Delivery of free amino acids into and through the stratum corneum of the skin using micro emulsions and microemulsion-based hydrogels: Formulation, characterization, and ex-vivo permeation studies

Free amino acids constitute the largest portion (40%) of the natural moisturizing factor. Their level might decline and cause dry skin condition. The treatment strategy involves the replenishment of these components to the skin, and, to our knowledge, there are no reports that involve dermal delivery of free amino acids. The purpose of the current study was therefore to prepare and characterize different micro-emulsions, micro-emulsion-based hydrogels, and hydrophilic creams loaded with free amino acids for dermal delivery. Oil-in-water microemulsions were prepared using carefully selected formulation components. Poloxamer® 407 and carbopol® 934 were used to prepare the hydrogels. All the formulations were characterized for physico-chemical, permeation and cytotoxicity properties. The results showed that the prepared microemulsions had desired droplet size, size distribution, zeta potential, refractive index, and pH. In the gel preparations, the elastic properties prevailed over the viscous behavior. The hydrogels had non-Newtonian shear-thinning behavior with some thixotropic properties. The free amino acids permeated into the deeper layers of the stratum corneum from the microemulsions, and microemulsion-based hydrogels as compared to conventional hydrophilic cream. The hydrogels were more effective than the microemulsions to deliver the FAAs to the desired site of the skin in a sustained manner. Poloxamer-based hydrogel permeated into deeper skin layers than Carbopol-based hydrogel. Formulations prepared using standard free amino acids and those extracted and purified from oyster mushroom had similar characteristics. All the formulations were stable and safe to be applied topically. In conclusion, microemulsions and microemulsion-based hydrogels can be considered as safe carrier systems for dermal delivery of free amino acids.

[Development of an ivermectin-containing syrup as an extemporaneous preparation for treatment of scabies in children]

BACKGROUND

Oral ivermectin can be used to treat scabies. Evidence for safe and effective use in young children in individual treatment situations has been developed and published. In order to also ensure a body weight-adapted dosage for children, an ivermectin-containing syrup was developed as an extemporaneous preparation.

MATERIALS AND METHODS

Since ivermectin is not available as a pure substance for the formulation, tablets containing active ingredient were used as a basic material for development. The formulation was designed according to pharmaceutical, regulatory and use-oriented criteria. An HPLC (high-pressure liquid chromatography) method was developed and validated to demonstrate chemical stability. In order to facilitate the practical implementation, information on suitable packaging material and application aids was also developed and the formulation was evaluated.

RESULTS

It has been demonstrated that the final formulation produced in the pharmacy was stable and can be stored for 3 weeks. No concerns were raised regarding the tolerability of the syrup formulation. The physicochemical properties and the taste of the formulation allow the intended use as a well-dosed syrup for children.

CONCLUSION

The developed formulation meets the requirements of the Apothekenbetriebsordnung (Pharmacy Work Rules; Section 7 ApBetrO) and enables an exact, body weight-adapted dosage of oral ivermectin in young children. Studies on human pharmacokinetics or clinical studies to demonstrate tolerability and/or efficacy are not available for the formulation.

Assessment of the applicability of HLB values for natural phospholipid emulsifiers for preparation of stable emulsions

Natural phospholipid (PL) excipients are native, biocompatible and relatively inexpensive alternatives to synthetic emulsifiers. A well-known PL excipient is lecithin, which primarily contains phosphatidylcholine (PC) and (depending on the purity grade) also contains a well-defined mixture of other PLs with a fatty acid composition, which reflects their natural source. Since all of these lipid species are emulsifiers, natural PLs can be considered as a mixture of (co-) emulsifiers. Many different HLB values for lecithins are given in the literature, which is why this needs to be clarified. To assess this, HLB values of thirteen different plant derived PLs differing in PC content were determined using a centrifugation stress method to determine the relative stability of an emulsion with the respective emulsifier and different oil phases. It could be shown that the studied PLs can be characterized by a broad HLB range, which may be linked to the composition of the PLs and the oil used. In order to emphasize the results of the HLB determination, it could be demonstrated that stable emulsions could be prepared with a wide range of oils using the plant-based PLs and that the preparation method of the emulsions is important in order to obtain stable emulsions. Therefore, assigning a specific exact HLB value to natural PLs instead of a wider range is inappropriate. The broad HLB ranges indicate the suitability of the studied PL emulsifiers for the preparation of oil-in-water emulsions for a wide range of oils: It is recommended to experimentally evaluate the suitability of these natural emulsifiers for the preparation of stable emulsions and to benefit from the wide range of HLB values of these emulsifiers instead of relying on inaccurate and confusing HLB values in the literature.

