Impairment of lysosome-pinocytic vesicle fusion in rat kidney proximal tubules after treatment with gentamicin at low doses

Pyruvate dehydrogenase is a potential mitochondrial off-target for gentamicin based on in silico predictions and in vitro inhibition studies

During the drug development process, organ toxicity leads to an estimated failure of one-third of novel chemical entities. Drug-induced toxicity is increasingly associated with mitochondrial dysfunction, but identifying the underlying molecular mechanisms remains a challenge. Computational modeling techniques have proven to be a good tool in searching for drug off-targets. Here, we aimed to identify mitochondrial off-targets of the nephrotoxic drugs tenofovir and gentamicin using different in silico approaches (KRIPO, ProBis and PDID). Dihydroorotate dehydrogenase (DHODH) and pyruvate dehydrogenase (PDH) were predicted as potential novel off-target sites for tenofovir and gentamicin, respectively. The predicted targets were evaluated in vitro, using (colorimetric) enzymatic activity measurements. Tenofovir did not inhibit DHODH activity, while gentamicin potently reduced PDH activity. In conclusion, the use of in silico methods appeared a valuable approach in predicting PDH as a mitochondrial off-target of gentamicin. Further research is required to investigate the contribution of PDH inhibition to overall renal toxicity of gentamicin.

Investigation the effects of 2-aminoethoxydiphenyl borate (2-APB) on aminoglycoside nephrotoxicity

Investigation the protective effect of transient receptor potential channel modulator 2-Aminoethoxydiphenyl Borate (2-APB) on aminoglycoside nephrotoxicity caused by reactive oxygen species, calcium-induced apoptosis and inflammation was aimed. Forty Wistar rats were divided (n=8) as follows: Control group; DMSO group; 2-APB group; Gentamicin group (injected 100 mg/kg gentamicin intramuscularly for 10 days); Gentamicin+ 2-APB group (injected 2 mg/kg 2-APB intraperitoneally, then after 30 minutes 100 mg/kg gentamicin was injected intramuscularly for 10 days). Blood samples were collected for biochemical analyses, kidney tissue samples were collected for light, electron microscopic and immunohistochemical investigations. In gentamicin group glomerular degeneration, tubular dilatation, vacuolization, desquamation of tubular cells and hyaline cast formation in luminal space and leukocyte infiltration were seen. Disorganization of microvilli of tubular cells, apical cytoplasmic blebbing, lipid accumulation, myelin figure like structure formation, increased lysosomes, mitochondrial swelling and disorganization of cristae structures, apoptotic changes and widening of intercellular space were found. TNF-α, IL-6 and caspase 3 expressions were increased. BUN and creatinine concentrations were increased. Increase in MDA levels and decrease in SOD activities were determined. Even though degeneration still continues in gentamicin+2-APB treatment group, severity and the area it occupied were decreased and the glomerular and tubule structures were generally preserved. TNF-α, IL-6, caspase 3 immunoreactivities and BUN, creatinine, MDA concentrations were reduced and SOD activities were increased markedly compared to gentamicin group. In conclusion, it has been considered that 2-APB can prevent gentamicin mediated nephrotoxicity with its anti-oxidant, anti-apoptotic and anti-inflammatory effects.

Proenkephalin-A secreted by renal proximal tubules functions as a brake in kidney regeneration

Organ regeneration necessitates precise coordination of accelerators and brakes to restore organ function. However, the mechanisms underlying this intricate molecular crosstalk remain elusive. In this study, the level of proenkephalin-A (PENK-A), expressed by renal proximal tubular epithelial cells, decreases significantly with the loss of renal proximal tubules and increased at the termination phase of zebrafish kidney regeneration. Notably, this change contrasts with the role of hydrogen peroxide (H2O2), which acts as an accelerator in kidney regeneration. Through experiments with penka mutants and pharmaceutical treatments, we demonstrate that PENK-A inhibits H2O2 production in a dose-dependent manner, suggesting its involvement in regulating the rate and termination of regeneration. Furthermore, H2O2 influences the expression of tcf21, a vital factor in the formation of renal progenitor cell aggregates, by remodeling H3K4me3 in renal cells. Overall, our findings highlight the regulatory role of PENK-A as a brake in kidney regeneration.

Generation and characterization of a high affinity anti-human FcRn antibody, rozanolixizumab, and the effects of different molecular formats on the reduction of plasma IgG concentration

Rozanolixizumab (UCB7665), a humanized high-affinity anti-human neonatal Fc receptor (FcRn) monoclonal antibody (IgG4P), has been developed to reduce pathogenic IgG in autoimmune and alloimmune diseases. We document the antibody isolation and compare rozanolixizumab with the same variable region expressed in various mono-, bi- and trivalent formats. We report activity data for rozanolixizumab and the different molecular formats in human cells, FcRn-transgenic mice, and cynomolgus monkeys. Rozanolixizumab, considered the most effective molecular format, dose-dependently and selectively reduced plasma IgG concentrations in an FcRn-transgenic mouse model (no effect on albumin). Intravenous (IV) rozanolixizumab dosing in cynomolgus monkeys demonstrated non-linear pharmacokinetics indicative of target-mediated drug disposition; single IV rozanolixizumab doses (30 mg/kg) in cynomolgus monkeys reduced plasma IgG concentration by 69% by Day 7 post-administration. Daily IV administration of rozanolixizumab (initial 30 mg/kg loading dose; 5 mg/kg daily thereafter) reduced plasma IgG concentrations in all cynomolgus monkeys, with low concentrations maintained throughout the treatment period (42 days). In a 13-week toxicology study in cynomolgus monkeys, supra-pharmacological subcutaneous and IV doses of rozanolixizumab (≤ 150 mg/kg every 3 days) were well tolerated, inducing sustained (but reversible) reductions in IgG concentrations by up to 85%, with no adverse events observed. We have demonstrated accelerated natural catabolism of IgG through inhibition of IgG:FcRn interactions in mice and cynomolgus monkeys. Inhibition of FcRn with rozanolixizumab may provide a novel therapeutic approach to reduce pathogenic IgG in human autoimmune disease. Rozanolixizumab is being investigated in patients with immune thrombocytopenia (NCT02718716) and myasthenia gravis (NCT03052751).

Reno-protective effects of ursodeoxycholic acid against gentamicin-induced nephrotoxicity through modulation of NF-κB, eNOS and caspase-3 expressions

Gentamicin (GNT) is a potent aminoglycoside antibiotic widely used to treat life-threatening bacterial infections. We aim to investigate the potential protective effect of ursodeoxycholic acid (UDCA) against GNT-induced nephrotoxicity. In this study, 24 male Wistar rats were used and randomly divided into four groups of six animals each. Control group received 0.5% carboxymethyl cellulose orally for 15 days, GNT group received GNT 100 mg/kg/day i.p. for 8 days, UDCA group received UDCA orally for 15 consecutive days at a dose of 60 mg/kg/day suspended in 0.5% carboxymethyl cellulose and UDCA-pretreated group received UDCA orally for 7 days then co-administered with GNT i.p. for 8 days at the same fore-mentioned doses. Serum levels of kidney function parameters (urea, creatinine, uric acid and albumin) were measured. Renal tissues were used to evaluate oxidative stress markers; malonaldehyde (MDA), reduced glutathione (GSH) and the anti-oxidant enzyme superoxide dismutase (SOD) activities and nuclear factor kappa light-chain enhancer of activated B cells (NF-κB) and kidney injury molecule-1 (KIM-1) mRNA levels. Immunohistochemical expression of endothelial nitric oxide synthase (eNOS) and caspase-3 and histological and ultrastructural examination were performed. Treatment with GNT increased the serum levels of renal function parameters and renal MDA, NF-κB and KIM-1 mRNA levels, while it decreased GSH and SOD activities. Marked immunohistochemical expression of caspase-3 was observed after GNT administration while it decreased eNOS expression. Histological and ultrastructural alterations were also evident in renal corpuscles and tubules. In contrast, pretreatment with UDCA reversed changes caused by GNT administration. These results suggest that UDCA ameliorates GNT-induced kidney injury via inhibition of oxidative stress, inflammation and apoptosis.

