Experiences with Freund's complete adjuvant test (FCAT) when screening for contact allergens in colophony

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.

An α,β-unsaturated oxime identified as a strong contact allergen

The aim of this study was to examine the possible skin sensitizing effect of oximes, employing an alpha,beta-unsaturated oxime as the model compound. Oximes are not frequently used as biologically active compounds. However, they have been shown to possess both anti-inflammatory and anti-allergic activities. Furthermore, in a recent study, a number of oximes and oxime-ethers of hydroxylated benzaldehydes and acetophenones were found to be powerful antioxidants suggested to be used in consumer products such as cosmetics and food. Although there are only few reports on the sensitizing effect of oximes, their ability to be hydrolyzed to the corresponding ketones or aldehydes makes them potential contact allergens. The oxime investigated in this study was demonstrated to be a strong contact allergen in both mice and guinea pigs, capable of sensitize the control animals after only one dermal exposure. In order to elucidate the mechanisms for the formation of the complete antigen, a variety of analogues with different reactivity were tested. The results indicate that alpha,beta-unsaturated oximes can react with proteins via several different pathways. Most likely, a metabolic transformation is involved. Due to the strong allergenic effect of the oxime investigated, we strongly advise against the use of such oximes in consumer products until a better understanding of their interactions with biological macromolecules has been obtained.

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.

A Conjugated Diene Identified as a Prohapten: Contact Allergenic Activity and Chemical Reactivity of Proposed Epoxide Metabolites

A hapten causing allergic contact dermatitis binds covalently to macromolecules via nucleophilic-electrophilic reactions or radical couplings. A prohapten can be seen as a chemically inert compound without electrophilic or radical forming properties. To exert its activity, the prohapten is activated, for example, metabolically, to the hapten. We have investigated the contact allergenic properties of a diene, (5R)-5-isopropenyl-2-methyl-1-methylene-2-cyclohexene (1), as a potential prohapten, and we found it to be a sensitizer in animal studies. The activity is likely to be exerted via epoxide metabolites. Thus, two potential metabolites of the investigated diene, (4S)-1,2-epoxy-4-isopropenyl-1-methyl-6-methylene-cyclohexane (3) and (7R)-7-isopropenyl-4-methyl-1-oxa-spiro[2.5]oct-4-ene (4), were synthesized and subjected to animal tests. Both epoxides were sensitizers. They also elicited significant reactions when tested in animals induced with 1, which indicates that they are formed from the diene in the skin. Furthermore, incubation of 1 with human liver microsomes produced both epoxides. The chemical reactivity of 1, 3, and 4 was investigated in relation to a hexapeptide, H-Pro-His-Cys-Lys-Arg-Met-OH. No adducts were obtained from reactions between the peptide and 1. However, epoxide 3 bound covalently to the cysteine residue and epoxide 4 to both the cysteine and proline residues. Since it is possible to relate the sensitizing capacity of a compound to its key physicochemical properties, knowledge-based expert systems have been developed to predict the toxicity of novel compounds by comparing the structure with activity data stored in the computer database. A diene related to 1 found in the knowledge-based expert system DEREK was considered as a nonsensitizer by this system. Our study indicates that conjugated dienes can be metabolized to contact allergens in the skin. Thus, when constructing predictive test methods based on SARs, it is important to analyze not only the virtual chemical structure of a compound but also its ability to act as a prohapten.

Studies on the autoxidation and sensitizing capacity of the fragrance chemical linalool, identifying a linalool hydroperoxide

Fragrances are among the most common causes of allergic contact dermatitis. The two monoterpenes linalool and d-limonene are the most frequently incorporated fragrance chemicals in scented products. Previous studies on d-limonene show that this monoterpene oxidizes on air exposure (autoxidation) and that allergenic oxidation products are formed. Due to structural similarities, linalool might also form allergenic oxidation products on air exposure. The aim of the present study was to study the autoxidation of linalool and to investigate the sensitizing potential of linalool before and after air exposure. Linalool was oxidized for 10 weeks and gas chromatographic analyses showed that the content of linalool decreased to about 80%. The chromatograms revealed the formation of other compounds during oxidation. One of the major oxidation products was isolated and identified as 7-hydroperoxy-3,7-dimethyl-octa-1,5-diene-3-ol. This substance is, to the best of our knowledge, described for the first time. In sensitization studies in guinea pigs, linalool of high purity gave no reactions, while linalool that had been oxidized for 10 weeks sensitized the animals. It is concluded that autoxidation of linalool is essential for its sensitizing potential.

