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Chemical and Dermatological Aspects of UV-Absorbing Compounds

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Chemical and Dermatological Aspects of UV-Absorbing Compounds Chemical and Dermatological Aspects of UV‐absorbing Compounds Studies of Photoallergens and Synthesis of a Natural UV‐filter ISABELLA KARLSSON DOCTORAL THESIS Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Chemistry Chemical and Dermatological Aspects of UV‐absorbing Compounds Studies of Photoallergens and Synthesis of a Natural UV‐filter ISABELLA KARLSSON Cover illustration: Proposed mechanism for activation of the commercial UV‐filters 4‐tert‐ butyl‐4’‐methoxy dibenzoylmethane and octocrylene by solar radiation resulting in the reaction with skin proteins and the formation of immunogenic complexes. © Isabella Karlsson ISBN: 978‐91‐628‐8349‐2 Available online at: http://hdl.handle.net/2077/26665 Department of Chemistry University of Gothenburg SE‐412 96 Göteborg Sweden Printed by Chalmers Reproservice Göteborg, Sweden, 2011 The most exciting phrase to hear in science, the one that heralds new discoveries, is not ‘Eureka!’ (I found if!) but ‘That’s funny…’ Isaac Asimov (1920‐1992) ABSTRACT The sun’s UV radiation is necessary for the existence of life on earth. However, too much UV exposure can lead to the development of skin cancer. Therefore, sunscreens are often used by the general population as protection from excessive UV radiation. Unfortunately, many of the chemical UV‐filters that are used in sunscreens today have the ability to induce contact and photocontact allergy. In this work two different chemical UV‐filters together with the anti‐inflammatory drug ketoprofen, all known to induce allergic reactions, have been studied to better understand the reason for these adverse effects. In addition, a synthetic route to the natural UV‐filter scytonemin has been developed. One of the most commonly used UVA‐filters today is the well known photoallergen 4‐tert‐ butyl‐4’‐methoxy dibenzoylmethane. We showed that it degrades when irradiated with UV light and that several different photodegradation products are formed. Of particular interest were arylglyoxals and benzils because they were unexplored as potential contact allergens. The benzils were found to be cytotoxic rather than allergenic, whereas the arylglyoxals were found to be strong sensitizers in the murine local lymph node assay (LLNA) used to assess their allergenic potency. Photocontact allergy to dibenzoylmethanes is therefore probably caused by the arylglyoxals that are formed upon photodegradation. Chemical reactivity experiments showed that the arylglyoxals have the ability to form immunogenic complexes via an electrophilic‐nucleophilic reaction with the amino acid arginine. A relatively new UV‐filter on the market is octocrylene that has grown in popularity, due to its ability to stabilize other UV‐filters such as 4‐tert‐butyl‐4’‐methoxy dibenzoylmethane. However, recent clinical reports suggest that it is the UV‐filter that causes most allergic reactions. Patch and photopatch testing of 172 patients with suspected skin reactions to sunscreens or ketoprofen was performed and 23 of these patients displayed a positive test reaction to octocrylene. Five patients were diagnosed with contact allergy and 18 with photocontact allergy. Notably, many of these patients also displayed a photoinduced reaction to ketoprofen. Without UV radiation, octocrylene was classified as a moderate allergen in the murine LLNA and it was shown to reacted with amines like lysine via a retro‐ aldol condensation. In presence of UV radiation, octocrylene also reacted with amines but via acyl substitution resulting in a different product outcome than the reaction in the dark. Both the clinical studies and the chemical reactivity experiments thereby indicate that octocrylene has the ability to induce both contact and photocontact allergy. The apparent photocross‐reactivity between octocrylene and ketoprofen observed in the clinical study could not be explained by the previous reactivity studies of octocrylene. Furthermore, according to other clinical reports, photosensitization to ketoprofen also leads to photocontact allergy to many other compounds. Ketoprofen was therefore irradiated in presence of five amino acid analogs and interestingly a reaction between the tryptophan and lysine analogs was substantially enhanced by ketoprofen. We believe that ketoprofen generates singlet molecular oxygen which activates the tryptophan analog that subsequently reacts with the lysine analog. The formation of an immunogenic complex not containing the allergen itself can explain many of the observed photocross allergies between ketoprofen and other structurally different compounds. In theory all compounds that are able to generate singlet molecular oxygen can promote the formation of the same immunogenic complex. V