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Probing the microenvironment of benzo[a]pyrene diol epoxide-DNA adducts by triplet excited state quenching methods.

Triplet flash photolysis techniques, coupled with quenching of the triplets by molecular oxygen, are utilized as probes of the microenvironment of polycyclic aromatic molecules bound covalently and non-covalently to DNA. The triplet-oxygen quenching properties of the following adducts in aqueous solutions at 25 +/- 1 degrees C were investigated: covalent adducts derived from the reaction of (+/-)-7 beta,8 alpha-dihydroxy-9 alpha,10 alpha-epoxy-7,8,9, 10-tetrahydrobenzo[a]pyrene (BaPDE) and of (+/-)-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BaPE) with DNA, and non-covalent intercalation complexes of acridine orange (AO) and DNA. In all cases the quenching follows the Stern-Volmer quenching law with a quenching constant of KTO2 approximately equal to 10(9) M-1 X S-1 for the covalent BaPDE-DNA and BaPE-DNA complexes in aqueous solution. This value of KTO2 is characteristic of free molecules (not bound to DNA) and indicates that the pyrene chromophore is totally accessible to oxygen, and is thus not located at an intercalation-type of binding site in these covalent adducts. In contrast, the AO-DNA complexes are characterized by values of KTO2 approximately equal to 10(8) M-1 X S-1 indicating that the intercalated AO molecules are about ten times less accessible to molecular oxygen than free AO molecules. The KTO2 values for the covalent BaPDE-DNA and BaPE-DNA adducts decrease when the DNA concentration is increased in the 1 X 10(-4)-3 X 10(-3) M range (expressed in nucleotide concentration). This effect is attributed to intermolecular DNA-DNA interactions in which segments of adjacent DNA molecules tend to cover the pyrene chromophores on other strands, thus decreasing their accessibility to oxygen. In contrast the values of KTO2 for the non-covalent AO-DNA intercalation complexes are independent of DNA concentration, as expected for interior binding sites.

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗

Effects of medicinal plant extracts from Chinese herbal medicines on the mutagenic activity of benzo[a]pyrene.

The effects of medicinal plants on the mutagenicity of benzo[a]pyrene were studied with Salmonella typhimurium tester strains. The chosen medicinal plants are very frequently used as Chinese herbal medicines. Each medicinal plant was extracted with hot water, which is similar to the method used in Chinese medicinal treatment. Cinnamomi cortex, Rhei rhizoma, Scutellariae radix and Rehmanniae radix were found to decrease the mutagenic activity of benzo[a]pyrene. Atractylodis rhizoma also reduced the mutagenicity of benzo[a]pyrene, but this was not certain, because it showed a killing effect on the cell survival test. Bupleuri radix and Aurantii nobilis pericarpium had an enhancing effect, but then neither of these extracts is itself mutagenic. Each medicinal plant extract showed a different effect on the mutagenicity of benzo[a]pyrene. These effects were classified into 5 types: (I) decreasing effect, (II) killing effect, (III) enhancing effect, (IV) enhancing and decreasing effect and (V) inactive.

Benzo(a)pyrene↗

Detection of 3,6-dinitrobenzo[a]pyrene in airborne particulates.

3,6-Dinitrobenzo[a]pyrene, a new mutagen, was detected in airborne particulates collected in Santiago (Chile). The quantity of the compound in the airborne particulates was very small, accounting for 0.01 micrograms/g of total particulates (0.002 ng/m3 of air) at the lowest concentration. It was found that 3,6-dinitrobenzo[a]pyrene is readily decomposed by UV irradiation at 312 nm. The decomposed product was identified as 3-nitrobenzo[a]pyrene-6-quinone by means of mass spectrometry and proton nuclear magnetic resonance analysis. The mutagenicity of 3,6-dinitrobenzo[a]pyrene was 137,000 revertants/nmole for Salmonella typhimurium strain TA98, less than that for strain TA98/1,8-DNP6, an acetyltransferase-deficient mutant, and more than that for strain YG1024, an acetyltransferase-rich mutant.

Air Pollutants↗

Immunosuppressive potential of several polycyclic aromatic hydrocarbons (PAHs) found at a Superfund site: new model used to evaluate additive interactions between benzo[a]pyrene and TCDD.

