Pharmacological and clinical aspects of heme oxygenase

Dimethoxycurcumin, a Synthetic Curcumin Analogue, Induces Heme Oxygenase-1 Expression through Nrf2 Activation in RAW264.7 Macrophages

Curcumin [1,7-bis(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione] induces heme oxygenase-1 (HO-1) expression via activation of the nuclear factor-erythroid-2-related factor 2 (Nrf2), whereas tetrahydrocurcumin [1,7-bis(4-hydroxy-3-methoxyphenyl)-3,5-heptanedione], one of curcumin in vivo metabolites, has no effect on HO-1 expression and Nrf2 activation. The aim of this study was to investigate whether dimethoxycurcumin [1,7-bis(4,3-dimethoxyphenyl)-1,6-heptadiene-3,5-dione], a synthetic curcumin analogue with higher metabolic stability over curcumin, could induce HO-1 expression to the same extent as curcumin in RAW264.7 macrophages. Dimethoxycurcumin and curcumin, but not tetrahydrocurcumin, induced HO-1 expression and Nrf2 nuclear translocation, suggesting that the unsaturated nature of the diarylheptanoid chain of the compounds are crucial for HO-1 expression and Nrf2 activation. Blockage of Nrf2 synthesis by small interfering RNA abolished HO-1 expression by dimethoxycurcumin, indicating that dimethoxycurcumin may induce HO-1 expression via Nrf2 activation. In comparison, dimethoxycurcumin and curcumin had about the same effect on HO-1 expression, suggesting that dimethoxycurcumin retains the HO-1-inducing activity of its parent compound curcumin in RAW264.7 macrophages.

Upregulation of heme oxygenase-1 combined with increased adiponectin lowers blood pressure in diabetic spontaneously hypertensive rats through a reduction in endothelial cell dysfunction, apoptosis and oxidative stress

This study was designed to investigate the effect of increased levels of HO-1 on hypertension exacerbated by diabetes. Diabetic spontaneously hypertensive rat (SHR) and WKY (control) animals were treated with streptozotocin (STZ) to induce diabetes and stannous chloride (SnCl₂) to upregulate HO-1. Treatment with SnCl₂ not only attenuated the increase of blood pressure (p<0.01), but also increased HO-1 protein content, HO activity and plasma adiponectin levels, decreased the levels of superoxide and 3-nitrotyrosine (NT), respectively. Reduction in oxidative stress resulted in the increased expression of Bcl-2 and AKT with a concomitant reduction in circulating endothelial cells (CEC) in the peripheral blood (p<0.005) and an improvement of femoral reactivity (response to acetylcholine). Thus induction of HO-1 accompanied with increased plasma adiponectin levels in diabetic hypertensive rats alters the phenotype through a reduction in oxidative stress, thereby permitting endothelial cells to maintain an anti-apoptotic environment and the restoration of endothelial responses thus preventing hypertension.

Heme oxygenase-1 induction prevents neuronal damage triggered during mitochondrial inhibition: role of CO and bilirubin

Heme oxygenase (HO) catalyzes the breakdown of heme to iron, carbon monoxide (CO), and biliverdin, the latter being further reduced to bilirubin (BR). A protective role of the inducible isoform, HO-1, has been described in pathological conditions associated with reactive oxygen species (ROS) and oxidative damage. The aim of this study was to investigate the role of HO-1 in the neurotoxicity induced by the mitochondrial toxin 3-nitropropionic acid (3-NP) in primary cultures of cerebellar granule neurons (CGNs). Toxicity of 3-NP is associated with ROS production, and this metabolic toxin has been used to mimic pathological conditions such as Huntington's disease. We found that cell death caused by 3-NP exposure was exacerbated by inhibition of HO with tin mesoporphyrin (SnMP). In addition, HO-1 up-regulation induced by the exposure to cobalt protoporphyrin (CoPP) before the incubation with 3-NP, prevented the cell death and the increase in ROS induced by 3-NP. Interestingly, addition of SnMP to CoPP-pretreated CGNs exposed to 3-NP, abolished the protective effect of CoPP suggesting that HO activity was responsible for this protective effect. This was additionally supported by the fact that CORM-2, a CO-releasing molecule, and BR, were able to protect against cell death and the increase in ROS induced by 3-NP. Our data clearly show that HO-1 elicits in CGNs a neuroprotective action against the neurotoxicity of 3-NP and that CO and BR may be involved, at least in part, in this protective effect. The present results increase our knowledge about the role of HO-1 in neuropathological conditions.

