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

Beyond Avoidance: Advanced Therapies for Contact Dermatitis

Contact dermatitis (CD) is a common and burdensome condition divided into irritant contact dermatitis and allergic contact dermatitis. Treatment relies on accurate diagnosis and identification of the trigger, because definitive treatment is irritant or allergen avoidance. However, avoidance is not always possible, such as when the patient is reacting to a necessary medical device, when the trigger is integral to the patient's occupation, and when avoidance is practically untenable. In these cases, treatment is particularly challenging, especially because the literature on treatments in this clinical scenario is limited. In addition, CD has a complex pathophysiology that varies according to the trigger type, leading to variable treatment efficacy. This article reviews the current literature on treatments for CD with a focus on treatments when trigger avoidance is not feasible.

Allergic contact dermatitis: From pathophysiology to development of new preventive strategies

As the body's first line of defense, the skin is the organ most frequently exposed to chemicals present in personal hygiene products, household products, or materials used in the work environment. In this context, skin disorders account for more than 40 % of all occupational and work-related diseases, constituting a significant public health burden. Among skin disorders, allergic contact dermatitis (ACD) is the most prevalent occupational disease and the most common form of immunotoxicity in humans. ACD is a T-cell-mediated skin inflammation resulting from the priming and expansion of allergen-specific CD4⁺ and CD8⁺ T cells. The clinical condition is characterized by local skin rash, itchiness, redness, swelling, and lesions, being mainly diagnosed by the patch test. Upon ACD diagnosis, avoiding the exposure to the triggering allergen is the mainstay of treatment to prevent future flares. In cases where avoidance is not possible, the use of a standard of care interim treatments such as steroid creams or ointments, barrier creams, and moisturizers are strongly recommended to alleviate symptoms. In this review, we sought to provide the reader with an overview of the pathophysiology of ACD as well as the currently available pharmacological treatment options. Furthermore, a comprehensive outline of several preventive strategies is also provided.

The role of the antioxidant ascorbic acid in the elicitation of contact allergic reactions to p-phenylenediamine

BACKGROUND

An allergic contact reaction is accompanied by high oxidative stress in the skin. Pretreatment of the skin with antioxidative substances could reduce the elicitation reaction.

OBJECTIVES

To investigate, in a proof-of-principle study, whether pretreatment of the skin with the antioxidant ascorbic acid reduces the elicitation reaction to a p-phenylenediamine (PPD)-containing hair dye in sensitized subjects.

METHODS

Twelve subjects with contact allergy to PPD, a documented skin reaction to a hair dye simulation exposure model and a history of hair dye-related skin complaints were included in this study. Skin areas on the forearms were, in a left versus right design, exposed to an emulsion with ascorbic acid and an emulsion without ascorbic acid, and then to a 2% PPD-containing hair dye testing formulation. In addition, control areas were exposed to the emulsions and to the PPD-containing hair dye formulation without pretreatment. Skin reactions were graded on day (D)2 and D3.

RESULTS

Pretreatment with ascorbic acid emulsion resulted in a reduction in the elicitation reaction in 7 of 12 subjects at D3 (p = 0.046). No statistically significant difference was observed at D2.

CONCLUSIONS

Pretreatment of the skin with the antioxidant ascorbic acid had an attenuating effect on the elicitation reaction to PPD in sensitized individuals.

Differential regulation of free radicals (reactive oxygen and nitrogen species) by contact allergens and irritants in human keratinocyte cell line

