IndexIntroductionResultDiscussionConclusionIntroductionHerpes simplex viruses type 1 and type 2 are one of the most common and contagious pathogens. the virus is transmitted through the mouth, the respiratory system, direct person-to-person contact, saliva, sexual contact. The primary infection usually appears in the form of labial on the skin or mucosa. These viruses can cause damage to the liver, adrenal glands, eyes of infants, and people with immunodeficiency disorders. It can also cause encephalitis, meningitis and death with attack on the central nervous system and brain. In most cases, the virus tends to remain in latent form in the sensory ganglia. An antiviral treatment for HSV infection is acyclovir which is still the most commonly used chemotherapy. In recent years, due to long-term treatments with aciclovir, the appearance of drug-resistant mutants has been reported. Drug-resistant mutants of the virus without thymidine kinase are being isolated from immunocompromised patients, which could pose a major problem in future years. Due to these problems there is a need to find new drugs with low side effects. Medicinal plant extracts and essential oils are increasingly interesting as antimicrobial and antiviral agents and have been widely used in traditional medicine. Medicinal plants produce a variety of chemical components with the potential to inhibit viral replication with low side effects. these plants represent a massive source of new bioactive components for the discovery of new drugs with low side effects. Say no to plagiarism. Get a tailor-made essay on "Why Violent Video Games Shouldn't Be Banned"? Get an original essay Melissa officinalis (lemon balm) is a member of the Lamiaceae family, and plants of this family are well known in antiviral herbal medicine. Melissa officinalis is a perennial herbaceous plant of the Lamiaceae family and is native to central-southern Europe, the Mediterranean basin, Iran and central Asia. The main components of lemon balm essential oil are citral (citronellol, linalool), geraniol and trepenes. Many studies report the antioxidant and antibacterial effects of extracts and essential oils from the Lamiaceae family. The antiviral activity of aqueous extracts and essential oils of lemon balm has been described previously, but details on the main effective component of the extract and essential oil are not available. In this study we compared the antiviral activity of essential oils of melissa officinalis and the two components of it, and the mode of antiviral action is analyzed at different stages of the viral infection cycle. Melissa officinalis essential oil was purchased from Primavera Life, Sulzberg, Germany who had previously analyzed with gas chromatography by Dr. Schnitzler and we used their analysis for our study. Melissa officinalis oil was dissolved in ethanol and added to the cell culture medium at a maximum final concentration of 1% ethanol. In this study we used the A549 cell line to evaluate the cytotoxicity and antiviral activity of our compounds. A monolayer of A549 (human lung carcinoma) cells was cultured with Dulbecco's modified Eagle medium (DMEM) supplemented with 5% fetal calf serum (FCS), 100 U/ml penicillin, and 100 mg/ml streptomycin. Herpes simplex virus type 1 (HSV-1) was used for the experiments, and the viruses were grown on A549 cells. Acyclovir was purchased from Sigma-Aldrich(Sigma-Aldrich, Germany) and dissolved in dimethyl sulfoxide (DMSO) to a maximum final concentration of 1% DMSO. initially the cytotoxicity of the compounds on the A549 cell was evaluated. for this purpose, A549 cells were seeded into a 96-well tissue culture plate and medium containing serial dilutions of the essential oil and compounds and were added onto A549 cells in eight replicates for each concentration of the drugs. Wells containing a medium with 1% ethanol but no compounds were also included on each plate as controls. After 72 h of incubation, the cytotoxicity of essential oil and other compounds were determined by MTT assay. The cytotoxic concentration of the drug that reduced the number of viable cells by 50% (CC50) was determined from the dose-response curves. Inhibition of HSV replication was examined by plaque reduction assay in 12-well culture plates. 25×104 cells were seeded into each well and incubated until reaching at least 90% confluence, then the virus was added at multiplicity of infection (MOI) 0.0002 to each well in 4 different stages, the cells were pretreated with essential oil before viral infection, viruses were incubated with essential oil before cell infection, essential oils and compounds were added after virus penetration into cells or during virus penetration into cells, cell pretreatment, cells and viruses were incubated together during adsorption, cells were pretreated with serial dilutions of essential oil before viral infection, viruses were incubated with essential oil before cell infection or after virus penetration into cells guests. For viral pretreatment, cellular pretreatment and treatment during penetration. After adsorption, the remaining inoculum was removed and the infected