New evaluation methods to assess anti-itching efficacy: validation with Activated Virgin Coconut oil
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Presented by: Anne Potter
Introduction:
Sensitive skin is a syndrome defined by the occurrence of unpleasant sensations (stinging, burning, pain, pruritus, and tingling sensations) in response to stimuli that normally should not provoke such sensations1. Sensitive skin is a major concern for more and more consumers, whose skin is frequently aggressed by the frequent usage of harsh cosmetic products or complex routines and by environmental stresses, like pollution or climate variations (wind, cold, temperatures). The aetiology of sensitive skin is poorly understood. There is a decrease in the “tolerance threshold” of the skin free from any immune or allergic mechanism2. The onset of unpleasant sensations is, at least partly, mediated by cutaneous unmyelinated C-fibers, localized in the epidermis, and equipped with sensory receptors called nociceptors. These nociceptors are also present and functional on keratinocytes which play a more and more evidenced role in skin surface perception3,4.
A consumer study performed in China showed that itchiness, one of the main symptoms of sensitive skin, concerns 26% of consumers and that there is a clear performance gap with the current cosmetic solutions which rely strongly on anti-inflammation actives.
Itching is a complex sensation involving several pathways. Among the main pathways is PAR2 receptor, involved in atopic dermatitis5, scalp seborrheic dermatitis6, activated by proteases such as those produced by plants or microflora
There is a need to develop new evaluation methods, to select cosmetic raw materials with potential soothing properties against itch. The aim of this study was to specifically assess the efficacy of several actives on the of inhibition of PAR2 pathway, through in vitro 2D model of keratinocytes and to confirm this efficacy in vivo in a clinical protocol with a natural trigger (cowhage) of PAR2 pathway.
Methods:
In vitro, several raw materials were evaluated in a 2D keratinocytes test, able to identify molecules modulating PAR2 nociceptor activation by quantifying inhibition of provoked Ca 2+ influx (generated by a discomfort-associated stimulus). More particularly, an Activated Virgin Coconut Oil (AVCO, derived from catalytic activity of lipase on virgin coconut oil) was compared to a Virgin coconut oil (VCO).
In vivo, a clinical protocol was set up to confirm the soothing efficacy of actives specifically via the PAR2 pathway. PAR2 can be specifically triggered by cowhage seedpod spicules (Mucuna pruriens). We evaluated the efficacy of a formula with 10% AVCO compared to a cosmetic reference (Laureth-9) on reducing itching sensations triggered by topical application of cowhage spicules. Laureth-9 (3%) was tested at the concentration used by Hawro et al.7. AVCO and Laureth 9 were formulated in the same vehicle. 45 women, 18-50 years old with healthy skin were recruited for this study. The formulae were applied on the volar forearm for 1h under occlusion prior to stimulating the surface of the skin with approximately 50 cowhage spicules.
The intensity of itching declared by the subjects was recorded every 30 sec using Visual Analogue Scale (VAS) for 20 min after induction. Area Under Curve were calculated and used to compare the treatments (AVCO and Laureth-9) with their vehicle and a non-treated control area.
Results:
Compared to Virgin Coconut Oil (VCO), it was demonstrated in vitro that Activated Virgin Coconut displayed an inhibition of Ca 2+ influx for PAR 2 nociceptor, with a dose effect. Pre-treating the skin with AVCO for 1h under occlusion significantly reduced the duration and intensity (AUC) of itch caused by cowhage compared to pretreating with vehicle (p<0.001, moderate effect) or not pre-treating (p<0.001, moderate effect). Pre-treating with vehicle was not different from not pre-treating. There was no significant difference between AVCO and Laureth-9.
Discussion/Conclusion:
A physical effect linked to the application of a concentrated formula rich in fatty compounds cannot be excluded. The next steps would be to evaluate clinically the soothing efficacy of dose effect of AVCO versus a formula containing 10% of VCO.
Nevertheless, inhibition of PAR 2 nociceptor activation is only one of the biological pathways to be considered in the treatment of itchiness. Different key players and possible targets have been identified: sensory neurons, mast cells and keratinocytes. An evaluation soothing architecture should encompass receptor tests, second intention cellular tests exploring other mechanisms (release of mediators) or targeting other cells such as mast cells or sensory neurons.
