Studies On Construction And Drug Delivery Mechanism Of Local Inner-ear Drug Delivery System With PLGA Nanoparticles As Vehicles

Currently, the treatment of inner ear and brain disorders heavily relies on systemicadministration. However, the existence of the blood-labyrinthine barrier (BLB) andblood-brain barrier (BBB) prevent the delivery of drugs from the blood to inner ear andbrain, which represent a fundamental obstacle to systemic application. The intratympanicadministration (IT) with round window membrane (RWM) injection, one of the main routesfor local drug delivery to the inner ear, is becoming of increasing interest in basic researchand in clinics, it can directly transport drugs to the perilymph (PL), and further transport tothe cerebrospinal fluid (CSF) through the cochlear aqueduct. This approach indicates thatinner ear administration can be used to the treatment of inner ear and brain disorders. Novelpoly(lactic-co-glycolic acid)(PLGA) nanoparticles of biodegradable and biocompatiblepolymers as promising drug delivery vehicles preferably reduce drug degradation, controldrug release, manipulate drug distribution and improve their bioavailability. Because oftheir advantages, PLGA nanoparticles as vehicles are being studied widely. In this paper,some kinds of drugs with different physicochemical properties were chosen as model drugs.One was lipid soluble micromolecular drug (coumarin-6), the other was water solublemacromolecular protein drug (Human recombinant interferon α-2b, IFNα-2b), the last wereefficient components from salvia miltiorrhiza and panax notoginseng (salvianolic acid B(Sal B), tanshinone IIA (TS IIA), notoginsenoside R1(R1), ginsenoside Rg1(Rg1), ginsenoside Rb1(Rb1)). PLGA nanoparticles loaded with different model drugs wereprepared and the drug delivery mechanism of local inner-ear drug delivery system withPLGA nanoparticles as vehicles was studied.Coumarin-6as a fluorescent probe was employed to PLGA nanoparticles using theemulsion/solvent evaporation method. Morphological characteristics of nanoparticles wereobserved using transmission electron microscope (TEM). It could be found thatnanoparticles formed spherical particles in a small size. The mean diameter and the sizedistribution of nanoparticles were determined by laser particle size analyzer. The averagesize of the nanoparticles was135nm with PDI0.17. The mean entrapment efficiency (EE)was determined by sephadex filtration method and EE was49.6%. In vitro leakage ofcoumarin-6from nanoparticles was less than2%. Coumarin-6can be used as afluorescence marker for in vivo tracing. After unilateral IT of coumarin-6into the cochleaof guinea pig, tissues (PL, contralateral PL, CSF, plasma) were collected at different timepoints. It was found that the transport pathway of fluorescent prob wasPL→CSF→contralateral PL. The Cmaxof coumarin-6in PL and CSF following IT ofnanoparticles was9.91and9.01-fold higher compared with coumarin-6solution. And therelative bioavailability was467%and850%, respectively. All these findings suggestedlocal bioavailability in inner ear and brain was enhanced remarkably by the PLGAnanoparticles delivery system after inner ear application.The double emulsion/solvent evaporation method was used to prepare the IFNα-2bloaded PLGA nanoparticles. These copolymers formed spherical shape. The mean diameterof these nanoparticles was about249nm with PDI0.13. EE was21.8%using sephadexfiltration method. After IFNα-2b nanoparticles guided into guinea pigs via IT andintravenous administration (IV), respectively, the AUC and Cmaxin PL, CSF and brain were70.98,209.89,0.73,0.46and2.34,0.21-fold higher compared with IV. The relativebioavailability of IFNα-2b in PL, CSF and brain following IT of IFNα-2b nanoparticleswas7121%,2193%,1863%compared with IT of IFNα-2b solution, respectively. PLGAnanoparticles could promote macromolecular drugs crossing the RWM into inner ear andbrain significantly. Effective components of salviae miltiorrhizae-panax notoginseng loaded PLGAnanoparticles were prepared by double emulsion/solvent evaporation method. Theoptimization of formulation was investigated by single factor method: inner water phasewas distilled water, oil phase/outer water phase ratio was1:3, LA/GA was50:50, span-80and LABRAFILM1994CS (1:1) as mixture emulsifier. These copolymers formedspherical shape. The mean diameter of these nanoparticles was about154nm with PDI0.007. Moreover, in vitro drug release behavior shown that it had a good sustained-releasecharacteristics. The EE of nanoparticles was determined by reverse dialysis method. TheEE was91.81%for TS IIA,92.88%for Sal B,37.87%for R1,44.98%for Rg1, and93.56%for Rb1, respectively. The concentrations of five components in PL, CSF and brain afternanoparticles via IT were significantly higher than nanoparticles via IV. Moreover, afternanoparticles via IT, the relative bioavailability of Sal B, TS IIA, R1, Rg1and Rb1in PLwas509%,6091%,2375%,1288%,2350%compared with compound solution via IT,respectively. In CSF, the relative bioavailability was524%,1165%,1422%,1185%,1232%, respectively. Moreover, the relative bioavailability of R1, Rg1and Rb1fromnanoparticles in brain was13599%,6063%,16690%compared with compound solution,respectively. These results showed that PLGA nanoparticles had powerful ability totransport multiple components to inner ear and brain through the RWM and resulted in anincreased absorption.Combination of bilateral common carotid artery occlusion with depressurization usingsodium nitroprusside was applied to prepare model of global cerebral ischemia reperfusioninjury. Evaluation the effect of PLGA nanoparticles loaded with effective components ofsalviae miltiorrhizae-panax notoginoside via IT on the treatment of cerebral ischemia. Maleguinea pigs were allocated into five groups randomly: sham group, I/R group, positivecontrol group, IT group, IV group. The serum and brain of guinea pigs were used formeasurement of SOD, MDA and NOS. Compared with I/R group and shame group,nanoparticles pretreatment via IT or IV resulted in a significant degradation in MDAcontent and NOS activity (P＜0.01) and elevation in SOD level (P＜0.01). Moreover, theeffect of IT group is significantly better than IV group (P＜0.01). Moreover, preliminary study on the toxicity of PLGA nanoparticles via IT was conducted. Guinea pigs weredivided into normal group, saline group and nanoparticles group. MDA content, SOD andNOS activities in the cochlea were determined. SOD, MDA and NOS level in saline groupor nanoparticles group have no significant differences compared to normal group (P＞0.05).The preliminary results showed that nanoaprticles did not cause cochlear injury via IT.In this paper, the results suggested that local inner-ear drug delivery system withPLGA nanoparticles as carrier could effectively carry micro-macromolecular drugs ormultiple components crossing the RWM and improve local bioavailability in inner ear andbrain. It is a beneficial attempt and new breakthrough for the drug delivery to inner ear andbrain.