Permeability changes caused by surfactants in liposomes that model the stratum corneum lipid composition

A comparative study of the in vitro permeation of 2-phenoxyethanol in the skin PAMPA model and mammalian skin

For permeation studies that use excised skin, experimental data may show variability associated with the use of biological tissues. As a consequence, achieving reproducible results and data interpretation may be challenging. The skin parallel artificial membrane permeability assay (skin PAMPA) model has been proposed as a high-throughput tool for predicting skin permeation of chemicals. A number of skin cleansing wipe formulations for the diaper area of infants contain 2-phenoxyethanol (PE) as a preservative and cetylpyridinium chloride (CPC) as a surfactant with antimicrobial activity. However, information regarding cutaneous absorption of PE and CPC in the scientific literatures is remarkably limited. The main aim of the present study was to assess the suitability of the skin PAMPA model for prediction of skin permeation of PE. A secondary aim was to investigate the influence of CPC on the dermal absorption of PE. PE (1 % w/w) was prepared in two vehicles, namely propylene glycol (PG) and water-PG (WP). Permeability of PE was investigated in vitro using the skin PAMPA membrane, porcine skin and human skin under finite dose conditions. The highest permeation of PE was observed for the water-PG preparation with 0.2 % w/w of CPC. This finding was consistently observed in the skin PAMPA model and in Franz cell studies using porcine skin and human skin. Permeation of CPC was not detected in the three permeation models. However, permeation of PE increased significantly (p < 0.05) in the presence of CPC compared with formulations without CPC. When comparing the skin PAMPA data and the mammalian skin data for the cumulative amount of PE permeated, the r² values for PAMPA-porcine skin and PAMPA-human skin were 0.84 and 0.89, respectively. The findings in this study demonstrate the capability of the skin PAMPA model to differentiate between various doses and formulations and are encouraging for further applications of this model as a high throughput screening tool in topical formulation development.

Liposomes: structure, composition, types, and clinical applications

Liposomes are now considered the most commonly used nanocarriers for various potentially active hydrophobic and hydrophilic molecules due to their high biocompatibility, biodegradability, and low immunogenicity. Liposomes also proved to enhance drug solubility and controlled distribution, as well as their capacity for surface modifications for targeted, prolonged, and sustained release. Based on the composition, liposomes can be considered to have evolved from conventional, long-circulating, targeted, and immune-liposomes to stimuli-responsive and actively targeted liposomes. Many liposomal-based drug delivery systems are currently clinically approved to treat several diseases, such as cancer, fungal and viral infections; more liposomes have reached advanced phases in clinical trials. This review describes liposomes structure, composition, preparation methods, and clinical applications.

How do dermatological vehicles influence the horny layer?

Emulsifying agents in aqueous solution lead to dehydration of the horny layer of the epidermis and damage to the barrier. This is only partly true if emulsifying agents are constituents of emulsions. Water-in-oil (W/O) emulsions cause an improvement in the hydration of the horny layer and barrier function. In the case of an additional effect of wash solutions, a partial or complete abolition of the drying out and barrier-damaging effect of the wash solution results. Oil-in-water (O/W) emulsions without glycerol have no effect on the moisture of the horny layer or indeed increase it, but they lead to considerable damage to the barrier and irritation. In wash tests, they do not induce any protective effect. With micro-emulsions this is still more the case and, moreover, they can also lead to exsiccation. As a result of the addition of glycerol, the barrier-damaging effect can be abolished. Also in stress tests with wash solutions, the damage to the horny layer is reduced by glycerol-containing O/W emulsions. Whereas the penetration-promoting effect of O/W emulsions without glycerol is best, only W/O emulsions or glycerol-containing O/W emulsions are suitable for atopic dermatitis. A hydrating effect on the stratum corneum was also found in a propylene glycol ointment.

Cleansing, dehydrating, barrier-damaging and irritating hyperaemising effect of four detergent brands: comparative studies using standardised washing models

BACKGROUND AND PROBLEM: It is well known that the damaging effect of surfactants on the stratum corneum varies according to the surfactant used. The present investigations aim to compare four standard commercial cleansing solutions (Esemptan Cleansing Lotion, Stephalen Shower Gel, Manipur Antimicrobial Cleansing Solution and Tork Mevon 55 Liquid Soap) with respect to their cleansing and skin barrier-damaging effects.