Sensitive skin is a syndrome defined by the occurrence of unpleasant sensations (stinging, burning, pain, pruritus, and tingling sensations) in response to stimuli that normally should not provoke such sensations1. Sensitive skin is a major concern for more and more consumers, whose skin is frequently aggressed by the frequent usage of harsh cosmetic products or complex routines and by environmental stresses, like pollution or climate variations (wind, cold, temperatures). The aetiology of sensitive skin is poorly understood. There is a decrease in the “tolerance threshold” of the skin free from any immune or allergic mechanism2. The onset of unpleasant sensations is, at least partly, mediated by cutaneous unmyelinated C-fibers, localized in the epidermis, and equipped with sensory receptors called nociceptors. These nociceptors are also present and functional on keratinocytes which play a more and more evidenced role in skin surface perception3,4.
A consumer study performed in China showed that itchiness, one of the main symptoms of sensitive skin, concerns 26% of consumers and that there is a clear performance gap with the current cosmetic solutions which rely strongly on anti-inflammation actives.
Itching is a complex sensation involving several pathways. Among the main pathways is PAR2 receptor, involved in atopic dermatitis5, scalp seborrheic dermatitis6, activated by proteases such as those produced by plants or microflora
There is a need to develop new evaluation methods, to select cosmetic raw materials with potential soothing properties against itch. The aim of this study was to specifically assess the efficacy of several actives on the of inhibition of PAR2 pathway, through in vitro 2D model of keratinocytes and to confirm this efficacy in vivo in a clinical protocol with a natural trigger (cowhage) of PAR2 pathway.
Methods:
In vitro, several raw materials were evaluated in a 2D keratinocytes test, able to identify molecules modulating PAR2 nociceptor activation by quantifying inhibition of provoked Ca 2+ influx (generated by a discomfort-associated stimulus). More particularly, an Activated Virgin Coconut Oil (AVCO, derived from catalytic activity of lipase on virgin coconut oil) was compared to a Virgin coconut oil (VCO).
In vivo, a clinical protocol was set up to confirm the soothing efficacy of actives specifically via the PAR2 pathway. PAR2 can be specifically triggered by cowhage seedpod spicules (Mucuna pruriens). We evaluated the efficacy of a formula with 10% AVCO compared to a cosmetic reference (Laureth-9) on reducing itching sensations triggered by topical application of cowhage spicules. Laureth-9 (3%) was tested at the concentration used by Hawro et al.7. AVCO and Laureth 9 were formulated in the same vehicle. 45 women, 18-50 years old with healthy skin were recruited for this study. The formulae were applied on the volar forearm for 1h under occlusion prior to stimulating the surface of the skin with approximately 50 cowhage spicules.
The intensity of itching declared by the subjects was recorded every 30 sec using Visual Analogue Scale (VAS) for 20 min after induction. Area Under Curve were calculated and used to compare the treatments (AVCO and Laureth-9) with their vehicle and a non-treated control area.
Results:
Compared to Virgin Coconut Oil (VCO), it was demonstrated in vitro that Activated Virgin Coconut displayed an inhibition of Ca 2+ influx for PAR 2 nociceptor, with a dose effect. Pre-treating the skin with AVCO for 1h under occlusion significantly reduced the duration and intensity (AUC) of itch caused by cowhage compared to pretreating with vehicle (p<0.001, moderate effect) or not pre-treating (p<0.001, moderate effect). Pre-treating with vehicle was not different from not pre-treating. There was no significant difference between AVCO and Laureth-9.
Discussion/Conclusion:
A physical effect linked to the application of a concentrated formula rich in fatty compounds cannot be excluded. The next steps would be to evaluate clinically the soothing efficacy of dose effect of AVCO versus a formula containing 10% of VCO.
Nevertheless, inhibition of PAR 2 nociceptor activation is only one of the biological pathways to be considered in the treatment of itchiness. Different key players and possible targets have been identified: sensory neurons, mast cells and keratinocytes. An evaluation soothing architecture should encompass receptor tests, second intention cellular tests exploring other mechanisms (release of mediators) or targeting other cells such as mast cells or sensory neurons.