SEED: An Operational Numerical Tool for Dosimetric Reconstruction in Case of External Radiological Overexposure

ABSTRACT

In the event of a radiological accident involving external exposure of one or more victims and potential high doses, it is essential to know the dose distribution within the body in order to sort the victims according to the severity of the irradiation and then to take them to the most suitable medical facilities. However, there are currently few techniques that can be rapidly deployed on field and capable of characterizing an irradiation. Therefore, a numerical simulation tool has been designed. It can be implemented by a doctor/physicist pairing, projected within a limited time as close as possible to the irradiation accident and emergency response teams. Called SEED (Simulation of External Exposures & Dosimetry), this tool (dedicated to dose reconstruction in case of external exposure) allows a rapid modeling of the irradiation scene and a visual exchange with the victims and witnesses of the event. The user can navigate in three dimensions in the accident scene thanks to a graphical user interface including a "first person" camera. To validate the performance of the SEED tool, two dosimetric benchmarking exercises were performed. The first consisted in comparing the dose value provided by SEED to that given by a reference calculation code: MCNPX. The purpose of the second validation was to perform an experiment irradiating a physical dummy equipped with dosimeters and to reconstruct this irradiation using SEED. These two validation protocols have shown satisfactory results with mean difference less than 2% and 12% for the first and second exercises, respectively. They confirm that this new tool is able to provide useful information to medical teams in charge of dosimetric triage in case of a major external exposure event.

Evolution and significance of circulating procalcitonin levels compared with IL-6, TNF alpha and endotoxin levels early after thermal injury

To determine the evolution and significance of circulating procalcitonin (ProCT), IL-6 TNF alpha and endotoxin levels early after thermal injury, we performed a prospective, single unit, longitudinal study. Forty burn patients with total body surface area (TBSA) > 30 per cent were studied, of whom 33 suffered an inhalation injury. Blood samples were taken on the day of admission, every 4 h during the first day and daily during the first week. All patients had increased ProCT and IL-6 levels without any proven infection. Endotoxin and TNF alpha levels remained very low or undetectable. ProCT and IL-levels correlated well with the severity of skin burn injury (respectively, p < 0.006 and p < 0.028, using the non-parametric Kruskal-Wallis test). ProCT levels are not associated with smoke inhalation. ProCT and IL6 are prognostic factors of mortality at the time of admission but less reliable than the clinical UBS (unit burn standard) score. Endotoxin and TNF alpha were undetectable, suggesting that the problem of the early gut bacterial translocation remains to be proven.

Immunological relevance of malonic dialdehyde (MDA): II. Precipitation reactions of human sera with MDA-crosslinked proteins

Using precipitation reactions in agarose gels (Bidimensional double diffusion: Ouchterlony. Counterimmunoelectrophoresis: CEP), we showed that: a) sera from normal human subjects contain components able to bind and precipitate with MDA-crosslinked lysozyme (ML) and not with native lysozyme, which indicates that the chemical structures involved in such bindings arise from reaction of MDA with lysozyme and probably include 1-amino-3-iminopropene (AIP) bridges. b) some if not all of these seric components are immunoglobulins. c) the F(ab')2 regions of these immunoglobulins are involved in their binding and precipitating properties. These results lead us to assume that sera from normal human subjects contain immunoglobulins with antibody-like specificity for MDA-crosslinked proteins. Nevertheless, this assumption remains to be assessed by further studies, especially about the "epitopes" involved in such reactions.

Immunological relevance of malonic dialdehyde (MDA): III. Immuno-enzymatic determination of human immunoglobulin binding to MDA-crosslinked proteins

Using immunoenzymatic reactions (ELISA) with MDA-crosslinked lysozyme (ML) or poly-L-lysine (MP) and with the corresponding native protein or polypeptide, we showed that sera from normal human subjects contain immunoglobulins with antibody-like specificity for MDA-modified proteins. Inhibition studies with ML and MP showed that the chemical structures recognized by these immunoglobulins include 1-amino-3-iminopropene (AIP) bridges resulting from reactions of MDA with primary amino groups. An ELISA technique for quantitation of these immunoglobulins was developed and applied to 32 sera from healthy humans, which provided an estimation of their normal levels. Variations of these levels under pathological conditions are now being investigated.

Immunological relevance of malonic dialdehyde. I. Preparation of Schiff's bases from lysozyme or polylysine reacted with malonic dialdehyde

Malonic dialdehyde (MDA) is produced in all mammalian tissues either as an end product of lipid peroxidation or as a by-product of arachidonic acid metabolism. It may either be quickly oxidized to carbon dioxide or combine covalently with primary amino groups of proteins, phospholipids or nucleic acids. In the latter case, fluorescent Schiff's bases with 1-amino-3-iminopropene (AIP) bridges are produced. MDA metabolism is now fairly well elucidated, while that of MDA-cross-linked biological molecules remains unknown. Aiming at investigating the fate of such cross-linked molecules in mammalian organisms, and their biological relevance, we tried in the present study to prepare reproducibly Schiff's bases from chicken egg white lysozyme reacted with MDA. The resulting mixture of different Schiff's bases (ML) was fractionated into single oligomeric fractions by gel-filtration chromatography. ML and the single oligomeric fractions obtained from this mixture were controlled by fluorescence measurements for their content of AIP bridges, and by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate (SDS-PAGE) for their content of different oligomers. ML contained monomers, dimers, trimers and other oligomers, as shown by SDS-PAGE. The corresponding single oligomeric fractions were satisfactorily separated by gel-filtration chromatography (purity better than 94%, as determined by SDS-PAGE). Schiff's bases from poly-L-lysine reacted with MDA (MP) were also prepared. Their fluorescence emission spectrum was similar to that of ML and to that of the single oligomeric fractions obtained from ML.