In vitro antiviral activity of Melaleuca alternifolia essential oil

Aims:  To investigate the in vitro antiviral activity of Melaleuca alternifolia essential oil (TTO) and its main components, terpinen-4-ol, α-terpinene, γ-terpinene, p -cymene, terpinolene and α-terpineol.
Methods and Results:  The antiviral activity of tested compounds was evaluated against polio type 1, ECHO 9, Coxsackie B1, adeno type 2, herpes simplex (HSV) type 1 and 2 viruses by 50% plaque reduction assay. The anti-influenza virus assay was based on the inhibition of the virus-induced cytopathogenicity. Results obtained from our screening demonstrated that the TTO and some of its components (the terpinen-4-ol, the terpinolene, the α-terpineol) have an inhibitory effect on influenza A/PR/8 virus subtype H1N1 replication at doses below the cytotoxic dose. The ID₅₀ value of the TTO was found to be 0·0006% (v/v) and was much lower than its CD₅₀ (0·025% v/v). All the compounds were ineffective against polio 1, adeno 2, ECHO 9, Coxsackie B1, HSV-1 and HSV-2. None of the tested compounds showed virucidal activity. Only a slight virucidal effect was observed for TTO (0·125% v/v) against HSV-1 and HSV-2.
Conclusions:  These data show that TTO has an antiviral activity against influenza A/PR/8 virus subtype H1N1 and that antiviral activity has been principally attributed to terpinen-4-ol, the main active component.
Significance and Impact of the Study:  TTO should be a promising drug in the treatment of influenza virus infection.     

Virucidal effect of peppermint oil on the enveloped viruses herpes simplex virus type 1 and type 2 in vitro

The virucidal effect of peppermint oil, the essential oil of Mentha piperita, against herpes simplex virus was examined. The inhibitory activity against herpes simplex virus type 1 (HSV-1) and herpes simplex virus type 2 (HSV-2) was tested in vitro on RC-37 cells using a plaque reduction assay. The 50% inhibitory concentration (IC50) of peppermint oil for herpes simplex virus plaque formation was determined at 0.002% and 0.0008% for HSV-1 and HSV-2, respectively. Peppermint oil exhibited high levels of virucidal activity against HSV-1 and HSV-2 in viral suspension tests. At noncytotoxic concentrations of the oil, plaque formation was significantly reduced by 82% and 92% for HSV-1 and HSV-2, respectively. Higher concentrations of peppermint oil reduced viral titers of both herpesviruses by more than 90%. A clearly time-dependent activity could be demonstrated, after 3 h of incubation of herpes simplex virus with peppermint oil an antiviral activity of about 99% could be demonstrated. In order to determine the mode of antiviral action of the essential oil, peppermint oil was added at different times to the cells or viruses during infection. Both herpesviruses were significantly inhibited when herpes simplex virus was pretreated with the essential oil prior to adsorption. These results indicate that peppermint oil affected the virus before adsorption, but not after penetration into the host cell. Thus this essential oil is capable to exert a direct virucidal effect on HSV. Peppermint oil is also active against an acyclovir resistant strain of HSV-1 (HSV-1-ACV(res)), plaque formation was significantly reduced by 99%. Considering the lipophilic nature of the oil which enables it to penetrate the skin, peppermint oil might be suitable for topical therapeutic use as virucidal agent in recurrent herpes infection.     

Anti-herpesvirus activities of Pseudomonas sp. S-17 rhamnolipid and its complex with alginate

The rhamnolipid biosurfactant PS-17 and its complex with the polysaccharide alginate, both produced by the Pseudomonas sp. S-17 strain, were studied for their antiviral activity against herpes simplex virus (HSV) types 1 and 2. They significantly inhibited the herpesvirus cytopathic effect (CPE) in the Madin-Darby bovine kidney (MDBK) cell line. The investigations were carried out according to the CPE inhibition assay protocol. The suppressive effect of the compounds on HSV replication was dose-dependent and occurred at concentrations lower than the critical micelle concentration of the surfactant. The 50% inhibitory concentration (IC50) of rhamnolipid PS-17 was 14.5 microg/ml against HSV-1 and 13 microg/ml against HSV-2. The IC50 values of the complex were 435 microg/ml for HSV-1 and 482 microg/ml for HSV-2. The inhibitory effects of the substances were confirmed by measuring the infectious virus yields with the multicycle virus growth experimental design as well: deltalog CCID50 of 1.84-2.0 against the two types of herpes simplex viruses by rhamnolipid PS-17 (20 microg/ml), and a strong reduction of the HSV-2 virus yield under the effect of the alginate complex at a concentration of 450 microg/ml. The results indicate that rhamnolipid PS-17 and its alginate complex may be considered as promising substances for the development of anti-herpetic compounds.     