MATERIAL AND METHODS

The cleansing effect of the solutions was determined in relation to their concentrations in a first experimental series involving 15 subjects using a standardised test method. The product concentrations with the most divergent cleansing effects were tested for their dehydrating (corneometry), epidermal barrier-damaging (TEWL) and irritating effects (laser Doppler) in a standardised washing test. In a second experimental series, the concentration used for the cleansing solutions was based on the quantity of cleansing solution obtained from dispenser actuations (six actuations/L). These concentrations were used to test the cleansing and damaging effect on the stratum corneum using the same methods as in the first experimental series.

RESULTS

There were no significant differences in the first experimental series. In the second experimental series, Stephalen Shower Gel showed disadvantages in terms of a small cleansing effect, but without evidence of a smaller stratum corneum-damaging effect, and Tork Mevon 55 Liquid Soap showed advantages in terms of a smaller stratum corneum-damaging effect, but without evidence of a smaller cleansing effect.

CONCLUSIONS

These studies showed that the relationship between the cleansing and the damaging effect on the stratum corneum can be properly assessed only by testing different concentrations. Furthermore, this experimental approach allowed to differentiate the four tested cleansing solutions.

Cleansing without compromise: the impact of cleansers on the skin barrier and the technology of mild cleansing

Cleanser technology has come a long way from merely cleansing to providing mildness and moisturizing benefits as well. It is known that harsh surfactants in cleansers can cause damage to skin proteins and lipids, leading to after-wash tightness, dryness, barrier damage, irritation, and even itch. In order for cleansers to provide skin-care benefits, they first must minimize surfactant damage to skin proteins and lipids. Secondly, they must deposit and deliver beneficial agents such as occlusives, skin lipids, and humectants under wash conditions to improve skin hydration, as well as mechanical and visual properties. While all surfactants tend to interact to some degree with lipids, their interaction with proteins can vary significantly, depending upon the nature of their functional head group. In vitro, ex vivo, and in vivo studies have shown that surfactants that cause significant skin irritation interact strongly with skin proteins. Based on this understanding, several surfactants and surfactant mixtures have been identified as "less irritating" mild surfactants because of their diminished interactions with skin proteins. Surfactants that interact minimally with both skin lipids and proteins are especially mild. Another factor that can aggravate surfactant-induced dryness and irritation is the pH of the cleanser. The present authors' recent studies demonstrate that high pH (pH 10) solutions, even in the absence of surfactants, can increase stratum corneum (SC) swelling and alter lipid rigidity, thereby suggesting that cleansers with neutral or acidic pH, close to SC-normal pH 5.5, may be potentially less damaging to the skin. Mildness enhancers and moisturizing agents such as lipids, occlusives, and humectants minimize damaging interactions between surfactants, and skin proteins and lipids, and thereby, reduce skin damage. In addition, these agents play an ameliorative role, replenishing the skin lipids lost during the wash period. The present review discusses the benefits of such agents and their respective roles in improving the overall health of the skin barrier.

[Effects of emulsions on the stratum corneum barrier and hydration]

The appearance of the skin depends greatly on the hydration of the stratum corneum which is regulated by water binding substances of the corneocytes and also by the quality of the stratum corneum lipids. Furthermore these lipids are responsible for the barrier function. In patients with atopic dermatitis, the water binding capacity and the barrier function of the stratum corneum are reduced even in clinically healthy skin areas. Emollients can damage the stratum corneum and lead to desiccation and a disturbance of the barrier. This effect is a result of an increased permeability of the barrier lipids and direct damage to the keratinocytes and corneocytes. The degree of damage of the barrier caused by emollients in dermatological vehicles has not been sufficiently investigated. As suggested by hypothetical considerations, such an effect is not expected and cannot be demonstrated in water-in-oil-emulsions. Oil-in-water-emulsions without glycerol as well as lipophilic and hydrophilic microemulsions do damage the barrier function. Both types of microemulsions additionally lead to a dehydration of the stratum corneum. The damaging effect of oil-in-water-emulsions can be reduced by the addition of glycerol and urea.