Pathogenic factors in aminoglycoside-induced nephrotoxicity

Toward an optimization of empirical antibiotic therapy in acute graft pyelonephritis: A retrospective multicenter study

OBJECTIVE

Acute graft pyelonephritis (AGPN) is the most frequent infectious complication in kidney transplant recipients (KTR). The treatment of acute community-acquired (CA) pyelonephritis is based on third-generation cephalosporins (3GC) and fluoroquinolones. Cefepime or a piperacillin-tazobactam combination are more often used in healthcare-associated (HCA) infections. However, these recommendations do not consider the resistance observed in KTRs. The objective of our study was to define the most appropriate empirical antibiotherapy for AGPN in KTRs according to the CA and HCA settings. To answer this question, we assessed the prevalence of resistance to different antibiotics usually recommended for urinary tract infections (UTIs) in the general population.

METHODS

Observational, retrospective, multicenter study covering all episodes of AGPN occurring in hospitalized KTRs in 2019.

RESULTS

A total of 210 patients were included in 7 centers and 244 episodes of AGPN were analyzed (158 CA-AGPN and 86 HCA-AGPN). The prevalence of 3GC and fluoroquinolone resistance was 23 % (n = 36) and 30 % (n = 50) in CA infections (n = 158), and 47 % (n = 40) and 31 % (n = 27) in HCA infections (n = 86), respectively. Cefepime resistance rate was 19 % (n = 30) in CA-AGPN and 29 % (n = 25) in HCA-AGPN. Piperacillin-tazobactam combination had resistance rates > 15 % in both CA and HCA infections. The only antimicrobials with resistance rates < 10 % were aminoglycosides and carbapenems.

CONCLUSION

None of the antibiotics recommended in empirical treatment in UTIs has shown a resistance rate of less than 10% with regard to AGPN. Therefore, none of them should be used as monotherapy. A combination therapy including amikacin could be an appropriate strategy in this setting.

Properties of Non-Aminoglycoside Compounds Used to Stimulate Translational Readthrough of PTC Mutations in Primary Ciliary Dyskinesia

Primary ciliary dyskinesia (PCD) is a rare disease with autosomal recessive inheritance, caused mostly by bi-allelic gene mutations that impair motile cilia structure and function. Currently, there are no causal treatments for PCD. In many disease models, translational readthrough of premature termination codons (PTC-readthrough) induced by aminoglycosides has been proposed as an effective way of restoring functional protein expression and reducing disease symptoms. However, variable outcomes of pre-clinical trials and toxicity associated with long-term use of aminoglycosides prompt the search for other compounds that might overcome these problems. Because a high proportion of PCD-causing variants are nonsense mutations, readthrough therapies are an attractive option. We tested a group of chemical compounds with known PTC-readthrough potential (ataluren, azithromycin, tylosin, amlexanox, and the experimental compound TC007), collectively referred to as non-aminoglycosides (NAGs). We investigated their PTC-readthrough efficiency in six PTC mutations found in Polish PCD patients, in the context of cell and cilia health, and in comparison to the previously tested aminoglycosides. The NAGs did not compromise the viability of the primary nasal respiratory epithelial cells, and the ciliary beat frequency was retained, similar to what was observed for gentamicin. In HEK293 cells transfected with six PTC-containing inserts, the tested compounds stimulated PTC-readthrough but with lower efficiency than aminoglycosides. The study allowed us to select compounds with minimal negative impact on cell viability and function but still the potential to induce PTC-readthrough.

A Uremic Goat Model Created by Subtotal Renal Artery Embolization and Gentamicin

A large animal model of (end-stage) kidney disease (ESKD) is needed for the preclinical testing of novel renal replacement therapies. This study aimed to create stable uremia via subtotal renal artery embolization in goats and induce a temporary further decline in kidney function by administration of gentamicin. Renal artery embolization was performed in five Dutch white goats by infusing polyvinyl alcohol particles in branches of the renal artery, aiming for the embolization of ~80% of one kidney and complete embolization of the contralateral kidney. Gentamicin was administered to temporarily further increase the plasma concentrations of uremic toxins. After initial acute kidney injury, urea and creatinine plasma concentrations stabilized 1.5 ± 0.7 months post-embolization and remained elevated (12 ± 1.4 vs. 5.6 ± 0.8 mmol/L and 174 ± 45 vs. 65 ± 5.6 µmol/L, resp.) during follow-up (16 ± 6 months). Gentamicin induced temporary acute-on-chronic kidney injury with a variable increase in plasma concentrations of small solutes (urea 29 ± 15 mmol/L, creatinine 841 ± 584 µmol/L, phosphate 2.2 ± 0.3 mmol/L and potassium 5.0 ± 0.6 mmol/L) and protein-bound uremic toxins representative of patients with ESKD. A uremic goat model characterized by stable moderate uremia was established via subtotal renal artery embolization with the induction of temporary severe acute-on-chronic kidney injury by the administration of gentamicin, allowing preclinical in vivo validation of novel renal replacement technologies.

Chronotoxicity of Streptomycin-Induced Renal Injury in Mice

The aim of the present study was to investigate the "chronotoxicity" of streptomycin (SM) in relation to its circadian periodicity. Male ICR mice were injected intraperitoneally with SM (780 mg/kg, one shot) one of six time points throughout the day. Mortality was monitored until 14 d after the injection and clearly differed depending on the timing of the injection (i.e., mice were more sensitive to injection during the dark phase). Moreover, when mice were administered with non-lethal doses of SM (550 mg/kg, every 24 h for 3 d, in the light phase or dark phase), the levels of nephrotoxicity indicators (blood urea nitrogen and renal levels of malondialdehyde and cyclooxygenase-2) were significantly increased by the injection in the dark phase, but not in the light phase. These results suggested that SM showed clear chronotoxicity. Our current data indicated that chronotoxicology may provide valuable information on the importance of injection timings for evaluations of toxicity and undesirable side effects.

