DMPC liposomes

Monnard and Deamer (2001) carried out further studies, using DMPC liposomes, to determine their properties under conditions of passive diffusion of dissolved molecules. The passage across the lipid bilayer is a precondition for the intake of nutrient substances via the vesicle envelope. The experiments showed that even polar molecules can enter the interior of the liposomes oligonucleotides, however, cannot cross the lipid bilayer of DMPC vesicles. 

PDA vesicles have been used to screen small molecules that are known to interact with membranes. Screening of almost 40 compounds against PDA/DMPC liposomes... 

Figure 2 Variation of P form fluorescence intensity of 1-naphthol ( - - ) and polarization (dP/dT) of DPH (A-A-A) with temperature in DMPC liposome membranes. (From Ref. 93a. Copyright 1998 American Chemical Society.)...

DSC has also been used to determine partition coefficients between phospholipids and water, avoiding radiolabeled solutes and high concentrations. One example is the partitioning of cardiac drugs into DMPC liposomes [48] (Table 3.9). The drug concentration in the liposomes was calculated using the following equation ... 

In another 1H-NMR study, the interaction of P-blockers with sonicated DMPC liposomes in the presence of Pr3+ was evaluated [122]. The presence of Pr3+ increased the splitting of the choline trimethylammonium group signals that arise from the phospholipid molecules located at the internal and external layer of the bilayer. The downfield shift of the external peak ( ) is considerably stronger than the upheld shift of the internal peak (i) (Figure 3.34). The difference in chemical shift of the two sig-... 

Fig. 3.44 Second-derivative absorption spectra oflOpM 4-hydroxytamoxifen in DMPC liposomes at different lipid concentrations. The nominal concentration of DM PC in suspensions was 0 (curve 0), 21 (1), 28 (2), 42 (3),...

I, DMPC liposomes II, DPPC liposomes III, DMPC/CHOL (1 1 mole ratio) liposomes ... 

To demonstrate polymerase activity in a model cell, Chakrabarti et al. [79] encapsulated polynucleotide phosphorylase in vesicles composed of dimyris-toylphosphatidylcholine (DMPC). This enzyme can produce RNA from nucleoside diphosphates such as adenosine diphosphate (ADP) and does not require a template, so it has proven useful for initial studies of encapsulated polymerase activity (Fig. 10a). Furthermore, DMPC liposomes are sufficiently permeable so that 5-10 ADP molecules per second enter each vesicle. Under these conditions, measurable amounts of RNA in the form of polyadenylic acid were synthesized and accumulated in the vesicles after several days incubation. The enzyme-catalyzed reaction could be carried out in the presence of a protease external to the membrane, demonstrating that the vesicle membrane protected the encapsulated enzyme from hydrolytic degradation. Similar behavior has been observed with monocarboxylic acid vesicles [80], and it follows that complex phospholipids are not required for an encapsulated polymerase system to function. 

Bomre L et al (2003) In vivo photosensitizing efficiency of a diphenylchlorin sensitizer Interest of a DMPC liposome formulation. Pharmacol Res 47 253-261... 

Log D membrane, or log D em/ is another way of measuring the lipophilicity of a compound, which is less frequently used than the octanol/water partition system. Log Dmem utilizes liposomes prepared from the synthetic phospholipids dimyristoylphosphatidylcholine (DMPC), and although the system is more physiologically relevant than octanol, it suffers from a lack of predictability. This method requires 1 mg of the compound, whereby a solution of the compound is equilibrated with a solution of DMPC liposomes at 37°C for two hours. The free and liposome-bound compounds are then separated by centrifugation, and the solutions are analyzed by high-performance liquid chromatography (HPLC). 

The interaction observed between oleuropein and DMPC liposomes may be due to the introduction of lipophilic molecules into the ordered structure of the lipid bilayer [55]. 

The structure and property of the porphinatoiron complex in the lipid bilayer of a liposome was studied for the liposome-embedded heme composed of DMPC and lipid-heme (DMPC liposome/lipid-heme) as follows... 

