Pentacyclic triterpenes in birch bark extract inhibit early step of herpes simplex virus type 1 replication M. Heidary Navid,.N. Laszczyk-Lauer, Reichling,. Schnitzler Abstract Antiviral
agents frequently applied for treatment of herpesvirus infections
include acyclovir and its derivatives. The antiviral effect of a
triterpene extract of birch bark and its major pentacyclic triterpenes,
i.e. betulin, lupeol and betulinic acid against acyclovir-sensitive
and acyclovir-resistant HSV type 1 strains was examined. The cytotoxic
effect of a phytochemically defined birch bark triterpene extract (TE)
as well as different pentacyclic triterpenes was analyzed in cell
culture, and revealed a moderate cytotoxicity on RC-37 cells. TE,
betulin, lupeol and betulinic acid exhibited high levels of antiviral
activity against HSV-1 in viral suspension tests with IC50 values
ranging between 0.2 and 0.5μg/ml. Infectivity of acyclovir-sensitive
and clinical isolates of acyclovir-resistant HSV-1 strains was
significantly reduced by all tested compounds and a direct
concentration- and time-dependent antiherpetic activity could be
demonstrated. In order to determine the mode of antiviral action, TE
and the compounds were added at different times during the viral
infection cycle. Addition of these drugs to uninfected cells prior to
infection or to herpesvirus-infected cells during intracellular
replication had low effect on virus multiplication. Minor virucidal
activity of triterpenes was observed, however both TE and tested
compounds exhibited high anti-herpetic activity when viruses were
pretreated with these drugs prior to infection. Pentacyclic triterpenes
inhibit acyclovir-sensitive and acyclovir-resistant clinical isolates
of HSV-1 in the early phase of infection. Source : Intl Journal of Phytotherapy and Phytopharmacology Link to Abstract