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Chen X, Li Z, Yang C, Yang D. Ionic liquids as the effective technology for enhancing transdermal drug delivery: Design principles, roles, mechanisms, and future challenges. Asian J Pharm Sci 2024; 19:100900. [PMID: 38590797 PMCID: PMC10999516 DOI: 10.1016/j.ajps.2024.100900] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2023] [Revised: 12/25/2023] [Accepted: 01/08/2024] [Indexed: 04/10/2024] Open
Abstract
Ionic liquids (ILs) have been proven to be an effective technology for enhancing drug transdermal absorption. However, due to the unique structural components of ILs, the design of efficient ILs and elucidation of action mechanisms remain to be explored. In this review, basic design principles of ideal ILs for transdermal drug delivery system (TDDS) are discussed considering melting point, skin permeability, and toxicity, which depend on the molar ratios, types, functional groups of ions and inter-ionic interactions. Secondly, the contributions of ILs to the development of TDDS through different roles are described: as novel skin penetration enhancers for enhancing transdermal absorption of drugs; as novel solvents for improving the solubility of drugs in carriers; as novel active pharmaceutical ingredients (API-ILs) for regulating skin permeability, solubility, release, and pharmacokinetic behaviors of drugs; and as novel polymers for the development of smart medical materials. Moreover, diverse action mechanisms, mainly including the interactions among ILs, drugs, polymers, and skin components, are summarized. Finally, future challenges related to ILs are discussed, including underlying quantitative structure-activity relationships, complex interaction forces between anions, drugs, polymers and skin microenvironment, long-term stability, and in vivo safety issues. In summary, this article will promote the development of TDDS based on ILs.
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Affiliation(s)
- Xuejun Chen
- Department of Pharmacy, Shantou University Medical College, Shantou 515041, China
| | - Ziqing Li
- Department of Pharmacy, Shantou University Medical College, Shantou 515041, China
| | - Chunrong Yang
- Department of Pharmacy, Shantou University Medical College, Shantou 515041, China
| | - Degong Yang
- Department of Pharmacy, Shantou University Medical College, Shantou 515041, China
- Guangdong Provincial Key Laboratory of Infectious Diseases and Molecular Immunopathology, Shantou University Medical College, Shantou 515041, China
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2
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Norlén L. Molecular Organization of the Skin Barrier. Acta Derm Venereol 2023; 103:adv13356. [PMID: 37987626 PMCID: PMC10680981 DOI: 10.2340/actadv.v103.13356] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2023] [Accepted: 10/19/2023] [Indexed: 11/22/2023] Open
Abstract
Cryo-electron microscopy of vitreous sections allows for investigation directly in situ of the molecular architecture of skin. Recently, this technique has contributed to the elucidation of the molecular organization of the skin's permeability barrier and its stepwise formation process. The aim of this review is to provide an overview of the procedure for cryo-electron microscopy of vitreous sections, its analysis using atomic detail molecular dynamics modelling and electron microscopy simulation, and its application in the investigation of the barrier structure and formation process of the skin.
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Affiliation(s)
- Lars Norlén
- Department of Cellular and Molecular Biology (CMB), Karolinska Institutet, Biomedicum, SE-171 77 Stockholm, Sweden.
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3
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Loo YS, Zahid NI, Madheswaran T, Ikeno S, Nurdin A, Mat Azmi ID. Coencapsulation of Gemcitabine and Thymoquinone in Citrem-Phosphatidylcholine Hexosome Nanocarriers Improves In Vitro Cellular Uptake in Breast Cancer Cells. Mol Pharm 2023; 20:4611-4628. [PMID: 37587099 DOI: 10.1021/acs.molpharmaceut.3c00333] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/18/2023]
Abstract
Lyotropic liquid crystalline nanoassemblies (LLCNs) are internally self-assembled (ISA)-somes formed by amphiphilic molecules in a mixture comprising a lipid, stabilizer, and/or surfactant and aqueous media/dispersant. LLCNs are unique nanoassemblies with versatile applications in a wide range of biomedical functions. However, they comprise a nanosystem that is yet to be fully explored for targeted systemic treatment of breast cancer. In this study, LLCNs proposed for gemcitabine and thymoquinone (Gem-TQ) co-delivery were prepared from soy phosphatidylcholine (SPC), phytantriol (PHYT), or glycerol monostearate (MYVR) in optimized ratios containing a component of citric and fatty acid ester-based emulsifier (Grinsted citrem) or a triblock copolymer, Pluronic F127 (F127). Hydrodynamic particle sizes determined were below 400 nm (ranged between 96 and 365 nm), and the series of nanoformulations displayed negative surface charge. Nonlamellar phases identified by small-angle X-ray scattering (SAXS) profiles comprise the hexagonal, cubic, and micellar phases. In addition, high entrapment efficiency that accounted for 98.3 ± 0.1% of Gem and 99.5 ± 0.1% of TQ encapsulated was demonstrated by the coloaded nanocarrier system, SPC/citrem/Gem-TQ hexosomes. Low cytotoxicity of SPC-citrem hexosomes was demonstrated in MCF10A cells consistent with hemo- and biocompatibility observed in zebrafish (Danio rerio) embryos for up to 96 h postfertilization (hpf). SPC/citrem/Gem-TQ hexosomes demonstrated IC50 of 24.7 ± 4.2 μM in MCF7 breast cancer cells following a 24 h treatment period with the moderately synergistic interaction between Gem and TQ retained (CI = 0.84). Taken together, biocompatible SPC/citrem/Gem-TQ hexosomes can be further developed as a multifunctional therapeutic nanodelivery approach, plausible for targeting breast cancer cells by incorporation of targeting ligands.
