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VCU Theses and Dissertations

Defects in genes mediating thyroid hormone biosynthesis result in dyshormonogenic congenital hypothyroidism (CH). Here, we report homozygous truncating mutations in SLC26A7 in 6 unrelated families with goitrous CH and show that goitrous hypothyroidism also occurs in Slc26a7-null mice. In both species, the gene is expressed predominantly in the thyroid gland, and loss of function is associated with impaired availability of iodine for thyroid hormone synthesis, partially corrected in mice by iodine supplementation. SLC26A7 is a member of the same transporter family as SLC26A4 (pendrin), an anion exchanger with affinity for iodide and chloride (among others), whose gene mutations cause congenital deafness and dyshormonogenic goiter. However, in contrast to pendrin, SLC26A7 does not mediate cellular iodide efflux and hearing in affected individuals is normal. We delineate a hitherto unrecognized role for SLC26A7 in thyroid hormone biosynthesis, for which the mechanism remains unclear.

To overcome the difficulty of assessing oncogene action in human epithelial cell types, such as thyroid, which have limited proliferative potential in culture, we have explored the use of temperature-sensitive (ts) mutants of simian virus 40 (SV40) early region to create conditionally immortalized epithelial cell lines. Normal primary cultures of human thyroid follicular cells were transfected with a plasmid containing the SV40 early region from mutant tsA58. Expanding epithelial colonies were observed after 2 to 3 months, all of which grew to greater than 200 population doublings without crisis. All showed tight temperature dependence for growth. After switch-up to the restrictive temperature (40.5 degrees C), no further increase in cell number was seen after 1 to 2 days. However, DNA synthesis declined much more slowly; the dissociation from cell division led to marked polyploidy. Viability was maintained for up to 2 weeks. Introduction of an inducible mutant ras gene into ts thyroid cells led, as expected, to morphological transformation at the permissive temperature when ras was induced. Interestingly, this was associated with a marked reduction in net growth rate. At the restrictive temperature, induction of mutant ras caused rapid cell death. These results demonstrate the utility of a ts SV40 mutant to permit the study of oncogene action in an otherwise nonproliferative target cell and reveal important differences in the interaction between ras and SV40 T in these epithelial cells compared with previously studied cell types.

Pentavalent 99 Tc m -dimercaptosuccinic acid ( 99 Tc m -(V)DMSA) has established uses in the detection and diagnosis of medullary thyroid carcinoma, osteosarcoma, amyloidosis and many soft tissue tumours, but is not readily available as a commercial kit. We have evaluated published methods for preparation of 99 Tc m -(V)DMSA that are based on the modification of 99 Tc m -(III)DMSA commercial kits. The criteria for assessment were achievement of satisfactory radiochemical purity and practical considerations regarding the ease of synthesis. Quantification of the desired product's activity was achieved via thin-layer chromatography (silica gel) with an n-butanol:acetic acid:water solvent system. The developed plates were imaged on a gamma camera and analysed using standard software. The methods investigated were designated as Birmingham, Cambridge and Canterbury: the latter two were very similar. With experience, the methods eventually produced similar radiochemical purities of > 90%. However, the Birmingham method was found to be more satisfactorv in terms of its reliabilitv and simplicity of synthesis.

In this paper we present a low-energy ion scattering (LEIS) study of the site exchange of Fe adatoms with Ag atoms from the Ag(100) surface. The time-of-flight (TOF) spectra obtained at low temperatures have been interpreted with a newly developed LEIS simulation program MATCH. After low temperature deposition (˜50 K) of Fe atoms oil the Ag(100) surface, the Fe atoms occupy adatom positions. These Fe adatoms exchange sites with Ag atoms from the first layer, starting at a temperature of 130(10) K.

In a pilot study of consistency in nuclear medicine reporting, a panel of three observers evaluated 60 bone scans carried out for detection of metastases. The bone scans had originated from 10 departments. Difficulties arose in evaluation of the quality of the images by the panel members because of the differing criteria each chose to adopt. This highlights the need to define strictly, in advance, the parameters to be included in quality assessment. All three panel members agreed on the lesions present in 54 out of 60 studies. The observers' consensus report showed material differences from the original departmental report in the number of lesions present in 10 out of 60 studies. Material differences in the interpretation of the study occurred between panel members in two cases and between the panel and the original report in four cases. The pilot study has shown an acceptable level of consistency in bone scan reporting in the departments contributing images. A national study assessing consistency of reporting would be difficult to organize but alternative, more local, schemes are suggested.

