Quinolone antibiotic photodynamic production of 8-oxo-7, 8-dihydro-2'-deoxyguanosine in cultured liver epithelial cells

Photosensitization Reactions of Biomolecules: Definition, Targets and Mechanisms

Photosensitization reactions have been demonstrated to be largely responsible for the deleterious biological effects of UV and visible radiation, as well as for the curative actions of photomedicine. A large number of endogenous and exogenous photosensitizers, biological targets and mechanisms have been reported in the past few decades. Evolving from the original definitions of the type I and type II photosensitized oxidations, we now provide physicochemical frameworks, classifications and key examples of these mechanisms in order to organize, interpret and understand the vast information available in the literature and the new reports, which are in vigorous growth. This review surveys in an extended manner all identified photosensitization mechanisms of the major biomolecule groups such as nucleic acids, proteins, lipids bridging the gap with the subsequent biological processes. Also described are the effects of photosensitization in cells in which UVA and UVB irradiation triggers enzyme activation with the subsequent delayed generation of superoxide anion radical and nitric oxide. Definitions of photosensitized reactions are identified in biomolecules with key insights into cells and tissues.

Oxidatively-generated damage to DNA and proteins mediated by photosensitized UVA

UVA accounts for about 95% of the solar ultraviolet (UV) radiation that reaches Earth and most likely contributes to human skin cancer risk. In contrast to UVB, which comprises the remaining 5% and is absorbed by DNA nucleobases to cause direct photodamage, UVA damages DNA indirectly. It does this largely through its interactions with cellular chromophores that act as photosensitisers to generate reactive oxygen species. Exogenously supplied chemicals, including some widely-prescribed medicines, may also act as photosensitisers and these drugs are associated with an increased risk of sun-related cancer. Because they amplify the effects of UVA on cells, they provide a means to investigate the mechanisms and effects of UVA-induced photodamage. Here, we describe some of the major lesions induced by two groups of UVA photosensitisers, the DNA thionucleotides and the fluoroquinolone antibiotics. In thionucleotides, replacement of the oxygen atoms of canonical nucleobases by sulfur converts them into strong UVA chromophores that can be incorporated into DNA. The fluoroquinolones are also UVA chromophores. They are not incorporated into DNA and induce a different range of DNA damages. We also draw attention to the potentially important contribution of photochemical protein damage to the cellular effects of photosensitised UVA. Proteins targeted for oxidation damage include DNA repair factors and we suggest that UVA-mediated protein damage may contribute to sunlight-induced cancer risk.

Use of centromeric and telomeric DNA probes in in situ hybridization for differentiation of micronuclei induced by lomefloxacin

Classification of micronuclei induced by lomefloxacin, a difluorinated quinolone bactericidal agent, in mouse bone marrow was performed by fluorescence in situ hybridization using DNA probes for the centromere repeated minor satellite DNA and the telomeric hexamer repeat (5'-TTAGGG-3'). Colchicine and mitomycin C were used as a positive control aneugen and clastogen, respectively, and these compounds produced the expected responses. Single doses of 40, 80, 160, or 320 mg/kg lomefloxacin were given via oral intubations and bone marrow was sampled at 24 and 48 hr after treatment. The micronuclei showed significant increases in both sampling times after doses of 320 mg/kg. A statistically significant increase of micronuclei frequency was also detected for 160 mg/kg lomefloxacin at 48 hr after treatment. The responses were directly correlated with bone-marrow cytotoxicity. Following treatment with 160 and 320 mg/kg lomefloxacin, 48.2 and 50.0% of the induced micronuclei, respectively, showed double labeling with centromeric signals and several telomeric signals, indicating that the induced micronuclei were composed of whole chromosomes. Similarly, 51.8 and 50.0% of the induced micronuclei, respectively, were centromere-negative, demonstrating that lomefloxacin not only induces chromosome loss but also chromosome breakage. The results also showed that chromosomes can be enclosed in a micronucleus before and after centromere separation. Overall, this study provides the first evidence of the potential of lomefloxacin to induce aneugenic effect in mice. However, given the high doses used in this study, the clinical significance of this finding is uncertain.

Photosensitized DNA damage: the case of fluoroquinolones

This review focuses on DNA damage photosensitized by the fluoroquinolone (FQ) antibacterial drugs. The in vivo evidence for photocarcinogenesis mediated by FQs is presented in the introduction. The different methods employed for detection of DNA-photodamage mediated by FQs are then summarized, including gel electrophoresis (with whole cells, with isolated DNA and with oligonucleotides) and chromatographic analysis (especially HPLC with electrochemical and MS/MS detection). The chemical mechanisms involved in the formation of the reported lesions are discussed on the basis of product studies and transient spectroscopic evidence. In general, the literature coverage is limited to the last decade, although some earlier citations are also included.

