Saudi Journal of Kidney Diseases and Transplantation

ORIGINAL ARTICLE
Year
: 2019  |  Volume : 30  |  Issue : 5  |  Page : 1022--1031

Correlation between serum sclerostin level and bone density status in children on regular hemodialysis


Manal Abd Elsalam1, Maha Zein El-Abden1, Eman Mahmoud2, Zakia Abo Zahab3, Heba Ahmed1,  
1 Department of Pediatrics, Faculty of Medicine, Al-Azhar University, Cairo, Egypt
2 Department of Endocrinology, Faculty of Medicine, Al-Azhar University, Cairo, Egypt
3 Department of Clinical Pathology, Faculty of Medicine, Al-Azhar University, Cairo, Egypt

Correspondence Address:
Manal Abd Elsalam
Department of Pediatrics, Faculty of Medicine, Al-Azhar University, Cairo
Egypt

Abstract

Bone disease is frequently observed in chronic kidney disease (CKD) and increases a patient’s risk for fracture. Sclerostin is an osteocyte-derived negative regulator of bone formation. We aimed to assess serum sclerostin level as a bone marker in children with CKD on regular hemodialysis (HD) and detect the association between this and bone density status. This cross-sectional comparative study was conducted on 25 children with CKD on HD and 25 age- and sex-matched healthy children, as controls. Their ages ranged from 4 to 18 years. Serum sclerostin levels were measured and dual-energy X-ray absorptiometry scan was performed in the same line with the traditional bone markers. There was a significant increase in serum sclerostin level in patients (1.754 ± 1.31 ng/mL) compared to controls (0.290 ± 0.074 ng/mL) with P = 0.001. Nine patients (36%) had low bone mineral density (BMD) with z score under -2.0, eight of whom had low BMD in both the neck of femur and lumbar spines. There was a significant increase in serum sclerostin levels in the patient-group with low BMD (2.38 ± 0.85 ng/mL) compared with patients with normal BMD (1.4 ± 0.98 ng/mL) (P = 0.001). A significant positive correlation was found between serum sclerostin level and alkaline phosphtase, parathormone with negative correlation with serum calcium. Sclerostin was 100% specific and sensitive in predicting CKD-mineral and bone disorder. Elevated sclerostin levels were consistent with low BMD and appear to be an independent predictor of reduced BMD in children on regular HD.



How to cite this article:
Elsalam MA, El-Abden MZ, Mahmoud E, Zahab ZA, Ahmed H. Correlation between serum sclerostin level and bone density status in children on regular hemodialysis.Saudi J Kidney Dis Transpl 2019;30:1022-1031


How to cite this URL:
Elsalam MA, El-Abden MZ, Mahmoud E, Zahab ZA, Ahmed H. Correlation between serum sclerostin level and bone density status in children on regular hemodialysis. Saudi J Kidney Dis Transpl [serial online] 2019 [cited 2019 Nov 21 ];30:1022-1031
Available from: http://www.sjkdt.org/text.asp?2019/30/5/1022/270256


Full Text



 Introduction



Bone disease is frequently observed in chronic kidney disease (CKD) and increases a patient’s risk for fracture, cardiovascular (CV) calcification, and mortality. The Kidney Disease Improving Global Outcomes foundation defined a new syndrome incorporating the bone, mineral, and CV disorders, namely CKD–mineral and bone disorders (CKD-MBDs).[1]

The quest for a modifiable reliable biomarker of CV and bone disease in CKD-MBD remains a nephrologist’s challenge. Numerous bone proteins have been associated with CKD-MBD in patients with CKD, such as osteoprotegerin (OPG),[2] fibroblast growth factor 23, bone-specific alkaline phosphatase (ALP),[3] and sclerostin.[4]

Sclerostin is a new and potentially important player in the well-known bone–vascular axis in CKD and end-stage renal disease (ESRD).[5]

Sclerostin is a 21-kDa glycoprotein that inhibits osteoblast differentiation and bone formation,[6],[7] and is secreted almost exclusively by osteocytes and to a lesser extent by other cell types including osteoclast precursors, renal and vascular cells.[8] In mouse models, dose-dependent decreases in osteocyte scierostin expression have been shown with mechanical loading, and conversely increased sclerostin expression occurs with mechanical unloading.[9],[10] Sclerostin blocks the Wnt signaling pathway in osteoblasts by binding to low-density lipoprotein receptor-related protein 5/6 (LRP-5/6) receptors.[5],[11],[12],[13]

Therefore, sclerostin is a potent inhibitor of bone formation and mineralization. Accordingly, rodent sclerostin deficiency models exhibit a strong bone phenotype. Moreover, blocking sclerostin represents a promising treatment perspective against osteoporosis.[14]

In the context of CKD, sclerostin concentrations clearly increase as glomerular filtration rate decreases; whether this is due to reduced renal clearance, increased skeletal production, or both is still a subject of debate. Therefore, the biological significance and interpretation of circulating sclerostin levels in CKD remain uncertain.[5]

Only a few studies have examined serum sclerostin levels in adult patients with CKD, with particularly few studies in dialysis patients,[15],[16],[17] in whom bone metabolism can be abnormally regulated under both high and low turnover conditions.[18] The hypothesis is that CKD-MBD is a complex disease that is not completely understood; however, the aim is to assess serum sclerostin level as one of the factors secreted by the osteocytes that may facilitate the understanding and management and correlate with bone density status.

