Gene expression profiling of skin and draining lymph nodes of rats affected with cutaneous contact hypersensitivity

Lack of ApoA-I in ApoEKO Mice Causes Skin Xanthomas, Worsening of Inflammation, and Increased Coronary Atherosclerosis in the Absence of Hyperlipidemia

Background:

HDL (high-density lipoprotein) and its major protein component, apoA-I (apolipoprotein A-I), play a unique role in cholesterol homeostasis and immunity. ApoA-I deficiency in hyperlipidemic, atheroprone mice was shown to drive cholesterol accumulation and inflammatory cell activation/proliferation. The present study was aimed at investigating the impact of apoA-I deficiency on lipid deposition and local/systemic inflammation in normolipidemic conditions.

Methods:

ApoE deficient mice, apoE/apoA-I double deficient (DKO) mice, DKO mice overexpressing human apoA-I, and C57Bl/6J control mice were fed normal laboratory diet until 30 weeks of age. Plasma lipids were quantified, atherosclerosis development at the aortic sinus and coronary arteries was measured, skin ultrastructure was evaluated by electron microscopy. Blood and lymphoid organs were characterized through histological, immunocytofluorimetric, and whole transcriptome analyses.

Results:

DKO were characterized by almost complete HDL deficiency and by plasma total cholesterol levels comparable to control mice. Only DKO showed xanthoma formation and severe inflammation in the skin-draining lymph nodes, whose transcriptome analysis revealed a dramatic impairment in energy metabolism and fatty acid oxidation pathways. An increased presence of CD4⁺ T effector memory cells was detected in blood, spleen, and skin-draining lymph nodes of DKO. A worsening of atherosclerosis at the aortic sinus and coronary arteries was also observed in DKO versus apoE deficient. Human apoA-I overexpression in the DKO background was able to rescue the skin phenotype and halt atherosclerosis development.

Conclusions:

HDL deficiency, in the absence of hyperlipidemia, is associated with severe alterations of skin morphology, aortic and coronary atherosclerosis, local and systemic inflammation.

Integrative transcriptome analysis deciphers mechanisms of nickel contact dermatitis

Background

Nickel‐induced allergic contact dermatitis (nACD) remains a major occupational skin disorder, significantly impacting the quality of life of suffering patients. Complex cellular compositional changes and associated immunological pathways are partly resolved in humans; thus, the impact of nACD on human skin needs to be further elucidated.

Methods

To decipher involved immunological players and pathways, human skin biopsies were taken at 0, 2, 48, and 96 hours after nickel patch test in six nickel‐allergic patients. Gene expression profiles were analyzed via microarray.

Results

Leukocyte deconvolution of nACD‐affected skin identified major leukocyte compositional changes at 48 and 96 hours, including natural killer (NK) cells, macrophage polarization, and T‐cell immunity. Gene set enrichment analysis mirrored cellular‐linked functional pathways enriched over time. NK cell infiltration and cytotoxic pathways were uniquely found in nACD‐affected skin compared to sodium lauryl sulfate–induced irritant skin reactions.

Conclusion

These results highlight key immunological leukocyte subsets as well as associated pathways in nACD, providing insights into pathophysiology with the potential to unravel novel therapeutic targets.

Topical Plant Polyphenols Prevent Type I Interferon Signaling in the Skin and Suppress Contact Hypersensitivity

