[D-Trp8]-gamma-melanocyte-stimulating hormone exhibits anti-inflammatory efficacy in mice bearing a nonfunctional MC1R (recessive yellow e/e mouse)

Two melanocortin receptors (MC1 and MC3R) have been identified as main transducers of the anti-inflammatory effects of natural and synthetic melanocortins. In this study, we have taken advantage of the recent description of the selective MC3R agonist [d-Trp(8)]-gamma-melanocyte-stimulating hormone (MSH) and of the recessive yellow (e/e) mouse, bearing a nonfunctional MC1R, thereby incrementing our knowledge on this topic. Culturing peritoneal macrophages of recessive yellow (e/e) mice with [d-Trp(8)]-gamma-MSH led to accumulation of cAMP, indicating MC3R receptor functionality: this effect was blocked by a neutralizing antibody against MC3R. Likewise, release of the chemokine KC by urate crystals was attenuated by [d-Trp(8)]-gamma-MSH, and this effect was prevented by synthetic [Ac-Nle(4)-c[Asp(5)-2'-Nal(7),Lys(10)]alpha-MSH(4-10)-NH(2) (SHU9119)] and natural [agouti-related protein (AGRP)] MC3R antagonists but not by the MC4R antagonist Ac-Cys-Nle-Arg-His-d-2-Nal-Arg-Trp-Cys-NH(2) (HS024). Systemic treatment of mice with [d-Trp(8)]-gamma-MSH inhibited KC release and polymorphonuclear cell accumulation elicited by urate crystals in the murine peritoneal cavity. SHU9119 and AGRP prevented the inhibitory actions of [d-Trp(8)]-gamma-MSH, whereas HS024 was inactive. We also demonstrate here that [d-Trp(8)]-gamma-MSH displays a dual mechanism of action by inducing the anti-inflammatory protein heme-oxygenase 1 (HO-1). Treatment with the HO-1 inhibitor zinc protoporphyrin IX exacerbated the inflammatory response elicited by urate crystals and abrogated the anti-inflammatory effects of [d-Trp(8)]-gamma-MSH. In conclusion, these data support the development of the selective MC3R agonist [d-Trp(8)]-gamma-MSH for the treatment of inflammatory pathologies, based on a dual mechanism of cytokine/chemokine inhibition and induction of the anti-inflammatory protein HO-1.

Up-regulation of heme oxygenase provides vascular protection in an animal model of diabetes through its antioxidant and antiapoptotic effects

Heme oxygenase (HO) plays a critical role in the regulation of cellular oxidative stress. The effects of the reactive oxygen species scavenger ebselen and the HO inducers cobalt protoporphyrin and stannous chloride (SnCl(2)) on HO protein levels and activity, indices of oxidative stress, and the progression of diabetes were examined in the Zucker rat model of type 2 diabetes. The onset of diabetes coincided with an increase in HO-1 protein levels and a paradoxical decrease in HO activity, which was restored by administration of ebselen. Up-regulation of HO-1 expressed in the early development of diabetes produced a decrease in oxidative/nitrosative stress as manifested by decreased levels of 3-nitrotyrosine, superoxide, and cellular heme content. This was accompanied by a decrease in endothelial cell sloughing and reduced blood pressure. Increased HO activity was also associated with a significant increase in the antiapoptotic signaling molecules Bcl-xl and phosphorylation of p38-mitogen-activated protein kinase but no significant increases in Bcl-2 or BAD proteins. In conclusion, 3-nitrotyrosine, cellular heme, and superoxide, promoters of vascular damage, are reduced by HO-1 induction, thereby preserving vascular integrity and protecting cardiac function involving an increase in antiapoptotic proteins.

Genetic suppression of HO-1 exacerbates renal damage: reversed by an increase in the antiapoptotic signaling pathway

