Usefulness of whole PTH assay in patients with renal osteodystrophy —Correlation with bone scintigraphy

Total Phosphate Elimination is Negatively Associated With Increased Serum Fibroblast Growth Factor 23 Levels in Patients who Undergo Peritoneal Dialysis

As fibroblast growth factor 23 (FGF23) has been shown to induce cardiovascular disease directly in patients with chronic kidney disease, identification of factors and treatments that can modulate serum FGF23 (sFGF23) level is clinically important. This retrospective longitudinal study investigated factors that modulate sFGF23 in 49 patients who underwent peritoneal dialysis (PD). sFGF23 ratio (sFGF23 at 18 months/baseline sFGF23) was used as an indicator of changes in sFGF23 level. Total phosphate elimination was the sum of both renal phosphate excretion and dialysate phosphate elimination. In multivariate analysis, log sFGF23 ratio was associated negatively with total phosphate elimination and the use of cinacalcet at baseline, and positively with the use of vitamin D receptor activators at baseline, even after adjusting for potential confounding factors. Our study indicates that maintaining phosphate elimination can prevent increased sFGF23_, thereby preventing cardiovascular events in patients who undergo PD.

Factors Associated with the Serum Myostatin Level in Patients Undergoing Peritoneal Dialysis: Potential Effects of Skeletal Muscle Mass and Vitamin D Receptor Activator Use

Myostatin is a member of the transforming growth factor-β family, which regulates synthesis and degradation of skeletal muscle proteins and is associated with the development of sarcopenia. It is up-regulated in the skeletal muscle of chronic kidney disease patients and is considered to be involved in the development of uremic sarcopenia. However, serum myostatin levels have rarely been determined, and the relationship between serum myostatin levels with clinical and metabolic factors remains unknown. This cross-sectional study investigated the association between serum myostatin level and clinical factors in 69 outpatients undergoing peritoneal dialysis. Serum myostatin level was determined by commercially available enzyme-linked immunosorbent assay (ELISA). Univariable and multivariable analysis were conducted to determine factors associated with serum myostatin levels. The factors included age, sex, diabetes mellitus, dialysis history, body mass index, residual kidney function, peritoneal dialysate volume, serum biochemistries, and the use of vitamin D receptor activators (VDRAs). Mean serum myostatin level was 7.59 ± 3.37 ng/mL. There was no association between serum myostatin level and residual kidney function. Serum myostatin levels were significantly and positively associated with lean body mass measured by the creatinine kinetic method and negatively associated with the use of VDRAs after adjustment for potential confounding factors. Our study indicated that serum myostatin levels are associated with skeletal muscle mass and are lower in patients treated with VDRAs. Further studies are necessary to determine the significance of measuring serum myostatin level in patients undergoing peritoneal dialysis.

Factors associated with serum soluble inhibitors of Wnt-β-catenin signaling (sclerostin and dickkopf-1) in patients undergoing peritoneal dialysis

AIM

Sclerostin and dickkopf-1 (Dkk-1) are soluble inhibitors of Wnt-β-catenin signaling and are involved in decreased bone formation and bone volume in patients with various bone diseases. The clinical characteristics of sclerostin and Dkk-1 and their impacts on mineral and bone metabolism remain undetermined in patients undergoing peritoneal dialysis (PD).

METHODS

This cross-sectional study investigated the association between serum sclerostin and Dkk-1 levels and mineral disorders in 74 outpatients under PD treatment. Levels of sclerostin and Dkk-1 in serum, urine, and peritoneal dialysate were determined using enzyme-linked immunosorbent assay kits. The associations between serum sclerostin and Dkk-1 levels and biochemical parameters were evaluated by linear regression analyses.

RESULTS

Median serum sclerostin and Dkk-1 levels were 138 pmol/L (range, 98.3-195.9 pmol/L) and 38.8 pmol/L (range, 28.5-47.1 pmol/L), respectively. Both sclerostin and Dkk-1 were excreted into urine and peritoneal dialysate. Multivariable linear regression analyses showed that serum sclerostin level was significantly associated with age, sex, parathyroid hormone level, and renal Kt/V. In contrast, serum Dkk-1 level was associated with platelet count and serum fibroblast growth factor 23 level but not with any of the bone metabolic markers.

CONCLUSION

Serum sclerostin was associated with serum intact parathyroid hormone, while Dkk-1 was associated with serum fibroblast growth factor 23 in patients undergoing PD. The utility of determining soluble Wnt-β-catenin inhibitors levels in patients undergoing PD requires further investigation.

Two Years of Cinacalcet Hydrochloride Treatment Decreased Parathyroid Gland Volume and Serum Parathyroid Hormone Level in Hemodialysis Patients With Advanced Secondary Hyperparathyroidism

The long-term effect of cinacalcet hydrochloride treatment on parathyroid gland (PTG) volume has been scarcely investigated in patients with moderate to advanced secondary hyperparathyroidism (SHPT). The present study was a prospective observational study to determine the effect of cinacalcet treatment on PTG volume and serum biochemical parameters in 60 patients with renal SHPT, already treated with intravenous vitamin D receptor activator (VDRA). Measurement of biochemical parameters and PTG volumes were performed periodically, which were analyzed by stratification into tertiles across the baseline parathyroid hormone (PTH) level or PTG volume. We also determined the factors that can estimate the changes in PTG volume and the achievement of the target PTH range by multivariable analyses. Two years of cinacalcet treatment significantly decreased the serum levels of PTH, calcium, and phosphate, followed by the improvement of achieving the target ranges for these parameters recommended by the Japanese Society for Dialysis Therapy. Cinacalcet decreased the maximal and total PTG volume by about 30%, and also decreased the serum PTH level independent of the baseline serum PTH level and PTG volume. Ten out of 60 patients showed 30% increase in maximal PTG after 2 years. Multivariable analysis showed that patients with nodular PTG at baseline and patients with higher serum calcium and PTH levels at 1 year were likely to exceed the target range of PTH at two years. In conclusion, cinacalcet treatment with intravenous VDRA therapy decreased both PTG volume and serum intact PTH level, irrespective of the pretreatment PTG status and past treatment history.

