Barrier function and immunology of the skin: skin health and skin disease Julia Schofield

Barrier function Why does it matter?

Childhood eczema Eczema is common Mild, moderate or severe 20% under one year olds Big impact on families Recent research shows importance of barrier function Relevant to eczema of all types in all ages

Barrier function and atopic eczema

A Healthy Skin Barrier NMF H2O NMF H2O NMF H2O Filaggrin Profilaggrin Swelled corneocytes Cornified envelope Intact Corneodesmosomes Lipid Lamellae pH 5.5 NMF H2O NMF H2O NMF H2O Degradatory Proteases Protease Inhibitors Profilaggrin Filaggrin Lipid delivery Lipid processing Corneocytes are filled with natural moisturising factor, a collection of natural humectants which maintain skin hydration The constituents of NMF are derived from profilaggrin, a structural component of the CE expressed during keratinocytes differentiation. NMF is important for maintaining an acid environment at the outer surface of the SC In order to balance the introduction of new cells in the basal layer of the epidermis, mature corneocytes are shed from the surface of the SC is a process referred to as desquamation. Desquamation involves the degradation of the extracellular corneodesmosomes by a cocktail of proteases regulated by protease inhibitors. The optimum pH for serine protease activity is slightly alkaline in contrast to the normal acidic pH of the skin. 5/28/2019 The Academic Unit of Dermatology Research, The University of Sheffield. 5

Lipid delivery & processing Natural moisturizing factor A Healthy Skin Barrier Lipid Lamellae Ceramide: cholesterol: fatty acids Cornified envelope Lipid delivery & processing Swelled corneocytes Filaggrin NMF H2O Natural moisturizing factor Urocanic acid, Pyrrolidone carboxylic acid, lactic acid, urea Intact corneodesmosomes pH 5.5 Degradatory proteases Protease inhibitors Corneocytes are filled with natural moisturising factor, a collection of natural humectants which maintain skin hydration The constituents of NMF are derived from profilaggrin, a structural component of the CE expressed during keratinocytes differentiation. NMF is important for maintaining an acid environment at the outer surface of the SC In order to balance the introduction of new cells in the basal layer of the epidermis, mature corneocytes are shed from the surface of the SC is a process referred to as desquamation. Desquamation involves the degradation of the extracellular corneodesmosomes by a cocktail of proteases regulated by protease inhibitors. The optimum pH for serine protease activity is slightly alkaline in contrast to the normal acidic pH of the skin. 5/28/2019 Danby SG & Cork MJ, The Academic Unit of Dermatology Research, The University of Sheffield. 6

Allergens & Irritants Water pH 5.5 NMF H2O The normal intact SC acts as an efficient barrier to the penetration of irritants and allergens and to the loss of water. Barrier function is often determined by measuring TEWL Water 5/28/2019 The Academic Unit of Dermatology Research, The University of Sheffield. 7

Brick => Corneocyte Mortar => Lipid Lamellae 3/26/09 The Academic Unit of Dermatology Research, University of Sheffield 8

Mortar => Lipid Lamellae Ceramides + Fatty acids Cholesterol 3/26/09 The Academic Unit of Dermatology Research, University of Sheffield 9

The Normal Skin Barrier 3/26/09 The Academic Unit of Dermatology Research, University of Sheffield Cork et al 2006 JACI 10

Irritants & allergens The normal intact SC acts as an efficient barrier to the penetration of irritants and allergens and to the loss of water. Barrier function is often determined by measuring TEWL 5/28/2019 Danby SG & Cork MJ, The Academic Unit of Dermatology Research, The University of Sheffield. 11

What goes wrong in childhood eczema?

Infant skin has a low epidermal barrier reserve (i) (i)Nikolovski J, Stamatas GN, Kollias N, Wiegand BC. J Invest Dermatol. 2008 Jul;128(7):1728-36 (picture:) Cork MJ, Danby SG, Vasilopoulos Y, Hadgraft J, Lane ME, Moustafa M, Guy RH, Macgowan AL, Tazi-Ahnini R, Ward SJ. Epidermal barrier dysfunction in atopic dermatitis. J Invest Dermatol. 2009 Aug;129(8):1892-908

When is the skin barrier not optimum? 5/28/2019 Danby SG & Cork MJ, The Academic Unit of Dermatology Research, The University of Sheffield. 14

A Defective Skin Barrier in AD Defective lipid lamellae Degraded Corneodesmosomes Abnormal cornified envelope (Reduced levels of ceramides) pH 7.0 NMF H2O NMF H2O NMF H2O Degradatory Proteases Protease Inhibitors Profilaggrin Filaggrin Lipid delivery Lipid processing (Reduced levels of ceramides) The defective epidermal barrier is characterised by: Abnormal expression of differentiation dependent proteins leading to corneocytes with an abnormal morphology and defective CE. There is defective LL with reduced levels of ceramides and altered FFA profiles. This affects the structure of the lamellar membranes and there ability to efficiently prohibit water permeation. The interaction between the corneocytes and the LL is also compromised. There is a reduced expression of profilaggrin leading to decreased filaggrin – structural defect, decreased NMF – reduced SC hydration – development of gaps between corneocytes. There is an elevated skin surface pH associated with the reduction in NMF – optimum for protease hyperactivity Increased protease activity leading to increased degradation of the corneodesmosomal junctions – barrier breakdown 5/28/2019 The Academic Unit of Dermatology Research, The University of Sheffield. 15

PAR = Proteinase-activated Receptor-2

An allergic response is elicited Allergens NMF H2O NMF H2O NMF H2O Th2 Th1 ? Cork, Danby et al (2009) In Skin Moisturization. Academic Unit of Dermatology Research, The University of Sheffield

Allergens & Irritants Water pH 7.0 NMF H2O NMF H2O NMF H2O The barrier defect in patients with AD leads to an increased risk of irritant and allergen penetration and increased loss of water. The skin is characterised by increased TEWL Water 5/28/2019 The Academic Unit of Dermatology Research, The University of Sheffield. 18

Irritants & allergens TEWL The normal intact SC acts as an efficient barrier to the penetration of irritants and allergens and to the loss of water. Barrier function is often determined by measuring TEWL 5/28/2019 The Academic Unit of Dermatology Research, The University of Sheffield. 19

What do we mean by irritants?

