Citrus bioflavonoid, hesperetin, as inhibitor of two thrombin-like snake venom serine proteases isolated from Crotalus simus

Biophysical characterization and in silico analysis of natural and synthetic compounds targeting Listeria monocytogenes HtrA protease

HtrA protein is a member of a serine protease family with dual functions as a protease and molecular chaperone. It is a virulence factor in many bacteria, including the food-borne pathogen Listeria monocytogenes (Lm), which induces listeriosis in humans. Hence, inhibitors of LmHtrA protease have great importance in the control of infection. Many natural compounds have been used in the inhibition studies of proteases; here, we have performed the inhibition studies of LmHtrA with 31 compounds from different origins. The spectrophotometric assays revealed that plant compounds are promising inhibitors of LmHtrA protease activity compared to other tested peptides and synthetic compounds. The green tea catechin, EGCG has been identified as an inhibitor of protease activity of LmHtrA with a low IC50 value of 0.754 ± 0.2 μM. The substrate cleavage analysis by SDS-PAGE and SPR experiments corroborates the spectrophotometric results by exhibiting protease inhibition and showing the micromolar affinity of EGCG with LmHtrA, respectively. The interaction between rLmHtrA and EGCG was investigated by fluorescence spectroscopy. The binding constant and the number of binding sites were determined as 1.86 × 10(5) M(-1) and 1.2, respectively. The molecular docking and dynamics results of LmHtrA-inhibitor complexes have provided new insights into the inhibition mechanism of LmHtrA compared with other serine proteases. The findings of this study may open up new avenues for the development of natural compound-based derivatives of LmHtrA inhibitors that might be more potent and less harmful to humans.

Exploring the Diversity and Function of Serine Proteases in Toxicofera Reptile Venoms: A Comprehensive Overview

Toxicofera reptile venoms are composed of several toxins, including serine proteases. These proteases are glycosylated enzymes that affect the prey's hemostatic system. Their actions extend across the coagulation cascade, the kallikrein-kinin system, and platelet activation. Despite their specificity for different substrates, these enzymes are homologous across all toxicoferans and display high sequence similarity. The aim of this review is to compile decades of knowledge about venom serine proteases, showing the diversity of biochemically and biophysically characterized enzymes, their structural characteristics, advances in understanding their origin and evolution, as well as methods of obtaining enzymes and their biotechnological applications.

Bioassay-guided identification of antithrombotic compounds from Cnidoscolus aconitifolius (Mill.) I. M. Jhonst.: molecular docking, bioavailability, and toxicity prediction

Cardiovascular diseases (CVDs) are the leading cause of death worldwide. Conventional antithrombotic therapy has reported hemorrhagic accidents. Ethnobotanical and scientific reports point to Cnidoscolus aconitifolius as an antithrombotic adjuvant. Previously, C. aconitifolius leaves ethanolic extract displayed antiplatelet, anticoagulant, and fibrinolytic activities. This work aimed to identify compounds from C. aconitifolius with in vitro antithrombotic activity through a bioassay-guided study. Antiplatelet, anticoagulant, and fibrinolytic tests guided the fractionation. Ethanolic extract was subjected to a liquid-liquid partitioning, followed by vacuum liquid, and size exclusion chromatography to obtain the bioactive JP10B fraction. The compounds were identified through UHPLC-QTOF-MS, and their molecular docking, bioavailability, and toxicological parameters were determined computationally. Kaempferol-3-O-glucorhamnoside and 15(S)-HPETE were identified; both showed affinity for antithrombotic targets, low absorption, and safety for human consumption. Further in vitro and in vivo evaluations will better understand their antithrombotic mechanism. This bioassay-guided fractionation demonstrated that C. aconitifolius ethanolic extract has antithrombotic compounds.Communicated by Ramaswamy H. Sarma.

