Discovery and Clinical Evaluation of MK-8150, A Novel Nitric Oxide Donor With a Unique Mechanism of Nitric Oxide Release

Background

Nitric oxide donors are widely used to treat cardiovascular disease, but their major limitation is the development of tolerance, a multifactorial process to which the in vivo release of nitric oxide is thought to contribute. Here we describe the preclinical and clinical results of a translational drug development effort to create a next‐generation nitric oxide donor with improved pharmacokinetic properties and a unique mechanism of nitric oxide release through CYP3A4 metabolism that was designed to circumvent the development of tolerance.

Methods and Results

Single‐ and multiple‐dose studies in telemetered dogs showed that MK‐8150 induced robust blood‐pressure lowering that was sustained over 14 days. The molecule was safe and well tolerated in humans, and single doses reduced systolic blood pressure by 5 to 20 mm Hg in hypertensive patients. Multiple‐dose studies in hypertensive patients showed that the blood‐pressure–lowering effect diminished after 10 days, and 28‐day studies showed that the hemodynamic effects were completely lost by day 28, even when the dose of MK‐8150 was increased during the dosing period.

Conclusions

The novel nitric oxide donor MK‐8150 induced significant blood‐pressure lowering in dogs and humans for up to 14 days. However, despite a unique mechanism of nitric oxide release mediated by CYP3A4 metabolism, tolerance developed over 28 days, suggesting that tolerance to nitric oxide donors is multifactorial and cannot be overcome solely through altered in vivo release of nitric oxide.

Clinical Trial Registration

URL: http://www.clinicaltrials.gov. Unique identifiers: NCT01590810 and NCT01656408.

What could mice tell us about goiter or other benign thyroid diseases?

Several lines of research have been developed by using mice as animal models, including goiter development and involution, nodules formation and congenital hypothyroidism. They are reviewed and discussed as potential tools to better understand the thyroid pathophysiology.

The non-obese diabetic (NOD) mouse: an animal model for autoimmune thyroiditis

The NOD mouse, an ideal model for insulin-dependent diabetes mellitus, is also useful to study the pathogenesis of autoimmune thyroiditis. Spontaneous thyroiditis greatly varies in frequency among NOD colonies, but Hashimoto-like thyroiditis can be induced in two experimental models: goiter involution after iodide administration and immunization by TSH receptor, described hereunder.

Destruction of contrast microbubbles by ultrasound: effects on myocardial function, coronary perfusion pressure, and microvascular integrity

BACKGROUND

Recent experimental data indicate that ultrasound-induced destruction of ultrasound contrast microbubbles can cause immediate rupture of the microvessels in which these microbubbles are located.

METHODS AND RESULTS

To examine the functional and morphological significance of these findings in the heart, isolated rabbit hearts were perfused retrogradely with buffer containing ultrasound contrast agents and were insolated at increasing levels of acoustic energy with a broadband transducer emitting at 1.8 MHz and receiving at 3.6 MHz and operated in the triggered mode (1 Hz). At the end of each experiment, the hearts were fixed in glutaraldehyde and examined with light microscopy. Neither exposure to ultrasound alone or to contrast alone affected left ventricular developed pressure. By contrast, simultaneous exposure to contrast and ultrasound resulted in a reversible, transient mechanical index (MI)-dependent decrease in left ventricular developed pressure (to 83+/-5% of baseline at an MI of 1.6) and a transient MI-dependent increase in coronary perfusion pressure (to 120+/-6% of baseline at an MI of 1.6). Myocardial lactate release also showed significant increases with increasing MIs. Macroscopically, areas of intramural hemorrhage were identified over the beam elevation in hearts exposed to both contrast and high-MI ultrasound. Light microscopy revealed the presence of capillary ruptures, erythrocyte extravasation, and endothelial cell damage. The mean percentage of capillaries ruptured at an MI of 1.6 was 3.6+/-1.4%.

CONCLUSIONS

Simultaneous exposure of isolated rabbit hearts to ultrasound and contrast agents results in an MI-dependent, transient depression of left ventricular contractile function, a rise in coronary perfusion pressure, an increase in lactate production, and limited capillary ruptures.

Neural morphological effects of long-term implantation of the self-sizing spiral cuff nerve electrode

The paper reports on the histological effects of chronic implantation of self-sizing spiral cuff nerve electrodes on the cat sciatic nerve. The implantation period is about 4.4 months. Four different experimental conditions are evaluated: control, sham, bare cuff (cuffs without contacts and leads) and full cuff. The total number of axons in the nerves of the control group is compared with the three other groups. The surface occupied by collagen fibres in the nerve section, perineurium thickness, fibre diameter and myelin thickness are also measured. The average number of axons in the control nerves is found to be 16,416 (+/- 1,509) and does not differ significantly from the three other groups (p > 0.1). Collagen measurements show an extrafascicular epineurial fibrosis in the two implanted groups that is found to be significantly different (p < 0.05). No differences are encountered in the perineurium thickness analysis. Fibre diameter distributions show a regular bimodal pattern for all groups. Centrality (mean and Pm) and dispersion statistics (P25 and P75) extracted from fibre diameter distributions do not reveal significant differences. Myelin thickness distributions are also similar for all groups, as well as centrality and dispersion statistics. The present morphometrical results suggest that the effects produced by a chronic spiral cuff implant on this animal model are negligible.

Duplex PCR for differential identification of Mycobacterium bovis, M. avium, and M. avium subsp. paratuberculosis in formalin- fixed paraffin-embedded tissues from cattle

We previously isolated and sequenced two genomic segments of Mycobacterium avium subsp. paratuberculosis, namely, f57, a species-specific sequence, and the p34 gene, coding for a 34-kDa antigenic protein. Comparison of sequences upstream of the p34 open reading frame (us-p34) from M. avium subsp. paratuberculosis and M. tuberculosis showed a 79-base deletion in M. tuberculosis. Sequence analysis of the p34 genes in another two species, M. bovis (strain BCG) and M. avium (strain D4), confirmed the differences observed between tuberculous and nontuberculous species. A duplex diagnostic PCR strategy based on coamplification of nonhomologous us-p34 and species-specific f57 sequences was therefore developed. Duplex PCR yielded three different patterns, specific either for tuberculous bacilli (M. tuberculosis, M. bovis, and M. africanum), for both nontuberculous mycobacteria M. avium and M. intracellulare, or for M. avium subsp. paratuberculosis. The specificity of this single-step DNA-based assay was assessed on DNA from cultured mycobacterial strains, as well as on a panel of formalin-fixed and paraffin-embedded tissues from cattle. Molecular assay results from tissular DNA were compared to conventional bacteriological and histological test results, including those obtained by Ziehl-Neelsen staining on tissue biopsy specimens. Molecular discrimination was successful and confirmed the value of duplex us-p34 and f57 sequence amplification for differential diagnosis of tuberculosis, paratuberculosis, or infections caused by other members of the M. avium complex.

Evidence for co-ordinated changes between vascular endothelial growth factor and nitric oxide synthase III immunoreactivity, the functional status of the thyroid follicles, and the microvascular bed during chronic stimulation by low iodine and propylthiouracyl in old mice

Vasoactive and angiogenic factors are involved in the autocrine/paracrine thyroid regulation of microvascular bed during goiter development. In the thyroid of old mice, the presence of slowly functioning ('cold') follicles allowed us to study the microvascular regulation of each follicle in correlation with the immunohistochemical expression of vascular endothelial growth factor (VEGF) and nitric oxide synthase III (NOSIII). Mice aged 20 months did or did not receive a goitrogenic treatment (low iodine diet and propylthiouracyl), and their thyroids were processed for light and electron microscopy, and for autoradiography. The relative volumes (Vv) of the capillaries, the number of vessels per follicular area, the mean capillary area and the number of [(3)H]thymidine labeled nuclei were measured separately for 'hot' and 'cold' follicles. Already in control mice, the capillary bed surrounding 'hot' follicles was significantly larger than that seen around 'cold' follicles, because of larger diameters and twice the number of capillaries. This difference persisted whatever the length of the stimulatory treatment. During this treatment, the Vv of the capillaries increased to a larger extent around 'hot' follicles than around 'cold' ones. All vascular changes around 'cold' follicles were less extended and the increase in the capillary diameter was delayed. In control mice, the 'cold' follicles were negative for NOSIII and positive for VEGF while 'hot' follicles were positive for both. During stimulation, all follicles became progressively NOSIII positive. These data support the concept of 'angio-follicular units' in the thyroid and demonstrate their differential regulation in chronic stimulation during which local secretion of VEGF and NO is clearly involved.

