Clinical and pathophysiologic aspects of aminoglycoside nephrotoxicity

[Therapeutics for acute tubular necrosis in 2020]

Acute kidney injury is a major cause of in-hospital morbidity and mortality because of the serious nature of the underlying illnesses and the high incidence of complications. The two major causes of acute kidney injury that occur in the hospital are prerenal disease and acute tubular necrosis. Acute tubular necrosis has a histological definition, even if a kidney biopsy is rarely performed. Kidney injuries occurring during acute tubular necrosis are underlined by different pathophysiological mechanisms that emphasize the role of hypoxia on the tubular cells such as apoptosis, cytoskeleton disruption, mitochondrial function and the inflammation mediated by innate immune cells. The microcirculation and the endothelial cells are also the targets of hypoxia-mediated impairment. Repair mechanisms are sometimes inadequate because of pro-fibrotic factors that will lead to chronic kidney disease. Despite all the potential therapeutic targets highlighted by the pathophysiological knowledge, further works remain necessary to find a way to prevent these injuries.

Nephroprotective effect of pigmented violacein isolated from Chromobacterium violaceum in wistar rats

The present study aimed to analyze the nephroprotective property of violacein obtained from the bacterium, Chromobacterium violaceum. The nephrotoxicity in the animal model was induced by gentamicin, potassium dichromate, mercuric chloride, and cadmium chloride-induced nephrotoxicity in the Wistar rats was analyzed by measuring the serum creatinine, uric acid, and urea level. The present investigation revealed the nephroprotective property on convoluted proximal tubule (S1 and S2 segments) and the straight proximal tubule (S3 segment). Also, violacein significantly improved the renal function by the renal protective property on S2 segment of proximal tubule from the nephrotoxicity stimulated by mercuric chloride, potassium dichromate, cadmium chloride and gentamicin in animal models. Animal model studies revealed that violacein at 20 and 40 mg/kg p.o improved the renal function and significantly reduced the increased amount of uric acid, creatinine, and blood urea compared to the control.

Genome-Scale Model-Based Identification of Metabolite Indicators for Early Detection of Kidney Toxicity

Identifying early indicators of toxicant-induced organ damage is critical to provide effective treatment. To discover such indicators and the underlying mechanisms of toxicity, we used gentamicin as an exemplar kidney toxicant and performed systematic perturbation studies in Sprague Dawley rats. We obtained high-throughput data 7 and 13 h after administration of a single dose of gentamicin (0.5 g/kg) and identified global changes in genes in the liver and kidneys, metabolites in the plasma and urine, and absolute fluxes in central carbon metabolism. We used these measured changes in genes in the liver and kidney as constraints to a rat multitissue genome-scale metabolic network model to investigate the mechanism of gentamicin-induced kidney toxicity and identify metabolites associated with changes in tissue gene expression. Our experimental analysis revealed that gentamicin-induced metabolic perturbations could be detected as early as 7 h postexposure. Our integrated systems-level analyses suggest that changes in kidney gene expression drive most of the significant metabolite alterations in the urine. The analyses thus allowed us to identify several significantly enriched injury-specific pathways in the kidney underlying gentamicin-induced toxicity, as well as metabolites in these pathways that could serve as potential early indicators of kidney damage.

Adverse Drug Reactions in the Intensive Care Unit

Adverse drug reactions (ADRs) are undesirable effects of medications used in normal doses [1]. ADRs can occur during treatment in an intensive care unit (ICU) or result in ICU admissions. A meta-analysis of 4139 studies suggests the incidence of ADRs among hospitalized patients is 17% [2]. Because of underreporting and misdiagnosis, the incidence of ADRs may be much higher and has been reported to be as high as 36% [3]. Critically ill patients are at especially high risk because of medical complexity, numerous high-alert medications, complex and often challenging drug dosing and medication regimens, and opportunity for error related to the distractions of the ICU environment [4]. Table 1 summarizes the ADRs included in this chapter.

Aminoglycosides: An Overview

Aminoglycosides are natural or semisynthetic antibiotics derived from actinomycetes. They were among the first antibiotics to be introduced for routine clinical use and several examples have been approved for use in humans. They found widespread use as first-line agents in the early days of antimicrobial chemotherapy, but were eventually replaced in the 1980s with cephalosporins, carbapenems, and fluoroquinolones. Aminoglycosides synergize with a variety of other antibacterial classes, which, in combination with the continued increase in the rise of multidrug-resistant bacteria and the potential to improve the safety and efficacy of the class through optimized dosing regimens, has led to a renewed interest in these broad-spectrum and rapidly bactericidal antibacterials.

Adverse effects of drugs on the kidney

The number of drugs presently marketed is countless, their prescription is relentlessly growing, such that the likelihood of adverse effects is strikingly increasing. As many drugs are cleared by the body through kidney excretion, renal adverse events are likely. In this review we shall concisely describe the pathophysiologic mechanisms of renal damage by drugs, the different clinical presentations outlining renal toxicity in the course of pharmacologic treatment, and the main offending agents.

