Release behaviour and biocompatibility of drug-loaded pH sensitive particles

https://doi.org/10.1016/j.ijpharm.2005.12.024Get rights and content

Abstract

The purpose of this work was to investigate the physical properties of drug-loaded poly(methacrylic acid-g-ethylene glycol) {P(MAA-g-EG)} particles, their biocompatibility with the gastrointestinal tract of rats and also the effects of these particles on the tight junctions of the rat intestinal epithelium. Model drugs such as diltiazem HCl, diclofenac Na, ciprofloxacin HCl and isoniazid were used in this study. P(MAA-g-EG) particles were prepared by free radical solution polymerization of methacrylic acid (MAA) and poly(ethylene glycol) (PEG). The loading efficiency of the model drugs in the particles and in vitro release profiles were investigated in pH 7.4 phosphate buffer and in gradually pH changing buffers (pH 1.2, 5.8, 6.8 and 7.4). The stability of free particles and drug-loaded particles was established by Fourier transform infrared spectroscopy (FT-IR) and differential scanning calorimetry (DSC). In conclusion, P(MAA-g-EG) particles controlled the release rate of small molecular weight model drugs according to the pH of the medium. Stability of those particles loaded with drugs did not change in accelerated stability conditions. Histopathological results indicated that loading drugs to the particles prevented cell and tissue damage after 20 h. Free particles showed no change of tight junctions after 2 and 10 h. The results of TEM showed that increasing the amount of P(MAA-g-EG) particles from 100 to 385 mg clearly opened the tight junction, but with serious epithelial cell disruption.

Introduction

Hydrogels are used as carriers for the delivery of drugs, peptides and proteins, as targeting agents for site-specific delivery, or as components for preparation of protein or enzyme conjugates (Peppas, 1997, Peppas, 1999, Nakamura et al., 2003). Copolymer networks of poly(methacrylic acid) grafted with poly(ethylene glycol) henceforth designated as P(MAA-g-EG), exhibit pH swelling due to the reversible formation/dissociation of interpolymer complexes. In the acidic environment of the stomach, the gels are in a complexed state. As the polymer passes from the stomach into the intestine, the environmental pH increases above the transition pKa of the gel. Then, the complexes dissociate and the network mesh size rapidly increases leading to the release of the drug (Peppas et al., 2001, Donini et al., 2002).

In this study, diltiazem HCl, diclofenac Na, ciprofloxacin HCl and isoniazid were chosen as model drugs since all were small molecules having different ionic properties at pH 7.4 and all commonly cause gastric irritation (Dukes, 1988).

P(MAA-g-EG) polymers are molecularly designed to contain poly(ethylene glycol) (PEG) chains promoting mucosal adhesion and poly(methacrylic acid) (PMAA) backbones with carboxylic pendant groups (–COOH), which can act as calcium binders leading to epithelial cell junction opening (Madsen and Peppas, 1999). ATR–FT-IR, atomic absorption spectroscopy and Caco-2 cell studies indicated that P(MAA-g-EG) particles could bind to calcium ions which increase the paracellular permeability of epithelial cell monolayers by opening the tight junctions (Madsen and Peppas, 1999, Sipahigil et al., 2002, Torres-Lugo et al., 2002, Foss and Peppas, 2004). These particles are investigated as potential carriers for protein drugs such as insulin and calcitonin (Lowman et al., 1999, Torres-Lugo and Peppas, 1999). Cell culture methods, also known as cytotoxicity tests, can be used to evaluate the toxicity of the hydrogels. The histological analysis of poly[N-(2-hydroxy ethyl)-dl-aspartamide] (PHEA) showed no gross lesion of the stomach or duodenum when observed 24 h. after their oral administration to rats (Giammona et al., 1997).

In this study P(MAA-g-EG) particles were used as carriers of small molecular drugs and also their biocompatibility with the gastrointestinal tract of the rats and their in vivo effect on tight junctions and cells of gastrointestinal system were investigated.

The objectives of this study were the following:

  • To evaluate the physical characteristics of P(MAA-g-EG) particles such as loading efficiency, release rates and the stability.

