Effects of Ultraviolet Radiation (UVA+UVB) on Young Gametophytes of Gelidium floridanum: Growth Rate,Photosynthetic Pigments,Carotenoids, Photosynthetic Performance,and Ultrastructure

This study investigated the effects of radiation (PAR+UVA+UVB) on the development and growth rates (GRs) of young gametophytes of Gelidium floridanum. In addition, photosynthetic pigments were quantified, carotenoids identified, and photosynthetic performance assessed. Over a period of 3 days, young gametophytes were cultivated under laboratory conditions and exposed to photosynthetically active radiation (PAR) at 80 μmol photons m^?2 s^?1 and PAR+UVA (0.70 W m^?2)+UVB (0.35 W m^?2) for 3 h per day. The samples were processed for light and electron microscopy to analyze the ultrastructure features, as well as carry out metabolic studies of GRs, quantify the content of photosynthetic pigments, identify carotenoids and assess photosynthetic performance. PAR+UVA+UVB promoted increase in cell wall thickness, accumulation of floridean starch grains in the cytoplasm and disruption of chloroplast internal organization. Algae exposed to PAR+UVA+UVB also showed a reduction in GR of 97%. Photosynthetic pigments, in particular, phycoerythrin and allophycocyanin contents, decreased significantly from UV radiation exposure. This result agrees with the decrease in photosynthetic performance observed after exposure to ultraviolet radiation, as measured by a decrease in the electron transport rate (ETR), where values of ETRmax declined approximately 44.71%. It can be concluded that radiation is a factor that affects the young gametophytes of G. floridanum at this stage of development.     

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.     

Medical UV Exposures and HIV Activation

This paper presents the first attempt to evaluate the potential of clinical UV exposures to induce the human immunodeficiency (HIV) promoter and, thus, to upregulate HIV growth in those skin cells that are directly affected by the exposure. Using the data for HIV promoter activation in vitro, we computed UVB and psoralen plus UVA (PUVA) doses that produce 50% of the maximal promoter activation (AD₅₀). Then, using (a) literature data for UV transmittance in the human skin, (b) a composite action spectrum for HIV promoter and pyrimidine dimer induction by UVB and (c) an action spectrum for DNA synthesis inhibition by PUVA, we estimated the distribution of medical UVB and PUVA doses in the skin. This allowed us to estimate how deep into the skin the HIV-activating doses might penetrate in an initial and an advanced stage of UVB or PUVA therapy. Such analysis was done for normal type II skin and for single exposures. The results allow us to predict where in the skin the HIV promoter may be induced by selected small and large therapeutic UVB or PUVA doses. To accommodate changes in skin topography due to disease and UV therapy, our considerations would require further refinements. For UVB we found that, when the incident dose on the surface of the skin is 500 J/m² (290–320nm) (initial stage of the therapy), the dose producing 50% of the maximal HIV promoter activation (AD^UVB₅₀) is limited to the stratum corneum. However, with an incident dose of 5000 J/m² (an advanced stage of the therapy), AD^UVB₅₀ may be delivered as far as the living cells of the epidermis and even to some parts of the upper dermis. For PUVA we found that, when the incident UVA doses are 25 or 100 kJ/m² (320–400nm) (an initial and an advanced stage of therapy, respectively), and the 8-methoxypsoralen concentration in the blood is 0.1 μg/mL (the desired level), the combined doses to the mid epidermis (and some areas of the upper dermis) are well below the 50% HIV promoter-activating PUVA dose (AD^PUVA₅₀). Only under the worst scenario conditions, i. e. an exceptionally high drug concentration in the patient's tissues and localization of HIV in the nearest proximity to the skin surface, would the combined PUVA dose expected during photochemotherapy exceed AD^PUVA₅₀. These results suggest that the probability of HIV activation in the epidermis by direct mechanisms is higher for UVB than for PUVA treatment. However, complexities of the UV-inducible HIV activation and immunomodulatory phenomena are such that our results by themselves should not be taken as an indication that UVB therapy carries a higher risk than PUVA therapy when administered to HIV-infected patients.     

