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 [(18)F]fluorodeoxyglucose ([(18)F]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. [(18)F]FDG uptake and total hexokinase activity was measured 20 min after PMA stimulation in the presence or absence of soluble RGD peptides (200 microg/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. [(18)F]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 [(18)F]FDG uptake or hexokinase activity. In contrast, without affecting respiratory burst activation, wortmannin inhibited PMA-stimulated [(18)F]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 [(18)F]FDG uptake and hexokinase activity or respiratory burst, which suggests the involvement of distinct signaling pathways. CONCLUSION: Neutrophil [(18)F]FDG uptake is enhanced by PMA through a mechanism that requires PI3K activity but is independent of integrin receptor occupancy or respiratory burst activation.
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 [(18)F]fluorodeoxyglucose ([(18)F]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. [(18)F]FDG uptake and total hexokinase activity was measured 20 min after PMA stimulation in the presence or absence of soluble RGD peptides (200 microg/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. [(18)F]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 [(18)F]FDG uptake or hexokinase activity. In contrast, without affecting respiratory burst activation, wortmannin inhibited PMA-stimulated [(18)F]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 [(18)F]FDG uptake and hexokinase activity or respiratory burst, which suggests the involvement of distinct signaling pathways. CONCLUSION: Neutrophil [(18)F]FDG uptake is enhanced by PMA through a mechanism that requires PI3K activity but is independent of integrin receptor occupancy or respiratory burst activation.