Megalin Contributes to Kidney Accumulation and Nephrotoxicity of Colistin

Polymyxin B is increasingly used as a treatment of last resort against multidrug-resistant Gram-negative infections. Using a mammalian kidney cell line, we demonstrated that polymyxin B uptake into proximal tubular epithelial cells was saturable and occurred primarily through the apical membrane, suggesting the involvement of transporters in the renal uptake of polymyxin B. Megalin might play a role in the uptake and accumulation of polymyxin B into renal cells. Multidrug-resistant Gram-negative infections are disseminating worldwide (1-3). This has necessitated the use of systemic polymyxin B as a treatment of last resort, despite the risk of nephrotoxicity (4-6). Polymyxin B is a polypeptide antibiotic commercially available as a mixture of several closely related cyclic amphiphilic molecules, of which polymyxin B1 (PB1) is the most abundant component (7). Our group previously studied the nephrotoxicity and renal disposition of polymyxin B in a rat model (8,9). We showed that polymyxin B had a tendency to persist in the kidneys (8). Using a dose fractionation design, we have also demonstrated the saturation of renal uptake with a clinically relevant dosing exposure (9), which suggested that the renal uptake of polymyxin B was unlikely a passive process. In addition, histological examination showed that renal injury was predominantly confined to the proximal tubular epithelial cells of the renal cortex. Based on these results, we postulated that polymyxin B was taken up primarily by proximal tubular epithelial cells. Collectively, these observations suggest a selective uptake process into renal cells, which can play a prominent role in the nephrotoxic potential of polymyxin B. The objective of this study was to characterize the cell uptake of polymyxin B in vitro. Understanding the mechanism of renal uptake might provide useful insights into minimizing the accumulation of polymyxin B and thus reducing its nephrotoxic potential.(This study was presented in part at the 53rd Interscience Conference on Antimicrobial Agents and Chemotherapy, Denver, CO, 10 -13 September 2013 [10].) Polymyxin B sulfate which met U.S. Pharmacopeia (USP) testing specifications, gentamicin sulfate (USP), and piperacillin sodium powder were purchased from Sigma-Aldrich (St. Louis, MO). A fluorescent polymyxin B derivative, polymyxin B Bodipy FL conjugate (FLPB), was purchased from Life Technologies (Grand Island, NY). Prior to each experiment, a fresh stock of each drug (100 mM, titrated to pH 5 by NaOH) was made with Dulbecco's phosphate-buffered saline (DPBS) with calcium and magnesium (Mediatech, Inc., Manassas, VA). Hanks' balanced salt solution (HBSS) was purchased from Sigma, supplemented with NaHCO 3 , glucose, and HEPES, and adjusted to pH 7.4 with NaOH at room temperature. Porcine kidney proximal tubular epithelial (LLC-PK1) cells were purchased from the ATCC (Manassas, VA). The cells were grown in medium 199 (Lonza, Walkersville, MD) supplemented with 3% fetal bovine serum (Thermo Scientific, Rockford, IL), 1% minimal essential...

mentioning

confidence: 84%

Uptake of Polymyxin B into Renal Cells

Abdelraouf

Chang

Yin

et al. 2014

“…6). An endocytic receptor megalin (MR) (66), polypeptide transporter 1 (PEPT1), and organic cation transporter 1 (OCTN1) (67) may mediate the substantial uptake of colistin by renal tubular cells. It is notable that oxidative stress and apoptosis play major roles in colistin-induced nephrotoxicity, while autophagy may protect renal tubular cells against the damage caused by colistin.…”

Section: Discussionmentioning

confidence: 99%

Colistin-Induced Nephrotoxicity in Mice Involves the Mitochondrial, Death Receptor, and Endoplasmic Reticulum Pathways

Dai

Tang

et al. 2014

150

157

c Nephrotoxicity is the dose-limiting factor for colistin, but the exact mechanism is unknown. This study aimed to investigate the roles of the mitochondrial, death receptor, and endoplasmic reticulum pathways in colistin-induced nephrotoxicity. Mice were intravenously administered 7.5 or 15 mg of colistin/kg of body weight/day (via a 3-min infusion and divided into two doses) for 7 days. Renal function, oxidative stress, and apoptosis were measured. Representative biomarkers involved in the mitochondrial, death receptor, and endoplasmic reticulum pathways were investigated, and the key markers involved in apoptosis and autophagy were examined. After 7-day colistin treatment, significant increase was observed with blood urea nitrogen, serum creatinine, and malondialdehyde, while activities of superoxide dismutase (SOD) and catalase decreased in the kidneys. Acute tubular necrosis and mitochondrial dysfunction were detected, and colistin-induced apoptosis was characterized by DNA fragmentation, cleavage of poly(ADP-ribose) polymerase (PARP-1), increase of 8-hydroxydeoxyguanosine (8-OHdG), and activation of caspases (caspase-8, -9, and -3). It was evident that colistin-induced apoptosis involved the mitochondrial pathway (downregulation of Bcl-2 and upregulation of cytochrome C [cytC] and Bax), death receptor pathway (upregulation of Fas, FasL, and Fasassociated death domain [FADD]), and endoplasmic reticulum pathway (upregulation of Grp78/Bip, ATF6, GADD153/CHOP, and caspase-12). In the 15-mg/kg/day colistin group, expression of the cyclin-dependent kinase 2 (CDK2) and phosphorylated JNK (p-JNK) significantly increased (P < 0.05), while in the 7.5-mg/kg/day colistin group, a large number of autophagolysosomes and classic autophagy were observed. Western blot results of Beclin-1 and LC3B indicated that autophagy may play a protective role in colistin-induced nephrotoxicity. In conclusion, this is the first study to demonstrate that all three major apoptosis pathways and autophagy are involved in colistin-induced nephrotoxicity.

“…In regard to the tubular reabsorption of colistin and PMB, it appears that megalin, an endocytic receptor expressed in the apical membrane domain of proximal tubular cells and involved in the reabsorption of proteins, peptides, and cationic compounds, is a key player in the reabsorption of the polymyxins (21)(22)(23). The affinity of polymyxin B for megalin appeared to be substantially greater than that of gentamicin (21), which is also a substrate of megalin (24).…”

Section: Why Do Polymyxins Have the Propensity To Cause Nephrotoxicity?mentioning

confidence: 99%

Nephrotoxicity of Polymyxins: Is There Any Difference between Colistimethate and Polymyxin B?

Zavascki

Nation

2017

174

120

Nephrotoxicity is a common adverse effect of the clinically used polymyxins, colistin and polymyxin B. This adverse effect is dose limiting for both polymyxins, as the plasma polymyxin concentrations associated with renal damage overlap those required for antibacterial effect. Since development of acute kidney injury (AKI) during therapy is highly undesirable, it is extremely important to know whether there is any difference between the nephrotoxic potential of colistin (administered as its inefficient prodrug, colistimethate) and polymyxin B (administered as the active form). Both polymyxins are cytotoxic to renal tubular cells and are prone to cause nephrotoxicity in vivo because of the renal handling mechanisms that facilitate accumulation of these compounds in these cells, processes that are reviewed in this article. Also reviewed are the emerging data that strongly suggest significantly higher rates of AKI in patients treated with colistimethate compared to patients treated with polymyxin B. This finding may be due to differences in pharmacokinetics and renal handling mechanisms of colistimethate and formed colistin versus polymyxin B, and consequently the relative amount of polymyxin material delivered to tubular cells. A lower risk of AKI with polymyxin B is one of several potential advantages over colistimethate. The relative safety and efficacy of the two agents require closer examination in well-designed clinical studies.