Biodegradable Intrascleral Implant of Triamcinolone Acetonide in Experimental Uveitis

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.

Evaluation of controlled-release triamcinolone acetonide-loaded mPEG-PLGA nanoparticles in treating experimental autoimmune uveitis

Uveitis is a recurrent, sight-threatening intraocular inflammatory disease and is treated with glucocorticoids in clinical practice. In the present study, methoxypoly(ethyleneglycol)-poly(dl-lactide-co-glycolic acid) (mPEG-PLGA) nanoparticles in combination with triamcinolone acetonide (TA) were fabricated using a modified double emulsification method. Further, we characterized the TA-loaded nanoparticles, and investigated the effects of TA-loaded nanoparticles on experimental autoimmune uveitis rats, including histopathological examination and the alterations in interleukin (IL)-17 and IL-10 at mRNA and protein levels in either aqueous humor or serum. As a result, the TA-loaded nanoparticles were a well-defined spherical shape with a mean particle size of 82 nm. The in vitro release profile showed that the TA-loaded nanoparticles could sustain for more than 45 days, and possessed higher anti-inflammatory effects compared to TA alone after pathological examination, resulting in decreased IL-17 and elevated IL-10 levels in both aqueous humor and serum. Based on these findings, it can be concluded that TA-loaded mPEG-PLGA nanoparticles can potentially provide a better anti-inflammatory effect in treating chronic and recurrent uveitis in clinical practice.

Episcleral drug film for better-targeted ocular drug delivery and controlled release using multilayered poly-ε-caprolactone (PCL)

Triamcinolone acetonide (TA) and poly-ε-caprolactone (PCL) were engineered into a micro drug film for episcleral application to better manage chronic vitreoretinal diseases such as proliferative vitreoretinopathy (PVR). Compared to an intravitreal drug injection, this drug film is much safer without breaking into ocular barriers. Compared to a traditional subtenon injection, this drug film demonstrated superior therapeutic duration, better drug bioavailability in the choroid and retina, and better-targeted drug delivery ability. The rabbit eye study demonstrated that using the PCL-TA film led to 5.6 and 3.4 times higher drug AUC in the choroid and the retina respectively than in eyes following a subtenon drug injection. The mean drug residence time in the rabbit choroid was also doubled by using the episcleral TA film (86days versus 43days). Remaining TA in the drug film was consistently higher than that in the subtenon space, indicating controlled release of TA by the PCL-TA film. The pharmacokinetics of triamcinolone in the choroid and retina were optimized from typical first-order kinetics to a more sustained release by use of this film. This episcleral film system worked better on rabbit eyes than on guinea pig eyes, indicating that scleral thickness and eye size may be crucial aspects to consider when choosing an animal model or when designing a transscleral delivery device for human use. This engineered drug film may be very useful in preventing and managing PVR associated with open globe trauma or surgical repair for retinal detachment.

STATEMENT OF SIGNIFICANCE

This study demonstrated a novel micro episcleral drug film that is made from the engineering of triamcinolone acetonide (TA) into poly-ε-caprolactone (PCL). The film can be conveniently placed at the injury or disease site during primary surgery and provide controlled release of TA for four months that covers the high-risk time window for developing proliferative vitreoretinopathy (PVR). This engineered drug film may be very useful in preventing and managing PVR associated with open globe trauma or intraocular surgery.

Overview of biopolymers as carriers of antiphlogistic agents for treatment of diverse ocular inflammations

Inflammation of the eye is a usual clinical condition that can implicate any part of the eye. The nomenclature of variety of such inflammations is based on the ocular part involved. These diseases may jeopardize normal functioning of the eye on progression. In general, corticosteroids, antihistamines, mast cell stabilizers and non-steroidal anti-inflammatory drugs (NSAIDs) are used to treat inflammatory diseases/disorders of the eye. There have been several attempts via different approaches of drug delivery to overcome the low ocular bioavailability resulting from shorter ocular residence time. The features like safety, ease of elimination and ability to sustain drug release have led to application of biopolymers in ocular therapeutics. Numerous polymers of natural origin such as gelatin, collagen, chitosan, albumin, hyaluronic acid, alginates etc. have been successfully employed for preparation of different ocular dosage forms. Chitosan is the most explored biopolymer amongst natural biopolymers because of its inherent characteristics. The emergence of synthetic biopolymers (like PVP, PACA, PCL, POE, polyanhydrides, PLA, PGA and PLGA) has also added new dimensions to the drug delivery strategies meant for treatment of ophthalmic inflammations. The current review is an endeavor to describe the utility of a variety of biomaterials/polymers based drug delivery systems as carrier for anti-inflammatory drugs in ophthalmic therapeutics.

Experimental uveitis can be maintained in rabbits for a period of six weeks after a safe sensitization method

PURPOSE

New treatments against long-lasting uveitis need to be tested. Our aim was to develop a six-week model of uveitis in rabbits.