Free radicals in antigen formation: reduction of contact allergic response to hydroperoxides by epidermal treatment with antioxidants

BACKGROUND

For patients with allergic contact dermatitis, the main therapy is anti-inflammatory steroids, a non-specific and symptomatic treatment. In contact allergy, the antigen formation is considered to be the binding of a chemical (hapten) to a biological macromolecule, e.g. a protein. Limonene-2-hydroperoxide (Lim-OOH) is a hapten with a known allergenic effect. It is likely to bind to proteins in the skin via a radical mechanism. It might be possible to inhibit the allergic reaction by epidermal application of substances that can trap free radicals, e.g. antioxidants such as ascorbic acid or alpha-tocopherol, prior to the application of the hapten.

OBJECTIVES

To study the influence of antioxidants on the allergenic effect of Lim-OOH in sensitization experiments on guinea pigs.

METHODS

Pretreatment with the antioxidants was performed before induction to study the effect on sensitization as well as before challenge testing to study the effect on elicitation.

RESULTS

A reduction in the response rate was found both at sensitization and at elicitation. The antioxidants had no effect on cobalt allergy or on the allergenic effect of haptens that form antigens via nucleophilic-electrophilic reactions. No reduction of the effect was seen for irritants.

CONCLUSIONS

The protective effect of antioxidants in elicitation could be of practical therapeutic value, as it indicates a possibility for the treatment of patients who have become sensitized to haptens that form full antigens via a radical mechanism.

Different physical forms of maleopimaric acid give different allergic responses

Endo-maleopimaric acid (MPA) is a contact allergen formed when colophonium is "modified" with maleic anhydride or fumaric acid. Previous patch testing showed a higher allergic response to petrolatum (pet.) preparations of MPA in amorphous form compared to MPA in crystalline form. In the present study, the impact of the physical form of MPA on the allergic response was investigated. Since the amorphous form is difficult to standardize, crystalline MPA mechanically incorporated or dissolved in pet. was used. A lower eliciting capacity was obtained from crystalline MPA, compared to that obtained from dissolved MPA, in guinea pigs intradermally induced with MPA. Using 3H-MPA a 3X difference in the dissolution into synthetic sweat from MPA dissolved in pet., compared to MPA mechanically incorporated, was demonstrated. A difference in bio-availability between dissolved and crystalline MPA could therefore be assumed. Crystalline MPA had a low sensitizing capacity compared to that seen for amorphous MPA in previous studies. The amorphous form of MPA is likely to have a larger surface area than crystalline MPA, with less ordered molecules, resulting in a higher dissolution rate and a greater bio-availability. Modified colophonium exists as amorphous solids and as viscous liquids. Thus, exposure will probably be to non-crystalline MPA and cases of contact allergy could be overlooked when screening with crystalline MPA.

Mechanism of the antigen formation of carvone and related alpha, beta-unsaturated ketones

In the present study, the mechanism for the antigen formation of alpha, beta-unsaturated ketones was investigated. A series of analogues of carvone ((5R)-5-isopropenyl-2-methyl-2-cyclohexenone) with altered chemical reactivity and with retained overall structure or with retained reactivity and altered three-dimensional structure were synthesized. These analogues were tested for cross-reactivity in carvone-sensitized animals. Cross-reactivity was observed for analogue 3 ((5R)-5-isopropyl-2-methyl-2-cyclohexen-1-one). No cross-reactions were observed for analogues 1 ((2R,5R)-5-isopropenyl-2-methyl cyclohexanone) and 4 ((5R)-2,3-dimethyl-5-isopropenyl-2-cyclohexene-1-one). Both those compounds also failed to induce sensitization. These findings demonstrate that alpha, beta-unsaturated ketones form antigens after a nucleophilic attack at the beta-carbon with soft nucleophiles such as thiol in cysteine and not with the formation of a Schiff's base after a nucleophilic attack at the carbonyl carbon with nitrogen nucleophiles. Furthermore, no cross-reactivity was observed between R- and S-carvone indicating the importance of the 3-dimensional structure of haptens (and antigens) in T-cell recognition. The analogues were also tested for cross-reactivity on patients allergic to carvone. The results from the animal study were confirmed.

