HO-1 induction ameliorates experimental murine membranous nephropathy: anti-oxidative, anti-apoptotic and immunomodulatory effects

Oxidative stress and inflammation are mediated via aryl hydrocarbon receptor signalling in idiopathic membranous nephropathy

Membranous nephropathy (MN) patients are diagnosed by the presence of phospholipase A2 receptor (PLA2R) before they progress to renal failure. However, the subepithelium-like immunocomplex deposit-mediated downstream molecular pathways are poorly understood. The aryl hydrocarbon receptor (AHR), NF-ƙB and Nrf2 pathways play central roles in the pathogenesis and progression of chronic kidney disease. However, their mutual effects on MN require further examination. Thus, we investigated the effect of AHR signalling on the NF-ƙB and Nrf2 pathways in IMN patients, cationic bovine serum albumin (CBSA)-injected rats and zymosan activation serum (ZAS)-treated podocytes. IMN patients show significantly decreased serum total protein and albumin levels, increased urine protein levels and intrarenal IgG4 and PLA2R protein expression in glomeruli compared with controls. IMN patients exhibited increased mRNA expression of intrarenal AHR and its target genes, including CYP1A1, CYP1A2, CYP1B1 and COX-2. This increase was accompanied by significantly upregulated protein expression of CD3, NF-ƙB p65 and COX-2 and significantly downregulated Nrf2 and HO-1 expression. Similarly, CBSA-induced rats showed severe proteinuria and activated intrarenal AHR signalling. This was accompanied by significantly upregulated protein expression of intrarenal p-IκBα, NF-κB p65 and its gene products, including COX-2, MCP-1, iNOS, 12-LOX, p47phox and p67phox, and significantly downregulated protein expression of Nrf2 and its gene products, including HO-1, catalase, GCLC, GCLM, MnSOD and NQO1. These results were further verified in ZAS-induced podocytes. Treatment with the AHR antagonist CH223191 and AHRsiRNA significantly preserved podocyte-specific protein expression and improved the NF-ƙB and Nrf2 pathways in ZAS-induced podocytes. In contrast, similar results were obtained in ZAS-induced podocytes treated with the NF-ƙB inhibitor BAY 11-7082 and NF-κBp65 siRNA. However, neither method had a significant effect on AHR signalling. Collectively, these results indicate that the NF-ƙB pathway is a downstream target of AHR signalling. Our findings suggest that blocking AHR signalling inhibits oxidative stress and inflammation, thereby improving proteinuria and renal injury.

Moshen granule ameliorates membranous nephropathy by regulating NF-ƙB/Nrf2 pathways via aryl hydrocarbon receptor signalling

Considerable achievements were realized in illuminating underlying pathological mechanisms of patients with idiopathic membranous nephropathy (IMN). Although IMN patients are well diagnosed before they reach renal failure, no currently available drug intervention is effective in halting IMN progression. In this study, we assess Moshen granule (MSG) effect on IMN patients and cationic bovine serum albumin (CBSA)-induced rats. Increasing studies has indicated that activation of aryl hydrocarbon receptor (AHR) was related to oxidative stress and inflammation. We further determine MSG effect on AHR, nuclear factor ƙB (NF-ƙB) and nuclear factor erythroid 2-related factor 2 (Nrf2) in the CBSA-induced rats. MSG markedly reduces proteinuria and improves kidney function in both IMN patients and rats induced by CBSA. MSG markedly inhibits increased mRNA expressions of intrarenal AHR and its four downstream target genes including CYP1A1, CYP1A2, CYP1B1 and COX-2 compared with untreated CBSA-induced rats. This is accompanied by markedly downregulated protein expressions of p-IƙBα and NF-ƙB p65 and its downstream gene products including MCP-1, COX-2, 12-LOX, iNOS, p47phox and p67phox, while markedly preserves protein expressions of Nrf2 and its downstream gene products including catalase, HO-1, GCLM, GCLC, MnSOD and NQO1 in the kidney tissues. These data suggests MSG blunts podocyte damage through inhibiting activation of NF-ƙB/Nrf2 pathway via AHR signaling. This finding may provide a promising therapy for treatment of IMN through oxidative stress and inflammation.

Cobalt Protoporphyrin Blocks EqHV-8 Infection via IFN-α/β Production

Equid alphaherpesvirus type 8 (EqHV-8) is the causative agent of severe respiratory disease, abortions, and neurological syndromes in equines and has resulted in huge economic losses to the donkey industry. Currently, there exist no therapeutic molecules for controlling EqHV-8 infection. We evaluated the potential antiviral activity of cobalt protoporphyrin (CoPP) against EqHV-8 infection. Our results demonstrated that CoPP inhibited EqHV-8 infection in susceptible cells and mouse models. Furthermore, CoPP blocked the replication of EqHV-8 via HO-1 (heme oxygenase-1) mediated type I interferon (IFN) response. In conclusion, our data suggested that CoPP could serve as a novel potential molecule to develop an effective therapeutic strategy for EqHV-8 prevention and control.

Metalloporphyrins Reduce Proteinuria in Podocyte Immune Injury: The Role of Metal and Porphyrin Moieties

Depending on their central metal atom, metalloporphyrins (MPs) can attenuate or exacerbate the severity of immune-mediated kidney injury, and this has been attributed to the induction or inhibition of heme oxygenase (HO) activity, particularly the inducible isoform (HO-1) of this enzyme. The role of central metal or porphyrin moieties in determining the efficacy of MPs to attenuate injury, as well as mechanisms underlying this effect, have not been assessed. Using an antibody-mediated complement-dependent model of injury directed against rat visceral glomerular epithelial cells (podocytes) and two MPs (FePPIX, CoPPIX) that induce both HO-1 expression and HO enzymatic activity in vivo but differ in their chelated metal, we assessed their efficacy in reducing albuminuria. Podocyte injury was induced using rabbit immune serum raised against the rat podocyte antigen, Fx1A, and containing an anti-Fx1A antibody that activates complement at sites of binding. FePPIX or CoPPIX were injected intraperitoneally (5 mg/kg) 24 h before administration of the anti-Fx1A serum and on days 1, 3, 6, and 10 thereafter. Upon completion of urine collection on day 14, the kidney cortex was obtained for histopathology and isolation of glomeruli, from which total protein extracts were obtained. Target proteins were analyzed by capillary-based separation and immunodetection (Western blot analysis). Both MPs had comparable efficacy in reducing albuminuria in males, but the efficacy of CoPPIX was superior in female rats. The metal-free protoporphyrin, PPIX, had minimal or no effect on urine albumin excretion. CoPPIX was also the most potent MP in inducing glomerular HO-1, reducing complement deposition, and preserving the expression of the complement regulatory protein (CRP) CD55 but not that of CD59, the expression of which was reduced by both MPs. These observations demonstrate that the metal moiety of HO-1-inducing MPs plays an important role in reducing proteinuria via mechanisms involving reduced complement deposition and independently of an effect on CRPs.

