[Transcorneal and transscleral iontophoresis of the dexamethasone phosphate into the rabbit eye]

PURPOSE

To evaluate the efficiency of the dexamethasone phosphate penetration into the rabbit eye after transcorneal and transscleral iontophoresis using a drug loaded hydrogel assembled on a portable iontophoretic Mini Ion device.

METHODS

lontophoresis of dexamethasone phosphate was studied in healthy rabbits using drug-loaded disposable HEMA hydrogel sponges and portable iontophoretic device. Corneal iontophoretic administration was performed with electric current of 1 mAmp for 1, 2, and 4 min. In the control group, the dexamethasone was applied in drops into the conjunctival sac. Transconjunctival and transscleral iontophoresis were performed in the pars plana area, through the conjunctiva or directly on the sclera. Dexamethasone concentrations were assayed using HPLC method. To study the anatomical changes after iontophoresis application, histological examinations of corneas excised 5 minutes and 8 hours after the procedure were performed.

RESULTS

Dexamethasone levels in the rabbits' corneas after a single transcorneal iontophoresis were up to 38 times higher compared to those obtained after topical eye drops instillation. High drug concentrations were obtained in the retina and sclera 4 hours after transscleral iontophoresis as well. There were no statistically significant differences in the drug concentration after transscleral and tranconjunctival iontophoresis. Histological examination of the corneas after the iontophoresis showed only discrete reversible changes of the epithelium and the stroma.

CONCLUSION

A short, low-current, non-invasive iontophoretic treatment using the dexamethasone-loaded hydrogels has a potential clinical value in increasing the drug's penetration into the anterior and posterior segment of the eye.

[Delivery of gentamicin to the rabbit eye using hydrogel and iontophoresis]

The aim of this study was to evaluate the use of solid hydrogel as a probe for the drug delivery to the rabbit eye upon application of low current iontophoresis. Hydroxyethyl methacrylate (HEMA), cross-linked with ethylenglycol dimethacrylate (EGDMA) were prepared to form solid hydrogels. The concentrations of gentamicin sulfate in different segments of rabbit eye after transconjunctival and transscleral iontophoresis were also studied. For iontophoresis we used a portable Mini Ion device (designed at Hebrew University of Jerusalem) and applied a current from 0 mA to 1.5 mA for pre-set period from 30 to 120 seconds and after application the concentrations of gentamicin in cornea were assayed. The rabbits in control group were treated with fortified gentamicin eye-drops (concentration 1.4 %). The highest concentration of gentamicin sulfate was reached after iontophoresis with current intensity of 1.5 mA applied for 60 s. High gentamicin concentration were found in the retina and in the sclera four hours after transscleral iontophoresis, the lowest concentration was obtained in vitreous. The delivery of gentamicin to the eye via iontophoresis with solid HEMA/EGDMA hydrogels seems to be promising method achieving high concentrations of the drug in the eye tissue.

New Formulations and Derivatives of Amphotericin B for Treatment of Leishmaniasis

The clinical treatment of leishmaniasis is based on a limited number of drugs, which are associated with adverse effects and have already induced resistance. Amphotericin B (AmB), a polyene antibiotic produced by Streptomyces sp, is the only anti-leishmanial drug which has not induced clinical resistance since its discovery in 1956. The limiting factor in the use of AmB is its toxic effects, mainly nephrotoxicity. The maximal dose of AmB for human use is 1.5 mg/kg which sometimes is not sufficient for cure. The mode of action of AmB is associated with its toxicity: it selectively binds to parasite membrane ergosterol but also, to a lesser extent, to human cholesterol. Apart from this mechanism, AmB has immunomodulatory effects, some of them are deleterious. Reduction of the toxic effects by using lipid formulations allows the infusion of higher doses of AmB. Unfortunately, these formulations are relatively expensive and therefore out of reach for patients in need, in the endemic areas. All the existing formulations are given parenterally, which has obvious disadvantages; most important is the need for hospitalization or multiple visits in the clinic. The current efforts to improve AmB are directed at the production of AmB aggregates in liquid solutions, encapsulation with lipid components, and solubilization by binding to soluble polymers. The expected improved treatment resulting from use of the new formulations is based on better pharmacokinetics, reduced toxicity originating from slow release, targeting to the infected organ and an altered pattern of immune responses (related to AmB). Of particular importance are the attempts to produce derivatives for oral treatment, which will decrease costs of hospitalization and improve applicability for children and the elderly population.