Apoptosis has been shown to contribute to the development of acute and chronic renal failure. The antiapoptotic action of the heme oxygenase (HO) system may represent an important protective mechanism in kidney pathology. We examined whether the lack of HO-1 would influence apoptosis in clipped kidneys of two-kidney, one-clip (2K1C) rats. Five-day-old Sprague-Dawley rats were injected in the left ventricle with approximately 5 x 10(9) colony-forming units/ml of retrovirus containing rat HO-1 antisense (LSN-RHO-1-AS) or control retrovirus (LXSN). After 3 mo, a 0.25-mm U-shaped silver clip was placed around the left renal artery. Animals were killed 3 wk later. Clipping the renal artery in LSN-RHO-1-AS rats did not result in increased HO-1 expression. In contrast to LXSN animals, 2K1C LSN-RHO-1-AS rats showed increased expression of cyclooxygenase 2 (COX-2) and higher 3-nitrotyrosine (3-NT) content as well as increased expression of the proapoptotic protein Apaf-1 and caspase-3 activity. Clipping the renal artery in LXSN rats resulted in increased expression of the antiapoptotic proteins Bcl-2 and Bcl-xl, while clipping the renal artery in LSN-RHO-1-AS rats did not change Bcl-2 levels and decreased the levels of Bcl-xl. Treatment of LSN-RHO-1-AS rats with cobalt protoporphyrin resulted in induction of renal HO-1, which was accompanied by decreases in blood pressure, COX-2, 3-NT, and caspase-3 activity, and increased expression of anti-apoptotic molecules (Bcl-2, Bcl-xl, Akt and p-Akt) in the clipped kidneys. These findings underscore the prominent role of HO-1 in counteracting apoptosis in this 2K1C renovascular hypertension model.

Portal hypertension produces an evolutive hepato-intestinal pro- and anti-inflammatory response in the rat

An inflammatory etiopathogeny can be suggested in portal hypertensive enteropathy since infiltration of the intestinal wall by mononuclear cells has been described in this condition. This work was carried out with the intention of shedding light on this matter. Male Wistar rats were divided into 4 control groups and 4 groups with partial portal vein ligation at 1, 2, 3 and 15 months. TNF-alpha, IL-1beta and IL-10 were quantified in liver and ileum by ELISA. CO and NO were measured in splanchnic and systemic vein by spectrophotometry and Griess reaction, respectively. Expression of constitutive and inducible isoforms of NO and HO were assayed by Western blot in liver and ileum. An increased hepatic release of proinflammatory mediators (TNF-alpha, IL-1beta and NO) associated with intestinal release of anti-inflammatory mediators (IL-10, CO) occurs in an early evolutive phase (1 month) of experimental portal hypertension. On the contrary, in the long-term (15 months), the increase in the intestinal release of proinflammatory mediators (TNF-alpha, IL-1beta) is associated with an increase in the hepatic release of anti-inflammatory mediators (IL-10, CO). These results suggest that experimental prehepatic portal hypertension presents changes in the serum and tissular (liver and small bowel) concentrations of mediators which are considered as pro- and anti-inflammatory.

Heme oxygenase induction and biliverdin excretion: implications for the bile fluorescence biomarker

The measurement of bile fluorescence has become a popular biomarker to demonstrate the exposure of fish to polycyclic aromatic hydrocarbons. Conflicting data have been published on how to normalize bile fluorescence. To investigate if normalization to biliverdin is a suitable method, experiments were performed to study the mechanisms related to biliverdin excretion in fish. Channel catfish (Ictalurus punctatus) were dosed with mixtures of benzo[a]pyrene and cadmium, chlorinated phenols or borneol. The results showed that under increasing toxicant stress, more biliverdin was excreted per amount of protein. To investigate if the increased biliverdin excretion was related to increased heme degradation, enzymatic activity of heme oxygenase (HO) was measured in liver homogenates. The fish dosed with chemical mixtures had significantly higher HO activity than the control fish, and a significant correlation was observed between HO activity and biliverdin concentration in the bile. It is concluded that chemical mixtures of environmental pollutants can induce HO activity and that this chemical stress leads to increased biliverdin excretion. The elucidation of this mechanistic pathway warrants that bile fluorescence is better expressed per amount of bile protein than per biliverdin absorption.

Downregulation of two novel genes in Sl/Sld and W(LacZ)/Wv mouse jejunum

Interstitial cells of Cajal (ICC) are the so-called pacemaker cells of the gut. W(LacZ)/Wv and Sl/Sld mice lack ICC surrounding the myenteric plexus (MP) in the jejunum. We compared the gene expression profile of wild type (WT) and W(LacZ)/Wv and Sl/Sld mice using suppression subtractive hybridization (SSH), generating a cDNA library of 1303 clones from which 48 unique sequences were differentially expressed with Southern blot. Among them, we identified heme oxygenase2, TROY, and phospholamban in ICC using immunohistochemistry. Using RT-qPCR, c-Kit and two new transcripts Dithp and prenylcysteine oxidase1 were significantly lower expressed in Sl/Sld and W(LacZ)/Wv versus WT. Prenylcysteine oxidase1 appeared cytotoxic for COS-7 cells and was highly expressed in liver while Dithp was mainly expressed in small intestine. The combination of SSH, Southern blot, RT-qPCR, and immunohistochemistry turned out to be a useful approach to identify rarely expressed genes and genes with small differences in expression.