Identification and allergenic activity of hydroxyaldehydes - a new type of oxidation product from an ethoxylated non-ionic surfactant

Ethoxylated alcohols, which are widely used as surfactants, are susceptible to oxidation on air exposure. A complex mixture of oxidation products is formed, among which alkylated aldehydes, alkylated formates, formaldehyde and peroxides have previously been identified by our group. In the present study, we have identified a new class of oxidation product from the nonionic ethoxylated surfactant C12E5. These oxidation products are highly water-soluble hydroxyaldehydes with the general formula HO(CH2CH2O)nCH2CHO, n=1-4. To facilitate the identification of the hydroxyaldehydes in oxidized C12E5, reference compounds were synthesized. The sensitizing potential of 1 of the identified hydroxyaldehydes, HO(CH2CH2O)3CH2CHO, was studied in guinea pigs and was found to be weak. A significant cross-reactivity between this aldehyde and the next shorter homologue, HO(CH2CH2O)2CH2CHO, was observed. Irritant components, present in the oxidation mixture, facilitate the skin penetration of allergens, which further accentuates the importance of controlling the conditions of storage and handling of ethoxylated surfactants, to reduce the formation of allergenic and irritant oxidation products.

Atmospheric oxidation of poly(oxyethylene) alcohols. Identification of ethoxylated formates as oxidation products and study of their contact allergenic activity

Ethoxylated alcohols are widely used as surfactants. In the present study we have continued our investigations on the degradation with time upon air exposure of the ethoxylated alcohols at normal storage and handling. As a result, a new group of ethoxylated formates with the general formula C12H25(OCH2CH2)nOCHO (n = 0-4) was identified in C12H25(OCH2CH2)5OH stored and handled at room temperature. To facilitate the identification work, reference compounds were synthesized. The formates showed no allergenic activity in the sensitization studies performed. In previous investigations on the same ethoxylated alcohol, we have identified formaldehyde and ethoxylated aldehydes among the oxidation products formed. Formaldehyde is a common contact allergen, and the ethoxylated aldehydes were shown to have a sensitizing capacity of the same magnitude as formaldehyde. The instability of the ethoxylated alcohols and formation of oxidation products may give an allergenic contribution to hand eczema caused by work with water and surfactants. To investigate the clinical significance in man an appropriate diagnostic patch testing in exposed humans is required.

Sensitizing potential of acetaldehyde and formaldehyde using a modified cumulative contact enhancement test (CCET)

The contact allergenic activity of acetaldehyde was investigated with a modified cumulative contact enhancement test (CCET) method in guinea pigs. Possible cross-reactivity between acetaldehyde and formaldehyde was also studied. In contrast to the original CCET protocol, we used sham-treated controls and the chemicals were tested with closed epicutaneous application at 1st challenge. The suitability of the method was verified with formaldehyde and the results were comparable with those previously found with the guinea pig maximization test (GPMT). For the 1st time, acetaldehyde was shown to be a contact allergen in predictive tests. No cross-reactivity was observed between acetaldehyde and formaldehyde. Acetaldehyde seems to be a rare sensitizer in man. However, its allergenic activity should be considered, since it might be present as an impurity in ethoxylated surfactants. As the CCET protocol involves topical induction and challenge, we regard the modified version as well suited to evaluation of the contact allergenic potential of chemicals.

