Aminoglycoside antibiotics and renal function: changes in urinary gamma-glutamyltransferase excretion

Polyphenolic fraction of Algerian propolis protects rat kidney against acute oxidative stress induced by doxorubicin

We evaluated the effects of propolis extract on renal oxidative stress induced by doxorubicin throughout an analytical and pharmacological study of the eastern Algerian propolis using thin layer chromatography, ultra-violet-high-performance liquid chromatography) and gas chromatography-mass spectrometry. The pharmacological study was carried out in vivo on Wistar rat pre-treated with propolis extract 100 mg/kg/day for seven days. Doxorubicin at 10 mg/kg of body weight was administered intravenously on Day 7. Serum creatinine concentration, scavenging effect of flavonoids, lipid peroxidation and glutathione concentration were measured. Chemical analysis allowed identification and quantification of the phenolic compounds including pinostrombin chalcone (38.91%), galangin (18.95%), naringenin (14.27%), tectochrysin (25.09%), methoxychrysin (1.14%) and a prenylated coumarin compound suberosin (1.65%). The total flavonoid concentration in the propolis extract was 370 mg (quercetin equivalents QE) /g dry weight (QE/g DWPE). Propolis extract restored the renal functions and reduced the toxic effect of doxorubicin. These data show a protective effect of Algerian propolis extract against doxorubicin-induced oxidative stress.

Attenuation of oxalate-induced nephrotoxicity by eicosapentaenoate-lipoate (EPA-LA) derivative in experimental rat model

Hyperoxaluria is one of the major risk factors for the formation of urinary calcium oxalate stones. Calcium oxalate crystals and their deposition have been implicated in inducing renal tubular damage. Lipoic acid (LA) and eicosapentaenoic acid (EPA) have been shown to ameliorate the changes associated with hyperoxaluria. This prompted us to investigate the nephroprotectant role of EPA-LA, a new derivative, in vivo in hyperoxaluric rats. Elevation in the levels of calcium, oxalate and phosphorus, the stone-forming constituents, were observed in calculogenic rats as a manifestation of crystal deposition. Tubular damage to the renal tissue was assessed byassaying the excretion of marker enzymes in the urine. Damage to the tubules was indicated by increased excretion of alkaline phosphatase (ALP), lactate dehydrogenase (LDH), gamma-glutamyl transferase (gamma-GT), beta-Glucuronidase (beta-GLU) and N-Acetyl beta-D glucosaminidase (NAG). Fibrinolytic activity was found to be reduced. Administration of EPA, LA and EPA-LA reduced the tubular damage and decreased the markers of crystal deposition markedly, which was substantiated by the reduction in weight of bladder stone formed. Our results highlight that EPA-LA is the most effective drug in inhibiting stone formation and mitigating renal damage caused by oxalate toxicity, thus confirming it as a nephroprotectant. Further work in this direction is warranted to establish the therapeutic effectiveness of this new derivative.

Once daily aminoglycoside therapy. Is it less toxic than multiple daily doses and how should it be monitored?

After 50 years of clinical experience with the aminoglycoside agents, there is continuing debate over the most appropriate administration regimen for these drugs. In recent years, once daily administration has been used increasingly, in the hope of both improving efficacy and reducing toxicity. At least 30 controlled clinical trials have compared once versus conventional multiple daily administration. Efficacy was assessed in some, but not all, studies using clinical and/or bacteriological cure. Toxicity was generally determined using rather nonsensitive end-points such as measurement of serum creatinine for nephrotoxicity and clinically detectable hearing loss for ototoxicity. The results of individual clinical trials and subsequent meta-analyses have been variable. However, 5 of 9 meta-analyses found clinical efficacy to be significantly better with once daily administration, and in 3 of the 9 there were significantly less nephrotoxicity with once daily administration. The results were not significant for ototoxicity in any of the meta-analyses. There is debate about how therapeutic drug monitoring should be performed, and whether it is still required with once daily administration. Previous experience with the aminoglycosides, especially in patients with impaired drug clearance caused by renal impairment, suggests that monitoring is still prudent. Results from the once daily administration trials appear to support this. Various methods of monitoring and dose adjustment have been proposed. The most common is to measure a 24-hour trough concentration and to adjust the dose to maintain the trough concentration below a value of 2, 1 or 0.5 mg/L. However, this method allows for greater total aminoglycoside exposure than has been permitted with conventional dosages, increasing the likelihood of toxicity in patients with impaired aminoglycoside clearance. Other methods measure drug concentrations at a time-point or points within the dose interval (when the concentration is still measurable), and adjust the dose according to concentration-time curve nomograms or to a target area under the concentration-time curve. This allows the use of higher doses in those with high drug clearance. Furthermore, in patients with impaired clearance, drug exposure is limited to the same extent as, or less than, that with conventional multiple daily administration. To date no controlled trials have compared methods of dose-individualisation. In summary, in addition to a slight overall improvement in efficacy, once daily administration has resulted in a small reduction in nephrotoxicity. In the studies using more sensitive measures of toxicity, the differences in toxicity were greater, strengthening the case for once daily administration. Therapeutic drug monitoring is probably required with once daily administration. Methods which use mid-dosage interval concentrations to gauge drug exposure would seem to be preferable over trough concentration measurement.

