Role of Transition Metals in UV‐B‐Induced Damage to Bacteria

The purpose of this study was to explore the possible link between metals and UV‐B‐induced damage in bacteria. The effect of growth in the presence of enhanced concentrations of different transition metals (Co, Cu, Fe, Mn and Zn) on the UV‐B sensitivity of a set of bacterial isolates was explored in terms of survival, activity and oxidative stress biomarkers (ROS generation, damage to DNA, lipid and proteins and activity of antioxidant enzymes). Metal amendment, particularly Fe, Cu and Mn, enhanced bacterial inactivation during irradiation by up to 35.8%. Amendment with Fe increased ROS generation during irradiation by 1.2–13.3%, DNA damage by 10.8–37.4% and lipid oxidative damage by 9.6–68.7%. Lipid damage during irradiation also increased after incubation with Cu and Co by up to 66.8% and 56.5% respectively. Mn amendment decreased protein carbonylation during irradiation by up to 44.2%. These results suggest a role of Fe, Co, Cu and Mn in UV‐B‐induced bacterial inactivation and the importance of metal homeostasis to limit the detrimental effects of ROS generated during irradiation.     

Novel aspects of intrinsic and extrinsic aging of human skin: beneficial effects of soy extract

Biochemical and structural changes of the dermal connective tissue substantially contribute to the phenotype of aging skin. To study connective tissue metabolism with respect to ultraviolet (UV) exposure, we performed an in vitro (human dermal fibroblasts) and an in vivo complementary DNA array study in combination with protein analysis in young and old volunteers. Several genes of the collagen metabolism such as Collagen I, III and VI as well as heat shock protein 47 and matrix metalloproteinase-1 are expressed differentially, indicating UV-mediated effects on collagen expression, processing and degradation. In particular, Collagen I is time and age dependently reduced after a single UV exposure in human skin in vivo. Moreover, older subjects display a lower baseline level and a shorter UV-mediated increase in hyaluronan (HA) levels. To counteract these age-dependent changes, cultured fibroblasts were treated with a specific soy extract. This treatment resulted in increased collagen and HA synthesis. In a placebo-controlled in vivo study, topical application of an isoflavone-containing emulsion significantly enhanced the number of dermal papillae per area after 2 weeks. Because the flattening of the dermal-epidermal junction is the most reproducible structural change in aged skin, this soy extract appears to rejuvenate the structure of mature skin.     

High frequency induction of CC to TT tandem mutations in DNA repair-proficient mammalian cells

The CC to TT tandem mutation is induced by UV radiation exposure, though at relatively low frequencies when compared with the more commonly induced C to T mutation. Induction of the tandem mutation by UV is enhanced in mammalian cells with certain genetic deficiencies; however, conditions have not been described in which the frequency of this mutation is enhanced in DNA repair-proficient mammalian cells. For this study, an integrated construct that detects C to T and CC to TT mutations at a single codon in mouse Aprt was used to examine UVB mutagenesis under various conditions. Oxidative stress, in the form of intracellular hydrogen peroxide, increased the frequency of UVB-induced CC to TT mutations. Surprisingly, exposure of the cells to two antioxidants (N-acetylcysteine and trolox), either alone or in combination, also enhanced UVB induction of CC to TT tandem mutations. These results demonstrate, for the first time, that the frequency of UVB-induced CC to TT tandem mutations can be enhanced dramatically in DNA repair-proficient mammalian cells, and suggest that the enhancing effect does not require direct damage to DNA.     