Identifying irritants: ask about skin care regime Bath or shower How often, per day, per week Products used for washing/showering, added to bath Products used for laundry

Common irritants

Common cause of irritancy! TOO MUCH WASHING!!!!

Itching: some simple tips STOP ALL IRRITANTS: Shower gels Soaps Biological washing powders Fabric conditioners Leave on moisturiser NOT AQUEOUS CREAM

The effect of topical products/treatments on pH and protease activity

A Healthy Skin Barrier NMF H2O NMF H2O NMF H2O Filaggrin Profilaggrin Swelled corneocytes Cornified envelope Intact Corneodesmosomes Lipid Lamellae pH 5.5 NMF H2O NMF H2O NMF H2O Degradatory Proteases Protease Inhibitors Profilaggrin Filaggrin Lipid delivery Lipid processing Corneocytes are filled with natural moisturising factor, a collection of natural humectants which maintain skin hydration The constituents of NMF are derived from profilaggrin, a structural component of the CE expressed during keratinocytes differentiation. NMF is important for maintaining an acid environment at the outer surface of the SC In order to balance the introduction of new cells in the basal layer of the epidermis, mature corneocytes are shed from the surface of the SC is a process referred to as desquamation. Desquamation involves the degradation of the extracellular corneodesmosomes by a cocktail of proteases regulated by protease inhibitors. The optimum pH for serine protease activity is slightly alkaline in contrast to the normal acidic pH of the skin. 5/28/2019 The Academic Unit of Dermatology Research, The University of Sheffield. 26

A Defective Skin Barrier in AD Defective lipid lamellae Degraded Corneodesmosomes Abnormal cornified envelope (Reduced levels of ceramides) pH 7.0 NMF H2O NMF H2O NMF H2O Degradatory Proteases Protease Inhibitors Profilaggrin Filaggrin Lipid delivery Lipid processing (Reduced levels of ceramides) The defective epidermal barrier is characterised by: Abnormal expression of differentiation dependent proteins leading to corneocytes with an abnormal morphology and defective CE. There is defective LL with reduced levels of ceramides and altered FFA profiles. This affects the structure of the lamellar membranes and there ability to efficiently prohibit water permeation. The interaction between the corneocytes and the LL is also compromised. There is a reduced expression of profilaggrin leading to decreased filaggrin – structural defect, decreased NMF – reduced SC hydration – development of gaps between corneocytes. There is an elevated skin surface pH associated with the reduction in NMF – optimum for protease hyperactivity Increased protease activity leading to increased degradation of the corneodesmosomal junctions – barrier breakdown 5/28/2019 The Academic Unit of Dermatology Research, The University of Sheffield. 27

Protease activity in the skin barrier (in the stratum corneum - no red stain) Nucleated layers (nuclear material stained red) Dermis The Academic Unit of Dermatology Research, University of Sheffield

The effect of pH on skin barrier protease activity: clinical relevance Acute AD pH 7.3 Current AD pH 5.7 Normal skin pH 5.0 The Academic Unit of Dermatology Research, University of Sheffield

The Effect of Washing with Liquid Soap on Skin Surface pH *p = <0.05; ***p = <0.001; n = 3 5/28/2019 Danby SG & Cork MJ, The Academic Unit of Dermatology Research, The University of Sheffield. 30

The Effect of Washing with Liquid Soap on Skin Surface pH Acute AD Current AD (non-lesional site) Clinical relevance* *p = <0.05; ***p = <0.001; n = 3 5/28/2019 Danby SG & Cork MJ, The Academic Unit of Dermatology Research, The University of Sheffield. 31

Aqueous cream – first appeared in the BNF in 1958 Its formulation containing SLS remains largely unchanged today

Aqueous Cream Leave-On compared with No Treatment for 4 weeks Skin Barrier Integrity: End Point 5/28/2019 The Academic Unit of Dermatology Research, The University of Sheffield 33

Atopic eczema and domestic water hardness. McNally NJ, Williams HC, Phillips DR, Smallman-Raynor M, Lewis S, Venn A, Britton J. Lancet. 1998 Aug 15;352(9127):527-31. “Living in a hard water area is significantly associated with an increased lifetime prevalence of AD” Confirmed by 2 replicate studies (in Japan and Spain) 5/28/2019 Danby SG & Cork MJ, The Academic Unit of Dermatology Research, The University of Sheffield. 34

A Randomised Controlled Trial of Ion-Exchange Water Softeners for the Treatment of Eczema in Children Kim S. Thomas, Tara Dean, Caroline O'Leary, Tracey H. Sach, Karin Koller, Anthony Frost, Hywel C. Williams, and the SWET Trial Team PLoS Med. 2011 February; 8(2): e1000395.

To summarise

Atopic eczema: pathophysiology BRICK WALL THEORY

Irritants penetrate and trigger inflammatory response The Brick Wall theory Leads to dry skin Irritants penetrate and trigger inflammatory response

Brick wall theory: correct barrier function Correcting barrier function reduces dry skin and penetration of irritants and inflammation

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