Heme oxygenase-1 enhances renal mitochondrial transport carriers and cytochrome C oxidase activity in experimental diabetes

Heme oxygenase, a novel target for the treatment of hypertension and obesity?

Heme oxygenase (HO) is the rate-limiting enzyme in the metabolism of heme-releasing bioactive molecules carbon monoxide (CO), biliverdin, and iron, each with beneficial cardiovascular actions. Biliverdin is rapidly reduced to bilirubin, a potent antioxidant, by the enzyme biliverdin reductase, and iron is rapidly sequestered by ferritin in the cell. Several studies have demonstrated that HO-1 induction can attenuate the development of hypertension as well as lower blood pressure in established hypertension in both genetic and experimental models. HO-1 induction can also reduce target organ injury and can be beneficial in cardiovascular diseases, such as heart attack and stroke. Recent studies have also identified a beneficial role for HO-1 in the regulation of body weight and metabolism in diabetes and obesity. Chronic HO-1 induction lowers body weight and corrects hyperglycemia and hyperinsulinemia. Chronic HO-1 induction also modifies the phenotype of adipocytes in obesity from one of large, cytokine producing to smaller, adiponectin producing. Finally, chronic induction of HO-1 increases oxygen consumption, CO(2), and heat production and activity in obese mice. This review will discuss the current understanding of the actions of the HO system to lower blood pressure and body weight and how HO or its metabolites may be ideal candidates for the development of drugs that can both reduce blood pressure and lower body weight.

Heme oxygenase, a novel target for the treatment of hypertension and obesity?

Heme oxygenase (HO) is the rate-limiting enzyme in the metabolism of heme-releasing bioactive molecules carbon monoxide (CO), biliverdin, and iron, each with beneficial cardiovascular actions. Biliverdin is rapidly reduced to bilirubin, a potent antioxidant, by the enzyme biliverdin reductase, and iron is rapidly sequestered by ferritin in the cell. Several studies have demonstrated that HO-1 induction can attenuate the development of hypertension as well as lower blood pressure in established hypertension in both genetic and experimental models. HO-1 induction can also reduce target organ injury and can be beneficial in cardiovascular diseases, such as heart attack and stroke. Recent studies have also identified a beneficial role for HO-1 in the regulation of body weight and metabolism in diabetes and obesity. Chronic HO-1 induction lowers body weight and corrects hyperglycemia and hyperinsulinemia. Chronic HO-1 induction also modifies the phenotype of adipocytes in obesity from one of large, cytokine producing to smaller, adiponectin producing. Finally, chronic induction of HO-1 increases oxygen consumption, CO(2), and heat production and activity in obese mice. This review will discuss the current understanding of the actions of the HO system to lower blood pressure and body weight and how HO or its metabolites may be ideal candidates for the development of drugs that can both reduce blood pressure and lower body weight.

Curcumin attenuates aluminum-induced oxidative stress and mitochondrial dysfunction in rat brain

Aluminum is neurotoxic both in animals and human beings primarily because of its interference with biological enzymes in key mechanisms of metabolic pathways. Mitochondrial dysfunction is one such mechanism that has been implicated in the pathogenesis of neurodegenerative diseases like Alzheimer's disease. Aluminum toxicity is very closely related to Alzheimer's disease. We evaluated the potentials of curcumin, a known cytoprotectant, against neurotoxic consequences of aluminum that acts through a wide range of mechanisms. Curcumin has been reported to be an antioxidant, and it is this property that is widely held to be responsible for its protective effects in tissue. Aluminum was administered by oral gavage at a dose level of 100 mg/kg body wt/day for a period of 8 weeks. Curcumin was administered in conjunction with aluminum at a dose of 50 mg/kg of body wt i.p. for a period of 8 weeks on alternate days. The effects of different treatments were studied on oxidative phosphorylation and reduced glutathione of different regions of rat brain. The study indicates reduced activity of NADH dehydrogenase (complex I), succinic dehydrogenase (complex II), and cytochrome oxidize (Complex IV) in all the three regions of rat brain, i.e., cerebral cortex, mid brain, and cerebellum. Curcumin supplementation to aluminum-treated rats was able to normalize significantly the activities of all the three mitochondrial complexes as well as reduced glutathione content in all the three regions of brain which were altered following aluminum treatment. We conclude that curcumin, by attenuating oxidative stress, as evident by hypoxia in histological observations and mitochondrial dysfunction holds a promise as an agent that can potentially reduce aluminum-induced adverse effects in brain.

A carbon monoxide-releasing molecule (CORM-3) uncouples mitochondrial respiration and modulates the production of reactive oxygen species

Carbon monoxide (CO), produced during the degradation of heme by the enzyme heme oxygenase, is an important signaling mediator in mammalian cells. Here we show that precise delivery of CO to isolated heart mitochondria using a water-soluble CO-releasing molecule (CORM-3) uncouples respiration. Addition of low-micromolar concentrations of CORM-3 (1-20 μM), but not an inactive compound that does not release CO, significantly increased mitochondrial oxygen consumption rate (State 2 respiration) in a concentration-dependent manner. In contrast, higher concentrations of CORM-3 (100 μM) suppressed ADP-dependent respiration through inhibition of cytochrome c oxidase. The uncoupling effect mediated by CORM-3 was inhibited in the presence of the CO scavenger myoglobin. Moreover, this effect was associated with a gradual decrease in membrane potential (ψ) over time and was partially reversed by malonate, an inhibitor of complex II activity. Similarly, inhibition of uncoupling proteins or blockade of adenine nucleotide transporter attenuated the effect of CORM-3 on both State 2 respiration and Δψ. Hydrogen peroxide (H₂O₂) produced by mitochondria respiring from complex I-linked substrates (pyruvate/malate) was increased by CORM-3. However, respiration initiated via complex II using succinate resulted in a fivefold increase in H₂O₂ production and this effect was significantly inhibited by CORM-3. These findings disclose a counterintuitive action of CORM-3 suggesting that CO at low levels acts as an important regulator of mitochondrial respiration.

Chronic HO-1 induction with cobalt protoporphyrin (CoPP) treatment increases oxygen consumption, activity, heat production and lowers body weight in obese melanocortin-4 receptor-deficient mice

Objective

Heme oxygenase-1 induction (HO-1) elicits chronic weight loss in several rodent models of obesity. Despite these findings, the mechanism by which HO-1 induction reduces body weight is unclear. Chronic HO-1 induction does not alter food intake suggesting other mechanisms such as increases in metabolism and activity may be responsible for the observed reduction of body weight. In this study, we investigated the mechanism of weight loss elicited by chronic HO-1 induction in a model of genetic obesity due to melanocortin-4 receptor (MC4R) deficiency.

