Selected oxidized fragrance terpenes are common contact allergens

Anti-inflammatory potential of a lipolotion containing coriander oil in the ultraviolet erythema test

SUMMARY BACKGROUND

Coriander oil is used as an antimicrobial agent and as a natural fragrance. The present study investigated the anti-inflammatory potency of coriander oil in the ultraviolet (UV) erythema test in vivo.

METHODS

40 volunteers were enrolled in this monocentric,randomized,placebo-controlled double-blind study.Test areas on the back were irradiated with the 1.5 fold minimal erythema dose UV-B. Subsequently, the test areas were treated under occlusion for 47 hours with a lipolotion containing 0.5% or 1.0% essential coriander oil. Hydrocortisone (1.0%) and betamethasone valerate (0.1%) in the vehicle served as positive controls.The vehicle was used as place-bo.The effect of the test substances on the UV-induced erythema was measured photometrically after 48 hours.Additionally,the skin tolerance of the test preparations was assessed on non-irradiated skin.

RESULTS

Compared to placebo, the lipolotion with 0.5% coriander oil significantly reduced the UV-induced erythema, but it was not as effective as hydrocortisone. The skin tolerance of both coriander oil concentrations was excellent.

CONCLUSIONS

The lipolotion containing coriander oil displayed a mild antiinflammatory effect in this study. It could be useful in the concomitant treatment of inflammatory skin diseases.

Autoxidation of linalyl acetate, the main component of lavender oil, creates potent contact allergens

BACKGROUND

Fragrances are among the most common causes of allergic contact dermatitis. We have in previous studies shown that linalool, present in lavender oil, autoxidizes on air exposure, forming allergenic oxidation products. Oxidized linalool was found to be a frequent cause of contact allergy in a patch test study on consecutive dermatitis patients. Linalyl acetate, the main component of lavender oil is commonly used as a fragrance chemical in scented products. Because of structural similarities, linalyl acetate should also be susceptible to oxidation on air exposure, forming similar oxidation products as linalool.

OBJECTIVE

The aim of the present study was to investigate the autoxidation of linalyl acetate and the influence of oxidation on its sensitizing potency.

METHODS

Analyses were performed using gas chromatography, nuclear magnetic resonance spectrometry and mass spectrometry. Sensitizing potencies of compounds were determined using the local lymph node assay (LLNA) in mice.

RESULTS

Analyses showed that the content of linalyl acetate decreased over time on air exposure and other compounds were formed. Hydroperoxides, an epoxide and an alcohol were identified as oxidation products from linalyl acetate. In the LLNA, linalyl acetate of high purity showed a weak sensitizing potency (EC3 25%). Autoxidation increased the sensitizing potency of linalyl acetate, and a 10 weeks oxidized sample gave an EC3 value of 3.6%. As for linalool, the hydroperoxides were shown to be the oxidation products with the highest sensitizing potency.

CONCLUSION

It is concluded that autoxidation of the weakly allergenic linalyl acetate leads to formation of allergenic oxidation products.

Allergic contact dermatitis--formation, structural requirements, and reactivity of skin sensitizers

Contact allergy is caused by a wide range of chemicals after skin contact. Its clinical manifestation, allergic contact dermatitis (ACD), is developed upon repeated contact with the allergen. This perspective focuses on two areas that have yielded new useful information during the last 20 years: (i) structure-activity relationship (SAR) studies of contact allergy based on the concept of hapten-protein binding and (ii) mechanistic investigations regarding activation of nonsensitizing compounds to contact allergens by air oxidation or skin metabolism. The second area is more thoroughly reviewed since the full picture has previously not been published. Prediction of the sensitizing capacity of a chemical is important to avoid outbreaks of ACD in the population. Much research has been devoted to the development of in vitro and in silico predictive testing methods. Today, no method exists that is sensitive enough to detect weak allergens and that is robust enough to be used for routine screening. To cause sensitization, a chemical must bind to macromolecules (proteins) in the skin. Expert systems containing information about the relationship between the chemical structure and the ability of chemicals to haptenate proteins are available. However, few designed SAR studies based on mechanistic investigations of prohaptens have been published. Many compounds are not allergenic themselves but are activated in the skin (e.g., metabolically) or before skin contact (e.g., via air oxidation) to form skin sensitizers. Thus, more basic research is needed on the chemical reactions involved in the antigen formation and the immunological mechanisms. The clinical importance of air oxidation to activate nonallergenic compounds has been demonstrated. Oxidized fragrance terpenes, in contrast to the pure terpenes, gave positive patch test reactions in consecutive dermatitis patients as frequently as the most common standard allergens. This shows the importance of using compounds to which people are exposed when screening for ACD in dermatology clinics.