Biochemical and hemostatic description of a thrombin-like enzyme TLBro from Bothrops roedingeri snake venom

Objective: The current study's objective is to characterize a new throm-bin-like enzyme called TLBro that was obtained from Bothrops roedingeris snake from a biochemical and hemostatic perspective. Methodology: One chromatographic step was used to purify it, producing the serine protease TLBro. Molecular mass was estimated by SDS-PAGE to be between reduced and unreduced by 35 kDa. Tryptic peptide sequencing using Swiss Prot provided the complete amino acid sequence. Expasy.org by conducting a search that is limited to Crotalinae snake serine proteases and displaying a high degree of amino acid sequence. Results: Ser (182) is inhibited by phenylmethylsulfonyl fluoride (PMSF), and TLBro demonstrated the presence of Asp (88) residues. It also deduced the positions of His (43) and Ser (182) in the set of three coordinated amino acids in serine proteases. It was discovered that this substrate had high specificity for BANA, Michaelis-Menten behavior with KM 0 point85 mM and Vmax 1 point89 nmoles -NA/L/min, and high stability between temperatures (15 to 70°C) and pHs (2 point0 to 10 point0). According to doses and incubation times, TLBro degraded fibrin preferentially on the B-chain; additionally, its activities were significantly diminished after preincubation with divalent ions (Zn2 and Cd2). When incubated with PMSF, a particular serine protease inhibitor, enzymatic activities and platelet aggregation were inhibited. Conclusion: The findings revealed distinct structural and functional differences between the serine proteases, adding to the information and assisting in the improvement of the structure-function relationship.

Kaempferol from Moringa oleifera demonstrated potent antivenom activities via inhibition of metalloproteinase and attenuation of Bitis arietans venom-induced toxicities

Bitis arietans venom (BAV) can induce severe pathophysiological disorders after envenoming. However, studies have shown that the Moringa oleifera fraction is effective against BAV toxicities and contains bioactive compounds with significant antivenom potency. This research aimed to identify the main active antivenom compound in the M. oleifera fraction responsible for neutralizing the toxicities induced by BAV. The compounds identified from M. oleifera fraction were docked in silico against the catalytic site of the Snake Venom Metalloproteinase (SVMP) to determine the lead inhibitor compound. The antivenom potency of the lead inhibitor compound was tested against BAV toxicities and metalloproteinase isolated from BAV using in vitro and in vivo methods, while EchiTab-Plus polyvalent antivenom served as a standard drug. The in silico prediction revealed kaempferol as the lead inhibitor compound with a docking score of -7.0 kcal/mol. Kaempferol effectively inhibited metalloproteinase activity at 0.2 mg/ml, compared to antivenom (0.4 mg/ml) and demonstrated significant antihaemorrhagic, antihaemolytic and coagulant effects against BAV activities. Furthermore, kaempferol showed a significant dose-dependent effect on altered haematological indices observed in rats challenged with LD50 of BAV. Envenomed rats also showed an increase in oxidative stress biomarkers and antioxidant enzyme activity in the heart and kidney. However, treatment with kaempferol significantly (P < 0.05) decreased malondialdehyde levels and SOD activity with concomitant enhancement of glutathione levels. Severe histopathological defects noticed in the organ tissues of envenomed rats were ameliorated after kaempferol treatment. Kaempferol is identified as the main active antivenom compound in M. oleifera, and this research highlights the potential of the compound as an effective alternative to snakebite treatment.

Pharmacologic Comparison of High-Dose Hesperetin and Quercetin on MDCK II Cell Viability, Tight Junction Integrity, and Cell Shape

The modulation of tight junction (TJ) integrity with small molecules is important for drug delivery. High-dose baicalin (BLI), baicalein (BLE), quercetin (QUE), and hesperetin (HST) have been shown to open TJs in Madin-Darby canine kidney (MDCK) II cells, but the mechanisms for HST and QUE remain unclear. In this study, we compared the effects of HST and QUE on cell proliferation, morphological changes, and TJ integrity. HST and QUE were found to have opposing effects on the MDCK II cell viability, promotion, and suppression, respectively. Only QUE, but not HST, induced a morphological change in MDCK II into a slenderer cell shape. Both HST and QUE downregulated the subcellular localization of claudin (CLD)-2. However, only QUE, but not HST, downregulated CLD-2 expression. Conversely, only HST was shown to directly bind to the first PDZ domain of ZO-1, a key molecule to promote TJ biogenesis. The TGFβ pathway partially contributed to the HST-induced cell proliferation, since SB431541 ameliorated the effect. In contrast, the MEK pathway was not involved by both the flavonoids, since U0126 did not revert their TJ-opening effect. The results offer insight for using HST or QUE as naturally occurring absorption enhancers through the paracellular route.