The role of medications and their management in acute kidney injury

Prior to 2002, the incidence of acute renal failure (ARF) varied as there was no standard definition. To better understand its incidence and etiology and to develop treatment and prevention strategies, while moving research forward, the Acute Dialysis Quality Initiative workgroup developed the RIFLE (risk, injury, failure, loss, end-stage kidney disease) classification. After continued data suggesting that even small increases in serum creatinine lead to worse outcomes, the Acute Kidney Injury Network (AKIN) modified the RIFLE criteria and used the term acute kidney injury (AKI) instead of ARF. These classification and staging systems provide the clinician and researcher a starting point for refining the understanding and treatment of AKI. An important initial step in evaluating AKI is determining the likely location of injury, generally classified as prerenal, renal, or postrenal. There is no single biomarker or test that definitively defines the mechanism of the injury. Identifying the insult(s) requires a thorough assessment of the patient and their medical and medication histories. Prerenal injuries arise primarily due to renal hypoperfusion. This may be the result of systemic or focal conditions or secondary to the effects of drugs such as nonsteroidal anti-inflammatory drugs, calcineurin inhibitors (CIs), and modulators of the renin-angiotensin-aldosterone system. Renal, or intrinsic, injury is an overarching term that represents complex conditions leading to considerable damage to a component of the intrinsic renal system (renal tubules, glomerulus, vascular structures, inter-stitium, or renal tubule obstruction). Acute tubular necrosis and acute interstitial nephritis are the more common types of intrinsic renal injury. Each type of injury has several drugs that are implicated as a possible cause, with antiinfectives being the most common. Postrenal injuries that result from obstruction block the flow of urine, leading to hydronephrosis and subsequent damage to the renal parenchyma. Drugs associated with tubular obstruction include acyclovir, methotrexate, and several antiretrovirals. Renal recovery from drug-induced AKI begins once the offending agent has been removed, if clinically possible, and is complete in most cases. It is uncommon that renal replacement therapy will be needed while recovery occurs. Pharmacists can play a pivotal role in identifying possible causes of drug-induced AKI and limit their toxic effect by identifying those most likely to cause or contribute to injury. Dose adjustment is critical during changes in renal function, and the pharmacist can ensure that optimal therapy is provided during this critical time.

Presence of tobramycin in blood and urine during selective decontamination of the digestive tract in critically ill patients, a prospective cohort study

INTRODUCTION

Tobramycin is one of the components used for selective decontamination of the digestive tract (SDD), applied to prevent colonization and subsequent infections in critically ill patients. Tobramycin is administered in the oropharynx and gastrointestinal tract and is normally not absorbed. However, critical illness may convey gut barrier failure. The aim of the study was to assess the prevalence and amount of tobramycin leakage from the gut into the blood, to quantify tobramycin excretion in urine, and to determine the association of tobramycin leakage with markers of circulation, kidney function and other organ failure.

METHODS

This was a prospective observational cohort study. The setting was the 20-bed closed format-mixed ICU of a teaching hospital. The study population was critically ill patients with an expected stay of more than two days, receiving SDD with tobramycin, polymyxin-E and amphotericin-B four times daily in the oropharynx and stomach. Tobramycin concentration was measured in serum (sensitive high performance liquid chromatography - mass spectrometry/mass spectrometry (HLPC-MS/MS) assay) and 24-hour urine (conventional immunoassay), in 34 patients, 24 hours after ICU admission, and in 71 patients, once daily for 7 days. Tobramycin leakage was defined as tobramycin detected in serum at least once (> 0.05 mg/L). Ototoxicity was not monitored.

RESULTS

Of the 100 patients with available blood samples, 83 had tobramycin leakage. Median highest serum concentration for each patient was 0.12 mg/L; 99% of the patients had at least one positive urinary sample (> 0.5 mg/L), 49% had a urinary concentration ≥ 1 mg/L. The highest tobramycin serum concentration was significantly associated with vasopressor support, renal and hepatic dysfunction, and C-reactive protein. At binary logistic regression analysis, high dopamine dose and low urinary output on Day 1 were the significant predictors of tobramycin leakage. Nephrotoxicity could not be shown.

CONCLUSIONS

The majority of acute critically ill patients treated with enteral tobramycin as a component of SDD had traces of tobramycin in the blood, especially those with severe shock, inflammation and subsequent acute kidney injury, suggesting loss of gut barrier and decreased renal removal. Unexpectedly, urinary tobramycin was above the therapeutic trough level in half of the patients. Nephrotoxicity could not be demonstrated.

Evaluation of efficacy of vitamin E and N-acetyl cysteine in gentamicin-induced nephrotoxicity in rats

Gentamicin (GM), an aminoglycoside, is widely employed in clinical practice for the treatment of serious gram-negative infections. The clinical utility of GM is limited by the frequent incidence of acute renal failure. This study was designed to investigate treatment and posttreatment renoprotective potential of vitamin E and N-acetyl cysteine (NAC) against GM-induced oxidative stress and renal dysfunction. Male Sprague-Dawley rats were divided into six groups: first group is the control group that received olive oil (0.1 mL/100 g B.W.), second is the one that was treated with GM (80 mg/kg/i.p./8 days), third is the one that was treated with GM (80 mg/kg/i.p./8 days) and vitamin E (50 mg/kg/i.p./8 days), fourth is the one that was treated with GM (80 mg/kg/i.p./8 days) and NAC (50 mg/kg/i.p./8 days), fifth is the one that was treated with GM (80 mg/kg/i.p./8 days), vitamin E (50 mg/kg/i.p./8 days), and NAC (50 mg/kg/i.p./8 days), and sixth is the one that was treated with GM initially for 8 days (at 80 mg/kg/i.p.) after which vitamin E (at 50 mg/kg/i.p.) and NAC (at 50 mg/kg/i.p.) were administered for 8 days. Serum creatinine, blood urea nitrogen, serum glucose, renal malondialdehyde, renal reduced glutathione, urine sodium, fractional excretion of sodium, and histopathological examination of kidney were performed after treatment. Gentamicin treatment caused nephrotoxicity as evidenced by marked elevation in serum creatinine, blood urea nitrogen, renal malondialdehyde, urine sodium, and fractional excretion of sodium. Study of renal morphology showed marked loss of epithelium in proximal convoluted tubule, inflammatory infiltrate in the form of lymphocytes, mainly in interstitium. Treatment and posttreatment with vitamin E and NAC significantly restored renal functions, reduced lipid peroxidation, enhanced reduced glutathione level, and restored the biochemical parameters. The results of this study demonstrate the therapeutic potential of vitamin E and NAC in gentamicin-induced nephrotoxicity.