β-sitosterol protects against carbon tetrachloride hepatotoxicity but not gentamicin nephrotoxicity in rats via the induction of mitochondrial glutathione redox cycling

Previous findings have demonstrated that β-sitosterol (BSS), an active component of Cistanches Herba, protected against oxidant injury in H9c2 cardiomyocytes and in rat hearts by enhancing mitochondrial glutathione redox cycling, possibly through the intermediacy of mitochondrial reactive oxygen species production. We therefore hypothesized that BSS pretreatment can also confer tissue protection against oxidant injury in other vital organs such as liver and kidney of rats. In this study, the effects of BSS pretreatment on rat models of carbon tetrachloride (CCl4) hepatotoxicity and gentamicin nephrotoxicity were investigated. The findings showed that BSS pretreatment protected against CCl4-induced hepatotoxicity, but not gentamicin nephrotoxicity in rats. The hepatoprotection afforded by BSS was associated with the improvement in mitochondrial glutathione redox status, presumably through the glutathione reductase-mediated enhancement in mitochondrial glutathione redox cycling. The hepatoprotection afforded by BSS was also accompanied by the improved mitochondrial functional ability in rat livers. The inability of BSS to protect against gentamicin nephrotoxicity was likely due to the relatively low bioavailability of BSS in rat kidneys. BSS may serve as potential mitohormetic agent for the prevention of oxidative stress-induced injury in livers.

Regulation of lipid accumulation by AMP-activated kinase [corrected] in high fat diet-induced kidney injury

AMP-activated protein kinase (AMPK) is an important energy sensor that may be critical in regulating renal lipid accumulation. To evaluate the role of AMPK in mediating renal lipid accumulation, C57BL/6J mice were randomized to a standard diet, a high-fat diet, or a high-fat diet plus AICAR (an AMPK activator) for 14 weeks. Renal functional and structural studies along with electron microscopy were performed. Mice given the high-fat diet had proximal tubule injury with the presence of enlarged clear vacuoles, and multilaminar inclusions concurrent with an increase of tissue lipid and overloading of the lysosomal system. The margins of the clear vacuoles were positive for the endolysosomal marker, LAMP1, suggesting lysosome accumulation. Characterization of vesicles by special stains (Oil Red O, Nile Red, Luxol Fast Blue) and by electron microscopy showed they contained onion skin-like accumulations consistent with phospholipids. Moreover, cholesteryl esters and phosphatidylcholine-containing phospholipids were significantly increased in the kidneys of mice on a high-fat diet. AMPK activation with chronic AICAR treatment prevented the clinical and structural effects of high-fat diet. Thus, high-fat diet contributes to a dysfunction of the lysosomal system and altered lipid metabolism characterized by cholesterol and phospholipid accumulation in the kidney. AMPK activation normalizes the changes in renal lipid content despite chronic exposure to lipid challenge.

Uriniferous tubule: structural and functional organization

The uriniferous tubule is divided into the proximal tubule, the intermediate (thin) tubule, the distal tubule and the collecting duct. The present chapter is based on the chapters by Maunsbach and Christensen on the proximal tubule, and by Kaissling and Kriz on the distal tubule and collecting duct in the 1992 edition of the Handbook of Physiology, Renal Physiology. It describes the fine structure (light and electron microscopy) of the entire mammalian uriniferous tubule, mainly in rats, mice, and rabbits. The structural data are complemented by recent data on the location of the major transport- and transport-regulating proteins, revealed by morphological means(immunohistochemistry, immunofluorescence, and/or mRNA in situ hybridization). The structural differences along the uriniferous tubule strictly coincide with the distribution of the major luminal and basolateral transport proteins and receptors and both together provide the basis for the subdivision of the uriniferous tubule into functional subunits. Data on structural adaptation to defined functional changes in vivo and to genetical alterations of specified proteins involved in transepithelial transport importantly deepen our comprehension of the correlation of structure and function in the kidney, of the role of each segment or cell type in the overall renal function,and our understanding of renal pathophysiology.

Recent progress in histochemistry and cell biology

Studies published in Histochemistry and Cell Biology in the year 2011 represent once more a manifest of established and newly sophisticated techniques being exploited to put tissue- and cell type-specific molecules into a functional context. The review is therefore the Histochemistry and Cell Biology's yearly intention to provide interested readers appropriate summaries of investigations touching the areas of tissue biology, developmental biology, the biology of the immune system, stem cell research, the biology of subcellular compartments, in order to put the message of such studies into natural scientific-/human- and also pathological-relevant correlations.

Role of oxidative stress in lysosomal membrane permeabilization and apoptosis induced by gentamicin, an aminoglycoside antibiotic

Gentamicin, an aminoglycoside antibiotic used to treat severe bacterial infections, may cause acute renal failure. At therapeutic concentrations, gentamicin accumulates in lysosomes and induces apoptosis in kidney proximal tubular cells. In gentamicin-treated renal LLC-PK1 cells, acridine orange release from lysosomes, previously interpreted as lysosomal membrane permeabilization, precedes the apoptotic cascade that develops during incubation with gentamicin. However, the link between gentamicin lysosomal accumulation and apoptosis remains unclear. We here examined if reactive oxygen species (ROS) production could account for gentamicin-induced acridine orange release and apoptosis, and the implication of iron in these events. We found that gentamicin induced ROS production prior to, and at lower drug concentrations than required for, acridine orange release and apoptosis. ROS antioxidant or scavenger, catalase, and N-acetylcysteine largely prevented these events. Vital confocal imaging revealed that gentamicin-induced ROS production occurs in lysosomes. Deferoxamine, an iron chelator, which is endocytosed and accumulates in lysosomes, largely prevented gentamicin-induced ROS production as well as apoptosis. Direct evidence for gentamicin-induced permeabilization of lysosomal membrane was provided by showing the release into the cytosol of Lucifer yellow, a membrane-impermeant endocytic tracer with a comparable molecular weight as gentamicin. Altogether, our data demonstrate a key role of lysosomal iron and early ROS production in gentamicin-induced lysosomal membrane permeabilization and apoptosis.

Transport of arylsulfatase A across the blood-brain barrier in vitro

Enzyme replacement therapy is an option to treat lysosomal storage diseases caused by functional deficiencies of lysosomal hydrolases as intravenous injection of therapeutic enzymes can correct the catabolic defect within many organ systems. However, beneficial effects on central nervous system manifestations are very limited because the blood-brain barrier (BBB) prevents the transfer of enzyme from the circulation to the brain parenchyma. Preclinical studies in mouse models of metachromatic leukodystrophy, however, showed that arylsulfatase A (ASA) is able to cross the BBB to some extent, thus reducing lysosomal storage in brain microglial cells. The present study aims to investigate the routing of ASA across the BBB and to improve the transfer in vitro using a well established cell culture model consisting of primary porcine brain capillary endothelial cells cultured on Transwell filter inserts. Passive apical-to-basolateral ASA transfer was observed, which was not saturable up to high ASA concentrations. No active transport could be determined. The passive transendothelial transfer was, however, charge-dependent as reduced concentrations of negatively charged monosaccharides in the N-glycans of ASA or the addition of polycations increased basolateral ASA levels. Adsorptive transcytosis is therefore considered to be the major transport pathway. Partial inhibition of the transcellular ASA transfer by mannose 6-phosphate indicated a second route depending on the insulin-like growth factor II/mannose 6-phosphate receptor, MPR300. We conclude that cationization of ASA and an increase of the mannose 6-phosphate content of the enzyme may promote blood-to-brain transfer of ASA, thus leading to an improved therapeutic efficacy of enzyme replacement therapy behind the BBB.

