Identification of a plasma microRNA profile in untreated pulmonary tuberculosis patients that is modulated by anti-mycobacterial therapy
Introduction
Tuberculosis (TB) continues to be a major global health problem with over 10 million new cases of active TB and 1.8 million deaths from TB each year1. The WHO has set the ambitious goal of reducing TB deaths by 95% and the incidence of new TB cases by 90% by 20352, but this will not be achieved without the development of new interventions, including new therapeutics to combat drug-resistant TB and shorten the length of therapy and a more effective vaccine. New biomarkers that could help identify individuals with active disease or predict the response to treatment would also aid efforts to control TB disease3. Diagnosing active TB can be challenging. Sputum can be difficult to collect from children, the elderly and HIV co-infected patients. Facilities for sputum culture are often not available. Most commonly TB is diagnosed based on symptoms and X-ray where available and WHO estimates that over 3 million individuals who develop TB every year go undiagnosed or unreported4. Therefore, a simple and reliable biomarker that correlates with the presence of active TB would be useful to prevent delay in diagnosis. Furthermore, biomarkers that correlate with the response to anti-microbial therapy may allow early recognition of treatment failure and possible drug resistance and be used as surrogate endpoints in late phase drug and vaccine studies, by greatly reducing the prolonged follow-up period currently required5, 6.
microRNAs (miRNAs) show great promise as both diagnostic and prognostic biomarkers7. miRNAs influence nearly all aspects of cell physiology, including cell proliferation, differentiation and apoptosis8. Mycobacterium tuberculosis infection of macrophages modifies the expression of multiple miRNAs, although the functions of most of these miRNAs are currently unknown. Some, such as miR-155 and miR-146, have been demonstrated to exert multiple effects on the inflammatory response to M. tuberculosis infection, both in vivo and in vitro9, 10. Studies have shown changes in blood miRNA levels in small numbers of patients with active TB that have biomarker potential11, 12, 13.
Patterns of expression of plasma miRNAs have proven to be reliable as a prognostic indicator for some malignancies and infectious diseases14, 15. The current study has examined the potential of a miRNA expression profile in the plasma to serve as a biomarker in patients with active pulmonary TB and to predict the response to therapy.
Section snippets
Study area and participants
This study was undertaken in Ningxia Hui Autonomous region (NHAR) in north-western China where Han make up the majority ethnic group and Hui (Chinese Muslims), ∼30%, the largest minority group. Participants were enrolled from five districts within NHAR. This study was undertaken with the approval of the University of Sydney Ethics Review Committee (Protocol No 2012/1076) and the Ningxia Medical University Human Ethics Committee (approval date 6/6/2013) between August 2013 and June 2014 and
Exploratory study
Twenty patients with newly diagnosed PTB and an average age of 46 (range 18–69) were recruited and compared to 20 healthy controls (Table 1). Plasma miRNAs were extracted and examined with the Plasma Focus miRNA PCR panel. QC analysis of the plasma, the miRNA and the miRNA plates excluded 7 samples from further analysis with 19 TB patients and 14 healthy controls included in the final analysis. Among the 175 miRNAs analysed, 87 miRNAs were identified with significantly altered expression
Discussion
The exploratory study demonstrated that M. tuberculosis disease resulted in significant changes in the levels of 47% plasma miRNAs examined demonstrating that miRNA expression is significantly modulated during active TB. The levels of 10 of these miRNA were then examined in a longitudinal confirmatory study of 100 PTB patients sampled at four time points during therapy. Of the ten selected miRNAs that were differentially expressed in the exploratory study, only six were significantly modulated
Funding
This work was supported by the National Health and Medical Research Council CRE-TB (APP1043225), The Rebecca L Cooper Medical Research Foundation (Scholarship for SB), The Australian Respiratory Council, and The Baxter Charitable Foundation.
Acknowledgments
We thank all the staff of The Infectious Disease Hospital of Ningxia, Yinchuan, and the surrounding Centre for Disease Control Clinics for their invaluable assistance in enrolling patients and the patients and donors who volunteered to take part in this study.
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