Urinary Guanidinoacetic Acid Excretion as an Indicator of Gentamicin Nephrotoxicity in Rats

The kidney is the main site of guanidinoacetic acid synthesis and excretion. The aim of this study was to examine whether urinary guanidinoacetic acid is a sensitive indicator for diagnosis of early-stage gentamicin nephrotoxicity. Early-stage renal injury was induced in rats by a single intravenous injection of 5, 10, or 30 mg/kg body weight gentamicin. Twenty-four hours after injection all rats were killed. Blood, urine and tissue guanidino compound concentrations were determined by high performance liquid chromatography. Glycine amidinotransferase activity in tissues was assayed according to the method of Pilsum. Urinary guanidinoacetic acid excretion was decreased in 5 mg/kg gentamicin-treated rats in comparison to that in control rats, whereas urine N-acetyl-beta-D-glucosaminidase activity and beta2-microglobulin were unchanged. Guanidinoacetic acid concentration and glycine amidinotransferase activity in the kidney were significantly decreased in 5, 10, and 30 mg/kg gentamicin-treated rats; the decreases were dose-dependent. These results suggest that the urine guanidinoacetic acid concentration is a more sensitive indicator of renal injury than conventional indicators such as urine N-acetyl-beta-D-glucosaminidase and beta2-microglobulin.

The epidemiology of drug-induced disorders: the kidney

The epidemiology of drug-induced renal disorders is a complex topic. Drug-associated nephrotoxicity accounts for 18 - 27% of all acute kidney injury cases in US hospitals. Medications can affect all aspects of the kidney, and drugs that are associated with renal dysfunction are used commonly in clinical practice. The article reviews six major mechanisms of drug-induced renal dysfunction as well as lists the major medications involved. NSAIDs, aminoglycosides, amphotericin B and calcineurin inhibitors are just some examples of drugs that contribute to renal dysfunction. The medical community must be aware of patient risk factors for nephrotoxicity, as well as the drug's inherent nephrotoxic potential, when prescribing and administering medications.

An evaluation of amikacin nephrotoxicity in the hematology/oncology population

Amikacin is an aminoglycoside commonly used to provide empirical double gram-negative treatment for febrile neutropenia and other suspected infections. Strategies of extended-interval and conventional dosing have been utilized extensively in the general medical population; however, data are lacking to support a dosing strategy in the hematology/oncology population. To evaluate amikacin-associated nephrotoxicity in an adult hematology/oncology population, a prospective, randomized, open-label trial was conducted at a university-affiliated medical center. Forty patients with a diagnosis consistent with a hematologic/oncologic disorder that required treatment with an aminoglycoside were randomized to either conventional or extended-interval amikacin. The occurrence of nephrotoxicity by means of an increase in serum creatinine and evaluation of efficacy via amikacin serum concentrations with respective pathogens were assessed. The occurrence of nephrotoxicity was similar between the conventional and extended-interval groups, at 10% and 5%, respectively (P = 1.00). Six patients in the conventional group had a positive culture, compared with none in the extended-interval group (P = 0.002). The occurrence of nephrotoxicity was similar between the two dosing regimens, but the distribution of risk factors was variable between the two groups. Efficacy could not be assessed.

Effect of Rheum emodi (Revand Hindi) on renal functions in rats

The renal effects of water-soluble (W-S) and water-insoluble (W-INS) portions of the alcoholic extract of Revand Hindi (Rheum emodi) were investigated on cadmium chloride, mercuric chloride, potassium dichromate and gentamicin-induced nephrotoxicity in rats and normal rats by monitoring the levels of urea nitrogen and creatinine in serum. The present investigations provide evidences that W-S fraction has nephroprotective effect on all the proximal tubule segments (S1, S2 and S3) possibly through antioxidant action of the tannins present in the fraction. W-INS also improved the renal function by protecting S2 segment of proximal tubule nephrotoxicity induced by metals viz cadmium chloride and mercuric chloride in rat models, however, this fraction has been found to enhance gentamicin nephrotoxicity.

Molecular Aspects of Renal Handling of Aminoglycosides and Strategies for Preventing the Nephrotoxicity

Aminoglycosides such as gentamicin and amikacin are the most commonly used antibiotics worldwide in the treatment of Gram-negative bacterial infections. However, serious complications like nephrotoxicity and ototoxicity are dose-limiting factors in the use of aminoglycosides. A relatively large amount of the intravenously administered dose is accumulated in the kidney (about 10% of dose), whereas little distribution of aminoglycosides to other tissues is observed. Aminoglycosides are taken up in the epithelial cells of the renal proximal tubules and stay there for a long time, resulting in nephrotoxicity. Acidic phospholipids are considered as a binding site for aminoglycosides in the brush-border membrane of the proximal tubular cells. More recently, it has been reported that megalin, a giant endocytic receptor abundantly expressed at the apical membrane of renal proximal tubules, plays an important role in binding and endocytosis of aminoglycosides in the proximal tubular cells. The elucidation of the aminoglycoside-binding receptor would help design a strategy to prevent against aminoglycoside-induced nephrotoxicity. In this review, we summarize recent advances in the understandings of the molecular mechanisms responsible for renal accumulation of aminoglycosides, especially megalin-mediated endocytosis. In addition, approaches toward prevention of aminoglycoside-induced nephrotoxicity are discussed, based on the molecular mechanisms of the renal accumulation of aminoglycosides.

A role for superoxide in gentamicin-mediated nephropathy in rats

Gentamicin is an antibiotic effective against Gram-negative infection, whose clinical use is limited by its nephrotoxicity. Oxygen free radicals are considered to be important mediators of gentamicin-mediated nephrotoxicity, but the exact nature of the radical in question is not known with certainty. We have investigated the potential role of superoxide in gentamicin-induced renal toxicity by using M40403, a low molecular weight synthetic manganese containing superoxide dismutase mimetic, which selectively removes superoxide. Administration of gentamicin at 100 mg/kg, s.c. for 5 days to rats induced a marked renal failure, characterised by a significant decrease in creatinine clearance and increased plasma creatinine levels, fractional excretion of sodium, lithium, urine gamma glutamyl transferase (gamma GT) and daily urine volume. A significant increase in kidney myeloperoxidase activity and lipid peroxidation was also observed in gentamicin-treated rats. M40403 (10 mg/kg, i.p. for 5 days) attenuated all these parameters of damage. Immunohistochemical localisation demonstrated nitrotyrosine formation and poly(ADP-ribose) synthetase (PARS) activation in the proximal tubule of gentamicin-treated rats. Renal histology examination confirmed tubular necrosis. M40403 significantly prevented gentamicin-induced nitrotyrosine formation, poly(ADP-ribose) synthetase activation and tubular necrosis. These results confirm our hypothesis that superoxide anions play an important role in gentamicin-mediated nephropathy and support the possible clinical use of low molecular weight synthetic superoxide dismutase mimetics in those conditions that are associated with over production of superoxide.