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Affiliation(s)
- Yan Shan Loo
- Department of Chemistry, Faculty of Science, Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia
| | - N Idayu Zahid
- Centre for Fundamental and Frontier Sciences in Nanostructure Self-Assembly, Department of Chemistry, Faculty of Science, Universiti Malaya, 50603 Kuala Lumpur, Malaysia
| | - Thiagarajan Madheswaran
- Department of Pharmaceutical Technology, School of Pharmacy, International Medical University, Jalan Jalil Perkasa 19, Bukit Jalil, 57000 Kuala Lumpur, Malaysia
| | - Shinya Ikeno
- Department of Biological Functions Engineering, Graduate School of Life Science and Systems Engineering, Kyushu Institute of Technology, 2-4 Hibikino, Wakamatsu, Kitakyushu, 808-01906 Fukuoka, Japan
| | - Armania Nurdin
- Department of Biomedical Science, Faculty of Medicine and Health Sciences, Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia
| | - Intan Diana Mat Azmi
- Department of Chemistry, Faculty of Science, Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia
- Centre of Foundation Studies for Agricultural Science, Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia
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4
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Pullmannová P, Čuříková-Kindlová BA, Ondrejčeková V, Kováčik A, Dvořáková K, Dulanská L, Georgii R, Majcher A, Maixner J, Kučerka N, Zbytovská J, Vávrová K. Polymorphism, Nanostructures, and Barrier Properties of Ceramide-Based Lipid Films. ACS OMEGA 2023; 8:422-435. [PMID: 36643519 PMCID: PMC9835644 DOI: 10.1021/acsomega.2c04924] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/03/2022] [Accepted: 12/02/2022] [Indexed: 06/17/2023]
Abstract
Ceramides belong to sphingolipids, an important group of cellular and extracellular lipids. Their physiological functions range from cell signaling to participation in the formation of barriers against water evaporation. In the skin, they are essential for the permeability barrier, together with free fatty acids and cholesterol. We examined the periodical structure and permeability of lipid films composed of ceramides (Cer; namely, N-lignoceroyl 6-hydroxysphingosine, CerNH24, and N-lignoceroyl sphingosine, CerNS24), lignoceric acid (LIG; 24:0), and cholesterol (Chol). X-ray diffraction experiments showed that the CerNH24-based samples form either a short lamellar phase (SLP, d ∼ 5.4 nm) or a medium lamellar phase (MLP, d = 10.63-10.78 nm) depending on the annealing conditions. The proposed molecular arrangement of the MLP based on extended Cer molecules also agreed with the relative neutron scattering length density profiles obtained from the neutron diffraction data. The presence of MLP increased the lipid film permeability to the lipophilic model permeant (indomethacin) relative to the CerNS24-based control samples and the samples that had the same lipid composition but formed an SLP. Thus, the arrangement of lipids in various nanostructures is responsive to external conditions during sample preparation. This polymorphic behavior directly affects the barrier properties, which could also be (patho)physiologically relevant.
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Affiliation(s)
- Petra Pullmannová
- Skin
Barrier Research Group, Charles University, Faculty of Pharmacy in Hradec Králové, Heyrovského 1203, 500 05Hradec Králové, Czech Republic
| | - Barbora A. Čuříková-Kindlová
- Faculty
of Chemical Technology, University of Chemistry
and Technology Prague, Technická 5, 166 28Prague, Czech Republic
| | - Veronika Ondrejčeková
- Skin
Barrier Research Group, Charles University, Faculty of Pharmacy in Hradec Králové, Heyrovského 1203, 500 05Hradec Králové, Czech Republic
| | - Andrej Kováčik
- Skin
Barrier Research Group, Charles University, Faculty of Pharmacy in Hradec Králové, Heyrovského 1203, 500 05Hradec Králové, Czech Republic
| | - Kristýna Dvořáková
- Faculty
of Chemical Technology, University of Chemistry
and Technology Prague, Technická 5, 166 28Prague, Czech Republic
| | - Lucia Dulanská
- Skin
Barrier Research Group, Charles University, Faculty of Pharmacy in Hradec Králové, Heyrovského 1203, 500 05Hradec Králové, Czech Republic
| | - Robert Georgii
- Heinz
Maier-Leibnitz Zentrum (MLZ), Technische
Universität München, Lichtenbergstr. 1, 85748Garching, Germany
| | - Adam Majcher
- Skin
Barrier Research Group, Charles University, Faculty of Pharmacy in Hradec Králové, Heyrovského 1203, 500 05Hradec Králové, Czech Republic
| | - Jaroslav Maixner
- Faculty
of Chemical Technology, University of Chemistry
and Technology Prague, Technická 5, 166 28Prague, Czech Republic
| | - Norbert Kučerka
- Faculty
of Pharmacy, Comenius University Bratislava, Odbojárov 10, 832 32Bratislava, Slovakia
- Frank
Laboratory of Neutron Physics, Joint Institute
for Nuclear Research, Joliot-Curie 6, 141980Dubna, Russia
| | - Jarmila Zbytovská
- Skin
Barrier Research Group, Charles University, Faculty of Pharmacy in Hradec Králové, Heyrovského 1203, 500 05Hradec Králové, Czech Republic
- Faculty
of Chemical Technology, University of Chemistry
and Technology Prague, Technická 5, 166 28Prague, Czech Republic
| | - Kateřina Vávrová
- Skin
Barrier Research Group, Charles University, Faculty of Pharmacy in Hradec Králové, Heyrovského 1203, 500 05Hradec Králové, Czech Republic
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5
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Ri JS, Choe CS, Choe SH, Jong KH, Hong SN, Schleusener J, Lademann J, Darvin ME. Lycopene, but not zeaxanthin, serves as a skeleton for the formation of an orthorhombic organization of intercellular lipids within the lamellae in the stratum corneum: Molecular dynamics simulations of the hydrated ceramide NS bilayer model. BIOCHIMICA ET BIOPHYSICA ACTA. BIOMEMBRANES 2023; 1865:184081. [PMID: 36342013 DOI: 10.1016/j.bbamem.2022.184081] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/26/2022] [Revised: 10/24/2022] [Accepted: 10/25/2022] [Indexed: 11/06/2022]
Abstract
