Studies On Quercetin-Loaded Solid Lipid Nanoparticles

Quercetin(QT,3,3',4',5,7-pentahydroxyflavone)is a natural flavonoid,which is known to have a variety of biological activities and pharmacological actions,such as dilating coronary arteries,decreasing blood lipid,anti-platelet aggregation,anticancer, antioxidation,antianemic action,anti-inflammation,anti-anaphylaxis.However, quercetin,with low hydrophilicity and lipophilic,can be absorbed little by the gastrointestinal tract,and its oral bioavailability is very low.As a result,the clinical application of the drug was seriously influenced.Solid lipid nanoparticles(SLN),a type of submicron particulate drug delivery system,are composed of physiological, biodegradable natural lipid material as drug carrier.The advantages of the system include high biocompatibility,high bioavailability,controlled release,no problems with respect to mult-ways administration.Quercetin-loaded solid lipid nanoparticles (QT-SLN)were prepared.The possibility of SLN as oral delivery carrier of quercetin was investigated through the study of absorption mechanism,absorption segment and pharmacokinetic experiment in vivo.The method of "emulsification and low-temperature solidification" was used to prepare QT-SLN.The morphous,particle size and entrapment efficiency(EE)were taken as criterions to evaluate the effects of surfantants,lipid materials,organic solvent, emulsifying temperature,emulsifying time,stirring velocity etc.on the properties of QT-SLN.As a result,the quantity of QT,the ratio of Glycerol Monostearate to Lecithin, amount of surfactants,the ratio of PEG400 to tween-80,emulsifying temperature and emulsifying time were proved to have great effects on the properties of QT-SLN.The uniform experimental design was applied to optimize the formulation based on the morphous,entrapment efficiency,drug loading and stability of QT-SLN.Three batches of QT-SLN were prepared using the optimized formulation.From the transmission electron microscope observation,the nanoparticles were spherically shaped,the particle size was 155.3nm,the entrapment efficiency and drug loading were 91.08%and 13.20%,the zeta potential was -32.23mV,which attained the predicted objective.The dialytic method was used to study drug release of QT-SLN in vitro and the curve fitting method was used to find the drug release equation.The results showed that the drug release of QT-SLN in vitro fit double phase kinetics model well.The equation was as follows:100-Q=98.8731e^-0.1042t+42.4531e^-0.0258t,(r_α=0.9994,r_β= 0.9937).The stability of QT-SLN was examined being stored under cold conditions, and the results showed that QT-SLN was stable within six months at least.The absorption of QT-SLN at the gastrointestinal tract was studied using in situ perfusion method in rats.It showed that the stomach was the worse absorption segment, and the absorption percent after 2h was only 6.20%.The intestinal absorption kineticses of QT-SLN with low,middle,high concentrantions were investigated and the Ka were 0.0784h^-1,0.0780 h^-1和0.0777 h^-1,respectively.So the principal mechanism of QT-SLN in intestinal absorption conformed to passive diffusion.The test of main segment indicated that QT-SLN could be absorbed by all the segments of the intestine, and the absorption percentages of duodenum,jejunum,ileum and colonic were (13.00±2.41)%,(17.57±1.84)%,(30.44±2.21)%,(22.03±1.77)%.The main segments of QT-SLN absorbed in intestine were ileum and colonic.The effects of QT-SLN on the structural properties of the intestinal mucosal membrane of rats were investigated by Fluorescence polarization and Circular dichroism in vitro.After being treated with samples,not only the fluidity of intestinal mucosal membrane increased but also the conformation of the membrane protein loosed which increased the gastrointestinal absorption of QT-SLN.The pharmacokinetic experiment of QT suspension and QT-SLN was carried on rats.The concentration of QT was examined by the HPLC.Program 3p97 was applied to calculate pharmacokinetic parameters and chose the best compartment method.The results showed that both preparations' pharmacokinetics processes were all fitted one-compartment model.In contrast to QT suspension,the absorption of QT-SLN was markedly improved,as a result, the circulating amount of the drug in blood was markedly increased and the relative bioavailability was 571.4%.The powder of the QT-SLN was prepared by lyophilization using mannitos as supporting agent in order to obtain better physical and chemical stabilities.The stability of QT-SLN was not affected by the lyophilization process with nearly unchanged entrapment efficiency,drug loading,pH,etc.The release trail in vitro was investigated and the results showed that the QT-SLN and freeze-dried powder have similar release kinetics and both releasing curves could be well explained by double phase kinetics model.Both preparations had sustained-release character.Currently,there has been no report about solid lipid nanoparticles using QT as model drug in the world.In this dissertation it was proved that solid lipid nanoparticles indeed increased the absorption of poorly soluble drugs through gastrointestinal tract after oral administration.So it is a new drug delivery system with great investigating value and potential.