UVA light-induced DNA cleavage by isomeric methylbenz[a]anthracenes

New Insights into the Phototoxicity of Anthracene-Based Chromophores: The Chloride Salt Effect†

Unraveling the causes underlying polycyclic aromatic hydrocarbon phototoxicity is an essential step in understanding the harmful effects of these compounds in nature. Toward this end, we have studied the DNA interactions and photochemistry of N1-(anthracen-9-ylmethyl)ethane-1,2-diaminium dichloride in the presence and absence of NaF, KF, NaCl, KCl, NaBr, KBr, NaI, and KI (350 nm hν, pH 7.0). Exposing pUC19 plasmid to UV light in solutions containing 400 mM KCl formed significantly more direct strand breaks in DNA compared to no-salt control reactions. In contrast, NaCl increased DNA damage moderately, while the sodium(I) and potassium(I) fluoride, bromide, and iodide salts generally inhibited cleavage (I- > Br- > F-). A halide anion-induced heavy-atom effect was indicated by monitoring anthracene photodegradation and by employing the hydroxyl radical (•OH) probe hydroxyphenyl fluorescein (HPF). These studies revealed that among no-salt controls and the eight halide salts, only NaCl and KCl enabled the anthracene to photosensitize the production of high levels of DNA-damaging reactive oxygen species (ROS). Pre-irradiation of N1-(anthracen-9-ylmethyl)ethane-1,2-diaminium dichloride at 350 nm increased the amounts of chloride salt-induced •OH detected by HPF in subsequent anthracene photoactivation experiments. Taking into consideration that •OH and other highly reactive ROS are extremely short-lived, this result suggests that the pre-irradiation step might lead to the formation of oxidized anthracene photoproducts that are exceedingly redox-active. The fluorometric probes HPF and Singlet Oxygen Sensor Green revealed that KCl concentrations ranging from 150 to 400 mM and from 100 to 400 mM, respectively, enhanced N1-(anthracen-9-ylmethyl)ethane-1,2-diaminium dichloride photosensitized •OH and singlet oxygen (1O2) production over no-salt controls. Considering the relatively high levels of Na+, K+, and Cl- ions that exist in the environment and in living organisms, our findings may be relevant to the phototoxic effects exhibited by anthracenes and other polycyclic hydrocarbons in vivo.

Natural aeolian dust particles have no substantial effect on atmospheric polycyclic aromatic hydrocarbons (PAHs): A laboratory study based on naphthalene

Natural aeolian dust (AD) particles are potential carriers of polycyclic aromatic hydrocarbons (PAHs) in the atmosphere. The heterogeneous interaction between them may lead to worsened air quality and enhanced cytotoxicity and carcinogenicity of ambient particulates in downwind areas, and this topic requires in-depth exploration. In this study, AD samples were collected from four Asian dust sources, and their physical properties and compositions were determined, showing great regional differences. The physical and chemical interactions of different AD particles with naphthalene (Nap; model PAH) were observed in aqueous systems. The results showed that AD particles from the Loess Plateau had weak adsorption to Nap, which was fitted by the Langmuir isotherm. There was no obvious adsorption to Nap found for the other three AD samples. This difference seemed to depend mainly on the specific surface area and/or the total pore volume. In addition, the Nap in the aqueous solution did not undergo chemical reactions under dark conditions and longwave ultraviolet (UV) radiation but degraded under shortwave UV radiation, and 2-formylcinnamaldehyde and 1,4-naphthoquinone were the first-generated products. The degradation of Nap in the aqueous solution was probably initiated by photoionization, and the reaction rate constant (between 1.44 × 10^-4 min^-1 and 8.55 × 10^-4 min^-1) was much lower than that of Nap with hydroxyl radicals. Instead of inducing or promoting the chemical change in Nap, the AD particles slowed photodegradation due to the extinction of radiation. Therefore, it is inferred that natural AD particles have no substantial effect on the transportation and transformation of PAHs in the atmosphere.

