Aerosolized, Gas-Phase, Intravitreal Methotrexate Reduces Proliferative Vitreoretinopathy in a Randomized Trial in a Porcine Model.

Purpose: To determine the effectiveness of aerosol-delivered methotrexate (AD-MTx) in a large-animal (porcine) model of proliferative vitreoretinopathy (PVR). Design: Prospective, randomized, interventional, double-masked, controlled, large-animal study with predetermined clinical and histopathologic outcome criteria. Controls: Half of the pigs were randomly assigned to receive an identical volume of aerosol-delivered normal saline (AD-NS) using identical delivery systems and treatment intervals. Methods: Proliferative vitreoretinopathy was surgically induced in 16 pigs (8 males and 8 females), randomly assigned to receive 2 doses (group A) or 3 doses (group B) of either AD-MTx (1.6 mg/0.4 ml) or normal saline (AD-NS). Group A pigs were euthanized at week 2 (n = 8), and group B pigs were euthanized at week 3 (n = 8). Masked clinical PVR scores (0-6) by a vitreoretinal surgeon and histopathology PVR scores (0-8) by a masked ophthalmic pathologist were used to determine outcomes. Main Outcome Measures: The mean, combined clinical and histopathology scores (both anterior and posterior) were used to determine the overall treatment effect between the groups. Results: The mean masked score (± standard deviation) when all grading end points (clinical + histopathology) were combined was a mean of 8.0 ± 2.3 in the AD-MTx group versus a higher 9.9 ± 2.0 in the AD-NS control group (P = 0.05). The clinical score was 3.88 ± 1.2 in the AD-MTx group versus 4.63 ± 1.6 in the AD-NS group (P = 0.16). The histopathology score for anterior PVR was 2.5 ± 0.8 in the AD-MTx group versus 2.5 ± 0.5 in the AD-NS group (P = 0.50), and the posterior PVR was 1.63 ± 1.6 in the AD-MTx group versus 2.75 ± 1.3 in the AD-NS group (P = 0.07). When the frequency of methotrexate dosing in group A (2 doses) was compared with that in group B (3 doses), the mean score was 8.75 versus 9.13 (P = 0.38), respectively, suggesting an insignificant difference. Conclusions: After surgical induction of PVR in an aggressive, high-risk, large-animal model, AD-MTx reduced posterior PVR formation compared with AD-NS. Additional dosing at week 3 did not improve the outcomes. No difference in anterior PVR formation was noted with intervention. This novel drug delivery system has implications for PVR reduction and warrants further investigation. Financial Disclosures: Proprietary or commercial disclosure may be found after the references.

Drug Tissue Distribution of TUDCA From a Biodegradable Suprachoroidal Implant versus Intravitreal or Systemic Delivery in the Pig Model.

Purpose: To determine local ocular tissue levels of the bile acid, tauroursodeoxycholic acid (TUDCA), in the pig model using oral, intravenous (IV), intravitreal injection (IVitI) and low- and high-dose suprachoroidal, sustained-release implants (SCI-L or SCI-H). Methods: Forty-six pigs (92 globes) were included in the study. TUDCA was delivered orally in 5 pigs, IV in 4, IVitI in 6, SCI-L in 17, and SCI-H in 14. Testing timeframes varied from the same day (within minutes) for IV; 1 to 6 days, oral; and 1 to 4 weeks, IVitI and SCI. Enucleated globes were dissected, specimens from specific tissues were separated, and TUDCA was extracted and quantified using mass spectrometry. Results: The highest TUDCA tissue levels occurred after IV delivery in the macula (252 ± 238 nM) and peripheral retina (196 ± 171 nM). Macular choroid and peripheral choroid levels were also high (1032 ± 1269 and 1219 ± 1486 nM, respectively). For IVitI delivery, macular levels at day 6 were low (0.5 ± 0.5 nM), whereas peripheral choroid was higher (15.3 ± 16.7 nM). Neither the SCI-L nor SCI-H implants delivered meaningful macular doses (≤1 nM); however, peripheral retina and choroid levels were significantly higher. Bile acid isoforms were found in the serum specimens. Conclusions: The highest TUDCA tissue levels in the pig model were obtained using IV delivery. Oral delivery was associated with reasonable tissue levels. Local delivery (IVitI and SCI) was able to achieve measurable local ocular tissue levels. Translational Relevance: Diffusional kinetics from the suprachoroidal space follow the choroidal blood flow, away from the macula and toward the periphery.

A Pharmacodynamic Analysis of Choroidal Neovascularization in a Porcine Model Using Three Targeted Drugs.

