Properties and Biological Effects of Liposomes and their uses in Pharmacology and Toxicology

Intranasal Nanoparticulate Systems as Alternative Route of Drug Delivery

There is always a need for alternative and efficient methods of drug delivery. The nasal cavity can be considered as a non-invasive and efficient route of administration. It has been used for local, systemic, brain targeting, and vaccination delivery. Although many intranasal products are currently available on the market, the majority is used for local delivery with fewer products available for the other targets. As nanotechnology utilization in drug delivery has rapidly spread out, the nasal delivery has become attractive as a promising approach. Nanoparticulate systems facilitate drug transportation across the mucosal barrier, protect the drug from nasal enzyme degradation, enhance the delivery of vaccines to the lymphoid tissue of the nasal cavity with an adjuvant activity, and offer a way for peptide delivery into the brain and the systemic circulation, in addition to their potential for brain tumor treatment. This review article aims at discussing the potential benefit of the intranasal nanoparticulate systems, including nanosuspensions, lipid and surfactant, and polymer-based nanoparticles as regards productive intranasal delivery. The aim of this review is to focus on the topicalities of nanotechnology applications for intranasal delivery of local, systemic, brain, and vaccination purposes during the last decade, referring to the factors affecting delivery, regulatory aspects, and patient expectations. This review further identifies the benefits of applying the Quality by Design approaches (QbD) in product development. According to the reported studies on nanotechnology-based intranasal delivery, potential attention has been focused on brain targeting and vaccine delivery with promising outcomes. Despite the significant research effort in this field, nanoparticle-based products for intranasal delivery are not available. Thus, further efforts are required to promote the introduction of intranasal nanoparticulate products that can meet the requirements of regulatory affairs with high patient acceptance.

α-Tocopherol liposomes alleviate LPS-induced hepatotoxicities

Gram-negative bacteria, in part through lipopolysaccharide (LPS) and tumor necrosis factor-alpha (TNFα), activate phagocytes to generate reactive oxygen species (ROS), which have been known to play a key role in the pathogenesis of liver injury. Accordingly, we hypothesized that the susceptibility of the liver to ROS should be reduced by augmenting its antioxidant status. Adult male Sprague-Dawley rats were pretreated with α-tocopherol liposomes (20 mg α-tocopherol/kg body weight, i.v.), plain liposomes or saline. 24 h after liposomal treatment, rats were injected intravenously with LPS (1 mg/kg, Escherichia coli: 0111:B4) and killed 2 h later. Livers of saline-pretreated animals challenged with LPS were damaged as demonstrated by increases in plasma alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activities. The hepatic injury appeared to be associated with oxidative stress-mediated mechanisms as evidenced by increases in lipid peroxidation and decreases in glutathione concentration in the liver, both indices of oxidative stress. Also, LPS injection resulted in increases in plasma TNFα and thromboxane B2 (TXB2) levels, as well as increases in hepatic myeloperoxidase (MPO) activity and chloramine concentration, suggestive of activation of the inflammatory response. Pretreatment of rats with plain liposomes, 24 h prior to LPS challenge, failed to protect against the LPS-induced liver injury. Although pretreatment of animals with α-tocopherol liposomes was not effective in preventing the LPS-induced inflammatory response, it conferred a partial protection against the LPS-induced changes in plasma AST and ALT activities as well as in hepatic levels of lipid peroxidation, glutathione and chloramine concentrations. These data appear to suggest that augmentation of the hepatic antioxidant status is effective in alleviating the LPS-induced liver injury.

Polymerized surfactant vesicles: novel membrane mimetic systems

Vesicles formed from dialkyl surfactants containing vinyl, methacrylate, diacetylene, isocyano, and styrene groups have been stabilized by polymerization across their bilayers of head groups. Polymerized vesicles have shelf lives of many months and controllable permeabilities and sizes. The kinetics of surfactant vesicle photopolymerzation have been determined, and the mechanism of photopolymerization has been discussed as a two-dimensional surface process. Polymerized surfactant vesicles concentrate reagents in their aqueous interiors, in bilayers, and in their inner or outer surfaces. This, in turn, leads to altered reaction rates and sites. Polymerized surfactant vesicles also provide a good media for the generation, in situ, of small, uniform, and efficient colloidal catalysts.

Preliminary investigation of the nasal delivery of liposomal leuprorelin acetate for contraception in rats

The purpose of the study was to investigate the nasal route as a non-invasive alternative for delivery of leuprorelin acetate (leuprolide acetate, LEU) and to achieve an effective concentration of leuprorelin acetate in blood after nasal administration for contraception in rats. The plain drug solution, physical mixture (plain drug along with constituents of liposomes), or drug encapsulated in either neutral or charged liposomes containing 5 μg leuprorelin acetate were administered to rats through the nasal route. The plain drug solution was administered subcutaneously (s.c.). Simultaneous evaluation was performed on the influence of a mucoadhesive agent (chitosan) on nasal absorption of the plain drug and the liposome-encapsulated drug. Blood samples were taken at regular time intervals and subjected to luteinising hormone (LH) analysis using a specific immunoassay kit. The plasma luteinising hormone concentration vs time data of nasal and subcutaneous treatments were plotted and compared with that of subcutaneous administration. Relative percentage of bioavailability (F) for nasal treatments was calculated from plasma concentration vs time plots. Sperm count and fertility performance studies were carried out for selected formulations in rats. Neutral liposomes (LLEU) and negatively-charged liposomes (LLEUn) showed higher relative percentage of bioavailability (F 27.83 and 21.30%, respectively) as compared with the plain drug and the physical mixture (F 10.89 and 10.96%, respectively) after nasal administration. Hence, work on neutral liposomes was continued. F was further improved after incorporation of chitosan i.e. 10.89 to 49.13% for plain leuprorelin acetate and 27.83 to 88.90% for liposomal leuprorelin acetate formulations. Liposomal chitosan formulation administered nasally and leuprorelin acetate solution subcutaneously achieved complete azoospermia. No implantation sites were observed after the mating of female rats with treated males. It was observed that in the treated female rats, the estrous cycles ceased with the same formulations from the first treatment cycle. The findings of these investigations demonstrated that the bioavailability of the nasally-administered liposomal leuprorelin acetate with chitosan formulation was comparable with that of the subcutaneously administered drug. Complete contraception was obtained in male and female rats that had been treated with either the nasally administered liposomal leuprorelin acetate with chitosan or the subcutaneously administered drug.

