Antiviral Activity Against Chikungunya Virus of Diterpenes from the Seaweed Dictyota menstrualis

Chikungunya virus infection has become one of the most challenging re-emergent viral infections. Given that there is as yet no vaccine or effective drugs against chikungunya virus, our group evaluated products from Dictyota menstrualis (Hoyt) Schnetter, Horning, & Weber-Peukert 1987, Dictyoteae, for their antiviral potential. We evaluated whether crude extracts, acetylated crude extracts, and their fractions could inhibit chikungunya virus replication. The F-5 and FAc-1 fractions, rich in cyclic diterpenes with aldehyde groupings, inhibited replication by >96%, in a dose-dependent manner and the concentration of a drug that gives half-maximal response (EC50) values of 0.90 (F-5) and 0.73 (FAc-1) mu g/ml. Virucidal assay, where 20 mu g/ml of F-5 showed a strong effect, reducing chikungunya virus infectivity by up to 88%. Associating F-5 and FAc-1 with ribavirin at suboptimal dosages produced a synergistic effect that completely inhibited viral replication. Time addition experiments demonstrate that F-5 was greater than 85% even if added at 16 h after infection. Our results indicate that these natural products have an excellent inhibitory potential against chikungunya virus replication.