Transdermal delivery of insulin using trypsin as a biochemical enhancer

Trypsin has been extensively used in laboratory settings for in vitro epidermal separation and keratinocyte isolation for over 50 years. The aim of this study was to assess the enhancing effect of trypsin on the transdermal delivery of insulin by applying its specific biochemical properties to react with the stratum corneum (SC) of skin. Bovine insulin was used as a model peptide to investigate in vitro permeation through rat skin and in vivo hypoglycemic effects of bovine insulin with or without the trypsin pretreatment. Trypsin significantly increased the transdermal permeability of bovine insulin in pH 3.0 solution, but no effect was observed in pH 6.0 solution. The permeation flux of bovine insulin from pH 3.0 solution was promoted 5.2-fold with 0.25% trypsin pretreatment when compared with the control. The enhancement of trypsin was dependent on the concentration in the range of 0.5-2.5%. Furthermore, with trypsin pretreatment, the plasma glucose level was reduced to less than 60% of the initial value after 8 h of in vivo permeation of bovine insulin with pH 3.0 solution, but did not return to the initial value during an 8-h experiment. Mechanistic studies with Fourier transform-infrared and attenuated total reflectance analysis and electrical resistance measurements suggest that trypsin alters the SC protein structure from the alpha- to the beta-form and decreases the electrical resistance of skin, thereby decreasing the SC barrier and enhancing the permeation of insulin. We conclude that trypsin would be effective as a biochemical enhancer for the transdermal delivery of peptide and protein drugs such as insulin.     

Effects of pretreatment of needle puncture and sandpaper abrasion on the in vitro skin permeation of fluorescein isothiocyanate (FITC)-dextran

Microneedle systems have gained attention as having many advantages over transdermal patches and hypodermic needles. The procedure provides adequate skin permeation rates without pain or severe infection. To obtain information for designing a microneedle system, macroneedles were used instead of microneedles to investigate the effects of pretreatment of needle puncture in the skin barrier stratum corneum on in vitro skin permeation of fluorescein isothiocyanate (FITC)-dextrans (4.3, 9.6 and 42.0 kDa) (FD-4, FD-10 and FD-40). The effect of sandpaper abrasion was also investigated for comparison. Both pretreatments on the skin barrier significantly increased the skin permeation of FDs. Lactate dehydrogenase (LDH) leaching was measured after pretreatment of macroneedle and sandpaper abrasion on the skin to evaluate the skin damage by these pretreatment methods. Lower leaching of LDH was observed after macroneedle puncture than after sandpaper abrasion. Next, a parallel permeation-resistance model of the skin barrier was established. Skin permeation of FD-10 was predicted by the model as a function of the number of pores in the skin barrier. Our results suggest that needle puncture may provide a safe, efficient and controllable alternative for increasing transdermal drug delivery.     

Enhanced transdermal delivery of triprolidine from the ethylene-vinyl acetate matrix.

Triprolidine-containing matrix was fabricated with ethylene-vinyl acetate (EVA) copolymer to control the release of the drug. The permeation rate of triprolidine in the stripped skin was greatly larger than that in the whole skin. Thus it showed that the stratum corneum acts as a barrier of skin permeation. The effect of penetration enhancer and stripping of skin on the permeation of triprolidine through the excised mouse skin was studied. Penetrating enhancers showed increased flux probably due to the enhancing effect on the skin barrier, the stratum corneum. Among enhancers used such as glycols, fatty acids and non-ionic surfactants, polyoxyethylene-2-oleyl ether showed the best enhancement. The permeability of triprolidine was markedly increased with stripping of the mouse skin to remove the stratum corneum that acts as a barrier of skin permeation. For the controlling transdermal delivery of triprolidine, the application of EVA membrane containing permeation enhancer could be useful in the development of transdermal drug delivery system.     