Nitric oxide-dependent pigment migration induced by ultraviolet radiation in retinal pigment cells of the crab Neohelice granulata

The purpose of this study was to verify the occurrence of pigment dispersion in retinal pigment cells exposed to UVA and UVB radiation, and to investigate the possible participation of a nitric oxide (NO) pathway. Retinal pigment cells from Neohelice granulata were obtained by cellular dissociation. Cells were analyzed for 30 min in the dark (control) and then exposed to 1.1 and 3.3 J cm⁻² UVA, 0.07 and 0.9 J cm⁻² UVB, 20 n m β-PDH (pigment dispersing hormone) or 10 μ m SIN-1 (NO donor). Histological analyses were performed to verify the UV effect in vivo . Cultured cells were exposed to 250 μ m L-NAME (NO synthase blocker) and afterwards were treated with UVA, UVB or β-PDH. The retinal cells in culture displayed significant pigment dispersion in response to UVA, UVB and β-PDH. The same responses to UVA and UVB were observed in vivo . SIN-1 did not induce pigment dispersion in the cell cultures. l-NAME significantly decreased the pigment dispersion induced by UVA and UVB but not by β-PDH. All retinal cells showed an immunopositive reaction against neuronal nitric oxide synthases. Therefore, UVA and UVB radiation are capable of inducing pigment dispersion in retinal pigment cells of Neohelice granulata and this dispersion may be nitric oxide synthase dependent.     

Differential Activation of Signaling Pathways by UVA and UVB Radiation in Normal Human Epidermal Keratinocytes(†)

Ultraviolet (UV) radiation from the solar spectrum is a major etiological factor for many cutaneous pathologies including cancer. By understanding changes in cell signaling pathways induced by UVA and UVB, novel strategies for prevention and treatment of UV‐related pathologies could be developed. However, much of the information in the literature from various laboratories cannot cross talk because of difficulties associated with the use of ill‐defined light sources and physiologically irrelevant light dosimetry. Herein, we have assessed the effect of exposure of normal human epidermal keratinocytes (NHEK) to UVA (2 and 4 J cm^?2) or UVB (20 and 40 mJ cm^?2) radiation. Employing western blot analysis, we found that exposure of NHEK to UVB, but not UVA, phosphorylates JNK1/2 at Th¹⁸³/Tyr¹⁸⁵, STAT3 at Ser⁷²⁷, AKT at Ser⁴⁷³ and increases c‐Fos expression, whereas exposure to UVA, but not UVB, phosphorylates AKT at Thr³⁰⁸. UVB as well as UVA exposure leads to increased phosphorylation of (1) ERK1/2 at Th²⁰²/Tyr²⁰⁴; (2) p38 at Th¹⁸⁰/Tyr²⁰⁴; (3) STAT3 at Tyr⁷⁰⁵; (4) mTOR at Thr²⁴⁴⁸; and (v) p70S6k at Thr⁴²¹/Ser⁴²⁴; enhanced expression of PI3K (p85) and c‐jun; and nuclear translocation of NFκB proteins. These findings could be considered as a beginning for understanding the differential effects of UVA and UVB in the human skin and may have implications both with respect to risk assessment from exposure to solar UV radiation, and to target interventions against signaling events mediated by UVA and UVB.     

UVA and UVB‐Induced 8‐Methoxypsoralen Photoadducts and a Novel Method for their Detection by Surface‐Enhanced Laser Desorption Ionization Time‐of‐Flight Mass Spectrometry (SELDI‐TOF MS)

