Sulforaphane protects the heart from doxorubicin-induced toxicity

Cardiotoxicity is one of the major side effects encountered during cancer chemotherapy with doxorubicin (DOX) and other anthracyclines. Previous studies have shown that oxidative stress caused by DOX is one of the primary mechanisms for its toxic effects on the heart. Since the redox-sensitive transcription factor, Nrf2, plays a major role in protecting cells from the toxic metabolites generated during oxidative stress, we examined the effects of the phytochemical sulforaphane (SFN), a potent Nrf2-activating agent, on DOX-induced cardiotoxicity. These studies were carried out both in vitro and in vivo using rat H9c2 cardiomyoblast cells and wild type 129/sv mice, and involved SFN pretreatment followed by SFN administration during DOX exposure. SFN treatment protected H9c2 cells from DOX cytotoxicity and also resulted in restored cardiac function and a significant reduction in DOX-induced cardiomyopathy and mortality in mice. Specificity of SFN induction of Nrf2 and protection of H9c2 cells was demonstrated in Nrf2 knockdown experiments. Cardiac accumulation of 4-hydroxynonenal (4-HNE) protein adducts, due to lipid peroxidation following DOX-induced oxidative stress, was significantly attenuated by SFN treatment. The respiratory function of cardiac mitochondria isolated from mice exposed to DOX alone was repressed, while SFN treatment with DOX significantly elevated mitochondrial respiratory complex activities. Co-administration of SFN reversed the DOX-associated reduction in nuclear Nrf2 binding activity and restored cardiac expression of Nrf2-regulated genes at both the RNA and protein levels. Together, our results demonstrate for the first time that the Nrf2 inducer, SFN, has the potential to provide protection against DOX-mediated cardiotoxicity.

Evidence Suggesting a Role of Iron in a Mouse Model of Nephrogenic Systemic Fibrosis

Nephrogenic systemic fibrosis is associated with gadolinium contrast exposure in patients with reduced kidney function and carries high morbidity and mortality. We have previously demonstrated that gadolinium contrast agents induce in vivo systemic iron mobilization and in vitro differentiation of peripheral blood mononuclear cells into ferroportin (iron exporter)-expressing fibrocytic cells. In the present study we examined the role of iron in a mouse model of nephrogenic systemic fibrosis. Chronic kidney disease was induced in 8-week-old male Balb/C mice with a two-step 5/6 nephrectomy surgery. Five groups of mice were studied: control (n = 5), sham surgery control (n = 5), chronic kidney disease control (n = 4), chronic kidney disease injected with 0.5 mmol/kg body weight of Omniscan 3 days per week, for a total of 10 injections (n = 8), and chronic kidney disease with Omniscan plus deferiprone, 125 mg/kg, in drinking water (n = 9). Deferiprone was continued for 16 weeks until the end of the experiment. Mice with chronic kidney disease injected with Omniscan developed skin changes characteristic of nephrogenic systemic fibrosis including hair loss, reddening, ulceration, and skin tightening by 10 to 16 weeks. Histopathological sections demonstrated dermal fibrosis with increased skin thickness (0.25±0.06 mm, sham; 0.34±+0.3 mm, Omniscan-injected). Additionally, we observed an increase in tissue infiltration of ferroportin-expressing, fibrocyte-like cells accompanied by tissue iron accumulation in the skin of the Omniscan-treated mice. The deferiprone-treated group had significantly decreased skin thickness (p<0.05) and significantly decreased dermal fibrosis compared to the Omniscan-only group. In addition, iron chelation prevented tissue infiltration of ferroportin-expressing, fibrocyte-like cells. Our in vitro experiments demonstrated that exposure to Omniscan resulted in the release of catalytic iron and this was prevented by the iron chelator deferiprone. Deferiprone inhibited the differentiation of human peripheral blood mononuclear cells into ferroportin-expressing cells by immunohistochemical staining and western blot analysis. Our studies support an important role of iron in the pathophysiology of gadolinium chelate toxicity and nephrogenic systemic fibrosis.

