Evidence for cytochrome P-450 as a source of catalytic iron in myoglobinuric acute renal failure

Heme Proteins and Kidney Injury: Beyond Rhabdomyolysis

Heme proteins, the stuff of life, represent an ingenious biologic strategy that capitalizes on the biochemical versatility of heme, and yet is one that avoids the inherent risks to cellular vitality posed by unfettered and promiscuously reactive heme. Heme proteins, however, may be a double-edged sword because they can damage the kidney in certain settings. Although such injury is often viewed mainly within the context of rhabdomyolysis and the nephrotoxicity of myoglobin, an increasing literature now attests to the fact that involvement of heme proteins in renal injury ranges well beyond the confines of this single disease (and its analog, hemolysis); indeed, through the release of the defining heme motif, destabilization of intracellular heme proteins may be a common pathway for acute kidney injury, in general, and irrespective of the underlying insult. This brief review outlines current understanding regarding processes underlying such heme protein-induced acute kidney injury (AKI) and chronic kidney disease (CKD). Topics covered include, among others, the basis for renal injury after the exposure of the kidney to and its incorporation of myoglobin and hemoglobin; auto-oxidation of myoglobin and hemoglobin; destabilization of heme proteins and the release of heme; heme/iron/oxidant pathways of renal injury; generation of reactive oxygen species and reactive nitrogen species by NOX, iNOS, and myeloperoxidase; and the role of circulating cell-free hemoglobin in AKI and CKD. Also covered are the characteristics of the kidney that render this organ uniquely vulnerable to injury after myolysis and hemolysis, and pathobiologic effects emanating from free, labile heme. Mechanisms that defend against the toxicity of heme proteins are discussed, and the review concludes by outlining the therapeutic strategies that have arisen from current understanding of mechanisms of renal injury caused by heme proteins and how such mechanisms may be interrupted.

Prominent Mitochondrial Injury as an Early Event in Heme Protein-Induced Acute Kidney Injury

Background

Mitochondrial injury occurs in and underlies acute kidney injury (AKI) caused by ischemia-reperfusion and other forms of renal injury. However, to date, a comprehensive analysis of this issue has not been undertaken in heme protein-induced AKI (HP-AKI). We examined key aspects of mitochondrial function, expression of proteins relevant to mitochondrial quality control, and mitochondrial ultrastructure in HP-AKI, along with responses to heme in renal proximal tubule epithelial cells.

Methods

The long-established murine glycerol model of HP-AKI was examined at 8 and 24 hours after HP-AKI. Indices of mitochondrial function (ATP and NAD+), expression of proteins relevant to mitochondrial dynamics, mitochondrial ultrastructure, and relevant gene/protein expression in heme-exposed renal proximal tubule epithelial cells in vitro were examined.

Results

ATP and NAD+ content and the NAD+/NADH ratio were all reduced in HP-AKI. Expression of relevant proteins indicate that mitochondrial biogenesis (PGC-1α, NRF1, and TFAM) and fusion (MFN2) were impaired, as was expression of key proteins involved in the integrity of outer and inner mitochondrial membranes (VDAC, Tom20, and Tim23). Conversely, marked upregulation of proteins involved in mitochondrial fission (DRP1) occurred. Ultrastructural studies, including novel 3D imaging, indicate profound changes in mitochondrial structure, including mitochondrial fragmentation, mitochondrial swelling, and misshapen mitochondrial cristae; mitophagy was also observed. Exposure of renal proximal tubule epithelial cells to heme in vitro recapitulated suppression of PGC-1α (mitochondrial biogenesis) and upregulation of p-DRP1 (mitochondrial fission).

Conclusions

Modern concepts pertaining to AKI apply to HP-AKI. This study validates the investigation of novel, clinically relevant therapies such as NAD+-boosting agents and mitoprotective agents in HP-AKI.

Serum catalytic iron and progression of chronic kidney disease: findings from the ICKD study

BACKGROUND

The non-transferrin bound catalytic iron moiety catalyses production of toxic reactive oxygen species and is associated with adverse outcomes. We hypothesized that serum catalytic iron (SCI) is associated with progression of chronic kidney disease (CKD).

METHODS

Baseline samples of the Indian Chronic Kidney Disease participants with at least one follow up visit were tested for total iron, iron binding capacity, transferrin saturation, SCI, ferritin and hepcidin. SCI was measured using the bleomycin-detectable iron assay that detects biologically active iron. Association with the incidence of major kidney endpoints, (MAKE, a composite of kidney death, kidney failure or > 40% loss of eGFR) was examined using Cox proportional hazards model adjusted for sex and age.

RESULTS

2002 subjects (49.9 ± 11.6 years, 68.1% males, baseline eGFR 41.01 ml/min/1.73m2) were enrolled. After a median follow up of 12.6 (12.2, 16.7) months, the composite MAKE occurred in 280 (14%). After adjusting for age and sex, increase from 25th to 75th percentile in SCI, transferrin saturation, ferritin and hepcidin were associated with 78% (43-122%), 34% (10-62%), 57% (24-100%) and 74% (35-124%) increase in hazard of MAKE, respectively. SCI was associated with MAKE and kidney failure after adjustment for occupational exposure, hypertension, diabetes, tobacco, alcohol use, history of AKI, baseline eGFR, uACR, and allowing baseline hazard to vary by centre.

CONCLUSIONS

SCI is strongly and independently associated with composite MAKE in patients with mild to moderate CKD. Confirmation in other studies will allow consideration of SCI as a risk marker and treatment target.

Iron deficiency exacerbates cisplatin- or rhabdomyolysis-induced acute kidney injury through promoting iron-catalyzed oxidative damage

Iron deficiency is the most common micronutrient deficiency worldwide. While iron deficiency is known to suppress embryonic organogenesis, its effect on the adult organ in the context of clinically relevant damage has not been considered. Here we report that iron deficiency is a risk factor for nephrotoxic intrinsic acute kidney injury of the nephron (iAKI). Iron deficiency exacerbated cisplatin-induced iAKI by markedly increasing non-heme catalytic iron and Nox4 protein which together catalyze production of hydroxyl radicals followed by protein and DNA oxidation, apoptosis and ferroptosis. Crosstalk between non-heme catalytic iron/Nox4 and downstream oxidative damage generated a mutual amplification cycle that facilitated rapid progression of cisplatin-induced iAKI. Iron deficiency also exacerbated a second model of iAKI, rhabdomyolysis, via increasing catalytic heme-iron. Heme-iron induced lipid peroxidation and DNA oxidation by interacting with Nox4-independent mechanisms, promoting p53/p21 activity and cellular senescence. Our data suggests that correcting iron deficiency and/or targeting specific catalytic iron species are strategies to mitigate iAKI in a wide range of patients with diverse forms of kidney injury.

Ferrotoxicity and Its Amelioration by Calcitriol in Cultured Renal Cells

Globally, acute kidney injury (AKI) is associated with significant mortality and an enormous economic burden. Whereas iron is essential for metabolically active renal cells, it has the potential to cause renal cytotoxicity by promoting Fenton chemistry-based oxidative stress involving lipid peroxidation. In addition, 1,25-dihydroxyvitamin D3 (calcitriol), the active form of vitamin D, is reported to have an antioxidative role. In this study, we intended to demonstrate the impact of vitamin D on iron-mediated oxidant stress and cytotoxicity of Vero cells exposed to iohexol, a low osmolar iodine-containing contrast media in vitro. Cultured Vero cells were pretreated with 1,25-dihydroxyvitamin D3 dissolved in absolute ethanol (0.05%, 2.0 mM) at a dose of 1 mM for 6 hours. Subsequently, iohexol was added at a concentration of 100 mg iodine per mL and incubated for 3 hours. Total cellular iron content was analysed by a flame atomic absorption spectrophotometer at 372 nm. Lipid peroxidation was determined by TBARS (thiobarbituric acid reactive species) assay. Antioxidants including total thiol content were assessed by Ellman’s method, catalase by colorimetric method, and superoxide dismutase (SOD) by nitroblue tetrazolium assay. The cells were stained with DAPI (4 ${}^{\prime }$ ,6-diamidino-2-phenylindole), and the cytotoxicity was evaluated by viability assay (MTT assay). The results indicated that iohexol exposure caused a significant increase of the total iron content in Vero cells. A concomitant increase of lipid peroxidation and decrease of total thiol protein levels, catalase, and superoxide dismutase activity were observed along with decreased cell viability in comparison with the controls. Furthermore, these changes were significantly reversed when the cells were pretreated with vitamin D prior to incubation with iohexol. Our findings of this in vitro model of iohexol-induced renotoxicity lend further support to the nephrotoxic potential of iron and underpin the possible clinical utility of vitamin D for the treatment and prevention of AKI.

