Gallic acid anti-myotoxic activity and mechanism of action, a snake venom phospholipase A2 toxin inhibitor, isolated from the medicinal plant Anacardium humile

Inhibitors and activators for myotoxic phospholipase A2-like toxins from snake venoms - A structural overview

Snakebite envenomations result in acute and chronic physical and psychological health effects on their victims, leading to a substantial socio-economic burden in tropical and subtropical countries. Local necrosis is one of the serious effects caused by envenomation, primarily induced by snake venoms from the Viperidae family through the direct action of components collectively denominated as myotoxins, including the phopholipase A2-like (PLA2-like) toxins. Considering the limitations of antivenoms in preventing the rapid development of local tissue damage caused by envenomation, the use of small molecule therapeutics has been suggested as potential first-aid treatments or as adjuvants to antivenom therapy. In this review, we provide an overview of the structural interactions of molecules exhibiting inhibitory activity toward PLA2-like toxins. Additionally, we discuss the implications for the myotoxic mechanism of PLA2-like toxins and the molecules involved in their activation, highlighting key differences between activators and inhibitors. Finally, we integrate all these results to propose a classification of inhibitors into three different classes and five sub-classes. Taking into account the structural and affinity information, we compare the different inhibitors/ligands to gain a deeper understanding of the structural basis for the effective inhibition of PLA2-like toxins. By offering these insights, we aim to contribute to the search for new and efficient inhibitor molecules to complement and improve current therapy by conventional antivenoms.

Antivenom Properties and Chemical Profiling via Molecular Networking of Mimosa gracilis Extracts

The species Mimosa gracilis var. capillipes (Benth.) Barneby is used for its antivenom properties in the Coqueiros community, municipality of Catalão, state of Goiás. This study focused on three varieties: M. gracilis Benth. var. gracilis, M. gracilis var. capillipes (Benth.) Barneby, and M. gracilis var. invisiformis Barneby. The chemical profiles of extracts from these varieties were analysed using molecular networking through liquid chromatography with tandem mass spectrometry. Additionally, the study investigated the inhibitory potential of these three varieties against the proteolytic, coagulant, and phospholipase activities of Bothrops and Crotalus venoms. In vitro results confirmed the antivenom potential of nine extracts. Remarkably, the ethanolic extracts of roots from M. gracilis var. capillipes (Benth.) Barneby and the leaves from M. gracilis Benth. var. gracilis exhibited 100 % inhibition of the tested activities. The study also revealed 19 annotated compounds through molecular networking, reported for the first time in the species M. gracilis.

Microwave-assisted extraction of mucilage from juá: Characterization and antioxidant activity

Microwave-assisted extraction of mucilage from juá was investigated using response surface methodology. The optimal conditions for extraction were a power of 300 W, an extraction time of 240 s, a pH of 8.0, and a water/sample ratio of 1/6, which achieved a 26.43% yield. The monosaccharide composition and antioxidant activity of the mucilage from juá fruits from different regions of Caatinga were investigated. The fruits from Agreste Paraibano showed the highest mucilage extraction yield (18.64%) compared to that of fruits from Mata Paraibana (MP) (12.37%), Borborema (BB) (11.47%), and Sertão Paraibano (8.31%) (p < 0.05). Glucose (32.8%-50.8%) and arabinose (19.3%-32.9%) were the main monosaccharides found in juá mucilage. The mucilage from fruits in the MP presented the highest antioxidant activity in the 2,2-diphenyl-1-picrylhydrazyl and oxygen radical absorbance capacity assays. Our results demonstrated the potential for the future exploration and application of juá mucilage in the food industry. PRACTICAL APPLICATION: Juá (Ziziphus joazeiro Mart.) mucilage contains phenolic compounds and antioxidant activity, and its extraction by MAE is efficient, as it contributed to a higher yield.

