Iron-based second-sphere contrast agents for magnetic resonance imaging: development of a model system and evaluation of iron (III) tris (tironate) complex in rats.

RATIONALE AND OBJECTIVES: Iron(III) complexes have been developed as magnetic resonance (MR) contrast agents based on the use of ligands capable of providing coordinative saturation at iron and allowing the second-sphere hydrogen bonding of water molecules. METHODS: Studies of solution-phase binding of a probe ion to a diamagnetic metal catecholate complex and molecular orbital calculations were performed. R1 values were determined. Toxicity studies of iron(III) tris(tironate) were conducted with rats. Excretion studies were performed by analysis of urine samples. MR measurements were made. RESULTS: Second-sphere coordination of a probe ion to a metal catecholate complex occurred in solution. Molecular orbital calculations suggested flexibility in design. Iron(III) tris (catecholate) complexes were shown to have high R1 values. Images of the kidneys and liver showed dose-dependent enhancement in T1-weighted images. The onset of toxicity was at approximately 0.30 mmol/kg. Urine analysis indicated essentially complete clearance (0.1-0.2 mmol/kg) within 24-48 hours. CONCLUSION: Interactions between water molecules and basic sites within a paramagnetic metal-ligand complex allow for application of suitable complexes as T1 agents.

Developmental toxicity evaluation of tiron (sodium 4,5-dihydroxybenzene-1,3-disulfonate) in mice.

Tiron (sodium 4,5-dihydroxybenzene-1,3-disulfonate), a chelating agent used in the treatment of experimental metal poisoning, was evaluated for developmental toxicity in pregnant Swiss mice. Tiron was administered intraperitoneally on gestational days 6 through 15 at doses of 0, 750, 1500, or 3000 mg/kg/day. Cesarean sections were performed on gestation day 18. All fetuses were examined for external, visceral, and skeletal malformations and variations. Treatment with Tiron resulted in maternal toxicity at 3000 mg/kg/day as evidenced by a high number of deaths, reduced body weight during gestation and increased relative liver and kidney weights. There were no significant differences between treated and control animals on the number of total implants, dead fetuses, or sex ratio. However, embryo fetotoxicity was evidenced at 3000 mg/kg/day by a significant increase in the number of resorptions per litter, and a significant decrease in the average fetal body weight. There were no significant changes in the incidence of abnormalities (expressed as total, individual, external, visceral, or skeletal). The no observable adverse effect level (NOAEL) for maternal and developmental toxicity was 1500 mg Tiron/kg/day.