In the span of just two decades, the world has grappled with three major outbreaks of coronavirus diseases, namely, Severe Acute Respiratory Syndrome (SARS), Middle East Respiratory Syndrome (MERS), and the COVID-19 pandemic caused by SARS-CoV-2 , , .
Among these, the COVID-19 pandemic stands out as the most devastating in terms of public health and economic impact, largely due to its rapid transmission and high mutation rate .
SARS-CoV-2, the virus responsible for COVID-19, enters human cells through the receptor-binding domain (RBD) of the spike protein binding to the angiotensin-converting enzyme 2 (ACE2) receptor. The virus has undergone numerous mutations, resulting in the emergence of several important variants, including Alpha, Beta, Delta, and most notably, the Omicron variant , , , .
The Omicron variant, in particular, has garnered significant attention due to its extensive RBD mutations and high affinity for the ACE2 receptor, leading to increased antibody evasion and rapid spread , .
While the Omicron variant exhibits high transmissibility, it appears to cause milder symptoms and reduced mortality rates, especially in vaccinated individuals. However, elderly patients infected with Omicron still face the risk of severe lung inflammation and other complications, contributing to increased mortality .
In the quest for effective COVID-19 treatments, scientists have explored various drugs and therapies. Initially, drugs like Remdesivir, hydroxychloroquine, and lopinavir-ritonavir were developed with pan-coronavirus inhibitory effects but proved controversial and unsatisfactory in clinical trials , , , , .
More promising results emerged with the use of interleukin-6 receptor inhibitors, tocilizumab and sarilumab, in increasing survival rates among severe COVID-19 patients . Paxlovid, an inhibitor of the SARS-CoV-2 main protease, also showed antiviral activity and reduced the risk of critical illness or death , , .
The rise of Omicron and its drug-resistant characteristics, along with ongoing concerns about new emerging variants, underscores the urgent need for the development of effective therapeutic agents against SARS-CoV-2 and its mutants.
Natural medicinal compounds, particularly those from Traditional Chinese Medicine (TCM), have a long history of use in combating epidemic infectious diseases. China has recommended several TCM formulations as potential COVID-19 therapeutics, although their scientific basis and effectiveness require further exploration.
Several antiviral and anti-inflammatory compounds, such as Oroxylin A, hesperetin, scutellarin, glycyrrhizic acid, and glycyrrhizin, have been identified in QFPD , , .
Triterpenoids like licorice-saponin A3 and glycyrrhetinic acid from licorice have been reported to inhibit SARS-CoV-2 infection by targeting the spike protein . This led to the exploration of 35 active compounds from QFPD for their potential as anti-coronavirus agents , , , , , , .
In this context, alisol B 23-acetate, an active compound from Alismatis Rhizoma, emerged as a potential candidate for further investigation. It demonstrated inhibitory effects on SARS-CoV-2 infection in vitro and possesses a range of beneficial properties, including antibiotic, anti-cancer, anti-inflammatory, and hepatoprotective activities , , , , .
Alisma herb extract and its constituent alisol B 23-acetate have also shown promise in attenuating allergic asthma and lung injuries , . Thus, it became essential to explore the potential of alisol A/B/C and their acetate derivatives in the treatment of COVID-19.
This investigation was designed to develop a novel therapeutic agent for COVID-19 treatment, with a specific focus on alisol B 23-acetate. The study aimed to determine whether alisol B 23-acetate could serve as a promising antiviral compound against COVID-19 by inhibiting viral entry and exhibiting anti-inflammatory activities.
- In vitro testing of inhibitory effects of alisol B 23-acetate on different coronavirus lineages.
- Utilization of pseudotyped Vesicular Stomatitis Virus (VSV) and receptors overexpressed cells to explore potential mechanisms of alisol B 23-acetate in viral entry.
- Application of HDX-MS techniques to verify the molecular interaction between alisol B 23-acetate and the ACE2 receptor.
- Establishment of various coronavirus-challenged animal models to evaluate the role of alisol B 23-acetate in ameliorating lung damage and inflammation caused by the virus.
In this comprehensive discussion, we delve into the findings and implications of our study, which focused on the potential of alisol B 23-acetate as an antiviral compound against various coronavirus species, including SARS-CoV-2 and its variants. We also explore the mechanisms underlying its antiviral activity, its structure-activity relationship with related compounds, and its potential role in modulating inflammation in COVID-19.
Antiviral Potential of Alisol B 23-Acetate
Our study began by screening 35 active compounds derived from QingFei PaiDu (QFPD) for their antiviral potential. Notably, alisol B 23-acetate emerged as the sole compound with inhibitory effects on SARS-CoV-2 infection in vitro. Subsequent investigations expanded its antiviral activity to include various coronavirus species, including MERS-CoV, the Alpha variant, the Delta variant, and the highly transmissible Omicron variant, both in vitro and in vivo. This broad-spectrum inhibitory effect is a promising characteristic of alisol B 23-acetate, suggesting its potential utility in the treatment of COVID-19 and its variants.