Metalloporphyrins as Tools for Deciphering the Role of Heme Oxygenase in Renal Immune Injury

Renal immune injury is a frequent cause of end-stage renal disease, and, despite the progress made in understanding underlying pathogenetic mechanisms, current treatments to preserve renal function continue to be based mainly on systemic immunosuppression. Small molecules, naturally occurring biologic agents, show considerable promise in acting as disease modifiers and may provide novel therapeutic leads. Certain naturally occurring or synthetic Metalloporphyrins (Mps) can act as disease modifiers by increasing heme oxygenase (HO) enzymatic activity and/or synthesis of the inducible HO isoform (HO-1). Depending on the metal moiety of the Mp employed, these effects may occur in tandem or can be discordant (increased HO-1 synthesis but inhibition of enzyme activity). This review discusses effects of Mps, with varying redox-active transitional metals and cyclic porphyrin cores, on mechanisms underlying pathogenesis and outcomes of renal immune injury.

Integrative analysis of miRNA-mRNA network in idiopathic membranous nephropathy by bioinformatics analysis

Background

Currently, several specific antigens, M-type receptor for secretory phospholipase A2(PLA2R1), thrombospondin type-1 domain-containing 7A(THSD7A), and neural epidermal growth factor-like 1 protein (NELL-1), are discovered associated with the onset of idiopathic membranous nephropathy (IMN). But the pathomechanisms of IMN still need to be further claried. Understanding the mechanisms of IMN is required to improve its diagnosis and treatment.

Methods

In this study, we constructed miRNA regulatory networks to investigate IMN development. Moreover, miRNAs and mRNAs that were differentially expressed between Idiopathic Membranous Nephropathy (IMN) patients and normal controls were examined using the GSE115857 dataset and our previous sequence study. DE miRNA target genes were determined based on the FUNRICH software, starBase, miRDB, and miRWalk, and an miRNA-mRNA network was designed using DE-mRNAs that were negatively correlated with DE-miRNAs. The miRNA-mRNA network contained 228 miRNA-mRNA pairs. Thereafter, we conducted KEGG pathway, GO functional annotation, immune-related gene screening, protein interaction networks, and potential hub gene analyses. Furthermore, 10 miRNAs and 10 genes were determined and preliminarily validated using the validation dataset from GEO. Finally, we identified which pair may offer more accurate diagnosis and therapeutic targets for IMN.

Results

Two miRNA-mRNA pairs, miR-155-5p-FOS and miR-146a-5p-BTG2, were differentially expressed in IMN, indicating that these genes may affect IMN through immune processes. These findings may offer more accurate diagnoses and therapeutic targets for IMN.

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.

Functional Metabolomics Analysis Elucidating the Metabolic Biomarker and Key Pathway Change Associated With the Chronic Glomerulonephritis and Revealing Action Mechanism of Rhein

Chronic glomerulonephritis (CGN) as the culprit of kidney failure can increase the mortality of critically ill patients and seriously threatens people’s health all over the world. This study using metabolomics strategy is to reveal the potential therapeutic mechanism-related targets to evaluate the effects of rhein (RH) on CGN rats. Changes of serum metabolites and pathways were analyzed by non-targeted metabolomic method based on liquid chromatography-mass spectrometry (LC-MS) combined with ingenuity pathway analysis. In addition, the levels of biochemical indicators were also detected. A total of 25 potential biomarkers were identified to express serum metabolic turbulence in CGN animal model, and then 16 biomarkers were regulated by RH trending to the normal states. From metabolite enrichment and pathway analysis, pharmacological activity of RH on CGN were mainly involved in six vital metabolic pathways including phenylalanine, tyrosine and tryptophan biosynthesis, phenylalanine metabolism, arachidonic acid metabolism, tricarboxylic acid cycle (TCA cycle), alanine, aspartate, and glutamate metabolism, arginine and proline metabolism. It suggested CGN treatment with RH, which may be mediated via interference with metabolic pathway such as amino acid metabolism, arachidonic acid metabolism, and TCA cycle to regulating inflammation, oxidation response and immune regulation against CGN. It showed that metabolomics method offer deeply insight into the therapeutic mechanisms of natural product.

Influence of Resveratrol on the Cardiovascular Health Effects of Chronic Kidney Disease

Cardiovascular disease (CVD) is closely related to chronic kidney disease (CKD), and patients with CKD have a high risk of CVD-related mortality. Traditional CVD risk factors cannot account for the higher cardiovascular risk of patients with CKD, and standard CVD interventions cannot reduce the mortality rates among patients with CKD. Nontraditional factors related to mineral and vitamin-D metabolic disorders provide some explanation for the increased CVD risk. Non-dialyzable toxins, indoxyl sulfate (IS) and p-cresol sulfate (PCS)—produced in the liver by colonic microorganisms—cause kidney and vascular dysfunction. Plasma trimethylamine-N-oxide (TMAO)—a gut microbe-dependent metabolite of dietary L-carnitine and choline—is elevated in CKD and related to vascular disease, resulting in poorer long-term survival. Therefore, the modulation of colonic flora can improve prospects for patients with CKD. Managing metabolic syndrome, anemia, and abnormal mineral metabolism is recommended for the prevention of CVD in patients with CKD. Considering nontraditional risk factors, the use of resveratrol (RSV), a nutraceutical, can be helpful for patients with CVD and CKD. This paper discusses the beneficial effects of RSV on biologic, pathophysiological and clinical responses, including improvements in intestinal epithelial integrity, modulation of the intestinal microbiota and reduction in hepatic synthesis of IS, PCS and TMAO in patients with CVD and CKD.

