Hemin pretreatment ameliorates aspects of the nephropathy induced by mercuric chloride in the rat

Heme Oxygenase 1: A Defensive Mediator in Kidney Diseases

The incidence of kidney disease is rising, constituting a significant burden on the healthcare system and making identification of new therapeutic targets increasingly urgent. The heme oxygenase (HO) system performs an important function in the regulation of oxidative stress and inflammation and, via these mechanisms, is thought to play a role in the prevention of non-specific injuries following acute renal failure or resulting from chronic kidney disease. The expression of HO-1 is strongly inducible by a wide range of stimuli in the kidney, consequent to the kidney's filtration role which means HO-1 is exposed to a wide range of endogenous and exogenous molecules, and it has been shown to be protective in a variety of nephropathological animal models. Interestingly, the positive effect of HO-1 occurs in both hemolysis- and rhabdomyolysis-dominated diseases, where the kidney is extensively exposed to heme (a major HO-1 inducer), as well as in non-heme-dependent diseases such as hypertension, diabetic nephropathy or progression to end-stage renal disease. This highlights the complexity of HO-1's functions, which is also illustrated by the fact that, despite the abundance of preclinical data, no drug targeting HO-1 has so far been translated into clinical use. The objective of this review is to assess current knowledge relating HO-1's role in the kidney and its potential interest as a nephroprotection agent. The potential therapeutic openings will be presented, in particular through the identification of clinical trials targeting this enzyme or its products.

Effect of hemin, baicalein and heme oxygenase-1 (HO-1) enzyme activity inhibitors on Cd-induced accumulation of HO-1, HSPs and aggresome-like structures in Xenopus kidney epithelial cells

Cadmium is a highly toxic environmental pollutant that can cause many adverse effects including cancer, neurological disease and kidney damage. Aquatic amphibians are particularly susceptible to this toxicant as it was shown to cause developmental abnormalities and genotoxic effects. In mammalian cells, the accumulation of heme oxygenase-1 (HO-1), which catalyzes the breakdown of heme into CO, free iron and biliverdin, was reported to protect cells against potentially lethal concentrations of CdCl₂. In the present study, CdCl₂ treatment of A6 kidney epithelial cells, derived from the frog, Xenopus laevis, induced the accumulation of HO-1, heat shock protein 70 (HSP70) and HSP30 as well as an increase in the production of aggregated protein and aggresome-like structures. Treatment of cells with inhibitors of HO-1 enzyme activity, tin protoporphyrin (SnPP) and zinc protoporphyrin (ZnPP), enhanced CdCl₂-induced actin cytoskeletal disorganization and the accumulation of HO-1, HSP70, aggregated protein and aggresome-like structures. Treatment of cells with hemin and baicalein, which were previously shown to provide cytoprotection against various stresses, induced HO-1 accumulation in a concentration-dependent manner. Also, treatment of cells with hemin and baicalein suppressed CdCl₂-induced actin dysregulation and the accumulation of aggregated protein and aggresome-like structures. This cytoprotective effect was inhibited by SnPP. These results suggest that HO-1-mediated protection against CdCl₂ toxicity includes the maintenance of actin cytoskeletal and microtubular structure and the suppression of aggregated protein and aggresome-like structures.

Heme Oxygenase-1 in Kidney Health and Disease

SIGNIFICANCE

Acute kidney injury (AKI) and chronic kidney disease (CKD) represent a considerable burden in healthcare. The heme oxygenase (HO) system plays an important role in regulating oxidative stress and is protective in a variety of human and animal models of kidney disease. Preclinical studies of the HO system have led to the development of several clinical trials targeting the enzyme or its products.

RECENT ADVANCES

Connection of HO, ferritin, and other proteins involved in iron regulation has provided important insight into mechanisms of damage in AKI. Also, HO-1 expression is important in the pathogenesis of hypertension, diabetic kidney disease, and progression to end-stage renal disease.

