Photodynamic therapy is a type of treatment approved for several types of cancer, such as skin (non-melanoma), esophageal, and lung. It is also used against fungal and bacterial skin infections (antimicrobial photodynamic therapy).
Broadly speaking, this therapy consists of the combination of a photosensitizing compound and visible light. The photosensitizing compound is excited when exposed to light, causing a cascade of photochemical reactions that lead to the formation of reactive oxygen species. These reactive species are ultimately responsible for the death of tumor cells or infectious agents.
Based on the foundations of photodynamic therapy, Beatriz Praena’s team, from the Autonomous University of Madrid (UAM) in Spain, has shown that a plant extract of St. John’s Wort, in combination with daylight, has a viricidal effect against HCoV-229E, a cold coronavirus similar in many ways to SARS-CoV-2.
The results of the UAM researchers show that, despite continuous exposure to daylight, the St. John’s Wort extract does not lose its virucidal properties, thus preventing viral infection of human cells for hours.
In these photos, cells infected with the coronavirus HCoV-229E glow green. The image on the left shows that all untreated cells are infected. In the image on the right, treatment using photodynamic therapy with St John’s wort extract and white light dramatically decreases the number of cells infected by this coronavirus (Images: UAM)
“This work has been carried out in the laboratory, but due to its efficacy, the plant extract of St. John’s wort in combination with sunlight is proposed as a promising candidate to fight against the transmission of SARS-CoV-2”, the authors emphasize.
St John’s wort extract comes from the aerial part of the Hypericum perforatum L. plant, also known as St. John’s wort. This extract is already used in medicine with different indications, mainly as an anxiolytic, antidepressant and anti-inflammatory.
Its properties are due to the action of several biologically active components, such as hypericin and hyperforin. The latter in particular has powerful photosensitizing properties and can be applied in combination with light in photodynamic therapy.
The new results were evaluated in vitro with human Huh-7 (human hepatocellular carcinoma) cells, susceptible to coronavirus infection. The exposure to white light was carried out directly in the laboratory using an appropriate light source for it. In addition, the researchers found that the treatment is not effective against other viruses such as herpes simplex type 1 (HSV-1).
“Although the work has been carried out in vitro, the results obtained encourage us to expand the studies to apply the extract to body regions exposed to light, including the upper respiratory tract, which is the entry route for some of the viruses studied, and thus prevent the spread of coronavirus ”, conclude the authors of the study.
The study is entitled “Potent In Vitro Virucidal Activity of Photodynamic Therapy with Hypericum Extract as Photosensitizer and White Light against Human Coronavirus HCoV-229E”. And it has been published in the academic journal Pharmaceutics. (Source: UAM)