Introduction
Ginkgolic acids are alkylphenol constituents of the leaves and fruits of Ginkgo biloba. Ginkgo biloba extracts (GBE) have been used as herbal supplements since at least the 16th century and remain widely in use1. Major constituents of GBE include terpine trilactones (ginkgolide A, B, C, J, and bilobalide), flavonoid glycosides (quercetin and rutin), as well as Ginkgolic acids2. Ginkgolic acids are a mixture of several 2-hydroxy-6-alkylbenzoic acids in which the most common alkyl chains contain 13, 15, or 17 carbons. The 15 and 17 carbon chains are unsaturated at positions 8 and 10, respectively. The 3 Ginkgolic acid (GA) structures are, therefore, designated C13:0, C15:1, and C17:1 (Table S1)3.
GA has shown pleiotropic effects in vitro, including: antitumor effects through inhibition of lipogenesis; decreased expression of invasion associated proteins through AMPK activation; potential rescue of amyloid-β (Aβ) induced synaptic impairment; and inhibition of HIV protease activity as well as HIV viral replication4–7. GA was also reported to have activity against Escherichia coli and Staphylococcus aureus8. Several ways in which GA works have been suggested including by SUMOylation inhibition activity; blocking formation of the E1-SUMO intermediate9; inhibition of fatty acid synthase10; non-specific SIRT inhibition11; and activation of protein phosphatase type-2C12.
Here we report that GA shows antiviral activity against Herpes simplex virus 1 (HSV-1), Human cytomegalovirus (HCMV), and Zika virus (ZIKV) primarily through viral fusion inhibition. In addition, we show inhibition of entry of a replication-defective non-enveloped adenovirus. The antiviral effects were observed below the cytotoxic threshold. We believe that broad spectrum antiviral activity is achieved through the inhibition of viral entry and that this effect could be therapeutically utilized systemically in the context of severe acute viral disease, or topically for the treatment of cutaneous viral lesions. We show a broad spectrum of fusion inhibition by GA of all three classes of fusion proteins13 including: pathogenic human enveloped viruses from Class I (ZIKV, HIV, EBOV, and influenza A virus (IAV)), Class II (Venezuelan equine encephalitis virus (VEEV) and Semliki Forest virus (SFV)), and Class III (vesicular stomatitis virus (VSV) and Epstein Barr virus (EBV)). Taken together, our experiments suggest that GA inhibits viral entry by blocking the initial fusion event.