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In vitro and in vivo antifungal activity of amphotericin B lipid complex: are phospholipases important?
C E Swenson1, W R Perkins, P Roberts
1The Liposome Company, Inc., Princeton, New Jersey 08540, USA.
Abstract:
Amphotericin B lipid complex for injection (ABLC) is a suspension of amphotericin B complexed with the lipids L-alpha-dimyristoylphosphatidylcholine (DMPC) and L-alpha-dimyristoylphosphatidylglycerol. ABLC is less toxic than amphotericin B deoxycholate (AmB-d), while it maintains the antifungal activity of AmB-d. Active amphotericin B can be released from ABLC by exogenously added (snake venom, bacteria, or Candida-derived) phospholipases or by phospholipases derived from activated mammalian vascular tissue (rat arteries). Such extracellular phospholipases are capable of hydrolyzing the major lipid in ABLC. Mutants of C. albicans that were resistant to ABLC but not AmB-d in vitro were deficient in extracellular phospholipase activity, as measured on egg yolk agar or as measured by their ability to hydrolyze DMPC in ABLC. ABLC was nevertheless effective in the treatment of experimental murine infections produced by these mutants. Isolates of Aspergillus species, apparently resistant to ABLC in vitro (but susceptible to AmB-d), were also susceptible to ABLC in vivo. We suggest that routine in vitro susceptibility tests with ABLC itself as the test material may not accurately predict the in vivo activity of ABLC and that the enhanced therapeutic index of ABLC relative to that of AmB-d in vivo may be due, in part, to the selective release of active amphotericin B from the complex at sites of fungal infection through the action of fungal or host cell-derived phospholipases.
Insights
Amphotericin B lipid complex (ABLC) shows reduced toxicity compared to conventional amphotericin B deoxycholate (AmB-d). Its effectiveness in treating fungal infections, even with resistant strains, is linked to phospholipase-mediated drug release at infection sites.
Area of Science:
- Mycology
- Pharmacology
- Biochemistry
Background:
- Amphotericin B lipid complex (ABLC) is a lipid-bound formulation of amphotericin B, designed to reduce toxicity.
- ABLC retains the broad-spectrum antifungal activity of conventional amphotericin B deoxycholate (AmB-d).
- The release of active amphotericin B from ABLC is proposed to be mediated by phospholipases.
Purpose of the Study:
- To investigate the role of phospholipase activity in the in vitro and in vivo efficacy of ABLC.
- To evaluate the predictive value of in vitro susceptibility testing for ABLC.
- To understand the mechanism behind ABLC's enhanced therapeutic index.
Main Methods:
- Assessing phospholipase activity in Candida albicans mutants using egg yolk agar and DMPC hydrolysis.
- Evaluating ABLC efficacy in murine models infected with ABLC-resistant mutants.
- Testing the in vitro and in vivo susceptibility of Aspergillus species to ABLC and AmB-d.
Main Results:
- Candida albicans mutants resistant to ABLC in vitro showed deficient extracellular phospholipase activity.
- ABLC was effective in treating murine infections caused by these phospholipase-deficient mutants.
- In vitro resistance to ABLC did not always correlate with in vivo susceptibility for Aspergillus species.
Conclusions:
- In vitro susceptibility testing using ABLC may not accurately predict in vivo outcomes.
- Fungal or host phospholipase activity is crucial for the selective release of amphotericin B from ABLC at infection sites.
- The enhanced therapeutic index of ABLC is likely due to localized drug release mediated by phospholipases.