Distribution study of peplomycin in rat kidney revealed by immunocytochemistry using monoclonal antibodies

Peplomycin (PEP), an anti-tumor antibiotic related structurally to bleomycin, is widely used, especially for squamous cell carcinoma but shows renal toxicity. We prepared monoclonal antibodies (mAbs) against N-(γ-maleimidobutyryloxy)succinimide-conjugated PEP. The mAbs were monospecific for PEP, but did not react with bleomycin and other anticancer antibiotics. The mAbs enabled us to develop an immunocytochemical (ICC) method for detecting the uptake of PEP in the rat kidney. Two hours after a single i.v. administration of PEP, ICC revealed immunostaining for PEP in irregularly shaped cytoplasmic granules of the proximal tubules in which the microvilli were also stained. Also, staining occurred in the distal tubules and collecting ducts, in both of which we observed scattered swollen cells, reminiscent of necrotic cells, in which both the nuclei and cytoplasm reacted strongly with the antibody. Twenty-four hours after injection, PEP in the proximal tubules completely vanished, but yet significant amounts of PEP remained in both the distal tubules and collecting ducts. Distribution patterns of PEP in cells of the kidneys resembled, in some ways, those of our recent ICC studies for an organic cation aminoglycoside antibiotic gentamicin. This ICC suggests that PEP taken up in the proximal tubule cells is localized in the lysosomes, and organic cation transporters and bleomycin hydrolase might be involved in entrance and/or disappearance of PEP in this cell type. Furthermore, the distal tubules and collecting ducts may be the sites readily affected by some chemotherapeutic agents.

Urinary levels of regenerating islet-derived protein III β and gelsolin differentiate gentamicin from cisplatin-induced acute kidney injury in rats

A key aspect for the clinical handling of acute kidney injury is an early diagnosis, for which a new generation of urine biomarkers is currently under development including kidney injury molecule 1 and neutrophil gelatinase-associated lipocalin. A further diagnostic refinement is needed where one specific cause among several potentially nephrotoxic insults can be identified during the administration of multidrug therapies. In this study we identified increases in regenerating islet-derived protein III beta (reg IIIb) and gelsolin as potential differential urinary markers of gentamicin's nephrotoxicity. Indeed, urinary levels of both reg IIIb and gelsolin distinguish between the nephrotoxicity caused by gentamicin from that caused by cisplatin where these markers were not increased by the latter. Reg IIIb was found to be overexpressed in the kidneys of gentamicin-treated rats and excreted into the urine, whereas urinary gelsolin originated from the blood by glomerular filtration. Our results illustrate an etiological diagnosis of acute kidney injury through analysis of urine. Thus, our results raise the possibility of identifying the actual nephrotoxin in critically ill patients who are often treated with several nephrotoxic agents at the same time, thereby providing the potential for tailoring therapy to an individual patient, which is the aim of personalized medicine.

The antibiotic gentamicin inhibits specific protein trafficking functions of the Arf1/2 family of GTPases

Gentamicin is a highly efficacious antibiotic against Gram-negative bacteria. However, its usefulness in treating infections is compromised by its poorly understood renal toxicity. Toxic effects are also seen in a variety of other organisms. While the yeast Saccharomyces cerevisiae is relatively insensitive to gentamicin, mutations in any one of ∼20 genes cause a dramatic decrease in resistance. Many of these genes encode proteins important for translation termination or specific protein-trafficking complexes. Subsequent inspection of the physical and genetic interactions of the remaining gentamicin-sensitive mutants revealed a network centered on chitin synthase and the Arf GTPases. Further analysis has demonstrated that some conditional arf1 and gea1 alleles make cells hypersensitive to gentamicin under permissive conditions. These results suggest that one consequence of gentamicin exposure is disruption of Arf-dependent protein trafficking.

Sub-nephrotoxic doses of gentamicin predispose animals to developing acute kidney injury and to excrete ganglioside M2 activator protein

We studied whether nephrotoxic drug administration sensitizes to acute renal failure (ARF) by administering a sub-nephrotoxic dose of gentamicin. This pre-treatment sensitized animals with no sign of renal injury to develop ARF when exposed to a second potential nephrotoxic drug, also given at sub-nephrotoxic doses that would be otherwise harmless to non-sensitized animals. We identified urinary ganglioside M2 activator protein (GM2AP) as a biomarker of an enhanced sensitivity to suffer ARF following sub-nephrotoxic treatment with gentamicin. Sub-nephrotoxic gentamicin did not alter renal GM2AP gene expression or protein levels, determined by reverse transcriptase-PCR, western blot, and immunostaining, nor was its serum level modified. The origin of increased GM2AP in the urine is thought to be a defective tubular handling of this protein as a consequence of gentamicin action. Hence, markers of acquired sensitivity may improve the prevention of ARF by enhancing our capacity to monitor for this condition, in a preemptive manner.

Light-microscopic immunocytochemistry for gentamicin and its use for studying uptake of the drug in kidney

Gentamicin (GM) is a widely used antibiotic but shows renal toxicity. We produced a serum against GM (anti-GM) conjugated to bovine serum albumin with N-(gamma-maleimidobutyryloxy)succinimide. The antiserum was monospecific for GM and did not cross-react with the analog streptomycin, tobramycin, kanamycin, or amikacin. The antiserum also detected glutaraldehyde-fixed GM, and this enabled us to develop an immunocytochemical method for detecting the uptake of GM in rat kidney. Twelve hours after a single intravenous administration of GM, immunocytochemistry revealed that GM accumulated in the S1, S2, and S3 segments of the proximal tubules, as well as in the distal tubules and collecting ducts. By 12 h after injection, the drug was detected in cytoplasmic granules of the proximal tubule cells. However, early (1 h) after injection, drug accumulation was detected in the microvilli of these cells. The distal tubules and collecting ducts contained scattered swollen cells, reminiscent of necrotic cells, in which both the nuclei and the cytoplasm reacted strongly with GM. No staining occurred in the kidneys of saline-injected control rats. These results agree with previous studies showing that GM is endocytosed in the proximal tubules and accumulates in lysosomes. Additionally, our results show that GM also accumulates in the distal tubules and collecting ducts. This was achieved by systematically varying the pretreatment conditions-an approach necessary for detecting GM in different subcellular compartments. This approach should be useful for accurately detecting the uptake and toxicity of the antibiotic in different tissues.

Renal cell apoptosis induced by nephrotoxic drugs: cellular and molecular mechanisms and potential approaches to modulation

Apoptosis plays a central role not only in the physiological processes of kidney growth and remodeling, but also in various human renal diseases and drug-induced nephrotoxicity. We present in a synthetic fashion the main molecular and cellular pathways leading to drug-induced apoptosis in kidney and the mechanisms regulating it. We illustrate them using three main nephrotoxic drugs (cisplatin, gentamicin, and cyclosporine A). We discuss the main regulators and effectors that have emerged as key targets for the design of therapeutic strategies. Novel approaches using gene therapy, antisense strategies, recombinant proteins, or compounds obtained from both classical organic and combinatorial chemistry are examined. Finally, key issues that need to be addressed for the success of apoptosis-based therapies are underlined.