Ferrotoxicity and Its Amelioration by Calcitriol in Cultured Renal Cells

Globally, acute kidney injury (AKI) is associated with significant mortality and an enormous economic burden. Whereas iron is essential for metabolically active renal cells, it has the potential to cause renal cytotoxicity by promoting Fenton chemistry-based oxidative stress involving lipid peroxidation. In addition, 1,25-dihydroxyvitamin D3 (calcitriol), the active form of vitamin D, is reported to have an antioxidative role. In this study, we intended to demonstrate the impact of vitamin D on iron-mediated oxidant stress and cytotoxicity of Vero cells exposed to iohexol, a low osmolar iodine-containing contrast media in vitro. Cultured Vero cells were pretreated with 1,25-dihydroxyvitamin D3 dissolved in absolute ethanol (0.05%, 2.0 mM) at a dose of 1 mM for 6 hours. Subsequently, iohexol was added at a concentration of 100 mg iodine per mL and incubated for 3 hours. Total cellular iron content was analysed by a flame atomic absorption spectrophotometer at 372 nm. Lipid peroxidation was determined by TBARS (thiobarbituric acid reactive species) assay. Antioxidants including total thiol content were assessed by Ellman's method, catalase by colorimetric method, and superoxide dismutase (SOD) by nitroblue tetrazolium assay. The cells were stained with DAPI (4',6-diamidino-2-phenylindole), and the cytotoxicity was evaluated by viability assay (MTT assay). The results indicated that iohexol exposure caused a significant increase of the total iron content in Vero cells. A concomitant increase of lipid peroxidation and decrease of total thiol protein levels, catalase, and superoxide dismutase activity were observed along with decreased cell viability in comparison with the controls. Furthermore, these changes were significantly reversed when the cells were pretreated with vitamin D prior to incubation with iohexol. Our findings of this in vitro model of iohexol-induced renotoxicity lend further support to the nephrotoxic potential of iron and underpin the possible clinical utility of vitamin D for the treatment and prevention of AKI.

Ferrotoxicity and its amelioration by endogenous vitamin D in experimental acute kidney injury

This work provides in-depth insights on catalytic iron-induced cytotoxicity and the resultant triggering of endogenous vitamin D synthesis in experimental acute kidney injury. Our results reveal significantly elevated levels of catalytic iron culminating in oxidant-mediated renal injury and a concomitant increase in 1,25-dihdyroxyvitamin D3 levels. Also, changes in other iron-related proteins including transferrin, ferritin, and hepcidin were observed both in the serum as well as in their mRNA expression. We consider all these findings vital since no connection between catalytic iron and vitamin D has been established so far. Furthermore, we believe that this work provides new and interesting results, with catalytic iron emerging as an important target in ameliorating renal cellular injury, possibly by timely administration of vitamin D. It also needs to be seen if these observations made in rats could be translated to humans by means of robust clinical trials.

Ferrotoxicity and its amelioration by endogenous vitamin D in experimental acute kidney injury

Acute kidney injury causes significant morbidity and mortality. This experimental animal study investigated the simultaneous impact of iron and vitamin D on acute kidney injury induced by iohexol, an iodinated, non-ionic monomeric radiocontrast agent in Wistar rats. Out of 36 healthy male Wistar rats, saline was injected into six control rats (group 1) and iohexol into the remaining 30 experimental rats (groups 2 to 6 comprising six rats each). Biochemical, renal histological changes, and gene expression of iron-regulating proteins and 1 α-hydroxylase were analyzed. Urinary neutrophil gelatinase-associated lipocalin (NGAL), serum creatinine, urine protein, serum and urine catalytic iron, 25-hydroxyvitamin D3, 1,25-dihydroxyvitamin D3, and tissue lipid peroxidation were assayed. Rats injected with iohexol showed elevated urinary NGAL (11.94 ± 6.79 ng/mL), serum creatinine (2.92 ± 0.91 mg/dL), and urinary protein levels (11.03 ± 9.68 mg/mg creatinine) together with histological evidence of tubular injury and iron accumulation. Gene expression of iron-regulating proteins and 1 α-hydroxylase was altered. Serum and urine catalytic iron levels were elevated (0.57 ± 0.17; 48.95 ± 29.13 µmol/L) compared to controls (0.49 ± 0.04; 20.7 ± 2.62 µmol/L, P < 0.001). Urine catalytic iron positively correlated with tissue peroxidation (r = 0.469, CI 0.122 to 0.667, P = 0.004) and urinary NGAL (r = 0.788, CI 0.620 to 0.887, P < 0.001). 25-hydroxyvitamin D3 (61.58 ± 9.60 ng/mL) and 1,25-dihydroxyvitamin D3 (50.44 ± 19.76 pg/mL) levels increased simultaneously. In a multivariate linear regression analysis, serum iron, urine catalytic iron, and tissue lipid peroxidation independently and positively predicted urinary NGAL, an acute kidney injury biomarker. This study highlights the nephrotoxic potential of catalytic iron besides demonstrating a concurrent induction of vitamin D endogenously for possible renoprotection in acute kidney injury.

Impact statement

This work provides in-depth insights on catalytic iron-induced cytotoxicity and the resultant triggering of endogenous vitamin D synthesis in experimental acute kidney injury. Our results reveal significantly elevated levels of catalytic iron culminating in oxidant-mediated renal injury and a concomitant increase in 1,25-dihdyroxyvitamin D3 levels. Also, changes in other iron-related proteins including transferrin, ferritin, and hepcidin were observed both in the serum as well as in their mRNA expression. We consider all these findings vital since no connection between catalytic iron and vitamin D has been established so far. Furthermore, we believe that this work provides new and interesting results, with catalytic iron emerging as an important target in ameliorating renal cellular injury, possibly by timely administration of vitamin D. It also needs to be seen if these observations made in rats could be translated to humans by means of robust clinical trials.

Iron Chelation as a Potential Therapeutic Strategy for AKI Prevention

AKI remains a major public health concern. Despite years of investigation, no intervention has been demonstrated to reliably prevent AKI in humans. Thus, development of novel therapeutic targets is urgently needed. An important role of iron in the pathophysiology of AKI has been recognized for over three decades. When present in excess and in nonphysiologic labile forms, iron is toxic to the kidneys and multiple other organs, whereas iron chelation is protective across a broad spectrum of insults. In humans, small studies have investigated iron chelation as a novel therapeutic strategy for prevention of AKI and extrarenal acute organ injury, and have demonstrated encouraging initial results. In this review, we examine the existing data on iron chelation for AKI prevention in both animal models and human studies. We discuss practical considerations for future clinical trials of AKI prevention using iron chelators, including selection of the ideal clinical setting, patient population, iron chelating agent, and dosing regimen. Finally, we compare the key differences among the currently available iron chelators, including pharmacokinetics, routes of administration, and adverse effects.

