Static histomorphometry allows for a diagnosis of bone turnover in renal osteodystrophy in the absence of tetracycline labels

Static histomorphometry parameters can identify bone turnover status in children and adults with chronic kidney disease

INTRODUCTION

Tetracycline labeling for bone biopsy facilitates quantification of the pace of new bone production. As tetracycline labeling needs to be done prior to biopsy, it cannot be used to assess bone turnover in patients presenting with fractures, yet knowing turnover rate in patients experiencing fractures - especially in those with chronic kidney disease (CKD) - may guide appropriate medical therapy after surgical repair. Therefore, we sought to determine the diagnostic accuracy of static markers of bone turnover relative to tetracycline labeling in a pediatric and adult cohort of patients with chronic kidney disease (CKD) undergoing iliac crest biopsy with histomorphometry.

METHODS

We evaluated two cohorts, one of 147 children and young adults ages 18±10 and another of 151 adults ages 49±13 who had undergone iliac crest biopsy with tetracycline labeling for clinical indications of CKD-mineral and bone disorders. We used bone formation rate relative to bone surface (BFR/BS) based on double tetracycline labeling as our gold standard marker of bone turnover. A blinded investigator used light microscopy without fluorescence to measure static bone turnover parameters. We compared the area under the ROC curve (AUC), sensitivity, and specificity of each static parameter with low and high bone turnover based on BFR/BS.

RESULTS

In the pediatric and adult cohorts, 35 (24 %) and 70 (46 %) had low bone turnover, respectively, and 18 (12 %) and 30 (20 %) had high bone turnover, respectively. The static parameters with the greatest AUCs for low and high turnover were osteoblast surface/bone surface (Ob.S/BS), osteoclast surface/bone surface (Oc.S/BS), eroded surface/bone surface (ES/BS), osteoid surface/bone surface (OS/BS), osteoid volume/bone volume (OV/BV), and osteoid thickness (O.Th.) in both cohorts. Ob.S/BS had the highest AUC for low and high turnover in the pediatric cohort (0.8204 and 0.8678, respectively) whereas Oc.S/BS had the highest AUC for low turnover (0.8325) and ES/BS had the highest AUC for high turnover (0.7360) in the adult cohort.

DISCUSSION

Static measures of histomorphometry that do not rely on tetracycline bone labeling can identify low and high bone turnover in children and adults with CKD with moderate to high accuracy. This approach may allow assessment of bone turnover in the setting of clinical fractures where clinicians may have access to bone tissue but where tetracycline labeling is not available.

Relationship between biochemical parameters of mineral bone disease and static bone histomorphometry in chronic kidney disease patients on hemodialysis: An Indian cross-section study

AIM

We estimated the relationship between routine biochemical laboratory parameters with static bone histomorphometric parameters and their high and low bone turnover capacity predictability in hemodialysis patients.

METHOD

It was a single-center cross-sectional study, included 28 hemodialysis patients. The routine biochemical parameters measured including calcium, phosphorous, alkaline phosphatase, intact PTH, and 25-hydroxycholecalciferol. The histomorphometric parameters assessed were osteoblasts perimeter, osteoclast perimeter, eroded perimeter, osteoid perimeter, bone fibrosis and bone volume.

RESULT

Total 28 hemodialysis patients underwent bone biopsy. Seventy percent were male, with a mean age was 33.07±10.42 yrs; serum alkaline phosphatase was 219.10±311.3IU/ml; vitamin D was 18.18±9.56ng/ml, and intact PTH was 650.7±466.0pg/ml. Intact PTH had a significant positive association with osteoblast, osteoclast, eroded surface, and osteoid perimeter. Serum alkaline phosphatase had a significant relationship with bone fibrosis (r=0.525, p-value=0.004). Intact PTH was significantly higher in females than males (1078.75±533.04 vs. 479.6±309.83; p-value=0.004). The osteoid surface was significantly high in females compared to males (p=0.038). Age had a significant impact on osteoblast and eroded surface (p=0.008 and p=0.031, respectively). Intact PTH is a reliable biomarkers for bone turnover compare to ALP (p<0.001 and p=0.554, respectively).