Formation of formaldehyde and peroxides by air oxidation of high purity polyoxyethylene surfactants

Ethoxylated alcohols are non-ionic surfactants. The majority are used in household cleaners, laundry products, toiletries and in industrial and institutional cleaners. In previous studies, an ethoxylated non-ionic surfactant of technical quality showed allergenic activity in guinea pig experiments. Chemical analysis revealed a content of formaldehyde, a well-known contact allergen, and peroxides in the surfactant. Most cases of occupational contact dermatitis are considered to be of irritant origin, caused by contact with water and surfactants, but if allergenic autoxidation products can be formed, allergic contact dermatitis cannot be excluded. The sensitizing potential of a chemically defined high purity ethoxylated alcohol was investigated and oxidation under various storage and handling conditions was studied for this and a homologous product. The pure surfactant showed no significant allergenic activity on predictive testing in guinea pigs. When ethoxylated alcohols were stored in the refrigerator, their deterioration was limited. At room temperature, their content of peroxides and formaldehyde increased with time. Levels of formaldehyde above those capable of causing positive patch test reactions were found. Since such surfactants have wide applications, resulting exposure to formaldehyde could be more frequent than is generally realized, contributing to persistence of dermatitis in individuals allergic to formaldehyde.

Lack of antagonism to Ni2+ and Co2+ contact allergy from other essential divalent metal ions

The potential antagonistic effects of Ca2+, Cu2+, Fe2+, Mg2+, Mn2+ and Zn2+ on contact allergy to Co2+ and Ni2+ were studied. The immune response was characterized by the Co2+ or Ni2+ mediated cellular [methyl-3H]thymidine uptake in peripheral blood mononuclear cell (PBMC) cultures from 6 subjects contact-allergic to Co2+ and Ni2+ and 6 non-allergic control individuals. Results from the in vitro experiments were further evaluated with Co2+-sensitized guinea pigs according to the modified Freund's complete adjuvant test. Ni2+ and Co2+ (10-50 microM) significantly increased the lymphocyte proliferation in PBMC cultures from contact-allergic subjects in comparison with those from control individuals. Pretreatment of the PBMCs with Ca2+, Fe2+, Mg2+ (10-100 microM) or Mn2+ (1-10 microM) did not influence, while Zn2+ (100 microM) enhanced, and Cu2+ (5 and 10 microM) markedly reduced the Ni2+ and Co2+ mediated cellular [methyl-3H]thymidine uptake. The inhibition of the Ni2+- and Co2+-induced cell proliferation by Cu2+ in vitro was probably related to toxicity, since the viability of the cells was significantly reduced by applied combinations of Ni2+ or Co2+ with Cu2+. Topical pretreatment of Co2+-sensitized guinea pigs with maximum non-irritating doses of CuCl2 x 2H2O (0.8%) did not affect the challenge testing to CoCl2 x 6H2O (0.1 and 0.3%). In conclusion, our combined in vitro and in vivo results indicate that Ca2+, Cu2+, Fe2+, Mg2+, Mn2+ and Zn2+ are not able to antagonise the formation of Ni2+ and Co2+ antigens.

Contact allergens from surfactants. Atmospheric oxidation of polyoxyethylene alcohols, formation of ethoxylated aldehydes, and their allergenic activity

Ethoxylated surfactants are susceptible to oxidation upon air exposure. We have previously studied the rate of peroxidation and formaldehyde formation in the chemically well-defined ethoxylated alcohol C12H25(OCH2CH2)5OH. Formaldehyde is a common cause of contact allergy. The aim of the present study was to identify other oxidation products that could be formed upon air exposure of the ethoxylated alcohol and to determine their allergenic activity. It was shown that air oxidation of C12H25(OCH2CH2)5OH gave all the theoretically possible aldehydes of the general formula C12H25(OCH2CH2)nOCH2CHO (n = 0-4) and that the major oxidation product was C12H25(OCH2CH2)4OCH2CHO, dodecyltetraoxyethyleneoxyacetaldehyde. The structure elucidation and synthesis of these aldehydes are here presented for the first time. The major aldehyde was shown to be a contact allergen with the same sensitizing capacity as that of formaldehyde. A dose-response relationship was observed in the sensitization studies. The allergens were formed from the surfactant itself and the skin reactions cannot be explained due to any impurities that may be present in a technical quality of the surfactant. Cases of allergic contact dermatits to ethoxylated surfactants have been reported. To avoid the formation of allergenic oxidation products it is important to control the conditions for storage, handling, and transportation of ethoxylated surfactants.

