Hyperoside as a UV Photoprotective or Photostimulating Compound-Evaluation of the Effect of UV Radiation with Selected UV-Absorbing Organic Compounds on Skin Cells.

Ultraviolet (UV) radiation is a non-ionizing radiation, which has a cytotoxic potential, and it is therefore necessary to protect against it. Human skin is exposed to the longer-wavelength components of UV radiation (UVA and UVB) from the sun. In the present paper, we focused on the study of eight organic UV-absorbing compounds: astragalin, beta-carotene, 2,4-dihydroxybenzophenone, 2-hydroxy-4-methoxybenzophenone, hyperoside, 3-(4-methylbenzylidene)camphor, pachypodol, and trans-urocanic acid, as possible protectives of skin cells against UVA and UVB radiation. Their protective effects on skin cell viability, ROS production, mitochondrial membrane potential, liposomal permeability, and DNA integrity were investigated. Only some of the compounds studied, such as trans-urocanic acid and hyperoside, had a significant effect on the examined hallmarks of UV-induced cell damage. This was also confirmed by an atomic force microscopy study of morphological changes in HaCaT cells or a study conducted on a 3D skin model. In conclusion, hyperoside was found to be a very effective UV-protective compound, especially against UVA radiation. Commonly used sunscreen compounds such as 2,4-dihydroxybenzophenone, 2-hydroxy-4-methoxybenzophenone, and 3-(4-methylbenzylidene)camphor turned out to be only physical UV filters, and pachypodol with a relatively high absorption in the UVA region was shown to be more phototoxic than photoprotective.

In Vitro Anti-Inflammatory and Antioxidant Activities of pH-Responsive Resveratrol-Urocanic Acid Nano-Assemblies.

Inflammatory environments provide vital biochemical stimuli (i.e., oxidative stress, pH, and enzymes) for triggered drug delivery in a controlled manner. Inflammation alters the local pH within the affected tissues. As a result, pH-sensitive nanomaterials can be used to effectively target drugs to the site of inflammation. Herein, we designed pH-sensitive nanoparticles in which resveratrol (an anti-inflammatory and antioxidant compound (RES)) and urocanic acid (UA) were complexed with a pH-sensitive moiety using an emulsion method. These RES-UA NPs were characterized by transmission electron microscopy, dynamic light scattering, zeta potential, and FT-IR spectroscopy. The anti-inflammatory and antioxidant activities of the RES-UA NPs were assessed in RAW 264.7 macrophages. The NPs were circular in shape and ranged in size from 106 to 180 nm. The RES-UA NPs suppressed the mRNA expression of the pro-inflammatory molecules inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2), interleukin-1ß (IL-1ß), and tumor necrosis factor-α (TNF-α) in lipopolysaccharide (LPS)-stimulated RAW 264.7 macrophages in a concentration-dependent manner. Incubation of LPS-stimulated macrophages with RES-UA NPs reduced the generation of reactive oxygen species (ROS) in a concentration-dependent manner. These results suggest that pH-responsive RES-UA NPs can be used to decrease ROS generation and inflammation.

Trans-urocanic acid facilitates spatial memory, implications for Alzheimer's disease.

Trans-urocanic acid (trans-UCA) is an isomer of cis-UCA and is widely distributed in the brain, predominantly in the hippocampus and prefrontal cortex. Previous studies have investigated the role of trans-UCA in non-spatial memory; however, its influence on spatial memory remains unclear. In the present study, network pharmacology strategy and behavioral testing were used to evaluate the role of trans-UCA in spatial memory and predict its possible mechanism. The results showed that there are 40 intersecting targets between trans-UCA and spatial memory identified by several databases and Venn diagram, indicating that trans-UCA may be involved in spatial memory. Behavioral results show that trans-UCA facilitates spatial working memory in the Y-maze test as well as spatial recognition memory acquisition, consolidation and retrieval in an object location recognition (OLR) task. Furthermore, PPI (protein-protein interaction) network analysis, GO (gene ontology) and KEGG (Kyoto encyclopedia of genes and genomes) pathway enrichment analyses show that the molecular mechanisms underlying the enhancing effect of trans-UCA on spatial memory are mainly associated with the regulation of insulin, mitogen-activated protein kinase (MAPK) and nuclear factor Kappa B (NF-κB) signaling pathways, serotonergic synapse and arginine and proline metabolism. The results of this study suggest that trans-UCA facilitates spatial memory in the Y-maze test and OLR task and may offer therapeutic potential for Alzheimer's disease (AD). The underlying mechanisms predicted by network pharmacology should be further verified.