Existence of heme oxygenase-carbon monoxide-cyclic guanosine monophosphate pathway in human trabecular meshwork cells in vitro

To confirm the existence of heme oxygenase (HO)- carbon monoxide (CO)- cyclic guanosine monophosphate (cGMP) pathway in the cultured human trabecular meshwork cells (HT-MCs) in vitro, and to evaluate the inductive role of hemin on this pathway, HTMCs of the third to fourth generation were cultured in vitro. Reverse transcripase-polymerase chain reaction (RT-PCR) was employed for detection of HO-1 and HO-2 mRNA. Immunohistochemical staining was used to detect HO-1 and HO-2 proteins. Hemin was added into the culture solution. The HO-1 mRNA levels were quantified by RT-PCR. The relative amount of carbon monoxide released into the media was measured with the quantifying carbon monoxide hemoglobin (HbCO) by spectrophotometry. Radioimmunoassay was used to determine changes of cGMP in HTMCs. The results showed that cultured cells had the specific characteristics of HTMCs. Both HO-1 and HO-2 genes were expressed in HTMCs, as well as HO-1 and HO-2 proteins in HTMCs. Hemin induced HO-1 mRNA, HbCO and cGMP in a dose-dependent manner. In conclusion, HO-CO-cGMP pathway exists in the cultured HTMCs and can be induced by hemin. Pharmacological stimulation of HO-CO-cGMP pathway may constitute a novel therapeutic approach to rescuing glaucoma.

Inhibition of the ERK/MAP kinase pathway attenuates heme oxygenase-1 expression and heme-mediated neuronal injury

Hemin is an oxidant that accumulates in intracranial hematomas. Its neurotoxicity is increased by its breakdown, which is catalyzed by the heme oxygenase (HO) enzymes. In this study we tested the hypothesis that inhibiting signaling events mediating HO-1 induction would protect cultured cortical neurons from hemin. A fivefold increase in HO-1 expression was observed in mixed neuron-astrocyte cultures 4h after hemin exposure. This was markedly reduced by the ERK pathway inhibitor U0126. The JNK inhibitor SP600125 had a weak but statistically significant effect, while the p38 inhibitor SB239063 was ineffective. Hemin neurotoxicity, as assessed by LDH release, propidium iodide staining, and malondialdehyde assay, was also prevented by U0126 but not by SB239063; SP600125 had little or no effect. Consistent with reduced iron release, ferritin expression was also attenuated by U0126, while cell hemin accumulation was increased. These results suggest that targeting the ERK pathway may prevent HO-1 induction in response to hemin, and reduce neuronal injury.

Bile fluorescence, heme oxygenase induction, and increased biliverdin excretion by mixtures of environmental toxicants

The measurement of bile fluorescence has become a popular biomarker to demonstrate the exposure of fish to polycyclic aromatic hydrocarbons. Conflicting data has been published on how to normalize bile fluorescence. To investigate if normalization to biliverdin is a suitable method, experiments were performed to study the mechanisms related to biliverdin excretion in fish. In two separate experiments channel catfish (Ictalurus punctatus) were dosed with mixtures of benzo[a]pyrene with cadmium, chlorinated phenols or borneol. The results showed linear relationships between bile protein and biliverdin for each treatment group, but the slope of this relationship was significantly increased when fish received more chemical stress. Thus, under increasing toxicant stress, more biliverdin was excreted per amount of protein. To investigate if the increased biliverdin excretion was related to increased heme degradation, enzymatic activity of heme oxygenase (HO) was measured in liver homogenates of the dosed fish. The fish dosed with chemical mixtures had a significantly higher HO activity than the control fish, and in both experiments a significant correlation was observed between HO activity and biliverdin concentration in the bile. It is concluded that mixtures of environmental pollutants can induce HO activity and that this chemical stress leads to increased biliverdin excretion. The elucidation of this mechanistic pathway warrants that bile fluorescence should not be expressed per biliverdin absorption, and that expression per bile protein would be a more reliable method.