Human keratinocytes were recently shown to respond to anti-EGFR (epidermal growth factor receptor) drugs with activation of an interferon-κ-driven autocrine loop, leading to enhanced expression of innate antiviral effectors and of the pro-inflammatory chemokines CXCL10 (C-X-C motif chemokine 10) and CCL2 (C-C motif ligand 2). Here we showed active type I interferon signaling in the skin lesions of cancer patients undergoing treatment with the anti-EGFR drug cetuximab. Strong nuclear positivity for Interferon Regulatory Factor 1 and phosphorylated Signal Transducer and Activator of Transcription 1, enhanced interferon-κ expression and CXCL10 was associated to the epidermal compartment. Notably, 50 micromolar resveratrol and quercetin fully suppressed the low constitutive levels of type I interferon signaling and prevented its activation by the anti-EGFR cetuximab or gefitinib in cultured keratinocytes. In sensitized mice undergoing DNFB (2,4-dinitro-1-fluorobenzene)-induced contact hypersensitivity, local administration of gefitinib prior to elicitation further amplified hapten-induced type I interferon activation, tissue edema, and infiltration by T cells, whereas resveratrol or quercetin suppressed this inflammatory cascade. Overall, these data suggest that topical application of resveratrol or quercetin could be potentially effective in preventing pathological conditions due to overactivation of type I IFN (interferon)-driven circuits in the skin, including the inflammatory manifestations of anti-EGFR drug-induced skin-targeted toxicity.

Pathomechanisms of Contact Sensitization

Contact sensitization is the initial process involved in the development of an allergic reaction to xenobiotic environmental substances. Here, we briefly describe the differences between irritant and allergic contact dermatitis. Then, we highlight the essential steps involved in the development of an ACD reaction, i.e., the protein binding of haptens, genetic factors influencing the penetration of sensitizers into the skin, the different mechanisms driving the initial development of an inflammatory cytokine micromilieu enabling the full maturation of dendritic cells, the role of pre- and pro-haptens, antigen presentation and T cell activation via MHC and CD1 molecules, dendritic cell (DC) migration, and potential LC contribution as well as the different T cell subsets involved in ACD. In addition, we discuss the latest publications regarding factors that might influence the sensitizing potential such as repeated sensitizer application, penetration enhancers, humidity of the skin, microbiota, Tregs, and phthalates. Last but not least, we briefly touch upon novel targets for drug development that might serve as treatment options for ACD.

Roles of alternatively activated M2 macrophages in allergic contact dermatitis

Alternatively activated macrophages (M2 macrophages) play key roles in the suppression of Th1 cell responses and the orchestration of tissue repair. However, recent studies have shown that M2 macrophages have potentials to produce high levels of proinflammatory cytokines such as IL-1β, IL-6, and TNF-α, suggesting that M2 macrophages may exacerbate inflammation in some settings. In this regard, we have recently shown that large numbers of M2 macrophages accumulate in the sites of hapten-induced contact hypersensitivity (CHS), an animal model of allergic contact dermatitis, and that M2 macrophages exacerbate hapten-induced CHS by producing matrix metalloproteinase 12 (MMP12). We have also shown that suppressor of cytokine signaling-3 (SOCS3), a member of SOCS family proteins that are cytokine-inducible negative regulators of the JAK/STAT signaling pathways, is highly and preferentially expressed in M2 macrophages in hapten-induced CHS and that SOCS3 expressed in M2 macrophages is involved in the attenuation of CHS by suppressing MMP12 production. These findings underscore the importance of M2 macrophage-derived MMP12 in the development of CHS, and suggest that inhibition of M2 macrophages or MMP12 could be a potential therapeutic strategy for the treatment of allergic contact dermatitis.

A nucleic acid-based medication for allergic skin diseases

Among allergic skin diseases, atopic dermatitis is the most difficult to cure. In the majority of patients, atopic dermatitis can be easily controlled by treatment based on three therapeutic approaches: avoidance of precipitating factors, skin care, and medication. In some adult patients, however, severe atopic dermatitis is refractory to treatment, and no fundamental effective treatment modality has yet been established for such cases. Chronic contact dermatitis without an identified causative hapten is also considered an allergic skin disease that is difficult to cure. Topical nucleic acid-based medications are currently being applied clinically, and an ointment containing nuclear factor-κB decoy oligodeoxynucleotides (hereafter referred to as Decoy) has reached clinical trials. In addition, synthetic double-stranded DNA with high affinity for signal transducers and activators of transcription 6 (STAT6) introduced in vivo as a decoy cis element to bind the transcriptional factor and block the activated gene that contributes to the onset and progression of atopic dermatitis functions as an effective therapeutic agent. We also introduce another STAT1 decoy treatment, cytosine-phosphate-guanine-ODN or STAT6 small interfering RNA therapy, for allergic skin diseases.

