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Unlabelled: The contribution of (18)F-FDG uptake by endothelial cells to uptake values measured by PET in various tissues is as yet unclear. We therefore sought to characterize (18)F-FDG uptake in an in vitro model of human endothelial cells., Methods: Commercially obtained human umbilical vein endothelial cells (HUVECs) were seeded in 6-multiwell plates 48-96 h before incubation with 1-2 MBq (18)F-FDG per well. Radioactivity measurements were performed after washing and mechanical dissolvation of the cellular monolayers. Cellular (18)F-FDG uptake was referred to protein concentration. This experimental protocol was subsequently varied to study the effect of different parameters of interest. Furthermore, radio-thin-layer chromatography was used to identify intracellular (18)F-FDG metabolites. (18)F-FDG uptake in HUVECs was compared with that by a human monocyte-macrophage (HMM) preparation and by glioblastoma cells (GLIOs) under identical experimental conditions., Results: (18)F-FDG accumulated in HUVECs in a time-dependent manner and was trapped mainly as (18)F-FDG-6-phosphate and (18)F-FDG-1,6-diphosphate. Unlabeled glucose and cytochalasin B competitively inhibited (18)F-FDG uptake, whereas phlorizin had no significant effect. Glucose deprivation significantly enhanced (18)F-FDG uptake by a factor of 2.7, whereas sodium depletion had no significant influence. HUVECs treated with vascular endothelial growth factor (VEGF) showed a significant 82% increase in (18)F-FDG accumulation after a 2-h exposure to 50 ng/mL VEGF. (18)F-FDG uptake in HUVECs was significantly higher than that in HMMs and in the range of the uptake values measured in GLIOs., Conclusion: (18)F-FDG accumulates in HUVECs by mechanisms analogous to those in neoplastic cells or neurons. VEGF significantly stimulates endothelial (18)F-FDG uptake. The observed differences in (18)F-FDG uptake between HUVECs, HMMs, and GLIOs are difficult to extrapolate to in vivo conditions but stimulate further studies on the contribution of endothelial (18)F-FDG uptake to the overall uptake of that tracer in neoplastic or vascular lesions.

Unlabelled: Activated monocytes with a high (18)F-FDG accumulation can affect the results of clinical PET studies. To better understand the mechanisms regulating monocytic (18)F-FDG uptake, we investigated the effect of priming and respiratory-burst generation and further evaluated the role of potential protein kinase pathways., Methods: Purified human monocytes were primed with interferon-gamma (IFN-gamma), and respiratory burst was generated by stimulation of primed cells with phorbol-12-myristate-13-acetate (PMA). Oxygen-intermediate generation was assessed by luminescence measurements after the addition of lucigenin. (18)F-FDG uptake after 30 min of incubation was measured for unprimed control cells, primed cells, and PMA-stimulated cells. The role of protein kinases was investigated using respective inhibitors., Results: PMA stimulation of primed monocytes dramatically increased oxygen-intermediate generation, leading to a 42.2 +/- 1.1 fold higher level of cumulative luminescence compared with unprimed control cells, whereas IFN-gamma priming alone resulted in low luminescence levels (13.9% +/- 4.6% of PMA-stimulated cells). In contrast, priming alone was sufficient to augment monocytic (18)F-FDG uptake to 273.3% +/- 16.7% of control levels (P < 0.001), and it was not further increased by PMA stimulation. The tyrosine kinase inhibitor, genistein, and the specific protein kinase C inhibitor, staurosporine, completely abolished the priming-induced enhancement of (18)F-FDG uptake and lowered uptake to control levels. Under the same conditions, wortmannin, a phosphatidylinositol 3 kinase (PI3 kinase)-specific inhibitor, and cycloheximide, a protein synthesis inhibitor, were associated with only minor reductions in the enhanced-uptake effect of priming., Conclusion: IFN-gamma priming alone, without stimulation of respiratory-burst activity, is sufficient to induce maximal augmentation of (18)F-FDG uptake in monocytes. Furthermore, this metabolic effect appears to involve tyrosine kinases and the protein kinase C pathway but is independent of the PI3 kinase pathway.