Shaping the biology of citrus: I. Genomic determinants of evolution

We performed genomic analyses on wild species of the genus Citrus to identify major determinants of evolution. The most notable effect occurred on the pathogen-defense genes, as observed in many other plant genera. The gene space was also characterized by changes in gene families intimately related to relevant biochemical properties of citrus fruit, such as pectin modifying enzymes, HDR (4-hydroxy-3-methylbut-2-enyl diphosphate reductase) genes, and O-methyltransferases. Citrus fruits are highly abundant on pectins and secondary metabolites such as terpenoids and flavonoids, the targets of these families. Other gene types under positive selection, expanded through tandem duplications and retained as triplets from whole genome duplications, codified for purple acid phosphatases and MATE-efflux proteins. Although speciation has not been especially rapid in the genus, analyses of selective pressure at the codon level revealed that the extant species evolved from the ancestral citrus radiation show signatures of pervasive adaptive evolution and is therefore potentially responsible for the vast phenotypic differences observed among current species.

Shaping the biology of citrus: II. Genomic determinants of domestication

We performed genomic analyses on species and varieties of the genus Citrus to identify several determinants of domestication, based on the pattern of pummelo [Citrus maxima (Burr. f) Merr] and mandarin (Citrus reticulata Blanco) admixture into the ancestral genome, as well as population genetic tests at smaller scales. Domestication impacted gene families regulating pivotal components of citrus flavor (such as acidity) because in edible mandarin varieties, chromosome areas with negative Tajimas values were enriched with genes associated with the regulation of citric acid. Detection of sweeps in edible mandarins that diverged from wild relatives indicated that domestication reduced chemical defenses involving cyanogenesis and alkaloid synthesis, thus increasing palatability. Also, a cluster of SAUR genes in domesticated mandarins derived from the pummelo genome appears to contain candidate genes controlling fruit size. Similarly, conserved stretches of pure mandarin areas were likely important as well for domestication, as, for example, a fragment in chromosome 1 that is involved in the apomictic reproduction of most edible mandarins. Interestingly, our results also support the hypothesis that various genes subject to selective pressure during evolution or derived from whole genome duplication events later became potential targets of domestication.

Reprogramming of Retrotransposon Activity during Speciation of the Genus Citrus

Speciation of the genus Citrus from a common ancestor has recently been established to begin ∼8 Ma during the late Miocene, a period of major climatic alterations. Here, we report the changes in activity of Citrus LTR retrotransposons during the process of diversification that gave rise to the current Citrus species. To reach this goal, we analyzed four pure species that diverged early during Citrus speciation, three recent admixtures derived from those species and an outgroup of the Citrus clade. More than 30,000 retrotransposons were grouped in ten linages. Estimations of LTR insertion times revealed that retrotransposon activity followed a species-specific pattern of change that could be ascribed to one of three different models. In some genomes, the expected pattern of gradual transposon accumulation was suddenly arrested during the radiation of the ancestor that gave birth to the current Citrus species. The individualized analyses of retrotransposon lineages showed that in each and every species studied, not all lineages follow the general pattern of the species itself. For instance, in most of the genomes, the retrotransposon activity of elements from the SIRE lineage reached its highest level just before Citrus speciation, while for Retrofit elements, it has been steadily growing. Based on these observations, we propose that Citrus retrotransposons may respond to stressful conditions driving speciation as a part of the genetic response involved in adaptation. This proposal implies that the evolving conditions of each species interact with the internal regulatory mechanisms of the genome controlling the proliferation of mobile elements.

Genomics of the origin and evolution of Citrus

The genus Citrus, comprising some of the most widely cultivated fruit crops worldwide, includes an uncertain number of species. Here we describe ten natural citrus species, using genomic, phylogenetic and biogeographic analyses of 60 accessions representing diverse citrus germ plasms, and propose that citrus diversified during the late Miocene epoch through a rapid southeast Asian radiation that correlates with a marked weakening of the monsoons. A second radiation enabled by migration across the Wallace line gave rise to the Australian limes in the early Pliocene epoch. Further identification and analyses of hybrids and admixed genomes provides insights into the genealogy of major commercial cultivars of citrus. Among mandarins and sweet orange, we find an extensive network of relatedness that illuminates the domestication of these groups. Widespread pummelo admixture among these mandarins and its correlation with fruit size and acidity suggests a plausible role of pummelo introgression in the selection of palatable mandarins. This work provides a new evolutionary framework for the genus Citrus.

Sequencing of diverse mandarin, pummelo and orange genomes reveals complex history of admixture during citrus domestication

Cultivated citrus are selections from, or hybrids of, wild progenitor species whose identities and contributions to citrus domestication remain controversial. Here we sequence and compare citrus genomes--a high-quality reference haploid clementine genome and mandarin, pummelo, sweet-orange and sour-orange genomes--and show that cultivated types derive from two progenitor species. Although cultivated pummelos represent selections from one progenitor species, Citrus maxima, cultivated mandarins are introgressions of C. maxima into the ancestral mandarin species Citrus reticulata. The most widely cultivated citrus, sweet orange, is the offspring of previously admixed individuals, but sour orange is an F1 hybrid of pure C. maxima and C. reticulata parents, thus implying that wild mandarins were part of the early breeding germplasm. A Chinese wild 'mandarin' diverges substantially from C. reticulata, thus suggesting the possibility of other unrecognized wild citrus species. Understanding citrus phylogeny through genome analysis clarifies taxonomic relationships and facilitates sequence-directed genetic improvement.

Performance vigilance task and sleepiness in patients with sleep-disordered breathing

Altered vigilance performance has been documented in patients with sleep-related breathing disorders (SRBDs). Sleep fragmentation, sleepiness, respiratory disturbances and nocturnal hypoxaemia have been suggested as the pathogenesis of these deficits, yet it remains difficult to find a good correlation between performance deficits and the above factors. In the present study, which performance measure better characterised SRBD patients and the main factors implicated in these disturbances were examined. The study group consisted of 152 patients and 45 controls, all examined using a performance vigilance task and subjective sleepiness assessment. Speed and accuracy in the psychomotor vigilance task (PVT) were measured in patients and controls. Objective daytime sleepiness was assessed in the patient group using the maintenance of wakefulness test. In comparison with controls, PVT accuracy rather than speed seems to be affected in SRBD patients, with lapses and false responses significantly greater in patients with more severe objective sleepiness and higher apnoea/hypopnoea index. Although slowing and increased variability in reaction time were associated with shorter sleep latency in the maintenance of wakefulness test, subjective sleepiness, sleep fragmentation, nocturnal hypoxaemia and apnoea/hypopnoea index influenced mainly PVT accuracy. It is concluded that vigilance impairment, sleep fragmentation and severity of disease may partially and differentially contribute to the diurnal performance consequences found in sleep-related breathing disorders. Since the psychomotor vigilance task worsening is more marked in accuracy that in speed, measurement of lapses and false responses would better characterise the degree of diurnal impairment in these patients.