Design

Experiments were performed on loxTB MC4R deficient mice as well as lean controls. Mice were administered cobalt protoporphyrin (CoPP, 5 mg/kg), an inducer of HO-1, once weekly from 4 to 23 weeks of age. Body weights were measured weekly and fasted blood glucose and insulin as well as food intake were determined at 18 weeks of age. O₂ consumption, CO₂ production, activity, and body heat production were measured at 20 weeks of age.

Results

Chronic CoPP treatment resulted in a significant decrease in body weight from 5 weeks on in loxTB mice. Chronic CoPP treatment resulted in a significant decrease in fasted blood glucose levels, plasma insulin, and a significant increase in plasma adiponectin levels in MC4R deficient mice. Chronic CoPP treatment increased O₂ consumption (47 ± 4 vs. 38 ± 3 ml/kg/min, P<0.05) and CO₂ production (44 ± 7 vs. 34 ± 4 ml/kg/min, P<0.05) in treated versus non-treated, MC4R deficient mice (n=4). Heat production (10%) and activity (18%) were also significantly (P<0.05) increased in CoPP treated MC4R deficient mice.

Conclusion

Our results suggest that chronic HO-1 induction with CoPP induction elicits weight loss by increasing metabolism and activity by an MC4R independent pathway.

Pharmacological preconditioning by low dose cobalt protoporphyrin induces heme oxygenase-1 overexpression and alleviates retinal ischemia-reperfusion injury in rats

PURPOSE

Retinal ischemia-induced neuronal death plays a crucial role in certain severe visual impairment diseases. The aims of this study were to investigate the effects of low dose cobalt protoporphyrin IX (CoPP), an inducer of heme oxygenase-1 (HO-1), on the retina of rats against ischemia-reperfusion (IR) injury.

METHODS

Retinal IR was achieved in rats by raising intraocular pressure for 60 min. CoPP (1 mg/ kg) was injected intraperitoneally 24 hr before IR. Retinal injury was assessed by the number of retinal ganglion cells (RGCs) seven days after reperfusion. TUNEL assay was used to detect the appearance of apoptotic cells 24 hr after reperfusion. The expressions of the HO-1 and Bax proteins were evaluated by Western blot.

RESULTS

Both HO-1 expression, examined by Western blot, and enzyme activity were increased strongly after CoPP administration. Rats treated with CoPP before IR had more RGCs (p = 0.034) and less apoptotic cells (p = 0.04) together with downregulated Bax protein levels (p = 0.03) compared to ischemic rats without CoPP. The protective effects of CoPP were HO-1 dependent because the upregulation of HO-1 and the RGC protection were both abolished by the HO-1 inhibitor tin protoporphyrin (SnPP).

CONCLUSIONS

In this study, we demonstrated that induction of HO-1 expression by low dose CoPP ameliorated retinal damage from IR injury. The favorable effect appears to be related with modulations of the apoptotic pathway.

Adipocyte heme oxygenase-1 induction attenuates metabolic syndrome in both male and female obese mice

Increases in visceral fat are associated with increased inflammation, dyslipidemia, insulin resistance, glucose intolerance, and vascular dysfunction. We examined the effect of the potent heme oxygenase (HO)-1 inducer, cobalt protoporphyrin (CoPP), on regulation of adiposity and glucose levels in both female and male obese mice. Both lean and obese mice were administered CoPP intraperitoneally (3 mg/kg once per week) for 6 weeks. Serum levels of adiponectin, tumor necrosis factor α (TNFa), interleukin (IL)-1β and IL-6, and HO-1, PPARγ, pAKT, and pAMPK protein expression in adipocytes and vascular tissue were measured. While female obese mice continued to gain weight at a rate similar to controls, induction of HO-1 slowed the rate of weight gain in male obese mice. HO-1 induction led to lowered blood pressure levels in obese male and female mice similar to that of lean male and female mice. HO-1 induction also produced a significant decrease in the plasma levels of IL-6, TNFα, IL-1β, and fasting glucose of obese females compared to untreated female obese mice. HO-1 induction increased the number and decreased the size of adipocytes of obese animals. HO-1 induction increased adiponectin, pAKT, pAMPK, and PPARγ levels in adipocyte of obese animals. Induction of HO-1 in adipocytes was associated with an increase in adiponectin and a reduction in inflammatory cytokines. These findings offer the possibility of treating not only hypertension, but also other detrimental metabolic consequences of obesity including insulin resistance and dyslipidemia in obese populations by induction of HO-1 in adipocytes.

Heme oxygenase-1 prevents non-alcoholic steatohepatitis through suppressing hepatocyte apoptosis in mice

Objective

Heme oxygenase-1 (HO-1), the rate-limiting enzyme in heme catabolism, has been reported to have potential antioxidant properties. However, the role of HO-1 on hepatocyte apoptosis remains unclear. We aim to elucidate the effects of HO-1 on oxidative stress related hepatocellular apoptosis in nutritional steatohepatitis in mice.

Methods

C57BL/6J mice were fed with methionine-choline deficient (MCD) diet for four weeks to induce hepatic steatohepatitis. HO-1 chemical inducer (hemin), HO-1 chemical inhibitor zinc protoporphyrin IX (ZnPP-IX) and/or adenovirus carrying HO-1 gene (Ad-HO-1) were administered to mice, respectively. Hepatocyte apoptosis was evaluated by terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) assay, the mRNA and protein expression of apoptosis related genes were assayed by quantitative real-time PCR and Western blot.

Results

Hepatocyte signs of oxidative related apoptotic injury were presented in mice fed with MCD diet for 4 weeks. Induction of HO-1 by hemin or Ad-HO-1 significantly attenuated the severity of liver histology, which was associated with decreased hepatic lipid peroxidation content, reduced number of apoptotic cells by TUNEL staining, down-regulated expression of pro-apoptosis related genes including Fas/FasL, Bax, caspase-3 and caspase-9, reduced expression of cytochrome p4502E1 (CYP2E1), inhibited cytochrome c (Cyt-c) release, and up-regulated expression of anti-apoptosis gene Bcl-2. Whereas, inhibition of HO-1 by ZnPP-IX caused oxidative stress related hepatic injury, which concomitant with increased number of TUNEL positive cells and up-regulated expression of pro-apoptosis related genes.

