Heme Oxygenase System Research Articles

Chronic Migraineurs Form Carboxyhemefibrinogen and Iron-Bound Fibrinogen.

Chronic migraine (CM) is a disabling painful condition that is associated with dementia and thrombotic disease. It has been proposed that carbon monoxide (CO) and iron may play a role in CM, and CO and iron are products of the heme oxygenase system which is widespread within the brain. Further, CO and iron enhance plasmatic coagulation in part via a fibrinogen-dependent mechanism. Thus, our goal was to determine whether patients with CM had experienced carboxyhemefibrinogen formation, iron bound fibrinogen formation and plasmatic hypercoagulability. Nonsmokers with CM were recruited after informed, written consent. Blood was collected, anticoagulated with sodium citrate, and then centrifuged with plasma stored at -80ºC. Carboxyhemefibrinogen formation, iron bound fibrinogen formation and coagulation kinetics were determined via thrombelastographic methods. Patient results were compared with laboratory values generated from normal control plasmas. Incidence (95% confidence intervals) of the various parameters was determined using the Clopper-Pearson method. Twenty-six CM patients (24 female) were recruited; they were 46±12 years old. With regard to fibrinogen modification, 88.5% (69.8%-97.6%) of CM patients had formation of carboxyhemefibrinogen, iron bound fibrinogen, or both. With regard to coagulation, 42.3% (23.4%-63.1%) of patients had abnormally decreased time to clot initiation, 80.8% (60.6%-93.4%) had abnormally large velocity of clot formation, and 46.2% (26.6%-66.7%) had abnormally strong clot strength. Patients with CM have a large incidence of carboxyhemefibrinogen and iron bound fibrinogen formation and hypercoagulability. Confirmatory and potential therapeutic clinical trials targeting CO and iron modified hypercoagulation as a source of pain and vascular disease in CM patients are indicated.

Cytoprotective responses in HaCaT keratinocytes exposed to high doses of curcumin

Wound healing is a complex process that involves the well-coordinated interactions of different cell types. Topical application of high doses of curcumin, a plant-derived polyphenol, enhances both normal and diabetic cutaneous wound healing in rodents. For optimal tissue repair interactions between epidermal keratinocytes and dermal fibroblasts are essential. We previously demonstrated that curcumin increased reactive oxygen species (ROS) formation and apoptosis in dermal fibroblasts, which could be prevented by pre-induction of the cytoprotective enzyme heme oxygenase (HO)-1. To better understand the effects of curcumin on wound repair, we now assessed the effects of high doses of curcumin on the survival of HaCaT keratinocytes and the role of the HO system. We exposed HaCaT keratinocytes to curcumin in the presence or absence of the HO-1 inducers heme (FePP) and cobalt protoporphyrin (CoPP). We then assessed cell survival, ROS formation, and caspase activation. Curcumin induced caspase-dependent apoptosis in HaCaT keratinocytes via a ROS-dependent mechanism. Both FePP and CoPP induced HO-1 expression, but only FePP protected against curcumin-induced ROS formation and caspase-mediated apoptosis. In the presence of curcumin, FePP but not CoPP induced the expression of the iron scavenger ferritin. Together, our data show that the induction of ferritin, but not HO, protects HaCaT keratinocytes against cytotoxic doses of curcumin. The differential response of fibroblasts and keratinocytes to high curcumin doses may provide the basis for improving curcumin-based wound healing therapies.

Induction and functional significance of the heme oxygenase system in pathological shear stress in vivo.

