So, the potential

synergistic effects between glucoevatromonoside and acyclovir were tested at different concentrations (Table 2). The results shown CI values <1 indicating synergism between these compounds. In the same way, Hartley et al. (2006) were able to demonstrate synergism between digoxin and furosemide and improvement of anti-adenovirus and anti-cytomegalovirus activity. These findings corroborate the potential antiherpetic activity of glucoevatromonoside and support its use Selleck MS 275 either alone or in combination with acyclovir for the treatment of herpes infections. Glucoevatromonoside is a natural cardiac glycoside, although its capacity of Na+K+ATPase inhibition has not been reported yet. Therefore, an anti-ATPase assay was performed to assess this potential Selleckchem Androgen Receptor Antagonist activity. Digoxigenin, digitoxin and digitoxin were used as positive controls (Pullen et al.,

2004), and digitoxose was used as a negative control. All tested cardenolides inhibited the Na+K+ATPase activity, and Table 3 shows the values of IC50. The Na+K+ATPase inhibition would justify the inhibition of virus release if the energy used by this process was obtained from this system (Nagai et al., 1972). Hence, the inhibition of viral protein synthesis caused by glucoevatromonoside could be explained by the reduction of K+ concentration into the cells, which is a consequence of the inhibition of this enzyme, since it is known that several enzymes, including those related to viral protein synthesis, require K+ for its activation (Di Cera, 2006). Due to the depletion of K+, it seems that the inhibition of viral

macromolecules by this cardenolide was not complete, because its antiviral activity was reversed when the K+ concentration was restored. Hence, we believe that the antiviral activity of glucoevatromonoside could be a consequence of its primary action on the cellular electrochemical gradient causing no damage to the host cells (Hartley Quinapyramine et al., 1993), and leading to a secondary action, which is the inhibition of viral replication. Accordingly, it acts discretely modifying the distribution and concentration of K+ intracellular ion, and also affecting the synthesis of essential co-factors in the viral replication. As it is well known, cardenolides have a long story of therapeutic applications and are frequently associated to systemic toxicity, but recent in vitro and in vivo toxicological results, and epidemiological data support new roles for such drugs in the treatment of several diseases, including cancer, neurological diseases and some viral infections ( Prassas and Diamandis, 2008). Taken together, the obtained results showed that glucoevatromonoside presents inhibitory effects of HSV-1 replication that seems to occur by the inhibition of viral protein synthesis (ICP27, UL42, gB and gD), the blockage of virus release, and the reduction of viral cell-to-cell spread.