Iron Homeostasis in Healthy Kidney and its Role in Acute Kidney Injury

Iron is required for key aspects of cellular physiology including mitochondrial function and DNA synthesis and repair. However, free iron is an aberration because of its ability to donate electrons, reduce oxygen, and generate reactive oxygen species. Iron-mediated cell injury or ferroptosis is a central player in the pathogenesis of acute kidney injury. There are several homeostatic proteins and pathways that maintain critical balance in iron homeostasis to allow iron's biologic functions yet avoid ferroptosis. Hepcidin serves as the master regulator of iron homeostasis through its ability to regulate ferroportin-mediated iron export and intracellular H-ferritin levels. Hepcidin is a protective molecule in acute kidney injury. Drugs targeting hepcidin, H-ferritin, and ferroptosis pathways hold great promise to prevent or treat kidney injury. In this review we discuss iron homeostasis under physiological and pathologic conditions and highlight its importance in acute kidney injury.

Iron, Hepcidin, and Death in Human AKI

BACKGROUND

Iron is a key mediator of AKI in animal models, but data on circulating iron parameters in human AKI are limited.

METHODS

We examined results from the ARF Trial Network study to assess the association of plasma catalytic iron, total iron, transferrin, ferritin, free hemoglobin, and hepcidin with 60-day mortality. Participants included critically ill patients with AKI requiring RRT who were enrolled in the study.

RESULTS

Of the 807 study participants, 409 (51%) died by day 60. In both unadjusted and multivariable adjusted models, higher plasma concentrations of catalytic iron were associated with a significantly greater risk of death, as were lower concentrations of hepcidin. After adjusting for other factors, patients with catalytic iron levels in the highest quintile versus the lowest quintile had a 4.06-fold increased risk of death, and patients with hepcidin levels in the lowest quintile versus the highest quintile of hepcidin had a 3.87-fold increased risk of death. These findings were consistent across multiple subgroups. Other iron markers were also associated with death, but the magnitude of the association was greatest for catalytic iron and hepcidin. Higher plasma concentrations of catalytic iron and lower concentrations of hepcidin are each independently associated with mortality in critically ill patients with AKI requiring RRT.

CONCLUSIONS

These findings suggest that plasma concentrations of catalytic iron and hepcidin may be useful prognostic markers in patients with AKI. Studies are needed to determine whether strategies to reduce catalytic iron or increase hepcidin might be beneficial in this patient population.

Early intraoperative iron-binding proteins are associated with acute kidney injury after cardiac surgery

OBJECTIVES

Iron regulation is an important modifier of renal ischemia-reperfusion injury, but the role of iron-binding proteins during cardiopulmonary bypass remains unclear. The goal was to characterize iron-binding proteins throughout ischemia-reperfusion injury to determine their association with acute kidney injury development.

METHODS

A prospective observational cohort of adult patients who underwent cardiac surgery (n = 301) was obtained, and acute kidney injury was defined by Kidney Disease Improving Global Outcomes. Serum ferritin, transferrin saturation, and urine hepcidin-25 were measured.

RESULTS

Intraoperative serum ferritin was lower at the start of cardiopulmonary bypass (P = .005) and 1-hour cardiopulmonary bypass (P = .001) in patients with acute kidney injury versus patients without acute kidney injury. Lower serum ferritin and higher transferrin saturation at 1-hour cardiopulmonary bypass were independent predictors of acute kidney injury (serum ferritin odds ratio, 0.66; 95% confidence interval [CI], 0.48-0.91; transferrin saturation odds ratio, 1.26; 95% CI, 1.02-1.55) and improved model discrimination (area under the curve [AUC], 0.76; 95% CI, 0.67-0.85) compared with clinical prediction alone (AUC, 0.72; 95% CI, 0.62-0.81; ΔAUC and net reclassification index, P = .01). Lower ferritin, higher transferrin saturation at 1-hour cardiopulmonary bypass, and lower urine hepcidin-25 at postoperative day 1 were also independent predictors for acute kidney injury development, and this model demonstrated an AUC of 0.80 (0.72-0.87), which was superior to clinical prediction (ΔAUC P = .002, integrated discrimination improvement and net reclassification index P = .003).

CONCLUSIONS

Our findings suggest that lower levels of intraoperative iron-binding proteins may reflect an impaired capacity to rapidly handle catalytic iron released during cardiopulmonary bypass, leading to kidney injury. These data highlight the importance of iron homeostasis in human ischemia-reperfusion injury and suggest it is a potentially modifiable risk during cardiac surgery. Intraoperative detection of incipient acute kidney injury may be feasible and could be used as an enrichment strategy for clinical trials.

Protective and antioxidant effects of copper-nicotinate complex against glycerol-induced nephrotoxicity in rats

Copper-nicotinate complex (CNC) has antioxidant activities through scavenging of free radicals formed inside the body. CNC also has anti-tumor and anti-inflammatory activities. The current study was designed to determine the effect of glycerol on rat kidney function and oxidative stress as well as, the potential nephroprotective effects of CNC. Forty male Wistar rats were randomly allocated into four equal groups. The groups of rats were as follows: GI was kept under normal control conditions; GII was orally given CNC at a dose of 0.043 mg kg^-1 body weight (BW), three times/week for 4 weeks; GIII was administered glycerol (topical application) at a dose of 3.15 ml kg^-1 BW daily for 4 weeks; and GIV was given CNC and glycerol with the same dose and route. The results revealed that CNC improves the renal dysfunctions induced by glycerol by recovering the levels of urea and creatinine to normal, as well as through the antioxidant status manifested by the normalization of catalase, superoxide dismutase, reduced glutathione, and malondialdehyde levels. Moreover, by its effect as an anti-oxidant, CNC reduces the effect of glycerol on the kidney by decreasing the fibrosis, degenerative changes and necrotic changes in the renal tubules. In conclusion, CNC could alleviate the side effects that might be caused by glycerol.

Physiological functions of ferroportin in the regulation of renal iron recycling and ischemic acute kidney injury

Renal iron recycling preserves filtered iron from urinary excretion. However, it remains debated whether ferroportin (FPN), the only known iron exporter, is functionally involved in renal iron recycling and whether renal iron recycling is required for systemic iron homeostasis. We deleted FPN in whole nephrons by use of a Nestin-Cre and in the distal nephrons and collecting ducts, using a Ksp-Cre, and investigated its impacts on renal iron recycling and systemic iron homeostasis. FPN deletion by Nestin-Cre, but not by Ksp-Cre, caused excess iron retention and increased ferritin heavy chain (FTH1) specifically in the proximal tubules and resulted in the reduction of serum and hepatic iron. The systemic iron redistribution was aggravated, resulting in anemia and the marked downregulation of hepatic hepcidin in elderly FPN knockout (KO)/Nestin-Cre mice. Similarly, in iron-deficient FPN KO/Nestin-Cre mice, the renal iron retention worsened anemia with the activation of the erythropoietin-erythroferrone-hepcidin pathway and the downregulation of hepatic hepcidin. Hence, FPN likely located at the basolateral membrane of the proximal tubules to export iron into the circulation and was required for renal iron recycling and systemic iron homeostasis particularly in elderly and iron-deficient mice. Moreover, FPN deletion in the proximal tubules alleviated ischemic acute kidney injury, possibly by upregulating FTH1 to limit catalytic iron and by priming antioxidant mechanisms, indicating that FPN could be deleterious in the pathophysiology of ischemic acute kidney injury (AKI) and thus may be a potential target for the prevention and mitigation of ischemic AKI.