Carotenoids play an important role in the protection of biomembranes against oxidative damage. Their function depends on the surroundings and the organization of the lipid membrane they are embedded in. Carotenoids are located parallel or perpendicular to the surface of the lipid bilayer. The influence of carotenoids on the organization of the lipid bilayer in the stratum corneum has not been thoroughly considered. Here, the orientation of the exemplary cutaneous carotenoids lycopene and zeaxanthin in a hydrated ceramide NS24 bilayer model and the influence of carotenoids on the lateral organization of the lipid bilayer model were studied by means of molecular dynamics simulations for 32 °C and 37 °C. The results confirm that lycopene is located parallel and zeaxanthin perpendicular to the surface of the lipid bilayer. The lycopene-loaded lipid bilayer appeared to have a strong orthorhombic organization, while zeaxanthin-loaded and pure lipid bilayers were organized in a disordered hexagonal-like and liquid-like state, respectively. The effect is stronger at 32 °C compared to 37 °C based on p-values. Therefore, it was assumed that carotenoids without hydroxyl polar groups in their structure facilitate the formation of the orthorhombic organization of lipids, which provides the skin barrier function. It was shown that the distance between carotenoid atoms matched the distance between atoms in the lipids, indicating that parallel located carotenoids without hydroxyl groups serve as a skeleton for lipid membranes inside the lamellae. The obtained results provide reasonable prediction of the overall qualitative properties of lipid model systems and show the importance of parallel-oriented carotenoids in the development and maintenance of the skin barrier function.
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Affiliation(s)
- Jin-Song Ri
- Faculty of Materials Science, Kim Il Sung University, Pyongyang, Democratic People's Republic of Korea
| | - Chun-Sik Choe
- Faculty of Materials Science, Kim Il Sung University, Pyongyang, Democratic People's Republic of Korea
| | - Se-Hyok Choe
- Faculty of Materials Science, Kim Il Sung University, Pyongyang, Democratic People's Republic of Korea
| | - Kwang-Hyok Jong
- Faculty of Physics, Kim Il Sung University, Pyongyang, Democratic People's Republic of Korea
| | - Song-Nam Hong
- Faculty of Materials Science, Kim Il Sung University, Pyongyang, Democratic People's Republic of Korea
| | - Johannes Schleusener
- Charité - Universitätsmedizin Berlin, Corporate Member of Freie Universität Berlin and Humboldt-Universität zu Berlin, Department of Dermatology, Venerology and Allergology, Center of Experimental and Applied Cutaneous Physiology, Charitéplatz 1, 10117 Berlin, Germany.
| | - Juergen Lademann
- Charité - Universitätsmedizin Berlin, Corporate Member of Freie Universität Berlin and Humboldt-Universität zu Berlin, Department of Dermatology, Venerology and Allergology, Center of Experimental and Applied Cutaneous Physiology, Charitéplatz 1, 10117 Berlin, Germany
| | - Maxim E Darvin
- Charité - Universitätsmedizin Berlin, Corporate Member of Freie Universität Berlin and Humboldt-Universität zu Berlin, Department of Dermatology, Venerology and Allergology, Center of Experimental and Applied Cutaneous Physiology, Charitéplatz 1, 10117 Berlin, Germany
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6
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Prado-Mantilla A, Lechler T. Polarity in skin development and cancer. Curr Top Dev Biol 2023; 154:317-336. [PMID: 37100522 DOI: 10.1016/bs.ctdb.2023.02.003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/12/2023]
Abstract
The epidermis is a stratified squamous epithelium that forms the outermost layer of the skin. Its primary function is to act as a barrier, keeping pathogens and toxins out and moisture in. This physiological role has necessitated major differences in the organization and polarity of the tissue as compared to simple epithelia. We discuss four aspects of polarity in the epidermis - the distinctive polarities of basal progenitor cells as well as differentiated granular cells, the polarity of adhesions and the cytoskeleton across the tissue as keratinocytes differentiate, and the planar cell polarity of the tissue. These distinctive polarities are essential for the morphogenesis and the function of the epidermis and have also been implicated in regulating tumor formation.
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7
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Miyauchi M, Ishikawa S, Kurachi T, Sakamoto K, Sakai H. Oral Absorption across Organotypic Culture Models of the Human Buccal Epithelium after E-cigarette Aerosol Exposure. ACS OMEGA 2022; 7:45574-45581. [PMID: 36530294 PMCID: PMC9753183 DOI: 10.1021/acsomega.2c06304] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 09/29/2022] [Accepted: 11/21/2022] [Indexed: 06/17/2023]
Abstract
Inhaled aerosols are absorbed across the oral cavity, respiratory tract, and gastrointestinal tract. The absorption across the oral cavity, which is one of the exposure routes, plays an important role in understanding pharmacokinetics and physiological effects. After aerosol exposure from e-cigarettes, tissue viability studies, morphological observation, and chemical analyses at the inner and outer buccal tissues were performed using organotypic 3D in vitro culture models of the buccal epithelium to better understand the deposition and absorption on the inner and outer buccal tissues. The aerosol exposures did not affect the tissue viability and had no change to the tissue morphology and structure. The deposition ratio at the buccal tissue surface is relatively low. This shows that majority of aerosol transfers to the airway tissues. The distribution from the inner tissue to the outer tissue has selectivity among various compounds, depending on the affinity with the liquid crystal structure of phospholipids and glucosylceramide. Although nicotine absorption in the aqueous solution was well known to increase as the unprotonated state of nicotine increased, the nicotine absorption after the aerosol exposure is irrelevant to the protonated-unprotonated state. Furthermore, the results showed that half of nicotine that adhered to the oral cavity transferred to the inner tissue via the oral epithelium and the other half transferred to the gastrointestinal tract accompanying multiple executions of swallowing, while majority of the water-soluble compounds with the hydroxyl group such as propylene glycol and benzoic acid that adhered to the oral cavity were eluted with the saliva and transferred to the gastrointestinal tract by swallowing.