Recent advances in liposomal dry powder formulations: preparation and evaluation

Liposomal drug dry powder formulations have shown many promising features for pulmonary drug administration, such as selective localization of drug within the lung, controlled drug release, reduced local and systemic toxicities, propellant-free nature, patient compliance, high dose carrying capacity, stability and patent protection. Critical review of the recent developments will provide a balanced view on benefits of liposomal encapsulation while developing dry powder formulations and will help researchers to update themselves and focus their research in more relevant areas. In liposomal dry powder formulations (LDPF), drug encapsulated liposomes are homogenized, dispersed into the carrier and converted into dry powder form by using freeze drying, spray drying and spray freeze drying. Alternatively, LDPF can also be formulated by supercritical fluid technologies. On inhalation with a suitable inhalation device, drug encapsulated liposomes get rehydrated in the lung and release the drug over a period of time. The prepared LDPF are evaluated in vitro and in vivo for lung deposition behavior and drug disposition in the lung using a suitable inhaler device. The most commonly used liposomes are composed of lung surfactants and synthetic lipids. Delivery of anticancer agents for lung cancer, corticosteroids for asthma, immunosuppressants for avoiding lung transplantation rejection, antifungal drugs for lung fungal infections, antibiotics for local pulmonary infections and cystic fibrosis and opioid analgesics for pain management using liposome technology are a few examples. Many liposomal formulations have reached the stage of clinical trials for the treatment of pulmonary distress, cystic fibrosis, lung fungal infection and lung cancer. These formulations have given very promising results in both in vitro and in vivo studies. However, modifications to new therapies for respiratory diseases and systemic delivery will provide new challenges in conducting well-designed inhalation toxicology studies to support these products, especially for chronic diseases.

Chapter 9 - Nanoliposomal dry powder formulations

Liposomal dry powder formulations (DPFs) have proven their superiority over conventional DPFs due to favorably improved pharmacokinetics and pharmacodynamics of entrapped drugs, and thus, reduced local and systemic toxicities. Nanoliposomal DPFs (NLDPFs) provide stable, high aerosolization efficiency to deep lung, prolonged drug release, slow systemic dilution, and avoid macrophage uptake of encapsulated drug by carrier-based delivery of nano-range liposomes. This chapter describes methods of preparation of nanoliposomes (NLs) and NLDPFs, using various techniques, and their characterization with respect to size distribution, flow behavior, in vitro drug release profile, lung deposition, cellular uptake and cytotoxicity, and in vivo pharmacokinetics and pharmacodynamics. Some examples have been detailed for better understanding of the methods of preparation and evaluation of NLDPFs by investigators.

A preliminary pharmacokinetic study of liposomal leuprolide dry powder inhaler: a technical note

The developed liposomal DPI of LEU (LLEUn-DPI) demonstrated approximately 50% bioavailability compared with SC route. The studies justify the role of the pulmonary route as a promising alternative to the presently available SC route. The components of liposomal vesicles may be suitably changed to achieve higher bioavailability. Pulmonary delivery of LEU is expected to help in improving patient compliance, self-administration and avoiding the complications related to injection procedure. The developed LEU-DPI may be employed for both male and female contraception and treatment of prostate cancer in men and early puberty in children. In women it may be used for ovarian, endometrial, pancreas, and breast cancer; endometriosis; Uterine Leiomyoma; and anemia due to uterine fibroid tumors. However, the role of LEU-DPI in clinical practice can only be justified only after in vivo studies on 2 species of animals followed by extensive clinical trials.

The choroidal circulation assessed by laser-targeted angiography

The choroid plays an important role in supplying nutrients to and removing waste products from the outer region of the retina. Abnormal choroidal blood flow can disrupt normal retinal function and lead to alterations in visual function. Visualization of the choriocapillaris in vivo is a great challenge to understanding its normal physiology and involvement in the disease process. Laser-targeted angiography (LTA) is a relatively new method used to visualize and analyze the choroidal circulation. Carboxyfluorescein (CF), encapsulated in heat-sensitive liposomes, is released locally in the choroid through the application of a heat beam provided by an infrared laser. Video angiograms are generated with excitation illumination provided by an argon laser. Obtained images are highly selective to the choriocapillaris and are sharply contrasted against underlying and overlying structures. The images can be obtained repetitively, during which period the circulating liposome concentration is sufficient to generate adequate angiograms. These high-quality images have revealed three distinct phases (filling, plateau, and draining) of the choriocapillaris. In the plateau phase, a cluster of lobules fed by a common arteriole has been uniformly illuminated. This defined cluster area does not change in size while an infrared laser is continuously applied to the same spot, which demonstrates that each cluster is functionally independent and no physiological communication exists between them. Only in posterior regions do the angiograms demonstrate during the filling and draining phases that each lobule is filled from a central spot and drained along a peripheral ring, showing honeycomb flow patterns. The regional differences in choriocapillaris flow patterns revealed by LTA suggests that the choriocapillaris provides a more highly efficient system of outflow in posterior regions than in peripheral regions. LTA is useful in analyzing choroidal circulation in vivo and has the potential for clinical application in the future. Additionally, LTA has a unique capability to image choroidal neovascularization in animal models and it promises potential application in age-related macular degeneration (AMD).

