AN ACTION SPECTRUM FOR ULTRAVIOLET INDUCED ELASTOSIS IN HAIRLESS MICE: QUANTIFICATION OF ELASTOSIS BY IMAGE ANALYSIS

To determine an action spectrum for ultraviolet (UV)-induced elastosis, four groups of 24 albino hairless mice each were exposed to four different spectra emitted by a xenon arc solar simulator fitted with cut-off filters (Schott WG 320, 335, 345, and 360). These filters progressively removed more of the shorter wavelengths until, in the final spectrum, only long wavelength UVA (greater than 335 nm) remained. Exposures continued up to 62 weeks. A fifth group of mice served as controls. Skin biopsies were taken at pre-determined dose points and were processed for light microscopy. Elastosis was quantified by computerized image analysis, yielding dose-response curves for each spectrum. The total energy required for a 50% increase in elastic tissue compared to controls was determined graphically for each spectrum. These were: WG 320, 65 J/cm2; WG 335, 865 J/cm2; WG 345, 1230 J/cm2; and WG 360, 2000 J/cm2. Our results were tested against published action spectra for erythema, photocarcinogenesis and elastosis. The erythema spectrum was the most predictive for elastosis except that the longer UVA wavelengths were less effective for elastosis than for erythema. Solar simulating radiation (WG 320 filter) with its UVB component was the most effective in inducing elastosis. Full spectrum UVA (WG 345) required 20 times more energy while long wavelength UVA (WG 360) required 30 times more energy to induce equivalent elastosis.     

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.     

A Five‐year Study of Solar Ultraviolet Radiation in Southern Chile (39° S): Potential Impact on Physiology of Coastal Marine Algae?

This study reports 5 years of (1998-2003) data on continuous solar-irradiation measurements from a scanning spectroradiometer (SUV-100) in Valdivia, Chile (39 degrees S), accompanied by evaluation of the impact of ultraviolet radiation (UVR) on marine macroalgae of this site. UVR conditions showed a strong seasonal variation, which was less pronounced toward longer wavelengths. Daily maximum dose rates (clear days) averaged in winter-summer: UV-B(290-315 nm) 0.30-2.1, UV-B(290-320 nm) 0.70-3.7, UV-A(315-400 nm) 20.6-62.1, UV-A(320-400 nm) 20.2-60.5 W m(-2), and photosynthetically active radiation (PAR) 969-2423 micromol m(-2) s(-1). The corresponding daily doses (all the days) ranged: UV-B(290-315 nm) 2.6-40.7, UV-B(290-320 nm) 6.7-78.5, UV-A(315-400 nm) 228-1539, UV-A(320-400 nm) 224-1501, and PAR 2008-13308 kJ m(-2) d(-1). Taking into consideration action spectra of a biological interest, the risk of UV exposure could be up to 37 times higher in summer than in winter. The photosynthetic activity (as maximum quantum yield of chlorophyll fluorescence, F(v)/F(m)) of the brown alga Lessonia nigrescens from the infralittoral zone was markedly more sensitive to UVR than of the green alga Enteromorpha intestinalis from the upper midlittoral, and the UV-B wave band increased markedly photoinhibition. In L. nigrescens, maximal photoinhibition (40%) took place at weighted (the action spectrum for photoinhibition of photosynthesis) UVR doses of 800 kJ m(-2), irrespective of the season (corresponding midsummer daily dose in Valdivia is 480 kJ m(-2)). In winter, when this alga was at its most sensitive, the weighted UV dose causing 35-40% photoinhibition was around 200 kJ m(-2). In E. intestinalis, weighted doses of 800 kJ m(-2) resulted in low photoinhibition (<10 %) and no clear seasonal patterns could be inferred. These results confirm that midday summer levels of UV-B and their daily doses in southern Chile are high enough to produce stress to intertidal macroalgae.     

