Pharmacokinetics and Tissue Distribution of Bee Venom-Derived Phospholipase A2 Using a Sandwich ELISA after Subcutaneous Injection of New Composition Bee Venom in Rats

Bee venom is a traditional drug used to treat the nervous system, musculoskeletal system, and autoimmune diseases. A previous study found that bee venom and one of its components, phospholipase A2, can protect the brain by suppressing neuroinflammation and can also be used to treat Alzheimer's disease. Thus, new composition bee venom (NCBV), which has an increased phospholipase A2 content of up to 76.2%, was developed as a treatment agent for Alzheimer's disease by INISTst (Republic of Korea). The aim of this study was to characterize the pharmacokinetic profiles of phospholipase A2 contained in NCBV in rats. Single subcutaneous administration of NCBV at doses ranging from 0.2 mg/kg to 5 mg/kg was conducted, and pharmacokinetic parameters of bee venom-derived phospholipase A2 (bvPLA2) increased in a dose-dependent manner. Additionally, no accumulation was observed following multiple dosings (0.5 mg/kg/week), and other constituents of NCBV did not affect the pharmacokinetic profile of bvPLA2. After subcutaneous injection of NCBV, the tissue-to-plasma ratios of bvPLA2 for the tested nine tissues were all <1.0, indicating a limited distribution of the bvPLA2 within the tissues. The findings of this study may help understand the pharmacokinetic characteristics of bvPLA2 and provide useful information for the clinical application of NCBV.

Bee Venom: From Venom to Drug

Insects of the order Hymenoptera have a defensive substance that contains many biologically active compounds. Specifically, venom from honeybees (Apis mellifera) contains many enzymes and peptides that are effective against various diseases. Different research papers stated the possibility of using bee venom (a direct bee sting or in an injectable form) in treating several complications; either in vivo or in vitro. Other reports used the active fractions of bee venom clinically or at labratory scale. Many reports and publications have stated that bee venom and its constituents have multiple biological activities including anti-microbial, anti-protozoan, anti-cancer, anti-inflammatory, and anti-arthritic properties. The present review aims to refer to the use of bee venom itself or its fractions in treating several diseases and counteracting drug toxicities as an alternative protocol of therapy. The updated molecular mechanisms of actions of bee venom and its components are discussed in light of the previous updated publications. The review also summarizes the potential of venom loaded on nanoparticles as a drug delivery vehicle and its molecular mechanisms. Finally, the products of bee venom available in markets are also demonstrated.

Bee Venom Phospholipase A2 Ameliorates Atherosclerosis by Modulating Regulatory T Cells

Atherosclerosis is a chronic inflammatory disease caused by lipids and calcareous accumulations in the vascular wall due to an inflammatory reaction. Recent reports have demonstrated that regulatory T (Treg) cells have an important role as a new treatment for atherosclerosis. This study suggests that bee venom phospholipase A2 (bvPLA2) may be a potential therapeutic agent in atherosclerosis by inducing Treg cells. We examined the effects of bvPLA2 on atherosclerosis using ApoE^-/- and ApoE^-/-/Foxp3^DTR mice. In this study, bvPLA2 increased Treg cells, followed by a decrease in lipid accumulation in the aorta and aortic valve and the formation of foam cells. Importantly, the effect of bvPLA2 was found to depend on Treg cells. This study suggests that bvPLA2 can be a potential therapeutic agent for atherosclerosis.

Illustrating Interfacial Interaction between Honey Bee Venom Phospholipase A2 and Supported Negatively Charged Lipids with Sum Frequency Generation and Laser Scanning Confocal Microscopy

Phospholipase A₂ is an important enzyme species which can widely be found in animals, plants, bacteria, and so on. A large number of studies have shown that phospholipase A₂ is highly catalytic toward the lipids. Here, sum frequency generation (SFG) vibrational spectroscopy and laser scanning confocal microscopy (LSCM) were applied to study the interaction between honey bee venom phospholipase A₂ (bvPLA₂) and the negatively charged DPPG bilayer. In both cases without and with the calcium ions (Ca²⁺), the bvPLA₂ molecules were adsorbed onto the outer leaflet surface with the orientational order, and the adsorbed bvPLA₂ molecules damaged the order of the packed outer leaflet. In comparison to the case without Ca²⁺, the addition of Ca²⁺ can accelerate the attaching process of bvPLA₂ to the outer leaflet surface and decelerate the process of damaging the outer leaflet order. The experimental result also confirmed, with the help of the Ca²⁺, the DPPG molecules in the outer leaflet were hydrolyzed, with both hydrolysates, that is, lysophospholipids and fatty acids, remaining at the interface, showing a distinct difference from previous published literatures regarding neutral lipids [Phys. Chem. Chem. Phys. 2018, 20, 63-67] and PLA₁ [Langmuir 2019, 35, 12831-12838].

Bee Venom Phospholipase A2 Induces Regulatory T Cell Populations by Suppressing Apoptotic Signaling Pathway

Bee venom phospholipase A2 is a lipolytic enzyme in bee venom that catalyzes hydrolysis of the sn-2 ester bond of membrane phospholipids to produce free fatty acid and lysophospholipids. Current evidence suggests that bee venom phospholipase A2 (bvPLA2) induces regulatory T cell expansion and attenuates several immune system-related diseases, including Alzheimer's disease. The induction of Treg cells is directly mediated by binding to mannose receptors on dendritic cells. This interaction induces the PGE2-EP2 signaling pathway, which promotes Treg induction in CD4⁺ T cells. In this study, we investigated the effects of bvPLA2 treatment on the apoptotic signaling pathway in Treg populations. Flow cytometry was performed to identify early apoptotic cells. As a result, early apoptotic cells were dramatically decreased in bvPLA2-treated splenocytes, whereas rapamycin-treated cells showed levels of apoptotic cells similar to those of PBS-treated cells. Furthermore, bvPLA2 treatment increased expression of anti-apoptotic molecules including CTLA-4 and PD-1. The survival rate increased in bvPLA2-treated Tregs. Our findings indicate that bvPLA2-mediated modulation of apoptotic signaling is strongly associated with the Treg induction, which exhibits protective effects against various immune-related diseases. To our knowledge, this study is the first to demonstrate that bvPLA2 is the major bee venom (BV) compound capable of inducing Treg expansion through altering apoptotic signal.

Polyunsaturated Phospholipid Modified Membrane Degradation Catalyzed by a Secreted Phospholipase A2

To optimize the compositions of the lipid-based nanomedicine and to advance understanding of the roles of polyunsaturated phospholipids in biological membranes, this study examined the effects of polyunsaturated phospholipids on the degradation of giant unilamellar vesicles catalyzed by a secreted phospholipase A2 (sPLA₂) using fluorescence microscopy. Molecular interfacial packing, interaction, and degradation of the films containing various mixing ratios of saturated and polyunsaturated phospholipids were quantified using a Langmuir trough integrated with synchrotron X-ray surface scattering techniques. It was found that a high molar fraction (0.63 and above) of polyunsaturated phospholipids not only enhanced the rate of sPLA₂-catalyzed vesicle degradation but also changed the vesicle deformation process and degradation product morphology. Hydrolysis of the saturated phospholipids generated highly ordered liquid crystal domains, which was reduced or prohibited by the presence of the polyunsaturated phospholipids in the reactant film.

