Solvent-Dependent Phytochemical Profiles, Antioxidant and Antimicrobial Bioactivities, and Melanoma-Selective Cytotoxicity of Inula helenium L. Root Extracts

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Inula helenium L. (elecampane) is a traditional medicinal plant whose roots contain both hydrophilic polyphenols and lipophilic sesquiterpene lactones. However, the influence of the raw material origin and the extraction solvent on its combined bioactivity profile remains unclear. Moreover, although isolated sesquiterpene lactones from I. helenium have been extensively investigated for their anticancer properties, the bioactivity of whole root extracts against human melanoma cells has remained largely underexplored. This study aimed to systematically compare the phytochemical characteristics and biological activity of I. helenium root extracts obtained from three distinct raw material sources and three solvents of increasing polarity, and to identify the main factors associated with the observed bioactivity through multivariate integration. In this study, I. helenium roots from three distinct sources—commercially available dried roots, wild-collected roots, and cultivated roots collected from the Botanical Garden of Vilnius University—were extracted with three solvents of increasing polarity (n-hexane, ethyl acetate, and 70% ethanol). Each extract was characterized by total phenolic content, four antioxidant assays (DPPH, ABTS, FRAP, CUPRAC), UV–Vis fingerprinting, antimicrobial testing against Staphylococcus aureus, Klebsiella pneumoniae, and Candida albicans, and a CCK-8 assay on SK-MEL-28 human melanoma and HEK293 non-cancerous cells. Multivariate integration (PCA, HCA, Spearman rank correlation) identified solvent polarity as the dominant driver of both the phytochemical and the biological profile (PC1 and PC2 together explained 87.9% of the total variance). Ethanolic extracts combined the highest phenolic content (up to 38.6 mg GAE/g dry extract) and the strongest antioxidant capacity across all four assays, with maximum values of 177.3 (DPPH), 328.9 (ABTS), 174.1 (FRAP), and 541.6 (CUPRAC) µmol TE/g DE (p ≤ 0.004). In the preliminary antimicrobial screening, ethanolic extracts showed near-complete to complete inhibition of S. aureus and C. albicans at 25 mg/mL, with MIC90 values as low as 12.5 mg/mL against S. aureus and 6.25 mg/mL against C. albicans, whereas K. pneumoniae showed only marginal growth inhibition (median values below 20% across the entire tested concentration range). Strikingly, n-hexane and ethyl acetate extracts—despite negligible antioxidant activity—produced concentration-dependent cytotoxic effects. Six of the nine extracts reduced SK-MEL-28 viability while sparing HEK293 cells, with the cultivated Botanical Garden n-hexane extract showing the greatest difference across the tested cell models (SI > 1.50, p = 0.0003). Targeted solvent selection thus enables a single plant material to yield two functionally distinct bioactive fractions: more polar extracts with pronounced antioxidant and antimicrobial activities and less polar extracts with preferential activity against SK-MEL-28 within the cell models tested.

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