Urocanic acid enhances memory consolidation and reconsolidation in novel object recognition task.

Urocanic acid (UCA) is an endogenous small molecule that is elevated in skin, blood and brain after sunlight exposure, mainly playing roles in the periphery systems. Few studies have investigated the role of UCA in the central nervous system. In particular, its role in memory consolidation and reconsolidation is still unclear. In the present study, we investigated the effect of intraperitoneal injection of UCA on memory consolidation and reconsolidation in a novel object recognition memory (ORM) task. In the consolidation version of the ORM task, the protocol involved three phases: habituation, sampling and test. UCA injection immediately after the sampling period enhanced ORM memory performance; UCA injection 6 h after sampling did not affect ORM memory performance. In the reconsolidation version of the ORM task, the protocol involved three phases: sampling, reactivation and test. UCA injection immediately after reactivation enhanced ORM memory performance; UCA injection 6 h after reactivation did not affect ORM memory performance; UCA injection 24 h after sampling without reactivation did not affect ORM memory performance. This UCA-enhanced memory performance was not due to its effects on nonspecific responses such as locomotor activity and exploratory behavior. The results suggest that UCA injection enhances consolidation and reconsolidation of an ORM task, which further extends previous research on UCA effects on learning and memory.

Ternary Cu(II) Complex with GHK Peptide and Cis-Urocanic Acid as a Potential Physiologically Functional Copper Chelate.

The tripeptide NH2-Gly-His-Lys-COOH (GHK), cis-urocanic acid (cis-UCA) and Cu(II) ions are physiological constituents of the human body and they co-occur (e.g., in the skin and the plasma). While GHK is known as Cu(II)-binding molecule, we found that urocanic acid also coordinates Cu(II) ions. Furthermore, both ligands create ternary Cu(II) complex being probably physiologically functional species. Regarding the natural concentrations of the studied molecules in some human tissues, together with the affinities reported here, we conclude that the ternary complex [GHK][Cu(II)][cis-urocanic acid] may be partly responsible for biological effects of GHK and urocanic acid described in the literature.

UV-B-Induced Inflammasome Activation Can Be Prevented by Cis-Urocanic Acid in Human Corneal Epithelial Cells.

Purpose: The cornea is continually exposed to highly energetic solar UV-B (280-320 nm). Our aim was to investigate whether UV-B triggers the activation of NLRP3 inflammasomes and the production of IL-1ß and/or IL-18 in human corneal epithelial (HCE) cells. Additionally, we studied the capability of cis-urocanic acid (cis-UCA) to prevent inflammasome activation or alleviate inflammation through other signaling pathways. Methods: HCE-2 cell line and primary HCE cells were primed using lipopolysaccharide or TNF-α. Thereafter, cells were exposed to UV-B before or after the addition of cis-UCA or caspase-1 inhibitor. Caspase-1 activity was measured from cell lysates by an enzymatic assay. IL-1ß, IL-18, IL-6, IL-8, and NLRP3 levels were detected using the ELISA method from cell culture media. Additionally, intracellular NLRP3 levels were determined by the Western blot technique, and cytotoxicity was measured by the LDH assay. Results: UV-B exposure significantly increased caspase-1 activity in TNF-α-primed HCE cells. This result was consistent with the concurrently induced IL-1ß secretion. Both caspase-1 activity and release of IL-1ß were reduced by cis-UCA. Additionally, UV-B stimulated the caspase-1-independent production of IL-18, an effect also reduced by cis-UCA. Cis-UCA decreased the release of IL-6, IL-8, and LDH in a time-dependent manner when administered to HCE-2 cells after UV-B exposure. Conclusions: Our findings demonstrate that UV-B activates inflammasomes in HCE cells. Cis-UCA can prevent the secretion of IL-1ß and IL-18 and therapeutically reduces the levels of IL-6, IL-8, and LDH in UV-B-stressed HCE cells.

