Kinetics of intracolloidal iodine in thyroid of iodine-deficient or equilibrated newborn rats. Direct imaging using secondary ion mass spectrometry.

The most significant impact of the Chernobyl accident is the increased incidence of thyroid cancers among children. In order to accurately estimate the radiation dose provided by radioiodines, it is important to examine how the distribution of newly incorporated iodine varies with time and if this distribution varies according to the iodine status. The kinetic distribution of intra colloidal newly organified iodine in the rat immature thyroid was recorded and analysed using the ionic nanoprobe NanoSims50. Our observations imply that in case of radioiodine contamination, the energy deposits vary (i) with time, (ii) from one follicle to another, and (iii) from one cell to another inside the same follicle regardless the iodine status. The kinetic heterogeneity of iodine distribution must be take in account in thyroid dose evaluation.

Analysis of the distribution of MRI contrast agents in the livers of small animals by means of complementary microscopies.

BACKGROUND: Magnetic resonance imaging (MRI) contrast agents contain magnetic molecules such as iron (Fe) or gadolinium (Gd) that are injected in vivo into rats or mice to study their distribution inside the liver. Fluorescent europium (Eu) can be used as a model of Gd to obtain comparable information of this distribution of corresponding contrast agents. In a similar approach, Fe can be attached to Texas Red and used as a model of ferumoxides and be detected by fluorescence. METHODS: To combine and compare the advantages of different microscopic imaging modes, characterization studies were carried out by means of a confocal laser scanning microscope (CLSM), a secondary ion mass spectrometric (SIMS) microscope, and an electron energy loss spectrometric (EELS) microscope. In the case of CLSM, the locations of fluorescent signals inside preparations were determined by factor analysis of biomedical image sequences (FAMIS) and selection of image sequences at emission. RESULTS: By CLSM and FAMIS, we distinguished chelated Eu and Texas Red attached to Fe. By SIMS microscopy, we distinguished Eu and Gd of chlorides and chelates and Fe of a ferumoxide. By EELS microscopy, we distinguished Eu and Gd of chlorides. CONCLUSIONS: Analysis of compounds inside correlative specimens by means of CLSM, SIMS, and EELS microscopes provided complementary results.

Microscopic distribution of iodine radioisotopes in the thyroid of the iodine deficient new-born rat: insight concerning the Chernobyl accident.

UNLABELLED: Thyroid cancer markedly increased in children exposed to iodine radioisotopes following the Chernobyl accident. This increase exceeded predictions based on dose estimates to the whole organ. We sought to investigate whether iodine deficiency may have influenced the pattern of microscopic distribution of radioiodines, which may be important to interpretation of the observed effects. Iodine-deficient new-born rats were injected with iodine-129 (129I) and the microscopic distribution in the thyroid tissue was studied at 24 hr and at one week after administration, using secondary ion mass spectrometry (SIMS). Twenty-four hr after administration, SIMS images showed large differences in 129I uptake among thyroid follicles, with more than a factor ten variation in the local concentration. In addition, the distribution of 129I inside follicles varied with time. At 24 hr, the highest concentration was found at the periphery of the colloid, close to the thyroid cells. There also was enhanced concentration of 129I at one pole of follicles. Distribution inside follicles was homogeneous at 7 days. CONCLUSIONS: 1/Dosimetric models, which assume uniform iodine uptake by thyroid follicles, give an oversimplified picture of radiation dosimetry in cases involving iodine deficiency, which induces patchy tissue irradiation. 2/The dynamic pattern of iodine distribution within thyroid follicles suggests that decay events from short-lived iodines will occur closer to thyroid cells than events resulting from iodine-131.

The perinatal thyroid in iodine deficient regions: risks of radioiodines--hazards of stable iodine overload. A study in the newborn rat.