The present study examined the heme oxygenase (HO) system in an in vivo murine model of pathological shear stress induced by partial carotid artery ligation. In this model, along with upregulation of vasculopathic genes, HO-1 is induced in the endothelium and adventitia, whereas HO-2 is mainly upregulated in the endothelium. Within minutes of ligation, NF-κB, a transcription factor that upregulates vasculopathic genes and HO-1, is activated. Failure to express either HO-1 or HO-2 exaggerates the reduction in carotid blood flow and exacerbates vascular injury. After artery ligation, comparable induction of HO-2 occurred in HO-1(+/+) and HO-1(-/-) mice, whereas HO-1 induction was exaggerated in HO-2(-/-) mice compared with HO-2(+/+) mice. Upregulation of HO-1 by an adeno-associated viral vector increased vascular HO-1 expression and HO activity and augmented blood flow in both ligated and contralateral carotid arteries. Acute inhibition of HO activity decreased flow in the ligated carotid artery, whereas a product of HO, carbon monoxide (CO), delivered by CO-releasing molecule-3, increased carotid blood flow. In conclusion, in the partial carotid artery ligation model of pathological shear stress, this study provides the first demonstration of 1) upregulation and vasoprotective effects of HO-1 and HO-2 and the vasorelaxant effects of CO as well as 2) vascular upregulation of HO-1 in vivo by an adeno-associated viral vector that is attended by a salutary vascular response. Induction of HO-1 may reside in NF-κB activation, and, along with induced HO-2, such upregulation of HO-1 provides a countervailing vasoprotective response in pathological shear stress in vivo.

The ameliorative effect of Heme Oxygenase System on early Diabetic Nephropathy in Streptozotocin-Induced Diabetic Rats

The ameliorative effect of Heme Oxygenase System on early Diabetic Nephropathy in Streptozotocin-Induced Diabetic Rats

Involvement of the heme oxygenase system in the development of preeclampsia and as a possible therapeutic target.

The enzyme heme oxygenase (HO) is an important regulatory molecule present in most nucleated mammalian cells which functions to break down the pro-oxidant molecule heme into three products, carbon monoxide (CO), biliverdin and free iron. The HO system has been associated with many physiologic functions, including vascular tone, regulation of inflammation and apoptosis, angiogenesis and antioxidant capabilities. Deficiencies in HO are associated with several pregnancy disorders, including preeclampsia. With no present cure, this disorder continues to affect 5-7% of all pregnancies worldwide, leading to maternal and fetal morbidity and mortality. Researchers continue to strive for therapeutic potentials and this review will outline the possible use of the HO/CO system as a target treatment/prevention of preeclampsia in the future.

Some mechanisms of the protective effect of ischemic preconditioning on rat liver ischemia-reperfusion injury.

Ischemia-reperfusion (I/R) injury is a multifactorial process that affects graft function after liver transplantation. An understanding of the mechanisms involved in I/R injury is essential for the design of therapeutic strategies to improve the outcome of liver transplantation. The generation of reactive oxygen species subsequent to reoxygenation inflicts tissue damage and initiates a cascade of deleterious cellular responses, leading to inflammation, cell death, and ultimate organ failure. Increasing experimental evidence has suggested that Kupffer cells and T-cells mediate activation of neutrophil inflammatory responses. Activated neutrophils infiltrate the injured liver in parallel with increased expression of adhesion molecules on endothelial cells. The heme oxygenase system is among the most critical of the cytoprotective mechanisms activated during cellular stress, exerting antioxidant and anti-inflammatory functions, modulating the cell cycle, and maintaining the microcirculation. Finally, the activation of toll-like receptors on Kupffer cells may play a fundamental role in exploring new therapeutic strategies based on the concept that hepatic I/R injury represents a case for host “innate” immunity. In the present study, there was a significant decrease in hepatic activity of glycogen in the I/R group as compared with corresponding values in the control group. On the other hand, there was a significant increase in the hepatic activity of glycogen in the I/R-IP (ischemic preconditioning) group as compared with corresponding values in the I/R group.

