Inhibition of vascular smooth muscle cell proliferation by chronic hemin treatment

A Thia-Analogous Indirubin N-Glycoside Disrupts Mitochondrial Function and Causes the Death of Human Melanoma and Cutaneous Squamous Cell Carcinoma Cells

Skin cancer is the most common malignant disease worldwide and, therefore, also poses a challenge from a pharmacotherapeutic perspective. Derivatives of indirubin are an interesting option in this context. In the present study, the effects of 3-[3'-oxo-benzo[b]thiophen-2'-(Z)-ylidene]-1-(β-d-glucopyranosyl)-oxindole (KD87), a thia-analogous indirubin N-glycoside, on the viability and mitochondrial properties of melanoma (A375) and squamous cell carcinoma cells (A431) of the skin were investigated. In both cell lines, KD87 caused decreased viability, the activation of caspases-3 and -7, and the inhibition of colony formation. At the mitochondrial level, a concentration-dependent decrease in both the basal and ATP-linked oxygen consumption rate and in the reserve capacity of oxidative respiration were registered in the presence of KD87. These changes were accompanied by morphological alterations in the mitochondria, a release of mitochondrial cytochrome c into the cytosol and significant reductions in succinate dehydrogenase complex subunit B (SDHB, subunit of complex II) in A375 and A431 cells and NADH:ubiquinone oxidoreductase subunit B8 (NDUFB8, subunit of complex I) in A375 cells. The effect of KD87 was accompanied by a significant upregulation of the enzyme heme oxygenase-1, whose inhibition led to a partial but significant reduction in the metabolic-activity-reducing effect of KD87. In summary, our data show a mitochondria-targeting effect of KD87 as part of the cytotoxic effect of this compound on skin cancer cells, which should be considered in future studies with this class of compounds.

Heme in Cardiovascular Diseases: A Ubiquitous Dangerous Molecule Worthy of Vigilance

Heme, the protoporphyrin IX iron complex is widely present in the human body and it is involved in oxygen storage, electron transfer, and enzymatic reactions. However, free heme can be toxic as it catalyzes the production of reactive oxygen species, oxidizes lipids and proteins, and causes DNA damage, thereby inducing a pro-inflammatory environment. The generation, metabolism, and degradation of heme in the human body are regulated by precise mechanisms to ensure that heme remains non-toxic. However, in several types of cardiovascular diseases, impaired metabolism and exposure to heme may occur in pathological processes, including neovascularization, internal hemorrhage, ischemia, and reperfusion. Based on years of research, in this review, we aimed to summarize the underlying mechanisms by which heme contributes to the development of cardiovascular diseases through oxidative stress, relative pathway gene expression regulation and phenotypic changes in cells. Excess heme plays a detrimental role in atherosclerosis, heart failure, myocardial ischemia-reperfusion injury, degenerative aortic valve stenosis, cardiac iron overload. Recent researches revealed that in some cases heme involved in cardiac damage though ferroptosis. Thus, heme concentrations beyond normal levels are dangerous. Further research on the role of heme in cardiovascular diseases is needed.

Cannabinoid-Induced Autophagy and Heme Oxygenase-1 Determine the Fate of Adipose Tissue-Derived Mesenchymal Stem Cells under Stressful Conditions

The administration of adipose tissue-derived mesenchymal stem cells (ADMSCs) represents a promising therapeutic option after myocardial ischemia or myocardial infarction. However, their potential is reduced due to the high post-transplant cell mortality probably caused by oxidative stress and mitogen-deficient microenvironments. To identify protection strategies for ADMSCs, this study investigated the influence of the non-psychoactive phytocannabinoid cannabidiol (CBD) and the endocannabinoid analogue R(+)-methanandamide (MA) on the induction of heme oxygenase-1 (HO-1) and autophagy under serum-free conditions. At a concentration of 3 µM, CBD induced an upregulation of HO-1 mRNA and protein within 6 h, whereas for MA only a late and comparatively lower increase in the HO-1 protein could be detected after 48 h. In addition, both cannabinoids induced time- and concentration-dependent increases in LC3A/B-II protein, a marker of autophagy, and in metabolic activity. A participation of several cannabinoid-binding receptors in the effect on metabolic activity and HO-1 was excluded. Similarly, knockdown of HO-1 by siRNA or inhibition of HO-1 activity by tin protoporphyrin IX (SnPPIX) had no effect on CBD-induced autophagy and metabolic activity. On the other hand, the inhibition of autophagy by bafilomycin A₁ led to a significant decrease in cannabinoid-induced metabolic activity and to an increase in apoptosis. Under these circumstances, a significant induction of HO-1 expression after 24 h could also be demonstrated for MA. Remarkably, inhibition of HO-1 by SnPPIX under conditions of autophagy deficit led to a significant reversal of apoptosis in cannabinoid-treated cells. In conclusion, the investigated cannabinoids increase metabolic viability of ADMSCs under serum-free conditions by inducing HO-1-independent autophagy but contribute to apoptosis under conditions of additional autophagy deficit via an HO-1-dependent pathway.

