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Biomedical subjects

A M McGregor

Publications and source records attributed to A M McGregor.

At least 19 recordsLinked to original sources
PubMed2005

The nadir growth hormone after an octreotide test dose predicts the long-term efficacy of somatostatin analogue therapy in acromegaly.

OBJECTIVE: In the treatment of acromegaly, a 'test dose' of octreotide is recommended prior to the use of depot somatostatin analogue (SSA) therapy. However, there remains no consensus regarding the criteria that predict a response to treatment. The ability to select patients who may benefit most from medical therapy is potentially of great value in clinical practice. The aim of the study was to determine the predictive value of both the nadir GH and the mean GH following an octreotide test dose in identifying patients who subsequently achieved disease remission with depot SSA therapy. Remission was defined as a mean GH < 5 mU/l (< 2 microg/l). DESIGN: Retrospective case-control study. PATIENTS: A group of 41 patients with acromegaly underwent an octreotide test dose where GH was measured hourly for a total of 6 h following an injection of octreotide 50 microg subcutaneously. Nadir GH and mean GH following the octreotide test dose were determined. Thirty-three patients were subsequently treated with depot SSA therapy and mean GH and IGF-I levels were determined at follow-up. RESULTS: The nadir GH demonstrated superior predictive power to that of mean GH across a range of GH cut-off values. A nadir GH < 5 mU/l demonstrated 80% sensitivity and 83% specificity in predicting remission with depot SSA therapy. A nadir GH < 10 mU/l demonstrated 100% sensitivity and 56% specificity. CONCLUSIONS: The nadir GH following an octreotide test dose is a useful predictive marker of achieving disease remission with depot SSA therapy used as either a primary or an adjuvant agent.

Acromegaly↗
PubMed2001

The pharmaceutical care of patients with hypertension: an examination of service models in primary care in the US.

BACKGROUND: In the UK, the delivery of health care in cardiovascular disease is guided by national service frameworks', which are a source of standards of practice and evidence that help to define and aid the implementation of service models capable of responding to public health goals. The revised British Hypertension Society guidelines reflect a lower target blood pressure consistent with those recommended in the US and by the WHO. The lowering of the target for the control of blood pressure has increased the estimated proportion of treated patients with inadequate control in the UK from 37% to 72%. OBJECTIVE: To identify the requirements for the provision of a pharmacy service that supports hypertension monitoring, and to gain insights into how such a service might be delivered as part of a wider provision of pharmaceutical care in the UK. METHOD: Two pharmacists followed a structured programme of observation involving three centres in the United States (Minnesota, Colorado and Iowa). Twelve clinical settings were observed, and the pharmacists who provided the services were also the subjects of documented interviews. The settings offered different models of pharmaceutical care from which issues relevant to the international development of such services were identified. FINDINGS: Differences noted between the service models observed included; physical environment of the community pharmacy, the use and type of documentation, methods of blood pressure measurement, extent of monitoring and follow-up, inter-professional communication and service orientation in terms of the provision of comprehensive pharmaceutical care to patients or specific disease management. CONCLUSION: If clearly defined operational models of pharmaceutical care practice in the primary care setting are to form part of a national public health strategy in the UK, they must also be capable of responding to local opportunities and patients' needs. Future development of models and services must be patient-centred and more widely informed by the range of practice experience gained elsewhere.

Blood Pressure Monitoring, Ambulatory↗
PubMed2000

Identification of an immunodominant region recognized by human autoantibodies in a three-dimensional model of thyroid peroxidase.

Autoimmune thyroid diseases (AITD) are characterized by the presence of autoantibodies to thyroid peroxidase (TPO). This response is dominated by autoantibodies to two conformational determinants, termed A and B, that have been defined by monoclonal antibodies but whose structures and location within TPO are unknown. We have modeled the three-dimensional structure of the extracellular region of TPO, raised antisera to prominent surface structures, and identified an epitope that we show to be a critical part of the B determinant. Antibodies to this epitope inhibit the binding to TPO of human autoantibodies in virtually all serum samples from 65 patients with AITD that were tested. This first description of a model of the three-dimensional structure and location of a major autoantigenic determinant within the TPO molecule may provide structural clues for identifying causative agents or developing novel therapeutic strategies.