ULTRAVIOLET LIGHT IRRADIATION OF DEFINED-SEQUENCE DNA UNDER CONDITIONS OF CHEMICAL PHOTOSENSITIZATION

Abstract— The formation of cyclobutane pyrimidine dimers and UV light-induced (6-4) products was examined under conditions of triplet state photosensitization. DNA fragments of defined sequence were irradiated with 313 nm light in the presence of either acetone qr silver ion. UV irradiation in the presence of both silver ion and acetone enhanced the formation of TT cyclobutane dimers, yet no (6-4) photoproducts were formed at appreciable levels. When photoproduct formation was also measured in pyrimidine dinucleotides, only cyclobutane dimers were formed when the dinucleotides were exposed to 313 nm light in the presence of photosensitizer. The relative distribution of each type of cyclobutane dimer formed was compared for DNA fragments that were irradiated with 254, 313, or 313 nm UV light in the presence of acetone. The dimer distribution for DNA irradiated with 254 and 313 nm UV light were very similar, whereas the distribution for DNA irradiated with 313 nm light in the presence of acetone favored TT dimers. Alkaline labile lesions at guanine sites were also seen when DNA was irradiated with 313 nm light in the presence of acetone.     

Fluorometric analysis of DNA unwinding (FADU) as a method for detecting repair-induced DNA strand breaks in UV-irradiated mammalian cells

Fluorometric analysis of DNA unwinding (FADU assay) was originally designed to detect X-ray-induced DNA damage in repair-proficient and repair-deficient mammalian cell lines. The method was modified and applied to detect DNA strand breaks in Chinese hamster ovary (CHO) cells exposed to ionizing radiation as well as to UV light. Exposed cells were allowed to repair damaged DNA by incubation for up to 1 h after exposure under standard growth conditions in the presence and in the absence of the DNA synthesis inhibitor aphidicolin. Thereafter, cell lysates were mixed with 0.15 M sodium hydroxide, and DNA unwinding took place at pH 12.1 for 30 min at 20 degrees C. The amount of DNA remaining double-stranded after alkaline reaction was detected by binding to the Hoechst 33258 dye (bisbenzimide) and measuring the fluorescence. After exposure to X-rays DNA strand breaks were observed in all cell lines immediately after exposure with subsequent restitution of high molecular weight DNA during postexposure incubation. In contrast, after UV exposure delayed production of DNA strand break was observed only in cell lines proficient for nucleotide excision repair of DNA photoproducts. Here strand break production was enhanced when the polymerization step was inhibited by adding the repair inhibitor aphidicolin during repair incubation. These results demonstrate that the FADU approach is suitable to distinguish between different DNA lesions (strand breaks versus base alterations) preferentially induced by different environmental radiations (X-rays versus UV) and to distinguish between the different biochemical processes during damage repair (incision versus polymerization and ligation).     

DNA DAMAGE IN RAT 9L CELLS TREATED WITH 8-METHOXYPSORALEN AND NEAR-UV LIGHT ASSAYED BY VISCOELASTOMETRY AND S1 NUCLEASE

–The techniques of viscoelastometry and S1 nuclease digestion were applied to the analysis of DNA damage in rat 9L cells treated with the combination of 8-MOP (8-methoxysporalen) and near-UV light. Treatment of cells with near-UV light alone resulted in a decrease in the viscoelastic retardation time under both denaturing and nondenaturing conditons. Exposure of cells to 8-MOP alone yielded a maximum in the plot of retardation time vs dose under nondenaturing conditions, similar to that found with ionizing radition. This observation suggests that treatment with 8-MOP alone leads to DNA strand breaks. Viscoelastic analysis of cell lysates under denaturing conditions demonstrated that treatment of cells with 8-MOP and UV radiation led to substantial increases in both the viscoelastic retardation time and recoil, consistent with formation of DNA interstrand cross-links. Viscoelastic analysis of cell lysates under nondenaturing conditions showed that exposure to long wavelength UV light in the presence of 8-MOP produced a decrease in retardation time. This decrease reflects the combined effect of strand breaks and interstrand cross-links. Results from the S1 nuclease assay confirmed these observations and permitted quantitation of DNA damage arising from single-strand breaks and DNA interstrand crosslinks. The importance of including the effect of strand breaks in the quantitation of cross-link formation is discussed.     