Formoterol restores mitochondrial and renal function after ischemia-reperfusion injury

Mitochondrial biogenesis may be an adaptive response necessary for meeting the increased metabolic and energy demands during organ recovery after acute injury, and renal mitochondrial dysfunction has been implicated in the pathogenesis of AKI. We proposed that stimulation of mitochondrial biogenesis 24 hours after ischemia/reperfusion (I/R)-induced AKI, when renal dysfunction is maximal, would accelerate recovery of mitochondrial and renal function in mice. We recently showed that formoterol, a potent, highly specific, and long-acting β2-adrenergic agonist, induces renal mitochondrial biogenesis in naive mice. Animals were subjected to sham or I/R-induced AKI, followed by once-daily intraperitoneal injection with vehicle or formoterol beginning 24 hours after surgery and continuing through 144 hours after surgery. Treatment with formoterol restored renal function, rescued renal tubules from injury, and diminished necrosis after I/R-induced AKI. Concomitantly, formoterol stimulated mitochondrial biogenesis and restored the expression and function of mitochondrial proteins. Taken together, these results provide proof of principle that a novel drug therapy to treat AKI, and potentially other acute organ failures, works by restoring mitochondrial function and accelerating the recovery of renal function after injury has occurred.

Suramin: a potential therapy for diabetic nephropathy

Objective

To determine whether delayed administration of a single dose of suramin, a drug that has been used extensively in humans to treat trypanosomiasis, attenuates renal injury in a leptin receptor deficient C57BLKS/J db/db type 2 diabetic nephropathy (T2DN) mouse model.

Research Design and Methods

Groups of female non-diabetic (control) db/m and diabetic db/db mice of 8 and 16 weeks of age, respectively, were treated with suramin (10 mg/kg) or saline i.v. All animals were euthanized one week later. Measurements in mice 1 week following treatment included the following: body weight; blood glucose; urinary protein excretion; pathological lesions in glomeruli and proximal tubules; changes in protein expression of pro-inflammatory transcription factor nuclear factor κB (NF-κB) and intracellular adhesion molecule-1 (ICAM-1), profibrotic transforming growth factor-β1 (TGF-β1), phospho-SMAD-3 and alpha-smooth muscle actin (α-SMA); and immunohistochemical analysis of leukocyte infiltration and collagen 1A2 (COL1A2) deposition.

Results

Immunoblot analysis revealed increased NF-κB, ICAM-1, TGF-β1, phospho-SMAD-3, and α-SMA proteins in both 9 and 17 week db/db mice as compared to db/m control mice. Immunohistochemical analysis revealed moderate leukocyte infiltration and collagen 1A2 (COL1A2) deposition in 9 week db/db mice that was increased in the 17 week db/db mice. Importantly, suramin significantly decreased expression of all these markers in 9 week db/db mice and partially decreased in 17 week db/db mice without altering body weight, blood glucose or urinary protein excretion. There was no difference in creatinine clearance between 9 week db/m and db/db mice ± suramin. Importantly, in the 17 week db/db mice suramin intervention reversed the impaired creatinine clearance and overt histological damage.

Conclusions

Delayed administration of a single dose of suramin in a model of T2DN attenuated inflammation and fibrosis as well as improved renal function, supporting the use of suramin in T2DN.

Transgenic expression of proximal tubule peroxisome proliferator-activated receptor-alpha in mice confers protection during acute kidney injury

Our previous studies suggest that peroxisome proliferator-activated receptor-alpha (PPARalpha) plays a critical role in regulating fatty acid beta-oxidation in kidney tissue and this directly correlated with preservation of kidney morphology and function during acute kidney injury. To further study this, we generated transgenic mice expressing PPARalpha in the proximal tubule under the control of the promoter of KAP2 (kidney androgen-regulated protein 2). Segment-specific upregulation of PPARalpha expression by testosterone treatment of female transgenic mice improved kidney function during cisplatin or ischemia-reperfusion-induced acute kidney injury. Ischemia-reperfusion injury or treatment with cisplatin in wild-type mice caused inhibition of fatty-acid oxidation, reduction of mitochondrial genes of oxidative phosphorylation, mitochondrial DNA, fatty-acid metabolism, and the tricarboxylic acid cycle. Similar injury in testosterone-treated transgenic mice resulted in amelioration of these effects. Similarly, there were increases in the levels of 4-hydroxy-2-hexenal-derived lipid peroxidation products in wild-type mice, which were also reduced in the transgenic mice. Similarly, necrosis of the S3 segment was reduced in the two injury models in transgenic mice compared to wild type. Our results suggest proximal tubule PPARalpha activity serves as a metabolic sensor. Its increased expression without the use of an exogenous PPARalpha ligand in the transgenic mice is sufficient to protect kidney function and morphology, and to prevent abnormalities in lipid metabolism associated with acute kidney injury.