Dicaprylyl maleate ? an emerging cosmetic allergen

Dicaprylyl maleate (DCM) has been reported rarely as a cause of allergic contact dermatitis. The objectives of this study were to identify patients from multiple centres with allergy to DCM in cosmetic products confirmed by patch testing and, in addition, to investigate the effect of testing with aged DCM. This is an international multicentre study of 22 patients with 26 reactions to products containing DCM. Patch testing was carried out to ingredients including DCM obtained from the manufacturer. Further testing was carried out with deliberately aged DCM in a sample of patients. 22 patients had clinical and positive patch test reactions at 4 days to a total of 26 cosmetic products containing DCM. 5 patients did not react to DCM prepared by the manufacturer from concurrent factory stock but did have positive reactions to a deliberately aged batch of DCM. DCM is an emerging cosmetic allergen. Testing with aged material yields a greater number of positive results. Co-operation between cosmetics manufacturers and clinicians is important in the identification of new allergens.

Fragrance ingredient labelling in products on sale in the U.K

BACKGROUND

The seventh amendment of the European Union (EU) Cosmetics Directive (March 2005) and the Detergents Regulations of the EU (October 2005) are now legal requirements in Europe. Cosmetic products and detergents must be labelled for 26 individual named fragrances, when present at concentrations of > 10 parts per million (p.p.m.) in leave-on products and > 100 p.p.m. in rinse-off products.

OBJECTIVES

To make an assessment of the exposure pattern to fragrance of the U.K. consumer and to determine the frequency with which the constituent fragrances of fragrance mix I (FM I) and fragrance mix II (FM II) are included in products currently sold in the U.K.

METHODS

A study of perfumed cosmetic and household products available on the shelves of U.K. retailers was carried out in January 2006. Products were included if 'parfum' or 'aroma' was listed among the ingredients. Three hundred products were surveyed and any of the 26 listed fragrances named on the label were recorded.

RESULTS

The top six most frequently labelled fragrances were linalool (190; 63%), limonene (189; 63%), citronellol (145; 48%), geraniol (126; 42%), butyl phenyl methyl propional (Lilial(trade mark)) (126; 42%) and hexyl cinnamal (125; (42%). One of these, geraniol, is present in FM I and two others, citronellol and hexyl cinnamal, in FM II, thus tested as part of the British Standard patch test series. The frequencies of other constituents of FM I were as follows: eugenol, 80 (27%); hydroxycitronellal, 52 (17%); isoeugenol, 27 (9%); cinnamic alcohol, 25 (8%); amyl cinnamal, 22 (7%); cinnamal, 17 (6%); Evernia prunastri (oak moss absolute), 13 (4%). The other constituents of FM II occurred as follows: coumarin, 90 (30%); hydroxyisohexyl-3-cyclohexene carboxaldehyde (Lyral(trade mark)), 88 (29%); citral, 74 (25%); farnesol, 23 (8%). Linalool (n = 46; 66%) was the most frequently found fragrance in 70 personal care products (soap, shampoo, shower gel). Linalool (n = 47; 80%) and limonene (n = 45; 76%) were the most frequent in 59 products for men (e.g. aftershave). Limonene (n = 29; 51%) predominated in 57 household products (washing-up liquid, detergent). Limonene (n = 43; 98%) and linalool (n = 42; 95%) were the most frequent fragrances in 44 perfumes for women. Alpha-isomethyl ionone (n = 28; 72%) was the most frequent in 39 cosmetics (foundation, lipstick, etc). Citronellol predominated (n = 15; 88%) in 17 deodorants and limonene (n = 9; 64%) was the commonest in 14 dental products (toothpaste and mouthwash). Thirty-four products (11%) contained none of the listed fragrances but were labelled as containing 'parfum' or 'aroma'.

