The medical importance of Zika virus (ZIKV) was fully highlighted during the recent epidemics in South Pacific islands and Americas due to ZIKV association with severe damage to fetal brain development and neurological complications in adult patients. A worldwide research effort has been undertaken to identify effective compounds to prevent or treat ZIKV infection. Fruits and vegetables may be sources of compounds with medicinal properties. Flavonoids are one class of plant compounds that emerge as promising antiviral molecules against ZIKV. In the present study, we demonstrated that flavonoid isoquercitrin exerts antiviral activity against African historical and Asian epidemic strains of ZIKV in human hepatoma, epithelial, and neuroblastoma cell lines. Time-of-drug addition assays showed that isoquercitrin acts on ZIKV entry by preventing the internalisation of virus particles into the host cell. Our data also suggest that the glycosylated moiety of isoquercitrin might play a role in the antiviral effect of the flavonoid against ZIKV. Our results highlight the importance of isoquercitrin as a promising natural antiviral compound to prevent ZIKV infection.

Zika virus (ZIKV) is a mosquito-borne flavivirus that recently emerged in the South Pacific, Americas, and Caribbean islands, where the larger epidemics were documented. ZIKV infection in humans is responsible for neurological disorders and microcephaly. Flavivirus NS1 is a non-structural glycoprotein that is expressed on the cell surface and secreted as a hexameric lipoprotein particle. Intracellular NS1 exists as a dimer that is required for viral replication, whereas the secreted NS1 hexamer interacts with host factors, leading to pathophysiological conditions. In an effort to dispose of specific anti-ZIKV NS1 immune serum, Vero cells were transduced with a lentiviral vector containing the NS1 gene from an epidemic strain of ZIKV. We showed that stably transduced Vero/ZIKV NS1 cell clone was efficient in the secretion of recombinant NS1 oligomer. Immunization of adult rat with purified extracellular NS1 developed anti-ZIKV antibodies that specifically react with the NS1 dimer produced in human cells infected with African and Asian strains of ZIKV. The rat antibody against ZIKV NS1 dimer is a reliable biological tool that enables the immunological detection of secreted NS1 from host-cells infected with ZIKV.

Heme oxygenase-1 (HO-1), a rate-limiting enzyme involved in the degradation of heme, is induced in response to a wide range of stress conditions. HO-1 exerts antiviral activity against a broad range of viruses, including the Hepatitis C virus, the human immunodeficiency virus, and the dengue virus by inhibiting viral growth. It has been reported that HO-1 displays antiviral activity against the Zika virus (ZIKV) but the mechanisms of viral inhibition remain largely unknown. Using a ZIKV RNA replicon with the Green Fluorescent Protein (GFP) as a reporter protein, we were able to show that HO-1 expression resulted in the inhibition of viral RNA replication. Conversely, we observed a decrease in HO-1 expression in cells replicating the ZIKV RNA replicon. The study of human cells infected with ZIKV showed that the HO-1 expression level was significantly lower once viral replication was established, thereby limiting the antiviral effect of HO-1. Our work highlights the capacity of ZIKV to thwart the anti-replicative activity of HO-1 in human cells. Therefore, the modulation of HO-1 as a novel therapeutic strategy against ZIKV infection may display limited effect.