Liposomes in pulmonary applications: physicochemical considerations, pulmonary distribution and antioxidant delivery

The Utilization of Plant-Material-Loaded Vesicular Drug Delivery Systems in the Management of Pulmonary Diseases

Medicinal plants have been utilized to treat a variety of conditions on account of the bioactive properties that they contain. Most bioactive constituents from plants are of limited effectiveness, due to poor solubility, limited permeability, first-pass metabolism, efflux transporters, chemical instability, and food-drug interactions However, when combined with vesicular drug delivery systems (VDDS), herbal medicines can be delivered at a predetermined rate and can exhibit site-specific action. Vesicular drug delivery systems are novel pharmaceutical formulations that make use of vesicles as a means of encapsulating and transporting drugs to various locations within the body; they are a cutting-edge method of medication delivery that combats the drawbacks of conventional drug delivery methods. Drug delivery systems offer promising strategies to overcome the bioavailability limitations of bioactive phytochemicals. By improving their solubility, protecting them from degradation, enabling targeted delivery, and facilitating controlled release, drug delivery systems can enhance the therapeutic efficacy of phytochemicals and unlock their full potential in various health conditions. This review explores and collates the application of plant-based VDDS with the potential to exhibit protective effects against lung function loss in the interest of innovative and effective treatment and management of respiratory illnesses.

Nano-antimicrobials: A New Paradigm for Combating Mycobacterial Resistance

BACKGROUND

Mycobacterium group contains several pathogenic bacteria including M. tuberculosis where the emergence of multidrug-resistant tuberculosis (MDR-TB) and extensively drug-resistant tuberculosis (XDR-TB) is alarming for human and animal health around the world. The condition has further aggravated due to the speed of discovery of the newer drugs has been outpaced by the rate of resistance developed in microorganisms, thus requiring alternative combat strategies. For this purpose, nano-antimicrobials have emerged as a potential option.

OBJECTIVE

The current review is focused on providing a detailed account of nanocarriers like liposome, micelles, dendrimers, solid lipid NPs, niosomes, polymeric nanoparticles, nano-suspensions, nano-emulsion, mesoporous silica and alginate-based drug delivery systems along with the recent updates on developments regarding nanoparticle-based therapeutics, vaccines and diagnostic methods developed or under pipeline with their potential benefits and limitations to combat mycobacterial diseases for their successful eradication from the world in future.

RESULTS

Distinct morphology and the underlying mechanism of pathogenesis and resistance development in this group of organisms urge improved and novel methods for the early and efficient diagnosis, treatment and vaccination to eradicate the disease. Recent developments in nanotechnology have the potential to meet both the aspects: nano-materials are proven components of several efficient targeted drug delivery systems and the typical physicochemical properties of several nano-formulations have shown to possess distinct bacteriocidal properties. Along with the therapeutic aspects, nano-vaccines and theranostic applications of nano-formulations have grown in popularity in recent times as an effective alternative means to combat different microbial superbugs.

CONCLUSION

Nanomedicine holds a bright prospect to perform a key role in global tuberculosis elimination program.

Exploring the potential benefit of natural product extracts in paraquat toxicity

Paraquat dichloride, a herbicide used for weed and grass control, is extremely toxic to humans and animals. The mechanisms of toxicity involve the redox cycling of paraquat resulting in the generation of reactive oxygen species and the depletion of the cellular NADPH. The major cause of death in paraquat poisoning is respiratory failure due to its specific uptake by and oxidative insult to the alveolar epithelial cells and inflammation with subsequent obliterating fibrosis. Paraquat also causes selective degeneration of dopaminergic neurons in the substantia nigra pars compacta, reproducing an important pathological feature of Parkinson disease. Currently, there are no antidotes for the treatment of paraquat poisoning and therapeutic management is mostly supportive and directed towards changing the disposition of the poison. The lack of effective treatments against paraquat poisoning has led to the exploration of novel compounds with antioxidant and/or anti-inflammatory properties. Recently, there is an interest in plant compounds, particularly those used in traditional medicine. Phytochemicals have been highlighted as a possible therapeutic modality for a variety of diseases due to their putative efficacies and safety. In this review, the status of plant extracts and traditional medicines in ameliorating the toxicity of paraquat is discussed.

