Liposomes in treatment of infectious diseases

Review: Liposomes in the prophylaxis and treatment of infectious diseases

Infectious diseases remain as one of the major burdens among health communities as well as in the general public despite the advances in prevention and treatment. Although vaccination and vector eliminations have greatly prevented the transmission of these diseases, the effectiveness of these strategies is no longer guaranteed as new challenges such as drug resistance and toxicity as well as the missing effective therapeutics arise. Hence, the development of new tools to manage these challenges is anticipated, in which nano technology using liposomes as effective nanostructure is highly considered. In this review, we concentrate on the advantages of liposomes in the drug delivery system and the development of vaccine in the treatment of three major infectious diseases; tuberculosis (TB), malaria and HIV.

Polyphenols against infectious diseases: Controlled release nano-formulations

The emergence of multi-drug resistant (MDR) pathogens has become a global threat and a cause of significant morbidity and mortality around the world. Natural products have been used as a promising approach to counter the infectious diseases associated with these pathogens. The application of natural products and their derivatives especially polyphenolic compounds as antibacterial agents is an active area of research, and prior studies have successfully treated a variety of bacterial infections using these polyphenolic compounds. However, delivery of polyphenolic compounds has been challenging due to their physicochemical properties and often poor aqueous solubility. In this regard, nanotechnology-based novel drug delivery systems offer many advantages, including improving bioavailability and the controlled release of polyphenolic compounds. This review summarizes the pharmacological mechanism and use of nano-formulations in developing controlled release delivery systems of naturally occurring polyphenols in infectious diseases.

Successful use of liposome encapsulated amphotericin to treat invasive aspergillosis following failure of conventional amphotericin

We describe a case of proven invasive pulmonary aspergillosis in a neutropenic patient in whom disease progression occurred during treatment with conventional amphotericin B despite neutrophil recovery. Treatment with liposomal encapsulated amphotericin B resulted in clinical and radiological improvement and the clearance of aspergillus spores from the sputum.

Biological evaluation of pyrazinamide liposomes for treatment of Mycobacterium tuberculosis

Pyrazinamide liposomes were prepared employing the phospholipid molar ratios; dipalmitoyl phosphatidyl choline (7):cholesterol (2) neutral and dipalmitoyl phosphatidyl choline (7):cholesterol (2):dicetyl phosphate (1) negatively charged. Swelling at 52 degrees C led to higher trapping efficiencies. An optimum sterilizing dose of 25 kGy was exhibited by gamma (gamma)-irradiation. Neutral pyrazinamide liposomes (7:2), swollen for 24 h, were employed in biological evaluation for treatment of mice infected by Mycobacterium tuberculosis. Liposomal pyrazinamide could effect highly significant reduction in bacterial counts (colony forming units/g lung), 10, 20 and 30 days after the last treatment dose. Histopathological examination of mice lungs showed highest severity of infection in drug-free liposomes (control) group > pyrazinamide liposomes > free pyrazinamide 6 days/week. The results indicate high therapeutic efficacy of pyrazinamide liposomes, injected twice weekly, in treatment of M. tuberculosis in mice.

Comparative study on the efficacy of AmBisome and Fungizone in a mouse model of pulmonary aspergillosis

OBJECTIVES

The aim of this study was to evaluate the efficacy and tissue concentration of AmBisome and Fungizone in murine pulmonary aspergillosis, and to investigate the localization of AmBisome at the infection site.

METHODS

Mice were infected intratracheally with Aspergillus fumigatus. A single dose of each of the antifungals was administered intravenously 4 h after infection. The efficacy of the antifungal treatment was assessed by the pulmonary fungal burden at 20 h post-treatment and the survival time over 1 month. The pulmonary amphotericin B (AMB) concentration was measured until 48 h after administration. The distribution of AmBisome in the lung was evaluated using rhodamine-labelled AmBisome and an anti-AMB antibody.

RESULTS

AmBisome at a dose of > or =1 mg/kg significantly prolonged the survival time of infected mice compared with the control group. At the maximum tolerated dose, 10 mg/kg AmBisome exhibited greater efficacy than 1 mg/kg Fungizone in terms of increasing survival and reducing the fungal burden. The pulmonary AMB concentration of 10 mg/kg AmBisome was higher than that of 1 mg/kg Fungizone. Tissue distribution analysis showed that AmBisome was localized at the infection site in the lung, and this might explain the potent in vivo efficacy in this infection model.

CONCLUSIONS

AmBisome is localized at the infection site in the lung and consequently may fully exhibit its in vivo activity. The efficacy of AmBisome is superior to that of Fungizone against pulmonary aspergillosis.

