PMA-enhanced neutrophil [ 18F]FDG uptake is independent of integrin occupancy but requires PI3K activity

Abstract

Objective While respiratory burst enhances neutrophil glucose utilization, many neutrophil functions are critically influenced by extracellular matrix interaction and phosphoinositide-3-OH kinase (PI3K) signaling. We thus evaluated the role of RGD integrin occupancy and PI3K inhibition on respiratory burst and [ 18F]fluorodeoxyglucose ([ 18F]FDG) uptake of stimulated neutrophils. Methods Human neutrophils were stimulated by 100 ng/ml phorbol–myristate–acetate (PMA), and respiratory burst was measured by cumulative luminescence with lucigenin. [ 18F]FDG uptake and total hexokinase activity was measured 20 min after PMA stimulation in the presence or absence of soluble RGD peptides (200 μg/ml) and/or the PI3K inhibitor wortmannin (200 nM). Results Phorbol–myristate–acetate induced a 71.7±0.9 fold increase in neutrophil oxygen intermediate generation. [ 18F]FDG uptake was increased to 194.6±3.7% and hexokinase activity to 145.0±2.0% of basal levels (both P<.0005). RGD peptides attenuated respiratory burst activation to 35.6±0.2% ( P<.005) but did not inhibit stimulated [ 18F]FDG uptake or hexokinase activity. In contrast, without affecting respiratory burst activation, wortmannin inhibited PMA-stimulated [ 18F]FDG uptake to 66.9±1.6% and hexokinase activity to 81.0±4.2% (both P<.0005), demonstrating its dependence on PI3K activity. Neither RGD nor wortmannin reversed the other's inhibitory effect on stimulated [ 18F]FDG uptake and hexokinase activity or respiratory burst, which suggests the involvement of distinct signaling pathways. Conclusion Neutrophil [ 18F]FDG uptake is enhanced by PMA through a mechanism that requires PI3K activity but is independent of integrin receptor occupancy or respiratory burst activation.