EFFECT OF CHRONIC UV EXPOSURE ON EPIDERMAL FORWARD SCATTERING-ABSORPTION INSK–1 HAIRLESS MOUSE SKIN

Abstract— Clinical and histological precancerous responses to UV irradiation are complicated dynamic functions of total dose, dose fractionation, fluence rate, and spectral distribution. This may be due, in large part, to the ability of UV to decrease epidermal-stratum corneum transmission by stimulation of hyperplasia. This work provides quantitative measurement of dose- and wavelength-dependent optical changes inSK–1 hairless mouse epidermis-stratum corneum occurring under irradiation with “monochromatic” UV wavebands, at 280, 290, 300, 307, and 313 nm. Mice were irradiated 5 days per week with a filtered Xenon-Hg high-intensity grating monochromator, starting with 0.9 minimal erythemal dose (MED), followed by incremental increases in the radiation dose by 20% of the original dose every tenth irradiation day, for2–8 consecutive weeks. Subsequent irradiations (for longer experiments) were followed by 30% incremental increases after the 8th week every 10th irradiation day until cessation of radiation at the end of 14 weeks. Irradiated and control full-thickness epidermis/ stratum corneum were examined histologically and by forward-scattering absorption spectroscopy. Chronic irradiation of hairless mice resulted in significant hyperplasia which was optically manifested by a general increase in forward-scattering absorbance. At moderate local doses (7.2 MED), the absorbance increase per MED was approximately the same for all excitation wavelengths, whereas at large total doses (? 100 MED) the optical increase per delivered MED progressively decreased in the order 313> 307> 300? 290> 280 nm. The increase in skin thickening, expressed as observed increase in absorption at 320 nm, correlated well with histological and clinical data. We propose that optical changes induced by UV-induced thickening can account in large part, if not entirely, for dynamic changes in action spectra for (pre) cancerous processes under chronic irradiation conditions.     

COMPARISON OF UV ACTION SPECTRA FOR LETHALITY AND MUTATION IN Salmonella typhimurium USING A BROAD BAND SOURCE AND MONOCHROMATIC RADIATIONS

Abstract— The UV-B region (280–320 nm) is thought to be primarily responsible for the mutagenic, lethal, and carcinogenic effects of solar radiation. We have conducted UV-B action spectroscopy for mutagenesis and survival of Ames' Salmonella typhimurium strain TA98 ( uvrB , pKM101) using both monochromatic radiation from a dye laser and broader bandwidth radiation emitted from FS-20 sunlamps. A series of optical filters having different transmission cut-offs together with the sunlamp source provided bandwidths having successively less short wavelength components from which a "broad band" action spectrum was deduced. The two sets of action spectra differed both qualitatively and quantitatively: in comparison to the monochromatic action spectra, the "broad band" spectra showed up to a 200-fold reduced efficiency for both mutation induction and lethality by UV-B wavelengths. These results suggest a large protective effect of the background UV-A and/or visible radiations which were present during the broad spectrum irradiations and which are also present in solar radiation. Additional experiments show that to the extent tested this protective effect is not due to photo-reactivation or irradiance (dose rate) effects     

Noninvasive Assessment of UV-induced Skin Damage: Comparison of Optical Measurements to Histology and MMP Expression

Acute exposure to UV radiation (UVR) causes visible skin damage such as erythema and results in local and systemic immunosuppression while chronic exposure can result in photocarcinogenesis. These deleterious effects can be quantified by histology and by bioassays of key biological markers, including matrix metalloproteinases (MMPs), or tryptophan moieties. We now report our results in quantifying UV skin damage with noninvasive optical methods based on reflectance and fluorescence spectroscopy and compare these noninvasive measurements to histopathology and MMP-13 expression. A solar simulator with spectral output nearly identical to that of solar radiation was developed and used in our experiments. SKH1 hairless mice were exposed to solar-simulated UVR at a total dose of 21 MED delivered over 10 weeks. Changes in oxygenated and deoxygenated hemoglobin were measured by diffuse reflectance spectroscopy, and tryptophan changes were monitored via a fluorescence monitor. Our results show that there is an increase in erythema, skin fluorescence, sunburn cells and MMP-13 after a series of suberythemal doses of UV irradiation on a hairless mouse animal model. Increased skin fluorescence is observed with increasing UV exposure. The levels of MMP-13 increase as the cumulative UV dose increases but their increase does not correspond to noninvasively measured changes.     