Photoirradiation of representative polycyclic aromatic hydrocarbons and twelve isomeric methylbenz[a]anthracene with UVA light: formation of lipid peroxidation

Polycyclic aromatic hydrocarbons (PAHs) are widespread genotoxic environmental pollutants, which require metabolic activation in order to exert biological activities, including mutagenicity and carcinogenicity. Photoactivation is another activation pathway that can lead to PAH genotoxicity. In this paper, we demonstrate that photoirradiation of a series of representative PAHs, with and without bearing a methyl substituent, with UVA light in the presence of methyl linoleate resulted in the formation of methyl linoleate hydroperoxides (a lipid peroxide). The lipid peroxide formation was inhibited by dithiothreitol (DTT) (free radical scavenger), NaN3 (singlet oxygen and free radical scavenger), and superoxide dismutase (SOD) (superoxide scavenger), but was enhanced by the presence of deuterium oxide (D2O) (extends singlet oxygen lifetime). These results suggest that photoirradiation of PAHs by UVA light generates reactive oxygen species (ROS), which induce lipid peroxidation.

Linking biochemical perturbations in tissues of the African catfish to the presence of polycyclic aromatic hydrocarbons in Ovia River, Niger Delta region

Petroleum hydrocarbons including polycyclic aromatic hydrocarbons (PAHs) are a pollution issue in the Niger Delta region due to oil industry activities. PAHs were measured in the water column of the Ovia River with concentrations ranging from 0.1 to 1055.6 ng L(-1). Attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy detected alterations in tissues of the African catfish (Heterobranchus bidorsalis) from the region showed varying degrees of statistically significant (P<0.0001, P<0.001, P<0.05) changes to absorption band areas and shifts in centroid positions of peaks. Alteration patterns were similar to those induced by benzo[a]pyrene in MCF-7 cells. These findings have potential health implications for resident local communities as H. bidorsalis constitutes a key nutritional source. The study provides supporting evidence for the sensitivity of infrared spectroscopy in environmental studies and supports their potential application in biomonitoring.

Ultraviolet A radiation potentiates the cytotoxic and genotoxic effects of 7 H-dibenzo[c,g]carbazole and its methyl derivatives

7H-Dibenzo[c,g]carbazole (DBC) is a heterocyclic aromatic hydrocarbon that is carcinogenic in many species and tissues. DBC is a common environmental pollutant, and is therefore constantly exposed to sunlight. However, there are limited data exploring the toxicity of DBC photoexcitation products. Here, we investigated the impact of ultraviolet (UV) A radiation on the biological activity of DBC and its methyl derivatives, 5,9-dibenzo[c,g]carbazole and N-methyl dibenzo[c,g]carbazole, on human skin HaCaT keratinocytes. Co-exposure of HaCaT cells to UVA and DBC derivatives resulted in a sharp dose-dependent decrease in cell survival and apparent changes in cell morphology. Under the same treatment conditions, significant increases in DNA strand breaks, intracellular reactive oxygen species, and oxidative damage to DNA were observed in HaCaT cells. Consistent with these results, an apparent inhibition in superoxide dismutase, but not glutathione peroxidase activity, was detected in cells treated with DBC and its derivatives under UVA irradiation. The photoactivation-induced toxicity of individual DBC derivatives correlated with the electron excitation energies approximately expressed as the energy difference between the highest occupied and the lowest vacant molecular orbital. Our data provide the first evidence that UVA can enhance the toxicity of DBC and its derivatives. Photoactivation-induced conversion of harmless chemical compounds to toxic photoproducts associated with reactive oxygen species generation may substantially amplify the adverse health effects of UVA radiation and contribute to increased incidence of skin cancer.

DNA dendrimer: an efficient nanocarrier of functional nucleic acids for intracellular molecular sensing

Functional nucleic acid (FNA)-based sensing systems have been developed for efficient detection of a wide range of biorelated analytes by employing DNAzymes or aptamers as recognition units. However, their intracellular delivery has always been a concern, mainly in delivery efficiency, kinetics, and the amount of delivered FNAs. Here we report a DNA dendrimer scaffold as an efficient nanocarrier to deliver FNAs and to conduct in situ monitoring of biological molecules in living cells. A histidine-dependent DNAzyme and an anti-ATP aptamer were chosen separately as the model FNAs to make the FNA dendrimer. The FNA-embedded DNA dendrimers maintained the catalytic activity of the DNAzyme or the aptamer recognition function toward ATP in the cellular environment, with no change in sensitivity or specificity. Moreover, these DNA dendrimeric nanocarriers show excellent biocompatibility, high intracellular delivery efficiency, and sufficient stability in a cellular environment. This FNA dendrimeric nanocarrier may find a broad spectrum of applications in biomedical diagnosis and therapy.