Photoimmunology: how ultraviolet radiation affects the immune system.

Ultraviolet (UV) radiation is a ubiquitous component of the environment that has important effects on a wide range of cell functions. Short-wavelength UVB radiation induces sunburn and is a potent immunomodulator, yet longer-wavelength, lower-energy UVA radiation also has effects on mammalian immunity. This Review discusses current knowledge regarding the mechanisms by which UV radiation can modify innate and adaptive immune responses and how this immunomodulatory capacity can be both beneficial in the case of inflammatory and autoimmune diseases, and detrimental in the case of skin cancer and the response to several infectious agents.

Chemoattractant activity of tris-(hydroxymethyl)aminomethane for Brugia pahangi infective third-stage larvae.

Urocanic acid (UCA) is known as a major chemoattractant for Strongyloides stercoralis infective third-stage larvae (L3). Since Brugia pahangi is a skin-penetrating parasitic nematode similar to S. stercoralis, UCA was expected to be a chemoattractant for B. pahangi L3. Thus, the chemoattractant activity of UCA for B. pahangi L3 was assessed. The chemotactic responses of B. pahangi L3 to UCA or acetic acid (CH3COOH) dissolved in amine solutions were assessed using an agar-plate assay. A test solution of 200 mm UCA dissolved in aqueous 270 mm tris(hydroxymethyl)aminomethane (Tris) significantly attracted B. pahangi L3 compared with deionized water (DW), while neither a solution of 200 mm UCA dissolved in aqueous 230 mm ammonia (NH3) nor 290 mm triethylamine (TEA) significantly attracted L3. Similarly, a test solution of 200 mm CH3COOH dissolved with 200 mm Tris significantly attracted L3, but neither a test solution of 200 mm CH3COOH plus 200 mm NH3 nor 200 mm TEA attracted L3. Furthermore, L3 were significantly attracted to 200 mm Tris alone, compared with DW, but avoided 200 mm NH3 and 200 mm TEA. Moreover, the chemoattractant activity of Tris for L3 was observed even at a low concentration of 25 mm, and it was observed in a mild alkaline condition but not in an acidic condition. The present study reveals that Tris is a potential chemoattractant for B. pahangi L3 while UCA is not. This finding will contribute to an understanding of the mechanisms of skin-penetrating infection of filarial L3.

[Experimental research of neutrophil gelatinase-associated lipocalin siRNA encapsulated by urocanic acid-coupled chitosan on colon cancer cells].

