In silico and in vitro neutralization of PLA2 activity of Daboxin P by butein, mimosine and bakuchiol

Proteomic diversity of Russell's viper venom: exploring PLA2 isoforms, pharmacological effects, and inhibitory approaches

Snakebite envenomation is a serious health concern in tropical regions, resulting in high mortality. The World Health Organization (WHO) has declared it a neglected tropical disease and is working on strategies to reduce mortality. Russell's viper (Daboia russelii) is one of the most abundant venomous snakes found across Southeast Asia. Proteomic analysis of Russell's viper venom has demonstrated variation, with phospholipase A2 (PLA2) being the most abundant toxin across geographic boundaries. PLA2, a major constituent of the low-molecular-weight fraction of snake venom, hydrolyses phospholipids at the sn-2 position, releasing arachidonic acid and lysophospholipids. They are reported to cause various pharmacological effects, including hemolysis, anticoagulation, neurotoxicity, myotoxicity, and oedema. Though administration of antivenoms (ASV) is the primary treatment for envenomation, it has many drawbacks. Besides causing hypersensitivity reactions and life-threatening anaphylaxis, treatment with ASV is further complicated due to its inability to neutralize low-molecular-weight toxins. Thus, there is a greater need to produce next-generation antivenoms that can target specific toxins in the venom. In this review, we explored the classification of Russell's viper and the variation in its proteomic profile across Southeast Asia to date. In addition, we have also summarized the mechanism of action of PLA2 and discussed various isoforms of PLA2 found across different regions with their respective pharmacological effects. Finally, the drawbacks of commercially available antivenoms and the molecules investigated for inhibiting the low-molecular-weight toxin, PLA2 are discussed.

Temperature effect in the inhibition of PLA2 activity of Bothrops brazili venom by Rosmarinic and Chlorogenic acids, experimental and computational approaches

Myotoxicity caused by snakebite envenoming emerges as one of the main problems of ophidic accidents as it is not well neutralized by the current serum therapy. A promising alternative is to search for efficient small molecule inhibitors that can act against multiple venom components. Phospholipase A2 (PLA2) is frequently found in snake venom and is usually associated with myotoxicity. Thus it represents an excellent target for the search of new treatments. This work reports the effect of temperature in the inhibition of catalytic properties of PLA2 from Bothrops brazili venom by Rosmarinic (RSM) and Chlorogenic (CHL) acids through experimental and computational approaches. Three temperatures were evaluated (25, 37 and 50 °C). In the experimental section, enzymatic assays showed that RSM is a better inhibitor in all three temperatures. At 50 °C, the inhibition efficiency decayed significantly for both acids. Docking studies revealed that both ligands bind to the hydrophobic channel of the protein dimer where the phospholipid binds in the catalytic process, interacting with several functional residues. In this context, RSM presents better interaction energies due to stronger interactions with chain B of the dimer. Molecular dynamics simulations showed that RSM can establish selective interactions with ARG112B of PLA2, which is located next to residues of the putative Membrane Disruption Site in PLA2-like structures. The affinity of RSM and CHL acids towards PLA2 is mainly driven by electrostatic interactions, especially salt bridge interactions established with residues ARG33B (for CHL) and ARG112B (RSM) and hydrogen bonds with residue ASP89A. The inability of CHL to establish a stable interaction with ARG112B was identified as the reason for its lower inhibition efficiency compared to RSM at the three temperatures. Furthermore, extensive structural analysis was performed to explain the lower inhibition efficiency at 50 °C for both ligands. The analysis performed in this work provides important information for the future design of new inhibitors.Communicated by Ramaswamy H. Sarma.

Bakuchiol targets mitochondrial proteins, prohibitins and voltage-dependent anion channels: New insights into developing antiviral agents