Administration of large quantities of stable iodine is an effective means of reducing the radiation burden on the thyroid in the event of a nuclear power-plant accident. Such administration may involve countries with low baseline dietary iodine intake. It is questioned whether stable iodine overload is safe, and in particular, what are its effects in newborn infants? Iodine-deficient newborn rats were submitted to a single acute administration of stable iodine (100 microg) on the second day of life. The effects on thyroid structure were studied, after 24 hr and after 7 days, using light microscopy. Compared to controls, the thyroids of animals submitted to stable iodine overload showed, 7 days after treatment, signs of acute toxicity including marked desquamation of epithelial cells and rupture of a large number of thyroid follicles. Our findings in iodine deficient newborn rats suggest that stable iodine overload may have side effects during perinatal life. This prophylactic measure should, therefore, be accompanied by follow-up of thyroid function. Thyroid hormones are critical for brain development, during the first period of life.

Tissular distributions and kinetics of two renal 99mTc-radiopharmaceuticals in rat.

A digital radioimager (RI), conventional radioautography (RA), and tracks microradioautography (MRA) were used to assess the biodistributions and kinetics of 99mTc-dimercaptosuccinic (99mTc-DMSA) and 99mTc-mercaptoacetyltriglycine (99mTc-MAG3) in rat at both macroscopic and microscopic levels. Three groups of male Wistar rats were studied. Using gamma-counting, kidney, liver, spleen and blood kinetics of both tracers were assessed in the three groups. Using RA and RI, renal slices were analyzed in group 1 the animals being sacrified from 2 to 60 min after injection of 99mTc-MAG3, and in group 2 the animals being sacrificed from 0.5 to 24 hr after injection of 99mTc-DMSA. Using MRA, renal slices were analyzed for 99mTc-DMSA (group 3). RA films and RI images displayed the variation with time of the cortical and medullary uptakes of the tracers. No regional heterogeneity within the different structures could be seen neither with RA films nor with MRA. The remaining activity in the blood 24 hr after injection of 99mTc-DMSA was evaluated. The tissular distributions of both tracer being homogenous, mean values of cortical uptake seems to be acceptable for dosimetric studies. Our results incite to use of 99mTc-MAG3 instead of 99mTc-DMSA when both tracers may be indicated.

Total body 4.5 Gy gamma irradiation-induced early delayed learning and memory dysfunction in the rat.

In an attempt to determine the consequences of total body radiation damage on learning and memory in the rat, twenty-eight male Wistar rats aged 4 months received 4.5 Gy total body gamma-irradiation (TBI) while 28 rats received sham irradiation. Sequential behavioral studies of negative reinforcement including a/ one- and b/ two-way avoidance tasks were undertaken. a/ One-way avoidance test: this test was performed before and after TBI. Prior to irradiation both groups were similar. At 20 days (D) and at 3 months post-TBI, irradiated rats had a significantly lower percentage of avoidance than controls but no statistical difference was found at 5 months post-TBI. b/ Two-way avoidance test: this test was performed only after TBI. At days 21, 22, 23, 24, (leaming) and at 4 or 6 months (recalls) post-TBI the mean percentage of avoidance was significantly lower in irradiated than in control rats. This study demonstrates that total-body exposure to 4.5 Gy gamma-irradiation induces behavioral dysfunction affecting learning and transitorily memory. These results suggest that a relatively low dose of total body irradiation can induce neurological complications, which persist 4-6 months later.

Early ultrastructural injuries in the thyroid of the normal rat radioinduced by diagnostic and/or therapeutic amounts of iodine-131.

After irradiation, two principal mechanisms of cytolytic cell death can be involved: apoptosis and necrosis. By using morphological criteria, cells undergoing apoptosis can be distinguished from cells dying by necrosis. In nuclear medicine 131I is used to ablate thyroid remnants or to treat well differentiated thyroid carcinoma. The aim of study was to describe the progressive morphological thyroid changes induced by a diagnostic and/or therapeutic amounts of 131I in the rat using electron microscopy, in an attempt to determine which is the cell death pathway and to analyse "stunned" thyroid tissue to elucidate this effect. Tissular and ultrastructural examinations show that damages induced by 131I irradiation of the normal thyroid gland are heterogeneous. Thyroid cells die by necrosis after this metabolic irradiation, and no signs of apoptosis were observed by electron microscopy. In the other hand, stunning effect did not seem to impair the effectiveness of 131I treatment.

