Phosphatidylethanolamine Liposomes Research Articles

The Use of Mannose-Grafted and Lipopetide-Conjugated PE Liposomes in the Delivery of Docetaxel for the Treatment of Glioblastoma Multiforme: A Research Protocol

Introduction: One of the biggest obstacles in delivering anti-cancer drugs to brain tumours is the penetration of the blood-brain barrier. Docetaxel is a promising drug used for glioblastoma multiforme that works by promoting mitotic arrest and cell death of tumorous cells, yet it encounters this obstacle presented by the selectivity of the blood-brain barrier. Due to the barrier’s highly selective nature and the imprecision of current cancer treatments, the use of nanoparticles in drug delivery has been an area of significant interest. To address these issues, we propose using mannose and lipopeptide-grafted phosphatidylethanolamine liposomes as a drug delivery mechanism to effectively eliminate the obstacle of penetrating the blood-brain barrier in the treatment of glioblastomas. The truncated fibroblast growth factor and GALA lipopeptides increase the precision of the chemotherapeutic agent in targeting the tumour cells. Simultaneously, the mannose allows the nanoparticle to be recognized by sugar receptors on the blood-brain barrier, enabling it to pass through. This novel drug delivery system broadens the variety and increases the effectiveness of anti-tumoral drugs used in the treatment of brain cancer. Methods: The lipopeptides are prepared through pyridyl disulfide reactions. The phosphatidylethanolamine liposomes are prepared using standard thin-film hydration in which the lipopeptides, docetaxel, and calcein (to track the drug delivery) are incorporated into the liposomal lumen. Mannose is then grafted onto the liposomal surfaces through the covalent coupling of p-aminophenyl-D-glycosides to phosphatidylethanolamine liposomes. The synthesized liposomes would be administered intravenously alongside radiation. Statistical analyses will be conducted to measure the growth of the tumour and the accuracy of drug delivery. Discussion: The tumour cells should display a greater level of fluorescence, indicating a more accurate administration of the drug. It is expected that the patients will respond favourably to the treatment with the tumorous tissues showing a reduced growth rate and greater bioavailability of the drug. Conclusion: The liposomal drug delivery mechanism presents a novel method by which anti-tumoral drugs can both cross the blood-brain barrier and precisely target the tumorous mass, thereby reducing the risk of drugs getting lost within the vasculature and expanding the horizons for brain tumour prognoses.

Abstract 15904: Echogenic Immunoliposome-targeted Mesenchymal Stem Cells for Imaging and Treatment of Atheroma

Background: Vascular stem cell dead impairs the regenerating capacity of the arterial wall with atherosclerosis. A patented technology has been developed to employ biofunctional echogenic immunoliposomes (BF-ELIP) for enhancing entry of stem cells to atherosclerotic lesions. Objective: Determine whethere ultrasound-enhanced delivery of BF-ELIP-targeted stem cells visualize and treat atheroma simultaneously. Methods and Results: BF-ELIP were prepared by conjugating thiolated antibodies specific for the mesenchymal marker CD146 and murine ICAM-1 to phosphatidyl-ethanolamine liposomes through a thioether linkage. CD146 + bone marrow-derived mesenchymal cells (BM-MSC) were prepared from green fluorescence protein (GFP)-transgenic mice. By fluorescence microscopy, BF-ELIP targeted CD146 + cells were clearly visualized being adherent on cultured human endothelial cells that expressed ICAM-1 induced by tumor necrosis factor alpha (TNF-α) (Fig. 1a). BM-MSC/BF-ELIP mixtures were intravenously injected into ApoE-/- mice (n=9). Ultrasound illustrated intense echo signals of BF-ELIP in the aortic arch 15 min after injection of the BM-MSC/BF-ELIP preparation into ApoE-knockout mice (Fig. 1b). Histopathology of the aorta analyzed by H&E and Oil-Red O staining of aortic sections showed that the BF-ELIP targeted MSC delivery reduced plaque sizes, inflammation and lipid loading. Neither normal wild type C57BL/6J nor ApoE-knockout mice without injection showed the intensified echo signals and histological changes in their aortic arch regions. Conclusions: BF-ELIP enhancement of vascular stem cell adherence to inflammatory endothelium facilitates vulnerable plaque detection and targeted stem cell therapy for atheroma. This proof of concept study illustrates on the development of ultrasound-enhanced, BF-ELIP-mediated stem cell delivery and therapeutic approach to stabilize atheroma.