Synthesis of solar light driven nanorod-zinc oxide for degradation of rhodamine B,industrial effluent and contaminated river water

Surface water contamination by various dyes and pigments is a global problem caused by rapid industry, particularly textile/dyeing. Bangladesh's export-oriented textile sector has exploded in recent decades, polluting local waterways significantly. In this study, nano-ZnO were prepared using surfactant-assisted sol–gel, hydrothermal and thermal methods. SEM, XRD, reflectance spectrophotometer, EDS and adsorption tests were used to characterize the synthesized nano-ZnO. BET isotherms were used to determine the surface area, pore volume, and pore size of the as-prepared nano-ZnO. The mixed surfactant assisted-sol gel method produced nanorod-ZnO, whereas the hydrothermal and/or thermal methods yielded clusters of needles ZnO, as proven by SEM images. XRD data revealed that the synthesized nanorod-ZnO had a mainly wurtzite crystalline structure and their size was estimated using the Scherrer equation to be about 23.90 nm. EDS spectra confirmed the synthesis of pure nanorod-ZnO. Using a UV–visible reflectance spectrophotometer, the band gap energy of the as-prepared nanorod-ZnO was found to be 3.35 eV. According to BET isotherms, the BET and Langmuir surface areas were 4 and 5.4 m²/g, respectively. Prior to analyzing photodegradation, the RB was adsorbing in the presence of various doses of the nanorod-ZnO in the dark, but no adsorption was observed. The photocatalytic activities of the synthesized nano-ZnO were compared to TiO₂ (anatase) for the degradation of RB in an aqueous system under solar light, UV, fluorescence, and tungsten filament light irradiation. Nanorod-ZnO showed exceptional photocatalytic activity in degrading RB in an aqueous solution under solar light irradiation. The results suggest that 0.01 g/50 mL nanorod-ZnO with a solution pH of 7.8 is the best combination for complete degradation of 2.00 × 10^-5 M RB under solar light irradiation. When nano-ZnO was exposed to light, the inhibiting effect of ethanol and/or tert-butanol on the degradation of RB confirmed the formation of mostly hydroxyl free radicals. The synthesized nanorod-ZnO shown substantial photocatalytic activity in the removal of pollutants from industrial effluents and contaminated river water under solar light irradiation. A mechanism of excellent photocatalytic activity of the nanorod-ZnO is discussed.     

The Effect of Tryptophan on UV-induced DNA Photodamage

Trp–DNA adducts resulting from UV irradiation of pyrimidine bases and nucleotides in the presence of tryptophan (Trp) have been the subject of previous research. However, the relative yield of the adducts compared with the UV screening effect of Trp has not been previously considered. To determine whether Trp–DNA adduct formation or absorption “screening” by Trp is the predominant process when DNA solutions are irradiated with UV light in the presence of Trp, we irradiated Trp-containing DNA oligonucleotide solutions with UVC light and incubated aliquots of those solutions with molecular beacons (MBs) to detect the damage. We observed a rapid decay of fluorescence of the MBs for pure DNA solutions, thereby indicating damage. However, in the presence of Trp, the fluorescence decay is prolonged, with time constants that increase exponentially with Trp concentration. The results are discussed in terms of a beneficial in vivo cellular protection rather than harmful adduct formation and suggest a net sacrificial absorption of UV light by Trp which actually protects the DNA from UV damage.     

UVA-Potentiated Damage to Calf Thymus DNA by Fenton Reaction System and Protection by para-Aminobenzoic Acid