The effect of hydrophilic penetration/diffusion enhancer on stratum corneum lipid models: Part II*: DMSO

To optimize dermal and transdermal administration of drugs, the barrier function of the skin, particularly the stratum corneum (SC), needs to be reduced reversibly. For this purpose, penetration/diffusion enhancers such as DMSO can be applied. However, there is the question whether DMSO is an aggressive penetration/diffusion enhancer in pharmaceutical and cosmetical relevant concentrations? Until now, it is unclear if this penetration/diffusion enhancement is caused by an interaction with the SC lipid matrix or related to effects within the corneocytes. Therefore, the effects of the hydrophilic enhancer DMSO on SC models with different dimensionality ranging from bilayers (liposomes) via oligo-layers to multilayers have been investigated in this study. The effects of DMSO should be compared to that of other relevant hydrophilic enhancers such as urea and taurine. An innovative spectrum of methods was applied to ascertain the mode of action of DMSO in relevant concentrations on a molecular scale. The experiments reveal that there is no specific interaction of 10% and 30% DMSO solutions with the SC model systems. Hence, if DMSO is applied in pharmaceutically and cosmetically relevant concentrations, it has no influence on the SC model systems used. Neither an additional water uptake in the head group region nor a decrease of the lipid chain packing density have been observed. The leakage studies on liposomes show that 10% DMSO is causing just a very slight leakage of 8%, lower than the leakage of 19.4% caused by 10% urea (Müller et al., 2016). Consequently, the interactions of DMSO with the SC model lipids used are very low in concentrations of 10% and 30%, respectively. Since the lipid composition in native SC lipid matrix is far more complex than this model mixture, the results can not be directly transferred to the native SC lipid matrix. However, the outcome of this study, together with various findings in the literature give rise to the assumption that the enhancing effect of DMSO concerning the diffusion of relevant hydrophilic drugs and actives appears to be realized via the corneocytes.

Pflanzliche Ceramide zur kosmetischen Anwendung

Die Bedeutung von Ceramiden als aktive Inhaltstoffe in kosmetischen Präparaten hat in den letzten Jahren erheblich an Bedeutung gewonnen. Im dermatologischen Kontext werden Ceramide meist in Kombination mit anderen Lipiden sowie weiteren kosmetischen Wirkstoffen in Präparaten zur Barriereprotektion und -regeneration bei chronisch-entzündlichen Hauterkrankungen bzw. bei Diabetes mellitus oder Altershaut eingesetzt. Da die Herstellung von synthetischen Ceramiden sehr kostenintensiv ist, kann die Verwendung von pflanzlichen Ceramiden mit vergleichbaren physikochemischen Eigenschaften eine Alternative darstellen. Neuere Verfahren ermöglichen die Glykosylierung dieser aus Pflanzenextrakten isolierten Ceramide und deren Einsatz in kosmetischen Zubereitungen. Weitere Untersuchungen müssen klären, ob sich glykosylierte pflanzliche Ceramide in die natürlichen Lipidmembranen im Stratum corneum integrieren und welche funktionellen Auswirkungen sie auf die Barrierefunktion haben. Die bisherigen Daten begründen ein großes Potenzial pflanzlicher Ceramide für die Barriere-protektive Anwendung in kosmetischen Präparaten.

Studies of the Corneocytary Pathway Across the Stratum Corneum. Part I: Diffusion of Amino Acids Into the Isolated Corneocytes

Amino acids (AAs), important constituents of natural moisturizing factors (NMFs) of the skin are decreased in diseased conditions such as psoriasis and atopic dermatitis. No study so far investigated the uptake of AAs into isolated corneocytes (COR). The present study was performed using 19 AAs, including taurine (TAU), to measure their amount diffused into the COR and binding of these AAs to keratin. Incubation of alanine, aspartic acid, asparagine, glutamine, glutamic acid, histidine, proline, serine and TAU with the isolated COR showed uptake after 24 h of 51.6, 95.4, 98.6, 94.1, 95.6, 90.1, 94.6, 72.9 and 57.8 %, respectively, into the COR but no binding with keratin. Uptake of TAU was validated by time dependent in-vitro diffusion models 'without COR and 'with COR'. The time dependent curve fitting showed that in in-vitro diffusion model 'without COR' there was no change in the total concentration of TAU until 72 hours, while in diffusion model 'with COR' the total conc. decreased to 37.8 % after 72 hours. The Pearson's correlation coefficient 'r' between the conc. curves of both in-vitro diffusion models was -0.54 that was an evidence of significant amount of TAU uptake by the COR. AAs as part of the NMFs have a great potential to be diffused into the COR. This property of the AAs can be employed in further dermatological research on diseased or aged skin conditions with NMFs deficiency.

Dermal peptide delivery using enhancer molecules and colloidal carrier systems - part V#: Influence of enhancers on the permeation of PKEK through snake skin

In a previous study, it was shown, that shed snake skin is a good alternative model membrane for the human stratum corneum (SC). In this study, the influence of the enhancers dimethyl sulfoxide (DMSO), 1,2-propanediol, 1,3-butanediol, 1,2-pentanediol, 1,2-hexanediol and 1,2-octanediol in a concentration of 10 % on the permeation of l-prolyl- l-lysyl-l-α-glutamyl-l-lysin (PKEK) through shed snake skin was conducted. Pharmacokinetic parameters (diffusion coefficient, permeation coefficient, t-lag, Flux) were calculated. All examinations were performed on the skin of an individual and thus allowed a very good comparability of the data. All enhancers have overcome the shed snake skin and could be proven in the acceptor. DMSO does not affect the permeability of the membrane. Nevertheless, PKEK permeates faster in the presence of DMSO than PKEK being used alone. PKEK permeated the same, no matter if an auxiliary material was added or not. Without their addition, in all other enhancers no significant difference towards permeation could be determined.

