Induction of heme oxygenase-1 is involved in anti-proliferative effects of paclitaxel on rat vascular smooth muscle cells

Heme Oxygenase-1, Cardiac Senescence, and Myocardial Infarction: A Critical Review of the Triptych

PURPOSE

Heme oxygenase-1 (HO-1) is a crucial enzyme in heme metabolism, facilitating the breakdown of heme into biliverdin, carbon monoxide, and free iron. Renowned for its potent cytoprotective properties, HO-1 showcases notable antioxidant, anti-inflammatory, and anti-apoptotic effects. In this review, the authors aim to explore the profound impact of HO-1 on cardiac senescence and its potential implications in myocardial infarction (MI).

RESULTS

Recent research has unveiled the intricate role of HO-1 in cellular senescence, characterized by irreversible growth arrest and functional decline. Notably, cardiac senescence has emerged as a pivotal factor in the development of various cardiovascular conditions, including MI. Notably, cardiac senescence has emerged as an important factor in the development of various cardiovascular conditions, including myocardial infarction (MI). The accumulation of senescent cells, spanning vascular endothelial cells, vascular smooth muscle cells, cardiomyocytes, and progenitor cells, poses a significant risk for cardiovascular diseases such as vascular aging, atherosclerosis, myocardial infarction, and ventricular remodeling. Inhibition of cardiomyocyte senescence not only reduces senescence-associated inflammation but also impacts other myocardial lineages, hinting at a broader mechanism of propagation in pathological remodeling. HO-1 has been shown to improve heart function and mitigate cardiomyocyte senescence induced by ischemic injury and aging. Furthermore, HO-1 induction has been found to alleviate H2O2-induced cardiomyocyte senescence. As we grow in our understanding of antiproliferative, antiangiogenic, anti-aging, and vascular effects of HO-1, we see the potential to exploit potential links between individual susceptibility to cardiac senescence and myocardial infarction.

CONCLUSIONS

This review investigates strategies for upregulating HO-1, including gene targeting and pharmacological agents, as potential therapeutic approaches. By synthesizing compelling evidence from diverse experimental models and clinical investigations, this study elucidates the therapeutic potential of targeting HO-1 as an innovative strategy to mitigate cardiac senescence and improve outcomes in myocardial infarction, emphasizing the need for further research in this field.

Regulatory effects of HIF-1α and HO-1 in hypoxia-induced proliferation of pulmonary arterial smooth muscle cells in yak

Hypoxia-inducible factor-1α (HIF-1α) and heme oxygenase-1 (HO-1) are important transcription regulators in hypoxic cells and for maintaining cellular homeostasis, but it is unclear whether they participate in hypoxia-induced excessive proliferation of yak pulmonary artery smooth muscle cells (PASMCs). In this study, we identified distribution of HIF-1α and HO-1 in yak lungs. Immunohistochemistry and immunofluorescence results revealed that both HIF-1α and HO-1 were mainly concentrated in the medial layer of small pulmonary arteries. Furthermore, under induced-hypoxic conditions, we investigated HIF-1α and HO-1 protein expression and studied their potential involvement in yak PASMCs proliferation and apoptosis. Western blot results also showed that both factors significantly increased in age-dependent manner and upregulated in hypoxic PASMCs (which exhibited obvious proliferation and anti-apoptosis phenomena). HIF-1α up-regulation by DMOG increased the proliferation and anti-apoptosis of PASMCs, while HIF-1α down-regulation by LW6 decreased proliferation and promoted apoptosis. More so, treatment with ZnPP under hypoxic conditions down-regulated HO-1 expression, stimulated proliferation, and resisted apoptosis in yak PASMCs. Taken together, our study demonstrated that both HIF-1α and HO-1 participated in PASMCs proliferation and apoptosis, suggesting that HO-1 is important for inhibition of yak PASMCs proliferation while HIF-1α promoted hypoxia-induced yak PASMCs proliferation.