Melatonin protects against gentamicin-induced nephrotoxicity in rats

Acute renal failure is a major complication of gentamicin (GEN), which is widely used in the treatment of gram-negative infections. A large body of in vitro and in vivo evidence indicates that reactive oxygen metabolites (or free radicals) are important mediators of gentamicin nephrotoxicity. In this study we investigated the role of free radicals in gentamicin-induced nephrotoxicity and whether melatonin, a potent antioxidant could prevent it. For this purpose female Sprague-Dawley rats were given intraperitoneally either gentamicin sulphate (40 mg/kg), melatonin (10 mg/kg), gentamicin plus melatonin or vehicle (control) twice daily for 14 days. The rats were decapitated on the 15th day and kidneys were removed. Blood urea nitrogen (BUN) and creatinine levels were measured in the blood and malondialdehyde (MDA) and glutathione (GSH) levels, protein oxidation (PO) and myeloperoxidase (MPO) activity were determined in the renal tissue. Gentamicin was observed to cause a severe nephrotoxicity which was evidenced by an elevation of BUN and creatinine levels. The significant decrease in GSH and increases in MDA levels, PO and MPO activity indicated that GEN-induced tissue injury was mediated through oxidative reactions. On the other hand simultaneous melatonin administration protected kidney tissue against the oxidative damage and the nephrotoxic effect caused by GEN treatment.

Effect of N-acetylcysteine on gentamicin-mediated nephropathy in rats

Studies were performed on the mechanisms of the protective effects of free-radical scavengers against gentamicin-mediated nephropathy. Administration of gentamicin, 100 mg/kg s.c., for 5 days to rats induced marked renal failure, characterised by a significantly decreased creatinine clearance and increased blood creatinine levels, fractional excretion of sodium Na(+), lithium Li(+), urine gamma glutamyl transferase and daily urine volume. A significant increase in kidney myeloperoxidase activity and lipid peroxidation was observed in gentamicin-treated rats. Immunohistochemical localisation demonstrated nitrotyrosine formation and poly(ADP-ribose)synthase activation in the proximal tubule from gentamicin-treated rats. Renal histology examination confirmed the tubular necrosis. N-acetylcysteine (10 mg/kg i.p. for 5 days) caused normalisation of the above biochemical parameters. In addition, N-acetylcysteine treatment significantly prevents the gentamicin-induced tubular necrosis. These results suggest that (1) N-acetylcysteine has protective effects on gentamicin-mediated nephropathy, and (2) the mechanisms of the protective effects can be, at least in part, related to interference with peroxynitrite-related pathways.

Malignancy and renal disease

A variety of renal diseases and electrolyte disorders may be associated with various malignancies or with treatment of malignancy with chemotherapeutic drugs or radiation. This article reviews renal disease in cancer patients, which constitutes a major source of morbidity and mortality.

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.

Differential toxic effects of gentamicin on cultured renal epithelial cells (LLC-PK1) on application to the brush border membrane or the basolateral membrane

Aminoglycoside antibiotics are generally accepted to accumulate in renal proximal tubule cells from the luminal surface and show toxic effects on the cells. The binding affinity and membrane permeability of aminoglycoside antibiotics are different at the brush border membrane (BBM) and the basolateral membrane (BLM) of proximal tubule cells. This study was performed, therefore, to investigate the differential effects of the aminoglycoside antibiotic gentamicin (GM) on cultured LLC-PK1 cells, a pig kidney proximal epithelial cell line, after addition to the BBM or the BLM side. LLC-PK1 cells were cultured on microporous membranes until forming confluent monolayers, and then GM was added to either the BBM or the BLM side. GM caused release of enzymes from the organelles, with a higher level of release observed following addition to the BBM side than that to the BLM side. Patterns of [3H]GM uptake by the cells differed in a manner dependent on whether it was added to the BBM or the BLM side. That is, the cellular uptake from the BBM side increased with incubation time, while that from the BLM side showed rapid saturation. These results suggested that aminoglycoside antibiotics show differential effects on cultured proximal epithelial cells and have differential patterns of cellular uptake when added to the BBM or the BLM side.

Renal pharmacology

Pharmacologic treatment of diseases of the urinary tract of horses is limited to administration of antibiotics for treatment of urinary tract infections (UTIs), administration of drugs that alter urine pH, administration of drugs that alter bladder smooth muscle function or urethral sphincter tone, and treatment of acute renal failure. The indications, mechanisms of action, pharmacokinetic characteristics, and adverse effects of these agents in each of these groups are discussed in this article. The use of the agents is discussed within the context of the pathophysiology of the disease being treated.

