Chelation therapy with 3,4,3-Li(1,2-HOPO) after pulmonary exposure to plutonium in rats.

Internal exposure to plutonium can occur through inhalation for the nuclear worker, but also for the public if the radionuclide was released into the atmosphere in the context of a nuclear accident or terrorist attack. DieThylenetriaminePentaAcetic acid (DTPA) is currently still the only authorized chelator that can be used to decorporate internalized plutonium. The Linear HydrOxyPyridinOne-based ligand named 3,4,3-Li(1,2-HOPO) remains the most promising drug candidate to replace it in the hopes of improving chelating treatment. This study aimed to assess the efficacy of 3,4,3-Li(1,2-HOPO) in removing plutonium from rats exposed to the lungs, depending on the timing and route of treatment, and almost always compared to DTPA at a ten-fold higher dose used as a reference chelator. First, early intravenous injection or inhalation of 3,4,3-Li(1,2-HOPO) demonstrated superior efficacy over DTPA in preventing plutonium accumulation in liver and bone in rats exposed by injection or lung intubation. However, this superiority of 3,4,3-Li(1,2-HOPO) was much less pronounced with delayed treatment. In rats given plutonium in the lungs, the experiments also showed that 3,4,3-Li-HOPO reduced pulmonary retention of plutonium more effectively than DTPA only when the chelators were injected early but not at delayed times, while it was always the better of the two chelators when they were inhaled. Under our experimental conditions, the rapid oral administration of 3,4,3-Li(1,2-HOPO) was successful in preventing systemic accumulation of plutonium, but not in decreasing lung retention. Thus, after exposure to plutonium by inhalation, the best emergency treatment would be the rapid inhalation of a 3,4,3-Li(1,2-HOPO) aerosol to limit pulmonary retention of plutonium and prevent extrapulmonary deposition of plutonium in target systemic tissues.

Actinide Decorporation: A Review on Chelation Chemistry and Nanocarriers for Pulmonary Administration.

Chelation is considered the best method for detoxification by promoting excretion of actinides (Am, Np, Pu, Th, U) from the human body after internal contamination. Chemical agents that possess carboxylic acid or hydroxypyridinonate groups play a vital role in actinide decorporation. In this review article, we provide considerable background details on the chelation chemistry of actinides with an aim to formulate better decorporation agents. Nanocarriers for pulmonary delivery represent an exciting prospect in the development of novel therapies for actinide decorporation that both reduce toxic side effects of the agent and improve its retention in the body. Recent studies have demonstrated the benefits of using a nebulizer or an inhaler to administer chelating agents for the decorporation of actinides. Effective chelation therapy with large groups of internally contaminated people can be a challenge unless both the agent and the nanocarrier are readily available from strategic national stockpiles for radiological or nuclear emergencies. Sunflower lecithin is particularly adept at alleviating the burden of administration when used to form liposomes as a nanocarrier for pulmonary delivery of diethylenetriamine-pentaacetic acid (DTPA) or hydroxypyridinone (HOPO). Better physiologically-based pharmacokinetic models must be developed for each agent in order to minimize the frequency of multiple doses that can overload the emergency response operations.

[High-Throughput Sequencing Combined with Metabonomics to Analyze the Effect of Heavy Metal Contamination on Farmland Soil Microbial Community and Function].

Heavy metal contamination affects microbial composition and diversity. The interaction between heavy metal contamination and soil microorganisms has been a hot topic in ecological research. Battery manufacturing has been going on for over six decades in Xinxiang City, resulting in severe soil heavy metal contamination due to battery wastewater runoff. Few studies have investigated the effect of heavy metal contamination due to long-term battery wastewater runoff on microbial diversity and metabolomics in Xinxiang City. In this study, we collected samples from three heavy metal contaminated sites in Xinxiang City and found that Cd and Pb exceeded the recommended thresholds by 34-66 fold and 1.5-2.32 fold, respectively. High-throughput sequencing showed that Bacillus, Arthrobacter, Sphingomonas, and Streptomyces were the dominant bacteria genera, while Olpidium, Plectosphaerella, and Gibellulopsis were the dominant fungi genera, indicating that heavy metal contaminated soil in Xinxiang City was rich in heavy metal tolerant bacteria and fungi due to the long-term heavy metal stress. Correlation analysis showed that total Cu, DTPA extract Cu, and water soluble Pb were significant factors in bacterial diversity, while total Cd, total Ni, total Pb, total Zn, DTPA extract Cu, and water soluble Pb were significant factors in fungal diversity. To better understand the effect of heavy metal contamination on the metabolism of soil microorganisms, we conducted non-targeted metabolomic profiling, which showed significant differences in metabolites across the samples. Pathway enrichment analysis showed that these differential metabolites were involved in pathways such as metabolism, environmental information processing, and genetic Information Processing, which may play a role in heavy metal stress mitigation and environmental adaptation.

