Use of molecular probes in the study of endocrine diseases

Clinically Non-Functioning Human Pituitary Adenomas

Clinically non-functioning pituitary adenomas are morphologically classified into two groups, those which have hormone immunoreactivity and ultrastructural features of known adenohypophysial cell types but are clinically silent, and those composed of cells that do not resemble nontumorous adenohypophysial cell types. Among the fomer are the silent somatotroph adenomas, silent corticotroph adenomas and silent gonadotroph adenomas; the latter include the silent type III adenomas, null cell adenomas and oncocytomas. We review their histological, immunohistochemical and ultrastructural features, the results of in situ hybridization to determine hormone synthesis by these tumors and data obtained from tissue culture characterizing their hormone release in vitro. Non-functioning adenomas represent a heterogeneous group. The discrepancies between morphology, immunoreactivity and lack of endocrine activity of silent adenomas are not clear. Oncocytomas are variants of null cell adenomas. We suggest that null cell adenomas and oncocytomas originate in uncommitted pluripotent precursor cells capable of undergoing multidirectional differentiation. The progenitor cells differentiate most frequently toward FSH / a-subunit producing cells; the mechanism of preferential differentiation is obscure.

Application of immunohistochemistry to thyroid neoplasms

CONTEXT

Thyroid lesions with nodular architecture and follicular pattern of growth often pose difficulties in accurate diagnosis during the assessment of cytologic and histologic specimens. The diagnosis of follicular neoplasm on cytology or of follicular tumor of uncertain malignant potential on histology is likely to cause confusion among clinicians and delay effective management of these lesions. Occasionally, thyroid tumors represent unusual or metastatic lesions and their accurate diagnosis requires immunohistochemical confirmation.

OBJECTIVE

To review the literature on the applications of immunohistochemistry in the differential diagnosis of thyroid tumors.

DATA SOURCES

Relevant articles indexed in PubMed (National Library of Medicine) between 1976 and 2006.

CONCLUSIONS

Our review supports the use of ancillary techniques involving a panel of antibodies suitable for immunohistochemistry and molecular analysis in the assessment of thyroid nodules. These tools can improve diagnostic accuracy when combined with standard morphologic criteria.

Practical markers used in the diagnosis of endocrine tumors

Endocrine tumors constitute a large group of neoplasms that are widely dispersed throughout the body. They are made up mostly of neuroendocrine tumors (NE), which are characterized by the presence of secretory granules and production of peptide hormones, and non-NE tumors such as those derived from thyroid follicular cells and adrenal cortical cells. Immunohistochemical markers have been used to characterize these lesions and distinguish them from other histologically similar tumors. Chromogranin and synaptophysin are the most widely used broad-spectrum neuroendocrine tumor markers. The use of antibodies to transcription factors, keratins, and specific peptides is quite valuable in the diagnosis of endocrine tumors. This article reviews the common markers used to characterize endocrine tumors and to recognize tumors involved in the differential diagnosis of specific lesions.

Practical markers used in the diagnosis of neuroendocrine tumors

Although there are many broad-spectrum neuroendocrine markers, chromogranin and synaptophysin are the principal ones used in diagnostic pathology. Other broad-spectrum neuroendocrine markers, transcription factors, and specific peptide markers used in the diagnosis of neuroendocrine tumors are reviewed. The use of different keratins in the differential diagnosis of endocrine tumors is also presented. The importance of using low-molecular-weight keratins such as CAM5.2 to avoid false-negative results in the workup of some neuroendocrine tumors is emphasized. Finally, the use of in situ hybridization in diagnostic pathology is briefly summarized.

Overview of Neuroendocrine Cells and Tumors

The diffuse neuroendocrine system (DNES) is composed of cells and tumors with secretory granules ranging from 50-400 nm in diameter. Members of the DNES commonly stain for chromogranin and synaptophysin by immunohistochemistry and may express a variety of peptide hormones. Recent studies have shown that the proprotein convertases (proconvertases or PCs) are good broad-spectrum markers for members of the DNES. Gene expression can be readily detecting in neuroendocrine cells and tumors by in situ hybridization (ISH). Newer techniques such as in situ polymerase chain reaction (PCR) can be used to detect gene products that are expressed in low copy numbers in neuroendocrine cells. The concept of multidirectional differentiation is an important notion that helps to explain multiple patterns of phenotypic expression observed in some neuroendocrine tumors.

