Nephrotoxic effects of aminoglycoside treatment on renal protein reabsorption and accumulation

Gentamicin nephrotoxicity in animals: Current knowledge and future perspectives

Due to high relative blood flow the kidney is prone to drug-induced damage. Aminoglycoside type antibiotic gentamicin is one of the leading cause of drug-induced nephrotoxicity. In recent years gentamicin nephrotoxicity is significantly reduced by shifting to once daily dosage as well as by eliminating known risk factors. Application of gentamicin is still related to serious side effects which are reported more often compared to other antibiotics. Because gentamicin is still heavily used and is highly efficient in treating infections, it is important to find mechanisms to reduce its nephrotoxicity. This aim can only be achieved through better understanding of kidney metabolism of gentamicin. This problem has been extensively researched in the last 20 years. The experimental results have provided evidence for almost complete understanding of mechanisms responsible for gentamicin nephrotoxicity. We now have well described morphological, biochemical and functional changes in kidney due to gentamicin application. During the years, this model has become so popular that now it is used as an experimental model for nephrotoxicity per se. This situation can mislead an ordinary reader of scientific literature that we know everything about it and there is nothing new to discover here. But quite opposite is true. The precise and complete mechanism of gentamicin nephrotoxicity is still point of speculation and an unfinished story. With emerge of new and versatile technics in biomedicine we have an opportunity to reexamine old beliefs and discover new facts. This review focuses on current knowledge in this area and gives some future perspectives.

Influence of the infusion rate on disposition of netilmicin in the isolated rat perfused kidney

A study of the disposition of netilmicin in the isolated rat kidney was carried out in order to establish the influence of the infusion rate on the drug profile in this tissue. A dose of 800 microg administered as a bolus injection or at infusion times of 5, 7.5 and 10 min, respectively, was injected through the afferent cannula into the isolated kidney. Analysis of outflow curves was carried out using different kinetic approaches. Comparison of statistical moments and derived parameters pointed to changes in the distribution process with the infusion rate. In contrast, elimination remained constant, since the extraction coefficient and relative area under the curve values did not change with the infusion rate, although the MTT (mean transit time) and distribution volume decreased for the longest infusion times. The UDF (unit disposition function) profiles were not superimposed for the different infusion rates and combined with the results of the kinetic analysis revealed that the behaviour of netilmicin in the isolated kidney depends on infusion rate. The apparent partition coefficients in renal cortex and medulla showed higher values for the slower perfusion rates. Yet, a progressive decrease in the absolute amount of netilmicin was predicted in the tubular epithelium compartment whereas the residence time tended to increase. The latter phenomenon could account for the higher aminoglycoside nephrotoxicity reported when these drugs are administered over longer infusion times.

Prevention of acute renal failure

Acute renal failure (ARF) induced by therapeutic agents that are nephrotoxic (e.g., gentamicin, cisplatin, amphotericin, and nonsteroidal anti-inflammatory drugs) or hypotension associated with anesthesia and surgery unfortunately occur with some regularity in small animal practice. Several clinical conditions have been identified that can increase the risk of hospital-acquired ARF in dogs. Recognition of these risk factors allows the clinician to assess the risk/benefit ratio for various drugs and/or procedures. Additionally, initiating protective measures and increasing the monitoring of renal function in those patients that require potentially harmful treatment may decrease the incidence of hospital-acquired ARF.

Effects of dietary protein conditioning on gentamicin pharmacokinetics in dogs

Eighteen, six-month-old male Beagles with normal renal function were randomly divided into three groups of 6. Each group was fed a diet that was similar except for protein content (high = 26%, medium = 13% and low = 9%, all on an as fed basis) throughout the experimental period. After a 21 day dietary protein conditioning period (including a terminal 2 day testing period), gentamicin was administered at a dosage of 10 mg/kg q. 8 h for 8 days. The first dose on days 1 and 7 was administered i.v. and all others were given i.m. Pharmacokinetic parameters were determined using blood samples collected over an 8 h period following the i.v. dose on day 1. The elimination rate constant was calculated on days 1 and 7. The data best fit a two-compartment open model for all dogs on day 1. The volume of distribution was higher and the clearance greater in the high protein group compared to the other two groups. No difference was found in the rate of elimination between days 1 and 7 for the high protein group; however, in the medium and low protein groups the rate of elimination decreased over the 7 days of treatment. Therefore, high dietary protein prior to and during gentamicin administration induced faster gentamicin clearance and a larger volume of distribution and preserved the ability to eliminate gentamicin in dogs with normal renal function.