Exposure to environmental pollution is rarely limited to a single compound or even a single class of compounds. The Superfund site located in Massena, NY, is contaminated by both halogenated aromatic hydrocarbons (HAHs) and polycyclic aromatic hydrocarbons (PAHs). Since representatives of both HAHs and PAHs are capable of binding to the aromatic hydrocarbon receptor (AhR), two well-documented AhR-mediated effects, immunosuppression and induction of hepatic aryl hydrocarbon hydroxylase (AHH) activity, were used to evaluate the individual and interactive toxicity of these compounds. Fifteen PAHs were first screened for their ability to suppress the antibody response in C57BL/6 (Ah+/+) mice immunized 12 h after a single oral dose of 0.1, 1, 10, or 100 mg/kg. Acenaphthene, anthracene, benzo[g,h,i]perylene, fluoranthene, fluorene, naphthalene, phenanthrene, and pyrene had little or no effect. Seven PAHs caused > 50% suppression at 100 mg/kg. Listed in order of decreasing potency they were benzo[k]fluoranthene, benzo[b]fluoranthene, indeno[1,2,3,c,d]pyrene, benzo[a]pyrene, chrysene, dibenzo[a,h]anthracene, and benz[a]anthracene. Chrysene and benzo[a]pyrene (B[a]P), were further evaluated to determine the dependence of these effects on the Ah phenotype by comparing responses of C57BL/6 and congenic B6.D2 (Ah-/-) mouse strains. Chrysene immunosuppression was maximal at 0.1 mg/kg and was Ah phenotype-independent whereas chrysene AHH induction was Ah phenotype-dependent, but a 100-fold less sensitive indicator of exposure. In contrast, B[a]P immunosuppression and AHH induction were coincident in B6 mice and Ah phenotype-dependent. In the final phase, a new approach was used to evaluate toxic interactions. This approach considers the mechanism of action of each compound and accounts for the fact that the extent of increase in toxic response caused by an incremental change of dose is determined by its position on the dose-response curve rather than on the absolute amount of dose administered. Thus, the immunotoxic effects of combined exposure to B[a]P and the AhR ligand, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), a representative HAH, were evaluated by combining the ED20 of B[a]P with the difference between the ED20 and ED40 of TCDD, and vice versa, to produce 40% suppression. The results of the combination were consistent with additivity regardless of the composite arrangement or phenotype although some antagonism could not be excluded with certainty.

Animals↗

Action of xanthine-xanthine oxidase system on microsomal benzo(a)pyrene metabolism in vitro.

The effect of superoxide anion-radical and other reactive oxygen species on the metabolism of benzo(a)pyrene was studied with isolated mouse liver microsomes. Reactive oxygen species were generated in vitro by xanthine-xanthine oxidase plus Fe3+ X FeEDTA and benzo(a)pyrene metabolism was followed by reverse-phase high pressure liquid chromatography. The following results were obtained: The reactive oxygen species induced one-electron oxidation of benzo(a)pyrene and increased production of free epoxide as well as protein-binding intermediates. The reactive oxygen species triggered microsomal lipid peroxidation in the presence of Fe3+ X FeEDTA. As a result of microsomal lipid peroxidation a decreased activity of cytochrome P-450, epoxide hydrolase and UDP-glucuronyltransferase was found. It is suggested that active oxygen species changed the balance between bioactivation and conjugation of benzo(a)pyrene metabolites causing accumulation of the epoxide and protein-binding intermediates. The role of iron ions and chelates in this process is discussed.

Animals↗

Effect of caffeine on the hepatic microsomal mixed function oxidase system during phenobarbital and benzo[a]pyrene treatment in rats.

