Transdermal Iontophoresis of Rotigotine Across Human Stratum Corneum in Vitro: Influence of pH and NaCl Concentration

PURPOSE: The aim of this study was to characterize the influence of pH and NaCl concentration on the transdermal iontophoretic transport of the dopamine receptor agonist rotigotine across human stratum corneum (HSC). METHODS: Rotigotine transport was studied in vitro in side by side diffusion cells according to the following protocol: 6 h of passive diffusion, 9 h of iontophoresis, and 5 h of passive diffusion. A current density of 0.5 mA cm(-2) was used. The influence of donor phase pH (4, 5, and 6) and different concentrations of NaCl (0.07 and 0.14 M) on rotigotine iontophoretic flux were examined. The acceptor phase was phosphate-buffered saline (PBS) at pH 7.4 except in one series of experiments aimed to study the effects of rotigotine solubility on its iontophoretic transport. In this study, PBS at pH 6.2 was used. In separate studies. 14C-mannitol was used as a marker to determine the role of electro-osmosis during iontophoresis. RESULTS: The estimated iontophoretic steady-state flux (Flux(ss)) of rotigotine was influenced by the pH of the donor solution. At a drug donor concentration of 0.5 mg ml(-1), the iontophoretic flux was 30.0 +/- 4.2 nmol cm(-2) h(-1) at pH 6 vs. 22.7 +/- 5.5 nmol cm(-2) h(-1) at pH 5. However, when the donor concentration was increased to 1.4 mg ml(-1), no significant difference in iontophoretic rotigotine transport was observed between pH 5 and 6. Increase of NaCl concentration from 0.07 M to 0.14 M resulted in a decrease of the rotigotine Flux(ss) from 22.7 +/- 5.5 nmol cm(-2) h(-1) to 14.1 +/- 4.9 nmol cm(-2) h(-1). The contribution of electro-osmosis was estimated less than 17%. Probably due to the lipophilic character of the drug, impeding the partitioning of rotigotine from HSC to the acceptor compartment, steady-state transport was not achieved during 9 h of iontophoresis. CONCLUSIONS: Both pH and NaCl concentration of the donor phase are crucial on the iontophoretic transport of rotigotine. Electro-repulsion is the main mechanism of the iontophoretic transport of rotigotine.     

Transdermal Delivery of Metoprolol by Electroporation

Electroporation, i.e., the creation of transient pores in lipid membranes leading to increased permeability, could be used to promote transdermal drug delivery. We have evaluated metoprolol permeation through full thickness hairless rat skin in vitro following electroporation with an exponentially decaying pulse. Application of electric pulses increased metoprolol permeation as compared to diffusion through untreated skin. Raising the number of twin pulses (300 V, 3 ms; followed after 1 s by 100 V, 620 ms) from 1 to 20 increased drug transport. Single pulse (100 V, 620 ms) was as effective as twin pulse application (2200 V, 1100 V or 300 V, 3 ms; followed after 1 s by 100 V, 620 ms). In order to investigate the effect of pulse voltage on metoprolol permeation, 5 single pulses (each separated by 1 min) were applied at varying voltages from 24 to 450 V (pulse time 620 ms). A linear correlation between pulse voltage and cumulative metoprolol transported after 4 h suggested that voltage controls the quantity of drug delivered. Then, the effect of pulse time on metoprolol permeation was studied by varying pulse duration of 5 single 100 V pulses from 80 to 710 ms (each pulse also separated by 1 min). Cumulative metoprolol transported after 4 h increased linearly with the pulse time. Therefore, pulse time was also a control factor of the quantity of drug delivered but to a lesser extent than the voltage at least at 100 V. The mechanisms behind improved transdermal drug delivery by electroporation involved reversible increased skin permeability, electrophoretic movement of drug into the skin during pulse application, and drug release from the skin reservoir formed by electroporation. Thus, electroporation did occur as shown by the increased transdermal permeation, on indicator of structural skin changes and their reversibility. Electroporation has potential for enhancing transdermal drug delivery.     