Determinants of altered quality of life in patients with sleep-related breathing disorders

Recent reports have suggested that altered quality of life and well-being are reported by patients with sleep-related breathing disorders (SRBD). There seems to be no data available in the literature on factors underlying these behavioural consequences. In this study, health-related quality of life (HRQL) scores were examined in SRBD patients in order to establish which factors are implicated in these disturbances. The study group consisted of 130 patients: 49 snorers and 81 patients with obstructive sleep apnoea. The Medical Outcome Survey Short Form-36 questionnaire was administered the morning after the sleep study and scores for the eight dimension scores were obtained. Patient's data were compared to normative sex- and age-matched data. In comparison with normal values, scores for all HRQL dimensions were decreased in SRBD patients, with a greater impact on subscores for "vitality", "physical role", "social functioning", "mental health" and "role emotional" dimensions. While impairment in physical function was mostly influenced by sleep stage and obesity, subjective daytime sleepiness mainly affected the other dimensions. The authors conclude that the altered health-related quality of life of sleep-related breathing disorder patients is a multifactorial phenomenon depending on the interaction of sleep stages, daytime sleepiness and obesity, with no significant contribution of sleep fragmentation, hypoxaemia and apnoea recurrence.

The role of stimulus type in age-related changes of visual working memory

Aging is accompanied by increasing difficulty in working memory associated with the temporary storage and processing of goal-relevant information. Face recognition plays a preponderant role in human behavior, and one might therefore suggest that working memory for faces is spared from age-related decline compared to socially less important visual stimulus material. To test this hypothesis, we performed working memory (n-back) tasks with two different visual stimulus types, namely faces and doors, and compared them to tasks with primarily verbal material, namely letters. Age-related reaction time slowing was comparable for all three stimulus types, supporting hypotheses on general cognitive and motor slowing. In contrast, performance substantially declined with age for faces and doors, but little for letters. Working memory for faces resulted in significantly better performance than that for doors and was more sensitive to on-line manipulation errors such as the temporal order. All together, our results show that even though face perception might play a specific role in visual processing, visual working memory for faces undergoes the same age-related decline as it does for socially less relevant visual material. Moreover, these results suggest that working memory decline cannot be solely explained by increasing vulnerability in prefrontal cortex related to executive functioning, but indicate an age-related decrease in a visual short-term buffer, possibly located in the temporal cortex.

Is waking electroencephalographic activity a predictor of daytime sleepiness in sleep-related breathing disorders?

No data are available in the literature assessing the potential use of waking electroencephalographic (EEG) activity in the detection of excessive daytime sleepiness (EDS) in patients with sleep-related breathing disorders (SRBD). The aim of this study was to evaluate whether waking EEG spectral power reflects the level of EDS in SRBD patients. The study was performed in 48 patients in whom quantitative EEG analysis, including the alpha attenuation coefficient (AAC), was performed. Sleepiness was assessed by the Epworth Sleepiness Scale, the Stanford Sleepiness Scale, the Visual Analogue Scale and the maintenance of wakefulness test. Although AAC and EEG spectral power tended to vary throughout the day, none of these variations correlated with EDS measures. Waking EEG measures were not different between snorers and apnoeic patients. Compared to nonsleepy patients, sleepy patients had greater theta and slow alpha powers, but the differences did not reach statistical significance. The EEG slowing was independent of hypoxaemia, severity of SRBD, or degree of sleep disruption. The authors conclude that waking electroencephalographic measures are not sensitive enough to predict variation in alertness or to differentiate sleepy from nonsleepy sleep-related breathing disorders patients. The degree of electroencephalographic slowing was related neither to sleep disruption nor to severity of sleep-related breathing disorders.

Cardiac activation during arousal in humans: further evidence for hierarchy in the arousal response

OBJECTIVES

One major subject of discussion in sleep studies is whether bursts of K-complexes (K-bursts) and delta waves (D-bursts), expressions of a subcortical arousal, truly reflect an arousal response during sleep. To address this question we studied the changes in heart rate (HR) during spontaneous arousals in healthy subjects.

METHODS

Twenty-seven healthy adults were examined. Arousals were graded in 4 levels, including the standard definition of a microarousal (MA), phases of transitory activation (PAT), D-bursts and K-bursts. HR was analyzed for 10 beats before and 20 beats during arousal. EEG spectral analysis was performed for all types of arousals, including in the analysis the 20 s period preceding the actual event.

RESULTS

Each type of arousal was associated with HR changes consisting of a tachycardia followed by a bradycardia. Changes were more pronounced during MA and PAT. Detailed analysis of the HR response showed that HR always increased before MA and PAT onset, associated with a rise in delta, theta and fast EEG activities, and suggesting a cerebral activation.

CONCLUSIONS

Our data suggest that such subcortical arousals represent a real arousal response inducing cardiac activation similar to that found during MA and PAT. During MA and PAT, a rise in HR appears before the onset of the actual arousal associated with an increase in EEG slow and fast activity. The link between EEG and HR variation during MA and PAT and the fluctuations in HR during subcortical arousal suggest a continuous spectrum in the arousal mechanisms, starting at the brainstem level and progressing to cortical areas.

[Somatosensory evoked potentials: interference and perceptual masking of cutaneous afferents in man]

Somatosensory evoked potentials (SEP) are attenuated following double electrical stimulation of the fingers (II + III). This effect is observed at cervical (N13), parietal (N20-P27) and frontal (P22-N30) levels. We simultaneously observed in the same subjects that cutaneous perception of the test-shock is completely suppressed with interstimulus intervals (ISI) within a 0-10 msec range. With 25-30 msec ISI, the perceptive function totally recovers, but SEP inhibition remains at 50 % of the control. The SEP reduction does not result in a perception deficit as long as the cortical-test response exceeds 50% of control. These results suggest that: SEP inhibition could be a local but durable phenomenon occurring at both cervical and cortical levels. Cutaneous perception does not necessitate a maximal SEP development. The perceptive process involves other associative areas (5,7...) and is activated when the primary cortical activation exceeds a certain threshold which was found at 50% of the unconditioned response voltage.

Solution conformation of the (+)-cis-anti-[BP]dG adduct in a DNA duplex: intercalation of the covalently attached benzo[a]pyrenyl ring into the helix and displacement of the modified deoxyguanosine

This paper reports on the solution structure of the (+)-cis-anti-[BP]dG adduct positioned opposite dC in a DNA oligomer duplex which provides the first experimentally based solution structure of an intercalative complex of a polycyclic aromatic hydrocarbon covalently bound to the N2 of deoxyguanosine. The combined NMR-energy minimization computation studies were undertaken on the (+)-cis-anti-[BP]dG adduct embedded in the same d(C5-[BP]G6-C7).d(G16-C17-G18) trinucleotide segment of the complementary 11-mer duplex studied previously with the stereoisomeric trans adducts. The exchangeable and nonexchangeable protons of the benzo[a]pyrenyl moiety and the nucleic acid were assigned following analysis of two-dimensional NMR data sets in H2O and D2O solution. The solution structure of the (+)-cis-anti-[BP]dG-dC 11-mer duplex has been determined by incorporating intramolecular and intermolecular proton-proton distances defined by upper and lower bounds deduced from NOESY data sets as restraints in energy minimization computations. The benzo[a]pyrene ring of [BP]dG6 is intercalated between intact Watson-Crick dC5.dG18 and dC7.dG16 base pairs in a right-handed DNA helix. The benzylic ring is in the minor groove while the pyrenyl ring sacks with flanking dC5 and dC7 bases on the same strand. The deoxyguanosine ring of [BP]dG6 is not Watson-Crick base paired but displaced into the minor groove with its plane parallel to the helix axis and stacks over the sugar ring of dC5. The dC17 base on the partner strand is displaced from the center of the helix toward the major groove by the intercalated benzo[a]pyrene ring. This intercalative structure of the (+)-cis-anti-[BP]dG-dC 11-mer duplex exhibits several unusually shifted proton resonances which can be readily accounted for by the ring current contributions of the deoxyguanosine and pyrenyl rings of the [BP]dG6 adduct. Several phosphorus resonances are shifted to low and high field of the unperturbed phosphorus spectral region and have been assigned to internucleotide phosphates centered about the [BP]dG6 modification site. These studies define the changes in the helix at the central trinucleotide segment needed to generate the intercalation site for the covalently bound (+)-cis-anti-[BP]dG adduct.(ABSTRACT TRUNCATED AT 400 WORDS)

