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.

Modeling radiation dose and effects from internal emitters in nuclear medicine: from the whole body to individual cells.

In nuclear medicine, proper application of radiation protection principles depends on balancing the potential risks of exposure to ionizing radiation against its possible benefits. Average doses to organs, in diagnostic or therapeutic applications, are not always representative of the doses received at the tissue or cellular level. Therefore, understanding of the relationship between the overall biological effect and absorbed dose delivered by the radiopharmaceutical may require study of doses at the organ, tissue, or cell level. In this paper, we review current models for radiation dose assessment, with consideration of the different models and assumptions employed for study at all levels of investigation.

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.

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.

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.

An experimental model of acute encephalopathy after total body irradiation in the rat: effect of liposome-entrapped Cu/Zn superoxide dismutase.

PURPOSE: To develop an experimental model of acute encephalopathy following total body irradiation in rats and to define the therapeutic effect of liposome-entrapped Cu/Zn superoxide dismutase. METHODS AND MATERIALS: A total of 120 4-month-old rats received 4.5 Gy total body irradiation (TBI) while 120 rats received sham irradiation. A behavioral study based on a conditioning test of negative reinforcement, the one-way avoidance test, was performed 5 hours before irradiation and repeated the following days. Subcutaneous treatment was started 1 hour after irradiation and repeated daily for 2 weeks. In both the irradiated and sham group, three subgroups were defined according to the treatment received: liposome-entrapped Cu/Zn superoxide dismutase (0.5 mg/kg), liposomes only, normal saline. RESULTS: This work comprised two consecutive studies. In study A (90 rats) the one-way avoidance test was administered daily from day 0 to day 4 with a recall session at day 14. In study B (validation phase in 150 rats) the behavioral test was performed only from day 0 to day 6. Before irradiation, all rats showed a similar behavioral response. Study A (6 groups of 15 rats): Following TBI, irradiated rats treated with liposomes only or saline demonstrated a significant delay in learning the one-way avoidance test in comparison with sham-irradiated rats (0.05 < p <0.001 depending upon the day of evaluation and the subgroup type). In contrast, irradiated rats treated with liposome-entrapped Cu/Zn superoxide dismutase did not differ from sham-irradiated rats. Study B (6 groups of 25 rats): The results were the same as those in study A, demonstrating a significant delay in the learning of the test in the liposome and saline-treated irradiated rats in comparison with sham-irradiated rats (0.02 < p < 0.001). The irradiated rats, treated with liposome-entrapped Cu/Zn superoxide dismutase did not differ from the sham-irradiated controls. CONCLUSION: This study indicates that a relatively low dose of total body irradiation induces a substantial acute learning dysfunction in the rat. This effect is prevented by the administration of liposome-entrapped Cu/Zn superoxide dismutase.

Absorption of ofloxacin isomers in the rat small intestine.

Ofloxacin, a chiral fluoroquinolone, possesses two optical isomers. The antibacterial activity of S-(-)-ofloxacin is 8 to 128 times higher than that of R-(+)-ofloxacin. In the rat, a saturable absorption process has been described for racemic ofloxacin. In the present study we investigated the mechanism underlying the in vivo intestinal absorption of ofloxacin enantiomers in the rat. Blood samples were collected from the portal vein. Our results show that the intestinal absorption of ofloxacin isomers is pH dependent, both enantiomers being best absorbed at neutral pH. S-(-)-Ofloxacin seems to have a greater affinity for the intestinal transporter (initial concentrations at 5 min [C(init)] are 0.17 +/- 0.04 and 0.12 +/- 0.03 microg/ml for S-(-)- and R-(+)-ofloxacin, respectively). Dipeptides fail to modify ofloxacin absorption, but amino acids reduce both isomers' absorption (C(init) is reduced by 53 and 33% with glycine for S-(-)- and R-(+)-ofloxacin, respectively, and by 59 and 42% with L-leucine). Gamma amino butyric acid interferes with the absorption of ofloxacin isomers, but less seriously than do amino acids. Furthermore, ofloxacin competes with other fluoroquinolones or P-glycoprotein substrates for a common secretory pathway, resulting in an increased rate of absorption for both ofloxacin isomers; this is probably an indirect result of their reduced efflux from the apical side of intestinal cells.

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.

Incidence of dysthyroidism during interferon therapy in chronic hepatitis C.

