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PubMed1982

Liposomes disposition in vivo. V. Liposome stability in plasma and implications for drug carrier function.

The kinetics of [14C]sucrose release from multilamellar liposomes of fixed diameter (approx. 0.23 micron) incubated in human plasma (serum and blood) were quantified. Composition was various ratios of phosphatidylcholine, phosphatidic acid and cholesterol with alpha-tocopherol included as antioxidant. Considerable intra-individual variability was noted for liposome stability in blood and its derived fluids, yet reproducible results were obtained for pooled samples. The destabilizing effects of plasma decreased with increasing lipid concentrations. Results of fitting a kinetic model to the data showed that four of five model parameters were linearly related to liposome cholesterol content. Liposomes depleted plasma of its destabilizing factors, and when pre-incubated with plasma were partially stabilized to the effects of a subsequent plasma addition. Plasma caused a rapid rise in liposome membrane permeability which then declined non-linearly, presumably because of a rearrangement of membrane lipids and adsorbed proteins to form their most stable configuration. The therapeutic availability of drugs administered encapsulated in liposomes, which can be governed by the kinetics of their in vivo extracellular release, may be directly proportional to--and predictable from--the time-course and extent of release in plasma. The kinetic model was used in conjunction with simple pharmacokinetic assumptions to show that the effectiveness of a liposome drug carrier cannot be predicted based simply on its plasma stability; more stable liposomes may not be more effective drug carriers. Interestingly, plasma-induced solute release from liposomes serendipitously mimics an important facet of ideal carrier behavior.

Cholesterol↗
PubMed2006

Integrity of liposomes in presence of cyclodextrins: effect of liposome type and lipid composition.

Liposome stability during incubation in presence of cyclodextrins (CDs) is studied. Dried-rehydrated vesicle (DRV), multilamellar vesicle (MLV) and small unilamellar vesicle (SUV) calcein-encapsulating liposomes, composed of different lipids are formulated, and retention of calcein is followed during vesicle incubation in hydroxypropyl-beta-CD (HP beta-CD), HP gamma-CD or methyl-beta-CD (Me beta-CD), for 24h. Results demonstrate that liposome integrity in cyclodextrins is affected by lipid composition and type. For the same lipid composition calcein release from vesicles is faster in the order: MLV > DRV > SUV. Me beta-CD influences liposome stability most, compared to the other CD's studied. Vesicles composed of saturated phospholipids were found more stable compared to phosphatidyl-choline (PC) liposomes, suggesting that phospholipid saturation and membrane rigidity influences the interaction between liposomal-lipids and CD molecules. Chol (cholesterol) addition in lipid membrane improves PC-liposome integrity, but has opposite or no effect on liposomes consisting of saturated lipids. Decrease of vesicle dispersion turbidity and size distribution in presence of CD, implies that Me beta-CD induces vesicle disruption and solubilization (to micelles). Turbidity measurements confirm that DRV liposomes are affected more than SUV.

2-Hydroxypropyl-beta-cyclodextrin↗
PubMed1998

The influence of the route of administration and liposome composition on the potential of liposomes to protect tissue against local toxicity of two antitumor drugs.

The present paper reports on the influence of the route of administration and liposome stability on the protective effect of liposome encapsulation of two model antitumor agents, mitoxantrone and doxorubicin. The results demonstrate that liposome encapsulation can protect surrounding tissue from the cytotoxic effects of the drugs after subcutaneous (s.c.) and intramuscular (i.m.) administration. The route of administration is an important factor influencing tissue damage. Liposomal mitoxantrone caused much less tissue irritation after im injection than after s.c. injection. Liposome stability is also an important factor. Liposomes composed of 'fluid-state' phospholipids only delayed the damaging effects of doxorubicin when injected sc. Liposomes with a more rigid nature were much more effective in preventing local tissue damage over a longer period of time when administered sc. Results suggest that slow release of liposome-associated drugs may eventually cause severe local tissue damage. The incorporation of the hydrophilic lipid derivative distearoylphosphatidylethanolamine-poly(ethyleneglycol) (PEG-PE) had no apparent effect on the protective effect of liposomes after sc administration.

