Molecular mechanisms of cis-urocanic acid and permethrin-induced alterations in cutaneous immunity

Uses of Polypodium leucotomos Extract in Oncodermatology

The effects of UV radiation on the skin and its damage mechanisms are well known. New modalities of exogenous photoprotection have been studied. It was demonstrated that Polypodium leucotomos extract acts as an antioxidant, photoprotectant, antimutagenic, anti-inflammatory, and immunoregulator. It is effective when taken orally and/or applied topically to support the prevention of skin cancers. It also has an important role in preventing photoaging. This review aims to report the mechanisms through which Polypodium leucotomos acts and to analyze its uses in oncodermatology with references to in vitro and in vivo studies. Additionally, alternative uses in non-neoplastic diseases, such as pigmentary disorders, photosensitivity, and atopic dermatitis, have been considered.

Fernblock (Polypodium leucotomos Extract): Molecular Mechanisms and Pleiotropic Effects in Light-Related Skin Conditions, Photoaging and Skin Cancers, a Review

Healthier life styles include increased outdoors time practicing sports and walking. This means increased exposure to the sun, leading to higher risk of sunburn, photoaging and skin cancer. In addition to topical barrier products, oral supplementations of various botanicals endowed with antioxidant activity are emerging as novel method of photoprotection. Polypodium leucotomos extract (PL, commercial name Fernblock^®, IFC Group, Spain) is a powerful antioxidant due to its high content of phenolic compounds. PL is administered orally, with proven safety, and it can also be used topically. Its mechanisms include inhibition of the generation and release of reactive oxygen species (ROS) by ultraviolet (UV) light. It also prevents UV- and ROS-induced DNA damage with inhibition of AP1 and NF-κB and protection of natural antioxidant enzyme systems. At the cellular level, PL decreases cellular apoptosis and necrosis mediated UV and inhibits abnormal extracellular matrix remodeling. PL reduces inflammation, prevents immunosuppression, activates tumor suppressor p53 and inhibits UV-induced cyclooxygenase-2 (COX-2) enzyme expression. In agreement with increased p53 activity, PL decreased UV radiation-induced cell proliferation. PL also prevents common deletions mitochondrial DNA damage induced by UVA, and MMP-1 expression induced Visible Light and Infrared Radiation. These cellular and molecular effects are reflected in inhibitions of carcinogenesis and photoaging.

cis-Urocanic acid attenuates acute dextran sodium sulphate-induced intestinal inflammation

On exposure to sunlight, urocanic acid (UCA) in the skin is converted from trans to the cis form and distributed systemically where it confers systemic immunosuppression. The aim of this study was to determine if administration of cis-UCA would be effective in attenuating colitis and the possible role of IL-10. Colitis was induced in 129/SvEv mice by administering 5% dextran sodium sulfate (DSS) for 7 days in drinking water. During this period mice received daily subcutaneously injections of cis-UCA or vehicle. To examine a role for IL-10, 129/SvEv IL-10^−/− mice were injected for 24 days with cis-UCA or vehicle. Clinical disease was assessed by measurement of body weight, stool consistency, and presence of blood. At sacrifice, colonic tissue was collected for histology and measurement of myeloperoxidase and cytokines. Splenocytes were analyzed for CD4+CD25+FoxP3+ T-regulatory cells via flow cytometry. Murine bone-marrow derived antigen-presenting cells were treated with lipopolysaccharide (LPS) ± UCA and cytokine secretion measured. Our results demonstrated that cis-UCA at a dose of 50 µg was effective in ameliorating DSS-induced colitis as evidenced by reduced weight loss and attenuated changes in colon weight/length. This protection was associated with reduced colonic expression of CXCL1, an increased expression of IL-17A and a significant preservation of splenic CD4+CD25+FoxP3+ T-regulatory cells. cis-UCA decreased LPS induced CXCL1, but not TNFα secretion, from antigen-presenting cells in vitro. UCA reduced colonic levels of IFNγ in IL-10^−/− mice but did not attenuate colitis. In conclusion, this study demonstrates that cis-urocanic acid is effective in reducing the severity of colitis in a chemically-induced mouse model, indicating that pathways induced by ultraviolet radiation to the skin can influence distal sites of inflammation. This provides further evidence for a possible role for sunlight exposure in modulating inflammatory disorders.

Recent advances in urocanic acid photochemistry, photobiology and photoimmunology

Urocanic acid (UCA), produced in the upper layers of mammalian skin, is a major absorber of ultraviolet radiation (UVR). Originally thought to be a 'natural sunscreen', studies conducted a quarter of a century ago proposed that UCA may be a chromophore for the immunosuppression that follows exposure to UVR. With its intriguing photochemistry, its role in immunosuppression and skin cancer development, and skin barrier function, UCA continues to be the subject of intense research effort. This review summarises the photochemical, photobiological and photoimmunological findings regarding UCA, published since 1998.

An action spectrum (290-320 nm) for TNFalpha protein in human skin in vivo suggests that basal-layer epidermal DNA is the chromophore

Terrestrial solar UVB radiation ( approximately 295-320 nm) readily induces cyclobutane pyrimidine dimers (CPDs) in human skin DNA that result in characteristic mutations associated with nonmelanoma skin cancer. The proinflammatory cytokine TNFalpha is important in mouse skin chemical carcinogenesis and is thought to also play a role in UVR-induced skin cancer by its immunomodulatory properties. There is some in vitro evidence that CPDs initiate the production of TNFalpha, and we tested this hypothesis by comparing the wavelength dependence (action spectrum) for TNFalpha protein induction in human skin in vivo with our earlier in vivo action spectra for CPD induction in four different epidermal layers of human skin. Normal volunteers (n = 35) were irradiated with physiologically relevant doses of monochromatic UVB (290-320 nm), and TNFalpha concentration was assessed, by high-sensitivity ELISA, in exudates from skin suction blisters raised 8 h after irradiation. An action spectrum, constructed from the slopes of the dose-response curves at the different wavelengths, showed maximal efficacy at 300 nm. An excellent match was observed for TNFalpha and the CPD action spectrum for cells in the lower basal epidermis. These data strongly suggest that UVB-induced photodamage to DNA in the epidermal basal layer is a major trigger for TNFalpha production. The TNFalpha may originate directly from the keratinocytes in this layer or inflammatory cells that are rapidly recruited into the upper dermis (e.g., neutrophils) as a consequence of DNA photodamage to basal-layer keratinocytes.