UVA photoirradiation of nitro-polycyclic aromatic hydrocarbons-induction of reactive oxygen species and formation of lipid peroxides

Nitro-polycyclic aromatic hydrocarbons (nitro-PAHs) are a class of genotoxic environmental contaminants. We have long been interested in determining the mechanisms by which nitro-PAHs induce genotoxicity. Although the metabolic activation of nitro-PAHs leading to toxicological activities has been well studied, the photo-induced activation of nitro-PAHs has seldom been reported. In this paper, we report photo-induced lipid peroxidation by 19 nitro-PAHs. The results indicated that all but two of the nitro-PAHs can induce lipid peroxidation. Mechanistic studies suggest that lipid peroxidation by nitro-PAHs is mediated by free radicals generated in the reaction. There was no structural correlation between the nitro-PAHs and their ability to induce lipid peroxidation upon UVA irradiation, or between the HOMO-LUMO gap and the ability to cause lipid peroxidation. Most of the nitro-PAHs are less potent in terms of causing lipid peroxidation than their parent PAHs. The lack of correlation is attributed to the complex photophysics and photochemistry of the nitro-PAHs and the yield of reactive oxygen species (ROS) and other factors.

Phototoxicity of herbal plants and herbal products

Plants are used by humans in daily life in many different ways, including as food, herbal medicines, and cosmetics. Unfortunately, many natural plants and their chemical constituents are photocytotoxic and photogenotoxic, and these phototoxic phytochemicals are widely present in many different plant families. To date, information concerning the phototoxicity and photogenotoxicity of many plants and their chemical constituents is limited. In this review, we discuss phototoxic plants and their major phototoxic constituents; routes of human exposure; phototoxicity of these plants and their constituents; general mechanisms of phototoxicity of plants and phototoxic components; and several representative phototoxic plants and their photoactive chemical constituents.

Phototoxicity and environmental transformation of polycyclic aromatic hydrocarbons (PAHs)-light-induced reactive oxygen species, lipid peroxidation, and DNA damage

Polycyclic aromatic hydrocarbons (PAHs) are a class of mutagenic and tumorigenic environmental contaminants. Although the mechanisms by which PAHs induce cancer in experimental animals have been extensively studied and the metabolic activation pathways have been determined, the environmental fate of PAHs and the phototoxicity exerted by PAHs, as well as their photoreaction products formed in the environment, have received much less attention. In this review, the formation of oxygenated PAHs, PAH quinones, nitro-PAHs, and halogenated PAHs from photoreaction of environmental PAHs are addressed. Upon light irradiation, PAHs and all PAH photoreaction products can absorb light energy to reach photo-excited states, which react with molecular oxygen, medium, and coexisting chemicals to produce reactive oxygen species (ROS) and other reactive intermediates, such as oxygenated PAHs and free radicals. These intermediates, including ROS, induce lipid peroxidation, and DNA damage including DNA strand breakage, oxidation to 8-oxo-2'-deoxyguanosine, and DNA-adducts. Since these toxicological endpoints are associated with age-related diseases, including cancer, environmental PAHs concomitantly exposed to sunlight may potentially promote human skin damage, leading to ageing and skin cancers. Thus, we suggest that (i) in addition to the widely recognized metabolic pathways, more attention must be paid to photoreaction as an important activation pathway for PAHs, (ii) risk assessment of environmental PAHs should take into consideration the complex photochemical reactions leading to mixtures of products that are also phototoxic; and (iii) the study of structure-toxicity relationships should be expanded to cover the complex photoreactions and extrinsic factors that affect phototoxicity endpoints.

