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Division of Nephrology, Pennsylvania State College of Medicine, Hershey; and Lebanon Veterans Affairs Medical Center, Lebanon, Pennsylvania
Submitted 5 November 2004 ; accepted in final form 3 February 2005
| ABSTRACT |
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(TNF-
). The pathway through which cisplatin mediates the production of TNF-
and injury is not known. Cisplatin activates p38 MAPK and induces apoptosis in cancer cells. p38 MAPK activation leads to increased production of TNF-
in ischemic injury and in macrophages. However, little is known concerning the role of p38 MAPK in cisplatin-induced renal injury. Therefore, we examined the effect of cisplatin on p38 MAPK activity and the role of p38 MAPK in mediating cisplatin-induced TNF-
production and renal injury. In vitro, cisplatin caused a dose-dependent activation of p38 MAPK in proximal tubule cells. Inhibition of p38 MAPK activation led to inhibition of TNF-
production. In vivo, mice treated with a single dose of cisplatin (20 mg/kg body wt) developed severe renal dysfunction at 72 h [blood urea nitrogen (BUN): 154 ± 34 mg/dl, creatinine: 1.4 ± 0.4 mg/dl], which was accompanied by an increase in kidney p38 MAPK activity and an increase in infiltrating leukocytes. However, animals treated with the p38 MAPK inhibitor SKF-86002 along with cisplatin showed less renal dysfunction (BUN: 55 ± 14 mg/dl, creatinine: 0.3 ± 0.02 mg/dl, P < 0.05), less severe histological damage, and fewer leukocytes compared with cisplatin+vehicle-treated animals. Serum levels of TNF-
, sTNFRI, and sTNFRII also increased significantly in cisplatin-treated mice compared with SKF-86002-treated mice (P < 0.05). Kidney mRNA levels of TNF-
were significantly increased in cisplatin-treated mice compared with either SKF-86002- or saline-treated animals. The hydroxyl radical scavenger DMTU (100 mg·kg body wt1·day1) prevented the activation of p38 MAPK by cisplatin both in vitro and in vivo. DMTU also completely prevented cisplatin-induced renal injury (BUN: 140 ± 27 vs. 22 ± 2 mg/dl, P < 0.005) and the increase in serum TNF-
(33 ± 7 vs. 4 ± 2 pg/ml, P < 0.005) and kidney TNF-
mRNA in vivo. We conclude that hydroxyl radicals, either directly or indirectly, activate p38 MAPK and that p38 MAPK plays an important role in mediating cisplatin-induced acute renal injury and inflammation, perhaps through production of TNF-
.
tumor necrosis factor-
; acute renal failure; antioxidants; gene expression; cytokines; protein kinases
We (3537) and others (7, 42, 43) demonstrated a role for inflammation in cisplatin-induced acute renal failure. In particular, cisplatin increases renal TNF-
production (7, 36, 42) and inhibition of TNF-
production reduces cisplatin nephrotoxicity (35, 36). p38 MAPK is involved in TNF-
production in a variety of models of inflammation (13, 15, 19, 46). However, the role of p38 MAPK in mediating cisplatin-induced TNF-
production has never been evaluated. Therefore, the second goal of the current study was to determine the role of p38 MAPK in cisplatin-induced TNF-
production both in vitro and in vivo.
Finally, there is substantial evidence supporting the role of reactive oxygen species (ROS) in mediating cisplatin-induced renal injury (35, 24). ROS are known to activate p38 MAPK in a variety of tissues (12, 18, 32) including kidney (43). Tsuruya et al. (43) recently demonstrated that ROS are involved in the production of TNF-
in response to cisplatin. However, the role of p38 MAPK in this process was not examined. Therefore, the third goal of the current studies was to determine the role of ROS in the activation of p38 MAPK and TNF-
production in response to cisplatin both in vitro and in vivo.
| MATERIALS AND METHODS |
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Animals and drug administrations.
Experiments were performed using 10- to 12-wk-old male C57BL/6 mice weighing
2530 g. Mice were maintained on a standard diet and water was freely available. Cisplatin was dissolved in saline at a concentration of 1 mg/ml. Mice were given a single intraperitoneal injection of either saline, cisplatin (20 mg/kg body wt) plus vehicle, cisplatin and SKF-86002, DMTU, or DMTU and cisplatin. SKF-86002 was dissolved in DMSO-Ethanol-saline (30:30:40 by volume) and injected subcutaneously at a dose of 20 mg·kg body wt1·day1. DMTU (100 mg·kg1·day1) was dissolved in saline and injected intraperitoneally. The initial doses of SKF-86002 and DMTU were administered 30 min before the cisplatin. Cisplatin-treated animals were administered the vehicles for SKF-86002 or DMTU on the same schedule. Animals were killed 72 h after cisplatin injection and blood and kidney tissues were collected. Kidney tissues were processed for histology, p38 activity, and RNA isolation. All animal protocols conformed with the American Physiological Societys Guiding Principles in the Care and Use of Laboratory Animals and were approved by the Institutional Animal Care and Use Committee of the Pennsylvania State College of Medicine.
