Methyl-β-cyclodextrin quaternary ammonium chitosan conjugate: nanoparticles vs macromolecular soluble complex

Abstract

Purpose: The present study aimed to compare a novel cyclodextrin-polymer-drug complex in solution with a dispersed supramolecular nanosize system, made of the same complex, for ability to carry dexamethasone (DEX) across excised rat intestine.

Results: Methyl-β-cyclodextrin-quaternary ammonium chitosan conjugate (QA-Ch-MCD) was obtained by covalent grafting through a 10-atom spacer. The conjugate was characterized by ¹H-NMR, resulting in 24.4% w/w of MCD content. Phase solubility profile analysis of the QA-Ch-MCD/DEX complex yielded an association constant of 14037 M^-1, vs 4428 M^-1 for the plain MCD/DEX complex. Nanoparticle (NP) dispersions resulted from ionotropic gelation of the QA-Ch-MCD/DEX complex by sodium tripolyphosphate, leading to 9.9%±1.4% drug loading efficiency. The mean diameter and zeta potential for NP were 299±32 nm (polydispersity index [PI] 0.049) and 11.5±1.1 mV, respectively. Those for QA-Ch-MCD/DEX were 2.7±0.4 nm (PI 0.048) and 6.7±0.6 mV. QA-Ch-MCD/DEX solutions and corresponding NP dispersions were compared in vitro for water-assisted transport through mucus, DEX permeation through excised rat intestine, and ex vivo mucoadhesivity. The complex showed higher mucoadhesion and lower transport rate through mucus; also, it provided faster drug permeation across excised rat intestine.

Conclusion: Carrier adhesion to mucus surface has played a most important role in favoring transepithelial permeation. Then, within the concerns of the present study, the use of NP seems not to provide any determinant advantage over using the simpler macromolecular complex.

Keywords: chitosan derivatives; cyclodextrin chitosan conjugates; dexamethasone cyclodextrin complex; mucoadhesive nanoparticles; mucoadhesive polymers.

Figure 1

DEX and QA-Ch-MCD structures. Abbreviations: DEX, dexamethasone; QA-Ch-MCD, methyl-β-cyclodextrin–quaternary ammonium chitosan.

Figure 2

¹H-NMR spectra of QA-Ch60 (A) and QA-Ch-MCD (B). Notes: QA-Ch60 (300 MHz, D₂O): δ = 4.5 (s, anomerics), 4.2–2.2 (m, protons of the pyranosidic ring, methylene protons of pendant quaternized chains –CH₂CH₂N⁺(CH₂CH₃)₂CH₂- and –CH₂N(CH₂CH₃)₂), 2.0 (s, methyl protons of N- acetylglucosamine), 1.6–1.1 (m, methyl protons of the ethyl moieties closed to ammonium pendants N⁺CH₂CH₃), and 1.1–0.8 ppm (m, methyl protons of the terminal part of DEAE chains N(CH₂CH₃)₂). QA-Ch-MCD (300 MHz, D₂O) δ = 5.13 and 4.95 (s, MCD anomerics), 4.2–2.6 (m, protons of the pyranosidic ring, methylene protons of pendant quaternized chains –CH₂CH₂N⁺(CH₂CH₃)₂CH₂- and –CH₂N(CH₂CH₃)₂, methylene protons closed to the N of the spacer –NHCH₂(CH₂)₄CH₂NH₂); 2.5 (s, methylene protons of not protonated N of the DEAE pendant –CH₂N(CH₂CH₃)₂), 2.0 (s, methyl protons of N-acetylglucosamine), 1.7–1.1 (m, methyl protons of the ethyl moieties close to ammonium pendants N⁺(CH₂CH₃)_2, and methylene protons of the central part of spacer chain –NHCH₂(CH₂)₄CH₂NH₂), and 1.0–−0.7 ppm (m, methyl protons of the terminal part of DEAE chains –N(CH₂CH₃)₂). Compounds in bold correspond to peaks in the spectra. Abbreviations: DEAE, 2-diethylaminoethyl chloride; MCD, methyl-β-cyclodextrin; QA-Ch60, quaternary ammonium-chitosan 60; QA-Ch-MCD, methyl-β-cyclodextrin–quaternary ammonium chitosan; s, singlet; m, multiplet.

Figure 3

Solubility profiles of DEX: intrinsic water solubility (DEX₀), solubility in presence of MCD (MCD/DEX), and in the presence of QA-Ch-MCD (QA-Ch-MCD/DEX). Abbreviations: DEX, dexamethasone; MCD, methyl-β-cyclodextrin; QA-Ch-MCD, methyl-β-cyclodextrin–quaternary ammonium chitosan.

Figure 4

DEX kinetics from dynamic interrupted dialysis studies on NP samples: DEX kinetics in each phase of dialysis: NP phase; NP DM; and RP. Note: Mean±SD of three runs. Abbreviations: DEX, dexamethasone; DM, dispersion medium; NP, nanoparticle; RP, receiving phase.

Figure 5

DEX kinetics from dynamic dialysis studies: comparison of ln[(C_d/Cd₀) × 100] vs time plots for DEX, derived from each formulation study. Abbreviations: DEX, dexamethasone; MCD, methyl-β-cyclodextrin; NP, nanoparticle; QA-Ch-MCD, methyl-β–cyclodextrin–quaternary ammonium chitosan.

Figure 6

Water-assisted transport in mucus of FITC-labeled carriers (QA-Ch-MCD/DEX and NP). Note: Mean±SD (n=3). Abbreviations: DEX, dexamethasone; FITC, fluorescein isothiocyanate; NP, nanoparticle; QA-Ch-MCD, methyl-β-cyclodextrin–quaternary ammonium chitosan.