Amphotericin B and Amphotericin B methylester: Effect on brush border membrane permeability

Amphotericin B and Amphotericin B methylester: Effect on brush border membrane permeability. In order to explain the nephrotoxicity of polyene antibiotics such as Amphotericin B (AM), an effect on the tubule membrane permeability has been postulated. However, studies on the action of AM have been complicated by the use of sodium deoxycholate (DOC), a membrane dissociating detergent as a solvent. Recently, a derivative, the methylester aspartate salt of Amphotericin B (AME) has been synthesized, which is highly water soluble in the absence of organic solvents. We have tested the action of AM, DOC, and AME on the sodium permeability of brush border (BBM) vesicles isolated from rat kidney cortex. It was found that both AM and AME increased the 22Na uptake as measured by a rapid filtration technique. However, a large fraction of the AM action was due to the effect of DOC on the BBM sodium permeability. We also investigated the time– and dose–dependent action of AME on 22Na and 3H-D-mannitol efflux from BBM vesicles. After 15sec of exposure, efflux from 22Na-preloaded vesicles was unchanged in the presence of 1 µg AME/mg protein compared to control vesicles. With 10, 50, and 100 µg AME/mg protein, the efflux increased 16, 25, and 35% respectively; 260 µg AME/mg protein did not elicit a further increment in the 22Na efflux. In the same membrane vesicles 3H-D-mannitol efflux did not change. After preincubation of the membranes for 60min with different concentrations of AME, the 15sec 22Na efflux increased 26% in the presence of 1 µg/mg protein AME with no change in the 3H-D-mannitol efflux. At higher concentrations of AME (200 and 300 µg/mg protein), an increase in 22Na efflux (36%), but also an increased 3H-D-mannitol efflux (26 and 63% respectively) was observed. These studies demonstrate that AME increases the Na permeability of BBM in a time– and dose–dependent manner. At higher concentrations and with longer incubation periods, AME additionally affects the overall membrane permeability. The increase in sodium permeability and the breakdown in membrane barrier may be among the factors responsible for the nephrotoxicity of Amphotericin B and its derivatives