Polyhydroxyethylaspartamide-based micelles for ocular drug delivery. Int J Pharm. 2009;378:177-186. [PMID: 19465101 DOI: 10.1016/j.ijpharm.2009.05.028]

Nanoengineered drug delivery systems for enhancing antibiotic therapy

Formulation scientists are recognizing nanoengineered drug delivery systems as an effective strategy to overcome limitations associated with antibiotic drug therapy. Antibiotics encapsulated into nanodelivery systems will contribute to improved management of patients with various infectious diseases and to overcoming the serious global burden of antibiotic resistance. An extensive review of several antibiotic-loaded nanocarriers that have been formulated to target drugs to infectious sites, achieve controlled drug release profiles, and address formulation challenges, such as low-drug entrapment efficiencies, poor solubility and stability is presented in this paper. The physicochemical properties and the in vitro/in vivo performances of various antibiotic-loaded delivery systems, such as polymeric nanoparticles, micelles, dendrimers, liposomes, solid lipid nanoparticles, lipid-polymer hybrid nanoparticles, nanohybirds, nanofibers/scaffolds, nanosheets, nanoplexes, and nanotubes/horn/rods and nanoemulsions, are highlighted and evaluated. Future studies that will be essential to optimize formulation and commercialization of these antibiotic-loaded nanosystems are also identified. The review presented emphasizes the significant formulation progress achieved and potential that novel nanoengineered antibiotic drug delivery systems have for enhancing the treatment of patients with a range of infections.

In-situ forming gel-like depot of a polyaspartamide-polylactide copolymer for once a week administration of sulpiride

Objectives

An in-situ forming gel-like depot, prepared by using an appropriate polyaspartamide-polylactide graft copolymer, has been employed to release in a sustained way sulpiride.

Methods

α,β-poly(N-2-hydroxyethyl)-D,L-aspartamide-g-polylactic acid (PHEA-g-PLA) has been used as a polymer component. Its physicochemical properties make possible to dissolve it in N-methyl-2-pyrrolidone, with the obtainment of a solution able to form a gel-like depot once injected into a physiological medium. Cell compatibility of PHEA-g-PLA depot has been investigated, using murine dermal fibroblasts as cell model. 3-(4,5-Dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium, inner salt assay and fluorescence microscopy have been employed to evaluate cell viability and morphology after contact with PHEA-g-PLA depot. Pharmacokinetic parameters of sulpiride released from depot have been determined following subcutaneous administration to rabbits and compared with corresponding parameters following administration of free sulpiride solution.

Key findings

It has been demonstrated that the system does not affect significantly the viability of fibroblasts and is able to sustain the release of sulpiride until a week, with a burst effect dependent on the initial weight ratio polymer/drug.

Conclusion

In-vivo release profiles and pharmacokinetic parameters suggest that PHEA-g-PLA depot could have interesting clinical applications for a once a week administration of poorly soluble drugs to humans or animals.

Controlled ocular drug delivery with nanomicelles

Many vision threatening ocular diseases such as age-related macular degeneration (AMD), diabetic retinopathy, glaucoma, and proliferative vitreoretinopathy may result in blindness. Ocular drug delivery specifically to the intraocular tissues remains a challenging task due to the presence of various physiological barriers. Nonetheless, recent advancements in the field of nanomicelle-based novel drug delivery system could fulfil these unmet needs. Nanomicelles consists of amphiphilic molecules that self-assemble in aqueous media to form organized supramolecular structures. Micelles can be prepared in various sizes (10-1000 nm) and shapes depending on the molecular weights of the core and corona forming blocks. Nanomicelles have been an attractive carrier for their potential to solubilize hydrophobic molecules in aqueous solution. In addition, small size in nanometer range and highly modifiable surface properties have been reported to be advantageous in ocular drug delivery. In this review, various factors influencing rationale design of nanomicelles formulation and disposition are discussed along with case studies. Despite the progress in the field, influence of various properties of nanomicelles such as size, shape, surface charge, rigidity of structure on ocular disposition need to be studied in further details to develop an efficient nanocarrier system.

CSM enhances the filtration bleb survival in rabbit model of experimental glaucoma surgery

PURPOSE

The aim of this study is to investigate whether CS-g-MMCs conjugate (CSM) could be a new agent to prevent the post-operative fibrosis in a rabbit model of experimental glaucoma filtration surgery.

