Transdermal immunisation with an integral membrane component, gap junction protein, by means of ultradeformable drug carriers, transfersomes.

Molecules greater than 500 Da normally do not cross the skin. This prevents epicutaneous delivery of the high molecular weight therapeutics as well as non-invasive transcutaneous immunisation. Extremely deformable vesicles prepared by the judicious combination of several materials provide a solution to this problem: the resulting agent carriers, transfersomes, are the only tested colloidal system that can transport even large macromolecules spontaneously through the skin in immunologically active form. Gap junction proteins (GJP) incorporated into transfersomes and applied to the intact skin surface thus give rise to specific antibody titres marginally higher than those elicited by subcutaneous injections of GJP in transfersomes, mixed lipid micelles or liposomes. The latter two carrier systems give no significant biological response after epicutaneous administration. Transcutaneous protein delivery by means of transfersomes also appears to increase the relative concentration of anti-GJP IgA in the serum.

Enhanced in vivo catalytic activity of PEG-modified cellulase complex from Trichoderma reesei.

The cellulase complex from Trichoderma reesei was polyethylene glycol (PEG)-modified with considerable retention of endo-beta-1,4-glucanase activity, as evaluated by the carboxymethylcellulase (CMCase) assay. While resistance towards heat denaturation was the same for either form, susceptibility towards proteolysis was slightly greater for the PEG-conjugate, in contrast to most reports using other enzymes. The circulatory life of endoglucanase activity associated with the complex was enhanced upon PEG-modification. This was confirmed by demonstrating degradation of chromogen-labelled substrate injected (i.v.) after 24hr of administration of the PEG-ylated enzymes; in contrast the substrate remained undegraded in mice pretreated with the native complex. The PEG-modified complex could be a good candidate for the treatment of pneumoconioses of textile workers exposed to cotton dust.

Transdermal immunization with large proteins by means of ultradeformable drug carriers.

By means of novel, ultradeformable and self-optimizing agent carriers called transfersomes, large molecules can be brought into the body through intact permeability barriers. This permits non-invasive immunization through normal skin and gives rise to a similar or even slightly higher antibody titer than subcutaneous injections of the same immunogen formulation. The former type of immunization also results in a higher IgA/IgG ratio in the blood than the repeated immunogen injections, as shown here for a soluble protein, human serum albumin, as well as for an integral membrane protein, gap junction protein, in mice.

Effect of elimination of phagocytic cells by liposomal dichloromethylene diphosphonate on aspergillosis virulence and toxicity of liposomal amphotericin B in mice.

The role of macrophages in the toxicity and efficacy of liposomal amphotericin B (L-Amp B) was studied in a murine aspergillosis model infection. Macrophages and polymorphonuclear phagocytes (PMN cells) were depleted in the liver and spleen of mice by the administration of liposome encapsulated dichloromethylene diphosphonate. Macrophage depletion had no effect on the lethality of Fungizone, a commercial deoxycholate preparation of Amp B, but significantly increased the lethality of L-Amp B (P < 0.01). Macrophage depletion led to an increase in the fungal loads in the lung, liver and kidney (P < 0.05) and to an increase in the virulence of aspergillosis (P < 0.05). Tissue distribution analysis of L-Amp B revealed that in macrophage/PMN-depleted mice there was a decrease in the concentration of Amp B in the liver, with concomitant increases in the circulation, spleen and lung, both in the uninfected and in the infected conditions. The results clearly demonstrate that depletion of macrophage/PMN cells increases the virulence of aspergillosis, as well as the toxicity of L-Amp B. Moreover, L-Amp B treatment does not improve the survival rate of macrophage/PMN-depleted mice subjected to aspergillosis challenge.

Enhanced intracellular stability and efficacy of PEG modified dextranase in the treatment of a model storage disorder.

A model for storage disorders was produced in the livers of mice by the administration of liposomally encapsulated FITC-dextran. Liposomally delivered dextranase was found to be more efficient in degrading the accumulated substrate as compared to the free enzyme. Dextranase was covalently modified with PEG, and liposomes were used as carriers for delivering the free and the modified enzyme to the liver at similar rates. The PEG-dextranase conjugate showed greater intracellular stability as compared to the native enzyme. Liposomally delivered PEG-dextranase, by virtue of its enhanced intracellular stability, could not only degrade the accumulated FITC-dextran, but could also prevent its further accumulation over a period of time. This enhanced intracellular stability of enzymes would be of importance in extending the catalytic life of therapeutically active enzymes and thereby improve their therapeutic potential for the treatment of intracellular storage disorders.

