Marija Brgles

Entrapment of Ovalbumin into Liposomes—Factors Affecting Entrapment Efficiency, Liposome Size, and Zeta Potential

Various amounts of Ovalbumin (OVA) were encapsulated into positively and negatively charged multilamellar liposomes, with the aim to investigate the entrapment efficiency in different buffers and to study their effects on the liposome size and zeta potential. Results showed that the entrapment efficiency of OVA in anionic liposomes was the same in 10 mM Phosphate Buffer (PB) as in Phosphate-Buffered Saline (PBS; PB + 0.15 M NaCl). Also, liposome size was approximately 1200 nm for all anionic liposomes incorporating OVA. The entrapment efficiency of OVA in cationic liposomes was highly dependent on ionic strength. The size of cationic liposomes was approximately 1200 nm in PBS, regardless of protein content, but increased with the amount of the incorporated protein in PB. Aggregation of cationic liposomes in PB was observed when the mass of the protein was 2.5 mg or greater. The zeta potential of anionic liposomes was negative and of cationic liposomes positive in the whole range of protein mass tested. These results show how different compositions of lipid and aqueous phases can be used to vary the entrapment efficiency, liposome size, and zeta potential—the factors that are of great importance for the use of liposomes as drug carriers.

Concentration and purification of rubella virus using monolithic chromatographic support.

The production of economically acceptable viral vaccines of high quality requires simple and efficient methods for purification and concentration of viral particles. Ion-exchange chromatography (IEC) has become one of commonly used methods for large-scale downstream purification of viruses. Viruses possess different biological and/or biochemical properties and therefore IEC conditions must be established specifically for each virus. Live attenuated rubella virus vaccines have been manufactured and successfully used widely to protect people from rubella and congenital rubella syndrome for almost 40 years. The aim of this study was to search for an efficient method for concentration and purification of rubella virus using IEC. The selected operating conditions using quaternary amine monolithic supports enabled highly efficient binding, purification and concentration of rubella virus from complex biological suspension without additional procedures. Eluted viral particles maintained their infectivity and viral recovery was almost 100%. At the same time, viral preparation was successfully depleted from host cell protein and DNA. This work indicates the possibility of using monoliths to improve the rubella virus yields in productions where high virus titers during cultivation can hardly be achieved.

Liposome fusogenicity and entrapment efficiency of antigen determine the Th1/Th2 bias of antigen-specific immune response.

Liposomes, either alone or in combination with additional immunostimulatory molecules, could be used for the delivery of antigens as vaccine adjuvants. The aim of this study was to investigate the influence of (a) composition (fusogenicity and charge) of large multilamellar liposomes, (b) antigen entrapment efficiency into cationic liposomes and (c) addition of immunostimulatory peptidoglycan monomer (PGM) into liposomal formulations on intensity and direction of antigen-specific humoral immune response. Ovalbumin (OVA) was used as a model antigen and liposomal formulations were tested in a well defined experimental mice model. It was shown that, by means of controlling ionic strength of the media, entrapment efficiency of OVA was enhanced and this lead to Th1 biased immune response. Also, by varying liposome composition and increasing fusogenicity of liposomes immune response was directed toward Th1. Addition of immunostimulatory PGM into liposomal formulation resulted in a switch toward Th2 type immune response.

Selectivity of monolithic supports under overloading conditions and their use for separation of human plasma and isolation of low abundance proteins

Human serum albumin (HSA) and immunoglobulin G (IgG) represent over 75% of all proteins present in human plasma. These two proteins frequently interfere with detection, determination and purification of low abundance proteins that can be potential biomarkers and biomarker candidates for various diseases. Some low abundance plasma proteins such as clotting factors and inhibitors are also important therapeutic agents. In this paper, the characterization of ion-exchange monolithic supports under overloading conditions was performed by use of sample displacement chromatography (SDC). If these supports were used for separation of human plasma, the composition of bound and eluted proteins in both anion- and cation-exchange mode is dependent on column loading. Under overloading conditions, the weakly bound proteins such as HSA in anion-exchange and IgG in cation-exchange mode are displaced by stronger binding proteins, and this phenomenon was not dependent on column size. Consequently, small monolithic columns with a column volume of 100 and 200 μL are ideal supports for high-throughput screening in order to develop new methods for separation of complex mixtures, and for sample preparation in proteomic technology.

