Acetaldehyde (AA), which is present in tobacco smoke, automobile exhaust gases and alcohol beverage, is a mutagen and carcinogen. AA reacts with 2′-deoxyguanosine (dG) in DNA to form N2-ethyl-dG ...(EtdG) and cyclic, 1, N2-propano-dG (CPrdG), which are considered to have a critical role in carcinogenesis induced by AA. In this study, we have developed a highly sensitive method for the quantitation of the two AA-derived DNA adducts by using liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS) in which hydrophilic interaction chromatography (HILIC) employing mobile phases of high organic solvent concentration was selected to improve the ionization efficiency in the ESI process. Fourteen times and 11 times larger peak areas for EtdG and CPrdG, respectively, in HILIC-ESI-MS/MS were obtained compared with those in reversed phase (RP)-LC-ESI-MS/MS. Furthermore, 6.9 times (for EtdG) and 2.4 times (for CPrdG) larger peak areas were also obtained as additional enhancement by varying additive compounds in the HILIC mobile phases from ammonium acetate to ammonium bicarbonate. In total, the enhancements in detected MS signal intensities by exchanging from the RP-LC system to the HILIC system are 97 times for EtdG and 26 times for CPrdG, respectively. Three commercially available HILIC columns with different polar functional groups were examined and sufficient separation between normal 2′-deoxynucleosides and the AA-derived DNA adducts was achieved by a carbamoyl-bonded HILIC column. Finally, we applied the established method to quantify EtdG and CPrdG in the damaged calf thymus DNA.
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•We developed a HILIC-MS/MS method for the acetaldehyde(AA)-derived DNA adducts.•The HILIC separation improved the sensitivity of the AA-derived DNA adducts.•The optimization of additive salts for mobile phase also improved the sensitivity.•The method was applied to the quantitation of the AA-derived DNA adducts in DNA.
The substrate selectivities of three endonucleases were studied quantitatively using capillary zone electrophoresis to find one giving N2-ethyl(Et)-2′-deoxyguanosine-5′-monophosphate (5′-dGMP) and ...cyclic 1,N2-propano(CPr)-5′-dGMP from DNAs damaged by acetaldehyde (AA). Six 2′-deoxyribonucleoside-5′-monophosphates to be quantified in the hydrolysis solutions of DNAs, namely, Et-5′-dGMP, CPr-5′-dGMP, and four authentic ones, were completely separated using a 100 mM borate running buffer solution having an optimized pH of 9.67. Using the present method, nuclease reactions of nuclease S1 (NS1), nuclease P1 (NP1), and nuclease Bal 31 to 2′-deoxyribonucleoside-5′-monophosphates from damaged Calf thymus (CT-) DNAs were monitored. The CT-DNAs were prepared by treatment with AA to generate Et-guanine or CPr-guanine internally. Bal 31 hydrolyzed the damaged CT-DNAs to yield Et-5′-dGMP and CPr-5′-dGMP quantitatively. The two 5′-dGMP adducts were not detected in the hydrolysis solutions using NS1 or NP1. Bal 31 can be a suitable nuclease for analyzing DNA damages caused by AA.
Scavenging of superoxide radical anion (O
) by tocopherols (TOH) and related compounds was investigated on the basis of cyclic voltammetry and in situ electrolytic electron spin resonance spectrum in
...,
-dimethylformamide (DMF) with the aid of density functional theory (DFT) calculations. Quasi-reversible dioxygen/O
redox was modified by the presence of TOH, suggesting that the electrogenerated O
was scavenged by α-, β-, γ-TOH through proton-coupled electron transfer (PCET), but not by δ-TOH. The reactivities of α-, β-, γ-, and δ-TOH toward O
characterized by the methyl group on the 6-chromanol ring was experimentally confirmed, where the methyl group promotes the PCET mechanism. Furthermore, comparative analyses using some related compounds suggested that the
-oxygen-atom in the 6-chromanol ring is required for a successful electron transfer (ET) to O
through the PCET. The electrochemical and DFT results in dehydrated DMF suggested that the PCET mechanism involves the preceding proton transfer (PT) forming a hydroperoxyl radical, followed by a PCET (intermolecular ET-PT). The O
scavenging by TOH proceeds efficiently along the PCET mechanism involving one ET and two PTs.