In Vitro and In Vivo Evaluation of DTPA-HPMA Copolymers as Potential Decorporating Agents for Prophylactic Therapy of Actinide Contamination.

The release of actinides into the environment represents a significant potential public health concern. Chelation therapy utilizing diethylenetriamine pentaacetate (DTPA) is a U.S. Food and Drug Administration (FDA)-approved therapy capable of mitigating the deposition of some absorbed actinides in the body. However, the pharmacokinetic profile of DTPA is not ideal for prophylactic applications. In this study, we examine the incorporation of DTPA into a HPMA copolymer (P-DTPA) to investigate if the enhanced blood circulation time can offer superior prophylactic protection and of improving in vivo radiometal decorporation. Utilizing lutetium-177 (177Lu) as an actinide model, the performance of P-DTPA and DTPA (control) were evaluated using selectivity studies in the presence of competing biological metals, chelation and stability assays in human serum and cytotoxicity studies using human umbilical vein endothelial cells (HUVEC). The in vivo decorporation efficiency of P-DTPA relative to DTPA and untreated controls was also evaluated over two weeks in CF-1 mice. In the experimental groups, the mice were prophylactically treated with P-DTPA or DTPA (30 µmol/kg) 6 or 24 h prior to 177LuCl3 administration. The in vitro results reveal that P-DTPA gives efficient complexation yields relative to DTPA with a tolerable cytotoxicity profile and good serum stability. The in vivo decorporation studies demonstrated enhanced total excretion of the 177Lu using P-DTPA compared to DTPA in both the 6 and 24 h prophylactic treatment study arms. This enhanced decorporation effect is certainly attributable to the expected prolonged biological half-life of DTPA when grafted to the HPMA polymer.

Determination of drug efficacy to dissolve cobalt oxide particles in cellular models: Towards a therapeutic approach to decrease pulmonary retention.

Following accidental inhalation of radioactive cobalt particles, the poorly soluble and highly radioactive Co3O4 particles are retained for long periods in lungs. To decrease their retention time is of crucial importance to minimize radiation-induced damage. As dissolved cobalt is quickly transferred to blood and eliminated by urinary excretion, enhancing the dissolution of particles would favor 60Co elimination. We evaluated the ability of ascorbic acid alone or associated with the chelating agents DTPA1, DFOB2 or EDTA3 to enhance dissolution of cobalt particles after macrophage engulfment, and the drug effects on the translocation of the soluble species CoCl2 through an epithelial barrier. We exposed differentiated THP-1 macrophage-like cells and Calu-3 lung epithelial cells cultured in a bicameral system to cobalt and selected molecules up to 7 days. DTPA, the recommended treatment in man, used alone showed no effect, whereas ascorbic acid significantly increased dissolution of Co3O4 particles. An additional efficacy in intracellular particles dissolution was observed for combinations of ascorbic acid with DTPA and EDTA. Except for DFOB, treatments did not significantly modify translocation of dissolved cobalt across the epithelial lung barrier. Our study provides new insights for decorporating strategies following radioactive cobalt particle intake.

Reversion of arterial calcification by elastin-targeted DTPA-HSA nanoparticles.

Generalized arterial calcification of infancy (GACI) and pseudoxanthoma elasticum (PXE) are characterized by pathologic calcifications in the media of large- and medium sized arteries. GACI is associated with biallelic mutations in ENPP1 in the majority of cases, whereas mutations in ABCC6 are known to cause PXE. Different treatment approaches including bisphosphonates and orally administered pyrophosphate (PPi) were investigated in recent years, but reversion of calcification could not be achieved. With this study, we pursued the idea of a combination of controlled drug delivery through nanoparticles and active targeting via antibody conjugation to develop a treatment for GACI and PXE. To establish a suitable drug delivery system, the chelating drug diethylenetriamine pentaacetic acid (DTPA) was conjugated to nanoparticles composed of human serum albumin (HSA) as biodegradable and non-toxic particle matrix. To accomplish an active targeting of the elastic fibers exposed through calcification of the affected areas, the nanoparticle surface was functionalized with an anti-elastin antibody. Cytotoxicity and cell interaction studies revealed favorable preconditions for the intended i.v. application. The chelating ability was evaluated in vitro and ex vivo on aortic ring culture isolated from two mouse models of GACI and PXE. The positive results led to the conclusion that the produced nanoparticles might be a promising therapy in the treatment of GACI and PXE.