Bioequivalence of marketed transdermal delivery systems for tulobuterol

Tulobuterol permeation through skin from various transdermal delivery systems has been compared for the bioequivalence among devices marketed. Both the permeation profiles across the hairless mouse skin and the release profiles from the devices were measured under well-controlled in vitro conditions. The release rate of the drug from the devices was appreciably higher than the penetration rate across the intact skin, indicating the skin-controlled delivery systems. However the deviation between the release rate and the permeation rate differs depending upon the system design. The brand patch showed the least difference between the release and permeation profiles among the brand and three generic devices examined. From the in vitro permeation profiles for both intact and stripped skins, the diffusion coefficient and the partition coefficient were evaluated on the basis of bi-layer skin model. The effect of the stratum corneum thickness was then simulated by SKIN-CAD. The simulated profile has suggested that the clinical performance for transdermal tulobuterol delivery is influenced not only by the thickness of the stratum corneum but by the device design as well. This is particularly the case for the stratum corneum, thinner than about 10 microm or damaged skin with the decreased barrier capacity. For the stratum corneum thicker than 20 microm, on the other hand, the clinical performance may not be significantly influenced by the device designs investigated in this study.     

Strategies for overcoming the stratum corneum

Transdermal drug delivery has many advantages over the oral administration of drugs. This is the reason why many researchers have extensively investigated the transdermal absorption of drugs. However, a much smaller number of drugs are marketed using this route of delivery, compared to oral dosage forms, because drug absorption across the skin is very low due to the stratum corneum (the main barrier for drug absorption across the skin). Overcoming the penetration barrier would significantly improve the development of an efficient transdermal drug delivery system. Several techniques have been developed, or are under development, to bypass the stratum corneum. Approaches that have been made to overcome the stratum corneum fit into five different categories: (i) device and formulation; (ii) modification of stratum corneum by chemical enhancers; (iii) ablation; (iv) bypassing the stratum corneum via appendages; and (v) electrically assisted methods such as iontophoresis and electroporation. Furthermore, possible combinatorial uses of several approaches have been studied. Although the safety issues of these synergistic approaches still require clarification, several combinations could be promising. Finally, there is a necessity to regulate the intradermal disposition of drugs to develop a more efficient transdermal drug delivery system after overcoming the skin barrier.     

长春西汀透皮贴剂的研制及体外释药机理的探讨

目的:制备长春西汀透皮贴剂,研究其体外释药机理.方法:在单层贴剂优化处方的基础上制备了单层、双层和三层贴剂,比较不同类型贴剂经不同皮肤的体外渗透速率,对三层贴剂进行了质量考察并研究了其释药机理.结果:三层贴剂和双层贴剂的经皮渗透量大于单层贴剂.去除角质层的皮肤对药物经皮渗透的屏障作用明显小于完整皮肤. 结论:长春西汀贴剂质量可控,刺激性小,药物经皮吸收的主要屏障为角质层,在经皮渗透中有较微弱的储库效应,其渗透行为主要是零级释药模式.     

Stratum corneum permeation and percutaneous drug delivery of hydrophilic molecules enhanced by cryopneumatic and photopneumatic technologies

Novel cryopneumatic technology (CPx) and photopneumatic technology (PPx) have been developed to enhance the permeation of the stratum corneum (SC) and percutaneous drug delivery (PDD). CPx produces micro-cracks at the skin surface by successively freezing and stretching the skin with vacuum suction. PPx combines stretching of the skin by vacuum suction with intense pulsed light. The enhancing effects of CPx and PPx were studied on ex vivo porcine skin and in vivo human skin models. Fluorescent hydrophilic macromolecules (FITC and FITC-Dextran) were used as drug surrogates. Fluorescent images of in vivo experiments show that the enhancing effect of CPx is due to drug permeation through the micro-cracks produced by freezing stretching cycles, while PPx could promote drug permeation through sweat glands. Both ex vivo and in vivo results strongly suggest that CPx and PPx can effectively enhance the permeation of the SC and PDD for the delivery of hydrophilic macromolecules.     