Conclusions

The present study provided evidences for the protective role of HO-1 in preventing nutritional steatohepatitis through suppressing hepatocyte apoptosis in mice.

Epoxyeicosatrienoic acid agonist regulates human mesenchymal stem cell-derived adipocytes through activation of HO-1-pAKT signaling and a decrease in PPARγ

Human mesenchymal stem cells (MSCs) expressed substantial levels of CYP2J2, a major CYP450 involved in epoxyeicosatrienoic acid (EET) formation. MSCs synthesized significant levels of EETs (65.8 ± 5.8 pg/mg protein) and dihydroxyeicosatrienoic acids (DHETs) (15.83 ± 1.62 pg/mg protein), suggesting the presence of soluble epoxide hydrolase (sEH). The addition of an sEH inhibitor to MSC culture decreased adipogenesis. EETs decreased MSC-derived adipocytes in a concentration-dependent manner, 8,9- and 14,15-EET having the maximum reductive effect on adipogenesis. We examined the effect of 12-(3-hexylureido)dodec-8(Z)-enoic acid, an EET agonist, on MSC-derived adipocytes and demonstrated an increased number of healthy small adipocytes, attenuated fatty acid synthase (FAS) levels (P < 0.01), and reduced PPARγ, C/EBPα, FAS, and lipid accumulation (P < 0.05). These effects were accompanied by increased levels of heme oxygenase (HO)-1 and adiponectin (P < 0.05), and increased glucose uptake (P < 0.05). Inhibition of HO activity or AKT by tin mesoporphyrin (SnMP) and LY2940002, respectively, reversed EET-induced inhibition of adipogenesis, suggesting that activation of the HO-1-adiponectin axis underlies EET effect in MSCs. These findings indicate that EETs decrease MSC-derived adipocyte stem cell differentiation by upregulation of HO-1-adiponectin-AKT signaling and play essential roles in the regulation of adipocyte differentiation by inhibiting PPARγ, C/EBPα, and FAS and in stem cell development. These novel observations highlight the seminal role of arachidonic acid metabolism in MSCs and suggest that an EET agonist may have potential therapeutic use in the treatment of dyslipidemia, diabetes, and the metabolic syndrome.

Image analysis to quantify histological and immunofluorescent staining of ex vivo skin and skin cell cultures

Image processing steps and analysis techniques were developed for the quantification of photomicrographs obtained from light and fluorescence microscopy. The substrates examined were either skin cell cultures, such as normal human keratinocytes (NHK) or fibroblasts, or ex vivo skin sections. Examples of the analyses are provided for the comparison of skincare active ingredient treated samples vs. placebo to demonstrate the utility of the methods to quantify and provide numerical data for a procedure that is typically qualitative in nature and based on observations by a histologist. Quantifiable experiments that are discussed include: Fontana Masson staining for melanin expression; Nile red staining to detect cellular lipid droplets; nuclei staining with diamidino-phenylindole (DAPI); and immunofluorescent staining of protein expression with a primary antibody directed against the protein (antigen) and a secondary antibody tagged with a fluorescent dye (Alexa Fluor 488) against the primary antibody.

Overexpression of heme oxygenase-1 increases human osteoblast stem cell differentiation

Human bone marrow mesenchymal stem cells (MSCs) are pleiotrophic cells that differentiate to either adipocytes or osteoblasts as a result of crosstalk by specific signaling pathways including heme oxygenase (HO)-1/-2 expression. We examined the effect of inducers of HO-1 expression and inhibitors of HO activity on MSC differentiation to the osteoblast and following high glucose exposure. MSC cultured in osteogenic medium increased expression of osteonectin, Runt-related transcription factor 2 (RUNX-2), osteocalcin, and alkaline phosphatase. HO-1 expression during differentiation was initially decreased and then followed by a rebound increase after 15 days of culture. Additionally, the effect of HO-1 on osteoblasts appears different to that seen in adipocyte stem cells. On addition of a cobalt compound, the resultant induction of HO-1 decreases adipogenesis. Moreover, glucose (30 mM) inhibited osteoblast differentiation, as evidenced by decreased bone morphogenetic protein (BMP)-2, osteonectin, osteocalcin, and osteoprotegerin (OPG). In contrast, MSC-derived adipocytes were increased by glucose. Increased HO-1 expression increased the levels of osteonectin, OPG, and BMP-2. Inhibition of HO activity prevented the increase in osteonectin and potentiated the decrease of osteocalcin and OPG in cells exposed to high glucose levels. Furthermore, targeting HO-1 expression increased pAMPK and endothelial nitric oxide synthase (eNOS) and restored osteoblastic markers. Our findings suggest that targeting HO-1 gene expression attenuates the hyperglycemia-mediated decrease in MSC-derived osteoblast differentiation. Finally, the mechanism underlying the HO-1-specific cell effect on osteoblasts and adipocytes is yet to be explored. Thus, the targeting of HO-1 gene expression presents a portal to increase osteoblast function and differentiation and attenuate osteoporosis by promoting bone formation.

Mitochondrial dysfunction in diabetes: from molecular mechanisms to functional significance and therapeutic opportunities

Given their essential function in aerobic metabolism, mitochondria are intuitively of interest in regard to the pathophysiology of diabetes. Qualitative, quantitative, and functional perturbations in mitochondria have been identified and affect the cause and complications of diabetes. Moreover, as a consequence of fuel oxidation, mitochondria generate considerable reactive oxygen species (ROS). Evidence is accumulating that these radicals per se are important in the pathophysiology of diabetes and its complications. In this review, we first present basic concepts underlying mitochondrial physiology. We then address mitochondrial function and ROS as related to diabetes. We consider different forms of diabetes and address both insulin secretion and insulin sensitivity. We also address the role of mitochondrial uncoupling and coenzyme Q. Finally, we address the potential for targeting mitochondria in the therapy of diabetes.

