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Urocanic Acid (urocanic + acid)

Distribution by Scientific Domains

Medical Sciences	37%

Selected Abstracts

The Effect of Molecular Environment on the Photoisomerization of Urocanic Acid,

PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 2 2004
Richard A. Wallis
ABSTRACT Urocanic acid, imidazole propenoic acid, is a metabolic product of histidine, which accumulates in skin and is excreted in sweat. It absorbs UV radiation at wavelengths shorter than 340 nm, and its principal photochemical reaction is a trans-cis isomerization about the propenyl double bond. This isomerization to the biologically active cis isomer is implicated in the photo-induced suppression of the immune system of skin. The kinetics of the trans,cis photoisomerization of urocanic acid has been determined in a number of solvents, spanning a range of polarities. The initial rates of isomerization and the photostationary trans-cis compositions, in all solvents except water, correlate linearly with solvent polarity. This indicates that the isomerization proceeds through a polar intermediate that is stabilized by coulombic interactions with the molecular environment. [source]

Topically Applied Eicosapentaenoic Acid Protects Against Local Immunosuppression Induced by UVB Irradiation, cis -Urocanic Acid and Thymidine Dinucleotides,

PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 1 2001
Ralf M. W. Moison
ABSTRACT UVB-induced immunosuppression, a promoter of photocarcinogenesis, involves the formation of pyrimidine dimers and cis -urocanic acid (cis -UCA), but reactive oxygen species (ROS) also plays an important role. Eicosapentaenoic acid (EPA) can inhibit photocarcinogenesis, but due to its polyunsaturated nature it is susceptible to oxidative damage by ROS. The antioxidant defense system may therefore be challenged upon ultraviolet-B (UVB) irradiation in the presence of EPA. We investigated whether topically applied EPA in mice could protect against local immunosuppression (contact hypersensitivity response to dinitrofluorobenzene) induced by UVB radiation (1.5 J/cm2), or topically applied cis -UCA (150 nmol/cm2) or thymidine dinucleotides (pTpT) (5 nmol/cm2). The influence of EPA on epidermal lipid peroxidation and antioxidant status was also measured. UVB irradiation, cis -UCA and pTpT all caused 70% immunosuppression. Topical pretreatment of mice with EPA partially protected against immunosuppression; the EPA dose needed to accomplish this was 10 nmol/cm2 for UVB irradiation, 100 nmol/cm2 for cis -UCA and 1000 nmol/cm2 for pTpT. Higher EPA doses caused higher UVB-induced lipid peroxidation and lower vitamin C levels. Glutathione only decreased with the highest EPA dose whereas vitamin E was not decreased after UVB irradiation. In conclusion, topically applied EPA protects against UVB-, cis -UCA- and pTpT-induced immunosuppression and maintenance of an adequate antioxidant defense seems to be an important prerequisite for the protective action by EPA. [source]

The Effect of Molecular Environment on the Photoisomerization of Urocanic Acid,

Screening of urocanic acid isomers in human basal and squamous cell carcinoma tumors compared with tumor periphery and healthy skin

EXPERIMENTAL DERMATOLOGY, Issue 10 2008
Juan Manuel Decara
Abstract:,Trans -urocanic acid is a major chromophore for ultraviolet (UV) radiation in human epidermis. The UV induces photoisomerization of trans -urocanic acid (tUCA) form to cis -urocanic acid (cUCA) and has been reported as an important mediator in the immunosuppression induced by UV. This immunomodulation has been recognized as an important factor related to skin cancer development. This is the first time that UCA isomers have been measured in epidermis of skin biopsies from patients with squamous cell carcinoma (SCC) and with basal cell carcinoma (BCC) and compared with the tumor periphery and biopsies of healthy photoexposed and non-photoexposed skin as controls. The UCA isomers were separated and quantified by high performance liquid chromatography. Analysis of UCA in healthy skin showed significant increase in total UCA content in non-photoexposed body sites compared with highly exposed skins. In contrast, the percentage of cUCA was higher in photoexposed body sites. Maximal levels of cUCA were found in cheek, forehead and forearm and lower levels in abdomen and thigh. No differences were found in total UCA concentration between the tumor samples and healthy photoexposed skin. However, differences were found in relation between isomers. Higher levels of cUCA were detected in SCC biopsies (44% of total UCA) compared with samples of BCC and that of healthy photoexposed skin (30%). These results suggest that the UV radiation exposure, a main factor in development of SCC can be mediated, apart from direct effect to cells (DNA damage), by immunosuppression pathways mediated by high production of cUCA. [source]

