Fatty acids-carotenoid complex: An effective anti-TB agent from the chlorella growth factor-extracted spent biomass of Chlorella vulgaris.

Abstract

The multidrug-resistant (MDR) pathogen, Mycobacterium tuberculosis, still remains as one of the major threat to mankind, despite the availability of a live attenuated vaccine and effective antibiotics. Marine microalgae, at all times, act as a key resource for valuable therapeutic compounds with limited side effects. The present explorative attempt is to isolate the biomolecules of pharmacological importance from the marine microalgae, Chlorella vulgaris, and to evaluate its effect on the ever dreadful disease, Tuberculosis. The study is also aimed to develop an economically feasible methodology for by-products extraction from microalgae. Fatty acids-carotenoid complexes (FACC), namely, FACC-1 (red oil) and FACC-2 (brown oil) were isolated, in addition to lipid and lutein from the Chlorella Growth Factor (CGF, a protein fraction enriched with vitamins, minerals and carbohydrates)-extracted spent biomass through column chromatography. FACC-1 is a complex of fatty acids such as oleic and linoleic acids, and carotenoids such as canthaxanthin and neoxanthin. FACC-2 is a complex of oleic, linoleic and linolenic acids and carotenoids (cryptoxanthin and echinenone). Initial screening for evaluation of minimum bactericidal concentration (MBC) of FACC-1 and -2 was performed against Mycobacterium tuberculosis strains such as H37Rv, SHRE sensitive clinical isolate and SHRE resistant clinical isolate. MBC was noted at 10μg/mL by FACC-1 and at 5μg/mL by FACC-2, determined using colony forming and Lucipherase Reporter Mycobacteriophages (LRP) assay. Testing in the PAN sensitive isolates indicated that the MBC was noted at 5μg/mL by FACC-1 and at 2.5μg/mL by FACC-2. Complete inhibition (100%) was observed at 100μg/mL by FACC-1 and at 50μg/mL by FACC-2. Testing of FACC-1 and FACC-2 individually as well as in combination on two different types of MDR strains confirmed the efficacy of the algal oils, wherein in MDR-strain 1, FACC-1 revealed 50% inhibition at 10μg/mL, while FACC-2 exhibited the same at 5μg/mL. Conversely, in the case of MDR strain-2, MBC of FACC-1 was at 500μg/mL and MBCof FACC-2 to be at 250μg/mL. No significant synergistic effect was observed on combining both the oils. The study signifies the development of a potent therapeutic agent comprising of a complex of anti-TB agent (fatty acids) and antioxidants (carotenoids) from the CGF-extracted spent biomass of C. vulgaris.