Gentamicin Nephrotoxicity

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    in agreement with those obtained by other investigators (15,37, 39, 40, 51, 52). Peak renal toxicity was observed whenaminoglycosides were injected in the middle of the rest periodof the experimental animals, while lower toxicity was foundwhen they were treated in the middle of the activity period.These data are also in agreement with those of Prins et al. (44),recently obtained for patients. In fact, they reported that neph-

    rotoxicity occurred more frequently when aminoglycosideswere administered to patients between midnight and 0730 hthan when administered at any other hour of the day.

    The temporal variations in the effectiveness of aminoglyco-sides have never been investigated for animals. Thus, the ob-jective of this study was to investigate the circadian variationsin the toxicity and the efficacy of gentamicin in an experimentalmodel of pyelonephritis in rats.

    MATERIALS AND METHODS

    Animals and treatment. Female Sprague-Dawley rats (Charles River BreedingLaboratories, Inc., Montreal, Quebec, Canada) aged 58 to 82 days and weighing185 to 250 g were used in this study. They had free access to food and waterthroughout the experiment. They were maintained on a 14-h-light (rest period)

    and a 10-h-dark (active period) schedule with the light on at 0600 h, for 1 weekbefore induction of pyelonephritis. Animals were divided into four groups on thebasis of the time of day that infection was induced and treatment was given.

    Pyelonephritis model. The bacterial strain used to induce pyelonephritis wasEscherichia coli Yale EY-9 (furnished by V. Andreoli, Yale University). Beforethe induction of pyelonephritis, animals were anesthetized with sodium pento-barbital (Nembutal sodium [Abbott Laboratories]) at 50 mg/kg of body weight,intraperitoneally (i.p.). The side of the animals was shaved and asepticized, anda small incision was made at the level of the kidney. The left kidney was exposed,and 0.05 ml of an inoculum containing 107 to 108 bacteria was injected throughthe upper and lower poles of the kidney. This technique, described previously byKaye (26), produces a constant and severe pyelonephritis in the left kidney withextensive inflammation and abscess formation induced by the direct inoculationofE. coliand a less severe pyelonephritis in the right kidney due to the reflux ofinfected urine. Pyelonephritis was induced at either 0700, 1300, 1900, or 0100 h,and the treatment was initiated exactly 24 h after the time of inoculation. TheMIC of gentamicin against the E. coli strain was 0.5 g/ml.

    Effectiveness study.Infected animals were treated with a single daily injection

    of gentamicin (20 and 40 mg/kg, i.p.) for 3 and 7 days at the same time of day atwhich the infection was previously induced: 0700, 1300, 1900, or 0100 h. Saline(NaCl [0.9%]) was injected into control animals in a volume of 0.2 ml at the samehour of the day as that for the aminoglycoside. Twenty-four hours after the lastinjection, a minimum of 10 rats per group were anesthetized as described above,blood was sampled by cardiac puncture, and animals were killed by decapitation.At the time of sacrifice, a midline abdominal incision was made and both kidneyswere aseptically removed, decapsulated, weighed, and homogenized in 3 ml ofsterile saline at 4C. Appropriate dilutions of homogenized kidneys were made,and 10-l samples were placed in triplicate on MacConkey agar. The number ofCFU ofE. coliin the kidneys was determined after an incubation of 18 h at 37C(the CFU per milliliter of homogenate were transformed into CFU per gram oftissue). The bacterial enumeration was done at the dilution that allowed us todetect between 30 and 300 CFU/g of kidney. The limit of detection was 30 CFU/g of kidney. Kidneys were considered sterile when no CFU were detected on theagar. The efficacy of gentamicin was assessed by comparing the number of CFUmeasured in the infected and treated rats with that of animals injected with salineat the same time. The efficacy of gentamicin was also evaluated by comparing the

    percentages of sterile kidneys in the infected and treated animals at the fourtimes of day.Nephrotoxicity study.Groups of rats were infected as described above at 0700,