Automatic morphometry of nerve histological sections

A method for the automatic segmentation, recognition and measurement of neuronal myelinated fibers in nerve histological sections is presented. In this method, the fiber parameters i.e. perimeter, area, position of the fiber and myelin sheath thickness are automatically computed. Obliquity of the sections may be taken into account. First, the image is thresholded to provide a coarse classification between myelin and non-myelin pixels. Next, the resulting binary image is further simplified using connected morphological operators. By applying semantic rules to the zonal graph axon candidates are identified. Those are either isolated or still connected. Then, separation of connected fibers is performed by evaluating myelin sheath thickness around each candidate area with an Euclidean distance transformation. Finally, properties of each detected fiber are computed and false positives are removed. The accuracy of the method is assessed by evaluating missed detection, false positive ratio and comparing the results to the manual procedure with sampling. In the evaluated nerve surface, a 0.9% of false positives was found, along with 6.36% of missed detections. The resulting histograms show strong correlation with those obtained by manual measure. The noise introduced by this method is significantly lower than the intrinsic sampling variability. This automatic method constitutes an original tool for morphometrical analysis.

Genetic immunization of outbred mice with thyrotropin receptor cDNA provides a model of Graves' disease

We performed genetic immunization of outbred NMRI mice, using a cDNA encoding the human thyrotropin receptor (TSHr). All mice produced antibodies capable of recognizing the recombinant receptor expressed at the surface of stably transfected Chinese hamster ovary (CHO) cells, and sera from most of the immunized mice blocked TSH-dependent stimulation of cAMP accumulation in cells expressing the TSHr. Five out of 29 female mice showed sign of hyperthyroidism including elevated total T4 and suppressed TSH levels. The serum of these mice contained thyroid-stimulating activity, as measured in a classic assay using CHO cells expressing recombinant TSHr. In contrast, only 1 male out of 30 had moderately elevated serum total T4 with undetectable TSH values. The hyperthyroid animals had goiters with extensive lymphocytic infiltration, characteristic of a Th2 immune response. In addition, these animals displayed ocular signs reminiscent of Graves' ophthalmopathy, including edema, deposit of amorphous material, and cellular infiltration of their extraocular muscles. Our results demonstrate that genetic immunization of outbred NMRI mice with the human TSHr provides the most convincing murine model of Graves' disease available to date.

Activation of Poly(ADP-Ribose)Polymerase in rat hepatocytes does not contribute to their cell death by oxidative stress

Oxidative stress induced by tert-butyl hydroperoxide (tBOOH) in freshly isolated rat hepatocytes caused DNA damage and loss of membrane integrity. Such DNA lesions are likely to be single strand breaks since neither caryolysis nor chromatine condensation was seen in electron micrographs from tBOOH-treated cells. In addition, pulsed field gel electrophoresis of genomic DNA from both control and tBOOH-treated hepatocytes showed similar profiles, indicating the absence of internucleosomal DNA cleavage, a classical reflection of apoptotic endonuclease activity. The activation of the repair enzyme poly(ADP-ribose)polymerase (PARP) following DNA damage by tBOOH induced a dramatic drop in both NAD(+) and ATP. The inhibition of PARP by 3-aminobenzamide enhanced DNA damage by tBOOH, restored NAD(+) and ATP levels, but did not result in better survival against cell killing by tBOOH. The lack of the protective effect of PARP inhibitor, therefore, does not implicate PARP in the mechanism of tBOOH-induced cytotoxicity. Electron micrographs also show no mitochondrial swelling in cells under oxidative stress, but such organelles were mainly located around the nucleus, a picture already observed in autoschizis, a new suggested kind of cell death which shows both apoptotic and necrotic morphological characteristics.

Protein S-thiolation can mediate the inhibition of protein synthesis induced by tert-butyl hydroperoxide in isolated rat hepatocytes

A rapid inhibition of protein synthesis is observed when isolated rat hepatocytes are incubated in the presence of 0.25-0.5 mM of tert-butyl hydroperoxide (tBOOH). Such an inhibition occurs in the absence of a cytolytic effect by tBOOH. Iron chelators (o-phenanthroline and desferrioxiamine), protected against oxidative cell death, but they did not modify the inhibition of protein synthesis caused by tBOOH (0.5 mM), suggesting that free radicals are less implicated in such an impairment. Electron micrographs of hepatocytes under oxidative stress show disaggregation of polyribosomes but not oxidative alterations, such as blebs or mitochondrial swelling. Protein synthesis inhibition is accompanied by a decrease in reduced glutathione (GSH) and an increase in glutathione disulfide (GSSG) and the level of protein S-thiolation (protein mixed disulfides formation). Such an increase of GSSG appears as a critical event since diethylmaleate (DEM) at 0.2 mM reduced GSH content by more than 50% but did not affect either GSSG content or protein synthesis. The addition of exogenous GSH and N-acetylcysteine (NAC) to tBOOH-treated hepatocytes significantly reduced the formation of protein mixed disulfides and restored the depressed protein synthesis either completely or partially. We suggest that S-thiolation of some key proteins may be involved in protein synthesis inhibition by tBOOH.

Detection of Mycobacterium avium subsp. paratuberculosis in infected tissues by new species-specific immunohistological procedures

We have previously described the cloning and sequencing of a gene portion coding for the terminal part of a 34-kDa protein of Mycobacterium avium subsp. paratuberculosis, the etiological agent of Johne's disease (P. Gilot, M. De Kesel, L. Machtelinckx, M. Coene, and C. Cocito, J. Bacteriol. 175:4930-4935, 1993). The recombinant polypeptide (a362) carries species-specific B-cell epitopes which do not cross-react with other mycobacterial pathogens (M. De Kesel, P. Gilot, M.-C. Misonne, M. Coene, and C. Cocito, J. Clin. Microbiol. 31:947-954, 1993). The present work describes the preparation of polyclonal and monoclonal antibodies directed against a362 and the use of these immunoglobulins for histopathological diagnosis of Johne's disease. The new immunohistological procedures herewith detailed proved to be able to identify M. avium subsp. paratuberculosis antigens in the intestinal tissues and lymph nodes of cattle affected by either the paucibacillary or pluribacillary form of the disease. They yielded negative responses not only with healthy animals but also with those affected by tuberculosis (Mycobacterium bovis). Both immunohistological procedures proved to be as sensitive as or more sensitive than Ziehl-Neelsen staining and, in addition, to be endowed with species specificity.

Antigoitrogenic effect of combined supplementation with dl-alpha-tocopherol, ascorbic acid and beta-carotene and of dl-alpha-tocopherol alone in the rat

The effects of the vitamins dl-alpha-tocopherol, ascorbic acid and beta-carotene, free radical scavengers and lipid peroxidation inhibitors, were analyzed in male Wistar rats made goitrous by feeding a low iodine diet (< 20 micrograms iodine/kg) and perchlorate (1% in drinking water) for 4, 8, 16, and 32 days. Groups of control or goitrous rats received for at least 16 days before killing a diet containing 0.6% vitamin E (as dl-alpha-tocopherol acetate), 1.2% vitamin C (ascorbic acid) and 0.48% beta-carotene, either simultaneously (vitamin cocktail) or separately. This treatment led to a 5-fold increase of vitamin E in the thyroid gland, a 24-fold increase in the liver and a 3-fold increase in the plasma. In control rats, vitamin cocktail administration increased slightly the thyroid weight with little changes in thyroid function parameters. During iodine deficiency, administration of the vitamin cocktail or vitamin E alone reduced significantly the rate of increase in thyroid weight, and DNA and protein contents, as well as the proportion of [3H]thymidine labeled thyroid follicular cells, but not that of labeled endothelial cells. Plasma tri-iodothyronine, thyroxine, TSH levels, thyroid iodine content and concentration as well as relative volumes of glandular compartments were not modified. The proportion of necrotic cells rose from 0.5% in normal animals to about 2% after 16 days of goiter development. No significant protective effect of the vitamins was observed. These results suggest that these vitamins, particularly vitamin E, modulate one of the regulatory cascades involved in the control of thyroid follicular cell growth, without interfering with the proliferation of endothelial cells.