MATERIALS AND METHODS

In a randomized, controlled, masked-observer study, 40 New Zealand White rabbits underwent trabeculectomy in the right eyes and randomly received subconjunctival injection of phosphate buffered saline, chitosan (CS), CSM (100 µg/ml), CSM (200 µg/ml) or Mitomycin C (100 µg/ml). Bleb characteristics and anterior chamber depth were evaluated by slit-lamp examination. The animals were killed on day 14 and 28. Histopathology and immunohistochemistry were performed to determine the amount of the scarring and fibrosis. Ocular toxicity was assessed by histopathology and electron microscope.

RESULTS

We found that the five groups were similar with respect to intraocular pressure and anterior chamber depth. The medians for survival days were: 5.5, 8, 17.5, 28 and 16 in the PBS, CS, CSM100, CSM200 and MMC groups, respectively. Both the CSM200 and the MMC group showed a significantly larger bleb area than the CSM100, CS and the PBS group. Less scarring was seen on day 14 and 28 in CSM200 and MMC group than in the PBS, CS and CSM100 group by histology and immunohistochemistry assessment. No damages were found in the rabbit eyes in each group.

CONCLUSIONS

Subconjunctival injection of CSM postoperatively can improve the filtration bleb survival in the rabbit model. It can be a safe and effective antimetabolite in glaucoma surgery.

Ocular drug delivery systems: An overview

The major challenge faced by today’s pharmacologist and formulation scientist is ocular drug delivery. Topical eye drop is the most convenient and patient compliant route of drug administration, especially for the treatment of anterior segment diseases. Delivery of drugs to the targeted ocular tissues is restricted by various precorneal, dynamic and static ocular barriers. Also, therapeutic drug levels are not maintained for longer duration in target tissues. In the past two decades, ocular drug delivery research acceleratedly advanced towards developing a novel, safe and patient compliant formulation and drug delivery devices/techniques, which may surpass these barriers and maintain drug levels in tissues. Anterior segment drug delivery advances are witnessed by modulation of conventional topical solutions with permeation and viscosity enhancers. Also, it includes development of conventional topical formulations such as suspensions, emulsions and ointments. Various nanoformulations have also been introduced for anterior segment ocular drug delivery. On the other hand, for posterior ocular delivery, research has been immensely focused towards development of drug releasing devices and nanoformulations for treating chronic vitreo-retinal diseases. These novel devices and/or formulations may help to surpass ocular barriers and associated side effects with conventional topical drops. Also, these novel devices and/or formulations are easy to formulate, no/negligibly irritating, possess high precorneal residence time, sustain the drug release, and enhance ocular bioavailability of therapeutics. An update of current research advancement in ocular drug delivery necessitates and helps drug delivery scientists to modulate their think process and develop novel and safe drug delivery strategies. Current review intends to summarize the existing conventional formulations for ocular delivery and their advancements followed by current nanotechnology based formulation developments. Also, recent developments with other ocular drug delivery strategies employing in situ gels, implants, contact lens and microneedles have been discussed.

How do polymeric micelles cross epithelial barriers?

Non-parenteral delivery of drugs using nanotechnology-based delivery systems is a promising non-invasive way to achieve effective local or systemic drug delivery. The efficacy of drugs administered non-parenterally is limited by their ability to cross biological barriers, and epithelial tissues particularly present challenges. Polymeric micelles can achieve transepithelial drug delivery because of their ability to be internalized into cells and/or cross epithelial barriers, thereby delivering drugs either locally or systematically following non-parenteral administration. This review discusses the particular characteristics of various epithelial barriers and assesses their potential as non-parenteral routes of delivery. The material characteristics of polymeric micelles (e.g., size, surface charge, and surface decoration) and of unimers dissociated from polymeric micelles determine their interactions (non-specific and/or specific) with mucus and epithelial cells as well as their intracellular fate. This paper outlines the mechanisms governing the major modes of internalization of polymeric micelles into epithelial cells, with an emphasis on specific recent examples of the transport of drug-loaded polymeric micelles across epithelial barriers.