    1300, 1900, and 0100 h. Exactly 24 h after the induction of the infection, groupsof at least six infected rats were treated with a single daily i.p. injection ofgentamicin (40 mg/kg) or saline for 7 days at the same time at which the infectionwas induced. During treatment, animals were placed individually in metaboliccages to collect urine over a 24-h period for the measurement of specific enzymeactivities as markers of toxicity. Urine was collected under mineral oil immedi-ately after the first gentamicin injection (day 1) and 24 h before sacrifice (day 7),and the volume was noted. All samples were centrifuged (1,340 g) for 15 min,and the enzymuria was assessed immediately after centrifugation. At the time ofsacrifice, a midline abdominal incision was made and the right kidney of eachanimal was rapidly removed and bisected. The blood was centrifuged, and theserum collected was quickly frozen at 20C for the determination of creatinineand blood urea nitrogen (BUN) levels. The cortex of the kidneys was dissected,and a piece of tissue was quickly frozen in dry ice for further determination ofsphingomyelinase activity and the [3H]thymidine/DNA ratio. Another part of thecortical tissue was cut into small blocks (approximately 1 mm3) in a drop of 0.5%

    glutaraldehyde0.1 M phosphate buffer (pH 7.4) and left overnight in the samefixative at 4C.

    Enzymuria. The activities of -galactosidase, N-acetyl--D-glucosaminidase,and -glutamyltransferase were measured as an index of tubular damages. Theactivities of -galactosidase and N-acetyl--D-glucosaminidase, lysosomal en-zymes, were measured by the method of Maruhn (35). The activity of -glutamyltranspeptidase, an enzyme of the brush border membrane, was evaluated by themethodology of Persijn and van der Slik (42).

    Biochemical analysis. The cellular regeneration in the renal cortex was eval-

    uated by measuring the radioactivity of [3H]thymidine incorporated into DNA asdescribed by Laurent et al. (29) on purified DNA obtained from the corticaltissue of the right kidney. Sphingomyelinase (EC 3.1.4.12) activity was assayed inthe renal cortex as described previously (28). Serum creatinine and BUN levelswere evaluated with a Hitachi 737 apparatus.

    Histology. Cubes previously fixed overnight were washed with phosphatebuffer (0.1 M, pH 7.4), fixed in 1% osmium tetroxide for 60 min at roomtemperature, dehydrated in ascending grades of alcohol, and embedded inAraldite 502 epoxy resin. Thick sections (1 m) were cut with an Ultracut Eultramicrotome (Leica Canada, Inc., Quebec, Quebec, Canada), stained with hottoluidine blue, and examined with a blind code to identify gross lesions. Micro-scopic renal lesions were scored on plastic sections at a magnification of400.Each slide was coded so that identification of the groups was not possible for theobserver. Slices came from three different pieces of renal cortex for each rat, andfive rats per group were used. The following lesions in the renal cortex wererecorded: isolated cell necrosis, tubular necrosis (proximal tubule with more than50% necrotic cells), tubular desquamation (proximal tubule with 100% necroticcells), the number of proximal tubules with metachromatic material in their

    lumens, and the number of interstitial cells (no specific identification of cell typewas made). The total number of proximal tubules was also measured on eachslice. The number of isolated necrotic cells, the number of necrotic proximaltubules, the number of desquamated proximal tubules, and the number of prox-imal tubules with metachromatic material in their lumens were recorded as thepercentages of the total number of proximal tubules on each respective slice andassigned a score as follows: 0 to 9%, 1; 10 to 19%, 2; 20 to 29%, 3; etc. The scorefor the interstitial cells was obtained by dividing the total number of interstitialcells (excluding endothelial capillary cells) by the total number of proximaltubules on each respective slice. The lesion scores were summed up to producea single toxicity score for each animal.

    Statistics. All statistical analyses were performed with the Stat-View SE Graphics 1988 program (Abacus Concepts, Inc., Berkeley, Calif.). Analysis ofvariance by a least-squares method was used to determine the statistical signif-icance of the difference between groups. Ap value smaller than 0.05 (P 0.05)was considered significant. Group comparisons were performed by Fishers pro-tected least significant difference test.

    RESULTS

    Effectiveness study.Figure 1 shows the effectiveness of gen-tamicin (20 and 40 mg/kg) given once daily to infected rats for3 days. In infected animals treated with gentamicin (20 mg/kg),the log CFU per gram was significantly lower than that for theinfected controls only when gentamicin was administered at0100 h (P 0.05). When gentamicin was injected at a dose of40 mg/kg, a significant reduction (P 0.05) in the log CFU pergram of tissue compared with that for control infected rats wasobserved at all injection times, but the reduction in the bacte-rial counts was slightly greater (not significant) when gentami-cin was injected at 0100 h than at other times of day.