Induction of heme oxygenase-1 is a beneficial response in a murine model of venous thrombosis

The induction of heme oxygenase-1 (HO-1) may protect against tissue injury. The present study examines the induction of HO-1 in a murine model of venous thrombosis and explores the downstream consequences of this induction. In a model of stasis-induced thrombosis created by ligation of the inferior vena cava, HO-1 expression is markedly induced. Such expression occurs primarily in smooth muscle cells in the venous wall and in leukocytes infiltrating the venous wall and clot. To determine the significance of HO-1 induction in venous thrombosis, this model was imposed in HO-1(+/+) and HO-1(-/-) mice. The initial clot size did not differ in either group by day 2, but was significantly larger in HO-1(-/-) mice by day 10, where an exaggerated inflammatory response in the venous wall was also observed. Following ligation of the inferior vena cava, HO-1(-/-) mice exhibited increased nuclear factor kappaB activation and markedly increased up-regulation of tissue factor, selectins, inflammatory cytokines, and matrix metalloproteinase-9, the latter incriminated in both clot lysis and vascular injury. We conclude that HO-1 deficiency impairs thrombus resolution and exaggerates the inflammatory response to thrombus formation. These findings offer insight into recent observations that polymorphisms in the HO-1 gene may increase the risk for recurrent venous thrombosis and dysfunction of hemodialysis arteriovenous fistulas, the latter caused, in part, by thrombosis.

Physiological significance of heme oxygenase in hypertension

The last decade has witnessed an explosion in the elucidation of the role that the heme oxygenase system plays in human physiology. This system encompasses not only the heme degradative pathway, including heme oxygenase and biliverdin reductase, but also the products of heme degradation, carbon monoxide, iron, and biliverdin/bilirubin. Their role in diabetes, inflammation, heart disease, hypertension, transplantation, and pulmonary disease are areas of burgeoning research. The research has focused not only on heme itself but also on its metabolic products as well as endogenous compounds involved in a vast number of genetic and metabolic processes that are affected when heme metabolism is perturbed. It should be noted, however, that although the use of carbon monoxide and biliverdin/bilirubin as therapeutic agents has been successful, these agents can be toxic at high levels in tissue, e.g., kernicterus. Care must be used to ensure that when these compounds are used as therapeutic agents their deleterious effects are minimized or avoided. On balance, however, the strategies to target heme oxygenase-1 as described in this review offer promising therapeutic approaches to clinicians for the effective management of hypertension and renal function. The approaches detailed may prove to be seminal in the development of a new therapeutic strategy to treat hypertension.

The lipocalin alpha1-microglobulin protects erythroid K562 cells against oxidative damage induced by heme and reactive oxygen species

Alpha(1)-microglobulin is a 26 kDa plasma and tissue glycoprotein that belongs to the lipocalin protein superfamily. Recent reports show that it is a reductase and radical scavenger and that it binds heme and has heme-degrading properties. This study has investigated the protective effects of alpha(1)-microglobulin against oxidation by heme and reactive oxygen species in the human erythroid cell line, K562. The results show that alpha(1)-microglobulin prevents intracellular oxidation and up-regulation of heme oxygenase-1 induced by heme, hydrogen peroxide and Fenton reaction-generated hydroxyl radicals in the culture medium. It also reduces the cytosol of non-oxidized cells. Endogeneous expression of alpha(1)-microglobulin was up-regulated by these oxidants and silencing of the alpha(1)-microglobulin expression increased the cytosol oxidation. alpha(1)-microglobulin also inhibited cell death caused by heme and cleared cells from bound heme. Binding of heme to alpha(1)-microglobulin increased the radical reductase activity of the protein as compared to the apo-protein. Finally, alpha(1)-microglobulin was localized mainly at the cell surface both when administered exogeneously and in non-treated cells. The results suggest that alpha(1)-microglobulin is involved in the defence against oxidative cellular injury caused by haemoglobin and heme and that the protein may employ both heme-scavenging and one-electron reduction of radicals to achieve this.

Oxidative stress in diseases of the human cornea

Intense exposure to light, robust metabolic activity, and high oxygen tension render the human eye particularly vulnerable to oxidative damage and the list of ophthalmological disorders implicating reactive oxygen and nitrogen species is rapidly expanding. Here, we review the roles of oxidative stress in the etiopathogeneses and pathophysiology of diseases of the human cornea including pterygium, keratoconus, trauma and chemical injury, and a host of inflammatory, metabolic, degenerative, and iatrogenic conditions. Data from animal and tissue culture experimentation germane to these conditions are also adduced.

