FK506 in a Biodegradable Glycolide-co-Clatide-co-Caprolactone Polymer for Prolongation of Corneal Allograft Survival

FK506-loaded PLGA nanoparticles improve long-term survival of a vascularized composite allograft in a murine model

Background

The side effects of life-long administration of FK506 limit the clinical practice of vascularized composite allografts (VCAs). This study aimed to evaluate the feasibility of FK506-loaded poly (lactic-co-glycolic acid) (PLGA) nanoparticles (FK506 NPs) for prolonging the long-term survival of VCAs and reducing the side effects of FK506.

Methods

PLGA nanoparticles loaded with FK506 were prepared by the solvent evaporation method. The characterization of FK506 NPs was evaluated by electron microscopy. To confirm the function and safety of FK506 NPs, these particles were administrated into rats by intraperitoneal injection. The survival time of the allograft, systemic concentration of FK506, anti-rejection activity, and side-effect of FK506 NPs were evaluated in a Brown Norway (BN)-to-Sprague Dawley (SD) epigastric VCA transplantation model.

Results

Compared with the nontreatment, PLGA control and FK506 groups, the median survival times (MST) of the FK506 NP groups were significantly prolonged. The FK506 NPs could maintain therapeutic drug concentration for 60 days. Moreover, cytokine concentrations, flow cytometry of regulatory T cells (Tregs) and histopathology of allografts revealed significantly prolonged immunosuppression by FK506 NPs. FK506 NPs also ameliorated FK506 nephrotoxicity.

Conclusions

FK506 NPs prolong the survival time of VCAs in a murine model with minimal nephrotoxicity, and provide a potential clinical strategy for ameliorating long-term side effects of immunosuppressive therapy.

Polymeric Implants for the Treatment of Intraocular Eye Diseases: Trends in Biodegradable and Non-Biodegradable Materials

Intraocular/Intravitreal implants constitute a relatively new method to treat eye diseases successfully due to the possibility of releasing drugs in a controlled and prolonged way. This particularity has made this kind of method preferred over other methods such as intravitreal injections or eye drops. However, there are some risks and complications associated with the use of eye implants, the body response being the most important. Therefore, material selection is a crucial factor to be considered for patient care since implant acceptance is closely related to the physical and chemical properties of the material from which the device is made. In this regard, there are two major categories of materials used in the development of eye implants: non-biodegradables and biodegradables. Although non-biodegradable implants are able to work as drug reservoirs, their surgical requirements make them uncomfortable and invasive for the patient and may put the eyeball at risk. Therefore, it would be expected that the human body responds better when treated with biodegradable implants due to their inherent nature and fewer surgical concerns. Thus, this review provides a summary and discussion of the most common non-biodegradable and biodegradable materials employed for the development of experimental and commercially available ocular delivery implants.

Multiphase Assembly of Small Molecule Microcrystalline Peptide Hydrogel Allows Immunomodulatory Combination Therapy for Long-Term Heart Transplant Survival

Combination therapies that target multiple pathways involved in immune rejection of transplants hold promise for patients in need of restorative surgery. Herein, a noninteracting multiphase molecular assembly approach is developed to crystallize tofacitinib, a potent JAK1/3 inhibitor, within a shear-thinning self-assembled fibrillar peptide hydrogel network. The resulting microcrystalline tofacitinib hydrogel (MTH) can be syringe-injected directly to the grafting site during surgery to locally deliver the small molecule. The rate of drug delivered from MTH is largely controlled by the dissolution of the encapsulated microcrystals. A single application of MTH, in combination with systemically delivered CTLA4-Ig, a co-stimulation inhibitor, affords significant graft survival in mice receiving heterotopic heart transplants. Locoregional studies indicate that the local delivery of tofacitinib at the graft site enabled by MTH is required for the observed enhanced graft survival.

Biomaterials for topical and transdermal drug delivery in reconstructive transplantation

Lifelong systemic immunosuppression remains the biggest challenge in vascularized composite allotransplantation (VCA) due to the adverse effects it causes. Since VCA is a life-enhancing procedure as compared with solid organ transplant which is life-saving; one needs to weigh the benefits and risks carefully. Thus, there is a huge unmet clinical need to design biomaterial-based vehicles that can deliver drugs more efficiently, topically and locally to eliminate adverse effects of systemic immune suppression. This review discusses several biomaterial-based systems that have been carefully designed, conceived and attempted to make VCA a more patient compliant approach. Variety of promising preclinical studies has shown the feasibility of the approaches, and clinical trials are required to bridge the gap. Several challenges for the future and new approaches have been discussed.