Increment of Lysosomal Biogenesis by Combined Extracts of Gum Arabic, Parsley, and Corn Silk: A Reparative Mechanism in Mice Renal Cells

Gum Arabic (GA), parsley, and corn silk have been traditionally used for renal failure patients worldwide. This study aimed at probing the mechanism of the combined extracts, namely, GA (3 g/kg/day), parsley (1 g/kg/day), and corn silk (200 mg/kg/day), as nephroprotective agents in mice after amikacin (1.2 g/kg) single dose through exploration of their action on G-protein coupled receptors (GPR) 41 and 43 and the ensuing lysosomal biogenesis. Western blotting was employed for renal levels of bcl-2-associated X protein (BAX) and cytosolic cathepsin D; cell death markers, nuclear transcription factor EB (TFEB), and lysosomal associated membrane protein-1 (LAMP-1); and lysosomal biogenesis indicators. Liquid chromatography–mass spectrometry (LC-MS) and docking were also employed. After amikacin treatment, BAX and cathepsin D levels were upregulated while LAMP-1 and nuclear TFEB levels were inhibited. The combined extracts inhibited BAX and cytosolic cathepsin D but upregulated LAMP-1 and nuclear TFEB levels. Docking confirmed GPR modulatory signaling. The combined extracts showed GPR signal modulatory properties that triggered lysosome synthesis and contributed to reversing the adverse effects of amikacin on renal tissues.

Use of 3D Human Liver Organoids to Predict Drug-Induced Phospholipidosis

Drug-induced phospholipidosis (PL) is a storage disorder caused by the formation of phospholipid-drug complexes in lysosomes. Because of the diversity of PL between species, human cell-based assays have been used to predict drug-induced PL in humans. We established three-dimensional (3D) human liver organoids as described previously and investigated their liver characteristics through multiple analyses. Drug-induced PL was initiated in these organoids and in monolayer HepG2 cultures, and cellular changes were systemically examined. Organoids that underwent differentiation showed characteristics of hepatocytes rather than HepG2 cells. The organoids also survived under PL-inducing drug conditions for 48 h and maintained a more stable albumin secretion level than the HepG2 cells. More cytoplasmic vacuoles were observed in organoids and HepG2 cells treated with more potent PL-induced drugs, but to a greater extent in organoids than in HepG2 cells. Lysosome-associated membrane protein 2, a marker of lysosome membranes, showed a stronger immunohistochemical signal in the organoids. PL-distinctive lamellar bodies were observed only in amiodarone-treated organoids by transmission electron microscopy. Human liver organoids are thus more sensitive to drug-induced PL and less affected by cytotoxicity than HepG2 cells. Since PL is a chronic condition, these results indicate that organoids better reflect metabolite-mediated hepatotoxicity in vivo and could be a valuable system for evaluating the phospholipidogenic effects of different compounds during drug development.

A systematic meta-analysis on the efficacy of pre-clinically tested nephroprotectants at preventing aminoglycoside nephrotoxicity

Nephrotoxicity limits the use of aminoglycoside antibiotics. Kidney damage is produced mainly in the renal tubule due to an inflammatory and oxidative process. At preclinical level, many drugs and natural products have been tested as prospective protectors of aminoglycoside nephrotoxicity. The main objective of this work was to make a systematic literature review of preclinical studies about aminoglycoside nephrotoxicity protection and a statistical analysis based on the meta-analysis methodology. Studies published up to January 2016 were identified. After applying inclusion criteria, 54 studies were chosen. The size of the experimental groups, means and standard deviations of data on renal function (i.e. plasma creatinine and blood urea nitrogen [BUN] concentrations) were extracted and registered in a database. The studies were grouped according to the mechanism of nephroprotection and their route of administration. The Mean Difference (95% confidence interval) was calculated for each study and group. 40 of 54 products tested produced an amelioration of aminoglycoside nephrotoxicity based on creatinine results. Also a dose dependent protective effect was observed (both in creatinine and BUN). Products orally administered were more effective than via i.p. Products with attributed antioxidant activity were the most used and those which proved statistically significant nephroprotection as a class effect. Aminoglycoside tubular reuptake inhibitors, excretion inducers and calcium channel blockers also showed a promising and rather homogeneous class tendency towards nephroprotection, although more research is necessary to obtain solid and conclusive results, based on a larger number of studies.

Aminoglycoside-stimulated readthrough of premature termination codons in selected genes involved in primary ciliary dyskinesia

Translational readthrough of premature termination codons (PTCs) induced by pharmacological compounds has proven to be an effective way of restoring functional protein expression and reducing symptoms in several genetic disorders. We tested the potential of different concentrations of several aminoglycosides (AAGs) for promoting PTC-readthrough in 5 genes involved in the pathogenesis of primary ciliary dyskinesia, an inherited disorder caused by the dysfunction of motile cilia and flagella. The efficiency of readthrough stimulation of PTCs cloned in dual reporter vectors was examined in 2 experimental settings: in vitro (transcription/translation system) and ex vivo (transiently transfected epithelial cell line). PTC-readthrough was observed in 5 of the 16 mutations analyzed. UGA codons were more susceptible to AAG-stimulated readthrough than UAG; no suppression of UAA was observed. The efficiency of PTC-readthrough in vitro (from less than 1% to ∼28% of the translation from the corresponding wild-type constructs) differed with the AAG type and concentration, and depended on the combination of AAG and PTC, indicating that each PTC has to be individually tested with a range of stimulating compounds. The maximal values of PTC suppression observed in the ex vivo experiments were, depending on AAG used, 3–5 times lower than the corresponding values in vitro, despite using AAG concentrations that were 2 orders of magnitude higher. This indicates that, while the in vitro system is sufficient to examine the readthrough-susceptibility of PTCs, it is not sufficient to test the compounds potential to stimulate PTC-readthrough in the living cells. Most of the tested compounds (except for G418) at their highest concentrations did not disturb ciliogenesis in the cultures of primary respiratory epithelial cells from healthy donors.