A quick and simple in vitro assay to predict bioavailability of actinides following accidental exposure.

Physicochemical properties of actinides highly influence internal intake and biodistribution. An a priori knowledge of the dissolution properties of compounds involved in accidental exposure would be of great help in early dose assessment. However, this information is rarely available, leading to difficulties in interpreting excretion data from contaminated victims. We developed an in vitro acellular assay to predict in vivo bioavailability of actinides and improve medical handling of the victims. Various actinides of different physicochemical properties were used to validate the reliability of the assay to mimic in vivo behavior of the contaminants. Our assay was designed as a dynamic muticompartmental system in which an agarose gel represents the retention compartment of actinides and a dynamic phase the transfer compartment. Relevant physiological conditions were obtained by introducing various components both in the static and dynamic phases. The proposed model may provide a good prediction of in vivo behavior and could be used as a first assessment to predict the fraction of actinides that could be potentially transferred from retention compartments, as well as the fraction available to chelating drugs.

Rapid Response, Dose Assessment, and Clinical Management of a Plutonium-contaminated Puncture Wound.

Internalization of radionuclides occurs not only by inhalation, ingestion, parenteral injection (i.e., administration of radioactive material for a medical purpose), and direct transdermal absorption, but also by contaminated wounds. In June 2010, a glove-box operator at the U.S. Department of Energy's Savannah River Site sustained a puncture wound while venting canisters containing legacy materials contaminated with Pu. To indicate the canisters had been vented, a flag was inserted into the vent hole. The shaft of the flag penetrated the protective gloves worn by the operator. Initial monitoring performed with a zinc-sulfide alpha detector indicated 300 dpm at the wound site. After being cleared by radiological controls personnel, the patient was taken to the site medical facility where decontamination was attempted and diethylenetriaminepentaacetic acid (DTPA) was administered intravenously within 1.5 h of the incident. The patient was then taken to the Savannah River Site In Vivo Counting Facility where the wound was counted with a Canberra GL 2820 high-purity germanium detector, capable of quantifying contamination by detecting low-energy x rays and gamma rays. In addition to the classic 13, 17, and 20 keV photons associated with Pu, the low-yield (0.04%) 43.5 keV peak was also detected. This indicated a level of wound contamination orders of magnitude above the initial estimate of 300 dpm detected with handheld instrumentation. Trace quantities of Am were also identified via the 59.5 keV peak. A 24 h urine sample collection was begun on day 1 and continued at varying intervals for over a year. The patient underwent a punch biopsy at 3 h postincident (14,000 dpm removed) and excisional biopsies on days 1 and 9 (removal of an additional 3,200 dpm and 3,800 dpm, respectively). The initial post-DTPA urine sample analysis report indicated excretion in excess of 24,000 dpm Pu. Wound mapping was performed in an effort to determine migration from the wound site and indicated minimum local migration. In vivo counts were performed on the liver, axillary lymph nodes, supratrochlear lymph nodes, and skeleton to assess uptake and did not indicate measurable activity. Seventy-one total doses of DTPA were administered at varying frequencies for 317 d post intake. After allowing 100 d for removal of DTPA from the body, five 24 h urine samples were collected and analyzed for dose assessment by using the wound model described in National Council on Radiation Protection and Measurements Report No. 156. The total effective dose averted via physical removal of the contaminant and DTPA administration exceeded 1 Sv, demonstrating that rapid recognition of incident magnitude and prompt medical intervention are critical for dose aversion.

Decorporation of Pu/Am Actinides by Chelation Therapy: New Arguments in Favor of an Intracellular Component of DTPA Action.

