Reeta Mehta

Toxicity and therapeutic effects in mice of liposome-encapsulated nystatin for systemic fungal infections.

The therapeutic activity of nystatin (NYS) incorporated in multilamellar liposomes (L-NYS) was studied in vivo. Hale-Stoner mice injected intravenously with various doses of L-NYS and free NYS showed a significant reduction in toxicity of NYS after the NYS was incorporated into liposomes (maximal tolerated doses, 16 and 4 mg/kg of body weight, respectively). The maximal tolerated dose of free NYS had no effect in the treatment of mice infected with Candida albicans, whereas L-NYS at an equivalent dose improved the survival of mice. A marked increase in survival was observed when L-NYS was administered in higher and multiple doses (total doses up to 80 mg/kg). Liposome encapsulation thus provided a means for intravenous administration of NYS, reducing its toxicity and making it an active systemic antifungal agent.

In vitro antifungal activities of amphotericin B and liposome-encapsulated amphotericin B.

The in vitro activities of liposome-encapsulated amphotericin B and free amphotericin B against Candida albicans 336 were comparable. Amphotericin B concentrations 12-fold and greater than 50-fold higher were required to kill the same organism when cholesterol and ergosterol were incorporated into the liposomes. The addition of cholesterol to liposomes caused a significant increase in the minimal fungicidal concentration of amphotericin B in 7 of 19 other yeast strains tested, whereas ergosterol caused an increase in 18 of the 19 strains.

Formulation, toxicity, and antifungal activity in vitro of liposome-encapsulated nystatin as therapeutic agent for systemic candidiasis

Multilamellar vesicles containing nystatin (NYS) were compared with vesicles containing the free drug for toxicity to erythrocytes and for antifungal activity in vitro. Liposomal nystatin was as active as free NYS was against a wide variety of yeasts and fungi. The antifungal activity against Candida albicans was maintained with different liposome compositions and without sterols. Liposome encapsulation also protected the erythrocytes from the toxicity of free NYS.

In vitro activities of free and liposomal drugs against Mycobacterium avium-M. intracellulare complex and M. tuberculosis.

We compared MICs and MBCs of various free- and liposome-incorporated antimicrobial agents against several patient isolates of Mycobacterium avium-M. intracellulare complex and certain American Type Culture Collection strains of M. avium, M. intracellulare, and Mycobacterium tuberculosis. Seven of 19 agents were selected for incorporation into liposomes. The MICs of these agents for 50 and 90% of isolates tested (MIC50s and MIC90s, respectively) ranged from 0.5 to 62 micrograms/ml. Members of the M. avium-M. intracellulare complex were resistant to killing by most of the other agents tested in the free form. However, clofazimine, resorcinomycin A, and PD 117558 showed complete killing of bacteria at concentrations ranging from 8 to 31 micrograms/ml, represented as MBC90s. Among the liposome-incorporated agents, clofazimine and resorcinomycin A had the highest killing effects (MBC90s, 8 and 16 micrograms/ml, respectively). Furthermore, both free and liposome-incorporated clofazimine had equivalent growth-inhibitory and killing effects on all American Type Culture Collection strains of M. avium, M. intracellulare, and M. tuberculosis tested. These results show that the antibacterial activities of certain drugs, particularly those of clofazimine and resorcinomycin, were maintained after the drugs were incorporated into liposomes.

Prophylaxis of Candida albicans infection in neutropenic mice with liposome-encapsulated amphotericin B.

The efficacy of liposome-encapsulated amphotericin B in the prophylaxis of disseminated Candida albicans infections in neutropenic mice was studied. The administration of liposome-encapsulated amphotericin B was associated with protection against infection with C. albicans when used at doses of greater than or equal to 2 mg of amphotericin B per kg of body weight. Neither empty liposomes nor free amphotericin B showed prophylactic efficacy.