Formal redox potentials E°′ involving neutral species R and radical anions R•– in ionic liquids (ILs) composed of ammonium, pyridinium, and imidazolium cations are discussed from the point of view of ...the adiabatic electron affinity as a molecular property. The dependence of the 1,4-benzoquinone (BQ)/BQ•– redox process in CH2Cl2 and CH3CN is primarily investigated over a wide concentration range of ILs as the supporting electrolyte. A logarithmic relationship involving a positive shift of E°′ with increasing concentration is obtained when the concentration is changed from 0.01 to 1.0 M. The relationship of E°′ at IL concentrations greater than 1.0 M gradually reaches a plateau and remains there even for the neat ILs. It is found that the E°′ values in the neat ILs are not influenced by the measurement conditions, and that they remain considerably dependent on the nature and concentration of the electrolyte when measured using the traditional method involving molecular solvents combined with a supporting electrolyte (0.1–0.5 M). The difference in the E°′ values observed in the ammonium and pyridinium ILs is only several millivolts. In addition, ESR and self-consistent isodensity polarized continuum model calculation results reveal that the potential shift toward positive values upon the transition from molecular solvents containing ILs to neat ILs is adequately accounted for by changes in the electrostatic interaction of R•– taken into the cavity composed of the solvent and IL. On the other hand, the first reduction waves of quinones, electron-accepting molecules, and polynuclear aromatic hydrocarbons are reversibly or quasi-reversibly observed in the ILs. The electrochemical stability of the ILs is exploited in the facile measurement of these quasi-reversible waves at quite negative potentials, such as for the naphthalene (NP)/NP•– couple. Notably, the E°′ values obtained in the ammonium ILs correlate well with the calculated standard redox potentials and are linearly fitted with high correlation over all classes of compounds using a single regression equation based on Koopmans’ theorem.
It is known that pyruvate kinase in muscle (PKM), which is a rate-limiting glycolytic enzyme, has essential roles in the Warburg effect and that expression of cancer-dominant PKM2 is increased by ...polypyrimidine tract-binding protein 1 (PTBP1), which is a splicer of the PKM gene. In other words, PKM2 acts as a promoter of the Warburg effect. Previously, we demonstrated that the Warburg effect was partially established by down-regulation of several microRNAs (miRs) that bind to PTBP1 and that ectopic expression of these miRs suppressed the Warburg effect. In this study, we investigated the functions of miR-1 and -133b, which are well known as muscle-specific miRs, from the viewpoint of the Warburg effect in colorectal tumors. The expression levels of miR-1 and -133b were relatively high in colon tissue except muscle and very frequently down-regulated in 75 clinical colorectal tumors samples, even in adenomas, compared with those of the adjacent normal tissue samples. The ectopic expression of these miRs induced growth suppression and autophagic cell death through the switching of PKM isoform expression from PKM2 to PKM1 by silencing PTBP1 expression both in vitro and in vivo. Also, we showed that the resultant increase in the intracellular level of reactive oxygen species (ROS) was involved in this mechanism. Furthermore, PTBP1 was highly expressed in most of the 30 clinical colorectal tumor samples examined, even in adenomas. Our results suggested that PTBP1 and PTBP1-associated miR-1 and -133b are crucial molecules for the maintenance of the Warburg effect in colorectal tumors.
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•H2Q derivatives efficiently react with O2•− through the 2PCET mechanism.•Both methyl and chloro substituents promote the 2PCET.•The I effect is not associated with the promotion of ...2PCET.•The +R effect is the main driving force behind the promotion of PCET.
Improving energy conversion technologies is pivotal for reducing the effects of global warming. The use of electron transfer catalysts based on electron carriers found in organisms, such as redox biomimetic quinone systems, is a promising route for truly efficient energy conversion. Herein, we report the density functional theory (DFT)-based analysis of the reaction between electrogenerated superoxide radical anion (O2•−) and methyl- or chloro-substituted benzene-1,4-diol (hydroquinone) derivatives in N,N-dimethylformamide. We investigate the electrochemical scavenging of O2•− by hydroquinone derivatives involving two proton transfers (PTs) and one electron transfer (ET). We show that chloro and methyl substituents promote a proton-coupled electron transfer (PCET) reaction with the effect increasing with the number of substituent groups. Our DFT results demonstrate that the substituent effect promotes either of the PT or ET processes, along a sequential PCET pathway. The electrochemical and DFT analyses of the substituent effect indicate that the concerted two-proton-coupled electron transfer (2PCET) promoted by an increasing number of the substituents is a plausible pathway for the reaction between electrogenerated O2•− and hydroquinone derivatives. In addition, our findings show that the resonance effect is the main driving force for the promotion of 2PCET.