Role of oxidative stress in chemical allergens induced skin cells activation

Allergic contact dermatitis (ACD) is an important occupational and environmental disease caused by topical exposure to chemical allergens. It describes the adverse effects that may results when exposure to a chemical elicits a T cell-mediated inflammatory skin disease. The ability of contact sensitizers to induce the oxidative stress pathway in keratinocytes and dendritic cells has been confirmed by several authors. Reactive oxygen species (ROS) can serve as essential second messengers mediating cellular responses resulting in immune cells activation. Oxidative stress may be the starter point, as it leads to the activation of transcription factors and signaling pathways, including NF-kB and p38 MAPK, which leads to the release of cytokines and chemokines. ROS are also involved in the activation of the NLRP3/NALP3 inflammasome, which is required to direct the proteolytic maturation of inflammatory cytokines such as IL-1β and IL-18, which are all integral to the process of dendritic cells mobilization, migration and functional maturation. Moreover, emerging evidence correlates ROS to changes in the constitution of the extracellular microenvironment found to facilitate ACD. The purpose of this review is to provide both conceptual and technical frameworks on the role of oxidative stress in chemical allergy.

Inflammatory and immune mechanisms in contact hypersensitivity (CHS) in rats

Contact hypersensitivity (CHS) is a T-cell-mediated skin inflammatory reaction to cutaneous exposure to small sensitizing chemicals, haptens. Majority of CHS studies were conducted in mice and there is paucity of data in other experimental animals. In this review, after a brief survey of murine CHS, hitherto known characteristics of CHS in rats were presented including inflammatory and immune mechanisms of both sensitization and elicitation phases. Survey of literature of rat CHS is presented, with our data concerning the importance of genetic background both in the induction and in the expression of reaction to dinitrochlorobenzene. The knowledge of CHS in rats, preferred animal in immunopharmacological studies, might help development of immunomodulatory intervention in contact allergy.

Extra domain A-positive fibronectin-positive feedback loops and their association with cutaneous inflammatory disease

Cutaneous inflammation can show Th1 or Th2 predominance, but the precise mechanisms by which such selectivity is determined are unknown. A recent study has demonstrated that Th1 cells, but not Th2 cells, produce an endogenous ligand for Toll-like receptor (TLR) 4, namely extradomain A+ fibronectin containing extra type III domain A (FnEDA+). As TLR4 stimulation leads to production of proinflammatory cytokines that recruit (via altered endothelial adhesion molecule expression and chemokine production) more Th1/Th17 cells, a positive feedback mechanism for Th1/Th17 inflammation exists. We propose that FnEDA+ positive feedback loops are a potential driver of Th1/Th17 inflammation. Conversely, the inflammatory EDA+ fibronectin loop is negatively regulated in atopic dermatitis, Th2 cytokines actively suppress TLR4 expression of Th1 cytokines, and recruited Th2 cells do not produce FnEDA+. In psoriasis, there are multiple FnEDA+ loops, comprising inflammatory, keratinocyte, and autoimmune loops. In allergic contact dermatitis, a single inflammatory loop operates. In atopic dermatitis, the FnEDA+ loop is actively suppressed by Th2 cytokines, and recruited Th2 cells do not "feedback" FnEDA+. We review endogenous ligands for TLR in relation to inflammatory disease, FnEDA+ function, and the potential role for FnEDA+ in psoriasis, allergic contact dermatitis, and atopic dermatitis.

