Inflammatory doses of UV may not be necessary for skin carcinogenesis

The UV wavelengths in sunlight are the main cause of skin cancer in humans. Sunlight causes gene mutations, immunosuppression and, at higher doses, inflammation. While it is clear that immunosuppression and gene mutations are essential biologic events via which UV causes skin cancer, the requirement for UV-induced inflammation is less certain. Both the UVB (290-320 nm) and UVA (320-400 nm) wavebands within sunlight can cause skin cancer, gene mutations and immunosuppression. However, UVB, but not UVA, at realistic doses can cause inflammation, and UVB induces skin cancer, immunosuppression and gene mutations at doses much lower than those required to cause inflammation. Inflammation enhances skin carcinogenesis, but may not be UV induced, and inflammatory mediators at doses too low to cause inflammation may be required. UV-induced mutations can cause epidermal cells to make proinflammatory factors or to induce them in the surrounding stroma, creating an oxidizing environment in which additional oncogenic mutations are likely to take place, even in the absence of UV. Our hypothesis is therefore that subinflammatory doses of both UVA and UVB cause benign skin tumors. One of the effects of sunlight-induced mutations may be the production of inflammatory mediators that enhance carcinogenesis.     

A Review of Sunscreen Safety and Efficacy

The use of sunscreen products has been advocated by many health care practitioners as a means to reduce skin damage produced by ultraviolet radiation (UVR) from sunlight. There is a need to better understand the efficacy and safety of sunscreen products given this ongoing campaign encouraging their use. The approach used to establish sunscreen efficacy, sun protection factor (SPF), is a useful assessment of primarily UVB (290–320 nm) filters. The SPF test, however, does not adequately assess the complete photoprotective profile of sunscreens specifically against long wavelength UVAI (340–400 nm). Moreover, to date, there is no singular, agreed upon method for evaluating UVA efficacy despite the immediate and seemingly urgent consumer need to develop sunscreen products that provide broad-spectrum UVB and UVA photoprotection. With regard to the safety of UVB and UVA filters, the current list of commonly used organic and inorganic sunscreens has favorable toxico-logical profiles based on acute, subchronic and chronic animal or human studies. Further, in most studies, sunscreens have been shown to prevent the damaging effects of UVR exposure. Thus, based on this review of currently available data, it is concluded that sunscreen ingredients or products do not pose a human health concern. Further, the regular use of appropriate broad-spectrum sunscreen products could have a significant and favorable impact on public health as part of an overall strategy to reduce UVR exposure.     

Radiation sources providing increased UVA/UVB ratios induce photoprotection dependent on the UVA dose in hairless mice

In studies involving mice in which doses of UVA (320-400 nm) and UVB (290-320 nm) radiation were administered alone or combined sequentially, we observed a protective effect of UVA against UVB-induced erythema/edema and systemic suppression of contact hypersensitivity. The UVA immunoprotection was mediated by the induction of the stress enzyme heme oxygenase-1 (HO-1) in the skin, protection of the cutaneous Th1 cytokines interferon-gamma (IFN-gamma) and IL-12 and inhibition of the UVB-induced expression of the Th2 cytokine IL-10. In this study, we seek evidence for an immunological waveband interaction when UVA and UVB are administered concurrently to hairless mice as occurs during sunlight exposure in humans. A series of spectra providing varying ratios of UVA/UVB were developed, with the UVA ratio increased to approximately 3.5 times the UVA component in solar simulated UV (SSUV). We report that progressively increasing the UVA component of the radiation while maintaining a constant UVB dose resulted in a reduction of both the erythema/edema reaction and the degree of systemic immunosuppression, as measured as contact hypersensitivity. The UVA-enhanced immunoprotection was abrogated in mice treated with a specific HO enzyme inhibitor. UVA-enhanced radiation also upregulated the expression of cutaneous IFN-gamma and IL-12 and inhibited expression of both IL-6 and IL-10, compared with the activity of SSUV. The results were consistent with the previously characterized mechanisms of photoprotection by the UVA waveband alone and suggest that the UVA component of solar UV may have beneficial properties for humans.     