Gastroprotective effect of orexin-A and heme oxygenase system

BackgroundOrexin-A, besides playing an important role in the mechanism of food intake, exhibits a potent gastroprotective action against the formation of acute gastric mucosal injury. The aim of the present study was to determine the effect of administered orexin-A against ischemia–reperfusion (I/R)-induced gastric injury on the expression of heme oxygenase (HO)-1 and HO-2 in gastric tissue. Materials and methodsWistar rats were subjected to 30 min of ischemia followed by 3 h reperfusion. Orexin-A was infused at a dose of 500 pmol/kg/min during the I/R period. The lesion area was measured by stereomicroscope. The myeloperoxidase activity and 4-hydroxinonenol-malondialdehyde content of gastric mucosa were evaluated spectrophotometrically, and the gastric tumor necrosis factor-α was measured by enzyme linked immune sorbent assay. The expression of HO-1 and HO-2 was determined by Western blotting analysis. ResultsOrexin-A significantly decreased the I/R-induced gastric lesions, myeloperoxidase activity, and 4-hydroxinonenol-malondialdehyde concentration in gastric tissue exposed to I/R. The gastroprotective effect of orexin-A in gastric I/R model was accompanied by the increase in HO-2 expression and the decrease in HO-1 expression. ConclusionsOrexin-A exerts a protective action on gastric mucosa subjected to I/R, and this effect is associated with the reduction of neutrophil infiltration and lipid peroxidation in gastric tissue in addition to the increase in HO-2 expression due to the administration of orexin-A.

The Role of the Heme Oxygenase System in the Metabolic Syndrome

Molecular chaperones and the heat shock response play a major role in the maintenance of cellular homeostasis under various pathological conditions. In particular, their role is to regulate protein conformation, protect proteins from misfolding and aggregation, and maintain signalling and organellarnetworks. Among variousheat shock proteins, Hsp32 also known as heme oxygenase-1 (HO-1), has demonstrated an important role in metabolic syndrome. In particular, the HO system seems to play a major role in the complex pathophysiological cascade involved in insulin resistance mechanisms, and adipocyte functions as measured by the release of important adipokynes. The aim of the present review is to point out the role of HO-1 in metabolic syndrome, and how to exploit its beneficial effects as a therapeutic strategy to prevent complicationsof andto improve insulin sensitivity.

Structural insights into heme oxygenase-1 inhibition by azole-based compounds

The development of heme oxygenase (HO) inhibitors, especially those that are isozyme-selective, promises powerful pharmacological tools to elucidate the regulatory characteristics of the HO system. HO is known to have cytoprotective properties with a role in several disease states; thus, it is an enticing therapeutic target. Traditionally, given their structural similarity with heme, the metalloporphyrins have been used as competitive HO inhibitors. However, given heme's important role in several other proteins (e.g. cytochromes P450, nitric oxide synthase), nonselectivity is an unfortunate side-effect. Reports that azalanstat and other non-porphyrin molecules inhibited HO led to a multi-faceted effort to develop novel compounds as potent, selective inhibitors of HO. This resulted in the creation of non-competitive HO-selective inhibitors, including a subset with isozyme selectivity for HO-1. Using X-ray crystallography, the structures of several complexes of HO-1 with novel inhibitors have been elucidated, providing insightful information regarding the salient features required for inhibitor binding. This included the structural basis for non-competitive inhibition, flexibility and adaptability of the inhibitor binding pocket, and multiple, potential interaction subsites, all of which can be exploited in future drug-design strategies. The structures revealed a common binding mode, despite different structural fragments, with the flexibility to accommodate bulkier substituents via "induced fit". Compounds bind to the distal side of heme through an azole ``anchor" which coordinates with the heme iron. Expansion of the distal pocket, mainly due to distal helix flexibility, allows accommodation of the compounds, with a distal hydrophobic pocket providing further stabilization yet without displacing heme or the critical Asp140 residue. Rather, binding displaces a catalytically critical water molecule and disrupts an ordered hydrogen-bond network involving Asp140.

The heme oxygenases: important regulators of pregnancy and preeclampsia.

The heme oxygenase system has long been believed to act largely as a housekeeping unit, converting prooxidant free heme from heme protein degradation into the benign bilirubin for conjugation and safe excretion. In recent decades, however, heme oxygenases have emerged as important regulators of cardiovascular function, largely through the production of their biologically active metabolites: carbon monoxide, bilirubin, and elemental iron. Even more recently, a number of separate lines of evidence have demonstrated an important role for the heme oxygenases in the establishment and maintenance of pregnancy. Early preclinical and clinical studies have associated defects in the heme oxygenase with the obstetrical complication preeclampsia, as well as failure to establish adequate placental blood flow, an underlying mechanism of the disorder. Several recent preclinical studies have suggested, however, that the heme oxygenase system could serve as a valuable therapeutic tool for the management of preeclampsia, which currently has few pharmacological options. This review will summarize the role of heme oxygenases in pregnancy and highlight their potential in advancing the management of patients with preeclampsia.

