Are free radicals and not quinones the haptenic species derived from urushiols and other contact allergenic mono- and dihydric alkylbenzenes? The significance of NADH, glutathione, and redox cycling in the skin

Investigation into Propolis Components Responsible for Inducing Skin Allergy: Air Oxidation of Caffeic Acid and Its Esters Contribute to Hapten Formation

Propolis is a resin-like material produced by bees from the buds of poplar and cone-bearing trees and is used in beehive construction. Propolis is a common additive in various biocosmetics and health-related products, despite the fact that it is a well-known cause of contact allergy. Caffeic acid and its esters have been the primary suspects behind the sensitization potency of propolis-induced contact allergy. However, the chemical structures of the protein adducts formed between these haptens and skin proteins during the process of skin sensitization remain unknown. In this study, the reactivity of three main contact allergens found in propolis, namely, caffeic acid (CA), caffeic acid 1,1-dimethylallyl ester (CAAE), and caffeic acid phenethyl ester (CAPE), was investigated. These compounds were initially subjected to the kinetic direct peptide reactivity assay to categorize the sensitization potency of CA, CAAE, and CAPE, but the data obtained was deemed too unreliable to confidently classify their skin sensitization potential based on this assay alone. To further investigate the chemistry involved in generating possible skin allergy-inducing protein adducts, model peptide reactions with CA, CAAE, and CAPE were conducted and analyzed via liquid chromatography-high-resolution mass spectrometry. Reactions between CA, CAAE, and CAPE and a cysteine-containing peptide in the presence of oxygen, both in closed and open systems, were monitored at specific time points. These studies revealed the formation of two different adducts, one corresponding to thiol addition to the α,β-unsaturated carbonyl region of the caffeic structure and the second corresponding to thiol addition to the catechol, after air oxidation to o-quinone. Observation of these peptide adducts classifies these compounds as prehaptens. Interestingly, no adduct formation was observed when the same reactions were performed under oxygen-free conditions, highlighting the importance of air oxidation processes in CA, CAAE, and CAPE adduct formation. Additionally, through NMR analysis, we found that thiol addition occurs at the C-2 position in the aromatic ring of the CA derivatives. Our results emphasize the importance of air oxidation in the sensitization potency of propolis and shed light on the chemical structures of the resultant haptens which could trigger allergic reactions in vivo.

Systemic contact dermatitis induced by Rhus allergens in Korea: exercising caution in the consumption of this nutritious food

Systemic contact dermatitis (SCD) develops when a person who was previously sensitized to an allergen is exposed to the same allergen via the systemic route. In East Asia, the use of lacquer for polishing furniture is common and a part of the traditional culture. Contact exposure to tableware polished with Rhus lacquer may lead to sensitization. In Korea, SCD is commonly observed after systemic exposure to Rhus, a nutritious food item consumed because of the common belief of it improving the immune system. In this study, we reviewed the medical records of 21 Korean patients with SCD caused by Rhus ingestion. We found that the most significant epidemiological factor for SCD was the season of the year. Furthermore, 66.67% of the patients presented with leucocytosis and 23.81% showed increased liver enzyme levels. It is important to educate people on the risks associated with the systemic ingestion of Rhus.

Structural influence on radical formation and sensitizing capacity of alkylic limonene hydroperoxide analogues in allergic contact dermatitis

Hydroperoxides are known to be strong contact allergens and a common cause of contact allergy. They are easily formed by the autoxidation of, for example, fragrance terpenes, compounds that are common in perfumes, cosmetics, and household products. A requirement of the immunological mechanisms of contact allergy is the formation of an immunogenic hapten-protein complex. For hydroperoxides, a radical mechanism is postulated for this formation. In our previous investigations of allylic limonene hydroperoxides, we found that the formation of carbon- and oxygen-centered radicals, as well as the sensitizing capacity, is influenced by the structure of the hydroperoxides. The aim of the present work was to further investigate the connection between structure, radical formation, and sensitizing capacity by studying alkylic analogues of the previously investigated allylic limonene hydroperoxides. The radical formation was studied in radical-trapping experiments employing 5,10,15,20-tetraphenyl-21H,23H-porphine iron(III) chloride as an initiator and 1,1,3,3-tetramethylisoindolin-2-yloxyl as a radical trapper. We found that the investigated hydroperoxides initially form carbon- and oxygen-centered radicals that subsequently form alcohols and ketones. Trapped carbon-centered radicals and nonradical products were isolated and identified. Small changes in structure, like the omission of the endocyclic double bond or the addition of a methyl group, resulted in large differences in radical formation. The results indicate that alkoxyl radicals seem to be more important than carbon-centered radicals in the immunogenic complex formation. The sensitizing capacities were studied in the murine local lymph node assay (LLNA), and all hydroperoxides tested were found to be potent sensitizers. For two of the hydroperoxides investigated, the recently suggested thiol-ene reaction is a possible mechanism for the formation of immunogenic complexes. For the third investigated, fully saturated, hydroperoxide, the thiol-ene mechanism is not possible for immunogenic complex formation. This strongly indicates that several radical reaction pathways for immunogenic complex formation of limonene hydroperoxides are active in parallel.

