Antimycobacterial Activity and Nitric Oxide Production Inhibition of Antarctic Seaweeds

The emergence of increasingly resistant strains of Mycobacterium tuberculosis (Mtb) makes the search for new antimycobacterial and host-directed therapies essential to help combat this disease. Antarctica extreme environmental conditions make seaweeds an important source for the discovery of bioactive compounds with the potential to treat various diseases caused by microorganisms. In this study, 29 lipophilic extracts of Antarctic seaweeds were evaluated for their potential as antituberculosis drug sources. The antimycobacterial and immunomodulatory activities (based initially on NO inhibition), as well as the chemical profiles of the algae were studied. Of all the extracts, 21 (72.4%) showed antimycobacterial activity with MIC₅₀ values lower than 25 μg/mL against Mtb H37Rv. And, 9 (31%) showed activity also against the hypervirulent strain Mtb M299. Regarding immunomodulation, 27 seaweed extracts (93.1%) inhibited NO production by suppressing iNOS expression with IC₅₀ values lower than 25 μg/mL. Six samples of the genera Desmarestia, Sarcopeltis, Iridaea, Pyropia, and Curdiea with dual activity and a selectivity index higher than ten were selected as promising, with Pyropia endiviifolia extract standing out against Mtb H37Rv and Mtb M299 (MIC₅₀ 2.1 ± 0.2 and 3.2 ± 0.7 μg/mL, respectively). GC-MS-based Molecular Networking indicated pentadecanoic acid, hexadecanoic acid, and cholesterol as the major known components of the promising samples. Our study demonstrates for the first time the potential of the secondary metabolites from Antarctic seaweeds against Mtb and encourages further investigation to characterize novel antitubercular agents from these extremophilic organisms.