Design of rolipram-loaded nanoparticles: comparison of two preparation methods

doi:10.1016/S0168-3659(01)00230-9

Journal of Controlled Release

Volume 71, Issue 3, 28 April 2001, Pages 297-306

https://doi.org/10.1016/S0168-3659(01)00230-9 Get rights and content

Abstract

The aim of the present work was to investigate the preparation of nanoparticles as a potential drug carrier and targeting system for the treatment of inflammatory bowel disease. Rolipram was chosen as the model drug to be incorporated within nanoparticles. Pressure homogenization–emulsification (PHE) with a microfluidizer or a modified spontaneous emulsification solvent diffusion method (SESD) were used in order to select the most appropriate preparation method. Poly(ε-caprolactone) has been used for all preparations. The drug loading has been optimized by varying the concentration of the drug and polymer in the organic phase, the surfactants (polyvinyl alcohol, sodium cholate) as well as the volume of the external aqueous phase. The rolipram encapsulation efficiency was high (>85%) with the PHE method in all cases, whereas with the SESD method encapsulation efficiencies were lower (<40%) when lower surfactant concentrations and reduced volume of aqueous phase were used. Release profiles were characterized by a substantial initial burst release with the PHE method (25–35%) as well as with the SESD method (70–90%). A more controlled release was obtained after 2 days of dissolution with the PHE method (70–90%), no further significant drug release was observed with the SESD method.

Introduction

Nowadays, the conventional treatment of inflammatory bowel disease requires the daily intake of anti-inflammatory drugs at high doses involving potential adverse effects. Therefore, one major strategy was to develop solid dosage forms releasing the drug in the colon in dependency of the pH or specific bacterial enzymes in the colon [1], [2]. However, the efficiency of this strategy is reduced in many cases owing to diarrhea, an assured symptom of inflammatory bowel disease [3], [4]. Since drug carriers with a nominal size below 200 μm are affected less by this symptom [4], smaller drug carriers could display a prolonged intestinal transit time. Indeed, it has been reported that particles with a diameter in the lower micron or nanometre range show an accumulation in the inflammatory areas of the colon in the case of ulcerative colitis in rats [5].

In the inflamed tissue an increased adherence of particles with a nominal size of 100 nm, 1 μm, and 10 μm was observed. The optimal particle size ranged between 100 nm and 1 μm. In this range, the particle deposition in the inflamed tissue of the colon was 5–6.5-fold higher than in the healthy control. Particles showed an increased accumulation mainly in the areas of ulceration and the surrounding tissue. This may be due either to the increased secretion of sticky mucus leading to an attachment or to the uptake of particles into the macrophages which are present in the inflamed tissue in a highly increased number. Moreover, a prolonged retention of the particles in the inflamed regions up to 3 days was found [6].

Consequently, an increased residence time at the inflammation sites can be postulated for nanoparticles (NP) compared with existing drug delivery systems. This should allow a dose reduction and local drug delivery to the inflamed tissue. For instance, since dexamethasone-containing microparticles showed promising results in a preliminary in-vivo study with colitis-induced mice [7]. Thus, drugs which are usually not administered orally owing to their strong side effects may be therefore encapsulated within polymeric particles with the aim of oral administration.

In several different diseases, the proinflammatory cytokine tumor necrosis factor-α (TNF) forms a necessary element in the chain of pathophysiologic events leading to inflammation. Among the agents known to inhibit TNF production rather than to block its function, attention has focused on cAMP elevating phosphodiesterase inhibitors. Compared with the nonspecific phosphodiesterase inhibitor pentoxifylline, the specific type IV phosphodiesterase inhibitor rolipram is a 500-fold more potent inhibitor of TNF synthesis in human mononuclear cells [8]. Rolipram has initially been developed and studied clinically as an antidepressant drug [9]. Recently, the potential therapeutic use of rolipram in TNF-dependent diseases has been demonstrated in several animal models [10], [11], [12].