Abstract— Calf thymus DNA was irradiated with low-intensity UVA (main output at 365 nm, 2 mW cm^?2 or 36 kj m ² for 30 min), and the role of metal ions, hydrogen peroxide and reactive oxygen species (ROS) was examined. DNA damage was measured as thiobarbituric acid-reactive substances (possibly from degradation of deoxyribose) and as changes in ethidium bromide-DNA fluorescence due to unwinding from strand breaks. Under the present experimental conditions, UVA alone or in the presence of H₂0₂ had no effect on DNA but slightly enhanced the damage by iron/EDTA. Ultraviolet A strongly enhanced DNA damage (ca four- to five-fold) by the Fenton reaction system (50 μM Fe²⁺/100 μM EDTA + 0.5 mM H₂0₂). The results suggest that the Fenton reaction system was “photosensitized” to damage DNA by low-intensity UVA radiation. The enhanced damage by UVA was attributed in part to the reduction of Fe³⁺ to Fe²⁺. Ultraviolet A had no effect when iron (ferric or ferrous) ions were replaced by Cu²⁺, Zn²⁺, Mn²⁺ or Cd²⁺. The ROS involved in the UVA-enhanced damage to DNA by the Fenton reagents were OH and, to a lesser extent, superoxide anions. The UVA-potentiated DNA damage by the Fenton reaction system was then used to examine the protective effect of para-aminobenzoate (PABA), a UVB-absorbing sunscreen that protects against photocarcinogenesis in hairless mice. The results show that PABA and mannitol dose-dependently inhibited the damage with concentrations required for 50% inhibition at 0.1 mM and 3 mM, respectively. The protection by PABA was attributed to its radical-scavenging ability because PABA does not absorb light in the UVA region. These findings may be relevant to the biological damage by UVA and suggest that PABA is useful in protection against photocarcinogenesis by wide-range UV radiation.     

Synergism between electricity and ionizing radiation

Weak direct electric currents which produce little (or no) lethal damage to Escherichia coli bacteria are shown to act synergistically with ionizing radiation, both electromagnetic radiation (X-ray) and charged particles (beta radiation). This synergism greatly enhances the lethal effect of ionizing radiation on bacteria. This is possibly due to increased single-strand breaks in DNA, as detected by the alkaline sucrose gradient method. It is also shown that in cells with thymidine-3H incorporated into their DNA and treated with electricity, the radioactivity is released from the acid-insoluble fraction to the acid-soluble fraction, so that the ratio of radioactivity in the soluble fraction to that in the insoluble fraction increases from 0.47 in the non-treated control cells to 3.46 in the cells treated with an electric current of 1.0 mA (3.0 V) for 30 min, which indicates extensive degradation of cellular DNA. No synergism is detected between electricity and 254 nm UV radiation nor between electricity and X-rays, when these two agents are used sequentially in any order. Electricity alone produces lesions in cell membranes, as shown by electron microscopy.     

Damage to rat retinal DNA induced in vivo by visible light

Intense visible light can damage retinal photoreceptor cells by photochemical or thermal processes, leading to cell death. The precise mechanism of light-induced damage is unknown; however, oxidative stress is thought to be involved, based on the protective effect of antioxidants on the light-exposed retina. To explore the in vivo effects of light on retinal DNA, rats were exposed to intense visible light for up to 24 h and the time courses of single-strand breaks in restriction fragments containing the opsin, insulin 1 and interleukin-6 genes were measured. All three gene fragments displayed increasing single-strand modifications with increasing light exposure. Treatment with the antioxidant dimethylthiourea prior to light exposure delayed the development of net damage. The time course of double-strand DNA damage was also examined in specific genes and in repetitive DNA. The appearance of discrete 140-200 base-pair DNA fragments after 20 h of light exposure implicated a nonrandom, possibly enzymatic damaging mechanism. The generation of nucleosome core-sized DNA fragments, in conjunction with single-strand breaks, suggests two phases of light-induced retinal damage, with random attack on DNA by activated oxygen species preceding enzymatic degradation.     