In vitro irradiation of blood with 99mTc: evaluation of dose and chromosome aberrations in irradiated lymphocytes.

The use of ionizing radiation for diagnostic or therapeutic purposes in medicine represents the principal source of artificial radiation to humans. Calculation of radiation dose is essential to the analysis of risks (biological effects) and benefits in any application, including nuclear medicine. The dose assessment in many cases is not necessarily straightforward. Many radiopharmaceuticals are labelled with radionuclides that undergo not only gamma-emission but also emission of Auger and internal conversion electrons. A typical example is technetium-99m (99mTc), which is used in more than 80% of nuclear medicine applications. In this work, in vitro studies have been carried out to evaluate the dose delivered to lymphocytes by human serum albumin microspheres (HSAM) labelled with 99mTc. Experiments were performed in order to score unstable chromosomal aberrations induced by 99mTc-HSAM, using conventional cytogenetic techniques. Henceforth, the relationship between activities introduced into blood samples and induced chromosomal aberrations were evaluated. To assess the dose absorbed in lymphocytes, electron and photon transport was performed in a simple model representing the system used for irradiating the cells using the MCNP Monte Carlo code. In this report, analysis of dose-effect curve demonstrates a linear quadratic response for unstable chromosome aberrations.

Keratinocyte growth factor and hepatocyte growth factor in bronchoalveolar lavage fluid in acute respiratory distress syndrome patients.

OBJECTIVES: To determine bronchoalveolar lavage (BAL) fluid concentrations of keratinocyte growth factor (KGF) and hepatocyte growth factor (HGF), two potent growth factors for alveolar type II epithelial cells, in patients with acute respiratory distress syndrome (ARDS). DESIGN: Prospective study. SETTING: An adult trauma/surgical intensive care unit in an urban teaching hospital. PATIENTS: A total of 32 ventilated patients with pulmonary infiltrates prospectively identified with ARDS (n = 17) or without ARDS (n = 15), including eight patients with hydrostatic edema (HE), and ten nonventilated patients serving as controls. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: BAL was performed 2.88 days +/- 2.4, 3.5 days +/- 2.4, and 2.3 days +/- 2.2 after the lung insult in ARDS, HE, and other non-ARDS patients respectively (p = .32). KGF was detected in BAL fluid in 13 of the 17 ARDS patients (median, 31.6 pg/mL), in one patient with HE, and in none of other non-ARDS patients. In ARDS patients, detection of KGF in BAL was associated in BAL fluid with the detection of type III procollagen peptide (PIIIP), a biological marker of fibroproliferation. In ARDS patients, detection of KGF in BAL was associated with death (p = .02). HGF was detected in 15 ARDS patients (median, 855 pg/mL), in seven patients with HE (median, 294 pg/mL; p = .05 for the comparison with ARDS group), in six of other non-ARDS patients (median, 849 pg/mL; p = .32 with ARDS group). HGF concentrations were higher in nonsurvivors than in survivors (p = .01). None of the ten BAL of controls contained either KGF or HGF. CONCLUSION: KGF was detected almost exclusively in BAL fluid from ARDS patients and correlated with a poor prognosis in this group. In contrast, HGF was detected in the BAL fluid from a majority of patients with or without ARDS. Elevated HGF concentrations were associated with a poor prognosis in the overall group.

Active intestinal elimination of ciprofloxacin in rats: modulation by different substrates.

