Studies of compounds that enhance sphingolipid metabolism in human keratinocytes1

Plant and Microalgae Derived Peptides Are Advantageously Employed as Bioactive Compounds in Cosmetics

Bioactive peptides (BP) are specific protein fragments that are physiologically important for most living organisms. It is proven that in humans they are involved in a wide range of therapeutic activities as antihypertensive, antioxidant, anti-tumoral, anti-proliferative, hypocholesterolemic, and anti-inflammatory. In plants, BP are involved in the defense response, as well as in the cellular signaling and the development regulation. Most of the peptides used as ingredients in health-promoting foods, dietary supplements, pharmaceutical, and cosmeceutical preparations are obtained by chemical synthesis or by partial digestion of animal proteins. This makes them not fully accepted by the consumers because of the risks associated with solvent contamination or the use of animal derived substances. On the other hand, plant and microalgae derived peptides are known to be selective, effective, safe, and well tolerated once consumed, thus they have got a great potential for use in functional foods, drugs, and cosmetic products. In fact, the interest in the plant and microalgae derived BP is rapidly increasing and in this review, we highlight and discuss the current knowledge about their studies and applications in the cosmetic field.

Skin diseases associated with the depletion of stratum corneum lipids and stratum corneum lipid substitution therapy

The skin is the largest organ of the body, whose main function is to protect the body against the loss of physiologically important components as well as harmful environmental insults. From the inside to the outside, the skin comprises three major structural layers: the hypodermis, the dermis and the epidermis. The epidermis contains four different sublayers, the stratum corneum (SC), stratum granulosum, stratum spinosum and stratum basale, where the barrier function of the skin mainly lies in the outermost layer of the epidermis, the SC. The SC contains corneocytes that are embedded in a lipid matrix existing in the form of lipid bilayers. The lipid bilayers are formed mainly from ceramides, free fatty acids and cholesterol, constitute the only continuous pathway across the SC and are responsible for the barrier function of the skin. However, the depletion or disturbance of SC lipids in the SC leads to a perturbation of the barrier function of the skin, and, conversely, several skin diseases such as psoriasis and atopic dermatitis are associated with the depletion of these SC lipids. Therefore, it is of paramount importance to understand the interrelationship between the depletion of SC lipids and skin diseases as well as factors that affect the composition and organization of SC lipids in order to assess the potential benefit of a direct replacement of the missing SC lipids as a means of treating affected, aged or diseased skin.

The lipid alterations in the stratum corneum of dogs with atopic dermatitis are alleviated by topical application of a sphingolipid-containing emulsion

BACKGROUND

Atopic dermatitis (AD) results from an altered skin barrier associated with defects in the lipid composition of the skin. Dogs with AD present similar clinical symptoms to humans, and may be a useful model for investigations into AD.

AIM

To analyse the changes occurring in the lipids of the stratum corneum (SC) of dogs with AE after 3 weeks of topical treatment with an emulsion containing ceramides, free fatty acids (FFAs) and cholesterol (skin lipid complex; SLC).

METHODS

Nonlesional SC was collected by tape stripping from control and treated areas. Free and protein-bound lipids were purified, and the various classes were isolated by column chromatography, analysed by thin-layer chromatography and assayed.

RESULTS

Ceramides, FFA and cholesterol were all found to be lower in the skin of untreated dogs with AD than in normal dogs, and the topical treatment resulted in significantly increased values for ceramides. Conversely, only trace amounts of glucosylceramides were present in normal SC, but a high concentration (27 μg per mg protein) was detected in canine atopic SC, which disappeared after treatment with SLC. There was a heterogeneous distribution of all of the lipids in the different layers of canine atopic SC, which was more pronounced for protein-bound than for free lipids. Following topical treatment, the protein-bound lipid content normalized.

CONCLUSIONS

Topical treatment with SLC resulted in a significant improvement of the lipid biosynthesis of keratinocytes in atopic dogs, thereby potentially enabling the formation of a tighter epidermal barrier.

Atopic dermatitis in dogs is associated with a high heterogeneity in the distribution of protein-bound lipids within the stratum corneum

The stratum corneum (SC) was taken from five atopic dogs by tape stripping (12 strips) of non-lesional areas of the abdomen. The free and protein-bound lipids were extracted and analyzed by thin-layer chromatography after fractionation on aminopropyl-bonded silica gel columns. A very frequent feature was the heterogeneity in the lipid content of consecutive layers. This was even more accentuated for the covalently bound lipids, with variations from one layer to another in the concentrations of cholesterol, omega hydroxylated ceramides and omega hydroxylated long-chain fatty acids. Among the free lipids, large amounts of glucosylceramides were present in canine atopic SC although they are nearly absent from the SC of normal dogs. A heterogeneous distribution of lipids was seen in canine atopic SC. These results suggest that strikingly deep variations occur in the lipid metabolism of keratinocytes in the skin of atopic dogs. In order to gain insight into this phenomenon, further studies should be focused on the activity of enzymes involved in both biosynthetic and catabolic processes.

Analysis of free and protein-bound ceramides by tape stripping of stratum corneum from dogs

The free and protein-bound ceramides of dog stratum corneum (SC) were analyzed by thin-layer chromatography after tape stripping of the abdomen of five dogs. The sphingoid bases were identified by gas-liquid chromatography as sphingosine, phytosphingosine, and 6-hydroxysphingosine. Electrospray ionization-ion trap mass spectrometry was used to characterize the protein-bound ceramides containing sphingosine and omega-hydroxy long-chain fatty acids. Although the molecular species were the same ones in all dogs, wide quantitative variations in the patterns of SC ceramides were observed in different breeds of dogs. The free ceramide concentration changed with the depth of SC, with a higher concentration in the deep layers, whereas the concentration of protein-bound ceramides remained constant. These results show that canine SC is close to that of humans with respect to ceramides.

The weak rate of sphingolipid biosynthesis shown by basal keratinocytes isolated from aged vs. young donors is fully rejuvenated after treatment with peptides of a potato hydrolysate

A new study was carried out to bring more information on the effect of the potato proteins ferment. Basal keratinocytes obtained from freshly excised skin samples of two groups of five donors, a young one (25-36-year-old) and an aged one (59-70-year-old) were established in culture. The results showed a downward trend in the content of all lipid fractions in untreated keratinocytes of aged donors when compared with young ones. We found major differences in the response of keratinocytes to potato proteins ferment treatment between young and old donors. Whereas the lipid content of cells from young donors increased either moderately or actually decreased in some cases in comparison with the untreated controls, the lipid biosynthesis was strongly stimulated in aged donors' keratinocytes whose lipid contents globally became close to those found in young donors. However, the changes elicited by potato proteins ferment treatment were not seen at the same extent for all lipid classes. Cholesterol content increased up to three-fold and alpha-hydroxy fatty acids were augmented up to seven-fold, whereas the increase in normal fatty acids was quite moderate. In sphingolipids labelled by incubation of keratinocytes in culture medium containing [(14)C]-serine, ceramides and glucosylceramides in cells from aged donors showed the highest uptake of radioactivity, with somewhat less incorporation in sphingomyelin and gangliosides. Therefore, it seems that potato proteins ferment has a much more potent stimulatory activity on the lipid biosynthesis of basal keratinocytes of aged donors, thereby normalizing the cellular lipid content that obviously decreases along with ageing. Although our results were obtained only with basal keratinocytes in this study, potato proteins ferment could be beneficial to maintain an efficient skin barrier in ageing people, provided that the peptides can get through to the basal membrane upon topical application.