Niosomes: a review of their structure, properties, methods of preparation, and medical applications

Target-specific drug-delivery systems for the administration of pharmaceutical compounds enable the localization of drugs to diseased sites. Various types of drug-delivery systems utilize carriers, such as immunoglobulins, serum proteins, synthetic polymers, liposomes, and microspheres. The vesicular system of niosomes, with their bilayer structure assembled by nonionic surfactants, is able to enhance the bioavailability of a drug to a predetermined area for a period. The amphiphilic nature of niosomes promotes their efficiency in encapsulating lipophilic or hydrophilic drugs. Other additives, such as cholesterol, can be used to maintain the rigidity of the niosomes’ structure. This narrative review describes fundamental aspects of niosomes, including their structural components, methods of preparation, limitations, and current applications to various diseases.

Antioxidant strategies in respiratory medicine

Pulmonary oxidant stress plays an important pathogenetic role in disease conditions including acute lung injury/adult respiratory distress syndrome (ALI/ARDS), hyperoxia, ischemia-reperfusion, sepsis, radiation injury, lung transplantation, COPD, and inflammation. Reactive oxygen species (ROS), released from activated macrophages and leukocytes or formed in the pulmonary epithelial and endothelial cells, damage the lungs and initiate cascades of pro-inflammatory reactions propagating pulmonary and systemic stress. Diverse molecules including small organic compounds (e.g. gluthatione, tocopherol (vitamin E), flavonoids) serve as natural antioxidants that reduce oxidized cellular components, decompose ROS and detoxify toxic oxidation products. Antioxidant enzymes can either facilitate these antioxidant reactions (e.g. peroxidases using glutathione as a reducing agent) or directly decompose ROS (e.g. superoxide dismutases [SOD] and catalase). Many antioxidant agents are being tested for treatment of pulmonary oxidant stress. The administration of small antioxidants via the oral, intratracheal and vascular routes for the treatment of short- and long-term oxidant stress showed rather modest protective effects in animal and human studies. Intratracheal and intravascular administration of antioxidant enzymes are being currently tested for the treatment of acute oxidant stress. For example, intratracheal administration of recombinant human SOD is protective in premature infants exposed to hyperoxia. However, animal and human studies show that more effective delivery of drugs to cells experiencing oxidant stress is needed to improve protection. Diverse delivery systems for antioxidants including liposomes, chemical modifications (e.g. attachment of masking pegylated [PEG]-groups) and coupling to affinity carriers (e.g. antibodies against cellular adhesion molecules) are being employed and currently tested, mostly in animal and, to a limited extent, in humans, for the treatment of oxidant stress. Further studies are needed, however, in order to develop and establish effective applications of pulmonary antioxidant interventions useful in clinical practice. Although beyond the scope of this review, antioxidant gene therapies may eventually provide a strategy for the management of subacute and chronic pulmonary oxidant stress.

Suppressing iron oxide nanoparticle toxicity by vascular targeted antioxidant polymer nanoparticles

The biomedical use of superparamagnetic iron oxide nanoparticles has been of continued interest in the literature and clinic. Their ability to be used as contrast agents for imaging and/or responsive agents for remote actuation makes them exciting materials for a wide range of clinical applications. Recently, however, concern has arisen regarding the potential health effects of these particles. Iron oxide toxicity has been demonstrated in in vivo and in vitro models, with oxidative stress being implicated as playing a key role in this pathology. One of the key cell types implicated in this injury is the vascular endothelial cells. Here, we report on the development of a targeted polymeric antioxidant, poly(trolox ester), nanoparticle that can suppress oxidative damage. As the polymer undergoes enzymatic hydrolysis, active trolox is locally released, providing a long term protection against pro-oxidant agents. In this work, poly(trolox) nanoparticles are targeted to platelet endothelial cell adhesion molecules (PECAM-1), which are able to bind to and internalize in endothelial cells and provide localized protection against the cytotoxicity caused by iron oxide nanoparticles. These results indicate the potential of using poly(trolox ester) as a means of mitigating iron oxide toxicity, potentially expanding the clinical use and relevance of these exciting systems.

