Tartrate-resistant acid phosphatase isoform 5b: a novel serum marker for monitoring bone disease in multiple myeloma

Changes in RANKL, OPG, and 25(OH)D Levels in Children with Leukemia from Diagnosis to Remission

BACKGROUND

The receptor activator of the nuclear factor-kB (RANK)/RANK ligand (RANKL)/osteoprotegerin (OPG) pathway is a determining pathway in the balance between bone formation and resorption, and disruptions in this complex can affect bone metabolism.

METHODS

This study analyzes the changes in RANKL, OPG, and 25(OH)D levels; the RANKL/OPG ratio; and other bone turnover markers (BTMs) from diagnosis to complete remission in children with acute lymphoblastic leukemia (ALL). This is a prospective observational cohort study, carried out at the Instituto Mexicano del Seguro Social, Mexico City, including 33 patients (4-17 years) with newly diagnosed B-cell ALL. The patients were treated with the HP09 chemotherapy protocol. Children who had previously been treated with corticosteroids were excluded. A peripheral blood sample at diagnosis and remission was collected to determine the 25(OH)D and BTM concentrations.

RESULTS

Increased RANKL (p = 0.001) and osteocalcin (p < 0.001) levels and RANKL/OPG ratio (<0.001) and a decreased OPG level (p = 0.005) were observed at remission, predominantly in the high-risk (HR) relapse and vitamin D deficiency groups. A negative association between RANKL and OPG (r = -0.454, p = 0.008) was observed.

CONCLUSIONS

we suggest that the RANKL/OPG ratio could serve as a bone remodeling marker in ALL patients.

The Impact of a 6-Week Nordic Walking Training Cycle and a 14-Hour Intermittent Fasting on Disease Activity Markers and Serum Levels of Wnt Pathway-Associated Proteins in Patients with Multiple Myeloma

Background: Multiple myeloma (MM) accounts for about 10-15% of all diagnosed hematologic malignancies and about 1-2% of all cancer cases. Approximately 80-90% of MM patients develop bone disease and the changes rarely regress. It is only possible to stop or slow their progression. A major role in bone destruction in MM is attributed to the Wnt signaling pathway, and its action can be modified by various types of interventions including training and diet. Therefore, the aim of this project was to evaluate the effects of a Nordic Walking (NW) training cycle and intermittent fasting (IF) on the levels of selected bone turnover markers associated with the Wnt pathway in patients with MM. Materials and methods: Results from 35 patients divided into training (NW and IF NW) and non-training (IF and control) groups were included in the analysis. A 6-week training cycle involving 60 min workouts 3 times a week was conducted. Body mass and composition as well as the levels of vitamin D, calcium and phosphorus, beta2-microglobulin, and albumin were examined before and after the completion of the training cycle. Markers of bone turnover were also determined: sclerostin (SOST), Dickkopf-related protein 1 (DKK-1), osteoprotegrin (OPG), osteopontin (OPN), and Tartrate-resistant acid phosphatase 5b (TRACP 5b). Results: There was no negative effect of IF or combined training and fasting on the nutritional status of the patients (the level of albumins was unchanged). Both training groups showed an increase in serum concentrations of the active metabolite of vitamin D (IF NW and NW: p = 0.001 and p = 0.022, respectively). The change in the concentration of this vitamin negatively correlated with the concentration of TRACP 5b (r = -0.413, p = 0.014). Evaluating the concentrations of markers related to bone turnover, a reduction in the concentrations of SOST (time: p = 0.026, time vs. group: p = 0.033) and TRACP 5b (time: p < 0.001, time vs. group p < 0.001) was indicated. Conclusions: The obtained results allow one to indicate the training with the poles as a safe and beneficial form of physical activity that should be recommended to patients suffering from MM. However, the results obtained in the present study are not sufficient to show the beneficial effect of IF applied without trainings.

Phosphorescence, fluorescence, and colorimetric triple-mode sensor for the detection of acid phosphatase and corresponding inhibitor

Acid phosphatase (ACP) as a clinical diagnostic biomarker for several pathophysiological diseases has aroused widespread interest. Compared to commonly developed single-mode ACP detection technology, the multi-mode detection method with self-validation can provide more reliable results. Herein, we proposed a triple-mode phosphorescence, fluorescence, and colorimetric method for ACP detection in combination with CDs@SiO₂. HAuCl₄ with oxidase-like activity can catalyze the oxidation of colorless 3,3',5,5'-tetramethylbenzidine (TMB) to the blue oxide TMB (TMBox), offering absorption signals and quenching the phosphorescence and fluorescence of CDs@SiO₂ based on the internal filtration effect (IFE). ACP can hydrolyze ascorbic acid 2-phosphate (AAP) to yield ascorbic acid (AA), thereby reducing TMBox to TMB, triggering solution fading and restoring phosphorescence and fluorescence signals. When the ACP inhibitor malathion is present, the reduction of TMBox is hindered, which successively led to the suppression of CDs@SiO₂ phosphorescence and fluorescence signal recovery. According to these principles, triple-mode ACP (LOD = 0.0026 mU mL^-1) and malathion detections (LOD = 0.039 μg mL^-1) with favorable accuracy and sensitivity are realized. With simplicity, robustness, and versatility, the triple-mode sensor can be extended to the detection of the AAP hydrolase family and the screening of corresponding inhibitors.

Sensitive acid phosphatase assay based on light-activated specific oxidase mimic activity

Acid phosphatase (ACP) is a key marker in the diagnosis of many diseases. However, exploiting a simple and sensitive sensor for the real-time quantitative analysis of ACP is still challenging. Herein, we attempted to develop a sensitive colorimetric sensing strategy for the detection of ACP based on light-activated oxidase mimic property of carbon dots (CDs). The synthesized CDs were proved to be capable of intrinsic light-activated oxidase mimic activity, which could generate reactive oxygen species to oxidize chromogenic substrate under ultraviolet light stimulation. Interestingly, this light-activated oxidase mimic behavior would be effectively suppressed by the antioxidant ascorbic acid (AA), a product from the hydrolysis of 2-phospho-L-ascorbic acid trisodium (AAP) mediated by ACP. Based on the above property, a facile and sensitive colorimetric sensing method for ACP was developed. Under the optimal conditions, the linear range for ACP 0.1-5.5 U/L, and the detection limit was 0.056 U/L. Compared with conventional nanozyme based ACP assay systems, the catalytic activity of light-activated nanozyme could be conveniently regulated by switching the light on and off, which made it easier to precisely control the extent of the reaction and ensured the accuracy of the assay. In addition, the proposed sensing system would be readout directly by the naked eye or smartphone-based RGB analysis system, and have been successfully applied to analyze diluted in diluted fetal bovine serum and urine samples spiked with ACP. All these results indicated that this approach holds good promise for future applications in clinical analysis and point-of-care (POC) biosensor platforms.