Ammodytagin, a heterodimeric metalloproteinase from Vipera ammodytes ammodytes venom with strong hemorrhagic activity

Ammodytagin, a hemorrhagic Zn(2+)-dependent metalloproteinase from Vipera ammodytes ammodytes (Vaa) venom, is a glycosylated heterodimer of 108 kDa, as determined by MALDI mass spectrometry. Partial amino acid sequencing by Edman degradation and MS/MS analysis identified sequences belonging to metalloproteinase, disintegrin-like and cysteine-rich domains, which in addition to its heterodimeric nature allows classification into the P-IIIc group of snake venom metalloproteinases (SVMPs). Only few members of that group have been described so far. Ammodytagin possesses potent azocaseinolytic activity which can be inhibited by Na(2)EDTA, Zn(2+) and DTT. It cleaves insulin B-chain, hydrolysing it at positions Gln(4)-His(5), His(10)-Leu(11) and Tyr(16)-Leu(17). Furthermore, ammodytagin acts as a strong hemorrhagin in both rats and mice. Investigation of a substrate specificity revealed that the hemorrhagic activity of the novel SVMP might be the result of its involvement in cleavage of basal membrane components and depletion of fibrinogen, prothrombin and factor X in blood circulation. Finally, antiserum raised against ammodytagin was able to completely neutralise the hemorrhagic activity of the whole venom, suggesting it might be one of the key molecules towards which effective Vaa specific antivenom should be directed.

The role of antibodies specific for toxic sPLA2s and haemorrhagins in neutralizing potential of antisera raised against Vipera ammodytes ammodytes venom

The contribution of antibodies directed against the two main toxic groups of proteins in the Vipera ammodytes ammodytes venom, haemorrhagic metalloproteinases (H) and neurotoxic sPLA2s (Atxs), to the overall protective efficacy of the whole venom antisera was investigated. Using ELISA assays we established a high correlation between the protective efficacy of the whole venom antisera in mice and their anti-Atxs antibody content. As the haemorrhage is the prevailing toxic effect of the venom in human, the lack of correlation also with anti-H IgG content exposed that the mouse model might not be optimal to evaluate the neutralizing potential of the venom-specific antisera for human therapy. We further revealed that Atxs and structurally very similar but non-toxic AtnI2 from the venom are not immuno cross-reactive.

Influence of charge ratio of liposome/DNA complexes on their size after extrusion and transfection efficiency

Background Physicochemical characteristics of liposome/DNA complexes influence transfection efficiency and affect each other in a very intricate way. The result of this is discrepancies in conclusions drawn about the individual influence of each one. Methods Aiming to elucidate the influence of liposome/DNA charge ratio and size on transfection efficiency and on each other, we used liposome/DNA complexes with charge ratio (+/−) in the range of 1–50 and extruded through membranes of 400, 200, and 100 nm. Plasmid DNA encoding green fluorescent protein was used to measure transfection efficiency by flow cytometry. Sizes of liposome/DNA complexes were measured by dynamic light scattering. Results Liposome size was reduced after extrusion but this was mainly driven by the charge ratio and not by the size of the membrane pores. Reduction of complex size at each charge ratio positively correlated with transfection efficiency. When the size of the complexes was approximately constant, increasing the charge ratio was found to promote transfection efficiency. Cationic lipid N-(1-(2,3-dioleoyloxy)propyl)N,N,N trimethylammonium chloride was used for modulation of positive charge and a cytotoxicity test showed that increasing its amount increases cytotoxicity. Conclusion It can be concluded that charge ratio dictates the size of the complex whereas overall size reduction and higher charge ratios promote transfection efficiency in vitro.

Identification of proteins interacting with ammodytoxins in Vipera ammodytes ammodytes venom by immuno-affinity chromatography.

