Alterations in lysosomal enzymes of the proximal tubule in gentamicin nephrotoxicity

Behind every smile there's teeth: Cathepsin B's function in health and disease with a kidney view

Cathepsin B (CatB) is a very abundant lysosomal protease with endo- and carboxydipeptidase activities and even ligase features. In this review, we will provide a general characterization of CatB and describe structure, structure-derived properties and location-dependent proteolytic actions. We depict CatB action within lysosome and its important roles in lysosomal biogenesis, lysosomal homeostasis and autophagy rendering this protease a key player in orchestrating lysosomal functions. Lysosomal leakage and subsequent escape of CatB into the cytosol lead to harmful actions, e.g. the role in activating the NLPR3 inflammasome, affecting immune responses and cell death. The second focus of this review addresses CatB functions in the kidney, i.e. the glomerulus, the proximal tubule and collecting duct with strong emphasis of its role in pathology of the respective segment. Finally, observations regarding CatB functions that need to be considered in cell culture will be discussed. In conclusion, CatB a physiologically important molecule may, upon aberrant expression in different cellular context, become a harmful player effectively showing its teeth behind its smile.

Drug-Induced Acute Kidney Injury

Medications are a common cause of AKI especially for patients admitted to hospital wards and the intensive care unit. Although drug-related kidney injury occurs through different mechanisms, this review will focus on three specific types of tubulointerstitial injury. Direct acute tubular injury develops from several medications, which are toxic to various cellular functions. Their excretory pathways through the proximal tubules contribute further to AKI. Drug-induced AKI may also develop through induction of inflammation within the tubulointerstitium. Medications can elicit a T cell-mediated immune response that promotes the development of acute interstitial nephritis leading to AKI. Although less common, a third pathway to kidney injury results from the insolubility of drugs in the urine leading to their precipitation as crystals within distal tubular lumens, causing a crystalline-related AKI. Intratubular obstruction, direct tubular injury, and localized inflammation lead to AKI. Clinicians should be familiar with the pathogenesis and clinical-pathologic manifestations of these forms of kidney injury. Prevention and treatment of AKI relies on understanding the pathogenesis and judiciously using these agents in settings where AKI risk is high.

Acute Kidney Injury in Septic Patients Treated by Selected Nephrotoxic Antibiotic Agents-Pathophysiology and Biomarkers-A Review

Acute kidney injury is a common complication in critically ill patients with sepsis and/or septic shock. Further, some essential antimicrobial treatment drugs are themselves nephrotoxic. For this reason, timely diagnosis and adequate therapeutic management are paramount. Of potential acute kidney injury (AKI) biomarkers, non-protein-coding RNAs are a subject of ongoing research. This review covers the pathophysiology of vancomycin and gentamicin nephrotoxicity in particular, septic AKI and the microRNAs involved in the pathophysiology of both syndromes. PubMED, UptoDate, MEDLINE and Cochrane databases were searched, using the terms: biomarkers, acute kidney injury, antibiotic nephrotoxicity, sepsis, miRNA and nephrotoxicity. A comprehensive review describing pathophysiology and potential biomarkers of septic and toxic acute kidney injury in septic patients was conducted. In addition, five miRNAs: miR-15a-5p, miR-192-5p, miR-155-5p, miR-486-5p and miR-423-5p specific to septic and toxic acute kidney injury in septic patients, treated by nephrotoxic antibiotic agents (vancomycin and gentamicin) were identified. However, while these are at the stage of clinical testing, preclinical and clinical trials are needed before they can be considered useful biomarkers or therapeutic targets of AKI in the context of antibiotic nephrotoxicity or septic injury.

Carbon monoxide: An emerging therapy for acute kidney injury

Treating acute kidney injury (AKI) represents an important unmet medical need both in terms of the seriousness of this medical problem and the number of patients. There is also a large untapped market opportunity in treating AKI. Over the years, there has been much effort in search of therapeutics with minimal success. However, over the same time period, new understanding of the underlying pathobiology and molecular mechanisms of kidney injury have undoubtedly helped the search for new therapeutics. Along this line, carbon monoxide (CO) has emerged as a promising therapeutic agent because of its demonstrated cytoprotective, and immunomodulatory effects. CO has also been shown to sensitize cancer, but not normal cells, to chemotherapy. This is particularly important in treating cisplatin-induced AKI, a common clinical problem that develops in patients receiving cisplatin therapies for a number of different solid organ malignancies. This review will examine and make the case that CO be developed into a therapeutic agent against AKI.

