SHANGHAI – A novel biomarker may help predict the course of asthma, suggests a Chinese study published in the European Respiratory Journal.

Recently, the chitinase-like protein YKL-40 has been identified as a novel biomarker in asthma. According to study results, patients who present with an acute asthma attack show not only increased total serum IgE levels and peripheral blood eosinophils but also significantly elevated levels of serum YKL-40. Moreover, levels of the proposed biomarker seem to correlate inversely with lung function.

The protein may contribute to asthma pathogenesis by mediating the inflammatory responses associated with the disease: “YKL-40 may be a biological characteristic of the exacerbation of asthma,” the study authors write.

The study included 62 asthmatic patients and 64 controls, who were followed up over a period of 2 years. The asthma patients were further divided into two subgroups: patients with known stable asthma and patients who had requested urgent medical care for an acute exacerbation either at a clinic or emergency room. Researchers of the Changzheng Hospital in Shanghai, China, evaluated levels of the YKL-40 protein in the different patient groups and the correlation between serum YKL-40 levels, total serum IgE levels, the percentage of peripheral blood eosinophils and lung function parameters.

They showed that during an asthma attack, serum YKL-40 levels are higher than during stable periods of asthmatics, and higher than serum levels of non-asthmatic subjects.
The minimum detection limit of the YKL-40 assay is 20 nanograms per milliliter. Overall, serum YKL-40 levels in patients with asthma were higher than those in controls.
Serum YKL-40 levels for patients in the exacerbation group were higher than those in the control group (83.72 (47.00–97.25) nanograms per milliliter versus 55.16 (34.25–70.75) nanograms per milliliter; p = 0.001) and those in the stable group (83.72 (47.00–97.25) nanograms per milliliter versus 60.25 (39.00–72.75) nanograms per milliliter; p = 0.043).

The serum YKL-40 levels of patients in the stable group were not different from those in the control group. 

“Elevated circulating YKL-40 levels have been implicated in patients with meningitis, pneumonia, rheumatoid arthritis, osteoarthritis, breast or lung cancer, and hepatic fibrosis. Furthermore, it has recently been shown that YKL-40 is strongly upregulated in the airway epithelium and alveolar macrophages of patients with asthma, and that serum YKL-40 levels are elevated in patients with asthma. Circulating YKL-40 levels are correlated with asthma severity, the thickness of the subepithelial basement membrane and pulmonary function, suggesting that circulating YKL-40 levels are a biomarker for asthma. “

Further studies should show whether serum levels of YKL-40 decrease in patients who are adequately controlled after an acute asthma attack, the authors conclude.

Reference:
Tang H et al. Eur. Respir. J. 2010 Apr;35(4):757-60.

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