Effect of electroporation on the electroosmosis across hairless mouse skin in vitro

Remote-controllable dosage management through a wearable iontophoretic patch utilizing a cell phone

With regard to medical treatment through operations, remote control is possible, however, the area of remote-controllable drug treatment is yet to be established. In this study, a prototyped remote-controllable dosage management system that allows patients and caregivers to administer therapeutic drugs via an internet line without touching the dosage device or formulation was developed. This system consists of a transmitter (System A) located away from the patient, and a dosage device (System B) equipped with a receiver (B1), dosage management unit (B2), and a drug treatment unit (B3) that can be installed on the patient. Additionally, Bluetooth® is adopted to communicate from System A to System B. In the present study, System A was incorporated into a cell phone, and System B was a constant-current iontophoresis (IP) device, which was applied on excised pig skin. Sodium salt of betamethasone phosphate (BP^-Na⁺) was selected as a model drug, and the in vitro skin permeation of BP^- was evaluated. As a result, by transmitting the administration information incorporated in System A through B1 to B2, the optimal current was passed between the IP electrodes in B3, and the skin permeation of BP^- was obtained by remote control. That is, the skin permeation of BP^- was obtained by the current flowing from the IP device. The permeation amount decreased when the voltage load was stopped. These results suggested that remote control from System A enables dosing management of bioactive substances from dosage devices applied on the skin, intracutaneously, or subcutaneously without being near the patient. Although various trials are still required to complete the remote-controlled system, the patient does not have to go to the hospital except to take injections. Such drug administrations would lead to decreased medical expenses and increased quality of life for patients.

Electrical aspects of skin as a pathway to engineering skin devices

Skin is one of the indispensable organs for life. The epidermis at the outermost surface provides a permeability barrier to infectious agents, chemicals, and excessive loss of water, while the dermis and subcutaneous tissue mechanically support the structure of the skin and appendages, including hairs and secretory glands. The integrity of the integumentary system is a key for general health, and many techniques have been developed to measure and control this protective function. In contrast, the effective skin barrier is the major obstacle for transdermal delivery and detection. Changes in the electrical properties of skin, such as impedance and ionic activity, is a practical indicator that reflects the structures and functions of the skin. For example, the impedance that reflects the hydration of the skin is measured for quantitative assessment in skincare, and the current generated across a wound is used for the evaluation and control of wound healing. Furthermore, the electrically charged structure of the skin enables transdermal drug delivery and chemical extraction. This paper provides an overview of the electrical aspects of the skin and summarizes current advances in the development of devices based on these features.

Needle-free iontophoresis-driven β-adrenergic sweat rate test

OBJECTIVES

Two CFTR-dependent β-adrenergic sweat rate tests applying intradermal drug injections were reported to better define diagnosis and efficacy of CFTR-directed therapies. The aim of this work was to develop and test a needle-free image-based test and to provide an accurate analysis of the responses.

METHODS

The modified method was conducted by applying two successive iontophoresis sessions using the Macroduct device. Efficiency of drug delivery was tested by evaporimetry. Cholinergically stimulated sweating was evoked by pilocarpine iontophoresis. β-adrenergically stimulated sweating was obtained by iontophoresis of isoproterenol and aminophylline in the presence of atropine and ascorbic acid. A nonlinear mixed-effects (NLME) approach was applied to model volumes of sweat and subject-specific effects displaying inter- and intra-subject variability.

RESULTS

Iontophoresis provided successful transdermal delivery of all drugs, including almost neutral isoproterenol and aminophylline. Pilocarpine was used at a concentration ∼130-times lower than that used in the classical Gibson and Cooke sweat test. Addition of ascorbic acid lowered the pH of the solution, made it stable, prevented isoproterenol degradation and promoted drug iontophoresis. Maximal secretory capacity and kinetic rate of β-adrenergic responses were blunted in CF. A cutoff of 5.2 minutes for ET50, the time to reach the half maximal secretion, discriminated CF from controls with a 100% sensitivity and specificity. Heterozygous showed an apparently reduced kinetic rate and a preserved secretory capacity.

CONCLUSION

We tested a safe, well-tolerated needle-free image-based sweat test potentially applicable in children. Modelling responses by NLME allowed evaluating metrics of CFTR-dependent effects reflecting secretory capacity and kinetic rate.

