**2.5 Protein biomarkers**

Heat shock protein 72 (HSP72) belongs to the Hsp70 family of heat shock proteins. It regulated protein expression during conditions of cell stress and acted as a protective factor by preventing abnormal protein aggregation, thus helping to refold damaged proteins, which was related to inflammation and obesity. Obesity was considered to be a risk factor for asthma, and serum and urine Hsp72 levels were significantly elevated in patients with severe asthma and obesityrelated asthma. Hsp72 also was an independent predictor of asthma severity and could be used as a simple, noninvasive biomarker for predicting and monitoring asthma severity in obese asthma patients [84].

Eosinophil cationic protein (ECP) was secreted by activated eosinophil and is a specific marker of EOS. Serum ECP levels were significantly increased in children and adults with allergic asthma during acute stage. ECP, as a strong alkalitoxic protein, had strong effects on airway and nasal epithelium and had been associated with AHR, eosinophilic chronic sinusitis, aspirinaggravated respiratory disease, and recurrent wheezing [85]. Elevated ECP concentrations in serum reflected EOS activation and were associated with asthma severity and allergen sensitization. In children with acute asthma, serum ECP was a more sensitive biomarker of asthma severity than blood EOS [86].

Periostein was a matrix protein that expressed in fibroblasts and epithelial cells, which was involved in a variety of biological processes, such as cell proliferation, cell invasion, and angiogenesis. In asthma patients, periostein associated with EOS migration and promoted production Th2 cytokines such as IL4 and IL13, lead to chronic allergic inflammation. It was found that the best cutoff value of sputum periostein which distinguished mild and moderate to severe asthma was 528.25 ng/mL [87]. Serum periostein was associated with AHR, blood EOS counts and FeNO in asthma children. The level of sputum periosteins was positively correlated with age, asthma course and sputum EOS increase, which was a surrogate biomarker and therapeutic target of severe eosinophil asthma.

High mobility group protein B1 (HMGB1) was a protein that specifically binds to nucleosome DNA junction region, it can enhance nucleosome stability and transcription factor interaction. In asthma, acute respiratory distress syndrome (ARDS), cystic fibrosis, lung cancer and other lung diseases, HMGB1 induced the production of proinflammatory cytokines and exacerbated airway inflammation, and antiHMGB1 can reduce the pathological features of asthma [88].

Serum chitinaselike protein YKL40, a member of the chitinase family, might be involved in the development of fibrosis and airway remodeling. YKL40 was involved in the pathogenesis of asthma by inducing IL8 in the epithelium and was considered as one of the biomarkers of asthma patients [89]. In addition, YKL40 also indicated neutrophil inflammation in asthma and was associated with asthma severity. Moreover, YKL40 was significantly negatively correlated with lung function [90].

CD14 was a marker of activation of monocytes or macrophages, which existed in membranebound form (mCD14) and soluble form (sCD14) and had a positive effect on the balance between Th1 and Th2 cytokines. Soluble CD14(sCD14) played

#### *The Blood Biomarkers of Asthma DOI: http://dx.doi.org/10.5772/intechopen.106807*

an important role in proliferation and activation of T and B cell. The level of sCD14 in asthma patients was significantly higher in the acute stage than in the convalescence stage. There was a significant correlation between plasma sCD14 level and the severity of asthma, lung function, asthma symptoms and signs in adults, and there was a negative correlation between sCD14 level and asthma severity [91]. Therefore, plasma sCD14 levels may be a potential biomarker for predicting asthma severity in adults.

Serum arginase I levels were significantly elevated in asthmatic patients compared with healthy controls and Creactive protein (CRP) was a common inflammatory marker for assessing systemic inflammation. In asthma patients, serum high sensitivity CRP (HSCRP) levels were elevated and associated with respiratory symptoms and airway inflammation. Serum arginase I level was positively correlated with HSCRP and negatively correlated with IgE in asthma patients. Elevated serum arginase I levels might be serve as a biomarker of airway inflammation in asthma [92].

The OX40 ligand (OX40L,) and its receptor OX40 were members of the tumor necrosis factor (TNF) receptor superfamily. Serum OX40L was positively correlated with serum IgE, IL6, percentage of EOS and NEU, TSLP, and negatively correlated with asthma severity and lung function. Inhaled corticosteroid (ICS) treatment can reduce serum OX40L levels, and the reduction of serum OX40L was more significant in steroidsensitive asthma than in steroidresistant asthma. High serum OX40L can be used as a biomarker for identifying glucocorticoid resistance in asthmatic patients. Changes in OX40L levels also reflect response to ICS treatment [93].

#### **2.6 Non-coding RNA biomarkers**

MicroRNAs (miRNAs) were small noncoding RNA molecules that were considered to be one of the basic regulatory mechanisms of gene expression. They were involved in many biological processes, such as signal transduction, cell proliferation and differentiation, apoptosis and stress response [94]. Sufficient evidence have been suggested that miRNA play a role in several key points of asthma, including the diagnosis of asthma, disease severity, and response to treatment [95].

Serum miRNA21 and miRNA155 levels were significantly elevated in asthma patients compared with healthy controls. The expression level of miRNA21 in serum of asthma patients was significantly positively correlated with the level of IL4. In addition, compared with steroidsensitive children, miRNA21 was significantly elevated in untreated and steroidresistant children, and miRNA21 could be a promising biomarker for diagnosis and response to inhaled corticosteroid therapy [96].

