Polyester nanocapsules as new topical ocular delivery systems for cyclosporin A

Phototoxicity and cytotoxicity of fullerol in human lens epithelial cells

The water-soluble, hydroxylated fullerene [fullerol, nano-C60(OH)22-26] has several clinical applications including use as a drug carrier to bypass the blood ocular barriers. We have assessed fullerol's potential ocular toxicity by measuring its cytotoxicity and phototoxicity induced by UVA and visible light in vitro with human lens epithelial cells (HLE B-3). Accumulation of nano-C60(OH)22-26 in the cells was confirmed spectrophotometrically at 405 nm and cell viability estimated using MTS and LDH assays. Fullerol was cytotoxic to HLE B-3 cells maintained in the dark at concentrations higher than 20 microM. Exposure to either UVA or visible light in the presence of >5 microM fullerol-induced phototoxic damage. When cells were pretreated with non-toxic antioxidants: 20 microM lutein, 1 mM N-acetyl cysteine, or 1 mM l-ascorbic acid prior to irradiation, only the singlet oxygen quencher-lutein significantly protected against fullerol photodamage. Apoptosis was observed in lens cells treated with fullerol whether or not the cells were irradiated, in the order UVA>visible light>dark. Dynamic light scattering (DLS) showed that in the presence of the endogenous lens protein alpha-crystallin, large aggregates of fullerol were reduced. In conclusion, fullerol is both cytotoxic and phototoxic to human lens epithelial cells. Although the acute toxicity of water-soluble nano-C60(OH)22-26 is low, these compounds are retained in the body for long periods, raising concern for their chronic toxic effect. Before fullerols are used to deliver drugs to the eye, they should be tested for photo- and cytotoxicity in vivo.

Charged nanoparticles delivery to the eye using hydrogel iontophoresis

Ocular iontophoresis has been investigated for many years as a non-invasive technique for enhancing ionized drug penetration through ocular tissues. In this study we assessed the penetration of charged fluorescent nanoparticles into rabbit eyes using hydrogel iontophoresis. Particle distribution into ocular tissues and penetration efficiency of negative nanoparticles compared with positive nanoparticles was also evaluated. Cathodal and anodal iontophoretic administrations were performed using polyacrylic hydrogels loaded with charged nanoparticle suspension (20-45 nm), applying a current intensity of 1.5 mA for 5 min onto the cornea and sclera. At pre-set time points post treatment, eyes were dissected and tissues were evaluated for fluorescence intensity. Strong fluorescence evidence was observed at anterior and posterior ocular tissues. Negative particle distribution profile revealed fast uptake into the outer ocular tissues, within 30 min post treatment, followed by particle migration into the inner tissues up to 12 h post treatment. The positively charged particles demonstrated better penetration abilities into inner ocular tissues compared to the negatively charge particles. This work provides an opening for the development of a new ocular therapeutic pathway using iontophoresis of extended release drug-loaded charged nanoparticles.

Timolol transport from microemulsions trapped in HEMA gels

Approximately 90% of all ophthalmic drug formulations are now applied as eye-drops. While eye-drops are convenient and well accepted by patients, about 95% of the drug contained in the drops is lost due to absorption through the conjunctiva or through the tear drainage. A major fraction of the drug eventually enters the blood stream and may cause side effects [J.C. Lang, Adv. Drug Delivery Rev. 16 (1995) 39-43; C. Bourlais, L. Acar, H. Zia, P.A. Sado, T. Needham, R. Leverge, Prog. Retinal Eye Res. 17 (1998) 33-58; M.P. Segal, FDA Consumer Mag. (1991)]. The drug loss and the side effects can be minimized by using microemulsion-laden soft contact lenses for ophthalmic drug delivery [D. Gulsen, A. Chauhan, Invest. Ophthalmol. Vis. Sci. 45 (2004) 2342-2347; D. Gulsen, A. Chauhan, Abstr. Pap. Am. Chem. Soc. 227 (2004) U875]. In order for microemulsion-laden gels to be effective, these should load sufficient quantities of drug and should release it a controlled manner. The presence of a tightly packed surfactant at the oil-water interface of microemulsions may provide barrier to drug transport, and this could be used to control the drug delivery rates. In this paper we focus on trapping ethyl butyrate in water microemulsions stabilized by Pluronic F127 surfactant in 2-hydroxyethyl methacrylate (HEMA) gels and measuring the transport rates of timolol, which is a beta-blocker drug that is used for treating a variety of diseases including glaucoma. The results described here show that microemulsion-laden gels could have high drug loadings, particularly for drugs such as timolol base which can either be dissolved in the oil phase or form the oil phase of the microemulsions. However, the surfactant covered interface of the Pluronic microemulsions does not provide sufficient barrier to impede the transport of timolol, perhaps due to the small size of this drug.