Effect of hyaluronic acid initial concentration on cross-linking efficiency of hyaluronic acid - based hydrogels used in biomedical and cosmetic applications

This work was aimed to explore the potential effect of hyaluronic acid (HA) initial concentration (7.0 - 14.0 % w/v) on cross-linking efficiency of HA hydrogels cross-linked with 1,4-butanediol diglycidyl ether (BDDE). The results revealed that the hydrogel prepared at 10.0 % HA concentration exhibited a slower degradation rate, a lower swelling ability and more regular porosity than those prepared at either lower or higher HA concentration. After four days incubating with hyaluronidase, the content of NAG (N-acetyl glucosamine) remaining in the 10.0 HA hydrogel was 25.1±1.9 % with respect to the total NAG content found in the original mass. In contrast, the hydrogels prepared at 7.0 % and 14.0 % HA concentration showed a less remaining content of NAG equaled to approximately 15.9±5.4 % and 19.5±2.6 % respectively. On the other hand, the swelling ability of tested hydrogels was steadily decreased with the increase of HA initial concentration until the 10.0 % HA hydrogel and then showed an opposite trend. Based on this finding, the 10.0 % HA hydrogel exhibited the lowest swelling ratio which was observed at 129±3.2 g/g in distilled water and at 116±2.4 g/g in phosphate buffer saline (PBS). The SEM images showed various morphologies within the entire range of tested hydrogels. However, the hydrogel prepared at 10.0 % HA concentration was more homogenous and appeared with narrower pore-size distribution ranged in diameter from less than 50 μm to approximately 300 μm. Finally, the effect of HA initial concentration was investigated by FTIR which confirmed that the 10.0 % HA hydrogel was subject to a greater loss of (- OH) at 3343 cm-1 than other hydrogels except the 11.0 % HA hydrogel. This phenomenon was probably attributed to the formation of pendants that allowed the 11.0 % HA hydrogel to appear with a lower peak intensity than the 10.0 % HA hydrogel in the FTIR spectra. In conclusion, the HA initial concentration plays a crucial role in determining the cross-linking efficiency of HA hydrogels cross-linked with BDDE.

Retarder action of isosorbide in a microemulsion for a targeted delivery of ceramide NP into the stratum corneum

Ceramide [NP] is an integral component of the stratum corneum (SC) lipid matrix and is capable of forming tough and stable lamellar structures. It was proven, that in skin diseases as psoriasis or atopic dermatitis different ceramide (CER) classes, including [NP], are degraded. It is obvious that topically application of CER on impaired skin is useful for repairing the skin barrier but a tendency for low penetration due to its poor solubility in conventional dosage forms was observed. Therefore, a stable and physiologic compatible colloidal carrier system, a microemulsion (ME), was developed and characterized. The increasing knowledge of the new colloidal systems in this last decade shows their benefits in dermal application. Isosorbide (Polysorb P) was incorporated into the ME developed. It was expected that Polysorb P has a retarder potential in order to accumulate the CER in the SC, the outermost layer of the skin. Thereby the CER [NP] would be able to interact with the affected skin layers to strengthen the skin barrier. The release and penetration behavior of the CER [NP] from the ME was assessed ex vivo in a Franz diffusion cell. The results of the study showed that CER [NP] penetrate largely in the upper layers of the skin (from SC to stratum basale), which was the desired region. A recovery in the acceptor could not be detected that underlines an accumulation in upper layers. Furthermore, significantly increased values for the SC for the ME with retarder were not received. No differences in the concentrations of CER [NP] were observed. However, the toxicity of MEs was investigated using heńs egg test chorioallantoic membrane (HET-CAM). For the isosorbide-containing ME no difference was obtained in comparison to the non-containing. The results showed that both MEs are safe to be used on the skin for the controlled penetration of CER [NP] into the skin. The isosorbide had no effect on the irritating effect as well as on the penetration of the used CER.

Dermal and transdermal delivery of pharmaceutically relevant macromolecules

The skin offers an attractive way for dermal and transdermal drug delivery that is why the drug still needs certain qualities to transcend the outermost layer of the skin, the stratum corneum. The requirements are: drugs with a maximum molecular weight of 1kDa, high lipophilicity and a certain polarity. This would restrict the use of a transdermal delivery of macromolecules, which would make the drug more effective in therapeutic administration. Various studies have shown that macromolecules without support do not penetrate the human skin. This effect can be achieved using physical and chemical methods, as well as biological peptides. The most popular physical method is the use of microneedles to create micropores in the skin and release the active agent in different sections. But also, other methods have been tested. Microjets, lasers, electroporation, sonophoresis and iontophoresis are also promising methods to successfully deliver dermal and transdermal macromolecules. Additionally, there are different penetration enhancer groups and biological peptides, which are also considered to be interesting approaches of enabling macromolecules to travel along the skin. All these methods will be described and evaluated in this review article.