ACTIVATION OF NF-KB IN HUMAN SKIN FIBROBLASTS BY THE OXIDATIVE STRESS GENERATED BY UVA RADIATION

We have examined the role of the nucleus and the membrane in the activation of nuclear factor (NF)-KB by oxidant stress generated via the UVA (320–380nm) component of solar radiation. Nuclear extracts from human skin fibroblasts that had been irradiated with UVA at doses that caused little DNA damage contained activated NF-KB that bound to its recognition sequence in DNA. The UVA radiation-dependent activation of NF-KB in enucleated cells confirmed that the nucleus was not involved. On the other hand, UVA radiation-dependent activation of NF-KB appeared to be correlated with membrane damage, and activation could be prevented by a-tocopherol and butylated hydroxytol-uene, agents that inhibited UVA radiation-dependent peroxidation of cell membrane lipids. The activation of NF-KB by the DNA damaging agents UVC (200–290nm) and UVB (290–320nm) radiation also only occurred at doses where significant membrane damage was induced, and, overall, activation was not correlated with the relative levels of DNA damage induced by UVC/UVB and UVA radiations. We conclude that the oxidative modification of membrane components may be an important factor to consider in the UV radiation-dependent activation of NF-KB over all wavelength ranges examined.     

Relevance of sunscreen application method, visible light and sunlight intensity to free-radical protection: A study of ex vivo human skin

With the continued rise in skin cancers worldwide there is a need for effective skin protection against sunlight damage. It was shown previously that sunscreens, which claimed UVA protection (SPF 20+), provided limited protection against UV-induced ascorbate radicals in human skin. Here the results of an electron spin resonance (ESR) investigation to irradiate ex vivo human skin with solar-simulated light are reported. The ascorbate radical signal in the majority of skin samples was directly proportional to the irradiance over relevant sunlight intensities (0.9-2.9 mW cm(-2)). Radical production (substratum-corneum) by UV (wavelengths < 400 nm) and visible components (> 400 nm) was approximately 67% and 33% respectively. Ascorbate radicals were in steady state concentration at low irradiance (approximately 1 mW cm(-2) equivalent to UK sunlight), but at higher irradiance (approximately 3 mW cm(-2)) decreased with time, suggesting ascorbate depletion. Radical protection by a four star-rated sunscreen (with UVA protection) was optimal when applied as a thin film (40-60% at 2 mg cm(-2)) but less so when rubbed into the skin (37% at 4 mg cm(-2) and no significant protection at 2 mg cm(-2)), possibly due to cream filling crevices, which reduced film thickness. This study validates ESR determinations of the ascorbate radical for quantitative protection measurements. Visible light contribution to radical production, and loss of protection when sunscreen is rubbed into skin, has implications for sunscreen design and use for the prevention of free-radical damage.     

Prompt and delayed nonsteroidal anti-inflammatory drug-photoinduced DNA damage in peripheral blood mononuclear cells measured with the comet assays

Nonsteroidal anti-inflammatory drug (NSAID)-photoinduced DNA damage in human peripheral blood mononuclear cells measured using the alkaline comet assay is presented. Whereas Tiaprofenic Acid-photoinduced DNA damage was promptly induced (i.e. observed at relatively low radiation doses), Ketoprofen-photoinduced DNA damage was delayed. This prompt and delayed effect is observed with UVA (320-400 nm), UVB (290-320 nm) and solar-simulated radiation and is attributed to the different photochemical properties of NSAID. The results from these experiments, carried out in living cells, confirm the speculations of NSAID-photoinduced DNA damage brought up by the many experiments conducted in solution.     