Base-sequence dependence of covalent binding of benzo[a]pyrene diol epoxide to guanine in oligodeoxyribonucleotides

The base-sequence dependence of the yield of the covalent binding reaction of (+)-anti-7 beta, 8 alpha-dihydroxy-9 alpha, 10 alpha-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene [(+)-anti-BPDE] with the exocyclic amino group of guanine surrounded by different flanking bases X and Y in the single-stranded oligonucleotide d(CTATXGYTATC) was investigated. With an initial ratio of [(+)-anti-BPDE]/[oligonucleotide strand] = 2, the percentage of modified strands varied from 20 +/- 2% when the modified dG was surrounded by pyrimidines to 5-7% when the central dG was surrounded by purines. The trans/cis ratio of (+)-anti-BPDE-N2-dG adducts was in the range of 3-5. The lower reaction yields observed when the modified guanine residues in single-stranded oligonucleotides are surrounded by purines rather than by pyrimidines is tentatively attributed (1) to steric effects arising from the presence of the bulkier purines flanking the reacting dG moieties on the 5'- and 3'-sides and/or (2) to noncovalent interactions between anti-BPDE and neighboring purines which decrease the probability of optimal alignment for covalent binding between the interacting moieties in the bimolecular transition-state complex. Noncovalent intercalation of (+)-anti-BPDE prior to the covalent binding reaction is not a relevant process in the case of single-stranded oligonucleotides and is therefore not a critical requirement for obtaining high yields of covalent trans- and cis-(+)-anti-BPDE-N2-dG adducts in these oligonucleotide sequences.

Direct synthesis and identification of benzo[a]pyrene diol epoxide-deoxyguanosine binding sites in modified oligodeoxynucleotides

Adducts derived from the reaction of the benzo[a]pyrene metabolite model compound (+)-anti-7 beta,8 alpha-dihydroxy-9 alpha,10 alpha-epoxy-7,8,9, 10-tetrahydrobenzo[a]pyrene [(+)-BPDE] with the single-stranded oligodeoxynucleotide 5'-d(TATGCGTAT) were obtained according to direct synthesis techniques described earlier [Cosman, M., Ibanez, V., Geacintov, N. E., and Harvey, R. G. (1990) Carcinogenesis 11, 1667-1672]. Four major adducts, involving trans and cis addition (trans/cis adduct ratio approximately 4.5) of (+)-BPDE to the exocyclic amino groups of guanines G4 and G6 (the numbers denote the positions of the guanines counted from the 5'-side) were obtained. These adducts can be separated from one another by reverse-phase high-performance liquid chromatography methods. The site of BPDE binding on either G4 or G6 can be determined from the electrophoresis band patterns on 20% polyacrylamide gels of the BPDE-modified oligonucleotides subjected to the G+A and G Maxam-Gilbert strand cleavage reactions [Maxam, A. M., and Gilbert, W. (1980) Methods. Enzymol. 65, 499-560]. The electrophoresis gel band patterns are different for unmodified DNA and the two different BPDE-modified oligonucleotides because (1) the strand cleavage fragments bearing BPDE residues migrate slower than the corresponding fragments derived from the unmodified oligonucleotide and (2) strand cleavage tends to be inhibited on the 5'-sides of BPDE-modified guanines in the G+A, but not the G reaction.

Isolated tremor and disruption of the nigrostriatal dopaminergic system: an 18F-dopa PET study

We measured striatal 18F-dopa influx constants (Ki) for 20 patients with isolated, predominantly postural, tremor (eight familial, 12 sporadic) and 11 with predominantly rest tremor. Results were compared with 30 controls and 16 Parkinson's disease (PD) patients. The eight familial essential tremor (ET) patients had normal striatal 18F-dopa uptake. Two of the 12 sporadic postural tremor patients had subnormal putamen 18F-dopa Ki, one (who later became akinetic) falling in the PD range. The mean putamen 18F-dopa uptake of the 11 rest tremor patients was reduced to PD levels (51% of normal). Our findings argue against an association between ET and PD, but support the existence of a "benign" tremulous variant of PD. The presence of low-amplitude rest tremor, cogwheel rigidity, reduced arm swing, and short tremor duration was not a useful predictor of nigral dysfunction in patients with postural tremor. In contrast, patients with predominantly rest tremor, particularly with onset in the leg, consistently showed reduced putamen 18F-dopa uptake.

Influence of benzo[a]pyrene diol epoxide chirality on solution conformations of DNA covalent adducts: the (-)-trans-anti-[BP]G.C adduct structure and comparison with the (+)-trans-anti-[BP]G.C enantiomer

Benzo[a]pyrene (BP) is an environmental genotoxin, which, following metabolic activation to 7,8-diol 9,10-epoxide (BPDE) derivatives, forms covalent adducts with cellular DNA. A major fraction of adducts are derived from the binding of N2 of guanine to the C10 position of BPDE. The mutagenic and carcinogenic potentials of these adducts are strongly dependent on the chirality at the four asymmetric benzylic carbon atoms. We report below on the combined NMR-energy minimization refinement characterization of the solution conformation of (-)-trans-anti-[BP]G positioned opposite C and flanked by G.C base pairs in the d(C1-C2-A3-T4-C5-[BP]G6-C7-T8-A9-C10-C11).d(G12-G13-T14++ +-A15-G16-C17- G18-A19-T20-G21-G22) duplex. Two-dimensional NMR techniques were applied to assign the exchangeable and non-exchangeable protons of the benzo[a]pyrenyl moiety and the nucleic acid in the modified duplex. These results establish Watson-Crick base pair alignment at the [BP]G6.C17 modification site, as well as the flanking C5.G18 and C7.G16 pairs within a regular right-handed helix. The solution structure of the (-)-trans-anti-[BP]G.C 11-mer duplex has been determined by incorporating intramolecular and intermolecular proton-proton distances defined by lower and upper bounds deduced from NOE buildup curves as constraints in energy minimization computations. The BP ring spans both strands of the duplex in the minor groove and is directed toward the 3'-end of the modified strand in the refined structure. One face of the BP ring of [BP]G6 stacks over the C17 residue across from it on the partner strand while the other face is exposed to solvent.(ABSTRACT TRUNCATED AT 250 WORDS)

Solution conformation of the major adduct between the carcinogen (+)-anti-benzo[a]pyrene diol epoxide and DNA

