Involvement of lipid rafts in macrophage apoptosis induced by cationic liposomes

We have demonstrated that protein kinase Cδ (PKCδ) could be involved in macrophage apoptosis induced by cationic liposomes composed of stearylamine (SA-liposomes), but the detailed mechanism of how SA-liposomes activate PKCδ has remained unclear. In this paper, we clarified whether lipid rafts are involved in the PKCδ activation induced by SA-liposomes. Co-localization of SA-liposomes and Cholera toxin B subunit (CBT), which specifically binds to ganglioside GM1 on lipid rafts, was found by microscopic observation. The incorporation of SA-liposomes into lipid rafts was clearly inhibited by the pretreatment of cells with an agent, 2,6-di-O-methyl-α-cyclodextrin (DM-α-CD) which disrupts lipid rafts. Activation of PKCδ and externalization of phosphatidylserine induced by SA-liposomes were also suppressed by DM-α-CD, which extracts sphingolipids and proteins from lipid rafts. Reactive oxygen species (ROS) generation, which could be involved in the macrophage apoptosis, was also inhibited by DM-α-CD. Furthermore, apoptosis induced by SA-liposomes was clearly inhibited when the cells were pre-treated with DM-α-CD, but not nystatin, a cholesterol-sequestering agent that disrupt lipid rafts. These findings suggest that sphingolipids in lipid rafts are involved in the activation of PKCδ which leads to apoptosis induced by cationic liposomes, SA-liposomes.     

Higly fusogenic cationic liposomes transiently permeabilize the plasma membrane of HeLa cells

Cationic liposomes can efficiently carry nucleic acids into mammalian cells. This property is tightly connected with their ability to fuse with negatively charged natural membranes (i.e. the plasma membrane and endosomal membrane). We used FRET to monitor and compare the efficiency of lipid mixing of two liposomal preparations — one of short-chained diC14-amidine and one of long-chained unsaturated DOTAP — with the plasma membrane of HeLa cells. The diC14-amidine liposomes displayed a much higher susceptibility to lipid mixing with the target membranes. They disrupted the membrane integrity of the HeLa cells, as detected using the propidium iodide permeabilization test. Morphological changes were transient and essentially did not affect the viability of the HeLa cells. The diC14-amidine liposomes were much more effective at either inducing lipid mixing or facilitating transfection.     

Immunostimulation of dendritic cells by cationic liposomes

A nano-aggregate liposome-polycation-DNA (LPD), composed of a cationic lipid, protamine and plasmid DNA was found to effectively deliver a human papillomavirus (HPV)-E7 epitope antigen to the antigen presenting cells of the immune system, eliciting enhanced anti-tumor immune responses in mouse models of cervical carcinoma. Both the cationic liposome and plasmid DNA were essential for the full immunostimulation activity of LPD. Interestingly, cationic liposomes alone could stimulate the antigen presenting dendritic cells (DC) leading to the expression of co-stimulatory molecules, CD80 and CD86. However, cationic lipids could not stimulate DC for the expression of pro-inflammatory cytokines. Moreover, they were unable to enhance the expression of NF-κB, suggesting that dendritic cells stimulation by cationic lipids is signaled through an NF-κB independent mechanism. DC stimulation was specific to cationic lipids, the zwitterionic and anionic lipids showed little or no activity. The ability of different cationic lipids to stimulate the expression of co-stimulatory molecules on DC varied significantly. In general, the cationic lipids bearing ethyl phosphocholine head groups were better stimulants than their trimethylammonium counterparts. In case of the cationic lipids bearing trimethyl ammonium head groups, the ones bearing unsaturated or shorter saturated hydrophobic chains exhibited enhanced immunostimulatory activity. The LPS-induced TNF-α expression by dendritic cells was inhibited by active cationic lipids but not the inactive ones, suggesting the possible involvement of lipopolysaccharide binding protein (LBP) in cationic lipid mediated DC stimulation. Based on the structure-specific activation of dendritic cells by cationic lipids, a model for the immunostimulation of DC by such lipids is proposed.     

