N-Acetylcysteine-Doped Microparticles Efficiently Rescue Oligodendrocyte Precursor Cell Redox State in an Oxidative Environment

Introduction: Overproduction of reactive oxygen species (ROS) is a major factor in the pathogenesis of multiple sclerosis¹. Localized antioxidant delivery is therapeutically relevant to counteract and neutralize ROS in such oxidant-stressed systems. Poly(lactic-co-glycolic acid) (PLGA) nanoparticles can provide a localized, controlled release of encapsulant, though reported encapsulation efficiencies of small-molecule therapeutics have been low: 12%² and 16%³ for dopamine and N-acetylcysteine (NAC), respectively. Here we investigate how modifying the traditional double-emulsion, solvent evaporation method by doping external water phases with the small-molecule drug affects encapsulation efficiency, temporal release profiles, released drug activity, and released drug protective effect on oligodendrocyte progenitor cell (OPC) viability after H₂O₂ stress. We aim to deliver NAC, a potent, cheap, FDA-approved antioxidant, with high efficiency and temporal control.

 

Materials and Methods: NAC-loaded PLGA nanoparticles with varying lactide:glycolide (L:G) ratios and inherent viscosities were prepared by the double-emulsion, solvent evaporation method. The solvent for all water phases was deionized water. Briefly, the internal water phase (10% w/v NAC) was dispersed via sonication within the oil phase (15% PLGA in dichloromethane). The primary emulsion was dispersed in the outer water phase (1% PVA with or without 2.5% NAC) via sonication. The secondary emulsion was stirred in 0.3% PVA with or without 5% NAC for 4 hours. Particles were washed 3x in either DI water or 2.5% NAC and lyophilized. Release was determined by incubating particles at 37°C in phosphate-buffered saline and measuring supernatant NAC via Ellman’s Reagent. LAP photoinitiator radical concentrations were measured via luminol to determine the dose response of NAC radical scavenging. OPC viability in response to oxidative conditions with and without the NAC antioxidant was measured via the CellGlo reagent.

 

Results and Discussion: Encapsulation efficiencies (relative to theoretical load without doped external phases) for NAC-loaded PLGA nanoparticles were greatest with external phase doping – reading greater than 300% of the case when undoped. With the doped particles, NAC was released for 14 days. NAC ranging from 0.5-1000 µM (the particle supernatant concentration range for each sample time) scavenged photoinitiated LAP radicals in a dose-dependent manner, with 0.5 µM and 1000 µM NAC scavenging 6.82% and 95.5% of radicals, respectively. Ongoing experiments show NAC-loaded nanoparticle antioxidant activity and protective effect on OPC viability.

 

Conclusions: Drug-doping of external water phases during the double emulsion, solvent evaporation method gave NAC-loaded PLGA nanoparticles with significantly higher encapsulation efficiencies than without doping, and up to 20-fold higher than previously reported values. NAC scavenged LAP radicals in a dose-dependent manner and was released from PLGA nanoparticles for at least two weeks. This indicates that these particles will provide a larger and more continuous small molecule dose longer than previously reported methods. Efficiently loaded antioxidant nanoparticles capable of controlled and localized delivery could have therapeutic potential in oxidant-stressed systems and bias progenitor cells such as OPCs toward a self-renewing fate.

 

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