Search PubMed⌕ Search

Biomedical subjects

T Akamizu

Publications and source records attributed to T Akamizu.

At least 19 recordsLinked to original sources
PubMed2006

Ghrelin prevents development of diabetes at adult age in streptozotocin-treated newborn rats.

AIMS/HYPOTHESIS: Ghrelin, a stomach-derived hormone, functions in multiple biological processes, including glucose metabolism and cellular differentiation and proliferation. In this study, we examined whether early treatment with ghrelin can regenerate beta cells of the pancreas in an animal model of diabetes mellitus, the n0-STZ model, in which neonatal rats are injected with streptozotocin (STZ) at birth. METHODS: Following administration of ghrelin to n0-STZ rats from postnatal days 2 to 8, we examined beta cell mass, mRNA expression levels of insulin and of pancreatic and duodenal homeobox 1 (Pdx1) gene, and pancreatic morphology on days 21 and 70. In addition, we investigated the effects of ghrelin on beta cell replication. RESULTS: By day 21, ghrelin treatment increased pancreatic expression of insulin and Pdx1 mRNA in n0-STZ rats. The number of replicating cells was also significantly increased in the ghrelin-treated n0-STZ model. At day 70, n0-STZ rats exhibited hyperglycaemia, despite slight increases in plasma insulin levels. Ghrelin treatment resulted in the improvement of plasma glucose levels, which were associated with normal plasma insulin levels. Pancreatic insulin mRNA and protein levels were significantly increased in ghrelin-treated n0-STZ model animals. CONCLUSIONS/INTERPRETATION: These findings suggest that ghrelin promotes regeneration of beta cells in STZ-treated newborn rats. Thus, early administration of ghrelin may help prevent the development of diabetes in disease-prone subjects after beta cell destruction.

Aging↗
PubMed2006

Plasma ghrelin levels in healthy elderly volunteers: the levels of acylated ghrelin in elderly females correlate positively with serum IGF-I levels and bowel movement frequency and negatively with systolic blood pressure.

Aging is associated with a decrease in growth hormone (GH) secretion, appetite and energy intake. As ghrelin stimulates both GH secretion and appetite, reductions in ghrelin levels may be involved in the reductions in GH secretion and appetite observed in the elderly. However, only preliminary studies have been performed on the role of ghrelin in elderly subjects. In this study, we sought to clarify the physiologic implications of the age-related alterations in ghrelin secretion by determining plasma ghrelin levels and other clinical parameters in healthy elderly subjects. Subjects were > or = 65 years old, corresponding to the SENIEUR protocol, had not had a resection of the upper gastrointestinal tract and had not been treated with hormones. One hundred and five volunteers (49 men and 56 women) were admitted to this study (73.4 +/- 6.3 years old). Plasma levels of acylated ghrelin in elderly female subjects positively correlated with serum IGF-I levels and bowel movement frequency and negatively with systolic blood pressure. In elderly men, desacyl ghrelin levels correlated only weakly with bowel movement frequency. These findings suggest that the plasma levels of the acylated form of ghrelin may influence the age-related alterations in GH/IGF-I regulation, blood pressure and bowel motility. These observational associations warrant further experimental studies to clarify the physiologic significance of these effects.

Acylation↗
PubMed2003

Recombinant monoclonal thyrotropin-stimulation blocking antibody (TSBAb) established from peripheral lymphocytes of a hypothyroid patient with primary myxedema.