Cannabidiol Promotes Endothelial Cell Survival by Heme Oxygenase-1-Mediated Autophagy

Cannabidiol (CBD), a non-psychoactive cannabinoid, has been reported to mediate antioxidant, anti-inflammatory, and anti-angiogenic effects in endothelial cells. This study investigated the influence of CBD on the expression of heme oxygenase-1 (HO-1) and its functional role in regulating metabolic, autophagic, and apoptotic processes of human umbilical vein endothelial cells (HUVEC). Concentrations up to 10 µM CBD showed a concentration-dependent increase of HO-1 mRNA and protein and an increase of the HO-1-regulating transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2). CBD-induced HO-1 expression was not decreased by antagonists of cannabinoid-activated receptors (CB₁, CB₂, transient receptor potential vanilloid 1), but by the reactive oxygen species (ROS) scavenger N-acetyl-L-cysteine (NAC). The incubation of HUVEC with 6 µM CBD resulted in increased metabolic activity, while 10 µM CBD caused decreased metabolic activity and an induction of apoptosis, as demonstrated by enhanced caspase-3 cleavage. In addition, CBD triggered a concentration-dependent increase of the autophagy marker LC3A/B-II. Both CBD-induced LC3A/B-II levels and caspase-3 cleavage were reduced by NAC. The inhibition of autophagy by bafilomycin A₁ led to apoptosis induction by 6 µM CBD and a further increase of the proapoptotic effect of 10 µM CBD. On the other hand, the inhibition of HO-1 activity with tin protoporphyrin IX (SnPPIX) or knockdown of HO-1 expression by Nrf2 siRNA was associated with a decrease in CBD-mediated autophagy and apoptosis. In summary, our data show for the first time ROS-mediated HO-1 expression in endothelial cells as a mechanism by which CBD mediates protective autophagy, which at higher CBD concentrations, however, can no longer prevent cell death inducing apoptosis.

Effects of haem oxygenase-1 expression on oxidative injury and biological behaviours of rat dermal fibroblasts

OBJECTIVE

This study investigated the effects of high haem oxygenase-1 (HO-1) expression on oxidative injury and the biological behaviours of rat dermal fibroblasts, under high glucose conditions.

METHOD

Rat dermal fibroblasts were cultured in normal glucose (1.0g/l), high glucose (4.5g/l) or haemin (5μm). A bilirubin kit, real-time polymerase chain reaction (RT-PCR) and Western blotting measured the protease activity, mRNA, and protein levels of HO-1, respectively. An enzyme-linked immunosorbent assay (ELISA) kit measured media levels of 8-hydroxydeoxyguanosine (8-OHdG), reactive oxygen species (ROS) and collagen (hydroxyproline) secretion. Cell proliferation was measured using flow cytometry. Cell apoptosis was measured using Hoechst 33258 staining and flow cytometry. The transwell method and scratch test evaluated cell migration.

RESULTS

HO-1 expression exhibited a time-dependent change that was lowest in the high glucose (HG) group at 96 hours compared with the normal glucose (NG) group. In the HG group, the 8-OHdG, ROS and cell apoptosis were increased, and collagen secretion, cell proliferation and cell migration (horizontal and vertical) were decreased compared with the NG group at 96 hours. Haemin treatment sustained high HO-1 expression for at least 96 hours, and the cells exhibited decreased 8-OHdG and ROS, increased collagen synthesis, improved proliferation and migration ability, and decreased apoptosis in the NG and haemin (NH) group/HG and haemin (HH) group compared with the NG/HG groups. These cells recovered from oxidative injury and biological behaviours dysfunction.

CONCLUSION

Haemin induces HO-1 expression in fibroblasts and it may influence the oxidative injury and biological behaviours of fibroblasts. These findings suggest that HO-1 may accelerate the healing of diabetic wounds via alleviation of oxidative injury and improvement of biological behaviours of fibroblasts.

Amelioration of estrogen-induced endometrial hyperplasia in female rats by hemin via heme-oxygenase-1 expression, suppression of iNOS, p38 MAPK, and Ki67

Although heme oxygenase-1 (HO-1) is part of an endogenous defense system implicated in the homeostatic response, its role in cell proliferation and tumor progression is still controversial. Endometrial hyperplasia (EH) is associated with high risk of endometrial cancer (EC). Therefore, we aimed to evaluate the effect of hemin, a HO-1 inducer, against EH. Thirty-two female rats (60-70 days old) were divided into 4 groups treated for 1 week: vehicle control group, hemin group (25 mg/kg; i.p. 3 times/week), estradiol valerate (EV) group (2 mg/kg per day, p.o.), and hemin plus EV group. Sera were obtained for reduced glutathione level. Uterine malondialdehyde, superoxide dismutase, total nitrite/nitrate, and interleukin-1β levels were estimated. HO-1 and p38 mitogen-activated protein kinase expressions were obtained in uterine tissue. Uterine histological and immunohistochemical assessment of iNOS and Ki67 were also done. Results demonstrated that upregulation of HO-1 expression in hemin plus EV rats led to amelioration of EH which was confirmed with histological examination. This was associated with significant decrease in oxidative stress parameters, p38 mitogen-activated protein kinase expression, and interleukin-1β level. Also, uterine iNOS and Ki67 expressions were markedly suppressed. In conclusion, upregulation of HO-1 expression via hemin has ameliorative effect against EH through its antioxidant, anti-inflammatory, and antiproliferative actions.

