Computer simulation of ESR signals of liver paramagnetic centers

Changes of paramagnetic centres concentration characterized by g-factors values of 1.94, 2.2, and 2.03 in the rat liver were studied by ESR method under acute intoxication by diethylnitrosamine (DENA) and at preliminary threefold treatment of animals with butylhydroxytoluene (BHT). A protective effect of BHT can be explained by its stabilizing action of the membrane structures. A comparison has been carried out with a similar study of paramagnetic centres in the experiment of chronic intoxication by DENA. A simulation was performed of the liver tissue ESR spectra by means of special computer program. The parameters of simulated ESR spectra of the liver tissue with due regard for ESR signal g 2.03 corresponded to the parameters of the experimental spectra. Confirmations were obtained for the nature and number of paramagnetic centres in the liver tissue.     

Comparative study of the ESR spectra of normal and regenerating liver tissue in mice

Low temperature ESR spectra of gamma-irradiated samples of mouse liver regenerating after partial hepatectomy were studied. As compared to ESR spectra of gamma-irradiated samples of health animals liver, in regenerating liver samples new ESR signals from paramagnetic centres S(2.0005) and S(2.0025) were revealed; these signals were earlier recorded by the authors in gamma-irradiated samples of hepatoma 22a. It is concluded that the paramagnetic centres S(2.0005) and S(2.0025) are typical of proliferating tissues of different ethiology.     

Sensitivity of the electron spin resonance technique as applied in histochemical research on normal and pathological calcified tissues

Summary The electron spin resonance (ESR) technique is proposed as a microchemical and/or histochemical method in research on mineralized tissues.It has been described in previous papers that ionizing radiation evokes stable paramagnetic centres in the crystalline fraction of mineral constituents of calcified tissues. These centres were used as a label in studies on resorption and creeping substitution of bone grafts.In this paper the sensitivity of the method and its application for determination of the crystallinity of various mammalian tissues were described.It was shown that: a) three single Haversian systems (osteons) isolated from a ca. 100 m thick undecalcified section of human compact bone weighing around 10^–4 g could be measured by the ESR technique; b) the crystallinity of mineral constituents of normal and pathological calcified tissues could be estimated as the ratio of the concentration of stable paramagnetic centres to the total ash content.Comparative ESR measurements were performed on compact bone of various mammalian species, human enamel and dentin, as well as on ageing bovine cartilage and atherosclerotic human aortas.     

Localization of unpaired electrons in molecules of lysozyme substrate-inhibitors. I. N-acetylglucosamine]

Electron structure of N-acetylglucoseamine molecule and its ion-radicals has been studied by quantum-chemical methods CNDO2 and JNDO, and by ESR as well. N-acetyl group is shown to be the only electron acceptor group of AGA molecule. Phototransformations of paramagnetic centres are studied at different pH values.     

Role of particle coating in controlling skin damage photoinduced by titania nanoparticles

TiO₂ nanoparticles hazard is associated to their photocatalytic activity causing release of DNA damaging ROS (Reactive Oxygen Species), lipid peroxidation and skin damage. Various coatings have been proposed to minimize photocatalysis, while keeping the potential to block UV radiations. Uncoated and variously coated commercial nano-titania have been classified on the basis of UVB-induced lipoperoxidation of linoleic acid. A selection of the most and the least protective specimens was then examined by ESR (Electron Spin Resonance) to evidence the presence of surface paramagnetic centres and the release of ROS in aqueous suspensions (spin trapping). Paramagnetic centres and ROS were correlated with the extent of lipid peroxidation. When tested on porcine skin (mimicking the human one), titania acted as on linoleic acid. The combined use of lipid peroxidation of simple fatty acids with ESR analysis is here proposed as a possible screening tool for the evaluation of the potential toxicity of nano-titania in sunscreen preparations.     

Detection of new metabolic paramagnetic centers in the lung tissue by ESR method

An ESR signal with g = 2.0025 and delta H = 0.2 mT was recorded at 77 K in lung tissues of guinea-pigs, mouse and rats. The signal intensity changed in the lung tissues of animals exposed to some chemicals. A relationship between new paramagnetic centres and the lung surfactant system is suggested to exist.     