Animals↗
PubMed1998

Lymphatic uptake and biodistribution of liposomes after subcutaneous injection . IV. Fate of liposomes in regional lymph nodes.

The ability of clodronate-containing liposomes to deplete lymph nodes of macrophages was used as a tool to investigate the fate of liposomes in regional lymph nodes after subcutaneous (s.c.) administration. Reduced lymph node localization of liposomes in macrophage-depleted lymph nodes confirmed that phagocytosis by macrophages plays an important role in lymph node retention of liposomes. Depletion of macrophages had less effect on lymph node localization of small liposomes than on the lymph node localization of large liposomes. Inclusion of distearoylphosphatidylethanolamine (DSPE)-poly(ethyleneglycol) (PEG-PE) into the liposomes, which is known to oppose macrophage uptake, did not affect lymph node localization in macrophage-depleted or control lymph nodes. We conclude that PEG-liposomes retained by lymph nodes are also taken up by lymph node macrophages. Morphological observations visualizing the uptake of PEG-liposomes by lymph node macrophages support this conclusion.

Animals↗
PubMed1991

Liposome chromatography: liposomes immobilized in gel beads as a stationary phase for aqueous column chromatography.

Liposomes have been used as a stationary phase for column chromatography with an aqueous mobile phase. They were immobilized in the pores of carrier gel beads by two methods: (A) hydrophobic ligands were coupled to the matrix of gel beads, which then were packed into a column and liposomes were applied and became associated with the ligands by hydrophobic interaction; and (B) phospholipids and detergent were dialysed in the presence of gel beads; many of the liposomes that formed in the pores of the beads were sterically immobilized by the gel matrix. Proteoliposomes containing red cell glucose transport protein in the lipid bilayers were immobilized in a column by method A. This column retained D-glucose longer than L-glucose. In contrast to L-glucose, D-glucose was transported into and out of the immobilized liposomes, causing an increased retention. Liposomes with (stearylamine)+ or (phosphatidylserine)- in their lipid bilayers were immobilized by method B and the gel beads were packed into a column. A protein of opposite charge was applied in excess. Under suitable conditions, the protein molecules became close-packed on the liposome surfaces. Ion-exchange chromatographic experiments with proteins showed that these sterically immobilized liposomes were also stable enough to be used as a stationary phase. The loss of lipids was 5-23% in the first run at high protein load and with sodium chloride gradient elution but was lower in subsequent runs. It is proposed that water-soluble molecules can be separated and their interactions with liposome surfaces studied by chromatography on immobilized liposomes in detergent-free aqueous solution. Membrane proteins can be inserted and ligands can be anchored in the lipid bilayers for chromatographic purposes.

Chemical Phenomena↗
PubMed2001

Separation and determination of liposomal and non-liposomal daunorubicin from the plasma of patients treated with Daunoxome.

Several liposomal formulations of anthracyclines have been developed recently and are currently used in the clinical setting. We describe a technique of separation and quantification of the liposomal and non-liposomal forms of daunorubicin in the plasma of patients treated with DaunoXome, a liposomal formulation of daunorubicin. The method we propose is based upon the property of liposomes to cross reversed-phase C18 silicagel cartridges without being retained, while non-liposomal drug is retained on the stationary phase and is eluted with methanol. Extraction of liposomal and non-liposomal daunorubicin from plasma, therefore, is performed in two steps. This technique is rapid, can be automated in order to handle large series of samples, and the plasma can be frozen after sampling by addition of glycerol. The recovery of liposomal daunorubicin as well as the precision, linearity and accuracy of the technique appear satisfactory for pharmacokinetic purposes.

