Myoglobinuric Acute Renal Failure Research Articles

Effects of fenoldopam on renal blood flow and its function in a canine model of rhabdomyolysis

Background and objective: Our hypothesis was that fenoldopam, a selective DA1 agonist, would protect against rhabdomyolysis-induced renal injury. Methods: We studied the effects of intravenous fenoldopam (0.1-1.0 μg kg−1 min−1) or saline on renal blood flow and function in 10 anaesthetized Labrador dogs in whom rhabdomyolysis and myoglobinuric acute renal failure had been induced by administration of glycerol 50% (10 mL kg−1) intramuscularly. Haemodynamic measurements including renal blood flow and derived parameters of renal function including creatinine clearance were recorded before and for the 30 min following glycerol injection, and during the 3 h following commencement of each infusion. Serum malondialdehyde concentrations were measured before and 15 min after glycerol intramuscularly, and 30 and 150 min after commencement of the infusion. Results: In the fenoldopam group, creatinine clearance was less than placebo at 1 and 2 h after commencing the infusion (12.7 ± 11.5 versus 31.3 ± 9.9 mL min−1, P = 0.04; 8.5 ± 5.3 versus 20.1 ± 7.4 mL min−1, P = 0.03). A 140-fold increase in serum malondialdehyde concentration occurred in one dog (fenoldopam group). Conclusion: Fenoldopam increased the severity of the renal injury in this canine model of myoglobinuric acute renal failure.

Catechin, a natural antioxidant protects against rhabdomyolysis-induced myoglobinuric acute renal failure

Rhabdomyolysis-induced myoglobinuric acute renal failure accounts for about 10–40% of all cases of acute renal failure (ARF). Reactive oxygen intermediates have been demonstrated to play an etiological role in myoglobinuric renal failure. This study was performed to explore the protective effect of catechin-a natural antioxidant in an experimental model of myoglobinuric ARF in rats. Four groups of rats were employed in this study, group 1 served as control, group 2 was given 50% glycerol (8 ml kg −1, i.m.), group 3, glycerol plus catechin (40 mg kg −1, p.o. for 4 days, twice a day) and group 4 was given only catechin (40 mg kg −1, p.o.), respectively. Renal injury was assessed by measuring serum creatinine, blood urea nitrogen (BUN), creatinine, and urea clearance. The oxidative stress was measured by renal malondialdehyde (MDA) levels, reduced glutathione levels and by enzymatic activity of catalase, glutathione reductase (GR) and superoxide dismutase (SOD). Glycerol administration resulted in a marked renal oxidative stress, significantly deranged the renal functions as well as renal morphology. All these factors were significantly improved by catechin treatment. Catechin, due to its antioxidative activity, reduced the toxicity of myoglobin in the renal tissues, and thus exerted a renoprotective effect in this rhabdomyolysis mimicking model.

Renal uptake of myoglobin is mediated by the endocytic receptors megalin and cubilin.

Nephrotoxicity of myoglobin is well recognized as playing a part in the development of acute renal failure in settings of myoglobinuria. However, the molecular mechanism of myoglobin uptake in renal proximal tubules has not been clarified. Here, we report that the endocytic receptors megalin and cubilin are involved in renal reabsorption of myoglobin. Both receptors were captured from solubilized renal brush-border membranes by affinity chromatography using myoglobin-Sepharose. Myoglobin bound to purified megalin and cubilin with Kd values of 2.0 and 3 microM, respectively, as evaluated by surface plasmon resonance analysis. Apomyoglobin bound to megalin with the same affinity, and the affinity of apomyoglobin to cubilin was reduced (Kd = 5 microM). Radioiodinated myoglobin could be displaced by apomyoglobin in inhibition studies using isolated renal brush-border membranes (Ki approximately 2 microM). Receptor-associated protein as well as antibodies directed against megalin and cubilin markedly inhibited the uptake of fluorescent-labeled myoglobin by cultured yolk sac BN-16 cells. The significance of megalin- and cubilin-mediated endocytosis for myoglobin uptake in vivo was demonstrated by use of kidney-specific megalin knockout mice. Injected myoglobin was extensively reabsorbed by megalin-expressing proximal tubular cells, whereas there was very little uptake in the megalin-deficient cells. In conclusion, this study establishes the molecular mechanism of myoglobin uptake in the renal proximal tubule involving the endocytic receptors megalin and cubilin. Identification of the receptors for tubular uptake of myoglobin may be essential for development of new therapeutic strategies for myoglobinuric acute renal failure.