Simultaneous administration of caffeine (100 mg/kg, i.p., 3 days) and phenobarbital (80 mg/kg, i.p., 3 days) to adult male rats resulted in a significant decrease in hepatic cytochrome P-450 and acetanilide hydroxylase activity, compared to phenobarbital administration alone. While simultaneous administration of caffeine and benzo[a]pyrene (20 mg/kg, i.p., 2 days) increased acetanilide hydroxylase, compared to benzo[a]pyrene administration, no change was seen in the cytochrome P-450 concentration. In vitro addition of 2.5 mM caffeine to microsomal incubations from untreated, phenobarbital- and benzo[a]pyrene-treated rats inhibited aminopyrine N-demethylase activity. No significant difference was seen in the extent of aminopyrine N-demethylase inhibition due to the in vitro addition of caffeine to microsomes from untreated or phenobarbital-treated rats, whereas inhibition in microsomes from benzo[a]pyrene-treated rats was greater.

Aminopyrine N-Demethylase↗

Effect of sulfamethazine on phenobarbital and benzo[a]pyrene induced hepatic microsomal mixed function oxidase system in rats.

Administration of sulfamethazine (300 mg/kg, i.p., single dose) to phenobarbital (80 mg/kg, i.p., 3 days) pretreated rats showed significant decrease in microsomal protein, electron transport components and drug metabolizing enzyme activities, compared with phenobarbital administration alone. Induction of mixed function oxidase enzymes due to phenobarbital was not affected by the pretreatment of sulfamethazine. Sulfamethazine administration to benzo[a]pyrene (20 mg/kg, i.p., 2 days in oil) pretreated rats showed no significant change, but there was a slight decrease in cytochrome P450 and aminopyrine N-demethylase activity, compared with benzo[a]pyrene administration alone. A significant inhibition was observed in aminopyrine N-demethylase activity due to in vitro addition of sulfamethazine (3.5 mM) to microsomal incubations from untreated, sulfamethazine, phenobarbital and benzo[a]pyrene-treated rats. The results indicate that the phenobarbital induced cytochrome P450 is more susceptible to sulfamethazine than benzo[a]pyrene induced cytochrome P450.

Animals↗

Pyrene lipids as markers of peroxidative processes in different regions of low and high density lipoproteins.

Three different pyrene derivatives, pyrene decanoyl phosphatidylcholine (P10PC), pyrene dodecanoyl sulfatide (P12CS) and cholesteryl pyrenyl hexanoate (P6Chol), were used to follow lipid peroxidation in low and high density lipoproteins. Probe-labelled lipoproteins were subjected to Cu2+ catalyzed peroxidation. In all cases the fluorescence of the probes progressively decreased due to the involvement of pyrene in the peroxidative reaction. Thus, we used the fluorescence decrease of P6Chol to monitor the lipid peroxidation in the hydrophobic core of LDL and HDL, and that of the amphipatic probes, P10PC and P12CS, to follow lipid peroxidation in the envelope of both lipoproteins. The possibility of following lipid peroxidation in individual lipoprotein regions could lead to more detailed information on the oxidative modifications that play an important role in the altered cholesterol homeostasis involved in the formation of atherosclerotic lesions. No differences were observed in the peroxidation kinetics of the hydrophobic core of HDL and LDL monitored with P6Chol. On the contrary kinetics obtained with P10PC and P12 CS demonstrated the HDL envelope to be more susceptible to Cu2+ -dependent lipid peroxidation than that of the LDL. This could be due to a greater radical generating capacity of the HDL envelope and can be explained on the basis of low vitamin E levels and large amounts of polyunsaturated fatty acids esterified on phospholipids determined in HDL, and on literature evidence that indicates HDL as the principal vehicle of circulating plasma lipids peroxides.

Adult↗

Metabolism of benzo(a)pyrene, dimethylbenzanthracene and aflatoxin B1 by camel liver microsomes.

The ability of camel liver microsomes to metabolise a range of common environmental carcinogens including benzo(a)pyrene, dimethylbenzanthracene and aflatoxin B1 has been investigated. The camel liver has shown the ability to metabolise benzo(a)pyrene, dimethylbenzanthracene and aflatoxin B1 to a number of metabolites. The major metabolites of benzo(a)pyrene produced by camel liver enzymes were identified as its mono-hydroxy derivatives and suggest that the metabolic detoxification pathways of carcinogen metabolism are predominant in this species. Benzo(a)pyrene metabolising activity in camel liver required NADPH and was inhibited by CO and alpha-naphthoflavone suggesting the involvement of cytochrome P450 in the metabolism of this carcinogen by camel liver. The cytochrome P450-dependent metabolism of carcinogen and other specific substrates such as ethoxyresorufin and ethoxycoumarin, by camel liver enzymes, was about 50% higher than that of rat liver enzymes. The cytochrome P450-dependent metabolism of a variety of carcinogenic and other substrates by camel liver demonstrated that there are multiple forms of cytochrome P450 enzymes involved in the metabolism of a wide array of xenobiotics and pollutants.

