Lipid microspheres loaded with antigenic membrane proteins of the Leishmania amazonensis as a potential biotechnology application

Production of glycosylphosphatidylinositol-anchored proteins for vaccines and directed binding of immunoliposomes to specific cell types

BACKGROUND

Liposomes are highly useful carriers for delivering drugs or antigens. The association of glycosylphosphatidylinositol (GPI)-anchored proteins to liposomes potentially enhances the immunogenic effect of vaccine antigens by increasing their surface concentration. Furthermore, the introduction of a universal immunoglobulin-binding domain can make liposomes targetable to virtually any desired receptor for which antibodies exist.

METHODS

We developed a system for the production of recombinant proteins with GPI anchors and histidine tags and Strep-tags for simplified purification from cells. This system was applied to i) the green fluorescent protein (GFP) as a reporter, ii) the promising Plasmodium falciparum vaccine antigen PfRH5 and iii) a doubled immunoglobulin Fc-binding domain termed ZZ from protein A of Staphylococcus aureus. As the GPI-attachment domain, the C-terminus of murine CD14 was used. After the recovery of these three recombinant proteins from Chinese hamster ovary (CHO) cells and association with liposomes, their vaccine potential and ability to target the CD4 receptor on lymphocytes in ex vivo conditions were tested.

RESULTS

Upon immunization in mice, the PfRH5-GPI-loaded liposomes generated antibody titers of 103 to 104, and showed a 45% inhibitory effect on in vitro growth at an IgG concentration of 600 µg/mL in P. falciparum cultures. Using GPI-anchored ZZ to couple anti-CD4 antibodies to liposomes, we created immunoliposomes with a binding efficiency of 75% to CD4+ cells in splenocytes and minimal off-target binding.

CONCLUSIONS

Proteins are very effectively associated with liposomes via a GPI-anchor to form proteoliposome particles and these are useful for a variety of applications including vaccines and antibody-mediated targeting of liposomes. Importantly, the CHO-cell and GPI-tagged produced PfRH5 elicited invasion-blocking antibodies qualitatively comparable to other approaches.

Biomedical applications of nanotechnology

The ability to investigate substances at the molecular level has boosted the search for materials with outstanding properties for use in medicine. The application of these novel materials has generated the new research field of nanobiotechnology, which plays a central role in disease diagnosis, drug design and delivery, and implants. In this review, we provide an overview of the use of metallic and metal oxide nanoparticles, carbon-nanotubes, liposomes, and nanopatterned flat surfaces for specific biomedical applications. The chemical and physical properties of the surface of these materials allow their use in diagnosis, biosensing and bioimaging devices, drug delivery systems, and bone substitute implants. The toxicology of these particles is also discussed in the light of a new field referred to as nanotoxicology that studies the surface effects emerging from nanostructured materials.

Liposomal systems as carriers for bioactive compounds

Since the revolutionary discovery that phospholipids can form closed bilayered structures in aqueous systems, the study of liposomes has become a very interesting area of research. The versatility and amazing biocompatibility of liposomes has resulted in their wide-spread use in many scientific fields, and many of their applications, especially in medicine, have yielded breakthroughs in recent decades. Specifically, their easy preparation and various structural aspects have given rise to broadly usable methodologies to internalize different compounds, with either lipophilic or hydrophilic properties. The study of compounds with potential biotechnological application(s) is generally related to evaluation and risk assessment of the possible cytotoxic or therapeutic effects of the compound under study. In most cases, undesirable side-effects are associated with an interaction of the liposome with the cell membrane and/or its absorption and subsequent interaction with a cellular biomolecule. Liposomal carrier systems have an unprecedented potential for delivering bioactive substances to specific molecular targets due to their biocompatibility, biodegradability and low toxicity. Liposomes are therefore considered to be an invaluable asset in applied biotechnology studies due to their potential for interaction with both hydrophilic and lipophilic compounds.