Photoirradiation of polycyclic aromatic hydrocarbon diones by UVA light leading to lipid peroxidation

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous genotoxic environmental pollutants and potentially pose a health risk to humans. In most if not all cases, PAHs in the environment can be oxidized into their corresponding PAH-diones. This process is considered a detoxification pathway with regard to tumorigenicity. Nevertheless, photo-induced toxicological activity of PAH-diones has not been systematically investigated. In this study, we show that 27 potential environmental PAH-diones induced lipid peroxidation, in a dose (light) response manner, when irradiated with UVA at 7 and 21 J cm(-2). Photoirradiation in the presence of sodium azide, deuterated methanol, or superoxide dismutase revealed that lipid peroxidation is mediated by reactive oxygen species. Electron spin resonance (ESR) spin trapping studies supported this observation. These results suggest that UVA photoirradiation of PAH-diones generates reactive oxygen species and induces lipid peroxidation.

Interaction of DNA and a series of aromatic donor-viologen acceptor molecules with and without the presence of CB[8]

A series of 1-ethyl-1'-arylmethyl-4,4'-bipyridinium compounds is synthesized, where the aryl is phenyl (BEV), 2-naphthyl (NEV), 2-anthracenyl (AEV) or 1-pyrenyl (PEV). Among them, PEV and AEV can bind with calf thymus DNA mainly through intercalation and groove-binding modes, and both of them can be observed to photocleave plasmid pBR 322 DNA significantly under irradiation with a xenon arc lamp. After inclusion of cucurbit[8]uril (CB[8]), all of the aromatic donor-viologen acceptor compounds exhibit efficient DNA photocleavage ability. The reason is that CB[8] can inhibit the intramolecular backwards electron transfer in the aromatic donor-viologen acceptor molecule, prolonging the lifetime of the charge separated excited state to some extent. These studies bring a new subject in DNA photocleavage research and a potential application of the host-guest supramolecular system.

Synthesis, characterization, and photoactivated DNA cleavage by copper (II)/cobalt (II) mediated macrocyclic complexes

We report the synthesis of new photonuclease consisting of two Co(II)/Cu(II) complexes of macrocyclic fused quinoline. Metal complexes are [MLX(2)], type where M = Co(II) (5), Cu(II) (6), and X = Cl, and are well characterized by elemental analysis, Fourier transform infrared spectroscopy, (1)H-NMR and electronic spectra. We have shown that photocleavage of plasmid DNA is markedly enhanced when this ligand is irradiated in the presence of Cu(II), and more so than that of cobalt. The chemistry of ternary and binary Co(II) complexes showing efficient light induced (360 nm) DNA cleavage activity is summarized. The role of the metal in photoinduced DNA cleavage reactions is explored by designing complex molecules having macrocyclic structure. The mechanistic pathways are found to be concentration dependent on Co(II)/Cu(II) complexes and the photoexcitation energy photoredox chemistry. Highly effective DNA cleavage ability of 6 is attributed to the effective cooperation of the metal moiety.

Effects of UVA and visible light on the photogenotoxicity of benzo[a]pyrene and pyrene

This study investigated the role of UVA/visible light (U, 320-800 nm) and visible light (V, 400-800 nm) in the phototoxicity and photogenotoxicity of two ubiquitous polycyclic aromatic hydrocarbons (PAH): benzo[a]pyrene (BaP) and Pyrene (Pyr). These mechanisms were evaluated by the WST-1 test and the comet assay on normal human keratinocytes (NHK) and by the micronucleus test on CHO cells. The production of reactive oxygen species (ROS) was assessed through the induction of 8-oxodeoxyguanine (8-oxodG) lesions by immunofluorescence staining in NHK. Results of the WST-1 test revealed the phototoxic properties of BaP and Pyr after irradiation with U and V lights. BaP presented the highest phototoxic properties. Results of the comet assay showed that U- and V-irradiated BaP and Pyr induced increasing rates of DNA single-strand breaks in NHK, in a dose dependent manner. The tested PAH could also induce increased levels of micronuclei in CHO cells after U and V irradiations. Increasing 8-oxodG levels were detected after U and V irradiations in BaP- and Pyr-treated keratinocytes and confirmed the involvement of ROS in the photogenotoxicity of PAH. Overall, this study highlighted the existence of an alternative pathway of PAH genotoxicity that is induced by UVA and/or visible light. Visible light is suggested to photoactivate PAH by a mechanism which is mainly based on oxidative reactions.

