Application of capillary electrophoresis-fluorescence line-narrowing spectroscopy for on-line spectral characterization of closely related analytes

Capillary electrophoresis (CE) interfaced with low-temperature (4.2 K) fluorescence line-narrowing spectroscopy (FLNS) is used for the separation and spectral characterization of closely related analytes. In this paper, the CE-FLNS system is applied to the analysis of a mixture of deuterated and protonated benzo[a]pyrene, a mixture of structurally similar benzo[a]pyrene and benzo[e]pyrene, and mixtures of dibenzo[a,l]pyrene-derived adenine DNA adducts. The CE-FLNS system provides on-line separation and high-resolution spectroscopic identification of CE-separated analytes, via fingerprint structure of vibrationally resolved FLN spectra at 4.2 K. The combination of the separation power of CE and the spectral selectivity of FLNS provide a methodology that has potential to become a powerful tool for molecular analyte characterization. The main applications of the CE-FLNS system, due to its selectivity, should be in the chemical analysis of structurally similar analytes and applications where analyte purity and detailed structural characterization are required.

Determination of benzo[a]pyrene- and 7,12-dimethylbenz[a]anthracene-DNA adducts formed in rat mammary glands

Both 7,12-dimethylbenz[a]anthracene (DMBA) and benzo[a]pyrene (BP) are carcinogenic in the rat mammary gland. The depurinating and stable adducts of DMBA and BP formed in vitro and in mouse skin were previously identified and quantitated. Identification and quantitation of the depurinating and stable DNA adducts of DMBA and identification of the depurinating adducts of BP formed in rat mammary glands in the 24 h after intramammillary injection of DMBA or BP are reported in this paper. The depurinating adducts of DMBA, which constitute 52% of all adducts detected, are DMBA bound at the 12-methyl group to the N-7 of adenine (Ade) or guanine (Gua), namely, 7-methylbenz[a]anthracene (MBA)-12-CH2-N7Ade (39%) and 7-MBA-12-CH2-N7Gua (13%). All of the stable adducts were formed from the diol epoxide(s) of DMBA. Depurinating adducts of BP with guanine, namely, 8-(BP-6-yl)-guanine (BP-6-C8Gua) and BP-6-N7Gua, were identified in rat mammary glands treated with BP. The major stable adduct, formed via the diol epoxide pathway, BP-diol epoxide-10-N2dG, accounted for over 64% of all the stable adducts. Three other BP-DNA stable adducts remain unidentified. Thus, rat mammary cells form depurinating adducts of DMBA and BP predominantly via their radical cations and stable adducts via the diol epoxides.

Conformational studies of stereoisomeric tetrols derived from syn- and anti-dibenzo[a,l]pyrene diol epoxides

An understanding of the conformational behavior of the stereoisomeric tetrols at the 11,12,13,14-positions of dibenzo[a,l]pyrene (DB[a,l]P) is essential for the spectroscopic identification of DNA adducts derived from the biologically highly active fjord region syn- and anti-DB[a,l]P-11,12-diol 13,14-epoxides. Conformational effects are expected to play an important role in DNA-DB[a,l]P diol epoxide reactivity, base-sequence specificity, and conformation dependent repair. The results of conformational studies on trans-anti-, cis-anti-, and cis-syn-DB[a,l]P tetrol isomers are presented and compared to the results obtained previously for trans-syn-DB[a,l]P tetrol (Carcinogenesis 17, 829-837, 1996). Molecular mechanics, dynamical simulations, and semiempirical calculations of electronic transitions are used to interpret the low-temperature fluorescence spectra and 1H NMR data. Molecular dynamics simulations (in vacuo) identified two conformers (I and II) for each of the tetrol isomers; in all conformations the aromatic ring system is severely distorted. Fluorescence line-narrowing (FLN) spectroscopy identified two distinct conformational species for the trans-anti isomer, one occurring in ethanol and the other occurring in a glycerol/water matrix. The corresponding structures are assigned based on the S1<--S0 transition energies calculated for conformers I and II, respectively. 1H NMR spectroscopy confirmed the structure of conformer I at room temperature. In contrast to trans-syn-DB[a,l]P tetrol (where the major conformation was identified as a boat structure), both conformations of trans-anti-DB[a,l]P tetrol feature a half-chair structure for the cyclohexenyl ring with different orientations of the hydroxyl groups. For cis-anti- and cis-syn-DB[a,l]P tetrols, only a single conformer is detected by FLN spectroscopy. The NMR results for the latter appear to be most consistent with a mixture of two half-chair conformers I and II, while for the cis-anti isomer a flattened, boatlike conformation was observed. The generally good agreement between the NMR coupling constants and those estimated theoretically indicates that these structures should serve as good starting points for spectroscopic or computational studies of DNA adducts derived from DB[a,l]P diol epoxides.