BthTX-I, a phospholipase A2-like toxin, is inhibited by the plant cinnamic acid derivative: chlorogenic acid

Snakebite is a significant health concern in tropical and subtropical regions, particularly in Africa, Asia, and Latin America, resulting in more than 2.7 million envenomations and an estimated one hundred thousand fatalities annually. The Bothrops genus is responsible for the majority of snakebite envenomings in Latin America and Caribbean countries. Accidents involving snakes from this genus are characterized by local symptoms that often lead to permanent sequelae and death. However, specific antivenoms exhibit limited effectiveness in inhibiting local tissue damage. Phospholipase A2-like (PLA2-like) toxins emerge as significant contributors to local myotoxicity in accidents involving Bothrops species. As a result, they represent a crucial target for prospective treatments. Some natural and synthetic compounds have shown the ability to reduce or abolish the myotoxic effects of PLA2-like proteins. In this study, we employed a combination approach involving myographic, morphological, biophysical and bioinformatic techniques to investigate the interaction between chlorogenic acid (CGA) and BthTX-I, a PLA2-like toxin. CGA provided a protection of 71.8% on muscle damage in a pre-incubation treatment. Microscale thermophoresis and circular dichroism experiments revealed that CGA interacted with the BthTX-I while preserving its secondary structure. CGA exhibited an affinity to the toxin that ranks among the highest observed for a natural compound. Bioinformatics simulations indicated that CGA inhibitor binds to the toxin's hydrophobic channel in a manner similar to other phenolic compounds previously investigated. These findings suggest that CGA interferes with the allosteric transition of the non-activated toxin, and the stability of the dimeric assembly of its activated state.

Unraveling snake venom phospholipase A2: an overview of its structure, pharmacology, and inhibitors

Snake bite is a neglected disease that affects millions of people worldwide. WHO reported approximately 5 million people are bitten by various species of snakes each year, resulting in nearly 1 million deaths and an additional three times cases of permanent disability. Snakes utilize the venom mainly for immobilization and digestion of their prey. Snake venom is a composition of proteins and enzymes which is responsible for its diverse pharmacological action. Snake venom phospholipase A2 (SvPLA2) is an enzyme that is present in every snake species in different quantities and is known to produce remarkable functional diversity and pharmacological action like inflammation, necrosis, myonecrosis, hemorrhage, etc. Arachidonic acid, a precursor to eicosanoids, such as prostaglandins and leukotrienes, is released when SvPLA2 catalyzes the hydrolysis of the sn-2 positions of membrane glycerophospholipids, which is responsible for its actions. Polyvalent antivenom produced from horses or lambs is the standard treatment for snake envenomation, although it has many drawbacks. Traditional medical practitioners treat snake bites using plants and other remedies as a sustainable alternative. More than 500 plant species from more than 100 families reported having venom-neutralizing abilities. Plant-derived secondary metabolites have the ability to reduce the venom's adverse consequences. Numerous studies have documented the ability of plant chemicals to inhibit the enzymes found in snake venom. Research in recent years has shown that various small molecules, such as varespladib and methyl varespladib, effectively inhibit the PLA2 toxin. In the present article, we have overviewed the knowledge of snake venom phospholipase A2, its classification, and the mechanism involved in the pathophysiology of cytotoxicity, myonecrosis, anticoagulation, and inflammation clinical application and inhibitors of SvPLA2, along with the list of studies carried out to evaluate the potency of small molecules like varespladib and secondary metabolites from the traditional medicine for their anti-PLA2 effect.

Structural basis of the myotoxic inhibition of the Bothrops pirajai PrTX-I by the synthetic varespladib

Varespladib (LY315920) is a potent inhibitor of human group IIA phospholipase A₂ (PLA₂) originally developed to control inflammatory cascades of diseases associated with high or dysregulated levels of endogenous PLA₂. Recently, varespladib was also found to inhibit snake venom PLA₂ and PLA₂-like toxins. Herein, ex vivo neuromuscular blocking activity assays were used to test the inhibitory activity of varespladib. The binding affinity between varespladib and a PLA₂-like toxin was quantified and compared with other potential inhibitors for this class of proteins. Crystallographic and bioinformatic studies showed that varespladib binds to PrTX-I and BthTX-I into their hydrophobic channels, similarly to other previously characterized PLA₂-like myotoxins. However, a new finding is that an additional varespladib binds to the MDiS region, a particular site that is related to muscle cell disruption by these toxins. The present results further advance the characterization of the molecular interactions of varespladib with PLA₂-like myotoxins and provide additional evidence for this compound as a promising inhibitor candidate for different PLA₂ and PLA₂-like toxins.