Effect of Combination of Low-Frequency Sonophoresis or Electroporation with Iontophoresis on the Mannitol Flux or Electroosmosis through Excised Skin

In vitro permeation studies of mannitol were conducted across excised hairless mouse skin to determine and compare the enhancing effect of electroporation (EP) or sonophoresis (SP) combined with iontophoresis (IP) on the electroosmotic flow, and to analyze the enhancement mechanism of these combined methods. Mannitol flux was utilized as an index for the electroosmotic flow due to its low molecular weight and no electrorepulsion effect. The combination of SP and IP (SP/IP) resulted in an apparent increase of electroosmotic flow (no effect was sometimes observed by SP/IP), while that of EP and IP (EP/IP) had no synergistic enhancing effect on the electroosmosis. Next, the combined effect of tape-stripping (TS) and IP (TS/IP) was examined in a similar manner to clarify the difference between the SP/IP and EP/IP effects on electroosmosis. When the TS number increased from 0 to 3, the electroosmotic flow increased with the TS number. However, no further increase was observed when the TS number became more than 3, and the flow started to decrease when the TS number became 5. The electric charge of the skin surface was then measured after SP or TS application. When SP was applied, the skin surface charge became much more negative and the electroosmotic flow by SP/IP was markedly increased. Thus, an increase in the electroosmotic flow across the skin during IP application can be obtained not by EP and TS, but by SP. The combined use of SP and IP is a promising means for the enhanced skin delivery of non-electrolyte drugs.

Alteration of electroosmotic volume flow through skin by polyethylene glycols

We have studied the effect of polyethylene glycols (PEGs) on the iontophoretic flux of acetaminophen (AAP) using conventional in vitro iontophoresis methodology. A series of PEGs with average molecular weight (MW) ranging from about 100 to 1,500 was studied. The results were analyzed to explain how PEGs affect the electroosmosis and flux through skin. As a marker molecule for the direction and magnitude of electroosmotic volume flow (EVF), AAP was used. PEG decreased both anodal and cathodal AAP flux markedly. The magnitude of this decrease in flux increased as the MW and the concentration of PEG increased. From the Helmholtz-Smoluchowski equation, it was expected that the increase in viscosity and the decrease in dielectric constant are thought to be the main reason for the decrease in EVF and the flux. The large increase in solubility of AAP in PEG solution may also play an important role, because this increase lowers the partition of AAP into the stratum corneum. When 30 % diethylene glycol solution was used, the magnitude of EVF was estimated to be about 1.5 μl/cm(2) h, and it decreased as the MW of the PEG increased. These results and discussions clearly suggest that the incorporation of organic solubilizers and penetration enhancers into the iontophoretic formulation should be carefully decided after a thorough understanding of their effect on flux. Overall, these results provide further mechanistic insights into the role of electroosmosis in flux through skin, and how they can be modulated by PEG and their MW.

A miniaturized flow-through cell to evaluate skin permeation of endoxifen

Endoxifen, an anti-estrogenic agent, has been recently implicated in the use of breast cancer. Its physicochemical properties make it a good candidate for transdermal delivery. However, as an investigative drug, its limited supply makes it difficult to conduct extensive pre-formulation studies. To address this issue, a miniaturized flow-through diffusion cell has been fabricated that utilized minimal amounts of the drug for in vitro skin permeation studies. The novel flow-through cells have been validated against horizontal diffusion cells and shown to cause no noticeable damage to the applied skin, as observed by histological sectioning. The cells were also demonstrated to be useful in search of suitable enhancers for endoxifen. Endoxifen permeation using permeation enhancers was tested by using this new device and limonene was found to achieve highest flux, attaining the requirement for clinical applications. The fabricated cells can thus be useful in carrying out pre-formulation studies for expensive, new drug entities, both in industrial as well as academic research.

Preparation and evaluation of liquid-crystal formulations with skin-permeation-enhancing abilities for entrapped drugs

The usefulness of liquid crystals (LC) in topical formulations for application to skin was evaluated by measuring the in vitro permeation profile of a model compound, calcein, entrapped in a LC formulation, through excised hairless rat skin and a three-dimensional cultured human-skin model; the viability was determined using the MTT assay. Two physically stable LCs were prepared from a mixture of mono-, di-, and tri-esters 1, and monoesters 2, composed of erythritol and phytanylacetic acid. Cryo-transmission electron microscopy (cryo-TEM), electron diffraction patterns, and small-angle X-ray diffraction (SAXS) observations of the LC nanodispersions showed that the structures of the LCs were reverse hexagonal (LC-A) and cubic (LC-B). The skin-permeation properties of calcein were enhanced by entrapping in the LCs as a result of the increase in calcein partition from the LC dispersion solution into the skin; the properties were analyzed using a skin-permeation-time profile. Drug partitioning could also be modified by the LC structure. No skin damage was caused by the LC formulation in these experiments.The present study suggests that LC dispersions are potential additives in topical drug formulations and cosmetic formulations.