Investigation in W/O developed microemulsions with DMSO as a cosurfactant

In this study the effect of dimethylsulfoxide (DMSO) radii on the droplets and on the required non-ionic surfactant volume for preparing water-in-oil microemulsions (MEs) was investigated. Five series of MEs were prepared either with the aid of isopropylpalmitate or medium chain triglycerides (MCTG) as continuous phases. The MEs were stabilized via either Tween80 or Span20 or a mixture of both. A mixture of water:DMSO (W:DMSO) with different ratios formed the colloidal phase of the first four MEs series. Only DMSO was used as colloidal phase of the fifth series. Dynamic light scattering (DLS) was used for measuring the radii of the droplets of MEs. The results showed that the consumed volumes of the surfactants were related to the W:DMSO ratio and the surfactant type. Moreover, the consumed surfactant volumes increased with decreasing radii of the droplets of the MEs. The MEs stabilized with Span20 had lower radii of the droplets (4-15 nm) than MEs stabilized by Tween80 (25-65 nm). It was evident that DMSO changed the interfacial tension which is reflected by changing the the volume of the surfactant consumed and by altering the droplets sizes. Consequently, DMSO acted as co-surfactant in stabilizing the MEs by reducing the required volumes of the surfactant which is important for reducing their toxicity.

Investigation of the molecular structure of the human stratum corneum ceramides [NP] and [EOS] by mass spectrometry

The aim of this study was to characterize the two ceramide (CER) subclasses CER[NP] and CER[EOS] of human stratum corneum and to identify the chemical structures of their subspecies. High-performance thin-layer chromatography and normal-phase high-performance liquid chromatography were used for the separation of CER fractions, whereas nanoelectrospray ionization tandem mass spectrometry was applied to investigate the chemical structures in detail. Thus, CER[EOS] fragmentation revealed that in addition to linoleic acid other esterified fatty acids occur in the ω-position. Of particular interest is the identification of a 17:2 fatty acid located in this part of the molecule. Several subspecies of CER[NP], including subspecies with odd numbers of carbon atoms in both chains, the non-α-hydroxylated fatty acid moiety (part N) and the phytosphingosine (part P), were identified. Furthermore, it was found that 12% of CER[NP] subspecies have an odd number of carbon atoms in both chains of the molecule. Similar results were obtained for CER[EOS]. Both the esterified fatty acid (part E) and the sphingosine base (part S) were found to contain odd-numbered chain lengths. These results underline the heterogeneity of the CER composition in the stratum corneum lipid bilayer.

FTIR microscopy and confocal Raman microscopy for studying lateral drug diffusion from a semisolid formulation

Fourier transform infrared (FTIR) microscopy was applied to obtain information on lateral drug diffusion of dithranol in artificial acceptor membranes. Lateral (2D) drug distribution into an artificial membrane was investigated on an area of 300microm x 1000microm with a lateral resolution of 25microm x 25microm by integrating a specific IR band located at 1430cm(-1). The concentration profiles show a heterogeneous distribution of dithranol particles resulting in non-uniform drug diffusion. Use of the FTIR microscope either in the transmission or in the reflection mode was restricted to a thickness of the DDC membrane <15microm. The third dimension (depth profile) was analysed by means of confocal Raman microscopy (CRM). In an artificial membrane, the depth range from a minimum of 1.5microm up to a maximum of 49microm was analysed for dithranol distribution.

Characterization and activity of cephalosporin metal complexes

Semi-synthetic cephalosporin antibiotics have structures similar to that of penicillins, and both groups of compounds are characterized by similar properties and determined by the same methods. Most antibiotics, including cephalosporins and their decomposition products, contain electron donor groups that can bind naturally occurring metal ions in vivo. Cephalosporin antibiotics exhibit a change in their toxicological properties and biological performance when they were tested as metal complexes. The proposed reason for such a behavior is the capability of chelate binding of the cephalosporins to the metals. In an attempt to understand the coordination mode of metals with cephalosporins, different spectroscopic techniques such as IR, UV-visible, NMR spectroscopy and voltammetric measurements were carried out to elucidate the structure of the metal-cephalosporin complexes. Synthesis, characterization and biological screening of the cephalosporins and of the cephalosporin-metal complexes are discussed in this review. However, little information is available on the influence of the metal ions on the pharmacokinetics of the cephalosporin derivatives.

Optical methods for measurements of skin penetration

Fourier transform infrared photoacoustic (PAS), photothermal deflection (PDS) and Raman spectroscopy belong to the modern innovative noninvasive analytical tools that are beginning to be recognized as highly potential techniques for the noninvasive study of biological tissues and human skin under in vivo conditions. They can be applied to obtain information regarding the molecular composition of the skin down to several hundred micrometers below the skin surface. All three methods allow depth-resolved investigations. While PAS and PDS use a frequency modulation of the excitation beam to reach deeper regions in the sample, the principle of confocal Raman microspectroscopy (CRM) is a movement of the specimen in the focal plane. In consideration of depth measurements PAS and PDS complete the applicable spectrum of CRM, since Raman microscopy requires particular transparent materials.

Hydrophilic silica aerogels as dermal drug delivery systems--dithranol as a model drug

A special class of porous silica materials, silica aerogels, was recently shown to be a potential candidate for oral drug delivery systems. It was demonstrated, that stability of drugs and their dissolution rate can essentially be improved through the adsorption on to these materials. In this work, drug loaded silica aerogels are firstly applied as dermal drug delivery systems. Dithranol is used as a representative drug since there is a need to enhance its dermal availability. The unstable and nearly water-insoluble drug exhibits a poor penetration. Release of dithranol from aerogels into various semi-solid formulations and its dissolution as well as the release and penetration into artificial membranes were investigated by Fourier-transform infrared attenuated total reflection (FTIR-ATR) spectroscopy. Two model membranes (one hydrophilic and one lipophilic) were applied. Several formulations were tested and the most promising one was used in order to study the penetration of dithranol into human stratum corneum (SC). Dithranol adsorbed on hydrophilic silica aerogels exhibited superior penetration behaviour compared to that of the standard ointment (dithranol in white soft paraffin).

