Journal of Clinical and Diagnostic Research (Jul 2019)
Superoxide Dismutase: A Biomarker for Early Diagnosis of Tuberculosis
Abstract
Introduction: Tuberculosis (TB) is a major public health concern in developing countries. Traditional diagnostic methods such as microscopic detection of organism and histopathological examination are limited in their capacity to provide information on prognosis and treatment efficiency. Abundantly secreted extracellular Superoxide Dismutase (SOD) protects the Mycobacterium tuberculosis (MTB), and elevated levels of the biomolecule are found in tissues and fluids of tubercular patients. Aim: To estimate the levels of serum SOD in lung control disease and tubercular patients; assess the diagnostic potential of SOD assay for detection of tuberculosis at an early onset stage and quantify the serum SOD activity to monitor the course of infection and determine the effectiveness of the anti-Tubercular (anti-TB) drug treatment. Materials and Methods: The present observational study was conducted on 180 participants at B.S. Medical College and Hospital, Bankura, West Bengal, India. The participants were divided into three groups: Group 1: Normal Control (n=30), Group 2: Disease Control/Lung-Disease Control (n=27) and Group 3: Tubercular Subjects (3A- Pulmonary TB and 3B- Extrapulmonary TB) (n=76). Serum SOD levels of the participants were measured spectrophotometrically. The serum SOD levels of the patients were re-measured after one-month of A-TB drug treatment. In addition, to increase the specificity of the test, the serum of tubercular subjects was incubated with different concentrations of Sodium Cyanide (NaCN) and then assayed for SOD activity. The level of significance was assessed using Student’s t-test. Results: The serum SOD level in tubercular subjects (both pulmonary and extra-pulmonary; with treatment started between 0-15 days) were significantly (p-value <0.01) elevated as compared to the control and lung-disease subjects. Significant decrease in serum SOD levels was observed after one-month of A-TB drug treatment signifying a decrease in mycobacterial load in host tissues. The iron co-factored SOD secreted by M.tuberculosisis was found to be resistant to NaCN whereas Copper-Zinc (Cu-Zn) co-factored SOD was inhibited by NaCN. Conclusion: The serum SOD assay, used in the present study, differentiated between human and mycobacterial origin-SOD, on incubation with NaCN, and diagnosed pulmonary as well as extra-pulmonary TB cases with confidence. Thus, it can be used as a simple, rapid, inexpensive, yet highly sensitive and specific- assay for detection of both human and bovine tuberculosis and primary and secondary drug-resistant cases.
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