Liposomes attached

The application of modified electrodes for the assay of antibodies in senun preparations using redox indicators encapsuled into antigene marked liposomes attached to an electrode surface was suggested First model studies towards this goal make use of ferricyanide ions entrapped in synthetic vesicles. 

Reppy MA, Pindzola BA (2006) Polydiacetylene liposomes attached to glass fibers for bioassays. Mater Res Soc Symp Proc 942(0942) W13-10... 

The sites of targeting of IL on hypoxic cardiocytes was visualized by fluorescent microscopy, using rhoda-mine labeled antimyosin immunoliposomes. Fig. 17 shows that only cells treated with antimyosin-rhoda-mine labeled IL were still confluent in the culture and that almost all cells were labeled with fluoresent liposomes. Those cells treated with rhodamine labeled PL showed extremely sparse number of cells still attached to the culture plates at 24 h of incubation, with essentially no or minimal fluorescence. Confocal microscopic examination of the cultures treated with rhodamine labeled IL showed that the cells still retained their morphology and shape with scattered fluorescent liposomes attached to the cell membranes (Fig. 18A). Those cells treated with rhodamine labeled PL were shrunken and only a few random cells showed some non-specific attachment of fluorescent PL (Fig. 18B). In this study, untreated hypoxic cells were all dead and since there was no fluorescent compounds added in them, no micrographs were obtained. 

We have studied the electrophysiological properties of outer mitochondria membranes incorporated in liposomes, using the patch-clamp technique. The proteoliposomes were prepared and enlarged in 150 mM KCl, 0.1 mM CaCh, and 20 mM HEPES, and the same solution was used in the recording pipette. Liposome-attached and inside-out patches were obtained. 

Fig. 12. Outer mitochondrial membrane incorporated in liposomes. A Multiple conductance levels obtained from a liposome-attached patch maintained at + 50 mV. At least four different conductance levels are revealed from the amplitude histogram of the current record 97 pS, 156pS, 244 pS, and 351 pS. B Current recorded from an inside-out patch during the application of a voltage ramp from —70 mV to 4-70 mV and back to —70 mV. The voltage dependence is appreciated from the higher frequency of high conductance events at negative potentials.

Nanotechnology has led to very efficient versions of liposomes. Tiny hollow spheres only nanometers in diameter hold even tinier capsules of medicine. The spheres are made of silica covered with gold nanoparticles and when they are coated with antibodies they attach to tumor cells. The spheres are sensitive to light of specific wavelengths and when the light is applied, either heat up and destroy the tumor, or burst, releasing the drugs within the capsules directly into the tumor. 

The "stealth" concept may offer two other opportunities for liposome application (1) Conventional immunoliposomes (see Sec. VI.C) have been shown to be removed rapidly firom the circulation by the MPS (Peeters et al., 1987). The combination of the stealth approach for longer circulation with the attachment of antibodies or antibody fragments may provide a means of delivery of drugs to their sites of action with a high degree of specificity. This could be useful for treating leukemia, graft-vs.-host diseases, and HIV disease. 

Fig. 13 Diagrammatic representation of two types of antibody-targeted systems. Drug is either covalently linked directly to the antibody or is contained in liposomes that are targeted by attached antibodies.

Antibodies were attached to liposomes by the CDI activation method via the gly-colipid tetradecylmelibionamide.[ 1513... 

The most useful form of liposomes for bioconjugate applications consists of small, spherical ULVs that possess layers of hydrophilic head groups on their inner and outer surfaces. The inside of each vesicle can contain hydrophilic molecules that are protected from the outer environment by the lipid shell. The outside surface can be derivatized to contain covalently attached molecules designed to target the liposome for specific interactions. 

Covalent attachment of antibody molecules to liposomes can provide a targeting capacity to the vesicle that can modulate its binding to specific antigenic determinants on cells or to molecules in solution. Antibody-bearing liposomes may possess encapsulated components that can be used for detection or therapy (Figure 22.17). For instance, fluorescent molecules encapsulated within antibody-targeted vesicles can be used as imaging tools or in flow cytometry... 

Covalent attachment of proteins to the surface of liposomal bilayers is done through reactive sites created on the head groups of phospholipids with the intermediary use of a crosslinker or other activating agent. The lipid functional groups described in Section 1 of this chapter are modified according to the methods discussed in Section 2 to be reactive toward specific target... 

Heath, T.D., Macher, B.A., and Papahadjopoulos, D. (1981) Covalent attachment of immunoglobulins to liposomes via glycosphingolipids. Biochim. Biophys. Acta 640, 66-81. 

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