Diethylenetriaminepentaacetic acid (DTPA) is currently still the only known chelating drug that can be used for decorporation of internalized plutonium (Pu) and americium (Am). It is generally assumed that chelation occurs only in biological fluids, thus preventing Pu/Am deposition in target tissues. We postulate that actinide chelation may also occur inside cells by a mechanism called "intracellular chelation". To test this hypothesis, rats were given DTPA either prior to (termed "prophylactic" treatment) or belatedly after (termed "delayed" treatment) Pu/Am injection. DTPA decorporation efficacy was systematically tested for both plutonium and americium. Both prophylactic and delayed DTPA elicited marked decreases in liver Pu/Am. These results can be explained by chelation within subcellular compartments where DTPA efficacy increased as a function of a favorable intracellular DTPA-to-actinide molar ratio. The efficacy of intracellular chelation of liver actinides decreased with the delay of treatment. This is probably explained by progressive actinide binding to the high-affinity ligand ferritin followed by migration to lysosomes. Intracellular chelation was reduced as the gap between prophylactic treatment and contamination increased. This may be explained by the reduction of the intracellular DTPA pool, which declined exponentially with time. Skeletal Pu/Am was also reduced by prophylactic and delayed DTPA treatments. This decorporation of bone actinides may mainly result from extracellular chelation on bone surfaces. This work provides converging evidence for the involvement of an intracellular component of DTPA action in the decorporation process. These results may help to improve the interpretation of biological data from DTPA-treated contamination cases and could be useful to model DTPA therapy regimens.

Inhibitory potential of three zinc chelating agents against the proteolytic, hemorrhagic, and myotoxic activities of Echis carinatus venom.

Viperbites undeniably cause local manifestations such as hemorrhage and myotoxicity involving substantial degradation of extracellular matrix (ECM) at the site of envenomation and lead to progressive tissue damage and necrosis. The principle toxin responsible is attributed to snake venom metalloproteases (SVMPs). Treatment of such progressive tissue damage induced by SVMPs has become a challenging task for researchers and medical practitioners who are in quest of SVMPs inhibitors. In this study, we have evaluated the inhibitory potential of three specific zinc (Zn(2+)) chelating agents; N,N,N',N'-tetrakis (2-pyridylmethyl) ethane-1,2-diamine (TPEN), diethylene triamine pentaacetic acid (DTPA), tetraethyl thiuram disulfide (TTD) on Echis carinatus venom (ECV) induced hemorrhage and myotoxicity. Amongst them, TPEN has high affinity for Zn(2+) and revealed potent inhibition of ECV metalloproteases (ECVMPs) in vitro (IC50: 6.7 µM) compared to DTPA and TTD. The specificity of TPEN towards Zn(2+) was confirmed by spectral and docking studies. Further, TPEN, DTPA, and TTD completely blocked the hemorrhagic and myotoxic activities of ECV in a dose dependent manner upon co-injection; whereas, only TPEN successfully neutralized hemorrhage and myotoxicity following independent injection. Histological examinations revealed that TPEN effectively prevents degradation of dermis and basement membrane surrounding the blood vessels in mouse skin sections. TPEN also prevents muscle necrosis and accumulation of inflammatory cells at the site of ECV injections. In conclusion, a high degree of structural and functional homology between mammalian MMPs and SVMPs suggests that specific Zn(2+) chelators currently in clinical practice could be potent first aid therapeutic agents in snakebite management, particularly for local tissue damage.

A drug-repositioning screening identifies pentetic acid as a potential therapeutic agent for suppressing the elastase-mediated virulence of Pseudomonas aeruginosa.

Pseudomonas aeruginosa, a Gram-negative bacterium of clinical significance, produces elastase as a predominant exoprotease. Here, we screened a library of chemical compounds currently used for human medication and identified diethylene triamine penta-acetic acid (DTPA, pentetic acid) as an agent that suppresses the production of elastase. Elastase activity found in the prototype P. aeruginosa strain PAO1 was significantly decreased when grown with a concentration as low as 20 µM DTPA. Supplementation with Zn(2+) or Mn(2+) ions restored the suppressive effect of DTPA, suggesting that the DTPA-mediated decrease in elastase activity is associated with ion-chelating activity. In DTPA-treated PAO1 cells, transcription of the elastase-encoding lasB gene and levels of the Pseudomonas quinolone signal (PQS), a molecule that mediates P. aeruginosa quorum sensing (QS), were significantly downregulated, reflecting the potential involvement of the PQS QS system in DTPA-mediated elastase suppression. Biofilm formation was also decreased by DTPA treatment. When A549 alveolar type II-like adenocarcinoma cells were infected with PAO1 cells in the presence of DTPA, A549 cell viability was substantially increased. Furthermore, the intranasal delivery of DTPA to PAO1-infected mice alleviated the pathogenic effects of PAO1 cells in the animals. Together, our results revealed a novel function for a known molecule that may help treat P. aeruginosa airway infection.

