Studies On The Oral Absorption Of Solid Lipid Nanoparticles Loading Saquinavir

In recent years, Solid Lipid Nanoparticles (SLNs) have been focused on as a new developed type of colloidal drug delivery systems. SLNs integrate the advantages of drug-containing microemulsions and liposomes, and can improve the bioavailability of drugs and physiological compatibility. Also the drug releasing can be controlled at the target site. The pharmacokinetics of a drug can be changed greatly when it is encapsulated into the nanoparticles for the controlled release of the drug from the nanoparticles and the change in the body distribution of the drug. In brief, SLNs, as an promising drug carrier for oral admnistration can effectively enhance the absorption and bioavailability of the loaded drug meanwhile lowering toxicity and side-effect of the drug for reduction of used dose.In this study, saquinavir, chosen as the model drug,was firstly mixed with phospholipid to form saquinavir-phospholipid complex by ionic interaction The solid lipid nanoparticles containing saquinavir (SQV-SLNs) with different polyethylene glycol (PEG) modification ratio were then prepared by the solvent diffusion method. The physiochemical properties such as particle size, morphology, drug encapsulation efficiency (EE%) and drug loading capacity (DL%) were described in the study In vivo release characteristics, pharmacokinetic behavior, bioavailability in rats and cellular transport behaviour across the intestinal epithelial cell were also studied in details.The resultant saquinavir-phospholipid complex was confirmed using Differential Scanning(DSC). The DSC results showed that saquinavir and phospholipids (1:1.5 m:m) had successfully mixed through combination of ionic bonds. The number average diameter of obtained SQV-SLNs and pSLNs in suspension was determined with Zetasizer and transmission electron microscopy (TEM). The results indicated that the number average diameter of SQV-SLNs was about 275 nm. And the incorporation of PEG2000-SA led to the formation of spherical nanoparticles with smallerparticle size. The number average diameter of pSLNs-10% was about 158 nm. EE% and DL% showed that the higher drug encapsulation efficiencies were achieved for water soluble drug, saquinavir using the preparation method combined ionic complex with solvent diffusion method, which were above 95%. SQV-SLNs gained the highest drug encapsulation efficiency, which was about 99.19%, and the drug encapsulation efficiency slightly decreased with increasing content of PEG2000-SA. The drug encapsulation efficiency of pSLNs-10% was about 95.23%. Moreover, the drug loading capacities were above 19%, which is much higher than that of conventional SLNs. In vitro drug release from SLNs was further measured by the dialysis bag method. It was clear that the saquinavir release behaviours from SQV-SLNs, pSLNs-5% and pSLNs-10% were slower than that of the diffusion for saquinavir from the dialysis bag.The pharmacokinetic study was also performed using male SD rats. Saquinavir content was determined by HPLC method. The key pharmacokinetic parameters obtained by a noncompartmental analysis after the oral administration of saquinavir suspension, SQV-SLNs, pSLNs-5% and pSLNs-10%. It was obviously the Cmax (peak plasma saquinavir concentration) and MRT (the mean residence time) were highly improved when the drug was encapsulated into SLNs, and which were significantly enhanced with increased PEG2000-SA content in SLNs. Comparing with saquinavir suspension, the Cmax of pSLNs-10% was increased by 24.52-fold, and the MRT0-t increased from 4.62 h to 51.68 h. The AUC and relative bioavailability of saquinavir was enhanced near 1-fold, however, which were highly improved by the PEGylation of SLNs.The relative bioavailability of saquinavir for pSLNs-10% was 101.15-fold higher than that of saquinavir suspension. The higher PEG2000-SA content led to the longer residence time and the higher AUC and relative bioavailability, which improved the transport efficiency across the gastrointestinal tract and prolonged blood circulation times by PEGylation.To illustrate that the oral bioavailability and improvement of the biological effect of saquinavir could be significantly increased by SLNs and pSLNs, the transport experiments of SLNs and pSLNs were conducted using madin-daby canine kidney (MDCK) cell as a model intestinal epithelial cell line. The cytotoxicity of saquinavir-loaded nanoparticles were determined by MTT assay. After drug loading, the nanoparticles indicated slight cytotoxicity, and the pSLNs showed less toxicity than that of SLNs. The 50% inhibition concentration (IC50) of SLNs can be calculated at 269.02 μg/mL, while the IC50 of pSLNs-5% and pSLNs-10% were 549.25 μg/mL and 550.47 μg/mL, respectively. The cytotoxicity was decreased with the increased ratio of PEG in SLNs. To investigate the transport efficacy of the nanoparticle across intestinal epithelial cell, the permeation properties of drug-loaded SLNs were evaluated by comparing SQV-SLNs, pSLNs-5% and pSLNs-10% with saquinavir solution in MDCK cell monolayers. The content of saquinavir was detected by HPLC. All of SLNs, pSLNs-5% and pSLNs-10% showed significantly higher drug permeation compared with saquinavir solution (0.09×10-5cm/s), whose were 0.18×10-5cm/s, 0.38×10-5cm/s,0.40×10-5cm/s. Furthermore, the drug transport ability across intestinal epithelial cell monolayer enhanced with increasing the PEG2000-SA content in SLNs. The increased cellular uptake ability due to increasing ratio of PEG was possibly because that the pSLNs had smaller sizes. It has been proven that a small particle size contributed to endocytosis. Result also demonstrated that the transport ability across intestinal epithelial cell monolayer of nanoparticles was increased by increasing the amount of PEG fraction on nanoparticles surface, which could improve the hydrophilicity of SLNs.The solid lipid nanoparticles loading saquinavir were successfully prepared using the combination of ionic complex and solvent diffusion method in an aqueous system, which had high drug encapsulation efficiencies and drug loading capacites. The higher PEG2000-SA content in SLNs led to smaller particle sizes, faster drug release behavior in initial stage, stronger cellular uptake and transport ability across intestinal epithelial cell monolayer, longer in vivo residence time, and higher relative bioavailability. These properties suggested that the PEGylated solid lipid nanoparticles loading saquinavir can be a new promising oral anti-HIV drug delivery system.