The number of people diagnosed with asthma has risen steadily within the last decade. In 2001, 7.3% of people were diagnosed with chronic asthma compared to 8.4% of people in 2010. Asthma is also more common in children, in women, and in those below the poverty line, according to the CDC.1 It is not clear why asthma is on the rise, and there may be environmental epigenetic regulations at work.2
Louten et al. studied chronic asthma in murine and non-human primate models.3 This research group was interested in identifying asthma biomarkers present during the early and chronic stages of asthma and determining if biomarkers could be predictors of asthma progression and treatment efficacy.
For these experiments, proximal fluids were obtained from thymic stromal lymphopoietin (TSLP) transgenic mice. The mice began showing signs of asthma by 5 weeks of age. By 9 weeks of age, all the hallmarks of chronic human asthma were present. Once the mice reached 9 weeks of age, fluid was taken via bronchoalveolar lavage (BAL) and analyzed by mass spectrometry.
Approximately 150 proteins were identified via shotgun proteomics, with 44 proteins whose expression was upregulated compared to wild-type littermate controls. Proteins discovered in the BAL fluid included enzymes (30%), transporters (10%), peptidases (6%), cytokines (2%), or kinases (2%), while remaining proteins were not easily categorized.
Of the 44 proteins, 18 were chosen to be evaluated further via western blot, ELISA, and quantitative reverse transcriptase-PCR. Proteins were chosen based on previous associations with pulmonary diseases, lack of association, and the availability of experimental reagents. The results of these experiments remained consistent and validated all 18 proteins as asthma biomarkers. Expression was also validated in the more established ovalbumin (OVA)-induced asthma mouse model, as well as in house dustmite allergen-asthma-induced non-human primates.
In summary, the group found and characterized new asthma biomarkers, including KLK1, Reg3γ, ITLN2, and LTF in asthmatic mice. MRNA studies using 5-week-old mouse models of early asthma found that Clca3, Chi3l4 (YM2), and Ear11 were the first lung biomarkers to increase. Treatment with the steroid dexamethasone in 12-week-old mice found that these particular biomarkers were also the last to decline in response to steroid therapy.
They also found that the presence of GP-39, LCN2, sICAM-1, YM1, and the upregulated expression of Epx, Mmp12, and Klk1 were good indicators of early therapeutic intervention. In nonhuman primates, AMCase, sICAM-1, CLCA1, and GP-39 were reduced upon treatment with corticosteroids.
Through the continued characterization of candidate biomarkers using animal models of asthma, researchers hope to better understand the mechanics of asthma in humans and be able to better maintain and possibly prevent asthma in the future.
1. Akinbami, L.J., et al. ‘Trends in asthma prevalence, health care use, and mortality in the United States, 2001-2010‘, Centers for Disease Control and Prevention, National Center for Health Statistics Data Brief, 94, (pp. 1-8)
2. Miller, R.L. and Ho, S.M., (2008) ‘Environmental epigenetics and asthma current concepts and call for studies‘, Respiratory and Critical Care Medicine, 177 (6), (pp. 567-73)
3. Louten, J., et al., (2012) ‘Biomarkers of disease and treatment in murine and cynomolgus models of chronic asthma‘, Biomarker Insights, 2012 (7), (pp. 87-104)