Integration of Quercetin-Iron Complexes into Phosphatidylcholine or Phosphatidylethanolamine Liposomes.

It is well known that flavonoids can chelate transition metals. Flavonoid-metal complexes exhibit a high antioxidative and therapeutic potential. However, the complexes are frequently hydrophobic ones and low soluble in water, which restricts their medical applications. Integration of these complexes into liposomes may increase their bioavailability and therapeutic effect. Here, we studied the interaction of quercetin-iron complexes with dimyristoylphosphatidylcholine (DMPC) or palmitoyl-oleoyl phosphatidylethanolamine (POPE) multilamellar liposomes. Differential scanning calorimetry (DSC) and freeze-fracture electron microscopy revealed that quercetin-iron complexes did not interact with liposomes. Quercetin however could penetrate lipid bilayers, when added to liposomes at a temperature above lipid melting. Iron cations added later penetrated into the lipid bilayers and produced complexes with quercetin in the liposomes. The quercetin-iron entry in POPE liposomes was improved when the suspension was heated above the temperature of the bilayer-hexagonal HII phase transition of the lipid. The approach proposed facilitates the integration of quercetin-iron complexes into liposomes and may promote their use in medicine.

Transport Rates of a Glutamate Transporter Homologue Are Influenced by the Lipid Bilayer

The aspartate transporter from Pyrococcus horikoshii (GltPh) is a model for the structure of the SLC1 family of amino acid transporters. Crystal structures of GltPh provide insight into mechanisms of ion coupling and substrate transport; however, structures have been solved in the absence of a lipid bilayer so they provide limited information regarding interactions that occur between the protein and lipids of the membrane. Here, we investigated the effect of the lipid environment on aspartate transport by reconstituting GltPh into liposomes of defined lipid composition where the primary lipid is phosphatidylethanolamine (PE) or its methyl derivatives. We showed that the rate of aspartate transport and the transmembrane orientation of GltPh were influenced by the primary lipid in the liposomes. In PE liposomes, we observed the highest transport rate and showed that 85% of the transporters were orientated right-side out, whereas in trimethyl PE liposomes, 50% of transporters were right-side out, and we observed a 4-fold reduction in transport rate. Differences in orientation can only partially explain the lipid composition effect on transport rate. Crystal structures of GltPh revealed a tyrosine residue (Tyr-33) that we propose interacts with lipid headgroups during the transport cycle. Based on site-directed mutagenesis, we propose that a cation-π interaction between Tyr-33 and the lipid headgroups can influence conformational flexibility of the trimerization domain and thus the rate of transport. These results provide a specific example of how interactions between membrane lipids and membrane-bound proteins can influence function and highlight the importance of the role of the membrane in transporter function.

The grape aquaporin VvSIP1 transports water across the ER membrane

Water diffusion through biological membranes is facilitated by aquaporins, members of the widespread major intrinsic proteins (MIPs). In the present study, the localization, expression, and functional characterization of a small basic intrinsic protein (SIP) from the grapevine were assessed. VvSIP1 was expressed in leaves and berries from field-grown vines, and in leaves and stems from in vitro plantlets, but not in roots. When expressed in tobacco mesophyll cells and in Saccharomyces cerevisiae, fluorescent-tagged VvSIP1 was localized at the endoplasmic reticulum (ER). Stopped-flow spectroscopy showed that VvSIP1-enriched ER membrane vesicles from yeast exhibited higher water permeability and lower activation energy for water transport than control vesicles, indicating the involvement of protein-mediated water diffusion. This aquaporin was able to transport water but not glycerol, urea, sorbitol, glucose, or inositol. VvSIP1 expression in Xenopus oocytes failed to increase the water permeability of the plasma membrane. VvSIP1-His-tag was solubilized and purified to homogeneity from yeast ER membranes and the reconstitution of the purified protein in phosphatidylethanolamine liposomes confirmed its water channel activity. To provide further insights into gene function, the expression of VvSIP1 in mature grapes was studied when vines were cultivated in different field conditions, but its transcript levels did not increase significantly in water-stressed plants and western-exposed berries. However, the expression of the aquaporin genes VvSIP1, VvPIP2;2, and VvTIP1;1 was up-regulated by heat in cultured cells.

