Gentamicin-induced nephrotoxicity: a cell biology approach

Gentamicin inhibition of Na+,K(+)-ATPase in rat kidney cells

Na,K(+)-ATPase activity is decreased in homogenized renal tissue from GM-treated rats. This study examines whether the site of the active effect of GM on Na,K(+)-ATPase activity in the kidney can be localized to the proximal convoluted tubules (PCT) where the drug is taken up and where it will produce necrosis. In rats treated with gentamicin (50 micrograms.kg-1.day-1 i.m.) for 7 days, PCT Na,K(+)-ATPase activity was reduced as compared to vehicle-treated rats but returned to control levels 7 days after treatment withdrawal. In another nephron segment, the medullary thick ascending limb of Henle (mTAL), where GM induced lesions are uncommon, Na,K(+)-ATPase activity was the same in GM- and vehicle-treated rats treatment. To study the in vitro effect of GM, dissected PCT and mTAL segments from untreated rats were preincubated for 30 min with GM 10(-3) M, a dose similar to the tissue concentration in chronically treated rats. In tubule segments that were permeabilized to allow the drug to enter the cells, GM 10(-3) M significantly inhibited Na,K(+)-ATPase activity both in PCT and mTAL. In non-permeabilized mTAL segments GM did not inhibit Na,K(+)-ATPase activity. GM inhibition of Na,K(+)-ATPase activity in permeabilized PCT segments persisted after the tubules were rinsed in GM free medium. GM does not inhibit Na,K(+)-ATPase partly purified from the renal cortex. Conclusion. Gentamicin inhibits Na,K(+)-ATPase activity in renal tubule cells when it has access to the cytoplasm. Treatment with GM will therefore cause a selective inhibition of Na,K(+)-ATPase in the proximal tubule cells.

Mild ischemia predisposes the S3 segment to gentamicin toxicity

The purpose of these studies was to determine if a functionally insignificant ischemic insult, occurring prior to gentamicin administration, enhanced gentamicin nephrotoxicity. Bilateral renal pedicle clamp studies demonstrated that 15 minutes of ischemia did not increase the plasma creatinine yet markedly enhanced gentamicin nephrotoxicity. Further studies, in uninephrectomized rats, demonstrated that following fifteen minutes of renal ischemia and four hours of reperfusion inulin clearance, FENa+ and cellular morphology were normal. This model, therefore, was used in all subsequent studies. While the plasma creatinine concentrations were normal 24 hours following 15 minutes of ischemia and only slightly increased following gentamicin administration (100 mg/kg, i.p.) gentamicin administered four hours following 15 minutes of renal ischemia resulted in significantly increased 24-hour plasma creatinine values. Light microscopic quantitation of tissue injury, performed 24 hours following experimental manipulation, was notable for S3 segment damage in the ischemia plus gentamicin group. This was not observed in either the ischemia group or the sham operated gentamicin group. Cortical gentamicin levels were elevated in the ischemia plus gentamicin group, despite similar plasma gentamicin half-lives. However, the elevation in cortical gentamicin levels was dissociated from the enhanced nephrotoxicity seen following mild ischemic injury. Taken together these data indicate that mild renal ischemia, occurring prior to gentamicin administration, greatly enhanced gentamicin nephrotoxicity with the greatest damage occurring to S3 cells.

Immediate and long-term renal effects of fetal exposure to gentamicin

Aminoglycoside antibiotics, like gentamicin, given to pregnant females cross the placenta and accumulate in the fetal kidney, which, like the adult kidney, was found to be the major site of deposition. In young guinea-pigs whose mothers were given gentamicin during the week following nephrogenesis in the fetus, nephron growth was found to be retarded temporarily. In rats whose mothers were given gentamicin during the period of fetal nephrogenesis, the final number of nephrons was reduced by about 20%. In both cases, renal development was impaired, although the concentration of gentamicin in the fetal kidney was lower than that measured in the kidney of human fetuses whose mothers had received a single injection of aminoglycoside. In rats exposed to gentamicin in utero, cellular damage of the undifferentiated and differentiating renal tissues was observed. It is, there are likely that the oligonephronia observed in animals born of gentamicin-treated mothers resulted from a direct effect of the drug at early stages of nephrogenesis. When gentamicin administration to the mother was prolonged, part of the oligonephronia observed at birth might have also resulted from fetal growth retardation, secondary to adverse effects of the drug on the mother. Providing it was not associated with fetal growth retardation, the presence of high gentamicin concentrations in the fetal kidney at late stages of nephrogenesis did not affect nephron differentiation. Long-term studies of rats born with gentamicin-induced oligonephronia showed that neither the antibiotic still present in kidney several weeks after birth, nor the injuries it caused, prevented renal growth and morphological adaptation of the nephrons to their reduced number.(ABSTRACT TRUNCATED AT 250 WORDS)

Streptomycin toxicity in primary cultures of flounder renal proximal tubule cells

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

Intracellular distribution of gentamicin within the rat kidney cortex: a cell fractionation study

The present study demonstrates that during the first 1.5-3 min after a single intraperitoneal administration of [3H]gentamicin to rats, most of the radioactivity in the kidney cortex is recovered in the cytosolic and microsomal fractions upon subcellular fractionation. Subsequently, the level of radioactivity recovered in the cytosolic fraction decreases markedly, whereas this level remains relatively unchanged in microsomes and increases somewhat in the nuclear and mitochondrial fractions. A steady state is apparently reached 13 hr after the injection. The high initial concentration of gentamicin in the cytosol may indicate that this substance is taken up to a large extent by diffusion. Such uptake is somewhat surprising, because of the polar nature of gentamicin. The small size of this drug may, however, allow it to diffuse through so-called pores and/or interaction with negatively charged phospholipids may be involved in the uptake of gentamicin. The initial total level of radioactivity recovered in microsomes after in vivo administration of [3H]gentamicin was considerably higher than in the nuclear and mitochondrial-lysosomal fractions. Furthermore, when gentamicin was added directly to kidney homogenate prepared from untreated rats, instead of being administered in vivo, this substance was still recovered in highest amounts in the total microsomal fraction. This observation may indicate that enrichment of gentamicin in the endoplasmic reticulum (or fragments thereof) reflects a special affinity of this drug for these membranes and is probably not the result of a particular in vivo process. There was no difference in the levels of radioactivity recovered in smooth and rough microsomes.(ABSTRACT TRUNCATED AT 250 WORDS)

Seasonal effects on the daily variations of gentamicin-induced nephrotoxicity

The effect on kidney damage of the season of year at which gentamicin was administered to rats was studied. Rats received a single intramuscular dose of 200 mg/kg gentamicin at four different times of the day (08.00, 14.00, 20.00 or 02.00 hours. Studies were carried out in January-February, March-April, June-July and October-November. The nephrotoxicity was assessed by the increase of three urinary enzymes: two brush border enzymes, gamma-glutamyl transferase and alanine aminopeptidase, and a lysosomal enzyme: N-acetyl-beta-D-glucosaminidase. The results show that when the injection is administered at 20.00 hours in the January-February and the October-November studies and at 08.00 hours in the March-April study and at 14.00 hours in the June-July study there is a significant increase in the excretion of these enzymes. The renal toxicity of gentamicin therefore has circadian variations as well as seasonal variations. The peak enzyme level is displaced from the start to the end of the rest period of rats depending upon the time of year.

