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

Topical and oral peroxisome proliferator-activated receptor-α agonist ameliorates diabetic corneal neuropathy

Diabetic corneal neuropathy (DCN) is a common diabetic ocular complication with limited treatment options. In this study, we investigated the effects of topical and oral fenofibrate, a peroxisome proliferator-activated receptor-α agonist, on the amelioration of DCN using diabetic mice (n = 120). Ocular surface assessments, corneal nerve and cell imaging analysis, tear proteomics and its associated biological pathways, immuno-histochemistry and western blot on PPARα expression, were studied before and 12 weeks after treatment. At 12 weeks, PPARα expression markedly restored after topical and oral fenofibrate. Topical fenofibrate significantly improved corneal nerve fibre density (CNFD) and tortuosity coefficient. Likewise, oral fenofibrate significantly improved CNFD. Both topical and oral forms significantly improved corneal sensitivity. Additionally, topical and oral fenofibrate significantly alleviated diabetic keratopathy, with fenofibrate eye drops demonstrating earlier therapeutic effects. Both topical and oral fenofibrate significantly increased corneal β-III tubulin expression. Topical fenofibrate reduced neuroinflammation by significantly increasing the levels of nerve growth factor and substance P. It also significantly increased β-III-tubulin and reduced CDC42 mRNA expression in trigeminal ganglions. Proteomic analysis showed that neurotrophin signalling and anti-inflammation reactions were significantly up-regulated after fenofibrate treatment, whether applied topically or orally. This study concluded that both topical and oral fenofibrate ameliorate DCN, while topical fenofibrate significantly reduces neuroinflammation.

Corneal elastic property investigated by terahertz technology

Terahertz (THz) spectroscopy technique has been applied in ex vivo biomechanical properties analysis of human corneas. Upon the application of light pressure on the cornea, the photo elastic birefringent effect, anisotropic deformation, thickness changes and hydration levels will contribute to the sudden phase changes of terahertz time domain signal. The shelf lifetime study shows that the phase shift is reduced and cornea loose the biomechanical properties with the increase of hydration level. Mechanical behaviors have been further studied based on the "fresh" cut corneas with the similar hydration levels. THz signal was collected by focusing inside of the cornea to avoid the phase shift due to light stress caused movement of the corneal surface. By this way, the amount of THz signal refractive index variation is correlated to the elastic property of the corneas. The correlation between the THz signal phase shift and refractive index shift due to the corneal strain can be used to derive the elastic Young's modulus. Our results demonstrated the THz spectroscopy, as a non-contact and non-invasive detection method, could be potential for understanding the mechanism of corneal deformation under the action of intraocular pressure in the physiological environment in future.

Femtosecond laser-assisted corneal transplantation with a low-energy, liquid-interface system

Femtosecond laser-assisted keratoplasty has been proposed as a treatment option for corneal transplantation. In this study, we investigated and compared the outcomes of Ziemer Z8 femtosecond laser (FSL)-assisted penetrating keratoplasty (PK) using a liquid interface versus flat interface. Thirty fresh porcine eyes underwent FSL-assisted PK with the Z8 using different levels of energies (30%, 90% or 150%) and different interfaces (liquid or flat). The real-time intraocular pressure (IOP) changes, incision geometry, corneal endothelial damage, as well as the accuracy of laser cutting and tissue reaction, were performed and compared. We found that the overall average IOP at all laser trephination stages was significantly higher with the flat interface, regardless of the energy used (68.9 ± 15.0 mmHg versus 46.1 ± 16.6 mmHg; P < 0.001). The overall mean laser-cut angle was 86.2º ± 6.5º and 88.2º ± 1.0º, for the liquid and flat platform respectively, indicating minimal deviation from the programmed angle of 90º. When high energy (150%) was used, the endothelial denuded area was significantly greater with the flat interface than with liquid interface (386.1 ± 53.6 mm² versus 139.0 ± 10.4 mm²P = 0.02). The FSL cutting did not cause obvious tissue reaction alongside the laser cut on histological evaluation. The results indicated a liquid interface is the preferable choice in FSL-assisted corneal transplantation.

Terahertz spectroscopy analysis of human corneal sublayers

SIGNIFICANCE

Corneal diseases is a major cause of reversible blindness in the world. Monitoring the progression of human corneal edema or corneal scarring to prevent the disease entering into the end stage is crucial.