UVA‐activated psoralens are used to treat hyperproliferative skin conditions due to their ability to form DNA photoadducts, which impair cellular processes and may lead to cell death. Although UVA (320–400 nm) is more commonly used clinically, studies have shown that UVB (280–320 nm) activation of psoralen can also be effective. However, there has been no characterization of UVB‐induced adduct formation in DNA alone. As psoralen derivatives have a greater extinction coefficient in the UVB region (11 800 cm^?1 M^?1 at 300 nm) compared with the UVA region (2016 cm^?1 M^?1 at 365 nm), a greater extent of adduct formation is expected. SELDI‐TOF, a proteomic technique that combines chromatography with mass spectrometry, was used to detect photoadduct formation in an alternating A–T oligonucleotide. 8‐Methoxypsoralen (8‐MOP) and DNA solutions were irradiated with either UVA or UVB. An adduct peak was obtained with SELDI‐TOF. For UVB‐activated 8‐MOP, the extent of adducts was three times greater than for UVA. HPLC ESI‐MS analysis showed that UVB irradiation yielded high levels of 3,4‐monoadducts (78% of total adducts). UVA was more effective than UVB at conversion of 4′,5′‐monoadducts to crosslinks (17% vs 4%, respectively). This report presents a method for comparing DNA binding efficiencies of interstrand crosslink inducing agents.     

Effects of Ultraviolet Radiation (UVA+UVB) and Copper on the Morphology,Ultrastructural Organization and Physiological Responses of the Red Alga Pterocladiella capillacea

The effect of ultraviolet (UV) radiation and copper (Cu) on apical segments of Pterocladiella capillacea was examined under two different conditions of radiation, PAR (control) and PAR+UVA+UVB (PAR+UVAB), and three copper concentrations, ranging from 0 (control) to 0.62, 1.25 and 2.50 μm . Algae were exposed in vitro to photosynthetically active radiation (PAR) at 70 μmol photons m^?2 s^?1, PAR + UVB at 0.35 W m^?2 and PAR +UVA at 0.70 W m^?2 during a 12‐h photocycle for 3 h each day for 7 days. The effects of radiation and copper on growth rates, content of photosynthetic pigments and photosynthetic performance were analyzed. In addition, samples were processed for light and transmission electron microscopy. The content of photosynthetic pigments decreased after exposure to radiation and Cu. Compared with PAR radiation and copper treatments modified the kinetics patterns of the photosynthesis/irradiance curve. The treatments also caused changes in the ultrastructure of cortical and subcortical cells, including increased cell wall thickness and accumulation of plastoglobuli, as well as changes in the organization of chloroplasts. The results indicate that the synergistic interaction between UV radiation and Cu in P. capillacea, led to the failure of protective mechanisms and causing more drastic changes and cellular imbalances.     

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.     

Long-wavelength Ultraviolet A1 and Visible Light Photoprotection: A Multimodality Assessment of Dose and Response

Human skin is exposed to visible light (VL; 400–700 nm) and long-wavelength ultraviolet A1 (UVA1) radiation (370–400 nm) after the application of organic broad-spectrum sunscreens. The biologic effects of these wavelengths have been demonstrated; however, a dose–response has not been investigated. Ten subjects with Fitzpatrick skin phototype IV-VI were enrolled. Subjects were irradiated with 2 light sources (80–480 J cm⁻²): one comprising VL with less than 0.5% UVA1 (VL+UVA1) and the other pure VL. Skin responses were evaluated for 2 weeks using clinical and spectroscopic assessments. 4-mm punch biopsies were obtained from nonirradiated skin and sites irradiated with 480 J cm⁻² of VL+UVA1 and pure VL 24 h after irradiation. Clinical and spectroscopic assessments demonstrated a robust response at VL+UVA1 sites compared with pure VL. Histology findings demonstrated a statistically significant increase in the marker of inflammation (P < 0.05) and proliferation (P < 0.05) at the irradiated sites compared with nonirradiated control. Threshold doses of VL+UVA1 resulting in biologic responses were calculated. Results indicate that approximately 2 h of sun exposure, which equates to VL+UVA1 dose (~400 J cm⁻²), is capable of inducing inflammation, immediate erythema and delayed tanning. These findings reinforce the need of photoprotection beyond the UV range.     