CRITICAL ISSUES

Despite intriguing discoveries, no drugs targeting the HO system have been translated to the clinic. Meanwhile, treatments for AKI and CKD are urgently needed. Many factors have likely contributed to challenges in clinical translation, including variation in animal models, difficulties in obtaining human tissue, and complexity of the disease processes being studied.

FUTURE DIRECTIONS

The HO system represents a promising avenue of investigation that may lead to targeted therapeutics. Tissue-specific gene modulation, widening the scope of animal studies, and continued clinical research will provide valuable insight into the role HO plays in kidney homeostasis and disease. Antioxid. Redox Signal. 25, 165-183.

Hemin attenuates cisplatin-induced acute renal injury in male rats

Background. The aim of this study is to investigate the protective effects of hemin (the heme oxygenase-1 [OH-1] inducer) against nephrotoxic effects induced by cisplatin [cis-diamminedichloroplatinum II (CP)] in male rats. Methods. The evaluation was performed through monitoring renal redox parameters: lipid peroxidation (LPO), glutathione peroxidase (GPx), superoxide dismutase (SOD), glutathione reductase (GR), and reduced glutathione (GSH). The work also examined renal function tests (urea and creatinine), tissue proinflammatory mediator like nitric oxide (NO), and kidney cytopathology. Results. A single intraperitoneal dose of CP (10 mg/kg b.w.) caused significant elevation of blood urea, serum creatinine, and renal LPO and NO, along with significant decline of the activities of GPx and GR, but renal SOD activity and GSH level were statistically insignificant as compared to control group. Subcutaneous injection of hemin (40 µmol/kg b.w.) partially ameliorated CP-induced renal damage, based on suppression of blood urea, serum creatinine, the renal MDA and NO levels, and increased antioxidant capacity in CP-treated rats. The results of histopathological and ultrastructural investigations supported the renoprotective effect of hemin against CP-induced acute toxicity. Conclusion. The induction of HO-1 by hemin is a promising approach in the treatment of CP-induced nephrotoxicity. However, further preclinical studies are warranted to test effectiveness of CP/hemin on the outcome of tumor chemotherapy.

Protective roles of CX3CR1-mediated signals in toxin A-induced enteritis through the induction of heme oxygenase-1 expression

The injection of Clostridium difficile toxin A into the ileal loops caused fluid accumulation with the destruction of intestinal epithelial structure and the recruitment of neutrophils and macrophages. Concomitantly, intraileal gene expression of CX3CL1/fractalkine (FKN) and its receptor, CX3CR1, was enhanced. When treated with toxin A in a similar manner, CX3CR1-deficient (CX3CR1(-/-)) mice exhibited exaggerated fluid accumulation, histopathological alterations, and neutrophil recruitment, but not macrophage infiltration. Mice reconstituted with CX3CR1(-/-) mouse-derived bone marrow cells exhibited exacerbated toxin A-induced enteritis, indicating that the lack of the CX3CR1 gene for hematopoietic cells aggravated toxin A-induced enteritis. A heme oxygenase-1 (HO-1) inhibitor, tin-protoporphyrin-IX, markedly increased fluid accumulation in toxin A-treated wild-type mice, indicating the protective roles of HO-1 in this situation. HO-1 expression was detected mainly in F4/80-positive cells expressing CX3CR1, and CX3CR1(-/-) mice failed to increase HO-1 expression after toxin A treatment. Moreover, CX3CL1/FKN induced HO-1 gene expression by isolated lamina propria-derived macrophages or a mouse macrophage cell line, RAW264.7, through the activation of the ERK signal pathway. Thus, CX3CL1/FKN could induce CX3CR1-expressing macrophages to express HO-1, thereby ameliorating toxin A-induced enteritis.