Amino Acid Sequence↗
PubMed1999

Distinct immunological and biochemical properties of thyroid peroxidase purified from human thyroid glands and recombinant protein produced in insect cells.

The biosynthesis of thyroid hormone from thyroglobulin is catalysed by thyroid peroxidase (TPO), an integral membrane protein. TPO is also a major autoantigen in autoimmune thyroid disease and autoantibodies to TPO are markers for disease activity. Large quantities of purified TPO are essential for elucidating its structure and understanding its role in disease activity. We describe the high yield purification of full-length recombinant human TPO from baculovirus infected insect cells and compare it to purified native TPO from human thyroid glands. In contrast to native human TPO, the human TPO produced in insect cells as a recombinant protein was insoluble and resistant to solubilisation in detergents. Reversible substitution of lysine residues with citraconic anhydride led to increased solubility of the recombinant TPO, allowing high-yield purification by monoclonal antibody chromatography. The purified enzyme preparation was shown to be TPO by its reactivity with monoclonal and polyclonal antibodies by enzyme linked immunosorbent assay and Western blotting. Both the human and recombinant purified TPO preparations also react with sera from patients with autoimmune thyroid disease, although the binding of conformational dependent autoantibodies was considerably lower to the recombinant TPO than to the native TPO. This suggests that the recombinant TPO may differ in some aspects of its tertiary structure. The purified recombinant TPO was devoid of enzyme activity, in contrast to the enzymatically active, purified human TPO preparations. Both preparations contained comparable amounts of haem (R(z)=0.269), but a shift in the Soret band of recombinant TPO (402 nm) from that of natural TPO (409 nm) indicates that the lack of enzymatic activity of the recombinant enzyme may be due to changes in the protein backbone surrounding the haem. Both the purified native and recombinant TPO, under non-denaturing conditions, show evidence of high molecular mass oligomers, although the latter preparation is prone to a greater degree of aggregation. In conclusion, our studies indicate that recombinant TPO generated in insect cells is conformationally distinct from the native TPO, is insoluble and enzymatically inactive, consistent with the difficulties associated with its purification and crystallisation.

Animals↗
PubMed1999

Direct binding of thyrotropin receptor autoantibody to in vitro translated thyrotropin receptor: a comparison to radioreceptor assay and thyroid stimulating bioassay.

Graves' disease is characterized by the presence of autoantibodies to the thyrotropin receptor (TSHR), which are pathogenic and responsible for disease activity. It is well recognized that the autoantibodies are heterogeneous and recognize a number of different conformational dependent epitopes on the TSHR. In this study, we have extended our previous observations to study the interaction of Graves' disease autoantibodies with TSHR ectodomain produced by in vitro transcription and translation reaction. The specific activity of the translated TSHR ectodomain has been increased by a log fold by adding an efficient ribosome binding Kozak sequence before the translation initiation codon as well as double labelling with 35S-methionine and 35S-cysteine during the translation reaction. Addition of canine pancreatic microsomes to the translation mix showed that the glycosylation of TSHR ectodomain did not occur efficiently for the nascent receptor protein. In order to determine the specificity and sensitivity of the improved assay with nonglycosylated TSHR ectodomain, we have studied 331 sera from Graves' disease patients and as controls 100 sera from patients with nonthyroid autoimmune disorders as well as sera from 200 normal control subjects with no family history of thyroid autoimmunity. With this large cohort of sera from Graves' disease and control individuals, 25% of Graves' disease sera immunoprecipitated the dual labeled, in vitro transcribed and translated TSHR ectodomain, exceeding the 98th percentile of the control sera. There was no correlation between the autoantibodies that immunoprecipitate the in vitro translated TSHR ectodomain and those that inhibit iodinated TSH binding in the radioreceptor assay and those with biological activity in a bioassay. The data are consistent with the finding that a proportion of Graves' disease autoantibodies can interact directly with TSHR ectodomain produced by in vitro transcription and translation. However, in contrast to the wide use of similar translation and immunoprecipitation assays to measure other autoantibodies for the diagnosis of autoimmune disorders, such as type 1 diabetes, the TSHR immunoprecipitation on its own is unsuitable for diagnosis of Graves' disease.

Animals↗
PubMed1998

Gene expression and serum levels of insulin-like growth factors (IGFs) and IGF-binding proteins in a case of non-islet cell tumour hypoglycaemia.