Sodium pentosan polysulphate--a novel inhibitor of urinary risk factors and enzymes in experimental urolithiatic rats

Sodium pentosan polysulphate (SPP) has been shown to inhibit calcium oxalate crystallization in vitro. Here, the effect of SPP was studied on in vivo crystallization. Ammonium oxalate was used as the inducer of calcium oxalate crystallization in rats and the effect of SPP on in vivo crystallization factor is reported. The increased excretions of stone forming constituents associated with urinary marker enzymes are the salient features observed in experimental rats. Sodium pentosan polysulphate administration brought about a significant reduction in urinary stone forming constituents. It also decreased the extent of renal tubular damage as evidenced from the reduced level of marker enzymes in urine. These observations highlight the inhibitory capacity of SPP against in vivo calcium oxalate crystallization.

Estimation of quantitative enzymuria in dogs with gentamicin-induced nephrotoxicosis using urine enzyme/creatinine ratios from spot urine samples

The correlation between 24-hour urinary excretion of N-acetyl-beta-D-glucosaminidase (NAG) and gamma-glutamyl transferase (GGT) with urine NAG and GGT/creatinine ratios was assessed in dogs with gentamicin-induced nephrotoxicosis. Eighteen 6-month-old male Beagles with normal renal function were randomly divided into 3 groups of 6. Each group was fed a different concentration of protein (high protein, 27.3%; medium protein, 13.7%; and low protein, 9.4%) for 21 days. After dietary conditioning, gentamicin was administered at a dose of 10 mg/kg IM tid for 8 days and each group was continued on its respective diet. Endogenous creatinine clearance and 24-hour urinary excretion of NAG and GGT were determined after dietary conditioning (day 0) and on days 2, 4, 6, and 8 of gentamicin administration. In addition, urine NAG and GGT/creatinine ratios (IU/L divided by mg/dL) were determined from catheterized spot urine samples obtained between 7 and 10 AM on the same days. The correlation between 24-hour urinary enzyme excretion and urine enzyme/creatinine ratio in the spot urine samples was evaluated by simple linear regression analysis. Spot sample urine enzyme/creatinine ratios were significantly correlated with 24-hour urinary enzyme excretion through day 4 for dogs on low dietary protein, through day 6 for those on medium protein, and through day 8 for those on high dietary protein. Mean +/- SD baseline values for urine NAG/creatinine ratio and 24-hour urinary NAG excretion were 0.06 +/- 0.04 and 0.19 +/- 0.14 IU/kg/24 hr, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Variations in urinary gamma glutamyl transferase/urinary creatinine ratio in horses with or without pleuropneumonia treated with gentamicin

The urinary GGT/urinary creatinine (uGGT/uCR) ratio was measured on Days 1, 3 and 10 in 4 adult, healthy horses; in 6 adult, healthy horses treated with gentamicin at recommended dosages and 9 adult horses treated for pleuropneumonia with gentamicin at recommended dosages. Plasma creatinine and gentamicin trough concentrations were measured on the same days. The uGGT/uCr ratio was higher in the normal horses (mean +/- s.d. 22.85 +/- 13.69) than previously reported normal values (10.5 +/- 6.8) (Adams and McClure 1985). Analysis of variance for repeated measures was used to compare the ratio in the 3 groups while controlling for the effect of time. Sick horses had a significantly higher uGGT/uCr ratio than either of the 2 groups of normal horses. Both groups of horses that were treated with gentamicin had similar percentage increases in uGGT/uCr ratio over the treatment period with the most marked increases found between treatment Days 1 and 3. The increase in uGGT/Cr ratio was predominantly a result of an increase in uGGT activity rather than a decrease in uCr concentration. The increase in uGGT activity and uGGT/uCr ratio occurred without abnormalities in serum creatinine or gentamicin trough concentrations. These findings demonstrate that urine GGT activity and uGGT/uCr ratio should be expected to increase in response to gentamicin therapy at recommended dosages without measurable changes in serum creatinine. This suggests that an elevation of the uGGT/uCr ratio in horses being treated with gentamicin would not necessarily require changes in, or withdrawal of, the gentamicin treatment as long as increases in the plasma creatinine do not exceed 0.3 g/l and gentamicin trough concentrations are < 2 micrograms/l.

