Indian Journal of Traditional Knowledge Vol. 17 (2), April 2018, pp 255-262 In vitro anti-herpes simplex virus activity, antioxidant potential and total phenolic compounds of selected Iranian medicinal plant extracts Mohammad-Taghi Moradi 1 , Ali Karimi 1 *, Somayeh Alidadi 2 & Leila Hashemi 3 1 Medical Plants Research Center; 2 Cellular and molecular Research Center; 3 Clinical Biochemistry Research Center, Basic Health Sciences Institute, Shahrekord University of Medical Science, Shahrekord, Iran E-mails: kakarimi42@gmail.com, mtmoradi65@gmail.com Received 11 September 2017, revised 17 January 2018 Drug resistant strains of herpes simplex virus-1 (HSV-1) have been increased recently. Essentially, medicinal plant-based new antiviral agents that are effective against HSV-1 infections are urgently required. Therefore, this research was conducted to evaluate in vitro anti HSV-1 activity of 25 plant extracts. In this study, the hydroalchoholic extracts of different parts of 25 medicinal plants belonging to 16 different families were prepared. Anti-HSV-1 activity was evaluated on Vero cell line using MTT (3-[4,5-dimethylthiazol–2-yl]-2,5-diphenyltetrazolium bromide) assay. The 50 % effective concentration (EC50) and 50 % cytotoxicity concentration (CC50) of the extract were determined using regression analysis. The inhibitory effect of the plant materials on adsorption and/or post-adsorption stages of HSV-1 replication cycle was determined. Antioxidant activity, total phenolic content, and total flavonoid content of the extracts were determined using 2, 2-diphenyl-1- picrylhydrazyl (DPPH) assay, Folin-Ciocalteu reagent, and aluminum chloride colorimetric method, respectively. Results showed that Pistacia atlantica Desf., Equisetum arvense L., Melissa officinalis L., Anthyllis vulneraria L., Punica granatum L., Syzygium aromaticum (L.) Merr. & L.M. Perry, Camellia sinensis (L.) Kuntze, and Crataegus azarolus L., were active against HSV-1. There was a significant association of total phenolic contents (R = 0.773, p < 0.001) and the free radical scavenging property (R = -0.684, p < 0.01) with the antiviral activity of the extracts. Some of the Iranian plant extracts studied showed potent antiviral activity against HSV-1 and can be used to develop new and effective anti-HSV-1 agents. Keywords: Antiviral activity, Herpes simplex virus, Antioxidant potential IPC Int. Cl. 8 : A61P31/12, C07K 14/035, A61K 39/245, C09K 15/00 Plants have the ability to synthesize a wide array of compounds and have long been used as remedies, with many of them being currently collected and examined to identify possible sources of herbal medicines 1 . Some medicinal plant extracts have been recently used for treatment of a few diseases 2 and some others have been evaluated to develop therapeutic agents with promising results 3-5 . Modern studies have shown that some of the medicinal plants with therapeutic application in traditional medicine 6-9 have antiviral effects. Many screening efforts have been made to seek out antiviral agents from natural sources 10-13 . Persia ancient civilization has a long history in identification of medicinal plants and treatment by these plants and Iranian scientists such as Avicenna have tried to develop this science. Infections caused by HSV-1 represent a public health concern worldwide. These infections range from mild to severe life threatening infections such as encephalitis 14 . During the past two decades, the mechanisms of replication and pathogenesis of HSV-1 and thus the potential antiviral targets in this virus have been thoroughly understood, leading to development of antiviral compounds for this virus 14 . A category of nucleoside analogues, acyclovir (ACV), is widely used to treat HSV-1 infections 15 . However, a major problem with the use of ACV, is the development of drug resistant HSV strains, particularly in AIDS patients 16 . This type of drug resistance may occur after long-term treatment and is mainly due to mutations in the HSV-1 thymidine kinase and/or DNA polymerase genes 17 . Therefore, antiviral, medicinal plant-based agents with active compounds that exhibiy different modes of action against viral infections are urgently needed. Iran is endowed with rich and diverse local health tradition, which is matched with its rich and diverse plant genetic source. Detailed investigations and documentation of plants used in local healthcare traditions and ethnopharmacological evaluation to —————— *Corresponding author