Commentary - Archives of Pharmacology and Therapeutics (2020) Volume 2, Issue 1
Beta-Sitosterol: As Immunostimulant, Antioxidant and Inhibitor of SARS-CoV-2 Spike Glycoprotein
Sharuk L. Khan*, Falak A. Siddiqui
New Montfort Institute of Pharmacy, Ashti, Wardha, Maharashtra, India-442202
- *Corresponding Author:
- Sharuk Khan
Received date: July 31, 2020; Accepted date: August 24, 2020
Citation: Khan SL, Siddiqui FA. Beta-Sitosterol: As Immunostimulant, Antioxidant and Inhibitor of SARS-CoV-2 Spike Glycoprotein. Arch Pharmacol Ther. 2020; 2(1):12-16.
Copyright: © 2020 Khan SL, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
As an extension to our recently published research work in Asian Journal of Pharmaceutical and Clinical Research, entitled “Β-Sitosterol: Isolation from Muntingia Calabura Linn. Bark Extract, Structural Elucidation, and Molecular Docking Studies as Potential Inhibitor of SARS-CoV-2 Mpro (COVID-19)”, we have investigated the role of β-sitosterol as immunostimulant, antioxidant and inhibitory potential against Receptor Binding Domain (RBD) of SARS-CoV-2 Spike Glycoprotein with the aid of molecular docking. There are many studies which reveals the antioxidant and immune boosting role of β-sitosterol especially in viral infection including pneumoniae. This commentary emphasis on further potential of β-sitosterol in treatment of COVID-19 through molecular docking studies. We have targeted RBD of spike glycoprotein and performed molecular docking studies of β-sitosterol to find out its inhibitory potential of SARS-CoV-2. β-sitosterol have showed binding affinity - 7.8 kcal/mol with 0 RMSD lower and upper bound. It formed one hydrogen bond with Ala-B:419 with bond length of 2.16A0. β-sitosterol has formed five alkyl bonds with Pro-C:384 (5.0A0, 4.66A0, 5.23A0, 4.27A0) and with Lys-C:378 (4.66A0). From present commentary, we have concluded that β-sitosterol can be used to enhance immunity against the SARS-CoV-2 infection as well as to restrict the viral invasion into the host cell through angiotensin converting enzyme-2 (ACE-2) by inhibiting spike glycoprotein. If we can increase the dietary intake of β-sitosterol and other phytosterols it can modulate the immunity which is todays need to face COVID-19.
β-sitosterol, SARS-CoV-2 spike glycoprotein, Molecular docking, 6VSB
This article is an extension to our recently published article in Asian Journal of Pharmaceutical and Clinical Research, entitled “Β-Sitosterol: Isolation from Muntingia Calabura Linn. Bark Extract, Structural Elucidation, and Molecular Docking Studies as Potential Inhibitor of SARSCoV- 2 Mpro (COVID-19)”. The article describes detailed procedure for the isolation (by Column Chromatography) and structural characterization (by FTIR, UV-Visible Spectroscopy and HPTLC) of β-sitosterol from Muntingia Calabura bark. The β-sitosterol was docked on SARSCoV- 2 Mpro to study the binding affinity (kcal/mol) in comparison with favipiravir. It has been found that favipiravir has a less binding affinity, i.e. 5.7 kcal/mol than β-sitosterol which has 6.9 kcal/mol. The number of hydrogen bonds formed by the favipiravir is much more, i.e., 4 than β-sitosterol which formed only 01 hydrogen bond with SARS-CoV-2 Mpro.
As an extension to this published research work, we have investigated the role of β-sitosterol as immunostimulant, antioxidant and inhibitory potential against receptor binding domain (RBD) of SARS-CoV-2 Spike Glycoprotein with the aid of molecular docking. There are many studies which reveals the antioxidant and immune boosting role of β-sitosterol especially in viral infection including pneumoniae. This commentary emphasized on further potential of β-sitosterol in treatment of COVID-19 through molecular docking studies.
Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) is a novel, zoonotic, positive-sense , single-stranded RNA beta-coronavirus  (subgenus Sarbecovirus, sub-family Orthocoronaviridae) . The disease caused due to SARS-CoV-2 is termed as COVID-19 . Almost every country of the world is now affected by SARS-CoV-2 infection. The World Health Organization (WHO) declared it a Public Health Emergency of International Concern on January 30, 2020, and on February 28, it upraised the worldwide threat of COVID-19 to the utmost level . A global pandemic was declared on March 11, 2020 . The N, E, M, and S proteins are the four structural proteins encoded by SARSCoV- 2 . This S protein of SARS-CoV-2 i.e. SARS-CoV-2 spike glycoprotein causes invasion to the host cell after binding with angiotensin converting enzyme-2 (ACE-2) . The SARS-CoV-2 spike glycoprotein is cleaved into two subunits during entry . The S1 subunit contains a receptor binding domain (RBD) and attaches to ACE-2 . The S2 subunit then facilitates membrane fusion [12-14]. Therefore, we have targeted RBD of spike glycoprotein and performed molecular docking studies of β-sitosterol to find out its inhibitory potential of SARS-CoV-2.