Antibiotics, Antineoplastic↗
PubMed2002

Encapsulation of an antivasospastic drug, fasudil, into liposomes, and in vitro stability of the fasudil-loaded liposomes.

The objectives of this work were to develop a liposomal fasudil, an antivasospastic drug, as a possible means to deliver the encapsulated drug to the brain, and to characterize the stability of the liposomal formulation in vitro. Transmembrane electrochemical gradients of H+ or ammonium sulfate were created, and their effect on the uptake of fasudil into preformed hydrogenated soy phosphatidylcholine/cholesterol (HSPC/CHOL) liposomes were examined. Fasudil was successfully loaded into preformed liposomes in response to sulfate ion (SO4(2-)) and, in part, by H+. Encapsulation levels approaching 100% could be achieved up to a drug to lipid ratio of 0.364 (mol/mol). A stability study of the fasudil-loaded liposomes was performed by storage at 4 degrees C in 4-(2-hydroxyethyl)-1-piperazineethanesulphonic acid (HEPES)-buffer (pH 7.4) and by incubation in human cerebrospinal fluid (CSF) at 37 degrees C. The formulations were stable with respect to drug retention as well as size alteration, for the period studied. A leakage study clearly showed the sustained release properties of the fasudil-loaded liposomes in human CSF. We recently reported that the intrathecal administration of liposomal fasudil significantly decreased ischemia, with no obvious adverse effect in a rat model [Neurol. Med. Chir. 41 (2001) 109]. Taken together, efficient encapsulation of fasudil into preformed liposomes, their long-term stability at 4 degrees C and the sustained release characteristics in CSF indicate that fasudil-loaded liposomes could be potential candidates for further clinical evaluation.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1981

Interaction of antibody-bearing small unilamellar liposomes with antigen-coated cells. The effect of antibody and antigen concentration on the liposomal and cell surface respectively.

Human blood lymphocytes were coated with increasing amounts of human kappa chain (2-85mug/10(7) cells) through the linking reagent CrCl(3). These cells were then exposed to small unilamellar liposomes composed of egg phosphatidylcholine, cholesterol and phosphatidic acid (molar proportions 7:7:1) containing carboxyfluorescein and/or (111)In-labelled bleomycin and bearing (131)I-labelled affinity chromatography-purified or non-purified anti-(kappa-chain) immunoglobulin G (IgG) [see the preceding paper, Gregoriadis, Meehan & Mah (1981) Biochem. J.200, 203-210]. In some experiments liposomes contained [(14)C]phosphatidylcholine. (1) Lymphocytes (10(7)) coated with 2-85mug of kappa chain and exposed to liposomes devoid of IgG or bearing non-purified anti-(kappa chain) IgG bound only a small proportion of the liposomal markers. Even with liposomes bearing the purified anti-(kappa chain) IgG, uptake of the labels improved only slightly for cells coated with up to 10mug of kappa chain. However, with higher concentrations of the antigen on the cell surface, binding was improved considerably to reach values of 31% ((111)In-labelled bleomycin) and 43% ((131)I-labelled IgG) of added liposomes for cells coated with 85mug of kappa chain. (2) Lymphocytes coated with kappa chain were exposed to liposomes bearing increasing amounts (0-180mug/0.9mg of egg phosphatidylcholine) of purified anti-(kappa chain) IgG. It was found that under the present conditions, binding of all three markers ((111)In-labelled bleomycin, (131)I-labelled IgG and [(14)C]phosphatidylcholine) was directly proportional to the concentration of IgG on the liposomal surface. However, uptake values remained unchanged above 90mug of IgG. (3) Antibody-mediated uptake of liposomes by cells coated with the corresponding antigen without loss of their metabolic activities may provide a method of efficient targeting.

Antigen-Antibody Reactions↗
PubMed2003

Sterically stabilized etoposide liposomes: evaluation of antimetastatic activity and its potentiation by combination with sterically stabilized pentoxifylline liposomes in mice.

