

Abnormalities in systemic mineral metabolism could alter both bone mass and bone quality in CKD patients. In particular, abnormal bone turnover and bone mineralization are predominantly caused by abnormal parathyroid and/or mineral metabolisms in this disease condition [10]. Thus, CKD-MBD may account for the increased risk of fragility fractures among CKD patients, at least in part.

However, reduced bone mass and abnormal systemic mineral metabolism, namely CKD-MBD, may not be the only cause of the increased bone fragility in CKD patients. This is because the material properties, including the chemical composition, relative amounts, and distributions of mineral and matrix, govern the mechanical properties of bone [11]. We previously reported that the mineral and matrix composition in the femoral diaphysis showed specific alterations in uremic rats without secondary hyperparathyroidism, and those material changes were tightly associated with bone mechanical deterioration [12], [13]. Moreover, such alterations in bone material composition and mechanical properties were at least partially rescued by administration of an oral adsorbent that reduced the circulating uremic toxin levels [13]. Thus, we hypothesized that the accumulation of uremic toxins is another possible candidate for the increased bone fragility.

Nevertheless, we did not intend to negate the role of CKD-MBD in the increased bone fragility in the CKD condition. Both abnormal systemic mineral metabolism and uremic toxins are possible candidates for the pathogenesis of the increased bone fragility in the uremic condition. Thus, we performed an in vivo experimental study using rats with chronic kidney injury and various degrees of parathyroid function. The aim of this study was to evaluate the roles of uremia and abnormal mineral/parathyroid metabolism in the development of bone abnormalities in the uremic condition.

Section snippets

Materials and methods

All experiments, including animal handling and testing, were approved by the Animal Care and Use Committee of the Biomedical Research Laboratories, Kureha Chemical Industry Co. Ltd., Japan.

Renal function and bone histomorphometry

Uremia determined by decreased levels of creatinine clearance was successfully created by the Nx procedure in both the LTB-Nx and HTB-Nx groups. Although the circulating PTH levels were increased in the HTB-Nx group, they stayed within comparable levels to the control LTB-Nx group (Table 1).

Cancellous bone histomorphometric analyses were conducted to confirm bone turnover using tibial samples at the end of the experiment (16 weeks). The dynamic parameters showed that bone turnover was higher in

Discussion

In this study, we examined the bone mechanical properties using DMA in two groups of uremic rats with quite different bone metabolism. Despite their different bone turnovers, both uremic groups showed reduced bone elastic mechanical properties. As shown in Table 1 and Fig. 3, the bone storage modulus and tan delta in the HTB-Nx group were attenuated along with the severity of renal injury. We could not find any evident differences in the magnitude of elastic mechanical property deterioration

Acknowledgments

We wish to thank Kiyoshi Miyashita for the technical advice on Raman spectroscopy. We also thank Mikio Sugano and Mieko Kuwahara for their technical assistance. This work was supported in part by a grant-in-aid from the Japanese Society for the Promotion of Science (no. 23591223 to YI and no. 123591215 to JJK) and from the Kidney Foundation Japan (no. JKFB10-21 to YI).

References (48)

  • M. Jadoul et al.

    Incidence and risk factors for hip or other bone fractures among hemodialysis patients in the Dialysis Outcomes and Practice Patterns Study

    Kidney Int.

    (2006)
  • Z.Z. Lin et al.

    Epidemiology and mortality of hip fracture among patients on dialysis: Taiwan National Cohort Study

    Bone

    (2014)
  • C.O. Stehman-Breen et al.

    Risk factors for hip fracture among patients with end-stage renal disease

    Kidney Int.

    (2000)
  • M.D. Danese et al.

    PTH and the risks for hip, vertebral, and pelvic fractures among patients on dialysis

    Am. J. Kidney Dis.

    (2006)
  • J.J. Kazama et al.

    Uremic osteoporosis

    Kidney Int. Suppl.

    (2013)
  • H.H. Malluche et al.

    Renal osteodystrophy: what's in a name? Presentation of a clinically useful new model to interpret bone histologic findings

    Clin. Nephorol.

    (2006)
  • J.J. Kazama

    Bone histology in chronic kidney disease-related mineral and bone disorder

    Ther. Apher. Dial.

    (2011)
  • K.E. Ensrud et al.

    Renal function and risk of hip and vertebral fractures in older women

    Arch. Intern. Med.

    (2007)
  • M. Wakasugi et al.

    Increased risk of hip fracture among Japanese hemodialysis patients

    J. Bone Miner. Metab.

    (2013)
  • NIH consensus Development Panel on Osteoporosis Prevention, Diagnosis, and Therapy

    Osteoporosis prevention, diagnosis, and therapy

    JAMA

    (2001)
  • S. Jamal et al.

    Bone mineral density by DXA and HR pQCT can discriminate fracture status in men and women with stages 3 to 5 chronic kidney disease

    Osteoporos. Int.

    (2012)
  • S. Iimori et al.

    Diagnostic usefulness of bone mineral density and biochemical markers of bone turnover in predicting fracture in CKD stage 5D patients—a single-center cohort study

    Nephrol. Dial. Transplant.

    (2012)
  • S.M. Ott

    Bone disease in CKD

    Curr. Opin. Nephrol. Hypertens.

    (2012)
  • S. Weiner et al.

    The material bone: structure–mechanical function relations

    Annu. Rev. Mater. Sci.

    (1998)
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    Funding information

    This work was supported in part by Grants-in-Aid from the Japanese Society for the Promotion of Science (No. 23591223 to YI and No. 123591215 to JJK) and the Kidney Foundation, Japan (No. JKFB10-21 to YI).

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