Heme Arginate Pretreatment Attenuates Pulmonary NF-κB and AP-1 Activation Induced by Hemorrhagic Shock via Heme Oxygenase-1 Induction

Hemorrhagic shock followed by resuscitation (HSR) induces oxidative stress that leads to acute lung injury. Heme oxygenase-1 (HO-1), the rate-limiting enzyme in heme catabolism, is induced by oxidative stress and is thought to play an important role in the protection from oxidative tissue injuries. We previously demonstrated that HO-1 induction by heme arginate (HA), a strong inducer of HO-1, ameliorated HSR-induced lung injury and inflammation. Cellular redox state is known to modulate the DNA biding activity of the transcription factors; nuclear factor-kappaB (NF-kappaB) and activator protein-1 (AP-1). In the present study, we treated rats with HA (30 mg/kg of hemin) 18 h prior to HSR and examined its effect on the DNA binding activity of NF-kappaB and AP-1 at 1.5 h after HSR. HSR significantly increased the DNA binding activity of NF-kappaB as well as AP-1, while HA pretreatment markedly attenuated the activities of these transcription factors. In contrast, administration of tin mesoporphyrin, a specific competitive inhibitor of HO activity, to HA-pretreated animals abolished the suppressive effect of HA on the activities of NF-kappaB and AP-1, and increased these activities to almost the same level as those in HSR animals. Our findings indicate that HA pretreatment can significantly suppress the increased activity of NF-kappaB and AP-1 induced by HSR by virtue of its ability to induce HO-1. Our findings also suggest that HO-1 induced by HA pretreatment ameliorates HSR-induced lung injury at least in part mediated through the suppression of the activities of these transcription factors.

Pyrrolidine dithiocarbamate reduces ischemia-reperfusion injury of the small intestine

AIM

To evaluate whether pyrrolidine dithiocarbamate (PDTC), an enhancer of HO production, attenuates intestinal IR injury.

METHODS

Eighteen male rats were randomly allocated into three groups: (a) sham; (b) IR, consisting of 30 min of intestinal ischemia, followed by 2-h period of reperfusion; and (c) PDTC treatment before IR. Intestinal microvascular perfusion (IMP) was monitored continuously by laser Doppler flowmetry. At the end of the reperfusion, serum samples for lactate dehydrogenase (LDH) levels and biopsies of ileum were obtained. HO activity in the ileum was assessed at the end of the reperfusion period.

RESULTS

At the end of the reperfusion in the IR group, IMP recovered partially to 42.5% of baseline (P<0.05 vs sham), whereas PDTC improved IMP to 67.3% of baseline (P<0.01 vs IR). There was a twofold increase in HO activity in PDTC group (2 062.66+/-106.11) as compared to IR (842.3+/-85.12) (P<0.001). LDH was significantly reduced (P<0.001) in PDTC group (585.6+/-102.4) as compared to IR group (1 973.8+/-306.5). Histological examination showed that the ileal mucosa was significantly less injured in PDTC group as compared with IR group.

CONCLUSION

Our study demonstrates that PDTC improves the IMP and attenuates IR injury of the intestine possibly via HO production. Additional studies are warranted to evaluate the clinical efficacy of PDTC in the prevention of IR injury of the small intestine.

Regulation and expression of heme oxygenase enzymes in aged-rat brain: age related depression in HO-1 and HO-2 expression and altered stress-response

The heme oxygenase isozymes, HO-1 and HO-2, oxidatively cleave the heme molecule to produce biliverdin and the gaseous messenger, CO. The cleavage results in the release of iron, a regulator of transferrin, ferritin, and nitric oxide (NO) synthase gene expression. Biliverdin reductase (BVR) then catalyzes the reduction of biliverdin, generating the potent intracellular antioxidant, bilirubin. We report an age-related decrease in HO-1 and HO-2 expression present in select brain regions including the hippocampus and the substantia nigra, that are involved in the high order cognitive processes of learning and memory. The age-related loss of monoxide-producing potential in select regions of the brain was not specific to the HO system but was also observed in neuronal NO-generating system. Furthermore, compared to 2-month old rats, the ability of aged brain tissue to respond to hypoxic/hyperthermia was compromised at both the protein and the transcription levels as judged by attenuated induction of HO-1 immunoreactive protein and its 1.8 Kb transcript. Neotrofin (AIT), a cognitive-enhancing and neuroprotective drug, caused a robust increase in HO-1 immunoreactive protein in select neuronal regions and increased the expression of HO-2 transcripts. The potential interplay between regulation of HO-2 gene expression and the serum levels of the adrenal steroids is discussed. We suggest the search for therapeutic agents that reverse the decline and aberrant stress response of HO enzymes may lead to effective treatment regimens for age-associated neuronal deficits.

Role of Heme Oxygenase in the Protection Afforded Skeletal Muscle During Ischemic Tolerance

OBJECTIVE

Ischemic tolerance (IT) is known to improve resistance to ischemia/reperfusion (I/R)-induced injury; however, the mechanisms remain unknown. The authors hypothesized that induction of heme oxygenase (HO), a heat shock protein, would provide anti-inflammatory benefits during IT, thereby preventing leukocyte-derived I/R injury.

