| Transdermal drug delivery system (TDDS) refers to the system that delivery drug in a controlled rate to the systemic circulation through the skin. Since the first transdermal patch containing scopolamine was introduced in 1981, the TDDS has developed rapidly with the developments of drug sustained-release theory, material science of pressure sensitive adhesive, drug analysis science in vivo, biopharmaceutics and other related technologies. Now there are some effective methodologies are developed to enhance the drug transdermal delivery, for example, physical enhancing strategies of iontophoresis, electroporation, ultrasound, microneedle, photomechanical waves, and so on; chemical enhancers such as Azone and pharmacetucal strategies of microemulsion, liposome, nanoparticles and prodrugs etc.With the development of biological technology and genetic engineering, study and application of protein and polypeptide drugs have attracted a lot of interest. However, the poor stability, short biological half-life, existing in polymer form and being unable to oral administration of these drugs result in their lower bioavailability and limited applications. The basic administration ways of these drugs are injection. In order to reduce the patients'body burden, psychological burden and financial burden, researchers are searching for the non-invasive administration way, say non-injection administration way.Electret is a functional dielectric material that can keep space and dipole charge for a long time. Electret can be used as a physical methodology to enhance the drug transdermal delivery because the electret can produce constant electrostatic field and microcurrent to form transient permeable holes in intercellular stratum corneum (SC) lipids and to expand the hair follicles. As a safe and effective enhancing strategy, electret has both the functions of iontophoresis and electroporation in transdermal enhancement of ionic drugs due to the effect of microcurrent and electrostatic effect, which provide a broad area for application of ionic drugs and polypeptide drugs.Since 2010, the model drugs employed in electret trasdermal system has turn to those drugs with the molecular weight higher than 1000Da. Now the electret transdermal system using cyclosporin A (CsA) and insulin which have the molecular weights of 1202.63Da and 5807.69Da respectively are under study.In order to study the enhancing effect of electret on protein and peptide drug systemically, to study the combined effect of electret with chemical enhancers, to clarify the mechanism of electret on transdermal delivery, and to provide theory and experimental support in preparation of protein and peptide electret transdermal formulation, we used CsA as model drug, polypropylene (PP) as a material to prepare electrets using the corona charging method under different charging conditions. The charge storage stabilities of the electrets were studied by isothermal surface charge decay measurement. The individual and combied enhancing effect of electret and chemical enhancers (Azone, ethyl oleate and monoolein) were studied through in vitro transdermal experiment and high performance liquid chromatography (HPLC) analysis. The micro-morphology and the structure change of the skin after application of electret were studied using inverted microscope. The mechanism of the electret on drug transdermal delivery was also studied using open thermally stimulated discharge (TSD) and differential thermal analysis (DTA).The result of eletret charge stability study indicated that (1) the effective surface potential decayed exponentially. (2) The higher the grid voltage used in corona charging, the worse was the charge storage stability of the PP electret with no aluminium coated on both sides. (3) PP electret has excellent charge storage stability, fitting for transdermal study of CsA.The in vitro transdermal experiment using improved Franz diffusion cell and high performance liquid chromatography indicated that (1) +2000V electret and -1000V electret groups had higher 24 hours'accumulated penetration amount of CsA of 9.4083μg/cm2 and 9.2753μg/cm2 respectively which were 1.50 and 1.48 times that of the CsA solution (control group) accordingly. The steady penetration rates of the +2000V electret and -1000V electret were 0.5364μg/cm2?h and 0.4822μg/cm2?h respectively, which were 1.52 and 1.37 times that of the control group(Js=0.3529μg/cm2?h), indicating that electret could enhance the transdermal delivery of CsA. (2) As compared with control group, the steady penetration rates of CsA for grouops of 1% Azone, 3% Azone and 5% Azone, 10% monoolein, and 10% ethyl oleate were 6.72, 2.11, 1.43, 7.735 and 14.55 that of the control group (P<0.05), ranged in order of 10% ethyl oleate > 10% monoolein> 1% Azone > 3% Azone > 5% Azone. The 24 hours'accumulated penetration amount were ranged in order of 10% ethyl oleate > 1% Azone > 10% monoolein > 3% Azone > 5% Azone. (3) The study of synergetic effect of electret with chemical enhancers indicated that combination of 10% monoolein with±500V electret and 10% ethyl oleate with±2000V electret showed excellent enhancing effects with a enhancement ratio of 8.87 and 19.59 as compared with control group. The enhancing abilities of these combined group were ranged in order of±2000V electret +10% ethyl oleate >±500V electret +10% monoolein (P<0.05). In addition, with the 19.59 enhancement ratio of±2000V electret +10% ethyl oleate group had a significant increase as compared with a 14.55 enhancement ratio of the 10% ethyl oleate (P<0.05), indicting a better synergetic effect of 10% ethyl oleate with±2000V electret on CsA transdermal delivery while electret had not with different concentrations of Azone.On basis of the in vitro transdermal study, we use inverted microscope to study the micro-morphology and the structure change of the skin after application of electret, and we use TSD and DTA to study the mechanism of the electret on transdermal enhancement. The inverted microscope observation showed that the microscopic structure of the rat skin changed after application of electret with the surface potentials of -1000V and 1000V in the action time of 2h to 16h. The SC become thinner, the inter-connection of the SC was loosed, and the outer layer of the SC detached. The change degree of the microscopic structure of the SC increased with the increase of electret action time. Electret could enhance the drug transdermal delivery by altering the barrier function of the skin, increase the permeability of the skin and drug penetration rate. The results of TSD studies showed that -500V electret could change the arrangement and fluidity of SC lipid and the space structure of protein, regulate the skin electret state, which decreased the barrier function of the skin and opened a certain transdermal route for easy drug penetration. The results of DTA studies indicated that±500V,±1000V and±2000V electrets could change the lipid structure from gel to liquid crystal to increase the fluidity and collaboration of the lipids, cause the attenuation and alteration of space conformation of the protein from right-handed helix to vertical stretching and parallel alignment which opened penetration route for drug transdermal delivery. Therefore, the microstructure studies of the skin indicated that negative electret had better biological effect than positive electret, especially for those eletrets with the surface potentials in a range of -500V to -1000V, And - 500V electret had the more outstanding comprehensive regulation effect in rat skin structure. As the protein regulation concerned, electrets with the surface potentials of 1000V to 2000V exhibited better action effects. In summary, electret had a"potential window"effect on change of the microscopic structure of the skin.In this study we first observed the transdermal behaviours of CsA after application of electrets with different polarity or voltage, application of different chemical enhancers and combined application of electret and chemical enhancer. The electret and chemical enhancer showed a better synergetic effect on CsA transdermal delivery. The studies of inverted microscope and thermal analysis technology confirmed further the influence of electret in skin microscopic structure and electret status, which supported the enhancing effect of electret on CsA transdermal delivery. We could indicate that electret had excellent effect on transdermal enhancement and could be used to prepare the transdermal formulation for protein and peptides.The study was supported by Nature Science Foundation of China (No.:50977089, 2010-2012), Nature Science Foundation of Shanghai (No.: 10ZR1437600, 2010-2011)and the"Eleven-Five-Year"International Collaboration Project of PLA (No. : 06H022, 1996-2010).
|
PDF Full Text Request