Prophylactic Effects of Bee Venom Phospholipase A2 in Lipopolysaccharide-Induced Pregnancy Loss

Spontaneous abortion represents a common form of embryonic loss caused by early pregnancy failure. In the present study, we investigated the prophylactic effects of bee venom phospholipase A2 (bvPLA2), a regulatory T cell (Treg) inducer, on a lipopolysaccharide (LPS)-induced abortion mouse model. Fetal loss, including viable implants, the fetal resorption rate, and the fetal weight, were measured after LPS and bvPLA2 treatment. The levels of serum and tissue inflammatory cytokines were determined. To investigate the involvement of the Treg population in bvPLA2-mediated protection against fetal loss, the effect of Treg depletion was evaluated following bvPLA2 and LPS treatment. The results clearly revealed that bvPLA2 can prevent fetal loss accompanied by growth restriction in the remaining viable fetus. When the LPS-induced abortion mice were treated with bvPLA2, Treg cells were significantly increased compared with those in the non-pregnant, PBS, and LPS groups. After LPS injection, the levels of proinflammatory cytokines were markedly increased compared with those in the PBS mouse group, while bvPLA2 treatment showed significantly decreased TNF-α and IFN-γ expression compared with that in the LPS group. The protective effects of bvPLA2 treatment were not detected in Treg-depleted abortion-prone mice. These findings suggest that bvPLA2 has protective effects in the LPS-induced abortion mouse model by regulating Treg populations.

Bee Venom Phospholipase A2 Alleviate House Dust Mite-Induced Atopic Dermatitis-Like Skin Lesions by the CD206 Mannose Receptor

Atopic dermatitis (AD) is a chronic inflammatory skin disease characterized by highly pruritic, erythematous, and eczematous skin plaques. We previously reported that phospholipase A2 (PLA2) derived from bee venom alleviates AD-like skin lesions induced by 2,4-dinitrochlorobenzene (DNCB) and house dust mite extract (Dermatophagoides farinae extract, DFE) in a murine model. However, the underlying mechanisms of PLA2 action in actopic dermatitis remain unclear. In this study, we showed that PLA2 treatment inhibited epidermal thickness, serum immunoglobulin E (IgE) and cytokine levels, macrophage and mast cell infiltration in the ear of an AD model induced by DFE and DNCB. In contrast, these effects were abrogated in CD206 mannose receptor-deficient mice exposed to DFE and DNCB in the ear. These data suggest that bvPLA2 alleviates atopic skin inflammation via interaction with CD206.

Protective Effects of Intratracheally-Administered Bee Venom Phospholipase A2 on Ovalbumin-Induced Allergic Asthma in Mice

Asthma is a common chronic disease characterized by bronchial inflammation, reversible airway obstruction, and airway hyperresponsiveness (AHR). Current therapeutic options for the management of asthma include inhaled corticosteroids and β2 agonists, which elicit harmful side effects. In the present study, we examined the capacity of phospholipase A2 (PLA2), one of the major components of bee venom (BV), to reduce airway inflammation and improve lung function in an experimental model of asthma. Allergic asthma was induced in female BALB/c mice by intraperitoneal administration of ovalbumin (OVA) on days 0 and 14, followed by intratracheal challenge with 1% OVA six times between days 22 and 30. The infiltration of immune cells, such as Th2 cytokines in the lungs, and the lung histology, were assessed in the OVA-challenged mice in the presence and absence of an intratracheal administration of bvPLA2. We showed that the intratracheal administration of bvPLA2 markedly suppressed the OVA-induced allergic airway inflammation by reducing AHR, overall area of inflammation, and goblet cell hyperplasia. Furthermore, the suppression was associated with a significant decrease in the production of Th2 cytokines, such as IL-4, IL-5, and IL-13, and a reduction in the number of total cells, including eosinophils, macrophages, and neutrophils in the airway.

A continuous spectrophotometric assay that distinguishes between phospholipase A1 and A2 activities

A new spectrophotometric assay was developed to measure, continuously and specifically, phospholipase A1 (PLA1) or phospholipase A2 (PLA2) activities using synthetic glycerophosphatidylcholines (PCs) containing α-eleostearic acid, either at the sn-1 position [1-α-eleostearoyl-2-octadecyl-rac-glycero-3-phosphocholine (EOPC)] or at the sn-2 position [1-octadecyl-2-α-eleostearoyl-rac-glycero-3-phosphocholine (OEPC)]. The substrates were coated onto the wells of microtiter plates. A nonhydrolyzable ether bond, with a non-UV-absorbing alkyl chain, was introduced at the other sn position to prevent acyl chain migration during lipolysis. Upon enzyme action, α-eleostearic acid is liberated and then solubilized into the micellar phase. The PLA1 or PLA2 activity was measured by the increase in absorbance at 272 nm due to the transition of α-eleostearic acid from the adsorbed to the soluble state. EOPC and OEPC differentiate, with excellent accuracy, between PLA1 and PLA2 activity. Lecitase(®), guinea pig pancreatic lipase-related protein 2 (known to be a PLA1 enzyme), bee venom PLA2, and porcine pancreatic PLA2 were all used to validate the assay. Compared with current assays used for continuously measuring PLA1 or PLA2 activities and/or their inhibitors, the development of this sensitive enzymatic method, using coated PC substrate analogs to natural lipids and based on the UV spectroscopic properties of α-eleostearic acid, is a significant improvement.

Regulatory T Cells Contribute to the Inhibition of Radiation-Induced Acute Lung Inflammation via Bee Venom Phospholipase A₂ in Mice

Bee venom has long been used to treat various inflammatory diseases, such as rheumatoid arthritis and multiple sclerosis. Previously, we reported that bee venom phospholipase A₂ (bvPLA₂) has an anti-inflammatory effect through the induction of regulatory T cells. Radiotherapy is a common anti-cancer method, but often causes adverse effects, such as inflammation. This study was conducted to evaluate the protective effects of bvPLA₂ in radiation-induced acute lung inflammation. Mice were focally irradiated with 75 Gy of X-rays in the lung and administered bvPLA₂ six times after radiation. To evaluate the level of inflammation, the number of immune cells, mRNA level of inflammatory cytokine, and histological changes in the lung were measured. BvPLA₂ treatment reduced the accumulation of immune cells, such as macrophages, neutrophils, lymphocytes, and eosinophils. In addition, bvPLA₂ treatment decreased inflammasome-, chemokine-, cytokine- and fibrosis-related genes' mRNA expression. The histological results also demonstrated the attenuating effect of bvPLA₂ on radiation-induced lung inflammation. Furthermore, regulatory T cell depletion abolished the therapeutic effects of bvPLA₂ in radiation-induced pneumonitis, implicating the anti-inflammatory effects of bvPLA₂ are dependent upon regulatory T cells. These results support the therapeutic potential of bvPLA₂ in radiation pneumonitis and fibrosis treatments.

Bee Venom Phospholipase A2: Yesterday's Enemy Becomes Today's Friend

Bee venom therapy has been used to treat immune-related diseases such as arthritis for a long time. Recently, it has revealed that group III secretory phospholipase A₂ from bee venom (bee venom group III sPLA₂) has in vitro and in vivo immunomodulatory effects. A growing number of reports have demonstrated the therapeutic effects of bee venom group III sPLA₂. Notably, new experimental data have shown protective immune responses of bee venom group III sPLA₂ against a wide range of diseases including asthma, Parkinson’s disease, and drug-induced organ inflammation. It is critical to evaluate the beneficial and adverse effects of bee venom group III sPLA₂ because this enzyme is known to be the major allergen of bee venom that can cause anaphylactic shock. For many decades, efforts have been made to avoid its adverse effects. At high concentrations, exposure to bee venom group III sPLA₂ can result in damage to cellular membranes and necrotic cell death. In this review, we summarized the current knowledge about the therapeutic effects of bee venom group III sPLA₂ on several immunological diseases and described the detailed mechanisms of bee venom group III sPLA₂ in regulating various immune responses and physiopathological changes.