Properties of ceramides and their impact on the stratum corneum structure. Part 2: stratum corneum lipid model systems

The stratum corneum (SC) represents the outermost layer of the mammalian skin, exhibits the main skin barrier and plays an important role in the water penetration pathway through the SC. Knowing the structure and properties of the SC at the molecular level is essential for studying drug penetration through the SC and for the development of new dermal drug delivery systems. Therefore, research interest is focused on the SC lipid matrix and on water diffusion through it. Thus, the ultimate aim is to design a lipid mixture that mimics the barrier properties of the human SC to a high extent and that can substitute the SC in drug delivery systems. This review summarizes various studies performed on either isolated animal or human ceramide based SC model systems, coming to the result that using synthetic lipids with a well-defined architecture allows good extrapolation to the in vivo situation. This review is the continuation of part 1 that is focused on a detailed description of the thermotropic and/or lyotropic phase behaviour of single ceramide types obtained by various experimental techniques. The objective of part 2 is to reflect the numerous studies on SC lipid model systems, namely binary, ternary and multicomponent systems, during the last decade. In this context, neutron diffraction as a prospective tool for analyzing the internal membrane structure is addressed in particular. Based on these new insights, current SC models are presented, whose validations are still under discussion. A profound knowledge about SC lipid organization at the molecular level is still missing.

Properties of Ceramides and Their Impact on the Stratum Corneum Structure: A Review

The lipid matrix of the stratum corneum (SC) is the major diffusion-rate-limiting pathway by which most drugs intracellularly pass the SC. The major lipid classes extracted from the SC are ceramides, cholesterol and free fatty acids. Ceramides that comprise nine subclasses play a crucial role in maintaining the barrier function of the skin. A profound knowledge of the physical properties of ceramides is essential for a deeper understanding of the impact of each ceramide species on the barrier function. The review summarizes the thermotropic and/or lyotropic behaviour of sphingosine-type ceramides (CER AS, CER NS) and phytosphingosine-type ceramides (CER AP, CER NP) revealed by differential scanning calorimetry, X-ray diffraction, Fourier transform infrared spectroscopy and Fourier transform Raman spectroscopy in past decades. Polymorphism is a characteristic feature of ceramides. At physiological temperatures, all crystalline phases of ceramides exhibit lamellar structures with highly ordered hydrocarbon chains. The differential behaviour of the head groups of ceramides may be an important determinant for the skin barrier function.

Sublimation of antimycotic agents as proved by various analytical methods

Qualitative and quantitative results demonstrate that the pure substances amorolfine base, amorolfine hydrochloride, two selected morpholine derivatives and terbinafine hydrochloride are clearly able to sublimate. As amorolfine hydrochloride is also capable to sublimate from galencial forms laquer and cream in this experimental setup, a clinical relevance of sublimation phenomenon at least for topical treatment of onychomycosis has to be considered. This phenomenon could be one reason for advantageous clinical and mycological cure rates of amorolfine nail laquer to comparable topical products reported in the literature.

Different physicochemical properties of antimycotic agents are relevant for penetration into and through human nails

This article reports the characterization of the physicochemical properties of two important antifungal topical drugs, amorolfine and ciclopirox. Furthermore, the release of the drugs from commercial lacquer formulations for treatment of onychomycosis was studied using the online FTIR-ATR technique. Based on the physicochemical background of these two drugs and their release from commercial lacquer formulations for treatment of onychomycosis, the suitability of these drugs for optimized local antifungal therapy to human nails is discussed. Amorolfine appears to be more suitable for drug delivery to human nails because it penetrates into the nails via the hydrophilic pathway. Furthermore amorolfine penetrates very well into fungal cells, due to the pH value of the nail, as well as the pKa value of this antimycotic agent and the lipophilic properties of its base form.

Overcoming the Stratum Corneum: The Modulation of Skin Penetration

It is preferred that topically administered drugs act either dermally or transdermally. For that reason they have to penetrate into the deeper skin layers or permeate the skin. The outermost layer of the human skin, the stratum corneum, is responsible for its barrier function. Most topically administered drugs do not have the ability to penetrate the stratum corneum. In these cases modulations of the skin penetration profiles of these drugs and skin barrier manipulations are necessary. A skin penetration enhancement can be achieved either chemically, physically or by use of appropriate formulations. Numerous chemical compounds have been evaluated for penetration-enhancing activity, and different modes of action have been identified for skin penetration enhancement. In addition to chemical methods, skin penetration of drugs can be improved by physical options such as iontophoresis and phonophoresis, as well as by combinations of both chemical and physical methods or by combinations of several physical methods. There are cases where skin penetration of the drug used in the formulation is not the aim of the topical administration. Penetration reducers can be used to prevent chemicals entering the systemic circulation. This article concentrates on the progress made mainly over the last decade by use of chemical penetration enhancers. The different action modes of these substances are explained, including the basic principles of the physical skin penetration enhancement techniques and examples for their application.

What can we learn about the lipid vesicle structure from the small-angle neutron scattering experiment?

