Estimation of relative biological effectiveness of tritium according to chromosome aberration frequency in human blood lymphocytes

The goal of this work was to determine the relative biological effectiveness (RBE) of tritium β-radiation according to the chromosome aberration frequency in the peripheral blood lymphocytes after in vitro and in vivo radiation exposures. The experimental RBE assessment of tritium β-radiation relative to ⁶⁰Co γ-radiation according to unstable chromosome aberration frequency in the peripheral blood lymphocytes under particular conditions is described. It has been demonstrated that tritium β-radiation is, in general, more effective in the dose range of up to 1 Gy, which is most pronounced at low doses. The RBE value of tritium β-radiation at minimum doses reached 2.2 and decreased at higher doses (1 Gy) to 1.25. The data on comparative analysis of the frequency of stable chromosome aberrations in the blood lymphocytes of professional nuclear workers (Sarov, Russia) after long-term chronic exposure to tritium β-radiation, as compared with γ-irradiation, are reported for the first time. The higher biological effectiveness of tritium β-radiation was demonstrated and was estimated as 2.5.     

The Presence of Aldehyde-Reacted Proteins in Normal and Multiple Sclerosis White Matter

The incorporation of tritium from NaB3H4 into the major protein components of myelin and the presence of weak fluorescence emission bands at wavelengths of approximately 440 and 500 nm from sodium dodecyl sulfate-solubilized, delipidated white matter are indicative of the presence of the products of aldehyde reactions with proteins. The incorporation of tritium from NaB3H4 into myelin proteins was confirmed by reaction with purified components of myelin basic protein or with lipophilin, a purified fraction of proteolipid protein. From the extent of tritium incorporation into the purified proteins, it is estimated that approximately 0.2 mol of tritium is incorporated/mol of myelin basic protein and approximately 0.4 mol of tritium/mol of proteolipid protein. There is approximately 50% greater incorporation of tritium into a more degraded, less positively charged form of the basic protein. The incorporation of tritium into normal and multiple sclerosis white matter was compared. There is a small but statistically significant difference in the percentage of the total counts incorporated into the major protein fractions for the two groups, with the multiple sclerosis samples showing a higher percentage of the counts in the Wolfgram protein and a lower percentage in the myelin basic protein compared with the normal samples.     

Possibility to study cell membrane topography using tritium planigraphy

The method of tritium planigraphy was adopted for the investigation of intact cells. Conditions for the incorporation of thermally activated tritium atoms in the erythrocytes are described. The accessibility of erythrocytes hemoglobin for tritium was compared to that of free hemoglobin. By comparing specific radioactivities of amino acids it was shown that the incorporation of the label into free hemoglobin was over 100 times higher than into that in erythrocytes. The cell membrane was highly tritiated. Thus the plasma membrane protects the cell inner regions from penetration of the hot tritium atoms. Tritium planigraphy can be used for studying the cell surface topography.     

Tritium release assay for oleic acid desaturation

The “tritium release” assay for the enzymic conversion of stearic acid into oleic acid introduced by Talamo and Bloch in 1969 (1) represented a major advance in the measurement of enzymic fatty acid desaturation. By measuring the release of tritium from the 9- and 10-positions of erythro-[9,10³H₂]stearic acid into water instead of isolating the oleic acid chromatographically, the processing time can be reduced from about 2–3 hr to 5–10 min per assay. Recently, Johnson and Gurr (2) showed that the release of tritium does not represent an absolute measure of enzymic activity due to a primary kinetic isotope effect discriminating against tritium. In that paper we recorded the magnitude of the isotope effect, described the synthesis and use of threo-[9,10³H₂]stearic acid, which increases the sensitivity of the assay, and demonstrated that release of tritium from this substrate was proportional to the formation of oleic acid.     