AIM

We present a method for sensing human corneal composition at different depths, namely focused on the epithelium and stromal layer, using high-sensitivity terahertz (THz) broadband spectroscopy.

APPROACH

From the proposed methodology, the THz temporal and absorption spectra of human corneas at different edema stages have been studied. THz wave signals were collected from the direct reflection and four other collection points along the THz wave propagation direction as reviewed from the simulation THz electrical field.

RESULT

Our results show that the epithelium layer acts as a good barrier to maintain hydration level of the stroma, and the quality of the epithelium can be used to predict the level of corneal swelling in corneal edema. At the detection points near to the incident point, the THz frequency spectra demonstrated interference oscillation behavior. At the final edema observing time, results showed that the epithelium lose its barrier properties. The intactness of the epithelium can be used to predict the edema severity in the final stage. When the detection points are further away from the incident point, the THz spectra are believed to contain information from stromal layer. Stromal absorption spectra demonstrated correlation with optical coherence tomography thickness results.

CONCLUSION

The hydration concentration from stromal layer was further quantitatively calculated. At the end of the experiment, all the corneal hydration levels reach to the same value which shows that the edema hydration has reached maximum saturation. The information of individual sublayers of the cornea is obtained by characterizing noninvasively with the use of THz spectroscopy. To our knowledge, this is the first report of using THz for noninvasive characterization of sublayers of the cornea.

Safety profiles of terahertz scanning in ophthalmology

Terahertz (THz) technology has emerged recently as a potential novel imaging modality in biomedical fields, including ophthalmology. However, the ocular biological responses after THz electromagnetic exposure have not been investigated. We conducted a rabbit study to evaluate the safety profiles of THz scanning on eyes, at a tissue, cellular, structural and functional level. Eight animals (16 eyes) were analysed after excessive THz exposure (control, 1 h, 4 h, and 1 week after continuous 4-h exposure; THz frequency = 0.3 THz with continuous pulse generated at 40 µW). We found that at all the time points, the corneas and lens remained clear with no corneal haze or lens opacity formation clinically and histopathologically. No thermal effect, assessed by thermographer, was observed. The rod and cone cell-mediated electroretinography responses were not significantly altered, and the corneal keratocytes activity as well as endothelial viability, assessed by in-vivo confocal microscopy, was not affected. Post-exposed corneas, lens and retinas exhibited no significant changes in the mRNA expression of heat shock protein (HSP)90AB1), DNA damage inducible transcript 3 (DDIT3), and early growth response (EGR)1. These tissues were also negative for the inflammatory (CD11b), fibrotic (fibronectin and α-smooth muscle actin), stress (HSP-47) and apoptotic (TUNEL assay) responses on the immunohistochemical analyses. The optical transmittance of corneas did not change significantly, and the inter-fibrillar distances of the corneal stroma evaluated with transmission electron microscopy were not significantly altered after THz exposure. These results provide the basis for future research work on the development of THz imaging system for its application in ophthalmology.

Nanotechnology for the Treatment of Allergic Conjunctival Diseases

Allergic conjunctivitis is one of the most common external eye diseases and the prevalence has been increasing. The mainstay of treatment is topical eye drops. However, low bioavailability, low ocular drug penetration, transient resident time on the ocular surface due to tear turnover, frequent topical applications and dependence on patient compliance, are the main drawbacks associated with topical administration. Nanotechnology-based medicine has emerged to circumvent these limitations, by encapsulating the drugs and preventing them from degradation and therefore providing sustained and controlled release. Using a nanotechnology-based approach to load the drug is particularly useful for the delivery of hydrophobic drugs such as immunomodulatory agents, which are commonly used in allergic conjunctival diseases. In this review, different nanotechnology-based drug delivery systems, including nanoemulsions, liposomes, nanomicelles, nanosuspension, polymeric and lipid nanoparticles, and their potential ophthalmic applications, as well as advantages and disadvantages, are discussed. We also summarize the results of present studies on the loading of immunomodulators or nonsteroidal anti-inflammatory drugs to nano-scaled drug delivery systems. For future potential clinical use, research should focus on the optimization of drug delivery designs that provide adequate and effective doses with safe and satisfactory pharmacokinetic and pharmaco-toxic profiles.