Glyoxal-induced modification enhances stability of hemoglobin and lowers iron-mediated oxidation reactions of the heme protein: An in vitro study

Glyoxal, a reactive α-oxoaldehyde, increases in diabetic condition. It reacts with different proteins to form advanced glycation end products (AGEs) following Maillard-like reaction. Considering the significance of AGE-mediated protein modification by glyoxal, here we have investigated the in vitro effect of the reactive α-oxoaldehyde (10, 20μM) on the heme protein hemoglobin (HbA₀) (100μM) after incubation for one week at 25°C. In comparison with HbA₀, glyoxal-treated HbA₀ exhibited decreased absorbance around 280nm, reduced intrinsic fluorescence and lower surface hydrophobicity. Glyoxal treatment was found to increase the stability of HbA₀ without significant perturbation of the secondary structure of the heme protein. In addition, H₂O₂-mediated iron release and subsequent iron-mediated oxidative (Fenton) reactions were found to be lower in presence of glyoxal-treated HbA₀ compared to HbA₀. Mass spectrometric studies revealed modification of arginine residues of HbA₀ (Arg-31α, Arg-40β) to hydroimidazolone adducts. AGE-induced modifications thus appear to be associated with the observed changes of the heme protein. Considering the increased level of glyoxal in diabetes mellitus as well as its high reactivity, glyoxal-derived AGE adducts might thus be associated with modifications of the protein including physiological significance.

Protective Role for Antioxidants in Acute Kidney Disease

Acute kidney injury causes significant morbidity and mortality in the community and clinic. Various pathologies, including renal and cardiovascular disease, traumatic injury/rhabdomyolysis, sepsis, and nephrotoxicity, that cause acute kidney injury (AKI), induce general or regional decreases in renal blood flow. The ensuing renal hypoxia and ischemia promotes the formation of reactive oxygen species (ROS) such as superoxide radical anions, peroxides, and hydroxyl radicals, that can oxidatively damage biomolecules and membranes, and affect organelle function and induce renal tubule cell injury, inflammation, and vascular dysfunction. Acute kidney injury is associated with increased oxidative damage, and various endogenous and synthetic antioxidants that mitigate source and derived oxidants are beneficial in cell-based and animal studies. However, the benefit of synthetic antioxidant supplementation in human acute kidney injury and renal disease remains to be realized. The endogenous low-molecular weight, non-proteinaceous antioxidant, ascorbate (vitamin C), is a promising therapeutic in human renal injury in critical illness and nephrotoxicity. Ascorbate may exert significant protection by reducing reactive oxygen species and renal oxidative damage via its antioxidant activity, and/or by its non-antioxidant functions in maintaining hydroxylase and monooxygenase enzymes, and endothelium and vascular function. Ascorbate supplementation may be particularly important in renal injury patients with low vitamin C status.

Cisplatin-Induced Nephrotoxicity; Protective Supplements and Gender Differences

Cisplatin (CDDP) has been widely used as a chemotherapeutic agent for solid tumors. The most common side effect of CDDP is nephrotoxicity, and many efforts have been made in the laboratory and the clinic to employ candidate adjuvants to CDDP to minimize this adverse influence. Many synthetic and herbal antioxidants as well as trace elements have been investigated for this purpose in recent years and a variety of positive and negative results have been yielded. However, no definitive supplement has so far been proposed to prevent CDDP-induced nephrotoxicity; however, this condition is gender related and the sex hormone estrogen may protect the kidney against CDDP damage. In this review, the results of research related to the effect of different synthetic and herbal antioxidants supplements are presented and discussed with suggestions included for future work.

Targeting Iron Homeostasis in Acute Kidney Injury

Iron is an essential metal involved in several major cellular processes required to maintain life. Because of iron's ability to cause oxidative damage, its transport, metabolism, and storage is strictly controlled in the body, especially in the small intestine, liver, and kidney. Iron plays a major role in acute kidney injury and has been a target for therapeutic intervention. However, the therapies that have been effective in animal models of acute kidney injury have not been successful in human beings. Targeting iron trafficking via ferritin, ferroportin, or hepcidin may offer new insights. This review focuses on the biology of iron, particularly in the kidney, and its implications in acute kidney injury.

Catalytic iron and acute kidney injury

Acute kidney injury (AKI) is a common and often devastating condition among hospitalized patients and is associated with markedly increased hospital length of stay, mortality, and cost. The pathogenesis of AKI is complex, but animal models support an important role for catalytic iron in causing AKI. Catalytic iron, also known as labile iron, is a transitional pool of non-transferrin-bound iron that is readily available to participate in redox cycling. Initial findings related to catalytic iron and animal models of kidney injury have only recently been extended to human AKI. In this review, we discuss the role of catalytic iron in human AKI, focusing on recent translational studies in humans, assay considerations, and potential therapeutic targets for future interventional studies.

Postischemic microvasculopathy and endothelial progenitor cell-based therapy in ischemic AKI: update and perspectives

Acute kidney injury (AKI) dramatically increases mortality of hospitalized patients. Incidences have been increased in recent years. The most frequent cause is transient renal hypoperfusion or ischemia which induces significant tubular cell dysfunction/damage. In addition, two further events take place: interstitial inflammation and microvasculopathy (MV). The latter evolves within minutes to hours postischemia and may result in permanent deterioration of the peritubular capillary network, ultimately increasing the risk for chronic kidney disease (CKD) in the long term. In recent years, our understanding of the molecular/cellular processes responsible for acute and sustained microvasculopathy has increasingly been expanded. The methodical approaches for visualizing impaired peritubular blood flow and increased vascular permeability have been optimized, even allowing the depiction of tissue abnormalities in a three-dimensional manner. In addition, endothelial dysfunction, a hallmark of MV, has increasingly been recognized as an inductor of both vascular malfunction and interstitial inflammation. In this regard, so-called regulated necrosis of the endothelium could potentially play a role in postischemic inflammation. Endothelial progenitor cells (EPCs), represented by at least two major subpopulations, have been shown to promote vascular repair in experimental AKI, not only in the short but also in the long term. The discussion about the true biology of the cells continues. It has been proposed that early EPCs are most likely myelomonocytic in nature, and thus they may simply be termed proangiogenic cells (PACs). Nevertheless, they reliably protect certain types of tissues/organs from ischemia-induced damage, mostly by modulating the perivascular microenvironment in an indirect manner. The aim of the present review is to summarize the current knowledge on postischemic MV and EPC-mediated renal repair.

Protective effects of formononetin against rhabdomyolysis-induced acute kidney injury by upregulating Nrf2 in vivo and in vitro

Acute kidney injury (AKI) is a well-known organ injury frequently observed after rhabdomyolysis (RM).

A study on the effect of cimetidine and L-carnitine on myoglobinuric acute kidney injury in male rats

Myoglobinuric acute renal failure is the most important life threatening complication of rhabdomyolysis. Iron, free radicals, nitric oxide and cytochrome p450 are involved in the pathogenesis of mARF. The aim of this study is to compare the effect of cimetidine, l-carnitine and both agents together on mARF in rats. Forty rats were divided into 5 groups; group I: control rats, group II: myoglobinuric ARF rats, group III: mARF rats received l-carnitine (200mg/kg, i.p.), group IV: mARF rats received cimetidine (150mg/kg i.p.) and group V: mARF rats received both agents together. 48h after glycerol injection, systolic blood pressure was measured. Urine and blood samples were collected to evaluate urine volume, GFR, BUN, creatinine, K, Na, serum creatine kinase, NO and glutathione levels. Kidney specimens were taken to investigate renal cytochrome p450 and for histological examinations. Cimetidine treatment significantly decreased creatinine, BUN, K, Na, SBP and creatine kinase and increased GFR and urine volume compared to group II. l-carnitine exerted similar changes except for the effect on K and GFR. NO was significantly decreased, while renal glutathione and cytochrome p450 were significantly increased in groups treated with l-carnitine or cimetidine as compared to group II. Combined treatment further improved renal functions, creatine kinase, oxidative stress parameters and SBP as compared to each therapy alone. The histological changes confirmed the biochemical findings. Cimetidine and l-carnitine have protective effects - almost equally - against mARF. Using both agents together, minimises the renal injury.