CNS myelin structural modification induced in vitro by phospholipases A2

Myelin is the self-stacked membrane surrounding axons; it is also the target of several pathological and/or neurodegenerative processes like multiple sclerosis. These processes involve, among others, the hydrolytic attack by phospholipases. In this work we describe the changes in isolated myelin structure after treatment with several secreted PLA2 (sPLA2), by using small angle x-ray scattering (SAXS) measurements. It was observed that myelin treated with all the tested sPLA2s (from cobra and bee venoms and from pig pancreas) preserved the lamellar structure but displayed an enlarged separation between membranes in certain zones. Additionally, the peak due to membrane asymmetry was clearly enhanced. The coherence length was also lower than the non-treated myelin, indicating increased disorder. These SAXS results were complemented by Langmuir film experiments to follow myelin monolayer hydrolysis at the air/water interface by a decrease in electric surface potential at different surface pressures. All enzymes produced hydrolysis with no major qualitative difference between the isoforms tested.

Analgesic Effects of Bee Venom Derived Phospholipase A(2) in a Mouse Model of Oxaliplatin-Induced Neuropathic Pain

A single infusion of oxaliplatin, which is widely used to treat metastatic colorectal cancer, induces specific sensory neurotoxicity signs that are triggered or aggravated when exposed to cold or mechanical stimuli. Bee Venom (BV) has been traditionally used in Korea to treat various pain symptoms. Our recent study demonstrated that BV alleviates oxaliplatin-induced cold allodynia in rats, via noradrenergic and serotonergic analgesic pathways. In this study, we have further investigated whether BV derived phospholipase A₂ (bvPLA₂) attenuates oxaliplatin-induced cold and mechanical allodynia in mice and its mechanism. The behavioral signs of cold and mechanical allodynia were evaluated by acetone and a von Frey hair test on the hind paw, respectively. The significant allodynia signs were observed from one day after an oxaliplatin injection (6 mg/kg, i.p.). Daily administration of bvPLA₂ (0.2 mg/kg, i.p.) for five consecutive days markedly attenuated cold and mechanical allodynia, which was more potent than the effect of BV (1 mg/kg, i.p.). The depletion of noradrenaline by an injection of N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine hydrochloride (DSP4, 50 mg/kg, i.p.) blocked the analgesic effect of bvPLA₂, whereas the depletion of serotonin by injecting DL-p-chlorophenylalanine (PCPA, 150 mg/kg, i.p.) for three successive days did not. Furthermore, idazoxan (α2-adrenegic receptor antagonist, 1 mg/kg, i.p.) completely blocked bvPLA₂-induced anti-allodynic action, whereas prazosin (α1-adrenegic antagonist, 10 mg/kg, i.p.) did not. These results suggest that bvPLA₂ treatment strongly alleviates oxaliplatin-induced acute cold and mechanical allodynia in mice through the activation of the noradrenergic system, via α2-adrenegic receptors, but not via the serotonergic system.

Effects of human Parvovirus B19 and Bocavirus VP1 unique region on tight junction of human airway epithelial A549 cells

As is widely recognized, human parvovirus B19 (B19) and human bocavirus (HBoV) are important human pathogens. Obviously, both VP1 unique region (VP1u) of B19 and HBoV exhibit the secreted phospholipase A2 (sPLA2)-like enzymatic activity and are recognized to participate in the pathogenesis of lower respiratory tract illnesses. However, exactly how, both VP1u from B19 and HBoV affect tight junction has seldom been addressed. Therefore, this study investigates how B19-VP1u and HBoV-VP1u may affect the tight junction of the airway epithelial A549 cells by examining phospholipase A2 activity and transepithelial electrical resistance (TEER) as well as performing immunoblotting analyses. Experimental results indicate that TEER is more significantly decreased in A549 cells by treatment with TNF-α (10 ng), two dosages of B19-VP1u and BoV-VP1u (400 ng and 4000 ng) or bee venom PLA2 (10 ng) than that of the control. Accordingly, more significantly increased claudin-1 and decreased occludin are detected in A549 cells by treatment with TNF-α or both dosages of HBoV-VP1u than that of the control. Additionally, more significantly decreased Na+/K+ ATPase is observed in A549 cells by treatment with TNF-α, high dosage of B19-VP1u or both dosages of BoV-VP1u than that of the control. Above findings suggest that HBoV-VP1u rather than B19 VP1u likely plays more important roles in the disruption of tight junction in the airway tract. Meanwhile, this discrepancy appears not to be associated with the secreted phospholipase A2 (sPLA2)-like enzymatic activity.

A sting in the tale of TH2 immunity

Allergies are widely considered misguided Th2 cell responses. In this issue, Palm et al. (2013) and Marichal et al. (2013) show that mice mount anti-venom Th2 cell responses that share components of the "allergic" response but confer protection.

Peptide-based immunotherapy: a novel strategy for allergic disease

The T-cell component of the antigen-specific immune response is the target of various novel interventions to modify chronic immunologic disorders, such as allergic diseases. Recent clinical trials have evaluated the safety and efficacy of therapeutic vaccines consisting of short, synthetic, allergen-derived peptides, corresponding to T-cell epitopes from the eliciting antigen. The main advantage of such an approach is the reduction in systemic, immunoglobulin E-mediated adverse events compared with existing whole allergen immunotherapy, often referred to as 'allergy shots'. T-cell peptide epitopes, although capable of inducing immunologic tolerance, are short linear structures that have reduced ability to cross-link mast cell- and basophil-bound immunoglobulin E. The precise mechanism of tolerance induction remains incompletely defined. However, recent data indicate that peptide therapy induces/expands a population of antigen-specific regulatory T-cells. A novel form of treatment combining efficacy with a substantially decreased occurrence of adverse events is likely to have a major impact on the management and prevalence of allergic diseases. Furthermore, the principles of epitope-specific therapy hold promise for the development of therapeutic vaccines for the treatment of autoimmune diseases.

Bee Venom Phospholipase A2, a Good "Chauffeur" for Delivering Tumor Antigen to the MHC I and MHC II Peptide-Loading Compartments of the Dendritic Cells: The Case of NY-ESO-1

Bee venom phospholipase A2 (bvPLA2) is a small, 15kDa enzyme which hydrolyses many phospholipids through interfacial binding. The mutated bvPLA2H34Q (bvPLA2m), in which histidine-34 is replaced by glutamine, is not catalytically active. This protein has been shown to be a suitable membrane anchor and has been suggested as a suitable tumor-antigen vector for the development of novel dendritic cell-based vaccines. To confirm this feature, in this study the fusion protein PNY, composed of NY-ESO-1(NY(s)) fused to the C-terminus of bvPLA2m, was engineered. bvPLA2m enhanced the binding of NY(s) to the membrane of human monocyte-derived dendritic cells (DCs) and, once taken up by the cells, the antigen fused to the vector was directed to both MHC I and MHC II peptide-loading compartments. bvPLA2m was shown to increase the cross-presentation of the NY(s)-derived, restricted HLA-A*02 peptide, NY-ESO-1157-165(NY157-165), at the T1 cell surface. DCs loaded with the fusion protein induced cross-priming of NY(s)-specific CD8 + T-cells with greater efficiency than DCs loaded with NY(s). Sixty-five percent of these NY(s)-specific CD8+ T-cell lines could also be activated with the DCs pulsed with the peptide, NY157-165. Of these CD8+ T-cell lines, two were able to recognize the human melanoma cell line, SK-MEL-37, in a context of HLA-A*02. Only a small number of bvPLA2m CD8+ T-cell lines were induced, indicating the low immunogenicity of the protein. It was concluded that bvPLA2m can be used as a membrane-binding vector to promote MHC class II peptide presentation and MHC class I peptide cross-presentation. Such a system can, therefore, be tested for the preparation of cell-based vaccines.

Bumblebee venom serine protease increases fungal insecticidal virulence by inducing insect melanization

Insect-killing (entomopathogenic) fungi have high potential for controlling agriculturally harmful pests. However, their pathogenicity is slow, and this is one reason for their poor acceptance as a fungal insecticide. The expression of bumblebee, Bombus ignitus, venom serine protease (VSP) by Beauveria bassiana (ERL1170) induced melanization of yellow spotted longicorn beetles (Psacothea hilaris) as an over-reactive immune response, and caused substantially earlier mortality in beet armyworm (Spodopetra exigua) larvae when compared to the wild type. No fungal outgrowth or sporulation was observed on the melanized insects, thus suggesting a self-restriction of the dispersal of the genetically modified fungus in the environment. The research is the first use of a multi-functional bumblebee VSP to significantly increase the speed of fungal pathogenicity, while minimizing the dispersal of the fungal transformant in the environment.

