[3H]gentamicin uptake in brush border and basolateral membrane vesicles from rat kidney cortex

Entry of aminoglycosides into renal tubular epithelial cells via endocytosis-dependent and endocytosis-independent pathways

Aminoglycoside antibiotics such as gentamicin and amikacin are well recognized as a clinically important antibiotic class because of their reliable efficacy and low cost. However, the clinical use of aminoglycosides is limited by their nephrotoxicity and ototoxicity. Nephrotoxicity is induced mainly due to high accumulation of the antibiotics in renal proximal tubular cells. Therefore, a lot of studies on characterization of the renal transport system for aminoglycosides so far reported involved various in-vivo and in-vitro techniques. Early studies revealed that aminoglycosides are taken up through adsorptive endocytosis in renal epithelial cells. Subsequently, it was found that megalin, a multiligand endocytic receptor abundantly expressed on the apical side of renal proximal tubular cells, can bind aminoglycosides and that megalin-mediated endocytosis plays a crucial role in renal accumulation of aminoglycosides. Therefore, megalin has been suggested to be a promising molecular target for the prevention of aminoglycoside-induced nephrotoxicity. On the other hand, recently, some reports have indicated that aminoglycosides are transported via a pathway that does not require endocytosis, such as non-selective cation channel-mediated entry, in cultured renal tubular cells as well as cochlear outer hair cells. In this commentary article, we review the cellular transport of aminoglycosides in renal epithelial cells, focusing on endocytosis-dependent and -independent pathways.

Gender difference in Cisplatin-induced nephrotoxicity in a rat model: greater intensity of damage in male than female

Background

Nephrotoxicity and hepatotoxicity are side effects of Cisplatin (CP) therapy.

Objectives

We investigated the role of gender in CP-induced nephrotoxicity and hepatotoxicity.

Materials and Methods

Low dose of CP (1 mg/kg/day; ip) was administered daily to male and female Wistar rats for 15 consecutive days. Serum creatinine (Cr), blood urea nitrogen (BUN), malondialdehyde (MDA), nitric oxide (NO) metabolite, and magnesium (Mg) levels were determined.

Results

The percentage of weight loss and the serum levels of MDA and nitrite in male and female animals were not statistically different. However, the serum levels of BUN, Cr, Mg, and kidney MDA levels, and kidney weight and damage score were significantly greater in males than in females (P < 0.05).

Conclusions

CP-induced nephrotoxicity is gender related for which the mechanisms should be determined.

Selective exposure of human proximal tubule cells to gentamicin provides evidence for a basolateral component of toxicity

The goal of the present study was to determine if cultured human proximal tubule (HPT) cells could provide evidence for a basolateral component of gentamicin toxicity. Six isolates of HPT cells were grown on Millicell filters and exposed to gentamicin either apically, basolaterally, or both apically and basolaterally. Toxicity was determined by the release of lactate dehydrogenase into the growth media. The results clearly demonstrated that basolateral exposure and combined apical and basolateral exposure to gentamicin resulted in significant levels of cell toxicity. In contrast, apical exposure to gentamicin elicited only marginal toxicity. The transepithelial flux of gentamicin was shown to be the same in either the apical to basolateral or the basolateral to apical direction. A two-step mechanism of gentamicin toxicity is proposed in order to integrate basolateral toxicity with known features of aminoglycoside 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.

Subcellular distribution of gentamicin in proximal tubular cells, determined by immunogold labeling

The subcellular distribution of gentamicin in rat renal proximal tubular cells was evaluated by immunogold labeling. The distribution of the drug was monitored from 10 min to 10 days following single (40 mg/kg of body weight) and multiple (5 and 20 mg/kg/12 h) injections of gentamicin. Animals were killed on day 11, and cubes of renal cortex tissue were fixed overnight in cold phosphate-buffered glutaraldehyde (0.5%), dehydrated in ethanol, and embedded in Araldite 502 epoxy resin. Ultrathin sections were made and incubated with sheep antigentamicin and then with protein A-gold (15 nm) complex. At 10 min after a single injection, the labeling was found over the brush border membrane and over the membranes of endocytic apical vesicles of proximal tubular cells. After 1 h, a similar distribution was observed and the labeling was also seen over small lysosomes located close to the brush border membrane. At 24 h, gold particles were found over large lysosomes of proximal tubular cells. Following 10 days of treatment, lysosomes of proximal tubular cells were densely labeled with gold particles. The labeling was distributed uniformly over the lysosomes, although a lower density of labeling was observed over the myeloid bodies inside the lysosomes. Necrotic proximal tubular cells showed labeling over intact lysosomes and also in the cytoplasms of the cells, in the mitochondria, and in the nucleoli. The various control experiments demonstrated the high specificity of these results. The present immunocytochemical study better documents the subcellular disposition of gentamicin in proximal tubular cells, as previously evaluated by subcellular fractionation and autoradiography. This technique will be useful for better understanding the relationship between drug disposition and drug-induced toxicity.