Tuftsin-bearing liposomes as drug vehicles in the treatment of experimental aspergillosis.

Encapsulation of amphotericin B in tuftsin-bearing liposomes greatly increased its efficacy in treatment of human aspergillosis in mice. Also, the drug efficacy was significantly increased by pretreating the animals with drug-free tuftsin-bearing liposomes. These results demonstrate that macrophage activation can considerably enhance the therapeutic efficacy of antifungal drugs, like amphotericin B.

Liposomal hamycin in the control of experimental aspergillosis in mice: effect of phosphatidic acid with and without cholesterol.

Hamycin incorporated into liposomes containing phosphatidylcholine (SPC) and phosphatidic acid (PA) had reduced toxicity and an enhanced antifungal activity in experimental aspergillosis in balb/c mice. Incorporation of cholesterol into liposomes led to a dose dependent decrease in the toxicity of hamycin. The LD50 (mg/kg) of hamycin contained in SPC/cholesterol/PA (molar ratio 4:5:1) liposomes was 2.8 whereas that in SPC/PA liposomes (molar ratio 9:1) was 0.35. Although the free drug had little or no protective effect on the animals, those administered liposomal hamycin at an equivalent dose (0.1 mg/kg) in the absence of cholesterol (SPC/PA; molar ratio 9:1) showed 90% survival after seven days of therapy. On the other hand the presence of cholesterol in the carrier phosphatidic acid liposomes (SPC/cholesterol/PA; molar ratio 4:5:1) at a similar dose (0.1 mg/kg) led to a 60% survival over the same time period. Hamycin incorporation in phosphatidic acid liposomes both in the presence or absence of cholesterol was found to be effective in reducing the fungal load in lung, liver, spleen and kidney. Studies with distribution of hamycin in various tissues by HPLC showed a significant reduction in the concentration of the liposomal drug in circulation as compared to those seem after administration of free drug.

Enhanced stability and therapeutic utility of proteins upon conjugation with hydrophilic polymers.

The Pharmacological utility of various exogenous proteins is considerably impeded, since upon infusion, they are liable to rapid systemic clearance, proteolysis, in addition to eliciting severe immunological reactions. Upon conjugation with hydrophilic polymers like polyethylene glycol and dextran, the altered topology of proteins, often hinders interaction with their corresponding complementary surfaces. This is manifest in their increased circulatory-lives, as a fall out of decreased binding to proteases, pre-existing antibodies and other opsonins that mediate clearance by the reticuloendothelial-system as well as receptors mediating specific organ uptake. Further, an increase in conjugate size beyond the threshold limit of 70 kDa, permits small proteins to escape clearance via renal filtration. Upon covalent modification, proteins are generally endowed with an intrinsic inertness which is reflected in their enhanced stability in extremes of pH and temperature, presence of proteases and other denaturing conditions. The enhanced intracellular stability of conjugates which may also be responsible for their altered immunological properties is likely to be a consequence of the changed physiochemical properties of the conjugates. The therapeutic efficacy of these conjugates in clinical trials indicate their tremendous utility in pharmacological procedures.

Mannosylated liposomes as carriers for hamycin in the treatment of experimental aspergillosis in Balb/C mice.

Hamycin incorporated into mannosylated liposomes produced less toxicity and enhanced antifungal activity in experimental aspergillosis in balb/c mice in vivo. Incorporation of cholesterol into mannosylated liposomes led to a decrease in hamycin toxicity. The LD50 (mg/kg) values of hamycin contained in SPC/Chol/DPPE-Man (molar ratio 4:5:1) lipsomes was 2.8 whereas that in SPC/DPPE-Man liposomes (molar ratio 9:1) was 1.4. Incorporation of cholesterol into mannosylated liposomes increased the survival rates of infected animals: 70% survival was recorded after 7 days therapy as well as reduced fungal load in lung, liver, spleen and kidney. HPLC studies of distribution of hamycin in various tissues showed a reduction in the concentration of the liposomal drug in circulation compared to that observed for free drug and neutral liposomes after 1 hour.