Sequential Release of Paclitaxel and Imatinib from Core-Shell Microparticles Prepared by Coaxial Electrospray for Vaginal Therapy of Cervical Cancer

To optimize the anti-tumor efficacy of combination therapy with paclitaxel (PTX) and imatinib (IMN), we used coaxial electrospray to prepare sequential-release core–shell microparticles composed of a PTX-loaded sodium hyaluronate outer layer and an IMN-loaded PLGA core. The morphology, size distribution, drug loading, differential scanning calorimetry (DSC), Fourier transform infrared spectra (FTIR), in vitro release, PLGA degradation, cellular growth inhibition, in vivo vaginal retention, anti-tumor efficacy, and local irritation in a murine orthotopic cervicovaginal tumor model after vaginal administration were characterized. The results show that such core–shell microparticles were of spherical appearance, with an average size of 14.65 μm and a significant drug-loading ratio (2.36% for PTX, 19.5% for IMN, w/w), which might benefit cytotoxicity against cervical-cancer-related TC-1 cells. The DSC curves indicate changes in the phase state of PTX and IMN after encapsulation in microparticles. The FTIR spectra show that drug and excipients are compatible with each other. The release profiles show sequential characteristics in that PTX was almost completely released in 1 h and IMN was continuously released for 7 days. These core–shell microparticles showed synergistic inhibition in the growth of TC-1 cells. Such microparticles exhibited prolonged intravaginal residence, a >90% tumor inhibitory rate, and minimal mucosal irritation after intravaginal administration. All results suggest that such microparticles potentially provide a non-invasive local chemotherapeutic delivery system for the treatment of cervical cancer by the sequential release of PTX and IMN.

Rosae multiflorae Fructus Extract Improves Trimellitic Anhydride-Induced Atopic Dermatitis-Like Symptoms

Allergic disorders, including atopic dermatitis (AD), are closely linked to the activation of type 2 helper T (Th2) cells. The aim of this study was to investigate the possibility of using Rosae multiflorae fructus extract (RMFE) for AD treatment in the AD-like mouse model induced by treatment with trimellitic anhydride (TMA). Oral treatment of RMFE reduced the increase in ear thickness and suppressed inflammatory cytokine expression (interleukin [IL]-1β and tumor necrosis factor [TNF]-α) and Th2-associated immune responses (immunoglobulin [Ig] E and IL-4) in mouse ears. Furthermore, messenger RNA (mRNA) expression levels such as IL-4, IL-5, and IL-13, in draining lymph nodes were decreased by RMFE. Furthermore, we found that RMFE increased the level of heme oxygenase-1 (HO-1) through ERK and p38 pathways, reducing IL-2 production and CD4⁺ T cell proliferation, and inhibited STAT6 phosphorylation. Therefore, this study suggested that RMFE could be an effective treatment of AD induced by Th2-mediated immune responses by suppressing proliferation of CD4⁺ T cells via increased HO-1.

Grape Seed Procyanidins Attenuates Cisplatin-induced Human Embryonic Renal Cell Cytotoxicity by Modulating Heme Oxygenase-1 in Vitro

Cisplatin is a widely used anti-cancer drug. However, cisplatin is limited in clinical treatment because of its severe nephrotoxicity. This study reported whether O-GSP can antagonize the cisplatin-induced cytotoxicity in HEK293 cells through inducing HO-1 protein expression. We previously demonstrated O-GSP can increase the survival rate of HEK293 and have protective effect on HEK293 cells. Herein, We found that O-GSP can antagonize cisplatin nephrotoxicity through regulating the expression of HO-1. O-GSP promotes the translocation of Nrf2 in the nucleus, and activates the ERKN JNK pathway and p38 MAPK pathway. Interestingly, p38 MAPK plays a major role in HO-1 expression induced by O-GSP. And O-GSP can modulate the decrease of Nrf2 and HO-1 expression induced by cisplatin, and improve the cisplatin-induced activity and apoptosis rate of cells by stimulating the expression of HO-1. However, the protective effects of O-GSP are inhibited by ZnPP IX. Collectively, the results indicated that O-GSP induced the expression of HO-1 through p38MAPK and Nrf2 pathway in HEK293 cells.

Effects of paclitaxel intervention on pulmonary vascular remodeling in rats with pulmonary hypertension

