Combined Anti-influenza Virus Effect of Synthetic and Natural Viral Inhibitors

The combined virus-inhibitory effects of a proteinaceous protease inhibitor, produced by Streptomyces sp. 225b (BF), rimantadine hydrochloride (Rim), ε-aminocaproic acid (ACA) and a polyphenol extract from Geranium sanguineum L. (PC) have been investigated on the reproduction of influenza virus A/Germany/34, strain Rostock (H7N1) in MDCK cell cultures. The simultaneous application of BF and PC, a plant preparation with established anti-influenza-virus activity, led to antagonistic virus-inhibitory effect. The combined use of BF and Rim, a selective anti-influenza drug, in doses, which by themselves do not suppress significantly viral replication, resulted in an additive increase of inhibition. The combinations BF+АСА, both of the preparations being proteolytic inhibitors, limited viral replication in a synergistic fashion. The results support the efficacy of combined chemotherapy; however to achieve a synergistic enhancement of the virusinhibitory effect it is essential to precisely select the doses of the individual components in the combinations. Introduction The∗ combined use of antiviral agents helps the enhancement of viral inhibition, the reduction of toxicity and the prevention of antiviral resistance. The application of natural and synthetic viral inhibitors in appropriate combinations also offers possibilities in this direction. This paper presents the results from the investigation of the combined virus-inhibitory effects of two synthetic inhibitors (rimantadine hydrochloride and ε-aminocaproic acid) and two inhibitors of natural ∗Abbreviation: BF protease inhibitor, produced by Streptomyces sp. 225b; CPE cytopathogenic effect; ACA ε-aminocaproic acid; IVY Infectious virus yield reduction assay; KIU Kunitz inhibitory units; MDCKMadin-Darby canine kidney cells; PC polyphenol extract from Geranium sanguineum L.; Rim rimantadine hydrochloride; TCID50 50% tissue culture infectious doses. origin (a protease inhibitor, produced by Streptomyces sp. 225b and a plant polyphenol extract). Materials and Methods Substances: Fermentation product from Streptomyces sp. 225b (BF): the strain is from the collection of the Department of Microbiology, Sofia University; the cultivation conditions and the partial purification were as in (1). Polyphenol extract from Geranium sanguineum L. (PC): the plant material and extraction were as in (7). Rimantadine hydrochloride (Rim) was purchased from Hoffman La Roche Inc., Nutley, NJ, USA. ε-aminocaproic acid (ACA) was a gift from Prof. V.P. Lozitsky, Odessa, Anti-plague Institute, Ukraine. Cells and Virus: MDCK cells, media for cultivation and influenza virus A/chicken/Germany/34, strain Rostock (H7N1) (A/Rostock) were as described in (1). Infectious virus yield (IVY) reduction