Tissue Responses and Wound Healing following Laser Scleral Microporation for Presbyopia Therapy

Purpose

To investigate the postoperative inflammatory and wound-healing responses after laser scleral microporation for presbyopia.

Methods

Thirty porcine eyes were used for the optimization of laser intensities first. Six monkeys (12 eyes) received scleral microporation with an erbium yttrium aluminum garnet (Er:YAG) laser, and half of the eyes received concurrent subconjunctival collagen gel to modulate wound-healing response. The intraocular pressure (IOP) and the laser ablation depth were evaluated. The animals were euthanized at 1, 6, and 9 months postoperatively. The limbal areas and scleras were harvested for histologic analysis and immunofluorescence of markers for inflammation (CD11b and CD45), wound healing (CD90, tenascin-C, fibronectin, and HSP47), wound contraction (α-smooth muscle actin [α-SMA]), vascular response (CD31), nerve injury (GAP43), and limbal stem cells (P63 and telomerase).

Results

In the nonhuman primate study, there was a significant reduction in IOP after the procedure. Overall, the ablation depth was 76.6% to 81.2% at 1 month and slightly decreased to 71.5% to 72.7% at 9 months. Coagulative necrosis around the micropores, as well as expression of CD11b, CD45, tenascin, fibronectin, HSP47, and GAP43, was distinct at 1 month but subsided with time. Collagen gel treatment significantly suppressed the upregulation of CD11b, CD45, fibronectin, and tenascin-C. The expression of CD90, α-SMA, and CD31 was minimal in all eyes.

Conclusions

The study demonstrated the course of inflammatory and wound-healing responses following laser scleral microporation. The tissue responses were small and self-limited, resolved with time, and were suppressed by concurrent collagen treatment. It provides a useful understanding of this new procedure.

Translational Relevance

The results would be helpful in the laser parameter modification to improve the long-term treatment stability.

Intraoperative Optical Coherence Tomography-Guided Femtosecond Laser-Assisted Deep Anterior Lamellar Keratoplasty

PURPOSE

To describe the feasibility and outcomes of intraoperative optical coherence tomography (OCT)-guided, femtosecond laser-assisted deep anterior lamellar keratoplasty in which the lamellar and tunnel cuts were completed by laser.

METHODS

The Ziemer Z8 system was used to scan the corneas intraoperatively and guide the stromal lamellar and tunnel cuts created by the laser. Thirty porcine eyes and 3 human cadaver globes were used to evaluate the accuracy of laser-created intrastromal tunnels and the feasibility of achieving big-bubble pneumatic dissection. The tunnel distance above the Descemet membrane (Dt-dm) was set at 100 and 130 μm, and the accuracy of laser cut was assessed by anterior segment OCT and histological sections. Fourteen patients with keratoconus or corneal scars were then included to evaluate the clinical outcomes.

RESULTS

The deviation from the targeted Dt-dm was 5.5% to 8.6% and 0.7% to 9.8% for the 100 and 130 μm groups, respectively. The achieved thickness had a significantly and positively strong correlation with the targeted thickness (r = 0.86; P < 0.001). In all cases, the anterior stromal lamella was removed without difficulty, except in the patients with corneal scars in whom some remaining stromal fiber attachments were observed. A type 1 big bubble was successfully achieved in all patients.

CONCLUSIONS

We present the accuracy and clinical outcomes of femtosecond laser-assisted, intraoperative OCT-guided deep anterior lamellar keratoplasty, in which controlled lamellar and tunnel cuts at desired depths were performed by laser in one step, and a successful big bubble was achieved.

Evaluation of a Sustained-Release Prednisolone Acetate Biodegradable Subconjunctival Implant in a Non-Human Primate Model

PURPOSE

We evaluate the toxicity and plasma toxicokinetic (TK) profile of a biodegradable subconjunctival microrod for sustained prednisolone acetate (PA) release over 12 weeks in a non-human primate model.