Glutathionylation of adenine nucleotide translocase induced by carbon monoxide prevents mitochondrial membrane permeabilization and apoptosis

The present work demonstrates the ability of CO to prevent apoptosis in a primary culture of astrocytes. For the first time, the antiapoptotic behavior can be clearly attributed to the inhibition of mitochondrial membrane permeabilization (MMP), a key event in the intrinsic apoptotic pathway. In isolated non-synaptic mitochondria, CO partially inhibits (i) loss of potential, (ii) the opening of a nonspecific pore through the inner membrane, (iii) swelling, and (iv) cytochrome c release, which are induced by calcium, diamide, or atractyloside (a ligand of ANT). CO directly modulates ANT function by enhancing ADP/ATP exchange and prevents its pore-forming activity. Additionally, CO induces reactive oxygen species (ROS) generation, and its prevention by beta-carotene decreases CO cytoprotection in intact cells as well as in isolated mitochondria, revealing the key role of ROS. On the other hand, CO induces a slight increase in mitochondrial oxidized glutathione, which is essential for apoptosis modulation by (i) delaying astrocytic apoptosis, (ii) decreasing MMP, and (iii) enhancing ADP/ATP translocation activity of ANT. Moreover, CO and GSSG trigger ANT glutathionylation, a post-translational process regulating protein function in response to redox cellular changes. In conclusion, CO protects astrocytes from apoptosis by preventing MMP, acting on ANT (glutathionylation and inhibition of its pore activity) via a preconditioning-like process mediated by ROS and GSSG.

The role of reactive oxygen species in apoptosis of the diabetic kidney

Increased levels of reactive oxygen species (ROS) by hyperglycemia can induce apoptosis of renal cells and diabetic nephropathy. The redox balance in the renal cell seems, therefore, of the utmost importance. ROS-mediated apoptosis may be further aggravated by an inadequate cytoprotective response against ROS. When there are insufficient cytoprotective and ROS scavenging molecules, ROS lead to considerable cellular damage and to a point of no return in apoptosis. Induction of cytoprotective proteins may prevent or attenuate apoptosis, renal cell injury, and finally diabetic nephropathy. Here, we discuss some mechanisms of apoptosis and several strategies that have been probed to ameliorate, or to prevent apoptosis in the diabetic kidney.

HO-1 expression increases mesenchymal stem cell-derived osteoblasts but decreases adipocyte lineage

Human bone marrow mesenchymal stem cells (MSC) are pleiotropic cells that differentiate to either adipocytes or osteoblasts as a result of cross-talk by specific signaling pathways including heme oxygenase (HO)-1/-2 expression. We examined the effect of inducers of HO-1 expression and inhibitors of HO activity on MSC differentiation to the osteoblast and adipocyte lineage. HO-1 expression is increased during osteoblast stem cell development but remains elevated at 25 days. The increase in HO-1 levels precedes an increase in alkaline phosphatase (AP) activity and an increase in BMP, osteonectin and RUNX-2 mRNA. Induction of HO-1 by osteogenic growth peptide (OGP) was associated with an increase in BMP-2 and osteonectin. Exposure of MSC to high glucose levels decreased osteocalcin and osteogenic protein expression, which was reversed by upregulation of the OGP-mediated increase in HO-1 expression. The glucose-mediated decrease in HO-1 resulted in decreased levels of pAMPK, pAKT and the eNOS signaling pathway and was reversed by OGP. In contrast, MSC-derived adipocytes were increased by glucose. HO-1 siRNA decreased HO-1 expression but increased adipocyte stem cell differentiation and the adipogenesis marker, PPARgamma. Thus, upregulation of HO-1 expression shifts the balance of MSC differentiation in favor of the osteoblast lineage. In contrast, a decrease in HO-1 or exposure to glucose drives the MSC towards adipogenesis. Thus, targeting HO-1 expression is a portal to increased osteoblast stem cell differentiation and to the attenuation of osteoporosis by the promotion of bone formation.

Heme oxygenase: the key to renal function regulation

Heme oxygenase (HO) plays a critical role in attenuating the production of reactive oxygen species through its ability to degrade heme in an enzymatic process that leads to the production of equimolar amounts of carbon monoxide and biliverdin/bilirubin and the release of free iron. The present review examines the beneficial role of HO-1 (inducible form of HO) that is achieved by increased expression of this enzyme in renal tissue. The influence of the HO system on renal physiology, obesity, vascular dysfunction, and blood pressure regulation is reviewed, and the clinical potential of increased levels of HO-1 protein, HO activity, and HO-derived end products of heme degradation is discussed relative to renal disease. The use of pharmacological and genetic approaches to investigate the role of the HO system in the kidney is key to the development of therapeutic approaches to prevent the adverse effects that accrue due to an impairment in renal function.

Effects of losartan, HO-1 inducers or HO-1 inhibitors on erectile signaling in diabetic rats

INTRODUCTION

Activation of the renin-angiotensin system which is common in diabetes mellitus might affect heme oxygenase (HO-1) gene expression.

AIM

Assessment of the effects of administration of angiotensin II (Ang II) receptor antagonist (losartan) with HO-1 inducer or inhibitor on erectile signaling in diabetic rats.

MATERIALS AND METHODS

Seventy male rats were divided equally into seven groups; healthy controls, streptozotocin-induced diabetic rats, rats on citrate buffer, diabetic rats on losartan, diabetic rats on HO-1 inducer (cobalt protoporphyrin [CoPP]), diabetic rats on losartan and CoPP, and diabetic rats on losartan and HO-1 inhibitor (stannus mesoporphyrin [SnMP]).

MAIN OUTCOME MEASURE

HO enzyme activity, HO-1 gene expression, cyclic guanosine monophosphate (cGMP) assay, intracavernosal pressure (ICP), and cavernous tissue sinusoids surface area.

RESULTS

HO-1 gene expression, HO enzymatic activity, and cGMP were significantly decreased in the cavernous tissue of diabetic rats. These parameters were significantly elevated with the use of CoPP that restored the normal control levels of HO enzyme activity. Administration of losartan exhibited a significant enhancing effect on these parameters compared with the diabetic group, but not restored to the control levels, whereas administration of CoPP combined with losartan led to the restoration of their normal levels. ICP demonstrated significant decline in diabetic rats. The use of CoPP and/or losartan led to its significant improvement compared with diabetic rats. Administration of either losartan and/or CoPP led to a significant increase in the cavernous sinusoids surface area of diabetic rats. Administration of losartan with SnMP significantly decreased the enhancing effect of losartan on the studied parameters.

CONCLUSION

The decline in erectile function in diabetes mellitus could be attributed to the downregulation of HO-1 gene expression. HO-1 induction added to Ang II receptor antagonist could improve erectile function.

Diabetes impairs the vascular recruitment of normal stem cells by oxidant damage, reversed by increases in pAMPK, heme oxygenase-1, and adiponectin

BACKGROUND

Atherosclerosis progression is accelerated in diabetes mellitus (DM) by either direct endothelial damage or reduced availability and function of endothelial progenitor cells (EPCs). Both alterations are related to increased oxidant damage.