Phenolic substances from Phagnalon rupestre protect against 2,4,6-trinitrochlorobenzene-induced contact hypersensitivity

2-isoprenylhydroquinone-1-glucoside (1), 3,5-dicaffeoylquinic acid (2), and 3,5-dicaffeoylquinic acid methyl ester (3), isolated from Phagnalon rupestre, improved the contact hypersensitivity response to 2,4,6-trinitrochlorobenzene in mice. These phenolics reduced ear swelling and IL-1β content by 50% 24 h after challenge; in addition, 2 inhibited tumor necrosis factor-α by 53%. All three compounds also reduced interleukin-2 content by 50% 72 h after challenge. Both 2 and 3 inhibited metalloproteinase-9 levels in the skin lesions by 66% and 41%, respectively, and lowered cyclooxygenase-2 expression by 44% and 49%, respectively, at 24 h. Moreover, 2 was effective against atopic dermatitis induced by repeated application of 2,4,6-trinitrochlorobenzene; it attenuated edema by over 40% from day 7 and inhibited inflammatory cell infiltration by 44% at day 22. In addition, 1-3 reduced metalloproteinase-9 expression in a dose-dependent manner in macrophages RAW 264.7 stimulated with lipopolysaccharide. Thus, compounds 2 and 3 were found to exhibit a greater activity against contact hypersensitivity than 1.

Genetic factors in contact allergy--review and future goals

The genetics of contact allergy are still only partly understood, despite decades of research; this might be a consequence of inadequately defined phenotypes used in the past. A recommendation is to study an extreme phenotype, namely, polysensitization (sensitization to three or more unrelated allergens). Another approach to unravel the genetics of contact allergy is the study of candidate genes. In this review, we summarize studies on the associations between genetic variation (e.g. single-nucleotide polymorphisms) in certain candidate genes and contact allergy. Polymorphisms and mutations affecting the following proteins were studied: (i) filaggrin; (ii) N-acetyltransferase (NAT) 1 and 2; (iii) glutathione-S-transferase (GST) M and T; (iv) manganese superoxide dismutase; (v) angiotensin-converting enzyme (ACE); (vi) tumour necrosis factor (TNF); and (vii) interleukin-16 (IL-16). The polymorphisms of NAT1, NAT2, GSTM, GSTT, ACE, TNF and IL-16 were shown to be associated with an increased risk of contact allergy. In one of our studies, the increased risk conferred by the TNF and IL-16 polymorphisms was confined to polysensitized individuals. Other relevant candidate genes may be identified by studying diseases related to contact allergy in terms of clinical symptoms, a more general pathology (inflammation), and possibly an overlapping genetic background, such as irritant contact dermatitis.

IL-33 and IL-33 receptors in host defense and diseases

Interleukin-33 (IL-33) is a member of the IL-1 cytokine family, which includes IL-1 and IL-18. IL-33 is considered to be crucial for induction of Th2-type cytokine-associated immune responses such as host defense against nematodes and allergic diseases by inducing production of such Th2-type cytokines as IL-5 and IL-13 by Th2 cells, mast cells, basophils and eosinophils. In addition, IL-33 is involved in the induction of non-Th2-type acute and chronic inflammation as a proinflammatory cytokine, similar to IL-1 and IL-18. In this review, we summarize and discuss the current knowledge regarding the roles of IL-33 and IL-33 receptors in host defense and disease development.

Gene expression profiles and pathways in skin inflammation induced by three different sensitizers and an irritant