Roles of hemodynamic and tubular factors in gentamicin-mediated nephropathy

Gentamicin (GM) often causes polyuric acute renal failure (ARF) in humans and animals. GM-mediated ARF in rats was accompanied with activated renin-angiotensin system, increased renal endothelin content, and enhanced lipid peroxidation. Suppression of the renin-angiotensin activity by desoxycorticosterone acetate and saline drinking, and treatment with superoxide dismutase attenuated the GM-induced decline in whole-kidney GFR with well-maintained RBF but did not reduce the severity of tubular necrosis. On the other hand, treatment with dimethylthiourea, a hydroxyl radical scavenger, attenuated the GM-mediated decline in GFR and lessened tubular necrosis but did not ameliorate the reduction in RBF. These data suggest contributions of both vascular and tubular factors to the GM-induced decline in GFR in rats. However, relative importance of these factors probably differs with different doses of the agent.

Nephrotoxicity of acyclovir and cis-diamminedichloroplatinum(II)--effect of co-administration in rats

The effect of co-administration of acyclovir and cis-diamminedichloroplatinum(II) (cisplatin) on nephrotoxicity in male Wistar rats was investigated. Animals received acyclovir (15 mg/kg body weight, s.c., three times per day for 5 days) or cisplatin (5 mg/kg body weight, i.p., one single injection) or a combination of both drugs. Acyclovir plasma levels were determined after one single acyclovir s.c. injection. Urines were monitored for volume, pH, osmolality and excretion of N-acetyl-beta-D-glucosaminidase (NAG), lysozyme and total protein. Concentrations of blood urea nitrogen and plasma creatinine were determined on day 6. Renal cortical slices were monitored to assess the accumulation of weak organic bases (tetraethylammonium) and acids (p-aminohippurate). Cisplatin induced a marked increase in the excretion of NAG, lysozyme and total protein and an increase in urine volume, plasma creatinine and blood urea nitrogen. Urine osmolality and accumulation of p-aminohippurate were depressed by cisplatin. Acyclovir treatment alone caused no significant symptoms of nephrotoxicity. Co-administration did not impair renal function more than cisplatin treatment alone, excepting a slight rise in lysozyme excretion on day 6. Short-term antiviral therapy with acyclovir, concomitant to cisplatin treatment, may bring, if at all, a slightly increased nephrotoxic risk.

Proteinuria: changes and mechanisms in toxic nephropathies

During the last few decades, considerable progress has been made in the understanding of the pathophysiological mechanisms of proteinuria. A great variety of hemodynamic or biochemical mechanisms acting at different sites of the nephron have been shown to alter the renal handling and the urinary excretion of proteins. The finding which perhaps has had most practical implications is that the pattern of protein excretion quantitatively and qualitatively varies with the site and severity of renal damage. This has led to the development of a large array of methods for the identification and quantitation of specific urinary proteins. These methods have been most extensively used by toxicologists in experimental, epidemiological, or clinical studies on potentially nephrotoxic chemicals (e.g., drugs, heavy metals, solvents, etc.). The present review summarizes the current state of knowledge on the mechanisms of proteinuria and the use of urinary proteins as indicators of nephrotoxicity.

Studies on the nephrotoxicity of aminoglycoside antibiotics and protection from these effects (9): Protective effect of inositol hexasulfate against tobramycin-induced nephrotoxicity