Correlation Between Lipid Profile and Heme Oxygenase System in Patients With Benign Prostatic Hyperplasia

To investigate the role of heme oxygenase (HO) system in moderate to severe benign prostatic hyperplasia and lower urinary tract symptom patients and the influence of metabolic syndrome (MetS) components on HO-1 or HO-2 prostatic levels. One hundred thirty-two consecutive patients who underwent transurethral resection of the prostate were prospectively enrolled. MetS was defined by the International Diabetes Federation. Patients were divided in 2 groups: group A (high-density lipoprotein-cholesterol [HDL-C]≥40 mg/dL and triglycerides<150 mg/dL) and group B (HDL-C<40 mg/dL and triglycerides≥150 mg/dL). Surgical specimens were collected for HO level determination. HO-1 levels were determined by enzyme-linked immunosorbent assay and HO-1 levels by Western blotting. Patients with MetS showed lower levels of HO-1 (5.29 vs 6.28 ng/mL; P=.04), HO-2 (1.01 vs 1.83 ng/mL; P=.04), phosphorylated activated protein kinase (pAMPK; 0.62 vs 1.11 AUI; P<.01), and HO-activity (61.43 vs 70.22 AUI; P<.01) with respect to normal. The Pearson correlation analysis showed that HO-1, HO-2, and HO activity were negatively associated with waist circumference (P<.05), body mass index (P<.05), triglycerides (P<.05) and positively with HDL-C (P<.05). Group B showed lower levels of HO-1 (4.7 vs 6.6 ng/mL; P<.05), HO-2 (1.4 vs 0.4 ng/mL; P=.03), HO-activity (69.63 vs 58.42 AUI; P=.04), and higher International Prostate Symptoms Score (21.4 vs 25.0; P<.05) with respect to group A. The enzyme-linked immunosorbent assay showed that HO-1 and HO activity levels were significantly lower in group B compared with group A. Reduced HDL-C and elevated triglyceride levels decreased HO-1 expression in the prostate tissue. Western blot analysis of tissue samples showed significant differences in basal protein expression levels of HO-2 and pAMPK in group B compared with group A. Alteration of serum triglycerides and HDL-C significantly impairs HO-1 and HO-2 levels in benign prostatic hyperplasia patients.

Heme oxygenase suppresses markers of heart failure and ameliorates cardiomyopathy in L-NAME-induced hypertension

Heart failure and related cardiac complications remains a great health challenge. We investigated the effects of upregulating heme-oxygenase (HO) on myocardial histo-pathological lesions, proinflammatory cytokines/chemokines, oxidative mediators and important markers of heart failure such as osteopontin and osteoprotergerin in Nω-nitro-l-arginine methyl ester (L-NAME)-induced hypertension. Treatment with the HO-inducer, heme-arginate improved myocardial morphology in L-NAME hypertensive rats by attenuating subendocardial injury, interstitial fibrosis, mononuclear-cell infiltration and cardiomyocyte hypertrophy. These were associated with the reduction of several inflammatory/oxidative mediators including chemokines/cytokines such as macrophage inflammatory protein-1 alpha (MIP-1α), macrophage chemoattractant protein-1 (MCP-1), tumor necrosis factor alpha (TNF-α), interleukin (IL)-6, IL-1β, endothelin-1, 8-isoprostane, nitrotyrosine, and aldosterone. Similarly, heme-arginate abated the elevated levels of extracellular matrix/remodeling proteins including transforming-growth factor beta (TGF-β1) and collagen-IV in the myocardium. These were accompanied by significant reduction of proteins of heart failure such as osteopontin and osteoprotegerin. Interestingly, the cardio-protective effects of heme-arginate were associated with the potentiation of adiponectin, atrial-natriuretic peptide (ANP), HO-1, HO-activity, cyclic gnanosine monophosphate (cGMP) and the total-anti-oxidant capacity, whereas the HO-inhibitor, chromium-mesoporphyrin nullified the effects of heme-arginate, exacerbating inflammatory injury and oxidative insults. We conclude that heme-arginate therapy protects myocardial damage by potentiating the HO-adiponectin-ANP axis, which in turn suppressed the elevated levels of aldosterone, pro-inflammatory chemokines/cytokines, mononuclear-cell infiltration and oxidative stress, with concomitant reduction of extracellular matrix/remodeling proteins and heart failure proteins. These data suggest a cardio-protective role of the HO system against L-NAME-induced hypertension that could be explored in the design of novel strategies against cardiomyopathy.