Sustained and targeted delivery of an anti-HIV agent using elastic liposomal formulation: mechanism of action

The present study is aimed at evaluating the transdermal route as an alternative to the oral route for improving the systemic bioavailability and sustaining the constant therapeutic plasma level of Zidovudine (AZT). Elastic liposomal formulations of AZT were prepared and characterized. The effect of different formulation variables on transdermal delivery of AZT from elastic liposomes was studied. To investigate the mechanism of skin permeation of elastic liposomes, Transmission Electron Microscopic (TEM) study was carried out. The optimized elastic liposomal formulation showed transdermal flux of 98.8+/-5.8 microg/cm2/hr across rat skin as compared to 5.72+/-0.3 microg/cm2/hr for free drug. Vesicle-skin interaction study showed that elastic vesicles influenced the ultra structure of stratum corneum. Distinct regions with lamellar stacks derived from vesicles were observed in intercellular spaces of the stratum corneum. These stacks disrupted the organization of skin bilayers leading to increased skin permeability, whereas no changes were observed in the underlying viable epidermis and dermis. Improved pharmacokinetic profile was observed when AZT was entrapped in elastic liposomes. The AUC0-24h for elastic liposomal formulation was found to be (12.63+/-1.2 microg h/mL), nearly twelve fold higher than the control (0.83+/-0.2 microg h/mL). Furthermore, the administration of elastic liposome encapsulated AZT resulted in substantially higher accumulation of AZT in target RES organs that play a key role in the pathogenesis of AIDS by providing long-term reservoir for the virus. The results of the present study demonstrated that elastic liposomes increased the transdermal flux, prolonged the release, improved the site specificity of AZT and represented an attractive strategy for sustained and targeted delivery of AZT.     

Transdermal Controlled Delivery of Propranolol from a Multilaminate Adhesive Device

The feasibility of transdermal controlled delivery of propranolol was investigated by conducting in vitro skin permeation studies using rabbit pinna (ear) skin. A new multilaminate adhesive device which is capable of releasing propranolol in a controlled fashion over a 24-hr period had been developed and was evaluated transdermally using rabbit pinna skin. Skin permeation of propranolol from the device was found to be controlled by the stratum corneum during the early phase of permeation and then by the adhesive device during steady-state permeation. The rabbit pinna skin was shown to be a good animal model for studying the transdermal permeation of propranolol from the device, when compared to human cadaver skin.     

Enhanced transdermal delivery of atenolol from the ethylene-vinyl acetate matrix

To enhance transdermal delivery of atenolol, ethylene-vinyl acetate (EVA) matrix of drug containing penetration enhancer was fabricated. Effect of penetration enhancer on the permeation of atenolol through the excised rat skin was studied. Penetrating enhancers showed the increased flux probably due to the enhancing effect on the skin barrier, the stratum corneum. Among enhancers used such as glycols, fatty acids and non-ionic surfactants, polyoxyethylene 2-oleyl ether showed the best enhancement. For the controlling transdermal delivery of atenolol, the application of EVA matrix containing permeation enhancer could be useful in the development of transdermal drug delivery system.     

Microneedles and transdermal applications

With the limitations of oral drug delivery and the pain and needle phobias associated with traditional injections, drug delivery research has focused on the transdermal delivery route. A formidable barrier to transdermal drug delivery is the stratum corneum, the superficial layer of the skin. In the last 10 years, microneedles were proposed as a mechanical tool to pierce through the stratum corneum, in order to create drug delivery channels without stimulating underlying pain nerves. Since then, the field of microneedles has rapidly evolved to spawn a plethora of potential transdermal applications. In this review, the authors provide an overview of the progress in microneedle research and design, and the advancements that have been made in employing this technology for transdermal applications.     

Transdermal Delivery of Molecules is Limited by Full Epidermis, Not Just Stratum Corneum

Purpose

Most methods to increase transdermal drug delivery focus on increasing stratum corneum permeability, without addressing the need to increase permeability of viable epidermis. Here, we assess the hypothesis that viable epidermis offers a significant permeability barrier that becomes rate limiting upon sufficient permeabilization of stratum corneum.

Methods

We tested this hypothesis by using calibrated microdermabrasion to selectively remove stratum corneum or full epidermis in pig and human skin, and then measuring skin permeability to a small molecule (sulforhodamine) and macromolecules (bovine serum albumin, insulin, inactivated influenza vaccine) in vitro.

Results

We found that removal of stratum corneum dramatically increased skin permeability to all compounds tested. However, removal of full epidermis increased skin permeability by another 1–2 orders of magnitude. We also studied the effects of removing skin tissue only from localized spots on the skin surface by covering skin with a mask containing 125-μm holes during tissue removal. Skin permeabilized in this less-invasive way showed similar results. This suggests that microdermabrasion of skin using a mask may provide an effective way to increase skin permeability.

