Significance of Bio-intact PTH(1-84) assay in hemodialysis patients

Significance of urinary C-megalin excretion in vitamin D metabolism in pre-dialysis CKD patients

Serum 1,25(OH)₂D and 24,25(OH)₂D are decreased in CKD. Megalin in proximal tubular epithelial cells reabsorbs glomerular-filtered 25(OH)D-DBP complex to convert 25(OH)D to 1,25(OH)₂D and 24,25(OH)₂D. Urinary C-megalin excretion is increased via exocytosis from injured nephrons overloaded with megalin-mediated protein metabolism. This study investigated the significance of urinary C-megalin excretion in vitamin D metabolism in 153 pre-dialysis CKD patients. Urinary C-megalin was positively associated with urinary protein, β₂MG and α₁MG, and exhibited negative correlations with serum 25(OH)D, 1,25(OH)₂D and 24,25(OH)₂D. Multiple regression analysis showed that urinary C-megalin had a significantly negative association with 25(OH)D. Serum 1,25(OH)₂D and 24,25(OH)₂D, as well as 1,25(OH)₂D/25(OH)D and 24,25(OH)₂D/25(OH)D ratios, showed positive correlations with eGFR. Additionally, wholePTH was positively associated with 1,25(OH)₂D/25(OH)D and 1,25(OH)₂D/24,25(OH)₂D, while FGF23 was positively associated with 24,25(OH)₂D/25(OH)D and negatively with 1,25(OH)₂D/24,25(OH)₂D. Urinary C-megalin emerged as an independent factor positively associated with 1,25(OH)₂D/25(OH)D and 1,25(OH)₂D/24,25(OH)₂D. Although 1,25(OH)₂D and 24,25(OH)₂D are decreased in CKD patient serum, our findings suggest that PTH and FGF23 retain their effects to regulate vitamin D metabolism even in the kidneys of these patients, while production of 1,25(OH)₂D and 24,25(OH)₂D from 25(OH)D is restricted due to either impairment of megalin-mediated reabsorption of the 25(OH)D-DBP complex or reduced renal mass.

Decreased cortical thickness, as estimated by a newly developed ultrasound device, as a risk for vertebral fracture in type 2 diabetes mellitus patients with eGFR of less than 60 mL/min/1.73 m2

Cortical porosity is increasingly recognized as an important risk for fracture in DM patients. The present study demonstrated that decreased cortical thickness, assessed using a newly developed quantitative ultrasonic bone densitometry, is a significant risk factor for vertebral fractures in type 2 diabetes mellitus patients with stage 3 or higher chronic kidney disease, but not in those without.

INTRODUCTION

Cortical porosity is increasingly recognized as an important risk factor for fracture in type 2 diabetes mellitus (T2DM) patients as well as in stage 3 chronic kidney disease (CKD) patients in whom serum parathyroid hormone (PTH) starts to increase. The present study aimed to clarify whether the coexistence of CKD might affect the relationship of decreased cortical thickness (CoTh) in the development of vertebral fractures (VF) in T2DM patients.

METHODS

In this cross-sectional study, trabecular bone mineral density (TrBMD), elastic modulus of trabecular bone (EMTb), and CoTh were estimated with a new quantitative ultrasound bone densitometry in 173 T2DM patients. VFs were identified radiographically.

RESULTS

Thirty-nine patients (22.5%) had VF. Those with estimated glomerular filtration rate (eGFR) <60 mL/min/1.73 m(2) (low eGFR) showed a significantly higher VF rate (32.4%) than those with eGFR ≥60 mL/min/1.73 m(2) (high eGFR, 16.2%). Serum PTH was significantly higher with low eGFR than with high eGFR. In those with high eGFR, EMTb was significantly lower in VF(+) than VF(-). In those with low eGFR, TrBMD, EMTb, and CoTh were significantly lower in VF(+) than in VF(-). In a multivariate logistic regression analysis, EMTb was independently and significantly associated with VF in T2DM patients with a high eGFR, in contrast to those with only CoTh with VF in T2DM with low eGFR.

CONCLUSION

This study demonstrated CoTh as a factor independently associated with VF in T2DM patients with low eGFR and increasing serum PTH levels.