Photosensitizing Potential of Ciprofloxacin at Ambient Level of UV Radiation

Ciprofloxacin is a widely used fluoroquinolone drug with broad spectrum antibacterial activities. Clinical experience has shown incidences of adverse effects related to skin, hepatic, central nervous system, gastrointestinal and phototoxicity. India is a tropical country and sunlight is abundant throughout the day. In this scenario exposure to ambient levels of ultraviolet radiation (UV-R) in sunlight may lead to harmful effects in ciprofloxacin users. Phototoxicity assessment of ciprofloxacin was studied by two mouse fibroblast cell lines L-929 and NIH-3T3. Generation of reactive oxygen species (ROS) like singlet oxygen (1O2), superoxide anion radical (O2*-) and hydroxyl radical (*OH) was studied under the exposure of ambient intensities of UV-A (1.14, 1.6 and 2.2 mW cm(-2)), UV-B (0.6, 0.9 and 1.2 mW cm(-2)) and sunlight (60 min). The drug was generating 1O2, O2*- and *OH in a concentration and dose-dependent manner. Sodium azide (NaN3) and 1,4-diazabicyclo 2-2-2-octane (DABCO) inhibited the generation of 1O2. Superoxide dismutase (SOD) inhibited 90-95% O2*- generation. The drug (5-40 microg mL(-1)) was responsible for linoleic acid peroxidation. Quenching study of linoleic acid peroxidation with SOD (25 and 50 U mL(-1)) confirms the involvement of ROS in drug-induced lipid peroxidation. The generation of *OH radical was further confirmed by using specific quenchers of *OH such as mannitol (0.5 M) and sodium benzoate (0.5 M). 2'-deoxyguanosine (2'-dGuO) assay and linoleic acid peroxidation showed that ROS were mainly responsible for ciprofloxacin-sensitized photo-degradation of guanine base. L-929 cell line showed 29%, 34% and 54% reduced cell viability at higher drug concentration (300 microg mL(-1)) under UV-A, UV-B and sunlight, respectively. 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay in NIH-3T3 cell line at higher drug concentration (300 microg mL(-1)) showed a decrease in cell viability by 54%, 56% and 59% under UV-A, UV-B and sunlight, respectively. Results of neutral red uptake assay (NRU) in L-929 cell line were in accordance with MTT assay. The NIH-3T3 cell line showed a higher photosensitizing potential than L-929. The phototoxicity end point shows a time- and concentration-dependent statistically significant (P<0.001) damage. Ciprofloxacin produced ROS by Type I and Type II photodynamic reactions, interacted with nucleic acid moiety and inhibited cell viability. Further, UV-induced photo-peroxidation of linoleic acid accorded the involvement of ROS in the manifestation of drug phototoxicity. Appearance of ciprofloxacin-induced phototoxicity at the ambient level of sunlight is a real risk for the people of India and for those of other tropical countries. We suggest that sunlight exposure should be avoided (especially peak hours) during ciprofloxacin treatment.

Photosensitized DNA Damage and its Protection via a Novel Mechanism†

UVA, which accounts for approximately 95% of solar UV radiation, can cause mutations and skin cancer. Based mainly on the results of our study, this paper summarizes the mechanisms of UVA-induced DNA damage in the presence of various photosensitizers, and also proposes a new mechanism for its chemoprevention. UVA radiation induces DNA damage at the 5'-G of 5'-GG-3' sequence in double-stranded DNA through Type I mechanism, which involves electron transfer from guanine to activated photosensitizers. Endogenous sensitizers such as riboflavin and pterin derivatives and an exogenous sensitizer nalidixic acid mediate DNA photodamage via this mechanism. The major Type II mechanism involves the generation of singlet oxygen from photoactivated sensitizers, including hematoporphyrin and a fluoroquinolone antibacterial lomefloxacin, resulting in damage to guanines without preference for consecutive guanines. UVA also produces superoxide anion radical by an electron transfer from photoexcited sensitizers to oxygen (minor Type II mechanism), and DNA damage is induced by reactive species generated through the interaction of hydrogen peroxide with metal ions. The involvement of these mechanisms in UVA carcinogenesis is discussed. In addition, we found that xanthone derivatives inhibited DNA damage caused by photoexcited riboflavin via the quenching of its excited triplet state. It is thus considered that naturally occurring quenchers including xanthone derivatives may act as novel chemopreventive agents against photocarcinogenesis.