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Affiliation(s)
- Masato Miyauchi
- Tobacco
Science Research Center, R&D Group, Japan Tobacco Inc., 6-2 Umegaoka, Aoba, Yokohama, Kanagawa 227-8512, Japan
| | - Shinkichi Ishikawa
- Scientific
Product Assessment Center, R&D Group, Japan Tobacco Inc., 6-2 Umegaoka, Aoba, Yokohama, Kanagawa 227-8512, Japan
| | - Takeshi Kurachi
- Scientific
Product Assessment Center, R&D Group, Japan Tobacco Inc., 6-2 Umegaoka, Aoba, Yokohama, Kanagawa 227-8512, Japan
| | - Kazutami Sakamoto
- Department
of Pure and Applied Chemistry, Faculty of Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510, Japan
| | - Hideki Sakai
- Department
of Pure and Applied Chemistry, Faculty of Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510, Japan
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8
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Kono T, Miyachi Y, Kawashima M. Clinical significance of the water retention and barrier function-improving capabilities of ceramide-containing formulations: A qualitative review. J Dermatol 2021; 48:1807-1816. [PMID: 34596254 PMCID: PMC9293121 DOI: 10.1111/1346-8138.16175] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2021] [Revised: 08/19/2021] [Accepted: 09/12/2021] [Indexed: 11/27/2022]
Abstract
A decrease in the ceramide content of the stratum corneum is known to cause dry and barrier-disrupted skin. In this literature review, the clinical usefulness of preparations containing natural or synthetic ceramides for water retention and barrier functions was evaluated. The PubMed, Cochrane Library, and Igaku Chuo Zasshi databases were searched using keywords such as "ceramide", "skincare products", "barrier + hydration + moisture + skin", and "randomized trial". All database searches were conducted in February 2019. Forty-one reports were selected based on the following criterion: comparative control studies that evaluated the effects of ceramide-containing formulations based on statistical evidence. Among the 41 reports, 12 were selected using the patient, intervention, comparison, and outcome approach. These 12 reports showed that external ceramide-containing preparations can improve dry skin and barrier function in patients with atopic dermatitis. However, a double-blinded comparative study with a large sample size is warranted for appropriate clinical use.
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Affiliation(s)
- Takeshi Kono
- Department of Dermatology, Aidu Chuo Hospital, Fukushima, Japan
| | - Yoshiki Miyachi
- Non-Profit Organization Health Institute Research of Skin, Tokyo, Japan.,Shizuoka Graduate University of Public Health, Shizuoka, Japan.,Kyoto University, Kyoto, Japan
| | - Makoto Kawashima
- Non-Profit Organization Health Institute Research of Skin, Tokyo, Japan.,Tokyo Women's Medical University, Tokyo, Japan
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9
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The Skin's Barrier: A Cryo-EM Based Overview of its Architecture and Stepwise Formation. J Invest Dermatol 2021; 142:285-292. [PMID: 34474746 DOI: 10.1016/j.jid.2021.06.037] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2021] [Revised: 06/28/2021] [Accepted: 06/30/2021] [Indexed: 01/22/2023]
Abstract
A major role of the skin is to serve as a barrier toward the environment. The skin's permeability barrier consists of a lipid structure positioned in the stratum corneum. Recent progress in high-resolution cryo-electron microscopy (cryo-EM) has allowed for elucidation of the architecture of the skin's barrier and its stepwise formation process representing the final stage of epidermal differentiation. In this review, we present an overview of the skin's barrier structure and its formation process, as evidenced by cryo-EM.
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10
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Narangifard A, Wennberg CL, den Hollander L, Iwai I, Han H, Lundborg M, Masich S, Lindahl E, Daneholt B, Norlén L. Molecular Reorganization during the Formation of the Human Skin Barrier Studied In Situ. J Invest Dermatol 2021; 141:1243-1253.e6. [DOI: 10.1016/j.jid.2020.07.040] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2020] [Revised: 07/01/2020] [Accepted: 07/13/2020] [Indexed: 12/25/2022]
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11
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Nováčková A, Sagrafena I, Pullmannová P, Paraskevopoulos G, Dwivedi A, Mazumder A, Růžičková K, Slepička P, Zbytovská J, Vávrová K. Acidic pH Is Required for the Multilamellar Assembly of Skin Barrier Lipids In Vitro. J Invest Dermatol 2021; 141:1915-1921.e4. [PMID: 33675786 DOI: 10.1016/j.jid.2021.02.014] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2020] [Revised: 02/18/2021] [Accepted: 02/23/2021] [Indexed: 11/19/2022]
Abstract
Lipid membrane remodeling belongs to the most fundamental processes in the body. The skin barrier lipids, which are ceramide dominant and highly rigid, must attain an unusual multilamellar nanostructure with long periodicity to restrict water loss and prevent the entry of potentially harmful environmental factors. Our data suggest that the skin acid mantle, apart from regulating enzyme activities and keeping away pathogens, may also be a prerequisite for the multilamellar assembly of the skin barrier lipids. Atomic force microscopy on monolayers composed of synthetic or human stratum corneum lipids showed multilayer formation (approximately 10-nm step height) in an acidic but not in a neutral environment. X-ray diffraction, Fourier transform infrared spectroscopy, and permeability studies showed markedly altered lipid nanostructure and increased water loss at neutral pH compared with that at acidic pH. These findings are consistent with the data on the altered organization of skin lipids and increased transepidermal water loss under conditions such as inadequate skin acidification, for example, in neonates, the elderly, and patients with atopic dermatitis.