The aim of the present study was to investigate the effects of paclitaxel (PTX), at a non-cytotoxic concentration, on pulmonary vascular remodeling (PVR) in rats with pulmonary hypertension (PAH), and to explore the mechanisms underlying the PTX-mediated reversal of PVR in PAH. A total of 36 rats were divided into control group (n=12), model group (n=12) receiving a subcutaneous injection of monocrotaline (60 mg/kg) in the back on day 7 following left pneumonectomy and PTX group (n=12) with PTX (2 mg/kg) injection via the caudal vein 3 weeks following establishing the model. The degree of PVR among all groups, as well as the expression levels of Ki67, p27^Kip1 and cyclin B1, were compared. The mean pulmonary artery pressure, right ventricular hypertrophy index [right ventricle/(left ventricle + septum) ratio] and the thickness of the pulmonary arterial tunica media in the model group were 58.34±2.01 mmHg, 0.64±0.046 and 65.3±3.3%, respectively, which were significantly higher when compared with 23.30±1.14 mmHg, 0.32±0.028 and 16.2±1.3% in the control group, respectively (P<0.01). The mean pulmonary artery pressure, right ventricular hypertrophy index and thickness of the pulmonary arterial tunica media in the PTX group were 42.35±1.53 mmHg, 0.44±0.029 and 40.5±2.6%, respectively, which were significantly lower when compared with the model group (P<0.01). Compared with the control group, the expression levels of Ki67 and cyclin B1 in the model group were significantly increased (P<0.01), while p27^Kip1 expression was significantly reduced (P<0.01). Following PTX intervention, the expression levels of Ki67 and cyclin B1 were significantly reduced when compared with the model group (P<0.01), while p27^Kip1 expression was significantly increased (P<0.01). The results of the present study suggest that PTX, administered at a non-cytotoxic concentration, may reduce PAH in rats, and prevent the effects of PVR in PAH. These effects of PTX may be associated with increased expression of p27^Kip1 and decreased expression of cyclin B1.

Vascular smooth muscle cell proliferation as a therapeutic target. Part 2: Natural products inhibiting proliferation

Many natural products have been so far tested regarding their potency to inhibit vascular smooth muscle cell proliferation, a process involved in atherosclerosis, pulmonary hypertension and restenosis. Compounds studied in vitro and in vivo as VSMC proliferation inhibitors include, for example indirubin-3'-monoxime, resveratrol, hyperoside, plumericin, pelargonidin, zerumbone and apamin. Moreover, taxol and rapamycin, the most prominent compounds applied in drug-eluting stents to counteract restenosis, are natural products. Numerous studies show that natural products have proven to yield effective inhibitors of vascular smooth muscle cell proliferation and ongoing research effort might result in the discovery of further clinically relevant compounds.

Metformin Sensitizes Non-small Cell Lung Cancer Cells to an Epigallocatechin-3-Gallate (EGCG) Treatment by Suppressing the Nrf2/HO-1 Signaling Pathway

Non-small cell lung cancer (NSCLC) is the most common type of lung cancer. (-)-Epigallocatechin-3-gallate (EGCG), a major polyphenol in green tea, is widely studied as a cancer chemopreventive agent with potential anti-cancer effects. The NF-E2-related factor 2 (Nrf2)/heme oxygenase-1 (HO-1) signaling pathway is considered to mediate cellular resistance to EGCG. Metformin, a classical antidiabetic drug, has been shown to prevent cancer progression. Researchers have not reported whether metformin potentiates the anti-cancer efficacy of EGCG. In this study, metformin inhibited HO-1 expression and augmented the anti-tumor effect of EGCG. Metformin also enhanced ROS (reactive oxygen species) generation induced by EGCG (100 μM), subsequently resulting in apoptosis. Based on the results of the in vivo study, size of xenografts treated with the combination of metformin and EGCG was smaller than other groups. Mechanistically, metformin modulated the EGCG-activated Nrf2/HO-1 pathway through Sirtuin 1 (SIRT1)-dependent deacetylation of Nrf2. Moreover, metformin upregulated SIRT1 expression partially through the NF-kB pathway. Comparatively, the combination of EGCG and metformin showed little impact on normal lung epithelial BEAS-2B cells. Based on our findings, metformin sensitized NSCLC cells to the EGCG treatment by suppressing the Nrf2/HO-1 signaling pathway.

Role of heme oxygenase-1 in the pathogenesis and tumorigenicity of Kaposi's sarcoma-associated herpesvirus

Kaposi's Sarcoma-associated Herpesvirus (KSHV) is the etiologic agent of several malignancies, including Kaposi's Sarcoma (KS), which preferentially arise in immunocompromised patients such as HIV+ subpopulation and lack effective therapeutic options. Heme oxygenase-1 (HO-1) has been reported as an important regulator of endothelial cell cycle control, proliferation and angiogenesis. HO-1 has also been found to be highly expressed in KSHV-infected endothelial cells and oral AIDS-KS lesions. We previously demonstrate that the multifunctional glycoprotein CD147 is required for KSHV/LANA-induced endothelial cell invasiveness. During the identification of CD147 controlled downstream genes by microarray analysis, we found that the expression of HO-1 is significantly elevated in both CD147-overexpressing and KSHV-infected HUVEC cells when compared to control cells. In the current study, we further identify the regulation of HO-1 expression and mediated cellular functions by both CD147 and KSHV-encoded LANA proteins. Targeting HO-1 by either RNAi or the chemical inhibitor, SnPP, effectively induces cell death of KSHV-infected endothelial cells (the major cellular components of KS) through DNA damage and necrosis process. By using a KS-like nude mouse model, we found that SnPP treatment significantly suppressed KSHV-induced tumorigenesis in vivo. Taken together, our data demonstrate the important role of HO-1 in the pathogenesis and tumorigenesis of KSHV-infected endothelial cells, the underlying regulatory mechanisms for HO-1 expression and targeting HO-1 may represent a promising therapeutic strategy against KSHV-related malignancies.