AIM

We examined if DM specifically impairs vascular signaling, thereby reducing the recruitment of normal EPCs, and if increases in antioxidant levels by induction of heme oxygenase-1 (HO-1) can reverse this condition.

METHODS

Control and diabetic rats were treated with the HO-1 inducer cobalt protoporphyrin (CoPP) once a week for 3 weeks. Eight weeks after the development of diabetes, EPCs harvested from the aorta of syngenic inbred normal rats and labeled with technetium-99m-exametazime were infused via the femoral vein to estimate their blood clearance and aortic recruitment. Circulating endothelial cells (CECs) and the aortic expression of thrombomodulin (TM), CD31, and endothelial nitric oxide synthase (eNOS) were used to measure endothelial damage.

RESULTS

DM reduced blood clearance and aortic recruitment of EPCs. Both parameters were returned to control levels by CoPP treatment without affecting EPC kinetics in normal animals. These abnormalities of EPCs in DM were paralleled by reduced serum adiponectin levels, increased numbers of CECs, reduced endothelial expression of phosphorylated eNOS, and reduced levels of TM, CD31, and phosphorylated AMP-activated protein kinase (pAMPK). CoPP treatment restored all of these parameters to normal levels.

CONCLUSION

Type II DM and its related oxidant damage hamper the interaction between the vascular wall and normal EPCs by mechanisms that are, at least partially, reversed by the induction of HO-1 gene expression, adiponectin, and pAMPK levels.

The L-4F mimetic peptide prevents insulin resistance through increased levels of HO-1, pAMPK, and pAKT in obese mice

We examined mechanisms by which L-4F reduces obesity and diabetes in obese (ob) diabetic mice. We hypothesized that L-4F reduces adiposity via increased pAMPK, pAKT, HO-1, and increased insulin receptor phosphorylation in ob mice. Obese and lean mice were divided into five groups: lean, lean-L-4F-treated, ob, ob-L-4F-treated, and ob-L-4F-LY294002. Food intake, insulin, glucose adipocyte stem cells, pAMPK, pAKT, CB1, and insulin receptor phosphorylation were determined. Subcutaneous (SAT) and visceral adipose tissue (VAT) were determined by MRI and hepatic lipid content by magnetic resonance spectroscopy. SAT and VAT volumes decreased in ob-L-4F-treated animals compared with control. L-4F treatment decreased hepatic lipid content and increased the numbers of small adipocytes (P < 0.05) and phosphorylation of insulin receptors. L-4F decreased CB1 in SAT and VAT and increased pAKT and pAMPK in endothelium. L-4F-mediated improvement in endothelium was prevented by LY294002. Inhibition of pAKT and pAMPK by LY294002 was associated with an increase in glucose levels. Upregulation of HO-1 by L-4F produced adipose remodeling and increased the number of small differentiated adipocytes. The anti-obesity effects of L-4F are manifested by a decrease in visceral fat content with reciprocal increases in adiponectin, pAMPK, pAKT, and phosphorylation of insulin receptors with improved insulin sensitivity.

Heme oxygenase-1 induction remodels adipose tissue and improves insulin sensitivity in obesity-induced diabetic rats

Obesity-associated inflammation causes insulin resistance. Obese adipose tissue displays hypertrophied adipocytes and increased expression of the cannabinoid-1 receptor. Cobalt protoporphyrin (CoPP) increases heme oxygenase-1 (HO-1) activity, increasing adiponectin and reducing inflammatory cytokines. We hypothesize that CoPP administration to Zucker diabetic fat (ZDF) rats would improve insulin sensitivity and remodel adipose tissue. Twelve-week-old Zucker lean and ZDF rats were divided into 4 groups: Zucker lean, Zucker lean-CoPP, ZDF, and ZDF-CoPP. Control groups received vehicle and treatment groups received CoPP (2 mg/kg body weight) once weekly for 6 weeks. Serum insulin levels and glucose response to insulin injection were measured. At 18 weeks of age, rats were euthanized, and aorta, kidney, and subcutaneous and visceral adipose tissues were harvested. HO-1 expression was measured by Western blot analysis and HO-1 activity by serum carbon monoxide content. Adipocyte size and cannabinoid-1 expression were measured. Adipose tissue volumes were determined using MRI. CoPP significantly increased HO-1 activity, phosphorylated AKT and phosphorylated AMP kinase, and serum adiponectin in ZDF rats. HO-1 induction improved hyperinsulinemia and insulin sensitivity in ZDF rats. Subcutaneous and visceral adipose tissue volumes were significantly decreased in ZDF rats. Adipocyte size and cannabinoid-1 expression were both significantly reduced in ZDF-CoPP rats in subcutaneous and visceral adipose tissues. This study demonstrates that HO-1 induction improves insulin sensitivity, downregulates the peripheral endocannabinoid system, reduces adipose tissue volume, and causes adipose tissue remodeling in a model of obesity-induced insulin resistance. These findings suggest HO-1 as a potential therapeutic target for obesity and its associated health risks.

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.

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.

Pharmacological and clinical aspects of heme oxygenase

This review is intended to stimulate interest in the effect of increased expression of heme oxygenase-1 (HO-1) protein and increased levels of HO activity on normal and pathological states. The HO system includes the heme catabolic pathway, comprising HO and biliverdin reductase, and the products of heme degradation, carbon monoxide (CO), iron, and biliverdin/bilirubin. The role of the HO system in diabetes, inflammation, heart disease, hypertension, neurological disorders, transplantation, endotoxemia and other pathologies is a burgeoning area of research. This review focuses on the clinical potential of increased levels of HO-1 protein and HO activity to ameliorate tissue injury. The use of pharmacological and genetic probes to manipulate HO, leading to new insights into the complex relationship of the HO system with biological and pathological phenomena under investigation, is reviewed. This information is critical in both drug development and the implementation of clinical approaches to moderate and to alleviate the numerous chronic disorders in humans affected by perturbations in the HO system.