We examined the protective effect of inositol hexasulfate (IS6) against tobramycin (TOB)-induced nephrotoxicity. In the electrophoretic analysis, TOB alone and IS6 alone were observed as single spots on the cathode and anode sides, respectively. However, in the mixture of TOB and IS6 preincubated at 37 degrees C for 3 hr, the tailing of the spots of TOB and IS6 were observed from the origin to the cathode and the anode sides, respectively, and the overlapping of the spots of TOB and IS6 was recognized at the origin. These results indicated that TOB directly interacted with IS6 in vitro. Assay of TOB binding to rat kidney brush border membranes (BBMs) indicated that IS6 inhibited the binding of TOB to BBMs through an interaction of TOB and IS6. No significant reduction in intrarenal TOB level was observed in the rats given TOB (90 mg/kg, s.c.) and IS6 (153 or 610 mg/kg, s.c.). However, the treatment of rats with a combination of TOB and IS6 reduced the degree of necrosis of renal tubular cells and also suppressed the increases in urinary protein, urinary enzyme activities, blood urea nitrogen and plasma creatinine induced by TOB. Additionally, we detected a complex of TOB and IS6 in the urine of rats given both compounds simultaneously. These results indicate that IS6 protects against TOB-induced nephrotoxicity and that the protective action of IS6 may be due to the inhibition of TOB binding to BBMs through an interaction of TOB with IS6.

Studies on the nephrotoxicity of aminoglycoside antibiotics and protection from these effects (6): A mechanism for the suppressive action of latamoxef on intrarenal tobramycin level

The mechanism by which latamoxef (LMOX) reduces intrarenal tobramycin (TOB) levels was studied. When TOB (90 mg/kg/day, s.c.) and LMOX (500 or 2000 mg/kg/day, s.c.) were given simultaneously at separate sites to rats, 20 to 30% reductions in intrarenal TOB concentration were found on the 1st and 3rd days, as compared with the results from using TOB alone. The treatment with the reaction mixture of TOB and LMOX, which was preincubated for 3 hr at 37 degrees C to form the complex of TOB and LMOX, resulted in a greater suppression of TOB level in the kidney than administration of TOB and LMOX concomitantly at separate sites. When LMOX was given to rats 0.5 or 1.5 hr before s.c. injection of TOB, there were significant reductions in intrarenal TOB concentration. However, treatment with LMOX 5 hr before, as well as 1.5 or 5 hr after TOB injection, was ineffective in reducing the accumulation of TOB in the kidney. In the rats given both drugs simultaneously, the urinary excretion pattern of TOB almost overlapped with that of LMOX. Additionally, we detected a complex of TOB and LMOX in the urine of rats given both drugs simultaneously. These results suggest that the suppressive action of LMOX on intrarenal TOB level is due to the interaction of TOB and LMOX.

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

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

Urinary excretion of beta-2-microglobulin in patients with active metabolic stone disease

The aim of the present work is to evaluate the function of the proximal tubule in patients with active metabolic stone disease (a.m.s.d.), recognizing the urinary excretion of beta-2-microglobulin (B2-M) as a sensitive marker of that function. The investigated group included 30 patients with a.m.s.d. accompanied by chronic pyelonephritis (CP) and 31 patients with a.m.s.d. without CP. The serum and urinary B2-M concentrations were estimated by radioimmunoassay. The clearance of B2-M (CB2-M) and the tubular reabsorption of B2-M (TRB2-M) were estimated. Patients with a.m.s.d. and CP showed an increased excretion of B2-M, significantly higher values of CB2-M and a significantly lower TRB2-M. The results indicate that the proximal tubular dysfunction in the group of patients with a.m.s.d. is a result of a chronic inflammatory process in the urinary tract.

Experience with brulamycin therapy in dialysed patients

Forty-two patients with chronic renal insufficiency were subjected to Brulamycin therapy to combat complications such as sepsis, infection of the lower respiratory tract (bronchopneumonia) or of the urinary tract, Cimino fistula inflammation or peritonitis when the pathogenic agent was sensitive to nothing but aminoglycosides. The proper Brulamycin dose was selected under close clinical and laboratory control so as to fit the dialysed patient and his state of impaired renal function. The various forms of dialysis have been studied to determine their Brulamycin blood level diminishing effects. Familiarity with these effects is as important as with the patient's age, sex, body weight and actual state of renal function. The results confirm the experience gained by other authors that Brulamycin treatment--in curative non-toxic doses as indicated by the blood level index--is useful against severe infectious complications in anuric patients.

