Altered tissue distribution of amphotericin B by liposomal encapsulation: comparison of normal mice to mice infected with Candida albicans

Polyene Antibiotics Physical Chemistry and Their Effect on Lipid Membranes; Impacting Biological Processes and Medical Applications

This review examined a collection of studies regarding the molecular properties of some polyene antibiotic molecules as well as their properties in solution and in particular environmental conditions. We also looked into the proposed mechanism of action of polyenes, where membrane properties play a crucial role. Given the interest in polyene antibiotics as therapeutic agents, we looked into alternative ways of reducing their collateral toxicity, including semi-synthesis of derivatives and new formulations. We follow with studies on the role of membrane structure and, finally, recent developments regarding the most important clinical applications of these compounds.

DectiSomes: Glycan Targeting of Liposomal Drugs Improves the Treatment of Disseminated Candidiasis

Candida albicans causes life-threatening disseminated candidiasis. Individuals at greatest risk have weakened immune systems. An outer cell wall, exopolysaccharide matrix, and biofilm rich in oligoglucans and oligomannans help Candida spp. evade host defenses. Even after antifungal treatment, the 1-year mortality rate exceeds 25%. Undoubtedly, there is room to improve drug performance. The mammalian C-type lectin pathogen receptors Dectin-1 and Dectin-2 bind to fungal oligoglucans and oligomannans, respectively. We previously coated amphotericin B-loaded liposomes, AmB-LLs, pegylated analogs of AmBisome, with the ligand binding domains of these two Dectins. DectiSomes, DEC1-AmB-LLs and DEC2-AmB-LLs, showed two distinct patterns of binding to the exopolysaccharide matrix surrounding C. albicans hyphae grown in vitro. Here we showed that DectiSomes were preferentially associated with fungal colonies in the kidneys. In a neutropenic mouse model of candidiasis, DEC1-AmB-LLs and DEC2-AmB-LLs delivering only one dose of 0.2 mg/kg AmB reduced the kidney fungal burden several fold relative to AmB-LLs. DEC1-AmB-LLs and DEC2-AmB-LLs increased the percent of surviving mice 2.5-fold and 8.3-fold, respectively, relative to AmB-LLs. Dectin-2 targeting of anidulafungin loaded liposomes, DEC2-AFG-LLs, and of commercial AmBisome, DEC2-AmBisome, reduced fungal burden in the kidneys several fold over their untargeted counterparts. The data herein suggest that targeting of a variety of antifungal drugs to fungal glycans may achieve lower safer effective doses and improve drug efficacy against a variety of invasive fungal infections.

Dectin-1-Targeted Antifungal Liposomes Exhibit Enhanced Efficacy

Aspergillus species cause pulmonary invasive aspergillosis resulting in nearly 100,000 deaths each year. Patients at the greatest risk of developing life-threatening aspergillosis have weakened immune systems and/or various lung disorders. Patients are treated with antifungals such as amphotericin B (AmB), caspofungin acetate, or triazoles (itraconazole, voriconazole, etc.), but these antifungal agents have serious limitations due to lack of sufficient fungicidal effect and human toxicity. Liposomes with AmB intercalated into the lipid membrane (AmB-LLs; available commercially as AmBisome) have severalfold-reduced toxicity compared to that of detergent-solubilized drug. However, even with the current antifungal therapies, 1-year survival among patients is only 25 to 60%. Hence, there is a critical need for improved antifungal therapeutics. Dectin-1 is a mammalian innate immune receptor in the membrane of some leukocytes that binds as a dimer to beta-glucans found in fungal cell walls, signaling fungal infection. Using a novel protocol, we coated AmB-LLs with Dectin-1's beta-glucan binding domain to make DEC-AmB-LLs. DEC-AmB-LLs bound rapidly, efficiently, and with great strength to Aspergillus fumigatus and to Candida albicans and Cryptococcus neoformans, highly divergent fungal pathogens of global importance. In contrast, untargeted AmB-LLs and bovine serum albumin (BSA)-coated BSA-AmB-LLs showed 200-fold-lower affinity for fungal cells. DEC-AmB-LLs reduced the growth and viability of A. fumigatus an order of magnitude more efficiently than untargeted control liposomes delivering the same concentrations of AmB, in essence decreasing the effective dose of AmB. Future efforts will focus on examining pan-antifungal targeted liposomal drugs in animal models of disease.IMPORTANCE The fungus Aspergillus fumigatus causes pulmonary invasive aspergillosis resulting in nearly 100,000 deaths each year. Patients are often treated with antifungal drugs such as amphotericin B (AmB) loaded into liposomes (AmB-LLs), but all antifungal drugs, including AmB-LLs, have serious limitations due to human toxicity and insufficient fungal cell killing. Even with the best current therapies, 1-year survival among patients with invasive aspergillosis is only 25 to 60%. Hence, there is a critical need for improved antifungal therapeutics. Dectin-1 is a mammalian protein that binds to beta-glucan polysaccharides found in nearly all fungal cell walls. We coated AmB-LLs with Dectin-1 to make DEC-AmB-LLs. DEC-AmB-LLs bound strongly to fungal cells, while AmB-LLs had little affinity. DEC-AmB-LLs killed or inhibited A. fumigatus 10 times more efficiently than untargeted liposomes, decreasing the effective dose of AmB. Dectin-1-coated drug-loaded liposomes targeting fungal pathogens have the potential to greatly enhance antifungal therapeutics.

Local Skin Inflammation in Cutaneous Leishmaniasis as a Source of Variable Pharmacokinetics and Therapeutic Efficacy of Liposomal Amphotericin B

Disfiguring skin lesions caused by several species of the Leishmania parasite characterize cutaneous leishmaniasis (CL). Successful treatment of CL with intravenous (i.v.) liposomal amphotericin B (LAmB) relies on the presence of adequate antibiotic concentrations at the dermal site of infection within the inflamed skin.

Disfiguring skin lesions caused by several species of the Leishmania parasite characterize cutaneous leishmaniasis (CL). Successful treatment of CL with intravenous (i.v.) liposomal amphotericin B (LAmB) relies on the presence of adequate antibiotic concentrations at the dermal site of infection within the inflamed skin. Here, we have investigated the impact of the local skin inflammation on the pharmacokinetics (PK) and efficacy of LAmB in two murine models of localized CL (Leishmania major and Leishmania mexicana) at three different stages of disease (papule, initial nodule, and established nodule). Twenty-four hours after the administration of one 25 mg/kg of body weight LAmB (i.v.) dose to infected BALB/c mice (n = 5), drug accumulation in the skin was found to be dependent on the causative parasite species (L. major > L. mexicana) and the disease stage (papule > initial nodule > established nodule > healthy skin). Elevated tissue drug levels were associated with increased vascular permeability (Evans blue assay) and macrophage infiltration (histomorphometry) in the infected skin, two pathophysiological parameters linked to tissue inflammation. After identical treatment of CL in the two models with 5 × 25 mg/kg LAmB (i.v.), intralesional drug concentrations and reductions in lesion size and parasite load (quantitative PCR [qPCR]) were all ≥2-fold higher for L. major than for L. mexicana. In conclusion, drug penetration of LAmB into CL skin lesions could depend on the disease stage and the causative Leishmania species due to the influence of local tissue inflammation.

Pharmacodynamics and Biodistribution of Single-Dose Liposomal Amphotericin B at Different Stages of Experimental Visceral Leishmaniasis

Visceral leishmaniasis is a neglected tropical disease that causes significant morbidity and mortality worldwide. Characterization of the pharmacokinetics and pharmacodynamics of antileishmanial drugs in preclinical models is important for drug development and use. Here we investigated the pharmacodynamics and drug distribution of liposomal amphotericin B (AmBisome) in Leishmania donovani-infected BALB/c mice at three different dose levels and two different time points after infection. We additionally compared drug levels in plasma, liver, and spleen in infected and uninfected BALB/c mice over time. At the highest administered dose of 10 mg/kg AmBisome, >90% parasite inhibition was observed within 2 days after drug administration, consistent with drug distribution from blood to tissue within 24 h and a fast rate of kill. Decreased drug potency was observed in the spleen when AmBisome was administered on day 35 after infection, compared to day 14 after infection. Amphotericin B concentrations and total drug amounts per organ were lower in liver and spleen when AmBisome was administered at the advanced stage of infection and compared to those in uninfected BALB/c mice. However, the magnitude of difference was lower when total drug amounts per organ were estimated. Differences were also noted in drug distribution to L. donovani-infected livers and spleens. Taken together, our data suggest that organ enlargement and other pathophysiological factors cause infection- and organ-specific drug distribution and elimination after administration of single-dose AmBisome to L. donovani-infected mice. Plasma drug levels were not reflective of changes in drug levels in tissues.