6-Azathymidine-4'-thionucleosides: synthesis and antiviral evaluation

The synthesis of dideoxy-6-azathymidine 4'-thionucleoside 1-(2,3-dideoxy-4-thio-beta-D-erythro-pentofuranosyl)-(6-azathymidine) (2), and the L-nucleoside, 1-(4-thio-beta-L-erythro-pentofuranosyl)-(6-azathymidine) (3) and their evaluation against a wide panel of antiviral assays are described. The L-thionucleoside (3) was devoid of antiviral activity. The dideoxy-thionucleoside (2) was moderately active against vaccinia virus (VV) and the herpes simplex virus strains HSV-1 (strain KOS) and HSV-2 (strain G) (MIC 12 microM) and retained inhibitory activity vs a thymidine kinase-deficient strain HSV-1/TK(-), suggesting that (2) is not dependent on viral TK-catalysed phosphorylation for antiviral activity and/or may use an alternative metabolic activation pathway.     

Inhibitory effect of sulfated galactans from the marine alga Bostrychia montagnei on herpes simplex virus replication in vitro.

Sulfated polysaccharides exhibit many biological properties such as antiviral and anticoagulant activities. Herein, we report the antiviral activity of sulfated galactans extracted from the red sea-weed Bostrychia montagnei against herpes simplex virus types 1 (strain F and the thymidine kinase-deficient strains Field and B2006) and 2 (strain G). Two crude extracts obtained with cold and hot water as well as some fractions obtained by anion exchange chromatography, inhibited significantly the replication of the different strains of herpesviruses as determined by plaque reduction assays. The inhibitory effect of the compounds studied here took place only when they were added during the adsorption period. They were found to be highly selective antiviral substances, causing no impairment of Vero cell viability. Furthermore, they had no direct inactivating effect on virions by incubation in a virucidal assay. The antiviral activity could be correlated with the molecular weight and sulfate content of the polysaccharides. Although sulfated polysaccharides are generally endowed with anticoagulant properties, the results of the activated partial thromboplastin time and the thrombine time assays indicated that the natural sulfated polysaccharides from Bostrychia montagnei have very low anticoagulant activity, confirming that there is no relation between the antiviral and anticoagulant properties.     

Structural features and in vitro antiviral activities of sulfated polysaccharides from Sphacelaria indica

Many viruses display affinity for cell surface heparan sulfate proteoglycans with biological relevance to virus entry. This raises the possibility of the application of sulfated polysaccharides in antiviral therapy. In this study, we have analyzed xylogalactofucan- and alginic acid-containing fractions from Sphacelaria indica, a marine alga. The xylogalactofucan that has apparent molecular mass of 26±5 kDa and negative specific rotation [α](D)(32) -71° (c 0.2, H(2)O) contains, inter alia, (1→3)-linked L-fucopyranosyl and D-galactopyranosyl residues. The algin (molecular mass: 21±5kDa) contains 41% guluronic and 59% mannuronic acid residues. The 50% inhibitory concentration (IC(50)) values of these macromolecules and their chemically sulfated derivatives against herpes simplex virus type 1 (HSV-1) were in the range of 0.6-10 μg ml(-1) and they lacked cytotoxicity at concentrations up to 200 μg ml(-1). The antiviral activity was dependent on the sulfate contents of the polysaccharides. The results support the feasibility of inhibiting HSV infection by direct interaction of polysaccharides with viral particles.     

Antiviral property and mechanisms of a sulphated polysaccharide from the brown alga Sargassum patens against Herpes simplex virus type 1

A sulphated polysaccharide (SP-2a) from the brown alga Sargassum patens (Kütz.) Agardh (Sargassaceae) was found to significantly inhibit the in vitro replication of both the acyclovir (ACV)-sensitive and -resistant strains of Herpes simplex virus type 1 (HSV-1), in dose-dependent manners, with 50% inhibitions occurring with 1.5–5.3 μg/ml of the polysaccharide. SP-2a exhibited extracellular virucidal activity only against the ACV-sensitive strains, but not the resistant strain, at the concentration of 100 μg/ml. The strongest antiviral activities against the different strains of HSV-1 were observed when this polysaccharide was present during and after adsorption of the virus to host cells. The inhibitory effect of SP-2a on virus adsorption occurred dose-dependently in all the HSV-1 strains tested, and the adsorption of the ACV-resistant DM2.1 strain was reduced by 81.9% (relative to control) with 4 μg/ml of the polysaccharide. This study clearly demonstrated that the antiviral mode of action of SP-2a is mediated mainly by inhibiting virus attachment to host cells, and this sulphated polysaccharide might have different modes of action against the ACV-sensitive and -resistant strains of HSV-1.     

