Optical imaging agents and potential application in the assessment of pancreatic beta cells

Diseases of the pancreas are life-threatening because of its central role in glucose homeostasis and digestion. Regulation of blood glucose falls within the purview of pancreatic beta cells, whose primary role is to produce insulin. Malfunctioning of beta cells can lead to diabetes, the severity of which has been shown to correlate with pancreatic beta cell mass (PBCM). Consequently, methods that can image PBCM would play a major role in the management of type 1 diabetes. To be successful, such imaging methods must be highly sensitive and specific because of the anatomical challenges and the small size of the pancreas. The desired sensitivity and specificity can be obtained in conjunction with molecular contrast effectors to decipher pathologic from normal tissues. Because of its high sensitivity, nuclear methods have been the dominant molecular imaging method for human applications. For this reason, a variety of radiopharmaceuticals has been developed. To minimize the exposure of patients to radioactivity, optical imaging is a complementary and viable alternative to nuclear methods. Optical methods are highly sensitive and use non-ionizing radiation to interrogate the molecular basis of pathogenesis. This review will focus on the development of molecular beacons and their potential application in the imaging of pancreatic beta cells. It is most likely that contrast-mediated optical imaging of pancreatic islet cells will combine molecular specificity with high sensitivity to furnish useful diagnostic and prognostic information by endoscopic methods. Alternatively, minimally invasive continuous organ function monitoring methods could be developed to assess indirectly the functional status of pancreatic beta cells by optical spectroscopy.