Rational design of immobilized lipases and phospholipases

Immobilization of lipases and phospholipases on, mainly, water insoluble carriers, helps in their economic reuse and in the development of continuous bioprocesses. Design of efficient lipases and phospholipases-immobilized system is rather a difficult task. A lot of research work has been done in order to optimize immobilization techniques and procedures and to develop an efficient immobilized system. A new rational design of immobilized derivatives strategy (RDID) has been conceived in favor of the successful synthesis of optimal lipases and phospholipases-immobilized derivatives, aiming prediction of the immobilized derivative's functionality and the optimization of load studies. RDID begins with the knowledge of structural and functional features of synthesis components (protein and carrier), and the practical goal of immobilized product. RDID was implemented in software named RDID ( 1.0 ). The employment of RDID allows selecting the most appropriate way to prepare immobilized derivatives more efficient in enzymatic bioconversion processes and racemic mixture resolution.

Gangliosides inhibit bee venom melittin cytotoxicity but not phospholipase A(2)-induced degranulation in mast cells

Sting accident by honeybee causes severe pain, inflammation and allergic reaction through IgE-mediated anaphylaxis. In addition to this hypersensitivity, an anaphylactoid reaction occurs by toxic effects even in a non-allergic person via cytolysis followed by similar clinical manifestations. Auto-injectable epinephrine might be effective for bee stings, but cannot inhibit mast cell lysis and degranulation by venom toxins. We used connective tissue type canine mast cell line (CM-MC) for finding an effective measure that might inhibit bee venom toxicity. We evaluated degranulation and cytotoxicity by measurement of β-hexosaminidase release and MTT assay. Melittin and crude bee venom induced the degranulation and cytotoxicity, which were strongly inhibited by mono-sialoganglioside (G(M1)), di-sialoganglioside (G(D1a)) and tri-sialoganglioside (G(T1b)). In contrast, honeybee venom-derived phospholipase A(2) induced the net degranulation directly without cytotoxicity, which was not inhibited by G(M1), G(D1a) and G(T1b). For analysis of distribution of Gα(q) and Gα(i) protein by western blotting, lipid rafts were isolated by using discontinuous sucrose gradient centrifuge. Melittin disrupted the localization of Gα(q) and Gα(i) at lipid raft, but gangliosides stabilized the rafts. As a result from this cell-based study, bee venom-induced anaphylactoid reaction can be explained with melittin cytotoxicity and phospholipase A(2)-induced degranulation. Taken together, gangliosides inhibit the effect of melittin such as degranulation, cytotoxicity and lipid raft disruption but not phospholipase A(2)-induced degranulation in mast cells. Our study shows a potential of gangliosides as a therapeutic tool for anaphylactoid reaction by honeybee sting.

Dual function of a bee venom serine protease: prophenoloxidase-activating factor in arthropods and fibrin(ogen)olytic enzyme in mammals

Bee venom contains a variety of peptides and enzymes, including serine proteases. While the presence of serine proteases in bee venom has been demonstrated, the role of these proteins in bee venom has not been elucidated. Furthermore, there is currently no information available regarding the melanization response or the fibrin(ogen)olytic activity of bee venom serine protease, and the molecular mechanism of its action remains unknown. Here we show that bee venom serine protease (Bi-VSP) is a multifunctional enzyme. In insects, Bi-VSP acts as an arthropod prophenoloxidase (proPO)-activating factor (PPAF), thereby triggering the phenoloxidase (PO) cascade. Bi-VSP injected through the stinger induces a lethal melanization response in target insects by modulating the innate immune response. In mammals, Bi-VSP acts similarly to snake venom serine protease, which exhibits fibrin(ogen)olytic activity. Bi-VSP activates prothrombin and directly degrades fibrinogen into fibrin degradation products, defining roles for Bi-VSP as a prothrombin activator, a thrombin-like protease, and a plasmin-like protease. These findings provide a novel view of the mechanism of bee venom in which the bee venom serine protease kills target insects via a melanization strategy and exhibits fibrin(ogen)olytic activity.

Interfacial binding dynamics of bee venom phospholipase A2 investigated by dynamic light scattering and quartz crystal microbalance

Bee venom phospholipase A(2) (bvPLA(2)) is part of the secretory phospholipase A(2) (sPLA(2)) family whose members are active in biological processes such as signal transduction and lipid metabolism. While controlling sPLA(2) activity is of pharmaceutical interest, the relationship between their mechanistic actions and physiological functions is not well understood. Therefore, we investigated the interfacial binding process of bvPLA(2) to characterize its biophysical properties and gain insight into how membrane binding affects interfacial activation. Attention was focused on the role of membrane electrostatics in the binding process. Although dynamic light scattering experiments indicated that bvPLA(2) does not lyse lipid vesicles, a novel, nonhydrolytic activity was discovered. We employed a supported lipid bilayer platform on the quartz crystal microbalance with dissipation sensor to characterize this bilayer-disrupting behavior and determined that membrane electrostatics influence this activity. The data suggest that (1) adsorption of bvPLA(2) to model membranes is not primarily driven by electrostatic interactions; (2) lipid desorption can follow bvPLA(2) adsorption, resulting in nonhydrolytic bilayer-disruption; and (3) this desorption is driven by electrostatic interactions. Taken together, these findings provide evidence that interfacial binding of bvPLA(2) is a dynamic process, shedding light on how membrane electrostatics can modulate interfacial activation.

Scalaradial, a dialdehyde-containing marine metabolite that causes an unexpected noncovalent PLA2 Inactivation

Several marine terpenoids that contain at least one reactive aldehyde group, such as manoalide and its congeners, possess interesting anti-inflammatory activities that are mediated by the covalent inactivation of secretory phospholipase A(2) (sPLA(2)). Scalaradial, a 1,4-dialdehyde marine terpenoid that was isolated from the sponge Cacospongia mollior, is endowed with a relevant anti-inflammatory profile, both in vitro and in vivo, through selective sPLA(2) inhibition. Due to its peculiar dialdehyde structural feature, it has been proposed that scalaradial exerts its enzymatic inactivation by means of an irreversible covalent modification of its target. In the context of our on-going research on anti-PLA(2) natural products and their interaction at a molecular level, we studied scalaradial in an attempt to shed more light on the molecular mechanism of its PLA(2) inhibition. A detailed analysis of the reaction profile between scalaradial and bee venom PLA(2), a model sPLA(2) that shares a high structural homology with the human synovial enzyme, was performed by a combination of spectroscopic techniques, chemical reactions (selective modifications, biomimetic reactions), and classical protein chemistry (such as proteolytic digestion, HPLC and mass spectrometry), along with molecular modeling studies. Unexpectedly, our data clearly indicated the noncovalent forces to be the leading event in the PLA(2) inactivation process; thus, the covalent modification of the enzyme emerges as only a minor side event in the ligand-enzyme interaction. The overall picture might be useful in the design of SLD analogues as new potential anti-inflammatory compounds that target sPLA(2) enzymes.

