Development of immunoassays for type-5 tartrate-resistant acid phosphatase in human serum

Alendronate (ALN) combined with osteoprotegerin (OPG) significantly improves mechanical properties of long bone than the single use of ALN or OPG in the ovariectomized rats

Background

Alendronate (ALN) is the most common form of bisphosphonates used for the treatment of osteoporosis. Osteoprotegerin (OPG) has also been shown to reduce osteoporotic changes in both humans and experimental animals after systemic administration. The aim of this current study was to test if the anti-resorption effects of ALN may be enhanced when used in combination with OPG.

Objectives

To investigate the effects of ALN, OPG or combined on bone mass and bone mechanical properties in ovariectomized (OVX) rats.

Methods

OVX rats were treated with ALN, OPG-Fc, or OPG-Fc and ALN. Biochemical markers, trabecular bone mass, biomechanics, histomorphometry and RANKL expression in the bone tissues were examined following the treatments.

Results

The treatment of ALN, OPG-Fc and ALN+OPG-Fc all prevented bone loss in the OVX-rats, there was no statistical difference among the three treatment groups in terms of vertebrae BMD, mineralizing surfaces, mineral apposition rate, BFR/BS. The ALN+OPG-Fc treatment group had significantly increased the mechanical strength of lumber vertebral bodies and femoral shafts when compared to the ALN and OPG-Fc treatment groups. The RANKL protein expression in the vertebral bones was significantly decreased in the ALN and ALN+OPG-Fc treatment groups, suggesting the combined use of OPG-Fc and ALN might have amplified inhibition of bone resorption through inhibiting RANKL-dependent osteoclastogenesis.

Conclusion

The combined use of OPG-Fc and ALN may be a new treatment strategy for reversing bone loss and restoring bone quality in osteoprotic disorders.

Biology and clinical significance of tartrate-resistant acid phosphatases: new perspectives on an old enzyme

Type 5 tartrate-resistant acid phosphatase (TRAP) has been a clinically relevant biomarker for about 50 years. It has always been a reliable and specific cytochemical marker for hairy cell leukemia and for differentiated cells of monocytic lineage. Only recently has the test for serum TRAP activity been accepted as sensitive and specific enough for clinical use as a marker of osteoclasts and bone resorption. This has come about through steady advances in knowledge about TRAP enzymology, structure, function, and molecular regulation and a consequent appreciation that TRAP isoforms 5a and 5b have very different clinical significance. As a measure of osteoclast number and bone resorption, TRAP 5b has diagnostic and prognostic applications in osteoporosis, cancers with bone metastasis, chronic renal failure, and perhaps other metabolic and pathologic bone diseases. Serum TRAP 5a, on the other hand, has no relationship to bone metabolism but seems instead to be a measure of activated macrophages and chronic inflammation. Exploration of the real clinical usefulness of serum TRAP 5a for diagnosis and disease management in a wide variety of chronic inflammatory diseases is only now beginning. This perspective traces the important basic scientific developments that have led up to the refinement of serum TRAP isoform immunoassays and their validation as biomarkers of disease. Many unanswered questions remain, providing a wealth of opportunity for continued research of this multifaceted enzyme.

Age-related changes of serum tartrate-resistant acid phosphatase 5b and the relationship with bone mineral density in Chinese women

AIM

Osteoclastic activity is mainly assessed by measurement of urinary markers (eg C-terminal cross-linked telopeptides of type I collagen, N-terminal crosslinked telopeptides of type I collagen, etc), the levels of which could often be affected by renal clearance. Recently, serum tartrate-resistant acid phosphatase 5b (TRACP5b) has been used as an alternative serum marker to evaluate osteoclastic activity. We investigated the age-related changes of TRACP5b level and its association with bone mineral density (BMD) in Chinese women.

METHODS

Seven-hundred and twenty-two Chinese mainland women aged 20-79 years were recruited in the study. Serum TRACP5b level was measured using immunoassay to evaluate the state of bone resorption. Bone mineral density (BMD) (g/cm2) at lumbar spine 1-4 and proximal femur were measured by duelenergy X-ray absorptiometry.