Spectroscopic characterization of the nickel and iron-sulphur clusters of hydrogenase from the purple photosynthetic bacterium Thiocapsa roseopersicina. 1. Electron spin resonance spectroscopy

The thermostable hydrogenase from Thiocapsa roseopersicina was examined by low-temperature ESR spectroscopy. Two types of signals were detected, from an oxidized iron-sulphur cluster and a nickel centre (Ni-A). In the oxidized protein additional signals were observed due to spin-spin interaction between the two paramagnetic centres. This interaction could be reversibly abolished by reduction to a redox potential below 105 mV. This implies that an additional redox centre is involved in the interaction, for which an Fe3+ ion is suggested. Reduction with hydrogen induced a second type of nickel ESR signal (Ni-C), corresponding to an intermediate redox state seen in other nickel hydrogenases. The Ni-C species was light-sensitive at cryogenic temperatures. At temperatures near to 4.2 K the Ni-C signal showed evidence of interaction with another paramagnetic centre, presumably a second iron-sulphur cluster. On reoxidation a signal due to a third Ni(III) species, Ni-B, increased in amplitude. These results establish that metal centres in the hydrogenase from T. roseopersicina are closely similar to those of the well-studied hydrogenase from Chromatium vinosum.     

Comparison of ESR1 Mutations in Tumor Tissue and Matched Plasma Samples from Metastatic Breast Cancer Patients

BACKGROUND: ESR1 mutation in circulating cell-free DNA (cfDNA) is emerging as a noninvasive biomarker of acquired resistance to endocrine therapy, but there is a paucity of data comparing the status of ESR1 gene in cfDNA with that in its corresponding tumor tissue. The objective of this study is to validate the degree of concordance of ESR1 mutations between plasma and tumor tissue. METHODS: ESR1 ligand-binding domain mutations Y537S, Y537N, Y537C, and D538G were analyzed using droplet digital PCR in 35 patients with metastatic breast cancer (MBC) (35 tumor tissue samples and 67 plasma samples). RESULTS: Of the 35 paired samples, 26 (74.3%) were concordant: one patient had detectable ESR1 mutations both plasma (ESR1 Y537S/Y537N) and tumor tissue (ESR1 Y537S/Y537C), and 25 had WT ESR1 alleles in both. Nine (25.7%) had discordance between the plasma and tissue results: five had mutations detected only in their tumor tissue (two Y537S, one Y537C, one D538G, and one Y537S/Y537N/D538G), and four had mutations detected only in their plasma (one Y537S, one Y537N, and two Y537S/Y537N/D538G). Furthermore, longitudinal plasma samples from 19 patients were used to assess changes in the presence of ESR1 mutations during treatment. Eleven patients had cfDNA ESR1 mutations over the course of treatment. A total of eight of 11 patients with MBC with cfDNA ESR1 mutations (72.7%) had the polyclonal mutations. CONCLUSION: We have shown the independent distribution of ESR1 mutations between plasma and tumor tissue in 35 patients with MBC.     

ESR imaging on a solid-tumor-bearing mouse using spin-labeled dextran

Imaging of a tumor with ESR was tried using two different types of spin probes, a low molecular weight spin probe, CPROXYL, and a polymer spin probe, TEMPO-DX. Spin probes were administered to a mouse bearing a solid tumor that was a transplanted Ehrlich's ascites carcinoma in the back, using two methods, conventional intraperitoneal injection and continuous intravenous injection with a micro-feeder. First, the accumulation of the probe was examined by X-band ESR. CPROXYL, which was administered to a mouse intraperitoneally, was exclusively retained in urine, showing that it was rapidly excreted into the bladder, while TEMPO-DX was absorbed from the peritoneal cavity with difficulty to the vessel. Using continuous intravenous injection, CPROXYL was also rapidly excreted, but it was confirmed that TEMPO-DX concentrated in tumor tissue because it has a long half-life in vivo. In addition, measurement of ESR imaging was done to measure the distribution of spin probes with continuous intravenous injection. The strongest spot of CPROXYL was observed on ESR images, showing the accumulation at the bladder, while the spot of TEMPO-DX was observed in the solid tumor of the back of the mouse. These results suggest that TEMPO-DX could stay much longer than a low molecular weight spin probe in vivo and concentrate at the tumor. TEMPO-DX may be useful for developing specific ESR imaging agents for tumor.     