CONCLUSION

Intact PTH strongly associated with bone formation, bone resorption parameters. Gender and age had significant impact on static histomorphometric parameters in our study.

Mild Chronic Kidney Disease Associated with Low Bone Formation and Decrease in Phosphate Transporters and Signaling Pathways Gene Expression

The initial phases of molecular and cellular maladaptive bone responses in early chronic kidney disease (CKD) remain mostly unknown. We induced mild CKD in spontaneously hypertensive rats (SHR) by either causing arterial hypertension lasting six months (sham-operated rats, SO6) or in its' combination with 3/4 nephrectomy lasting two and six months (Nx2 and Nx6, respectively). Sham-operated SHRs (SO2) and Wistar Kyoto rats (WKY2) with a two-month follow-up served as controls. Animals were fed standard chow containing 0.6% phosphate. Upon follow-up completion in each animal, we measured creatinine clearance, urine albumin-to-creatinine ratio, renal interstitial fibrosis, inorganic phosphate (Pi) exchange, intact parathyroid hormone (PTH), fibroblast growth factor 23 (FGF23), Klotho, Dickkopf-1, sclerostin, and assessed bone response by static histomorphometry and gene expression profiles. The mild CKD groups had no increase in renal Pi excretion, FGF23, or PTH levels. Serum Pi, Dickkopf-1, and sclerostin were higher in Nx6. A decrease in trabecular bone area and osteocyte number was obvious in SO6. Nx2 and Nx6 had additionally lower osteoblast numbers. The decline in eroded perimeter, a resorption index, was only apparent in Nx6. Significant downregulation of genes related to Pi transport, MAPK, WNT, and BMP signaling accompanied histological alterations in Nx2 and Nx6. We found an association between mild CKD and histological and molecular features suggesting lower bone turnover, which occurred at normal levels of systemic Pi-regulating factors.

Time for Revival of Bone Biopsy with Histomorphometric Analysis in Chronic Kidney Disease (CKD): Moving from Skepticism to Pragmatism

Bone Biopsy (BB) with histomorphometric analysis still represents the gold standard for the diagnosis and classification of different forms of renal osteodystrophy. Bone biopsy is the only technique able to provide comprehensive information on all bone parameters, measuring static and dynamic parameters of turnover, cortical and trabecular microarchitecture, and mineralization defects. In nephrological practice, bone biopsy yields relevant indications to support therapeutic choices in CKD, heavily impacting the management and prognosis of uremic patients. Unfortunately, the use of bone biopsy has decreased; a lack of expertise in performing and interpreting, perceived procedure invasiveness and pain, and reimbursement issues have all contributed to this decline. Nevertheless, both bone biomarkers and instrumental images cannot be considered reliable surrogates for histological findings, being insufficiently accurate to properly evaluate underlying mineral and bone disorders. This is a multidisciplinary position paper from the Nephrology and Osteoporosis Italian Scientific Societies with the purpose of restating the role of bone biopsy in CKD patient management and of providing strong solutions to allow diffusion of this technique in Italy, but potentially also in other countries. The Italian approach through the optimization and standardization of bone biopsy procedure, the construction of the Italian Hub and Spoke network, and a request for adjustment and national homogenization of reimbursement to the Italian Health Ministry has led the way to implement bone biopsy and to improve CKD patient management and prognosis.

Natural History of Bone Disease following Kidney Transplantation

BACKGROUND

Knowledge of the effect of kidney transplantation on bone is limited and fragmentary. The aim of this study was to characterize the evolution of bone disease in the first post-transplant year.

METHODS

We performed a prospective, observational cohort study in patients referred for kidney transplantation under a steroid-sparing immunosuppressive protocol. Bone phenotyping was done before, or at the time of, kidney transplantation, and repeated at 12 months post-transplant. The phenotyping included bone histomorphometry, bone densitometry by dual-energy x-ray absorptiometry, and biochemical parameters of bone and mineral metabolism.