Anti-TSH receptor antibodies (TRAbs) have been known to be involved in Graves' disease and primary hypothyroidism. We previously isolated and reconstituted immunoglobulin (Ig) genes of Epstein-Barr virus-transformed B cell clones producing monoclonal TRAbs obtained from Graves' patients. In the present study, we performed a similar experiment using a B cell clone, 32A-5, derived from a patient with primary hypothyroidism. The variable region genes of Ig heavy (H) and light (L) chains were isolated and sequenced from the 32A-5 clone. A significant number of somatic mutations were found in variable regions of H and L chain gene segments. Each pair of H and L chain cDNAs was ligated into an expression vector for IgG1 production and stably introduced into myeloma cells. The transfectants were injected ip into BALB/c mice to yield ample volume of the antibody for following applications. Interactions of recombinant 32A-5 with Graves' sera with varying thyroid-stimulating antibody (TSAb) activities were studied. The recombinant antibody tended to suppress TSAb activities in 10 of 15 Graves' sera, in which four were significantly inhibited. In summary, this is the first study to analyze human monoclonal TSH-stimulation blocking antibodies (TSBAb) at the molecular level. Use of human recombinant monoclonal TSBAb may be an analytical tool for molecular-basis etiology and an alternative therapeutic path for Graves' disease.

Animals↗
PubMed2002

Drug-induced neutropenia associated with anti-neutrophil cytoplasmic antibodies (ANCA): possible involvement of complement in granulocyte cytotoxicity.

Although antineutrophil antibodies are thought to be involved in drug-induced neutropenia, neither the precise mechanisms nor the particular antigens on the neutrophil surface have yet been clarified. Recently, we examined a patient with Graves' disease who developed antineutrophil cytoplasmic antibodies (ANCA) after propylthiouracil treatment and exhibited neutropenia. Because several target antigens of ANCA are expressed on the surface of neutrophils, it was suggested that ANCA might contribute to neutropenia. The patient's serum bound specifically to neutrophils and HL-60 cells differentiated into granulocytes, and lysed the HL-60 cells via a complement-mediated mechanism. Furthermore, two representative ANCA antigens, proteinase 3 and myeloperoxidase, significantly inhibited both the binding and cytotoxicity of the serum. Finally, tumour necrosis factor-alpha, which is known to up-regulate cell surface expression of several ANCA antigens, enhanced both the binding and cytotoxicity of the serum. These findings suggest that ANCA induced by propylthiouracil contributed to leucopenia through a complement-mediated mechanism.

Antibodies, Antineutrophil Cytoplasmic↗
PubMed2001

Identification of susceptibility loci for autoimmune thyroid disease to 5q31-q33 and Hashimoto's thyroiditis to 8q23-q24 by multipoint affected sib-pair linkage analysis in Japanese.

Autoimmune thyroid disease (AITD), including Graves' disease (GD) and Hashimoto's thyroiditis (HT), is caused by multiple genetic and environmental factors. The clinical and immunological features of GD and HT are distinct; however, there are multiplex families with both GD and HT, and cases in which GD evolves into HT. Thus, there may be specific susceptibility loci for GD or HT, and common loci controlling the susceptibility to both GD and HT may exist. A genome-wide analysis of data on 123 Japanese sib-pairs affected with AITD was made in which GD- or HT-affected sib-pairs (ASPs) were studied to detect GD- or HT-specific susceptibility loci, and all AITD-ASPs were used to detect AITD-common susceptibility loci. Our study revealed 19 regions on 14 chromosomes (1, 2, 3, 5, 6, 8, 9, 10, 11, 12, 13, 15, 18 and 22) where the multipoint maximum LOD score (MLS) was >1. Especially, chromosome 5q31-q33 yielded suggestive evidence for linkage to AITD as a whole, with an MLS of 3.14 at D5S436, and chromosome 8q23-q24 yielded suggestive evidence for linkage to HT, with an MLS of 3.77 at D8S272. These observations suggest the presence of an AITD susceptibility locus at 5q31-q33 and a HT susceptibility locus at 8q23-q24.

Abatacept↗
PubMed2001

Characterization of the secretable ectodomain of thyrotropin receptor produced by the recombinant baculovirus system.