Endocytosis of gentamicin in a proximal tubular renal cell line

The mechanisms by which aminoglycosides are accumulated in renal proximal tubular cells remain unclear. Adsorptive mediated endocytosis, via a common pathway for cationic proteins, or receptor endocytosis, mediated by the glycoprotein 330/megalin, have been proposed to be involved in gentamicin transport in renal cells. We used the LLC-PK1 cell line, derived from the pig proximal tubule, to explore further the regulation of gentamicin endocytosis in these cells and to determine the role of clathrin mediated endocytosis and G proteins in this function. Gentamicin endocytosis was strictly temperature dependent, whereas total uptake (endocytosis plus binding) did not significantly differ at 4 or 37 degrees C. Substances that suppress receptor mediated, clathrin dependent endocytosis, such as monensin, phenylarsine oxide and dansylcadaverine, or inhibit caveolae mediated endocytosis, such as nystatin, did not affect gentamicin entrance in LLC-PK1 cells. Among substances that disrupt the actin cytoskeleton, only cytochalasin D, that is active also on fluid phase endocytosis, significantly reduced the intracellular concentrations of the aminoglycoside. Other maneuvers that perturb clathrin dependent endocytosis without affecting clathrin independent pathway, such as acidification of cytosol or incubation in hypertonic medium, were also without effect. Mastoparan, a well known stimulator of heterotrimeric G proteins, strongly increased endocytosis of gentamicin, and the same effect was evident with two other G protein stimulators, aluminum fluoride and fluoride alone; however the effect seems not to be mediated by an activation of adenylyl cyclase. In conclusion, gentamicin endocytosis in LLC-PK1 cells is probably clathrin independent, limited by cytochalasin D, which interacts with cytoskeleton, and increased by substances like mastoparan and aluminum fluoride, which activate heterotrimeric G proteins.

Does vancomycine increase aminoglycoside nephrotoxicity?

Vancomycine and amikacin combined is an effective antibiotic combination used in the treatment of serious Gram-positive bacteremia in childhood. However, both drugs may have a potential nephrotoxic effect when used individually. The present study investigates whether the nephrotoxicity of these drugs that display a nephrotoxic effect when used separately increases when used in a combined manner. Ten 2-month-old rats were subjected to intraperitoneal injections of vancomycine (100 mg/kg) and amikacin (80 mg/kg) and ten other 2-month-old rats were administered amikacin (80 mg/kg) for a period of 15 days. The control group of animals consisting of five 2-month old rats were untreated. The renal tissues obtained by laparotomy were processed for both light and electron microscopy. Paraffin sections and ultrathin sections were evaluated in order to determine the renal structure of the control and the experimental groups. In addition, serum creatinine and blood, urea and nitrogen (BUN) levels were measured in blood samples obtained from the rats. In the amikacin and combined amikacin-vancomycine treatment groups, renal morphological changes were observed at the glomerular and tubular levels when compared to the control group, and the serum creatinine and BUN levels were also higher in these groups. Although both experimental groups were different from the control group, they had similar morphological and biochemical features. It was concluded that vancomycine did not influence the nephrotoxic effect of amikacin and both drugs could be used in a combined manner.

Drug-induced nephrotoxicity

Drug-induced renal dysfunction is not an uncommon event, which can cause significant morbidity and can be easily overlooked. Many medications can lead to renal dysfunction through various mechanisms. The most common medications or classes of medications along with their clinical presentations are discussed in this article. As can be noted, many drugs can cause nephropathy in more than one way. Because it is difficult to discuss nephrotoxicities of every reported medication, Tables 1, 2, and 3 are provided; although these tables are by no means comprehensive, they may serve as further reference. This article is intended to provide a broad overview of the spectrum of presentation associated with drug-induced nephrotoxicity to guide the clinician to familiarity with this entity.

Aminoglycoside prescription, therapeutic monitoring and nephrotoxicity at a university hospital in Saudi Arabia

We studied the use of aminoglycosides at King Abdulaziz University Hospital (KAUH), Jeddah, Saudi Arabia, including prescriptions, dosage, serum levels, toxic factors and treatment outcome. Two hundred and fifty-six patients on aminoglycosides were involved in the study period November-December 1994: 24 (9.4%) patients were on amikacin and 232 (90.6%) patients were on gentamicin. The serum concentration was below the therapeutic range in 75% of the patients on amikacin and 50% on gentamicin. Serum concentrations within the therapeutic range (> 20 micrograms/ml; < 35 micrograms/ml for amikacin, and > 6 micrograms/ml and < 10 micrograms/ml for gentamicin) were achieved in 4% and 44% of patients respectively. The dosage was adjusted during therapy for 57% of the patients because of low levels, and for 43% of the patients because of toxic levels. More than 30% of the patients had their serum monitored for the first time 3 days after starting aminoglycoside therapy. Aminoglycosides were discontinued before the end of the course in 157 (62%) patients because 24% of them had developed toxic levels and 24% had not responded to the treatment. Successful outcome was achieved in 170 (66%) of the patients, however, 50% of them had inappropriate serum levels. The risk factors that are significantly associated with aminoglycoside nephrotoxicity were duration of therapy (P = 0.008), renal, liver diseases and ampicillin given concurrently with the aminoglycosides (P = < 0.05).

Interactions of drugs with the developing kidney

Interactions between drugs and the kidney are necessary for renal drug elimination, metabolism, and occasionally for therapeutic effect. These interactions may result also in renal toxicity. Understanding the kidney's role in drug-handling helps the clinician to be aware of potential drug interactions and toxicity. Drug disposition, elimination, and toxicity may differ with development and are to be considered when prescribing drugs for children. Nephrotoxicity associated with drugs, although common, is usually reversible with discontinuation of the drug; however, when drug therapy with a well-known nephrotoxic drug (e.g., cisplatin) is necessary, pharmacologic modulators may play a role in limiting the associated nephrotoxicity.

Guanidinoacetic acid (GAA) synthesis in rat tubular suspension as a system for evaluating gentamicin (GM) nephrotoxicity

Since guanidinoacetic acid (GAA), a precursor of creatine, is synthesized mainly in the proximal tubule of the kidney where gentamicin (GM) nephrotoxicity often occurs, GM-induced renal cell damage was investigated using GAA synthesis in tubular suspension as an indicator. Results obtained were as follows: (1) GAA synthesis was significantly suppressed with 1 mM GM; (2) GM-induced decrease in GAA synthesis was recognized during incubation longer than 15 min; (3) furosemide significantly enhanced the suppression of GAA synthesis by GM. The results obtained parallel with those in the whole animal thus making GAA synthesis in tubular suspension a valid system for evaluating the GM-induced proximal tubular damage.