Rufloxacin-induced photosensitization in yeast

The fluoroquinolone Rufloxacin (RFX) is active as specific inhibitor of bacterial gyrase. The adverse effects of the photosensitization induced by fluoroquinolones are well known. A predominant type II photosensitizing activity of Rufloxacin has already been demonstrated on simpler models (free nucleosides, calf thymus DNA), whereas a cooperative mechanism was corroborated on more complex ones (plasmid and fibroblast). The purpose of this study is to examine the drug photocytoxicity in another complex cellular model, a wild-type eukaryotic fast-growing microorganism whose cultivation is cheap and easily managed, Saccharomyces cerevisiae. This work represents the first report of the potential photogenotoxicity of Rufloxacin. Particular emphasis was given to DNA modifications caused in yeast by the formation of Rufloxacin photomediated toxic species, such as hydrogen peroxide and formaldehyde. Drug phototoxicity on yeast was evaluated by measuring DNA fragmentation (single/double strand breaks) using single cell gel electrophoresis assay and 8-OH-dGuo, a DNA photooxidation biomarker, by HPLC-ECD. Cellular sensitivity was also assessed by cell viability test. The extra- and intracellular RFX concentration (as well as its main photoproduct) was verified by HPLC-MS, whereas the cytotoxic species were evaluated by colorimetric assays. The results confirm the phototoxicity of Rufloxacin on yeast cell and are in agreement with those previously obtained with human fibroblast and with simpler models used recently, and provide a clear link between DNA photosensitization and overall phototoxicity.

Cellular aspects of photocarcinogenesis

Many aspects are involved in photocarcinogenesis. Historically, genetic change caused by UV-B-induced pyrimidine photoproducts have been paid much attention. Indeed they are very important factors. However, recent reports indicate the involvement of many other factors. First, UV-B induces not only pyrimidine photoproducts but also DNA lesions modified by reactive oxygen species (ROS). Several reports pointed out that types of mutations that are not theoretically caused by pyrimidine photoproducts are frequently observed in the human skin cancers of sun-exposed areas and UV-B-induced murine skin cancers. In addition to transition-type mutations at dipyrimidine sites, mutations which may be induced by the presence of oxidative DNA damage, are frequently observed in the ras oncogene and p53 tumor suppressor gene in human skin cancers of sun-exposed area and in UV-induced mouse skin cancers. Second, recent studies have shown that not only UV-B but also UV-A is involved in photocarcinogenesis based on animal experiments whereas UV-B has been considered mostly responsible. UV-A induces indirect DNA damage via ROS and lipid peroxidation. ROS have been associated not only with initiation, but promotion and progression in the multistage carcinogenesis model. Third, biological responses other than direct influence by UV such as inflammatory and immunological responses and oxidative modifications of DNA and proteins appears also responsible for carcinogenesis. Persistent oxidative stress in cancer may also cause activation of transcription factors and protooncogenes such as c-fos and c-jun as well as genetic instability. Such a stress may also contribute to maintain their malignant characteristics. An integrated model for photocarcinogenesis is proposed.

The photocarcinogenesis of antibiotic lomefloxacin and UVA radiation is enhanced in xeroderma pigmentosum group A gene-deficient mice

Lomefloxacin (LFLX) is phototoxic and phototumorigenic, but the mechanisms of phototumorigenesis of quinolone drugs have not been fully elucidated. Formation of cyclobutane pyrimidine dimers (CPD) by UVB radiation is primarily involved in the carcinogenesis of ultraviolet (UV) radiation. On the other hand, UVA region is responsible to photobiologic reactions of quinolone drugs. To know if CPD can be formed by UVA radiation in the presence of LFLX and is involved in the phototumorigenesis, we used xeroderma pigmentosum (XP) group A gene-deficient (XPA-/-) mouse, which is defective in nucleotide excision repair. XPA-/- and XPA+/+ mice were irradiated to 5 J per cm2-UVA with or without the administration of LFLX. In XPA-/- mice treated with LFLX, the first skin tumor appeared after exposures to 75 J per cm2 in 5 wk. In XPA+/+ mice treated with LFLX, the first tumor appeared after exposures to 345 J per cm2 in 23 wk. Immunohistochemically, CPD formation was observed after UVA-exposure in the skin of XPA+/+ as well as XPA-/- mice which had been given LFLX. The CPD disappeared, however, earlier from XPA+/+ mice than from XPA-/- mice. The acute inflammatory reaction after LFLX administration and exposure to UVA were greatly enhanced in XPA-/- mice. These results indicate that UVA exposure induces DNA damage in the form of CPD in the presence of LFLX, which exerts phototoxicity and phototumorigenesis.

