Clearance of osteocalcin by peritoneal dialysis in children with end-stage renal disease

Current use of bone turnover markers in the management of osteoporosis

The adult bone is continuously being remodelled to repair microdamage, preserve bone strength and mechanical competence as well as maintain calcium homeostasis. Bone turnover markers are products of osteoblasts (bone formation markers) and osteoclasts (bone resorption markers) providing a dynamic assessment of remodelling (turnover). Resorption-specific bone turnover markers are typically degradation products of bone collagen molecules (N- [NTX] and C-telopeptide cross-linked type 1 collagen [CTX]), which are released into the circulation and excreted in urine; or enzymatic activities reflecting osteoclastic resorption, tartrate-resistant acid phosphatase [TRACP]. Formation-specific bone turnover markers embrace different osteoblastic activities: type 1 collagen synthesis (Procollagen type I N- propeptide [PINP]), osteoblast enzymes (bone-specific alkaline phosphatase [BALP]), or bone matrix proteins [osteocalcin]. Among individuals not receiving osteoporosis treatment, resorption and formation markers are tightly linked and highly correlated (r= 0.6-0.8). Significant biological variability was reported in the past, but these issues have been greatly improved with automated assays and attention to pre-analytical and analytical factors that are known to influence bone turnover marker levels. Bone turnover markers are not useful in the diagnosis of osteoporosis, the individual prediction of bone loss, fracture, or rare complications, or in the selection of pharmacological treatment. Despite remaining issues with reference intervals and assays harmonization, bone turnover markers have proven to be useful in elucidating the pharmacodynamics and effectiveness of osteoporosis medications in clinical trials. As an alternative to BMD testing, BTMs may be useful to monitor osteoporosis therapies.

Clearance of Sclerostin, Osteocalcin, Fibroblast Growth Factor 23, and Osteoprotegerin by Dialysis

INTRODUCTION

Fibroblast growth factor (FGF23), sclerostin, osteocalcin, and osteoprotegerin are important factors that control mineral bone metabolism. End-stage renal disease is associated with the pronounced dysregulation of mineral bone metabolism; however, the impact and clearance of mineral bone metabolism factors during dialysis remain largely undescribed.

METHODS

In a cross-sectional study, 10 chronic hemodialysis patients were treated with hemodialysis for 8 h using a high-flux filter and a dialysate bath of 50% calculated total body water continuously recycled at a rate of 500 mL/min. Plasma and dialysate concentrations of FGF23, sclerostin, osteoprotegerin, and osteocalcin were measured at 1, 2, 4, 6, and 8 h permitting the estimation of dialysis clearance.

RESULTS

Clearance of FGF23 was 7.7 mL/min, of sclerostin was 7.6 mL/min, of osteoprotegerin was 1.2 mL/min, and of osteocalcin was 19.7 mL/min. Clearance of FGF23 was correlated to sclerostin and osteoprotegerin clearance and also to the ultrafiltration rate. Although, osteocalcin blood concentrations decreased during dialysis, they rebounded within 6 h. Overall, no significant changes in blood concentrations of the measure mineral bone metabolism factors were observed.

CONCLUSIONS

The intradialytic clearance of osteocalcin, FGF23, sclerostin, and osteoprotegerin occurs; however, only clearance of FGF23 is directly correlated with the ultrafiltration rate. The effects of dialytic clearance on mineral bone metabolism are, however, uncertain and intradialytic plasma concentrations of the studied substrates remained largely unchanged.

Effect of chronic renal failure on bone turnover and bone alkaline phosphatase isoforms

BACKGROUND

Biochemical markers of bone turnover are used to monitor metabolic bone disease associated with renal failure. We have applied a comprehensive panel of markers to patients with chronic renal failure (CRF), with particular focus on the isoforms of bone alkaline phosphatase (BALP).