Hepcidin Mitigates Renal Ischemia-Reperfusion Injury by Modulating Systemic Iron Homeostasis

Iron-mediated oxidative stress is implicated in the pathogenesis of renal ischemia-reperfusion injury. Hepcidin is an endogenous acute phase hepatic hormone that prevents iron export from cells by inducing degradation of the only known iron export protein, ferroportin. In this study, we used a mouse model to investigate the effect of renal ischemia-reperfusion injury on systemic iron homeostasis and determine if dynamic modulation of iron homeostasis with hepcidin has therapeutic benefit in the treatment of AKI. Renal ischemia-reperfusion injury induced hepatosplenic iron export through increased ferroportin expression, which resulted in hepatosplenic iron depletion and an increase in serum and kidney nonheme iron levels. Exogenous hepcidin treatment prevented renal ischemia-reperfusion-induced changes in iron homeostasis. Hepcidin also decreased kidney ferroportin expression and increased the expression of cytoprotective H-ferritin. Hepcidin-induced restoration of iron homeostasis was accompanied by a significant reduction in ischemia-reperfusion-induced tubular injury, apoptosis, renal oxidative stress, and inflammatory cell infiltration. Hepcidin -: deficient mice demonstrated increased susceptibility to ischemia-reperfusion injury compared with wild-type mice. Reconstituting hepcidin-deficient mice with exogenous hepcidin induced hepatic iron sequestration, attenuated the reduction in renal H-ferritin and reduced renal oxidative stress, apoptosis, inflammation, and tubular injury. Hepcidin-mediated protection was associated with reduced serum IL-6 levels. In summary, renal ischemia-reperfusion injury results in profound alterations in systemic iron homeostasis. Hepcidin treatment restores iron homeostasis and reduces inflammation to mediate protection in renal ischemia-reperfusion injury, suggesting that hepcidin-ferroportin pathway holds promise as a novel therapeutic target in the treatment of AKI.

Increased plasma catalytic iron in patients may mediate acute kidney injury and death following cardiac surgery

Catalytic iron, the chemical form of iron capable of participating in redox cycling, is a key mediator of acute kidney injury (AKI) in multiple animal models, but its role in human AKI has not been studied. Here we tested in a prospective cohort of 250 patients undergoing cardiac surgery whether plasma catalytic iron levels are elevated and associated with the composite outcome of AKI requiring renal replacement therapy or in-hospital mortality. Plasma catalytic iron, free hemoglobin, and other iron parameters were measured preoperatively, at the end of cardiopulmonary bypass, and on postoperative days 1 and 3. Plasma catalytic iron levels, but not other iron parameters, rose significantly at the end of cardiopulmonary bypass and were directly associated with bypass time and number of packed red blood cell transfusions. In multivariate analyses adjusting for age and preoperative eGFR, patients in the highest compared with the lowest quartile of catalytic iron on postoperative day 1 had a 6.71 greater odds of experiencing the primary outcome, and also had greater odds of AKI, hospital mortality, and postoperative myocardial injury. Thus, our data are consistent with and expand on findings from animal models demonstrating a pathologic role of catalytic iron in mediating adverse postoperative outcomes. Interventions aimed at reducing plasma catalytic iron levels as a strategy for preventing AKI in humans are warranted.

Plasma catalytic iron, AKI, and death among critically ill patients

BACKGROUND AND OBJECTIVES

Catalytic iron has been hypothesized to be a key mediator of AKI. However, the association between plasma catalytic iron levels and AKI has not been well studied in humans.

DESIGN, SETTINGS, PARTICIPANTS, & MEASUREMENTS

A single-center, prospective, nonconsecutive cohort study of 121 critically ill patients admitted to intensive care units (ICUs) between 2008 and 2012 was performed. Plasma catalytic iron, free hemoglobin, and other iron markers were measured on ICU days 1 and 4. The primary end point was in-hospital mortality or AKI requiring RRT. Secondary end points included mortality (assessed during hospitalization, at 30 days, and 1 year) and incident AKI, defined by modified Kidney Disease Improving Global Outcomes criteria.

RESULTS

ICU day 1 plasma catalytic iron levels were higher among patients who reached the primary end point (median, 0.74 µmol/l [interquartile range, 0.31-3.65] versus 0.29 µmol/l [0.22-0.46]; P<0.01). ICU day 1 plasma catalytic iron levels were associated with number of packed red blood cell transfusions before ICU arrival (rs=0.29; P<0.001) and plasma free hemoglobin levels on ICU day 1 (rs=0.32; P<0.001). Plasma catalytic iron levels on ICU day 1 were significantly associated with in-hospital mortality or AKI requiring RRT, even after adjusting for age, enrollment eGFR, and number of packed red blood cell transfusions before ICU arrival (13 events; adjusted odds ratio per 1-SD higher ln[catalytic iron], 3.33; 95% confidence interval, 1.79 to 6.20). ICU day 1 plasma catalytic iron levels were also significantly associated with incident AKI, RRT, hospital mortality, and 30-day mortality.

CONCLUSIONS

Among critically ill patients, elevated plasma catalytic iron levels on arrival to the ICU are associated with a greater risk of incident AKI, RRT, and hospital mortality.

Caffeic acid phenethyl ester as a protective agent against nephrotoxicity and/or oxidative kidney damage: a detailed systematic review

Caffeic acid phenethyl ester (CAPE), an active component of propolis, has been attracting the attention of different medical and pharmaceutical disciplines in recent years because of its antioxidant, anti-inflammatory, antiproliferative, cytotoxic, antiviral, antifungal, and antineoplastic properties. One of the most studied organs for the effects of CAPE is the kidney, particularly in the capacity of this ester to decrease the nephrotoxicity induced by several drugs and the oxidative injury after ischemia/reperfusion (I/R). In this review, we summarized and critically evaluated the current knowledge regarding the protective effect of CAPE in nephrotoxicity induced by several special medicines such as cisplatin, doxorubicin, cyclosporine, gentamycin, methotrexate, and other causes leading to oxidative renal injury, namely, I/R models and senility.

Inhibition of cytochrome P450 2E1 and activation of transcription factor Nrf2 are renoprotective in myoglobinuric acute kidney injury

Rhabdomyolysis accounts for ∼10% of acute kidney injuries. In glycerol-induced myoglobinuric acute kidney injury, we found an increase in the nuclear factor erythroid 2-related factor 2 (Nrf2) nuclear protein, a key redox-sensitive transcription factor, and Nrf2-regulated genes and proteins including upregulation of heme oxygenase-1. In in vitro studies, pretreatment of LLC-PK1 cells with an activator of Nrf2 before myoglobin exposure significantly decreased oxidant generation and cytotoxicity, whereas Nrf2 inhibition and gene silencing exacerbated the injury. Chlormethiazole, a specific CYP2E1 transcription inhibitor, prevented an increase in catalytic iron in the kidneys, decreased oxidative stress, blocked nuclear translocation of the Nrf2 protein, decreased heme oxygenase-1 upregulation, and provided functional and histological protection against acute kidney injury. CYP2E1 inhibitors and gene silencing in renal tubular epithelial cells significantly decreased reactive oxygen species generation and provided marked protection against myoglobin-induced cytotoxicity. Thus, during CYP2E1-induced oxidative stress, the transcription factor Nrf2 has a pivotal role in the early adaptive response. Inhibition of CYP2E1 coupled with the prior induction of Nrf2 may be a valuable tool to reduce CYP2E1-mediated rhabdomyolysis-induced acute kidney injury.

Hemojuvelin modulates iron stress during acute kidney injury: improved by furin inhibitor

AIMS

Free iron plays an important role in the pathogenesis of acute kidney injury (AKI) via the formation of hydroxyl radicals. Systemic iron homeostasis is controlled by the hemojuvelin-hepcidin-ferroportin axis in the liver, but less is known about this role in AKI.

RESULTS

By proteomics, we identified a 42 kDa soluble hemojuvelin (sHJV), processed by furin protease from membrane-bound hemojuvelin (mHJV), in the urine during AKI after cardiac surgery. Biopsies from human and mouse specimens with AKI confirm that HJV is extensively increased in renal tubules. Iron overload enhanced the expression of hemojuvelin-hepcidin signaling pathway. The furin inhibitor (FI) decreases furin-mediated proteolytic cleavage of mHJV into sHJV and augments the mHJV/sHJV ratio after iron overload with hypoxia condition. The FI could reduce renal tubule apoptosis, stabilize hypoxic induced factor-1, prevent the accumulation of iron in the kidney, and further ameliorate ischemic-reperfusion injury. mHJV is associated with decreasing total kidney iron, secreting hepcidin, and promoting the degradation of ferroportin at AKI, whereas sHJV does the opposite.

