Hypotonically Loaded Rat Erythrocytes Deliver Encapsulated Substances into Peritoneal Macrophages

Abstract

Previous work has shown increased uptake of hypotonically loaded rat RBCs by the spleen and liver "in vivo," suggesting that the cells of MPS are involved in their elimination from the circulation. In order to elucidate the mechanism of such elimination, we have undertaken studies on the interaction of such loaded RBCs, in comparison with native RBCs, with peritoneal macrophages. Erythrophagocytosis assays were performed in well plates to which thioglycollate-induced peritoneal macrophages had adhered. Native or loaded 51Cr-RBCs were added under different opsonization conditions to monolayer adherent macrophages, and then the amount of RBCs that were recognized was determined, with separation into adhesion and phagocytosis fractions. Native RBCs are slightly recognized by peritoneal macrophages, about one RBC per macrophage (Mphi). Osmotic treatment of rat RBCs used for encapsulation (independently of the encapsulated substance, 125I-CA or FITC-dextran) produces some modification in the erythrocyte membrane that induces higher recognition of these cells, about three loaded RBCs per macrophage. Consequently, both fluorescent (FITC-Dx) and radioactive (125I-CA) substances previously encapsulated in RBCs were transferred to M(phi)s. The fluorescence microscopic observations confirmed these results. Moreover, in the case of carrier 51Cr-cells loaded with 125I-CA, the amount of 125I-radioactivity delivered into M(phi)s was relatively higher than that of 51Cr. The highest ratio, 125I-CA (encapsulated substance)/51Cr-RBCs (carrier cells), present in M(phi)s means there was a stronger interaction with macrophages of RBCs that carry a higher amount of encapsulated CA, as a function of the heterogeneity of the loaded rat RBCs population previously reported. Finally, the adhesion and phagocytosis of loaded RBCs seem not to involve complement receptors or Fc receptors on the macrophages.

Drug delivery by red blood cells: vascular carriers designed by mother nature

“…As expected, modifications that altered RBC surface antigens and membrane plasticity (e.g., treatment with cross-linking agents) resulted in their rapid phagocytosis by macrophages in the RES71,72, providing a mechanism to deliver encapsulated drugs into lysosomes in these and other cell types with active internalization processes including tumor cells26,73 (see section below). Pilot studies showed that microparticles made from RBC ghosts facilitate delivery of cytotoxic agents to malignant cells74.…”

Immune cells as tumor drug delivery vehicles

“…Some degree of targeting of the MPS is described e.g. via cell surface modifications which mimic damaged or senescent RBCs [116,117].…”

Delivery of Drugs Bound to erythrocytes: New Avenues for an Old Intravascular Carrier

“…Making lemonade from lemons, modified RBC carriers destined for phagocytosis can be used to deliver drugs to macrophages [78,92]. Examples of these approaches include attempts to deliver enzymes therapy for lysosomal storage diseases, with variable success in animal studies [18,93], antimicrobial and antiviral agents [24,94–97], antigens to boost the immune response [98] and anti-inflammatory drugs [99].…”