Cytotoxic activity of chemotherapeutic agents can be enhanced by site-specific delivery or by combination with other less toxic agents. In the present study, enhancement in the antimetastatic activity of etoposide (ETP) by encapsulation in sterically stabilized liposomes was evaluated in the murine experimental B16F10 melanoma model. Further, potentiation of its antimetastatic activity by combination with pentoxifylline (PTX) solution or sterically stabilized PTX liposomes was evaluated in the same animal model. Upon intravenous administration, ETP solution and ETP liposomes inhibited pulmonary tumor nodule formation in a dose-dependent manner. Encapsulation of ETP in liposomes resulted in significant enhancement in its antimetastatic activity at doses of 0.5 mg/kg and 0.75 mg/kg as compared to ETP solution at similar doses. In combination therapy, the effect of sequence of administration of the drugs, ETP and PTX, was evaluated. Enhancement of antimetastatic activity of ETP solution when used in combination with PTX solution was effected by the sequence in which the solutions were administered. However, a combination of ETP liposomes and PTX liposomes led to potentiation of antimetastatic activity in a sequence-independent manner. The results indicate that antimetastatic activity of ETP is significantly enhanced by encapsulation in liposomes. Administration of ETP liposomes with PTX liposomes further potentiated the activity, suggesting the usefulness of this combination in clinical practice for reducing the dose-limiting toxic effects of ETP.

Animals↗
PubMed1982

Liposomal membranes. XII. Adsorption of polysaccharides on liposomal membranes as monitored by fluorescence depolarization.

Under specific conditions where neither induced aggregation nor fusion is brought about, the adsorption of polysaccharides on liposomal membranes was investigated by the fluorescence depolarization technique using fluoresceinylthiocarbamoyl-dextrans (FITC-dex) as probes. The adsorption of FITC-dex on liposomes significantly increased the fluorescence polarization of FITC fluorophore due to the restriction of the mobility of the dextrans. Dextran with larger molecular weight was efficiently adsorbed on liposomes, in good agreement with the tendency for polysaccharide-induced aggregation of liposomes (Sunamoto et al. (1980) J. Biochem. 88, 1219--1226). The adsorption seemed to be related to the fluidity of liposomal membranes, since dextrans were adsorbed more efficiently on egg lecithin liposomes than dipalmitoyl lecithin liposomes at 25.0 degrees C. However, the adsorption of dextrans did not cause a significant change in the fluidity of the liposomal membrane itself under the specific conditions adopted in this work; this was ascertained from the mobility of sodium 8-anilino-1-naphthalenesulfonate (ANS) intercalated close to the surface of liposomes.

Chemical Phenomena↗
PubMed1994

Delivery of cytokines by liposomes. I. Preparation and characterization of interleukin-2 encapsulated in long-circulating sterically stabilized liposomes.

In an attempt to enhance the therapeutic efficacy of interleukin-2 (IL-2), recombinant human IL-2 was encapsulated either in large conventional liposomes or in small (mean diameter 65 nm), unilamellar, long-circulating, extravasating liposomes [referred to as sterically stabilized liposomes (SSLs)]. The SSL-IL-2 activity was assessed in vitro and in mice in comparison with soluble IL-2, IL-2 in conventional liposomes (non-SSL-IL-2), and pegilated IL-2 (PEG-IL-2). The main observations were as follows: (a) SSLs were far better carriers than conventional liposomes with regard to encapsulation efficiency and pharmacokinetics; (b) > 85% of IL-2 biological activity was consistently encapsulated in SSLs; (c) SSL-IL-2 was much more stable than soluble IL-2 at 4 and 37 degrees C; (d) SSL-IL-2, but not "empty" liposomes, bound in vitro to IL-2 receptor-bearing T-cells, indicating that the domain of the cytokine molecule involved in binding to the receptor is exposed on the outer liposome membrane; (e) release of IL-2 from the liposomes was not required for its in vitro biological activity; (f) plasma half-lives (t1/2 alpha, t1/2 beta) and area under the curve (AUC) of SSL-IL-2 were 10-30 times greater than those of soluble IL-2 and similar to those of PEG-IL-2; and (g) IL-2 is released from the SSLs in vivo with a t1/2 of approximately 40 min, although the SSL-IL-2s retained their steric stabilization in the plasma for > 4 h, with little liposome accumulation in the reticuloendothelial system. These data, together with the improved immunomodulatory and antitumor activity of SSL-IL-2 in mice, suggest that SSL-IL-2 might be a therapeutic agent superior to soluble IL-2.