9,10-Dimethyl-1,2-benzanthracene↗

Effects of in vivo benzo(a)pyrene treatment on liver microsomal mixed-function oxidase activities of gilthead seabream (Sparus aurata).

Benzo(a)pyrene [B(a)P] treatment of gilthead seabream, 25 mg/kg, i.p. for 5 consecutive days, did not cause any significant changes in ethylmorphine N-demethylase and aniline 4-hydroxylase activities of liver microsomes. The same treatment did not alter the liver microsomal cytochrome b5 content, NADH-cytochrome b5 reductase and NADPH-cytochrome P450 reductase activities. However, benzo(a)pyrene treatment caused a 2-3-fold increase in 7-ethoxyresorufin O-deethylase (7-EROD) activity of gilthead seabream liver microsomes. Although, upon treatment, total cytochrome P450 content of liver microsomes increased about 1.7-fold in 1990 fall, no such increase was observed in spring 1991. However, a new cytochrome P450 with an apparent M(r) of 58,000 was observed on SDS-PAGE of liver microsomes obtained from benzo(a)pyrene treated gilthead seabream. Besides, in vitro addition of 0.2 x 10(-6) M benzo(a)pyrene to the incubation mixture inhibited 7-ethoxyresorufin O-deethylase activity by 93%. Gilthead seabream liver microsomal 4-ethoxyresorufin O-deethylase activity was characterized with respect to substrate concentration, amount of enzyme, type of buffer used, incubation period and temperature.

Animals↗

Removal of fluoranthene and pyrene by different microalgal species.

In this work, the efficiency of four microalgal species, namely, Chlorella vulgaris, Scenedesmus platydiscus, Scenedesmus quadricauda, and Selenastrum capricornutum to remove fluoranthene (1.0 mg l(-1)), pyrene (1.0 mg l(-1)), and a mixture of fluoranthene and pyrene (each at a concentration of 0.5 mg l(-1)) was evaluated. Results showed that removal was algal species specific and was also toxicant-dependent. Se. capricornutum was the most effective species while C. vulgaris was the least efficient species in removing and transforming polycyclic aromatic hydrocarbons (PAHs). PAHs removal in 7-days of treatment was 78% and 48%, respectively by these two. All species, except S. platydiscus exhibited higher fluoranthene removal efficiency than pyrene, indicating the latter PAH was generally more stable and recalcitrant. The removal efficiency of fluoranthene and pyrene in a mixture was comparable, or higher than the respective single compound, suggesting that the presence of one PAH stimulated the removal of the other PAH.

Chlorophyta↗

Novel method for determining pyrene biodegradation using synchronous fluorimetry.

To study the biodegradation rate of pyrene dissolved in liquid medium supplemented with mineral salts, a synchronous fluorimetry (SF) method was established. The limit of detection for pyrene dissolved in mineral salts medium (MSM) was determined as 0.19 ng/ml with a relative standard deviation of less than 1.3% (n = 9). The pyrene degrading rates of four bacterial strains were investigated using this method under the same experimental conditions. The degradation rates of the three active strains ranged from 76% to 87% after a 14-h incubation. The results were confirmed by the gas chromatography with a flame ionized detector (GC/FID) method. This implies that pyrene degradation can be directly monitored by the SF method without the solvent extraction of samples. The advantages of SF are that it is less laborious, faster, and less expensive than the GC/FID determination method with solvent extraction. The SF method provides a new tool for studying the degradation of polynuclear aromatic hydrocarbons (PAHs) in the natural environment and under experimental conditions.

Bacteria↗

Effects of riboflavin on the phototransformation of benzo[a]pyrene.