METHODS

The biodegradable copolymer poly(l-lactide-co-ε-caprolactone) (PLC) and 40-wt% PA microrods were used and fashioned into 8 and 16 mm lengths. Twelve monkeys were divided into two treatment groups of PA-loaded and blank microrods, with six monkeys each receiving either 8- or 16-mm microrods subconjunctively implanted into both eyes. TK and hematology parameters were analyzed. Ophthalmic clinical evaluation, including slit-lamp and ophthalmoscopy examinations, was performed.

RESULTS

Over the study period of 12 weeks, the mean area under the plasma concentration-time curve was 45.7% higher, and the maximum plasma concentration was 17.2% lower for the animals treated with 40-wt% PA 16-mm microrods compared to 8-mm microrods (251.44 versus 172.54 hours × nanograms per milliliter and 8.53 versus 10.30 ng/mL, respectively). The PA release was significantly below the levels of assumed toxicity. There was no significant difference in the time to reach maximum concentration between the 8- and 16-mm microrod groups (7.33 and 8 hours; P = 0.421). Findings from clinical evaluation, hematology, and histopathology showed no ocular side effects and no significant adverse systemic effects.

CONCLUSION

The PA biodegradable microrods demonstrated safe toxicokinetics even with the larger size implant containing a higher amount of drug. The PA implant may be considered as a safe alternative to the application of topical PA eyedrops.

TRANSLATIONAL RELEVANCE

The results provide the evidence of the safety of implanting a steroid delivery system subconjunctively, offering an alternative to topical PA eyedrops.

The Blockade of Vascular Endothelial Growth Factor C Effectively Inhibits Corneal Lymphangiogenesis and Promotes Allograft Survival

PURPOSE

To explore the inhibitory effects of antivascular endothelial growth factor C (VEGF-C) therapy on corneal lymphangiogenesis and allograft rejection in rats.

METHODS

Fischer 344 rat corneas were transplanted into Lewis rat eyes. After corneal transplantation, Lewis rats (the recipients) were randomly and equally divided into 2 groups: anti-VEGF-C treatment (group A) and control (group B). Corneal hemangiogenesis and lymphangiogenesis were characterized using whole-mount immunofluorescence, and the immune rejection of the grafts was examined using a slit lamp and evaluated by scoring the rejection index (RI). In addition, the expression of VEGF-C was examined by immunohistochemistry and real-time polymerase chain reaction. The association of corneal lymphangiogenesis and hemangiogenesis with VEGF-C in transplanted corneas was also characterized.

RESULTS

VEGF-C expression was markedly downregulated after anti-VEGF-C therapy. The outgrowth of corneal lymphangiogenesis dramatically decreased in group A. There was a significant relationship between VEGF-C reduction and the decrease in the lymphatic vessel area (r=0.55, P<0.05), whereas the relationship between the reduction of VEGF-C and the decrease in blood vessel area was not significant (r=0.11, P>0.05). In addition, the RI scores were significantly lower in group A compared with group B at 7, 10, and 14 days after transplantation. The graft survival time in group A rats (20.33±1.37 days) was significantly longer than that in group B rats (12.83±1.47 days; P<0.05).

CONCLUSIONS

The results suggested that VEGF-C blockade had a significant role in preventing corneal lymphangiogenesis in corneal beds, which resulted in higher allograft survival rates.

Electrospun nanofibrous SF/P(LLA-CL) membrane: a potential substratum for endothelial keratoplasty

Background

Cornea transplant technology has progressed markedly in recent decades, allowing surgeons to replace diseased corneal endothelium by a thin lamellar structure. A thin, transparent, biocompatible, tissue-engineered substratum with corneal endothelial cells for endothelial keratoplasty is currently of interest. Electrospinning a nanofibrous structure can simulate the extracellular matrix and have beneficial effects for cell culture. Silk fibroin (SF) has good biocompatibility but poor mechanical properties, while poly(l-lactic acid-co-ε-caprolactone) (P(LLA-CL)) has good mechanical properties but poor biocompatibility. Blending SF with P(LLA-CL) can maintain the advantages of both these materials and overcome their disadvantages. Blended electrospun nanofibrous membranes may be suitable for regeneration of the corneal endothelium. The aim of this study was to produce a tissue-engineered construct suitable for endothelial keratoplasty.