RESULTS

Paired data were obtained for 97 patients (median age 55 years; 72% male; 21% of patients had diabetes). Bone turnover remained normal or improved in the majority of patients (65%). Bone histomorphometry revealed decreases in bone resorption (eroded perimeter, mean 4.6% pre- to 2.3% post-transplant; P<0.001) and disordered bone formation (fibrosis, 27% pre- versus 2% post-transplant; P<0.001). Whereas bone mineralization was normal in all but one patient pretransplant, delayed mineralization was seen in 15% of patients at 1 year post-transplant. Hypophosphatemia was associated with deterioration in histomorphometric parameters of bone mineralization. Changes in bone mineral density were highly variable, ranging from -18% to +17% per year. Cumulative steroid dose was related to bone loss at the hip, whereas resolution of hyperparathyroidism was related to bone gain at both spine and hip.

CONCLUSIONS

Changes in bone turnover, mineralization, and volume post-transplant are related both to steroid exposure and ongoing disturbances of mineral metabolism. Optimal control of mineral metabolism may be key to improving bone quality in kidney transplant recipients.

CLINICAL TRIAL REGISTRY NAME AND REGISTRATION NUMBER

Evolution of Bone Histomorphometry and Vascular Calcification Before and After Renal Transplantation, NCT01886950.

Contemporary kidney transplantation has a limited impact on bone microarchitecture

Bone microarchitecture is an important component of bone quality and disturbances may reduce bone strength and resistance to trauma. Kidney transplant recipients have an excess risk of fractures, and bone loss affecting both trabecular and cortical bone compartments have been demonstrated after kidney transplantation. The primary aim of this study was to investigate the impact of kidney transplantation on trabecular and cortical bone microarchitecture, assessed by histomorphometry and micro computed tomography (μCT). Iliac crest bone biopsies, analyzed by bone histomorphometry and μCT, were performed at time of kidney transplantation and 12 months post-transplantation in an unselected cohort of 30 patients. Biochemical markers of mineral metabolism and bone turnover were measured at both time-points. At 12 months post-transplantation, bone turnover was low in 5 (17%) and normal in 25 (83%) patients. By histomorphometry, bone remodeling normalized, with decreases in eroded perimeters (4.0 to 2.1%, p = 0.02) and number of patients with marrow fibrosis (41 to 0%, p < 0.001). By μCT, trabecular thickness (134 to 125 μM, p = 0.003) decreased slightly. Other parameters of bone volume and microarchitecture, including cortical thickness (729 to 713 μm, p = 0.73) and porosity (10.2 to 9.5%, p = 0.15), remained stable. We conclude that kidney transplantation with current immunosuppressive protocols has a limited impact on bone microarchitecture.

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Bone structure after kidney transplantation was explored using biopsy, μCT, and DXA.

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Modest trabecular bone loss was detected in the first post-transplant year.

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Cortical thickness and porosity were overall stable post-transplant.

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Contemporary kidney transplantation has minimal impact on bone microarchitecture.

Bone Biopsy for Histomorphometry in Chronic Kidney Disease (CKD): State-of-the-Art and New Perspectives

The use of bone biopsy for histomorphometric analysis is a quantitative histological examination aimed at obtaining quantitative information on bone remodeling, structure and microarchitecture. The labeling with tetracycline before the procedure also allows for a dynamic analysis of the osteoblastic activity and mineralization process. In the nephrological setting, bone biopsy is indicated to confirm the diagnosis of subclinical or focal osteomalacia and to characterize the different forms of renal osteodystrophy (ROD). Even if bone biopsy is the gold standard for the diagnosis and specific classification of ROD, the use of this approach is very limited. The main reasons for this are the lack of widespread expertise in performing or interpreting bone biopsy results and the cost, invasiveness and potential pain associated with the procedure. In this regard, the sedation, in addition to local anesthesia routinely applied in Italian protocol, significantly reduces pain and ameliorates the pain perception of patients. Concerning the lack of widespread expertise, in Italy a Hub/Spokes model is proposed to standardize the analyses, optimizing the approach to CKD patients and reducing the costs of the procedure. In addition, new tools offer the possibility to evaluate the osteogenic potential or the ability to form bone under normal and pathological conditions, analyzing mesenchymal stem cells and their ability to differentiate in the osteogenic lineage. In the same way, circulating microRNAs are suggested as a tool for exploring osteogenic potential. The combination of different diagnostic approaches and the optimization of the bioptic procedure represent a concrete solution to spread the use of bone biopsy and optimize CKD patient management.