Biomedical subjects

Antonella Maffei

Publications and source records attributed to Antonella Maffei.

7 recordsLinked to original sources

PubMed2006

Longitudinal noninvasive PET-based beta cell mass estimates in a spontaneous diabetes rat model.

Diabetes results from an absolute or relative reduction in pancreatic beta cell mass (BCM) leading to insufficient insulin secretion and hyperglycemia. Measurement of insulin secretory capacity is currently used as a surrogate measure of BCM. However, serum insulin concentrations provide an imprecise index of BCM, and no reliable noninvasive measure of BCM is currently available. Type 2 vesicular monoamine transporters (VMAT2) are expressed in human islet beta cells, as well as in tissues of the CNS. [11C]Dihydrotetrabenazine ([11C]DTBZ) binds specifically to VMAT2 and is a radioligand currently used in clinical imaging of the brain. Here we report the use of [11C]DTBZ to estimate BCM in a rodent model of spontaneous type 1 diabetes (the BB-DP rat). In longitudinal PET studies of the BB-DP rat, we found a significant decline in pancreatic uptake of [11C]DTBZ that anticipated the loss of glycemic control. Based on comparison of standardized uptake values (SUVs) of [11C]DTBZ and blood glucose concentrations, loss of more than 65% of the original SUV correlated significantly with the development of persistent hyperglycemia. These studies suggest that PET-based quantitation of VMAT2 receptors provides a noninvasive measurement of BCM that could be used to study the pathogenesis of diabetes and to monitor therapeutic interventions.

Animals↗

PubMed2006

Effect of interferon alpha on MHC class II gene expression in ex vivo human islet tissue.

Type 1 diabetes (T1D) is caused by autoimmune destruction of the insulin-producing beta-cells of the islets of Langerhans. One still open question is where naive islet-reactive T cells encounter antigens and become stimulated. In this report we have re-examined the expression of MHC class II (MHCII) genes in human islets to further explore the possibility that non-professional antigen presenting cells (APCs) within islets contribute to autoimmunity. Since development of T1D has been linked to viral infections, we also studied ex-vivo MHCII expression in response to interferon-alpha (IFNalpha) in islet tissue and in different APCs. The findings are: first, MHCII genes expression in human islets is linked with the expression of the class II transactivator isoform transcribed from the promoter IV, similar to that described in non-professional APCs. Second, there is IFNalpha-mediated lineage-specific regulation of MHCII genes expression, seen as a decrease in the accumulation of MHCII transcripts in pancreatic islets opposite to an increase in dendritic cells and B-lymphoblastoid cell lines. Third, there is allele-specific regulation of the HLA-DQA1 gene by IFNalpha in islet tissue. These findings may begin to explain the molecular events that create favorable conditions for organ-specific autoimmunity and explain the incomplete penetrance of T1D susceptibility alleles.

Alleles↗

PubMed2006

Visualizing pancreatic beta-cell mass with [11C]DTBZ.

Beta-cell mass (BCM) influences the total amount of insulin secreted, varies by individual and by the degree of insulin resistance, and is affected by physiologic and pathologic conditions. The islets of Langerhans, however, appear to have a reserve capacity of insulin secretion and, overall, assessments of insulin and blood glucose levels remain poor measures of BCM, beta-cell function and progression of diabetes. Thus, novel noninvasive determinations of BCM are needed to provide a quantitative endpoint for novel therapies of diabetes, islet regeneration and transplantation. Built on previous gene expression studies, we tested the hypothesis that the targeting of vesicular monoamine transporter 2 (VMAT2), which is expressed by beta cells, with [11C]dihydrotetrabenazine ([11C]DTBZ), a radioligand specific for VMAT2, and the use of positron emission tomography (PET) can provide a measure of BCM. In this report, we demonstrate decreased radioligand uptake within the pancreas of Lewis rats with streptozotocin-induced diabetes relative to their euglycemic historical controls. These studies suggest that quantitation of VMAT2 expression in beta cells with the use of [11C]DTBZ and PET represents a method for noninvasive longitudinal estimates of changes in BCM that may be useful in the study and treatment of diabetes.

Animals↗

PubMed2006

Current progress in non-invasive imaging of beta cell mass of the endocrine pancreas.

The increasing incidence of diabetes requires a better understanding of the pathogenesis of the clinical disease. Studies in prevention and treatment have been hampered by the single end-point of diagnosis of diabetes and hyperglycemia. The common pathology in both type 1 and type 2 diabetes is insufficient beta-cell mass to meet the metabolic demand. Unfortunately, current diagnostic methods rely on metabolic responses that do not accurately reflect true beta-cell mass. Recent advances in beta-cell imaging have utilized multiple modalities in experimental and clinical settings. While no "gold-standard" exists to measure beta-cell mass, modalities such as single photon emission computed tomography, optical and fluorescent imaging, magnetic resonance imaging, and positron emission tomography have been used with mixed success. Many of the methods are limited by the inability to translate to the clinical setting, poor discrimination between the exocrine and endocrine pancreas, or a poor measurement of beta-cell mass. However, promising new "neurofunctional imaging" approaches have emerged as improved measures of beta-cell mass. We review the current understanding of the pathogenesis and evaluation of diabetes, as well as experimental approaches to assessing beta-cell mass.