Rufloxacin induced photosensitization in bio-models of increasing complexity

Rufloxacin belongs to the class of fluoroquinolones that act mainly as specific inhibitors of bacterial Topoisomerase II. These drugs are widely known to be involved in various diseases ranging from cutaneous reactions to aging. The type II photosensitizing activity of Rufloxacin has been already demonstrated on calf thymus DNA and free nucleosides. The aim of this study is to examine in control untreated and UVA irradiated human fibroblasts the modifications on DNA status induced by Rufloxacin added in the culture medium. This allows to investigate the photosensitizing activity of Rufloxacin in a more complex cell model. Fibroblasts, either in the presence or in the absence of Rufloxacin, were exposed to UVA irradiation for different times. An experimental protocol was followed in order to evaluate the amount of single-strand breaks (SSB) and double-strand breaks (DSB) DNA fragmentation by comet assay, and plasmid photocleavage. The presence of oxidized bases was also evaluated using the 8-OH-dGuo test. The comet assay test was also employed to assess cellular repair capacity. The intracellular drug concentration was verified by HPLC-MS. The results confirming the role of Rufloxacin as photosensitizer were: (i) a time-dependent increase in DNA fragmentation when fibroblasts were irradiated in the presence of Rufloxacin; (ii) the efficiency of the cellular repair machinery to be exhaustive after 2 h (whereas no correlation between irradiation time and DNA damage repair was observed with a higher level of DNA fragmentation after shorter irradiation times); (iii) the increased number of cells exhibiting high DNA fragmentation, seen as comets with long tails, was not accompanied by a similar large extent of oxidised DNA base formation, as measured by 8-OH-dGuo analysis; (iv) the double helix SSB, formed in plasmid photosensitization, agreed with the comet assay results, pointing out a good correlation among the cell system and the simpler models used.

Enhanced antitumor activity of ultrasonic irradiation in the presence of new quinolone antibiotics in vitro

To determine if there is any synergistic antitumor effect of ultrasound (US) in the presence of new quinolone (NQ) antibiotics, 0.2 mM solutions of lomefloxacin hydrochloride (LFLX), sparfloxacin (SPFX), ciprofloxacin hydrochloride (CPFX), and gatifloxacin hydrate (GFLX) were tested as sonodynamic agents against sarcoma 180 cells in vitro. After US irradiation at 2 W/cm(2) for 30 and 60 s, the survival rates of tumor cells in the presence of NQ antibiotics were significantly lower than those in their absence (P < 0.001). In May-Giemsa smears, most of the tumor cells remained intact in the control group. However, in the 0.2 mM SPFX group, the tumor cells were mostly fragmented. The synergistic antitumor effect of SPFX was dose-dependent. Furthermore, when D-mannitol was used with SPFX, the survival rate of tumor cells after irradiation was comparable with that when SPFX alone was applied, but when L-histidine was used concurrently, the survival rate of tumor cells was significantly higher than that when SPFX alone was applied. These findings suggest that NQ antibiotics would exhibit useful antitumor activity under US irradiation, and that generation of singlet oxygen is involved in the process of cell damage.

Role of reactive oxygen species in skin carcinogenesis

Reactive oxygen species (ROS) are associated not only with initiation, but also with promotion and progression in the multistage carcinogenesis model. In the present review, we will focus on the involvement of ROS in skin carcinogenesis, especially that induced by ultraviolet (UV) radiation. UV-specific DNA damage has been well studied thus far. However, recent reports have revealed the previously unknown participation of oxidative stress in UV-induced skin carcinogenesis. Indeed, in addition to transition-type mutations at dipyrimidine sites, G:C to T:A transversions, which may be induced by the presence of 8-oxoguanine during DNA replication, are frequently observed in the ras oncogene and p53 tumor suppressor gene in human skin cancers of sun-exposed areas and in UV-induced mouse skin cancers. Recent studies have shown that not only UV-B, but also UV-A is involved in UV-induced carcinogenesis. A wide variety of biological phenomena other than direct influence by UV, such as inflammatory and immunological responses and oxidative modifications of DNA and proteins, appear to play roles in UV-induced skin carcinogenesis. Furthermore, it has become clear that genetic diseases such as xeroderma pigmentosum show deficient repair of oxidatively modified DNA lesions. The involvement of ROS in skin carcinogeneisis caused by arsenic and chemical carcinogens will also be discussed.

Genotoxicity of lomefloxacin--an antibacterial drug in somatic and germ cells of Swiss albino mice in vivo

The in vivo genotoxicity of lomefloxacin, a diflourinated antibacterial drug, was evaluated by employing mouse in vivo chromosomal aberration test in bone marrow cells and dominant lethal mutation assay in germ cells. Statistically significant reduction in mitotic index, increase in chromosomal aberrations (CAs)/cell and percent abnormal metaphase was observed only at the highest dose (160 mg/kg b.w.) of the drug. In the dominant lethal mutation assay, a statistically significant decrease in the number of implants/female, compared to vehicle control, was noticed only in the females mated with males treated with 32 mg/kg b.w. during the third week of mating, while statistically significant reduction in live implants/female was noticed at both the doses during the second and third weeks of mating. Nevertheless, no significant change in the number of dead implants/female was observed after lomefloxacin treatment. These results seems to indicate that lomefloxacin is a weak clastogen in the bone marrow cells and non-mutagenic in the germ cells of mouse in vivo.

