Renal proximal tubules are targets for toxicity due in part to the expression of transporters that mediate the secretion and reabsorption of xenobiotics. Alterations in transporter expression and/or function can enhance the accumulation of toxicants and sensitize the kidneys to injury. This can be observed when xenobiotic uptake by carrier proteins is increased or efflux of toxicants and their metabolites is reduced. Nephrotoxic chemicals include environmental contaminants (halogenated hydrocarbon solvents, the herbicide paraquat, the fungal toxin ochratoxin, and heavy metals) as well as pharmaceuticals (certain beta-lactam antibiotics, antiviral drugs, and chemotherapeutic drugs). This review explores the mechanisms by which transporters mediate the entry and exit of toxicants from renal tubule cells and influence the degree of kidney injury. Delineating how transport proteins regulate the renal accumulation of toxicants is critical for understanding the likelihood of nephrotoxicity resulting from competition for excretion or genetic polymorphisms that affect transporter function.

The success of cisplatin-containing regimens to treat solid tumors is limited, in part, by nephrotoxicity. In rodents, several urinary proteins have emerged as more sensitive indicators of cisplatin-induced kidney injury. We sought to characterize time-dependent changes in the urinary concentrations of 12 proteins including KIM-1, calbindin, β2M, and TFF3 after cisplatin therapy. Urine was collected at baseline, 3 (range: 2-5), and 10 (range: 9-11) days from 57 patients with solid tumors receiving outpatient cisplatin therapy (≥ 25 mg/m2). Serum creatinine was largely unchanged after cisplatin infusion. However, compared to baseline values, several novel biomarkers were significantly increased in the urine including β2M, which was 3-fold higher by day 3 (p<0.0001). Urinary KIM-1 and TFF3 were elevated 2-fold by day 10 (p=0.002 and p=0.002, respectively) whereas calbindin levels were increased 8-fold (p<0.0001). We report novel time-dependent changes in the urinary excretion of noninvasive markers of subclinical kidney injury after cisplatin treatment.

Despite recent progress in the development of novel approaches to treat cancer, traditional antineoplastic drugs, such as cisplatin, remain a mainstay of regimens targeting solid tumors. Use of cisplatin is limited by acute kidney injury, which occurs in approximately 30% of patients. Current clinical measures, such as serum creatinine and estimated glomerular filtration rate, are inadequate in their ability to detect acute kidney injury, particularly when there is only a moderate degree of injury. Thus, there is an urgent need for improved diagnostic biomarkers to predict nephrotoxicity. There is also interest by the U.S. Food and Drug Administration to validate and implement new biomarkers to identify clinical and subclinical acute kidney injury in patients during the drug approval process. This minireview provides an overview of the current literature regarding the utility of urinary proteins (albumin, beta-2-microglobulin, N-acetyl-D-glucosaminidase, kidney injury molecule-1, neutrophil gelatinase-associated lipocalin, and cystatin C) as biomarkers for cisplatin-induced AKI. Many of the well-studied urinary proteins (KIM-1, NGAL, B2M, albumin) as well as emerging biomarkers (calbindin, monocyte chemotactic protein-1, and trefoil factor 3) display distinct patterns of time-dependent excretion after cisplatin administration. Implementation of these biomarker proteins in the oncology clinic has been hampered by a lack of validation studies. To address these issues, large head-to-head studies are needed to fully characterize time-dependent responses and establish accurate cutoff values and ranges, particularly in cancer patients. Impact statement There is growing interest in using urinary protein biomarkers to detect acute kidney injury in oncology patients prescribed the nephrotoxic anticancer drug cisplatin. We aim to synthesize and organize the existing literature on biomarkers examined clinically in patients receiving cisplatin-containing chemotherapy regimens. This minireview highlights several proteins (kidney injury molecule-1, beta-2-microglobulin, neutrophil gelatinase-associated lipocalin, calbindin, monocyte chemotactic protein-1, trefoil factor 3) with the greatest promise for detecting cisplatin-induced acute kidney injury in humans. A comprehensive review of the existing literature may aid in the design of larger studies needed to implement the clinical use of these urinary proteins as biomarkers of kidney injury.