Probing phospholipase a(2) with fluorescent phospholipid substrates

The Foerster resonance energy transfer-based sensor, PENN, measures intracellular phospholipase A(2) (PLA(2)) activity in living cells and small organisms. In an attempt to modify the probe for the detection of particular isoforms, we altered the sn-2 fatty acid in such a way that either one or three of the Z double bonds in arachidonic acid were present in the sensor molecule. Arachidonic-acid-mimicking fatty acids were prepared by copper-mediated coupling reactions. Probes with a single double bond in the 5-position exhibited favorable substrate properties for secretory PLA(2)s. In vitro experiments with the novel unsaturated doubly labeled phosphatidylethanolamine derivatives showed preferred cleavage of the sensor PENN2 (one double bond) by the physiologically important group V sPLA(2), while the O-methyl-derivative PMNN2 was accepted best by the isoform from hog pancreas. For experiments in living cells, we demonstrated that bioactivation via S-acetylthioethyl (SATE) groups is essential for probe performance. Surprisingly, membrane-permeant versions of the new sensors that contained double bonds, PENN2 and PENN3, were only cleaved to a minor extent in HeLa cells while the saturated form, PENN, was well accepted.

DNA vaccines and allergic diseases

1. Allergic diseases are characterized by inappropriate immune responses to common environmental antigens. The prevalence of these diseases has been increasing worldwide for reasons that are not exactly clear. 2. Current treatment is largely symptomatic. Because the initial observation that simple plasmid DNA injections resulted in in vivo protein expression and induction of adaptive immune responses to the encoded antigen, the potential of modifying the allergic immune responses by DNA vaccination so as to treat and prevent these diseases has been explored extensively. 3. In the present paper we review preclinical studies using animal models of allergic diseases, with an emphasis on DNA vaccine design, for house dust mite allergens-related allergic asthma.

A protective allergy vaccine based on CpG- and protamine-containing PLGA microparticles

PURPOSE

Allergen-specific immunotherapy (SIT) requires dozens of subcutaneous injections over 3 to 5 years in order to control IgE-mediated hypersensitivity, which is a T-helper 2 (Th2)-associated pathology. This study investigates the use of poly(lactide-co-glycolide) (PLGA) microparticles combined with immunostimulatory oligodeoxynucleotide (CpG), as well as protamine in SIT.

MATERIALS AND METHODS

We prepared microparticle formulations with the major allergen of bee venom, phospholipase A2 (PLA2), and analyzed the effect of co-encapsulated or admixed CpG in both naïve and bee venom allergic mice.

RESULTS

Mice immunized with microparticles containing only PLA2 induced weak antibody responses. In contrast, the combination with CpG resulted in strong PLA2-specific antibody responses. The presence of CpG was required for the induction of the Th1-associated isotype IgG2a, and the titers of IgG2a in sensitized mice correlated with a better protection against an allergen challenge. The effect of CpG was further strengthened when protamine was co-encapsulated for complexation of CpG.

CONCLUSIONS

This study shows that allergen-specific immunotherapy with a PLGA-based allergen-delivery system in combination with CpG enhanced the induction of protective IgG2a immune responses. This may improve SIT compliance and shorten its duration.

Towards abolition of immunogenic structures in insect cells: characterization of a honey-bee (Apis mellifera) multi-gene family reveals both an allergy-related core alpha1,3-fucosyltransferase and the first insect Lewis-histo-blood-group-related antigen-synthesizing enzyme

Glycoproteins from honey-bee (Apis mellifera), such as phospholipase A2 and hyaluronidase, are well-known major bee-venom allergens. They carry N-linked oligosaccharide structures with two types of alpha1,3-fucosylation: the modification by alpha1,3-fucose of the innermost core GlcNAc, which constitutes an epitope recognized by IgE from some bee-venom-allergic patients, and an antennal Lewis-like GalNAcbeta1,4(Fucalpha1,3)GlcNAc moiety. We now report the cloning and expression of two cDNAs encoding the relevant active alpha1,3-FucTs (alpha1,3-fucosyltransferases). The first sequence, closest to that of fruitfly (Drosophila melanogaster) FucTA, was found to be a core alpha1,3-FucT (EC 2.4.1.214), as judged by several enzyme and biochemical assays. The second cDNA encoded an enzyme, most related to Drosophila FucTC, that was shown to be capable of generating the Le(x) [Galbeta1-4(Fucalpha1-3)GlcNAc] epitope in vitro and is the first Lewis-type alpha1,3-FucT (EC 2.4.1.152) to be described in insects. The transcription levels of these two genes in various tissues were examined: FucTA was found to be predominantly expressed in the brain tissue and venom glands, whereas FucTC transcripts were detected at highest levels in venom and hypopharyngeal glands. Very low expression of a third homologue of unknown function, FucTB, was also observed in various tissues. The characterization of these honey-bee gene products not only accounts for the observed alpha1,3-fucosylation of bee-venom glycoproteins, but is expected to aid the identification and subsequent down-regulation of the FucTs in insect cell lines of biotechnological importance.

Characterization of the N-glycans of recombinant bee venom hyaluronidase (Api m 2) expressed in insect cells

Honeybee venom hyaluronidase (Api m 2) is a major glycoprotein allergen. Previous studies have indicated that recombinant Api m 2 expressed in insect cells has enzyme activity and IgE binding comparable with that of native Api m 2. In contrast, Api m 2 expressed in Escherichia coli does not. In this study, we characterized the carbohydrate side chains of Api m 2 expressed in insect cells, and compared our data with the established carbohydrate structure of native Api m 2. We assessed both the monosaccharide and the oligosaccharide content of recombinant Api m 2 using fluorophore-assisted carbohydrate electrophoresis and HPLC. To identify the amino acid residues at which glycosylation occurs, we digested recombinant Api m 2 with endoproteinase Glu-C and identified the fragments that contained carbohydrate by specific staining. Recombinant Api m 2 expressed in insect cells contains N-acetylglucosamine, mannose, and fucose, as well as trace amounts of glucose and galactose, and the oligosaccharide analysis is consistent with heterogeneous oligosaccharide chains consisting of two to seven monosaccharides. No sialic acid or N-acetylgalactosamine were detected. These results are similar to published data for native Api m 2, although some monosaccharide components appear to be absent in the recombinant protein. Analysis of proteolytic digests indicates that of the four candidate N-glycosylation sites, carbohydrate chains are attached at asparagines 115 and 263. Recombinant Api m 2 expressed in insect cells has enzymic activity and IgE binding comparable with the native protein, and its carbohydrate composition is very similar.

Isoform-specific membrane insertion of secretory phospholipase A2 and functional implications

Despite increasing evidence that the membrane-binding mode of interfacial enzymes including the depth of membrane insertion is crucial for their function, the membrane insertion of phospholipase A(2) (PLA(2)) enzymes has not been studied systematically. Here, we analyze the membrane insertion of human group IB PLA(2) (hIBPLA(2)) and compare it with that of a structurally homologous V3W mutant of human group IIA PLA(2) (V3W-hIIAPLA(2)) and with a structurally divergent group III bee venom PLA(2) (bvPLA(2)). Increasing the anionic charge of membranes results in a blue shift of the fluorescence of Trp(3) of hIBPLA(2), a decrease in quenching by acrylamide, and an increase in enzyme activity, reflecting an enhancement in the membrane binding of PLA(2). Fluorescence quenching by brominated lipids indicates significant penetration of Trp(3) into fluid POPC/POPG membranes but little insertion into the solid DPPC/DPPG membranes. Increased membrane fluidity also supports hIBPLA(2) activity, suggesting that membrane insertion of hIBPLA(2) is controlled by membrane fluidity and is necessary for the full activity of the enzyme. Trp fluorescence quenching of the V3W-hIIAPLA(2) and bvPLA(2) by water- and membrane-soluble quenchers indicates substantial membrane insertion of Trp(3) of V3W-hIIAPLA(2), similar to that found for hIBPLA(2), and no insertion of tryptophans of bvPLA(2). Our results provide evidence that (a) structurally similar group IB and IIA PLA(2)s, but not structurally diverse group III PLA(2), significantly penetrate into membranes; (b) membrane insertion is controlled by membrane fluidity and facilitates activation of IB and IIA PLA(2)s; and (c) structurally distinct PLA(2) isoforms may employ different tactics of substrate accession/product release during lipid hydrolysis.

