First structural evidence of a specific inhibition of phospholipase A2 by alpha-tocopherol (vitamin E) and its implications in inflammation: crystal structure of the complex formed between phospholipase A2 and alpha-tocopherol at 1.8 A resolution

Advances in the Therapeutic Application of Small-Molecule Inhibitors and Repurposed Drugs against Snakebite

The World Health Organization has declared snakebite as a neglected tropical disease. Antivenom administration is the sole therapy against venomous snakebite; however, several limitations of this therapy reinforce the dire need for an alternative and/or additional treatment against envenomation. Inhibitors against snake venoms have been explored from natural resources and are synthesized in the laboratory; however, repurposing of small-molecule therapeutics (SMTs) against the principal toxins of snake venoms to inhibit their lethality and/or obnoxious effect of envenomation has been garnering greater attention owing to their established pharmacokinetic properties, low-risk attributes, cost-effectiveness, ease of administration, and storage stability. Nevertheless, SMTs are yet to be approved and commercialized for snakebite treatment. Therefore, we have systematically reviewed and critically analyzed the scenario of small synthetic inhibitors and repurposed drugs against snake envenomation from 2005 to date and proposed novel approaches and commercialization strategies for the development of efficacious therapies against snake envenomation.

The allosteric activation mechanism of a phospholipase A2-like toxin from Bothrops jararacussu venom: a dynamic description

The activation process of phospholipase A₂-like (PLA₂-like) toxins is a key step in their molecular mechanism, which involves oligomeric changes leading to the exposure of specific sites. Few studies have focused on the characterization of allosteric activators and the features that distinguish them from inhibitors. Herein, a comprehensive study with the BthTX-I toxin from Bothrops jararacussu venom bound or unbound to α-tocopherol (αT) was carried out. The oligomerization state of BthTX-I bound or unbound to αT in solution was studied and indicated that the toxin is predominantly monomeric but tends to oligomerize when complexed with αT. In silico molecular simulations showed the toxin presents higher conformational changes in the absence of αT, which suggests that it is important to stabilize the structure of the toxin. The transition between the two states (active/inactive) was also studied, showing that only the unbound BthTX-I system could migrate to the inactive state. In contrast, the presence of αT induces the toxin to leave the inactive state, guiding it towards the active state, with more regions exposed to the solvent, particularly its active site. Finally, the structural determinants necessary for a molecule to be an inhibitor or activator were analyzed in light of the obtained results.

Ultrasound Assisted Cascade Extraction of Oil, Vitamin E, and Saccharides from Roselle (Hibiscus Sabdariffa L.) Seeds

Roselle seeds, a waste biomass of the roselle calyx processing industry, were utilized to recover valuable compounds of oil, vitamin E, and water-soluble saccharides. Firstly, ultrasound-assisted extraction (UAE) and conventional stirring extraction were conducted for saccharide extraction, and the advantage of UAE was confirmed. Secondly, oil, vitamin E, and saccharides extracted from Vietnamese roselle seeds by UAE were analyzed for the first time. Oil of tri-, di-, and mono-glycerides, fatty acids of linoleic-, oleic-, palmitic-, and stearic-acids, vitamin E of γ- and α-tocopherol, and saccharides of sucrose, raffinose, stachyose, etc. were identified, and the amounts of these components were compared with those in other country's roselle seeds. Thirdly, cascade extraction of oil, vitamin E, and saccharides by UAE was investigated with solvents of hexane, hexane:ethyl acetate binary solvent, and water. The results indicated that the order of using solvents was very important for high and selective extraction: the best order to recover oil (almost 100%), vitamin E (95.7%), and saccharides (86.2%) was hexane, and then water.

Vanillic acid as phospholipase A2 and proteases inhibitor: In vitro and computational analyses