Phagocyte Transport as Mechanism for Enhanced Therapeutic Activity of Liposomal Amphotericin B

Liposomal amphotericin B (L-AmB) is emerging as one of the most attractive new antifungal agents. We have attempted to show that phagocytic cells circulating in blood play an important role in transport and accumulation of L-AmB at inflammatory sites in vivo. Free AmB or L-AmB was injected intravenously to mice, and the amount of AmB in peritoneal exudate cells was quantitated by high-performance liquid chromatography. Higher levels of AmB were detected in a higher number of mice injected with L-AmB. The presence of L-AmB in inflammatory peritoneal cells after intravenous administration of fluorescence-labeled L-AmB also suggested that macrophages play an important role in the transport of intravenously administered L-AmB to inflammatory sites.

Synergistic antifungal activity and reduced toxicity of liposomal amphotericin B combined with gramicidin S or NF.

Amphotericin B (AmpB) disrupts membrane integrity by binding to sterols in fungal and mammalian cell membranes. The gramicidins, which form pores in all membranes but exhibit poor antifungal activity, are too toxic to mammalian cells to be used systemically. This study demonstrated synergistic antifungal activity of free and liposomal forms of AmpB when combined with the free and liposomal forms of gramicidin S and gramicidin NF against five Candida strains. In vitro erythrocyte lysis was prevented by using the liposomal forms of all drugs tested alone or in combination. Presumably, AmpB increases accessibility of the fungal cell membrane to the gramicidins, while liposome encapsulation decreases the rate of transfer of the drugs to the mammalian cell membrane. Liposome encapsulation of inactive or toxic drugs, used in combination with liposomal AmpB, may give new life to drugs previously believed to be inactive or too toxic for therapeutic consideration.

Formulation and Toxicity of Liposomes Containing Rifampicin

AbstractRFP was incorporated in liposomes and the effect of lipid composition on incorporation of drug and stability of the vesicles was studied. The amount of RFP incorporated is dependent on the lipid composition, being higher when charged lipids were used. RFP incorporation increased as the fluidity of the vesicles increased. Stability in saline was related to liposomes with high encapsulation of RFP, while stability in serum was superior when phospholipids with a Tc higher than 37°C were used. In vitro RFP and L-RFP were not toxic to erythrocytes; however, L-RFP was less toxic than RFP to CHO cells and to macrophages. In concentrations up to 340 mg x Kg-1, L-RFP was not toxic to mice.

Effects of free and liposomal amphotericin B and gramicidin S alone and in combination on potassium leakage from human erythrocytes and Candida albicans.

We studied the toxic effects of amphotericin B and gramicidin S, alone and in combination, using free and liposome-encapsulated drugs. In vitro toxic effects of the drugs on human erythrocytes and Candida albicans were determined by measuring leakage of intracellular potassium ions (K+). Liposomal formulations of both drugs greatly reduced K+ leakage from human erythrocytes, whereas liposomal gramicidin S, but not liposomal amphotericin B, prevented K+ leakage from C. albicans. In both free and liposomal forms, the combinations of drugs produced decreased toxicity to erythrocytes compared with the drugs alone. This protective effect was more apparent with liposomal combinations than with free drug combinations. A significant increase in fungal cell toxicity was observed, however, when free and liposomal drug combinations were tested against C. albicans. The results suggest that optimal concentrations of liposomal drug combinations (amphotericin B and gramicidin S) may provide increased toxicity against fungal cells and simultaneously protect mammalian cells.

Liposomes as drug carriers for polyene antibiotics

Abstract Despite the advent of powerful antibiotics, infections are still a major cause of morbidity and mortality. The widespread use of immunosuppressive therapy has made fungal infections a familiar aspect of many branches of medicine. The development of useful antifungal agents has been hampered by the fact that drugs lethal to the fungal cells are frequently toxic to the eukaryotic host cells. In addition to the obvious need for new drugs, modifications in the formulation of established or newer drugs and use of combination therapy have been proposed as alternative approaches to improve the therapy of infectious diseases. One recent promising development in the modification of drug formulation has been the use of liposomes. We have used liposomes as carriers for polyene antibiotics in the treatment of systemic candidiasis. The use of liposome-encapsulated polyenes in other areas still remains to be explored. This review will focus on the problems related to antifungal therapy with polyenes and the use of liposomes as drug carriers for polyene macrolide antibiotics alone or in combination with other drugs or biological molecules. The possible use of liposome-encapsulated polyenes in the treatment of other diseases has also been discussed, as has the effect of liposome encapsulation on the toxicity and antifungal activity of certain polyenes.