Pulmonary absorption of liposomal levonorgestrel

The purpose of these studies was to achieve desired bioavailability after pulmonary administration of Levonorgestrel (LN) and to provide prolonged effective concentration of the drug in plasma and to reduce reported side effects of orally administered drug. The plain drug suspension, physical mixture (plain drug with liposomal constituents), and drug-encapsulated liposomes containing 10 micro g of drug were instilled intratracheally in rats. Similarly, 10- micro g drug suspension (LO) was administered orally. The blood samples were withdrawn at specific time intervals and were subjected to LN analysis by spectrofluorimetric technique. The plasma drug concentration data of both the treatments were plotted, and pharmacokinetics data were calculated and compared with that of oral administration. Percentage relative bioavailability (F*) of 97.6%, 98.6%, and 109.9% were observed after pulmonary administration of plain drug formulation (LP1), physical mixture (plain drug along with constituents of liposomes [LP2]), and liposomal (LP3) formulations of the drug, respectively. Following oral administration, Cmax of 14.4 +/- 0.6 ng/mL was observed at 2.1 +/- 0.2 hours followed by subtherapeutic concentration beyond 30 +/- 0.2 hours, while after pulmonary administration of LP1, LP2, and LP3 formulations, Cmax of 4.4 +/- 0.4 ng/mL, 4.2 +/- 0.5 ng/mL, and 4.4 +/- 0.6 ng/mL were observed at 6.0 +/- 0.2 hours, 7.0 +/- 0.2 hours, and 6.8 +/- 0.2 hours, respectively, followed by maintenance of effective plasma drug concentration up to 60 +/- 2 hours. These studies demonstrate superiority of pulmonary drug delivery with regards to maintenance of effective therapeutic concentration of the LN in the plasma over a period of 6 to 60 hours. Hence, the pulmonary delivery is expected to reduce frequency of dosing and systemic side effects associated with oral administration of LN.

Nasal delivery of levonorgestrel for contraception: an experimental study in rats

OBJECTIVE

To ascertain the nasal bioavailability of Levonorgestrel and change formulation components to provide long-term effective concentrations of the drug in blood. An experimental study was conducted on rats to reduce dose and/or frequency of drug administration to reduce expected side effects reported in humans.

DESIGN

In vivo study in rats.

SETTING

Centre of Relevance & Excellence in new drug delivery systems, Pharmacy Dept., G.H. Patel Budg., Faculty of Technology and Engineering, M.S. University of Baruda, Fatehgunj, Vadodara, Gujarat, India.

ANIMAL(S)

Rats of proven fertility.

INTERVENTION(S)

Formulations containing 10-microg of levonorgestrel were administered in rats via the nasal route. Similarly, a 10-microg drug suspension was administered orally. The influence of the mucoadhesive agents chitosan and carbopol 934p on nasal absorption of the drug was also evaluated.

MAIN OUTCOME MEASURE(S)

Plasma drug concentration and pharmacokinetics.

RESULT(S)

Relative bioavailabilities of 29.93%, 32.14%, and 25.97% were observed after nasal administration of plain drug, physical mixture, and liposomal formulations, respectively. Mucoadhesive agents in nasal formulations were found to produce a threefold increase in drug bioavailability. Bioavailability was improved from 29.93% to 101.70% and 99.42%, respectively, for chitosan (0.5%) and carbopol 934p (0.5%) formulations, with a significantly improved plasma half life from 7.0 hours to 55.7 hours and 52.9 hours, respectively. Pharmacodynamic studies indicate that the dosing interval can be changed from daily oral administration to nasal administration once every 2 days without changing the dose.

CONCLUSION(S)

Levonorgestrel with mucoadhesive agents administered nasally in rats is superior for maintaining effective drug concentrations over an extended period of time when compared with the presently available orally administered form.

Liposomal alpha-tocopherol alleviates the progression of paraquat-induced lung damage

The present study was carried out to investigate the efficacy of liposome-associated alpha-tocopherol in treating pulmonary damage caused by paraquat exposure. alpha-Tocopherol liposomes (8 mg alpha-tocopherol/kg body weight) or plain liposomes were intratracheally instilled into the lungs of rats 24 h after paraquat treatment (20 mg/kg, ip); treated animals were killed 8, 24 or 48 h after administration of the liposomal preparations. Lungs of animals exposed to paraquat were extensively damaged as evidenced by an increase in lung weight and decreases in pulmonary angiotensin converting enzyme and alkaline phosphatase activities. Also, paraquat treatment resulted in a significant reduction in glutathione (GSH) concentration in the lung and an elevation in microsomal lipid peroxidation levels, as measured by the formation of diene conjugates. Treatment of paraquat-injected rats with plain liposomes did not significantly alter paraquat-induced changes of all parameters examined. On the other hand, treatment of rats with alpha-tocopherol liposomes, 24 h after paraquat administration, resulted in a significant increase in pulmonary alpha-tocopherol concentrations as well as a reduction in paraquat-induced changes in lipid peroxidation, GSH concentration, and lung angiotensin converting enzyme and alkaline phosphatase activities. The results of the present study suggest that alpha-tocopherol, administered directly to the lung in a liposomal form, may serve as a potentially effective pharmacological agent in the treatment of paraquat-induced lung injury.