Enzymatic inhibition by natural compounds may represent a valuable adjuvant in snakebite serum therapy. The objective in this work was to evaluate possible in vitro interactions between vanillic acid and enzymes from Bothrops spp. and Crotalus durissus terrificus venoms, and also suggest a theory as how they interact based on molecular docking. Vanillic acid inhibited the phospholipase activity induced by Bothrops alternatus (∼25% inhibition); the caseinolytic activity induced by Bothrops atrox (∼30%), Bothrops jararacussu (∼44%), and C. d. terrificus (∼33%); the fibrinogenolysis induced by B. jararacussu, B. atrox, and C. d. terrificus (100%); the serine protease activity induced by Bothrops moojeni (∼45%) and Bothrops jararaca (∼66%); the hemolytic activity induced by B. moojeni (∼26%); the thrombolysis activity induced by B. atrox (∼30%) and B. jararacussu (∼20%); and the thrombotic activity induced by C. d. terrificus (∼8%). The compound was also capable of delaying the coagulation time in citrated plasma by 60, 35, and 75 Sec, when incubated with B. moojeni, B. atrox, and B. jararaca, respectively. The results obtained expand the possibilities for future pharmaceutical use of vanillic acid, considering the high homology degree among human and snake venom phospholipases A₂ and proteases (involved in chronic inflammatory diseases). Also, this compound can be used as adjuvant to improve currently available treatments for ophidism victims.

Depigmentation and Anti-aging Treatment by Natural Molecules

Natural molecules are becoming more accepted choices as cosmetic agents, many products in the market today claim to include natural components. Plants include many substances that could be of a value in the whitening of the skin and working as anti-aging agents. A wide range of articles related to natural skin whitening and anti-aging agents have been reviewed. Many plant-derived and natural molecules have shown to affect melanin synthesis by different mechanisms, examples include Arbutin, Ramulus mori extract, Licorice extract, Glabridin, Liquiritin, Kojic acid, Methyl gentisate, Aloesin, Azelaic acid, Vitamin C, Thioctic acid, Soya bean extracts, Niacinamide, α and β-hydroxy acids, Lactic acid, Chamomile extract, and Ellagic acid. Some of the widely used natural anti-aging products as natural antioxidants, collagen, hyaluronic acid, and coenzyme Q can counteract the effects of reactive oxygen species in skin cells and have anti-aging properties on the skin. It was concluded that many natural products including antioxidants can prevent UV-induced skin damage and have whitening and anti-aging effects. It is very important to develop and stabilize appropriate methods for the evaluation of the whitening and anti-aging capacity of natural products and their exact mechanism of action to ensure real efficacy based on evidence-based studies. The attention should be oriented on the formulations and the development of an appropriate vehicle to ensure suitable absorption of these natural products in addition to evaluating the suitable concentration of these molecules required having the desired effects without causing harmful side effects.

Excitotoxicity, neuroinflammation and oxidant stress as molecular bases of epileptogenesis and epilepsy-derived neurodegeneration: The role of vitamin E

Glutamate-mediated excitotoxicity, neuroinflammation, and oxidative stress are common underlying events in neurodegeneration. This pathogenic "triad" characterizes the neurobiology of epilepsy, leading to seizure-induced cell death, increased susceptibility to neuronal synchronization and network alterations. Along with other maladaptive changes, these events pave the way to spontaneous recurrent seizures and progressive degeneration of the interested brain areas. In vivo models of epilepsy are available to explore such epileptogenic mechanisms, also assessing the efficacy of chemoprevention and therapy strategies at the pre-clinical level. The kainic acid model of pharmacological excitotoxicity and epileptogenesis is one of the most investigated mimicking the chronicization profile of temporal lobe epilepsy in humans. Its pathogenic cues include inflammatory and neuronal death pathway activation, mitochondrial disturbances and lipid peroxidation of several regions of the brain, the most vulnerable being the hippocampus. The importance of neuroinflammation and lipid peroxidation as underlying molecular events of brain damage was demonstrated in this model by the possibility to counteract the related maladaptive morphological and functional changes of this organ with vitamin E, the main fat-soluble cellular antioxidant and "conditional" co-factor of enzymatic pathways involved in polyunsaturated lipid metabolism and inflammatory signaling. The present review paper provides an overview of the literature supporting the potential for a timely intervention with vitamin E therapy in clinical management of seizures and epileptogenic processes associated with excitotoxicity, neuroinflammation and lipid peroxidation, i.e. the pathogenic "triad".

The rise, the fall and the renaissance of vitamin E

This review deals with the expectations of vitamin E ability of preventing or curing, as a potent antioxidant, alleged oxidative stress based ailments including cardiovascular disease, cancer, neurodegenerative diseases, cataracts, macular degeneration and more. The results obtained with clinical intervention studies have highly restricted the range of effectiveness of this vitamin. At the same time, new non-antioxidant mechanisms have been proposed. The new functions of vitamin E have been shown to affect cell signal transduction and gene expression, both in vitro and in vivo. Phosphorylation of vitamin E, which takes place in vivo, results in a molecule provided with functions that are in part stronger and in part different from those of the non-phosphorylate compound. The in vivo documented functions of vitamin E preventing the vitamin E deficiency ataxia (AVED), slowing down the progression of non-alcoholic steato-hepatitis (NASH), decreasing inflammation and potentiating the immune response are apparently based on these new molecular mechanisms. It should be stressed however that vitamin E, when present at higher concentrations in the body, should exert antioxidant properties to the extent that its chromanol ring is unprotected or un-esterified.