Synthesis and anti-herpes simplex viral activity of monoglycosyl diglycerides

Based on the discovery of antiviral beta-galactosyl diglycerides from Clinacanthus nutans leaves, 19 monoglycosyl diglycerides were synthesized and examined for inhibitory effect on herpes simplex virus types 1 and 2 (HSV-1, HSV-2). A study of the structure-activity relationships of the synthetic monoglycosyl diglycerides indicated that the fatty acyl moieties were critical for inhibitory action with higher activity displayed as the acyl groups became more olefinic in character. The sugar moiety was also important for anti-HSV action; however, the type of sugar (glucose or galactose) did not affect activity. The stereochemistry at C-2 of the glycerol backbone displayed no significant effect on anti-HSV activity. Among the compounds synthesized, 1,2-O-dilinolenoyl-3-O-beta-D-glucopyranosyl-sn-glycerol showed the highest inhibitory activity against HSV-1 and HSV-2 with IC50 values of 12.5+/-0.5 and 18.5+/-1.5 microg/ml, respectively.     

In vitro antiherpetic and antirotaviral activities of a sulfate prepared from Mimosa scabrella galactomannan

A chemically sulfated galactomannan (BRS) from seeds of Mimosa scabrella had in vitro antiviral activity against Herpes simplex virus 1 (HSV-1), but not against Simian rotavirus A/SA11 (SiRV-A/SA11). It was examined by ¹³C NMR spectroscopy, which showed the sulfate groups to be mainly at C-6 of galactose residues. BRS had a selective inhibition against HSV-1 during its attachment step, having an IC₅₀ lower than 2.5 μg/ml, determined by plaque reduction, and a selectivity index of greater than 181, suggesting that the antiviral effect is likely due to interactions between the virus and BRS, being influenced its overall surface charge.     

Synthesis and anti-HSV activity of tricyclic penciclovir and hydroxybutylguanine derivatives

A series of tricyclic penciclovir (PCV) and hydroxybutylguanine (HBG) derivatives have been prepared with enhanced lipophilicity following an efficient synthetic route. All the novel tricyclic derivatives were evaluated for inhibitory activity against herpes simplex virus 1 and 2 (HSV-1, HSV-2) and thymidine kinase deficient (ACV resistant) HSV-1. The tricyclic HBG derivatives were devoid of inhibitory activity however several of the tricyclic PCV derivatives showed promising antiviral activity, in particular 9g (R?=?4-MeO-C₆H₄) displayed good inhibitory activity (HSV-1 EC₅₀ 1.5?μM, HSV-2 EC₅₀ 0.8?μM) and retained inhibitory activity in HSV-1 TK^? cells (EC₅₀ 0.8?μM). Computational docking experiments supported the biological data observed and this preliminary study provides useful data for further development of tricyclic acyclic nucleoside derivatives with improved lipophilicity and retention of activity in HSV-1 TK deficient strains. Also, the new tricyclic derivatives were evaluated against a broad range of other DNA and RNA viruses, but were found to be inactive at subtoxic concentrations. In addition, weak to moderate cytostatic effect was observed for the new compounds.     

Antiviral properties of fucoidan fractions from Leathesia difformis.

Three fractions of fucoidans isolated from the brown seaweed Leathesia difformis (Ee, Ec and Ea) were found to be selective antiviral agents against herpes simplex virus (HSV) types 1 and 2 and human cytomegalovirus. Fraction Ea was the most active, with IC50 values in the range 0.5-1.9 microg/ml without affecting cell viability at concentrations up to 400 microg/ml. The antiherpetic activity of Ea was assessed by three different methods, plaque reduction, inhibition of virus yield and prevention of HSV-2 induced shut-off of cell protein synthesis, demonstrating that the inhibitory effect was independent of the antiviral assay and the multiplicity of infection. The mode of action of Ea could be ascribed to an inhibitory action on virus adsorption. The fucoidans did not inhibit the blood coagulation process even at concentrations exceeding more than 100 times the IC50 value.     