CONCLUSIONS

There is ongoing consumer exposure to the most frequent sensitizers in FM I: E. prunastri, isoeugenol and the cinnamon fragrances cinnamal and cinnamic alcohol. Hydroxyisohexyl-3-cyclohexene carboxaldehyde (Lyral(trade mark)) is present at significant concentrations in almost one-third of products. Linalool and limonene, fragrance terpenes which are significant allergens in their oxidized state, are the most frequent fragrances encountered by individuals living in the U.K. The current exposure pattern of the U.K. consumer suggests that we should add oxidized limonene and oxidized linalool to the test series for patients suspected to have fragrance allergy.

Sensitization to 26 fragrances to be labelled according to current European regulation

To study the frequency of sensitization to 26 fragrances to be labelled according to current European regulation. During 4 periods of 6 months, from 1 January 2003 to 31 December 2004, 26 fragrances were patch tested additionally to the standard series in a total of 21 325 patients; the number of patients tested with each of the fragrances ranged from 1658 to 4238. Hydroxymethylpentylcyclohexene carboxaldehyde (HMPCC) was tested throughout all periods. The following frequencies of sensitization (rates in %, standardized for sex and age) were observed: tree moss (2.4%), HMPCC (2.3), oak moss (2.0), hydroxycitronellal (1.3), isoeugenol (1.1), cinnamic aldehyde (1.0), farnesol (0.9), cinnamic alcohol (0.6), citral (0.6), citronellol (0.5), geraniol (0.4), eugenol (0.4), coumarin (0.4), lilial (0.3), amyl-cinnamic alcohol (0.3), benzyl cinnamate (0.3), benzyl alcohol (0.3), linalool (0.2), methylheptin carbonate (0.2), amyl-cinnamic aldehyde (0.1), hexyl-cinnamic aldehyde (0.1), limonene (0.1), benzyl salicylate (0.1), gamma-methylionon (0.1), benzyl benzoate (0.0), anisyl alcohol (0.0). 1) Substances with higher sensitization frequencies were characterized by a considerable number of '++/+++' reactions. 2) Substances with low sensitization frequencies were characterized by a high number of doubtful/irritant and a low number of stronger (++/+++) reactions. 3) There are obviously fragrances among the 26 which are, with regard to contact allergy, of great, others of minor, and some of no importance at all.

Compositae dermatitis from airborne parthenolide

BACKGROUND

Compositae dermatitis confined to exposed skin has often been considered on clinical grounds to be airborne. Although anecdotal clinical and plant chemical reports suggest true airborne allergy, no proof has been procured. Feverfew (Tanacetum parthenium) is a European Compositae plant suspected of causing airborne contact allergy, and its most important allergen is the sesquiterpene lactone (SQL) parthenolide (PHL).

OBJECTIVES

The aims of this study were to (i) assess the allergenicity of feverfew-derived monoterpenes and sesquiterpenes and their oxidized products in feverfew-allergic patients and (ii) re-assess the role of PHL and other SQLs in airborne contact allergy.

PATIENTS AND METHODS

Feverfew-allergic patients were patch tested with extracts and fractions containing volatile monoterpenes and sesquiterpenes as well as extracts of airborne particles from flowering feverfew plants, obtained by fractionation of ether extracts, dynamic headspace and high-volume air sampler (HIVAS) technique, respectively.

RESULTS

Among 12 feverfew-allergic patients, eight had positive patch-test reactions to a HIVAS filter extract, while two tested positive to a headspace extract. Subsequent analysis of the HIVAS extract by gas chromatography and mass spectrometry detected PHL in a concentration of 510 ng mL(-1) in the HIVAS extract. Testing with a dilution series of PHL showed positive reactions down to 8.1 ng in selected patients. None of the 12 patients tested positive to monoterpenes or sesquiterpenes, whether they were oxidized or not.