Heme Oxygenase System and Hypertension: A Comprehensive Insight

Hypertension is a complex interplay of interrelated etiologies, and the leading risk factor for many cardiovascular morbidity and mortality worldwide. Cardinal pathophysiological features of hypertension include enhanced vascular inflammation, vascular remodeling, vascular contractility and increased oxidative stress. In response to oxidative, inflammatory or other noxious stimuli, many physiological pathways like the heme oxygenase (HO) system are activated in an attempt to counteract tissue insults. However, the pathophysiological activation of the HO system only results to a transient increase of HO activity that fall below the necessary threshold capable of activating the downstream signaling components of the HO system like the soluble guanylyl cyclase (sGC)/cyclic guanosine monophosphate (cGMP) secondary messenger system. Therefore, a more robust potentiation of the HO system by pharmacological agents such as hemin, heme-arginate, cobalt protoporphyrin or through retroviral HO-1 gene delivery would be needed to surmount the threshold for cytoprotection. The HO system modulates cellular homeostasis. Importantly, the HO system plays a vital role in a wide spectrum of physiologic including the regulation of blood vessel tone. Alterations in the activity and expression of HO has been correlated to pathophysiology of hypertension and related complications such as hypertrophy, myocardial infarction and heart failure. Moreover, the cytoprotection exerted by HO is attributable to its catabolic products namely, carbon monoxide, bilirubin/biliverdin, and ferritin that are known to modulate immune, inflammatory and oxidative insults. The growing incidence of hypertension and associated cardiometabolic complications has prompted the need for the exploration of alternative therapeutic strategies like substances capable of potentiating the HO system. This review briefly, highlights the functional significance of the HO system and its downstream signaling molecules including bilirubin/biliverdin, carbon monoxide and ferritin as potential therapeutic modalities for the management of hypertension and its related co-morbid conditions.

A Critical and Comprehensive Insight on Heme Oxygenase and Related Products Including Carbon Monoxide, Bilirubin, Biliverdin and Ferritin in Type-1 and Type-2 Diabetes

The increased prevalence of diabetes and associated complications presents a major health risk worldwide, and requires an efficient management protocol. Type-1 and type-2 diabetes have several common pathophysiological denominators including hyperglycemia, elevated oxidative stress, increased inflammation and apoptosis. These pathological factors are implicated in the progression and worsening of the disease, and the related cardiometabolic complications associated with it. Despite the advancement in management of type-1 and type-2 diabetes, the high incidence of diabetes and related complications calls for novel therapeutic strategies. Recent findings suggest that the pharmacological modulation of the microsomal heme oxygenase (HO) system may be an important therapeutic avenue to explore. The HO system and related products such as carbon monoxide, bilirubin, biliverdin, biliverdin reductase and ferritin have been shown to abate inflammation, oxidative stress, and apoptosis and reduce hyperglycemia. In addition, the HO system also enhances insulin sensitivity and increase pancreatic beta cell insulin production in experimental models of type-1 and type-2 diabetes. This review is an effort to provide evidence of the regulatory and cytoprotective role of the HO system in type-1 and type-2 diabetes, and will highlight the multifaceted mechanisms implicated in the anti-diabetic effects of the HO system.

