Renal brush border membrane vesicle aminoglycoside binding and nephrotoxicity

The in vitro binding affinity (KD) of aminoglycoside (AG) antibiotics to renal brush border membranes (BBM) has previously been correlated with several variables (sex, age and toxic potential of specific antibiotics) influencing in vivo AG nephrotoxicity in rats. The initial intent of our study was to extend this correlation to the in vivo difference in sensitivity to tobramycin recently observed between two strains of rats. However, the tobramycin binding affinity (KD) failed to correlate with the in vivo strain difference in AG nephrotoxicity. In addition, a comparison of BBM vesicle tobramycin binding affinity between sexes failed to correlate with an earlier report of in vivo gender differences in tobramycin nephrotoxicity. Comparison of binding capacities for male Sprague-Dawley rats and male Fischer rats yielded the only instance where binding parameters correlated with the reports of in vivo nephrotoxicity comparisons. Preliminary examinations of tobramycin binding using renal BBM vesicles derived from a single human kidney revealed binding kinetics and characteristics similar to rat BBM binding. Tobramycin binding was rapid and saturable for each type of BBM vesicle preparation. Scatchard analyses indicated low affinity, high capacity binding characteristics, as well as a single binding site in each case. Polyaspartic acid, which blocks in vitro BBM tobramycin binding as well as in vivo nephrotoxicity in rats, also blocked binding of tobramycin to human BBM vesicles. These data indicate that AG binding is qualitatively similar for rat and human BBM vesicle preparations. However, examination of the quantitative kinetic aspects of AG binding to BBM vesicles (KD and binding capacities) suggests that these parameters may not be critical determinants in the pathogenesis of Ag nephrotoxicity.