Effects of daptomycin and vancomycin on tobramycin nephrotoxicity in rats

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

Model of gentamicin-induced nephrotoxicity and its amelioration by calcium and thyroxine

The exact mechanism of gentamicin-induced acute renal failure is presently unknown; various mechanisms have been proposed but there is no proposed commonality between them. In animals, dietary calcium loading and L-thyroxine administration have been shown to ameliorate toxicity, with again no common process. A mechanism of competitive displacement of calcium and other cations from anionic phospholipids at the plasma and organelle membrane level, resulting in a decrease in Na+ -K+ ATPase, adenylate cyclase, mitochondrial function and ATP production, protein synthesis, solute reabsorption and overall cellular function is proposed. A further proposal is dietary calcium loading and thyroxine (which increases intracellular calcium) reverse gentamicin-induced acute renal failure by increasing the calcium and solute flux, thereby competitively inhibiting the primary lesion: anionic phospholipid binding.

Reversible, hepatic, lysosomal phospholipidosis in rat induced by subchronic daily administration of trospectomycin sulfate

Trospectomycin sulfate is an experimental aminocyclitol antibiotic which has been shown previously to induce the formation of cytoplasmic lamellar bodies in rat and dog liver in subchronic experiments. The effect of repeated daily administration of trospectomycin sulfate on hepatic phospholipid levels and activities of marker enzymes for subcellular organelles was examined. Rats were treated for 30 or 90 days with 0, 50, or 250 mg/kg/day of trospectomycin sulfate prior to being killed, and another group was dosed for 90 days and then allowed to recover for 79 days prior to sacrifice. Transmission electron microscopy showed the presence of lamellar bodies in hepatocytes in both 50 and 250 mg/kg groups at 90 days but no other apparent changes in cellular morphology. Total phospholipids were increased significantly (1.6-fold) only at 90 days (P less than 0.01) and only in the 250 mg/kg group. Phosphatidylcholine, phosphatidylinositol, and two acidic lysosomal phospholipids, bis(monoacylglycero)phosphate and acylphosphatidylglycerol, accounted for 42, 35, and 21% of the increase in total phospholipids. Changes in the activities of marker enzymes were generally confined to the 250 mg/kg group at 90 days, with the largest and most significant increases being in the lysosomal enzymes acid phosphatase and hexosaminidase (P less than 0.01). Levels of all phospholipids and marker enzymes, with the exception of succinate dehydrogenase, were not significantly different from controls 79 days after cessation of dosing, and lamellar bodies had disappeared. We conclude that repeated trospectomycin sulfate treatment in rat induces a reversible, dose- and time-dependent lysosomal phospholipidosis in liver which is characterized by an increase in lysosomal enzymes and selected anionic phospholipids.

Isolation of myelin bodies from the kidney cortex of gentamicin-treated rats

Myelin bodies have been isolated from the kidney cortex of gentamicin-treated rats (100 mg gentamicin sulfate/kg body weight i.p. twice daily for 3 days) by a simple procedure involving differential centrifugation followed by equilibrium density centrifugation on a discontinuous sucrose gradient. Electron microscopy and assay of acid phosphatase suggest that the myelin bodies were obtained in virtually quantitative yield, essentially uncontaminated by other cellular structures and relatively intact. The method developed here may also prove applicable for the isolation of myelin bodies arising in connection with other drug treatments and may provide information on a number of toxic side-effects of clinical importance.

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.

Effects of anti-lipid A human monoclonal antibody on lipopolysaccharide-induced toxicity to the kidney

Studies were done to evaluate the effects of the human monoclonal anti-lipid A IgM antibody A6(H4C5) on several components of the hemodynamic and renal toxicity of the cell wall lipopolysaccharide of E. coli 0111:B4. Antibody (0.25 to four mg./kg. BW) was administered 0.5 hour before, or premixed for one hour with, lipopolysaccharide (0.05 mg./kg., a 14 to 18% lethal dose), and the following measurements made over 0.5 to 3.5 hours of study: systemic arterial blood pressure, renal plasma flow, and glomerular filtration. The proximal tubular cell cytotoxicity of 90 mg./kg. of the cephalosporin cephaloridine was also quantified in similarly treated animals sacrificed 48 hours later. While one mg./kg. of antibody prevented the reduction by the lipopolysaccharide of renal plasma flow, it did not prevent the nephrotoxic synergy with cephaloridine, and four times the antibody dose did not prevent lipopolysaccharide-induced hypotension or reduced glomerular filtration. These amounts of this antibody protect leukopenic rabbits against the lethality of the slow onset bacteremic model of Pseudomonas conjunctivitis. It is suggested that the incompleteness of protection in this study may be the result of the sensitivity of the assay methods used and/or the acute endotoxemia produced in these animals.

Modulation of gentamicin nephrotoxicity by chronic inhibition of angiotensin-I-converting enzyme in rat

Perindopril, a new specific and potent inhibitor of angiotensin-I-converting enzyme, was used to evaluate the possible participation of inhibition of the renin-angiotensin system in the development of aminoglycoside-induced renal failure. Kidney function, morphology and biochemistry were evaluated at regular intervals throughout the study. Perindopril was given orally to rats at a daily dose of 2 mg/kg for 15 days prior to and during 15-day gentamicin treatment given intraperitoneally at a daily dose of 50 mg/kg. Perindopril treatment alone induced no modification in renal function or structure. Gentamicin treatment alone induced typical renal lesions which were scored as moderate and a slight but significant decrease in ACE blood levels. Concurrent treatment with perindopril and gentamicin induced a greater drop in ACE blood levels than after the administration of perindopril alone and produced more marked renal impairment than after the administration of gentamicin alone. These observations suggest that the integrity of the renin-angiotensin system may play an important role in limiting kidney injury during aminoglycoside-induced nephrotoxicity.

Metabolism of complement factor D in renal failure

Factor D is an essential enzyme of the alternative pathway of complement. Its plasma concentration increases approximately tenfold in end-stage renal failure (ESRF). To analyze its metabolism in humans, we injected purified radiolabelled factor D into 5 healthy individuals and 12 patients with various renal diseases or renal failure. Fractional metabolic rates (FMR) and extravascular/intravascular distributions (EV/IV) were calculated using a compartmental model. The FMR was very rapid in normal individuals (mean 59.6%/hr; range 74.1 to 50.5), significantly diminished in the five patients with ESRF (5.7%/hr; 7.0 to 2.8; P less than 0.004), and correlated well with the creatinine clearance (r = 0.89; P less than 0.001). The extrarenal catabolic rate was not modified in renal failure. Despite a significant inverse correlation between plasma levels of factor D and creatinine clearance [r = 0.68; P less than 0.002], factor D levels were not a sensitive indicator of renal function because the synthesis rate (SR) varied widely from one individual to another (mean SR: 62.9 micrograms/kg/hr; 14.9 to 136.5). Factor D synthesis was not significantly altered by renal function, and did not correlate with C-reactive protein, suggesting that factor D is not an acute phase protein. The proportion of intact factor D elimination in the urine was increased in patients with tubular dysfunction (up to 15% compared to less than 0.2% in normal individuals) confirming that under normal circumstances factor D is filtered through the glomerulus and catabolized by tubular cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of antibiotics on the binding of pargyline to monoamine oxidase in cultured hepatocytes