Finally, the first total synthesis of the dimeric alkaloid scytonemin was developed. This natural occurring UV‐filter enables the survival of different species of cyanobacteria in areas of intense solar radiation. The planed structure activity studies of scytonemin and derivatives thereof will hopefully lead to the development of a stable UV‐filter that does not cause contact or photocontact allergy. Keywords: Contact allergy, Dibenzoylmethane, Immunogenic complex, Ketoprofen, Local Lymph Node Assay, Octocrylene, Patch testing, Photoallergen, Photocontact Allergy, Photodegradation, Photopatch testing, Photostability, Scytonemin, UV‐filter. VI LIST OF PUBLICATIONS This thesis is based on the following papers, which are referred to in the text by their Roman numbers I‐V. The papers are appended at the end of the thesis and reprints are made with permission from the publishers. I. Photodegradation of Dibenzoylmethanes: Potential Cause of Photocontact Allergy to Sunscreens Isabella Karlsson, Lisa Hillerström, Anna‐Lena Stenfeldt, Jerker Mårtensson, and Anna Börje. Chemical Research in Toxicology 22, 1881‐1892 (2009) II. Clinical and Experimental Studies of Octocrylene’s Allergenic Potency Isabella Karlsson, Katrien Vanden Broecke, Jerker Mårtensson, An Goossens, and Anna Börje. Contact Dermatitis 64, 343‐352 (2011) III. Investigation of the Sunscreen Octocrylene’s Interaction with Amino Acid Analogs in the Presence of UV radiation Isabella Karlsson, Jerker Mårtensson, and Anna Börje. Submitted for publication IV. Ketoprofen Induced Formation of Amino Acid Photoadducts: Possible Explanation for Photocontact Allergy to Ketoprofen Isabella Karlsson, Elin Persson, Jerker Mårtensson, and Anna Börje. Manuscript in preparation V. Oxidative Coupling as a Biomimetic Approach to the Synthesis of Scytonemin Andreas Ekebergh, Isabella Karlsson, Rudi Mete, Ye Pan, Anna Börje, and Jerker Mårtensson. Organic Letters 13, 4458‐4461 (2011) VII CONTRIBUTION REPORT Paper I. Contributed to the formulation of the research problem; performed or supervised the synthesis of test compounds, the development of analytical methods, the chemical reactivity experiments, the LLNA experiments; planed the cell viability experiments; major contribution to interpretation the results; wrote the manuscript. Paper II. Major contribution to the formulation of the research problem; developed the analytical methods, performed the chemical reactivity experiments and the LLNA experiment; major contribution to interpretation of the results and to the writing of the manuscript. Paper III. Formulated the research problem; performed all the experimental work; interpreted the results, and wrote the manuscript. Paper IV. Major contribution to the formulation of the research problem; performed or supervised all the experimental work; interpreted the results, and wrote the manuscript. Paper V. Minor contribution to the formulation of the research problem; contributed to the experimental work, the interpretation of the results, and to writing of the manuscript. VIII ABBREVIATIONS ACD Allergic contact dermatitis ACN Acetonitrile Arg Arginine Cys Cysteine DCM Dichloromethane DMSO Dimethyl sulfoxide DodSMe n‐Dodecyl methyl sulfide dpm Disintegrations per minute EtOH Ethanol FDA US Food and Drug Administration GC Gas chromatography HEPES 4‐(2‐hydroxyethyl)‐1‐piperazineethanesulfonic acid His Histidine HPLC High performance liquid chromatography LDA Lithium diisopropyl amide LLNA Local lymph node assay Lys Lysine MeOH Methanol MI Methylisothiazolinone MS Mass spectrometry MTS 3‐(4,5‐Dimethylthiazol‐2‐yl)‐5‐(3‐carboxymethoxyphenyl)‐2‐(4‐sulfophenyl)‐2H‐ tetrazolium, inner salt NSAID Non‐steroidal anti‐inflammatory drug PMS Phenazine methosulfate OECD Organization for Economic Co‐operation and Development PACD Photoallergic contact dermatitis PIDA Phenyliodine diacetate PBS Phosphate buffered saline THF Tetrahydrofuran TiO2 Titanium dioxide TMANO Trimethylamine N‐oxide Trp Tryptophan Tyr Tyrosine UV Ultraviolet ZnO Zinc oxide IX CONTENTS 1 INTRODUCTION .................................................................................................................. 1 1.1 Solar UV radiation ........................................................................................................ 1 1.1.1 Effects of solar UV radiation on human skin ........................................................ 1 1.2 Sunscreens ................................................................................................................... 1 1.3 The Natural UV‐filter Scytonemin ............................................................................... 3 1.4 Allergic Contact Dermatitis .......................................................................................... 3 1.4.1 Immunological mechanism .................................................................................
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