We describe a case of non-islet cell tumour hypoglycaemia (NICTH) associated with a renal cell carcinoma. Serum insulin-like growth factors (IGFs) (including IGF-II E peptide), IGF-binding proteins (IGFBPs), insulin and C-peptide were measured before and after surgical removal of the tumour. IGFBPs were visualized by Western ligand blotting. Preoperatively 'big' IGF-II and IGFBP-2 levels were raised. IGF-I, IGFBP-1 and IGFBP-3 were low, while insulin, C-peptide and GH were undetectable. These changes were reversed by 2 days postoperatively. Protease assays showed little IGFBP-3 protease activity preoperatively. Preoperatively, neutral chromatography demonstrated most of the immunoassayable IGFBP-3 in a high molecular weight form with a small amount of IGF-II. Most of the IGF-II and big IGF-II eluted in lower molecular weight forms. Postoperative samples showed a shift in IGF-II which became increasingly associated with IGFBP-3 in both low and high molecular weight complexes. By Northern blotting, expression of all species of IGF-II mRNA in the tumour was 10-fold greater than in normal human liver. The tumour did not express IGFBP-1 or IGFBP-2. IGFBP-3 was expressed in small amounts, while the expression of IGFBP-4 was two-fold higher than in liver. In conclusion, we have confirmed high levels of big IGF-II and IGFBP-2 in NICTH, changes which are reversed postoperatively. The IGF-II is derived from the tumour which overexpresses these genes but IGFBP-2 probably arises from extratumour upregulation.

Aged↗
PubMed1998

Induction of thyroiditis in mice with thyrotropin receptor lacking serologically dominant regions.

Grave's disease (GD) is characterized by pathogenic autoantibodies to the human thyrotropin receptor (hTSH-R), and is frequently associated with a lymphocytic infiltrate of the thyroid gland. In attempts to establish a murine model of GD, we and others have previously shown that immunization of mice with recombinant preparations of the hTSH-R ectodomain induces high titres of specific antibodies, which, however, are not pathogenic, nor is the response accompanied by the development of thyroiditis. Since earlier reports identified the serological immunodominant determinants within the N- and C-terminal regions of hTSH-R ectodomain, we reasoned that immunization of mice with truncated fragments of ectodomain lacking these dominant regions might result in skewing of the response to other determinants of the molecule, with consequent induction of immunopathological features present in GD. We show here that multiple challenge of BALB/c mice with an amino acid fragment of residues 43-282 generates antibodies directed at hTSH-R peptides 37-56, 157-176, 217-236 and 232-251. This reactivity pattern is distinct from that induced previously with the whole ectodomain of hTSH-R in BALB/c animals. Thyroid function remained unaffected in these mice, suggesting that pathogenic antibodies were not being induced. Interestingly, some animals developed lymphocytic infiltration of the thyroid gland, clearly indicating the presence of pathogenic T cell determinants within the 43-282 fragment. Challenge with the related fragment 43-316 produced the same pattern of serological response to the synthetic peptides as fragment 43 282, but was not accompanied by thyroiditis. The results demonstrate: (i) the presence of thyroiditogenic determinants within hTSH-R, and (ii) that these pathogenic determinants are likely to be cryptic, as their effect is exhibited only when the hierarchy of immunodominance within hTSH-R is drastically altered.

Animals↗
PubMed1998

Agonist-induced endocytosis and recycling of the gonadotropin-releasing hormone receptor: effect of beta-arrestin on internalization kinetics.