Nanoencapsulation II. Biomedical applications and current status of peptide and protein nanoparticulate delivery systems

The concept of polymeric nanoparticles for the design of new drug delivery systems emerged a few years ago, and recent rapid advances in nanotechnology have offered a wealth of new opportunities for diagnosis and therapy of various diseases. Recent progress has made possible the engineering of nanoparticles to allow the site-specific delivery of drugs and to improve the pharmacokinetic profile of numerous compounds with biomedical applications such as peptide and protein drugs. Biologically active peptides and their analogues are becoming an increasingly important class of drugs. Their use for human and animal treatment is problematic, however, because some of these drugs are generally ineffective when taken orally and thus have been administered chiefly by the parenteral route. This review covers some of the historical and recent advances of nanotechnology and concludes that polymeric nanoparticles show great promise as a tool for the development of peptide drug delivery systems.

Oral evaluation in rabbits of cyclosporin-loaded Eudragit RS or RL nanoparticles

The hydrophobic cyclic undecapeptide cyclosporin A (CyA) used in the prevention of graft rejection and in the treatment of autoimmune diseases was encapsulated by nanoprecipitation within non-biodegradable polymeric nanoparticles. The effect of polymers (Eudragit RS or RL) and additives within the alcoholic phase (fatty acid esters and polyoxyethylated castor oil) on the size, zeta potential and the encapsulation efficiency of the nanoparticles was investigated. The mean diameter of the various CyA nanoparticles ranged from 170 to 310 nm. The size as well as the zeta potential increased by adding fatty acid ester and polyoxyethylated castor oil within the organic phase. No significant differences in surface potential were observed for all formulations tested. Probably due to the very low water solubility of the drug, high encapsulation efficiencies were observed in a range from 70 to 85%. The oral absorption of CyA from these polymeric nanoparticles was studied in rabbits and compared to that of Neoral capsule. Based on comparison of the area under the blood concentration-time curve values, the relative bioavailability of CyA from each nanoparticulate formulation ranged from 20 to 35%.

Ocular Pharmacokinetics and Safety of Ciclosporin, a Novel Topical Treatment for Dry Eye

Ciclosporin is a potent immunomodulator that acts selectively and locally when administered at the ocular surface. 0.05% ciclosporin ophthalmic emulsion has recently been approved by the US FDA for treatment of keratoconjunctivitis sicca (KCS) [dry-eye disease]. After topical application, ciclosporin accumulates at the ocular surface and cornea, achieving concentrations (>/=0.236 microg/g) that are sufficient for immunomodulation. Very little drug penetrates through the ocular surface to intraocular tissues. Ciclosporin is not metabolised in rabbit or dog eyes and may not be prone to metabolism in human eyes. Cultured human corneal endothelial and stromal cells exposed to ciclosporin in vitro exhibited no adverse effects and only minor effects on DNA synthesis. No ocular or systemic toxicity was seen with long-term ocular administration of ciclosporin at concentrations up to 0.4%, given as many as six times daily for 6 months in rabbits and 1 year in dogs. Systemic blood ciclosporin concentration after ocular administration was extremely low or undetectable in rabbits, dogs and humans, obviating concerns about systemic toxicity. In 12-week and 1-year clinical safety studies in dry-eye patients, the most common adverse event associated with the ophthalmic use of ciclosporin emulsion was ocular burning. No serious drug-related adverse events occurred. These data from in vitro, nonclinical and clinical studies indicate effective topical delivery of ciclosporin to desired target tissues along with a favourable safety profile, making 0.05% ciclosporin ophthalmic emulsion a promising treatment for KCS.