Gentamicin causes apoptosis at low concentrations in renal LLC-PK1 cells subjected to electroporation

Gentamicin accumulates in the lysosomes of kidney proximal tubular cells and causes apoptosis at clinically relevant doses. Gentamicin-induced apoptosis can be reproduced with cultured renal cells, but only at high extracellular concentrations (1 to 3 mM; 0.4 to 1.2 g/liter) because of its low level of uptake. We recently showed that gentamicin-induced apoptosis in LLC-PK1 cells involves a rapid (2-h) permeabilization of lysosomes and activation of the mitochondrial pathway of apoptosis (10 h). We now examine whether the delivery of gentamicin to the cytosol by electroporation would sensitize LLC-PK1 cells to apoptosis. Cells were subjected to eight pulses (1 ms) at 800 V/cm (square waves) in the presence of gentamicin (3 microM to 3 mM; 1.2 mg/liter to 1.2 g/liter); returned to gentamicin-free medium; and examined at 8 h for their Bax (a marker of mitochondrial pathway activation) contents by Western blotting and competitive reverse transcriptase PCR and at 24 h for apoptosis by 4',6'-diamidino-2'-phenylindole staining (confirmed by electron microscopy) and for necrosis (by determination of lactate dehydrogenase release). Nonelectroporated cells were incubated with gentamicin for 8 and 24 h. Significant increases in Bax levels (8 h) and apoptosis (24 h) were detected with 0.03 mM (13.2 mg/liter) gentamicin in electroporated cells compared with those achieved with 2 mM (928 mg/liter) in incubated cells. The increase in the Bax level was not associated with an increase in the level of its mRNA but was associated with the accumulation of ubiquitinated forms (probably as a result of impairment of its degradation by the proteasome). Assay of cell-associated gentamicin showed a marked, immediate, but transient accumulation in electroporated cells, whereas a slow, steady uptake was detected in incubated cells. The data indicate that cytosolic gentamicin triggers apoptosis. Sequestration of gentamicin in lysosomes would, to some extent, protect against apoptosis.

Gentamicin-induced apoptosis in LLC-PK1 cells: Involvement of lysosomes and mitochondria

Gentamicin accumulates in lysosomes and induces apoptosis in kidney proximal tubules and renal cell lines. Using LLC-PK1 cells, we have examined the concentration- and time-dependency of the effects exerted by gentamicin (1-3 mM; 0-3 days) on (i) lysosomal stability; (ii) activation of mitochondrial pathway; (iii) occurrence of apoptosis (concentrations larger than 3 mM caused extensive necrosis as assessed by the measurement of lactate dehydrogenase release). Within 2 h, gentamicin induced a partial relocalization [from lysosomes to cytosol] of the weak organic base acridine orange. We thereafter observed (a) a loss of mitochondrial membrane potential (as from 10 h, based on spectrophotometric and confocal microscopy using JC1 probe) and (b) the release of cytochrome c from granules to cytosol, and the activation of caspase-9 (as from 12 h; evidenced by Western blot analysis). Increase in caspase-3 activity (assayed with Ac-DEVD-AFC in the presence of z-VAD-fmk]) and appearance of fragmented nuclei (DAPI staining) was then detected as from 16 to 24 h together with nuclear fragmentation. Gentamicin produces a fast (within 4 h) release of calcein from negatively-charged liposomes at pH 5.4, which was slowed down by raising the pH to 7.4, or when phosphatidylinositol was replaced by cardiolipin (to mimic the inner mitochondrial membrane). The present data provide temporal evidence that gentamicin causes apoptosis in LLC-PK1 with successive alteration of the permeability of lysosomes, triggering of the mitochondrial pathway, and activation of caspase-3.

Cocaine induces a mixed lysosomal lipidosis in cultured fibroblasts, by inactivation of acid sphingomyelinase and inhibition of phospholipase A1

This paper reports that cocaine may induce a lysosomal storage disorder. Indeed, culture of Rat-1 fibroblasts with 250-500 microM cocaine induced after 2-3 days a major accumulation in lysosomes of electron-dense lamellar structures. By subcellular fractionation, this was reflected by a selective decrease of the buoyant density of several lysosomal enzymes, indicating lysosomal lipid overload. Biochemical analysis confirmed an increased cellular content of major phospholipids and sphingomyelin, but not of cholesterol. Cocaine, a membrane-permeant weak base, is concentrated by acidotropic sequestration, because its accumulation was abrogated by the proton ionophore, monensin and the vacuolar ATPase inhibitor, bafilomycin A1. At its estimated lysosomal concentration, cocaine almost completely inhibited phospholipase A1 activity on liposomes. Cell incubation with cocaine, but not with its inactive metabolite, benzoylecgonine, rapidly inactivated acid sphingomyelinase, as reflected by a 10-fold decrease in Vmax with identical Km. Acid sphingomyelinase inactivation was fully prevented by the thiol proteinases inhibitors, leupeptin and E64, indicating that cocaine induces selective sphingomyelinase proteolysis. Upon cocaine removal, acid sphingomyelinase activity was rapidly restored, pointing to its fast turnover. In contrast, the cellular content of several other lysosomal hydrolases was increased up to 2-fold. Together, these data show that acidotropic accumulation of cocaine in lysosomes rapidly inhibits acid phospholipase A1 and inactivates acid sphingomyelinase, which can explain induction of a mixed lysosomal lipidosis.

Proteomic analysis of rat kidney cortex following treatment with gentamicin

The regionally specific structure and function of the kidney renders it susceptible to toxic exposure. To characterize these changes at the proteome level, we have investigated the effects on protein expression following treatment with gentamicin. The more than 20 proteins identified were involved in the citric acid cycle, gluconeogenesis, fatty acid synthesis, and transport or cellular stress responses. These results strongly support the notion that energy production is impaired and mitochondrial dysfunction is involved in gentamicin-induced nephrotoxicity.

Gentamicin causes endocytosis of Na/Pi cotransporter protein (NaPi-2)

BACKGROUND

Renal toxicity is a major side-effect of aminoglycoside antibiotics and is characterized by an early impairment in proximal tubular function. In a previous study, we have shown that gentamicin administration to the rat causes an early impairment in sodium gradient-dependent phosphate (Na/Pi) cotransport activity. The purpose of our current study was to determine the molecular mechanisms of the impairment in Na/Pi cotransport activity, specifically the role of the proximal tubular type II Na/Pi cotransporter.

METHODS

Rats were treated for one, two, and three days with two daily injections of 30 mg/kg body weight gentamicin or the vehicle.

RESULTS

Gentamicin caused a progressive decrease in superficial cortical apical brush-border membrane (SC-BBM) Na/Pi cotransporter activity (856 +/- 93 in control vs. 545 +/- 87 pmol/mg BBM protein in 3-day gentamicin, P < 0.01). Western blot analysis showed a parallel and progressive decrease in SC-BBM Na/Pi cotransporter protein abundance, a 50% decrease after one day of treatment, a 63% decrease after two days of treatment, and an 83% decrease after three days treatment with gentamicin. In contrast, gentamicin treatment had no effect on Na/Pi cotransport activity or Na/Pi cotransporter protein abundance in BBM isolated from the juxtamedullary cortex (JMC-BBM). Immunofluorescence microscopy showed a major decrease in the expression of Na/Pi cotransporter protein in the apical membrane of the proximal convoluted tubule, with progressive intracellular accumulation of Na/Pi protein. Colocalization studies showed that in gentamicin-treated rats, Na/Pi protein was colocalized in the early endosomes and especially in the lysosomes. Northern blot analysis of cortical RNA interestingly showed no reduction in Na/Pi cotransporter mRNA abundance even after three days of gentamicin treatment.

CONCLUSION

We conclude that gentamicin inhibits Na/Pi cotransport activity by causing a decrease in the expression of the type II Na/Pi cotransport protein at the level of the proximal tubular apical BBM and that inhibition of Na/Pi cotransport activity is most likely mediated by post-transcriptional mechanisms.