X-ray Scattering Analysis of Human Stratum Corneum Treated by High Voltage Pulses

Pharmaceutical Research -     

In Vitro Cutaneous Application of ISCOMs on Human Skin Enhances Delivery of Hydrophobic Model Compounds Through the Stratum Corneum

This study aimed to investigate the effect of a novel kind of immune-stimulating complexes (ISCOMs) on human skin penetration of model compounds in vitro to evaluate their potential as a delivery system, ultimately for transcutaneous vaccination. Special focus was on elucidating the mechanisms of penetration. Preparation of ISCOMs was done by dialysis and subsequent purification in a sucrose density gradient. The penetration pathways of acridine-labeled ISCOMs were visualized using confocal laser scanning microscopy (CLSM). Transmission electron microscopy (TEM) was used to evaluate the ultrastructural changes in the skin after application of the ISCOMs with or without hydration. Transcutaneous permeation of the model compound, methyl nicotinate, was evaluated in diffusion cells. The prepared ISCOMs were 42–52 nm in diameter as evaluated by dynamic light scattering with zeta potentials of −33 to −26.1 mV. TEM investigations verified the presence of ISCOM structures. Penetration of acridine into skin was greatly increased by incorporation into ISCOMs as visualized by CLSM. Permeation of methyl nicotinate was enhanced in the presence of ISCOMs. Ultrastructural changes of the intercellular space in the stratum corneum after exposure of ISCOMs were observed on micrographs, especially for hydrated skin. In conclusion, cutaneous application of ISCOMs leads to increased penetration of hydrophobic model compounds through human stratum corneum and thus shows potential as a transcutaneous delivery system. The increased penetration seems to be reflected by a change in the intercellular space between the corneocytes, and the effect is most likely caused by the components of the ISCOMs rather than intact ISCOMs.Key words: CLSM, penetration, Posintro™, TEM, vaccine     

Lecithin-Based Microemulsions for Targeted Delivery of Ceramide AP into the Stratum Corneum: Formulation, Characterizations, and In Vitro Release and Penetration Studies

Purpose

To improve the solubility and penetration of Ceramide AP (CER [AP]) into the stratum corneum that potentially restores the barrier function of aged and affected skin.

Methods

CER [AP] microemulsions (MEs) were formulated using lecithin, Miglyol® 812 (miglyol) and water-1,2 pentandiol (PeG) mixture as amphiphilic, oily and hydrophilic components, respectively. The nanostructure of the MEs was revealed using electrical conductivity, differential scanning calorimeter (DSC) and electron paramagnetic resonance (EPR) techniques. Photon correlation spectroscopy (PCS) was used to measure the sizes and shape of ME droplets. The release and penetration of the CER into the stratum corneum was investigated in vitro using a multi-layer membrane model.

Results

The MEs exhibited excellent thermodynamic stability (>2 years) and loading capacity (0.5% CER [AP]). The pseudo-ternary phase diagrams of the MEs were obtained and PCS results showed that the droplets are spherical in shape and bigger in size. In vitro investigations showed that the MEs exhibited excellent rate and extent of release and penetration.

Conclusions

Stable lecithin-based CER [AP] MEs that significantly enhance the solubility and penetration of CER [AP] into the stratum corneum were developed. The MEs also have better properties than the previously reported polyglycerol fatty acid surfactant-based CER [AP] MEs.     

Investigator Impact on Reproducibility of Drug Bioavailability in Stratum Corneum Sampling by Tape Stripping

Pharmaceutical Research - Skin sampling by tape stripping measures the local bioavailability of topical drug products in the stratum corneum (SC). The goal of the current study was to evaluate the...     

胰岛素脂质体的制备及在电致孔下的经皮渗透

采用反相蒸发法制备了平均粒径122.7nm的胰岛素脂质体,并考察了电致孔经皮转运情况.结果表明,在电致孔条件下,胰岛素脂质体2h累积渗透量是载药脂质体被动扩散的1倍;是原药及其与空白脂质体混合物的2～3倍.     

