Activation of Fc receptor-mediated phagocytosis by mouse peritoneal macrophages following the intraperitoneal administration of liposomes

Effect of treatment with free and liposomized albendazole on selected immunological parameters and cyst growth in mice infected with Echinococcus multilocularis

Selected immunological parameters in healthy mice and mice infected with Echinococcus multilocularis and the effect of free and liposomized albendazole (lip.ABZ) upon these parameters in relation to the reduction of parasite growth were investigated over 26 weeks. Proliferative response of splenic T and B lymphocytes, number of CD4+ and CD8+ spleen T cell subpopulations, serum concentration of IFN-gamma and IL-5, and generation of superoxide anion (O2-) by peritoneal macrophages were the chosen parameters. Both drug forms were given to mice at a dose of 10 mg kg(-1) twice a week from week 4 to week 10 post infection (p.i.) (6 weeks in total). The reduction of cyst growth after treatment with ABZ and lip.ABZ was similar up to week 4 after last dose, but the parasitostatic effect of lip.ABZ lasted 4 weeks longer than the effect of free drug. After administration of both drug forms, the proliferative responses of T and B cells were restored, and also the number of CD4+ and CD8+ increased markedly. In lip.ABZ-treated mice, stimulation of mentioned lymphocyte parameters, except that of CD8+ numbers, persisted for longer period than after ABZ therapy, where values peaked at week 12 p.i., then declined more rapidly. A very strong stimulatory effect was seen on B lymphocytes during the period of lip.ABZ administration, although interestingly, numbers of CD8+ cells were higher in free ABZ-treated group. Low concentrations of IFN-gamma (Th1 response) were present in infected, untreated mouse serum. Only moderate IFN-gamma elevation was observed after treatment with free ABZ. A profound increase of its concentration was seen shortly after administration of lip.ABZ, and persisted until the experiment ended. In infected untreated mice, concentration of IL-5 (Th2 response) was highest on week 2 p.i. Significantly more IL-5 was recorded in serum of mice treated with free ABZ treatment than with lip.ABZ from week 12 to 18 p.i. (weeks 2-8 after the last dose). After the initial increase of superoxide anions (weeks 4-11 p.i.), generation of O2- by peritoneal macrophages was gradually inhibited by E. multilcoularis infection. In general, treatment abolished this suppression and macrophages from lip.ABZ-treated mice produced elevated amounts of O2- over a longer period than macrophages from ABZ-treated mice. Our data indicate that anthelmintic potency of ABZ could be increased after incorporation into liposomes, not only because of improved pharmacokinetics and consequent bioavailability, but also because of significant stimulation of Th1-type cytokine IFN-gamma response and effector macrophage functions.

Modulation of liver fibrosis and pathophysiological changes in mice infected with Mesocestoides corti (M. vogae) after administration of glucan and liposomized glucan in combination with vitamin C

The effects of glucan and liposomized glucan, alone or co-administered with vitamin C, and empty liposomes on hepatic fibrosis in mice infected with Mesocestoides corti (M. vogae) tetrathyridia were studied. Preparations were administered every third day from day 7 to day 31 post-infection (p.i.), nine doses in total. Activities of alanine aminotransferase (ALT), aspartate aminotransferase (AST) and cholesterol levels were measured in sera collected on days 11, 15, 21, 28, 32, 42, 50 and 65 p.i. Liver fibrosis was studied on the same days by measuring hydroxyproline concentration, which is considered a marker for collagen content. Larvicidal effects of the glucan and liposome preparations were estimated on day 65 p.i. in the liver and peritoneal cavity. Glucan formulations significantly enhanced collagen content, most prominently after administration of liposomized glucan in combination with vitamin C. Activities of both enzymes and cholesterol levels were slightly modified after administration of glucan alone. Liposomized glucan with vitamin C significantly increased ALT and AST activity and cholesterol levels up to days 28-32 p.i., after which they plateaued or declined. The most pronounced decrease was after administration of liposomized glucan and vitamin C. The same pattern of biochemical parameters in serum was observed after administration of empty liposomes, however, collagen content was not modified significantly. Larval counts in the liver and the peritoneal cavity were significantly reduced after treatment with either glucan formulation, but were unaffected following treatment with empty liposomes. In summary, intense fibrosis in the liver of mice treated with liposomized glucan and vitamin C did not result in the most extensive parenchymal cell injury but, rather in the highest efficacy of treatment. Liposomal lipids were probably utilized in the reparation of the damaged parenchymal cells, while glucan stimulated phagocytic cells.

