Vasopressin: physiology, assessment and osmosensation.

Vasopressin (AVP) plays a major role in the regulation of water and sodium homeostasis by its antidiuretic action on the kidney, mediated by V2 receptors. AVP secretion is stimulated by a rise in plasma osmolality, a decline in blood volume or stress. V1a receptors are expressed in vascular smooth muscle cells, but the role of vasopressin in blood pressure regulation is still a matter of debate. AVP may also play a role in some metabolic pathways, including gluconeogenesis, through its action on V1a receptors expressed in the liver. It is now understood that thirst and arginine vasopressin (AVP) release are regulated not only by the classical homeostatic, intero-sensory plasma osmolality negative feedback, but also by novel, extero-sensory, anticipatory signals. AVP measurement is time-consuming, and AVP level in the blood in the physiological range is often below the detection limit of the assays. Recently, an immunoassay has been developed for the measurement of copeptin, a fragment of the pre-provasopressin molecule that is easier to measure. It has been shown to be a good surrogate marker of AVP.

Gender-specific co-activation of arginine vasopressin and the hypothalamic-pituitary-adrenal axis during stress.

OBJECTIVE: To study the interaction between copeptin and hypothalamic-pituitary-adrenal (HPA) activation in men and women during hypoglycaemic stress. DESIGN AND PATIENTS: A prospective study in 118 patients (mean age 47·7 ± 13·6 years, n = 52 women) undergoing insulin tolerance testing for suspected pituitary dysfunction. MEASUREMENTS: Serum copeptin was measured in serially collected blood samples and assessed in relation to ACTH, cortisol and other endocrine parameters. RESULTS: Symptomatic hypoglycaemia (mean glucose nadir, 1·6 ± 0·5 mmol/l) resulted in a rapid significant increase of serum copeptin. Individuals with impaired pituitary function had lower stress-induced copeptin levels (median, 6·26 pmol/l) than patients with intact pituitary (8·46 pmol/l, P < 0·001). A weak overall correlation between stress-induced copeptin and cortisol levels was observed (rs  = 0·31, P < 0·001). In female individuals, there was a positive correlation between stress-induced copeptin and ACTH (rs  = 0·47, P < 0·001) or cortisol levels (rs  = 0·42, P = 0·002), while in males, no correlation with ACTH levels (rs  = 0·03, P = 0·75) and poor correlation with cortisol levels (rs  = 0·24, P = 0·045) was observed. Patients with central diabetes insipidus showed lowest baseline (2·20 pmol/l) and stimulated copeptin levels (3·68 pmol/l). CONCLUSIONS: The data from this study indicate that stress-induced release of AVP in women, but not in men, is linked to the co-activation of the hypothalamic-pituitary-adrenal system.

Copeptin, a marker of vasopressin, in abdominal obesity, diabetes and microalbuminuria: the prospective Malmö Diet and Cancer Study cardiovascular cohort.

BACKGROUND: High plasma copeptin (copeptin), the C-terminal fragment of arginine vasopressin pro-hormone, has been associated with the metabolic syndrome (MetS), diabetes mellitus (DM) development and nephropathy. Here we tested whether elevated copeptin level is associated with later development of the MetS, its individual components and microalbuminuria. METHODS: We analysed copeptin at baseline (1991-1994) in the population-based Malmö Diet and Cancer Study cardiovasular cohort and re-examined 2064 subjects 15.8 years later (mean age 72.8 years, 59% women) with oral glucose tolerance test and measurement of MetS and its individual components. RESULTS: After age and sex adjustment, increasing quartiles of copeptin at baseline (the lowest quartile as reference) were associated with MetS (P for trend=0.008), incident abdominal obesity (P for trend=0.002), DM (P for trend=0.001) and microalbuminuria (P for trend=0.002). After additional adjustment for all the MetS components at baseline, increasing copeptin quartiles predicted incident abdominal obesity (odds ratios 1.55, 1.30 and 1.59; P for trend=0.04), DM (odds ratios 1.18, 1.32 and 1.46; P for trend=0.04) and microalbuminuria (odds ratios 1.05, 1.08 and 1.65; P for trend=0.02) but not MetS (P for trend=0.19) at the reexamination. Further, the relationship between copeptin and microalbuminuria was independent of baseline C-reactive protein, incident DM and incident hypertension. CONCLUSION: Copeptin independently predicts DM and abdominal obesity but not the cluster of MetS. Apart from predicting DM and abdominal obesity, elevated copeptin signals increased risk of microalbuminuria. Interestingly, the association between copeptin and later microalbuminuria was independent of both prevalent and incident DM and hypertension. Our findings suggest a relationship between a dysregulated vasopressin system and cardiometabolic risk, which could have implications for risk assessment and novel preventive treatments.