Rapid Temporal Control of Transdermal Drug Delivery by Electroporation

Pharmaceutical Research -     

Enhancement by Terpenes of 5-Fluorouracil Permeation through the Stratum Corneum: Model Solvent Approach

5-Fluorouracil permeates the stratum corneum through the intercellular pathway. 5-Fluorouracil is hydrophilic and, therefore, its partitioning from the aqueous region into the hydrocarbon interior of stratum corneum lipids is expected to be an important stage of its permeation and a target for some permeation enhancers. It has also been reported that complexation plays a role in the enhancement effect of some accelerants. These mechanisms have been investigated. For partitioning-permeation studies, isooctane was chosen as a model of the hydrocarbon interior of stratum corneum lipid bilayers and the effects of 26 different terpene enhancers on the solubility of 5-fluorouracil in isooctane were measured. Results were then compared with the effects of the same enhancers on the permeation of 5-fluorouracil through the epidermis in man. The stoichiometry of interaction of cineole and limonene with 5-fluorouracil were also studied to reveal possible complex formation. Solubility studies revealed good correlation between solubility and enhancement ratios for the majority of terpenes, indicating that one mechanism by which terpenes increase permeation of the stratum corneum by 5-fluorouracil is by improvement of partitioning. Stoichiometry studies showed that cineole can form 1:1 or higher complexes with 5-fluorouracil. With limonene, only a weak 1:1 complex was indicated. Data obtained using epidermis from man show that the enhancement effect of cineole toward 5-fluorouracil is much higher than that of limonene. These data reveal that terpenes might increase the permeation of 5-fluorouracil through the stratum corneum as a result of complex formation and a form of facilitated transport.     

Interaction of Antidepressant Drug,Clomipramine, with Model and Biological Stratum Corneum Membrane as Studied by Electron Paramagnetic Resonance

The interactions of tricyclic antidepressant drug, clomipramine (CLO), with pig ear stratum corneum (SC) and model membranes were investigated by electron paramagnetic resonance (EPR) spin labeling to get some insight into the possible application of this drug in transdermal delivery. The changes in membrane characteristics caused by CLO in the regions that are close to the water–lipid interfaces and the central parts of the membranes were searched. The experimental results were supported by computer simulation of EPR spectra, which showed heterogeneity of the membranes composed of regions with different fluidity characteristics. CLO was effective in both parts of the layers, indicating intercalation of the drug into model membranes as well as into the pig ear SC. Introduction of various molar ratios of CLO caused a decrease in the order parameter and an increase in the rotational diffusion of nitroxide moiety in different membrane regions as well as an increase in the polarity of spin probe environment. It also changed the number of resolved spectral components, which reflects the heterogeneity of the membrane. The fluidizing effect of CLO on pig ear SC throughout the whole membrane layers indicates that CLO penetrates into the SC, which is important for its transdermal delivery.     

应用ATR-FTIR考察壳聚糖及其衍生物对角质层含水量的影响

目的：用衰减全反射傅立叶红外光谱考察壳聚糖（CS）及其衍生物对小鼠角质层含水量的影响，以初步探讨其作为透皮吸收促进剂的作用机理。方法：合成不同取代度的N-三甲基壳聚糖（TMC）和N-羧甲基壳聚糖（MCC）；酶消化法提取小鼠角质层，分别用2．5％TMC、MCC、CS溶液处理之后进行ATR—FTIR分析，计算酰胺基Ⅰ吸光度和酰胺基Ⅱ吸光度之比。结果：TMC20，TMCA0，TMC60，MCC，CS，H20（作为对照）处理之后，角质层酰胺基Ⅰ吸光度和酰胺基Ⅱ吸光度之比分别在8，4，8，6，6，6h达到最大值：1．7286，1．6190，1．6690，1．6460，1．6103，1．5905。结论：壳聚糖及其衍生物可使角质层含水量增加，可能是其具备透皮吸收促进作用的原因之一。     

The Role of Protein and Lipid Domains in the Uptake of Solutes by Human Stratum Corneum