Modeling photoinduced toxicity of PAHs based on DFT-calculated descriptors

Quantitative structure-activity relationships (QSARs) were established for photoinduced toxicity of polycyclic aromatic hydrocarbons (PAHs) to two aquatic species. Partial least squares (PLS) regression and molecular structural parameters calculated by density functional theory (DFT) were employed for model development. Two QSAR models were established and their high R(2) and Q(CUM)(2) values indicated their good goodness-of-fit, robustness and internal predictive power. The descriptors that describe the partition behavior, light absorbance, and generation of reactive free radicals were found to be successful in modeling the photoinduced toxicity. The average molecular polarizability (alpha), energy gap (E(GAP)) between the energy of the lowest unoccupied molecular orbital and the highest occupied molecular orbital, lowest triplet excitation energy (E(T1)) and vertical electron affinity at the lowest excited triplet (VEA(T1)) were the main molecular structural factors. Polarizability which determines the partition of PAHs between water and lipid governs the photoinduced toxicity of selected PAHs. Moreover, the photoinduced toxicity increased with the decreasing of E(GAP) probably due to better spectral overlap. The parameter, VEA(T1) that characterizes the ability of PAH anion radical (PAH(*-)) generation from excited triplet state PAH ((3)PAH(*)), is also related with the photoinduced toxicity. This investigation will make us gain more insight into the photoinduced toxicity mechanism and assess the applicability of various DFT-based descriptors to toxicological QSARs.

Light-Induced Toxic Effects of Tamoxifen: A Chemotherapeutic and Chemopreventive Agent

Tamoxifen is a powerful drug used to treat breast cancer patients, and more than 500,000 women in the U. S. are being treated with this drug. In our study, tamoxifen is found to be photomutagenic in Salmonella typhimurium TA102 at concentrations as low as 0.08 muM and reaches maximum photomutagenicity at 0.4 muM under a light dose equivalent to 20 min sunlight. These concentrations are comparable to the plasma tamoxifen concentration of 0.4 to 3 muM for patients undergoing tamoxifen therapy. The toxicity seems to be the result of DNA damage and/or lipid peroxidation caused by light irradiation of tamoxifen. The DNA damage caused by irradiation of PhiX174 DNA in the presence of tamoxifen appears to be formation of DNA-tamoxifen covalent adducts, not single strand/double strand cleavages, and there is no oxygen involvement. This is confirmed by EPR experiments that carbon-centerd radicals are formed by light irradiation of tamoxifen and there is no singlet oxygen formation. Although superoxide radical is formed, it is not involved in DNA damage.

Light-induced cytotoxicity of 16 polycyclic aromatic hydrocarbons on the US EPA priority pollutant list in human skin HaCaT keratinocytes: relationship between phototoxicity and excited state properties

The photocytotoxicity of 16 polycyclic aromatic hydrocarbons (PAHs) on the priority pollutant list of the United States Environmental Protection Agency (US EPA) were tested in human skin HaCaT keratinocytes. A selected PAH was mixed with HaCaT cells and irradiated with a solar simulator lamp for a dose equivalent to 5 min of outdoor sunlight and the cell viability was determined immediately and also after 24 h of incubation. For the cells without incubation after the treatments, it is found that all PAHs with three rings or less, except anthracene, are not photocytotoxic, while the four or five-ring PAHs (except chrysene), benz[a]anthracene, dibenzo[a,h]anthracene, benzo[ghi]perylene, benzo[a]pyrene, indeno[1,2,3-cd]pyrene, benzo[b]fluorenthene, fluorenthene, and pyrene, are photocytotoxic to the human skin HaCaT keratinocytes. If the cells were incubated for 24 h after the treatments, the photocytotoxic effect of the PAHs was greatly amplified in comparison to the nonincubated cells. For the 24 h incubated cells, all PAHs except naphthalene exhibit photocytotoxicity to some extent. Exposure to 5 microM of the 4- and 5-ring PAHs (except chrysene) and 3-ring anthracene more than 80% of the cells lose viability. The photocytotoxicity of the PAHs correlates well with several of their excited state properties: light absorption, excited singlet-state energy, excited triplet-state energy, and HOMO-LUMO energy gap. All the photocytotoxic PAHs absorb light at >300 nm, in the solar UVB and UVA region. There is a threshold for each of the three excited state descriptors of a photocytotoxic PAH: singlet energy <355 kJ/mol (corresponding to 337 nm light), triplet energy <230 kJ/mol (corresponding to 520 nm light), HOMO-LUMO gap <3.6 eV (corresponding to 344 nm light) obtained at the Density Functional Theory B3LYP/6-31G(d) level.