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.

Hapten-protein binding: from theory to practical application in the in vitro prediction of skin sensitization

In view of the forthcoming European Union ban on in vivo testing of cosmetic and toiletry ingredients, following the publication of the 7th amendment to the Cosmetics Directive, the search for practical, alternative, non-animal approaches is gathering pace. For the end-point of skin sensitization, the ultimate goal, i.e. the development and validation of alternative in vitro/in silico assays by 2013, may be achieved through a better understanding of the skin sensitization process on the cellular and molecular levels. One of the key molecular events in skin sensitization is protein haptenation, i.e. the chemical modification of self-skin protein(s) thus forming macromolecular immunogens. This concept is widely accepted and in theory can be used to explain the sensitizing capacity of many known skin sensitizers. Thus, the principle of protein or peptide haptenation could be used in in vitro assays to predict the sensitization potential of a new chemical entity. In this review, we consider some of the theoretical aspects of protein haptenation, how mechanisms of protein haptenation can be investigated experimentally and how we can use such knowledge in the development of novel, alternative approaches for predicting skin sensitization potential in the future.

Lipoxygenase-catalyzed polymerization of phenolic lipids suggests a new mechanism for allergic contact dermatitis induced by urushiol and its analogs

Lipoxygenase was found to catalyze the oxidative polymerization of phenolic lipids containing a (Z,Z)-pentadiene in the side chain, the model compounds of urushiol and its analog, yielding methanol-soluble and insoluble polymers. The structural analysis of the resulted polymers suggested that the polymerization occurred at both the phenol and the unsaturated side chain. The key step of the polymerization was the generation of the hydroperoxide at the unsaturated side chain by lipoxygenase. The decomposition of hydroperoxide and concomitant dehydrogenation of phenol ring catalyzed by lipoxygenase might produce radicals that could be coupled to form cross-linked polymers. This lipoxygenase-mediated reaction implies a new mechanism for contact allergy of urushiol and its analogs.

Clinical and immunologic features of systemic contact dermatitis from ingestion of Rhus (Toxicodendron)

Oral or parenteral exposure to certain contact allergens may elicit an eczematous skin reaction in sensitized individuals. This phenomenon has been called systemic contact dermatitis (SCD) and is relatively rare when compared with classical contact dermatitis. We reviewed and analysed the clinical and immunologic features of 42 patients with SCD caused by ingestion of Rhus (Toxicodendron), 24 males and 18 females, average age 44 years (range 24-72). Several of such patients (33%) had a known history of allergy to lacquer. The patients developed skin lesions such as generalized maculopapular eruptions (50%), erythroderma (29%), vesiculobullous lesions (14%) and erythema multiform (EM)-like lesions (7%). Many patients (57%) developed leucocytosis with neutrophilia (74%). In some patients (5%), abnormalities of liver function developed. We also analysed lymphocyte subsets in the peripheral blood of 12 patients. The lymphocyte subsets studied were T cells (CD3), B cells (CD19), natural killer (NK) cells (CD3-CD16+/CD56+), helper/inducer cells (CD4), cytotoxic/suppressor cells (CD8) and helper/suppressor ratio (CD4/CD8). The lymphocyte subsets of all 12 patients studied were within the normal range. Moreover, there were no differences between patients with a history of allergy to lacquer and those without a history of allergy to lacquer. Therefore, rather than an immunologic response, the skin eruption seems to be caused by a toxic reaction because of Rhus.