Renal dysplasia associated with in utero exposure to gentamicin and corticosteroids

We report on a patient with renal cystic dysplasia, whose mother was given gentamicin and corticosteroids early in pregnancy. We speculate that these drugs may be implicated in abnormal nephrogenesis in humans. This speculation is based on gentamicin-induced small kidneys (oligonephronia) in the rat. Renal cystic disease has been demonstrated following glucocorticoid administration early in gestation. We realize that there is no proof for a casual relationship between gentamicin and/or glucocorticoids in the pathogenesis of this patient's renal disease. However, it is possible that renal cystic dysplasia in humans is not solely the result of a genetic defect.

Antioxidants attenuate endotoxin-gentamicin induced acute renal failure in rats

The synergistic mechanism by which endotoxin enhances the nephrotoxic potential of gentamicin is unknown. In this study, we attempted to shed light on this mechanism by injecting rats with endotoxin plus gentamicin. Renal injury was assessed by measuring creatinine, inulin and PAH clearance, NADH levels and electrolyte reabsorption, for 24 hr following this injection. Gentamicin alone (20 mg/100 g) induced no renal injury, while endotoxin without gentamicin (0.075 mg/100 g) induced mild injury. However, endotoxin plus gentamicin resulted in acute renal failure. In an attempt to halt the progressive renal dysfunction, the antioxidants NAO (5 mg/100 g), Vitamin E (0.2 mg/100 g per day) and dimethylthiourea (DMTU-50 mg/100 g) were administered, or early endotoxin tolerance was induced before injecting the rats with endotoxin plus gentamicin. The reduction in renal function was markedly slower in rats administered with antioxidants compared with untreated rats. Similar results were obtained with endotoxin tolerance. These data suggest that NAO, vitamin E, DMTU and endotoxin tolerance are potentially beneficial in arresting progressive renal damage associated with endotoxin plus gentamicin.

Influence of intraperitoneal gentamicin on peritoneal transport in IPD patients

We have investigated the effect of intraperitoneal gentamicin on dialysis efficiency in 10 intermittent peritoneal dialysis (IPD) patients. The following parameters were measured: net ultrafiltration (UF); concentration ratios (D/P) of urea, creatinine, potassium; peritoneal clearances (ml/min) of urea, creatinine, potassium; mass transfer of sodium (MTNa); sodium sieving index (SCNa). It has been found that gentamicin significantly decreased D/P urea (p < 0.056) and D/P creatinine (p < 0.05). We found also a significant decrease of mean clearances of urea (p < 0.05) and creatinine (p < 0.05). The mean clearance of potassium did not significantly change. There was no significant change in UF, MTNa and SCNa. Our preliminary data suggest that gentamicin decreases the permeability of the peritoneum for certain low molecules in IPD patients, which may have a negative impact on dialysis efficiency.

Apically and basolaterally internalized aminoglycosides colocalize in LLC-PK1 lysosomes and alter cell function

Aminoglycosides bind to apical and basolateral (BL) membranes of renal epithelial cells. However, little is known regarding differential uptake and intracellular processing after internalization across these distinct surface membrane domains. To examine these processes independently, LLC-PK1 cells were grown on porous filters, which allow selective access to both domains. Apical and BL membrane uptakes of gentamicin (0.5 mM), quantified using [3H]gentamicin, were linear from 2 to 24 h (r = 0.99). The 4-h apical gentamicin uptake was 667 +/- 59 pmol/mg protein, the BL 748 +/- 26 pmol/mg protein, and concurrent apical and BL uptake 1,389 +/- 22 pmol/mg protein. Aminoglycoside uptake, documented using indirect immunogold techniques, occurred via the apical and BL endocytic systems and colocalized with cationic ferritin. Aminoglycosides internalized via the apical (gentamicin) and BL (tobramycin) membrane converged at the lysosomal level. Gentamicin incorporated via either domain significantly decreased lysosomal N-acetylglucosaminidase below control values (P < 0.05). We conclude that, after binding, aminoglycosides are internalized equally across apical and BL membranes of LLC-PK1 cells via receptor-mediated endocytosis, colocalize within the lysosomal compartment, and alter cellular function similarly.

Aminoglycoside-induced Fanconi's syndrome

Nephrotoxicity manifested by renal insufficiency is a well-known consequence of aminoglycoside administration in hospitalized patients. We report two cases of aminoglycoside-induced nephrotoxicity as manifested by proximal tubular dysfunction (Fanconi's syndrome). In the two patients reported, the tubular dysfunction occurred at the extremes of renal function. In both patients, tubular function returned to normal when the antibiotic was discontinued. Because of the widespread use of these antibiotics in the critically ill patient, it may be prudent to recognize this disorder when managing fluids, electrolytes, and nutrition.

Time-dependent change in the toxic effects of amikacin on renal functions

The present study was undertaken to examine whether there was a time-dependent change in the toxic effects of amikacin, an aminoglycoside, on renal functions. Male Wistar rats were maintained under conditions of light from 7 am to 7 pm and dark from 7 pm to 7 am. Amikacin (1.2 g/kg) was injected intraperitoneally to animals at 4 am, 10 am, 4 pm or 10 pm. Glomerular function estimated by creatinine clearance (Clcr) and tubular function estimated by urinary excretion of a loop diuretic, furosemide, which was excreted in urine mainly by tubular secretion, were determined before and 24 hours after amikacin injection. The values of these parameters were reduced by amikacin at each observation point. The magnitude of these decrements was greatest at 4 pm both for Clcr and urinary furosemide excretion. These results suggest that the toxic effects of amikacin on renal glomerular and tubular functions vary with its time of administration.