Comparative study of aminoglycoside nephrotoxicity in normal rats and rats with experimental cirrhosis

Several authors have suggested that the risk of developing aminoglycoside nephrotoxicity is greater in cirrhotic patients than in the noncirrhotic population. However, this has not been confirmed by other investigators. To compare the intensity and characteristics of aminoglycoside nephrotoxicity in cirrhotic and normal rats, 31 rats with carbon tetrachloride-induced cirrhosis with ascites and 35 control rats were treated with gentamicin. Each group of rats was divided into two subgroups in order to receive 10 or 40 mg per kg per day of gentamicin, and different subsets of animals were killed on Days 4, 8 and 12 of treatment for renal histological examination and determination of renal tissue gentamicin concentration. Urine volume, osmolality, sodium excretion and N-acetyl-beta-D-glucosaminidase activity were measured daily throughout the study. Creatinine clearance and trough plasma concentration of gentamicin were determined in each animal immediately before killing. There were no significant differences between cirrhotic and control rats in relation to the magnitude of changes in urine volume, osmolality, sodium excretion and N-acetyl-beta-D-glucosaminidase activity and creatinine clearance during gentamicin administration. The values of a histopathological score semiquantitatively assessing the renal morphological changes observed by light microscopy were not significantly different in cirrhotic and control rats. In addition, similar trough plasma and renal cortical tissue concentrations of gentamicin were observed in both groups of animals. These results suggest that, in this experimental model, cirrhosis does not increase the risk for aminoglycoside nephrotoxicity.

Effects of gentamicin on the renal uptake of endogenous and exogenous protein in conscious rats

To study the effect of gentamicin on the renal uptake of proteins, Sprague-Dawley female rats were intravenously injected with solutions containing unlabeled human beta 2-microglobulin (beta 2-m), retinol-binding protein, and increasing amounts of gentamicin (from 0.063 up to 31.5 mg/kg). The concentrations of human proteins and that of endogenous beta 2-m, albumin, and IgG in the urine collected during the 2 hr following the injection were determined by immunoassays. Gentamicin transiently increased the urinary excretion of rat and human beta 2-m in a dose-dependent manner. The mean relative increase of rat beta 2-m excretion ranged from 2 at a gentamicin dose of 0.06 mg/kg up to 500 at a gentamicin dose of 31.5 mg/kg. By contrast, the urinary excretion of other proteins was only increased by a factor of 2 to 5 at the highest dose of gentamicin. The relative increase of the urinary excretion of proteins was positively correlated with the fractional reabsorption of the proteins by the rat kidney. The inhibitory effect of gentamicin on the renal uptake of protein was very similar to that observed in rats injected with polycationic proteins like lysozyme and cytochrome C. These observations, combined with the fact that gentamicin, like proteins, enters the tubular cell by adsorptive endocytosis, strongly suggest that this drug competes with proteins for common binding sites on the apical tubular membrane and for subsequent endocytosis. Furthermore, the iv injection of large amounts of gentamicin and polycationic proteins induces a lysosomal enzymuria which very likely is a manifestation of an increased exocytosis.

Comparative oto-vestibular effects in the pigmented guinea pig after dibekacin and netilmicin treatment

We treated groups of pigmented guinea pigs with either intramuscular netilmicin or dibekacin at 100 and 150 mg/kg per day for 3 weeks. Saline was used as the control solution. All animals were tested weekly for both vestibular and auditory functions. The vestibular function was evaluated by the duration of post-rotatory nystagmus (PRN) elicited by interrupting the rotation of the animal around the vertical axis; auditory function was evaluated by the threshold response for the Preyer's pinna reflex (PPR). All animals were then sacrificed and either their labyrinths or Corti organs were processed for further investigations using the scanning electron microscope (SEM). The duration of PRN decreased over the treatment period in all of the groups as a result of adaptation. However, 150 mg/kg dibekacin produced a significant decrease of the PRN responses as compared to the control and other groups. This effect also continued during the recovery period. Likewise, the PPR threshold of the animals receiving 150 mg/kg dibekacin showed a significant increase at the end of the treatments and during the recovery period, while the other dibekacin group had no significant auditory impairment. Netilmicin at both doses did not significantly affect responses following either vestibular or auditory stimulations. SEM observations demonstrated that the sensory epithelia of the labyrinths and Corti organs affected by 150 mg/kg dibekacin had great losses of stereocilia, while comparable doses of netilmicin (150 mg/kg) had only very moderate losses of stereocilia in the labyrinths but not in the Corti organs.