Costimulation of adenylyl cyclase and phospholipase C by a mutant alpha 1B-adrenergic receptor transgene promotes malignant transformation of thyroid follicular cells

Proliferation of thyroid follicular cells is controlled by three intra-cellular cascades [cAMP, inositol 1,4,5-triphosphate (IP3)/Ca2+/diacylglycerol (DAG), and tyrosine kinases] that are activated by distinct extracellular signals and receptors. We had previously generated a transgenic mouse model in which the cAMP cascade was permanently stimulated in thyroid cells by an adenosine A2a receptor (Tg-A2aR model). In the present work, we have generated a transgenic model characterized by the chronic stimulation of both adenylyl cyclase and phospholipase C in thyroid follicular cells. The bovine thyroglobulin gene promoter was used to direct the expression of a constitutively active mutant of the alpha 1B adrenergic receptor, which is known to couple to both cascades in transfected cell lines. The expression of the transgene resulted, as expected, in the activation of phospholipase C and adenylyl cyclase, as demonstrated by the direct measurement of IP3 and cAMP in thyroid tissue. The phenotype resulting from this dual stimulation included growth stimulation, hyperfunction, cell degeneracy attributed to the overproduction of free radicals, and the development of malignant nodules invading the capsule, muscles, and blood vessels. Differentiated metastases were found occasionally in old animals. The development of malignant lesions was more frequent and of earlier onset than in our previous Tg-A2aR model, in which only the cAMP cascade was stimulated. These observations demonstrate that the cAMP and IP3/Ca2+/DAG cascades can cooperate in vivo toward the development of thyroid follicular cell malignancies.

Cyclic feeding behaviour and changes in hypothalamic galanin and neuropeptide Y gene expression induced by zinc deficiency in the rat

Dietary zinc-deficiency induces a striking reduction and a cyclic pattern of food intake in rodents. To elucidate the mechanisms for these effects, we studied the hypothalamic content, synthesis, and distribution of galanin (GAL) and neuropeptide Y (NPY) during zinc deficiency and refeeding in the rat. In Wistar rats, three weeks of zinc-deprivation consistently induced a reduction and a cyclic pattern of night- and day-time food intake, as well as of water intake. This was accompanied in zinc-deficient (ZD) rats, and to a lesser extent in pair-fed (PF) rats, by a decrease of hypothalamic GAL mRNA concentration (CTR: 100 +/- 8, ZD: 61 +/- 4, PF: 78 +/- 2 arbitrary densitometric units, ADU, P < 0.01) and an increase of hypothalamic NPY (CTR: 100 +/- 11, ZD: 154 +/- 10, PF: 126 +/- 4 ADU, P < 0.05), without peptide modification. The two neuropeptidergic systems were not affected by the cycles of feeding, with the exception of the NPY-immunoreactivity in the suprachiasmatic nuclei (geniculo-hypothalamic tract), that was inversely correlated to the food intake in both ZD and PF animals. In a second experiment, we showed that zinc-repletion for 4 days suppressed the behaviour induced by a two-week zinc-deprivation, and reversed the increase of NPY mRNA in ZD animals. We finally demonstrated that zinc-deficiency induced a similar behaviour in Zucker rats. However, in these rats whose synthesis of NPY is constitutively up-regulated, no change of NPY synthesis was observed in ZD rats, suggesting that the increase observed in Wistar is adaptative rather than instrumental to the abnormal food intake. In conclusion, we have further characterized the cyclic feeding behaviour of the zinc-deficient Wistar rats, and shown in these animals a decreased activity of the GAL system and an increased activity of the NPY system, likely corresponding to a compensatory response of the two neuropeptidergic systems, as observed in food-deprived animals. As spontaneous food intake of ZD rats does not increase, a resistance to NPY could also be present. These behavioural and neuropeptidergic changes were partially reversed by reintroduction of zinc in the diet. In Zucker rats, the same behaviour occurred despite an insensitivity of the NPY system to the zinc-deficiency. In addition, we describe a nutritional regulation of the NPY-immunoreactivity in the geniculo-hypothalamic tract, that could constitute the substrate of circadian rhythm modulation by timed feeding.

Selenium deficiency and thyroid fibrosis. A key role for macrophages and transforming growth factor beta (TGF-beta)

Free radical damage and fibrosis caused by selenium deficiency are thought to be involved in the pathogenesis of myxoedematous cretinism. So far, no pathway explains the link between selenium deficiency and tissue fibrosis. Pharmacological doses of iodine induce necrosis in iodine-deficient thyroids. Necrosis is much increased if the glands are also selenium-deficient, which then evolve to fibrosis. This rat model was reproduced to explore the role of selenium deficiency in defective tissue repair. At first, proliferation indexes of epithelial cells and fibroblasts were comparable between selenium-deficient and control groups. Then, in selenium-deficient thyroids the inflammatory reaction was more marked being mainly composed of macrophages. The proliferation index of the epithelial cells decreased, while that of the fibroblasts increased. These thyroids evolved to fibrosis. TGF-beta immunostaining was prominent in the macrophages of selenium-deficient rats. Anti TGF-beta antibodies restored the proliferation indexes, and blocked the evolution to fibrosis. In selenium deficiency, an active fibrotic process occurs in the thyroid, in which the inflammatory reaction and an excess of TGF-beta play a key role.

Early occurrence of metastatic differentiated thyroid carcinomas in transgenic mice expressing the A2a adenosine receptor gene and the human papillomavirus type 16 E7 oncogene

We report here the characterization of a transgenic mouse model (Tg-A2aR/Tg-E7) resulting from the coexpression of two oncogenic transgenes in the thyroid. The two transgenes (Tg-A2aR and Tg-E7) were placed under control of the thyroid specific thyroglobulin gene promoter, and directed the expression of either the A2a adenosine receptor that constitutively activates the cAMP pathway, or the E7 protein of the human papillomavirus type 16, that binds and inactivates the retinoblastoma susceptibility gene product (Rb1). Transgenic mice expressing both transgenes were generated by interbreeding the Tg-A2aR and Tg-E7 transgenic lines, generated and characterized previously (Ledent et al., 1992, 1995). These mice develop a larger goiter than that of the two parental lines, and a severe hyperthyroidism comparable to that observed in the Tg-A2aR parental line. The main feature of the Tg-A2aR/Tg-E7 mice is the rapid occurrence of malignant lesions, and the dissemination of malignant thyroid tissue through the blood stream, generating multiple differentiated and functional metastases in the lung. These metastases appeared as early as 2 months after birth and their frequency increased to 75% over 3 months. They were associated with the presence of large vascular lakes in the thyroid. Electron microscopy of the malignant cells revealed nuclear features similar to those of human thyroid papillary carcinoma. These mice, in which two oncogenes are co-expressed in the thyroid, represent the first genetic animal model developing metastatic differentiated carcinomas of the thyroid with a high frequency.

Expression of nitric oxide synthase isoforms in the thyroid gland: evidence for a role of nitric oxide in vascular control during goiter formation

The thyroid gland is a highly vascular tissue, and its blood flow changes dramatically in various pathological conditions. Although the mechanisms regulating these changes in vascularity and blood flow are not well understood, candidate mediators include endothelin-1 (ET-1) and nitric oxide (NO). In the present study, we used a reverse transcriptase-polymerase chain reaction assay to determine which components of these vasoregulatory pathways are present in the thyroid and to analyze changes in gene expression in an experimental model of goiter formation and involution. Expression of messenger RNAs (mRNAs) encoding ET-1, ET receptors (ETA and ETB), ET-converting enzyme, and the three nitric oxide synthase (NOS) isoforms (NOS I, NOS II, and NOS III) was readily detected in the rat thyroid. After goiter formation was induced by thiouracil and a low iodine diet, there was increased expression of the genes encoding ET-related proteins (ET-1, 3.2-fold; ETA, 2.9-fold; ETB, 3.5-fold) as well as two of the three NOS isoforms (NOS I, 2.7-fold; NOS III, 4.9-fold). During iodide-induced involution, the ET-related mRNA levels remained elevated, whereas those of the two NOS isoforms returned to basal values. ET-converting enzyme, NOS II, and thyroglobulin mRNAs were minimally affected in this model, providing evidence for selective regulation of these genes. To assess whether NO plays a role in vascular changes during goiter formation, animals were treated with a NOS inhibitor, N-nitro-L-arginine methyl ester (NAME). NOS activity in the thyroid was inhibited by more than 75% after treatment with NAME. Thyroid hormone and TSH levels were unchanged. Although NAME had little effect on overall thyroid size, vascular expansion during goiter formation was decreased by 36%. We conclude that the thyroid gland expresses a complex network of vasoactive genes whose expression is regulated dynamically during thyroid goiter formation and involution. NO production and probably other locally produced vasoactive substances are involved in changes in thyroid vascularization.