Wavelength- and Tissue-dependent Variations in the Mutagenicity of Cyclobutane Pyrimidine Dimers in Mouse Skin

The cyclobutane pyrimidine dimer (CPD) is a main mutagenic photolesion in DNA produced by UVR. We previously studied the wavelength-dependent kinetics of mutation induction efficiency using monochromatic UVR sources and transgenic mice developed for mutation assay and established the action spectra of UVR mutagenicity in the mouse epidermis and dermis. Here, we further established the action spectra of CPD and pyrimidine(6-4)pyrimidone photoproduct formation in the same tissues and in naked DNA using the same sources and mouse strain. Quantitative ELISA helped us estimate the photolesion formation efficiencies on a molecule-per-nucleotide basis. Using these action spectra, we confirmed that the UVR mutation mostly depends on CPD formation. Moreover, the mutagenicity of a CPD molecule (CPD mutagenicity) was found to vary by wavelength, peaking at approximately 313 nm in both the epidermis and dermis with similar wavelength-dependent patterns. Thus, the CPD formation efficiency is a main determinant of UVR mutagenicity in mouse skin, whereas a wavelength-dependent variation in the qualitative characteristics of CPD molecules also affects the mutagenic consequences of UVR insults. In addition, the CPD mutagenicity was always higher in the epidermis than in the dermis, suggesting different cellular responses to UVR between the two tissues irrespective of the wavelength.     

Analysis of Compact Fluorescent Lights for Use by Patients with Photosensitive Conditions

Ultraviolet radiation (UVR) is hazardous to patients with photosensitive skin disorders, such as lupus erythematosus, xeroderma pigmentosum and skin cancer. As such, these patients are advised to minimize their exposure to UVR. Classically, this is accomplished through careful avoidance of sun exposure and artificial tanning booths. Indoor light bulbs, however, are generally not considered to pose significant UVR hazard. We sought to test this notion by measuring the UV emissions of 19 different compact fluorescent light bulbs. The ability to induce skin damage was assessed with the CIE erythema action spectrum, ANSI S(λ) generalized UV hazard spectrum and the CIE photocarcinogenesis action spectrum. The results indicate that there is a great deal of variation amongst different bulbs, even within the same class. Although the irradiance of any given bulb is low, the possible daily exposure time is rather lengthy. This results in potential daily UVR doses ranging from 0.1 to 625 mJ cm⁻², including a daily UVB (290–320 nm) dose of 0.01 to 15 mJ cm⁻². Because patients are exposed continually over long time frames, this could lead to significant cumulative damage. It would therefore be prudent for patients to use bulbs with the lowest UV irradiance.     

Know your standard: clarifying the CIE erythema action spectrum

The standard erythema action spectrum provides an internationally accepted representation of the erythema-inducing effectiveness of wavelengths in the UV part of the spectrum. The action spectrum forms the basis of the UV index used for public health information, defines the standard erythema dose unit and the minimum erythema dose and is the default response spectrum aspired to by a range of UV radiometer manufacturers. However, there are several versions of this erythema action spectrum in use, and only one of them has been endorsed as a standard. While the differences in erythemally weighted radiation incurred by choice of action spectrum will be no more than a few percent, this uncertainty is unnecessary. Here we detail the differences in the different versions of erythema action spectra, illustrate the resulting effects in quantifying UV doses and encourage readers to use only the standard version of the action spectrum in the future.     

OBSERVED AND PREDICTED MINIMAL ERYTHEMA DOSES: A COMPARATIVE STUDY

Abstract This study compared how well minimal erythema doses predicted using the reference action spectrum for UV erythema proposed by the International Commission on Illumination (CIE) in 1987 agreed with those observed in phototesting a large number of subjects with normal responses to sunlight to six different wavelengths of UV radiation (UVR) between 300 and 400 nm. It was found that, within the limits of experimental error, the hypothesis that the CIE reference action spectrum is a valid predictor of the erythemal effectiveness of different wavelengths of UVR could not be dismissed. There is no strong reason, therefore, why the CIE action spectrum should not continue to be used as a reference to compare the erythemal effectivenesses of different broadband sources. However, close examination of the residuals from the regression analysis suggested that the erythemal sensitivity of skin at longer UV wavelengths (>350 nm) in the population studied here is greater than predicted from the CIE reference action spectrum.     