Evolution of Total Antioxidant Status in a Model of Acute Renal Insufficiency in Rats

Background. Accurate estimation of the Total Antioxidant Status (TAS) in the myoglobinuric acute renal failure (ARF) is necessary because its pathogenesis is believed to be mediated, at least in part, by the development of oxidative stress resulting from the generation of oxygen free radicals and reduced antioxidant defense system. The purpose of this study is to examine the TAS 24 and 72 h after glycerol injection in a model of myoglobinuric-ARF. Experimental Design. The study was conduced in 28 Sprague-Dawley rats. In group 1 (n = 7) rats were placed into individual metabolic cages and deprived of water during 24 h, afterwards an intramuscular injection of glycerol was administrated (50% vol/vol in sterile saline) 10 mg/100 g of body weight and 24 h later blood samples were collected for biochemical measurements (urea, creatinine, creatine-kinase, and TAS levels). In group 2 (n = 7), rats followed the same conditions than group 1 ones but blood samples were collected 72 h after glycerol injection. In groups 3 (n = 7) and 4 (n = 7) rats didn't receive glycerol injection, and blood samples were collected within 24 and 72 h respectively after they were placed into metabolic cages. Results. In groups 1 and 2 we observed a renal function decrease, with higher serum levels of urea and creatinine in group 2 (urea levels: 269 ± 16 mg/dL vs. 586 ± 147 mg/dL; p < 0.001. Creatinine levels: 2.8 ± 0.2 mg/dL vs. 5.8 ± 0.7 mg/dL; p<0.001). TAS levels in groups 2, 3, and 4 were similar, but in group 1 was significantly lower (group 1: 0.81 ± 0.2 mmol/L; group 2: 1.3 ± 0.1 mmol/L; group 3: 1.2 ± 0.3 mmol/L, and group 4: 1.2 ± 0.2 mmol/L; p<0.005). Conclusion. In the model of glycerol induced myoglobinuric-ARF we observed a decrease of serum TAS level within 24 h with spontaneous recuperation 72 h after.

Hand-assisted laparoscopic radical nephrectomy-associated rhabdomyolysis with ARF

Intraoperative rhabdomyolysis with resultant acute renal failure is a rare complication seen, most commonly, with urologic surgical procedures. Since the early 1990s, the refinement of laparoscopic techniques has permitted their application more broadly. Among the procedures to benefit from these less invasive surgical methods has been radical nephrectomy. In general, this has resulted in less postoperative pain and shorter convalescence. Nonetheless, laparoscopic radical nephrectomy still represents major surgery and is not free from operative risks. To highlight one of these risks, we present a case of a young, obese man with renal cell carcinoma who underwent a hand-assisted laparoscopic radical nephrectomy that was complicated by rhabdomyolsis resulting in acute renal failure (ARF). We discuss the clinical insults that contributed to the development of azotemia with particular attention paid to our current understanding of the pathogenesis of myoglobinuric ARF. In addition, we review the literature concerning surgery-associated, rhabdomyolytic ARF with the aim of providing clinicians guidance for the avoidance and early recognition of this rare, but very serious, surgical complication. Am J Kidney Dis 41:E5. © 2003 by the National Kidney Foundation, Inc.