Reduction in dermal fibrosis in the tight-skin (Tsk) mouse after local application of halofuginone

The effect of dermal application of halofuginone-an inhibitor of collagen type I synthesis-on skin collagen and collagen alpha1(I) gene expression in an animal model of scleroderma and chronic graft versus host disease (cGvHD) was evaluated. Halofuginone-containing cream was applied on the tight-skin mouse (Tsk) and skin biopsies were taken for collagen staining by sirius red and for collagen alpha1(I) gene expression by in situ hybridization. In addition, cell proliferation was evaluated by immunostaining for proliferation cell nuclear antigen (PCNA) alone or in combination with collagen alpha1(I) probe. The number of mast cells was assessed by toluidine blue. Dermal application of halofuginone (0.01%) for 60 days was as good as systemic administration (1 microg/mouse/day) in reducing collagen alpha1(I) gene expression in skin biopsy and almost as good in reducing skin width. Halofuginone was stable and effective only at acidic pH. The effect of halofuginone (0.03%) was time-dependent. After 40 days of daily treatment, a significant reduction in the collagen alpha1(I) gene expression was observed and further decrease was observed after 60 days. The reduction in collagen alpha1(I) gene expression and the reduction in the proliferation of dermal fibroblasts probably occur in the same subset of cells. No effect of halofuginone on the proliferation of keratinocytes or on mast cell number was observed. These results suggest that target-oriented application of halofuginone may become a novel therapy for fibrotic disorders in general and for scleroderma in particular.

The treatment of animal models of malaria with iron chelators by use of a novel polymeric device for slow drug release

The hydrophilic desferrioxamine (DFO) and the lipophilic salicylaldehyde isonicotinoyl hydrazone (SIH) are iron chelators which inhibit in vitro proliferation of Plasmodium falciparum with similar potency (IC50 approximately 20 microM in 24- to 48-h tests). The in vivo assessment of these drugs was performed on Swiss mice infected with Plasmodium vinckei petteri with novel modes of drug administration and release. The drugs were delivered postpatently either by multiple i.p. injections or by a single i.p. or s.c. insertion of a drug-containing polymeric device which released most of the drug within 7 days at apparently first-order rates. A regimen of three daily i.p injections of 5 mg DFO for 3 consecutive days or a 70-mg dose of the drug given as an i.p. or s.c. polymer implant evoked similar delay and reduction in peak parasitemias and reduced mortality with no apparent signs of toxicity. Relatively faster, but otherwise similar results were obtained with the less hydrophilic SIH. In combination, the two drugs apparently potentiated each other. The polymeric devices were particularly useful for treating Plasmodium berghei K173-infected C57Bl mice, a suggested model of cerebral malaria, in which classical methods of DFO delivery were ineffective. The insertion of a 140-mg DFO-containing device on day 6 postinfection (parasitemia approximately 1%) led to a marked reduction in parasite proliferation, appearance of neurological sequelae and mortality of mice. Our studies indicate that polymeric devices for slow drug release might be highly advantageous for both hydrophilic and lipophilic drugs whose antimalarial efficacy might depend on the maintenance of sustained blood levels. The results obtained with slow-release devices have implications for malaria chemotherapy as well as for iron chelation therapy in iron overload conditions.

Nanotechnology for biomaterials engineering: structural characterization of amphiphilic polymeric nanoparticles by 1H NMR spectroscopy

Nanoparticles composed of diblock poly(D,L-lactide-co-glycolide)-poly(ethylene glycol) (PLGA-PEG) or a branched, multiblock PLA-(PEG)3 were prepared by the single emulsion technique. Results of previous studies of these nanoparticles suggested that their structure is of the core-corona type with a polyester core and an outer PEG coating. In the present study, 1H NMR spectroscopy was utilized to provide direct evidence of the structure of these nanoparticles suspended in an aqueous environment. The results confirm the existence of the core-corona structure under these conditions, and show that the PEG moieties extend out from the nanoparticle core into the aqueous environment, and exhibit chain mobility similar to that of PEG in solution.