Depurinating and stable benzo[a]pyrene-DNA adducts formed in isolated rat liver nuclei

Polycyclic aromatic hydrocarbons are bound to DNA by two major pathways, one-electron oxidation and monooxygenation, to form adducts that are stable in DNA under normal conditions of isolation and depurinating adducts that are released from DNA by cleavage of the bond between the purine base and deoxyribose. Isolated rat liver nuclei have been used as an in vitro model for studying covalent binding of aromatic hydrocarbons to DNA, but the depurinating adducts formed by nuclei have not been identified or compared to those formed by the more commonly used rat liver microsomes. To examine the profiles of stable and depurinating adducts, nuclei from the livers of 3-methylcholanthrene-induced male MRC Wistar rats were incubated with [3H]benzo[a]pyrene (BP) and NADPH. Three depurinating adducts, 8-(BP-6-yl)Gua, 7-(BP-6-yl)Gua, and 7-(BP-6-yl)Ade, were obtained from the nuclei, as seen previously with rat liver microsomes or in mouse skin. The profile of stable adducts analyzed by the 32P-postlabeling method was qualitatively similar to that found in the microsomal activation of BP or in mouse skin treated with BP. Low-temperature fluorescence studies of the nuclear DNA revealed the presence of stable BP adducts originating from syn- and anti-BP diol epoxide.

Expanded analysis of benzo[a]pyrene-DNA adducts formed in vitro and in mouse skin: their significance in tumor initiation

This paper reports expanded analyses of benzo[a]pyrene (BP)-DNA adducts formed in vitro by activation with horseradish peroxidase (HRP) or 3-methylcholanthrene-induced rat liver microsomes and in vivo in mouse skin. The adducts formed by BP are compared to those formed by BP-7,8-dihydrodiol and anti-BP diol epoxide (BPDE). First, activation of BP by HRP produced 61% depurinating adducts: 7-(benzo[a]pyrene-6-yl)guanine (BP-6-N7Gua), BP-6-C8Gua, BP-6-N7Ade, and the newly identified BP-6-N3Ade. As a standard, the last adduct was synthesized along with BP-6-N1Ade by electrochemical oxidation of BP in the presence of adenine. Second, identification and quantitation of BP-DNA adducts formed by microsomal activation of BP showed 68% depurinating adducts: BP-6-N7Ade, BP-6-N7Gua, BP-6-C8Gua, BPDE-10-N7Ade, and the newly detected BPDE-10-N7Gua. The stable adducts were mostly BPDE-10-N2dG (26%), with 6% unidentified. BPDE-10-N7Ade and BPDE-10-N7Gua were the depurinating adducts identified after microsomal activation of BP-7, 8-dihydrodiol or direct reaction of anti-BPDE with DNA. In both cases, the predominant adduct was BPDE-10-N2dG (90% and 96%, respectively). Third, when mouse skin was treated with BP for 4 h, 71% of the total adducts were the depurinating adducts BP-6-N7Gua, BP-6-C8Gua, BP-6-N7Ade, and small amounts of BPDE-10-N7Ade and BPDE-10-N7Gua. These newly detected depurinating diol epoxide adducts were found in larger amounts when mouse skin was treated with BP-7,8-dihydrodiol or anti-BPDE. The stable adduct BPDE-10-N2dG was predominant, especially with anti-BPDE. Comparison of the profiles of DNA adducts formed by BP, BP-7,8-dihydrodiol, and anti-BPDE with their carcinogenic potency indicates that tumor initiation correlates with the levels of depurinating adducts, but not with stable adducts. Furthermore, the levels of depurinating adducts of BP correlate with mutations in the Harvey-ras oncogene in DNA isolated from mouse skin papillomas initiated by this compound [Chakravarti et al. (1995) Proc. Natl. Acad. Sci. U.S.A. 92, 10422-10426]. The depurinating adducts formed by BP in mouse skin appear to be the key adducts leading to tumor initiation.

High pressure studies of energy transfer and strongly coupled bacteriochlorophyll dimers in photosynthetic protein complexes

High pressure is used with hole burning and absorption spectroscopies at low temperatures to study the pressure dependence of the B800→B850 energy transfer rate in the LH2 complex of Rhodobacter sphaeroides and to assess the extent to which pressure can be used to identify and characterize states associated with strongly coupled chlorophyll molecules. Pressure tuning of the B800-B850 gap from ∼750 cm(\s-1) at 0.1 MPa to ∼900 cm(-1) at 680 MPa has no measurable effect on the 2 ps energy transfer rate of the B800-850 complex at 4.2 K. An explanation for this resilience against pressure, which is supported by earlier hole burning studies, is provided. It is based on weak coupling nonadiabatic transfer theory and takes into account the inhomogeneous width of the B800-B850 energy gap, the large homogeneous width of the B850 band from exciton level structure and the Franck-Condon factors of acceptor protein phonons and intramolecular BChl a modes. The model yields reasonable agreement with the 4.2 K energy transfer rate and is consistent with its weak temperature dependence. It is assumed that it is the C9-ring exciton levels which lie within the B850 band that are the key acceptor levels, meaning that BChl a modes are essential to the energy transfer process. These ring exciton levels derive from the strongly allowed lowest energy component of the basic B850 dimer. However, the analysis of B850s linear pressure shift suggests that another Förster pathway may also be important. It is one that involves the ring exciton levels derived from the weakly allowed upper component of the B850 dimer which we estimate to be quasi-degenerate with B800. In the second part of the paper, which is concerned with strong BChl monomer-monomer interactions of dimers, we report that the pressure shifts of B875 (LH2), the primary donor absorption bands of bacterial RC (P870 of Rb. sphaeroides and P960 of Rhodopseudomonas viridis) and B1015 (LH complex of Rps. viridis) are equal and large in value (∼-0.4 cm(01)/MPa at 4.2 K) relative to those of isolated monomers in polymers and proteins (< -0.1 cm(01)/MPa). The shift rate for B850 at 4.2 K is-0.28 cm(-1)/MPa. A model is presented which appears to be capable of providing a unified explanation for the pressure shifts.

