morphological and molecular structure of the Stratum corneum

Transcription

1 New insights into the morphological and molecular structure of the Stratum corneum Prof. Dr. Dr. h.c.. Reinhard H. H. Neubert Institute of Pharmacy of the Martin Luther University, Halle-Wittenberg

2 Content: 1. Introduction 2. Structure of the Stratum corneum - Morphology - Molecular architecture 3. Influence on Penetration - Penetration Pathways -Enhancer -Vehicle 4. Summary

3 Principles of drug administration to the skin 1. Effects at the surface of the skin - Cleaning 2. Dermal therapy - Effects in viable epidermis e.g.. Psoriasis, Atopic dermatitis - Effects in the folliculae 3. Transdermal therapy - Administration to the skin, systemic effects

4 Structure of the human skin

5 Main barrier of the skin: Stratum corneum (SC)

6 Main barrier of the skin: Stratum corneum (SC) Brick and mortar model of the Stratum corneum (horny( layer) according to Elias (1981), to understand barrier function: Corneocytes: the bricks bricks Intercellular Lipids: the mortar mortar

7 H H H Penetration pathways into and through the Stratum corneum (SC) The intercellular lipid are highly ordered: they form bilayers Intercellular pathway: Route of drug penetration intercellular route transcellular route plasma membrane cytoplasma fatty acid water ceramides intracellular room lipid water cholesterol triglycerides lipid matrix keratin

8 Stratum corneum Lipids Ceramides (Sphingolipids) 30% C H 3 C H 3 HN Free fatty acids 30 % H 3 C Cholesterol and Derivatives 30 % H CH CH CH 3 3 CH 3 3 H 3 C

9 Ceramides of the Stratum corneum Fatty acid HN Sphingoidbase Fatty acid α-hydroxylated (A) Non α-hydroxylated (N) ω-esterified (E) Sphingoid base Sphingosine (S) Phytosphingosine (P) 6-Hydroxy-Sphingosine (H)

10 Ceramides of the Stratum corneum

11 Research work of the recent years shows: 1. The brick and mortar model has to be re-evaluated 2. the mechanical stability and the barrier function of the SC are realised by: A. Hook like structures of the corneocytes, B. The existence of the corneodesmosomesand C. The bilayer structure of the SC lipids. Neubert und Wepf,, PZ 152, (2007)

12 Research work of the recent years shows: The mechanical stability (adhesion) of the SC (horny layer) is realised by A. Hook like structures of the corneocytes KindlysuppliedbyDr. R. Wepf, ETH Zürich

13 Research work of the recent years shows: The mechanical stability(adhesion) of the SC (horny layer) is realised by: B. Corneodesmosomes: Rivets consisting of a proteinframework: 1 corneodesmosome/µm 2 = corneodesmosomes/corneocyte

14 Research work of the recent years shows: The mechanical stability (adhesion) of the SC (horny layer) is realised by: C. The bilayer structure of the Stratum corneum Methods: - New results using neutron scattering (NS) and SC lipid bilayers at a quartz surface show new insights. Co-operation with JINR in Dubna, Russia Helmholtz-Zentrum für Material und Energie, Berlin

15 The Bilayer of the Stratum corneum: New results using Neutron scattering (NS) and a SC lipid bilayer on a quartz surface allow new insights at V1 Diffractometer, HZ Berlin. θ d 2θ d 4 Intensität, a.u Q, Å -1

16 Stratum corneum Lipid Model Membranes HN C 55% Ceramide AP 15% Palmitic acid H Na S 25% Cholesterol 5% Cholesterol sulfate

17 Stratum corneum Lipid Model Membranes Diffractogram: Five diffraction orders detectable! 14 I III Intensity a.u IV V II q [A -1 ] Ceramide AP/Cholesterol/Palmitic acid/cholesterol sulfate T=32 o C, 60% humidity, 8% D 2

18 Stratum corneum Lipid Model Membranes Neutron scatteringlengthdensityprofile: SC-lipid modelsystem CER[AP]/Chol/SA/CholS, T = 32 C, 60% relative humidity H H H NH CH 3 ρ(x), a.u H 3 C CH 3 H 3 C x, Å 8 % D 2 20 % D 2 50 % D 2 HN

19 Stratum corneum Lipid Model Membranes Model calculations of the neutron scattering length density of the model system (CER[AP], CHL, behenic acid and Cholesterol sulfate) H 2 /D 2 (98/2) ρ s (x), a.u polare head groups Cholesterol CH 2 chains CH 3 groups x, Å

20 Stratum corneum Lipid Model Membranes Neutron scattering allows new insights into the molecular structure of the SC bilayer 1.0 Å nonpolar region 28 Å water layer 19.2 Å polar region Neubert et al., Eur. Biophys. J. 34, 1030 (2005)

21 Stratum corneum Lipid Model Membranes Influence of long-chain ceramides C H 3 HN Ceramide [AP] C H 3 H 3 C Ceramide [ES] H 3 C HN 15% Fatty acid (C26), C(24), C(22), e.g. Cerotic acid