Structures and binding studies of the complexes of phospholipase A2 with five inhibitors

Phospholipase A2 (PLA2) catalyzes the hydrolysis of phospholipids into arachidonic acid and lysophospholipids. Arachidonic acid is used as a substrate in the next step of the multistep pathway leading to the production of eicosanoids. The eicosanoids, in extremely low concentrations, are required in a number of physiological processes. However, the increase in their concentrations above the essential physiological requirements leads to various inflammatory conditions. In order to prevent the unwanted rise in the concentrations of eicosanoids, the actions of PLA2 and other enzymes of the pathway need to be blocked. We report here the structures of five complexes of group IIA PLA2 from Daboia russelli pulchella with tightly binding inhibitors, (i) p-coumaric acid, (ii) resveratrol, (iii) spermidine, (iv) corticosterone and (v) gramine derivative. The binding studies using fluorescence spectroscopy and surface plasmon resonance techniques for the interactions of PLA2 with the above five compounds showed high binding affinities with values of dissociation constants (KD) ranging from 3.7×10(-8) M to 2.1×10(-9) M. The structure determinations of the complexes of PLA2 with the above five compounds showed that all the compounds bound to PLA2 in the substrate binding cleft. The protein residues that contributed to the interactions with these compounds included Leu2, Leu3, Phe5, Gly6, Ile9, Ala18, Ile19, Trp22, Ser23, Cys29, Gly30, Cys45, His48, Asp49 and Phe106. The positions of side chains of several residues including Leu2, Leu3, Ile19, Trp31, Lys69, Ser70 and Arg72 got significantly shifted while the positions of active site residues, His48, Asp49, Tyr52 and Asp99 were unperturbed.

A metabolomic investigation of the effects of vitamin E supplementation in humans

Background

Vitamin E is a nutrient with both antioxidant and non-antioxidant activities and has been shown to modulate the function of a number of cell types in vitro and in human studies. However studies have also shown vitamin E to have detrimental interactions and therefore it is important to establish the extent to which this nutrient influences metabolism. Metabolomics can potentially identify nutrient-metabolism interactions and therefore the aim of this study was to use a non-targeted metabolomic approach to identify changes to the plasma metabolome following vitamin E supplementation in humans.

Methods

A relatively homogenous healthy adult male population (n = 10) provided a fasting blood sample immediately before and after a 4-week vitamin E supplementation regime (400 mg/d of RRR-α-tocopheryl acetate)) on top of their habitual diet. Plasma samples were analysed for vitamin E and clinical markers. Plasma underwent non-targeted metabolite profiling using liquid chromatography/mass spectroscopy and data was processed using multivariate statistical analysis.

Results

Plasma vitamin E concentrations were significantly increased following supplementation (p < 0.001). A partial least squares-discriminant analysis (PLS-DA) model was able to discriminate between samples taken pre and post vitamin E supplementation (goodness of fit R²Y = 0.82, predictive ability Q² = 0.50). Variable influence on projection and PLS-DA loadings highlighted a number of discriminating ions that were confirmed as discriminatory through pairwise analysis. From database searches and comparison with standards these metabolites included a number of lysophosphatidylcholine species (16:0, 18:0, 18:1, 18:2, 20:3 and 22:6) that were increased in intensity post supplementation by varying degrees from 4% to 29% with the greatest changes found for lysoPC 22:6 and 20:3.

Conclusions

Although a small scale study, these results potentially indicate that vitamin E supplementation influences phospholipid metabolism and induces lysoPC generation; a general pro-inflammatory response. Moreover the study identifies novel areas of vitamin E interactions and highlights the potential of metabolomics for elucidating interactions between nutrients and metabolic pathways in nutritional research.

Anti-inflammatory effect of (E)-4-(3,7-dimethylocta-2,6-dienylamino)phenol, a new derivative of 4-nerolidylcatechol

Objectives

We have investigated the anti-inflammatory and antinociceptive effects of (E)-4-(3,7-dimethylocta-2,6-dienylamino)phenol (LQFM-015), which was designed through molecular simplification strategy from 4-nerolidylcatechol.