The laser dye rhodamine 123 has been used to establish that the binding of [3H]pargyline to monoamine oxidase is a more sensitive indicator of mitochondrial perturbation than measurements of protein synthesis, secretion, or degradation. The amount of monoamine oxidase labelled depends on the antibiotic used. The labelling was considerably lower in the presence of gentamycin than in the presence of either chloramphenicol or of penicillin and streptomycin. The accumulation of gentamycin within the cells was the cause of the reduced labelling of monoamine oxidase which was not accompanied by an alteration in the metabolism of pargyline. The gentamycin effect can be prevented by incubating the cells in medium supplemented with methylamine prior to adding the monoamine oxidase inhibitor. Long term culture of cells with gentamycin can result in the cell culture medium becoming dark brown. Under these conditions the monoamine oxidase labelling is increased due to an inhibition of pargyline metabolism. The results indicate that the choice of antibiotic is important in patients being treated with both antibiotics and monoamine oxidase inhibitors.

Acute hepatocellular effects of erythromycin, gentamicin, and trospectomycin in the perfused rat liver: lack of correlation between lamellar body induction potency and cytotoxicity

The formation of multilamellar inclusion bodies in cytoplasm is a generalized cellular response to treatment with a variety of chemical agents. The present study was conducted to determine if a correlation exists between acute lamellar body induction potency and cytotoxicity in the perfused rat liver. Livers were perfused for 3 hrs with various concentrations of erythromycin, gentamicin, sulfate, or trospectomycin sulfate, all of which are known to produce lamellar bodies in the rat in vivo. At the end of the experiments, the livers were perfusion fixed for transmission electron microscopy. Based on the bile flow rate, perfusion rate at constant pressure, and cytoplasmic enzyme release, neither gentamicin nor trospectomycin was hepatotoxic at concentrations up to 1.8 mM, whereas erythromycin was toxic at 0.1 mM. Gentamicin caused no ultrastructural changes compared to controls, but trospectomycin caused the dose-dependent formation of lamellar bodies in hepatocytes without other cytoplasmic alterations. Erythromycin caused cellular degeneration accompanied by an increase in the number of secondary lysosomes, but these lacked lamellated inclusions. It is concluded that hepatic lamellar bodies can be induced in acute ex vivo experiments, but that their formation does not appear to be linked with acute cytotoxicity.

Aminoglycoside-induced alterations in apical membranes of kidney epithelial cell line (LLC-PK1)

Aminoglycoside-induced renal cell injury was investigated using the LLC-PK1 pig kidney epithelial cell line. The development of aminopeptidase and gamma-glutamyltransferase, marker enzymes for apical membranes, was inhibited in the LLC-PK1 cells cultured with gentamicin. The inhibitory effect of gentamicin on the enzyme activities was dose dependent and was related to its accumulation within the cells. The development of Na+ -dependent active transport of alpha-methyl-D-glucoside, a nonmetabolizable hexose, was also inhibited by treatment with gentamicin. Inhibitions in apical membrane enzyme activities and Na+ -dependent transport of alpha-methyl-D-glucoside were associated with the elevation of cytosolic free calcium, determined with a fluorescent indicator fura-2. The correlation between the alterations in apical membrane functions and the increase in cytosolic free calcium concentration was also supported by the study using the calcium ionophore A23187. The present data suggest that aminoglycoside-induced alterations in apical membranes of the LLC-PK1 cells are related to the increase in cytosolic free calcium levels.

In utero aminoglycosides-induced nephrotoxicity in rat neonates

Pregnant Wistar females were treated with gentamicin (G), netilmicin (N) or amikacin (A) during two periods of pregnancy covering organogenesis and the beginning of nephrogenesis. Deliveries occurred normally. We studied functional effects--influence of sex, litter size, diuresis, creatinine clearance, G-kidney concentration, and kidney morphological alterations--in rat neonates on day 1 of life. After G and N, the creatinine clearance of the neonates was decreased according to the dosage given to the mother. Whatever the aminoglycoside, kidneys presented proximal tubular alterations (close to those observed in adults) at protonic microscopy and, with electron microscopy, some modifications of distal tubules and of mature and immature glomeruli. It is concluded that the developing kidney can be altered after treating pregnant mothers with aminoglycosides. This model of in utero-induced nephrotoxicity is dose-dependent. Mature and/or immature structures could be affected. The toxicity of the investigated antibiotics could be asserted as G greater than or equal to N greater than A.

Cationic amphiphilic drug-induced renal cortical lysosomal phospholipidosis: an in vivo comparative study with gentamicin and chlorphentermine

Daily subcutaneous injection of gentamicin (100 mg/kg) for 2 days produced a significant decrease in the activities of alkaline phosphatase, a brush-border membrane marker, and Na+-K+ ATPase, a basolateral membrane marker, in adult rat kidney cortex. Analysis of homogenate and lysosomal fractions revealed a significant rise in the concentration of total renal cortical phospholipid, phosphatidylserine, phosphatidylcholine, and phosphatidylinositol. In the lysosomal fraction, an increase in the levels of phosphatidylglycerol and phosphatidylethanolamine was also noted. Daily, oral chlorphentermine (60 mg/kg) administration for 5 days significantly reduced renal Na+-K+ ATPase without a marked change in alkaline phosphatase. As in the case of gentamicin, chlorphentermine produced a significant elevation in phosphatidylserine, phosphatidylcholine, and phosphatidylinositol as well as total phospholipid in both the homogenate and lysosomal fractions of kidney cortex. The observed chlorphentermine- or gentamicin-induced renal phospholipidosis was associated with a significant reduction in the activity of phosphatidylinositol-specific phospholipase C. The drug-induced inhibition of phospholipase C was quantitatively equal in the renal cortical homogenate and lysosomal fractions. In addition, gentamicin significantly inhibited the activity of phosphatidylserine-phospholipase C and phosphatidylcholine-phospholipase C in renal cortical homogenate. In contrast, only the activity of phosphatidylinositol-specific phospholipase C was decreased in chlorphentermine-treated kidneys. Evidence thus indicates that the gentamicin-induced accumulation of phospholipid in renal cortical lysosomes is associated with inhibition of various forms of phospholipase C, while in the case of chlorphentermine the inhibition of different phospholipases may be involved in phospholipid accumulation.

Inhibition of alkaline phosphatase activity and D-glucose uptake in rat renal brush-border membrane vesicles by aminoglycosides

The binding of aminoglycoside antibiotics to, and their effects on, the plasma membrane were studied using isolated rat renal brush-border membrane vesicles. Dibekacin was noted to bind with brush-border membrane vesicles having a single class of many binding sites. 3H-labeled dibekacin binding was inhibited competitively by unlabeled dibekacin, gentamicin or amikacin. The inhibition constants obtained from the Dixon plots followed the order of gentamicin approximately equal to dibekacin greater than amikacin. The alkaline phosphatase activity of brush-border membrane vesicles was inhibited by gentamicin significantly, as was also observed by a histochemical study. Sodium-dependent D-glucose uptake by brush-border membrane vesicles was significantly inhibited by the addition of gentamicin.