Inhaled antibiotics to treat lung infection

The development of inhaled antibiotics to treat lung infection is an active field, with four approved products in the USA and more in the late stages of clinical development. The efficacies of TOBI® tobramycin (Novartis) and Cayston® aztreonam lysate (Gilead), the approved inhaled antibiotics for cystic fibrosis (CF) patients colonized with Pseudomonas aeruginosa, have been well documented. Recent approvals for a second-generation tobramycin solution, Bethkis®, and a tobramycin powder formulation in a dry-powder inhaler (DPI), TOBI Podhaler®, indicate that the inhaled antibiotic marketplace in CF is becoming very competitive. Other indications are also receiving interest. While there have been a number of recent reviews from a clinical, technical or regulatory perspective in the field of inhaled antibiotics, as well as others focused on a specific product or data from a recent clinical trial, there have not been any that describe the patent coverage of these products. This review addresses that missing piece.

Liposomal formulations for inhalation

No marketed inhaled products currently use sustained release formulations such as liposomes to enhance drug disposition in the lung, but that may soon change. This review focuses on the interaction between liposomal formulations and the inhalation technology used to deliver them as aerosols. There have been a number of dated reviews evaluating nebulization of liposomes. While the information they shared is still accurate, this paper incorporates data from more recent publications to review the factors that affect aerosol performance. Recent reviews have comprehensively covered the development of dry powder liposomes for aerosolization and only the key aspects of those technologies will be summarized. There are now at least two inhaled liposomal products in late-stage clinical development: ARIKACE® (Insmed, NJ, USA), a liposomal amikacin, and Pulmaquin™ (Aradigm Corp., CA, USA), a liposomal ciprofloxacin, both of which treat a variety of patient populations with lung infections. This review also highlights the safety of inhaled liposomes and summarizes the clinical experience with liposomal formulations for pulmonary application.

Nanomedicine and veterinary science: the reality and the practicality

Nanomedicine is a rapidly expanding field with a promising future that is already permeating veterinary science. This review summarises the current applications for nanoparticles in human medicine and explores their potential applicability for veterinary use. The principles underlying the use of nanoparticles in drug delivery, imaging and as vaccine adjuvants are explored along with the unique issues surrounding nanoparticle toxicity and regulatory approval. A brief overview of the properties of different nanoparticle systems including, liposomes, micelles, emulsions and inorganic nanoparticles, is provided, along with a description of their current and potential future applications in veterinary medicine.

Development of alpha-tocopherol acetate nanoparticles: influence of preparative processes

We studied different methods of preparing alpha-tocopherol acetate (ATA) nanoparticles, which are to be used in targeting the lungs as aerosols in order to prevent cigarette smoke toxicity. Poly-(lactide) nanoparticles were prepared using nanoprecipitation and solvent evaporation techniques, which produced, respectively, too small and too large nanoparticles to be aerosolized. The emulsification-diffusion method produced 2 months stable nanoparticles with a size between (500-700 nm). Increasing ATA concentration (1-7 mg/mL) induced a decrease in the association rate (97-93%) and in the adsorbed ATA rate (7-4.5%), which was associated with variations of Zeta potentials (-27.5 to -24.3 mV) and decrease in polymeric wall thickness and density.

Pulmonary delivery of insulin by liposomal carriers

Growing attention has been given to the potential of a pulmonary route as a non-invasive administration for systemic delivery of therapeutic agents (mainly peptides and proteins). The lungs provide a large absorptive surface area, extremely thin absorptive mucosal membrane, and good blood supply. The non-invasive nature of this pathway makes it especially valuable for the delivery of large molecular protein. However, pulmonary delivery of peptides and proteins is complicated by the complexity of the anatomic structure of the human respiratory system and the effect of disposition exerted by the respiration process. In this study, novel nebulizer-compatible liposomal carrier for aerosol pulmonary drug delivery of insulin was developed and characterized. Experimental results showed that insulin could be efficiently encapsulated into liposomes by preformed vesicles and detergent dialyzing method. The optimal encapsulation efficiency was achieved when 40% ethanol was used. The particle size of liposomal aerosols from ultrasonic nebulizer approximated to 1 mum. Insulin was stable in the liposomal solution. Animal studies showed that plasma glucose level was effectively reduced when liposomal insulin was delivered by inhalation route of using aerosolized insulin-encapsulated liposomes. Including fluorescent probe (phosphatidylethanolamine-rhodamine) into liposome, we found that the liposomal carriers were effectively and homogeneously distributed in the lung aveolar. Liposome-mediated pulmonary drug delivery promotes an increase in drug retention-time in the lungs, and more importantly, a reduction in extrapulmonary side-effects which invariably results in enhanced therapeutic efficacies.