Methods

The possible anti-inflammatory and antinociceptive effects were assayed on carrageenan-induced paw oedema and pleurisy, acetic acid-induced abdominal writhing and formalin tests in mice.

Key findings

LQFM-015 reduced the activity of PLA2 enzyme in vitro by 18%. Docking studies into the catalytic site of PLA2 were used to identify the binding mode of the LQFM-015. LQFM-015 showed a moderate antinociceptive effect, since this compound reduced the number of writhings by approximately up to 40% in the acetic acid-induced pain model; this antinociceptive activity also emerged in the second phase of the formalin-induced pain model (58% of inhibition). The anti-inflammatory action of LQFM-015 was confirmed in acute inflammation models, in which it reduced the formation of oedema to 52.78 ± 8.6 and 46.64 ± 5.2 at the second and third hour of carrageenan-induced paw oedema, respectively. Also in the carrageenan-induced pleurisy model, LQFM-015 reduced the migration of leucocytes by 26.0% and decrease myeloperoxidase activity by 50%. LQFM-015 showed different concentrations to inhibit 50% of isoenzyme cyclooxygenase activity (IC50); COX-1 IC50 = 36 μm) and COX-2 IC50 = 28 μm.

Conclusions

LQFM-015 demonstrated inhibition of both PLA2 and COX enzymes; thus, the moderate antinociceptive effect of this compound could be attributed to its anti-inflammatory activity.

A novel pharmacophore model to identify leads for simultaneous inhibition of anti-coagulation and anti-inflammatory activities of snake venom phospholipase A(2)

In addition to catalytic action, snake venom phospholipase A(2) induces several pharmacological effects including neurotoxicity, cardiotoxicity as well as anti-coagulant and anti-platelet aggregation effects. Therefore, strategy to identify dual inhibitor for this enzyme will be of much importance in medical research. In this paper, structure-based pharmacophore mapping, molecular docking, protein-ligand interaction fingerprints, binding energy calculations, and binding affinity predictions were employed in a virtual screening strategy to identify new hits for dual inhibition of anti-coagulation and inflammation of phospholipase A(2) . A structure-based pharmacophore map was modeled which comprised of important interactions as observed in co-crystal of phospholipase A(2) and its dual inhibitor indomethacin. The generated model was used to retrieve molecules from ChemBridge, a free database of commercially available compounds. A total of 381 molecules mapped on the developed pharmacophore model from ChemBridge database. The hits retrieved were further screened by molecular docking, protein-ligand interaction fingerprints, binding energy calculations, and binding affinity predictions using Genetic Optimization for Ligand Docking and moe. Based on these results, 32 chemo-types molecules were predicted as potential lead scaffolds for developing novel, potent and structurally diverse dual inhibitor of phospholipase A(2.).

In silico identification of viper phospholipaseA2 inhibitors: validation by in vitro, in vivo studies

Snake venom, particularly of vipers from the Indian subcontinent, contains Phospholipase A2 (PLA2) as one its constituents which is widely implicated in hemorrhagic, cardiac arrest and death. Development of inhibitors of the protein can facilitate the weakening or annihilation of the venom toxicity and save many human lives. In the present communication, our studies relate to the design and development of structure-based ligands as inhibitors of PLA2 of Viper venom. The study involves the computational approach towards evaluating a library of molecules comprising of natural products, and synthetic molecules through docking studies on the venom protein PDB ID: 1OXL (a dimer, available in the literature). In silico experiments have resulted in the identification of several of them as PLA2 inhibitors. The inhibitory effect of PLA2 by these compounds is attributed to a great extent to their interaction with the residues Phe 46 and Val47 of chain B of the target protein and hence these two residues are identified as the key contributor for the said activity. In order to validate the in silico findings, a selected panel of compounds have been tested by in vitro and in vivo experiments against the venom, which has led to the observance of significant corroboration between the wet lab and in silico findings, validating thereby the in silico approach used in the present study.

