In vitro uptake of gentamicin by rat renal cortical tissue

Interactions of drugs with the developing kidney

Interactions between drugs and the kidney are necessary for renal drug elimination, metabolism, and occasionally for therapeutic effect. These interactions may result also in renal toxicity. Understanding the kidney's role in drug-handling helps the clinician to be aware of potential drug interactions and toxicity. Drug disposition, elimination, and toxicity may differ with development and are to be considered when prescribing drugs for children. Nephrotoxicity associated with drugs, although common, is usually reversible with discontinuation of the drug; however, when drug therapy with a well-known nephrotoxic drug (e.g., cisplatin) is necessary, pharmacologic modulators may play a role in limiting the associated nephrotoxicity.

Renal handling of tobramycin in the isolated perfused rat kidney

The renal handling of tobramycin (TOB), an aminoglycoside antibiotic (AG), was studied using a single-pass isolated perfused rat kidney with moment analysis. In the bolus administration study at tracer concentration (7.4 microM), 32% of the glomerular-filtrated TOB remained in the lumen, but no TOB was found in the vein. This ratio of the luminal uptake was reduced in a dose-dependent manner. Other aminoglycosides such as gentamicin inhibited this uptake, but tetraethylammonium and glucosamine had no effect. In addition, under the alkalinuria condition, TOB uptake was decreased to 67% of the control value. This indicated that TOB has mainly been taken into the renal epithelial cells from their luminal site and that this uptake process was saturable and specific for AGs which have more than one cationic group. The present findings should be helpful in developing a method to reduce the nephrotoxicity of AGs and to identify their toxicity mechanisms.

The effect of guanidine on the accumulation of amikacin in guinea pig renal cortical slices

The role of a recently identified organic ion transport system in the accumulation of the aminoglycoside (AG), amikacin (AK) in the kidney was investigated in the present study. Because this transport system has been characterized as being a carrier for the organic cation, guanidine, the effect of guanidine on the uptake of AK into renal slices from guinea pig was examined. Renal slices incubated in medium containing AK concentrated the drug against a concentration gradient (i.e. slice:medium ratio (S/M) greater than 1.0). This uptake was significantly reduced when an equimolar concentration (1 x 10(-5) M) of another AG, gentamicin was added to the incubation medium. In contrast, AK uptake was relatively insensitive to the presence of the cation, tetraethylammonium (TEA) in the medium. Guanidine was also ineffective at inhibiting AK uptake into slices and reduced AK uptake by only 22% at guanidine concentrations of 1 x 10(-2) M. In comparison, TEA was slightly more sensitive to the presence of guanidine in the incubation media since TEA uptake was reduced by 22% at guanidine concentrations of 1 x 10(-3) M and reduced by approximately 70% at guanidine concentrations of 1 x 10(-2) M. Thus, the results of the present study suggest that the guanidine transport system does not play a role in the renal accumulation of AK since the presence of guanidine in the incubation medium had little effect on the accumulation of AK into renal cortical slices.

Correlation between renal membrane binding and nephrotoxicity of aminoglycosides

The kinetics of aminoglycoside binding to renal brush border and basolateral membrane vesicles from rat renal cortex were studied by using [3H]amikacin. [3H]amikacin binding to renal membranes was found to be a rapid, saturable process with a fourfold greater affinity for basolateral membranes than for brush border membranes (Kd basolateral = 607 microM; Kd brush border = 2,535 microM). Renal membranes prepared from immature rats (2 to 3 weeks old) exhibited a significantly lower affinity compared with membranes from adults (Kd basolateral = 2,262 microM; Kd brush border = 6,216 microM). Additionally, the inhibitory behavior of several aminoglycosides versus [3H]amikacin binding to brush border membranes revealed the following rank order of potency: neomycin greater than tobramycin approximately gentamicin approximately netilmicin greater than amikacin approximately neamine greater than streptomycin. The relative insensitivity of immature rats to aminoglycoside-induced nephrotoxicity in vivo and the comparative nephrotoxicity of the various aminoglycosides suggest that renal membrane-binding affinity is closely correlated to the nephrotoxic potential of these antibiotics.