Up-regulation of heme oxygenase-1 expression and inhibition of disease-associated features by cannabidiol in vascular smooth muscle cells

Aberrant proliferation and migration of vascular smooth muscle cells (VSMC) have been closely linked to the development and progression of cardiovascular and cancer diseases. The cytoprotective enzyme heme oxygenase-1 (HO-1) has been shown to mediate anti-proliferative and anti-migratory effects in VSMC. This study investigates the effect of cannabidiol (CBD), a non-psychoactive cannabinoid, on HO-1 expression and disease-associated functions of human umbilical artery smooth muscle cells (HUASMC). HO-1 protein and mRNA were significantly increased by CBD in a time- and concentration-dependent manner. Although the expression of several cannabinoid-activated receptors (CB₁, CB₂, G protein-coupled receptor 55, transient receptor potential vanilloid 1) was verified in HUASMC, CBD was shown to induce HO-1 via none of these targets. Instead, the CBD-mediated increase in HO-1 protein was reversed by the glutathione precursor N-acetylcysteine, indicating the participation of reactive oxygen species (ROS) signaling; this was confirmed by flow cytometry-based ROS detection. CBD-induced HO-1 expression was accompanied by inhibition of growth factor-mediated proliferation and migration of HUASMC. However, neither inhibition of HO-1 activity nor knockdown of HO-1 protein attenuated CBD-mediated anti-proliferative and anti-migratory effects. Indeed, inhibition or depletion of HO-1 resulted in induction of apoptosis and intensified CBD-mediated effects on proliferation and migration. Collectively, this work provides the first indication of CBD-mediated enhancement of HO-1 in VSMC and potential protective effects against aberrant VSMC proliferation and migration. On the other hand, our data argue against a role of HO-1 in CBD-mediated inhibition of proliferation and migration while substantiating its anti-apoptotic role in oxidative stress-mediated cell fate.

SB202190 inhibits endothelial cell apoptosis via induction of autophagy and heme oxygenase-1

Activation of the p38 mitogen-activated protein kinase (MAPK) pathway has been implicated in various detrimental events finally leading to endothelial dysfunction. The present study therefore investigates the impact of the p38 MAPK inhibitor SB202190 on the expression of the cytoprotective enzyme heme oxygenase-1 (HO-1) as well as metabolic activity, apoptosis and autophagy of endothelial cells. Using human umbilical vein endothelial cells (HUVEC) SB202190 was found to cause a time- and concentration-dependent induction of HO-1 protein. Induction of HO-1 protein expression was mimicked by SB203580, another p38 MAPK inhibitor, but not by SB202474, an inactive structural analogue of p38 MAPK inhibitors. HO-1 induction by both SB202190 and SB203580 was also demonstrated by analysis of mRNA expression. On the functional level, SB202190 was shown to increase metabolic activity and autophagy of HUVEC along with diminishing basal apoptosis. Treatment of cells with tin protoporphyrin IX (SnPPIX), a well-characterised HO-1 enzymatic inhibitor, or HO-1 siRNA left SB202190-modulated metabolic activity and autophagy virtually unaltered but caused a significant reversal of the anti-apoptotic action of SB202190. Conversely, however, HO-1 expression by SB202190 became completely suppressed by the autophagy inhibitor bafilomycin A1. Bafilomycin A1 likewise fully reversed effects of SB202190 on metabolic activity and apoptosis, albeit significantly inducing apoptosis per se. Collectively, this work demonstrates SB202190 to confer upstream induction of autophagy followed by HO-1 induction resulting in potential protective effects against apoptosis. On the other hand, our data oppose HO-1 to contribute to SB202190-mediated increases in metabolic activity and autophagy, respectively.

Multiple mechanisms mediating carbon monoxide inhibition of the voltage-gated K+ channel Kv1.5

The voltage-gated K+ channel has key roles in the vasculature and in atrial excitability and contributes to apoptosis in various tissues. In this study, we have explored its regulation by carbon monoxide (CO), a product of the cytoprotective heme oxygenase enzymes, and a recognized toxin. CO inhibited recombinant Kv1.5 expressed in HEK293 cells in a concentration-dependent manner that involved multiple signalling pathways. CO inhibition was partially reversed by superoxide dismutase mimetics and by suppression of mitochondrial reactive oxygen species. CO also elevated intracellular nitric oxide (NO) levels. Prevention of NO formation also partially reversed CO inhibition of Kv1.5, as did inhibition of soluble guanylyl cyclase. CO also elevated intracellular peroxynitrite levels, and a peroxynitrite scavenger markedly attenuated the ability of CO to inhibit Kv1.5. CO caused nitrosylation of Kv1.5, an effect that was also observed in C331A and C346A mutant forms of the channel, which had previously been suggested as nitrosylation sites within Kv1.5. Augmentation of Kv1.5 via exposure to hydrogen peroxide was fully reversed by CO. Native Kv1.5 recorded in HL-1 murine atrial cells was also inhibited by CO. Action potentials recorded in HL-1 cells were increased in amplitude and duration by CO, an effect mimicked and occluded by pharmacological inhibition of Kv1.5. Our data indicate that Kv1.5 is a target for modulation by CO via multiple mechanisms. This regulation has important implications for diverse cellular functions, including excitability, contractility and apoptosis.

