Bupleurum turcicum: A Rich Source of Saikosaponin A and D with Potential Use as Adjunct for the Management of Acute Respiratory Diseases: A Meta Review

COVID-19 pandemic caused by SARS-CoV-2 has resulted in unprecedented havoc worldwide with significant morbidity and mortality. Till now, no effective antivirals are at disposal prompting researchers to explore potential lead molecules including from bioactive phytochemicals. An extensive literature search was carried out utilizing online resources; Google Scholar and PubMed to collect published reports on pharmacological potential of saikosaponin particularly in underexplored Bupleurum species. A number of molecular docking studies have reported promising antiviral effects of saikosaponins particularly of saikosaponin A, D, U and V with tremendous potential to be developed as anti-SARS-CoV-2 therapy. The search for potential sources of saikosaponin A and D led to the identification of Bupleurum turcicum; an unexplored, underutilized and endemic Bupleurum species. The observation that B. turcicum root extract contains highest amount of SSa and SSd among endemic Bupleurum species found in Turkey (Bupleurum sulphureum, Bupleurum lycaonicum, Bupleurum turcicum, Bupleurum heldreichii, Bupleurum pauciradiatum) and presence of significant amounts of antioxidant compounds led to the proposition of using B. turcicum extracts as adjust therapy in the management of COVID-19. The proposal also relies on the evidence of SSa and SSd being effective against a number of viruses including SARS-CoV. This review discusses phytochemical composition of B. turcicum root, antiviral, immunomodulatory and anti-inflammatory potential of saikosaponins in view of its plausible usefulness in the management of COVID-19. B. turcicum is an underutilized species rich in saikosaponin A and D with potential antiviral properties which could be effective alternative therapy in COVID-19 management.

Saikosaponin A, a Triterpene Saponin, Suppresses Angiogenesis and Tumor Growth by Blocking VEGFR2-Mediated Signaling Pathway

Saikosaponin A (SSA), a main triterpenoid saponin component from Radix Bupleurum, has been revealed to have a variety of pharmacological activities. However, whether SSA can inhibit angiogenesis, a key step in solid tumor progression, remains unknown. In this study, we demonstrated that SSA could powerfully suppress the proliferation, migration, and tube formation of human umbilical vein endothelial cells. SSA also significantly inhibited angiogenesis in the models of the chick embryo chorioallantoic membrane and Matrigel plugs. Moreover, SSA was found to inhibit tumor growth in both orthotopic 4T1 breast cancer and subcutaneous HCT-15 colorectal tumor by the inhibition of tumor angiogenesis. Western blot assay indicated the antiangiogenic mechanism of SSA in the suppression of the protein phosphorylation of VEGFR2 and the downstream protein kinase including PLCγ1, FAK, Src, and Akt. In summary, SSA can suppress angiogenesis and tumor growth by blocking the VEGFR2-mediated signaling pathway.

Glycan Epitopes and Potential Glycoside Antagonists of DC-SIGN Involved in COVID-19: In Silico Study

Glycosylation is an important post-translational modification that affects a wide variety of physiological functions. DC-SIGN (Dendritic Cell-Specific Intercellular adhesion molecule-3-Grabbing Non-integrin) is a protein expressed in antigen-presenting cells that recognizes a variety of glycan epitopes. Until now, the binding of DC-SIGN to SARS-CoV-2 Spike glycoprotein has been reported in various articles and is regarded to be a factor in systemic infection and cytokine storm. The mechanism of DC-SIGN recognition offers an alternative method for discovering new medication for COVID-19 treatment. Here, we discovered three potential pockets that hold different glycan epitopes by performing molecular dynamics simulations of previously reported oligosaccharides. The “EPN” motif, “NDD” motif, and Glu354 form the most critical pocket, which is known as the Core site. We proposed that the type of glycan epitopes, rather than the precise amino acid sequence, determines the recognition. Furthermore, we deduced that oligosaccharides could occupy an additional site, which adds to their higher affinity than monosaccharides. Based on our findings and previously described glycoforms on the SARS-CoV-2 Spike, we predicted the potential glycan epitopes for DC-SIGN. It suggested that glycan epitopes could be recognized at multiple sites, not just Asn234, Asn149 and Asn343. Subsequently, we found that Saikosaponin A and Liquiritin, two plant glycosides, were promising DC-SIGN antagonists in silico.