Inhibitory effect of gentamicin on gluconeogenesis from pyruvate, propionate, and lactate in isolated rabbit kidney-cortex tubules

The effect of gentamicin on glucose production in isolated rabbit renal tubules was studied with lactate, propionate, malate, 2-oxoglutarate, and succinate as substrates. This antibiotic at 5 mM concentration inhibited gluconeogenesis from lactate by about 60% and that from either pyruvate or propionate by about 30%. In contrast, it did not alter the rate of glucose formation from other substrates studied. The rate of gluconeogenesis was higher at 1 mM propionate than at increasing concentrations of this substrate and was stimulated in the presence of 1 mM carnitine. However, the addition of carnitine did not affect the degree of inhibition of glucose formation by gentamicin. Since the mitochondrial free coenzyme A level was significantly lower in the presence of 10 than 1 mM propionate and increased on the addition of carnitine to the reaction medium, the inhibitory effect of propionate concentrations above 1 mM on gluconeogenesis in rabbit renal tubules may be due to a depletion of the free mitochondrial coenzyme A level, resulting in an inhibition of the mitochondrial coenzyme A-dependent reactions. In intact rabbit kidney cortex mitochondria incubated in State 4 as well as in Triton X-100-treated mitochondria, 5 mM gentamicin inhibited by about 30-40% the incorporation of 14CO2 into both pyruvate and propionate. The results indicate that the inhibitory effect of gentamicin on glucose formation in isolated kidney tubules incubated with lactate, pyruvate, or propionate is likely due to a decrease of the rate of carboxylation reactions.

Failure of inhibition of lipid peroxidation by vitamin E to protect against gentamicin nephrotoxicity in the rat

We tested the hypothesis that accelerated lipid peroxidation, possibly at the level of the lysosome, is linked causally to the pathogenesis of aminoglycoside nephrotoxicity by investigating whether administration of vitamin E would inhibit lipid peroxidation and prevent or ameliorate gentamicin-induced proximal tubular cell injury. Five groups of rats were injected with either saline, vitamin E (600 mg/kg per day) for 6 days, gentamicin (100 mg/kg per day) for 6 days, vitamin E for 6 days plus gentamicin for 6 days or vitamin E for 12 days and gentamicin for the last 6 days. Gentamicin alone induced a 16% increase in renal cortical phospholipids; vitamin E had no significant effect on this change. Gentamicin alone caused accelerated lipid peroxidation evident by a doubling of renal cortical malondialdehyde to 1.23 nmol/mg protein, and a sharp decline of esterified polyunsaturated fatty acids, especially arachidonic acid which fell 43%. These changes were accompanied by depressions of superoxide dismutase, catalase, and total glutathione and a shift from reduced to oxidized glutathione. Concurrent treatment of rats with vitamin E plus gentamicin for 6 days had no significant effect on the gentamicin-induced alterations of malondialdehyde, superoxide dismutase, catalase or the glutathione cascade; however, the shift from polyunsaturated to saturated fatty acids was largely reversed. In rats pretreated with vitamin E for 6 days, gentamicin failed to raise renal cortical malondialdehyde above that of saline-treated rats. The changes in esterified fatty acids were prevented almost entirely, and there were no significant alterations from control of the glutathione cascade. The depressions of superoxide dismutase and of catalase, however, were not reversed. Vitamin E did not affect the amount of gentamicin accumulated in renal cortex nor did it prevent the gentamicin-induced rise of serum creatinine. Examination of renal cortex by light and electron microscopy revealed that vitamin E did not prevent or even reduce the severity of gentamicin-induced proximal tubular cell lesions and necrosis. These results confirm those we obtained in a previous study with the antioxidant diphenyl-phenylenediamine. The observation that inhibition of lipid peroxidation by two distinct antioxidants failed to prevent proximal tubular cell injury and renal dysfunction associated with gentamicin administration leads us to conclude that lipid peroxidation is a consequence and not a cause of gentamicin-induced nephrotoxicity.

Normal values for urinary N-acetyl-beta-glucosaminidase excretion in preterm and term babies

Urinary N-acetyl-beta-glucosaminidase (NAG) excretion was measured in 14 healthy, preterm, male neonates with gestational ages between 32 and 35 weeks. Daily NAG excretion increased significantly during the first four weeks of life. No correlation was observed between urinary NAG:creatinine ratio and postnatal age regardless of whether measurements were taken from the whole 24 hour urine collection or from an isolated urine spot sample at the same time on each day. When the preterm infants were compared with a group of 20 healthy, full term, male infants at a postnatal age of 7 days the NAG:creatinine ratio was significantly higher in the preterm group, the measurements having been taken from single urine spot samples. We suggest that this variable be used in the evaluation of renal tubular integrity during the neonatal period.

Biochemical effects of gentamicin on rat kidney cortex. II. Analytical subfractionation after short-term, high-dose treatment

As a first step in studies on the molecular mechanism(s) underlying gentamicin toxicity, the effect of treating rats with this aminoglycoside antibiotic (100 mg/kg once or twice daily for 3 days) on the analytical subfractionation of the kidney cortex has been examined. DNA was used as a marker for the nuclei, cytochrome oxidase for mitochondria, acid phosphatase for lysosomes, catalase for peroxisomes (with reservations; see the companion paper), NADPH-cytochrome c reductase for the endoplasmic reticulum, p-nitrophenyl-alpha-mannosidase (at pH 5.5) for the Golgi apparatus, AMPase for the plasma membrane in general and alkaline phosphatase for the brush border, and lactate dehydrogenase for the cytosol. In addition, the presumptive lysosomal hydrolases N-acetyl-beta-D-glucosaminidase, p-nitrophenyl-alpha-mannosidase (at pH 4.5), cathepsin D, and DNase II were monitored. Electron microscopy was also performed on the subfractions obtained. The only significant biochemical changes brought about by gentamicin treatment were that N-acetyl-beta-D-glucosaminidase demonstrated both a greater total activity and a larger enrichment in the 104,000gav pellet, while p-nitrophenyl-alpha-mannosidase at pH 4.5 demonstrated the same total activity and a greater enrichment in the 104,000gav pellet. Since myeloid bodies were shown by electron microscopy to sediment primarily with the 500gav and 10,000gav pellets, the biochemical changes seen cannot be associated with these morphological structures. These findings suggest that selective changes in a certain subpopulation(s) of lysosomes or in certain lysosomal enzymes may be involved in the early stages of gentamicin toxicity. On the other hand, no lysosomal membrane damage was observed here, since both the latency of acid phosphatase and the recovery of this activity in the soluble cytosol were unchanged. The present investigation may also have relevance for the dosage and duration of gentamicin treatment chosen in clinical situations.

