2-deoxy-2-[18F]fluoro-D-glucose Positron Emission Tomography to Monitor Lung Inflammation and Therapeutic Response to Dexamethasone in a Murine Model of Acute Lung Injury

Abstract

Purpose: To image inflammation and monitor therapeutic response to anti-inflammatory intervention using 2-deoxy-2-[¹⁸F]fluoro-D-glucose ([¹⁸F]FDG) positron emission tomography (PET) in a preclinical model of acute lung injury (ALI).

Procedures: Mice were intratracheally administered lipopolysaccharide (LPS, 2.5 mg/kg) to induce ALI or phosphate-buffered saline as the vehicle control. A subset of mice in the ALI group received two intraperitoneal doses of dexamethasone 1 and 24 h after LPS. [¹⁸F]FDG PET/CT was performed 2 days after the induction of ALI. [¹⁸F]FDG uptake in the lungs was quantified by PET (%ID/mL_mean and standardized uptake value (SUV_mean)) and ex vivo γ-counting (%ID/g). The severity of lung inflammation was determined by quantifying the protein level of inflammatory cytokines/chemokines and the activity of neutrophil elastase and glycolytic enzymes. In separate groups of mice, flow cytometry was performed to estimate the contribution of individual immune cell types to the total pulmonary inflammatory cell burden under different treatment conditions.

Results: Lung uptake of [¹⁸F]FDG was significantly increased during LPS-induced ALI, and a decreased [¹⁸F]FDG uptake was observed following dexamethasone treatment to an intermediate level between that of LPS-treated and control mice. Protein expression of inflammatory biomarkers and the activity of neutrophil elastase and glycolytic enzymes were increased in the lungs of LPS-treated mice versus those of control mice, and correlated with [¹⁸F]FDG uptake. Furthermore, dexamethasone-induced decreases in cytokine/chemokine protein levels and enzyme activities correlated with [¹⁸F]FDG uptake. Neutrophils were the most abundant cells in LPS-induced ALI, and the pattern of total cell burden during ALI with or without dexamethasone therapy mirrored that of [¹⁸F]FDG uptake.

Conclusions: [¹⁸F]FDG PET noninvasively detects lung inflammation in ALI and its response to anti-inflammatory therapy in a preclinical model. However, high [¹⁸F]FDG uptake by bone, brown fat, and myocardium remains a technical limitation for quantification of [¹⁸F]FDG in the lungs.

Keywords: Acute lung injury; Inflammation; Positron emission tomography; [18F]FDG.