Effects of aminoglycoside treatment on renal protein reabsorption and accumulation

Renal damage caused by gentamicin: a study of the effect in vitro using isolated rat proximal tubular fragments

The clinical use of gentamicin (G) is limited because of its nephrotoxic potential. The administration of G (50 mg/kg) to rats in a 10-day daily treatment gave a biphasic pattern of lactate dehydrogenase (LDH) and N-acetyl-beta-D-glucosaminidase (NAG) excretion. Alkaline phosphatase (ALP) was highly elevated during the corresponding second phase while a slight and statistically insignificant increase in glutamate dehydrogenase (GDH) was obtained. The kidneys of such rats were isolated and tubules prepared and incubated for a specific period of time at 37 degrees C in Kreb's Henseleit bicarbonate buffer, pH 7.4. Results indicate a considerable loss of protein (P < 0.01) after the 3rd and 10th days of treatment with G, elevated and significant increase of ALP after the 1st (P < 0.05) and 3rd (P < 0.01) days and significant increase (P < 0.05) of GDH after the 10th day of treatment. The release of GDH, LDH and NAG from tubules of rats after a single dose of G was lower than the control rats while other treatments produced a significant increase in ALP, LDH and NAG over the period of incubation. In vitro incubation of tubules in the presence of several concentrations (5, 50, 500, 5000 micrograms/g of wet cortex) of G indicated a time-dependent leakage of enzyme only at the highest concentration of G. Our results clearly indicate that cellular damage caused by G as evidenced by urinary enzyme excretion and marker enzyme release from isolated tubules occurs at very high concentration in vivo or in vitro and is time-dependent.

Model of gentamicin-induced nephrotoxicity and its amelioration by calcium and thyroxine

The exact mechanism of gentamicin-induced acute renal failure is presently unknown; various mechanisms have been proposed but there is no proposed commonality between them. In animals, dietary calcium loading and L-thyroxine administration have been shown to ameliorate toxicity, with again no common process. A mechanism of competitive displacement of calcium and other cations from anionic phospholipids at the plasma and organelle membrane level, resulting in a decrease in Na+ -K+ ATPase, adenylate cyclase, mitochondrial function and ATP production, protein synthesis, solute reabsorption and overall cellular function is proposed. A further proposal is dietary calcium loading and thyroxine (which increases intracellular calcium) reverse gentamicin-induced acute renal failure by increasing the calcium and solute flux, thereby competitively inhibiting the primary lesion: anionic phospholipid binding.