Lipofectin: direct gene transfer to higher plants using cationic liposomes

Summary It has recently been shown that lipofectin, a commercially available preparation of cationic liposomes is capable of animal and plant cell line transfection. Here, it is analyzed with respect to its toxicity for higher plant protoplasts and used for transient expression and stable transformation experiments with mesophyll protoplasts of Nicotiana tabacum and Nicotiana plumbaginifolia. Transient expression of the -glucuronidase gene (GUS) under control of the CaMV-35S-promoter was lower than after introduction of the same gene by polyethylene glycol. By transferring the neomycin phosphotransferase gene (NPTII) and subsequent culture and regeneration under selection with kanamycin, stably transformed plants were recovered after using Lipofectin in various protocols with or without additional application of electroporation. Efficiencies of stable transformation were comparable to those achieved with PEG and/or electroporation. Confirmation of transformants included assaying the enzyme activity of the gene product, genomic blotting, and transfer of the resistant phenotype to the progeny produced from selfed primary transformants.     

Visualization of intracellular trafficking of exogenous DNA delivered by cationic liposomes

To visualize the intracellular trafficking of exogenous DNAs delivered by cationic liposomes, rhodamine-labeled DNAs were transfected into NIH3T3 cells and observed by confocal laser microscopy. After 0.5- to 1-h incubations, the DNAs reached the nucleus with a much higher frequency than that expected from the cell division rate. This result suggests that DNAs can enter the nucleus in the presence of the nuclear membrane. Interestingly, some DNAs appeared to extend through the nuclear membrane in the aggregated form which were much larger than the nuclear pore complex. The DNAs which have passed through the nuclear membrane were stained with SYTO 24, a DNA labeling reagent. The stained part may be "naked" DNA that is free of lipids or proteins. This observation indicates that a complex containing DNA fuses with the nuclear membrane and then naked DNA is released into the nucleus.     

Potential effect of cationic liposomes on interactions with oral bacterial cells and biofilms

Context: Although oral infectious diseases have been attributed to bacteria, drug treatments remain ineffective because bacteria and their products exist as biofilms. Cationic liposomes have been suggested to electrostatically interact with the negative charge on the bacterial surface, thereby improving the effects of conventional drug therapies. However, the electrostatic interaction between oral bacteria and cationic liposomes has not yet been examined in detail.

Objective: The aim of the present study was to examine the behavior of cationic liposomes and Streptococcus mutans in planktonic cells and biofilms.

Materials and methods: Liposomes with or without cationic lipid were prepared using a reverse-phase evaporation method. The zeta potentials of conventional liposomes (without cationic lipid) and cationic liposomes were ?13 and 8?mV, respectively, and both had a mean particle size of approximately 180?nm. We first assessed the interaction between liposomes and planktonic bacterial cells with a flow cytometer. We then used a surface plasmon resonance method to examine the binding of liposomes to biofilms. We confirmed the binding behavior of liposomes with biofilms using confocal laser scanning microscopy.

Results: The interactions between cationic liposomes and S. mutans cells and biofilms were stronger than those of conventional liposomes. Microscopic observations revealed that many cationic liposomes interacted with the bacterial mass and penetrated the deep layers of biofilms.

Discussion and conclusion: In this study, we demonstrated that cationic liposomes had higher affinity not only to oral bacterial cells, but also biofilms than conventional liposomes. This electrostatic interaction may be useful as a potential drug delivery system to biofilms.     

