Water is the most ubiquitous component. As universal biological solvent, it is an important and essential for all living cells. Water allows chemical reactions inside cells (enzymatic reactions…) and stability of all living systems (like cells and membranes…) is always controlled by a sensible balance of hydrophilic and hydrophobic interactions. In human biology as in plant biology, hydration corresponds to water absorption by the organism, improving water intake and/or reducing water loss. Different strategies exist to maintain water in the tissue, in or outside the cells. The number of potential H-bonds helps to reticulate molecules of water, thanks to osmolytes for example. Well represented in plant or human biology, they are small molecules composed by organic matter, and soluble in intracellular media. They play a role against different environmental stress such as dehydration. In this case, lack of water could threaten cellular integrity, proteins conformation and stability. Through their structure, osmolytes offer numerous free terminations –OH, and/or pairs of electrons in doublet (-O-; -S-; -N=) to stabilize proteins but also water molecules. Osmolytes family can be divided into three groups: (1) small-sized carbohydrates (such as trehalose, polyols, glycerol, inositol etc. and their derivatives); (2) amino-acids (glycine, proline, taurine etc.); (3) methylamines (glycine betaine). We focused on myoinositol and taurine, that are really conserved and the main represented in epidermal keratinocytes.
Myoinositol is an isomer from the simple sugar inositol (C6H12O6), presenting 6 hydroxyl terminations. It is named phytic acid in plant physiology. The sodium-dependent myoinositol transporter (SMIT) is known to be expressed by human keratinocytes under different stress conditions (osmolality and Ultra-Violet, UV). In another hand, taurine is a sulphur containing derivative from amino acid (NH2-CH2-CH2-SO3H). Literature indicates the presence of taurine and of its transporter (TAUT) in the epidermis and relates that the accumulation of taurine as one potential mechanism protecting epidermal keratinocytes from dehydration. Cultured human keratinocytes accumulated taurine in a concentration- and osmolarity-dependent manner. A high level of taurine protects cultures of keratinocytes from both osmotically induced and UV-induced apoptosis. This so-called osmolytes strategy requires not only the expression of specific osmolytes but also the expression of their specific transporting systems. Both are important for keratinocytes capacity to maintain cell volume homeostasis in several stress conditions. Aging and especially photo-aging is characterized by the deterioration of tissue structure and function. Reduction in keratinocyte cell size with age and a downregulation of osmolytes transporters SMIT and TAUT with UV exposure were reported. This confirms that osmolytes play a critical role in cutaneous age‐related.
In this study we present results concerning a biotechnological active ingredient obtained from butterfly lavender (Lavendula stoechas) dedifferentiated cells. First, using full transcriptomic analysis after 24h of contact on human keratinocytes, we demonstrated an increase of cluster genes linked to osmolytes metabolism. Our extract stimulated BAAT, CDO1, GADL1 genes that are coding for taurine precursors. It increased the transcription of taurine but also the expression of the corresponding protein by 27% (ELISA method). Using RT-qPCR we demonstrated the improvement of TAUT, and SMIT in parallel. Then, we wanted to focus on the cellular consequences and on the effects on skin. We obtained very impressive pictures of treated keratinocytes. After their analysis, we showed the increase of cellular surface up to 36%*** (p<0.001) in condition of treatment. If keratinocytes were put in dehydrated conditions, water lost corresponded to 42%*** and if they were also treated by the extract the loss of water was reduced by 50%, to reach only 21% of loss. Raman spectroscopy helped us to demonstrate the improvement of water reserves in skin explants due to the treatment. There were 69%* (p<0.1) more signal corresponding to water signature in the tissue. Finally, we used epidermal reconstructed models that we submitted to osmotic stress. Treated models showed a fully increased thickness of living epidermis but also of stratum corneum, a stimulated viability by 89%*** and an alteration of nuclei (pyknotic cells) reduced by 38%** (p<0.01).
In this study, we confirmed the importance of osmolytes in skin biology and homeostasis. Water management by osmolytes induced reduction of markers for stress and aging.