Limonene hydroperoxide analogues differ in allergenic activity

A lipidomic approach towards identifying the effects of fragrance hydroperoxides on keratinocytes

BACKGROUND

Limonene and linalool are used in cosmetic products for their floral scents, but their oxidation products are strong contact allergens whose mechanisms of action are still not fully understood.

OBJECTIVES

The effects of limonene hydroperoxide (Lim-2-OOH) and linalool hydroperoxides (Lin-6/7-OOH) on the lipid profile of a human keratinocyte cell line (HaCaT) were evaluated. 2,4-Dinitrofluorobenzene (DNFB) was also included.

METHODS

Lim-2-OOH and Lin-6/7-OOH were synthesised according to previous methods. HaCaT cells were treated with allergens (10 μM) for 24 h and the cellular lipid extracts were analysed by C18 liquid chromatography with tandem mass spectrometry (LC-MS/MS). Data analysis was performed using Lipostar software. Statistical analysis was carried out using Metaboanalyst and R software.

RESULTS

All three sensitisers used caused significant changes in the lipidome of HaCaT cells in a similar trend. There was an upregulation in several plasmanyl/plasmenyl phospholipids (O-/P-phosphatidylcholines [PC] and O-/P-phosphatidylethanolamines [PE]), sphingolipids (HexCer) and triacylglycerol lipid species, and a decrease in some polyunsaturated fatty acids-containing phospholipid (PE and PC) species suggesting oxidative stress and inflammation.

CONCLUSIONS

This study is the first to evaluate the plasticity of the HaCaT cell lipidome in response to allylic hydroperoxide allergens Lim-2-OOH and Lin-6/7-OOH, together with the experimental contact allergen DNFB. These allergens are able to upregulate and downregulate certain lipid classes to a varying degree.

Transcriptome analysis of Reticulitermes flaviceps exposed to Mentha spicata essential oil and carvone indicates a potential neurotoxic mechanism of action characterized by intracellular calcium influx mediated by dopamine receptors

Reticulitermes flaviceps is an economically important pest in agriculture, forestry, and construction. Recent studies have shown an increase in research focusing on the anti-termite properties of plant essential oils, however, there remains a lack of information regarding the specific molecular mechanism involved. In this study, RNA-seq analysis was conducted on termites exposed to Mentha spicata essential oil (EO) and carvone, leading to the discovery of various genes that were expressed differentially under different treatment conditions. Numerous genes that exhibited a response to M. spicata EO and carvone found to be associated with stress-related pathways, such as drug metabolism cytochrome P450, glutathione metabolism, fatty acid metabolism, citric acid cycle, neuroactive ligand-receptor interaction, cell apoptosis, the AMPK signalling pathway, the mTOR signalling pathway, the longevity regulation pathway, ubiquitin-mediated protein hydrolysis, and the calcium signalling pathway. The up-regulation of genes (SPHK) associated with calcium channels, such as SPHK, indicates a potential mechanism of neurotoxicity, while the up-regulation of apoptosis-associated genes, including ACTB_G1, PYG, SQSTM1, RNF31, suggests a potential mechanism of cytotoxicity. The metabolism of M. spicata EO induces oxidative stress, elevates free Ca2+ levels in mitochondria, and initiates the generation of reactive oxygen species (ROS), ultimately resulting in programmed cell necrosis and apoptosis, as well as facilitating cellular autophagy. The monoterpenes exhibited neurotoxic and cytotoxic effects on R. flaviceps and could be exploited to advance termiticide development and eco-friendly termite control.