Plasma procalcitonin and the risk of cardiovascular events and death: a prospective population-based study.

OBJECTIVES: A number of inflammatory biomarkers such as C-reactive protein (CRP) are independent predictors of cardiovascular risk. The inflammatory biomarker procalcitonin (PCT) has previously been shown to be associated with coronary atherosclerosis and the metabolic syndrome. We evaluated the ability of PCT to predict future cardiovascular events in a population of apparently healthy individuals. DESIGN: We measured plasma PCT levels in 3713 subjects with no previous history of cardiovascular disease, randomly selected from the Malmö Diet and Cancer cohort. The correlation between PCT concentration and the incidence of coronary events, stroke and cardiovascular death over a median follow-up period of 13.7 years was studied using a Cox regression analysis corrected for age, sex, CRP level, traditional risk factors and renal function. RESULTS: Age and sex were strong determinants of PCT; the concentration of PCT was significantly higher in men than in women. PCT was associated with several of the established cardiovascular risk factors (CRP, hypertension, diabetes and renal function) as determined by multivariate linear regression. Of note, PCT was inversely correlated with HDL and smoking. We found significant correlations between PCT levels, coronary events and cardiovascular death. However, these relationships lost statistical significance when the analysis was corrected for CRP and the traditional risk factors. CONCLUSIONS: This is the largest population-based prospective study to demonstrate a positive association between plasma PCT levels and cardiovascular risk in subjects with no previous history of acute cardiovascular events. However, the high degree of covariation between PCT and other cardiovascular risk factors limits the value of PCT as an independent cardiovascular risk predictor.

Comparison of midregional pro-atrial natriuretic peptide with N-terminal pro-B-type natriuretic peptide in the diagnosis of heart failure.

OBJECTIVES: The concentration of atrial natriuretic peptide (ANP) in the circulation is approximately 10- to 50- fold higher than B-type natriuretic peptide (BNP). We sought to compare the accuracy of midregional pro-atrial natriuretic peptide (MRproANP) measured with a novel sandwich immunoassay with N-terminal pro-B-type natriuretic peptide (NTproBNP) in the diagnosis of heart failure. DESIGN: The diagnosis of heart failure was adjudicated by two independent cardiologists using all available clinical data (including BNP levels) in 287 consecutive patients presenting with dyspnoea to the emergency department (ED). MRproANP and NTproBNP levels were determined at presentation in a blinded fashion. RESULTS: Heart failure was the adjudicated final diagnosis in 154 patients (54%). Median MRproANP was significantly higher in patients with heart failure as compared to patients with other causes of dyspnoea (400 vs. 92 pmol L(-1), P < 0.001). The diagnostic accuracy of MRproANP was very high with an area under the receiver operating characteristic curve of 0.92 and was comparable with that of NTproBNP (0.92, P = 0.791). Moreover, MRproANP provided incremental diagnostic information to BNP and NTproBNP in patients presenting with BNP levels in the grey zone between 100 and 500 pg mL(-1). CONCLUSION: Midregional pro-atrial natriuretic peptide is as accurate in the diagnosis of heart failure as NTproBNP. MRproANP seems to provide incremental information on top of BNP or NT-proBNP in some subgroups and should be further investigated in other studies.

Following brain trauma, copeptin, a stable peptide derived from the AVP precusor, does not reflect osmoregulation but correlates with injury severity.