Liposome-encapsulated antibiotics

Encapsulation of certain antibiotics in liposomes can enhance their effect against microorganisms invading cultured cells and in animal models. We describe the incorporation of amikacin, streptomycin, ciprofloxacin, sparfloxacin, and clarithromycin in a variety of liposomes. We delineate the methods used for the evaluation of their efficacy against Mycobacterium avium-intracellulare complex (MAC) infections in macrophages and in the beige mouse model of MAC disease. We also describe the efficacy of pH-sensitive liposomes incorporating sparfloxacin or azithromycin. We summarize studies with other antibiotics, including rifampicin, rifabutin, ethambutol, isoniazid, clofazimine, and enrofloxacin, and their use against MAC, as well as other infection models, including Mycobacterium tuberculosis.

Determination of Intracellular Concentrations of Free and Two Types of Liposome-Encapsulated Enrofloxacin in Anatolian Shepherd Dog Monocytes

In this study, it was evaluated the accumulation of free and two types of liposome-encapsulated enrofloxacin (LEE) at the doses of 0.25, 0.5 and 1 microg/ml, which were clinically relevant concentrations into monocytes of healthy Anatolian shepherd dogs. Enrofloxacin was encapsulated with two different types of liposome in multilamellar large vesicles (MLV). Type A MLV composed of 15 mg egg phosphatidylcholine and 35 mg cholesterol, Type B MLV composed of phosphatidylcholine (PC), cholesterol and enrofloxacin, in a molar ratio of 1 : 1 : 1. The mean sizes of Type A and Type B liposome were found to be 7.65 and 4.27 microm, respectively. However, the mean encapsulation rate determined of Type A (13 +/- 2%) was found lower than Type B liposome (44 +/- 3%). The amounts of intracellular enrofloxacin concentrations were determined by high performance liquid chromatography. Type B LEE accumulated significantly higher level into monocytes when compared to free drug or Type A liposome. This study showed that Type B LEE markedly concentrated within monocytes and may improve the antibacterial efficacy of the antibiotic.

Biodistribution of liposomes of terbutaline sulfate in guinea pigs

A series of liposomes was prepared with various lipid (egg phosphatidyl choline [egg PC], phosphatidyl glycerol [PG], dipalmitoyl phosphatidyl choline [DPPC], distearoyl phosphatidyl choline [DSPC], dipalmitoyl phosphatidyl glycerol [DPPG], phosphatidyl ethanolamine [PE], cholesterol [CH], and stearylamine [SA]) compositions, such as egg PC:PG:CH (55:5:40), DPPC:PG:CH (55:5:40), DSPC:DSPG:CH (55:5:40) egg PC:SA:CH (55:5:40), DSPE:DSPG:CH (55:5:40) in molar ratio. Liposomal formulations were administered to guinea pigs intravenously; 3 hr after the treatment, serum samples and various organs (e.g., liver, spleen, lung) were removed and analyzed for drug concentration by a high-performance liquid chromatographic (HPLC) method. Based on the above study, a liposomal preparation with better lung specificity was selected, and the time profile of these liposomes was determined in guinea pigs. Three hours postadministration, a significant difference in blood levels was observed between free terbutaline sulfate and the various liposomal formulations. Localization of the drug in the lungs increased considerably when encapsulated drug was used, and the highest percentage localization was observed with DSPC:DSPG:CH (55:5:40) liposomes. The percentage recovery of the drug in the lungs with egg PC:CH:SA (55:40:5) liposomes did not change significantly when compared with egg PC:CH:PG (55:40:5) liposomes. To establish the time course of disposition of the liposomes, DSPC:DSPG:CH (55:5:40) liposomes were selected. Terminal half-life t1/2 of the drug in blood with free drug solution was about 12 hr, whereas with liposomes, a twofold increase in t1/2 was observed. The disposition data indicated that the clearance of the drug was delayed by 1.5 times when incorporated into liposomes.

Liposome encapsulation of clofazimine reduces toxicity in vitro and in vivo and improves therapeutic efficacy in the beige mouse model of disseminated Mycobacterium avium-M. intracellulare complex infection

Disseminated infections caused by the Mycobacterium avium-M. intracellulare complex (MAC) are the most frequent opportunistic bacterial infections in patients with AIDS. MAC isolates are resistant to many of the standard antituberculous drugs. Failure to obtain significant activities of certain drugs is due to difficulty in achieving high concentrations at the sites where the infections reside. New and improved agents for the treatment of mycobacterial infections are therefore required. Earlier, the anti-MAC activities of various agents in free or liposomal form were studied; liposomes were used as drug carriers to ultimately target the drugs to macrophages where mycobacterial infections reside. Clofazimine was chosen for further studies because it could be effectively encapsulated and its activity was well maintained in liposomal form. The present studies with both erythrocytes and macrophages as the model systems show that liposomal drug is far less toxic in vitro than the free drug. The in vivo toxicity of clofazimine was also significantly reduced after liposome encapsulation. The therapeutic efficacies of free and liposomal drugs were compared in a beige mouse model of disseminated MAC infection. An equivalent dose of liposomal drug (10 mg/kg of body weight) was more effective in eliminating the bacterial from the various organs studied, particularly from the liver. Moreover, because of the reduced toxicity of liposomal drug, higher doses could be administered, resulting in a significant reduction in the numbers of CFU in the liver, spleen, and kidneys. The data demonstrate that liposomal clofazimine is highly effective in the treatment of MAC infections, even if the treatment is initiated after a disseminated infection has been established. The present studies thus suggest the potential usefulness of liposomal clofazimine for the treatment of disseminated MAC infections.