Induction of 8-Oxo-7,8-Dihydro-2'-Deoxyguanosine by Ultraviolet Radiation in Calf Thymus DNA and HeLa Cells

Abstract— The levels of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo) in purified calf thymus DNA and HeLa cells were measured following exposure to either UVC, UVB or UVA wavelengths. This DNA damage was quantitated using HPLC coupled with an electrochemical detector. The 8-oxodGuo was induced in purified DNA in a linear dose-dependent fashion by each portion of the UV spectrum at yields of 100, 0.46 and 0.16 8-oxodGuo per 10⁵ 2'-deoxyguanosine (dGuo) per kJ/m² for UVC, UVB and UVA, respectively. However, the amount of 8-oxodGuo in HeLa cells irradiated with these UV sources decreased to approximately 2.0, 0.013 and 0.0034 8-oxodGuo per 10⁵ dGuo per kJ/m², respectively. In contrast, the levels of cyclobutyl pyrimidine dimers were similar in both irradiated DNA and cells. Therefore, 8-oxodGuo is induced in cells exposed to wavelengths throughout the UV spectrum although it appears that protective precesses exist within cells that reduce the UV-induced formation of this oxidative DNA damage. Cell survival was also measured and the number of dimers or 8-oxodGuo per genome per lethal event determined. These calculations are consistent with the conclusion that dimers play a major role in cell lethality for UVC- or UVB-irradiated cells but only a minor role in cells exposed to UVA wavelengths. In addition, it was found that the relative yield of 8-oxodGuo to dimers increased nearly 1000-fold in both UVA-irra-diated cells and DNA compared with cells subjected to either UVC or UVB. These results are supportive of the hypothesis that 8-oxodGuo, and possible other forms of oxidative damage, play an important role in the induction of biological effects caused by wavelengths in the UVA portion of the solar spectrum.     

Absence of photoreactivation of pyrimidine dimers in the epidermis of hairless mice following exposures to ultraviolet light

Abstract—The influence of photoreactivating light on the fate of UV-induced DNA damage has been measured in the epidermis of hairless mice using damage-specific endonuclease from Micrococcus luteus. Groups of mice were exposed to varying fluences of UV at 297nm or from an FS40 fluorescent sun lamp to induce UV photoproducts. The same fluence-dependent DNA damage was observed in high molecular weight epidermal DNA regardless of whether the mice were killed immediately, or maintained in the dark or under photoreactivating light for 20 h after UV. Thus, no detectable photoreactivation of UV-induced pyrimidine dimers could be demonstrated in mouse epithelial cells in vivo.     

MEASUREMENT OF DNA CROSSLINKS BY S1 NUCLEASE: INDUCTION AND REPAIR IN PSORALEN-PLUS-360 nm LIGHT TREATED ESCHERICHIA COLI

Abstract—DNA crosslinks in Escherichia coli cells. exposed to 4.5',8-trimethylpsoralen plus 360 nm light, were measured using a rapid and sensitive new approach. The assay is based on the specificity of S₁ nuclease from Aspergillus oryzae to single-stranded DNA. Bacterial cells were lysed and the DNA denatured by alkali. Following acid neutralization. crosslinked DNA undergoes spontaneous renaturation and is rendered S₁-nuclease resistant and therefore acid-precipitable. The single-stranded fraction after denaturation by alkali decreases with increasing near UV light exposure in the presence of TMP following first order kinetics. The kinetics were faster when exposure was at 4°C rather than at 20°C. This suggests that excision of crosslinks occurs during exposure at the higher temperature. Indeed. since the rate of DNA crosslinking in a uvr B mutant which is excision-deficient was higher than in wild type bacteria at 4°C, some excision must have occurred even in the cold. DNA from excision-proficient cells incubated at 37°C following exposure to TMP-plus-near UV at 4° showed a greater single stranded fraction than that from non-incubated cells. This indicates repair of DNA crosslinks. which proceeded with a half-time of 8 min at 37°C and was unaffected by substitution of thymine in DNA by 5-bromouracil.     

