Ultraviolet radiation induces a change in cell membrane potential in vitro: a possible signal for ultraviolet radiation induced alteration in cell activity

Burn Injury: Mechanisms of Keratinocyte Cell Death

Cutaneous burn injury is associated with epidermal loss in the zone of coagulation zone and delayed tissue loss in the zone of stasis. Thus, thermal stress can trigger both necrosis and regulated cell death (RCD) or apoptosis. Experimental in vitro and in vivo work has clearly demonstrated apoptotic events of thermally injured keratinocytes that are accompanied by morphological and biochemical markers of regulated cell death. However, in vivo data for the different pathways of regulated cell death are sparse. In vitro experiments with heat-stressed human keratinocytes have demonstrated death receptor involvement (extrinsic apoptosis), calcium influx, and disruption of mitochondrial membrane potential (intrinsic apoptosis) in regulated cell death. In addition, caspase-independent pathways have been suggested in regulated cell death. Keratinocyte heat stress leads to reduced proliferation, possibly as a result of reduced keratinocyte adhesion (anoikis) or oncogene involvement. Understanding the underlying mechanisms of RCD and the skin’s responses to thermal stress may lead to improved strategies for treating cutaneous burn trauma.

Identifying conserved UV exposure genes and mechanisms

Studies have been showing how changes in ultraviolet (UV) affect the terrestrial system, mostly focusing on higher plants and indirect effects, e.g. UV changed food quality/decomposition. Much less attention has been given to direct effect on terrestrial species, although the negative effects have been recognized for some earthworms. Further, the actual mechanisms of UV toxicity to soil invertebrates are even less understood. We here studied the effect of UV on the soil oligochaete Enchytraeus crypticus, and attempted to identify the possible mechanisms of toxicity using high-throughput gene expression. Applying a UV dose equivalent to UV during the winter months in northern Europe we observed an 80% decrease in reproduction. For these organisms, approximately 5% of the genes were differentially expressed. Among the observations was an activation of the DNA repair mechanisms, nucleotide excision repair, which correlated with survival of the organisms. An observed repressing of apoptosis seems to have deleterious effects (e.g. because it may lead to the accumulation of aberrant cells) leading to a decline in reproduction. The mechanisms activated by UV were similar to those mechanisms activated in humans, showing conservation across species.

Effect of ultraviolet-B radiation in laboratory on morphological and ultrastructural characteristics and physiological parameters of selected cultivar of Oryza sativa L

Ultraviolet-B radiation (UVBR) affects plants in many important ways, including reduction of growth rate and primary productivity, and changes in ultrastructures. Rice (Oryza sativa) is one of the most cultivated cereals in the world, along with corn and wheat, representing over 50% of agricultural production. In this study, we examined O. sativa plants exposed to ambient outdoor radiation and laboratory-controlled photosynthetically active radiation (PAR) and PAR + UVBR conditions for 2 h/day during 30 days of cultivation. The samples were studied for morphological and ultrastructural characteristics, and physiological parameters. PAR + UVBR caused changes in the ultrastructure of leaf of O. sativa and leaf morphology (leaf index, leaf area and specific leaf area, trichomes, and papillae), plant biomass (dry and fresh weight), photosynthetic pigments, phenolic compounds, and protein content. As a photoprotective acclimation strategy against PAR + UVBR damage, an increase of 66.24% in phenolic compounds was observed. Furthermore, PAR + UVBR treatment altering the levels of chlorophylls a and b, and total chlorophyll. In addition, total carotenoid contents decreased after PAR + UVBR treatment. The results strongly suggested that PAR + UVBR negatively affects the ultrastructure, morphology, photosynthetic pigments, and growth rates of leaf of O. sativa and, in the long term, it could affect the viability of this economically important plant.