Two-step development of Hashimoto-like thyroiditis in genetically autoimmune prone non-obese diabetic mice: effects of iodine-induced cell necrosis

The administration of a high iodide dose (HID; 10 micrograms/day) to goitrous mice is known to induce thyroid cell necrosis and inflammation, which, in most strains, is transient. In this study, we analyzed the effects of iodide in autoimmune prone non-obese diabetic (NOD) mice. Control NOD mice fed a standard diet (MID; 1 microgram I/day) or HID did not spontaneously develop thyroiditis. In NOD mice previously made goitrous, HID provoked thyroid cell necrosis and diffuse inflammation within 4 days. Inflammatory cells consisted of MHC-class II+ antigen-presenting cells, CD4+ T helper cells and CD8+ T suppressor/cytotoxic cells. After 96 days of treatment with HID, thyroiditis similar to Hashimoto's disease was obtained in 100% of the animals, with destruction of thyroid follicles, large clusters of T and B cells, and antithyroid antibodies in the plasma. When treating goitrous mice with MID, no cell necrosis was observed and no autoimmune thyroiditis was obtained. The early iodide-induced cell necrosis and inflammation may thus be considered as an important factor in the induction and persistence of autoimmune thyroiditis in individuals carrying a genetic susceptibility to autoimmune disease.

Molecular cloning of an orphan G-protein-coupled receptor that constitutively activates adenylate cyclase

A human gene encoding an orphan G-protein-coupled receptor named ACCA (adenylate cyclase constitutive activator) was isolated from a genomic library using as a probe a DNA fragment obtained by low-stringency PCR. Human ACCA (hACCA) is a protein of 330 amino acids that exhibits all the structural hallmarks of the main family of G-protein-coupled receptors. Expression of hACCA resulted in a dramatic stimulation of adenylate cyclase, similar in amplitude to that obtained with other Gs-coupled receptors fully activated by their respective ligands. This stimulation was obtained in a large variety of stable cell lines derived from various organs, and originating from different mammalian species. hACCA was found to be the human homologue of a recently reported mouse orphan receptor (GPCR21). The mouse ACCA (mACCA) was therefore recloned by PCR, and expression of mACCA in Cos-7 cells demonstrated that the mouse receptor behaved similarly as a constitutive activator of adenylate cyclase. It is not known presently whether the stimulation of adenylate cyclase is the result of a true constitutive activity of the receptor or, alternatively, is the consequence of a permanent stimulation by a ubiquitous ligand. The tissue distribution of mACCA was determined by RNase protection assay. Abundant transcripts were found in the brain, whereas lower amounts were detected in testis, ovary and eye. Various hypotheses concerning the constitutive activity of ACCA and their potential biological significance are discussed.

Effects of selenium deficiency on thyroid necrosis, fibrosis and proliferation: a possible role in myxoedematous cretinism

It has been suggested that selenium deficiency is a co-factor to iodine deficiency in the pathogenesis of myxoedematous cretinism. The mechanism proposed is that the generation of hydrogen peroxide is greatly increased in iodine-deficient thyroid glands, and that selenium is involved in the control of hydrogen peroxide and its derived free radicals. This study was carried out to investigate the effect of the possibly impaired cellular defence mechanism associated with selenium deficiency on thyroid necrosis and tissue repair. For this purpose, we studied thyroid tissue from selenium- (SE-) and/or iodine-deficient (I-) rats before and after an acute toxic iodine overload. In I- thyroids, necrotic cells were numerous. Acute iodine administration increased this effect. Necrosis was associated with transient infiltration of inflammatory cells. In I-SE+ thyroids the tissue resumed its normal appearance. In I-SE- thyroid glands, the iodide toxicity was stronger, with greater necrosis and inflammatory reaction. The inflammation resolved but was replaced by fibrotic tissue. Fifteen days after the toxic overload, the connective tissue volume was twice the control value. Before iodide overload, the proportion of dividing cells was equal in I-SE+ and I-SE- thyroids. Three days after the iodide overload, this proportion was increased in I-SE+ thyroids but reduced in the I-SE- thyroids. Overall, the I-SE- thyroids had four times fewer dividing cells than the I-SE+ thyroids. In summary, selenium deficiency coupled to iodine deficiency increased necrosis, induced fibrosis and impeded compensatory epithelial cell proliferation. These results are compatible with histological and functional description of thyroid tissue from myxoedematous cretins.

Site-dependent pathological differences in smooth muscles and skeletal muscles of the adult mdx mouse

This study presents a survey of the morphometric characteristics, the regeneration rate, and the extent of muscle dystrophy in several smooth and skeletal muscles from adult mdx mice, an animal model of the Duchenne muscular dystrophy (DMD). Smooth muscles from adult mdx mice showed neither cell necrosis nor fibrosis. As compared to control C57 mice, the thickness of the mdx smooth muscle was normal in the vascular and urogenital layers but significantly reduced in the digestive layers, a finding relevant to clinical reports of gastrointestinal dilatation in DMD patients, and suggesting that gastrointestinal dysfunctions should be systemically searched for in DMD patients. Adult mdx skeletal muscles, however, presented different patterns of muscle suffering: either absent (esophagus); very mild (trunk and limb muscles); or severe (diaphragm). In these three conditions we studied the fiber diameters, the nuclei locations, and the regeneration rate. From this comparative study, it seems that severe dystrophy occurs in muscle tissues showing large fiber diameter and peripheral location of the nuclei. We showed that this combination occurs in the mouse diaphragm which is thus a realistic model for human DMD muscles.

Sex-steroid control of galanin in the rat hypothalamic-pituitary axis

To further investigate how sex steroids regulate galanin (GAL) in the rat pituitary and hypothalamus, we examined the effects of prepubertal gonadectomy (Gx) and long-term (9 weeks) replacement with estradiol (E2) or testosterone (T) on pituitary and hypothalamic GAL concentrations in Wistar rats (5-6/group). Sham-operated animals served as controls (CTR). Pituitary GAL concentration was markedly higher in random-cycling CTR-females than in CTR-males (1391 +/- 247 vs 39 +/- 5 pg/mg protein, P < 0.01) and decreased after Gx only in females (20 +/- 3 pg/mg protein, P < 0.01). E2 strongly increased pituitary GAL in Gx-females and Gx-males (4470 +/- 365 and 3853 +/- 347 pg/mg protein, P < 0.01), whereas T had no effect. Inversely, hypothalamic GAL was higher in CTR males than in CTR females (5.4 +/- 0.3 vs 4.0 +/- 0.5 ng/mg protein, P < 0.05), and decreased significantly after gonadectomy in males (3.7 +/- 0.2 ng/mg protein, P < 0.01). The only steroid treatment that significantly modified hypothalamic GAL in Gx animals was administration of E2 to females (5.7 +/- 0.4 ng/mg protein, P < 0.01 vs non-treated Gx). We also studied in hypophysectomized (Hx) rats (8/group) the effects of sex steroids on hypothalamic GAL concentration and distribution. The low hypothalamic GAL concentration observed in male and female Hx rats (1.0 +/- 0.1 ng/mg protein) was significantly increased by T in males and in females (respectively, by 40% and by 50%, P < 0.02) and by E2 in males (by 60%, P < 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)

Expression of the endothelin-1 gene in the rat thyroid gland and changes in its peptide and mRNA levels in goiter formation and iodide-induced involution