It is often difficult to discriminate between chemically induced skin irritation and sensitization due to their similar clinical, pathological, and immunological responses. More information than that currently available from local lymph node assays (LLNAs), such as data from gene expression and pathway analysis, can provide more insightful data than the assay itself for distinguishing skin sensitization from skin irritation. This study investigated the gene expression profiles and pathways in ear skins of mice topically exposed daily for three consecutive days to the known strong contact sensitizer 1-chloro-2,4-dinitrobenzene, the skin contact sensitizer 2-phenyl-4-ethoxymethylene-5-oxazolone, the skin or respiratory sensitizer toluene 2,4-diisocyanate, or to the non-sensitizing irritant croton oil. All the sensitizers induced histological changes in ear tissues similar to those induced by the croton oil. In gene expression microarrays, sensitizers up-regulated 193 genes and down-regulated 61 genes in ear skin following chemical exposure. 13 genes whose expression was affected by more than two-fold by all three of the sensitizers, but not by the irritant, were selected by microarray analysis. Microarray and real-time RT-PCR analyses revealed that, of these genes, the allergic inflammation-related genes Oasl2 and Zbp1 were up-regulated in skin inflammation by the sensitizers. In gene expression pathway analysis of all the sensitizers and the croton oil, the top functions of the 48 genes were related to cytokine and cytokine receptors interactions, and only two genes (Cxcl9 and Cxcl10) were specific to skin sensitizer-induced skin inflammation. Thus, although contact sensitizer-induced skin inflammation is similar to irritant-induced responses in terms of histological changes and gene expression profiles, the regulation of allergic inflammation-related gene transcripts, such as those of Oasl2 and Zbp1 or Cxcl9 and Cxcl10, could help to discriminate skin sensitization from chemically induced skin inflammation.

Intracellular expression of cytokines and granzyme B in auricular lymph nodes draining skin exposed to irritants and sensitizers

The murine local lymph node assay (LLNA) has been extensively utilized to evaluate sensitizing chemicals. However, there have been some concerns that its use to discriminate between classes of chemicals is minimal. It is thus desirable to identify better or alternative immune endpoints with in LLNA itself. Here, we evaluated the protein and/or mRNA levels of cytokines and granzyme B (GzmB), a cytotoxic lymphocyte product, to discriminate between sensitizers and irritants and to characterize the chemical sensitizers when used as supplemental indicators in LLNA endpoints. For this, CBA/N mice were topically treated daily with a well-known chemical sensitizer such as a strong contact sensitizer 1-chloro-2,4-dinitrobenzene (DNCB), a skin contact sensitizer 2-phenyl-4-ethoxymethylene-5-oxazolone (OXA), and a skin or respiratory sensitizer toluene 2,4-diisocyanate (TDI), and the non-sensitizing irritants, croton oil (CRO) and nonanoic acid (NA), for 3 consecutive days. The protein and/or mRNA levels in auricular lymph nodes draining the ear skin were then analyzed by real-time RT-PCR and immunoassay. The sensitizers, but not the irritants, evoked pronounced interleukin (IL)-2, IL-3 and IL-4 or interferon (IFN)-gamma. Significantly, different sensitizers evoked different cytokine patterns of IL-4 and IFN-gamma, as DNCB strongly up-regulated both IFN-gamma and IL-4, OXA up-regulated IFN-gamma strongly but IL-4 weakly, and TDI up-regulated IL-4 strongly but IFN-gamma weakly. The sensitizers also strongly up-regulated GzmB mRNA, while the irritants had a much weaker effect. Thus, these cytokines and GzmB mRNA may be useful as additional endpoints for discriminating between irritants and sensitizers or contact and respiratory sensitizers in the LLNA.

Sensitive gene expression profiling of human T cell subsets reveals parallel post-thymic differentiation for CD4+ and CD8+ lineages

The differentiation of CD4(+) or CD8(+) T cells following priming of naive cells is central in the establishment of the immune response against pathogens or tumors. However, our understanding of this complex process and the significance of the multiple subsets of differentiation remains controversial. Gene expression profiling has opened new directions of investigation in immunobiology. Nonetheless, the need for substantial amount of biological material often limits its application range. In this study, we have developed procedures to perform microarray analysis on amplified cDNA from low numbers of cells, including primary T lymphocytes, and applied this technology to the study of CD4 and CD8 lineage differentiation. Gene expression profiling was performed on samples of 1000 cells from 10 different subpopulations, defining the major stages of post-thymic CD4(+) or CD8(+) T cell differentiation. Surprisingly, our data revealed that while CD4(+) and CD8(+) T cell gene expression programs diverge at early stages of differentiation, they become increasingly similar as cells reach a late differentiation stage. This suggests that functional heterogeneity between Ag experienced CD4(+) and CD8(+) T cells is more likely to be located early during post-thymic differentiation, and that late stages of differentiation may represent a common end in the development of T-lymphocytes.

