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

Mapping Adverse Outcome Pathways for Kidney Injury as a Basis for the Development of Mechanism-Based Animal-Sparing Approaches to Assessment of Nephrotoxicity

In line with recent OECD activities on the use of AOPs in developing Integrated Approaches to Testing and Assessment (IATAs), it is expected that systematic mapping of AOPs leading to systemic toxicity may provide a mechanistic framework for the development and implementation of mechanism-based in vitro endpoints. These may form part of an integrated testing strategy to reduce the need for repeated dose toxicity studies. Focusing on kidney and in particular the proximal tubule epithelium as a key target site of chemical-induced injury, the overall aim of this work is to contribute to building a network of AOPs leading to nephrotoxicity. Current mechanistic understanding of kidney injury initiated by 1) inhibition of mitochondrial DNA polymerase γ (mtDNA Polγ), 2) receptor mediated endocytosis and lysosomal overload, and 3) covalent protein binding, which all present fairly well established, common mechanisms by which certain chemicals or drugs may cause nephrotoxicity, is presented and systematically captured in a formal description of AOPs in line with the OECD AOP development programme and in accordance with the harmonized terminology provided by the Collaborative Adverse Outcome Pathway Wiki. The relative level of confidence in the established AOPs is assessed based on evolved Bradford-Hill weight of evidence considerations of biological plausibility, essentiality and empirical support (temporal and dose-response concordance).

Gentamicin-induced nephrotoxicity in rats ameliorated and healing effects of resveratrol

In this study, we aimed to investigate the possible protective effect of resveratrol on gentamicin induced nephrotoxicity. Experiments were carried out in male Wistar rats weighing 200-250 g. Gentamicin sulfate (80 mg/kg per day i.p.), resveratrol (10 mg/kg per day i.p.) and gentamicin together with resveratrol were administered for 6 d. The animals were sacrificed 24 h after the last injection. Urine, blood samples and tissue samples were collected from the animals on the seventh day of the treatment before they were sacrificed. Kidneys were collected for histopathological studies and fixed in 10% buffered formalin solution. Tissue samples were stored at -70 degrees C in liquid nitrogen for the determination of glutathione (GSH), glutathione-S-transferase (GST), malondialdehyde (MDA) and catalase (CAT). Glutathione assay was determined by the method of Beutler et al. GST amounts were measured by the method of Habig et al. Catalase activity was tested by Aebi's method and MDA was determined according to Thayer's method. Blood urea level was significantly increased in the gentamicin treated group. The study showed lowered levels of urea and creatinine levels in resveratrol administered groups when compared with gentamicin administered rats, and the difference was statistically significant. It has been determined that resveratrol caused statistically significant decrease in lipid peroxidation and reduced the level of catalase. Histopathological examination showed that resveratrol prevented partly gentamicin induced tubular damage. The results histopathologically demonstrated that resveratrol has a protective effect against gentamicin induced nephrotoxicity, lipid peroxidation and cellular damage in rats.

Protective effects of vitamin e and probucol against gentamicin-induced nephrotoxicity in rats

Gentamicin (GM) is widely used as a bactericidal agent for the treatment of severe gram negative infections, however, its clinical use is partially limited due to its nephrotoxicity. Recent evidence suggests a role of reactive oxygen metabolites in GM nephrotoxicity. The present study was designed to investigate a possible potential protective role of vitamin E and/or probucol against GM nephrotoxicity. GM was administered to rats in a single dose of (150 mg kg(-1)i.p.), while vitamin E (250 mg kg(-1)i.m.) and/or probucol (60 mg kg(-1)i.m.) were given once daily for 3 consecutive days prior to GM administration. GM-induced nephrotoxicity was evidenced by marked elevations in serum urea and creatinine levels, urinary activity of N-acetyl-beta- d -glucosaminidase (NAG) and gamma-glutamyl-transferase (gamma-GT). Also, GM caused significant increases in kidney content of malondialdehyde (MDA), and significant decreases in kidney content of reduced non-protein sulphydryls (NPSH) and superoxide dismutase (SOD) activity. Vitamin E pretreatment significantly lowered the elevated serum urea and creatinine levels, and urinary activity of NAG and gamma-GT. In addition, vitamin E ameliorated the rise in renal content of MDA and enhanced the renal NPSH content as well as SOD activity. Similarly, probucol significantly inhibited the elevations in urea and creatinine levels and enhanced renal NPSH content and SOD activity. Simultaneous use of vitamin E and probucol was more effective in mitigating disturbances in the assessed parameters. The present work indicates that, due to their antioxidant activity, vitamin E and probucol have potential protective effects against GM nephrotoxicity.