Time dependent effect of gentamicin on enzymes of carbohydrate metabolism and terminal digestion in rat intestine

Gentamicin (GM) is an aminoglycoside antibiotic commonly used against life threatening gram negative bacterial infections, however, nephrotoxicity remains the major concern for its long term use. Although its effects on kidney are well characterized but there have been no studies regarding its effects on intestine. We hypothesize that GM causes adaptive coordinated effect on enzymes of carbohydrate metabolism and terminal digestion/ absorption in rat intestine. Rats were administerd a nephrotoxic dose of GM (80 mg /kg body weight) daily for 15 days and a time dependent effect was observed on various enzyme activities. Activities of lactate (LDH), malate (MDH) and isocitrate (ICDH) dehydrogenases, significantly increased and peaked at different time intervals of GM treatment. Whereas LDH activity remained higher, MDH and ICDH activity slowly declined from their peak values. Activities of fructose-1,6-bisphosphatase, glucose-6-phosphatase and glucose-6-phosphate dehydrogenase increased but malic enzyme decreased in a time dependent manner. Activity of alkaline phosphatase and sucrase significantly increased but γ-glutamyl transpeptidase activity decreased. GM administration increased lipid peroxidation, glutathione peroxidase but decreased superoxide dismutase and catalase activities. The results indicate that GM treatment selectively upregulated certain enzymes of carbohydrate metabolism and terminal digestion/absorption and perturbed antioxidant defenses. Human & Experimental Taxicology, ( 2007) 26, 587—593.

Cardiotrophin-1 therapy prevents gentamicin-induced nephrotoxicity in rats

Aminoglycosides are very effective antibiotics for the treatment of severe infections, but they rank among the most frequent causes of drug-induced nephrotoxicity. Thus, prevention of aminoglycoside nephrotoxicity is an unmet therapeutic objective. Cardiotrophin-1 (CT-1), a member of the IL-6 family of cytokines, has been reported to protect the kidney against toxic and ischemic acute kidney injury (AKI). We have assessed the effect of rat CT-1 in the severity of gentamicin (G)-induced AKI. Groups of male Wistar rats received the following for 6 consecutive days: i) isotonic saline solution (group CONT), ii) G, 150mg/kg/day, i.p. (group G), iii) CT-1, 100μg/kg/day i.v. (group CT-1), or iv) G and CT-1 at the doses described above. The G group showed a manifest AKI characterized by low creatinine clearance, high plasma creatinine and urea levels, increased urinary excretion of proteins, glucose and AKI markers such as N-acetyl-glucosaminidase, neutrophil gelatinase-associated lipocalin, kidney-injury molecule-1 and T-gelsolin, increased kidney levels of CD-68, iNOS, IL-1β and TNF-α, and markedly higher histological renal damage and leukocyte infiltration than the CONT and CT-1 groups. Administration of CT-1 together with G reduced almost all of the above-described manifestations of G-induced AKI. The results of this study have potential clinical application, as CT-1 is near to being used as a drug for organ protection.

Effect of Kidney Function on Drug Kinetics and Dosing in Neonates, Infants, and Children

Neonates, infants, and children differ from adults in many aspects, not just in age, weight, and body composition. Growth, maturation and environmental factors affect drug kinetics, response and dosing in pediatric patients. Almost 80% of drugs have not been studied in children, and dosing of these drugs is derived from adult doses by adjusting for body weight/size. As developmental and maturational changes are complex processes, such simplified methods may result in subtherapeutic effects or adverse events. Kidney function is impaired during the first 2 years of life as a result of normal growth and development. Reduced kidney function during childhood has an impact not only on renal clearance but also on absorption, distribution, metabolism and nonrenal clearance of drugs. 'Omics'-based technologies, such as proteomics and metabolomics, can be leveraged to uncover novel markers for kidney function during normal development, acute kidney injury, and chronic diseases. Pharmacometric modeling and simulation can be applied to simplify the design of pediatric investigations, characterize the effects of kidney function on drug exposure and response, and fine-tune dosing in pediatric patients, especially in those with impaired kidney function. One case study of amikacin dosing in neonates with reduced kidney function is presented. Collaborative efforts between clinicians and scientists in academia, industry, and regulatory agencies are required to evaluate new renal biomarkers, collect and share prospective pharmacokinetic, genetic and clinical data, build integrated pharmacometric models for key drugs, optimize and standardize dosing strategies, develop bedside decision tools, and enhance labels of drugs utilized in neonates, infants, and children.

A histological study of the effect of exogenous melatonin on gentamicin induced structural alterations of proximal tubules in rats

The aim of this research was to assess the reactive changes of rat proximal tubules caused by gentamicin and the effect of relatively low doses of melatonin. 48 adult male Wistar rats were distributed into six groups of equal size which all received one of the following daily intraperitoneal injections: vehicle (5% ethanol in Ringer solution) during 11 days (C); gentamicin (80 mg/kg) during 8 days (G), two groups which concomitantly received gentamicin (80 mg/kg) during 8 days and melatonin in two different test doses (5 or 20 mg/kg) during 11 days (GM1, GM2) and two groups treated only with melatonin in two different doses (5 or 20 mg/kg) during 11 days (M1, M2). Histological analysis included qualitative and semi-quantitative light microscopy analysis of proximal tubules. Exogenous melatonin had no significant effect on the microstructure, independently of dosis. The changes of proximal tubules microstructure induced by gentamicin were expressed in the form of granulovacuolar degeneration, necrosis and desquamation. The grade of proximal tubular changes was smaller in animals who besides gentamicin received melatonin. Melatonin has a dose dependent protective effect on the structural alterations of proximal tubules of the kidney induced by gentamicin.

New tides: using zebrafish to study renal regeneration

Over the past several decades, the zebrafish has become one of the major vertebrate model organisms used in biomedical research. In this arena, the zebrafish has emerged as an applicable system for the study of kidney diseases and renal regeneration. The relevance of the zebrafish model for nephrology research has been increasingly appreciated as the understanding of zebrafish kidney structure, ontogeny, and the response to damage has steadily expanded. Recent studies have documented the amazing regenerative characteristics of the zebrafish kidney, which include the ability to replace epithelial populations after acute injury and to grow new renal functional units, termed nephrons. Here we discuss how nephron composition is conserved between zebrafish and mammals, and highlight how recent findings from zebrafish studies utilizing transgenic technologies and chemical genetics can complement traditional murine approaches in the effort to dissect how the kidney responds to acute damage and identify therapeutics that enhance human renal regeneration.