Thyrotropin receptor (TSHR) is a member of the glycoprotein hormone receptor family and an autoantigen of Graves' disease. Various attempts have been made to obtain a large amount of soluble ectodomain of TSHR in insect or mammalian cells, but most of them failed to secrete the overexpressed ectodomain. In the present study, we observed that about one-third of the ectodomain protein (sTSHR-gp), in which the signal peptide of TSHR was replaced by the baculovirus-encoded glycoprotein 67-signal peptide, was secreted into the culture medium and the remainder stayed within cells in the recombinant baculovirus system. Microsequencing the N-terminal of the purified protein confirmed that the baculovirus signal peptide was cleaved at the expected site. Carbohydrate studies using several glycosidases and lectins revealed that the secreted form of the ectodomain had biantennary carbohydrate, whereas the non-secreted form had high-mannose. Moreover, the secreted form of sTSHR-gp exhibited high-affinity ligand binding, whereas the non-secreted form did not show any significant ligand binding. Regarding the interactions of TSHR ectodomains with anti-TSHR antibodies, both the secreted and non-secreted forms of sTSHR-gp, almost completely neutralized the stimulatory and inhibitory anti-TSHR antibody activities. In conclusion, we succeeded in secreting the ectodomain of TSHR into culture medium, which was capable of binding to TSH and neutralizing anti-TSHR antibody activities.

Amino Acid Sequence↗
PubMed2001

Antithyrotropin receptor antibody: an update.

Numerous studies have reported the characteristics and significance concerning antithyrotropin receptor antibodies (TSHR-Abs), which cause Graves' disease and in some cases primary hypothyroidism. However, many unsolved questions concerning those antibodies remain. Here, recent developments in the study of TSHR-Abs are reviewed based on three aspects: mechanisms of TSHR-Ab production, antibody binding epitopes, and clinical TSHR-Ab assays. Mechanisms of TSHR-Ab production are discussed from five points of view: aberrant expression of the major histocompatibility complex, dysregulation of T cells, molecular mimicry, bystander effect, and expansion of autoreactive B cells. Regarding epitopes, unique TSHR-Abs have been reported that may explain the complicated pathophysiology of patients with TSHR-Ab diseases. Finally, recent efforts to improve TSHR-Ab measurements are introduced. Such efforts will contribute to clinical examinations and treatments for thyroid diseases as well as experimental methods of thyroidology.

Animals↗
PubMed2001

Stomach is a major source of circulating ghrelin, and feeding state determines plasma ghrelin-like immunoreactivity levels in humans.

Ghrelin, an endogenous ligand for the GH secretagogue receptor, was isolated from rat stomach and is involved in a novel system for regulating GH release. Although previous studies in rodents suggest that ghrelin is also involved in energy homeostasis and that ghrelin secretion is influenced by feeding, little is known about plasma ghrelin in humans. To address this issue, we studied plasma ghrelin-like immunoreactivity levels and elucidated the source of circulating ghrelin and the effects of feeding state on plasma ghrelin-like immunoreactivity levels in humans. The plasma ghrelin-like immunoreactivity concentration in normal humans measured by a specific RIA was 166.0 +/- 10.1 fmol/ml. Northern blot analysis of various human tissues identified ghrelin mRNA found most abundantly in the stomach and plasma ghrelin-like immunoreactivity levels in totally gastrectomized patients were reduced to 35% of those in normal controls. Plasma ghrelin-like immunoreactivity levels were increased by 31% after 12-h fasting and reduced by 22% immediately after habitual feeding. In patients with anorexia nervosa, plasma ghrelin-like immunoreactivity levels were markedly elevated compared with those in normal controls (401.2 +/- 58.4 vs. 192.8 +/- 19.4 fmol/ml) and were negatively correlated with body mass indexes. We conclude that the stomach is a major source of circulating ghrelin and that plasma ghrelin-like immunoreactivity levels reflect acute and chronic feeding states in humans.

Adult↗
PubMed2001

Substantial production of ghrelin by a human medullary thyroid carcinoma cell line.