Poly-epsilon-caprolactone microspheres and nanospheres: an overview

Poly-epsilon-caprolactone (PCL) is a biodegradable, biocompatible and semicrystalline polymer having a very low glass transition temperature. Due to its slow degradation, PCL is ideally suitable for long-term delivery extending over a period of more than one year. This has led to its application in the preparation of different delivery systems in the form of microspheres, nanospheres and implants. Various categories of drugs have been encapsulated in PCL for targeted drug delivery and for controlled drug release. Microspheres of PCL either alone or of PCL copolymers have been prepared to obtain the drug release characteristics. This article reviews the advancements made in PCL-based microspheres and nanospheres with special reference to the method of preparation of these and their suitability in developing effective delivery systems.

Cyclosporine A delivery to the eye: a pharmaceutical challenge

Systemic administration of cyclosporine A (CsA) is commonly used in the treatment of local ophthalmic conditions involving cytokines, such as corneal graft rejection, autoimmune uveitis and dry eye syndrome. Local administration is expected to avoid the various side effects associated with systemic delivery. However, the currently available systems using oils to deliver CsA topically are poorly tolerated and provide a low bioavailability. These difficulties may be overcome through formulations aimed at improving CsA water solubility (e.g. cyclodextrins), or those designed to facilitate tissue drug penetration using penetration enhancers. The use of colloidal carriers (micelles, emulsions, liposomes and nanoparticles) as well as the approach using hydrosoluble prodrugs of CsA have shown promising results. Solid devices such as shields and particles of collagen have been investigated to enhance retention time on the eye surface. Some of these topical formulations have shown efficacy in the treatment of extraocular diseases but were inefficient at reaching intraocular targets. Microspheres, implants and liposomes have been developed to be directly administered subconjunctivally or intravitreally in order to enhance CsA concentration in the vitreous. Although progress has been made, there is still room for improvement in CsA ocular application, as none of these formulations is ideal.

Design of poly-epsilon-caprolactone nanospheres coated with bioadhesive hyaluronic acid for ocular delivery

This study was performed to design a new ocular drug delivery system based on poly-epsilon-caprolactone (PCL) biodegradable nanospheres (NS) coated with a bioadhesive polymer, hyaluronic acid (HA), in order to combine ophthalmic prolonged action with the ease of application. The aim of this work was to investigate three strategies to attach HA on NS surface: (1) coating the core by chain entanglement with HA; (2) coating NS by HA adsorption; (3) coating NS by electrostatic interactions between negatively charged HA and a cationic surfactant (stearylamine, SA, or benzalkonium chloride, BKC). A radioimmunoassay technique, usually used for HA quantification in serum, was transposed to determine the amount of HA on the NS. The results show that HA is strongly attached on NS positively charged by cationic surfactant. This system is stable and not influenced by dilution. These results show the possibility of using cationic surfactants to obtain a HA coating by electrostatic interactions. BKC, approved for ophthalmic administration, was retained because it was more firmly anchored within the PCL matrix and the amount of HA attached was high (41.6 microg HA/mg PCL). Moreover, the yield of fixation reached 50%. Therefore, by using a simple preparation method, it was possible to obtain stable HA and intact HA-coated NS.

Chitosan nanoparticles: a new vehicle for the improvement of the delivery of drugs to the ocular surface. Application to cyclosporin A

Present limitations in the management of extraocular diseases include the inability to provide long-term extraocular drug delivery without compromising intraocular structures and/or systemic drug exposure. In the present study, the potential of chitosan (CS) nanoparticles as a new vehicle for the improvement of the delivery of drugs to the ocular mucosa was investigated. Cyclosporin A (CyA) was chosen as a model compound because of its potential usefulness for the treatment of these local diseases. An ionic gelation technique was conveniently modified in order to produce CyA-loaded CS nanoparticles. These nanoparticles had a mean size of 293 nm, a zeta potential of +37 mV and high CyA association efficiency and loading (73 and 9%, respectively). In vitro release studies, performed under sink conditions, revealed a fast release during the first hour followed by a more gradual drug release during a 24-h period. In vivo experiments showed that, following topical instillation of CyA-loaded CS nanoparticles to rabbits, it was possible to achieve therapeutic concentrations in external ocular tissues (i.e., cornea and conjunctiva) during at least 48 h while maintaining negligible or undetectable CyA levels in inner ocular structures (i.e., iris/ciliary body and aqueous humour), blood and plasma. These levels were significantly higher than those obtained following instillation of a CS solution containing CyA and an aqueous CyA suspension. From these results, we can conclude that CS nanoparticles may represent an interesting vehicle in order to enhance the therapeutic index of clinically challenging drugs with potential application at extraocular level.

