Ethnomedicinal products in the development of anti-herpesvirus agents
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BAY57-1293 inhibit helicase-primase of herpesvirus with potent in vitro and in vivo antiherpetic activity [Betz et al., 2002]; while n-docosanol is approved as a topical agent for herpes labialis by FDA [Sacks et al., 2001]. All these findings indicated that the herbal products are still potential sources for new antiherpetic agents. Due to the amazing structural diversity and broad range of bioactivities herbal medicinal products can be explored as a source of complementary antiherpetic agents, as many of them inhibit several steps of replication cycle and certain cellular factors of herpesviruses [Chattopadhyay & Khan, 2008]. The objective of this review is to summarize the potential uses of natural products, especially derived from herbal sources, for the prevention and treatment of infections caused by herpesviruses, especially the HSV-1 and HSV-2.
Screening models for herbal anti-HSV agents and their value in drug discovery In vitro primary screening assays Several in vitro and in vivo methods are available to study the antiherpetic activities of plant-derived products, but the most commonly used in vitro method for preliminary screening of extracts or compounds is the study of cytopathic effect (CPE) by plaque reduction assay on HSV-infected cells. Here the Hep2 or Vero Cells were grown in suitable cell culture media with incubation at 37 °C for 24 h. Confluent cell monolayers are then infected with 100-200 plaque-forming units (PFU) of the virus. After 1h incubation (to allow viral adsorption), the cells are washed with phosphate buffer saline (PBS) and overlaid with agar in cell culture medium containing twofold dilutions of the extracts or test compounds, and recultured at 370C, until plaques appeared. Finally the monolayer cells are fixed with formalin, stained, dried and the number of plaques are microscopically counted. The percentage inhibition of plaque formation [(mean number of plaques in control − mean number of plaques in test)/(mean number of plaques in control) × 100], or the effective concentration for 50% plaque reduction [EC50; the lowest extract concentration that reduced plaque number by 50% in the treated cultures compared to untreated ones], or the 50% inhibitory concentration [IC50; the extract concentration required to reduce the virus plaque number by 50%] is calculated. When different herbal preparations (cold aqueous, hot aqueous, ethanolic, acid ethanolic, and methanolic) were analyzed by plaque reduction assay, it was observed that the ethanolic extract of Rheum officinale and methanol extract of Paeonia suffruticosa inhibit attachment and penetration of HSV-1; while the aqueous extract of P. suffruticosa and ethanolic extract of Melia toosendan inhibit attachment and replication of HSV-1 and HSV-2 [Hsiang et al.,