Fragrance Contact Allergy - A Review Focusing on Patch Testing

Fragrance materials are widely used in various types of products in daily life and many of them can be contact sensitizers. Contact allergy to fragrances has been reported to be common worldwide. Unlike other groups of contact allergens such as metals and preservatives, fragrance materials in consumer products can be present as single fragrance chemicals or in the form of mixtures known as natural complex substances. Due to the complexity of the fragrance materials and the high number of fragrance substances known to cause contact sensitization, selecting suitable materials for patch testing is challenging. Emerging fragrance markers have been additionally introduced in different baseline series for screening to enhance the rate of fragrance contact allergy detection. Moreover, there have been continual updates on basic knowledge, clinical perspectives, sources of exposure, and regulations on the use of fragrance materials. Avoiding pitfalls while performing patch testing with fragrance test materials is also crucial and should not be overlooked. Therefore, this review aims to update knowledge to provide a high-quality holistic approach to fragrance contact allergy diagnosis and management.

Protein Haptenation and Its Role in Allergy

Humans are exposed to numerous electrophilic chemicals either as medicines, in the workplace, in nature, or through use of many common cosmetic and household products. Covalent modification of human proteins by such chemicals, or protein haptenation, is a common occurrence in cells and may result in generation of antigenic species, leading to development of hypersensitivity reactions. Ranging in severity of symptoms from local cutaneous reactions and rhinitis to potentially life-threatening anaphylaxis and severe hypersensitivity reactions such as Stephen-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN), all these reactions have the same Molecular Initiating Event (MIE), i.e. haptenation. However, not all individuals who are exposed to electrophilic chemicals develop symptoms of hypersensitivity. In the present review, we examine common chemistry behind the haptenation reactions leading to formation of neoantigens. We explore simple reactions involving single molecule additions to a nucleophilic side chain of proteins and complex reactions involving multiple electrophilic centers on a single molecule or involving more than one electrophilic molecule as well as the generation of reactive molecules from the interaction with cellular detoxification mechanisms. Besides generation of antigenic species and enabling activation of the immune system, we explore additional events which result directly from the presence of electrophilic chemicals in cells, including activation of key defense mechanisms and immediate consequences of those reactions, and explore their potential effects. We discuss the factors that work in concert with haptenation leading to the development of hypersensitivity reactions and those that may act to prevent it from developing. We also review the potential harnessing of the specificity of haptenation in the design of potent covalent therapeutic inhibitors.

DFT Studies of the Activity and Reactivity of Limonene in Comparison with Selected Monoterpenes

Nowadays, the effective processing of natural monoterpenes that constitute renewable biomass found in post-production waste into products that are starting materials for the synthesis of valuable compounds is a way to ensure independence from non-renewable fossil fuels and can contribute to reducing global carbon dioxide emissions. The presented research aims to determine, based on DFT calculations, the activity and reactivity of limonene, an organic substrate used in previous preparative analyses, in comparison to selected monoterpenes such as cymene, pinene, thymol, and menthol. The influence of the solvent model was also checked, and the bonds most susceptible to reaction were determined in the examined compounds. With regard to EHOMO, it was found that limonene reacts more easily than cymene or menthol but with more difficultly than thymol and pienene. The analysis of the global chemical reactivity descriptors "locates" the reactivity of limonene in the middle of the studied monoterpenes. It was observed that, among the tested compounds, the most reactive compound is thymol, while the least reactive is menthol. The demonstrated results can be a reference point for experimental work carried out using the discussed compounds, to focus research on those with the highest reactivity.

Patterns of simultaneous contact allergies in patients with contact sensitization to oxidised linalool and oxidised limonene

BACKGROUND

Contact allergy rates of linalool and limonene hydroperoxides (HPs) have increased.

OBJECTIVES

To demonstrate the patterns of simultaneous positive patch test (PT) reactions and prevalences of multiple contact allergies (MCAs) in patients with contact allergy to linalool and/or limonene HPs.

METHODS

A retrospective analysis of consecutive dermatitis patients in 2015-2020 was performed.

RESULTS

Of all 4192 patients, 1851 had at least one positive PT reaction. Of these, 410 (22.2%) had MCAs, significantly related to a higher age (p-value = 0.003). Patients with an exclusively positive reaction to linalool HPs but not limonene HPs were shown to have MCAs (p-value <0.001, odds ratio (95% confidence interval) = 4.15 (3.01-5.73)). Patients with simultaneous contact allergies to both linalool and limonene HPs had contact allergies to many other screening and fragrance allergens.