Prevention of phorbol myristate acetate-induced acute lung injury by alpha-tocopherol liposomes

Phorbol-myristate acetate (PMA) is commonly used to produce experimental edema and other tissue injuries in the lung. Lung injuries induced by the administration of PMA has been shown to be mediated mainly by neutrophils. Neutrophils recruited to the lower respiratory tract may damage lung tissues by releasing reactive oxygen species, neutral proteases, and lysosomal enzymes. The present study was conducted to investigate whether alpha-tocopherol, entrapped in dipalmitoylphosphatidylcholine liposomes and delivered directly to the lung, could counteract some of the PMA-induced lung injuries. Plain liposomes or alpha-tocopherol containing liposomes (8 mg alpha-tocopherol/kg body weight) were intratracheally instilled into the lungs of rats 24 hr prior to PMA exposure (25 micrograms/kg) and treated rats were killed 3 hr later. Lungs of control animals exposed to PMA developed an increase in lung weight and lipid peroxidation as well as a decrease in lung angiotensin converting enzyme (ACE) and alkaline phosphatase (AKP) activities. PMA treatment also caused an increase in myeloperoxidase (MPO) activity in the lung, suggestive of neutrophil infiltration. Pretreatment of PMA-treated rats with plain liposomes had no effect on PMA-induced injuries. In contrast, pretreatment of rats with liposomal alpha-tocopherol, 24 hr prior to PMA administration, resulted in a significant elevation of pulmonary alpha-tocopherol concentration, accompanied by a concomitant reduction in MPO activity and reversal of PMA-induced changes in lung edema, lipid peroxidation, ACE and AKP activities. These results appear to demonstrate that the intratracheal administration of a liposome-associated lipophilic antioxidant, such as alpha-tocopherol, can significantly ameliorate the toxic effects of reactive oxygen species, putatively released from PMA-stimulated pulmonary target cells and infiltrating neutrophils.

Distribution of free and liposome-encapsulated cefoxitin in experimental intra-abdominal sepsis in rats

The distributions of radiolabelled free cefoxitin (FC) and liposome-encapsulated cefoxitin (LC) were compared in an animal model of intra-abdominal sepsis. Intraperitoneally administered LC was initially retained in the peritoneal cavity with subsequent preferential drug targeting to the liver (14% injected LC) and spleen (6% injected LC) by 3 h post-injection. Differing patterns of liposomal drug and lipid retention indicated that drug release from the liposome complex occurred within the peritoneum, liver and spleen. Intraperitoneal FC was rapidly taken up into the systemic circulation, with peak recovery in the blood (9% injected FC) and liver (5% injected FC) at 1 h post-injection. FC was also rapidly eliminated; 7% of the injected drug was recovered in the kidney 1 h post-injection. A negligible amount of FC was recovered in the spleen and very little FC or LC was found in the lungs of treated animals. Unlike FC, LC was found to provide a sustained bactericidal drug level (> 40 micrograms mL-1) in the peritoneal fluid for up to 5 h post-injection. LC also achieved significantly higher drug levels, compared with FC, within the liver at 3 and 5 h post-injection. Since severe intra-abdominal sepsis is often characterized by the presence of intraphagocytic bacteria in hepatic and splenic reticuloendothelial systems, the enhanced delivery of liposome-encapsulated anti-microbial agents, such as cefoxitin, to the liver and spleen may provide a more effective treatment for the septic condition.

Pulmonary uptake of liposome-associated alpha-tocopherol following intratracheal instillation in rats

This study examined the uptake and subcellular distribution of alpha-tocopherol in the lung following intratracheal instillation of liposome-associated alpha-tocopherol in rats. The liposomal suspension was composed of dipalmitoylphosphatidylcholine (DPPC) and alpha-tocopherol (molar ratio 7:3), labelled with [3H]alpha-tocopherol and [14C]cholesterol. Following intratracheal administration of the liposomal preparation (2 mg alpha-tocopherol/animal), the recovery of [3H]alpha-tocopherol in the lung was maximal (87% of initial dose) 1 h after treatment; thereafter, alpha-tocopherol levels remained relatively high (no less than 73% of initial dose) for the rest of the 72-h experimental period. This treatment effect/resulted in a 16-fold increase in pulmonary total alpha-tocopherol concentration 72 h post-instillation. No radioactivity was detected in the blood, liver, kidney, pancreas, spleen and heart of animals during the 72-h experimental period. [3H]alpha-Tocopherol was recovered largely from cytosolic (45%) and nuclear (36%) fractions of lung and to a lesser extent, from microsomal (11%) and mitochondrial (9%) fractions. Chromatographic analysis of the subcellular fractions revealed that [3H]alpha-tocopherol was co-eluted with 14C-labelled liposomal lipids. Our in-vitro study, involving the incubation of Fe(3+)-ADP (a pro-oxidant) with mitochondrial or microsomal fractions isolated from lung tissues of animals treated with liposome-associated alpha-tocopherol, provided evidence that alpha-tocopherol levels present in the membranes of these subcellular fractions were sufficient to protect against oxidant-induced lipid peroxidation.(ABSTRACT TRUNCATED AT 250 WORDS)

Protective effect of liposome-associated alpha-tocopherol against paraquat-induced acute lung toxicity