Conformational studies of depurinating DNA adducts from syn-dibenzo[a,l]pyrene diolepoxide

One of the major DNA adducts from the extremely potent aromatic carcinogen dibenzo[a,l]pyrene (DB[a,l]P) is the depurinating adduct syn-DB[a,l]P diolepoxide-14-N7Ade. Low-temperature fluorescence spectra of this adduct (and related derivaties bound to N3-adenine and N7-guanine) showed two distinct (0,0) origin bands with different excited-state vibrational frequencies, as measured by means of fluorescence line narrowing spectroscopy. The relative intensity of the two origin bands was solvent dependent. The hypothesis that this phenomenon could be due to a conformational equilibrium was tested using molecular mechanics, dynamical simulations and semi-empirical quantum-mechanical calculations. The hydrolyzed metabolite DB[a,l]P tetraol was also studied for comparison. It was found that the syn-DB[a,l]P diolepoxide-14-N7Ade adduct is formed via trans addition to the epoxide. Exploration of the conformational space indeed produced two potential energy minima; both corresponding to structures in which the aromatic ring system is severely distorted. In conformation I the proximity of the distal ring forces the adenine base into a pseudo-axial position and the cyclohexenyl ring adopts a half-boat structure. In conformation II the distal ring is bent in the opposite direction, allowing the cyclohexenyl ring to adopt a half-chair structure with the base in a pseudo-equatorial position, partially stacked over the distal ring. THe difference in (0,0) transition energy calculated for the two conformers agrees very well with the spectroscopic data, and the relative orientations of the hydrogens bound to the cyclohexenyl ring in the major (half-boat) conformation I are in full agreement with the experimentally observed proton NMR coupling constants.

Conformational studies of the (+)-trans, (-)-trans, (+)-cis, and (-)-cis adducts of anti-benzo[a]pyrene diolepoxide to N2-dG in duplex oligonucleotides using polyacrylamide gel electrophoresis and low-temperature fluorescence spectroscopy

Using polyacrylamide gel electrophoresis (PAGE) and low-temperature, laser-induced fluorescence line narrowing (FLN) and non-line narrowing (NLN) spectroscopic methods, the conformational characteristics of stereochemically defined and site-specific adducts derived from the binding of 7 beta,8 alpha-dihydroxy-9 alpha,10 alpha-epoxy-7,8,9,10- tetrahydrobenzo[a]pyrene (anti-BPDE, a metabolite of the environmental carcinogen benzo[a]pyrene), to DNA were studied. The focus of these studies was on the four stereochemically distinct anti-BPDE modified duplexes 5'-d(CCATCGCTACC).(GGTAGCGATGG), where G denotes the lesion site derived from trans or cis addition of the exocyclic amino group of guanine to the C10 position of either (+) or (-)-anti-BPDE. PAGE experiments under non-denaturing conditions showed that the (+)-trans adduct causes a significantly greater retardation in the electrophoretic mobility than the other three adducts, probably the result of important adduct-induced distortions of the duplex structure. Low-temperature fluorescence studies in frozen aqueous buffer matrices showed that the (+)-trans adduct adopts primarily an external conformation with only minor interactions with the helix, but a smaller fraction (approximately 25%) appears to exists in a partially base-stacked conformation. The (-)-trans adduct exists almost exclusively (approximately 97%) in an external conformation. Both cis adducts were found to be intercalated; strong electron-phonon coupling observed in their FLN spectra provided additional evidence for significant pi-pi stacking interactions between the pyrenyl residues and the bases. FLN spectroscopy is shown to be suitable for distinguishing between trans and cis adducts, but lesions with either (+)- or (-)-trans, or (+)- or (-)-cis stereochemical characteristics showed very similar vibrational patterns.(ABSTRACT TRUNCATED AT 250 WORDS)

Formation and persistence of benzo[a]pyrene-DNA adducts in mouse epidermis in vivo: importance of adduct conformation