Gentamicin inhibits renal protein and phospholipid metabolism in rats: implications involving intracellular trafficking

Studies were undertaken to characterize the mechanism of aminoglycoside-induced nephrotoxicity. Early time points in gentamicin treatment (1 to 3 d) were used to investigate the development of toxic events without the complication of gross morphologic cellular alterations. Enzyme activities of cortical homogenates and brush border membrane (BBM) preparations documented little effect on specific activities or the ability to isolate representative membrane fractions. In vivo protein synthesis experiments demonstrated that gentamicin reduced cellular protein synthesis after 2 d of treatment. This inhibition increased to 50% on the third day. Total cellular proteins synthesis was inhibited to the same extent as BBM protein synthesis. However, gentamicin had different effects on homogenate versus BBM phospholipids. The total phospholipid contents in cortical homogenates and BBM from treated animals were increased, compared with control animals. A significant decrease in phospholipid synthesis was observed only in homogenates from treated animals. When effects on individual phospholipids were investigated, only an increase in phosphatidylinositol levels was observed in cortical homogenates from treated rats. However, gentamicin treatment was demonstrated to increase the levels of phosphatidylinositol and phosphatidylcholine, while decreasing the level of sphingomyelin (SPH), in BBM. Incorporation of (32)P into SPH, phosphatidylserine, and phosphatidylethanolamine was inhibited in cortical homogenates from gentamicin-treated animals; among BBM phospholipids, however, a significant decrease was observed only for SPH synthesis. It was concluded that inhibition of phospholipid degradation was quantitatively the major contributor to the effects of gentamicin on phospholipid metabolism. Confocal microscopic studies, using tracer amounts of fluorescently labeled gentamicin, revealed gentamicin in large, mostly basal structures. Correlative electron microscopic studies, using photo-oxidation techniques, demonstrated that these structures consisted of lysosomal, Golgi complex, and mitochondrial structures. These observations suggest retrograde trafficking of gentamicin and indicate a general mechanism of gentamicin-induced nephrotoxicity.

Inhibition of in vitro endosomal vesicle fusion activity by aminoglycoside antibiotics

The effects of two aminoglycoside antibiotics, neomycin and Geneticin, on the endocytic pathway were studied using a cell-free assay that reconstitutes endosome-endosome fusion. Both drugs inhibit the rate and extent of endosome fusion in a dose-dependent manner with IC50 values of approximately 45 microM and approximately 1 mM, respectively. Because the IC50 for neomycin falls within the range of affinities reported for its binding to acidic phospholipids, notably phosphatidylinositol 4,5-bisphosphate (PIP2), these data suggest that negatively charged lipids are required for endosome fusion. A role for negatively charged lipids in membrane traffic has been postulated to involve the activity of a PIP2-dependent phospholipase D (PLD) stimulated by the GTP-binding protein ADP-ribosylation factor (ARF). Although neomycin blocks endosome fusion at a stage of the in vitro reaction that is temporally related to steps inhibited by cytosolic ARFs when they bind guanosine-5'-gamma-thiophosphate (GTPgammaS), these inhibitors appear to act in a synergistic manner. This idea is confirmed by the fact that addition of a PIP2-independent PLD does not suppress neomycin inhibition of endosome fusion; moreover, in vitro fusion activity is not affected by the pleckstrin homology domain of phosphoinositide-specific phospholipase C delta1, which binds to acidic phospholipids, particularly PIP2, with high affinity. Thus, although aminoglycoside-sensitive elements of endosome fusion are required at mechanistic stages that are also blocked by GTPgammaS-bound ARF, these effects are unrelated to inhibition of the PIP2-dependent PLD activity stimulated by this GTP-binding protein. These results argue that there are additional mechanistic roles for acidic phospholipids in the endosomal pathway.

Attenuation of gentamicin-induced nephrotoxicity in rats by fleroxacin

The effect of fleroxacin on gentamicin-induced nephrotoxicity was evaluated with female Sprague-Dawley rats. Animals were injected during 4 or 10 days with saline (NaCl; 0.9%), gentamicin alone at doses of 10 and 40 mg/kg of body weight/12 h (subcutaneously), fleroxacin alone at a dose of 25 mg/kg/12 h (intraperitoneally), or the combination gentamicin-fleroxacin in the same regimen. Gentamicin induced a dose- and time-dependent renal toxicity as evaluated by gentamicin cortical levels, sphingomyelinase activity in the renal cortex, histopathologic and morphometric analysis, blood urea nitrogen and serum creatinine levels, and cellular regeneration ([3H]thymidine incorporation into DNA of cortical cells). The extent of these changes was significantly reduced when gentamicin was given in combination with fleroxacin. Although the mechanisms by which fleroxacin reduces the nephrotoxic potential of gentamicin are unknown, we propose that the fleroxacin-gentamicin combination enhances exocytosis activity in proximal tubular cells, as suggested by the higher excretion of urinary enzymes and lower cortical levels of gentamicin observed in animals treated with the combination fleroxacin-gentamicin compared with those treated with gentamicin alone. The protective effect of fleroxacin on gentamicin nephrotoxicity should be investigated further.

Rapid and complete fusion of macrophage lysosomes with phagosomes containing Salmonella typhimurium

The virulence of Salmonella typhimurium for mice results, in part, from its ability to survive after phagocytosis by macrophages. Although it is generally agreed that intracellular bacteria persist in membrane-bound phagosomes, there remains some question as to whether these phagosomes fuse with macrophage lysosomes. This report describes the maturation of phagosomes containing S. typhimurium inside mouse bone marrow-derived macrophages. Macrophages were infected briefly and incubated for various intervals; then they were examined by fluorescence microscopy for colocalization of bacteria with lysosomal markers. These markers included LAMP-1, cathepsin L, and fluorescent proteins or dextrans preloaded into lysosomes by endocytosis. By all measures, phagosomes containing S. typhimurium merged completely with the lysosomal compartment within 20 min of phagocytosis. The rate of phagosome-lysosome fusion was similar to the rate for phagocytosed latex beads. Phagolysosomes remained accessible to fluid-phase probes and contained lysosomal markers for many hours. Moreover, a large percentage of the wild-type bacteria that were viable 20 min after infection survived longer incubations inside macrophages, indicating that the survivors were not a minor subpopulation that avoided phagosome-lysosome fusion. Therefore, we conclude that S. typhimurium survives within the lysosomal compartments of macrophages.

Aminoglycoside antibiotics prevent the formation of non-bilayer structures in negatively-charged membranes. Comparative studies using fusogenic (bis(beta-diethylaminoethylether)hexestrol) and aggregating (spermine) agents

Aminoglycoside antibiotics cause aggregation but not fusion of negatively-charged liposomes at an extent proportional to their capacity to interact with acidic phospholipids (Van Bambeke et al., 1995, Eur. J. Pharmacol., 289, 321-333). To understand why aggregation is not followed by fusion, we have examined here the influence of two aminoglycosides with markedly different toxic potential (gentamicin > isepamicin) on lipid phase transition in negatively-charged liposomes using 31P-NMR spectroscopy, in comparison with spermine (an aggregating agent) and bis(beta-diethylaminoethylether)hexestrol or DEH (a fusogenic cationic amphiphile). Gentamicin, spermine, and, to a lesser extent, isepamicin inhibit the appearance of the isotropic signal seen upon warming of control liposomes and denoting the presence of mobile structures. This non-bilayer signal appeared most prominently when liposomes were incubated with DEH, a strong fusogenic agent. We conclude that aminoglycosides, like spermine, have the potential to prevent membrane fusion, by inhibiting the development of a critical change in membrane organization, which is associated with fusion. We suggest that this capacity could be a determinant in aminoglycoside toxicity.