In vivo photochemical micronucleus induction due to certain quinolone antimicrobial agents in the skin of hairless mice

The skin micronucleus test combined with irradiation due to a sunlight simulator having a spectrum almost identical to solar irradiation was used as a novel in vivo testing method for detecting or comparing the photochemical chromosome damage of quinolone antibacterial agents (quinolones). Eight-week-old male SKH1 hairless mice were orally administered once lomefloxacin (LFLX), a strong in vitro photochemical clastogen, at 25 or 50 mg/kg, followed by light irradiation at 7.9-9.4J/cm2 of ultraviolet A (UVA). Animals were killed on Days 2, 3, 4, 5 or 8 (the dosing day was designated as Day 1), and the incidence of micronucleus in the epidermis was determined. As results, LFLX at either dose caused significant increases in the micronucleus frequency, which peaked on Day 4. These changes tended to return to the control level on Day 8. Then, the micronucleus induction potential of the quinolone derivatives levofloxacin (LVFX) and clinafloxacin (CLFX) at 10, 20 or 40 mg/kg was assessed on Day 4 under the same experimental conditions as for LFLX. Although LVFX was negative even at 40 mg/kg, CFLX dose-dependently induced significant increases in micronucleus frequency at all doses. The correlation of magnitude among the three quinolones in the skin micronucleus test with light irradiation was similar to that in our previous in vitro photochemical clastogenicity study. No significant increase in micronucleus frequency was observed in any of three quinolones employed without light irradiation. In conclusion, the experimental method presented here would be a useful tool for detecting in vivo photochemical chromosome damage and for research on photochemical carcinogenesis of chemicals.

In vitro photochemical clastogenicity of quinolone antibacterial agents studied by a chromosomal aberration test with light irradiation

The photochemical clastogenic potential of 12 quinolone antibacterial agents with or without light irradiation was assessed by an in vitro chromosomal aberration test using cultured CHL cells. Exposure to all test compounds, except for DK-507k, increased the incidence of cells with structural aberrations excluding gap (TA) following light irradiation. Test compounds used in the present study under light irradiation were divided into three groups based on their ED(50) values, doses inducing chromosomal aberrations in 50% of cells. The first group with ED(50) values below 30 microg/ml includes sparfloxacin (SPFX), clinafloxacin (CLFX), gemifloxacin (GMFX), lomefloxacin (LFLX), sitafloxacin (STFX), grepafloxacin (GPFX) and fleroxacin (FLRX); the second group with ED(50) values of 100 microg/ml, enoxacin (ENX) and levofloxacin (LVFX); the third group with little or no potency, moxifloxacin (MFLX), trovafloxacin (TVFX) and DK-507k. The photochemical clastogenicity of these compounds correlates well with their reported in vivo phototoxic potentials. In the chemical structure and clastogenicity relationships, substitution of a methoxy group at the C-8 position in the quinolone nucleus was confirmed to reduce not only photochemical clastogenicity, but also the clastogenic potential of quinolone antibacterial agents.

Analysis of fluoroquinolone-mediated photosensitization of 2'-deoxyguanosine, calf thymus and cellular DNA: determination of type-I, type-II and triplet-triplet energy transfer mechanism contribution

Fluoroquinolone (FQ) antibacterials are known to exhibit photosensitization properties leading to the formation of oxidative damage to DNA. In addition, photoexcited lomefloxacin (Lome) was recently shown to induce the formation of cyclobutane pyrimidine dimers via triplet-triplet energy transfer. The present study is aimed at gaining further insights into the photosensitization mechanisms of several FQ including enoxacin (Enox), Lome, norfloxacin (Norflo) and ofloxacin (Oflo). This was achieved by monitoring the formation of DNA base degradation products upon UVA-mediated photosensitization of 2'-deoxyguanosine, isolated and cellular DNA. Oflo and Norflo act mainly via a Type-II mechanism whereas Lome and, to a lesser extent, Enox behave more like Type-I photosensitizers. However, the extent of oxidative damage was found to be relatively low. In contrast, it was found that cyclobutane thymine dimers represent the major class of damage induced by Enox, Lome and Norflo within isolated and cellular DNA upon UVA irradiation. This striking observation confirms that FQ are able to promote efficient triplet energy transfer to DNA. The levels of photosensitized formation of strand breaks, alkali-labile sites and oxidative damage to cellular DNA, as measured by the comet assay, were confirmed to be rather low. Therefore, we propose that the phototoxic effects of FQ are mostly accounted for energy transfer mechanism rather than by Type-I or -II photosensitization processes.

Oxidative DNA damage: endogenous and chemically induced

A variety of types of DNA oxidation occur endogenously and mediated by xenobiotics. Certain forms are mutagenic and carcinogenic and may lead to other pathologies.