CONCLUSIONS

Simultaneous positive PT reactions to allergens in baseline series and fragrances are common in patients with the HPs contact allergy, especially linalool HPs. The pattern of simultaneous PT reactions principally suggested the co-sensitization of the cosmetic allergens.

Influence of vegetation on the composition of essential oil from (Melissa officinalis L.)

Lemon balm (Melissa officinalis L.) is a perennial plant of the family Lamiaceae, which is used in folk medicine and the food industry, as well as being processed to obtain essential oil. The aim of the special work is to monitor the influence of vegetation on the composition of the essential oil. The chemical composition of essential oils, obtained by steam distillation from lemon balm cultivated in North-eastern Bulgaria, has been determined. The plants were harvested in two periods of vegetation - the first at the end of June and second - at the end of August 2020. The main components in the oil from the first cut are geranial (26.41%), neral (19.55%), (E)-β-caryophyllene (17.46%), germacrene D (7.86%) and β-citronellal (3.24%). In the oil from the second cut, the main components are geranial (37.26%), neral (28.46%), (E)-β- caryophyllene (6.65%), geraniol (4.72%), and β-citronellal (3.04%). The oil from the second harvest has a high content of the main components of geranial, neral and geraniol and a lower content of (E)-β- caryophyllene and germacrene D. Variations in the amounts are also present in other compounds.

Flavonoid glycosides and other bioactive compounds in Citrus reticulate 'Chachi' peel analysed by tandem mass spectrometry and their changes during storage

The peel of Citrus reticulate 'Chachiennsis' (Chachi) is a well-known functional food with multiple health benefits in Asia. There is an old saying "the longer time Chachi is stored, the better health benefits it has". Is it convincible? What are the critical bioactive compounds in Chachi? To answer these questions, gas chromatography-mass spectrometry (GC-MS) and ultrahigh performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) were used to qualify and quantify the flavonoid glycosides and other bioactive compounds of Chachi with storage time of 5-20 years. Limonene was the representative volatile compound. The level of most volatile compounds decreased along with storage. Sixteen flavonoids glycosides and twenty flavonoids were identified. Nobiletin, hesperitin, tetramethoxy flavone and pentamethoxy flavone were characteristic bioactive compounds for Chachi. Most of them accumulated during 10-year storage, thereafter decreased. Ten years could be the optimal storage time. These results indicated that the old saying should be corrected.

Contact allergy to oxidized linalool and oxidized limonene: Patch testing in consecutive patients with dermatitis

BACKGROUND

Contact allergy to oxidized (ox.) linalool and ox. limonene has been reported to have a high prevalence, raising the question of inclusion into the baseline series. However, several important issues should be clarified and further investigated before inclusion can be warranted.

OBJECTIVES

To report the trends of ox. terpenes allergy in patients with dermatitis, features of the patch test reactions, and clinical characteristics of the patients.

METHODS

A retrospective analysis of 5773 patients was performed. All patients were patch tested with baseline series, individual ingredients of fragrance mix I and II, ox. linalool, and ox. limonene from 2013 to 2020.

RESULTS

The prevalence rates of contact allergy to ox. linalool and ox. limonene were 7.0% and 5.1%, respectively. Significantly increasing trends of contact allergy were observed. More than 95% of contact allergy cases were identified on Day 3/4. Patients with contact allergy to ox. linalool and ox. limonene were significantly younger than those with contact allergy to other fragrances and were predominantly female. Strong reactions were associated with older age and multiple fragrance allergies.

CONCLUSIONS

Contact allergy to ox. linalool and ox. limonene is becoming increasingly important, and findings show intriguing features. More studies concerning the clinical relevance before recommending these substances for screening are required.