Excessive dietary lipid intake provokes an acquired form of lysosomal lipid storage disease in the kidney

Obesity and dyslipidaemia are features of the metabolic syndrome and risk factors for chronic kidney disease. The cellular mechanisms connecting metabolic syndrome with chronic kidney disease onset and progression remain largely unclear. We show that proximal tubular epithelium is a target site for lipid deposition upon overnutrition with a cholesterol-rich Western-type diet. Affected proximal tubule epithelial cells displayed giant vacuoles of lysosomal or autophagosomal origin, harbouring oxidised lipoproteins and concentric membrane layer structures (multilamellar bodies), reminiscent of lysosomal storage diseases. Additionally, lipidomic analysis revealed renal deposition of cholesterol and phospholipids, including lysosomal phospholipids. Proteomic profiles of renal multilamellar bodies were distinct from those of epidermis or lung multilamellar bodies and of cytoplasmic lipid droplets. Tubular multilamellar bodies were observed in kidney biopsies of obese hypercholesterolaemic patients, and the concentration of the phospholipidosis marker di-docosahexaenoyl (22:6)-bis(monoacylglycerol) phosphate was doubled in urine from individuals with metabolic syndrome and chronic kidney disease. The enrichment of proximal tubule epithelial cells with phospholipids and multilamellar bodies was accompanied by enhanced inflammation, fibrosis, tubular damage markers, and higher urinary electrolyte content. Concomitantly to the intralysosomal lipid storage, a renal transcriptional response was initiated to enhance lysosomal degradation and lipid synthesis. In cultured proximal tubule epithelial cells, inhibition of cholesterol efflux transport or oxysterol treatment induced effects very similar to the in vivo situation, such as multilamellar body and phospholipid amassing, and induction of damage, inflammatory, fibrotic, and lipogenic molecules. The onset of phospholipidosis in proximal tubule epithelial cells is a novel pathological trait in metabolic syndrome-related chronic kidney disease, and emphasises the importance of healthy lysosomes and nutrition for kidney well-being. Copyright © 2018 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Intracellular organelles in health and kidney disease

Subcellular organelles consist of smaller substructures called supramolecular assemblies and these in turn consist of macromolecules. Various subcellular organelles have critical functions that consist of genetic disorders of organelle biogenesis and several metabolic disturbances that occur during non-genetic diseases e.g. infection, intoxication and drug treatments. Mitochondrial damage can cause renal dysfunction as ischemic acute renal injury, chronic kidney disease progression. Moreover, mitochondrial dysfunction is an early event in aldosterone-induced podocyte injury and cardiovascular disease due to oxidative stress in chronic kidney disease. Elevated production of reactive oxygen species could be able to activate NLRP3 inflammasome representing new deregulated biological machinery and a novel therapeutic target in hemodialysis patients. Peroxisomes are actively involved in apoptosis and inflammation, innate immunity, aging and in the pathogenesis of age related diseases, such as diabetes mellitus and cancer. Peroxisomal catalase causes alterations of mitochondrial membrane proteins and stimulates generation of mitochondrial reactive oxygen species. High concentrations of hydrogen peroxide exacerbate organelles and cellular aging. The importance of proper peroxisomal function for the biosynthesis of bile acids has been firmly established. Endoplasmic reticulum stress-induced pathological diseases in kidney cause glomerular injury and tubulointerstitial injury. Furthermore, there is a link between oxidative stress and inflammations in pathological states are associated with endoplasmic reticulum stress. Proteinuria and hyperglycemia in diabetic nephropathy may induce endoplasmic reticulum stress in tubular cells of the kidney. Due to the accumulation in the proximal tubule lysosomes, impaired function of these organelles may be an important mechanism leading to proximal tubular toxicity.

Previous aminoglycoside use and acute kidney injury risk in non-critically ill children

OBJECTIVES

Aminoglycosides (AG) are a group of bactericidal antibiotics with nephrotoxic effects that are commonly used in the treatment of hospitialized children. We have examined previous AG treatment as a risk factor for acute kidney injury (AKI) during current AG treatment.

STUDY DESIGN

We performed a retrospective cohort study of children ranging in age from 1 month to 18 years who were treated with AG between October 2008 and April 2012 at Montreal's Children's Hospital. Children for whom no serum creatinine data (SCr) were available and those with baseline renal disease were excluded from the analysis. Main exposures were prior AG use (number and hours of prior treatments) and time since last AG treatment. The main outcome was AKI, defined on the basis of the Kidney Disease: Improving Global Outcomes guidelines. Logistic regression was used to examine exposure-outcome associations.