We have synthesized, separated, and purified approximately 10 mg of a deoxyundecanucleotide duplex containing a single centrally positioned covalent adduct between (+)-anti-benzo[a]pyrene (BP) diol epoxide and the exocyclic amino group of guanosine. Excellent proton NMR spectra are observed for the (+)-trans-anti-BP diol epoxide-N2-dG adduct positioned opposite dC and flanked by G.C pairs in the d[C1-C2-A3-T4-C5-(BP)G6-C7-T8-A9-C10-C11].d[12- G13-T14-A15-G16-C17-G18-A19-T20-G 21-G22] duplex +ADdesignated (BP)G.C 11-mer+BD. We have determined the solution structure centered about the BP covalent adduct site in the (BP)G.C 11-mer duplex by incorporating intramolecular and intermolecular proton-proton distance bounds deduced from the NMR data sets as constraints in energy minimization computations. The BP ring is positioned in the minor groove and directed toward the 5' end of the modified strand. One face of the BP ring of (BP)G6 is stacked over the G18 and A19 sugar-phosphate backbone on the partner strand and the other face is exposed to solvent. A minimally perturbed B-DNA helix is observed for the d[T4-C5-(BP)G6-C7-T8].d[A15-G16-C17-G18-A19] segment centered about the adduct site with Watson-Crick alignment for both the (BP)G6.C17 pair and flanking G.C pairs. A widening of the minor groove at the adduct site is detected that accommodates the BP ring whose long axis makes an angle of approximately 45 degrees with the average direction of the DNA helix axis. Our study holds future promise for the characterization of other steroisomerically pure adducts of BP diol epoxides with DNA to elucidate the molecular basis of structure-activity relationships associated with the stereoisomer-dependent spectrum of mutational and carcinogenic activities.

Striatal D2 receptor status in patients with Parkinson's disease, striatonigral degeneration, and progressive supranuclear palsy, measured with 11C-raclopride and positron emission tomography

Equilibrium striatal: cerebellar 11C-raclopride (RAC) uptake ratios reflect the density of striatal dopamine D2 binding sites. Using positron emission tomographic scanning we have measured striatal RAC uptake in 6 untreated patients with Parkinson's disease (PD), 5 chronically treated patients with PD and a fluctuating response to L-dopa, 10 patients with striatonigral degeneration (SND), and 9 patients with progressive supranuclear palsy (PSP). Regional cerebral blood flow was determined also, with C15O2. Mean striatal: cerebellar RAC uptake was not significantly different from normal in untreated patients with PD, though 2 of these 6 patients showed significantly increased putamen tracer binding. Mean caudate and putamen: cerebellar RAC uptake ratios of the group with PD and a fluctuating response to L-dopa were significantly reduced by 30% and 18%, respectively. The patients with SND had lesser, but significant, 10% and 11% decreases in mean caudate and putamen: cerebellar RAC uptake ratios, respectively, whereas patients with PSP showed 24% and 9% reductions in caudate and putamen: cerebellar RAC binding. Striatal and frontal blood flow were significantly reduced in patients with PSP, but not in patients with PD or SND. In conclusion, striatal D2 binding potential is normal or raised in untreated patients with PD, but reduced in patients with PD and a fluctuating response to L-dopa. Patients with SND and PSP show a decrease in striatal RAC binding, but to a lesser extent than patients with PD and a fluctuating response to treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Spectroscopic characteristics and site I/site II classification of cis and trans benzo[a]pyrene diolepoxide enantiomer-guanosine adducts in oligonucleotides and polynucleotides

The highly tumorigenic isomer (+)-7,8-dihydroxy-anti-9, 10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene [(+)-anti-BPDE] and its non-tumorigenic enantiomer (-)-anti-BPDE are known to react predominantly with the exocyclic amino group (N2) of deoxyguanine in DNA and to form adducts of different conformations. The spectroscopic characteristics (UV absorbance, fluorescence and circular dichroism) of stereochemically defined (+)-trans, (-)-trans, (+)-cis and (-)-cis d(5'-CACATGBPDETACAC) adducts in the single-stranded form, or complexed with the complementary strand d(5'-GTGTACATGTG) in aqueous solution, were investigated. The spectroscopic characteristics of the double-stranded d(5'-CACATGBPDETACAC).d(5'-GTGTACATGTG) adducts can be interpreted in terms of two types of conformations. In site I-type conformations, there is an approximately 10 nm red shift in the absorption maxima, which is attributed to significant pyrenyl residue-base interactions; in site II-type adducts, the red shift is only approximately 2-3 nm, and the pyrene ring system is located at external, solvent-exposed binding sites. The spectroscopic characteristics of the BPDE-modified duplexes are of the site II type for the (+)- and (-)-trans, and of the site I type for the (+)- and (-)-cis adducts. In adducts derived from the binding of (+)-anti-BPDE to poly(dG-dC).(dG-dC) and poly(dG).(dC), the trans/cis BPDE-N2-dG adduct ratio is 6 +/- 1; in the case of (-)-anti-BPDE this ratio is only 0.4 +/- 0.1 and 0.6 +/- 0.15 in poly(dG-dC).(dG-dC) and poly(dG).(dC) respectively. The spectroscopic properties of these BPDE-modified polynucleotide adducts are consistent with those of the BPDE-modified oligonucleotide complexes; the cis adducts are correlated with site I adduct conformations, while the trans adducts are of the site II type. The correlations between adduct characteristics and biological activities of the two BPDE enantiomers are discussed.

Presynaptic and postsynaptic striatal dopaminergic function in neuroacanthocytosis: a positron emission tomographic study

Using [18F]dopa, [11C]raclopride, C15O2, and positron emission tomography, we have assessed striatal dopamine storage capacity, dopamine D2-receptor integrity, and regional cerebral blood flow, respectively, of 6 patients with neuroacanthocytosis. The patients with neurocanthocytosis all had chorea and variable combinations of seizures, dementia, axonal neuropathy, and orolingual self-multiation. [18F]dopa positron emmission tomographic findings were compared with 30 normal controls and 16 patients with sporadic, L-dopa-responsive, Parkinson's disease. Caudate and anterior putamen [18F]dopa uptake were normal in patients with neuroacanthocytosis, but mean posterior putamen [18F]dopa uptake was reduced to 42% of normal, similar to that in patients with Parkinson's disease. In patients with neuroacanthocytosis, mean equilibrium caudate: cerebellum and putamen: cerebellum [11C]raclopride uptake ratios were reduced to 54% and 62% of normal, compatible with a 65% and 53% loss of caudate and putamen D2-receptor-binding sites, respectively. Striatal and frontal blood flow was also depressed. The severe loss of D2-receptor-bearing striatal neuron, with concomitant loss of dopaminergic projections from the nigra to the posterior putamen, is consistent with both chorea and extrapyramidal rigidity being features of patients with neuroacanthocytosis.