Femtosecond Laser-Assisted Keratolimbal Allograft Transplantation for the Treatment of Total Limbal Stem Cell Deficiency

PURPOSE

To investigate the surgical procedure and therapeutic efficacy of femtosecond (FS) laser-assisted keratolimbal allograft (KLAL) transplantation in the treatment of eyes with total limbal stem cell deficiency.

METHODS

Ten eyes from 10 patients who underwent FS laser-assisted KLAL transplantation were enrolled. The best-corrected visual acuity (BCVA), ocular surface stability, corneal transparency, and postoperative complications were recorded.

RESULTS

The keratolimbal grafts prepared using the FS laser were even in thickness and width. After the surgery, glucocorticoid and tacrolimus eye drops were administered locally to the eyes with concentration gradients, and a medium dose was prescribed for maintenance. Within the mean follow-up period of 16.8 ± 7.3 months, 9 of 10 eyes (90.0%) maintained a stable ocular surface and showed significant improvements in corneal transparency and BCVA. Persistent corneal edema only occurred in one eye because of repeated epithelial defects, and the BCVA of this eye did not improve. Confocal microscopy revealed activated dendritic cells in the Bowman membrane at the limbus, but they were always low in density with small dendritic processes. No acute immune rejection, cataracts, or elevation of intraocular pressure were detected.

CONCLUSIONS

The FS laser-assisted KLAL technique can produce ring-shaped grafts with an even depth and width, resulting in a stable ocular surface and good visual prognosis. After surgery, glucocorticoids and potent immunosuppressive eye drops were administered locally with concentration gradients and effectively inhibited acute immune rejection.

Laser Scanning In Vivo Confocal Microscopy of Clear Grafts after Penetrating Keratoplasty

PURPOSE

To evaluate the changes of keratocytes and dendritic cells in the central clear graft by laser scanning in vivo confocal microscopy after penetrating keratoplasty (PK).

METHODS

Thirty adult subjects receiving PK at Shandong Eye Institute and with clear grafts and no sign of immune rejection after surgery were recruited into this study, and 10 healthy adults were controls. The keratocytes and dendritic cells in the central graft were evaluated by laser scanning confocal microscopy, as well as epithelium cells, keratocytes, corneal endothelium cells, and corneal nerves (especially subepithelial plexus nerves).

RESULTS

Median density of subepithelial plexus nerves, keratocyte density in each layer of the stroma, and density of corneal endothelium cells were all lower in clear grafts than in controls. The dendritic cells of five (16.7%) patients were active in Bowman's membrane and stromal membrane of the graft after PK.

CONCLUSIONS

Activated dendritic cells and Langerhans cells could be detected in some of the clear grafts, which indicated that the subclinical stress of immune reaction took part in the chronic injury of the clear graft after PK, even when there was no clinical rejection episode.

A biodegradable, sustained-released, prednisolone acetate microfilm drug delivery system effectively prolongs corneal allograft survival in the rat keratoplasty model

Frequent and long-term use of topical corticosteroids after corneal transplantation is necessary to prevent graft rejection. However, it relies heavily on patient compliance, and sustained therapeutic drug levels are often not achieved with administration of topical eye drops. A biodegradable drug delivery system with a controlled and sustained drug release may circumvent these limitations. In this study, we investigated the efficacy of a prednisolone acetate (PA)-loaded poly (d,l-lactide-co-ε-caprolactone) (PLC) microfilm drug delivery system on promoting the survival of allogeneic grafts after penetrating keratoplasty (PK) using a rat model. The drug release profiles of the microfilms were characterized (group 1). Subsequently, forty-eight PK were performed in four experimental groups: syngeneic control grafts (group 2), allogeneic control grafts (group 3), allogeneic grafts with subconjunctivally-implanted PA microfilm (group 4), and allogeneic grafts with PA eye drops (group 5; n = 12 in each). PA-loaded microfilm achieved a sustained and steady release at a rate of 0.006-0.009 mg/day, with a consistent aqueous drug concentration of 207-209 ng/ml. The mean survival days was >28 days in group 2, 9.9±0.8 days in group 3, 26.8±2.7 days in group 4, and 26.4±3.4 days in group 5 (P = 0.023 and P = 0.027 compared with group 3). Statistically significant decrease in CD4+, CD163+, CD 25+, and CD54+ cell infiltration was observed in group 4 and group 5 compared with group 3 (P<0.001). There was no significant difference in the mean survival and immunohistochemical analysis between group 4 and group 5. These results showed that sustained PA-loaded microfilm effectively prolongs corneal allograft survival. It is as effective as conventional PA eye drops, providing a promising clinically applicable alternative for patients undergoing corneal transplantation.