Induction of partial protection against Leishmania donovani by promastigote antigens in negatively charged liposomes

Negatively charged liposomes, proposed as potential vaccine adjuvants, have been extensively studied in association with various antigens. In the present study, we investigated the adjuvanicity of negatively charged liposomes to enhance the protective immunity of membrane antigens of Leishmania donovani promastigotes (LAg). In comparison to the control mice immunized with phosphate-buffered saline and empty liposomes, immunization with free LAg led to significant levels of protection against infection with virulent promastigotes. Encapsulation of LAg in liposomes also induced effective protection. However, the level of protection by LAg-liposome was not significantly different from that induced by free LAg. Investigation of the immune responses showed, in contrast to free LAg, that immunization with LAg-liposome elicited strong antibody responses. IgG isotype analysis revealed the presence of all 4 isotypes. However, the titer of IgG1 was significantly higher than IgG2a, IgG2b, and IgG3. Following infection, stimulation of IgG and IgG isotypes did not differ in the different immunization groups. Delayed-type hypersensitivity (DTH) analysis after immunization showed significant induction by LAg and LAg-liposomes, in comparison to controls. With infection, again, the level of DTH in all the groups became almost comparable. Stimulation of insufficient cellular response, as reflected by DTH and potentiation of IgG1 over IgG2a, IgG2b, and IgG3 suggest a dominance of Th2 response with this liposome-antigen formulation, resulting in weak protection against visceral leishmaniasis.

Distribution of [3H]cholesterol-labelled liposomes with or without praziquantel in mice infected with Mesocestoides corti (Cestoda) tetrathyridia

The anthelmintic drug praziquantel (PZQ) has a short half-life in the circulation, necessitating repeated daily administration of PZQ for the therapy of larval stages of cestodes. The effect of incorporation of PZQ into multilamellar liposomes on their biodistribution in Mesocestoides corti (syn. M. vogae) infected mice has been examined using [3H]cholesterol as a liposomal marker. Incorporation of PZQ significantly increased the average size of liposomes with 70.3% of [3H]lip.PZQ particles up to 1.9 microm, whereas higher portion of [3H]liposomes (66.3% of total) were of smaller (up to 1.3 microm). Both liposome preparations were given intraperitoneally to avoid rapid sequestration in the liver. There were significant differences between [3H]liposomes and [3H]lip.PZQ-associated radioactivity in peritoneal adherent cells, liver- and peritoneal larvae, liver, spleen and lymph nodes within 16 days of examination. The highest uptake (about 2-fold more [3H]lip.PZQ than [3H]liposomes from the total dose) was found in peritoneal cells on day 1 post therapy (p.t.) followed by a rapid decline. The kinetic of decline in these cells recovered on day 1 p.t. was studied also in vitro. Disappearance of the marker due to the breakdown of liposomes and efflux of lipids and PZQ from cells was slower for [3H]lip.PZQ in comparison with drug-free liposomes and was not completed after 4 days-incubation. Significantly increased levels of radioactivity, more in [3H]liposomes treated groups, were recorded in the liver- and peritoneal larvae between days 8-16 p.t. indicating re-utilization of cholesterol by the larvae. The data suggest that incorporation of PZQ into liposomes contributes to the enlargement of liposome average size and slows down their degradation in phagocytosing cells. In this respect, these cells could serve as the secondary circulating depots for PZQ releasing it slowly to the circulation.