Vitamin E, signalosomes and gene expression in T cells

CD4+T cells from aged humans or mice show significant reductions in IL-2 production upon activation. The resulting decreased proliferation is linked to higher risks of infection in the elderly. Several lines of evidence indicate that intrinsic defects preferentially affecting the naïve subset of CD4+T cells contribute to this reduced IL-2 production. Comparison of the biochemical pathways that transduce activation signals from the T cell receptor to the IL-2 promoter in young and old CD4+T cells has demonstrated age-related impairments at initial molecular events, in particular the phosphorylation of kinases and adapter proteins involved in the formation of signalosomes - complex multiprotein assemblies that provide the framework for effective signal transduction. Confocal microscopy has demonstrated a series of age-related impairments in effective immune synapse formation. Vitamin E can reverse many of these CD4+T cell age-associated defects, including reduced levels of phosphorylation of critical signaling/adapter proteins as well as defective immune synapse formation. Vitamin E also enhances IL-2 production, expression of several cell cycle control proteins, and proliferation. Although the precise mechanisms underlying this effect are not understood, it is possible that this antioxidant lipophilic vitamin can prevent the propagation of polyunsaturated fatty acid peroxidation in the cell membrane, influence the biochemical characteristics of specific lipid bilayer microdomains involved in signal transduction, modulate the activity of kinases/phosphatases, or interact with intracellular receptors.

Enzymatic toxins from snake venom: structural characterization and mechanism of catalysis

Snake venoms are cocktails of enzymes and non-enzymatic proteins used for both the immobilization and digestion of prey. The most common snake venom enzymes include acetylcholinesterases, l-amino acid oxidases, serine proteinases, metalloproteinases and phospholipases A(2) . Higher catalytic efficiency, thermal stability and resistance to proteolysis make these enzymes attractive models for biochemists, enzymologists and structural biologists. Here, we review the structures of these enzymes and describe their structure-based mechanisms of catalysis and inhibition. Some of the enzymes exist as protein complexes in the venom. Thus we also discuss the functional role of non-enzymatic subunits and the pharmacological effects of such protein complexes. The structures of inhibitor-enzyme complexes provide ideal platforms for the design of potent inhibitors which are useful in the development of prototypes and lead compounds with potential therapeutic applications.

Vitamin E and adiponectin: proposed mechanism for vitamin E-induced improvement in insulin sensitivity

Insulin resistance and type 2 diabetes have been treated with the PPARγ agonists thiazolidinediones, or TZDs, since the 1990s. One mechanism by which these drugs may work is through PPARγ-mediated upregulation of adiponectin, an endogenous adipokine that has been shown to increase insulin sensitivity. Interestingly, α- and γ-tocopherol, two vitamin E vitamers, have structural similarities to the TZDs and have also been linked to enhanced insulin sensitivity. A recent study identified a novel function of α- and γ-tocopherol in 3T3-L1 preadipocytes: upregulation of an endogenous ligand involved in activating PPARγ. This study also found that tocopherols dramatically enhanced adiponectin expression and that this effect was mediated through a PPARγ-dependent process. These findings illustrate a possible mechanistic link between vitamin E and insulin sensitivity.

Present trends in vitamin E research

Nearly after one century of research and thousands of publications, the physiological function(s) of vitamin E remain unclear. Available evidence suggests a role in cell homeostasis that occurs through the modulation of specific signaling pathways and genes involved in proliferative, metabolic, inflammatory, and antioxidant pathways. Vitamin E presence in the human body is under close metabolic control so that only alpha-tocopherol and, to a lower extent, gamma-tocopherol are retained and delivered to tissues. Other vitamin E forms that are not retained in the body in significant amounts, exhibit responses in vitro that are different form those of alpha-tocopherol and may include tumor cell specific toxicity and apoptosis. These responses provide a therapeutic potential for these minor forms, either as such or metabolically modified, to produce bioactive metabolites. These cellular effects go beyond the properties of lipophilic antioxidant attributed to alpha-tocopherol particularly investigated for its alleged protective role in atherosclerosis or other oxidative stress conditions. Understanding signaling and gene expression effects of vitamin E could help assign a physiological role to this vitamin, which will be discussed in this review. Besides vitamin E signaling, attention will be given to tocotrienols as one of the emerging topics in vitamin E research and a critical re-examination of the most recent clinical trials will be provided together with the potential use of vitamin E in disease prevention and therapy.