Pro-healing potential of hemin: an inducer of heme oxygenase-1

Hemin induces heme oxygenase (HO), an enzyme which degrades heme in a rate-limiting manner and has an important role in cellular protection against oxidative stress and apoptosis. This HO inducer may be of potential therapeutic value in wound healing and inflammation. To identify the beneficial activity of HO vis a vis wound healing, hemin was used as inducer of HO in rats using a full-thickness cutaneous wound model. Hemin treatment increased cellular proliferation and collagen synthesis as evidenced by increase in wound contraction and hydroxyproline and glucosamine contents. mRNA expression of cytokines endorsed fast healing as was indicated by inhibition of pro-inflammatory cytokines such as ICAM-1 and TNF-alpha and up-regulation of anti-inflammatory cytokine IL-10.

Therapeutic potential of hemin in acetaminophen nephrotoxicity in rats

The therapeutic potential of hemin, the heme oxygenase-1 inducer, was investigated against renal damage induced by acute acetaminophen overdose in rats. Nephrotoxicity was induced by a single oral dose of acetaminophen (2.5g/kg). Hemin was given as a single s.c. injection (40μmol/kg), 1h following acetaminophen administration. Hemin treatment restored blood urea nitrogen and serum creatinine levels that were elevated by acetaminophen. Hemin also compensated deficits in the antioxidant defense mechanisms (reduced glutathione, and catalase and superoxide dismutase activities), and suppressed lipid peroxidation in renal tissue resulted from acetaminophen administration. Hemin attenuated the acetaminophen-induced elevations in renal tumor necrosis factor-α and nitric oxide levels, and caspase-3 activity. Additionally, hemin ameliorated acetaminophen-induced renal damage observed by light microscopic examination. The therapeutic effect afforded by hemin was abolished by prior administration of zinc protoporphyrin-IX, the heme oxygenase-1 inhibitor. It was concluded that hemin represents a potential therapeutic option to protect renal tissue from the detrimental effects of acute acetaminophen overdose.

Bimoclomol ameliorates mercuric chloride nephrotoxicity through recruitment of stress proteins

Bimoclomol (BIM), is a stress proteins coinducer, that acts synergistically with a mild stressor to activate cytoprotective stress proteins. BIM has been successfully utilized in animal models for the treatment of various nervous, cardiac and cerebrovascular diseases. Mercuric chloride (HgCl(2)) induces acute renal failure in rats by a single dosage. The present in vivo study was conducted to assess the efficacy of BIM against acute HgCl(2) nephrotoxicity. At different times after BIM and/or HgCl(2) exposure we evaluated renal morphology and the localization/abundance of three stress proteins (HSP72, GRP75, HSP60) by electron microscopy, immunohistochemistry and Western blot analysis. BIM delivery to rats 6h before mercury, ameliorated damage to renal ultrastructure, with recovery of tubular and mitochondrial membranes 24h after mercury treatment. In rats pretreated with BIM prior to HgCl(2) exposure, HSP72 was significantly overexpressed in proximal tubules in a time-dependent manner. In contrast, the amounts of GRP75 and HSP60 after BIM pretreatment were comparable to the group treated with mercury alone, but these stress proteins had translocated to the nuclei at 14 and 24h, respectively. These novel findings suggest that BIM mitigates HgCl(2) nephrotoxicity in rats through the early recruitment of stress proteins in midcortical proximal tubules that are the main renal mercury-targets.

Heme oxygenase-1: a provenance for cytoprotective pathways in the kidney and other tissues

