Deuterium-depletion has no significant impact on the mutation rate of Escherichia coli, deuterium abundance therefore has a probabilistic, not deterministic effect on spontaneous mutagenesis

Deuterium (D), the second most abundant isotope of hydrogen is present in natural waters at an approximate concentration of 145-155 ppm (ca. 1.5E-4 atom/atom). D is known to influence various biological processes due to its physical and chemical properties, which significantly differ from those of hydrogen. For example, increasing D-concentration to >1000-fold above its natural abundance has been shown to increase the frequency of genetic mutations in several species. An interesting deterministic hypothesis, formulated with the intent of explaining the mechanism of D-mutagenicity is based on the calculation that the theoretical probability of base pairs to comprise two adjacent D-bridges instead of H-bridges is 2.3E-8, which is equal to the mutation rate of certain species. To experimentally challenge this hypothesis, and to infer the mutagenicity of D present at natural concentrations, we investigated the effect of a nearly 100-fold reduction of D concentration on the bacterial mutation rate. Using fluctuation tests, we measured the mutation rate of three Escherichia coli genes (cycA, ackA and galK) in media containing D at either <2 ppm or 150 ppm concentrations. Out of 15 pair-wise fluctuation analyses, nine indicated a significant decrease, while three marked the significant increase of the mutation/culture value upon D-depletion. Overall, growth in D-depleted minimal medium led to a geometric mean of 0.663-fold (95% confidence interval: 0.483-0.911) change in the mutation rate. This falls nowhere near the expected 10,000-fold reduction, indicating that in our bacterial systems, the effect of D abundance on the formation of point mutations is not deterministic. In addition, the combined results did not display a statistically significant change in the mutation/culture value, the mutation rate or the mutant frequency upon D-depletion. The potential mutagenic effect of D present at natural concentrations on E. coli is therefore below the limit of detection using the indicated methods.

Deuterium content of water increases depression susceptibility: the potential role of a serotonin-related mechanism

Environmental factors can significantly affect disease prevalence, including neuropsychiatric disorders such as depression. The ratio of deuterium to protium in water shows substantial geographical variation, which could affect disease susceptibility. Thus the link between deuterium content of water and depression was investigated, both epidemiologically, and in a mouse model of chronic mild stress. We performed a correlation analysis between deuterium content of tap water and rates of depression in regions of the USA. Next, we used a 10-day chronic stress paradigm to test whether 2-week deuterium-depleted water treatment (91 ppm) affects depressive-like behavior and hippocampal SERT. The effect of deuterium-depletion on sleep electrophysiology was also evaluated in naïve mice. There was a geographic correlation between a content of deuterium and the prevalence of depression across the USA. In the chronic stress model, depressive-like features were reduced in mice fed with deuterium-depleted water, and SERT expression was decreased in mice treated with deuterium-treated water compared with regular water. Five days of predator stress also suppressed proliferation in the dentate gyrus; this effect was attenuated in mice fed with deuterium-depleted water. Finally, in naïve mice, deuterium-depleted water treatment increased EEG indices of wakefulness, and decreased duration of REM sleep, phenomena that have been shown to result from the administration of selective serotonin reuptake inhibitors (SSRI). Our data suggest that the deuterium content of water may influence the incidence of affective disorder-related pathophysiology and major depression, which might be mediated by the serotoninergic mechanisms.

8-Hydroxydeoxyguanosine formation at the 5' site of 5'-GG-3' sequences in double-stranded DNA by UV radiation with riboflavin

DNA damage caused by UV radiation in the presence of riboflavin or hematoporphyrin was characterized by the DNA sequencing technique using 32P-labeled DNA fragments and the analysis of 8-hydroxydeoxyguanosine (8-OH-dG) formation in calf thymus DNA. Exposure of double-stranded DNA to 365 or 302 nm radiation in the presence of riboflavin induced the sequence-specific DNA cleavage which is different from that caused by 302 or 254 nm irradiation in the absence of a sensitizer. The specific cleavage sites were the guanine residues located 5' to guanine. On the other hand, when denatured single-stranded DNA was irradiated at 365 nm with riboflavin or hematoporphyrin, cleavages occurred at most guanine residues. With D2O, the sequence-specific damage of double-stranded DNA by riboflavin was not enhanced, whereas the damage to single-stranded DNA by hematoporphyrin was greatly enhanced. Photodynamic action of riboflavin caused the formation of 8-OH-dG in double-stranded DNA. The enhancing effect of D2O on 8-OH-dG formation was not observed with riboflavin. By contrast, hematoporphyrin plus 365-nm light induced the 8-OH-dG formation only in denatured single-stranded DNA and the 8-OH-dG yield was increased about 2-fold in D2O. ESR spin destruction experiments suggested that photoexcited riboflavin reacts with dGMP to produce riboflavin anion radical and guanine cation radical, but not with other mononucleotides. The estimated ratio of 8-OH-dG yield to total guanine loss indicates that the photoexcited riboflavin induces 8-OH-dG formation specifically at the guanine residue located 5' to guanine through electron transfer. The mechanism was discussed in relation to UV carcinogenesis.