Melatonin prevents ultraviolet radiation-induced alterations in plasma membrane potential and intracellular pH in human keratinocytes

Melatonin exhibits protective effects against ultraviolet radiation (UVR) via modulation of proinflammatory mediators and its free radical scavenging capacity. To date, several reports presented protective mechanisms of this agent against UVR-induced alterations in mitochondria and nuclei. This investigation evaluates the potent preventing action of melatonin regarding early-stage UVR-mediated perturbations in plasma membrane potential (mbΔψ) and intracellular (cytosolic) pH (pH i) analyzed by flow cytometry. Experiments were carried out in a dose- and time-dependent manner using human keratinocytes [HaCaT and normal human epidermal keratinocytes (NHEK)]. First investigations, which used viability/cytotoxicity assays, showed the gradual mortality with increasing UVR doses and cultivation time. Pre-incubation with melatonin (10(-3) m) prior to UVR exposure reduced lactate dehydrogenase release by 30% (HaCaT) and 28% (NHEK) at the dose of 50 mJ/cm(2) after 48 hr (P < 0.001). Furthermore, UVR caused hyperpolarization of mbΔψ immediately (0 hr) after irradiation (25 or 50 mJ/cm(2)). At the dose of 50 mJ/cm(2), cells cultivated for 48 hr manifested a marked increase in mbΔψ by 112% (HaCaT) and 123% (NHEK). The presence of melatonin significantly protected the cells by 12% (HaCaT) and 14% (NHEK) (P < 0.001). Simultaneously, 50 mJ/cm(2) induced dramatic acidification reaching after 24 hr the level of 6.40 (without melatonin), 6.56 (with melatonin) for HaCaT and 6.11 (without melatonin), 6.43 (with melatonin) for NHEK. The results presented provide information about the protective mechanisms of melatonin itself on one hand and, combined with data reported so far, confirm the potent antiapoptotic action of melatonin.

Alterations in architecture and metabolism induced by ultraviolet radiation-B in the carragenophyte Chondracanthus teedei (Rhodophyta, Gigartinales)

The in vivo effect of ultraviolet radiation-B (UVBR) in apical segments of Chondracanthus teedei was examined. Over a period of 7 days, the segments were cultivated and exposed to photosynthetically active radiation (PAR) at 80 μmol photons m(-2) s(-1) and PAR + UVBR at 1.6 W m(-2) for 3 h per day. The samples were processed for electron microscopy and histochemistry; also was analyzed growth rates, mitochondrial activity, protein levels, content of photosynthetic pigments and photosynthetic performance. UVBR elicited increased cell wall thickness and accumulation of plastoglobuli, changes in mitochondrial organization and destruction of chloroplast internal organization. Compared to controls, algae exposed to PAR + UVBR showed a growth rate reduction of 55%. The content of photosynthetic pigments, including chlorophyll a and phycobiliproteins, decreased after exposure to PAR + UVBR. This result agrees with the decreased photosynthetic performance observed after exposing algae to PAR + UVBR. Irradiation also elicited increased activity of the antioxidant enzyme glutathione peroxidase and decreased mitochondrial NADH dehydrogenase activity, which correlated with the decreased protein content in plants exposed to PAR + UVBR. Taken together, these findings strongly indicate that UVBR negatively affects the architecture and metabolism of the carragenophyte C. teedei.

A self-reported clinical trial investigates the efficacy of 1072 nm light as an anti-ageing agent

BACKGROUND

Previous laboratory research has shown that human lymphocytes pre-irradiated with 1072 nm light are afforded some protection against subsequent ultraviolet light toxicity.

OBJECTIVE

To investigate the possibility that 1072 nm light can prevent or reverse skin ageing which itself is known to be accelerated by ultraviolet light.

METHODS

A randomized, prospective, double-blind, placebo-controlled, self-reporting study was performed to assess the effect of one daily treatment episode for a period of between 6 and 8 weeks on wrinkles and fine lines around the eyes as well as the appearance of bags under the eyes.

RESULTS

Between 52% and 57% of volunteers were able to accurately identify an improvement in the fine lines and wrinkles of the treated areas of skin. Fewer volunteers, between 37% and 46%, observed an improvement in the bags under the treated eye or eyes, albeit with an emphatic statistical significance.

CONCLUSION

Regular application of a non-thermal quantity of 1072nm light around the eyes demonstrated efficacy as an anti-ageing agent.