Skin sensitization to linalyl hydroperoxide: support for radical intermediates

In order to better understand the skin sensitization mechanism of allylic hydroperoxides, linalyl hydroperoxide (1) and several of its potential rearrangement products-epoxylinalool (2), epoxynerol (3), epoxygeraniol (4), and furan (5) and pyran (6) derivatives-were synthesized. The sensitizing properties of these molecules have been screened on mice using the local lymph node assay (LLNA) and further evaluated on guinea pigs using the Freund's complete adjuvant test (FCAT). Linalyl hydroperoxide (1) and linalyl epoxide (2) were found to be sensitizers, while the other compounds were classified as mild sensitizers or nonsensitizers. In the guinea pigs, no cross-reactions were observed between skin sensitizers 1 and 2. Radical-trapping experiments were carried out on linalyl hydroperoxide (1) using TTBP as trapping agent and Fe(3+)-TPP as radical inducer. The major reaction taking place is the formation of a furan ring by intramolecular reaction of the oxygen-centered radical with the isoprenyl double bond with the formation of a tertiary radical. Reaction of this intermediate with radicals derived from TTBP gave compounds 10a,b in 25% yield. The second important reaction, accounting for 14%, is taking place on the allylic double bond with the formation of a less stable primary radical which is not trapped by a TTBP-derived radical but by a hydroxy radical to give a mixture of epoxides 3 and 4. These results are in favor of the formation of a carbon-centered reactive radical as intermediate in the skin sensitization to linalyl hydroperoxide.

Contact allergenic activity of Tween 80 before and after air exposure

Tween 80 is an ethoxylated hydrophilic non-ionic surfactant, which is used for the preparation of oil-in-water emulsions in pharmaceutical products, cosmetics, and industrial detergents. Ethoxylated surfactants are polyethers and are thus easily oxidized by atmospheric oxygen to a variety of hydroperoxides, peroxides and carbonyl compounds. The aim was to investigate the formation of oxidation products and the allergenic potential of Tween 80 before and after air exposure. The formation of peroxides and formaldehyde was followed with chemical analyses during air and pure oxygen exposure of water solutions of Tween 80 of technical quality. A complex mixture of compounds was formed when Tween 80 was oxidized. Formaldehyde was detected in amounts that may be eliciting in allergic individuals. Acetaldehyde was identified in Tween 80 before oxygen exposure, whereafter the amount gradually decreased. The contact allergenic activity was determined in experimental sensitization studies in guinea pigs. Non-oxidized as well as oxidized Tween 80 of technical quality showed allergenic activity. The results indicate that allergens are present in Tween 80 before oxidation and that new allergens are formed in the oxidation process. No obvious dose-response relationship was found in the sensitization studies. The possibility that allergenic compounds can be formed during storage and handling of products containing ethoxylated surfactants should be taken into consideration.

Environmentally friendly paper may increase risk of hand eczema in rosin-sensitive persons

BACKGROUND

A connection between patch test reactions to paper extracts and contact allergy to rosin (colophony) has been demonstrated.

OBJECTIVE

We wanted to determine whether a difference in the allergenic activity of various types of paper is related to a difference in the pulp.

METHODS

Patients with dermatitis who were frequently exposed to paper were patch tested with extracts from various papers and the standard series. The extracts were also tested in volunteers with or without contact allergy to rosin and in animals. The rosin compounds in the papers were analyzed by gas chromatography.

RESULTS

The subjects reacting to paper extracts also reacted to rosin. Most reactions were found to the papers produced from mechanical pulps, which contained the highest analyzed amounts of rosin compounds. Animals sensitized to rosin reacted only to paper from mechanical pulp.