The formation and repair of benzo[a]pyrene diol epoxide-N2-deoxyguanosine adducts (BPDE-N2-dG) in DNA isolated from the skin of mice treated topically with benzo[a]pyrene (BP) was studied by 32P-postlabeling and by low-temperature fluorescence spectroscopy under low resolution and under high resolution fluorescence line narrowing (FLN) conditions. In agreement with earlier studies, total BP-DNA binding reached a maximum at 24 h after treatment (dose: 1 mumol/mouse), then declined rapidly until 4 days after treatment and much more slowly thereafter. An HPLC method was developed which resolved the 32P-postlabeled (-)-trans- from (-)-cis-anti-BPDE-N2-dG, and (+)-trans-from (+)-cis-anti-BPDE-N2-dG. High performance liquid chromatography analysis of the major TLC adduct spot (containing > 80% of the total adducts) obtained by postlabeling BP-modified mouse skin DNA showed that it consisted of a major component that coeluted with (-)-cis-/(+)-trans-anti-BPDE-N2-dG and a minor component that coeluted with (-)-trans-/(+)-cis-anti-BPDE-N2-dG and that the minor component was repaired at a slower rate than the major component. Low-temperature fluorescence spectroscopy of the intact DNA identified the major adduct as (+)-trans-anti-BPDE-N2-dG and the minor adduct fraction consisted mainly of (+)-cis-anti-BPDE-N2-dG. In agreement with the 32P-postlabeling results it was observed by fluorescence spectroscopy that the (+)-cis-adducts were repaired more slowly than most other adducts. Moreover, the (+)-trans-adducts exhibited a broad distribution of base-stacked, partially base-stacked and helix-external conformations. Mouse skin DNA samples obtained at early timepoints (2-8 h) after treatment with BP contained substantially more of the 'external' adducts, while samples at later timepoints (24-48 h) contained relatively more adducts in the base-stacked conformation, indicating also that the latter adducts are repaired less readily than the former. The possible biological significance of these novel observations of conformation-dependent rates of DNA adduct repair and their possible dependence on DNA sequence, are discussed.

Identification and quantitation of dibenzo[a,l]pyrene--DNA adducts formed by rat liver microsomes in vitro: preponderance of depurinating adducts

Dibenzo[a,l]pyrene (DB[a,l]P) is the most potent carcinogen known among aromatic hydrocarbons. DB[a,l]P-11,12-dihydrodiol, precursor to the bay-region diol epoxide, is slightly less carcinogenic than the parent compound. DB[a,l]P and its 11,12-dihydrodiol were covalently bound to DNA by cytochrome P-450 in 3-methylcholanthrene-induced rat liver microsomes, and DB[a,l]P was also bound to DNA by horseradish peroxidase. The "stable" (remaining intact in DNA under normal conditions of purification) and "depurinating" (released from DNA by cleavage of the glycosidic link between the purine base and deoxyribose) adducts were identified and quantified. Stable adducts were analyzed by the 32P-postlabeling technique. Depurinating adducts were identified by comparison of their retention times with those of standard adducts on HPLC in two solvent systems. Confirmation of their identity was obtained by means of fluorescence line-narrowing spectroscopy. When DB[a,l]P was activated by horseradish peroxidase, the depurinating adducts 3-(DB[a,l]P-10-yl)adenine (DB[a,l]P-10-N3Ade, 33%), 7-(DB[a,l]P-10-yl)adenine (DB[a,l]P-10-N7Ade, 27%), and 7-DB[a,l]P-10-yl)guanine (DB[a,l]P-10-N7Gua, 5%) were formed. Unidentified stable adducts comprised the remaining 35% of the detected adducts. When DB[a,l]P was activated by microsomes, the one-electron oxidation depurinating adducts DB[a,l]P-10-N3Ade (28%), DB[a,l]P-10-N7Ade (14%), DB[a,l]P-10-N7Gua (2%), and DB[a,l]P-10-C8Gua (6%), as well as the diol epoxide depurinating adducts (+/-)-syn-DB[a,l]P-diol epoxide (DE)-14-N7Ade (31%) and (+/-)-anti-DB[a,l]PDE-14-N7Gua (3%), were formed. Stable adducts predominantly formed via the DB[a,l]PDE pathway represented 16% of the adducts detected.(ABSTRACT TRUNCATED AT 250 WORDS)

Flanking base effects on the structural conformation of the (+)-trans-anti-benzo[a]pyrene diolepoxide adduct to N2-dG in sequence-defined oligonucleotides

Conformations of the trans adduct of (+)-anti-benzo[a]pyrene -7,8-dihydrodiol-9,10-epoxide (BPDE) to N2-guanine, the major stable DNA adduct of the environmental carcinogen benzo[a]pyrene, were studied as a function of flanking bases in single-stranded and in double-stranded oligonucleotides. Three 11mer oligonucleotides d(CTAT-G1G2G3TATC) were synthesized containing the (+)-trans-anti-BPDE adduct at one specific guanine of the GGG sequence (a known mutational hot spot). Polyacrylamide gel electrophoresis of the three single-stranded oligonucleotides showed that the adduct bound to G2 or G3 (5'-flanking base guanine) caused significantly stronger retardation than the same adduct bound to G1 (5'-flanking base thymine). The strength of the carcinogen-base interaction was reflected in the spectroscopic properties of the pyrenyl moiety. Low temperature fluorescence measurements under line-narrowing (FLN) or non-line-narrowing (NLN) conditions showed that in single-stranded form the adduct at G2 or G3 (5'-flanking base guanine) adopts a conformation with strong interaction with the bases. This was also observed for the same adduct at the sequence AGA. In contrast, the (+)-trans-anti-BPDE adduct with a 5'-flanking thymine exists in a primarily helix-external conformation. Similar differences were observed in the double-stranded oligonucleotides: the adducts at G2 and G3 were found to exist in similar conformational equilibria, again with significant carcinogen-base interactions, while the adduct at G1 showed a predominantly external conformation. The nature of the 3'-flanking base appeared to have little influence on the conformational equilibrium of the (+)-trans-anti-BPDE-guanine adduct. The results could provide insight into the mutational specificity and flanking base effects observed for (+)-anti-BPDE.