DETECTION OF UVR-INDUCED DNA DAMAGE IN MOUSE EPIDERMIS in vivo USING ALKALINE ELUTION

Abstract— Alkaline elution has been used to detect ultraviolet radiation (UVR)-induced DNA damage in the epidermis of C3H/Tif hr/hr mice. This technique detects DNA damage in the form of single-strand breaks and alkali-labile sites (SSB) formed directly by UVA (320–400 nm) or indirectly by UVB (280–320 nm). The latter induces DNA damage such as cyclobutane pyrimidine dimers and pyrimidine-pyrimidone (6–4)-photoproducts, which are then converted into transient SSB by cellular endonucleases, during nucleotide excision repair (NER). The irradiation system used had a spectral output similar in effect to solar UVR, with the UVB component inducing 94% of the edema response observed in mice. Consequently, the majority of SSB detected were those formed via NER of UVB-induced photoadducts. The number of SSB detected immediately after 8 kj/m² (2.7 minimum erythema doses determined at 48 h post-UVR [MED]) was low, indicating the formation of only small numbers of transient SSB. When DNA repair inhibitors hydroxyurea and 1 -β-D-arabinofuranosylcytosine were administered (intraperi-toneally) to mice 30 min before UVR, they prevented sealing of the DNA SSB formed during NER. A four-fold increase in the number of SSB detected resulted, which was found to be linearly related to the UVR dose. The SSB induced by 2 kj/m² (less than an MED) were readily detected, with the ear showing lower numbers of SSB than the dorsum. When repair inhibitors were added post-UVR, the rate of formation of SSB declined rapidly with time of administration, reflecting repair of DNA lesions. After a UVR dose of 6 kj/m² (2 MED), 50% of the initial repair-dependent SSB had been removed after approximately 2 h in the ear and 4 h in the dorsum; no more SSB appeared to be incised by 24 h post-UVR. The technique described is an efficient and highly sensitive one for the quantification of SSB induced in UV-irradiated skin samples in vivo.     

ACTION SPECTRUM FOR ERYTHEMA IN HUMANS INVESTIGATED WITH DYE LASERS

Abstract— Erythema reactions of human skin were reevaluated with improved experimental methods: a tunable, highly monochromatic irradiation source as well as an instrumental measurement of skin reactions were used. The irradiation system consisted of an excimer laser pumped dye laser and a U V fiber optic system. The skin color after irradiation was determined with a colorimeter in the three-dimensional norm system of the Commission Internationale d'Eclairage (CIE). The wavelength dependence for delayed erythema was investigated in the UVB and UVA region from 294 nm to 374 nm in skin type II and III individuals. The maximum of the action spectrum in the UVB range was measured at 298.5 nm and an additional maximum was found at 362 nm in the UVA range. The action spectrum is compared with previous spectra from the literature and with the current standard erythema curve of the CIE as well as with other photobiological action spectra. Our results suggest a UVA/UVB boundary at 330 nm.     

LACK OF CORRELATION BETWEEN SUPPRESSION OF CONTACT HYPERSENSITIVITY BY UV RADIATION AND PHOTOISOMERIZATION OF EPIDERMAL UROCANIC ACID IN THE HAIRLESS MOUSE

Abstract The immunological consequences of exposure to UVA (320–400 nm) radiation are unclear. This study describes the relationship between the generation of epidermal cis -urocanic acid and the ability to respond to a contact-sensitizing agent, in hairless mice exposed to different UV radiation sources, which incorporate successively greater short-wavelength cutoff by filtration of the radiation from fluorescent UV tubes. Mice were exposed to these radiation sources at doses systematically varying in UVB radiation content but supplying increasing proportions of UVA radiation. All radiation sources were found to generate approximately 35% cis -urocanic acid in the epidermis, thus normalizing the sources for cis -urocanic acid production. However, only those sources richest in short-wavelength UVB resulted in suppression of the systemic contact hypersensitivity response. These sources also induced the greatest erythema reaction, measured as its edema component, in the exposed skin. A strong correlation was thus demonstrated between the induction of edema and the suppression of contact hypersensitivity, but there appeared to be no correlation between the generation of epidermal cis-urocanic acid and suppression of contact hypersensitivity. The sources richest in UVA content did not result in suppression of contact hypersensitivity: furthermore mice previously irradiated with such UVA-rich sources were refractory to the immunosuppressive action of exogenous cis-urocanic acid. A protective effect of the increased UVA content thus appeared to be inhibiting immunosuppression by the available endogenously generated or exogenously applied cⁱs-urocanic acid.     