Comprehensive identification of immune-associated biomarkers based on network and mRNA expression patterns in membranous glomerulonephritis

BACKGROUND

Membranous glomerulonephritis (MGN) is the most common cause of nephrotic syndrome in adult patients. Despite extensive evidences suggested that many immune-related genes could serve as effective biomarkers in MGN, the potential has not been sufficiently understood because of most previous studies have concentrated on individual gene and not the entire interaction network.

METHODS

Here, we integrated multiple levels of data containing immune-related genes, MGN-related genes, protein-protein interaction (PPI) networks and gene expression profiling data to construct an immune or MGN-directed neighbor network (IOMDN network) and an MGN-related genes-directed network (MGND network).

RESULTS

Our analysis suggested that immune-related genes in the PPI network have special topological characteristics and expression pattern related to MGN. We also identified five network modules which showed tighter network structure and stronger correlation of expression. In addition, functional and drug target analyses of genes in modules indicated that the potential mechanism for MGN.

CONCLUSIONS

Collectively, these results indicated that the strong associations between immune and MGN and showed the potential of immune-related genes as novel diagnostic and therapeutic targets for MGN.

Raspberry ketone induces brown-like adipocyte formation through suppression of autophagy in adipocytes and adipose tissue

Promoting white adipose tissue (WAT) to acquire brown-like characteristics is a promising approach for obesity treatment. Although raspberry ketone (RK) has been reported to possess antiobesity activity, its effects on the formation of brown-like adipocytes remain unclear. Therefore, we investigated the effects and underlying mechanism of RK on WAT browning in 3T3-L1 adipocytes and rats with ovariectomy (Ovx)-induced obesity. RK (100 μM) significantly induced browning of 3T3-L1 cells by increasing mitochondrial biogenesis and the expression of browning-specific proteins (PR domain containing 16, PRDM16; peroxisome proliferator-activated receptor gamma coactivator 1-alpha, PGC-1α; uncoupling protein-1, UCP-1) and lipolytic enzymes (hormone-sensitive lipase and adipose triglyceride lipase). RK significantly reduced the expression of the autophagy-related protein Atg12 and increased the expression of p62 and heme oxygenase 1 (HO-1). Additionally, these effects of RK were reversed by the HO-1 inhibitor SnPP (20 μM). In addition, RK (160 mg/kg, gavage, for 8 weeks) significantly reduced body weight gain (Ovx+RK, 191.8 ± 4.6 g vs. Ovx, 223.6 ± 5.9; P < .05), food intake, the amount of inguinal adipose tissue (Ovx+RK, 9.05 ± 1.1 g vs Ovx, 12.9 ± 0.92 g; P < .05) and the size of white adipocytes in Ovx rats. Moreover, compared to expression in the Ovx group, the levels of browning-specific proteins were significantly higher and the levels of autophagy-related proteins were significantly lower in the Ovx+RK group. Therefore, this study elucidated the mechanism associated with RK-induced WAT browning and thus provides evidence to support the clinical use of RK for obesity treatment.

Renal-targeted delivery of triptolide by entrapment in pegylated TRX-20-modified liposomes

Previously, 3,5-dipentadecyloxybenzamidine hydrochloride (TRX-20)-modified liposomes were reported to specifically target mesangial cells (MCs) in glomeruli. To further gain a better understanding of the characteristics and potential application for glomerular diseases of TRX-20-modified liposomes, we synthesized TRX-20 and prepared TRX-20-modified liposomes (TRX-LPs) with different molar ratios - 6% (6%-TRX-LP), 11% (11%-TRX-LP), and 14% (14%-TRX-LP) - of TRX-20 to total lipid in the present study. All TRX-LPs exhibited concentration-dependent toxicity against the MCs at a lipid concentration ranging from 0.01 to 1.0 mg/mL with IC50 values of 3.45, 1.13, and 0.55 mg/mL, respectively. Comparison of the cell viability of TRX-LPs indicated that high levels of TRX-20 caused severe cell mortality, with 11%-TRX-LP showing the higher cytoplasmic accumulation in the MCs. Triptolide (TP) as a model drug was first loaded into 11%-TRX-LP and the liposomes were further modified with PEG5000 (PEG-TRX-TP-LP) in an attempt to prolong their circulation in blood and enhance TP-mediated immune suppression. Due to specific binding to MCs, PEG-TRX-TP-LP undoubtedly showed better anti-inflammatory action in vitro, evidenced by the inhibition of release of nitric oxide (NO) and tumor necrosis factor-α from lipopolysaccharide-stimulated MCs, compared with free TP at the same dose. In vivo, the PEG-TRX-TP-LP effectively attenuated the symptoms of membranous nephropathic (MN) rats and improved biochemical markers including proteinuria, serum cholesterol, and albumin. Therefore, it can be concluded that the TRX-modified liposome is an effective platform to target the delivery of TP to glomeruli for the treatment of MN.

Betulinic acid, isolated from the leaves of Syzygium cumini (L.) Skeels, ameliorates the proteinuria in experimental membranous nephropathy through regulating Nrf2/NF-κB pathways

Membranous nephropathy (MN) is associated with increased oxidative stress and inflammatory markers in the kidney. Betulinic acid (BA) is a potent antioxidant and anti-inflammatory compound isolated from the leaves of Syzygium cumini (L.) Skeels. In the present study, we investigated the effects of BA on experimental MN in rats and explored the mechanisms by which it enhances antioxidant activities and resolves inflammatory condition in experimental MN. Passive Heymann nephritis (PHN) was induced in Sprague-Dawley rats by a single tail vein injection of anti- Fx1A antiserum. The rats were orally administered BA (25 and 50 mg kg ^-1 d ^-1) or dexamethasone (DEX; 0.07 mg kg-1, reference compound) for 4 weeks after the induction of PHN. Blood, urine, and kidney tissue were collected for analysis at the end of the study. Treatment of PHN rats with BA or DEX significantly attenuated renal dysfunction, histopathological alterations and reduced immune complex deposition in the kidneys. Furthermore, BA ameliorated mRNA and protein expression of NF-κB, iNOS, TNF-α, Nrf2, HO-1 and NQO1 in the kidney. BA also restored malondialdehyde level and antioxidant enzyme activities in the kidney. In a nutshell, the protective effect of BA can be explained by its anti-inflammatory and anti-oxidant activities, which in turn is due to downregulation of NF-κB pathway and activation of Nrf2. The results indicated that BA can effectively suppress experimental PHN in rats by regulating Nrf2/NF-κB pathways.

