Serum metabolic disparity between pulmonary Sarcoidosis (SAR) and Tuberculosis (TB) revealed by NMR based metabolomics study

Tuberculosis (TB) -a pulmonary granulomatous disease- is the leading cause of death worldwide from a single infectious disease agent especially in developing countries such as India. Current diagnostic methodologies often lack specificity and sensitivity; therefore, there is an immense clinical interest to investigate alternative biomarker signatures for obtaining a conclusive and suggestive diagnosis of TB. Particular challenge arises for treating physicians while differentiating TB from sarcoidosis (SAR) which is an uncommon granulomatous disease and shares the similar clinical, radiological and pathological features with TB. Symptoms common in TB such as cough, fever, fatigue, and weight-loss are often manifested in sarcoidosis as well. As India accounts for more than 26% of global burden of TB cases and epidemiological data about sarcoidosis is unknown, most of the sarcoidosis patients end up receiving anti tubercular therapy (ATT) erroneously, leading to delayed proper treatment and considerable risk of drug induced toxicity, whereas lung damage continues to progress in this backdrop. Therefore, there is an urgent unmet need to identify non-invasive biomarker(s) for differentiating sarcoidosis from TB. Metabolomics analysis of serum holds great potential to provide distinctive patterns of metabolic profiles relevant to underlying disease processes and thus may aid in rapid clinical diagnosis and guiding appropriate treatment.

Starting our efforts in this direction, the serum metabolic profiles of sarcoidosis and active TB patients were measured using 800 MHz NMR Spectroscopy and compared using the multivariate and univariate statistical analysis tools. The partial least square discriminatory analysis (PLS-DA) revealed significant serum metabolic disparity between SAR and TB with respect to normal control subjects [1-5]. Compared to SAR, the sera of TB patients were characterized by (a) elevated levels of lactate, acetate, 3-hydroxybutyrate (3HB), glutamate and succinate (b) decreased levels of glucose, citrate, pyruvate, glutamine, and various lipid and membrane metabolites (such as very-low/low density lipoproteins (VLDL/LDL), polyunsaturated fatty acids, etc.).

The altered circulatory levels of glucose (decreased) and lactate (increased) were found well consistent with previous report [6] demonstrating that infection with Mycobacterium tuberculosis (MTb) induces the Warburg effect in mouse lungs. A very recent study reported increased production of glutamate from mitochondrial glutaminolysis and pleiotropic roles of glutamine metabolism in the metabolic reprogramming of MTb infected M1-like macrophages [7]. A previous study published in Science [8] reported the suppression of oxidative stress by 3HB. Another study published in scientific report demonstrated that of Mycobacterium tuberculosis (MTb) secretory protein ESAT-induces GLUT-1 mediated enhanced glucose uptake by macrophages and increased fatty acid biosynthesis (to drive foamy macrophage differentiation) which in turn results in release of 3HB in the extracellular environment [9]. Based on previously reported metabolic derangements in MTb infected systems and our results derived from NMR-based serum metabolomics, the following remarks have been drawn:

• Active TB infection induces Warburg effect as inferred from the decreased serum levels of glucose and elevated levels of lactate
• Active TB infection causes increased biosynthesis of fatty acids as inferred from the decreased serum levels of citrate and increased levels of acetate and 3-Hydroxybutyrate (3-HB)
• Active TB infection manipulates oxidative stress (OS) induced pathogen killing host-defense mechanism as inferred from decreased circulatory phenylalanine-to-tyrosine ratio (PTR) and 3HB (known to suppress OS)
• Active TB infection induces augmented utilization of glutamine (an immunomodulatory nutrient) as inferred from the decreased serum levels of glutamine and increased serum levels of glutamate and succinate
• Active TB infection induces dyslipidemia as inferred from the decreased NMR signals of very-low/low density lipoproteins (VLDL/LDL) and polyunsaturated fatty acids (PUFAs)

References:

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