Activation of intrinsic and extrinsic pathways in apoptotic signaling during UV-C-induced death of Jurkat cells: the role of caspase inhibition

We have examined UV irradiation-induced cell death in Jurkat cells and evaluated the relationships that exist between inhibition of caspase activity and the signaling mechanisms and pathways of apoptosis. Jurkat cells were irradiated with UV-C light, either with or without pretreatment with the pan-caspase inhibitor, z-VAD-fmk (ZVAD), or the more selective caspase inhibitors z-IETD-fmk (IETD), z-LEHD-fmk (LEHD), and z-DEVD-fmk (DEVD). Flow cytometry was used to examine alterations in viability, cell size, plasma membrane potential (PMP), mitochondrial membrane potential (DeltaPsi(mito)), intracellular Na(+) and K(+) concentrations, and DNA degradation. Processing of pro-caspases 3, 8, and 9 and the pro-apoptotic protein Bid was determined by Western blotting. UV-C irradiation of Jurkat cells resulted in characteristic apoptosis within 6 h after treatment and pretreatment of cells with ZVAD blocked these features. In contrast, pretreatment of the cells with the more selective caspase inhibitors under conditions that effectively blocked DNA degradation and inhibited caspase 3 and 8 processing as well as Bid cleavage had little protective effect on the other apoptotic characteristics examined. Thus, both intrinsic and extrinsic pathways are activated during UV-induced apoptosis in Jurkat cells and this redundancy appears to assure cell death during selective caspase inhibition.     

Induction of apoptosis in macrophages by cationic liposomes

The effects of liposomes on apoptosis in macrophages were evaluated from DNA content and DNA fragmentation. Cationic liposomes composed of different kinds of cationic lipids induced apoptosis in mouse splenic macrophages and the macrophage-like cell line, RAW264.7 cells. Generation of reactive oxygen radicals from macrophages treated with cationic liposomes was detected using flow cytometry, and further apoptosis was inhibited by the addition of oxidant scavenger, N-acetylcysteine. From these findings, the production of reactive oxygen species may be important in the regulation of apoptosis induced by cationic liposomes.     

PS exposure increases the susceptibility of cells to fusion with DOTAP liposomes

Cationic liposomes are used as efficient carriers for gene delivery into mammalian cells due to their ability to bind nucleic acids, adsorb onto the cell surface and fuse with negatively charged membranes. This last property enables the release and escape of their cargo from endosomal compartments. The efficiency of this fusion mainly depends on the surface charge of the target membranes. Here, we report that cells of two different lines, epithelial adenocarcinoma HeLa and lymphocytic leukemia Jurkat T, which externalize PS, are more susceptible to fusion with DOTAP liposomes than control cells. We compared the ability to undergo fusion of untreated and apoptotic cells. Apoptosis was induced by various pro-apoptotic agents and treatments, namely: incubation in the presence of MnCl(2), cytostatic drugs fludarabine and mitoxantrone, staurosporine and serum depletion in the case of HeLa cells. Jurkat T cells were treated similarly except apoptosis was additionally induced by incubation in the presence of 4% EtOH. Epithelial cells fused with the highest efficiencies of lipid mixing, when pretreated with staurosporine. Jurkat T cells were less susceptible to fusion, but they also displayed an increase in fusion efficiency after the induction of apoptosis. Alternatively, we treated the cells with metabolic inhibitors causing ATP-depletion in order to inactivate aminophospholipid translocase. After ATP-depletion, HeLa and Jurkat T cells fused with DOTAP liposomes with higher efficiencies than control cells. Our conclusion is that the lipid asymmetry of natural membranes may limit fusion with cationic liposomes.     

Characterization of cationic liposomes. Influence of the bilayer composition on the kinetics of the liposome breakdown

The cationic large unilamellar mixed liposomes from 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC) and didodecyldimethylammonium bromide (DDAB) or dioctadecyldimethylammonium bromide (DODAB) were prepared. The influence of the addition of Triton X-100 (TX-100) or octaethylene glycol mono-n-dodecylether (C₁₂E₈) on the membrane integrity was investigated turbidimetrically. The stability of the liposomal systems was estimated by monitoring fluorimetrically at 25 °C the rate of spontaneous and surfactant-induced release of entrapped 5(6)-carboxyfluorescein (CF). In order to evaluate the interaction of the cationic DODAB guest with the host POPC membrane, the main phase transition temperatures (T_m) were determined by electron paramagnetic resonance spectroscopy (EPR). All the results obtained show that the presence of DODAB and DDAB stabilizes the POPC liposomes. The extent of stabilization depends on the concentration and nature of the cationic guest.     