Butein induction of HO-1 by p38 MAPK/Nrf2 pathway in adipocytes attenuates high-fat diet induced adipose hypertrophy in mice

Adipose tissue inflammation and oxidative stress are key components in the development of obesity and insulin resistance. Heme oxygenase (HO)-1 in adipocytes protects against obesity and adipose dysfunction. In this study, we report the identification of butein, a flavonoid chalcone, as a novel inducer of HO-1 expression in adipocytes in vitro and in vivo. Butein upregulated HO-1 mRNA and protein expression in 3T3-L1 adipocytes, accompanied by Kelch-Like ECH-Associated Protein (Keap) 1 degradation and increase in the nuclear level of nuclear factor erythroid 2-related factor 2 (Nrf2). Butein modulation of Keap1 and Nrf2 as well as HO-1 upregulation was reversed by pretreatment with p38 MAPK inhibitor SB203580, indicating the involvement of p38 MAPK in butein activation of Nrf2 in adipocytes. In addition, HO-1 activation by butein led to the inhibitions of reactive oxygen species and adipocyte differentiation, as evidenced by the fact that butein repression of reactive oxygen species and adipogenesis was reversed by pretreatment with HO-1 inhibitor SnPP. Induction of HO-1 expression by butein was also demonstrated in the adipose tissue of C57BL/6 mice fed a high-fat diet administered along with butein for three weeks, and correlated with the inhibitions of adiposity and adipose tissue inflammation, which were reversed by co-administration of SnPP. Altogether, our results demonstrate that butein activates the p38 MAPK/Nrf2/HO-1 pathway to act as a potent inhibitor of adipose hypertrophy and inflammation in a diet-induced obesity model and thus has potential for suppressing obesity-linked metabolic syndrome.

Heme oxygenase 1-mediated novel anti-inflammatory activities of Salvia plebeia and its active components

ETHNOPHARMACOLOGICAL RELEVANCE

Salvia plebeia R. Br. (SP) has been widely used as a traditional folk medicine for the treatment of infectious diseases and pain. An anti-inflammatory potential of SP has remains largely unknown.

AIM OF THE STUDY

We tried to elucidate the principle mechanism and the active ingredients underlying the anti-inflammatory activities of SP.

MATERIALS AND METHODS

We investigated the protective activities of SP methanolic extract (SPME) and seven representative ingredients against inflammation. Quantitative analysis using HPLC-DAD-ESI/MS was conducted to determine the relative amounts of these seven active ingredients in SPME. Both in vitro murine macrophages and in vivo mouse models were employed to elucidate SP- and active ingredient-mediated anti-inflammatory effects.

RESULTS

SPME significantly reduced inflammatory processes both in vivo in a TPA-induced ear edema model and in vitro in lipopolysaccharide (LPS)-activated macrophages. SPME decreased the release of nitric oxide (NO) and prostaglandin E2 (PGE2) and expression of inducible nitric oxide synthase (iNOS). Seven active components (luteoloside (C1), nepitrin (C2), homoplantagenin (C3), luteolin (C4), nepetin (C5), hispidulin (C6), and eupatorin (C7)) of SPME were analyzed and their relative concentrations were determined, demonstrating that C2, C3, C5 and C6 were present in higher amounts than were C1, C4, and C7. These major compounds inhibited NO and PGE2 production, and iNOS and COX-II protein expression through heme oxygenase-1 (HO-1) induction via activation of nuclear factor erythroid 2-related factor2 (Nrf2).

CONCLUSION

Our data demonstrate that SPME possesses potent in vitro and in vivo anti-inflammatory activities. Nepetin and hispidulin, and their glycosides are the major active compounds in SPME, and their effects are mediated by Nrf2/HO-1 signaling. Taken together, we propose that SPME and its active ingredients may serve as novel therapeutic candidates for diseases associated with excessive inflammation.

Photobiomodulation Mitigates Diabetes-Induced Retinopathy by Direct and Indirect Mechanisms: Evidence from Intervention Studies in Pigmented Mice

Objective

Daily application of far-red light from the onset of diabetes mitigated diabetes-induced abnormalities in retinas of albino rats. Here, we test the hypothesis that photobiomodulation (PBM) is effective in diabetic, pigmented mice, even when delayed until weeks after onset of diabetes. Direct and indirect effects of PBM on the retina also were studied.

Methods

Diabetes was induced in C57Bl/6J mice using streptozotocin. Some diabetics were exposed to PBM therapy (4 min/day; 670 nm) daily. In one study, mice were diabetic for 4 weeks before initiation of PBM for an additional 10 weeks. Retinal oxidative stress, inflammation, and retinal function were measured. In some mice, heads were covered with a lead shield during PBM to prevent direct illumination of the eye, or animals were treated with an inhibitor of heme oxygenase-1. In a second study, PBM was initiated immediately after onset of diabetes, and administered daily for 2 months. These mice were examined using manganese-enhanced MRI to assess effects of PBM on transretinal calcium channel function in vivo.

Results

PBM intervention improved diabetes-induced changes in superoxide generation, leukostasis, expression of ICAM-1, and visual performance. PBM acted in part remotely from the retina because the beneficial effects were achieved even with the head shielded from the light therapy, and because leukocyte-mediated cytotoxicity of retinal endothelial cells was less in diabetics treated with PBM. SnPP+PBM significantly reduced iNOS expression compared to PBM alone, but significantly exacerbated leukostasis. In study 2, PBM largely mitigated diabetes-induced retinal calcium channel dysfunction in all retinal layers.

Conclusions

PBM induces retinal protection against abnormalities induced by diabetes in pigmented animals, and even as an intervention. Beneficial effects on the retina likely are mediated by both direct and indirect mechanisms. PBM is a novel non-pharmacologic treatment strategy to inhibit early changes of diabetic retinopathy.