DNA ligand Hoechst-33342 enhances UV induced cytotoxicity in human glioma cell lines

The effects of minor groove binding ligand bisbenzimidazole derivative Hoechst-33342 on the cellular response to UV damage have been studied in two human glioma cell lines BMG-1 and U-87 grown as monolayer cultures. Treatment induced cell death (macro-colony assay) and growth inhibition, potential lethal damage recovery, cytogenetic damage (micronuclei formation) and proliferation kinetics were studied as parameters for cellular response. Pre and post-irradiation treatment with Hoechst-33342 (1-20 microM) enhanced the UV-induced growth inhibition and cell death in a concentration dependent manner in both cell lines. At higher Hoechst-33342 concentrations (>5 microM), the cytotoxic effects of the combination (Hoechst-33342+UV) were highly synergistic and mainly mediated through apoptosis implying the possible interactions of lesions caused by both the agents. The enhanced cell death due to Hoechst-33342 was accompanied by a significant increase (2-3 folds at 5 microM) in UV-induced micronuclei formation in BMG-1 cells. Under these conditions, Hoechst-33342 also enhanced the UV-induced cell cycle delay, mainly due to S and G(2) blocks. The increase in UV-induced micronuclei formation observed after treatment with Hoechst-33342 indicates that the DNA bound Hoechst-33342 may interfere with the rejoining of DNA strand breaks. Since the treatment of cells with the replication inhibitor aphidicolin reduced the enhancement of UV induced cytotoxicity by Hoechst-33342, ongoing DNA replication appears to stimulate Hoechst-33342 and UV-induced cytotoxicity.     

Simple photografting method to chemically modify and micropattern the surface of SU-8 photoresist

SU-8 has gained widespread acceptance as a negative photoresist. It is also finding increasing use as a structural material in microanalytical devices. Consequently, methods to tailor the surface properties of SU-8 as well as to micropattern coatings on the surface of SU-8 are needed. The SU-8 photoresist consists of EPON SU-8 resin mixed with the photoacid generator triarylsulfonium hexafluoroantimonate. This photoacid generator can also serve as a photoinitiator generating free radicals when illuminated with UV light. Under the appropriate conditions, sufficient triarylsulfonium hexafluoroantimonate remains within cured SU-8 to act as a source of free radicals and initiate UV-mediated grafting of polymers onto the surface of the SU-8. UV-mediated grafting was used to coat SU-8 surfaces with poly(acrylic acid) and other water-soluble monomers. The SU-8 surface was chemically micropatterned by placing a mask between the UV light and SU-8. The X-Y spatial resolution of micropatterned poly(acrylic acid) on the SU-8 surface was 2 mum. Three applications of these chemically modified SU-8 surfaces were demonstrated. In the first, poly(ethylene glycol) was used to protect the SU-8 from interactions with proteins, yielding a surface resistant to biofouling. In the second demonstration, the SU-8 surface was micropatterned with a cell-resistant layer to guide cellular attachment and growth. In the final application, SU-8 micropallets were encoded with polymer lines. The bar codes were read by either absorbance or fluorescence measurements. Thus, UV-mediated graft polymerization is an efficient and effective method to micropattern coatings onto the surface of SU-8.     

Enhancement of the Efficacy of Photodynamic Inactivation of Candida albicans with the Use of Biogenic Gold Nanoparticles

This study reports on successful photodynamic inactivation of planktonic and biofilm cells of Candida albicans using Rose Bengal (RB) in combination with biogenic gold nanoparticles synthesized by the cell‐free filtrate of Penicillium funiculosum BL1 strain. Monodispersed colloidal gold nanoparticles coated with proteins were characterized by a number of techniques including SEM–EDS, TEM, UV–Vis absorption and fluorescence spectroscopy, as well as Fourier transform infrared spectroscopy to be 24 ± 3 nm spheres. A Xe lamp (output power of 20mW, delivering intensity of 53 mW cm^?2) was used as a light source to study the effects of RB alone, the gold nanoparticles alone and the RB‐gold nanoparticle mixture on the viability of C. albicans cells. The most effective reduction in the number of planktonic cells was found after 30 min of Xe lamp light irradiation (95.4 J cm^?2) and was 4.89 log₁₀ that is 99.99% kill for the mixture of RB with gold nanoparticles compared with 2.19 log₁₀ or 99.37% for RB alone. The biofilm cells were more resistant to photodynamic inactivation, and the highest effective reduction in the number of cells was found after 30 min of irradiation in the presence of the RB–gold nanoparticles mixture and was 1.53 log₁₀, that is 97.04% kill compared with 0.6 log₁₀ or 74.73% for RB. The probable mechanism of enhancement of RB‐mediated photodynamic fungicidal efficacy against C. albicans in the presence of biogenic gold nanoparticles is discussed leading to the conclusion that this process may have a multifaceted character.     