Effect of the iontophoresis of a chitosan gel on doxorubicin skin penetration and cytotoxicity

The aim of this work was to investigate doxorubicin (DOX) percutaneous absorption and retention in the skin following iontophoresis. The convective flow contribution to the overall electrotransport of DOX was also elucidated for a non-ionic hydroxyethylcellulose gel and a cationic chitosan gel. Moreover, the cytotoxicity of DOX and its formulations, with and without low electrical current, was verified. It was observed that iontophoresis of DOX significantly increased the skin permeation and retention of the drug. In addition, the electroosmotic flow was dramatically reduced when DOX was added to the non-ionic gel, thereby indicating that the drug interacted with negative charges in the skin. Interestingly, electroosmosis was also significantly reduced when the iontophoresis was performed in the presence of the chitosan gel, but in the absence of DOX. Consequently, the transport of an electroosmotic marker from this gel almost disappeared when the positively charged drug was added to the cationic gel. These results indicated that chitosan appeared to interact with negative charges in the skin. Hence, this carrier not only reduced electroosmotic flow, but also released DOX from ionic interactions with these sites and improved its diffusion to deeper skin layers. The application of the low electrical current directly to melanoma cells increased DOX cytotoxicity by nearly three-fold, which was probably due to membrane permeation.

[Recent trend of transdermal drug delivery system development]

The potential of transdermal drug delivery systems has been demonstrated in recent years with the approval of several medicines for use by patients who are unable to use conventional dosage routes, like oral administration or injection. To enhance the TDDS (Transdermal Drug Delivery System) potential to include other drug candidates, many researchers have been exploring enhancement approaches to increase the permeability of various drugs through the skin. Recently, physical enhancement systems are being reported as having big potential by many researchers. In particular, iontophoresis is a very attractive way of delivering ionized drugs by the application of an electric field to the skin. This has been marketed with some topical and systemic drugs (lidocaine and fentanyl). Sonophoresis is also an attractive method to deliver a drug through the skin using ultrasound. Besides these technologies, various physical approaches are under study. Such technologies can be expected to deliver not only small MW compounds but also macromolecules like peptides. In this article, after looking back through the history of TDDS development, I would like to summarize with new physical and chemical approaches and outline of the new trend of TDDS development with those enhancement system.

Dermatopharmacokinetics of salicylate following topical injection in rats: Effect of osmotic pressure and injection volume on salicylate disposition

Using advanced topical formulations containing potential chemical enhancer(s) or physical penetration-enhancing tools capable of delivering entrapped drug(s) directly into skin tissues with little influence of the stratum corneum barrier, local and systemic drug disposition may be markedly similar to direct injection into the skin and muscle. The objective of this study is to investigate the dermatopharmacokinetics and systemic drug disposition after topical application and topical injection. Salicylate (SA) disposition in the skin and muscle as administration sites, and in the systemic circulation were evaluated following intracutaneous (i.c.) injection of an isotonic solution of SA-Na (dose; 3.08 micromol). Subcutaneous (s.c.) and intramuscular (i.m.) injection were also evaluated for comparison. Dermatopharmacokinetics and systemic disposition of SA after i.c. and s.c. injections were analyzed using a 4-compartment model consisting of skin, muscle, and central and peripheral compartments, whereas SA disposition after i.m. injection was analyzed using a 3-compartment model consisting of muscle, and central and peripheral compartments. Moreover, the absorption rate constant of SA after i.c. injection (0.073 min(-1)) was slightly lower than that after s.c. injection (0.083 min(-1)), and much lower than that after i.m. injection (0.327 min(-1)). In addition, higher osmolarity and a larger volume of SA-Na injectant increased the retention of SA in the skin and decreased the absorption rate to the systemic circulation after i.c. injection. The effect of injection volume on SA disposition after i.c. injection was not so marked compared with that of osmotic pressure. These results are useful to design an injection-type topical delivery system.

Effect of electroporation and pH on the iontophoretic transdermal delivery of human insulin

The synergistic effect of electroporation (EP) and iontophoresis (IP) on the in vivo percutaneous absorption of human insulin was evaluated in rats. Passive diffusion and IP alone (0.4 mA/cm(2)) resulted in almost no skin permeation of insulin at pH 7, whereas EP treatment (150 or 300 V, 10 ms, and 10 pulses) resulted in a high plasma level of insulin and the combined use of EP and IP led to a further increase of the plasma level of insulin compared with that measured after EP alone. Interestingly, a much higher plasma level was observed when the pH of the insulin solution at 7 was increased to 10. One of the reasons was the different aggregation properties of insulin at pH 7 and pH 10. The nonassociation ratio of insulin was significantly higher at pH 10 than at pH 7. Insulin monomers and dimers were observed in addition to the normal form of insulin, hexamer, albeit in low percentages, at pH 10, whereas most of the insulin was in the hexamer form at pH 7. To confirm the influence of the aggregation properties of insulin, the commercially available human insulin analogue insulin lispro was then evaluated. Its skin permeation was found to be extremely high compared to that of conventional human insulin without increasing the solution pH. Marked decreases in blood glucose levels reflecting the increases in the plasma concentration of insulin were also observed after EP/IP treatment. The present study suggests that percutaneous absorption of insulin is synergistically enhanced by a combined use of EP and IP and that altering the aggregation properties of insulin is important to enhance the percutaneous absorption of insulin by IP and/or EP.