RESULTS

AG treatments episodes with Stage 1, 2, and 3 AKI, respectively, were associated with a median of 98 [interquartile range (IQR) 339], 231 (IQR 688), and 111 (IQR 505) h of prior AG treatment, respectively, versus non-AKI (median 0, IQR 54 h) (p < 0.0001). AKI episodes were associated with a mean (± standard deviation) of 1.5 ± 1.8 AG treatments in the previous 6 months, versus 0.9 ± 1.6 AG treatments for non-AKI. The number of AG-treatment days during the preceding 6 months [adjusted odds ratio (adjOR) 1.04, 95 % confidence interval (CI) 1.03-1.06; p < 0.001], younger age (adjOR 0.96, 95 % CI 0.93-0.99; p = 0.009), admission to hematology-oncology department (adjOR 3.88, 95 % CI 2.17-6.96; p < 0.001), and tobramycin use (adjOR 1.77, 95 % CI 1.04-3.02; p = 0.04) were independently associated with AKI. Episodes with Stage 1 and 2 AKI were associated with fewer days since last treatment compared to non-AKI treatment (p < 0.02 and p < 0.005, respectively; Mann-Whitney test).

CONCLUSIONS

Based on these results, prior AG treatment is a risk factor for AKI and should be considered when dosing and monitoring hospitalized children being treated with AG.

TMBIM6 (transmembrane BAX inhibitor motif containing 6) enhances autophagy and reduces renal dysfunction in a cyclosporine A-induced nephrotoxicity model

Cyclosporine A (CsA) is widely used as an immunosuppressor in transplantation. Previous studies reported that CsA induces autophagy and that chronic treatment with CsA results in accumulation of autophagosomes and reduced autophagic clearance. Autophagy is a prosurvival process that promotes recovery from acute kidney injury by degrading misfolded proteins produced in the kidney. In the present study, we used TMBIM6-expressing HK-2, human kidney tubular cells (TMBIM6 cells) and Tmbim6 knockout (tmbim6(-/-)) mice. When exposed to CsA, the TMBIM6 cells maintained autophagy activity by preventing autophagosome accumulation. With regard to signaling, PRKKA/AMPK phosphorylation and mechanistic target of rapamycin (serine/threonine kinase) complex 1 (MTORC1) expression and its downstream target TFEB (transcription factor EB), a lysosome biogenesis factor, were regulated in the TMBIM6 cells. Lysosomal activity was highly increased or stably maintained in the presence of TMBIM6. In addition, treatment of tmbim6(-/-) mice with CsA resulted in increased autophagosome formation and decreased lysosome formation and activity. We also found that tmbim6(-/-) mice were susceptible to CsA-induced kidney injury. Taken together, these results indicate that TMBIM6 protects against CsA-induced nephrotoxicity both in vitro and in vivo by inducing autophagy and activating lysosomes.

Acute kidney injury: not just acute renal failure anymore?

Until recently, no uniform standard existed for diagnosing and classifying acute renal failure. To clarify diagnosis, the Acute Dialysis Quality Initiative group stated its consensus on the need for a clear definition and classification system of renal dysfunction with measurable criteria. Today the term acute kidney injury has replaced the term acute renal failure, with an understanding that such injury is a common clinical problem in critically ill patients and typically is predictive of an increase in morbidity and mortality. A classification system, known as RIFLE (risk of injury, injury, failure, loss of function, and end-stage renal failure), includes specific goals for preventing acute kidney injury: adequate hydration, maintenance of renal perfusion, limiting exposure to nephrotoxins, drug protective strategies, and the use of renal replacement therapies that reduce renal injury.

Acute kidney insufficiency in the critically ill

Acute kidney insufficiency (AKI), or injury, is common in the critically ill patient. Minimal increases in serum creatinine (Scr) have been associated with greater morbidity, mortality, and hospital cost. In 2002, the Acute Dialysis Quality Initiative (ADQI) proposed a consensus definition (the RIFLE classification) which was modified after continuing evidence suggested that small changes in Scr (≥0.3 mg/dL) led to worsening outcomes. This group, known as the Acute Kidney Injury Network (AKIN), suggests 3 stages of worsening kidney function. Such definitions may aid in identifying patients at greatest risk and further the development of preventive strategies. This review will focus on the epidemiology and etiology of AKI as well as provide a mechanistic description of drug-induced AKI. In addition, a brief review of continuous renal replacement therapies is provided.