Liposome encapsulation circumvents the hepatic clearance mechanisms of all-trans-retinoic acid

All-trans-retinoic acid (ATRA) has been proven active against a range of malignancies in isolated tissue culture systems and in human clinical trials, but the duration of its effects has been transient. Recent evidence indicates that the basis for the limited duration of ATRA's activity, at least in one form of leukemia, is a pharmacological adaptation that results in reduced serum concentration after prolonged treatment. This finding suggests that an i.v. formulation of ATRA may significantly improve the potency and duration of ATRA's activity in leukemia and, potentially, other malignancies as well. Liposomal ATRA (L-ATRA) was developed to provide a formulation of this retinoic acid isomer that can be administered intravenously to provide potential pharmacological advantages over the oral formulation. When L-ATRA was administered to rats over a prolonged period, the blood levels of the drug did not change over time. In vitro studies of isolated liver microsomes revealed that catabolism of the drug was not altered in rats that were repeatedly administered the L-ATRA formulation. Whereas microsomes isolated from animals that were orally administered free ATRA the same number of times with the same doses showed a significant increase in metabolism of the drug. These results suggest that an i.v. formulation of ATRA such as L-ATRA could be extremely useful in inducing long-term remissions in patients with APL.

Liposomes as carriers of antimicrobial agents or immunomodulatory agents in the treatment of infections

Targeting of antimicrobial agents by means of liposomes is under investigation and may be of importance in the treatment of infections that prove refractory to conventional forms of antimicrobial treatment. The ability to achieve a significantly longer residence time of liposomes in plasma and limited uptake of liposomes by the mononuclear phagocyte system opens up new areas of investigation and potential therapeutic application. By manipulating the liposomal composition, rates of uptake and intracellular degradation can be influenced and thereby the rates at which liposome-encapsulated agents are released and become available to exert their therapeutic action. With respect to the targeting of macrophage modulators at the mononuclear phagocyte system by means of liposomes for maximal stimulation of the nonspecific antimicrobial resistance, experimental evidence is now available of the potential usefulness of liposomes as carriers of these agents. This approach may also be of importance for the potentiation of treatment of severe infections.

Enhanced localization of liposomes with prolonged blood circulation time in infected lung tissue

In an experimental model of unilateral pneumonia caused by Klebsiella pneumoniae in rats we investigated whether intravenous administration of liposomes with prolonged blood circulation time resulted in significant localization of liposomes in infected lung tissue. Liposomes (100 nm) composed of hydrogenated phosphatidylinositol:hydrogenated phosphatidylcholine:cholesterol (molar ratio, 1:10:5) radiolabeled with gallium-67-deferoxamine showed relatively long blood circulation time. The degree of localization of these long circulating liposomes in the infected left lung was significantly higher compared to that of localization of 110 nm egg phosphatidylglycerol:egg phosphatidylcholine:cholesterol (molar ratio, 1:10:5) liposomes which exhibited relatively short blood circulation time. At 16 h after administration of the long circulating liposomes (when 10% of the injected dose was still present in the bloodstream) localization of liposomes in the infected left lung was increased up to 10-fold compared to the left lung of uninfected rats, and appeared to be highly correlated with the intensity of the infection. In the uninfected right lung the localization of long circulating liposomes was not increased. The degree of localization of liposomes in the infected tissue is dependent on the residence time of liposomes in the blood compartment. The extent of localization of long circulating liposomes in infected tissue appeared to be dependent on the liposomal dose administered.