Alteration of renal respiratory Complex-III during experimental type-1 diabetes

BACKGROUND

Diabetes has become the single most common cause for end-stage renal disease in the United States. It has been established that mitochondrial damage occurs during diabetes; however, little is known about what initiates mitochondrial injury and oxidant production during the early stages of diabetes. Inactivation of mitochondrial respiratory complexes or alteration of their critical subunits can lead to generation of mitochondrial oxidants, mitochondrial damage, and organ injury. Thus, one goal of this study was to determine the status of mitochondrial respiratory complexes in the rat kidney during the early stages of diabetes (5-weeks post streptozotocin injection).

METHODS

Mitochondrial complex activity assays, blue native gel electrophoresis (BN-PAGE), Complex III immunoprecipitation, and an ATP assay were performed to examine the effects of diabetes on the status of respiratory complexes and energy levels in renal mitochondria. Creatinine clearance and urine albumin excretion were measured to assess the status of renal function in our model.

RESULTS

Interestingly, of all four respiratory complexes only cytochrome c reductase (Complex-III) activity was significantly decreased, whereas two Complex III subunits, Core 2 protein and Rieske protein, were up regulated in the diabetic renal mitochondria. The BN-PAGE data suggested that Complex III failed to assemble correctly, which could also explain the compensatory upregulation of specific Complex III subunits. In addition, the renal F0F1-ATPase activity and ATP levels were increased during diabetes.

CONCLUSION

In summary, these findings show for the first time that early (and selective) inactivation of Complex-III may contribute to the mitochondrial oxidant production which occurs in the early stages of diabetes.

STAT3 attenuates EGFR-mediated ERK activation and cell survival during oxidant stress in mouse proximal tubular cells

We have shown that renal epithelial cell survival depends on the sustained activation of the extracellular signal-regulated protein kinase (ERK) and lack of this activation was associated with death during oxidative stress. ERK is activated via the canonical epidermal growth factor receptor (EGFR)-Ras-MEK pathway, which could be attenuated by oxidants. We now show that the failure to activate ERK in a sustained manner during severe oxidative stress is owing to the activation of the signal transducer and activator of transcription-3 (STAT3) rather than the failure to activate the EGFR. Tyrosine phosphorylation of the EGFR and STAT3 was studied in hydrogen peroxide (H(2)O(2))-treated mouse proximal tubule (TKPTS) cells or in mouse kidney after ischemia/reperfusion (I/R) injury by Western blotting. STAT3 activation was inhibited by either pharmacologically (AG490) through its upstream janus kinase (JAK2) or by a dominant-negative STAT3 adenovirus. EGFR was inhibited by AG1478. Survival was determined by fluorescence-activated cell sorter analysis and trypan blue exclusion. We found that the EGFR was phosphorylated on its major autophosphorylation site (Tyr1173) regardless of the H(2)O(2) dose. On the other hand, both I/R and severe oxidative stress - but not moderate stress - increased tyrosine phosphorylation of STAT3 in an EGFR and JAK2-dependent manner. Inhibition of JAK2 or STAT3 lead to increased ERK activation and survival of TKPTS cells during severe oxidative stress. Our data suggest a role of tyrosine-phosphorylated STAT3 in the suppression of ERK activation. These data suggest that the STAT3 pathway might represent a new target for improved survival of proximal tubule cells exposed to severe oxidant injury.

Disruption of renal peritubular blood flow in lipopolysaccharide-induced renal failure: role of nitric oxide and caspases

Acute renal failure (ARF) is a frequent and serious complication of endotoxemia caused by lipopolysaccharide (LPS) and contributes significantly to mortality. The present studies were undertaken to examine the roles of nitric oxide (NO) and caspase activation on renal peritubular blood flow and apoptosis in a murine model of LPS-induced ARF. Male C57BL/6 mice treated with LPS ( Escherichia coli) at a dose of 10 mg/kg developed ARF at 18 h. Renal failure was associated with a significant decrease in peritubular capillary perfusion. Vessels with no flow increased from 7 ± 3% in the saline group to 30 ± 4% in the LPS group ( P < 0.01). Both the inducible NO synthase inhibitor l- N6-1-iminoethyl-lysine (l-NIL) and the nonselective caspase inhibitor benzyloxycarbonyl-Val-Ala-Asp fluoromethylketone (Z-VAD) prevented renal failure and reversed perfusion deficits. Renal failure was also associated with an increase in renal caspase-3 activity and an increase in renal apoptosis. Both l-NIL and Z-VAD prevented these changes. LPS caused an increase in NO production that was blocked by l-NIL but not by Z-VAD. Taken together, these data suggest NO-mediated activation of renal caspases and the resulting disruption in peritubular blood flow are an important mechanism of LPS-induced ARF.

