Gingko Biloba is an ideal candidate to be used as adjuvants in the treatment of COVID-19 due its antiviral and anti-inflammatory properties.
Ginkgolic acid (GA) an important phytochemical found in Gingko Biloba can function as an antiviral by inhibiting the fusion and synthesis of viral proteins.
Ginkgolic acid (GA) is able to inhibit the Herpes Simplex Virus type1 (HSV-1), genome replication in Human Cytomegalovirus (HCMV) and the infections of the Zika Virus (ZIKV).
It is also able to inhibits the wide spectrum of fusion by inhibiting the three types of proteins that have been linked to induced fusion as seen in Influenza A Virus [IAV], Epstein Barr Virus [EBV], HIV and Ebola Virus [EBOV]).
The secondary mechanism of GA targeting inhibition of the RNA or DNA and protein synthesis in virus, have been related to its strong effects, even afterward the beginning of the infection, therefore, it potentially treats the acute viral contaminations like (Measles and COVID-19).
Another past study has shown that Ginko Biloba is able to inhibit the coronavirus strain 229E infection of human epithelial lung cells. https://www.mdpi.com/1424-8247/14/10/980
Here, we report that GA in the range of 1 to 15 µM inhibits HCoV-229E CPE, viral RNA, and viral protein production in a dose-dependent manner. This effect is retained when cells are treated with 15 µM GA two hours post-infection with the virus. FIPV3-70 antibody binds to the nucleoprotein (N protein) of SARS-CoV-2 (~46kDa).
The N protein is conserved among the alpha, beta, and gamma genera of coronaviruses, suggesting a common structural and functional role for N protein domains . Furthermore, 15 µM GA completely inhibited coronavirus N protein expression on days 3 and 6 in post-infection treated MRC-5 cells. We previously reported that Ginkgolic acid’s antiviral mechanism of action involves inhibiting the initial virus-to-cell fusion event and preventing the spread of cell-to-cell infection .
In addition, we also reported that GA has broad-spectrum antiviral activity against all three classes of fusion proteins , which may explain its ability to inhibit coronavirus S protein, a class I fusion protein, which plays a role in cell entry . Furthermore, our results also indicate that pre- or post-treatment with GA inhibits virus progeny production and protein expression evaluated on days 3 to 6 days post-infection.
As we reported, GA inhibits the synthesis of viral proteins ; other researchers have also shown a potential secondary mechanism of action of GA involving inhibition of viral DNA and protein synthesis, which may explain the strong and successful inhibition of HCoV-229E and its potential to inhibit SARS-CoV-2 infection [15,17,18,23,24].
Increased degrees of severity of SARS-CoV-2 infections have been attributed to comorbidities (diabetes, hypertension, and obesity) arising from dysregulation, and thought to be compounded by an age-dependent decrease in metabolic processes [25,26,27]. Previous studies have revealed that GA inhibits de novo lipogenesis in pancreatic cancer (Panc-1), BxPC-3, and hepatocellular carcinoma (HepG2) cell lines by inducing the activation of 5′-adenosine monophosphate-activated protein kinase (AMPK) signaling and downregulating the expression of acetyl-CoA carboxylase (ACC) and fatty acid synthase (FASN) .
AMPK plays an essential role in the regulation of cellular energy metabolism. Coronavirus maintains a high ATP/AMP ratio following infection, reducing phosphorylation of AMPK (p-AMPK), AMPK substrates, and downstream targets. SARS-CoV-2 infection has been shown to influence components of the AMPK/mechanistic target of the rapamycin complex 1 (mTORC1) pathway.
Downstream, coronaviruses activate autophagy inhibitors while reducing autophagy-enhancing proteins, proteins responsible for membrane nucleation, phagophore formation, and autophagosome-lysosome fusion [26,27]. GA has also been shown to activate AMPK in SW480 colon cancer cells and to decrease expression of invasion-associated proteins, including matrix metalloproteinase (MMP)-2, MMP-9, urinary-type plasminogen activator (uPa), and C-X-C chemokine receptor type 4 (CXCR4) in the SW480 cells.
The effect of GA has been shown to be reversible following small interfering RNA (siRNA) silencing of AMPK expression, which suggests that GA can inhibit migration, invasion, and proliferation of colon cancer cells . We propose that GA-induced activation of AMPK may hinder coronavirus propagation in primary human lung cells.
Liu et al. (2018) reported that GA directly binds and inhibits the SUMOylation E1 enzyme, thus inhibiting SUMOylation in both HEK293 and mBMSCs cells. SUMOylation is a post-translational modification by which small ubiquitin modifiers (SUMOs) are conjugated to protein targets by the E1, E2, and E3 sumoylation enzymes . SUMOylation is known to play a role in cellular processes such as nuclear translocation, transcription regulation, apoptosis, stress response, protein stability, pluripotency, differentiation, and maintenance of stem/progenitor cells .