The use of renal tubule fragments isolated from the rat to investigate aspects of gentamicin nephrotoxicity

A suspension of renal tubule fragments from the rat was prepared by a method involving collagenase digestion of the excised renal cortex and dispersion of the digest by passage through a nylon mesh. Through the use of scanning electronmicroscopy it was confirmed that the tubular lumena were patent, thus ensuring access of medium to both the luminal and the contraluminal membranes of the tubular cells. The viability of the tubule fragments was ascertained by measuring the rate of formation of glucose from pyruvate as substrate and the uptake of [14C] L-lysine against a concentration gradient. The uptake of L-lysine was unimpaired in the presence of gentamicin (10(-3) M), suggesting that there is no competition between this basic amino acid and the polycationic aminoglycoside for transport into tubular cells. The uptake of [3H] gentamicin was studied and found to be reduced in the presence of 2,4-dinitrophenol, potassium cyanide, and ouabain. The reduced uptake in the presence of ouabain was interpreted to mean that a component of gentamicin uptake, which occurs at the luminal membrane, may be driven by the Na+ gradient created by Na+-K+ATPase activity at the contraluminal membrane. This renal tubule preparation offers advantages over the kidney-slice technique for studies into the mechanisms of aminoglycoside nephrotoxicity.

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.

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.

Increased nephrotoxicity of gentamicin in pyelonephritic rats

Multiple factors may increase the nephrotoxic potential of aminoglycosides. We studied gentamicin susceptibility of kidneys infected with E. coli. Several parameters of renal function, histological changes on light and electron microscopy, and drug levels in renal parenchyma were compared in pyelonephritic and normal rats treated with low doses (10 mg/kg/Q8 hr for 3 days), or high doses (60 mg/kg/day for 14 days), of gentamicin. A significant increase (P less than 0.01) in beta-galactosidase and protein excreted in urine over a period of 17 days associated with severe changes in diuresis and osmolality was noted in the infected treated rats (low doses) compared with normal, treated, infected or control animals. Histological modifications compatible with gentamicin nephrotoxicity were more persistent in the infected treated animals. A significant decrease in 14C inulin (P less than 0.01) and 3H-PAH clearance and secretion (P less than 0.02) was observed in the infected treated rats receiving high doses of antibiotics. Cellular necrosis and tubular desquamation also were more severe in this group. Gentamicin levels in the cortex and medulla of infected animals were significantly higher than in the normals (P less than 0.01) and might have been responsible for the increased toxicity noted in the pyelonephritic animals. Infected kidneys appeared to be more susceptible to the nephrotoxic potential of gentamicin.

Determination of aminoglycosides in rat renal tissue by enzyme immunoassay

The enzyme-multiplied immunoassay technique for the determination of gentamicin or amikacin in serum was evaluated for use in rat renal tissue. After the addition of either gentamicin or amikacin to tissue homogenate, the assay of the supernatant showed a reduced recovery, depending on the amount of renal tissue present per milliliter of homogenate. The recovery was independent of the amount of aminoglycoside added. This reduction could be due to either protein binding or interference with the enzyme-multiplied immunoassay technique by substances released from the renal tissue. When the enzyme-multiplied immunoassay technique is used for aminoglycoside assay in renal tissue, care should be taken to minimize the amount of tissue present in the homogenate or to correct for the decreased recovery.

Clinical and pathophysiologic aspects of aminoglycoside nephrotoxicity

Aminoglycoside antibiotics continue to be a mainstay of therapy in the clinical management of gram negative infections, but a major factor in the clinical use of aminoglycosides is their nephrotoxicity. With gram negative organisms accounting for the majority of hospital acquired infections, the occurrence of aminoglycoside induced acute renal failure has become commonplace. Presently at least 10% of all cases of acute renal failure can be attributed to these antibiotics. This article will cover the renal handling of the aminoglycosides, the pathogenetic mechanisms of nephrotoxicity, and the clinical aspects of aminoglycoside induced acute renal failure with particular emphasis on recent data which have increased our understanding of the interaction of aminoglycosides with the renal tubular cell and the effects of this interaction on cellular function and integrity.