22 Stratum corneum Lipid Model Membranes Influence of long-chain ceramides Polar headgroup region Polar headgroup region ρ s (x), a.u x, Å CER[AP]/ CHL/ PA/ ChS CER[ES]/ CER[AP]/ CHL/ BA Schröter et al. 2009, BiophysJ. 97

23 New structure model of the SC: Armature reinforcement model Composition CER[AP]/CHL/PA/ChS CER[NS]/CHL/PA/ChS CER[ES]/CER[AP]/CHL CER[ES]/CER[NS]/CER[AP]/CHL CER[ES]/CER[AP]/CHL/PA CER[ES]/CER[AP]/CHL/BA Membrane thickness 45.6 Å 57.0 Å 45.2 Å 44.0 Å 45.0 Å 46.5 Å

24 New structure model of the SC: Armature reinforcement model CER[AP] CHL CER[ES] Behenic acid 48.3 Å

25 New model of the SC bilayer Structure Armature reinforcement model 1. Ceramide [AP]: Most hydrophilic ceramide, four groups, H-bridges stabilize the hair pin structure 2. Ceramide [AP]: Fully extended conformation stabilizes the bilayer structure 3. Ceramide [ES]: The long alkyl chain penetrates into the next bilayer

26 New Asymmetry model by L. Norlén

27 New Asymmetry model by L. Norlén

28 New model of the SC bilayer structure Asymmetry model according to L. Norlén: Å-Bilayer:Consisting on the long chain of CER[NP] and of the free fatty acids (mainly: lignoceric acid, C24) Å-Bilayer:Consisting on the short chain of CER[NP] and of cholesterol

29 New Asymmetry model Does CER[NP] C18/C24exists in the Hairpin or fully extended conformation in model membranes? CH 3 H H NH CH 3 Hair pin conformation H 3 C H NH CH 3 H Fully extended conformation

30 SC Lipid model membranes: CER[NP]C18,C24 /CHL /lignoceric/ acid CER[NP] C18,C24/ cholesterol/ lignoceric acid (equimolar) Intensity [a.u.] L1a L1b L2a L2b L3a Twolamellarphases: d 1 = 54.5 Å d 2 = Å Asymmetry L3b L4b L4a L5b L5a L6a L6b Scattering angle 2Θ [deg] % D 2 50% D 2 100% D 2

31 Structural architecture of the lipids: CER[NP]C18,C24/ cholesterol/ lignoceric acid (C24) n 54.5 Å 42.9 Å CER[NP] C18/C24-molecules present in the fully extended conformation! The localisationof cholesterol and lignocericacid has to be identified by applying deuterated derivatives.

32 Effect of Penetration enhancers vercoming the skin barrier essential for transdermal drug administration Increased drug flux realized e.g. by PENETRATIN ENHANCERS Mode of action not yet fully elucidated on molecular level Assumptions: Fluidization of SC lipids Increase of lamellar disorder Induction of phase separation Isopropyl myristate leic acid Limonene

33 Effect of Penetration enhancers leic acid Model membrane(massratio): CER[AP]/CHL/PA/ChS 55/25/15/ % leic acid( Quat_Basic_A ) + 10 % leic acid-9,10-d2 ( Basic_A-D2 ) D D 100 % D 2, T=32 C, 58 % rh Lamellar repeat distance d Quat_ Basic_A-d ±0.08 Å

34 Effect of Penetration enhancers leic acid Model membrane(massratio): CER[AP]/CHL/PA/ChS 55/25/15/ % leic acid( Quat_Basic_A ) + 10 % leic acid-9,10-d2 ( Basic_A-D2 ) ρ(x), arbitrary units (a.u.) 40x H D D x D = ± 8.6 Å D D x, Å Quat_Basic_A-d2 Quat_Basic_A Deuterium-Distribution

35 Conclusion I Mechanical stability of the SC realized at three levels: - Hook like structures, - Desmosmes and -Bilayers of thesc lipids. Neutron scattering allows new insights into the molecular architecture of the SC bilayers. A new model of the SC bilayer structure was created: The armature reinforcement model.

36 Conclusion II Ceramide [AP]: Most hydrophilic ceramide, four groups, H-bridges stabilize the hair pin structure conformation stabilizes the bilayer structure. Ceramide [ES]: The long alkyl chain penetrates into the next bilayer. Ceramide [NP]:This ceramide, three -groups, seems to force asymmetric bilayer structures in fully extended structure.

37 Conclusion III Penetration enhancers: Can be studied on a molecular level. Structure models: Has to be confirmed using specifically deuterated ceramides (CER[AP], CER[NP], CER[ES]).

38 Thanks to: Prof. Dr. Johannes Wohlrab, Depart. Dermatology, MLU Prof. Dr. Anatolyi Balagurov, JINR, Dubna, Russia Dr. Mikael Kiselev, JINR, Dubna, Russia Dr. Thomas Hauß, HZ Berlin Dr. Annett Schröter, Department of Pharmacy, MLU Dr. Doreen Keßner, Department of Pharmacy, MLU Tanja Engelbrecht, Department of Pharmacy, MLU

39 Thank you very much for your attention! Available at: