A Simple, Rapid, Comparative Evaluation of Multiple Products for Decontamination of Actinide-contaminated Rat Skin Ex Vivo

ABSTRACT

Decontamination of skin is an important medical countermeasure in order to limit potential internal contamination by radionuclides such as actinides. Minimizing skin surface contamination will ultimately prevent internal contamination and subsequent committed effective dose as well as contamination spreading. The decontamination agents tested on a rat skin ex vivo model ranged from water to hydrogel wound dressings. A surfactant-containing cleansing gel and calixarene nanoemulsion with chelation properties demonstrated marked decontamination efficacies as compared with water or the chelator DTPA. Based on efficacy to remove different actinide physicochemical forms from skin, the results demonstrate that all products can remove the more soluble forms, but a further component of emulsifying or tensioactive action is required for less soluble forms. This indicates that for practical purposes, successful decontamination will depend on identification of the actinide element, the physicochemical form, and possibly the solvent. This study offers a simple, quick, cheap, reproducible screening method for efficacy evaluation of multiple products for removal of a variety of contaminants.

DTPA Treatment of Wound Contamination in Rats with Americium: Evaluation of Urinary Profiles Using STATBIODIS Shows Importance of Prompt Administration

ABSTRACT

In the nuclear industry, wound contamination with americium is expected to increase with decommissioning and waste management. Treatment of workers with diethylenetriaminepentaacetic acid (DTPA) requires optimization to reduce internal contamination and radiation exposure. This work aimed at evaluating and comparing different DTPA protocol efficacies after wound contamination of rats with americium. Wound contamination was simulated in rats by depositing americium nitrate in an incision in the hind limb. Different routes, times, and frequencies of DTPA administration were evaluated. Individual daily urinary americium excretion and tissue retention were analyzed using the statistical tool STATBIODIS. Urinary profiles, urinary enhancement factors, and inhibition percentages of tissue retention were calculated. A single DTPA administration the day of contamination induced a rapid increase in americium urinary excretion that decreased exponentially over 7 d, indicating that the first DTPA administration should be delivered as early as possible. DTPA treatment limited americium uptake in systemic tissues irrespective of the protocol. Liver and skeleton burdens were markedly reduced, which would drive reduction of radiation dose. Local or intravenous injections were equally effective. Inherent difficulties in wound site activity measurements did not allow identification of a significant decorporating effect at the wound site. Repeated intravenous injections of DTPA also increased americium urinary excretion, which supports the use of multiple DTPA administrations shortly after wound contamination. Results from these statistical analyses will contribute to a better understanding of americium behavior in the presence or absence of DTPA and may aid optimization of treatment for workers.

Comparison of Local and Systemic DTPA Treatment Efficacy According to Actinide Physicochemical Properties Following Lung or Wound Contamination in the Rat

Purpose: In cases of occupational accidents in nuclear facilities or subsequent to terrorist activities, the most likely routes of internal contamination with alpha-particle emitting actinides, such as plutonium (Pu) and americium (Am), are by inhalation or following wounding. Following contamination, actinide transfer to the circulation and subsequent deposition in skeleton and liver depends primarily on the physicochemical nature of the compound. The treatment remit following internal contamination is to decrease actinide retention and in consequence potential health risks, both at the contamination site and in systemic retention organs as well as to promote elimination. The only approved drug for decorporation of Pu and Am is the metal chelator diethylenetriaminepentaacetic acid (DTPA). However, a limited efficacy of DTPA has been reported following contamination with insoluble actinides, irrespective of the contamination route. The objectives of this work are to evaluate the efficacy of prompt local and/or systemic DTPA treatment regimens following lung or wound contamination by actinides with differing solubility. The conclusions are drawn from retrospective analysis of experimental studies carried out over 10 years. Materials and Methods: Rat lungs or wounds were contaminated either with poorly soluble Mixed OXide (U, Pu O2) or more soluble forms of Pu (nitrate or citrate). DTPA treatment was administered promptly after contamination, locally to lungs by insufflation of a powder or inhalation of aerosolized solution or by injection directly into the wound site. Intravenous injections of DTPA were given either once or repeated in combination with the local treatment. Doses ranged from 1 to 30 µmol/kg. Animals were euthanized from day 7-21 and alpha activity levels were measured in urine, lungs, wound, bone and liver for determination of decorporation efficacy. Results: Different experiments confirmed that whatever the route of contamination, most of the activity is retained at the entry site after insoluble MOX contamination as compared with contamination with more soluble forms which results in very low activities reaching the systemic compartment and subsequent retention in bone and liver. Several DTPA treatment regimens were evaluated that had no significant effect on either lung or wound levels compared with untreated animals. In contrast, in all cases systemic retention (skeleton and liver) was reduced and urinary excretion were enhanced irrespective of the contamination route or DTPA treatment regimen. Conclusion: The present study demonstrates that despite limitation of retention in systemic organs, different DTPA protocols were ineffective in removing insoluble actinides deposited in lungs or wound site. For moderately soluble actinides, local or intravenous DTPA treatment reduced activity levels both at contamination and at systemic sites.

Research on the Radiotoxicology of Plutonium Using Animals: Consideration of the 3Rs-Replace, Reduce, Refine

To characterize the health effects of incorporated plutonium, many experiments have been conducted using different animal models. These range from (1) applied (tissue uptake/retention determination, decorporation therapy efficacy), (2) fundamental (gene expression, cancer induction), and (3) dosimetry models. In recent years, the use of animals for scientific purposes has become a public concern. The application of the 3Rs - Replace (use of alternative methods or animals not considered capable of experiencing pain, suffering, and distress), Reduce (reduction in animal numbers), and Refine (better animal welfare and minimization of suffering, pain and distress) - has increased to address ethical concerns and legislative requirements. The introduction of novel non-animal technologies is also an important factor as complementary options to animal experimentation. In radiotoxicology research, it seems there is a natural tendency to Replace given the possibility of data reuse obtained from contamination cases in man and animal studies. The creation of "registries" and "repositories" for nuclear industry workers (civil and military) is now a rich legacy for radiotoxicological measurements. Similarly, Reduction in animal numbers can be achieved by good experimental planning with prior statistical analyses of animal numbers required to obtain robust data. Multiple measurements in the same animal over time (external body counting, excreta collection) with appropriate detection instruments also allow Reduction. In terms of Refinement, this has become "de rigueur" and a necessity given the societal and legal concerns for animal welfare. For research in radiotoxicology, particularly long-term studies, better housing conditions within the constraints of radiation protection issues for research workers are an important concern. These are all pertinent considerations for the 3Rs remit and future research in radiotoxicology.

Americium biodistribution in rats after wound contamination with different physicochemical forms in the presence or absence of plutonium: analyses using STATBIODIS

Americium (Am) biodistribution data obtained after wound contamination in rats were analysed to evaluate and quantify the influence of different physicochemical forms of Am in the presence or absence of plutonium (Pu). The biodistribution data were individual Am daily urinary excretion and tissue retention. The data were analysed with STATBIODIS, a statistical tool developed in the laboratory and based on the R language. Non-parametric methods were selected to comply with the data characteristics. Am systemic tissue retention and urinary excretion data were much greater for contamination with soluble physicochemical forms than insoluble forms. Meanwhile, Am relative biodistribution between the main retention tissues (skeleton, liver and kidney) remained the same. Hence, after absorption into blood the radionuclide behaviour was independent of the physicochemical form. The presence of Pu did not change the Am biodistribution. Comparisons of the biodistribution data from the laboratory with mean values published by other laboratories showed that soluble to moderately soluble forms of Am resulted in similar urine excretion after contamination, whether it was intravenous, intramuscular, subcutaneous injection or incision. Findings from this work will contribute to improve the understanding and interpretation of wound contamination cases with different physicochemical forms and mixtures of actinides including Am.

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.

Actinide-contaminated Skin: Comparing Decontamination Efficacy of Water, Cleansing Gels, and DTPA Gels

Skin contamination by alpha-emitting actinides is a risk to workers during nuclear fuel production and reactor decommissioning. Also, the list of items for potential use in radiological dispersal devices includes plutonium and americium. The actinide chemical form is important and solvents such as tributyl phosphate, used to extract plutonium, can influence plutonium behavior. This study investigated skin fixation and efficacy of decontamination products for these actinide forms using viable pig skin in the Franz cell diffusion system. Commonly used or recommended decontamination products such as water, cleansing gel, diethylenetriamine pentaacetic acid, or octadentate hydroxypyridinone compound 3,4,3-LI(1,2-HOPO), as well as diethylenetriamine pentaacetic acid hydrogel formulations, were tested after a 2-h contact time with the contaminant. Analysis of skin samples demonstrated that more plutonium nitrate is bound to skin as compared to plutonium-tributyl phosphate, and fixation of americium to skin was also significant. The data show that for plutonium-tributyl phosphate all the products are effective ranging from 80 to 90% removal of this contaminant. This may be associated with damage to the skin by this complex and suggests a mechanical/wash-out action rather than chelation. For removal of americium and plutonium, both Trait Rouge cleansing gel and diethylenetriamine pentaacetic acid are better than water, and diethylenetriamine pentaacetic acid hydrogel is better than Osmogel. The different treatments, however, did not significantly affect the activity in deeper skin layers, which suggests a need for further improvement of decontamination procedures. The new diethylenetriamine pentaacetic acid hydrogel preparation was effective in removing americium, plutonium, and plutonium-tributyl phosphate from skin; such a formulation offers advantages and thus merits further assessment.

Actinide bioimaging in tissues: Comparison of emulsion and solid track autoradiography techniques with the iQID camera

This work presents a comparison of three autoradiography techniques for imaging biological samples contaminated with actinides: emulsion-based, plastic-based autoradiography and a quantitative digital technique, the iQID camera, based on the numerical analysis of light from a scintillator screen. In radiation toxicology it has been important to develop means of imaging actinide distribution in tissues as these radionuclides may be heterogeneously distributed within and between tissues after internal contamination. Actinide distribution determines which cells are exposed to alpha radiation and is thus potentially critical for assessing absorbed dose. The comparison was carried out by generating autoradiographs of the same biological samples contaminated with actinides with the three autoradiography techniques. These samples were cell preparations or tissue sections collected from animals contaminated with different physico-chemical forms of actinides. The autoradiograph characteristics and the performances of the techniques were evaluated and discussed mainly in terms of acquisition process, activity distribution patterns, spatial resolution and feasibility of activity quantification. The obtained autoradiographs presented similar actinide distribution at low magnification. Out of the three techniques, emulsion autoradiography is the only one to provide a highly-resolved image of the actinide distribution inherently superimposed on the biological sample. Emulsion autoradiography is hence best interpreted at higher magnifications. However, this technique is destructive for the biological sample. Both emulsion- and plastic-based autoradiography record alpha tracks and thus enabled the differentiation between ionized forms of actinides and oxide particles. This feature can help in the evaluation of decorporation therapy efficacy. The most recent technique, the iQID camera, presents several additional features: real-time imaging, separate imaging of alpha particles and gamma rays, and alpha activity quantification. The comparison of these three autoradiography techniques showed that they are complementary and the choice of the technique depends on the purpose of the imaging experiment.

Analysis methodology and development of a statistical tool for biodistribution data from internal contamination with actinides

The aim of this work was to develop a computational tool that integrates several statistical analysis features for biodistribution data from internal contamination experiments. These data represent actinide levels in biological compartments as a function of time and are derived from activity measurements in tissues and excreta. These experiments aim at assessing the influence of different contamination conditions (e.g. intake route or radioelement) on the biological behavior of the contaminant. The ever increasing number of datasets and diversity of experimental conditions make the handling and analysis of biodistribution data difficult. This work sought to facilitate the statistical analysis of a large number of datasets and the comparison of results from diverse experimental conditions. Functional modules were developed using the open-source programming language R to facilitate specific operations: descriptive statistics, visual comparison, curve fitting, and implementation of biokinetic models. In addition, the structure of the datasets was harmonized using the same table format. Analysis outputs can be written in text files and updated data can be written in the consistent table format. Hence, a data repository is built progressively, which is essential for the optimal use of animal data. Graphical representations can be automatically generated and saved as image files. The resulting computational tool was applied using data derived from wound contamination experiments conducted under different conditions. In facilitating biodistribution data handling and statistical analyses, this computational tool ensures faster analyses and a better reproducibility compared with the use of multiple office software applications. Furthermore, re-analysis of archival data and comparison of data from different sources is made much easier. Hence this tool will help to understand better the influence of contamination characteristics on actinide biokinetics. Our approach can aid the optimization of treatment protocols and therefore contribute to the improvement of the medical response after internal contamination with actinides.

Forecasting the In Vivo Behavior of Radiocontaminants of Unknown Physicochemical Properties Using a Simple In Vitro Test

An understanding of the "bioavailability" of disseminated radiocontaminants is a necessary adjunct in order to tailor treatment and to calculate dose. A simple test has been designed to predict the bioavailability of different actinide forms likely to be found after dissemination of radioactive elements by dispersal devices or nuclear reactor incidents. Plutonium (Pu) or Americium (Am) nitrate or MOX (U,PuO2) are immobilized in culture wells using a static gel phase simulating biological compartments (lung, wound, etc.). Gels are incubated in a fluid phase representing physiological media (plasma, sweat, etc.). Transfer of radionuclide from static to fluid phase reflects contaminant bioavailability. After 48 h of incubation in physiological saline, Am transfer from static to fluid phase was greater than for Pu (70% vs. 15% of initial activity). Transfer of Pu or Am was markedly less from the oxide form of the two elements (1% Am and 0.05% Pu transferred). Medium representing intracellular lysosomal fluid (pH 4) increased transfer of Pu and Am, whereas culture medium including serum reduced actinide transfer. Actinide transfer was also reduced by elements of the extracellular matrix present in the static gel phase. Increasing DTPA concentrations (5 to 500 μM) to the fluid phase significantly enhanced transfer of Pu and Am. Although this agarose gel cannot fully represent in vivo complexity, this simple test can be used to investigate and predict the behavior in vivo of radiocontaminants to support medical treatments and medical forensic investigations.

Penetration and decontamination of americium-241 ex vivo using fresh and frozen pig skin

Skin contamination is one of the most probable risks following major nuclear or radiological incidents. However, accidents involving skin contamination with radionuclides may occur in the nuclear industry, in research laboratories and in nuclear medicine departments. This work aims to measure the penetration of the radiological contaminant Americium (²⁴¹Am) in fresh and frozen skin and to evaluate the distribution of the contamination in the skin. Decontamination tests were performed using water, Fuller's earth and diethylene triamine pentaacetic acid (DTPA), which is the recommended treatment in case of skin contamination with actinides such as plutonium or americium. To assess these parameters, we used the Franz cell diffusion system with full-thickness skin obtained from pigs' ears, representative of human skin. Solutions of ²⁴¹Am were deposited on the skin samples. The radioactivity content in each compartment and skin layers was measured after 24 h by liquid scintillation counting and alpha spectrophotometry. The Am cutaneous penetration to the receiver compartment is almost negligible in fresh and frozen skin. Multiple washings with water and DTPA recovered about 90% of the initial activity. The rest remains fixed mainly in the stratum corneum. Traces of activity were detected within the epidermis and dermis which is fixed and not accessible to the decontamination.

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.

Macrophages as key elements of Mixed-oxide [U-Pu(O2)] distribution and pulmonary damage after inhalation?

Abstract Purpose: To investigate the consequences of alveolar macrophage (AM) depletion on Mixed OXide fuel (MOX: U, Pu oxide) distribution and clearance, as well as lung damage following MOX inhalation.

MATERIALS AND METHODS

Rats were exposed to MOX by nose only inhalation. AM were depleted with intratracheal administration of liposomal clodronate at 6 weeks. Lung changes, macrophage activation, as well as local and systemic actinide distribution were studied up to 3 months post-inhalation.

RESULTS

Clodronate administration modified excretion/retention patterns of α activity. At 3 months post-inhalation lung retention was higher in clodronate-treated rats compared to Phosphate Buffered Saline (PBS)-treated rats, and AM-associated α activity was also increased. Retention in liver was higher in clodronate-treated rats and fecal and urinary excretions were lower. Three months after inhalation, rats exhibited lung fibrotic lesions and alveolitis, with no marked differences between the two groups. Foamy macrophages of M2 subtype [inducible Nitric Oxide Synthase (iNOS) negative but galectin-3 positive] were frequently observed, in correlation with the accumulation of MOX particles. AM from all MOX-exposed rats showed increased chemokine levels as compared to sham controls.

CONCLUSION

Despite the transient reduced AM numbers in clodronate-treated animals no major differences on lung damage were observed as compared to non-treated rats after MOX inhalation. The higher lung activity retention in rats receiving clodronate seems to be part of a general inflammatory response and needs further investigation.

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.

Actinide handling after wound entry with local or systemic decorporation therapy in the rat

BACKGROUND

Treatment of actinide-contaminated wounds may be problematic because of contaminant physicochemical properties, dissemination and anatomical localization. This study investigates different chelation/resection protocols after contamination of rats with americium (Am) or plutonium (Pu) nitrate or mixed oxide (MOX; uranium (U), Pu oxide).

METHODS

Anesthetized rats were contaminated with Am or Pu nitrate (moderately soluble) or MOX (insoluble) following wounding of hind leg muscle. DTPA (diethylene triamine pentaacetic acid) treatment (30 μmol/kg) was immediate or delayed, systemic or local and combined or not with wound resection. Actinide urinary and tissue levels were measured.

RESULTS

Comparison of Pu nitrate and MOX dissemination at the wound site indicated a more heterogeneous localization of MOX particles. In all cases DTPA treatment reduced target tissue (bone, liver) activity levels even if DTPA treatment was started 7 days after contamination. Surgery alone increased urinary excretion suggesting release from the wound site but no subsequent increases in organ retention (bone, liver) were observed. The combination of surgery and DTPA increased Pu excretion and reduced tissue levels markedly.

CONCLUSION

This rodent model of actinide wound contamination has been used to test different treatments. It provides evidence of activity release as a result of surgery that seems not to lead to increased organ retention.

Increased retention of americium in kidneys as compared with plutonium in an actinide wound contamination model in the rat

PURPOSE

Americium-241 ((241)Am) presents a potential risk for nuclear industry workers associated with reactor decommissioning and aging combustible materials. The purpose of this study was to investigate Am renal retention after actinide contamination by wounding in the rat.

MATERIALS AND METHODS

Anesthetized rats were contaminated with Mixed Oxide (MOX) (7.1% Plutonium [Pu] by mass and containing 27% Am as % total alpha activity), Pu or Am nitrate following an incision wound of the hind leg. Times of euthanasia ranged from 2 hours to 5 months after contamination. Pu and Am levels were quantified following radiochemistry and alpha-spectrophotometry.

RESULTS

Initial data show that over the experimental period the proportion of Am in kidneys as a fraction of total kidney alpha activity was elevated as compared to MOX powder indicating a specific retention in this organ. The percentage of Pu was similar to the powder. After MOX contamination, kidney to liver ratios appeared to increase more markedly for Am (from 0.2 at 7 days to 0.6 at 90 days) as compared with Pu (0.1 at 7 days to 0.2 at 90 days). In accordance with tissue actinide retention the dose from Am to the kidney increases with time. For comparison, the ratio of estimated equivalent doses due to Am to kidney is 1.5-fold greater than for Pu (around 90 versus 60 mSv).

CONCLUSION

After actinide contamination of wounds, Am is concentrated in the kidneys as compared to Pu leading to potential exposure of renal tissue to both alpha particles and gamma radiation.

Internal contamination by actinides after wounding: a robust rodent model for assessment of local and distant actinide retention

Internal contamination by actinides following wounding may occur in nuclear fuel industry workers or subsequent to terrorist activities, causing dissemination of radioactive elements. Contamination by alpha particle emitting actinides can result in pathological effects, either local or distant from the site of entry. The objective of the present study was to develop a robust experimental approach in the rat for short- and long- term actinide contamination following wounding by incision of the skin and muscles of the hind limb. Anesthetized rats were contaminated with Mixed OXide (MOX, uranium, plutonium oxides containing 7.1% plutonium) or plutonium nitrate (Pu nitrate) following wounding by deep incision of the hind leg. Actinide excretion and tissue levels were measured as well as histological changes from 2 h to 3 mo. Humid swabs were used for rapid evaluation of contamination levels and proved to be an initial guide for contamination levels. Although the activity transferred from wound to blood is higher after contamination with a moderately soluble form of plutonium (nitrate), at 7 d most of the MOX (98%) or Pu nitrate (87%) was retained at the wound site. Rapid actinide retention in liver and bone was observed within 24 h, which increased up to 3 mo. After MOX contamination, a more rapid initial urinary excretion of americium was observed compared with plutonium. At 3 mo, around 95% of activity remained at the wound site, and excretion of Pu and Am was extremely low. This experimental approach could be applied to other situations involving contamination following wounding including rupture of the dermal, vascular, and muscle barriers.

Late-occurring pulmonary pathologies following inhalation of mixed oxide (uranium + plutonium oxide) aerosol in the rat

Accidental exposure by inhalation to alpha-emitting particles from mixed oxide (MOX: uranium and plutonium oxide) fuels is a potential long-term health risk to workers in nuclear fuel fabrication plants. For MOX fuels, the risk of lung cancer development may be different from that assigned to individual components (plutonium, uranium) given different physico-chemical characteristics. The objective of this study was to investigate late effects in rat lungs following inhalation of MOX aerosols of similar particle size containing 2.5 or 7.1% plutonium. Conscious rats were exposed to MOX aerosols and kept for their entire lifespan. Different initial lung burdens (ILBs) were obtained using different amounts of MOX. Lung total alpha activity was determined by external counting and at autopsy for total lung dose calculation. Fixed lung tissue was used for anatomopathological, autoradiographical, and immunohistochemical analyses. Inhalation of MOX at ILBs ranging from 1-20 kBq resulted in lung pathologies (90% of rats) including fibrosis (70%) and malignant lung tumors (45%). High ILBs (4-20 kBq) resulted in reduced survival time (N = 102; p < 0.05) frequently associated with lung fibrosis. Malignant tumor incidence increased linearly with dose (up to 60 Gy) with a risk of 1-1.6% Gy for MOX, similar to results for industrial plutonium oxide alone (1.9% Gy). Staining with antibodies against Surfactant Protein-C, Thyroid Transcription Factor-1, or Oct-4 showed differential labeling of tumor types. In conclusion, late effects following MOX inhalation result in similar risk for development of lung tumors as compared with industrial plutonium oxide.

Persistence of altered 5-hydroxytryptamine turnover following hemibody X-irradiation in the rat distal colon

PURPOSE

Acute gastrointestinal responses to ionizing radiation exposure include a role for 5-hydroxytryptamine (5-HT), but it is not known whether involvement of 5-HT persists and contributes to late effects. The aim was to investigate the acute and later effects of lower hemibody irradiation on 5-HT turnover and the biological effect in the rat distal colon.

MATERIALS AND METHODS

Rats were exposed to 10 Gy lower hemibody X-radiation. 5-HT and 5-hydroxyindole acetic acid tissue levels were measured in the distal colon along with the serotonin re-uptake transporter and tryptophan hydroxylase mRNA. 5-HT-containing cells and crypt cell numbers were estimated in addition to 5-HT-stimulated short-circuit current responses in isolated mucosa. Studies were performed from 3 days to 3 months post-exposure.

RESULTS

During the acute phase, at 3 days post-irradiation, reductions in cell number, tissue resistance, serotonin re-uptake transporter expression and secretory responses to 5-HT were observed. However, at later times when secretory responses were normal, 5-HT tissue levels and enterochromaffin cell numbers were increased.

CONCLUSIONS

The results provide evidence that after 10 Gy hemibody irradiation, modifications persist past the acute phase. In particular, 5-HT turnover in the distal colon is altered during a longer period.

Imbalance of the antioxidant network of mouse small intestinal mucosa after radiation exposure

The aim of this study was to investigate acute variations in antioxidant defense systems in the intestinal mucosa after abdominal radiation exposure and the role played by radiation-induced inflammation in these variations. Antioxidant defense systems of mouse small intestinal mucosa were studied at 6 h and 4 days after abdominal radiation exposure. Superoxide dismutases, glutathione peroxidases, catalase, metallothioneins and thioredoxins were followed in terms of mRNA expression, protein expression and enzyme activities. Dexamethasone was administered to investigate the relationship between variations in mucosal antioxidant capacity and radiation-induced inflammation. Six hours after exposure, only mitochondrial-associated antioxidant systems were induced (the superoxide dismutase and thioredoxin 2). Four days after exposure, during the inflammatory phase, superoxide dismutases were decreased and modulations of the second line of the antioxidant network were also observed: Catalase was decreased and glutathione peroxidases and metallothioneins were induced. Dexamethasone treatment modulated only glutathione peroxidase expression and did not influence either metallothionein or superoxide dismutase expression. Our findings provide direct in vivo evidence that antioxidant mechanisms of the small intestinal mucosa were not markedly mobilized during the very acute tissue radiation response. During the radiation-induced acute inflammatory response, the antioxidant capacity appeared to be dependent on inflammatory status to a certain extent.

Maintenance of differentiation capacity of HT-29 cells after radiation exposure

PURPOSE

Following ionizing radiation exposure, intestinal crypt regeneration is possible but it is still not known if regenerating crypts give rise to differentiated functional epithelial cells on villi. The aim of this study was to demonstrate that irradiated progeny of enterocytic precursor cells are capable of proliferation and subsequent differentiation using the HT-29?cell line.

MATERIALS AND METHODS

Cells were cultured, irradiated (5 Gy or 10 Gy) and incubated in the presence or absence of butyrate (5 mM). Cell numbers, cell cycle parameters, alkaline phosphatase (ALP) activity, occludin labelling and gene expression were determined at different times post-exposure.

RESULTS

Butyrate-induced inhibition of cell growth and arrest in G0 phase was comparable in both sham and irradiated cells in addition to similar development of ALP activity and expression. Cells also formed a monolayer with tight junctions post-irradiation. Butyrate-stimulated modulation of integrin expression during differentiation was unchanged after radiation exposure. Genes known to be implicated in differentiation mechanisms, i.e., growth and transcription factors (vascular Epidermal Growth Factor, v-EGF ; Activating Transcription Factor 4, ATF4), cell cycle genes (Cyclin-Dependent Kinase Inhibitor 1A, CDKN1A/p21(Cip1/waf1)), were studied. Most responded similarly to the differentiation stimulus whether irradiated or not.

CONCLUSION

These results demonstrate that irradiated HT-29 cells still respond to butyrate to form a differentiated, functional epithelium.

Functional and structural alterations of epithelial barrier properties of rat ileum following X-irradiation

Irradiation of the digestive system leads to alterations of the small intestine. We have characterized the disruption of the barrier integrity in rat ileum from 1 to 14 days following irradiation ranging from 6 to 12 Gy. The intestinal permeability to 14C-mannitol and 3H-dextran 70 000 was measured in vitro in Ussing chambers. In parallel to these functional studies, immunohistochemical analyses of junctional proteins (ZO-1 and beta-catenin) of ileal epithelium were performed by confocal microscopy. Irradiation with 10 Gy induced a marked decrease in epithelial tissue resistance at three days and a fivefold increase in mannitol permeability, without modifications of dextran permeability. A disorganization of the localization for ZO-1 and beta-catenin was also observed. At 7 days after irradiation, we observed a recovery of the organization of junctional proteins in parallel to a return of intestinal permeability to control value. In addition to these time-dependent effects, a gradual effect on epithelial integrity of the radiation doses was observed 3 days after irradiation. This study shows a disruption of the integrity of the intestinal barrier in rat ileum following abdominal X-irradiation, depending on the time postirradiation and on the delivered dose. The loss of barrier integrity was characterized by a disorganization of proteins of tight and adherent junctions, leading to increased intestinal permeability to mannitol.

Differential qualitative and temporal changes in the response of the hypothalamus-pituitary-adrenal axis in rats after localized or total-body irradiation

Stress such as exposure to ionizing radiation is able to activate the hypothalamus-pituitary-adrenal axis. The present study sought to examine the effects of different configurations of a 10-Gy gamma irradiation in rats on the hypothalamus-pituitary-adrenal axis to understand the mechanism of negative feedback by glucocorticoids induced by ionizing radiation. Specifically, we determined adrenocorticotropin and corticosterone levels in plasma as well as corticotrophin-releasing factor expression in the paraventricular nucleus of the hypothalamus by in situ hybridization from 6 h to 4 days after total-body, abdominal or head irradiation. In this study, we found an activation of the hypothalamus-pituitary-adrenal axis after radiation exposure. Plasma adrenocorticotropin and corticosterone levels were significantly increased after total-body and abdominal irradiation 3 days after exposure, in parallel with decreased labeling of corticotrophin-releasing factor mRNA in the parvocellular region of the paraventricular nucleus of the hypothalamus. Our results suggest that ionizing radiation activates the neuroendocrine system to protect the organism from the occurrence of radiation-induced inflammation.

Use of Reference Gene Expression in Rat Distal Colon after Radiation Exposure: A Caveat

Research on the effects of ionizing radiation exposure includes transcriptome studies using real-time reverse transcription polymerase chain reaction (RT-PCR). These studies require the use of a reference gene that normalizes for cDNA quantity and corrects for transcription between different samples. In this study, several criteria are reviewed that allow the choice of a reference gene. With the example of five genes selected from the widely used standard housekeeping genes, Gapd (glyceraldehyde-3-phosphate dehydrogenase), Hprt (hypoxanthine-guanine phosphoribosyl transferase), cyclophilin A, AcRP0 (acidic ribosomal protein P0) and 18S, we show that the use of a reference gene without a preliminary study is hazardous. We have shown in rat colon after a hemi-body irradiation that expression of a gene of interest, the serotonin receptor type 1F (5-HT(1F)), was either increased or unchanged, with the result depending on the reference gene used. This work has led us to propose the use of two reference genes, a ribosomal gene, 18S, and another gene with a level of expression closer to that of the gene of interest. The methodology reported here may be applied to other studies of gene expression levels to evaluate the effects of experimental treatment on the expression of potential reference genes.

Screening of a large panel of gastrointestinal peptide plasma levels is not adapted for the evaluation of digestive damage following irradiation

The aim of this study was to assess the potential of gastrointestinal peptide plasma levels as biomarkers of radiation-induced digestive tract damage. To this end, plasma levels of substance P, GRP, motilin, PYY, somatostatin-28, gastrin, and neurotensin were followed for up to 5 days in pigs after a 16-Gy whole-body X-irradiation, completed by a histopathological study performed at 5 days. Each peptide gave a specific response to irradiation. The plasma levels of GRP and substance P were not modified by irradiation exposure; neither were those of motilin and PYY. Concerning gastrin, a 2-3-fold increase of plasma concentration was observed in pig, which presented the most important histological alterations of the stomach. The plasma levels of somatostatin, unchanged from 1 to 4 days after irradiation, was also increased by 130% at 5 days. In contrast, a diminution of neurotensin plasma levels was noted, firstly at 1 day (-88%), and from 3 days after exposure (-50%). The present study suggested that changes in gastrin and neurotensin plasma levels were associated with structural alterations of the stomach and ileum, respectively, indicating that they may be relevant biological indicators of radiation-induced digestive damage to these segments.

Alteration of the enterohepatic recirculation of bile acids in rats after exposure to ionizing radiation

The aim of this work was to study acute alterations of the enterohepatic recirculation (EHR) of bile acids 3 days after an 8-Gy radiation exposure in vivo in the rat by a washout technique. Using this technique in association with HPLC analysis, the EHR of the major individual bile acids was determined in control and irradiated animals. Ex vivo ileal taurocholate absorption was also studied in Ussing chambers. Major hepatic enzyme activities involved in bile acid synthesis were also measured. Measurements of bile acid intestinal content and intestinal absorption efficiency calculation from washout showed reduced intestinal absorption with significant differences from one bile acid to another: absorption of taurocholate and tauromuricholate was decreased, whereas absorption of the more hydrophobic taurochenodeoxycholate was increased, suggesting that intestinal passive diffusion was enhanced, whereas ileal active transport might be reduced. Basal hepatic secretion was increased only for taurocholate, in accordance with the marked increase of CYP8B1 activity in the liver. The results are clearly demonstrate that concomitantly with radiation-induced intestinal bile acid malabsorption, hepatic bile acid synthesis and secretion are also changed. A current working model for pathophysiological changes in enterohepatic recycling after irradiation is thus proposed.Key words: irradiation, bile acids, intestine, liver, enterohepatic recycling.

Effect of radiation on cAMP, cGMP and Ca(2+)(i) pathways and their interactions in rat distal colon

The secretory response implicated in the intestinal response to luminal attack is altered by radiation. The cAMP, cGMP and Ca(2+)(i) pathways leading to secretion as well as the interactions between the cAMP pathway and the cGMP or Ca(2+)(i) pathway were studied in the rat distal colon 4 days after a 9-Gy abdominal X irradiation, when modifications mainly occurred. The secretory response in Ussing chambers and cAMP and cGMP accumulation in single isolated crypts were measured. The muscarinic receptor characteristics were determined in mucosal membrane preparations. The secretory response by the cAMP pathway (stimulated by vasoactive intestinal peptide or forskolin) and the cAMP accumulation in crypts were decreased (P < 0.05) after irradiation. The weak secretory response induced by the cGMP pathway (stimulated by nitric oxide or guanylin) was unaltered by radiation, and the small amount of cGMP determined in isolated crypts from the control group became undetectable in the irradiated group. Inducible NOS was not involved in the hyporesponsiveness to VIP after irradiation (there was no effect of an iNOS inhibitor). The secretory response by the Ca(2+)(i) pathway (stimulated by carbachol) was unaffected despite a decreased number and increased affinity of muscarinic receptors. The non-additivity of VIP and carbachol co-stimulated responses was unmodified. In contrast, VIP and SNP co-stimulation showed that NO enhanced the radiation-induced hyporesponsiveness to VIP through a reduced accumulation of cAMP in crypts. This study provides further understanding of the effect of ionizing radiation on the intracellular signaling pathways.

'In-field' and 'out-of-field' functional impairment during subacute and chronic phases of experimental radiation enteropathy in the rat

PURPOSE

To investigate subacute and chronic functional consequences of localized irradiation of rat small intestine on exposed and shielded segments (proximal and distal).

MATERIALS AND METHODS

The surgical model of a scrotal hernia was used. The ileal loop was exposed to single doses of 18, 21 or 29.6 Gy X-irradiation. Epithelial structure and transport capacity were followed 2 and 26 weeks post-exposure.

RESULTS

Irradiated segments showed mucosal ulceration followed by transmural fibrosis. Transport capacity was impaired from 2 to 26 weeks. Subacute functional impairment was noticed in the proximal segment, without either morphological alteration or neutrophil influx. At 26 weeks, both proximal and distal segments showed impaired epithelial transport capacity, with neutrophil influx in the submucosa in cases of 21-Gy exposure and in the submucosa and muscularis propria after 29.6 Gy.

CONCLUSIONS

Radiation enteritis was characterized by functional impairment, within as well as outside, the irradiation field. During the subacute phase, the irradiated segment may be a source of mediators which might influence intestinal function outside the site of injury via the blood stream and/or enteric nervous system. The development of an intestinal occlusion syndrome during the chronic phase might be responsible for intestinal dysfunction but it does not rule out a possible inflammatory process developing in the shielded parts of the small intestine.

Alterations in water and electrolyte absorption in the rat colon following neutron irradiation: influence of neutron component and irradiation dose

PURPOSE

To study the absorptive function of rat colon following whole-body exposure to neutron irradiation, either to the same total dose with varying proportion of neutrons or to the same neutron proportion with an increasing irradiation dose.

MATERIALS AND METHODS

Different proportions of neutron irradiation were produced from the reactor SILENE using a fissile solution of uranium nitrate (8, 47 and 87% neutron). Water and electrolyte fluxes were measured in the rat in vivo under anaesthesia by insertion into the descending colon of an agarose gel cylinder simulating the faeces. Functional studies were completed by histological analyses. In the first set of experiments, rats received 3.8 Gy with various neutron percentages and were studied from 1 to 14 days after exposure. In the second set of experiments, rats were exposed to increasing doses of irradiation (1-4Gy) with a high neutron percentage (87%n) and were studied at 4 days after exposure.

RESULTS AND CONCLUSIONS

The absorptive capacity of rat colon was diminished by irradiation at 3-5 days, with a nadir at 4 days. The results demonstrate that an increase in the neutron proportion is associated with an amplification of the effects. Furthermore, a delay in the re-establishment of normal absorption was observed with the high neutron proportion (87%n). A dose-dependent reduction of water absorption by rat colon was also observed following neutron irradiation (87%n), with a 50% reduction at 3 Gy. Comparison of this dose-effect curve with the curve obtained following gamma (60)Co-irradiation indicates an RBE of 2.2 for absorptive colonic function in rat calculated at 4 days after exposure.

Potential role of the membrane in the development of intestinal cellular damage after whole-body gamma irradiation of the rat

Our study emphasizes the effect of gamma irradiation on intestinal cell membrane fluidity and addresses the potential relationships existing between radiation-induced lipoperoxidation, membrane fluidity, and changes in membrane protein activities. Male Wistar rats were exposed to an 8-Gy total body irradiation (60Co source) and studied 1, 4, and 7 days after irradiation (D1, D4, and D7). Membrane enzyme activities and fluorescence anisotropy were determined on small intestinal crude membrane preparations. The supernatants of membrane preparations as well as plasma were used for malonedialdehyde (MDA) quantification. The effect of carbamylcholine on electrical parameters was estimated on distal ileum placed in Ussing chambers. We observed a decrease in fluorescence anisotropy for at least 7 days, an increase in membrane production of MDA at D4, a decrease in membrane enzyme activities at D4, but an amplification of carbamylcholine-induced increase in short-circuit current at D4 and D7. Furthermore, correlations were observed between the 1,6-diphenyl-1,3,5-hexatriene anisotropy coefficient and sucrase activity and between MDA levels and leucine aminopeptidase activity. Thus, total body irradiation induces changes in intestinal membrane fluidity and an increase in lipoperoxidation. These modifications may have an impact on the activity of membrane proteins involved in intestinal function.

Alterations of the VIP-stimulated cAMP pathway in rat distal colon after abdominal irradiation

Ionizing radiation induces hyporesponsiveness of rat colonic mucosa to vasoactive intestinal peptide (VIP). Possible mechanisms responsible for this hyporesponsiveness of the cAMP communication pathway in rat colon were investigated. VIP- and forskolin-stimulated short-circuit current (I(sc)) responses were studied after a 10-Gy abdominal irradiation in Ussing chambers as well as in single, isolated crypts. Adenylyl cyclase (AC) activity and VIP receptor characteristics were determined in mucosal membrane preparations. In addition, alterations in crypt morphology were studied. Impaired secretory responses to VIP and forskolin were observed 4 days after irradiation (decrease of 80%). cAMP analog-stimulated I(sc) responses were unchanged. In isolated crypts, VIP- and forskolin-stimulated cAMP accumulation was markedly reduced by 80 and 50%, respectively. VIP-stimulated AC activity and VIP receptor number were decreased in membrane preparations. No major change of cellularity was associated with these functional alterations. In conclusion, the decreased secretory responses to VIP of rat colon are associated with reduced cAMP accumulation, decreased AC activity, and diminution of VIP receptor numbers without a marked decrease of crypt cell number.

The recovery of the neurally evoked secretory response of rat colonic mucosa after irradiation is independent of mast cells

The ability of the enteric submucosal plexus to influence the transport of water and electrolytes in the colon was investigated in rats for 1 week after acute whole-body gamma irradiation. The involvement of neuroimmune links in the epithelial responses to nerve stimulation was confirmed by the sensitivity of the tissue to tetrodotoxin, mepyramine and doxantrazole. At 1 and 3 days after irradiation, colon tissues were hyporesponsive to nerve stimulation. This was associated with a drastic diminution of mucosal mast cell numbers, tissue histamine levels, and rat mast cell protease II (RMCP II) levels, and by a decreased maximal epithelial response to exogenously added histamine. The responses to electric-field stimulation were insensitive to both mepyramine and doxantrazole. At 7 days, neurally evoked responses recovered, despite the virtual absence of mast cells, tissue histamine and RMCP II, and the continuing decreased response to histamine. The responses were insensitive to doxantrazole but were decreased by mepyramine. This study showed that the establishment of a normal epithelial response to neural stimulation can occur despite the radiation-induced depletion of mucosal mast cells. The recovery of the epithelial response, which was sensitive to mepyramine, may be ascribed to the reappearance of an unknown histaminergic pathway, which probably has indirect effects on epithelial transport but is independent of nerve-mast cell connections.

Effect of granisetron on radiation-induced alterations of colonic motility and fluid absorption in rats

BACKGROUND

Radiation-induced diarrhoea is attributed to both mucosal injury and alterations of intestinal motility. Previous reports have indicated that 5-hydroxytryptamine is released following irradiation, which may contribute to these changes.

AIMS

To investigate the effects of granisetron (5-hydroxytryptamine type-3 receptor antagonist) on colonic motility, fluid absorption and 5-hydroxytryptamine colonic content following abdominal irradiation (10 Gy) in rats.

METHODS

In vivo measurements of motility and fluid absorption in the proximal and distal colon, respectively, diarrhoea score and 5-hydroxytryptamine tissue levels were performed 3 and 7 days after abdominal irradiation. The effects of post-irradiation granisetron (0.3 mg/kg subcutaneously) were also evaluated.

RESULTS

Colonic motility and fluid/Na(+) absorption were reduced 3 and 7 days after irradiation. All rats developed diarrhoea (3 days) concomitant with increased colonic mucosal 5-hydroxytryptamine levels. Granisetron prevented diarrhoea, attenuated decreased colonic motility and reduced 5-hydroxytryptamine levels on day 3, although fluid absorption was only slightly improved. On day 7, colonic motility and fluid/Na(+) absorption were restored in granisetron-dosed animals.

CONCLUSIONS

These results indicate that radiation-induced diarrhoea involves alterations of both colonic motility and fluid/Na(+) absorption. 5-Hydroxytryptamine could be one of the mediators implicated in these alterations, as post-irradiation dosage with a 5-hydroxytryptamine type-3 receptor antagonist improved colonic motility and prevented diarrhoea on day 3.

Evidence for modulation of pericryptal sheath myofibroblasts in rat descending colon by transforming growth factor beta and angiotensin II

BACKGROUND

Absorption of water and Na+ in descending colonic crypts is dependent on the barrier function of the surrounding myofibroblastic pericryptal sheath. Here the effects of high and low Na+ diets and exposure to whole body ionising radiation on the growth and activation of the descending colonic pericryptal myofibroblasts are evaluated. In addition the effect of a post-irradiation treatment with the angiotensin converting enzyme inhibitor Captopril was investigated.

METHODS

The levels of Angiotensin II type 1 receptor (AT1), ACE, collagen type IV, transforming growth factor-beta type 1 receptor (TGF-betaR1), OB cadherin and alpha-smooth muscle actin in both descending colon and caecum were evaluated, using immunocytochemistry and confocal microscopy, in rats fed on high and low Na+ diets (LS). These parameters were also determined during 3 months post-irradiation with 8Gy from a 60Co source in the presence and absence of the angiotensin converting enzyme inhibitor, Captopril.

RESULTS

Increases in AT1 receptor (135.6% +/- 18.3, P < 0.001); ACE (70.1% +/- 13.1, P < 0.001); collagen type IV (49.6% +/- 15.3, P < 0.001); TGF-+/-beta1 receptors (291.0% +/- 26.5, P < 0.001); OB-cadherin (26.3% +/- 13.8, P < 0.05) and alpha-smooth muscle actin (82.5% +/- 12.4, P < 0.001) were observed in the pericryptal myofibroblasts of the descending colon after LS diet. There are also increases in AT1 receptor and TGF-beta1 receptor, smooth muscle actin and collagen type IV after irradiation. Captopril reduced all these effects of irradiation on the pericryptal sheath and also decreased the amount of collagen and smooth muscle actin in control rats (P < 0.001).

CONCLUSIONS

These results demonstrate an activation of descending colonic myofibroblasts to trophic stimuli, or irradiation, which can be attenuated by Captopril, indicative of local trophic control by angiotensin II and TGF-beta release.

Characterization of altered absorptive and secretory functions in the rat colon after abdominal irradiation: comparison with the effects of total-body irradiation

The aim of this work was to determine the alterations in the absorptive and secretory functions of the rat colon after abdominal irradiation and to compare the effects of abdominal and whole-body irradiation. Rats received an abdominal irradiation with 8 to 12 Gy and were studied at 1, 4 and 7 days after exposure. Water and electrolyte absorption was measured in vivo by insertion of an agarose cylinder into the colons of anesthetized rats. In vitro measurements of potential difference, short-circuit current and tissue conductance were performed in Ussing chambers under basal and agonist-stimulated conditions. Most of the changes appeared at 4 days after abdominal irradiation. At this time, a decrease in water and electrolyte absorption in the colon was observed for radiation doses > or = 9 Gy. The response to secretagogues (VIP, 5-HT and forskolin) was attenuated after 10 and 12 Gy. Epithelial integrity, estimated by potential difference and tissue conductance, was altered from 1 to 7 days after 12 Gy abdominal irradiation. These results show that the function of the colon was affected by abdominal irradiation. Comparison with earlier results for total-body irradiation demonstrated a difference of 2 Gy in the radiation dose needed to induce changes in the function of the colon.

Dose dependence effects of ionizing radiation on bile acid metabolism in the rat

PURPOSE

To study radiation dose-related changes of individual or total bile acids in various physiological fluids in order to identify potential bio-indicators of radiation-induced gastrointestinal injuries.

MATERIALS AND METHODS

Wistar rats were sham- or whole-body gamma irradiated (1-12Gy). Total and individual bile acids were quantified, 3 days after exposure, in bile collected after catheterization of the bile duct. Total bile acid concentrations were also measured in plasma and colonic contents 1, 2 and 3 days after irradiation. These concentrations were determined by an enzymatic method whereas individual bile acids were quantified by HPLC.

RESULTS

In bile, whereas total bile acid concentration remained unchanged after irradiation whatever the dose, the proportion of dihydroxy bile acids in the pool of total bile acids was gradually increased with the irradiation dose, especially from 8 Gy. In plasma samples, total bile acid concentrations fell for doses higher than 10 Gy. In colonic contents, bile acid concentrations increased progressively with time (from 1 to 3 days) and with irradiation dose (from 1 to 12Gy), reaching a plateau 3 days after exposure for doses higher than 10 Gy.

CONCLUSIONS

These results show that changes in colonic bile acid concentrations which are reflected in faeces are perhaps a useful parameter to improve diagnosis and prognosis of radiation-induced gastrointestinal damage since it probably reflects directly intestinal bile acid malabsorption.

The example of gastrointestinal damage induced by ionising radiation: are there accessible markers?

Ionising radiation exposure occurs during radiotherapy, diagnostic tests or by accident. In all cases the gastrointestinal tract, which is highly sensitive to radiation, may be at risk. Each region may respond differently to radiation exposure which to some extent is reflected by clinical symptoms. The evaluation of injury, whether acute or chronic, depends on the utilization of a variety of techniques. It appears that no definitive tests exist and that a multiparametric analysis should be undertaken. This review addresses the question of accessible markers associated with radiation-induced intestinal pathologies. Several approaches are discussed which include clinical observations, measurement of faecal parameters, changes in inflammatory mediators and possible applications of imaging techniques.

Absence of protective role of afferent nerves in early intestinal mucosal alterations induced by abdominal irradiation in rats

PURPOSE

To assess the early effects of primary afferent nerve suppression by systemic treatment with the neurotoxin capsaicin in an acute model of abdominal irradiation in rats (10Gy, gamma).

MATERIALS AND METHODS

Changes in myeloperoxidase (MPO) activity, calcitonin gene-related peptide (CGRP) tissue content, number of mast cells and apoptotic cells were determined in jejunum and ileum in four groups of rat male Wistar (vehicle sham-irradiated, vehicle irradiated, capsaicin sham-irradiated and capsaicin irradiated) at 1 and 3 days post-irradiation.

RESULTS

In vehicle irradiated rats, CGRP was significantly increased from the first day after irradiation in jejunal mucosa; MPO activity increased in both segments at day 3 but not at day 1 after irradiation; the number of detectable mucosal mast cells dropped to nearly zero on days 1 and 3, while the apoptotic cells in the intestinal mucosa were significantly increased at day 1. Similar results were obtained for mast cells and apoptosis in capsaicin irradiated rats as compared to capsaicin sham-irradiated rats, while MPO activity was significantly increased and CGRP concentration in jejunal mucosa significantly decreased from the first day in these rats in comparison with capsaicin sham-irradiated rats.

CONCLUSIONS

Intestinal sensory innervation seems not to have a major protective role against a radiation-induced intestinal inflammatory reaction.