Ferritin heavy chain mediates the protective effect of heme oxygenase-1 against oxidative stress

The phenomenon that heme oxygenase-1 (HO-1) protects cell from injury yet its enzymatic product, iron, may facilitate generation of free radical has been long puzzling. Here we establish a functional connection between ferritin heavy chain (FHC) and HO-1. In human lupus nephritis HO-1 and FHC are colocalized within the glomeruli. In rodent anti-Thy1 (thymocyte antigen 1) induced glomerulonephritis, heme oxygenase blockade lowers the expression of FHC and accelerates mesangial cell death. Stimulation of heme oxygenase in cultured rat mesangial cell enhances its resistance to hydrogen peroxide, whereas FHC knockdown by RNA interference compromises this salutary effect. RNA interference of HO-1 makes the cell more susceptible to hydrogen peroxide, which can be rescued by forced expression of wild-type FHC but not mutants that lose the capacity of iron storage and ferroxidase activity. Phosphorylation of JunD was not sustained in these cells. Microarray analysis identifies four candidate transcriptional factors that may regulate the HO-1-induced transcription of FHC. Our results support the role of FHC in neutralizing the iron toxicity as well as mediating the protective effect of HO-1 in response to oxidative stress.

Pterostilbene and allopurinol reduce fructose-induced podocyte oxidative stress and inflammation via microRNA-377

High dietary fructose is an important causative factor in the development of metabolic syndrome-associated glomerular podocyte oxidative stress and injury. Here, we identified microRNA-377 (miR-377) as a biomarker of oxidative stress in renal cortex of fructose-fed rats, which correlated with podocyte injury and albuminuria in metabolic syndrome. Fructose feeding increased miR-377 expression, decreased superoxide dismutase (SOD) expression and activity, and caused O2(-) and H2O2 overproduction in kidney cortex or glomeruli of rats. This reactive oxygen species induction increased p38 MAPK phosphorylation and thioredoxin-interacting protein (TXNIP) expression and activated the NOD-like receptor pyrin domain-containing 3 (NLRP3) inflammasome to produce interleukin-1β in kidney glomeruli of fructose-fed rats. These pathological processes were further evaluated in cultured differentiated podocytes exposed to 5mM fructose, or transfected with miR-377 mimic/inhibitor and TXNIP siRNA, or co-incubated with p38 MAPK inhibitor, demonstrating that miR-377 overexpression activates the O2(-)/p38 MAPK/TXNIP/NLRP3 inflammasome pathway to promote oxidative stress and inflammation in fructose-induced podocyte injury. Antioxidants pterostilbene and allopurinol were found to ameliorate fructose-induced hyperuricemia, podocyte injury, and albuminuria in rats. More importantly, pterostilbene and allopurinol inhibited podocyte miR-377 overexpression to increase SOD1 and SOD2 levels and suppress the O2(-)/p38 MAPK/TXNIP/NLRP3 inflammasome pathway activation in vivo and in vitro, consistent with the reduction of oxidative stress and inflammation. These findings suggest that miR-377 plays an important role in glomerular podocyte oxidative stress, inflammation, and injury driven by high fructose. Inhibition of miR-377 by antioxidants may be a promising therapeutic strategy for the prevention of metabolic syndrome-associated glomerular podocyte injury.

Resveratrol ameliorates renal damage, increases expression of heme oxygenase-1, and has anti-complement, anti-oxidative, and anti-apoptotic effects in a murine model of membranous nephropathy

Background

Idiopathic membranous nephropathy (MN) is an autoimmune-mediated glomerulonephritis and a common cause of nephrotic syndrome in adults. There are limited available treatments for MN. We assessed the efficacy of resveratrol (RSV) therapy for treatment of MN in a murine model of this disease.

Methods

Murine MN was experimentally induced by daily subcutaneous administration of cationic bovine serum albumin, with phosphate-buffered saline used in control mice. MN mice were untreated or given RSV. Disease severity and pathogenesis was assessed by determination of metabolic and histopathology profiles, lymphocyte subsets, immunoglobulin production, oxidative stress, apoptosis, and production of heme oxygenase-1 (HO1).

Results

MN mice given RSV had significantly reduced proteinuria and a marked amelioration of glomerular lesions. RSV also significantly attenuated immunofluorescent staining of C3, although there were no changes of serum immunoglobulin levels or immunocomplex deposition in the kidneys. RSV treatment of MN mice also reduced the production of reactive oxygen species (ROS), reduced cell apoptosis, and upregulated heme oxygenase 1 (HO1). Inhibition of HO1 with tin protoporphyrin IX partially reversed the renoprotective effects of RSV. The HO1 induced by RSV maybe via Nrf2 signaling.

Conclusion

Our results show that RSV increased the expression of HO1 and ameliorated the effects of membranous nephropathy in a mouse model due to its anti-complement, anti-oxidative, and anti-apoptotic effects. RSV appears to have potential as a treatment for MN.

Disruption of the cytochrome P-450 1B1 gene exacerbates renal dysfunction and damage associated with angiotensin II-induced hypertension in female mice

Recently, we demonstrated in female mice that protection against ANG II-induced hypertension and associated cardiovascular changes depend on cytochrome P-450 (CYP)1B1. The present study was conducted to determine if Cyp1b1 gene disruption ameliorates renal dysfunction and organ damage associated with ANG II-induced hypertension in female mice. ANG II (700 ng·kg(-1)·min(-1)) infused by miniosmotic pumps for 2 wk in female Cyp1b1(+/+) mice did not alter water consumption, urine output, Na(+) excretion, osmolality, or protein excretion. However, in Cyp1b1(-/-) mice, ANG II infusion significantly increased (P < 0.05) water intake (5.50 ± 0.42 ml/24 h with vehicle vs. 8.80 ± 0.60 ml/24 h with ANG II), urine output (1.44 ± 0.37 ml/24 h with vehicle vs. 4.30 ± 0.37 ml/24 h with ANG II), and urinary Na(+) excretion (0.031 ± 0.016 mmol/24 h with vehicle vs. 0.099 ± 0.010 mmol/24 h with ANG II), decreased osmolality (2,630 ± 79 mosM/kg with vehicle vs. 1,280 ± 205 mosM/kg with ANG II), and caused proteinuria (2.60 ± 0.30 mg/24 h with vehicle vs. 6.96 ± 0.55 mg/24 h with ANG II). Infusion of ANG II caused renal fibrosis, as indicated by an accumulation of renal interstitial α-smooth muscle actin, collagen, and transforming growth factor-β in Cyp1b1(-/-) but not Cyp1b1(+/+) mice. ANG II also increased renal production of ROS and urinary excretion of thiobarburic acid-reactive substances and reduced the activity of antioxidants and urinary excretion of nitrite/nitrate and the 17β-estradiol metabolite 2-methoxyestradiol in Cyp1b1(-/-) but not Cyp1b1(+/+) mice. These data suggest that Cyp1b1 plays a critical role in female mice in protecting against renal dysfunction and end-organ damage associated with ANG II-induced hypertension, in preventing oxidative stress, and in increasing activity of antioxidant systems, most likely via generation of 2-methoxyestradiol from 17β-estradiol.

