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Microscopic localization of PEG-liposomes in a rat model of focal infection
P Laverman1, E T Dams, G Storm
1Department of Nuclear Medicine, University Medical Center Nijmegen, P.O. Box 9101, 6500 HB, Nijmegen, The Netherlands. p.laverman@nugen.azn.nl
Abstract:
In the present study the microscopic localization of polyethylene glycol (PEG) liposomes in infected tissues was studied with both light microscopy (LM) and transmission electron microscopy (TEM) in rats with focal intramuscular Staphylococcus aureus infection. PEG-liposomes containing colloidal gold were prepared and injected intravenously in rats with focal S. aureus infection and tissues were dissected at 24 h post injection. Sections were cut and liposomes were visualized for microscopic evaluation using silver enhancement. Uptake of PEG-liposomes was visualized by both scintigraphy and LM in the abscess, liver and spleen. In the infected area, the liposomes were mainly found in the vicinity of blood vessels. TEM showed that the liposomes were localized in the macrophages and to a lesser extent in endothelial cells in the infectious tissue. In the liver, the liposomes appeared mainly localized in Kupffer cells. In the spleen, uptake was only seen in cells of the red pulp and in cells around the central arteries. Our microscopic observations indicate that uptake and retention of PEG-liposomes in the infectious focus is a result of enhanced extravasation due to increased vascular permeability and subsequent phagocytosis of PEG-liposomes by macrophages in the infected tissue.
Insights
Polyethylene glycol (PEG) liposomes accumulate in Staphylococcus aureus infection sites, primarily within macrophages and endothelial cells. This uptake is driven by increased vascular permeability and phagocytosis in infected tissues.
Area of Science:
- Biomedical Engineering
- Microscopy
- Infectious Diseases
Background:
- Liposomes are widely investigated drug delivery systems.
- Polyethylene glycol (PEG) modification enhances liposome circulation time.
- Understanding liposome localization in infection is crucial for targeted therapy.
Purpose of the Study:
- To investigate the microscopic distribution of PEG-liposomes in Staphylococcus aureus infected tissues.
- To elucidate the cellular mechanisms of PEG-liposome uptake in infection models.
Main Methods:
- Intravenous injection of colloidal gold-labeled PEG-liposomes into rats with S. aureus infection.
- Microscopic evaluation using light microscopy (LM) and transmission electron microscopy (TEM).
- Scintigraphy for macroscopic uptake visualization.
Main Results:
- PEG-liposomes were detected in abscesses, liver, and spleen 24 hours post-injection.
- In infected tissues, liposomes localized near blood vessels, within macrophages, and endothelial cells.
- Kupffer cells in the liver and specific spleen cells showed significant liposome uptake.
Conclusions:
- PEG-liposome accumulation in infectious foci is facilitated by enhanced extravasation.
- Increased vascular permeability in infected tissues promotes liposome leakage.
- Subsequent phagocytosis by macrophages is a key mechanism for liposome retention in infection sites.