Sequence dependence of benzo[a]pyrene diol epoxide-DNA adduct conformer distribution: a study by laser-induced fluorescence/polyacrylamide gel electrophoresis

Low-temperature laser-induced fluorescence techniques in combination with polyacrylamide gel electrophoresis (LIF/PAGE) were used to study the binding of (-)-anti- and (+)-anti-benzo[a]pyrene 7,8-dihydrodiol 9,10-epoxide (anti-BPDE) to several sequence-defined duplex oligomers. Two of the oligomers contain central 5'-RAGGAR-3' sequences (R = purine) which appear to be frequently mutated by racemic (+/-)-anti-BPDE in endogenous genes of cells cultured in vitro. Two contain a central 5'-CCGG-3' or 5'-TGGT-3' sequence which are strongly preferred for covalent binding but appear to be not so frequently mutated. Binding of the two enantiomers to the latter two sequences yielded a distribution of BPDE-N2-dG adduct conformations similar to those from binding to highly polymerized, random sequence DNA in vitro which, for (+/-)-anti-BPDE, means that the helix-external conformation of the N2-dG adduct is dominant. Binding of (-)-anti-BPDE to the 5'-RAGGAR-3' sequences yielded more partially base-stacked and less base-stacked (quasi-intercalated) conformer than observed for random sequence DNA. Importantly, the (+)-anti-BPDE in binding to the more mutagenically inclined 5'-RAGGAR-3' sequences yielded little external-type adduct in comparison to the other two sequences and random sequence DNA. Moreover, an unusually high proportion of the (+)-anti-BPDE adducts formed with the 5'-RAGGAR-3' sequences result from cis stereoaddition, which yields a partially base-stacked configuration. Since the (+)-anti-BPDE appears to be the more mutagenic, this result suggests a possible role of internal adduct conformations in mutagenesis.

Identification and quantitation of benzo[a]pyrene-DNA adducts formed in mouse skin

The DNA adducts of benzo[a]pyrene (BP) formed in vitro were previously identified and quantitated. In this paper, we report the identification and quantitation of the depurination adducts of BP, 8-(benzo[a]pyren-6-yl)guanine (BP-6-C8Gua), BP-6-N7Gua, and BP-6-N7Ade, formed in mouse skin by one-electron oxidation, as well as the major stable adduct formed via the diolepoxide pathway, BP diolepoxide bound at C-10 to the 2-amino of dG (BPDE-10-N2dG). Identification of the depurination adducts was achieved by HPLC and fluorescence line narrowing spectroscopy. The depurination adducts, BP-6-C8Gua (34%), BP-6-N7Gua (10%), and BP-6-N7Ade (30%), constituted 74% of the adducts found in mouse skin 4 h after treatment with BP. The stable adduct BPDE-10-N2dG accounted for 22% of the adducts. Treatment of the skin with BP-7,8-dihydrodiol or BP diolepoxide yielded almost exclusively the stable adduct BPDE-10-N2dG. When BP or BP-7,8-dihydrodiol was bound to RNA or denatured DNA in reactions catalyzed by rat liver microsomes, no depurination adducts were detected. The profiles of stable adducts were similar both qualitatively and quantitatively with native or denatured DNA. With activation of BP by horseradish peroxidase, the profiles of stable adducts differed with native and denatured DNA. The total amount of adducts with denatured DNA was only 25% of the amount detected with native DNA. No depurination adducts were detected with denatured DNA or RNA in the peroxidase system.(ABSTRACT TRUNCATED AT 250 WORDS)

Identification and quantitation of 7,12-dimethylbenz[a]anthracene-DNA adducts formed in mouse skin

Identification and quantitation of the depurination and stable DNA adducts of 7,12-dimethylbenz[a]anthracene (DMBA) formed by cytochrome P450 in rat liver microsomes previously established one-electron oxidation as the predominant mechanism of activation of DMBA to bind to DNA. In this paper we report the identification and quantitation of the depurination and stable DMBA-DNA adducts formed in mouse skin. The depurination adducts, which constitute 99% of all the adducts detected, are DMBA bound at the 12-methyl group to the N-7 of adenine or guanine, namely, 7-methylbenz[a]anthracene (MBA)-12-CH2-N7Ade and 7-MBA-12-CH2-N7Gua. The depurination adducts were identified by HPLC and fluorescence line narrowing spectroscopy. The stable DNA adducts were analyzed by the 32P-postlabeling method. Almost 4 times as much of the depurination adduct 7-MBA-12-CH2-N7Ade (79%) was formed compared to 7-MBA-12-CH2-N7Gua (20%). The stable adducts accounted for only 1% of all the adducts detected and 80% of these were formed from DMBA diolepoxide. The binding of DMBA to DNA specifically at the 12-CH3 group is consistent with the results of carcinogenicity experiments in which this group plays a key role. When DMBA was bound to RNA or denatured DNA in reactions catalyzed by microsomes or by horseradish peroxidase (HRP), no depurination DNA adducts of DMBA were detected. The amount of stable DNA adducts observed with denatured DNA was 70% lower in the HRP system and 30% lower in the microsomal system compared to native DNA.(ABSTRACT TRUNCATED AT 250 WORDS)