1. Two in vivo models, in the rat, were used to investigate, in the presence of different substrates, the overall and net intestinal elimination of ciprofloxacin: an open-intestinal perfusion model and an intestinal loop model respectively. 2. In the presence of quinidine, verapamil and cyclosporin (substrates of the P-glycoprotein (P-gp)), plasma AUCs of ciprofloxacin were 1.5 - 2 fold increased, while biliary clearance (1.5 - 2 fold), intestinal overall and net clearances (2 - 4 fold and 1.5 - 8 fold respectively) decreased. The weak effect obtained with cyclosporin as compared to verapamil and especially quinidine, suggests, for ciprofloxacin, the existence of transport systems distinct from the P-gp, as the OCT1 transporter which could be inhibited by quinidine. 3. With cephalexin and azlocillin, two beta-lactam antibiotics, plasma AUCs of ciprofloxacin increased and biliary and intestinal overall clearances decreased in a similar fashion (1.3 - 2 fold), suggesting the involvement of organic anion and/or cation transporters. 4. In the presence of structural analogues, the effect was dependent on the compound administered: Sparfloxacin had no effect on intestinal clearance of ciprofloxacin. In contrast, with pefloxacin, overall intestinal clearance of ciprofloxacin was decreased and net intestinal clearance increased. 5. The specificity of ciprofloxacin intestinal transport appears to be different from P-gp as outlined by the lack of competition with sparfloxacin, a P-gp substrate. Ciprofloxacin intestinal elimination seems to be mediated by organic anion and/or cation transporters and a mechanism sensitive to quinidine and verapamil.

Biological consequences of irradiation by low doses of technetium 99m: ultrastructural studies, p53 protein expression and cytogenetic effects.

Few studies concerning the potential genetic effects of diagnostic radionuclides used in nuclear medicine have been reported. The aim of this study was to evaluate the biological and cytogenetic consequences of two technetium 99m-labelled radiopharmaceuticals. Ultrastructural modifications of pulmonary cells were first investigated after injection of 99mTc labelled microspheres in the rat. On the same irradiated cells, nuclear expression of p53 protein was assessed using immunohistochemistry. Despite very high previously calculated doses delivered to pulmonary cells, no morpholological cell damage and no significant increase of nuclear expression of the p53 were noted. There was no correlation between the calculated dose and the ultrastructural biological damage. Secondly, a specific in vitro curve, activity/number of unstable chromosomal aberrations, corresponding to physical characteristics of 99mTc, was established to verify the potentiality of 99mTc to induce such aberrations. In vivo, cytogenetic effects were assessed on blood samples of 5 patients with various arthrosic and periarthrosic diseases obtained after bone scintigraphy. Aberration frequencies of both in vitro and in vivo irradiated lymphocytes were determined using the classical Fluorescence Plus Giemsa technique. No cytogenetic effects appeared with the routinely 99mTc injected activities as predicted by the in vitro curve.

Quantitative autoradiography using a radioimager based on a multiwire proportional chamber.

Determination of the biodistribution of radiopharmaceuticals is an important issue for the evaluation of their performance in diagnosis and therapy. In this study, we evaluated a digital radioimager (RI) based on a multiwire proportional chamber for quantitative autoradiography (AR). The RI allows direct detection of electronic emissions of gamma emitters. Its qualitative and quantitative performances were tested on 99mTc and (111)In labelled sections and compared with conventional film AR. Linearity of count rate versus activity was verified over a 104 range of activity. As compared with film AR, a substantial improvement of the detection limit was obtained even for acquisition periods up to 20 times less than film exposure times. We provided the basis for quantitative analysis with tissue equivalent paste standards: the 99mTc and (111)In RI counting efficiencies were respectively 1.19% and 2.35%. We illustrated the respective values of RI and film AR in two rat studies: 99mTc-DMSA in kidney and dual-isotope 99mTc-MIBI and (111)In-antimyosin in heart. Calculated activity concentrations on sections of rat organs confirmed good correlation to gamma counting (deviation less than 12%). We suggest RI as a convenient technique for fast localization of single or dual-isotope tracers and determination of activity distribution.

Biological consequences of the heterogeneous irradiation of lymphocytes during technetium-99m hexamethylpropylene amine oxime white blood cell labelling.