Combined drug and surgery treatment of plutonium-contaminated wounds: indications obtained using a rodent model.

There is an important requirement following accidental actinide contamination of wounds to limit the dissemination and retention of such alpha-emitting radionuclides. To reduce wound and systemic contamination, treatment approaches include chelation therapy with or without wound excision. However, it has been hypothesized that wound excision could lead to increased contaminant release and systemic organ retention. This study in the rat addresses this question. Anesthetized rats were contaminated with plutonium nitrate following wounding by deep incision of hind leg muscle. Excision of tissue at the contaminated site was performed 7 d later with or without Diethylene Triamine Pentaacetic Acid (DTPA) treatment (30 µmol kg⁻¹ i.v.). Pu urinary excretion was then measured for a further 3 d, and animals were euthanized at 14 d after contamination. Tissue samples were evaluated for Pu activity and histology. At 7 d after contamination, around 50% of the initial activity remained at the wound site. An average of 16% of this activity was then removed by surgery. Surgery alone resulted in increased urinary excretion, suggesting release from the wound site, but no subsequent increases in organ retention (bone, liver) were observed at 14 d. Indeed, organ Pu activity was slightly reduced. The combination of surgery and DTPA or DTPA treatment alone was much more effective than excision alone as shown by the markedly increased urinary Pu excretion and decreased tissue levels. This is the first report in an experimental rodent model of resection of Pu-contaminated wound. Urinary excretion data provide evidence for the release of activity as a result of surgery, but this does not appear to lead to further Pu organ retention. However, a combination of prior DTPA treatment with wound excision is particularly effective.

Efficacy of reversal of aortic calcification by chelating agents.

Elastin-specific medial vascular calcification, termed "Monckeberg's sclerosis," has been recognized as a major risk factor for various cardiovascular events. We hypothesize that chelating agents, such as disodium ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA), and sodium thiosulfate (STS) might reverse elastin calcification by directly removing calcium from calcified tissues into soluble calcium complexes. We assessed the chelating ability of EDTA, DTPA, and STS on removal of calcium from hydroxyapatite (HA) powder, calcified porcine aortic elastin, and calcified human aorta in vitro. We show that both EDTA and DTPA could effectively remove calcium from HA and calcified tissues, while STS was not effective. The tissue architecture was not altered during chelation. In the animal model of aortic elastin-specific calcification, we further show that local periadventitial delivery of EDTA loaded in to poly(lactic-co-glycolic acid) nanoparticles regressed elastin-specific calcification in the aorta. Collectively, the data indicate that elastin-specific medial vascular calcification could be reversed by chelating agents.

Efficacy of a novel chelator BPCBG for removing uranium and protecting against uranium-induced renal cell damage in rats and HK-2 cells.

Chelation therapy is a known effective method to increase the excretion of U(VI) from the body. Until now, no any uranium chelator has been approved for emergency medical use worldwide. The present study aimed to evaluate the efficacy of new ligand BPCBG containing two catechol groups and two aminocarboxylic acid groups in decorporation of U(VI) and protection against acute U(VI) nephrotoxicity in rats, and further explored the detoxification mechanism of BPCBG for U(VI)-induced nephrotoxicity in HK-2 cells with comparison to DTPA-CaNa3. Chelating agents were administered at various times before or after injections of U(VI) in rats. The U(VI) levels in urine, kidneys and femurs were measured 24 h after U(VI) injections. Histopathological changes in the kidney and serum urea and creatinine and urine protein were examined. After treatment of U(VI)-exposed HK-2 cells with chelating agent, the intracellular U(VI) contents, formation of micronuclei, lactate dehydrogenase (LDH) activity and production of reactive oxygen species (ROS) were assessed. It was found that prompt, advanced or delayed injections of BPCBG effectively increased 24 h-urinary U(VI) excretion and decreased the levels of U(VI) in kidney and bone. Meanwhile, BPCBG injection obviously reduced the severity of the U(VI)-induced histological alterations in the kidney, which was in parallel with the amelioration noted in serum indicators, urea and creatinine, and urine protein of U(VI) nephrotoxicity. In U(VI)-exposed HK-2 cells, immediate and delayed treatment with BPCBG significantly decreased the formation of micronuclei and LDH release by inhibiting the cellular U(VI) intake, promoting the intracellular U(VI) release and inhibiting the production of intracellular ROS. Our data suggest that BPCBG is a novel bi-functional U(VI) decorporation agent with a better efficacy than DTPA-CaNa3.