The reaction of hydrogen peroxide with hemoglobin induces extensive alpha-globin crosslinking and impairs the interaction of hemoglobin with endogenous scavenger pathways

Cell-free hemoglobin (Hb) enhances the oxidation-related toxicity associated with inflammation, ischemia, and hemolytic disorders. Hb is highly vulnerable to oxidative damage, and irreversible structural changes involving iron/heme oxidation, heme-adduct products, and amino acid oxidation have been reported. Specific structural features of Hb, such as unconstrained alpha-chains and molecular size, determine the efficiency of interactions between the endogenous Hb scavengers haptoglobin (Hp) and CD163. Using HPLC, mass spectrometry, and Western blotting, we show that H(2)O(2)-mediated Hb oxidation results in the formation of covalently stabilized globin multimers, with prominent intramolecular crosslinking between alpha-globin chains. These structural alterations are associated with reduced Hp binding, reduced CD163 interaction, and severely impaired endocytosis of oxidized Hb by the Hp-CD163 pathway. As a result, when exposed to oxidized Hb, CD163-positive HEK293 cells and human macrophages do not increase hemeoxygenase-1 (HO-1) expression, the physiological anti-oxidative macrophage response to Hb exposure. Failed Hb clearance, inadequate HO-1 expression, and the subsequent accumulation of oxidatively damaged Hb species might thus contribute to pathologies related to oxidative stress.

Prevention of cadmium accumulation in retinal pigment epithelium with manganese and zinc

Age-related macular degeneration (AMD) is a leading cause of irreversible blindness in the elderly. Risk factors include old age, female gender, obesity, smoking, low dietary intakes of antioxidants and increased exposure to the toxic metal cadmium (Cd(2+)). Supplementation with high-dose zinc (80 mg) provides some protection, but the mechanism(s) underlying such protection has not been fully elucidated. The present study had a focus on the human retinal pigment epithelial (RPE) cell line ARPE-19 in an attempt to demonstrate a reduction in intracellular Cd(2+) effect associated with heme oxygenase-1 (HO-1) expression by co-exposure with zinc (Zn(2+)) or manganese (Mn(2+)), which is known to be a more potent inhibitor of Cd(2+) uptake than Zn(2+). Our results indicated that co-exposure of 10 microM Cd(2+) with 5 microM Mn(2+) reduced the intracellular Cd(2+) effect by 50-60%, possibly by limiting the amounts of Cd(2+) entering cells through Mn(2+) transporter protein (ZIP8). A similar reduction in a Cd(2+) effect was achieved by co-exposure with 20 microM Zn(2+) while co-exposure with 5 and 10 microM Zn(2+) ions was ineffective. Mn(2+) ions as low as 2.5 microM were found to cause an increase in HO-1 mRNA expression levels in ARPE-19 cells, demonstrating for the first time that Mn(2+) is an inducer of HO-1. Mn(2+) ions at 1 microM induced HO-1 mRNA expression in the HEK293 human embryonic kidney cells. In contrast, Zn(2+) in 5, 10 or 20 microM concentrations did not induce expression of HO-1 in ARPE-19 cells or any other cells tested. These data suggest the superiority of Mn(2+) over Zn(2+) in preventing Cd(2+) uptake and accumulation in RPE to toxic levels. Further, induction of HO-1 by Mn(2+) could provide RPE with some resistance to enhanced oxidative stress arising from Cd(2+) accumulation in RPE as HO-1 is one of the frontline cellular antioxidant defense mechanisms.