DNA damage induced by coexposure to PAHs and light

Polycyclic aromatic hydrocarbons (PAHs) are widely distributed in the environment as pollutants in air, water and soil, and some are carcinogenic, being associated with various types of cancer. A majority of the research concerning the biological effects of PAHs has focused on the metabolic activation and DNA adducts leading to mutation and transformation. Although the role of the PAHs as photosensitizers has received much less attention, investigators have shown that PAHs excited by sunlight induced significant cytotoxicity and several kinds of DNA damage. Some PAHs were recently proved to be photomutagenic. In this review, we discuss the influence of PAHs in combination with sunlight focusing on the phototoxicity and cellular DNA damage produced.

Photoirradiation of polycyclic aromatic hydrocarbons with UVA light - a pathway leading to the generation of reactive oxygen species, lipid peroxidation, and dna damage

Polycyclic aromatic hydrocarbons (PAHs) are a class of genotoxic environmental contaminants. We have long been interested in determining the mechanisms by which PAHs induce genotoxicity. Although the metabolic activation of PAHs leading to biological activities has been well studied, the photo-induced activation pathway has seldom reported. In this paper, we review the study of photoirradiation of PAHs with UVA irradiation results in (i) cytotoxicity and DNA damage (ii) DNA single strand cleavage; (iii) formation of 8-hydroxy-2'-deoxyguanosine adduct (8-OHdG), and (iv) formation of lipid peroxidation. Evidence has been shown that these photobiological activities are mediated by reactive oxygen species (ROS).

DNA adducts and lung cancer risk: a prospective study

Objectives were to investigate prospectively the ability of DNA adducts to predict cancer and to study the determinants of adducts, especially air pollutants. DNA adducts were measured in a case-control study nested in the European Prospective Investigation into Cancer and Nutrition (EPIC) investigation. Cases included newly diagnosed lung cancer (n = 115), upper respiratory cancers (pharynx and larynx; n = 82), bladder cancer (n = 124), leukemia (n = 166), and chronic obstructive pulmonary disease or emphysema deaths (n = 77) accrued after a median follow-up of 7 years among the EPIC former smokers and never-smokers. Three controls per case were matched for questionnaire analyses and two controls per case for laboratory analyses. Matching criteria were gender, age, smoking status, country of recruitment, and follow-up time. Individual exposure to air pollution was assessed using concentration data from monitoring stations in routine air quality monitoring networks. Leukocyte DNA adducts were analyzed blindly using 32P postlabeling technique. Adducts were associated with the subsequent risk of lung cancer, with an odds ratio (OR) of 1.86 [95% confidence interval (95% CI), 0.88-3.93] when comparing detectable versus nondetectable adducts. The association with lung cancer was stronger in never-smokers (OR, 4.04; 95% CI, 1.06-15.42) and among the younger age groups. After exclusion of the cancers occurring in the first 36 months of follow-up, the OR was 4.16 (95% CI, 1.24-13.88). A positive association was found between DNA adducts and ozone (O3) concentration. Our prospective study suggests that leukocyte DNA adducts may predict lung cancer risk of never-smokers. Besides, the association of DNA adduct levels with O3 indicates a possible role for photochemical smog in determining DNA damage.