Pathogenesis of renal failure due to aminoglycosides and contrast media used in roentgenography

The etiology of acute renal failure has changed in recent years due to the recognition of drug nephrotoxicity as a more common cause. In this communication we emphasize recent information concerning the pathophysiology of nephrotoxic acute renal failure produced by aminoglycoside antibiotics and the contrast media used in roentgenography. The aminoglycosides are excreted primarily by glomerular filtration; however, net tubular reabsorption and renal parenchymal accumulation do occur. The exact mechanism of uptake is not clear, but the luminal membrane seems primarily involved. The pathogenesis of nephrotoxicity, although probably linked to cortical accumulation, is complex since experimental animals recover from gentamicin-induced renal failure despite continued administration of the drug. Knowledge of the precise cellular mechanisms of injury awaits further studies. Histologic damage is usually limited to proximal tubular necrosis and, clinically, the renal failure is nonoliguric. Although reports of the contrast media used in roentgenography producing acute renal failure have increased, the pathogenesis is unclear. Evidence supporting various theories is reviewed.

Renal tubular transport of gentamicin in the rat

The renal handling of gentamicin in the rat was examined by clearance, microinjection, and renal cortical-slice techniques. The steady-state renal clearance of 14C-gentamicin, when corrected for the 7.5% binding to plasma protein, was not significantly different from that of 3H-inulin. At the end of the renal clearance experiments, the cortical concentration of gentamicin was 93 +/- 7 microgram/g of tissue (N = 7), a concentration threefold greater than that of the medulla and 20-fold greater than that of serum. Absorption of 3H-gentamicin along the proximal convoluted tubule and loop of Henle was demonstrated by the tubular microinjection technique. No reabsorption of 3H-gentamicin was detected beyond the early distal convoluted tubule. The tubular absorption of 3H-gentamicin was load dependent. Fractional absorption of 3H-gentamicin averaged 30.1 +/- 2.7% when the dose of 3H-gentamicin injected into early proximal tubular convolutions averaged 132 +/- 17 pg. It was decreased to 13.6 +/- 2.6% when the microinjected dose of gentamicin was increased to 1996 +/- 388 pg. No evidence of transtubular absorption of 3H-gentamicin was detected during the microinjection experiments. Microperfusion of pertubular capillaries failed to demonstrate urinary precession of 3H-gentamicin over 14C-inulin, a finding which argues against a rapid transtubular secretory flux of gentamicin. Significant uptake of gentamicin was demonstrated by renal cortical slices incubated in medium containing 14C-gentamicin. The accumulation of 14C-gentamicin by renal cortical slices was not inhibited by probenecid or N1-methylnicotinamide but was inhibited by netilmicin and tobramycin. These data support the conclusion that the renal accumulation of gentamicin reflects transport of gentamicin across both the apical and basolateral membranes of proximal tubular epithelium.

Influence of single or multiple doses of gentamicin and netilmicin on their cortical, medullary, and papillary distribution

In this study, the comparative intrarenal distribution and accumulation of both gentamicin and netilmicin were investigated in normal rats. The animals received 1, 3, or 14 injections of 10 mg of gentamicin or netilmicin per kg. A total of 324 animals and 648 kidneys were analyzed. These animals were sacrificed at from 1 h to 25 days after the intraperitoneal injections. At each timed interval, the serum, urine, cortex, medulla, and papilla were analyzed for antimicrobial content. The peak serum values of gentamicin (8 to 12 mug/ml) and netilmicin (9 to 14 mug/ml) were close to those found in humans. There was a progressive increase in the cortical concentrations of both antibiotics from a low of 53 mug/g to a high of 719 mug/g when the animals were given increasing doses of the agents. At most timed intervals, the concentrations of gentamicin within the cortex were slightly lower than those of netilmicin. The accumulation of the drugs was also demonstrated in the medulla, where therapeutic levels could be detected for up to 25 days after the cessation of therapy. Even though gentamicin and netilmicin were transiently present in the papilla after 1 or 3 injections, both drugs could still be detected in the papilla on day 25 after 14 doses. The urinary concentration closely paralleled the papillary concentration. If applicable to humans, the persistence of high levels of both drugs within the medulla and papilla may have therapeutic implications.