cells were covered with medium containing 1% methylcellulose and for the post-infection phase covered with medium containing 1% methylcellulose and was added a serial dilution of essential oil and compounds. for each plate there were 2 wells of positive control infected with the virus and treated with acyclovir, 2 wells of mock control to which no viruses and compounds had been added, and 2 wells of untreated control which had not been treated with essential oils and compounds used as an untreated control to determine plaque reduction in serial dilutions of essential oil and compounds. the positive control, untreated control, and sham control always contained 1% ethanol to eliminate the effect of ethanol on the cells or virus. After 3 days of incubation, cells were fixed with 10% formalin and stained with 1% crystal violet, and then plaques were counted. the concentration of the test compound that inhibited plaque number by 50% (IC50) was determined from the dose-response curves. The selectivity index (SI) was determined as the ratio of CC 50 /IC 50. Result Melissa Officinalis oil and some selected terpene compounds and their mixture were serially diluted in ethanol and added to the culture medium cell to examine the effect on the growth and viability of cells in tissue culture, always resulting in an ethanol concentration of less than 1% which had no effect on cells and viruses. Cell monolayers were grown in medium containing different concentrations of these drugs. After 3 days of incubation, the cell viability of A549 cells was determined by the MTT assay. The maximum noncytotoxic concentrations of these drugs were determined to be 40 μg/ml for citral and 50 μg/ml for citral.beta-caryophyllene, 0.004% for lemon balm oil and 0.006% for the mixture of citral and beta-caryophyllene. The potential antiviral effect of several essential oils and some selected components has been determined in vitro against herpes simplex virus type 1 (HSV-1). HSV-1 was incubated for 1 hour at room temperature with various concentrations of lemon balm oil, citral and beta-caryophyllene mixture, beta-caryophyllene, and citral. In all assays, untreated virus-infected cells were used as controls. Subsequently, aliquots of each dilution were added to the cells for 1 hour, then the cells were washed and covered with drug-free medium and incubated for 3 days at 37ºC. The 50% inhibitory concentrations (IC50) for HSV-1 were determined over a wide range below the maximum non-cytotoxic concentration. Results are presented as virus reduction and represent the average of three independent experiments. In plaque reduction tests, all essential oils and terpenes showed a concentration-dependent antiviral effect, beta-caryophyllene was the most effective drug. Selectivity indices for oils and different terpenes were calculated as the TC50/IC50 ratio, the highest selectivity index of 30 was determined for beta-caryophyllene. Herpesvirus replication is characterized by a complex sequence of several steps in which antiviral agents could interfere. To study the inhibitory effects on the herpes simplex virus in detail, all drugs were added at different stages during the viral infection. For comparison, all untreated controls contained the same concentration of ethanol as the drug-treated viruses, in order to exclude any influence of ethanol. When host cells were pretreated with drugs before infection, some of the drugs tested showed minor effects on viral infection. On the other hand, pretreatment of HSV-1 with oils or terpene compounds for 1 hour before infection caused a significant reduction in plaque formation. Aciclovir showed the highest antiviral activity when added during the replication period with an inhibition of viral replication of 98.6%. This drug specifically inhibits viral DNA polymerase during the replication cycle when new viral DNA is synthesized. However, only minor effects on viral infection were detected when cells or viruses were pretreated with acyclovir (data not shown). In contrast, when oils or compounds were added to the covering medium after virus penetration into host cells, plaque formation was not significantly reduced. The drugs were applied to HSV-1-infected cells after the viruses had penetrated the cells for 3 days. The number of viral plaques was determined 3 days after infection and compared with the untreated control. Results are expressed as percentage plaque reduction. These experiments were repeated independently, and the data presented represent the average of three experiments. HSV was incubated for 1 hour at room temperature with maximal noncytotoxic drug concentrations. The number of viral plaques was determined 3 days after infection and compared with the untreated control. Results are expressed as percentage plaque reduction. These experiments were repeated independently and the data presented represent the average of three experiments. Prior to viral infection, cells were incubated with maximal noncytotoxic concentrations of drugs for 1 h at 37°C. The number of viral plaques was determined 3 days after infection and compared with the untreated control..