Technetium-99m hexamethylpropylene amine oxime (99mTc-HMPAO) labelling of white blood cells, routinely used for the detection of infection, results in the incorporation of radioactivity by polymorphonuclear leucocytes and also lymphocytes and can induce cell lesions in the latter case. The aim of this study was therefore to acquire data on the morphological and functional status of labelled lymphocytes present in the 99mTc-HMPAO leucocyte mixture and to determine the cellular consequences of labelling. The mean radioactivity associated with lymphocytes was 325 +/- 10.8 kBq/10(6) lymphocytes under standard labelling conditions. Microautoradiographic studies showed that labelling was heterogeneous (4% intensely labelled cells), which prevented calculation of the mean absorbed dose. The frequency of chromosomal aberrations (dicentrics and rings) in the labelled lymphocytes for 380 kBq/10(6) cells was 1.08 +/- 0.09 but no abnormality was observed in the unlabelled control lymphocytes. The plating efficiency of labelled lymphocytes was reduced, as compared with that for control cells, but some lymphocytes were still able to form clones and were still "alive" by radiobiological definition. It is therefore suggested that lymphocytes should be removed from 99mTc-HMPAO cell preparations before administration to patients.

Heterogeneous distribution of technetium-99m-labeled microspheres in rat lungs: microautoradiographic evidence and dosimetric consequences.

UNLABELLED: The heterogeneity of 99mTc-labeled microspheres distribution within rat lung was visualized and quantified using a microautoradiographic "track" method (MAR). METHODS: MAR was used to study the uptake of radioactivity by individual microspheres, thereby enabling calculation of the range of particle activity. MAR was also used to visualize in rat lung sections the intrapulmonary distribution of the microspheres within the lungs after intravenous administration. The mean doses delivered to the cells in close contact with the labeled microspheres were calculated taking only the 99mTc electron emissions into account. RESULTS: All the microspheres were labeled. Nevertheless, the spectrum of visible tracks varied by a factor of 10, inducing a variable activity per microsphere from < 36 Bq to 325 Bq (mean activity-94 Bq/microsphere). No correlation existed between the radioactivity uptake and the size of microspheres. A very heterogeneous tridimensional distribution of the microspheres within the lungs were demonstrated with interparticle distances ranging from 57-4400 microns. On the other hand, only 1 of 2000 rat lung capillaries was obstructed. Using the mean activity, calculated delivered doses were found to reach approximately 6 Gy for the closest endothelial cells and 2 Gy for epithelial cells. However, such high doses were delivered to only a few cells. CONCLUSION: The number of obstructed capillaries in human lungs is lower than in rat lungs; the distances between microspheres should be larger. Nevertheless, the individual doses absorbed by the pulmonary cells closest to the microspheres should be very important.

Mutual contribution by "track" microradioautography method (MRA) and secondary ion mass spectrometry (SIMS) microscopy: prospects in technetium dosimetry at-the cellular level.

The determination of cellular uptake sites of radioligands used for cell labelling for diagnostic purposes is an essential prerequisite for evaluating the radiation dose to the cell nucleus and cytoplasm. The distribution of 99mTc-HMPAO in labelled leukocytes was studied by two microscopic imaging techniques on the same biological material: the "track" microradioautographic method (MRA) and Secondary Ion Mass Spectrometry (SIMS) microscopy. The "track" method used internal conversion electrons of 99mTc, leading to the formation of silver grains in a thick layer nuclear emulsion deposited onto cellular smear. In order to improve the specificity of the "track" detection, a minimum of 5 consecutive silver grains was required. In SIMS Microscopy, mapping with 99Tc "daughter" nuclide of 99mTc (half-life: 2.13.10(5) years) was obtained after sputtering of superficial molecular layers on embedded specimen sections. A mass resolution of about 5,000 was needed to circumvent polyatomic ion interferences. Both methods were able to demonstrate a very heterogeneous distribution of technetium from one cell to another. The sensitivity and signal/noise ratios were excellent for both methods. The lateral resolution of SIMS microscopy (0.5 microns) was far better than that of MRA. Therefore, only SIMS is able to distinguish between nuclear and cytoplasmic localization. On the other hand, quantification was not achieved for SIMS, although semi-quantification is possible with MRA. The field of view of MRA is far larger, allowing a better statistical approach for quantification. Both methods appear to be complementary to determine the distribution of technetium at the cell level. MRA is simpler and better fitted to the study of a cell population or a tissue. The unique spatial resolution of SIMS allows to focus the study on subcellular structures.