    Figure 2 shows the effectiveness of a once-daily gentamicin

    (40 mg/kg) injection of infected rats for 7 days. Gentamicinproduced a significant reduction (P 0.05) of the log CFU pergram of tissue in all treated groups (Fig. 2, dotted line) incomparison to that of their time-matched controls (solid line).Figure 2 shows also that gentamicin injected at 0100 h steril-ized 40% of infected kidneys, while the percentage of sterilekidneys was 25, 0, and 33% in animals treated at 0700, 1300,and 1900 h, respectively.

    Nephrotoxicity study. Figure 3 shows excretion of-galac-tosidase, N-acetyl--D-glucosaminidase, and -glutamyltrans-ferase in the 24-h urine of infected rats treated for 7 days withgentamicin (40 mg/kg/day) at 0700, 1300, 1900, and 0100 h.The excretion of each enzyme was significantly higher inurine of animals injected at 1300 than in urine of animalsinjected at any other time of day. Similar effects were observed

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    on the first day of treatment, but the level was much greater onday 7.

    The inhibition of sphingomyelinase activity, the cellular re-generation, and the histopathological scores measured in therenal cortex of rats treated for 7 days are presented in Fig. 4.The inhibition of sphingomyelinase activity was significantlymore severe when gentamicin was injected at 1300, 1900, and0100 h than when animals were injected with gentamicin at0700 h (P0.01). In comparison to their time-matched con-trols, the animals treated at 1300 h were the only ones to show

    a significant inhibition of the sphingomyelinase activity (P0.01). The cellular regeneration was significantly higher in therenal cortex of animals treated with gentamicin at 1300 than intheir time-matched controls (P 0.01) and in other treatedgroups (P 0.01). The histopathological nephrotoxicity scoreswere also significantly higher for animals treated with genta-micin at 1300 h than for their time-matched controls (P 0.01)

    and for the other groups treated at the other times of day (P0.01).

    Figure 5 shows plastic sections of the left renal cortex ofinfected nontreated animals (controls) (A) and the renal cor-tex of infected animals treated with gentamicin for 7 days at0100 (B) or 1300 (C) h. The renal cortex of infected controlanimals shows typical signs of pyelonephritis such as the pres-ence of intensive peritubular infiltration with inflammatorycells and the loss of the structural integrity of the tissue. Theperitubular cell infiltration was less severe in gentamicin-

    treated infected rats. In infected animals treated with genta-micin at 1300 h, the renal cortex still shows peritubular cellinfiltration as well as signs of gentamicin toxicity such as des-quamated and necrotic proximal tubular cells (Fig. 5C) whilethese changes were not observed for animals treated with gen-tamicin at 0100 h (Fig. 5B). However, large lysosomes can beobserved in proximal tubular cells in the latter group (Fig. 5B).

    FIG. 1. Log CFU per gram of kidney ( standard deviations [SD]) of animals infected withE. coliand treated with either saline (infected) or a single daily injection

    of gentamicin (infected and treated) at doses of 20 and 40 mg/kg for 3 days at either 0700, 1300, 1900, or 0100 h. Treatment was initiated 24 h after the induction ofinfection. , significantly different from time-matched infected and treated animals (P 0.05). Open boxes, light period; closed boxes, dark period.

    FIG. 2. Log CFU per gram of kidney ( standard deviations [SD]) and percentages of sterile kidneys (treated animals only) of animals infected with E. coli andtreated with either saline (infected) or a single daily injection of gentamicin (infected and treated) at doses of 40 mg/kg for 7 days at either 0700, 1300, 1900, or 0100 h., significantly different from time-matched infected and treated animals (P 0.05). Open box, light period; closed box, dark period.

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    These observations are consistent with the data for the his-topathological quantification of the cellular toxicity induced bygentamicin presented in Fig. 4.

    Renal function.Figure 6 shows creatinine and BUN levels in

    FIG. 3. Twenty-four-hour urinary excretion of-galactosidase (A),N-acetyl--D-glucosaminidase (B), and -glutamyl transpeptidase (C) in infected ratstreated for 7 days with saline or gentamicin. Gentamicin was given as a singledaily dose of 40 mg/kg/day i.p. at either 0700, 1300, 1900, or 0100 h. Theenzymuria was expressed as a percentage of control animals standard devia-tion (SD). , significantly different from the respective time-matched controls(P 0.01); , statistical differences (P 0.05) between the groups under theextremities of the line. Open boxes, light period; closed boxes, dark period.