Ghrelin, an endogenous ligand for the GH secretagogue receptor, is a novel acylated peptide produced in the gastrointestinal endocrine cells as well as neuroendocrine cells in the hypothalamus. The Ser(3) residue of ghrelin is modified by n-octanoic acid, a modification necessary for hormonal activity. Human medullary thyroid carcinoma is known to produce a variety of gastrointestinal and neuroendocrine peptides. In the present study we investigated ghrelin production in the thyroid gland, especially in human medullary thyroid carcinoma. PCR amplification demonstrated prepro-ghrelin gene transcripts in normal human thyroid tissue and two medullary thyroid carcinoma cell lines (human TT cells and rat 6-23 cells), but not in a rat thyroid follicular cell line. TT cells showed the expression of prepro-ghrelin mRNA of about 0.6 kb by Northern blot analysis. Furthermore, production of ghrelin in TT cells was demonstrated by RIA and immunocytochemistry. Accumulation of des-n-octanoyl ghrelin in the cultured medium of the cells was confirmed. Finally, human medullary thyroid carcinoma surgical specimens showed significantly higher des-n-octanoyl ghrelin contents than normal thyroid tissues. In conclusion, we revealed that ghrelin was produced by the human thyroid parafollicular carcinoma cell line, TT cells. These findings suggest that ghrelin is produced in the thyroid C cells as well as in medullary thyroid carcinoma and may provide opportunities to investigate its physiological role in the thyroid gland.

Carcinoma, Medullary↗
PubMed2001

Identification of the peptides that inhibit the function of human monoclonal thyroid-stimulating antibodies from phage-displayed peptide library.

Autoantibodies against TSH receptor (TSHR) are known to be involved in the occurrence of Graves' disease. It is obvious that mapping of epitopes of the autoantibodies found in the patients with Graves' disease is an important step in elucidating possible mechanism of generation of the autoantibodies against TSHR as well as in developing effective diagnostic and therapeutic approaches for Graves' disease. In this report we have identified the peptide sequences that bind to two human monoclonal thyroid-stimulating antibodies (mTSAbs; B6B7 and 101-2) from a disulfide-constrained phage-displayed peptide library. The peptides selected by three rounds of biopanning showed half-maximal inhibitory activities for cAMP synthesis induced by mTSAbs at about 0.1 micromol/L. SPWTLGA and TQWNMQH selected for B6B7 and 101-2, respectively, show specificity for their respective antibodies. This means that different clones of mTSAbs may have different epitopes for TSHR. The IgG of the patient from whom B6B7 was derived binds with specificity to the respective immobilized peptide in an enzyme-linked immunosorbant assay format, and its cAMP generation was also inhibited by selected peptide. It may be possible that the epitopes of TSAbs identified from the phage-displayed peptide library could be used for the classification of different clones of TSAbs present in patients with Graves' disease and for development of drugs to treat Graves' disease.

Amino Acid Sequence↗
PubMed2001

A low dose of ghrelin stimulates growth hormone (GH) release synergistically with GH-releasing hormone in humans.

The synergistic relationship between GH-releasing secretagogue (GHS) and GH-releasing hormone (GHRH) with respect to GH secretion is well known. In the present study, we report a similar relationship between GHRH and ghrelin, a recently identified endogenous ligand for the GHS receptor. In normal male adults, various doses of ghrelin were intravenously administered alone or together with 1.0 microg/kg GHRH. At small doses of 0.08 and 0.2 microg/kg ghrelin, combined administration of the two peptides significantly stimulated GH release in a synergistic manner; the mean GH response values of the two peptide combinations were more than the summed mean GH response values of each peptide alone (P < 0.05). In addition, at 1.0 microg/kg ghrelin, the tendency of the synergistic effect was observed, although the comparison was not statistically significant probably due to a submaximal dose ceiling effect. No synergistic effects with respect to ACTH or prolactin secretion were observed. In conclusion, the synergistic interaction between ghrelin and GHRH was clearly shown and might be useful for a provocation test to diagnose GH deficiency.