This has shown promise as a suppressor of cancer cell growth and migration . Recent structural-based studies have examined posttranscriptional modifications of coronavirus proteins to understand the mechanism of virion assembly and virus-host interactions. The SUMOylation site in SARS-CoV was mapped to the lysine (62 amino acid) residue of the N protein .
N protein dimerizes and binds to genomic RNA, forming a nucleocapsid, which plays a significant role in viral genome replication and evasion of the immune response . In SARS-CoV, post-transcriptional modification of N protein plays a vital regulatory role in viral replication cycles by interfering with host cell division .
Thus, we propose that the SUMOylation inhibition activity of GA may suppress post-transcriptional modification of the HCoV-229E conserved N protein, thereby disturbing the viral replication cycle.
The anti-inflammatory effects of GA and other Ginkgo Biloba extracts have been thoroughly examined in cell culture [29,30] and animal models [31,32]. GA significantly inhibits the production of NO, PGE2, proinflammatory cytokines (TNF-α, IL-1β, and IL-6) and suppresses the activation of iNOS and COX-2 in oxidized low-density lipoprotein (ox-LDL)-stimulated HUVEC cells.
Application of GA in ox-LDL-induced HUVEC cells inhibits the degradation of IκB-α, preventing the translocation of NF-κB from the cytoplasm to the nucleus. GA also inhibits the phosphorylation of JNK, p38 MAPK, ERK, and Akt, thus strongly suppressing the activation of NF-κB . The pathophysiology of SARS-CoV-2 resembles SARS-CoV infections.
The onset of Acute Respiratory Distress Syndrome (ARDS) results from damage to the airways by aggressive inflammatory responses. Nuclear Factor Kappa B (NF-κB) is one of the major transcription factors activated in ARDS, and it plays a vital role in mediating immune responses to inflammation and other cellular activities. NF-κB activation can induce cytokine production, which leads to a positive autoregulatory loop that exacerbates the inflammatory response.
Papain-like protease (PLP) of SARS-CoV has been shown to block phosphorylation and activation of interferon regulatory factor 3 (IRF3), thereby antagonizing interferon (IFN)-β induction [33,34]. Some reports have suggested that the ubiquitin-like domain of PLP is insufficient to block the activation of NF-κB, thus perpetuating the aggressive host inflammatory response to COVID-19 infection [33,34].
Thus, we postulate that GA could inhibit and suppress inflammation caused by severe SARS-CoV-2 infections by downregulating the expression of proinflammatory cytokines by suppressing the activation of the NF-κB signaling pathway. This approach should be tested in a relevant in vivo model of SARS-CoV-2 infection.
A recent study using a high-throughput screen has identified GA and anacardic acid as irreversible inhibitors of SARS-CoV-2 PLP and 3-chymotrypsin-like protease (3-CLP) in Vero-E6 and BL21 (DE3) cells [35,36], thereby providing further evidence of the multifaceted role of GA as an antiviral inhibitor of coronaviruses.
Ginkgo Biloba can also reduce the risk of infection by several mechanisms; these mechanisms involve Ginkgo Biloba containing quercetin and other constituents, which have anti-inflammatory and immune modulator effects by reducing pro-inflammatory cytokines concentrations.
Cytokines cause inflammation which have been induced the injuries in lung lining. Some observational studies confirmed that Ginkgo Biloba reduced the risk of asthma, sepsis and another respiratory disease as well as it reduced the risk of cigarette smoking on respiratory symptoms.
A new COVID-19 Herbs study by researchers from Florida Polytechnic University-USA, University of Baghdad-Iraq, Poznan University of Medical Sciences-Poland and Damanhour University and the Damanhour-Egypt has also showed that Gingko Biloba can be used to treat COVID-19 severity.
SARS-CoV-2 infections are linked with inflammatory disorders and the development of oxidative stress in extreme cases. Therefore, anti-inflammatory and antioxidant drugs may alleviate these complications. Ginkgo biloba L. folium extract (EGb) is a herbal medicine containing various active constituents.
The study review aimed to provide a critical discussion on the potential role of EGb in the management of coronavirus disease 2019 (COVID-19). The antiviral effect of EGb is mediated by different mechanisms, including blocking SARS-CoV-2 3-chymotrypsin-like protease that provides trans-variant effectiveness.
The study found that EGb moreover impedes the development of pulmonary inflammatory disorders through the diminution of neutrophil elastase activity, the release of proinflammatory cytokines, platelet aggregation, and thrombosis. Thus, EGb can attenuate the acute lung injury and acute respiratory distress syndrome in COVID-19.
The study findings concluded that EGb offers the potential of being used as adjuvant antiviral and symptomatic therapy. Nanosystems enabling targeted delivery, personalization, and booster of effects provide the opportunity for the use of EGb in modern phytotherapy.
The study findings were published in the peer reviewed journal: Archiv der Pharmazie.