One hundred years of allergic contact dermatitis due to oxidized terpenes: What we can learn from old research on turpentine allergy

Although in recent years the focus on sensitizing terpene oxidation products has been on oxidized limonene and linalool, the autoxidation of terpenes in relation to allergic contact dermatitis is not new and dates back to the early part of the 20th century with the use of turpentine causing occupational contact dermatitis in painters. This review is written in a way as to allow us to get closer to the work of the scientists in earlier days, to participate in the successes, and also to observe the weak points. The researchers concluded that the main culprit in Scandinavian turpentine was Δ³ -carene hydroperoxides. This explains its high sensitizing effect compared with French turpentine which is of the Iberian type with no or only traces of Δ³ -carene. Historical exposure to turpentine showed that ending the industrial exposure stopped the occupational skin sensitization. Patch test studies demonstrated that monoterpene hydroperoxides, far from being an obsolete source of contact allergy solely related to turpentine, is a common cause of contact allergy in the population. A hundred years of extensive chemical and clinical studies worldwide should be sufficient to meet the evidence requirement regarding allergic contact dermatitis caused by terpenes. HIGHLIGHTS: The autoxidation of terpenes in relation to allergic contact dermatitis is not new and dates back to the early part of the 20th century with the use of turpentine. The main culprit in Scandinavian turpentine was Δ³ -carene hydroperoxides. This explains its high sensitizing effect compared with French turpentine with no or only traces of Δ³ -carene. Recent patch test studies demonstrated that monoterpene hydroperoxides, far from being an obsolete source of contact allergy solely related to turpentine, is a common cause of contact allergy in the population.

Rhizobacteria Mediate the Phytotoxicity of a Range of Biorefinery-Relevant Compounds

Advances in engineering biology have expanded the list of renewable compounds that can be produced at scale via biological routes from plant biomass. In most cases, these chemical products have not been evaluated for effects on biological systems, defined in the present study as bioactivity, that may be relevant to their manufacture. For sustainable chemical and fuel production, the industry needs to transition from fossil to renewable carbon sources, resulting in unprecedented expansion in the production and environmental distribution of chemicals used in biomanufacturing. Further, although some chemicals have been assessed for mammalian toxicity, environmental and agricultural hazards are largely unknown. We assessed 6 compounds that are representative of the emerging biofuel and bioproduct manufacturing process for their effect on model plants (Arabidopsis thaliana, Sorghum bicolor) and show that several alter plant seedling physiology at submillimolar concentrations. However, these responses change in the presence of individual bacterial species from the A. thaliana root microbiome. We identified 2 individual microbes that change the effect of chemical treatment on root architecture and a pooled microbial community with different effects relative to its constituents individually. The present study indicates that screening industrial chemicals for bioactivity on model organisms in the presence of their microbiomes is important for biologically and ecologically relevant risk analyses. Environ Toxicol Chem 2019;38:1911-1922. © 2019 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC.

Limonene Hydroperoxides

Limonene is a fragrance widely used in cosmetics and household products. Until recently, contact allergy to limonene was considered rare because positive patch tests to it were infrequently observed. In recent years, however, it has been demonstrated that exposure of limonene to oxygen (air) results in the formation of a number of oxidation products, of which the hydroperoxides have a far stronger sensitizing potency than the pure compound. By routine testing of patients suspected of contact dermatitis with hydroperoxides of limonene, high frequencies of positive reactions were found, indicating that these chemicals are important fragrance allergens. It should be realized, however, that a number of "positive" reactions may well be false-positive, irritant responses.

Formation of methyl radicals derived from cumene hydroperoxide in reconstructed human epidermis: an EPR spin trapping confirmation by using 13C-substitution

