Monday, December 5, 2022 - 22:28

December 5, 2022

Natural products derived from essential oils and extracts of medicinal plants are natural sources well tolerated by humans. In this sense, plant essential oils have been extensively studied and are reported to have antiviral activities. Among them, the essential oil and bioactive terpenes present in Eucalyptus leaves have shown great potential as antiviral therapies. Inhalation of steam from Eucalyptus essential oil has previously shown a positive impact on treating difficulties derived from viral infections, such as cold, bronchiolitis, rhinosinusitis, and asthma. Therefore, they represent a good alternative to treat infections caused by viruses, either to alleviate symptoms or to affect different pharmacological targets of these pathogens.

Eucalyptus is a genus of trees belonging to the Myrtaceae family native to Australia and Tasmania that includes 900 species and subspecies cultivated in different areas of the world with subtropical and Mediterranean climates. Various species of Eucalyptus are recognized for their high biomass production, rapid growth rate, good adaptation to various environmental conditions, and excellent wood quality to produce paper and derived products. In turn, some species of the genus (e.g., Eucalyptus polybractea, Eucalyptus smithii, and Eucalyptus globulus) have received particular attention as sources of essential oils for use in pharmaceutical and cosmetic products.

Numerous examples illustrate the phytopharmacological potential of essential oils obtained from Eucalyptus. These compounds are recognized for their broad spectrum of action, such as antibacterial, antifungal, antiviral, anti-inflammatory, anti-immunomodulatory, antioxidant, and wound healing properties. They are commonly used for the treatment of respiratory tract diseases such as the common cold, nasal congestion, sinusitis, pulmonary tuberculosis, bronchitis, asthma, influenza, acute respiratory distress syndrome (ARDS), and chronic obstructive pulmonary disease (COPD). Regardless of the route of administration of preparations of Eucalyptus essential oil, after being absorbed, the components exert their antiseptic, anti-inflammatory, and expectorant activities, which justifies the interest by researchers in the use of Eucalyptus essential oil to treat respiratory diseases.

According to the studies Eucalyptus essential oil has inhibitory potential against the coronavirus. SARS-CoV-2 is highly contagious, causing more than 3.8 million deaths worldwide, emerging as the most critical health and humanitarian crisis since the 1918 influenza pandemic. Viral influenza is an infectious respiratory disease with symptoms such as fever, runny nose, sore throat, muscle pain, headache, cough, and fatigue but can progress to pneumonia and other complications such as ARDS, COPD, rhinosinusitis, meningitis, encephalitis, and worsening of preexisting health problems such as asthma and cardiovascular disease. Due to limited therapeutic management for these viral infections, current strategies focus on developing and testing new drugs or reusing available drugs against possible viral therapeutic targets. However, compared with synthetic drugs, medicines from natural sources, such as essential oils, generate fewer side effects in humans and are often commercially profitable. In this context, interest has increased in the medicinal use of essential oils from Eucalyptus, especially as a complement for the treatment of viral diseases, either to relieve symptoms caused by infection or to exert effects on possible viral therapeutic targets.

Eucalyptus essential oil is generally obtained from steam distillation or hydrodistillation of leaves and less frequently from fruits, flowers, and stems. At least 300 species of Eucalyptus contain volatile oils in their leaves, with a chemical composition comprising a mixture of volatile bioactive compounds, mainly monoterpenoids. For medicinal purposes Eucalyptus oil is commonly extracted from the leaves of  Eucalyptus polybractea, Eucalyptus smithii, or  Eucalyptus globulus because the content of the main bioactive monoterpene, 1,8-cineole (eucalyptol), in these species is greater than 70% (v/v) of the total oil. The pharmacopoeias of many countries, including the United States, Spain, the United Kingdom, Germany, France, Belgium, the Netherlands, Australia, Japan, and China, have ruled on the benefits and applications, i.e., infusion, inhalation (steam), and topical application, of these oils. Eucalyptus globulus is the main species used in the phytopharmacological industry to obtain essential oil of high medicinal value, primarily because the species is widely cultivated worldwide and has been subjected to genetic selection processes in breeding programs to optimize different wood productivity characteristics. There are numerous products prepared with the essential oil of  Eucalyptus globulus or with its main component (1,8-cineole), both for internal use (tablets, capsules, or syrups) and external use (nasal drops and ointments). In recent years, medications such as 1,8-cineole and Myrtol® standardized capsules (300 mg capsule that has at least 75 mg of 1,8-cineole, 75 mg of limonene, and 20 mg of α-pinene), sold commercially as GeloMyrtol® and GeloMyrtol forte®, have received substantial attention due to their therapeutic benefits in various respiratory conditions. Due to the multiple clinical studies that support their phytomedicinal use, Eucalyptus essential oil and products containing its derivatives have been classified as highly safe.

Influenza Virus infections are primarily treated with mantadine, rimantadine, oseltamivir (Tamiflu®), and zanamivir (Relenza®), all neuraminidase inhibitors. However, their use has been limited by side effects and the emergence of resistant viral strains. Although vaccination is the most effective means of protection against influenza, the vaccines must be administered annually; therefore, the use of natural products for the treatment of Influenza viruses  could provide supplemental protection. Several studies have reported the anti- Influenza Virus capacity of Eucalyptus essential oil. For example, it was  investigated the antiviral activity of Eucalyptus polybractea against influenza A virus in air. Their results showed that when the pure essential oil was actively diffused with a nebulizer for 15 s (oil concentration: 125 µg/L of air in the chamber), Influenza Virus was completely inactivated in the air. Saturated oil vapor was slightly less effective, achieving a viral inactivation of 86% after one day of exposure. However, it was concluded that both aerosol and Eucalyptus polybractea oil vapor could be used as effective natural antiviral agents for disinfection applications. Also it was demonstrated the anti-influenza A activity of Eucalyptus globulus essential oil, both in the liquid phase and in the vapor phase, and a 94% reduction in viral infection was observed after 10 min of exposure of the virus to 250 µL of oil vapor. Therefore Eucalyptus essential oil has demonstrated incredible health benefits and, because of this, is widely used in traditional medicine to treat symptoms of airborne infectious diseases, including the common cold, pulmonary tuberculosis, nasal congestion, sinusitis, bronchial disease, and asthma, and is also used as a disinfectant, antioxidant, and antiseptic agent, especially in the treatment of respiratory tract infections.

Antiviral Activities of Eucalyptus Essential Oils: Their Effectiveness as Therapeutic Targets against Human Viruses (