Attenuation of Glycerol-Induced Acute Renal Failure in Rats by Trimetazidine and Deferoxamine

The pathogenesis of glycerol-induced myoglobinuric acute renal failure involves, among other causes, ischaemia, vascular congestion, and reactive oxygen metabolites. The aim of this study was to investigate the roles of ischaemia and iron-induced oxidative stress by employing trimetazidine, an anti-ischemic drug with an additional antioxidant effect, and deferoxamine, an iron chelator, in glycerol-induced acute renal failure in rats. Five groups of rats were employed in this study: group 1 served as control group, group 2 was given 50% glycerol alone (8 ml/kg i.m.), group 3 was given glycerol plus trimetazidine (3 mg/kg), and groups 4 and 5 were given glycerol plus deferoxamine (50 and 100 mg/kg, respectively). Renal injury was assessed by measuring plasma creatinine and blood urea nitrogen levels and creatinine and urea clearances. The oxidative stress was measured on the basis of the renal malondialdehyde and reduced glutathione levels and the activities of catalase, glutathione reductase, and superoxide dismutase. Glycerol treatment resulted in marked renal oxidative stress and deranged renal functions which significantly improved by trimetazidine and deferoxamine treatments. Deferoxamine, by interacting with Fenton reaction chemistry, and trimetazidine, by its anti-ischaemic and antioxidative properties, protected the kidney against the oxidative stress and the resultant renal dysfunction produced by glycerol. Based on these results, this study points towards renal ischaemia and iron as potential mediators and demonstrates the potential beneficial effects of deferoxamine and trimetazidine in glycerol-induced acute renal failure in rats.

Nephroprotective effects of pentoxifylline in experimental myoglobinuric acute renal failure

The nephroprotective effects of pentoxifylline, a methylxantine, were studied in glycerol-induced acute renal failure. Glycerol treated rats exhibited collecting duct and medullary ascending limb dilation and casts, with focal tubular damage, confined mainly to the superficial cortex. In the interstitium focal mononuclear infiltration was observed. In some glomeruli there was swelling of mesangial spaces and mesangial cells. Pentoxifylline injected to glycerol pretreated rats exerted a protective effect. Only few groups of proximal tubules in the subcapsulary region of renal cortex showed necrosis and tubulorhexis. There were not leukocyte infiltrations or vascular congestion. Morphometric analysis showed increased surface area fraction of tubular lumen in rats treated with glycerol ( p < 0.01) compared to those in controls. Intratubular cast formations in rats treated with glycerol alone were significantly higher than in rats given pentoxifylline in addition to glycerol. Kidney cortex ectopeptidases (APA, APN and DPP IV) were not significantly changed after glycerol administration. Serum creatinine and blood urea were markedly increased in glycerol treated rats, however, pentoxifylline reduced significantly their levels. This study in glycerol-induced acute renal failure showed a marked renal morphologic and functional protection by pentoxifylline.

Altered cholesterol localization and caveolin expression during the evolution of acute renal failure

Renal cortical/proximal tubule cholesterol accumulation, with preferential localization within plasma membrane "detergent resistant microdomains" (DRMs: rafts/caveolae), is a hallmark of the maintenance phase of acute renal failure (ARF). This study addressed two related issues: (1) Are maintenance-phase cholesterol increases accompanied by an up-regulation of caveolin, a DRM/caveolar-associated cholesterol binding protein? (2) Is DRM cholesterol/caveolin homeostasis acutely altered during the induction phase of ARF? Mouse kidneys were subjected to ischemia +/- reperfusion (I/R) followed by assessment of cholesterol DRM partitioning. Acute cell injury effects on potential caveolin release from isolated proximal tubules or into urine also were assessed. Finally, renal cortical/isolated proximal tubule caveolin levels were determined 18 hours after I/R or myoglobinuric ARF. Acute ischemia causes a rapid shift of cholesterol into cortical DRMs (>22%). Cholesterol migration into DRMs also was observed in ATP-depleted cultured proximal tubule (HK-2) cells. Acute hypoxic or toxic tubule injury induced plasma membrane caveolin release (Western blot). By the maintenance phase of ARF, marked renal cortical/proximal tubule caveolin increases resulted. Acute proximal tubular injury damages caveolar/DRM structures, as determined by cholesterol maldistribution and caveolin release. Post-injury, there is a dramatic up-regulation of renal cortical/proximal tubule caveolin, suggesting an increased caveolar mass. These findings indicate, to our knowledge for the first time, that dysregulation of caveolae/raft microdomain expression is a correlate of, and potential participant in, the induction and maintenance phases of ischemic and toxic forms of experimental ARF.