THE ACTION SPECTRA FOR UV-INDUCED SUPPRESSION OF MLR and MECLR SHOW THAT IMMUNOSUPPRESSION IS MEDIATED BY DNA DAMAGE

-Ultraviolet-B (UVB,280–320 nm) radiation can promote the induction of skin cancer by two mechanisms: damage of epidermal DNA and suppression of the immune system, allowing the developing tumor to escape immune surveillance. The mixed lymphocyte reaction (MLR) and the mixed epidermal cell lymphocyte reaction (MECLR) are commonly used methods to study the immunosuppressive effects of UVB radiation. To obtain a better understanding of the mechanism by which UVB radiation decreases the alloactivating capacity of in vitro-irradiated cells, action spectra for the MLR and MECLR were determined. Suspensions of peripheral blood mononuclear cells or epidermal cells were irradiated with monochromatic light of 254, 297, 302 or 312 nm and used as stimulator cells in the MLR or MECLR. Using dose-response curves for each wavelength, the action spectra were calculated. Both MLR and MECLR action spectra had a maximum at 254 nm and a relative sensitivity at 312 nm that was a thousand times lower than at 254 nm. Strikingly, the action spectra corresponded very closely to the action spectra that were found by Matsunaga et al. (Photochem. Photobiol. 54,403–410, 1991) for the induction of thymine dimers and (6-4)photoproducts in irradiated calf thymus DNA solutions, strongly suggesting that the UV-induced abrogation of the MLR and MECLR responses is mediated by UV-induced DNA damage. Furthermore, the action spectra for the MLR and MECLR were similar, suggesting that they share a common mechanism for UV-induced suppression.     

ULTRAVIOLET ACTION SPECTRA FOR PHOTOBIOLOGICAL EFFECTS IN CULTURED HUMAN LENS EPITHELIAL CELLS

Abstract— The action spectrum for cell killing by UV radiation in human lens epithelial (HLE) cells is not known. Here we report the action spectrum in the 297–365 nm region in cultured HLE cells with an extended lifespan (HLE B-3 cells) and define their usefulness as a model system for photobiological studies. Cells were irradiated with monochromatic radiation at 297, 302, 313, 325, 334 and 365 nm. Cell survival was determined using a clonogenic assay. Analysis of survival curves showed that radiation at 297 nm was six times more effective in cell killing than 302 nm radiation; 297 nm radiation was more than 260, 590, 1400 and 3000 times as effective in cell killing as 313, 325, 334 and 365 nm radiation, respectively. The action spectrum was similar in shape to that for other human epithelial cell lines and rabbit lens epithelial cells. The effect of UV radiation on crystallin synthesis was also determined at different wavelengths. To determine whether exposure to UV radiation affects the synthesis of β-crystallin, cells were exposed to sublethal fluences of UV radiation at 302 and 313 nm, labeled with [³⁵S]methionine and the newly synthesized βY-crystallin was analyzed by immunoprecipitation and western blotting using an antibody to β-crystallin. The results show a decrease in crystallin synthesis in HLE cells irradiated at 302 and 313 nm at fluences causing low cytotoxicity. The effect of radiation on membrane perturbation was determined by measuring enhancement of synthesis of prostaglandin E₂ (PGE₂). Synthesis of PGE₂ occurs at all UV wavelengths tested in the 297–365 nm region. The slope of the PGE₂ response curves was higher than that of cell killing curves in cultured HLE cells. These data show that cultured HLE cells with extended lifespan are a suitable system for investigating photobiological responses of cells to UV radiation.     

MINIMUM DOSES OF ULTRAVIOLET RADIATION REQUIRED TO INDUCE MURINE SKIN EDEMA and IMMUNOSUPPRESSION ARE DIFFERENT and DEPEND ON THE ULTRAVIOLET EMISSION SPECTRUM OF THE SOURCE*