Small-angle neutron scattering (SANS) on the unilamellar vesicle (ULV) populations (diameter 500 and 1,000 A) in D2O was used to characterize lipid vesicles from dimyristoylphosphatidylcholine (DMPC) at three phases: gel Lbeta', ripple Pbeta' and liquid Lalpha. Parameters of vesicle populations and internal structure of the DMPC bilayer were characterized on the basis of the separated form factor (SFF) model. Vesicle shape changes from nearly spherical in the Lalpha phase to elliptical in the Pbeta' and Lbeta' phases. This is true for vesicles prepared via extrusion through pores with the diameter 500 A. Parameters of the internal bilayer structure (thickness of the membrane and the hydrophobic core, hydration and the surface area of the lipid molecule) were determined on the basis of the hydrophobic-hydrophilic (HH) approximation of neutron scattering length density across the bilayer rhox and of the step function (SF) approximation of rhox. DMPC membrane thickness in the Lalpha phase (T = 30 degrees C) demonstrates a dependence on the membrane curvature for extruded vesicles. Prepared via extrusion through 500 A diameter pores, vesicle population in the Lalpha phase has the following characteristics: average value of minor semi-axis 266 +/- 2 A, ellipse eccentricity 1.11 +/- 0.02, polydispersity 26%, thickness of the membrane 48.9 +/- 0.2 A and of the hydrophobic core 19.9 +/- 0.4 A, surface area 60.7 +/- 0.5 A2 and number of water molecules 12.8 +/- 0.3 per DMPC molecule. Vesicles prepared via extrusion through pores with the diameter 1,000 A have polydispersity of 48% and membrane thickness of 45.5 +/- 0.6 A in the Lalpha phase. SF approximation was used to describe the DMPC membrane structure in Lbeta' (T = 10 degrees C) and Pbeta' (T = 20 degrees C) phases. Extruded DMPC vesicles in D2O have membrane thickness of 49.6 +/- 0.5 A in the Lbeta' phase and 48.3 +/- 0.6 A in the Pbeta' phase. The dependence of the DMPC membrane thickness on temperature was restored from the SANS experiment.

Antioxidant and photoprotective properties of an extract from buckwheat herb (Fagopyrum esculentum MOENCH)

In recent years, the incidence of skin cancer has risen remarkably. Sun light, especially the included ultraviolet (UV)-radiation, is seen as important trigger for the development of skin cancer. Thus, there is an increasing interest in the development of UV-protective substances to use them as sun care products. One approach is the topical application of herbal antioxidants. Plant-derived antioxidants are often extracts and therefore contain a complex mixture of constituents, like flavonoids and polyphenols, which contribute to the overall activity of the extract. In the present study an extract from buckwheat herb was compared to rutin, which is the main constituent of the extract, regarding their antioxidant and radical scavenging activity. Additionally, the photoprotective properties of the extract were compared to those of a commercial UV absorber. The antioxidant activity was quantified regarding the reactivity versus the 1,1-diphenyl-2-picryl-hydrazyl radical (DPPH). The photoprotective properties of the extract were examined by the inhibition of the photosensitized lipid peroxidation of linolic acid. In the DPPH assay, the extract had significantly better antioxidant activity than pure rutin. The extract prevented more effectively the UV-induced peroxidation of linolic acid than rutin itself or the commercial UV absorber. The use of the extract from buckwheat herb seems to be more beneficial than the use of pure rutin. This can be referred to the presence of minor phenolic compounds in the extract. The results indicate that it is advisable to use antioxidants rather than only UV absorber to obtain a maximum of photo protection.

Polymorphism of ceramide 6: a vibrational spectroscopic and X-ray powder diffraction investigation of the diastereomers of N-(alpha-hydroxyoctadecanoyl)-phytosphingosine

A preparative chromatographic method was developed for the quantitative isolation of the diastereomers of synthetic N-(alpha-hydroxyoctadecanoyl)-phytosphingosine (DL-CER6). The L- and the D-compound were studied each by means X-ray powder diffraction, FT-Raman and FT-IR spectroscopy. The diastereomers exhibit different thermotropic polymorphism. Three lamellar crystalline and a lamellar liquid crystalline phase were found for L-CER6. The natural occurring D-CER6 forms an Lalpha phase with a larger repeating distance than the L-CER6. The two lamellar crystalline phases of the D-compound have a significant larger dimension than those of the L-compound. The addition of water lowers the phase transition temperatures but does not induce structural changes such as incorporation into the lamellar sheets.

Interaction of water with different cellulose ethers: a Raman spectroscopy and environmental scanning electron microscopy study

Different non-ionic cellulose ethers like methyl cellulose (MC), hydroxypropyl cellulose (HPC) and hydroxypropylmethyl cellulose (HPMC) were investigated. The characterization of the cellulose ethers was carried out by thermogravimetry and sorption/desorption isotherms. Differences in the properties of the cellulose ether films were described by time-dependent contact angle measurements. Changes in molecular structure of the raw materials, gels and films caused by water contact were studied using Raman spectroscopy. Differences between the substitution types and changes due to the gel or film formation were observed. An environmental scanning electron microscopy (ESEM) technique was used to distinguish the morphological behaviour of the cellulose ether films in contact with water. Based on in-situ ESEM experiments, the swelling and drying behaviour of the various stages of cellulose ether films (film-hydrated film-dried film) were quantified by using image analysis.

