Conifer Essential Oils Modulate Oxidative Stress and Erythrocyte Stability in Human Blood in Vitro

Essential oils (EOs) derived from conifers of the Pinaceae family are complex bioactive mixtures known for their antioxidant and antimicrobial properties. However, their impact on human redox homeostasis, particularly in blood, remains poorly understood. This study aimed to compare the redox-modulating and membrane-stabilising effects of essential oils from Scots pine (PEO), European spruce (SEO), and European silver fir (FEO) using an in vitro human blood model.

The chemical composition of each EO was characterised using gas chromatography-mass spectrometry (GC-MS), proton-transfer-reaction mass spectrometry (PTR-MS), and Fourier-transform infrared spectroscopy (FTIR). Human blood samples were incubated with different EO concentrations, and oxidative stress biomarkers, antioxidant enzyme activities, and erythrocyte membrane stability were evaluated.

All EOs exhibited terpene-rich profiles dominated by α-pinene, β-pinene, borneol, and bornyl acetate, with distinct species-specific differences. The oils displayed concentration-dependent biphasic redox effects. At moderate concentrations, PEO and SEO enhanced total antioxidant capacity and increased catalase and ceruloplasmin activities by 15-25% (p < 0.05). In contrast, higher doses-particularly of FEO-induced lipid peroxidation and protein oxidation by 40-60% (p < 0.05), indicating pro-oxidant behaviour. Erythrocyte haemolysis assays revealed that SEO exerted the strongest membrane-stabilising effect (haemolysis reduced by 18%), whereas FEO increased membrane fragility (haemolysis increased by 27%).

Pinaceae-derived essential oils exhibit dual antioxidant and pro-oxidant activity dependent on concentration and species. Among them, PEO showed the most balanced redox profile. These findings highlight both the therapeutic potential and the importance of controlled dosing when considering such oils for biomedical applications.