Redox-modulated pathways in inflammatory skin diseases

Inflammatory skin diseases account for a large proportion of all skin disorders and constitute a major health problem worldwide. Contact dermatitis, atopic dermatitis, and psoriasis represent the most prevalent inflammatory skin disorders and share a common efferent T-lymphocyte mediated response. Oxidative stress and inflammation have recently been linked to cutaneous damage in T-lymphocyte mediated skin diseases, particularly in contact dermatitis. Insights into the pathophysiology responsible for contact dermatitis can be used to better understand the mechanism of other T-lymphocyte mediated inflammatory skin diseases, and may help to develop novel therapeutic approaches. This review focuses on redox sensitive events in the inflammatory scenario of contact dermatitis, which comprise for example, several kinases, transcription factors, cytokines, adhesion molecules, dendritic cell surface markers, the T-lymphocyte receptor, and the cutaneous lymphocyte-associated antigen (CLA). In vitro and animal studies clearly point to a central role of several distinct but interconnected redox-sensitive pathways in the pathogenesis of contact dermatitis. However, clinical evidence that modulation of the skin's redox state can be used therapeutically to modulate the inflammatory response in contact dermatitis is presently not convincing. The rational for this discrepancy seems to be multi-faceted and complex and will be discussed.

Molecular mechanisms of CD8+ T cell-mediated delayed hypersensitivity: implications for allergies, asthma, and autoimmunity

Delayed-type hypersensitivity (DTH) is defined as the recruitment of T cells into tissues to be activated by antigen-presenting cells to produce cytokines that mediate local inflammation. CD8+ T cells are now known to mediate DTH responses in allergic contact dermatitis, drug eruptions, asthma, and autoimmune diseases. This inflammatory effector capability of CD8+ cytotoxic T cells was previously poorly recognized, but there is now considerable evidence that these diseases may be mediated by CD8+ DTH. The difference between CD8+ T cells and CD4+ T cells mediating DTH relates to the molecular mechanisms by which antigens are processed and presented to the T cells. Antigens external to the cell are phagocytosed and processed for presentation on MHC class II molecules (eg, HLA-DR) to CD4+ T cells. In contrast, internal cytoplasmic antigens are processed by the endogenous pathway for presentation on MHC class I molecules (eg, HLA-A, -B, and -C) to CD8+ T cells. External allergens can also enter the endogenous pathway to be presented to CD8+ T cells. These include many contact sensitizers, chemical and protein respiratory allergens, viral antigens, metabolic products of drugs, and autoantigens. The resulting CD8+ T-cell response explains the role of CD8+ T-cell DTH mechanisms in allergic contact dermatitis, asthma, drug eruptions, and autoimmune diseases.

Free radicals as potential mediators of metal-allergy: Ni2+- and Co2+-mediated free radical generation

The generation of free radicals by Ni(2+) and Co(2+) was studied at physiological pH in H(2)O(2)-containing solutions in the absence and presence of various radical-mediating ligands and in human peripheral blood mononuclear cell (PBMC) cultures. With ESR spectroscopy, free radical species were identified and quantitated by spin trapping with 5,5-dimethyl-1-pyrroline-N-oxide (DMPO). Co(2+) generated hydroxyl radicals from H(2)O(2) in PBS solutions containing glutathione (GSH) or histidine (His). Omission of GSH or His from the reaction mixture significantly reduced the ESR-signal, indicating the importance of metal-chelation in free radical generation. Carnosine did not significantly enhance the reactivity of Co(2+) toward H(2)O(2), whereas cysteine (Cys) and N-acetylcysteine (NAC) suppressed free radical generation. Under identical reaction conditions, Ni(2+) was markedly less reactive toward H(2)O(2) in comparison with Co(2+). GSH, His, Cys and NAC did not enhance free radical generation of Ni(2+) from H(2)O(2). However, in the presence of carnosine weak but significantly enhanced ESR intensities were found. Incubation of PBMC cultures from healthy subjects with Co(2+) (10-50 microM) yielded the DMPO-.OH adduct, suggesting Co(2+)-mediated hydroxyl radical generation. In contrast, incubation of PBMC cultures with Ni(2+) (10-50 microM) did not produce a detectable ESR-signal. Ascorbic acid efficiently inhibited Co(2+)-mediated free radical generation in PBS solutions and PBMC cultures. The observed difference in free radical generating capacity between Ni(2+) and Co(2+) is of interest with respect to the absence of cross-reactivity between the two metal-ions in experimental allergic contact dermatitis.