Transcriptional upregulation centra of HO-1 by EGB via the MAPKs/Nrf2 pathway in mouse C2C12 myoblasts

Long-term abuse of alcohol results in chronic alcoholic myopathy which is associated with increased oxidative stress. Ginkgo biloba extract (EGB) is widely used as a therapeutic agent to treat certain cardiovascular and neurological disorders. Although EGB is known to possess antioxidant functions and potent cytoprotective effects, its protective mechanism on alcohol-induced oxidative damage in C2C12 myoblasts remains unclear. In this study, we investigated the cytoprotective mechanisms of EGB against alcohol-derived oxidative stress in mouse C2C12 myoblasts. Challenge with alcohol (100mM) caused an increase in intracellular reactive oxygen species in mouse C2C12 myoblasts, which was not alleviated by treatment with EGB. These results indicate that EGB does not seem to act as an ROS scavenger in this experimental model. Additionally, EGB produced activation of ERK and JNK [two major mitogen-activated protein kinases (MAPKs)], an increase in the nuclear level of nuclear factor erythroid-2-related factor 2 (Nrf2) and upregulation of heme oxygenase-1 (HO-1, a stress-responsive protein with antioxidant function). Pretreatment with inhibitors of MAPKs PD98059 (a specific inhibitor of ERK), SP600125 (a specific inhibitor of JNK) abolished both EGB-induced Nrf2 nuclear translocation and HO-1 up-regulation. We conclude that EGB confers cytoprotective effects from oxidative stress induced by alcohol in mouse C2C12 myoblasts depend on transcriptional upregulation of HO-1 by EGB via the MAPKs/Nrf2 pathway.

Ferulic Acid, an Angelica sinensis-Derived Polyphenol, Slows the Progression of Membranous Nephropathy in a Mouse Model

Membranous nephropathy (MN) is a leading cause of adult nephrotic syndrome but lacks adequate treatment. Different extracts of Angelica sinensis (AS) and one of its active compounds, ferulic acid (FA), were used to evaluate the therapeutic effects in a MN mouse model. The MN model was grouped into three subgroups: no treatment (N-T), treatment at induction of MN (Pre-T), and treatment after full-blown MN (Post-T). The results showed that the methanol (ME) layer of AS extract exhibited a therapeutic effect on MN-induced proteinuria. The ME layer-enriched compound, FA, improved the hypoalbuminemia, hyperlipidemia, and proteinuria in both Pre-T and Post-T groups. Ferulic acid also reduced the formation of oxidative protein products and increased the synthesis of antioxidant enzymes in groups Pre-T and Post-T. Regarding angiogenesis factors, the antiangiogenic factors in renal glomeruli were increased in group N-T, but, after FA treatment, only one of the antiangiogenic factors, thrombospondin-1, showed a significant decrease. Furthermore, the expression of Th2 predominant showed significant decrease in both Pre-T and Post-T groups when compared to that of N-T group. In summary, FA retarded the progression of MN, and the mechanisms involved the regulation of oxidative stresses, angiogenic and antiangiogenic factors, and attenuation of Th2 response.

Melatonin enhances endogenous heme oxygenase-1 and represses immune responses to ameliorate experimental murine membranous nephropathy

Idiopathic membranous nephropathy (MN), an autoimmune-mediated glomerulonephritis, is one of the most common causes of nephrotic syndrome in adults. Therapeutic agents for MN remain ill defined. We assessed the efficacy of melatonin therapy for MN. Experimental murine MN was induced with cationic bovine serum albumin, and the mice were immediately administered 20 mg/kg melatonin or phosphate-buffered saline subcutaneously once a day. Disease severity was verified by examining serum and urine metabolic profiles and renal histopathology. The expression of cytokines and oxidative stress markers, cell apoptosis, and the associated mechanisms were also determined. Mice treated with melatonin displayed a significant reduction in proteinuria and a marked amelioration of glomerular lesions, with attenuated immunocomplex deposition. The subpopulations of T cells were not altered, but the CD19(+) B-cell subpopulation was significantly reduced in the MN mice treated with melatonin. The expression of cytokine mRNAs in splenocytes indicated that melatonin reduced the expression of proinflammatory cytokines and increased the expression of anti-inflammatory cytokines (interleukin 10). The production of reactive oxygen species and TUNEL-positive apoptotic cells in the kidney were also significantly reduced in the melatonin-treated MN mice. Melatonin also upregulated heme oxygenase 1 (HO1) and ameliorated MN. The blockade of HO1 expression with SnPP, a HO1 inhibitor, attenuated HO1 induction by melatonin and thus mitigated its renoprotective effects during MN. Our results suggest that melatonin treatment ameliorates experimental MN via multiple pathways, including by its antioxidative, antiapoptotic, and immunomodulatory effects. Melatonin should be considered a potential therapeutic intervention for MN in the future.

Contributions of heme oxygenase-1 in postconditioning-protected ischemia-reperfusion injury in rat liver transplantation

BACKGROUND

Heme oxygenase-1 (HO-1), an oxidative stress-response gene up-regulated by various physiological and exogenous stimuli, has cytoprotective activities. Ischemic postconditioning (Postcon) can protect an organ from ischemia-reperfusion (I/R) injury. In the present study, we investigated the potential contributions of HO-1 to Postcon-dependent protection against I/R injury in rat liver transplantation models.

MATERIALS AND METHODS

Adult male Sprague-Dawley rats were randomly divided into four groups: sham group with laparotomy for liver exposure; I/R group with 24-hour cold ischemia of the donor liver; Postcon group with the same treatment as the I/R group plus ischemic Postcon; and zinc protoporphyrin (ZnPP HO-1 inhibitor) + Postcon group treated the same as the Postcon cohort with donors pretreated using ZnPP 24 hours before the I/R injury. We measured liver tissue and peripheral blood samples collected at 6 hours after reperfusion and serum transaminase levels, histopathology, liver tissue malondialdehyde (MDA) content, superoxide dismutase (SOD) activity and HO-1 expression in the liver.