The Effect of Molecular Environment on the Photoisomerization of Urocanic Acid,

Topically Applied Eicosapentaenoic Acid Protects Against Local Immunosuppression Induced by UVB Irradiation, cis -Urocanic Acid and Thymidine Dinucleotides,

Sunscreens containing the broad-spectrum UVA absorber, Mexoryl® SX, prevent the cutaneous detrimental effects of UV exposure: a review of clinical study results

PHOTODERMATOLOGY, PHOTOIMMUNOLOGY & PHOTOMEDICINE, Issue 4 2008
Anny Fourtanier
Background: UVA exposure of human skin mainly produces reactive oxygen species (ROS) leading to DNA, cell and tissue damage. It alters immune function, pigmentation and it is certainly responsible for a large part of photoaging changes. Moreover UVA is implicated in the etiology of several photodermatoses. As a consequence, to provide adequate protection, sunscreens or skin care products for daily use protective products need UVA absorbers combined with UVB ones. Aim: To assess the efficacy of sunscreens containing a broad-spectrum UVA absorber the Mexoryl® SX or ecamsule and to compare formulations with and without it through a large number of clinical studies in human volunteers and patients. Methods: The following assessments were conducted: ,Prevention of excessive pigmentation induced by UV exposure in Caucasian and Asian skins using a method that measures pigmentation protection factors (PPF). ,Efficacy against DNA damage by measurement of pyrimidine dimer formation and p53 protein accumulation. ,Protection of immune system using delayed type hypersensitivity (DTH) reactions to recall antigens, isomerization of urocanic acid (UCA), alteration of Langerhans cells (LC) density, morphology and function. ,Reduction of epidermal and dermal alterations induced by repeated UVA or UV solar simulated radiation (SSR) using histology or immunohistology. ,Prevention of the polymorphous light eruption (PMLE) in patients prone to develop this disease. Results: Mexoryl® SX-containing formulations showed a dose-dependent level of protection against pigmentation. For a same sun protection factor (SPF) the higher the UVA protection was, the higher was the PPF. Pyrimidine dimer formation and p53 accumulation were significantly reduced by formulations with Mexoryl® SX. In the studies looking at the suppression of DTH reactions to recall antigens by the different UV spectra, the LC alterations and the cis UCA formation, Mexoryl® SX formulations always showed a higher protective potency than sunscreen without it even when the protection against erythema was similar (products with same SPF). Mexoryl® SX formulations also prevented or significantly decreased to minimal, ferritin, tenascin and lysozyme expression induced by repeated UVA or SSR exposure. It also reduced the enhancement of collagenase 2 mRNA expression induced by SSR exposure. Finally PMLE study demonstrated that UVA protection was essential for the prevention of this photodermatose. Conclusion: Mexoryl® SX formulated in sunscreens or daily use products have been shown to be an effective UV absorber, leading to an increased efficacy of these products against a large number of biological damage induced by UVA, SSR or sun exposure. [source]

UV-induced skin changes due to regular use of commercial sunbeds

PHOTODERMATOLOGY, PHOTOIMMUNOLOGY & PHOTOMEDICINE, Issue 5 2002
J. Ruegemer
Background/aim: Increased pigmentation and thickening of the epidermis are the most important photoprotective skin reactions induced by ultraviolet (UV) radiation. The present study was designed to find out what changes are induced by regular use of commercial sunbeds twice weekly over a period of 6 weeks. Methods: The parameters analysed were skin pigmentation measured by chromametry, minimal erythema dose (MED) as a parameter of light sensitivity, epidermal thickening as determined by histology, induction of keratinocyte apoptosis as determined by TUNEL staining and antioxidant metabolism as measured by changes of cis - and trans -urocanic acid (UCA) content of the skin. Results: As expected, chromametry confirmed the clinically obvious increased skin pigmentation. However, no increase in MED was observed. In addition, neither epidermal thickening nor sunburn cells were seen. Significant detectable changes in proportion of the UCA isomer content of the UV-exposed skin were seen. The total UCA and cis -UCA content increased significantly between nearly all points of measurement. The amount of trans -UCA first decreased, then increased significantly between the different time points. Conclusion: Our data indicate that sunbed-induced tanning is non-protective, which has to be addressed for persons looking for this effect before planning a stay in a sunny climate. However, sunbed-induced tanning may influence immunological reactions. [source]