Electronic effects in transition metal porphyrins. 10. Effect of ortho substituents on the temperature dependence of the NMR spectra of a series of spin-admixed perchloratoiron(III) tetrakis(2,6- or 2,4,6-phenyl substituted)porphyrinates

The perchloratoiron(III) complexes of a series of 2,6-disubstituted tetraphenylporphyrin ligands, where the 2,6-phenyl substituents were -H, -F, -Cl, -Br, or -OMe, as well as two 2,4,6-phenyl-substituted complexes, where the substituents were -Me and -OMe, have been investigated as a function of temperature by 1H NMR spectroscopy. Curvature in the 1/T dependence was evident in most cases. Forced linear extrapolation of the temperature dependence observed over the range of the study yielded Curie plots that include negative slopes with very large positive 1/T intercepts (Cl approximately Br > Me > H) to negative slope with near zero intercept (tri-OMe) to positive slope with very large negative intercept (F, di-OMe). The NMR results were combined with EPR spectroscopic data and curve-fitting procedures based on an expanded Curie law to arrive at a consistent overview of the variety of temperature-dependence behaviors observed. This overview relies upon the premise that, in addition to the ground state observed by EPR spectroscopy, one (or more) thermally accessible excited state(s) are populated to varying degrees over the temperature range of the NMR measurements. If only one excited state is considered, the analysis is consistent with the ground state being a largely intermediate-spin state (S = 3/2) for the majority of the complexes but a largely high-spin state (S = 5/2) for ((2,6-F2)4TPP)FeOClO3 and ((2,6-(OMe)2)4TPP)FeOClO3.

Quantitation of 1,N6-ethenoadenine in rat urine by immunoaffinity extraction combined with liquid chromatography/electrospray ionization mass spectrometry

A fast, highly specific analytical method was developed to quantify 1,N6-ethenoadenine (epsilonA) in urine of rats. epsilonA is a highly mutagenic DNA adduct generated by vinyl chloride (VC) exposures as well as endogenously from lipid peroxidation. epsilonA was concentrated through extraction from rat urine by immunoaffinity chromatography and quantitated by liquid chromatography/electrospray ionization mass spectrometry (LC/ESI-MS). The average epsilonA recovery by immunoaffinity extraction was 66%. The LC/ESI-MS selected-ion monitoring (SIM) of the response ratio of epsilonA to its isotopically labeled internal standard [15N5]epsilonA was linear (r2 = 0.999) and reproducible from 0.15 to 30 pmol/injection. The detection limit obtained in the routine analysis of urine of unexposed rats was 270 fmol/sample with a signal-to-noise ratio (S/N) 3:1. The concentration of endogenous epsilonA was determined to be 21.6 +/- 14.8 pmol/mL (3 rats). Following portal injection of chloroethylene oxide (CEO; the putative active metabolite of VC), the rate of epsilonA excretion in urine was greatest from 0 to 24 h, with approximately 90% of the CEO-induced epsilonA excreted. By 132 h, the excretion of epsilonA was similar to pretreatment amounts. The accuracy of the quantitation was 107 +/- 6% (n = 4), established by analyzing urine of an unexposed rat spiked with authentic epsilonA. These data indicate that the LC/ESI-MS with immunoaffinity extraction method is precise and accurate for epsilonA quantification. The measurement of epsilonA in urine provides a potential biomarker for exposure to chemicals and processes that form this adduct.

Usefulness of ST-segment elevation in lead III exceeding that of lead II for identifying the location of the totally occluded coronary artery in inferior wall myocardial infarction

The presence of ST-segment elevation in lead III exceeding that of lead II, particularly if combined with ST elevation in lead V1, proved to be a powerful marker for occlusion of the proximal or midportion of the right coronary artery. These findings helped to determine the extent of myocardium at risk in inferior wall myocardial infarction and may further guide the decision to administer thrombolytics.

