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

Ultraviolet-A1 irradiation therapy for systemic lupus erythematosus

Systemic lupus erythematosus (lupus, SLE) is a chronic autoimmune disease characterized by the production of autoantibodies, which bind to antigens and are deposited within tissues to fix complement, resulting in widespread systemic inflammation. The studies presented herein are consistent with hyperpolarized, adenosine triphosphate (ATP)-deficient mitochondria being central to the disease process. These hyperpolarized mitochondria resist the depolarization required for activation-induced apoptosis. The mitochondrial ATP deficits add to this resistance to apoptosis and also reduce the macrophage energy that is needed to clear apoptotic bodies. In both cases, necrosis, the alternative pathway of cell death, results. Intracellular constituents spill into the blood and tissues, eliciting inflammatory responses directed at their removal. What results is “autoimmunity.” Ultraviolet (UV)-A1 photons have the capacity to remediate this aberrancy. Exogenous exposure to low-dose, full-body, UV-A1 radiation generates singlet oxygen. Singlet oxygen has two major palliative actions in patients with lupus and the UV-A1 photons themselves have several more. Singlet oxygen depolarizes the hyperpolarized mitochondrion, triggering non-ATP-dependent apoptosis that deters necrosis. Next, singlet oxygen activates the gene encoding heme oxygenase (HO-1), a major governor of systemic homeostasis. HO-1 catalyzes the degradation of the oxidant heme into biliverdin (converted to bilirubin), Fe, and carbon monoxide (CO), the first three of these exerting powerful antioxidant effects, and in conjunction with a fourth, CO, protecting against injury to the coronary arteries, the central nervous system, and the lungs. The UV-A1 photons themselves directly attenuate disease in lupus by reducing B cell activity, preventing the suppression of cell-mediated immunity, slowing an epigenetic progression toward SLE, and ameliorating discoid and subacute cutaneous lupus. Finally, a combination of these mechanisms reduces levels of anticardiolipin antibodies and protects during lupus pregnancy. Capping all of this is that UV-A1 irradiation is an essentially innocuous, highly manageable, and comfortable therapeutic agency.

Wavelength dependence of cellular responses in human melanocytes and melanoma cells following exposure to ultraviolet radiation

PURPOSE

To examine the wavelength dependence of cellular responses in human melanocytes and human melanoma cells exposed to ultraviolet radiation (UVR).

MATERIALS AND METHODS

Primary human melanocytes and G361 human melanoma cells were exposed to ultraviolet-C (UVC), ultraviolet-B (UVB), or ultraviolet-A (UVA) radiation. Dose-response relationships for clonal cell survival were assessed, and flow cytometry was used to monitor cell cycle distributions for up to one week post-irradiation. Chromosomal aberrations were scored in exposed and unexposed melanoma cells.

RESULTS

G361 melanoma cells were more sensitive than melanocytes to killing by UVB and UVC radiation. This difference in sensitivity between cell types was much less marked following UVA irradiation. The melanoma cells showed a sustained, dose-dependent G2/M block following exposure with all wavelengths; in addition, transit through S phase was slowed following UVA irradiation. There was no apparent block to G1 cells entering S phase at any wavelength. Melanocytes, on the other hand, showed a marked G1 arrest, particularly following UVA irradiation. Cytogenetic results showed a dose-dependent increase in chromatid-type aberrations, mostly gaps, breaks and exchanges, in exposed melanoma cells.

CONCLUSION

These results show that G361 malignant melanoma cells have lost the ability to regulate the cell cycle at the G1/S checkpoint and are more sensitive than melanocytes to cell killing by UVC and UVB but not UVA radiation. Similarly, exposure of these melanoma cells to UVC and UVB, and to a much lesser extent UVA, induced chromatid aberrations. UVA nevertheless induced strong cell cycle delays in both cell types, indicating that UVA exposure can significantly affect genome metabolism.