 Materials and Methods



This is a cross-sectional comparative study, conducted during the period from February 2016 to August 2016. Samples were selected from the nephrology and hemodialysis (HD) units, and from the outpatient pediatric clinic of Alzahraa University Hospital. The study children were divided into two groups: Group I, dialysis group): This included 25 children with ESRD [(estimated glomerular filtration rate) <15 mL/min/l.73 m2] on regular HD for more than three months at the time of the study.[19] They were on regular HD for 4 h, three times weekly, with polysulfone low flux membrane dialyzer, their ages ranged from 5 to 17 years. Furthermore, the study included 25 age- and sex-matched healthy children who served as controls. Children on steroid therapy, children with congenital bone deformity, other chronic illness, and recent fracture were excluded from the study. The study patients were subjected to full history (etiology and duration of CKD and dialysis), and bone symptoms (aches, deformities, and medications).

Informed consent was obtained from the participating parents in adherence to the guidelines of the ethical committee of Alzhraa University Hospital, Al-Azhar University, Cairo, Egypt.

Investigations

Sample collection

Blood samples were drawn in the morning after an overnight fast of at least 12 h before the start of the mid-week HD session. A 5 mL venous blood sample was withdrawn; 2 mL was mixed with EDTA solution and tested for complete blood picture. 3 mL of the samples was left to clot and serum was separated without delay and analyzed for biochemical parameters on the same day, including serum urea creatinine, calcium, phosphorus, ALP, and parathormone (PTH). All samples were tested on HITACHII auto-analyzer.

Two milliliters of the serum sample was stored at −20°C after careful labeling till the time of sclerostin assay; quantitative determination of serum sclerostin concentrations was performed using the ELISA technique. Kits were delivered by Glory bioscience (www. glorybioscience.com).

This study was conducted with the participation of pediatric (nephrology and HD), endocrinology and clinical pathology departments.

Dual X-ray absorptiometry

For the assessment of bone mineral density (BMD), DEXA test was performed by dual-energy X-ray absorptiometry (DEXA) device in the endocrinology department and Alzharaa University Hospital. All BMD measurements were carried out by an experienced technician by using a GE Lunar prodigy DF +16170 DEXA scanner (Norland) with advanced fan-beam technology, the examination was conducted with the patient lying in supine and lateral decubitus positions. The measurement of BMD was carried out on the lumbar spine, and the anteroposterior (AP) images were generated in all patients. Z-score <-2, which was below the expected range for age, was indicative of the diagnosis.[20]

The recommendations included were:

  1. Measurement at two sites (hip, spine)
  2. AP images of L1–L4 were used for spine BMD measurement
  3. Proximal neck of the left femur was used for the hip
  4. The scanner calculated BMD in grams per square centimeter
  5. A reference database was consulted, and values and curves were obtained.


 Statistical Analysis



Data were collected, revised, coded, and entered the Statistical Package for the Social Science version 20 (IBM Corp., Armonk, NY, USA). Spearman correlation coefficients were used to assess the correlation between two studied parameters in the same group. Receiver operating characteristic (ROC) curve was used to assess the best cutoff point with sensitivity and specificity.

Interpretation of probability values were as follows: P >0.05 as nonsignificant, P <0.05 as significant and P <0.01 as highly significant.

 Results



There was significant increase in the serum PTH, ALP, and sclerostin levels in the patients-group compared to controls with no significant difference in the serum calcium (Ca) level. There was also a significant increase in serum sclerostin levels in males compared to females among the patients-group [Table 1].{Table 1}

[Table 2] shows that nine patients (36%) had low BMD, eight of whom had low BMD in both neck of femur and lumbar spine and one patient had low BMD in lumbar spine only.{Table 2}

[Table 3] shows comparison between patients with normal BMD and those with low BMD regarding the traditional bone markers; it revealed no significant difference between the two groups regarding the serum level of serum Ca, phosphate, PTH and ALP. [Table 3] also shows the comparison between patients with normal and those with low BMD regarding sclerostin level; it shows a significant increase in serum sclerostin level in the patients-group with low BMD.{Table 3}

