Nanoparticles from alkylglyceryl-modified polysaccharides for drug delivery to the brain
Student thesis: Doctoral Thesis
The loading of therapeutic actives into polymeric nanoparticles represents one of the approaches towards drug transport through the blood-brain barrier – the main obstacle to drug delivery into the central nervous system. The non-toxic, biocompatible and biodegradable polysaccharides chitosan and dextran were modified with permeation-enhancing alkylglyceryl pendant chains through reaction with epoxide precursors. The modified polysaccharides were characterised by spectroscopic methods (1H-, 13C-NMR and FT-IR). These polysaccharides were further formulated into nanoparticles using three methods, namely: nanoprecipitation, solvent displacement via dialysis and electrospraying. The resultant colloidal systems formed were characterised using Dynamic Light Scattering, Nanoparticle Tracking Analysis and Electrophoretic Mobility Measurements. Dried nanoparticles were further characterised by Scanning Electron Microscopy and Atomic Force Microscopy. Formulations of alkylglyceryldextran derivatives were found to be stable at the physiologically relevant pH of 7.4. Over the same range of pH values, formulations of alkyglyceryl-chitosans formed aggregates. Respectively dependent upon the method of formulation and the pH, nanoparticles from poly(lactic acid)-graft-butylglyceryl-modified dextran exhibited diameters in the range 100-400 nm and zeta potentials of between -15 and -30 mV. The preparation of nanoparticulate congeners that incorporated a fluorescent marker molecule (Doxorubicin, Rhodamine B or Fluorescein) allowed the studies of the capabilities of nanoparticles to accommodate and release a model therapeutic load. Rhodamine B-loaded nanoparticles further allowed the study of the uptake of nanoformulations by mouse (bEnd3) brain endothelial cells. The interactions of nanoparticles with modelled blood-brain barriers (mouse bEnd3 and human hCMEC/D3) were studied by Electric Cell Substrate Impedance Sensing and also by means of the Transwell model. Data from MTT and Presto Blue assays were consistent with the absence of nanoparticle-induced cytotoxic effects. An in ovo study that used 3-day chicken embryos indicated the absence of whole-organism acute toxicity effects but failed to unmask the biodistribution profile of nanoparticles. The results have shown that poly(lactic)-graft-alkylglyceryl- modified dextran nanoparticles possess some promising features (size, stability, loading capacity, and toxicity) that render them candidates for further evaluation as biocompatible nanocarriers for drug delivery to the brain.
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