METHODS

Rabbits were presensitized with an s.c. injection of Mycobacterium tuberculosis H37RA emulsified with TiterMax Gold adjuvant. Uveitis was induced at day 28 and 50, by intravitreal challenges of antigen suspension. Ocular inflammation was assessed till euthanasia at day 71 after s.c. injection of M. tuberculosis H37RA by: (a) the number of inflammatory cells in aqueous humor (AH); (b) the protein concentration in AH; (c) the clinical score (mean of conjunctival hyperaemia, conjunctival chemosis, oedema and secretion); (d) the microscopical score (mean presence of fibrin and synechiae, aqueous cell density and aqueous flare grade, as scored by slit lamp).

RESULTS

At the sites of presensitization injection, rabbits presented flat nodules which progressively vanished. The first challenge induced a significant increase in the four parameters (p < 0.05 the Wilcoxon/Kruskal-Wallis test). The AH contained 764 ± 82 cells/µl and 32 ± 0.77 mg protein/ml. During the following days, inflammatory parameters decreased slightly. The second intravitreal challenge increased inflammation (3564 ± 228 cells/µl AH and 31 ± 1 mg protein/ml), which remained at a high level for a longer period of time.

CONCLUSION

We developed a model of long-term uveitis, which could be maintained in rabbits for at least six weeks. Such a model could be used to test the efficacy of either new drugs or various drug delivery systems intended to deliver active agents during a few months.

Evaluation of sustained release of PLC-loaded prednisolone acetate microfilm on postoperative inflammation in an experimental model of glaucoma filtration surgery

PURPOSE

To evaluate the effect of a biodegradable microfilm with sustained release of prednisolone acetate (PA) on postoperative wound healing after experimental glaucoma filtration surgery (GFS).

METHODS

Biodegradable microfilms composed of poly (D-, L-lactide-co-caprolactone) (PLC) were fabricated and then pre-loaded PA-20% total weight. Fourteen New Zealand White rabbits were randomly divided into 3 treatment groups: GFS alone (n=4), GFS with PLC microfilms (n=4) and GFS with PA-loaded microfilm (n=6). Microfilms were inserted subconjunctivally, adjacent to the filtering surgical site. We monitored all eyes with slit-lamp examination, bleb photography and anterior segment optical coherence tomography (AS-OCT). Histology with immunohistochemistry was performed to determine the presence of any inflammation.

RESULTS

Prednisolone acetate 20%-loaded microfilms exhibited steady, sustained release in vitro. Eyes implanted with PA-loaded microfilms showed a significantly better bleb survival (100% vs. 37.5%, p<0.001) and reduced bleb vascularity (58%; 95% CI 54-62% vs. 30%; 95% CI 23-37%, p=0.001) compared to the control at 30 days postoperatively. Histology and immunohistochemistry demonstrated less T-cell infiltration in the eye implanted with PA-loaded microfilms.

CONCLUSION

Subconjunctival insertion of a PA-loaded biodegradeable microfilm exhibit sustained release of PA to reduce postoperative inflammation and prolong bleb survival in rabbit GFS.

Advancements in ocular drug delivery

This review covers both noninvasive and invasive ophthalmic drug delivery systems that can have application to therapy of veterinary ophthalmic diseases. Noninvasive approaches include gel technologies, permeation enhancement via pro-drug development, solubilization agents and nanoparticle technologies, iontophoresis, microneedles, drug-eluting contact lenses and eye misters, and microdroplets. More invasive systems include both eroding implants and noneroding technologies that encompass diffusion based systems, active pumps, intraocular lenses, suprachoroidal drug delivery, and episcleral reservoirs. In addition to addressing the physiologic challenges of achieving the necessary duration of delivery, tissue targeting and patient compliance, the commercial development factors of biocompatibility, sterilization, manufacturability and long-term stability will be discussed.

Novel NSAIDs ophthalmic formulation: flurbiprofen axetil emulsion with low irritancy and improved anti-inflammation effect

The aim of this study was to design and formulate a novel low-irritant NSAIDs ophthalmic emulsion of flurbiprofen axetil (FBA), the prodrug of flurbiprofen (FB). FBA ophthalmic emulsion (FBA-EM) was prepared by high-pressure homogenization with caster oil as oil phase and tween 80 as emulsifying agent. Results from the stability evaluation suggested the protect effect of oil droplets on the stability of FBA. Compared with FBA-oil solution, the AUC(0→10h) of FB in aqueous humor administered in FBA-EMs exhibited 6.7-fold (F2), 4.5-fold (F3) and 4.6-fold (F4) increase. With the increment of oil content, the MRT also prolonged, which of FBA-EM F2-F4 were 5.14 ± 2.23, 5.73 ± 3.35 and 8.71 ± 0.94 h, respectively. No significant difference was found between the ocular bioavailability of FBA-EM F2 and 0.03% FB-Na eye drops. Ocular irritation evaluation revealed that FBA-EM F2 had better ocular biocompatibility than 0.03% FB-Na eye drops, even though the FBA concentration was up to 0.1%. Intraocular anti-inflammation effect evaluation showed that FBA-EM F2 had a quite good anti-inflammation effect. In conclusion, FBA-EM F2 with elevated FBA concentration to be 0.1% might represent a promising NSAIDs ophthalmic emulsion with low irritancy and improved anti-inflammation effect.