Molecular imaging of lymphoid organs and immune activation by positron emission tomography with a new [18F]-labeled 2′-deoxycytidine analog

Monitoring immune function with molecular imaging could have a considerable impact on the diagnosis and treatment evaluation of immunological disorders and therapeutic immune responses. Positron emission tomography (PET) is a molecular imaging modality with applications in cancer and other diseases. PET studies of immune function have been limited by a lack of specialized probes. We identified [(18)F]FAC (1-(2'-deoxy-2'-[(18)F]fluoroarabinofuranosyl) cytosine) by differential screening as a new PET probe for the deoxyribonucleotide salvage pathway. [(18)F]FAC enabled visualization of lymphoid organs and was sensitive to localized immune activation in a mouse model of antitumor immunity. [(18)F]FAC microPET also detected early changes in lymphoid mass in systemic autoimmunity and allowed evaluation of immunosuppressive therapy. These data support the use of [(18)F]FAC PET for immune monitoring and suggest a wide range of clinical applications in immune disorders and in certain types of cancer

AMPK modulates glucose-sensing in insulin-secreting cells by altered phosphotransfer to KATP channels

Glucose-sensing (GS) behaviour in pancreatic β-cells is dependent on ATP-sensitive K(+) channel (KATP) activity, which is controlled by the relative levels of the KATP ligands ATP and ADP, responsible for closing and opening KATP, respectively. However, the mechanism by which β-cells transfer energy status from mitochondria to KATP, and hence to altered electrical excitability and insulin secretion, is presently unclear. Recent work has demonstrated a critical role for AMP-activated protein kinase (AMPK) in GS behaviour of cells. Electrophysiological recordings, coupled with measurements of gene and protein expression were made from rat insulinoma cells to investigate whether AMPK activity regulates this energy transfer process. Using the whole-cell recording configuration with sufficient intracellular ATP to keep KATP closed, raised AMPK activity induced GS electrical behaviour. This effect was prevented by the AMPK inhibitor, compound C and required a phosphotransfer process. Indeed, high levels of intracellular phosphocreatine or the presence of the adenylate kinase (AK) inhibitor AP5A blocked this action of AMPK. Using conditions that maximised AMPK-induced KATP opening, there was a significant increase in AK1, AK2 and UCP2 mRNA expression. Thus we propose that KATP opening in response to lowered glucose concentration requires AMPK activity, perhaps in concert with increased AK and UCP2 to enable mitochondrial-derived ADP signals to be transferred to plasma membrane KATP by phosphotransfer cascades