title: Calcium is a competitive inhibitor of gentamicin-renal membrane binding interactions and dietary calcium supplementation protects against gentamicin nephrotoxicity.
abstract: The divalent cations, Ca++ and Mg++, are known to competitively inhibit a large number of aminoglycoside-membrane interactions, so that Ca++ prevents both the neurotoxic and ototoxic effects of these antibiotics acutely in vitro. Since gentamicin-induced plasma and subcellular membrane damage appear to be critical pathogenetic events in gentamicin nephrotoxicity, Ca++ may play a similar protective role in gentamicin-induced acute renal failure. To test this possibility in vivo, rats (group 2) were given a 4% calcium (in the form of CaCO3) supplemented diet to increase delivery of Ca++ to the kidney and administered single daily subcutaneous injections of gentamicin, 100 mg/kg, for 10 d. Compared with a simultaneously studied group (group 1) of rats receiving identical gentamicin dosages and normal diets, Ca++ supplementation ameliorated gentamicin-induced acute renal failure. After 10 doses of gentamicin, blood-urea nitrogen values in group 1 averaged 213 +/- 15 (SE) and 25 +/- 3 (P less than 0.001) in group 2. The progressive decline in renal excretory function, as measured by BUN, in group 1 animals was accompanied by simultaneous declines in renal cortical mitochondrial function and elevations in renal cortex and mitochondrial Ca++ content, quantitative indices of the degree of renal tubular cell injury. Oral Ca++ loading markedly attenuated these gentamicin-induced derangements. After eight and 10 doses of gentamicin, mitochondria isolated from the renal cortex of group 2 rats had significantly higher rates of respiration supported by pyruvate-malate, succinate and N,N,N',N'-tetramethyl-p-phenyldiamine-ascorbate, higher rates of dinitrophenol-uncoupled respiration and greater acceptor control ratios than those measured in mitochondria isolated from the renal cortex of group 1 animals. Similarly, after 8 and 10 doses, renal cortex and renal cortical mitochondrial Ca++ content of group 2 was significantly lower than values observed in group 1. Thus, dietary calcium supplementation significantly protected against gentamicin-induced renal tubular cell injury and, consequently, gentamicin-induced acute renal failure. The mechanism for this protective effect of Ca++ may relate to the manner in which this polycationic antibiotic interacts with anionic sites, primarily the acidic phospholipids of renal membranes. In this regard, Ca++ was found to be a competitive inhibitor both of 125I-gentamicin binding to renal brush border membranes, the initial site of interaction between gentamicin and renal proximal tubule cells, with a composite inhibition constant (Ki) of 12 mM and of 125I-gentamicin binding to phosphatidic acid, an important membrane acidic phosph
mesh_terms: D058186:Acute Kidney Injury / Q000178:diet therapy* / Q000378:metabolism / Q000503:physiopathology; D000818:Animals; D001485:Basement Membrane / Q000378:metabolism; D001667:Binding, Competitive; D002118:Calcium / Q000008:administration & dosage / Q000378:metabolism / Q000494:pharmacology*; D002413:Cations, Divalent; D005839:Gentamicins / Q000032:analysis / Q000378:metabolism / Q000633:toxicity*; D007672:Kidney Cortex / Q000187:drug effects / Q000378:metabolism*; D007677:Kidney Function Tests; D008274:Magnesium / Q000494:pharmacology; D008297:Male; D008928:Mitochondria / Q000378:metabolism; D010101:Oxygen Consumption / Q000187:drug effects; D051381:Rats; D011919:Rats, Inbred Strains; D012965:Sodium Chloride / Q000008:administration & dosage
chemical_list: D002413:Cations, Divalent; D005839:Gentamicins; D012965:Sodium Chloride; D008274:Magnesium; D002118:Calcium