Polyphenol Profiling, Antibacterial Activity, and In Vitro Cytotoxic Effects of a Diethyl Ether Fraction from Juniper Cone Berries

Modern research on medicinal plants aims to expand their applications beyond traditional usage. Juniper (Juniperus communis L.) cone berries have a background in the phytotherapy of skin diseases. The present study investigated a diethyl ether fraction (JC-DEE) obtained by sequential solvent partitioning of an ethanolic extract from Juniperus communis L. cone berries. Phytochemical characterization was performed using Fourier-transform infrared (FTIR) spectroscopy, HPLC–MS, and total phenolic content determination. The antimicrobial activity of JC-DEE and its effects on cell viability and morphology in HaCaT keratinocytes and A375 melanoma cells were evaluated, alongside an exploratory DPPH spectrophotometric assessment. Targeted HPLC–MS analysis identified eleven selected constituents, seven of which were quantified within the validated calibration range, with apigenin (1.971 ± 0.150 µg/mL), protocatechuic acid (1.070 ± 0.049 µg/mL), and luteolin (0.560 ± 0.046 µg/mL) showing the highest concentrations in the analyzed solution. The antimicrobial assay revealed limited inhibitory effects against the tested microorganisms, with inhibition zones ranging from 7 to 10 mm. Exploratory DPPH measurements revealed time- and concentration-associated variations in apparent absorbance reduction. In the cellular assays, JC-DEE produced a concentration-dependent reduction in viability in both human A375 melanoma cells and HaCaT keratinocytes, with estimated IC50 values of 102.7 μg/mL and 129.3 μg/mL, respectively. Phase-contrast microscopy revealed concentration-related morphological alterations, while immunofluorescence analysis at 100 μg/mL demonstrated cytoskeletal and nuclear changes, including nuclear condensation and fragmentation, with apoptotic body-like structures particularly evident in A375 cells. Overall, JC-DEE represents a phytochemically characterized fraction exhibiting limited antimicrobial effects and concentration-dependent cytotoxicity in the investigated cellular models, while its antioxidant potential remains to be validated. Further studies are required to identify the constituents responsible for these effects, clarify the mechanisms of cell death, and assess selectivity and safety in additional non-malignant cellular models.