Combined chemical and electrical enhancement modulates stratum corneum structure

Optimization of Metronidazole Emulgel

The purpose of the present study was to develop and optimize the emulgel system for MTZ (Metronidazole), a poorly water soluble drug. The pseudoternary phase diagrams were developed for various microemulsion formulations composed of Capmul 908 P, Acconon MC8-2, and propylene glycol. The emulgel was optimized using a three-factor, two-level factorial design, the independent variables selected were Capmul 908 P, and surfactant mixture (Acconon MC8-2 and gelling agent), and the dependent variables (responses) were a cumulative amount of drug permeated across the dialysis membrane in 24 h (Y₁) and spreadability (Y₂). Mathematical equations and response surface plots were used to relate the dependent and independent variables. The regression equations were generated for responses Y₁ and Y₂. The statistical validity of the polynomials was established, and optimized formulation factors were selected. Validation of the optimization study with 3 confirmatory runs indicated a high degree of prognostic ability of response surface methodology. Emulgel system of MTZ was developed and optimized using 2³ factorial design and could provide an effective treatment against topical infections.

Study on the mechanisms of chitosan and its derivatives used as transdermal penetration enhancers

The efficacy of chitosan (CS) and its derivatives used as transdermal penetration enhancers has been confirmed in our previous research. This study investigated the mechanisms of penetration enhancement by CS and its derivatives, i.e., N-trimethyl chitosan (TMC) with different degree of quaternization (DQ) and mono-N-carboxylmethyl chitosan (MCC). After treatment with CS, TMCs or MCC, the secondary structure changes of keratin in stratum corneum (SC) from mice were examined by an Attenuated Total Reflection-Fourier Transform Infrared (ATR-FTIR) combined with the application of the second-order derivative, deconvolution and curve-fitting. The water content in the SC was also studied by ATR-FTIR. HaCaT cell lines were employed as the cell models in the study. HaCaT cells were first treated with blank D-Hanks solution, CS or its derivatives, and were then fluorescent labeled with DiBAC(4) (3). The change of membrane potential was measured by a flow cytometer (FCM). Alternatively, the treated HaCaT cells were labeled with NBD-C(6)-HPC and the change of membrane fluidity was examined under a Confocal Laser Scanning Microscope (CLSM). It was found that CS, TMCs and MCC could significantly affect the secondary structure of keratin in SC in different ways. Although the amide II absorption peak of keratin moved to a lower wave number following treatment with CS, TMCs, or MCC, the beta-turning structure of keratin was converted to beta-sheeting and random coiling after treatment with TMCs and was converted to beta-sheeting and alpha-helix following treatment with MCC and CS. At the same time, CS and its derivatives all could increase the water content of SC, decrease HaCaT cells membrane potentials and enhance HaCaT cells membrane fluidity significantly. The effect of TMCs appeared to be independent of their DQ. The results suggest that the mechanisms of transdermal enhancement of CS, TMCs and MCC are closely related to their effects on the secondary structure of keratin and water content in SC, cell membrane potential and fluidity.

Depth Dependence of Stratum Corneum Lipid Ordering: A Slow-Tumbling Simulation for Electron Paramagnetic Resonance

We investigated the structural ordering of stratum corneum (SC) lipid by means of electron paramagnetic resonance (EPR) slow-tumbling simulation in conjunction with spin probe studies. The SC of human mid-volar forearm was stripped consecutively from three to six times. The EPR probe method detected a characteristic peak of sebaceous matter in the first SC stripping. The order parameter values obtained by the slow-tumbling simulation (S(0)) showed significant differences between each layer compared with those indicated by the conventional order parameter (S) using hyperfine couplings. Although the conventional S values were in the range of 0.56 (outermost layer) to 0.61 (bottom layer), the S(0) values by the simulation changed from 0.22 to 0.96. The present results suggest that the structural ordering of the outermost SC layer is less tight, whereas the structure of inner layers becomes more rigid. Therefore, we concluded that the EPR probe method recognizes sebaceous matters, whereas EPR in conjunction with the simulation allows quantitative evaluation of SC lipid ordering in relation to skin depth.

An extended model based on the modified Nernst-Planck equation for describing transdermal iontophoresis of weak electrolytes