Cutaneous tolerance to nitroxide free radicals and nitrone spin traps in the guinea pig

The attempts to use nitroxide free radicals and nitrone spin traps topically in skin requires analysis of their potential cutaneous adverse effects. The objective of this study was to investigate the skin irritation and sensitizing potential of nitroxides and nitrones in the guinea pig. The following unsubstituted nitroxides were investigated: 2,2,6,6-tetramethyl-1-piperidinoxyl (Tempo), 2,2, 5,5-tetramethyl-3-oxazolidinoxyl (Doxo), 2,2,5,5-tetramethyl-1-dihydro-pyrrolinoxyl (Proxo), 2,2,3,4,5,5-hexamethyl-imidazoline-1-yloxyl (Imidazo) and the nitrones: 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) and N-tert.-butyl-phenylnitrone (PBN). Cutaneous irritation was determined following the modified Draize protocol. The response was evaluated clinically as well as by a biophysical method analyzing transepidermal water loss (TEWL). The nitroxides and nitrones were classified clinically from non-irritant (Proxo, Imidazo, DMPO) to slightly irritant (Tempo, Doxo, PBN) according to the Draize protocol. In agreement with the clinical scoring, the TEWL values were significantly increased by Tempo, Doxo and PBN. TOLH, the hydroxylamine of Tempo and its major skin metabolite, did not cause skin irritation. The sensitizing effect was evaluated according to the Magnusson and Kligman test. The results showed no cutaneous hypersensitivity to all nitroxides and nitrones, indicating a weak sensitizing potential. That concludes that the nitroxides and nitrones tested in this study have a low potential of acute skin intolerance.

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.

Modulation of fatty acid oxidation alters contact hypersensitivity to urushiols: role of aliphatic chain beta-oxidation in processing and activation of urushiols

Lithraea caustica, or litre, a tree of the Anacardiaceae family that is endemic to the central region of Chile, induces a severe contact dermatitis in susceptible human beings. The allergen was previously isolated and characterized as a 3-(pentadecyl-10-enyl) catechol, a molecule belonging to the urushiol group of allergens isolated from poison ivy and poison oak plants. Because urushiols are pro-electrophilic haptens, it is believed that the reactive species are generated intracellularly by skin keratinocytes and Langerhans cells. The active species are presumed to modify self proteins which, after proteolytic processing, would generate immunogenic peptides carrying the hapten. The presence of a 15-carbon-length hydrophobic chain should impair antigen presentation of self-modified peptides by class I MHC molecules, either by steric hindrance or by limiting their sorting to the ER lumen. We have proposed that the shortening of the aliphatic chain by beta-oxidation within peroxisomes and/or mitochondria should be a requirement for the antigen presentation process. To test this hypothesis we investigated the effect of drugs that modify the fatty acid metabolism on urushiol-induced contact dermatitis in mice. Clofibrate, a peroxisomal proliferator in mice, increased the immune response to the urushiols from litre by 50%. Conversely, tetradecyl glycidic acid, an inhibitor of the uptake of fatty acids by mitochondria, decreased the hypersensitivity to the hapten. An increase in the level in glutathione by treatment of the animals with 2-oxotiazolidin-4-carboxilic acid lowered the response. Those findings strongly support a role for the fatty acid oxidative metabolism in the processing and activation of urushiols in vivo.

Paraphenylene diamine, a contact allergen, induces oxidative stress in normal human keratinocytes in culture

During the course of evaluating the interaction between allergens and keratinocytes in the pre-immunological phase of contact sensitization, we have studied the effects of paraphenylene diamine (pPD) on membrane lipid peroxidation and on intracellular antioxidant levels in cultured human keratinocytes. pPD is an aromatic amine which undergoes spontaneous oxidation in culture medium, generating short-lived free radical species including oxyradicals. Following exposure to non-toxic concentrations of pPD (0.5-10 micrograms/ml), we have evaluated the fatty acid pattern of membrane phospholipids as a target of peroxidative damage, and the intracellular level of reduced glutathione (GSH), the activity of superoxide dismutase (SOD), and that of catalase (CAT) as parameters of the antioxidant system. Depending on pPD concentration and the period of exposure, peroxidative damage with a significant decrease in membrane polyunsaturated fatty acids, was detected. Concentrations between 0.5 and 2 micrograms/ml produced an initial increase and then a decrease in both SOD and CAT activities, and in the oxidation of GSH, up to 12 h. After 24 h, when all the pPD had decomposed, recovery of the initial levels of the antioxidants was detected. Concentrations over 5 micrograms/ml induced a progressive decrease in both the enzymatic activities and the GSH concentrations. These results are consistent with the view that oxidative stress can be an essential event in the pre-immunological phase of contact sensitization.