Separation and identification of DNA-carcinogen adduct conformers by polyacrylamide gel electrophoresis with laser-induced fluorescence detection

We have developed a separation protocol utilizing high-resolution polyacrylamide gel electrophoresis (PAGE) to isolate stable anti-benzo[a]pyrene diol epoxide adducts of oligodeoxynucleotides. Both enantiomers produced multiple adduct species. The distribution of adduct types could be quantitated by densitometry of autoradiograms or Cerenkov counting of eluted oligomers modified by anti-BPDE isomers. Laser-induced fluorescence (LIF) spectra of eluted adducts at 4.2 K (fluorescence line-narrowing spectroscopy) and 77 K revealed that bands corresponded to pure conformers of pyrene chromophore. Carcinogen-modified oligodeoxynucleotides were single-stranded, but there were often considerable stacking interactions between the pyrenyl residues and the oligonucleotide bases, indicating that electrophoresed oligomers were single-stranded but in a native, versus random coil, conformation. The ability to identify and quantitate adducts by PAGE-LIF, coupled with the high resolution and sensitivity of both techniques, makes PAGE and LIF in tandem a potentially powerful tool in the study of chemical carcinogenesis or other ligand-DNA interactions.

Evidence of involvement of multiple sites of metabolism in the in vivo covalent binding of dibenzo[a,h]pyrene to DNA

The in vivo formation of dibenzo[a,h]pyrene-DNA adducts in mouse skin was assessed by laser-excited fluorescence spectroscopy at 77 and 4.2 K. Two adducts were identified with fluorescence origin bands at approximately 383.5 and 407.2 nm, and these were shown to possess pyrene and benzo[a]pyrene (B[a]P) chromophores, respectively. Both DNA-bound chromophores displayed considerable electron-phonon coupling and likely assume a highly base-stacked or quasi-intercalated configuration within DNA duplexes. The presence of B[a]P and pyrene aromatic systems indicates that two-electron or monooxygenation metabolism occurred on either the a or h benzo moieties (which are equivalent) in the former case, and on both these rings in the latter case. The presence of two adduct species agrees with 32P-postlabeling analysis of the DNA, which showed the presence of two major adducts in both thin-layer and high-performance liquid chromatographic separations.

Identification and quantitation of benzo[a]pyrene-DNA adducts formed by rat liver microsomes in vitro

The two DNA adducts of benzo[a]pyrene (BP) previously identified in vitro and in vivo are the stable adduct formed by reaction of the bay-region diol epoxide of BP (BPDE) at C-10 with the 2-amino group of dG (BPDE-10-N2dG) and the adduct formed by reaction of BP radical cation at C-6 with the N-7 of Gua (BP-6-N7Gua), which is lost from DNA by depurination. In this paper we report identification of several new BP-DNA adducts formed by one-electron oxidation and the diol epoxide pathway, namely, BP bound at C-6 to the C-8 of Gua (BP-6-C8Gua) and the N-7 of Ade (BP-6-N7Ade) and BPDE bound at C-10 to the N-7 of Ade (BPDE-10-N7Ade). The in vitro systems used to study DNA adduct formation were BP activated by horseradish peroxidase or 3-methylcholanthrene-induced rat liver microsomes, BP 7,8-dihydrodiol activated by microsomes, and BPDE reacted with DNA. Identification of the biologically-formed depurination adducts was achieved by comparison of their retention times on high-pressure liquid chromatography in two different solvent systems and by comparison of their fluorescence line narrowing spectra with those of authentic adducts. The quantitation of BP-DNA adducts formed by rat liver microsomes showed 81% as depurination adducts: BP-6-N7Ade (58%), BP-6-N7Gua (10%), BP-6-C8Gua (12%), and BPDE-10-N7Ade (0.5%). Stable adducts (19% of total) included BPDE-10-N2dG (15%) and unidentified adducts (4%). Microsomal activation of BP 7,8-dihydrodiol yielded 80% stable adducts, with 77% as BPDE-10-N2dG and 20% of the depurination adduct BPDE-10-N7Ade. The percentage of BPDE-10-N2dG (94%) was higher when BPDE was reacted with DNA, and only 1.8% of BPDE-10-N7Ade was obtained.(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanism of metabolic activation of the potent carcinogen 7,12-dimethylbenz[a]anthracene

