Manipulation of Kupffer cells by liposome encapsulated clodronate and propamidine—synergistic and antagonistic effects of liposomal phospholipids and drugs

Targeted liposomal drug delivery to monocytes and macrophages

As the role of monocytes and macrophages in a range of diseases is better understood, strategies to target these cell types are of growing importance both scientifically and therapeutically. As particulate carriers, liposomes naturally target cells of the mononuclear phagocytic system (MPS), particularly macrophages. Loading drugs into liposomes can therefore offer an efficient means of drug targeting to MPS cells. Physicochemical properties including size, charge and lipid composition can have a very significant effect on the efficiency with which liposomes target MPS cells. MPS cells express a range of receptors including scavenger receptors, integrins, mannose receptors and Fc-receptors that can be targeted by the addition of ligands to liposome surfaces. These ligands include peptides, antibodies and lectins and have the advantages of increasing target specificity and avoiding the need for cationic lipids to trigger intracellular delivery. The goal for targeting monocytes/macrophages using liposomes includes not only drug delivery but also potentially a role in cell ablation and cell activation for the treatment of conditions including cancer, atherosclerosis, HIV, and chronic inflammation.

Macrophages in spleen and liver direct the migration pattern of rat neutrophils during inflammation

OBJECTIVE

The exact fate of polymorphonuclear neutrophilic granulocytes (PMN; neutrophils) after their mobilization from the bone marrow is not known. It is believed that they, after a relatively short lifespan (1-3 d), become apoptotic and phagocytosed by macrophages. We have recently shown that transfused neutrophils sequestrate not only in lungs, liver and spleen, but also to a large extent in the bone marrow, possibly because of uptake by macrophages. Hence, we studied if inactivation of macrophages would alter the pattern of neutrophil migration.

METHODS

We used transfused congenic or syngeneic neutrophils in rats with or without sterile peritonitis, induced by a casein preparation (Bacto-Tryptone). To perturb macrophage function, we either killed them with liposome-encapsulated clodronate or overloaded them with inert phagocytosable particles. Transfused neutrophils were tracked with flow cytometric or radiometric methods.

RESULTS

Not more than a small portion of the neutrophils migrated to the inflamed peritoneal cavity under any circumstance. Their ecotaxis to liver and spleen was reduced in rats with liver and spleen macrophages either congested with polystyrene particles or depleted by clodronate. The bone marrow uptake and blood retention of transfused neutrophils were increased in macrophage-depleted rats 18 h after transfusion. In rats depleted of liver macrophages only, the sequestration in the liver was reduced, without detectably changed uptake in bone marrow and spleen.

CONCLUSION

Macrophages are instrumental to the neutrophil migration stream in the organism, and their function in this regard is robust and not easily decreased by inert phagocytosable particles or a killing agent.

A method for the selective depletion of perivascular and meningeal macrophages in the central nervous system

The perivascular (PVM) and meningeal (MM) macrophages form a distinct population of resident CNS cells, selectively expressing the mature macrophage marker ED2 in the rat. In order to elucidate the role of the PVM and MM in rats during normal functioning of the brain and pathology, we have developed a strategy employing a single intraventricular injection of clodronate liposomes. This resulted in a complete depletion of the PVM and MM. Clodronate liposomes did not deplete the microglial cells. In other parts of the body, a temporal and mild depletion effect was observed, which was restored within 1 week. Detailed analysis of the elimination and repopulation kinetics of the PVM and MM revealed a slow repopulation of the CNS, starting at 14 days post depletion. This selective depletion method of the PVM and MM will enable us to get direct insight in their functions during normal and pathologic conditions of the CNS.

Treatment with liposome-encapsulated clodronate as a new strategic approach in the management of immune thrombocytopenic purpura in a mouse model

Immune thrombocytopenic purpura (ITP) is an autoimmune disease related to the presence of elevated levels of platelet-associated immunoglobulin, or autoantibodies. In recent years the importance of macrophage Fcγ receptors in the uptake of platelets in ITP has been confirmed. Although in patients with ITP the platelet destruction occurs in liver and spleen, in this present experimental mouse model the liver was the principal organ of sequestration of sensitized platelets. The uptake in the spleen, bone marrow, lung, and kidneys was negligible and not different from that in control animals. In addition, the trapped platelets did not return to circulation, and new cells derived from the platelet-storage pool or new thrombocytogenesis were necessary to restore the platelet count. The depletion of splenic and hepatic murine macrophages by liposome-encapsulated clodronate (lip-clod) was studied as a new strategy for ITP treatment. Lip-clod inhibits, in a dose-dependent manner, the antibody-induced thrombocytopenia. Moreover, lip-clod treatment rapidly restored (24 hours) the platelet count in thrombocytopenic animals to hematologic safe values, and despite additional antiplatelet antiserum treatment, mice were able to maintain this level of platelets at least up to 48 hours. The bleeding times in lip-clod–treated animals was not different from those in controls, demonstrating that the hemostasis was well controlled in these animals. The results presented in this study demonstrate that lip-clod treatment can be effective in the management of experimental ITP.

Treatment with liposome-encapsulated clodronate as a new strategic approach in the management of immune thrombocytopenic purpura in a mouse model

Immune thrombocytopenic purpura (ITP) is an autoimmune disease related to the presence of elevated levels of platelet-associated immunoglobulin, or autoantibodies. In recent years the importance of macrophage Fcγ receptors in the uptake of platelets in ITP has been confirmed. Although in patients with ITP the platelet destruction occurs in liver and spleen, in this present experimental mouse model the liver was the principal organ of sequestration of sensitized platelets. The uptake in the spleen, bone marrow, lung, and kidneys was negligible and not different from that in control animals. In addition, the trapped platelets did not return to circulation, and new cells derived from the platelet-storage pool or new thrombocytogenesis were necessary to restore the platelet count. The depletion of splenic and hepatic murine macrophages by liposome-encapsulated clodronate (lip-clod) was studied as a new strategy for ITP treatment. Lip-clod inhibits, in a dose-dependent manner, the antibody-induced thrombocytopenia. Moreover, lip-clod treatment rapidly restored (24 hours) the platelet count in thrombocytopenic animals to hematologic safe values, and despite additional antiplatelet antiserum treatment, mice were able to maintain this level of platelets at least up to 48 hours. The bleeding times in lip-clod–treated animals was not different from those in controls, demonstrating that the hemostasis was well controlled in these animals. The results presented in this study demonstrate that lip-clod treatment can be effective in the management of experimental ITP.