PET imaging of acute and chronic inflammation in living mice.
OBJECTIVE
In this study, we evaluated the 12-O-tetradecanoyl-phorbol-13-acetate (TPA)-induced acute and chronic inflammation in living mice by PET imaging of TNF-alpha and integrin alpha(v)beta(3) expression.


METHODS
TPA was topically applied to the right ear of BALB/c mice every other day to create the inflammation model. (64)Cu-DOTA-etanercept and (64)Cu-DOTA-E{E[c(RGDyK)](2)}(2) were used for PET imaging of TNF-alpha and integrin alpha(v)beta(3) expression in both acute and chronic inflammation. Hematoxylin and eosin staining, ex vivo autoradiography, direct tissue sampling, and immunofluorescence staining were also performed to confirm the non-invasive PET imaging results.


RESULTS
The ear thickness increased significantly and the TNF-alpha level more than tripled after a single TPA challenge. MicroPET imaging using (64)Cu-DOTA-etanercept revealed high activity accumulation in the inflamed ear, reaching 11.1 +/- 1.3, 13.0 +/- 2.0, 10.9 +/- 1.4, 10.2 +/- 2.2%ID/g at 1, 4, 16, and 24 h post injection, respectively (n = 3). Repeated TPA challenges caused TPA-specific chronic inflammation and reduced (64)Cu-DOTA-etanercept uptake due to lowered TNF-alpha expression. (64)Cu-DOTA-E{E[c(RGDyK)](2)}(2) uptake in the chronically inflamed ears (after four and eight TPA challenges) was significantly higher than in the control ears and those after one TPA challenge. Immunofluorescence staining revealed increased integrin beta(3) expression, consistent with the non-invasive PET imaging results using (64)Cu-DOTA-E{E[c(RGDyK)](2)}(2) as an integrin alpha(v)beta(3)-specific radiotracer. Biodistribution and autoradiography studies further confirmed the quantification capability of microPET imaging.


CONCLUSIONS
Successful PET imaging of TNF-alpha expression in acute inflammation and integrin alpha(v)beta(3) expression in chronic inflammation provides the rationale for multiple target evaluation over time to fully understand the inflammation processes.
Cao
Qizhen
Q
The Molecular Imaging Program at Stanford, Department of Radiology and Bio-X Program, Stanford University School of Medicine, Stanford, CA 94305-5484, USA.
Cai
Weibo
W
Li
Zi-Bo
ZB
Chen
Kai
K
He
Lina
L
Li
Hui-Cheng
HC
Hui
Mizhou
M
Chen
Xiaoyuan
X
D000818:Animals; D003301:Copper Radioisotopes / Q000493:pharmacokinetics; D000068800:Etanercept; D007074:Immunoglobulin G / Q000378:metabolism*; D007249:Inflammation / Q000000981:diagnostic imaging* / Q000378:metabolism*; D039302:Integrin alphaVbeta3 / Q000378:metabolism*; D008657:Metabolic Clearance Rate; D051379:Mice; D008807:Mice, Inbred BALB C; D009928:Organ Specificity; D049268:Positron-Emission Tomography / Q000379:methods*; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics; D018124:Receptors, Tumor Necrosis Factor / Q000378:metabolism*; D014018:Tissue Distribution; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism*
D003301:Copper Radioisotopes; D007074:Immunoglobulin G; D039302:Integrin alphaVbeta3; D019275:Radiopharmaceuticals; D018124:Receptors, Tumor Necrosis Factor; D014409:Tumor Necrosis Factor-alpha; D000068800:Etanercept