Management of aminoglycosides in the intensive care unit

Antibacterial resistance is increasing throughout the world, while the development of new agents is slowly progressing. In addition, the increasing prevalence of fluoroquinolone resistance may force many practitioners to choose an aminoglycoside agent in gram-negative regimens. Aminoglycosides are bactericidal agents with potent activity against gram-negative infections and activity against gram-positive infections when added to a cell wall active antimicrobial-based regimen. These agents may be dosed multiple times a day or consolidated as high-dose, extended-interval dosing to maximize pharmacokinetic and pharmacodynamic properties to achieve possible improved efficacy with reduced toxicity. Clinical application includes the treatment of bacteremia, endocarditis, health-care and nosocomial pneumonias, intra-abdominal infections, and others. Nephrotoxicity and ototoxicity are potential risks of aminoglycoside therapy that may be minimized with serum monitoring and short courses of therapy.

Identification of genes involved in gentamicin-induced nephrotoxicity in rats--a toxicogenomic investigation

For the application of microarray technology as an additional endpoint in toxicological studies, there is a need to understand associations between pathological processes and gene expression alterations. In the current study, we investigated gentamicin as a nephrotoxic model compound. Gene expression changes of the kidney in response to a dose of 80 mg/kg gentamicin were analyzed by using DNA microarray technology and alterations in gene expression were associated with results from conventional histopathological investigations and with the described pathomechanisms of gentamicin. Under the conditions of our experiment, the mRNA level of 211 genes were found to be deregulated by gentamicin. The gentamicin-induced affection of proximal convoluted tubules was associated with a strong up-regulation of mRNAs encoding for proteins which are used as nephrotoxicity markers in urine and plasma such as Kim-1, Osteopontin and TIMP1. Candidate marker genes for nephrotoxicity such as GATM were deregulated. Gentamicin-induced lysosomal phospholipidosis was indicated by deregulation of lysosomal located gene products such as ATP6V1D, a subunit of the lysosomal H+ transporting ATPase. Effects on glucose transport and metabolism were indicated by the down-regulation on SGLT-2 and glucose-6-phosphatase. Renal cell apoptosis was indicated by up-regulated genes as TP53 and BAX. The role of oxidative stress in gentamicin toxicity was reflected by deregulation of transferrin receptor and heme oxygenase. The results of the study show the potential of microarray technology to study a complex mechanism of toxicity in a single study.

An overview of drug-induced acute kidney injury

The complex nature of critical illness often necessitates the use of multiple therapeutic agents, many of which may individually or in combination have the potential to cause renal injury. The use of nephrotoxic drugs has been implicated as a causative factor in up to 25% of all cases of severe acute renal failure in critically ill patients. Acute tubular necrosis is the most common form of renal injury from nephrotoxin exposure, although other types of renal failure may be seen. Given that this is a preventable cause of a potentially devastating complication, a comprehensive strategy should be used to avoid nephrotoxicity in critically ill patients including: accurate estimation of pre-existing renal function using serum creatinine-based glomerular filtration rates, avoidance of nephrotoxins if possible, ongoing monitoring of renal function, and immediate discontinuation of suspected nephrotoxins in the event of renal dysfunction.

Comparison of kidney injury molecule-1 and other nephrotoxicity biomarkers in urine and kidney following acute exposure to gentamicin, mercury, and chromium

Sensitive biomarkers are needed to detect kidney injury at the earliest stages. The objective of this study was to determine whether the appearance of kidney injury molecule-1 (Kim-1) protein ectodomain in urine and kidney injury molecule-1/hepatitis A viral cellular receptor-1 (Kim-1/Havcr1) gene expression in kidney tissue may be more predictive of renal injury after exposure to nephrotoxicants when compared to traditionally used biomarkers. Male Sprague-Dawley rats were injected with a range of doses of gentamicin, mercury (Hg; HgCl2), or chromium (Cr; K2Cr2O7). The results showed that increases in urinary Kim-1 and kidney Kim-1/Havcr1 gene expression paralleled the degree of severity of renal histopathology and were detected at lower doses of nephrotoxicants when compared to blood urea nitrogen (BUN), serum creatinine, and urinary N-acetyl-beta-D-glucosaminidase (NAG). In a time course study, urinary Kim-1 was elevated within 24 h after exposure to gentamicin (100 mg/kg), Hg (0.25 mg/kg), or Cr (5 mg/kg) and remained elevated through 72 h. NAG responses were nephrotoxicant dependent with elevations occurring early (gentamicin), late (Cr), or no change (Hg). At 72 h, after treatment with any of the three nephrotoxicants, there was increased Kim-1 immunoreactivity and necrosis involving approximately 50% of the proximal tubules; however, only urinary Kim-1 was significantly increased, while BUN, serum creatinine, and NAG were not different from controls. In rats treated with the hepatotoxicant galactosamine (1.1 mg/kg), serum alanine aminotransferase was increased, but no increase in urinary Kim-1 was observed. Urinary Kim-1 and kidney Kim-1/Havcr1 expression appear to be sensitive and tissue-specific biomarkers that will improve detection of early acute kidney injury following exposure to nephrotoxic chemicals and drugs.