Aminoglycoside-induced alterations of phosphoinositide metabolism

There exists a strong interaction between aminoglycosides and phosphoinositides, and these membrane lipids are even considered as the drug receptors. To shed some light on the role of such an interaction in the drug nephrotoxicity, we have investigated the influence of aminoglycosides on phosphoinositide metabolism in kidney proximal tubules where these compounds accumulate. Experiments were carried out by measuring 32P labelling of phosphatidylinositol 4-phosphate (PI-P) and of phosphatidylinositol 4,5-bisphosphate (PI-P2) after incubation of homogenates of isolated proximal tubules with [gamma-32P] ATP. The treatment of rabbits with neomycin, gentamicin and amikacin (50, 50 and 300 mg/kg/day, respectively for seven days) promoted a decrease in 32P-PI-P2 and an increase in 32P-PI-P, when compared to the respective values observed in tubules from untreated rabbits. Under these conditions, the extent of modifications in lipid labelling was similar with the three drugs tested. In in vitro experiments, the exogenous addition of the above aminoglycosides to the incubation medium containing tubule homogenates from untreated rabbits also produced, in a dose dependent manner, a decrease in 32P-PI-P2 and an increase in 32P-PI-P. In the in vitro experiments, however, amikacin and gentamicin appeared to be less potent than neomycin. The results indicated moreover that phosphoinositide metabolism was more sensitive to the in vivo (vs. in vitro) action of the drugs. Phosphoinositides are involved in Ca2+ transport and/or mobilization processes, and aminoglycosides are known to interfere with the Ca2+ binding to membranes.(ABSTRACT TRUNCATED AT 250 WORDS)

Uptake of aminoglycoside antibiotics into brush-border membrane vesicles and inhibition of (Na+ + K+)-ATPase activity of basolateral membrane

The effects of aminoglycoside antibiotics on plasma membranes were studied using rat renal basolateral and brush-border membrane vesicles. 3',4'-Dideoxykanamycin was bound to the basolateral membrane and brush-border membrane vesicles. They had a single class of binding sites with nearly the same constant, and the basolateral membrane vesicles had more binding sites than those of the brush-border membrane. Dideoxykanamycin B was transported into the intravesicular space of brush-border membrane vesicles, but not into that of basolateral membrane vesicles. The (Na+ + K+)-ATPase activity of the plasma membrane fraction prepared from the kidney of rat administered with dideoxykanamycin B intravenously decreased significantly. Aminoglycoside antibiotics entrapped in the basolateral membrane vesicles inhibited (Na+ + K+)-ATPase activity, but those added to the basolateral membrane vesicles externally failed to do so. The activity of (Na+ + K+)-ATPase was non-competitively inhibited by gentamicin. It is thus concluded that aminoglycoside antibiotics are taken up into the renal proximal tubular cells across the brush-border membrane and inhibit the (Na+ + K+)-ATPase activity of basolateral membrane. This inhibition may possibly disrupt the balance of cellular electrolytes, leading to a cellular dysfunction, and consequently to the development of aminoglycoside antibiotics' nephrotoxicity.

The role of cell calcium overload in nephrotoxic renal tubular cell injury

Data on the role of cell Ca++ overload in the pathogenesis of nephrotoxic renal tubular injury and methodologic considerations for studying this process were reviewed. It was concluded that: A consistent pattern of Ca++ uptake and resultant functional changes are attributable to the interactions of Ca++ with mitochondria during their isolation, unless specific measures are taken to prevent these interactions. The simplest approach to prevent in vitro Ca++ from occurring during isolation of mitochondria from injured tissues having high Ca++ levels is to include ruthenium red in the homogenizing solution used to prepare the mitochondria, although this will still permit some surface binding of Ca++ to mitochondria. By comparing mitochondrial Ca++ levels and functional parameters of mitochondria isolated after in vivo nephrotoxic injury with those of control mitochondria isolated at similar homogenate Ca++ levels, the components of mitochondrial Ca++ overload and functional deterioration solely attributable to in vivo events can be identified. These were detailed for gentamicin- and mercuric chloride-induced nephrotoxicity. Tissue and mitochondrial Ca++ overload are relatively late events during the development of renal tubule cell injury secondary to aminoglycosides or to mercuric chloride, occurring only when lethal cell injury is present by morphologic criteria. Since it correlates with lethal cell injury, the presence of tissue Ca++ overload can be of value in assessing this process, but care must be exercised in drawing conclusions about the extent of lethal cell injury, because the degree of Ca++ overload can be modified by factors, such as saline intake, independently of changes in the number of lethally injured cells.

Purification of lysosomal phospholipase A and demonstration of proteins that inhibit phospholipase A in a lysosomal fraction from rat kidney cortex

Phospholipase A has been isolated from a crude lysosomal fraction from rat kidney cortex and purified 7600-fold with a recovery of 9.8% of the starting activity. The purified enzyme is a glycoprotein having an isoelectric point of pH 5.4 and an apparent molecular weight of 30,000 by high-pressure liquid chromatography gel permeation. Naturally occurring inhibitors of lysosomal phospholipase A are present in two of the lysosomal-soluble protein fractions obtained in the purification. They inhibit hydrolysis of 1,2-di[1-14C]oleoylphosphatidylcholine by purified phospholipase A1 with IC50 values of 7-11 micrograms. The inhibition is abolished by preincubation with trypsin at 37 degrees C, but preincubation with trypsin at 4 degrees C has no effect, providing evidence that the inhibitors are proteins. The results suggest that the activity of lysosomal phospholipase A may be regulated in part by inhibitory proteins. Lysosomal phospholipase A from rat kidney hydrolyzes the sn-1 acyl group of phosphatidylcholine, does not require divalent cations for full activity, and is not inhibited by ethylenediaminetetraacetic acid. It has an acid pH optimum of 3.6-3.8. Neither p-bromophenacyl bromide, diisopropyl fluorophosphate, nor mercuric ion inhibits phospholipase A1. In contrast to rat liver, which has two major isoenzymes of acid phospholipase A1, kidney cortex has only one isoenzyme of lysosomal phospholipase A1.

Autoradiography of tobramycin uptake by the proximal and distal tubules of normal and endotoxin-treated rats

Multiple factors may modify the pharmacokinetics of aminoglycosides and increase their nephrotoxic potential. In the present study, the influence of Escherichia coli endotoxin on the renal handling of [3H]tobramycin was investigated. The accumulation of [3H]tobramycin in proximal tubules, distal tubules, and collecting ducts was compared in both normal and endotoxin-injected (0.25 mg/kg) rats. Histological observations were also made. Blood pressure and cardiac frequency were recorded, and renal function was evaluated with labeled inulin and p-aminohippuric acid. Following administration of endotoxin, disturbed intrarenal localization of the drug was noted. Grain counts were affected in both proximal and distal tubules. Increased labeling was observed at all time intervals in the proximal tubules. In the distal tubules of endotoxemic animals we could detect higher amounts of drug at 10 and 60 min in the medulla and at 10 min in the cortex. Not all of the tubules were labeled to the same extent. No histological lesion was noted on light microscopy in animals receiving either normal saline or endotoxin. The dose of endotoxin used resulted in very fine physiological disturbance. Both blood pressure and cardiac frequency were minimally affected by endotoxin. Decreases in glomerular filtration rate and renal plasma flow were observed. However, none of these changes was statistically significant. The present study has shown that low doses of endotoxin alter the renal handling of aminoglycosides in the absence of any major physiological disturbance or histological changes. By increasing the total amount of drug within the kidney, endotoxin might increase the nephrotoxic potential of aminoglycosides.