Dependence of conformations of benzo[a]pyrene diol epoxide-DNA adducts derived from stereoisomers of different tumorigenicities on base sequence

The conformations of covalent adducts derived from the binding of the highly tumorigenic stereoisomer (+)-trans-7,8-dihydroxy-anti-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyren e [(+)-anti-BPDE] and its nontumorigenic (-)-anti-BPDE isomer with poly[(dG).(dC)], poly[(dG-dC).(dG-dC)], poly[(dT-dC).(dG-dA)], and poly[(dA-dC).(dG-dT)] were investigated by employing UV absorbance and linear dichroism methods. The degrees of orientation of the BPDE residues (bound covalently to N2 of deoxyguanosine), relative to the DNA bases, are most pronounced in the alternating and nonalternating (dG).(dC) polymers and decrease in polymers with neighboring dA.dT base pairs. The tumorigenic (+)-anti-BPDE isomer gives rise predominantly to external (solvent-exposed) site II adducts, while the (-)-enantiomer gives rise predominantly to site I adducts with significant carcinogen-nucleoside interactions. In the mixed (dA-dC).(dG-dT) and (dT-dC).(dG-dA) copolymers, the (+)-anti-BPDE isomer also binds predominantly to N2 of deoxyguanosine, but the adducts are weakly oriented with respect to the DNA bases. The incidence of site II adducts is considerably reduced as compared to the (dG).(dC) and (dG-dC).(dG-dC) polymers, and there is a greater proportion of site I adducts; the presence of a significant proportion of unordered adduct forms is also suggested from the diffuseness and broadness of the absorption spectra in the dA.dT base pair containing polymers. The preference of formation of site II adducts in dG-rich sequences in the case of the biologically highly active (+)-anti-BPDE isomer is discussed in terms of the known binding and mutation spectra.

Clinical and positron emission tomographic studies in the 'extrapyramidal syndrome' of dementia of the Alzheimer type

Extrapyramidal signs, particularly rigidity and tremor, have been reported in a proportion of patients with dementia of the Alzheimer type. To test the hypothesis that these extrapyramidal signs are similar clinically and neurochemically to the extrapyramidal signs of Parkinson's disease, a group of 20 patients satisfying clinical criteria for probable Alzheimer's disease were studied and assessed clinically for the presence of rigidity, tremor, and bradykinesia. In those patients with extrapyramidal signs, qualitative differences were observed between the signs in these patients and in subjects with Parkinson's disease. Fifteen of 20 patients underwent fluoro-18-dopa scans, which showed no significant difference in fluoro-18-dopa uptake into the caudate and putamen between normal subjects and the rigid and nonrigid patients with Alzheimer's disease, in contrast to the marked reduction in fluoro-18-dopa uptake into the putamen that is observed in Parkinson's disease. This provides clinical and in vivo neurochemical support for the hypothesis that extranigral factors may be involved in the pathogenesis of rigidity in Alzheimer's disease.

Differing patterns of striatal 18F-dopa uptake in Parkinson's disease, multiple system atrophy, and progressive supranuclear palsy

Using positron emission tomography (PET), we studied regional striatal 18F-dopa uptake in 16 patients with L-dopa-responsive Parkinson's disease (PD), 18 patients with multiple system atrophy, and 10 patients with progressive supranuclear palsy. Results were compared with those of 30 age-matched normal volunteers. The patients with PD showed significantly reduced mean uptake of 18F-dopa in the caudate and putamen compared to controls, but while function in the posterior part of the putamen was severely impaired (45% of normal), function in the anterior part of the putamen and in the caudate was relatively spared (62% and 84% of normal). Mean 18F-dopa uptake in the posterior putamen was depressed to similar levels in all patients. Unlike patients with PD, the patients with progressive supranuclear palsy showed equally severe impairment of mean 18F-dopa uptake in the anterior and posterior putamen. Caudate 18F-dopa uptake was also significantly lower in patients with progressive supranuclear palsy than in patients with PD, being depressed to the same level as that in the putamen. Mean 18F-dopa uptake values in the anterior putamen and caudate in patients with multiple system atrophy lay between PD and progressive supranuclear palsy levels. Locomotor disability of individual patients with PD or multiple system atrophy correlated with decline in striatal 18F-dopa uptake, but this was not the case for the patients with progressive supranuclear palsy. We conclude that patients with PD have selective nigral pathological features with relative preservation of the dopaminergic function in the anterior putamen and caudate, whereas there is progressively more extensive nigral involvement in multiple system atrophy and progressive supranuclear palsy.(ABSTRACT TRUNCATED AT 250 WORDS)

Preparation and isolation of adducts in high yield derived from the binding of two benzo[a]pyrene-7,8-dihydroxy-9,10-oxide stereoisomers to the oligonucleotide d(ATATGTATA)

The reaction of the (+)- and (-)-enantiomers of BDPE trans-7,8-dihydroxy-anti-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene) with the oligodeoxynucleotide d(ATATGTATA) in aqueous buffer solutions gives rise predominantly to trans and cis addition products at the exocyclic amino group of the single deoxyguanosine residue. The trans/cis ratios are 7:1 in the case of (+)-BPDE, and 2:1 in the case of (-)-BPDE, while the reaction yields correspond to 34 and 15% respectively, of modified strands. These relatively high reaction efficiencies, at least for this particular type of oligonucleotide sequence, offer the possibilities of synthesizing relatively large amounts of well-defined covalent BPDE-oligonucleotide adducts (with different sequences of nucleotides flanking the modified base) for detailed spectroscopic and biochemical studies.

Differences in conformations of covalent adducts derived from the binding of 5- and 6-methylchrysene diol epoxide stereoisomers to DNA

The conformations of adducts derived from the covalent binding of four different isomeric diol epoxide derivatives of 5- or 6-methylchrysene to native double-stranded calf thymus DNA were studied by linear dichroism techniques. Out of four isomers investigated here, only the R,S,S,R enantiomer of anti-1,2-dihydroxy-3,4-epoxy-1,2,3,4-tetrahydro-5-methylchrysene, (+)-5-MeCDE, is highly tumorigenic and mutagenic toward Salmonella typhimurium TA100; the S,R,R,S enantiomer, (-)-5-MeCDE, and the corresponding R,S,S,R and S,R,R,S enantiomers of anti-1,2,-dihydroxy-3,4-epoxy-1,2,3,4-tetrahydro-6-methylchrysene are non-tumorigenic and much less mutagenic than (+)-5-MeCDE. [Melikian et al., (1988) Cancer Res., 48, 1781-1787] Only the DNA adducts derived from the binding of (+)-5-MeCDE are characterized by a pronounced positive linear dichroism signal at 308 nm due to the phenanthrenyl residue which is tilted at an angle of 45-48 degrees with respect to the average orientations of the axes of unoriented DNA segments. The phenanthrenyl residues derived from the covalent binding to DNA of the other three inactive or less active isomers appear to be unoriented. The defined orientation of the covalently bound phenanthrenyl residues derived from (+)-5-MeCDE corresponds to adduct conformations which are similar to those obtained from the binding of the highly tumorigenic trans-7,8-dihydroxy-anti-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene stereoisomer and other highly active bay-region diol epoxide derivatives to DNA. These findings provide further evidence that there is a correlation between DNA adduct conformation and biological activities for these series of polycyclic aromatic diol epoxide derivatives with R,S,S,R absolute configuration and which are known to bind predominantly to N2 of guanine.