UVA irradiation induces energy-independent phospholipid-flip in mammalian plasma membrane

Translocation from the outer to the inner membrane leaflet (flip) of phospholipids after ultraviolet A (UVA) irradiation was investigated in Chinese hamster ovary cells. Fluorescent 1-palmitoyl-2-[6-[(7-nitro-2-1,3-benzox- adiazol-4-yl)amino]caproyl]-sn-glycero-3-phosphoserine (NBD-labeled phosphatidylserine [NBD-PS]) was used to assay transbilayer lipid movement. A marked increase in flip of NBD-PS was observed immediately after low-dose UVA irradiation which was not lethal and returned to the basal level after 6 h. UVA-induced flip was not attributed to the increase of permeability by UVA irradiation because cells that were negative for staining with propidium iodide also showed increased flip of NBD-PS. Furthermore, the enhancement was independent of adenosine 5'-triphosphate, demonstrating the lack of involvement of phospholipid translocase. Marked increases were also observed in flip of both NBD-phosphatidylethanolamine and NBD-phosphatidylcholine immediately after UVA irradiation, showing that the increase was independent on the head groups of phospholipids. These findings indicated that UVA changes the flip-flop of phospholipids and that the cell membrane is a molecular and cellular target of UVA.

Bilirubin- and light induced cell death in a murine lymphoma cell line

Cells from the mouse lymphoma cell line L5178Y-R were exposed to blue light from phototherapy lamps in the presence of solutions of 160 microM bilirubin supplemented with serum albumin. HPLC analysis showed that the bilirubin solution was photooxidised as a function of increasing light dose. The cells were stained with trypan blue to score necrosis, and apoptosis was assayed by the terminal deoxynucleotide transferase assay (TdT) or by studying the nuclear structure in cells stained with propidium iodide. A rapidly developing apoptosis was observed after light doses killing 60-80% of the cells as judged from the trypan blue exclusion test. The fraction of apoptotic cells was smaller than the fraction of necrotic cells. Exposure of the cells to fractions of light at a high dose rate was compared to the effect of the same total dose at a lower dose rate given as a single fraction. No large differences were found, however, there was a tendency of a higher degree of necrosis as well as apoptosis in the cells receiving the light in fractions at a high dose rate.

Glutathione modulates the level of free radicals produced in UVA-irradiated cells

We have developed an assay to detect reactive oxygen species (ROS) generated by UVA radiation utilising chemical probes which become fluorescent upon oxidation. Using a human bladder carcinoma cell line (MGH-U1) and spontaneously immortalised keratinocytes (HaCaT), we have shown a UVA (narrow band 365+/-5 nm) dose-dependent increase in fluorescence by flow cytometry following loading of the cells with either dihydrorhodamine 123 (DHR) or 2',7'-dichlorodihydrofluorescein diacetate (DCFH-DA). The UVA response of both DHR and DCFH was enhanced by elevation of intracellular levels of the photosensitiser protoporphyrin IX by incubation for 2.5 h with 5-aminolaevulinic acid. Depletion of the antioxidant glutathione (GSH) using the inhibitor D,L-buthionine-sulphoximine (BSO), resulted in an increase in the UVA-induced fluorescence of DCF but not of rhodamine 123. Conversely, raising intracellular GSH levels with N-acetyl cysteine (NAC) had relatively little protective effect in terms of degree of induced fluorescence.

PUVA (psoralen + UVA) photochemotherapy: processes triggered in the cells

Photochemotherapy using psoralens and UVA is a treatment used widely in some skin diseases, in cutaneous lymphomas and in autoimmune diseases. This review has selected recent publications dealing with the photochemical processes triggered in the cells by UVA radiation and psoralen treatment. The photochemical changes initiated in the cell membranes were described.