Heme Oxygenases in Cardiovascular Health and Disease

Heme oxygenases are composed of two isozymes, Hmox1 and Hmox2, that catalyze the degradation of heme to carbon monoxide (CO), ferrous iron, and biliverdin, the latter of which is subsequently converted to bilirubin. While initially considered to be waste products, CO and biliverdin/bilirubin have been shown over the last 20 years to modulate key cellular processes, such as inflammation, cell proliferation, and apoptosis, as well as antioxidant defense. This shift in paradigm has led to the importance of heme oxygenases and their products in cell physiology now being well accepted. The identification of the two human cases thus far of heme oxygenase deficiency and the generation of mice deficient in Hmox1 or Hmox2 have reiterated a role for these enzymes in both normal cell function and disease pathogenesis, especially in the context of cardiovascular disease. This review covers the current knowledge on the function of both Hmox1 and Hmox2 at both a cellular and tissue level in the cardiovascular system. Initially, the roles of heme oxygenases in vascular health and the regulation of processes central to vascular diseases are outlined, followed by an evaluation of the role(s) of Hmox1 and Hmox2 in various diseases such as atherosclerosis, intimal hyperplasia, myocardial infarction, and angiogenesis. Finally, the therapeutic potential of heme oxygenases and their products are examined in a cardiovascular disease context, with a focus on how the knowledge we have gained on these enzymes may be capitalized in future clinical studies.

H2S does not regulate proliferation via T-type Ca2+ channels

T-type Ca(2+) channels (Cav3.1, 3.2 and 3.3) strongly influence proliferation of various cell types, including vascular smooth muscle cells (VSMCs) and certain cancers. We have recently shown that the gasotransmitter carbon monoxide (CO) inhibits T-type Ca(2+) channels and, in so doing, attenuates proliferation of VSMC. We have also shown that the T-type Ca(2+) channel Cav3.2 is selectively inhibited by hydrogen sulfide (H2S) whilst the other channel isoforms (Cav3.1 and Cav3.3) are unaffected. Here, we explored whether inhibition of Cav3.2 by H2S could account for the anti-proliferative effects of this gasotransmitter. H2S suppressed proliferation in HEK293 cells expressing Cav3.2, as predicted by our previous observations. However, H2S was similarly effective in suppressing proliferation in wild type (non-transfected) HEK293 cells and those expressing the H2S insensitive channel, Cav3.1. Further studies demonstrated that T-type Ca(2+) channels in the smooth muscle cell line A7r5 and in human coronary VSMCs strongly influenced proliferation. In both cell types, H2S caused a concentration-dependent inhibition of proliferation, yet by far the dominant T-type Ca(2+) channel isoform was the H2S-insensitive channel, Cav3.1. Our data indicate that inhibition of T-type Ca(2+) channel-mediated proliferation by H2S is independent of the channels' sensitivity to H2S.

T-Type Ca2+ Channel Regulation by CO: A Mechanism for Control of Cell Proliferation

T-type Ca(2+) channels regulate proliferation in a number of tissue types, including vascular smooth muscle and various cancers. In such tissues, up-regulation of the inducible enzyme heme oxygenase-1 (HO-1) is often observed, and hypoxia is a key factor in its induction. HO-1 degrades heme to generate carbon monoxide (CO) along with Fe(2+) and biliverdin. Since CO is increasingly recognized as a regulator of ion channels (Peers et al. 2015), we have explored the possibility that it may regulate proliferation via modulation of T-type Ca(2+) channels.Whole-cell patch-clamp recordings revealed that CO (applied as the dissolved gas or via CORM donors) inhibited all 3 isoforms of T-type Ca(2+) channels (Cav3.1-3.3) when expressed in HEK293 cells with similar IC(50) values, and induction of HO-1 expression also suppressed T-type currents (Boycott et al. 2013). CO/HO-1 induction also suppressed the elevated basal [Ca(2+) ](i) in cells expressing these channels and reduced their proliferative rate to levels seen in non-transfected control cells (Duckles et al. 2015).Proliferation of vascular smooth muscle cells (both A7r5 and human saphenous vein cells) was also suppressed either by T-type Ca(2+) channel inhibitors (mibefradil and NNC 55-0396), HO-1 induction or application of CO. Effects of these blockers and CO were non additive. Although L-type Ca(2+) channels were also sensitive to CO (Scragg et al. 2008), they did not influence proliferation. Our data suggest that HO-1 acts to control proliferation via CO modulation of T-type Ca(2+) channels.