The reactivity of 5-(E)-2-(4-hydroxyphenyl)ethen-1-ylbenzene-1,3-diol (trans-resveratrol) and related compounds toward electrogenerated superoxide radical anion (O2 •–) were investigated using ...electrochemistry, in situ electrolytic electron spin resonance, and in situ electrolytic ultraviolet–visible spectral measurements, in N,N-dimethylformamide (DMF) with the aid of density functional theory (DFT) calculations. The quasi-reversible cyclic voltammogram of dioxygen/O2 •– was modified by the presence of trans-resveratrol, suggesting that the electrogenerated O2 •– was scavenged by trans-resveratrol through proton-coupled electron transfer (PCET) via three phenolic hydroxy groups (OH) on the stilbene moiety. The reactivity of trans-resveratrol toward O2 •– characterized by the OHs was experimentally confirmed in comparative analyses using some related compounds, pinosylvin, pterostilbene, p-coumaric acid, and so on, in DMF. The electrochemical and DFT results suggested that a concerted PCET mechanism via 4′OH of trans-resveratrol proceeds, where the coplanarity of the two phenolic rings in the stilbene moiety linked by an ethylene bridge is essential for a successful O2 •– scavenging.
Background: Changes in the plasma adenosine concentration and the effects on left ventricular (LV) function and remodeling in patients with acute myocardial infarction (AMI) remain unclear. Methods ...and Results: In 58 patients with AMI and 14 subjects without cardiac disease (controls), we measured the plasma adenosine concentration by LC-MS/MS. Blood samples were taken from the antecubital vein on days 0, 1, 7, and 14 after AMI, and from the controls on admission. Cardiac echocardiography was performed in the acute (within 7 days) and chronic (6 months) phases of AMI. There were no significant differences in the plasma adenosine concentrations among days 0 (211.5±150.2 nmol/L), 1 (192.7±141.3 nmol/L), 7 (218.8±154.1 nmol/L), and the controls (136.0±50.9 nmol/L). The plasma adenosine concentration increased significantly on day 14 (321.1±195.4 nmol/L) after AMI as compared with days 0, 1 and 7. AMI patients with a greater increase in the plasma adenosine concentration in the subacute phase showed an attenuation of LV dilation in the chronic phase. The plasma adenosine concentration in the acute phase did not affect the LV ejection fraction in the chronic phase. Conclusions: The plasma adenosine concentration significantly increased 14 days after AMI, which may contribute to attenuation of LV dilation in the chronic phase.
•12H2NQ and 14H2NQ scavenge electrogenerated O2•− forming H2O2 and NQ•− through a concerted two-proton-coupled electron transfer (2PCET) mechanism.•Generation of O2•− via electron transfer from NQ•− ...to O2 was electrochemically observed.•Along with O2•− scavenging through 2PCET and the subsequent O2•− generation, production of H2O2 from O2 is catalyzed by 12H2NQ and 14H2NQ.•The expanded π-conjugated plane on the naphthalene ring contributes to the redox catalysis between oxygen species and NQ.
We have carried out an electrochemical and theoretical study on the reactivity of 1,2-, 1,3-, and 1,4-dihydroxynaphthalenes (1nH2NQ, n = 2, 3, 4) toward electrogenerated superoxide radical anion (O2•−) in N,N-dimethylformamide. Cyclicvoltammetry and in situ electrolytic electron spin resonance measurements revealed that the quinone–hydroquinone π-conjugation plays an important role in a successful O2•− scavenging by 12H2NQ and 14H2NQ through proton-coupled electron transfer (PCET) reaction. The reactivities of 12H2NQ and 14H2NQ toward O2•− were mediated by the ortho- (catechol) or para-diphenol (hydroquinone) moieties, as experimentally confirmed in comparative analyses with catechol, hydroquinone, and 13H2NQ, aided by density functional theory (DFT) calculations. The electrochemical and DFT results suggested that a concerted PCET mechanism involving two-proton transfers and one-electron transfer proceeds, demonstrating a successful O2•− scavenging by 12H2NQ and 14H2NQ. Furthermore, a subsequent electron transfer between molecular dioxygen and product-naphthoquinone-radicals was observed, where O2•− was regenerated. The DFT analysis suggested that the spin distribution on the planar naphthalene ring embodies the superior kinetics of the PCET and the subsequent generation of O2•− from dioxygen demonstrated in the electrochemical results.
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