Direct amphotericin B-mediated tubular toxicity: Assessments of selected cytoprotective agents

Direct amphotericin B-mediated tubular toxicity: Assessments of selected cytoprotective agents. Amphotericin B (AB) may induce acute renal failure by vasoconstrictive and tubulo-toxic effects. Although mannitol, Ca 2+ channel blockers, and lipid-based AB preparations have been suggested to mitigate in vivo AB nephrotoxicity, whether they confer direct tubular cytoprotection has not been defined. Therefore, this study assessed the impact of mannitol, verapamil/extracellular Ca 2+ , and cholesteryl sulfate (CS) AB binding on AB cytotoxicity, employing an isolated rat proximal tubular segment (PTS) preparation. After 30 to 60 minutes of incubation, 0.2 mg/ml of AB (Fungizone) caused marked toxicity, as assessed by LDH release (29 to 44%) and ATP depletion (>90%). Approximately 40% of the LDH release could be attributed to deoxycholate, the standard AB (Fungizone) solubilizing agent. Both 100 mM mannitol and 100 mM glucose decreased AB-mediated LDH release, despite having a quantitatively trivial impact on ATP concentrations (increments of 2+ removal from the PTS buffer had a protective effect. CS binding completely eliminated AB's toxicity (no LDH or ATP losses). The effect of AB and CS-AB on concomitant O 2 deprivation/reoxygenation (30 min/15 min) PTS injury was also assessed. AB and hypoxia/reoxygenation caused additive, not synergistic, LDH release whereas CS-AB had no adverse effect. We conclude that: (1) AB (Fungizone) is directly toxic to PTS, due, in part, to an independent deoxycholate effect; (2) mannitol blunts AB cytotoxicity, presumably via an osmotic, not anti-oxidant or ATP enhancing effect; (3) extracellular Ca2 + does not mediate AB PTS toxicity and thus, verapamil confers no protection; (4) AB and O 2 deprivation cause additive, not synergistic, PTS injury; and (5) CS binding completely blocks AB's direct tubulo-toxic effects.