Development of Phosphatidylethanolamine Liposomes That Efficiently Retain Encapsulated Vinorelbine Bitartrate

A hydrophilic and temperature-induced degradation drug, vinorelbine bitartrate (VB)-loaded phosphatidylethanolamin sterically stabilized liposomes (PSLs) were prepared by the thin film hydration method. Liposomes were made of phosphatidylethanolamine: cholesteryl: oleic acid (PE: CHOL: OA, 6:4:3 mass/mass). The mean particle size of the PSLs ranged from 600 to 650 nm. The transmission electron microscope (TEM) images displayed that the shape of the PSLs was multilamellar vesicles with smooth surface. The highest entrapment efficiency (EE) and drug loading capacity (DL) could reach up to 81.2 and 16.6%, respectively. The studies of drug release showed that the drug release could last for much more than 48 hours. The PSLs was evaluated by comparing the rate of release of encapsulated VB in different phosphate buffer solution (PBS).

Membrane surface charge dictates the structure and function of the epithelial Na+/H+exchanger

The Na(+)/H(+) exchanger NHE3 plays a central role in intravascular volume and acid-base homeostasis. Ion exchange activity is conferred by its transmembrane domain, while regulation of the rate of transport by a variety of stimuli is dependent on its cytosolic C-terminal region. Liposome- and cell-based assays employing synthetic or recombinant segments of the cytosolic tail demonstrated preferential association with anionic membranes, which was abrogated by perturbations that interfere with electrostatic interactions. Resonance energy transfer measurements indicated that segments of the C-terminal domain approach the bilayer. In intact cells, neutralization of basic residues in the cytosolic tail by mutagenesis or disruption of electrostatic interactions inhibited Na(+)/H(+) exchange activity. An electrostatic switch model is proposed to account for multiple aspects of the regulation of NHE3 activity.

Crystal structure of the receptor binding domain of the botulinum C–D mosaic neurotoxin reveals potential roles of lysines 1118 and 1136 in membrane interactions

The botulinum neurotoxins (BoNTs) produced by different strains of the bacterium Clostridium botulinum are responsible for the disease botulism and include a group of immunologically distinct serotypes (A, B, E, and F) that are considered to be the most lethal natural proteins known for humans. Two BoNT serotypes, C and D, while rarely associated with human infection, are responsible for deadly botulism outbreaks afflicting animals. Also associated with animal infections is the BoNT C–D mosaic protein (BoNT/CD), a BoNT subtype that is essentially a hybrid of the BoNT/C (∼two-third) and BoNT/D (∼one-third) serotypes. While the amino acid sequence of the heavy chain receptor binding (HCR) domain of BoNT/CD (BoNT/CD-HCR) is very similar to the corresponding amino acid sequence of BoNT/D, BoNT/CD-HCR binds synaptosome membranes better than BoNT/D-HCR. To obtain structural insights for the different membrane binding properties, the crystal structure of BoNT/CD-HCR (S867-E1280) was determined at 1.56Å resolution and compared to previously reported structures for BoNT/D-HCR. Overall, the BoNT/CD-HCR structure is similar to the two sub-domain organization observed for other BoNT HCRs: an N-terminal jellyroll barrel motif and a C-terminal β-trefoil fold. Comparison of the structure of BoNT/CD-HCR with BoNT/D-HCR indicates that K1118 has a similar structural role as the equivalent residue, E1114, in BoNT/D-HCR, while K1136 has a structurally different role than the equivalent residue, G1132, in BoNT/D-HCR. Lysine-1118 forms a salt bridge with E1247 and may enhance membrane interactions by stabilizing the putative membrane binding loop (K1240-N1248). Lysine-1136 is observed on the surface of the protein. A sulfate ion bound to K1136 may mimic a natural interaction with the negatively changed phospholipid membrane surface. Liposome-binding experiments demonstrate that BoNT/CD-HCR binds phosphatidylethanolamine liposomes more tightly than BoNT/D-HCR.