The Heme Oxygenase System and Type-1 Diabetes

Diabetes is a complex endocrine/metabolic disease with many related complications including micro-vascular and macrovascular problems such as cardiomyopathy, nephropathy, neuropathy and retinopathy. Generally, type-1 diabetes is caused by autoimmune- mediated destruction of pancreatic beta cells leading to insulin deficiency. This is usually accompanied by dyslipidemia, enhanced hyperglycemia-mediated oxidative stress, endothelial-cell dysfunction and apoptosis. For decades, type-1 diabetes has been traditionally known as insulin-dependent, while type-2 as non-insulin dependent diabetes. However, it is becoming increasingly clear that insulin deficiency and insulin resistance are manifested in both forms of diabetes at different stages. Thus, it may be time revisit the nomenclature and adjust it to reflect these observations of insulin deficiency and insulin resistance in both forms of diabetes to avoid ambiguity when discussing forms of diabetes. Emerging evidence indicates that the heme-oxygenase (HO) system and related products including carbon monoxide, ferritin and biliverdin are capable of suppressing immune/inflammatory response, and abate oxidative stress and apoptosis. More importantly, upregulating the HO-system increases pancreatic beta-cell insulin release and reduce hyperglycemia in different diabetic models. Similarly, carbon monoxide, a product of the HO-catalyzed degradation of heme also enhances insulin production and improves glucose metabolism. Since excessive immune/inflammatory responses coupled to elevated apoptosis are among the cardinal pathophysiological features of type-1 diabetes, this review highlights the role of the HO-system and related products such as carbon monoxide and bilirubin in the modulation of apoptosis and immune response, and the beneficial effects of the HO-system in the pathogenesis of type-1 diabetes and related cardiometabolic complications.

The Heme Oxygenase System Selectively Modulates Proteins Implicated in Metabolism, Oxidative Stress and Inflammation in Spontaneously Hypertensive Rats

Although recent studies have underscored the role of the heme-oxygenase (HO) inducer hemin, on insulin-signaling and glucose metabolism, the underlying mechanisms are not completely understood. In this study, two-dimensional-gel electrophoresis, massspectrometry and MSACOT-analyses were used to identify and characterize novel proteins modulated by hemin in spontaneoushypertensive rat (SHR), a model of essential hypertension with insulin resistance/impaired glucose metabolism. In addition, the effects of hemin on endothelin-1 (ET-1), protein-tyrosine-phosphatase-1B (PTP-1B), atrial-natriuretic-peptide (ANP) and its surrogate-marker urinary cGMP, and inflammatory cytokines including TNF-α, IL-6 and IL-1β were investigated. In hemin-treated SHR, several proteins related to oxidative-stress and metabolism were modulated. Particularly, hemin enhanced aldolase- B, fumarylacetoacetate hydrolase, purine-nucleoside phosphorylase, adenosine-kinase, argininosuccinate synthetase and carbonic anhydrase-3 all of which are enzymes involved in glucose/energy metabolism and pH homeostasis. Similarly, hemin potentiated antioxidant pathways including, NADP(+)-dependant isocitrate-dehydrogenase, catalase, glutathione-S-transferase-Yb1 and hsp70, a pleiotropic agent that regulates protein-folding, oxidative/pro-inflammatory events. Hemin also increased enzymes implicated in cell-growth such as the nitrilase-protein-family, but reduced betaine-homocysteine methyltransferase, an enzyme associated with insulin resistance and dysfunctional glucose metabolism. Furthermore, hemin increased ANP and its surrogate marker, urinary cGMP, but reduced ET-1, PTP-1B, TNF-α, IL-6, IL-1β, whereas the HO-inhibitor, chromium-mesoporphyrin abolished the effects. The potentiation of ANP, urinary-cGMP, aldolade-B, fumarylacetoacetate hydrolase, purine-nucleoside phosphorylase, adenosine-kinase, argininosuccinate synthetase, carbonic anhydrase-3, hsp70 and the corresponding reduction of betaine-homocysteine methyltransferase, PTP-1B, TNF-α, IL-6, IL-1β, and ET-1 may be responsible for the improved glucose metabolism in hemin-treated animals. Collectively, these findings underscore the pleiotropic effects of the HO-system in cellular homeostasis with important roles in metabolism and defence.

