Development of a New Immunoassay for Human Cathepsin K-Generated Periostin Fragments as a Serum Biomarker for Cortical Bone

Higher serum levels of a cathepsin K-generated periostin fragment are associated with fractures in postmenopausal women with primary hyperparathyroidism: a pilot study

The only difference between fractured and non-fractured postmenopausal women with PHPT of same sex, age, and BMI was a significantly mean higher serum k-periostin level. K-periostin value was associated with fracture at any site (odds ratio 1.044, 95% CI 1.005-1.091, p = 0.03).

INTRODUCTION

To assess serum k-periostin fragment levels in patients with primary hyperparathyroidism (PHPT), fractured and non-fractured matched for sex, age, and body mass index.

METHODS

Twenty-five Caucasian fractured postmenopausal women with PHPT (group Fx) and 25 PHPT non-fractured (group NFx) were enrolled. Each patient underwent DXA scan at lumbar, hip, and forearm, spine X-ray, and biochemical evaluation of calcium metabolism. For k-periostin analyses, we utilized a specific ELISA test that detects CatK-generated fragment levels in the bloodstream.

RESULTS

We found no difference in mean BMD and bone turnover marker values between Fx and NFx groups. Prevalence of osteoporosis was not significantly different in Fx vs NFx (72% vs 60%, p = 0.55). Among Fx, 16% reported multiple fractures, 28% morphometric vertebral fractures, 4% femoral fractures, 28% non-vertebral non-femoral fractures, and 8% wrist fractures. The only detectable difference between Fx and NFx group was a significantly mean higher k-periostin serum level (46.2 ± 21.4 vs 34.7 ± 13.5 ng/ml, p = 0.02). K-periostin was associated with fracture at any site (odds ratio 1.044, 95% CI 1.005-1.091, p = 0.03). No difference in mean k-periostin values was found between patients with vertebral fracture vs those with non-vertebral fracture, and between those with multiple fractures vs those with single fracture.

CONCLUSION

Serum k-periostin is significantly associated with fracture in PHPT. If confirmed by further studies, k-periostin could be considered a new marker of bone fragility in PHPT, independently of BMD.

The role of biochemical markers of joint tissue remodelling to predict progression and treatment efficacy in inflammatory rheumatic diseases

Structural damage is a hallmark in RA, spondyloarthropy (SpA) and psoriatric arthritis (PsA). Its progression is difficult to predict and current radiological or inflammatory biological markers lack sensitivity. Biochemical markers of bone, cartilage and synovial tissues provide a dynamic indication of the anabolism and catabolism of joint tissues and can be easily measured by immunoassays. Novel biochemical markers including post-translational modifications of matrix proteins and enzyme-generated neoepitopes with increased tissue and/or biological pathway specificity have been developed. Their evaluation in clinical trials of novel biologic therapies and epidemiological studies indicated that their measurements could be useful to predict progression of structural damage and treatment efficacy, independently of current clinical, radiological and biological indices of disease activity. In this paper we briefly describe the latest developments in biochemical markers and critically analyse the clinical data assessing the utility of established and novel biochemical markers in RA, SpA and PsA.

Tartrate-resistant acid phosphatase 5b, but not periostin, is useful for assessing Paget's disease of bone

BACKGROUND

Periostin is a matricellular protein with a preferential location in cortical bone and periosteal tissue, and tartrate-resistant acid phosphatase 5b (TRAP5b) is a marker of osteoclast numbers. In Paget's disease of bone (PDB), there is increased cortical thickening and probably increased periosteal apposition, along with increased osteoclast numbers.

OBJECTIVES

To analyse if circulating periostin is a biomarker for PDB, and if it is associated with disease activity and involvement of long bones that represent major cortical contribution. Also, to analyse whether TRAP5b, a scarcely explored bone resorption marker, is useful in the assessment of PDB.

PATIENTS AND METHODS

We recruited 42 patients with PDB (13F/29M; 71 ± 11.6 yrs). 71.4% had active disease, 66.6% had polyostotic disease and 54.8% had long bone involvement. Blood and urine samples were taken between 8:00 and 10:00 A.M. after an overnight fast. Periostin and TRAP5b were measured in serum, using commercial ELISA assays (Biomedica and IDS, respectively). Serum total ALP, PINP, CTX, bone ALP and urinary NTX were measured. Reference values for periostin and TRAP5b were obtained from 45 healthy subjects.