  • To characterize the histopathology of the ileum after free particles or pure drugs and drug-loaded particles were administered orally to rats.

  • To examine the effect of drugs and particles on epithelial tight junctions in vivo by TEM (Jeol, 1200 EX).

Section snippets

Materials

Methacrylic acid (MAA) and poly(ethylene glycol) monomethacrylate (PEGMA) were purchased from Polysciences Inc. (Warrington, PA). Tetra(ethylene glycol) dimethacrylate (TEGDMA) was purchased from Aldrich Chemical Co. (Milwaukee, WI). Irgacure 184® (1-hydroxy cyclohexyl phenyl ketone) was purchased from Ciba-Geigy Corp. (Hawthorne, NY). Diltiazem HCl, diclofenac Na, ciprofloxacin HCl and isoniazid were obtained respectively from İlsan İltaş A.Ş., Fako, Koçak and Deva, Turkey as a gift. All

Size and drug loading

Since particles were crushed, they were shapeless and only sieved particles having 180 μm diameter were used throughout the study.

Drug-loading percentage (w/w ± S.D.) of P(MAA-g-EG) particles were 2.09 ± 0.06, 1.79 ± 0.21, 0.93 ± 0.11 and 0.54 ± 0.05 mg for isoniazid, diltiazem HCl, diclofenac Na and ciprofloxacin HCl, respectively. Raising the initial drug concentration up to five times did not change the percentage of loaded drug amount. Among the drug-loaded particles, loading efficiencies of diltiazem

Conclusions

It can be concluded that P(MAA-g-EG) particles can control the release rate of small molecular weight model drugs according to the pH of the medium. The stability of these particles loaded with drugs did not change in accelerated conditions.

According to the literature, this study is the only in vivo investigation on P(MAA-g-EG) particles histopathologically and for their effect on epithelial tight junction of rats.

Histopathological investigation of free particles showed cell damage in the ileum

Acknowledgments

The authors thank Ms. N. Özkan and Mrs. E. Şalva for their technical assistance.

References (23)

  • C.A. Foss et al.

    Investigation of the cytotoxicity and insulin transport of acrylic-based copolymer protein delivery systems in contact with Caco-2 cultures

    Eur. J. Pharm. Biopharm.

    (2004)
  • Cited by (18)

    • PH-sensitive polymeric nanoparticles to improve oral bioavailability of peptide/protein drugs and poorly water-soluble drugs

      2012, European Journal of Pharmaceutics and Biopharmaceutics
      Citation Excerpt :

      Poly(methacrylic acid-g-ethylene glycol) (P(MAA-g-EG)) [51,13] is also a pH-sensitive material. Sipahigil [51] prepared P(MAA-g-EG) particles by free radical solution polymerization of methacrylic acid and poly(ethylene glycol). Model drugs such as diltiazem HCl, diclofenac Na, ciprofloxacin HCl and isoniazid were embedded in the particles.

    • Impact of absorption and transport on intelligent therapeutics and nanoscale delivery of protein therapeutic agents

      2009, Chemical Engineering Science
      Citation Excerpt :

      This behavior was attributed to the presence of negatively charged carboxylic acid in the polymer network. The presence of the microparticles has been shown to prevent cell and tissue damage for extended periods of time (Sipahigil et al., 2006). The similar system of acrylic acid and poly(ethylene glycol), or P(AA-g-PEG), has been shown to demonstrate some of these beneficial properties as well (Foss et al., 2004; Serra et al., 2006; Thomas et al., 2007).

    • Down-regulation of PPARγ2-induced adipogenesis by PEGylated conjugated linoleic acid as the pro-drug: Attenuation of lipid accumulation and reduction of apoptosis

      2006, Archives of Biochemistry and Biophysics
      Citation Excerpt :

      In fact, 99.5% of PCLA-NPs were distributed in up to 115 nm, as shown in Table 1. Generally, the most often employed pro-drugs are based on hydrolyzable or enzymatically cleaveable bonds such as esters, carbonates, carbamates, and hydrazones [29–31]. Based on these early concepts, we further investigated whether the PCLA can act as a pro-drug.

    View all citing articles on Scopus
    View full text