Encapsulation of Essential Oils within a Polymeric Liposomal Formulation for Enhancement of Antimicrobial Efficacy

Essential oils and their constituents are known to possess antimicrobial activity; however, their inherent volatility is a limiting factor. In order to exploit the antimicrobial efficacy of essential oils, encapsulation within polymeric liposomal systems was undertaken. The liposomes were subsequently polymer-coated in order to further enhance the stability of the formulations. Essential oils distilled from Artemisia afra, Eucalyptus globulus and Melaleuca alternifolia were encapsulated into diastearoyl phosphatidylcholine and diastearoyl phosphatidylethanolamine liposomes employing a reverse phase evaporation methodology. A polyelectrolyte coating was then applied via the layer-by-layer self-deposition technique. A batch of the liposomes was polymer-coated with a 0.15%w/v chitosan solution. Using the minimum inhibitory concentration assay, the liposome-encapsulated, unencapsulated and polymer-coated liposome-encapsulated essential oils were compared in order to observe whether the antimicrobial efficacy was improved with encapsulation and polymer coating. Fractional inhibitory concentrations (FICs) were calculated in order to determine the antimicrobial interactions amongst the lipoid components, polymer coating and essential oils (synergistic, additive, indifferent and antagonistic interactions). With the exception of A. afra, microbial growth was inhibited at lower concentrations for the encapsulated formulations in comparison with the nonencapsulated oils. Synergistic to additive interactions were noted for encapsulated E. globulus (sigmaFIC values 0.25-0.45) and M alternifolia (sigmaFIC values 0.26-0.52) formulations. The addition of the polymer coating did not enhance antimicrobial activity, but owing to their positive effects on membrane stability, its presence is important as a means of extending the shelf life of these formulations. Additionally, the presence of the polymeric coating availed the essential oil at a slower rate. This investigation is a stepping stone towards the promotion of the antimicrobial use of essential oils. The added benefits are that essential oils not only provide effective antimicrobial efficacy, but also promote a "greener" consumerism. Within liposomes, they will enhance dermato-cosmetic properties and increase the marketing image of the final product.

Lipid Composition Regulates the Orientation of Transmembrane Helices in HorA, an ABC Multidrug Transporter

ATP-binding cassette (ABC) transporters constitute a large class of molecular pumps whose central role in chemotherapy resistance has highlighted their clinical relevance. We investigated whether the lipid composition of the membrane affects the function and structure of HorA, a bacterial ABC multidrug transporter. When the transporter was reconstituted in a bilayer where phosphatidylethanolamine (PE), the main lipid of the bacterial membrane, was replaced with phosphatidylcholine (PC), ATP hydrolysis and substrate transport became uncoupled. Although ATPase activity was maintained, HorA lost its ability to extrude the prototypical substrate Hoechst33342. Attenuated Total Reflection-Fourier Transform Infrared spectroscopy (ATR-FTIR) revealed that, although the secondary structure of the protein was unaffected, the orientation of the transmembrane helices (TM) was modified by the change in lipid composition. The orientation of the backbone carbonyls indicated that the helices opened wider in PE versus PC-containing liposomes, with 10 degrees difference. This was supported by hydrogen/deuterium exchange studies showing increased protection of the backbone from the solvent in PC-containing liposomes. Electron Paramagnetic Resonance was used to further probe the structural change. In the PC-containing liposomes we observed increased mobility of the spin label in TM4, along with increased exposure to molecular oxygen, used as a hydrophobic quencher. This indicates that the lipid change induced modification of the orientation of TM4, exposing Cys-180 to the lipid phase. The lipid composition of the bilayer thus modulates the structure of HorA, and in turn its ability to extrude its substrates.

Physiological pH and Acidic Phospholipids Contribute to Substrate Specificity in Lipidation of Atg8

Yeast Atg8 and its mammalian homolog LC3 are ubiquitin-like proteins involved in autophagy, a primary pathway for degradation of cytosolic constituents in vacuoles/lysosomes. Whereas the lipid phosphatidylethanolamine (PE) was identified as the sole in vivo target of their conjugation reactions, in vitro studies showed that the same system can mediate the conjugation of these proteins with phosphatidylserine as efficiently as with PE. Here, we show that, in contrast to PE conjugation, the in vitro phosphatidylserine conjugation of Atg8 is markedly suppressed at physiological pH. Furthermore, the addition of acidic phospholipids to liposomes also results in the preferential formation of the Atg8-PE conjugate. We have successfully captured authentic thioester intermediates, allowing us to elucidate which step in the conjugation reaction is affected by these changes in pH and membrane lipid composition. We propose that these factors contribute to the selective formation of Atg8-PE in the cell.