Increased Bone Volume by Ixazomib in Multiple Myeloma: 3-Month Results from an Open Label Phase 2 Study

Multiple myeloma (MM) is an incurable bone marrow cancer characterized by the development of osteolytic lesions due to the myeloma-induced increase in osteoclastogenesis and decrease in osteoblastic activity. The standard treatment of MM often involves proteasome inhibitors (PIs), which can also have a beneficial off-target bone anabolic effect. However, long-term treatment with PIs is unadvised due to their high side-effect burden and inconvenient route of administration. Ixazomib is a new-generation, oral PI that is generally well tolerated; however, its bone effect remains unknown. Here, we describe the 3-month results of a single-center phase II clinical trial investigating the effect of ixazomib treatment on bone formation and bone microstructure. Thirty patients with MM in stable disease not receiving antimyeloma treatment for ≥3 months and presenting ≥2 osteolytic lesions received monthly ixazomib treatment cycles. Serum and plasma samples were collected at baseline and monthly thereafter. Sodium ¹⁸ F-Fluoride positron emission tomography (NaF-PET) whole-body scans and trephine iliac crest bone biopsies were collected before and after three treatment cycles. The serum levels of bone remodeling biomarkers suggested an early ixazomib-induced decrease in bone resorption. NaF-PET scans indicated unchanged bone formation ratios; however, histological analyses of bone biopsies revealed a significant increase in bone volume per total volume after treatment. Further analyses of bone biopsies showed unchanged osteoclast number and COLL1A1^High -expressing osteoblasts on bone surfaces. Next, we analyzed the superficial bone structural units (BSUs), which represent each recent microscopic bone remodeling event. Osteopontin staining revealed that following treatment, significantly more BSUs were enlarged (>200,000 μm² ), and the distribution frequency of their shape was significantly different from baseline. Overall, our data suggest that ixazomib induces overflow remodeling-based bone formation by decreasing the level of bone resorption and promoting longer bone formation events, making it a potentially valuable candidate for future maintenance treatment. © 2023 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

A feasible self-assembled near-infrared fluorescence sensor for acid phosphatase detection and cell imaging

The single signal amplification strategy is significant for detecting various disease biomarkers but is restricted by its limited accuracy. The multi-signal and multi-mode methods have overcome this deficiency. Acid phosphatase (ACP) is an important intracellular enzyme but one-step cell imaging material-based probes are scarce for ACP. Herein, we designed a one-step self-assembled polymer probe using neutral red (NR), modified-(pyridoxal-5'-phosphate (PLP)) and Eu³⁺. The polymer exhibited non-emission and excellent stability. Upon the catalytic hydrolysis reaction of ACP, the polymer exhibited two strong fluorescence signals at 373 nm and 613 nm and an appreciable decline of absorbance at 395 nm. The probe has excellent selectivity and higher sensitivity with a limit of detection as low as 0.02 mU mL^-1. It possesses favorable biocompatibility and has been successfully used to detect and image intracellular ACP in several living cells.

From Glucose to Lactate and Transiting Intermediates Through Mitochondria, Bypassing Pyruvate Kinase: Considerations for Cells Exhibiting Dimeric PKM2 or Otherwise Inhibited Kinase Activity

A metabolic hallmark of many cancers is the increase in glucose consumption coupled to excessive lactate production. Mindful that L-lactate originates only from pyruvate, the question arises as to how can this be sustained in those tissues where pyruvate kinase activity is reduced due to dimerization of PKM2 isoform or inhibited by oxidative/nitrosative stress, posttranslational modifications or mutations, all widely reported findings in the very same cells. Hereby 17 pathways connecting glucose to lactate bypassing pyruvate kinase are reviewed, some of which transit through the mitochondrial matrix. An additional 69 converging pathways leading to pyruvate and lactate, but not commencing from glucose, are also examined. The minor production of pyruvate and lactate by glutaminolysis is scrutinized separately. The present review aims to highlight the ways through which L-lactate can still be produced from pyruvate using carbon atoms originating from glucose or other substrates in cells with kinetically impaired pyruvate kinase and underscore the importance of mitochondria in cancer metabolism irrespective of oxidative phosphorylation.

Cathepsin K regulates localization and secretion of Tartrate-Resistant Acid Phosphatase (TRAP) in TRAP-overexpressing MDA-MB-231 breast cancer cells

Background

Tartrate–resistant acid phosphatase (TRAP/ ACP5) belongs to the binuclear metallophosphatase family and is present in two isoforms. The primary translation product is an uncleaved TRAP 5a isoform with low phosphatase activity. TRAP 5a can be post-translationally processed to a cleaved TRAP 5b isoform with high phosphatase activity by e.g. cysteine proteinases, such as Cathepsin K (CtsK). The relevance of the phosphatase activity of TRAP 5b has been demonstrated for proliferation, migration and invasion of cancer cells. TRAP-overexpressing MDA-MB-231 breast cancer cells displayed higher levels of TRAP 5a and efficient processing of TRAP 5a to TRAP 5b protein, but no changes in levels of CtsK when compared to mock-transfected cells. In TRAP-overexpressing cells colocalization of TRAP 5a and proCtsK was augmented, providing a plausible mechanism for generation of TRAP 5b. CtsK expression has been associated with cancer progression and has been pharmacologically targeted in several clinical studies.

Results

In the current study, CtsK inhibition with MK-0822/Odanacatib did not abrogate the formation of TRAP 5b, but reversibly increased the intracellular levels of a N-terminal fragment of TRAP 5b and reduced secretion of TRAP 5a reversibly. However, MK-0822 treatment neither altered intracellular TRAP activity nor TRAP-dependent cell migration, suggesting involvement of additional proteases in proteolytic processing of TRAP 5a. Notwithstanding, CtsK was shown to be colocalized with TRAP and to be involved in the regulation of secretion of TRAP 5a in a breast cancer cell line, while it still was not essential for processing of TRAP 5a to TRAP 5b isoform.

Conclusion

In cancer cells multiple proteases are involved in cleaving TRAP 5a to high-activity phosphatase TRAP 5b. However, CtsK-inhibiting treatment was able to reduce secretion TRAP 5a from TRAP-overexpressing cancer cells.

