Skip to main content

Gd-based protein cage nanoparticles provide enhanced r1 relaxivity and detect experimental atherosclerosis


Develop a highly sensitive T1 contrast agent based on chemically attaching a multitude of chelated Gd molecules constrained within a protein cage structure.


A T1 nanoparticle contrast agent showing high r1 relaxivity is desired to provide more sensitive molecular/cellular imaging with reduced Gd dose, and may have more clinical utility than T2* (e.g., iron-based) approaches. Tethering multiple Gd-chelates to a supramolecular platform is a promising strategy to increase r1 relaxivity, as rotational correlation time of the Gd ions can become significantly larger which is highly favorable for efficient r1 relaxivity. Here we utilize a small heat shock protein cage (Hsp) with a 12nm exterior diameter and a 9nm interior cavity, as a platform to anchor Gd-DTPA.


1) Material development and evaluation

Hsp was purified from an E. coli expression system. An azide-alkyne based click reaction is cycled to produce a branched polymer network in the interior of the protein cage (Fig 1). The polymer results in a stable network containing Gd-DTPA, as the azide-containing monomer has the Gd chelate attached prior to polymer generation.

Figure 1

Illustration of Hsp-brach polymer with Gd.

2) In vivo imaging of vascular inflammation

FVB mice underwent left carotid ligation after 4 weeks of high-fat diet and diabetes induction by streptozotocin. Two weeks later, Hsp-Gd or Magnevist (Gd-DTPA) was intravenously injected at a dose of 20µmol Gd/kg (one-fifth the typical clinical dose). Mice were imaged on a whole-body 3T MRI scanner (Signa HDx, GE Healthcare) with a 50mT/m, 150T/m/s gradient system and a phased array mouse coil (RAPID MR International), using a T1-weighted fast spin echo sequence (TR/TE=400ms/15ms, slice thickness=1mm, FOV=3cm, matrix=256x256) before injection and 4h after injection.


In vitro analysis of Hsp-Gd showed about 160 Gd-DTPA molecules per cage. At 0.73T, the ionic (per Gd) r1 value is 25mM-1sec-1 and the particle r1 value is 4,200mM-1sec-1 (Fig 2). At 3T, the ionic and particle r1 values are 9.7 mM-1sec-1 and 1600 mM-1sec-1, respectively. The ionic r1 value is nearly 3 times higher than that of Magnevist. The macrophage-rich left carotid lesion, but not the non-ligated right carotid, was clearly detected on T1-weighted MR imaging 4h after injection of Hsp-Gd, whereas the same lesion was hardly detected after Magnevist injection (Fig. 3).

Figure 2

Graph of r1 measurement at varying field.

Figure 3

T1-weighted FSE MRI of ligated left carotids in mice before and after injection of Hsp-Gd (top) or Magnevist (bottom). The macrophage-rich left carotid lesion was clearly enhanced by Hsp-Gd, but not in the non-ligated right carotid artery or either carotid artery after Magnevist injection.


Gd can be effectively incorporated into polymer-incorporated protein cage nanoparticles providing high r1 relaxivity. Hsp-Gd allows positive contrast imaging of macrophage-rich carotid atherosclerosis with low Gd dosing. Thus, Gd-based protein cages are promising atherosclerosis imaging agents.

Author information



Corresponding author

Correspondence to Masaki Uchida.

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Liepold, L.O., Uchida, M., Abedin, M.J. et al. Gd-based protein cage nanoparticles provide enhanced r1 relaxivity and detect experimental atherosclerosis. J Cardiovasc Magn Reson 13, P370 (2011).

Download citation


  • Small Heat Shock Protein
  • Protein Cage
  • Exterior Diameter
  • Nanoparticle Contrast
  • Nanoparticle Contrast Agent