RESULTS

Postcon significantly diminished the elevation of serum transaminases levels after I/R injury when compared with I/R and ZnPP+Postcon groups. Postcon treated rats showed significantly lower MDA production and higher SOD activity. HO-1 was induced in rat livers exposed to Postcon; its levels were obviously overexpressed after 6 hours in Postcon rats. Inhibiting the expression of HO-1, negated the protective effects of Postcon.

CONCLUSIONS

Induction of HO-1 in the Postcon condition played a protective role against hepatic I/R injury and enhanced the early antioxidative activity. The protective effects of Postcon were significantly associated with greater intrahepatic HO-1 expression.

Guggulsterone induces heme oxygenase-1 expression through activation of Nrf2 in human mammary epithelial cells: PTEN as a putative target

Guggulsterone (GS) [4,17(20)-pregnadiene-3,16-dione] is a phytosterol found in the gum resin of the Commiphora mukul. GS exists naturally in two stereoisomers: E-GS (cis-GS) and Z-GS (trans-GS). In this study, the effects of both isomers on expression of the cytoprotective enzyme heme oxygenase-1 (HO-1) were evaluated in human mammary epithelial (MCF10A) cells. NF-E2-related factor 2 (Nrf2) is considered a master regulator in activating antioxidant response element (ARE)-driven expression of HO-1 and many other antioxidant/cytoprotective proteins. cis-GS upregulated the transcription and protein expression of HO-1 to a greater extent than did trans-GS. cis-GS treatment enhanced nuclear translocation and ARE-binding activity of Nrf2. MCF10A cells transfected with an ARE luciferase construct exhibited significantly elevated Nrf2 transcriptional activity upon cis-GS treatment compared with cells transfected with the control vector. In addition, silencing of the Nrf2 gene abrogated cis-GS-induced expression of HO-1. Incubation of MCF10A cells with cis-GS increased phosphorylation of Akt. The pharmacological inhibition of phosphoinositide 3-kinase (PI3K), an upstream kinase responsible for Akt phosphorylation, abrogated cis-GS-induced Nrf2 nuclear translocation. Pretreatment with the thiol-reducing agents attenuated Akt phosphorylation, Nrf2 activation and HO-1 expression, suggesting that cis-GS may cause thiol modification of an upstream signaling modulator. Phosphatase and Tensin Homologue Deleted on Chromosome 10 (PTEN) is a negative regulator of the PI3K-Akt axis. The mutation in cysteine 124 present in the catalytic domain of PTEN abolished cis-GS-induced HO-1 expression as well as Akt phosphorylation. Whether this cysteine is a 'bona fide' target of cis-GS in its activation of Nrf2 needs additional investigation.

Epigallocatechin-3-gallate prevents lupus nephritis development in mice via enhancing the Nrf2 antioxidant pathway and inhibiting NLRP3 inflammasome activation

Patients with lupus nephritis show an impaired oxidative status and increased levels of interleukin (IL)-1β and IL-18, which are closely linked to inflammation and correlated with disease activity. Although epigallocatechin-3-gallate (EGCG), the major bioactive polyphenol present in green tea with antioxidant and free radical scavenging activities, has been reported to have anti-inflammatory effects by inhibiting nuclear factor-kappa B (NF-κB)-mediated inflammatory responses in vivo, its effectiveness for the treatment of lupus nephritis is still unknown. In the present study, 12-week-old New Zealand black/white (NZB/W) F1 lupus-prone mice were treated daily with EGCG by gavage until sacrificed at 34 weeks old for clinical, pathological, and mechanistic evaluation. We found that the administration (1) prevented proteinuria, renal function impairment, and severe renal lesions; (2) increased renal nuclear factor E2-related factor 2 (Nrf2) and glutathione peroxidase activity; (3) reduced renal oxidative stress, NF-κB activation, and NLRP3 mRNA/protein expression and protein levels of mature caspase-1, IL-1β, and IL-18; and (4) enhanced splenic regulatory T (Treg) cell activity. Our data clearly demonstrate that EGCG has prophylactic effects on lupus nephritis in these mice that are highly associated with its effects of enhancing the Nrf2 antioxidant signaling pathway, decreasing renal NLRP3 inflammasome activation, and increasing systemic Treg cell activity.

Antroquinonol reduces oxidative stress by enhancing the Nrf2 signaling pathway and inhibits inflammation and sclerosis in focal segmental glomerulosclerosis mice

Oxidative stress, inflammation, and fibrosis are involved in the development and progression of focal segmental glomerulosclerosis (FSGS), a common form of idiopathic nephrotic syndrome that represents a therapeutic challenge because it has a poor response to steroids. Antroquinonol (Antroq), a purified compound, is a major active component of a mushroom, namely Antrodia camphorata, that grows in the camphor tree in Taiwan, and it has inhibitory effects on nitric oxide production and inflammatory reactions. We hypothesized that Antroq might ameliorate FSGS renal lesions by modulating the pathogenic pathways of oxidative stress, inflammation, and glomerular sclerosis in the kidney. We demonstrate that Antroq significantly (1) attenuates proteinuria, renal dysfunction, and glomerulopathy, including epithelial hyperplasia lesions and podocyte injury; (2) reduces oxidative stress, leukocyte infiltration, and expression of fibrosis-related proteins in the kidney; (3) increases renal nuclear factor E2-related factor 2 (Nrf2) and glutathione peroxidase activity; and (4) inhibits renal nuclear factor-κB (NF-κB) activation and decreases levels of transforming growth factor (TGF)-β1 in serum and kidney tissue in a mouse FSGS model. Our data suggest that Antroq might be a potential therapeutic agent for FSGS, acting by boosting Nrf2 activation and suppressing NF-κB-dependent inflammatory and TGF-β1-mediated fibrosis pathways in the kidney.

