Stinging nettle extract inhibits SARS-CoV-2 cell fusion

In a recent study posted to the bioRxiv* preprint server, researchers at Ghent University and KU Leuven, Belgium, demonstrated that Urtica dioica agglutinin (UDA), a monomeric lectin extracted from stinging nettle rhizomes, inhibited severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants of concern (VOCs) cell to cell fusion.

Study: Carbohydrate-Binding Protein from Stinging Nettle as Fusion Inhibitor for SARS-CoV-2 Variants of Concern. Image Credit: Craig Walton / Shutterstock

Background

From the initial 41 coronavirus disease 2019 (COVID-19) patients in Hubei province, China, the SARS-CoV-2 quickly expanded to become a global pandemic with over 556 million confirmed infections and more than 6.35 million fatalities in just over two and a half years.

The current study's authors previously identified plant lectins as a distinct class of antiviral compounds. A carbohydrates-attaching tiny monomeric protein called UDA was discovered in the rhizomes of stinging nettle plants. 

UDA selectively hinders the replication of numerous viruses, including coronaviruses, in different cell kinds. Prior studies with respiratory syncytial virus (RSV), human immunodeficiency virus (HIV), and influenza virus demonstrated that UDA impedes viral entry, possibly by blocking virus fusion.

Notably, the ongoing SARS-CoV-2 pandemic emphasizes the necessity for a broad-spectrum antiviral agent that can be employed immediately to quickly reduce viral transmission when an epidemic associated with a (re-)emerging virus arises.

About the study

In the present study, the researchers looked into UDA's potential as a broad-spectrum SARS-CoV-2 antiviral drug. Determining if the lectin was a viable wide-ranging antiviral inhibitor requires resolving its precise mode of action in depth. The team assessed UDA against a screen of SARS-CoV-2 variants in several cell types.

Initially, the plant lectin UDA was assessed against pseudotyped SARS-CoV-2. Subsequently, the antiviral effectiveness of UDA was examined against the wild-type virus. The team also evaluated UDA against the SARS-CoV-2 Omicron and Delta VOCs.

To further explore the antiviral potency of UDA, the researchers assessed UDA's antiviral function in differentiated cells in three-dimensional (3D)-like structures that were air-exposed, known as air-liquid-interface (ALI) cultures. To identify which region of the SARS-CoV-2 spike (S) protein or cellular receptor was in charge of UDA's antiviral effect, they utilized surface plasmon resonance (SPR).

The investigators next evaluated UDA's potential to block cell-cell SARS-CoV-2 fusion utilizing a split neon-green molecular platform to better comprehend the precise molecular focus of UDA in SARS-CoV-2 entrance. They also determined which carbohydrates on the S protein were necessary for UDA binding.

Results and conclusions

The study results indicated that in A549 angiotensin-converting enzyme 2 (ACE2) transmembrane protease serine 2 (TMPRSS2) cells, UDA effectively prevents entry of pseudotyped SARS-CoV-2 with half-maximal inhibitory concentration (IC50) values varying from 0.32 to 1.22 microM.

Further, UDA inhibited the replication of the early SARS-CoV-2 Wuhan-Hu-1 strain in Vero E6 cells with an IC50 value of 225 nM, and the SARS-CoV-2 Beta, Alpha, and Gamma VOCs with an IC50 range of 115 to 171 nM. Moreover, UDA has antiviral activity in U87.ACE2+ cells against the latest Omicron and Delta VOCs, with IC50 values of 0.9 and 1.6 microM, respectively.

Interestingly, UDA maintained antiviral efficacy against the SARS-CoV-2 20A.EU2 variant within the nanomolar range when evaluated in ALI primary lung epithelial cell cultures. According to SPR investigations, UDA binds to the S protein of the SARS-CoV-2 in a concentration-reliant manner, perhaps interfering with cell adhesion or subsequent viral entry.

Moreover, in subsequent mechanistic studies using cell-cell fusion tests, UDA prevented SARS-CoV-2 S protein-facilitated membrane fusion. According to the current cell-cell fusion investigations, a saturating concentration of UDA was necessary for the dynamic fusion process to elicit an almost full inhibitory effect. The scientists found that the inhibitory potential of UDA significantly decreased when unbound UDA was removed ahead of the start of cell-cell fusion. Furthermore, N-glycosylation deletions across the S2 subunit of the S protein in pseudotyped SARS-CoV-2 mutants did not affect their sensitivity to UDA's antiviral effects.

To conclude, the present work demonstrated that UDA was a potent and wide-spectrum SARS-CoV-2 fusion inhibitor. The study findings depicted that UDA efficaciously prevents SARS-CoV-2 from entering target cells. Besides, the current observation that UDA retained antiviral effectiveness against various SARS-CoV-2 VOCs shows that UDA should be regarded as an antiviral with an intriguing pan-character that could be a beneficial tool for combating present and prospective SARS-CoV-2 variants.

*Important notice

bioRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Written by

Shanet Susan Alex

Shanet Susan Alex, a medical writer, based in Kerala, India, is a Doctor of Pharmacy graduate from Kerala University of Health Sciences. Her academic background is in clinical pharmacy and research, and she is passionate about medical writing. Shanet has published papers in the International Journal of Medical Science and Current Research (IJMSCR), the International Journal of Pharmacy (IJP), and the International Journal of Medical Science and Applied Research (IJMSAR). Apart from work, she enjoys listening to music and watching movies.