METHODS

Male Wistar rats were randomly assigned to sham (n = 4), I/R (n = 9), preconditioning (PC)+I/R (n = 7), chromium mesoporphyrin, to inhibit HO (CrMP; n = 4), or PC+I/R+CrMP (n = 6) groups. PC consisted of 5 cycles of I/R, each lasting 10 min, induced by tightening a tourniquet placed above the greater trochantor of the hindlimb. Twenty-four hours later, the hindlimb underwent 2 h of no-flow ischemia followed by intravital microscopy during 90 min reperfusion to assess capillary perfusion (#/mm), tissue injury (ratio of ethidium bromide to bisbenzimide labeled cells/100 microm2), leukocyte rolling (Lr, #/1000 microm2), and adhesion (La, #/1000 microm2) in postcapillary venules of the extensor digitorum longus (EDL) muscle.

RESULTS

In the I/R group, Lr was significantly increased (7.1 +/- 0.4) compared to sham (3.1 +/- 0.4). PC+I/R increased Lr (10.8 +/- 0.72), which was further exacerbated by the removal of HO (14.2 +/- 1.3). La (7.8 +/- 2.0) was significantly increased compared to sham (2.4 +/- 0.9), while PC returned La back to sham levels (1.9 +/- 0.7). Removal of HO activity, via CrMP, had no significant effect on La (3.9 +/- 0.7). However, CrMP removed the protection to microvascular perfusion (I/R = 9.4 +/- 1.1, PC = 16.6 +/- 1.8, sham = 20.5 +/- 2.8, PC+CrMP+I/R = 12.3 +/- 2.3) and prevented protection from ischemia-induced tissue injury.

CONCLUSION

The data suggest that HO is an important protective mechanism during IT in skeletal muscle, but such protection was by mechanisms other than altered leukocyte-endothelial cell interaction.

Increased HO-1 Expression and Decreased iNOS Expression in the Hippocampus From Adult Spontaneously Hypertensive Rats

Brain expression of heme oxygenase (HO) and nitric oxide synthase (NOS) in hypertension may participate in the pathogenesis of hypertension-related neuronal disorders, such as vascular dementia. In the present study, expression levels of HO and NOS in spontaneously hypertensive rats (SHR) were investigated using Western immunoblotting assay. Expression level of inducible HO-1 in hippocampus of 4-wk prehypertensive SHR was about twofold of that in age-matched Sprague-Dawley (SD) rats (p < 0.01). In 23-wk SHR with fully developed hypertension, hippocampal HO-1 level was significantly greater than that of age-matched SD rats (p < 0.05), but not different from 4-wk SHR. There was no difference in expression levels of hippocampal HO-2 between SHR and SD rats at different ages. Total enzymatic activity of hippocampal HO was significantly greater in 23-wk SHR than in age-matched SD rats or 4-wk SD/SHR (p < 0.01). Although hippocampal expression of nNOS protein was relatively unchanged, iNOS expression in 23-wk SHR was about fourfold lower than that in age-matched SD rats and 4-wk SD/SHR (p < 0.01). Total enzymatic activity of hippocampal NOS was significantly lower in 23-wk SHR than in age-matched SD rats or 4-wk SD/SHR (p < 0.01). Significantly suppressed Morris water maze performance was found in 23-wk SHR in comparison with age-matched SD rats. Because SHR has been used as a model of vascular dementia and hippocampus is essential for spatial learning and memory, understanding of altered HO/CO and NOS/NO systems in the hippocampus of adult SHR may shed light on the pathogenic development of memory deficits associated with vascular dementia.

[Effect of heme oxygenase-1 expression and activity on the heart function in ischemia-reperfusion]

The purpose of this study was to determine the protective effects of heme oxygenase-1 (HO-1) expression against postischemic myocardial dysfunction. We also investigated HO-1 expression in cardiac tissue from the left and right ventricles of myocardium. Rat hearts were isolated and perfused according to Langendorff technique to evaluate the recovery of myocardial function after 20 min of global ischemia and 40 min of reperfusion. We found that HO-1 expression was more expressed in left ventricles of myocardium in basic conditions and after ischemia/reperfusion as well as after its previous induction by hemin. Upregulation of the inducible isoform of HO-1 and increase its activity after treatment of animals with hemin 24 h before ischemia ameliorated myocardial function (raised left ventricular developed pressure, decreased end-diastolic pressure, attenuated vasoconstriction) and reduced oxydative stress in cardiac tissue during reperfusion of isolated hearts. Zinc protoporphyrin IX, an inhibitor of heme oxygenase activity, completely abolished the HO-1 expression in left ventricles of myocardium and increased postischemic myocardial dysfunction. Likewise, cardiac tissue injury was exacerbated by treatment with zinc protoporphyrin IX through significant inhibition of HO activity and increasing of hydroxyl radical production on reperfusion. The treatment of animals with hemin and following ischemia/reperfusion resulted in 5-6-times increase of HO-1 expression in the left ventricle of myocardium whereas in right ventricle only in 3-times. Our data provide strong evidence for a primary role of HO-1 in cardioprotection against reperfusion injury and show different HO-1 expression in left and right ventricles of myocardium.

