Nano Drug Delivery Systems For Enhancing Transdermal Delivery And Skin Targeting Of Drugs

Recently, the rapid development in transdermal drug delivery systems (TDDS) has been made in pharmaceutical science. TDDS are of advantage to reduce adverse side effects and to enhance therapy index and convenience for clinical uses. Much attention has been paid on transdermal delivery, topical delivery and dermal delivery in TDDS. The transdermal delivery of peptides and proteins with large molecular weights and skin targeting delivery of drugs for the therapy of skin diseases are attractive challenges in TDDS. Nano drug delivery systems (NDDS) are used to conquer these challenges due to the rapid development of nanotechnology.In this dissertation, the insulin-loaded nanovesicles were prepared, characterized and used to improve the permeation rates of insulin through skins with the enhancement of microneedle, iontophoresis or their combination. The change of blood glucose levels of diabetic rats were evaluated using in vivo animal experiments. The penetration mechanisms of insulin-loaded nanovesicles through skins were also explored using fluorescence imaging. In addition, podophyllotoxin-loaded hydrogel-thickened microemulsions (HTM) and solid lipid nanoparticles (SLN) were constructed and characterized. The dermal delivery of podophyllotoxin-loaded HTM and SLN was evaluated and their permeation mechanisms were also explored. Furthermore, Compritol 888 ATO was used to costruct novel HTM based on solid lipid for dermal delivery. The following are main results:(1) The nanovesicles were respectively prepared using high shear, ultrasound and high pressure homogenization methods. The nanovesicles with average diameters of 91.0 nm, 143.0 nm and 175.9 nm were constructed. The nanovesicles with zeta potentials of +27.8 mV, -25.3 mV and -50.5 mV were also prepared by modifying the surface charges of nanovesicles. The microstructures of nanovesicles were investigated by quantum dots (QDs)-based trace method and high resolution transmission electron microscopy (HR-TEM). The lipid membranes were found to have the thickness of 3～5 nm and insulin molecules distributed both inside and outside membranes. The entrapment efficiency of insulin-loaded nanoveiscles from Sephadex G25 column was (89.05±0.91)%. Insulin can passively penetrate through skins from nanovesicles at a low permeation rate of 0.19±0.01μg/(cm2·h).(2) The microneedles-pretreated microchannels could reduce the barrier of stratum corneum and increase the permeation rate of insulin from nanovesicles 86～166 times and the highest permeation rate was 31.68±0.79μg/(cm2·h). The permeation time lag ranged from 0.9 h to 1.2 h and the penetration accorded with Fick's first law of diffusion. The iontophoresis could also enhance the permeation rates of insulin from nanovesicles 3.9～4.3 times and the highest permeation rate was 0.97±0.05μg/(cm2·h). The microneedles had more powerful ability to enhance the permeation rates of insulin from nanovesicles when compared with iontophoresis. The permeation rates of insulin from nanovesicles combined with the microneedles or iontophoresis were 3.3～13.0 times higher than those from control solution and the nanovesicles significantly contributed to the permeation enhancement. Microneedles could enhance the diffusion coefficient of insulin in skins and nanovesicles could improve both diffusion coefficient and partition coefficient of insulin. The nanovesicles with positive charges had more powerful permeation ability when compared with those with negative charges, when microneedles or iontophoresis were used.(3) The penetration of insulin from nanovesicles enhanced by the combination of microneedles and iontophoresis followed with Fick's first law of diffusion and the permeation time lag ranged from 1.0 h to 1.3 h. The permeation rates of insulin were 60.23～106.99μg/(cm2·h), which were 3.9～7.0, 3.4～7.1, 92.5～134.9 and 359.6～713.3 times, respectively, when compared with those from control solution at passive diffusion, nanovesicles combined with microneedles alone, nanovesicles combined with iontophoresis alone and nanovesicles at passive diffusion. The combination of microneedles, iontophoresis and nanovesicles resulted in synergetic effects on the penetration of insulin (P<0.01). The synergetic effect could result in significant decrease of blood glucose levels (BGL) (P<0.01). The values of BGL at 3～6 h were 28.3～41.7% of initial values, which were comparable to those of rats administrated by subcutaneous injection and higher than that of the other groups. Fluorescence imaging showed that the synergetic effects of nanovesicles, microneedles and iontophoresis resulted in the enrichment of insulin in skins. Both the skin microchannels and stratum corneum showed high permeability for the penetration of insulin. The synergetic effect might attribute to several factors. The microneedle-pretreated skin microchannels acted as one of the main routes for insulin-loaded nanovesicles. The nanovesicles with charges propelled by iontophoresis could penetrate into deep skins along the microchannels and also lead to the enrichment of insulin in skins and reduce the barriers of stratum corneum. The high entrapment efficiency of nanovesicles could also improve the partition coefficient and avoid the charge reversal of insulin under the electric field of iontophoresis.(4) The podophyllotoxin-loaded hydrogel-thickened microemulsions (HTM) were constructed and characterized. The hydrogel have no significant influence on the microstructure of microemulsion and the permeation ability. The permeation rates of podophyllotoxin through skins increased with the increase of the accumulative amounts of drug in skin when the concentrations of Tween 80 were changed. The further studies should be performed for enhancing the skin targeting ability of HTM. In addition, podophyllotoxin-loaded solid lipid nanoparticles (SLN) were constructed using poloxamer 188 (P-SLN) and Tween 80 (T-SLN) as stabilizers. The average diameters of P-SLN and T-SLN were 73.4 nm and 123.1 nm, respectively. Atomic force microscopy and scanning electron microscopy showed that both SLN had spherical morphology and P-SLN had good physical stability. The in vitro permeation studies showed both P-SLN and T-SLN coult not penetrate through skins and avoid the systemic absorption of podophyllotoxin. But the tincture resulted in high permeation rates of podophyllotoxin. The accumulative amounts of podophyllotoxin from P-SLN and T-SLN in skins were 23.38±0.55μg and 6.82±0.34μg, respectively. Both SLN showed more powerful skin targeting than HTM. The fluorescence imaging found that P-SLN resulted in the local distribution of podophyllotoxin in epidermis and showed an epidermal targeting ability. The epidermal targeting might contribute to the penetration of SLN into stratum corneum and further change the partition coefficient besides their occlusive effects and sustained release.(5) The melt Compritol 888 ATO as an oily phase was used to construct a hot HTM. A novel HTM based on solid lipid (SHTM) were obtained by cooling the hot HTM at various temperature. The size distributions of SHTM obtained at the cooling temperature of -20℃and 5℃were 20～50 nm and 20～200 nm, respectively. SHTM obtained at -20℃had a narrow size distribution. But SHTM obtained at 5℃showed significant increases of diameters and broad size distribution because of possible coalescence between droplets during cooling. The in vitro permeation studies showed that SHTM could enhance the accumulative amounts of triptolide in skins, reduce the permeation rates and show a good skin targeting. The studies about microstructure, drug release and skin targeting of SHTM should be valuable in future.The results of this dissertation show that the penetration strategy of insulin-loaded nanovesicles enhanced by the combination of microneedles and iontophoresis would be significantly valuable for transdermal delivery of insulin and also be promising for transdermal delivery of the other peptides and proteins with large molecular weights. The research on the drug-loaded nanocarriers with skin targetings for the therapy of skin diseases affords a novel strategy in development of novel formulations with low toxicity and good curative effects.