Conclusions

We conclude that viable epidermis offers a significant permeability barrier that becomes rate limiting upon removal of stratum corneum.     

Touch-actuated microneedle array patch for closed-loop transdermal drug delivery

To date, only approximately 20 drugs synthesized with small molecules have been approved by the FDA for use in traditional transdermal patches (TTP) owing to the extremely low permeation rate of the skin barrier for macromolecular drugs. A novel touch-actuated microneedle array patch (TMAP) was developed for transdermal delivery of liquid macromolecular drugs. TMAP is a combination of a typical TTP and a solid microneedle array (MA). High doses of liquid drug formulations, especially heat-sensitive compounds can be easily filled and stored in the drug reservoir of TMAPs. TMAP can easily penetrate the skin and automatically retract from it to create microchannels through the stratum corneum (SC) layer using touch-actuated ‘press and release’ actions for passive permeation of liquid drugs. Comparison of subcutaneous injection, TTP, solid MA, and dissolvable MA, indicated that insulin-loaded TMAP exhibited the best hypoglycemic effect on type 1 diabetic rats. A ‘closed-loop’ permeation control was also provided for on-demand insulin delivery based on feedback of blood glucose levels (BGLs). Twenty IU-insulin-loaded TMAP maintained the type 1 diabetic rats in a normoglycemic state for approximately 11.63?h, the longest therapeutic duration among all previously reported results on microneedle-based transdermal patches. TMAP possesses excellent transdermal drug delivery capabilities.     

Novel reverse electrodialysis-driven iontophoretic system for topical and transdermal delivery of poorly permeable therapeutic agents

Topical and transdermal drug delivery has great potential in non-invasive and non-oral administration of poorly bioavailable therapeutic agents. However, due to the barrier function of the stratum corneum, the drugs that can be clinically feasible candidates for topical and transdermal delivery have been limited to small-sized lipophilic molecules. Previously, we fabricated a novel iontophoretic system using reverse electrodialysis (RED) technology (RED system). However, no study has demonstrated its utility in topical and/or transdermal delivery of poorly permeable therapeutic agents. In this study, we report the topical delivery of fluorescein isothiocyanate (FITC)–hyaluronic acid (FITC–HA) and vitamin C and the transdermal delivery of lopinavir using our newly developed RED system in the in vitro hairless mouse skin and in vivo Sprague–Dawley rat models. The RED system significantly enhanced the efficiency of topical HA and vitamin C and transdermal lopinavir delivery. Moreover, the efficiency and safety of transdermal delivery using the RED system were comparable with those of a commercial ketoprofen patch formulation. Thus, the RED system can be a potential topical and transdermal delivery system for various poorly bioavailable pharmaceuticals including HA, vitamin C, and lopinavir.     

Changes in electrophysiological properties of rat skin with age

The age-related changes in the electrical and physiological properties of the skin were examined in rats at the ages of 5, 10, 21, 90, and 180 d. The resistance of the stratum corneum, the resistance of the viable skin (epidermis and dermis), and the capacitance of the stratum corneum were analyzed from skin impedance data using an equivalent circuit. With development and aging, the resistance of the stratum corneum and the viable skin increased, whereas the capacitance of the stratum corneum decreased. Physiological characteristics such as the thickness of skin strata and the content of lipid and water in the stratum corneum were also measured. The lipid content in the stratum corneum was constant at all ages. The water content in the stratum corneum decreased, and the thickness of skin strata increased with age. Comparison between electrical data and physiological properties suggested that the increase in the resistance of the stratum corneum with aging is primarily caused by the decrease in the water content and that the capacitance of the stratum corneum and the resistance of the viable skin depend on age-related increases in the thickness of skin strata. In conclusion, the age dependency of cutaneous electrical properties may affect the permeation profile of drugs through the skin, and impedance analysis can be used to estimate age-related changes in transdermal drug delivery.     