The incidence of water and electrolyte disturbances following traumatic brain injury (TBI) is considerable and has been attributed to a dysregulation of the hypothalamic peptide arginine-vasopressin (AVP). Copeptin, the C-terminal part of the AVP prohormone, reflects AVP activity. In 71 TBI patients we measured copeptin in serum by a sandwich immunoassay. Injury severity was assessed by Glasgow Coma Score (GCS) and computed tomography, and recovery by Glasgow Outcome Score (GOS). Neuroendocrine and osmoregulation regulation were examined on day 0, 3 and 7, and 24 months post-injury. Copeptin was highest on admission (40.0 +/- 72.3 pmol/l), stabilized on day 3 and 7 (21.2 +/- 18.3 resp. 20.3 +/- 17.1 pmol/l), and normalized at follow-up (4.2 +/- 1.7 pmol/l). On admission, there was a correlation between serum sodium and urine excretion (p = 0.003), but the correlation got lost on day 3 and 7. Copeptin did not reflect the individual 24 h urine excretion or serum sodium levels indicating an uncoupling of copeptin/AVP release and renal water excretion. High copeptin level on day 3 were correlated with a low GCS (p < 0.001), midline shift (p = 0.019), intracerebral hemorrhage (p = 0.026), SAPS score (p = 0.001), as well as with a low GOS (p = 0.031). Copeptin was significantly decreased following skullbase fracture (p = 0.016).Our data reveal a loss of hypothalamic osmoregulation following TBI. The measurement of Copeptin/AVP release reveals a significant predictive function for the severity of TBI.

Microarray analysis of multiple candidate genes and associated plasma proteins for nephropathy secondary to type 2 diabetes among Chinese individuals.

AIMS/HYPOTHESIS: Evolving research suggests that common and rare alleles jointly constitute the genetic landscape of complex disease. We studied the association between 43 pathway-related candidate genes with 'intermediate phenotype' (i.e. corresponding plasma protein) and diabetic nephropathy in a customised microarray of 1,536 SNPs. METHODS: In this case-control study of type 2 diabetic Chinese individuals with and without diabetic nephropathy, cases (n = 545) were defined on the basis of a spot urinary albumin/creatinine ratio (ACR) > 113 mg/mmol; the value for controls (n = 503) was ACR < 3.3 mg/mmol. Genotyping was performed using Illumina GoldenGate assay. RESULTS: No single nucleotide polymorphism (SNP) remained significant in single locus analysis after correction for multiple testing. Therefore, we explored the best approximately 1% SNPs. Of these 13 SNPs, four clustered to a 5' end NADPH oxidase homologue 4 (NOX4) haplotype (GGCC frequency = 0.776) with estimated OR for diabetic nephropathy of 2.05 (95% CI 1.04-4.06) (heterozygous) and 2.48 (1.27-4.83) (homozygous) (p = 0.0055). The haplotype was correlated with plasma Cu/Zn superoxide dismutase (SOD) concentration, suggesting increased oxidative burden. Endothelin-1 SNP (rs1476046G>A, frequency = 0.252) was correlated with plasma C-terminal pro-endothelin-1 concentrations with an estimated OR for diabetic nephropathy of (heterozygous) 1.26 (0.96-1.66) and (homozygous) 1.87 (1.13-3.12) (p = 0.0072). Nitric oxide synthase 1 (NOS1) 5' haplotype (TGTC frequency = 0.38) also revealed a suggestive association with diabetic nephropathy: heterozygous 1.26 (0.95-1.67), homozygous 1.57 (1.04-2.35) (p = 0.0073). A rare NADPH oxidase homologue 1 (NOX1)-coding non-synonymous SNP (Arg315His, frequency = 0.006) was found exclusively among cases. CONCLUSIONS/INTERPRETATION: Our preliminary observations suggest that common haplotypes from NOX4 and endothelin-1 SNP correlated with plasma Cu/Zn SOD and C-terminal pro-endothelin-1 concentrations, respectively, and might have conferred diabetic nephropathy susceptibility. Common NOS1 and rare NOX1 variants also revealed a suggestive association with diabetic nephropathy. Future studies to validate our observation are needed.

B-type natriuretic peptide and C-terminal-pro-endothelin-1 for the prediction of severely impaired peak oxygen consumption.