Heme oxygenase-1 ameliorates dextran sulfate sodium-induced acute murine colitis by regulating Th17/Treg cell balance

Inflammatory bowel disease (IBD), including ulcerative colitis and Crohn's disease, is a group of autoimmune diseases characterized by nonspecific inflammation in the gastrointestinal tract. Recent investigations suggest that activation of Th17 cells and/or deficiency of regulatory T cells (Treg) is involved in the pathogenesis of IBD. Heme oxygenase (HO)-1 is a protein with a wide range of anti-inflammatory and immune regulatory function, which exerts significantly protective roles in various T cell-mediated diseases. In this study, we aim to explore the immunological regulation of HO-1 in the dextran sulfate sodium-induced model of experimental murine colitis. BALB/c mice were administered 4% dextran sulfate sodium orally; some mice were intraperitoneally pretreated with HO-1 inducer hemin or HO-1 inhibitor stannum protoporphyrin IX. The results show that hemin enhances the colonic expression of HO-1 and significantly ameliorates the symptoms of colitis with improved histological changes, accompanied by a decreased proportion of Th17 cells and increased number of Tregs in mesenteric lymph node and spleen. Moreover, induction of HO-1 down-regulates retinoic acid-related orphan receptor γt expression and IL-17A levels, while promoting Treg-related forkhead box p3 (Foxp3) expression and IL-10 levels in colon. Further study in vitro revealed that up-regulated HO-1 switched the naive T cells to Tregs when cultured under a Th17-inducing environment, which involved in IL-6R blockade. Therefore, HO-1 may exhibit anti-inflammatory activity in the murine model of acute experimental colitis via regulating the balance between Th17 and Treg cells, thus providing a possible novel therapeutic target in IBD.

Heme oxygenase-1 regulates cell proliferation via carbon monoxide-mediated inhibition of T-type Ca2+ channels

Induction of the antioxidant enzyme heme oxygenase-1 (HO-1) affords cellular protection and suppresses proliferation of vascular smooth muscle cells (VSMCs) associated with a variety of pathological cardiovascular conditions including myocardial infarction and vascular injury. However, the underlying mechanisms are not fully understood. Over-expression of Ca_v3.2 T-type Ca²⁺ channels in HEK293 cells raised basal [Ca²⁺]_i and increased proliferation as compared with non-transfected cells. Proliferation and [Ca²⁺]_i levels were reduced to levels seen in non-transfected cells either by induction of HO-1 or exposure of cells to the HO-1 product, carbon monoxide (CO) (applied as the CO releasing molecule, CORM-3). In the aortic VSMC line A7r5, proliferation was also inhibited by induction of HO-1 or by exposure of cells to CO, and patch-clamp recordings indicated that CO inhibited T-type (as well as L-type) Ca²⁺ currents in these cells. Finally, in human saphenous vein smooth muscle cells, proliferation was reduced by T-type channel inhibition or by HO-1 induction or CO exposure. The effects of T-type channel blockade and HO-1 induction were non-additive. Collectively, these data indicate that HO-1 regulates proliferation via CO-mediated inhibition of T-type Ca²⁺ channels. This signalling pathway provides a novel means by which proliferation of VSMCs (and other cells) may be regulated therapeutically.

Heme oxygenase-1 exerts a protective role in ovalbumin-induced neutrophilic airway inflammation by inhibiting Th17 cell-mediated immune response

Allergic asthma is conventionally considered as a Th2 immune response characterized by eosinophilic inflammation. Recent investigations revealed that Th17 cells play an important role in the pathogenesis of non-eosinophilic asthma (NEA), resulting in steroid-resistant neutrophilic airway inflammation. Heme oxygenase-1 (HO-1) has anti-inflammation, anti-oxidation, and anti-apoptosis functions. However, its role in NEA is still unclear. Here, we explore the role of HO-1 in a mouse model of NEA. HO-1 inducer hemin or HO-1 inhibitor tin protoporphyrin IX was injected intraperitoneally into ovalbumin-challenged DO11.10 mice. Small interfering RNA (siRNA) was delivered into mice to knock down HO-1 expression. The results show that induction of HO-1 by hemin attenuated airway inflammation and decreased neutrophil infiltration in bronchial alveolar lavage fluid and was accompanied by a lower proportion of Th17 cells in mediastinal lymph nodes and spleen. More importantly, induction of HO-1 down-regulated Th17-related transcription factor retinoic acid-related orphan receptor γt (RORγt) expression and decreased IL-17A levels, all of which correlated with a decrease in phosphorylated STAT3 (p-STAT3) level and inhibition of Th17 cell differentiation. Consistently, the above events could be reversed by tin protoporphyrin IX. Also, HO-1 siRNA transfection abolished the effect of hemin induced HO-1 in vivo. Meanwhile, the hemin treatment promoted the level of Foxp3 expression and enhanced the proportion of regulatory T cells (Tregs). Collectively, our findings indicate that HO-1 exhibits anti-inflammatory activity in the mouse model of NEA via inhibition of the p-STAT3-RORγt pathway, regulating kinetics of RORγt and Foxp3 expression, thus providing a possible novel therapeutic target in asthmatic patients.