CONCLUSION

Papers based on mechanical pulps that are considered to be environmentally friendly have a greater potential to elicit positive patch test reactions than papers made from other pulps. The increased use of mechanical pulps in different applications may increase the incidence of rosin-related hand eczema.

15-hydroperoxydehydroabietic acid--a contact allergen in colophony from pinus species

A new hydroperoxide, 15-hydroperoxydehydroabietic acid (15-HPDA), with contact allergenic properties has been detected in rosin obtained from Pinus species. Detection was facilitated using a synthetic preparation of 15-HPDA for reference purposes. The synthesis and the detection (HPLC and GC) of 15-HPDA in rosin are described. The allergenic activity of 15-HPDA was studied in an experimental sensitization test on guinea-pigs.

Hydroperoxides in oxidized d-limonene identified as potent contact allergens

Hydroperoxides of d-limonene were shown to be potent contact allergens when studied in guinea-pigs. Limonene-2-hydroperoxide (2-hydroperoxy-p-mentha-6,8-diene, a mixture of trans and cis isomers) was synthesized for the first time. The ratio between the trans and cis forms was 3:1. These two hydroperoxides were identified as the major hydroperoxides in autoxidized d-limonene. In photo-oxidized d-limonene, they constituted a minor part of the hydroperoxide fraction. Hydroperoxides may bind to proteins of the skin to make antigens either via a radical mechanism or after reactions to give epoxides. The cross-reactivity between the epoxide limonene-1,2-oxide, a potent contact allergen, and the hydroperoxides was therefore studied. No significant pattern of cross-reactivity was found. Further studies to identify and test the allergenicity of single hydroperoxides are needed to elucidate the mechanism of the allergenicity.

Rosin allergy: identification of a dehydroabietic acid peroxide with allergenic properties

A peroxide of dehydroabietic acid was isolated from rosin using flash chromatography and preparative HPLC. It was identified by 1H-NMR and MS. In animal experiments, this peroxide cross-reacted with a previously identified allergen in rosin, 15-hydroperoxyabietic acid (15-HPA), despite differences in molecular weight and unsaturation. Both substances are able to react via a radical mechanism generating structurally similar molecules. In patch testing of patients, no reactions were observed to the peroxide. Low skin penetration of the peroxide could be the explanation for this. The peroxide seems of little clinical importance. The observed cross-reactivity is an indication of antigen generation via a radical mechanism. Only a few compounds that react with radical mechanisms to form antigens are described in the literature.

Air oxidation of d-limonene (the citrus solvent) creates potent allergens

Products containing as much as 95% of d-limonene are used for, e.g., degreasing metal before industrial painting and for cleaning assemblies. Experimental studies on the sensitizing potential of limonene show diverging results. In a previous study, we found that the sensitizing potential of d-limonene increased with prolonged air exposure. The aim of this study was to make further chemical analyses, to identify compounds formed by air exposure of d-limonene and to study their allergenic potential. d-limonene was found to be a sensitizer after prolonged exposure to air according to 2 Freund's complete adjuvant test (FCAT) experiments and 1 guinea pig maximization test (GPMT) study. No significant response was obtained to d-limonene not air exposed, even if the animals were sensitized to oxidized d-limonene. 5 main oxidation products of d-limonene were identified. (R)-(-)-carvone and a mixture of cis and trans isomers of (+)-limonene oxide were found to be potent sensitizers, while no significant reactions were obtained in the animals induced with a mixture of cis and trans isomers of (-)-carveol. It can be concluded that air oxidation of d-limonene is essential for its sensitizing potential, and that potent allergens are created.

Maleopimaric acid--a potent sensitizer in modified rosin

The allergenicity of the maleic-modified rosins and their esters has been studied. The unesterified resins are mainly used in paper size and the esters in printing inks, varnishes and adhesives. The levopimaric-maleic anhydride Diels-Alder adduct (maleopimaric acid) is the main component obtained in the maleic-modified rosins. This compound was synthesized and its structure was determined. Its sensitizing potential was investigated in guinea pigs according to different methods. It was shown that maleopimaric acid is a very potent sensitizer, comparable with the strongest allergen isolated from unmodified gum rosin. The allergen may also be present after esterification unless the process is carried out to completion. The animals sensitized to maleopimaric acid did not react to unmodified rosin, which shows that maleopimaric acid is structurally different from the allergens in rosin.