Dermal exposure to cumene hydroperoxide (CumOOH) during manufacturing processes is a toxicological issue for the industry. Its genotoxicity, mutagenic action, ability to promote skin tumour, capacity to induce epidermal hyperplasia, and aptitude to induce allergic and irritant skin contact dermatitis are well known. These toxic effects appear to be mediated through the activation to free radical species such as hydroxyl, alkoxyl, and alkyl radicals characterised basically by electron paramagnetic resonance (EPR) and spin-trapping (ST) techniques. To be a skin sensitiser CumOOH needs to covalently bind to skin proteins in the epidermis to form the antigenic entity triggering the immunotoxic reaction. Cleavage of the O-O bond allows formation of unstable CumO^•/CumOO^• radicals rearranging to longer half-life specific carbon-centred radicals R^• proposed to be at the origin of the antigen formation. Nevertheless, it is not still clear which R^• is precisely formed in the epidermis and thus involved in the sensitisation process. The aim of this work was to elucidate in conditions closer to real-life sensitisation which specific R^• are formed in a 3D reconstructed human epidermis (RHE) model by using ¹³C-substituted CumOOH at carbon positions precursors of potentially reactive radicals and EPR-ST. We demonstrated that most probably methyl radicals derived from β-scission of CumO^• radicals occur in RHE through a one-electron reductive pathway suggesting that these could be involved in the antigen formation inducing skin sensitisation. We also describe a coupling between nitroxide radicals and β position ¹³C atoms that could be of an added value to the very few examples existing for the coupling of radicals with ¹³C atoms.

Sensitization potential and potency of terpene hydroperoxides in the cocultured activation test method

BACKGROUND

Positive patch test reactions to mixtures of oxidized terpenes containing allergenic hydroperoxides are frequently reported. However, human sensitization data for these hydroperoxides are not available.

OBJECTIVES

To analyse and evaluate the human sensitization potential and potency of hydroperoxides in vitro by using human cells.

MATERIALS/METHODS

Limonene-1-hydroperoxide, limonene-2-hydroperoxide, citronellol-7-hydroperoxide, cumene hydroperoxide, 1-(1-hydroperoxy-1-methylethyl)cyclohexene and mixtures of citronellol hydroperoxides (isomers at positions 6 and 7) and linalool hydroperoxides (isomers at positions 6 and 7) were studied. All compounds were synthesized except for cumene hydroperoxide, which was commercially available. Their potential and potency to activate dendritic cells (DCs) was evaluated by measuring the upregulation of CD86 and CD54 on THP-1 cells upon exposure in the cocultured activation test (COCAT) consisting of HaCaT cells (human keratinocyte cell line) and THP-1 monocytes (as a surrogate for DCs).

RESULTS

Hydroperoxides upregulated CD86 and/or CD54 on cocultured THP-1 cells in a concentration-dependent manner. The results are comparable with their sensitization potency ranking in predictive animal models.

CONCLUSIONS

For the first time, the human sensitization potential and potency of several hydroperoxides were determined by the use of human cells and the COCAT method.

Biotransformation and bioactivation reactions - 2016 literature highlights

We are pleased to present a second annual issue highlighting a previous year's literature on biotransformation and bioactivation. Each contributor to this issue worked independently to review the articles published in 2016 and proposed three to four articles, which he or she believed would be of interest to the broader research community. In each synopsis, the contributing author summarized the procedures, analyses and conclusions as described in the original manuscripts. In the commentary sections, our authors offer feedback and highlight aspects of the work that may not be apparent from an initial reading of the article. To be fair, one should still read the original article to gain a more complete understanding of the work conducted. Most of the articles included in this review were published in Drug Metabolism and Disposition or Chemical Research in Toxicology, but attempts were made to seek articles in 25 other journals. Importantly, these articles are not intended to represent a consensus of the best papers of the year, as we did not want to make any arbitrary standards for this purpose, but rather they were chosen by each author for their notable findings and descriptions of novel metabolic pathways or biotransformations. I am pleased that Drs. Rietjens and Dalvie have again contributed to this annual review. We would like to welcome Grover P Miller as an author for this year's issue, and we thank Tom Baillie for his contributions to last year's edition. We have intentionally maintained a balance of authors such that two come from an academic setting and two come from industry. Finally, please drop us a note if you find this review helpful. We would be pleased to hear your opinions of our commentary, and we extend an invitation to anyone who would like to contribute to a future edition of this review. This article is dedicated to Professor Thomas Baillie for his exceptional contributions to the field of drug metabolism.