Noninvasive in vivo monitoring of drug release and polymer erosion from biodegradable polymers by EPR spectroscopy and NMR imaging

Biodegradable polymers have attracted much attention as implantable drug delivery systems. Uncertainty in extrapolating in vitro results to in vivo systems due to the difficulties of appropriate characterization in vivo, however, is a significant issue in the development of these systems. To circumvent this limitation, noninvasive magnetic resonance techniques, electron paramagnetic resonance (EPR) and magnetic resonance imaging (MRI), were applied to characterize drug release and polymer degradation in vitro and in vivo. MRI makes it possible to monitor water content, tablet shape, and response of the biological system such as edema and encapsulation. The results of the MRI experiments give the first direct proof in vivo of postulated mechanisms of polymer erosion. Using nitroxide radicals as model drug releasing compounds, information on the mechanism of drug release and microviscosity inside the implant can be obtained by means of 1.2 GHz EPR spectroscopy. To be able to attribute nitroxide mobility to a particular layer of the implant, sandwich-like tablets were manufactured, taking advantage of the distinct spectral features of nitroxides containing different isotopes of nitrogen (15N vs 14N). The use of both noninvasive methods to monitor processes in vivo leads to new insights in understanding the mechanisms of drug release and polymer degradation.

Gamma-sterilization-induced radicals in biodegradable drug delivery systems

Electron paramagnetic resonance (EPR) spectroscopy (1.2 and 9.25 GHz, 25 degrees C) was used to characterize free radicals in gamma-ray sterilized biodegradable polymers of the type which are in clinical use. Free radicals were detected in all irradiated polymer samples. The temperature of irradiation (25 degrees C vs dry ice temperature) had only a minor influence on the yield of radicals and the shape of the EPR spectra. In contrast, the composition of the polymers and the drugs incorporated in them did strongly influence the amount of radiation-induced free radicals and their reactivity. In general, polymers with high melting points and crystallinity had the highest yields of radicals observable at room temperature. We were able to use the free radicals induced by the usual sterilization procedures to follow the penetration of water and the degradation of the polymers in vitro and in vivo. The ability of in vivo EPR to follow drug delivery noninvasively and continuously in vivo, using the free radicals induced in the usual sterilization process indicates that this approach could be applied immediately for the characterization of these drug delivery systems in experimental animals and in the near future should be able to be used in human subjects.

Polymer-iodine inactivation of the human immunodeficiency virus

BACKGROUND

Hospital and laboratory equipment that come in contact with body fluids of patients with human immunodeficiency virus (HIV) are potentially infective and require special measures for decontamination and disposal. Human immunodeficiency virus is sensitive to several chemicals but requires a continuous exposure to the disinfectant to effective inactivation. Polymers have the capacity to release viricidal chemicals in a sustained fashion for prolonged periods of time, and may be used to coat patient care items before their use. Iodine was chosen because of its universal antimicrobial potential; it was incorporated into polyurethane polymers and the effectiveness of the polymer-iodine against HIV-1 3B was assayed.

STUDY DESIGN

Iodine was loaded into polyurethane polymers by two different methods: polyurethane-complexing, where the iodine is released through a desorption mechanism, and polyurethane-matrixing, where the iodine is released through a diffusion mechanism. The pharmacokinetics of the iodine release were studied in each case. Twenty-four-well viral culture plates used for HIV-1 3B assays were coated with both types of polyurethane-iodine polymers. Their effectiveness against HIV was assessed by MT4 cell viability and reverse transcriptase assays.

RESULTS

The polymer-iodine combination remained stable as long as it was dry: the iodine release started only when the plates came in contact with an aqueous environment. The release from the polyurethane-iodine complex was large and rapid, resulting in inactivation of the HIV-1 3B within 15 to 30 minutes, as determined both by reverse transcriptase and the MT4 cytopathic cell cultures assays. The release from the polyurethane-iodine matrix was slower and had no significant antiviral effect.