Antigen processing: the gateway to the immune response

The T-lymphocyte response to an antigen is governed by the source of that antigen and the way in which it is processed. Before recognition by T lymphocytes, proteins must be degraded to peptides by antigen-presenting cells. The peptides are then presented on major histocompatibility complex (MHC) molecules for recognition by the T cells. Antigens arising outside the cell (e.g., bacteria) are phagocytosed and processed by the exogenous pathway for presentation on MHC class II molecules (e.g., DR) to CD4+ cells. Antigens derived from the cytoplasm (e.g., viral proteins) are processed by the endogenous pathway for presentation by MHC class I molecules (e.g., HLA-A, -B, -C) to CD8+ cells. The response to a hapten or drug is a function of the antigen processing pathway and is determined by its chemical properties. Antigen processing also governs the T-cell response to pathogens, vaccines, and autoimmune conditions.

The chemistry of contact allergy: why is a molecule allergenic?

This review concentrates on some specific aspects of the chemistry of allergic contact dermatitis. The way low molecular weight chemicals react with skin proteins to form complete antigens will be discussed and the development of molecular modelling techniques to analyse molecular recognition presented. Subsequently, how knowledge of the chemical structure can be used to estimate the allergenic activity of a molecule will be considered. This aspect includes work with qualitative and quantitative structure-activity relationships (SAR) in the field of contact allergy.

Processing of urushiol (poison ivy) hapten by both endogenous and exogenous pathways for presentation to T cells in vitro

The antigen processing requirements for urushiol, the immunogen of poison ivy (Toxicodendron radicans), were tested by presentation of urushiol to cultured human urushiol-responsive T cells. Urushiol was added to antigen-presenting cells (APC) either before or after fixation with paraformaldehyde. Three distinct routes of antigen processing were detected. CD8+ and CD4+ T cells, which were dependent upon processing, proliferated if urushiol was added to APC before fixation, but did not proliferate when urushiol was added to APC after fixation. Processing of urushiol for presentation to CD8+ T cells was inhibited by azide, monensin, and brefeldin A. This suggests that urushiol was processed by the endogenous pathway. In contrast, presentation of urushiol to CD4+ T cells was inhibited by monensin but not by brefeldin A. This was compatible with antigen processing by the endosomal (exogenous) pathway. Finally, certain CD8+ T cells recognized urushiol in the absence of processing. These cells proliferated in response to APC incubated with urushiol after fixation. Classification of contact allergens by antigen processing pathway may predict the relative roles of CD4+ and CD8+ cells in the immunopathogensis of allergic contact dermatitis.

Perturbation of glutathione status and generation of oxidative stress in mouse skin following application of contact allergenic sesquiterpene lactones and isothiocyanates

1. The sensitizing or non-sensitizing status of selected sesquiterpene lactones and isothiocyanates was confirmed in mouse by open epicutaneous application. 2. Glutathione status of mouse skin was determined 12 h after lactone/isothiocyanate application; glutathione S-transferase activity also was determined 12 h after lactone application. 3. NAD(P)H utilization by rat liver microsomal preparations exposed to the sesquiterpene lactones and isothiocyanates was measured. 4. A correlation was observed between sensitizing status and the ability to perturb glutathione status, to induce glutathione S-transferase activity, and to stimulate NAD(P)H utilization. 5. It was concluded that sensitizing sesquiterpene lactones and isothiocyanates could induce oxidative stress in mouse skin, possibly as a result of their reductive metabolism.

