Penetration Of Liposomes Research Articles

Efficacy of Gel Formulations Containing free and Liposomal Foscarnet in a Murine Model of Cutaneous HSV-1 Infection

The efficacy of gel formulations containing free and liposomal foscarnet has been evaluated in a murine model of cutaneous Herpes simplex virus type-1 infection. Both formulations were applied topically 3 times daily for 4 days and initiated 24 h post-infection. The penetration of liposomes incorporated into the gel in infected skin tissues was better than that of liposomes dispersed in buffer. Therein, their localization mostly matched that of viral antigen detected by immunoperoxydase staining. Despite these facts, the efficacy of gel formulations of both free and liposomal foscarnet in preventing the development of a zosteriform rash in mice was similar. Electron microscopic examination revealed that liposomes incorporated into the gel formed aggregates together with the micelles of gel. Diffusion studies showed that liposomes were trapped within these aggregates and were hardly able to diffuse across a polycarbonate membrane. In addition, although the liposomes were shown to be highly stable in vitro, the formation of these aggregates destabilized their membrane resulting in a premature release of foscarnet from liposomes. The efficacy of both gel formulations was higher than that of solutions of free or liposomal foscarnet suggesting that the gel formulation is a suitable matrix for the delivery of drugs. Thus, strategies aimed at reducing the interaction of liposomes with the gel could be a convenient approach to improve the efficacy of liposome-encapsulated drug over the free drug.

Interaction of liposomes with human skin in vitro — The influence of lipid composition and structure

Liposomes have been suggested as a vehicle for dermal and transdermal drug delivery, but the knowledge about the interaction between lipid vesicles and human skin is poor. Therefore, we visualized liposome penetration into the human skin by confocal laser scanning microscopy (CLSM) in vitro. Liposomes were prepared from phospholipids in different compositions and labeled with a fluorescent lipid bilayer marker, N-Rh-PE (l-α-phosphatidylethanolamine-N-lissamine rhodamine B sulfonyl). Fluorescently labelled liposomes were not able to penetrate into the granular layers of epidermis. However, the fluorescence from liposome compositions containing DOPE (dioleylphosphatidyl ethanolamine) was able to penetrate deeper into the stratum corneum than that from liposomes without DOPE. Pretreatment of skin with unlabeled liposomes containing DOPE or lyso-phosphatidyl choline (lyso-PC) enhanced the subsequent penetration of the fluorescent markers, N-Rh-PE and sulforhodamine B into the skin, suggesting possible enhancer activity, while most liposomes did not show such enhancement. Resonance energy transfer (RET) and calcein release assay between stratum corneum lipid liposomes (SCLLs) and the phospholipid vesicles suggested that the liposomes containing DOPE may fuse or mix with skin lipids in vitro and loosen the SCLL bilayers, respectively. Among the factors not affecting stratum corneum penetration were: negative charge, cholesterol inclusion and acyl chain length of the phospholipids. In conclusion, fusogenicity of the liposome composition appears to be a prerequisite for the skin penetration.

Percutaneous penetration of liposomes using the tape stripping technique

The reservoir capacity of the stratum corneum was studied by topical application of sodium fluorescein encapsulated in vesicles in order to elucidate the mechanism involved in the (trans)dermal transport of drugs when vesicles are applied to the skin. The penetration profile of sodium fluorescein in the different strips was found to be logarithmic with both the constant and the slope of the regression curves, accounting for the superficial non-penetration content and for the penetration rate inside the stratum corneum, respectively. The results show a small but significantly enhanced penetration of these vesicle structures for the release of hydrophilic substances. Moreover, similar values obtained when the same liposomes with a varying encapsulation content were applied could lend support to the penetration mechanism where the vesicle enhancement is mainly due to stratum corneum structural modification.

Interaction of phospholipid liposomes with lipid model mixtures for stratum corneum lipids

Differential scanning calorimetry (DSC) and 2H-NMR experiments were performed on lipid vesicles prepared from a lipid mixture resembling the lipid composition of stratum corneum lipids in the epidermis. This lipid mixture showed a broad phase transition with a transition range from 40 to approx. 80°C. 2H-NMR spectroscopy revealed that the transition occurs from a lamellar gel-like phase to a cubic phase at high temperature. Both phases coexist over a broad temperature range. Mixing of populations of different soy bean phosphatidylcholine or dipalmitoylphosphatidylcholine vesicles with the vesicles made from the model mixture for stratum corneum lipids resulted in the mixing of lipid components, induced either by heating the vesicles to 95°C, or by incubation of the vesicle mixtures at 37°C for 2–24 h. The mixing of lipid components apparently proceeds by monomer exchange through the water phase. 2H-NMR spectroscopy showed that the resulting mixed lipid system has different phase characteristics, being in a liquid-crystalline state at 37°C and transforming apparently to an inverted hexagonal phase at higher temperature. The consequences for the penetration of liposomes through the stratum corneum of the skin are discussed. Mixing of liposomes with the lipids in the intercellular layers could be one mechanism contributing to the enhancement of the permeability of the skin to lipid vesicles.