Reno-protective role of flunarizine (mitochondrial permeability transition pore inactivator) against gentamicin induced nephrotoxicity in rats

This study was aimed to evaluate the role of flunarizine on gentamicin (GEM) induced nephrotoxicity in rat. Administration of GEM (40 mg/kg, s.c. for 10 consecutive days) significantly increased blood urea nitrogen (BUN), N-acetyl β-d-glucosaminidase (NAG), thiobarbituric acid reactive substances (TBARS) and total calcium whereas, decreased body weight, fractional excretion of sodium (FrNa), creatinine clearance (CrCl), reduced glutathione (GSH), mitochondrial cytochrome c oxidase (Cyt-C oxidase) and ATP levels resulting in nephrotoxicity. Further, flunarizine (100, 200 and 300 µmol/kg, p.o.) was administered to evaluate its renoprotective effect against GEM induced nephrotoxicity and the results were compared with cylcosporin A (CsA, 50 µmol/kg, p.o.). Flunarizine resulted in the attenuation of renal dysfunction and oxidative marker changes in rats subjected to GEM induced nephrotoxicity in a dose dependent manner. Medium and higher doses of flunarizine produced significant renal protective effect which was comparable to cyclosporin A. The results of this study clearly revealed that flunarizine protected the kidney against the nephrotoxic effect of GEM via mitochondrial permeability transition pore (MPTP) inactivation potential.

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.

New insights into the mechanism of aminoglycoside nephrotoxicity: an integrative point of view

Nephrotoxicity is one of the most important side effects and therapeutical limitations of aminoglycoside antibiotics, especially gentamicin. Despite rigorous patient monitoring, nephrotoxicity appears in 10-25% of therapeutic courses. Traditionally, aminoglycoside nephrotoxicity has been considered to result mainly from tubular damage. Both lethal and sub-lethal alterations in tubular cells handicap reabsorption and, in severe cases, may lead to a significant tubular obstruction. However, a reduced glomerular filtration is necessary to explain the symptoms of the disease. Reduced filtration is not solely the result of tubular obstruction and tubular malfunction, resulting in tubuloglomerular feedback activation; renal vasoconstriction and mesangial contraction are also crucial to fully explain aminoglycoside nephrotoxicity. This review critically presents an integrative view on the interactions of tubular, glomerular, and vascular effects of gentamicin, in the context of the most recent information available. Moreover, it discusses therapeutic perspectives for prevention of aminoglycoside nephrotoxicity derived from the pathophysiological knowledge.

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.

Induction of Apoptosis by Cationic Amphiphilic Drugs Amiodarone and Imipramine

Phospholipidosis is the excessive accumulation of intracellular phospholipids in cell lysosomes. Drugs that induce this disease often share common physiochemical properties and are collectively classified as cationic amphiphilic drugs (CADs). Although the cause of phospholipidosis and morphologic appearance of affected lysosomes have been studied extensively, less is known about the physiologic effects of the condition. In the current study, U-937 cells were incubated with the CADs amiodarone (2.5-10 microg/mL) and imipramine (2.5-20 microg/mL). Treatment of U-937 cells with these compounds for 96 h resulted in concentration-related increases in phospholipids, as assessed by flow cytometry using the fluorophore nile red. These results were verified by measuring the concentrations of choline-derived phospholipids, which were significantly increased in drug-treated cells. Cell number in amiodarone (10 microg/mL) and imipramine (20 microg/mL) cultures following the 96-h incubation period were markedly reduced compared to control cultures. These observations suggested that accumulation of cellular phospholipids could inhibit cell proliferation. Flow cytometric analysis revealed a decrease in the percentage of cells in the S-phase of the cell cycle following drug treatment, yet DNA replication still occurred in a significant portion of cells. Interestingly, amiodarone and imipramine induced apoptosis in U-937 cells as shown by annexin V-FITC staining and DNA fragmentation. Enzymatic assays demonstrated that amiodarone and imipramine induced the activity of caspases 2 and 3. These results suggest that disruption of cell lysosomes in U-937 cells following accumulation of phospholipids does not cause a cell cycle arrest but instead induces apoptosis by activation of caspase pathways.

Studies on the protective effect of dietary fish oil on gentamicin-induced nephrotoxicity and oxidative damage in rat kidney

Gentamicin (GM)-induced nephrotoxicity limits its long-term clinical use. Several agents/strategies were attempted to prevent GM nephrotoxicity but were not found suitable for clinical practice. Dietary fish oil (FO) retard the progression of certain types of cancers, cardiovascular and renal disorders. We aimed to evaluate protective effect of FO on GM-induced renal proximal tubular damage. The rats were pre-fed experimental diets for 10 days and then received GM (80 mg/kg body weight/day) treatment for 10 days while still on diet. Serum/urine parameters, enzymes of carbohydrate metabolism, brush border membrane (BBM), oxidative stress and phosphate transport in rat kidney were analyzed. GM nephrotoxicity was recorded by increased serum creatinine and blood urea nitrogen. GM increased the activities of lactate and glucose-6-phosphate dehydrogenases whereas decreased malate, isocitrate dehydrogenases; glucose-6 and fructose-1,6-bisphosphatases; superoxide dismutase, catalase, glutathione peroxidase and BBM enzymes. In contrast, FO alone increased enzyme activities of carbohydrate metabolism, BBM and oxidative stress. FO feeding to GM treated rats markedly enhanced resistance to GM elicited deleterious effects and prevented GM-induced decrease in 32Pi uptake across BBM. Dietary FO supplementation ameliorated GM-induced specific metabolic alterations and oxidative damage due to its intrinsic biochemical/antioxidant properties.

Glomerular nephrotoxicity of aminoglycosides

Aminoglycoside antibiotics are the most commonly used antibiotics worldwide in the treatment of Gram-negative bacterial infections. However, aminoglycosides induce nephrotoxicity in 10-20% of therapeutic courses. Aminoglycoside-induced nephrotoxicity is characterized by slow rises in serum creatinine, tubular necrosis and marked decreases in glomerular filtration rate and in the ultrafiltration coefficient. Regulation of the ultrafiltration coefficient depends on the activity of intraglomerular mesangial cells. The mechanisms responsible for tubular nephrotoxicity of aminoglycosides have been intensively reviewed previously, but glomerular toxicity has received less attention. The purpose of this review is to critically assess the published literature regarding the toxic mechanisms of action of aminoglycosides on renal glomeruli and mesangial cells. The main goal of this review is to provide an actualized and mechanistic vision of pathways involved in glomerular toxic effects of aminoglycosides.