Changes in renal enzyme activities following the administration of gentamicin to unilateral nephrectomized rats

The effects of unilateral nephrectomy and the impact of gentamicin administration on renal tissue enzyme activities in adult Wistar rats were investigated. Gentamicin 200 mg/kg body wt. or an equivalent volume of saline to control rats was administered subcutaneously on three consecutive days, followed by unilateral nephrectomy. Rats were killed on day 3, 7 or 14 following nephrectomy. Alkaline phosphatase, predominantly a proximal tubular brush border enzyme, rose in both the experimental and control groups, however, significantly less in the gentamicin treated rats. Aspartate aminotransferase activity, an enzyme participating in renal glucogenesis, increased transiently in the control but remained unchanged in the experimental group. No difference in glucose-6-phosphate dehydrogenase activity between the two groups was observed, probably reflecting the localization of this enzyme to distal tubular segments, a site unaffected by gentamicin. Significant and similar increases in Mg2+ and Na+ K+ ATPase were observed on day 14 in both groups. The administration of the drug resulted in a marked reduction in oxygen consumption, with a higher oxidation to phosphorylation ratio (P/O). Serum creatinine concentration was significantly higher on days 3 and 7 in the experimental group reverting to control values on the 14th day. Urea concentration increased significantly on days 3 and 7, decreasing on the 14th day to values slightly, but significantly, higher than those of the controls.

The effect of gentamicin on human renal proximal tubular cells

Human renal proximal tubular cells were exposed to gentamicin (0, 0.1, 0.5, 1.0, 5.0, 10.0 mg/ml medium) for 3, 7, 10, and 14 days. Cells were counted and cell viability was estimated by lactate dehydrogenase release. In addition, brush border-associated (gamma-glutamyltransferase) and lysosomal (acid phosphatase, N-acetyl-beta-glucosaminidase, and sphingomyelinase) enzyme activities were measured (0.01, 1.0, 3.3 mg/ml gentamicin for 3, 7, 10 and 14 days). The number of cells did not change significantly after gentamicin treatment. Cell viability, however, significantly decreased after 3 and 7 days exposure to 5 and 10 mg/ml gentamicin. Total lactate dehydrogenase activity was significantly decreased at 7, 10, and 14 days exposure to gentamicin greater than or equal to 5.0 mg/ml. gamma-Glutamyltransferase, acid phosphatase, and sphingomyelinase were decreased at 3, 7, and 10 days exposure to gentamicin greater than or equal to 1.0 mg/ml. Continued exposure to gentamicin less than or equal to 1.0 mg/ml appeared to have little or no effect on the activity of these enzymes at 14 days. N-Acetyl-beta-glucosaminidase activity, in contrast, was elevated (120-140% control) in the gentamicin-treated (greater than or equal to 1.0 mg/ml) groups at all time periods studied. Thus, gentamicin exposure resulted in changes in some of the enzyme activities in human renal proximal tubular cell cultures, but longer exposure (14 days) to gentamicin (less than or equal to 1.0 mg/ml) resulted in a return to control levels of some activities.

Aminoglycoside nephrotoxicity

Aminoglycosides are life-saving antibiotics in patients with gram negative sepsis. Renal dysfunction occurs in approximately 10% of all clinical courses of aminoglycosides. Because of close pharmacokinetic and toxicologic similarities, rats are excellent human surrogates for comparing the nephrotoxic potentials of these antibiotics. Comparisons in rats are also more sensitive than clinical comparisons due to the insensitivities of clinical renal function tests, the confounding influences present in seriously-ill patients and the inability to make morphologic comparisons in the clinic. The pathogenesis of aminoglycoside nephrotoxicity is still evolving despite extensive world-wide investigations. However, these investigations have facilitated the identification of several inhibitors of aminoglycoside nephrotoxicity. The clinical usefulness of these inhibitors must still be established.

Influence of endotoxin on the intrarenal distribution of gentamicin, netilmicin, tobramycin, amikacin, and cephalothin

Multiple factors may modify the pharmacokinetics of aminoglycosides and increase their nephrotoxic potential. In this study, we investigated the influence of Escherichia coli endotoxin on the renal handling of several aminoglycosides and one cephalosporin. Drug levels in the renal parenchyma, as well as several parameters of renal function and histology, were compared in rats treated with endotoxin (0.25 mg/kg) and normal rats treated with either gentamicin (10 mg/kg), netilmicin (10 mg/kg), tobramycin (10 mg/kg), amikacin (50 mg/kg), or cephalothin (100 mg/kg). Blood pressure and pulse rate were recorded. Endotoxin was associated with a decrease in the half-life and in the apparent volume of distribution of gentamicin. The endotoxin-injected animals accumulated significantly (P less than 0.05) more aminoglycosides in their kidneys than the normal animals. The amount of cephalothin recovered in the renal parenchyma was identical in both groups. Slight decreases in the glomerular filtration rate and renal plasma flow were observed after endotoxin treatment. Blood pressure and cardiac frequency were minimally affected by endotoxin. No histological lesions were observed by light microscopy in animals receiving endotoxin. Thus, endotoxin modifies the renal handling of aminoglycosides in the absence of any major physiological disturbance or histological change. By increasing the total amount of drug within the kidneys, endotoxin might increase the nephrotoxic potential of aminoglycosides.

Nephrotoxic tubular and interstitial lesions: morphology and classification

Nephrotoxic renal injury, and especially drug nephrotoxicity is now a common cause of acute renal failure. The most common patterns of renal injury produced by nephrotoxins, tubular damage, and interstitial nephritis, are discussed here. Toxic agents which are primarily tubular toxins include certain antibiotics, cisplatinum, anesthetics, and radiocontrast agents. In tubules injured by toxins, alterations range from subtle ultrastructural abnormalities to extensive tubular necrosis. Mechanisms of tubular injury include direct tubular cell toxicity, and alterations in intrarenal blood flow producing secondary tubular damage. Other commonly used therapeutic agents, including the penicillins, other antibiotics, and non-steroidal anti-inflammatory agents, produce renal dysfunction by inducing interstitial nephritis. Long-term analgesic abuse is associated with a particularly striking interstitial damage with frank papillary necrosis. Criteria for differentiating primary tubular injury with inflammation and primary interstitial nephritis with tubular injury are discussed. Individual commonly-used therapeutic agents are considered in some detail, with discussion of both clinical and morphological aspects of drug nephrotoxicity.