Simultaneous inhibition of anti-coagulation and inflammation: crystal structure of phospholipase A2 complexed with indomethacin at 1.4 A resolution reveals the presence of the new common ligand-binding site

A novel ligand-binding site with functional implications has been identified in phospholipase A(2) (PLA(2)). The binding of non-steroidal anti-inflammatory agent indomethacin at this site blocks both catalytic and anti-coagulant actions of PLA(2). A group IIA PLA(2) has been isolated from Daboia russelli pulchella (Russell's viper) which is enzymatically active as well as induces a strong anti-coagulant action. The binding studies have shown that indomethacin reduces the effects of both anti-coagulant and pro-inflammatory actions of PLA(2). A group IIA PLA(2) was co-crystallized with indomethacin and the structure of the complex has been determined at 1.4 A resolution. The structure determination has revealed the presence of an indomethacin molecule in the structure of PLA(2) at a site which is distinct from the conventional substrate-binding site. One of the carboxylic group oxygen atoms of indomethacin interacts with Asp 49 and His 48 through the catalytically important water molecule OW 18 while the second carboxylic oxygen atom forms an ionic interaction with the side chain of Lys 69. It is well known that the residues, His 48 and Asp 49 are essential for catalysis while Lys 69 is a part of the anti-coagulant loop (residues, 54-77). Indomethacin binds in such a manner that it blocks the access to both, it works as a dual inhibitor for catalytic and anti-coagulant actions of PLA(2). This new binding site in PLA(2) has been observed for the first time and indomethacin is the first compound that has been shown to bind at this novel site resulting in the prevention of anti-coagulation and inflammation.

Effect of umbelliferone (7-hydroxycoumarin, 7-HOC) on the enzymatic, edematogenic and necrotic activities of secretory phospholipase A2 (sPLA2) isolated from Crotalus durissus collilineatus venom

Flavonoids, coumarins and other polyphenolic compounds are powerful antioxidants both in hydrophilic and lipophylic environments with diverse pharmacological properties including anti-inflammatory activity. Despite being widely used as powerful therapeutic agents for blood coagulation disorders, more specifically to control some serine protease enzymes, the mechanism of anti-inflammatory activity of coumarins is unknown, unlike that of flavonoids. Although their controlling effect on serine proteases is well acknowledged, their action on secretory phospholipase A2 (sPLA2) remains obscure. The present study describes the interaction between umbelliferone (7-HOC) and the sPLA2 from Crotalus durissus collilineatus venom. In vitro inhibition of sPLA2 enzymatic activity by 7-HOC was estimated using 4N3OBA as substrate, resulting in an irreversible decrease in such activity proportional to 7-HOC concentration. The biophysical interaction between 7-HOC and sPLA2 was examined by fluorescent spectral analysis and circular dichroism studies. Results from both techniques clearly showed that 7-HOC strongly modified the secondary structure of this enzyme and CD spectra revealed that it strongly decreased sPLA2 alpha-helical conformation. In addition, two-dimensional electrophoresis indicated an evident difference between HPLC-purified native and 7-HOC-treated sPLA2s, which were used in pharmacological experiments to compare their biological activities. In vivo anti-inflammatory activity was assessed by the sPLA2-induced mouse paw edema model, in which 7-HOC presented an effect similar to those of dexamethasone and cyproheptadine against the pro-inflammatory effect induced by native sPLA2 on the mouse paw edema, mast cell degranulation and skin edema. On the other hand, 7-HOC exhibited a more potent inhibitory effect on sPLA2 than that of p-bromophenacyl bromide (p-BPB). Our data suggest that 7-HOC interacts with sPLA2 and causes some structural modifications that lead to a sharp decrease or inhibition of the edematogenic and myotoxic activities of this enzyme, indicating its potential use to suppress inflammation induced by sPLA2 from the snake venom.

Vitamin E: the shrew waiting to be tamed

Vitamin E is the last of all vitamins whose essentiality is not yet understood. Its widely accepted role as a lipophilic antioxidant has been questioned, since proof of its in vivo relevance remained scarce. The influence of vitamin E on biomarkers of oxidative stress in vivo is inconsistent and metabolites of vitamin E having reacted as an antioxidant are hardly detectable. Novel functions of vitamin E include the regulation of enzymes, most of which are membrane bound or activated by membrane recruitment. Also, expression of genes responds to vitamin E. The search for a transcription factor common to all regulated genes failed so far and a receptor that specifically binds vitamin E has not yet been identified. According to microarray data, pathways preferentially affected by the vitamin E status are the inflammatory response and cellular traffic. A role of vitamin E in cellular trafficking could best explain the neurological symptoms seen in vitamin E deficiency. Emerging knowledge on vitamin E is compiled here with the perspective to unravel the molecular mechanisms that could more likely explain the essentiality of the vitamin than its ability to scavenge free radicals.

