The old pharmaceutical oleoresin labdanum of Cistus creticus L. exerts pronounced in vitro anti-dengue virus activity.

ETHNOPHARMACOLOGICAL RELEVANCE: The haemorrhagic dengue fever affects up to 500 million patients, annually causing 20.000 deaths, with no chemotherapeutic agent available. The oleoresin labdanum of Cistus creticus L. has been established as an anti-infective agent since antiquity in Mediterranean ethnopharmacology. MATERIALS AND METHODS: We tested several extracts and fractions of labdanum - standardised on labdane-type diterpenes via GC-MS - on their activity against the dengue virus (DENV-2 strain 00st-22A) in in vitro Vero cell cultures (96-well-plates, 5 days). Preliminary experiments with a labdanum diethyl ether raw-extract did not yield measureable results due to cytotoxic effects against Vero cells. In all following experiments, cell viability was constantly checked using the MTT-test. Fractionation of this raw-extract by liquid-liquid-extraction and column-chromatography on silica-gel (gradient elution with hexane, EtOAc, CHCl3, MeOH) succeeded in separating the anti-viral activity of labdanum from its cytotoxic effect. RESULTS: In the most active fraction GS5 at 30 µg/ml, dengue virus proliferation was 100% suppressed and cell viability was over 90%. Structural elucidation of major constituents of GS5 is currently ongoing, but thin-layer chromatography showed that this fraction is mainly dominated by manoyloxides, a class of labdane-type diterpenes with known antimicrobial activity. Claims concerning the antiviral activity of above ground parts of C. creticus have been made previously, but these generally ascribe this activity to hot water soluble polyphenols and propose an unspecific tanning effect of the viral surface proteins as the mechanism of action. However, the water soluble fraction enhanced viral proliferation. CONCLUSION: We therefore describe a direct, pharmacological, antiviral activity of a diethyl ether extract of labdanum against a virulent haemorrhagic fever like dengue for the first time.

Inhibitory effect of the green tea molecule EGCG against dengue virus infection.

Dengue virus (DENV) infection is a major public health problem worldwide; however, specific antiviral drugs against it are not available. Hence, identifying effective antiviral agents for the prevention of DENV infection is important. In this study, we showed that the reportedly highly biologically active green-tea component epigallocatechin gallate (EGCG) inhibited dengue virus infection regardless of infecting serotype, but no or minimal inhibition was observed with other flaviviruses, including Japanese encephalitis virus, yellow fever virus, and Zika virus. EGCG exerted its antiviral effect mainly at the early stage of infection, probably by interacting directly with virions to prevent virus infection. Our results suggest that EGCG specifically targets DENV and might be used as a lead structure to develop an antiviral drug for use against the virus.