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Comparison of particle clearance and macrophage phagosomal motion in liver and lungs of rats
1Department of Environmental Science and Physiology, Harvard University School of Public Health, Boston, Massachusetts 02115.
Abstract:
Magnetic particles and magnetometry were used to noninvasively measure motion of particle-containing organelles in macrophages as well as to monitor the disappearance of particles from tissues. We compared these parameters in the liver (where macrophages are attached to the endothelium) and in the lungs (where macrophages were mobile on epithelial surfaces). Submicrometric magnetic particles were injected intravenously (1.5 mg/kg) into rats; 94% was taken up by the liver. Rats were also instilled intratracheally (1.0 mg/kg) with the same particles. Ultrastructural analyses showed that almost all particles were ingested by macrophages in both organs. Periodically, the retained particles were magnetized and aligned with an external magnet. After the magnet was removed, the decay of the resulting remanent field (relaxation) was followed for 25 min. Relaxation parameters (t1/2 and lambda 0) in the liver were constant from 30 min to 30 days after particle administration, but relaxation in lungs showed a time-dependent increase during the 1st day due to the slower rate of particle phagocytosis. Relaxation in both organs primarily reflects the motion of particle-containing organelles as they are rotated by the cytoskeleton. Relaxation in the lungs may also reflect cell translocation or even changes in alveolar shape. Clearance of particles from the lungs or liver was measured by following B0 (initial magnetic field strength). After correction for growth, the clearance t1/2 was 17.7 and 27.3 days for the lungs and liver, respectively. Bulk transport of particles is probably a more important clearance mechanism in the lungs than in the liver.
Insights
Magnetometry noninvasively measures particle movement within macrophages in rat lungs and liver. Liver particle clearance was slower than in lungs, indicating different macrophage dynamics and particle transport mechanisms.
Area of Science:
- Biophysics
- Cell Biology
- Nanotechnology
Background:
- Macrophages play crucial roles in tissue homeostasis and particle clearance.
- Noninvasive techniques are needed to study intracellular dynamics and particle fate in vivo.
- Magnetometry offers a sensitive method to probe magnetic particle behavior within biological systems.
Purpose of the Study:
- To compare particle-macrophage interactions and clearance kinetics in the liver and lungs using magnetometry.
- To investigate the influence of macrophage location and mobility on particle dynamics.
- To assess the utility of magnetic particle relaxation for monitoring cellular processes.
Main Methods:
- Submicrometric magnetic particles were administered intravenously and intratracheally to rats.
- Magnetometry was used to measure magnetic particle relaxation and initial magnetic field strength (B0).
- Ultrastructural analysis confirmed particle uptake by macrophages in both organs.
Main Results:
- Liver macrophages showed constant magnetic relaxation parameters, while lung macrophages exhibited time-dependent changes, suggesting slower phagocytosis.
- Particle clearance half-life was 17.7 days in lungs versus 27.3 days in the liver.
- Relaxation primarily reflected organelle motion, with lung relaxation also influenced by cell translocation and alveolar shape.
Conclusions:
- Magnetometry effectively quantifies intracellular organelle motion and tissue particle clearance noninvasively.
- Macrophage mobility and tissue architecture significantly impact particle dynamics and clearance rates.
- Findings highlight distinct clearance mechanisms in the lungs and liver, with bulk transport being more significant in the lungs.