Investigation of self-association between new glycosurfactant N-acetyl-β-d-glucosaminyl-PEG-docosanate and soybean phosphatidylcholine into vesicles

https://doi.org/10.1016/j.colsurfa.2014.11.052Get rights and content

Highlights

  • The self-assembly of phosphatidylcholine and a new glycosylated amphiphile was investigated.

  • The procedure yielded to 100 nm-diameter carbohydrate-decorated vesicles.

  • The supramolecular nanostructures are stable against aggregation processes.

  • The amphiphile orders the lipid phosphate region.

  • The amphiphile disorders the carbonyl and methylene groups.

Abstract

This work describes the investigation of self-assembly between phosphatidylcholine-purified soybean lecithin (PC) and the new glycosylated polymeric amphiphile N-acetyl-β-d-glucosaminyl-PEG900-docosanate conjugate (C22PEG900GlcNAc). Our results indicate that a mixture of PC and C22PEG900GlcNAc undergoes spontaneous self-assembly in aqueous solution, forming vesicles with a mean diameter of 100 nm. Dynamic light scattering (DLS), transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS) were used to investigate the structure of the self-assembled vesicles. The effects of the C22PEG900GlcNAc on the molecular dynamics of the vesicle's PC groups were monitored by HATR-FTIR and 1H NMR. Our results indicate that PC and C22PEG900GlcNAc mixed vesicles have colloidal stability against aggregation processes. The stronger interaction of C22PEG900GlcNAc with the soybean phosphatidylcholine phosphate suggests an attractive force between this lipidic region and the nitrogen groups of the polymer. However, the enhancement of the hydrogen bonds on the PC carbonyl region may result from a discrete interaction with the hydroxyl and carbonyl regions of the C22PEG900GlcNAc. A disorder on PC carbonyl region and acyl methylene groups was observed and may be related to a C22PEG900GlcNAc-induced restriction on the lipid intermolecular contact, at interfacial and hydrophobic regions. These findings support the great potential of biosourced lipids in the design of PEG-ester carbohydrate-decorated vesicles with surfaces allowing the site-directed vectorization of active molecules through receptor–ligand binding.

Introduction

In aqueous media, lipids spontaneously self-assemble to form bilayers structures commonly referred to as vesicles that present intrinsic similarities to biological membranes [1]. Because of their composition, vesicles have lower toxicity than other matrices, making them interesting systems to deliver a wide range of drugs used for specific treatments with controlled circulation times, reduced side effects and optimized drug action [1], [2], [3], [4], [5], [6]. Vesicles can offer wide structural variety considering their sizes, membrane compositions, bilayer fluidities, surface charges and ability to incorporate lipophilic, amphiphilic and/or hydrophilic compounds [7], [8]. Although vesicles are frequently used to encapsulate polar drugs inside their aqueous cores, non-polar substances can be protected from metabolic degradation when inserted into the bilayers [7], [8]. Knowledge of the physicochemical properties of vesicles is important because it contributes to improving the parameters of pharmacological systems for drug targeting and membrane stability.

In recent years, many studies have reported that the insertion of polymers within vesicles may improve the stability of these vesicles [9], [10], [11], [12], [13], [14], [15]. Polyethylene glycol and its derivatives are especially important in various biological, chemical and pharmaceutical settings due to their wide range of solubilities in both organic and aqueous media, their ease of excretion from living organisms, and their lack of toxicity, immunogenicity, and biodegradability. PEG is often used as a covalent modifier of a variety of substrates, producing conjugates that combine some of the properties of both the starting substrate and the polymer. The blood lifetime of PEGylated vesicles, nanoparticles, and proteins can be significantly extended and their uptake by reticuloendothelial system (RES) organs, liver and spleen diminished [6], [16], [17], [18], [19], [20].

Systems containing amphiphilic carbohydrate-based graft- or block-copolymers have thus received attention as site-directed drug carriers [10]. For example, glycosylated amphiphiles have been incorporated into vesicles to target lectins from a synthetic PEG ester [19]. Lectins are proteins that bind to cell-surface carbohydrates and could be a promising method for the site-directed vectorization of drug-loaded nanostructures [19], [21]. Thus, to develop nanocarriers with improved site-directed vectorization capacity, it is necessary to understand the molecular properties and the effects that can influence it, such as size, charge potential, order, phase state and mobility.

As a first part of our investigation, the present study concerns the interaction between new glycosylated polymeric amphiphiles, prepared by click-chemistry grafting of propargylated carbohydrates onto azido-PEG900-docosanate (C22PEG900GlcNAc), and phosphatidylcholine-purified soybean lecithin (PC). The physico-chemical properties of the liposomal systems were characterized using transmission electron microscopy, zeta potential and light and X-ray scattering. The effects of the C22PEG900GlcNAc polymer on the molecular dynamics of the liposomal PC groups were monitored by HATR-FTIR and 1H NMR.

Section snippets

Materials

Phosphatidylcholine (PC) from soybean lecithin (95% phosphatidylcholine, 5% lysophosphatidylcholine and phosphatidic acid) was a gift from Solae do Brasil S.A. The molecular composition of the soybean PC is around 75% distearoylphosphatidylcholine (DSPC, 18:0), 12% dioleoylphosphatidylcholine (DOPC, 18:2) and 8% dipalmitoylphosphatidylcholine (DPPC, 16:0) [22].

All reagents were of commercial grade and were used as received unless otherwise noticed. The solvents were dried and distilled prior to

Characterization of vesicles: size, morphology and surface charge

The accurate morphology of the self-assembled objects was previously determined via TEM and SAXS analysis. Representative data for PC + C22PEG900GlcNAc is given in Fig. 1. The TEM image evidences the spherical shape of the objects and the formation of vesicular structures was further confirmed by SAXS data. The scattering pattern portrayed in Fig. 1B could be fitted by using the bilayered vesicle form factor implemented in the SASfit software. The adjustable parameters were Rc – radius of the

Conclusion

The work described the preparation of mixed vesicles containing the new glycosurfactant C22PEG900GlcNAc and phosphatidylcholine-purified soybean lecithin. The results point out that a mixture of PC and C22PEG900GlcNAc spontaneously self-assemble in water into vesicles as evidenced by SAXS and TEM. The negligible influence of the carbohydrate groups on size and morphology of the vesicles suggests that the protocol can be easily applied to other saccharidic ligands targeting different receptors.

Acknowledgments

The authors wish to thank Conselho Nacional de Pesquisa e Desenvolvimento (CNPq– Brazil) (440619/2014-9) for financial support. The LNLS is acknowledged for supplying the SAXS beam time (proposal 16960). A.G.D.B acknowledges the financial support from FAPESC 3805/2012 and F.C.G. acknowledges the financial support from FAPESP (grant 2012/14087-8).

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