LONG-WAVELENGTH UVA RADIATION INDUCES OXIDATIVE STRESS,CYTOSKELETAL DAMAGE and HEMOLYSIS*

Abstract— We investigated the ability of the different wavelength regions of UV radiation, UVA(320–400 nm), UVB(290–320 nm) and UVC(200–290 nm), to induce hemolysis. Sheep erythrocytes were exposed to radiation from either a UVA1 (>340 nm) sunlamp, a UVB sunlamp, or a UVC germicidal lamp. The doses used for the three wavelength regions were approximately equilethal to the survival of L5178Y murine lymphoma cells. Following exposure, negligible hemolysis was observed in the UVB- and UVC-irradiated erythrocytes, whereas a decrease in the relative cell number (RCN), indicative of hemolysis, was observed in the UVA 1-exposed samples. The decrease in RCN was dependent on dose(0–1625 kj/m²), time(0–78 h postirradiation) and cell density (10⁶-10⁷ cells/mL). Hemolysis decreased with increasing concentration of glutathione, hemoglobin or cell number, while the presence of pyruvate drastically enhanced it. Because scanning spectroscopy(200–700 nm) showed that hemoproteins and nicotinamide adenine dinucleotides were oxidized, cytoplasmic oxidative stress was implicated in the lytic mechanism. Further evidence of oxidation was obtained from electron micrographs, which revealed the formation of Heinz bodies near the plasma membrane. The data demonstrate that exposure of erythrocytes to UVA1, but not UVB or UVC, radiation causes oxidation of cytoplasmic components, which results in cytoskeletal damage and hemolysis.     

Both solar UVA and UVB radiation impair conidial culturability and delay germination in the entomopathogenic fungus Metarhizium anisopliae.

The entomopathogenic hyphomycete Metarhizium anisopliae has been used in programs of agricultural pest and disease vector control in several countries. Exposure to simulated solar radiation for a few hours can completely inactivate the conidia of the fungus. In the present study we determined the effect of exposures to full-spectrum sunlight and to solar ultraviolet A radiation at 320-400 nm (UVA) on the conidial culturability and germination of three M. anisopliae strains. The exposures were performed in July and August 2000 in Logan, UT. The strains showed wide variation in tolerance when exposed to full-spectrum sunlight as well as to UVA sunlight. Four-hour exposures to full-spectrum sunlight reduced the relative culturability by approximately 30% for strain ARSEF 324 and by 100% for strains ARSEF 23 and 2575. The relative UV sensitivity of the two more sensitive strains was different under solar UV from that under ultraviolet B radiation at 280-320 nm (UVB) in the laboratory. Four-hour exposures to solar UVA reduced the relative culturability by 10% for strain ARSEF 324, 40% for strain ARSEF 23 and 60% for strain ARSEF 2575. Exposures to both full-spectrum sunlight and UVA sunlight delayed the germination of the surviving conidia of all three strains. These results, in addition to confirming the deleterious effects of UVB, clearly demonstrate the negative effects of UVA sunlight on the survival and germination of M. anisopliae conidia under natural conditions. The negative effects of UVA in sunlight also emphasize that the biological spectral weighting functions for this fungus must not neglect the UVA wavelengths.     

Examination of Solar Simulators Used for the Determination of Sunscreen UVA Efficacy

The U.S. FDA recently proposed both in vivo and in vitro UVA efficacy tests for sunscreen products with the lower result used to establish the sunscreen's labeled UVA protection claim. The FDA stated their rationale for dual tests was concern that the in vivo test method overemphasizes UVA-2 (320–340 nm) photoprotection. We attribute FDA's observation to the relative lack, compared to sunlight, of UVA-1 (340–400 nm) radiation in the current JCIA UVA solar simulator specification, allowing the method to generate higher UVA protection factors than sunscreens will provide in sunlight. Our work is based upon comparisons of Air Mass 1.0 sunlight to variously filtered UVA solar simulators. Sources near the JCIA UVA-2/UVA limits (8–20%) had a goodness of fit to solar UVA of only 67–79%. We propose that instead of using ratios of UVA-2 to UVA the standard should be a goodness of fit to the UVA region of an Air Mass 1 solar reference spectrum. As the spectral distribution of solar UVA varies much less than UVB, sunlight of reasonable zenith angles of ≤60° will have similar spectral shapes and approximate risk spectrum. Goodness of fit to this spectrum will produce UVA protection values predictive to those actually achieved in sunlight of different zenith angles.     