Coexposure to benzo[a]pyrene and UVA induces phosphorylation of histone H2AX

Phosphorylation of histone H2AX (termed gamma-H2AX) was recently identified as an early event after induction of DNA double strand breaks (DSBs). We have previously shown that co-exposure to benzo[a]pyrene (BaP), a wide-spread environmental carcinogen, and ultraviolet A (UVA), a major component of solar UV radiation, induced DSBs in mammalian cells. In the present study, we examined whether co-exposure to BaP and UVA generates gamma-H2AX in CHO-K1 cells. Single treatment with BaP (10(-9)-10(-7)M) or UVA ( approximately 2.4 J/cm(2)) did not result in gamma-H2AX, however, co-exposure drastically induced foci of gamma-H2AX in a dose-dependent manner. gamma-H2AX could be detected even at very low concentration of BaP (10(-9)M) plus UVA (0.6J/cm(2)), which did not change cell survival rates. NaN(3) effectively inhibited the formation of gamma-H2AX induced by co-exposure, indicating the contribution of singlet oxygen. This is the first evidence that co-exposure to BaP and UVA induced DSBs, involving gamma-H2AX.

Photochemical Reaction of 7,12-Dimethylbenz[a]anthracene (DMBA) and Formation of DNA Covalent Adducts

DMBA, 7,12-dimethylbenz[a]anthracene, is a widely studied polycyclic aromatic hydrocarbon that has long been recognized as a probable human carcinogen. It has been found that DMBA is phototoxic in bacteria as well as in animal or human cells and photomutagenic in Salmonella typhimurium strain TA102. This article tempts to explain the photochemistry and photomutagenicity mechanism. Light irradiation converts DMBA into several photoproducts including benz[a]anthracene-7,12-dione, 7-hydroxy-12-keto-7-methylbenz[a]anthracene, 7,12-epidioxy-7,12-dihydro-DMBA, 7-hydroxymethyl-12-methylbenz[a]anthracene and 12-hydroxymethyl-7-methylbenz[a]anthracene. Structures of these photoproducts have been identified by either comparison with authentic samples or by NMR/MS. At least four other photoproducts need to be assigned. Photo-irradiation of DMBA in the presence of calf thymus DNA was similarly conducted and light-induced DMBA-DNA adducts were analyzed by ³²P-postlabeling/TLC, which indicates that multiple DNA adducts were formed. This indicates that formation of DNA adducts might be the source of photomutagenicity of DMBA. Metabolites obtained from the metabolism of DMBA by rat liver microsomes were reacted with calf thymus DNA and the resulting DNA adducts were analyzed by ³²P-postlabeling/TLC under identical conditions. Comparison of the DNA adduct profiles indicates that the DNA adducts formed from photo-irradiation are different from the DNA adducts formed due to the reaction of DMBA metabolites with DNA. These results suggest that photo-irradiation of DMBA can lead to genotoxicity through activation pathways different from those by microsomal metabolism of DMBA.

Effect of co-existing biologically relevant molecules and ions on DNA photocleavage caused by pyrene and its derivatives

Inorganic ions, coenzymes, amino acids, and saccharides could co-exist with toxic environmental chemicals, such as polycyclic aromatic hydrocarbons (PAHs), in the cell. The presence of these co-existing chemicals can modulate the toxicity of the PAHs. One of the genotoxic effects by PAHs is light-induced cleavage, or photocleavage, of DNA. The effect of inorganic ions I-, Na+, Ca2+, Mg2+, Fe3+, Mn2+, Cu2+, and Zn2+ and biological molecules riboflavin, histidine, mannitol, nicotinamide adenine dinucleotide (NAD), glutathione, and glutamic acid on the DNA photocleavage by pyrene, 1-hydroxypyrene (1-HP), and 1-aminopyrene (1-AP), is studied. The non-transition metal ions Na+, Ca2+, and Mg2+, usually have very little inhibitory effects, while the transition metal ions Fe3+, Cu2+, and Zn2+ enhance, Mn2+ inhibits the DNA photocleavage. The effect by biological molecules is complex, depending on the photochemical reaction mechanisms of the compounds tested (1-AP, 1-HP and pyrene) and on the chemical nature of the added biological molecules. Riboflavin, histidine, and mannitol enhance DNA photocleavage by all three compounds, except that mannitol has no effect on the photocleavage of DNA by pyrene. Glutathione inhibits the DNA photocleavage by 1-AP and 1-HP, but has no effect on that by pyrene. NAD enhances the DNA photocleavage by 1-AP, but has no effect on that by 1-HP and pyrene. Glutamic acid enhances the DNA photocleavage by 1-AP and pyrene, but inhibits that by 1-HP. These results show that the co-existing chemicals may have a profound effect on the toxicity of PAHs, or possibly on the toxicity of many other chemicals. Therefore, if one studies the toxic effects of PAHs or other toxic chemicals, the effect of the co-existing chemicals or ions needs to be considered.