Suspected Pulmonary Infection with Trichoderma longibrachiatum after Allogeneic Stem Cell Transplantation

Aspergillus and Candida species are the main causative agents of invasive fungal infections in immunocompromised human hosts. However, saprophytic fungi are now increasingly being recognized as serious pathogens. Trichoderma longibrachiatum has recently been described as an emerging pathogen in immunocompromised patients. We herein report a case of isolated suspected invasive pulmonary infection with T. longibrachiatum in a 29-year-old man with severe aplastic anemia who underwent allogeneic stem cell transplantation. A direct microscopic examination of sputum, bronchoaspiration, and bronchoalveolar lavage fluid samples revealed the presence of fungal septate hyphae. The infection was successfully treated with 1 mg/kg/day liposomal amphotericin B.

Delivery of negatively charged liposomes into the atherosclerotic plaque of apolipoprotein E-deficient mouse aortic tissue

Liposomes have been used to diagnose and treat cancer and, to a lesser extent, cardiovascular disease. We previously showed the uptake of anionic liposomes into the atheromas of Watanabe heritable hyperlipidemic rabbits within lipid pools. However, the cellular distribution of anionic liposomes in atherosclerotic plaque remains undescribed. In addition, how anionic liposomes are absorbed into atherosclerotic plaque is unclear. We investigated the uptake and distribution of anionic liposomes in atherosclerotic plaque in aortic tissues from apolipoprotein E-deficient (ApoE(-/-)) mice. To facilitate the tracking of liposomes, we used liposomes containing fluorescently labeled non-silencing small interfering RNA. Confocal microscopy analysis showed the uptake of anionic liposomes into atherosclerotic plaque and colocalization with macrophages. Transmission electron microscopy analysis revealed anionic liposomal accumulation in macrophages. To investigate how anionic liposomes cross the local endothelial barrier, we examined the role of clathrin-mediated endocytosis in human coronary artery endothelial cells (HCAECs) treated with or without the inflammatory cytokine tumor necrosis factor (TNF)-α. Pretreatment with amantadine, an inhibitor of clathrin-mediated endocytosis, significantly decreased liposomal uptake in HCAECs treated with or without TNF-α by 77% and 46%, respectively. Immunoblot analysis showed that endogenous clathrin expression was significantly increased in HCAECs stimulated with TNF-α but was inhibited by amantadine. These studies indicated that clathrin-mediated endocytosis is partly responsible for the uptake of liposomes by endothelial cells. Our results suggest that anionic liposomes target macrophage-rich areas of vulnerable plaque in ApoE(-)(/)(-) mice; this finding may lead to the development of novel diagnostic and therapeutic strategies for treating vulnerable plaque in humans.

Delivery of negatively charged liposomes into the atheromas of Watanabe heritable hyperlipidemic rabbits

Liposomes have been used as imaging and therapeutic agents in various tissues but only infrequently in the cardiovascular system. We prepared a liposome to target atheromas in a Watanabe heritable hyperlipidemic (WHHL) rabbit model. Liposomes labeled with rhodamine and nanogold were injected intra-arterially into the descending thoracic aortas of WHHL rabbits. The arterial segments of interest were perfusion-fixed and evaluated with immunohistochemistry, light microscopy, and electron microscopy. Deconvolution microscopy showed that rhodamine label was concentrated in the plaque shoulder regions of advanced-stage atheromas; however, rhodamine label was not found in adjacent, non-atherosclerotic aorta. Transmission electron microscopy revealed liposome remnants and the highest concentration of nanogold label in lipid-laden areas of atheromas. Liposomes were concentrated in areas of lipoprotein-associated phospholipase A2 expression. We conclude that modified liposomes can be delivered to the shoulder regions of advanced atheromas in WHHL rabbits and may be useful therapeutically for targeting metabolically active plaque.

Comparison between concentrations of amphotericin B in infected lung lesion and in uninfected lung tissue in a patient treated with liposomal amphotericin B (AmBisome)

Generally, the primary lesion of a mold infection is in the airway, an extravascular site. Therefore, the antifungal drug concentration at the actual tissue lesion of a mold infection is as important as in the blood compartment. Although our antifungal armamentarium has expanded recently, polyenes are still often needed in clinical practice because of their potent fungicidal activity and the rarity of resistance. Nevertheless, the distribution of amphotericin B (AmB) in infected lung tissue has not yet been evaluated. Using high-performance liquid chromatography analysis, we determined the concentrations of AmB in plasma and infected and uninfected tissues of resected lung simultaneously, in a patient with pulmonary aspergillosis treated with liposomal amphotericin B (L-AmB). The AmB concentration in the infected lesion of the lung was approximately 5.2 times higher than that in plasma and 3.7 times higher than in uninfected lung tissue. L-AmB accumulated in the infected lesion of the lung at a higher concentration. Although our data are from only one patient, they may be useful in helping to develop better strategies for the use of L-AmB against pulmonary fungal infections.

The pharmacokinetics and pharmacodynamics of micafungin in experimental hematogenous Candida meningoencephalitis: implications for echinocandin therapy in neonates

BACKGROUND

Hematogenous Candida meningoencephalitis (HCME) is a relatively frequent manifestation of disseminated candidiasis in neonates and is associated with significant mortality and neurodevelopmental abnormalities. The outcome after antifungal therapy is often suboptimal, with few therapeutic options. Limited clinical data suggest that echinocandins may have role to play in the treatment of HCME.

METHODS

We studied the pharmacokinetics and pharmacodynamics of micafungin in a rabbit model of neonatal HCME and bridged the results to neonates by use of population pharmacokinetics and Monte Carlo simulation.

RESULTS

Micafungin exhibited linear plasma pharmacokinetics in the range of 0.25-16 mg/kg. Micafungin penetrated most compartments of the central nervous system (CNS), but only with doses >2 mg/kg. Micafungin was not reliably found in cerebrospinal fluid. With few exceptions, drug penetration into the various CNS subcompartments was not statistically different between infected and noninfected rabbits. A dose-microbiological response relationship was apparent in the brain, and near-maximal effect was apparent with doses of 8 mg/kg. Monte Carlo simulations revealed that near-maximal antifungal effect was attained at human neonatal doses of 12-15 mg/kg.

CONCLUSIONS

These results provide a foundation for clinical trials of micafungin in neonates with HCME and a model for antimicrobial bridging studies from bench to bedside in pediatric patients.