Renal function. Renal function was assessed by measurements of blood urea nitrogen (BUN; VITROS DT60II Chemistry slides, Ortho-clinical Diagnostics) and serum creatinine (DZ072B, Diazyme Labs).
Quantitation of mRNA by real-time PCR.
Real-time PCR was performed in an Applied Biosystem 7700 sequence detection system; 1.5 µg of total RNA was reverse transcribed in a reaction volume of 20 µl using Omniscript reverse transcriptase kit (Qiagen) and random primers. The product was diluted to a volume of 150 µl and either 2-µl (actin) or 10-µl (all others) aliquots were used as templates for amplification using SYBR Green PCR amplification reagent and gene-specific primers. The primer sets used were: actin (forward: CATGGATGACGATATCGCT; reverse: CATGAGGTAGTCTGTCAGGT), TNF-
(forward: GCATGATCCGCGACGTGGAA; reverse: AGATCCATGCCGTTG GCCAG), IL-1
(forward: 5'-CTCCATGAGCTTTGTACAAGG-3; reverse: 5'-TGCTGATGTACCAGTTGGGG-3'), ICAM-1 (forward: 5'-GATCACATTCACGGTGCTG-3'; reverse: 5'-CTTCAGAGGCAGGAAACAGG-3'), MCP-1 (foward: 5'-ATGCAGGTCCCTGTCATG-3'; reverse: 5'-GCTTGAGGTGGTTGTGGA-3'), TGF-
1 (forward: 5'-TGACGTCACTGGAGTTGTACGG-3'; reverse: 5'- GGTTCATGTCATGGATGG TGC-3'), heme oxygenase-1 (forward: AGCATGCCCCAGGATTTG; reverse: AGCTCAATGTTGAGCAGGA). The amount of RNA was normalized to actin amplified in a separate reaction.
TNF-
, soluble TNFR1 and TNFR2 quantitation by ELISA.
The levels of TNF-
, sTNF RI, and sTNF RII were quantitated using an ELISA assay (Quantikine Mouse TNF-
kit, Quantikine Mouse sTNF RI and sTNF RII kit, R&D System, Minneapolis, MN) according to the manufacturers instructions.
p38 MAPK assay in kidney tissue extract. p38 MAPK activity was measured by immunoprecipitation and phosphorylation of ATF-2 (p38 MAPK assay kit, cat. no. 9820, Cell Signaling Technologies, Beverly, MA). Briefly, kidney was homogenized in 6 ml of lysis buffer and incubated on ice for 10 min. The homogenate was centrifuged at 10,000 rpm for 5 min and the supernatant was transferred to a fresh tube; 400 µg of supernatant protein in 300-µl volume were immunoprecipitated using immobilized p38 antibody beads. The mixture was centrifuged and washed with lysis buffer twice and kinase buffer twice. The pellet was resuspended in 50 µl of kinase buffer containing 200 µM ATP and 2 µg of ATF-2 fusion protein and incubated for 30 min at 30°C. The reaction was arrested by adding SDS-sample loading buffer and then separated on a 412% polyacrylamide gel. Proteins were transfered onto a PVDF membrane and probed with anti-phospho ATF-2 antibody. Phospho ATF-2 was visualized using ECL reagents.
Histology and immunohistochemistry. Kidney tissue was fixed in buffered 10% formalin for 12 h and then embedded in paraffin wax. For assessment of injury, 5-µm sections were stained with PAS. Tubular injury was assessed in PAS-stained sections using a semiquantitative scale (16, 17, 34) in which the percentage of cortical tubules showing epithelial necrosis was assigned a score: 0 = normal; 1 = <10%; 2 = 1025%; 3 = 2675%; 4 = >75%. Sections were scored independently by two investigators who were blinded to the treatment of the animal. To quantitate leukocyte infiltration, sections were stained with naphthol AS-D choroacetate esterase (Sigma kit no. 91C), which identifies neutrophils and monocytes. Twenty-five x40 fields of esterase-stained sections were examined for quantitation of leukocytes. For ATF-2 immunohistochemistry, sections were deparaffinized and rehydrated. Antigen retreval was performed by heating the sections in 10 mM sodium citrate buffer (pH 6.0) at 95°C for 10 min. The sections were washed and incubated with 1% hydrogen peroxide in 90% methanol for 10 min to block endogenous peroxidases. Sections were then blocked with 5% goat serum/1% BSA in PBS, followed by incubation overnight at 4°C with an anti-phospho ATF-2 antibody (diluted 1:50 in blocking buffer). Slides were washed and then incubated with a biotinylated secondary antibody for 1 h followed by ABC reagent. Color was developed with a metal-enhanced DAB reagent (Pierce), counterstained with hematoxylin, and mounted.