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Affiliation(s)
- Anna Nováčková
- Faculty of Pharmacy in Hradec Králové, Charles University, Hradec Králové, Czech Republic
| | - Irene Sagrafena
- Faculty of Pharmacy in Hradec Králové, Charles University, Hradec Králové, Czech Republic
| | - Petra Pullmannová
- Faculty of Pharmacy in Hradec Králové, Charles University, Hradec Králové, Czech Republic
| | | | - Anupma Dwivedi
- Faculty of Pharmacy in Hradec Králové, Charles University, Hradec Králové, Czech Republic
| | - Anisha Mazumder
- Faculty of Pharmacy in Hradec Králové, Charles University, Hradec Králové, Czech Republic
| | - Karolína Růžičková
- Faculty of Pharmacy in Hradec Králové, Charles University, Hradec Králové, Czech Republic
| | - Petr Slepička
- Faculty of Chemical Technology, University of Chemistry and Technology Prague, Prague, Czech Republic
| | - Jarmila Zbytovská
- Faculty of Pharmacy in Hradec Králové, Charles University, Hradec Králové, Czech Republic; Faculty of Chemical Technology, University of Chemistry and Technology Prague, Prague, Czech Republic
| | - Kateřina Vávrová
- Faculty of Pharmacy in Hradec Králové, Charles University, Hradec Králové, Czech Republic.
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12
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Wertz PW. Lipid Metabolic Events Underlying the Formation of the Corneocyte Lipid Envelope. Skin Pharmacol Physiol 2021; 34:38-50. [PMID: 33567435 DOI: 10.1159/000513261] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2020] [Accepted: 11/22/2020] [Indexed: 11/19/2022]
Abstract
Cornified cells of the stratum corneum have a monolayer of an unusual lipid covalently attached to the outer surface. This is referred to as the corneocyte lipid envelope (CLE). It consists of a monolayer of ω-hydroxyceramides covalently attached to the outer surface of the cornified envelope. The CLE is essential for proper barrier function of the skin and is derived from linoleate-rich acylglucosylceramides synthesized in the viable epidermis. Biosynthesis of acylglucosylceramide and its conversion to the cornified envelope is complex. Acylglucosylceramide in the bounding membrane of the lamellar granule is the precursor of the CLE. The acylglucosylceramide in the limiting membrane of the lamellar granule may be oriented with the glucosyl moiety on the inside. Conversion of the acylglucosylceramide to the CLE requires removal of the glucose by action of a glucocerebrosidase. The ester-linked fatty acid may be removed by an as yet unidentified esterase, and the resulting ω-hydroxyceramide may become ester linked to the outer surface of the cornified envelope through action of transglutaminase 1. Prior to removal of ester-linked fatty acids, linoleate is oxidized to an epoxy alcohol through action of 2 lipoxygenases. This can be further oxidized to an epoxy-enone, which can spontaneously attach to the cornified envelope through Schiff's base formation. Mutations of genes coding for enzymes involved in biosynthesis of the CLE result in ichthyosis, often accompanied by neurologic dysfunction. The CLE is recognized as essential for barrier function of skin, but many questions about details of this essentiality remain. What are the relative roles of the 2 mechanisms of lipid attachment? What is the orientation of acylglucosylceramide in the bounding membrane of lamellar granules? Some evidence supports a role for CLE as a scaffold upon which intercellular lamellae unfold, but other evidence does not support this role. There is also controversial evidence for a role in stratum corneum cohesion. Evidence is presented to suggest that covalently bound ω-hydroxyceramides serve as a reservoir for free sphingosine that can serve in communicating with the viable epidermis and act as a potent broad-acting antimicrobial at the skin surface. Many questions remain.
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13
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Gutowska-Owsiak D, Podobas EI, Eggeling C, Ogg GS, Bernardino de la Serna J. Addressing Differentiation in Live Human Keratinocytes by Assessment of Membrane Packing Order. Front Cell Dev Biol 2020; 8:573230. [PMID: 33195206 PMCID: PMC7609878 DOI: 10.3389/fcell.2020.573230] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2020] [Accepted: 09/15/2020] [Indexed: 01/12/2023] Open
Abstract
Differentiation of keratinocytes is critical for epidermal stratification and formation of a protective stratum corneum. It involves a series of complex processes leading through gradual changes in characteristics and functions of keratinocytes up to their programmed cell death via cornification. The stratum corneum is a relatively impermeable barrier, comprised of dead cell remnants (corneocytes) embedded in lipid matrix. Corneocyte membranes are comprised of specialized lipids linked to late differentiation proteins, contributing to the formation of a stiff and mechanically strengthened layer. To date, the assessment of the progression of keratinocyte differentiation is only possible through determination of specific differentiation markers, e.g., by using proteomics-based approaches. Unfortunately, this requires fixation or cell lysis, and currently there is no robust methodology available to study keratinocyte differentiation in living cells in real-time. Here, we explore new live-cell based approaches for screening differentiation advancement in keratinocytes, in a "calcium switch" model. We employ a polarity-sensitive dye, Laurdan, and Laurdan general polarization function (GP) as a reporter of the degree of membrane lateral packing order or condensation, as an adequate marker of differentiation. We show that the assay is straightforward and can be conducted either on a single cell level using confocal spectral imaging or on the ensemble level using a fluorescence plate reader. Such systematic quantification may become useful for understanding mechanisms of keratinocyte differentiation, such as the role of membrane in homogeneities in stiffness, and for future therapeutic development.