N-acetyl-L-cysteine prevents DNA damage induced by UVA, UVB and visible radiation in human fibroblasts

The thiol N-acetyl-L-cysteine (NAC) is a source of cysteine for the synthesis of the endogenous antioxidant glutathione (GSH) which is depleted by ultraviolet radiation. It is also associated with the scavenging of reactive oxygen species (ROS). In this study the effects of NAC were examined in cultured human fibroblasts during prolonged exposure to ultraviolet B (UVB), ultraviolet A (UVA) and visible irradiation (280-700 nm), delivered by a 150 W xenon-arc lamp. The alkaline comet assay was used to assess the DNA damage in individual cells. It was found that incubating skin and lung fibroblasts at 37 degrees C for 1 h with an optimal 6 mM NAC supplement prior to light exposure, significantly reduced the level of DNA damage in both cell types, however, the skin fibroblasts were less sensitive to xenon-arc lamp irradiation than lung fibroblasts. NAC incubation resulted in an initial delay in DNA damage when the cells were irradiated. There was also a significant reduction in the overall levels of DNA damage observed with continued irradiation. NAC significantly reduced the DNA damage produced in lung fibroblasts depleted of normal GSH protection by the glutamylcysteinyl synthetase inhibitor, L-buthionine-[S,R]-sulfoximine. Although the specific mechanism of NAC protection has not yet been elucidated, these results support the hypothesis that NAC may protect the cells directly, by scavenging ROS induced by UVA and visible radiation, and indirectly by donating cysteine for GSH synthesis.     

Cell Cycle Effects and Concomitant p53 Expression in Hairless Murine Skin after Longwave UVA (365 nm) Irradiation: A Comparison with UVB Irradiation

Abstract— Ultraviolet A (UVA,315–400 nm) radiation is known to be a complete carcinogen, but in contrast to UVB (280-315 nm) radiation, much of the cell damage is oxygen dependent (mediated through reactive oxygen species), and the dominant premutational DNA lesion(s) remains to be identified. To investigate further the basic differences in UVA and UVB carcinogenesis, we compared in vivo cellular responses, viz. cell cycle progression and transient p53 expression in the epidermis, after UVA1 (340-400 nm) exposure with those after broadband UVB exposure of hairless mice. Using flow cytometry we found a temporary suppression of bromodeoxyuridine (BrdU) uptake in S-phase cells both after UVB and UVA1 irradiation, which only in the case of UVB is followed by an increase to well over control levels. With equally erythemogenic doses (1-2 MED), the modulation of BrdU uptake was more profound after UVB than after UVA1 irradiation. Also, a marked transient increase in the percentage of S-phase cells occurred both after UVB and after UVA1 irradiation, but this increase evolved more rapidly after UVA1 irradiation. Further, p53 expression increased both after UVB and UVA1 irradiations, with peak expression already occurring from 12 to 24 h after UVA1 exposure and around 24 h after UVB exposure. Overall, UVA1 radiation appears to have less of an impact on the cell cycle than UVB radiation, as measured by the magnitude and duration of changes in DNA synthesis and cells in S phase. These differences are likely to reflect basic differences between UVB and UVA1 in genotoxicity and carcinogenic action.     

Cell Cycle Kinetics Following UVA Irradiation in Comparison to UVB and UVC Irradiation