Endothelin-1 (ET-1) is a major vasoconstrictor peptide, first found in endothelial cells, and later in many other tissues, including the thyroid gland. We analysed the expression of the ET-1 gene in the rat thyroid gland and changes in ET-1 mRNA and peptide levels in goiter development and involution, two circumstances characterised by vascular changes. Thyroid hyperplasia was induced in adult Wistar rats by feeding a low iodine diet (LID) supplemented with 0.25% thiouracil for 10 days, and LID alone for 2 further days (H.12 group). Involution was induced by injecting 100 micrograms iodide and refeeding a normal diet during 6 h, 12 h, and 24 h (I.6h, I.12h, I.24h groups). Rats fed a normal iodine diet were used as controls. A specific 488 bp cDNA corresponding to the known sequence of pre-pro ET-1 was found by RT-PCR from RNA extracts in all thyroid experimental groups, as well as in lung and kidney which were used as positive controls. RP-HPLC analysis showed that ET-1 immunoreactivity eluted similarly as mature ET-1. During hyperplasia, ET-1 mRNA and peptide levels were increased 3.5- and 5-fold respectively. The relative volume of the vascular bed was more than doubled. During iodide-induced involution, the glandular ET-1 mRNA level remained elevated. The concentration of ET-1 peptide increased and was significantly greater at 12 h involution than in the H.12 group. At this time, the capillary reticulum reverted to individual capillaries and the vascular bed was significantly reduced. These data demonstrate that the ET-1 gene is expressed in the rat thyroid gland and that the ET-1 mRNA and peptide levels are increased during thyroid hyperplasia and remain elevated during a phase of rapid iodide-induced involution. These data suggest that changes in ET-1 production may play a role in control of thyroid gland trophic regulation and vascularity.

Pituitary-dependent hormonal regulation of galaninergic neurons in the rat hypothalamus

To investigate whether pituitary-dependent hormones may regulate galanin (GAL) content, synthesis and distribution in the hypothalamus, female hypophysectomized Wistar rats were treated for 2 weeks with subcutaneous injections of thyroxine (T4, 2 x 1 microgram), bovine growth hormone (GH, 2 x 125 micrograms), cortisol (C, 50 micrograms), subcutaneous implants of beta-estradiol (E2, 5-mm implant, dilution 1:1), or with the combinations [T4+GH], [T4+GH+C+E2] or [T4+GH+C+E2 + rat PRL, 2 x 125 micrograms] (doses/100 g BW/day). Concentrations of GAL in the hypothalamus were measured by radioimmunoassay (RIA) and GAL mRNA abundance was quantified by Northern blot (6 rats/group); 2 rats/group were used for immunohistochemistry. Hypophysectomy caused decreases of hypothalamic GAL peptide and mRNA concentrations (by 70 and 50%, respectively; p < 0.05 vs. intact rats). GAL immunoreactivity disappeared in the median eminence (ME), but increased in the neurohypophyseal magnocellular neurons of hypophysectomized rats. Substitution with T4, GH, [T4+GH], C or E2 had no significant effect on total hypothalamic GAL peptide and GAL mRNA concentrations. A treatment combining [T4+GH+C+E2] increased hypothalamic GAL (1.9 +/- 0.1 vs. 1.2 +/- 0.1 ng/mg protein in untreated hypophysectomized rats; p < 0.01) and GAL mRNA concentrations (127 +/- 19 vs. 59 +/- 2 densitometric units in untreated rats, p < 0.001). Addition of PRL to this combined treatment had no further effect. Treatment with T4, GH, [T4+GH] or E2 enhanced GAL labeling in the ME of hypophysectomized rats. The effect of estrogens was restricted to the GnRH-rich lateral regions of the ME. The combined treatment with [T4+GH+C+E2] restored the ME GAL immunoreactivity to levels observed in intact rats. In contrast, the increased GAL labeling observed in magnocellular neurons after hypophysectomy was not influenced by any hormonal treatment. In conclusion, hypophysectomy leads to marked reductions of hypothalamic GAL and GAL mRNA concentrations, and of GAL immunoreactivity in the ME. These reductions are prevented in part by a combined hormonal treatment associating T4, GH, C and E2, but not by any hormone given alone. This suggests specific pituitary hormone-dependent regulation of the hypophysiotropic GAL neurons. In contrast, the increased GAL labeling in magnocellular neurons of hypophysectomized rats persists despite hormonal treatment and likely represents a lesional effect on the neurohypophyseal GAL system.

Subtypes of Madin-Darby canine kidney (MDCK) cells defined by immunocytochemistry: further evidence for properties of renal collecting duct cells

The Madin-Darby canine kidney (MDCK) cell line has been proposed as a model for studying intercalated (IC) cells of the renal cortical collecting duct. The IC cells are characterized by peanut lectin (PNA) binding capacity, carbonic anhydrase (CA) activity and Cl(-)-HCO3- exchange mediated by a band 3-related protein. It has been suggested that these properties are also expressed in MDCK cells. So far however, the nature of the specific protein involved in Cl(-)-HCO3- exchange, the type of CA isozyme and the relationship between these two characteristics and PNA binding, have not been investigated in MDCK cells by immunocytochemical methods. Using two antibodies raised against human erythrocyte band 3 protein and two against human erythrocyte CA I and II isozymes, our study provides evidence that a protein related to band 3 is expressed in about 5% of cultured MDCK cells; these band 3-positive cells do not bind PNA and are not reactive for CAI or CAII. About 30% of the MDCK cells bind PNA, two-thirds of which are also CAII-positive. A majority (about 65%) of MDCK cells is not reactive for the three markers used; their density is increased after incubation with aldosterone. These data indicate (i) that the Cl(-)-HCO3- exchange of the MDCK cells could be related to human erythrocyte band 3, (ii) that the CA activity of the MDCK cell line bears antigenic identity with the erythrocyte CA II isozyme and (iii) that the latter is always co-localized with PNA binding.(ABSTRACT TRUNCATED AT 250 WORDS)

Involvement of T cell immunity in the transient thyroid inflammation induced by iodide in goitrous BALB/C and nude mice

To evaluate the involvement of T cell immunity in the thyroiditis induced in goitrous mice by iodide administration, we analyzed the immunological changes happening in the thyroid glands and lymph nodes during goiter involution in balb/c and athymic nude mice of similar background. In both balb/c and nude mice, goiter involution was characterized by thyroid cell necrosis and inflammation. In balb/c mice, the inflammatory infiltrate was made of numerous Ia+ cells. Their number was unchanged during goiter development, but was significantly increased after 2 days of involution and remained high after 8 days. CD4+ and CD8+ T cells were also observed, some of which were clearly activated since they expressed the receptor for Interleukin-2 (IL-2R). The numbers of CD4+, CD8+ and IL-2R+ T cells were increased during goiter as compared to control mice, and they reached a maximum at day 1 of involution. In nude mice, unexpectedly, CD4+ and CD8+ T cells were also found in the thyroid. Their numbers, as well as the number of Ia+ cells, were significantly increased at the onset of involution, but they remained systematically lower than in the corresponding groups of balb/c mice. Iodide treatment of goitrous mice also induced modifications of the lymph nodes draining the thyroid: enlargement of the paracortical T zone, presence of germinal centers in cortical follicles, and increase of the density of IL-2R+ cells. Mesenteric lymph nodes taken as controls were unchanged. Thus, three observations suggest the involvement of T cell immunity in iodine-induced thyroid inflammation: 1. Infiltration of Ia+, CD4+, CD8+ and IL-2R+ cells. 2. Signs of stimulation in thyroid lymph nodes, 3. Significant differences between balb/c and nude mice, in which the inflammatory reaction is weaker.