OBJECTIVE: To assess the utility of B-type natriuretic peptide (BNP) and C-terminal-pro-endothelin-1 (CT-proET-1) to predict a severely impaired peak oxygen consumption (peak VO(2), < 14 mL kg(-1) min(-1)) in patients referred for cardiopulmonary exercise testing. DESIGN: Cross-sectional study. SETTING: Tertiary care center. METHODS: Peak VO(2), BNP and CT-proET-1 were assessed in 141 consecutive patients referred for cardiopulmonary exercise testing. RESULTS: B-type natriuretic peptide [median (interquartile range) 48 (38-319) vs. 33 (15-86) pg mL(-1); P = 0.002] and CT-proET-1 [87 (76-95) vs. 60 (52-74) pmol L(-1); P < 0.001] were higher in patients with a peak VO(2) < 14 mL kg(-1) min(-1) (n = 30) than in those with a peak VO(2) > or = 14 mL kg(-1) min(-1) (n = 111). CT-pro-ET-1 had a higher area under the receiver-operator-characteristics curve (AUC) to predict a peak VO(2) < 14 mL kg(-1) min(-1) than BNP (0.79 vs. 0.68; P = 0.04). The optimal BNP cut-off of 37.2 pg mL(-1) had a sensitivity of 80% and a specificity of 56%. The optimal CT-proET-1 cut-off of 74.4 pmol L(-1) had a sensitivity of 80% and specificity of 76%. A five-item score composed of body mass index, diabetes, forced expiratory volume within the first second, alveolo-arterial oxygen pressure difference, and BNP had an AUC of 0.88 to predict a peak VO(2) < 14 mL kg(-1) min(-1). Adding CT-proET-1 to the score resulted in an AUC of 0.92. CONCLUSIONS: C-terminal-pro-endothelin-1 is superior to BNP for the prediction of a peak VO(2) < 14 mL kg(-1) min(-1) in patients referred for CPET. A score incorporating body mass index, diabetes status, spirometry, blood gases, BNP and CT-proET-1 improves the prediction of a peak VO(2) < 14 mL kg(-1) min(-1) based on single biomarkers.

The T393C polymorphism of the Galphas gene (GNAS1) is associated with the course of Graves' disease.

Genotypes of the T393C SNP of GNAS1, a gene that encodes for the Galphas subunit of G proteins have been significantly associated with the clinical course in a variety of cancers. Since this SNP may also influence the course of Graves' disease (GD) and, especially, Graves' ophthalmopathy (GO), we determined genotype and allele frequency in a series of 359 patients, which were referred to our clinic within 6 months of the onset of GO. Among them, 336 patients also suffered from associated hyperthyroidism. Data on relapse and remission rates 12 months after termination of a 1 year antithyroid drug therapy was available for 276 patients. As controls, 820 healthy individuals were recruited. Our data suggest that the T393C SNP does not represent a risk factor for the development of both GD and GO. It was, however, significantly associated with the course of hyperthyroidism (p=0.013) and a similar trend was evident for the course of GO (p=0.093). Homozygous TT carriers showed a significantly increased risk (p=0.03) for hyperthyroidism to relapse (OR 2.4; 95% CI 1.1-5.4). Also, the TT genotype was associated with significantly increased serum TRAb levels (CC+CT: 5.4 IU/l vs. TT: 9.3 IU/l). This is probably caused by increased G-Protein susceptibility to TSHR-mediated stimulation through TRAb. Genotyping of the T393C SNP of GNAS1 may become a useful additional tool to predict the clinical course of GD and GO. This may allow the clinician to identify patients at risk for more severe courses of disease and to come to more timely decisions for treatment.

Adrenomedullin and endothelin-1 are related to inflammation in chronic heart failure.

BACKGROUND: Adrenomedullin (ADM) and endothelin-1 (ET-1) are novel promising peptide biomarkers in chronic heart failure (CHF). According to recent studies among their pleiotropic effect they play roles in the regulation of inflammation. The aim of the study was to measure the above mentioned two vasoactive peptides in parallel in a well characterized population of patients with CHF, and study their associations with inflammatory markers. MATERIALS AND METHODS: A total of 186 patients (138 male, 48 female) with <45% left ventricular ejection fraction (LVEF), and without acute inflammatory disease, were enrolled. Plasma midregional-proADM (MR-proADM) and C-terminal-proET-1 (CT-proET-1) were determined by a novel sandwich immunoluminometric assay. RESULTS: Increased MR-proADM and CT-proET-1 plasma levels were measured in patients with severe CHF (NYHA III-IV) as compared to the group of NYHA I-II (p<0.0001). MR-proADM and CT-proET-1 levels showed significant negative correlation with serum albumin and prealbumin levels (p

Graves' disease and Hashimoto's thyroiditis in monozygotic twins: case study as well as transcriptomic and immunohistological analysis of thyroid tissues.