Effect of temperature on the photoreduction of centres A and B in Photosystem I,and the kinetics of recombination

When spinach Photosystem I particles, frozen in the dark with ascorbate, are illuminated at low temperatures, one electron is transferred from P-700 to either iron-sulphur centre A or B. It was found that the proportion of centre A or B reduced depended on the temperature of illumination. At 25 K, reduction of centre A, as detected by ESR spectroscopy, was strongly preferred. At higher temperatures, at about 150K, there was an increased proportion of reduced centre B. Reduction of B was more strongly preferred in particles frozen in 50% glycerol. The kinetics of dark reoxidation of A^? and B^? at various temperatures were followed by observing the radical signal of P-700⁺, and also by periodically cooling to 25 K to measure the ESR spectra of the iron-sulphur centres. The recombination of A^? and P-700⁺ occurred at lower temperatures than that at of B^?; at 150–200 K, centre B was the more stable electron trap. Dark reoxidation of both centres was more rapid in samples that were illuminated at 25 K than in samples illuminated at 150–215 K. In no case was net electron transfer between centres A and B observed. Differences in g values of the ESR spectra in particles illuminated at 25 and 200 K indicate that the iron-sulphur centres are in altered conformational states. It is concluded firstly that, in the frozen state, the rates of dark electron transfer decrease in the sequence A^? → P-700⁺ > B^? → P-700⁺ > B^? → A; secondly, that when centres A or B are photoreduced, a temperature-dependent conformational change takes place which slows down the rate of recombination with P-700⁺.     

Studies on the conformational changes of metalloproteins induced by electrons in water-ethylene glycol solutions at low temperatures. III. Adrenal ferredoxin.

The reduction of adrenal ferredoxin (adrenodoxin) at low temperatures was investigated in order to separate local modifications of the active centre of the protein on its reduction, from the conformational transition which seems to accompany the change of the redox state of the irons; The ESR spectra of the states of the protein, where the reduced active centre is to be found by the "oxidized" conformation of the apoprotein, were obtained. The transition from the states of the protein to the state which occurs on its chemical reduction at room temperature was also investigated. The results of the work support the view that conformational changes in proteins (enzymes) which take place while they are functioning proceed after modifications of the active centres (change of the redox state, adsorption of a substrate, etc.), and are essentially caused by them. Adrenal ferredoxin was the third subject in our studies of the intermediate states of proteins which appear after reduction of their active centres by means of electrons trapped in water-ethylene glycol mixtures at the temperature of liquid nitrogen [1, 2]. In the reduced state, the active centre of the protein has an ESR signal with a g-factor of 1.94 [3, 4] which is convenient for our purposes.     

Supernarrow EPR spectrum of aqueous protein solutions, UV-irradiated at 77 K

The nature was studied of paramagnetic centres photoinduced in aqueous solutions of proteins, amino acids and peptides at 77 K, having a supernarrow ESR spectrum with the width 8 mkTl and g = 1.9988 +/- 0.0002. It has been shown that seized electrons localized in deep traps are responsible for this signal. It is suggested that these are metal ions whose nucleus magnetic moment equals zero.     

Effect of hyperbaric oxygenation on paramagnetic centers in the rabbit myocardium during experimental myocardial infarction

Changes in paramagnetic centres (PC) concentration in rabbit's myocardial muscle were studied under experimental myocardial infarction during 168 hours by means of ESR-spectroscopy. PC characterized by ESR signal with g = 3.0 was found. It was shown that hyperbaric oxygenation did not affect PC content in the infarction zone, and resulted in an increase of PC concentration with g = 1.94 and g = 2.0 in the intact myocardial zone.     