Lambda interferon (IFN-lambda), a type III IFN, is induced by viruses and IFNs and displays potent antiviral activity against select virus infections in vivo

Type III interferons (IFNs) (interleukin-28/29 or lambda interferon [IFN-lambda]) are cytokines with IFN-like activities. Here we show that several classes of viruses induce expression of IFN-lambda1 and -lambda2/3 in similar patterns. The IFN-lambdas were-unlike alpha/beta interferon (IFN-alpha/beta)-induced directly by stimulation with IFN-alpha or -lambda, thus identifying type III IFNs as IFN-stimulated genes. In vitro assays revealed that IFN-lambdas have appreciable antiviral activity against encephalomyocarditis virus (EMCV) but limited activity against herpes simplex virus type 2 (HSV-2), whereas IFN-alpha potently restricted both viruses. Using three murine models for generalized virus infections, we found that while recombinant IFN-alpha reduced the viral load after infection with EMCV, lymphocytic choriomeningitis virus (LCMV), and HSV-2, treatment with recombinant IFN-lambda in vivo did not affect viral load after infection with EMCV or LCMV but did reduce the hepatic viral titer of HSV-2. In a model for a localized HSV-2 infection, we further found that IFN-lambda completely blocked virus replication in the vaginal mucosa and totally prevented development of disease, in contrast to IFN-alpha, which had a more modest antiviral activity. Finally, pretreatment with IFN-lambda enhanced the levels of IFN-gamma in serum after HSV-2 infection. Thus, type III IFNs are expressed in response to most viruses and display potent antiviral activity in vivo against select viruses. The discrepancy between the observed antiviral activity in vitro and in vivo may suggest that IFN-lambda exerts a significant portion of its antiviral activity in vivo via stimulation of the immune system rather than through induction of the antiviral state.     

Antiviral activity against dengue virus of diverse classes of algal sulfated polysaccharides

Diverse classes of sulfated polysaccharides obtained from the red seaweeds (Rhodophyta) Grateloupia indica, Scinaia hatei and Gracilaria corticata, the brown seaweeds (Phaeophyta) Stoechospermum marginatum and Cystoseira indica and the green seaweed (Chlorophyta) Caulerpa racemosa were assayed for antiviral activity against the four serotypes of dengue virus (DENV). DENV-2 was the most susceptible serotype to all polysulfates, with inhibitory concentration 50% values in the range 0.12-20μg/mL. The antiviral potency of the sulfated polysaccharides depended on the sulfate content, the position of sulfate group, the sugar composition, and the molar mass. Independently of the sugar composition, the antiviral effect was mainly exerted during DENV-2 adsorption and internalization.     

In vitro inhibition of herpes simplex virus type 1 replication by Mentha suaveolens essential oil and its main component piperitenone oxide

Several essential oils exert in vitro activity against bacteria and viruses and, among these latter, herpes simplex virus type 1 (HSV-1) is known to develop resistance to commonly used antiviral agents. Thus, the effects of the essential oil derived from Mentha suaveolens (EOMS) and its active principle piperitenone oxide (PEO) were tested in in vitro experimental model of infection with HSV-1. The 50% inhibitory concentration (IC₅₀) was determined at 5.1 μg/ml and 1.4 μg/ml for EOMS and PEO, respectively. Australian tea tree oil (TTO) was used as control, revealing an IC₅₀ of 13.2 μg/ml. Moreover, a synergistic action against HSV-1 was observed when each oil was added in combination with acyclovir. In order to find out the mechanism of action, EOMS, PEO and TTO were added to the cells at different times during the virus life-cycle. Results obtained by yield reduction assay indicated that the antiviral activity of both compounds was principally due to an effect after viral adsorption. Indeed, no reduction of virus yield was observed when cells were treated during viral adsorption or pre-treated before viral infection. In particular, PEO exerted a strong inhibitory effect by interfering with a late step of HSV-1 life-cycle. HSV-1 infection is known to induce a pro-oxidative state with depletion of the main intracellular antioxidant glutathione and this redox change in the cell is important for viral replication. Interestingly, the treatment with PEO corrected this deficit, thus suggesting that the compound could interfere with some redox-sensitive cellular pathways exploited for viral replication. Overall our data suggest that both EOMS and PEO could be considered good candidates for novel anti-HSV-1 strategies, and need further exploration to better characterize the targets underlying their inhibition.     

