Serum osteoprotegerin levels in school-aged children with asthma

Abstract

Background

Various inflammatory biomarkers have been used in asthma cases for evaluating inflammation, however it has been determined that the majority of these biomarkers are insufficient for putting forth the course and severity of the disease. Osteoprotegerin is a glycoprotein mediator in the lung and macrophages. As far as we know, there are no studies about the role played by osteoprotegerin in child patients with asthma.

Objective

It was planned to examine the relationship between osteoprotegerin levels in childhood asthma and respiratory functions and airway inflammation and to assess its use as a biomarker.

Methods

The study included patients aged 6–16 years who were diagnosed with asthma at the pediatric allergy outpatient clinic of Bagcilar Training and Research Hospital in Turkey. The correlation analyses for the osteoprotegerin levels of asthma patients and their respiratory functions were examined.

Results

The age average of asthma cases was 10.61 ± 3.04 years and 51.2 % were female. No statistically significant difference was observed between the osteoprotegerin levels of the groups (p > 0.05). A negative and statistically significant correlation was observed between the FEV1 and FVC values and osteoprotegerin levels (p = 0.015, p = 0.003).

Conclusions

This was the first study to examine the relationship between osteoprotegerin levels and airway inflammation in children with asthma. We believe that there is a need for wider scale studies in which clinical symptoms and more parameters are evaluated for defining the role played by osteoprotegerin level in children with asthma and for determining its usability as a biomarker.

Introduction

Asthma is a heterogenic, chronic inflammatory disease characterized by reversible obstruction and airway hypersensitivity.¹ The identification of similar biological biomarkers which play a role in inflammation in asthma patients is important with regard to both diagnosis and the developments it will provide for treatment. The identification of special non-invasive biomarkers that will enable monitoring and follow up is of greater importance, especially in childhood asthma cases. Spirometric measurements used frequently for this purpose require effective cooperation and therefore cannot be sufficiently evaluated in children. Similarly, current methods such as bronchoalveolar lavage cannot be routinely used because they are invasive.2, 3, 4, 5 Hence, there is a need for non-invasive methods that may be used for the follow up of these diseases.

Initially, osteoprotegerin (OPG) is a polypeptide synthesized with 401 amino acids. A mature protein composed of 380 amino acids is formed after removing the 21 amino acid propeptide section. It is secreted extracellularly as a homodimeric, soluble glycoprotein with 60 kDa monomeric and 120 kDa disulfite bond. OPG is a member of the tumor necrosis factor receptors (TNFR) super family but does not contain transmembrane and cytoplasmic sections like the other receptors of the TNFR super family.6, 7 OPG is synthesized by many different tissues, including hematopoietic and immune cells such as osteoblasts, bone marrow, kidney, spleen, brain, lung and cardiovascular system (heart, arteries and veins).8, 9 The primary function of OPG is known as osteoclast differentiation and activation inhibition, however the role played by OPG synthesized in other tissues is not known for sure. OPG synthesis in large arteries’ media layers and different vascular cell types such as coronary artery smooth muscles and endothelium cells indicate its function at the vascular bed.¹⁰

The role played by OPG, a glycoprotein mediator in the lung and macrophages, in childhood asthma and the relationship between its level and disease severity is not known. The number of studies with invasive bronchoscopy techniques in children is limited, hence studies have focused more on identifying various markers for determining airway inflammation. In this study it was planned to evaluate the relationship between OPG levels and airway inflammation in childhood asthma and the assessment of its usability as a biomarker.