Synthesis and evaluation of Gd-DTPA-labeled arabinogalactans as potential MRI contrast agents.

Arabinogalactan derivatives conjugated with gadolinium-diethylenetriaminepentaacetic acid (Gd-DTPA) by ethylenediamine (Gd-DTPA-CMAG-A2) or hexylamine (Gd-DTPA-CMAG-A6) have been synthesized and characterized by means of Fourier transform infrared spectra (FTIR), 13C nuclear magnetic resonance (13C NMR), size exclusion chromatography (SEC), and inductively coupled plasma atomic emission spectrometry (ICP-AES). Relaxivity studies showed that arabinogalactan-bound complexes possessed higher relaxation effectiveness compared with the clinically used Gd-DTPA, and the influence of the spacer arm lengths on the T1 relaxivities was studied. Their stability was investigated by competition study with Ca2+, EDTA, and DTPA. MR imaging of Wistar rats showed remarkable enhancement in rat liver and kidney after i.v. injection of Gd-DTPA-CMAG-A2 (0.079+/-0.002 mmol/kg Gd3+): The mean percentage enhancement of the liver parenchyma and kidney was 38.7+/-6.4% and 69.4+/-4.4% at 10-30 min. Our preliminary in vivo and in vitro study indicates that the arabinogalactan-bound complexes are potential liver-specific contrast agents for MRI.