Effect of cyclophosphamide treatment on selected lysosomal enzymes in the kidney of rats

The anti-cancer drug cyclophosphamide (CYP) is nephrotoxic besides being urotoxic thereby limiting its clinical utility. Since the nephrotoxicity of CYP is less common compared to its urotoxicity, not much importance has been given for the study of mechanism of CYP-induced nephrotoxicity. The aim of the present study is to investigate the possible role of lysosomal enzymes in CYP-induced renal damage. Adult female Wistar rats weighing 200-250 g were used for the study. The rats were administered single-intraperitoneal injection of CYP at the dose of 150 mg/kg body wt and sacrificed at various time intervals 6, 16 or 24 h after the dose of CYP. The control rats were administered saline alone. Nephrotoxicity was assessed by measuring plasma creatinine and urea and histopathology of the kidney. The kidney was weighed and used for the assay of lysosomal enzymes namely acid phosphatase, beta-glucuronidase and N-acetylglucosaminidase and total protein content. Histologically, the CYP-treated rat kidneys showed progressive renal damage with increase in time after treatment. Glomerular nephritis, cortical tubular vacuolization and interstitial edema were observed in the CYP-treated rats. Surprisingly, a significant drastic decrease (instead of an increase) in the activities of lysosomal enzymes was observed in the kidneys of CYP-treated rats at 16 and 24 h as compared with the control. A highly significant increase (270%) in protein content was observed in the kidneys of the CYP-treated rats as compared with the control. Decrease in the activities of lysosomal protein digestive enzymes may contribute to CYP-induced renal damage. The accumulation of abnormal amounts of the protein in the kidney may be due at least in part to defect in lysosomal enzyme activity and contribute to renal damage.

Protective Effect of L-Arginine Intake on the Impaired Renal Vascular Responses in the Gentamicin-Treated Rats

The purpose of this study was to investigate the effect of gentamicin (100 mg/kg/day, i.p.) treatment on endothelium-dependent and -independent vasodilation in isolated perfused rat kidney, and the effect of amino acid L-arginine (in the drinking water, 2.25 g/l) on renal dysfunction induced by gentamicin. When gentamicin-treated groups were compared with the control group, it was observed that BUN and creatinine levels increased significantly. Also, the relaxant responses induced by acetylcholine, sodium nitroprusside and pinacidil decreased. Histopathological examination indicated acute tubular necrosis in this group. In animals treated with gentamicin together with L-arginine, there was a significant amelioration in the BUN and creatinine levels. The vasodilator responses were similar to those of the control group. Histopathological examination indicated only hydropic degeneration in tubular epithelium of kidney. Co-administration of L-NG-nitroarginine methyl ester (L-NAME) (112.5 mg/l), an inhibitor of nitric oxide synthase, and L-arginine to rats treated with gentamicin did not change the protective effect of L-arginine. In rats receiving L-NAME alone, the level of BUN and creatinine and vasodilation to acetylcholine were not significantly different when compared to those of the control group, while relaxant responses to sodium nitroprusside and pinacidil were increased. These results suggest that gentamicin leads to an impairment in vascular smooth muscle relaxation in addition to acute tubular necrosis in the rat kidney. Supplementation of L-arginine has an important protective effect on gentamicin-induced nephropathy.

Prediction of potential toxicity and side effect protein targets of a small molecule by a ligand-protein inverse docking approach

Determination of potential drug toxicity and side effect in early stages of drug development is important in reducing the cost and time of drug discovery. In this work, we explore a computer method for predicting potential toxicity and side effect protein targets of a small molecule. A ligand-protein inverse docking approach is used for computer-automated search of a protein cavity database to identify protein targets. This database is developed from protein 3D structures in the protein data bank (PDB). Docking is conducted by a procedure involving multiple conformer shape-matching alignment of a molecule to a cavity followed by molecular-mechanics torsion optimization and energy minimization on both the molecule and the protein residues at the binding region. Potential protein targets are selected by evaluation of molecular mechanics energy and, while applicable, further analysis of its binding competitiveness against other ligands that bind to the same receptor site in at least one PDB entry. Our results on several drugs show that 83% of the experimentally known toxicity and side effect targets for these drugs are predicted. The computer search successfully predicted 38 and missed five experimentally confirmed or implicated protein targets with available structure and in which binding involves no covalent bond. There are additional 30 predicted targets yet to be validated experimentally. Application of this computer approach can potentially facilitate the prediction of toxicity and side effect of a drug or drug lead.