Comparative sensitizing potencies of fragrances, preservatives, and hair dyes

The local lymph node assay (LLNA) is used for assessing sensitizing potential in hazard identification and risk assessment for regulatory purposes. Sensitizing potency on the basis of the LLNA is categorized into extreme (EC3 value of ≤0.2%), strong (>0.2% to ≤2%), and moderate (>2%). To compare the sensitizing potencies of fragrance substances, preservatives, and hair dye substances, which are skin sensitizers that frequently come into contact with the skin of consumers and workers, LLNA results and EC3 values for 72 fragrance substances, 25 preservatives and 107 hair dye substances were obtained from two published compilations of LLNA data and opinions by the Scientific Committee on Consumer Safety and its predecessors. The median EC3 values of fragrances (n = 61), preservatives (n = 19) and hair dyes (n = 59) were 5.9%, 0.9%, and 1.3%, respectively. The majority of sensitizing preservatives and hair dyes are thus strong or extreme sensitizers (EC3 value of ≤2%), and fragrances are mostly moderate sensitizers. Although fragrances are typically moderate sensitizers, they are among the most frequent causes of contact allergy. This indicates that factors other than potency need to be addressed more rigorously in risk assessment and risk management.

Can contact allergy to p-phenylenediamine explain the high rates of terpene hydroperoxide allergy? - An epidemiological study based on consecutive patch test results

BACKGROUND

Contact allergy to linalool hydroperoxides (Lin-OOHs) and limonene hydroperoxides (Lim-OOHs) is common. Similarly to what occurs with the terpene hydroperoxides, reactive intermediates formed from p-phenylenediamine (PPD) can cause oxidative modifications of tryptophan residues on proteins in mechanistic studies.

OBJECTIVES

To test the hypothesis that patients sensitized to PPD are at increased risk of concomitant reactivity to either of the terpene hydroperoxides, owing to a 'common pathway' of skin protein oxidation.

METHODS

A database study of consecutively patch tested eczema patients (n = 3843) from 2012 to 2015, tested concomitantly with PPD, Lim-OOHs and Lin-OOHs, was performed. Associations were examined by level of concordance and odds ratios (ORs) adjusted for age, sex, and contact allergy to fragrance mix I and fragrance mix II.

RESULTS

Concomitant reactions to PPD were seen in 2.2% of Lim-OOH-positive patients and in 4.9% of Lin-OOH-positive patients. Neither proportion was higher than expected by chance. No association existed between PPD and Lim-OOH patch test reactivity. In a multiple logistic regression analysis, PPD allergy was associated with an insignificantly increased risk (OR 2.11, 95%CI:0.92-4.80) of a positive patch test reaction to Lin-OOHs.

CONCLUSIONS

PPD sensitization cannot explain the high rates of sensitization to Lin-OOHs and/or Lim-OOHs. Contact allergy to oxidized linalool is more strongly associated with fragrance allergy than with PPD allergy.

Oxidized limonene and oxidized linalool - concomitant contact allergy to common fragrance terpenes

BACKGROUND

Limonene and linalool are common fragrance terpenes. Both oxidized R-limonene and oxidized linalool have recently been patch tested in an international setting, showing contact allergy in 5.2% and 6.9% of dermatitis patients, respectively.

OBJECTIVE

To investigate concomitant reactions between oxidized R-limonene and oxidized linalool in consecutive dermatitis patients.

METHODS

Oxidized R-limonene 3.0% (containing limonene hydroperoxides 0.33%) and oxidized linalool 6% (linalool hydroperoxides 1%) in petrolatum were tested in 2900 consecutive dermatitis patients in Australia, Denmark, Singapore, Spain, Sweden, and the United Kingdom.

RESULTS

A total of 281 patients reacted to either oxidized R-limonene or oxidized linalool. Of these, 25% had concomitant reactions to both compounds, whereas 29% reacted only to oxidized R-limonene and 46% only to oxidized linalool. Of the 152 patients reacting to oxidized R-limonene, 46% reacted to oxidized linalool, whereas 35% of the 200 patients reacting to oxidized linalool also reacted to oxidized R-limonene.