Adrenocorticotropic Hormone↗
PubMed2001

Simultaneous onset of type 1 diabetes mellitus and painless thyroiditis following acute pancreatitis.

A 24-year-old female suffered from acute pancreatitis, followed by simultaneous onset of painless goiter, elevation of thyroid hormones and diabetic ketoacidosis. Two months later, her insulin secreting function was severely decreased and positive for anti-GAD and anti-islet cell antibodies, whereas the serum glucagon level was normal, suggesting an autoimmune-related destruction specifically of beta cells. In addition, the initial hyperthyroid state was followed by a hypothyroid phase which later recovered to an euthyroid state, suggesting an initial destruction of thyroid cells. Because anti-thyroidal antibodies were positive, it is likely that the thyroidal destruction was also autoimmune-related. This case implies common pathogenic mechanisms in the autoimmunity related destruction of beta cells and thyroid cells.

Acute Disease↗
PubMed2001

[Association study on candidate loci of susceptible genes of autoimmune thyroid diseases in a Japanese population].

Autoimmune thyroid diseases(AITD), which include Graves' disease(GD), Hashimoto's thyroiditis(HT), primary hypothyroidism with blocking-type anti-thyrotropin receptor antibody and idiopathic myxedema, are believed to be a multifactorial disease with a significant genetic and environmental component. Several genetic factors associated with AITD susceptibility have been tentatively identified, including the HLA genes and the cytotoxic T lymphocyte associated-4(CTLA-4) gene. More recently, as part of a genome scan, five additional chromosomal locations, i.e., chromosome 5, 8, 9, 15 and X, have recently been reported in a Japanese population. In the present study, in order to confirm evidence obtained by the genome scan, we performed an association study regarding these five candidate loci identified as regions where susceptible genes of AITD exist. Five microsatellite markers, which are located in these loci, were genotyped in a set of 487 unrelated Japanese AITD patients and 218 Japanese controls. Markers located in chromosome 5, 15 and X showed association in AITD patients with significant increase in particular alleles (p < 0.01), while markers in chromosome 8 and 9 did not consistently show significant association. These findings partly support evidence by the previous genome scan that attempted to identify loci of susceptible genes of AITD in a Japanese population; presence of an AITD susceptibility locus at 5q31-33 was suggested. Genotyping using other markers located in these loci would be helpful not only to confirm regions of AITD susceptible genes but also to narrow the regions.

Adolescent↗
PubMed2000

Thyrotropin regulation of cyclic adenosine monophosphate production in human coronary artery smooth muscle cells.

Thyroid disease has been associated with the occurrence of pathophysiologic changes in the vasculature that may result in part from altered serum thyroid hormone and serum lipid levels. Thyrotropin (TSH) levels are also altered in thyroid disease, but a direct effect of TSH on vascular smooth muscle has not previously been considered. In the present study, human coronary artery smooth muscle cells (CASMC) were induced into two morphologically distinct forms by culturing in either (1) growth factor supplemented, 0.5% serum medium (SmGM-3) or (2) basal medium (SmBM) plus 10% fetal bovine serum (FBS). Intracellular cyclic adenosine monophosphate (cAMP) accumulation was determined by radioimmunoassay after exposure to increasing doses of bovine TSH. Cells grown in SmBM/10% FBS for 3 days exhibited a dose-dependent increase in intracellular cAMP that reached a level 10 times higher than baseline at the highest dose examined (100 mIU/mL). In contrast, cells grown in SmGM-3 medium exhibited no change in intracellular cAMP on exposure to increasing TSII. Low serum (0.5% FBS) reduced the ability of TSH to stimulate cAMP above the control value in CASMC. Pretreatment of CASMC with either transforming growth factor-beta1 (TGF-beta1) or tumor necrosis factor-alpha (TNF-alpha) lowered basal levels of cAMP production, but did not inhibit the ability of TSH to stimulate cAMP production. Human, but not rat aortic smooth muscle cells in culture also responded to TSH with a significant increase in cAMP. The results of this study suggest that TSH may exert direct effects on vascular smooth muscle mediated by adenylate cyclase activation that could conceivably affect the progression of vascular disease associated with thyroid dysfunction.