Conformationally Restricted (+)-Cacospongionolide B Analogues. Influence on Secretory Phospholipase A2 Inhibition

A new approach to (+)-cacospongionolide was developed to access conformationally restricted variants of the natural product. The flexible aliphatic region between the decalin and side chain portion of the natural product was replaced with alkenyl and alkynyl linkers to probe the influence of structural rigidity in the inhibition of secretary phospholipase A2 (sPLA2). It was found that when the aliphatic section is replaced with a Z-olefin or an alkyne, sPLA2 inhibitory activity suffered relative to the natural product; however, an E-olefin-containing analogue led to an enhanced activity. These results suggest that preferred sPLA2 binding conformation of the natural product is similar to the geometry of the E-olefin-containing analogue.

The Molecular Mechanism of Bee Venom Phospholipase A2 Inactivation by Bolinaquinone

The molecular basis of the inactivation of bee venom PLA2 by the marine natural product bolinaquinone (BLQ) was studied by several spectral techniques (CD, fluorescence, and NMR spectroscopy, mass spectrometry), biomimetic reactions, and molecular modeling. Our data suggest competitive inhibition based on a BLQ-PLA2 noncovalent molecular recognition. However, BLQ is also able to react selectively with Lys133 through conjugate addition followed by a beta elimination. The biological implications of both the covalent and noncovalent molecular events are discussed.

PLA2 Inhibitory Activity of Marine Sesterterpenoids Cladocorans, Their Diastereomers and Analogues

Inhibition of secretory phospholipase A(2) (sPLA(2)) by cladocorans A and B and their diastereomers almost equaled that of manoalide.

Regulation of human T helper cell differentiation by antigen-presenting cells: the bee venom phospholipase A2 model

Whereas some individuals develop immunity to bee sting and mount protective IgG4- mediated antibody responses to bee venom phospholipase A2 (PLA), others produce large amounts of PLA-specific IgE antibodies and become allergic to this, otherwise, innocuous antigen. PLA-specific IgE responses are the result of imbalanced T helper (Th)2-cell differentiation. There are multiple mechanisms driving the differentiation of naive CD4+ T cells into Th1- or Th2-cell phenotypes. Most of them are linked to the conditions occurring during initial or repeated encounters with the allergen, in the context of an antigen-presenting cell (APC). The different types of APC and their availability to display particular cytokine production profiles, pattern recognition receptors, costimulatory molecules and specific HLA haplotypes are key determinants for human Th1- and Th2-cell polarization.

Amino acid residues that are important for Hyal2 function as a receptor for jaagsiekte sheep retrovirus

Background

Infection by jaagsiekte sheep retrovirus (JSRV) and by enzootic nasal tumor virus (ENTV) depends on cell-surface expression of the virus entry receptor, hyaluronidase 2 (Hyal2). Human Hyal2 binds the envelope (Env) proteins of these viruses and is functional as a receptor, but Hyal2 from mice does not bind Env nor does it mediate entry of either virus. Here we have explored the amino acid determinants that account for the difference in receptor function.

Results

Analysis of human-mouse Hyal2 chimeric proteins showed that amino acid differences responsible for the difference in Hyal2 receptor activity were localized to the central third of Hyal2. Human Hyal2 mutants containing single or double amino acid replacements with the respective mouse amino acids were generated across this region and were assayed for activity. None of the single or double mutation reduced the receptor activity of human Hyal2 by more than 10-fold, whereas mouse Hyal2 activity is reduced 1,000-fold from that of human Hyal2. While the 3-dimensional structures of mammalian Hyal2 proteins are unknown, bee venom hyaluronidase shows significant amino acid similarity to human and mouse Hyal2 and its structure has been determined. Many mutations having the largest negative effects on human Hyal2 function mapped to a small region of the bee venom hyaluronidase close to but not overlapping the active site of the enzyme, suggesting that this site represents the binding site for Env. Analysis of synonymous and non-synonymous nucleotide substitutions in the coding sequences of multiple mammalian Hyal2 proteins shows that the proteins are undergoing strong selection for amino acid conservation. We found no evidence for positive selection of amino acid changes that might reflect evolution of mammalian hosts to resist JSRV or ENTV infection.

Conclusion

These results show that the greatly reduced receptor activity of mouse Hyal2 in comparison to that of human Hyal2 is determined by multiple amino acid changes acting in concert. In particular, no one amino acid change blocks infection. However, the most important amino acids map to a small patch on a predicted 3-dimensional Hyal2 structure, which may represent the binding site for Env.

Expression and regulation of phospholipase A2 in venom gland of the chinese honeybee, Apis cerana cerana

Phospholipase A(2) (PLA(2)) is one of the components of bee venom with a wide range of pharmacological functions. It operates as a major allergen working with other venom components to defend the colony from intruder. In the present study, the cDNA sequence of the Ac-pla(2) gene from cDNA library of the venom gland of Apis cerana was compared with the amplified corresponding region of genomic DNA. The result showed that the Ac-pla(2) gene consisted of four exons and three introns. Southern blot showed that the Ac-pla(2) gene was a single copy per haploid genome. The most active transcription period was during the first 8 days of adults, which correspondingly was the period of sharp increase of PLA(2) protein. ELISA analysis revealed that the PLA(2) was undetectable in pupal stage and the newly eclosed adult, but increased sharply to a maximum of 10-12 mug per honeybee by 8-10 days of adult life, followed by a gradual decrease to 8 mug for the rest of adult life. Transcriptional or post transcriptional regulation is the key step for Ac-pla(2) expression. The early secreted Ac-PLA(2) showed a low degree of post-translational modification; with increasing age, glycosylation was detected by Western blot and glycoprotein staining analysis. Different post-translational modifications were found among different individuals in A. cerana when compared to A. mellifera.

Sulphated oligosaccharides as inhibitors of hyaluronidases from bovine testis, bee venom and Streptococcus agalactiae

Potent and specific inhibitors of hyaluronidases, a group of enzymes preferentially catalysing the hydrolysis of hyaluronic acid, are not known so far. Such compounds could be useful as pharmacological tools for studying the physiological and pathophysiological role of both hyaluronan and hyaluronidases. The effects of sulphated and non-sulphated structurally different oligosaccharides on bovine testicular hyaluronidase, hyaluronidase from bee venom and hyaluronate lyase from Streptococcus agalactiae (hylB (4755)) were studied with the Morgan-Elson reaction. Several active compounds were identified within a series of sulphated beta-(1,4)-galacto-oligosaccharides. The determined IC (50) values of these sulphated oligosaccharides ranged from 4 microM to 630 microM for all hyaluronan-degrading enzymes. Sulphated oligosaccharides like verbascose, planteose and neomycin showed comparable inhibition on all hyaluronidases, thereby possessing 100 - 500 times the activity of the widely accepted hyaluronidase inhibitor apigenin.

Dendritic-cell activation by secretory phospholipase A2

Dendritic cells (DCs), also referred to as the sentinels of the immune system, induce and coordinate important functions of immune surveillance. DCs acquire immunity-initiating capacity only after a process of maturation usually induced by ligands that bind to members of the tumor necrosis factor (TNF) or toll-like receptor families. Secretory phospholipase A2 (sPLA2), which hydrolyzes the sn-2 ester bond of glycerophospholipids, regulates a variety of cellular functions including migration of endothelial cells and neurite outgrowth. In the present study we investigated the role of sPLA2 in DC biology. We report that human monocyte-derived DC cultures lack sPLA2 activity but respond to exogenous sPLA2. sPLA2 alone and in cooperation with TNF-α and interleukin 1 β (IL-1β) induced fatty acid release from DC membranes, which was accompanied by upregulation of surface markers and by an increase in the migratory and immunostimulatory capacity of the DCs. Our findings indicate that secreted enzymes such as sPLA2 can contribute to DC maturation and emphasize the role of lipid mediators in the regulation of immune responses. This observation may also have implications for DC-based vaccine development.