Carbon monoxide donors or heme oxygenase-1 (HO-1) overexpression blocks interleukin-18-mediated NF-kappaB-PTEN-dependent human cardiac endothelial cell death

The objective of this study was to determine whether heme oxygenase-1 (HO-1) or heme metabolites exert cytoprotective effects on interleukin-18-mediated endothelial cell (EC) death. Treatment with interleukin (IL)-18 increased NF-kappaB activation and PTEN induction, suppressed Akt activation, and stimulated EC death. While ectopic expression of p65 enhanced PTEN transcription, adenoviral transduction of dnIkappaB-alpha, dnp65, or dnIKKbeta was inhibitory. Furthermore, IL-18 suppressed HO-1 mRNA expression via enhanced mRNA degradation. Overexpression of HO-1, treatment with HO-1 inducer hemin, or the CO donor cobalt (III) protoporphyrin IX all reversed IL-18-mediated NF-kappaB activation, PTEN induction, Akt suppression, and EC death. Furthermore, hemin induced HO-1 expression, and HO-1 knockdown, HO-1 inhibition, or CO scavengers all reversed the prosurvival effects of hemin. In addition, the CO donors CORM-1 and CORM-3 and the heme metabolites biliverdin and bilirubin attenuated IL-18-induced EC death via a similar signaling pathway. IL-18 induced p38alpha MAPK activation, and suppressed p38beta isoform expression. While p38alpha knockdown attenuated, p38beta knockdown potentiated IL-18-mediated EC death. Hemin and HO-1 reversed IL-18-mediated p38alpha induction and restored p38beta levels. These results demonstrate that IL-18 suppresses HO-1 expression and induces EC death. HO-1 overexpression, HO-1 induction, or treatment with heme metabolites all reverse IL-18-mediated p38alpha MAPK and NF-kappaB activation, PTEN induction, Akt suppression, and EC death. Thus, HO-1 inducers and CO donors may have the therapeutic potential to effectively block IL-18 signaling and reduce IL-18-dependent vascular injury and inflammation.

The TRPV1 receptor is associated with preferential stress in large dorsal root ganglion neurons in early diabetic sensory neuropathy

Chronic diabetic neuropathy is associated with peripheral demyelination and degeneration of nerve fibers. The mechanism(s) underlying neuronal injury in diabetic sensory neuropathy remain poorly understood. Recently, we reported increased expression and function of transient receptor potential vanilloid 1 (TRPV1) in large dorsal root ganglion (DRG) neurons in diabetic sensory neuropathy. In this study, we examined the effects of TRPV1 activation on cell injury pathways in this subpopulation of neurons in the streptozotocin-induced diabetic rat model. Large DRG neurons from diabetic (6-8 weeks) rats displayed increased oxidative stress and activation of cell injury markers compared with healthy controls. Capsaicin (CAP) treatment induced decreased labeling of MitoTracker Red and increased cytosolic cytochrome c and activation of caspase 3 in large neurons isolated from diabetic rats. CAP treatment also induced oxidative stress in large diabetic DRG neurons, which was blocked by pre-treatment with caspase or calpain inhibitor. In addition, both mu-calpain expression and calpain activity were significantly increased in DRG neurons from diabetic rats after CAP treatment. Treatment with capsazepine, a competitive TRPV1 antagonist, markedly reduced these abnormalities in vitro and prevented activation of cell injury in large DRG neurons in diabetic rats in vivo. These results suggest that activation of the TRPV1 receptor activates pathways associated with caspase-dependent and calpain-dependent stress in large DRG neurons in STZ-diabetic rats. Activation of the TRPV1 receptor may contribute to preferential neuronal stress in large DRG neurons relatively early in diabetic sensory neuropathy.

Akt activation improves oxidative phosphorylation in renal proximal tubular cells following nephrotoxicant injury

Previously, we showed that protein kinase B (Akt) activation increases intracellular ATP levels and decreases necrosis in renal proximal tubular cells (RPTC) injured by the nephrotoxicant S-(1, 2-dichlorovinyl)-l-cysteine (DCVC) (Shaik ZP, Fifer EK, Nowak G. Am J Physiol Renal Physiol 292: F292-F303, 2007). This study examined the role of Akt in improving mitochondrial function in DCVC-injured RPTC. Our data show a novel observation that phosphorylated (active) Akt is localized in mitochondria of noninjured RPTC, both in mitoplasts and the mitochondrial outer membrane. Mitochondrial levels of active Akt decreased in nephrotoxicant-injured RPTC, and this decrease was associated with mitochondrial dysfunction. DCVC decreased basal, uncoupled, and state 3 respirations; ATP production; activities of complexes I, II, and III; the mitochondrial membrane potential (DeltaPsi(m)); and F(0)F(1)-ATPase activity. Expressing constitutively active Akt in DCVC-injured RPTC increased the levels of phosphorylated Akt in mitochondria, reduced the decreases in basal and uncoupled respirations, increased complex I-coupled state 3 respiration and ATP production, enhanced activities of complex I, complex III, and F(0)F(1)-ATPase, and improved DeltaPsi(m). In contrast, inhibiting Akt activation by expressing dominant negative (inactive) Akt or using 20 microM LY294002 exacerbated decreases in electron transport rate, state 3 respiration, ATP production, DeltaPsi(m), and activities of complex I, complex III, and F(0)F(1)-ATPase. In conclusion, our data show that Akt activation promotes mitochondrial respiration and ATP production in toxicant-injured RPTC by 1) improving integrity of the respiratory chain and maintaining activities of complex I and complex III, 2) reducing decreases in DeltaPsi(m), and 3) restoring F(0)F(1)-ATPase activity.

Targeting endothelial cells with heme oxygenase-1 gene using VE-cadherin promoter attenuates hyperglycemia-mediated cell injury and apoptosis

Risk factors for cardiovascular diseases include hyperglycemia, TNF, and reactive oxygen species (ROS), which collectively contribute to vascular endothelial cell dysfunction and apoptosis. We examined, in vascular endothelial cells, whether the selective expression of heme oxygenase-1 (HO-1) offers cytoprotection against glucose- and TNF-mediated cell death. An adenoviral vector expressing human HO-1 was constructed using a VE-cadherin (VECAD) promotor fragment, and cell-specific expression of the recombinant adenovirus was examined using endothelial and vascular smooth muscle cells. The effects of HO-1 transduction (Ad-VECAD-HO-1 gene) on HO-1 expression, HO activity, and the response to TNF and hyperglycemia were studied. Human HO-1 gene was selectively expressed in endothelial cells after infection with the Ad-VECAD-HO-1 vector. Selective expression of HO-1 prevented TNF- and hyperglycemia-mediated superoxide (O2-) formation, DNA degeneration, and upregulation of caspase, but increased the expression of pAkt and Bcl-xL, proteins responsible for endothelial dysfunction in diabetes. These results demonstrate that endothelial cell survival after oxidative stress injury may be enhanced by targeting HO-1 expression, thus blocking inflammation, apoptosis, and thereby attenuating cardiovascular risk factors.