OBJECTIVE: To explore the impact of neutrophil gelatinase-associated lipocalin (NGAL) knockdown by NGAL siRNA encapsulated with urocanic acid-modified chitosan nanoparticles (UAC) on the proliferation, migration and apoptosis of human colon cancer cells. METHODS: NGAL siRNA was encapsulated by UAC and chitosan (CTS) respectively, and then was transfected into human colon cancer cell lines HT29. The NGAL mRNA was detected by real-time quantitative PCR (RT-QPCR). Relationships of NGAL gene silencing with the proliferation, migration and apoptosis of HT29 cell were analyzed. RESULTS: Under the fluorescence microscope, the transfection efficiency of siRNA in UAC group was (37.52±7.17)%, which was significantly higher than (11.32±3.39)% in CTS group (t=6.102, P=0.005). Forty-eight hours after transfection, RT-QPCR examination showed that the level of NGAL mRNA expression was 0.350 in UAC group and 0.529 in CTS group with significant difference (t=-3.743, P=0.02), meanwhile both levels were significantly lower as compared to control group(F=163.538, P<0.001). Proliferation analysis revealed that after silencing NGAL gene, proliferation rate of UAC group and CTS group was slightly lower than control group, and no significant differences were found (F=9.520, P=0.438). However, migration assay demonstrated that the 24-hour migration rate of UAC group and CTS group was significantly lower than that of control group (F=6.756, P=0.029), meanwhile the migration rate of UAC group was slightly lower than that of CTS group [(77.90±7.14)% vs. (87.67±3.98)%, t=-1.704, P=0.164]. Apoptosis detection revealed that the apoptosis rate in UAC group was significantly higher than that in CTS group and the control group 2 days after transfection [(15.800±1.054)% vs. (12.900±0.656)%, (11.933±1.914)%, F=7.004, P=0.027]. CONCLUSIONS: The encapsulated ability and transfection efficiency of chitosan modified by urocanic acid elevate significantly. Silencing NGAL gene by UAC carrier can down-regulate the expression of NGAL mRNA in HT29 colon cell line, inhibit their migration and facilitate their apoptosis.

Intravesical treatment with cis-urocanic acid improves bladder function in rat model of acute bladder inflammation.

AIMS: The aim was to study the effect of intravesically instilled cis-urocanic acid (cis-UCA) on bladder function in an experimental rat model of acute bladder inflammation. Hyaluronic acid (HA) was used as a comparator compound. METHODS: Bladder irritation was induced in female rats by intravesical hydrochloric acid (HCl) infusion. Vehicle, 0.5% HA, or 2% cis-UCA solutions were infused intravesically twice a day for three consequent days. On the fourth day, urodynamical measurements were performed, the animals were sacrificed, and the bladders were removed for histopathological assessment. RESULTS: HCl treatment caused significant impairment of bladder function indicated by decreased micturition intervals and voided urine volumes and induced severe voiding dysfunction observed as occurrence of overflow incontinence. These functional changes were accompanied by increased bladder weight, hemorrhage, and infiltration of inflammatory cells into the urothelium. Intravesical cis-UCA treatment recovered bladder function by significantly prolonging the micturition interval, increasing the voided volume, and reducing the occurrence of overflow incontinence. All these changes were comparable to the effects of HA. CONCLUSIONS: Intravesical administration of cis-UCA was able to partially recover bladder function impaired by chemical irritation. Cis-UCA may offer a novel intravesical treatment option in some inflammatory conditions of the bladder. Neurourol. Urodynam. 35:786-791, 2016. © 2015 Wiley Periodicals, Inc.

Protective Effect of Chitin Urocanate Nanofibers against Ultraviolet Radiation.

Urocanic acid is a major ultraviolet (UV)-absorbing chromophore. Chitins are highly crystalline structures that are found predominantly in crustacean shells. Alpha-chitin consists of microfibers that contain nanofibrils embedded in a protein matrix. Acid hydrolysis is a common method used to prepare chitin nanofibrils (NFs). We typically obtain NFs by hydrolyzing chitin with acetic acid. However, in the present study, we used urocanic acid to prepare urocanic acid chitin NFs (UNFs) and examined its protective effect against UVB radiation. Hos: HR-1 mice coated with UNFs were UVB irradiated (302 nm, 150 mJ/cm²), and these mice showed markedly lower UVB radiation-induced cutaneous erythema than the control. Additionally, sunburn cells were rarely detected in the epidermis of UNFs-coated mice after UVB irradiation. Although the difference was not as significant as UNFs, the number of sunburn cells in mice treated with acetic acid chitin nanofibrils (ANFs) tended to be lower than in control mice. These results demonstrate that ANFs have a protective effect against UVB and suggest that the anti-inflammatory and antioxidant effects of NFs influence the protective effect of ANFs against UVB radiation. The combination of NFs with other substances that possess UV-protective effects, such as urocanic acid, may provide an enhanced protective effect against UVB radiation.