CONCLUSIONS

The polyurethane polymer provided a sustained release of iodine that effectively inactivated HIV. The coating may be applied at the time of manufacturing to specific hospital and laboratory items that are to come in contact with blood from patient-contaminated fluids. This technology is attractive for decontamination, especially in situations where appropriate and rapid disposal of medical waste is not readily available. Further research is in progress to speed the release of the iodine from the polymer and the subsequent inactivation of the virus.

The controlled intravenous delivery of drugs using PEG-coated sterically stabilized nanospheres

Injectable blood persistent particulate carriers have important therapeutic application in site-specific drug delivery or medical imaging. However, injected particles are generally eliminated by the reticuloendothelial system within minutes after administration and accumulate in the liver and spleen. To obtain a coating that might prevent opsonization and subsequent recognition by the macrophages, sterically stabilized nanospheres were developed using amphiphilic diblock or multiblock copolymers. The nanospheres are composed of a hydrophilic polyethylene glycol coating and a biodegradable core in which various drugs were encapsulated. Hydrophobic drugs, such as lidocaine, were entrapped up to 45 wt% and the release kinetics were governed by the polymer physico-chemical characteristics. Plasma protein adsorption was drastically reduced on PEG-coated particles compared to non-coated ones. Relative protein amounts were time-dependent. The nanospheres exhibited increased blood circulation times and reduced liver accumulation, depending on the coating polyethylene glycol molecular weight and surface density. They could be freeze-dried and redispersed in aqueous solutions and possess good shelf stability. It may be possible to tailor "optimal" polymers for given therapeutic applications.

Effectiveness of controlled release of a cyclophosphamide derivative with polymers against rat gliomas

Most malignant gliomas grow despite treatment by standard chemotherapeutic agents. The authors explored the use of an innovative drug, 4-hydroperoxycyclophosphamide (4HC), delivered via a controlled-release biodegradable polymer to determine whether local delivery would enhance efficacy. This drug is an alkylator-type chemotherapeutic agent derived from cyclophosphamide. Unlike the parent drug, which requires activation by hepatic microsomes, 4HC is active in vitro. Two rat glioma cell lines, 9L and F98, were treated in cell culture with medium containing 4HC. Both cell lines were more sensitive to 4HC than to a nitrosourea, BCNU, an agent of established value in the local therapy of gliomas. Ninety Fischer 344 rats implanted with 9L or F98 gliomas were treated with an intracranial polymer implant containing 0% to 50% loaded 4HC in the polymer, and it was found that 20% 4HC-loaded polymers caused minimum local brain toxicity and maximum survival. These polymers were then used to compare the in vivo efficacy of 4HC to BCNU in rats implanted with 9L glioma. Animals with brain tumors treated with 4HC had a median survival span of 77 days compared to the median survival of 21 days in BCNU-treated animals and median survival of 14 days in untreated animals. Long-term survival for more than 80 days was 40% in the 4HC-treated rats versus 30% in the BCNU-treated rats. The polymer carrier used in this study was a copolyanhydride of dimer erucic acid and sebacic acid 1:1, which was able to maintain the hydrolytically unstable 4HC in a stable state for local delivery. Thus, it is concluded that 4HC-impregnated polymers provide an effective and safe local treatment for rat glioma.

Erosion of a new family of biodegradable polyanhydrides

Studies investigating the erosion mechanism of the newly developed poly (fatty acid dimer: sebacic acid) polyanhydride (p:[FAD:SA]) are described. The overall erosion of different monomer compositions of p(FAD:SA) copolymers was examined to determine whether and to what extent copolymer properties affected polymer erosion. Increasing the hydrophobic monomer (FAD) content up to 50 wt% in the copolymer resulted in longer erosion, whereas further increases up to 70 wt% decreased the erosion period. Polymer crystallinity depended on copolymer FAD content. Copolymer degradation was studied by examining anhydride bond hydrolysis using infrared spectroscopy. Much faster hydrolysis was found in p(FAD:SA) 70:30 compared with more crystalline copolymers of higher SA content. Light microscopy indicates the presence of an erosion zone, a distinct area where mass loss occurs. This erosion zone moves from the outside toward the interior of the polymer matrix. It plays an important role in erosion because any water or monomer must diffuse through this eroded layer.

