In vitro evidence of the influence of complexation of Pu and Am on uptake by human lung epithelial cells Calu-3

Understanding the mechanisms involved in retention and clearance of actinides from the lungs after accidental intake is essential for the evaluation of the associated radiological risks. Although the absorption of radioelements has been shown in vivo to depend on their nature and physico-chemical properties, their mechanisms of translocation remain unknown. In this study, we have evaluated in vitro the binding and uptake by bronchial epithelial cells Calu-3 of 2 transuranic actinides, plutonium (Pu) and americium (Am), as the first steps of translocation across the pulmonary barrier. For this purpose, Calu-3 cells grown to confluence in 24-well plates were exposed to the radioelements for 24 h under various culture conditions. Two compartments were identified for the association of actinides to cells, corresponding to the membrane bound and internalized fractions. Binding of Pu was slightly higher than of Am, and depended on its initial chemical form (nitrate, citrate, colloids). Uptake of Pu and Am nitrate was higher in serum-free conditions than in supplemented medium, with an active mechanism involved in Pu internalization. Overall, our results suggest that complexation of actinides to bioligands may have an influence on their uptake by pulmonary epithelial cells, and therefore possibly on their subsequent absorption into blood.

ICRP Publication 141: Occupational Intakes of Radionuclides: Part 4

The 2007 Recommendations (ICRP, 2007) introduced changes that affect the calculation of effective dose, and implied a revision of the dose coefficients for internal exposure, published previously in the Publication 30 series (ICRP, 1979a,b, 1980a, 1981, 1988) and Publication 68 (ICRP, 1994b). In addition, new data are now available that support an update of the radionuclide-specific information given in Publications 54 and 78 (ICRP, 1989a, 1997) for the design of monitoring programmes and retrospective assessment of occupational internal doses. Provision of new biokinetic models, dose coefficients, monitoring methods, and bioassay data was performed by Committee 2 and its task groups. A new series, the Occupational Intakes of Radionuclides (OIR) series, will replace the Publication 30 series and Publications 54, 68, and 78. OIR Part 1 (ICRP, 2015) describes the assessment of internal occupational exposure to radionuclides, biokinetic and dosimetric models, methods of individual and workplace monitoring, and general aspects of retrospective dose assessment. OIR Part 2 (ICRP, 2016), OIR Part 3 (ICRP, 2017), this current publication, and the final publication in the OIR series (OIR Part 5) provide data on individual elements and their radioisotopes, including information on chemical forms encountered in the workplace; a list of principal radioisotopes and their physical half-lives and decay modes; the parameter values of the reference biokinetic models; and data on monitoring techniques for the radioisotopes most commonly encountered in workplaces. Reviews of data on inhalation, ingestion, and systemic biokinetics are also provided for most of the elements. Dosimetric data provided in the printed publications of the OIR series include tables of committed effective dose per intake (Sv per Bq intake) for inhalation and ingestion, tables of committed effective dose per content (Sv per Bq measurement) for inhalation, and graphs of retention and excretion data per Bq intake for inhalation. These data are provided for all absorption types and for the most common isotope(s) of each element. The online electronic files that accompany the OIR series of publications contains a comprehensive set of committed effective and equivalent dose coefficients, committed effective dose per content functions, and reference bioassay functions. Data are provided for inhalation, ingestion, and direct input to blood. This fourth publication in the OIR series provides the above data for the following elements: lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), actinium (Ac), protactinium (Pa), neptunium (Np), plutonium (Pu), americium (Am), curium (Cm), berkelium (Bk), californium (Cf), einsteinium (Es), and fermium (Fm).

Updated biokinetic model for systemic americium

The biokinetic model for systemic americium (Am) currently recommended by the International Commission on Radiological Protection (ICRP) for application to occupational intake of Am is based on information available through the early 1990s. Much additional information on Am biokinetics has been developed in the past 25 y, including measurements of retention and excretion of ²⁴¹Am in many workers with ²⁴¹Am burdens and post mortem measurements of ²⁴¹Am in tissues of some of those workers. The ICRP's current Am model is reasonably consistent with the updated information, with the main exception that the current model apparently overestimates 24-hour urinary Am as a fraction of skeletal or systemic Am at late times after intake. This paper provides an overview of current information on the systemic kinetics of Am in adult human subjects and laboratory animals and presents an updated biokinetic model for systemic Am that addresses the discrepancies between the current database and current ICRP systemic model for Am. This model is applied in Part 4 (to appear) of an ICRP series of reports on intake of radionuclides by workers called the OIR (Occupational Intake of Radionuclides) series.

Orally administered DTPA penta-ethyl ester for the decorporation of inhaled (241)Am

Diethylenetriaminepentaacetic acid (DTPA) is an effective decorporation agent to facilitate the elimination of radionuclides from the body, but its permeability-limited oral bioavailability limits its utility in mass-casualty emergencies. To overcome this limitation, a prodrug strategy using the penta-ethyl ester form of DTPA is under investigation. Pharmacokinetic and biodistribution studies were conducted in rats by orally administering [(14) C]DTPA penta-ethyl ester, and this prodrug and its hydrolysis products were analyzed as a single entity. Compared with a previous reporting of intravenously administered DTPA, the oral administration of this prodrug resulted in a sustained plasma concentration profile with higher plasma exposure and lower clearance. An assessment of the urine composition revealed that the bioactivation was extensive but incomplete, with no detectable levels of the penta- or tetra-ester forms. Tissue distribution at 12 h was limited, with approximately 73% of the administered dose being associated with the gastrointestinal tract. In the efficacy study, rats were exposed to aerosols of (241) Am nitrate before receiving a single oral treatment of the prodrug. The urinary excretion of (241) Am was found to be 19% higher than with the control. Consistent with prior reports of DTPA, the prodrug was most effective when the treatment delays were minimized.

The distribution and retention of plutonium, americium and uranium in CBA/H mice

Groups of male and female CBA/H mice were given intraperitoneal injections of 40 kBq kg-1 of 239Pu, 241Am and 233U citrate solutions and the retention and distribution of the three radionuclides compared at times up to 448 days. Similar results were obtained for males and females and showed that: 1. Whole body retention at 448 days was very similar for 239Pu and 241Am, accounting for about 20% of injected activity for each nuclide; retention of 233U was much lower at about 3%. 2. The skeleton accounted for 85% or more of retained 239Pu, 241Am and 233U activity from 6 weeks after injection. 3. The greatest concentrations of each radionuclide were measured in the main body of the spine, limb girdles and ribs, with lowest concentrations in the paw bones, head bones and caudal vertebrae. The inhomogeneity of distribution was in the order Pu > U > Am; with a trend to more uniform activity with time. 4. Average bone doses to 448 days were calculated as about 1.6 and 1.7 Gy for 239Pu and 241Am, respectively, and 0.3 Gy for 233U, with ranges for individual bones of 0.7-3.0 Gy, 1.1-2.5 Gy and 0.1-0.6 Gy, respectively. Average liver doses to 448 days were calculated as about 0.9 Gy, 0.6 Gy and 0.007 Gy for 239Pu, 241Am and 233U respectively, whilst the dose to the kidney for 233U was about 0.1 Gy. 5. Autoradiographic studies of the distribution of the nuclides in the femur showed differences in their initial distribution and subsequent movement. Initially, concentrations of 239Pu were greater on endosteal than periosteal surfaces while 241Am distributed more evenly on bone surfaces. The initial deposition of 233U on all surfaces was uneven with concentrations probably on active surfaces. Burial of all three nuclides in areas of bone growth was observed. Transfer of activity to the marrow was greatest for 239Pu and least for 233U.