The influence of aphakia and vitrectomy on experimental retinal toxicity of aminoglycoside antibiotics

To study the effect of lens and vitreous surgery on the dose threshold of aminoglycoside-induced retinal toxicity, we performed extracapsular lens extraction (Group 1) or lensectomy and vitrectomy (Group 2) on Dutch Belted rabbits. A single dose of amikacin or gentamicin ranging from 100 to 4,000 micrograms was administered intravitreally. Retinal toxicity was examined by light and transmission electron microscopy seven days after injection. Both groups showed retinal toxicity after 400 micrograms of gentamicin or 1,500 micrograms of amikacin, doses identical to those causing toxicity in intact, phakic rabbit eyes. Thus, neither surgical procedure increased the toxic threshold of injected aminoglycoside. Given the accelerated aminoglycoside clearance reported in aphakic eyes, these findings imply that the mechanism of aminoglycoside toxicity may be related to peak drug concentration rather than duration of tissue exposure.

The nephrotoxic potential of gentamicin in the cat: enzymuria and alterations in urine concentrating capability

This study investigated the potential for nephrotoxicity of gentamicin in cats by measuring marker enzyme concentrations, [Na], [K], osmolality, and pH of the urine, and blood urea nitrogen (BUN) levels. Gentamicin was administered i.m. at 4.4 mg/kg once daily (s.i.d.) or twice daily (b.i.d.) for 7 days. Concentrations of lactic dehydrogenase (LDH), lysozyme (LZM), alkaline phosphatase (AP), and glutamate dehydrogenase (GD) were measured as total 24-h excretions. The s.i.d. regimen produced only a slight increase in LDH excretion after 5 days, whereas the b.i.d. regimen caused an increase in the excretion of all enzymes. The greatest elevations were observed for LZM and LDH. Of the enzymes studied, these appeared to be the most appropriate to monitor for potential nephrotoxicity, except that urinary concentrations did not correlate well with duration of gentamicin administration. Only slight elevations in BUN were observed for either regimen. Single daily administration increased urine osmolality slightly, but b.i.d. treatment caused a marked and immediate decrease in urine osmolality, [Na], and total Na excretion. Urinary [K] was also depressed, as was total K excretion after 6 days. Urine pH was not substantially affected. This study showed that the recommended daily dose of 4.4 mg/kg produced little if any evidence of nephrotoxicity as indicated by the parameters measured. Twice daily dosing, however, produced elevations in urine enzyme concentrations, and markedly decreased urine osmolality and Na and K excretion. Compared to other species studied, the cat appears particularly sensitive to urine concentrating alterations resulting from repeated gentamicin administration.

Effect of gentamicin on lipid peroxidation in rat renal cortex

We examined the hypothesis that lipid peroxidation participates in the pathogenesis of aminoglycoside-induced nephrotoxicity. Male Sprague-Dawley rats were injected subcutaneously with gentamicin, 100 mg/kg per day, for 1-4 days. Twenty-four or forty-eight hours after the last injection the rats were killed and the renal cortex was processed for total phospholipids, malondialdehyde (MDA), phospholipid fatty acid composition, superoxide dismutase, catalase and glutathione. Gentamicin induced a significant increase in total renal cortical phospholipids which was evident after a single injection and by the third injection reached a plateau 17% above the baseline level. MDA, an end product of lipid peroxidation, increased from 0.674 +/- 0.021 nmole/mg protein in the control group to 0.931 +/- 0.053 nmole/mg protein (P less than 0.001) 48 hr after the fourth injection. As another index of lipid peroxidation, we determined the shift from polyunsaturated to saturated fatty acids of renal cortical phospholipids. By the second injection of gentamicin we detected a significant decline of arachidonic acid (20:4) present in phospholipid. By the fourth injection, arachidonic acid had fallen 48% below control and was accompanied by reciprocal increases of more saturated fatty acids including linoleic (18:2), oleic (18:1) and palmitic (16:0) acids. The number of double bonds per mole of fatty acid declined from a baseline value of 1.62 +/- 0.01 to 1.20 +/- 0.02 (P less than 0.001) by the fourth injection of drug. Superoxide dismutase showed no consistent alteration, whereas catalase activity (k) fell from the control value of 0.221 +/- 0.007 min to 0.155 +/- 0.009 min (P less than 0.01) by the third injection, where k is the first-order rate constant. Total and reduced glutathione declined after the fourth injection of gentamicin accompanied by a shift to oxidized glutathione with an increase in the ratio of oxidized to total glutathione. These data support the conclusion that accelerated lipid peroxidation occurs early in the course of gentamicin administration and raise the possibility that lipid peroxidation is a proximal event in the injury cascade of gentamicin nephrotoxicity.

Comparative toxicity of intravitreal aminoglycoside antibiotics

We compared the toxicity of the aminoglycoside antibiotics (tobramycin, amikacin, netilmicin, and kanamycin) by ophthalmoscopy, light and electron microscopy, and electro-retinography after intravitreal injection in rabbits in doses ranging from 100 to 3,000 micrograms. The earliest manifestations of toxicity were confined to the outer retina with each drug, with lamellar lysosomal inclusions in the retinal pigment epithelium as the earliest finding. However, the aminoglycosides displayed marked differences in the threshold dose required to produce toxic reactions, permitting the following ordering of toxicity: (most toxic) gentamicin greater than netilmicin = tobramycin greater than amikacin = kanamycin (least toxic).

Early monitoring of human renal transplantations by N-acetyl-beta-D-glucosaminidase isoenzyme activities in urines

Monitoring of variations in N-acetyl-beta-D-glucosaminidase (NAG) urinary activity, following renal transplantation, has been proposed for the early diagnosis of rejection episodes. In this study, the measurement of urinary NAG-B activity was conducted as a complement to total NAG (A + B) measurement, which is normally used alone. Selective measurement of NAG-B activity is carried out after fixation of NAG-A on ion exchanger in test tubes. Results of NAG (A + B) activity confirm that the assay of urinary NAG is a useful indicator of rejection, but a positive correlation between NAG-B and NAG (A + B) activities was observed during the various complications which can occur after transplantation. The specific measurement of this isoenzyme does not, therefore, seem to provide additional information in the early monitoring of human renal transplantations. Apart from rejection episodes, other factors are likely to produce marked NAG-B excretion, e.g. gentamicin therapy.

Distribution of gentamicin among subcellular fractions from rat renal cortex

A substantial amount of data is available to suggest that lysosomal sequestration of aminoglycoside antibiotics plays a role in the pathogenesis of aminoglycoside-induced renal tubule cell injury; however, relatively little information is available on the subcellular distribution of aminoglycosides in the kidney during treatment protocols of the type that ultimately go on to produce extensive lethal renal tubule cell injury and acute renal failure in experimental animals. This study assessed the distribution of gentamicin and subcellular membranes on a discontinuous sucrose density gradient after in vivo exposure of rats to four daily 100 mg/kg doses of gentamicin as compared to in vitro exposure of normal rat renal cortex to gentamicin during tissue homogenization at drug levels comparable to those seen after in vivo treatment. After both in vivo and in vitro exposure, major localization of gentamicin, the lysosomal marker enzyme N-acetyl-beta-D-glucosaminidase (NAG), and the endoplasmic reticulum marker enzyme NADPH-cytochrome c reductase, occurred in a very light membrane fraction. Within this membrane fraction, gentamicin was more closely associated with the NAG than with the NADPH-cytochrome c reductase. The results could not be explained by complete lysosomal disruption during subcellular fractionation after in vivo gentamicin. These data provide additional insights into both the possibilities for subcellular interactions of aminoglycosides in the kidney, and into the methodology required to optimally assess such interactions.