The Value of the Ratio of UVA to UVB in Sunlight

The objective of this communication is to present the calculated ratio between UVA and UVB irradiance from sunrise to sunset and under a number of weather conditions. UVA plays an important role in the sun spectrum and a lot of attention has been paid lately regarding the protection of people from UVA. Solar spectra were collected in Kuwait City located at 29.3^oNorth latitude (similar to that of Houston, TX) over a period of 8 months and under various weather conditions. Spectra were collected from 260 nm to 400 nm in 2 nm increments for solar elevation angles from 10^o to 90^o using a calibrated Optronics Laboratories OL‐742 Spectroradiometer. The measurements reported in this study the ratio of UVA (320–400 nm) to UVB (280–320 nm) in solar terrestrial radiation remains essentially constant and equal to 20 for the part of the day when the solar elevation is greater than 60^o. Consequently the value of the ratio of solar UVA/UVB should be considered as equal to 20 for studies in photobiology and photomedicine. When the wavelength limiting the range of UVA and UVB is 315 nm (i.e. UVB: 280–315 nm and UVA: 315–400 nm) the ratio of UVA to UVB becomes equal to 41.     

Effects and Mechanism of Nicotinamide Against UVA‐ and/or UVB‐mediated DNA Damages in Normal Melanocytes

Melanoma incidences are increasing rapidly, and ultraviolet (UV) radiation from the sun is believed to be its major contributing factor. UV exposure causes DNA damage in skin which may initiate cutaneous skin cancers including melanoma. Melanoma arises from melanocytes, the melanin‐producing skin cells, following genetic dysregulations resulting into hyperproliferative phenotype and neoplastic transformation. Both UVA and UVB exposures to the skin are believed to trigger melanocytic hyperplasia and melanomagenesis. Melanocytes by themselves are deficient in repair of oxidative DNA damage and UV‐induced photoproducts. Nicotinamide, an active form of vitamin B3 and a critical component of the human body's defense system has been shown to prevent certain cancers including nonmelanoma skin cancers. However, the mechanism of nicotinamide's protective effects is not well understood. Here, we investigated potential protective effects and mechanism of nicotinamide against UVA‐ and/or UVB‐ induced damage in normal human epidermal melanocytes. Our data demonstrated an appreciable protective effect of nicotinamide against UVA‐ and/or UVB‐ induced DNA damage in melanocytes by decreasing both cyclobutane pyrimidine dimers and 8‐hydroxy‐2′‐deoxyguanosine levels. We found that the photoprotective response of nicotinamide was associated with the activation of nucleotide excision repair genes and NRF2 signaling. Further studies are needed to validate our findings in in vivo models.     

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.     

Sunscreen Protection Against Ultraviolet Radiation-induced Pyrimidine Dimers in Mouse Epidermal DNA

Pyrimidine dimers were measured in epidermal DNA of SKH:HRI mice following exposure to solar-simulated UV radiation (SSUV, 290–400 nm) or to UVA (320–400 nm). Mice were exposed to SSUV or UVA after topical application (2 mg/cm²) of vehicle, a UVB absorber (5% 2-ethylhexyl p-methoxycinnamate [2-EHMC]), or a broad-spectrum UVA absorber (5% Mexoryl®SX). The rates of induction of pyrimidine dimers in untreated animals were 5.4 ± 0.57 times 10^-4 (mean ± SEM) and 7.6 ± 0.95 times 10^-6 dimers per 10⁸ Da of epidermal DNA per J/m² of SSUV and UVA, respectively. Topical application of Mexoryl®SX reduced the rate of induction of pyrimidine dimers in SSUV-exposed animals to 4.7 ± 0.44 times 10^-5 dimers per 10⁸ Da per J/m² for a dimer induction protection factor (PF) of 11.5 (5.4 times 10 ⁴/4.7 times 10^-5). The rate of dimer induction in Mexoryl®SX-treated, UVA-ex-posed mice was 0.95 ± 0.2 times 10^-6 dimers per 10⁸ Da per J/m² (PF = 8.0). The 2-EHMC at a concentration of 5% (wt/wt) was significantly less effective than Mexoryl®SX in preventing the induction of pyrimidine dimers in animals exposed to either SSUV or UVA. The rates of dimer induction in 2-EHMC-treated mice were 8.2 ± 1.1 times 10^-5 and 3.8 ± 0.33 times 10^-6 dimers per Da per J/m² of SSUV (PF = 6.6) and UVA (PF = 2.0), respectively. Upon normalizing to the efficacy for edema induction, UVA induced approximately one-fourth the number of pyrimidine dimers per equivalent edematous response when compared to SSUV.     

