A novel assay for improved detection of sputum periostin in patients with asthma.

BACKGROUND: Serum periostin associates with type-2 inflammation in asthmatic airways, but also reflects whole body periostin levels originating from multiple sources. Less is known about sputum periostin as a biomarker in asthma as detection levels are low using currently available periostin assays. We aimed to investigate detection of sputum periostin using ELISA assays targeting different periostin epitopes and relate levels to clinical characteristics. METHODS: Two ELISA systems were developed using antibodies detecting whole periostin or cleavage products, the molecular weight and amino acid sequences of which were confirmed. The ELISA assays were applied to sputum from 80 patients with mild-to-moderate and severe asthma enrolled in the European, multi-center study BIOAIR. Results were related to clinical characteristics. RESULTS: Sputum was found to contain smaller periostin fragments, possibly due to proteolytic cleavage at a C-terminal site. Comparing ELISA methodology using antibodies against cleaved versus whole periostin revealed detectable levels in 90% versus 44% of sputum samples respectively. Sputum periostin showed associations with blood and sputum eosinophils. Furthermore, sputum, but not serum, periostin correlated with reduced lung function and sputum IL-13 and was reduced by oral corticosteroid treatment. CONCLUSIONS: We present an ELISA method for improved analysis of sputum periostin by detecting cleavage products of the periostin protein. Using this assay, sputum periostin was detectable and associated with more disease-relevant parameters in asthma than serum periostin. Sputum periostin is worth considering as a phenotype-specific biomarker in asthma as its proximity to the airways may eliminate some of the confounding factors known to affect serum periostin.

Establishment of a novel ELISA system for measuring periostin independently of formation of the IgA complex.

BACKGROUND: Periostin, a matricellular protein that modulates cell functions having various pathophysiological roles, has the potential to be a useful biomarker for various diseases. We recently found that periostin forms a complex with IgA in human serum, which may affect the periostin measurement. METHODS: We investigated (1) whether the formation of the periostin-IgA complex affects the original periostin ELISA system, decreasing the values of serum periostin? (2) bow each domain of periostin affects periostin measurement by the original periostin ELISA system? (3) whether we can establish a novel ELISA system that is not affected by formation of the IgA complex? RESULTS: The periostin value at the reducing condition was significantly higher than that of the non-reducing condition, demonstrating that formation of the IgA complex affects periostin measurement. The monoclonal antibodies (mAbs) for periostin recognizing the EMI and R1 domains immunoprecipitated serum periostin in the reducing condition more than in the non-reducing condition, whereas the mAbs recognizing the R2 or R3 domain immunoprecipitated comparable amounts of serum periostin in the reducing and non-reducing conditions, suggesting the EMI and R1 domains contribute to formation of the complex with IgA. Using SS16A recognizing the R3 domain combined with SS17B recognizing the R4 domain, we established an ELISA system that was able to measure periostin independently of the IgA complex. CONCLUSIONS: We have established a novel ELISA system that measures periostin independently of the IgA complex. This system is promising in identifying periostin as a biomarker for various diseases.

Pathological Roles and Clinical Usefulness of Periostin in Type 2 Inflammation and Pulmonary Fibrosis.

Periostin is known to be a useful biomarker for various diseases. In this article, we focus on allergic diseases and pulmonary fibrosis, for which we and others are now developing detection systems for periostin as a biomarker. Biomarker-based precision medicine in the management of type 2 inflammation and fibrotic diseases since heterogeneity is of utmost importance. Periostin expression is induced by type 2 cytokines (interleukin-4/-13) or transforming growth factor-ß, and plays a vital role in the pathogenesis of allergic inflammation or interstitial lung disease, respectively, andits serum levels are correlated disease severity, prognosis and responsiveness to the treatment. We first summarise the importance of type 2 biomarker and then describe the pathological role of periostin in the development and progression of type 2 allergic inflammation and pulmonary fibrosis. In addition, then, we summarise the recent development of assay methods for periostin detection, and analyse the diseases in which periostin concentration is elevated in serum and local biological fluids and its usefulness as a biomarker. Furthermore, we describe recent findings of periostin as a biomarker in the use of biologics or anti-fibrotic therapy. Finally, we describe the factors that influence the change in periostin concentration under the healthy conditions.

Periostin forms a functional complex with IgA in human serum.

BACKGROUND: Periostin is a matricellular protein belonging to the fasciclin family, playing a role for the pathogenesis of allergic diseases by binding to integrins on cell surfaces. Serum periostin is elevated in various allergic diseases reflecting type 2 inflammation and tissue remodeling so that for allergic diseases, periostin is expected to be a novel biomarker for diagnosis, assessing severity or prognosis, and predicting responsiveness to treatments. We have previously shown that most serum periostin exists in the oligomeric form by intermolecular disulfide bonds. METHODS: In this study, we examined how periostin forms a complex in serum, whether the periostin complex in serum is functional, and whether the complex formation interferes with reactivity to anti-periostin Abs. RESULTS: We found that periostin formed a complex with IgA1 at a 1:1 ratio. The periostin in the serum complex contained at least five different isoforms. However, IgA was not essential for the oligomeric formation of periostin in mouse serum or in IgA-lacking serum. The periostin-IgA complex in human serum was functional, sustaining the ability to bind to αVß3 integrin on cell surfaces. Moreover, periostin formed the complex with IgA broadly, which interferes the binding of the Abs recognizing all of the domains except the R4 domain to periostin. CONCLUSIONS: Periostin is a novel member of the IgA-associated molecules. These results are of great potential use to understand the pathological roles of periostin in allergic diseases and, from a practical standpoint, to develop diagnostics or therapeutic agents against periostin.

The usefulness of monomeric periostin as a biomarker for idiopathic pulmonary fibrosis.

The natural course of idiopathic pulmonary fibrosis (IPF) is variable. Predicting disease progression and survival in IPF is important for treatment. We previously demonstrated that serum periostin has the potential to be a prognostic biomarker for IPF. Our aim was to use monomeric periostin in a multicenter study to evaluate its efficacy in diagnosing IPF and predicting its progression. To do so, we developed a new periostin kit to detect only monomeric periostin. The subjects consisted of 60 IPF patients in a multicenter cohort study. We applied monomeric periostin, total periostin detected by a conventional kit, and the conventional biomarkers-KL-6, SP-D, and LDH-to diagnose IPF and to predict its short-term progression as estimated by short-term changes of %VC and % DL, CO. Moreover, we compared the fraction ratios of monomeric periostin to total periostin in IPF with those in other periostin-high diseases: atopic dermatitis, systemic scleroderma, and asthma. Monomeric periostin showed the greatest ability to identify IPF comparable with KL-6 and SP-D. Both monomeric and total periostin were well correlated with the decline of %VC and % DL, CO. Clustering of IPF patients into high and low periostin groups proved useful for predicting the short-term progression of IPF. Moreover, the relative ratio of monomeric periostin was higher in IPF than in other periostin-high diseases. Measuring monomeric periostin is useful for diagnosing IPF and predicting its short-term progression. Moreover, the ratio of monomeric periostin to total periostin is elevated in IPF compared to other periostin-high diseases.