Gentamicin-induced nephrotoxicity: A cell biology approach

Abstract

By autoradiography of microdissected isolated nephrons, we show that gentamicin distributes almost exclusively in the proximal tubule, where an increasing concentration grdient takes place from the initial to the distal part. On isopycnic centrifugation of homogenates from isolated tubules, the drug is found exclusively associated with the lysosomes 6 hours after injection. At a shorter time, the distribution is slightly bimodal and consistent with an association of part of the drug with brush border. This agrees with the suggestion that gentamicin enters cells and accumulates in lysosomes by absorptive pinocytosis. In gentamicin-treated animals, we showed (1) a decrease of the latency of lysosomes; (2) a decrease of the activity of lysosomal sphingomyelinase and, at large doses, of cathepsin B and α-D-galactosidase; (3) a decrease of the activity of alanylaminopeptidase and γ-glutamyl-transpeptidase. Unlike the others, the latter effect is not dose-related. All these alterations showed complete reversibility within 15 to 21 days after gentamicin withdrawal. These findings are consistent with the proposal that a central feature of the mechanism of gentamicin nephrotoxicity involves the accumulation of the drug in the lysosomes of the cells of the proximal tubule, leading to an extensive dysfunction of these cells through (1) the subsequent inhibition of the activities of the enzymes that are involved in the degradation of polar lipids, (2) the alteration of the properties of the lysosomal membrane permeability. From in vitro studies on cultured cells (fibroblasts), these alterations of the cell metabolism seem to be relevant for cell necrosis and cell death.