Abstract
The peptide (CKGGRAKDC-NH2) specifically targets the brown adipose tissue (BAT). Here we applied this peptide coupled with polyethylene glycol (PEG)-coated ultrasmall superparamagnetic iron oxide (USPIO) nanoparticles to detect BAT in vivo by magnetic resonance imaging (MRI). The peptide was conjugated with PEG-coated USPIO nanoparticles to obtain targeted USPIO nanoprobes. Then the nanoprobes for BAT were evaluated in mice. T2⁎-weighted images were performed, precontrast and postcontrast USPIO nanoparticles. Finally, histological analyses proved the specific targeting. The specificity of targeted USPIO nanoprobes was observed in mice. The T2⁎ relaxation time of BAT in the targeted group decreased obviously compared to the controls (P<0.001). Prussian blue staining and transmission electron microscope confirmed the specific presence of iron oxide. This study demonstrated that peptide (CKGGRAKDC-NH2) coupled with PEG-coated USPIO nanoparticles could identify BAT noninvasively in vivo with MRI.
Highlights
TEM images showed that the ultrasmall superparamagnetic iron oxide (USPIO) were well dispersed (Figure 1(a)) and the mean core size was 7.56±0.92 nm (Figure 1(b))
The hydrodynamic diameters of untargeted USPIO nanoparticles and targeted USPIO nanoprobes were 17.50±5.90 nm and 20.55±5.70nm, respectively, which were within the range of ultrasmall particles of iron oxide (10-40nm) [16]
Transmission electron microscopy demonstrated that iron particles were located in brown adipose tissue (BAT) while no obvious particles were found in the controls, which were consistent with the results of Prussian blue staining and magnetic resonance imaging (MRI) results (Figure 4)
Summary
[18F]DG PET-CT imaging only shows activated BAT and is not sensitive to BAT in the nonactivated thermoneutral state. The PET-CT imaging depends on high glucose utilization which is associated with metabolic activity. Another limitation of PET imaging is owing to the use of ionizing radiation [7]. Various nanoparticulate contrast agents for MR molecular imaging have been developed, like ultrasmall superparamagnetic iron oxide (USPIO), lutetium oxide nanoparticles, BioMed Research International and so on [9,10,11]. We innovatively conjugated the targeted peptide (CKGGRAKDC-NH2) with polyethylene glycol (PEG)coated USPIO nanoparticles to synthesize BAT-targeted USPIO nanoprobe and investigated its potential application in detecting BAT with MRI in vivo
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