Stratum corneum molecular mobility in the presence of natural moisturizers.

The outermost layer of the skin, the stratum corneum (SC), is a lipid-protein membrane that experiences considerable osmotic stress from a dry and cold climate. The natural moisturizing factor (NMF) comprises small and polar substances, which like osmolytes can protect living systems from osmotic stress. NMF is commonly claimed to increase the water content in the SC and thereby protect the skin from dryness. In this work we challenge this proposed mechanism, and explore the influence of NMF on the lipid and protein components in the SC. We employ natural-abundance (13)C solid-state NMR methods to investigate how the SC molecular components are influenced by urea, glycerol, pyrrolidone carboxylic acid (PCA), and urocanic acid (UCA), all of which are naturally present in the SC as NMF compounds. Experiments are performed with intact SC, isolated corneocytes and model lipids. The combination of NMR experiments provides molecularly resolved qualitative information on the dynamics of different SC lipid and protein components. We obtain completely novel molecular information on the interaction of these NMF compounds with the SC lipids and proteins. We show that urea and glycerol, which are also common ingredients in skin care products, increase the molecular mobility of both SC lipids and proteins at moderate relative humidity where the SC components are considerably more rigid in the absence of these compounds. This effect cannot be attributed to increased SC water content. PCA has no detectable effect on SC molecular mobility under the conditions investigated. It is finally shown that the more apolar compound, UCA, specifically influences the mobility of the SC lipid regions. The present results show that the NMF components act to retain the fluidity of the SC molecular components under dehydrating conditions in such a way that the SC properties remain largely unchanged as compared to more hydrated SC. These findings provide a new molecular insight into how small polar molecules in NMF and skin care products act to protect the human skin from drying.

Modulation of multiple sclerosis by sunlight exposure: role of cis-urocanic acid.

The role of cis-urocanic acid (UCA) as a UV-mediated immunomodulator in MS patients was investigated. Plasma levels of cis-UCA were significantly lower in MS patients compared to controls. Stimulation of MBP- and MOG-specific T cells in the presence of cis-UCA, significantly increased IL-10, and inhibited IFN-γ production. PBMCs cultured in the presence of cis-UCA increased CD4(+)CD25(+)FoxP3(+) regulatory T cell percentages. Dendritic cells cultured in the presence of cis-UCA significantly reduced Ag presentation capacity. Finally, cis-UCA activated the 5-HT2A receptor, inducing the increase in phosphorylated forms of ERK 1/2 and JNK2. Thus, in addition to vitamin D, cis-UCA also appears to be an additional UV-mediated immunomodulator.

Topical cis-urocanic acid attenuates oedema and erythema in acute and subacute skin inflammation in the mouse.

BACKGROUND: cis-Urocanic acid (cis-UCA) is an endogenous immunosuppressive molecule of the epidermis. OBJECTIVES: We investigated the effects of topical cis-UCA creams (2·5% and 5%) in acute and subacute mouse models of skin inflammation. METHODS: Acute skin irritation was induced by applying dimethyl sulphoxide (DMSO) on the earlobe of CD-1 mice. Topical cis-UCA, hydrocortisone (1%) or tacrolimus (0·1%) were applied 10 min later. In another model, subacute inflammation was provoked and maintained by three applications of 12-O-tetradecanoylphorbol-13-acetate (TPA) on the ears of NMRI mice on days 1, 2 and 4. The test products were applied topically twice a day during 6 days. RESULTS: In the acute DMSO model, cis-UCA creams suppressed ear swelling at 1 h significantly more efficiently than hydrocortisone (P < 0·01) and tacrolimus (P < 0·001). Ear swelling was significantly inhibited by cis-UCA (P < 0·001) in the subacute TPA model as well. The 5% cream also decreased erythema, whereas tacrolimus enhanced skin reddening. Treatments with cis-UCA did not affect TPA-induced infiltration of neutrophils to the skin. In contrast to hydrocortisone, cis-UCA did not reduce epidermal thickness. CONCLUSIONS: The results suggest that cis-UCA - unlike hydrocortisone and tacrolimus - is efficient in both acute and subacute skin inflammation, attenuating skin oedema and erythema. Topical drug therapy with cis-UCA may provide a safe and effective drug treatment modality in inflammatory skin disorders.