A First Look at the Inhibitory Potential of Urospatha sagittifolia (Araceae) Ethanolic Extract for Bothrops atrox Snakebite Envenomation

Bothrops atrox snakebites are a relevant problem in the Amazon basin. In this biodiverse region, the ethnomedicinal approach plays an important role as an alternative to antivenom therapy. Urospatha sagittifolia (Araceae) is a plant used for this purpose; however, its neutralizing properties have not been scientifically accessed. To fill this gap, we investigated the ability of U. sagittifolia to modulate the catalytic activity of Bothrops atrox venom, and their toxic consequences, such as local damage and lethality. The venom profile of B. atrox was assessed by chromatography and electrophoresis. Inhibition of the three main enzymatic and medically important toxins from the venom was evaluated using synthetic substrates and quantified by chromogenic activity assays. Additionally, the neutralization of lethality, hemorrhage and edema were investigated by in vivo assays. The possible interactions between venom proteins and plant molecules were visualized by polyacrylamide gel electrophoresis. Finally, the phytochemical constituents present in the ethanolic extract were determined by qualitative and quantitative analyses. The ethanolic extract reduced the activity of the three main enzymes of venom target, achieving ranges from 19% to 81% of inhibition. Our in vivo venom neuralizations assays showed a significant inhibition of edema (38.72%) and hemorrhage (42.90%). Additionally, lethality was remarkably counteracted. The highest extract ratio evaluated had a 75% survival rate. Our data support the biomedical value of U. sagittifolia as a source of natural enzyme inhibitors able to neutralize catalytically active B. atrox venom toxins and their toxic effects.

Separation and Analytical Techniques Used in Snake Venomics: A Review Article

The deleterious consequences of snake envenomation are due to the extreme protein complexity of snake venoms. Therefore, the identification of their components is crucial for understanding the clinical manifestations of envenomation pathophysiology and for the development of effective antivenoms. In addition, snake venoms are considered as libraries of bioactive molecules that can be used to develop innovative drugs. Numerous separation and analytical techniques are combined to study snake venom composition including chromatographic techniques such as size exclusion and RP-HPLC and electrophoretic techniques. Herein, we present in detail these existing techniques and their applications in snake venom research. In the first part, we discuss the different possible technical combinations that could be used to isolate and purify SV proteins using what is known as bioassay-guided fractionation. In the second part, we describe four different proteomic strategies that could be applied for venomics studies to evaluate whole venom composition, including the mostly used technique: RP-HPLC. Eventually, we show that to date, there is no standard technique used for the separation of all snake venoms. Thus, different combinations might be developed, taking into consideration the main objective of the study, the available resources, and the properties of the target molecules to be isolated.

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.

Prospects and Challenges of Developing Plant-Derived Snake Antivenin Natural Products: A Focus on West Africa

Snakebite envenomation (SBE) is an important public health issue that is now receiving renewed attention following its reclassification as a Neglected Tropical Disease (NTD). Most incidences occur in rural areas of resource-limited countries, as such, timely and appropriate medical care for SBE is often inaccessible. The administration of anti-snake venom serum (ASV) is the only effective definitive treatment of SBE, but treatment failure to available ASVs is not uncommon. Emerging evidence highlights the potential of small-molecule compounds as inhibitors against toxins of snake venom. This presents an encouraging prospect to develop an alternative therapeutic option for the treatment SBE, that may be amenable for use at the point of care in resource-constraint settings. In view of the pivotal role of natural products in modern drug discovery programmes, there is considerable interest in ethno-pharmacological mining of medicinal plants and plant-derived medicinal compounds toward developing novel snake venom-neutralising therapeutics. In this review, we compile a collection of medicinal plants used in the treatment of SBE in West Africa and highlight their promise as potential botanical drugs or as sources of novel small-molecule compounds for the treatment of SBE. The challenges that must be surmounted to bring this to fruition including the need for (sub) regional collaboration have been discussed.

Hesperetin as an inhibitor of the snake venom serine protease from Bothrops jararaca

The majority (90%) of the snakebite envenomation in Brazil accounts for Bothrops from the Viperidae family. Some snake venom serine proteases provoke blood coagulation in ophidian accident victims because of their fibrinolytic activity, one of those proteases from Bothrops jararaca (B. jararaca) has been chosen for this study. Our objectives were to isolate and characterize the target serine protease; isolate, purify, and characterize the orange bagasse flavone (hesperetin, Hst), and investigate the interactions between the targets, enzyme, and hesperetin. The purified serine protease was named BjSP24 because of its molecular mass and proteolytic activity. BjSP24 was folded and characterized using circular dichroism and showed low alpha-helix contents (7.7%). BjSP24 exhibited sequence similarity to other known snake venom serine proteases as measured in the enzyme tryptic peptides' LC-MS/MS run. Hesperetin was obtained within the expected yield and with the predominance of 2S isomer (82%). It acted as a mixed inhibitor for the serine protease (SVSP) from Bothrops jararaca snake venom observed in three different in vitro experiments, fluorescence, kinetics, and SSTD-NMR. It is still to determine if hesperetin might aid-in reverting the on site blood clotting problems just after snakebite accidents.