Adenine adducts with diepoxybutane: isolation and analysis in exposed calf thymus DNA

1,3-Butadiene (BD) is a high-volume industrial chemical and a common environmental pollutant. Although BD is classified as a "probable human carcinogen", only limited evidence is available for its tumorigenic effects in occupationally exposed populations. Animal studies show a surprisingly high sensitivity of mice to the carcinogenic effects of BD compared to rats (approximately 10(3)-fold), making interspecies extrapolations difficult. Identification and quantitation of specific BD-induced DNA adducts are important for improving our understanding of the mechanisms of BD biological effects and for explaining the observed species differences. Covalent binding of BD to DNA is probably due to its two epoxy metabolites: 3,4-epoxy-1-butene (EB) and 1,2:3,4-diepoxybutane (DEB). Both EB and DEB are direct mutagens producing frameshift and point mutations at both A:T and G:C base pairs. DEB is 100 times more mutagenic than EB and is found in quantity only in tissues of the most sensitive species (mouse). This has led to the suggestion that the higher sensitivity of mice to BD could be due to greater exposure to DEB. The present work was initiated in order to isolate and structurally characterize DEB-induced adenine adducts. The adducts were formed by reacting DEB with free adenine (Ade), 2'-deoxyadenosine (2'-dAdo), and calf thymus DNA followed by HPLC separation and analysis of the products by UV spectrophotometry, electrospray ionization mass spectrometry, and nuclear magnetic resonance. The adenine reaction resulted in three products which were identified as N-3-, N-7-, and N-9-(2'-hydroxy-3',4'-epoxybut-1'-yl)adenine. These adducts underwent acid-catalyzed hydrolysis to their corresponding (2',3',4'-trihydroxybut-1'-yl)adenines upon heating or storage. The 2'-dAdo reaction with DEB followed by acid hydrolysis yielded a single adduct, N6-(2',3',4'-trihydroxybut-1'-yl)adenine (N6-DEB-Ade). N-3-DEB-Ade and N6-DEB-Ade were also found in hydrolysates of calf thymus DNA exposed to DEB. The amounts of N-3-DEB-Ade (13/10(3) normal Ade) and N6-DEB-Ade (5/10(3) normal Ade) were slightly lower than those of the corresponding EB-induced adducts in similar experiments, suggesting comparable reactivity of the two epoxy metabolites of BD toward adenine in DNA. The findings of this study provide a basis for future analyses of BD-induced adenyl DNA adducts in vitro and in vivo.

Compound I and Compound II Analogues from Porpholactones

The tetraaza macrocycles 2-oxa-3-oxotetramesitylporphine (|H(2) 1|) and 2-oxa-3-oxotetrakis(2,6-dichlorophenyl)porphine (|H(2) 2|) and the corresponding iron complexes (|Fe(III)(X) 1| and |Fe(III)(X) 2|; X= Cl(-), OH(-), or SO(3)CF(3)(-)) have been synthesized. These macrocycles are derived from porphyrins by transformation of one pyrrole ring to an oxazolone ring. The resulting lactone functionality serves to restrict but not completely block pi-conjugation around the periphery. These complexes thus share properties with both porphyrins and chlorins. The ferric and high-valent iron complexes have been characterized by a variety of spectroscopic techniques. The molecular structure of |Fe(III)(Cl) 2| has been obtained by X-ray crystallography and shows that the structural changes at the macrocycle periphery do not perturb the coordination sphere of iron relative to the corresponding porphyrin complexes. This is illustrated by the observation that Fe-O frequencies in the resonance Raman spectra of the porpholactone analogues of compounds I and II are not substantially different from those of porphyrins and by the axial appearance of the EPR signals of the high-spin ferric complexes. This is consistent with reports that the Fe=O unit of oxidized porphyrins and chlorins is relatively insensitive to alteration of macrocycle symmetry. Nevertheless, probes of properties of the porpholactone macrocycle ((1)H NMR, resonance Raman skeletal modes) show effects of the asymmetry induced by the oxazolone ring. On the basis of (1)H NMR, EPR, Mössbauer, and resonance Raman data, the singly occupied molecular orbital of oxoferryl porpholactone pi-cation radicals correlates with the a(1u) molecular orbital of porphyrins under D(4)(h)() symmetry. Moreover, the paramagnetic properties and the intramolecular exchange interaction of ferryl iron and the porpholactone pi-radical have been characterized by EPR and magnetic Mössbauer measurements and spin-Hamiltonian analyses. The values J(0) = 17 cm(-)(1) and J(0) = 11 cm(-)(1) obtained for the exchange coupling constants of the oxoferryl porpholactone pi-cation radical complexes |Fe(IV)=O 1|(+) and |Fe(IV)=O 2|(+), respectively, are among the lowest found for synthetic compound I analogues.