Renal platinum content. Platinum content was measured in kidneys removed 72 h after cisplatin injection and in cells harvested after 6 h of cisplatin treatment. Tissues and cells were digested in a mixture of Ultrex trace metal grade nitric acid and hydrochloric acid for 1 h at 100°C. The digested samples were diluted with high-purity water and subjected to inductively coupled plasma/mass spectroscopy (Perkin Elmer Elan 6000 ICP/MS) to determine the platinum content.
Statistical methods. All assays were performed in duplicate. The data are reported as means ± SE. Statistical significance was assessed by unpaired, two-tailed Students t-test for single comparison or ANOVA for multiple comparisons.
| RESULTS |
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expression in vivo and in vitro.
p38 MAPK activation leads to TNF-
production in number of cell types (13, 15, 19, 27, 46). To determine whether p38 MAPK mediates TNF-
expression in renal proximal tubule cells in response to cisplatin, TKPTS cells were treated with cisplatin along with the p38 MAPK inhibitor SB-203580 for 12 h. As shown in Fig. 3, cisplatin induced an 8- to 10-fold increase in TNF-
mRNA levels. SB-203580 significantly blunted the cisplatin-induced TNF-
mRNA expression and reduced TNF-
protein secretion into the culture supernatant. SB-203580 did not affect the cellular uptake of cisplatin (222 ± 22 vs. 257 ± 20 ng Pt/mg protein, cisplatin vs. cisplatin + SB-203580, P = NS). Similarly, mice treated with cisplatin had increased amounts of renal TNF-
protein and mRNA which were significantly reduced by the p38 inhibitor SKF-86002 (Fig. 3B). SKF-86002 also significantly reduced the cisplatin-induced increases in serum levels of TNF-
, sTNFRI and sTNFRII (Table 1).
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, IL-1
, MCP-1, ICAM-1, and TGF-
1 were upregulated after cisplatin injection (Fig. 6). TNF-
expression was reduced significantly (P < 0.05) by SKF-86002. Although the expression of the other genes was also reduced by SKF-86002, these differences did not reach statistical significance.
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concentrations and the increase in kidney TNF-
mRNA in cisplatin-treated mice (Fig. 10). Heme oxygenase-1, known to be upregulated in cisplatin nephrotoxicity (1), was measured as a marker of oxidative stress. DMTU completely prevented the cisplatin-induced upregulation of HO-1 (Fig. 10).
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| DISCUSSION |
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in response to cisplatin is a central element in renal injury (36). Inhibition or deletion of TNF-
reduces cisplatin-induced renal dysfunction, epithelial cell necrosis and apoptosis and infiltration of leukocytes (35, 36). The pathways by which cisplatin induces TNF-
production are poorly understood. p38 MAP kinase is activated in cisplatin nephrotoxicity and mediates the production of TNF-
in a number of other settings. However, the role p38 MAPK in cisplatin nephrotoxicity and in cisplatin-induced TNF-
production, in particular, is unknown. The current studies were performed to address these issues. We determined that p38 MAPK activity is increased in response to cisplatin both in vitro and in vivo. Arany et al. (2) recently reported that cisplatin increased p38 MAPK phosphorylation in TKPTS cells, the same cells used in the present study, and in kidney of cisplatin-treated mice. Our studies, which measured actual enzyme activity in addition to phosphorylated enzyme, confirm their findings. In addition, using immunocytochemistry, we determined that p38 MAPK was activated in cells of the proximal tubule in vivo, the predominant site of cisplatin-induced injury. A significant finding of our study is that pharmacological inhibition of p38 MAPK resulted in a substantial reduction in cisplatin nephrotoxicity in vivo as assessed by either functional (Fig. 4) or structural (Fig. 5) parameters. These results indicate that p38 MAPK signaling contributes to cisplatin-induced renal injury in vivo. Similarly, p38 MAPK is believed to contribute to the tumorcidal activity of cisplatin in cancer cells (23). p38 MAPK activation has also been observed after renal ischemia-reperfusion (27, 29, 47) and likely plays a role in injury in that setting. Furuichi et al. (11) reported that inhibition of p38 MAPK reduced renal ischemia-reperfusion injury. Similarly, brief periods of ischemia that precondition the kidney to resist subsequent ischemic injury are associated with a marked reduction in p38 MAPK activation (29). Thus p38 MAPK activation may be a common element in the mechanism of acute renal injury.