The impact of ultraviolet light on bacterial adhesion to glass and metal oxide-coated surface

Biofouling of glass and quartz surfaces can be reduced when the surface is coated with photocatalytically active metal oxides, such as TiO2 (anatase form) or SnO2. We measured the attachment of eight strains of bacteria to these two metal oxides (TiO2 and SnO2), and to an uncoated glass (control; designated Si-m) before and after exposure to UV light at wavelengths of 254 nm (UVC) or 340 nm UV (UVA). TiO2-coated surfaces were photocatalytically active at both 254 and 340 nm as evidenced by a decrease in the water contact angle of the surface from 59 degrees +/-2 to <5 degrees. The water contact angle of the SnO2 surface was reduced only at 254 nm, while contact angle of the Si-m glass surface was not altered by light of either wavelength. Bacterial adhesion decreased by 10-50% to photocatalyzed glass surfaces. In all cases, bacteria exposed to the UV light were completely killed due to a combination of exposure to UV light and the photocatalytic activity of the glass surfaces. These results show that UV light irradiation of TiO2-coated surfaces can be an effective method of reducing bacterial adhesion.     

DNA DAMAGE AND REPAIR IN HUMAN CELLS EXPOSED TO SUNLIGHT

Cultured human cells were treated with direct sunlight under conditions which minimised the hypertonic, hyperthermic and fixative effects of solar radiation. Sunlight produced similar levels of DNA strand breaks as equitoxic 254 nm UV in two fibroblast strains and a melanoma cell line, but DNA repair synthesis and inhibition of semiconservative DNA synthesis and of DNA chain elongation were significantly less for sunlight-exposed cells. DNA breaks induced by sunlight were removed more rapidly. Thus, the repair of solar damage differs considerably from 254 nm UV repair. Glass-filtered sunlight (> 320 nm) was not toxic to cells and did not induce repair synthesis but gave a low level of short-lived DNA breaks and some inhibition of DNA chain elongation; thymidine uptake was enhanced. Filtered sunlight slightly enhanced UV-induced repair synthesis and UV toxicity; photoreactivation of UV damage was not found. Attempts to transform human fibroblasts using sunlight, with or without phorbol ester, were unsuccessful.     

Induced and photoinduced DNA damage by quinolones: ciprofloxacin, ofloxacin and nalidixic acid determined by comet assay

Quinolones are degraded by light with loss of their antimicrobial activity, generating active species or radicals. Evidence exists that some fluoroquinolones (lomefloxacin, fleroxacin and enoxacin) induce damage to the cellular membrane and DNA cleavage by photosensitization. In this study, the genotoxic potential of the quinolones ofloxacin, nalidixic acid and ciprofloxacin (three antimicrobials frequently used in therapy) was evaluated upon irradiation with UV light by using the comet assay on cells of the Jurkat line. The results demonstrate that there are significant differences between the control groups (positive control with 50 microM H2O2, negative controls without drug and with and without irradiation) and the groups of irradiated quinolones (ofloxacin 2.76 x 10(-5) M, nalidixic acid 2.15 x 10(-4) M and ciprofloxacin 2.01 x 10(-5) M), indicating that, at the dose of irradiation employed (necessary to produce 50% photodegradation), the photodecomposition of the quinolones enhanced DNA damage. The unirradiated drugs also exhibited genotoxicity significantly different from that of the negative control.