Induction of apoptosis in WEHI 231 cells by cationic liposomes

PURPOSE

Liposomes are of considerable interest as drug carriers and immunoadjuvants. However, few investigators have studied the changes exerted by liposomes in the cells with which they interact. The purpose of this study was to investigate whether liposomes induce apoptosis in B cells.

METHODS

The mouse immature B cell line WEHI 231 cells and mouse splenic B cells were treated with liposomes, and the induction of apoptosis was evaluated by monitoring changes in DNA content, DNA fragmentation and chromatin condensation by flow cytometry, agarose gel electrophoresis and by morphological investigation.

RESULTS

Cationic liposomes induced apoptosis in WEHI 231 cells, but neutral and anionic liposomes did not. A contact time of 30 min between WEHI 231 cells and cationic liposomes was sufficient to induce apoptosis, and 80% of the cells showed hypodiploid DNA content. Apoptosis induced by cationic liposomes composed of stearylamine was inhibited by addition of the oxidant scavenger, N-acetyl-cysteine.

CONCLUSIONS

Cationic liposomes induced apoptosis in WEHI 231 cells, and the production of reactive oxygen species is important in the regulation of apoptosis induced by cationic liposomes. It is well known that cationic liposomes show cytotoxicity, and apoptosis may be one of the causes of this toxicity.

Activation of the mononuclear phagocyte system by poloxamine 908: its implications for targeted drug delivery

PURPOSE

To investigate the effect of poloxamine 908 on the MPS activity and the importance of its mode of presentation to the immune system.

METHODS

Solutions of endotoxin free poloxamine 908 were injected daily intravenously to rats, and the effect on the degree of sequestration by the liver of I125 labelled, poloxamine 908-coated 60 nm polystyrene particles was investigated by studying effect of dosing regimen(s) and assessment of opsonic activity.

RESULTS

After 3 or 4 days repeated dosing with poloxamine 908 (0.7 mg) in solution, the poloxamine 908-coated polystyrene particles (60 nm) were rapidly cleared from the circulation. The increase sequestration of the particles by the liver lasted for more than 7 days after last dosing with the poloxamine 908 solution. In subsequent studies, it was found that a single dose of poloxamine 908 (0.7 mg) in solution was sufficient to activate the MPS 4 days after the injection. The increased uptake was found not be mediated by a serum component, nor was it due to proliferation of the Kupffer cells in the liver.

CONCLUSIONS

The results provide evidence that a solution of endotoxin-free poloxamine 908 activates the MPS so that 4 days after injection otherwise long-term circulating poloxamine 908-coated particles are sequestered by the liver. This finding has implications for use of such coated systems in therapeutic situations.

alpha 2-macroglobulin stimulation of protein tyrosine phosphorylation in macrophages via the mannose receptor for Fc gamma receptor-mediated phagocytosis activation

Macrophage phagocytic activity has previously been shown to be increased by binding of modified alpha 2-macroglobulin (alpha 2M) with mannose residues at termini of sugar chains to mannose receptors on macrophages, with a subsequent increase in the number of Fc gamma receptors at the cell surface. In the present study, an examination was made of the association of protein tyrosine kinase with the increase in number of Fc gamma receptors following binding of modified alpha 2M to mannose receptors. The phagocytosis of IgG-opsonized sheep red blood cells through the action of the Fc gamma receptor by modified alpha 2M was inhibited by mannose and herbimycin A and slightly so by genistein. The mannose receptor would thus appear to be associated with tyrosine kinase activity. By Western blotting, tyrosine phosphorylated proteins with molecular weights of 32000, 34000, 36000, 65000, 85000 and 110000 appeared or increased upon treating macrophages with modified alpha 2M. The degree of tyrosine phosphorylated proteins was the same for control macrophages following incubation in the presence of mannose and herbimycin A. Genistein treatment affected only tyrosine phosphorylated proteins of 65000 and 110000. The binding of modified alpha 2M to mannose receptors was demonstrated by the inducement of tyrosine kinase activation that was sensitive to herbimycin A, followed by an increase in Fc gamma receptors and consequently greater phagocytosis.