The DNA adducts of 7,12-dimethylbenz[a]anthracene (DMBA) previously identified in vitro and in vivo are stable adducts formed by reaction of the bay-region diol epoxides of DMBA with dG and dA. In this paper we report identification of several new DMBA-DNA adducts formed by one-electron oxidation, including two adducts lost from DNA by depurination, DMBA bound at the 12-methyl to the N-7 of adenine (Ade) or guanine (Gua) [7-methylbenz[a]anthracene (MBA-12-CH2-N7Ade or 7-MBA-12-CH2-N7Gua, respectively]. The in vitro systems used to study DNA adduct formation were DMBA activated by horseradish peroxidase or 3-methyl-cholanthrene-induced rat liver microsomes. The biologically-formed depurination adducts were identified by high-pressure liquid chromatography and by fluorescence line narrowing spectroscopy. Stable DMBA-DNA adducts were analyzed by the 32P-postlabeling method. Quantitation of DMBA-DNA adducts formed by microsomes showed about 99% as depurination adducts: 7-MBA-12-CH2-N7Ade (82%) and 7-MBA-12-CH2-N7Gua (17%). Stable adducts (1.4% of total) included one adduct spot that may contain adduct(s) formed from the diol epoxide (0.2%) and unidentified adducts (1.2%). Activation of DMBA by horseradish peroxidase afforded 56% of stable unidentified adducts and 44% of depurination adducts, with 36% of 7-MBA-12-CH2-N7Ade and 8% of 7-MBA-12-CH2-N7Gua. Adducts containing the bond to the DNA base at the 7-CH3 group of DMBA were not detected.(ABSTRACT TRUNCATED AT 250 WORDS)

Heterogeneous distributions and dispersive photodissociation rates of benzo[a]pyrene diol-epoxide enantiomer-DNA and -poly(dG-dC).poly(dG-dC) adducts

Two types of heterogeneity of adducts are illustrated and discussed utilizing non-line narrowed (S2----S0 laser excitation) and line-narrowed (excitation into the (0,0) origin band) fluorescence spectra at low temperatures. The first type (type A) is due to structurally distinct and/or energetically inequivalent conformers. The second one (type B) is provided by an inhomogeneous environment of DNA and polynucleotides. In light of the above, the non-exponential photodissociation kinetics of the (+/-)-anti-BPDE-DNA and -polynucleotide adducts have been reanalyzed in terms of a dispersive first order chemical reaction, where the inhomogeneous effects are explicitly included. It is demonstrated that the DNA structure shows considerable inhomogeneous broadening, and that type B heterogeneity is responsible for the dispersive photodissociation process. The latter is accounted for by a Gaussian distribution of activation energies, with the center of the distribution at approximately 600 meV and the full width at half-maximum equal to approximately 50 meV (approximately 2 kT). Photolabile (+/-)-anti-BPDE-DNA and -polynucleotide adducts are identified as quasi-intercalated (site I) (+)- and (-)-cis-BPDE. The calculated concentrations of cis-BPDE adducts in DNA and polynucleotides from the kinetic data are in very good agreement with the cis-BPDE adduct concentrations obtained from the spectral and/or chemical analysis. The average photodissociation rate and the photodissociation quantum yield of cis- and trans-BPDE adducts are also estimated.

Comparative laser spectroscopic study of DNA and polynucleotide adducts from the (+)-anti-diol epoxide of benzo[a]pyrene

A recently developed methodology [Jankowiak, R., Lu, P., Small, G. J., and Geacintov, N. E. (1990) Chem. Res. Toxicol. 3, 39-46], which combines fluorescence line narrowing spectroscopy at 4.2 K with non-line-narrowed (S2----S0 laser excitation) fluorescence spectroscopy at 77 K and fluorescence quenching, is used to characterize adducts formed from (+)-anti-BPDE and the alternating copolymers poly(dG-dC).poly(dG-dC) and poly(dA-dT).poly(dA-dT), the nonalternating poly (dG).poly(dC), single-strand poly(dG), and the oligonucleotide d(ATATGTATA). Detailed comparisons of the fluorescence spectra and quenching (with acrylamide) of the properties of the adducts with those of (+)-anti-BPDE-DNA adducts are made. Fluorescence spectra of the trans and cis isomers of the adduct formed from guanosine monophosphate and the adducts of d(ATATGTATA) are used to assign the stereochemistry of the two major DNA adducts as trans-N2-dG moieties which occupy two different DNA sites. Evidence for the existence of minor cis-type guanine adducts is provided. Finally, a fourth type of DNA adduct (minor) is identified and assigned as trans-N6-dA.

Effects of detergent on the excited state structure and relaxation dynamics of the photosystem II reaction center: A high resolution hole burning study

Low temperature (4.2 K) absorption and hole burned spectra are reported for a stabilized preparation (no excess detergent) of the photosystem II reaction center complex. The complex was studied in glasses to which detergent had and had not been added. Triton X-100 (but not dodecyl maltoside) detergent was found to significantly affect the absorption and persistent hole spectra and to disrupt energy transfer from the accessory chlorophyll a to the active pheophytin a. However, Triton X-100 does not significantly affect the transient hole spectrum and lifetime (1.9 ps at 4.2 K) of the primary donor state, P680(*). Data are presented which indicate that the disruptive effects of Triton X-100 are not due to extraction of pigments from the reaction center, leaving structural perturbations as the most plausible explanation. In the absence of detergent the high resolution persistent hole spectra yield an energy transfer decay time for the accessory Chl a QY-state at 1.6 K of 12 ps, which is about three orders of magnitude longer than the corresponding time for the bacterial RC. In the presence of Triton X-100 the Chl a QY-state decay time is increased by at least a factor of 50.