Characterization of peptides resulting from digestion of human skin elastin with elastase

Several pathological disorders are associated with abnormalities in elastic fibers, which are mainly composed of elastin. Understanding the biochemical basis of such disorders requires information about the primary structure of elastin. Since the acquisition of structural information for elastin is hampered by its extreme insolubility in water or any organic solvent, in this study, human skin elastin was digested with elastase to produce water-soluble peptides. Tandem mass spectrometry (MS/MS) experiments were performed using conventional electrospray ionization (ESI) and nano-ESI techniques coupled with ion trap and quadrupole time-of-flight (qTOF) mass analyzers, respectively. The peptides were identified from the fragment spectra using database searching and/or de novo sequencing. The cleavage sites of the enzyme and, for the first time, the extent and location of proline hydroxylation in human skin elastin were determined. A total of 117 peptides were identified with sequence coverage of 58.8%. It has been observed that 25% of proline residues in the sequenced region are hydroxylated. Elastase cleaves predominantly at the C-terminals of the amino acids Gly, Val, Leu, Ala, and Ile, and to a lesser extent at Phe, Pro, Glu, and Arg. Our results confirm a previous report that human skin elastin lacks amino acid sequences expressed by exon 26A.

Comparative in vitro investigation of the forces exerted by eye drops and eye spray

Topical administration of ophthalmic drugs is predominantly carried out in the form of eye drops. The application of an eye spray represents a feasible alternative to drop instillation with regard to the clinical efficacy. In this study the forces exerted during the application of eye drops and eye spray to a surface were measured in vitro and compared with each other. Whereas the maximal forces that occurred with a falling drop tended to increase with greater application distance, the forces decreased with spraying. From an application distance of 3 cm the eye spray proved to have a more favorable mechanical force effect than the eye drops. In view of the loss of experimental liquid caused by spray application as well as the diameter of the spray cone, a spray distance of from 4 cm to 5 cm can be deemed to be optimal.

New insights into the structure and hydration of a stratum corneum lipid model membrane by neutron diffraction

The structure and hydration of a stratum corneum (SC) lipid model membrane composed of N-(alpha-hydroxyoctadecanoyl)-phytosphingosine (CER6)/cholesterol (Ch)/palmitic acid (PA)/cholesterol sulfate (ChS) were characterized by neutron diffraction. The neutron scattering length density across the SC lipid model membrane was calculated from measured diffraction peak intensities. The internal membrane structure and water distribution function across the bilayer were determined. The low hydration of the intermembrane space is a major feature of the SC lipid model membrane. The thickness of the water layer in the SC lipid model membrane is about 1 A at full hydration. For the composition 55% CER6/25% Ch/15% PA/5% ChS, in a partly dehydrated state (60% humidity) and at 32 degrees C, the lamellar repeat distance and the membrane thickness have the same value of 45.6 A . The hydrophobic region of the membrane has a thickness of 31.2 A . A decrease of the Ch content increases the membrane thickness. The water diffusion through the SC lipid model multilamellar membrane is a considerably slow process relative to that through phospholipid membranes. In excess water, the membrane hydration follows an exponential law with two characteristic times of 93 and 44 min. At 81 degrees C and 97% humidity, the membrane separates into two phases with repeat distances of 45.8 and 40.5 A . Possible conformations of CER6 molecules in the dry and hydrated multilayers are discussed.

Characterization of the force effect of aqueous and oily eye drops

During the instillation of eye drops the drop impact affects a mechanical irritation on the eye surface. The force impact occurring in the moment of impact may be measured in vitro. Four commercially available eye drop preparations of different consistency and viscosity were tested. In dependance on the drip distance, the quantity of force impact was determined as well as the maximally effecting force during impact in each case. Whereas the force impact increased with all preparations with rising drip distance, only the higher viscosity solutions showed an approximate linear increase of the maximal force. With the aqueous low-viscosity eye drops, peak forces were ascertained. The drop oscillation was considered as the cause. The test results show that the consistency of eye drop preparations and their resulting physical-chemical properties like viscosity influence the quantity of the maximal force during the drop impact.

Properties of ternary phospholipid/dimethyl sulfoxide/water systems at low temperatures

X-ray diffraction, neutron diffraction and differential scanning calorimetry were used to investigate phase transitions in the ternary system phospholipid/dimethyl sulfoxide (DMSO)/water under cooling for three homologous phospholipids: dimyristoylphosphatidylcholine (DMPC), dipalmitoylphosphatidylcholine (DPPC), and distearoylphosphatidylcholine (DSPC). Below the temperature of ice formation from -40 to -113 degrees C, a new lamellar phase of DPPC and DSPC was found at and above a DMSO molar fraction of X(DMSO) = 0.05. Below X(DMSO) = 0.05 only a single dehydrated Lc-phase exists after ice formation. The new phase has an increased membrane repeat distance and coexists with a dehydrated Lc-phase. DPPC with a DMSO molar fraction of X(DMSO) = 0.07 shows a membrane repeat distance of the new phase of d = 6.61 +/- 0.03 nm. The value of d increases at the increase of X(DMSO). The new phase was not observed in the ternary system with DMPC. No correlation between the new phase and the glass transition of bound water in the intermembrane space was detected. The new phase was detected only in the systems with excess of water. The creation of the new phase demonstrates the specific DMSO interaction with hydrocarbon chains.