In order to perform their function, proteins frequently interact with other proteins. Various methods are used to reveal protein interacting partners, and affinity chromatography is one of them. Snake venom is composed mostly of proteins, and various protein complexes in the venom have been found to exhibit higher toxicity levels than respective components separately. Complexes can modulate envenomation activity of a venom and/or potentiate its effect. Our previous data indicate that the most toxic components of the Vipera ammodytes ammodytes (Vaa) venom isolated so far—ammodytoxins (Atxs)—are contributing to the venom’s toxicity only moderately; therefore, we aimed to explore whether they have some interacting partner(s) potentiating toxicity. For screening of possible interactions, immuno-affinity chromatography combined with identification by mass spectrometry was used. Various chemistries (epoxy, carbonyldiimidazole, ethylenediamine) as well as protein G functionality were used to immobilize antibodies on monolith support, a Convective Interaction Media disk. Monoliths have been demonstrated to better suit the separation of large biomolecules. Using such approach, several proteins were indicated as potential Atx-binding proteins. Among these, the interaction of Atxs with a Kunitz-type inhibitor was confirmed by far-Western dot-blot and surface plasmon resonance measurement. It can be concluded that affinity chromatography on monolithic columns combined with mass spectrometry identification is a successful approach for screening of protein interactions and it resulted with detection of the interaction of Atx with Kunitz-type inhibitor in Vaa venom for the first time.

Studying disulfide bond rearrangement by MALDI‐RTOF PSD and MALDI‐TOF/RTOF high‐energy CID (20 keV) experiments of peptides derived from ammodytoxins

Ammodytoxins (Atxs) are presynaptically neurotoxic phospholipases present in Vipera ammodytes ammodytes snake venom. Atxs show a high sequence homology and contain 14 cysteines which form seven biologically relevant disulfide bridges-connecting non-neighboring cysteines. Formic acid cleavage was performed to confirm protein sequences by MALDI RTOF MS and resulted in 95.6% sequence coverage exhibiting only few formylations. Cysteine-containing peptides showed adjacent signals 2 and/or 4 Da lower (according to the number of cysteines present in the peptide) than the theoretical molecular weight indicating disulfide bridge rearrangement. Post-source decay (PSD) and high-energy collision-induced dissociation (CID) at 20 keV experiments showed fragmentation pattern unique for the reduced, thiol group containing and the oxidized, disulfide bridge harboring peptides. Besides typical low-energy fragment ions observed during PSD experiments (a-, b-, y-type ions), additional high-energy fragment ions (c-, x-, w-, d-type and internal fragments) of significant intensity were generated during fragmentation at 20 keV. In the case of charge directing N- and C-termini, x- and w-type ions were also observed during PSD. Good and up to complete sequence coverage was achieved for all studied peptides from Atxs in the case of high-energy CID, whereas PSD lacked information particularly for larger peptides.

The standard mouse assay of anti-venom quality does not measure antibodies neutralising the haemorrhagic activity of Vipera ammodytes venom

The venom of Vipera ammodytes ammodytes (Vaa), like the venoms of other Viperinae snakes, is largely haemorrhagic and necrotising, and only to a lesser extent neurotoxic to humans. The components most extensively studied so far, and most probably involved in generating the observed pathologies, are haemorrhagins (H), members of the metalloproteinase group of enzymes, and neurotoxic ammodytoxins (Atxs), that belong to the secretory phospholipases A2. Rabbit antisera were prepared containing functional antibodies specific for each class of pathology-inducing venom constituents and for both classes together. The involvement of these antibodies in neutralising the toxicity of whole Vaa venom was assessed using the ED50 assay in mice. This assay is the only regulatorily approved assay for estimating anti-venom potency and as such has the task to quantify the active compound neutralising venom-induced pathology of the anti-venom. Fully functional anti-Atx antibodies were shown to be responsible for neutralising the portion of venom toxicity, while anti-H antibodies were not protective in this assay. Thus, the mouse ED50 assay, intended to measure the active principle of the anti-venom, does not measure antibodies specific for Vaa venom haemorrhagins, and consequently does not fulfil its primary task from the regulatory point of view.