Heme oxygenase (HO) is the rate-limiting enzyme in the degradation of heme, converting heme to biliverdin, during which iron is released and carbon monoxide (CO) is emitted; biliverdin is subsequently converted to bilirubin by biliverdin reductase. At least two isozymes possess HO activity: HO-1 represents the isozyme induced by diverse stressors, including ischemia, nephrotoxins, cytokines, endotoxin, oxidants, and vasoactive substances; HO-2 is the constitutive, glucocorticoid-inducible isozyme. HO-1 is upregulated in the kidney in assorted conditions and diseases. Interest in HO is driven by the capacity of this system to protect the kidney against injury, a capacity likely reflecting, at least in part, the cytoprotective properties of its products: in relatively low concentrations, CO exerts vasorelaxant, antiapoptotic, and anti-inflammatory effects while bile pigments are antioxidant and anti-inflammatory metabolites. This article reviews the HO system and the extent to which it influences the function of the healthy kidney; it summarizes conditions and stimuli that elicit HO-1 in the kidney; and it explores the significance of renal expression of HO-1 as induced by ischemia, nephrotoxins, nephritides, transplantation, angiotensin II, and experimental diabetes. This review also points out the tissue specificity of the HO system, and the capacity of HO-1 to induce renal injury in certain settings. Studies of HO in other tissues are discussed insofar as they aid in elucidating the physiologic and pathophysiologic significance of the HO system in the kidney.

Opposite roles of neutrophils and macrophages in the pathogenesis of acetaminophen-induced acute liver injury

Neutrophils and macrophages infiltrate after acetaminophen (APAP)-induced liver injury starts to develop. However, their precise roles still remain elusive. In untreated and control IgG-treated wild-type (WT) mice, intraperitoneal APAP administration (750 mg/kg) caused liver injury including centrilobular hepatic necrosis and infiltration of neutrophils and macrophages, with about 50% mortality within 48 h after the injection. APAP injection markedly augmented intrahepatic gene expression of inducible nitric oxide synthase (iNOS) and heme oxygenase (HO)-1. Moreover, neutrophils expressed iNOS, which is presumed to be an aggravating molecule for APAP-induced liver injury, while HO-1 was mainly expressed by macrophages. All anti-granulocyte antibody-treated neutropenic WT and most CXC chemokine receptor 2 (CXCR2)-deficient mice survived the same dose of APAP, with reduced neutrophil infiltration and iNOS expression, indicating the pathogenic roles of neutrophils in APAP-induced liver injury. However, APAP caused more exaggerated liver injury in CXCR2-deficient mice with reduced macrophage infiltration and HO-1 gene expression, compared with neutropenic WT mice. An HO-1 inhibitor, tin-protoporphyrin-IX, significantly increased APAP-induced mortality, implicating HO-1 as a protective molecule for APAP-induced liver injury. Thus, CXCR2 may regulate the infiltration of both iNOS-expressing neutrophils and HO-1-expressing macrophages, and the balance between these two molecules may determine the outcome of APAP-induced liver injury.

Products of heme oxygenase and their potential therapeutic applications

Heme oxygenase 1 (HO-1) is induced in response to cellular stress and is responsible for converting the prooxidant heme molecule into equimolar quantities of biliverdin (BV), carbon monoxide (CO), and iron. BV is then converted to bilirubin (BR) by the enzyme biliverdin reductase. Experimental evidence suggests that induction of the HO system is an important endogenous mechanism for cytoprotection and that the downstream products of heme degradation, CO, BR, and BV, may mediate these powerful beneficial effects. These molecules, which were once considered to be toxic metabolic waste products, have recently been shown to have dose-dependent vasodilatory, antioxidant, and anti-inflammatory properties that are particularly desirable for tissue protection during organ transplantation. In fact, recent work has demonstrated that administration of exogenous CO, BR, or BV may offer a simple, inexpensive method to substitute for the cytoprotective effects of HO-1 in a variety of clinically applicable models. This review will attempt to summarize the relevant biochemical and cytoprotective properties of CO, BR, and BV, and will discuss emerging studies involving the therapeutic applications of these molecules in the kidney and other organ systems.