Dosing time-dependent nephrotoxicity of cyclosporin A during 21-day administration to Wistar rats

The incidence of cyclosporine A (CsA) nephrotoxicity with reference to the temporal stage of administration was studied during a chronic 21-day treatment in male Wistar rats. Oral administration (20 mg/kg/day) was given at four different times: 1, 7, 13, or 19 hours after light onset (HALO). Plasma creatinine and blood urea nitrogen (BUN) levels were determined at regular intervals over the 24 h: before treatment (day 0); 7, 14, and 21 days after the beginning of treatment (days 7, 14, and 21); and 7 and 14 days after CsA withdrawal (days 28 and 35). At the same times, creatinine clearance and g-glutamyl transferase urinary excretion were determined in the groups of animals treated at 7 and 19 HALO. Residual concentrations of CsA in the renal tissue were measured at the end of the treatment period (day 21) in all groups. Nephrotoxicity of CsA was dependent on the temporal stage of administration. The renal vasoconstriction showed by the increase in plasma creatinine and BUN levels and the decrease in creatinine clearance was maximal when the CsA was given at 7 and 19 HALO and was correlated to the tissue concentrations of CsA. Tubular injury seems to occur earlier and the return to normal function less rapidly in animals treated at 19 HALO compared with animals treated at 7 HALO.

Aminoglycoside antibiotics alter the electrogenic transport properties of cultured human proximal tubule cells

Monolayers of human proximal tubule (HPT) cells, when grown on permeable supports and mounted in Ussing chambers, spontaneously display a transepithelial potential difference (PD) and short-circuit current (Isc). These electrical parameters were used in the present study to determine if aminoglycoside exposure altered electrogenic sodium transport by HPT cells. The results of this determination demonstrated that exposure to gentamicin, at levels below that producing cell necrosis, caused a marked reduction in Isc and that this reduction followed the known in vivo nephrotoxicities of the aminoglycosides streptomycin, gentamicin, and neomycin. It was concluded through a similar analysis on a total of 14 isolates of HPT cells that the aminoglycosides repeatably reduced the electrogenic sodium transport of HPT cells. It was further determined that this alteration in electrogenic transport by gentamicin was mediated through exposure of the drug to the basolateral cell surface and that apical exposure had little effect. Evidence was obtained against the involvement of Na+, K(+)-ATPase, adenosine 3',5'-cyclic monophosphate, and sodium-coupled substrate transport in this alteration in electrogenic transport by the aminoglycosides. The basolaterally located Na+: CO3(-2):HCO3(-1) symporter is a possible site for aminoglycoside-induced nephrotoxicity.

Renal tolerance of rubidium chloride: short-term clinical evaluation

The rubidium and lithium ions are known to have opposite effects on a wide range of biochemical and behavioral parameters in experimental animals. Based on the proven effectiveness of lithium as an antimanic agent, several trials have been conducted with rubidium in the acute treatment of the depressive phase of bipolar illness. The results to date are promising. However, the 30- to 60-day biologic half-life of rubidium has mandated careful studies of potential toxicity before engaging in long-term administration of this ion to depressive subjects. One area of potential concern is the possibility of renal toxicity, which could be expressed as unexpectedly increased retention of rubidium. The data in this paper show that after 15 days of rubidium administration, there are no changes beyond the normal range in a variety of kidney function tests, including in four enzymes which are specific markers of tubule cell function.

Urinary excretion of enzymes in cirrhotics with renal failure

We studied the significance of urinary enzyme measurements in diagnosing proximal tubular damage in cirrhosis of the liver. Urinary excretion (u-enzyme) and fractional urinary excretion (FEenzyme) of gamma-glutamyltranspeptidase (GGT), leucine aminopeptidase (LAP), alkaline phosphatase (AP) and beta-glucuronidase (B-GLU) were quantified in 14 control subjects (group I), 12 cirrhotics with functional renal failure (group II), 13 cirrhotics with renal tubular damage (group III) and 7 non-liver patients with renal tubular damage (group IV). Urinary enzyme excretion and fractional enzyme excretion were significantly higher in the cirrhotics of group III than in the controls or group II. In group III, these tests usually reached values within the range of group IV. The sensitivity of urinary enzyme excretion was 0.92 and specificity ranged from 0.75 (u-LAP) to 1 (u-GGT; u-B-GLU). The sensitivity of fractional enzyme excretion was between 0.61 (FEB-GLU) and 0.84 (FEGGT; FELAP), while specificity was from 0.91 (FELAP; FEAP) to 1 (FEGGT; FEB-GLU). The results indicate that measurement of urinary enzymes may be very useful in diagnosing renal tubular damage in cirrhotic patients with impaired renal function.