Heme oxygenase-1 (Hsp32) is involved in the protection of small intestine by whole body mild hyperthermia from ischemia/reperfusion injury in rat

AIM

The aim of the present study was to explore whether heme oxygenase-1 (HO-1) is involved in the hyperthermia-provided protection of the small intestine from ischemia/reperfusion injury in rats.

METHODS

Intestinal damage was induced in male Sprague-Dawley rats by clamping both the superior mesenteric artery and the celiac trunk for 30 min, followed by reperfusion. Whole-body hyperthermia was induced in anesthetized rats by placement in a temperature-controlled water bath. Whole-body hyperthermia to a core temperature of 42-43 degrees C for 15 min was followed by passive cooling. We started the hyperthermic treatment 6 h before the vascular clamping. The severity of the mucosal injury was evaluated by several biochemical markers and histological findings. Hyperthermia-induced heat-shock proteins were detected by Western blotting. We also investigated the effect of zinc protoporphyrin IX (an HO-1 inhibitor) on the protective effect of hyperthermia.

RESULTS

The rats, which were killed after ischemia/reperfusion, had severe intestinal inflammation. Hyperthermia significantly induced the production of Hsp70 and HO-1 in intestinal mucosa and significantly reduced ischemia/reperfusion-induced mucosal injury. The combination of zinc protoporphyrin IX with hyperthermia extinguished the protective effects of hyperthermia on ischemia/reperfusion injury.

CONCLUSION

Hyperthermia protects against ischemia/reperfusion injury in rat small intestine through the expression of heat-shock proteins, especially HO-1.

Dynamic changes in expression of heme oxygenases in mouse heart and liver during hypoxia

Heme oxygenase cleaves heme to form biliverdin, carbon monoxide (CO), and iron, and consists of two structurally related isozymes, HO-1 and HO-2. HO-2 is also known as a potential oxygen sensor. Here we show that the relative CO content in arterial blood, which reflects the total amount of endogenous heme degradation, dynamically changes in mice during acclimatization to normobaric hypoxia (10% O2), with the two peaks at 1 day and 21 days of hypoxia. The expression levels of HO-1 and HO-2 proteins were decreased by 20% and 40%, respectively, in the mouse liver at 7 days of hypoxia, which returned to the basal levels at 14 days. On the other hand, HO-1 and HO-2 proteins were increased 2-fold and 1.3-fold, respectively, in the heart at 28 days of hypoxia. Thus, hypoxia induces or represses the expression of HO-1 and HO-2 in vivo, depending on cellular microenvironments.

A physiological model to study iron recycling in macrophages

Following erythrophagocytosis (EP) of senescent red blood cells (RBCs), heme iron is recycled to the plasma by tissue macrophages. This process is critical for mammalian iron homeostasis but remains elusive. We characterized a cellular model using artificially-aged murine RBCs and murine bone marrow-derived macrophages (BMDMs) and study mRNA and protein expression of HO-1, ferroportin and ferritin after EP. In vitro ageing of RBCs was obtained by raising intracellular calcium concentration. These RBCs exhibit several features of erythrocyte senescence including externalization of phosphatidyl-serine, specific binding and phagocytosis by BMDMs. During the first hours of EP, we observed a rapid increase of HO-1 and ferroportin mRNAs and proteins, whereas ferritin protein expression was progressively induced with no major changes in RNA levels. At later stages after EP, a different pattern of expression was observed with a net decrease of ferroportin, a sustained high level of HO-1, and a strong increase in ferritins. Taken together, these results suggest that after EP, iron is rapidly extracted from heme and exported by ferroportin. Surprisingly, the gene expression profile at late stages after EP, which is indicative of iron storage, is reminiscent of what is observed in inflammation. However, phagocytosis of artificially-aged red blood cells seems to repress the proinflammatory response of macrophages.