Biodegradable nanoparticles as a delivery system for cyclosporine: preparation and characterization

Cyclosporine (CyA) was incorporated into polycaprolactone nanoparticles (PCL-NP) in order to increase its oral bioavailability and to control drug distribution, thereby potentially reducing its toxicity. Prior to in vivo studies, the carrier was optimized and characterized by using different techniques. Light scattering (LS) and transmission and scanning electron microscopy (TEM and SEM) indicated the NP were spherical in shape with a mean size of approximately 100 nm. The influence of the solvent evaporation conditions and the polymer and drug amounts on CyA incorporation was established in order to optimize drug loading. When acetone and excess water were removed at constant temperature, no aggregation phenomena were observed. A value of 180 mg PCL was the minimum polymer amount necessary to encapsulate 95% of the drug initially added to the preparation. Under these conditions, HPLC analysis revealed that approximately 130 microg CyA per mg PCL were incorporated for a total CyA concentration of 2.5 mg/ml, being part of the drug adsorbed onto the particle surface. No structural changes or instability of the components during NP preparation were detected by gel permeation chromatography (GPC) and differential scanning calorimetry (DSC). However, GPC studies showed a competition between poloxamer and CyA for adsorption onto the carrier. In addition, DSC results suggested that at least part of the drug associated to NP remained in its crystal form. Therefore, CyA-loaded NP were easily manufactured and characterized and allow for the administration of therapeutic drug doses to experimental animals.

Therapeutic applications of colloidal drug carriers

Colloidal drug carriers such as liposomes and nanoparticles can be used to improve the therapeutic index of both established and new drugs by modifying their distribution, and thus increasing their efficacy and/or reducing their toxicity. This is because the drug distribution then follows that of the carrier, rather than depending on the physicochemical properties of the drug itself. If these delivery systems are carefully designed with respect to the target and the route of administration, they may provide one solution to some of the delivery problems posed by new classes of active molecules, such as peptides and proteins, genes and oligonucleotides. They may also offer alternative modes for more conventional drugs, such as highly hydrophobic small molecules. This review discusses the use of colloidal, particulate carrier systems (25 nm to 1 µm in diameter) in such applications.

Reversion of multidrug resistance by co-encapsulation of doxorubicin and cyclosporin A in polyalkylcyanoacrylate nanoparticles

Individual and combined polyalkylcyanoacrylate nanoparticle formulation of cyclosporin A and doxorubicin were prepared and evaluated in an attempt to show improved growth inhibition efficacy in a resistant cell culture line. The drug loaded nanoparticles were prepared using the well established emulsion polymerization process without using any modification for the hydrophilic doxorubicin drug whereas the incorporation of cyclosporin A needed to wait a moment after the polymerization reaction started. This was necessary to avoid cyclosporin A precipitation and polymer aggregation. Cyclosporin A release from the nanoparticles was rapid probably because the drug was adsorbed onto the nanoparticles surface rather than embedded into the polymeric core. Doxorubicin displayed also a burst effect but with a slower second phase probably related with the nanoparticles bioerosion rate owing to its entrapment in the polymeric network. Finally, it was shown in resistant cell culture experiments that the association of both cyclosporin A and doxorubicin within a single nanoparticle formulation elicited the most effective growth rate inhibition as compared to other combinations of both drugs while using a lower amount of polymer compared to separated nanoparticle formulations. This result was probably due to the synergistic effect achieved by combining the chemo-sensitizing compound cyclosporin A, with an effective cytotoxic drug like doxorubicin.

Primidone-loaded poly-epsilon-caprolactone nanocapsules: incorporation efficiency and in vitro release profiles

This paper describes the preparation of primidone-loaded poly-epsilon-caprolactone nanocapsules according to the interfacial deposition technique. The colloidal suspension obtained showed a monomodal size distribution with a mean diameter ranging from 308 to 352 nm. By adjusting the process parameters, the encapsulation efficiency was about 74% with good reproducibility. Primidone release from the nanocapsules was found to be slower as compared to the oily control solution despite an important burst-effect. The release profile was not influenced by the pH of the release medium.

