Receptor induced magnetization

Figure 7 Receptor-induced magnetization enhancement mechanism. The contrast agent consists of two parts the Gdm chelate and the protein-binding moiety. Within the bloodstream, the agent binds to the protein. The bound form is in equilibrium with the small amount of free form, which can be renally excreted steadily over time. The bound form has high relaxivity by virtue of its slow rotation (reproduced by permission of the American Chemical Society from Chem. Rev., 1999, 99, 2293).

This modified CR is targeted for blood. This modified CR designated as MS-325 exploits the relaxivity, r, the coefficient which relates the H20 T to the concentration of CR in vitro. The r of free MS-325 is 6.6 (mM) 1 S-1 but the value increases to SOSO (mM) 1 S 1 when the CR is bound to albumin. This means that the CR is reversibly activated on binding to human serum albumin and is very much more effective in reducing H20 T value. Hence the detection is made easy at much lower levels. This effect, known as proton relaxation enhancement (or the receptor-induced magnetization enhancement), is due to the reduced rate of rotation of CR molecule bound to a macromolecule, and in this case, the rotation rate may be reduced by two orders of magnitude. 

Receptor-induced magnetization enhancement (RIME) describes the binding of CAs to biomolecules, such as proteins or receptors. This leads to an increase in the concentration and retention time of CAs in a particular region. It also results in an increase in tr and has a tremendous effect on increasing the relaxivity [64]. 

It is generally believed that cellular imaging with either coated or uncoated nanoparticles of iron oxide is equivalent since the biology of the cell is assumed to be unperturbed by the introduction of the magnetic label inside the cell. However, the recent report of Berry et that uncoated and dextran-coated iron oxide nanoparticles induce different cell response is a cautionary one. Moreover, anionic nanoparticles show a significantly higher affinity for some cells than dextran-coated particles, while van den Bos et have investigated the efficacy of cationic hposomes. The transferrin receptor... 

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