[Figure 1] shows significant positive correlation between serum sclerostin and PTH levels. [Figure 2] shows significant negative correlation between serum sclerostin and calcium levels. [Figure 3] shows significant positive correlation between serum sclerostin and ALP levels. [Figure 4] shows BMD of lumbar spine in the control with z score of 1.8 and [Figure 5] shows BMD of the lumbar spine in the patient-group with z score of 2.8. [Figure 6] and [Figure 7] show BMD in the neck of femur in one of the controls and the patient-group, z score was 0.8 and -2.6, respectively.{Figure 1}{Figure 2}{Figure 3}{Figure 4}{Figure 5}{Figure 6}{Figure 7}

[Table 4] and [Table 5] and [Figure 8] show the cutoff point, sensitivity, and specificity of serum sclerostin level and BMD of lumbar spine and the head of femur in children on HD for the prediction of CKD-MBD; it was >0.383, 100%, 100%;0.3, 96%, 68%; 0.4, 84%, 85%, respectively.{Table 4}{Table 5}{Figure 8}

 Discussion



To our knowledge, this is the first study reporting serum sclerostin level in children on HD and consequently, the associations between serum sclerostin levels and BMD in these patients. Compared with healthy controls, significant increase in level of serum sclerostin was detected in the HD group. Claes et al[21] reported that plasma concentration of sclerostin tends to increase across the stages of CKD, and is significantly elevated in maintenance HD patients.[22]

The study results were also in agreement with Thambiah et al[23] and Pelletier et al,[17] who reported significant increase in serum sclerostin level in CKD patients, which reveal accumulation of levels with declining renal filtration; whether this is due to decreased clearance or excess production has not yet been fully assessed.[15] These data originate solely in adults.

In the present study, sclerostin levels are significantly higher in boys than in girls; however, age was not associated significantly. Kirmanı et al[24] reported similar findings in a cross-sectional sample of healthy boys and girls aged 6–21 years, in adults; Modder et al[25] also reported similar findings.

On the other hand, Fischer et al[26] reported that sclerostin levels were independent of age and gender.

The reasons for higher serum sclerostin in males than females are unclear, but it might reflect total-body skeletal mass; the larger skeleton in men simply may produce and release more sclerostin into the circulation.[26] We found that sclerostin levels positively correlated with PTH and ALP levels and negatively correlated with serum Ca and PTH, which is a central regulator of bone homeostasis and inhibits sclerostin expression. Numerous studies have revealed that osteocytes are crucial target cells for the actions of PTH. PTH promotes new bone formation by down-regulating the expression of sclerostin.[27],[28]

Chronic excess of PTH, as in primary hyper-parathyroidism or secondary to Ca deficiency, increases the rate of bone remodeling, and can result in loss of bone.[29]

Our results are similar to the report of Kim et al,[30] but are inconsistent with the reports of Mirza et al and,[31] Gennari et al,[32] who reported that PTH correlates negatively with serum sclerostin levels. Jean et al[33] did not observe any association between serum sclerostin and PTH levels.

The cause of this discrepancy is unknown but may be attributed to the observation that uremia leads to skeletal resistance to PTH, and decreases in PTH signaling activity might result in increased production of sclerostin in CKD patients.[30]

In the present study, we measured BMD of the anterior-posterior lumbar spine (L1–L4), and the neck of femur, by DEXA. About 36% of the study patients had low BMD; similarly, Andrade et al,[34] Bakr.[35] and Shepetov et al[36] respectively, reported that 25%, 59.1% and 53.1% of children with CKD had low BMD.

It is not surprising to see significant association between low BMD and serum sclerostin levels in pediatric patients on HD with no significant association with the traditional markers; the main action of sclerostin is a decrease in bone formation through inhibiting osteoblast proliferation, differentiation, and promoting osteoblast apoptosis.[37] There are some studies however, linking the increased plasma sclerostin concentrations in CKD with the development of renal osteodystrophy.[16],[38] It has been demonstrated that serum sclerostin levels correlated negatively with the histomorphometric parameters of bone turnover and osteoblastic number in bone biopsies from HD patients.

Some studies[16],[39] unexpectedly found that serum sclerostin levels were associated positively with BMD; the disparity may due to older patients studied and longer duration on HD.

ROC curve analysis revealed that the cutoff point of sclerostin between patients and controls is >0.383 (ng/mL) with 100% specificity and sensitivity as a new marker of CKD MBD.

In conclusion, serum sclerostin levels are increased in children on HD with significant association with low BMD values. This study provides a base for further research to elucidate whether changes in sclerostin levels play a significant role in the pathogenesis in growing uremic children.

 Limitations of the Study



Some limitations of the study include: no information could be obtained related to this subject since no data have been published on sclerostin in the pediatric population on HD. In addition, the number of participants was relatively small.

Conflict of interest: None declared.

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