Characterisation of the skin s polar. GB Kasting The James L. Winkle College of Pharmacy University of Cincinnati

Transcription

1 Characterisation of the skin s polar pathway GB Kasting The James L. Winkle College of Pharmacy University of Cincinnati

2 Acknowledgements In regards to this presentation, the investigators have no conflict of g p g interest to disclose. The conclusions are those of the authors and do not represent the positions of the sponsors of this research.

3 Proposed polar pathways in human stratum corneum Inset picture: Warner et al., JID, 2003

4 Why study it? Allergic contact dermatitis Metals Hair dyes (cationic) Topical and transdermal drug delivery Passive Iontophoresis Sonophoresis 4

5 How this talk is organized Polar pathway phenomenology SC electrical lproperties Temperature dependence of SC permeability Size selectivity for hydrophilic permeants NMF extraction from the SC Accumulation of charged dyes in the SC My concept of what it looks like. Alternative hypothesis 5

6 Stratum corneum electrical properties 6

7 Skin resistivity in vivo 5 min exposure in normal saline ~400 cf. 1 phospholipid bilayer 1 M cm 2 Huang, 1964; Tsong, 1991 n = 9 n = 9 n = RT Tregear, Nature,

8 Human skin resistivity in vitro Time course in normal saline; 20 Hz AC, 7 A rms 300 Res sistance (k k cm 2 ) Max 95% CL Mean (n = 6) Min Time (min) TD LaCount & GB Kasting, J Pharm Sci,

9 Current Pathways in Skin Dyes driven electrically into the skin preferentially stain pores and follicles. HA Abramson and MH Gorin J HA Abramson and MH Gorin, J Phys Chem 44: (1940).

10 Current pathways, cont. Scheuplein (1978) provided an in vitro demonstration of this phenomenon. RJ Scheuplein, in: The Physiology and Pathophysiology of the Skin, Vol. 5. Copyright 1978 Academic Press Press. 2 Fe K3 Fe CN 6 2K KFe2( CN) 6 Prussian blue

11 Current pathways, cont. Metal foil electrodes placed over the skin can be preferentially etched at the site of ecrine sweat glands. S Grimnes, Acta Derm Venereol 64:93 98 (1984).

12 Current pathways, cont. Invitro microelectrode studies have shown high current densities at pores in human skin and hair follicles in rodent skin. Burnette and Ongpipattanakul, J Pharm Sci 77: See also Cullander and Guy, 1991; Scott et al

13 Skin electrical properties p Electrical resistance of the skin falls rapidly during iontophoretic treatment, then recovers e gradually. GB Kasting and LA Bowman, Pharm Res 7: (1990).

14 Electrical properties, p cont. The steady state current voltage characteristic is approximately exponential. GB Kasting and LA Bowman, Pharm Res 7: (1990).

15 Temperature dependence of SC permeability 15

16 16

17 Arrhenius plot urea in HEM Peck et al., 1995

18 Two temperature protocol urea Peck et al., 1995

19 Two temperature protocol corticosterone Peck et al., 1995

20 Permeability ratio vs. skin resistance corticosterone urea mannitol TEA Peck et al., 1995

21 Urea permeability vs. Skin resistance The slope of this log log g plot is almost 1, supporting that urea traverses a similar pathway to sodium and chloride ions. Peck et al., 1995

22 Size eselectivity ect ty for hydrophilic permeants ea 22

23 23

24 Peck et al.,

25 Peck et al.,

26 26

27 Iontophoretic permeability coefficients versus molecular volume Cations Lai and Roberts,

28 Iontophoretic permeability coefficients versus molecular volume Anions Lai and Roberts,

29 Iontophoretic permeability coefficients versus molecular volume Uncharged solutes Lai and Roberts,

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31 Skin/solution mobility ratio a Salt u skin/u soln 100 K Na Ni Cr Cl 1.24 NO SO CrO Cr 2 O a Temperature-adjusted to 32 LaCount & Kasting, J Pharm Sci, 2013

32 Effect of permeant size on mobilities 3 n 100 u sk kin /u soln 2.5 anions: cations r² = 0.06 anions cations: cations: r² = r 2 = Ionic radius (Å) LaCount & Kasting, J Pharm Sci, 2013

33 NMF extraction from the stratum corneum 33

34 The desmosome degradation process A. First strip, fully degraded DS B. Second strip, lipids encapsulating DS C. Second strip, partially degraded DS D. Third strip, normal DS Rawlings et al., J Soc Cosmet Chem,

35 The desmosome degradation process D. Third strip, normal DS; lipid envelopes in direct contact withds DS. Note the boundary between the DS and the corneocyte. Rawlings et al., J Soc Cosmet Chem,

36 Extraction of NMF components from the SC Log Kow = 3.19 Robinson et al., J Cosmet Sci,

37 Accumulation of charged dyes in the stratum corneum Farahmand S and Kasting GB COLIPA Investigators Workshop Brussels,

38 Test dataset A test set composed of 78 in vitro permeation studies involving 64 chemicals used in rinse off cosmetic products (primarily hair dyes) was used for model evaluation. 34 direct hid hair dyes 22 oxidative hair dyes 8 cationic hair dyes 5 products of oxidative hair dye coupling 4 preservatives 2 solubilizers 3 reference compounds (cinnamaldehyde, PPD(2))

39 In vitro protocol Split thickness human or pig skin Franzdiffusion cells Compounds applied at various concentrations in fully formulated products (mostly hair dye formulations) Skin was washed thoroughly after 30 min. Samples collected after 24 hours. Most studies involved radiochemicals.