In Vitro Anti-Venom Potentials of Aqueous Extract and Oils of Toona ciliata M. Roem against Cobra Venom and Chemical Constituents of Oils

There are high mortality and morbidity rates from poisonous snakebites globally. Many medicinal plants are locally used for snakebite treatment in Uganda. This study aimed to determine the in vitro anti-venom activities of aqueous extract and oils of Toona ciliata against Naja melanoleuca venom. A mixture of venom and extract was administered intramuscularly in rats. Anticoagulant, antiphospholipase A2 (PLA2) inhibition assay, and gel electrophoresis for anti-venom activities of oils were done. The chemical constituents of the oils of ciliata were identified using Gas chromatography-tandem mass spectroscopy (GC-MS/MS). The LD50 of the venom was 0.168 ± 0.21 µg/g. The venom and aqueous extract mixture (1.25 µg/g and 3.5 mg/g) did not cause any rat mortality, while the control with venom only (1.25 µg/g) caused death in 1 h. The aqueous extract of T. ciliata inhibited the anticoagulation activity of N. melanoleuca venom from 18.58 min. to 4.83 min and reduced the hemolytic halo diameter from 24 to 22 mm. SDS-PAGE gel electrophoresis showed that oils completely cleared venom proteins. GC-MS/MS analysis showed that the oils had sesquiterpene hydrocarbons (60%) in the volatile oil (VO) and oxygenated sesquiterpenes (48.89%) in the non-volatile oils (NVO). Some major compounds reported for the first time in T. ciliata NVOs were: Rutamarin (52.55%), β-Himachalol (9.53%), Girinimbine (6.68%) and Oprea1 (6.24%). Most compounds in the VO were reported for the first time in T. ciliata, including the major ones Santalene (8.55%) and Himachal-7-ol (6.69%). The result showed that aqueous extract and oils of T. ciliata have anti-venom/procoagulant activities and completely neutralized the venom. We recommend a study on isolation and testing the pure compounds against the same venom.

Structural and functional studies of a snake venom phospholipase A2-like protein complexed to an inhibitor from Tabernaemontana catharinensis

Snake envenomation is an ongoing global health problem and tropical neglected disease that afflicts millions of people each year. The only specific treatment, antivenom, has several limitations that affects its proper distribution to the victims and its efficacy against local effects, such as myonecrosis. The main responsible for this consequence are the phospholipases A₂ (PLA₂) and PLA₂-like proteins, such as BthTX-I from Bothrops jararacussu. Folk medicine resorts to plants such as Tabernaemontana catharinensis to palliate these and other snakebite effects. Here, we evaluated the effect of its root bark extract and one of its isolated compounds, 12-methoxy-4-methyl-voachalotine (MMV), against the in vitro paralysis and muscle damage induced by BthTX-I. Secondary and quaternary structures of BthTX-I were not modified by the interaction with MMV. Instead, this compound interacted in an unprecedented way with the region inside the toxin hydrophobic channel and promoted a structural change in Val31, loop 58-71 and Membrane Disruption Site. Thus, we hypothesize that MMV inhibits PLA₂-like proteins by preventing entrance of fatty acid into the hydrophobic channel. These data may explain the traditional use of T. catharinensis extract and confirm MMV as a promising candidate to complement antivenom or a structural guide to develop more effective inhibitors.

Lys49 myotoxins, secreted phospholipase A2-like proteins of viperid venoms: A comprehensive review

Muscle necrosis is a potential clinical complication of snakebite envenomings, which in severe cases can lead to functional or physical sequelae such as disability or amputation. Snake venom proteins with the ability to directly damage skeletal muscle fibers are collectively referred to as myotoxins, and include three main types: cytolysins of the "three-finger toxin" protein family expressed in many elapid venoms, the so-called "small" myotoxins found in a number of rattlesnake venoms, and the widespread secreted phospholipase A₂ (sPLA₂) molecules. Among the latter, protein variants that conserve the sPLA₂ structure, but lack such enzymatic activity, have been increasingly found in the venoms of many viperid species. Intriguingly, these sPLA₂-like proteins are able to induce muscle necrosis by a mechanism independent of phospholipid hydrolysis. They are commonly referred to as "Lys49 myotoxins" since they most often present, among other substitutions, the replacement of the otherwise invariant residue Asp49 of sPLA₂s by Lys. This work comprehensively reviews the historical developments and current knowledge towards deciphering the mechanism of action of Lys49 sPLA₂-like myotoxins, and points out main gaps to be filled for a better understanding of these multifaceted snake venom proteins, to hopefully lead to improved treatments for snakebites.

Utilization of gallic acid to inhibit some toxic activities caused by Bothrops jararaca or B. jararacussu snake venoms

Snake bite envenoming is a serious public health issue, affecting thousands of people worldwide every year, especially in rural communities of tropical and subtropical countries. Injection of venom into victims may cause hemorrhaging, blood coagulation imbalance, inflammation, pain, edema, muscle necrosis, and eventually, death. The official validated treatment recommended by governments is the administration of antivenom that efficiently prevents morbidity and mortality. However, this therapy does not effectively neutralize the local effects of Viperidae venoms which constitute one of the leading causes of disability or amputation of the affected limb. Thus, bioprospecting studies seeking for alternative therapies to complement antivenom should be encouraged, especially those investigating the blockage of local venomic toxicity. Plants produce a great diversity of metabolites with a wide range of pharmacological and biological properties. Therefore, the objective of this study was to assess the utilization of gallic acid, which is widely found in plants, against some toxic in vitro (coagulation, proteolytic, and hemolytic) or in vivo (edematogenic, hemorrhagic, and lethal) activities of Bothrops jararaca or B. jararacussu venom. Gallic acid was incubated with B. jararaca or B. jararacussu venom (incubation protocol), after which, in vitro or in vivo assays were performed. Additionally, a gel containing gallic acid was developed and topically applied over the skin of mice after injection of B. jararaca or B. jararacussu venom (treatment protocol), and then, a hemorrhagic assay was carried out. As a result, gallic acid inhibited the toxic activities, with variable efficacy, and the gallic acid gel neutralized B. jararaca or B. jararacussu venom-induced hemorrhagic activity. Gallic acid was devoid of in vitro toxicity as shown through a hemocompatibility test. Thus, these findings demonstrate the potential of gallic acid in the development of an alternative agent to treat victims of snake bites inflicted by Bothrops species.

Gallic Acid as a Non-Selective Inhibitor of α/β-Hydrolase Fold Enzymes Involved in the Inflammatory Process: The Two Sides of the Same Coin

(1) Background: Gallic acid (GA) has been characterized as an effective anti-inflammatory, antivenom, and promising drug for therapeutic use. (2/3) Methods and Results: GA was identified from ethanolic extract of fresh pitanga (Eugenia uniflora) leaves, which was identified using commercial GA. Commercial GA neutralized the enzymatic activity of secretory PLA2 (sPLA2) by inhibiting the active site and inducing changes in the secondary structure of the enzyme. Pharmacological edema assays showed that GA strongly decreased edema when the compound was previously incubated with sPLA2. However, prior treatment of GA (30 min before) significantly increased the edema and myotoxicity induced by sPLA2. The molecular docking results of GA with platelet-acetylhydrolase (PAF-AH) and acetylcholinesterase reveal that this compound was able to interact with the active site of both molecules, inhibiting the hydrolysis of platelet-activating factor (PAF) and acetylcholine (ACh). (4) Conclusion: GA has a great potential application; however, our results show that this compound can also induce adverse effects in previously treated animals. Additionally, the increased edema and myotoxicity observed experimentally in GA-treated animals may be due to the inhibition of PAF-AH and Acetylcholinesterase.

The potential of phenolic acids in therapy against snakebites: A review

Ophidism is a serious health problem worldwide and is included in the World Health Organization's (WHO's) list of Neglected Tropical Diseases. Although snakebite envenoming requires emergency treatment, currently the only treatment recommended by WHO is serotherapy, which has some disadvantages such as low access to the rural population, low effectiveness in neutralizing local effects, and high cost. In this context, new alternatives for the treatment of snakebites are required. The use of plant-derived compounds to inhibit the effects caused by snake venoms has been the object of a number of studies in recent years. This review aims to provide an up-to-date overview of the use of phenolic acids with therapeutic application against envenomation by snakes of different species. In this sense, structural analysis in silico and biological activities in vivo and in vitro were reported. The acids were subdivided into derivatives of benzoic and cinnamic acids, with derivatives of cinnamic acids being the most studied. Studies have revealed that these compounds are capable of inhibiting local and systemic effects induced by envenomation, and structural analyses indicate that the acids interact with important sites responsible for the action of toxins. Thus, it was reported that phenolic acids showed antiophidic potential, providing insights for future research to develop complementary drugs for the treatment of snakebites.