Cyclosporine A-induced toxicity in two renal cell culture models (LLC-PK1 and MDCK)

Renal damage caused by therapeutic treatment with cyclosporine A has been well documented. Clinical experiences have shown that cyclosporine A nephrotoxicity is determined by interstitial fibrosis with tubular atrophy. However, the exact mechanism by which this drug causes nephrotoxicity has not yet been clarified. This study used an in vitro model in an attempt to identify the cellular mechanisms underlying kidney cyclosporine A damage. We used two cell lines with the characteristics of proximal and distal tubule cells (pig kidney proximal tubular epithelial cell line [LLC-PK1] and Madin-Darby canine kidney cell line [MDCK]. The cell lines were treated with cyclosporine A for 24 h. After the treatment, the cells were stained with Trypan Blue to estimate cell viability and processed by histochemical reactions to evaluate their cellular metabolism. Four enzymes (acid phosphatase, alkaline phosphatase, lactate dehydrogenase and succinate dehydrogenase) were considered. The cell viability assay showed that the LLC-PK1 cell line was more sensitive to cyclosporine A than MDCK. Remarkably, the LLC-PK1 cells disappeared with cyclosporine A treatment. As for the hydrolytic enzymes, only acid phosphatases showed an increased positivity in the treated LLC-PK1 cells. Similarly, lactate dehydrogenase showed a different activity histochemically. No statistically significant alterations were observed in the succinate dehydrogenase reaction. The cyclosporine A-treated MDCK cell lines did not show any difference in either their hydrolytic or succinate dehydrogenase enzyme positivity with respect to the control line. In contrast, there was a significant increase in lactate dehydrogenase activity. This study allowed the possible mechanism of cyclosporine A-induced damage in renal tubular cells to be evaluated. The enzymatic changes happened rapidly (during the 24 h of treatment), suggesting that this alteration was one of the steps by which cyclosporine A induced toxicity. Moreover, since acid phosphatase is a marker of protein catabolism, the variation in the activity of this enzyme, in the LLC-PK1 line only, showed that cyclosporine can induce alterations leading to cellular toxicity. The modifications in lactate dehydrogenase activity, in both lines, suggested that this drug caused cell stress, inducing the production of lactic acid from glucose in the presence of oxygen. In conclusion, cyclosporine A treatment may force LLC-PK1 and MDCK cells to use anaerobic glycolysis preferentially. Further, these enzyme alterations may represent an epiphenomenon or a consequence of cyclosporine A toxicity.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

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

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

Pathophysiology and management of renal insufficiency in the perioperative and critically ill patient

Acute renal failure remains a common, devastating complication of the postoperative period and in the critically ill patient. The most common cause is the progression of prerenal insufficiency to ATN. Despite improved understanding of the pathogenic mechanisms, including impaired hemodynamic autoregulation, medullary hypoxia, and proximal tubular obstruction and transtubular backleak, the treatment, to date, remains largely supportive. Avoidance by ensuring hemodynamic stability, with provision of adequate renal perfusion, provides the best means for minimizing the complications of this organ dysfunction.

Renal catabolism of advanced glycation end products: the fate of pentosidine

Advanced glycation end products (AGEs) generated through the Maillard reaction significantly alter protein characteristics. Their accumulation has been incriminated in tissue injury associated with aging, diabetes, and renal failure. However, little is known about their clearance from the body. The present study delineates the catabolic pathway of a well-defined AGE product, pentosidine. Synthesized pentosidine given intravenously in rats with normal renal function was rapidly eliminated from the circulation through glomerular filtration, but was undetectable in the urine by chemical analysis. Immunohistochemistry with anti-pentosidine antibody disclosed that pentosidine accumulated transiently in the proximal renal tubule one hour after its administration, but had disappeared from the kidney at 24 hours. After an intravenous load of radiolabeled pentosidine, radioactivity peaked in the kidney at one hour and subsequently decreased, whereas it rose progressively in the urine. Over 80% of the radioactivity was recovered in the 72-hour collected urine. However, only 20% of urine radioactivity was associated with intact pentosidine chemically or immunochemically. In gentamicin-treated rats with tubular dysfunction, up to 30% of the pentosidine load was recovered as intact pentosidine in the urine. The present study suggests that free pentosidine (and possibly other AGEs) is filtered by renal glomeruli, reabsorbed in the proximal tubule where it is degraded or modified, and eventually excreted in the urine. Kidney thus plays a key role in pentosidine disposal.