Interaction among heme oxygenase, nuclear factor-kappaB, and transcription activating factors in cardiac hypertrophy in hypertension

Deoxycorticosterone acetate-induced hypertension is a volume overload and human primary aldosteronism model characterized by severe cardiac lesions attributed to elevated inflammation, oxidative stress, fibrosis, and hypertrophy. An important cytoprotective pathway that counteracts tissue insults is the heme oxygenase (HO) system. Although the HO-1 gene promoter contains consensus binding sites for proinflammatory/oxidative transcription factors like nuclear factor-kappaB, activating protein (AP)-1, and AP-2, the effects of HO inducers on these transcription factors in cardiac lesions of deoxycorticosterone acetate hypertension are not fully understood. Hemin therapy normalized systolic blood pressure and markedly reduced the left:right ventricular ratio, left ventricular wall thickness, and left ventricle:body weight ratio, whereas the HO blocker, chromium mesoporphyrin, exacerbated cardiac fibrosis/hypertrophy in deoxycorticosterone acetate-hypertensive rats. The cardioprotection by hemin was accompanied by increased HO-1, HO activity, cGMP, superoxide dismutase, catalase, the total antioxidant capacity alongside the reduction of 8-isoprostane, AP-1, AP-2, nuclear factor-kappaB, and c-Jun-NH(2)-terminal kinase, whereas chromium mesoporphyrin abolished the hemin effects. Furthermore, hemin therapy attenuated transforming growth factor-beta(1) and extracellular matrix proteins like fibronectin and collagen, with a corresponding reduction of histopathologic lesions, including longitudinal/cross-sectional muscle fiber thickness, scarring, muscular hypertrophy, coronary arteriolar thickening, and collagen deposition. The suppression of AP-1, AP-2, nuclear factor-kappaB, and c-Jun-NH(2)-terminal kinase proinflammatory/oxidative mediators in the left ventricle of hemin-treated animals is a novel observation that may account for cardioprotection in deoxycorticosterone acetate hypertension. By concomitantly upregulating HO activity and cGMP and potentiating the total antioxidant status, hemin therapy reduced hypertension, suppressed oxidative stress, and attenuated extracellular matrix and remodeling proteins, with a reduction of histopathologic lesions that characterize cardiac fibrosis, hypertrophy, and end-stage organ damage.

Carbon monoxide and nitric oxide mediate cytoskeletal reorganization in microvascular cells via vasodilator-stimulated phosphoprotein phosphorylation: evidence for blunted responsiveness in diabetes

OBJECTIVE

We examined the effect of the vasoactive agents carbon monoxide (CO) and nitric oxide (NO) : n the phosphorylation and intracellular redistribution of vasodilator-stimulated phosphoprotein (VASP), a critical actin motor protein required for cell migration that also controls vasodilation and platelet aggregation.

RESEARCH DESIGN AND METHODS

We examined the effect of donor-released CO and NO in endothelial progenitor cells (EPCs) and platelets from nondiabetic and diabetic subjects and in human microvascular endothelial cells (HMECs) cultured under low (5.5 mmol/l) or high (25 mmol/l) glucose conditions. VASP phosphorylation was evaluated using phosphorylation site-specific antibodies.

RESULTS

In control platelets, CO selectively promotes phosphorylation at VASP Ser-157, whereas NO promotes phosphorylation primarily at Ser-157 and also at Ser-239, with maximal responses at 1 min with both agents on Ser-157 and at 15 min on Ser-239 with NO treatment. In diabetic platelets, neither agent resulted in VASP phosphorylation. In nondiabetic EPCs, NO and CO increased phosphorylation at Ser-239 and Ser-157, respectively, but this response was markedly reduced in diabetic EPCs. In endothelial cells cultured under low glucose conditions, both CO and NO induced phosphorylation at Ser-157 and Ser-239; however, this response was completely lost when cells were cultured under high glucose conditions. In control EPCs and in HMECs exposed to low glucose, VASP was redistributed to filopodia-like structures following CO or NO exposure; however, redistribution was dramatically attenuated under high glucose conditions.

CONCLUSIONS

Vasoactive gases CO and NO promote cytoskeletal changes through site- and cell type-specific VASP phosphorylation, and in diabetes, blunted responses to these agents may lead to reduced vascular repair and tissue perfusion.

Physicochemical properties, pharmacokinetics, and pharmacodynamics of intravenous hematin: a literature review

INTRODUCTION

Intravenous (i.v.) hematin has been used in the treatment of acute intermittent porphyria (AIP) since the early 1970s and commercially available as Panhematin (hemin for injection; Ovation Pharmaceuticals, Inc., USA) since 1983, yet no publication to date has attempted to summarize the known pharmacodynamics and toxicological actions of hematin and the implications on treatment. It is the objective of this literature review to identify, consolidate, and summarize the available scientific literature regarding the physicochemical properties, pharmacokinetics, toxicology, and hemostatic effects of i.v. hematin injections.

METHODS

A comprehensive search of the available literature was performed and resulting data were summarized. Furthermore, previously unpublished toxicology data extracted from the original New Drug Application were included.

