الفهرس 
Formulation and characterization of rivastigmine loaded lipid polymer hybrid nanoparticlesOnly 14 pages are availabe for public view
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Abstract
Rivastigmine (Riv) is a hydrophilic drug used in the treatment of dementia in Alzheimer’s disease (AD). Riv’s limitations mainly lie in its restricted access to the brain. The main goal of this research was to efficiently deliver Riv to the brain and increase its residence time while minimizing its accumulation in other organs (like kidneys and spleen).Meanwhile, the secondary goal was to achieve high encapsulation efficiency of Riv into hybrid nanoparticles (NPs).Enabling such brain targeted treatments, allows for higher efficacy, minimum side effects, less toxicity and, therefore, lesser treatment expenses. In this work, we investigated the potential of a tailored lipid polymer hydrid nanocarriers in overcoming the robust brain guard; the BBB. We also overcame the challenge of loading a hydrophilic moiety (Riv), and efficiently targeted a high payload of the drug to the brain. The surface modification of the tailored hybrid system with the biocompatible molecules, DX and CA gave a high potential for brain targeting. This was proven by comparing the surface modified system to a non-modified one.
In chapter I:
A single step modified nanoprecipitation technique was adopted for the preparation of nanoparticles (NPs). First, conventional NPs were optimized and used as a template for the preparation of hybrid NPs. Conventional poly-lactic-co-glycolic acid (PLGA) NPs were optimized by manipulating the following factors: organic solvent type, polymer (PLGA) concentration, dielectric constant (DEC) of anti-solvents, type and concentration of surface active agents (SAA). The size and polydispersity index (PDI) were the main factors being studied. Second, introducing a layer of lipids took place. Small hybrid PLGA NPs (in the size of 100 nm) hybrid were optimized by manipulating the following: the DEC of anti-solvent, type of phospholipids, the addition of bio-SAA, sodium cholate (NaC) and the addition of drug. Two-drug-feed concentrations and the addition of SAA were set as independent factors affecting entrapment efficiency. Thereafter, surface morphology and structure of selected formulae (conventional and hybrid PLGANPs) were characterized, using scanning electron microscope (SEM) and transmission electron microscope (TEM).
In chapter II:
Synthesis of cholic acid modified dextran (MDX) took place using an esterification reaction based on the use of DCC and the solvent DMSO. The prepared amphiphile was characterized using Fourier transform-infra red (FT-IR) and H-NMR. The later was used to determine the degree of substitution as well as the conjugation. Hereafter, surface modification of the previously prepared hybrid NPs, using the MDX, took place. To yield the optimum size and EE% (in the range of 100-150 nm and above 60%, respectively); two types of organic solvents, different PLGA and MDX concentrations, addition of B-SAA, and the manipulation of the DEC of the solvent/non-solvent system, were evaluated. Particle size, measured using zeta-sizer, was the main determinant. Meanwhile, Riv was assayed using the HPLC system. The optimum formula was evaluated for its in-vitro release in PBS PH-7. Finally, TEM and FT-IR were used for the structure and morphology characterization.
In chapter III:
In-vivo evaluation of Riv-loaded hybrid NPs with or without MDX modification was carried out in comparison to the free drug solution. Localization of Riv in the brain, as well as its delocalization in other organ tissues was evaluated through the biodistribution study. In the meantime, the absorption, distribution and elimination of Riv were studied in the pharmacokinetics study, in male albino rats. Intervals were up to 24h. Parameters: Cmax, Tmax, AUC0-inf, Kel= rate of elimination, MRT and t1⁄2, were calculated. Finally, the brain targeting efficiency was evaluated by calculating the AUC of the drug formula and drug solution.
The results showed the following
In chapter I:
Rapid mixing (of organic solvent) combined with high turbulence (in the non-solvent) reduced the NPs size. Meanwhile, when acetone was compared to acetonitrile, the later had a significant (P<0.05) effect on reducing PS. Moreover, the ratio of 1:2 (acetonitrile/ 15% ethanol) was the optimum in regards to PS and particles distribution. Upon comparing different types of surfactant (SAA), the anionic biosurfactant (B-SAA), Na-cholate, displayed the least size, while the ratio of 2/1 SAA: PLGA has optimized the PDI to the least possible value. Hence, these optimum parameters were used for the preparation of the lipid polymer hybrid NPs. PLGA concentration in the range of 0.1%-0.5% w/v has shown small size, when used with the appropriate ratios of lipid. Lipid layer made up of egg derived phosphatidylcholine (EPC) in the ratio of 2/20; L/P displayed the least possible size as compared to other phospholipids. Addition of NaC on the lipid layer in 15% ethanol has shown further reduction in size.
Chapter II:
MDX was successfully synthesized using the solvent DMSO. The degree of substitution varied with the variation of the process conditions. An amphiphile with a degree of substitution not exceeding 30% was selected in this work based on previous literature. The integration of MDX into the lipid layer was afforded by placing the MDX in the organic solvent DMSO. In the meantime, 100 % ethanol was used as a non-solvent. Though the former increased the EE%, yet it enlarged the size of NPs up to 300 nm. Nonetheless, EE% varied with the addition of MDX and NaC on a fixed lipid/PLGA ratio. PLGA in low concentrations increased the EE% of Riv. However, based on the ratio of MDX and NaC, size of NPs varied. Thus, viscosity of PLGA was raised through the reduction of organic solvent volume, where the ratio of organic/aqueous (60% ethanol) was 1:8. Finally, the system successfully yielded negatively charged NPs, with a size and EE% around 100 nm and 70%, respectively. This formula had successfully extended the in-vitro release of Riv up to 72 h.
Chapter III:
Compared to the drug solution, higher drug accumulation in brain was achieved with the hybrid NPs (both unmodified and surface modified) following the iv administration in rats. This was due to the probable uptake by endocytosis/transcytosis. However, modified hybrid Riv-loaded NPs enhanced Riv’s brain penetration and diffused into the brain at a faster rate compared to the non-modified. Surface modification prolonged the circulation time of Riv and probably has enhanced brain permeability for the system. This was reflected in the AUC in the brain tissues, which were found to be: 1250.2 µg /mL.min for the modified hybrid NPs compared to 296.5 and 124 (µg /ml.min) for the unmodified and the free drug soln, respectively. Furthermore, Riv modified hybrid NPs showed the highest concentration in the brain (715.48 ng/ g) after 45. Meanwhile, the unmodified and free drug was 447 and 346 ng/g after 60 min, respectively. High selectivity of Riv modified hybrid NPs to the brain was also seen in the targeting efficiency of 184%, meanwhile, that of the unmodified and free drug was 61.5% and 34%, respectively. Surface functionalization of the hybrid NPs were able to accumulate the drug in the brain for up to 40.7 h, as compared to 5.1 h in the free drug.
The modifications applied to the hybrid system allowed to load high percentage of the hydrophilic Riv and selectively penetrate the brain, while minimizing its biodistribution in non-targeted organs, with a reduction in side and toxic effects. The developed dextran surface modified lipid polymer hybrid nanocarrier present an integrated promising carrier for efficient treatments of AD as well as other brain diseases.