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Affiliation(s)
- Danuta Gutowska-Owsiak
- University of Gdansk, Intercollegiate Faculty of Biotechnology of University of Gdansk and Medical University of Gdansk, Gdansk, Poland
- Medical Research Council Human Immunology Unit, National Institute for Health Research Oxford Biomedical Research Centre, Medical Research Council Weatherall Institute of Molecular Medicine, University of Oxford, Oxford, United Kingdom
| | - Ewa I. Podobas
- Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Warsaw, Poland
- Faculty of Biology, Institute of Genetics and Biotechnology, University of Warsaw, Warsaw, Poland
| | - Christian Eggeling
- Medical Research Council Human Immunology Unit, National Institute for Health Research Oxford Biomedical Research Centre, Medical Research Council Weatherall Institute of Molecular Medicine, University of Oxford, Oxford, United Kingdom
- Institute of Applied Optics and Biophysics, Friedrich-Schiller-University Jena, Jena, Germany
- Leibniz Institute of Photonic Technologies e.V., Jena, Germany
| | - Graham S. Ogg
- Medical Research Council Human Immunology Unit, National Institute for Health Research Oxford Biomedical Research Centre, Medical Research Council Weatherall Institute of Molecular Medicine, University of Oxford, Oxford, United Kingdom
| | - Jorge Bernardino de la Serna
- Medical Research Council Human Immunology Unit, National Institute for Health Research Oxford Biomedical Research Centre, Medical Research Council Weatherall Institute of Molecular Medicine, University of Oxford, Oxford, United Kingdom
- Faculty of Medicine, National Heart and Lung Institute, Imperial College London, London, United Kingdom
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14
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Kitaoka M, Oka A, Goto M. Monoolein Assisted Oil-Based Transdermal Delivery of Powder Vaccine. Pharmaceutics 2020; 12:E814. [PMID: 32867263 PMCID: PMC7558954 DOI: 10.3390/pharmaceutics12090814] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2020] [Revised: 08/24/2020] [Accepted: 08/25/2020] [Indexed: 11/17/2022] Open
Abstract
An increasing number of protein vaccines have been researched for cancer, inflammation, and allergy therapies. Most of the protein therapeutics are administered through injection because orally-administered proteins are metabolized by the digestive system. Although transdermal administration has received increasing attention, the natural barrier formed by the skin is an obstacle. Monoolein is a common skin penetration enhancer that facilitates topical and transdermal drug delivery. Conventionally, it has been used in an aqueous vehicle, often with polyhydric alcohols. In the current study, monoolein was dissolved in an oil vehicle, isopropyl myristate, to facilitate the skin permeation of powder proteins. The skin permeabilities of the proteins were examined in-vivo and ex-vivo. Monoolein concentration-dependently enhanced the skin permeation of proteins. The protein permeability correlated with the zeta potential of the macromolecules. Dehydration of the stratum corneum (SC), lipid extraction from the SC, and disordering of ceramides caused by monoolein were demonstrated through Fourier transform infrared spectroscopic analysis and small-angle X-ray scattering analysis. An antigen model protein, ovalbumin from egg white, was delivered to immune cells in living mice, and induced antigen-specific IgG antibodies. The patch system showed the potential for transdermal vaccine delivery.
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Affiliation(s)
- Momoko Kitaoka
- Department of Applied Chemistry, Graduate School of Engineering, Kyushu University, Fukuoka 819-0395, Japan; (M.K.); (A.O.)
| | - Atsushi Oka
- Department of Applied Chemistry, Graduate School of Engineering, Kyushu University, Fukuoka 819-0395, Japan; (M.K.); (A.O.)
| | - Masahiro Goto
- Department of Applied Chemistry, Graduate School of Engineering, Kyushu University, Fukuoka 819-0395, Japan; (M.K.); (A.O.)
- Advanced Transdermal Drug Delivery System Center, Kyushu University, Fukuoka 819-0395, Japan
- Center for Future Chemistry, Kyushu University, Fukuoka 819-0395, Japan
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15
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Badhe Y, Gupta R, Rai B. Development and application of coarse-grained MARTINI model of skin lipid ceramide [AP]. J Mol Model 2020; 26:182. [PMID: 32583227 DOI: 10.1007/s00894-020-04435-z] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2019] [Accepted: 06/02/2020] [Indexed: 01/10/2023]
Abstract
Stratum corneum (SC), the outermost layer of the skin, contains large variety of lipids, endowing them with the amphiphilic properties, needed to fulfil their key role in skin's barrier function. The individual role of lipid types in the barrier function is difficult to understand due to the immense heterogeneity and complexity of the lipid's organization within the SC. The lipid organization is being explored using both computational (molecular dynamics simulations) and experimental (neutron diffraction) techniques. Even though atomistic simulations provide unprecedented atomic level details, the major limitation is time and length scale that can be achieved with decent computational facility. Alternatively, coarse-grain (CG) models are currently being used to capture physics at bigger time and length scale without losing essential underlined structural information. In this study, a CG model of α-hydroxy phytosphingosines (CER[AP]) is developed based on philosophy of MARTINI force field. At first, the model is validated with various atomistic simulations and available experimental data. Later on, the model's compatibility with other major skin lipids, cholesterol, and free fatty acid (palmitic acid) is checked by simulating a mixture of lipid multilayer in presence and absence of water. The developed model of CER[AP] is able to predict key structural properties within the acceptable error limits. The phenomena of ceramide conformation transformation, cholesterol flip-flop, and specificity of lipid arrangement within the multilayered systems is observed during the simulation. This signifies the importance of model in capturing higher order structural transformations.