ACYCLIC/CARBOCYCLIC GUANOSINE ANALOGUES AS ANTI-HERPESVIRUS AGENTS

Several guanosine analogues, i.e. acyclovir (and its oral prodrug valaciclovir), penciclovir (in its oral prodrug form, famciclovir) and ganciclovir, are widely used for the treatment of herpesvirus [i.e. herpes simplex virus type 1 (HSV-1), and type 2 (HSV-2),varicella-zoster virus (VZV) and/or human cytomegalovirus (HCMV)] infections. In recent years, several new guanosine analogues have been developed, including the 3-membered cyclopropylmethyl and-methenyl derivatives (A-5021 and synguanol) and the 6-membered D-and L-cyclohexenyl derivatives. The activity of the acyclic/carbocyclic guanosine analogues has been determined against a wide spectrum of viruses, including the HSV-1, HSV-2, VZV, HCMV, and also human herpesviruses type 6 (HHV-6), type 7 (HHV-7) and type 8 (HHV-8), and hepatitis B virus (HBV). The new guanosine analogues (i.e. A-5021 and D- and L-cyclohexenyl G) were found to be particularly active against those viruses (HSV-1, HSV-2, VZV) that encode for a specific thymidine kinase (TK), suggesting that their antiviral activity (at least partially) depends on phosphorylation by the virus-induced TK. Marked antiviral activity was also noted with A-5021 against HHV-6 and with D- and L-cyclohexenyl G against HCMV and HBV. The antiviral activity of the acyclic/carbocyclic nucleoside analogues could be markedly potentiated by mycophenolic acid, a potent inhibitor of inosine 5′-monophosphate (IMP) dehydrogenase. The new carbocyclic guanosine analogues (i.e. A-5021 and D- andL-cyclohexenyl G) hold great promise, not only as antiviral agents for the treatment of herpesvirus infections, but also an antitumor agents for the combined gene therapy/chemotherapy of cancer, provided that (part of) the tumor cells have been transduced by the viral (HSV-1, VZV) TK gene.     

Acyclic/carbocyclic guanosine analogues as anti-herpesvirus agents

Several guanosine analogues, i.e. acyclovir (and its oral prodrug valaciclovir), penciclovir (in its oral prodrug form, famciclovir) and ganciclovir, are widely used for the treatment of herpesvirus [i.e. herpes simplex virus type 1 (HSV-1), and type 2 (HSV-2), varicella-zoster virus (VZV) and/or human cytomegalovirus (HCMV)] infections. In recent years, several new guanosine analogues have been developed, including the 3-membered cyclopropylmethyl and -methenyl derivatives (A-5021 and synguanol) and the 6-membered D- and L-cyclohexenyl derivatives. The activity of the acyclic/carbocyclic guanosine analogues has been determined against a wide spectrum of viruses, including the HSV-1, HSV-2, VZV, HCMV, and also human herpesviruses type 6 (HHV-6), type 7 (HHV-7) and type 8 (HHV-8), and hepatitis B virus (HBV). The new guanosine analogues (i.e. A-5021 and D- and L-cyclohexenyl G) were found to be particularly active against those viruses (HSV-1, HSV-2, VZV) that encode for a specific thymidine kinase (TK), suggesting that their antiviral activity (at least partially) depends on phosphorylation by the virus-induced TK. Marked antiviral activity was also noted with A-5021 against HHV-6 and with D- and L-cyclohexenyl G against HCMV and HBV. The antiviral activity of the acyclic/carbocyclic nucleoside analogues could be markedly potentiated by mycophenolic acid, a potent inhibitor of inosine 5'-monophosphate (IMP) dehydrogenase. The new carbocyclic guanosine analogues (i.e. A-5021 and D- and L-cyclohexenyl G) hold great promise, not only as antiviral agents for the treatment of herpesvirus infections, but also an antitumor agents for the combined gene therapy/chemotherapy of cancer, provided that (part of) the tumor cells have been transduced by the viral (HSV-1, VZV) TK gene.     

Activity of Porphyridium sp. polysaccharide against herpes simplex viruses in vitro and in vivo.

