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Different components in human serum inhibit multiplication of Cryptococcus neoformans and enhance fluconazole
F Nassar1, E Brummer, D A Stevens
1Department of Medicine, Santa Clara Valley Medical Center, San Jose, California 95128-2699, USA.
Abstract:
The inhibitory effect of human serum on the multiplication of Cryptococcus neoformans and the interaction with fluconazole were studied. Compared with cryptococcal multiplication in RPMI 1640 medium alone, 5% human serum in medium inhibited multiplication by 76% +/- 6% (n = 8). The inhibitory effect of human serum was donor independent, [corrected] heat stable (56 degrees C, 30 min), and not due to albumin or globulin. Bovine and murine sera were not inhibitory at that concentration. A fungistatic concentration of fluconazole (5.0 micrograms/ml) in medium plus 5% human serum resulted in 40% +/- 5% (n = 8) killing (reduction of inoculum CFU) in a 24-h assay. Bovine or murine sera did not have the enhancing effect, and this human serum activity was heat stable and donor independent. At 2.5 micrograms of fluconazole per ml, fungistasis by fluconazole plus human serum was significantly greater than with either alone. Higher serum concentrations [corrected] potentiated fluconazole more. At higher fluconazole concentrations (e.g., 20 micrograms/ml) fluconazole alone could kill, but serum potentiated this. A fluconazole-resistant isolate (MIC, 100 micrograms/ml) was not killed by fluconazole (5.0 micrograms/ml) in 5% human serum, but human serum potentiated the partial fluconazole inhibition. When human serum was dialyzed (molecular weight cutoff, 6,000 to 8,000) against phosphate-buffered saline, it lost the ability to synergize with fluconazole for killing Cryptococcus organisms but not the capacity to inhibit multiplication. Filtration of serum suggested the filtrate with a molecular weight of < 10,000 could interact synergistically with fluconazole for killing but could not inhibit cryptococcal multiplication. These findings indicate that human serum has two components, one (macromolecular) with a unique ability to inhibit C. neoformans and a low-molecular-weight component that enhances fluconazole anticryptococcal activity.
Insights
Human serum inhibits Cryptococcus neoformans growth and enhances fluconazole
Area of Science:
- Mycology
- Immunology
- Pharmacology
Background:
- Cryptococcus neoformans is a fungal pathogen causing life-threatening infections.
- Fluconazole is a primary antifungal drug, but resistance is emerging.
- The role of human serum in antifungal activity is not fully understood.
Purpose of the Study:
- To investigate the inhibitory effect of human serum on Cryptococcus neoformans.
- To determine the interaction between human serum and fluconazole against C. neoformans.
- To identify components within human serum responsible for these effects.
Main Methods:
- In vitro assays measuring C. neoformans growth inhibition and killing.
- Testing varying concentrations of human serum and fluconazole.
- Fractionation of human serum by dialysis and filtration to identify active components.
Main Results:
- Human serum significantly inhibited C. neoformans multiplication (76%).
- Human serum synergistically enhanced fluconazole's fungicidal activity.
- A low-molecular-weight component (<10,000 Da) of serum enhanced fluconazole killing, while a macromolecular component inhibited growth.
Conclusions:
- Human serum possesses dual activity against C. neoformans: growth inhibition and fluconazole potentiation.
- These activities are mediated by distinct serum components.
- Understanding these interactions may lead to improved antifungal therapies for cryptococcosis.