This study examined the dynamics of endocytotic and recycling events associated with the GnRH receptor, a unique G protein-coupled receptor (GPCR) without the intracellular carboxyl-terminal tail, after agonist stimulation, and investigated the role of beta-arrestin in this process. Subcellular location of fluorescently labeled epitope-tagged GnRH receptors stably expressed in HEK 293 cells was monitored by confocal microscopy, and the receptor/ligand internalization process was quantified using radioligand binding and ELISA. Agonist stimulation resulted in reversible receptor redistribution from the plasma membrane into the cytoplasmic compartment, and colocalization of internalized GnRH receptors with transferrin receptors was observed. Internalization experiments for the GnRH receptor and another GPCR possessing a carboxy-terminal tail, the TRH receptor, showed that the rate of internalization for the GnRH receptor was much slower than for the TRH receptor when expressed in both HEK 293 and COS-7 cells. TRH receptor internalization could be substantially increased by coexpression with beta-arrestin in COS-7 cells, while GnRH receptor internalization was not affected by coexpression with beta-arrestin in either cell type. Coexpression of the GnRH receptor with the dominant negative beta-arrestin (319-418) mutant did not affect its ability to internalize, and activated GnRH receptors did not induce time-dependent redistribution of beta-arrestin/green fluorescent protein to the plasma membrane. However, the beta-arrestin mutant impaired the internalization of the TRH receptor, and activated TRH receptors induced the beta-arrestin/green fluorescent protein translocation. This study demonstrates that, despite having no intracellular carboxy-terminal tail, the GnRH receptor undergoes agonist-stimulated internalization displaying distinctive characteristics described for other GPCRs that internalize via a clathrin-dependent mechanism and recycle through an acidified endosomal compartment. However, our data indicate that the GnRH receptor may utilize a beta-arrestin-independent endocytotic pathway.

Animals↗
PubMed1997

Purification and crystallisation of the autoantigen thyroid peroxidase from human Graves' thyroid tissue.

Milligram quantities of the human membrane autoantigen thyroid peroxidase (TPO) have been purified to a high degree of homogeneity by a combination of detergent solubilisation, monoclonal antibody affinity, and ion exchange chromatography, from pooled Graves' disease thyroid glands. The purified TPO of greater than 90% purity was enzymatically active as judged by its ability to oxidise guaiacol. Crystals of TPO have been grown from solutions of the protein solubilised in sodium deoxycholate, in the presence of ammonium sulphate. The crystals exhibited birefringence under polarised light, indicative of molecular order. Crystallisation of this large, membrane autoantigen represents the first step in delineating the complete three-dimensional structure of a human autoantigen involved in destructive thyroiditis.

Autoantigens↗
PubMed1997

Human thyroid peroxidase (TPO) isoforms, TPO-1 and TPO-2: analysis of protein expression in Graves' thyroid tissue.

Thyroid peroxidase (TPO) is the key enzyme involved in the biosynthesis of thyroid hormones and is an important autoantigen in autoimmune thyroid disease. Different messenger RNA species coding for TPO are present in thyroid tissue, including the species coding for a 933-amino acid protein (termed TPO-1) and a second in which exon 10 is deleted and which is 57 residues shorter (termed TPO-2). However, it is not known whether the smaller, TPO-2 isoform is expressed as a protein in thyroid cells. In SDS-PAGE under reducing conditions, TPO appears in the thyroid microsome and purified protein preparations as a closely migrating double band of approximately 105 (larger form) and 100 kilodaltons (smaller form). We investigated the presence of the isoform TPO-2 polypeptide in Graves' thyroid tissue using rabbit antisera to three different synthetic peptides from exon 10 (specific for TPO-1) and a polyclonal rabbit and monoclonal anti-TPO antibody (both of which are specific for the two forms of TPO). The larger and smaller forms of TPO were purified by electroelution after gel electrophoresis of highly purified natural TPO from Graves' thyroid microsomes. Both of the purified forms of TPO react with all three anti-exon 10 peptide antibodies, the polyclonal anti-TPO and the monoclonal antibody anti-TPO. This shows that both forms of TPO contain exon 10-encoded polypeptide of TPO-1. Interestingly, the proportion of the larger and smaller forms of TPO varied in different Graves' thyroid microsome preparations. To investigate the presence of the smaller TPO-2 isoform in the purified natural TPO preparation, affinity depletion of TPO-1 using the anti-exon 10 peptide antibodies was carried out. The binding of anti-exon 10 peptide antibodies to the immunodepleted TPO-1 fraction was considerably diminished in comparison to binding of polyclonal anti-TPO, suggesting the presence of small amounts (< 10%) of TPO-2 expressed as a protein in thyroid cells. Our results extend previous observations by showing that the alternatively spliced form of TPO, in which exon 10 is excised, is expressed at low levels in Graves' thyroid tissue. Furthermore, we confirm that both the larger and smaller forms of TPO observed on gel electrophoresis contain TPO-1, suggesting that the difference is caused by posttranslational modifications. The presence of small amounts of TPO-2 in Graves' thyroid glands argues for its role in thyroid function, which remains to be clarified.