A study of hydrogen peroxide generation by, and antioxidant activity of, Granuflex (DuoDERM) Hydrocolloid Granules and some other hydrogel/hydrocolloid wound management materials

The effect of Granuflex Hydrocolloid Granules (0.01-0.50% w/v) on the rate of proliferation of murine (L929) fibroblasts was examined. The dose-response curve showed a significant (P < 0.02) pro-proliferant effect at 0.05%, and a significant (P < 0.02) antiproliferant effect at 0.50%, mirroring the dose-response curve produced by hydrogen peroxide in the concentration range 10(-9) - 10(-4) mol/l. The antiproliferant effect at 0.20% w/v was abolished by catalase, suggesting that the biological activity of Granuflex was mediated by the in situ generation of hydrogen peroxide. Formation of hydrogen peroxide by Granuflex was confirmed by performing the scopoletin-horseradish peroxidase assay in the presence and absence of catalase. The total concentration of hydrogen peroxide detected was about 8 x 10(-6) mol/l (using 0.5% w/v Granuflex) after 48 h at 37 degrees C. In contrast, when hydrogen peroxide itself was added to L929 cultures, a similar antiproliferant activity was observed at concentrations between 10(-4) and 10(-5) mol/l. These results suggested that Granuflex was undergoing autoxidation in the culture medium, and hence that it might possess antioxidant activity. In assays for antioxidant activity using 1,1-diphenyl-2-picrylhydrazyl (DPPH), Granuflex, and two other hydrocolloid dressings (Comfeel Powder and Bard Absorption Dressing) showed significant ability to reduce DPPH to DPPH2. These three dressings also displayed superoxide scavenging activity in a nitroblue tetrazolium reduction assay. We conclude that, in addition to providing a moist wound-healing environment, Granuflex and certain other hydrocolloids might contribute to the establishment and maintenance of the reducing environment necessary for energy production and hence cell division.(ABSTRACT TRUNCATED AT 250 WORDS)

Toxicity of L-ascorbic acid to L929 fibroblast cultures: relevance to biocompatibility testing of materials for use in wound management

Fibroblast cultures are often used to evaluate materials intended for medical use, cytotoxicity being taken as an indicator of bioincompatibility. Such an approach has previously been taken with ascorbic acid in determining its value in wound healing. We have now reexamined the toxicity of L-ascorbic acid to L929 fibroblast cells in culture. Concentrations of ascorbic acid between 0.5 mM and 11 mM were tested. At concentrations above 2 mM, ascorbic acid was found to inhibit cell proliferation, with cell viability decreasing as the concentration was increased. This effect could be prevented by the addition of either superoxide dismutase or catalase to the culture medium. Assays of glutathione and glutathione disulfide were carried out on 8 day old cultures exposed for 24 h to the same concentrations of ascorbic acid. A dose-related depletion of glutathione occurred whilst glutathione disulfide levels remained essentially constant. Lactate dehydrogenase and glucose-6-phosphate dehydrogenase activities were induced by ascorbic acid at all concentrations tested but the ratio of NADP to NADPH nevertheless increased as the concentration of ascorbic acid increased. Finally, ATP in cells from 8-day-old cultures became depleted in the presence of ascorbic acid at concentrations in excess of about 5 mM when assayed after 24 h incubation. These biochemical changes and the concomitant cytostatic/cytotoxic effects may be ascribed to the reactive oxygen species produced by the autoxidation of ascorbic acid in the culture medium. Ascorbic acid breakdown products appeared not to be directly involved. In addition, our results suggested that superoxide acted cooperatively with hydroxyl to elicit these effects on the fibroblasts. It is evident from this study that the microenvironment surrounding fibroblasts in culture may differ fundamentally from that surrounding fibroblasts in a healing wound, making it impossible to extrapolate directly to an in vivo situation and hence to make any recommendations from these results concerning the use of ascorbic acid in wound healing.

Biochemical responses of skin to allergenic and non-allergenic nitrohalobenzenes. Evidence that an NADPH-dependent reductase in skin may act as a prohapten-activating enzyme

Using a selection of 'classic' haptens (dinitrohalobenzenes and picryl chloride) and related non-sensitizing analogous, we examined changes in levels of glutathione (GSH) and glutathione disulphide (GSSG) in mouse skin 12 h after their epicutaneous application. We observed that elevation of GSSG levels and/or depletion of GSH levels correlated well with contact allergenic potential. Non-sensitizing analogous failed to perturb GSH/GSSG status. In vitro assays using mouse skin and rat liver microsomal preparations indicated that only the allergenic nitrohalobenzenes initiated NADPH-dependent oxygen utilization, with the activity falling off in the order picryl chloride >> DNIB > DNBB > DNCB > DNFB. In addition, an examination of the colour of mouse skin homogenates ex vivo after application of the dinitrohalobenzenes showed significant yellowing (consistent with aromatic nucleophilic substitution) only with DNFB. Our results indicate that, while an aromatic nucleophilic substitution reaction with skin protein can possibly account for the allergenicity of DNFB, it does not seem to occur with DNCB, DNBB or DNIB. These may instead behave mainly as prohaptens which are activated enzymically by NADPH-dependent reductase(s) within the skin, with the concomitant generation of superoxide and hydrogen peroxide, to form potentially protein-reactive free radical and other metabolites. Picryl chloride appears capable of both conjugating directly with proteins by aromatic nucleophilic substitution and undergoing NADPH-dependent metabolism to other potentially protein-reactive metabolites.