Increased active PTH(1-84) fraction as a predictor of poor mortality in male hemodialysis patients

We reported previously that serum parathyroid hormone [PTH(1-84)]/intact PTH[PTH(1-84) + PTH(7-84)] ratio provides the better marker for parathyroid function and bone turnover state than serum PTH level itself. The present study demonstrated that higher PTH(1-84)/intact PTH ratio, but not serum PTH(1-84) and intact PTH, predicted higher all-cause mortality in 177 male hemodialysis patients.

INTRODUCTION

We reported that PTH(1-84)/intact PTH ratio provides a clinically relevant marker for parathyroid function and the resultant bone turnover state. The purpose of our study was to investigate the association of PTH(1-84)/intact PTH ratio with all-cause mortality (ACM) in male hemodialysis patients.

METHODS

The study was performed for 70 months. Serum PTH in 177 male hemodialysis patients was measured with PTH(1-84)-specific whole PTH assay and intact PTH assay which cross-reacts with N-truncated PTH including PTH(7-84).

RESULTS

The patients (n = 177) were divided into higher and lower halves based on serum levels of PTH(1-84)/intact PTH ratio (cutoff value, 0.484), intact PTH (143.8 pg/mL), and PTH(1-84) (64.1 pg/mL). In Kaplan-Meier analysis, the higher group in whole PTH/intact PTH ratio had significantly higher ACM than the lower group (P = 0.020 by log-rank test), in contrast with the insignificant difference between the higher and lower groups in intact PTH and PTH(1-84). Multivariate Cox regression hazard analysis identified higher log [PTH(1-84)/intact PTH ratio], but not log intact PTH or log PTH(1-84) as a significant independent predictor [hazard ratio 14.428 (95% CI 2.486-83.728)] for ACM after adjustment for various factors including age, hemodialysis duration, presence/absence of diabetes mellitus, BMI, log C-reactive protein, serum albumin, calcium, and phosphate. The association existed between log [PTH(1-84)/intact PTH ratio] and ACM in those without vitamin D administration (n = 95).

CONCLUSION

Higher PTH(1-84)/intact PTH ratio, which provides a relevant marker for parathyroid function, may be a significant predictor of ACM in male hemodialysis patients.

Comparison between a second and a third generation parathyroid hormone assay in hemodialysis patients

OBJECTIVE

Third generation parathyroid hormone (PTH) assays are new generation assays that do not recognize the PTH7-84 fragment whereas second generation assays detect both PTH1-84 and PTH7-84 fragments. Despite the excellent correlation between both assays in chronic renal failure (CRF) subjects, the mean PTH levels are typically 50% lower with the third compared to the second generation assays. The assessment of third generation PTH assays has not been extensively studied in hemodialysis subjects. The purpose of our study was to compare a third generation PTH assay to a second generation one in a population of hemodialysis subjects.

MATERIALS AND METHODS

92 haemodialysis subjects (36 women and 56 men) with a mean age of 67±12.9 years were included in this study. Anthropometric and clinical parameters (Body Mass Index (BMI) and blood pressure) were measured. Second and third generation PTH assays (Cis biomedical and Diasorin respectively) were performed in each subject. In addition, the following biochemical tests were measured: 25-hydroxyvitamin D (25-(OH)D), 1,25-hydroxyvitamin D (1,25-(OH)2D), crosslaps and alkaline phosphatase.

RESULTS

The mean second and third generation PTHs are respectively 211±205 pg/ml and 151±164 pg/ml. The mean third generation PTH values are 28.4% lower compared to the second generation ones. Both methods are strongly correlated (r=0.923, p<0.001). This correlation persisted without any significant difference after controlling for gender, age, BMI and Blood Pressure. However, the difference between both methods increases when baseline PTH increases. Each of the second and third generation method is significantly correlated with hemodialysis duration (p<0.01), crosslaps (p<0.001), alkaline phosphatase (p<0.05), but not with age, BMI, Blood Pressure, 25-(OH)D or 1,25-(OH) 2D levels.

CONCLUSION

Our results show that both second and third generation PTH methods are strongly correlated in hemodialysis patients mainly when PTH values are low. However, the difference between both methods increases when PTH values are high. More research is needed to establish which method is the gold standard when PTH values are high.