Liposomes loaded with P. falciparum merozoite-derived proteins are highly immunogenic and produce invasion-inhibiting and anti-toxin antibodies

The formulation of an effective vaccine against malaria is still a significant challenge and the induction of high anti-parasite antibody titers plus a sustained T cell response is mandatory for the success of such a vaccine. We have developed a nanoliposome-based structure which contains plasma membrane-associated proteins (PfMNP) of Plasmodium falciparum merozoites on its surface. Incorporation of parasite-derived proteins led to a significant increase in the size and dispersity of particles. Immunization of particles in BalbC and C57BL/6 mice led to high anti-MSP119 IgG titers (10(4)) after the first dose and reached a plateau (>10(6)) after the third dose. While very high titers were observed against the C-terminal domain of the vaccine candidate MSP1, only modest titers (≤10(3)) were detected against MSP2. The induced antibodies showed also a strong growth-inhibiting effect in reinvasion assays. In addition, PfMNP immunization generated antibodies which partially blocked the inflammatory response, probably by blocking TLR-induced activation of macrophages by malarial toxins such as GPI anchors. The results underline the potential of nanoliposome-based formulations as anti-malarial vaccines.

Biodegradable multi-liposomal containers

Structure of multiliposomal nanocontainer on base of anionic liposomes, polycation and polylactide.

Proteoliposomes in nanobiotechnology

Proteoliposomes are systems that mimic lipid membranes (liposomes) to which a protein has been incorporated or inserted. During the last decade, these systems have gained prominence as tools for biophysical studies on lipid-protein interactions as well as for their biotechnological applications. Proteoliposomes have a major advantage when compared with natural membrane systems, since they can be obtained with a smaller number of lipidic (and protein) components, facilitating the design and interpretation of certain experiments. However, they have the disadvantage of requiring methodological standardization for incorporation of each specific protein, and the need to verify that the reconstitution procedure has yielded the correct orientation of the protein in the proteoliposome system with recovery of its functional activity. In this review, we chose two proteins under study in our laboratory to exemplify the steps necessary for the standardization of the reconstitution of membrane proteins in liposome systems: (1) alkaline phosphatase, a protein with a glycosylphosphatidylinositol anchor, and (2) Na,K-ATPase, an integral membrane protein. In these examples, we focus on the production of the specific proteoliposomes, as well as on their biochemical and biophysical characterization, with emphasis on studies of lipid-protein interactions. We conclude the chapter by highlighting current prospects of this technology for biotechnological applications, including the construction of nanosensors and of a multi-protein nanovesicular biomimetic to study the processes of initiation of skeletal mineralization.

Dermaseptin 01 as antimicrobial peptide with rich biotechnological potential: study of peptide interaction with membranes containing Leishmania amazonensis lipid-rich extract and membrane models

This article addresses the interactions of the synthetic antimicrobial peptide dermaseptin 01 (GLWSTIKQKGKEAAIAAA- KAAGQAALGAL-NH(2) , DS 01) with phospholipid (PL) monolayers comprising (i) a lipid-rich extract of Leishmania amazonensis (LRE-La), (ii) zwitterionic PL (dipalmitoylphosphatidylcholine, DPPC), and (iii) negatively charged PL (dipalmitoylphosphatidylglycerol, DPPG). The degree of interaction of DS 01 with the different biomembrane models was quantified from equilibrium and dynamic liquid-air interface parameters. At low peptide concentrations, interactions between DS 01 and zwitterionic PL, as well as with the LRE-La monolayers were very weak, whereas with negatively charged PLs the interactions were stronger. For peptide concentrations above 1 µg/ml, a considerable expansion of negatively charged monolayers occurred. In the case of DPPC, it was possible to return to the original lipid area in the condensed phase, suggesting that the peptide was expelled from the monolayer. However, in the case of DPPG, the average area per lipid molecule in the presence of DS 01 was higher than pure PLs even at high surface pressures, suggesting that at least part of DS 01 remained incorporated in the monolayer. For the LRE-La monolayers, DS 01 also remained in the monolayer. This is the first report on the antiparasitic activity of AMPs using Langmuir monolayers of a natural lipid extract from L. amazonensis.