Riboflavin (Vitamin B2) is a natural dye-sensitizer habitually present in natural waters. Effects of riboflavin as photosensitizer on the transformation of benzo[a]pyrene (BaP) (10 microM) in the aqueous-organic solvent (water/acetonitrile/methanol 50/40/10) were investigated in this study. The photolysis half life of BaP in solution containing 50 microM riboflavin was 5 min, compared to 98 min in the absence of riboflavin. The rate of phototransformation of BaP increased as the concentration of riboflavin was raised from 10 microM to 100 microM under both natural sunlight and UVA irradiation. The half life of BaP in the presence of 50 microM riboflavin was 10.6 min and 43.1 min when exposed to visible range of natural sunlight and UVA irradiation respectively. Riboflavin decomposes under natural sunlight. Lumichrome, a principal photoproduct of riboflavin, was shown to photosensitize BaP under natural sunlight after photolysis of riboflavin. Our study indicated that other photoproducts from riboflavin, such as lumiflavin, were also involved in the phototransformation of BaP under sunlight when riboflavin diminished. The major photoproducts in the photolysis of BaP were identified as 1,6-benzo[a]pyrene-dione, 3,6-benzo[a]pyrene-dione, 6,12-benzo[a]pyrene-dione by using high performance liquid chromatography (HPLC). All these products were detected in the samples which were irradiated under different light sources and in the presence or absence of riboflavin. The possible phototransformation mechanism was discussed.

Benzo(a)pyrene↗

Plant-accelerated dissipation of phenanthrene and pyrene from water in the presence of a nonionic-surfactant.

Plant-accelerated dissipation of phenanthrene and pyrene in water in the presence of a nonionic-surfactant (Brij35) was studied. The mechanisms involved were evaluated, based on the investigation of plant uptake of these compounds from water with Brij35. The presence of ryegrass (Lolium multiflorum Lam) clearly enhanced the dissipation of tested PAHs in water with 0-296 mg l(-1) Brij35. The first-order rate constants (K), calculated from the first-order kinetic models for these PAH degradation (all significant at P < 0.05, n=8), of phenanthrene and pyrene in the presence of ryegrass were 16.7-50% and 47.1-108% larger than those of plant-free treatments, whereas half-lives (T1/2) of the former were 14.3-33.4% and 32.0-52.0% smaller than the latter, respectively. However, the promotion of PAH dissipation by ryegrass was found to significantly decrease with increasing Brij35 concentrations. In the range of 0-296 mg l(-1), low concentrations (< or = 74.0 mg l(-1)) of Brij35 generally enhanced plant uptake and accumulation of phenanthrene and pyrene, based on the observed plant concentrations and accumulated amounts of these chemicals from water. In contrast, Brij35 at relatively high concentrations (> or = 148 mg l(-1)) markedly restricted plant uptake of these PAHs. Plant accumulation of phenanthrene and pyrene accounted for 6.21-35.0% and 7.66-24.3% of the dissipation enhancement of these compounds from planted versus unplanted water bodies. In addition, plant metabolism was speculated to be another major mechanism of plant-accelerated dissipation of these PAHs in water systems. Results obtained from this study provided some insight with regard to the feasibility of phytoremediation for PAH contaminated water bodies with coexisted contaminants of surfactants.

Biomass↗

A method for determining pyrene in mucus using synchronous fluorimetry with multiple standard additions.

A new method was proposed to determine pyrene in mucus, which combined the synchronous fluorimetry with the multiple standard addition method (SFMSA). The method was used to determine pyrene in mucus directly without pretreatment. The method detection limit (MDL) for pyrene in mucus was measured as 0.47 ng/ml with a relative standard deviation of 12.7% (n = 7). The standard addition graph was linear in the range 0.05-50.00 ng/ml (r(2) = 0.9989). SFMSA was validated using a GC/MS method as a reference method, and nice agreement was found. The pyrene in mucus can be directly monitored by SFMSA without solvent extraction of samples. This indicates that SFMSA is more timesaving, less laborious and cheaper than the GC/MS method with solvent extraction. SFMSA has lower MDL and higher average recovery than the GC/MS method.

Animals↗

The ability of dissolved organic matter (DOM) to influence benzo[a]pyrene bioavailability increases with DOM biodegradation.

