Gadolinium modulates gentamicin uptake via an endocytosis-independent pathway in HK-2 human renal proximal tubular cell line

Evaluation of biomarkers for in vitro prediction of drug-induced nephrotoxicity in RPTEC/TERT1 cells

There have been intensive efforts to identify in vivo biomarkers that can be used to monitor drug-induced kidney damage before significant impairment occurs. Kidney injury molecule-1, neutrophil gelatinase-associated lipocalin, clusterin, β2-microglobulin and cystatin C (CysC) have been validated as clinical or preclinical biomarkers in urinary and plasma predictive of acute and chronic kidney injuries and diseases. A high-throughput in vitro assay predictive of nephrotoxicity could potentially be implemented in early drug discovery stage to reduce attrition at later stages of drug development. To assess the potential of these known in vivo biomarkers for in vitro evaluation of drug-induced nephrotoxicity, we selected four nephrotoxic agents (cisplatin, cyclosporin, aristolochic acid I and gentamicin) and detected their effects on the protein levels of nephrotoxic biomarkers in RPTEC/TERT1 cells. The protein levels of clusterin, CysC, GSTπ and TIMP-1 significantly increased in the conditioned media of RPTEC/TERT1 cells treated with cisplatin, cyclosporin, aristolochic acid I and gentamicin. The messenger RNA levels of clusterin, CysC, GSTπ and TIMP-1 also increased in RPTEC/TERT1 cells treated with cisplatin, cyclosporin, aristolochic acid I and gentamicin, indicating that drug-induced upregulation involves transcriptional activation. Taken together, the results clearly demonstrate that among the known in vivo nephrotoxic biomarkers, clusterin, CysC, GSTπ and TIMP-1 can be effectively used as in vitro biomarkers for drug-induced nephrotoxicity in RPTEC/TERT1 cells.

Vinpocetine Improves Oxidative Stress and Pro-Inflammatory Mediators in Acute Kidney Injury

Background:

Gentamicin-induced-acute kidney injury (AKI) is a multifaceted phenomenon which previously linked to the oxidative stress only. Vinpocetine prevents reactive free radical generation which contributed in reduction of damage. Therefore, objective of the present study was to investigate the renoprotective effect of vinpocetine on gentamicin-induced-AKI in rats.

Methods:

Thirty Sprague Dawley Male rat were divided into three groups. Control group (n = 10): Rats treated with distilled water + intra-peritoneal injection of normal saline 2 ml/kg/day. Gentamicin group (n = 10): Rats treated with distilled water + intra-peritoneal injection of gentamicin 100 mg/kg/day. Vinpocetine group (n = 10): Rats treated with vinpocetine + intra-peritoneal injection of gentamicin 100 mg/kg/day. Blood urea and serum creatinine were estimated by auto-analyzer. Serum malondialdehyde (MDA), superoxide dismutase (SOD), Neutrophil Gelatinase Associated Lipocalin (NGAL), kidney injury molecules (KIM-1), and Cystatin-c were measured by ELISA kit methods.

Results:

Vinpocetine led to significant renoprotective effect on gentamicin induced-AKI through amelioration of blood urea and serum creatinine compared with gentamicin group P < 0.01. Vinpocetine improved oxidative stress through reduction of MDA serum level and elevation of SOD significantly compared with gentamicin group P = 0.001 and P = 0.03, respectively. Indeed, vinpocetine reduced glomerular and renal tubular injury via reduction of inflammatory biomarkers including KIM-1, NGALand Cystatin-c sera levels significantly P < 0.01 compared to gentamicin group.

Conclusions:

Vinpocetine leads to significant attenuation of gentamicin-induced-AKI through modulation of oxidative stress and pro-inflammatory pathway.

An in vitro method for nephrotoxicity evaluation using HK-2 human kidney epithelial cells combined with biomarkers of nephrotoxicity

The kidney is one of the major target organs for drug-induced toxicity. During drug development, the traditional markers of nephrotoxicity indicate only severe and late damage, which leads to high costs. The new biomarkers are needed for a more sensitive and reliable evaluation of nephrotoxicity, especially for the regulatory accepted and validated in vitro model. We developed an in vitro model based on the HK-2 cell using the biomarkers of nephrotoxicity as endpoints for the evaluation of nephrotoxicity. The predictive performance of the biomarkers including LDH, GGT, KIM-1, clusterin, CysC, NGAL, TIMP-1, GSTπ and osteopontin was evaluated with 22 well characterized compounds. The area under the curve (AUC) values of KIM-1, clusterin, CysC and osteopontin ranged between 0.79 and 0.84. The combination of clusterin, KIM-1 and/or osteopontin improved the AUC value (ranging between 0.88 and 0.95) compared to one biomarker. Taken together, these results suggest that the model based on the HK-2 cell using clusterin, osteopontin, CysC and KIM-1 as endpoints would allow the prediction of nephrotoxicity at early preclinical stages.

Nanostructured lipid carrier (NLC)-based novel hydrogels as potential carriers for nepafenac applied after cataract surgery for the treatment of inflammation: design, characterization and in vitro cellular inhibition and uptake studies

Schematic illustration of the novel formulation (nanostructured lipid carriers-based novel hydrogels) instills into the surface of eyes and the results of cytotoxicity and cell uptake for optimal formulation.