Agents ameliorating or augmenting experimental gentamicin nephrotoxicity: some recent research

Despite its nephrotoxic potential, the aminoglycoside antibiotic gentamicin (GM) is still considered to be an important agent against life-threatening infections. The goal of reducing or protecting against its nephrotoxicity has attracted much effort and attention during the last decade. This article reviews some of the literature published during the last decade on the effects of agents that ameliorate or augment GM nephrotoxicity. Notable among the ameliorating agents are antioxidant agents. These include different classes of compounds that include beta blockers (e.g. carvedilol), superoxide dismutase mimetic agents (e.g. M40403), hormones (e.g. melatonin), iron chelators (e.g. deferrioxamine), vitamins (vitamin C and E) and medicinal plants (e.g. garlic). Other ameliorating agents include antibiotics (e.g. ceftriaxone), antiplatelet drugs (e.g. trapidil) and Ca++ agents that may augment GM nephrotoxicity include cyclosporin and the Ca++-channel blocker verapamil.

Drug-induced phospholipidosis: are there functional consequences?

Phospholipidosis induced by drugs with a cationic amphiphilic structure is a generalized condition in humans and animals that is characterized by an intracellular accumulation of phospholipids and the concurrent development of concentric lamellar bodies. The primary mechanism responsible for the development of phospholipidosis is an inhibition of lysosomal phospholipase activity by the drugs. While the biochemical and ultrastructural features of the condition have been well characterized, much less effort has been directed toward understanding whether the condition has adverse effects on the organism. While there are a few cationic amphiphilic drugs that have been reported to cause phospholipidosis in humans, the principal concern with this condition is in the pharmaceutical industry during preclinical testing. While this class of drugs should technically be referred to as cationic lipophilic, the term cationic amphiphilic is widely used and recognized in this field, and for this reason, the terminology cationic amphiphilic drugs (CADs) will be employed in this Minireview. The aim of this Minireview is to provide an evaluation of the state of knowledge on the functional consequences of CAD-induced phospholipidosis.

Confounding factors in toxicity testing

The necessity for understanding normal human functions and the mechanisms which underlie dysfunction in these processes is essential in the promotion of a healthier lifestyle. To achieve this goal utilization of a suitable animal model is necessary in order to develop new pharmaceutical agents to alleviate diseases or chemicals to enhance the quality of life. It is incumbent upon investigators to choose a species in which pharmacokinetic principles are established and it is important that these phenomena resemble those of the humans. The choice of rats has specific advantages in that these rodents possess similar pharmacodynamic parameters to humans. Other advantages include availability, low cost, ease of breeding, and an extensive literature data-base to enable comparisons to present findings. However, in the interpretation of data from animals to humans, there are factors which need to be recognized as playing important roles in chemical-induced outcomes. The confounding factors include strain, supplier, age, gender, hormonal status and dietary intake. The aim of this article is to demonstrate that there are differences in the responsiveness of rat stock/strains to chemicals and that lack of consideration of confounding factors yields inappropriate conclusions regarding risk assessment for humans.

Localization of the nephron site of gentamicin-induced hypercalciuria in the rat: a micropuncture study

In vivo renal micropuncture techniques were used to locate the nephron site of hypercalciuria induced by acute gentamicin infusion in anaesthetized Sprague Dawley rats. Three series of experiments were conducted. The effect of gentamicin on calcium reabsorption in the proximal tubule (Series I) and loop of Henle (Series II) was investigated using in vivo microperfusion whereas the effect on distal calcium handling (Series III) was studied using in vivo microinfusion. In all three experimental series, acute systemic gentamicin infusion at 0.28 mg kg(-1) min(-1) caused significant hypercalciuria within 30 min of commencing drug infusion. Gentamicin had no effect on the rates of urine flow or sodium excretion. Acute gentamicin infusion had no effect on unidirectional calcium reabsorption in the proximal tubule or loop of Henle despite a simultaneous and highly significant hypercalciuria at the whole kidney level. Net fluid reabsorption was also unaffected by the drug in these nephron segments. Acute gentamicin infusion significantly increased the urinary recovery of calcium following microinfusion into early distal tubules, whereas urinary calcium recovery was decreased after microinfusion into late distal tubules. We conclude that acute gentamicin-induced hypercalciuria is mediated by a decrease in calcium reabsorption in the early distal tubule. Thus, the acute hypercalciuric effect of gentamicin occurs at a different nephron site to the nephrotoxic effects associated with longer-term administration of the drug. It is, therefore, unlikely that gentamicin-induced hypercalciuria is involved in the pathogenesis of subsequent proximal tubular cell injury.

Human kallikrein gene delivery protects against gentamycin-induced nephrotoxicity in rats

The tissue kallikrein-kinin system has been shown to play important roles in cardiovascular and renal function. The aim of this study was to investigate potential protective effects of kallikrein gene delivery in gentamycin-induced nephrotoxicity. Rats were injected subcutaneously with gentamycin daily for 10 to 14 days. Adenovirus, Ad.CMV-cHK carrying the human tissue kallikrein gene or Ad.CMV-LacZ carrying the beta-galactosidase gene under the control of the cytomegalovirus promoter, were delivered intravenously on the first day of gentamycin administration. The expression of human tissue kallikrein mRNA was identified in the kidney, aorta, heart and liver and immunoreactive human kallikrein levels were measured in the serum and urine of rats receiving kallikrein gene delivery. Adenovirus-mediated kallikrein gene delivery significantly increased the renal blood flow, glomerular filtration rates, and urine flow while it attenuated renal tubular damage, cellular necrosis, lumenal protein casts and reduced ventricular weight and cardiomyocyte size. Kallikrein gene delivery caused a decrease in blood urea nitrogen levels and increases in urinary kinin and nitrite/nitrate levels. This study shows that kallikrein gene delivery exhibits protection against gentamycin-induced nephrotoxicity, and raises the potential for kallikrein gene therapy to treat drug-induced renal diseases.