Wavelength-specific synergy between ultraviolet radiation and interleukin-1 alpha in the regulation of matrix-related genes: mechanistic role for tumor necrosis factor-alpha

Ultraviolet light causes both acute and chronic changes in extracellular matrix. We sought to examine the effects of different ultraviolet wavelengths on expression of matrix-related genes in fibroblasts. We previously reported that tropoelastin gene expression in vivo decreases with acute ultraviolet B exposure, and interleukin-1 alpha-mediated upregulation of tropoelastin is blocked in vitro after ultraviolet B radiation. In this study, we found that only ultraviolet B, but not ultraviolet A or ultraviolet A1, blocked the ability of interleukin-1 alpha to stimulate tropoelastin expression in vitro. Ultraviolet B and interleukin-1 alpha synergistically increased tumor necrosis factor-alpha secretion by fibroblasts, a finding not seen with ultraviolet B alone nor with ultraviolet A or ultraviolet A1 combined with interleukin-1 alpha. Keratinocytes showed a similar ultraviolet B-specific induction of tumor necrosis factor-alpha production. Addition of tumor necrosis factor-alpha to cultured fibroblasts blocked interleukin-1 alpha-induced stimulation of tropoelastin message, and addition of anti-tumor necrosis factor-alpha antibodies restored the responsiveness of tropoelastin and collagen messages to exogenous interleukin-1 alpha after ultraviolet B exposure. We conclude that interleukin-1 alpha in combination specifically with ultraviolet B induces fibroblasts to secrete tumor necrosis factor-alpha, and that this ultraviolet B-specific induction of tumor necrosis factor-alpha secretion is responsible for effects of ultraviolet B on the expression of matrix-related genes in the skin.

Near-visible ultraviolet light induces a novel ubiquitous calcium-permeable cation current in mammalian cell lines

1. We studied the immediate and short-term effects of UV light in the near-visible range at the cellular and membrane level using the whole-cell patch-clamp technique in combination with digital fluorescence imaging. 2. Illumination with monochromatic UVA light (340-380 nm) induced a sustained non-saturable increase in membrane conductance dependent on wavelength and light intensity in several different mammalian cell types including RBL, mast, HEK, PC12 and 3T3 cells. 3. The current was non-selective for cations and permeable to Ca2+, but was inhibited by trivalent cations and was not due to the activation of an endogenous ion channel. We termed this novel current ILiNC for light-induced non-selective cation current. 4. A similar current was evoked by chemical peroxidants such as hydrogen peroxide and tertbutylhydroperoxide, but not by cytosolic oxidized glutathione. 5. The free-radical scavengers tocopherol (vitamin E) and ascorbic acid (vitamin C) significantly reduced the UV light effect. 6. The generation of the current was membrane delimited since it could be induced by the same UVA treatment in cell-free membrane patches showing a similar wavelength dependence. 7. These results suggest that ILiNC is activated by UVA light-induced generation of free radicals acting through lipid or protein peroxidation, and may represent a ubiquitous mechanism by which Na+ and Ca2+ can enter cells after phototoxic or free radical-induced membrane damage.

Survival of Cloudman mouse melanoma cells after irradiation by solar wavelengths of light

A number of variants of Cloudman S91 mouse melanoma cells that differ with respect to the amount of pigment produced are available for study. In this report, we compare the photobiological responses of S91/amel, which contains about 1 pg of melanin per cell, with S91/I3, which contains about 3 pg/cell. Earlier studies had shown that UVC induced more oxidative damage (in the form of thymine glycols) in cell line S91/I3 than in S91/amel and that cell line S91/amel was more resistant to killing by UVC than S91/I3. The present study finds that S91/amel cells are also relatively resistant to killing by near monochromatic UVB from a Philips TL01 fluorescent lamp and by near monochromatic UVA from a Philips HPW125 lamp. However, when the cells are irradiated with a Westinghouse FS20 polychromatic lamp, the S91/I3 cells are more resistant than the S91/amel cells. These findings cannot be explained on the basis of pigment induction because in S91/I3 this is about the same after UVB and FS20, although the maximum is reached earlier after UVB. Nor can our findings be explained on the basis of pyrimidine dimer formation, which is comparable in the two cell lines regardless of the type of irradiation. These results suggest that, with a pigment such as melanin, which absorbs light across the visible and ultraviolet ranges of the spectrum, cellular responses to monochromatic light do not necessarily predict responses to polychromatic mixtures.