Immune responses to chemicals resulting in sensitization and the appearance of allergic responses following subsequent exposures are dependent upon activation of T lymphocytes. On the contrary, irritant responses are independent of immune response. The aim of this project was to identify the differential signaling cascade operated in allergic and irritant contact dermatitis. Recently, we have shown that keratinocyte cell line A431 can function as an antigen presenting cell (APC) and hence can be used as a model to differentiate between an allergen and irritant molecule. Allergen- and irritant-induced regulation of reactive oxygen species (ROS) and nitric oxide (NO) has been explored. Irritants induce release of ROS even at noncytotoxic concentration. ROS generation by allergens was not detected at nontoxic concentration but as the concentration was increased to a toxic dose there was a drastic increase in the ROS level compared to the untreated cells. Hence, the regulation of ROS is not significant in allergic responses but important in irritant responses. The major difference exists in the fact that the source of ROS for irritants is mitochondria, while that of allergens is mostly cytosolic. Antioxidant-induced protection from irritant-induced cell death has also been demonstrated. NO level was found to increase by allergens and irritants in a concentration-dependent manner. Hence, the regulation of ROS and NO can be used as important mediators in contact allergic and irritant dermatitis.

Dissolution of cemented carbide powders in artificial sweat: implications for cobalt sensitization and contact dermatitis

Skin exposure to cobalt-containing materials can cause systemic immune sensitization and upon repeat contact, elicitation of allergic contact dermatitis (ACD). Data on cobalt dissolution rates are needed to calculate uptake through skin and for development of models to understand risk of sensitization or dermatitis. The purpose of this research was to measure the dissolution kinetics of feedstock and process-sampled powders encountered in the production of hard metal alloys using artificial sweat. The physicochemical properties of each material were characterized prior to evaluation of dissolution behavior. Variations in artificial sweat solvent pH and chemistry were used to understand critical factors in dissolution. Dissolution of cobalt, tungsten, and tungsten carbide was often biphasic with the initial rapid phase being up to three orders of magnitude faster than the latter long-term phase. Artificial sweat pH did not influence dissolution of cobalt or tungsten carbide. Solvent composition had little influence on observed dissolution rates; however, vitamin E suppressed the dissolution of cobalt and tungsten carbide from sintered particles obtained from a chamfer grinder. There was no effect of particle size on dissolution of feedstock cobalt, tungsten, tungsten carbide, and admixture powders. Particle physicochemical properties influenced observed dissolution rates with more cobalt and tungsten carbide dissolving from chamfer grinder particles compared to the feedstock powders or admixture powder. Calculations using the observed dissolution rates revealed that skin exposure concentrations were similar to concentrations known to induce cobalt sensitization and elicit ACD. Observed dissolution rates for cobalt in artificial sweat indicate that dermal uptake may be sufficient to induce cobalt sensitization and allergic dermatitis.

In vivo skin irritation potential of a Castanea sativa (Chestnut) leaf extract, a putative natural antioxidant for topical application

Topical application of natural antioxidants has proven to be effective in protecting the skin against ultraviolet-mediated oxidative damage and provides a straightforward way to strengthen the endogenous protection system. However, natural products can provoke skin adverse effects, such as allergic and irritant contact dermatitis. Skin irritation potential of Castanea sativa leaf ethanol:water (7:3) extract was investigated by performing an in vivo patch test in 20 volunteers. Before performing the irritation test, the selection of the solvent and extraction method was guided by the 1,1-diphenyl-2-picryl hydrazyl (DPPH) free radical scavenging test and polyphenols extraction (measured by the Folin Ciocalteu assay). Iron-chelating activity and the phenolic composition (high performance liquid chromatography/diode array detection) were evaluated for the extract obtained under optimized conditions. The extraction method adopted consisted in 5 short extractions (10 min.) with ethanol:water (7:3), performed at 40 degrees. The IC(50) found for the iron chelation and DPPH scavenging assays were 132.94 +/- 9.72 and 12.58 +/- 0.54 microg/ml (mean +/- S.E.M.), respectively. The total phenolic content was found to be 283.8 +/- 8.74 mg GAE/g extract (mean +/- S.E.M.). Five phenolic compounds were identified in the extract, namely, chlorogenic acid, ellagic acid, rutin, isoquercitrin and hyperoside. The patch test carried out showed that, with respect to irritant effects, this extract can be regarded as safe for topical application.