The Effects of the Broadband UVA Radiation on Myeloid Leukemia Cells: The Possible Role of Protein Kinase C in Mediation of UVA-lnduced Effects

Abstract— We examined the effects of broadband UVA radiation (320–400 nm) on a rat myeloid leukemia cell line–chlo-roma (ChL). A Phillips face tanner model HB 171/A was used as a light source. Chloroma were irradiated through a 5 mm thick glass Alter that cut off all of the UVB contamination. The irradiances were measured, from 250 to 400 nm, with a well-characterized and calibrated double-grating spectroradiometer Optronic 742. The overall uncertainty of dose evaluation was estimated to be <15% (2s?). The cells were irradiated with UVA doses of 4 and 8 J/cm² and cultured thereafter for 24 h. After this period of time, a marked decline up to 50% was observed in cell proliferation in UVA-irradiated ChL cultures. The cell proliferation decline was found to be caused by simultaneously occurring G2/M phase cell cycle arrest and apoptosis in part of the UVA-irradiated ChL population. Concomitantly, with the decline in cell proliferation, an increase was observed in the expression of the major histocompatibility (MHC) class I and II antigens. Because protein kinase C (PKC) is known to regulate cell proliferation, apoptosis and expression of MHC antigens, and because UVA was shown to regulate PKC activity/expression, we therefore examined whether UVA irradiation has any effect on the expression of isozymes of PKC. Western blots revealed that ChL express α, βI, δ, α, γ, and π isozymes of PKC and that expression of all isozymes declined 24 h after UVA irradiation (8 J/cm²). Finally, PKC activation in ChL by exposure to phorbol ester caused cell cycle arrest in G1 phase but did not induce apoptosis. This suggests that the previously shown UVA-induced PKC activation in ChL might be responsible for the induction of MHC antigens but the simultaneously observed ChL apoptosis is likely to be mediated by PKC down-regulation. All together, our results suggest that UVA, at irradiance levels that resemble the outdoor exposure, may have profound effects on the immune-related properties of leukocytes. Thus, we speculate that in vivo the immune functions of leukocytes passing through dermal capillaries might be altered by exposure to solar UVA radiation.     

Red Light Interferes in UVA‐Induced Photoaging of Human Skin Fibroblast Cells

The possible regulation mechanism of red light was determined to discover how to retard UVA‐induced skin photoaging. Human skin fibroblasts were cultured and irradiated with different doses of UVA, thus creating a photoaging model. Fibroblasts were also exposed to a subtoxic dose of UVA combined with a red light‐emitting diode (LED) for five continuous days. Three groups were examined: control, UVA and UVA plus red light. Cumulative exposure doses of UVA were 25 J cm^?2, and the total doses of red light were 0.18 J cm^?2. Various indicators were measured before and after irradiation, including cell morphology, viability, β‐galactosidase staining, apoptosis, cycle phase, the length of telomeres and the protein levels of photoaging‐related genes. Red light irradiation retarded the cumulative low‐dose UVA irradiation‐induced skin photoaging, decreased the expression of senescence‐associated β‐galactosidase, upregulated SIRT1 expression, decreased matrix metalloproteinase MMP‐1 and the acetylation of p53 expression, reduced the horizon of cell apoptosis and enhanced cell viability. Furthermore, the telomeres in UVA‐treated cells were shortened compared to those of cells in the red light groups. These results suggest that red light plays a key role in the antiphotoaging of human skin fibroblasts by acting on different signaling transduction pathways.     