Reduction of whole PTH/intact PTH ratio as a predictor of bone metabolism in cinacalcet treatment of hemodialysis patients with secondary hyperparathyroidism

In cinacalcet treatment of hemodialysis (HD) patients with secondary hyperparathyroidism (SHPT), not only intact parathyroid hormone (I-PTH), whole PTH (W-PTH), and bone markers, but also W-PTH/I-PTH ratio as proportion of active PTH(1-84) molecules were decreased. Changes in W-PTH/I-PTH ratio significantly correlated and predicted changes in bone marker.

INTRODUCTION

Cinacalcet partly suppresses the secretion of PTH by enhancing PTH(1-84) degradation into N-truncated fragments. The objectives of this study is to investigate the significance of the N-truncated PTH/PTH(1-84) ratio for the prediction of the effect of cinacalcet in HD patients.

METHODS

Serum parameters were measured during 12 weeks of oral cinacalcet administration at 25 mg daily in 39 HD patients with SHPT.

RESULTS

Serum Ca, Pi, W-PTH, I-PTH, and W-PTH/I-PTH ratio all decreased significantly in a time-dependent manner during cinacalcet administration. Serum tartrate-resistant acid phosphatase (TRAP) 5b reflected these changes more precisely than serum N-telopeptide of type-I collagen. At 1 week, changes in I-PTH and W-PTH correlated significantly with those in serum Pi, but not Ca. Changes in serum Pi (but not Ca) and serum W-PTH also correlated significantly with changes in serum TRAP5b at both 4 and 12 weeks, while changes in serum I-PTH correlated significantly with those in serum TRAP5b only at 12 weeks. Changes in the serum W-PTH/I-PTH ratio correlated significantly with those in serum TRAP5b at both 4 and 12 weeks, and changes in serum W-PTH/I-PTH ratio at 4 weeks showed a tendency for a correlation with changes in serum TRAP5b at 12 weeks. HD patients with a reduced W-PTH/I-PTH ratio after 4 weeks had a significantly greater reduction of TRAP5b over 12 weeks.

CONCLUSION

W-PTH and the W-PTH/I-PTH ratio allow estimation of the potency of cinacalcet in enhancement of PTH degradation, and thus no less reliable markers than I-PTH for reflecting cinacalcet-induced bone resorption.

The administration of an active vitamin D(3) analogue reduced the serum concentrations of 1-84 and truncated parathyroid hormone in pseudohypoparathyroidism type Ib patients

Serum calcium is one of major regulators of PTH amino-terminal (N-terminal) truncation and secretion of full-length (1-84)PTH from parathyroid glands. However, the effect of active vitamin D(3) on PTH truncations remains controversial. To determine whether active vitamin D(3) accelerates the truncation of PTH, the vitamin D(3) analogue alfacalcidol was administered to patients with pseudohypoparathyroidism type Ib (PHP Ib). Both the (1-84)PTH molecule and N-terminally truncated fragments such as (7-84)PTH can be measured by commercially available two-site total PTH (T-PTH) assays. The development of whole PTH (W-PTH) assays specific for full-length (1-84)PTH has enabled us to distinguish between N-terminally truncated PTH and full-length (1-84)PTH. W-PTH/T-PTH ratios were calculated and used as an index of PTH N-terminal truncations. Both serum W-PTH and T-PTH levels were elevated in untreated PHP Ib patients. The administration of alfacalcidol reduced both the W-PTH and T-PTH levels; however, the W-PTH/T-PTH ratios were stable. Serum calcium levels were significantly and negatively correlated with both the W-PTH and T-PTH levels, but not with the W-PTH/T-PTH ratios. Thus, the administration of an active vitamin D(3) analogue did not seem to have a major effect on the rate of PTH N-terminal truncation, even though it did reduce the secretion of both full-length and truncated PTH. Possibly, active vitamin D(3) attenuates the effect of elevated calcium on PTH N-terminal truncation in PHP Ib patients.