MiR20a5p was significantly downregulated in the lungs and OVAstimulated cells of mouse models of OVA induced asthma, and miR20a5p may be a promising biomarker and therapeutic target during asthma progression by targeting ATG7's involvement in autophagyinduced apoptosis, fibrosis and inflammation [97]. MiR-5825p was strongly upregulated in nasal epithelial cells of children with severe acute asthma [98]. MiR1455p was associated with lung function in children with asthma and also increased proliferation of airway smooth muscle cell. This suggests that the decreased expression of miR1455p was a risk factor for early decline in longterm lung function [99]. MiR124 contributed to the development and maintenance of antiinflammatory phenotypes of asthmatic lung macrophages, and was negatively correlated with the risk of exacerbation, severity and inflammation in asthma patients [100].

MiRNA155, a key regulator of type 2 innate lymphocytes in a mouse model of allergic airway inflammation, was elevated in serum samples from allergic asthma patients compared with nonallergic asthma patients and healthy individuals. Expression of miR155 was altered by allergic stimulation or glucocorticoid treatment, which can be used as biomarkers for steroids resistance/neutrophilic asthma [101]. MiRNA223 was significantly upregulated in patients with moderate asthma compared with healthy controls, and no significant difference in miR223 expression was found between patients with severe asthma and healthy controls, which could serve as a potential biomarker for the diagnosis of moderate asthma [102]. The level of miR192 in asthma children was lower than that in healthy children, and miR192 blocked the activation pathway of Tfh cells by targeting CXCR5 [103]. Serum miRNA-11653P levels were significantly elevated in asthma patients compared to healthy controls. In addition, Serum miR11653p levels were also significantly elevated in patients with allergic rhinitis (AR) or allergic bronchopulmonary aspergillosis (ABPA), suggesting that serum miR11653p may be used as a noninvasive biomarker to help diagnose and characterize allergic asthma [104]. MiRNA3934 levels in peripheral blood mononuclear cells of asthma patients were significantly decreased, and miRNA3934 levels in PBMCs could distinguish asthma patients, especially severe asthma patients from control group. MiRNA3934 levels in PBMCs of asthma patients were negatively correlated with serum IL6, IL8 and IL33 levels, respectively, which might also be a potential diagnostic biomarker for asthma [105]. In addition, upregulation of MiR11653p reduced AHR and airway inflammation by directly targeting IL13. MiR1855p was involved in calcium signaling by targeting NFAT and CaMKII proteins in cardiomyocytes and may play a role in muscle cell hyperplasia, proliferation and cell contraction in asthma, suggesting that these candidate biomarkers play a role in the pathogenesis of asthma [106]. Overexpression of MiRNA126 in acute asthma was associated with signs of immune imbalance and can predicted disease severity, suggesting that it can be used as a potential serologic marker for the diagnosis and evaluation of asthma [107].

Long noncoding RNA (lncRNAs) affected the regulation of immune response, airway inflammation and other pathological processes related to asthma. PTTG3P was highly expressed in peripheral blood of children with asthma and promoted the progression of childhood asthma by targeting miR1923p/CCNB1 axis and may serve as a potential diagnostic and therapeutic biomarker for childhood asthma [108]. LncRNA NEAT1 was upregulated in patients with asthma exacerbation compared with healthy controls and patients with asthma in remission stage, which was positively correlated with the severity of asthma exacerbation, TNFα, IL1β and IL17, but negatively correlated with predicted IL10, FEV1/FVC and FEV1%. Circulating lncRNA NEAT1 may be a novel biomarker for increased risk and severity of asthma exacerbations [100]. LncRNAANRIL/MiR125a axis was upregulated in patients with acute asthma compared with those in remission and healthy subjects, and the LncRNA ANRIL/MiR125a axis had good predictive value for the risk of bronchial asthma disease progression [109]. Compared with nonsevere asthma patients, the expression of lncRNA GAS5 in PBMCs of severe asthma patients was increased. After treatment with CS in vitro, the expression of GAS5 was downregulated in severe asthma patients, while upregulated in nonsevere asthma patients, highlighting the potential role of GAS5 as a biomarker for the diagnosis of severe asthma patients [110]. Compared with the healthy control group, the level of lncRNAMEG3 in CD4+T cells of asthma patients was significantly increased, and the degree of Treg/ Th17 imbalance was correlated with the severity of asthma mice symptoms. LncRNA-MEG3 can be used as a competitive endogenous RNA to inhibit the level of miRNA17, miRNA17 inhibits Th17 expression by directly targeting nuclear orphan receptor γ

*The Blood Biomarkers of Asthma DOI: http://dx.doi.org/10.5772/intechopen.106807*

T (RORγ T). Thus affecting Treg/Th17 balance in asthma, monitoring lncrNAMEG3 in asthma patients can be used to judge the course of disease or recovery of patients [111]. The level of lncBAZ2B in children with allergic asthma was significantly higher than that in healthy children. LncBAZ2B can aggravate allergeninduced pulmonary allergic inflammation by promoting the activation of M2 macrophages, which is positively correlated with the severity of asthma and blood eosinophil count. Thus, LncBAZ2B plays a key role in exacerbating the progression of allergic asthma and may serve as a potential diagnostic marker for childhood asthma [112].