Length polymorphism in heme oxygenase-1 is associated with arteriovenous fistula patency in hemodialysis patients

Heme oxygenase-1 (HO-1) is a rate-limiting enzyme in heme degradation, producing carbon monoxide (CO), which carries potent antiproliferative and anti-inflammatory effects in the vascular walls. Transcription of the HO-1 gene is regulated by the length polymorphism of dinucleotide guanosine thymine repeat (GT)(n) in the promoter region, which was measured in this study to determine its association with arteriovenous fistula (AVF) failure in Chinese hemodialysis (HD) patients in Taiwan. L allele means (GT)(n)>or=30 and S allele means (GT)n<30. Therefore, there are two L alleles for L/L genotype, one L and one S allele for L/S genotype, and two S alleles for S/S genotype. Among the 603 HD patients who were enrolled in this study, 178 patients had history of AVF failure, while 425 patients did not. Significant associations were found between AVF failure and the following factors (hazard ratio): longer HD duration (1.004 month), lower pump flow (0.993 ml/min), higher dynamic venous pressure (1.010 mmHg), location of AVF on the right side (1.587 vs left side) and upper arm (2.242 vs forearm), and L/L and L/S genotypes of HO-1 (2.040 vs S/S genotype). The proportion of AVF failure increased from 20.3% in S/S genotype and 31.0% in L/S genotype to 35.4% in L/L genotype (P=0.011). Relative incidences were 1/87.6 (1 episode per 87.6 patient-months), 1/129, and 1/224.9 for HD patients with L/L, L/S, and S/S genotypes, respectively (P<0.002). The unassisted patency of AVF at 5 years decreased significantly from 83.8% (124/148) to 75.1% (223/297) and 69% (109/158) in S/S, L/S, and L/L genotypes, respectively (P<0.0001). In comparison with HD patients with S/S genotype, those with L/L genotype had a higher prevalence of coronary artery disease (29.1 vs 14.2%; P=0.005). A longer length polymorphism with (GT)(n) >or=30 in the HO-1 gene was associated with a higher frequency of access failure and a poorer patency of AVF in HD patients. The longer GT repeat in the HO-1 promoter might inhibit gene transcription, and consequently offset the CO-mediated protective effect against vascular injury.

Hemin induces heme oxygenase-1 in spinal cord vasculature and attenuates barrier disruption and neutrophil infiltration in the injured murine spinal cord

Heme oxygenase-1 (HO-1) has been shown to alter vascular function in part by attenuating inflammation. We induced HO-1 in blood vessels in the spinal cord by systemic administration of hemin. Twenty-four hours later, immediately prior to euthanasia, fluorescence conjugated Lycopersicon esculentum (tomato) lectin was given intravenously to label the vasculature. HO-1 was induced in blood vessels, particularly in the white matter, as evidenced by the immunolocalization of HO-1 in lectin positive vessels. Western blots confirmed the hemin-mediated induction of HO-1 in the uninjured spinal cord. We next examined the extent to which treatment with hemin or vehicle, 24 h prior to a moderate contusion injury, influenced early vascular dysfunction in the injured cord. All animals were euthanized 24 h after injury. Luciferase, a marker of barrier integrity, was given intravenously 30 min prior to euthanasia. The spinal cord was either prepared for quantification of luciferase activity or fixed by vascular perfusion and prepared for the immunolocalization of neutrophils. There was a significant attenuation of barrier permeability to luciferase and a significant reduction in the number of neutrophils in hemin treated animals as compared to the vehicle treated group. Together, these findings demonstrate that vascular induction of HO-1 modulates barrier function and neutrophil infiltration and suggest that this protein may be useful for limiting the early vascular dysfunction and inflammation that occurs in the acutely injured spinal cord.

Acute renal hemodynamic effects of dimanganese decacarbonyl and cobalt protoporphyrin

BACKGROUND

Heme oxygenase (HO) products have a protective role in acute renal failure (ARF) that may be hemodynamically mediated because the HO-derived carbon monoxide (CO) is an important control system of arteriolar tone. The vascular effects of HO may be caused directly through changes in CO synthesis, and indirectly by alterations in nitric oxide (NO) release. The present study evaluated in vivo the renal effects of a heme oxygenase inhibitor, Co(III)Protoporphyrin (CoPP) alone or in combination with the CO donor dimanganese decacarbonyl (Mn2(CO)10).