Effects of hypophysectomy on galaninergic neurons in the rat hypothalamus

To understand better the relationship between hypothalamic galaninergic neurons and the pituitary gland, we studied the effects of hypophysectomy on hypothalamic galanin (GAL) content and distribution by radioimmunoassay and immunohistochemistry, and on GAL mRNA by Northern blot analysis. Three weeks after hypophysectomy, performed at 5 or 8 weeks of age, the hypothalamic concentrations of GAL and GAL mRNA were reduced by 30-50% in both male and female rats, compared to age- and sex-matched controls. Similar reverse-phase HPLC retention times of hypothalamic GAL were observed in intact and hypophysectomized rats. The reduction of hypothalamic GAL concentration following hypophysectomy was time-dependent, as peptide levels were unaffected one week after surgery. Immunohistochemistry showed regional differences in the effect of hypophysectomy on galaninergic neurons. In the hypophysiotropic hypothalamus, the scarce GAL immunoreactivity normally observed in the arcuate nuclei was no longer detectable in hypophysectomized rats, and the intense GAL immunoreactivity of the external zone of the median eminence progressively decreased and completely disappeared 3 and 6 weeks after hypophysectomy. In contrast, in the neurohypophyseal system, there was an increase of GAL labelling of the perikarya and emerging axons in the supraoptic and lateral-paraventricular nuclei, 1 and 3 weeks after hypophysectomy, that disappeared 6 weeks after hypophysectomy. An increase of GAL immunoreactivity was also observed in the internal zone of the median eminence 1 week but not 3 weeks after hypophysectomy. We conclude that hypophysectomy reduces the content of GAL and GAL mRNA in the rat hypothalamus. These changes are time-dependent and clearly detected after 3 weeks. The neurohypophyseal and hypophysiotropic galaninergic systems respond differently to hypophysectomy.(ABSTRACT TRUNCATED AT 250 WORDS)

High frequency of thymic ectopy in thyroids from autoimmune prone nonobese diabetic female mice

BACKGROUND

The female nonobese diabetic (NOD) mouse, a well known experimental model to study autoimmune type 1 diabetes, also spontaneously develops thyroiditis. In this study, we report an abnormally high frequency of thymic ectopy in thyroids from NOD mice.

EXPERIMENTAL DESIGN

Thyroids and thymuses from NOD mice and from control mice of different strains were processed for light and electron microscopy and for immunohistochemistry.

RESULTS

Ectopic thymic tissue was observed in the thyroids of 80% of female NOD mice, whereas it was not found in control age-paired female mice from various other strains. The thymic tissue was present beneath the capsule as a large and unique fragment consisting of both a cortical dark one and a medullary light region. Thymic ectopies, as the thymus itself, contained thymocytes expressing both L3T4 and Lyt2 antigens, specific respectively for T helper and T suppressor/cytotoxic cells. Cortical and medullary epithelial cells were also easily identified by electron microscopy and by immunohistochemical staining using ER-TR4 and ER-TR5 monoclonal antibodies.

CONCLUSIONS

Our observation could be an indication for a relation between abnormal thymus development and autoimmune disorder such as thyroiditis.

Selenium deficiency aggravates the necrotizing effects of a high iodide dose in iodine deficient rats

The effect of selenium deficiency associated with various iodide intake was investigated in rats in order to better understand its possible role in the etiopathogeny of myxedematous cretinism. Groups of rat pups were fed from birth a low selenium diet (Se-) and submitted to goitrogenic treatment (1% perchlorate in water) for one month. Some animals were refed iodide after perchlorate withdrawal. The gland morphology was analyzed in correlation with the glutathione peroxidase (GPX) activity and the thyroid hormone plasma levels. In all Se- rats, the GPX activity was strongly reduced as compared to selenium sufficient (Se+) animals (P < 0.01). Goitrous rats were hypothyroid whatever the selenium intake. After iodide refeeding, plasma T4 and T3 levels were increased by 160% in Se- rats and by respectively 330% and 580% in Se+ rats. The thyroid morphology was different according to the selenium intake: necrotic cells were about three times more numerous in Se- than in Se+ rats (P < 0.01) and the inflammatory reaction was increased. These experimental data demonstrate the detrimental role of selenium deficiency in one experimental case of thyroid disease. Such reduction of cell defences could contribute to the thyroid failure of African myxedematous cretins.

Localization of a Band 3-related protein in the mitochondria-rich cells of amphibian skin epithelium

Based on immunoblotting procedure, the isolated epithelium of amphibian skin was found to contain a 180 kDa protein which cross-reacts with a polyclonal antiserum raised against human erythrocyte Band 3. Immunoperoxidase and immunofluorescence staining techniques indicated that the Band 3-related protein was localized in the mitochondria-rich cells (MRC) of this epithelium, with characteristic apical labelling pattern. Our findings show that the putative apical anion exchanger of the MRC is immunologically related to the band 3 multigenic family, which catalyzes Cl(-)-HCO3- transmembranous exchange. It thus suggests a molecular basis for the role played by these cells in the transepithelial Cl- pathway and acid-base regulation.

In vitro study of acute toxic effects of high iodide doses in human thyroid follicles

The acute effects of increasing doses of sodium iodide were studied on human thyroid follicles isolated from normal paranodular tissue. After 24 h incubation in culture medium, follicles isolated from most thyroids maintained their capacity for 125I accumulation and organification and a normal cellular ultrastructure. 125I accumulation was significantly increased after addition of TSH, whereas 125I organification was not affected. In presence of TSH, numerous follicles had large empty-looking follicular lumina unlabeled on autoradiographies. Follicles incubated for 24 h in the presence of a low concentration (10(-7) M) of iodide retained their function and morphology. However, incubation with a high dose of iodide (10(-3) M) caused marked inhibition of 125I accumulation and organification reaching values similar to those obtained in presence of inhibitors of iodide trapping and organification. At high doses, iodide induced necrosis of thyroid epithelial cells: the percentage of necrotic cells was significantly increased with 10(-5) M and doubled with 10(-3) M as compared to values measured at 10(-7) M. Ultrastructural lesions such as apical blebbing, cytoplasmic fragments desquamation, endoplasmic reticulum vesiculation, and accumulation of lipofuscin in secondary lysosomes were also present. The necrotic effect and the ultrastructural alterations also occurred in the presence of TSH but were prevented by the addition of inhibitors of iodide trapping or organification. These results demonstrate a direct acute toxic effect of iodide in human thyroid cells. The nature of the ultrastructural alterations is in agreement with a mechanism of toxicity involving a free radical attack and lipid peroxidation as observed in other tissues.

Detection and identification of endothelin-1 immunoreactivity in rat and porcine thyroid follicular cells

Endothelin-1 immunoreactivity (irET-1) was observed in rat and porcine thyroid glands. Using a radioimmunoassay for endothelin-1, the mean concentration in extracts of rat and porcine thyroid glands were 0.75 pg/mg +/- 0.03 (n = 4) and 1.5 pg/mg +/- 0.2 (n = 8) (mean +/- SE) respectively. Gel-filtration and reverse-phase HPLC showed that ir ET-1 eluted in a position identical to synthetic endothelin-1. In addition, immunohistochemical study showed that irET-1 is located within epithelial follicular cells. No immunostaining was seen in parafollicular C-cells nor in parathyroid.

Changes in cAMP-dependent and Ca2(+)-phospholipid-dependent protein kinase activities in suspension cultures of porcine thyroid cells

The morphological and functional characteristics and the activities of cyclic AMP- (PKA I and PKA II) and calcium and phospholipid-dependent (PKC) protein kinases were studied in 2-day-old suspension cultures of porcine thyroid cells and were compared with those in freshly dissociated cells and intact glands. Thyroid cell morphology changed during the 2-day culture in the absence of specific regulators. This is characterized by a loss of cellular polarity, exo- and endocytotic vesicles and membranes of the rough endoplasmic reticulum, and an increase in the number of lysosomes, pseudomyelinic structures, lipidic inclusions and free ribosomes. Functional changes are characterized by a progressive decrease in protein iodination and its sensitivity to TSH stimulation. The total PKA activity in the cytosols of these cultures was slightly greater than that of freshly prepared tissue, due to the selective and significant accumulation of PKA I in cultured cells. In the particulate fraction the PKA activity was unchanged. PKC is the major kinase activity in porcine thyroids, and remains so in cultured cells. The slight drop in its activity in cytosols was offset by a significant increase in the particulate fraction, suggesting an intracellular redistribution of this kinase in cultured cells. The PKC activity is also partly activated in both the cytosol and particulate fraction, which results in an increased basal activity. The changes in PKA and PKC activities greatly modified the PKC/PKA ratios in the cytosols and the particulate fractions of cultured cells. These modifications could be partly responsible for the changes in sensitivity of cultured cells to the agents which control their activity.