40 Available data (24 h samples) All dt data expressed as % of applied dose Stratum t corneum content t(from tape strippings) ti i Viable epidermis + dermis content Receptor fluid content

41 Data were analyzed using a three layer skin diffusion i model dl Dancik et al., ADDR, 2012

42 Model assumptions Aqueous vehicles, 20 L per 0.8 cm 2 diffusion cell ½ of vehicle evaporates during 30 minute exposure Partially hydrated skin Indoor wind velocity (0.17 m/s)

43 Results of diffusion model analysis 43

44 Receptor solution content log 10 Ob bserved 3 Human in vitro skin 073 PPD A43 PE-1&2 permeation B72 (receptor level) of A09-2 AR52 A09-1 uncharged dhid hair dyes D9 PC1 and associated B37 PC2 A33 compounds was moderately well described. r 2 = s=0.73 p-value< log 10 Predicted Farahmand S and Kasting GB COLIPA Investigators Workshop Brussels,

45 Receptor solution content Log 10 Observed predicted %dose in receptor fluid not considering polar pathway contribution. predicted %dose in receptor fluid considering polar pathway contribution. Cationics However, the permeation of cationic hair dyes was greatly underestimated Log 10 Predicted Line of perfect fit Farahmand S and Kasting GB COLIPA Investigators Workshop Brussels,

46 Stratum corneum concentration rved Log 10 Obse A43 B DEGME HO1 PC3 DB1 B24-2 A19 A11 B24-1 A99 D8 D10 SC concentrations of these compounds and a few others was also greatly underestimated Log 10 Predicted B37 Line of perfect fit Farahmand S and Kasting GB COLIPA Investigators Workshop Brussels,

47 Implications of analysis Permanently charged hair dyes not only permeated human skin in vitro, but also accumulated ltdin the stratum t corneum. 47

48 My picture of the epolar pathway ay 48

49 Start with a recent bricks andmortar model of the SC From C. Harding (2004) Dermatologic Therapy 17:6 15

50 Add appendageal shunts Skin appendage (hair follicle or sweat gland) Intercellular l lipid ddf defects; possibly desmosomal Epithelial cell membrane defects 50

51 Simplify to essential components Component 1: Component 2: transcellular transappendageal Both routes deposit permeants in viable ibl skin tissues, bypassing the intercellular SC lipids. 51

52 An alternative hypothesis* *Recently advanced by the skin research group from China Agricultural University (includes Dr. Lian from Unilever) 52

53 The CAU group has developed a stratum corneum microscopic i model dlthat t accommodates polar solutes. See also: Chen et al., Ind Eng Chem Res, 2008 Chen et al., AIChE J, 2010 Wang et al., Int J Pharm,

54 CAU Model This model accounts for the steady state permeation rates of hydrophilic solutes within a brick and mortar structure. How is this accomplished? 54

55 The CAU model employs a geometry very similar to that t proposed by the MIT group in Johnson et al., J Pharm Sci,

56 But unlike the MIT analysis (or our own), lipid phase diffusion i in the CAU model dlis isotropic. i Model 1 (MIT) Model 2 (UB/UC) a a Wang et al., J Pharm Sci, 2006; Wang et al., J Pharm Sci,

57 Corneocytes are permeable in the CAU model, but tbarely so. The fiber matrix ti diffusion i model dl for D cor was adapted from another MIT group [1]. Property MIT CAU UB/UC a Partial UB/UC Full hydration hydration Sucrose D cor 10 6, cm 2 s 1 NA 6.13E K cor [1]. 57

58 The parameters and in the Johnson et al. model dlwere modified d in order to match thbulk lksc permeabilities for 8 selected solutes. Chen et al., AIChEJ J,

59 The result was a diffusion model that was much more restrictive titi to transport tthan the original ii version. Chen et al., AIChEJ J,

60 Lipids are much more permeable to ALL solutes in the CAU model dlthan in the UB/UC model. dl The difference lies in the transverse mass transfer coefficient (effective diffusivity = k trans ). Property MIT CAU UB/UC Partial UB/UC Full hydration hydration Sucrose D lt 9 lat 10, cm 2 s k trans 10 9, cm 2 s 1 [5.91] b 0.235E E 03 K lip 15.4E E E E 04 60

61 Consequences of parameter selection The CAU and UB/UC models both predict that diffusion through the SC is primarily transcellular. (MIT was strictly intercellular.) The limiting resistance in the CAU model is diffusion in the corneocytes; the limiting factor for UB/UC is transbilayer hopping in the lipid phase. CAU accommodates the permeation of hydrophilic solutes, whereas MIT and UB/UC do not. But at what cost? 61

62 Issues raised by CAU model Long time lags for hydrophilic permeants High permeability of delipidized SC Temperature dependence Electrical l conductance of pores and follicles l 62

63 Questions?