Surface plasmon resonance analysis of botulinum neurotoxin binding for lipid receptors

Botulinum neurotoxins (BoNTs) are the most potent protein toxins. There are seven serotypes of BoNTs, termed A to G (BoNT/A to BoNT/G). The carboxyl-terminal half of the heavy chain (Hc) of the neurotoxin recognizes its specific receptor on the plasma membrane. We have previously demonstrated that BoNT/C binds to gangliosides GD1b and GT1b under physiological conditions, while BoNT/D interacts with phosphatidylethanolamine (PE). In this study, the binding specificities of BoNT-Hc for GT1b or PE were determined by surface plasmon resonance (SPR) using a receptor-including liposome. Unlike microtiter plate and thin layer chromatography overlay assays, the SPR/liposome methodology allows for real-time analysis of toxin binding under conditions that mimic the natural cell surface of these interactions and without any requirement for labeling of toxin or receptor. BoNT/C-Hc showed the binding specificity to GT1b liposome but not PE liposome. On the other hand, BoNT/D-Hc bound to only PE liposome. The SPR analysis also yielded rate and affinity constants which are not attainable by conventional assays. Complex binding profiles were observed in that the association and dissociation rate constants. The affinities of BoNTs for liposome-anchored gangliosides or PE were attributable largely to very fast dissociation rate constants. The SPR/liposome analysis should have general applicability in the study of lipid–protein interactions.

Enzyme-induced shedding of a poly(amino acid)-coating triggers contents release from dioleoyl phosphatidylethanolamine liposomes

The enzymatically degradable poly(amino acid)–lipid conjugate poly(hydroxyethyl l-glutamine)– N-succinyl-dioctadecylamine (PHEG–DODASuc) has been shown to effectively prolong liposome circulation times. In this paper, we investigated whether PHEG–DODASuc can stabilize liposomes composed of the fusogenic, non-bilayer-forming lipid dioleoyl phosphatidylethanolamine (DOPE). Moreover, we evaluated the release of an entrapped compound after enzyme-induced shedding of the PHEG-coating, interbilayer contact and membrane destabilizing phase changes. Contents release was monitored using the fluorescent model compound calcein. Liposome destabilization and lipid mixing was studied by dynamic light scattering (DLS), fluorescence resonance energy transfer (FRET) and cryogenic-temperature transmission electron microscopy (cryo-TEM). It was shown that PHEG–DODASuc is able to stabilize DOPE-based liposomes and that contents release can be triggered by shedding of the PHEG-coating.

An Hg-sensitive channel mediates the diffusional component of glucose transport in olive cells

In several organisms solute transport is mediated by the simultaneous operation of saturable and non-saturable (diffusion-like) uptake, but often the nature of the diffusive component remains elusive. The present work investigates the nature of the diffusive glucose transport in Olea europaea cell cultures. In this system, glucose uptake is mediated by a glucose-repressible, H +-dependent active saturable transport system that is superimposed on a diffusional component. The latter represents the major mode of uptake when high external glucose concentrations are provided. In glucose-sufficient cells, initial velocities of d- and l-[U- 14C]glucose uptake were equal and obeyed linear concentration dependence up to 100 mM sugar. In sugar starved cells, where glucose transport is mediated by the saturable system, countertransport of the sugar pairs 3- O-methyl- d-glucose/ d-[U- 14C]glucose and 3- O-methyl- d-glucose/3- O-methyl- d-[U- 14C]glucose was demonstrated. This countertransport was completely absent in glucose-sufficient cells, indicating that linear glucose uptake is not mediated by a typical sugar permease. The endocytic inhibitors wortmannin-A and NH 4Cl inhibited neither the linear component of d- and l-glucose uptake nor the absorption of the nonmetabolizable glucose analog 3- O-methyl- d-[U- 14C]glucose, thus excluding the involvement of endocytic mediated glucose uptake. Furthermore, the formation of endocytic vesicles assessed with the marker FM1–43 proceeded at a very slow rate. Activation energies for glucose transport in glucose sufficient cells and plasma membrane vesicles were 7 and 4 kcal mol − 1 , respectively, lower than the value estimated for diffusion of glucose through the lipid bilayer of phosphatidylethanolamine liposomes (12 kcal mol − 1 ). Mercury chloride inhibited both the linear component of sugar uptake in sugar sufficient cells and plasma membrane vesicles, and the incorporation of the fluorescent glucose analog 2-NBDG, suggesting protein-mediated transport. Diffusive uptake of glucose was inhibited by a drop in cytosolic pH and stimulated by the protein kinase inhibitor staurosporine. The data demonstrate that the low-affinity, high-capacity, diffusional component of glucose uptake occurs through a channel-like structure whose transport capacity may be regulated by intracellular protonation and phosphorylation/dephosphorylation.