The contact allergen dinitrochlorobenzene (DNCB) and respiratory allergy in the Th2-prone Brown Norway rat

All LMW respiratory allergens known to date can also induce skin allergy in test animals. The question here was if in turn skin allergens can induce allergy in the respiratory tract. Respiratory allergy was tested in Th2-prone Brown Norway (BN) rats by dermal sensitization with the contact allergen dinitrochlorobenzene (DNCB; 1%, day 0; 0.5%, day 7) and a head/nose-only inhalation challenge of 27mg/m3 of DNCB (15 min, day 21), using a protocol that successfully identified chemical respiratory allergens. Skin allergy to DNCB was examined in BN rats and Th1-prone Wistar rats in a local lymph node assay followed by a topical patch challenge of 0.1% DNCB. Sensitization of BN rats via the skin induced DNCB-specific IgG in serum, but not in all animals, and an increased number of CD4+ cells in the lung parenchyma. Subsequent inhalation challenge with DNCB did not provoke apneas or allergic inflammation (signs of respiratory allergy) in the BN rats. However, microarray analysis of mRNA isolated from the lung revealed upregulation of the genes for Ccl2 (MCP-1), Ccl4 (MIP-1beta), Ccl7 and Ccl17. Skin challenge induced considerably less skin irritation and allergic dermatitis in the BN rat than in the Wistar rat. In conclusion, the Th2-prone BN rat appeared less sensitive to DNCB than the Wistar rat; nevertheless, DNCB induced allergic inflammation in the skin of BN rats but even a relatively high challenge concentration did not induce allergy in the respiratory tract, although genes associated with allergy were upregulated in lung tissue.

Signal transducer and activator of transcription 1 decoy oligodeoxynucleotide suppression of contact hypersensitivity

BACKGROUND

Cytokines play a pivotal role in allergy development through activating signaling mechanisms, such as the Janus kinase/signal transducer and activator of transcription (STAT) pathway, which controls the expression of numerous proinflammatory genes.

OBJECTIVE

In comparison with 2 different corticosteroids and a calcineurin inhibitor, the efficacy of a STAT1 decoy oligodeoxynucleotide (dODN)-containing ointment on hapten-induced contact hypersensitivity was examined in 3 different animal models.

METHODS

After sensitization, the test compounds were administered before hapten challenge, after hapten challenge, or both to different sites of the animal skin. Subsequent erythema and edema formation was scored macroscopically, microscopically, or by a shift in ear weight. Biopsy specimens were taken and processed for histopathology, immunohistochemistry, and real-time PCR analyses.

RESULTS

Treatment with the STAT1 dODN but not the corresponding control ODN markedly improved the clinical signs of inflammation in all 3 animal models in a dose-related manner. In guinea pig skin this was accompanied by a distinct decrease in leukocyte infiltration into the dermis after 24 hours. In addition, expression of CD40, IFN-gamma, IL-1beta, IL-8, IL-12, and TNF-alpha was strongly attenuated. The dODN was equally effective in the domestic pig model when administered therapeutically, and its preventive effect in the mouse model lasted for more than 48 hours.

CONCLUSIONS

Altogether, treatment with the dODN proved to be at least as effective as treatment with the reference compounds.

