Neil K. Gibbs

The role of urocanic acid in UV-induced immunosuppression: recent advances (1992-1994).

Abstract— Cis ‐ urocanic acid (UCA), formed in the epidermis by UV irradiation of trans‐UCA, has been implicated as a mediator of the immunosuppression induced by UV exposure of the skin. This review covers recent work in which the wavelength dependence of cis‐UCA formation, the interaction of UCA isomers with DNA, the effects of UCA isomers on the immune system and their interaction with histamine are examined. Results are frequently conflicting, particularly when considering the possible mode of action of cis‐UCA but, overall, a multifaceted role for UCA in immunomodulation by UV radiation is substantiated.

Transcriptional activation of tyrosinase and TRP‐1 by p53 links UV irradiation to the protective tanning response

We are exposed constantly to potentially harmful compounds and radiations. Complex adaptive protective responses have evolved to prevent such agents causing cellular damage, including potentially oncogenic mutation. The p53 tumour suppressor appears to have a role in co‐ordinating such responses: it is activated by diverse insults and it acts as a transcriptional regulator of downstream genes that facilitate cellular adaptation. Ultraviolet (UV) light is a particularly potent inducer of p53 expression. In addition, UV light induces the production of melanin as a protection against further irradiation‐induced damage. This study shows that the promoters of the genes coding for the enzymes crucial in melanin biosynthesis, namely tyrosinase and tyrosinase‐related protein‐1 (TRP‐1), are activated by wild‐type p53. Both promoters have p53‐responsive elements and are activated in vivo in a dose‐dependent manner by wild‐type p53, as well as by the p53 homologues p73α and p63α. Copyright

Action spectra for the trans to cis photoisomerisation of urocanic acid in vitro and in mouse skin.

Urocanic acid (UCA) is a major UV chromophore in the upper layers of the skin where it is found predominantly as the trans isomer. UV irradiation induces photoisomerisation of trans‐UCA to cis‐UCA which has been shown to mimic some of the immunosuppressive properties of UV exposure. We examined the wavelength dependence for trans‐UCA to cis‐UCA photoisomerisation in vitro and in mouse skin in vivo over the spectral range270–340 nm. The resulting action spectra were very similar with maximal effectiveness at300–315 nm and equal activity at 270 nm and325–330 nm, demonstrating that UVA‐II radiation (320–340nm) is efficient at UCA photoisomerisation. These action spectra differed markedly from the trans‐UCA absorption spectrum in vitro and also the reported action spectrum for UV suppression of contact hypersensitivity in mice. These findings suggest that the relationship between cis‐UCA formation in skin and UV‐induced immunosuppression may be complex.

Photogenotoxicity of Skin Phototumorigenic Fluoroquinolone Antibiotics Detected Using the Comet Assay

Abstract— The fluoroquinolone(FQ) antibiotics photosensitize human skin to solar UV radiation and are reported to photosensitize tumor formation in mouse skin. As tumor initiation will not occur without genotoxic insult, we examined the potential of ciprofloxacin, lomefloxacin, fle‐roxacin, BAYy3118 (a recently developed monofluori‐nated quinolone) and nalidixic acid to photosensitize DNA damage in V79 hamster fibroblasts in vitro. Cells were exposed to 37.5 kj/m2 UVA (320‐400 nm; glass filtered Sylvania psoralen + UVA (PUVA) tubes; calibrated Waldmann radiometer) at 4AoC in the presence of FQ and immediately afterwards embedded in agarose, lysed and placed in an electrophoretic field at pH 12. Under these denaturing conditions, the presence of DNA single‐strand breaks (SSB), alkali‐labile sites (ALS) and double‐strand breaks (DSB) can be visualized as DNA migrating away from the nucleus (characteristic “comet” appearance) after staining with a specific fluorochrome. At FQ concentrations that induced minimal loss of cell viability (neutral red uptake assay) the compounds tested induced comets with a rank order of BAYy3118 norfloxacin ciprofloxacin lomefloxacin fleroxacin nalidixic acid. If cells were incubated after treatment for 1 h at 37oC, the comet score decreased, suggesting efficient removal of SSB/ALS/DSB. Addition of the DNA polymerase, inhibitor, aphidicolin, to cells treated with either ciprofloxacin alone or ciprofloxacin + UVA resulted in an accumulation of SSB due to the endo/exonuclease steps of excision repair. We have demonstrated that the FQ are photogenotoxic in mammalian cells but that FQ‐pho‐tosensitized SSB are efficiently repaired. Preliminary evidence that ciprofloxacin photosensitizes the formation of DNA lesions warranting excision repair may indicate production of more mutagenic lesions.

