Studies On PEGylation Of Lipid Nanoparticles In Improving The Oral Absorption Of Fenofibrate

Lipid nanoparticles are a new drug delivery carrier based on researches in liposomes and microemulsions that have been extensively developed. Because of multiple advantages such as high drug loading, good biocompatibility, relatively large surface area and small particle size, lipid nanoparticles can increase the adhesion of formulation by the intestinal mucosa, therefore improving the oral bioavailability of drugs. Lipid nanocarriers are playing a more and more important role in formulation development of lipophilic drugs.Conventional lipid nanocarriers degrade rapidly after oral administration because of the presence of pancreatic lipase in the gastrointestinal(GI) tract, resulting in significant drug exposure in the GI cavity or drug precipitation that reduce the overall absorption of drugs and variable bioavailability. PEGylation by modifying drug structure or fabricating PEGylated formulations has also been shown to increase the bioavailability of the drug. But it remains largely unclear how lipid nanoparticles(with or without PEG modification) are processed in the GI tract.In this study, different techniques were used to prepare PEGylated lipid nanoparticles(PLNs) and conventional lipid nanoparticles(CLNs) loading fenofibrate(FN), a BCS II drug. In vitro release in medium with and without pancreatic lipase, lipolytic experiment and mucin binding feature were performed to elucidate the performance of PEGylated lipid nanocarriers. Pharmacokinetic behaviors of PLNs and CLNs were further investigated and compared in rats by gavage, for the sake of revealing the possible implications of PEGylation for oral delivery of lipophilic drugs.In the first chapter, the analytical methods on FN determination and entrapment efficiency were established. The methodology of FN quantification was validated carefully. The results showed that the method established by us could meet the requirements of the study. HPLC spectra exhibited excellent resolution and there was no interference from excipients.In the second chapter, FN as BCS II drug model was used to prepare PLNs by solvent diffusion method. Various factors that impact the performance of preparation were adopted to optimize the formulation using particle size and PDI as indices. FTIR spectroscopy, DSC, TEM and in vitro release were utilized to characterize the formulations. The results showed that FN-PLNs was 186.7 nm in particle size(PDI=0.207) with entrapment efficiency >95%. The ratio of each component significantly affected the particle size, stability and entrapment efficiency of PLNs. FN-PLNs appeared spherical or spherical structure as observed by TEM. The majority of particles were less than 342 nm, with no particularly large particle existence. Release study of FN from lipid nanoparticles was carried out using the reverse bulk equilibrium dialysis technique using 0.5% SDS solution. The results showed that FN-PLNs experienced a similar release feature to FN-CLNs, and there was no significant difference between them. The f2 value(similarity factor) between two preparations was calculated to be 58, revealing that their releases were comparable.In the third chapter, the GI transportation fate of lipid nanoparticles was investigated. After incubation with the extracted rat intestinal fluids at 37°C, the change in particle size was recorded. The release of FN in media with or without pancreatic lipid enzyme was tested to estimate the drug release or linkage from nanocarriers. Lipolytic experiment was further adopted to measure the damage of nanoparticle structure and the action of PEGylation on retarding enzymatic degradation. The results showed that FN-PLNs were affected less by the extracted intestinal fluids in comparison with FN-CLNs. Reversely, the release of FN-CLNs in medium containing lipid enzymes was faster than FN-PLNs. There was a significant difference in release rate between two preparations(f2 = 33). The lipolytic results also demonstrated that PEGylated lipid nanoparticles could resist degradation from lipd enzymes. Taken together, the function of PEGylation that serves as a protective shell was definite, especially in reducing the binding of free mucin and inhibiting the lipolysis of lipids by digestive enzymes.In the fourth chapter, the pharmacokinetics of FN-PLNs was studied in rats by gavage with FN-CLNs as a reference. The relative bioavailability of FN-PLNs was calculated by contrast with the commercial preparation(Lipanthyl® capsules). The results showed that the bioavailability of FN-PLNs and FN-CLNs were up to 157.0% and 123.9%, respectively, relative to Lipanthyl® capsules. The area under blood drug concentration versus time of FN-PLNs(AUC0–t=51.04 μg·h/m L) was significantly higher than those of FN-CLNs(AUC0–t=41.19 μg·h/m L) and Lipanthyl®(AUC0–t=32.52 μg·h/m L), suggesting that PEGylation of FN-loaded lipid nanoparticles can further enhance the oral bioavailability of FN. The in vitro and in vivo correlation of drug release and its absorption was also analyzed, reaching a conclusion that PEGylation of lipid nanoparticles is able to reduce the capture by GI free mucins and inhibit lipolysis of lipid nanoparticles by masking the approach of digestive enzymes, thereby improving the overall bioavailability of BCS II drugs.This study presented a better understanding of lipid nanocarriers in the body’s disposition process. When lipid nanoparticles were PEGylated, they can reduce the binding of free mucin and retard the lipolysis of lipids used in the formulation, thereby preserving the structure of nanoparticles that is favorable to enhance the oral bioavailability of drugs. This study gave a forward investigation on the effect of PEGylation of lipid nanoparticles on the oral absorption of poorly water-soluble drugs. The pharmacokinetic results also lent a strong support that PEGylation of lipid nanoparticles are provided with great potential in enhancement of oral absorption for BCSII drugs. Our findings will provide a valuable reference for design and development of poorly water-soluble drugs.