Contact allergy due to colophony (III). Sensitizing potency of resin acids and some related products

7 resin acids, 3 synthetically prepared derivatives and the neutral fraction of Chinese colophony were studied by experimental sensitization using a modified FCA method. 4 resin acids, laevopimaric, abietic, podocarpic and tetrahydroabietic, proved to be weak sensitizers. Neoabietic, dehydroabietic, isopimaric acid and larixol remained negative. However, the derivatives, methyl abietate and calcium abietate, were shown to be moderate sensitizers, and the maleic-modified adduct to be a moderate to strong sensitizer. As laevopimaric acid plays only a minor rôle in colophony, abietic acid must be considered a major, even if weak, allergen in non-modified colophony. The neutral fraction of colophony is also partially involved in colophony allergy.

Propolis allergy. (III). Sensitization studies with minor constituents

87% of the propolis product "LB-1", originally reported to be 1,1-dimethyl-allyl caffeic acid ester, was shown by GC/MS analysis to consist of 3 isomeric pentenyl caffeates, 63% of which are 1,1-dimethylallyl caffeate. These pentenyl caffeates proved to be the major sensitizers of propolis and of poplar bud secretion in our previous study. In addition, 3 further minor allergens have now been investigated. Experimental sensitization indicates that phenylethyl caffeate is as strong a sensitizer as the major allergen "LB-1", while benzyl salicylate is a moderate sensitizer. Benzyl cinnamate plays only a subordinate role. At least 3 further esters of caffeic acid or cinnamic acid remain to be studied. Interestingly, relationships between propolis and balsam of Peru were found. 8 compounds are common to both materials. Thus "cross-reactions" or concomitant reactions in propolis-sensitive individuals to balsam of Peru are explainable.

Contact allergy to dehydroabietic acid derivatives isolated from Portuguese colophony

7-oxodehydroabietic acid and 15-hydroxydehydroabietic acid were isolated as their methyl esters from Portuguese colophony of the gum rosin type and identified as contact allergens. Another oxidation product of dehydroabietic acid, 15-hydroxy-7-oxodehydroabietic acid, was synthesized and identified as a component of Portuguese gum rosin. 7-oxodehydroabietic acid was found to a be a grade III allergen according to the GPMT method. Guinea pigs induced with gum rosin showed only a low response to the isolated compounds, while patients with a known allergy to gum rosin reacted to a greater extent. The results imply that the content of oxidized dehydroabietic acids in gum rosin is too low to give a marked sensitization in the animals. However, the patients might have come in contact with the allergens in technically modified rosins. The compounds showed a pattern of cross-reactivity in the animal experiments as well as among the patch tested patients.

Hydrogenation reduces the allergenicity of colophony (rosin)

Abietic acid is the main component of rosin. It is readily oxidized by air and its oxidation products are considered to be mainly responsible for the allergenic effect. Hydrogenation of the conjugated double bonds of abietic acid decreases its susceptibility to air oxidation and would thus reduce the allergenicity of rosin. Portuguese gum rosin was therefore hydrogenated and its allergenicity was compared with that of unmodified rosin in animal experiments and by patch testing in humans. Its sensitizing potential was determined in 2 studies. No response was found according to the FCAT method while the GPMT gave significant response in the animals challenged with the highest test concentration. Hydrogenated rosin showed no eliciting activity in animals induced with unmodified rosin according to the GPMT method. A marked decrease was found in the frequency of allergic reactions to hydrogenated rosin compared to the reactions to unmodified rosin in patients with known allergy to gum rosin. We conclude that elimination of the unsaturated non-aromatic compounds by hydrogenation considerably reduces the allergenicity of Portuguese gum rosin.