Activation liposomes

The SPDP-activated liposomes may be used immediately to couple with sulfhydryl-containing molecules such as proteins (see Section 7.7, this chapter), or they may be stored in a lyophilized state in the presence of sorbitol (Friede et al., 1993) for latter use. 

Figure 22.16 SMPB-activated liposomes may be modified with peptide hapten molecules containing cysteine thiol groups. The resultant immunogen may be used for immunization purposes to generate an antibody...

Purify the activated liposomes from excess glutaraldehyde by gel filtration (using Sephadex G-50) or by dialysis against PBS, pH 6.8. 

Dissolve the protein or peptide to be conjugated at a concentration of lOmg/ml in 0.5M sodium carbonate, pH 9.5. Mix the activated liposome suspension with the polypeptide solution at the desired molar ratio to effect the conjugation. Mixing the equivalent of 4 mg of protein per mg of total lipid usually results in acceptable conjugates. 

Figure 22.26 SPDP-activated liposomes can be used to couple sulfhydryl-containing proteins, forming disulfide linkages.

Figure 22.27 SMPB-activated liposomes may be used to couple thiol-containing protein molecules, forming stable thioether linkages.

Figure 22.28 The reaction of an SMCC-activated liposome with a sulfhydryl-containing protein forms stable thioether bonds.

Figure 22.29 SIAB-activated liposomes can couple with sulfhydryl-containing proteins to produce thioether linkages.

We then examined the effect of phospholipid composition on the transfection activity. Liposomes containing various combinations of phospholipids were tested for transfection activity on BHK-21 and HeLa-S3 cells. As described in HVJ-AVE liposomes, the cationic liposomes containing all of ePC, DOPE, and eSph in equal molar amounts showed the highest transfection efficiency both with BHK-21 and HeLa-S3 cells. The same results were obtained with Ltk-, HEK 293, and NB-1 cells. We also examined other phospholipids, but none was observed to be more effective. We then examined the effect of the cholesterol/phospholipid ratio on the transfection efficiency. The phospholipid composition (ePC DOPE eSph = 1 1 1) and DC-Chol content (10% of total... 

Active lipids—mostly with anticancer activity—have also been added in liposome membrane for production of active liposomes. Examples of such lipids are ether lipids [18] and arsonolipids [19]. 

One requirement for liposomes to respond to US stimulation is the presence of a US-sensitive vehicle. Thus, early research showed that acoustically active liposomes can be used as contrast agents for US image enhancement [91], Also, subsequent studies revealed that such liposomes encapsulate air — which is responsible for their acoustic activity — in their structure [92]. These acoustically active liposomes have the potential to carry drugs and their acoustic activity allows them to respond to US stimulation by releasing their contents. 

A Liposomes (active) Liposomes (placebo) Aqueous (D) Dose applied... 

Fig. 3. Encapsulation efficiency of calcein (left) and echogenicity of acoustically active liposomes (EggPC DPPE DPPG CFI 69 8 8 15) (right) made by freeze-drying in the presence of different concentrations of mannitol. Mean SD. n=Q. Reproduced with permission from (3)...

Dilute 100 piL of the 10 mg lipid/mL calcein-containing, acoustically active liposomes, to 500 pL with 50 mM 3-mor-pholinepropanesulphonic acid (MOPS) buffer containing 110 mM NaCl (to maintain isosmolality with the liposomal contents of 320 mM mannitol and 0.1 mM calcein) into the transwell chamber. 

Fig. 7. Ultrasound-triggered release of calcein and air from acoustically active liposomes composed of EggPC DPPE DPPG CH at molar ratio of 69 8 8 15 including 4% DHPC. Mean SD, n=6. Internal control non-acoustically active liposomes were evaluated for calcein release. Reproduced with permission from (3)...

Huang SL, MacDonald RC (2004) Acoustically active liposomes for drug encapsulation and ultrasoimd-triggered release. Biochim Biophys Acta 1665 134-141... 

Heat-activated liposomal MR contrast agent initial in vivo results in rabbit Kver and kidney. Radiology 230(3) 743-752... 

Figure 7. Liposome-assisted catalysis. (A) Dependency of the initial hydrolysis rate of C16-O Np (nitrophenyl-pamitate) catalyzed by 1 mM carbobenzoxy-Phe-His-Leu-OH on the substrate concentration, in 0.05 M borate buffer pH 8.5. The filled circles are relative to the self-hydrolysis (no peptide, no liposomes). Open triangles are without liposomes, open squares with liposomes. (B) The pseudo-enzymatic turnover of the catalytically active liposomes. The catalytic activity results primarily from the binding (and solubilization) of a very hydrophobic histidin-containing peptide and the very hydrophobic substrate.

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