Accumulation of manganese in the brain of mice after intravenous injection of manganese-based contrast agents.
Because the manganese-based contrast agents used in magnetic, resonance imaging are unstable in vivo, some concern exists about the potential toxicity coming from the Mn2+ released by the complexes. This potential problem arises because the manganese is known to accumulate in the brain of people intoxicated by this metal (manganism): this central accumulation leads to neurological disorders (i.e., parkinsonism-like syndrome). The aim of this study was to assess the amount of Mn found in the brain after administration of MnCl2 or different chelates of Mn in normal mice as well as in mice with impaired biliary elimination. Male NMRI mice received an intravenous injection in a caudal vein of 5 mumol/kg of 54Mn compounds as MnCl2, manganese-diethylenetriaminepentaacetate (Mn-DTPA), or manganese-dipyridoxal diphosphate (Mn-DPDP). The radiolabeled complexes (1:1) were prepared by direct chelation (Mn-DTPA) or transchelation of preformed complex (Mn-DPDP), and the radiochemical purity was assessed by paper chromatography. The mice were killed at various times post-exposure (0-3 months), and the radioactivity present in the organs was determined by gamma counting. For each compound analyzed in the present study, we observed an accumulation of Mn (0.25-0.3% of the amount injected/g of tissue) in the mouse brain, reaching a plateau after 24 h, while the Mn content in the liver was decreasing with time. The amount of Mn accumulated in the brain remained unchanged 1 month later, but decreased to 40% of the maximum amount 3 months after the exposure. In mice whose bile ducts had been ligated 24 h before the administration of the manganese compound, we observed, 1 week after the injection, an amount of manganese accumulated in the brain 2 times higher than in normal mice.