A Novel Sandwich ELISA for Tartrate-Resistant Acid Phosphatase 5a and 5b Protein Reveals that Both Isoforms are Secreted by Differentiating Osteoclasts and Correlate to the Type I Collagen Degradation Marker CTX-I In Vivo and In Vitro

Tartrate-resistant acid phosphatase type 5 (TRAP) exists as two isoforms, 5a and 5b. 5b is a marker of osteoclast number and 5a of chronic inflammation; however, its association with bone resorption is unknown. In this study, a double-TRAP 5a/5b sandwich ELISA measuring 5a and 5b protein in the same sample was developed. TRAP 5a and 5b protein levels were evaluated as osteoclast differentiation/activity markers in serum and in culture, and their correlation to the resorption marker CTX-I was examined. Serum TRAP 5a and 5b concentrations in healthy men were 4.4 ± 0.6 ng/ml and 1.3 ± 0.2 ng/ml, respectively, and they correlated moderately to each other suggesting that their secretion is coupled under healthy conditions. A correlation was also observed between serum TRAP 5a and 5b with CTX-I, suggesting that both TRAP isoforms associate with osteoclast number. During osteoclast differentiation on plastic/bone, predominantly 5b increased in media/lysate from M-CSF/RANKL-stimulated CD14+ PBMCs. However, substantial levels of 5a were detected at later stages suggesting that both isoforms are secreted from differentiating OCs. More TRAP 5b was released on bone indicating a connection to osteoclast resorptive activity, and a peak in TRAP 5b/5a-ratio coincided with rapid CTX-I release. At the end of the culture period of M-CSF + RANKL-stimulated CD14+ PBMCs, there was a correlation between the secretion of TRAP 5a and 5b proteins with CTX-I. The correlation of not only 5b but also 5a with collagen degradation, both in serum and osteoclast cultures indicates that a considerable proportion of the TRAP 5a originates from osteoclasts and may reflect a hitherto undisclosed regulatory mechanism during bone resorption and bone remodeling.

Adiponectin inhibits the differentiation and maturation of osteoclasts via the mTOR pathway in multiple myeloma

The present study sought to investigate the correlation between adipose cytokines (visfatin, leptin and adiponectin) and markers of multiple myeloma bone disease, and to determine the effects and mechanism of action of adiponectin on the differentiation and maturation of osteoclasts in multiple myeloma (MM). The levels of visfatin, leptin and adiponectin were measured. Their association with the indices of myeloma tumor load and bone disease were analyzed. Reverse transcription-quantitative PCR was used to detect the expression of receptor activator of nuclear factor-κB ligand (RANKL), osteoclast associated Ig-like receptor (OSCAR), tartrate-resistant acid phosphatase (TRAP) and Cathepsin K genes. Flow cytometry was used to detect the expression of adiponectin receptor 1 (AdipoR1) and the phosphorylation of the mechanistic target of rapamycin kinase (mTOR) pathway-associated proteins mTOR and eukaryotic translation initiation factor 4E-binding protein (4EBP1). There were no significant correlations among leptin, visfatin and the indexes of myeloma tumor load and bone disease. Serum adiponectin levels were significantly lower in patients with newly diagnosed multiple myeloma compared with healthy volunteers (12.37±3.13 vs. 13.80±0.95; P<0.05). The number of mature osteoclasts in the adiponectin group was lower compared with in the control group. Adiponectin also inhibited the mRNA expression of the osteoclast-associated factors RANKL, OSCAR, TRAP and Cathepsin K. Comparison between the non-adiponectin group and the adiponectin group revealed that adiponectin increased the expression of AdipoR1 on the surface of osteoclast precursor cells (26.21±4.27% vs. 29.86±6.23%; P<0.05) and reduced the expression of phosphorylated (p-)mTOR (7.89±1.00% vs. 5.91±1.26%; P<0.05) and p-4EBP1 (26.78±5.00% vs. 22.49±4.24%; P<0.05). The p-mTOR and p-4EBP1 levels in the adiponectin + MHY1485 (an mTOR signaling pathway-specific agonist) group were significantly higher compared with those in the adiponectin group. It was revealed that adiponectin may inhibit osteoclast differentiation and maturation via the mTOR pathway. In conclusion, adiponectin inhibits the differentiation and maturation of osteoclasts by increasing the expression of AdipoR1 and reducing the phosphorylation levels of mTOR and 4EBP1 in patients with MM.

PdPt bimetallic nanowires with efficient oxidase mimic activity for the colorimetric detection of acid phosphatase in acidic media

PdPt bimetallic alloy nanowires (Pd/Pt NWs) were found to exhibit excellent oxidase-like activity and can be applied to sensitively detect the activity of acid phosphatase (ACP) in acidic media.

Identification of inhibitors of Tartrate-resistant acid phosphatase (TRAP/ACP5) activity by small-molecule screening

Tartrate-resistant acid phosphatase (TRAP/ACP5) occurs as two isoforms-TRAP 5a with low enzymatic activity due to a loop interacting with the active site and the more active TRAP isoform 5b generated upon proteolytic cleavage of this loop. TRAP has been implicated in several diseases, including cancer. Thus, this study set out to identify small-molecule inhibitors of TRAP activity. A microplate-based enzymatic assay for TRAP 5b was applied in a screen of 30,315 compounds, resulting in the identification of 90 primary hits. After removal of promiscuous compounds, unwanted groups, and false positives by orthogonal assays and three-concentration validation, the properties of 52 compounds were further investigated to better understand their mechanism of action. Full-concentration-response curves for these compounds were established under different enzyme concentrations and (pre)incubation times to remove compounds with inconsistent results and low potencies. Full-concentration-response curves were also performed for both isoforms, to examine isoform prevalence. Filtering led to six prioritized compounds, representing different clusters. One of these, CBK289001 or (6S)-6-[3-(2H-1,3-benzodioxol-5-yl)-1,2,4-oxadiazol-5-yl]-N-(propan-2-yl)-1H,4H,5H,6H,7H-imidazo[4,5-c]pyridine-5-carboxamide, demonstrated efficacy in a migration assay and IC₅₀ values from 4 to 125 μm. Molecular docking studies and analog testing were performed around CBK289001 to provide openings for further improvement toward more potent blockers of TRAP activity.