Distinct mechanisms of guanine-specific DNA photodamage induced by nalidixic acid and fluoroquinolone antibacterials

Fluoroquinolone antibacterials, which have been used for the treatment of a variety of infectious diseases, are reported to be photocarcinogenic. We investigated the mechanisms of DNA damage by UVA radiation (365 nm) plus fluoroquinolone antibacterials using 32P-labeled DNA fragments obtained from the human c-Ha-ras-1 proto-oncogene and the p53 tumor suppressor gene. Photocarcinogenic nalidixic acid (NA), which is an old member of synthetic quinolone antibacterials, caused DNA damage specifically at 5'-GG-3' sequences, whereas lomefloxacin (LFLX) did not exhibit the site preference for consecutive guanines. LFLX-induced DNA photodamage was inhibited by sodium azide and enhanced in D2O, suggesting that singlet oxygen plays the key role in the DNA damage. LFLX plus UVA induced the formation of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) depending on LFLX concentrations, and 8-oxodG formation was enhanced in single-stranded DNA. In contrast, NA induced larger amounts of 8-oxodG in double-stranded DNA. ESR spin destruction method revealed that NA induced DNA photodamage through electron transfer but LFLX did not. These findings indicate that DNA damage induced by photoactivated LFLX and NA plays an important role in expression of their photocarcinogenicity.

Photochemical decomposition of lomefloxacin in vitro and in vivo

To obtain an idea of the photostability of Lomefloxacin (Lom) under in vivo conditions the compound was exposed to UV-A (310-360 nm) in PBS buffer pH 7.4. Exposure of 10 microg/ml of Lom in PBS pH 7.4 led to more than 50% decomposition within 10 min. Loss of the fluorine atom at C-8 and partial breakdown of the piperazine ring occurred. The only two photoproducts formed under these conditions were AEA, 1-ethyl-6-fluoro-1,4-dihydro-7-(2-aminoethyl-amino)-4-oxo-3-quinolinecarboxylic acid, and APA, 1-ethyl-6-fluoro-1,4-dihydro-7-(2-aminopropyl-amino)-4-oxo-3-quinolinecarboxylic acid. When Lom was exposed in whole blood in vitro, the same photochemical decomposition was observed in the plasma as in PBS buffer: APA and AEA were the only products. During UV-A exposure, Lom was shown to be taken up by the leukocytes. This process appeared to be less rapid during UV-A exposure than in the dark. As soon as UV-A exposure commenced, AEA and APA were found. As in the plasma, the total amount of Lom and the two photoproducts in the leukocytes was not significantly different from the amount of Lom found in unexposed cells at the same time point. The erythrocytes did not take up Lom, but exposure of whole blood to Lom and UV-A under the above conditions led to more than 7% haemolysis. Treatment of rats with a combination of Lom and UV-A demonstrated photodecomposition of Lom in vivo. In urine produced during exposure and by the irradiated rats during the twilight period after exposure, a considerable amount of AEA and APA was found. The blood plasma from rats exposed simultaneously to UV-A and Lom proved to contain AEA and APA and, in the leukocytes, APA. This was not the case with animals kept in twilight.

The application of the micronucleus test in Chinese hamster V79 cells to detect drug-induced photogenotoxicity

Recent reports on the photochemical carcinogenicity and photochemical genotoxicity of fluoroquinolone antibacterials led to an increasing awareness for the need of a standard approach to test for photochemical genotoxicity. In this study the micronucleus test using V79 cells was adapted to photogenotoxicity testing. Results of using different UVA/UVB relationships enabled us to identify a suitable irradiation regimen for the activation of different kinds of photosensitizers. Using this regimen, 8-methoxypsoralen and the fluoroquinolones lomefloxacin, grepafloxacin and Bay Y 3118 were identified to cause micronuclei and toxicity upon photochemical activation. Among the phenothiazines tested, chlorpromazine and 2-chlorophenothiazine, were positive for both endpoints, whereas triflupromazine was only slightly photoclastogenic in the presence of strong phototoxicity. Among the other potential human photosensitizers tested (oxytetracycline, doxycycline, metronidazole, emodin, hypericin, griseofulvin), only hypericin was slightly photogenotoxic. Photochemical toxicity in the absence of photochemical genotoxicity was noted for doxycycline and emodin. With the assay system described, it is possible to determine photochemical toxicity and photochemical genotoxicity concomitantly with sufficient reliability.

Oxidative DNA damage and mutations induced by a polar photosensitizer, Ro19-8022

The oxidative DNA damage induced by the polar photosensitizer Ro19-8022 in the presence of light was studied and correlated with the associated mutagenicity. Both in isolated DNA and AS52 Chinese hamster ovary cells, photoexcited Ro19-8022 gave rise to a DNA damage profile that was similar to that caused by singlet oxygen: base modifications sensitive to the repair endonuclease Fpg protein, which according to high-performance liquid chromatography (HPLC) analysis were predominantly 8-hydroxyguanine (8-oxoG) residues, were generated in much higher yield than single-strand breaks, sites of base loss (AP sites) and oxidative pyrimidine modifications sensitive to endonuclease III. Fifty percent of the Fpg-sensitive modifications were repaired within 2 h. Under conditions that induced 10 Fpg-sensitive modifications per 10(6) bp (six 8-oxoG residues per 10(6) bp), approximately 60 mutations per 10(6) cells were induced in the gpt locus of the AS52 cells. A rather similar mutation frequency was observed when a plasmid carrying the gpt gene was exposed to Ro19-8022 plus light under cell-free conditions and subsequently replicated in bacteria. Sequence analysis revealed that GC-->TA and GC-->CG transversions accounted for 90% of the base substitutions. A significant generation of micronuclei was detectable in AS52 cells exposed to the photosensitizer plus light as well.