Methods

Five scaffolds containing different SF:P(LLA-CL) blended ratios (100:0, 75:25, 50:50, 25:75, 0:100) were manufactured. A human corneal endothelial (B4G12) cell line was cultured on the membranes. Light transmission, speed of cell adherence, cell viability (live-dead test), cell proliferation (Ki-67, BrdU staining), and cell monolayer formation were detected on membranes with the different blended ratios, and expression of some functional genes was also detected by real-time polymerase chain reaction.

Results

Different blended ratios of scaffolds had different light transmittance properties. The 25:75 blended ratio membrane had the best transmittance among these scaffolds. All electrospun nanofibrous membranes showed improved speed of cell adherence when compared with the control group, especially when the P(LLA-CL) ratio increased. The 25:75 blended ratio membranes also had the highest cell proliferation. B4G12 cells could form a monolayer on all scaffolds, and most functional genes were also stably expressed on all scaffolds. Only two genes showed changes in expression.

Conclusion

All blended ratios of SF:P(LLA-CL) scaffolds were evaluated and showed good biocompatibility for cell adherence and monolayer formation. Among them, the 25:75 blended ratio SF:P(LLA-CL) scaffold had the best transmittance and the highest cell proliferation. These attributes further the potential application of the SF:P(LLA-CL) scaffold for corneal endothelial transplantation.

Slow-release drug delivery through Elvax 40W to the rat retina: implications for the treatment of chronic conditions

Diseases of the retina are difficult to treat as the retina lies deep within the eye. Invasive methods of drug delivery are often needed to treat these diseases. Chronic retinal diseases such as retinal oedema or neovascularization usually require multiple intraocular injections to effectively treat the condition. However, the risks associated with these injections increase with repeated delivery of the drug. Therefore, alternative delivery methods need to be established in order to minimize the risks of reinjection. Several other investigations have developed methods to deliver drugs over extended time, through materials capable of releasing chemicals slowly into the eye. In this investigation, we outline the use of Elvax 40W, a copolymer resin, to act as a vehicle for drug delivery to the adult rat retina. The resin is made and loaded with the drug. The drug-resin complex is then implanted into the vitreous cavity, where it will slowly release the drug over time. This method was tested using 2-amino-4-phosphonobutyrate (APB), a glutamate analogue that blocks the light response of the retina. It was demonstrated that the APB was slowly released from the resin, and was able to block the retinal response by 7 days after implantation. This indicates that slow-release drug delivery using this copolymer resin is effective for treating the retina, and could be used therapeutically with further testing.

Evaluation of a prednisolone acetate-loaded subconjunctival implant for the treatment of recurrent uveitis in a rabbit model

AIM

To assess the efficacy of a biodegradable, prednisolone acetate implant in a rabbit uveitis model.

METHODS

Randomized, controlled study of biodegradable microfilms preloaded with prednisolone acetate (PA) in a rabbit uveitis model. Experimental uveitis was induced by unilateral intravitreal injection of Mycobacterium tuberculosis H37Ra antigen (50 ug; 1 ug/uL) in preimmunized rabbits. PA-loaded poly[d,l-lactide-co-ε-caprolactone] (PLC) microfilms (n = 10) and blank microfilms (n = 6) were implanted subconjunctivally. An estimate of PA release in vivo was calculated from measured residual PA amounts in microfilms after the rabbits were sacrificed. The eyes were clinically monitored for ocular inflammation for 28 days. Histopathological examination of the enucleated eyes was performed at the end of the study period.

RESULTS

In vitro studies revealed that sandwich PA-loaded microfilm formulations exhibited higher release kinetic compared to homogenous PA-loaded microfilms. The 60-40-60% microfilm released an average of 0.034 mg/day of PA over the period of 60 days in vitro; and we found that approximately 0.12 mg/day PA was released in vivo. Animals implanted with the PA-loaded microfilms exhibited significantly lowered median inflammatory scores when compared against the control group in this model for recurrent uveitis (P<0.001). The implants were clinically well tolerated by all the animals. Histology results showed no significant scarring or inflammation around the PA-loaded microfilms.

CONCLUSION

Our pilot study demonstrated that a subconjunctival PA-loaded implant is effective in suppressing inflammation in the rabbit model of uveitis, by providing therapeutic levels of PA that attenuated the inflammatory response even after a rechallenge. Longer term studies are now needed to establish the therapeutic potential of such a delivery system for treatment of ocular inflammation.