Comparative action spectrum for ultraviolet light killing of mouse melanocytes from different genetic coat color backgrounds

The photobiology of mouse melanocyte lines with different pigment genotypes was studied by measuring colony-forming ability after irradiation. The cell lines were wild-type black (melan-a) and the mutants brown (melan-b) and albino (melan-c). Four lamps emitting various UV wavelengths were used. These were germicidal (UVC, 200-280 nm), 82.3% output at 254 nm, TL01 (UVB, 280-320 nm), 64.2% at 310-311 nm, FS20, broadband with peak output at 312 nm and Alisun-S (UVA, 320-400 nm), broadband with peak output at 350-354 nm. Appropriate filtration reduced the contaminating UVC to nonlethal levels for the longer waverange lamps. Wild-type melan-a was resistant to UVC and UVA compared to the other two cell lines, but the differences were small. The melan-c cell line was more resistant to UVB and markedly more resistant to FS20 than the pigmented lines. With the exception of FS20 responses, melan-b was more sensitive than melan-a to killing by the various UV lamps. There were more pyrimidine dimers (cyclobutane dimers and 6-4 photoproducts) produced in melan-a than in melan-c cells by UVC, UVB and FS20 lamps. Unlike melan-c, melan-a and melan-b showed a strong free radical signal of melanin character with a detectable contribution of pheomelanin-like centers. The contribution of pheomelanin was higher in melan-b than in melan-a, while the total melanin content in these two cell lines was comparable. The abundant melanin granules of wild-type melan-a melanocytes were well melanized and ellipsoidal, whereas those of melan-b melanocytes tended to be spherical. In the albino line (melan-c) the melanocytes contained only early-stage melanosomes, all of which were devoid of melanin. The results indicate that pigment does not protect against direct effect DNA damage in the form of pyrimidine dimers nor does it necessarily protect against cell death. High pigment content is not very protective against killing by UVC and UVA, and it may photosensitize in UVB the very wavelength range that is of greatest concern with respect to the rising incidence in skin cancer, especially melanoma. It is clear from these studies that, in pigment cells, monochromatic results cannot predict polychromatic responses and that cell death from solar irradiations is a complex phenomenon that depends on more than DNA damage.

Photosensitized decontamination of blood with the silicon phthalocyanine Pc 4: no activation of the human immunodeficiency virus promoter

Photochemical decontamination of red blood cell concentrates (RBCC) with the silicon phthalocyanine Pc 4 and red light is being studied to enhance the viral safety of blood transfusion. Recent reports indicate that treatments with radiation and various phototsensitizing agents can activate the promoter of human immunodeficiency virus (HIV). This raises the possibility that an inadequate, sublethal photochemical treatment of RBCC could induce HIV in latently infected cells. This question has been addressed using HeLa cells stably transfected with the chloramphenicol acetyl transferase gene under the control of the HIV promoter. In control studies, 8-methoxypsoralen (8-MOP) excited by UVA light caused activation of the HIV promoter in a dose- and time-dependent manner. At 0.1 microgram/mL of 8-MOP, maximal activation occurred with 18 J/cm2, 30 h after light exposure, With Pc 4 at 20 nM, over 90% of HeLa cells were killed after 24 h when exposed to 1 J/cm2 of red light. During that time interval and over a wide range of light doses no activation of the HIV promoter occurred. It is concluded that RBCC sterilization with Pc 4 and red light is unlikely to induce HIV production in latently infected cells.