The heme oxygenase system suppresses perirenal visceral adiposity, abates renal inflammation and ameliorates diabetic nephropathy in Zucker diabetic fatty rats.

The growing incidence of chronic kidney disease remains a global health problem. Obesity is a major risk factor for type-2 diabetes and renal impairment. Perirenal adiposity, by virtue of its anatomical proximity to the kidneys may cause kidney disease through paracrine mechanisms that include increased production of inflammatory cytokines. Although heme-oxygenase (HO) is cytoprotective, its effects on perirenal adiposity and diabetic nephropathy in Zucker-diabetic fatty rats (ZDFs) remains largely unclear. Upregulating the HO-system with hemin normalised glycemia, reduced perirenal adiposity and suppressed several pro-inflammatory/oxidative mediators in perirenal fat including macrophage-inflammatory-protein-1α (MIP-1α), endothelin (ET-1), 8-isoprostane, TNF-α, IL-6 and IL-1β. Furthermore, hemin reduced ED1, a marker of pro-inflammatory macrophage-M1-phenotype, but interestingly, enhanced markers associated with anti-inflammatory M2-phenotype such as ED2, CD206 and IL-10, suggesting that hemin selectively modulates macrophage polarization towards the anti-inflammatory M2-phenotype. These effects were accompanied by increased adiponectin, HO-1, HO-activity, atrial-natriuretic peptide (ANP), and its surrogate marker, urinary-cGMP. Furthermore, hemin reduced renal histological lesions and abated pro-fibrotic/extracellular-matrix proteins like collagen and fibronectin that deplete nephrin, an important transmembrane protein which forms the scaffolding of the podocyte slit-diaphragm allowing ions to filter but not massive excretion of proteins, hence proteinuria. Correspondingly, hemin increased nephrin expression in ZDFs, reduced markers of renal damage including, albuminuria/proteinuria, but increased creatinine-clearance, suggesting improved renal function. Conversely, the HO-blocker, stannous-mesoporphyrin nullified the hemin effects, aggravating glucose metabolism, and exacerbating renal injury and function. The hemin effects were less-pronounced in Zucker-lean controls with healthy status, suggesting greater selectivity of HO in ZDFs with disease. We conclude that the concomitant reduction of pro-inflammatory/oxidative mediators, macrophage infiltration and profibrotic/extracellular-matrix proteins, coupled to increased nephrin, adiponectin, ANP, cGMP and creatinine clearance may account for improved renal function in hemin-treated ZDFs. These findings suggest that HO-inducers like hemin may be explored against the co-morbidity of perirenal adiposity and diabetic nephropathy.

A review on hemeoxygenase-2: focus on cellular protection and oxygen response.

Hemeoxygenase (HO) system is responsible for cellular heme degradation to biliverdin, iron, and carbon monoxide. Two isoforms have been reported to date. Homologous HO-1 and HO-2 are microsomal proteins with more than 45% residue identity, share a similar fold and catalyze the same reaction. However, important differences between isoforms also exist. HO-1 isoform has been extensively studied mainly by its ability to respond to cellular stresses such as hemin, nitric oxide donors, oxidative damage, hypoxia, hyperthermia, and heavy metals, between others. On the contrary, due to its apparently constitutive nature, HO-2 has been less studied. Nevertheless, its abundance in tissues such as testis, endothelial cells, and particularly in brain, has pointed the relevance of HO-2 function. HO-2 presents particular characteristics that made it a unique protein in the HO system. Since attractive results on HO-2 have been arisen in later years, we focused this review in the second isoform. We summarize information on gene description, protein structure, and catalytic activity of HO-2 and particular facts such as its cellular impact and activity regulation. Finally, we call attention on the role of HO-2 in oxygen sensing, discussing proposed hypothesis on heme binding motifs and redox/thiol switches that participate in oxygen sensing as well as evidences of HO-2 response to hypoxia.