Role of O-acetyltransferase in activation of oxidised metabolites of the genotoxic environmental pollutant 1-nitropyrene

The genotoxic environmental contaminant 1-nitropyrene is metabolised in mammalian systems by pathways more complex than the straightforward nitroreduction which accounts for most of its biological activity in bacteria. In order to evaluate the role of O-acetyltransferase (OAT) activity in generation of genotoxic intermediates from 1-nitropyrene, the mutagenicity of the major primary oxidised metabolites of 1-nitropyrene was characterised in the Ames Salmonella typhimurium plate incorporation assay with strain TA98, and with variants of TA98 deficient (TA98/1,8-DNP6) or enhanced (YG1024) in O-acetyltransferase. 1-Nitropyren-3-ol was more mutagenic in the absence than in the presence of S9, while 1-nitropyren-4-ol, 1-nitropyren-6-ol and 1-nitropyren-8-ol required S9 for maximum expression of mutagenicity. 1-Nitropyren-4-ol (176 rev/nmol without S9, 467 rev/nmol with S9 in TA98) and 1-nitropyren-6-ol (13 rev/nmol without S9, 266 rev/nmol with S9 in TA98) were overall the most potent nitropyrenol isomers assayed. 1-Acetamidopyren-8-ol and 1-acetamidopyrene 4,5-quinone were only minimally active. 1-Acetamidopyren-3-ol exhibited direct-acting mutagenicity. 1-Acetamidopyren-6-ol, previously shown to be a major contributor to mutagenicity in the urines of rats dosed with 1-nitropyrene (Ball et al., 1984b), was confirmed as a potent (359 rev/nmol) S9-dependent mutagen. Both the direct-acting and the S9-dependent mutagenicity of all the compounds studied was enhanced in the OAT-overproducing strain and much diminished (though not always entirely lost) in the OAT-deficient strain, showing that OAT amplifies expression of the genotoxicity of these compounds. 1-Acetamidopyren-6-ol required both S9 and OAT activity in order to exhibit any mutagenicity; this finding strongly implicates N-hydroxylation followed by O-esterification, as opposed to further S9-catalyzed ring oxidation, as a major route of activation for urinary metabolites of 1-nitropyrene.

Influence of Meso Substituents on Electronic States of (Oxoferryl)porphyrin pi-Cation Radicals

A series of (oxoferryl)porphyrin pi-cation radicals generated from porphyrins substituted at the meso positions with highly electron-withdrawing aryl groups has been characterized: tetrakis-5,10,15,20-(2,6-dichlorophenyl)-, 5-(2-chloro-6-nitrophenyl)-10,15,20-tris(2,6-dichlorophenyl)-, and 5-(2,6-dinitrophenyl)-10,15,20-tris(2,6-dichlorophenyl)porphyrins (porphyrins 1-3, respectively). The physical-chemical properties of the oxidized complexes of 1-3 are compared to those of two (oxoferryl)porphyrin pi-cation radical complexes substituted with electron-releasing aryl groups: tetramesitylporphyrin (TMP) and 2-iodotetramesitylporphyrin (2-iodoTMP). While all of the complexes examined show close correspondance in a number of spectroscopic parameters, some significant differences were observed. In contrast to observations for the oxidized complexes of TMP and 2-iodoTMP, the resonance Raman marker bands nu(2) and nu(11), which are indicators of symmetry state of porphyrin pi-cation radicals of 1-3, do not show the expected downfrequency shifts for oxidation to compound I analogs in a(2u) symmetry states. The upfield hyperfine NMR shifts of the pyrrole beta-proton signals of the compound I analogs of 1-3 are much larger than those for TMP and 2-iodoTMP. These data may be explained by admixture of some a(1u) character into the ground state of radical cations of 1-3, consistent with the hypothesis that electron-withdrawing meso substituents lower the energy of the a(2u) molecular orbital, favoring an a(1u) admixture.