Association of reduction in bone mineral density with mortality in male hemodialysis patients

In the present study we examined the relationship of bone mineral density (BMD) reduction with increased mortality in hemodialysis patients. A single-center prospective observational study was conducted on 269 male hemodialysis patients. The BMD in the distal third of the radius (DR1/3) and in the ultradistal radius (UR), which are enriched with cortical and cancellous bone, respectively, was measured twice using dual-energy X-ray absorptiometry (DXA) with a 1-year interval. Subjects were divided into two groups based on the presence or absence of BMD reduction. Survival was followed for 61.0 months, after which time 104 patients (39%) had died. A significant BMD reduction at the UR and DR1/3 occurred in 182 (68%) and 195 (72%) patients, respectively. Patients with BMD reduction in the UR, in contrast to the DR1/3, had a significantly lower survival rate than those without BMD reduction (P = 0.01). In Cox regression analysis, the rate of BMD change at the UR, in addition to patient age, diabetes mellitus, and serum albumin, emerged as an independent predictor for increased mortality (HR = 0.970, 95% CI 0.945-0.996). Our results suggest that BMD reduction at the UR might be a clinically relevant marker that predicts an increased risk of mortality in male hemodialysis patients.

Utility of serum tartrate-resistant acid phosphatase (TRACP5b) as a bone resorption marker in patients with chronic kidney disease: independence from renal dysfunction

BACKGROUND

Serum tartrate-resistant acid phosphatase (TRACP) 5b levels were assessed in predialysis patients with chronic kidney disease (CKD). The aim of the study was to establish the usefulness of a new assay for TRACP5b in assessing bone turnover in these patients.

METHODS

Serum concentrations of two bone resorption markers, TRACP5b and N-terminal cross-linking telopeptide of type I collagen (NTX); two bone formation markers, bone specific alkaline phosphatase (bone ALP) and intact osteocalcin (OC[1-49]); and PTH were measured in 98 predialysis CKD patients.

RESULTS

Log serum TRACP5b and other bone markers were significantly negatively correlated with glomerular filtration rate (GFR) and positively correlated with log serum PTH, suggesting an increase in serum bone markers with development of secondary hyperparathyroidism. Multiple regression analysis including age, gender, BMI, the presence of diabetes, GFR and log serum PTH showed an association of log serum PTH with log serum TRACP5b and other bone markers. GFR was associated with log serum NTX and log OC[1-49], but not with log serum TRACP5b or log bone ALP. These data show that renal dysfunction does not influence serum TRACP5b and bone ALP, but has an influence on NTX and OC[1-49].

CONCLUSION

Serum TRACP5b may be a good marker for serum bone resorption in predialysis CKD patients, as it is not affected by renal dysfunction.

Association of increased active PTH(1-84) fraction with decreased GFR and serum Ca in predialysis CRF patients: modulation by serum 25-OH-D

As the serum calcium and glomerular filtration rate decreased, the proportion of active PTH(1-84) molecules in PTH immunoreactivity increased in serum from predialysis uremic patients, particularly those with vitamin D insufficiency.

INTRODUCTION

The PTH(1-84) fraction was altered in predialysis patients with chronic renal failure (CRF).

METHODS

Serum PTH in predialysis CRF patients without any medication was measured by PTH(1-84)-specific whole PTH assay and intact PTH assay cross-reacting with N-truncated PTH.

RESULTS

In CRF patients, the glomerular filtration rate (GFR) correlated positively with serum Ca and 1,25-dihydroxyvitamin D (1,25(OH)(2)D), and inversely with serum Pi, log intact PTH, and log whole PTH. In multiple regression analysis, including age, gender, body mass index, GFR, Ca, and Pi and 1,25(OH)(2)D as independent variables, serum Ca and GFR associated significantly with serum log whole PTH and intact PTH. Serum log whole PTH/intact PTH ratio, which increased as serum Ca and GFR decreased, retained a negative correlation in those with serum 25-hydroxyvitamin D levels below 20 ng/ml, but not in those above 20 ng/ml. The ratio also correlated positively with serum log tartrate-resistant acid-phosphatase-5b, log cross-linked N-telopeptide of type-I collagen, and log bone alkaline-phosphatase.

CONCLUSION

As GFR declined with suppression of serum Ca, the proportion of active PTH molecules increased in predialysis CRF patients, particularly those with vitamin D insufficiency.