Arabidopsis thaliana plants possess a specific farnesylcysteine lyase that is involved in detoxification and recycling of farnesylcysteine

In plants, prenylated proteins are involved in actin organization, calcium-mediated signal transduction, and many other biological processes. Arabidopsis thaliana mutants lacking functional protein prenyltransferase genes have also revealed roles for prenylated proteins in phytohormone signaling and meristem development. However, to date, the turnover of prenylated plant proteins and the fate of the prenylcysteine (PC) residue have not been described. We have detected an enzyme activity in Arabidopsis plants that metabolizes farnesylcysteine (FC) to farnesal, which is subsequently reduced to farnesol. Unlike its mammalian ortholog, Arabidopsis FC lyase exhibits specificity for FC over geranylgeranylcysteine (GGC), and recognizes N-acetyl-FC (AFC). FC lyase is encoded by a gene on chromosome 5 of the Arabidopsis genome (FCLY, At5g63910) and is ubiquitously expressed in Arabidopsis tissues and organs. Furthermore, T-DNA insertions into the FCLY gene cause significant decreases in FC lyase activity and an enhanced response to abscisic acid (ABA) in seed germination assays. The effects of FCLY mutations on ABA sensitivity are even greater in the presence of exogenous FC. These data suggest that plants possess a specific FC detoxification and recycling pathway.     

Estimated yield of double-strand breaks from internal exposure to tritium

Internal exposure to tritium may result in DNA lesions. Of those, DNA double-strand breaks (DSBs) are believed to be important. However, experimental and computational data of DSBs induction by tritium are very limited. In this study, microdosimetric characteristics of uniformly distributed tritium were determined in dimensions of critical significance in DNA DSBs. Those characteristics were used to identify other particles comparable to tritium in terms of microscopic energy deposition. The yield of DSBs could be strongly dependent on biological systems and cellular environments. After reviewing theoretically predicted and experimentally determined DSB yields available in the literature for low-energy electrons and high-energy protons of comparable microdosimetric characteristics to tritium in the dimensions relevant to DSBs, it is estimated that the average DSB yields of 2.7 × 10(-11), 0.93 × 10(-11), 2.4 × 10(-11) and 1.6 × 10(-11) DSBs Gy(-1) Da(-1) could be reasonable estimates for tritium in plasmid DNAs, yeast cells, Chinese hamster V79 cells and human fibroblasts, respectively. If a biological system is not specified, the DSB yield from tritium exposure can be estimated as (2.3 ± 0.7) × 10(-11) DSBs Gy(-1) Da(-1), which is a simple average over experimentally determined yields of DSBs for low-energy electrons in various biological systems without considerations of variations caused by different techniques used and obvious differences among different biological systems where the DSB yield was measured.     

Coordination of cell proliferation and cell fate decisions in the angiosperm shoot apical meristem.

A unique feature of flowering plants is their ability to produce organs continuously, for hundreds of years in some species, from actively growing tips called apical meristems. All plants possess at least one form of apical meristem, whose cells are functionally analogous to animal stem cells because they can generate specialized organs and tissues. The shoot apical meristem of angiosperm plants acts as a continuous source of pluripotent stem cells, whose descendents become incorporated into organ primordia and acquire different fates. Recent studies are unveiling some of the molecular pathways that specify stem cell fate in the center of the shoot apical meristem, that confer organ founder cell fate on the periphery, and that connect meristem patterning elements with events at the cellular level. The results are providing important insights into the mechanisms through which shoot apical meristems integrate cell fate decisions with cellular proliferation and global regulation of growth and development.     

Arsenic transformations in the soil-rhizosphere-plant system: fundamentals and potential application to phytoremediation

This paper reviews major processes that potentially affect the fate of arsenic in the rhizosphere of plants. Rhizosphere interactions are deemed to play a key role in controlling bioavailability to crop plants and for a better understanding and improvement of phytoremediation technologies. Substantial progress has been made towards an understanding of As transformation processes in soils. However, virtually no information is available that directly addresses the fate of As in the rhizosphere. We are proposing a conceptual model of the fate of As in the soil-rhizosphere-plant system by integrating the state-of-the art knowledge available in the contributing disciplines. Using this model and recent studies on hyperaccumulation of As, we discuss research needs and the potential application of rhizosphere processes to the development of phytoremediation technologies for As-polluted soils.     