CONCLUSIONS

The majority of the patients (75%) reacted to only one of the oxidation mixtures, thus supporting the specificity of the reactions. The concomitant reactions to the two fragrance allergens suggest multiple sensitizations, which most likely reflect the exposure to the different fragrance materials in various types of consumer products. This is in accordance with what is generally seen for patch test reactions to fragrance materials.

Acute Limonene Toxicity in Escherichia coli Is Caused by Limonene Hydroperoxide and Alleviated by a Point Mutation in Alkyl Hydroperoxidase AhpC

Limonene, a major component of citrus peel oil, has a number of applications related to microbiology. The antimicrobial properties of limonene make it a popular disinfectant and food preservative, while its potential as a biofuel component has made it the target of renewable production efforts through microbial metabolic engineering. For both applications, an understanding of microbial sensitivity or tolerance to limonene is crucial, but the mechanism of limonene toxicity remains enigmatic. In this study, we characterized a limonene-tolerant strain of Escherichia coli and found a mutation in ahpC, encoding alkyl hydroperoxidase, which alleviated limonene toxicity. We show that the acute toxicity previously attributed to limonene is largely due to the common oxidation product limonene hydroperoxide, which forms spontaneously in aerobic environments. The mutant AhpC protein with an L-to-Q change at position 177 (AhpC(L177Q)) was able to alleviate this toxicity by reducing the hydroperoxide to a more benign compound. We show that the degree of limonene toxicity is a function of its oxidation level and that nonoxidized limonene has relatively little toxicity to wild-type E. coli cells. Our results have implications for both the renewable production of limonene and the applications of limonene as an antimicrobial.

Air-oxidized linalyl acetate - an emerging fragrance allergen?

BACKGROUND

Linalyl acetate is a fragrance chemical that is prone to autoxidation. Exposure to linalyl acetate occurs through cosmetic products and essential oils, but is difficult to assess, as linalyl acetate is not labelled in the EU.

OBJECTIVE

To investigate the frequencies of contact allergy to oxidized linalyl acetate among dermatitis patients, and to investigate the autoxidation of linalyl acetate in terms of hydroperoxide formation and sensitization potency.

PATIENTS AND METHODS

Hydroperoxide formation in air-exposed linalyl acetate was determined with high-performance liquid chromatography. The sensitization potencies of hydroperoxides were determined with the local lymph node assay. One thousand seven hundred and seventeen patients were patch tested with oxidized linalyl acetate at 6.0% in petrolatum.

RESULTS

Of the patients, 2.2% showed positive reactions to oxidized linalyl acetate. Forty-three per cent of the positive patients also had positive patch test reactions to other fragrance markers. Linalyl acetate hydroperoxides were detected early in the autoxidation process, and accumulated to a concentration of 37% after 42 weeks of air exposure. The linalyl acetate hydroperoxides were classified as moderate sensitizers.

CONCLUSIONS

The frequency of positive reactions to oxidized linalyl acetate is comparable to that of previously studied oxidized fragrance terpenes. Oxidized linalyl acetate could thus be a common fragrance contact allergen.

Occupational contact dermatitis caused by D-limonene

BACKGROUND

Limonene is widely used as a fragrance substance and solvent in cleansing products. Oxidized limonene is a frequent contact allergen among consumers of cosmetics, personal care products, and scented household cleaning products. Less is known about the sources of occupational exposure and occupational contact dermatitis caused by limonene.

OBJECTIVE

To report 14 patients with occupational contact allergy to limonene.

METHODS

The patients were examined in 2008-2013. An in-house preparation of oxidized limonene was patch tested as 3% and 5% in petrolatum from 2008 to August 2010, and after this as 3%, 1% and 0.3% pet. From 2012 onwards, a commercial test substance of limonene hydroperoxides was also used. We assessed the patients' occupational and domestic exposure to limonene.