Linear dichroism properties and orientations of different ultraviolet transition moments of benzo[a]pyrene derivatives bound noncovalently and covalently to DNA

Linear dichroism and absorption methods are used to study the orientations of transition moments of absorption bands of polycyclic aromatic epoxide derivatives which overlap with those of the DNA band in the 240-300 nm region. Both the short and long axes of the pyrene residues of 1-oxiranylpyrene (1-OP) and the (+) and (-) enantiomers of trans-7,8-dihydroxy-anti-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BPDE) noncovalently bound to double-stranded native DNA are oriented approximately perpendicular to the axis of the DNA helix, consistent with intercalative modes of binding. The covalent binding of these three epoxide derivatives to DNA is accompanied by reorientations of both the short and long axes of the pyrene residues. Covalent adducts derived from the highly mutagenic (+)-anti-BPDE are characterized by tilts of the short axis within 35 degrees or less, and of the long axis by more than 60-80 degrees, with respect to the planes of the DNA bases. In the adducts derived from the binding of the less mutagenic (-)-anti-BPDE and 1-OP epoxide derivatives to DNA, the long axes of the pyrenyl rings are predominantly oriented within 25 degrees of the planes of the DNA bases; however, in the case of the (-) enantiomer of BPDE, there is significant heterogeneity of conformations. In the case of the 1-OP covalent DNA adducts, the short axis of the pyrene ring system is tilted away from the planes of the DNA bases, and the pyrene ring system is not intercalated between DNA base-pairs as in the noncovalent complexes. The stereochemical properties of the saturated 7,8,9,10-ring in BPDE, or the lack of the 7 and 8 carbon atoms in 1-OP, do not seem to affect noncovalent intercalative complex formation which, most likely, is influenced mainly by the flat pyrenyl residues. These structural features, however, strongly influence the conformations of the covalent adducts, which in turn may be responsible for the differences in the mutagenic activities of these molecules.

Interactions of the dimethyldiazaperopyrenium dication with nucleic acids. 2. Binding to double-stranded polynucleotides

The interactions of dimethyldiazaperopyrenium dication (1) with DNA have been studied by spectroscopic methods: absorption, static and dynamic fluorescence, and linear dichroism. 1 binds strongly to DNA at 250 mM NaCl, with a higher affinity for G-C pairs as compared to A-T pairs. The dye fluorescence is enhanced when it is bound to A-T pairs, whereas the emission is quenched in the vicinity of G-C pairs. Evidence for intercalation has been obtained via energy transfer and linear dichroism measurements.

Base-sequence dependence of noncovalent complex formation and reactivity of benzo[a]pyrene diol epoxide with polynucleotides

The base-sequence selectivity of the noncovalent binding of (+/-)-trans-7,8-dihydroxy-anti-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyr ene (BPDE) to a series of synthetic polynucleotides in aqueous solutions (5 mM sodium cacodylate buffer, 20 mM NaCl, pH 7.0, 22 degrees C) was investigated. The magnitude of a red-shifted absorbance at 353 nm, attributed to intercalative complex formation, was utilized to determine values of the association constant Kic. Intercalation in the alternating pyridine-purine polymers poly(dA-dT).(dA-dT) (Kic = 20,000 M-1), poly(dG-dC).(dG-dC) (4200 M-1), and poly(dA-dC).(dG-dT) (9600 M-1) is distinctly favored over intercalation in their nonalternating counterparts poly(dA).(dT) (780 M-1), poly(dG).(dC) (1800 M-1), and poly(dA-dG).(dT-dC) (5400 M-1). Methylation at the 5-position of cytosine gives rise to a significant enhancement of intercalative binding, and Kic is 22,000 M-1 in poly(dG-m5dG).(dG-m5dC). In a number of these polynucleotides, values of Kic for pyrene qualitatively follow those exhibited by BPDE, suggesting that the pyrenyl residue in BPDE is a primary factor in determining the extent of intercalation. Both BPDE and pyrene exhibit a distinct preference for intercalating within dA-dT and dG-m5dC sequences. The catalysis of the chemical reactions of BPDE (hydrolysis to tetrols and covalent adduct formation) is enhanced significantly in the presence of each of the polynucleotides studied, particularly in the dG-containing polymers. A model in which catalysis is mediated by physical complex formation accounts well for the experimentally observed enhancement in reaction rates of BPDE in the alternating polynucleotides; however, in the nonalternating polymers a different or more complex catalysis mechanism may be operative.(ABSTRACT TRUNCATED AT 250 WORDS)

Properties of covalent benzo[a]pyrene diol epoxide-DNA adducts investigated by fluorescence techniques

The spectroscopic absorption and fluorescence properties of adducts derived from the covalent binding of (+/-)trans-7,8-dihydroxy-anti-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyre ne (BPDE) to DNA are re-examined in view of conflicting interpretations regarding the conformations of these adducts which currently exist in the literature. The fluorescence decay profiles were accurately determined utilizing synchrotron-pulsed light source excitation and the time-correlated single photon counting technique. The conformational properties of the adducts were probed by determining their accessibilities to acrylamide, a known fluorescence quencher, and by comparing the accessibilities of the BPDE-DNA adducts with those of known model systems with intercalative, partially intercalative and minor groove binding conformations. In contrast to any of these model systems, the fluorescence of the aromatic pyrenyl residues in the covalent BPDE-DNA adducts exhibit significant sensitivity to acrylamide, suggesting that these residues are located at binding sites with significant solvent exposure. A quantitative analysis of the acrylamide fluorescence quenching according to a dynamic Stern-Volmer quenching model suggests the following characteristics: the major (65%) component (1.4 ns lifetime) is characterized by significant exposure to the solvent environment; the second component (6-7 ns lifetime) can be subdivided into a solvent-accessible and a solvent-inaccessible component, the inaccessible fraction being attributed to minor adducts, possibly with a quasi-intercalative conformation. The amplitude of the third, long-lived (200-ns) component is variable; it arises from the photochemical decomposition of the adducts which gives rise to tetraols (7,8,9,10-tetrahydro-tetrahydroxybenzo[a]pyrene). The variable content of these degradation products accounts for most discrepancies in the fluorescence properties of the covalent BPDE-DNA adducts previously reported.

Orientation and linear dichroism characteristics of porphyrin-DNA complexes

The linear dichroism spectra of complexes of tetrakis(N-methyl-4-pyridinio)prophine (H2TMpyP) and its zinc(II) derivative (ZnTMpyP) with DNA oriented in a flow gradient have been investigated. The dichroism of H2TMpyP determined within the Soret band and the Qy band system is consistent with an intercalative conformation in which the plane of the porphyrin ring system is nearly parallel to the planes of the DNA bases. In the case of ZnTMpyP on the other hand, the porphyrin ring system is inclined at angles of 62-67 degrees with respect to the axis of the DNA helix. The pyridyl groups in both cases are characterized by a low degree of orientation with respect to the axis of the helix. In contrast to H2TMpyP which does not significantly affect the degree of alignment of the DNA in the flow gradient, the binding of ZnTMpyP causes a significant decrease (about 50% for a base pair/ZnTMpyP ratio of 20) in the intrinsic dichroism at 260 nm due to the oriented DNA bases; the binding of ZnTMpyP to DNA either gives rise to regions of higher flexibility or causes bends or kinks at the binding sites. Increasing the ionic strength has little influence on the linear dichroism of the ZnTMpyP-DNA complexes, but the number of molecules bound at intercalation sites diminishes in the case of the H2TMpyP-DNA complexes; the accompanying changes in the linear dichroism characteristics suggest that external H2TMpyP complexes are formed at the expense of intercalation complexes.(ABSTRACT TRUNCATED AT 250 WORDS)

[Somatosensory evoked potentials in intraspinal tumors]