Effect of experimental diabetes mellitus on gentamicin-induced acute renal functional changes in the anaesthetized rat

1. Rats with streptozotocin (STZ) diabetes are protected from gentamicin (GEN) nephrotoxicity. Because the chronic renal damage from GEN is preceded by acute renal functional changes (notably hypercalciuria), the present study aims to determine whether diabetes may also protect against the acute effects of the drug. If there is a link between the rapid physiological actions of GEN and its subsequent nephrotoxicity, the former may also be affected by the diabetic condition. 2. Standard renal clearance techniques were performed on anaesthetized rats that had been injected with STZ or vehicle 2 weeks previously. All animals were infused with 0.9% NaCl for 5 h and then either GEN (0.28 mg/kg per min) or 0.9% NaCl alone for 2 h. 3. Baseline fractional calcium excretion (FE(Ca)) of diabetic rats was three-fold that of control animals (6.6+/-0.2 vs 2.2+/-0.2%, respectively; P<0.01, MANOVA). Following GEN infusion, a comparable increase in FE(Ca) occurred in control and diabetic rats (5.3+/-0.6 vs 5.3+/-0.8%, respectively; NS). 4. Streptozotocin diabetes, therefore, does not alter the acute hypercalciuric response to GEN. This may suggest that the acute effects of GEN on renal calcium handling do not contribute to the subsequent nephrotoxicity. However, the higher baseline FE(Ca) seen in diabetic rats may afford protection against the renal injury caused by gentamicin.

Acute gentamicin-induced hypercalciuria and hypermagnesiuria in the rat: dose-response relationship and role of renal tubular injury

1. Standard renal clearance techniques were used to assess the dose-response relationship between acute gentamicin infusion and the magnitude of hypercalciuria and hypermagnesiuria in the anaesthetized Sprague-Dawley rat. Also investigated were whether these effects occurred independently of renal tubular cell injury. 2. Acute gentamicin infusion was associated with a significant hypercalciuria and hypermagnesiuria evident within 30 min of drug infusion. The magnitude of these responses was related to the dose of drug infused (0.14-1.12 mg kg(-1) min[-1]). Increased urinary electrolyte losses resulted from a decreased tubular reabsorption of calcium and magnesium. 3. A rapid dose-related increase in urinary N-acetyl-beta-D-glucosaminidase (NAG) excretion was also observed in response to gentamicin infusion. However, there was no evidence of renal tubular cell injury and no myeloid bodies were observed within the lysosomes of the proximal tubular cells. Gentamicin may thus interfere with the mechanisms for cellular uptake and intracellular processing of NAG causing increased NAG release into the tubular lumen. 4. The absence of changes in renal cellular morphology indicates that the excessive renal losses of calcium and magnesium were an effect of gentamicin per se and not the result of underlying renal tubular injury. The renal effects described in this paper were apparent after administration of relatively low total drug doses, and with plasma concentrations calculated to be within the clinical range. These findings suggest that disturbances of plasma electrolyte homeostasis could occur in the absence of overt renal injury in patients receiving aminoglycoside antibiotics.

Effect of superoxide dismutase treatment on gentamicin nephrotoxicity in rats

The effect of administration of superoxide dismutase (SOD) on gentamicin nephrotoxicity was examined in rats. SOD was administered at a dose of 2000 i.u/kg or 8000 i.u/kg for 10 consecutive days, and nephrotoxicity was induced by daily i.m. injections of gentamicin at a dose of 80 mg/kg during the last 6 days of the experimental period. Gentamicin induced significant increases in plasma creatinine and urea and protein urinary concentrations, and significant decreases in creatinine clearance and kidney cortical alkaline phosphatase activity and reduced glutathione (GSH) concentrations. The antibiotic also produced marked necrosis of the renal proximal tubules. SOD treatment (8000 i.u/kg) reversed most of these variables, indicating that it was effective in ameliorating gentamicin nephrotoxicity. However, at a dose of 2000 i.u./kg it was mostly ineffective.

Gentamicin nephrotoxicity in the rat: influence of age and diabetes mellitus

1. This work examines the influence of age on some nephrotoxic signs of gentamicin in normal and diabetic rats (aged 1 and 24 months). 2. Gentamicin (80 mg-1 kg-1 day for 6 days, intramuscularly) produced the typical pattern of nephrotoxicity; significantly increasing the plasma concentrations of creatinine and urea, and the urinary excretion of protein, copper and zinc and significantly reducing creatinine clearance and cortical alkaline phosphatase activity. The antibiotic produced a marked damage in the proximal renal tubules. Nearly all of these effects were more marked in the old than in the young rats. Cortical gentamicin concentration in the young was about 67% of that in the old. 3. Streptozotocin-induced diabetes significantly ameliorated the signs of nephrotoxicity of gentamicin in young rats. In old rats, diabetes had significantly less protective effect on the gentamicin-induced nephrotoxic signs than in the young rats. Gentamicin nephrotoxicity in diabetic old rats induced mortality in about a third of the animals used, whereas no mortality was seen in young diabetic rats treated with gentamicin.

Gentamicin nephrotoxicity in humans and animals: some recent research

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

Aminoglycoside-associated nephrotoxicity in extrahepatic obstructive jaundice

Experimental data demonstrate that biliary obstruction increases renal sensitivity to gentamicin. In the present study the incidence of and risk factors for aminoglycoside nephrotoxicity were prospectively studied in patients with extrahepatic obstructive jaundice. Two hundred and thirty-seven hospitalized adult patients were classified into three groups. Group I consisted of 84 patients with extrahepatic obstructive jaundice, who received aminoglycoside (gentamicin or tobramycin). Group II consisted of 81 patients with extrahepatic obstructive jaundice, who received either antibiotics other than aminoglycoside or no antimicrobial therapy. Group III consisted of 72 noncholestatic patients receiving aminoglycosides for different disorders. Nephrotoxicity developed in 27 patients (32%) in group I vs 9 patients (11%) in group II and 4 patients (5.6%) in group III (p < 0.00001). In group I, a comparison of patients with and without nephrotoxicity revealed significantly higher values in the former for mean serum bilirubin concentration, initial steady-state trough aminoglycoside concentration and estimated half-life. Stepwise multivariate analysis with nephrotoxicity status as the dependent variable determined that the most significant variable for predicting nephrotoxicity was serum total bilirubin level. In extrahepatic cholestasis a high serum bilirubin level is a distinct factor predisposing to aminoglycoside nephrotoxicity.