Phototoxicity assessment of drugs and cosmetic products using E. coli

A gram negative bacteria Escherichia coli (Dh5alpha strain) was developed as an alternate test system of phototoxicity. Eight drugs (antibiotics) and cosmetic products (eight face creams) were examined for their phototoxicity using this test system. Five known phototoxic compounds were used to validate the test system. UVA-radiation induced phototoxicity of these compounds was tested by agar gel diffusion assay. Decrease in colony forming units (CFU) was taken as an end point of phototoxicity. The phototoxic compounds and antibiotics produced significant reduction in CFU (p<0.001) at 80 microg/ml concentrations under exposure to UVA-radiation (5.4-10.8 J/cm(2)). One face cream was found phototoxic and produced significant decrease in CFU of E. coli at 1.0mg/ml concentration under UVA exposure (10.8 J/cm(2)). The minimum effective concentration of tetracycline and dose of UVA-radiation were also determined by observing growth inhibition of E. coli through disc diffusion assay. The observations suggested that E. coli can be used as an alternative test system for phototoxicity evaluation of chemicals. A battery of test systems is required to conclude the toxic/phototoxic potential of a chemical agent. In view of the speed, easiness, sensitivity and low cost, E. coli is introduced as one of the alternate test system for phototoxicity studies in safety evaluation of various chemical ingredients or formulations used in cosmetics and drugs.

A randomised double-blind study comparing the effect of 1072-nm light against placebo for the treatment of herpes labialis

BACKGROUND

Previous research demonstrated that 1072-nm narrowband laser light is effective in the treatment of cold sores.

AIM

To evaluate the efficacy of an over-the-counter cold-sore treatment device (Virulite CS) incorporating 1072-nm light-emitting diodes.

METHODS

A randomised, prospective, double-blind, self-reported study was performed to compare the efficacy of at least six 3-min treatments of 1072-nm narrowband light against placebo, in the treatment of herpes labialis.

RESULTS

The 1072-nm light-emitting diode device reduced cold-sore healing time to 6.3 days compared with 9.4 days for placebo (P=0.048). The time the cold sore took to form a crust was also reduced from 2.00 days for those treated with 1072-nm light, compared with 2.88 days for placebo (P=0.059)

CONCLUSIONS

The significant difference between the mean healing times in the two groups demonstrates that the Virulite CS device is an effective means of treating herpes labialis.

Effect of UVB radiation on human erythrocytes in vitro

In order to evaluate the UVB radiation induced phototoxic effect, the human erythrocytes (RBCs) were used an alternate biological model and rate of photohaemolysis was assessed in vitro at various intensities of UVB radiation (0-2.0 mW/cm2) for an exposure period of 0-240 min. The alterations of biochemical activities in RBC membrane (ghosts), caused by its exposure under an average incident intensity of UVB radiation (0.5 mW/cm2) in sunlight at earth surface, were also determined to understand the possible mechanism of photohaemolysis. We observed UVB dose dependent lysis of erythrocytes by recording haemoglobin and methemoglobin (oxidized form of haemoglobin) in photohaemolysate. We also observed significant inhibition in ATPase, acetylcholinesterase, glucose-6-phosphate dehydrogenase activites and an increased amount of thiobarbituric acid-reactive substance (TBA-RS) in RBC ghosts exposed to UVB radiation (0.5 mW/cm2) for a period of 0-100 min (doses: 0, 0.33, 0.66, 1.0, 1.5 and 3.0 J). The changes were found UVB dose dependent. A decrease of glutathione content in RBC ghosts at low dose level of UVB exposure (0.33 J) was found to be recovered at higher dose levels (0.66-1.5 J). These observations suggested, UVB dose dependent toxicity to human erythrocytes in vitro. Thus the erythrocytes can be used for an assessment of UVB induced biological effects and to understand possible mechanism of the phototoxicity.

Analysis of genes responding to ultraviolet B irradiation of HaCaT keratinocytes using a cDNA microarray

BACKGROUND

Ultraviolet (UV) B irradiation causes many important biological changes in skin, which lead to pathophysiological alterations of the homeostatic environment.