Correlated morphological and functional study of isolated rat thyroid follicles in suspension culture

Rat thyroid follicles were isolated by collagenase digestion and cultured in suspension on agarose for 1-12 days with 0-0.1-1 mU/ml thyrotropin (TSH). After a 4 h exposure to Na125I they were processed for light and electron microscopy, autoradiography and biochemical analysis. Follicular 125I accumulation (A) and organification (PBI) were measured. Thyroglobulin (Tg) content of follicles and 125I-labelled amino acids in Tg were analyzed by high-performance liquid chromatography (HPLC). Without TSH, follicular lumina and cell polarity persisted. From day 3, the rough endoplasmic reticulum (RER) and ribosomes disappeared while autophagic vacuoles appeared: 125I accumulation and PBI were significantly reduced. From day 6, ultrastructural cell dedifferentiation occurred. At day 12, autoradiographic labelling was found over very few lumina; half of the 125I accumulated was still organified. With 1 mU TSH, follicles formed aggregates with narrow densely labelled lumina lined by tall cells. The RER was well developed up to day 12. 125I accumulation, PBI and iodothyronine (T3, T4) formation in Tg remained significantly higher than in follicles cultured without TSH, showing a transient decrease at days 6 and 9. Monoiodotyrosine/diiodotyrosine (MIT/DIT) and T3/T4 ratios in Tg were not modified, suggesting the persistence in the follicles of a significant iodine pool available for iodination. With 0.1 mU TSH, alterations of cell morphology and reduction of functional properties occurred later than without TSH. In the presence of TSH, morphological signs of new follicle formation were seen. These data demonstrate that closed follicles keep their follicular structure up to 12 days of culture, even without TSH. However, TSH is necessary to maintain iodine accumulation and organification.

Correlated autoradiographic and ion-microscopic study of the role of iodine in the formation of "cold" follicles in young and old mice

The role of iodine in the formation of "cold" follicles (not labeled on autoradiograms after radioiodine administration) was analysed in ICR female mice during aging and involution of thyroid hyperplasia, by use of light and electron microscopy and by comparing autoradiographic and analytical ion-microscopic images for the same follicle in serial sections. The proportion of "cold" and "partly cold" (displaying a patchy or ring labeling pattern on autoradiograms) follicles increased significantly during aging. This increase was more pronounced in old mice fed an iodine-rich diet as compared to mice fed a moderate iodine diet. Similarly, during goiter involution produced by refeeding iodine, the follicular heterogeneity of iodine metabolism was more accentuated with a high dose of iodine, regardless of the age of the mice. The follicular lumina of "hot" and "cold" follicles had the same concentration of stable iodine, as shown by analytical ion microscopy, and the cells of both types of follicles formed colloid droplets in response to TSH. Furthermore, when a goitrogenic treatment was induced in aged mice, some "cold" follicles persisted after 8 days, but all follicles resumed "hot" after 16 days. By analytical ion microscopy, 127iodine was also found inside thyroid cells of old mice, but the cytoplasmic patches of 127iodine were not labeled with 125iodine. They corresponded to lipofuscin pigments and secondary lysosomes, as observed in serial sections at the electron-microscopic level. This intracellular stable iodine could constitute a slow turnover compartment not used for hormone synthesis.

Effects of iodide on class II-MHC antigen expression in iodine deficient hyperplastic thyroid glands

The expression of major histocompatibility complex class II molecules (Ia antigen) has been analyzed by immunoperoxidase staining in thyroids of normal C3H mice, of iodine-deficient mice with a hyperplastic goiter and of mice during goiter involution induced by administration of either a high iodide dose (HID, 10 micrograms/day) for 0.5 to 8 days or a moderate iodide dose (MID, 1 microgram/day) or triiodothyronine (T3, 1 micrograms/day) for 2 days. In normal and in hyperplastic thyroids, few interstitial cells were Ia positive (monoclonal antibodies, mAb, M5/114, ER-TR3). Their number was unchanged when goiter involution was induced by MID or by T3, but was significantly increased (p less than 0.05) after HID. It was maximal at days 1 and 2 of involution, decreased thereafter but remained higher (p less than 0.05) than in controls after 8 days. The Ia positive cells were mainly macrophages and, to a lesser extent, dendritic cells. Macrophages were identified by their heterogeneous content and their numerous lysosomes. They were stained with anti-Mac-1 (M1/70) and anti-Mac-2 (M3/38) mAb. Dendritic cells were characterized by their slender cytoplasmic processes, indented nucleus and pale cytoplasm. They were positive for NLDC-145 and MIDC-8 mAb whose specificity for dendritic cells has been demonstrated in lymphoid organs. During the whole period of involution analyzed, Ia antigens were not expressed on follicular cells. Since macrophages and dendritic cells are known to be involved in the pathogenesis of immune disorders, the inflammation induced by administration of HID to iodine-deficient mice could be considered as the early step of an immunological reaction.

Effects of iodide and thyroxine on iodine-deficient mouse thyroid: a morphological and functional study

The effects of iodide and thyroxine (T4) on female mice fed a low iodine diet (LID) for 8 weeks were analysed by morphological, stereological and biochemical methods. Iodide was given at a dose of 10 micrograms/day (HID) or 1 microgram/day (MID), either alone or together with daily injections of 1 microgram T4 for 8 or 40 days. With HID, the thyroid weight and the numbers of follicles and cells remained higher than in controls, although cell necrosis occurred. Colloid volume increased and iodine was stored within the gland: a colloid goitre with non-functioning follicles was produced. With MID, the glands resumed an almost normal appearance. With T4 and LID, progressive normalization occurred, but after 40 days thyroid weight and numbers of follicles and cells remained higher than in controls. Glandular iodine content slowly increased and reached control value. The proportions of 125I-labelled tri-iodothyronine (T3) and T4 in thyroglobulin were reduced. With T4 and HID, the glands resumed a normal appearance. Neither necrosis nor folliculoneogenesis was noted. The proportions of 125I-labelled T3 and T4 in thyroglobulin were reduced, but T3 and T4 serum levels were higher than with HID. With T4 and MID, a normal state was obtained as early as day 8. After 40 days the gland was morphologically and functionally inactive. In conclusion, the association of T4 and iodide seems to be the best way to obtain a rapid and complete involution of thyroid hyperplasia. The administration of T4 prevents the deleterious effects of an excess of iodine on follicular cells, and causes the gland to enter a slow-functioning state.

Direct toxic effect of iodide in excess on iodine-deficient thyroid glands: epithelial necrosis and inflammation associated with lipofuscin accumulation

Involution of thyroid hyperplasia (induced by a low iodine diet and a goitrogen, propylthiouracil, PTU) was obtained in mice by administering a high or a moderate dose of iodide (HID or MID, respectively). In HID involuting glands, vasoconstriction was observed after 12 hr whereas necrosis and inflammation were very abundant as early as after 6 hr and maximal after 48 hr. They were not prevented by papaverine by which vasoconstriction was inhibited, but were inhibited by the continuation of PTU by which iodide oxidation and organification were inhibited. Lipofuscin inclusions in thyroid and inflammatory cells were always associated with necrosis. On the contrary, when involution was induced by MID or by HID + triiodothyronine (T3), or by T3 alone, neither necrosis nor inflammation occurred and apoptosis was the only mode of cell deletion. No lipofuscin inclusion occurred. Our results demonstrate that iodide in excess, after being oxidized or organified, is directly toxic for iodine-deficient thyroid cells. The presence of lipofuscin suggests that its toxicity is mediated by lipid peroxidation, a consequence of production of free radicals in excess.