Arany et al. (2) found that inhibition of ERK, but not p38 MAPK, reduced cisplatin-induced cell death in vitro. The effects of MAPK inhibition in vivo were not examined in that study. In the present study, we focused on the role of p38 MAPK on cisplatin nephrotoxicity in vivo. It is likely that direct cytotoxicity, as studied in vitro, is only one component of a complex mechanism of renal injury in vivo (40). Therefore, our finding that p38 MAPK is involved in nephrotoxicity in vivo does not contradict the results of Arany et al. (2). Rather, p38 MAPK may be involved in other processes, such as inflammation or hemodynamic alterations, which are not recapitulated by in vitro models.
TNF-
is produced in response to cisplatin and plays an important role in the pathogenesis of renal injury. Inhibition of TNF-
production or action reduces nephrotoxicity and reduces the infiltration of leukocytes within the kidney (3537). Therefore, we examined whether the protective effect of p38 MAPK inhibition in cisplatin nephrotoxicity is associated with a reduction in TNF-
production and a reduction in renal inflammation. Indeed, we found that cisplatin led to the upregulation of both TNF-
mRNA and protein in TKPTS cells in vitro and in kidney in vivo and that p38 MAPK inhibition markedly reduced TNF-
mRNA and protein levels in both settings. Inhibition of p38 MAPK also markedly reduced the influx of inflammatory cells into the kidney. Although cisplatin is known to stimulate p38 MAPK activity in a variety of cells (30, 39, 44), and leads to Fas ligand expression in ovarian cancer cells (23), this is the first report, to our knowledge, of cisplatin stimulating TNF-
production through p38 MAPK. p38 MAPK has previously been implicated in TNF-
production after renal ischemia (11, 27) and in a murine model of lupus (15). Thus p38 MAPK may be an important mediator of TNF-
production in a variety of forms of renal injury. The mechanism whereby p38 MAPK increases TNF-
production is cell and stimulus specific. p38 MAPK has been reported to increase TNF-
production through effects on transcription, mRNA stability, and translation (10, 21, 41). Further studies will be required to determine the precise mechanism for p38 MAPK stimulation of TNF-
production in proximal tubule cells in response to cisplatin.
Oxidants are potent activators of MAPKs, including p38 MAPK (12, 18, 32). Cisplatin stimulates the production of ROS, including hydroxyl radicals. The formation of hydroxyl radicals in cisplatin-treated kidney cells, both in vitro and in vivo, involves the release of iron from the heme groups of cytochrome P-450 2E1 (22). Earlier studies by Matsushima et al. (24) showed that DMTU, a hydroxyl radical scavenger, prevented accumulation of malondialdehhyde, tubular damage, and renal dysfunction in cisplatin toxicity. In another study, DMTU reduced cisplatin-induced apoptotic cell death and the expression of death receptors (TNFR1 and Fas) and their ligands in the kidney (43). However, a possible role for p38 MAPK in that process was not examined. In the present study, we confirmed that DMTU reduced cisplatin-induced renal injury and TNF-
production. We also demonstrated that DMTU prevented the activation of p38 MAPK by cisplatin. This finding, along with the demonstration that p38 MAPK is required for cisplatin-induced TNF-
production, is consistent with the view that hydroxyl radicals stimulate p38 MAPK, which in turn, increases TNF-
production.
The mechanism whereby hydroxyl radicals activate p38 MAPK in kidney cells is not known. In macrophages, oxidant stress activates p38 MAPK via src (18). Arany et al. (2) reported recently that cisplatin-induced activation of ERK was mediated through src. Although cisplatin also stimulated p38 MAPK in that study, the effect of src inhibition on p38 MAPK activity was not reported. We believe that different mechanisms mediate the activation of p38 MAPK and ERK in response to cisplatin. In this regard, we noted that DMTU completely inhibited the activation of p38 MAPK by cisplatin (Fig. 7), but did not prevent the phosphorylation of ERK (preliminary studies). Alternatively, or in addition to src, oxidants might activate p38 MAPK via ASK1. ASK1 is a member of the MAPKKK family and activates both the p38 MAPK and the JNK signaling pathways (14). Under normal conditions, ASK1 forms an inactive complex with thioredoxin. In the presence of oxidant stress, cysteine residues of thioredoxin are oxidized, resulting in dissociation of thioredoxin from ASK1 and activation of ASK1 (25). Further studies will be required to determine the elements of the signaling pathway upstream of p38 MAPK activated in response to cisplatin.
In conclusion, we demonstrated that cisplatin stimulates TNF-
production in the kidney through a mechanism that involves the production of hydroxyl radicals and the subsequent activation of p38 MAPK. Inhibition of p38 MAPK not only reduces TNF-
production but also provides marked protection against cisplatin-induced renal injury in vivo. Inhibitors of p38 MAPK are in clinical trials (9). Accordingly, p38 MAPK may be an attractive target for the prevention of cisplatin nephrotoxicity.
| GRANTS |
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| ACKNOWLEDGMENTS |
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| FOOTNOTES |
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The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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