In vitro and in silico Evaluation of ACE2 and LOX Inhibitory Activity of Eucalyptus Essential Oils, 1,8-Cineole, and Citronellal

Eucalyptus essential oils are well-known and used especially in upper respiratory tract pathologies or diseases as herbal drug preparations. In the present study, the in vitro angiotensin-converting enzyme 2 (ACE2) and lipoxygenase (LOX) enzyme inhibitory potentials of commercial Eucalyptus globulus Labill. and Eucalyptus citriodora Hook. essential oils were evaluated for their potential anti-coronavirus disease 2019 (COVID-19), and anti-inflammatory effects. In addition, the major components, 1,8-cineole and citronellal, were evaluated for their ability to bind at the active site of either human ACE2 or human 5-LOX using an in silico setting. Before activity evaluation, Eucalyptus globulus and E citriodora essential oils were analysed by GC/FID and GC/MS, where 1,8-cineole (30%), and citronellal (80%) were identified as the major components, respectively. The in vitro ACE2 inhibition was calculated as 94.9% for E globulus, and that of E citriodora essential oil as 83.4%. In vitro LOX inhibition experiments for essential oils in the same order showed inhibitions of 71.3 and 91.4%, respectively, at 20 mu g/mL test concentrations in microplate-based fluorometric assays. In addition, protein-ligand docking, and interaction profiling was used to gain structural and mechanistic insights into the in silico ACE2 and LOX inhibitory potentials of the major Eucalyptus essential oil constituents, 1,8-cineole as well as citronellal. The resulting data supported the in vitro findings; however, further in vivo studies are needed to confirm the activity.