RESULTS

Hematin, reconstituted with sterile water, rapidly degrades and it is hypothesized that the degradation products lead to morbidities such as thrombophlebitis, thrombocytopenia, and transient anticoagulation. Reconstitution with human serum albumin produces a well-tolerated hematin preparation and improves its stability significantly. The clearance of i.v. hematin infusions are shown to fit a two-compartment model consisting of a rapid initial rate followed by a slower and prolonged second phase. This model is supported by the evidence demonstrating that hematin is first bound by hemopexin and, upon saturation, second by albumin. The highest i.v. human hematin dose reported in the literature was 12.2 mg/kg (1000 mg) and resulted in acute gastrointestinal pain, paresthesia, and acute tubercular necrosis. The patient's renal function returned to normal over the following 15 hours.

CONCLUSION

Hematin, at doses approved by the US Food and Drug Administration, is generally well tolerated. Reconstitution with albumin produces a significantly more stable preparation than reconstitution with sterile water and may lead to a more tolerable administration with less hemostatic interference. Hematin, once administered, is cleared hepatically and is best represented pharmacokinetically by a two-compartment model comprised of a rapid initial phase followed by a slower second phase.

Heme oxygenase metabolites inhibit tubuloglomerular feedback (TGF)

Tubuloglomerular feedback (TGF) is the mechanism by which the macula densa (MD) senses increases in luminal NaCl concentration and sends a signal to constrict the afferent arteriole (Af-Art). The kidney expresses constitutively heme oxygenase-2 (HO-2) and low levels of HO-1. HOs release carbon monoxide (CO), biliverdin, and free iron. We hypothesized that renal HOs inhibit TGF via release of CO and biliverdin. Rabbit Af-Arts and attached MD were simultaneously microperfused in vitro. The TGF response was determined by measuring Af-Art diameter before and after increasing NaCl in the MD perfusate. When HO activity was inhibited by adding stannous mesoporphyrin (SnMP) to the MD perfusate, the TGF response increased from 2.1+/-0.2 to 4.1+/-0.4 microm (P=0.003, control vs. SnMP, n=7). When a CO-releasing molecule, (CORM-3; 50 microM), was added to the MD perfusate, the TGF response decreased by 41%, from 3.6+/-0.3 to 2.1+/-0.2 microm (P<0.001, control vs. CORM-3, n=12). When CORM-3 at 100 microM was added to the perfusate, it completely blocked the TGF response, from 4.2+/-0.4 to -0.2+/-0.3 microm (P<0.001, control vs. CORM-3, n=6). When biliverdin was added to the perfusate, the TGF response decreased by 79%, from 3.4+/-0.3 to 0.7+/-0.4 microm (P=0.001, control vs. biliverdin, n=6). The effects of SnMP and CORM-3 were not blocked by inhibition of nitric oxide synthase. We concluded that renal HO inhibits TGF probably via release of CO and biliverdin. HO regulation of TGF is a novel mechanism that could lead to a better understanding of the control of renal microcirculation and function.

Exacerbated corneal inflammation and neovascularization in the HO-2 null mice is ameliorated by biliverdin

Heme oxygenase (HO-1 and HO-2) represents an intrinsic cytoprotective and anti-inflammatory system based on its ability to modulate leukocyte migration and to inhibit expression of inflammatory cytokines and proteins. HO-2 deletion leads to unresolved corneal inflammation and chronic inflammatory complications including ulceration, perforation and neovascularization. We examined the consequences of HO-2 deletion on hemangiogenesis and lymphangiogenesis in the model of suture-induced inflammatory neovascularization. An 8.0 silk suture was placed at the corneal apex of wild type and HO-2 null mice. Neovascularization was assessed by vital microscopy and quantified by image analysis. Hemangiogenesis and lymphangiogenesis were determined by immunofluorescence staining using anti-CD31 and anti-LYVE-1 antibodies, respectively. Inflammation was quantified by histology and myeloperoxidase activity. The levels of HO-1 expression and inflammatory cytokines were determined by real time PCR and ELISA, respectively. Corneal sutures produced a consistent inflammatory response and a time-dependent neovascularization. The response in HO-2 null mice was associated with a greater increase compared to the wild type in the number of leukocytes (827,600+/-129,000 vs. 294,500+/-57,510; p<0.05), neovessels measured by vital microscopy (21.91+/-1.05 vs. 12.77+/-1.55 mm; p<0.001) 4 days after suture placement. Hemangiogenesis but not lymphangiogenesis was more pronounced in HO-2 null mice compared to wild type mice. Induction of HO-1 in sutured corneas was greatly attenuated in HO-2 null corneas and treatment with biliverdin diminished the exaggerated inflammatory and neovascular response in HO-2 null mice. The demonstration that the inflammatory responses, including expression of proinflammatory proteins, inflammatory cell influx and hemangiogenesis are exaggerated in HO-2 knockout mice strongly supports the notion that the HO system is critical for controlling the inflammatory and neovascular response in the cornea. Hence, pharmacological amplification of this system may constitute a novel therapeutic strategy for the treatment of corneal disorders associated with excessive inflammation and neovascularization.