CONCLUSIONS

The clinical results have proved that some feverfew-allergic patients are sensitive to airborne particles released from the plant, and isolation of PHL from the particle-containing HIVAS extract in allergenic amounts is strong evidence of PHL as the responsible allergen.

Not only oxidized R-(+)- but also S-(?)-limonene is a common cause of contact allergy in dermatitis patients in Europe

Limonene, one of the most often used fragrance terpenes in any kind of scented products, is prone to air-oxidation. The oxidation products formed have a considerable sensitizing potential. In previous patch test studies on consecutively tested dermatitis patients, oxidized R-limonene has been proven to be a good and frequent indicator of fragrance-related contact allergy. The current study extends these investigations to 6 European clinics of dermatology, where the oxidation mixture of both enantiomers of limonene (R and S) have been tested in 2411 dermatitis patients. Altogether, 63 out of 2411 patients tested (2.6%) reacted to 1 or both the oxidized limonene preparations. Only 2.3% reacted to the oxidized R-limonene and 2.0% to the oxidized S-limonene. In 57% of the cases, simultaneous reactions were observed to both oxidation mixtures. Concomitant reactions to the fragrance mix, colophonium, Myroxylon pereirae, and fragrance-related contact allergy were common in patients reacting to 1 or both the oxidized limonene enantiomers. Our study provides clinical evidence for the importance of oxidation products of limonene in contact allergy. It seems advisable to screen consecutive dermatitis patients with oxidized limonene 3% petrolatum, although this patch test material is not yet commercially available.

Identification and classification of skin sensitizers: identifying false positives and false negatives

The first step in regulatory evaluation of substances involves the identification of their intrinsic hazards, including the potential for skin sensitization. This is, quite properly, entirely different from assessment of the risks to human health, which might arise from incorporation of substances in products. EU guidance on regulations concerning the classification of skin sensitizers suggests a range of sources of information be deployed in the hazard identification process. These include chemical structure, predictive animal tests, and various types of human data. Where the information is clear-cut, then uncertainties rarely arise. However, for some materials, discordant information arises, perhaps because the substance is on the borderline of test sensitivity and classification (sensitizing materials of insufficient potency do not classified according to the EU scheme), due to conflicting results in predictive tests or for other reasons. In this study, we review data on a number of substances where a classification decision is complicated by such discordances and seek to use these examples to demonstrate how best to make a weight of evidence decision on whether a substance should, or should not, be classified as a skin sensitizer.

Theoretical Investigation of Linalool Oxidation

This study concerns the autoxidation of one of the most used fragrances in daily life, linalool (3,7-dimethyl-1,6-octadien-3-ol). It reacts with O2 to form hydroperoxides, which are known to be important contact allergens. Pathways for hydroperoxide formation are investigated by means of quantum mechanical electronic structure calculations. Optimized molecular geometries and harmonic vibrational frequencies are determined using density functional theory (DFT). Insight into how the addition of O2 to linalool occurs is obtained by establishing a theoretical framework and systematically investigating three smaller systems: propene, 2-methyl-2-butene, and 2-methyl-2-pentene. 2-Methyl-2-pentene was chosen as a model system and used to compare with linalool. This theoretical study characterizes the linalool-O2 biradical intermediate state, which constitutes a branching point for the further oxidation reactions pathways. Thus, the observed linalool oxidation product spectrum is discussed in terms of a direct reaction path, the ene-type mechanism, and the radical mechanism. The major hydroperoxide found in experiments is 7-hydroperoxy-3,7-dimethyl-octa-1,5-diene-3-ol, and the calculated results support this finding.