Spectroscopic characterization of DMPC/DOTAP cationic liposomes and their interactions with DNA and drugs

Gene and synthetic drug-delivery vectors have been developed and characterized to treat several genetic diseases and cancers. Our study aims at characterizing cationic liposomes containing the zwitterionic phospholipid DMPC and the cationic lipid DOTAP as well as their interactions with two types of DNA and a new class of antineoplastic agents derived from arylchloroethylureas (CEU). Results obtained using FTIR spectroscopy as well as ³¹P and ²H NMR indicate that DMPC and DOTAP form cationic liposomes in a highly disordered fluid phase at a molar ratio of 1:1. In addition, the FTIR results indicate that the presence of DNA or CEUs within the liposomes does not significantly affect the conformational order of both the DMPC and DOTAP acyl chains. Our results therefore provide a detailed characterization of complexes between cationic liposomes and both DNA and drugs and indicate that these complexes are stable and fluid assemblies.     

Involvement of protein kinase Cδ in induction of apoptosis by cationic liposomes in macrophage-like RAW264.7 cells

We have recently demonstrated that reactive oxygen species (ROS) play an important role in RAW264.7 cell apoptosis induced by cationic liposomes composed of stearylamine (SA-liposomes). In this study, we investigated whether protein kinase Cδ PKCδ) is involved in apoptosis induced by cationic liposomes. Tyrosine phosphorylation, nuclear localization, and cleavage of PKCδ were observed following the treatment of cells with SA-liposomes, suggesting that SA-liposomes activate PKCδ. Rottlerin, a specific inhibitor of PKCδ, inhibited ROS generation and also suppressed apoptosis. Cell surface proteoglycans may contribute to PKCδ activation by SA-liposomes. These findings suggest that PKCδ is strongly associated with apoptosis induced by SA-liposomes.     

Nano-chemotherapy using cationic liposome that strategically targets the cell membrane potential of pancreatic cancer cells with negative charge

Negatively charged phosphatidylserine (PS) and sialic acid-containing glycosphingolipids (GM1) were observed to be over represented on the cell membranes of pancreatic cancer cells (BxPC-3) as opposed to normal pancreatic cells. Cationic liposomes (CL) were also found to selectively accumulate into the negatively charged cell membranes of BxPC-3 cells and inhibited their growth but have no effect on the viability of normal pancreatic cells. CL induced apoptosis in BxPC-3 cells via activation of caspase-3, -8, and -9 and mitochondrial events and inhibited tumor enlargement in xenograft mouse models of pancreatic cancer.     

Binding of antibodies in liposomes to extracellular matrix antigens

We have incorporated antibodies against fibronectin or laminin into liposomes and studied their interaction with insoluble forms of these antigens. The antibodies, after modification by palmitoylchloride, were incorporated into the lipid bilayer by the cholate dialysis method. The antibodies in the liposomes recognized their specific antigen with little reaction to the alternative attachment protein or to albumin (less than 2%). The binding of antibody-containing liposomes to insoluble antigen was inhibited by soluble antibodies to the respective antigens but not by antibodies to other antigens. The affinity constant of the liposome-antibody complex with the antigen was estimated at 1-10 X 10(-9) M liposomes. Thus, antibodies in liposomes retain their reactivity and specificity, and the reaction constant is comparable to that observed for immune complexes.     