Assessing the antifungal activity, pharmacokinetics, and tissue distribution of amphotericin B following the administration of Abelcet® and AmBisome® in combination with caspofungin to rats infected with Aspergillus fumigatus

The purpose of this study was to assess the antifungal activity, pharmacokinetics, and tissue distribution of amphotericin B (AmpB) following the administration of Abelcet and AmBisome alone and in combination with Caspofungin to rats infected with Aspergillus fumigatus. Aspergillus fumigatus inoculum (2.1-2.5 x 10(7) colony forming units [CFU]) was injected via the jugular vein; 48 h later male albino Sprague-Dawley rats (350-400 g) were administered either a single intravenous (i.v.) dose of Abelcet (5 mg AmpB/kg; n = 6), AmBisome (5 mg AmpB/kg; n = 6), Caspofungin (3 mg/kg; n = 5), Abelcet (5 mg AmpB/kg) plus Caspofungin (3 mg/kg) (n = 6), AmBisome (5 mg AmpB/kg) plus Caspofungin (3 mg/kg) (n = 7), or physiologic saline (non-treated controls; n = 6) once daily for 4 days. Antifungal activity was assessed by organ CFU concentrations and plasma galactomannan levels. Plasma and tissue samples were taken from each animal for AmpB pharmacokinetic analysis and tissue distribution determinations. Abelcet treatment significantly decreased total fungal CFU concentrations recovered in all the organs added together by 73% compared to non-treated controls. Ambisome treatment significantly decreased total fungal CFU concentrations recovered in all the organs added together by 69% compared to non-treated controls. Caspofungin treatment significantly decreased total fungal CFU concentrations recovered in all the organs added together by 80% compared to non-treated controls. Abelcet plus Caspofungin treatment significantly decreased total fungal CFU concentrations recovered in all the organs added together by 81% compared to non-treated controls. Ambisome plus Caspofungin treatment significantly decreased total fungal CFU concentrations recovered in all the organs added together by 98% compared to non-treated controls. Abelcet treatment significantly decreased plasma galactomannan levels by 50 and 75% 96 h following the initiation of treatment in the absence and presence of Caspofungin co-therapy, respectively. AmBisome treatment significantly decreased plasma galactomannan levels by 73 and 78% 96 h following the initiation of treatment in the absence and presence of Caspofungin co-therapy, respectively. Co-administration of Caspofungin with Abelcet and AmBisome did not significantly alter the plasma concentration-time profile, pharmacokinetic parameters, and tissue distribution of AmpB. Taken together, our findings suggest that an alternative mechanism, possibly at the cellular level rather than altered AmpB disposition, may be an explanation for the differences in organ CFU concentrations following Abelcet plus Caspofungin versus AmBisome plus Caspofungin administration.

Assessing the antifungal activity and toxicity profile of amphotericin B lipid complex (ABLC; Abelcet®) in combination with caspofungin in experimental systemic aspergillosis

The purpose of this study was to assess the antifungal activity and renal and hepatic toxicity of amphotericin B lipid complex (ABLC; Abelcet) following co-administration of Caspofungin to rats infected with Aspergillus fumigatus. Aspergillus fumigatus inoculum (1.3-2.3 x 10(7) colony forming units [CFU]) was injected via the jugular vein; 48 h later male albino Sprague-Dawley rats (350-400 g) were administered either a single intravenous (i.v.) dose of Fungizone(R) (1 mg AmpB/kg), ABLC (1 or 5 mg AmpB/kg), or an equivalent volume of normal saline (NS) (vehicle control) once daily for 4 days. Rats were further randomized into groups to receive 3 mg/kg Caspofungin or physiologic saline i.v. once daily for 4 days. To assess antifungal activity, brain, lung, heart, liver, spleen, and kidney sections were homogenized with NS (2 mL; 1 g of each tissue/mL) and a 0.1-mL aliquot was spread plated onto a Sabouraud dextrose agar plate. The plates were incubated for 48 h at 37 degrees C, at which time the numbers of CFU were determined and corrected for tissue weight. To assess renal and hepatic toxicity, serum creatinine and aspartate aminotransferase levels were determined. Fungizone and ABLC at a dosing regimen of 1 mg/kg i.v. once daily for four consecutive days and Caspofungin at a dosing regimen of 3 mg/kg i.v. once daily for four consecutive days had similar effectiveness in decreasing the total number of Aspergillus fumigatus CFUs found in all organs analyzed compared to non-treated controls. A combination of ABLC (1 mg/kg i.v. x 4 days) and Caspofungin (3 mg/kg i.v. x 4 days) significantly decreased the total number of Aspergillus fumigatus CFUs found in all organs analyzed compared to Caspofungin alone and non-treated controls. ABLC at a dosing regiment of 5 mg/kg i.v. once daily for four consecutive days was more effective in decreasing the total number of Aspergillus fumigatus CFUs found in all organs analyzed compared to Fungizone or ABLC alone at 1 mg/kg and Caspofungin alone at 3 mg/kg. However, a combination of ABLC (5 mg/kg i.v. x 4 days) and Caspofungin (3 mg/kg i.v. x 4 days) was not more effective than ABLC at 5 mg/kg or the combination of ABLC at 1 mg/kg and Caspofungin 3 mg/kg in reducing the total number of Aspergillus fumigatus CFUs compared to controls. Except for non-treated infected control rats, none of the treatment groups tested displayed a greater than 50% increase in serum creatinine concentrations from baseline. In addition, only ABLC at a dosing regimen of 1 mg/kg i.v. once daily for four consecutive days displayed a greater than 50% increase in AST concentration from baseline. Taken together, these findings suggest that ABLC at 5 mg/kg once daily x 4 days appears to be the best therapeutic choice in this animal model.

Pharmacokinetics, excretion, and mass balance of liposomal amphotericin B (AmBisome) and amphotericin B deoxycholate in humans

The pharmacokinetics, excretion, and mass balance of liposomal amphotericin B (AmBisome) (liposomal AMB) and the conventional formulation, AMB deoxycholate (AMB-DOC), were compared in a phase IV, open-label, parallel study in healthy volunteers. After a single 2-h infusion of 2 mg of liposomal AMB/kg of body weight or 0.6 mg of AMB-DOC/kg, plasma, urine, and feces were collected for 168 h. The concentrations of AMB were determined by liquid chromatography tandem mass spectrometry (plasma, urine, feces) or high-performance liquid chromatography (HPLC) (plasma). Infusion-related side effects similar to those reported in patients, including nausea and back pain, were observed in both groups. Both formulations had triphasic plasma profiles with long terminal half-lives (liposomal AMB, 152 +/- 116 h; AMB-DOC, 127 +/- 30 h), but plasma concentrations were higher (P < 0.01) after administration of liposomal AMB (maximum concentration of drug in serum [C(max)], 22.9 +/- 10 microg/ml) than those of AMB-DOC (Cmax, 1.4 +/- 0.2 microg/ml). Liposomal AMB had a central compartment volume close to that of plasma (50 +/- 19 ml/kg) and a volume of distribution at steady state (Vss) (774 +/- 550 ml/kg) smaller than the Vss of AMB-DOC (1,807 +/- 239 ml/kg) (P < 0.01). Total clearances were similar (approximately 10 ml hr(-1) kg(-1)), but renal and fecal clearances of liposomal AMB were 10-fold lower than those of AMB-DOC (P < 0.01). Two-thirds of the AMB-DOC was excreted unchanged in the urine (20.6%) and feces (42.5%) with >90% accounted for in mass balance calculations at 1 week, suggesting that metabolism plays at most a minor role in AMB elimination. In contrast, <10% of the liposomal AMB was excreted unchanged. No metabolites were observed by HPLC or mass spectrometry. In comparison to AMB-DOC, liposomal AMB produced higher plasma exposures and lower volumes of distribution and markedly decreased the excretion of unchanged drug in urine and feces. Thus, liposomal AMB significantly alters the excretion and mass balance of AMB. The ability of liposomes to sequester drugs in circulating liposomes and within deep tissue compartments may account for these differences.

In situ liposomal preparation containing amphotericin B: related toxicity and tissue disposition studies

The purpose of this research was to develop a novel hydroalcoholic method for the preparation of liposome entrapping inclusion complex of amphotericin B (AmB) with a view to obtaining reduced toxicity and superior tissue distribution of AmB in vivo. The method involves initial preparation of AmB-hydroxypropyl-beta-cyclodextrin (AmB-HPBCD) intercalated proliposome which is subsequently converted into a liposome dispersion by single dilution method. The AmB-liposome (L-AmB) derived from proliposome exhibited a superior entrapment efficiency (94.8 +/- 0.7%) compared to liposomes prepared by employing a conventional solvent-based technique (89.7 +/- 2.9%). The dose that was lethal to 50% of subjects (LD50) (mg/kg) value of AmB contained in stabilized proliposome-based liposomes was 18.6 +/- 0.25, whereas that in conventional solvent-based liposomes was 7.8 +/- 0.25. Incorporation of AmB-HPBCD into hydroalcoholic liposomes enhanced antifungal activity in experimental aspergillosis in Balb/c mice in vivo: 80% survival was recorded after 7 days of therapy and the fungal load in lung was reduced. The results clearly demonstrate that preferential uptake of L-AmB entrapped inclusion complex (AmB-HPBCD) by the reticulo endothelial system correlated with diminished levels of AmB in infected (p > 0.05) and noninfected (p > 0.001) kidney after 24 hr compared to that observed with conventional solvent-based L-AmB. Therefore, proliposome-based liposome entrapping inclusion complex of AmB with HPBCD offered an improved therapeutic efficacy by lowering toxicity as well as by altering the tissue distribution pattern.