    FIG. 4. Inhibition of sphingomyelinase activity (A), cellular regeneration(B), and total histopathologic nephrotoxicity scores (C) in renal cortices ofinfected rats treated for 7 days with gentamicin. Gentamicin was given once dailyat either 0700, 1300, 1900, or 0100 h at a dose of 40 mg/kg/day. The data arepresented as the means standard deviations (SD) and expressed as the per-centages of the values measured for control animals. , significantly differentfrom the respective time-matched controls (P 0.01); , statistical differences(P 0.01) between the groups under the extremities of the line. Open boxes,light period; closed boxes, dark period.

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    serum as well as the creatinine clearance of infected ratstreated with a single daily injection of gentamicin at a dose of40 mg/kg for 7 days. Serum BUN and creatinine levels weresignificantly higher in animals treated with gentamicin at1300 h than in their time-matched controls (P 0.05) and inrats treated at 0700 and 0100 h (P 0.05). The creatinineclearance was significantly lower in animals treated with gen-tamicin at 1300 than in their time-matched controls (P 0.05)and in rats treated at 0700 and 0100 h (P 0.05). Furthermore,the creatinine clearance was significantly lower in animals

    treated with gentamicin at 1900 than in animals treated at0700 h (P 0.05).

    DISCUSSION

    The objective of our study was to evaluate the effects of thetime of administration on the effectiveness and the renal tox-

    icity of gentamicin in an experimental model of pyelonephritisin rats. Our data show that both the effectiveness and thetoxicity of gentamicin varied over the 24-h period and that theefficacy was best at the time when the toxicity of the drug wasthe lowest. Data indicated also that the presence of infectiondoes not modify the circadian rhythm of aminoglycoside tox-icity.

    Temporal variations in the renal toxicity of aminoglycosideshave been reported for experimental animals since 1982.Briefly, Nakano and Ogawa (37) showed for the first time thatthe survival rate of mice treated once daily with gentamicin washigher when the drug was injected in the middle of the activityperiod (0200 h) and lower when gentamicin was injected in themiddle of the rest period (1400 h) of the animals. Similarresults were reported by Cambar and his colleagues (13, 39)with high doses of gentamicin, dibekacin, and netilmicin. Tem-poral variations in the nephrotoxicity of aminoglycosides werealso observed with lower doses of gentamicin (19, 40, 51),amikacin (14, 16), and isepamicin (52). In all these studies, thehigh acute doses of aminoglycosides produced greater toxicitywhen they were injected in the middle of the rest period, whiletoxicity was less when the antibiotics were injected in the mid-dle of the activity period of the experimental animals. Studiesdone in our laboratory showed similar results, as we injecteddaily small doses of aminoglycosides over 7 to 10 days. In fact,our data showed that tobramycin (30, 33) and isepamicin (49)induced higher toxicity when injected at 1400 h than when thesame dose was injected at 0200 h. Recently, Prins et al. showedfor the first time that the incidence of nephrotoxicity was sig-

    nificantly higher in patients receiving aminoglycosides duringtheir sleeping period (midnight to 0730 h) than in patientsreceiving drugs at other times of day (44).

    The mechanisms responsible for the temporal variation inrenal toxicity of aminoglycosides are still unknown. Some au-thors suggested that circadian rhythms in the urinary excretionof water, electrolyte, and renal perfusion (45); in membranestructure and fluidity (17); and in the number and size ofautophagic vacuoles in the cytoplasm of tubular cells (43)might be responsible for the temporal variations in the renaltoxicity of aminoglycosides. Temporal variations in the phar-macokinetics of aminoglycosides in serum could also be in-volved in the time-dependent changes in aminoglycoside neph-rotoxicity. Such changes were found in the levels of theseantibiotics in plasma in animals (24, 30, 38, 46, 52) and in

    humans (34, 38, 50). Time-dependent changes were also foundin the cortical accumulation (30, 40, 51, 52) and in the kineticsof the intracortical accumulation rate (31) of different amino-glycosides.

    Other experiments in our laboratory showed that the 24-hvariation in the serum corticosterone levels or changes in thesubcellular distribution of aminoglycosides could not explainthe chrononephrotoxicity of aminoglycosides (6). However,our data showed that a time-restricted feeding schedule in-duced a shift in the maximal and minimal levels of gentamicinnephrotoxicity in animals injected at different times of the day(5). Furthermore, fasting abolished the 24-h variations in thenephrotoxicity of gentamicin (4). Fasting was also associatedwith higher levels of tobramycin in the serum and cortex (32).We thus concluded that the time of dosing of gentamicin rel-

    FIG. 5. Plastic sections of the right renal cortex of infected control animals

    (A) and infected animals treated for 7 days with gentamicin at either 0100 h (B)or 1300 h (C). G, glomerulus; PT, proximal tubule; DT, distal tubule; NPT,necrotic proximal tubule; DPT, desquamated proximal tubule. Arrowheads,metachromatic material in tubular lumen. Magnification, ca. 300.