METHODS

Twenty CRF patients undergoing hemodialysis (N = 9) and peritoneal dialysis (N = 11) were measured for serum parathyroid hormone (PTH), osteocalcin, total ALP, and four BALP isoforms (B/I, B1x, B1, and B2) by high-performance liquid chromatography. These BALP isoforms were also compared with BALP measured by three commercial immunoassays (Alkphase-B, Tandem-R Ostase, and Tandem-MP Ostase). Type I collagen turnover was assessed by serum samples using the type I procollagen intact amino- and carboxy-terminal propeptides (PINP and PICP) and two fragments (ICTP and CrossLaps) derived from the carboxy-terminal telopeptide of mature matrix collagen by different degradative pathways.

RESULTS

Mean levels of bone turnover markers were elevated in CRF, with marked increases in those markers, osteocalcin, ICTP, and CrossLaps, cleared by the kidney. Total ALP activities were increased corresponding to elevated B/I and B2 isoform levels. The B1 isoform level was not significantly different from healthy controls. B1x was detected in 60% of the patients but was not resolved in healthy individuals. Kendall's tau rank correlation showed that B1x correlated significantly (P < 0.05) with B1 (0.53) and PINP (0.55), and was the only marker to correlate with PTH (0.49). B1x was not significantly correlated with any of the commercial BALP immunoassays. Interestingly, the immunoassay calibrators contained high activities of the B/I peak (39 to 80%) compared with human serum (4%).

CONCLUSION

There are selective differences between the BALP isoforms in CRF compared with healthy adults. The commercial BALP immunoassays are comparable with each other but are unable to distinguish the BALP isoform-specific differences in CRF patients.

Bone mineral density and biochemical markers of bone turnover in patients with predialysis chronic renal failure

BACKGROUND

Metabolic bone disease might commence early in the course of renal failure. This study therefore examined the frequency and severity of the skeletal changes in predialysis chronic renal failure by measurements of bone mineral density (BMD), biochemical markers of bone turnover (osteocalcin, bone-specific alkaline phosphatase, carboxy terminal propeptide of type I collagen, and carboxy-terminal telopeptide of type I collagen), parathyroid hormone (PTH), ionized calcium (Ca++), phosphate (P), and vitamin D metabolites.

METHODS

The study was performed in 113 patients (male/female: 82/31) with chronic renal diseases [mean glomerular filtration rate (GFR) of 37 ml/min] and in 89 matched, normal control subjects.

RESULTS

The patients had significantly (P<0.05) reduced BMD in the spine (-6.3%), the femur (-12.1%), the forearm (-5.7%), and the total body (-4.2%) as compared with the control subjects. Dividing the patients into quartiles according to GFR revealed that BMD decreased with the gradual decline in renal function at all the measured skeletal sites, but was most pronounced in the femur: 0.63+/-0.03, 0.74+/-0.02, 0.77+/-0.02, and 0.82+/-0.03 g/cm2 in each quartile from lowest to highest GFR compared with 0.82+/-0.02 g/cm2 in the control group (P<0.0001). All of the measured bone markers showed increasing plasma levels with the more advanced stages of renal failure. Serum PTH and serum P levels increased, whereas serum Ca++ and 1,25-dihydroxyvitamin D decreased. BMD Z-scores of the femur and of the forearm correlated to the biochemical markers and to PTH (P<0.05 to P<0.0001). The biochemical markers all showed strong correlations to PTH, also when corrected for the effect of the decline in GFR (r = 0.40 to 0.92, P<0.01 to P< 0.0001).

CONCLUSION

Skeletal changes are initiated at an early stage of chronic renal failure, as estimated from reduced BMD and elevated levels of PTH and from the biochemical markers of both bone formation and bone resorption.