Purpose: To compare the efficacy of microneedle-delivered suprachoroidal (SC) pazopanib to intravitreal (Ivit) delivery of pazopanib, bevacizumab, or a fusion protein hI-con1 versus vehicle controls on choroidal neovascularization (CNV) growth in a pig model. Methods: Forty-one pigs were injected on the day of CNV induction (hI-con1 on postinduction day 14) with either 2.5 mg Ivit bevacizumab (n = 9), 1 mg Ivit pazopanib (n = 9), 300 Ivit µg hI-con1 (n = 4), or 1 mg SC pazopanib (n = 9), vs. 10 vehicle controls (3 SC + 7 Ivit = 10). Pigs were euthanized at week 2 (11), 3 (8), 4 (11), and 8 (11), and eyes were fixed for histology. The size of the CNV was determined from histology, and CNV height was the primary outcome measure. Immunostaining for cytotoxic T-cells was performed in the hI-con1 study. Results: In 39 of 41 (95%) eyes, type 2 CNV lesions were identified. One CNV lesion was lost during dissection. One animal was euthanized due to surgical complications. For mean CNV size comparisons, Ivit pazopanib had smaller mean height measurements (90 ± 20 µm) versus controls (180 ± 20 µm; P = 0.009), and Ivit pazopanib had smaller maximum CNV height (173 ± 43 µm) compared to SC pazopanib (478 ± 105 µm; P = 0.018). The mean lesion size in hI-con1-treated animals trended smaller than in controls (P = 0.11). Immunostaining did not detect cytotoxic T-cells. Conclusions: Intravitreal pazopanib and to a lesser extent hI-con1 reduced the size of CNV lesions. The pig model has nearly a 100% rate of type 2 CNV induction and is a reliable preclinical model with pharmacodynamics similar to humans.

The effect of air tamponade on the ingress of ocular surface pathogens in sutureless transconjunctival microincisional vitrectomy.

PURPOSE: To assess the effect of air versus fluid tamponade on the intraocular migration of india ink particles through nonsutured transconjunctival 23-gauge sclerotomies in living porcine eyes. METHODS: Both eyes (n = 20) underwent 3-port, transconjunctival, 23-gauge vitrectomy. An angled trocar insertion technique was used in all cases. In each animal, one eye underwent a partial fluid-air exchange at the conclusion of the vitrectomy, yielding an air fill of approximately 80% (n = 10), whereas the other was left fluid filled (n = 10). After removal of the instruments and trocar cannulae, india ink was applied to the ocular surface. Animals were allowed to partially recover from anesthesia and resume normal blinking behavior. Animals were then reanesthetized, euthanized, and enucleated. Histopathologic examination was performed in a masked fashion. The presence and location of ink was noted for each identified sclerotomy. RESULTS: Ink was identified on the ocular surface in 18 of 20 eyes. Sclerotomy wounds were identified in 16 of 20 eyes. Ink penetration was seen in 2 of 16 sclerotomy wounds, 1 in an air-filled globe and 1 in a fluid-filled globe. In both eyes, the ink was identified along the outer one third of the wound. There was no penetration of ink along the inner two thirds of the sclerotomy wound or in the posterior segment of any eyes. CONCLUSION: In an experimental, in vivo, porcine model, india ink migration into angled transconjunctival sclerotomy incisions was minimal, regardless of the use of an 80% fluid-air exchange at the conclusion of the case.

Pharmacokinetics of pars plana intravitreal injections versus microcannula suprachoroidal injections of bevacizumab in a porcine model.

PURPOSE: To compare the pharmacokinetics and tissue response between intravitreal and microcannulation injections into the suprachoroidal space using bevacizumab. METHODS: Sixty-two pigs were studied. Either a pars plana intravitreal bevacizumab or a viscoelastic-enhanced microcannula suprachoroidal injection was performed with either 1.25 mg (group 1) or 3 mg (group 2). In group 1, six animals were euthanatized at 0.5, 7, 30, 60, 90, and 120 days after injection (n = 36). In group 2, six animals were euthanatized at 0.5, 7, 14, and 32 days (n = 24). Eyes were enucleated, dissected, and snap-frozen, or they were fixed for histology. Analysis of drug tissue levels was performed at two separate laboratories using masked specimens. RESULTS: Both laboratories were confirmatory. Intravitreal bevacizumab pharmacokinetics demonstrated a gradual decline in tissue levels over 30 to 60 days in both groups 1 and 2. In addition, suprachoroidal bevacizumab tissue levels declined rapidly and were not measurable at or beyond 7 days. Vitreitis and granulomatous vasculitis were noted in 7 of 30 intravitreal injection eyes. Immunohistology suggested a distinctive drug distribution. CONCLUSIONS: Direct intravitreal injection of bevacizumab has a more sustained pharmacologic profile than does a similar dose delivered to the suprachoroidal space. Intravitreal injections distributed more to the inner retina, whereas suprachoroidal delivery occurred primarily at the choroid, retinal pigment epithelium, and photoreceptor outer segments. Sustained release formulation of larger biological molecules should be considered to optimize suprachoroidal delivery. Inflammation from injections is granulomatous, seen only with intravitreal injections, and may result from either an altered immune response or a dose-related effect.