Amphotericin B lipid complex or amphotericin B multiple-dose administration to rabbits with elevated plasma cholesterol levels: pharmacokinetics in plasma and blood, plasma lipoprotein levels, distribution in tissues, and renal toxicities

The purpose of the present study was to determine if a relationship exists between the plasma cholesterol concentration, the severity of amphotericin B (AmpB)-induced renal toxicity, and the pharmacokinetics of AmpB in plasma in hypercholesterolemic rabbits administered multiple doses of amphotericin B (AmB) deoxycholate (Doc-AmB) and AmB lipid complex (ABLC). After 7 days of administration of a cholesterol-enriched diet (0.50% [wt/vol]) or a regular rabbit diet, each rabbit was administered a single intravenous bolus of Doc-AmB (n = 8) or ABLC (n = 10) (1.0 mg/kg of body weight) daily for 7 consecutive days (a total of eight doses). Blood samples were obtained daily before and 24 h after the administration of each dose and serially thereafter following the administration of the last dose for the assessment of pharmacokinetics in plasma, kidney toxicity, plasma lipoprotein levels, and drug distribution in tissue. The pharmacokinetics of AmB in blood following the administration of ABLC were also determined in rabbits fed cholesterol-enriched and regular diets (n = 3 each group). Before drug treatment, cholesterol-fed rabbits demonstrated marked increases in total, low-density lipoprotein (LDL), and triglyceride-rich lipoprotein (TRL) cholesterol levels in plasma compared with the levels in rabbits on a regular diet. No significant differences in total plasma triglyceride levels were observed. Significant increases in plasma creatinine levels were observed in rabbits fed a cholesterol-enriched diet (P < 0.05) and rabbits fed a regular diet (P < 0.05) when administered AmB. However, the magnitude of this increase was twofold greater in rabbits fed a regular diet than in rabbits fed a cholesterol-enriched diet. An increase in plasma creatinine levels was observed only in rabbits on a cholesterol-enriched diet administered ABLC. The pharmacokinetics of AmB were significantly altered in rabbits on a cholesterol-enriched diet administered Doc-AmB or ABLC compared to those in rabbits on a regular diet administered each of these compounds. The pharmacokinetics of AmB in blood were significantly different following ABLC administration but not following Doc-AmB administration in both rabbits fed cholesterol-enriched diets and rabbits fed regular diets compared to their corresponding pharmacokinetics in plasma. An increased percentage of AmB was recovered in the TRL fraction when Doc-AmB was administered to rabbits fed a cholesterol-enriched diet than when it was administered to rabbits fed a regular diet. Furthermore, an increased percentage of AmB was recovered in the LDL and TRL fractions when ABLC was administered to rabbits fed a cholesterol-enriched diet rabbits fed a regular diet. These findings suggest that an increase in plasma cholesterol levels modifies the pharmacokinetics of AmB and renal toxicity following the administration of multiple intravenous doses of Doc-AmB and ABLC.

Persistently positive cultures and outcome in invasive neonatal candidiasis

BACKGROUND

A persistently positive culture >24 h after starting antibiotic therapy has been correlated with adverse outcome in several invasive bacterial infections, but few reports address persistent positivity and outcome in infections caused by fungi and other pathogens that replicate more slowly and therefore may succumb less quickly to therapy.

METHODS

To assess whether positive culture >24 h after achieving target doses (amphotericin > or =0.5 mg/kg/day or fluconazole > or =6 mg/kg/day) of systemic antifungal therapy predicts focal infectious complication(s) or death from infection, we compared neonatal intensive care unit infants who had persistent (P+) or nonpersistent (P-) positive cultures with invasive candidiasis (clinical signs of infection and recovery of Candida from a normally sterile site) at this center from January 1, 1981, through June 30, 1999. Infants who died < or = 24 h after attaining target dosing, recovered without therapy, had a focal infectious complication already present at the time target dosing was achieved or were diagnosed with invasive candidiasis only postmortem were excluded.

RESULTS

We identified 58 P+ (29, 12 and 7 had positive cultures for >7, >14 and > or =21 days, respectively) and 38 P- infants. No differences were found between P+ and P- for birth weight; gestational age; gender; onset age; central vascular catheters; necrotizing enterocolitis, surgery or bacterial sepsis; or duration of parenteral nutrition, antibiotics, tracheal intubation or postnatal steroids. P+ were more likely to have blood or cerebrospinal fluid involvement (68 vs. 45%, P = 0.03). Distribution of Candida species was similar (albicans in 53 vs. 63% for P+ vs. P-). P+ were significantly more likely to develop later "fungus ball" uropathy (16 of 56 vs. 2 of 32, P = 0.01), to develop renal infiltration (11 of 56 vs. 1 of 32, P = 0.03) and to die from invasive candidiasis (11 of 58 vs. 0 of 38, P = 0.003) than P-. P+ were also more likely to develop endocarditis, abscess, ventriculitis and invasive dermatitis, although P > 0.05. Focal complication increased as duration of P+ increased (48, 55, 67 and 71% at >1, >7, >14 and > or =21 days, P = 0.06). When comparing only those with positive blood and/or cerebrospinal fluid culture, similar patterns were observed, although only death and focal complication or death from invasive candidiasis attained significance.

CONCLUSIONS

These observations suggest that in neonatal invasive candidiasis: (1) cultures usually remain positive >24 h after attaining target antifungal doses; (2) aggressive imaging for focal complications may be reserved for infants with persistently positive cultures after several days of antifungal therapy at target doses or have signs strongly suggestive of focal complication; (3) focal complications and/or death from candidiasis increase with persistence; (4) focal complications increase with duration of persistence; (5) serial culture of infected site(s) helps predict outcome and the need for aggressive surveillance and intervention for focal complications.

Compartmental pharmacokinetics and tissue distribution of multilamellar liposomal nystatin in rabbits

The plasma pharmacokinetics of multilamellar liposomal nystatin were studied in normal, catheterized rabbits after single and multiple daily intravenous administration of dosages of 2, 4, and 6 mg/kg of body weight, and drug levels in tissues were assessed after multiple dosing. Concentrations of liposomal nystatin were measured as those of nystatin by a validated high-performance liquid chromatography method, and plasma concentration data were fitted into a two-compartment open model. Across the investigated dosage range, liposomal nystatin demonstrated nonlinear kinetics with more than proportional increases in the AUC(0-24) and decreasing clearance, consistent with dose-dependent tissue distribution and/or a dose-dependent elimination process. After single-dose administration, the mean C(max) increased from 13.07 microg/ml at 2 mg/kg to 41.91 microg/ml at 6 mg/kg (P < 0.001); the AUC(0-24) changed from 11.65 to 67.44 microg. h/ml (P < 0.001), the V(d) changed from 0.205 to 0. 184 liters/kg (not significant), the CL(t) from 0.173 to 0.101 liters/kg. h (P < 0.05), and terminal half-life from 0.96 to 1.51 h (P < 0.05). There were no significant changes in pharmacokinetic parameters after multiple dosing over 14 days. Assessment of tissue concentrations of nystatin near peak plasma levels after multiple dosing over 15 days revealed preferential distribution to the lungs, liver, and spleen at that time point. Substantial levels were also found in the urine, raising the possibility that renal excretion may play a significant role in drug elimination. Liposomal nystatin administered to rabbits was well tolerated and displayed nonlinear pharmacokinetics, potentially therapeutic peak plasma concentrations, and substantial penetration into tissues. Pharmacokinetic parameters were very similar to those observed in patients, thus validating results derived from infection models in the rabbit and allowing inferences to be made about the treatment of invasive fungal infections in humans.