The current and future applications of microorganism in the bioremediation of cyanide contamination

Inorganic cyanide and nitrile compounds are distributed widely in the environment, chiefly as a result of anthropogenic activity but also through cyanide synthesis by a range of organisms including higher plants, fungi and bacteria. The major source of cyanide in soil and water is through the discharge of effluents containing a variety of inorganic cyanide and nitriles. Here the fate of cyanide compounds in soil and water is reviewed, identifying those factors that affect their persistence and which determine whether they are amenable to biological degradation. The exploitation of cyanides by a variety of taxa, as a mechanism to avoid predation or to inhibit competitors has led to the evolution in many organisms of enzymes that catalyse degradation of a range of cyanide compounds. Microorganisms expressing pathways involved in cyanide degradation are briefly reviewed and the current applications of bacteria and fungi in the biodegradation of cyanide contamination in the field are discussed. Finally, recent advances that offer an insight into the potential of microbial systems for the bioremediation of cyanide compounds under a range of environmental conditions are identified, and the future potential of these technologies for the treatment of cyanide pollution is discussed.     

Base analysis of ribopolynucleotides by tritium incorporation following analytical polyacrylamide gel electrophoresis

A procedure is described for tritium base composition analysis of major and modified constituents of 4S RNA following extraction of the RNA from analytical slab gels. Gel electrophoresis and isolation of RNA are shown not to lead to chemical alterations of RNA bases, degradation or preferential losses of RNA species.     

Relative biological effectiveness of tritium oxide based on nucleic acid metabolic indices

Relative biological effectiveness (RBE) of tritium oxide, as compared to gamma-rays (137Cs), with regard to LD50/30 is 2,32 +/- 0,69 for rats. The RBE coefficients for tritium oxide are obtained with regard to some indices of nucleic acid metabolism in the thymus and spleen during the dose formation (0-14 days). The RBE of tritium oxide increases with a decrease in radiation dose as determined according to the concentration and content of DNA per organ and activity of thymus DNAases.     

Incorporation of Tritium from Thymidine-methyl-H3 into DNA,RNA, Lipids and Protein in Logarithmic and Stationary Phase Tetrahymena pyriformis,Strain W*

SYNOPSIS. Numerous reports may be found in the literature on cytoplasmic and non-DNA utilization of tritium from H³-thymidine. Such reports underscore the need to clarify the metabolic fate of H³-thymidine. This investigation outlines the fate of thymidinemethyl-H³ (TMH³) in logarithmic phase and stationary phase Tetrahymena pyriformis, strain W. Isotope identification by liquid scintillation spectrometry in chemically derived fractions of log phase cultures grown thruout the initial 48 hours of population growth with TMH³ revealed the majority of the radioactivity (90% of intracellular recovery) to be in the DNA fraction. The remainder of the intracellular label was recovered in the acid soluble fraction, lipid fraction, and a small amount in the RNA and cell residue. On chromatographs, tritium appeared only in the thymine moiety of the nucleic acid derivatives. Hence in dividing cells, thymidine-methyl-H³ is “essentially” specific for DNA at the dosage used although some incorporation into other compounds was detected. Fractionation of the lipid extract from the above experiment on a florisil column localized most of the label to the triglyceride and phospholipid fractions with some recovery in the cholesterol-esters. Similar scintillation counting of the various fractions of early stationary phase cells incubated for the last 48 hours of culture with TMH³ revealed limited tritium distribution in all fractions.     

Plant stem cell niches

Stem cells are required to support the indeterminate growth style of plants. Meristems are a plants stem cell niches that foster stem cell survival and the production of descendants destined for differentiation. In shoot meristems, stem cell fate is decided at the populational level. The size of the stem cell domain at the meristem tip depends on signals that are exchanged with cells of the organizing centre underneath. In root meristems, individual stem cells are controlled by direct interaction with cells of the quiescent centre that lie in the immediate neighbourhood. Analysis of the interactions and signaling processes in the stem cell niches has delivered some insights into the molecules that are involved and revealed that the two major niches for plant stem cells are more similar than anticipated.     