Calorimetric study of the interaction of binary DMTAP/DOTAP cationic liposomes with plasmid DNA

Cationic liposomes have been suggested as possible agents for nonviral gene transfer. The interaction of plasmid DNA (pDNA) with dispersions of stable unilamellar cationic liposomes based on the binary lipid system 1,2-dimyristoyl-3-trimethyl-ammonium-propane (DMTAP):1,2-dioleoyl-3-trimethyl-ammonium-propane (DOTAP) has been studied by using isothermal titration calorimetry (ITC), high-precision differential scanning calorimetry (DSC), dynamic light scattering (DLS), and circular dichroism (CD). Systematic calorimetric and DLS exploration of the DMTAP:DOTAP binary system reveals that single-bilayer liposomes are stable at the 4:1 molar ratio, exhibiting the main lipid-phase transition temperature at ~25.3°C, and a total enthalpy change δH = 8.5 ± 0.4 kcal/mol. The interaction of pDNA with unilamellar DMTAP:DOTAP vesicles was investigated by ITC experiments, which clearly distinguished endothermic binding between the phosphate and the ammonium groups from exothermic processes, driven by slow kinetics, corresponding to interliposomal, DNA-triggered aggregation that leads to the formation of large multilamellar liposome/pDNA assemblies. Lipid-added-to-pDNA and pDNA-added-to-lipid experiments have been carried out in order to systematically explore the interaction mechanisms. Complex ITC profiles are revealed, which may be linked to packing rearrangements of the pDNA molecules bound at the outer liposomal surface, possibly due to binding to more than one liposome or due to p-DNA-enhanced heterogeneity in the local lipid concentration. DNA-mediated aggregation effects are detected at high [ammonium]/[phosphate] molar ratios in the case of lipid-added-to-pDNA interactions and at relatively low [phosphate]/[ammonium] molar ratios in the case of pDNA-added-to-lipid.     

Cationic liposomes produced via ethanol injection method for dendritic cell therapy

Cationic liposomes can be designed and developed in order to be an efficient gene delivery system for mammalian cells. Dendritic cell (DC) vaccines can be used to treat cancer, as cationic liposomes can deliver tumor antigens to cells while cells remain active. However, most methods used for liposome production are not able to reproduce in large scale the physicochemical and biological properties of liposomes produced in laboratory scale. In this context, ethanol injection method achieved promising results, although requiring post-treatment for size reduction and/or to remove residual ethanol. Thus, the purpose of this study was to generate cationic liposomes suitable for gene therapies via ethanol injection method in only one step (VEI) and compared to those submitted to a size reduction processes by microfluidization (MFV). For this, the method to produce cationic liposomes composed of egg phosphatidylcholine (EPC), 1,2-dioleoyl-3-trimethylammonium propane (DOTAP) and 1,2-dioleoylphosphatidylethanolamine (DOPE) was optimized using a statistical design approach. As a result, the size of VEI decreased from 290?nm to 110?nm and the polydispersity from 0.54 to 0.17. In the case of MFV, size decreased from 128?nm to 107?nm and polydispersity from 0.40 to 0.18. ST and MFV before and after optimization were also characterized in terms of morphology by transmission electron microscopy (TEM) and structure by differential scanning calorimetry (DSC). Finally, to show their potential in gene/immune therapies applications, DCs were stimulated by such liposomes. Cells internalized liposomes, increasing expression of the costimulatory molecule CD86 and inducing T lymphocyte proliferation.     

Enzyme-assisted photosensitization activates different apoptotic pathways in Rose Bengal acetate treated HeLa cells

Photosensitization of tumor cells after incubation with Rose Bengal acetate (RB-Ac) induces multiple organelle photodamage followed by apoptotic cell death. We used immunocytochemical techniques in multicolor fluorescence microscopy to elucidate whether this occurs through the simultaneous activation of different apoptotic pathways, in HeLa cells. We detected in situ the activated forms of caspases 9 and 3, and the translocation from the mitochondria to the nucleus of the apoptosis inducing factor; DNA electrophoretic techniques were also used to assess the occurrence of nuclear DNA cleavage into either high- or low-molecular-weight fragments. Both the caspase-dependent and caspase-independent apoptotic pathways are activated. The genomic DNA is degraded into high molecular weight molecules only, without the formation of oligonucleosome-sized fragments. The ability of RB-Ac to induce the simultaneous release of apoptogenic signals from different photodamaged organelles makes it an especially powerful cytotoxic agent.     