High-performance liquid chromatographic determination of liposomal nystatin in plasma and tissues for pharmacokinetic and tissue distribution studies

A reliable reversed-phase high-performance liquid chromatographic method was developed for the determination of liposomal nystatin in plasma. Nystatin is extracted by 1:2 (v/v) liquid-liquid extraction with methanol. Separation is achieved by HPLC after direct injection on a muBondapak C18 analytical column with a mobile phase composed of 10 mM sodium phosphate, 1 mM EDTA, 30% methanol and 30% acetonitrile adjusted to pH 6. Detection is by ultraviolet absorbance at 305 nm. Quantitation is based on the sum of the peak area concentration of the two major isomers of nystatin, which elute at 7.5-8.5 and 9.5-10.5 min. The assay was linear over the concentration range of 0.05 to 50 microg/ml. The lower limit of quantitation was 0.05 microg/ml, sufficient for investigating the plasma pharmacokinetics of liposomal nystatin in preclinical studies. Accuracies and intra- and inter-day precision showed good reproducibility. With minor modifications, this method also was used for assaying nystatin in various non-plasma body fluids and tissues.

Preparation, relative toxicity and therapeutic efficacy in mice and rats of liposomal HA-1-92, a new oxohexaene polyene macrolide antibiotic

HA-1-92, a new polyene oxohexaene macrolide antibiotic isolated from Streptomyces CDRIL-312, was incorporated into liposomes containing phosphotidyl choline and cholesterol. The liposomal incorporated HA-1-92 considerably decreased toxicity when compared with free HA-1-92 in mice. Liposomal HA-1-92 showed improved pharmacokinetic profiles in rats. When administered to aspergillosis- and cryptococcosis-infected Balb/c mice, liposomal HA-1-92 showed increased antifungal activity, compared with free HA-1-92, with improved survival rate and decreased colony-forming units in lung, liver, spleen and kidney. These results suggest that liposomal HA-1-92 is more effective than free HA-1-92 in controlling experimental aspergillosis and cryptococcosis in Ba1b/c mice.

Effect of fasting on temporal variation in the nephrotoxicity of amphotericin B in rats

Evidence for temporal variation in the nephrotoxicity of amphotericin B was recently reported in experimental animals. The role of food in these variations was determined by studying the effect of a short fasting period on the temporal variation in the renal toxicity of amphotericin B. Twenty-eight normally fed and 28 fasted female Sprague-Dawley rats were used. Food was available ad libitum to the fed rats, while the fasted animals were fasted 12 h before and 24 h after amphotericin B injection to minimize stress for the animals. Water was available ad libitum to both groups of rats, which were maintained on a 14-h light, 10-h dark regimen (light on at 0600 h). Renal toxicity was determined by comparing the levels of excretion of renal enzyme and the serum creatinine and blood urea nitrogen (BUN) levels at the time of the maximal (0700 h) or the minimal (1900 h) nephrotoxicity after the intraperitoneal administration of a single dose of dextrose (5%; control group) or amphotericin B (50 mg/kg of body weight; treated group) to the rats. The nephrotoxicities obtained after amphotericin B administration at both times of day were compared to the nephrotoxicities observed for time-matched controls. In fed animals, the 24-h urinary excretion of N-acetyl-beta-D-glucosaminidase and beta-galactosidase was significantly higher when amphotericin B was injected at 0700 and 1900 h. The excretion of these two enzymes was reduced significantly (P < 0.05) in fasting rats, and this effect was larger at 0700 h (P < 0.05) than at 1900 h. The serum creatinine level was also significantly higher (P < 0.05) in fed animals treated at 0700 h than in fed animals treated at 1900 h. Fasting reduced significantly (P < 0.05) the increase in the serum creatinine level, and this effect was larger in the animals treated at 0700 h. Similar data were obtained for BUN levels. Amphotericin B accumulation was significantly higher (P < 0.05) in the renal cortexes of fed rats than in those of fasted animals, but there was no difference according to the time of injection. These results demonstrated that fasting reduces the nephrotoxicity of amphotericin B and that food availability is of crucial importance in the temporal variation in the renal toxicity of amphotericin B in rats.

Pharmacokinetics, distribution in serum lipoproteins and tissues, and renal toxicities of amphotericin B and amphotericin B lipid complex in a hypercholesterolemic rabbit model: single-dose studies

The purpose of this study was to determine if a relationship exists among total serum and lipoprotein cholesterol concentration, the severity of amphotericin B (AmpB)-induced renal toxicity, and the serum pharmacokinetics of AmpB in hypercholesterolemic rabbits administered AmpB and AmpB lipid complex (ABLC). After 10 days of cholesterol-enriched diet (0.50% [wt/vol]) or regular rabbit diet (control), each rabbit was administered a single intravenous bolus of AmpB or ABLC (1.0 mg/kg of body weight). Blood samples were obtained before administration and serially thereafter for the assessment of serum pharmacokinetics, kidney toxicity, and serum lipoprotein distribution. Rabbits were humanely sacrificed after all blood samples were obtained, and tissues were harvested for drug analysis. Before drug treatment, cholesterol-fed rabbits demonstrated marked increases in total serum cholesterol and low-density lipoprotein (LDL) cholesterol levels compared with levels in rabbits on a regular diet. No significant differences in triglyceride levels were observed. A significant increase in serum creatinine levels was observed in cholesterol-fed and regular diet-fed rabbits administered AmpB. However, the magnitude of this increase was 2.5-fold greater in cholesterol-fed rabbits than in regular diet-fed rabbits. No significant differences in triglyceride levels were observed. A significant increase in serum creatinine levels was observed in cholesterol-fed and regular diet-fed rabbits administered ABLC. Whereas AmpB pharmacokinetics were significantly altered in cholesterol-fed rabbits administered free AmpB, similar AmpB pharmacokinetics were observed in both rabbit groups administered ABLC. Renal AmpB levels were significantly increased in cholesterol-fed rabbits administered AmpB compared with those in all other groups. Hepatic and lung AmpB levels were elevated in cholesterol-fed rabbits administered free AmpB compared to controls. In addition, hepatic, lung, and spleen AmpB levels were significantly decreased in cholesterol-fed rabbits administered ABLC compared to controls. An increased percentage of AmpB was recovered in LDL-very-low-density lipoprotein fraction when free AmpB was administered to cholesterol-fed rabbits compared with those in all other groups. These findings suggest that increases in cholesterol, specifically, LDL cholesterol levels, modify the disposition and renal toxicity of free AmpB. However, the pharmacokinetics and renal toxicity of ABLC were independent of elevations in total and LDL cholesterol levels.

High-performance liquid chromatographic determination of amphotericin B in plasma and tissue. Application to pharmacokinetic and tissue distribution studies in rats

A sensitive HPLC method with piroxicam as internal standard was developed for assaying amphotericin B in plasma and tissue. An Ultrabase-C18 column and a simple mobile phase consisting of an acetonitrile-acetic acid (10%)-water (41:43:16) mixture were used. The flow-rate was 1 ml/min and the effluent was monitored at 405 nm. The linearity of the assay method was up to 1000 ng/ml and 100 micrograms/g for plasma and tissue, respectively. Intra-day and inter-day RSDs were below 10% for all the sample types. This HPLC assay has been applied to determine amphotericin B in plasma and tissue samples taken during pharmacokinetic and tissue distribution studies in rats.