Vitamina C

Vitamin C or ascorbic acid is a hydrosoluble vitamin derived from glucose metabolism. It acts as a reductor agent required for synthesis of collagen fibers through hydroxylation of proline and lysine. It also protects the body against damage caused by the free radicals. Humans cannot synthesize ascorbic acid as they lack an enzyme called gulonolactone oxidase. Concentrations in plasma and leukocytes reflect the levels of the diet and body deposits respectively of this vitamin. Among foods with high vitamin C levels are tomatoes, potatoes, and citrus fruits such as limes, oranges and lemons. The current recommendation of daily intake of vitamin C is 90 mg/d for men and 75 mg/d for women. Patients with chronic diseases such as cancer or diabetes or those who smoke need higher doses in their usual diet. Ascorbic acid deficiency gives rise to the appearance of scurvy. This disease is rarely seen in developed countries. The symptoms develop with plasma levels below 0.15 mg/dL. Scurvy is characterized by the presence of weakness, joint pain or skin lesions in form of petechias, gum bleeding, ease of developing bruises or delay in wound healing. The most characteristic skin manifestations are purpuric perifollicular hyperkeratotic papules and the presence of kinky hair.

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.

The antioxidant potential of Sutherlandia frutescens

One of the best-known multi-purpose medicinal plants in Southern Africa, Sutherlandia frutescens subsp. microphylla (family: Fabaceae/Leguminosa), is used for a wide range of conditions, including cancer, viral diseases and inflammatory conditions. Little scientific data has been documented on the mechanism by which Sutherlandia frutescens acts on the immune system. Phagocyte derived reactive oxygen species, such as hydrogen peroxide and superoxide radicals, are responsible for the pathogenesis of various inflammatory conditions. Anti-inflammatory properties of various medicinal-plant extracts have been explained, at least in part, by their antioxidant activities. We investigated the effects of a hot water extract of Sutherlandia frutescens on both luminol and lucigenin enhanced chemiluminescence of neutrophils stimulated with L-formyl-L-methionyl-L-leucyl-L-phenylalanine (FMLP) as well as its superoxide and hydrogen peroxide scavenging properties in a cell free system. The results indicate that Sutherlandia frutescens extract possesses superoxide as well as hydrogen peroxide scavenging activities at concentrations as low as 10 microg/ml, which could account for some of the anti-inflammatory properties that have been described.

Structure elucidation, synthesis, and contact allergenic activity of a major hydroperoxide formed at autoxidation of the ethoxylated surfactant C12E5

Ethoxylated alcohols, widely used as surfactants, are known to be susceptible to oxidation when exposed to air. At autoxidation, a complex mixture is formed, in which alkyl poly(ethylene glycol) aldehydes, alkyl poly(ethylene glycol) formates, hydroxyaldehydes, and formaldehyde have previously been identified. These compounds are all secondary oxidation products, some of which have been shown to be skin sensitizers and irritants. The primary oxidation products from ethoxylated alcohols are described in the literature as peroxides and hydroperoxides, but their structures have not been elucidated more closely. Peroxides and hydroperoxides are usually reactive species and can be suspected to be biologically active as skin sensitizers and irritants. In the present investigation, we studied the autoxidation of the pure ethoxylated alcohol pentaethylene glycol mono-n-dodecyl ether (C(12)E(5)), using NMR and HPLC-MS. On the basis of experience from previous studies on a small model compound, diethyleneglycol monoethyl ether (C(2)E(2)), the hydroperoxide expected to be found in the highest amount in autoxidized C(12)E(5) was synthesized and used as a reference substance in the analyses. This same hydroperoxide, 16-hydroperoxy-3,6,9,12,15-pentaoxaheptacosan-1-ol, was identified in the autoxidation mixture of C(12)E(5), and its sensitizing capacity was determined. It was found to be a moderate allergen in experimental sensitization studies in guinea pigs. Our data further indicate the presence of at least three additional hydroperoxides in the autoxidation mixture of C(12)E(5), one of which was identified as 1-hydroperoxy-3,6,9,12,15-pentaoxaheptacosan-1-ol. The results accentuate the importance of controlling the storage, transportation, and handling conditions of ethoxylated surfactants, to avoid the formation of allergenic and skin irritant oxidation products.