Heme oxygenase-1 protects against radiocontrast-induced acute kidney injury by regulating anti-apoptotic proteins

Radiocontrast agents are thought to induce acute kidney injury in part through increased production of reactive oxygen species and increased cellular apoptosis. In this study we determined whether heme oxygenase-1 could prevent or reduce radiocontrast-induced acute kidney injury and, if so, what were the mechanisms by which this can occur. Sodium iothalamate was administered to uninephrectomized, salt-depleted male Sabra rats to initiate acute kidney injury. Heme oxygenase-1 was induced with cobalt protoporphyrin or inhibited with stannous mesoporphyrin. Inhibition of heme oxygenase exacerbated kidney injury as measured by an increase in plasma creatinine and in superoxide production. Heme oxygenase-1 induction prevented the increase in plasma creatinine and in superoxide in both the cortex and medulla compared to untreated rats with acute kidney injury. This protective effect of heme oxygenase-1 was associated with increased anti-apoptotic proteins Bcl-2 and Bcl-xl and a decrease of pro-apoptotic caspase-3 and caspase-9 along with increased expression of inactive BAX. Our study suggests that increased levels of heme oxygenase-1 are protective against acute kidney injury due to radiocontrast exposure.

Interdiction of the diabetic state in NOD mice by sustained induction of heme oxygenase: possible role of carbon monoxide and bilirubin

The aims of the present study were to assess whether sustained HO-1 expression could moderate or prevent diabetes in an animal model of the disease and, if so, to examine the possible mechanisms involved. Our results showed that HO-1 expression and HO activity were upregulated in the pancreas of non-obese diabetic (NOD) mice by the weekly administration of cobalt protoporphyrin (CoPP). Blood glucose levels in CoPPtreated mice decreased to normal, but continuously increased in untreated controls. Beta-cell numbers were preserved in the islets of CoPP-treated mice, whereas no beta cells were found in untreated diabetic mice. The number of CD11c(+) dendritic cells was significantly decreased in the pancreas of CoPP-treated NOD mice, but this effect was reversed by the inhibition of HO activity. Increased levels of HO-1 produced a new pancreatic phenotype, as reflected by increases in phosphorylated AKT, BcL-xL and RSK levels, and decreases in O(2)- and 3-NT levels. These novel findings provide a link between the increase in HO-1 activity, with its concurrent enhanced production of carbon monoxide (CO) and bilirubin, a decrease in infiltrated CD11c(+) dendritic cells and an increase in anti-apoptotic proteins, including RSK and BcL-xL, in the interdiction of the diabetic state.

Oxidative stress biology and cell injury during type 1 and type 2 diabetes mellitus

Diabetes mellitus (DM) affects approximately 170 million individuals worldwide and is expected to alter the lives of at least 366 million individuals within a future span of 25 years. Of even greater concern is the premise that these projections are underestimated since they assume obesity levels will remain constant. Type 1 insulin-dependent DM accounts for only 5-10 percent of all diabetics but represents a highly significant health concern, since this disorder begins early in life and leads to long-term complications. In contrast, Type 2 DM is recognized as the etiology of over 80 percent of all diabetics and is dramatically increasing in incidence as a result of changes in human behavior and increased body mass index. Yet, the pathological consequences of these disorders that involve the both the neuronal and vascular systems are intimately linked through the pathways that mediate oxidative stress. Here we highlight some of the relevant oxidative pathways that determine insulin resistance through reactive oxygen species, mitochondrial dysfunction, uncoupling proteins, and endoplasmic reticulum stress. These pathways are ultimately linked to protein kinase B (Akt) and the insulin signaling pathways that determine the initial onset of glucose intolerance and the subsequent course to apoptotic cell injury. Through the elucidation of these targets, improvement in current strategies as well as the development of future clinical applications can move forward for both the prevention and treatment of Type 1 and Type 2 DM.

Impact of silencing HO-2 on EC-SOD and the mitochondrial signaling pathway

The contribution of heme oxygenase HO-2, the primary source of bilirubin and carbon monoxide (CO) under physiological conditions, to the regulation of vascular function has remained largely unexplored. Using siRNA HO-2, we examined the effect of suppressed levels of HO-2 on vascular antioxidant and survival proteins. In vivo HO-2 siRNA treatment decreased the basal levels of EC-SOD, pAKT proteins (serine-473 and threonine-308), without changing Akt protein expression. HO-2 siRNA treatment increased 3-nitrotyrosine (3-NT) and apoptotic signaling kinase-1 (ASK-1) (P < 0.01). HO activity was decreased by the use of siRNA HO-2. We extended these studies to the mitochondria, examining for the presence of HO-1 and its role in the regulation of pro- and anti-apoptotic proteins. HO activity was increased by the administration of CoPP resulting in the translocation of HO-1 into the mitochondria, mainly to the inner face of the mitochondrial inner membrane. These findings suggest that HO-2 is critical in the maintenance of heme homeostasis and also the regulation of apoptosis by controlling levels of EC-SOD, Akt, 3-NT, and ASK-1. In addition, localization of HO-1 in the mitochondrial compartment plays a critical role in mitochondria-mediated apoptosis.

Nanoparticles and cells: good companions and doomed partnerships

Engineered nanoparticles are emerging as useful tools for different purposes in life sciences, medicine and agriculture. Nanomedicine, an emerging discipline, involves the application of nanotechnology (usually regarded within the size range of 1-1000 nm) in the design of systems and devices that can facilitate our understanding of disease pathophysiology, nano-imaging, nanomedicines and nano-diagnostics. Among the different nanomaterials used to construct nanoparticles, are organic polymers, co-polymers and metals. Some of these materials can self assemble, and depending on the conditions under which the self-assembly process occurs, a vast array of shapes can be formed. Frequently, the nanoparticle morphology is spherical or tubular, mimicking the shape, but thus far, not the functions of subcellular organelles. We discuss here several representative nanoparticles, made of block copolymers and metals, highlighting some of their current uses, advantages and limitations in medicine. Nano-oncology and nano-neurosciences will also be discussed in more detail in the context of the intracellular fate of nanoparticles and possible long-term consequences on cell functions.