Conformational changes in a bacterial multidrug transporter are phosphatidylethanolamine-dependent.

LmrP is an electrogenic H(+)/drug antiporter that extrudes a broad spectrum of antibiotics. Five carboxylic residues are implicated in drug binding (Asp142 and Glu327) and proton motive force-mediated restructuring (Asp68, Asp128 and Asp235). ATR-FTIR (Attenuated Total Reflection - Fourier Transform Infrared) and tryptophan quenching experiments revealed that phosphatidylethanolamine (PE) is required to generate the structural intermediates induced by ionization of carboxylic residues. Surprisingly, no ionization-induced conformational changes were detectable in the absence of PE, suggesting either that carboxylic acid residues do not ionize or that ionization does not lead to any conformational change. The mean pKa of carboxylic residues evaluated by ATR-FTIR spectroscopy was 6.5 for LmrP reconstituted in PE liposomes, whereas the pKa calculated in the absence of PE was 4.6. Considering that 16 of the 19 carboxylic residues are located in the extramembrane loops, the pKa values obtained in the absence and in the presence of PE suggest that the interaction of the loop acid residues with the membrane interface depends on the lipid composition.

Cisplatin encapsulated in phosphatidylethanolamine liposomes enhances the in vitro cytotoxicity and in vivo intratumor drug accumulation against melanomas

Cisplatin is a potent anticancer drug for treating melanoma. The aim of this study was to evaluate the possibility of using liposomes, for intratumoral distribution in a melanoma, composed of phosphatidylethanolamine (PE), for its cytotoxicity. The in vitro drug release, in vitro cytotoxicity against melanoma, and in vivo residence time in the tumor of liposome-encapsulated cisplatin were investigated. The liposomes were prepared and characterized in terms of their morphology, size, zeta potential, and drug loading. The size of the PE liposomes attained a level of approximately 100 nm. The concentration of cisplatin encapsulated in PE liposomes was 50-70% dependent on the presence or absence of polyethylene glycol (PEG) derivatives. On the other hand, no or negligible cisplatin molecules were encapsulated in egg phosphatidylcholine (EPC) liposomes. PE liposomes had higher cytotoxicity than classic liposomes or free cisplatin. Images of confocal laser scanning microscopy confirmed the great potency of PE liposomes to deliver cisplatin into cells. The incorporation of PEG derivatives completely inhibited the proliferation of melanoma cells. With in vivo intratumoral administration, the cisplatin concentration in the tumor tissue was maintained at a high level for 72 h after application of the PE liposomes. The PE liposomes delivered cisplatin into the tumor approximately 3.6 times more efficiently than the free drug. These results demonstrate that PE liposomes represent a potentially useful strategy for targeting cisplatin delivery into melanomas.

Novel therapeutic approaches in pediatric and young adult sarcomas

Novel therapy as part of sarcoma treatment schemas can enhance quality of life and is important in improving outcomes of high-risk sarcomas. Additional chemotherapy and biotherapy options to reduce tumor burden and prevent metastases include intra-arterial chemotherapy in osteosarcoma; intrapleural chemotherapy, aerosol 9-nitrocamptothecin, or protracted irinotecan and temozolomide in Ewing's sarcoma; continuous hyperthermic peritoneal perfusion for malignancy involving the peritoneum, such as desmoplastic small round cell tumor; and ifosfamide with muramyl tripeptide phosphatidyl ethanolamine liposomes in osteosarcoma. These treatments bring improved control of symptoms, including reduction in nausea, mucositis, cardiotoxicity, and central nervous system toxicity. Portable infusion devices have facilitated introduction of outpatient doxorubicin, ifosfamide, and methotrexate regimens and home-infusion irinotecan. Physical approaches to eliminate sarcoma tumors and metastases are critical for durable responses. Novel local control measures include embolization before surgery, radiosensitization, anti-vascular endothelial growth factor therapy during chemo-radiotherapy, proton therapy, samarium, thermal ablation (radiofrequency ablation), and cryoablation.