Carbon monoxide inhibition of Cav3.2 T-type Ca2+ channels reveals tonic modulation by thioredoxin

T-type Ca(2+) channels play diverse roles in tissues such as sensory neurons, vascular smooth muscle, and cancers, where increased expression of the cytoprotective enzyme, heme oxygenase-1 (HO-1) is often found. Here, we report regulation of T-type Ca(2+) channels by carbon monoxide (CO) a HO-1 by-product. CO (applied as CORM-2) caused a concentration-dependent, poorly reversible inhibition of all T-type channel isoforms (Cav3.1-3.3, IC50 ∼3 μM) expressed in HEK293 cells, and native T-type channels in NG108-15 cells and primary rat sensory neurons. No recognized CO-sensitive signaling pathway could account for the CO inhibition of Cav3.2. Instead, CO sensitivity was mediated by an extracellular redox-sensitive site, which was also highly sensitive to thioredoxin (Trx). Trx depletion (using auranofin, 2-5 μM) reduced Cav3.2 currents and their CO sensitivity by >50% but increased sensitivity to dithiothreitol ∼3-fold. By contrast, Cav3.1 and Cav3.3 channels, and their sensitivity to CO, were unaffected in identical experiments. Our data propose a novel signaling pathway in which Trx acts as a tonic, endogenous regulator of Cav3.2 channels, while HO-1-derived CO disrupts this regulation, causing channel inhibition. CO modulation of T-type channels has widespread implications for diverse physiological and pathophysiological mechanisms, such as excitability, contractility, and proliferation.

Heme oxygenase-1 transgenic overexpression did not prevent artery injury induced by electric stimulation and pressure overload in mice

Heme oxygenase-1 (HO-1) shows multiple beneficial effects on cardiovascular diseases. However, the effect of HO-1 on the injury of artery has never been identified. In the present study, we established systemic HO-1 overexpression transgenic mice and investigated the effect of HO-1 on the injury of artery induced by electric stimulation and pressure-overload in transgenic mice. Artery injury was induced by electric stimulation and pressure overload. The contractive function, endothelium-dependent and -independent relaxation of arteries were measured through an isometric force transducer connected to a multichannel acquisition and analysis system. Western blot results showed that HO-1 protein level in transgenic mice arteries was significantly higher than that in wild type mice arteries, while no difference of HO-2 protein level in the arteries of transgenic and wild type mice. Arterial reendothelialization after electric injury was accelerated in transgenic mice. No significant difference in contractive function, endothelium-dependent and -independent relaxation of arteries was observed between wild type and transgenic mice at day 7 after electric injury and 4 weeks after pressure overload. We concluded that HO-1 overexpression accelerated the reendothelialization, but did not prevent the functional impairment of injured artery in mice.

Neferine inhibits angiotensin II-stimulated proliferation in vascular smooth muscle cells through heme oxygenase-1

AIM

To explore the effect of neferine on angiotensin II (Ang II)-induced vascular smooth muscle cell (VSMC) proliferation.

METHODS

Human umbilical vein smooth muscle cells (HUVSMCs) were used. Cell proliferation was determined by using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and flow cytometry analysis. Heme oxygenase (HO)-1 protein expression was tested by Western blot analysis. Extracellular signal-regulated protein kinase 1/2 (ERK1/2) activation was determined by using immunoblotting.

RESULTS

Pre-incubation of HUVSMCs with neferine (0.1, 0.5, 1.0, and 5.0 micromol/L) significantly inhibited Ang II-induced cell proliferation in a concentration-dependent manner and neferine 5.0 micromol/L increased HO-1 expression by 259% compared with control. The antiproliferative effect of neferine was significantly attenuated by coapplication of zinc protoporphyrin IX (ZnPP IX, an HO-1 inhibitor) with neferine. Ang II-enhanced ERK1/2 phosphorylation was markedly reversed by neferine. By inhibiting HO-1 activity with ZnPP IX, the inhibitive effect of neferine on ERK1/2 phosphorylation was significantly attenuated. Cobalt-protoporphyrin (CoPP), an HO-1 inducer, significantly decreased Ang II-induced ERK1/2 phosphorylation and inhibited Ang II-induced cell proliferation. The ERK1/2 pathway inhibitor PD98059 significantly blocked Ang II-enhanced ERK1/2 phosphorylation and inhibited cell proliferation.

CONCLUSION

These findings suggest that neferine can inhibit Ang II-induced HUVSMC proliferation by upregulating HO-1, leading to the at least partial downregulation of ERK1/2 phosphorylation.