Plasma lipoprotein distribution of liposomal nystatin is influenced by protein content of high-density lipoproteins

The plasma lipoprotein distribution of free nystatin (Nys) and liposomal nystatin (L-Nys) in human plasma samples with various lipoprotein lipid and protein concentrations and compositions was investigated. To assess the lipoprotein distributions of Nys and L-Nys, human plasma was incubated with Nys and L-Nys (equivalent to 20 microg/ml) for 5 min at 37 degreesC. The plasma was subsequently partitioned into its lipoprotein and lipoprotein-deficient plasma fractions by step-gradient ultracentrifugation, and each fraction was analyzed for Nys content by high-pressure liquid chromatography. The lipid and protein contents and compositions of each fraction were determined with enzymatic kits. Following the incubation of Nys and L-Nys in human plasma the majority of Nys recovered within the lipoprotein fractions was recovered from the high-density lipoprotein (HDL) fraction. Incorporation of Nys into liposomes consisting of dimyristoylphosphatidylcholine and dimyristoylphosphatidylglycerol significantly increased the percentage of drug recovered within the HDL fraction. Furthermore, it was observed that as the amount of HDL protein decreased the amounts of Nys and L-Nys recovered within this fraction decreased. These findings suggest that the preferential distribution of Nys and L-Nys into plasma HDL may be a function of the HDL protein concentration.

Physical characteristics and lipoprotein distribution of liposomal nystatin in human plasma

The physical characteristics and lipoprotein distribution of free nystatin (NYS) and liposomal NYS (L-NYS) in human plasma were investigated. To determine the percentage of NYS that was lipid associated following incubation in human plasma, C18 reverse-phase extraction columns were used. To assess plasma drug distribution, NYS and L-NYS (20 microg/ml) were incubated in human plasma for 5, 60, and 120 min at 37 degrees C. After each interval, plasma was removed and separated into its lipoprotein and lipoprotein-deficient plasma (LPDP) fractions by ultracentrifugation and assayed for NYS by high-pressure liquid chromatography. Further studies evaluated the liposome structure of L-NYS by filtering through a 0.14-microm-pore-size microfilter before and after the addition of human plasma. When reconstituted L-NYS (mean particle diameter +/- standard deviation, 321 +/- 192 nm) was applied to a C18 column, 67% +/- 4% of the initial NYS concentration was associated with the lipid. When plasma samples containing L-NYS that had been incubated for 5 to 120 min at 37 degrees C were applied to C18 columns, 66 to 76% of the NYS was lipid associated. Incubation of NYS in human plasma for 5 min at 37 degrees C resulted in 3% +/- 1% of the initial NYS concentration incubated in the low-density lipoprotein (LDL) fraction, 23% +/- 4% of that in the high-density lipoprotein (HDL) fraction, and 66% +/- 10% of that in the LPDP fraction. In contrast, the distribution of NYS following incubation of L-NYS in human plasma for 5 min was 13% +/- 2% in the LDL fraction, 44% +/- 5% in the HDL fraction, and 42% +/- 5% in the LPDP fraction. Similar results were observed following 60 and 120 min of incubation. In addition, the liposome structure of L-NYS was quickly lost when mixed with plasma. These findings suggest that rapid disruption of the L-NYS structure upon incubation in human plasma is consistent with its rapid distribution in plasma. The preferential distribution of NYS into the HDL fraction upon incubation of L-NYS may be a function of its phospholipid composition.

Diversity of lipid-based polyene formulations and their behavior in biological systems

Patients with cancer and infectious disease often display dyslipidemias that result in changes in their plasma lipoprotein-lipid composition. It is likely that the interactions of liposomal polyenes with plasma lipoproteins may be responsible for the far different pharmacokinetics and pharmacodynamics of these compounds when they are administered to infected patients rather than to animals or healthy volunteers. Amphotericin B (AmpB) and nystatin are examples of such polyenes. Amphotericin B initially distributes with the high-density lipoprotein (HDL) fraction upon incubation in plasma. Over time, AmpB redistributes from HDLs to low-density lipoproteins (LDLs). This redistribution appears to be regulated by lipid transfer protein. However, when AmpB is incorporated into liposomes composed of negatively or positively charged phospholipids, not only is the capability of LTP to transfer AmpB from HDL to LDL diminished, but AmpB remains retained with only the HDL fraction. However, when liposomal nystatin is incubated in plasma, over 50% of nystatin distributes with HDLs. Over time, nystatin redistributes from HDL to the lipoprotein-deficient plasma fraction, which is composed of mainly aqueous plasma proteins. The lipid composition selected for the drug appears to be a vital constituent in regulating the drug's interaction with biological fluids. Furthermore, liposome (or liposomal particle) size, fluidity, and other physiochemical characteristics also play a role in altering the pharmacokinetics and pharmacological effects of lipid-based drug formulations. Armed with this understanding, a rational approach to clinical development of these formulations could be facilitated.

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.

Evaluation of renal toxicity and antifungal activity of free and liposomal amphotericin B following a single intravenous dose to diabetic rats with systemic candidiasis

Since fungal infections are prevalent in diabetic patients, in whom treatment is often complicated by underlying renal disease and dyslipidemias, the purpose of the present study was to determine if the antifungal activity and nephrotoxic effects of amphotericin B (AmB) and liposomal AmB (L-AmB) are different in nondiabetic (normolipidemic) rats compared with those in diabetic (dyslipidemic) rats with systemic candidiasis. Non diabetic and diabetic rats infected with Candida albicans received a single intravenous dose of either AmB (0.8 mg of AmB per kg of body weight), L-AmB (0.8, 2, or 4 mg of AmB per kg), or an equivalent volume of normal saline (1 ml). Renal function was assessed by insulin clearance, and antifungal activity was determined by measuring the numbers of CFU of C. albicans that were present in the right kidney following drug treatment. AmB at 0.8 mg/kg and L-AmB at 0.8, 2, and 4 mg/kg are effective antifungal agents in both diabetic and nondiabetic rats. However, while there was approximately a 4-fold decline in the mean number of CFU per gram of kidney in nondiabetic rats, there was only approximately a 2.5-fold decline for the comparable dose (AmB, 0.8 mg/kg) in diabetic rats. There also appeared to be a similar fold reduction of L-AmB at all of the dosages tested. AmB treatment significantly improved renal function in diabetic and nondiabetic rats with systemic candidiasis. Although L-AmB at all doses tested significantly improved renal function in diabetic rats with systemic candidiasis, only L-AmB at doses of 2 and 4 mg/kg significantly improved renal function in nondiabetic rats with systemic candidiasis. These findings suggest that following administration of a single intravenous dose, AmB and L-AmB appear to be less effective in killing C. albicans isolates in diabetic than in nondiabetic rats, while they were found to improve the renal functions of rats in both treatment groups.

Cyclosporin A in fat emulsion carriers: experimental studies on pharmacokinetics and tissue distribution

In the commercially available intravenous formulation of Cyclosporin A (Sandimmun), polyoxyethylated castor oil (Cremophor EL) is used as a solubilizing agent. We have recently reported that the acute nephrotoxic effect of this preparation was alleviated by replacing Cremophor EL with a soybean oil-based fat emulsion in a rat model. To further explore the potential of fat emulsions as carriers for cyclosporin A, data on the in vivo pharmacokinetics and tissue distribution are required. In this study in pigs, the pharmacokinetics of soybean oil-cyclosporin A was compared to that of Sandimmun. The two formulations seemed bioequivalent, as there were no significant differences in the systemic clearances, volumes of distribution or elimination half-lives. Moreover, the tissue distributions of soybean oil-cyclosporin A and Sandimmun were compared in rats. These studies also included two additional lipid-based carriers: one based on iodized ester of poppy seed oil and the other on a liposomal preparation. The tissue distributions were found to be similar regardless of the carriers used. Fat emulsion carriers seem to offer possibilities for preparing better tolerated intravenous formulations of cyclosporin A while maintaining the same characteristics concerning pharmacokinetics and tissue distribution.