Fig, 5. Electron microscopic photographs for the liposome-embedded heme (DMPC liposome/ lipid-heme) a) single-wall, b) multilamellar... 

The formation of the liposome (single-walled type) was confirmed by NMR measurements. When europium ion (Eu ) is added to a liposome solution, interacts with the choUne groups of the outward facing phospholipid and shifts the NMR signal of choline methyl groups upfield The same shift was observed for DMPC liposome/lipid-heme with the addition of Eu ". This result means the liposome formation for the hposome-embedded heme solution. The liposome formation was also supported by the sharp P-NMR spectrum (0.8 ppm), which.was caused by the spherical geometry of the phosphatidyl group. 

The Fourier-transform H-NMR spectrum of DMPC liposome/lipid-heme at 37 °C showed the absorption signal at —0.1 ppm assigned to the P-dimethyl group of the heme beside the signals based on DMPC. This suggests that the heme complex is molecularly dispersed in the bilayer of the DMPC hposome. 

The DSC thermogram of the liposome-embedded heme was measured to estimate the phase transition of the lipid bilayer of the liposome-embedded heme . The DMPC-liposome showed the endothermic peak at 24 °C, which was corresponding to the gel-liquid crystal phase transition temperature (T,) of the liposome . But for the liposome in which a simple heme such as I was embedded, the phase transition peak was broadened and shifted to lower temperature (22 °C). On the other hand, the peak was also observed at 24 °C for the DMPC liposome/lipid-heme. This suggests that the orientation of the phospholipid in the liposome is equivalent for the DMPC-liposome and the DMPC liposome/lipid-heme and that the compatibility of the lipid-heme with the phospholipid is large enough to form a stable liposome. 

The results mentioned above lead to the following conclusion The lipid-heme complex is included and molecularly dispersed in the hydrophobic environment of the liposome which protects the heme-oxygen adduct from the irreversible oxidations [Eqs. (3) and (4). The geometry of the lipid-heme derivative is assumed to emphasize the incorporation of the porphinatoiron into the phospholipid bilayer of the liposome. The following result also supports this conclusion. The lipid-heme complex was more efficiently taken into the DMPC liposome than the heme complex I of l-lauryl-2-methylimidazole was only 20 moles of DMPC were enough to solubilize one mole of the lipid-heme completely in water, while more than 100 moles were necessary for... 

In another H-NMR study the interaction of 3-blockers with sonicated dimyristoyl-phosphatidylcholine (DMPC) liposomes in the presence of Pr has been reported [83]. The presence of Pr " increased the splitting of the choline trimethylammonium group... 

The difference in chemical shift of the two signals (A Hz) increased, linearly with increasing Pr concentration up to 10 mM (data not shown). Upon addition of the P-blockers the effect of is reversed and propranolol (PPL) has the strongest effect. (P-blockers are presented in Table 11-7 together with their partition coefficients into DMPC liposomes and into octanol). 

PNPase has been entrapped inside extruded DMPC liposomes, which are fed by externally added ADP. In order to increase the entrance of ADP, liposomes were kept at 23 °C (i.e., at the TJ. 

T7 RNA polymerase has been entrapped inside DMPC liposomes, together with DNA template, and fed by externally added NTPs. In order to favour the entrance of NTPs, liposomes were incubated at cycling temperature (from 23 to 37°C). RNA was therefore then observed within DMPC vesicles. 

Tanaka M, Sato T, Yonezawa Y. 1996a. Specific photoresponse of dmpc liposomes doped with azobenzene derivative around the phase transition temperature. Thin Solid Films 284/285 829 832. 

Chauhan et al. proposed to disperse dimyristoylphosphatidylcholine (DMPC) liposomes into the CL material. However, the procedure suggested in this study requires the use of radicals for the polymerization of the CL matrix, which cannot be used with drugs sensitive to radicals. 

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