The biodegradation of two substrates and the ability of dissolved organic matter (DOM) to influence benzo[a]pyrene bioavailability as DOM biodegradation progressed were monitored in reactors. Substrates were composed of algae extracts and an artificial substrate that mimics raw wastewater, which were considered to be autochthonous and anthropogenic allochthonous models for DOM, respectively. The soluble microbial products formed during biomass activity were also studied. The aromaticity of DOM was investigated with specific ultraviolet absorbance. Partitioning coefficients between DOM and benzo[a]pyrene, K(DOC)(biol), were biologically determined by means of 4-h bioaccumulation experiments on Daphnia magna. Parent and degraded substrates always significantly reduced the bioaccumulation of benzo[a]pyrene at environmental DOM concentrations. Soluble microbial products also significantly affected the benzo[a]pyrene bioaccumulation. K(DOC)(biol) ranged between 2 x 10(4) and 4 x 10(5) L/kg. As the artificial wastewater biodegraded, DOM aromaticity increased, as did K(DOC)(biol). During the biodegradation of algae extract DOM, K(DOC)(biol) increased, whereas their aromaticity slightly decreased.

Algorithms↗

Studies on bovine serum albumin-sodium dodecyl sulfate complexes using pyrene fluorescence probe and 5-doxylstearic acid spin probe.

Interactions and characteristics of 0.1% bovine serum albumin (BSA)-sodium dodecyl sulfate (SDS) in 20 mM phosphate buffer solution were investigated by means of fluorescence spectroscopy and electron spin resonance (ESR) spectroscopy. In BSA-SDS system, the intensity ratio, Im3/Im1, of the third vibronic band of the pyrene monomer to the first vibronic band showed a small peak at about 0.1 mM SDS in the phosphate buffer below cmc. In accordance with this Im3/Im1 ratio, the intensity ratio, Ie/Im1, of fluorescence from the pyrene excimer to that from the monomer showed a pseudo-plateau (0.08-0.8 mM) and suggested the existence of micelle-like aggregates below the cmc. Temperature dependence of ln(Ie/Im1) in pyrene fluorescence in the SDS-BSA system was examined as a function of SDS concentration. The activation energy of pyrene diffusion for excimer formation in a micelle was estimated to be 19.2 kJ mol(-1) for the BSA-SDS system. ESR spectra of 5-doxylstearic acid (5-DSA) showed that the probe location is restricted at SDS concentrations above the cmc, and that the probe also is highly restricted in motion for BSA-bound SDS micelles.

Animals↗

Interactions of rice (Oryza sativa L.) and PAH-degrading bacteria (Acinetobacter sp.) on enhanced dissipation of spiked phenanthrene and pyrene in waterlogged soil.

The effects of cultivation of rice (Oryza sativa L.) and PAH-degrading bacteria (Acinetobacter sp.) separately, and in combination, on the dissipation of spiked phenanthrene and pyrene (0, 50+50, 100+100, 200+200 mg kg(-1)) in waterlogged soil were studied using pot trials. The population of introduced PAH-degrading bacteria remained at 10(5) CFU g(-1) dry soil after 20 days of treatment with Acinetobacter sp. only, but increased to 10(6) when planted with rice simultaneously. Shoot and root biomass of rice when grown alone was adversely affected by spiked PAHs, but significantly increased by 2-55% and 8-409%, respectively, when inoculated with Acinetobacter sp.. Phenanthrene and pyrene concentrations in roots ranged from 1-27 and 20-98 mg kg(-1), respectively, while their concentrations in shoots were generally lower than 0.2 mg kg(-1). The dissipation of phenanthrene was mainly due to abiotic loss as 70-78% phenanthrene was lost from the control soil at the end of 80 days, while removal of 86-87% phenanthrene had been achieved after 40 days in the treatment co-cultivated with Acinetobacter sp. and rice. Compared with the control where only 6-15% of pyrene was removed from soil, a much higher dissipation of pyrene (43-62%) was attained for the treatments co-cultivated with Acinetobacter sp. and rice at the end of 80 days. The results demonstrated that co-cultivation of rice and PAH-degrading bacteria may have a great potential to accelerate the bioremediation process of PAH-contaminated soil under waterlogged conditions.

Acinetobacter↗