OBJECTIVE: To report on the rare simultaneous occurrence of Graves' disease (GD) and Hashimoto's thyroiditis (HT) in monozygotic twins. DESIGN: We compared the pattern of thyroid tissue-derived cDNAs to gain insight into previous and ongoing immune destruction and reconstruction processes using microarrays. The results were confirmed by immunohistology and real-time PCR. RESULTS: Destruction of thyroid tissue in HT reduced levels of thyrocyte-related cDNAs and cDNAs encoding extracellular matrix components, but increased levels of proteases involved in extracellular matrix degradation compared with GD. Lymphocytic infiltrates forming ectopic follicles replaced the thyroid tissue almost completely in HT. Thus, lymphocyte-related cDNA levels were higher in HT than in GD. The same was true for many chemokines and their receptors, which not only enable migration towards the thyroid but also maintain the lymphocytic infiltrate. HT also showed increased levels of cDNAs encoding molecules related to apoptosis than did GD. Surprisingly, the Th1- and Th2-specific cytokine profiles suggested for HT and GD respectively could not be confirmed. cDNAs encoding factors and receptors involved in angiogenesis were increased in GD compared with HT. CONCLUSIONS: Comparison of gene expression reflects the cellular differences between the two types of autoimmune thyroid disease in twins with identical genetic and similar environmental background.

Copeptin as a biomarker and a diagnostic tool in the evaluation of patients with polyuria-polydipsia and hyponatremia.

Copeptin is part of the 164 amino acid precursor protein preprovasopressin together with vasopressin and neurophysin II. During precursor processing, copeptin is released together with vasopressin. Copeptin concentrations respond as rapidly as vasopressin to changes in osmolality, a decrease in blood pressure or stress and there is a close correlation of vasopressin and copeptin concentrations. For these reasons, copeptin is propagated as a surrogate marker for vasopressin in the differential diagnosis of the polyuria-polydipsia syndromes and hyponatremia. Results of prospective studies show that a baseline copeptin level without prior fluid deprivation >20 pmol/L is able to identify patients with nephrogenic diabetes insipidus, whereas osmotically stimulated copeptin levels differentiate between patients with partial central diabetes insipidus and primary polydipsia with a high sensitivity and specificity >94%. In hyponatremia, low copeptin levels point to primary polydipsia and high levels to hypovolemic hyponatremia. The copeptin to urinary sodium ratio differentiates accurately between volume-depleted and normovolemic disorders.

Pro-A-type and N-terminal pro-B-type natriuretic peptides in different thyroid function states.

QUESTIONS UNDER STUDY: Natriuretic peptides are produced predominantly in the heart and secreted in response to volume expansion and pressure overload. A wide spectrum of cardiac changes is observed in thyroid dysfunctions. This study investigates mid regional pro A-type (proANP) and N-terminal pro-B-type natriuretic peptide (NTproBNP) levels in different thyroid states and evaluates the effect of L-thyroxine treatment on natriuretic peptides in patients with subclinical hypothyroidism. METHODS: Case-control and double-blind, placebo-controlled trial. Sera from 161 female patients (35 with overt, 63 with subclinical hypothyroidism; 10 with overt, 14 with subclinical hyperthyroidism; 40 euthyroid controls) were analysed. ProANP and NT-proBNP were measured at baseline and 48 weeks after L-thyroxine treatment in subclinical hypothyroidism. RESULTS: Circulating proANP and NT-proBNP levels were higher in hyperthyroid patients than in hypothyroid and euthyroid patients (p <0.001). Plasma proANP levels tended to be lower in overt hypothyroidism than in subclinical hypothyroidism. ProANP and NT-proBNP levels correlated weakly to thyroid stimulating hormone (TSH) (r = -0.3 and -0.2, respectively). The natriuretic peptide levels of subclinical and overt hypothyroid subjects showed no difference with those of euthyroid subjects. L-thyroxine treatment had no effect on natriuretic peptide levels in subclinical hypothyroidism. CONCLUSION: Natriuretic peptide levels are altered in different thyroid states with a more pronounced effect in hyperthyroidism than in hypothyroidism. Hyperthyroidism should be considered in patients presenting with unclear symptoms and mildly elevated natriuretic peptide levels, as overt hyperthyroidism results in increased serum A- and B-type natriurectic peptide levels, typically seen in mild heart failure.

