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Magnetic starch microspheres, biodistribution and biotransformation. A new organ-specific contrast agent for magnetic
A K Fahlvik1, E Holtz, U Schrøder
1Department of Pharmacology, University of Oslo, Norway.
Abstract:
The biodistribution and elimination of magnetic starch microspheres (MSM) were studied qualitatively and quantitatively by radioiron tracer studies and relaxation time measurements. One hour after injection of MSM (1 mg/kg of Fe), 85% +/- 5% of the dose was accumulated in the liver and 6.5% +/- 1.3% [corrected] in the spleen. The hepatic clearance led to 50% reduction in the T2 relaxation time of liver tissue. This T2 effect was halved after 24 hours and T2 reversed to baseline value within 5 days after injection. The radioiron was gradually cleared from the liver with a t1/2 of 4 to 5 days. Six weeks after injection of MSM, 72% +/- 7% of the radioiron dose was detected in the circulation in a nonsuperparamagnetic form associated with the erythrocytes. The results indicate a redistribution of iron from the liver and spleen via the erythroid bone marrow to the erythrocytes after injection of MSM.
Insights
Magnetic starch microspheres (MSM) primarily accumulate in the liver and spleen after injection. Iron from MSM is later redistributed to red blood cells, impacting liver T2 relaxation times during clearance.
Area of Science:
- Biomedical Engineering
- Radiopharmacology
- Materials Science
Background:
- Magnetic starch microspheres (MSM) are investigated for potential biomedical applications.
- Understanding the in vivo fate of nanomaterials is crucial for safety and efficacy.
- Radioiron labeling allows for quantitative tracking of biodistribution and elimination.
Purpose of the Study:
- To determine the biodistribution and elimination kinetics of magnetic starch microspheres (MSM) in vivo.
- To assess the impact of MSM accumulation on liver tissue characteristics using MRI relaxation times.
- To trace the long-term fate of iron derived from MSM.
Main Methods:
- Qualitative and quantitative biodistribution studies using radioiron tracer techniques.
- Measurement of T2 relaxation times in liver tissue to monitor MSM clearance.
- Pharmacokinetic analysis of radioiron elimination from the liver and circulation.
Main Results:
- MSM rapidly accumulated in the liver (85%) and spleen (6.5%) within 1 hour post-injection.
- Hepatic T2 relaxation time decreased significantly due to iron accumulation, returning to baseline within 5 days.
- Radioiron exhibited a half-life of 4-5 days in the liver and was found associated with erythrocytes 6 weeks post-injection.
Conclusions:
- MSM demonstrate a specific biodistribution pattern favoring the reticuloendothelial system.
- The observed T2 changes in the liver reflect the clearance dynamics of iron from MSM.
- A significant portion of iron from MSM is ultimately incorporated into circulating erythrocytes, suggesting potential for iron delivery.