Hydroperoxides form specific antigens in contact allergy

Concomitant positive reactions to colophonium, oxidized limonene, and/or oxidized linalool are recorded in patch test studies. The main allergens in these patch test mixtures are hydroperoxides, which form antigens by a radical pathway. Theoretically, concomitant reactions can be explained not only by concomitant sensitization or by true cross-reactions but also by the hydroperoxides acting as oxidizing agents on skin proteins to form non-specific antigens without hapten-protein binding. The aim of this study was to explore concomitant reactions and cross-reactivity patterns among hydroperoxide haptens. We investigated whether individuals allergic to the main allergen in colophonium, 15-hydroperoxyabietic acid, would also react to limonene hydroperoxide or linalool hydroperoxide. Only 1 of 29 individuals reacted to more than 1 hydroperoxide. The cross-reactivity pattern among cumene hydroperoxide, limonene hydroperoxide, 1-(1-hydroperoxy-1-methylethyl) cyclohexene (cyclohexene hydroperoxide), and 15-hydroperoxydehydroabietic acid was investigated in guinea-pigs. No general cross-reactivity was observed. Cross-reactions between cumene hydroperoxide and cyclohexene hydroperoxide show that similarity in the overall structure and the way of antigen formation are needed. Quantum calculations were used to determine the formation energies of the intermediary radicals. We concluded that hydroperoxides form specific antigens and that formation of non-specific antigens is unlikely. The concomitant patch test reactions described in the literature are best explained as a result of multiple sensitizations.

Ozone's impact on public health: contributions from indoor exposures to ozone and products of ozone-initiated chemistry

OBJECTIVE

The associations between ozone concentrations measured outdoors and both morbidity and mortality may be partially due to indoor exposures to ozone and ozone-initiated oxidation products. In this article I examine the contributions of such indoor exposures to overall ozone-related health effects by extensive review of the literature as well as further analyses of published data.

FINDINGS

Daily inhalation intakes of indoor ozone (micrograms per day) are estimated to be between 25 and 60% of total daily ozone intake. This is especially noteworthy in light of recent work indicating little, if any, threshold for ozone's impact on mortality. Additionally, the present study estimates that average daily indoor intakes of ozone oxidation products are roughly one-third to twice the indoor inhalation intake of ozone alone. Some of these oxidation products are known or suspected to adversely affect human health (e.g., formaldehyde, acrolein, hydroperoxides, fine and ultrafine particles). Indirect evidence supports connections between morbidity/mortality and exposures to indoor ozone and its oxidation products. For example, cities with stronger associations between outdoor ozone and mortality tend to have residences that are older and less likely to have central air conditioning, which implies greater transport of ozone from outdoors to indoors.

CONCLUSIONS

Indoor exposures to ozone and its oxidation products can be reduced by filtering ozone from ventilation air and limiting the indoor use of products and materials whose emissions react with ozone. Such steps might be especially valuable in schools, hospitals, and childcare centers in regions that routinely experience elevated outdoor ozone concentrations.

Aqueous Solubility of Liquid Monoterpenes at 293 K and Relationship with Calculated Log P Value

Aqueous solubility is often a limiting factor in any concentration-dependent process and n-octanol/water partition coefficient, usually expressed as log P, is equilibrium between surrogate of nonaqueous biophases and water phase. The aqueous solubility of seven liquid monoterpenes: (+/-)-beta-citronellol, (+/-)-linalool, linalyl acetate, (-)-alpha-pinene, (-)-beta-pinene, eucalyptol and terpinen-4-ol were experimentally determined at 293 K. The obtained aqueous solubility data correlate well with log P values calculated by ACD/Log P software.

Photoallergic contact dermatitis from ketoprofen in southern Sweden

The non-steroidal anti-inflammatory drug ketoprofen is widely used for topical treatment. In Sweden, ketoprofen has been available for topical application since 1995. Photoallergic contact dermatitis from ketoprofen-containing topical preparations usually includes severe eczematous reactions. Ketoprofen is derived from propionic acid, and it is also a substituted benzophenone and therefore structurally similar to fenofibrate and sunscreen agents based on benzophenones. During the last 2 years, 35 patients have been refereed to our department with suspected photoallergic or allergic reactions after having used ketoprofen-containing gels. Photopatch testing with the photopatch standard series, the ketoprofen-containing gels and their ingredients, fenofibrate, benzophenone-3, benzophenone-10 and benzophenone-4, was performed. Photoallergic reactions to ketoprofen were noted in 35 patients and a simultaneous contact allergy to ketoprofen in 2 patients. Simultaneous photoallergy to fentichlor, tetrachlorosalicylanilide and fenofibrate was registered in 74%, 40% and 73% of the patients, respectively.