Concentrations of lysosomal cysteine proteases are decreased in renal cell carcinoma compared with normal kidney

Renal cell carcinoma contains significantly lower concentrations of the lysosomal cysteine proteases, cathepsins B, C, H, L and S, than does normal kidney, as shown by several methods, such as activity determination, enzyme-linked immunosorbent assay, immunoblotting and immunohistochemistry. The same low levels of enzyme activity and concentration have been determined in renal cell carcinoma metastases in the lung. Our results on the decreased concentration of cysteine peptidases at the protein level would seem to conflict with earlier results on an increased concentration of the cathepsin L mRNA in renal cell carcinoma.

N-acetyl-beta-D-glucosaminidase (NAG) isoenzymes in primary cultures of rabbit kidney proximal tubule cells: a cellular model for studies on nephrotoxicity?

N-Acetyl-beta-D-glucosaminidase (NAG) isoenzyme profile in primary cultures of rabbit kidney proximal tubule cells was studied. Confluent cells had high levels of NAG activity, but ion exchange chromatography showed that the NAG isoenzyme profile in cultured cells was different from that of rabbit renal cortex homogenates and freshly isolated cells. Confluent cultured cells contained an atypical acidic isoform, absent in homogenates and freshly isolated cells in which the predominant isoform is NAG-A (a heterodimer alpha beta). The fact that this atypical isoform was able to hydrolyse the synthetic substrate 4-methylumbelliferyl-beta-N-acetylglucosaminide-6-sulphate indicated that it probably was an alpha-subunit homodimer. These results suggest subunit rearrangement within NAG polypeptide chains linked to down-regulation of beta-subunit production in cultured rabbit proximal cells. The change in isoenzyme profile in cultured cells may make it difficult to use primary cultures of rabbit proximal tubule cells to establish correlations between in vitro and in vivo studies using NAG isoenzymes as a nephrotoxicity index, as illustrated by the effects of 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.

Cultured proximal cells derived from transgenic mouse provide a model to study drug toxicity

The effects of gentamicin on N-acetyl-beta-D-glucosaminidase (NAG) and acid phosphatase (AcP), two lysosomal enzymes present in proximal renal tubule cells, were studied in the PKSV-PCT cell line derived from proximal convoluted tubules from the kidney of a transgenic mouse carrying SV40 large T antigen under the control of the L-type pyruvate kinase gene. Gentamicin (400 micrograms/ml for 72 hr) did not alter cell viability, but significantly reduced cell growth and favored the formation of myeloid bodies. Gentamicin (50 to 800 micrograms/ml for 72 hr) decreased in a dose-dependent manner the cellular NAG in PKSV-PCT cells and stimulated its secretion by 20 to 60%. Chloroquine (50 to 100 microns) and ammonium chloride (NH4Cl, 30mM), two lysosomotropic amines known to stimulate the secretion of lysosomal enzymes in fibroblasts and macrophages, also stimulated secreted NAG in PKSV-PCT cells. However, the effect of chloroquine was less marked in PKSV-PCT cells than in cultured mouse 3T3 fibroblasts. Gentamicin induced lysosomal alkalinization but, in contrast to chloroquine and NH4Cl, the aminoside strongly stimulated the secretion of AcP. The secretion induced by gentamicin was nonpolarized, since the percentage of secreted NAG significantly increased from both the apical and basal sides of PKSV-PCT cells grown on permeable filters. Thus, these data suggest that gentamicin alters the secretion of NAG and AcP by a non-specific pathway and indicate that the PKSV-PCT cell line is a suitable system to examine the cellular action of drugs in kidney proximal tubule cells.

Plasminogen deficiency causes severe thrombosis but is compatible with development and reproduction

Plasminogen (Plg)-deficient mice were generated to define the physiological roles of this key fibrinolytic protein and its proteolytic derivatives, plasmin and angiostatin, in development, hemostasis, and reproduction. Plg-/- mice complete embryonic development, survive to adulthood, and are fertile. There is no evidence of fetal loss of Plg-/- mice based on the Mendelian pattern of transmission of the mutant Plg allele. Furthermore, embryonic development continues to term in the absence of endogenous, sibling-derived, or maternal Plg. However, Plg-/- mice are predisposed to severe thrombosis, and young animals developed multiple spontaneous thrombotic lesions in liver, stomach, colon, rectum, lung, pancreas, and other tissues. Fibrin deposition in the liver was a uniform finding in 5- to 21-week-old mice, and ulcerated lesions in the gastrointestinal tract and rectal tissue were common. A remarkable finding, considering the well-established linkage between plasmin and the proteolytic activation of plasminogen activators, was that the level of active urokinase-type plasminogen activator in urine was unaffected in Plg-/- mice. Therefore, Plg plays a pivotal role in fibrinolysis and hemostasis but is not essential for urokinase proenzyme activation, development, or growth to sexual maturity.