Saikosaponin A and D Inhibit Adipogenesis via the AMPK and MAPK Signaling Pathways in 3T3-L1 Adipocytes

Obesity is a lipid metabolism disorder caused by genetic, medicinal, nutritional, and other environmental factors. It is characterized by a complex condition of excess lipid accumulation in adipocytes. Adipogenesis is a differentiation process that converts preadipocytes into mature adipocytes and contributes to excessive fat deposition. Saikosaponin A (SSA) and saikosaponin D (SSD) are triterpenoid saponins separated from the root of the Bupleurum chinensis, which has long been used to treat inflammation, fever, and liver diseases. However, the effects of these constituents on lipid accumulation and obesity are poorly understood. We investigated the anti-obesity effects of SSA and SSD in mouse 3T3-L1 adipocytes. The MTT assay was performed to measure cell viability, and Oil Red O staining was conducted to determine lipid accumulation. Various adipogenic transcription factors were evaluated at the protein and mRNA levels by Western blot assay and quantitative reverse transcription polymerase chain reaction (qRT-PCR). Here, we showed that SSA and SSD significantly inhibited lipid accumulation without affecting cell viability within the range of the tested concentrations (0.938–15 µM). SSA and SSD also dose-dependently suppressed the expression of peroxisome proliferator-activated receptor gamma (PPARγ), CCAAT/enhancer binding protein alpha (C/EBPα), sterol regulatory element binding protein-1c (SREBP-1c), and adiponectin. Furthermore, the decrease of these transcriptional factors resulted in the repressed expression of several lipogenic genes including fatty acid binding protein (FABP4), fatty acid synthase (FAS), and lipoprotein lipase (LPL). In addition, SSA and SSD enhanced the phosphorylation of adenosine monophosphate-activated protein kinase (AMPK) and its substrate, acetyl-CoA carboxylase (ACC), and inhibited the phosphorylation of extracellular-regulated kinase 1/2 (ERK1/2) and p38, but not c-Jun-N-terminal kinase (JNK). These results suggest that SSA and SSD inhibit adipogenesis through the AMPK or mitogen-activated protein kinase (MAPK) pathways in the early stages of adipocyte differentiation. This is the first study on the anti-adipogenic effects of SSA and SSD, and further research in animals and humans is necessary to confirm the potential of saikosaponins as therapeutic agents for obesity.

Antitumor Effect of Saikosaponin A on Human Neuroblastoma Cells

Objective. Neuroblastoma (NB) is a highly metastatic tumor in children that develops in the sympathetic nervous system and has a low curative rate. Saikosaponin A (SSA), an active ingredient isolated from the root of Radix Bupleuri, is a natural compound with various pharmacological activities and shows good application prospects in antitumors. This study investigated the antihuman NB activity of SSA and underlying mechanisms associated with its actions. Materials and Methods. The MTT method was used to detect the activity of SSA in inhibiting human NB cell SK-N-AS proliferation. Cell morphology was observed. The flow cytometry technology was used in analyzing the cell apoptosis rate. The Transwell assay evaluated cell migration and invasion following SSA treatment, apoptosis-related protein expression, and angiogenesis-related protein expression, and EMT-related proteins were detected by western blot analysis. Results. SSA showed an inhibitory effect on SK-N-AS cells with the IC50 values of 14.14 μM at 24 h and 12.41 μM at 48 h. Results indicated that SSA has proapoptotic activity, and its proapoptotic activity is positively correlated with the Bax/Bcl-2/caspase-9/caspase-7/PARP pathway. Furthermore, SSA inhibited the invasion and migration of SK-N-AS cells via regulating the angiogenesis-related VEGFR2/Src/Akt pathway and the epithelial-mesenchymal transition- (EMT-) related protein expression. Conclusion. SSA exerts an antihuman NB effect and thus provides foundations for NB treatment.

In Silico Comparison of Separate or Combinatorial Effects of Potential Inhibitors of the SARS-CoV-2 Binding Site of ACE2

Background: The COVID-19 is a pandemic viral infection with a high morbidity rate, leading to many worldwide deaths since the end of 2019. The RBD (Receptor Binding Domain) of SARS-CoV-2 through its spike utilizes several host molecules to enter host cells. One of the most important ones is the angiotensin-converting enzyme 2 (ACE2), an enzyme normally engaged in renin angiotensin pathway and is responsible for hypertension regulation. As different articles have analyzed separate compounds which can bind ACE2 as the potential virus entry blockers, and each one with a different molecular docking algorithm, in this study we compared all candidate compounds individually as well as their combinations using a unique validated software to introduce most promising ones. Methods: We collected and prepared a list of all available compounds which potentially can inhibit RBD binding site of the ACE2 from different studies and then reanalyzed and compared them using the Patchdock (ver. 1.3) as a suitable molecular docking algorithm for analysis of separate compounds or their combinations. Results: Saikosaponin A (e.g. in Bupleurum chinense), Baicalin (e.g. in several species in the genus Scutellaria), Glycyrrhizin (Glycyrrhiza glabra), MLN-4760 and Umifenovir better occupied ACE2 to inhibit viral RBD binding and are suggested as the top five inhibitors of the SARS-CoV-2 binding site of ACE2. Their combinatory effects were also inspiring concurrent ACE2 blockade. Conclusion: The results propose greatest compounds and their combinatory anti-SARS-CoV-2 effects in order to decrease the time and expenses required for further experimental designs.