It was stated that ulcerous tissues contain high concentrations of positively charged proteins that increased the affinity to negatively charged substances [13]. For this reason a strong negative charge surface of NP might be suitable. Coating particles with anionic surfactants could be therefore a promising alternative. Owing to its interesting interfacial properties, its natural origin and consequently its biocompatibility, sodium cholate (SC) might be a suitable candidate. Surprisingly, only very little attention has been paid to its use for particle preparation so far [14]. The interest in SC consisted mainly in its ability to attract lipase and colipase to the particle surface in order to degrade solid lipid nanoparticles [15].

The aim of this work was the preparation and optimization of rolipram-containing NP. In order to develop NP with a strong negative surface charge, it was of high interest to optimize and characterize SC NP for their potential as a drug carrier system in inflammatory bowel disease. Comparing two different preparation methods should allow to develop an optimal carrier with a view to particle size, surface charge and release profile.

Due to the mainly lipophilic nature of rolipram, two emulsification techniques were directly compared: the pressure homogenization–emulsification (PHE) by using a microfluidizer and a modified spontaneous emulsification solvent diffusion method (SESD) based on nanoprecipitation. Since it is expected that nanoparticles could accumulate in the inflamed regions in the colon, the use of a biodegradable polymer was advised. Thus, NP were prepared with poly[ε-caprolactone] (PCL), a biocompatible and biodegradable polymer [16], [17]. NP were compared in terms of size, polydispersity, surface potential, encapsulation efficiency and drug release. NP prepared with polyvinyl alcohol (PVA) under the same conditions were used as standard formulations due to its wide use as surfactant in the preparation of NP. Moreover, polyvinyl alcohol-coated NP were found to be very efficient in protecting NP from degradation during the passage through the gastrointestinal tract [18].

Section snippets

Materials

The biodegradable polymer poly[ε-caprolactone] (M_w 10,000 Da) was purchased from Fluka (Steinheim, Germany). Polyvinyl alcohol (M_w 20,000 Da, 80% hydrolyzed) and sodium cholate (M_w 430.6 Da) chosen as surface active agents were respectively supplied by Sigma (Steinheim, Germany) and Fluka (Steinheim, Germany). Rolipram (solubility in distilled water: 473.8±29.1 μg/ml; n=6) was received as a gift from Schering AG (Berlin, Germany). All other chemical reagents were obtained from Sigma, Nacalai

Oil/water emulsion pressure homogenization technique

As shown in Fig. 1, nanoparticles prepared by the PHE method had a submicron size and were relatively monodispersed with the two surfactants used for their preparation.

Since drug loss from the internal organic to the external aqueous phases should be kept to a minimum during the emulsification step, the stability of the emulsion is crucial. During the solvent evaporation process, there is a gradual decrease of the dispersion volume and consequently a subsequent increase of the viscosity of the

Conclusions

The present nanoparticulate formulations can be expected to be used as colloidal drug carriers of rolipram when prepared by an o/w homogenization emulsification or nanoprecipitation solvent extraction method. These NP were found to be attractive for peroral or transmucosal applications because of their monodispersed submicron-sized structure. Their biodegradability should prevent any complication in the case of long-term deposition of the NP inside the ulcerated tissue during gut passage.

Acknowledgements

Alf Lamprecht acknowledges the ‘Monbusho Research Fellowship for Young Foreign Researchers’ grant from the Japanese Ministry of Education, Science and Culture.

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Design of rolipram-loaded nanoparticles: comparison of two preparation methods

Abstract

Introduction

Section snippets

Materials

Oil/water emulsion pressure homogenization technique

Conclusions

Acknowledgements

Int. J. Pharm.

Int. J. Immunopharmacol.

Neuropharmacology

Biomaterials

Int. J. Pharm.

J. Control. Release

Int. J. Pharm.

J. Control. Release

J. Control. Release

Colonic drug delivery

Drug Dev. Ind. Pharm.

Colonic drug targeting

J. Drug Target.

Gastrointestinal transit of small tablets in patients with ulcerative colitis

Int. J. Pharm.

Site specific targeting of microparticles to the inflamed colonic mucosa: a novel approach to the treatment of inflammatory bowel disease

Proc. Int. Symp. Control. Release Bioact. Mater.