The possible role of changes in TGF-beta expression in the multistage development of thyroid cancer was assessed. The presence of TGF-beta 1 in thyroid epithelial cells was analyzed in sections of normal and tumor tissue using an immunoperoxidase technique employing an antibody directed against the amino-terminal 30 amino acids of mature TGF-beta 1. Specific immunostaining was clearly detected in epithelial cells in 58% of malignant thyroid tumours (including follicular, papillary, and anaplastic variants). However, no positive cells were seen in any of 7 benign tumors nor in any normal thyroid epithelium. Within the cancer group as a whole, there was no significant correlation with pathological grade or clinical stage of tumor but in one subgroup--follicular carcinomas--a significant association was noted between TGF-beta immunostaining and the presence of a specific mutation of the H-ras oncogene (codon 61, gln----arg). We conclude that a major alteration in expression of TGF-beta occurs specifically in the malignant stage of tumor development in thyroid follicular epithelium and speculate on its possible role in this process.

The possibility of an association between restriction fragment length polymorphisms (RFLPs) at the Ha-ras gene locus and susceptibility to develop colorectal cancer has been investigated. Leucocyte DNA from 46 carcinoma patients and 49 controls was analysed by Southern blotting to determine the size distribution of restriction fragments containing the variable tandem repeat 3' to the Ha-ras gene. Four predominant allelic fragments were found in both groups (in AvaII digests having sizes of 1.55, 2.0, 2.65 and 3.15 kilobases [kb]), together with a variety of 'rare' alleles (with individual frequencies less than 5%). The overall prevalence of rare alleles was not significantly different between cancer and control groups. The distribution of the common alleles, however, differed significantly. The combined frequency of the two larger alleles (a3 and a4) was approximately twice as high in the cancer group (34%) as in controls (18%) (P less than 0.025), which was reflected in a highly significant increase in the proportion of individuals carrying an a3 or a4 allele. Images Figure 2 Figure 3

A recombinant murine retroviral vector encoding the SV40 virus large T antigen was used to infect stably an immortal line of differentiated rat thyroid epithelial cells, FRTL-5. Expression of SV40 T transformed these cells to anchorage independence and tumorigenicity but did not alter morphology or abolish tissue-specific functions and growth factor requirements. The resulting phenotype provides a model of well-differentiated human thyroid cancer. Images Figure 1 Figure 3

A questionnaire was sent to all the estimated 200 hospital departments providing nuclear medicine imaging services in the UK. Replies were received from 162 (81%). The questionnaire was brief, but covered a wide range of aspects of a nuclear medicine service. While all responses showed departments to have some quality control procedures in operation, they were often not used correctly. In most departments there appears to be scope for improvement so that departmental managers can monitor more closely the quality of service provided.

125I emits no β rays but part of its soft γ radiation is transformed into low energy electrons. Considering the short tissue path length (2-5 μm) of these electrons, it was postulated that its radiation effect on the thyroid might be different from that of 131I (path length 2000 μm). An experiment was designed to compare the biological effect of several dose levels of radiation from 125I on the rat thyroid gland with that from 131I. The effect of varying doses of each isotope on goitrogenesis (methylthiouracil induced) and on thyroid/serum radioiodide concentration (T/S) ratio was measured in animals radiated while on either a normal or a low iodide diet. In relation to 131I, the effect of 125I on goitrogenesis generally was much less than its effect on function. The low iodide diet group given 125I, surprisingly, showed markedly less inhibition of goitrogenesis than the normal diet group, an opposite effect to that attained with 131I. We suggest that the observed differences are due to the gradient of energy absorption in the follicular cell from irradiation from 125I stored in the colloid. The apical cytoplasm would absorb much more energy than the basal cytoplasm and the nucleus, in contrast to the uniform absorption of energy from 131I across the cell. The comparatively lower effect of 125I on goitrogenesis, and the paradoxical reduction in its effect in the low iodide diet groups, may be due to the low energy absorption by the nucleus, especially when, in a taller cell, the nucleus is farther from the colloid.

The applicability of a hapten-antihapten sandwich technique incorporating a monoclonal antihapten bridge antibody to localisation of tissue antigen is described. The results show that the method is both versatile and selective and has the potential of being even more sensitive than currently used immunoperoxidase methods.

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Publisher Summary This chapter discusses the role of 5-hydroxyindoles on thyroid gland. It presents a link between the morphology, histogenesis, and function of parafollicular cells with medullary carcinoma of the thyroid. It is suggested (1) that the lateral thyroid anlage plays a significant role in the development of the human thyroid, and that some of its derivatives persist throughout life; (2) that some cells from the lateral thyroid anlage give rise to the parafollicular system, which differs in morphology and function from the follicular. This cell system is able to concentrate 5-HTP and has a high content of 5-HT together with its enzymes of synthesis and degradation, 5-HTP decarboxylase and monoamine oxidase (MAO); (3) that medullary carcinoma of the thyroid is a tumor of parafollicular cells. It is associated with a clinical syndrome of watery diarrhea and may be associated with a raised 5-HIAA excretion; and (4) that the morphology, histogenesis, and function of medullary carcinoma distinguish it from other types of thyroid carcinoma.