Decorporation approach following rat lung contamination with a moderately soluble compound of plutonium using local and systemic Ca-DTPA combined chelation.

Decorporation efficacy of prompt pulmonary delivery of DTPA dry powder was assessed following lung contamination with plutonium nitrate and compared to an intravenous injection of DTPA solution and a combined administration of both DTPA compounds. In addition, efficacy of a delayed treatment was assessed. In case of either early or late administration, insufflated DTPA was more efficient than intravenously injected DTPA in reducing the plutonium lung burden due to its high local concentration. Prompt treatment with DTPA powder was also more effective in limiting extrapulmonary deposits by removing the early transportable fraction of plutonium from lungs prior its absorption into blood. Translocation of DTPA from lungs to blood may also contribute to the decrease in extrapulmonary retention, as shown by reduced liver deposit after delayed pulmonary administration of DTPA. Efficacy of DTPA dry powder was further increased by the combined intravenous administration of DTPA solution for reducing extrapulmonary deposits of plutonium and promoting its urinary excretion. According to our results, the most effective treatment protocol for plutonium decorporation was the early pulmonary delivery of DTPA powder supplemented by an intravenous injection of DTPA solution. Following inhalation of plutonium as nitrate chemical form, this combined chelation therapy should provide a more effective method of treatment than conventional intravenous injection alone. At later stages following lung contamination, pulmonary administration of DTPA should also be considered as the treatment of choice for decreasing the lung burden.

Allosteric effects of sulfonate anions on the rates of iron release from serum transferrin.

Serum transferrin is the protein that transports ferric ion through the bloodstream and is thus a potential target for iron chelation therapy. However, the release of iron from transferrin to low-molecular-weight chelating agents is usually quite slow. Thus a better understanding of the mechanism for iron release is important to assist in the design of more effective agents for iron removal. This paper describes the effect of sulfonate anions on the rates of iron removal from C-terminal monoferric transferrin by acetohydroxamic acid, deferiprone, nitrilotriacetic acid (NTA), and diethylenetriaminepentaacetic acid at 25°C in 0.1M N-(2-hydroxyethyl)piperazine-N'-(2-ethanesulfonic acid) (Hepes) buffer at pH 7.4. These ligands remove iron via a combination of pathways that show saturation and first order dependence on the ligand concentration. The kinetic effects of the anions methanesulfonate, methylenedisulfonate, and ethylenedisulfonate were evaluated. All these anions increase the overall rates of iron release, presumably by binding to an allosteric anion binding site on the protein. The two disulfonates produce a larger acceleration in iron release than the monosulfonate. More detailed studies using methylenedisulfonate show that this anion accelerates the rate of iron release via the saturation pathway. The addition of methylenedisulfonate results in the appearance of a large saturation pathway for iron release by NTA, which otherwise removes iron by a simple first-order process. The sulfonate group was selected for these studies because it represents an anionic functional group that can be covalently linked to a therapeutic ligand to accelerate iron release in vivo. The current studies indicate that the binding of the sulfonates to the allosteric site on the protein is quite weak, so that one would not expect a significant acceleration in iron release at clinically relevant ligand concentrations.

Zinc deprivation impairs growth factor-stimulated calcium influx into murine 3T3 cells associated with decreased cell proliferation.

Zinc plays a critical role in growth, a process that depends primarily on cell proliferation. Murine fibroblasts, Swiss 3T3 cells, were used to explore the hypothesis that a critical role of zinc in cell proliferation relates to its function in calcium influx. Cells were deprived of zinc by an impermeant chelator, diethylenetriaminepentaacetate (0.6 mmol/L), and low-calcium status was achieved by using a low- (<5 µmol/L) calcium medium. Cells were stimulated by a composite of growth factors (GF): platelet-derived GF, insulin-like GF-I, and epidermal GF. GF stimulation of cell proliferation was assessed by the incorporation of tritiated thymidine and calcium influx by the increase in fluorescence of cells loaded with Fluo-4. Proliferation was dependent on both zinc and calcium and they interacted in this process. GF stimulated an immediate sharp increase in intracellular calcium, indicative of internal calcium release, which peaked within 1 min and decreased to an elevated plateau, a pattern typical of a store-operated calcium channel. The sustained calcium influx of zinc-deprived cells was markedly lower than that of supplemented cells. Verapamil, a calcium channel blocker, also depressed both cell proliferation and calcium influx. In summary, zinc deficiency impaired GF-stimulated calcium influx into murine fibroblasts in association with decreased cell proliferation.