Treatment of obese diabetic mice with a heme oxygenase inducer reduces visceral and subcutaneous adiposity, increases adiponectin levels, and improves insulin sensitivity and glucose tolerance

OBJECTIVE

We hypothesized that the induction of heme oxygenase (HO)-1 and increased HO activity, which induces arterial antioxidative enzymes and vasoprotection in a mouse and a rat model of diabetes, would ameliorate insulin resistance, obesity, and diabetes in the ob mouse model of type 2 diabetes.

RESEARCH DESIGN AND METHODS

Lean and ob mice were intraperitoneally administered the HO-1 inducer cobalt protoporphyrin (3 mg/kg CoPP) with and without the HO inhibitor stannous mesoporphyrin (2 mg/100 g SnMP) once a week for 6 weeks. Body weight, blood glucose, and serum cytokines and adiponectin were measured. Aorta, adipose tissue, bone marrow, and mesenchymal stem cells (MSCs) were isolated and assessed for HO expression and adipogenesis.

RESULTS

HO activity was reduced in ob mice compared with age-matched lean mice. Administration of CoPP caused a sustained increase in HO-1 protein, prevented weight gain, decreased visceral and subcutaneous fat content (P < 0.03 and 0.01, respectively, compared with vehicle animals), increased serum adiponectin, and decreased plasma tumor necrosis factor-alpha (TNF-alpha), interleukin (IL)-6, and IL-1beta levels (P < 0.05). HO-1 induction improved insulin sensitivity and glucose tolerance and decreased insulin levels. Upregulation of HO-1 decreased adipogenesis in bone marrow in vivo and in cultured MSCs and increased adiponectin levels in the culture media. Inhibition of HO activity decreased adiponectin and increased secretion of TNF-alpha, IL-6, and IL-1beta levels in ob mice.

CONCLUSIONS

This study provides strong evidence for the existence of an HO-1-adiponectin regulatory axis that can be manipulated to ameliorate the deleterious effects of obesity and the metabolic syndrome associated with cardiovascular disease and diabetes.

Biliverdin is the endogenous ligand of human serum alpha1-acid glycoprotein

alpha(1)-Acid glycoprotein (AAG), an acute phase component of the human serum, is a prominent member of the lipocalin family of proteins showing inflammatory/immunomodulatory activities and promiscuous drug binding properties. Both three-dimensional structure of AAG and its precise biological function are still unknown and only a few endogenous AAG ligands have been described to date. CD spectroscopic studies performed with commercial AAG and the separated genetic variants revealed high-affinity binding of biliverdin (BV) and biliverdin dimethyl ester to the 'F1/S' fraction of the protein. The preferential accommodation of the right-handed, P-helicity conformers of the pigments by the protein matrix resulted in strong induced CD activity, which was utilized for estimation of the binding parameters and to locate the binding site. It was concluded that both pigments are bound in the central beta-barrel cavity of AAG, held principally by hydrophobic interactions. Possible biological implications of the BV binding ability of AAG with special emphasis on the heme oxygenase-1 pathway are discussed.