Interaction of methylglyoxal and hydrogen sulfide in rat vascular smooth muscle cells

Hydrogen sulfide (H(2)S) is a gasotransmitter with multifaceted physiological functions, including the regulation of glucose metabolism. Methylglyoxal (MG) is an intermediate of glucose metabolism and plays an important role in the pathogenesis of insulin resistance syndromes. In the present study, we investigated the effect of MG on H(2)S synthesis and the interaction between these two endogenous substances. In cultured vascular smooth muscle cells (VSMCs), MG (10, 30, and 50 microM) significantly decreased cellular H(2)S levels in a concentration-dependent manner, while H(2)S donor, NaHS (30, 60, and 90 microM), significantly decreased cellular MG levels. The expression level and activity of H(2)S-producing enzyme, cystathionine gamma-lyase (CSE), were significantly decreased by MG treatment. NaHS (30-90 microM) significantly inhibited MG (10 or 30 microM)-induced ROS production. Cellular levels of GSH, cysteine, and homocysteine were also increased by MG or NaHS treatment. Furthermore, direct reaction of H(2)S with MG in both concentration- and time-dependent manners were observed in in vitro incubations. In conclusion, MG regulates H(2)S level in VSMCs by downregulating CSE protein expression and directly reacting with H(2)S molecule. Interaction of MG with H(2)S may be one of future directions for the studies on glucose metabolism and the development of insulin resistance syndromes.

Hemin prevents in-stent stenosis in rat and rabbit models by inducing heme-oxygenase-1

OBJECTIVE

The introduction of drug-eluting stents (DES) has largely added benefit to the percutaneous coronary intervention. Questions about the long-term safety of DES have been raised, however, particularly with respect to late stent thrombosis. Research efforts are now being directed toward therapeutics that can impede smooth muscle proliferation and promote vascular healing. Emerging data suggest that heme oxygenase-1 (HO-1), an inducible oxidoreductase enzyme system, can exert cytoprotective effects on endothelial cells and limit smooth muscle cell proliferation. We assessed the ability of hemin, a potent HO-1 inducer, to reduce in-stent stenosis without compromising re-endothelialization.

METHODS

Rat aorta and rabbit iliac arteries were stented. Animals received ongoing treated with intraperitoneal hemin (50 mg/kg) or vehicle. At 7 to 28 days after surgery, stented arterial segments were collected and processed for histologic, electron microscopy, or protein analysis.

RESULTS

In both models, treatment with hemin reduced neointima growth without compromising re-endothelialization of the stented arteries. In the rat aorta, analysis of protein expression at 7 and 28 days after stenting revealed that hemin increased HO-1 expression and limited the early inflammatory, apoptotic, and proliferative cellular events that are common to in-stent stenosis. Hemin treatment decreased the expression of the Ki-67 protein and the activity of key regulators of smooth muscle cell proliferation, including p42/44, RhoA, and up-regulated the expression of cyclin-dependent kinase inhibitors. The beneficial effects of hemin were abolished in the presence of tin-protoporphyrin IX, an HO inhibitor. Finally, treatment with tricarbonylchloro(glycinato)ruthenium(II), a carbon monoxide donor, reduced in-stent stenosis in the rat aorta, suggesting that carbon monoxide, a by-product of heme degradation, might contribute to the protective effect of hemin.

CONCLUSION

These results suggest that HO-1 is important in limiting in-stent stenosis and can be regarded as a new therapeutic target.

Heme oxygenase-1/p21WAF1 mediates peroxisome proliferator-activated receptor-gamma signaling inhibition of proliferation of rat pulmonary artery smooth muscle cells

Activation of peroxisome proliferator-activated receptor (PPAR)-gamma suppresses proliferation of rat pulmonary artery smooth muscle cells (PASMCs), and therefore ameliorates the development of pulmonary hypertension in animal models. However, the molecular mechanisms underlying this effect remain largely unknown. This study addressed this issue. The PPARgamma agonist rosiglitazone dose-dependently stimulated heme oxygenase (HO)-1 expression in PASMCs, 5 microm rosiglitazone inducing a 12.1-fold increase in the HO-1 protein level. Cells pre-exposed to rosiglitazone showed a dose-dependent reduction in proliferation in response to serotonin; this was abolished by pretransfection of cells with sequence-specific small interfering RNA against HO-1. In addition, rosiglitazone stimulated p21(WAF1) expression in PASMCs, a 2.34-fold increase in the p21(WAF1) protein level being achieved with 5 microm rosiglitazone; again, this effect was blocked by knockdown of HO-1. Like loss of HO-1, loss of p21(WAF1) through siRNA transfection also reversed the inhibitory effect of rosiglitazone on PASMC proliferation triggered by serotonin. Taken together, our findings suggest that activation of PPARgamma induces HO-1 expression, and that this in turn stimulates p21(WAF1) expression to suppress PASMC proliferation. Our study also indicates that rosiglitazone, a medicine widely used in the treatment of type 2 diabetes mellitus, has potential benefits for patients with pulmonary hypertension.