RESULTS

Serum periostin did not differ between patients and controls (989.4 ± 173.2 vs. 966.9 ± 195.4 pMol/L, p = 0.572). No significant differences were observed between patients with and without active disease (964.5 ± 168.8 vs.1051.6 ± 175.6 pMol/L, p = 0.143), involvement or not of long bones (1022.2 ± 145.8 vs 949.7 ± 198.2 pMol/L, p = 0.181) and monostotic or polyostotic disease (963.8 ± 198.7 vs 1002.2 ± 161.4 pMol/L, p = 0.505). There were significant correlations between serum periostin and all bone turnover markers (bone ALP, PINP, uNTX, sCTX and TRAP5b) in PDB patients with active disease, but not in the inactive PDB group. Serum TRAP5b was significantly higher in PDB patients than in controls (4.43 ± 1.76 vs. 3.21 ± 1.02 U/L, p < 0.001), in those with active disease (4.98 ± 1.76 vs. 3.07 ± 0.72 U/L, p < 0.001) and in patients with polyostotic disease than in those with monostotic disease (4.81 ± 1.79 vs 3.68 ± 1.5 U/L, p = 0.005). TRAP5b levels were not influenced by previous bisphosphonate treatment (4.14 ± 1.42 vs. 4.84 ± 2.02 U/L, p = 0.206).

CONCLUSIONS

Periostin is not useful for assessing PDB, whilst TRAP5b, which has been a scarcely explored bone turnover marker until now, may be useful in the analysis of this disease, providing new information on the resorption process. In addition, periostin levels correlate with all classical BTMs in active PDB, suggesting that this marker may reflect periosteal and cortical metabolism in accelerated bone turnover states.

Periostin Mediates Right Ventricular Failure through Induction of Inducible Nitric Oxide Synthase Expression in Right Ventricular Fibroblasts from Monocrotaline-Induced Pulmonary Arterial Hypertensive Rats

Pulmonary arterial hypertension (PAH) leads to lethal right ventricular failure (RVF). Periostin (POSTN) mRNA expression is increased in right ventricles (RVs) of monocrotaline (MCT)-induced PAH model rats. However, the pathophysiological role of POSTN in RVF has not been clarified. We investigated the effects of POSTN on inducible nitric oxide (NO) synthase (iNOS) expression and NO production, which causes cardiac dysfunction, in right ventricular fibroblasts (RVFbs). Male Wistar rats were intraperitoneally injected with MCT (60 mg/kg) or saline. Three weeks after injection, RVFbs were isolated from RVs of MCT- or saline-injected rats (MCT-RVFb or CONT-RVFb). In MCT-RVFb, iNOS expression and phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2), c-Jun N-terminal kinase (JNK) and nuclear factor-kappa B (NF-κB) were higher than those in CONT-RVFb. Recombinant POSTN increased iNOS expression and NO production, which were prevented by a pharmacological inhibition of ERK1/2, JNK or NF-κB in RVFbs isolated from normal rats. Culture medium of POSTN-stimulated RVFbs suppressed Ca²⁺ inflow through l-type Ca²⁺ channel (LTCC) in H9c2 cardiomyoblasts. We demonstrated that POSTN enhances iNOS expression and subsequent NO production via ERK1/2, JNK, and NF-κB signaling pathways in RVFbs. POSTN might mediate RVF through the suppression of LTCC activity of cardiomyocytes by producing NO from RVFbs in PAH model rats.

The C-Terminal Intact Forms of Periostin (iPTN) Are Surrogate Markers for Osteolytic Lesions in Experimental Breast Cancer Bone Metastasis

Periostin is an extracellular matrix protein that actively contributes to tumor progression and metastasis. Here, we hypothesized that it could be a marker of bone metastasis formation. To address this question, we used two polyclonal antibodies directed against the whole molecule or its C-terminal domain to explore the expression of intact and truncated forms of periostin in the serum and tissues (lung, heart, bone) of wild-type and periostin-deficient mice. In normal bones, periostin was expressed in the periosteum and specific periostin proteolytic fragments were found in bones, but not in soft tissues. In animals bearing osteolytic lesions caused by 4T1 cells, C-terminal intact periostin (iPTN) expression disappeared at the invasive front of skeletal tumors where bone-resorbing osteoclasts were present. In vitro, we found that periostin was a substrate for osteoclast-derived cathepsin K, generating proteolytic fragments that were not recognized by anti-periostin antibodies directed against iPTN. In vivo, using an in-house sandwich immunoassay aimed at detecting iPTN only, we observed a noticeable reduction of serum periostin levels (- 26%; P < 0.002) in animals bearing osteolytic lesions caused by 4T1 cells. On the contrary, this decrease was not observed in women with breast cancer and bone metastases when periostin was measured with a human assay detecting total periostin. Collectively, these data showed that mouse periostin was degraded at the bone metastatic sites, potentially by cathepsin K, and that the specific measurement of iPTN in serum should assist in detecting bone metastasis formation in breast cancer.