Seventy-nine patients (40 males, 39 females) were enrolled in a prospective study of lymphoblastoid interferon-alpha (IFN), 3-5 MU three times weekly. They were randomly assigned to receive either 12 months of IFN therapy, or to 6 months of observation followed by 6 months of IFN therapy. The thyroid functional and immunological status was checked every other month during and after treatment. Before treatment, antithyroid antibodies were found in 6 patients (7.5%). Two were hypothyroid and were excluded from the study before starting IFN therapy. Seventy-seven patients received IFN therapy. Of these, thyroid abnormalities appeared in 6 (7.5%). Hyperthyroidism was observed in 3 patients. Two recovered within a few months, but 1 developed subsequent hypothyroidism. Hypothyroidism was observed in 2 patients. TSH blood values were persistently abnormal, but thyroid antibody levels remained increased and fluctuating. Thyroid function usually recovered within a few months; but 2 patients required hormonal therapy and 1 was treated with carbimazole. In 1 patient, a small thyroid papillary carcinoma was observed, but no evidence of relationship with the liver disease or with IFN therapy was found. In a patient with chronic hepatitis C, systematic thyroid assessment should be performed before initiating IFN therapy, including clinical examination, and measurement of TSH and anti-thyroperoxidase antibodies (TPO Ab). During treatment, a TSH assay every other month appears to be necessary and sufficient.

Intestinal elimination of ofloxacin enantiomers in the rat: evidence of a carrier-mediated process.

The aim of this work was to examine the mechanism involved in intestinal elimination of the two optical isomers of ofloxacin in the rat. An intestinal segment was isolated in situ and perfused with saline, while drug solution was administered via the carotid artery. Blood samples and intestinal effluents were collected and analyzed by a high-performance liquid chromatography method. We observed saturable and stereoselective intestinal elimination of the ofloxacin enantiomers. The elimination process favored the R-(+) form of the molecule. After a parenteral dose of 20 mg of racemic ofloxacin per kg of body weight, intestinal clearances were 0.23 +/- 0.03 versus 0.30 +/- 0.03 ml/min for S-(-)- and R-(+)-ofloxacin, respectively. Ciprofloxacin and pefloxacin interfered with ofloxacin elimination and significantly reduced the intestinal clearance of S-(-)- and R-(+)-ofloxacin. With concomitant ciprofloxacin, intestinal clearances became 0.13 +/- 0.02 versus 0.17 +/- 0.03 ml/min and 0.14 +/- 0.01 versus 0.19 +/- 0.05 ml/min with pefloxacin for S-(-)- and R-(+)-ofloxacin, respectively. Those findings argue for the presence of a common transport system in the rat intestine with variable affinities for fluoroquinolones. In addition, verapamil and quinidine, two P-glycoprotein blockers, significantly reduced the intestinal elimination of both ofloxacin isomers (with concomitant verapamil, intestinal clearances were 0.12 +/- 0.02 versus 0.18 +/- 0.03 ml/min for S-(-)- and R-(+)-ofloxacin, respectively, while with concomitant quinidine, values were 0.18 +/- 0.01 versus 0.23 +/- 0.01 ml/min without modifying their areas under the concentration-time curve in serum. Similar results were found with another fluoroquinolone, ciprofloxacin, in previous work. P-glycoprotein appears to be involved in the intestinal elimination of fluoroquinolones in rats. The characterization of fluoroquinolone intestinal elimination has significant clinical relevance for the better evaluation of the influence of this secretory pathway on antibiotic efficacy and selection of resistant bacteria within the intestinal flora.

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.

[Natural history of dysthyroidism during interferon treatment of chronic hepatitis C]. / Histoire naturelle des dysthyroïdies survenant sous interféron dans le traitement des hépatites chroniques C.

Thyroid dysfunction developed in 35 patients among a series of 300 (190 men and 110 women) treated with alpha-interferon (35/300 = 12%. No relationship was observed between the type of alpha-interferon, the dose, or hepatic response, but there were more women (24/35). Antithyroid antibody levels were frequently elevated before treatment (8/35, 23%). Hypothyroidism developed in 27 patients, 7 with clinical hypothyroidism, 10 with moderate hypothyroidism and 5 with elevated TSH only. Patients with severe symptoms and highly elevated thyroid antibodies were more prone to develop sustained or irreversible hypothyroidism (10 patients). Twelve patients recovered a normal thyroid function within a few months, but antibody levels fell more slowly. Primary hyperthyroidism of variable severity appeared in 13 patients. In 8 patients, normal thyroid function was recovered within a few weeks but thyroid antibodies remained high for at least one year. In 5 others spontaneous hypothyroidism occurred within a few weeks ("biphasic" hypothyroidism). Direct toxicity appears to be less probable than an autoimmune mechanism; elevated antithyroid antibodies were observed in only 20 patients (57%). In clinical practice, TSH levels should be regularly monitored during and after alpha-interferon therapy.