Relevance of lipid polar headgroups on boron-mediated changes in membrane physical properties

Using liposomes composed of either brain phosphatidylcholine (PC), or binary mixtures of PC and phosphatidylserine (PS), galactolipids (GL), phosphatidylinositol (PI), cardiolipin (CL), phosphatidic acid (PA), or phosphatidylethanolamine (PE), we investigated the effects of graded amounts of boric acid (B, 0.5–1000 μM) on the following membrane physical properties: (a) surface potential, (b) lipid rearrangement through lateral phase separation, (c) fluidity, and (d) hydration. Incubation of the different populations of vesicles with B was associated with a small, but statistically significant, increase in membrane surface potential in PC, PC:PS, PC:GL, PC:PI, PC:PA, and PC:PE liposomes. B-induced lipid lateral rearrangement through lateral phase separation in PC, PC:PA, and PC:PE liposomes; but had no effects on PC:PS, PC:GL, and PC:PI liposomes. In PC liposomes B affected membrane fluidity at the water–lipid interface without affecting the hydrophobic core of the bilayer. In all the other binary liposomes studied, B increased membrane fluidity in both, the hydrophobic portion of the membrane and in the anionic domains. The above was associated with a decrease in the fluidity of the cationic domains. B (10–1000 μM) decreased membrane hydration regardless the composition of the liposomes. The obtained results demonstrate the ability of B to interact with membranes, and induce changes in membrane physical properties. Importantly, the extent of B-membrane interactions and the consequent effects were dependent on the nature of the lipid molecule; as such, B had greater affinity with lipids containing polyhydroxylated moieties such as GL and PI. These differential interactions may result in different B-induced modulations of membrane-associated processes in cells.

Receptor-mediated targeting of lipobeads bearing acetohydroxamic acid for eradication of Helicobacter pylori

In the present context, phosphatidyl ethanolamine (PE) liposomes anchored polyvinyl alcohol (PVA) xerogel beads (lipobeads) bearing acetohydroxamic acid (AHA) was developed as a receptor-mediated drug delivery system for use in blocking adhesion of Helicobacter pylori and thereby preventing the sequelae of chronic gastric infections. PVA beads containing AHA were prepared by emulsification followed by low temperature crystallization method. Surface acylation with fatty acid chain was accomplished by treating PVA bare beads with palmitoyl chloride. The completion of this reaction was characterized by attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) which confirmed the formation of an ester bond. Final formation of lipobeads was accomplished by combining acylated PVA beads with a PE liposome suspension. To confirm the specific binding propensity of lipobeads towards the PE specific surface receptors of H. pylori, we have performed in situ adherence assay and radiolabelling assay with human stomach cells and KATO-III cells, respectively. In both of these studies, pretreatment of H. pylori with lipobeads completely inhibited the adhesion of H. pylori to human stomach cells and KATO-III cells. These assays could serve as suitable in-vitro models for the study of binding efficacy of lipobeads with H. pylori surface receptors . In addition, the antimicrobial activity of the formulations was evaluated by growth inhibition (GI) studies with isolated H. pylori strain. The inhibitory efficacy of lipobeads was significantly higher compared to that of PVA bare beads. These results suggest that lipobeads could be a potential targeted drug delivery system in the treatment of H. pylori.

Mechanism of pH-Triggered Collapse of Phosphatidylethanolamine Liposomes Stabilized by an Ortho Ester Polyethyleneglycol Lipid

The mechanism of pH-triggered destabilization of liposomes composed of a polyethyleneglycol-orthoester-distearoylglycerol lipid (POD) and phosphatidyl ethanolamine (PE) has been studied using an ANTS/DPX leakage and a lipid-mixing assay. We developed a kinetic model that relates POD hydrolysis to liposome collapse. This minimum-surface-shielding model describes the kinetics of the pH-triggered release of POD/PE liposomes. In the model, when acid-catalyzed hydrolysis lowers the mole percentage of POD on the liposome surface to a critical level, intervesicular lipid mixing is initiated, resulting in a burst of contents release. Two phases of content leakage are observed: a lag phase and a burst phase. During the lag phase, less than 20% of liposomal contents are released and the leakage begins to accelerate when approaching to the transition point. During the burst phase, the leakage rate is dependent on interbilayer contact. The burst phase occurs when the surface density of the PEG lipid is 2.3 ± 0.6 mol%, regardless of the pH. Vesicles containing 4 mol% of a pH- insensitive PEG-lipid conjugate and 10% POD did not leak contents or collapse at any pH. These data are consistent with the stalk theory to describe the lamellar-to-inverted hexagonal phase transition and set a lower bound of ∼16 PE lipids on the external monolayer as the contact site required for lipid mixing between two bilayers.