Pharmacokinetic/pharmacodynamic evaluation of inhalation drugs: application to targeted pulmonary delivery systems

Inhaled therapy with either glucocorticoids and/or beta(2)-adrenergic drugs remains the mainstay of asthma treatment. In the last few years, a number of new products have been introduced into the market with the goal of improving efficacy and safety. This review article summarises the pharmacokinetic and pharmacodynamic properties of inhaled drugs for topical delivery necessary to achieve this goal. Pharmacokinetic properties include a high pulmonary deposition, low oral bioavailability, optimised pulmonary residence time and a very high systemic clearance. Optimisation of pharmacodynamic properties, such as receptor selectivity, may also yield drugs with improved pulmonary selectivity. As existing drugs also provide high efficacy and safety profiles, future developments will represent only slight improvements and quantum leap improvements are unlikely to occur.

Therapeutic uses of antioxidant liposomes

This review will focus on the therapeutic uses of antioxidant liposomes. Antioxidant liposomes have a unique ability to deliver both lipid- and water-soluble antioxidants to tissues. This review will detail the varieties of antioxidants which have been incorporated into liposomes, their modes of administration, and the clinical conditions in which antioxidant liposomes could play an important therapeutic role. Antioxidant liposomes should be particularly useful for treating diseases or conditions in which oxidative stress plays a significant pathophysiological role because this technology has been shown to suppress oxidative stress. These diseases and conditions include cancer, trauma, irradiation, retinotherapy or prematurity, respiratory distress syndrome, chemical weapon exposure, and pulmonary infections.

Therapeutic uses of antioxidant liposomes

This chapter focuses on the use of antioxidant liposomes in the general area of free radical biology and medicine. The term antioxidant liposome is relatively new and refers to liposomes containing lipid-soluble chemical antioxidants, water-soluble chemical antioxidants, enzymatic antioxidants, or combinations of these various antioxidants. The role of antioxidants in health and disease has been extensively discussed, and many excellent reviews and books are available (1–3). Antioxidant liposomes hold great promise in the treatment of many diseases in which oxidative stress plays a prominent role. Oxidative stress is a physiological condition in which the production of damaging free radicals exceeds the in vivo capacity of antioxidant protection mechanisms to prevent pathophysiology. Free radicals are molecules with unpaired electrons, often highly reactive and damaging to biological systems. The biological membranes of subcellular organelles are a major site of free radical damage but proteins and DNA are also significant targets. Moreover, free radicals can alter cellular signal transduction pathways and stimulate the synthesis of inflammatory cytokines. Oxygen radicals and other reactive oxygen species (ROS) arise from the single electron reductions of oxygen.

Oxidants and antioxidant therapy

The nature of organ injury during critical illness would suggest that antioxidant therapy might be effective as prophylaxis and therapy. To date, the results of human trials with these agents have yielded somewhat disappointing results. Future trials using better-defined primary endpoints for outcome and newly developed agents and modes of administration may result in successes in this field.

Controlled-release, pegylation, liposomal formulations: new mechanisms in the delivery of injectable drugs

OBJECTIVE

To review recent developments in novel injectable drug delivery mechanisms and outline the advantages and disadvantages of each.

DATA SOURCES

A MEDLINE (1995-January 2000) search using the terms polyethylene glycol, liposomes, polymers, polylactic acid, and controlled release was conducted. Additional references were identified by scanning bibliographies.

STUDY SELECTION AND DATA EXTRACTION

All articles were considered for inclusion. Abstracts were included only if they were judged to add critical information not otherwise available in the medical literature.