Case study: three acute 241Am inhalation exposures with DTPA therapy.

Three workers incurred inhalation exposures to Am oxide as a result of waste sorting and compaction activities. The exposure magnitudes were not fully recognized until the following day when an in-vivo lung count identified a significant lung deposition of Am in a male worker, and DTPA chelation therapy was initiated. Two additional workers (one female and one male) were then identified as sufficiently exposed to also warrant therapy. In-vivo bioassay measurements were performed over the ensuing 6 mo to quantify the 241Am activity in the lungs, liver, and skeleton. Urine and fecal samples were collected and showed readily detectable 241Am. Clinical lab tests and medical evaluations all showed normal results. There were no significant adverse clinical health effects from the therapy. The estimated 241Am inhalation intakes for the three workers were 1,800 Bq, 630 Bq, and 150 Bq. Lung retention showed somewhat longer pulmonary clearance half-times than standard inhalation class W or absorption Type M assumptions. The three subjects underwent slightly different therapy regimens, with therapy effectiveness factors (defined as the ratio of the reference doses without therapy relative to the final assessed doses) of 4.5, 1.9, and 1.7, respectively.

Preferential decorporation of americium by pulmonary administration of DTPA dry powder after inhalation of aged PuO(2) containing americium in rats.

After inhalation of plutonium oxides containing various percentages of americium in rats, we identified an acellular transient pulmonary compartment, the epithelial lining fluid (ELF), in which a fraction of actinide oxides dissolve prior to absorption and subsequent extrapulmonary deposit. Chelation therapy is usually considered to be poorly efficient after inhalation of actinide oxides. However, in the present study, prompt pulmonary administration of diethylenetraminepentaacetic acid (DTPA) as a dry powder led to a decrease in actinide content in ELF together with a limitation of bone and liver deposits. Because americium is more soluble than plutonium, higher amounts of americium were found in ELF, extrapulmonary tissues and urine. Our results also demonstrated that the higher efficacy of DTPA on americium compared to plutonium in ELF induced a preferential inhibition of extrapulmonary deposit and a greater urinary excretion of americium compared to plutonium. All together, our data justify the use of an early and local DTPA treatment after inhalation of plutonium oxide aerosols in which americium can be in high proportion such as in aged compounds.

Biomimetic actinide chelators: an update on the preclinical development of the orally active hydroxypyridonate decorporation agents 3,4,3-LI(1,2-HOPO) and 5-LIO(Me-3,2-HOPO).

The threat of a dirty bomb or other major radiological contamination presents a danger of large-scale radiation exposure of the population. Because major components of such contamination are likely to be actinides, actinide decorporation treatments that will reduce radiation exposure must be a priority. Current therapies for the treatment of radionuclide contamination are limited and extensive efforts must be dedicated to the development of therapeutic, orally bioavailable, actinide chelators for emergency medical use. Using a biomimetic approach based on the similar biochemical properties of plutonium(IV) and iron(III), siderophore-inspired multidentate hydroxypyridonate ligands have been designed and are unrivaled in terms of actinide-affinity, selectivity, and efficiency. A perspective on the preclinical development of two hydroxypyridonate actinide decorporation agents, 3,4,3-LI(1,2-HOPO) and 5-LIO(Me-3,2-HOPO), is presented. The chemical syntheses of both candidate compounds have been optimized for scale-up. Baseline preparation and analytical methods suitable for manufacturing large amounts have been established. Both ligands show much higher actinide-removal efficacy than the currently approved agent, diethylenetriaminepentaacetic acid (DTPA), with different selectivity for the tested isotopes of plutonium, americium, uranium and neptunium. No toxicity is observed in cells derived from three different human tissue sources treated in vitro up to ligand concentrations of 1 mM, and both ligands were well tolerated in rats when orally administered daily at high doses (>100 micromol kg d) over 28 d under good laboratory practice guidelines. Both compounds are on an accelerated development pathway towards clinical use.