Identification and quantitation of 7-(benzo[a]pyren-6-yl)guanine in the urine and feces of rats treated with benzo[a]pyrene

The major identified benzo[a]pyrene (BP)-DNA adduct formed by cytochrome P-450 contains BP bound at the C-6 position to the N-7 position of guanine (BP-N7Gua). This adduct is rapidly depurinated from DNA. When rats were treated with [14C]BP, about 0.02% of the administered dose of BP was excreted as BP-N7Gua in feces and urine within 5 days. Chloroform extracts of the urine and feces were analyzed by high-pressure liquid chromatography. The structure of the adduct was established by cochromatography with electrochemically prepared BP-N7Gua and by fluorescence line narrowing spectrometry. This study represents the first demonstration that BP-N7Gua is formed in vivo in animals treated with BP.

Fluorescence line-narrowing spectrometry: a versatile tool for the study of chemically initiated carcinogenesis

An important initiating step in the induction of tumors is believed to be the covalent binding of an active carcinogenic species to a cellular macromolecule, e.g. DNA. Therefore, a spectroscopic technique which allows for positive identification of the intact (macromolecular) DNA adduct and/or isolated damaged nucleosides/nucleotides is highly desirable. It is shown that fluorescence line-narrowing spectroscopy (FLNS) is a rapid, versatile, highly sensitive and selective analytical technique, which can be used directly to characterize DNA adducts and isolated nucleosides. FLNS possesses sufficient resolution to distinguish between the major DNA adducts derived from different enantiomers of benzo[a]pyrene diol-epoxide (BPDE). With the present limit of detection (approximately 1 adducted base per 10(8) normal base pairs for 100 micrograms of DNA), the technique is applicable to in vivo samples. Analysis of liver DNA from fish exposed to benzo[a]pyrene (BP) (100 mg BP/kg fish) showed that a major DNA adduct is derived from syn-BPDE.

Laser spectroscopic studies of DNA adduct structure types from enantiomeric diol epoxides of benzo[a]pyrene

A methodology based on 77 K laser-excited fluorescence spectroscopy, fluorescence quenching, and fluorescence line narrowing is shown to be a highly selective and sensitive approach for the study of polycyclic aromatic carcinogen-DNA complexes. Three and five different DNA adducts derived from (+)-trans-7,8-dihydroxy-anti-9,10-epoxy-7,8,9,10-tetrahydrobenzo [a]pyrene and its (-)-enantiomer are identified, respectively. Two different methods are used to classify the adducts as type I (interior) or type II (exterior), and both yield consistent results. The first high-resolution fluorescence excitation spectra are reported for DNA adducts. These spectra are suggested to be useful for characterizing the strength of the interaction between the fluorescent chromophores and the DNA bases. The above methodology has the potential for monitoring the fates of different adducts as a function of time in repair-competent cells.

Fluorescence line narrowing spectrometric analysis of benzo[a]pyrene-DNA adducts formed by one-electron oxidation

Fluorescence line narrowing (FLN) was demonstrated for five benzo[a]pyrene (BP)-nucleoside adducts synthesized by one-electron oxidation of BP in the presence of guanosine, deoxyguanosine, and deoxyadenosine. The standard FLN spectra were used to prove that a major depurination adduct from the binding of BP to DNA in rat liver nuclei is 7-(benzo[a]pyren-6-yl)guanine (N7Gua). The structural characterization was performed with only 20 pg of the adduct. Metabolic activation of BP by one-electron oxidation in the horseradish peroxidase catalyzed reaction of BP with DNA (in vitro) was also investigated. The major adduct identified was 8-(benzo[a]pyren-6-yl)guanine (C8Gua).

Fluorescence line narrowing-nonphotochemical hole burning spectrometry: femtomole detection and high selectivity for intact DNA-PAH adducts

A new fluorescence line narrowing (FLN) apparatus is described and evaluated through experiments on intact DNA-PAH (polycyclic aromatic hydrocarbon) and globin-PAH adducts, as well as polar PAH metabolites. A detection limit of approximately 3 modified bases in 10(8) for a DNA adduct formed with a diol-epoxide of benzo[a]pyrene (BPDE-DNA) is reported for 20 micrograms of DNA at a spectral resolution of approximately 8 cm-1. The methodology employed avoids or minimizes spectral degradation and loss of sensitivity due to photooxidation and nonphotochemical hole burning (NPHB). A new double selection technique that employs both FLN and NPHB is described and found to lead to a significant improvement in selectivity over that obtained with conventional FLN.

Hole-Burning Spectroscopy and Relaxation Dynamics of Amorphous Solids at Low Temperatures

The magnitude and temperature dependence of most of the properties of amorphous solids are anomalous at very low temperatures ( less, similar1 Kelvin). Phonon-assisted tunneling of a distribution of glassy bistable configurations, or two-level systems, can account for these anomalies. A unified understanding of the low-temperature properties is required for an understanding of the glassy state. Persistent nonphotochemical hole burning of impurity optical transitions allows a glass state to be produced that is thermally inaccessible to the preburn state, and that allows the probing of tunneling dynamics on time scales that range between picoseconds and days. These data combined with recently obtained distribution functions for the two-level systems offer new insights into the tunneling dynamics.