Expression of VjbR under nutrient limitation conditions is regulated at the post-transcriptional level by specific acidic pH values and urocanic acid.

VjbR is a LuxR homolog that regulates transcription of many genes including important virulence determinants of the facultative intracellular pathogen Brucella abortus. This transcription factor belongs to a family of regulators that participate in a cell-cell communication process called quorum sensing, which enables bacteria to respond to changes in cell population density by monitoring concentration of self produced autoinducer molecules. Unlike almost all other LuxR-type proteins, VjbR binds to DNA and activates transcription in the absence of any autoinducer signal. To investigate the mechanisms by which Brucella induces VjbR-mediated transcriptional activation, and to determine how inappropriate spatio-temporal expression of the VjbR target genes is prevented, we focused on the study of expression of vjbR itself. By assaying different parameters related to the intracellular lifestyle of Brucella, we identified a restricted set of conditions that triggers VjbR protein expression. Such conditions required the convergence of two signals of different nature: a specific pH value of 5.5 and the presence of urocanic acid, a metabolite involved in the connection between virulence and metabolism of Brucella. In addition, we also observed an urocanic acid, pH-dependent expression of RibH2 and VirB7, two additional intracellular survival-related proteins of Brucella. Analysis of promoter activities and determination of mRNA levels demonstrated that the urocanic acid-dependent mechanisms that induced expression of VjbR, RibH2, and VirB7 act at the post-transcriptional level. Taken together, our findings support a model whereby Brucella induces VjbR-mediated transcription by modulating expression of VjbR in response to specific signals related to the changing environment encountered within the host.

Cis-urocanic acid inhibits SAPK/JNK signaling pathway in UV-B exposed human corneal epithelial cells in vitro.

PURPOSE: The cornea is sensitive to ultraviolet B (UV-B) radiation-induced oxidative stress and inflammation. Its clinical manifestations are photokeratitis and climatic droplet keratopathy. Urocanic acid (UCA) is a major endogenous UV-absorbing chromophore in the epidermis and it is also an efficacious immunosuppressant. We have previously shown that cis-UCA can suppress UV-B-induced interleukin-6 and -8 secretion and cytotoxicity in human corneal epithelium (HCE) cells. In the current study, we further wanted to investigate the effects of cis-UCA on UV-B-induced inflammatory and apoptotic responses in HCE-2 cells, focusing on the nuclear factor kappa B (NF-κB) and AP-1 (subunits c-Fos and c-Jun) signaling pathways. METHODS: After exposing HCE-2 cells to UV-B and cis-UCA, DNA binding of c-Fos, c-Jun and NF-κB was measured with ELISA. In addition, the endogenous levels of phosphorylated stress-activated protein kinase/c-Jun N-terminal kinase (phospho-SAPK/JNK) and phospho-c-Jun were determined. The proliferative capacity of HCE-2 cells was also quantified, and the cytotoxicity of the cis-UCA and UV-B treatments was monitored by measuring the release of lactate dehydrogenase enzyme in the culture medium. RESULTS: UV-B irradiation induced the binding of transcription factors c-Jun, c-Fos, and NF-κB to DNA. Cis-UCA inhibited the binding of c-Jun and c-Fos but not that of NF-κB. Moreover, UV-B increased the levels of phospho-c-Jun and phospho-JNK, and the expression of both was attenuated by cis-UCA. Cis-UCA also alleviated the UV-B-induced apoptosis and proliferative decline in human corneal cells. CONCLUSIONS: The results from this study suggest that cis-UCA suppresses JNK signaling pathway, which provides potential for treating UV-B-induced inflammatory defects in human corneal cells.