Induced melanin reduces mutations and cell killing in mouse melanoma

When melanin absorbs light energy, it can produce potentially damaging active oxygen species. There is little doubt that constitutive pigment in dark-skinned individuals is photoprotective against skin cancer, but induced pigment-as in tanning-may not be. The first step in cancer induction is mutation in DNA. The most suitable systems for evaluating the role of melanin are those in which pigment can be varied and mutations can be measured. Several cell lines from Cloudman S91 mouse melanoma can be induced to form large quantities of melanin pigment after treatment with a number of different agents enabling comparison of mutant yields in the same cells differing principally in pigment concentration. In these studies, melanin was induced with synthetic alpha-melanocyte-stimulating hormone and with isobutyl methyl xanthine in the cell line S91/mel. The former inducer produced about 50% more pigment than the latter. Survival and mutation induction at the Na+/K(+)-ATPase locus were studied using ethyl methane sulfonate (EMS), a standard mutagen and five UV lamps emitting near monochromatic and polychromatic UV light in the three wave-length ranges of UV. There was greater protection against killing and mutation induction in the more heavily pigmented cells after exposure to EMS and after irradiation with monochromatic UVC and UVB. There was significant protection against killing by polychromatic UVB + UVA (FS20), but the small degree of protection against mutation was not significant. No significant change in killing and mutation using the same protocol was seen in S91/amel, a related cell line that does not respond to these inducers. No mutants were produced by either monochromatic or polychromatic UVA at doses that killed 50% of the cells. Our results show that induced pigment-shown earlier to be eumelanin (K. A. Cieszka et al., Exp. Dermatol. 4, 192-198, 1995)-is photo- and chemoprotective, but it is less effective in protection against mutagenesis by polychromatic UVB + UVA in a spectrum that more nearly approximates the solar spectrum.

In vitro photooxidation of nucleic acids by ultraviolet A radiation

Although ultraviolet A radiation (UVA, 315-400 nm) has been shown to induce oxidative stress in mammalian cells and skin, the critical chromophore(s) and molecular target(s) involved have not been identified. We examined the role of oxidative damage to nucleic acids induced by UVA. To assess photooxidation of cellular DNA and RNA by UVA, we irradiated human skin fibroblasts with up to 765 kJ/m2 UVA. Cellular DNA and RNA were isolated immediately and enzymatically hydrolyzed to nucleosides. 8-Oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG), a primary oxidation product in DNA, and 8-oxo-7,8-dihydroguanosine (8-oxoG), resulting from hydroxylation of guanine in RNA, were measured by HPLC with electrochemical detection. We determined that irradiation of skin fibroblasts with levels of UVA that produced moderate toxicity also resulted in significant levels of guanine hydroxylation in RNA. Lower levels of photooxidation were observed in DNA. These results suggest that measurement of guanine hydroxylation in nucleic acids, particularly in cellular RNA, may be a powerful tool for investigating the photobiological activity of UVA.

Preprogrammed and programmed cell death mechanisms of apoptosis: UV-induced immediate and delayed apoptosis

Equitoxic doses (10% clonogenic survival) of UV radiation (UVR) from the three waveband regions, i.e. UVA1 (340-400 nm), UVB (290-320 nm) and UVC (200-290 nm), were shown to induce immediate or delayed apoptosis in L5178Y-R murine lymphoma cells. Membrane and DNA damage were shown to be the most probable initiators of UVA1-induced immediate or UVR-induced delayed apoptosis, respectively. These UV-induced apoptotic processes appeared to utilize two different "core" biochemical mechanisms; however, one core mechanism could be initiated at two distinct sites (e.g. membrane or DNA) and result in disparate kinetics. In an attempt to resolve this mechanistic issue, the dependence on macromolecular synthesis of each UV-induced apoptotic mechanism was investigated. In the absence of UVR, inhibition of either transcription (actinomycin D) or translation (cycloheximide) induced apoptosis in a concentration- and time-dependent manner. These results suggest that an apoptotic mechanism exists that does not require macromolecular synthesis postinsult (constitutive). The UVR data demonstrate that UVA1-induced immediate apoptosis utilizes this constitutive mechanism (preprogrammed), while UVR-induced delayed apoptosis utilizes the well-known inducible mechanism (programmed). Therefore, there are two different core biochemical mechanisms of apoptotic death available to each cell: preprogrammed (constitutive) and programmed (inducible) cell death.