Intraocular nanoparticle drug delivery: a pilot study using an aerosol during pars plana vitrectomy.

PURPOSE: To describe a method of drug delivery to the retina via aerosolized nanoparticles in the gas phase during the gas-exchange stage of vitrectomy in a porcine model. METHODS: An ultrasonically atomized and dried sodium fluorescein aerosol was produced with a concentration of 12 ng/mL and a mass median particle size of 407 nm. Eighteen porcine eyes were randomly divided into six groups and subjected to standard three-port pars plana vitrectomy. After the air-fluid exchange and during the gas exchange, the eyes were exposed to the aerosol, either as a steady flow through the chamber (3.6 microg/min) or as a single fill (50 ng) at three exposure times (three eyes/time point). RESULTS: The flow-through delivery mode provided a relatively uniform deposition of aerosol on the inner surface of the retina, and longer delivery time led to an increase in the quantity deposited, with greater than 40 ng total deposition by 10 minutes. The single-fill method had uniform deposition but lower total delivery, approximately 10 ng by 60 minutes. Modeling of the data suggests that deposition in the flow-through mode is successful if the vitreous chamber contents are well mixed. The single-fill delivery was described by diffusion in a quiescent state. CONCLUSIONS: This study demonstrates a novel method of drug delivery to the posterior pole by using aerosolized nanoparticles that may be used in the gas phase of vitrectomy. Therapeutic applications include antimetabolites for modulation of proliferative vitreoretinopathy, antimicrobial agents for endophthalmitis, antiangiogenic compounds for vasoproliferative disorders, corticosteroid delivery, and other pharmacotherapies directed at the retina and choroid.

Stimulated growth of human and pig epidermal nerve fibers by tape stripping.

Nerve growth studies in adults usually rely upon nerve regeneration that follows axon disruption. In this study elongation of the epidermal nerve fibers occurred in human and pig epidermis stimulated to hypertrophy by removing the stratum corneum with repetitive applications of tape (tape stripping). Epidermal thickening was accompanied by elongation of the epidermal nerve fibers. This study demonstrates that changing the cellular and chemical environment of nerves by tape stripping is a feasible method to study nerve fiber growth in a physiological manner.

Cannulation of the suprachoroidal space: a novel drug delivery methodology to the posterior segment.

PURPOSE: To describe, test, and evaluate the pharmacokinetics of a novel posterior drug delivery system (PDS) by means of microcannulation of the suprachoroidal space in both the primate and pig animal model. DESIGN: Animal study. METHODS: A rhesus macaque (Macaca mulatta) (n = 1) and pig model (n = 93) were used to evaluate the PDS, a microcannula that combines a drug delivery channel with a fiber-optic illumination and optimal transition properties. The surgical technique, safety profile, histopathology, retinal and choroidal blood flow, injection of tracer dyes, and triamcinolone pharmacokinetics were studied. Pre- and postsurgical high-speed video confocal scanning laser ophthalmoscopy (cSLO) that used fluorescein and indocyanine green (ICG) imaging and wide-field fundus imaging studies were performed. Globes were enucleated for either histopathology or pharmacokinetics. RESULTS: Cannulation was performed in 93 of 94 animals. Complications included: endophthalmitis (1/94), choroidal tear (1/94), choroidal blood flow irregularities (4/94), postoperative inflammation (6/94), scleral ectasia (4/94), wound abscess (1/94), and others. Histopathology demonstrated normal anatomy in uncomplicated cases. Triamcinolone remains in the local ocular tissue for at least 120 days, and measurable at very low levels in the systemic circulation. CONCLUSIONS: Accessing the suprachoroidal space by the microcannulation system can be performed in a safe and reproducible manner by using careful surgical technique. Forceful PDS tip impact into connective tissues in the macular and optic nerve regions should be avoided. Triamcinolone pharmacokinetics are unique and suggest long-term local tissue levels with low systemic levels. PDS access to the suprachoroidal space represents a novel drug delivery method, applicable to a wide variety of pharmacotherapies to the macula, optic nerve, and posterior pole.