Chemical Profiles of Serbian Nepeta cataria Essential Oils, Structural Characterization of trans-cis-Nepetalactone, and Preliminary In Vitro Bioactivity

Essential oils from three wild populations of Nepeta cataria L. (NC1–NC3) in southern and southeastern Serbia were obtained by hydrodistillation and analyzed by GC-FID and GC-MS. trans,cis-Nepetalactone (4aα,7α,7aβ-nepetalactone; NL) was isolated from NC1, and its constitution and relative configuration were established by NMR spectroscopy and iterative full-spin analysis; its absolute configuration was not determined. Its presence across the profiles was confirmed by co-injection with the isolated and characterized pure compound. NL accounted for 91.5%, 12.9%, and 87.9% of the relative GC-FID peak area in NC1, NC2, and NC3, respectively, whereas NC2 contained larger proportions of two additional provisionally annotated nepetalactone components, D (41.0%) and E (16.4%), whose configurations remain unresolved. In exploratory in vitro experiments, both the essential oils (NC1–NC3) and the isolated NL were evaluated using a cell-free lipid peroxidation model (TBA–MDA assay) and a cytokinesis-block micronucleus (CBMN) assay on lymphocytes from four male donors. All tested samples inhibited AAPH-induced lipid peroxidation. Preliminary CBMN screenings revealed a distinct non-monotonic profile: lower concentrations (1–2 µg/mL) reduced baseline micronucleus frequency, while 4 µg/mL caused an increase. These preliminary biological observations do not establish cytoprotection or safety. The findings document marked chemical variation among the analyzed Serbian samples, pointing to a complex, dose-dependent trend that requires confirmation with independent cytotoxicity measurements and a larger donor cohort.