Stereospecific binding of MRI contrast agents to human serum albumin: The ease of Gd-(S)-EOB DTPA (Eovist) and its (R) isomer

The water proton relaxation rate enhancement of the hepatospecific Gd-(S)-E OB-DTPA (Eovist) and of its (R) isomer in aqueous solutions free of protein , in serum and in 4% human serum albumin solution, are compared. In the abs ence of proteins, both compounds exhibit, as expected, the same proton rela xivity, as measured by the nuclear magnetic relaxation dispersion (NMRD) pr ofiles. In serum and albumin solution, non-covalent binding of the paramagn etic complexes to macromolecules is observed. Both isomers are likely to bi nd to the same site of human serum albumin, but the affinity of the (S) iso mer is larger than for the (R) isomer.