Inhibition of the Friend retrovirus by antisense oligonucleotides encapsulated in liposomes: mechanism of action.

Proliferation of the Friend retrovirus was specifically inhibited by the env mRNA complementary oligonucleotide encapsulated in pH-sensitive liposomes. This observation was made using the focus immunoassay (FIA) and the reverse transcriptase test. The key finding of the present study was the dramatic impact on liposome penetration. For chronic or de novo infection, the point at which the penetration of liposomes began corresponded to the time needed for the virus to leave the cell. In the absence of the virus, liposomes remained adsorbed onto the cell surface without any internalization. Regardless of the mechanism involved, the fact that a retroviral infection stimulates the cellular uptake of oligonucleotide liposomes widens the spectrum of strategies for specific antiviral action.

Preservative activity and in vivo percutaneous penetration of butylparaben entrapped in liposomes.

Butylparaben (BP) was added to liposomes prepared by the hydration method from egg phosphatidylcholine (egg PC), cholesterol, and dicetylphosphate in a molar ratio of 4 : 2 : 1 for the purpose of antimicrobial preservation. Most of the BP was entrapped in liposomes near the polar surface of the lipid bilayers, and rapid equilibrium was observed in its distribution between liposomes and the outer aqueous phase.The antimicrobial activities of liposomes containing BP were studied qualitatively against eight kinds of microorganisms. Although the liposome suspension without BP (empty liposomes) had no effect on the microorganisms, liposome suspensions with BP showed antimicrobial activities. The preservative effect was roughly proportional to the free cencentration (not the total concentration) of BP.Percutaneous penetration of liposomes containing BP after topical application was studied in vivo in guinea pigs by autoradiography. 14C-BP in liposomes as observed to penetrate into the body, but no difference was found in its distribution pattern in comparison with that after administratoin as an ointment. On the other hand, 14C-dipalmitoylphosphatidylcholine, a marker of egg PC, remained on the skin surface and was scarcely detected in the body, suggesting that the percutaneous penetration of liposomes themselves did not occur.

Intracellular penetration of liposomes containing a water insoluble antimitotic drug in L1210 cells

To demonstrate the possibility of cell delivery of water insoluble products, L 1210 cells were incubated with liposomes containing Nocodazole ® (NCL), an experimental drug totally insoluble in water. Liposomes of various lipid compositions readily incorporated NCL, but only those formed from dipalmitoyl phosphatidylcholine, cholesterol and stearylamine (molar ratio 4:3:1) had a clear affinity for L 1210 cells, as shown by fluorescence studies. This affinity is mediated by the degree of both cell and liposome membrane fluidity. Cytoplasmic and intranuclear location of these liposomes containing NCL or drug-free and subcellular changes induced by their presence were demonstrated by ultrastructural studies.

Cholesterol stimulation of penetration of unilamellar liposomes by hydrophobic compounds

The incorporation of cholesterol into unilamellar liposomes greatly increased the transmembranous movement of hydrophobic ionophores such as nigericin. In reconstituted liposomes containing rhodopsin as the only protein, the presence of cholesterol lowers by 10-fold or more the amount of negericin required to eliminate the light-driven proton gradient. These effects are seen both above and below the transition temperature of the phospholipid used for reconstitution. Cholesterol similarly increases the ability of A-23187, 1799, or NH4SCN to collapse the proton gradient of bacteriorhodopsin vesicles. Cholesterol also lowers the concentration of nigericin or valinomycin required for a rapid translocation of Rb+ into protein-free liposomes. It also lowers the concentration of A-23187 required for the release of Ca45 trapped in protein-free liposomes. In contrast to these observations and in confirmation of previous findings, we observed that cholesterol decreased the permeability of liposomes for glucose. Thus the effects of cholesterol on the permeability of the membrane vary with the chemical nature of the permeating compounds. We have also confirmed that in multilamellar liposomes cholesterol decreases the permeability of Rb+ in the presence of valinomycin. It therefore appears that the effect of cholesterol changes with the size and structural features of the model membranes.