Actins↗
PubMed2000

Association of autoimmune thyroid disease with microsatellite markers for the thyrotropin receptor gene and CTLA-4 in Japanese patients.

In a previous study we identified a microsatellite marker near the thyrotropin receptor (TSHR) gene. Studies with this marker, TSHR-CA, revealed a significant association between autoimmune thyroid disease (AITD) in Japanese patients and one specific allele (allele 1; 180 base pair [bp]) of the microsatellite sequence. In addition, weak evidence for association of AITD with two alleles of the CTLA-4 gene was observed. In the present study, TSHR-CA has been mapped to approximately 600 kb of the TSHR gene using radiation hybrid mapping. TSHR-CA and another TSHR microsatellite marker, TSHR-AT, which is located in intron 2 of TSHR gene, were genotyped in a set of 349 unrelated Japanese AITD patients and 218 Japanese controls. The TSHR-AT marker showed association in this Japanese AITD population with a significant increase in allele 5 (294 bp; p < 0.05) and a significant decrease in allele 7 (298 bp; p < 0.05). The association of allele 5 of TSHR-AT was also significant in hypothyroid patients (thyrotropin-binding inhibitory immunoglobulin-positive [TBII+], P < 0.01; thyrotropin-binding inhibitory immunoglobulin-negative [TBII-], p < 0.05). The association of allele 7 of TSHR-AT were also significant for the hypothyroid TBII+ patients (p < 0.05). The CTLA-4 gene was also genotyped in this expanded set of Japanese AITD patients and controls. Association between AITD susceptibility and allele 2 (102 bp; p < 0.01) and allele 4 (106 bp; p < 0.01) were observed. These associations were also observed with GD patients (allele 2, p < 0.01; allele 4, p < 0.01). Associations with TSHR-CA were observed for Hashimoto's thyroiditis (HT) patients with respect to alleles 3 (179 bp; p < 0.05) and 5 (175 bp; p < 0.05) and with hypothyroid TBII- patients for allele 4 (177 bp; p < 0.05). The presence of specific alleles of TSHR-CA, TSHR-AT, and CTLA-4 contribute significant increase in risk of development of AITD. These results confirm and expand on our previous study suggesting that alleles of the TSHR and CTLA-4 genes, or genes near them contribute to AITD susceptibility and set the stage for future studies of interactions between these genes and AITD.

Abatacept↗
PubMed2000

Ghrelin strongly stimulates growth hormone release in humans.

Ghrelin is a recently identified endogenous ligand for the GH secretagogue receptor and is involved in a novel system for regulating GH release. However, little is known about its GH-releasing activity and other endocrine effects in humans. To address this issue, we studied the GH, ACTH, cortisol, PRL, LH, FSH, and TSH responses to synthetic human ghrelin. In four normal male adults (28-37 yr), iv ghrelin administration released GH in a dose-dependent manner and 0.2, 1.0, and 5.0 microg/kg ghrelin produced 43.3 +/- 6.0, 81.5 +/- 12.7, and 107.0 +/- 10.7 ng/mL of the GH peak values at 30 min, respectively. ACTH, cortisol, and PRL levels were also elevated after ghrelin injection, while the lowest dose (0.2 microg/kg) resulted in only minimum peak values of these hormones (22.8 +/- 3.0 pg/mL, 9.4 +/- 1.9 microg/dL, and 4.6 +/- 0.6 ng/mL, respectively). There were no significant changes in LH, FSH, or TSH levels. This is the first study showing evidence that ghrelin strongly stimulates GH release in humans.

Adrenocorticotropic Hormone↗