We previously reported that bakuchiol, a phenolic isoprenoid anticancer compound, and its analogs exert anti-influenza activity. However, the proteins targeted by bakuchiol remain unclear. Here, we investigated the chemical structures responsible for the anti-influenza activity of bakuchiol and found that all functional groups and C6 chirality of bakuchiol were required for its anti-influenza activity. Based on these results, we synthesized a molecular probe containing a biotin tag bound to the C1 position of bakuchiol. With this probe, we performed a pulldown assay for Madin-Darby canine kidney cell lysates and purified the specific bakuchiol-binding proteins with SDS-PAGE. Using nanoLC-MS/MS analysis, we identified prohibitin (PHB) 2, voltage-dependent anion channel (VDAC) 1, and VDAC2 as binding proteins of bakuchiol. We confirmed the binding of bakuchiol to PHB1, PHB2, and VDAC2 in vitro using Western blot analysis. Immunofluorescence analysis showed that bakuchiol was bound to PHBs and VDAC2 in cells and colocalized in the mitochondria. The knockdown of PHBs or VDAC2 by transfection with specific siRNAs, along with bakuchiol cotreatment, led to significantly reduced influenza nucleoprotein expression levels and viral titers in the conditioned medium of virus-infected Madin-Darby canine kidney cells, compared to the levels observed with transfection or treatment alone. These findings indicate that reducing PHBs or VDAC2 protein, combined with bakuchiol treatment, additively suppressed the growth of influenza virus. Our findings indicate that bakuchiol exerts anti-influenza activity via a novel mechanism involving these mitochondrial proteins, providing new insight for developing anti-influenza agents.

In Silico Evaluation of Quercetin Methylated Derivatives on the Interaction with Secretory Phospholipases A2 from Crotalus durissus terrificus and Bothrops jararacussu

Quercetin derivatives have already shown their anti-inflammatory potential, inhibiting essential enzymes involved in this process. Among diverse pro-inflammatory toxins from snake venoms, phospholipase A2 is one of the most abundant in some species, such as Crotalus durissus terrificus and Bothrops jararacussu from the Viperidae family. These enzymes can induce the inflammatory process through hydrolysis at the sn-2 position of glycerophospholipids. Hence, elucidating the main residues involved in the biological effects of these macromolecules can help to identify potential compounds with inhibitory activity. In silico tools were used in this study to evaluate the potential of quercetin methylated derivatives in the inhibition of bothropstoxin I (BthTX-I) and II (BthTX-II) from Bothrops jararacussu and phospholipase A2 from Crotalus durissus terrificus. The use of a transitional analogous and two classical inhibitors of phospholipase A2 guided this work to find the role of residues involved in the phospholipid anchoring and the subsequent development of the inflammatory process. First, main cavities were studied, revealing the best regions to be inhibited by a compound. Focusing on these regions, molecular docking assays were made to show main interactions between each compound. Results reveal that analogue and inhibitors, Varespladib (Var) and p-bromophenacyl bromide (BPB), guided quercetins derivatives analysis, revealing that Leu2, Phe5, Tyr28, glycine in the calcium-binding loop, His48, Asp49 of BthTX-II and Cdtspla2 were the main residues to be inhibited. 3MQ exhibited great interaction with the active site, similar to Var results, while Q anchored better in the BthTX-II active site. However, strong interactions in the C-terminal region, highlighting His120, seem to be crucial to decreasing contacts with phospholipid and BthTX-II. Hence, quercetin derivatives anchor differently with each toxin and further in vitro and in vivo studies are essential to elucidate these data.

iTRAQ Quantitative Proteomic Analysis of Different Expressed Proteins and Signal Pathways in Bakuchiol-Induced Hepatotoxicity

Bakuchiol (BAK) is an abundant natural compound. BAK has been reported to have several biological activities such as anticancer, antiaging, anti-inflammatory, and prevention of bone loss. However, it causes hepatotoxicity, the mechanism of which is not known. In this study, we explored the mechanism of BAK hepatotoxicity by treating rats with 52.5 mg/kg and 262.5 mg/kg of BAK, administered continuously for 6 weeks. We examined the liver pathology and biochemical composition of bile to determine toxicity. Mechanisms of BAK hepatotoxicity were analyzed based on relative and absolute quantification (iTRAQ) protein equivalent signatures and validated in vitro using LO2 cells. iTRAQ analysis revealed 281 differentially expressed proteins (DEPs) in liver tissue of the BAK-treated group, of which 215 were upregulated, and 66 were downregulated. GO and KEGG enrichment analysis revealed that bile secretion, lipid metabolism, and cytochrome P450 signaling pathways were enriched in DEPs. Among them, peroxisome proliferator-activated receptor α (PPARα), farnesoid X receptor (FXR), and cholesterol 7α-hydroxylase (CYP7a1) were closely associated with the development and progression of BAK-induced hepatic metabolic dysfunction and abnormal bile metabolism. This study shows that BAK can induce hepatotoxicity through multiple signaling pathways.