[Liberation of hydrocortisone acetate from different commercial formulations]

Liberation of hydrocortisone acetate from different commercial formulations In this article the release of hydrocortisone acetate (HC-acetate) from three commercial semisolid formulations (Ebeno-ointment, Soventol HC cream and Fenistil hydrocortisone ointment) was measured by means of a multilayer membrane system (MLMS) described in the literature. The formulations are different regarding rate and extent of the release of HC-acetate. The release of HC-acetate form the Soventol HC cream is very fast and results in high topical availability. In contrast, HC-acetate shows a sustained release from the Fenistil hydrocortisone ointment. The release of HC-acetate from the Ebenol-ointment is between that of the Soventol HC cream and that of the Fenistil-ointment. In summary, HC-acetate shows a shorter mean liberation time (MDT) and a higher topical availability from Soventol HC cream in comparison to the other formulations studied.

Mass spectrometric examinations of stratum corneum lipid models exposed to ultraviolet irradiation

Lipid model systems consisting of the major components of the stratum corneum intercellular lipid matrix were studied to investigate the ultraviolet-radiation-mediated damage of these biomolecules. Pure lipids and liposomes were irradiated using a lamp emitting a solar radiation spectrum. The influences of the irradiation and the effects of added iron ions were studied by electrospray ionization mass spectrometry (MS) with an ion trap analyser. Exact mass measurements were carried out using a time-of-flight mass spectrometer. Only linolenic acid and cholesterol were found to be subject to oxidative changes caused by UV irradiation whereas the other lipids examined (dipalmitoylphosphatidylcholine, ceramide III and cholesterol sulphate) were stable to oxidative stress. Several lipid adducts were observed upon analysis of the liposomes. The composition of these adducts was identified by MS/MS experiments.

Biopharmaceutical characterization of some synthetic purine drugs

Hydrophilic-lipophilic properties (water solubility, n-octanol/water partition coefficient, transport across membranes) of some mercaptopurines (6-MP, 6-TG, AZA and a new AZA derivative--metazathioprine (MAZA) were determined. MAZA is the most lipophilic compound due to low aqueous solubility and high n-octanol/water partition coefficient. The fluxes from the donor medium into the membrane and from the membrane into the acceptor medium are highest for MAZA as well. The partition coefficients of the other purines decrease in the order: AZA > 6-TG > 6-MP.

Evaluation of the anti-microbial and anti-inflammatory activities of the medicinal plants Dodonaea viscosa, Rumex nervosus and Rumex abyssinicus

The crude extracts of the leaves of Dodonaea viscosa and Rumex nervosus as well as of the root of Rumex abyssinicus were tested for anti-microbial and anti-inflammatory activities. It was observed that the three plants possess antibacterial activity against Streptococcus pyogenes and Staphylococcus aureus and strong activity against Coxsackie virus B3 and influenza A virus. In contrast, none of them exhibited anti-fungal activity. The anti-inflammatory activity test results verified that only R. abyssinicus inhibited the synthesis of prostaglandin (PG) E(2).

Adhesive backing foil interactions affecting the elasticity, adhesion strength of laminates, and how to interpret these properties of branded transdermal patches

Standard tensile strength and peel adhesion tests were carried out to investigate interactions of pressure-sensitive adhesives (PSAs) with several backing foils used for transdermal patches. Seven branded transdermal patches (Alora, Cutanum, Estraderm MX 50, Estraderm TTS 50, Fem7 -50 micrograms, Menorest, Oesclim) were included in the investigation. Their skin adhesion measured in several clinical trials was compared with the results of the laboratory measurements according to PSTC-1 (Peel Adhesion for Single Coated Tapes 180 degrees Angle, Pressure Sensitive Tape Council, Illinois, 1996), such as Young's modulus at 3% elongation and peel adhesion to stainless steel. Data obtained for the PSA-coated backings (laminates) show increasing elasticity with increasing PSA thickness. Interactions of PSAs with backing foil became evident in significant changes in Young's modulus by low PSA thickness, as seen for the silicone adhesive. The Young's moduli of the laminates were found to be influenced not only by the elasticity of the backing foil but also by the chemical structure of the PSA. There was no correlation between the elasticity and peel adhesion of both the laminates and the branded patches. Likewise, for the branded patches the peel adhesion to stainless steel does not correlate with skin adhesion values obtained from clinical trials. The Young's modulus of the branded patches was between 4 N/mm2 (Oesclim) and 501 N/mm2 (Fem7). For the branded transdermal patches no correlation was found between Young's modulus and both the peel force on stainless steel and the skin adhesion reported in studies.

Evaluation of the release profiles of flavonoids from topical formulations of the crude extract of the leaves of Dodonea viscosa (Sapindaceae)

Quercetin and isorhamnetin are found in adequately large concentrations in the plant Dodonea viscosa (Sapindaceae). Plants that contain flavonoids are effective in the topical treatment of skin or mucous membrane inflammation. In this study, the release profiles of quercetin and isorhamnetin from hydrophilic, amphiphilic and lipophilic creams of the crude extract of Dodonea viscosa were determined using a multilayer membrane system. The results revealed that the hydrophilic cream provided the highest rate of release of both flavonoids while there was practically no release from the lipophilic cream. The hydrophilic cream may, therefore, serve most in delivering flavonoids to a diseased skin.