Evaluation of diethylenetriaminepentaacetic acid–manganese(II) complexes modified by narrow molecular weight distribution of chitosan oligosaccharides as potential magnetic resonance imaging contrast agents

Novel conjugates of narrow molecular weight distribution of chitosan oligosaccharides (CSn; n=6, 8, 11) with manganese–diethylenetriaminepentaacetic acid (Mn–DTPA) as potential magnetic resonance imaging (MRI) contrast agents were synthesized. The structures were characterized by means of Fourier transform infrared spectra, 13C nuclear magnetic resonance, size exclusion chromatography and inductively coupled plasma atomic emission spectrometry. The characterization results showed that Mn–DTPA was successfully linked to aminated CSn by an amide function. The magnetic properties were characterized by in vitro and T1-weighted FLASH image experiments. Relaxivities studies indicated that Mn–DTPA–CSn (n=8, 11) provided higher relaxivity, either in aqueous or bovine serum albumin solution (0.725 mM), than commercial contrast agent Gd–DTPA. The stability results showed that Mn–DTPA–CSn in aqueous were stable enough to prevent MnII ions from releasing. The preliminary in vitro and T1-weighted FLASH image studies suggested that Mn–DTPA–CSn had the advantage of becoming promising MRI contrast agents.