The synergistic effect of nsP2-L618, nsP3-R117, and E2-K187 on the large plaque phenotype of chikungunya virus

Attenuation of neurovirulence of chikungunya virus by a single amino acid mutation in viral E2 envelope protein

BACKGROUND

Chikungunya virus (CHIKV) has reemerged as a major public health concern, causing chikungunya fever with increasing cases and neurological complications.

METHODS

In the present study, we investigated a low-passage human isolate of the East/ Central/South African (ECSA) lineage of CHIKV strain LK(EH)CH6708, which exhibited a mix of small and large viral plaques. The small and large plaque variants were isolated and designated as CHIKV-SP and CHIKV-BP, respectively. CHIKV-SP and CHIKV-BP were characterized in vitro and in vivo to compare their virus production and virulence. Additionally, whole viral genome analysis and reverse genetics were employed to identify genomic virulence factors.

RESULTS

CHIKV-SP demonstrated lower virus production in mammalian cells and attenuated virulence in a murine model. On the other hand, CHIKV-BP induced higher pro-inflammatory cytokine levels, compromised the integrity of the blood-brain barrier, and led to astrocyte infection in mouse brains. Furthermore, the CHIKV-SP variant had limited transmission potential in Aedes albopictus mosquitoes, likely due to restricted dissemination. Whole viral genome analysis revealed multiple genetic mutations in the CHIKV-SP variant, including a Glycine (G) to Arginine (R) mutation at position 55 in the viral E2 glycoprotein. Reverse genetics experiments confirmed that the E2-G55R mutation alone was sufficient to reduce virus production in vitro and virulence in mice.

CONCLUSIONS

These findings highlight the attenuating effects of the E2-G55R mutation on CHIKV pathogenicity and neurovirulence and emphasize the importance of monitoring this mutation in natural infections.

Antiviral Activity of Kappaphycus alvarezii Seaweed against ZIKV

INTRODUCTION

Zika virus (ZIKV) is a flavivirus transmitted through the bites of infected Aedes mosquitoes. These viruses can also be transmitted through sexual contact, vertical transmission, and possibly transfusion. Most cases are asymptomatic, but symptoms can include rash, conjunctivitis, fever, and arthralgia, which are characteristic of other arboviruses. Zika infection can lead to complications such as microcephaly, miscarriage, brain abnormalities, and Guillain-Barré syndrome (GBS).

OBJECTIVE

The aim is to determine the inhibitory potential of the algae Kappaphycus alvarezii (K. alvarezii) on ZIKV replication.

METHODOLOGY

Cytotoxicity experiments were performed using Vero cells to determine the CC50, and ZIKV replication inhibition assays (ATCC® VR-1839™) were conducted to determine the EC50. The mechanism of action was also studied to assess any synergistic effect with Ribavirin.

RESULTS

K. alvarezii demonstrated low toxicity with a CC50 of 423 μg/mL and a potent effect on ZIKV replication with an EC50 of 0.65 μg/mL and a Selectivity Index (SI) of 651, indicating the extract's safety. Virucidal effect assays were carried out to evaluate the possible mechanism of action, and the compound addition time was studied, showing the potential to delay the treatment of infected cells by up to 6 hours. A potential synergistic effect was observed when K. alvarezii extract was combined with suboptimal concentrations of Ribavirin, resulting in 99% inhibition of viral replication.

CONCLUSION

Our data demonstrate the significant potential of K. alvarezii extract and highlight the need for further studies to investigate its mechanism of action. We propose this extract as a potential anti-Zika compound.

Pyrimidone inhibitors targeting Chikungunya Virus nsP3 macrodomain by fragment-based drug design

The macrodomain of nsP3 (nsP3MD) is highly conserved among the alphaviruses and ADP-ribosylhydrolase activity of Chikungunya Virus (CHIKV) nsP3MD is critical for CHIKV viral replication and virulence. No small molecule drugs targeting CHIKV nsP3 have been identified to date. Here we report small fragments that bind to nsP3MD which were discovered by virtually screening a fragment library and X-ray crystallography. These identified fragments share a similar scaffold, 2-pyrimidone-4-carboxylic acid, and are specifically bound to the ADP-ribose binding site of nsP3MD. Among the fragments, 2-oxo-5,6-benzopyrimidine-4-carboxylic acid showed anti-CHIKV activity with an IC50 of 23 μM. Our fragment-based drug discovery approach provides valuable information to further develop a specific and potent nsP3 inhibitor of CHIKV viral replication based on the 2-pyrimidone-4-carboxylic acid scaffold. In silico studies suggest this pyrimidone scaffold could also bind to the macrodomains of other alphaviruses and coronaviruses and thus, have potential pan-antiviral activity.

In Vitro Antiviral Activity Against Zika Virus From a Natural Product of the Brazilian Brown Seaweed Dictyota menstrualis

Natural products isolated from seaweeds have shown great antiviral potential against numerous viruses such as human type 1 herpes, human immunodeficiency virus, and dengue. Diterpenes produced by the brown seaweeds Dictyota and Canistrocarpus, in particular, have shown antiviral or virucidal activity. Recently, the Zika virus (ZIKV) has become a major public health concern due to its widespread dissemination throughout the Americas. Since no vaccines are available, and no drugs have effectively treated recent cases of infection, our group evaluated products from Dictyota menstrualis for their antiviral potential, alone and in combination with Ribavirin. We first evaluated the compounds’ cytotoxicity at high concentrations, and then evaluated the inhibition of ZIKV replication by crude extracts and acetylated crude extracts and their fractions at 20 μg/mL. The F-6 and FAc-2 fractions, rich in cyclic diterpenes with aldehyde groupings, inhibited ZIKV replication by >74%, with inhibition behaving in a dose-dependent manner and the 50% effective concentration (EC50) values of 2.80 (F-6) and 0.81 (FAc-2) μg/mL. Regarding the mechanism of action, FAc-2 had strong virucidal potential, and F-6 inhibited viral adsorption. Associating FAc-2 with Ribavirin at suboptimal dosages produced a strong synergistic effect that completely inhibited viral replication. Our results indicate that these natural products have excellent inhibitory potential against ZIKV replication and may be promising for developing affective therapies.