Effect of metronidazole and local irradiation of the tumor on paramagnetic metal complexes of the liver and tumor tissues

A study was made of changes in the intensity of the ESR signals in tissues of sarcoma-37 and liver of mice after radiation of the tumor, administration of metronidazole, and after the combined effect of the two factors. The most pronounced changes in the ESR signals were induced by metronidazole. An appreciable increase in the content of nitrosyl complexes in the tumor was noted after the combined effect of metronidazole and radiation which was indicative of the radiation-induced formation of a large number of metronidazole anion-radicals in the tumor.     

A study of free radicals in paraffin embedded and deparaffinized human heart muscle tissue using electron spin resonance (ESR)

Free radicals (spectroscopic splitting factor; g factor = 2.003-2.005) were investigated in formol-fixed, paraffin embedded heart-muscle tissue sections using electron spin resonance (ESR) spectra. Changes in signal amplitude, g factor and line width were registered during deparaffinization, chloroform-methanol extraction, vapour treatment and bromination. An attempt was made to identify the source of the ESR signals by a correlation between the signal amplitude and number of fluorescent and/or Sudan-black-positive granules counted in the tissue sections. An increase in signal amplitude, g value and line narrowing were characteristic of the ascorbyl radical after deparafinization in air. Vapour treatment revelated that the broader signal has lower g factor, a characteristic that is tentatively assigned to oxidized lipids. The bromination resistant minor fraction of free radical centres with small g factor might be associated with the pigment content of the samples.     

Photolysis of N-methyl and N-acetyl substituted amino acids

Summary Experiments on the production of free radicals in aqueous solutions of N-methyl and N-acetyl substituted amino acids by UV light are reported. The ESR spectra observed at 77 K show that the bond of the CH_3–group of these substances is ruptured to a great deal compared with other bond ruptures producing paramagnetic centres. But in N-methyl substituted amino acids the methyl radical is less predominant than in N-acetyl substituted ones. At temperatures higher than 200 K the ESR spectra of all substances studied in our experiments are similar. It is supposed that a radical is formed with an unpaired spin near an oxygen atom.A part of this paper was reported at a Congress in Freiburg i. Br. (Germany) organized by the Deutsche Gesellschaft für Biophysik, October 2–4, 1974.     

Synthesis, characterisation and structural studies of [Cu(dach)(μ-NCS)(NCS)]n and [Cu(dach)2(N3)]ClO4 (dach=1,4-diazacycloheptane)

A new singly bridging complex [Cu(dach)(μ-NCS)(NCS)]_n (dach=1,4-diazacycloheptane) has been synthesised and its crystal structure determined. There are many examples of double NCS bridged polymeric chains, but fewer singly bridged ones. IR, ESR and temperature variable magnetic studies are described but no magnetic interaction was found between the copper centres. [Cu(dach)₂(N₃)]ClO₄ has also been characterised by IR, ESR spectra and magnetic studies. The crystal structure determination shows that it is a penta-coordinated monomeric species with an axially coordinated azide linked to the perchlorate counterion by hydrogen bonding.     

ESR studies of molecular interactions of copper(II) nirvanol and copper(II) diisopropylsalicylate with Ehrlich ascites tumor cells

ESR spectra have been obtained after addition of either a cupric phenylhydantoin or a cupric diisopropylsalicylate complex to Ehrlich ascites tumor cells. It is shown that some of the complex remains in the cupric state. Because the ESR parameters of these complexes in the presence of cells differ from the ESR parameters for these complexes in the absence of cells, in the presence of cells either adducts or new cupric complexes are formed. The fast motion of these complexes, as determined from room temperature ESR spectra, is characteristic of complexes with molecular weights less than 1500.     

用ESR自旋捕集技术研究正常人和病人血清中的SOD活力

本文探讨了用ESR自旋捕集技术测定SOD活力的有关实验条件,并研究了正常人,疾病和恶性肿瘤病人血清中SOD活力的变化,发现恶性肿瘤病人血清SOD活力明显升高,某些疾病患者亦有升高,各组间有显著统计学差异.与化学发光法测定结果比较表明,ESR法测定SOD活力的特异性优于化学发光法.