Animals↗

PubMed2004

Identification of tissue-restricted transcripts in human islets.

The purpose of our study was to identify transcripts specific for tissue-restricted, membrane-associated proteins in human islets that, in turn, might serve as markers of healthy or diseased islet cell masses. Using oligonucleotide chips, we obtained gene expression profiles of human islets for comparison with the profiles of exocrine pancreas, liver, and kidney tissue. As periislet presence of type 1 interferon is associated with the development of type 1 diabetes, the expression profile of human islets treated ex vivo with interferon-alpha2beta (IFNalpha2beta) was also determined. A set of genes encoding transmembrane- or membrane-associated proteins with novel islet-restricted expression was resolved by determining the intersection of the islet set with the complement of datasets obtained from other tissues. Under the influence of IFNalpha2beta, the expression levels of transcripts for several of the identified gene products were up- or down-regulated. One of the islet-restricted gene products identified in this study, vesicular monoamine transporter type 2, was shown to bind [3H]dihydrotetrabenazine, a ligand with derivatives suitable for positron emission tomography imaging. We report here the first comparison of gene expression profiles of human islets with other tissues and the identification of a target molecule with possible use in determining islet cell masses.

Culture Techniques↗

PubMed2003

Shifting gene expression profiles during ex vivo culture of renal tumor cells: implications for cancer immunotherapy.

The use of cultured tumor cells rather than original tumor tissue for the preparation of therapeutic cancer vaccines represents an obvious solution to the problem of availability of adequate quantities of autologous tumor. In this study we investigated possible changes in gene expression accompanying the transition of renal cell carcinoma cells from the original tissue to cell populations in culture. In our study we employed cDNA microarray technology to compare the gene expression pattern of ex vivo cultured renal carcinoma cells to that of the original solid tumor tissue from which the cells were derived. Using this approach we detected changes in the expression of many genes mostly related to the cell lines' physiological properties. Some of the products of those genes showing differential expression between tumor-derived cell line and original tumor are known human autoantigens or tumor-associated antigens. Furthermore, analysis of overexpressed genes revealed the presence of several transcripts with restricted normal tissue distribution, representing self-antigens with potential to elicit autoimmunity. Our results suggest that adapting tumor tissue to culture can result in changes in the level of transcripts specific for known antigens and that more information regarding the composition of tumor cells and their byproducts used in vaccine trials is needed before the efficacy and safety of such procedures can truly be determined.

Adaptation, Physiological↗

PubMed2003

Gene expression profiling and functional activity of human dendritic cells induced with IFN-alpha-2b: implications for cancer immunotherapy.

PURPOSE: In this study, we have compared patterns of gene expression and functional activity of human dendritic cells (DCs) cultured under defined conditions in IFN-alpha-2b and recombinant human granulocyte macrophage colony-stimulating factor (DCA) with cells grown in granulocyte macrophage colony-stimulating factor and IL-4 (DC4) as an initial step in evaluating the clinical utility of DCA in cancer immunotherapy. EXPERIMENTAL DESIGN AND RESULTS: Comparison of mRNA transcript profiles between DCA and DC4 revealed different expression patterns for cytokines, chemokines, chemokine receptors, costimulatory molecules, and adhesion proteins. Many genes involved in antigen (Ag) processing were equally expressed in both populations; however, expression of transcripts involved in Ag presentation was increased in DCA. DCA also showed up-regulation of Toll-like receptor 2 and 3, as well as several tumor necrosis factor family ligands. Consistent with expression profiling, functional assays demonstrated that DCAs were more potent stimulators of naive T-cell responses than DC4 in an interleukin 15 and interleukin 1beta-dependent manner. DCA-mediated tumor cell-directed cytotoxicity induced apoptosis in different human tumor cell lines and internalized apoptotic bodies to a greater extent than DC4. Lastly, in vitro priming experiments, using apoptotic cells or peptide as sources of Ag, showed that DCA drove the expansion of tumor peptide Ag-specific autologous CD8+ T cells to a greater extent than DC4. CONCLUSIONS: The unique phenotype conferred by culturing DCs in IFN-alpha-2b may be useful in adoptive transfer regimens where the destruction of tumor cells in situ, initiation of T-cell responses toward tumor tissue with unknown Ags, and/or enhancement of pre-existing Ag-specific memory responses are desired outcomes.

Apoptosis↗