Intestinal and colonic motor alterations associated with irradiation-induced diarrhoea in rats

Localized application of ionizing radiation to the gastrointestinal tract frequently elicits responses, which include diarrhoea. The origin of this symptom is not clear but has been attributed to loss of epithelial integrity, together with alterations in motility and increased secretion. The purpose of this study was to examine whether a 10 Gy abdominal gamma irradiation leads to an inflammatory reaction, and to compare intestinal and colonic motility in controls and abdominally irradiated rats 1, 3 and 7 days after irradiation, using an electromyographic technique. The motility parameters analysed were the frequency and velocity of propagation of migrating myoelectric complexes (MMC) in the jejunum and colonic spike activity (long spike bursts; LSB) per 10 min in fasted rats. The MMC frequency was significantly reduced on days 1 and 7 after irradiation and the MMC pattern was markedly disrupted on day 3. The frequency of colonic LSB was significantly reduced on days 1, 3 and 7. Mouth to anus transit was significantly accelerated on day 3 only and diarrhoea was observed at this time. Myeloperoxidase activity in the jejunum and colon was also increased on this day only. It is concluded that irradiation-induced diarrhoea occurs contemporaneously with disruption of MMC in the small intestine.

Radiation induced cytochrome c release causes loss of rat colonic fluid absorption by damage to crypts and pericryptal myofibroblasts

BACKGROUND

Therapeutic or accidental exposure to radiation commonly causes gastrointestinal disturbances, including diarrhoea. Rats subjected to whole body ionising radiation at a dose of 8 Gy lose their capacity to absorb fluid via the descending colon after four days. After seven days, fluid absorption recovers to control levels.

AIMS

To investigate the effect of ionising radiation on colonic permeability together with its effect on mitochondria dependent apoptotic signals and intercellular adhesion molecules.

METHODS

Rats were irradiated with doses of 0-12 Gy. Colonic permeability was measured by accumulation of fluorescein isothiocyanate (FITC) dextran in crypt lumens. Changes in levels of cytochrome c, caspase 3, E and OB cadherin, beta-catenin smooth muscle actin, and collagen IV were assessed using immunocytochemistry with confocal microscopy.

RESULTS

Cytosolic cytochrome c increased after 8 Gy (t(1/2) 1.4 (0.6) hours) and peaked at approximately six hours. Caspase 3 increased more slowly, particularly in crypt epithelial cells (t(1/2) 57 (14.5) hours). Pericryptal myofibroblasts disintegrated within 24 hours as was evident from loss of OB cadherin and smooth muscle actin. This coincided with increased crypt permeability to dextran. Intercellular adhesion between crypt luminal cells was not lost until day 4 when both beta-catenin and E-cadherin were minimal. The half maximal dose-response for these effects was in the range 2-4 Gy. Recovery of colonic transport was concurrent with recovery of pericryptal smooth muscle actin and OB cadherin. The pan caspase inhibitor Z-Val-Ala-Asp.fluoromethylketone (1 mg/kg per day) had a small effect in conserving the pericryptal sheath myofibroblasts and sheath permeability but had no systemic therapeutic effects.

CONCLUSIONS

These data suggest that radiation damage to the colon may be initiated by mitochondrial events. Loss of crypt fluid absorption and increased permeability coincided with decreased intercellular adhesion between crypt epithelial cells and loss of pericryptal sheath barrier function.

Functional changes in the rat distal colon after whole-body irradiation: dose-response and temporal relationships

The aim of this study was to determine the acute radiation response of the rat distal colon by in vivo and in vitro measurements of the functions of the colon over a range of radiation doses. Rats received a whole-body irradiation of 2 to 12 Gy and were studied from 1 to 7 days after exposure. In vivo water and electrolyte absorption was measured by insertion of an agarose cylinder in the colon of anesthetized rats. In vitro transepithelial electrical parameters (potential difference, short-circuit current, transepithelial conductance) were measured in Ussing chambers in basal and agonist-stimulated conditions. In vivo and in vitro functional studies were completed by standard histological analyses. The majority of functional modifications appeared at 4 days after exposure. At this time, a dose-dependent decrease in absorption of water and sodium/chloride ions in the colon was noted. In contrast, a twofold increase in potassium secretion was observed for every radiation dose studied. The response to secretagogues was attenuated at doses >8 Gy. Modifications of basal transepithelial electrical parameters together with marked histological alterations were observed at 4 days with the higher doses (>/=10 Gy). In conclusion, these results show that functions of the colon are affected by irradiation and may contribute to diarrhea induced by ionizing radiation.

Changes in 5-HT-mediated pathways in radiation-induced attenuation and recovery of ion transport in rat colon

Whole body exposure to high doses of ionizing radiation is associated with small intestinal and colonic dysfunction, the etiology of which remains unknown. In this study, we investigated the role of both neural and nonneural 5-hydroxytryptamine (5-HT)-mediated pathways in radiation-induced attenuation and recovery of colonic secretory function. Rats were exposed to whole body 10-Gy gamma irradiation, and distal colonic tissues were studied in Ussing chambers 1, 3, and 7 days after exposure. Tissue responses to exogenously added 5-HT (nonneural pathway) and electrical field stimulation (EFS; neural pathway) were performed, and 5-HT receptor subtypes implicated in both responses were determined using three different 5-HT receptor antagonists: methysergide (5-HT(2/1C)), granisetron (5-HT(3)), and SDZ-205,557 (5-HT(4)). Maximal responses to exogenously added 5-HT were decreased at 1 and 3 days and returned to control values at 7 days. Responses to exogenous 5-HT were insensitive to both 5-HT(2/1C) and 5-HT(3) antagonists and to TTX but were totally inhibited by SDZ-205, 557 in both control and irradiated tissues. Responses to EFS were decreased 1 and 3 days after exposure and returned to control values at 7 days. In control tissues and 1 and 3 days after exposure, EFS responses were insensitive to both 5-HT(2/1C) and 5-HT(4) antagonists but reduced by granisetron in control (51%) and at 1 (64%) and 3 days (58%) after exposure. Granisetron was more effective at 7 days (73% inhibition), which was concomitant with the appearance of a 5-HT(4) antagonist-sensitive pathway (40% inhibition). In conclusion, neural and nonneural 5-HT-mediated pathways involve 5-HT(3) and 5-HT(4) receptors, respectively, in control as well as in irradiated tissues 1 and 3 days after exposure. Conversely, the recovery of colonic transport is associated with additional 5-HT(3)-mediated pathways, probably in combination with 5-HT(4) receptors.

Modified absorptive and secretory processes in the rat distal colon after neutron irradiation: in vivo and in vitro studies

Impaired fluid and electrolyte transport in the intestine is a well-recognized characteristic of radiation-induced pathologies in the gastrointestinal tract. The aim of this study was to investigate the responsiveness of the epithelium of the colon of the rat to electrical and pharmacological (serotonin, carbachol) stimulation concomitantly with in vivo assessment of the absorptive capacity of the colon at 1, 3, 5 and 7 days after 3.8 Gy whole-body exposure to neutrons. The responsiveness of rat colon in vitro to electrical stimulation and the number of mast cells were measured to examine the role of neuroimmune networks in radiation-induced dysfunction. Animals showed an impaired capacity of the colon to absorb water and sodium from 3 to 5 days after irradiation together with decreased responsiveness to electrical and pharmacological stimulation. The time course of decreased responsiveness to neural stimulation was similar to that of impaired absorption observed in vivo, but it was not correlated with variations in mast cell numbers. Histological (mast cells) and biochemical analyses (myeloperoxidase and NO synthase activities) did not find evidence of a marked infiltration and/or activation of inflammatory cells. Thus the impaired absorptive capacity of the colon observed after irradiation occurs concomitantly with decreased neural influence, and is possibly related to reduced epithelial functional capacity but not to decreased mast cell numbers.