Heated (20 min at 70 degrees C)
amphotericin B-desoxycholate (
hAMB-DOC) was further characterized, as was another formulation obtained after centrifugation (60 min, 3000 x g), hcAMB-DOC. Conventional AMB-DOC consisted of individual
micelles (approximately 4 nm in diameter) and threadlike aggregated
micelles, as revealed by cryo-transmission electron microscopy. For both
hAMB-DOC and hcAMB-DOC, pleiomorphic cobweb structures were observed with a mean particle size of approximately 300 nm as determined by
laser diffraction. The potent antifungal activity of AMB-DOC against Candida albicans is not reduced by heating. Effective killing of C. albicans (>99.9% within 6 h) was obtained at 0.1 mg/liter with each of the AMB formulations. For AMB-DOC,
hAMB-DOC, and hcAMB-DOC,
cation release ((86)Rb(+)) from C. albicans of > or =50% was observed at 0.8, 0.4, and 0.4 mg/liter, respectively. After heating of AMB-DOC, toxicity was reduced 16-fold as determined by red blood cell (RBC) lysis. For AMB-DOC,
hAMB-DOC, and hcAMB-DOC,
hemolysis of > or =50% was observed at 6.4, 102.4, and 102.4 mg/liter, respectively. In contrast, AMB-DOC and its derivates showed similar toxicities in terms of
cation release from RBC. For AMB-DOC,
hAMB-DOC, and hcAMB-DOC,
cation release ((86)Rb(+)) of > or =50% was observed at 1.6, 0.8, and 0.8 mg/liter, respectively. In persistently leukopenic mice with severe
invasive candidiasis, higher dosages of both
hAMB-DOC and hcAMB-DOC were tolerated than those of conventional AMB-DOC (3 versus 0.8 mg/kg of
body weight, respectively), resulting in significantly improved therapeutic efficacy. In conclusion, this new approach of heating AMB-DOC may be of great value for further optimizing the treatment of severe
fungal infections.