In vitro study of Hesperetin and Hesperidin as inhibitors of zika and chikungunya virus proteases

The potential outcome of flavivirus and alphavirus co-infections is worrisome due to the development of severe diseases. Hundreds of millions of people worldwide live under the risk of infections caused by viruses like chikungunya virus (CHIKV, genus Alphavirus), dengue virus (DENV, genus Flavivirus), and zika virus (ZIKV, genus Flavivirus). So far, neither any drug exists against the infection by a single virus, nor against co-infection. The results described in our study demonstrate the inhibitory potential of two flavonoids derived from citrus plants: Hesperetin (HST) against NS2B/NS3pro of ZIKV and nsP2pro of CHIKV and, Hesperidin (HSD) against nsP2pro of CHIKV. The flavonoids are noncompetitive inhibitors and the determined IC50 values are in low µM range for HST against ZIKV NS2B/NS3pro (12.6 ± 1.3 µM) and against CHIKV nsP2pro (2.5 ± 0.4 µM). The IC50 for HSD against CHIKV nsP2pro was 7.1 ± 1.1 µM. The calculated ligand efficiencies for HST were > 0.3, which reflect its potential to be used as a lead compound. Docking and molecular dynamics simulations display the effect of HST and HSD on the protease 3D models of CHIKV and ZIKV. Conformational changes after ligand binding and their effect on the substrate-binding pocket of the proteases were investigated. Additionally, MTT assays demonstrated a very low cytotoxicity of both the molecules. Based on our results, we assume that HST comprise a chemical structure that serves as a starting point molecule to develop a potent inhibitor to combat CHIKV and ZIKV co-infections by inhibiting the virus proteases.

Catechin and epicatechin as an adjuvant in the therapy of hemostasis disorders induced by snake venoms

Snake toxins, such as phospholipases A₂ and proteases, are used as research tools to evaluate biological activities and to understand physiopathological processes of natural compounds better. In the present study, the phenolic compounds catechin and epicatechin were incubated with snake venoms to evaluate their inhibition against different substrates. Catechin and epicatechin exerted inhibitions between 20% and 95% on the activity of phospholipases A₂ present in the venom of Bothrops alternatus. In the hemolytic activity, catechin exerted inhibitions between 20% and 25% in all proportions evaluated on the B. jararacussu venom, whereas epicatechin inhibited 20% of the venom activity. Coagulation induced by B. atrox and B. jararacussu venoms was significantly inhibited by catechin and epicatechin, where the time for coagulation was two to three times higher after previous incubation of the venoms with the compounds. The most significant inhibitions for the proteolytic activity on casein were 17% and 27%, respectively, by both compounds. Catechin inhibited serine protease activity induced by B. atrox venom by 64% and epicatechin by 65%. Regarding B. atrox-induced thrombolysis, catechin exerted 40% inhibition and epicatechin around 30%. The fibrinogen proteolysis was completely inhibited by catechin acting on the B. atrox venom in the proportion of 1:1 and by epicatechin on B. jararacussu venom. Catechin and epicatechin showed promising inhibitory action on proteases and phospholipases A₂ . Therefore, these compounds can be explored as an adjuvant for serum therapy or pharmaceutical purposes, once they act on homologous enzymes that are present in humans.

Application of omeprazole combined with hemocoagulase in respiratory failure complicated with upper gastrointestinal bleeding

BACKGROUND

Patients with respiratory failure usually have elevated partial pressure of carbon dioxide and decreased partial pressure of oxygen, and hypoxia occurs when respiratory failure symptoms worsen. When patients suffer from hypoxia, the sympathetic nerve in brain tissue will be more excited, and the secretion of gastric hormones and catecholamines will increase, which will lead to contraction and spasm of small blood vessels in the gastric wall and significantly reduce the blood in tissues. As a result, the metabolism in gastric mucosal cells will be abnormal, the secretion of mucus will be affected, and the barrier of the gastric mucosa will be damaged. Due to the damage to the gastric mucosa, erosion, bleeding, edema, and congestion will occur. In addition, CO₂ retention leads to the occurrence of hypercapnia, improves the biological activity of carbonic anhydrase, increases gastric hydrogen ions, and breaks the acid-base balance of the stomach and the protective barrier of gastric mucosa, leading to gastrointestinal bleeding symptoms.

