INTERACTION OF CULTURED HUMAN KERATINOCYTES WITH LIPOSOMES ENCAPSULATING SILVER SULFADIAZINE - PROOF OF THE UPTAKE OF INTACT VESICLES

There is evidence to suggest that human keratinocytes grown in vitro a re capable of engulfing and subsequently disintegrating intact liposom es. However, as the liposomes used in this context did not carry an el ectron-dense marker, the possibility that the lamellar structures seen within the keratinocytes were composed of material produced within th e cell could not be excluded. We therefore decided to investigate lipo some-keratinocyte interaction using an electron-dense marker. Human ke ratinocytes obtained from juvenile foreskins were cultured in a serum- free medium, and subconfluent cultures were exposed to liposomally enc apsulated and free silver sulphadiazine 1% (SSD), and a corresponding vehicle, for 5 min to 24 h. After fixation ultra-thin sections were an alysed electron microscopically at magnifications of up to x85,000. Ma ny keratinocytes treated with liposomal and free SSD showed marked dam age to the plasma membranes and the cell organelles, The phagocytosis of intact liposomes was demonstrated by the appearance of silver-label led unilamellar vesicles within the cytoplasm of undamaged keratinocyt es. The labelled liposomes were found enclosed in cellular unit membra nes, i.e. in lysosomes, In addition, perinuclear disintegration and re lease of the entrapped marker were observed, Silver particles, as pres ent in liposomally encapsulated SSD, were found to be adequate markers for electron microscopy. Our results confirm the phagocytosis of inta ct liposomes by keratinocytes in vitro. In addition, the cytotoxic eff ects of liposomal (intended for the treatment of burns) and free SSD o n human keratinocytes were studied in detail. Many keratinocytes treat ed for 10 min or more were severely affected.