Many photoimmunological studies have used UV radiation sources that emit nonsolar UV spectral energy and UV doses based on nonimmunological endpoints, e.g. erythema and skin edema. Interpretation of these data has led to misunderstanding when extrapolated to hypothetical effects in humans exposed to solar UV. The purpose of this study was to: (1) establish UV dose response relationships for murine skin edema and immunosuppression, and (2) determine how different UV spectra affect these relationships. Back skin and ear minimum edema doses (MEdD) for Kodacel-filtered FS20 sunlamp UV (290–400nm) were greater than two-fold higher than those for unfiltered FS20 sunlamp UV (250–400nm). Xenon arc solar simulator UV (295–400nm) MEdD were > 10-fold higher than those for unfiltered sunlamp UV. Back skin and ear MEdD differed two- to five-fold between C3H/ HeN, SWR/J and HRA/Skh-1 mice. The minimum immunosuppression doses (MISD) in C3H mice showed similar UV source spectrum dependence. The solar simulator UV MISD was 5.4- and 1.5-fold higher than for unfiltered and Kodacel-filtered sunlamp UV MISD, respectively. Furthermore, MISD were from 3- to 50-fold higher than the MEdD for the three UV sources. The UV bioeffectiveness spectra indicated that UVC energy (250–290nm) contributed 12% and 18%, respectively, of the total skin edema and immunosuppression UV energy. These data demonstrate the variability in UV sensitivity among mouse strains, the significant differences between murine MEdD and MISD and how these differences are influenced by nonsolar regions (below 295 nm) of the UV spectrum.     

The Evaluation of Noninvasive Measurements of Erythema as a Potential Surrogate for DNA Damage in Repetitively UV‐exposed Human Skin

Erythema (i.e. visible redness) and DNA damage caused by ultraviolet radiation (UVR) in human skin have similar action spectra and show good correlation after a single exposure to UVR. We explored the potential to use instrumental assessments of erythema as a surrogate for DNA damage after repeated exposures to UVR. We exposed 40 human subjects to three different exposure schedules using two different UVR sources. Cyclobutane‐pyrimidine dimers (CPDs) in skin biopsies were measured by immunofluorescence, and erythema was assessed by both the Erythemal Index (EI) and the Oxy‐hemoglobin (Oxy‐Hb) content. Surprisingly, the skin with the highest cumulative dose ended up with the lowest level of DNA damage, and with the least erythema, as assessed by Oxy‐Hb (but not EI) 24 h after the last UV exposure. Although the level of CPDs, on average, paralleled Oxy‐Hb (R² = 0.80–0.94, P = 0.03–0.11), the correlation did not hold for the pooled individual measurements (R² = 0.009, P = 0.37) due to potential individual differences in UV‐induced photoadaptation. We suggest that the methodology may be optimized to improve the correlation between DNA damage level and erythema to enable noninvasive risk assessment based on erythema/Oxy‐Hb content for individual human subjects.     

ACTION SPECTRUM FOR ANTHRACENE-INDUCED PHOTOSENSITIZATION OF HUMAN SKIN

Abstract— The action spectrum for photosensitization by topically applied anthracene was determined in human volunteers. Spectral reactivity was demonstrated in the range between 320 and 380 nm, with peak activity at around 360 nm. Three distinct inflammatory responses viz. immediate transient erythema, delayed erythema, and wealing were evoked following exposure to effective wavelengths. The action spectra for these responses were similar but the threshold doses were different. Prior treatment with a mast cell degranulating agent (codeine) abolished anthracene-UVA induced wealing but did not influence the erythema response. These findings suggest that photosensitized damage to cutaneous mast cells may be partially responsible for some of the observed inflammatory responses, but other sites of photochemical injury are also involved.     

ACTION SPECTRA IN ULTRAVIOLET WAVELENGTHS (150-250 nm) FOR INACTIVATION AND MUTAGENESIS OF Bacillus subtilis SPORES OBTAINED WITH SYNCHROTRON RADIATION

Bacillus subtilis spores were exposed in vacuo to monochromatic UV radiation from synchrotron radiation in the wavelength range of 150 nm to 250 nm. Survival and frequency of mutation to histidine-independent reversion were analysed for three types of spores differing in DNA-repair capabilities. UVR spores (wild-type DNA repair capability) exhibited nearly equal sensitivity to the lethal effects of far-UV (220 nm and 250 nm) and of vacuum-UV radiation (150 and 165 nm), but showed marked resistance to 190 nm radiation. UVS spores (excision-repair and spore-repair deficient) and UVP spores (a DNA polymerase I-defective derivative of UVS) exhibited similar action spectra; pronounced sensitivity at 250 and 220 nm, insensitivity at 190 nm and a gradual increase of the sensitivity as the wavelength decreased to 165 nm. In all strains, the action spectra for mutation induction paralleled those for the inactivation, indicating that vacuum-UV radiation induced lethal and mutagenic damages in the spore DNA. The insensitivity of the spores to wavelengths around 190 nm may be explicable by assuming that radiation is absorbed by materials surrounding the core in which DNA is situated.