The effect of thyroxine or carbimazole treatment on gentamicin nephrotoxicity in rats

1. This study examines the effect of treating rats with gentamicin (80 mg kg-1 day-1 intramuscularly (i.m.), for 6 days) alone or with either L-thyroxine or the anti-thyroid drug carbimazole. 2. Gentamicin produced significant increases in serum creatinine and urea concentrations, and significantly reduced the activity of Na+,K+ATPase in renal cortex. The concentration of serum triiodothyronine (T3) was unaffected by graded doses (20, 40 and 80 mg kg-1) of the antibiotic. Histopathologically, gentamicin produced necrosis of proximal tubules in the renal cortical tissues of treated rats. 3. Treatment of rats with either L-thyroxine or carbimazole alone did not significantly affect any of the biochemical variables investigated. Carbimazole alone produced only mild tubular necrosis. 4. Treatment of rats with either L-thyroxine (100 micrograms kg-1 day-1, subcutaneously) for 10 days, and gentamicin (80 mg kg-1, i.m. daily during the last 6 days of treatment significantly reduced the gentamicin-induced increases in serum creatinine and urea concentrations, and increased the activity of cortical N+,K+ATPase to control levels. Histopathologically, the severity of gentamicin-induced tubular necrosis was reduced by L-thyroxine treatment. 5. Carbimazole (12 mg ml-1 in drinking water for 21 days) and gentamicin (80 mg kg-1 i.m.) daily during the last 6 days of treatment, stimulated the increase in serum urea concentration produced by gentamicin, but did not significantly affect the gentamicin-induced changes in serum creatinine or cortical N+,K+ATPase.

Influence of iron, deferoxamine and ascorbic acid on gentamicin-induced nephrotoxicity in rats

1. Nephrotoxicity was induced in rats by injecting gentamicin intramuscularly (i.m.) at a dose of 80 mg/kg for 6 days. Treated animals demonstrated a typical pattern of nephrotoxicity characterized by increased serum creatinine and urea concentrations, and by necrosis of proximal tubular epithelium. 2. Pretreatment of rats with iron (Fe3+) at daily i.m. doses of 2, 4 and 8 mg/kg for 14 days, with gentamicin given during the last 6 days of treatment, significantly potentiated the gentamicin-induced increases in creatinine and urea concentrations and exacerbated renal histological damage. 3. Gentamicin significantly increased serum Fe3+ concentration in rats treated with Fe3+ and gentamicin, compared to Fe(3+)-treated rats. 4. The Fe3+ antidote deferoxamine (100 mg/kg, i.m.) given with gentamicin was ineffective in antagonizing the potentiating effect of Fe3+ on gentamicin-induced nephrotoxicity. 5. Ascorbic acid (50 mg/kg, i.m. for 14 days) was ineffective in altering the nephrotoxicity of gentamicin (80 mg/kg) given during the last 6 days of treatment. At a dose of 100 mg/kg for 14 days, ascorbic acid significantly reduced gentamicin-induced increases in creatinine and urea levels, and ameliorated proximal tubular damage. However, at a dose of 200 mg/kg, ascorbic acid exacerbated gentamicin-induced increases in creatinine and urea levels and increased the severity of the histological damage.

Selective exposure of human proximal tubule cells to gentamicin provides evidence for a basolateral component of toxicity

The goal of the present study was to determine if cultured human proximal tubule (HPT) cells could provide evidence for a basolateral component of gentamicin toxicity. Six isolates of HPT cells were grown on Millicell filters and exposed to gentamicin either apically, basolaterally, or both apically and basolaterally. Toxicity was determined by the release of lactate dehydrogenase into the growth media. The results clearly demonstrated that basolateral exposure and combined apical and basolateral exposure to gentamicin resulted in significant levels of cell toxicity. In contrast, apical exposure to gentamicin elicited only marginal toxicity. The transepithelial flux of gentamicin was shown to be the same in either the apical to basolateral or the basolateral to apical direction. A two-step mechanism of gentamicin toxicity is proposed in order to integrate basolateral toxicity with known features of aminoglycoside nephrotoxicity.

Aminoglycoside antibiotics alter the paracellular transport properties of cultured human proximal tubule cells

Cell cultures retaining properties of the human proximal tubule were utilized to determine whether or not the aminoglycoside antibiotics alter paracellular transport. The transepithelial resistance (RT) of the human proximal tubule (HPT) cell monolayers was determined by Ussing chamber analysis of cells grown on permeable supports. This analysis revealed that RT was reduced as a result of aminoglycoside exposure and that the reduction corresponded to the known clinical nephrotoxicities of the aminoglycosides. Variation in the aminoglycoside concentration necessary to elicit this response was documented using 14 individual cell isolates. Ultrastructural analysis provided evidence indicating that the alterations in RT were not associated with general damage to the HPT cells. An examination of the structure of the tight junctions by freeze-fracture analysis demonstrated only minimal alteration of the sealing strands as a result of aminoglycoside exposure. Consequently, the reductions in RT were not directly associated with discernible tight junction structural alterations. Alteration in the paracellular route of transport, as indicated by altered RT values, was clearly documented as a result of aminoglycoside exposure. In addition, this alteration was accompanied by an increased density of intramembrane particles within the apical cell membrane.