DATA SYNTHESIS

A number of systems that alter the delivery of injectable drugs have been developed in attempts to improve pharmacodynamic and pharmacokinetic properties of therapeutic agents. New drug delivery systems can be produced either through a change in formulation (e.g., continuous-release products, liposomes) or an addition to the drug molecule (e.g., pegylation). Potential advantages of new delivery mechanisms include an increased or prolonged duration of pharmacologic activity, a decrease in adverse effects, and increased patient compliance and quality of life. Injectable continuous-release systems deliver drugs in a controlled, predetermined fashion and are particularly appropriate when it is important to avoid large fluctuations in plasma drug concentrations. Encapsulating a drug within a liposome can produce a prolonged half-life and a shift of distribution toward tissues with increased capillary permeability (e.g., tumors, infected tissue). Pegylation provides a method for modification of therapeutic proteins to minimize many of the limitations (e.g., poor stability, short half-life, immunogenicity) associated with these agents.

CONCLUSIONS

Pegylation of therapeutic proteins is an established process with new applications. However, not all pegylated proteins are alike, and each requires optimization on a protein-by-protein basis to derive maximum clinical benefit. The language required to describe each pegylated therapeutic protein must be more precise to accurately distinguish each protein's differential pharmacologic properties.

Liposomes promote pulmonary glucocorticoid delivery

The beneficial effects of glucocorticoids in treating pulmonary inflammatory disorders are complicated by systemic adverse effects. Thus, a possible reduction in dosage and dosing frequency would be advantageous, particularly for patients requiring high doses of the drug. We believe that this can be achieved by developing formulations that increase the retention of glucocorticoids in the lung and a liposome-based drug delivery system may be useful. In the present study, we examined the pulmonary delivery of a liposomal glucocorticoid formulation. Male adult rats were intratracheally instilled with free [3H]dexamethasone (DEX) or [14C]liposome-entrapped [3H]dexamethasone (L-DEX) (800 microg DEX kg body weight) and animals were killed at different times within a 72-h treatment period. Pulmonary retention of [3H]DEX in animals instilled with free DEX was found to be approximately 1.5% of the administered dose 4 h post-instillation, with no radioactivity detectable 24 h post-instillation. Liposome encapsulation of the drug altered the pulmonary retention of DEX with about 34% and 8% of radioactivity remaining in the lung at 4 and 24h post-instillation, respectively. The intratracheal instillation of free DEX or L-DEX reduced the number of leukocytes in peripheral blood to a similar extent (50% of control values) at 4h. However, unlike free-DEX-treated animals whose leukocyte counts returned to control levels by 24h, the circulating leukocyte counts of L-DEX-treated animals remained depressed in the same period. Furthermore, DEX-induced changes in ACTH levels were less evident in animals treated with the liposomal formulation than those treated with free DEX. Our data suggest that the administration of liposome-entrapped DEX has the distinct advantage of enhancing the anti-inflammatory activity of the drug and therefore, possibly reducing its need for frequent administration.

Distribution of free and liposomal cefoxitin in plasma and peritoneal fluid in a porcine intra-abdominal sepsis model

The plasma and peritoneal fluid pharmacokinetic parameters obtained after the intravenous administration of free and liposomal cefoxitin were studied in a porcine model of intraabdominal sepsis. No prior assumptions were made to predict the number of compartments pertaining to drug clearance from the administration of either cefoxitin formulation. The experimental data obtained were applied to fit mathematical models of multiexponential drug clearance and the pharmacokinetic data were found to best fit a two-compartment open model. Liposomal encapsulation significantly altered the plasma drug distribution pattern resulting in changes in the magnitude of a number of pharmacokinetic parameters examined. The mean post-distributive half-life of liposomal cefoxitin was substantially longer than that of free cefoxitin by at least 3 times. The peritoneal cavity appeared to provide a reservoir for the initial distributive phase of rapid drug clearance from the plasma compartment followed by a less-rapid post-distributive phase. The cumulative drug level, as determined by the area under the concentration curve (AUC) as a function of time, in the plasma of animals treated with liposomal cefoxitin was about 3-4 fold as high as that of animals treated with free cefoxitin. The differences in pharmacokinetic parameters appeared to account for the improved therapeutic efficacy of liposomal cefoxitin in this animal model.

