Non-invasive imaging of the endocrine pancreas (Review)

The non-invasive imaging of the endocrine pancreas is currently considered by concerned institutions as a priority theme of research. Because the endocrine pancreas represents only about one percent of the pancreatic gland, highly specific tools are required for labelling the insulin-producing cells. The present review deals with the possible use of D-mannoheptulose for the non-invasive quantification of insulin-producing cells in the pancreas. This heptose is transported into hepatocytes and insulin-producing cells, but not other cell types, at the intervention of GLUT2. Its uptake coincides with the intracellular accumulation of acidic metabolites generated by phosphorylation of D-mannoheptulose. These metabolites remain in the islet cells after prolonged washing, suggesting that imaging of the pancreas at a relatively late time after intravenous administration of D-mannoheptulose could avoid significant extracellular contamination. Using tritiated D-mannoheptulose as tracer, a new method was designed for quantification of the total mass of insulin-producing cells in either isolated perfused rat pancreata or isolated pancreatic islets. Likewise, a preferential labelling of hepatocytes and insulin-producing transplanted cells can be achieved in vivo after administration of tritiated D-mannoheptulose. In the light of results obtained with 6-deoxy-6-iodo-D-glucose, it is proposed that 7-deoxy-7-iodo-D-mannoheptulose could be used for the non-invasive imaging of the endocrine pancreas.