Animals↗
PubMed1994

Incorporation of alpha-tocopherol in liposomes promotes the retention of liposome-encapsulated glutathione in the rat lung.

The present study was undertaken to investigate whether alpha-tocopherol incorporated in liposomes could improve the retention of entrapped glutathione (GSH) in the lung following intratracheal instillation in rats. Rats were treated with a single dose of [3H]GSH entrapped in liposomes with or without 30 mol% alpha-tocopherol and killed 0, 24 or 48 h later. The retention of GSH in the lung was assessed by measuring the recovery of either 3H-label or GSH in the lung. Animals instilled with free [3H]GSH were found to retain only 2% of the administered dose at 24 h after treatment and no detectable radioactivity at 48 h. Liposome encapsulation altered the pulmonary retention of GSH with 18 and 10% of radioactivity remaining in the lung at 24 and 48 h post-treatment, respectively. The instillation of GSH encapsulated in alpha-tocopherol-containing liposomes resulted in the highest level of GSH retention in the lung, namely 37 and 30% of the administered GSH dose at 24 and 48 h, respectively. Results from Sepharose 4B column chromatography revealed that lung homogenates, obtained from rats instilled with GSH entrapped in alpha-tocopherol-containing liposomes, 24 and 48 h earlier, contained 2 eluted GSH-related components--one associated with the liposomal lipid marker in the void volume and the other as free GSH tripeptide, suggesting a slow sustained release effect mediated by the liposomal formulation. The same liposome preparation containing both alpha-tocopherol and GSH also conferred better protection against FeADP-induced lipid peroxidation than liposomes containing either alpha-tocopherol or GSH alone, indicative of a potentially effective antioxidant formulation for treating oxidative lung injury.

Animals↗
PubMed1987

Effect of lipid composition and liposome size on toxicity and in vitro fungicidal activity of liposome-intercalated amphotericin B.

Intercalation of amphotericin B into liposomes at a 10 mol% drug/lipid ratio decreased its cytotoxicity by 3- to 90-fold in cultured murine cells and reduced its lethality by 2- to 8-fold in a median lethal dose (LD50) test in mice when compared with the commercial deoxycholate-solubilized drug (LD50 = 2.3 mg/kg). The cytotoxicity and lethality of the liposomal preparations were a function of their lipid composition and diameter. There was no correlation between the reduction of toxicity in the tissue culture assay and the reduction of lethality in the LD50 test. The rank order of reduction of lethality was sterol-containing liposomes greater than solid liposomes greater than fluid liposomes. In general, small sterol-containing vesicles were less lethal than large vesicles of the same composition. Intercalation of amphotericin B in sterol or solid liposomes increased not only the LD50 but also the time to death. The organ distribution of amphotericin B 24 h after intravenous administration was similar whether the drug was given as the commercial deoxycholate preparation or in liposomes. Finally, there were no differences among any of the formulations in their fungicidal activity against Candida tropicalis and Saccharomyces cerevisiae in vitro. The lesser and slower lethality of the liposomal and detergent-solubilized drug suggests that the mechanism by which liposomes reduce the lethality of amphotericin B is by slowing its rate of transfer to a sensitive cellular target.

Amphotericin B↗
PubMed1997

Modulation of noninduced and phorbol ester-induced generation of superoxide anion by free liposomes and liposomes containing dexamethasone.