Lack of effect of thyroxine in patients with Graves' hyperthyroidism who are treated with an antithyroid drug

BACKGROUND

Antithyroid drugs are effective in patients with hyperthyroidism due to Graves' disease, but the rate of recurrence after treatment is high. In a recent Japanese study, adjunctive treatment with thyroxine (T4) was associated with a recurrence rate 20 times lower than that among patients who received only an antithyroid drug. If these results are confirmed, combined therapy with an antithyroid drug and T4 might become the treatment of choice for all patients with Graves' hyperthyroidism.

METHODS

We treated 111 patients (89 women and 22 men) who had Graves' hyperthyroidism. All patients initially received 40 mg of carbimazole daily for one month. Then one group received carbimazole alone for 17 months (52 patients), and the other group received carbimazole plus T4 for 17 months and T4 alone for 18 months (59 patients). In the carbimazole group, the dose was adjusted after one month to maintain a normal serum thyrotropin concentration. In the carbimazole-T4 group, the dose of carbimazole was not changed, but 100 micrograms of T4 per day was added to the regimen and the dose was adjusted to maintain an undetectable serum thyrotropin concentration (< 0.04 microU per milliliter).

RESULTS

At the time of our analysis, 53 of the 111 patients had completed at least 3 months of follow-up (median, 12 months) after carbimazole was withdrawn. Hyperthyroidism recurred in eight patients in each group after a mean (+/- SD) of 6 +/- 4 months in the carbimazole group and 7 +/- 4 months in the carbimazole-T4 group. There was no difference between the recurrence rates in the two groups, despite the fact that serum thyrotropin concentrations were undetectable in 73 percent of patients in the carbimazole-T4 group on at least 75 percent of their visits.

CONCLUSIONS

The administration of T4 to patients with Graves' disease during carbimazole treatment and after its withdrawal neither delays nor prevents the recurrence of hyperthyroidism.

Efficient reactivation of Xenopus erythrocyte nuclei in Xenopus egg extracts

Rapid genome replication is one of the hallmarks of the frog embryonic cell cycle. We report here that complete reactivation of quiescent somatic cell nuclei in Xenopus egg extracts depends on prior restructuring of the nuclear substrate and prior preparation of cytoplasmic extract with the highest capacity to initiate and sustain DNA synthesis. Nuclei from mature erythrocytes swell, replicate their DNA efficiently, and enter mitosis in frozen/thawed extracts prepared from activated Xenopus eggs, provided the nuclei are first treated with trypsin, heparin, and an extract prepared from unactivated, meiotically arrested, eggs. Optimal replicating extracts are prepared from large batches of unfertilized eggs that are synchronously activated into the cell cycle for 28 minutes (at 20 degrees C). Because the Xenopus cell cycle progresses so rapidly, extracts prepared just a few minutes before or after this time have substantially lower DNA synthetic capacities. At the optimal time and temperature, eggs have just reached the G1/S boundary of the first cell cycle. This fact was revealed by injecting and replicating an SV40 plasmid in intact unfertilized eggs as described previously. We estimate that under optimal conditions approximately 6.14 × 10(9) base pairs of DNA/per nucleus are synthesized in 30–40 minutes, a rate that rivals that observed in the zygotic nucleus. The findings reported here are one step in our long term effort to develop a new in vitro/in vivo approach to nuclear transplantation. Nuclear transplantation in amphibian embryos has been used to establish that the genomes of many types of differentiated somatic cells are pluripotent. But very few such nuclei have ever developed into advanced tadpoles or adult frogs, probably because somatic nuclei injected directly into activated eggs fail to reactivate quickly enough to avoid being damaged during first mitosis. We have already shown that unfertilized eggs can be injected prior to activation of the first cell cycle. Future experiments will reveal whether in vitro reactivated somatic cell nuclei transplanted into such eggs reliably reach advanced stages of development.

Synthesis of [4,5,6,8-(13)C4]guanine, a reagent for the production of internal standards of guanyl DNA adducts

Using readily available labeled compounds, [4,5,6,8-(13)C4]guanine was synthesized in high overall yield. Intermediates as well as the final product were characterized by 1H NMR, 13C NMR, and high resolution mass spectrometry. The labeled guanine was used to generate [13C4]-labeled analogs of the guanine adducts, N2,3-ethenoguanine and 7-(2-hydroxyethyl)guanine. The application of such adducts in isotope dilution mass spectrometry was illustrated with DNA samples from rats exposed to two different mutagenic compounds, vinyl chloride and ethylene oxide.