Cross-presentation of a CMV pp65 epitope by human dendritic cells using bee venom PLA2 as a membrane-binding vector

We have used bee venom phospholipase A2 as a vector to load human dendritic cells ex vivo with a major histocompatibility complex (MHC) class I-restricted epitope fused to its C-terminus. The fusion protein bound to human monocyte-derived dendritic cells and was internalized into early endosomes. In vitro immunization experiments showed that these dendritic cells were able to generate specific CD8 T cell lines against the epitope carried by the fusion protein. Cross-presentation did not require proteasome, transporter associated with antigen processing, or endosome proteases, but required newly synthesized MHC molecules. Comparison of the antigen presentation pathway observed in this study to that followed by other toxins used as vectors is discussed.

Medicinal application of long synthetic peptide technology

This review covers the latest developments of long synthetic peptide technology for the rapid identification and development of malaria vaccine candidates and immunological modulators. A brief description of the two most common solid-phase synthetic procedures, together with the latest advances in optimisation of peptide chain assembly and analytical instrumentation, is given, with special attention to non-specialists. Several examples of vaccine candidates developed in the authors' or their collaborators' laboratories are also provided.

Real-Time Observation for the Enzymatic Reaction of Phospholipid Membrane: Application of the Time-Resolved Quasi-Elastic Laser Scattering Method

An analytical technique to measure reactions in biological membranes was developed and applied to monitoring the hydrolysis reaction of phospholipids (dipalmitoylphosphatidylcholine, DPPC) by phospholipase A(2). The technique uses the time-resolved quasi-elastic laser scattering (TR-QELS) method to measure an oil/phospholipid monolayer/water membrane system by monitoring the change of interfacial tension under a noncontact condition and in real time. When the TR-QELS method is used with the newly developed oil/phospholipid monolayer/water membrane system, measurement of the hydrolysis reaction of phospholipids with long alkyl chains (C >or=16), which are the major components in biological membranes, becomes possible. The reaction progress is monitored by the increase of interfacial tension at the oil/water interface caused by the decrease of surface-active DPPC molecules due to the reaction. The characteristic phases, namely, lag, burst, and equilibrium, are observed. The relationship between the duration of the lag phase (the rate-limiting step of the reaction) and the concentration of calcium ion (an essential cofactor of the reaction) is also investigated. Increase of calcium ion concentration in the subphase is found to shorten the duration of the lag phase. In addition, the real-time measurement simplifies the estimation process for the reaction activation energy.

Further insights on the structural aspects of PLA2 inhibition by γ-hydroxybutenolide-containing natural products: a comparative study on petrosaspongiolides M–R

Petrosaspongiolides M-R (PM-PR, 1-5) are marine sesterterpenes structurally characterised by a gamma-hydroxybutenolide moiety. They have shown an in vitro and in vivo potent anti-inflammatory activity, mediated by specific inhibition of secretory phospholipase A(2) (sPLA(2) enzymes). The molecular mechanism underlying the sub-micromolar irreversible inhibition of the bee-venom PLA(2) (bvPLA(2)) by PM has been clarified combining mass spectrometry (MS) and molecular modelling approaches. The N-terminal amino group (Ile-1 residue), recently identified as the unique PM covalent binding site on this enzyme, selectively delivers a nucleophilic attack onto the masked aldehyde at C-25 of the pharmacophoric gamma-hydroxybutenolide ring of PM, giving rise to a Schiff base. In the attempt of broadening the knowledge of the mechanism at molecular level of PLA(2) inactivation by this family of compounds, we performed a comparative analysis on petrosaspongiolides M-R, whose results are discussed in this paper. Firstly, the amount of bvPLA(2) enzyme covalently modified after incubation with each of petrosaspongiolides M-R was measured and resulted to be in good agreement with pharmacological in vitro data. Then, a full characterisation of the bvPLA(2) adduct with PR, one of the least active and most structurally different among petrosaspongiolides, by LC-MS, MS(n), and computational methods, confirmed the same inhibition mechanism and covalent binding site already found for PM. Finally, extensive molecular docking studies performed in comparison on the PM-PLA(2) and PR-PLA(2) complexes provided critical insight on how the balance between non-covalent and covalent inhibitor-enzyme interactions may affect the final potency exhibited by the various compounds of the petrosaspongiolide family.

Secretory phospholipases A2 induce neurite outgrowth in PC12 cells

sPLA(2)s (secretory phospholipases A(2)) belong to a broad and structurally diverse family of enzymes that hydrolyse the sn -2 ester bond of glycerophospholipids. We previously showed that a secreted fungal 15 kDa protein, named p15, as well as its orthologue from Streptomyces coelicolor (named Scp15) induce neurite outgrowth in PC12 cells at nanomolar concentrations. We report here that both p15 and Scp15 are members of a newly identified group of fungal/bacterial sPLA(2)s. The phospholipid-hydrolysing activity of p15 is absolutely required for neurite outgrowth induction. Mutants with a reduced PLA(2) activity exhibited a comparable reduction in neurite-inducing activity, and the ability to induce neurites closely matched the capacity of various p15 forms to promote fatty acid release from live PC12 cells. A structurally divergent member of the sPLA(2) family, bee venom sPLA(2), also induced neurites in a phospholipase activity-dependent manner, and the same effect was elicited by mouse group V and X sPLA(2)s, but not by group IB and IIA sPLA(2)s. Lysophosphatidylcholine, but not other lysophospholipids, nor arachidonic acid, elicited neurite outgrowth in an L-type Ca(2+) channel activity-dependent manner. In addition, p15-induced neuritogenesis was unaffected by various inhibitors that block arachidonic acid conversion into bioactive eicosanoids. Altogether, these results delineate a novel, Ca(2+)- and lysophosphatidylcholine-dependent neurotrophin-like role of sPLA(2)s in the nervous system.

A low-barrier hydrogen bond between histidine of secreted phospholipase A2 and a transition state analog inhibitor

This work describes in-depth NMR characterization of a unique low-barrier hydrogen bond (LBHB) between an active site residue from the enzyme and a bound inhibitor: the complex between secreted phospholipase A(2) (sPLA(2), from bee venom and bovine pancreas) and a transition-state analog inhibitor HK32. A downfield proton NMR resonance, at 17-18 ppm, was observed in the complex but not in the free enzyme. On the basis of site-specific mutagenesis and specific 15N-decoupling, this downfield resonance was assigned to the active site H48, which is part of the catalytic dyad D99-H48. These results led to a hypothesis that the downfield resonance represents the proton (H(epsilon 2) of H48) involved in the H-bonding between D99 and H48, in analogy with serine proteases. However, this was shown not to be the case by use of the bovine enzyme labeled with specific [15N(epsilon 2)]His. Instead, the downfield resonance arises from H(delta1) of H48, which forms a hydrogen bond with a non-bridging phosphonate oxygen of the inhibitor. Further studies showed that this proton displays a fractionation factor of 0.62(+/-0.06), and an exchange rate protection factor of >100 at 285 K and >40 at 298 K, which are characteristic of a LBHB. The pK(a) of the imidazole ring of H48 was shown to be shifted from 5.7 for the free enzyme to an apparent value of 9.0 in the presence of the inhibitor. These properties are very similar to those of the Asp em leader His LBHBs in serine proteases. Possible structural bases and functional consequences for the different locations of the LBHB between these two types of enzymes are discussed. The results also underscore the importance of using specific isotope labeling, rather than extrapolation of NMR results from other enzyme systems, to assign the downfield proton resonance to a specific hydrogen bond. Although our studies did not permit the strength of the LBHB to be accurately measured, the data do not provide support for an unusually strong hydrogen bond strength (i.e. >10 kcal/mol).