Abstract— There is limited information about the carcinogenic effect of longwave ultraviolet radiation (UVA: 315-400 nm). In particular very little is known about the relevant genotoxic damage caused by physiological doses of UVA radiation. A general response of cells to DNA damage is a delay or arrest of the cell cycle. Conversely, such cellular responses after UVA irradiation would indicate significant genotoxic damage. The aim of this study is to compare cell cycle kinetics of human fibroblasts after UVC (190-280 nm radiation), UVB (280-315 nm radiation) and UVA irradiation. Changes in the cell cycle kinetics were assessed by bivariate flow cytometric analysis of DNA synthesis and of DNA content. After UVC, UVB or UVA irradiation of human fibroblasts a suppression was seen of bromodeoxyuridine (BrdU) incorporation at all stages of S phase. The magnitude of this suppression appeared dose dependent. Maximum suppression was reached at 5-7 h after UVB exposure and directly after UVA exposure, and normal levels were reached 25 h after UVB and 7 h after UVA exposure. The lowered BrdU uptake corresponded with a lengthening of the S phase. No dramatic changes in percentages of cells in G₁, S and G₂/M were seen after the various UV irradiations. Apparently, UVA irradiation, like UVB and UVC irradiation, can temporarily inhibit DNA synthesis, which is indicative of genotoxic damage.     

Oxidation of guanine in cellular DNA by solar UV radiation: biological role.

The formation of cyclobutane pyrimidine dimers (CPD) and 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo) was investigated in Chinese hamster ovary cells upon exposure to either UVC, UVB, UVA or simulated sunlight (SSL). Two cell lines were used, namely AT3-2 and UVL9, the latter being deficient in nucleotide excision repair and consequently UV sensitive. For all types of radiation, including UVA, CPD were found to be the predominant lesions quantitatively. At the biologically relevant doses used, UVC, UVB and SSL irradiation yielded 8-oxodGuo at a rather low level, whereas UVA radiation produced relatively higher amounts. The formation of CPD was 10(2) and 10(5) more effective upon UVC than UVB and UVA exposure. These yields of formation followed DNA absorption, even in the UVA range. The calculated relative spectral effectiveness in the production of the two lesions showed that efficient induction of 8-oxodGuo upon UVA irradiation was shifted toward longer wavelengths, in comparison with those for CPD formation, in agreement with a photosensitization mechanism. In addition, after exposure to SSL, about 19% and 20% of 8-oxodGuo were produced between 290-320 nm and 320-340 nm, respectively, whereas CPD were essentially (90%) induced in the UVB region. However, the ratio of CPD to 8-oxodGuo greatly differed from one source of light to the other: it was over 100 for UVB but only a few units for UVA source. The extent of 8-oxodGuo and CPD was also compared to the lethality for the different types of radiation. The involvement of 8-oxodGuo in cell killing by solar UV radiation was clearly ruled out. In addition, our previously reported mutation spectra demonstrated that the contribution of 8-oxodGuo in the overall solar UV mutagenic process is very minor.     

Evaluation of the protective effect of sunscreens on in vitro reconstructed human skin exposed to UVB or UVA irradiation

We have previously shown that skin reconstructed in vitro is a useful model to study the effects of UVB and UVA exposure. Wavelength-specific biological damage has been identified such as the formation of sunburn cells (SBC) and pyrimidine dimers after UVB irradiation and alterations of dermal fibroblasts after UVA exposure. These specific effects were selected to evaluate the protection afforded by two sunscreens after topical application on the skin surface. Simplified formulations having different absorption spectra but similar sun protection factors were used. One contained a classical UVB absorber, 2-ethylhexyl-p-methoxycinnamate. The other contained a broad-spectrum absorber called Mexoryl SX, characterized by its strong absorbing potency in the UVA range. Both filters were used at 5% in a simple water/oil vehicle. The evaluation of photoprotection on in vitro reconstructed skin revealed good efficiency for both preparations in preventing UVB-induced damage, as shown by SBC counting and pyrimidine dimer immunostaining. By contrast, only the Mexoryl SX-containing preparation was able to efficiently prevent UVA-specific damage such as dermal fibroblast disappearance. Our data further support the fact that skin reconstructed in vitro is a reliable system to evaluate the photoprotection provided by different sunscreens against specific UVB and UVA biological damage.     