Insights into the role of oligomeric state on the biological activities of crotoxin: crystal structure of a tetrameric phospholipase A2 formed by two isoforms of crotoxin B from Crotalus durissus terrificus venom

Crotoxin B (CB or Cdt PLA(2)) is a basic Asp49-PLA(2) found in the venom of Crotalus durissus terrificus and it is one of the subunits that constitute the crotoxin (Cro). This heterodimeric toxin, main component of the C. d. terrificus venom, is completed by an acidic, nontoxic, and nonenzymatic component (crotoxin A, CA or crotapotin), and it is related to important envenomation effects such as neurological disorders, myotoxicity, and renal failure. Although Cro has been crystallized since 1938, no crystal structure of this toxin or its subunits is currently available. In this work, the authors present the crystal structure of a novel tetrameric complex formed by two dimers of crotoxin B isoforms (CB1 and CB2). The results suggest that these assemblies are stable in solution and show that Ser1 and Glu92 of CB1 and CB2, respectively, play an important role in the oligomerization. The tetrameric and dimeric conformations resulting from the association of the isoforms may increase the neurotoxicity of the toxin CB by the creation of new binding sites, which could improve the affinity of the molecular complexes to the presynaptic membrane.

Synthesis and evaluation of nitrostyrene derivative compounds, new snake venom phospholipase A2 inhibitors

Several nitrostyrene derivatives were synthesized and their inhibitive activities on phospholipase A(2) (PLA(2)) from Bothrops jararacussu venom were evaluated. Some compounds were very efficient as inhibition agents against edema-inducing, enzymatic and myotoxic activities. Data revealed that the size of the substitute and substitution position in the nitrostyrene moiety had important influence on the inhibition capacities. The enzymatic kinetic studies show that the nitrostyrene derivatives compounds inhibit PLA(2) in a non-competitive manner. The electronic, molecular and topologic parameters were calculated using ab initio quantum calculations (density functional theory-DFT) and analyzed by chemometric methods (principal component analysis (PCA) and hierarchical cluster analysis (HCA)) in order to build models able to establish relationships between the electronic features and the structure-activity presented by the target compound. Compounds with the nitro group in the ortho, meta and para position (compounds 2-4) on the aromatic ring were more efficient in the inhibition of PLA(2) activity in all tests. These results indicate that the influence of the nitro group in the aromatic ring is, in fact, important. In addition, quantum chemistry calculations show that compounds with a higher capacity of inhibiting PLA(2) present lower values of highest occupied molecular orbital (HOMO) energy and polarizability, suggesting the formation of a charge-transferring complex between the nitrostyrene compounds and PLA(2).

Tocopherols and tocotrienols in membranes: a critical review

The familiar role of tocols (tocopherols and tocotrienols) as lipid-soluble chain-terminating inhibitors of lipid peroxidation is currently in the midst of a reinterpretation. New biological activities have been described for tocols that apparently are not dependent on their well-established antioxidant behaviour. These activities could well be real, but there remain large gaps in our understanding of the behaviour of tocols in membranes, especially when it comes to the alpha-, beta-, gamma-, delta-chroman methylation patterns and the seemingly special nature of tocotrienols. It is inappropriate to make conclusions and develop models based on in vivo (or cell culture) results with reference to in vitro measurements of antioxidant activity. When present in biological membranes, tocols will experience a large variation in the local composition of phospholipids and the presence of neutral lipids such as cholesterol, both of which would be expected to change the efficiency of antioxidant action. It is likely that tocols are not homogeneously dispersed in a membrane, but it is still not known whether any specific combination of lipid head group and acyl chains are conferred special protection from peroxidation, nor do we currently appreciate the structural role that tocols play in membranes. Tocols may enhance curvature stress or counteract similar stresses generated by other lipids such as lysolipids. This review will outline what is known about the location and behaviour of tocols in phospholipid bilayers. We will draw mainly from the biophysical literature, but will attempt to extend the discussion to biologically relevant phenomena when appropriate. We hope that it will assist researchers when designing new experiments and when critically assessing the results, in turn providing a more thorough understanding of the biochemistry of tocols.