Interaction between the renal excretion rates of beta 2-microglobulin and tobramycin in man

The renal excretion rate of beta 2-microglobulin in man is 127 +/- 98 ng/min at alkaline urine pH (pH 7). Tobramycin, up to intravenous doses of 160 mg (2 mg/kg) does not increase the renal excretion rate of beta 2-microglobulin. Tobramycin must have less affinity than gentamicin for the tubular system for active reabsorption of amino groups containing organic compounds. Due to this reduced affinity tobramycin will be absorbed less by the proximal tubular cells, which may be one of the reasons for tobramycin being less toxic than gentamicin. beta 2-Microglobulin excretion can be used as a parameter for the relative binding affinity of aminoglycosides.

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.

Nephrotoxicity of drugs, evaluated by renal enzyme excretion studies

Via various pathways, urinary enzymatic activities are changed by drugs. Nephrotoxic effects may be determined by such investigations. Numerous experimental series have formed the basis for the clinical application of this method. The pertinent data collected with analgesics and antibiotics, alone or in combinations, are discussed in this paper. The data from the literature were compared with personal investigations, in animals as well as in man. It is concluded that - under certain precautions - the nephrotoxicity of drugs can be evaluated by renal enzyme excretion studies.

Structural, functional, and clinical aspects of gamma-glutamyltransferase

GGT catalyses the transfer of gamma-glutamyl residues to amino acids or small peptides. A number of publications report the purification of GGT, the rat kidney enzyme being the best characterized. Bromelain treatment liberates an active form with a molecular weight of 68,000 separable into two nonidentical glycopeptides with molecular weights of 46,000 and 22,000; the latter contains the gamma-glutamyl binding site. GGT is intimately concerned in the synthesis and metabolism of glutathione through the gamma-glutamyl cycle. There is good evidence that this plays a role in the absorption of amino acids from the glomerular filtrate and from the intestinal lumen through a translocation mechanism. Many studies indicate that the GGT content of liver is increased by enzyme-inducing drugs and that this increase is reflected in elevated activity of the enzyme in blood serum. The serum assay has potential in monitoring drug compliance. Increased serum GGT activity encountered in chronic alcoholics seems to be partly due to microsomal enzyme induction. Utility of the assay in detecting alcoholism is controversial, but it is a useful index to compliance with therapy. Dramatic increases in activity are found in many chemically-induced animal tumors, and can be recognized in premalignant cells long before any morphological changes become evident. It has been used as a test for hepatic metastases, but its predictive value has shown a wide range in the hands of many authors. A similar controversy applies to its role in monitoring cancer therapy. Many synthetic substrates have been used to measure serum GGT activity. Currently, L-gamma-glutamyl-p-nitroanilide is the most popular. Males have higher values than females; activity is very high in the neonate and rather low in pregnancy. The most universal application of serum GGT assay is in diagnosis of liver and biliary tract disease. It is widely believed that higher values occur in biliary obstruction than in parenchymal disease. However, the percentage incidence of abnormalities and the overlap of values in individual cases in different disease categories are so great that the enzyme cannot be recommended for this purpose. Isoenzyme analyses have been performed in an attempt to improve the diagnostic specificity of the serum GGT assay. Tissue-specific patterns have not been described, and disease-specific patterns cannot be reproduced with confidence. Whereas exciting advances are being made in understanding the molecular structure, mechanism, and functions of the enzyme it has yet to find a genuinely useful diagnostic role substantiated by a convincing body of scientific data.

[Tobramycin concentrations in human renal tissue (author's transl)]

Investigation of kidneys from 20 patients revealed relatively low tobramycin concentrations in cortex and medulla after one day of treatment. After administration for several days a significant accumulation was observed in only one of three patients. Attention is drawn to the higher tobramycin concentrations found in renal parenchyma which has undergone chronic inflammatory changes compared to the "normal" values in kidneys infiltrated by tumours. A higher accumulation thus occurs in renal tissue which has already undergone structural damage as a result of bacterial inflammation.

Effect of anticonvulsant drugs on urinary excretion of gamma-glutamyl transferase in women

Excretion of gamma-glutamyl transferase was found to be significantly higher in a group of epileptic patients on long-term anticonvulsant therapy than in normal subjects. The losses, which may reflect renal enzyme induction, were unrelated to drug dose or duration of therapy and were significantly lower than those found in normal healthy pregnant women at term.