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Affiliation(s)
- Yogesh Badhe
- Physical Science Research Area, TCS Research, Tata Research Development and Design Centre, Tata Consultancy Services, 54B, Hadapsar Industrial Estate, Pune, 411013, India
| | - Rakesh Gupta
- Physical Science Research Area, TCS Research, Tata Research Development and Design Centre, Tata Consultancy Services, 54B, Hadapsar Industrial Estate, Pune, 411013, India.
| | - Beena Rai
- Physical Science Research Area, TCS Research, Tata Research Development and Design Centre, Tata Consultancy Services, 54B, Hadapsar Industrial Estate, Pune, 411013, India
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16
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Li Q, Fang H, Dang E, Wang G. The role of ceramides in skin homeostasis and inflammatory skin diseases. J Dermatol Sci 2019; 97:2-8. [PMID: 31866207 DOI: 10.1016/j.jdermsci.2019.12.002] [Citation(s) in RCA: 52] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2019] [Accepted: 12/02/2019] [Indexed: 10/25/2022]
Abstract
Ceramides, members of sphingolipid family, are not only the building blocks of epidermal barrier structure, but also bioactive metabolites involved in epidermal self-renewal and immune regulation. Hence, abnormal ceramide expression profile is recognized to defect extracellular lipid organization, disturb epidermal self-renewal, exacerbate skin immune response and actively participate in progression of several inflammatory dermatoses, exemplifying by psoriasis and atopic dermatitis. Here, we discuss recent advances in understanding skin ceramides and their regulatory roles in skin homeostasis and pathogenic roles of altered ceramide metabolism in inflammatory skin diseases. These insights provide new opportunities for therapeutic intervention in inflammatory dermatoses.
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Affiliation(s)
- Qingyang Li
- Department of Dermatology, Xijing Hospital, Fourth Military Medical University, Xi'an, China
| | - Hui Fang
- Department of Dermatology, Xijing Hospital, Fourth Military Medical University, Xi'an, China
| | - Erle Dang
- Department of Dermatology, Xijing Hospital, Fourth Military Medical University, Xi'an, China
| | - Gang Wang
- Department of Dermatology, Xijing Hospital, Fourth Military Medical University, Xi'an, China.
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17
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Shin ES, Lee JY, Lee SJ, Nam SH. Non-invasive method to monitor molecular changes in human stratum corneum during acute barrier disruption using reflectance NIR spectroscopy. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2019; 2018:1542-1545. [PMID: 30440687 DOI: 10.1109/embc.2018.8512567] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Stratum corneum is the outer most part of skin for barrier function. Disorder in stratum corneum is related with many skin diseases including acne, atopic dermatitis and psoriasis. In developed countries, about 20% of the population has disorder in the barrier function of stratum corneum. Adhesive tape stripping is a method to disrupt skin barrier function in studying disorder in stratum corneum. In this study, we obtained NIR (Near-Infrared) spectrum of human skin after tape stripping. Changes in skin spectra after barrier disruption were investigated through principal component analysis (PCA) of spectrum. PCA analysis revealed that peaks for -NH stretching and -CH vibration mainly contributed to the spectral variation caused by barrier disruption. Furthermore, second derivative of spectrum revealed that acute barrier disruption contributes to spectral changes in the region related with secondary structure of protein, lipid and water associated with lipid in stratum corneum. We demonstrated that acute barrier disruption affected features in NIR spectrum. These spectral changes revealed that acute barrier disruption affected keratin protein and ceramide in human stratum corneum. These results suggest that NIR spectroscopy can be used to monitor changes in filamentous network and lamellar structure in stratum corneum. NIR spectroscopy can provide non-invasive method to investigate skin disease related with barrier disruption by monitoring disturbance in protein and lipid structure in stratum corneum.
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18
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Mechanistic skin penetration model by the COSMOperm method: Routes of permeation, vehicle effects and skin variations in the healthy and compromised skin. ACTA ACUST UNITED AC 2019. [DOI: 10.1016/j.comtox.2019.02.004] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
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19
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Severe Skin Permeability Barrier Dysfunction in Knockout Mice Deficient in a Fatty Acid ω-Hydroxylase Crucial to Acylceramide Production. J Invest Dermatol 2019; 140:319-326.e4. [PMID: 31356814 DOI: 10.1016/j.jid.2019.07.689] [Citation(s) in RCA: 26] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2019] [Revised: 07/08/2019] [Accepted: 07/22/2019] [Indexed: 12/20/2022]
Abstract
The skin permeability barrier is indispensable for maintaining water inside the body and preventing the invasion of pathogens and allergens; abnormalities lead to skin disorders such as atopic dermatitis and ichthyosis. Acylceramide is an essential lipid for skin barrier formation, and CYP4F22 is a fatty acid ω-hydroxylase involved in its synthesis. Mutations in CYP4F22 cause autosomal recessive congenital ichthyosis, although the symptoms vary among mutation sites and types. Here, we generated knockout mice deficient in Cyp4f39, the mouse ortholog of human CYP4F22, to investigate the effects of completely abrogating the function of the fatty acid ω-hydroxylase involved in acylceramide production on skin barrier formation. Cyp4f39 knockout mice died within 8 hours of birth. Large increases in transepidermal water loss and penetration of a dye from outside the body were observed, indicating severe skin barrier dysfunction. Histologic analyses of the epidermis revealed impairment of lipid lamella formation, accumulation of corneodesmosomes in the stratum corneum, and persistence of periderm. In addition, lipid analyses by mass spectrometry showed almost complete loss of acylceramide and its precursor ω-hydroxy ceramide. In conclusion, our findings provide clues to the molecular mechanisms of skin barrier abnormalities and the pathogenesis of ichthyosis caused by Cyp4f39 and CYP4F22 by association.
