Abstract
BackgroundInfluenza is a significant cause of morbidity and mortality. The recent pandemic of a novel H1N1 influenza virus has stressed the importance of the search for effective treatments for this disease. Essential oils from aromatic plants have been used for a wide variety of applications, such as personal hygiene, therapeutic massage and even medical practice. In this paper, we investigate the potential role of an essential oil in antiviral activity.MethodsWe studied a commercial essential oil blend, On Guard™, and evaluated its ability in modulating influenza virus, A/PR8/34 (PR8), infection in Madin-Darby canine kidney (MDCK) cells. Influenza virus was first incubated with the essential oil and infectivity in MDCK cells was quantified by fluorescent focus assay (FFA). In order to determine the mechanism of effects of essential oil in viral infection inhibition, we measured hemagglutination (HA) activity, binding and internalization of untreated and oil-treated virus in MDCK cells by flow cytometry and immunofluorescence microscopy. In addition, the effect of oil treatment on viral transcription and translation were assayed by relative end-point RT-PCR and western blot analysis.ResultsInfluenza virus infectivity was suppressed by essential oil treatment in a dose-dependent manner; the number of nascent viral particles released from MDCK cells was reduced by 90% and by 40% when virus was treated with 1:4,000 and 1:6,000 dilutions of the oil, respectively. Oil treatment of the virus also decreased direct infection of the cells as the number of infected MDCK cells decreased by 90% and 45% when virus was treated with 1:2,000 and 1:3,000 dilutions of the oil, respectively. This was not due to a decrease in HA activity, as HA was preserved despite oil treatment. In addition, oil treatment did not affect virus binding or internalization in MDCK cells. These effects did not appear to be due to cytotoxicity of the oil as MDCK cell viability was only seen with concentrations of oil that were 2 to 6 times greater than the doses that inhibited viral infectivity. RT-PCR and western blotting demonstrated that oil treatment of the virus inhibited viral NP and NS1 protein, but not mRNA expression.ConclusionsAn essential oil blend significantly attenuates influenza virus PR8 infectivity in vitro without affecting viral binding or cellular internalization in MDCK cells. Oil treated virus continued to express viral mRNAs but had minimal expression of viral proteins, suggesting that the antiviral effect may be due to inhibition of viral protein translation.
Highlights
Influenza is a significant cause of morbidity and mortality
Protective essential oil suppressed progeny virus production The effect of oil treatment on viral infectivity was first determined by measuring the release of nascent viral particles following infection of Madin-Darby canine kidney (MDCK) cells with untreated, oil treated, or control oil treated virus for 48 h
Quantification of infectious particles produced in virus-exposed MDCK supernatant was done by transfer of the infected cell supernatant to a separate culture of MDCK cells followed by Fluorescent focus assay (FFA)
Summary
The recent pandemic of a novel H1N1 influenza virus has stressed the importance of the search for effective treatments for this disease. We investigate the potential role of an essential oil in antiviral activity. The recent pandemic of a novel H1N1 influenza emphasizes the urgency of identifying effective approaches to prevent viral infection. Between 1990 and 1999 in the United States, non-pandemic influenza A virus (IAV) infected 5-20% of people and caused approximately 36,000 deaths and 226,000 hospitalizations annually [1,2]. IAV infection is initiated with a binding of the viral hemagglutinin (HA) to sialic acid on the cell surface; and virus particles are internalized through receptormediated endocytosis. Viral HA protein is activated and the virus fuses with endosomal membranes. As a result, infected cells die by apoptosis or cytolysis
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