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.

Intravitreal devices for the treatment of vitreous inflammation

The eye is a well-suited organ for local delivery of therapeutics to treat vitreous inflammation as well as other pathologic conditions that induce visual loss. Several conditions are particularly challenging to treat and often require chronic courses of therapy. The use of implantable intravitreal devices for drug delivery is an emerging field in the treatment of vitreous inflammation as well as other ophthalmologic diseases. There are unique challenges in the design of these devices which include implants, polymers, and micro- and nanoparticles. This paper reviews current and investigational drug delivery systems for treating vitreous inflammation as well as other pathologic conditions that induce visual loss. The use of nonbiodegradable devices such as polyvinyl alcohol-ethylene vinyl acetate polymers and polysulfone capillary fibers, and biodegradable devices such as polylactic acid, polyglycolic acid, and polylactic-co-glycolic acid, polycaprolactones, and polyanhydrides are reviewed. Clinically used implantable devices for therapeutic agents including ganciclovir, fluocinolone acetonide, triamcinolone acetonide, and dexamethasone are described. Finally, recently developed investigational particulate drug delivery systems in the form of liposomes, microspheres, and nanoparticles are examined.

Biodegradable implants for sustained drug release in the eye

The safety and effectiveness of systemic and topical medical therapies for ocular disorders are limited due to poor ocular drug uptake, nonspecificity to target tissues, systemic side effects, and poor adherence to therapy. Intravitreal injections can enhance ocular drug delivery, but the need for frequent retreatment and potential injection-related side effects limit the utility of this technique. Sustained-release drug delivery systems have been developed to overcome these limitations; such systems can achieve prolonged therapeutic drug concentrations in ocular target tissues while limiting systemic exposure and side effects and improving patient adherence to therapy. A critical factor in the development of safe and effective drug delivery systems has been the development of biocompatible polymers, which offer the versatility to tailor drug release kinetics for specific drugs and ocular diseases. Ocular implants include nonbiodegradable and biodegradable designs, with the latter offering several advantages. The polymers most commonly used in biodegradable delivery systems are synthetic aliphatic polyesters of the poly-α-hydroxy acid family including polylactic acid, polyglycolic acid, and polylactic-co-glycolic acid. The characteristics of these polymers for medical applications as well as the pharmacological properties, safety, and clinical effectiveness of biodegradable drug implants for the treatment of ocular diseases are reviewed herein.

Establishment of a murine model of chronic corneal allograft dysfunction

BACKGROUND

To establish a murine model of chronic corneal allograft dysfunction (CCAD) that permits molecular evaluation of chronic allograft dysfunction after corneal transplantation.

METHODS

C57BL/6 (allogeneic), CB6F1 (semiallogeneic) and BALB/c (syngeneic) corneal grafts were transplanted orthotopically to BALB/c recipients and to the BALB/c mice as a control group. The follow-up time was more than 100 days. Graft survival time was monitored. Corneal endothelium was examined by alizarin red and PI/Hoechst stain. CD4(+) and CD8(+) T lymphocytes were examined by immunohistochemistry. Ultra-structure changes of the grafts were examined by electron microscopy.

RESULTS

Median graft survival times were 17 days, 85.5 days, and >100 days in allogeneic, semiallogeneic, and syngeneic groups respectively. Acute rejection episodes were observed only in the allogeneic group. A large amount of CD4(+) and CD8(+) T lymphocyte infiltration was present in allografts only in the allogeneic group, and few CD4(+) and CD8(+) T lymphocytes were observed in grafts in other groups. Large amounts of apoptotic and necrotic cells could be seen in the allogeneic group. Endothelial cell density decreased, and few apoptotic cells could be detected in semiallogeneic and syngeneic groups. No apoptotic or necrotic endothelial cells were found in the control group. Ultra-structural characteristic changes mainly included fibrosis formation, endothelium atrophy, and degeneration in failed grafts among transplant groups, as determined by electron microscopy.