METHODS

All drugs were administered into the renal artery of anesthetized rats. Changes in renal cortical nitric oxide concentration were measured in vivo electrochemically.

RESULTS

The intrarenal administration of the CO donor Mn2(CO)10 increased blood carboxyhemoglobin levels (+74%), renal blood flow (+54%), glomerular filtration (+38%), and urinary cGMP excretion (+128%). On the other hand, the inhibition of renal HO with CoPP progressively induced an ARF characterized by a drop in renal blood flow (-77%), glomerular filtration (-93%), and urinary cGMP excretion (-93%). These deleterious effects of HO inhibition on renal function were nearly abolished by supplementing CO with the coadministration of Mn2(CO)10+ CoPP, indicating that they may be caused by inhibition of CO synthesis and the resulting hemodynamic changes. In addition, CoPP lowered the renal cortical NO concentration (-21%) and also decreased the urinary excretion of nitrates/nitrites, while Mn2(CO)10 increased renal NO levels (+20%) and raised the excretion of nitrates/nitrites, suggesting that changes in NO release may contribute to the renal effects of the HO-CO system.

CONCLUSION

These results indicate that heme oxygenase-derived CO plays a cardinal role in the control of renal hemodynamics and glomerular filtration.

Effect of heme oxygenase-1 inducer hemin on chronic renal failure rats

The role of HO-1 inducer, hemin, in chronic renal failure (CRF) rats and its possible mechanism of action was studied. 5/6 subtotal nephrectomy was performed to establish chronic renal failure model. Rats were randomly assigned to 4 groups: sham-operated group, CRF group, ferrous gluconate group and hemin group. At the 10th week after operation, serum creatinine, BUN, RBC, HGB and HCT were measured. Renal pathologic changes were observed. RT-PCR and immunohistochemistry were used to detect the expression and distribution of HO-1. RT-PCR and radioimmunoassay was used to determine the expression of ET-1 in the kidney and plasma. The results showed that as compared with CRF group, serum creatinine and BUN in hemin group were reduced significantly and nephrogenic anemia was improved markedly. Glomerular mesangial proliferation and interstitial lesion were also ameliorated significantly. Hemin not only increased the expression of HO-1 but also reduced the expression of ET-1 in the kidney. The level of ET-1 protein in the plasma was also reduced after hemin treatment. Most of these indexes were not obviously changed in ferrous gluconate group. It was suggested that through inducing the expression of HO-1 and reducing the level of ET-1 in the kidney and plasma, hemin plays an important protective role in 5/6 subtotal nephrectomized rats.

The story so far: Molecular regulation of the heme oxygenase-1 gene in renal injury

Heme oxygenases (HOs) catalyze the rate-limiting step in heme degradation, resulting in the formation of iron, carbon monoxide, and biliverdin, the latter of which is subsequently converted to bilirubin by biliverdin reductase. Recent attention has focused on the biological effects of product(s) of this enzymatic reaction, which have important antioxidant, anti-inflammatory, and cytoprotective functions. Two major isoforms of the HO enzyme have been described: an inducible isoform, HO-1, and a constitutively expressed isoform, HO-2. A third isoform, HO-3, closely related to HO-2, has also been described. Several stimuli implicated in the pathogenesis of renal injury, such as heme, nitric oxide, growth factors, angiotensin II, cytokines, and nephrotoxins, induce HO-1. Induction of HO-1 occurs as an adaptive and beneficial response to these stimuli, as demonstrated by studies in renal and non-renal disease states. This review will focus on the molecular regulation of the HO-1 gene in renal injury and will highlight the interspecies differences, predominantly between the rodent and human HO-1 genes.