Interstitial taxol delivered from a biodegradable polymer implant against experimental malignant glioma

Taxol is a novel antitumor agent with demonstrated efficacy against ovarian, breast, and non-small cell lung cancers in Phase II clinical trials, but which has been shown not to cross the blood-brain barrier. To adapt taxol as a therapy for brain tumors, we have incorporated it into a biodegradable polyanhydride matrix for intracranial implantation and evaluated this formulation in a rat model of malignant glioma. Fischer 344 rats bearing intracranial 9L glioma tumors were treated with 10 mg poly[bis(p-carboxyphenoxy)propane-sebacic acid] (20:80) copolymer discs, containing 20-40% taxol by weight, 5 days after tumor implantation. The taxol-loaded polymers doubled (38 days, 40% taxol loading, P < 0.02) to tripled (61.5 days, 20% taxol loading, P < 0.001) the median survival of rats bearing tumor relative to control rats (19.5 days). Drug loadings of 20-40% taxol by weight released intact taxol for up to 1000 h in vitro. In rats followed up to 30 days postimplant, the polymer maintained a taxol concentration of 75-125 ng taxol/mg brain tissue (100-150 microM taxol) within a 1-3-mm radius of the disc. At points more distant from the disc (up to 8 mm away, the size limit of the rat brain), the polymer maintained a taxol concentration of greater than 4 ng taxol/mg brain tissue (5 microM). We conclude that taxol shows promise as a therapy for malignant glioma when delivered interstitially from a biodegradable polymer.

Injectable polyanhydride granules provide controlled release of water-soluble drugs with a reduced initial burst

A method for preparing polyanhydride granules of an injectable size was developed. The resulting granules permitted a nearly constant release of low-molecular-weight, water-soluble drugs without an initial burst. The polyanhydrides used were poly(fatty acid dimer), poly(sebacic acid), and their copolymers. The dyes acid orange 63 and p-nitroaniline were used as model compounds for drugs. Polymer degradation and drug release for disks and variously sized granules of copolymers containing drugs, prepared by a water-in-oil (W/O) emulsion method, were compared with those for devices prepared by the usual compression method. In the W/O emulsion method, a mixture of aqueous drug solution and polymer-chloroform solution was emulsified by probe sonication to prepare a very fine W/O emulsion. The powder obtained by freeze-drying of the W/O emulsion was pressed into circular disks. In the compression method, the drug was mechanically mixed with the polymer, and the mixture was compressed into circular disks. The resulting disks were ground to prepare granules of different sizes. The granules encapsulated more than 95% of the drug, irrespective of the preparation method. Both methods were effective in preparing polymer disks capable of controlled drug release without any initial burst. However, as the granule size decreased to an injectable size (diameter, < 150 microns), a large difference in the drug release profile was observed between the two preparation methods. The injectable granules obtained by the W/O emulsion method showed nearly constant drug release without any large initial burst, in contrast to those prepared by the compression method, irrespective of the drug type.(ABSTRACT TRUNCATED AT 250 WORDS)

Bioerodible polyanhydrides for antibiotic drug delivery: in vivo osteomyelitis treatment in a rat model system