The role of oxidative DNA damage in human arsenic carcinogenesis: detection of 8-hydroxy-2'-deoxyguanosine in arsenic-related Bowen's disease

Arsenic is widely distributed in nature in the form of either metalloids or chemical compounds, which cause a variety of pathologic conditions including cutaneous and visceral malignancies. Recently, reactive oxygen species have been hypothesized to be one of the causes of arsenic-induced carcinogenesis. 8-Hydroxy-2'-deoxyguanosine is one of the major reactive oxygen species-induced DNA base-modified products that is widely accepted as a sensitive marker of oxidative DNA damage. We studied the presence of 8-hydroxy-2'-deoxyguanosine by immunohistochemistry using N45.1 monoclonal antibody in 28 cases of arsenic-related skin neoplasms and arsenic keratosis as well as in 11 cases of arsenic-unrelated Bowen's diseases. The frequency of 8-hydroxy-2'-deoxyguanosine positive cases was significantly higher in arsenic-related skin neoplasms (22 of 28; 78%) than in arsenic-unrelated Bowen's disease (one of 11; 9%) (p < 0.001 by chi2 test). 8-Hydroxy-2'-deoxyguanosine was also detected in normal tissue adjacent to the arsenic-related Bowen's disease lesions. Furthermore, arsenic was detected by neutron activation analysis in the deparaffined skin tumor samples of arsenic-related disease (four of five; 80%), whereas arsenic was not detected in control samples. Our results strongly suggest the involvement of reactive oxygen species in arsenic-induced human skin cancer. Key word: neutron activation analysis.

In vitro photogenotoxic activity of clinafloxacin: a paradigm predicting photocarcinogenicity

Fluoroquinolone antiinfective drugs exhibit phototoxic, photogenotoxic, and photocarcinogenic activities in experimental systems which may be interrelated. Clinafloxacin (CLX), a new fluoroquinolone, is a potent antiinfective agent being developed for use in life-threatening infections. While this drug has previously been demonstrated to be phototoxic, this report evaluated the photogenotoxic and photocarcinogenic potential of CLX. When Skh-1 mice were administered CLX in the presence of ultraviolet light (UVA) at the maximum tolerated dose expected for a photocarcinogenicity bioassay, induction of DNA strand breakage was noted in keratinocytes isolated from these animals. When compared with other well-studied fluoroquinolones in vitro, CLX and Lomefloxacin (LMX) were equally effective in producing chromosome damage and DNA strand breakage in Chinese hamster ovary (CHO) cells exposed to UVA. Treatment of CHO cells with CLX in the presence of UVA also resulted in hydroxyl radical formation. However, coincubation of CHO cells with CLX and various antioxidants markedly reduced hydroxyl radical formation, but inhibited photogenotoxicity only to a limited extent. Thus, while reactive oxygen species contribute to the photogenotoxic activity of CLX, other factors may be involved. Since CLX exhibits both phototoxic and photogenotoxic activity, we predict that CLX would be photocarcinogenic in vivo. The present study suggests that under conditions of human exposure, the potential risk for CLX-induced photocarcinogenicity is small.

Hydroxyl radicals and DNA base damage

Modified purine and pyrimidine bases constitute one of the major classes of hydroxyl-radical-mediated DNA damage together with oligonucleotide strand breaks, DNA-protein cross-links and abasic sites. A comprehensive survey of the main available data on both structural and mechanistic aspects of.OH-induced decomposition pathways of both purine and pyrimidine bases of isolated DNA and model compounds is presented. In this respect, detailed information is provided on both thymine and guanine whereas data are not as complete for adenine and cytosine. The second part of the overview is dedicated to the formation of.OH-induced base lesions within cellular DNA and in vivo situations. Before addressing this major point, the main available methods aimed at singling out.OH-mediated base modifications are critically reviewed. Unfortunately, it is clear that the bulk of the chemical and biochemical assays with the exception of the high performance liquid chromatographic-electrochemical detection (HPLC/ECD) method have suffered from major drawbacks. This explains why there are only a few available accurate data concerning both the qualitative and quantitative aspects of the.OH-induced formation of base damage within cellular DNA. Therefore, major efforts should be devoted to the reassessment of the level of oxidative base damage in cellular DNA using appropriate assays including suitable conditions of DNA extraction.