Protective effects of cyclodextrin sulphates against gentamicin-induced nephrotoxicity in the rat

The effects of cyclodextrin sulphates on the development of rat renal dysfunction induced with gentamicin, an aminoglycoside antibiotic, were studied. Daily subcutaneous injection of gentamicin (100 mg kg-1, 14 days) developed nephrotoxicity in the rat as assessed by an increase in serum urea nitrogen and histopathological changes in the renal cortex. When cyclodextrin sulphates were given intraperitoneally at 300 mg kg-1 at 6 h intervals after gentamicin administration, they protected the rat against the drug-induced renal impairment, while the parent cyclodextrins were ineffective. Since post-administration of cyclodextrin sulphates did not reduce the total amount of gentamicin accumulated in the kidney, the protection may occur through interference with intracellular events leading from the drug accumulation to nephrotoxicity. These results suggest that cyclodextrin sulphates are particularly effective in preventing renal failure associated with aminoglycoside treatment.

Primary culture of rabbit proximal tubules as a cellular model to study nephrotoxicity of xenobiotics

The effects of gentamicin treatment on functions of the plasma membrane-bound proteins in situ were investigated in primary culture of rabbit proximal tubular cells (PTC), a recognized model of renal epithelial cells. Activities of apical and basolateral enzymes, activities of phosphate, glucose and alanine sodium-coupled transport systems and leakage of the cytosolic enzyme lactate dehydrogenase (LDH) were determined in PTC grown in glucose-free culture medium as confluent monolayers and incubated with the aminoglycoside. Gentamicin altered in a concentration- and time-dependent manner the activity of dipeptidyl peptidase IV (DPP IV), neutral aminopeptidase (NAP), Na+K(+)-ATPase and the Vmax of sodium-dependent glucose and phosphate uptake, whereas gamma-glutamyl-transpeptidase (GGT) and sodium-dependent alanine uptake were unaffected. Identical concentration of gentamicin was required to induce LDH leakage and cell functions impairment. In contrast, under short time exposure, a condition where the enzyme activities were untouched, mercuric chloride inhibited to a similar extent the activity of the three sodium-coupled transport systems. These data suggest that whereas alterations in membrane fluidity might mediate the effects of gentamicin on membrane functions, the inhibition of transports by mercuric chloride rather reflects an effect on sodium permeability of the apical membrane. They also suggest that study of Na(+)-coupled transports in proximal tubular cells grown in primary culture is a simple and sensitive in vitro model to assess drug-induced nephrotoxicity.

Potassium and anaesthesia

Potassium is the principle intracellular ion, and its concentration and gradients greatly influence the electrical activity of excitable membranes. Because anaesthesia is so intimately involved with electrically active cells, potassium concentrations in surgical patients have received considerable attention in diagnostic and therapeutic applications. With the ongoing evolution in the indications for potassium, it is important to review the role of potassium in cellular activity, in storage and regulation, in diseases that alter potassium homeostasis, and in the therapeutic implications of perioperative alterations of potassium concentration. A rational approach to abnormal potassium values and the use of potassium in the operating room is sought, based on a physiological understanding of risks and benefits.

Aminoglycoside dosing considerations in intensive care unit patients

OBJECTIVE

Factors affecting aminoglycoside dosing requirements in critically ill adult patients were reviewed.

DATA SOURCES

A literature search was performed from 1979 to 1992 and articles pertaining to aminoglycoside dosing were obtained.

STUDY SELECTION

Only studies appearing in peer-reviewed journals were selected. Topics selected included: bactericidal kill kinetics, once-daily dosing regimens, critical illness, toxicity, aminoglycosides, intensive care unit, and lung penetration.

CONCLUSIONS

Studies suggest that larger initial aminoglycoside doses are necessary in critically ill patients (tobramycin/gentamicin 3 mg/kg or amikacin 9 mg/kg) to achieve adequate peak serum concentrations. Current studies have not shown an increase in the incidence of aminoglycoside toxicity when using these larger initial doses. Follow-up monitoring is dependent upon the patient's physiology and risk factors for aminoglycoside-induced toxicity.

Protection by antibiotics against myeloperoxidase-dependent cytotoxicity to lung epithelial cells in vitro

Myeloperoxidase, in the presence of noncytotoxic concentrations of H2O2, was used to induce cytotoxicity to the lung epithelial cell line, AKD. When the cationic aminoglycosides, tobramycin and gentamicin were added to the cells in the presence of myeloperoxidase and H2O2, cytotoxicity was completely inhibited. In addition, tobramycin prevented cytotoxicity induced by cystic fibrosis sputum and H2O2. Protection against myeloperoxidase and H2O2 was also observed with the thioether-containing antibiotics, ticarcillin and ceftazidime, but at higher concentrations than with the aminoglycosides. Analysis of spectral properties, dimethylsulfoxide-mediated reduction, and ethyl acetate/NaCl partitioning, demonstrated that aminoglycosides converted HOCl to hydrophilic noncytotoxic chloramines, but were unable to prevent the oxidation of sulfhydryls and methionine by HOCl. In contrast, ticarcillin and ceftazidime were highly effective inhibitors of HOCl-mediated sulfhydryl and methionine oxidation. These results suggest that aminoglycosides protect lung epithelial cells against myeloperoxidase-dependent oxidant injury by binding to anionic cell surfaces and converting HOCl to hydrophilic noncytotoxic chloramines, whereas penicillins and cephalosporins are potent HOCl scavengers capable of protecting critical extracellular molecules against oxidation.

