Reducing sensitive skin discomfort

This special skin condition includes uncomfortable manifestations like prickling, burning, tingling, pain or itching, and occasional erythema and flush, which negatively affect the quality of the sufferer’s personal life. These alterations can be induced by several environmental agents (pollution, UV radiation, dryness, heat and others), lifestyle substances (cosmetics, soap), psychological conditions (like stress) and hormonal factors.1 Due to the variety of causes that can stimulate the appearance of the mentioned distressing symptoms, an increasing number of products are oriented to relieve sensitive skin, therefore reducing its undesired effects. Sensitive skin may worsen and give rise to inflammatory and/or pruritic chronic disorders such as atopic dermatitis (AD), dry skin and acne, which also share a common pattern of barrier impairment and increased vascular reactivity. During inflammation, a specific type of sensory neurons release peptides and neurotransmitters that act on target cells liberating several products such as cytokines, leading to further inflammation. Proteinase activated receptor 2 (PAR-2) participates in the release of some cytokines, such as interleukin-6 (IL-6) and IL-8, and it is also involved in the delay of the barrier function recovery. PAR-2 is expressed in keratinocytes of the skin, afferent neurons and inflammatory cells among others, and enzymatic and non-enzymatic compounds can activate it.2 Proteases from plants, mites or human inflammatory cells (e.g., mast cell tryptase) can activate PAR-2. When activated in nociceptive neurons, it increases cellular excitability and may sensitise their responses to agonists of other receptors involved in inflammatory processes, such as the transient receptor potential vanilloid-1 (TRPV1). TRPV1 is a non-selective plasmamembrane cationic and heat-sensitive ion-channel that mediates responses to stimuli, including heat, protons and chemical irritants, such as capsaicin, which cause burning, pain or pruritus.3 Its over-activation can stimulate neurogenic inflammation by releasing neuropeptides in the periphery such as calcitonin gene-related peptide (CGRP) and substance P (SP), leading to neurogenic inflammation.3 They also interact with many non-neuronal cells, including endothelial cells, keratinocytes, mast cells, immune cells and arterioles, which contribute additional inflammatory elements such as the cytokines IL-6 and IL-8.4,5 CGRP also potentiates the release of SP that stimulates the liberation of proteases, activating PAR-2 and exacerbating the neurogenic inflammation. SP and CGRP are also further released due to UV radiation. Additionally, PAR-2 activation delays barrier recovery and inhibits lamellar bodies’ secretion. Moreover, serine proteases degrade the key lipid processing enzymes required for normal permeabilit barrier homeostasis, and acute barrier disruption raises the ambient pH of normal SC, activating serine proteases, which, in turn, activate PAR-2. Diminishing PAR-2 activity could improve the proliferation and differentiation of keratinocytes, helping to repair the skin barrier function.2 When skin is exposed to allergens, PAR-2 is stimulated inducing allergic inflammation and directly affecting the structure and function of epidermal barrier. They could break down the skin barrier via PAR-2, facilitating further penetration of allergens through the defective skin barrier propagating the vicious cycle of proteasemediated permeability barrier defect. Delisens (acetyl hexapeptide-46) is a novel hexapeptide for cosmetic products especially designed by Lipotec for sensitive skin, which was identified by a combinatorial chemistry approach using a high throughput screening (HTS) assay. The combinatorial peptide library was screened for PAR-2 activity inhibition in a keratinocyte cell model based on fluorescence detection of calcium mobilisation. This effective peptide diminishes PAR-2-induced release of pro-inflammatory mediators, attenuating neurogenic inflammation and relieving the itch in sensitive skin. It also facilitates the restoration of the damaged barrier function, preventing further inflammation.

Materials and methods

Inhibition of PAR-2 activity The efficacy of acetyl hexapeptide-46 in inhibiting PAR-2 activity was tested in human keratinocytes. Cells were incubated with a vehicle or the hexapeptide for 1 hour before 100 L of a mixture containing the fluo-4 NW indicator and probenecid was added to the wells. Then, they were incubated for 30 minutes at 37°C. Afterwards, PAR-2 was activated by the treatment with 1 M PAR-2 agonist I and its activation was evaluated by fluorescence using the FLUOstar Galaxy microplate fluorimeter, set for excitation at 500 nm and emission at 520 nm. Non-treated cells activated with a PAR-2 agonist were used as a control.