Aminoglycoside antibiotics induce aggregation but not fusion of negatively-charged liposomes

The binding of aminoglycoside antibiotics to acidic phospholipids of membranes is an essential step in the development of both their renal and auditory toxicities, which could be associated with critical modifications of the membrane properties. This work examines the capacity of aminoglycosides to induce membrane aggregation and fusion. Three techniques were used in parallel: (i) measurement of the dequenching rate of a lipid-soluble fluorescent probe (octadecylrhodamine B) incorporated at self-quenched concentration in membranes; (ii) measurement of the increase in the energy transfer between two fluorescent derivatives of phospholipids; and (iii) electron microscopy of negatively-stained replicas. The results were compared with those obtained with spermine (an aggregating polycation) and melittin (a fusogenic peptide). The three approaches indicate that aminoglycosides induce liposomes aggregation, but not fusion. Aggregation is related to the capacity of each drug studied to bind phosphatidylinositol, as evaluated by its energy of interaction with this acidic phospholipid, and to its toxic potential. Membrane aggregation occurring in vivo could therefore contribute to, or be a determinant of this toxicity, which could rationally be screened for new derivatives by the methods applied here.

Molecular parameters involved in aminoglycoside nephrotoxicity

Aminoglycoside antibiotics are hydrophilic molecules consisting of an animated cyclitol associated with amino sugar. They bind in vivo as well as in vitro to negatively charged membranes. Their use as chemotherapeutic agents is unfortunately accompanied by oto- and nephrotoxic reactions, and the purpose of this review is to examine the role of the molecular interactions between aminoglycosides and membranes in the development of nephrotoxicity. 31P Nuclear magnetic resonance (NMR) and fluorescence depolarization have been used to characterize the effect of aminoglycosides on phosphate heads and fatty acyl chains of phospholipids. 15N NMR has been used to obtain interesting information on regioselective interactions of amino groups of antibiotics with phospholipids. The binding of aminoglycosides with negatively charged membranes is associated with impairment of phospholipid catabolism, change in membrane permeability, and membrane aggregation. Biochemical analysis and 1H NMR spectroscopy have brought information on the molecular mechanism involved in the impairment of phospholipid catabolism. Nephrotoxic aminoglycosides could induce sequestration of phosphatidylinositol and therefore reduce the amount of negative charge available for optimal lysosomal phospholipase activity toward phosphatidylcholine included in liposomes that also contain cholesterol and sphingomyelin. Conformational analysis shows that aminoglycosides, which have a high potency to inhibit lysosomal phospholipase activity, adopt an orientation parallel to the lipid/water interface. This orientation of the aminoglycoside molecule at the interface is also critical to explain the marked increase of membrane permeability induced by less nephrotoxic aminoglycosides such as isepamicin and amikacin. This effect is indeed only observed with aminoglycosides oriented perpendicular to this interface, probably related to the creation of a local condition of disorder. The impairment of phospholipid catabolism, which is considered to be an early and significant step in the development of aminoglycoside toxicity, is therefore not related to the change in membrane permeability. However, the role of this latter phenomenon and of membrane aggregation for aminoglycoside nephrotoxicity could be further investigated.

Ceftriaxone protects against tobramycin nephrotoxicity

The effect of ceftriaxone on tobramycin-induced nephrotoxicity was investigated. Female Sprague-Dawley rats were treated during 4 and 10 days with saline (NaCl, 0.9%), ceftriaxone at a dose of 100 mg/kg of body weight/12 h subcutaneously, tobramycin at doses of 40 and 60 mg/kg/12 h intraperitoneally, or the combination ceftriaxone-tobramycin. Creatinine levels in serum were significantly higher in animals treated with tobramycin alone given at 60 mg/kg/12 h during 10 days, compared with control animals (P < 0.01) or animals receiving the combination tobramycin-ceftriaxone (P < 0.01). After 10 days of treatment, ceftriaxone did not accumulate in renal tissue but did reduce the renal intracortical accumulation of tobramycin (P < 0.05). Tobramycin given alone at either 40 or 60 mg/kg/12 h induced a significant inhibition of sphingomyelinase activity compared with control animals (P < 0.05). However, this enzyme activity was significantly less inhibited when tobramycin was injected in combination with ceftriaxone (P < 0.05). Ceftriaxone alone had no effect on the activity of this enzyme. The [3H]thymidine incorporation into the DNA of renal cortex was also significantly lower in animals treated with tobramycin-ceftriaxone compared with animals receiving tobramycin alone (P < 0.05). The 24-h urinary excretion of beta-galactosidase was significantly reduced in animals treated with the combination tobramycin-ceftriaxone compared with the administration of tobramycin alone at 40 and 60 mg/kg/12 h after 5 and 10 days (P < 0.05). Histologically, ceftriazone induced very few cellular alterations and reduced considerably the presence of typical signs of tobramycin nephrotoxicity. This investigation demonstrated that ceftriaxone protects animals against tobramycin-induced nephrotoxicity.

Daptomycin may attenuate experimental tobramycin nephrotoxicity by electrostatic complexation to tobramycin

The lipopeptidic antibiotic daptomycin is reported to reduce experimental tobramycin nephrotoxicity (D. Beauchamp, M. Pellerin, P. Gourde, M. Pettigrew and M. G. Bergeron, Antimicrob. Agents Chemother. 34:139-147, 1990; C. A. Wood, H. C. Finkbeiner, S. J. Kohlhepp, P. W. Kohnen, and D. C. Gilbert, Antimicrob. Agents Chemother. 33:1280-1285, 1989). In an attempt to explain these results, the in vivo and in vitro interactions between daptomycin and tobramycin were studied. Tobramycin alone and preincubated with negatively charged phospholipid bilayers (liposomes) was dialyzed against increasing concentrations of daptomycin in buffer at pH 5.4. A significant drop in the concentration of tobramycin was observed when daptomycin was added to the opposite half cells. Furthermore, daptomycin induced a concentration-dependent release of lipid-bound tobramycin. Gold labeling experiments showed that daptomycin could be incorporated into phospholipid layers. Female Sprague-Dawley rats were treated with daptomycin alone, with tobramycin alone, or with the combination over 2 to 10 days. Levels of daptomycin and tobramycin in serum were similar in all groups. The levels of tobramycin in the renal cortex increased significantly with time and, on day 10, reached values of 654 +/- 122 and 844 +/- 298 micrograms/g of tissue (mean +/- standard deviation; not significant) in animals treated with tobramycin and the combination of daptomycin-tobramycin, respectively. No significant difference was observed in the levels of tobramycin in the kidneys between animals treated with tobramycin or the daptomycin-tobramycin combination at any time. By contrast, daptomycin levels were significantly higher in the renal cortexes of animals treated with daptomycin-tobramycin in comparison with those in the renal cortexes of animals treated with daptomycin alone on days 6,8, and 10 (P < 0.01). For immunogold labeling studies, animals were killed 4 h after a single injection of daptomycin alone or daptomycin in combination with tobramycin. Daptomycin was found throughout the matrixes of the lysosomes of proximal tubular cells of animals treated with daptomycin alone. In animals treated with the combination of daptomycin and tobramycin, daptomycin was associated with intralysosomal myeloid bodies. Our results suggest that daptomycin might attenuate experimental aminoglycoside nephrotoxicity by interacting with the aminoglycoside, perhaps electrostatically, and thereby protecting intracellular targets of toxicity.

