Tolerance of high and low amounts of PLGA microspheres loaded with mineralocorticoid receptor antagonist in retinal target site.

Mineralocorticoid receptor (MR) contributes to retinal/choroidal homeostasis. Excess MR activation has been shown to be involved in pathogenesis of central serous chorioretinopathy (CSCR). Systemic administration of MR antagonist (MRA) reduces subretinal fluid and choroidal vasodilation, and improves the visual acuity in CSCR patients. To achieve long term beneficial effects in the eye while avoiding systemic side-effects, we propose the use of biodegradable spironolactone-loaded poly-lactic-co-glycolic acid (PLGA) microspheres (MSs). In this work we have evaluated the ocular tolerance of MSs containing spironolactone in rat' eyes. As previous step, we have also studied the tolerance of the commercial solution of canrenoate salt, active metabolite of spironolactone. PLGA MSs allowed in vitro sustained release of spironolactone for 30days. Rat eyes injected with high intravitreous concentration of PLGA MSs (10mg/mL) unloaded and loaded with spironolactone maintained intact retinal lamination at 1month. However enhanced glial fibrillary acidic protein immunostaining and activated microglia/macrophages witness retinal stress were observed. ERG also showed impaired photoreceptor function. Intravitreous PLGA MSs concentration of 2mg/mL unloaded and loaded with spironolactone resulted well tolerated. We observed reduced microglial/macrophage activation in rat retina compared to high concentration of MSs with normal retinal function according to ERG. Spironolactone released from low concentration of MSs was active in the rat retina. Low concentration of spironolactone-loaded PLGA MSs could be a safe therapeutic choice for chorioretinal disorders in which illicit MR activation could be pathogenic.

Development of an intravitreal peptide (BQ123) sustained release system based on poly(2-hydroxyoctanoic acid) aiming at a retinal vasodilator response.

PURPOSE: Development of a novel formulation for intravitreal administration, in which the endothelinA receptor antagonist BQ123 is incorporated in a biodegradable and injectable polymer drug delivery system, poly(2-hydroxyoctanoic acid), aiming at a prolonged retinal vasodilator response. METHODS: BQ123 was incorporated in poly(2-hydroxyoctanoic acid), leading to an easily injectable, homogenous mixture. In vitro release profiles were obtained in porcine vitreous humor (n=6). The ex vivo biocompatibility was studied by placing the formulation in contact with porcine retinal tissues and performing histology. In a pilot in vivo study, the change in retinal vessel diameter of mini pigs (n=2) was followed over 3 h after an intravitreal injection of the formulation, as well as the release of BQ123 from the polymer system for approximately 7 days (n=6). RESULTS: In vitro, a constant release profile was obtained, releasing approximately 91% of BQ123 within 7 days. Histology on the porcine retinal tissues showed good ex vivo biocompatibility. In vivo, a vasodilative response was observed, with a retinal vessel diameter increase from 14% after 15 min, for approximately 39% after 3 h. At t=3 h, the BQ123 concentration in the vitreous humor was 0.7±0.2 µg/mL, followed by 1.5±1.0 and 1.1±0.8 µg/mL after 3 and 7 days, respectively. 39.9%±6.0% of BQ123 was still present in the polymer depot at t=7 days. CONCLUSIONS: The results show that an intravitreal injection of this drug delivery system leads to a prolonged vasodilative response and a BQ123 release over 7 days, suggesting its therapeutic potential in the management of retinal ischemic conditions.

Design and in vitro assessment of L-lactic acid-based copolymers as prodrug and carrier for intravitreal sustained L-lactate release to reverse retinal arteriolar occlusions.

Ophthalmic conditions in which the retinal vasculature is obstructed generally lead to vision loss. Administration of the vasodilator L-lactate might offer a treatment strategy by restoring the blood flow, but unfortunately its effect after single intravitreal injection is short-lived. This study describes a concept in which the sustained release of L-lactic acid from a biodegradable copolymer system is investigated. The 50:50 (n/n) copolymer system, composed of L-lactic acid and L,D-2-hydroxyoctanoic acid, is a viscous injectable that will form an intravitreal drug depot. Hydrolysis of the copolymer will automatically lead to the release of L-lactic acid, which will convert to L-lactate at physiological pH, thereby providing a carrier and pro-drug in one. In vitro and ex vivo release studies demonstrate an L-lactic acid release over several weeks. Biocompatibility of the co-polymer and its degradation products is shown on a human retinal pigment epithelial cell line and on ex vivo retinal tissues. A low molecular weight copolymer (1200 g/mol) with low polydispersity has promising properties with a constant release profile, good biocompatibility and injectability.