Protective effect of SnCl2 on K2Cr2O7-induced nephrotoxicity in rats: the indispensability of HO-1 preinduction and lack of association with some antioxidant enzymes

We have shown that the ameliorative effect of stannous chloride (SnCl2) pretreatment on potassium dichromate (K2Cr2O7)-induced renal damage 24 h after K2Cr2O7 injection was associated with the induction of heme oxygenase-1 (HO-1). In this work we evaluated: (a) if the protective effect of SnCl2 (given 12 h before K2Cr2O7) is associated with changes in the renal activity of HO-1, superoxide dismutase (SOD), glutathione peroxidase (GPx), glutathione reductase (GR), and catalase (CAT) 24 and 48 h after K2Cr2O7 injection, and (b) if HO-1 induction is indispensable before K2Cr2O7 injection. It was found that the protective effect of SnCl2 on renal function was observed both at 24 and 48 h reaching its maximum at 24 h when HO-1 expression was higher. Cu,Zn-SOD, Mn-SOD, and GR activities remained unchanged whereas GPx and CAT activities decreased at 48 h in K2Cr2O7-treated rats. The activity of Cu,Zn-SOD, Mn-SOD, GPx, CAT, and GR was unchanged in the SnCl2-treated rats. To fulfill the objective (b) groups of rats treated with K2Cr2O7 and SnCl2 (given at the same time or 12 h after K2Cr2O7) were studied 24 h after K2Cr2O7-injection. The simultaneous injections of SnCl2 and K2Cr2O7 had no protective effect whereas the injection of SnCl2 12 h after K2Cr2O7 exacerbated renal damage. In conclusion, the protective effect of SnCl2 on K2Cr2O7-induced nephrotoxicity is associated with HO-1 induction and not with other antioxidant enzymes (Cu,Zn-SOD, Mn-SOD, GPx, GR, and CAT) and SnCl2 has a preventive and not a therapeutic effect on renal damage induced by K2Cr2O7.

HO-1 induction attenuates renal damage and oxidative stress induced by K2Cr2O7

Heme oxygenase (HO) is the rate-limiting enzyme in the degradation of heme; its inducible isozyme HO-1 protects against some types of acute tissue injury. The expression and functional role of HO-1 in rats with renal injury induced by potassium dichromate (K(2)Cr(2)O(7)) was investigated in this work. Rats were studied 24 h after a single injection of K(2)Cr(2)O(7). To address the possible protective effect of HO-1 in this experimental model, this enzyme was induced by an injection of stannous chloride (SnCl(2)) 12 h before K(2)Cr(2)O(7) administration. The functional role of HO-1 in K(2)Cr(2)O(7) + SnCl(2)-treated animals was tested by inhibiting HO activity with an injection of zinc (II) protoporphyrin IX (ZnPP) 18 h before K(2)Cr(2)O(7). In K(2)Cr(2)O(7)-treated rats: (i) renal HO-1 content, measured by Western blot, increased 2.6-fold; and, (ii) renal nitrotyrosine and protein carbonyl content, markers of oxidative stress, increased 3.5- and 1.36-fold, respectively. Renal damage and oxidative stress were ameliorated and HO-1 content was increased in the K(2)Cr(2)O(7) + SnCl(2) group. The attenuation of renal injury and oxidative stress was lost by the inhibition of HO activity in K(2)Cr(2)O(7) + SnCl(2) + ZnPP-treated animals. Our data suggest that HO-1 overexpression induced by SnCl(2) is responsible for the attenuation of renal damage and oxidative stress induced by K(2)Cr(2)O(7).

Preconditioning with tin-protoporphyrin IX attenuates ischemia/reperfusion injury in the rat kidney

BACKGROUND

Heme oxygenase (HO)-1 is induced as a unique stress response and leads to a transient resistance against oxidative damage, including ischemia and reperfusion (I/R) injury. In the present study, we examined whether HO-1 induction may confer a protection against I/R injury in the rat kidney.