Polymorphic light eruption occurs in 18% of Europeans and does not show higher prevalence with increasing latitude: multicenter survey of 6,895 individuals residing from the Mediterranean to Scandinavia.

Schneider MR, Antsiferova M, Feldmeyer L, Dahlhoff M, Bugnon P, Hasse S et al. (2008a) Betacellulin regulates hair follicle development and hair cycle induction and enhances angiogenesis in wounded skin. Journal of Investigative Dermatology 128:1256–65 Schneider MR, Werner S, Paus R, Wolf E (2008b) Beyond wavy hairs: the epidermal growth factor receptor and its ligands in skin biology and pathology. Am J Pathol 173:14–24

Estimation of the effect of increasing UVB exposure on the human immune system and related resistance to infectious diseases and tumours

Exposure to UV light has, besides some beneficial effects (vitamin D production), many harmful effects on human health. UVB irradiation has been shown to suppress both systemic and local immune responses to a variety of antigens, including some microorganisms. However, it is still not known whether such immunomodulating effects may lead to an increase in the number and severity of certain tumours and/or infections in humans. We report herein the data provided by a project that was funded by the European Union (Programme Environment), and that was aimed at the estimation of the risk associated with increased UVB exposure due to ozone depletion regarding the deleterious effects on the immune system and related resistance to tumours and infections in humans. The data, obtained by the different research groups involved, were assembled and used to calculate for the first time a risk assessment for increased environmental exposure to UVB in human subjects.

Effects of phototherapy on the production of cytokines by peripheral blood mononuclear cells and on systemic antibody responses in patients with psoriasis.

Exposure to ultraviolet B (UVB) radiation results in the suppression of many cell‐mediated immune responses, and recent studies using mice and murine cells in vitro suggest a shift from a T‐helper 1 (Th1) to a Th2 type of response on irradiation. Active psoriasis is considered to be a Th1‐type disorder, chiefly on the basis of the cytokines produced by inflammatory cells in psoriatic lesions. We investigated the effect of phototherapy in patients with psoriasis on the cytokine profile of mitogen‐stimulated mononuclear cells from peripheral blood and the concentration of IgG subclasses and IgE in the plasma. Eight patients were irradiated with a broad‐band UV source (Sylvania UV6; 280–400 nm) three times a week and another eight with a narrow‐band UVB source (Philips TL‐01; 311–313 nm). Peripheral blood was collected before therapy started and after 1–4 weeks of therapy. Peripheral blood mononuclear cells were stimulated in vitro with phytohemagglutinin; proliferation was measured by incorporation of tritiated thymidine and culture supernatants assayed for interleukin (IL)−2, −4 and −10 and γ‐interferon (IFN) by enzyme‐linked immunosorbent assays. Lymphoproliferation was not consistently affected by 4 weeks of UV6 therapy, and there was also no consistent change in the production of IL‐2, IL‐10 or γ‐IFN. In contrast, 4 weeks of TL‐01 therapy significantly suppressed lymphoproliferative responses. In addition the production of IL‐2, IL‐10 and γ‐IFN was lowered after 1 week of TL‐01 therapy, and this was even more apparent after the treatment had been extended to 4 weeks. IL‐4 concentrations were below detectable levels in all the samples throughout the study. The amounts of IgG1, −2, −3 and −4 and IgE in the plasma of the patients did not vary with either of the two phototherapies. Thus, although no evidence was obtained to indicate that UV6 exposure affected T‐helper subsets in psoriasis, TL‐01 inhibited the activity of both Th1 and Th2 subsets while not altering plasma antibody concentrations.

Damage to skin extracellular matrix induced by UV exposure.