RESULTS

Occupational limonene allergy was observed in workers who used limonene-containing machine-cleaning detergents and hand cleansers, and in workers who used limonene-containing surface cleaners and dishwashing liquids similar to those used by consumers. In 3 cases, the occupational limonene allergy resulted from work-related use of limonene-containing, leave-on cosmetic products.

CONCLUSIONS

Limonene is a frequent occupational sensitizer in hand cleansers and cleaning products. Occupational limonene contact allergy may also be caused by exposure to cosmetic products scented with limonene.

Air-oxidized linalool elicits eczema in allergic patients - a repeated open application test study

BACKGROUND

Linalool is a commonly used fragrance terpene that forms potent sensitizers upon oxidation. In a recent multicentre study, we found that 7% of 2900 patients showed positive patch test reactions to oxidized linalool at 6.0%. No elicitation studies have been performed.

OBJECTIVE

To identify threshold concentrations for elicitation of allergic contact dermatitis caused by oxidized linalool in allergic individuals with repeated exposures.

METHODS

Repeated open application tests were performed in 6 participants previously diagnosed with contact allergy to oxidized linalool. Creams containing 3.0%, 1.0% and 0.30% oxidized linalool (corresponding to 0.56%, 0.19% and 0.056% linalool hydroperoxides, respectively) and 'fine fragrance' containing 1.0%, 0.30% and 0.10% oxidized linalool (corresponding to 0.19%, 0.056% and 0.019% linalool hydroperoxides, respectively) were used twice daily for up to 3 weeks. Patch testing with a dilution series of oxidized linalool was performed.

RESULTS

Five of 6 participants reacted to the cream containing 3% oxidized linalool. With 1% oxidized linalool, a reaction was seen in 3 (cream) and 4 (fine fragrance) participants, respectively. With 0.3% oxidized linalool, 2 (cream) and 1 (fine fragrance) participants reacted.

CONCLUSION

Repeated exposure to low concentrations of oxidized linalool can elicit allergic contact dermatitis in previously sensitized individuals.

Ketoprofen-induced formation of amino acid photoadducts: possible explanation for photocontact allergy to ketoprofen

Photocontact allergy is a well-known side effect of topical preparations of the nonsteroidal anti-inflammatory drug ketoprofen. Photocontact allergy to ketoprofen appears to induce a large number of photocross allergies to both structurally similar and structurally unrelated compounds. Contact and photocontact allergies are explained by structural modification of skin proteins by the allergen. This complex is recognized by the immune system, which initiates an immune response. We have studied ketoprofen's interaction with amino acids to better understand ketoprofen's photoallergenic ability. Irradiation of ketoprofen and amino acid analogues resulted in four different ketoprofen photodecarboxylation products (6-9) together with a fifth photoproduct (5). Dihydroquinazoline 5 was shown to be a reaction product between the indole moiety of 3-methylindole (Trp analogue) and the primary amine benzylamine (Lys analogue). In presence of air, dihydroquinazoline 5 quickly degrades into stable quinazolinone 12. The corresponding quinazolinone (17) was formed upon irradiation of ketoprofen and the amino acids N-acetyl-l-Trp ethyl ester and l-Lys ethyl ester. The formation of these models of an immunogenic complex starts with the ketoprofen-sensitized formation of singlet oxygen, which reacts with the indole moiety of Trp. The formed intermediate subsequently reacts with the primary amino functionality of Lys, or its analogue, to form a Trp-Lys adduct or a mimic thereof. The formation of a specific immunogenic complex that does not contain the allergen but that can still induce photocontact allergy would explain the large number of photocross allergies with ketoprofen. These allergens do not have to be structurally similar as long as they can generate singlet oxygen. To the best of our knowledge, there is no other suggested explanation for ketoprofen's photoallergenic properties that can account for the observed photocross allergies. The formation of a specific immunogenic complex that does not contain the allergen is a novel hypothesis in the field of contact and photocontact allergy.