β-sitosterol as Immunostimulant, as Antiviral and as Antioxidant
Cheng et al. investigated the effects of dietary β-sitosterol at different levels on serum lipid levels, immune function, oxidative status, and intestinal morphology in broilers. They have concluded that dietary β-sitosterol supplementation could regulate serum cholesterol level, promote immune function, and improve intestinal oxidative status and morphology in broilers . Fraile et al. reported that β-sitosterol can be considered an immunomodulator in pigs . Bouic and Lamprecht reported that this phytosterol complex seems to target specific T-helper lymphocytes, the Th1 and Th2 cells, helping normalize their functioning and resulting in improved T-lymphocyte and natural killer cell activity. The re-establishment of these immune parameters may be of help in numerous disease processes relating to chronic immune-mediated abnormalities, including chronic viral infections, tuberculosis, rheumatoid arthritis, allergies, cancer, and autoimmune diseases . Bouic et al. concluded that phytosterols could be used to prevent the subtle immunosuppression associated with excessive physical stress . There are many studies which have reported the immunostimulant activity of the phytosterols [19-24].
Li et al. reported that β-sitosterol is a candidate for the development of anti-virulence agents against pathogens that rely on cholesterol-dependent toxins for successful infections . Zhou et al. reported that β-sitosterol blocks the immune response mediated by RIG-I signaling and deleterious IFN production, providing a potential benefit for the treatment of influenza . Parvez et. al. reported the antioxidative and hepatoprotective efficacy of of G. senegalensis leaves extract. HPTLC analysis of β-amyrin, β-sitosterol, lupeol and ursolic acid strongly supported the anti-HBV efficacy of GSLE via abating the cellular oxidative stress molecules . There are many studies that have reported the antioxidant activity of β-sitosterol [27-34].
Molecular Docking Studies of β-sitosterol with RBD of SARS-CoV-2 Spike Glycoprotein
Autodock vina 1.1.2 in PyRx-Virtual Screening Tool 0.8 were used to perform the docking studies . The active amino acid residues in the protein were identified and noted using BIOVIA Discovery Studio Visualizer (version-220.127.116.1187) . The complete docking procedure along with ligand preparation and target preparation have been performed as described in the reference article . The recently elucidated structure pre-fusion 2019-nCoV (SARS-CoV-2) spike glycoprotein with a single receptor-binding domain up was obtained from the RCSB Protein Data Bank (PDB ID: 6VSB) which was released on 26 February 2020 (https://www.rcsb. org/structure/6VSB) . RBD from SARS-CoV-2 spike glycoprotein was identified from the official website of Protein Data Bank in Europe (EMBL-EBI) (https:// www.ebi.ac.uk/pdbe/entry/pdb/6vsb). There were three sequence domains in the 6VSB crystal structure; Spike receptor binding domain; Spike glycoprotein N-terminal domain; Coronavirus spike glycoprotein S1, C-terminal, along with three chains in the structure (Chain A, B, C). For molecular docking simulation, the three-dimensional grid box (size_x = 76.1623A°; size_y = 84.3011A°; size_z = 62.4413A°) was designed (to define area for interactions) around the RBD (to occupy) using Autodock tool 1.5.6 with exhaustiveness value of 8 [35,36].
Results and Discussion
RBD comprises of amino acid residues from chain A, chain B, and chain C as well, therefore, the most potent inhibitor will be the one which interacts with amino acid residues from all the chains. β-sitosterol has showed a binding affinity of 7.8 kcal/mol with 0 RMSD lower and upper bound. The 2D- and 3D-Docking poses of the β-sitosterol represented in figure 1A & 1B respectively. It formed one hydrogen bond with Ala-B:419 with bond length of 2.16A0. β-sitosterol has formed five alkyl bonds with Pro-C:384 (5.0A°, 4.66A°, 5.23A°, 4.27A°) and with Lys-C:378 (4.66A°). It also shows van der Waals attraction with Thr-C:385, Ser-C:383, Asp-A:985, Thr-B:415, Phe-C:377, Cys-C:379, Glu-A:988, Gln-B:414, Gly-B:413, Pro-A:987, Lys-B:424, Asp-B:420, Leu-B:461, Asn-B:460. As β-sitosterol is interacting with amino acids from every chain (A, B, C), it indicates that it is a potent inhibitor of RBD of SARS-CoV-2 spike glycoprotein. The interacting residues, bond length, and binding affinity are represented in table 1.
|Types of Bond||Active Amino Residues with Bond Length (A°)|
|β-sitosterol||-7.8||Hydrogen Bond||Ala-B:419 (2.16A°)|
|Alkyl Bond||Pro-C:384 (5.0A°, 4.66A°, 5.23A0, 4.27A°), Lys-C:378 (4.66A°)|
|Van Der Waals||Thr-C:385, Ser-C:383, Asp-A:985, Thr-B:415, Phe-C:377,|
Cys-C:379, Glu-A:988, Gln-B:414, Gly-B:413, Pro-A:987,
Lys-B:424, Asp-B:420, Leu-B:461, Asn-B:460
Table 1: Binding Affinity (kcal/mol), types of bond and active amino acid residues with bond length (A0)..
Currently, there is no specific treatment available for SARS-CoV-2 infection. Use of immunostimulants, antivirals, and antioxidants can help to reduce the risk of COVID-19. Literature supports the immunostimulant, antiviral, and antioxidant activity of the β-sitosterol.
Also, molecular docking studies have found very good binding affinity of β-sitosterol with RBD of SARS-CoV-2 spike glycoprotein which can restrict the viral invasion into the host cell. It has formed one hydrogen bond with Ala-B:419, which is good for better inhibition. From present commentary, we have concluded that β-sitosterol can be used to enhance immunity against the SARS-CoV-2 infection as well as to restrict the viral invasion into the host cell through angiotensin converting enzyme-2 (ACE- 2) by inhibiting spike glycoprotein. If we can increase the dietary intake of β-sitosterol and other phytosterols it can modulate the immunity which is todays need to face COVID-19.
Conflict of Interest
The authors have no conflicts of interest.
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