Ultraviolet action spectra for photobiological effects in cultured human lens epithelial cells

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 beta-crystallin, cells were exposed to sublethal fluences of UV radiation at 302 and 313 nm, labeled with [35S]methionine and the newly synthesized beta-crystallin was analyzed by immunoprecipitation and western blotting using an antibody to beta-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.(ABSTRACT TRUNCATED AT 250 WORDS)

Spectral dependence of UV-induced immediate and delayed apoptosis: the role of membrane and DNA damage

The phototoxicity of each waveband region of UV radiation (UVR), i.e., UVA (320-400 nm), UVB (290-320 nm) and UVC (200-290 nm), was correlated with an apoptotic mechanism using equilethal doses (10% survival) on murine lymphoma L5178Y-R cells. Apoptosis was qualitatively monitored for DNA "ladder" formation (multiples of 200 base pair units) using agarose gel electrophoresis, while the percentages of apoptotic and membrane-permeabilized cells were quantified over a postexposure time course using flow cytometry. The UVA1 radiation (340-400 nm) induced both an immediate (< 4 h) and a delayed (> 20 h) apoptotic mechanism, while UVB or UVC radiation induced only the delayed mechanism. The role of membrane damage was examined using a lipophilic free-radical scavenger, vitamin E. Immediate apoptosis and membrane permeability increased in a UVA1 dose-dependent manner, both of which were reduced by vitamin E. However, vitamin E had little effect on UVR-induced delayed apoptosis. In contrast, the DNA damaging agents 2,4- and 2,6-diaminotoluene exclusively induced delayed apoptosis. Thus, immediate apoptosis can be initiated by UVA1-induced membrane damage, while delayed apoptosis can be initiated by DNA damage. Moreover, the results suggest that immediate and delayed apoptosis are two independent mechanisms that exist beyond the realm of photobiology.

A multitherapy resistance factor from melanoma reveals that killing by near UV is different from genotoxic agents

A diffusible multitherapy resistance factor (MTRF) is produced by Cloudman S91 melanoma cells in vitro. The MTRF decreases sensitivity of the target cell line, S91/amel, to gamma-irradiation, UVC (200-280 nm) and mitomycin C (MMC). In the present study, we demonstrate that MTRF also increases the survival of S91/amel after exposure to actinomycin D (AMD) and vinblastine (VBL). The MTRF is thus effective when target cells have been exposed to five genotoxic agents that act by different mechanisms. It does not alter the response to the same five agents of the S91/I3 producer cells, which are presumably saturated with the factor. The factor has no effect on the survival of S91/amel cells that have been exposed to lethal doses of near monochromatic UVB (280-320 nm) or UVA (320-400 nm) or to polychromatic FS20 lamps. The lack of effectiveness of MTRF after cells have been exposed to near (300-400 nm) UV radiation indicates that in this wavelength range, S91 melanoma cells are killed by mechanisms that are different from the lethal effects of the five genotoxic agents (gamma-irradiation, UVC, MMC, AMD and VBL) to which the target cells demonstrate a response.

Both UVA and UVB induce cytoskeleton-dependent surface blebbing in epidermoid cells

Data on the morphological changes induced by UVA or UVB irradiation of A431 epidermoid cells in culture are presented. After irradiation with different doses of UVB (120-2400 J m-2) or UVA (10(4)-10(5) J m-2), the membrane and cytoskeleton of these cells were analysed by immunofluorescence and scanning electron microscopy at different times after exposure (0-48 h). Both UVA and UVB alter microtubules and microfilaments and surface blebs are formed after UV irradiation. In particular, UVB induces multiple small blebs on the cells, while UVA induces one single large bleb on each cell. Since cytoskeletal damage and surface blebbing of this type are also induced by oxidative stress, these results add to the body of evidence indicating that UV radiation is capable of pro-oxidant behaviour. Specifically, the morphological changes described in this paper are reminiscent of the modifications which accompany epidermal keratinocytes during their transformation to sunburn cells after UV irradiation. The physiological implications of these findings are discussed.