Gentamicin nephrotoxicity in humans and animals: some recent research

It would appear from the literature cited in this article, that interest in gentamicin nephrotoxicity is still thriving. Despite extensive studies, the mechanism(s) of the nephrotoxicity is uncertain. Several clinical and experimental strategies have been employed in order to ameliorate or abolish the signs of gentamicin nephrotoxicity. Most of these were unsuccessful, impractical or unsafe. Therefore there is still a need for further studies to elucidate the mechanism(s) of action of the drugs nephrotoxicity, and to discover safe, practical and effective agents to ameliorate the nephrotoxicity in patients at risk.

Alterations in membrane permeability induced by aminoglycoside antibiotics: studies on liposomes and cultured cells

Aminoglycoside antibiotics bind to negatively-charged membranes in vitro as well as in vivo. We have examined if this binding could be associated with a change in the properties of membrane permeability. We have used a series of aminoglycoside derivatives and two independent test systems, namely (i) the release of calcein and of Mn2+ from phosphatidylinositol-containing large unilamellar vesicles, and (ii) the influx of Ca2+ into cultured macrophages. We found that certain aminoglycosides (e.g., streptomycin, isepamicin) markedly increase the membrane permeability whereas others (e.g., gentamicin) barely or do not influence it. This increase, when it occurs, is slower or less extensive than observed with pore-forming agents (mellitin, nystatin) or a Ca(2+)-ionophore (ionomycin). It is not observed with an agent [bis(beta-diethylaminoethylether)hexestrol] known to cause membrane fusion, and is not associated with any detectable change in membrane fluidity. In computer-aided conformational analysis of mixed monolayers between phosphatidylinositol and the aminoglycosides studied, it was found that those derivatives inducing an increase in membrane permeability in our experiments adopted an orientation rather perpendicular to the interface, whereas those with no or only a moderate effect were placed in a parallel orientation to this interface. The perpendicular orientation might cause a local condition of disorder which could explain the effects observed.

Drug-phospholipid interactions: role in aminoglycoside nephrotoxicity

Aminoglycoside antibiotics are known to be transported and accumulated within lysosomes of renal proximal tubular cells and to cause proximal tubular cell injury and necrosis. The pathogenesis of aminoglycoside nephrotoxicity is postulated to be related to the capacity of these organic polycations to interact electrostatically with membrane anionic phospholipids and to disrupt membrane structure and function. Aminoglycoside antibiotics have been shown to bind to anionic phospholipids of model membranes and to alter membrane permeability and promote membrane aggregation. In vivo these drugs induce phospholipiduria and a renal cortical phospholipidosis. The latter reflects the accumulation of phospholipid-containing myeloid bodies within the lysosomal compartment consequent to aminoglycoside-induced inhibition of lysosomal phospholipases. The mechanism of drug-induced inhibition of phospholipases has been shown to be secondary to the binding of these cationic drugs to anionic phospholipids. As the lysosomes became progressively distended with myeloid bodies, they become unstable and eventually rupture, which results in the release of acid hydrolases as well as high concentrations of aminoglycosides into the cytoplasm where they interact with and disrupt the function of other membranes and organelles including mitochondria and microsomes. It is postulated that the redistribution of drug from the lysosomal compartment to organellar membranes is the critical event which triggers the irreversible injury cascade. Polyaspartic acid is a polyanionic peptide which when administered in vitro or in vivo forms electrostatic complexes with aminoglycoside antibiotics and prevents these drugs from interacting with anionic phospholipids, from perturbing phospholipid metabolism and from causing cell injury and necrosis.