Osteocalcin: a non-invasive index of metabolic bone disease in patients treated by CAPD

Serum osteocalcin has been found to correlate with bone formation. However, present literature gives only limited data on osteocalcin and bone histomorphometry in patients undergoing peritoneal dialysis. This study assessed serum osteocalcin, dialysate osteocalcin, peritoneal clearance of osteocalcin (Clp-osteocalcin) and mass transfer of osteocalcin (MTp-osteocalcin), and evaluated relationships between these values and bone histomorphometry. Eighteen patients were treated by continuous ambulatory peritoneal dialysis (CAPD). Bone biopsies, serum and dialysate osteocalcin, serum levels of parathyroid hormone, alkaline phosphatase, aluminum, phosphate, Ca2+ and vitamin D3 metabolites were measured at the start and in 10 of the patients a year later. Serum osteocalcin was found to be elevated. Osteocalcin was detected in the dialysate resulting in significant values of Clp-osteocalcin and MTp-osteocalcin. Serum and dialysate levels of osteocalcin correlated significantly (r = 0.66, P < 0.001) and like MTp-osteocalcin with serum levels of alkaline phosphatase and PTH. Histomorphometry showed that osteitis fibrosa was the predominant bone disease detected. Serum concentration of osteocalcin correlated with osteoid thickness, eroded and osteoclast surfaces, aluminum staining, and some of the bone dynamic parameters. Dialysate osteocalcin, MTp-osteocalcin, PTH and alkaline phosphatase correlated with practically the same histomorphometric parameters as serum osteocalcin. No correlations were seen between Clp-osteocalcin and any histomorphometric parameters. Serum osteocalcin was elevated above the normal range, and significant positive correlations between serum osteocalcin and bone formation parameters were found. Serum osteocalcin correlated with almost the same histomorphometric parameters as PTH. Thus, serum levels of PTH and osteocalcin gave additional information to one another as non-invasive parameters in this group of patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Parathyroid hormone and osteocalcin levels in plasma and ultrafiltrate during hemofiltration

The effects of hemofiltration (HF) on serum levels of intact parathyroid hormone (PTH), as well as its mid-C regional and C-terminal fragments and bone Gla-protein (bone gamma-carboxyglutamic acid, osteocalcin), were investigated in 17 patients during one session of HF. During HF there was a significant decrease in the serum concentrations of both intact PTH (p < 0.01), mid-C regional PTH (p < 0.01) and C-terminal PTH (p < 0.01) as well as in the osteocalcin concentrations (p < 0.01). There was a significant increase in serum calcium (p < 0.05) during the procedure and this increase correlated with the reduction in PTH (r = 0.56, p < 0.05). Mid-C regional PTH and osteocalcin were found in the ultrafiltrate of all patients, while intact PTH was found in the ultrafiltrate of 8 of 17 patients and C-terminal PTH was detected only in the ultrafiltrate of one patient. The data demonstrate that the permeability of HF membranes is high enough to cause filtration of both intact PTH, PTH fragments and osteocalcin. An inhibited secretion of PTH probably played a major part in reducing intact PTH in serum during HF.

Serum osteocalcin concentrations in children with chronic renal insufficiency who are not undergoing dialysis. Growth Failure in Children with Renal Diseases Study

This report describes the serum osteocalcin values in children with mild to moderate, but relatively stable, renal dysfunction followed in the Growth Failure in Children With Renal Diseases Study. This report is derived from data obtained during the control period (6 months) before the initiation of vitamin D therapy. Up to three measurements per patient were obtained. Serum osteocalcin concentration was compared with creatinine clearance (glomerular filtration rate) calculated by the Schwartz formula; with serum concentrations of alkaline phosphatase, parathyroid hormone, and bicarbonate; and with the percentages of the recommended dietary allowances of calories and protein ingested. By standard correlation techniques, there appeared to be an inverse correlation between calculated creatinine clearance and serum osteocalcin concentration, and a direct correlation between serum osteocalcin and parathyroid hormone values. However, when we employed a statistical technique that takes into account repeated measures in the same patient, no correlation was found between calculated glomerular filtration rate and serum osteocalcin concentration, and no direct correlation was found between serum osteocalcin and parathyroid hormone values. The lack of a correlation between calculated glomerular filtration rate and serum osteocalcin values may be due to large fluctuations in the serum osteocalcin concentration, even though renal function is relatively stable.