Comparative tissue distribution and elimination of amphotericin B colloidal dispersion (Amphocil) and Fungizone after repeated dosing in rats

The pharmacokinetic profiles of amphotericin B (AmB) after administration of Amphocil, an AmB/cholesteryl sulfate colloidal dispersion (ABCD) and the micellar AmB/deoxycholate (Fungizone) were compared after repeated dosing in rats. After administration of ABCD and Fungizone at an equal AmB dose (1 mg/kg), AmB concentrations in plasma and most tissues were lower for the ABCD dose, especially in the kidneys where reduced drug concentration correlated with reduced nephrotoxicity. In contrast, AmB concentrations in the liver were substantially higher when ABCD was administered; however, without an accompanying increase in hepatotoxicity. Daily administration of ABCD for 14 days did not lead to AmB accumulation in plasma; while a slight accumulation was observed after multiple administration of Fungizone. AmB was eliminated more slowly from the plasma and various tissues and urinary and fecal recoveries of AmB were reduced after ABCD administration. These results suggest that ABCD may be stored in tissues in a form that is less toxic and is eliminated from the systemic circulation by a different mechanism than the free and protein-bound AmB in plasma. AmB accumulation in the spleen was observed when higher, doses of ABCD (5 mg/kg) were administered, which could be due to saturation of hepatic uptake of AmB. Comparison of spleen concentrations of AmB between ABCD and Fungizone at 5 mg/kg AmB doses was not possible because of Fungizone's toxicity in rats. In all other organs, AmB concentrations reached or approached a steady state within two weeks of dosing with ABCD. Urinary and fecal clearences of AmB were not different between ABCD and Fungizone administration.(ABSTRACT TRUNCATED AT 250 WORDS)

Concentrations in serum and distribution in tissue of free and liposomal amphotericin B in rats during continuous intralipid infusion

The influences of Intralipid (IL) and 0.45% normal-saline infusions on the concentration in serum and distribution in tissue of amphotericin B (AmpB) and liposomal amphotericin B (L-AmpB) in rats were compared. In animals receiving a continuous IL infusion, concentrations of AmpB in kidneys and lungs were significantly higher, but the concentration of AmpB in serum was significantly lower in animals administered AmpB versus those given L-AmpB. In animals receiving a continuous normal-saline infusion concentrations of AmpB in kidneys and the spleen were significantly higher, but the concentration of AmpB in serum was significantly lower in animals administered AmpB versus those given L-AmpB. These results suggest that the increased total serum cholesterol and high-density lipoprotein cholesterol during the IL infusion decreased the clearance of AmpB from the bloodstream and decreased the L-AmpB concentration in the kidney and lung.

Modification of amphotericin B's therapeutic index by increasing its association with serum high-density lipoproteins

AmpB remains one of the drugs of choice in the treatment of systemic fungal infection; however, its therapy is limited by the development of renal toxicity. When AmpB was incorporated into negatively charged liposomes composed of DMPC and DMPG (L-AmpB), it was less toxic but as effective as free AmpB. However, the mechanism of L-AmpB's enhanced therapeutic index remains unknown. We have demonstrated that AmpB predominantly associates with HDL when incorporated into positively and negatively charged liposomes. To further understand the therapeutic importance of AmpB predominantly associating with HDL, we next examined the influence of lipoproteins on the antifungal activity and renal cytotoxicity of AmpB. The antifungal activity of AmpB and L-AmpB was not altered in the presence of HDL or LDL. The reduced nephrotoxicity associated with the use of L-AmpB, however, was related to a decreased uptake of AmpB by renal cells when AmpB was associated with HDL, and it may be a result of the low expression of HDL receptors in the LLC PK1 renal cells.

Decreased toxicity of liposomal amphotericin B due to association of amphotericin B with high-density lipoproteins: role of lipid transfer protein

Previously, we have shown that liposomal amphotericin B (L-AmpB) composed of dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylglycerol (DMPG) was less nephrotoxic but equally as effective as Fungizone, which consists of amphotericin (AmpB) and deoxycholate. We have also observed that AmpB predominantly associates with high-density lipoproteins (HDL) in human serum and that the amount of AmpB associated with HDL increases when AmpB is incorporated into negatively charged liposomes. Furthermore, we observe that AmpB was less toxic in vitro to pig kidney cells when associated with HDL, but still toxic when associated with LDL. To further understand why HDL-associated AmpB causes reduced renal toxicity, we first examined LLC PK1 cells for the presence of LDL and HDL receptors and then the cytotoxic effects of HDL- and LDL-associated AmpB following trypsin treatment of LLC PK1 renal cells, which removed only the high-affinity LDL receptors. We found that LLC PK1 renal cells expressed high- and low-affinity LDL receptors but only low-affinity HDL receptors. Furthermore, when LLC PK1 cells were treated with trypsin, HDL- and LDL-associated AmpB were less toxic to the cells than was AmpB. The reduced renal cell toxicity of HDL-associated AmpB may be due to its lack of interaction with renal cells because of the absence of HDL receptors. Since AmpB interacts with cholesteryl esters (CE) whose transfer among lipoproteins is regulated by lipid transfer protein (LTP), the role of LTP on the distribution of AmpB to HDL and LDL was next investigated. We observed that LTP facilitated the transfer of AmpB, but not L-AmpB, from HDL to LDL.(ABSTRACT TRUNCATED AT 250 WORDS)

Beneficial effects of myristic, stearic or oleic acid as part of liposomes on experimental infection and antitumor effect in a murine model

Liposomes consisting of dicetyl-phosphate, cholesterol, lecithin and stearic or myristic or oleic acid, exert a protective effect for mice against experimental infection by Salmonella typhimurium, and delay both the onset and mortality B16 melanoma in these animals. Liposomes labelled with 3H-myristic acid were used as probes in the spleen and liver. We found that the treatment schedule rather than route of administration of liposomes, is important. The results show that in order to induce protection, preventive treatment must start at least three days before. Longer treatments do not increase the degree of protection, and treatments started at the same time as, or following experimental infection or tumor transplantation, have no effect.

The interaction of liposomal amphotericin B and serum lipoproteins within the biological milieu

Previously, we have shown that liposomal amphotericin B (L-AmpB) is less nephrotoxic than and equally as effective as free AmpB as treatment of patients with systemic fungal infections; The mechanism of L-AmpB's enhanced therapeutic index, however, remains unknown. This review discusses AmpB's association with lipoproteins, predominantly high-density lipoproteins (HDL) and the biological relevance of transferring AmpB to HDL. We observed that AmpB was less toxic to pig kidney cells when associated with HDL but still remains toxic when associated with low-density lipoproteins (LDL). AmpB's association with HDL or LDL does not alter its antifungal activity. We further found that these kidney cells express high- and low-affinity LDL receptors but only low-affinity HDL receptors. The reduced renal cytotoxicity of HDL-associated AmpB may be due to its lack of interaction with the renal cells, since they have no HDL receptors. Since AmpB interacts with cholesteryl esters in serum, whose transfer between HDL and LDL is regulated by lipid transfer protein (LTP), we addressed the role of this protein on the distribution of AmpB between HDL and LDL. The addition of LTP altered the lipoprotein distribution of AmpB but not of L-AmpB. Furthermore L-AmpB, but not AmpB (except at 20 micrograms/ml), inhibited the LTP-mediated transfer of cholesterol esters from HDL to LDL. It appears therefore, that the decreased nephrotoxicity associated with L-AmpB administration is related to its predominant distribution to HDL, which is regulated by inhibiting of LTP-mediated cholesterol esters transfer activity.

Roles of liposome composition and temperature in distribution of amphotericin B in serum lipoproteins

The role of liposome composition and temperature in the distribution of amphotericin B (AmB) with serum lipoproteins and the role of particle charge in AmB transfer to serum lipoproteins were determined. Serum obtained from healthy volunteers was incubated with known concentrations of AmB or different liposomal formulations of AmB (1 to 100 micrograms/ml) at 37 degrees C for various time intervals (5, 10, 20, 30, 45, and 60 min). After each interval, serum was removed and separated into high-density lipoprotein (HDL) and low-density lipoprotein (LDL) fractions by an LDL-direct assay. The distribution of AmB (Fungizone) at 5 min through 1 h of incubation at 25 degrees C remained constant and was similar in the HDL and LDL fractions. At 37 degrees C, at 5 through 45 min of incubation, 54 to 61% of AmB was recovered in the HDL fraction; however, at 1 h more than 75% of the AmB concentration was recovered in the HDL fraction. In contrast, 87.5 to 92% AmB was recovered in the HDL fraction throughout the incubation when negatively charged liposomal AmB (dimyristoylphosphatidylcholine [DMPC]:dimyristoylphosphatidylglycerol [DMPG], 7:3 [wt/wt]) was used. With positively charged liposomes, 75 to 87.7% of AmB was recovered in the HDL fraction through the different time points studied. AmB incorporated into DMPC (neutral) and DMPG (negative) liposomes, and AmB was distributed in an HDL:LDL ratio of 6:4 following 1 h of incubation. Ninety percent of AmB and 80% of the lipid were found in the HDL fraction in a 3:1 molar DMPG:AmB ratio and in the LDL fraction in a 6:1 molar ratio. Lipid charge and temperature play a role in AmB distribution into serum lipoproteins. AmB and DMPG may contransfer as an intact drug-lipid complex to serum lipoproteins.