We tested the relative efficacy of free dexamethasone, dexamethasone containing liposomes and free liposomes in preventing superoxide anion, O-2 generation by neutrophils. O-2 production by 5 x 10(5) neutrophils, whether primed or not with lipopolysaccharide, was stimulated by phorbol 12-myristate 13-acetate (PMA) to 13.4 +/- 1.3 nmoles after 15 minutes compared to 1.2 +/- 0.3 nmoles with nonstimulated cells. Free liposomes but not dexamethasone (dexa) decreased non-stimulated as well as PMA-induced O-2 generation. Dexa-containing phosphatidylcholine from egg yolk: phosphatidylserine from bovine brain (PC:PS 7:3) liposomes, unlike free dexa, diminished PMA-stimulated O-2 production in a dose-dependent manner with a maximal effect at 37.5 micrograms/ml phospholipid (6.6 +/- 1.6 nmoles). The kinetics of cytochrome-c reduction revealed that decreased O-2 production resulted from an extended lag-time of release to almost 8 minutes with PMA induction and consequently led to the conclusion that liposomes modified the activity of NADPH oxidase as well as that of protein kinase C. Liposomes prepared with PC and PS of natural origin had a greater inhibitory effect on O-2 generation by neutrophils than dipalmitoylphosphatidylcholine (DPPC) and phosphatidylethanolamine from egg yolk (PE):PC (3:1) liposomes. When 100 microM of Ca2+ was added to the medium, the inhibitory action of liposomes prepared with egg yolK PC and DPPC was increased by 30 and 60% respectively, while that of PS and PE:PC was prevented. We also verified that liposomes by themselves, even if phagocytized, did not induce O-2 generation or its concentration was too low to be detected by this technique. From the clinical point of view, some formulations delayed non-induced and PMA-induced O-2 generation, thus adding to the anti-inflammatory effect of the glucocorticoid they transported.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1991

Comparison of dynamics of lecithin liposomes and brain total lipid liposomes with synaptosomal membranes. An EPR spectroscopy study.

Dynamics and/or order of the hydrophobic part of phosphatidylcholine (PC) liposomes and rat brain total lipid (TL) liposomes and synaptosomes were studied and compared by EPR spectroscopy using the spin probes 5 or 16-doxyl stearic acid and 14-doxyl phosphatidylcholine. The dynamics and/or order of the hydrophobic part of TL liposomes or synaptosomes were similar but differed largely from those of PC liposomes. The dynamics of the hydrophobic part of the liposomes decreased gradually with the increasing TL/PC ratio in the sample. To obtain in TL liposomes or synaptosomes the same EPR spectrum parameters as in PC liposomes at 37 degrees C, the formers have to be heated to temperatures of approximately 50-60 degrees C. The dynamics and/or order of the hydrophobic part of lecithin liposomes at 5-10 degrees C were comparable with those of TL liposomes or synaptosomes at 37 degrees C. The results emphasize the role of the lipid composition in studies concerning drug-lipid and protein-lipid interactions in model and biological membranes.

Animals↗
PubMed1990

Effect of liposome composition and other factors on the targeting of liposomes to experimental tumors: biodistribution and imaging studies.