Modulation of the activity of secretory phospholipase A2 by antimicrobial peptides

The antimicrobial peptides magainin 2, indolicidin, and temporins B and L were found to modulate the hydrolytic activity of secretory phospholipase A(2) (sPLA(2)) from bee venom and in human lacrimal fluid. More specifically, hydrolysis of phosphatidylcholine (PC) liposomes by bee venom sPLA(2) at 10 micro M Ca(2+) was attenuated by these peptides while augmented product formation was observed in the presence of 5 mM Ca(2+). The activity of sPLA(2) towards anionic liposomes was significantly enhanced by the antimicrobial peptides at low [Ca(2+)] and was further enhanced in the presence of 5 mM Ca(2+). Similarly, with 5 mM Ca(2+) the hydrolysis of anionic liposomes was enhanced significantly by human lacrimal fluid sPLA(2), while that of PC liposomes was attenuated. These results indicate that concerted action of antimicrobial peptides and sPLA(2) could improve the efficiency of the innate response to infections. Interestingly, inclusion of a cationic gemini surfactant in the vesicles showed an essentially similar pattern on sPLA(2) activity, suggesting that the modulation of the enzyme activity by the antimicrobial peptides may involve also charge properties of the substrate surface.

Bee venom phospholipase inhibits malaria parasite development in transgenic mosquitoes

Malaria kills millions of people every year, and new control measures are urgently needed. The recent demonstration that (effector) genes can be introduced into the mosquito germ line to diminish their ability to transmit the malaria parasite offers new hope toward the fight of the disease (Ito, J., Ghosh, A., Moreira, L. A., Wimmer, E. A. & Jacobs-Lorena, M. (2002) Nature, 417, 452-455). Because of the high selection pressure that an effector gene imposes on the parasite population, development of resistant strains is likely to occur. In search of additional antiparasitic effector genes, we have generated transgenic Anopheles stephensi mosquitoes that express the bee venom phospholipase A2 (PLA2) gene from the gut-specific and blood-inducible Anopheles gambiae carboxypeptidase (AgCP) promoter. Northern blot analysis indicated that the PLA2 mRNA is specifically expressed in the guts of transgenic mosquitoes with peak expression at approximately 4 h after blood ingestion. Western blot and immunofluorescence analyses detected PLA2 protein in the midgut epithelia of transgenic mosquitoes from 8 to 24 h after a blood meal. Importantly, transgene expression reduced Plasmodium berghei oocyst formation by 87% on average and greatly impaired transmission of the parasite to naive mice. The results indicate that PLA2 may be used as an additional effector gene to block the development of the malaria parasite in mosquitoes.

A molecular assembly system that renders antigens of choice highly repetitive for induction of protective B cell responses

Virus like particles (VLPs) are known to induce potent B cell responses in the absence of adjuvants. Moreover, epitope-specific antibody responses may be induced by VLPs that contain peptides inserted in their immunodominant regions. However, due to steric problems, the size of the peptides capable of being incorporated into VLPs while still permitting capsid assembly, is rather limited. While peptides genetically fused to either the N- or C-terminus of VLPs present fewer assembly problems, the immune responses obtained against such epitopes are often limited, most likely because the epitopes are not optimally exposed. In addition, such particles may be less stable in vivo. Here, we show that peptides and proteins engineered to contain a free cys can be chemically coupled to VLPs formed from the hepatitis B core antigen (HBcAg) containing a lys in the immuno-dominant region. By using this approach steric hindrance of capsid assembly is abrogated. Peptides or protein coupled to VLPs in an oriented fashion are shown to induce strong and protective B cell responses even against self-epitopes in the absence of adjuvants. This molecular assembly system may be used to induce strong B cell responses against most antigens.

Molecular basis of phospholipase A2 inhibition by petrosaspongiolide M

Petrosaspongiolide M (PM) is an anti-inflammatory marine metabolite that displays a potent inhibitory activity toward group II and III secretory phospholipase A(2) (PLA(2)) enzymes. The details of the mechanism, which leads to a covalent adduct between PLA(2) and gamma-hydroxybutenolide-containing molecules such as PM, are still a matter of debate. In this paper the covalent binding of PM to bee venom PLA(2) has been investigated by mass spectrometry and molecular modeling. The mass increment observed for the PM-PLA(2) adduct is consistent with the formation of a Schiff base by reaction of a PLA(2) amino group with the hemiacetal function (masked aldehyde) at the C-25 atom of the PM gamma-hydroxybutenolide ring. Proteolysis of the modified PLA(2) by the endoprotease LysC followed by HPLC MS analysis allowed us to establish that the PLA(2) alpha-amino terminal group of the Ile-1 residue was the only covalent binding site for PM. The stoichiometry of the reaction between PM and PLA(2) was also monitored and results showed that even with excess inhibitor, the prevalent product is a 1:1 (inhibitor:enzyme) adduct, although a 2:1 adduct is present as a minor component. The 2:1 adduct was also characterized, which showed that the second site of reaction is located at the epsilon -amino group of the Lys-85 residue. Similar results in terms of the reaction profile, mass increments, and location of the PLA(2) binding site were obtained for manoalide, a paradigm for irreversible PLA(2) inhibitors, which suggests that the present results may be considered of more general interest within the field of anti-inflammatory sesterterpenes that contain the gamma-hydroxybutenolide pharmacophore. Finally, a 3D model, constrained by the above experimental results, was obtained by docking the inhibitor molecule into the PLA(2) binding site through AFFINITY calculations. The model provides an interesting insight into the PM-PLA(2) inhibition process and may prove useful in the design of new anti-inflammatory agents that target PLA(2) secretory enzymes.

Analysis of N-glycosylation of phospholipase A2 from venom of individual bees by microbore high-performance liquid chromatography-electrospray mass spectrometry using an ion trap mass spectrometer

The N-linked oligosaccharides were released from the phospholipase A2 (PLA) with glycopeptidases and reductively aminated with the chromophore, p-aminobenzoic acid ethyl ester (ABEE). The ABEE-labeled oligosaccharides were separated by microbore high-performance liquid chromatography (micro-HPLC) using a reversed-phase column and analyzed by electrospray mass spectrometry. Differentiation between alpha-1,3 and alpha-1,6 core-fucosylated glycans was achieved by comparison the glycans released by glycopeptidases peptide-N-glycanase A (PNase A) and peptide-N-glycanase F (PNase F). All N-linked oligosaccharides except 3B and 3C could be identified in this approach. The analysis of PLA oligosaccharides from the venom of individual bees indicated that glycosylation patterns between the younger and the older bees were similar.

Occupational allergy to bumblebees: allergens of Bombus terrestris

BACKGROUND

With the increase in commercial vegetable production in greenhouses, occupational sensitization to bumblebee venom is becoming more common. Studies using sera from subjects thus sensitized allow evaluation of the allergenic specificity of bumblebee sensitization.

OBJECTIVE

The purposes of this study were to determine the degree of species group specificity of bumblebee venom allergens in sera of allergic patients and to investigate the structural basis of this specificity.

METHODS

Allergens were purified from bumblebee venom, studied serologically by direct binding and inhibition techniques, and characterized by enzyme analysis and amino acid sequencing. Three-dimensional models of the phospholipases were constructed and analyzed.

RESULTS

Bombus terrestris venom contains phospholipase A(2), venom protease, hyaluronidase, and acid phosphatase allergens. The protease and phospholipase A(2) allergens contain IgE-reactive epitopes that are different from those seen in Bombus pennsylvanicus, a North American species. Bumblebee phospholipase A(2) is only 53% identical to honeybee phospholipase A(2). The results of 3-dimensional modeling are consistent with the immunologic observations.

CONCLUSIONS

Patients with primary bumblebee sensitization should be diagnosed and treated with venom from the appropriate species group of bumblebees. Bumblebee venom phospholipase A(2) and protease are antigenically distinct from honeybee venom proteins. There are significant species group-specific epitopes on bumblebee venom proteins.