The present study was undertaken to investigate whether alpha-tocopherol, entrapped in liposomes and delivered directly to the lung, could protect against paraquat-induced lung damage in the rat. Plain liposomes (composed of dipalmitoylphosphatidylcholine, DPPC) or DPPC/alpha-tocopherol liposomes were administered intratracheally to animals 24 hr prior to an intraperitoneal injection of paraquat (20 mg/kg); rats were killed 24 or 48 hr after paraquat treatment. Results of this study showed that lungs of animals treated with paraquat were damaged extensively as evidenced by an increase in lung weight and a significant reduction in lung angiotensin-converting enzyme (ACE) activity and cytochrome P450 concentration. Furthermore, paraquat treatment resulted in a significant decrease in reduced glutathione (GSH) concentrations and a marked elevation in microsomal lipid peroxidation levels as measured by the formation of diene conjugates. Pretreatment of rats with DPPC liposomes alone did not alter significantly the paraquat-induced changes of all parameters examined. On the other hand, pretreatment of rats with DPPC/alpha-tocopherol liposomes 24 hr prior to paraquat challenge resulted in a significant increase in pulmonary alpha-tocopherol concentrations and antagonized paraquat-induced changes in lipid peroxidation, GSH/GSSG ratio, lung ACE activity and cytochrome P450 concentrations. Results of this study suggested that alpha-tocopherol, delivered directly to the lung in a liposomal formulation 24 hr prior to paraquat administration, confers protection against paraquat-induced lung damage.

The effect of blood on the uptake of liposomal lipid by perfused rat liver

Liposomes have been prepared from dipalmitoylphosphatidylcholine (DPPC) and its mixtures with phosphatidylinositol (PI) and stearylamine. The absorption of the liposomes by perfused rat liver has been studied as a function of blood level (0-7% haematocrit). It has been found that the rate constant for uptake of liposomes (perfusion constant, kp) is markedly reduced by addition of blood to the perfusate particularly in the haematocrit range 0-3%. The perfusion constant is dependent on the liposome composition and decreases with incorporation of PI and increases with incorporation of stearylamine into DPPC liposomes, but is independent of the initial size of the liposomes in the range of weight-average diameter from 40-400 nm. The possible effects of blood components on the liposomes and their subsequent absorption by the liver are discussed.

A new method for delivering alkanes to mammalian cells: preparation and preliminary characterization of an inclusion complex between beta-cyclodextrin and pristane (2,6,10,14-tetramethylpentadecane)

Pristane (2,6,10,14-tetramethylpentadecane) is an isoalkane which induces plasma cell tumorigenesis in genetically susceptible strains of mice. Attempts to study the biological activity of pristane on cells in vitro have been hindered by the extreme hydrophobicity and hence complete immiscibility of the compound in aqueous cell culture media. In comparing different solubilization protocols such as using organic solvents, liposomes, and molecular encapsulation into beta-cyclodextrin (beta-CyD), it was found that beta-CyD/pristane inclusion complexes were optimal for delivery of the hydrocarbon to cells. After solubilization in beta-CyD, pristane was cytotoxic (51Cr release assay) to murine B lymphocyte lines in culture (P388, NSF-1, and SJL-4) and inhibited the lipopolysaccharide-induced stimulation of splenic B lymphocyte proliferation and blast formation (Coulter counter analysis) when added in the micromolar concentration range. Moreover, sub-toxic concentrations of beta-CyD/pristane inclusion complexes were found to have a small but reproducible mitogenic effect [( 3H]thymidine incorporation) on SJL-4 and 308 (murine initiated keratinocyte) cells in culture but not on P388 cells. The results indicate that molecular encapsulation of pristane into beta-CyD provides a new and effective method for delivering low concentrations of alkanes to mammalian cells in vitro.

Endocytosis of liposomes by macrophages: binding, acidification and leakage of liposomes monitored by a new fluorescence assay

The interaction of liposomes with macrophage cells was monitored by a new fluorescence method (Hong, K., Straubinger, R.M. and Papahadjopoulos, D., J. Cell Biol. 103 (1986) 56a) that allows for the simultaneous monitoring of binding, endocytosis, acidification and leakage. Profound differences in uptake, cell surface-induced leakage and leakage subsequent to endocytosis were measured in liposomes of varying composition. Pyranine (1-hydroxypyrene-3,6,8-trisulfonic acid, HPTS), a highly fluorescent, water-soluble, pH sensitive dye, was encapsulated at high concentration into the lumen of large unilamellar vesicles. HPTS exhibits two major fluorescence excitation maxima (403 and 450 nm) which have a complementary pH dependence in the range 5-9: the peak at 403 nm is maximal at low pH values while the peak at 450 nm is maximal at high pH values. The intra- and extracellular distribution of liposomes and their approximate pH was observed by fluorescence microscopy using appropriate excitation and barrier filters. The uptake of liposomal contents by cells and their subsequent exposure to acidified endosomes or secondary lysosomes was monitored by spectrofluorometry via alterations in the fluorescence excitation maxima. The concentration of dye associated with cells was determined by measuring fluorescence at a pH independent point (413 nm). The average pH of cell-associated dye was determined by normalizing peak fluorescence intensities (403 nm and 450 nm) to fluorescence at 413 nm and comparing these ratios to a standard curve. HPTS-containing liposomes bound to and were acidified by a cultured murine macrophage cell line (J774) with a t1/2 of 15-20 min. The acidification of liposomes exhibited biphasic kinetics and 50-80% of the liposomes reached an average pH lower than 6 within 2 h. A liposomal lipid marker exhibited a rate of uptake similar to HPTS, however the lipid component selectively accumulated in the cell; after an initial rapid release of liposome contents, 2.5-fold more lipid marker than liposomal contents remained associated with the cells after 5 h. Coating haptenated liposomes with antibody protected liposomes from the initial release. The leakage of liposomal contents was monitored by co-encapsulating HPTS and p-xylene-bis-pyridinium bromide, a fluorescence quencher, into liposomes. The time course of dilution of liposome contents, detected as an increase in HPTS fluorescence, was coincident with the acidification of HPTS. The rate and extent of uptake of neutral and negatively charged liposomes was similar; however, liposomes opsonized with antibody were incorporated at a higher rate (2.9-fold) and to a greater extent (3.4-fold).(ABSTRACT TRUNCATED AT 400 WORDS)