EFFECTS OF N-ACETYLCYSTEINE ON MYOGLOBINURIC-ACUTE RENAL FAILURE IN RATS

Oxygen metabolites play an important role in renal injury during myoglobinuric acute renal failure (ARF). This study was designed to determine the protective influence of N-acetylcysteine (NAC), a hydroxyl radical scavenger, and treatment in an experimental model of myoglobinuric-ARF induced by intramuscular injection of hypertonic glycerol in rats. The rats were randomly distributed into five groups: Group 0 (n = 10), was assigned to receive 2 mL saline (0,9%) intraperitoneally (ip); Group 1 (n = 10), NAC ip in a dose of 10 mg/100 g of body weight 30 min before the intramuscular (im) injection of 50% glycerol (10 mg/kg); Group 2 (n = 10), received saline 0,9% ip in a equivalent volume of NAC in Group 1 before the im injection of glycerol; Group 3 (n = 10), received NAC ip in a dose of 10 mg/100 g after im injection of glycerol; Group 4 (n = 10), saline 0,9% ip in a equivalent volume of NAC of the Group 3 after im administration of glycerol. After 24 h rats were sacrificed and kidney morphology and renal function were determined. A severe renal failure was produced by glycerol injection in the Groups 1, 2, 3, and 4, with significant tubular proximal necrosis and cast formation, and creatinine and urea concentrations were elevated in these groups without significant differences among groups, but Group 0 where the values were significantly lower. The results of this study suggests that ip administration of NAC in rats before or after glycerol injection do not confer protection against impairment of renal function under these conditions in this model of myoglobinuric-ARF.

EFFECTS OF MELATONIN ADMINISTRATION TO RATS WITH GLYCEROL-INDUCED ACUTE RENAL FAILURE

Melatonin, the pineal hormone with antioxidative properties was administered to rats with glycerol-induced myoglobinuric acute renal failure (Gly-ARF). This model is characterized by acute tubular necrosis mediated by heme-iron oxidative stress. Rats received melatonin (20 mg/kg) concomitant and 3 h after glycerol injection. Gly-ARF rats showed at 24 h a 78% reduction in glomerular filtration rate, whereas this decrement was significantly reduced to 35% in the melatonin treated Gly-ARF rats. Tubular function evaluated by tubular reabsorption of sodium and lithium was also preserved in melatonin treated rats. The histologic analysis revealed extensive cortical tubular necrosis that was significantly reduced by melatonin treatment. The renal concentration of malondialdehyde (MDA) was increased 6 h after glycerol injection in Gly-ARF and this elevation was prevented when melatonin was administered. Renal concentration of reduced glutathione (GSH) was decreased at 6 h in Gly-ARF and melatonin did not reverse this decrease. It was concluded that melatonin administration attenuated the renal injury in the glycerol model of acute renal failure and reduced kidney oxidative stress through a GSH-independent mechanism.

Acute renal failure due to crush injury and prolonged positional compression on a muscle group

Widespread muscle crush injury and prolonged positional compression on a muscle group are often associated with myoglobinuric acute renal failure (ARF). Treatment consists of early massive volume replacement and forced alkaline solute diuresis. With this regimen it is possible to increase survival of life and limbs, and prevent myoglobinuric ARF.