AIM

To investigate the efficacy of omeprazole combined with hemocoagulase in the treatment of respiratory failure complicated with upper gastrointestinal bleeding.

METHODS

Eighty patients with respiratory failure complicated with upper gastrointestinal bleeding were randomly divided into either a control group or a study group. The control group was treated with lafutidine, and the study group was treated with omeprazole combined with hemocoagulase. Therapeutic efficacy, mortality, and incidence of side effects were compared between the two groups.

RESULTS

The general data of the two groups were comparable (P > 0.05). The effective rate was significantly better in the study group than in the control group (95.0% vs 80.0%, P < 0.05). The mortality rate of the study group was significantly lower than that of the control group (10.0% vs 30.0%, P < 0.05). The incidence of side effects was also significantly lower in the study group than in the control group (2.5% vs 17.5%, P < 0.05).

CONCLUSION

Omeprazole combined with hemocoagulase is effective in the treatment of respiratory failure complicated with upper gastrointestinal hemorrhage.

Effects of hemocoagulase agkistrodon on the coagulation factors and its procoagulant activities

Objective

Hemocoagulase agkistrodon (HCA), a thrombin-like enzyme (TLE) from the venom of the Chinese moccasin snake (Deinagkistrodon acutus), has been used in clinical practice as a hemostatic compound. The aim of this study was to further investigate the pharmacological properties of HCA.

Materials and methods

Sodium dodecyl sulfate or native polyacrylamide gel electrophoresis (SDS- or N-PAGE) as well as enzyme linked immunosorbent assays (ELISAs) were conducted to study the effects of HCA on the human plasma fibrinogen and prothrombin levels, as well as its in vitro interactions with some coagulation factors. In addition, the bleeding time effects of HCA in the mouse tail-bleeding model as well as its effects on the fibrinogen levels in rabbits were determined in vivo.

Results

In vitro results revealed that HCA exerts its procoagulant activities by hydrolyzing fibrinogen into segments that are easier to be absorbed, reducing the risk of thrombus formation. Besides, HCA could significantly inhibit the activation of prothrombin at the concentration of 0.3 μM. Unexpectedly, we also found that HCA was able to strongly bind to factor X/Xa (in a ratio of 1:1) and thus inhibit the acceleration of active factor X to tissue plasminogen activator-catalyzed plasminogen activation, demonstrating that it could be less likely to lead to thrombus formation. Finally, in vivo results indicated that HCA could significantly shorten the bleeding time in the mouse tail-bleeding model and had no effect on the fibrinogen levels in rabbits.

Conclusion

In summary, HCA, a unique and new family member of TLEs, may become a new clinical drug for the prevention and treatment of hemorrhage due to its unique and complex interactions with the blood system. Clarification of these features will enable us to further understand the mechanism of action of HCA and then promote its further application in clinical practice as a therapeutic drug.

Thrombin-like enzymes from snake venom: Structural characterization and mechanism of action

Snake venom thrombin-like enzymes (SVTLEs) constitute the major portion (10-24%) of snake venom and these are the second most abundant enzymes present in the crude venom. During envenomation, these enzymes had shown prominently the various pathological effects, such as disturbance in hemostatic system, fibrinogenolysis, fibrinolysis, platelet aggregation, thrombosis, neurologic disorders, activation of coagulation factors, coagulant, procoagulant etc. These enzymes also been used as a therapeutic agent for the treatment of various diseases such as congestive heart failure, ischemic stroke, thrombotic disorders etc. Although the crystal structures of five SVTLEs are available in the Protein Data Bank (PDB), there is no single article present in the literature that has described all of them. The current work describes the structural aspects, structure-based mechanism of action, processing and inhibition of these enzymes. The sequence analysis indicates that these enzymes show a high sequence identity (57-85%) with each other and low sequence identity with trypsin (36-43%), human alpha-thrombin (29-36%) and other snake venom serine proteinases (57-85%). Three-dimensional structural analysis indicates that the loops surrounding the active site are variable both in amino acids composition and length that may convey variable substrate specificity to these enzymes. The surface charge distributions also vary in these enzymes. Docking analysis with suramin shows that this inhibitor preferably binds to the C-terminal region of these enzymes and causes the destabilization of their three-dimensional structure.