Evidence from Liposome Encapsulation for Transport-Limited Microbial Metabolism of Solid Alkanes

The recalcitrance of xenobiotics may be caused by an absence of transforming enzymes or by their inability to enter microbial cells. A nondestructive method for differentiating between these two possibilities is described. The solid n -alkanes octadecane (C 18 ) and hexatriacontane (C 36 ) were encapsulated into phosphatidylcholine bilayers (liposomes). The uptake and metabolism rates of encapsulated and unencapsulated substrates were then compared. During 1 h at 25°C, a Pseudomonas isolate took up 1.3% of radiolabeled and unencapsulated C 18 (solid state) versus 23.5% of labeled and encapsulated C 18 . Growth at 25°C occurred with an apparent k s of 2453 ± 148 mg/liter. Liposome encapsulation decreased this K s to 60 ± 12 mg/liter. At 34°C, growth on C 18 (liquid state) occurred with an apparent K s of 819 ± 83 mg/liter and on the readily available carbon source succinate, K s values were 80 ± 10 and 13 ± 7 mg/liter at 25 and 34°C, respectively. At 25°C, the isolate grew on C 36 with an apparent K s of 2,698 ± 831 mg/liter. Liposome encapsulation decreased the K s more than 60-fold to 41 ± 7 mg/liter, resulting in the complete utilization of 400 mg of C 36 per liter in 16 h. Since controls excluded the metabolic utilization of phosphatidylcholine, the results clearly identify transport limitation as the cause for C 36 recalcitrance.

Potential pitfalls in in vitro antitumor activity testing of free and liposome-entrapped doxorubicin

This paper addresses several potential problems which may play a critical role in the outcome of in vitro studies designed to investigate the antitumor activity of drugs. These problems were demonstrated to exist in in vitro assays developed for the evaluation of antitumor activity of free and liposome-entrapped doxorubicin (DXR). The stability of DXR-containing liposomes against drug leakage into the culture medium, as well as the chemical stability and extent of adsorption to tissue culture plastics of both free and liposomal DXR during the liposome-tumor cell incubation, were investigated. It is concluded that a full understanding of these processes is required for a reliable interpretation of the experimental results.

Externally triggered release of dye and drugs from liposomes into the eye. An in vitro and in vivo study

Temperature-sensitive liposomes were made with carboxyfluorescein (CF) (100 mM) entrapped in the aqueous compartment. This liposome dye system was used in vitro to evaluate the feasibility of using microwaves as a triggering mechanism for the release of drugs in the anterior chamber of the eye. The in vitro study demonstrated that CF can be released from liposomes in response to a localized temperature rise induced by microwave irradiation. In an in vivo study in rabbits, CF and the antineoplastic agent, cytosine arabinoside, were administered intravenously and selectively released by increasing the temperature of the ciliary body with microwaves. In the eyes receiving liposome-encapsulated dye, the average concentration of CF in the anterior chamber of the heated eyes was 8.0 times higher than in the contralateral unheated control eyes. In the eyes receiving liposome-encapsulated drug, the average concentration of cytosine arabinoside in the aqueous of the heated eyes was 4.1 times higher than the concentration in the contralateral unheated control eyes. The importance of this finding lies in the potential for a new method of targeting the delivery of dyes and drugs to specific sites in the eye.

Liposomes as membrane model for study of lipid peroxidation

This article describes the properties, production and characterization of liposomes with special reference to their use as membrane model for the study of lipid peroxidation. It presents briefly the methods that can be used for the assay of liposomal lipid peroxidation and brings out the special advantages these liposomes provide in elucidating the mechanism of lipid peroxidation by different physical and chemical agents. Studies involving liposomal lipid peroxidation by different agents and the consequent changes in the structure and function of liposomal membrane have been reviewed briefly.

Targeting of anti-Thy 1.1 monoclonal antibody conjugated liposomes in Thy 1.1 mice after intravenous administration

125I-labeled liposomes, conjugated to an anti-Thy 1.1 monoclonal antibody (MRCOX7), demonstrated up to 7.4-fold greater lymph node uptake than liposomes conjugated to non-specific monoclonal antibody (R-10) after intravenous injection into Thy 1.1 (AKR-J) mice. Uptake of anti-Thy 1.1-conjugated liposomes by the lymph nodes of AKR-J mice was 3-times greater than their uptake by lymph nodes of Thy 1.2 (AKR-Cu) mice. Lymph node localization of anti-Thy 1.1-liposomes was equal to that of control monoclonal antibody-liposomes in Thy 1.2 mice. Conjugation to either monoclonal antibody substantially increased liposome clearance by the liver, while decreasing liposome uptake in a number of organs outside the reticuloendothelial system. Changes in liposome size and phospholipid composition did not significantly alter these results. Administration of a large predose of unconjugated liposomes prior to injection of MRCOX7-conjugated liposomes increased blood levels and reduced liver uptake of the monoclonal antibody-liposome conjugates, but did not further enhance lymph node uptake. This study demonstrates that targeting of liposomes by conjugation to the appropriate monoclonal antibody, can significantly increase their uptake in lymph nodes which contain high levels of cells expressing the target antigen. However, conjugation to monoclonal antibody also increases clearance of liposomes by the liver. To increase the uptake of monoclonal antibody-conjugated liposomes in target tissue, substantial reduction of their clearance by the reticuloendothelial system will be required.