Protective effect of zinc-induced metallothionein synthesis on gentamicin nephrotoxicity in rats

Wistar rats were used to study the protective effect of zinc-induced metallothionein (MT) synthesis on gentamicin nephrotoxicity. We found that s.c. pre-injection of ZnSO4 (Zn 10 mg/kg/day) for 5 days could ameliorate proximal tubular necrosis and acute renal failure caused by an 8-day s.c. injection of gentamicin (100 mg/kg/day), while preinjection of saline instead of zinc or zinc and gentamicin together could not. In the zinc-pretreated rats (n = 6), renal cortical metallothionein level was significantly higher than that of normal (n = 8, p less than 0.001) and the saline controls (n = 6, p less than 0.001). Since MT is a scavenger of hydroxyl radical, it is proposed that hydroxyl radical plays a role in the pathogenesis of gentamicin nephrotoxicity and that preinjection of zinc could ameliorate gentamicin nephrotoxicity via the induction of renal cortical MT synthesis.

Effect of gentamicin on the lysosomal system of cultured human proximal tubular cells. Endocytotic activity, lysosomal pH and membrane fragility

Gentamicin treatment results in significant changes in lysosomal morphology and enzyme activity in renal tubular epithelium both in vivo and in vitro. In this study, cultured human proximal tubular cells (PTC) were treated with gentamicin (0, 0.01, 0.1, and 1.0 mg/ml) for 3, 7, 10 and 14 days, and the endocytotic activity, pH, and membrane fragility of the lysosomal system were examined. Fluorescein isothiocyanate-labeled dextran (FITC-dextran) was used to estimate endocytotic activity and intralysosomal pH. The fragility of isolated lysosomes was estimated by the release of N-acetyl-beta-glucosaminidase (NAG, EC3.2.1.30) into the medium. Gentamicin content was measured and correlated with the changes seen in lysosomal function. Gentamicin treatment caused a slight decrease in the rate with which human PTC accumulated FITC-dextran and a slight increase in intralysosomal pH. Treatment of human PTC with NH4Cl, a lysosomotropic compound, significantly increased the lysosomal pH; the NH4Cl-induced increase in the lysosomal pH of gentamicin-treated PTC, however, was not significantly different from control (0 mg gentamicin/ml). Lysosomes isolated from human PTC cultures released NAG upon incubation for 60 min at 37 degrees. There was no significant effect on the fragility of lysosomes isolated from cultures exposed to gentamicin for less than or equal to 7 days. Significantly increased fragility was seen, however, after 10 days of treatment with 1.0 mg gentamicin/ml and especially after a 14-day exposure to 0.01, 0.1, and 1.0 mg gentamicin/ml. Human PTC accumulated 0.47, 2.05 and 10.30 micrograms gentamicin/mg protein with 10 days of exposure to 0.01, 0.1 and 1.0 mg gentamicin/ml medium respectively. Gentamicin treatment associated with increased numbers of morphologically altered lysosomes, i.e. myeloid bodies, did not affect significantly the endocytotic activity and pH of lysosomes in cultured human PTC. Prolonged exposure (14 days) of human PTC to gentamicin, however, did increase the fragility of lysosomes after isolation. The increased numbers of morphologically altered lysosomes with increased fragility were not associated with any significant in vitro cell death. Therefore, it would appear that these lysosomal alterations are not directly responsible for the in vivo nephrotoxicity.

Effect of two gold compounds on lysosomes

The effect of two gold(I) compounds on stability of lysosomes in vitro was studied. Lysosomes from homogenates of rat kidney cortex were isolated by differential centrifugation. These lysosomes were incubated at 37 degrees C with widely varied concentrations of sodium aurothiomalate and sodium aurothiosulphate for 5, 35, and 65 minutes. Acid phosphatase activities were measured and used as an indication of lysosomal membrane stability in the presence and absence of drugs. The enhanced release of acid phosphatase from lysosomes by aurothiomalate and aurothiosulphate was related to dose, but the drugs differed substantially in their potencies. The disruptive effect on lysosomes was more marked for aurothiosulphate than for aurothiomalate. In addition, both drugs inhibited acid phosphatase activities at relatively high gold concentrations. Aurothiomalate had a moderate and aurothiosulphate a weaker inhibitory effect on the enzyme. Our results indicate that aurothiomalate and aurothiosulphate exert their beneficial effect in the treatment of rheumatoid arthritis through mechanism(s) other than lysosomal membrane stabilisation.