SIGNIFICANCE Chronic exposure to environmental ultraviolet radiation (UVR) plays a key role in both photocarcinogenesis and induction of accelerated skin aging. Although the spatiotemporal consequences of UVR exposure for the composition and architecture of the dermal extracellular matrix (ECM) are well characterized, the pathogenesis of photoaging remains poorly defined. Given the compelling evidence for the role of reactive oxygen species (ROS) as mediators of photoaging, UVR-exposed human skin may be an accessible model system in which to characterize the role of oxidative damage in both internal and external tissues. RECENT ADVANCES Although the cell-mediated degradation of dermal components via UVR-induced expression of ECM proteases has long been identified as an integral part of the photoaging pathway, the relative importance and identity of cellular and extracellular photosensitizers (direct hit and bystanders models, respectively) in initiating this enzymatic activity is unclear. Recently, both age-related protein glycation and relative amino-acid composition have been identified as potential risk factors for photo-ionization and/or photo-sensitization. Here, we propose a selective multi-hit model of photoaging. CRITICAL ISSUES Bioinformatic analyses can be employed to identify candidate UVR targets/photosensitizers, but the action of UVR on protein structure and/or ROS production should be verified experimentally. Crucially, in the case of biochemically active ECM components such as fibronectin and fibrillin, the downstream effects of photo-degradation on tissue homeostasis remain to be confirmed. FUTURE DIRECTIONS Both topical antioxidants and inhibitors of detrimental cell signaling may be effective in abrogating the effects of specific UVR-mediated protein degradation in the dermis.

Low-dose ultraviolet radiation selectively degrades chromophore-rich extracellular matrix components.

Photoageing of human skin due to chronic exposure to ultraviolet radiation (UVR) is characterized histologically by extensive remodelling of the dermal elastic fibre system. Whilst enzymatic pathways are thought to play a major role in mediating extracellular matrix (ECM) degeneration in UV‐exposed skin, the substrate specificity of UVR‐up‐regulated and activated matrix metalloproteinases (MMPs) is low. It is unclear, therefore, how such cell‐mediated mechanisms alone could be responsible for the reported selective degradation of elastic fibre components such as fibrillin‐1 and fibulin‐5 during the early stages of photoageing. Here we use atomic force microscopy (AFM) and scanning transmission electron microscopy (STEM) to demonstrate that physiologically attainable doses (20–100 mJ/cm2) of direct UV‐B radiation can induce profound, dose‐dependent, changes in the structure of, and mass distribution within, isolated fibrillin microfibrils. Furthermore, using reducing and native PAGE in combination with AFM, we show that, whilst exposure to low‐dose UV‐B radiation significantly alters the macromolecular and quaternary structures of both UV chromophore (Cys, His, Phe, Trp and Tyr)‐rich fibrillin microfibrils (fibrillin‐1, 21.0%) and fibronectin dimers (fibronectin, 12.9%), similar doses have no detectable effect on UV chromophore‐poor type I collagen monomers (2.2%). Analysis of the published primary amino acid sequences of 49 dermal ECM components demonstrates that most elastic fibre‐associated proteins, but crucially neither elastin nor members of the collagen family, are rich in UV chromophores. We suggest, therefore, that the amino acid composition of elastic fibre‐associated proteins [including the fibrillins, fibulins, latent TGFβ binding proteins (LTBPs) and the lysyl oxidase family of enzymes (LOK/LOXLs)] may predispose them to direct degradation by UVR. As a consequence, this selective acellular photochemical pathway may play an important role in initiating and/or exacerbating cell‐mediated ECM remodelling in UVR‐exposed skin. Copyright

A review of studies on the effects of ultraviolet irradiation on the resistance to infections: evidence from rodent infection models and verification by experimental and observational human studies

Recent studies on the immunosuppressive effects of ultraviolet radiation (UVR) and the related resistance to infections in rodents and humans are presented. The waveband dependency of trans-to-cis isomerisation of urocanic acid in the stratum corneum and the role of DNA damage in UVR-induced erythema and immunosuppression were investigated to further elucidate the underlying mechanisms. Furthermore, human experimental studies on UVR-induced immunomodulation were performed. It appeared that the doses needed to suppress various immune parameters in humans (e.g. NK activity, contact hypersensitivity) were higher than those needed in experiments in rodents. Still, extrapolation of experimental animal data to the human situation showed that UVR may impair the resistance to different systemic infections at relevant outdoor doses. In observational human studies we aimed to substantiate the relevance of UVR for infections in humans. It was shown that sunny season was associated with a slightly retarded but clinically non-relevant antibody response to hepatitis B vaccination. Furthermore, sunny season appeared to be associated with a small decline in the number of CD4+ T-helper cells in a cohort of HIV-infected persons and a higher recurrence of herpes simplex and herpes zoster in a cohort of renal transplant recipients. However, in a study among young children a higher exposure to solar UVR was associated with a lower occurrence of upper respiratory tract symptoms. As disentangling the effects of UVR from other relevant factors is often impossible in observational studies, concise quantitative risk estimations for the human situation cannot be given at present.