Abstract
Aminoglycoside-induced renal damage is enhanced in animals with Escherichia coli pyelonephritis. Bacterial endotoxin is liberated during antibiotic therapy. The toxic effect of endotoxin and tobramycin, alone or in combination, was investigated in primary cultures of rabbit proximal tubular cells grown to confluence in serum-free medium. Sodium-dependent uptakes of Pi and alpha-methylglucopyranoside (MGP) and enzymatic activities (lactate dehydrogenase [LDH] released as a marker of cell necrosis and gamma-glutamyltransferase [GGT] and N-acetyl-beta-D-glucosaminidase [NAG] present in the homogenate as markers of brush border membrane and lysosome integrity) were measured. Cells were exposed to (i) endotoxin (20 mg/liter), tobramycin (1 mM), or endotoxin plus tobramycin for 48 h, or (ii) endotoxin (100 mg/liter), tobramycin (4 mM), or endotoxin plus tobramycin for 72 h. Endotoxin alone did not alter Pi uptake, but tobramycin inhibited Pi uptake through a decrease in Vmax. The effect was not enhanced by the combination of endotoxin and tobramycin. Endotoxin and tobramycin alone exerted no significant effect upon MGP uptake, but strong inhibition of the Vmax was observed after exposure to a combination of endotoxin plus tobramycin, without alteration of the Km. Endotoxin decreased residual GGT activity in the cell homogenate. Tobramycin increased LDH release in the medium and NAG activity in the homogenate. Endotoxin plus tobramycin resulted in an additive effect upon LDH and NAG activities. In conclusion, by disturbing apical membrane integrity, endotoxin increased tobramycin toxicity in vitro in the absence of serum hormonal mediator.
Highlights
N-acetyl-p-D-glucosaminidase [NAG] present in the homogenate as markers of brush border membrane and lysosome integrity) were measured
After 48 h of incubation with both low and high concentrations of tobramycin and endotoxin, the lactate dehydrogenase (LDH) supernatant concentrations were significantly higher in the presence of both tobramycin and endotoxin as compared with the concentrations found with tobramycin alone
The purpose of our study was to determine in vitro the interaction between endotoxin and tobramycin on proximal tubular cells
Summary
N-acetyl-p-D-glucosaminidase [NAG] present in the homogenate as markers of brush border membrane and lysosome integrity) were measured. Since most of the damage exhibited by aminoglycosides is in the proximal tubule, this model was adapted to estimate more precisely the mechanisms of their toxicity at the cellular level This technique allowed the study of a relatively homogeneous population of renal epithelial cells under carefully controlled conditions and offered the possibility of evaluating the alteration of renal cells in the absence of hormonal mediators liberated in vivo after endotoxin exposure. These primary cultures, grown in welldefined medium without serum, exhibit many physiological functions and possess several enzymes typical of proximal tubular cells [4, 14]. (This work was presented in part at the 28th Interscience Conference on Antimicrobial Agents and Chemotherapy, Los Angeles, Calif., 23 to 26 October 1988, abstr. 291.)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