Effects of fenoldopam on renal blood flow and function using a canine model of myoglobinuric acute renal failure

Effects of fenoldopam on renal blood flow and function using a canine model of myoglobinuric acute renal failure

Changes in Free and Esterified Cholesterol: Hallmarks of Acute Renal Tubular Injury and Acquired Cytoresistance

Acute tubular cell injury is accompanied by plasma membrane phospholipid breakdown. Although cholesterol is a dominant membrane lipid which interdigitates with, and impacts, phospholipid homeostasis, its fate during the induction and recovery phases of acute renal failure (ARF) has remained ill defined. The present study was performed to ascertain whether altered cholesterol expression is a hallmark of evolving tubular damage. Using gas chromatographic analysis, free cholesterol (FC) and esterified cholesterol (CE) were quantified in: 1) isolated mouse proximal tubule segments (PTS) after 30 minutes of hypoxic or oxidant (ferrous ammonium sulfate) injury; 2) cultured proximal tubule (HK-2) cells after 4 or 18 hours of either ATP depletion/Ca(2+) ionophore- or ferrous ammonium sulfate-mediated injury; and 3) in renal cortex 18 hours after induction of glycerol-induced myoglobinuric ARF, a time corresponding to the so-called "acquired cytoresistance" state (ie, resistance to further renal damage). Hypoxic and oxidant injury each induced approximately 33% decrements in CE (but not FC) levels in PTS, corresponding with lethal cell injury ( approximately 50 to 60% LDH release). When comparable CE declines were induced in normal PTS by exogenous cholesterol esterase treatment, proportionate lethal cell injury resulted. During models of slowly evolving HK-2 cell injury, progressive CE increments occurred: these were first noted at 4 hours, and reached approximately 600% by 18 hours. In vivo myoglobinuric ARF produced comparable renal cortical CE (and to a lesser extent FC) increments. Renal CE accumulation strikingly correlated with the severity of ARF (eg, blood urea nitrogen versus CE; r, 0.84). Mevastatin blocked cholesterol accumulation in injured HK-2 cells, indicating de novo synthesis was responsible. Acute tubule injury first lowers, then raises, tubule cholesterol content. Based on previous observations that cholesterol has cytoprotectant properties, the present findings have potential relevance for both the induction and maintenance phases of ARF.

Rhabdomyolysis.

Rhabdomyolysis.

Role of glomerular nitric oxide in glycerol-induced acute renal failure

Myoglobinuric acute renal failure remains one of the least understood clinical syndromes and the mediators involved remain obscure. The aim of the present study was to assess the role of nitric oxide in glycerol-induced acute renal failure under normal conditions and after uninephrectomy. Acute renal failure was induced in rats by injection of 50% glycerol (10 mL x kg(-1) body weight). Half of the animals were subjected to uninephrectomy two days before glycerol injection. Two days after the induction of acute renal failure, glomeruli from some animals were isolated and glomerular nitrite production was measured. Another group of animals was used for acute clearance studies. In this case, the effect of infusing either L-NAME or L-arginine was assayed. Glomerular nitrite production was significantly decreased in glycerol-induced acute renal failure. Glomeruli from uninephrectomized animals showed an increase in nitrite production, both in normal conditions and after glycerol injection, as compared with glomeruli from non-nephrectomized animals. L-NAME infusion worsened renal function in all the study groups, but more slowly in animals with glycerol-induced acute renal failure than in control rats. In uninephrectomized animals L-NAME reduced renal function more than in animals with two kidneys. In conclusion, in this model of acute renal failure the decrease in glomerular nitric oxide production plays an important role in the decrease in renal function. After uninephrectomy, an increase in glomerular nitric oxide synthesis plays a protective role against glycerol-induced acute renal failure.