CREB mediates ERK-induced survival of mouse renal tubular cells after oxidant stress

BACKGROUND

We showed that extracellular signal-regulated protein kinase (ERK) is prosurvival during oxidant stress both in the kidney and in cultured mouse proximal tubule (TKPTS) cells and demonstrated concomitant activation of ERK as well as the cyclic adenosine monophosphate (cAMP)-responsive element binding protein (CREB), during survival in vitro. We now show that CREB is a necessary prosurvival target of ERK.

METHODS

Ischemia/reperfusion (I/R) injury was induced in 129Sv mice. Oxidant stress was induced by hydrogen peroxide (H(2)O(2)) in TKPTS cells. Activation of CREB was determined by immunohistochemistry and Western blotting. Inhibition and activation of CREB was achieved by mutant or activated CREB-containing adenoviruses in vitro. The effects of oxidant stress on cell survival, CREB binding, and CREB-mediated transcription was determined by cell counting, gelshift analysis, and luciferase assay, respectively.

RESULTS

I/R activates CREB in the surviving distal nephron segments of the kidney. Inhibition of ERK and CREB abrogates survival after 0.5 mmol/L H(2)O(2) treatment, while overexpression of CREB ameliorates necrotic death caused by 1 mmol/L H(2)O(2). Inhibition of ERK also inhibited CREB activation. Binding of phosphorylated CREB to a CREB oligonucleotide was significantly increased after 0.5 mmol/L H(2)O(2) but decreased after 1 mmol/L H(2)O(2). Similarly, CREB-mediated transcription was significantly increased after 0.5 mmol/L H(2)O(2) treatment, while 1 mmol/L H(2)O(2) inhibited it. Interestingly, transcription from the CREB-driven bcl-2 promoter was unchanged after 0.5 mmol/L but decreased after 1 mmol/L H(2)O(2) treatment in agreement with Western blot studies.

CONCLUSION

We show that survival during oxidant stress is mediated through CREB and identification of its downstream targets will reveal important survival pathways.

Activation of ERK or inhibition of JNK ameliorates H(2)O(2) cytotoxicity in mouse renal proximal tubule cells

BACKGROUND

Our previous studies suggest that the balance between the activation of extracellular signal-regulated kinase (ERK) and the c-Jun N-terminal/stress-activated protein kinase (JNK) might determine cell fate following oxidant injury in vivo.

METHODS

The mouse proximal tubule cell line (TKPTS) was used to study hydrogen peroxide (H(2)O(2))-induced death and survival. The role of ERK and JNK in this process was studied by using adenoviruses that contain either a constitutively active mitogen-activated protein kinase kinase 1 (MEK1) or a dominant-negative JNK. Acridine orange plus ethidium bromide staining was applied to distinguish between viable, apoptotic, and necrotic cells following H(2)O(2) treatment. We analyzed cell cycle events by fluorescence-activated cell sorter (FACS) analysis and the phosphorylation status of ERK and JNK by Western blotting.

RESULTS

TKPTS cells survived a moderate level of oxidative stress (0.5 mM/L H(2)O(2)) via temporary growth arrest, while high dose of H(2)O(2) (1 mM/L) caused extensive necrosis. Survival was associated with activation of both ERK and JNK, while death was associated with JNK activation only. Prior adenovirus-mediated up-regulation of ERK or inhibition of JNK function increased the survival (8- or 7-fold, respectively) of TKPTS cells after 1 mmol/L H(2)O(2) treatment. Interestingly, ERK activation and, thus, survival was associated with growth arrest not proliferation.

CONCLUSION

We demonstrate that oxidant injury-induced necrosis could be ameliorated by either up-regulation of endogenous ERK or by inhibition of JNK-related pathways. These results directly demonstrate that the intracellular balance between prosurvival and prodeath mitogen-activated protein kinases (MAPKs) determine proximal tubule cell survival from oxidant injury and reveal possible mediators of survival.

Cisplatin-induced cell death is EGFR/src/ERK signaling dependent in mouse proximal tubule cells