Increased follicular heterogeneity in experimental colloid goiter produced by refeeding iodine excess after thyroid hyperplasia

Delayed morphological changes induced in mouse hyperplastic thyroid by refeeding iodine were analyzed by light and electron microscopy, stereology, and autoradiography. Thyroid hyperplasia was induced by a low iodine diet supplemented with 0.25% propylthiouracil for 10 days. Involution was obtained by discontinuing the propylthiouracil and returning either to a moderate iodine diet [(MID) 1 microgram I/day] or to an iodine-rich diet [(HID) 10 micrograms I/day] for 40 days. In other experiments, three cycles of hyperplasia (8 days) and subsequent involution (8 days) with MID or HID were brought about. Control animals were fed MID or HID. All animals were killed when 12-14 weeks old after injection of 10-50 microCi 125I. Double labeling, with repeated injections of [3H]thymidine from day 0 to day 7 of involution followed by 125I injection 4 h before killing, was also performed. When involutions were performed with MID, most morphological variables returned to control values. However, when involution was brought about with HID, the glandular weight, the number of follicles, and the relative volume of follicular lumina remained larger than in controls. Moreover, the 125I-labeling pattern of the follicles was altered. The proportions of unlabeled, and unevenly or partly labeled, follicles, which were fewer than 5% in control groups, represented 25-35% of all follicles after involution with HID, whereas they were unchanged with MID. In unlabeled follicles the epithelium was flattened, with a reduced number of microvilli. Partly labeled follicles were of two types. In some follicles a persistent ring reaction was observed, suggesting an abnormally slow mixing of thyroglobulin. In others, the 125I labeling was restricted to areas adjacent to the apex of a reduced number of cells, suggesting that some cells were iodinating thyroglobulin, whereas others were not. There was no relationship between the follicular 125I labeling and the frequency of [3H]thymidine-labeled cells. These results indicate that refeeding iodine excess after hyperplasia leads to the formation of a colloid goiter with new follicles, and to an increased heterogeneity of iodine metabolism among follicles and among cells.

Morphometric studies of normal sural nerves in children

Quantitative histologic studies of biopsies of normal sural nerves were performed on nine children aged 4 days to 17 years. Stereologic computerized procedures were used to determine total endoneurial area, size distribution and number of myelinated, unmyelinated fibers and Schwann cell nuclei per nerve and per square millimeter, and the ratio of myelin thickness to axonal diameter. There was an inverse linear relationship between the number of myelinated fibers per square millimeter and increasing age. A stronger correlation was found between the number of Schwann cell nuclei per nerve (P less than 0.01) and per square millimeter (P less than 0.001) and the logarithm of age. The slope of myelin thickness/axon diameter regression lines (P less than 0.001) changed with age in linear relationship (correlation coefficient: P less than 0.001). There were no age-dependent changes in the number and density of unmyelinated fibers, but the number of unmyelinated axons per Schwann cell subunit decreased with age. Size distribution histograms for myelinated fibers showed a unimodal profile in the newborn. A second peak at 6-7 micron appeared at age 3 months, shifting progressively to 9-11 micron at 14 years. The distribution of unmyelinated fibers was unimodal, with a peak around 0.8 micron, irrespective of age. There were marked individual variations in endoneurial area.

Morphological and functional changes during thyroid hyperplasia and involution in C3H mice: effects of iodine and 3,5,3'-triiodothyronine during involution

Involution of thyroid hyperplasia was induced in mice by discontinuing a goitrogenic treatment (low iodine diet plus 0.25% propylthiouracil for 10 days) and returning either to a moderate iodine diet (MID; 1 microgram I/day) alone or associated with T3 administration (1 microgram/day) or to a high iodine diet (HID; 10 micrograms I/day) alone or associated with T3 treatment. Thyroid involution was studied by morphological, stereological, and biochemical methods after 2, 4, 6, and 8 days of involution. Age-paired, HID-fed animals were used as controls. When the involution was induced by MID, the glands resumed a normal morphological aspect. The synthesis and secretion of T3 were highly stimulated on day 2, but decreased thereafter. Plasma T4 levels reached a plateau at 50% of the control value from days 2-8. The administration of T3 together with MID accelerated the involution of hyperplasia and colloid accumulation in the follicular lumina. The synthesis and secretion of T3 and T4 remained lower than those in controls. When the involution was induced by HID, the thyroid weight remained higher than that in controls or in any involuting groups. The number of follicles and epithelial cells as well as the glandular thyroglobulin content were twice the control values. A Wolff-Chaikoff effect was evident on day 4, and hypothyroidism persisted. When HID was supplemented with T3 treatment, glandular weight and morphology were normal, but the Wolff-Chaikoff effect occurred earlier. In conclusion, the iodine dose given after a goitrogenic treatment must be carefully controlled; a high but physiological dose can have deleterious effects, whereas a small dose is beneficial. T3 prevents the deleterious effects of HID, but the thyroid enters a resting state.

Precocity of the endothelial proliferation during a course of rapid goitrogenesis

Thyroid hyperplasia was induced in C3H mice by a low iodine diet feeding supplemented with propylthiouracil. The morphological modifications associated to the development of hyperplasia were analyzed at light microscopical level and the cellular proliferation was studied by autoradiography after a pulse labelling with [3H]thymidine. The initial modification during the course of hyperplasia is the development of the vascularization. It includes the dilatation of the capillaries, which occurs before any extended modification of the follicular cells and any change of the thyroid weight, and the proliferation of endothelial cells which starts earlier than that of follicular cells.

Morphological and functional changes during thyroid hyperplasia and involution in C3H Mice: evidence for folliculoneogenesis during involution

Involution of thyroid hyperplasia was induced in C3H mice by discontinuing a goitrogenic treatment (low iodine diet supplemented with 0.25% propylthiouracil) and refeeding a normal iodine diet. Thyroid involution was studied by morphological, histochemical, autoradiographic, and stereological methods. The onset of the involution was characterized by an early accumulation of colloid, the presence of necrotic cells in the follicular lumina, and the appearance of homogeneous microcavities in the epithelial layers. The intraepithelial microcavities had the same morphological and functional properties as the follicular lumina. They were limited by a membrane covered with microvilli; polysaccharides and peroxidase activity were detected on their membranes, and 125I-labeling was marked in their lumina. Thin serial sections demonstrated that the microlumens originated from the intercellular space; plasma membranes differentiated into junctional complexes, and a narrow lumen limited by a membrane covered with short microvilli was formed in the intercellular space between the junctions. Later on, the newly formed microlumens fused to form new follicles with a cloverleaf pattern. As a consequence of the folliculogenesis, the total number of follicles doubled after 8 days of involution. This increase in number was mainly due to the presence of a population of small follicles. The folliculogenesis was associated in the first 4 days of involution with an active cellular multiplication which compensated for the early cell necrosis and led to a doubled number of epithelial cells. The increase in the total number of follicles and cells could partially explain the persistence of a relatively high thyroid weight after involution of hyperplasia.

Morphometry of nuclear pore complexes in thyroid cells during hyperplasia and involution

Nuclear pore complexes were analyzed in freeze-fractured replicas of thyroid follicular cells of C3H mice in different physiological states. Thyroid stimulation induced a rapid and simultaneous increase of the nuclear surface and volume and of the total number of pore complexes. The numerical density (Na) of pore complexes increased at the 6th day of stimulation, but after that time the proportion of cells with an increased Na was always higher than the proportion of 3H-labelled nuclei. During thyroid involution, all the nuclear parameters, including the Na, returned to normal values. These results indicate that the total number of pore complexes and their Na are correlated with the cellular activity rather than with the cell cycle. They also suggest that 2 different mechanisms are involved in the generation of pore complexes: first, an addition of new membranes with a low density of pore complexes; later, a formation of new pore complexes in preexisting membranes. However, during involution, parts of the nuclear membranes and pore complexes in the remaining parts disappear synchronously. In freeze-fractured thyroid nuclear membranes, 2 neighbouring pore complexes were always separated by a distance of 105 nm. Clusters of pore complexes were not observed. A comparison of the distances between pore complexes and between randomly generated points never showed any significant differences indicating that pore complexes were randomly distributed.

Morphological changes in mice thyroid induced by iodine deficiency

Goitrogenesis induced in mice by iodine deficiency took place in two distinct phases. The first phase lasted four weeks and was characterized histologically by the classic signs of hyperplasia: colloid resorption, increase in the height of the epithelium and enlargment of the capillaries. After the fourth week, the morphological changes in the thyroid were different in males and females. In the male, pluristratified follicles, secondary follicular cavities and papillary projections were observed. In the female, most of the follicles retained their hyperplastic appearance, while papillary projections were observed in very few follicles.