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20
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Structural and barrier properties of the skin ceramide lipid bilayer: a molecular dynamics simulation study. J Mol Model 2019; 25:140. [PMID: 31041534 DOI: 10.1007/s00894-019-4008-5] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2018] [Accepted: 03/29/2019] [Indexed: 10/26/2022]
Abstract
Skin provides excellent protection against the harsh external environment and foreign substances. The lipid matrix of the stratum corneum, which contains various kinds of ceramides, plays a major role in the barrier function of the skin. Here we report a study of the effects of ceramide type on the structural and transport properties of ceramide bilayers using molecular dynamics (MD) simulations. Specifically, the effects of headgroup chemistry (number and positions of hydroxyl groups) and tail structure (unsaturation of the sphingoid moiety) on the structural and transport properties of various ceramide bilayers at 310 K were analyzed. Theoretical results for structural properties such as area per lipid, bilayer thickness, lateral arrangement, order parameter, and hydrogen bonding are reported here and compared with corresponding experimental data. Our study revealed that the presence of a double bond disrupts the bilayer packing, which leads to a low area compressibility modulus, a large area per lipid, and low bilayer thickness. Furthermore, the effect of structural changes on water permeation was studied using steered MD simulations. Water permeation was found to be influenced by headgroup polarity, chain packing, and the ability of the water to hydrogen bond with the ceramides. The molecular-level information obtained from the current study should aid the design of mixed bilayer systems with desired properties and provide the basis for the development of higher order coarse-grained models.
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21
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Yamamoto K, Klossek A, Fuchs K, Watts B, Raabe J, Flesch R, Rancan F, Pischon H, Radbruch M, Gruber AD, Mundhenk L, Vogt A, Blume-Peytavi U, Schrade P, Bachmann S, Gurny R, Rühl E. Soft X-ray microscopy for probing of topical tacrolimus delivery via micelles. Eur J Pharm Biopharm 2019; 139:68-75. [PMID: 30849430 DOI: 10.1016/j.ejpb.2019.03.006] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2018] [Revised: 01/04/2019] [Accepted: 03/04/2019] [Indexed: 12/27/2022]
Abstract
The penetration of topically applied tacrolimus formulated in micelles into murine skin is reported, measured by X-ray microscopy. Tacrolimus and micelles are probed for the first time by this high spatial resolution technique by element-selective excitation in the C 1s- and O 1s-regimes. This method allows selective detection of the distribution and penetration depth of drugs and carrier molecules into biologic tissues. It is observed that small, but distinct quantities of the drug and micelles, acting as a drug carrier, penetrate the stratum corneum. A comparison is made with the paraffin-based commercial tacrolimus ointment Protopic®, where local drug concentrations show to be low. A slight increase in local drug concentration in the stratum corneum is observed, if tacrolimus is formulated in micelles, as compared to Protopic®. This underscores the importance of the drug formulations for effective drug delivery. Time-resolved penetration shows presence of drug in the stratum corneum 100 min after formulation application, with penetration to deeper skin layers at 1000 min. High resolution micrographs give indications for a penetration pathway along the lipid membranes between corneocytes, but also suggest that the compound may penetrate corneocytes.
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Affiliation(s)
- K Yamamoto
- Physikalische Chemie, Freie Universität Berlin, Arnimallee 22, 14195 Berlin, Germany
| | - A Klossek
- Physikalische Chemie, Freie Universität Berlin, Arnimallee 22, 14195 Berlin, Germany
| | - K Fuchs
- Apidel SA, c/o The Business Harbour, 29 Quai du Mont Blanc, 1201 Geneva, Switzerland
| | - B Watts
- Swiss Light Source, Paul Scherrer Institut, Forschungsstraße 111, 5232 Villigen PSI, Switzerland
| | - J Raabe
- Swiss Light Source, Paul Scherrer Institut, Forschungsstraße 111, 5232 Villigen PSI, Switzerland
| | - R Flesch
- Physikalische Chemie, Freie Universität Berlin, Arnimallee 22, 14195 Berlin, Germany
| | - F Rancan
- Clinical Research Center for Hair and Skin Science, Department of Dermatology and Allergy, Charité - Universitätsmedizin Berlin, Corporate Member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, 10117 Berlin, Germany
| | - H Pischon
- Institute of Veterinary Pathology, Freie Universität Berlin, Robert-von-Ostertag-Str. 15, 14163 Berlin, Germany
| | - M Radbruch
- Institute of Veterinary Pathology, Freie Universität Berlin, Robert-von-Ostertag-Str. 15, 14163 Berlin, Germany
| | - A D Gruber
- Institute of Veterinary Pathology, Freie Universität Berlin, Robert-von-Ostertag-Str. 15, 14163 Berlin, Germany
| | - L Mundhenk
- Institute of Veterinary Pathology, Freie Universität Berlin, Robert-von-Ostertag-Str. 15, 14163 Berlin, Germany
| | - A Vogt
- Clinical Research Center for Hair and Skin Science, Department of Dermatology and Allergy, Charité - Universitätsmedizin Berlin, Corporate Member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, 10117 Berlin, Germany
| | - U Blume-Peytavi
- Clinical Research Center for Hair and Skin Science, Department of Dermatology and Allergy, Charité - Universitätsmedizin Berlin, Corporate Member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, 10117 Berlin, Germany
| | - P Schrade
- Abteilung für Elektronenmikroskopie at CVK, 13353 Berlin, Germany
| | - S Bachmann
- Abteilung für Elektronenmikroskopie at CVK, 13353 Berlin, Germany
| | - R Gurny
- Apidel SA, c/o The Business Harbour, 29 Quai du Mont Blanc, 1201 Geneva, Switzerland
| | - E Rühl
- Physikalische Chemie, Freie Universität Berlin, Arnimallee 22, 14195 Berlin, Germany
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