Cisplatin treatment induces extensive death of the proximal tubules in mice. We also demonstrated that treatment of immortalized mouse proximal tubule cells (TKPTS) with 25 microM cisplatin induces apoptotic death in vitro. Here, we demonstrate that members of the MAPKs such as ERK, JNK, and p38 are all activated after cisplatin treatment both in vivo and in vitro. Because MAPKs mediate cell survival and death, we studied their role in cisplatin-induced cell death in vitro. Apoptosis was confirmed by cell morphology, fluorescence-activated cell-sorting analysis, annexin V/propidium iodide binding, and caspase-3 activation in TKPTS cells. Inhibition of ERK, but not JNK or p38, abolished caspase-3 activation and apoptotic death, suggesting a prodeath role of ERK in cisplatin-induced injury. We also determined that cisplatin-induced ERK as well as caspase-3 activation are epidermal growth factor receptor (EGFR) and c-src dependent because inhibition of these genes inhibited ERK and caspase-3 activation and attenuated apoptotic death. These results suggest that caspase-3 mediates cisplatin-induced cell death in TKPTS cells via an EGFR/src/ERK-dependent pathway. We also suggest that the prodeath effect of ERK is injury type dependent because during oxidant injury, ERK supports survival rather than death in the same cells. We propose that injury-specific outcome diverges downstream from ERK in cisplatin- or H(2)O(2)-mediated cell survival and death.

Differentiation-dependent expression of signal transducers and activators of transcription (STATs) might modify responses to growth factors in the cancers of the head and neck

Overexpression of the epidermal growth factor receptor (EGFR) in the cancers of the head and neck is well demonstrated. In addition, copy numbers of the EGFR mRNA were significantly higher in poorly differentiated tumors than in tumors that had a differentiated phenotype. Studies by others also showed that the constitutively activated signal transducer and activator of transcription-3 (STAT3), but not STAT1, is required for EGFR-mediated cell growth. Our aim was to reveal if STAT expression is differentiation-dependent and thus, might respond to exogenous stimuli in a differentiation-dependent manner. Both reverse transcription-polymerase chain reaction (RT-PCR) and immunohistochemistry revealed that expression of STAT1 was high in well/moderately differentiated tumors in vivo. In contrast, STAT3 was expressed in poorly differentiated tumors. In vitro experiments showed that differentiated primary oral keratinocytes expressed higher levels of STAT1, but lower levels of STAT3 than did their undifferentiated counterparts. Epidermal growth factor treatment of oral keratinocytes with various degrees of differentiation showed the maximal induction of cyclin D1 in undifferentiated cells. Our findings suggest that the level of differentiation might modulate the outcome of EGFR signaling (i.e. cyclin D1 transcription), due to the differentiation-associated intracellular balance of transcriptional regulators (STAT1 versus STAT3).

Cloning and expression of rat caspase-6 and its localization in renal ischemia/reperfusion injury

BACKGROUND

Caspase-6 is an important member of the executioner caspases in the caspase family of cell death proteases. The executioner caspases are the major active caspases detected in apoptotic cells and are generally considered to mediate the execution of apoptosis by cleaving and inactivating intracellular proteins. However, the complete characterization of mRNA and protein of caspase-6 in rat and its expression in normal kidney and in disease state has not been previously elucidated.

METHODS

A rat kidney cortex lambdagt10 cDNA library was screened to isolate the full-length caspase-6 cDNA. The recombinant caspase-6 protein was characterized by expression in bacteria and by transient transfection in mammalian cells. The expression in various tissues was analyzed by Northern blot, and localization in normal and ischemic kidney was performed by immunohistochemistry.

RESULTS

The predicted amino acid sequence of rat caspase-6 contains 277 amino acids, with two potential glycosylation sites, an integrin binding site (KGD), the caspase active site pentapeptide QACRG and the caspase family signature, HX2-4(S,C) X4(L,I,V,M,F)2(S,T)HG (HVDADCFVCVFLSHG). Rat caspase-6 is unique among known caspases by possessing a relatively long 5' untranslational region. Among various tissues tested, cas-pase-6 was expressed in varying levels in kidney, liver, spleen, heart, muscle, testis, and lung. Bacterial expression of recombinant rat caspase-6 resulted in production of both of the pro-form and active form of the enzyme suggesting autoactivation. Transient overexpression of rat caspase-6 in COS-1 cells induced DNA fragmentation, a hallmark of apoptosis. We also examined the localization and expression of caspase-6 by immunohistochemistry in kidneys subjected to 40 minutes of ischemia followed by 24 hours of reperfusion injury. Normal kidney showed mostly cytoplasmic and some nuclear staining of the tubules. Kidneys 24 hours after 40 minutes of ischemia showed more intense and diffused cytoplasmic staining with prominent nuclear staining, indicating increased expression and translocation from the cytoplasm to the nuclei. The staining in glomeruli was negative in both normal and ischemic kidney.

CONCLUSIONS

These studies demonstrate cloning, expression and characterization of the full-length rat caspase-6 and its localization in normal kidneys and kidneys subjected to ischemia/reperfusion injury. Since caspase-6 is involved in the degradation of nuclear matrix proteins and in activation of caspase-3, it may play an important role during renal ischemic injury.