amphotericin-b and sucrose-monolaurate

The effects of four monoesters of sucrose with different acyl chain lengths (palmitate, C16; myristate, C14; laurate, C12; and caprate, C10) on the aggregation state of amphotericin B (AmB), its binding to cholesterol and ergosterol, its toxicity to cells, and its lethality to mice were determined. In solution, all four of these esters inhibited AmB binding to cholesterol more than to ergosterol; this effect correlated with the ester-induced shift from the mainly aggregated form of AmB to the mainly monomeric form. In experiments with cells, the esters inhibited the toxicity of AmB to mouse erythrocytes and cultured mouse fibroblast L-929 cells more than its toxicity to Candida albicans cells. When injected intravenously with AmB, these esters decreased AmB lethality to mice. In all of these assays, the ester with the shortest chain length (caprate) was much less potent than the other three esters. Our results indicate a correlation between in vitro and in vivo assays and suggest that the in vitro and in vivo selectivity of AmB may be enhanced by surface-active agents which modulate the aggregation state of AmB.

Topics: Amphotericin B; Animals; Cholesterol; Ergosterol; Erythrocytes; Esters; Female; Hemoglobins; L Cells; Lethal Dose 50; Mice; Potassium; Sterols; Structure-Activity Relationship; Sucrose

A mild detergent, the monolauryl ester of sucrose (LS), at concentrations which ranged from 0.008 to 0.03%, enhanced amphotericin B (AmB) toxicity against Saccharomyces cerevisiae and Cryptococcus neoformans cells. At higher concentrations, 0.06 to 2.5%, LS inhibited AmB effects on these two fungi. We analyzed changes in the absorption spectrum of AmB induced by LS at these two concentration ranges by comparing ratios (R values) of AmB absorbance at 409 nm, the wavelength characteristic of non-aggregated (monomeric) AmB, to absorbance at 328 nm, the wavelength characteristic of aggregated AmB. Low concentrations of LS caused a decrease in R, whereas the higher LS concentrations increased R. Therefore, LS had concentration-dependent dual effects on the antifungal activity of AmB which correlated with shifts in the physical states of AmB. The concentration range of LS required to inhibit the antifungal effects of AmB was about 1000-fold greater than the previously reported concentrations required to inhibit AmB toxicity to mammalian cells (Gruda, I., Gauthier, E., Elberg, S., Brajtburg, J. and Medoff, G. (1988) Biochem. Biophys. Res. Commun. 154, 954-958). This suggests that LS may be a useful agent to decrease AmB toxicity to host cells without affecting the antifungal effects. Moreover, increase in AmB toxicity induced by low concentrations of LS suggests the possibility that synergistic interaction between fatty acid esters and polyene antibiotics may have therapeutic value.

Topics: Amphotericin B; Antifungal Agents; Dose-Response Relationship, Drug; Drug Synergism; Saccharomyces cerevisiae; Spectrophotometry, Ultraviolet; Sucrose

Amphotericin B (AmB) is a potent antifungal agent used to treat patients with systemic mycoses. The cytotoxicity of AmB is related to its binding to membrane sterols and its clinical usefulness is based on its greater affinity to ergosterol, the fungal sterol, compared to the mammalian cell sterol, cholesterol (1-3). Here we report that sucrose monolaurate (L.S.) decreased the binding of AmB to cholesterol without interfering with its binding to ergosterol. Furthermore, the toxicity of AmB for mouse erythrocytes (RBC) and cultured mouse fibroblasts, L-929, cells was significantly decreased by low concentrations of L.S., whereas under the same conditions, its toxicity for Candida albicans was unaffected. We observed a very good correlation between the spectroscopic and cell studies. The results reported here on the effects of L.S. on the selectivity of AmB toxicity for fungal cells compared to animal cells and the relative nontoxic nature of sugar esters suggest a potential for compounds of this type to enhance the therapeutic index of AmB.

Topics: Amphotericin B; Animals; Candida albicans; Cell Survival; Cholesterol; Ergosterol; Erythrocytes; Hemoglobins; Hemolysis; L Cells; Mice; Sterols; Sucrose