SEPs have been recorded in 15 patients with spinal cord tumors (mostly ependymomas) and in 5 patients with cord compression due to meningiomas (3 cas), neuromas (1 case) or neurosarcoma (1 cas). All the patients have been operated on so that precise informations were available on the histology and the location of the tumor. SEPs were monitored during surgery in 8 patients. The main conclusions of this study are as follows: There was a good correlation between the somatosensory troubles for touch, vibration sense and joint position sense, and SEPs abnormalities, however, SEPs may be clearly abnormal in the absence of any somatosensory deficit when the dorsal columns are compressed and not infiltrated by the tumor. In the latter situation the reverse dissociation (i.e., normal SEPs with somatosensory troubles) may be observed. The possibility of a dissociation between normal N11 and N13 cervical components and absent P14 far field components (non-cephalic reference) has been confirmed in 6 patients with cervicomedullary tumors. In 3 of them, this dissociation was found to be reversible and early SEPs returned to normal after surgery. Peroperative monitoring of scalp SEPs recorded with a non-cephalic reference electrode allowed the detection of transient SEP abnormalities related with a traction on the dorsal columns of the cord. SEP monitoring is recommended for any surgical removal of tumor that needs a posterior myelotomy.

The acute deafness of definite multiple sclerosis: BAEP patterns

Of 705 patients with or suspected of multiple sclerosis who underwent evoked potential recording during a 5 year period, 12 patients with definite multiple sclerosis experienced an acute hearing loss during a relapse of the demyelinating disease. Hearing loss was unilateral in all of the 12 cases but one; tinnitus was associated with hearing loss in 9 of the 12 patients. Deafness is an unfrequent symptom in the course of multiple sclerosis, being estimated to be no more than 3% in large series of multiple sclerosis. Brain-stem auditory evoked potentials were recorded in all 12 patients, during the relapse with acute hearing loss in 4 of them, after the relapse with hearing loss in the 8 others. During the relapse with hearing loss, BAEP abnormalities were present ipsilateral to the hearing loss in all 4 patients, wave I being absent in 2 of them. BAEPs were drastically improved when recorded after the relapse with hearing loss in 2 of the 3 patients in whom repeated records were made. BAEPs were abnormal on the side of the previous hearing loss in 5 out of the 8 patients recorded after the relapse with hearing loss. Clinical and BAEP data suggest that, in accordance with the anatomical organization of the auditory pathways, the lesion causing unilateral hearing loss in multiple sclerosis could be situated in the cochlear nerve or close to its entry zone in the brain-stem. However, dissociation between unilateral hearing loss and a normal peak I and I-III interval may occur.

Mechanisms of reaction of benzo(a)pyrene-7,8-diol-9,10-epoxide with DNA in aqueous solutions

The physical and chemical reaction pathways of the metabolite model compound benzo(a)pyrene-7,8-diol-9,10-epoxide (BPDE) in aqueous (double-stranded) DNA solutions was investigated as a function of temperature (0-30 degrees C), pH (7.0-9.5), sodium chloride concentration (0-1.5M) and DNA concentration in order to clarify the relationships between the multiple reaction mechanisms of this diol epoxide in the presence of nucleic acids. The reaction pathways are (1) noncovalent intercalative complex formation with DNA, characterized by the equilibrium constant K, and Xb the fraction of molecules physically bound; (2) accelerated hydrolysis of BPDE bound to DNA; (3) covalent binding to DNA; and (4) hydrolysis of free BPDE(kh). The DNA-induced hydrolysis of BPDE to tetraols and the covalent binding to DNA are parallel pseudo-first-order reactions. Following the rapid (millisecond time scale) noncovalent complex formation between BPDE and DNA, a much slower (approximately minutes) H+-dependent (either specific or general acid catalysis) formation of a DNA-bound triol carbonium ion (rate constant k3) occurs. At pH 7.0 the activation energy of k3 is 8.7 +/- 0.9 kcal/mol, which is lower than the activation energy of hydrolysis of free BPDE in buffer solution (14.2 +/- 0.7 kcal/mol), and which thus partially accounts for the acceleration of hydrolysis of BPDE upon complexation with DNA. The formation of the triol carbonium ion is followed by a rapid reaction with either water to form tetraols (rate constant kT), or covalent binding to DNA (kc). The fraction of BPDE molecules which undergo covalent binding is fcov approximately equal to kc/(kc + kT) = 0.10 and is independent of the overall BPDE reaction rate constant k = kh(1 - Xb) + k3Xb if Xb----1.0, or is independent of Xb as long as k3Xb much greater than kh(1 - Xb). Thus, at Xb = 0.9, fcov is independent of pH (7.0-9.5) even though k exhibits a 70-fold variation in this pH range and k----kh above pH 9 (k3 = kh). Similarly, fcov is independent of temperature (0-30 degrees C), while k varies by a factor of approx. 3. In the range of 0-1.5 M NaCl, fcov decreases from 0.10 to 0.04. These variations are attributed to a combination of salt-induced variations in the factors k3, Xb and the ratio kc/kT.

Conformations of adducts and kinetics of binding to DNA of the optically pure enantiomers of anti-benzo(a)pyrene diol epoxide

Kinetic flow dichroism studies indicate that the (+) enantiomer of 7 beta, 8 alpha-dihydroxy-9 alpha, 10 alpha-epoxy-7,8,9,10-tetrahydrobenzo(a)pyrene physically bound at intercalative-type sites in double-stranded DNA undergoes covalent binding reactions to form adducts at external binding sites. The conformation of the non-covalent complex derived from the (-) stereoisomer is also intercalative in nature, but the conformations of the covalent adducts are heterogeneous and are characterized by both intercalative-type and external conformations. It is suggested that the distinctly higher biological activity of the (+) enantiomer relative to the activity of the (-) enantiomer may be related to the preponderance of 7,8,9-triol benzo(a)pyrene residues covalently linked to deoxyguanine and located at external binding sites in the DNA adducts.

Stereoselective covalent binding of anti-benzo(a)pyrene diol epoxide to DNA conformation of enantiomer adducts

The conformation of adducts derived from the reactions and covalent binding of the (+) and (-) enantiomers of 7 beta, 8 alpha-dihydroxy-9 alpha, 10 alpha-epoxy-7,8,9,10-tetrahydrobenzo(a)pyrene (anti-BaPDE) with double-stranded calf thymus DNA in vitro were investigated utilizing the electric linear dichroism technique. The linear dichroism and absorption spectra of the covalent DNA complexes are interpreted in terms of a superposition of two types of binding sites. One of these conformations (site I) is a complex in which the plane of the pyrene residue is close to parallel (within 30 degrees) to the planes of the DNA bases (quasi-intercalation), while the other (site II) is an external binding site; this latter type of adduct is attributed to the covalent binding of anti-BaPDE to the exocyclic amino group of deoxyguanine (N2-dG), while site I adducts are attributed to the O6-deoxyguanine and N6-deoxyadenine adducts identified in the product analysis of P. Brookes and M.R. Osborne (Carcinogenesis (1982) 3, 1223-1226). Site II adducts are dominant (approximately 90% in the covalent complexes derived from the (+) enantiomer), but account for only 50 +/- 5% of the adducts in the case of the (-)-enantiomer. The orientation of site II complexes is different by 20 +/- 10 degrees in the adducts derived from the binding of the (+) and the (-) enantiomers to DNA, the long axis of the pyrene chromophore being oriented more parallel to the axis of the DNA helix in the case of the (+) enantiomer. These findings support the proposals by Brookes and Osborne that the difference in spatial orientation of the N2-dG adducts of (-)-anti-BaPDE together with their lower abundance may account for the lower biological activity of the (-) enantiomer. The external site II adducts, rather than site I adducts, appear to be correlated with the biological activity of these compounds.