Tumor genes and their proteins in cytologic and surgical specimens: relevance and detection systems

Oncogenesis is the consequence of a series of genetic alterations that allow unrestrained cellular growth, tissue invasion, and eventual metastases. Tumor-related genes can be classified into functional categories. Proto-oncogenes/oncogenes have a stimulatory role in cell growth, and the inactivation of cancer-suppressor genes/antioncogenes results in the loss of cell cycle regulation. More recently, three other groups of tumor-related genes have been recognized. They include the antiapoptosis genes which protect from programmed cell death, the antimetastasis genes, and multidrug resistance genes. Besides aiding in tumor diagnosis, the detection of such tumor-associated genes and their products allows the identification of individuals with an inherited predisposition to neoplastic growths, and the overexpression of many of these oncogene products has been shown to be a potential marker of tumor behavior and a predictor of treatment outcome and response. The ability to utilize DNA and RNA probes for nucleic acid hybridization and polymerase chain reaction procedures in cell and tissue preparations of solid tumors and lymphoid proliferations expands and complements the information provided by immunohistochemical techniques. These probes allow direct visualization and correlation of specific genes and their protein products with cytomorphologic features, and form a powerful addition to the armamentarium of the cytopathologist and surgical pathologist.

Comparison of in situ hybridization and immunocytochemistry for the detection of residual beta cells in the pancreas of streptozotocin-treated diabetic rats

The relative efficacy of immunocytochemistry versus in situ hybridization in identifying residual beta cells was studied in rats with streptozotocin-induced diabetes. Consecutive sections of pancreas of streptozotocin-treated diabetic rats and control animals were alternately subjected to in situ hybridization (synthetic oligonucleotides complementary to rat preproinsulin mRNA) and immunocytochemistry (monoclonal antibodies to insulin). The results obtained with both methods were quantitated with the use of computer-assisted image analysis, and the ratio of cells positive by immunocytochemistry to those positive by in situ hybridization was determined. Under normoglycaemic conditions the values obtained by immunocytochemistry correlated well with those obtained by in situ hybridization (immuno/in situ > 95%). In the streptozotocin diabetic animals, however, immunocytochemistry resulted in a distinct underestimation of the number of residual beta cells (immuno/in situ < 80%). This difference was even more striking in small islet cell clusters (< 100 microns) (immuno/in situ 20%). These results suggest that in situ hybridization for prohormone mRNA is the method of choice for the identification of residual or regenerating beta cells with very low insulin content. Caution should be used when interpreting quantitative data in diabetic conditions that are based exclusively on immunocytochemical detection methods.

In situ hybridization at light and electron microscopic levels: identification of human papillomavirus nucleic acids

A comparison of the sensitivities of biotinylated and 32P-labelled human papillomavirus type 6b DNA probes was made. Slot blot hybridization results showed that the sensitivity of biotinylated probes was consistent with that of 32P-labelled, that is, 0.1 pg of pBR 322 plasmid containing 8 kbp HPV cDNA. In situ hybridization using 35S-labelled probes was applied to tissue from condylomata acuminata. After autoradiography, many silver grains were seen concentrated over the superficial koilocytic nuclei with some grains present in the cytoplasm. Biotinylated probes were visualized by 4 different means, i.e., streptavidin alkaline phosphatase, streptavidin biotinylated horseradish peroxidase, monoclonal anti-biotin antibody with 15 nm colloidal gold and streptavidin 5 nm colloidal gold. Strong reaction products were localized in the superficial nuclei while the cytoplasm of koilocytes showed weak hybridization signal. Pre-embedding methods were carried out for electron microscopic studies in which numerous granular diaminobenzidine (DAB) products were present in the nuclear chromatin while viral particles themselves had much fewer DAB products. This suggested that hybridization occurred more efficiently to yet unassembled viral genomes than to matured virions. Post-embedding methods using 15 nm colloidal gold were performed and showed singly scattered or clustered gold particles in superficial koilocytic nuclei.