Fibroblast growth factor 23, but not parathyroid hormone, is associated with urinary phosphate regulation in patients on peritoneal dialysis

Fibroblast growth factor (FGF) 23 plays an important role in regulation of renal phosphate excretion in patients with chronic kidney disease. However, it remains undetermined whether FGF23 is closely linked to renal phosphate handling in patients with low glomerular filtration rate (GFR). The present cross-sectional study included 52 outpatients undergoing peritoneal dialysis with urine volume ≥ 100 mL/day. The primary outcome was level of urinary phosphate excretion, and the secondary outcomes were tubular maximal reabsorption of phosphate normalized to GFR (TmP/GFR), an index of the renal threshold for phosphate excretion, and level of peritoneal phosphate excretion. Variates of interest were serum FGF23 and parathyroid hormone (PTH) levels. The median and interquartile range of serum FGF23 level, TmP/GFR, and total urinary and peritoneal phosphate excretion were 5610 (1493-11 430) ng/mL, 1.30 (0.44-1.86) mg/dL, 117 (40-234) mg/day, and 208 (156-250) mg/day, respectively. Multivariate linear regression analysis revealed that serum FGF23 level was significantly (P < 0.05) associated with TmP/GFR negatively and significantly (P < 0.05) associated with urinary phosphate excretion positively, even after adjusting for confounders. In contrast, none of the three outcome variates was associated with serum PTH level. Neither serum FGF23 nor PTH level was associated with peritoneal phosphate excretion. The present study indicates that FGF23, but not PTH, is involved in urinary phosphate regulation, even in patients on peritoneal dialysis with residual renal function.

Relationship between residual renal function and serum fibroblast growth factor 23 in patients on peritoneal dialysis

Fibroblast growth factor 23 (FGF23) levels in dialysis patients are influenced by various factors, including phosphorus load. However, the clinical parameters that determine serum FGF23 levels in patients on peritoneal dialysis (PD) remain unclear. The aim of the present study was to examine the effects of clinical factors, on serum FGF23 levels, with an emphasis on residual renal function (RRF). This cross-sectional study included 56 outpatients undergoing PD therapy. Urine volume ≥ 100 mL/day or renal creatinine (Cr) clearance was used as a surrogate marker for RRF. Clinical characteristics were compared between patients with and without RRF. Linear regression analysis was conducted with serum FGF23 level as the dependent variable and renal Cr clearance as the main independent variable. The median and interquartile range of serum FGF23 levels were 5970 (1451-11,688) pg/mL. Patients with RRF showed higher urinary and total phosphate eliminations, and lower serum FGF23 and phosphate levels than patients without RRF. Multivariate linear regression analysis showed that the renal Cr clearance and serum phosphate and dialysis history were negatively associated with serum FGF23 levels, even after adjusting for potential confounders including peritoneal Cr clearance. Further, the predictabilities of serum FGF23 were comparable among renal Cr clearance, Kt/V for urea, and renal phosphate clearance. RRF determined by renal Cr clearance or residual urine volume is an independent negative determinant of serum FGF23 levels in PD patients.

The clinical utility of serum tartrate-resistant acid phosphatase 5b in the assessment of bone resorption in patients on peritoneal dialysis

OBJECTIVES

Serum tartrate-resistant acid phosphatase 5b (TRACP5b) is a bone resorption marker used in the assessment of bone metabolic status. The present study was designed to determine the clinical characteristics and utility of measuring serum TRACP5b levels in peritoneal dialysis (PD) patients.

DESIGN

Cross-sectional study.

PATIENTS

Forty-one patients receiving PD treatment in a single centre.

MEASUREMENT

Serum levels of the bone turnover markers TRACP5b, N-terminal cross-linking telopeptide of type 1 collagen (NTX), bone-specific alkaline phosphatase (BAP), and parathyroid hormone (PTH) were simultaneously measured. The correlation of serum TRACP5b with other established bone markers was analysed after logarithmic transformation. Multivariate linear regression analysis was performed to examine the effects of both renal and peritoneal Kt/V (an index for solute clearance) for urea on bone markers using age, sex, body mass index, and PTH as covariates. Bone markers were also measured in three patients before and after treatment with cinacalcet hydrochloride, alphacalcidol, and raloxifene hydrochloride.

RESULTS

Log TRACP5b was significantly correlated with log NTX, log BAP and log PTH. In the multivariate analysis, peritoneal Kt/V was not correlated with log NTX, log BAP or log TRACP5b. In contrast, renal Kt/V was significantly correlated with log NTX only. Responses to drug treatment were more accurately determined from serum TRACP5b and BAP than from serum NTX.

CONCLUSIONS

Serum TRACP5b and BAP are potentially useful biomarkers for the evaluation of bone turnover in PD patients because they correlate well with other established bone markers and they are not influenced by renal and peritoneal clearances.