Effect of physicochemical properties of cyclic terpenes on their ex vivo skin absorption and elimination kinetics

BACKGROUND

The terpenes disturb lipid arrangement in the intercellular region of the stratum corneum (SC) that leads to the increased permeability of the skin. This effect is used in technology of transdermal drug forms and depends on physicochemical properties of terpenes and their amounts penetrated to the stratum corneum; however terpenes do not need penetrate into viable skin tissue and this event is not even desired.

OBJECTIVE

To correlate skin absorption and elimination kinetics of four cyclic terpenes, namely alpha-pinene, beta-pinene, eucalyptol and terpinen-4-ol, applied as neat substance with their physicochemical properties.

METHODS

The terpenes were applied onto the human skin in vitro, and after 1-4 h their content in the separated by a tape-stripping method stratum corneum layers and in the epidermis/dermis was determined using GC. Similarly, the amounts of terpenes in the skin were analysed during 4 h following 1 h absorption.

RESULTS

The fastest and progressive penetration into all skin layers was observed for terpinen-4-ol. All studied terpenes are absorbed in the viable epidermis/dermis, however penetration into this layers is time-dependent process, constantly increasing during 4 h. Like for stratum corneum, the largest cumulation in epidermis/dermis was observed for terpinen-4-ol. The elimination of terpenes from the stratum corneum was fast, especially in deeper layers, and much faster if the initial cumulation was small.

CONCLUSION

Investigated cyclic terpenes represent different penetration and elimination characteristics and do not permeate across the skin to the acceptor medium due to large cumulation in the skin tissue. The penetration of terpenes into stratum corneum is greater if their log P-value is close to 3.

Colophonium and Compositae mix as markers of fragrance allergy: Cross-reactivity between fragrance terpenes, colophonium and Compositae plant extracts

The aim of this study was to assess the strength of any association between sensitization to 'new' fragrance compounds and sensitization to Compositae, fragrance mix, Myroxylon pereirae resin and colophonium, respectively. Consecutive eczema patients were tested with a series of essential oils and selected fragrance compounds and another series of oxidized terpenes in connection with European multicentre fragrance projects. Contact allergy to either series was frequently detected, in 5% of 318 and 4.6% of 262 persons tested, and both had a statistically significant association with Compositae, colophonium and fragrance mix sensitization. The individual results indicated that simultaneously occurring positive reactions to essential oils, colophonium and Compositae were based on cross-reactivity rather than concomitant sensitization. Thus, all patients with positive reaction to the rare fragrance sensitizer beta-caryophyllene had positive colophonium reactions, and cross-reactivity between essential oils and Compositae was related to the Compositae plant extracts of the Compositae mix and not the pure sesquiterpene lactones of the standard series. The implication is that Compositae mix and colophonium may be markers of fragrance allergy, which is important to know when assessing the relevance of positive reactions to Compositae plant extracts and colophonium.

The fragrance chemical beta-caryophyllene-air oxidation and skin sensitization

Fragrances are common causes of allergic contact dermatitis. beta-Caryophyllene is a sesquiterpene that is used as a fragrance chemical. Analogous to the monoterpenes R-limonene and linalool, it can be expected to autoxidize when air exposed. The aim of the present study was to investigate the autoxidation of beta-caryophyllene and to evaluate the effect on the contact allergenic activity. beta-Caryophyllene started to oxidize immediately when air exposed and after 5 weeks almost 50% of the original compound was consumed. Caryophyllene oxide was found to be the major oxidation product. Hydroperoxides of beta-caryophyllene could not be detected in the oxidation mixture. Caryophyllene oxide was shown to be an allergen of moderate strength and beta-caryophyllene air exposed for 10 weeks showed a weak sensitizing capacity in the local lymph node assay. The study reveals that the allergenic activity of beta-caryophyllene is affected by autoxidation, but to a lesser extent when compared to R-limonene and linalool. The present findings support our results in clinical studies showing oxidized beta-caryophyllene to be a rather rare sensitizer compared to oxidized R-limonene and linalool.