The Autophagy Receptor Adaptor p62 is Up‐regulated by UVA Radiation in Melanocytes and in Melanoma Cells

UVA (315–400 nm) is the most abundant form of UV radiation in sunlight and indoor tanning beds. However, much remains to be understood about the regulation of the UVA damage response in melanocytes and melanoma. Here, we show that UVA , but not the shorter waveband UVB (280–315 nm), up‐regulates adaptor protein p62 in an Nrf2‐ and reactive oxygen species (ROS )‐dependent manner, suggesting a UVA ‐specific effect on p62 regulation. UVA ‐induced p62 up‐regulation was inhibited by a mitochondria‐targeted antioxidant or Nrf2 knockdown. In addition, p62 knockdown inhibited UVA ‐induced ROS production and Nrf2 up‐regulation. We also report here a novel regulatory feedback loop between p62 and PTEN in melanoma cells. PTEN overexpression reduced p62 protein levels, and p62 knockdown increased PTEN protein levels. As compared with normal human skin, p62 was up‐regulated in human nevus, malignant melanoma and metastatic melanoma. Furthermore, p62 was up‐regulated in melanoma cells relative to normal human epidermal melanocytes, independent of their BRAF or NRAS mutation status. Our results demonstrated that UVA up‐regulates p62 and induces a p62‐Nrf2 positive feedback loop to counteract oxidative stress. Additionally, p62 forms a feedback loop with PTEN in melanoma cells, suggesting p62 functions as an oncogene in UVA ‐associated melanoma development and progression.     

Measurements of UV-generated free radicals/reactive oxygen species (ROS) in skin

Free radicals/reactive oxygen species (ROS) generated in skin by UV irradiation were measured by electron spin resonance (ESR). To increase the sensitivity of measurement the short life free radicals/ROS were scavenged and accumulated by using the nitroxyl probe 3-carboxy-2,2,5,5-tetrametylpyrrolidine-1-oxyl (PCA). The spatial distribution of free radicals/ROS measured in pig skin biopsies with ESR imaging after UV irradiation corresponds to the intensity decay of irradiance in the depth of the skin. The main part of free radicals/ROS were generated by UVA (320-400 nm) so that the spatial distribution of free radicals reaches up to the lower side of the dermis. In vivo measurements on human skin were performed with a L-band ESR spectrometer and a surface coil integrating the signal intensities from all skin layers to get a sufficient signal amplitude. Using this experimental arrangement the protection of UVB and UVA/B filter against the generation of free radicals/ROS in skin were measured. The protection against ROS and the repair of damages caused by them can be realized with active antioxidants characterized by a high antioxidative power (AP). The effect of UV filter and antioxidants corresponding to their protection against free radicals/ROS in skin generated by UVAB irradiation can be quantified by the new radical sun protection factor (RSF). The RSF indicates the increase of time for staying in the sun to generate the same number of free radicals/ROS in the skin like for the unprotected skin. Regarding the amount of generated free radicals/ROS in skin as an biophysical endpoint the RSF characterizes both the protection against UVB and UVA radiation.     

ULTRAVIOLET RADIATION-INDUCED PHOSPHOLIPASE A2 ACTIVATION OCCURS IN MAMMALIAN CELL MEMBRANE PREPARATIONS

Ultraviolet erythema in human skin is mediated in part by membrane derivatives of arachidonic acid (AA). UVA (320–400nm) and UVB (290–320nm) have been shown to induce release of AA from intact mammalian cells in culture. In order to investigate the mechanism of this release we examined the effect of UVA and UVB on release of [³H] AA from membrane preparations of murine fibroblasts. C3H 10T1/2 cells were prelabelled for 24 h with [³H] AA. The membrane fractions of the cells were separated after lysis by differential centrifugation. The membranes were irradiated in suspension and the [³H] AA released from the membranes was determined by scintillation spectroscopy of supernatants3–4 h after irradiation. Both UVA and UVB induced release of AA from the membrane preparations. The response to UVB was small but significant, reaching levels approximately 150% of control release at doses of 1,200-4,000 J/m². The response to UVA was larger; doses of 2.5-5.0 J/cm² induced release equal to twice control (200%) levels, while doses of10–20 J/cm² induced maximal release at levels approximately 400% of control. Time course studies with UVB and UVA showed maximal release at 4 h after irradiation. When the membrane preparations were incubated with a polyclonal anti-phospholipase A₂ antibody the UV induced release of [³H] AA was completely inhibited in both UVB (1200 J/m²) and UVA (10 J/cm²) treated cells. These data suggest that activation of phospholipase A₂ is responsible for the UV induced release of AA in mammalian cells and that the mechanism of this activation is due, in part at least, to direct photon-membrane interaction.     