In vivo biocompatibility, sustained-release and stability of triptorelin formulations based on a liquid, degradable polymer.

Hexylsubstituted poly(lactic acid) (hexPLA) is a viscous polymer, which degrades in the presence of water similar to the structure related poly(lactic acid). With hydrophilic active compounds, like Triptorelin acetate, the lipophilic polymer was formulated in form of parenterally injectable suspensions. This first in vivo study toward the biocompatibility of hexPLA implants in rats over 3 months in comparison to in situ forming poly(lactic-co-glycolic acid) (PLGA) formulations is presented here. The hexPLA implants showed only a mild acute inflammation at the injection site after application, which continuously regressed. In contrast to the PLGA formulations, hexPLA did not provoke an encapsulation of the implant with extracellular matrix. Prior to the formulation application, the stability of Triptorelin inside the hexPLA matrix was assessed under different storage conditions and in the presence of buffer to simulate a peptide degrading environment. At 5°C Triptorelin showed a stability of 98% inside the polymer for at least 6 months. The stability was still 78% at an elevated temperature of 40°C. HexPLA protected the incorporated peptide from the surrounding aqueous environment, which resulted in 20% less degradation inside the polymer compared to the solution. This protection effect supports the use of Triptorelin-hexPLA formulations for parenteral sustained-release formulations. In a second in vivo evaluation in Wistar Hannover rats, formulations containing 5% and 10% Triptorelin in the polymeric matrix released the active compound continuously for 6 months. The formulations showed a higher release during the initial 7 days, which is necessary for the clinical use to down-regulate all GnRH-receptors. Afterwards, a zero order drug release was observed over the first 3 months. After 3 months, the plasma levels decreased slowly but remained at effective concentrations for the total of 6 months. Furthermore, a qualitative in vitro-in vivo correlation was observed, possibly facilitating future optimization of the Triptorelin-hexPLA sustained-release formulations.

Single processing step toward injectable sustained-release formulations of Triptorelin based on a novel degradable semi-solid polymer.

Poly(lactic acid) is a widely used polymer for parenteral sustained-release formulations. But its solid state at room-temperature complicates the formulation process, and elaborate formulation systems like microparticles and self-precipitating implants are required for administration. In contrast, hexylsubstituted poly(lactic acid) (hexPLA) is a viscous, biodegradable liquid, which can simply be mixed with the active compound. In this study, the feasibility to prepare injectable suspension formulations with peptides was addressed on the example of the GnRH-agonist Triptorelin. Two formulation procedures, of which one was a straight forward one-step cryo-milling-mixing process, were compared regarding the particle size of the peptide in the polymer matrix, distribution, and drug release. This beneficial method resulted in a homogeneous formulation with an average particle diameter of the incorporated Triptorelin of only 4.1 µm. The rheological behavior of the Triptorelin-hexPLA formulations was assessed and showed thixotropic and shear-thinning behavior. Viscosity and injectability were highly dependent on the drug loading, polymer molecular weight, and temperature. Nine formulations with drug loadings from 2.5% to 10% and hexPLA molecular weights between 1500 and 5000 g/mol were investigated in release experiments, and all displayed a long-term release for over 3 months. Formulations with hexPLA of 1500 g/mol showed a viscosity-dependent release and hexPLA-Triptorelin formulations of over 2500 g/mol a molecular weight-dependent release profile. In consequence, the burst release and rate of release were controllable by adapting the drug loading and the molecular weight of the hexPLA. The degradation characteristics of the hexPLA polymer during the in vitro release experiment were studied by following the molecular weight decrease and weight loss. Triptorelin-hexPLA formulations had interesting sustained-release characteristics justifying further investigations in the drug-polymer interactions and the in vivo behavior.