Calcium supplementation and thyroid hormone protect against gentamicin-induced inhibition of proximal tubular Na+,K(+)-ATPase activity and other renal functional changes

Gentamicin can cause proximal tubule necrosis. We have shown that inhibition of PT Na+,K(+)-ATPase activity is rapidly induced by gentamicin. We have now investigated whether manipulations known to attenuate the negative effects of gentamicin on renal excretory capacity, i.e. high calcium intake and L-thyroxine treatment, will also attenuate gentamicin-induced inhibition of Na+,K(+)-ATPase activity and ameliorated signs of proximal tubule damage. Rats were gentamicin- or vehicle-treated for 7 days. Sub-groups were given 4% calcium (Ca) supplements or L-thyroxine 20 micrograms 100 g-1 body weight daily. Gentamicin significantly reduced the glomerular filtration rate and increased the urinary excretion of the proximal tubule lysosomal enzyme, N-acetyl-beta-D-glucosaminidase. Gentamicin significantly reduced proximal tubule Na+,K(+)-ATPase activity, measured in single permeabilized proximal tubule segments. Sodium excretion was inversely correlated to proximal tubule Na+,K(+)-ATPase activity. Both calcium and L-thyroxine alleviated all gentamicin-induced side-effects on renal function as well as on proximal tubule Na+,K(+)-ATPase activity. Calcium and L-thyroxine had no significant effect on renal function. L-thyroxine, but not calcium, increased proximal tubule Na+,K(+)-ATPase activity in control rats. Renal cortical tissue gentamicin concentration was not influenced by calcium but was significantly lowered by L-thyroxine. Two procedures which, via different mechanisms, afford protection from gentamicin-induced changes in renal function also give protection from gentamicin-induced inhibition of Na+,K(+)-ATPase activity. This suggests that loss of integrity of the Na+,K(+)-ATPase enzyme contributes to gentamicin-induced nephrotoxicity.

Streptomycin toxicity in primary cultures of flounder renal proximal tubule cells

The aminoglycoside antibiotic streptomycin is a known nephrotoxin in vivo and a common component of cell culture media. The effects of streptomycin (100 micrograms/ml) on transepithelial electrical properties, glucose transport, glycolytic metabolism, and morphology were examined in primary proximal tubule cell cultures from winter flounder (Pseudopleuronectes americanus) kidney. Streptomycin treatment on either Days 2 to 12 or Days 8 to 13 abolished the transepithelial potential difference and short-circuit current across the monolayer but had no effect on transepithelial resistance in confluent 12 to 13-d cultures, suggesting the loss of active transepithelial transport. Consistent with these findings, mucosal-to-serosal glucose fluxes were greatly reduced in streptomycin-treated cultures and insensitive to the transport inhibitor phlorizin, indicating the absence of the apical Na-dependent glucose transport system associated with net glucose reabsorption. In addition to transport processes, antibiotic treatment also interfered with cellular energy metabolism as judged by the rapid reduction in glycolytic lactate production observed in the presence of streptomycin. Scanning and transmission electron microscopy revealed that streptomycin-treated cultures were composed of cuboidal-to-columnar shaped cells which maintained intact tight junctions similar to control cultures. However, apical microvilli, the presumed sites of mucosal transport systems, were severely reduced in number in streptomycin-treated cultures. We concluded that streptomycin, at a dose commonly used in cell culture, inhibited the expression of differentiated function by flounder proximal tubule cell cultures. These cell cultures may provide a suitable model system for examination of the mechanisms of aminoglycoside nephrotoxicity.

Aminoglycosides: another perspective

Despite the introduction of several new classes of antimicrobial agents, aminoglycosides are still recognized as first-line therapeutic agents in the management of severe gram-negative sepsis. The major obstacle limiting the use of aminoglycoside antibiotics has been, and continues to be, the possibility of drug-induced ototoxicity and nephrotoxicity. This review critically examines the definitions used to establish the diagnosis of aminoglycoside-induced nephrotoxicity and ototoxicity and the clinical significance of these adverse reactions. The review also focuses on the practical and economic issues surrounding therapeutic drug monitoring practices. We conclude that aminoglycoside antibiotics remain an effective and economical form of therapy for severe infections and that if careful criteria are used in the selection of these agents, the benefits of therapy outweigh the risk of toxicity.

Neomycin inhibits mastoparan-induced lactate dehydrogenase release, ethidium bromide accumulation, and intracellular fluorescein depletion in MDCK cells

Mechanisms of cell death induced by toxins probably involve one or more processes such as inhibition of protein synthesis and impairment of plasma membrane integrity leading to an increase in membrane permeability. Since one of the possible actions of mastoparan, a cationic tetradecapeptide from wasp venom, is to perturb membrane phospholipids resulting in an increase in membrane permeability, we studied the effect of chemically synthesized mastoparan on lactate dehydrogenase release (LDH), ethidium bromide and fluorescein accumulation in Madin-Darby Canine Kidney (MDCK) cultured cells. Our results demonstrated that mastoparan induced cytosolic LDH release, ethidium bromide accumulation and intracellular fluorescein depletion in MDCK cells. Neomycin, a polycationic aminoglycoside, interacts with anionic polyphosphoinositides at the plasma membrane. Since both mastoparan and neomycin are cationic peptides and react with the negatively charged membrane phospholipids, we studied the interaction of these two peptides on membrane permeability. Our results demonstrated that neomycin inhibited mastoparan-induced LDH release, ethidium bromide accumulation and intracellular fluorescein depletion.

Differential susceptibility to gentamicin toxicity within the proximal convoluted tubule

The proximal convoluted tubule (PCT) is the major target for injury in gentamicin nephrotoxicity but the necrosis is often patchy and focal. The PCT is structurally, functionally, and metabolically heterogeneous, and the possibility of differential vulnerability to gentamicin-induced necrosis based on this heterogeneity has not been examined. A quantitative analysis comparing the extent of necrosis in the initial portion of the PCT (S1) to that in the more distal PCT (S2) and comparing necrosis in the PCT of superficial nephrons to that in juxtamedullary nephrons was done in rats after eight daily intraperitoneal doses of 100 mg gentamicin/kg rat weight. The results indicate that the PCT of superficial nephrons are more susceptible to necrosis than the PCT of juxtamedullary nephrons and that the initial S1 segment even in the superficial nephrons is remarkably resistant to injury. These findings suggest that some aspects of the functional or metabolic heterogeneity within the PCT may be related to either differential rates of uptake of the drug or to differences in intrinsic susceptibility to its toxic effects.