Linear dichroism studies of conformations of carcinogen-DNA adducts application to covalent complexes derived from the reactions of the two enantiomers of 9,10-epoxy-9,10,11,12-tetrahydrobenzo(e)pyrene with DNA

The conformations of the adducts derived from the covalent binding of the two enantiomeric forms of 9,10-epoxy-9,10,11,12-tetrahydrobenzo(e)pyrene (BePE) with native DNA were investigated by the electric linear dichroism technique. Both enantiomers give rise to two major adducts, one of which appears to be a quasi-intercalative site (I) while the other one is an external binding site (II). While the overall linear dichroism spectra are similar, in the case of the (-) enantiomer there is a greater contribution of site II adducts. These results are markedly different from the ones obtained with the two enantiomers of anti-benzo(a)pyrene-7,8-diol-9,10-epoxide (BaPDE), where the (+) enantiomer gives rise almost exclusively to site II binding, while the (-) enantiomer gives rise to both site I and site II covalent binding. The differences in the heterogeneity of binding between BePE and anti-BaPDE enantiomers may be due to the absence of hydroxyl groups in BePE which, in the case of BaPDE, are an important factor in determining the stereoselective properties of the covalent binding to double-stranded DNA.

Noncovalent binding of 7 beta, 8 alpha-dihydroxy-9 alpha, 10 alpha-epoxytetrahydrobenzo[a]pyrene to deoxyribonucleic acid and its catalytic effect on the hydrolysis of the diol epoxide to tetrol

In the presence of native DNA the hydrolysis of benzo[a]pyrene-7,8-diol 9,10-epoxide (BPDE) to tetrols (BPT) is markedly accelerated (by a factor of up to approximately 80 at 25 degrees C, pH 7.0, in 5 mM sodium cacodylate buffer solution). When stopped-flow kinetic techniques are utilized, it is shown that the pseudo-first-order hydrolysis rate constant kH is smaller by a factor of approximately 3 in the presence of equivalent concentrations of denatured DNA, by a factor of 8-25 in the presence of nucleotides, and by a factor of 35-45 in the presence of nucleosides (depending on the nucleotide or nucleoside). In the presence of native DNa, kH increases with increasing DNA concentration and reaches a limiting value of kH = 0.684 +/- 0.04 s-1 at DNA concentrations in excess of approximately 5 x 10(-4) M (expressed in concentration of nucleotides). A kinetic model based on (1) rapid formation of a noncovalent BPDE-DNA complex followed by (2) slower hydrolysis of BPDE to BPT at these binding sites is consistent with the experimental data. It is shown furthermore that the DNA concentration dependence of kH and of noncovalent intercalative binding of BPDE to DNA is similar and that addition of magnesium ions (which is known to reduce intercalative binding of planar aromatic molecules to DNA) also reduces kH. These results suggest, but do not necessarily prove, that the DNA binding sites at which the hydrolysis of BPDE (to BPT) is catalyzed are intercalative in nature.

Application of fluorescence and linear dichroism techniques to the characterization of the covalent adducts derived from interaction of (+/-)-trans-9,10-dihydroxy-anti-11,12-epoxy-9,10,11,12-tetrahydro-benzo[e]pyrene with DNA

Spectroscopic techniques including absorption, fluorescence excitation and emission spectra, fluorescence decay profiles (determined by single photon counting techniques), and electric linear dichroism are applied to a study of the conformation of covalent adducts derived from a reaction of 9,10-dihydroxy-11,12-epoxy-9,10,11,12-tetrahydro[e]pyrene (B[e]PDE) with DNA. The characteristics of non-covalent adducts obtained from the intercalative binding of 9,10,11,12-tetrahydroxytetrahydrobenzo[e]pyrene (B[e]PT) (derived from the hydrolysis of B[e]PDE) with DNA are compared to those of the covalent B[e]PDE--DNA adducts. It is shown that there are two types of binding sites in B[e]PDE--DNA adducts: (1) an exterior binding site similar to the one observed with the isomeric 7,8-dihydroxy-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (B[a]PDE)--DNA adducts, and (2) a quasi-intercalative type of binding site in which the properties of the pyrene chromophore are similar to those of an intercalated pyrene moiety, but in which the red shift in the absorption maximum, and fluorescence quenching are less pronounced. This latter conformation is not observed in covalent B[a]PDE--DNA adducts. It is shown that the DNA concentration is an important parameter in determining the relative number of pyrene chromophores at these two binding sites. The extent of covalent binding of B[e]PDE is 4-8 times less than the binding of B[a]PDE to DNA under the same experimental conditions. The reduced reactivity of B[e]PDE is tentatively attributed to steric hindrance due to quasi-diaxial conformations of the two hydroxyl groups in one of the two bay-regions of B[e]PDE.

Spectroscopic characterizations and comparisons of the structures of the covalent adducts derived from the reactions of 7, 8-dihydroxy-7,8,9,10-tetrahydrobenzo [a] pyrene-9,10-oxide, and the 9, 10-epoxides of 7,8,9,10-tetrahydrobenzo [a] pyrene and 9.10,11,12-tetrahydrobenzo [e] pyrene with DNA

The conformation of covalent adducts derived from the reactions of racemic 7 beta,8 alpha-dihydroxy-9 alpha, 10 alpha-epoxy-7,8,9,10-tetrahydrobenzo [a] pyrene (BaPDE), 9,10-epoxy-7,8,9,10-tetrahydrobenzo [a] pyrene (BaPE), and 9,10-epoxy-9,10,11,12-tetrahydrobenzo [e] pyrene (BePE) with calf thymus DNA in aqueous buffer solution (25 degrees C, pH 7.0) were investigated and compared by means of absorption, fluorescence and electric linear dichroism techniques. Two types of conformations are recognized. Site I is characterized by a red shift (approximately 10 nm) in the absorption maximum of the pyrene nucleus, a significantly reduced fluorescence yield, and a negative electric linear dichroism signal (delta A); this site is presumed to involve a near-parallel (within 25 degrees) orientation of the planar pyrene residue with the planes of the DNA bases, and a relatively strong interaction between the phi electrons of the nucleic acid bases and the pyrene residue. In site II, there is only a small red-shift in the absorption maximum (approximately 2 nm), a non-zero fluorescence yield, and a positive delta A throughout the absorption region of the pyrene residue; in this conformation the pyrene residue is presumed to lie on the outside of the DNA molecule, possibly in one of the grooves. The BaPDE-DNA complex displays predominantly a site II-type conformation while the BaPE- and BePE-DNA complexes display both site I and site II adducts, with site I conformations predominating. The lack of hydroxyl groups in BaPE and BePE lead to a loss in stereospecificity in covalent adduct formation. The 7 and 8 hydroxyl groups in covalent adduct formation. The 7 and 8 hydroxyl groups in BaPDE appear to reduce the probability of formation of site I-type of covalent adducts, and appear to be, at least in part, responsible for the enantiomeric stereospecificity in the covalent reaction between BaPDE and DNA.