Deficient invariant natural killer T cells had impaired regulation on osteoclastogenesis in myeloma bone disease

Recent research showed that invariant natural killer T (iNKT) cells take part in the regulation of osteoclastogenesis. While the role of iNKT cells in myeloma bone disease (MBD) remains unclear. In our study, the quantity of iNKT cells and the levels of cytokines produced by them were measured by flow cytometry. iNKT cells and osteoclasts were induced from peripheral blood mononuclear cells after activation by α‐GalCer or RANKL in vitro. Then, gene expressions and the levels of cytokines were determined by RT‐PCR and ELISA, respectively. The results showed that the quantity of iNKT and production of IFN‐γ by iNKT cells were significantly decreased in newly diagnosed MM (NDMM), and both negatively related with severity of bone disease. Then, the osteoclasts from healthy controls were cultured in vitro and were found to be down‐regulated after α‐GalCer‐stimulated, while there was no significant change with or without α‐GalCer in NDMM patients, indicating that the regulation of osteoclastogenesis by iNKT cells was impaired. Furthermore, the inhibition of osteoclastogenesis by iNKT cells was regulated by IFN‐γ production, which down‐regulated osteoclast‐associated genes. In conclusion, the role of α‐GalCer‐stimulated iNKT cells in regulation of osteoclastogenesis was impaired in MBD, as a result of iNKT cell dysfunction.

Monocyte chemotactic protein-1 deficiency attenuates and high-fat diet exacerbates bone loss in mice with Lewis lung carcinoma

Bone loss occurs in obesity and cancer-associated complications including wasting. This study determined whether a high-fat diet and a deficiency in monocyte chemotactic protein-1 (MCP-1) altered bone structural defects in male C57BL/6 mice with Lewis lung carcinoma (LLC) metastases in lungs. Compared to non-tumor-bearing mice, LLC reduced bone volume fraction, connectivity density, trabecular number, trabecular thickness and bone mineral density and increased trabecular separation in femurs. Similar changes occurred in vertebrae. The high-fat diet compared to the AIN93G diet exacerbated LLC-induced detrimental structural changes; the exacerbation was greater in femurs than in vertebrae. Mice deficient in MCP-1 compared to wild-type mice exhibited increases in bone volume fraction, connectivity density, trabecular number and decreases in trabecular separation in both femurs and vertebrae, and increases in trabecular thickness and bone mineral density and a decrease in structure model index in vertebrae. Lewis lung carcinoma significantly decreased osteocalcin but increased tartrate-resistant acid phosphatase 5b (TRAP 5b) in plasma. In LLC-bearing mice, the high-fat diet increased and MCP-1 deficiency decreased plasma TRAP 5b; neither the high-fat diet nor MCP-1 deficiency resulted in significant changes in plasma concentration of osteocalcin. In conclusion, pulmonary metastasis of LLC is accompanied by detrimental bone structural changes; MCP-1 deficiency attenuates and high-fat diet exacerbates the metastasis-associated bone wasting.

Chitosan-stabilized platinum nanoparticles as effective oxidase mimics for colorimetric detection of acid phosphatase

Capping molecules on the surface of nanomaterials not only enhance the dispersion and stability of nanomaterials but also greatly facilitate their surface modification and biological applications. However, most capping molecules can severely block the active sites of the catalytic core, thereby decreasing the enzymatic activity of nanomaterial-based enzyme mimics. This work demonstrates the superiority of chitosan (Ch) as a capping molecule for synthesizing catalytic platinum nanoparticles (PtNPs). The experimental results show that Ch simultaneously exhibits an excellent stabilizing effect and enhances the oxidase-like activity of PtNPs. Kinetic studies indicate that Ch-PtNPs have a higher affinity for 3,3',5,5'-tetramethylbenzidine (TMB) than other kinds of oxidase mimics. Furthermore, the TMB chromogenic reaction catalyzed by Ch-PtNPs is found to be much faster in an acidic medium, thus adapting well to the optimal pH for acid phosphatase (ACP). Therefore, a novel colorimetric approach for ACP determination is developed for the first time, which is based on the Ch-PtNP-catalyzed oxidation of TMB, the inhibitory effect of ascorbic acid (AA) on the oxidase-like activity of Ch-PtNPs, and the ACP-catalyzed hydrolysis of AA 2-phosphate (AAP) into AA. The linear range for ACP is 0.25-2.5 U L^-1 and the limit of detection is measured to be 0.016 U L^-1. This new colorimetric method is utilized to detect ACP in real biological samples and to screen ACP inhibitors. We believe that these new PtNPs, which exhibit high colloidal stability, excellent catalytic performance, good biocompatibility, simple preparation, and easy modification, can be promising candidates for a broad range of applications in optical sensing, environmental monitoring, clinical diagnosis, and drug discovery.

CYR61/CCN1 stimulates proliferation and differentiation of osteoblasts in vitro and contributes to bone remodeling in vivo in myeloma bone disease

Cysteine-rich 61 (CYR61/CCN1), a secreted protein in bone marrow (BM) microenvironment, has diverse effects on many cellular activities such as growth and differentiation. However, the effect of CCN1 on osteoblasts (OBs) in myeloma bone disease remains unclear. In our study, the level of CCN1 in multiple myeloma (MM) patients was detected by ELISA and RT-PCR. The proliferation and differentiation of OBs from MM patients were observed after stimulated by CCN1 in vitro. The myeloma cells transduced with CYR61 gene (RPMI‑8226/CYR61) were injected in a mouse model to evaluate the efficacy of CCN1 in vivo and compare with zoledronic acid. The results showed that CYR61/CCN1 levels in BM supernatant and OBs both elevated significantly in all newly diagnosed MM patients, especially in patients without bone disease (P=0.001 and P<0.001). After 30 ng/l CCN1 stimulation for 24 h, the quantity and mineralization of OBs increased significantly in vitro (P=0.046 and 0.048). The transcription factors of Wnt pathway, runt-related transcription factor 2 (Runx2) and β-catenin were upregulated in OBs after CCN1 stimulation (P=0.012 and 0.011). After injection of RPMI‑8226 cells, bone lesions were observed obviously by microCT and histochemistry at 7 weeks. Radiographic analysis of the bones showed decreased resorption in CCN1 overexpression group and zoledronic acid group, while severe resorption in negative control. Furthermore, trabecular bone volume in CCN1 overexpression group (1.7539±0.16949) was significantly higher than zoledronic acid group (1.2839±0.077) (P=0.012). In conclusion, CCN1 can stimulate the proliferation and differentiation of OBs in vitro and contribute to bone remodeling in vivo in MBD.