OBJECTIVES

To gain more insight into the molecular events provoked by UVB irradiation, we performed cDNA microarray analysis.

METHODS

Immortalized HaCaT keratinocytes were irradiated with a high cytotoxic dose of UVB (50 mJ cm(-2)), and total RNA was isolated. Fluorescently labelled probes were prepared by reverse transcription and were hybridized with cDNA microarray slides made using 840 cDNA clones.

RESULTS

Time-course cDNA microarray analysis revealed the global gene expression profile after UVB exposure. Of 840 genes tested, 192 genes showed changes in their expression levels at one or more of four time points. The genes were clustered into four groups according to their expression patterns in a self-organizing maps analysis. Classification of these genes into nine functional categories revealed that UVB irradiation affected several biological processes. The genes that were first upregulated and then returned to normal levels included several genes related to the inhibition of cell growth and the proteasome pathway. Conversely, the expressions of many genes involved in the cytoskeleton, signal transduction, metabolism and transcription were first downregulated or unchanged and then upregulated later, reflecting the recovery of UVB-damaged cellular activities.

CONCLUSIONS

These results demonstrate the complexity of the transcriptional profile of the UVB response, and provide a basis for the global characterization of UV-regulated gene expression.

Tubifex: a sensitive model for UV-B-induced phototoxicity

The natural increase of UV-B radiation levels due to depletion of the ozone layer in the atmosphere may impose additional stress for the survival of zooplanktons which serve as a major constituent of the aquatic food chain. To study the adverse effects of UV-B radiation on the aquatic biomass, studies were conducted using the aquatic organism Tubifex as a model, as UV-B radiation is known to penetrate into the natural waters. UV-B radiation induced mortality in tubifex and the production of activated oxygen species by these organisms. Alterations in DNA, RNA, protein, glutathione (GSH), hydrogen peroxide H(2)O(2), thiobarbituric acid-reactive substance (TBA-RS), ATPase, AChE, GST, and LDH activities in Tubifex at various doses (0-2.0 J) of UV-B radiation were found. LC(50) value for UV-B-induced mortality of Tubifex was 0.80+/-0.15 J and the threshold dose was 0.35+/-0.05 J; mortality began within 3h postirradiation. UV-B dose-dependent production of singlet oxygen, superoxide anion, and hydroxyl radicals by Tubifex was observed. DNA, RNA, protein, and GSH contents were found to decrease significantly (P<0.001) while H(2)O(2) and TBA-RS increased (P<0.01) under the influence of UV-B radiation. The activities of ATpase, AChE, and GST enzymes were inhibited (P<0.01) and LDH activity was significantly increased (P<0.001) in Tubifex exposed to UV-B radiation. The results suggest that an increase in UV-B radiation alters several biochemical processes, leading to the mortality of the organism. Tubifex could be useful as a sensitive alternate model for studying UV-B-induced phototoxicity and possible mechanisms of action.

Intracellular pH changes induced in Propionibacterium acnes by UVA radiation and blue light

The intracellular pH changes induced in the Gram-positive skin bacterium Propionibacterium acnes by blue light and UVA radiation were studied. Two methods (31P nuclear magnetic resonance (NRM) spectroscopy and fluorescence spectroscopy using a pH-sensitive fluoroprobe (2',7'-bis-(2-carboxyethyl)-5-(and -6-)-carboxyfluorescein)) were used to determine the intracellular pH. The pH changes induced by irradiation were found to be a function of cell survival. These changes as a function of cell survival followed the same pattern for blue light and UVA radiation. A reduction of the pH gradient across the cell membrane (inside alkaline) was found for lethal doses (less than 15% survival). This reduction corresponded to a decrease in intracellular pH and may indicate a proton influx. An increase in the pH gradient, which corresponded to an increase in the intracellular pH, was observed for sublethal doses. This increase appears to be reversible. Thus two separate mechanisms, which appear to be the same in UVA and blue light regions, may be responsible for the irradiation-induced pH alterations.