The uptake of a series of hydrocortisone esters varying in lipophilicity from water into untreated and delipidized human stratum corneum has been determined. The partition coefficients of solutes into fully hydrated stratum corneum are postulated to represent the separate contributions of three structurally distinct domains—the extractable lipids, protein, and the solvent domain. The solvent domain was assumed to have the properties of bulk water. The relative affinities of the protein and lipid domains of stratum corneum for solutes varying in structure were determined by comparing solute uptake in untreated and delipidized stratum corneum. Partitioning into the extracted lipids was also examined. Solute uptake into stratum corneum may be governed by the protein domain, the lipid domain, or a combination of the two, depending on solute lipophilicity. Due to differences in the selectivity of the two domains, a change in uptake mechanism occurs with increasing solute lipophilicity from protein-dominated uptake for hydrophilic solutes to lipid domain-dominated uptake for lipophilic solutes. The stratum corneum lipid content, which varies dramatically from individual to individual (3–46% in this study), is an important determinant of the affinity of the stratum corneum for highly lipophilic solutes but has no effect on the uptake of hydrophilic solutes.Prakash V. Raykar: In partial fulfillment of the Ph.D. degree of pharmaceutics, College of Pharmacy, University of Utah.     

Transdermal Delivery of Insulin to Alloxan-Diabetic Rabbits by Ultrasound Exposure

Pharmaceutical Research -     

Physicochemical Modulation of Skin Barrier by Microwave for Transdermal Drug Delivery

Purpose

To investigate mechanism of microwave enhancing drug permeation transdermally through its action on skin.

Methods

Hydrophilic pectin-sulphanilamide films, with or without oleic acid (OA), were subjected to drug release and skin permeation studies. The skins were untreated or microwave-treated, and characterized by infrared spectroscopy, Raman spectroscopy, thermal, electron microscopy and histology techniques.

Results

Skin treatment by microwave at 2450?MHz for 5?min promoted drug permeation from OA-free film without incurring skin damage. Skin treatment by microwave followed by film loaded with drug and OA resulted in permeation of all drug molecules that were released from film. Microwave exerted spacing of lipid architecture of stratum corneum into structureless domains which was unattainable by OA. It allowed OA to permeate stratum corneum and accumulate in dermis at a greater ease, and synergistically inducing lipid/keratin fluidization at hydrophobic C-H and hydrophilic O-H, N-H, C-O, C=O, C-N regimes of skin, and promoting drug permeation.

Conclusion

The microwave technology is evidently feasible for use in promotion of drug permeation across the skin barrier. It represents a new approach in transdermal drug delivery.     

Improvement of Transdermal Delivery of Tetragastrin by Lipophilic Modification with Fatty Acids

The in-vitro permeability of chemically modified tetragastrin with fatty acids through the rat skin was studied. The permeability of these compounds through intact skin and stripped skin of rat was determined with a Franz-type diffusion cell. The permeation of tetragastrin across the intact skin was improved by chemical modification with acetic acid and butyric acid. However, tetragastrin and caproyl-tetragastrin did not permeate across the intact skin up to the end of experiment. The permeation of tetragastrin across the stripped skin was improved by chemical modification, the skin flux of these acyl derivatives being in the order: acetyl > butyroyl > caproyl. The stability of tetragastrin in skin homogenate was also significantly improved by chemical modification with fatty acids. These results suggest that chemical modification of tetragastrin with fatty acids increases its lipophilicity, which makes it permeable across the stratum corneum. Moreover, the chemical modification reduced the degradation of tetragastrin in the viable skin, resulting an increase in permeation of tetragastrin across the skin.     

Transdermal Delivery of Fentanyl by Electroporation I. Influence of Electrical Factors

Purpose. Electroporation, a method of reversibly permeabilizing lipid bilayers by the application of an electric pulse, has been shown to induce increased transdermal passage of molecules. The aim of the present report was to study in vitro with hairless rat skin the potential of electroporation for transdermal delivery of fentanyl. Results. The application of electric pulses can strongly promote transdermal delivery of fentanyl compared to passive diffusion through untreated skin. We also point out that the choice of the waveform of the electric pulses is important: at the same applied energy, a few exponentially-decaying (ED) pulses increased fentanyl permeation more than a few square-wave pulses and to the same extent as the repeated application of higher voltage-shorter duration ED pulses. A factorial design showed that the voltage, duration, and number of ED pulses allowed control of the quantity of drug transported through the skin. Conclusions. Skin electroporation could be a good way to improve the transdermal diffusion of fentanyl.     