Photocleavage of DNA by the fluoroquinolone antibacterials

We have determined the relative efficiencies for the formation of single strand breaks (ssbs) after the UVA irradiation of pBR322 DNA and various fluoroquinolone (fleroxacin, lomefloxacin, norfloxacin) and naphthyridine (nalidixic acid, enoxacin) antibacterials. After correcting for the differences in absorption, the relative order for DNA photocleaving activity under anaerobic conditions is: fleroxacin, lomefloxacin > nalidixic acid >> norfloxacin > enoxacin. In general, fluoroquinolones having fluorine substituents at the C-6 and C-8 positions (lomefloxacin and fleroxacin) are 10-fold more efficient in generating ssbs than those having only a C-6 fluorine atom (norfloxacin). The effect of oxygen on photoinduced DNA damage caused by these antibacterials is complex, but our data imply that active oxygen species are not necessary for DNA scission by these molecules, and indeed, may sometimes inhibit it. Lomefloxacin ethyl ester, which cannot undergo decarboxylation, is as active as lomefloxacin itself. Thus the free radical generated by decarboxylation is unlikely to be the active species involved in photoinduced fluoroquinolone DNA cleavage. For lomefloxacin and fleroxacin, DNA damage probably results from the generation of a carbene at C-8 as a result of photoinduced loss of their F8 atom as fluoride upon UVA irradiation. Fluoroquinolones lacking a C-8 fluorine atom must operate by a different mechanism. While photocleavage of pBR322 DNA does not necessarily mean that duplex DNA will be cleaved under the same conditions, nevertheless lomefloxacin and fleroxacin, the two most photogenotoxic fluoroquinolones, did cause the most damage to the plasmid DNA.

Proposed mechanism for the photodynamic generation of 8-oxo-7,8-dihydro-2'-deoxyguanosine produced in cultured cells by exposure to lomefloxacin

In this study, lomefloxacin (LMX), a widely used quinolone antibiotic with a high frequency of clinical phototoxicity, was investigated by measuring the effects of several antioxidants on its ability to form of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxo-dG) in cultured adult rat liver cells after exposure to UVA. In the current study the observed DNA damage, reflected by the formation of 8-oxo-dG, was almost completely inhibited by co-incubation of LMX and cultured cells with sodium azide (NaN3) that specifically quenches singlet oxygen. Vitamin E (alpha-tocopherol), known to quench both superoxide and singlet oxygen, inhibited 8-oxo-dG formation by approximately 54%. Mannitol, a hydroxyl radical scavenger, inhibited 8-oxo-dG formation by 64%. Butylated hydroxyanisole (BHA), a scavenger of hydroxyl, peroxy and alkoxy radicals, showed no inhibition of 8-oxo-dG formation but in fact enhanced levels of 8-oxo-dG by 169%. The results of this study suggest that the mechanism for the photodynamic generation of 8-oxo-dG by LMX is mediated, at least in part, by both singlet oxygen and hydroxyl radical and involves both type I and type II photosensitization.

Nuclear and non-nuclear targets of genotoxic agents in the induction of gene expression. Shared principles in yeast, rodents, man and plants

The interplay between environmental cues and the genetic response is decisive for the development, health and well-being of an organism. For some environmental factors a narrow margin separates beneficial and toxic impacts. With the increasing exposure to UV-B this dichotomy has reached public attention. This review will be concerned with the mechanisms that mediate a cellular genetic response to noxious agents. The toxic stimuli find access to the regulatory network inside cells by interacting at several points with cellular molecules - a process that converts the 'outside information' into 'cellular language'. As a consequence of such interactions, many adverse agents cause massive signal transduction and changes of gene expression. There is an interesting conservation of the mechanisms from yeast to man. An understanding of the genetic programs and of their phenotypic consequences is lagging behind.

A fluoroquinolone antibiotic with a methoxy group at the 8 position yields reduced generation of 8-oxo-7,8-dihydro-2'-deoxyguanosine after ultraviolet-A irradiation

We have previously reported that two fluoroquinolone antibiotics gave rise to 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxo-dG) in DNA of cells concurrently exposed to UV-A and that this correlated with clinical phototoxicity. To determine the structural basis for generation of oxidative damage, the ability of two synthetic fluoroquinolone candidate antibiotics, Bayer 12-8039 (12-8039) and Bayer Y3118 (Y3118), to give rise to 8-oxo-dG in cultured liver epithelial cells was compared. 12-8039 contains a methoxy group at the 8 position of the quinolone nucleus, whereas Y3118 contains a chlorine group at the same position. Y3118 produced dose-dependent increases in 8-oxo-dG formation in cultured cells after UVA irradiation, whereas the 8-OCH3-substituted 12-8039 produced no increase. Also, after exposure to 20 J/cm2 UVA, UV spectral scans of both compounds revealed that Y3118 underwent photodegradation whereas 12-8039 was stable. These results demonstrate that the presence of an 8-OCH3 group on the quinolone nucleus is important for the reduction of photogeneration of oxidative DNA damage and photodegradation in the presence of UVA irradiation. From this, we suggest that 12-8039 has little phototoxic potential.