INNOVATION

This study suggests the ratio of mHJV/sHJV affects the iron deposition during acute kidney injury and sHJV could be an early biomarker of AKI.

CONCLUSION

Our findings link endogenous HJV inextricably with renal iron homeostasis for the first time, add new significance to early predict AKI, and identify novel therapeutic targets to reduce the severity of AKI using the FI.

Proximal tubule H-ferritin mediates iron trafficking in acute kidney injury

Ferritin plays a central role in iron metabolism and is made of 24 subunits of 2 types: heavy chain and light chain. The ferritin heavy chain (FtH) has ferroxidase activity that is required for iron incorporation and limiting toxicity. The purpose of this study was to investigate the role of FtH in acute kidney injury (AKI) and renal iron handling by using proximal tubule-specific FtH-knockout mice (FtH(PT-/-) mice). FtH(PT-/-) mice had significant mortality, worse structural and functional renal injury, and increased levels of apoptosis in rhabdomyolysis and cisplatin-induced AKI, despite significantly higher expression of heme oxygenase-1, an antioxidant and cytoprotective enzyme. While expression of divalent metal transporter-1 was unaffected, expression of ferroportin (FPN) was significantly lower under both basal and rhabdomyolysis-induced AKI in FtH(PT-/-) mice. Apical localization of FPN was disrupted after AKI to a diffuse cytosolic and basolateral pattern. FtH, regardless of iron content and ferroxidase activity, induced FPN. Interestingly, urinary levels of the iron acceptor proteins neutrophil gelatinase-associated lipocalin, hemopexin, and transferrin were increased in FtH(PT-/-) mice after AKI. These results underscore the protective role of FtH and reveal the critical role of proximal tubule FtH in iron trafficking in AKI.

Impact of catalytic iron on mortality in patients with acute coronary syndrome exposed to iodinated radiocontrast-The Iscom Study

BACKGROUND

Catalytic iron (CI) mediates vascular injury by generating reactive oxygen species. We evaluated role of CI in predicting mortality in patients with acute coronary syndrome (ACS) and studied association of contrast nephropathy with CI levels.

METHODS

We investigated 806 patients with ACS undergoing contrast exposure for a cardiac procedure who were followed up for 30 days.

RESULTS

Overall mortality was 1.6% at 30 days. Catalytic iron at baseline predicted mortality with CI levels significantly higher in those who died, 0.45 μmol/L (0.37, 0.68) compared with survivors 0.31 μmol/L (0.21, 0.40); P = .004. Catalytic iron was associated with increased risk of death in the highest quartile compared with lower 3 quartiles (hazard ratio 7.88, P = .001) after adjustment for age, diabetes, ST deviation, Killip class, ejection fraction, baseline creatinine, hemoglobin level, and troponin. Fifty-five patients (6.8%) developed contrast nephropathy. Patients with contrast nephropathy had a 27% increase in median CI levels from baseline up to 48 hours compared with a marginal 2.9% increase in those without contrast nephropathy (0.37, 0.14 μmol/L to 0.47, 0.20 μmol/L versus 0.35, 0.12 μmol/L to 0.36, 0.14 μmol/L, P < .0001). Patients with contrast nephropathy had significantly higher mortality compared with those without contrast nephropathy (9.1% vs 1.1%, P = .001).

CONCLUSION

High baseline CI levels predicted mortality in patients with ACS. Occurrence of contrast nephropathy was associated with rise in CI levels and higher mortality. Therapeutic options to buffer or chelate CI may have beneficial effects on mortality in this setting.

Methemoglobinemia-Induced Acute Kidney Injury

Introduction

Methemoglobinemia refers to the presence of increased levels of methemoglobin (Fe3+) in the blood. Methemoglobinemia can cause cyanosis, dyspnea, fatigue, seizure, arrhythmia, coma, and even death. Although methemoglobinemia is shown to cause acute kidney injury in experimental settings, human case reports are exceedingly rare. In addition, morphological features of methemoglobinemia-induced renal disease in humans remain undefined.

Case Presentation

A 76-year-old man with a history of chronic obstructive pulmonary disease underwent bronchoscopy following local anesthesia with a benzocaine spray. The patient developed benzocaine-induced methemoglobinemia and acute renal failure. Urinalysis disclosed numerous dysmorphic erythrocytes, erythrocyte casts, and granular casts. Urine protein excretion was approximately 1.1 g/day. Serologic tests were negative. Renal biopsy demonstrated minor glomerular abnormalities, severe acute tubular necrosis, and numerous erythrocyte casts in the tubules. Despite supportive care, renal function deteriorated necessitating hemodialysis. Four months later, the patient remained on hemodialysis. To exclude a superimposed pathology, renal biopsy was repeated and showed numerous erythrocyte casts in the tubules and severe tubular damage.

Conclusion

Methemoglobinemia can cause acute kidney injury in humans. Morphological features resemble those observed in methemoglobin-induced acute kidney injury in experimental settings. This case calls for a heightened awareness of potential adverse effects of methemoglobinemia on renal function.

Prognostic evaluation of catalytic iron in patients with acute coronary syndromes

BACKGROUND

The potential of iron to generate reactive oxygen species has motivated a long-standing interest in whether excess iron is causally linked to atherosclerotic heart disease. Circulating catalytic iron ("free" iron) is that which is not bound to transferrin or ferritin and is available to generate reactive oxygen species that may have deleterious vascular effects.

HYPOTHESIS

We hypothesized that increased levels of catalytic iron would be associated with increased cardiovascular events.

METHODS

We investigated the association of catalytic iron with clinical outcomes in 1701 patients with unstable angina, non-ST-segment elevation myocardial infarction (MI), or ST-segment elevation MI who were followed for a median of 10 months. All endpoints were adjudicated by a blinded Clinical End Points Committee.

RESULTS

The median catalytic iron level was significantly higher in those who died, 0.45 µmol/L (0.37, 0.57), compared with survivors, 0.37µmol/L (0.31, 0.46; P = 0.016). Catalytic iron was associated with a stepwise increased risk of death, with the highest quartile at an almost 4-fold risk compared with baseline (hazard ratio: 3.94, P = 0.035), which persisted after adjustment for age, diabetes, prior MI, prior congestive heart failure, ST-segment deviation, creatinine clearance, B-type natriuretic peptide, smoking, and Killip class (adjusted hazard ratio: 3.97, P = 0.036). There was no association between catalytic iron and risk of MI, recurrent ischemia, heart failure, or bleeding.

CONCLUSIONS

Increasing catalytic iron levels were associated with increased all-cause mortality. Although our findings suggest that catalytic iron is not likely to add to available tools as a routine biomarker for risk stratification of recurrent ischemic events, its association with mortality is intriguing and leaves open the question of whether cardiovascular therapeutics aimed at catalytic iron may be useful. The TIMI Study Group has received research grant support from the Muljibhai Patel Society for Research in Nephro-Urology.