Gene Expression Time Course in the Human Skin during Elicitation of Allergic Contact Dermatitis

Genes involved in the inflammatory response resulting in allergic contact dermatitis (ACD) are only partly known. In this study, we introduce the use of high-density oligonucleotide arrays for gene expression profiling in human skin during the elicitation of ACD. Skin biopsies from normal and nickel-exposed skin were obtained from seven nickel-allergic patients and five nonallergic controls at four different time points during elicitation of eczema. Each gene expression profile was analyzed by hybridization to high-density oligonucleotide arrays. Cluster analysis of 74 genes found to be differentially expressed in the patients over time revealed that the patient samples may be categorized into two groups: an early time-point group (no clinical reaction) and a late time-point group (clinical reaction). Bioinformatics analyses unraveled the potential involvement of signal transducers and activator of transcription and small/mothers against decepentaplegic (SMAD) transcription factors in the late time-point gene expression patterns. Concerning specific genes, the homeostatic chemokine CCL19 was unexpectedly found to be highly expressed in cells scattered in the deep dermis of the late time-point samples. Taken together, these findings suggest hitherto unknown roles of SMAD transcription factors and of CCL19 in the elicitation phase of ACD.

Tissue inhibitors of matrix metalloproteinase-1 levels are increased in serum of patients with allergic contact dermatitis

Allergic contact dermatitis (ACD) is an antigen-specific, T-cell-mediated skin inflammatory disease. Matrix metalloproteinases (MMPs) and their tissue inhibitors of matrix metalloproteinases (TIMPs) play a role in degradation of extracellular matrix and subsequent tissue remodelling during inflammatory process. The objective of this study was to examine a possible role of TIMP-1 and MMP-9 in the pathogenesis of ACD. The serum levels of MMP-9 and TIMP-1 have been measured using enzyme-linked immunosorbent assay in patients with disseminated ACD during exacerbation of skin lesions and the remission stage (n= 20) and were compared with healthy subjects (n= 20). The mean serum levels of TIMP-1 were significantly higher in patients with ACD than in control group (42.8 +/- 4.9 ng/ml). This difference was more prominent in patients with ACD during remission (69.01 +/- 6.99 ng/ml, P < 0.0001) than in patients with exacerbation of disease (46.8 +/- 3.6 ng/ml, P= 0.0054). Mean values of serum MMP-9 did not differ significantly between patients with ACD, both in the acute and in the remission stage, compared with healthy persons (P= 0.76 and P= 0.29, respectively). TIMP-1 might be involved in pathogenesis of ACD. It seems that moderately increased levels of TIMP-1 could reflect degree of activity of skin inflammation, whereas markedly increased levels could contribute to the maintenance of the remission of disease.

Effects of plant alkylphenols on cytokine production, tyrosine nitration and inflammatory damage in the efferent phase of contact hypersensitivity

BACKGROUND AND PURPOSE

The phenolic compounds isoprenylhydroquinone glucoside (IHG), 3,5-dicaffeoylquinic acid (DCA), and its methyl ester (DCE) have previously been shown to inhibit both contact hypersensitivity (CHS) and peroxynitrite reactivity. The present work seeks to establish a relationship between the anti-inflammatory effect and the release of cytokines and tyrosine nitration in skin.

EXPERIMENTAL APPROACH

Murine CHS was developed by means of sensitization and challenge with dinitrofluorobenzene (DNFB) or oxazolone. Ear swelling was measured 24 and 96 h after challenge. Interleukin (IL)-1beta, IL-4, and tumour necrosis factor (TNF)-alpha were measured by ELISA; and the expression of inducible nitric oxide synthase (iNOS) was detected by Western blotting. Histological samples were analysed for 3-nitrotyrosine.

KEY RESULTS

In the oxazolone model, DCE reduced the 24 h swelling by 54% whereas the effect of DCA was lower (40% inhibition). All the test compounds reduced IL-1beta values 24 h after challenge with DNFB or oxazolone, DCE particularly inhibited IL-4 production (74% and 78%, respectively; P<0.01). Tyrosine nitration was also markedly reduced by DCE. In general, the test compounds limited the presence of polymorphonuclear (PMN) leukocytes in the skin.

CONCLUSIONS AND IMPLICATIONS

These results suggest that the effect of 3,5-dicaffeoylquinic esters on CHS is associated with a decrease in the production of interleukins, but not with the inhibition of iNOS expression. Moreover, esterification of the carboxyl group at C-1 enhanced protection against tyrosine nitration in the skin.