Detection of growth hormone, prolactin and human beta-chorionic gonadotropin messenger RNA in growth-hormone-secreting pituitary adenomas by in situ hybridization

In a series of 39 adenomas from patients with the clinical hyperfunction syndrome of acromegaly and in one from a case of prolactinoma we studied the mRNA expression of growth hormone (GH), prolactin (PRL) and beta-human chorionic gonadotropin (HCG) by using this technique of in situ hybridization (ISH). This technique allows the direct identification and localization of cells expressing mRNA and thus synthesizing the respective hormone. The aim of our study was to demonstrate the frequent co-expression of PRL mRNA and HCG mRNA in pituitary adenomas of acromegalic patients. Probes for ISH of the above-mentioned hormones were obtained by subcloning cDNA fragments into pGEM plasmids. Subsequent Sp6-polymerase catalysed in vitro transcription with 35S-CTP revealed radiolabelled single-stranded antisense RNA probes [the probe for beta HCG detects beta-luteinizing hormone (beta LH) simultaneously because of a sequence homology of 90%]. To localize the labelled hybrids, autoradiography was carried out. Light microscopical evaluation of the tissue sections demonstrated positive signals in all cases for GH, in 80% of cases for PRL and in 25% of cases for HCG [LH] mRNA. The comparison of mRNA content shown by ISH with immunocytochemical (ICC) hormone detection revealed that in all cases the detection of GH corresponded to GH mRNA content of the cells. For PRL and HCG [LH] positive mRNA detection (ISH) and negative hormone detection (ICC) occurred in some cases (PRL 17.5%; HCG [LH] 15%). In contrast, negative mRNA detection (ISH) and positive hormone content (ICC) was also demonstrated (PRL 5%; HCG [LH] 37.5%). The remaining adenomas showed both mRNA and the respective hormone, as well as negative ISH and ICC.

Demonstration of insulin and glucagon mRNA in routinely fixed and processed pancreatic tissue by in-situ hybridization

Human insulin and glucagon mRNA were identified in routinely processed pancreatic tissue by non-radioactive in-situ hybridization using digoxigenin-labelled oligonucleotide probes. Cocktails of synthetic oligonucleotides complementary to human insulin and glucagon mRNA were labelled with digoxigenin using terminal deoxynucleotidyl transferase (Tdt). Specific hybrids were detected with alkaline phosphatase-labelled anti-digoxigenin antibody and visualized by BCIP-nitroblue tetrazolium indicator substrate. The results showed highly sensitive and specific staining of islet cells on a range of routinely formalin-fixed and paraffin-embedded tissues. Post-mortem pancreatic tissue from adults and stillborn neonates yielded acceptable signals as long as tissue morphology was well preserved. Preliminary investigations using pancreatic endocrine cell tumours gave clear easily interpretable signals which were comparable to conventional immunostaining. The application of this technique promises to be of value in the investigation of pancreatic disease.

The future anatomic pathology laboratory for molecular diagnosis and prognosis: circa 1990-95

Molecular biology provides analytical tools for the study of human disease. These clinical assays can help make a diagnosis, predict a prognosis, or elucidate the pathogenesis of poorly understood diseases. The detection and/or quantitation of specific genes, messenger RNA's, and their protein products provide diagnostic and prognostic information for physicians. Illustrative applications of some of these techniques in human virus infection and breast cancer will suggest the future direction that an anatomic pathology laboratory should consider if it is to provide optimal and competitive service to physicians.

The utility of some modern techniques in understanding thyroid pathology

A number of evaluating techniques have moved from the research laboratory into the purview of the diagnostic pathologist and have been applied to the analysis of thyroid lesions. Some of these have already proved diagnostically and prognostically useful, whereas some have produced insights into pathogenesis of specific thyroid lesions and disorders. Rapid proliferation and application of these techniques should allow for increased understanding of human thyroid disease in the near future.

Pituitary cells producing more than one hormone human pituitary adenomas

The existence of cells capable of producing more than one hormone in nontumorous human adenohypophyses and pituitary adenomas has been conclusively proved. In light of the evidence, current concepts on pituitary structure, function, and regulation as well as adenoma cytogenesis and classification have to be reconsidered.