Stable isotopes in clinical research: safety reaffirmed

Approaching half a century of stable-isotope usage in human metabolic studies has been without documented significant adverse effect. Side-effects with acute D dosing are transitory with no demonstrated evidence of permanent deleterious action. The threshold of D toxicity has been defined in animals and is far in excess of concentrations conceivably used in human studies. The possibility that D may have additional beneficial pharmacological applications cannot be excluded. For isotopes other than D, evidence of observed toxicity remains to be produced even at dosages far in excess of the range used in metabolic studies. Absence of adverse effect may be attributable to small mass differences and the similar properties of tracer and predominantly abundant isotope. Absolute determination of stable isotope toxicity in humans is rendered impossible by ethical considerations. Also, the precision of extrapolating toxicity thresholds from animal studies remains unknown. However, should perturbation of the delicate homoeostatic characteristic of living organisms occur with use of stable isotopes, it is almost undoubtedly at some level of administration greatly in excess of those administered currently in biomedical research.

Effects of deuteration on hematopoiesis in the mouse

Mice ingesting 30 to 50% D2O (heavy water, deuterium oxide) developed a dose-dependent depression of formed peripheral blood elements in 4 to 9 days. The principal mechanism of anemia and thrombocytopenia is impaired hematopoiesis. Despite pancytopenia in the peripheral blood, bone marrow cellularity and morphology remained normal. Upon replacement of D2O with tap water, platelet and neutrophil concentrations returned to normal within 48 to 72 hr. In contrast, blood lymphocyte concentrations remained low for several weeks. B-lymphocytes may be more affected by deuteration than other lymphocyte subsets. In vivo reticuloendothelial cell function, as assessed by 51Cr-labeled sheep erythrocyte clearance, was unaffected by D2O. Although a dose-dependent decrease in fluid intake occurred during deuteration, hematocytopenia was not a consequence of dehydration. In view of the known kinetics of D2O in biological systems, the rapid response of myeloid elements to deuteration must be due primarily to the solvent (nonmetabolic) isotope effect. Prolonged deuteration has proven toxic when included in regimens for treatment of neoplasia, including leukemia, in animal models. The present study shows that modulation of hematopoiesis by D2O is possible without invoking the toxicities associated with prolonged deuteration.

Cytogenetic toxicity of D2O in human lymphocyte cultures. Increased sensitivity in Fanconi's anemia

Chromosomal aberrations were scored in lymphocyte cultures from healthy individuals, patients with Bloom syndrome, and patients with Fanconi's anemia, after 4-5 h exposure to culture medium containing 90% heavy water (D2O). D2O treatment resulted in occasional pulverization of metaphases, and increased frequencies of chromosomal breakage. Patients with Fanconi's anemia were particularly sensitive to the chromosome breaking effect of D2O.

The production of deuterated E. coli

Our results indicate that the preparation of deuterated macromolecules for neutron scattering from E. coli can be done easily and relatively cheaply. The entry of deuterium into macromolecules of differing species during cell growth can be controlled by varying the D2O content of the medium and the choice of carbon sources, all in minimal medium. Considering the range of deuterations obtainable with simple protonated carbon sources, there seems to be no reason to use deuterated carbon sources except for the rare occasions when a fully deuterated specimen is required.

The action of D2O on the motility of human spermatozoa

The effect of 25%, 50%, 75% and 100% D2O on the survival of human spermatozoa was investigated. More spermatozoa were affected and died more quickly as the concentration of D2O increased. Spermatozoa died instantly in 100% D2O.