Clinical significance of osteoblast precursors and osteoclast precursors in earlier diagnosis and monitoring of myeloma bone disease

Bone disease is the most common complication of multiple myeloma (MM). In order to diagnose and monitor the bone damages earlier, we detected circulating osteoclast precursors (OCPs) and osteoblast precursors (OBPs) by flow cytometry, comparing with special biochemical markers, such as tartrate-resistant acid phosphatase isoform 5b (TRACP-5b), carboxy-terminal cross-linking telopeptide of type I collagen (CTX), osteocalcin (OCN), and procollagen I amino-terminal propeptide (PINP). The results showed that the circulating OBPs in the newly diagnosed MM patients significantly decreased compared with the normal controls (7.14 vs 12.82 %, P = 0.045), while circulating OCPs in the newly diagnosed patients and remission patients were significantly increased than the normal controls (2.46 vs 0.17 %, P = 0.000; 1.87 vs 0.17 %, P = 0.000, respectively). According to X-ray, newly diagnosed patients were divided into stages A and B (without and with osteolytic lesions). Compared with the normal controls, the circulating OBPs in stages A and B reduced (12.82 vs 7.47 %, P = 0.041; 12.82 vs 7.14 %, P = 0.010, respectively), while the circulating OCPs elevated (0.17 vs 2.31 %, P=0.010; 0.17 % vs 2.71 %, P=0.001, respectively). The levels of TRACP-5b and CTX in the newly diagnosed patients were higher than the normal controls (P = 0.014, P = 0.037) and remission patients (P = 0.025, P = 0.003), and they were significantly higher in stage B than the normal controls (P = 0.015, P = 0.002). However, the PINP and OCN levels had no significant changes in different stages. In conclusion, abnormal circulating OBPs and OCPs were found earlier before X-ray in MM and still existed in remission patients, indicating that they may be novel predictive markers for early diagnosing and monitoring bone disease.

High Uric Acid (UA) Negatively Affects Serum Tartrate-Resistant Acid Phosphatase 5b (TRACP 5b) Immunoassay

Background

Bone metastases often occur in the majority of patients with advanced cancer, such as prostate cancer, lung cancer and breast cancer. Serum tartrate-resistant acid phosphatase 5b (TRACP 5b), a novel bone resorption marker, has been used gradually in the clinics as a specific and sensitive marker of bone resorption for the early diagnosis of cancer patients with bone metastasis. Here, we reported that high concentrations of uric acid (UA) lead to decrease of TRACP 5b levels and determined whether TRACP 5b level was associated with UA in interference experiment.

Methods

A total of 77 patients with high concentrations of UA and 77 healthy subjects were tested to evaluate the differences in their TRACP 5b levels. Serial dilutions of UA were respectively spiked with a known concentration of TRACP 5b standard sample, then Serum TRACP 5b was detected by using bone TRAP^® Assay. A correction equation was set to eliminate UA-derived TRACP 5b false-decrease. The effect of this correction was evaluated in high-UA individuals.

Results

The average TRACP level of the high-UA individuals (1.47± 0.62 U/L) was significantly lower than that of the healthy subjects (2.62 ± 0.63 U/L) (t-test, p<0.0001). The UA correction equation derived: ΔTRACP 5b = -1.9751lgΔUA + 3.7365 with an R² = 0.98899. Application of the UA correction equation resulted in a statistically non-significant difference in TRACP 5b values between the healthy subjects and high-UA individuals (p = 0.24).

Conclusions

High UA concentrations can falsely decrease TRACP 5b levels due to a method-related systematic error. To avoid misdiagnoses or inappropriate therapeutic decisions, increased attention should be paid to UA interference, when TRACP 5b is used for early diagnosis of cancer patients with bone metastasis, evaluation of the aggressiveness of osteosarcoma or prediction of survival in prostate cancer and breast cancer with bone metastases.

Osteoprotegerin is a significant prognostic factor for overall survival in patients with primary systemic amyloidosis independent of the Mayo staging

Bone metabolism has not been systematically studied in primary (AL) amyloidosis. Thus we prospectively evaluated bone remodeling indices in 102 patients with newly diagnosed AL amyloidosis, 35 healthy controls, 35 newly diagnosed myeloma and 40 monoclonal gammopathy of undetermined significance patients. Bone resorption markers (C-telopeptide of type-1 collagen, N-telopeptide of type-1 collagen) and osteoclast regulators (soluble receptor activator of nuclear factor-κB ligand (sRANKL), osteoprotegerin (OPG)) were increased in AL patients compared with controls (P<0.01), but bone formation was unaffected. Myeloma patients had increased bone resorption and decreased bone formation compared with AL patients, while sRANKL/OPG ratio was markedly decreased in AL, due to elevated OPG in AL (P<0.001). OPG correlated with N-terminal pro-brain natriuretic peptide (P<0.001) and was higher in patients with cardiac involvement (P=0.028) and advanced Mayo stage (P=0.001). OPG levels above the upper value of healthy controls was associated with shorter survival (34 versus 91 months; P=0.026), while AL patients with OPG levels in the top quartile had very short survival (12 versus 58 months; P=0.024). In Mayo stage 1 disease, OPG identified patients with poor survival (12 versus >60 months; P=0.012). We conclude that increased OPG in AL is not only a compensation to osteoclast activation but may also reflect early cardiac damage and may identify patients at increased risk of death within those with earlier Mayo stage.

Myeloma bone disease

Bone destruction is a hallmark of multiple myeloma, and recent studies demonstrated a strong interdependence between tumor progression and bone resorption. Increased bone resorption as a major characteristic of multiple myeloma is caused by osteoclast activation and osteoblast inhibition (uncoupling). Myeloma cells alter the local regulation of bone metabolism by increasing the receptor activator of NF-kappaB ligand (RANKL) and decreasing osteoprotegerin (OPG) expression within the bone marrow microenvironment, thereby stimulating the central pathway for osteoclast formation and activation. In addition, they produce the chemokines MIP-1alpha, MIP-1beta and SDF-1alpha, which also increase osteoclast activity. Furthermore, myeloma cells suppress osteoblast function by the secretion of osteoblast inhibiting factors, e.g. Dickkopf (DKK)-1. The resulting bone destruction releases several cytokines, which in turn promote myeloma cell growth. Therefore, the inhibition of bone resorption could stop this vicious circle and not only decrease myeloma bone disease, but also the tumor progression. Preclinical studies provided strong evidence that the suppression of the osteoclast activity using bisphosphonates, RANKL blockade or inhibition of MIP-1alpha or MIP-1beta is effective both in reducing myeloma bone disease and tumor growth and therefore may offer an important treatment strategy in multiple myeloma.

