Plant Essential Oils: Possible COVID-19 Therapeutics

COVID-19 is the current pandemic sweeping the world caused by the coronavirus SARS-CoV-2. As of January 12, 2021, the virus has been responsible for 91 439 729 cases leading to 1 956 201 deaths (https://www.worldometers.info/coronavirus/). Although at least three vaccines have received emergency approval in the Western countries, questions remain as to the long-term efficacy of the vaccine(s), whether viral mutations can render the vaccines ineffective, and whether the vaccines will be equally effective for all ages and races of people. Finally, since all the vaccines need to be administered in 2 doses and with the current world population at 7.8 billion, that calls for 15.6 billion doses of the vaccines, which may prove to be a daunting task.

Drugs in the form of tablets or capsules can easily be prepared in large amounts very quickly, and, since they are more transportable, they are easily available and can possibly be more affordable to the general population. However, despite a number of promising leads (like flavonoids) in in silico studies, such therapeutic(s) for COVID-19 have not yet taken practical prospects for treatment. In this context, we would like to point out that plant essential oils (EOs) are known for their antiviral components and one or more of the EOs may prove to be potential cures for COVID-19.

A recent review has pointed out that aromatic plants and their EOs are active against a diverse variety of viruses including herpes simplex viruses 1 and 2, adenoviruses, human immunodeficiency virus, Junin virus, enterovirus, hepatitis B virus, and even SARS-CoV-1. Some active components of the EOs are terpinenes, pinenes, caryophyllene, eugenol, linalool, and camphor. EO components of Laurus nobilis L. (Lauraceae), like β-ocimene, α- and β-pinene, and 1,8-cineole have been hypothesized to be potential therapeutics against COVID-19 through inhibiting the main protease (Mpro) of the virus. ¹ In an in silico study with 171 EO components from various plants, best docking scores to Mpro were observed with (E)-β-farnesene, (E,E)-α-farnesene, (E,E)-farnesol, and (E)-nerolidol. ²

EOs can act in multiple ways. Being lipophilic, they can possibly disrupt the SARS-CoV-2 membrane, as well as either individually or synergistically acting against viral targets and so inhibiting viral replication. Thus far, the data on EOs are preliminary and more in vitro and in vivo studies are necessary to explore the full potential of the EOs and their components against SARS-CoV-2. ³ Any problem of targeted release of essential oils to sites in the human body necessary to combat the virus may be solved through encapsulation of EOs through a nanoprecipitation method. ⁴ EOs can be inhaled as vapor following boiling in water and so reach the lungs directly; individual bio-active components of EOs may be absorbed from the gastro-intestinal tract.