Plant-Derived Toxin Inhibitors as Potential Candidates to Complement Antivenom Treatment in Snakebite Envenomations

Snakebite envenomations (SBEs) are a neglected medical condition of global importance that mainly affect the tropical and subtropical regions. Clinical manifestations include pain, edema, hemorrhage, tissue necrosis, and neurotoxic signs, and may evolve to functional loss of the affected limb, acute renal and/or respiratory failure, and even death. The standard treatment for snake envenomations is antivenom, which is produced from the hyperimmunization of animals with snake toxins. The inhibition of the effects of SBEs using natural or synthetic compounds has been suggested as a complementary treatment particularly before admission to hospital for antivenom treatment, since these alternative molecules are also able to inhibit toxins. Biodiversity-derived molecules, namely those extracted from medicinal plants, are promising sources of toxin inhibitors that can minimize the deleterious consequences of SBEs. In this review, we systematically synthesize the literature on plant metabolites that can be used as toxin-inhibiting agents, as well as present the potential mechanisms of action of molecules derived from natural sources. These findings aim to further our understanding of the potential of natural products and provide new lead compounds as auxiliary therapies for SBEs.

Bakuchiol - a natural meroterpenoid: structure, isolation, synthesis and functionalization approaches

Bakuchiol is an emblematic meroterpene class of natural product extracted from Psoralea corylifolia. It has been reported to possess a broad range of biological and pharmacological properties and is considered as a leading biomolecule. It is highly desirable to devise an efficient approach to access bakuchiol and its chemical biology applications. In this review we provided structural features, isolation methods, various chemical routes and late-stage functionalization (LSF) approaches for bakuchiol and its derivatives. Moreover, this review encompasses the structure-activity relationships (SAR), value-added contributions and future perspectives of bakuchiol.

Do Uncommon Plant Phenolic Compounds Have Uncommon Properties? A Mini Review on Novel Flavonoids

Unique plants and their properties, once considered synonymous to medicine, remain a potent source for new compounds in modern science. Plant polyphenols and natural products continue to be investigated for effective treatments for the most persistent of human ailments. In this review, fifty novel plant phenolic compounds have been compiled and briefly described from the previous five years. Select compounds and notable plant species from genus Morinda and Sophora are further expanded on. Traditional medicine plants often contain rich and diverse mixtures of flavonoids, from which rare compounds should receive attention. The bioactivity of crude plant extracts, purified compounds and mixtures can differ greatly, requiring that these interactions and mechanisms of action be investigated in greater detail. Novel applications of uncommon natural products, namely mimosine and juglone, are explored within this review. The 2019 coronavirus pandemic has resulted in abrupt spike of related scientific publications: speculation is made regarding plant natural products and future of antiviral drug discovery.

Neutralization of Daboxin P activities by rationally designed aptamers

Inefficacy and associated risks of current antivenom has raised the need for alternative approaches of snakebite management. Aptamers are one such alternative which is being pursued for therapeutic interventions as well as for design of diagnostic kits due to its high specificity. Present study focussed on designing and validating nucleic acid aptamers against snake venom PLA_2, a hydrolytic enzyme present in all venomous snakes. The aptamers were designed by adding nucleic acid chain on the surface of Daboxin P, a major PLA₂ enzyme of Daboia russelii venom. Binding characteristics of the aptamers were confirmed by docking to Daboxin P as well as acidic and basic PLA₂s from different snake species using in silico docking. The aptamers folded into different tertiary structures and bound to the active and Ca²⁺ binding site of PLA₂ enzymes. Molecular dynamics simulation analysis of Daboxin P-aptamer complexes showed that the complexes were stable in an aqueous environment. The electrophoretic mobility shift assay further confirmed the binding of the synthetic aptamers to Daboxin P and other snake venom PLA₂ enzymes. The aptamers inhibited the sPLA₂ activity with an IC₅₀ value ranging between 0.52 μM and 0.77 μM as well as the anticoagulant activity of Daboxin P. The aptamers could also inhibit the PLA₂ activity of Echis carinatus crude venom and anti-coagulant activity of Bungarus caeruleus crude venom, members of big four snakes. However, the aptamers didn't inhibit fibrinogenolytic or proteolytic activity of big four venom as well as the coagulation and hemolytic activities. Thus, aptamers can be rationally designed to inhibit the biochemical and biological activities of snake venom proteins.