Effects of gentamicin on glomerular renin release

Gentamicin nephrotoxicity is associated with impaired glomerular function. To examine whether the effects of gentamicin on glomerular function are mediated through alterations in the renal-angiotensin system, basal and stimulated glomerular renin release was assessed in isolated glomeruli from control and gentamicin-treated rats. Male Sprague-Dawley rats (220 +/- 20 g) were studied immediately after treatment with gentamicin sulfate (4 mg/kg BW/day, n = 6) for 1 or 2 consecutive weeks and after 1 week of recovery from 2 weeks of treatment. Control rats received an equivalent volume of saline (n = 9). After the respective treatment, renal renin content was measured. In addition, glomeruli from control and gentamicin-treated rats were isolated and glomerular renin release was measured under basal conditions and after stimulation with the calmodulin inhibitor trifluoperazine (1 x 10(-4) M). Renin concentration was determined in aliquots of the supernatant by measuring the generation of angiotensin I using radioimmunoassay techniques at 15-min intervals. Renal renin content was significantly increased after 2 weeks of gentamicin treatment (+47%) and remained elevated (+62%) 1 week after discontinuing a 2-week gentamicin treatment. Both basal and stimulated glomerular renin release were lower in glomeruli isolated from gentamicin-treated rats. The effect of gentamicin added in vitro to glomeruli isolated from untreated rats was also evaluated. Exposure of normal glomeruli to in vitro gentamicin (1 mM) resulted in a significant inhibition of both basal (-47%, p < .05) and stimulated (-84%, p < .05) glomerular renin release. To determine whether the inhibitory action of gentamicin on glomerular renin release was dependent on extracellular calcium concentration, the effects of gentamicin on glomerular renin release were also assessed in the absence of extracellular calcium. Our data revealed that in the absence of extracellular calcium, the inhibitory effect of gentamicin on both basal and stimulated glomerular renin release was abolished. Taken together, these findings strongly suggest an inhibitory effect of gentamicin on glomerular renin release. Furthermore, the inhibition of glomerular renin release induced by gentamicin appears to be dependent on extracellular calcium.

Nephrotoxicity of low doses of tobramycin in rats: effect of the time of administration

The circadian and the circannual variations of the nephrotoxicity of tobramycin were studied in female Sprague-Dawley rats. Animals were maintained on a light-dark period of 14/10 hrs (light on: 06h00 to 20h00). They were injected once daily for 4 and 10 days with saline or tobramycin at a dose of 40 mg/kg/day i.p. at either 08h00, 14h00, 20h00 and 02h00, in April 1991, July 91, October 91, January 92. In April 91, tobramycin injected at 14h00 during 10 days induced a significant increase of [3H]-thymidine incorporation into DNA of renal cortex as compared to other groups (p < 0.01): toxicity was highest at 14h00 and lowest at 02h00. No temporal change was observed in the renal cortical accumulation of tobramycin, and in serum creatinine after the 4 or 10 days of treatment. In experiments done in April, July and October 1991 and in January 1992, no circannual variation was found in tobramycin cortical levels but peaks of toxicity were observed at 02h00 in April and October 1991 and at 14h00 in July 1991 and January 1992. There was no linear correlation between the toxicity and the tobramycin accumulation in the renal cortex (r = 0.21). The data suggest that the circadian changes in tobramycin toxicity are due to temporal changes in the susceptibility of renal cells to tobramycin.

Aminoglycoside antibiotics alter the electrogenic transport properties of cultured human proximal tubule cells

Monolayers of human proximal tubule (HPT) cells, when grown on permeable supports and mounted in Ussing chambers, spontaneously display a transepithelial potential difference (PD) and short-circuit current (Isc). These electrical parameters were used in the present study to determine if aminoglycoside exposure altered electrogenic sodium transport by HPT cells. The results of this determination demonstrated that exposure to gentamicin, at levels below that producing cell necrosis, caused a marked reduction in Isc and that this reduction followed the known in vivo nephrotoxicities of the aminoglycosides streptomycin, gentamicin, and neomycin. It was concluded through a similar analysis on a total of 14 isolates of HPT cells that the aminoglycosides repeatably reduced the electrogenic sodium transport of HPT cells. It was further determined that this alteration in electrogenic transport by gentamicin was mediated through exposure of the drug to the basolateral cell surface and that apical exposure had little effect. Evidence was obtained against the involvement of Na+, K(+)-ATPase, adenosine 3',5'-cyclic monophosphate, and sodium-coupled substrate transport in this alteration in electrogenic transport by the aminoglycosides. The basolaterally located Na+: CO3(-2):HCO3(-1) symporter is a possible site for aminoglycoside-induced nephrotoxicity.

Changes in concentration of essential metals in kidneys and urine as indices of gentamicin nephrotoxicity in female Wistar rats

Wistar rats were treated with gentamicin in single (80 mg/kg) or repeated doses (7 x 40 mg/kg) subcutaneously. Total protein as well as excretion of essential metals (Cu, Zn) with the urine were determined 24 hr after 1, 3 and 7 dosages as well as 3 and 7 days after the termination of administration. At the same time kidneys were examined histopathologically by light microscopy. Simultaneously, Cu, Zn and metallothionein levels in kidneys and liver were determined. Rats receiving gentamicin demonstrated progressive renal proximal tubular necrosis at the end of 7 days administration. At the same time elevated copper and zinc levels were observed in urine. These essential metals seem to be an indicator of gentamicin nephrotoxicity.

Effect of interaction between gentamicin and pyridoxal-5-phosphate on functional and metabolic parameters in kidneys of female Sprague-Dawley rats

Daily intraperitoneal (i.p.) injection of genatmicin at a dose of 70 mg/kg for 11 days produced nephrotoxicity in female Sprague-Dawley rats as evidenced by increased excretion of urinary protein and trypsin inhibitory activity as well as rise in renal individual class and total phospholipid. The observed proteinuria was associated with a significant twofold fall in creatinine clearance and histopathological changes, including the presence of hyaline casts and flattened epithelial cells within the lumen of proximal convoluted tubules. Although pyridoxal-5-phosphate (50 mg/kg) administered i.p. did not significantly alter creatinine clearance, histopathology, proteinuria, and urinary trypsin inhibitory activity, an increase in individual class and total phospholipid was noted in kidney. In rats simultaneously administered gentamicin and pyridoxal-5-phosphate, the observed fall in renal gentamicin content was associated with a return of individual class and total phospholipid to control values. However, the decline in creatinine clearance, enhanced proteinuria, and increase in urinary trypsin inhibitory activity in the simultaneous-treated group was similar or greater than that seen in the gentamicin-only injected rats. Morphological examination of simultaneous-treated rats revealed extensive alterations in proximal tubules including numerous mitotic figures, large vesicular nucleii, and prominent nucleoli in epithelial cells as well as hyaline casts within the lumen. Our data combined with results of previous studies suggest that sex and type of rat strain are important factors in aminoglycoside-induced nephrotoxicity. It is evident that a specific concentration of pyridoxal-5-phosphate may be necessary to provide protection against all manifestations of aminoglycoside-induced renal damage.