Detection of benzo(a)pyrene photodegradation products using DNA electrochemical sensors.

The reactivity of photodegradation products of benzo(a)pyrene vs. DNA has been assessed using both genomic and oligonucleotide based DNA electrochemical sensors. The kinetic of a photooxidation reaction of benzo(a)pyrene (BaP) carried out in controlled conditions using a 6 W UV lamp peaked at 365 nm has been studied using LC with fluorimetric detection. Degradation of benzo(a)pyrene by both UV and UV/H(2)O(2) exhibited pseudo-first-order reaction kinetics with half-lives ranging from 3.0 to 9.8h depending on the pH and on the amount of H(2)O(2). The oxidation products of benzo(a)pyrene obtained in different conditions were tested on genomic ssDNA electrochemical sensors obtained via immobilisation of salmon testis ss-DNA on graphite screen-printed electrodes. Guanines oxidation signals obtained using chronopotentiometry were used to detect the interaction of the products with DNA. The dose-response curve obtained with benzo(a)pyrene incubated 24 h at pH 4.7 was different from that of the parent compound indicating a different type of interaction with DNA. A DNA hybridisation sensor was also assembled using a thiolated/biotynilated 24-mer oligonucleotide immobilised on a gold screen-printed electrode and avidin-alkaline phosphatase conjugate. A voltammetric detection of naphtol was used to detect the hybridisation reaction. A net inhibition of the hybridisation reaction was observed after incubation with benzo(a)pyrene oxidation products that was attributed to the formation of stable adducts with the guanines of the biotinylated strand. LC-MS-MS studies of the oxidation products confirmed the presence of chemical species potentially forming adducts with DNA. The data reported demonstrate that DNA electrochemical sensors have the potential to be used to monitor remediation processes and to assess the potential toxicity vs. DNA of chemicals forming stable DNA adducts.

Properties of 16,17-disubstituted dihydroviolanthrones formed by reaction of violanthrones with photogenerated radicals.

The photophysical and photochemical properties of violanthrone (V1) and two 16,17-R derivatives with R = OC(8)H(17) and OCOC(17)H(35) (V2 and V3, respectively) in solution were examined. The fluorescence quantum yield of V3 is Phi(f) = 0.2, while that of V1 is low (0.01) and V2 even lower. A radical-induced reduction takes place in the presence of a photosensitizer, such as acetone, acetophenone or benzophenone, and an alcohol as donor. The reduction quantum yield in an argon-saturated solution, e.g. in 1-phenylethanol and glycerol triacetate, is close to unity. The products are the corresponding dihydroquinones (VH(2)s), which fluoresce strongly at 560-600 nm, Phi(f) = 0.6-1, and undergo back-oxidation on the admission of oxygen. The flash photolysis of violanthrones in the presence of both sensitizer and donor reveals ketyl radicals after the pulse, the intermediacy of the semiquinone radicals (VH*) at 650-750 nm and the formation of VH(2)s in the 0-1 ms range.

Photochemical transformations of benzo[e]pyrene in solution and adsorbed on silica gel and alumina surfaces.

The photodegradation of benzo[e]pyrene (BeP), a ubiquitous polycyclic aromatic hydrocarbon (PAH) contaminant, was investigated in solution and adsorbed on surfaces modeling the atmospheric particulate matter to provide fundamental information that could help to clarify its fate in the atmosphere. Diones, diols, and hydroxy derivatives were identified as the major photoproducts of BeP irradiated under simulated atmospheric conditions. The relative distribution of the products and the photodegradation rates of BeP were affected by the average pore size of the surface. Major photoproducts characterized in samples adsorbed on silica gel and alumina surfaces were not observed in irradiated solutions of BeP in hexane. In acetonitrile, the photodegradation rate was faster than in hexane, and one of the diones was observed. Different photoreaction pathways seem to take place in polar versus nonpolar microenvironments.

Photochemical generation of nitric oxide from 6-nitrobenzo[a]pyrene.

Photolabile 6-nitrobenzo[a]pyrene (6-nitroBaP) released nitric oxide (NO) under visible-light irradiation. The generation of NO and the concomitant formation of the 6-oxyBaP radical were confirmed by ESR. BaP quinones were also detected as further oxidized products of the 6-oxyBaP radical. No such photodegradation was observed with other nitrated BaPs, such as 1-nitroBaP and 3-nitroBaP. DNA-strand breakage, caused by photoexcited 6-nitroBaP, was closely related to its NO-releasing activity. MO calculations of nitrated BaP suggest that the perpendicular conformation of the nitro substituent to the aromatic ring is important for the release of NO with light. These findings may be useful for the development of a new type of NO donor.

The generation of oxidation products of benzo[a]pyrene by lipid peroxidation: a study using gamma-irradiation.

