Requirement of macromolecular complex formation for selective lymphatic transfer of bleomycin from large intestine by bifunctional delivery system.

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Abstract
The requirement of complex formation for the selective transfer of bleomycin from the large intestine of rat by a bifunctional delivery system was investigated. The delivery system developed by us is a combination of macromolecular dextran sulfate, mean molecular weight (MW), 500000, as a lymphotropic carrier forming an ionic complex with bleomycin, and lipid-surfactant mixed micelles as an absorption promoter. Co-existence of the bifunctional delivery system (bleomycin dextran sulfate complex+mixed micelles) with saline resulted in the dissociation of the complex. Administration of this system with saline into the lumen of the large intestine showed no selective rise of lymph level of bleomycin compared with the blood level, and pretreatment with dextran sulfate into the lumen did not increase the lymphatic transfer of bleomycin. Lower molecular weight dextran sulfate (MW, 5000) formed a complex with bleomycin, like macromolecular dextran sulfate (MW, 500000). However, administration of this complex with mixed micelles failed to selectively enhance the lymphatic transfer of bleomycin. Co-administration of bleomycin with other macromolecules (dextran or diethylaminoethyl dextran, MW, 500000) that do not form a complex with bleomycin also failed to selectively increase the lymphatic transfer of bleomycin. These findings suggest that the complex formation of bleomycin with a macromolecule over a certain molecular weight is required for the selective transfer of bleomycin into the lymphatics from the large intestine by a bifunctional delivery system.

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