Efficacy of topical cyclosporine-loaded nanocapsules on keratoplasty rejection in the rat

PURPOSE

To evaluate the efficacy of a topical formulation of nanocapsules loaded with 1% cyclosporine A (CsA), which has been previously demonstrated to enhance CsA corneal penetration, compared to 1% CsA in migliol oil on a penetrating keratoplasty rejection model in the rat.

METHODS

Lewis rats received orthotopic corneal allografts from inbred Fisher donors. Rats were treated with 10 microliters of the following topical solutions four times daily for 30 days, starting one day before surgery: Group 1 (n = 9), 1% CsA-loaded nanocapsules; group 2 (n = 13), 1% CsA dissolved in migliol oil; group 3 (n = 12), migliol oil; group 4 (n = 13), no treatment. Rejection index, mean survival time and rejection percentage were calculated for each group, and CsA levels in blood were measured.

RESULTS

The rejection percentage was 84.6% for group 2, 91.7% for group 3, and 100% for groups 1 and 4, with no significant differences among groups. Mean graft survival time was 7.3 days for group 1, 15.5 days for group 2, 8.36 days for group 3, and 7.69 days for group 4, with significant differences between group 2 and the other groups. Systemic CsA levels were only detectable in group 2.

CONCLUSIONS

CsA formulated in migliol oil delayed corneal rejection onset, but blood levels were evident in this group. CsA loaded-nanocapsules showed no effect on rejection and the drug was not detectable in blood. These data, along with the current concepts on corneal graft rejection immunology, suggest that the immunomodulatory effect of topical CsA in the prevention of corneal graft rejection may be systemically-mediated.

Ophthalmic drug delivery systems--recent advances

Eye-drops are the conventional dosage forms that account for 90% of currently accessible ophthalmic formulations. Despite the excellent acceptance by patients, one of the major problems encountered is rapid precorneal drug loss. To improve ocular drug bioavailability, there is a significant effort directed towards new drug delivery systems for ophthalmic administration. This chapter will focus on three representative areas of ophthalmic drug delivery systems: polymeric gels, colloidal systems, cyclodextrins and collagen shields. Hydrogels generally offer a moderate improvement of ocular drug bioavailability with the disadvantage of blurring of vision. In situ activated gel-forming systems are preferred as they can be delivered in drop form with sustained release properties. Colloidal systems including liposomes and nanoparticles have the convenience of a drop, which is able to maintain drug activity at its site of action and is suitable for poorly water-soluble drugs. Among the new therapeutic approaches in ophthalmology, cyclodextrins represent an alternative approach to increase the solubility of the drug in solution and to increase corneal permeability. Finally, collagen shields have been developed as a new continuous-delivery system for drugs that provide high and sustained levels of drugs to the cornea, despite a problem of tolerance. It seems that new tendency of research in ophthalmic drug delivery systems is directed towards a combination of several drug delivery technologies. There is a tendency to develop systems which not only prolong the contact time of the vehicle at the ocular surface, but which at the same time slow down the elimination of the drug. Combination of drug delivery systems could open a new directive for improving results and the therapeutic response of non-efficacious systems.

Effect of lysozyme on the stability of polyester nanocapsules and nanoparticles: stabilization approaches

The efficacy of colloidal particles as drug carriers is closely related to their interaction with proteins and enzymes in different body fluids. In the present work, we analysed the interaction phenomenon between lysozyme (LZM), a positively charged enzyme that is highly concentrated in mucosas, and two different drug carriers: nanocapsules made of an oily core coated by the polymer poly-epsilon-caprolactone (PECL) and nanoparticles made solely of PECL. Results showed that the interaction of LZM with these colloidal drug carriers is highly affected by their surface charge. Nanocapsules, because of their important negative charge (-40 mV), adsorbed a great amount of LZM, which is positively charged. This adsorption process, which was also evidenced by the significant reduction of the nanocapsules' negative surface charge, led to the degradation of the polymer coating and the aggregation of the nanocapsules. In contrast, nanoparticles had a low negative surface charge (-8 mV) and adsorbed only a small amount of LZM, which did not cause the destabilization of the system. Furthermore, the molecular weight of the polymer forming the nanoparticles did not change. Finally, it was observed that the destabilizing effects caused by the adsorption of LZM onto the nanocapsules can be prevented by previous adsorption of the cationic poly(amino acid) poly-L-lysine. Using this approach the adsorption of LZM was hindered and its consequences avoided.