Renal cortical hemopexin accumulation in response to acute kidney injury

Hemopexin (Hpx) is a liver-generated acute phase reactant that binds and neutralizes prooxidant free heme. This study tested whether acute kidney injury (AKI) triggers renal Hpx accumulation, potentially impacting heme Fe-mediated tubular injury. Mice were subjected to glycerol, cisplatin, ischemia-reperfusion (I/R), or endotoxemic [lipopolysaccharide (LPS)] AKI. In each instance, 3- to 30-fold renal cortical and isolated proximal tubule segment (PTS) Hpx increases resulted. Although renal cortex and PTS showed variable Hpx mRNA increases, due, in part, to increased mRNA stability, mRNA levels did not correlate with renal Hpx protein accumulation. Conversely, AKI evoked three- to fourfold increases in hepatic Hpx gene induction, which corresponded with three- to fourfold plasma Hpx increases. Renal immunohistochemistry, and increased urinary Hpx excretion, indicated that circulating Hpx gains tubule luminal/urinary access, followed by proximal tubule endocytic uptake. Paradoxically, in cultured renal cells (HK-2, HEK-293), Fe depletion, and not free heme excess, increased Hpx mRNA. LPS acutely increased HK-2 cell Hpx mRNA. This finding, coupled with observations that LPS evoked ∼30-fold greater renal Hpx mRNA increases than any other AKI model, suggests that inflammation, not heme exposure, activates the renal Hpx gene. Each form of AKI evoked early increases in circulating free heme, which subsequently fell to subnormal levels as plasma Hpx rose. In addition, purified Hpx blunted free Fe-mediated HK-2 cell death. In sum, these data indicated that AKI-associated hepatic stress generates Hpx, which gains renal tubule access. Given its ability to bind free heme and mitigate free Fe toxicity, Hpx loading can potentially confer cytoprotective effects.

NGAL-Siderocalin in kidney disease

Kidney damage induces the expression of a myriad of proteins in the serum and in the urine. The function of these proteins in the sequence of damage and repair is now being studied in genetic models and by novel imaging techniques. One of the most intensely expressed proteins is lipocalin2, also called NGAL or Siderocalin. While this protein has been best studied by clinical scientists, only a few labs study its underlying metabolism and function in tissue damage. Structure-function studies, imaging studies and clinical studies have revealed that NGAL-Siderocalin is an endogenous antimicrobial with iron scavenging activity. This review discusses the "iron problem" of kidney damage, the tight linkage between kidney damage and NGAL-Siderocalin expression and the potential roles that NGAL-Siderocalin may serve in the defense of the urogenital system. This article is part of a Special Issue entitled: Cell Biology of Metals.

Mechanism-based therapeutic approaches to rhabdomyolysis-induced renal failure

Rhabdomyolysis-induced renal failure represents up to 15% of all cases of acute renal failure. Many studies over the past 4 decades have demonstrated that accumulation of myoglobin in the kidney is central in the mechanism leading to kidney injury. However, some discussion exists regarding the mechanism mediating this oxidant injury. Although the free-iron-catalyzed Fenton reaction has been proposed to explain the tissue injury, more recent evidence strongly suggests that the main cause of oxidant injury is myoglobin redox cycling and generation of oxidized lipids. These molecules can propagate tissue injury and cause renal vasoconstriction, two of the three main conditions associated with acute renal failure. This review presents the evidence supporting the two mechanisms of oxidative injury, describes the central role of myoglobin redox cycling in the pathology of renal failure associated with rhabdomyolysis, and discusses the value of therapeutic interventions aiming at inhibiting myoglobin redox cycling for the treatment of rhabdomyolysis-induced renal failure.

Cytochrome P450 2B1 mediates complement-dependent sublytic injury in a model of membranous nephropathy

Membranous nephropathy is a disease that affects the filtering units of the kidney, the glomeruli, and results in proteinuria accompanied by loss of kidney function. Passive Heymann nephritis is an experimental model that mimics membranous nephropathy in humans, wherein the glomerular epithelial cell (GEC) injury induced by complement C5b-9 leads to proteinuria. We examined the role of cytochrome P450 2B1 (CYP2B1) in this complement-mediated sublytic injury. Overexpression of CYP2B1 in GECs significantly increased the formation of reactive oxygen species, cytotoxicity, and collapse of the actin cytoskeleton following treatment with anti-tubular brush-border antiserum (anti-Fx1A). In contrast, silencing of CYP2B1 markedly attenuated anti-Fx1A-induced reactive oxygen species generation and cytotoxicity with preservation of the actin cytoskeleton. Gelsolin, which maintains an organized actin cytoskeleton, was significantly decreased by complement C5b-9-mediated injury but was preserved in CYP2B1-silenced cells. In rats injected with anti-Fx1A, the cytochrome P450 inhibitor cimetidine blocked an increase in catalytic iron and ROS generation, reduced the formation of malondialdehyde adducts, maintained a normal distribution of nephrin in the glomeruli, and provided significant protection at the onset of proteinuria. Thus, GEC CYP2B1 contributes to complement C5b-9-mediated injury and plays an important role in the pathogenesis of passive Heymann nephritis.

Cytochrome-P450 2B1 gene silencing attenuates puromycin aminonucleoside-induced cytotoxicity in glomerular epithelial cells

Previously, we demonstrated that cytochrome P450 2B1 (CYP2B1) can generate reactive oxygen species in puromycin aminonucleoside (PAN)-induced nephrotic syndrome, an animal model of minimal-change disease in humans. In this study we found that overexpression of CYP2B1 in rat glomerular epithelial cells in vitro significantly increased PAN-induced reactive oxygen species generation, cytotoxicity, cell death, and collapse of the actin cytoskeleton. All of these pathological changes were markedly attenuated by siRNA-induced CYP2B1 silencing. The cellular CYP2B1 protein content was significantly decreased whereas its mRNA level was markedly increased, suggesting regulation by protein degradation rather than transcriptional inhibition in the PAN-treated glomerular epithelial cells. This degradation of CYP2B1 was accompanied by the induction of heme oxygenase-1, an important indicator of heme-induced oxidative stress. In PAN-treated CYP2B1-silenced glomerular epithelial cells the induction of heme oxygenase-1 and caspase-3 activity were significantly decreased. Further, cleavage of the stress-induced pro-apoptotic endoplasmic reticulum-specific pro-caspase-12 was prevented in the silenced cells. Our results support a pivotal role of CYP2B1 for reactive oxygen species production in the endoplasmic reticulum in PAN-induced cytotoxicity.

Progressive histone alterations and proinflammatory gene activation: consequences of heme protein/iron-mediated proximal tubule injury

Rhabdomyolysis (Fe)-induced acute renal failure (ARF) causes renal inflammation, and, with repetitive insults, progressive renal failure can result. To gain insights into these phenomena, we assessed the impact of a single episode of glycerol-induced rhabdomyolysis on proinflammatory/profibrotic [TNF-alpha, monocyte chemoattractant protein-1 (MCP-1), and transforming growth factor-beta1 (TGF-beta1)] gene expression and the time course of these changes. CD-1 mice were studied 1-7 days after glycerol injection. Normal mice served as controls. RNA polymerase II (Pol II) binding to the TNF-alpha, MCP-1, and TGF-beta1 genes, "gene-activating" histone modifications [histone 3 lysine 4 (H3K4) trimethylation (H3K4m3) and histone 2 variant H2A.Z], and cognate mRNA levels were assessed. Results were contrasted to changes in anti-inflammatory heme oxygenase-1 (HO-1). Glycerol produced severe ARF (blood urea nitrogen approximately 150-180 mg/dl) followed by marked improvement by day 7 (blood urea nitrogen approximately 40 mg/dl). Early increases in TNF-alpha, MCP-1, and TGF-beta1 mRNAs, Pol II gene binding, and H3K4m3/H2A.Z levels were observed. These progressed with time, despite resolution of azotemia. Comparable early HO-1 changes were observed. However, HO-1 mRNA normalized by day 7, and progressive Pol II binding/histone alterations did not occur. Fe-mediated injury to cultured proximal tubule (HK-2) cells recapitulated these in vivo results. Hence, this in vitro model was used for mechanistic assessments. On the basis of these studies, it was determined that 1) the H3K4m3/H2A.Z increases are early events (i.e., they precede mRNA increases), 2) subsequent mRNA elevations reflect transcription, not mRNA stabilization (actinomycin D assessments), and 3) increased transcription, per se, helps sustain elevated H2A.Z levels. We conclude that 1) Fe/glycerol-induced tubular injury causes sustained proinflammatory gene activation, 2) decreasing HO-1 expression, as reflected by mRNA levels, may facilitate this proinflammatory state, and 3) gene-activating histone modifications are early injury events and progressively increase at selected proinflammatory genes. Thus they may help sustain a proinflammatory state, despite resolving ARF.