High-performance liquid chromatographic analysis of amphotericin B in plasma, blood, urine and tissues for pharmacokinetic and tissue distribution studies

A sensitive and reproducible high-performance liquid chromatographic method was developed to assay ampherotericin B in plasma, blood, urine and various tissue samples. Amphotericin B was isolated from each sample matrix by solid-phase extraction (Bond-Elut). The eluate from Bond-Elut containing amphotericin B was injected onto a reversed-phase C18 column (Waters, mu Bondpak, 10 microns, 300 mm x 3.9 mm I.D.) with a mobile phase of 45% acetonitrile in 2.5 mM Na2EDTA at 1 ml/min. Detection of amphotericin B was by ultraviolet absorption at 382 nm. Blood and tissues were homogenized and extracted with methanol prior to Bond-Elut extraction. The extraction efficiencies of amphotericin B from plasma, blood and tissues were approximately 90, 70 and 75%, respectively. The sensitivity of the assay was less than or equal to 5 ng/ml for plasma, less than or equal to 25 ng/ml for blood, 2.5 ng/ml for urine and 50 ng/g for tissues. The linearity of the assay method was up to 2.5 micrograms/ml for plasma, 5 micrograms/ml for blood, 500 ng/ml for urine and 500 micrograms/g for tissues. The assay was reproducible with an intra-day coefficient of variation (C.V., n = 3) of less than 5% in general for plasma, blood and tissues. The inter-day C.V. of the assay was less than 5% for plasma (n = 5), less than 10% for blood (n = 4) and less than 5% for tissues (n = 3). The overall variability in the urine assay was generally less than 10%. This method has demonstrated significant improvement in the sensitivity and reproducibility in assaying amphotericin B in plasma and especially in blood, urine and tissues. We have employed this assay to compare the pharmacokinetic and tissue distribution profiles of amphotericin B in rats and dogs following administration of Fungizone and ABCD (amphotericin B-cholesteryl sulfate colloidal dispersion), a lipid-based dosage form. In addition, the assay method for plasma and urine samples can also be applied to pharmacokinetics studies of amphotericin B in man.

Relationship of pharmacokinetics and drug distribution in tissue to increased safety of amphotericin B colloidal dispersion in dogs

The safety, pharmacokinetics, and distribution in tissue of an amphotericin B (AmB)-cholesteryl sulfate colloidal dispersion (ABCD) were compared with those of micellar amphotericin B-deoxycholate (m-AmB). Dogs received 14 daily injections of ABCD (0.6 to 10 mg/kg of body weight per day) or m-AmB (0.6 mg/kg/day). Safety was evaluated by monitoring body weight, hematology, clinical chemistry, and urinalysis during the study and by microscopic examination of tissues at the time of necropsy (day 16). AmB concentrations in plasma were measured in some groups on days 1, 7, and 14 and in necropsy tissue samples. ABCD produced a spectrum of toxic effects in the kidneys, gut, and liver similar to those of m-AmB, but ABCD was eightfold safer than m-AmB. The highest tolerated dose of ABCD (5.0 mg/kg/day) produced effects similar to those of m-AmB (0.6 mg/kg/day). ABCD produced lower concentrations in plasma than an equal dose of m-AmB did. Clearances on days 7 and 14 were higher for ABCD (304 and 295 ml/h.kg) than they were for m-AmB (67 and 53 ml/h.kg). Concentrations in plasma reached steady state after ABCD administration, but they increased after repeated dosing with m-AmB. Diurnal fluctuations in AmB concentrations in plasma were observed 4 to 8 h after the time of dosing. ABCD resulted in lower AmB concentrations in tissue than m-AmB did, except in the reticuloendothelial system. Up to 90% of AmB administered as ABCD was recovered from the liver and spleen on day 16. Reduced drug levels in the kidneys and gut correlated with reduced indications of toxicity in these organs after ABCD administration. Although ABCD increased concentrations of AmB in the reticuloendothelial system, increased toxicity was not observed in these organs.

Cyclosporine A in fat emulsion carrier: immunosuppressive effect in vitro

We have recently shown in a rat model that the acute decrease in glomerular filtration rate caused by intravenous Sandimmun can be avoided if Cyclosporine A (CyA) is given in a fat emulsion carrier instead. The present study was undertaken to determine the immunosuppressive effect in vitro of this new formulation. The inhibitory effect on the lymphocyte responsiveness of CyA in fat emulsion carrier was compared with that of CyA dissolved in alcohol, using mitogens as well as alloantigens as stimuli. In the mixed lymphocyte culture and cell-mediated lympholysis tests and in the interleukin-2 assay, both formulations seemed equally effective. CyA in fat emulsion was somewhat less effective than CyA in alcohol in the mitogen tests. In clinical practice the fat emulsion would be rapidly metabolized, and to further evaluate our new formulation, studies in experimental organ transplantation are needed.

Limited protection by small unilamellar liposomes against the renal tubular toxicity induced by repeated amphotericin B infusions in rats

Amphotericin B (AMB), either alone or incorporated into small unilamellar vesicles of pure dipalmitoylphosphatidyl choline (DPPC SUV-AMB), was administered intravenously to male Sprague-Dawley rats once daily for 5 days. Either 1.5 or 3.5 mg of AMB or DPPC SUV-AMB per kg was given, since these concentrations corresponded, respectively, to the lowest nephrotoxic dose and the sublethal dose of AMB in our model. Tubular functions were evaluated daily, and AMB concentrations in plasma, urine, and tissues were measured by high-performance liquid chromatography. AMB at both doses induced tubular toxicity, hyposthenuria being the earliest symptom. DPPC SUV-AMB at 1.5 mg/kg/day was atoxic, but the tubular alterations induced by 3.5 mg of DPPC SUV-AMB per kg were similar to those observed with 3.5 mg of AMB per kg, except that the ability to concentrate urine was partly restored 72 h after the last infusion. Incorporating AMB into DPPC SUV did not influence the pharmacokinetics of the drug. Using this lipidic AMB formulation, we thus observed a beneficial effect toward limiting the renal tubular toxicity of repeated low doses of AMB but, unexpectedly, not that of high doses. These results indicate that tubular renal functions and electrolyte serum values should be closely monitored in patients treated with AMB liposomal formulations, especially high-dose regimens.

Comparative pharmacokinetics of amphotericin B after administration of a novel colloidal delivery system, ABCD, and a conventional formulation to rats

The pharmacokinetics and tissue distribution of two amphotericin B dosage forms were compared in rats. A novel lipid-based colloidal delivery system for amphotericin B (Amphotericin B Colloidal Dispersion [ABCD]) which reduces the toxicity of amphotericin B in animals was compared with a conventional micellar formulation. Male Sprague-Dawley rats received a single intravenous injection of 1.0 mg of ABCD, 5.0 mg of ABCD, or 1.0 mg of micellar amphotericin B per kg. Plasma and tissue samples were obtained at 0.5 to 96 h after dosing and analyzed for amphotericin B by high-pressure liquid chromatography. Animals receiving ABCD demonstrated reduced peak levels in plasma, a three- to sevenfold reduction in amphotericin B delivery to the kidneys (the major target organ for toxicity), and prolonged residence time compared with those receiving the micellar formulation. In contrast, amphotericin B concentrations in the liver were two- to threefold higher with ABCD than with the micellar formulation: nearly 100% of the amphotericin B administered as ABCD was recovered from the liver 30 min after dosing. These results suggest that the colloidal particles of ABCD are taken up by the liver, which then acts as a reservoir of amphotericin B.