Amino Acid Sequence↗
PubMed1997

Characterisation of the antibody response to the extracellular region of recombinant thyrotropin receptor.

Autoantibodies to the human thyrotropin receptor (TSH-R) are pathogenic in a number of autoimmune thyroid diseases including Graves' disease. We have characterised polyclonal antisera to TSH-R for antibodies which may mimic those present in autoimmune thyroid disease. For immunisations, recombinant extracellular region of human TSH-R which does not interact with its ligand TSH was used. The induced antibodies react with the full length membrane receptor in transfected mammalian cells by flow cytometry showing the presence of antibody capable of recognising the native functional receptor. The properties of the generated antibodies have been compared after two injections or following a multiple immunisation protocol with the receptor in adjuvant. High titre antisera were readily generated after the short injection protocol and further immunisations did not lead to any change in antibody titers. Analysis of the epitopes recognised using synthetic peptides confirmed previous observations that the immunodominant determinants localise to the amino and the carboxyl terminal part of the extracellular region of the receptor. Antisera from both rabbits contain TSH blocking antibody as assessed by inhibition of TSH mediated cAMP stimulation. There was an increase in TSH binding inhibitory immunoglobulin (TBII) activity with multiple injections. Furthermore, the increase in TBII activity was not related to spreading of the antibody response to new determinants on TSH-R. Our results support previous observations on the difficulties in reproducing, by adjuvant immunisation with recombinant TSH-R preparations, the fine specificity of antibodies to TSH-R present in autoimmune disorders such as Graves' disease or primary myxoedema.

Animals↗
PubMed1996

The isoform-specific expression of the tri-iodothyronine receptor in osteoblasts and osteoclasts.

Hyperthyroidism is associated with an increase in both osteoblast and osteoclast activity. We have previously shown that, in vitro, osteoclasts do not respond directly to tri-iodothyronine to increase bone resorption but that the effect is mediated by another bone cell, probably the osteoblast. To investigate this issue further we have studied the isoform-specific expression of thyroid receptor (TR) protein in human osteoclasts derived from an osteoclastoma (giant cell tumour of bone) and the expression of TR mRNA and protein in the osteoblastic cell lines MG 63 and UMR 106. Three major TR receptor variants have been described; TR alpha 1 and TR beta are functional receptors whereas c-erbA alpha 2 is a non-functional variant. Northern blot analysis using [32P]-cDNA probes against human TR alpha 1, c-erbA alpha 2 and TR beta demonstrated specific binding of these probes to mRNA from MG 63 and UMR 106. mRNA for all three receptor variants was observed in both cell lines, in UMR 106 multiple mRNA transcripts were present for TR alpha 1 and TR beta. Immunohistochemical staining with antibodies recognizing a common TR alpha epitope and specific c-erbA alpha 2 and TR beta epitopes extended these observations by demonstrating receptor protein in both osteoblasts and osteoclasts. These findings are consistent with previous observations of TR expression in osteoblast-like-cells and are the first direct demonstration of TR in osteoclasts.

Animals↗
PubMed1996

Analysis of the thyrotropin receptor as a candidate gene in familial Graves' disease.

Familial clustering of Graves' disease indicates a genetic etiology. Searches for genetic factors additional to the known human leukocyte antigen (HLA) association have implicated the gene for the TSH receptor (TSHR). We analyzed the linkage and association among three recently described microsatellite markers within the TSHR introns in Graves' disease in large multiply affected Welsh and English families (223 members, 44 affected individuals). Linkage analysis under a dominant model strongly rejected the hypothesis that TSHR is linked to Graves' disease in these families (lod score = -4.53). More detailed analyses also failed to provide evidence for linkage; these included combined segregation and linkage analysis, correction for HLA-DR3 status, allowance for the levels of thyroid autoantibodies in unaffected pedigree members, consideration of a recessive model for the disease, and linkage disequilibrium between disease and marker alleles. We also considered the possibility of a genetic heterogeneity of Graves' disease and thus analyzed separately the different families with a similar result. Although these results cannot eliminate a minor role of the TSHR gene locus in the genetics of Graves' disease, they argue against it being a major genetic determinant in this pathology.

Adolescent↗
PubMed1996

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.

Animals↗