Serum levels of TRAP5b, a new bone resorption marker unaffected by renal dysfunction, as a useful marker of cortical bone loss in hemodialysis patients

Tartrate-resistant acid phosphatase (TRAP) 5b is a new marker of bone resorption that is unaffected by renal dysfunction. The significance of TRAP5b was assessed in hemodialysis (HD) patients. Serum concentrations of TRAP5b and cross-linked N-telopeptide of type I collagen (NTX) were determined as bone resorption markers, and those of bone alkaline phosphatase (BAP) and intact osteocalcin (OC) were measured as bone formation markers in 58 HD patients. Bone mineral density (BMD) was measured by dual-energy X-ray absorptiometry twice in the distal third of the radius, with a 2-year interval between measurements. Serum TRAP5b correlated significantly with BAP, intact OC, intact parathyroid hormone (PTH), and especially serum NTX. TRAP5b, NTX, BAP, and intact OC all correlated significantly with BMD at the time of the second measurement; and TRAP5b, NTX, and intact OC, but not BAP and intact PTH, correlated significantly with the annual change in BMD during the 2-year period. Among the bone markers, patients in the highest tertile for serum TRAP5b and intact OC showed the fastest rate of cortical bone loss. The sensitivity and specificity for detection of rapid bone loss were 57.9% and 76.9%, respectively, for serum TRAP5b. Measurement of serum TRAP5b, as well as intact OC, may be a clinically relevant assay for estimation of bone metabolic status in HD patients, although serum intact OC accumulates in uremic serum.

Influence of nutritional status on serum large N-truncated PTH, but not PTH(1–84) in hemodialysis patients

BACKGROUND

Serum level of parathyroid hormone (PTH), measured by second-generation intact PTH (I-PTH), is known to be associated with nutritional status in hemodialysis (HD) patients. We investigated whether PTH(7-84) and larger N-truncated PTH or PTH(1-84) might be affected by nutritional status in HD patients.

METHODS

Serum PTH was determined in 170 male HD patients by either a Bio-intact PTH (Bio-PTH) or I-PTH assay. Lean body mass in the trunk region was measured as a nutritional marker by dual X-ray absorptiometry.

RESULTS

The serum PTH(7-84) level was theoretically obtained from the difference between serum I-PTH and Bio-PTH because I-PTH assay cross-reacted with PTH(7-84) with the same degree as PTH(1-84), although N-truncated PTH fragment larger than PTH(7-84) might affect theoretical serum PTH(7-84) level, although slightly. Serum PTH(1-84) was directly obtained from the serum Bio-PTH value because of its exclusive reaction with PTH(1-84). Serum PTH(7-84) correlated significantly with nutritional markers such as body weight, albumin, protein catabolic rate (PCR), TACBUN, BUN, phosphate, and lean body mass in the trunk, whereas PTH(1-84) correlated only with phosphate. Multiple regression analysis revealed that PCR, body weight, and lean body mass in the trunk region are significant factors independently associated with PTH(7-84), but not with PTH(1-84).

CONCLUSIONS

The results suggest that serum levels of PTH(7-84) and larger N-truncated PTH fragments, but not PTH(1-84), might be affected by the nutritional state in HD patients, which might explain the reported correlation of serum I-PTH levels with nutritional markers.

Role of fibroblast growth factor-23 in peripheral vascular calcification in non-diabetic and diabetic hemodialysis patients

INTRODUCTION

Fibroblast growth factor (FGF) 23 is a recently identified circulating factor that regulates phosphate (Pi) metabolism. Since the derangement of Pi control is an important risk factor for vascular calcification, we investigated the importance of plasma FGF-23 in the development of vascular calcification in the aorta and peripheral artery in hemodialysis patients with and without diabetes mellitus (DM).

METHODS

Male hemodialysis patients with DM (n=32) and without DM (n=56) were examined. Plasma samples were obtained before the start of dialysis sessions, and the FGF-23 levels were determined by enzyme-linked immunosorbent assay. Roentgenography of the aorta and hand artery was performed, and visible vascular calcification was evaluated by one examiner, who was blinded to the patient characteristics.

