Extracts from Helenium aromaticum and Orthopterygium huaucui as potential antimycobacterial agents

Tuberculosis remains one of the leading causes of mortality worldwide. The emergence of drug-resistant Mycobacterium tuberculosis strains and increasing infections caused by Mycobacterium kansasii, especially in immunocompetent individuals and people living with HIV, underscore an urgent need for novel therapeutic options. Medicinal plants represent a valuable source of antimicrobial compounds, offering promising alternatives against resistant mycobacterial pathogens. Extracts from Peruvian (Orthopterygium huaucui) and Chilean (Helenium aromaticum) species were evaluated for antimycobacterial activity against M. tuberculosis and M. kansasii. Cytotoxicity was assessed using MTT assay in RAW 264.7 macrophages, showing dose-dependent responses. The vehicle (3% ethanol in DMSO) was non-toxic at 0.5%. O. huaucui extract showed the lowest cytotoxicity (CC₅₀ > 100 µg/mL), while H. aromaticum extracts displayed moderate cytotoxicity (CC₅₀ > 40.4 ± 0.1 µg/mL). Two H. aromaticum extracts showed exceptional performance against M. tuberculosis H37Rv. Dichloromethane root extract exhibited potent activity (MIC₅₀ of 3.9 ± 0.9 µg/mL; SI = 17.2), while ethyl acetate flower extract demonstrated greater potency (MIC₅₀ 1.5 ± 0.8 µg/mL; SI = 37.3). These extracts also showed inhibitory effects against a clinical isolate of the Beijing sublineage (MIC₅₀ of 1.8 ± 0.5 and 3.4 ± 0.8 µg/mL, respectively). Furthermore, O. huaucui methanolic stem extract achieved selectivity index of 20.4 against M. kansasii. Most remarkably, H. aromaticum dichloromethane root extract exhibited extraordinary potency against hypervirulent Mkan 8835 strain (MIC50 = 0.7 ± 0.2 µg/mL; SI = 95.8), while methanolic leaf/stem extract demonstrated significant activity (MIC₅₀ = 2.3 ± 0.6 µg/mL; SI = 30.0). Differential scanning calorimetry analyses revealed that active extracts interact with dimyristoylphosphatidylcholine and dimyristoylphosphatidylglycerol model membranes, altering thermodynamic parameters of lipid phase transitions, suggesting a membrane-disruptive mechanism. Mass spectrometry identified sesquiterpene lactones and flavonoids in H. aromaticum, and terpenes and flavonoids in O. huaucui, known for their antimicrobial properties. These findings support the potential of these South American plants as sources of novel antimycobacterial agents.