CONCLUSIONS

The changes in semiallogeneic and syngeneic groups after transplantation were similar to those observed during clinical study. Although differences between mouse strains and clinical situations remain to be explored, this murine model provides the basis for understanding the pathogenesis of CCAD.

Recent perspectives in ocular drug delivery

Anatomy and physiology of the eye makes it a highly protected organ. Designing an effective therapy for ocular diseases, especially for the posterior segment, has been considered as a formidable task. Limitations of topical and intravitreal route of administration have challenged scientists to find alternative mode of administration like periocular routes. Transporter targeted drug delivery has generated a great deal of interest in the field because of its potential to overcome many barriers associated with current therapy. Application of nanotechnology has been very promising in the treatment of a gamut of diseases. In this review, we have briefly discussed several ocular drug delivery systems such as microemulsions, nanosuspensions, nanoparticles, liposomes, niosomes, dendrimers, implants, and hydrogels. Potential for ocular gene therapy has also been described in this article. In near future, a great deal of attention will be paid to develop non-invasive sustained drug release for both anterior and posterior segment eye disorders. A better understanding of nature of ocular diseases, barriers and factors affecting in vivo performance, would greatly drive the development of new delivery systems. Current momentum in the invention of new drug delivery systems hold a promise towards much improved therapies for the treatment of vision threatening disorders.

Corneal Graft Rejection

Penetrating keratoplasty is the most widely practiced type of transplantation in humans. Irreversible immune rejection of the transplanted cornea is the major cause of human allograft failure in the intermediate and late postoperative period. This immunological process causes reversible or irreversible damage to the grafted cornea in several cases despite the use of intensive immunosuppressive therapy. Corneal graft rejection comprises a sequence of complex immune responses that involves the recognition of the foreign histocompatibility antigens of the corneal graft by the host's immune system, leading to the initiation of the immune response cascade. An efferent immune response is mounted by the host immune system against these foreign antigens culminating in rejection and graft decompensation in irreversible cases. A variety of donor- and host-related risk factors contribute to the corneal rejection episode. Epithelial rejection, chronic stromal rejection, hyperacute rejection, and endothelial rejection constitute the several different types of corneal graft rejection that might occur in isolation or in conjunction. Corneal graft failure subsequent to graft rejection remains an important cause of blindness and hence the need for developing new strategies for suppressing graft rejection is colossal. New systemic pharmacological interventions recommended in corneal transplantation need further evaluation and detailed guidelines. Two factors, prevention and management, are of significant importance among all aspects of immunological graft rejection. Preventive aspects begin with the recipient selection, spread through donor antigenic activity, and end with meticulous surgery. Prevention of corneal graft rejection lies with reduction of the donor antigenic tissue load, minimizing host and donor incompatibility by tissue matching and suppressing the host immune response. Management of corneal graft rejection consists of early detection and aggressive therapy with corticosteroids. Corticosteroid therapy, both topical and systemic, is the mainstay of management. Addition of immunosuppressive to the treatment regimen helps in quick and long term recovery. Knowledge of the immunopathogenesis of graft rejection may allow a better understanding of the immunological process thus helping in its prevention, early detection and management.

Intraocular implants for extended drug delivery: therapeutic applications

An overview of ocular implants with therapeutic application potentials is provided. Various types of implants can be used as slow release devices delivering locally the needed drug for an extended period of time. Thus, multiple periocular or intraocular injections of the drug can be circumvented and secondary complications minimized. The various compositions of polymers fulfilling specific delivery goals are described. Several of these implants are undergoing clinical trials while a few are already commercialized. Despite the paramount progress in design, safety and efficacy, the place of these implants in our clinical therapeutic arsenal remains limited. Miniaturization of the implants allowing for their direct injection without the need for a complicated surgery is a necessary development avenue. Particulate systems which can be engineered to target specifically certain cells or tissues are another promising alternative. For ocular diseases affecting the choroid and outer retina, transscleral or intrasscleral implants are gaining momentum.