Erythropoietin enhances endogenous haem oxygenase-1 and represses immune responses to ameliorate experimental autoimmune encephalomyelitis

Both erythropoietin (EPO) and haem oxygenase-1 (HO-1), an anti-oxidative stress protein, have proven protective roles in experimental autoimmune encephalomyelitis (EAE), a reliable animal model of multiple sclerosis. In this study, EPO delivered intraperitoneally could reduce disease severity in myelin oligodendrocyte glycoprotein (MOG)–EAE mice. To assess the effect of EPO on endogenous HO-1 in EAE, we investigated expression of HO-1 mRNA by real-time polymerase chain reaction (RT–PCR), protein expression centrally and peripherally by Western blot and immunohistochemistry and mean fluorescence intensity of splenic HO-1 by flow cytometry. A significantly higher expression of HO-1 in both the central nervous system (CNS) and spleen was shown in EPO-treated MOG–EAE mice than in controls.We further examined the immunomodulatory effect of EPO in EAE, and via RT–PCR demonstrated significantly lower expression of interferon-γ, interleukin (IL)-23, IL-6 and IL-17 mRNA, and significantly higher expression of IL-4 and IL-10 mRNA in CNS of EPO-treated MOG–EAE mice than in controls. Using flow cytometry, we also observed a significantly decreased ratio of both T helper type 1 (Th1) and Th17 lymphocyte subsets isolated from CNS and a significantly increased ratio of splenic regulatory CD4 T cells in EPO-treated MOG–EAE mice. In addition, we demonstrated that MOG-specific T cell proliferation was lower in the EPO-treated group than in controls and showed amelioration of EAE by adoptive transfer of splenocytes from EPO-treated MOG–EAE mice. Together, our data show that in EAE, EPO induction of endogenous HO-1 and modulation of adaptive immunity both centrally and peripherally may involve the repression of inflammatory responses.

Approaching biomarkers of membranous nephropathy from a murine model to human disease

Background. Membranous glomerulonephropathy (MN) is the most prevalent cause of nephrotic syndrome in adult humans. However, the specific biomarkers of MN have not been fully elucidated. We examined the alterations in gene expression associated with the development of MN. Methods. Murine MN was induced by cationic bovine serum albumin (cBSA). After full-blown MN, cDNA microarray analysis was performed to identify gene expression changes, and highly expressed genes were evaluated as markers both in mice and human kidney samples. Results. MN mice revealed clinical proteinuria and the characteristic diffuse thickening of the glomerular basement membrane. There were 175 genes with significantly different expressions in the MN kidneys compared with the normal kidneys. Four genes, metallothionein-1 (Mt1), cathepsin D (CtsD), lymphocyte 6 antigen complex (Ly6), and laminin receptor-1 (Lamr1), were chosen and quantified. Mt1 was detected mainly in tubules, Lamr1 was highly expressed in glomeruli, and CtsD was detected both in tubules and glomeruli. The high expressions of Lamr1 and CtsD were also confirmed in human kidney biopsies. Conclusion. The murine MN model resembled the clinical and pathological features of human MN and may provide a tool for investigating MN. Applying cDNA microarray analysis may help to identify biomarkers for human MN.

Pivotal Advance: Heme oxygenase 1 expression by human CD4+ T cells is not sufficient for their development of immunoregulatory capacity

HO-1 is the only inducible one of three isoenzymes that catalyzes the oxidative degradation of heme. HO-1 is inducible by various cellular stress factors and exerts cytoprotective and immunomodulatory effects. Recent publications demonstrated that HO-1 is constitutively expressed by CD4(+)CD25(+) T(regs) and induced in CD4(+)CD25(-) T cells upon FoxP3 transfection. Here, we investigated whether HO-1 was essential and sufficient for human T(regs) to exert immunosuppression in vitro. PGJ(2) induced pronounced expression of HO-1 in CD4(+)CD25(-) T cells without accompanying FoxP3 induction. Treatment of CD4(+)CD25(-) T cells with PGJ(2) decreased their proliferation, whereas the HO-1 inhibitor SnPP enhanced the proliferation of HO-1-expressing T(regs), suggesting that HO-1 may modulate the proliferative capacity of T lymphocytes. HO-1 modulation by SnPP treatment of T(regs) or PGJ(2) treatment of CD4(+)CD25(-) T cells neither suppressed nor induced immune-modulatory function in these cells, respectively, as measured by responder-cell proliferation and/or IL-2 production. In summary, these data suggest that HO-1 expression by T(regs) might contribute to their typical reluctance to proliferate but does not account independently for their suppressive functions.

Heme oxygenase-1 accelerates cutaneous wound healing in mice

Heme oxygenase-1 (HO-1), a cytoprotective, pro-angiogenic and anti-inflammatory enzyme, is strongly induced in injured tissues. Our aim was to clarify its role in cutaneous wound healing. In wild type mice, maximal expression of HO-1 in the skin was observed on the 2(nd) and 3(rd) days after wounding. Inhibition of HO-1 by tin protoporphyrin-IX resulted in retardation of wound closure. Healing was also delayed in HO-1 deficient mice, where lack of HO-1 could lead to complete suppression of reepithelialization and to formation of extensive skin lesions, accompanied by impaired neovascularization. Experiments performed in transgenic mice bearing HO-1 under control of keratin 14 promoter showed that increased level of HO-1 in keratinocytes is enough to improve the neovascularization and hasten the closure of wounds. Importantly, induction of HO-1 in wounded skin was relatively weak and delayed in diabetic (db/db) mice, in which also angiogenesis and wound closure were impaired. In such animals local delivery of HO-1 transgene using adenoviral vectors accelerated the wound healing and increased the vascularization. In summary, induction of HO-1 is necessary for efficient wound closure and neovascularization. Impaired wound healing in diabetic mice may be associated with delayed HO-1 upregulation and can be improved by HO-1 gene transfer.

Heme oxygenase and renal disease

The cellular content of heme, derived from the breakdown of heme proteins, is regulated via the heme oxygenase (HO) enzyme system. HO catalyzes the rate-limiting step in heme degradation resulting in the formation of iron, carbon monoxide, and biliverdin. Recent studies have focused on the biologic effects of product(s) of this reaction, which have important antioxidant, antiapoptotic, anti-inflammatory, and cytoprotective properties. Two isoforms of the HO enzyme have been described: an inducible isoform (HO-1) and a constitutively expressed isoform (HO-2). Induction of HO-1 occurs as a beneficial response to several injurious stimuli and has been implicated in many clinically relevant disease states including sepsis, hypertension, atherosclerosis, and acute lung and kidney injury. This review focuses on the role of HO-1 in kidney diseases.