The influence of extracorporeal clearance techniques on elimination of radiocesium after internal contamination.

Radiocesium, an isotope released after nuclear accidents such as Chernobyl, causes damage to the health of humans after internal contamination. As a result of an internal deposit of radiocesium these persons are continuously irradiated and noxious effects may occur. Removal of this internal radiation source will reduce immediate (short-term) and future damage (long-term). In order to obtain data with respect to cesium kinetics in vivo, data obtained in dogs by Nold et al. were fitted by a computer program. On the basis of these data, simulations were carried out to evaluate the influences of extracorporeal clearance on cesium kinetics. The influence of various treatments on the committed effective dose [E(50)] as a measure of radiation harm was simulated. For this purpose an equivalence between the committed effective dose and the area under the curve, a kinetic parameter, was derived. This equivalence only holds when comparisons are made for different treatments of one subject contaminated with one isotope. Treatment with orally administered Prussian Blue salts reduces the committed effective dose by 29% (50 y). This can be insufficient to prevent deterministic effects as a result of a severe internal contamination with radiocesium. For this purpose other methods are evaluated. In simulations, extracorporeal clearance (e.g. hemoperfusion or hemodialysis) proved to be more effective in reducing E(50) (> 50%, 50 y). Extracorporeal clearance also seems to be effective in the early dose reduction and its consequent deterministic effects. Simulations revealed that effectiveness is improved when the treatment is started earlier and continued for a longer period. Effective extracorporeal clearance may be considered to be a promising method to treat victims of nuclear accidents internally contaminated with radiocesium.

Hemodialysis as a potential method for the decontamination of persons exposed to radiocesium.

Radiocesium may be deposited in the environment as a result of accidents in nuclear installations, for example, as in Chernobyl. Significant internal contamination with radiocesium poses a serious risk to human health, and, therefore, expedient removal is essential to reduce the radiation body burden. In vitro hemodialysis was tested as a potential method to remove radiocesium from a pasteurized plasma solution of bovine or human blood. Clearance values were calculated by a flow independent method. Hemodialysis appears to be a good method to remove radiocesium from blood: within 4 h more than 90% of the administered radiocesium is removed from blood or plasma. Radiocesium in dialysis fluid can be concentrated on Prussian Blue coated columns that were tested previously for hemoperfusion. Radioactive waste disposal problems can be solved by concentration of radiocesium on these columns. In vivo experiments are necessary to confirm these in vitro results.

In vitro binding of radiocesium to Prussian Blue coated strips and Prussian Blue containing hemoperfusion columns as a potential tool for the treatment of persons internally contaminated with radiocesium.

Cellulose or nylon strips coated with three different Prussian Blue salts were prepared with cellulose nitrate as binding material. These strips were evaluated for their usefulness for the development of an extracorporal clearance device for radiocesium, a radionuclide often released after accidents in nuclear installations (for example in Chernobyl). Extracorporeal clearance can be used to enhance the elimination of radiocesium from internally contaminated persons. The stability of these strips and their binding characteristics for radiocesium were investigated. In all studies strips coated with Fe4[Fe(CN)6]3 proved to be the most suitable for further development of an extracorporeal clearance device: the strips are stable, have a high binding capacity for radiocesium, and can be sterilized. On the basis of these results, hemoperfusion colums containing Fe4[Fe(CN)6]3-coated strips were developed and tested. In in vitro experiments these columns proved to be successful in removing radiocesium from a pasteurized plasma solution (clearance was approximately 100 ml/min). The binding capacity of these columns is relatively high. In 4 h the columns are able to bind approximately 0.3 TBq of radiocesium. They are a promising development for the enhancement of the removal of radiocesium from the human body. They can also be used for the decontamination of other fluids of chemical or biological origin. Further research is, however, still necessary.

Bioactivation of 2-nitrofluorene to reactive intermediates that bind covalently to DNA, RNA and protein in vitro and in vivo in the rat.