The role which active oxygen and radicals generated by the peroxidation of unsaturated fatty acids could play in the oxidation of benzo[a]pyrene has been studied using gamma-irradiation. Irradiation of benzo[a]pyrene resulted in the formation of benzo[a]pyrene 1,6-, 3,6- and 6,12-quinones and other more polar products which were analysed by h.p.l.c. OH. radicals are believed to be involved in this oxidation. The presence of polyunsaturated fatty acids and polyunsaturated lipids stimulated the formation of benzo[a]pyrene products following gamma-irradiation. Oxidation of benzo[a]pyrene also occurred over a period of days in the presence of autoxidising mackerel oil. The rate of benzo[a]pyrene oxidation was related to the extent of lipid peroxidation as determined by malonaldehyde formation. Malonaldehyde production as a result of peroxidising lipids was inhibited by benzo[a]pyrene which suggested that benzo[a]pyrene reacted directly with lipid peroxy radicals or hydroperoxides generated in the process of lipid peroxidation. These results demonstrate that oxidation products of the peroxidation of lipids and fatty acids are able to react directly with benzo[a]pyrene to form products including benzo[a]pyrene quinones without the presence of enzymes such as the cytochrome P-450 mixed function oxidase system and prostaglandin synthetase. It is possible that benzo[a]pyrene may be activated by these types of reactions in vivo or in vitro when benzo[a]pyrene is in contact with polyunsaturated lipids in foodstuffs or the intestinal lumen and peroxidation of unsaturated fats may play an important role in human carcinogenesis.

Reactions induced in vitro between model DNA and benzo[a]pyrene by near-ultraviolet radiation.

Near-ultraviolet (300--480 nm wavelength) irradiation of the single-strand polydeoxynucleotide poly[d(A,C,G,T)] and carbon-14 labeled benzo[alpha]-pyrene (B[alpha] P) in aqueous dimethylsulfoxide (DMSO) solution led to appreciable binding of labeled hydrocarbon to the polynucleotide. Nuclease digests of polydeoxynucleotide-B[alpha]P complexes were examined by chromatography on Sephadex LH-20; at high fluences of near-ultraviolet light deoxyguanosine (dG) residues of the polymer were largely destroyed when the hydrocarbon was present. Approximately 85% of the B[alpha] P of the digests were recovered as hydrophilic derivatives not adsorbed by Sephadex LH-20. Elution of the columns with an aqueous-methanol gradient indicated that substances similar to the covalent deoxynucleoside-B[alpha] P adducts formed between microsomally-oxidized B[alpha] P and DNA were likewise present in the digests. When the deoxyadenosine (dA), deoxycytidine (dC) or dG moieties of the polymer were tritium-labeled, substances doubly-labeled with tritium and carbon-14 were found; ratios of the two radioactivities indicated that equimolar amounts of deoxynucleoside and hydrocarbon were present.

[Decomposition of polycyclic aromatic hydrocarbons by means of radiation]. / Décomposition par irradiation des hydrocarbures aromatiques polycycliques.

BaP decomposes rapidly after exposure to solar illuminations or in simulated atmosphere. The kinetics of degradation depend upon the nature of the support material, the radiant energy, the light wavelength and the presence of other components in the mixture on the same support.

[The phototoxic activity of carcinogenic polycyclic hydrocarbons and their degradation products in the biological test (author's transl)]. / Die Phototoxizität kanzerogener polyzyklischer Aromate und ihrer Umwandlungsprodukte im biologischen Modellversuch.

The phototoxic activity of carcinogenic polycyclic hydrocarbons was evaluated using ciliates of the species Tetrahymena pyriformis maintained in sterile, semisynthetic media. This ciliate-light-test was developed into and standardized for a rapid microbiological assay of carcinogenic activity of polycyclic aromatic hydrocarbons. --In this fashion, six polycyclic aromatic compounds with differing carcinogenic activities were tested:benzo(a)-pyrene, benzo(b)fluoranthene, indeno(1,2,3-c,d)pyrene, benzo(a)anthracene, fluoranthene, and cyclopenteno (c,d)pyrene. An essential parallelism between phototoxic and carcinogenic activities, resp., was clearly obvious. --The combined effects of benzo(a)pyrene and fluoride ions was also investigated using the ciliate-light-test. Fluoride ions in the concentration of 1 ppm did not affect the phototoxicity of benzo(a)pyrene, suggesting that fluorides possess no cocarcinogenic activities. --Degradation products of benzo(a)pyrene obtained by UV-irradiation (mixtures of quinones) were also tested for phototoxic activity. It could be shown that such degradation products entirely free from benzo(a)pyrene still possessed 50% of the activity of the original, non-irradiated solution. This is taken to indicate that the degradation products products resulting of UV-irradiation may still retain a measure of carcinogenic activity, --a finding of considerable importance from the viewpoint of environmental hygiene.

Benzo(a)pyrene free-radicals formation in the presence of butylated hydroxyanisole and their possible importance in carcinogenesis.

By the method of UV irradiation of benzopyrene in the presence of butylated hydroxyanisole, the benzopyrene EPR spectra was investigated and the possible mechanism by which the carcinogenic activity of benzopyrene in the presence of butylated hydroxyanisole is lowered, was studied.