Nanotechnology in corneal neovascularization therapy--a review

Nanotechnology is an up-and-coming branch of science that studies and designs materials with at least one dimension sized from 1-100 nm. These nanomaterials have unique functions at the cellular, atomic, and molecular levels. The term "nanotechnology" was first coined in 1974. Since then, it has evolved dramatically and now consists of distinct and independent scientific fields. Nanotechnology is a highly studied topic of interest, as nanoparticles can be applied to various fields ranging from medicine and pharmacology, to chemistry and agriculture, to environmental science and consumer goods. The rapidly evolving field of nanomedicine incorporates nanotechnology with medical applications, seeking to give rise to new diagnostic means, treatments, and tools. Over the past two decades, numerous studies that underscore the successful fusion of nanotechnology with novel medical applications have emerged. This has given rise to promising new therapies for a variety of diseases, especially cancer. It is becoming abundantly clear that nanotechnology has found a place in the medical field by providing new and more efficient ways to deliver treatment. Ophthalmology can also stand to benefit significantly from the advances in nanotechnology research. As it relates to the eye, research in the nanomedicine field has been particularly focused on developing various treatments to prevent and/or reduce corneal neovascularization among other ophthalmologic disorders. This review article aims to provide an overview of corneal neovascularization, currently available treatments, and where nanotechnology comes into play.

Novel strategies for anterior segment ocular drug delivery

Research advancements in pharmaceutical sciences have led to the development of new strategies in drug delivery to anterior segment. Designing a new delivery system that can efficiently target the diseased anterior ocular tissue, generate high drug levels, and maintain prolonged and effective concentrations with no or minimal side effects is the major focus of current research. Drug delivery by traditional method of administration via topical dosing is impeded by ocular static and dynamic barriers. Various products have been introduced into the market that prolong drug retention in the precorneal pocket and to improve bioavailability. However, there is a need of a delivery system that can provide controlled release to treat chronic ocular diseases with a reduced dosing frequency without causing any visual disturbances. This review provides an overview of anterior ocular barriers along with strategies to overcome these ocular barriers and deliver therapeutic agents to the affected anterior ocular tissue with a special emphasis on nanotechnology-based drug delivery approaches.

Production of polymeric micelles by microfluidic technology for combined drug delivery: application to osteogenic differentiation of human periodontal ligament mesenchymal stem cells (hPDLSCs)

The current paper reports the production of polymeric micelles (PMs), based on pluronic block-copolymers, as drug carriers, precisely controlling the cellular delivery of drugs with various physico-chemical characteristics. PMs were produced with a microfluidic platform to exploit further control on the size characteristic of the PMs. PMs were designed for the co-delivery of dexamethasone (Dex) and ascorbyl-palmitate (AP) to in vitro cultured human periodontal ligament mesenchymal stem cells (hPDLSCs) for the combined induction of osteogenic differentiation. Mixtures of block-copolymers and drugs in organic, water miscible solvent, were conveniently converted in PMs within microfluidic channel leveraging the fast mixing at the microscale. Our results demonstrated that the drugs can be efficiently co-encapsulated in PMs and that different production parameters can be adjusted in order to modulate the PM characteristics. The comparative analysis of PM produced by microfluidic and conventional procedures confirmed that the use of microfluidics platforms allowed the production of PMs in a robust manner with improved controllability, reproducibility, smaller size and polydispersity. Finally, the analysis of the effect of PMs, containing Dex and AP, on the osteogenic differentiation of hPDLSCs is reported. The data demonstrated the effectiveness and safety of PM treatment on hPDLSC. In conclusion, this report indicates that microfluidic approach represents an innovative and useful method for PM controlled preparation, warrant further evaluation as general methodology for the production of colloidal systems for the simultaneous drug delivery.

Novel Nanomicellar Formulation Approaches for Anterior and Posterior Segment Ocular Drug Delivery

One of the most challenging areas of pharmaceutical research is ocular drug delivery. The unique anatomy and physiology of the eye impedes drug permeation to deeper ocular tissues. Nanosized carrier systems such as nanoparticles, liposomes, suspensions, dendrimers, and nanomicelles are being explored for ocular drug delivery. In this review, we have focused on application of emerging nanomicellar carrier systems in ocular drug delivery. Nanomicelles are nanosized vesicular carriers formed from amphiphilic monomer units. Surfactant and polymeric micellar nanocarriers provide an amenable means to improve drug solubilization, develop clear aqueous formulations and deliver drugs to anterior and posterior ocular tissues. Nanomicelles due to their amphiphilic nature encapsulate hydrophobic drugs and aid in drug delivery. Various methods are employed to develop nanosized micellar formulations depending upon the physicochemical properties of the drug. Nanomicellar carriers appear to be promising vehicles with potential applications in ocular drug delivery. In this review, we attempted to discuss about the progress in ocular drug delivery research using nanomicelles as carriers from the published literature and issued patents. Also, with regards to ocular static and dynamic barriers which prevent drug permeation, a brief discussion about nanomicelles, types of nanomicelles, their methods of preparation and micellar strategy to overcome ocular barriers, delivering therapeutic levels of drugs to anterior and posterior ocular tissues are discussed.