Low frequency of autoantibodies to the human Na(+)/I(-) symporter in patients with autoimmune thyroid disease.

Several studies suggest that the sodium-iodide symporter (NIS) may represent a major autoantigen in autoimmune diseases of the thyroid. The aim of the present paper was to investigate the importance of autoantibodies to human NIS (hNIS-Ab) in patients suffering from Hashimoto's thyroiditis (HT) and Graves' disease (GD). Full-length human NIS (hNIS) was cloned from thyroid tissue, expressed by in vitro transcription and translation in the presence of [(35)S]methionine, and used to analyze autoantibodies in a direct binding assay. The structurally similar glucose transporter, GLUT-2, was produced in the same system as control protein. Autoradiography revealed that full-length hNIS was expressed, recognized by a NIS monoclonal antibody, and strongly bound by some sera from patients with autoimmune thyroid disease, which did not react with the GLUT-2 control protein. Using the 95.2th percentile of healthy controls as threshold for positivity, 19 of 177 (10.7%) patients with GD and 15 of 72 (20.8%) patients with HT had hNIS-Ab, respectively. Applying more stringent cut-off criteria (99.4th percentile of normal controls), hNIS-Ab were found in only 5.6% of patients with GD and 6. 9% of patients with HT. In HT significantly higher hNIS-Ab levels were observed compared with GD and normal controls (P: < 0.001). There was no correlation between hNIS-Ab and TSH receptor antibodies and only a weak correlation to thyroid peroxidase antibodies (P: < 0. 05). Comparison of hNIS-Ab, thyroid peroxidase, and TSH receptor antibodies in individual sera revealed that the additional detection of hNIS-Ab did not increase the diagnostic power for GD or HT. Our data indicate that hNIS is not a major antigen in autoimmune thyroid disease, as it is the target of humoral autoimmunity in only a few patients with GD and HT. The frequency of hNIS-Ab may be lower than that reported in previous studies.

Rarity of anti- Na+/I- symporter (NIS) antibody with iodide uptake inhibiting activity in autoimmune thyroid diseases (AITD).

The search for antibody against the Na+/I- symporter (NIS) has seen conflicting results over the years. Prior to cloning of NIS, Raspe et al found iodide uptake inhibiting sera were rare in autoimmune thyroid diseases (AITD) while post-cloning, others reported the presence of antibody in 12-15% of Hashimoto's thyroiditis (HT) and 30-84% of Graves' disease (GD). To evaluate the role of NIS as a potential antigen in AITD, a stable COS 7 cell line expressing high level of functional hNIS was established which allowed the screening of large number of sera for iodide uptake inhibiting activity in a 96-well plate format. Five hundred and fourteen serum samples taken from normal subjects and patients with AITD, non-autoimmune thyroid diseases, and non-thyroid autoimmune diseases were assayed for presence of iodide uptake inhibiting activity. Under the influence of these sera, iodide uptake showed a normal frequency distribution and diminution of uptake 2 SDs below the mean of controls was observed with 14 sera. Among these, 7 that were available for further study were re-evaluated after dialysis and/or Ig G extraction. All 7 sera lost their iodide uptake inhibiting activity, indicating that the effects were not antibody mediated and unknown serum factors had been responsible. In conclusion, contrary to previous results, the present study indicates that antibodies capable of modulating NIS activity are rare in AITD.

Binding of antithyrotropin receptor autoantibodies in Graves' disease serum to nascent, in vitro translated thyrotropin receptor: ability to map epitopes recognized by antibodies.