We have examined the distribution of radiolabeled liposomes in tumor-bearing mice after i.v. injection. Two mouse tumors (B16 melanoma, J6456 lymphoma) and a human tumor (LS174T colon carcinoma) inoculated i.m., s.c., or in the hind footpad were used in these studies. When various liposome compositions with a mean vesicle diameter of approximately 100 nm were compared using a radiolabel of gallium-67-deferoxamine, optimal tumor localization was obtained with liposomes containing a phosphatidylcholine of high phase-transition temperature and a small molar fraction of monosialoganglioside or hydrogenated phosphatidylinositol (HPI). At 24 h after injection, average values of tumor uptake higher than 10% of the injected dose per g and liver-to-tumor ratios close to 1 were reproducibly obtained. Increasing the molar fraction of HPI from 9% to 41% of the total phospholipid resulted in enhancement of liver uptake and decrease of tumor uptake. Methodological aspects that influence vesicle size appear to affect significantly liposome localization in the tumor. However, varying the phospholipid dose within a 10-fold range caused only minor changes in the percent of injected dose recovered in the tumor. A high uptake by tumors was also observed using other radiolabels [[3H]inulin and indium-111-labeled bleomycin (111In-Bleo)] in monosialoganglioside- and HPI-containing liposomes. In the case of 111In-Bleo, encapsulation in liposomes resulted in approximately 20- to 40-fold increase in tumor accumulation of the radiolabel at 24 h after injection. The marked localization of liposomes in the mouse footpad inoculated with tumor as opposed to the contralateral mock-injected footpad was also documented by imaging experiments with gallium-67-deferoxamine and 111In-Bleo-labeled liposomes. These results support the contention that some glycolipid-containing liposomes previously shown to have long circulating half-lives accumulate significantly in a variety of tumors and are promising tools for the delivery of anti-tumor agents.

Animals↗
PubMed1987

[Basic studies on chemotherapy of brain tumors by means of liposomes: affinity of sulfatide-inserted liposomes to human glioma cells].

In order to utilize liposomes for the treatment of brain tumors, we examined the interaction between the cells and the liposomes prepared from phosphatidylcholine, cholesterol, and sulfatide (molar ratio, 7:2:1), which were able to deliver the encapsulated materials into the brain through the blood-brain barrier. With a variety of human cell lines, the incorporation of the liposomes and the release of the liposomal contents into cells were studied by spectrofluorometry and flow cytometry by use of encapsulated 6-carboxy-fluorescein. It was found that the amounts of liposomes incorporated into cells were dependent on the dose of liposomes and type of cells. At the same concentration of liposomes, the highest incorporation was found for glioma cells, which was further confirmed by electron microscopy with ferritin-containing liposomes. These results indicate that the liposomes composed of sulfatide, phosphatidylcholine and cholesterol have a high affinity for human glioma cells and should be useful for the chemotherapy of glioma when antitumor drugs are encapsulated into them.

Antineoplastic Agents↗
PubMed1987

Liposomes as adjuvants with immunopurified tetanus toxoid: influence of liposomal characteristics.

The effect of various manipulations of liposomes composed of equimolar phospholipid and cholesterol on immune responses to the incorporated immunopurified tetanus toxoid was investigated in BALB/c mice. In studies designed to establish proper dosage for immunization and to reveal the roles of the liposomal phospholipid to toxoid mass ratio, gel-liquid crystalline transition temperatures (Tc) of the liposomal phospholipids and mode of antigen incorporation into liposomes on immune responses, animals were injected intramuscularly with various amounts of the toxoid, free, entrapped in multilamellar dehydration-rehydration vesicles (DRV) or covalently linked to the surface of multilamellar vesicles (MLV) prepared by the classical procedure. Two identical injections separated by 4 weeks were given and IgG1 and IgG2b antibodies specific for the toxoid assayed in sera by an enzyme-linked immunosorbent assay. Results suggest that the adjuvant effect of liposomes is improved considerably when liposomal phospholipid to toxoid mass ratios are as high as 2049:1; however, adjuvanticity is reduced to reach very low levels for much higher ratios (e.g. 90,361:1); antibody responses are similar for liposomes (phospholipid to toxoid mass ratios: 14.3-33.1) made of a variety of phospholipids with Tcs ranging from -32 degrees to 41.5 degrees but are low or non-existent when liposomes are made of distearoyl phosphatidylcholine (Tc, 54 degrees) (however, see Discussion); there are no differences in antibody responses between liposomes with entrapped and surface-linked toxoid.

Adjuvants, Immunologic↗