14 SKIN MICROBIOME The modulation of skin bacteria


subjected to air pollution (PM2.5 and PM10) was shown in an ex vivomodel by counting and identifying skin bacteria by MALDI-TOF. These results revealed that pollution caused an imbalance of skin microbiota through a total drop of S. epidermidis and an increase of environmental bacteria comparatively to the untreated skin explants. The level of these bacteria was restored at basal rate in skin explants treated with Kalmethic® The positive modulation of skin


22000000


n Control n PM2.5/PM10 n Kalmethic®


+333% *


-41% *


165000000


+97% *


(Fig 2).


microbiota interaction thanks to Kalmethic rebalancing skin bacteria and promoting the growth symbiotic bacteria, may suggest its ability to preserve skin homeostasis.


Signalization pathway between bacteria and epidermis The beneficial relationship between bacteria and the skin can be seen through the innate capacity of the epithelium to detect microorganism with Toll-like receptors (TLRs). Stimulation of TLRs induces distinct patterns of gene expression that leads to the activation of a variety of immune responses. Commensalism and mutualism


interactions of microbes are an important part of the skin immune shield. Indeed, skin commensal interactions are able to amplify the innate immune response of keratinocytes by increased induction of antimicrobial expression and NF-kB pathway. It is likely that both mechanisms act in an additive or synergistic way to amplify immune response in human skin. The activation of keratinocyte TLRs


immediately initiates the innate immune response resulting in cell-to-cell communication activation, transmitted to the deep layers of the skin by several molecules such as endogenous skin antimicrobial peptides (AMPs), cytokines, chemokines.3 S. epidermidis, a normal inhabitant of


the skin, may have a uniquely structured TLR2 ligand that maximizes anti- inflammatory action yet minimizes the capacity to initiate inflammation. The activation of TLR2 in keratinocytes has its own beneficial effect in maintaining skin homeostasis. The bacteria-epidermis communication


has been highlighted in vitro (nHEK) based on of NF-kB, TLR2, TLR3 and 4TLR mRNAs quantification. Compared to control, NF-kB, TLR2, 3


and 4 expression significantly increased by 61%, 106%, 92% and 106% respectively) (Fig 3). Results indicated that Kalmethic (now referred to as ‘the sensitive skin cosmetic ingredient') improved the interaction pathway involved in skin microbiota communication. Interestingly, the upregulation of NF-kB did not induce


PERSONAL CARE NORTH AMERICA 11000000 0.4% + PM2.5/PM10


5500000


+97% *


0 Staphylococcus epidermidis Figure 2: Evaluation of the beneficial effects of Kalmethic® Environmental bacteria on cutaneous bacteria in skin explants


subjected to atmospheric pollution (PM2.5 & PM10). 43-year-old normal adult human skin explants (control in light grey profile), treated with PM2.5 & PM10 (pink profile) and treated with Kalmethic®


0.4% (gold profile), were maintained in an incubator


equilibrated with 5% CO2 at 37°C in a specific Explant Medium. Skin bacteria were counted and identified by MALDI-TOF. The SEM bars are represented in black lines on each histogram. The statistical analysis was performed using T-test (* p-value<0.05, n=3).


n Control n Kalmethic® 2.5


+106% **


2


+61% ***


1.5


+92% *


+100% *


0.04%


1


0.5


0 NF-kB TLR2 TLR3 TLR4


Figure 3: Evaluation on the level of NF-kB, TLR2, 3 and 4 mRNA in keratinocytes. 40-year-old normal Adult Human Primary Epidermal Keratinocyte (nHEK) (control in light grey profile) and treated with Kalmethic®


0.04% (gold profile), were maintained in an incubator equilibrated with


5±1.5% CO2 at 37±2°C in a specific medium « Dermal Cell Basal Medium » supplemented with Keratinocyte Growth kit components. Target mRNA were purified and then quantified using RT-qPCR. mRNA levels are expressed as induced arbitrary unit compared to control. The SEM bars are represented in black lines on each histogram. The statistical analysis was performed using T-test (* p-value<0.05; ** p-value<0.01; *** p-value<0.001 vs control, n=3).


neither in vitro nor ex vivo the expression of inflammatory markers suggesting positive role of NF-kB in cellular migration and reparation (data not shown). Activation of TLRs induces NF-kB signalization pathway which activates inflammation via the transcription of several proinflammatory cytokines but is also required for the proper


generation of epidermal appendages. This transcription factor NF-kB presents a complex picture in skin with two-faced behavior: both activation and inhibition of pathways associated with inflammation.4-5 The commensal bacterium


S. epidermidis, has been described to modulate the host innate immune


October 2020


Skin bacteria quantification (CFU/g) mRNA expression level


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