Soluble rank ligand produced by myeloma cells causes generalised bone loss in multiple myeloma

Patients with multiple myeloma commonly develop focal osteolytic bone disease, as well as generalised osteoporosis. The mechanisms underlying the development of osteoporosis in patients with myeloma are poorly understood. Although disruption of the RANKL/OPG pathway has been shown to underlie formation of focal osteolytic lesions, its role in the development of osteoporosis in myeloma remains unclear. Increased soluble RANKL in serum from patients with myeloma raises the possibility that this molecule plays a key role. The aim of the present study was to establish whether sRANKL produced by myeloma cells contributes directly to osteoporosis. C57BL/KaLwRij mice were injected with either 5T2MM or 5T33MM murine myeloma cells. 5T2MM-bearing mice developed osteolytic bone lesions (p<0.05) with increased osteoclast surface (p<0.01) and reduced trabecular bone volume (p<0.05). Bone volume was also reduced at sites where 5T2MM cells were not present (p<0.05). In 5T2MM-bearing mice soluble mRANKL was increased (p<0.05), whereas OPG was not altered. In contrast, 5T33MM-bearing mice had no changes in osteoclast surface or trabecular bone volume and did not develop osteolytic lesions. Soluble mRANKL was undetectable in serum from 5T33MM-bearing mice. In separate experiments, RPMI-8226 human myeloma cells were transduced with an human RANKL/eGFP construct, or eGFP alone. RPMI-8226/hRANKL/eGFP cells, but not RPMI-8226/eGFP cells, stimulated osteoclastic bone resorption (p<0.05) in vitro. Sub-cutaneous injection of NOD/SCID mice with RPMI-8226/hRANKL/eGFP or RPMI-8226/eGFP cells resulted in tumour development in all mice. RPMI-8226/hRANKL/eGFP-bearing mice exhibited increased serum soluble hRANKL (p<0.05) and a three-fold increase in osteoclast number (p<0.05) compared to RPMI-8226/eGFP-bearing mice. This was associated with reduced trabecular bone volume (27%, p<0.05), decreased trabecular number (29%, p<0.05) and increased trabecular thickness (8%, p<0.05). Our findings demonstrate that soluble RANKL produced by myeloma cells causes generalised bone loss, suggesting that targeting RANKL may prevent osteoporosis in patients with myeloma.

A molecular description of acid phosphatase

Acid phosphatase is ubiquitous in distribution in various organisms. Although it catalyzes simple hydrolytic reactions, it is considered as an interesting enzyme in biological systems due to its involvement in different physiological activities. However, earlier reviews on acid phosphatase reveal some fragmentary information and do not give a holistic view on this enzyme. So, the present review summarizes studies on biochemical properties, structure, catalytic mechanism, and applications of acid phosphatase. Recent advancement of acid phosphatase in agricultural and clinical fields is emphasized where it is presented as potent agent for sustainable agricultural practices and diagnostic marker in bone metabolic disorders. Also, its significance in prostate cancer therapies as a therapeutic target has been discussed. At the end, current studies and prospects of immobilized acid phosphatase are included.

Bone disease in multiple myeloma and precursor disease: novel diagnostic approaches and implications on clinical management

The manifestations of bone involvement in patients with multiple myeloma (MM) can have devastating clinical effects and increase mortality. Recent studies demonstrate that patients with the precursor conditions smoldering MM (SMM) and monoclonal gammopathy of undetermined significance (MGUS) show evidence of bone disease and increased risk of fractures. The understanding of the pathogenesis of bone disease in MM has expanded in recent years. The traditional skeletal survey will probably be replaced by newer and more sensitive imaging techniques, which may have a prognostic impact and change our definition of MGUS and SMM. Bisphosphonates are recommended to prevent skeletal events in patients with MM, and have also been studied in SMM and MGUS. This article summarizes the current knowledge of bone disease in plasma cell disorders, and discusses the current standard and future role of novel imaging techniques, as well as the evidence and current guidelines for bisphosphonates in MM, SMM and MGUS.

Prognostic significance of bone markers in patients with lung cancer metastatic to the skeleton: a review of published data

The presence of bone metastases significantly affects clinical outcome and quality of life parameters in patients with lung cancer. In this review, we aimed to evaluate the predictive value of markers of bone turnover in skeletal morbidity and clinical parameters, including disease-free survival (DFS) and overall survival (OS), in patients with lung cancer metastatic to the skeleton who were receiving bisphosphonate treatment. A comprehensive overview of all articles published from 1995 to date in 3 medical databases (PubMed, Scopus, and Cochrane) was performed using the keywords bone markers and lung cancer. Most bone formation markers (including bone alkaline phosphatase [bALP], osteocalcin [OC], and osteoprotegerin [OPG]), most bone absorption markers (including urinary calcium, osteopontin [OPN], receptor activator of nuclear factor κ-B ligand [RANKL], tartrate-resistant acid phosphatase isoform-5b [TRACP 5b]), and the metabolites of type I collagen had elevated concentrations in patients with lung cancer and bone metastases compared with patients without skeletal involvement. Two large studies showed that urinary N-terminal telopeptide (NTX) levels are a valid diagnostic method for early detection of bone metastases and a more consistent prognosticator than bALP. Treatment with zoledronic acid reduces NTX, TRACP-5b, RANKL, and OPG levels. Furthermore posttherapeutic reduction of urinary NTX levels seems to correlate with lower risk of skeletal-related events (SREs). Levels of markers of bone remodeling reflect the presence of bone metastases and may contribute to early detection of occult skeletal disease or monitor the effect of bisphosphonate treatment. However their ability to predict SREs, as well as DFS and OS, remains debatable.

Consensus on the utility of bone markers in the malignant bone disease setting

Biochemical markers of bone turnover provide insight into ongoing rates of skeletal metabolism and tumor-bone interactions in patients with malignant bone disease. This article reviews the available recent evidence assessing the potential of bone markers for detecting and monitoring malignant bone lesions in patients with advanced cancers, and for assessing overall skeletal health and response to antiresorptive therapies in patients at all stages of cancer progression. Most data thus far are for urinary N-terminal cross-linked telopeptide of type I collagen (NTX) in predicting risks of skeletal morbidity and death and monitoring response to zoledronic acid in patients with bone metastases. Ongoing studies are evaluating such correlations for other markers and therapies. Emerging evidence suggests that bone markers may help identify patients at high risk for bone metastasis or bone lesion progression, thereby allowing improved follow-up. Results from ongoing clinical trials evaluating such potential applications of bone markers are awaited.

