Raphael Leschiera

Antioxidant and anti-inflammatory effects of Ruta chalepensis L. extracts on LPS-stimulated RAW 264.7 cells

Ruta chalepensis L. is used in the traditional herbal treatment of various diseases. The aim of this work is to investigate the effect of different extracts of R. chalepensis L. on inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) gene expressions and their antioxidant capacity on murine RAW 264.7 macrophage challenged with lipopolysaccharide (LPS). In fact, this study shows that the ethanol and ethyl acetate extracts of R. chalepensis L. considerably decreased the nitric oxide (NO) production in murine RAW 264.7 macrophages stimulated with lipopolysaccharide. Thus, the treatment with both extracts significantly suppressed the levels of iNOS and COX-2 gene expressions through the inhibition of the nuclear factor-κB (NF-κB) activation. The preincubation of RAW 264.7 cells with various concentrations of ethanol and ethyl acetate extracts decreased the production of thiobarbituric acid-reactive substances (TBARS) in a dose-dependent manner. It also increased the activities of antioxidative enzymes, including superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) in LPS-stimulated macrophages, compared to those in the cells treated only with LPS. Besides, the 1H NMR spectra of both extracts have demonstrated the presence of aromatic signals, thus confirming the existence of phenolic compounds such as flavonoids and polyphenols. So, the ethanol and ethyl acetate extracts of R. chalepensis L. have been shown to possess enough antioxidant and anti-inflammatory activities to prevent LPS-induced oxidative stress and inflammation in RAW 264.7 macrophages.

What about physical contacts between epidermal keratinocytes and sensory neurons

Recent studies have demonstrated that keratinocytes closely participate in sensory transduction, and therefore, intra‐epidermal free nerve endings are not exclusive transducers of pain. This discovery implies the existence of close afferent communication from keratinocytes to sensory neurons. Although reciprocal interactions between keratinocytes and intra‐epidermal free nerve endings via soluble mediators are well established, little attention has been paid to physical contacts between keratinocytes and intra‐epidermal free nerve endings. This review proposes to consider the ultrastructural and functional knowledge of these contacts, in both human skin biopsies and keratinocyte‐sensory neuron cocultures to speculate on the possible existence of synaptic contacts.

In vitro models to study cutaneous innervation mechanisms

The skin is densely innervated to transmit all sensations (touch, temperature, pressure, pain, and pruritus) but not only it. Indeed, innervation plays a major role in the structuration of the epidermis, in its renewal, and in the process as wound healing. There are increasing evidences that skin cells and cutaneous nerve endings are in close interactions each other. So, to study them is an important issue to better understand the behavior of the skin and its both physiological and pathological processes. However, due to scientific, technical, ethical, or economic reasons, the study of these interactions in human or animals in vivo remains quite impossible. So, the development of in vitro models is crucial to better understand them. Since several years, all the actors of these interactions, skin cells such as keratinocytes, fibroblasts, melanocytes, Merkel cells or stem cells, and sensory neurons, could be extracted and cultured independently or together so named 2-D cocultures. Other cocultures, the 3-D cocultures, could also be considered by the use of the epidermis or dermis or whole portions of native or reconstructed skin. These 3-D models offer also an alternative by the use of compartmented cocultures to only analyze the biochemical communication between the different types of cells. After a description of the different models available, this chapter will give some clues to define the best model(s) depending of the applications and, finally, will discuss of the advantages and the limitations of these types of cultures to study cutaneous innervation mechanisms.

Major Role for TRPV1 and InsP3R in PAR2-Elicited Inflammatory Mediator Production in Differentiated Human Keratinocytes

PAR2 activation in basal keratinocytes stimulates inflammation via the Ca2+-dependent production of mediators such as IL-1β, TNF-α, and TSLP. In this study, we investigated PAR2 calcium signaling and the consequent production of inflammatory mediators in differentiated human primary keratinocytes (DhPKs). Stimulation with the PAR2-activating peptide SLIGKV promoted Ca2+ store depletion in both undifferentiated human primary keratinocytes and DhPKs. SLIGKV-evoked Ca2+ store depletion did not trigger the store-operated Ca2+ entry (i.e., SOCE) through ORAI1 in DhPKs compared with undifferentiated human primary keratinocytes. The inhibition of phospholipase C and the concomitant inhibition of TRPV1 and inositol triphosphate receptor in DhPKs abrogated the SLIGKV-evoked Ca2+ store depletion; NF-κB activity; and the production of inflammatory mediators such as IL-1β, TNF-α, and TSLP. Taken together, these results indicate a key role for both InsP3R and TRPV1 in Ca2+ internal stores in the PAR2-evoked Ca2+ release and consequent skin inflammation in DhPKs. These findings may provide clues to understanding the pathological role of DhPKs in skin disorders in which PAR2 is known to be involved, such as atopic dermatitis, Netherton syndrome, and psoriasis.

A new tool to test active ingredient using lactic acid in vitro, a help to understand cellular mechanism involved in stinging test: An example using a bacterial polysaccharide (Fucogel®)

The stinging test is an in vivo protocol that evaluates sensitive skin using lactic acid (LA). A soothing sensation of cosmetics or ingredients can be also appreciated through a decrease in stinging score. To predict the soothing sensation of a product before in vivo testing, we developed a model based on an LA test and substance P (SP) release using a co‐culture of human keratinocytes and NGF‐differentiated PC12 cells. A bacterial fucose‐rich polysaccharide present in Fucogel® was evaluated as the soothing molecule in the in vivo stinging test and our in vitro model. Excluding toxic concentrations, the release of SP was significant from 0.2% of lactic acid for the PC12 cells and from 0.1% of lactic acid for the keratinocytes. When the pH was adjusted to approximately 7.4, LA did not provoke SP release. At these concentrations of LA, 0.1% of polysaccharide showed a significant decrease in SP release from the two cellular types and in co‐cultures without modifying the pH of the medium. In vivo, a stinging test using the polysaccharide showed a 30% decrease in prickling intensity vs the placebo in 19 women between the ages of 21 and 69. Our in vitro model is ethically interesting and is adapted for cosmetic ingredients screening because it does not use animal experimentation and limits human volunteers. Moreover, Fucogel® reduced prickling sensation as revealed by the in vivo stinging test and inhibits the neurogenic inflammation as showed by our new in vitro stinging test based on SP release.