Subcellular distribution of daptomycin given alone or with tobramycin in renal proximal tubular cells

Previous studies in experimental animals showed that daptomycin, a lipopeptide antibiotic, protects against aminoglycoside nephrotoxicity (C. A. Wood, H. C. Finkbeiner, S. J. Kohlhepp, P. W. Kohnen, and D. N. Gilbert, Antimicrob. Agents Chemother. 33:1280-1285, 1989; D. Beauchamp, M. Pellerin, P. Gourde, M. Pettigrew, and M. G. Bergeron, Antimicrob. Agents Chemother. 34:139-147, 1990). In order to better understand the mechanism involved in this protective effect, the subcellular distribution of daptomycin was investigated in the proximal tubular cells of animals treated with daptomycin alone or in combination with tobramycin. A first group of female Sprague-Dawley rats received a single intravenous injection of daptomycin at a dose of 100 mg/kg of body weight and were killed at 10 min, 1 h, or 24 h after the injection. Other groups of rats were treated during 10 days with saline (NaCl, 0.9%), tobramycin at dosages of 20 mg/kg/12 h, daptomycin at dosages of 10 mg/kg/12 h, or the combination tobramycin-daptomycin at the same dosages. At the time of sacrifice, the renal cortex of the right kidney of each animal was dissected, and small blocks of tissue were fixed, dehydrated, and embedded in Araldite 502 epoxy resin. The subcellular distribution of daptomycin and tobramycin was determined on ultrathin sections by immunogold labeling. Ten minutes after the injection of daptomycin alone, gold particles were seen over the brush border membrane and on the membranes of the endocytic vacuoles of proximal tubular cells. One hour after the injection, a similar distribution was seen and numerous gold particles were found over the lysosomes of proximal tubular cells. The results suggest that daptomycin might protect against aminoglycoside nephrotoxicity by interfering with the interaction between the aminoglycoside and phospholipids inside the lysosomes of proximal tubular cells.

Distribution of gentamicin to the cochlea of the chicken embryo

Aminoglycoside antibiotics are ototoxic in mammals and birds, including recently hatched chicks, but chicken embryos are insensitive to the ototoxicity of gentamicin, kanamycin, and streptomycin. To determine whether or not the insensitivity is due to a lack of antibiotic distribution to the avian cochlea, the distribution of gentamicin to the cochlea of the White Leghorn chicken embryo was compared to the distribution to the cochlea of the recently hatched White Leghorn chick. Fertile eggs were injected with a maximally tolerated dose of gentamicin sulfate (0.1 mg/egg/day) on incubation days 10-18, and the chicks were injected subcutaneously with either 5 mg (non-ototoxic) or 100 mg (ototoxic) gentamicin sulfate/kg body weight on days 1-9 after hatching. Gentamicin sulfate was histochemically detected within the basilar papilla (the avian equivalent of the organ of Corti) in all treated chicken embryos and chicks by 1 day after the first injection, and the staining was intense after 3 days of treatment. By ultrastructural immunocytochemistry, mild, diffuse labeling for gentamicin sulfate was detected within the endoplasmic reticulum of short and tall hair cells of chicken embryos by incubation day 17. Moderate labeling of gentamicin sulfate was detected in the infracuticular region of lysosomes of hair cells in chicks receiving 5 treatments of gentamicin sulfate at 5.0 mg/kg body weight and after 1 treatment of gentamicin sulfate at 100 mg/kg body weight.(ABSTRACT TRUNCATED AT 250 WORDS)

Accessibility of aminoglycosides, isolated and in interaction with phosphatidylinositol, to water. A conformational analysis using the concept of molecular hydrophobicity potential

The mode of interaction between aminoglycosides and negatively charged phospholipids plays a critical role in the inhibition of lysosomal phospholipases induced by these antibiotics and therefore in their nephrotoxicity. Previous works suggested that accessibility of the drug interacting with phospholipids to water could be crucial in this respect. We have used the concept of molecular hydrophobicity potential described by Brasseur [J Med Chem 266: 16120-16127, 1991] to visualize the hydrophobic and hydrophilic envelopes around aminoglycosides assembled with phosphatidylinositol molecules, and to obtain a three-dimensional representation of the complex formed. Using a series of different aminoglycosides, we showed that molecules with a lower inhibitory potential (gentamicin B, amikacin and isepamicin) are surrounded by both hydrophobic and hydrophilic envelopes whereas aminoglycosides which are more inhibitory are enveloped primarily by either hydrophilic (kanamycin A or B) or hydrophobic (gentamicin C1a) envelopes. This approach, which is here for the first time applied to the study of drug-lipid complexes, could help in the better understanding of the molecular mechanism of lysosomal phospholipase inhibition induced by aminoglycosides.

Subcellular localization of tobramycin and vancomycin given alone and in combination in proximal tubular cells, determined by immunogold labeling

The subcellular localization of tobramycin and vancomycin in the renal cortices of rats was determined with ultrathin sections by immunogold labeling. Four groups of four rats each were treated for 10 days with saline (NaCl, 0.9%), tobramycin at dosages of 20 mg/kg of body weight per 12 h intraperitoneally, vancomycin at dosages of 25 mg/kg/12 h subcutaneously, or the combination tobramycin-vancomycin. On day 11, the animals were killed, and cubes of renal cortex were fixed overnight in phosphate-buffered glutaraldehyde (0.5%), dehydrated in ethanol, and embedded in Araldite 502 resin. Ultrathin sections were made and incubated with sheep antitobramycin antibody followed by protein A-gold (15-nm diameter) complex or rabbit antivancomycin antibody followed by gold (30-nm diameter)-labeled goat anti-rabbit antibody. For the double labeling, incubations were made on opposite sides of the grid. Tobramycin was detected over the lysosomes of proximal tubular cells, but the labeling was concentrated into small areas in the matrix of the lysosomes. Vancomycin was seen over the lysosomes of proximal tubular cells and was distributed uniformly throughout the matrix of the lysosomes. In rats treated with tobramycin-vancomycin, both drugs were still detected in lysosomes of proximal tubular cells. It is concluded that tobramycin and vancomycin accumulate in lysosomes of proximal tubular cells throughout 10 days of treatment and that vancomycin has no effect on the subcellular distribution of tobramycin.

Tubular injury and regeneration in the rat kidney following acute exposure to gentamicin: a time-course study

Aminoglycoside antibiotics act as nephrotoxic drugs, inducing a lysosomal phospholipidosis and necrotic lesions essentially in convoluted proximal tubules. Previous studies have demonstrated that tubular injury caused by these compounds elicits a process of renal tissue repair (tubular regeneration) involving an increase of cell turnover in tubular epithelium. The present study was performed in order to: (i) achieve further insight into the temporal relationship between aminoglycoside-induced phospholipidosis, tubular necrosis, and tubular regeneration; and (ii) approach the control of tubular regeneration after nephrotoxin-induced insult. To investigate the latter point, we examined by immunocytochemistry the intrarenal distribution of epidermal growth factor (EGF) during tubular regeneration. Five groups of female Sprague-Dawley rats (n = 5) were treated for 4 days with gentamicin i.p. at a daily dose of 50 mg/kg delivered in 2 injections per day. Sham-treated animals (n = 5) received an equivalent amount of vehicle (0.9% NaCl) according to the same protocol. Groups of treated rats, and controls, were terminated 16 h (day 1), 4 days, 7 days, 14 days, and 21 days after the end of gentamicin administration. One hour prior to necropsy, each animal was given an i.p. injection of 40 mg 5-bromo-2'-deoxyuridine (BrdU) for the immunocytochemical demonstration of S-phase cells, using an anti-BrdU monoclonal antibody. Renal tissue was processed for light microscopy analysis, namely: a computer-aided morphometry of lysosomes in proximal tubular cells, a single-blind evaluation of gentamicin-induced tubular injury, the measurement of cell proliferation by immunocytochemical detection of BrdU-labeled nuclei, the demonstration of EGF-like immunoreactive material in renal tissue by using anti-rat EGF antiserum and immunogold-silver staining. As revealed by the morphometry of lysosomes in proximal tubular epithelium, the degree of gentamicin-induced phospholipidosis was maximum at day 1 (relative area occupied by lysosomes was increased 25-fold over mean control value) and declined thereafter. In contrast, tubular necrosis reached a peak 4 days after the end of drug administration. In proximal tubular epithelium, the stimulation of cell turnover associated with tubular regeneration showed a peak at day 7 (15-fold the mean control value). Tubular regeneration was also accompanied by mild interstitial hyperplasia. Three weeks after treatment with gentamicin, morphological evidence of drug-induced injury had disappeared due to the tissue repair process, except for the occasional presence of small hyperplastic foci in renal cortex interstitium. In both treated animals and controls, EGF immunoreactivity as revealed by immunocytochemical staining was associated with distal tubules (renal cortex and outer medulla).(ABSTRACT TRUNCATED AT 400 WORDS)

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.