An extended model for iontophoretic enhancement of transdermal drug permeation under constant voltage is described based on the previously modified Nernst-Planck equation, which included the effect of convective solvent flow. This model resulted in an analytical expression for the enhancement factor as a function of applied voltage, convective flow velocity due to electroosmosis, ratio of lipid to aqueous pathway passive permeability, and weighted average net ionic valence of the permeant in the aqueous epidermis domain. The shift of pH in the epidermis compared to bulk caused by the electrical double layer at the lipid-aqueous domain interface was evaluated using the Poisson-Boltzmann equation. This was solved numerically for representative surface charge densities and yielded pH differences between bulk and epidermal aqueous domain between 0.05 and 0.4 pH units. The developed model was used to analyze the experimental enhancement of an amphoteric weak electrolyte measured in vitro using human cadaver epidermis and a voltage of 250 mV at different pH values. Parameter values characterizing the involved factors were determined that yielded the experimental enhancement factors and passive permeability coefficients at all pH values. The model provided a very good agreement between experimental and calculated enhancement and passive permeability. The deduced parameters showed (i) that the pH shift in the aqueous permeation pathway had a notable effect on the ionic valence and the partitioning of the drug in this domain for a high surface charge density and depending on the pK(a) and pI of the drug in relation to the bulk pH; (ii) the magnitude and the direction of convective transport due to electroosmosis typically reflected the density and sign, respectively, of surface charge of the tissue and its effect on enhancement was substantial for bulk pH values differing from the pI of epidermal tissue; (iii) the aqueous pathway predominantly determined passive permeability of the studied compound despite its measurable lipophilicity and therefore the lipid pathway did not notably affect enhancement. Hence, the proposed model can provide a good quantitative insight into the interplay between different phenomena and permeant properties influencing iontophoresis and can potentially be used as a predictive tool of the process.

Visualization studies of human skin in vitro/in vivo under the influence of an electrical field

The aim of this study was to investigate the local changes in the ultrastructure of human skin after iontophoresis, using cryo-scanning, transmission and freeze fracture electron microscopy in human skin in vitro and in vivo. Human dermatomed skin was subjected to passive diffusion for 6 hours followed by nine hours of iontophoresis at 0.5 mA/cm2. The skin was processed and examined using both cryo-scanning electron microscopy (Cryo-SEM) and transmission electron microscopy (TEM). In addition, iontophoresis patches were applied to healthy volunteers for 3.5h with 0.5h of passive delivery followed by 3h of iontophoresis at a current density of 0.25 mA/cm2. Subsequently, a series of tape stripping were performed, which were visualized by freeze fracture transmission electron microscopy (FFTEM). In vitro, the cryo-scanning electron microscopy study revealed that electric current induced changes in the water distribution in the stratum corneum. Transmission electron microscopy showed no local changes in the ultrastructure of the stratum corneum; however, layers of detached corneocytes were frequently observed especially at the anodal site. In vivo, there was no evidence of perturbation of the stratum corneum lipid organization; however, changes in the fracture were noticed deeper in the stratum corneum at the anodal side, indicating a weakening of the desmosomal structure. The in vitro/in vivo studies suggest that iontophoresis results in the formation of intercellular water pools (in vitro observation) and a weakening of the desmosomal structure (in vivo observation) only in the upper part of the stratum corneum. However, no changes in the lipid organization were observed in vitro and in vivo at the current densities of 0.5 and 0.25 mA/cm2, respectively. Therefore, even at relatively high current densities, no drastic changes in the ultrastructure of the stratum corneum are observed. As far as structural changes in stratum corneum are concerned iontophoresis is therefore a safe method at the experimental conditions we used.

Transdermal iontophoresis

Iontophoresis is a technique used to enhance the transdermal delivery of compounds through the skin via the application of a small electric current. By the process of electromigration and electro-osmosis, iontophoresis increases the permeation of charged and neutral compounds, and offers the option for programmed drug delivery. Interest in this field of research has led to the successful delivery of both low (lidocaine) and high molecular drugs, such as peptides (e.g., luteinising hormone releasing hormone, nafarelin and insulin). Combinations of iontophoresis with chemical enhancers, electroporation and sonophoresis have been tested in order to further increase transdermal drug permeation and decrease possible side effects. In addition, rapid progress in the fields of microelectronics, nanotechnology and miniaturisation of devices is leading the way to more sophisticated iontophoretic devices, allowing improved designs with better control of drug delivery. Recent successful designing of the fentanyl E-TRANS iontophoretic system have provided encouraging results. This review will discuss basic concepts, principles and applications of this delivery technique.

Transdermal iontophoretic delivery of apomorphine in patients improved by surfactant formulation pretreatment

The objective of the present study is to evaluate the efficacy and the safety of transdermal iontophoretic delivery of R-apomorphine, a potent dopamine agonist, in combination with surfactant pretreatment in patients with advanced Parkinson's disease. Iontophoresis patches were applied in 16 patients for 3.5 h, with 0.5 h of passive delivery followed by 3 h of current application at a current density of 250 microA/cm2. Eight of these patients were treated with a surfactant formulation prior to iontophoresis. The pharmacokinetics, pharmacodynamic effects, systemic and local side effects of R-apomorphine were assessed. The plasma concentration vs. time profiles upon iontophoresis of R-apomorphine were described successfully by a novel pharmacokinetic model. The model suggests that only 1.9% of the dose that has been released from the patch accumulated in the skin. The patients treated with the surfactant formulations showed a statistically significant increase of bioavailability (from 10.6+/-0.8% to 13.2+/-1.4%) and of the steady state input rate (from 75.3+/-6.6 to 98.3+/-12.1 nmol/cm2 h) compared to the control patients (iontophoresis without absorption enhancers). In five out of eight patients in the study group and in three out of eight patients in the control group, clinical improvement was observed.