Enhanced transdermal delivery of loratadine from the EVA matrix

Various enhancers, such as fatty acids (saturated, unsaturated), glycerides, propylene glycols, and non-ionic surfactants, have been incorporated in the loratadine-EVA matrix to increase the rate of skin permeation of loratadine from an EVA matrix. The enhancing effects of these enhancers on the skin permeation of loratadine were evaluated using a modified Keshary-Chien cell fitted with intact excised rat skin. The penetration enhancers showed a higher flux, probably due to the enhancing effect on the skin barrier, the stratum corneum. Among the enhancers used, such as the fatty acids, glycols, propylene glycols, and non-ionic surfactants, linoleic acid showed the best enhancement. For the enhanced transdermal delivery of loratadine, application of an EVA matrix containing a permeation enhancer might be useful in the development of a transdermal drug delivery system.     

Prodrug strategy for enhancing drug delivery via skin

Skin as a route for drug delivery has been extensively investigated. However, because of the predominant barrier function of stratum corneum in skin, the clinical application is limited. One strategy to solve this problem of drug permeation via skin is the use of prodrugs. Prodrugs are inactive compounds which are metabolized either chemically or enzymatically in a controlled or predictable manner to its parent active drug. Prodrugs can enhance dermal/transdermal drug delivery via different mechanisms, including increased skin partitioning, increased aqueous solubility, and reduced crystallization, etc. Besides the prodrug itself, the optimization of vehicle is important as well. The prodrug partitioning between skin and vehicle as well as prodrug-vehicle interaction may influence the enhancing efficacy on skin permeation. This review explores the synthesis and enhancing mechanisms of prodrugs for topical drug delivery. The prodrugs categorized by the therapeutic use of the parent drugs, including anticancer drugs, analgesics, anti-inflammatory drugs and vitamins, are systemically introduced in this review.     

盐酸尼卡地平贴剂的制备及体外透皮释药

目的：制备盐酸尼卡地平透皮贴剂,研究其释药影响因素。方法：利用Ｆｒａｎｚ扩散池,进行离体皮肤体外渗透实验,通过改变皮肤的状态,研究其体外透皮释药。结果：盐酸尼卡地平贴剂中药物的渗透可用Ｈｉｇｕｃｈｉ方程来表达,去除角质层皮肤的药物渗透远大于完整皮肤,而完整皮肤的贮库效应大于去角质层皮肤。结论：盐酸尼卡地平在经皮渗透过程中存在贮库效应,渗透的主要屏障为角质层。     

Skin permeation of ketotifen applied from stick-type formulation.

A stick-typed long lasting device for both transdermal and topical drug delivery has been developed. Ketotifen fumarate (KT) was used as a model drug. The effect of a variety of permeation enhancers was investigated using hairless mouse skin in vitro. Polyoxyethylene oleyl ether (POE), among the enhancers used, most enhanced the skin permeation of KT. The permeation enhancement was mainly due to the increase in the drug solubility in the stratum corneum and the resulting increase in the partition coefficient. The rate of skin permeation of KT was approximately proportional to the loading dose of the drug.     

新型经皮传递胰岛素透明质酸微针制剂的制备及性能考察

目的证明透明质酸微针制剂在药物经皮传递系统方面的应用前景。方法通过皮肤及微针的显微照片考察微针刺入皮肤的性能和在大鼠体内的溶解性能;用皮肤刺激性实验评价透明质酸微针的安全性;以人的离体皮肤为透皮释药模型,通过体外经皮通透实验考察微针对模型药物胰岛素经皮吸收的促进作用。结果微针能够均匀刺穿角质层,在皮肤表面产生与微针一致的阵列形状,在皮肤断面可观察到直至真皮层的通道;在大鼠体内使用1 h后,针体能够完全溶解,皮肤刺激性指数为1.7,属于轻度刺激性;体外经皮实验中,微针中的胰岛素能够以活性形式释放,与同剂量的溶液相比,微针对胰岛素的体外经皮吸收具有显著的促进作用,稳态通透速率达75.33×10-6U.cm-2.h-1。结论以透明质酸为基质制备的微针具有良好的皮肤刺入性、溶解性和轻度的刺激性,对于生物大分子类药物的经皮吸收有明显的促进作用,具有良好的开发前景。