Self-assembled carbohydrate-based vesicles for lectin targeting

https://doi.org/10.1016/j.colsurfb.2016.08.053Get rights and content

Highlights

  • Biocompatible vesicles designed for lectin targeting.

  • Self-assembled vesicles with glycosylated surfaces has been successfully achieved.

  • The glycosylated vesicles are easily recognized by the Bauhinia variegata lectin (BVL).

  • The enhance specificity of vesicles for lectins highlights their potential use in site vectorization targeted drug delivery.

Abstract

This study examined the physicochemical interactions between vesicles formed by phosphatidylcholine (PC) and glycosylated polymeric amphiphile N-acetyl-β-d-glucosaminyl-PEG900-docosanate (C22PEG900GlcNAc) conjugated with Bauhinia variegata lectin (BVL). Lectins are proteins or glycoproteins capable of binding glycosylated membrane components. Accordingly, the surface functionalization by such entities is considered a potential strategy for targeted drug delivery. We observed increased hydrodynamic radii (RH) of PC + C22PEG900GlcNAc vesicles in the presence of lectins, suggesting that this aggregation was due to the interaction between lectins and the vesicular glycosylated surfaces. Furthermore, changes in the zeta potential of the vesicles with increasing lectin concentrations implied that the vesicular glycosylated surfaces were recognized by the investigated lectin. The presence of carbohydrate residues on vesicle surfaces and the ability of the vesicles to establish specific interactions with BVL were further explored using atomic force microscopy (AFM) and small-angle X-ray scattering (SAXS) analysis. The results indicated that the thickness of the hydrophilic layer was to some extent influenced by the presence of lectins. The presence of lectins required a higher degree of polydispersity as indicated by the width parameter of the log-normal distribution of size, which also suggested more irregular structures. Reflectance Fourier transform infrared (HATR-FTIR), differential scanning calorimetry (DSC), nuclear magnetic resonance (NMR) and ultraviolet-visible (UV–vis.) analyses revealed that the studied lectin preferentially interacted with the choline and carbonyl groups of the lipid, thereby changing the choline orientation and intermolecular interactions. The protein also discretely reduced the intermolecular communication of the hydrophobic acyl chains, resulting in a disordered state.

Introduction

The surface functionalization of nanoparticles and liposomes has become of increasing importance since Ehrlich publicized his vision of the “Magic Bullet” [1]. Vesicles and liposomes (phospholipid-based vesicles) have been extensively studied due to their widespread application as controlled drug delivery vehicles in the pharmaceutical industry and as biomembranes [2], [3], [4]. Because of their lipid composition, vesicles have lower toxicity than other vehicles, making them promising systems for the delivery of a wide range of drugs requiring specific treatments, controlled circulation times, reduced side effects and optimum drug action [5], [6], [7], [8], [9], [10], [11]. The possibility of directing a drug toward targeted tissues without changing its structure and hence, its biological activity, is fundamental for therapeutic applications [12]. Thus, efforts have been directed toward improving the vectorization of drug delivery systems to specific target tissues. In this context, the surface functionalization of vesicles with natural or synthetic glycolipids has been proposed to enhance the specificity of vesicles for lectins [12], [13]. Lectins are non-immunological proteins or glycoproteins that specifically recognize sugar molecules and are capable of binding glycosylated membrane components. They are widely used to characterize carbohydrates on cell surfaces [14]. The Bauhinia variegata lectin (BVL) is particularly found in Caesalpinoideae plants. Its subunit has molecular weight of ∼33 kDa and diffraction patter similar to related lectins such as Bauhinia purpurea agglutinin (BPA) [15]. The carbohydrate-lectin binding typically involves two or three terminal sugar residues of mammalian glycans, including galactose, mannose, N-acetyl-neuraminic acid, fucose, and N-acetyl-glucosamine [16], [17].

High levels of lectins, such as galectin-3, have been detected in various cancers [12]. The specificity of the carbohydrate-lectin interaction has been exploited to convey glycosylated liposomes to tumor cells [12], [18], [19], [20]. Therefore, the development of nanoparticles with outer shells decorated with glycoconjugates for lectin targeting is considered a promising means to improve the delivery and internalization of antitumor drugs [16], [21]. Previously, our research group described the physicochemical interactions between vesicles composed of phosphatidylcholine-purified soybean lecithin and the glycosylated polymeric amphiphile N-acetyl-β-d-glucosaminyl-PEG900-docosanate conjugate (C22PEG900GlcNAc). Structurally, the ∼100 nm composite vesicles self-assemble via attractive force between the lipidic region and the nitrogen groups of C22PEG900GlcNAc. The results also suggested discrete interaction among the hydroxyl and carbonyl regions of C22PEG900GlcNAc [22]. Amphiphiles containing PEG chains have become a topic of interest due to their biocompatibility and anomalous behavior in water [23]. Through the PEGylation of vesicles, nanoparticles, and proteins, the residence times of these carriers can be significantly extended and diminish their uptake by the organs (e.g., liver and spleen) of the reticulo endothelial system (RES) [24], [25].

This present work reports on the interaction between self-assembled vesicles (composed of phosphatidylcholine-purified soybean lecithin and the glycosylated polymeric amphiphile, C22PEG900GlcNAc) and BVL. The physicochemical properties of the phosphatidylcholine-based vesicle system containing C22PEG900GlcNAc and lectin were investigated by several techniques, including zeta potential, dynamic light scattering (DLS), atomic force microscopy (AFM), small-angle X-ray scattering (SAXS), horizontal attenuated total reflectance Fourier transform infrared (HATR-FTIR), differential scanning calorimetry (DSC), nuclear magnetic resonance (NMR) and ultraviolet-visible (UV-vis.) spectroscopy measurements. The physicochemical properties of these self-assembled vesicles presented herein could contribute to improved vectorizations of drug delivery systems in cancer therapy.

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 was approximately 75% distearoylphosphatidylcholine (DSPC, 18:0), 12% dioleoylphosphatidylcholine (DOPC, 18:2) and 8% dipalmitoylphosphatidylcholine (DPPC, 16:0) [26]. All reagents were of commercial grade and were used as received unless otherwise noted. The native Bauhinia variegata (BVL)

Lectin effect on vesicle charge and size

The zeta potential (ZP) was used to evaluate the surface charge of the PC + C22PEG900GlcNAc vesicles in the presence of lectin. The zeta potential of PC + C22PEG900GlcNAc vesicles in phosphate buffer saline was −47 ± 2 mV, indicating stable assemblies in suspension due to electrostatic repulsion between particles, resulting in relative colloidal stability, as previously reported by the authors [22]. Fig. 1 shows the zeta potential values with increasing amounts of lectin. As the lectin concentration

Conclusion

We investigated the interaction between vesicles formed by phosphatidylcholine (PC) and the glycosylated polymeric amphiphile N-acetyl-β-d-glucosaminyl-PEG900-docosanate conjugate (C22PEG900GlcNAc) with the lectin BVL. Our results suggested that the lectin molecules recognized the glycosylated surfaces of the vesicles. Furthermore, the lectin molecules were located between the lipid choline and carbonyl groups, thereby changing the choline orientation and ordering the lipid polar head and

Conflicts of interest

The authors declare no conflicts of interest.

Acknowledgments

The authors wish to thank the Conselho Nacional de Pesquisa e Desenvolvimento (CNPq– Brazil) (440619/2014-9) for financial support. The LNLS is acknowledged for supplying the SAXS beam time (proposals 20150020 and 20150021). A.G.D.B acknowledges the financial support from FAPESC 3805/2012, and F.C.G. thanks FAPESP (grant 2014/22983-9).

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