RESULTS

The serum TRACP5b level reached a bottom value in premenopausal women aged 30-39, gradually increased in women aged 40-49, rapidly rose in women aged 50-59, and culminated with a maximum value in women aged 60-69 before a slow drop in women aged 70- 79. The average level of TRACP5b was significantly higher in postmenopausal women [(3.29+/-1.07) U/L] than in premenopausal women ([1.70+/-0.59] U/L). The levels of TRACP5b were inversely correlated with BMD at all measured sites (P<0.001). Furthermore, the level of TRACP5b was obviously higher in women with osteoporosis and osteopenia than those with normal bone mass (P<0.001).

CONCLUSION

We have established the reference values of serum TRACP5b in Chinese mainland women, and found that postmenopausal women had higher TRACP5b concentration than younger women. The results showed that serum TRACP5b was a sensitive and useful parameter for the evaluation of age-related changes of bone absorption.

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.

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.

Development of immunoassays for serum tartrate-resistant acid phosphatase isoform 5a

BACKGROUND

Serum tartrate-resistant acid phosphatase (TRACP) consists of 2 structurally related isoforms, TRACP 5a and 5b. TRACP 5b is from bone-resorbing osteoclasts. TRACP 5a may be a macrophage product of inflammation. We used a novel antibody to TRACP 5a to standardize immunoassays for serum TRACP 5a activity and protein.

METHODS

Biotinylated anti-TRACP antibodies were used to immobilize serum TRACP isoforms. TRACP activity was measured using 4-nitrophenyl phosphate as substrate. TRACP 5a protein was measured with an independent peroxidase-conjugated anti-TRACP antibody. Immunoassays were standardized for linearity of serum dose response, sensitivity and precision. Reference ranges for TRACP 5a were established from serum of 50 healthy males and 50 healthy age-matched females. Serum TRACP 5a activity and protein were determined in 29 cases of rheumatoid arthritis.

RESULTS

Serum matrix interference in both TRACP 5a assays required dilution to 10% serum to approach linearity. Intra-assay and inter-assay CV% were <10%. Mean serum TRACP 5a activity and protein were significantly higher in healthy men than women. There was a slight, but significant age related increase in both serum TRACP 5a and 5b among females, but not males, from age 20 to 70 years. TRACP 5a activity was positively correlated to TRACP 5a protein in healthy sera. Neither TRACP 5a activity nor protein was correlated strongly to TRACP-5b activity. TRACP 5a protein was significantly increased in 8/29 RA sera, whereas TRACP 5a and 5b activities were not. TRACP 5a activity and protein were not significantly correlated in RA sera.

CONCLUSIONS

Although TRACP 5a and 5b are related biosynthetically, their circulating levels in healthy humans were independent, suggesting differential regulation of expression. In chronic diseases, increased TRACP 5a may represent pathological processes of inflammation unrelated to bone metabolism.

Changes in receptor activator of nuclear factor-kappaB, and its ligand, osteoprotegerin, bone-type alkaline phosphatase, and tartrate-resistant acid phosphatase in ovariectomized rats

We investigated time-course changes in the expression of receptor activator of nuclear factor-kappaB (RANK), its ligand (RANKL), osteoprotegerin (OPG), bone-type alkaline phosphatase (BAP), and tartrate-resistant acid phosphatase (TRAP) in ovariectomized (OVX) rats. Samples of sera and coccyges were used for analysis of the enzyme activities and expression levels of proteins and mRNAs, and an immunohistochemical analysis was also performed. Serum BAP activity increased to 158.6% of the pre-operation value at 1 week after OVX, and then decreased to 38.7% at 8 weeks after OVX. On the other hand, the serum TRAP activity increased to 130.9% of the pre-operation level at 1 week after OVX, and was maintained at a high level, compared with the pre-operation level. The patterns of BAP and TRAP activity in the coccyges specimens were similar to those seen in the sera. The expression profiles of TRAP, RANK, and RANKL proteins in the coccyx specimens were similar to the pattern of serum TRAP activity, while the profiles of the BAP and OPG proteins were similar to the pattern of serum BAP activity in OVX rats. The changes in the mRNA expression levels of the osteogenic proteins were similar to those for protein expression. These biochemical changes in OVX rats were confirmed by immunohistochemical studies. Our results suggest that not only osteoclastogenesis accelerated but also osteoblastogenesis transiently increased during the early phase of osteoporosis.