Renal disposition of gentamicin, dibekacin, tobramycin, netilmicin, and amikacin in humans

The tubular disposition of five aminoglycosides was studied in humans to establish a possible relationship between tubular reabsorption and the nephrotoxicity that has been described in the literature. Thirty-three healthy male volunteers received a continuous intravenous infusion of isotonic saline with inulin, followed 1 h later by inulin plus gentamicin, dibekacin, tobramycin, netilmicin, or amikacin (1 mg/kg per h) or amikacin (4 mg/kg per h) over a period of 2 h. Brain-stem-evoked response audiometry was performed both before and at the end of each infusion. The latency of wave V remained constant whichever antibiotic was considered. The glomerular filtration rate did not vary significantly during the infusion of each drug. The percent fractional excretion was 79 +/- 6, 81 +/- 22, 85 +/- 5, and 99 +/- 9 for gentamicin, dibekacin, tobramycin, and netilmicin, respectively, and 83 +/- 4 and 124 +/- 13 for amikacin at concentrations of 1 and 4 mg/kg per h, respectively. Net balance and renal clearance were similar for the five aminoglycosides when administered at a rate of 1 mg/kg per h. With gentamicin only, fractional excretion was correlated with the urinary flow rate. We can conclude that (i) gentamicin, generally considered the most nephrotoxic agent, had the highest degree of net reabsorption; (ii) netilmicin exhibited a net zero tubular balance; (iii) amikacin had different patterns of tubular disposition according to the dose, i.e., reabsorption at 1 mg/kg per h and secretion at 4 mg/kg per h, raising the hypothesis of a saturable process of reabsorption; and (iv) these differences in tubular reabsorption could account at least in part for the known different nephrotoxic potentials of these five aminoglycosides in humans.

Interaction of gentamicin and spermine with bilayer membranes containing negatively charged phospholipids

We measured the electrophoretic mobility of multilamellar phospholipid vesicles, the 31P NMR spectra of both sonicated and multilamellar vesicles, and the conductance of planar bilayer membranes to study the binding of spermine and gentamicin to membranes. Spermine and gentamicin do not bind significantly to the zwitterionic lipid phosphatidylcholine. We measured the concentrations of gentamicin and spermine that reverse the charge on vesicles formed from a mixture of phosphatidylcholine and either phosphatidylserine or phosphatidylinositol. From these measurements, we determined that the intrinsic association constants of the cations with these negative lipids are all about 10 M-1. This value is orders of magnitude lower than the apparent binding constants reported in the literature by other groups because the negative electrostatic surface potential of the membranes and the resultant accumulation of these cations in the aqueous diffuse double layer adjacent to the membranes have not been explicitly considered in previous studies. Our main conclusion is that the Gouy-Chapman-Stern theory of the aqueous diffuse double layer can describe surprisingly well the interaction of gentamicin and spermine with bilayer membranes formed in a 0.1 M NaCl solution if the negative phospholipids constitute less than 50% of the membrane. Thus, the theory should be useful for describing the interactions of these cations with the bilayer component of biological membranes, which typically contain less than 50% negative lipids. For example, our results support the suggestion of Sastrasinh et al. [Sastrasinh, M., Krauss, T. C., Weinberg, J. M., & Humes, H. D. (1982) J. Pharmacol. Exp. Ther. 222, 350-358] that phosphatidylinositol is the major binding site for gentamicin in renal brush border membranes.

Recovery of cortical phospholipidosis and necrosis after acute gentamicin loading in rats

The recovery from gentamicin-induced phospholipidosis in the rat kidney cortex was characterized both morphologically and biochemically after a single 12-hr drug infusion. Total dosages administered were 10, 60, or 140 mg/kg, achieving constant serum concentrations of 3, 11, and 27 micrograms/ml, respectively. At the end of the 12-hr infusion, the cortical drug concentrations corresponding to the three dosages were 124, 450, and 993 micrograms/g of wet tissue. At the low dose (10 mg/kg), myeloid bodies were seen inside lysosomes of proximal tubular cells, along with a modest decrease of lysosomal sphingomyelinase activity. The cortical drug level declined steadily following first-order kinetics along with a disappearance of myeloid bodies and return of sphingomyelinase activity to control levels. At the high dose (140 mg/kg), we observed a sustained loss of sphingomyelinase activity (37% of controls), a subsequent increase of phospholipid concentration in the kidney cortex (up to 117% of controls 2 days after) and a prominent accumulation of myeloid bodies inside the lysosomes of proximal tubular cells (up to 4% of cell volume). Tubular regeneration and interstitial infiltration became detectable by histology and the increase of DNA synthesis as from day 1, along with an apparent reduction of the phospholipidosis at days 3 and 4. Drug cortical concentrations showed a sharp decline 2 days after infusion. An intermediate behavior was observed at 60 mg/kg. It is concluded that the proximal tubular cells behave in a fundamentally different way after gentamicin loading with low and high doses. At the low dose there is a regression of the drug-induced changes in the absence of any sign of necrosis-regeneration. Above a threshold in cortical drug concentration there is further development of the alterations leading to cell death-regeneration.

Induction and inhibition of pinocytosis by aminoglycoside antibiotics

We investigated whether differences in induction or stimulation of pinocytosis by six amino-glycosides reflected reported differences in their nephrotoxicity. Pinocytosis induced by antibiotics, Na+, K+ or Ca2+ was quantified by the number of pinocytotic channels in Amoeba proteus, a cell suitable for the study of the pinocytotic process. The aminoglycosides were potent inducers of pinocytosis. They were effective in the order of their cationic charge: neomycin greater than gentamicin greater than netilmicin = tobramycin greater than kanamycin greater than streptomycin. Factors which reduced the charge of the molecules, i.e. alkaline pH and combination with carbenicillin or heparin, diminished pinocytosis. Like La3+ the antibiotics inhibited Na+ -induced pinocytosis. The order of efficacy was netilmicin greater than gentamicin greater than neomycin. A similar rank order, which is the reverse of the order of nephrotoxicity, was observed for inhibition of Ca2+ -stimulated, Na+ -induced pinocytosis. Netilmicin was also the most potent inhibitor of the Ca2+-induced pinocytosis in cells treated with concanavalin A. Inhibition of Ca2+ -stimulated pinocytosis by netilmicin was reversed by Ca2+, the calcium ionophore A 23187, or 4-aminopyridine. We have shown that several nephrotoxic cations are strong inducers of pinocytosis in the amoeba, that aminoglycosides in Ringer solution induce pinocytosis in the approximate order of their nephrotoxicity and that factors which are known to diminish toxicity reduce pinocytosis. It, therefore, appears that the mechanism of aminoglycoside nephrotoxicity is related to their ability to induce pinocytosis in the amoeba. Low inducing potency and strong Ca2+ -antagonism, as for netilmicin, are qualities which may reduce the tendency of polycationic compounds to damage proximal tubular cells.