Ubiquitin-proteasome system mediates heme oxygenase-1 degradation through endoplasmic reticulum-associated degradation pathway

The present study investigated the cellular mechanism underlying the degradation of heme oxygenase-1 (HO-1), an endoplasmic reticulum (ER)-anchored protein. The turnover of HO-1 induced in vascular smooth muscle cells (VSMCs) was significantly attenuated by proteasome inhibitors, suggesting the involvement of a proteasome-mediated pathway. High molecular weight ubiquitin conjugates were co-immunoprecipitated with HO-1 from VSMCs after proteasome inhibition, and HO-1 ubiquitination was confirmed in HEK293 cells overexpressing His-tagged HO-1 and HA-tagged ubiquitin. Endogenous p97, an ATPase, and Ufd1, both implicated as essential components in the ER-associated degradation pathway (ERAD), were co-eluted with His-tagged HO-1 from metal affinity resin. Knockdown of either p97 or Ufd1 in HEK293 cells using specific siRNA significantly prolonged the half-life of endogenously induced HO-1 and slowed the degradation of ubiquitinated HO-1. HO-1 ubiquitination in HEK293 cells was enhanced by zinc chloride, but suppressed with a zinc chelator (N,N,N',N'-tetrakis(2-pyridylmethyl)ethyl-enediamine), suggesting the involvement of a RING-E3 ligase in this process. Collectively, these data indicate that HO-1 protein turnover is regulated by the ubiquitin-proteasome system through the ERAD pathway.

L-4F treatment reduces adiposity, increases adiponectin levels, and improves insulin sensitivity in obese mice

We hypothesized that the apolipoprotein mimetic peptide L-4F, which induces arterial anti-oxidative enzymes and is vasoprotective in a rat model of diabetes, would ameliorate insulin resistance and diabetes in obese mice. L-4F (2 mg/kg/d) administered to ob/ob mice for 6 weeks limited weight gain without altering food intake, decreased visceral (P < 0.02) and subcutaneous (P < 0.045) fat content, decreased plasma IL-1beta and IL-6 levels (P < 0.05) and increased insulin sensitivity, resulting in decreased glucose (P < 0.001) and insulin (P < 0.036) levels. In addition, L-4F treatment increased aortic and bone marrow heme oxygenase (HO) activity and decreased aortic and bone marrow superoxide production (P < 0.001). L-4F treatment increased serum adiponectin levels (P < 0.037) and decreased adipogenesis in mouse bone marrow (P < 0.039) and in cultures of human bone marrow-derived mesenchymal stem cells (P < 0.022). This was manifested by reduced adiposity, improved insulin sensitivity, improved glucose tolerance, increased plasma adiponectin levels, and reduced IL-1beta and IL-6 levels in obese mice. This study highlights the existence of a temporal relationship between HO-1 and adiponectin that is positively affected by L-4F in the ob/ob mouse model of diabetes, resulting in the amelioration of the deleterious effects of diabetes.

Heme oxygenase-mediated increases in adiponectin decrease fat content and inflammatory cytokines tumor necrosis factor-alpha and interleukin-6 in Zucker rats and reduce adipogenesis in human mesenchymal stem cells

Adiponectin, an abundant adipocyte-derived plasma protein that modulates vascular function in type 2 diabetes, has been shown to provide cytoprotection to both pancreatic and vascular systems in diabetes. Therefore, we examined whether up-regulation of heme oxygenase (HO)-1 ameliorates the levels of inflammatory cytokines and influences serum adiponectin in Zucker fat (ZF) rats. ZF rats displayed a decrease in both HO activity and HO-1 and HO-2 protein levels and an increase in tumor necrosis factor (TNF)-alpha and interleukin (IL)-6 compared with Zucker lean (ZL) rats. Treatment of ZF animals with 2 mg/kg cobalt protoporphyrin IX (CoPP) increased protein levels of HO-1 and HO activity, but HO-2 was unaffected. The increase in HO-1 was associated with a decrease in superoxide levels (p < 0.05) and an increase in plasma adiponectin (p < 0.005), compared with untreated ZF rats. CoPP treatment decreased visceral and s.c. fat content, and it reduced weight gain (p < 0.01). In addition, the inflammatory cytokines TNF-alpha and IL-6 were decreased (p < 0.04 and p < 0.008, respectively). Treatment of human bone marrow-derived adipocytes cultured with CoPP resulted in an increase in HO-1 and a decrease in superoxide levels. Up-regulation of HO-1 caused adipose remodeling, smaller adipocytes, and increased adiponectin secretion in the culture medium of human bone marrow-derived adipocytes. In summary, this study demonstrates that the antiobesity effect of HO-1 induction results in an increase in adiponectin secretion, in vivo and in vitro, a decrease in TNF-alpha and IL-6, and a reduction in weight gain. These findings highlight the pivotal role and symbiotic relationship of HO-1 and adiponectin in the modulation of the metabolic syndrome phenotype.