Organic Cation Transporter 2 Overexpression May Confer an Increased Risk of Gentamicin-Induced Nephrotoxicity

Nephrotoxicity is a relevant limitation of gentamicin, and obese patients have an increased risk for gentamicin-induced kidney injury. This damage is thought to depend on the accumulation of the drug in the renal cortex. Obese rats showed substantially higher levels of gentamicin in the kidney than did lean animals. This study characterized the role of organic cation transporters (OCTs) in gentamicin transport and elucidated their possible contribution in the increased renal accumulation of gentamicin in obesity. The mRNA and protein expression levels of the organic cation transporters Oct2 (Slc22a2) and Oct3 (Slc22a3) were increased in kidney samples from obese mice fed a high-fat diet. Similarly, OCT2 (∼2-fold) and OCT3 (∼3-fold) showed increased protein expression in the kidneys of obese patients compared with those of nonobese individuals. Using HEK293 cells overexpressing the different OCTs, human OCT2 was found to transport [(3)H]gentamicin with unique sigmoidal kinetics typical of homotropic positive cooperativity (autoactivation). In mouse primary proximal tubular cells, [(3)H]gentamicin uptake was reduced by approximately 40% when the cells were coincubated with the OCT2 substrate metformin. The basolateral localization of OCT2 suggests that gentamicin can enter proximal tubular cells from the blood side, probably as part of a slow tubular secretion process that may influence intracellular drug concentrations and exposure time. Increased expression of OCT2 may explain the higher accumulation of gentamicin, thereby conferring an increased risk of renal toxicity in obese patients.

Fatty acid-bearing albumin but not fatty acid-depleted albumin induces HIF-1 activation in human renal proximal tubular epithelial cell line HK-2

Recently, we found that albumin overload induces expression of the transcription factor hypoxia-inducible factor-1α (HIF-1α) protein and several HIF-1 target genes in human renal proximal tubular epithelial cell line HK-2. In this study, the role of albumin-bound fatty acids in the albumin-induced HIF-1 activation was studied. The enhancing effect of fatty acid-bearing human serum albumin [FA(+)HSA] treatment on HIF-1α protein expression was much greater than that of fatty acid-depleted human serum albumin [FA(-)HSA] treatment. The FA(+)HSA treatment induced HIF-1 target gene mRNAs such as those of glucose transporter 1 (GLUT1), glyceraldehyde 3-phosphate dehydrogenase (GAPDH), and breast cancer resistance protein (BCRP) in concentration-dependent manners, while FA(-)HSA caused no significant increases in these mRNAs. Consistent with increased GLUT1 mRNA, GLUT1 protein expression and GLUT inhibitor cytochalasin B-sensitive d-[(3)H]glucose uptake activity were significantly enhanced by treatment with FA(+)HSA, but not with FA(-)HSA. These findings indicate that fatty acids bound to albumin play a crucial role in albumin-induced HIF-1 activation followed by changes in HIF-1 target gene expression and protein product activity.

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.

Drug-induced nephrotoxicity: clinical impact and preclinical in vitro models

The kidney is a major target for drug-induced toxicity. Drug-induced nephrotoxicity remains a major problem in the clinical setting, where the use of nephrotoxic drugs is often unavoidable. This leads frequently to acute kidney injury, and current problems are discussed. One strategy to avoid such problems would be the development of drugs with decreased nephrotoxic potential. However, the prediction of nephrotoxicity during preclinical drug development is difficult and nephrotoxicity is typically detected only late. Also, the nephrotoxic potential of newly approved drugs is often underestimated. Regulatory approved or validated in vitro models for the prediction of nephrotoxicity are currently not available. Here, we will review current approaches on the development of such models. This includes a discussion of three-dimensional and microfluidic models and recently developed stem cell based approaches. Most in vitro models have been tested with a limited number of compounds and are of unclear predictivity. However, some studies have tested larger numbers of compounds and the predictivity of the respective in vitro model had been determined. The results showed that high predictivity can be obtained by using primary or stem cell derived human renal cells in combination with appropriate end points.

Albumin overload induces expression of hypoxia-inducible factor 1α and its target genes in HK-2 human renal proximal tubular cell line

The aim of this study was to investigate the effect of human serum albumin (HSA) overload on the expression of the transcription factor hypoxia-inducible factor-1α (HIF-1α) in human renal proximal tubular cell line HK-2. First, the cell viability and cytotoxic activity were examined to assess the cellular conditions in HK-2 cells with HSA treatment employed in this study. HSA treatment for 48h decreased the cell viability and increased the leakage of lactate dehydrogenase (LDH) into the medium in a concentration-dependent manner, but the toxicity was relatively mild. Western Blot analysis revealed that HSA treatment induced the expression of HIF-1α protein in a concentration-dependent manner without a change in β-actin protein expression. Confocal microscopy analysis revealed that HIF-1α protein was predominantly localized in the nucleus but was also observed in the cytoplasm. The HIF-1 target gene mRNAs, glucose transporter 1 and glyceraldehyde 3-phosphate dehydrogenase, were up-regulated by HSA treatment, leading to the increases in the protein expression levels. In addition, the mRNA of HIF-1α was increased by HSA treatment. In conclusion, albumin loading induces HIF-1α in HK-2 cells, resulting in the increases in the expression of proteins of its target genes.