Enhanced intracellular stability of dextran-horse radish peroxidase conjugate: an approach to enzyme replacement therapy.

Horse radish peroxidase (HRP), a mannose-containing glycoprotein was covalently modified by conjugation with dextran. The rapid uptake of HRP by the liver is markedly inhibited by mannan. The uptake of dextran-HRP conjugate by the liver, though lower compared to that of the free enzyme, is also partially inhibited by mannan. Liposomes were therefore used as carriers for delivering the free and the modified HRP to the liver. The dextran-HRP conjugate showed greater stability intracellularly as compared to the free enzyme. The enhanced stability of enzymes upon their extensive glycosylation with nondegradable sugar polymers would be of importance in extending the catalytic life of therapeutically active enzymes and thereby improve their therapeutic potential for the treatment of certain enzyme deficiency disorders.

Liposomal hamycin in the control of experimental aspergillosis in mice: relative toxicity, therapeutic efficacy and tissue distribution of free and liposomal hamycin.

Therapeutic efficacy of liposomal Hamycin has been evaluated in an animal model system for aspergillosis in Balb/c mice. Hamycin was intercalated into soya phosphatidyl choline (SPC), SPC: choline (1:1, vol./vol.) and DMPC liposomes. A single dose of either 0.1 mg/kg, 0.25 mg/kg or 0.5 mg/kg of liposomal Hamycin and 0.1 mg/kg of free Hamycin was injected (i.v.) into animals infected with Aspergillus fumigatus. An increase in the survival rate of animals along with decrease in fungal count in various organs was observed with liposomal administration. Incorporation of cholesterol into liposomes decreased the in vivo toxicity of Hamycin in a dose dependent manner. However, antifungal activity both in the presence and absence of cholesterol showed marked variation as compared to that of non-aromatic polyenes, e.g. amphotericin B. Analysis of Hamycin distribution by HPLC in various tissues revealed higher blood concentration of this drug, when given in free form, compared to its liposomised form. These studies suggest that liposomal Hamycin is more effective than free Hamycin in controlling the experimental Aspergillosis.

Liposome immune lysis assay (LILA) for gelonin.

A complement-mediated liposome immune lysis assay using entrapped calcein was developed for a plant toxin gelonin. Gelonin was covalently coupled to DPPE, and then adsorbed on to the surface of liposomes. Such antigen-bearing liposomes when incubated with anti-gelonin antibody in the presence of guinea pig complement undergo lysis. The detection range is from 3 ng to 60 ng. The method was used to monitor isolation of gelonin by affinity chromatography. It was observed that a minor peak in addition to the major one comes with gelonin, shared common epitopes/epitope with gelonin in immunological reaction. This was further confirmed by SDS-gel electrophoresis indicating the former being an isoform of gelonin. A comparative study of the immunocross-reactivity of ricin and ricin A chain with anti-gelonin antibody was carried out. It was found that while ricin A chain cross-reacted extensively with gelonin antibody and intact ricin elicited little or no cross-reactivity. It is suggested that the present LILA may be employed for the detection and quantitation of ricin A chain by this LILA method.

Macrophages in host defence--an overview.

The importance of macrophages in host defence is well documented. They are distributed in various tissues where they perform functions in normal steady state as well as in diseased condition. Macrophages secrete a number of enzymes, plasma proteins, complement and coagulation factors which regulate the effector functions of the macrophages. Exposure of macrophages to pathogens results in further metabolic changes which activate the former to secrete oxygen metabolites leading to their augmented microbicidal activity. Macrophages respond to the external stimuli by expressing a large repertoire of surface receptors which play an important role in the activation, recognition and endocytosis of foreign microorganisms. A large number of intracellular pathogens are harboured in the macrophages which can reside and replicate in them. A variety of strategem has been employed to target drugs to vacuolar apparatus of the macrophages in order to combat intracellular pathogens. This review covers some of these aspects particularly in relation to hose defence and methods by which therapeutic agents could be specifically delivered to macrophages.

Design of liposomes for circumventing the reticuloendothelial cells.