The clinical relevance of immunosuppression by UV irradiation

Ultraviolet light has been shown to modify the immune system. Photo immunosuppression occurs already when the skin is exposed to low doses of UVB. The physiological role of this suppression may be to prevent the occurrence of an inflammatory reaction after UVB exposure which could damage the sun-exposed skin. The pathogenic consequences of UVB radiation can be observed in the exacerbation of infectious diseases and the development of skin cancer. Especially for immunocompromised patients the additional role of photo immunosuppression is of great clinical importance. Renal transplant recipients have a highly increased risk for the development of squamous cell carcinomas and the great majority of these tumours are present on sun-exposed skin. In many of the skin lesions DNA of human papilloma virus (HPV) is present, suggesting that UVB light affects the local immune response and renders the skin unable to reject (pre)malignant HPV. The pathogenic consequences of photo immunosuppression in other patient groups and in the general population have still to be determined.

ArF-excimer laser-induced secondary radiation in photoablation of biological tissue

Secondary radiation, emitted during and after the irradiation of corneal, dermal, and dental tissue by an ArF-excimer laser (193 nm), was qualitatively and quantitatively characterized. Emission of secondary radiation was found in the range of 200-800 nm. The intensity of secondary radiation in the range of 200-315 nm (UVC and UVB) is approximately 20% of the total intensity at high laser fluences (> 2 J/cm2), and approximately 50% at moderate laser fluences (< 500 mJ/cm2); 10 muJ/cm2 in the UVC and UVB were measured at the sample surface, at fluences (< 1J/cm2) which are of relevance for clinical procedures on soft tissues. In dental tissue processing, very high fluences (> 5 J/cm2) are required. As a consequence, laser-induced plasma formation can be observed. Secondary radiation can be used as a visible guide for selective removal of carious altered tissue. The data we have found might be of assistance in estimating potential hazards for future mutagenic studies in the field.

Non-nuclear damage and cell lysis are induced by UVA, but not UVB or UVC, radiation in three strains of L5178Y cells

The potential to induce non-nuclear changes in mammalian cells has been examined for (1) UVA1 radiation (340-400 nm, UVASUN 2000 lamp), (2) UVA+UVB (peak at 313 nm) radiation (FS20 lamp), and (3) UVC (254 nm) radiation (G15T8 lamp). The effects of irradiation were monitored in vitro using three strains of L5178Y (LY) mouse lymphoma cells that markedly differ in sensitivity to UV radiation. Comparisons were made for the effects of approximately equitoxic fluences that reduced cell survival to 1-15%. Depending on the cell strain, the fluences ranged from 830 to 1600 kJ/m2 for the UVASUN lamp, 75 to 390 J/m2 for the FS20 lamp and 3.8 to 17.2 J/m2 for the G15T8 lamp. At the exposure level used in this study, irradiation with the UVASUN, but not the FS20 or G15T8, lamp induced a variety of non-nuclear changes including damage to cytoplasmic organelles and increased plasma membrane permeability and cell lysis. Cell lysis and membrane permeabilization were induced by the UVA1 emission of the UVASUN lamp, but not by its visible+IR components (> 400 nm). The results show that the plasma membrane and other organelles of LY cells are highly sensitive to UVA1 but not to UVB or UVC radiation. Also UVA1, but not UVB or UVC radiation, causes rapid and extensive lysis of LY cells. In conclusion, non-nuclear damage contributes substantially to UVA cytotoxicity in all three strains of LY cells.

An action spectrum for UV-induced attachment of V79 Chinese hamster cells to a substratum

When cells growing in monolayers are exposed to ultraviolet radiation (UV) their binding to the substratum is increased in strength. An action spectrum for such UV-induced binding was determined, using the time needed for trypsin-EDTA to detach the cells as a measure of the binding strength. This action spectrum was significantly different from the action spectrum for cell inactivation, which was also determined. At the shortest wavelengths (297/302, 313 nm) lethal fluences were needed to induce measurable binding while at the longest wavelengths (365, 405 nm) completely nonlethal fluences induced strong and persistent binding. Thus, different chromophores are involved in the two processes: while DNA may be the main chromophore for cell inactivation, other and unidentified chromophores may be more important for induction of increased cell binding to the substratum.