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    ative to the time of feeding seems to be a more importantmodulator of aminoglycoside nephrotoxicity than is the light-dark cycle.

    In this study, we showed again that gentamicin inducedhigher toxicity when injected in the middle of the rest period(1300 h) and that toxicity was lower when the drug was injectedin the middle of the activity period (0100 h). Moreover, no

    temporal variations in the cortical accumulation of gentamicinwere observed in the present study (data not shown), as re-cently demonstrated with tobramycin (33). As these data wereobserved for animals suffering from pyelonephritis, it can thusbe concluded that the presence of infection did not modify thetemporal variations in the renal toxicity of gentamicin.

    Our results also demonstrate a circadian rhythm in the ther-apeutic efficacy of gentamicin in the treatment of experimentalE. coli pyelonephritis. The effectiveness of gentamicin wasevaluated by two methods: (i) the log CFU of bacteria in therenal tissue in the treated animals compared to those in theirtime-matched infected controls and (ii) the percentage of ster-ile kidneys, observed at the end of therapy. In fact, the per-centage of sterile kidneys was higher when the drug was in-jected at 0100 h than when it was injected at 0700, 1300, and1900 h. Thus, the effectiveness of gentamicin was highest dur-ing the activity period in animals treated with gentamicin atdoses of 40 mg/kg for 7 days.

    Several factors might explain the temporal variations in theeffectiveness of gentamicin in this experimental model. First,the higher water and food intake, resulting in a higher urineoutput, might have contributed to increasing the efficacy anddecreasing the toxicity of gentamicin in infected animals wheninjected during the activity period. In fact, it might have con-tributed also to increasing the clearance of bacteria from thekidney and increasing the efficacy of gentamicin during thisperiod of the day. However, since no temporal variations wereobserved in the cortical accumulation of gentamicin in thepresent study, these drug levels could not contribute to the

    temporal variations in the effectiveness of the drug. It is inter-esting to note that Hosokawa et al. (24) also showed temporalvariations in the effectiveness of a single dose of amikacin in anexperimental model of i.p. infection with Pseudomonas aerugi-nosa. In infected mice, the 50% effective dose of amikacin waslower in the midlight phase (1300 h) at time of lower clearancethan in the middark phase (0100 h), when clearance washigher.

    Based on our studies and on the evidence available in thecurrent literature, it is quite clear that the renal toxicity ofaminoglycosides can be reduced by giving the drug as a singledaily injection when patients are active. Even if extrapolationof experimental data to humans is always uncertain, it is rea-sonable to believe that the administration of gentamicin in thebeginning or the middle of the day in humans may reduce renal

    toxicity and increase the efficacy of these antibiotics. In fact,some chronopharmacologic studies have already been appliedto patients with very conclusive results (34, 38, 50). In humans,the clearance of aminoglycosides was lower during the night(in the rest period) and maximal during the activity period(day). These results perfectly correlate with those obtained forexperimental animals. The prospective study of Prins et al. (44)clearly showed that the incidence of toxicity in 179 patients wassignificantly higher when the drug was given as a once-dailyinjection during the sleeping period of patients. Further inves-tigations must be done to investigate the effect of the time ofadministration on aminoglycoside effectiveness in patients, butphysicians should already be careful when administering ami-noglycosides to patients at night. The clinical applications ofthese results may be eventually extended to pathologies such as

    FIG. 6. BUN level (A), serum creatinine level (B), and creatinine clearance(C) of infected rats treated for 7 days with saline or gentamicin. Gentamicin wasgiven as a single daily dose of 40 mg/kg at either 0700, 1300, 1900, or 0100 h. Thedata are presented as the means standard deviations (SD) and expressed as thepercentages of the values measured for control animals. , significantly differentfrom the respective time-matched controls (P 0.05); , statistical differences(P 0.05) between the groups under the extremities of the line. Open boxes,light period; closed boxes, dark period.

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    pyelonephritis and pneumonia that could be treated with once-a-day aminoglycosides.

    ACKNOWLEDGMENTS

    This study was supported by the Kidney Foundation of Canada. M.LeBrun is the recipient of a studentship from the Fonds pour laFormation de Chercheurs et lAide a la Recherche (F.C.A.R.).

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