The binding of Graves' disease autoantibodies and xenogeneic antibodies to the human TSH receptor (TSH-R) has been studied using receptor preparations generated in an in vitro transcription and translation reaction. The complementary DNAs encoding for the full-length (764 amino acids) and the extracellular region of TSH-R (amino acids 20-414, lacking the signal sequence) were used to generate the translated receptor antigen. Stable [35S]methionine-labeled nascent protein for full-length and extracellular regions of TSH-R of approximate size 87 and 50 kDa, respectively, together with other smaller proteins were generated. The 87- and 50-kDa translated receptor proteins react by immunoprecipitation analysis with monoclonal antibodies, polyclonal antisera, and unfractionated Graves' disease serum containing autoantibody to TSH-R. The translated products of the extracellular TSH-R were examined in detail. Using three well characterized murine monoclonal antibodies whose epitopes encompass the amino-, central, and carboxyl-terminals of the extracellular region of the receptor led to immunochemical identification of the smaller translated products to derive from internal methionine start sites of TSH-R. These smaller, N-terminal-truncated translated proteins were also recognized by polyclonal antisera generated against recombinant TSH-R, thus allowing epitope mapping of some antibodies. A large proportion of Graves' disease autoantibodies (> 70%) bind to the translated extracellular region of TSH-R. This indicates that the majority of pathogenic anti-TSH-R autoantibody binds the nascent translated extracellular region of TSH-R, which is not influenced by the lack of glycosylation of the receptor.

Human B cells secreting immunoglobulin G to glutamic acid decarboxylase-65 from a nondiabetic patient with multiple autoantibodies and Graves' disease: a comparison with those present in type 1 diabetes.

Antibodies to glutamic acid decarboxylase-65 (GAD65) are present in a number of autoimmune disorders, such as insulin-dependent (type 1) diabetes mellitus (IDDM), stiff man syndrome, and polyendocrine autoimmune disease. Antibodies to GAD in IDDM patients usually recognize conformation-dependent regions on GAD65 and rarely bind to the second isoform, glutamic acid decarboxylase-67 (GAD67). In contrast, those present in stiff man syndrome and polyendocrine disease commonly target the second isoform (GAD67) and include antibodies that are less dependent on the conformation of the molecule. By immortalizing peripheral blood B cells with Epstein-Barr virus, we have generated three human IgG autoantibodies, termed b35, b78, and b96, to GAD65 from one patient with multiple autoantibodies to endocrine organs and Graves' disease. All three autoantibodies are of the IgG1 isotype, with islet cell activity, and do not react with GAD67. The regions on GAD65 recognized by the three autoantibodies have been investigated by immunoprecipitation with a series of chimeras, by binding to denatured and reduced antigens, and using protein footprinting techniques. Using chimeric GAD proteins, we have shown that b35 targets the IDDM-E1 region of GAD65 (amino acids 240-435) whereas both b78 and b96 target the IDDM-E2 region of GAD65 (amino acids 451-570). Furthermore, examination of binding to recombinant GAD65 and GAD67 by Western blotting revealed some differences in epitope recognition, where only b78 bound denatured and reduced GAD65. However, b35, b78, and b96 autoantibodies had different footprinting patterns after trypsin treatment of immune complexes with GAD65, again indicating different epitope recognition. Our results indicate that antibodies to GAD65 present in nondiabetic patients with multiple autoantibodies to endocrine organs show similarities to those in IDDM (by targeting IDDM-E1 and IDDM-E2 regions of GAD65) as well as subtle differences in epitope recognition (such as binding to denatured and reduced GAD65 and by protein footprinting). Thus, the GAD65 epitopes recognized by autoantibodies in different autoimmune diseases may overlap and be more heterogeneous than previously recognized.

Human immunoglobulin G autoantibodies to the thyrotropin receptor from Epstein-Barr virus-transformed B lymphocytes: characterization by immunoprecipitation with recombinant antigen and biological activity.

