A prodelphinidin-rich extract from Pelargonium sidoides DC, EPs® 7630 (Umckaloabo®), which is licensed to treat respiratory tract infections such as acute bronchitis, was investigated for its antiviral effects. EPs® 7630 showed dose-dependent anti-influenza activity at non-toxic concentrations against pandemic H1N1, oseltamivir-sensitive and -resistant seasonal H1N1, seasonal H3N2 and the laboratory H1N1 strain A/Puerto Rico/8/34, while it had no antiviral activity against adenovirus or measles virus. The extract inhibited an early step of influenza infection and impaired viral hemagglutination as well as neuraminidase activity. However, EPs® 7630 did not exhibit a direct virucidal effect, as virus preincubation (unlike cell preincubation) with the extract did not influence infectivity. Importantly, EPs® 7630 showed no propensity to resistance development in vitro. Analysis of EPs® 7630 constituents revealed that prodelphinidins represent the active principle. Chain length influenced antiviral activity, as monomers and dimers were less effective than oligo- and polymers. Importantly, gallocatechin and its stereoisomer epigallocatechin exert antiviral activity also in their monomeric form. In addition, EPs® 7630 administered by inhalation significantly improved survival, body weight and body temperature of influenza-infected mice, without obvious toxicity, demonstrating the benefit of EPs® 7630 in treatment of influenza.
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