Differences in the sensitivity of Fischer and Sprague-Dawley rats to aminoglycoside nephrotoxicity

Because of the anecdotal but unconfirmed inferences of the greater sensitivity of Fischer rats to aminoglycoside nephrotoxicity, an intrastudy comparison of the sensitivity of Fischer and Sprague-Dawley rats to aminoglycoside nephrotoxicity was undertaken. Tobramycin was administered at 3 dose levels to each strain of rat for 10 days. Nephrotoxicity was evaluated utilizing a spectrum of both functional and morphologic assessments of renal proximal tubular integrity. The results confirm that the aged matched Fischer rat is more sensitive to the nephrotoxic effect of tobramycin than the Sprague-Dawley. These results also suggest an opportunity to study quantitative and perhaps qualitative differences in pathogenic mechanisms of aminoglycoside nephrotoxicity in a single laboratory animal species.

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.

Effects of interleukin-1 alpha and cyclosporin A in vivo and in vitro on bone and lymphoid tissues in mice

The purpose of this study was to investigate the effects of interleukin-1 alpha (IL-1 alpha) infusion and the ability of cyclosporin A (CYA) to alter IL-1 alpha-induced effects on bone in vivo and in vitro and lymphoid organs in vivo. Mice were administered: IL-1 alpha (2, 4, or 6 days), CYA (6 days), or IL-1 alpha and CYA (6 days). Hypercalcemia was induced in mice treated with IL-1 alpha compared to controls and CYA treated mice, and decreased urinary calcium excretion was present in IL-1 alpha and CYA groups. Osteoclastic bone resorption was increased with a resultant loss of total bone area and bone formation (as measured by mineral apposition rate) was decreased in mice infused with IL-1 alpha. Although CYA-treatment increased bone formation as compared to IL-1 alpha-treatment; CYA in combination with IL-1 alpha did not alter the reduction in mineral apposition rate caused by IL-1 alpha, IL-1 alpha also stimulated bone resorption in vitro which was significantly inhibited by cyclosporin A. IL-1 alpha-induced splenic granulopoiesis, peripheral blood neutrophilia, thymic atrophy, and lymphoid hyperplasia in lymph nodes. CYA-treatment resulted histologically in a severe depletion of lymphocytes in the thymus, a moderate depletion of lymphocytes in lymph nodes but no difference in the histology of the spleen compared to controls. In summary, interleukin-1 alpha was effective in stimulating hypercalcemia and bone resorption both in vivo and in vitro but cyclosporin A was effective in inhibiting IL-1 alpha-mediated bone resorption only in vitro. IL-1 alpha also had marked effects on spleen, thymus, and circulating blood cells; however, most parameters were not affected by the concurrent administration of cyclosporin A.

Selective membrane toxicity of aminoglycoside antibiotics in membrane vesicles isolated from proximal renal tubules of the rat

A considerable body of evidence suggests that the nephrotoxic potential of aminoglycoside antibiotics may be associated with the degree of membrane binding and subsequent membrane damage in the renal tubules. In this study, we isolated functional basolateral and luminal membrane vesicles from rat renal cortex, incubated each membrane type in the presence of 1 mM concentrations of either neomycin, netilmicin, gentamicin, hydroxygentamicin, or amikacin, and monitored the activities of the marker enzymes alkaline phosphatase (ALP) and lambda-glutamyltransferase (GGT) (luminal) or ouabain-sensitive Na+,K+-ATPase (basolateral) to determine if there were any selective drug-related alterations of enzyme activities. While none of the five aminoglycosides had any substantive effect upon enzyme activities of luminal vesicles, all five drugs inhibited the basolateral marker enzyme. Neomycin produced the greatest inhibition, hydroxygentamicin and amikacin the least, and gentamicin and netilmicin were intermediate in the inhibition of the enzyme. These results are in accordance with the known relative nephrotoxicity of these same drugs and indicate the usefulness of isolated renal membrane vesicles for in vitro toxicological studies of novel aminoglycosides.

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.