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.

Possible origin of the skin sensitization potential of isoeugenol and related compounds. (I). Preliminary studies of potential reaction mechanisms

Although many simple chemicals can give rise to the phenomenon of allergic contact dermatitis, it is rare that the mechanism of reaction between the chemical hapten and skin protein is known. A further complication is that metabolic processes may produce substantial changes to a chemical penetrating skin. Thus the skin contactant may be regarded as a prohapten which will give rise to the true hapten in vivo. In this study, the possible reaction mechanisms for a number of related simple aromatic chemicals have been investigated. The approach taken was to evaluate potential reaction mechanisms by assessing the degree to which chemicals could cross-react in sensitization tests. By careful choice of chemicals, it was then possible to confirm (or reject) options. Using this approach, a number of reaction schemes were investigated for eugenol, isoeugenol, dihydroeugenol, anethole and several related chemicals. The patterns of sensitization obtained and the cross-reactions observed indicated clearly that electrophile/nucleophile interactions were unlikely to provide a complete explanation of the sensitization processes. Eugenol and isoeugenol are not mutually cross-reactive, yet both cross-reacted with dihydroeugenol. Examination of the possible reaction mechanisms allows the speculation that eugenol reacts in part via a phenolic radical mechanism, whilst isoeugenol reacts largely via formation of an orthoquinone. Both reaction mechanisms are proposed for dihydroeugenol.

Further investigation of the prohapten concept: reactions to benzene derivatives in man

p-Phenylenediamine (PPDA) is a strong contact sensitizer which is included in the standard patch test tray and which can also act as an indicator of allergy to related substances by virtue of cross-reactions. In a previous study, the pattern of cross-reactions between PPDA and related substances was investigated in the guinea pig to evaluate the prohapten concept. The results provided some support for this concept, but also indicated that a number of reactive intermediates might be behaving as haptens. This work has now been extended to an examination of the prohapten concept in man in PPDA-allergic subjects. These subjects were tested with 7 substituted benzenes, plus PPDA. Of these, the 1,4-substituted benzenes hydroquinone, Metol, PPDA and p-aminophenol are all capable theoretically of giving rise to benzoquinone by oxidation (after demethylation in the case of Metol). However, as had been the case in the guinea pig, only a limited degree of cross-reaction was observed. Only one of the subjects allergic to PPDA gave a clearly positive allergic reaction to benzoquinone. The data provided only limited support for the prohapten concept in terms of benzoquinone as the ultimate hapten for a range of 1,4-substituted benzenes. As indicated in the guinea pig, a range of reaction intermediates or indeed other oxidation products may be involved. So, for each molecule, the sensitizing activity and potential to give rise to cross-reactions may depend on the balance between routes of skin metabolism.

Propolis allergy (IV). Studies with further sensitizers from propolis and constituents common to propolis, poplar buds and balsam of Peru

26 different compounds have been investigated experimentally for their sensitizing capacity in guinea pigs. 19 of these occur in propolis as well as in poplar bud exudates, and 14 of them are also found in balsam of Peru. 4 caffeates and benzyl isoferulate were found to be strong sensitizers. 7 compounds were moderate, and 13 compounds showed only weak sensitizing potency. Methyl cinnamate was negative. Patch tests in 11 propolis-sensitive patients once more revealed 3-methyl-2-butenyl caffeate and phenylethyl caffeate as the major sensitizers. In addition to the 8 compounds already known to occur in propolis as well as in balsam of Peru, we detected 5 further substances that both materials have in common. Among these, benzyl isoferulate is considered a noteworthy sensitizer. Coniferyl benzoate, which was shown to be a moderate sensitizer, is present in fresh samples of balsam of Peru, while in propolis it has been detected only once so far. The flavonoid aglycones occurring in poplar bud exudates, and hence also in propolis, are weak sensitizers which play only a minor role in propolis hypersensitivity.