Liposomes for the sustained drug release in vivo

New lipidic carriers suitable for the sustained drug release in vivo are presented. They consist of middle sized, compact phospholipid vesicles with one or up to few lipid bilayers which are sterically stabilized with a small amount of large-head phospholipids. As an example, phosphatidylcholine (PC) liposomes casted with up to 10 mol% of phosphatidylethanolamine with a covalently attached polyethyleneglycol 5000 headgroup (PE-PEG) are discussed. Such vesicles exhibit a very long circulation time after an i.v. administration in mice; the improvement over pure phosphatidylcholine liposomes within the first 24 h exceeds 8000%, at this point nearly 25% of the applied PE-PEG liposomes being still in the circulation. This advantage is a consequence of reduced phagocytosis of the lipidic carriers, as shown by an in vitro assay with blood monocyte cells in the flow cytometric experiments. For example, after 6 h incubation with THP-1 monocyte cells in human plasma the difference between the uptake of standard distearoylphosphatidylcholine (DSPC) and novel liposomes containing 10% distearoylphosphatidylethanolamine-PEG is by 1000%. Vesicles with 2.5 mol% DSPE-PEG are also taken-up via phagocytosis relatively slowly. But the latter vesicles, moreover, retain most of the enclosed model-drug carboxyfluorescein after an incubation in plasma. The rate of permeation of the encapsulated substance from such DSPE-PEG liposomes is below 2.4% per h. This is by approximately a factor of two less than for pure DSPC liposomes; vesicles with a higher PE-PEG content are inferior in this respect. Long circulation time and high retention of the newly developed liposomes open up ways for the future systemic use as such stabilized drug carriers for the therapeutic applications in vivo.

Chloroquine blood levels after administration of the liposome-encapsulated drug in relation to therapy of murine malaria

In a previous report (P. A. M. Peeters, C. W. E. M. Huiskamp, W. M. C. Eling, and D. J. A. Crommelin. Parasitology, 1989, in press) an increase in therapeutic and prophylactic potential was found when chloroquine (CQ) was encapsulated in fluid-state liposomes (lipCQ) and tested in Plasmodium berghei-infected mice in comparison to intraperitoneal (i.p.) administration of the free drug. In this study, the same model was used to demonstrate that encapsulation of CQ into gel-state liposomes further increased the preventive and therapeutic effect considerably. CQ determinations in whole blood, plasma, and red blood cells (RBC) after i.p. administration of fluid- or gel-state lipCQ revealed a prolonged availability of the drug in comparison to administration of free CQ. The CQ concentrations were related to the CQ levels needed for prevention or therapy of Plasmodium berghei infections in mice.

Effect of lipid composition on activity of liposome-entrapped ampicillin against intracellular Listeria monocytogenes

The effect of lipid composition on the intracellular antibacterial activity of ampicillin-containing liposomes was studied in vitro by using mouse peritoneal macrophages infected with Listeria monocytogenes. Two types of liposomes, a fluid type, consisting of cholesterol-phosphatidylcholine-phosphatidylserine (5:4:1), and a solid type, consisting of cholesterol-distearoylphosphatidylcholine-dipalmitoylphosphatidylglyc ero l (10:10:1), were used. Although the cellular uptake of both types of liposomes was similar, they differed with respect to the rate of intracellular degradation. A correlation was found between the relatively slow degradation of the solid liposomes and a delayed intracellular release of the encapsulated ampicillin, as reflected in absent or delayed intracellular killing of L. monocytogenes.

Enhanced effect of liposome-encapsulated amikacin on Mycobacterium avium-M. intracellulare complex infection in beige mice

We examined the therapeutic effects of free and liposome-encapsulated amikacin on Mycobacterium avium-M. intracellulare complex infection by using the beige-mouse model of the disease. In the first series of studies, intravenous administration of four weekly doses of 5 mg of amikacin per kg encapsulated in large (approximately 0.4-micron diameter), unilamellar liposomes arrested the growth of M. avium-M. intracellulare complex organisms in the liver, as measured by CFU counts. M. avium-M. intracellulare complex levels in untreated animals and in those treated with the same dose of free amikacin increased by several orders of magnitude over 8 weeks. Liposome-encapsulated amikacin was also effective against M. avium-M. intracellulare complex organisms in the spleen and kidneys, reducing the CFU counts by about 1,000-fold compared with those of both untreated controls and free-drug-treated mice. In the lungs, a slight reduction in CFU was observed in the liposome-encapsulated-amikacin-treated group, but only at the 8-week point. Neither free nor liposome-encapsulated amikacin reduced the colony counts in the lymph nodes compared with those of control animals. Reductions in CFU in all organs greater than those caused by the liposome preparation could be achieved by intramuscular administration of free amikacin, but only at a 10-fold-higher dose given 6 days a week for 8 weeks. In the second series of studies, we investigated the effects of (i) doubling the dose of liposome-encapsulated amikacin and (ii) increasing the size of the liposomes and prolonging the treatment to five injections. Administration of 10 mg of amikacin per kg in liposomes 2 to 3 micrometer in diameter was more effective in the liver than 5 or 10 mg of amikacin per kg in liposomes 0.2 micrometer in diameter. A slight reduction in the CFU levels in the lungs was observed with the higher dose, irrespective of liposome size. Our results indicate that liposome-based delivery of amikacin enhances its anti-M. intracellulare complex activity, particularly in the liver, spleen, and kidney, and may therefore improve the therapy of this disease.