REVERSAL OF EXPERIMENTAL MYOGLOBINURIC ACUTE RENAL FAILURE WITH BIOFLAVONOIDS FROM SEEDS OF GRAPE

Rhabdomyolysis may account for about 10% of all cases of acute renal failure (ARF). This study was performed to explore the protective influence of proanthocyanidins from seeds of grape in an experimental model of myoglobinuric ARF. Rats were injected with 50% glycerol (8 mL/Kg, im) followed immediately and daily in the next three days by ip proanthocyanidins (20 mg/kg) or saline. After 96 h rats were sacrificed and kidney morphology, kidney cortex peptidase activities, and malondialdehyde (MDA) content were determined. A moderate renal failure was produced by glycerol injection with blood urea of 31.8 ± 11.0 vs. 7.68 ± 0.24 mmol/L, and serum creatinine of 153.6 ± 38.2 vs. 39.6 ± 9.0 μmol/L, in glycerol-induced ARF vs. control rats, respectively. Rats that received proanthocyanidins in addition to glycerol had significantly lower (p < 0.01) blood urea and serum creatinine levels compared to those receiving glycerol alone. These functional differences between the glycerol and glycerol plus proanthocianidins groups were also confirmed histologically. Kidney cortex dipeptidylpeptidase IV (DPP IV) activity was not significantly changed in glycerol-induced ARF, however, markedly increased after proanthocyanidins treatment. Kidney cortex malondialdehyde content was found significantly increased in glycerol-induced ARF over control level, and was markedly reduced by proanthocyanidin treatment. Taken together, these results provide strong evidence for the protective role of proanthocyanidins from seeds of grape in glycerol-induced ARF. The effect is probably due to the antioxidant activity of proanthocyanidins and to increased expression of kidney cortex DPP IV with effective degradation of TNF-α. This may provide therapeutic opportunities of preventing and/or treating myoglobinuric ARF in humans.

Role of glomerular nitric oxide in glycerol-induced acute renal failure

Myoglobinuric acute renal failure remains one of the least understood clinical syndromes and the mediators involved remain obscure. The aim of the present study was to assess the role of nitric oxide in glycerol-induced acute renal failure under normal conditions and after uninephrectomy. Acute renal failure was induced in rats by injection of 50% glycerol (10 mL x kg(-1) body weight). Half of the animals were subjected to uninephrectomy two days before glycerol injection. Two days after the induction of acute renal failure, glomeruli from some animals were isolated and glomerular nitrite production was measured. Another group of animals was used for acute clearance studies. In this case, the effect of infusing either L-NAME or L-arginine was assayed. Glomerular nitrite production was significantly decreased in glycerol-induced acute renal failure. Glomeruli from uninephrectomized animals showed an increase in nitrite production, both in normal conditions and after glycerol injection, as compared with glomeruli from non-nephrectomized animals. L-NAME infusion worsened renal function in all the study groups, but more slowly in animals with glycerol-induced acute renal failure than in control rats. In uninephrectomized animals L-NAME reduced renal function more than in animals with two kidneys. In conclusion, in this model of acute renal failure the decrease in glomerular nitric oxide production plays an important role in the decrease in renal function. After uninephrectomy, an increase in glomerular nitric oxide synthesis plays a protective role against glycerol-induced acute renal failure.

Protective Effect of a Bioflavonoid Proanthocyanidin-BP1 in Glycerol-Induced Acute Renal Failure in the Rat: Renal Stereological Study

