18F-fluoro-2-deoxyglucose PET informs neutrophil accumulation and activation in lipopolysaccharide-induced acute lung injury

Abstract

Introduction: Molecular imaging of the earliest events related to the development of acute lung injury (ALI)/acute respiratory distress syndrome (ARDS) could facilitate therapeutic development and patient management. We previously reported that ¹⁸F-fluoro-2-deoxyglucose (¹⁸F-FDG) PET identifies ALI/ARDS prior to radiographic abnormalities. The purpose of this study was to establish the time courses of ¹⁸F-FDG uptake, edema and neutrophil recruitment in an endotoxin-induced acute lung injury model and to examine molecular events required for ¹⁴C-2DG uptake in activated neutrophils.

Methods: Lung uptake of ¹⁸F-FDG was measured by PET in control male Sprague Dawley rats and at 2, 6 and 24h following the intraperitoneal injection of 10mg/kg LPS. Lung edema (attenuation) was measured by microCT. Neutrophil influx into the lungs was measured by myeloperoxidase assay. Control and activated human donor neutrophils were compared for uptake of ¹⁴C-2DG, transcription and content of hexokinase and GLUT isoforms and for hexokinase (HK) activity.

Results: Significant uptake of ¹⁸F-FDG occurred by 2h following LPS, and progressively increased to 24h. Lung uptake of ¹⁸F-FDG preceded increased CT attenuation (lung edema). Myeloperoxidase activity in the lungs, supporting neutrophil influx, paralleled ¹⁸F-FDG uptake. Activation of isolated human neutrophils resulted in increased uptake of ¹⁴C-2DG, expression of GLUT 3 and GLUT 4 and expression and increased HK1 activity.

Conclusion: Systemic endotoxin-induced ALI results in very early and progressive uptake of ¹⁸F-FDG, parallels neutrophil accumulation and occurs earlier than lung injury edema. Activated neutrophils show increased uptake of ¹⁴C-2DG, expression of specific GLUT3, GLUT4 and HK1 protein and HK activity. ADVANCES IN KNOWLEDGE AND IMPLICATIONS FOR PATIENT CARE: ¹⁸F-FDG pulmonary uptake is an early biomarker of neutrophil recruitment in ALI and is associated with specific molecular events that mediate ¹⁴C-2DG uptake in activated neutrophils. ¹⁸F-FDG PET may provide a potential mechanism for early diagnosis and therapeutic assessment of ALI/ARDS.

Keywords: 18F-fluordeoxyglucose; ARDS; Acute lung injury; FDG; Lipopolysaccharide; Neutrophils.