Early expression of heme oxygenase-1 in leukocytes correlates negatively with oxidative stress and predicts hepatic and renal dysfunction at late stage of sepsis

Oxidative stress triggered by septic insult may be the major cause of multiple organ dysfunction syndrome (MODS) in intensive unit care patients. The inducible form of heme oxygenase-1 (HO-1) can be induced by cytokines, lipopolysaccharide, and reactive oxygen species during sepsis. These facts raise the question of whether the expression of HO-1 in leukocytes can indicate the level of oxidative stress of multiple organs in sepsis. Clinical peritonitis was simulated in an animal model by cecal ligation and puncture (CLP). The level of oxidative stress was examined by plasma lipid peroxidation (LPO). Liver function was analyzed by plasma aspartate aminotransferase, alanine aminotransferase, total bilirubin, and direct bilirubin. Lung function was evaluated by severity of edema. Renal function was measured by blood urea nitrogen and creatinine. The correlation between early HO-1 induction and LPO level or organ functional indicators of the same rat at late sepsis was analyzed by linear regression. The results showed that the protein content of HO-1 increased at 9 h after CLP, whereas expression of HO-1 mRNA in leukocytes was significantly increased (P < 0.01) at 6 h after CLP. Plasma level of LPO and the indices of hepatic, pulmonary, and renal function were significantly increased at 18 h after CLP. Moreover, highly negative correlations were observed between HO-1 mRNA expression at 6 h after CLP and level of LPO or severity of hepatic/renal dysfunction at 18 h after CLP. These results suggest that early HO-1 mRNA expression in leukocytes may represent oxidative stress and may predict the severity of liver and renal dysfunction during sepsis.

Induction of heme oxygenase-1 in the donor reduces graft immunogenicity

There is increasing evidence that the induction of the enzyme heme oxygenase-1 (HO-1) improves both graft function and survival. Although it has been shown that HO-1 promotes graft protection, it remains unknown whether it reduces graft immunogenicity by modulating dendritic cells. In the current experiment, we investigated the impact of HO-1 induction on frequencies and trafficking of donor-derived dendritic cells (DCs). Kidneys from DA rats were transplanted into untreated Lewis recipients. Donor animals were treated with cobalt protoporphyrin (CoPP; 5 mg/kg IP) 24 hours prior to organ harvesting to induce HO-1. Controls remained untreated or received zinc protoporphyrin (ZnPP; 20 mg/kg, IP) to block HO-1 induction. Analyses of grafts, spleens, lymph nodes and blood of Lewis recipients were performed at days 1 and 3 posttransplantation. Donor-specific DCs were determined by flow cytometry using haplotype-specific mAb against RT1(ab) and mAb against OX62(+) antigens. Cell markers (CD4/CD8(+) T cells, ED1(+) monocytes, MHC class II(+) CD86(+) DC) were measured by immunohistochemical staining. T-cell alloreactivity of recipient splenocytes was measured by ELISPOT. Induction of HO-1 reduced frequencies of donor-derived DCs in the graft and recipient compartments, which was associated with reduced frequencies of CD4(+) T cells and CD8(+) T cells and alloreactivity. Expression of costimulatory molecule CD86 and MHC class II antigens were also reduced, although not significantly. Thus, induction of HO-1 reduced graft immunogenicity. These mechanisms may explain the protective effects of HO-1 induction.

Expression of allograft inflammatory factor-1 and haeme oxygenase-1 in brains of rats infected with the neurotropic Borna disease virus

Experimental infection of Lewis rats with Borna disease virus (BDV) causes an immune-mediated nonpurulent meningoencephalitis. Viral persistence in the central nervous system is accompanied by mononuclear infiltrates, activated monocytic/microglial cells and reactive astrocytes. The immune-mediated process was further characterized by expression analysis of allograft inflammatory factor-1 (AIF-1), a novel marker of monocyte/microglial activation and of glial fibrillary acid protein (GFAP) between day 3 and day 50 post infection (p.i.). Potential neuroprotective effects of these cells were studied by the induction of haeme oxygenase-1 (HO-1), a defensive molecule against oxidative stress in various brain insults. In BDV-infected rat brains, mononuclear infiltrates and AIF-1 expression increased up to day 28 p.i. During early time points p.i., AIF-1 expression was mainly found in inflammatory lesions and adjacent brain parenchyma. Already 24 days p.i., a widespread upregulation of AIF-1 was observed which declined only moderately beyond day 28 p.i. HO-1 induction was maximal between days 18 and 28 p.i. Increased amounts of GFAP-positive astrocytes were present beyond 24 days p.i. Viral antigen expression increased simultaneously to the inflammatory reaction and persisted up to 50 days p.i. Widespread upregulation of AIF-1 indicates an early, long-lasting microglial activation, which might be involved in the immunesurveillance of the immune-mediated inflammatory events. The early peak of HO-1 most likely represents a neuroprotective, anti-inflammatory response by invading monocytes, microglial cells and astrocytes during the formation of encephalitic lesions and acute viral replication.