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

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

Heme oxygenase-1 induced by aprotinin inhibits vascular smooth muscle cell proliferation through cell cycle arrest in hypertensive rats

Spontaneous hypertensive rats (SHR) are an established model of genetic hypertension. Vascular smooth muscle cells (VSMC) from SHR proliferate faster than those of control rats (Wistar-Kyoto rats; WKY). We tested the hypothesis that induction of heme oxygenase (HO)-1 induced by aprotinin inhibits VSMC proliferation through cell cycle arrest in hypertensive rats. Aprotinin treatment inhibited VSMC proliferation in SHR more than in normotensive rats. These inhibitory effects were associated with cell cycle arrest in the G1 phase. Tin protoporphyrin IX (SnPPIX) reversed the anti-proliferative effect of aprotinin in VSMC from SHR. The level of cyclin D was higher in VSMC of SHR than those of WKY. Aprotinin treatment downregulated the cell cycle regulator, cyclin D, but upregulated the cyclin-dependent kinase inhibitor, p21, in VSMC of SHR. Aprotinin induced HO-1 in VSMC of SHR, but not in those of control rats. Furthermore, aprotinin-induced HO-1 inhibited VSMC proliferation of SHR. Consistently, VSMC proliferation in SHR was significantly inhibited by transfection with the HO-1 gene. These results indicate that induction of HO-1 by aprotinin inhibits VSMC proliferation through cell cycle arrest in hypertensive rats.

Enhanced susceptibility of cyclin kinase inhibitor p21 knockout mice to high fat diet induced atherosclerosis

Cyclin kinase inhibitor p21 is one of the most potent inhibitors of aortic smooth muscle cell proliferation, a key mediator of atherosclerosis. This study tests if p2l deficiency will result in severe atherosclerosis in a mouse model. p21-/- and strain matched wild type mice were fed with high fat diet for 21 weeks. Analysis for biochemical parameters (cholesterol, triglycerides) in serum and mRNA expression of CD36, HO-1, TGF-beta, IFN-gamma, TNF-alpha, PPAR-gamma and NADPH oxidase components (p22phox, NOX-1 and Rac-1) was performed in aortic tissues by Real Time PCR. p21-/- mice gained significantly (p < 0.01) more weight than wild type mice, triglycerides (p < 0.05) and cholesterol levels (p < 0.01) were more pronounced in the sera of p21-/- compared to wild type mice fed with high fat diet. High fat diet resulted in significantly decreased TGF-beta (p < 0.02), HO-l (p < 0.02) and increased CD36 (p < 0.03) mRNA expression in aortic tissues of p21-/- mice compared to animal fed with regular diet. IFN-gamma mRNA expression (235 +/- 11 folds) increased significantly in high fat diet fed p21-/- mice and a multifold modulation of PPAR-gamma(136 +/- 7), p22phox, NOX-1 and Rac-1 (15-35-folds) mRNA in aortic tissues from p21-/- mice compared to the wild type mice. Severity of atherosclerotic lesions was significantly higher in p21-/- compared to wild type mice. The results demonstrate that the deficiency of p21 leads to altered expression of pro-atherogenic genes, and severe atherosclerosis in mice fed with high fat diet. This opens the possibility of p21 protein as a therapeutic tool to control progression of atherosclerosis.

Cobalt protoporphyrin inhibition of lipopolysaccharide or lipoteichoic acid-induced nitric oxide production via blocking c-Jun N-terminal kinase activation and nitric oxide enzyme activity

In the present study, low doses (0.5, 1, and 2 microM) of cobalt protoporphyrin (CoPP), but not ferric protoporphyrin (FePP) or tin protoporphyrin (SnPP), significantly inhibited lipopolysaccharide (LPS) or lipoteichoic acid (LTA)-induced inducible nitric oxide (iNOS) and nitric oxide (NO) production with an increase in heme oxygenase 1 (HO-1) protein in RAW264.7 macrophages under serum-free conditions. IC(50) values of CoPP inhibition of NO and iNOS protein individually induced by LPS and LTA were around 0.25 and 1.7 microM, respectively. This suggests that CoPP is more sensitive at inhibiting NO production than iNOS protein in response to separate LPS and LTA stimulation. NO inhibition and HO-1 induction by CoPP were blocked by the separate addition of fetal bovine serum (FBS) and bovine serum albumin (BSA). Decreasing iNOS/NO production and increasing HO-1 protein by CoPP were observed with CoPP pretreatment, CoPP co-treatment, and CoPP post-treatment with LPS and LTA stimulation. LPS- and LTA-induced NOS/NO productions were significantly suppressed by the JNK inhibitor, SP600125, but not by the ERK inhibitor, PD98059, through a reduction in JNK protein phosphorylation. Transfection of a dominant negative JNK plasmid inhibited LPS- and LTA-induced iNOS/NO production and JNK protein phosphorylation, suggesting that JNK activation is involved in LPS- and LTA-induced iNOS/NO production. Additionally, CoPP inhibition of LPS- and LTA-induced JNK, but not ERK, protein phosphorylation was identified in RAW264.7 cells. Furthermore, CoPP significantly reduced NO production in a cell-mediated, but not cell-free, iNOS enzyme activity assay accompanied by HO-1 induction. However, attenuation of HO-1 protein stimulated by CoPP via transfection of HO-1 siRNA did not affect NO's inhibition of CoPP against LPS stimulation. CoPP effectively suppressing LPS- and LTA-induced iNOS/NO production through blocking JNK activation and iNOS enzyme activity via a HO-1 independent manner is first demonstrated herein.