Toxicity of non-drug-containing liposomes for cultured human cells

The effects of non-drug-containing liposomes of different compositions and sizes on the proliferation of nine cancer-derived and one normal cultured human cell lines were determined. Stearylamine- and cardiolipin-containing liposomes were toxic (ID50) at 200 microM liposomal lipid concentrations or less, whereas phosphatidylglycerol- and phosphatidylserine-containing liposomes were toxic in the range 130-3000 microM. Phosphatidylcholine or dipalmitoylphosphatidylcholine liposomes were not toxic at 3000-4000 microM. In general, small liposomes were more toxic than large ones. The results indicate that there are wide variations in toxicity of non-drug-containing liposomes for cultured human cells. The potential for nonspecific toxicity due to the liposomes themselves should be carefully considered if human administration of drug-containing liposomes is to be done.

Liposomes in treatment of infectious diseases

In reviewing the literature about the potential of liposomes in the therapy of infections caused by protozoa, bacteria, fungi and viruses, it can be concluded that liposomal encapsulation may improve the therapeutic index of anti-infectious drugs. The improved therapeutic index may be a result of a reduction in drug toxicity and/or an enhanced drug delivery at the intracellular site of infection. Furthermore, attention is paid to the therapeutic utility of liposome-encapsulated immunomodulators in treatment of infections.

Efficient radiolabeling of mammalian cells using 111In-tagged liposomes

When indium-111 oxine labeled neutral liposomes were incubated with Chinese hamster V79 cells in the presence of 100 mM calcium, the cell-associated radioactivity increased approximately 75-fold over that observed in the absence of calcium. This is considerably higher (approximately 20 times) than the cellular uptake obtained when these cells are incubated in the presence of 111In-oxine alone. The highest uptake of radioactivity occurred when no bovine serum albumin was present in the medium, while as little as 0.001% of the protein greatly reduced the cell-liposome association. These efficient cell labeling conditions were not found to affect the survival of the cells.

The absorption of phospholipid vesicles by perfused rat liver depends on vesicle surface charge

Two types of sonicated vesicle have been prepared from dipalmitoylphosphatidylcholine (DPPC) by incorporation of phosphatidylinositol (PI) to give negatively charged vesicles and stearylamine to give positively charged vesicles. The absorption of the vesicles by rat liver has been investigated by perfusion techniques. A steady state of vesicle absorption is rapidly established in approx. 2 min and the initial rates of absorption decrease with PI content of the vesicles and increase with stearylamine content. In the steady state, the uptake of vesicles by the liver is similarly dependent on vesicle charge, being inhibited by PI and enhanced by incorporation of stearylamine in the vesicles. Fractionation of the liver into subcellular fractions following perfusion showed that most of the vesicular lipid could be found associated with a nuclear (plus plasma membrane) fraction. The suppression of vesicle absorption by PI may be of value as a means of bypassing the liver in relation to the use of vesicles as a delivery system.

The effect of incorporation of cloxacillin in liposomes on treatment of experimental staphylococcal mastitis in mice

The effect of incorporation of cloxacillin in liposomes on the treatment of staphylococcal mastitis was assessed bacteriologically 18 h after treatment of experimental infections in mice caused by two strains of Staphylococcus aureus. Intramammary treatments were cloxacillin incorporated in liposomes, cloxacillin in combination with liposomes, empty liposomes, cloxacillin in saline and saline alone. In none of the experiments did entrapment of cloxacillin within liposomes enhance its antibacterial effects. Electron microscopic studies demonstrated the presence of liposomes in neutrophils which also contained staphylococci. The results support the hypothesis that intracellular staphylococci are metabolically dormant and therefore not susceptible to the action of inhibitors of cell wall synthesis such as cloxacillin.

Inhibition of liver metastases of M 5076 tumor by liposome-entrapped adriamycin

The toxicity and therapeutic efficacy of free adriamycin (AM) and AM entrapped in standardized liposomes (AM-MLV) were evaluated in normal mice and in mice bearing M 5076 murine tumor, which metastasizes to the liver after i.v. and s.c. transplants of tumor cell suspensions. Acute and chronic toxicity to AM could be reduced by drug encapsulation in liposomes. The data indicated that at approximately equitoxic doses of free AM (10 mg/kg) and AM-MLV (greater than 20 mg/kg), the increase in survival times of mice transplanted i.v. with tumor cells were 25% and 100%, respectively. Furthermore, only in the AM-MLV-treated mice were long-term survivors observed. In contrast AM-MLV were equally effective as free AM in mice transplanted s.c. with tumor cell suspensions. AM-MLV, however, were more effective than free AM against liver metastases in mice bearing s.c. tumor, indicating differential antitumor activities against the same tumor type growing at different locations in the same animals.