Subcellular distribution of gentamicin in proximal tubular cells, determined by immunogold labeling

The subcellular distribution of gentamicin in rat renal proximal tubular cells was evaluated by immunogold labeling. The distribution of the drug was monitored from 10 min to 10 days following single (40 mg/kg of body weight) and multiple (5 and 20 mg/kg/12 h) injections of gentamicin. Animals were killed on day 11, and cubes of renal cortex tissue were fixed overnight in cold phosphate-buffered glutaraldehyde (0.5%), dehydrated in ethanol, and embedded in Araldite 502 epoxy resin. Ultrathin sections were made and incubated with sheep antigentamicin and then with protein A-gold (15 nm) complex. At 10 min after a single injection, the labeling was found over the brush border membrane and over the membranes of endocytic apical vesicles of proximal tubular cells. After 1 h, a similar distribution was observed and the labeling was also seen over small lysosomes located close to the brush border membrane. At 24 h, gold particles were found over large lysosomes of proximal tubular cells. Following 10 days of treatment, lysosomes of proximal tubular cells were densely labeled with gold particles. The labeling was distributed uniformly over the lysosomes, although a lower density of labeling was observed over the myeloid bodies inside the lysosomes. Necrotic proximal tubular cells showed labeling over intact lysosomes and also in the cytoplasms of the cells, in the mitochondria, and in the nucleoli. The various control experiments demonstrated the high specificity of these results. The present immunocytochemical study better documents the subcellular disposition of gentamicin in proximal tubular cells, as previously evaluated by subcellular fractionation and autoradiography. This technique will be useful for better understanding the relationship between drug disposition and drug-induced toxicity.

Effect of acidic phospholipids on the activity of lysosomal phospholipases and on their inhibition by aminoglycoside antibiotics--I. Biochemical analysis

Aminoglycoside antibiotics accumulate in lysosomes of kidney and cultured cells and cause an impairment of phospholipid catabolism which is considered to be an early and significant step in the development of their toxicity. Using liposomes, wer previously demonstrated that the activity of lysosomal phospholipases A1 and A2 towards phosphatidylcholine was markedly enhanced by the inclusion of phosphatidylinositol in the bilayer, and that gentamicin impaired this activity by binding to phosphatidylinositol. Since gentamicin-induced inhibition was inversely related to the amount of phosphatidylinositol included in the liposomes, we proposed that gentamicin impairs activity of phospholipases by decreasing the quantity of available negative charges carried by the bilayer surface (Mingeot-Leclercq et al., Biochem Pharmacol 37: 591-599, 1988). We now extend these observations to phosphatidylserine and phosphatidic acid, and compare the inhibition caused by gentamicin, amikacin and streptomycin towards lysosomal phospholipases on the hydrolysis of phosphatidylcholine in the presence of each of these acidic phospholipids. Inclusion of phosphatidic acid in liposomes, and, to a lesser extent, phosphatidylserine, caused a larger increase in phospholipases activity than phosphatidylinositol. In parallel, the three aminoglycosides tested were found less inhibitory towards phospholipases activity measured on phosphatidic acid-or phosphatidylserine-containing liposomes than was previously observed with phosphatidylinositol, even though equilibrium dialysis experiments failed to demonstrate significant difference in binding parameters of the drug towards each of these liposomes populations. Yet, as for phosphatidylinositol-containing liposomes, the inhibition was inversely related to the amount of phosphatidic acid or phosphatidylserine included in the bilayer and the inhibitory potency of the three drugs was consistently gentamicin greater than amikacin greater than streptomycin with the three types of negatively-charged liposomes used. We conclude that impairment of lysosomal phospholipases activity towards phosphatidylcholine included in negatively-charged membranes by aminoglycoside antibiotics is dependent upon drug binding to the bilayer, but that it is modulated by the nature of the acidic phospholipid that binds the drug as well as by that of the drug itself. A companion paper (Mingeot-Leclercq et al., Biochem Pharmacol 40: 499-506, 1990) will examine by computer-aided conformational analysis the parameters (drug-phospholipid energy of interaction, position of the drug in a monolayer and its accessibility to the aqueous phase) which may be important for these effects.

Increased levels of protein- and lipid-bound sialic acids in the renal cortex of rats injected with low doses of gentamicin

Administration of the aminoglycoside antibiotic, gentamicin, even at therapeutic doses, causes renal lysosomal phospholipidosis. We now report that protein- and lipid-bound sialic acid levels are increased significantly in a time-dependent fashion in the renal cortex of rats injected with gentamicin (10 mg/kg body wt. per day) for 4-10 days and a significant relationship could be observed between these two parameters. This elevation was not due to tissue regeneration, since it was not observed in cisplatin-treated animals.

Effects of daptomycin and vancomycin on tobramycin nephrotoxicity in rats

Daptomycin is a new biosynthetic antibiotic which belongs to a new class of drugs known as lipopeptides. The objective of this study was to evaluate the effects of daptomycin and vancomycin on tobramycin-induced nephrotoxicity. Female Sprague-Dawley rats were treated during 4 and 10 days with either saline (NaCl, 0.9%) or tobramycin at doses of 4 and 40 mg/kg per day (given every 12 h [q12h] intraperitoneally). Each treatment was combined with saline, daptomycin at a dose of 20 mg/kg per day (given q12h subcutaneously), and ancomycin at a dose of 50 mg/kg per day (given q12h subcutaneously). Daptomycin and vancomycin had no effect on the intracortical accumulation of tobramycin. Daptomycin did not accumulate in renal tissue even after 10 days of treatment. Tobramycin given at a dose of 40 mg/kg per day during 10 days induced a significant inhibition of sphingomyelinase activity in the renal cortex (P less than 0.01) and increased cellular regeneration (P less than 0.01), as measured by the incorporation of [3H]thymidine into DNA of the renal cortex. These changes were minimal when daptomycin was combined with tobramycin. Histologically, signs of tobramycin toxicity were also less severe in the presence of daptomycin. The intracortical accumulation of vancomycin was not modified by tobramycin. The sphingomyelinase activity was significantly more inhibited (P less than 0.01) when vancomycin was associated with tobramycin (4 and 40 mg/kg) without affecting the rate of [3H]thymidine incorporation into DNA. Histologically, signs of tobramycin toxicity were not affected by vancomuycin, but the cellular vacuolizations which were also observed in vancomycin-treated animals were still present in the proximal tubular cells of animals that were treated with the combination vancomycin-tobramycin. This study strongly suggests that daptomycin protects animals from tobramycin-induced nephrotoxicity but that vancomycin may enhance the effect of tobramycin. We conclude that daptomycin is safe and protects kidney cells from tobramycin-induced nephrotoxicity.

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.