IMMUNOGENICITY OF GADOLINIUM-BASED CONTRAST AGENTS FOR MAGNETIC-RESONANCE-IMAGING - INDUCTION AND CHARACTERIZATION OF ANTIBODIES IN ANIMALS

To evaluate the immunogenic potential of gadolinium-based magnetic resonance imaging (MRI) contrast agents, Sprague-Dawley rats were sensitized with gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA) dimeglumine and with Gd-DTPA covalently linked to either human serum albumin, dextran, or polylysine. IgG antibodies directed against Gd-DTPA were detected in immune sera by an enzyme-linked immunosorbent assay (ELISA), and were confirmed by competitive inhibition of antibody binding using free Gd-DTPA dimeglumine. Antiserum induced by immunization with human serum albumin-(Gd-DTPA) was characterized by a monophasic competition curve with 50% inhibition (IC50) = 5.5 x 10(-4) M when Gd-DTPA dimeglumine was used as both the well-coating and the displacing agent in a competition ELISA. Antiserum induced by Gd-DTPA dimeglumine alone was characterized by a biphasic competition curve with IC50 = 6.5 x 10(-7) M and 7.9 x 10(-4) M. Antisera obtained after exposure to either dextran-(Gd-DTPA) or polylysine-(Gd-DTPA) were of insufficient titer for characterization. The detection of antibodies specific for Gd-DTPA suggests in vivo protein binding with formation of hapten-carrier conjugates. This hypothesis is supported by increased relativity values observed when Gd-DTPA dimeglumine is incubated in serum rather than in water. Gd-DTPA dimeglumine and albumin-(Gd-DTPA) are immunogenic in rats under idealized experimental conditions. Additional studies will be necessary to determine the Potential for immunologic response in humans to gadolinium chelates under conditions of exposure inherent in clinical use.