Modulation of interferon-gamma-induced HLA-DR expression on the human keratinocyte cell line SCC-13 by ultraviolet radiation

Cell surface expression of major histocompatibility determinants on epidermal keratinocytes is a characteristic feature of a number of inflammatory dermatoses and in all likelihood is caused by diffusion of human leukocyte antigen (HLA)-DR-inducing cytokines from cells present in the dermal mononuclear cell infiltrate. Many of these same disorders respond to ultraviolet (UV) radiation phototherapy. Using the human SCC-13 keratinocyte cell line as a model, UV radiation was found to inhibit interferon-gamma-induced HLA-DR expression. Inhibition correlated closely with decreased steady-state levels of HLA-DR mRNA. These findings provide evidence that the therapeutic effect of UV radiation phototherapy may be mediated by its capacity to down-regulate cytokine-induced keratinocyte HLA-DR expression.

Irradiation of Langmuir-Blodgett multilayer preparations of phospholipids and a fatty acid. 1: Effect of UV radiation

Langmuir-Blodgett (LB) preparations containing stacked monolayers of phospholipids or stearic acid were irradiated with UV light and the electric conductance perpendicular to the planes of the monolayers was measured. There was no observable change of conductance when LB preparations of stearic acid were irradiated. For LB preparations of phospholipids, a rise of conductance, dependent on dose rate, was observed, reaching an equilibrium level after a few hours. After irradiation the conductance fell with a temperature-dependent time constant, and eventually reached a final level a little above the initial value. A three-state model is proposed for the LB phospholipid preparations. This suggests that the absorption of one photon raises a molecule from the ground to an excited state; and the absorption of a second photon carries it into a damaged but repairable or metastable state.

Scotopic spectral sensitivity of phakic and aphakic observers extending into the near ultraviolet

Despite interest in ultraviolet (UV) damage and UV vision in lower vertebrates, there are few recent publications on human UV sensitivity. We obtained dark-adapted spectra from 4 aphakic and 5 normal eyes at 8.8 degrees off-fovea using the staircase method. Our measurements extended from 314.5 nm, near the limit imposed by corneal UV absorbance, to 650 nm. Phakic and aphakic sensitivities resembled the traditional rod spectrum at long wavelengths with a peak around 500 nm. However, aphakic subjects were much more sensitive than phakic observers below 420 nm. From phakic volunteers ranging in age from 22 to 43 we deduced lens absorbance which depressed sensitivity at 350 nm by approx. 4 log units (n = 7 phakic runs on 5 eyes, average age = 30) as expected. We show a maximum lens absorbance at 355-360 nm and a UV window in the lens absorbance at 315 nm consistent with data on optical density of human lenses.

UV-induced protein alterations and lipid oxidation in erythrocyte membranes

Certain ultraviolet radiation-induced effects in skin may result from primary photochemical alterations in cell membranes. We have studied isolated erythrocyte membranes in order to determine the UV-fluence and wavelength dependence for protein alterations and lipid oxidation. Protein crosslinking was detected as high molecular weight protein (greater than 200,000 DA) on polyacrylamide/agarose gel electrophoresis. Spectrin decreased more rapidly than the other membrane proteins upon exposure to lambda = 250-380 nm radiation. Nitrogen-purging inhibited the UV-induced decrease in spectrin by 60% and decreased crosslinking to an even greater degree. The decrease in spectrin was not inhibited by superoxide dismutase, catalase, or sodium azide. Radiation at 280 nm was most effective for spectrin loss, 265 and 297 nm were less effective and 254 and 313 nm were not effective. Prior irradiation at 280 nm did not sensitize the membranes to subsequent irradiation at 313 nm indicating that photodecomposition products of tryptophan are not involved. Lipid photooxidation was measured with the thiobarbituric acid assay and was induced at higher fluences of UV radiations than those required for loss of spectrin. These results indicate that the major effects of UV radiation on cell membranes are alterations of proteins and suggest that tryptophan is the major chromophore for these alterations.