Differential expression of tartrate-resistant acid phosphatase isoforms 5a and 5b by tumor and stromal cells in human metastatic bone disease

Tartrate-resistant acid phosphatase (TRAP) exists in human serum as two major isoforms, monomeric 5a and proteolytically processed enzymatically active 5b. The 5b isoform is secreted by osteoclasts and has recently been advocated as a serum marker for bone metastasis in breast cancer patients. The 5a isoform, on the other hand, is not bone-derived and has been proposed to be a marker of activated macrophages and chronic inflammation. In this study, expression of TRAP protein and enzymatic activity in bone metastases from different primary sites was examined. TRAP activity was high in bone metastases from prostate cancer, intermediate in breast cancer, and low in lung and kidney cancers. The partially purified TRAP from breast cancer bone metastasis samples exhibited the enzymatic characteristics of purple acid phosphatase. Both 5a and 5b isoforms were expressed in bone metastases of different histogenetic origins, i.e. prostate, breast, lung and kidney, and also a novel previously unreported 42 kDa variant of the TRAP 5a isoform was identified in bone metastases. This novel TRAP 5a isoform was absent in human bone, indicating that the 42 kDa variant is specific to metastatic cancer tissue. Immunohistochemistry revealed that metastatic cancer cells were the predominant source of TRAP 5a, whereas tumor-associated macrophages and occasionally multinucleated giant cells in the tumor stroma preferentially expressed the proteolytically processed TRAP 5b variant. Our results indicate the presence of a previously unstudied variant of monomeric TRAP 5a in cancer cells, which may have functional and diagnostic implications. Moreover, the presence of TRAP-positive macrophages in bone metastases could, together with cancer cells and osteoclasts, contribute to the elevated levels of serum TRAP activity observed in patients with bone metastases.

Loss of osteoclasts contributes to development of osteosarcoma pulmonary metastases

We conducted a transcriptomic screen of osteosarcoma (OS) biopsies and found that expression of osteoclast-specific tartrate-resistant acid phosphatase 5 (ACP5/TRAP) is significantly downregulated in OS compared with nonmalignant bone (P < 0.0001). Moreover, lesions from OS patients with pulmonary metastases had 2-fold less ACP5/TRAP expression (P < 0.018) than lesions from patients without metastases. In addition, we found a direct correlation (P = 0.0166) between ACP5/TRAP expression and time to metastasis. Therefore, we examined whether metastasis-competent (MC) OS cells could induce loss of ACP5(+) osteoclasts and contribute to metastasis. We found that MC OS cell lines can inhibit osteoclastogenesis in vitro and in vivo. In addition, osteoclasts can inhibit the migration of MC OS cells in vitro. Finally, ablation of osteoclasts with zoledronic acid increases the number of metastatic lung lesions in an orthotopic OS model, whereas fulvestrant treatment increases osteoclast numbers and reduces metastatic lesions. These data indicate that the metastatic potential of OS is determined early in tumor development and that loss of osteoclasts in the primary lesion enhances OS metastasis.

Multiple myeloma: changes in serum C-terminal telopeptide of collagen type I and bone-specific alkaline phosphatase can be used in daily practice to detect imminent osteolysis

Objective: Monitoring of bone disease in multiple myeloma is becoming increasingly important because bone-protecting treatment with bisphosphonate is becoming restricted after the awareness of osteonecrosis of the jaw. Despite the potential of biochemical markers of bone remodeling to monitor dynamic bone turnover, they are not used in everyday practice. Here, we investigate their usefulness to detect imminent progressive osteolysis in relapsing patients with multiple myeloma. Methods: In an unselected cohort of 93 patients, we measured the bone resorption markers C-terminal telopeptide of collagen type I (CTX-I), C-terminal cross-linked telopeptide of type-I collagen generated by MMPs (ICTP), N-terminal cross-linked telopeptide of type-I collagen (NTX-I), and the bone formation marker bone-specific alkaline phosphatase (bALP) monthly for 2 yr. Retrospectively, we identified 40 cases where patients had progressive disease. We investigated how the bone markers developed prior to disease progression. Results: We observed that CTX-I and bALP changed significantly before progressive disease were recognized. More interestingly, these changes differed depending on whether concurrent progressive osteolysis was present. In patients with progressive osteolysis, there was a large increase in bone resorption which was not compensated by increased bone formation. In contrasts, patients with stable bone disease had only a slight increase in bone resorption which was compensated by concurrent increased bone formation. By calculating a patient-specific CTX-I/bALP ratio, we quantified the risk a patient experiences if the ratio increases. Conclusion: By analyzing patient-specific changes in the ratio of CTX-I/bALP, we might tailor treatment with bone-protecting agents in the individual patient.

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.

Can Elevated Serum Tracp-5B Levels Predict Stress Fractures? A Cohort Study

Background and Aims:

Stress fracture is a common overuse injury in athletes and military conscripts. The reliable diagnosis of stress fractures is often difficult, however, because it is usually based solely on radiographic findings. Biochemical markers of bone resorption reflect bone degradation and may also reflect the rate of bone loss. The aim of the study was to examine whether elevated serum tartrate-resistant acid phosphatase isoform 5b (TRACP-5b) levels reflect enhanced bone remodeling and predict the occurrence of stress fractures in military conscripts.

Material and Methods:

Randomly selected military conscripts [mean age, 19.8 (range 18–28) years; n = 820] were followed for 3 months. Baseline blood samples were drawn upon arrival to the service. Four subsequent samples were obtained from subjects that developed stress fractures and one sample each was obtained from two asymptomatic control subjects for each fracture case.

Results:

Plain radiography was used to diagnose stress fractures in 20 of the 820 conscripts (2.4%). Follow-up data were available for 14 subjects with 21 stress fractures and 28 control subjects. Subjects with proportionally increasing serum TRACP-5b levels had an 8-fold greater probability of stress fracture than controls. No statistically significant difference was detected.

Conclusions:

Although assessing serum TRACP-5b levels appears to be a promising method to predict bone stress injuries, the present study failed to give a conclusive statement of its usefulness as a diagnostic tool.

Serum bone turnover markers may be involved in the metastatic potential of lung cancer patients

The aim of this study was to investigate several bone markers in Non-Small Cell Lung (NSCLC) and Small Cell Lung (SCLC) patients experiencing or not secondary bony disease. Fasting serum levels of bone formation, bone resorption, and osteoclastogenesis markers were determined in 22 NSCLC patients with bone metastases, 18 without bone metastasis, and 28 SCLC patients. A total of 29 healthy volunteers were also included in the study. Decreased osteocalcin (OC) serum levels and increased osteopontin and ligand of the receptor of nuclear factor kB (RANKL) serum levels were detected in NCSLC patients with bone metastases while increased C-terminal cross-linking telopeptide of type I collagen and increased RANKL/OPG (osteoprotegerin) ratio were detected in SCLC patients. Increased serum levels of OPG were observed in all lung cancer patients. OPG may be actively involved in the development of lung cancer metastasis. Furthermore, OC, OPN, and RANKL in NSCLC and CTX and RANKL in SCLC patients may also have a broader role in the pathogenesis and spread of lung cancer. They also provide useful information in identifying the group of patients that may benefit from a more rigorous treatment.

