Preparation And Characterization Of Solid Lipid Nanoparticles Containing Hydrophilic Peptide

In recent years, many new pharmaceutically active polypeptides have been developed due to the progress of biotechnological techniques and genetic engineering. These new therapeutic biomolecules are usually characterized by large size, short plasma half-life, limited ability to cross cell membranes, and frequent injection of drug over a long therapeutic period are generally required when they are used to treat disease. Therefore, the design of a new dosage form leading to prolonged release should be suitable to overcome such a practical disadvantage.Solid lipid nanoparticles (SLN) are colloidal carrier system for controlled drug delivery and followed by the development of emulsion, liposomes, microparticles and nanoparticles based on synthetic polymers. They combine advantages of ernulsions, liposomes and polymeric nanoparticles. Identical to polymeric nanoparticles, their solid matrix protects incorporated active ingredients against chemical degradation and provides the highest flexibilities in the modulation of the drug release profiles. Similar to emulsions and liposomes, they are composedof well physiologically tolerated excipients and can be produced on large industrial scale by high pressure homogenization.Solid lipid nanoparticles (SLN) are a biodegradable particulate drug delivery system. Compared to other particulate carriers the SLN has more advantages for drug delivery system, such as a good tolerability and biodegradation, a high bioavailability by ocular administration, a targeting effect on brain. In recent years, the study on SLN has markedly increased, especially with the method of high pressure homogenization. Due to the lipophilic material of SLN, only a few investigations have been studied regarding the incorporation of peptides into SLN and few research has been reported the drug release from peptide-loaded SLN.The present study prepared several stable SLN using different kinds of lipids. Monostearin SLN were prepared by solvent diffusion method in aqueous system. The hydrophilic model drugs were incorporated to study the recovery of nanoparticles, entrapment efficacy, zeta potential (charge) and drug delivery characterization. lipid A-lipid B-lipid C SLN was prepared by the same solvent diffusion technique and the compound was successfully formulated into nanoparticles by solvent diffusion method. The recovery of nanoparticles, entrapment efficacy, zeta potential (charge) and drug delivery characterization were studied. The optimal cryoprotectant was selected by freeze-thaw test and reconstitution of the lyophilized products. The relative bioavailability of the INS-SLN given by gavage was studied with a commercially available INSsolution product as a reference formulation.Monostearin solid lipid nanoparticles were quickly prepared by a novel solventdiffusion method in aqueous system. The SLN were monodispersed spheres. The number mean diameter and the volume mean diameter were 400.1 run and 403.2 nm, respectively. SLN could be separated completely by centrifuge of 22,000 rmin"1 at the condition of the acidic dispersed aqueous medium with pH 1.10. Atthis time, the zeta potential value of drug loaded SLN is approached zero and forming aggregation of SLN. As DSC measurement with powdered SLN, we found that the endothermic peak presented at the same temperature point as the original drug crystal. It means that the original drug crystal lattice is forming after preparation. Up to 69.4% of drug can be incorporated. In vitro release of drug from SLN is slow. In the test solution of a pH6.8 phosphate buffer, the drug-release behavior from SLN suspension exhibited a biphasic pattern. After burst release at the first 2 h at a percentage of 13.3% of loaded drug, a distinctly prolonged release over a monitored period of 14 days was observed and nearly 3.97% drug was released in each day. These findings indicated that the internal structure of the SLN was a polymeric lipid matrix. As some drug adsorbed on the surface of nanoparticles, the dissolution profile of the SLN exhibited a burst of drug during initial stage. During the later stage, the drug release rate was determined by the diffusion of drug from the rigid matrix structure.PEG2000-monostearin SLNs were prepared by solvent diffusion method too. When the percentage of PEG2000 in preparation is 10%, the particles prepared under the acidic condition exhibited bimodal particle size distribution, with a number mean diameter of 141.0nm (83.7%) and 416.5 run (16.3%), respectively. And the volume mean diameter is 142.6nm (24.1%) and 415.3nm (75.9%), respectively. The amount of salbutamol sulfate incorporated into SLN is also correlated with the percentage of PEG2000 (w/w) in the organic phase during the preparation process and decreased with an increasing proportion of PEG2000 in the organic phase, which is attributed to PEG2000 increased leakage of hydrophilic drug into the outer aqueous phase. Since PEG2000 is a significant hydrophilic component of the carrier system, this modification also led to a reduction in entrapment efficiency, varying from 41.1% to 33.6 %, when the percentage of PEG2000 in the resultant organic preparation solution went from0% to 30% (w/w). Drug release from PEG2000-modified SLN was faster. After modification of the SLN matrix with PEG2000, e.g. when 30% (w/w) of PEG2000 was present in the organic phase, nearly 100% of the drug was released from SLN in only 5 days, following the similar biphasic pattern as with monosteann SLN. These results demonstrate that modification with PEG2000 can accelerate release of hydrophilic drugs from SLN.When the SLN were modified by 5% lipid C in preparation, the particles exhibited bimodal particle size distribution. The number mean diameters are 102.6 nm (95.7%) and 413.6 nm (4.3%), respectively. And the volume mean diameters are 137.7 nm (28.6%) and 415.3 nm (71.4%), respectively. When the percentage of lipid C in preparation was up to 10%, the size of SLN was decreased. The average entrapment efficiency of monostearin-SLN is 33.6%. Lipid C modification led to the increasing in entrapment efficiency, varying from 33.6% to 90.5 %, when the percentage of lipid C in the resultant organic preparation solution went from 0% to 20% (w/w). The improved drug encapsulation efficiency or loading capacity and faster drug release rate were observed by increasing the amount of liquid lipid SLN loaded. Results confirmed that, the improved drug loading capacity of SLN was related with their crystal order disturbance by liquid lipid.In vitro release of drug from SLN modified by lipid C in preparation was faster than monostearin-SLN. In the test solution of a phosphate buffer, the drug-release behavior from SLN suspension exhibited a triphasic pattern. After burst drug release at the first 12 hours, which was concerned with the percentage of lipid C in preparation, a distinctly prolonged release was observed, which had nothing to do with the percentage of lipid C in preparation. For example the model drug insulin was incorporated in monostearin-SLN. When the percentage of lipid C inthe resultant organic preparation solution was 0% (w/w), after burst release at the first 1 hour at a percentage of 37.2% of loaded drug, a diffusion controlled release at the next 12 hour a percentage of 82.7% of loaded drug. After 12 hours, the release rate of drug was slowing over a monitored period of 24 hours. When the percentage of lipid C in the resultant organic preparation solution was up to 20% (w/w), after burst release at the first 4 hours at a percentage of 90.3 % of loaded drug, the release rate of drug was slowing over a monitored period of 24 hours.Increased drug loading capacity and controlled drug release properties of SLN were achieved by controlling the amount of liquid lipid added to the formulation. Further, a novel preparation method in the present research for peptide-loaded SLN was established. These results also demonstrate the principle suitability of SLN as a controlled release formulation for hydrophilic peptide drugs.