Phototoxicity and DNA damage induced by the cosmetic ingredient chemical azulene in human Jurkat T-cells

Previous study showed that the cosmetic ingredient chemical azulene and its derivative gauiazulene exhibited photomutagenicity four- to five-fold higher than spontaneous mutation in Salmonella typhimurium TA102. In this study, phototoxicity including photogenotoxicity of azulene in human Jurkat T-cells is reported. When the cell suspensions are irradiated by light (UVA plus visible light) in the presence of azulene, an azulene dose-dependent cellular DNA damage is observed. At the highest azulene concentration of 50 microM, the average DNA fragmentation is 33 +/- 10%, determined by single cell gel electrophoresis (Comet assay). Cell viability assay using fluorescein diacetate indicates that the cells could endure the damage and remain viable. Further study revealed that the combination of light and azulene can cause single-strand cleavage on pure PhiX174 plasmid DNA in solution. Studies using scavengers reveal that singlet oxygen and free radicals are involved in causing DNA cleavage. This suggests that the photomutagenicity of azulene in S. typhimurium TA102 could be due to DNA fragmentation caused by the concurrent exposure to azulene and light.

Photomutagenicity of 16 polycyclic aromatic hydrocarbons from the US EPA priority pollutant list

The photomutagenicity of 16 polycyclic aromatic hydrocarbons (PAHs), all on the United States Environmental Protection Agency (US EPA) priority pollutant list, was studied. Concomitant exposing the Salmonella typhimurium bacteria strain TA102 to one of the PAHs and light (1.1 J/cm2 UVA+2.1 J/cm2 visible) without the activation enzyme S9, strong photomutagenic response is observed for anthracene, benz[a]anthracene, benzo[ghi]perylene, benzo[a]pyrene, indeno[1,2,3-cd]pyrene, and pyrene. Under the same conditions, acenaphthene, acenaphthylene, benzo[k]fluoranthene, chrysene, and fluorene are weakly photomutagenic. Benzo[b]fluoranthene, fluoranthene, naphthalene, phenanthrene, and dibenz[a,h]anthracene are not photomutagenic. These results indicate that PAHs can be activated by light and become mutagenic in Salmonella TA102 bacteria. At the same time, the mutagenicity for all the 16 PAHs was examined with the standard mutagenicity test with 10% S9 as the activation system. Benzo[b]fluoranthene, benzo[k]fluoranthene, chrysene, acenaphthylene, and fluorene are weakly mutagenic, while the rest of the PAHs are not. In general, the photomutagenicity of PAHs in TA102 does not correlate with their S9-activated mutagenicity in either TA102 or TA98/TA100 since they involve different activation mechanisms.

Environmental carcinogenic polycyclic aromatic hydrocarbons: photochemistry and phototoxicity

Polycyclic aromatic hydrocarbons (PAHs) are a class of environmental contaminants that has long been of interest in the fields of organic chemistry, theoretical chemistry, physical chemistry, environmental science, toxicology, cancer research, and energy sciences. Concerning environmental science and cancer research, majority of the research has focused on the occurrence, environmental fate, degradation/remediation, chemical transformation, genotoxicity, metabolism and metabolic activation, DNA adduct formation, mutagenesis, and carcinogenesis. Although many books and reviews on these subjects have been published, PAH photochemistry and phototoxicity have received much less attention. Therefore, it is intended for this article to provide an up-to-date source of photochemical reaction, photo-transformation, and phototoxicity of PAHs and their oxygenated, nitrated, halogenated, and amino substituted derivatives on a molecular basis. A perspective for future work is also discussed.