Tartrate-resistant acid phosphatase (TRACP 5b): a biomarker of bone resorption rate in support of drug development: modification, validation and application of the BoneTRAP kit assay

A commercial kit assay of tartrate-resistant acid phosphatase (TRACP 5b) used for the diagnosis of bone resorption was modified with a 'Fit-For-Purpose' approach for drug development of anti-resorptive therapeutics. The modifications included changing the standard matrix from buffer to serum, using a consistent bulk reference material to prepare standards and quality controls (QC), and adding sample controls (SC) prepared from authentic sample pools. Method validation experiments were conducted for: inter- and intra-assay accuracy and precision, establishment of SC, range finding of different population groups, selectivity tests, parallelism and stability. The analytical range was 1.00-10.0 U/L and the total errors of lower limit of quantification (LLOQ) and upper limit of quantification (ULOQ) validation samples were 8% and 21%, respectively. Data of range finding experiment showed that serum samples should be collected in tubes instead of bags. Selectivity results showed accurate spike recovery among the majority of test samples from target populations. Samples were demonstrated to be stable for up to four freeze/thaw cycles and for 24 months at -70+/-10 degrees C. Our results show that the modified TRACP 5b method is reliable for the quantification of TRACP 5b in human serum samples to support clinical trials of bone resorptive effect reflected by TRACP 5b activities. The method was robust with similar assay performance characteristics shown in three bioanalytical laboratories.

Bone markers and their prognostic value in metastatic bone disease: clinical evidence and future directions

BACKGROUND

Bone metastases are prevalent among patients with advanced solid tumors. Metastatic bone disease alters bone homeostasis, resulting in reduced bone integrity and, consequently, increased skeletal complications. Biochemical markers of bone metabolism may meet an unmet need for useful, noninvasive, and sensitive surrogate information for following patients' skeletal health.

MATERIALS AND METHODS

Data for this review were identified by searches of PubMed, and references from relevant articles using the search terms "bone markers" or individual bone marker nomenclature, "cancer," and "metastases." Abstracts and reports from meetings were included only when they related directly to previously published work. Only papers published in English between 1990 and 2007 were included.

RESULTS

Recent retrospective analyses with bisphosphonates, and particularly with zoledronic acid, have shown significant correlations between biochemical markers of bone metabolism levels and clinical outcomes, especially for bone resorption markers. Clinical results for biochemical markers of bone formation and resorption and other emerging markers of bone metabolism including bone sialoprotein, receptor-activator of nuclear factor-kappaB ligand, osteoprotegerin, and other markers are presented. However, biochemical markers of bone metabolism are not yet an established surrogate endpoint for treatment efficacy.

CONCLUSIONS

Biochemical markers of bone metabolism may allow physicians to identify which patients with metastatic bone disease are at high risk for skeletal-related events or death and who may be responding to therapy. Prospective randomized clinical trials are underway to further assess the utility of markers of bone metabolism in patients with bone metastases.

Myeloma bone disease and proteasome inhibition therapies

Bone disease is one of the most debilitating manifestations of multiple myeloma. A complex interdependence exists between myeloma bone disease and tumor growth, creating a vicious circle of extensive bone destruction and myeloma progression. Proteasome inhibitors have recently been shown to promote bone formation in vitro and in vivo. Preclinical studies have demonstrated that proteasome inhibitors, including bortezomib, which is the first-in-class such agent, stimulate osteoblast differentiation while inhibiting osteoclast formation and bone resorption. Clinical studies are confirming these observations. Bortezomib counteracts the abnormal balance of osteoclast regulators (receptor activator of nuclear factor-κB ligand and osteoprotegerin), leading to osteoclast inhibition and decreased bone destruction, as measured by a reduction in markers of bone resorption. In addition, bortezomib stimulates osteoblast function, possibly through the reduction of dickkopf-1, leading to increased bone formation, as indicated by the elevation in bone-specific alkaline phosphatase and osteocalcin. The effect of bortezomib on bone disease is thought to be direct and not only a consequence of the agent's antimyeloma properties, making it an attractive agent for further investigation, as it may combine potent antimyeloma activity with beneficial effects on bone. However, the clinical implication of these effects requires prospective studies with specific clinical end points.

The effect of novel anti-myeloma agents on bone metabolism of patients with multiple myeloma

Immunomodulatory drugs (IMiDs) and bortezomib have been recently used in the management of patients with both newly diagnosed and relapsed/refractory multiple myeloma. Except of their direct anti-myeloma effect, these agents also alter the interactions between myeloma cells and marrow microenvironment. Several recent studies have investigated their potential effect on myeloma bone disease. Preclinical studies have demonstrated that IMiDs reduce osteoclast formation and function in vitro. Clinical studies have confirmed that thalidomide reduces markers of bone resorption, while lenalidomide induces osteoclast arrest in myeloma patients. However, IMiDs seem to have no effect on osteoblast exhaustion present in myeloma. The proteasome inhibitor bortezomib restores abnormal bone remodeling through the inhibition of osteoclast function and the increase in osteoblast differentiation and activity in vitro. In myeloma patients, bortezomib reduces biochemical markers of bone resorption and normalizes the RANKL/osteoprotegerin ratio, while at the same time increases bone formation markers reducing levels of dickkopf-1 protein. Whether these effects are direct and not only a consequence of the agents' antimyeloma activity is not totally clear. This review summarizes all available data for these attractive agents that combine potent anti-myeloma activity with beneficial effects on bone and may alter the way of management of myeloma-related bone disease.

Clinical Utility of Biochemical Markers of Bone Metabolism for Improving the Management of Patients with Advanced Multiple Myeloma

Osteolytic bone lesions from advanced multiple myeloma (MM) result in significant skeletal morbidity. Therefore, biochemical markers of bone metabolism, such as the N-terminal and C-terminal telopeptides of type I collagen, bone-specific alkaline phosphatase, and osteocalcin, have been investigated as tools for evaluating the extent of bone disease, risk of skeletal morbidity, and response to antiresorptive treatment. Several studies have shown that the majority of biochemical markers of bone metabolism are increased in patients with MM with osteolytic bone lesions, thus reflecting changes in bone metabolism associated with tumor growth. There is also a growing body of evidence that markers of bone metabolism correlate with the risk of skeletal complications, disease progression, and death. In addition, bone markers could potentially be used as a tool for early diagnosis of bone lesions. The aim of this review is to improve our understanding of bone markers as a clinical tool for the management of malignant bone disease in patients with MM.