Comparative topical anaesthesia of EMLA and liposome-encapsulated tetracaine

BACKGROUND

The eutectic mixture of local anaesthetics (EMLA) provides effective topical anaesthesia after a minimum of 60 to 90 min application. Since liposome-encapsulated tetracaine (LET) can provide rapid dermal penetration, the goal of this study was to compare the local anaesthetic effects of EMLA and LET in human volunteers after 60 min application.

METHODS

After obtaining institutional approval and informed consent, healthy volunteers were recruited in a double blind, crossover, randomized trial. The study creams (0.5 ml EMLA and 0.5 ml LET 5%) were applied randomly to opposite arms for 60 min. The discomfort of i.v. catheterization was assessed using a visual analogue pain score (VAS). Cutaneous side effects of the creams were recorded.

RESULTS

Sixty-one subjects were studied. Twenty-one were excluded because of technical difficulties. Forty subjects completed the study and were included in the data analysis. The mean ( +/- SD) VAS was lower for LET than for EMLA (10.9 +/- 9.0 mm vs 22.7 +/- 17.1 mm, P < 0.001). Erythema secondary to vasodilatation occurred more frequent in the LET group than in the EMLA group (33 vs 3, P < 0.001). One subject with a history of atopy developed a rash at the LET application site.

CONCLUSION

Liposome-encapsulated tetracaine can provide a more effective topical anaesthesia than EMLA for intravenous catheterization after 60 min application. Clinical evaluations are necessary to determine the efficacy and safety of LET in providing topical anaesthesia for various invasive percutaneous procedures in other patient populations.

Modulation of silica-induced pulmonary toxicity by dexamethasone-containing liposomes

Human exposure to silica (SI) is of great occupational concern because it is marked by pulmonary inflammation and fibrosis. Our objective was to determine if early pharmacological intervention altered the inflammatory and fibrotic responses to silica in rats. Male Fisher-344 rats received intratracheal (IT) instillations of the anti-inflammatory steroid, dexamethasone (DEX), incorporated into a novel liposomal (LIP) delivery system (DEX-LIP), or buffer as control (HBSS) on Day-1 and every fourth day until euthanization. On Day 0, the DEX-LIP group received IT instillations of SI (10 mg/100g body wt, DEX-LIP-SI); half of the HBSS group received SI (10 mg/100g body wt, HBSS-SI) and the other half saline (HBSS-SAL). On Day 10 or 20, bronchoalveolar lavage (BAL) was performed for cellular, biochemical, and functional analyses of inflammation and damage. HBSS-SI rats had significant elevations in the neutrophil cell count over HBSS-SAL rats at both times. DEX-LIP treatment markedly reduced these values, indicating that DEX-LIP protected against SI-induced inflammation. In contrast, DEX-LIP did not protect against biochemical (albumin concentration, and beta-glucuronidase and lactate dehydrogenase activities) and functional (luminol-dependent chemiluminescence) indices of SI-induced damage. At Day 20, the DEX-LIP treatment significantly reduced the SI-induced increase in right lung/total body weight ratio and right lung hydroxyproline content, a biochemical index of fibrosis. This attenuation of fibrosis was confirmed histopathologically on preserved left lungs from these same animals. These results show that administration of liposomes containing dexamethasone attenuated SI-induced pulmonary inflammation and fibrosis in rats, and that this protection is independent of some biochemical and functional parameters of damage.

Liposomal aerosols in the management of pulmonary infections

The combination of liposomes and aerosols has been utilized to directly target the lungs with chemotherapeutic agents that might not have been used because of low solubility or toxicity. There are a variety of antibacterials, antifungals, and antivirals that have good in vitro activity, but are not effective because of their systemic toxicity and/or poor penetration into the lungs. Incorporation of many lipophilic drugs into liposomes decreases their toxicity without affecting effectiveness, thus increasing the therapeutic index. We have focused on aerosol delivery of amphotericin B (ampB) for the treatment of pulmonary and systemic fungal diseases. We have tested a variety of ampB-lipid formulations for the optimal treatment regimen for Cryptococcus and Candida infections in mouse models. The AeroTech II nebulizer (MMADs of 1.8-2.2 microns) produced aerosols with the highest concentrations in the breathable range. Pharmacokinetic studies revealed that pulmonary drug was present for hours to weeks. AmBisome retained its anticryptococcal activity even when animals were challenged 14 days after aerosol treatment. Aerosols may also be effective in systemic diseases. In our Candida-mouse model, systemic candidiasis and mortality were reduced by aerosolized ampB-liposome treatment. The ability to utilize lipophilic drugs, to deliver high concentrations of drug directly to the site of infection, and to reduce toxicity makes aerosol liposomes an attractive, alternative route of administration.