N-glycosylation influences the latency and catalytic properties of mammalian purple acid phosphatase

Purple acid phosphatase (PAP), also known as tartrate-resistant acid phosphatase or uteroferrin, contains two potential consensus N-glycosylation sites at Asn(97) and Asn(128). In this study, endogenous rat bone PAP was found to possess similar N-glycan structures as rat recombinant PAP heterologously expressed in baculovirus-infected Sf9 insect cells. PAP from Sf9 cells was shown to contain two N-linked oligosaccharides, whereas PAP expressed by mammalian CHO-K1 cells was less extensively glycosylated. The extent of N-glycosylation affected the catalytic properties of the enzyme, as N97Q and N128Q mutants, containing a single oligosaccharide chain, exhibited a lower substrate affinity and catalytic activity compared to those of the fully glycosylated PAP in the native, monomeric state. The differences in substrate affinity and catalytic activity were abolished and partially restored, respectively, by proteolytic cleavage in the loop domain, indicating that the extent of N-glycosylation influences the interaction of the repressive loop domain with catalytically important residues.

Tartrate-Resistant Acid Phosphatase 5b is a Useful Serum Marker for Extensive Bone Metastasis in Breast Cancer Patients

Purpose: Previous studies showed that serum tartrate-resistant acid phosphatase 5b (TRACP5b) activity was increased in 70% to 94% of breast cancer (BC) patients with bone metastasis (BM). This study aims to determine whether serum TRACP5b is useful for identifying limited or extensive BM in BC patients.

Experimental Design: Serum TRACP5b activity was measured in 168 BC patients, including 81 who were newly diagnosed with early BC, 20 with extraosseous metastasis, 24 with limited BM, and 43 with extensive BM. Serum TRACP5b activity was also measured monthly in 151 patients with early BC until they developed BM. Four hundred and twenty-seven (427) healthy women ages 18 to 90 served as control. One-way ANOVA was used to compare serum TRACP5b among groups. The sensitivity and specificity of serum TRACP5b as a marker for BM were estimated by receiver operator characteristic (ROC) curves.

Results: Serum TRACP5b increased with age in healthy women ( P &lt; 0.0001). It was significantly elevated in patients with extensive BM compared with all other groups ( P &lt; 0.0001). ROC analysis established a cutoff value of 4.026 units/L to identify patients with extensive BM with a specificity of 98% and a sensitivity of 93% (area under the curve = 0.9807; 95% CI = 0.9698-0.9915). Among the 151 patients with early BC, 6 developed limited BM and 2 developed extensive BM during the follow-up period. Serum TRACP5b remained below the cutoff value in patients with limited BM, but became significantly increased in those whose BM became extensive.

Conclusion: Serum TRACP5b activity is a useful diagnostic marker for extensive BM in patients with BC.

Alternative immunoassay for tartrate-resistant acid phosphatase isoform 5b using the fluorogenic substrate naphthol ASBI-phosphate and heparin

OBJECTIVE

Our purpose was to develop a specific immunoassay for tartrate-resistant acid phosphatase (TRACP) 5b using naphthol ASBI phosphate (N-ASBI-P) as a selective substrate for isoform 5b and heparin as a selective inhibitor of isoform 5a.

METHODS

Serum TRACP 5a and 5b and recombinant TRACP 5a were used to optimize and standardize the immunoassay for specificity, linearity, analytical recovery, sensitivity and reproducibility. Serum N-telopeptide cross-links (NTX) and bone alkaline phosphatase (bone ALP) were also measured. The clinical sensitivity and specificity were assessed in healthy control subjects and patients with osteoarthritis (OA), rheumatoid arthritis (RA) and endstage renal disease (ESRD).

RESULTS

TRACP 5b specificity was achieved at pH 6.3 with 2.5 mmol/l substrate and 25 U/ml heparin. Isoform 5b specificity was increased over our original immunoassay using 4-nitrophenyl phosphate (4-NPP) without heparin. The alternative immunoassay was linear with 110% analytical recovery and no serum matrix effects. The average intra-assay error was 10.65%; the average inter-assay error was 10.11% for values of 1-3 U/l and 6.5% for values of 7-11 U/l. Mean serum TRACP 5b in OA and RA were not significantly different from control using either immunoassay. Mean serum TRACP 5b was significantly increased in ESRD with both immunoassays. Serum TRACP 5b levels correlated significantly with NTX and bone ALP in the disease groups, but not always in the control group.

CONCLUSION

This alternative immunoassay for TRACP 5b activity is highly specific. It should have applications in evaluating patients with bone disease and will improve our understanding of the biological significance of TRACP 5b expression in health and disease.