Nitric oxide (NO) is derived from multiple isoforms of the Nitric Oxide Synthases (NOSs) within the lung for a variety of functions; however, NOS2-derived nitrogen oxides seem to play an important role in inflammatory regulation. In this study, we investigate the role of NOS2 in pulmonary inflammation/fibrosis in response to intratracheal bleomycin instillation (ITB) and to determine if these effects are related to macrophage phenotype. Systemic NOS2 inhibition was achieved by administration of 1400 W, a specific and potent NOS2 inhibitor, via osmotic pump starting six days prior to ITB. 1400 W administration attenuated lung inflammation, decreased chemotactic activity of the broncheoalveolar lavage (BAL), and reduced BAL cell count and nitrogen oxide production. S-nitrosylated SP-D (SNO-SP-D), which has a pro-inflammatory function, was formed in response to ITB; but this formation, as well as structural disruption of SP-D, was inhibited by 1400 W. mRNA levels of IL-1β, CCL2 and Ptgs2 were decreased by 1400 W treatment. In contrast, expression of genes associated with alternate macrophage activation and fibrosis Fizz1, TGF-β and Ym-1 was not changed by 1400 W. Similar to the effects of 1400 W, NOS2−/− mice displayed an attenuated inflammatory response to ITB (day 3 and day 8 post-instillation). The DNA-binding activity of NF-κB was attenuated in NOS2−/− mice; in addition, expression of alternate activation genes (Fizz1, Ym-1, Gal3, Arg1) was increased. This shift towards an increase in alternate activation was confirmed by western blot for Fizz-1 and Gal-3 that show persistent up-regulation 15 days after ITB. In contrast arginase, which is increased in expression at 8 days post ITB in NOS2−/−, resolves by day 15. These data suggest that NOS2, while critical to the development of the acute inflammatory response to injury, is also necessary to control the late phase response to ITB.

Nephrotoxicity is a dose limiting side effect associated with the use of cisplatin in the treatment of solid tumors. The degree of nephrotoxicity is dictated by the selective accumulation of cisplatin in renal tubule cells due to: (1) uptake by organic cation transporter 2 (OCT2) and copper transporter 1 (CTR1); (2) metabolism by glutathione S-transferases (GSTs) and γ-glutamyltransferase 1 (GGT1); and (3) efflux by multidrug resistance-associated protein 2 (MRP2) and multidrug and toxin extrusion protein 1 (MATE1). The purpose of this study was to determine the significance of single nucleotide polymorphisms that regulate the expression and function of transporters and metabolism genes implicated in development of acute kidney injury (AKI) in cisplatin treated patients. Changes in the kidney function were assessed using novel urinary protein biomarkers and traditional markers. Genotyping was conducted by the QuantStudio 12K Flex Real-Time PCR System using a custom open array chip with metabolism, transport, and transcription factor polymorphisms of interest to cisplatin disposition and toxicity. Traditional and novel biomarker assays for kidney toxicity were assessed for differences according to genotype by ANOVA. Allele and genotype frequencies were determined based on Caucasian population frequencies. The polymorphisms rs596881 (SLC22A2/OCT2), and rs12686377 and rs7851395 (SLC31A1/CTR1) were associated with renoprotection and maintenance of estimated glomerular filtration rate (eGFR). Polymorphisms in SLC22A2/OCT2, SLC31A1/CTRI, SLC47A1/MATE1, ABCC2/MRP2, and GSTP1 were significantly associated with increases in the urinary excretion of novel AKI biomarkers: KIM-1, TFF3, MCP1, NGAL, clusterin, cystatin C, and calbindin. Knowledge concerning which genotypes in drug transporters are associated with cisplatin-induced nephrotoxicity may help to identify at-risk patients and initiate strategies, such as using lower or fractionated cisplatin doses or avoiding cisplatin altogether, in order to prevent AKI.