Breakdown of the blood-ocular barrier as a strategy for the systemic use of nanosystems

Several drug delivery systems have been proposed to overcome physiological barriers, improving ocular bioavailability. Systemic routes are seldom used due to the blood-ocular barrier. Novel drug delivery systems based on nanotechnology techniques have been developed to overcome ocular physiological barriers. This non-systematic review suggests the utilization of a transitory blood-ocular breakdown to allow the access of drugs by nanotechnology drug delivery systems via the systemic route. We discuss the possible ways to cause the breakdown of the blood-ocular barrier: acute inflammation caused by intraocular surgery, induced ocular hypotony, and the use of inflammatory mediators. The suitability of use of the systemic route and its toxic effects are also discussed in this article.

Peculiar mechanism of solubilization of a sparingly water soluble drug into polymeric micelles. Kinetic and equilibrium studies

Complementary kinetic and equilibrium studies on the solubilization process of the sparingly water soluble tamoxifen (TAM) drug in polymeric aqueous solutions have been performed by using the spectrophotometric method. In particular, the amphiphilic copolymers obtained by derivatization of polymeric chain of poly(N-2-hydroxyethyl)-dl-aspartamide, PHEA, with poly(ethylene glycol)s, PEG (2000 or 5000 Da), and/or hexadecylamine chain, C16, namely PHEA-PEG2000-C16, PHEA-PEG5000-C16, PHEA-C16, have been employed. Preliminary to the kinetic and equilibrium data quantitative treatment, the molar absorption coefficient of TAM in polymeric micelle aqueous solution has been determined. By these studies the solubization sites of TAM into the polymeric micelles have been determined and the solubilization mechanism has been elucidated through a nonconventional approach by considering the TAM partitioned between three pseudophases, i.e., the aqueous pseudophase, the hydrophilic corona, and the hydrophobic core. The simultaneous solution of the rate laws associated with each step of the proposed mechanism allowed the calculation of the rate constants associated with the involved processes, the values of which are independent of both the copolymer concentration and nature, with the exception of the rate of the TAM transfer from the corona to the core. This has been attributed to the steric barrier, represented by the corona, which hampers the solubilization into the core. The binding constant values of the TAM to the hydrophilic corona of the polymeric micelles, calculated through the quantitative analysis of the equilibrium data, depend on the thickness of the hydrophilic headgroup, while those of the hydrophobic core are almost independent of the copolymer type. Further confirmation to the proposed solubilization mechanism has been provided by performing the kinetic and equilibrium measurements in the presence of PHEA-PEG2000 and PHEA-PEG5000 copolymers.

Synthesis of a novel CS-g-MMCs conjugate and the inhabitation on the proliferation of Tenon's capsule fibroblasts in vitro

A novel anti-proliferative macromolecular conjugate, CS-g-MMCs, was synthesized in order to decrease the cytotoxicity of Mitomycin C (MMC) which was a traditional anti-proliferative agent of fibroblast in trabeculectomy. The structure of CS-g-MMCs was characterized by (1)H NMR, FT-IR spectroscopy and GPC analysis. The grafting degree (dg) of MMC onto chitosan (CS) was determined to be in the range of 2.8-11.3%, which could be controlled by variation of the molar ratios of MMC to oxidized chitosan (CS-CHO). In the drug release profiles of CS-g-MMCs in vitro, an initial burst followed by slow leakage was observed, and addition of acid or lysozyme obviously accelerated the MMC release. The MTS assay indicated that CS-CHO of 8 mg/ml has no cytotoxicity against human Tenon's capsule fibroblasts (HTCFs). The inhibition of HTCFs proliferation by CS-g-MMCs increased along with increasing the dg of conjugate. The CS-g-MMCs also caused the apoptosis of HTCFs and interfered in the active DNA synthesis in HTCFs. Furthermore, the expression of a-SMA at gene and protein levels were obviously lower when HTCFs were treated with CS-g-MMCs, as compared to MMC or blend of MMC/CS-CHO (p<0.05). Our results primarily demonstrated that the CS-g-MMCs conjugates have low cytotoxicity and have the effect to inhibit fibroblast proliferation.