Acute and chronic osteomyelitis can be difficult to treat by conventional means. Current methods of treatment involve the use of systemic antibiotics, the local implantation of non-degradable drug carriers, and surgical débridement. Each method has specific drawbacks. We report on the use of a new controlled release system utilizing gentamicin and bioerodible, biocompatible polymers (polyanhydrides) designed for drug delivery applications for the treatment of clinical osteomyelitis. We compared this system's ability to reduce bacterial levels in infected bone with that of conventional non-degradable delivery systems based on polymethylmethacrylate (PMMA) and gentamicin. Polyanhydride copolymers of bis-carboxyphenoxypropane and sebacic acid P loaded with gentamicin sulfate and PMMA/gentamicin matrices were implanted in the long bones of Sprague-Dawley rats infected with a strain of Staphylococcus aureus. After 3 weeks of implantation, the polymeric delivery devices were removed and quantitative cultures were used to determine bacterial levels in bone. The polyanhydride/gentamicin matrices demonstrated significant degradation over the 3 week implantation period. Levels of bacteria, measured in colony forming units, were significantly lower in bone implanted with the polyanhydride/gentamicin release system than in long bones of control animals without an implant (p < 0.01), of animals with a polyanhydride polymer implant alone (p < 0.01), and of animals with a PMMA/gentamicin implant (p = 0.03). Bioerodible polyanhydrides show promise as a new treatment modality for infections in bone.

Poly(anhydride) administration in high doses in vivo: studies of biocompatibility and toxicology

Poly(anhydrides) proposed for use as vehicles for controlled drug delivery were administered subcutaneously in Sprague-Dawley rats at two dosage levels (800 mg/kg rat and 2400 mg/kg rat) for a period of eight weeks. Biocompatibility was assessed using a number of methods. Thirty-six clinical chemistry and hematology parameters were monitored throughout the study. Blood values were statistically analyzed for any possible effects due to the implanted polymer. After 8 weeks, rats were sacrificed and complete necropsies were performed. Histological evaluations of 33 organ sites including heart, lung, liver, kidney, and brain were performed. In addition, subcutaneous implant sites were excised and examined both grossly and microscopically. Results from evaluations of blood chemistry and hematology data, organ analyses and local implant site analyses overall demonstrated that the poly(anhydride) biomaterial possessed excellent in vivo biocompatibility.

Ectopic induction of cartilage and bone by water-soluble proteins from bovine bone using a polyanhydride delivery vehicle

Controlled release delivery vehicles for water-soluble osteogenic proteins from demineralized bovine bone matrix were constructed using polyanhydride polymers. The water-soluble proteins were isolated from a 4 M guanidine hydrochloride extract of bone matrix. The water-soluble proteins possessed Chondrogenic Stimulating Activity (CSA) when tested in stage 24 chick limb bud cell cultures, but were incapable of inducing cartilage or bone in vivo when implanted intramuscularly into mice by themselves. The polyanhydride polymers alone were also incapable of inducing ectopic cartilage or bone. However, when the water-soluble proteins were incorporated into the polymeric delivery vehicle, the combination was capable of inducing cartilage and bone up to 50% of the time. These results demonstrate that it is possible to use polyanhydride polymers as controlled-release delivery vehicles for soluble bioactive factors that interact with a local cell population.

Biocompatibility of a biodegradable, controlled-release polymer in the rabbit brain

The biodegradable polyanhydrides are a new class of controlled release polymers developed for the interstitial delivery of drugs to their target site in the brain or other organs over periods ranging from days to years. These polymers can release molecules of any size in a predictable fashion. Their degradation products are non-cytotoxic and biocompatible. The biocompatibility of a biodegradable polyanhydride, the copolymer of poly[bis(p-carboxyphenoxy)propane] anhydride and sebacic acid (PCPP-SA) in a 50:50 formulation, was studied in the rabbit brain. Twenty adult New Zealand White male rabbits underwent implantation of PCPP-SA in a frontal lobe and absorbable gelatin sponge (Gelfoam) in the other frontal lobe. The animals were evaluated daily until the time of sacrifice. Groups of four animals were sacrificed sequentially on post-operative days 1, 3, 7, 21, and 60, and the brains processed for histological evaluation. None of the animals showed behavioral changes or neurological deficits suggestive of toxicity and all that received implants survived to their date of sacrifice. The histological examination showed no significant differences between the tissue reaction from PCPP-SA compared to Gelfoam. The polymers were also tested in the rabbit cornea bioassay and did not induce an inflammatory response. We conclude that PCPP-SA (50:50), a new biodegradable polymeric matrix that can be surgically implanted for the interstitial delivery of drugs in the brain, is biocompatible in the rabbit brain.