EPR Detection of Free Radicals in UV-lrradiated Skin: Mouse Versus Human

Abstract— Ultraviolet radiation produces free radicals in Skh-1 mouse skin, contributing to photoaging and carcinogenesis. If a mouse model is a general indicator of free radical processes in human skin photobiology, then radical production observed in mouse and human skin should be directly comparative. In this work we show that UV radiation (Λ > 300 nm, 14 μW/cm² UVB; 3.5 mW/cm² UVA) increases the ascorbate free radical (Asc^.-) electron paramagnetic resonance (EPR) signal in both Skh-1 mouse skin (45%) and human facial skin biopsies (340%). Visible light (Λ > 400 nm; 0.23 mW/cm² UVA) also increased the Asc^.- signal in human skin samples (45%) but did not increase baseline mouse Asc^.-, indicating that human skin is more susceptible to free radical formation and that a chromophore for visible light may be present. Using EPR spin-trapping techniques, UV radiation produced spin adducts consistent with trapping lipid alkyl radicals in mouse skin (α-[4-pyridyl 1-oxide]-N-tert-butyl nitrone/alkyl radical adduct; a^N= 15.56 G and a^H= 2.70 G) and lipid alkoxyl radicals in human skin (5,5-dimethylpyrroline-l-oxide/alkoxyl radical adduct; a^N= 14.54 G and a^H= 16.0 G). Topical application of the iron chelator Desferal to human skin significantly decreases these radicals (±50%), indicating a role for iron in lipid peroxidation; Desferal has previously been shown to decrease radical production in mouse skin. This work supports the use of the Skh-1 mouse as a predictive tool for free radical formation in human skin. These results provide the first direct evidence for UV radiation-induced free radical formation at near physiological temperatures in human skin and suggest that iron chelators may be useful as photoprotective agents.     

COMPARISON OF EFFECTS OF UVA, UVB AND UVC ON GROWTH AND VIABILITY OF MITOGEN-STIMULATED HUMAN PERIPHERAL BLOOD CELLS

Abstract— Peripheral blood mononuclear cells were irradiated with UVA, UVB or UVC. The highest exposure dose used in each waveband reduced the number of viable cells to one-third the control cell population after 3 days in culture. Exposure of these cells to half as much UV from each waveband resulted in an equivalent or greater degree of inhibition of their proliferative response to mitogen as measured by lymphoblast transformation, [³H]-thymidine uptake and viable cell number on day 3 in culture. The pattern of inhibition was distinct for each waveband. UVA interfered with blastogenesis on the first 2 days of culture at doses which had considerably less effect on viable cell number. UVA also depressed the first round of DNA synthesis, which was detectable on the second day of culture. By day 3 in culture, however, the UVA-induced reduction in both the number of lymphoblasts and the uptake of [³H]-thymidine was a direct reflection of reduced numbers of viable cells. UVB did not interfere with blastogenesis in mitogen-stimulated cultures to the same degree as did UVA. Only the highest dose of UVB depressed blast transformation more than viable cell number on day 1; by day 2 lower doses were also inhibitory. In contrast UVC had little effect on blastogenesis at any time; a reduced number of lymphoblasts observed on days 2 and 3 in culture was a direct reflection of a reduced number of viable cells rather than a reduced percent of these cells undergoing blast transformation. As with UVA-irradiated, mitogen-stimulated cells, [³H]-thymidine uptake was also depressed in both UVB and UVC irradiated, mitogen-stimulated cells on day 2. However, only UVB continued to depress DNA synthesis more than viable cell number after 3 days of culture. These results suggest that UVA, UVB and UVC may interfere with any one or more of the signals involved in the response to mitogen, be they the recognition of mitogen by T cells or accessory cells, the transformation of lymphocytes into lymphoblasts or the activation of lymphoblasts to synthesize DNA.