Uptake of antineoplastic agents into large unilamellar vesicles in response to a membrane potential

Many drugs exhibit lipophilic and cationic (basic) characteristics. Previous studies have shown that lipophilic cations can be accumulated into model membrane 'liposomal' (vesicular) systems in response to establishing a membrane potential (inside negative) across the vesicle membrane. We demonstrate here that the anticancer drugs, adriamycin and vinblastine, can be rapidly accumulated into egg phosphatidylcholine large unilamellar vesicles in response to a valinomycin-dependent K+ diffusion potential (delta psi) to achieve high effective interior concentrations. Further, trapping efficiencies approaching 100% can be easily achieved. The influence of lipid composition and the requirement for valinomycin have been examined for adriamycin. Equimolar cholesterol levels inhibit the uptake process at 20 degrees C. However, incubation at higher temperature results in enhanced uptake. Similarly, the presence of egg phosphatidylserine or incubation at elevated temperatures results in significant adriamycin uptake in the absence of valinomycin. It is shown that the adriamycin retention time in the vesicles is enhanced by an order of magnitude or more when actively trapped by the presence of a membrane potential in comparison to passive trapping procedures. It is suggested that such active trapping procedures may be of use for loading liposomal systems for drug delivery applications, and may provide avenues for controlled release of encapsulated material.

The potential use of liposome-mediated antiviral therapy

The natural targeting of liposomes to cells of the reticuloendothelial system should be exploited to examine whether selective delivery of antiviral or immunomodulatory agents could be beneficial for the treatment of virus diseases. In this review we discuss the potential use of liposomes in the treatment of virus diseases, the targeting of liposome-encapsulated immunomodulators to macrophages in order to render these cells cytolytic for virus-infected cells, and the targeting of liposome-encapsulated antiviral drugs to macrophages to achieve direct suppression of virus replication with in these cells.

Influence of liposome charge on the association of liposomes with Kupffer cells in vitro. Effects of divalent cations and competition with latex particles

We studied the interaction of large unilamellar liposomes carrying different surface charges with rat Kupffer cells in maintenance culture. In addition to 14C-labeled phosphatidylcholine, all liposome preparations contained either 3H-labeled inulin or 125I-labeled bovine serum albumin as a non-degradable or a degradable aqueous space marker, respectively. With vesicles carrying no net charge, intracellular processing of internalized liposomes caused nearly complete release of protein label into the medium in acid-soluble form, while phospholipid label was predominantly retained by the cells, only about one third being released. The presence of the lysosomotropic agent, ammonia, inhibited the release of both labels from the cells. At 4 degrees C, the association and degradation of the vesicles were strongly reduced. These results are very similar to what we reported on negatively charged liposomes (Dijkstra, J., Van Galen, W.J.M., Hulstaert, C.E., Kalicharan, D., Roerdink, F.H. and Scherphof, G.L. (1984) Exp. Cell Res. 150, 161-176). The interaction of both types of vesicles apparently proceeds by adsorption to the cell surface followed by virtually complete internalization by endocytosis. Similar experiments with positively charged vesicles indicated that only about half of the liposomes were taken up by the endocytic route, the other half remaining adsorbed to the cell-surface. Attachment of all types of liposomes to the cells was strongly dependent on the presence of divalent cations; Ca2+ appeared to be required for optimal binding. Neutral liposomes only slightly competed with the uptake of negatively charged vesicles, both at 4 degrees and 37 degrees C, whereas negatively charged small unilamellar vesicles and negatively charged latex beads were found to compete very effectively with the large negatively charged liposomes. Neutral vesicles competed effectively for uptake with positively charged ones. These results suggest that neutral and positively charged liposomes are largely bound by the same cell-surface binding sites, while negatively charged vesicles attach mainly to other binding sites.

Ocular drug bioavailability from topically applied liposomes

During the past decade liposomes have been investigated extensively for their ability to improve drug utilization by the body, first in the area of chemotherapeutics and most recently in the area of ophthalmology. Liposomes are vesicle-like structures with a concentric series of alternating compartments of aqueous spaces and phospholipid bilayers. To date, liposomes have been found to both promote and reduce ocular drug absorption, indicating that a definite need exists for further studies to evaluate the interplay of drug, liposomes, and the corneal surface in determining the effectiveness of liposomes as vehicles for topically applied ophthalmic drugs. The purpose of this review is to place in perspective the role of liposomes in topical ocular drug delivery. As background material, the factors influencing ocular drug bioavailability and the features of liposomes pertinent to their effectiveness as drug carriers are reviewed.

An approach to the therapy of metastases from cancer of the upper rectum: a working hypothesis

Previously reported analyses of autopsy data gathered from patients dying from the sequelae of adenocarcinomas of the upper rectum revealed a step-wise sequence in the development of distant metastases. First, dissemination via the portal vein led to secondary hepatic metastases. Cancer cells from these liver metastases (not the primary cancer) disseminated via the inferior vena cava to generate tertiary pulmonary metastases. Cancer cells from the lung metastases (not the primary or secondary cancers) then disseminated via the arterial route to give rise to metastases in other organs. We propose a protocol for the treatment of patients with upper rectal carcinomas, based on the expectation that, at different times after diagnosis, some patients will have no distant metastases, metastases in the liver only, or in the liver and lungs only. The protocol for therapy is based on currently available liposome technology, by means of which high doses of drugs can be targeted to the liver and lungs containing the metastases, yet distinct from the metastases. It is argued that selective local delivery of this type would increase the dose of cytotoxic agent delivered, thereby increasing the chances of overcoming the relative drug-resistance of the metastatic cancer cells and, at the same time, reduce the risk of nonspecific toxicity. Liver and lung-selective liposomes could, when necessary, be delivered at the same time, in the same systemic venous infusion.