Binding of 124-kilodalton oat phytochrome to liposomes and chloroplasts

Binding of the radio-iodinated 124-kDa oat ( Avena sativa L. cv. Garry) phytochrome to liposomes and chloroplasts was investigated as a model system in order to understand the molecular affinity of phytochrome toward cellular organelles in plants. The binding of intact (124 kDa) phytochrome to liposomes and chloroplasts is hydrophobic in nature, as in the case of the degraded (118/114 kDa) phytochrome, but electrostatic interactions play a greater role in the intact phytochrome. The physiologically active P_fr form of the intact phytochrome showed a binding preference over the inactive P_r form with neutral liposomes and chloroplasts. However, the P_fr form of intact phytochrome exhibits smaller binding preference than the P_fr form of degraded phytochrome over their respective P_r forms (see Kim, I.-S. and Song, P.-S. 1981, Biochemistry 20: 5482–5489, for degraded phytochrome binding). These results indicate that the 6/10 kDa N-terminus segment, which is lost in the degraded phytochrome, plays an important role in determining the protein surface properties of the intact phytochrome. A competitive binding study on phytochrome also suggested that the P_fr form had a greater binding affinity for chloroplasts than the P_r form. However, the physiological activity of the P_fr form may not be explained simply by the observed difference in binding affinity between the two forms of phytochrome.     

Binding and photocleavage of cationic porphyrin-phenylpiperazine hybrids to DNA

The binding properties of cationic porphyrin-phenylpiperazine hybrids to calf thymus (CT) DNA were investigated by using absorption, fluorescence and circular dichroism (CD) spectra, and the apparent affinity binding constants (K(app)) of the porphyrins for CT DNA were determined by using a competition method with ethidium bromide (EB). Intercalation of porphyrin into CT DNA occurred when two phenylpiperazines were introduced at cis position onto the periphery of cationic porphyrin. The photocleavages of pBR322 plasmid DNA by the porphyrins were consistent with the values of K(app). With [porphyrin]/[DNA base pairs] ratio increased, the binding mode tended to be outside binding, and the cleavage abilities of the porphyrins varied. In the presence of sodium azide, a quencher of 1O2, the cleavage of DNA by the porphyrin of intercalation was less inhibited.     

Plasmid DNA activates murine macrophages to induce inflammatory cytokines in a CpG motif-independent manner by complex formation with cationic liposomes

Plasmid DNA (pDNA) is very important in non-viral gene therapy and DNA vaccination. Unmethylated CpG motifs in bacterial DNA, but not in vertebrate DNA, are known to trigger an inflammatory response, which inhibits gene expression while improving immunological consequences. In this report, we investigated the cytokine secretion induced by pDNA/cationic liposome complexes using murine macrophages. Naked CpG DNA induced tumor necrosis factor-alpha (TNF-alpha) secretion from the macrophages, but DNA without CpG motif did not, demonstrating that the cytokine induction was mediated by CpG motifs. pDNA complexed with cationic liposomes, but not the cationic liposomes alone, produced a significant amount of TNF-alpha from the macrophages. Surprisingly, methylated pDNA and calf thymus DNA complexed with the cationic liposomes were also able to induce TNF-alpha production, indicating that these responses were not dependent on CpG motifs. Taken together, the present study demonstrated that for the first time DNA can stimulate murine macrophages in a CpG motif-independent manner when it is complexed with the cationic liposomes.