Transport and fate of microplastics in wastewater treatment plants: implications to environmental health

Global studies of microplastic (MP) pollution confirm wastewater treatment plants serve as pathways for microplastics entering terrestrial and aquatic ecosystems. The behaviour, transport and fate of microplastics in wastewater effluents remain mostly unknown, rendering wastewater-derived microplastics as a contaminant of significant concern. We critically examine the literature to understand the sources and fate of microplastics in wastewater treatment plants (WWTPs) and the implications of treated effluents admitted to soil and aquatic systems. The transport of chemical and biological contaminants is also discussed in detail, using fundamental principles of vector relationships. For the removal and reduction of microplastics, profound knowledge is required from source to solution. This review presents a comprehensive overview of the significance of microplastics as a vector of water-borne contaminants in WWTPs.     

Solid phase catalytic hydrogen isotope exchange in dalargin

A [3H]Dalargin preparation with a molar radioactivity of 52 Ci/mmol was obtained by the high temperature solid-state catalytic isotope exchange (HSCIE) of tritium for hydrogen at 150 degrees C. This tritium-labeled peptide was shown to completely retain its biological activity in the test of binding to opioid receptors from rat brain. The dissociation constant of the Dalargin-opioid receptor complex was found to be 4.3 nM. The dependencies of the chemical yield and the molar radioactivity on the reaction time and temperature of HSCIE were determined. The activation energy of the HSCIE reaction for the peptide was calculated to be 32 kcal/mol. The amino acid analysis showed that tritium is distributed between all the amino acid residues of [3H]Dalargin at the HSCIE reaction, with the temperature growth significantly increasing the total tritium incorporation and, especially, enhancing the radioactivity incorporation into aromatic residues.     

Synthesis and activity of 2-[4-(4-[3H]-2-cyanophenyl)piperazinyl]-N-(2,4,6-[3H]3-3-methylphenyl)acetamide: a selective dopamine D4 receptor agonist and radioligand

The first selective dopamine D4 agonist radioligand is described. The synthesis of these piperazine radioligands relied on the transformation of brominated precursors 4a and 4b with tritium gas in the presence of a sensitive cyano functional group. The specific activity of these two radioligands was measured and [3H]6b found to be suitable for use in D4 saturation and competition binding studies. The synthesis, biological, and radioactivity of this new agonist radioligand as well as preliminary SAR will be discussed.     

Brief Report: Differential oxidations of estradiol-17β by the chimpanzee in vivo

The metabolism of estradiol-17β is primarily an oxidative process at either carbon-2 or carbon-16 in the human. The objective of this study was to determine the relative importance of these two oxygenation pathways in the chimpanzee. The rate of oxidation of estradiol-17β at each position was determined by measuring the release of tritium into body water from carbon-2 or carbon-16. [2-³H]-Estradiol-17β or [16-³H]-estradiol-17β was injected intravenously into three adult male chimpanzees, and blood samples were obtained at several time intervals between 1 and 48 hr. The blood was lyophilized, and the release of tritium from the specifically labeled estrogens into the body fluid pool was determined. The release of tritium from the 16α-position was very low and did not exceed 3% in any animal. The release of tritium from the carbon-2 was much faster, amounting to 29%, 34%, and 35%, respectively, by 24 hr. The ratio of tritium released from carbon-2:carbon-16 was 5.0, 13.2 and 16.9, respectively, at 24 hr after injection of the specifically labeled estradiol-17β. These results demonstrate clearly that the major pathway for oxidative metabolism of estradiol-17β in the chimpanzee is via oxygenation at carbon-2, with the formation of catechol estrogens, as in the human.     

The solid-state catalytic isotope exchange of hydrogen in dalargin

A [³H]Dalargin preparation with a molar radioactivity of 52 Ci/mmol was obtained by the high temperature solid-state catalytic isotope exchange (HSCIE) of tritium for hydrogen at 150°C. This tritium-labeled peptide was shown to completely retain its biological activity in the test of binding to opioid receptors from rat brain. The dissociation constant of the Dalargin-opioid receptor complex was found to be 4.3 nM. The dependences of the chemical yield and the molar radioactivity on the reaction time and temperature of HSCIE were determined. The activation energy of the HSCIE reaction for the peptide was calculated to be 32 kcal/mol. The amino acid analysis showed that tritium is distributed between all the amino acid residues of [³H]Dalargin at the HSCIE reaction, with the temperature growth significantly increasing the total tritium incorporation and, especially, enhancing the radioactivity incorporation into aromatic residues.