Phytochemistry and Bioactivity of Essential Oil and Methanolic Extracts of Origanum vulgare L. from Central Italy

Abstract

Origanum vulgare L. is an important aromatic plant traditionally used in folk medicine since ancient times. Its growing interest for the scientific community is mainly attributed to its distinctive chemical profile, which includes bioactive compounds, such as polyphenols (phenolic acids and flavonoids) and volatile compounds (essential oil). These components collectively contribute to oregano’s wide spectrum of biological activities. In this study, the volatile components of the essential oil (WEO_OR) and the polyphenolic fraction of the methanolic extract (ME_OR) obtained from leaves and inflorescences of wild Origanum vulgare collected in central Italy were characterized using GC-MS and UHPLC-DAD, respectively. Carvacrol was identified as the major compound in the essential oil, while rosmarinic acid was predominant in the methanolic extract. A comparative analysis was also carried out with a commercially available essential oil (CEO_OR), aiming to evaluate potential differences in chemical composition and antioxidant activity (DPPH, ABTS, and FRAP assays). ME_OR showed the strongest antioxidant activity (DPPH IC50 = 0.052 mg mL−1; ABTS = 3.94 mg TE mL−1; FRAP = 30.58 mg TE g−1), followed by CEO_OR (DPPH IC50 = 0.45 mg mL−1; ABTS = 9.57 mg TE mL−1; FRAP = 7.33 mg TE g−1), while WEO_OR displayed the lowest values (DPPH IC50 = 1.54 mg mL−1; ABTS = 0.10 mg TE mL−1). Furthermore, ME_OR and WEO_OR were tested in vitro using the human hepatoblastoma cell line HepG2 to assess their potential biological activities related to cell survival and oxidative stress. The results indicated that at the tested doses, neither the ME nor the EO showed significant toxicity, as evidenced by the unchanged proliferation rate of HepG2 cells. However, the ME at low doses (50 and 100 μg mL−1) and the EO (0.005%), administered as a pre-treatment, exhibited a protective effect against oxidative stress, as inferred from the reduction in 8-OHdG levels, a marker of oxidative damage to nucleic acids.