Roselle (Hibiscus sabdariffa) seed oil is a rich source of gamma-tocopherol

The antioxidant potential of roselle (Hibiscus sabdariffa L.) extracts was studied. Different plant organs, including seeds, stems, leaves, and sepals, were analyzed with respect to their water-soluble antioxidant capacity, lipid-soluble antioxidant capacity, and tocopherol content, revealing that roselle seeds are a good source of lipid-soluble antioxidants, particularly gamma-tocopherol. Roselle seed oil was extracted and characterized, and its physicochemical parameters are summarized: acidity, 2.24%; peroxide index, 8.63 meq/kg; extinction coefficients at 232 (k(232)) and 270 nm (k(270)), 3.19 and 1.46, respectively; oxidative stability, 15.53 h; refractive index, 1.477; density, 0.92 kg/L; and viscosity, 15.9 cP. Roselle seed oil belongs to the linoleic/oleic category, its most abundant fatty acids being C18:2 (40.1%), C18:1 (28%), C16:0 (20%), C18:0 (5.3%), and C19:1 (1.7%). Sterols include beta-sitosterol (71.9%), campesterol (13.6%), Delta-5-avenasterol (5.9%), cholesterol (1.35%), and clerosterol (0.6%). Total tocopherols were detected at an average concentration of 2000 mg/kg, including alpha-tocopherol (25%), gamma-tocopherol (74.5%), and delta-tocopherol (0.5%). The global characteristics of roselle seed oil suggest that it could have important industrial applications, adding to the traditional use of roselle sepals in the elaboration of karkade tea.

Tocopherol functions in photosynthetic organisms

During the past decade, the genes required for tocopherol (vitamin E) synthesis in plants and cyanobacteria have been identified. A series of mutants in which specific pathway steps are disrupted have been generated, providing new insights into tocopherol functions in photosynthetic organisms. Tocopherols are essential for controlling non-enzymatic lipid peroxidation during seed dormancy and seedling germination. Their absence results in elevated levels of malondialdehyde and phytoprostanes, and in inappropriate activation of plant defense responses. Surprisingly, tocopherol deficiency in mature leaves has limited consequences under most abiotic stresses, including high intensity light stress. The cell wall development of phloem transfer cells under cold conditions is, however, severely impaired in mature leaves of tocopherol-deficient mutants, indicating that tocopherols are required for proper adaptation of phloem loading at low temperatures.

Antioxidant modulation of oxidant-stimulated uptake and release of arachidonic acid in eicosapentaenoic acid-supplemented human lymphoma U937 cells

Omega-3 polyunsaturated fatty acids (PUFA) are increasingly finding use as treatments for a variety of medical conditions. PUFA supplementation can, however, result in increased oxidative stress causing elevated turnover rate of membrane phospholipids, impairment of membrane integrity and increased formation of inflammatory mediators. The aim of this study was to determine which antioxidant compounds were most effective in ameliorating the stimulation of phospholipid turnover by oxidative stress. U937 cells were supplemented with eicosapentaenoic acid and either ascorbic acid, alpha-tocopherol, beta-carotene or astaxanthin prior to being challenged with oxidant. Although all antioxidants were found to be effective in decreasing oxidant-stimulated peroxide formation, only alpha-tocopherol significantly decreased oxidant-stimulated release of 3H-labeled arachidonic acid (AA), while ascorbic acid markedly increased release. All antioxidants except alpha-tocopherol decreased oxidant-stimulated 3H-AA uptake. Our data suggest that antioxidants are not equally effective in combating the effects of oxidative stress upon membrane phospholipid turnover, and that optimal protection will require mixtures of antioxidants.

Modulation of signal transduction by vitamin E

The ability of vitamin E to modulate signal transduction and gene expression has been observed in numerous studies; however, the detailed molecular mechanisms involved are often not clear. The eight natural vitamin E analogues and synthetic derivatives affect signal transduction with different potency, possibly reflecting their different ability to interact with specific proteins. Vitamin E modulates the activity of several enzymes involved in signal transduction, such as protein kinase C, protein kinase B, protein tyrosine kinases, 5-, 12-, and 15-lipoxygenases, cyclooxygenase-2, phospholipase A2, protein phosphatase 2A, protein tyrosine phosphatase, and diacylglycerol kinase. Activation of some these enzymes after stimulation of cell surface receptors with growth factors or cytokines can be normalized by vitamin E. At the molecular level, the translocation of several of these enzymes to the plasma membrane is affected by vitamin E, suggesting that the modulation of protein-membrane interactions may be a common theme for vitamin E action. In this review the main effects of vitamin E on enzymes involved in signal transduction are summarized and the possible mechanisms leading to enzyme modulation evaluated. The elucidation of the molecular and cellular events affected by vitamin E could reveal novel strategies and molecular targets for developing similarly acting compounds.