Further studies of the response of kidney Lysosomes to aminoglycosides and other cations

Rat renal cortical lysosomes were isolated in 0.3 M sucrose containing 1 mM EDTA by differential centrifugation. Lysosomes were incubated in isotonic sucrose or isotonic glycine with various concentrations of endogenous and exogenous compounds at 37° for 1 hr. Lysosomes were resedimented, and the N-acetyl-β-glucosaminidase (NAG) activity was measured in the supernatant fraction and the disrupted pellet and the percentage of total NAG released was calculated. Gentamicin and its C₁ and C₂ components had similar potencies for inhibiting NAG release from lysosomes at low concentrations. The release of alpha-galactosidase and beta-galactosidase from lysosomes was also inhibited by streptomycin and gentamicin. Mepacrine at low concentrations stabilized lysosomes and at high concentrations disrupted lysosomes. This drug also enhanced the effect of low concentrations of gentamicin on lysosomes. Inositol hexaphosphoric acid was a potent antagonist of the effect of low concentrations of gentamicin and mepacrine on lysosomes. Rats were treated with gentamicin at doses of 40, 80 and 160 mg/kg for 1 and 3 days. NAG excretion in gentamicin-treated groups as compared to saline controls was unchanged at day 1. Only the 160 mg/kg treatment group showed a tendency toward elevated renal cortical NAG at day 1 (P < 0.06). All treatment groups had elevated renal cortical NAG at day 3, while the 160 mg/kg group also had elevated NAG excretion. Lysine, arginine, l-canavanine and polymyxin B all affected NAG release from lysosomes in vitro. Lysine enhanced the disruptive effect of high gentamicin concentrations on lysosomes. Ferric and ferrous ions, tested over widely varied concentrations, inhibited NAG release at low concentrations while enhancing NAG release at high concentrations. We therefore conclude that the nephrotoxicity of aminoglycoside and other endogenous and exogenous renally excreted cationic compounds may be produced by their effects on lysosomes in the proximal renal tubule.