Renal ischemia as well as oxygen metaholites ploy an important role in renal Injury during myoglobinuric acute renal failure (ARF). On the other hand, flavonoids. a diverse group of constituents naturally occurring in plants, have a strong antioxidative activity, and have been implicated in vascular relaxation. In this study the protective effect of a new bioflavonoid proanthocvanidin-BP1 (BP1), extracted from seeds of grapes, was evaluated in glycerol-induced ARF in rats. Stereological methods were used to quantify changes in renal morphology associated with ARF. Volume density of tubular lumen and intratubular cast formations, nuclear parameters (area, diameter, volume) of epithelial cells in the cortical proximal tubules, and glomerular parameters (surface area, diameter, volume, perimeter) were estimated on kidney sections of rats treated either with 50% glycerol (8 ml/kg i.m.) alone. BP1 (20 mg/kg i.p.) in addition to glycerol, or BP1 alone. It was noted that the volume density of tubular lumen and cast formations were significantly lower (p < 0.001) in kidneys of the rats treated with BP1 in addition to glycerol, compared with those treated with glycerol alone. There were no significant differences in glomerular and nuclear parameters between glycerol treated, and BP1 in addition to glycerol treated rats. Renal function was significantly improved in rats treated with BP1 in addition to glycerol. The results suggest that BP1 is a protective agent in glycerol model of ARF. This effect is probably due to the antioxidative activity of BP1 and reduced toxicity of myoglobin in renal tissue. Moreover, it is possible that the ability of BP1 to protect the kidney is dependent upon renal vascular relaxation. The potential beneficial effects of bioflavonoid-BP1 demonstrated in experimental ARF could be considered in therapy of myoglobinuric ARF.

Acute Renal Failure Due to Nontraumatic Rhabdomyolysis Following Binge Drinking

Nontraumatic rhabdomyolysis is an important but under-recognized cause of acute renal failure. In alcoholics, rhabdomyolysis most frequently develop following muscle necrosis during alcohol-induced coma, but has also been described rarely in those without prolonged coma or seizures. We describe a patient who developed myoglobinuric acute renal failure requiring dialysis following binge drinking in the absence of convulsions or coma. The renal biopsy showed acute tubular necrosis with pigment casts.

Differential effects of glutathione and cysteine on Fe2+, Fe3+, H2O2 and myoglobin-induced proximal tubular cell attack

Glutathione (GSH) is widely advocated as a cytoprotectant for preventing oxidant forms of renal damage. However, in the case of myoglobinuric tubular injury, both beneficial and adverse effects have been noted. The purpose of this study was to help elucidate this seeming paradox by assessing the impact on thiol supplementation on normal tubules and on tubules subjected to individual components of heme protein-induced oxidant attack (Fe2+, Fe3+, and H2O2). Isolated mouse proximal tubular segments (PTS) were exposed to either GSH or cysteine under normal conditions or in the presence of exogenous Fe2+, Fe3+, or H2O2. Lethal cell injury (LDH release) and lipid peroxidation (malondialdehyde) were then assessed. GSH and cysteine exerted iron dependent, H2O2 independent, pro-oxidant effects on normal PTS. Both were also pro-oxidant in the presence of an exogenous Fe3+ challenge. In contrast, each attenuated Fe2+ cytotoxicity. The importance of iron's redox status on the expression of tubular injury was further underscored by the fact that Fe3+ partially blocked Fe2+'s cytotoxic effects. GSH mitigated H2O2 toxicity (consistent with a fueling of GSH peroxidase activity). Conversely, cysteine promoted H2O2's injurious effects. To assess the impact of thiol supplementation on a fully integrated model of heme protein toxicity, proximal tubular (HK-2) cells were cultured with myoglobin x 24 hours +/- test reactants. Exogenous GSH worsened, while GSH depletion (BSO) protected, against myoglobin toxicity (indicating a predominance of GSH's pro-oxidant effects). Conversely, cysteine (but not homocysteine) decreased myoglobin toxicity. These GSH/cysteine effects were confirmed in LLC-PK1 cells subjected to iron attack. We conclude that: (1) GSH and cysteine can exert pro- and anti-oxidant effects, depending on the nature of the oxidant challenge and iron's redox status; (2) Fe3+ can function as a cytoprotectant, partially offsetting Fe2+ toxicity; and (3) cysteine, although potentially pro-oxidant, can mitigate heme protein-induced injury. Since the kidney rapidly catabolizes GSH to cysteine, the latter may be at least partially responsible for GSH's reported cytoprotective actions against myoglobinuric acute renal failure.