The activation of 2-nitrofluorene (2-NF) to reactive intermediates that bind covalently to DNA, RNA and protein has been investigated both in vitro and in the rat in vivo. In vitro, such binding was catalyzed by the hepatic microsomal fraction, was NADPH dependent and could be inhibited by SKF 525A, an inhibitor of cytochrome P450. The generation of reactive intermediates therefore is most likely catalyzed by cytochrome P450. Covalent binding of 2-NF could not be prevented by glutathione, N-acetylcysteine and other thiol-containing compounds. It could be partially prevented by guanosine, presumably because it traps the reactive intermediate(s). Under normal oxygenation conditions 2-NF was also covalently bound in freshly isolated hepatocytes; pretreatment of rats with an inducer of cytochrome P450, Aroclor 1254, gave rise to a higher rate of covalent binding in hepatocytes. Covalent binding of 2-NF to cellular macromolecules also occurred in vivo, both after oral and i.v. administration. Pentachlorophenol, a selective sulfation inhibitor, did not influence the covalent binding of 2-NF; therefore, the reactive intermediate is not formed by sulfation of N-hydroxy-2-acetylaminofluorene, which could be a metabolite of 2-NF. It is concluded that the reactive intermediates most likely can be formed from 2-NF by the cytochrome P450 enzyme system.

In vitro cyanide release of four prussian blue salts used for the treatment of cesium contaminated persons.

Prussian blue salts are used in clinical practice as an antidote for the treatment of humans contaminated with radioactive cesium. A decomposition product of these Prussian blue salts may be the highly toxic cyanide. A method to simulate gastrointestinal cyanide-release was applied to four different Prussian blue salts: K3Fe[Fe(CN)6], Fe4[Fe(CN)6]3, NH4Fe[Fe(CN)6] (pur. and unpur.). Cyanide-release was higher in artificial gastric juice than in water and artificial intestinal juice. Under all conditions cyanide-release from Fe4[Fe(CN)6]3 was the lowest. Since Fe4[Fe(CN)6]3 also binds more cesium, it appears to be the most suitable Prussian blue salt for use as an antidote after radiocesium contamination in humans.

DNA adduct formation in liver following the administration of [3H]2-nitrofluorene to rats in vivo.

The formation of RNA and DNA adducts by the environmental pollutant 2-nitrofluorene (2-NF) has been investigated in rat liver in vivo. The adduct pattern was studied after trifluoroacetic acid hydrolysis of DNA or RNA, followed by analysis of the adducts by HPLC. This was also done by enzymatic hydrolysis of DNA, followed by 32P-postlabeling. Both after oral and i.v. administration of [3H]2-NF, one major adduct was found. This adduct did not co-migrate with one of the known adducts of 2-(acetyl)-aminofluorene, N-deoxyguanosin-8-yl-2-aminofluorene (dG-C8-AF), which could have been formed after nitroreduction of 2-NF. 32P-Postlabeling revealed that two minor adducts were also formed, one of which was dG-C8-AF. The observation that the major adduct was also formed after i.v. administration of 2-NF to bile duct-catheterized rats makes a role for the intestinal microflora in the formation of this adduct very unlikely. In vitro experiments with inhibitors of the enzyme epoxide hydrolase indicated that epoxidation of 2-NF may play a role in the microsomal bioactivation of this compound.

Photoactivation of 2-nitrofluorene in vitro and in the rat in vivo. UVA-induced formation of reactive intermediates that bind covalently to RNA and protein.

2-Nitrofluorene (2-NF), an environmental pollutant, can be activated by UV light to reactive intermediates that bind covalently to RNA and protein in vitro: high levels of covalent binding were obtained. This covalent binding was not dependent on the presence of oxygen in the solution and could be decreased by glutathione. Hydrolysis of the in vitro modified RNA and subsequent analysis of the liberated bases by HPLC revealed that approximately 15% of the covalent binding of 2-NF to RNA could be attributed to the formation of a guanosine adduct of nitroreduced 2-NF, N-(deoxyguanosin-8-yl)-2-aminofluorene. Many other adducts are formed of which the structure and mechanism of formation are as yet unknown. The possibility of photoactivation of 2-NF in the rat in vivo was also investigated. Photoactivation increased covalent binding of 2-NF in the skin but not in other organs. The mechanism of the photoactivation of 2-NF is discussed.