Mechanistic insights into diabetes mellitus and oxidative stress

Diabetes mellitus (DM) is a significant healthcare concern worldwide that affects more than 165 million individuals leading to cardiovascular disease, nephropathy, retinopathy, and widespread disease of both the peripheral and central nervous systems. The incidence of undiagnosed diabetes, impaired glucose tolerance, and impaired fasting glucose levels raises future concerns in regards to the financial and patient care resources that will be necessary to care for patients with DM. Interestingly, disease of the nervous system can become one of the most debilitating complications and affect sensitive cognitive regions of the brain, such as the hippocampus that modulates memory function, resulting in significant functional impairment and dementia. Oxidative stress forms the foundation for the induction of multiple cellular pathways that can ultimately lead to both the onset and subsequent complications of DM. In particular, novel pathways that involve metabotropic receptor signaling, protein-tyrosine phosphatases, Wnt proteins, Akt, GSK-3beta, and forkhead transcription factors may be responsible for the onset and progression of complications form DM. Further knowledge acquired in understanding the complexity of DM and its ability to impair cellular systems throughout the body will foster new strategies for the treatment of DM and its complications.

Angiotensin-induced hypoxia in the kidney: functional and structural changes of the renal circulation

Recent studies emphasize the role of chronic hypoxia in the kidney as a final common pathway to end-stage renal disease (ESRD). Hypoxia of tubular cells leads to apoptosis or epithelial-mesenchymal transdifferentiation. This in turn exacerbates fibrosis of the kidney with loss of peritubular capillaries and subsequent chronic hypoxia, setting in train a vicious cycle whose end point is ESRD. To support this notion, our studies utilizing various techniques such as hypoxia-sensing transgenic rats revealed hypoxia of the kidney in various disease models. While fibrotic kidneys with advanced renal disease are devoid of peritubular capillary blood supply and oxygenation to the corresponding region, imbalances in vasoactive substances and associated intrarenal vasoconstriction can cause chronic hypoxia even at the early phase of kidney disease. Among various vasoactive substances, local activation of RAS is especially important because it can lead to constriction of efferent arterioles, hypoperfusion of postglomerular peritubular capillaries, and subsequent hypoxia of the tubulointerstitium in the downstream compartment. Recent studies using BOLD-MRI showed an immediate decrease of oxygen tension in the kidney after angiotensin II infusion. In addition, angiotensin II induces oxidative stress via activation of NADPH oxidase. Oxidative stress damages endothelial cells directly, causing the loss of peritubular capillaries. Oxidative stress also results in relative hypoxia due to inefficient cellular respiration. Thus, angiotensin II induces renal hypoxia via both hemodynamic and nonhemodynamic mechanisms. While the beneficial effects of blockade of RAS in kidney disease are, at least in part, mediated by amelioration of hypoxia, recent studies have also elucidated the mechanism of hypoxia-induced gene regulation via the HIF-HRE system. This has given hope for the development of novel therapeutic approaches against hypoxia in the kidney.

HO-2 provides endogenous protection against oxidative stress and apoptosis caused by TNF-α in cerebral vascular endothelial cells

Tumor necrosis factor-α (TNF-α) causes oxidative stress and apoptosis in a variety of cell types. Heme oxygenase (HO) degrades heme to bilirubin, an antioxidant, and carbon monoxide (CO), a cell cycle modulator, and a vasodilator. Newborn pig cerebral microvascular endothelial cells (CMVEC) highly express constitutive HO-2. We investigated the role of HO-2 in protection against TNF-α-induced apoptosis in cerebral vascular endothelium. In CMVEC from mice and newborn pigs, 15 ng/ml TNF-α alone, or with 10 μg/ml cycloheximide (CHX) caused apoptosis detected by nuclear translocation of p65 NF-κB, caspase-3 activation, DNA fragmentation, cell-cell contact destabilization, and cell detachment. TNF-α did not induce HO-1 expression in CMVEC. CMVEC from HO-2 knockout mice showed greater sensitivity to apoptosis caused by serum deprivation and TNF-α than did wild-type mice. TNF-α increased reactive oxygen species generation, including hydrogen peroxide and superoxide radicals, as detected by dihydrorhodamine-123 and dihydroethidium. The TNF-α response was inhibited by superoxide dismutase and catalase suggesting apoptosis is oxidative stress related. Inhibition of endogenous HO-2 in newborn pig CMVEC increased oxidative stress and exaggerated apoptosis caused by serum deprivation and TNF-α. In HO-1-overexpressing CMVEC (HO-1 selective induction by cobalt portophyrin), TNF-α did not cause apoptosis. A CO-releasing compound, CORM-A1, and bilirubin blocked TNF-α-induced reactive oxygen species accumulation and apoptosis consistent with the antioxidant and antiapoptotic roles of the end products of HO activity. We conclude that HO-2 is critical for protection of cerebrovascular endothelium against apoptotic changes induced by oxidative stress and cytokine-mediated inflammation.

Role of Bach1 and Nrf2 in up-regulation of the heme oxygenase-1 gene by cobalt protoporphyrin

Heme oxygenase (HO) catalyzes the conversion of heme to biliverdin with the release of iron and carbon monoxide. HO-1 is highly inducible by a large number of physical and chemical factors. CoPP is known to be a potent and effective inducer of HO-1 activity in many tissues. Here we report that CoPP up-regulates HO-1 via Bach1 and Nrf2 in human liver cells. CoPP did not influence hepatic Bach1 or Nrf2 mRNA levels, but markedly reduced Bach1 protein levels by increasing degradation of Bach1 protein (t(1/2) from 19 h to 2.8 h), and increased Nrf2 by decreasing degradation of Nrf2 protein (t(1/2) from 2.5 h to 9 h). Silencing Bach1 by Bach1-siRNA significantly increased levels of HO-1 mRNA and protein, and addition of CoPP up-regulated HO-1 mRNA and protein further. However, silencing Nrf2 mRNA by Nrf2-siRNA did not significantly change baseline HO-1 mRNA or protein levels, but significantly decreased 5-10 microM CoPP-mediated up-regulation of HO-1 mRNA levels compared with CoPP alone. Transfection with equal amounts of non-Bach1 or non-Nrf2 related control siRNA did not reduce Bach1 or Nrf2 mRNA or protein, confirming the specificity of Bach1- and Nrf2-siRNA in Huh-7 cells. We conclude that the pathway of CoPP-mediated induction of HO-1 involves the repression of Bach1 and up-regulation of the Nrf2 protein by post-transcriptional site(s) of action. Because CoPP, unlike heme, is neither a prooxidant nor a substrate for HO-1, it might be considered as a potential therapeutic agent in situations where up-regulation of HO-1 is desired.

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.