Palatability of a meal influences release of beta-endorphin, and of potential regulators of food intake in healthy human subjects.

The effect of the palatability of a meal was tested on the post-prandial release of several gut hormones or neuropeptides which are known to have an effect on intake and satiety. Hormonal response was determined in plasma during the 3 h after a highly palatable and energy-rich meal or after the same meal served cold in a poorly acceptable form, as well as while fasting. The early post-prandial pancreatic polypeptide and neurotensin response was significantly higher after the highly palatable meal than after the cold one. Later responses differed only for pancreatic polypeptide. No difference was observed in cholecystokinin and neuropeptide Y levels. Post-prandial levels of beta-endorphin were elevated only after the cold meal and were associated with an elevated response of ACTH. We suggest that beta-endorphin might be secreted in response to an aversion towards the non-palatable cold meal. This could, subsequently, inhibit the cephalic phase of pancreatic polypeptide response and the early post-prandial response of neurotensin by a central anticholinergic effect. This study evidences an effect of palatability on the modulation of the digestive hormonal response after a meal.

Cell surface carbohydrates modulate neutrophil adherence to alveolar type II cells in vitro.

We characterized the influence of phosphorylated sugars and cell surface sialic acids on the adherence of human polymorphonuclear leukocyte (PMN) to rat alveolar type II cell (ATII cells) and human-derived A549 cell monolayers in vitro. Percent adherence of radiolabeled polymorphonuclear leukocytes was assessed after incubating cells with the carbohydrates, enzymes, or lectins to be tested. Lactose-1-phosphate (Lact1P) and maltose-1-phosphate (Malt1P) (10 mM) inhibited adherence of PMN to ATII cells and A549 cells. Maximal inhibition followed treatment of both PMN and rat ATII cells and amounted to 85 +/- 7% with Lact1P and 92 +/- 3% with Malt1P. Inhibition was concentration dependent. Incubation of PMN with mannose-6-phosphate reduced adherence to rat ATII cells and A549 cells by 36 +/- 11 and 39 +/- 8%, respectively. Maximal concentrations of sugars did not alter cellular viability. Neuraminidase-induced desialilation of ATII cells increased adherence of PMN by 36 +/- 7% to rat ATII cells and by 86 +/- 18% to A549 cells. Masking of terminal sialic acids on rat ATH cells with Limulus polyphemus agglutinin (100 micrograms/ml) increased adherence by 50 +/- 2%. These results indicate that cell surface carbohydrates are involved in the regulation of the adhesive interaction between PMN and ATII cells in vitro.

Dosimetry at the cellular level of Kupffer cells after technetium-99m-sulphur colloid injection.

The radiation dose to Kupffer cells was estimated at the cellular level after intravenous injection of 99mTc labeled sulphur colloids in rats. The results were then compared with those obtained using macroscopic dosimetry. From the microscopy appearance observed using a "track" microautoradiographic method (MAR), it was shown that only 0.2% of the Kupffer cells were actually involved in the pinocytosis of radioactive colloids. For each electronic emission from 99mTc (Auger and internal conversion), the fraction of the emitted energy actually absorbed within the Kupffer cell was calculated using the values provided by Berger. About 15% of the total energy emitted by electrons was absorbed in 0.2% of the Kupffer cells. If these results are extrapolated to humans, the dose absorbed by the labeled cells can be estimated to be between 0.5 and 0.9 Gy/MBq. This represents about 15,000 times the average electron dose to the liver as estimated from macrodosimetric methods. In cases such as this one where an important distribution heterogeneity is expected, dosimetric estimations at a cellular level may be particularly useful.