Dissociation between respiratory burst activity and deoxyglucose uptake in human neutrophil granulocytes: implications for interpretation of (18)F-FDG PET images

Abstract

Neutrophil granulocytes play a key role in the pathogenesis of a wide variety of pulmonary diseases. In many such conditions, the injury observed reflects the activation status rather than the total number of inflammatory cells present. The metabolic activity of neutrophils can now be assessed noninvasively using PET to measure the regional uptake of (18)F-FDG after intravenous injection.

Methods: To understand the mechanism responsible for the increased (18)F-FDG signal, we have measured the uptake of tritiated deoxyglucose (DG) in neutrophils isolated from human peripheral blood and sought to determine which aspects of neutrophil function correlate with an increase in DG uptake.

Results: Our results show that formyl-methionyl-leucyl-phenylalanine (fMLP)-stimulated respiratory burst activity and (3)H-DG uptake are temporally dissociated, that neutrophil-priming agents such as tumor necrosis factor-alpha (TNFalpha) cause an identical increase in (3)H-DG uptake compared with fMLP without affecting respiratory burst activity, and that fMLP stimulation of TNFalpha-primed cells causes major upregulation of superoxide anion generation (O(2)(-)) yet no incremental increase in (3)H-DG uptake. Furthermore, direct activation of reduced nicotinamide adenine dinucleotide phosphate oxidase activity with the ester phorbol 12-myristate 13-acetate resulted in a concentration-dependent loss of cell-associated (3)H-DG, and preincubation of neutrophils with the phosphoinositide 3-kinase inhibitor wortmannin, which abolished both agonist-stimulated superoxide anion generation and degranulation, had no effect on TNFalpha- or fMLP-stimulated (3)H-DG uptake. In contrast, the fMLP-stimulated change in neutrophil shape was not influenced by priming or wortmannin, and of the functional responses examined, this appeared to correlate most closely with (3)H-DG uptake.

Conclusion: DG uptake occurs in both primed and activated neutrophils. It does not correlate with respiratory burst or secretory activity but may reflect the polarization and migrational status of these cells. These data have important implications for the analysis of (18)F-FDG signals in vivo.