Differential effects of UVA1 and UVB radiation on Langerhans cell migration in mice

The UVB (280-315 nm)- and UVA1 (340-400 nm)-induced migration of Langerhans cells (LC) from the epidermis and accumulation of dendritic cells (DC) in the lymph nodes draining the exposed skin site of C3H/HeN mice have been investigated. One minimum erythemal dose (MED) of UVB (1.5 kJ/m2) and of UVA1 (500 kJ/m2) were chosen, which have been shown previously to suppress delayed hypersensitivity (DTH). UVB irradiation resulted in a reduction in epidermal LC numbers, local to the site of the exposure, which was most apparent 12 h after exposure, but, in contrast, UVA1 had no significant effect even at 72 h after exposure. UVA1 did not exert any protection against the UVB-mediated depletion in LC numbers. The reduction in local LC following UVB exposure was prevented by systemic (intraperitoneal) treatment of mice with neutralising antibodies to either tumor necrosis factor (TNF)-alpha or interleukin (IL)-beta 2 h prior to the irradiation. It has been reported previously that UVB exposure caused an increase in the number of dendritic cells (DC) in the lymph nodes draining the irradiated skin site. In the present study we have shown that UVA1 had a similar effect. Pretreatment of the mice with neutralising antibodies to IL-1beta (by intraperitoneal injection) substantially inhibited DC accumulation induced by both UV regimens. However, anti-TNF-alpha antibodies affected only the UVB-induced increase, and did not alter the elevation in DC numbers observed following UVA1 exposure. These results indicate that UVB causes the migration of LC from the epidermis and an accumulation of DC in the draining lymph nodes by a mechanism that requires both TNF-alpha and IL-1beta. In contrast, UVAI does not cause LC migration from the epidermis and the accumulation of DC in the draining lymph nodes observed following UVA1 exposure requires IL-1beta, but not TNF-alpha. It is likely therefore that UVA1 acts through a different mechanism from UVB and may target a cutaneous antigen presenting cell other than LC, such as the dermal DC.     

Effects of ultraviolet-A exposure on ultraviolet-B-induced accumulation of specific flavonoids in Brassica napus.

Many plant species are able to acclimate to changes in ultraviolet-B radiation (UVB) (290-320 nm) exposure. Due to the wide range of targets of UVB, plants have evolved diverse repair and protection mechanisms. These include increased biosynthesis of UVB screening compounds, elevated antioxidant activity and increased rates of DNA repair. We have shown previously that Brassica napus L. cv Topas plants can acclimate quite effectively to environmentally relevant increases in UVB through the accumulation of specific flavonoids in the leaf epidermis. However, B. napus was found to lose other flavonoids when plants are exposed to ultraviolet-A radiation (UVA) (320-400 nm) and/or UVB (Wilson et al. [1998] Photochem. Photobiol. 67, 547-553). In this study we demonstrate that the levels of all the extractable flavonoids in the leaves of B. napus plants are decreased in a dose-dependent manner in response to UVA exposure. Additionally, the accumulation of the extractable flavonoids was examined following a shift from photosynthetically active radiation (PAR) + UVA to PAR + UVB to assess if preexposure to UVA affected UVB-induced flavonoid accumulation. UVA preexposures were found to impede UVB-induced accumulation of some flavonoids. This down regulation was particularly evident for quercetin-3-O-sophoroside and quercetin-3-O-sophoroside-7-O-glucoside, which is interesting because quercetins have been demonstrated to be induced by UVB and correlated with UVB tolerance in some plant species. The photobiological nature of these UVA-mediated effects on flavonoid accumulation implies complex interactions between UVA and UVB responses.