CROSS-LINKING TREATMENT OF LOADED ERYTHROCYTES INCREASES DELIVERY OF ENCAPSULATED SUBSTANCE TO MACROPHAGES

Previous investigation has shown that osmotically loaded erythrocytes can act as drug carriers in systemic circulation, whereas chemically m odified erythrocytes can be targeted to organs of the mononuclear phag ocytic system because of changes introduced in the membrane that are r ecognized by macrophage cells, In this study we have examined the deli very of I-125-labelled carbonic anhydrase (I-125-CA) carried by mouse erythrocytes, either loaded, or loaded and cross-linked with bis(sulph osuccinimidyl)suberate (BS3) and 3,3'-dithiobis(sulphosuccinimidyl pro pionate), into homologous peritoneal macrophages maintained in culture . The hypotonically loaded mouse erythrocytes show a slight recognitio n by macrophages, similar to native erythrocytes, CA loaded into eryth rocytes is thus delivered to a limited extent into macrophages, Neithe r the number of recognized loaded Cr-51-labelled erythrocytes nor the amount of delivered I-125-CA is affected by the presence of serum comp onents or IgG, In contrast, cross-linking these loaded erythrocytes re sults in a greater phagocytosis by macrophages as assessed by microsco pic observations, producing a markedly increased amount of targeted en zyme. The amount of CA delivered into macrophages, after BS3 cross-lin ker treatment of erythrocytes, is dependent on the presence of serum c omponents in the incubation medium. Thus these cross-linking treatment s improve the capacity of loaded mouse erythrocytes to deliver signifi cant amounts of targeted enzyme to macrophage cells, increasing the th erapeutic potential of carrier erythrocytes.