Melatonin Reduces Nitric Oxide via Increasing Arginase in Rhabdomyolysis-Induced Acute Renal Failure in Rats

Melatonin, the chief secretory product of the pineal gland, is a direct free radical scavenger. In addition to a direct scavenging effect on nitric oxide (NO), its inhibitory effect on nitric oxide synthase (NOS) activity has been also reported. L-arginine is the substrate for both NOS and arginase. It has been suggested that there is a competition between arginase and NOS and that they control each other's level. NO plays a crucial role in the pathogenesis of myoglobinuric acute renal failure (ARF). In this study, the authors aimed to investigate the effect of melatonin on arginase activity, ornithine, and NO levels on the myoglobinuric ARF formed by intramuscular (i.m.) injection of hypertonic glycerol. Forty rats were randomly divided into four groups. Rats in SHAM were given saline, and those in groups ARF, ARF-M5, and ARF-M10 were injected with glycerol (10 mL/kg) i.m. Concomitant and 24 hours after glycerol injection for the ARF-M5 and ARF-M10 groups, melatonin--5 mg/kg and 10 mg/kg, respectively--was administrated intraperitoneally. Forty-eight hours after the glycerol injection, kidneys of the rats were taken under anesthesia. Arginase activity, ornithine, and NO levels in the kidney tissue were determined. Melatonin had an increasing effect on kidney tissue arginase activities and ornithine levels while decreasing NO concentration. It is possible that besides the direct scavenging effect, the stimulatory effect of melatonin on arginase activity may result in an inhibition of NOS activity and, finally, a decrease in the kidney NO level.

Effects of Exogenous Melatonin on Myoglobinuric Acute Renal Failure in the Rats

Free oxygen radicals and nitric oxide (NO) play a crucial role in the pathogenesis of myoglobinuric acute renal failure (ARF). In this study, we aimed to investigate the effect of melatonin, a potent free radical scavenger, on the myoglobinuric ARF formed by injecting hypertonic glycerol intramuscularly (i.m.). The rats were randomly divided into 4 Groups. Rats in Group 1 were given saline and those in Groups 2, 3, and 4 were injected with glycerol (10 mL/kg) i.m. Concomitant and 24 hours after glycerol injection Group 3 (5 mg/kg) and Group 4 (10 mg/kg) were administrated melatonin intraperitoneally. Forty-eight hours after the glycerol injection, the blood and kidneys of the rats were taken under anesthesia. Kidney morphology and the levels of urea, creatinine and nitric oxide metabolites (NOx) in the plasma and the enzyme activities of superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx) and the level of malondialdehyde (MDA) in the kidney were determined. In both groups of melatonin administration, there was no protective effect of melatonin. Moreover, melatonin significantly decreased the level of NO. As a result, we suggest that the decreasing effect of melatonin on NO, which is a strong vasodilatator, may further increase the renal ischemia in this model. Thus, melatonin may have worsening rather than beneficial effects on myoglobinuric ARF.

Identification of radicals formed in the reaction mixture of bovine kidney microsomes with NADPH

In order to explore the mechanism of myoglobinuric renal toxicity, detection and identification of free radicals was performed for the reaction mixtures of bovine kidney microsomes. EPR measurements showed prominent signals for the control reaction mixture containing 2.0 mg protein/ml bovine kidney microsomes, 5 mM NADPH, 0.1 M 4-POBN and 29 mM phosphate buffer (pH 7.4). Addition of myoglobin (Mb) to the control reaction mixture resulted in increase of EPR peak height. The result indicates that Mb enhances the radical formation. An HPLC-EPR measurement showed three peaks with retention times of 29.4 min (P(1)), 32.4 min (P(2)) and 46.6 min (P(3)). HPLC-EPR-MS analyses of P(1) and P(2) gave ions at m/z 282. The results show that 4-POBN/hydroxypentyl radical adducts form in the reaction mixture. An HPLC-EPR-MS analysis of P(3) gave ions at m/z 266, indicating that 4-POBN/pentyl radical adduct forms in the reaction mixture.

Therapeutic antioxidant medical gas

Medical gases are pharmaceutical gaseous molecules which offer solutions to medical needs and include traditional gases, such as oxygen and nitrous oxide, as well as gases with recently discovered roles as biological messenger molecules, such as carbon monoxide, nitric oxide and hydrogen sulphide. Medical gas therapy is a relatively unexplored field of medicine; however, a recent increasing in the number of publications on medical gas therapies clearly indicate that there are significant opportunities for use of gases as therapeutic tools for a variety of disease conditions. In this article, we review the recent advances in research on medical gases with antioxidant properties and discuss their clinical applications and therapeutic properties.

Carbon monoxide-saturated preservation solution protects lung grafts from ischemia-reperfusion injury

OBJECTIVES

In previous work we have demonstrated that delivery of low concentrations (250 ppm) of carbon monoxide by means of inhalation to donors, recipients, or both protects transplanted lungs from ischemia-reperfusion injury (improved gas exchange, diminished intragraft and systemic inflammation, and retention of graft vascular endothelial cell ultrastructure). In this study we examined whether delivery of carbon monoxide to lung grafts in the preservation solution could protect against lung ischemia-reperfusion injury.

METHODS

Orthotopic left lung transplantation was performed in syngeneic Lewis to Lewis rats. Grafts were preserved in University of Wisconsin solution with or without (control solution) carbon monoxide at 4 degrees C for 6 hours. Carbon monoxide gas (5% or 100%) was bubbled into University of Wisconsin solution at 4 degrees C for 5 minutes before use.

RESULTS

In control animals, ischemia-reperfusion injury resulted in significant deterioration of graft function and was associated with a massive cellular infiltrate 2 hours after reperfusion. Grafts stored in University of Wisconsin solution with carbon monoxide (5%), however, demonstrated significantly better gas exchange and significantly reduced intragraft inflammation (reduced inflammatory mediators and cellular infiltrate). Experiments demonstrated that the protective effects afforded by 100% University of Wisconsin solution with carbon monoxide were not as potent as those of 5% University of Wisconsin solution with carbon monoxide.

CONCLUSIONS

This study demonstrates that 5% carbon monoxide as an additive to the cold flush/preservation solution can impart potent anti-inflammatory and cytoprotective effects after cold preservation and transplantation of lung grafts. Such ex vivo treatment of lung grafts with carbon monoxide can minimize concerns associated with carbon monoxide inhalation and might offer the opportunity to significantly advance the application of carbon monoxide in the clinical setting.

Ex vivo carbon monoxide prevents cytochrome P450 degradation and ischemia/reperfusion injury of kidney grafts

Renal ischemia/reperfusion injury is a major complication of kidney transplantation. We tested if ex vivo delivery of carbon monoxide (CO) to the kidney would ameliorate the renal injury of cold storage that can complicate renal transplantation. Orthotopic syngeneic kidney transplantation was performed in Lewis rats following 24 h of cold preservation in University of Wisconsin solution equilibrated without or with CO (soluble CO levels about 40 microM). Ischemia/reperfusion injury in control grafts resulted in an early upregulation of inflammatory mediator mRNAs and progressive deterioration of graft function. In contrast, the grafts preserved with CO had significantly less oxidative injury and this was associated with improved recipient survival compared to the control group. Renal injury in the control group showed considerable degradation of cytochrome P450 heme proteins, active heme metabolism and increased detrimental intracellular free heme levels. Kidney grafts preserved in CO-equilibrated solution maintained their cytochrome P450 protein levels, had normal intracellular heme levels and had less lipid peroxidation. Our results show that CO-mediated suppression of injurious heme-derived redox reactions offers protection of kidney grafts from cold ischemia/reperfusion injury.