Two different aspects of liposomal drug delivery to non-RES cells have been described. In one of the systems, by incorporating neutral glycolipids, with terminal beta-galactoside residue into liposomes, it is possible to target liposomes to the liver parenchymal cells, partially bypassing the RES. Asialoganglioside seems to be the most suited for this purpose. In another approach, various factors that prolong the lifespan of circulating liposomes have been discussed. It is possible to design such liposomes by imparting hydrophilicity to the liposomal surface. The effectiveness of a number of possible candidates, such as dextran, GM1 ganglioside and PEG, has been discussed in this context.

Conjugation of proteins and enzymes with hydrophilic polymers and their applications.

The efficacy of a number of therapeutically active proteins and peptides is severely limited due to their instability in circulation. Of the various approaches used to stabilise these proteins, the one more successful is covalent modification of the protein or enzyme with some hydrophilic polymers such as dextran or PEG. These conjugates are more stable than the native protein both in vitro as well as in vivo. They exhibit enhanced resistant to proteolytic degradation, have a long-life in circulation and exhibit reduced immunogenicity. The therapeutic efficacy of these conjugates is also greatly enhanced compared to the native protein or enzyme.

Polyene antibiotics in the membrane environment.

The cytotoxic activity of the polyene antibiotics mainly depends on the appearance of the drug species which arises from drug-sterol complexation. The unsaturation and intact macrolide ring of the polyenes are the requirements for the biological activity. All the polyene antibiotics can form the complex with the sterol having 3 beta-OH group, and planar ring and a hydrophobic side chain. Aromatic polyene antibiotics with positively charged head group have been considered as most potential antifungal agents.

Targeting of liposomes to hepatocytes.

We began our investigations about 15 years ago with the concept that it should be possible to deliver drugs or enzymes intracellularly into lysosomes for diseases associated with lysosomal enzymes (e.g., sphingolipidosis). The results have been very gratifying. It now has been possible to extend our in vitro studies on the kinetics of lectin-liposome interaction to the targeting of glycolipid liposomes to specific liver cell types in vivo by simply varying the sugar residue on the surface of liposome. Nevertheless, much remains to be done to ascertain the stability of the external enzyme and the expression of its activity after the delivery into the lysosomes.

Targeting of plant glycoside-bearing liposomes to specific cellular and subcellular sites.

The possibility of using liposomes as an effective drug delivery system has been studied by incorporation of two plant glycosides of varying terminal sugar residues onto the surface of liposomes and examination of their distribution in different tissues. The two glycosides, corchorusin D and asiaticoside having glucose and rhamnose respectively at the terminal ends wee selected for the purpose. The hepatic uptake of liposomes made from egg lecithin, cholesterol and dicetyl phosphate and either of the two glycosides was compared. The hepatic uptake of asiaticoside bearing liposomes was reduced, whereas that of corchorusin D bearing liposomes was enhanced and was specific for glucose. Liver perfusion followed by cell separation showed that the uptake is mostly into the non-parenchymal cells of liver. The distribution of corchorusin D bearing liposomes was maximal in the lysosomal fraction of the non-parenchymal cells. Ways of using corchorusin D bearing liposomes as delivery systems for drugs or enzymes to lysosomes have been sought.

Effect of cholesterol in various liposomal compositions on the in vivo toxicity, therapeutic efficacy, and tissue distribution of amphotericin B.

The effect of cholesterol in neutral, positively and negatively charged liposomes on the toxicity, therapeutic efficacy, and alteration in the tissue distribution pattern of amphotericin B (Amp-B) in normal and infected mice was studied. It was observed that inclusion of cholesterol (CHOL) into egg phosphatidylcholine (EPC) liposomes increased the LD50 of Amp-B from 5.3 to 8.5 mg/kg body weight. In the case of phosphatidylserine (PS) liposomes as well as stearylamine (SA) liposomes, cholesterol incorporation had no effect in altering the toxicity of the drug. The survival pattern of animals with all types of liposomal formulation of Amp-B was similar. The tissue distribution studies indicated that in the case of normal mice, cholesterol inclusion in all types of liposomes increased the organ concentration of the drug in various tissues. In infected animals, the concentration of Amp-B in all organs was increased when cholesterol was included in EPC and EPC/PS liposomes. The organ concentration of Amp-B in lung and liver after 1 h of injection was the same in the case of EPC/SA and EPC/SA/CHOL liposomes. Considering the observations on toxicity, therapeutic efficacy, and tissue distribution, it was suggested that cholesterol had a beneficial therapeutic effect on neutral EPC liposomes.