The cell wall sulfated polysaccharide of the red microalga Porphyridium sp. exhibited impressive antiviral activity against herpes simplex virus types 1 and 2 (HSV-1 and -2) both in vitro (cell culture) and in vivo (rats and rabbits). Depending on the concentration, this polysaccharide completely inhibited or slowed down the development of the cytopathic effect in HSV-infected cells, but did not show any cytotoxic effects on vero cells even when a concentration as high as 250 μg/ml was used. There was indirect evidence for a strong interaction between the polysaccharide and HSV and a weak interaction with the cell surface. When tested in vivo, Porphyridium sp. polysaccharide conferred significant and efficient protection against HSV-1 infection: at a concentration as low as 100 μg/ml, it prevented the appearance and development of symptoms of HSV-1 infection in rats and rabbits. The polysaccharide did not exhibit any cytotoxic effects at a concentration of 2 mg/ml in vivo.     

Synthesis and in vitro anti-HSV-1 activity of a novel Hsp90 inhibitor BJ-B11

In this study, a novel Hsp90 inhibitor BJ-B11, was synthesized and evaluated for in vitro antiviral activity against several viruses. Possible anti-HSV-1 mechanisms were also investigated. BJ-B11 displayed no antiviral activity against coxsackievirus B₃ (CVB₃), human respiratory syncytial virus (RSV) and influenza virus (H1N1), but exhibited potent anti-HSV-1 and HSV-2 activity with EC₅₀ values of 0.42 ± 0.18 μM and 0.60 ± 0.21 μM, respectively. Additionally, the inhibitory effects of BJ-B11 against HSV-1 were likely to be introduced at early stage of infection. Our results indicate that BJ-B11 with alternative mechanisms of action is potent as an anti-HSV clinical trial candidate.     

The enantiomers of carbocyclic 5'-norguanosine: activity towards Epstein-Barr virus

(-)-5'-noraristeromycin (1) has shown antiviral activity towards, particularly cytomegalovirus, vaccinia virus and measles while its (+)-enantiomer (2) is effective towards hepatitis B virus. To determine if the antiviral characteristics of 1 and 2 extended to the guanine analogues (3 and 4), these enantiomers were prepared and evaluated against herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2), cytomegalovirus (CMV), varicella zoster virus (VZV), Epstein-Barr virus (EBV), human herpes virus type 6 (HHV-6), human herpes virus type 8 (HHV-8), vaccinia virus (VV), cowpox virus (CV), vesicular stomatitis virus (VSV), respiratory syncytial virus (RSV), hepatitis B virus (HBV), and human immunodeficiency virus type 1 (HIV-1) and type 2 (HIV-2). The only activity found for 3 was for Epstein-Barr virus in VCA Elisa (EC50 0.78 microg/mL), immunofluorescence assay for VCA or gp 350/250 (1.8-4.0 microg/mL) and DNA hybridization (EC50 0.82 microg/mL) assays with no accompanying toxicity seen in the host Daudi cells. No activity was noted for 4.     

Comparison of disc diffusion, Etest and broth microdilution for testing susceptibility of carbapenem-resistant P. aeruginosa to polymyxins

Background

New prophylactic and therapeutic tools are needed for the treatment of herpes simplex virus infections. Several essential oils have shown to possess antiviral activity in vitro against a wide spectrum of viruses.

Aim

The present study was assess to investigate the activities of the essential oil obtained from leaves of Artemisia arborescens against HSV-1 and HSV-2

Methods

The cytotoxicity in Vero cells was evaluated by the MTT reduction method. The IC₅₀ values were determined by plaque reduction assay. In order to characterize the mechanism of action, yield reduction assay, inhibition of plaque development assay, attachment assay, penetration assay and post-attachment virus neutralization assay were also performed.

Results

The IC₅₀ values, determined by plaque reduction assay, were 2.4 and 4.1 μg/ml for HSV-1 and HSV-2, respectively, while the cytotoxicity assay against Vero cells, as determined by the MTT reduction method, showed a CC₅₀ value of 132 μg/ml, indicating a CC₅₀/IC₅₀ ratio of 55 for HSV-1 and 32.2 for HSV-2. The antiviral activity of A. arborescens essential oil is principally due to direct virucidal effects. A poor activity determined by yield reduction assay was observed against HSV-1 at higher concentrations when added to cultures of infected cells. No inhibition was observed by attachment assay, penetration assay and post-attachment virus neutralization assay. Furthermore, inhibition of plaque development assay showed that A. arborescens essential oil inhibits the lateral diffusion of both HSV-1 and HSV-2.

Conclusion

This study demonstrates the antiviral activity of the essential oil in toto obtained from A. arborescens against HSV-1 and HSV-2. The mode of action of the essential oil as antiherpesvirus agent seems to be particularly interesting in consideration of its ability to inactivate the virus and to inhibit the cell-to-cell virus diffusion.