The TSH receptor (TSH-R) is the target antigen for disease-related autoantibodies in Graves' disease and primary myxoedema, but the repertoire of the antibodies or the nature of the precise antigenic epitopes is not known. We have immortalized peripheral blood B cells from six different autoimmune thyroid disease patients with Epstein-Barr virus and selected IgG-producing B cells by magnetic selection on anti-IgG-coated beads. Purified recombinant insect cell-derived extracellular region of TSH-R was used to identify the positive wells for expansion in culture. Stable B cell lines (n = 11) were obtained, which after limiting dilution led to two stable B cell clones. B cell lines and clones secreted IgG antibody that were shown to react biochemically with metabolically labeled or in vitro translated, nascent extracellular region of TSH-R, giving strong, confirmatory evidence of the presence of anti-TSH-R antibody. Supernatants from lines contained thyroid-stimulating activity, thyroid-blocking activity (as assessed by inhibition of TSH-mediated cAMP stimulation), or both of these activities. Interestingly, antibodies with stimulating activity were generated from a primary myxoedema patient, and antibodies of blocking specificities were obtained from newly diagnosed thyrotoxic Graves' disease patients. Our results favor a fine balance between stimulating and blocking autoantibody activities in determining the clinical presentation observed in patients with autoimmune thyroid disease patients who have these antibodies present in their serum.

Development of a luminescent bioassay for thyroid stimulating antibodies.

The hyperthyroidism of Graves Disease (GD) is due to thyroid stimulating antibodies (TSAb) which are thyrotropin (TSH) agonists. They are detected routinely by measuring their ability to inhibit TSH binding to the receptor (TBII), which does not reflect their true biological activity. Current bioassays which measure cAMP by RIA, are not suitable for routine use. We have developed a luminescent bioassay for TSAb, by introducing a cAMP responsive luciferase construct into CHO cells stably expressing the human TSH receptor (TSHR). Clone lulul displays dose dependent TSH response detectable from 10 microU/ml and maximal at 10 mU/ml when a >25 fold increase in light output is obtained. 34 euthyroid sera were tested to determine a reference range, with values >1.5 relative light units (R.L.U.) being considered positive. An international TSAb standard responded in a dose dependent manner with 10 mIU/ml giving an R.L.U. of >10. The assay was adapted to a 96 well format for automatic readout and 100 treated GD samples (50 TBII negative and 50 TBII positive) were tested, 73% being positive. In contrast only 4% of 79 control sera from individuals with Hashimoto's, non-thyroid autoimmunity or multinodular goitre produced R.L.U. >1.5. When 44 of the GD sera were compared in a traditional salt-free bioassay, 61% were positive compared with 75% in the new luminescent assay. In conclusion, we have developed a luminescent bioassay for TSAb, using unfractionated serum which is capable of high throughput suitable for routine use.

Second generation assay for thyrotropin receptor antibodies has superior diagnostic sensitivity for Graves' disease.

Detection of autoantibodies to the TSH receptor (TSH-R) in Graves' disease has found widespread use in clinical routine and is performed mostly by commercial RRAs measuring TSH binding inhibitory activity. We report in this study on a second generation TSH binding inhibitory assay using the human recombinant TSH-R with two major improvements: 1) superior diagnostic sensitivity for Graves' disease, and 2) for the first time, nonradioactive and radioactive coated tube (CT) technology. Full-length human recombinant TSH-R was expressed in the K562 leukemia cell line and grown in suspension at a high density. A murine monoclonal antibody was selected for binding to the native TSH-R without interfering with autoantibodies or TSH and was coated to polystyrene tubes. After detergent extraction, TSH-R was affinity immobilized on antibody-coated tubes. The binding of TSH to the TSH-R could be demonstrated by the addition of 125I- or acridinium ester-labeled bovine TSH, and this binding could be inhibited by sera from patients with Graves' disease up to 95%. Subsequently, these novel assays, a CT RRA and a CT luminescence receptor assay, were compared to the conventional RRA based on porcine antigen in a blinded clinical multicenter trial. Sera from 328 patients with Graves' disease (86 untreated, 116 treated, and 126 in remission) and 520 controls (comprised of healthy blood donors and patients with autoimmune diseases or goiter) were tested in all 3 assays. Receiver-operating characteristic plot analysis resulted in a specificity of 99.6% with a sensitivity of 98.8% for both CT assays, compared to 99.6% specificity and 80.2% sensitivity for the conventional RRA (P < 0.001). In all 3 groups of patients with Graves' disease, the 2 CT assays were significantly more sensitive for the disease than the conventional assay, without loss of specificity in the control groups. This increase in sensitivity and the nonradioactive or radioactive CT format constitute a significant improvement over the currently available assays.