Molecular Interaction with ACE2 Receptor
To understand the mechanism behind the antiviral activity of alisol B 23-acetate, we employed HDX-MS (hydrogen-deuterium exchange mass spectrometry) techniques. Our results indicated that alisol B 23-acetate interacts with the ACE2 receptor at specific sites, particularly in α-helical regions and areas near the binding domain of ACE2 linking to the spike protein receptor-binding domain (RBD).
This interaction is crucial in blocking the entry of SARS-CoV-2 and its variants into host cells. Furthermore, alisol B 23-acetate disrupted several hydrogen bonds between ACE2 and the SARS-CoV-2 RBD, further hindering the virus’s ability to attach to host cells.
Importantly, the acetoxy group of alisol B 23-acetate formed a polar connection with a specific residue (497) in ACE2, influencing the receptor’s flexibility. This interaction strongly suggests that alisol B 23-acetate exerts its antiviral effects by disrupting the S-ACE2 interaction, preventing viral entry.
To gain insights into the structure-activity relationship, we investigated related compounds, alisol A/B/C, and their acetate derivatives. While alisol B and alisol B 23-acetate exhibited dose-dependent reductions in viral load, other structurally similar compounds like alisol A/alisol A 24-acetate and alisol C/alisol C 23-acetate did not display any inhibitory effect on viral load. The key structural difference between these compounds lies in the presence of the acetoxy group and carbonyl group. Specifically, the acetoxy group in alisol B 23-acetate formed a polar connection with ACE2 residue 497, enhancing its antiviral activity. The role of these specific chemical groups in antiviral bioactivity warrants further investigation.
Implications for COVID-19 Treatment
The ACE2 receptor plays a pivotal role in the entry of SARS-CoV-2 into host cells. Alisol B 23-acetate’s ability to interfere with this interaction has significant implications for COVID-19 treatment. By blocking the entry of the virus into host cells, alisol B 23-acetate offers a potential strategy to limit viral spread and reduce disease severity. Importantly, it may also play a role in preventing future emerging coronavirus variants from gaining a foothold in host populations.
Consideration of Other Mediators
While ACE2 is a crucial mediator for viral entry, cellular serine protease TMPRSS2 also plays a role in spike protein priming. Our results suggest that TMPRSS2 may not be directly involved in the antiviral bioactivity of alisol B 23-acetate. Recent research has identified neuropilin1 and furin as co-factors for viral entry, particularly in cells with low ACE2 expression. Further investigation is needed to determine whether alisol B 23-acetate affects these co-factors.
Amelioration of Inflammation and Cytokine Storm
Inflammatory responses and cytokine storms are major contributors to severe COVID-19 outcomes. Proinflammatory T cells, specifically Th1 and Th17 cells, are implicated in driving inflammation in COVID-19 patients. Our study demonstrated that alisol B 23-acetate has the potential to dampen these responses, reducing the production of proinflammatory cytokines such as IFNγ and IL17. This modulation of the immune response may help mitigate the severe lung inflammation associated with COVID-19.
The safety of any potential drug is a paramount concern. Alisol B 23-acetate displayed a satisfactory safety profile in our acute toxicity experiments, showing no adverse effects on body weight, organ functions, or tissue morphology at therapeutic dosages. Previous pharmacokinetic studies also indicate reasonable safety profiles for this compound. Nonetheless, comprehensive studies on long-term safety, pharmacodynamics, metabolic kinetics, and potential side effects are essential before considering clinical trials. Moreover, pharmaceutical investigations, such as the development of nasal spray or sustained-release preparations, will be crucial for translational applications of alisol B 23-acetate.
Limitations and Future Directions
We acknowledge certain limitations of our study. The selection of 35 compounds from QFPD may not have identified the most effective anti-coronavirus compound within the formula. The concentration and bioavailability of alisol B 23-acetate in QFPD remain unknown, and caution must be exercised in extrapolating our results to the broader formula. Future research should focus on understanding the pharmacokinetics, pharmacodynamics, and toxicity profiles of alisol B 23-acetate to facilitate its development as a therapeutic agent. Additionally, the formulation of alisol B 23-acetate for practical use, such as intranasal administration, should be explored.
In the face of the evolving COVID-19 pandemic and the emergence of highly transmissible variants like Omicron, the search for effective therapeutic agents remains critical. Alisol B 23-acetate, with its potential to inhibit viral entry and alleviate inflammation, presents a promising avenue for COVID-19 treatment.
Further research and clinical trials are warranted to validate its effectiveness and safety in combating the disease, not only for the current pandemic but also to prepare for potential new coronavirus variants in the future. This study underscores the importance of exploring natural compounds, like those from Traditional Chinese Medicine, as potential sources of novel therapeutics in the battle against COVID-19.
reference link : https://www.sciencedirect.com/science/article/pii/S2090123223002941#s0105