Inhibition by lithium of neomycin-induced release of N-acetyl-beta-glucosaminidase in the rat heart

The effects of neomycin, lithium and concurrent therapy of these drugs on subcellular distribution of lysosomal enzyme, N-acetyl-beta-glucosaminidase (NAG) in the heart was studied. Released activity of NAG was used as a marker for assessing myocardial lysosomal integrity. The activity of NAG was determined in non-sedimentable and sedimentable fractions after centrifugation of the tissue extracted for assessment of the subcellular distribution of the lysosomal enzyme. Daily intraperitoneal injection of 100 mg/kg/day of neomycin increased the ratio of the non-sedimentable activity (free) to the non-sedimentable plus sedimentable activities (total) of NAG. Daily intraperitoneal injection of lithium decreased the total activity of NAG but did not affect the ratio of free: total activities of the enzyme. Lithium in doses of 2 and 4 mM/kg/day one hour prior to neomycin reduced the neomycin-induced enhancement of the ratio of free: total activity of NAG. Neomycin like other aminoglycosides altered the acidic phospholipid metabolism in lysosomal membranes and/or impairment of some important lysosomal functions. In this regard, the protective effects of lithium may be due to interference of this ion with phosphoinositide cycle.

Side-effects of peptidoglycan monomer (PGM) treatment in mice

The influence of single (4 mg/mouse) and multiple (1 mg/mouse per day for 5 consecutive days) injections of PGM on some hepatic enzymes, lipid peroxide generation in serum and liver, sialic acid concentration in serum and spleen and hepatic lysosomal membrane permeability was investigated. The studies performed showed that a single injection of PGM in vivo changed temporarily the permeability of lysosomal membranes, lipid peroxidation products and sialic acid concentration, and when administered in vitro modulated superoxide anion production and did not affect the activity of lysosomal membrane enzymes. Multiple injections of PGM did not cause significant changes in the examined parameters. Although the metabolic changes were time-limited and from the toxicological point of view, provoked transient effects, the results obtained may be of importance when using PGM in combined chemo-immunotherapy.

Gentamicin administered during gestation alters glomerular basement membrane development

Gentamicin during gestation alters glomerular basement membrane development. A drug-induced nephrotoxicity was described for neonates after gentamicin was given intraperitoneally to pregnant Wistar rats; glomerular alterations and changes in permselectivity were important. We investigated the ultrastructure of the glomerular basement membrane (GBM), the arrangement of anionic sites, and the urinary proteins at two ages, with 1-day- and 12-month-old control and prenatally exposed animals. For neonates, the pattern of glomerular differentiation was similar, anionic sites were made of heparan sulfate proteoglycans, and the GBM had the same total thickness in both groups. After transplacental gentamicin exposure, the lamina densa was larger; the laminae rarae were thinner; the density of anionic sites was increased; the levels of hydroxyproline, sulfate, and hexuronic acid in the kidney were increased; and the immunoelectrophoresis of urinary proteins was abnormal. For adults, prenatal exposure to gentamicin led to altered juxta-medullary glomeruli with a larger GBM and abundant anionic sites, especially in the lamina densa, and to a protein excretion different from that of controls. Thus, gentamicin administered during pregnancy leads to permanent alterations of the GBM with modifications of both the layers and the anionic sites, possibly because of a perturbed protein metabolism. These altered glomeruli are at risk during life and could be the starting point for a kidney disease.

The effect of Met-enkephalin on mice liver lysosomes

The unsedimentable activities of acid phosphatase (AP) and beta-glucosidase (BG), from mice liver lysosomes significantly increased 6 h after a single i/p injection of Met-enkephalin (MENK). The activity of AP in the serum at the same time remained unchanged. Multiple injections of MENK (8 x 10 mg/kg) induced a significant decrease in AP activity in the serum and no change in the unsedimentable activities of AP or BG. MENK did not elicit any significant extracellular release of lactate dehydrogenase (LDH) either, indicating that, under the experimental conditions described, the cells remained intact. Other parameters, such as the activities of AP and BG in the liver and total sialic acid content in the serum and spleen remained unaltered. Moreover, MENK in concentrations of 10(-12) M, 10(-8) M, 10(-6) M or 10(-4) M did not change the activities of the lysosomal enzyme markers AP or BG in vitro. These data indicate far less pronounced transient effects of MENK on lysosomal membranes and enzymes compared to Leu-enkephalin which may be relevant for the use of MENK in combined chemo-immunotherapy.