[Moderation is best also in sunbathing]. / Kohtuus on parasta auringonotossakin.

There is more discussion and writing about the disadvantages of solar ultraviolet radiation than its benefits. Melanoma and other skin cancers have received most attention. Skin wrinkles and other signs of ageing or their prevention are being discussed. Instead only little attention has been paid on the anti-inflammatory properties and anticancer activity of UV radiation. Recent research has focused on sunscreen products, antioxidants preventing sunburn and its consequences, and urocanic acid, the skin's indigenous anti-inflammatory agent.

Systemic low-dose UVB inhibits CD8 T cells and skin inflammation by alternative and novel mechanisms.

Exposure to UVB radiation before antigen delivery at an unirradiated site inhibits functional immunological responses. Mice treated dorsally with suberythemal low-dose UVB and immunized with ova in abdominal skin generated ova-specific CD8 T cells with a significantly decreased activation, expansion, and cytotoxic activity compared with unirradiated mice. UVB also impaired the delayed-type hypersensitivity (DTH) reaction to ova. Transfer of CD4⁺CD25⁺cells from UVB-exposed mice did not suppress the ova-specific CD8 T-cell response or DTH reaction in unexposed mice, confirming that systemic low-dose UVB does not induce long-lived functional regulatory CD4⁺CD25⁺ T cells. Repairing cyclobutane pyrimidine dimer-type DNA damage and blocking aryl hydrocarbon receptor signaling also did not reverse the immunosuppressive effect of UVB on ova-specific CD8 T cells and DTH, suggesting that cyclobutane pyrimidine dimers and the aryl hydrocarbon receptor are not required in systemic low-dose UVB-induced immunosuppression. The known UVB chromophore, cis-urocanic acid, and reactive oxygen species triggered the inhibition of DTH caused by UVB, but they were not involved in the modulation of CD8 T cells. These findings indicate that systemic low-dose UVB impedes the primary response of antigen-specific CD8 T cells by a novel mechanism that is independent of pathways known to be involved in systemic suppression of DTH.

cis-Urocanic acid enhances prostaglandin E2 release and apoptotic cell death via reactive oxygen species in human keratinocytes.

Urocanic acid (UCA) is a major UVR-absorbing skin molecule that undergoes trans to cis photoisomerization in the epidermis following UVR exposure. Murine studies have established that cis-UCA is an important mediator of UVR-induced immune suppression, but little is known about its signaling pathway. We have previously demonstrated that treatment of normal human epidermal keratinocytes with cis-UCA resulted in increased synthesis of prostaglandin E(2) (PGE(2)) and cell death. Here, using immortalized human keratinocytes, we report that cis-UCA but not trans-UCA generates reactive oxygen species (ROS) in a dose-dependent manner and that the natural antioxidant α-tocopherol can reduce this ROS generation, subsequent PGE(2) release, and apoptotic cell death. Western blot analysis revealed that cis-UCA leads to a transient phosphorylation of EGFR as well as downstream mitogen-activated protein kinases (MAPKs), extracellular signal-regulated kinase (ERK) and p38. Pharmacological inhibition of their activity attenuated PGE(2) release induced by cis-UCA. After transient activation, cis-UCA downregulated EGFR protein expression that corresponded to activation of caspase-3. In addition, pretreatment with α-tocopherol inhibited EGFR downregulation and caspase-3 activation induced by cis-UCA. These results suggest that cis-UCA exerts its effects on human keratinocytes via intracellular ROS generation that modulates EGFR signaling and subsequently induces PGE(2) synthesis and apoptotic cell death.