Novel O-palmitoylscleroglucan-coated liposomes as drug carriers: Development, characterization and interaction with leuprolide

doi:10.1016/j.ijpharm.2006.06.040

International Journal of Pharmaceutics

Volume 325, Issues 1–2, 15 November 2006, Pages 155-162

https://doi.org/10.1016/j.ijpharm.2006.06.040 Get rights and content

Abstract

Polysaccharide-coated liposomes have been studied for their potential use for peptide drug delivery by the oral route because they are able to minimize the disruptive influences on peptide drugs of gastrointestinal fluids. The aim of this work was to synthesize and characterize a modified polysaccharide, O-palmitoylscleroglucan (PSCG), and to coate unilamellar liposomes for oral delivery of peptide drugs.

To better evaluate the coating efficiency of PSCG, also scleroglucan (SCG)-coated liposomes were prepared.

We studied the surface modification of liposomes and the SCG- and PSCG-coated liposomes were characterized in terms of size, shape, ζ potential, influence of polymer coating on bilayer fluidity, stability in serum, in simulated gastric and intestinal fluids and against sodium cholate and pancreatin.

Leuprolide, a synthetic superpotent agonist of luteinizing hormone releasing hormone (LHRH) receptor, was chosen as a model peptide drug.

After polymer coating the vesicle dimensions increased and the ζ potential shifted to less negative values. These results indicate that both SCG- and PSCG-coated liposomes surface and DSC results showed that PSCG was anchored on the liposomal surface.

The stability of coated-liposomes in SGF, sodium cholate solution and pancreatin solution was increased.

From this preliminary in vitro studies, it seems that PSCG-coated liposomes could be considered as a potential carrier for oral administration.

Introduction

Liposomes have been extensively studied for their potential use as drug carriers and development of stable liposomes is fundamental for this purpose. Many attempts have been made to enhance the stability of liposomes (New, 1990, Gregoriadis, 1991, Park et al., 1992, Sivakumar and Panduranga Rao, 2001). Among them, surface modification of liposomes is an attractive method to enhance vesicle in vitro and in vivo stability (Jones, 1995, Sagristá et al., 2000, Kato et al., 2004, Lukyanov et al., 2004, Han et al., 2006).

Liposomes have been studied for intraperitoneal and intravenous administration for the delivery of therapeutic or diagnostic agents to specific target tissues. However, there has been increased interest in their potential use for peptide drug delivery by the oral route because they are composed of physiological materials (Fukunaga et al., 1991).

The main problem associated with orally-administered liposomes is their poor stability in the gastrointestinal tract, due to pH, bile salts and pancreatic lipase presence in the GI tract (Kato et al., 1993).

To enhance liposome stability in order to decrease the leakage of entrapped solute and to improve the cellular uptake of liposomes, natural polysaccharides (i.e. mannan, pullulan, amylopectin, dextran, chitosan) were used to coat the outermost surface of liposomal vesicle (Vyas et al., 2005, Vyas et al., 2004, Venkatesan and Vyas, 2000, Cansell et al., 1999, Guo et al., 2003).

Coating liposomes with polypeptides or ligands is also an important biomimetic strategy to realize molecular recognition on liposome surface and also to strengthen the mechanical properties of liposomes.

On the other hand, polysaccharide anchoring by adsorption was found to be thermodynamically unstable and pharmaceutically unacceptable (Sihorkar and Vyas, 2001). In order to eliminate these limitations, chemically modified polysaccharide were used to coat liposomes (Sunamoto and Iwamoto, 1986, Lee et al., 2005). In these partially hydrophobized polysaccharides acyl chains were allowed to react covalently with natural polysaccharides and subsequently integrate with the lipid constituents of liposome bilayer.

Scleroglucan is a biocompatible and biodegradable polymer of low toxicity, thus it has been extensively used in the pharmaceutical field (Maggi et al., 1996, Coviello et al., 1998, Coviello et al., 2005).

Scleroglucan (SCG) (Fig. 1), a microbial polysaccharide, is a linear chain of 1,3-β linked d-glucopyranose units with single d-glucopyranose residues 1,6-β linked to every third unit of the chain.

The aim of this work was to synthesize and characterize a modified polysaccharide, O-palmitoylscleroglucan (PSCG), to coat unilamellar liposomes for oral delivery of peptide drugs.

To better evaluate the coating efficiency of PSCG, also scleroglucan (SCG)-coated liposomes were prepared.

The SCG- and PSCG-coated liposomes were characterized in terms of size, shape, ζ potential, influence of polymer coating on bilayer fluidity, stability in serum and in simulated gastric and intestinal fluids and against sodium cholate and pancreatin.

Leuprolide, a synthetic superpotent agonist of luteinizing hormone releasing hormone (LHRH) receptor, was chosen as a model peptide drug.

Section snippets

Materials

Phospholipon 90 (Ph90) was a gift of Nattermann (Germany), cholesterol (CHOL) was purchased from Carlo Erba (Italy), calcein; HEPES salt {N-(2-idroxyethyl)-piperazine-N′-(2-ethanesulfonicacid)}; Sepharose 4B; Sephadex G-75; pancreatin (from porcine pancreas) and bovine serum were Sigma–Aldrich (Italy) products, sodium 5,6-carboxyfluorescein was purchased by Kodak, scleroglucan (SCG) was provided by Degussa (Germany), Leuprolide was a generous gift of Abbott (USA). All other products and

Characterization of PSCG

The palmitoylscleroglucan was characterized by IR and ¹H NMR.

The IR analysis (Table 2) was used to identify carbonyl groups and to establish that scleroglucan is covalently bound to palmitoyl residues; in particular a characteristic stretching vibration of C double bond O is observed at about 1735 cm⁻¹ (Pavia et al., 1979). However in the PSCG, the stretching vibration was observed at 1655 cm⁻¹. This shift in frequency could be ascribed to a consequence of intramolecular hydrogen bonds between carbonyl and

Conclusions

In this study, scleroglucan and O-palmitoylscleroglucan-coated liposomes were prepared, characterized and evaluated for their potential use in oral drug delivery. Scleroglucan, a natural polysaccharide, was chemically modified into its palmitoyl derivative and used for the coating of liposomes.

After polymer coating the vesicle dimensions increased and the ζ potential shifted to less negative values. These results indicate that both SCG and PSCG coated liposome surface and DSC results showed

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Pharmaceutical NanotechnologyNovel O-palmitoylscleroglucan-coated liposomes as drug carriers: Development, characterization and interaction with leuprolide

Abstract

Introduction

Section snippets

Materials

Characterization of PSCG

Conclusions

Biochim. Biophys. Acta

Int. J. Pharm.

Int. J. Pharm.

J. Control. Release

Int. J. Pharm.

J. Colloid Interf. Sci.

Int. J. Pharm.

Eur. J. Pharm. Biopharm.

Biochim. Biophys. Acta: Biomembr.

Adv. Colloid Interf. Sci.

Eur. J. Pharm. Sci.

J. Biosci. Bioeng.

J. Control. Release

Int. J. Pharm.

Biophys. J.

Int. J. Pharm.

J. Colloid Interf. Sci.

Anal. Biochem.

Int. J. Pharm.

Pharmaceutical Nanotechnology
Novel O-palmitoylscleroglucan-coated liposomes as drug carriers: Development, characterization and interaction with leuprolide