A single-dose of cobalt-protoporphyrin protects islet beta cells from glucocorticoid suppression

This study examined whether treating donor mice with a single-dose of cobalt protoporphyrin (CoPP) could induce heme oxygenase-1 (HO-1) and thus protect islet cells from suppression by high-dose glucocorticoid. Islets were isolated from mice receiving either a single dose of CoPP (20 mg/kg body weight) (CoPP-islets) or isotonic sodium chloride solution (control islets) at 24 hours before isolation. Following incubation in the absence or presence of methylprednisolone (100 and 1000 ng/mL) for 24 hours, glucose-stimulated insulin secretion and insulin content of cultured islets were determined. Data were expressed as the mean +/- standard error. HO-1 protein level of CoPP-islets was significantly higher than that of normal islets at 12 hours (P < .005) and 30 hours (P < .05) but not at 56 hours after CoPP administration (P = NS). The expression of CPP-32, an apoptosis inducer, was significantly inhibited in CoPP-islets at 24 hours after CoPP administration. Compared to the control islets, CoPP-islets secreted significantly more insulin in response to glucose stimulation following 24-hour incubation with 100 and 1000 ng/mL of methylprednisolone (P < .05 and P < .05). The insulin content of both control and CoPP-islets did not differ significantly after 24-hour incubation with methylprednisolone. In conclusion, a single-dose treatment with cobalt-protoporphyrin for the induction of heme oxygenase-1 protects islets against the suppressive effect of methylprednisolone.

Sequential induction of heme oxygenase-1 and manganese superoxide dismutase protects cultured astrocytes against nitric oxide

Nitric oxide (NO) is a widely recognized mediator of physiological and pathophysiological signal transmission. In an attempt to better understand the molecular actions of NO in astrocytes, stress protein expression in response to NO donor sodium nitroprusside was investigated. Heme oxygenase-1 (HO-1) has been identified as an inducer of manganese superoxide dismutase (MnSOD), playing a cytoprotective role under the condition of nitrosative stress. We present evidence that the sequential induction of HO-1 and MnSOD protects astrocytes from NO toxicity: (1) both HO-1 and MnSOD expression were induced by NO; (2) NO-mediated increase in MnSOD activity was partly abolished by HO-1 inhibitor Zn(II) protoporphyrin IX (ZnPP); (3) pretreatment of astrocytes with a nontoxic dose of NO protected the cells against the later treatment with a toxic dose of NO; (4) inhibition of HO-1 by ZnPP sensitized astrocytes to the nontoxic dose of NO resulting in a marked cytotoxicity; and (5) adenovirus-mediated overexpression of MnSOD protected astrocytes from the NO toxicity. The molecular action of NO in astrocytes appears to be dose-dependent. While a high dose of NO exerts cytotoxicity leading to the tissue damage in the central nervous system, a low dose of NO may act as an important signaling molecule in astrocytes with concurrent induction of cytoprotective proteins such as HO-1 and MnSOD.

The nonthiazolidinedione PPARgamma agonist L-796,449 is neuroprotective in experimental stroke

Some agonists of the peroxisome proliferator-activated receptor gamma (PPARgamma) belonging to the thiazolidinedione (TZD) family, as well as the cyclopentenone prostaglandin 15-dPGJ2, have been shown to cause neuroprotection in animal models of stroke. We have tested whether the TZD-unrelated PPARgamma agonist L-796,449 is neuroprotective after permanent middle cerebral artery occlusion (MCAO) in the rat brain. Our results show that L-796,449 decreases MCAO-induced infarct size and improves neurologic scores. This protection is concomitant to inhibition of MCAO-induced brain expression of inducible NO synthase (iNOS) and the matrix metalloproteinase MMP-9 and to upregulation of the cytoprotective stress protein heme oxygenase-1 (HO-1). Analysis of the NF-kappaB p65 monomer and the NF-kappaB inhibitor IkappaBalpha protein levels as well as gel mobility shift assays indicate that L-796,449 inhibits NF-kappaB signaling, and that it may be recruiting both PPARgamma-dependent and independent pathways. In summary, our results provide new insights for stroke treatment.