Enhanced Transdermal Delivery of Diazepam by Submicron Emulsion (SME) Creams

Diazepam, a lipophilic drug with CNS activity, serves here as a model to investigate the efficacy of SubMicron Emulsion (SME) as a novel transdermal vehicle. Diazepam was formulated in various topical regular creams and SubMicron Emulsion creams of different compositions. The different formulations were applied topically and protection against Pentamethylenetetrazole induced convulsive effects in mice was monitored. The efficacy of Diazepam applied topically in emulsion creams strongly depends on the oil droplet size and to a lesser degree - on the formulation composition and the oil type. Processing medium-chain-triglyceride (MCT) emulsion with a high-pressure homogenizer causes a drastic reduction in the droplet size, thereby significantly increasing the transdermal activity of Diazepam. In this case both the high-pressure homogenization and the presence of lecithin, an efficient dispersant, contribute to the effective droplet size reduction of below 1 micron, usually between 100–300 nm. The SubMicron Emulsions as vehicles for transdermal delivery of Diazepam generate significant systemic activity of the drug as compared with regular creams or ointments. Transdermal delivery of Diazepam via SME formulations is very effective, and the activity may reach the range of parenteral delivery. A single application of Diazepam in SME cream to mice skin provides pronounced transdermal drug delivery and prolonged protective activity up to 6 hours.     

Effect of Charge and Molecular Weight on Transdermal Peptide Delivery by Iontophoresis

Purpose The study was conducted to investigate the impact of charge and molecular weight (MW) on the iontophoretic delivery of a series of dipeptides. Methods Constant current iontophoresis of lysine and 10 variously charged lysine- and tyrosine-containing dipeptides was performed in vitro. Results Increasing MW was compensated by additional charge; for example, Lys (MW = 147 Da, +1) and H-Lys-Lys-OH (MW = 275 Da, +2) had equivalent steady-state fluxes of 225 ± 48 and 218 ± 40 nmol cm⁻² h⁻¹, respectively. For peptides with similar MW, e.g., H-Tyr-d-Arg-OH (MW = 337 Da, +1) and H-Tyr-d-Arg-NH₂ (MW = 336 Da, +2), the higher valence ion displayed greater flux (150 ± 26 vs. 237 ± 35 nmol cm⁻² h⁻¹). Hydrolysis of dipeptides with unblocked N-terminal residues, after passage through the stratum corneum, suggested the involvement of aminopeptidases. The iontophoretic flux of zwitterionic dipeptides was less than that of acetaminophen and dependent on pH. Conclusions For the series of dipeptides studied, flux is linearly correlated to the charge/MW ratio. Data for zwitterionic peptides indicate that they do not behave as neutral (“charge-less”) molecules, but that their iontophoretic transport is dependent on the relative extents of ionization of the constituent ionizable groups, which may also be affected by neighboring amino acids.     

HPLC法测定醋酸泼尼松龙微乳中醋酸泼尼松龙的含量

目的:建立醋酸泼尼松龙微乳经皮给药制剂中醋酸泼尼松龙含量的测定方法。方法:采用高效液相色谱法。色谱柱为H醋y酸pe泼rsi尼lO松D龙S-检2C测18浓柱度,流在动0相.5～为1甲0.醇0μ-g水·(m6L5-∶13范5)围,检内测与波峰长面为积积24分3n值m呈,流良速好为的1线.0性m关L?m系(inr-=1,柱0.9温99为9)2;5低℃、,中进、样高量平为均加20样μL回。收结率果分:别为98.96%、99.50%、99.31%。结论:该方法准确可靠、方便快捷,可用于醋酸泼尼松龙微乳中主药的含量测定。