Alleviation of paraquat-induced lung injury by pretreatment with bifunctional liposomes containing alpha-tocopherol and glutathione

Reactive oxygen species are known to play a key role in the development of acute lung injury, and such injury can be alleviated by pretreating the lung with a suitable antioxidant preparation. In this study, we evaluated and compared the antioxidant efficacy of two liposomal preparations: liposomes containing only alpha-tocopherol versus bifunctional liposomes containing both alpha-tocopherol and glutathione (GSH). alpha-Tocopherol liposomes (2 mg alpha-tocopherol/animal) or liposomes containing both alpha-tocopherol and GSH (2 mg alpha-tocopherol and 10 mumol GSH/animal) were intratracheally instilled into the lungs of rats 30 min prior to a challenge with paraquat dichloride (30 mg/kg, i.p.); animals were killed 24 hr post-paraquat challenge. Lungs of paraquat-challenged animals were damaged extensively as evidenced by increases in lung weight, indicative of edema, and decreases in lung activities of angiotensin converting enzyme (ACE) and alkaline phosphatase (AKP), indicative of endothelial and alveolar type II epithelial cell injuries, respectively. While the pretreatment of rats with alpha-tocopherol liposomes or liposomes containing both alpha-tocopherol and GSH significantly attenuated paraquat-induced changes in lung ACE activity to more or less the same extent, the bifunctional liposomal preparation conferred additional protection to alveolar type II epithelial cells, as evidenced by a significantly higher pulmonary AKP activity. Our results also showed that both liposomal preparations failed to ameliorate paraquat-induced lung edema despite a significant protection of pulmonary endothelial cells, suggesting that paraquat-induced edema formation may be independent of endothelial cell damage. In conclusion, liposome-associated antioxidants can protect the lung against an oxidant challenge, and the extent of protection appears to be related to the characteristics of each antioxidant formulation.

The pulmonary uptake of intravenously administered liposomal alpha-tocopherol is augmented in acute lung injury

The present study was carried out to investigate whether the intravenous administration of liposomal alpha-tocopherol can result in a significant localization of the antioxidant in the injured lung. Male Sprague-Dawley rats were injected with paraquat dichloride (20 mg/kg, ip.) and 4, 24 or 48 h later, they were given an intravenous injection of a liposomal alpha-tocopherol preparation (20 mg alpha-tocopherol in 128 mumoles liposomal lipid/kg) labelled with [14C]dipalmitoylphosphatidylcholine (DPPC) and [3H]alpha-tocopherol. Animals were killed and their lungs removed for analysis 24 h after liposomal treatment. To demonstrate whether the extent of uptake of radioactive alpha-tocopherol liposomes was directly related to the extent of residual lung injury, additional groups of animals were also injected with higher doses (30 and 40 mg/kg body weight) of paraquat dichloride and 48 h later, were treated with liposomal alpha-tocopherol; animals were then killed 24 h after liposomal alpha-tocopherol treatment. The intraperitoneal injection of paraquat dichloride resulted in time- and dose-dependent decreases in angiotensin converting enzyme and alkaline phosphatase activities suggesting that the toxicant injures both the capillary endothelial cells and alveolar type II epithelial cells, respectively. The recovery of intravenously administered radioactive alpha-tocopherol in the lungs of saline-treated animals was found to be about 2% of the initial dose 24 h post-liposomal treatment. However, in paraquat-treated animals, there was an increased localization of the labelled alpha-tocopherol to the lung, resulting in a difference of pulmonary delivery by as much as 2-3 fold compared to that in a normal lung. The 3H/14C ratio, representing the recovery of [3H]alpha-tocopherol and [14C]liposomes, was practically constant and there was a linear relationship between the measurable lung injury index and the corresponding recovery of radiolabelled alpha-tocopherol in the lung. Our results appear to suggest that the residual pulmonary injury augments the delivery of liposomal alpha-tocopherol to the lung.

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.