METHODS

Lewis rats were divided into four groups as follows: (1) vehicle group; (2) group treated with ferri-protoporphyrin IX (hemin), an inducer of HO; (3) group treated with low-dose tin-protoporphyrin IX (SnPP), an inhibitor of HO; and (4) group treated with high-dose SnPP. Renal warm ischemia for 60 minutes was performed 24 hours after each treatment.

RESULTS

At 24 hours after treatment, hemin induced a significant increase in renal HO activity, but failed to induce HO-1 protein synthesis. Although both low- and high-dose SnPP reduced HO activity, a marked HO-1 expression was observed only in the high-dose SnPP-treated kidney. Hemin exacerbated the renal function after reperfusion, while high-dose SnPP significantly suppressed the intercellular adhesion molecule (ICAM)-1 expression, the infiltration of ED-1-positive macrophages and the expression of activated caspase-3, which resulted in attenuation of apoptotic cell death and ameliorated I/R injury.

CONCLUSION

These results suggest that prior induction of HO-1 protein by high-dose SnPP may lead to anti-inflammatory and antiapoptotic effects on warm renal I/R injury independently of its enzyme activity, and that HO enzyme activation may not always act as an antioxidant, especially under I/R-induced oxidative stress.

Differential induction of heme oxygenase-1 in macrophages and hepatocytes during acetaminophen-induced hepatotoxicity in the rat: effects of hemin and biliverdin

Heme oxygenase-1 (HO-1), also known as heat shock protein 32, has been shown to protect against oxidant-induced tissue injury. In the present studies, we analyzed expression of this enzyme in macrophages and hepatocytes following acetaminophen administration and its potential role in hepatotoxicity. Treatment of rats with a hepatotoxic dose of acetaminophen (1 g/kg, ip) resulted in a time-dependent induction of HO-1 in the liver. This was observed within 6 h of acetaminophen administration in both hepatocytes and macrophages. Hepatocytes were found to be more sensitive than macrophages to the effects of acetaminophen on HO-1. Up regulation of HO-1 in the liver following acetaminophen administration correlated with induction of ferritin and manganese superoxide dismutase (MnSOD). To determine if HO-1 was hepatoprotective, rats were pretreated with hemin (30 micromol/kg, ip), a potent inducer of the enzyme. Following hemin treatment, we observed a time-dependent increase in HO-1 protein in the liver and in serum bilirubin levels. Pretreatment of rats with hemin was found to prevent acetaminophen-induced hepatotoxicity, as measured histologically and biochemically by decreased serum transaminase levels. This was correlated with more rapid increases in expression of hepatic ferritin and MnSOD. Heme metabolism via HO-1 generates biliverdin, which is rapidly converted to bilirubin by biliverdin reductase. Pretreatment of rats with biliverdin (40 micromol/kg, ip) was also found to block acetaminophen-induced injury. These data suggest that HO-1 is an important component of antioxidant defense during acetaminophen-induced hepatotoxicity.

Heme oxygenase and the kidney

Heme plays a significant pathogenic role in several diseases involving the kidney. The cellular content of heme, derived either from the delivery of filtered heme proteins such as hemoglobin and myoglobin, or from the breakdown of ubiquitous intracellular heme proteins, is regulated via the heme oxygenase enzyme system. Heme oxygenases catalyze the rate-limiting step in heme degradation, resulting in the formation of iron, carbon monoxide, and biliverdin, which is subsequently converted to bilirubin by biliverdin reductase. Recent attention has focused on the biological effects of product(s) of this enzymatic reaction, which have important antioxidant, anti-inflammatory, and cytoprotective functions. Three isoforms of heme oxygenase (HO) enzyme have been described: an inducible isoform, HO-1, and two constitutively expressed isoforms, HO-2 and HO-3. Induction of HO-1 occurs as an adaptive and beneficial response to several injurious stimuli, and has been implicated in many clinically relevant disease states including atherosclerosis, transplant rejection, endotoxic shock, hypertension, acute lung injury, acute renal injury, as well as others. This review will focus predominantly on the role of HO-1 in the kidney.