The heme oxygenase system rescues hepatic deterioration in the condition of obesity co-morbid with type-2 diabetes.

The prevalence of non-alcoholic fatty-liver disease (NAFLD) is increasing globally. NAFLD is a spectrum of related liver diseases that progressive from simple steatosis to serious complications like cirrhosis. The major pathophysiological driving of NAFLD includes elevated hepatic adiposity, increased hepatic triglycerides/cholesterol, excessive hepatic inflammation, and hepatocyte ballooning injury is a common histo-pathological denominator. Although heme-oxygenase (HO) is cytoprotective, its effects on hepatocyte ballooning injury have not been reported. We investigated the effects of upregulating HO with hemin or inhibiting it with stannous-mesoporphyrin (SnMP) on hepatocyte ballooning injury, hepatic adiposity and inflammation in Zucker-diabetic-fatty rats (ZDFs), an obese type-2-diabetic model. Hemin administration to ZDFs abated hepatic/plasma triglycerides and cholesterol, and suppressed several pro-inflammatory cytokines and chemokines including, TNF-α, IL-6, IL-1β, macrophage-inflammatory-protein-1α (MIP-1α) and macrophage-chemoattractant-protein-1 (MCP-1), with corresponding reduction of the pro-inflammatory M1-phenotype marker, ED1 and hepatic macrophage infiltration. Correspondingly, hemin concomitantly potentiated the protein expression of several markers of the anti-inflammatory macrophage-M2-phenotype including ED2, IL-10 and CD-206, alongside components of the HO-system including HO-1, HO-activity and cGMP, whereas the HO-inhibitor, SnMP abolished the effects. Furthermore, hemin attenuated liver histo-pathological lesions like hepatocyte ballooning injury and fibrosis, and reduced extracellular-matrix/profibrotic proteins implicated in liver injury such as osteopontin, TGF-β1, fibronectin and collagen-IV. We conclude that hemin restore hepatic morphology by abating hepatic adiposity, suppressing macrophage infiltration, inflammation and fibrosis. The selective enhancement of anti-inflammatory macrophage-M2-phenotype with parallel reduction of pro-inflammatory macrophage-M1-phenotype and related chemokines/cytokines like TNF-α, IL-6, IL-1β, MIP-1α and MCP-1 are among the multifaceted mechanisms by which hemin restore hepatic morphology.

A Focus on Heme Oxygenase-1 (HO-1) Inhibitors

The aim of this review is to highlight the advances in the field of heme oxygenase-1 (HO-1) inhibitors over the past years, particularly from a medicinal chemistry point of view; progresses made in the field strongly helped to clarify physiological roles of the heme oxygenase (HO) system. HO is a family of ubiquitously expressed enzymes which regulate the regiospecific catabolism of heme leading to the formation of equimolar amounts of carbon monoxide (CO), ferrous iron (Fe⁺⁺), and biliverdin. HO exists in two distinct, catalytically active isoforms: HO-1 and HO-2. HO-1 is an inducible 32-kDa protein, while HO-2 is a constitutively synthesized 36-kDa protein and generally is unresponsive to any of the inducers of HO-1. A third isoform, HO-3, is still an elusive protein. The HO system, along with its catabolism products, is involved in a variety of crucial physiological functions, including cytoprotection, inflammation, anti-oxidative effects, apoptosis, neuro-modulation, immune-modulation, angiogenesis, and vascular regulation. The use of selective HO inhibitors is a very important tool to clarify the role of the HO system and the mechanisms underlying its physiological effects and pathological involvement; due to the inducible nature of HO-1, selective inhibition of HO-1 isoform is generally preferable. Notably, HO-1 inhibitors may be also beneficial in therapeutic applications and have been mainly studied for treatment of hyperbilirubinemia and certain types of cancer. Historically, the first molecules used as non selective HO-1 inhibitors were metalloporphyrins (Mps). The subsequent development of the imidazole-dioxolane derivatives afforded the first generation of non-porphyrin based, isozyme selective HO-1 inhibitors.