RESULTS

In the 56 non-DM hemodialysis patients, vascular calcification was found in the hand artery in 5 patients (8.9%) and in the aorta in 23 patients (41.1%). These levels were significantly lower (p<0.05) than in the 32 DM patients, of whom, 19 (59.4%) and 21 (65.6%) had vascular calcification of the hand artery and aorta, respectively. Multiple regression analyses performed separately in the non-DM and DM patients showed that the plasma FGF-23 level, CaxPi product, and body weight are independent factors significantly associated with hand-artery calcification and that diastolic blood pressure is associated with aorta calcification in non-DM patients. In DM patients, the plasma FGF-23 level and hemodialysis duration emerged as independent factors associated with hand-artery calcification and diastolic blood pressure was associated with aorta calcification. The independent association of the plasma FGF-23 level with hand-artery calcification was retained in both non-DM and DM patients when adjusted for the CaxPi product.

CONCLUSION

Our findings show that the plasma FGF-23 level is an independent factor negatively associated with peripheral vascular calcification in the hand artery, but not in the aorta, in both male non-DM and DM hemodialysis patients, even when adjusted for the CaxPi product. This study raises the possibility that the plasma FGF-23 level may provide a reliable marker for Moenckeberg's medial calcification in male hemodialysis patients, independent of its regulatory effect on Pi metabolism.

Overproduction and Secretion of a Novel Amino-Terminal Form of Parathyroid Hormone from a Severe Type of Parathyroid Hyperplasia in Uremia

Measurement of bioactive parathyroid hormone (PTH) is essential for optimal management of bone abnormalities in dialysis patients. This can be accomplished by PTH measurements using third-generation PTH assays, which detect more or less of the first six amino acids of the PTH structure. Such assays do not detect non-(1-84) PTH fragments, such as human PTH (7-84), which are recognized by the second-generation PTH assays that use a detection antibody that recognizes an epitope within the 13-34 region of the PTH structure. Therefore, third-generation PTH results are expected to be lower than those that are obtained with second-generation PTH assays. Rare exceptions to this rule have been reported for patients with severe primary hyperparathyroidism or parathyroid cancer. Sera and gland extracts were analyzed from a dialysis patient with high bone turnover disease and with surprising higher PTH levels by a third-generation assay than by a second-generation assay. This finding normalized after the surgical removal of an enlarged gland with a single nodule, an advanced type of nodular hyperplasia. HPLC fractionation of sera and gland extracts revealed the overproduction and secretion of a PTH molecule with an intact amino-terminus structure distinct from (1-84) PTH. This form of PTH was readily detectable by third-generation PTH assays but was poorly reactive in second-generation PTH assays. Therefore, parathyroid glands with advanced uremic nodular hyperplasia may overproduce and secrete a novel, biologically active form of PTH with an intact 1-6 region but a presumably modified 12-18 region required for the detection in second-generation PTH assays.

Positive correlation of serum bio-intact PTH(1-84) but not intact PTH with parathyroid gland size in hemodialysis patients

To evaluate the usefulness of newly-developed bio-intact parathyroid hormone (Bio-PTH) assay, which measures exclusively intact PTH(1-84) molecule, serum PTH level determined by Bio-PTH assay, in comparison with second-generation intact PTH (I-PTH) assay, was examined for its correlation with parathyroid gland size. Serum PTH was determined in 46 male HD patients, together with bone formation markers bone alkaline phosphatase, intact osteocalcin, N-terminal propeptide of type I collagen, and bone resorption markers deoxypyridinoline, pyridinoline, beta-crossLaps. Maximal diameter of parathyroid gland was determined with ultrasonography as the parathyroid gland size. Serum Ca and Pi correlated significantly with parathyroid gland size rationalizing our method to define parathyroid gland size. Serum Bio-PTH was correlated significantly in a positive manner with parathyroid gland size (R = 0.308, P = 0.0474), whereas serum I-PTH did not. Furthermore, parathyroid gland size did not exhibit a significant correlation with any of bone formation markers or bone resorption markers. The lack of correlation between bone markers and parathyroid gland size in HD patients may be explained by the occurrence of refractoriness of bone to PTH. In conclusion, serum Bio-PTH assay could provide a better assay than I-PTH assay to estimate parathyroid function in HD patients, due mainly to its exclusive correlation with parathyroid gland size.