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.

Effects of Eicosapentaenoic Acid on the Cytoprotection Through Nrf2-Mediated Heme Oxygenase-1 in Human Endothelial Cells

Consumption of omega-3 polyunsaturated fatty acid, particularly eicosapentaenoic acid (EPA), is associated with a significant reduction in the risk of developing cardiovascular disease. The aim of this study was to investigate whether heme oxygenase-1 (HO-1) induction contributes to the cytoprotective effects of EPA in endothelial cells threatened with oxidative damage. In this study, we investigated the effect of EPA on the induction of HO-1 by NF-E2-related factor 2 (Nrf2) in human umbilical vein endothelial cells. In cells treated with low concentrations of EPA (10-25 μM), HO-1 expression increased in a time- and concentration-dependent manner. Additionally, EPA treatment increased Nrf2 nuclear translocation and antioxidant response element activity, leading to the upregulation of HO-1 expression. Furthermore, treatment with EPA reduced hydrogen peroxide (H(2)O(2))-induced cell death. The reduction in cell death was reversed by treatment with zinc protoporphyrin, an inhibitor of HO-1, indicating that HO-1 contributed to the protective effect of EPA. These data suggest that EPA protects against H(2)O(2)-induced oxidative stress in endothelial cells by activating Nrf2 and inducting HO-1 expression.

A clinical prognostic scoring system for resectable gastric cancer to predict survival and benefit from paclitaxel- or oxaliplatin-based adjuvant chemotherapy

Background

Gastrectomy with D2 lymphadenectomy is a standard procedure of curative resection for gastric cancer (GC). The aim of this study was to develop a simple and reliable prognostic scoring system for GC treated with D2 gastrectomy combined with adjuvant chemotherapy.

Methods

A prognostic scoring system was established based on clinical and laboratory data from 579 patients with localized GC without distant metastasis treated with D2 gastrectomy and adjuvant chemotherapy.

Results

From the multivariate model for overall survival (OS), five factors were selected for the scoring system: ≥50% metastatic lymph node rate, positive lymphovascular invasion, pathologic TNM Stage II or III, ≥5 ng/mL preoperative carcinoembryonic antigen level, and <110 g/L preoperative hemoglobin. Two models were derived using different methods. Model A identified low- and high-risk patients for OS (P<0.001), while Model B differentiated low-, intermediate-, and high-risk patients for OS (P<0.001). Stage III patients in the low-risk group had higher survival probabilities than Stage II patients. Both Model A (area under the curve [AUC]: 0.74, 95% confidence interval [CI]: 0.69–0.78) and Model B (AUC: 0.79, 95% CI: 0.72–0.83) were better predictors compared with the pathologic TNM classification (AUC: 0.62, 95% CI: 0.59–0.71, P<0.001). Adjuvant paclitaxel- or oxaliplatin-based or triple chemotherapy showed significantly better outcomes in patients classified as high risk, but not in those with low and intermediate risk.

Conclusion

A clinical three-tier prognostic risk scoring system was established to predict OS of GC treated with D2 gastrectomy and adjuvant chemotherapy. The potential advantage of this scoring system is that it can identify high-risk patients in Stage II or III who may benefit from paclitaxel- or oxaliplatin-based regimens. Prospective studies are needed to confirm these results before they are applied clinically.

Drugs and acute porphyrias: reasons for a hazardous relationship

The porphyrias are a group of metabolic diseases caused by inherited or acquired enzymatic deficiency in the metabolic pathway of heme biosynthesis. Simplistically, they can be considered as storage diseases, because the partial enzymatic defect gives rise to a metabolic "bottleneck" in the biosynthetic pathway and hence to an accumulation of different metabolic intermediates, potentially toxic and responsible for the various (cutaneous or neurovisceral) clinical manifestations observed in these diseases. In the acute porphyrias (acute intermittent porphyria, hereditary coproporphyria, variegate porphyria, and the very rare delta-aminolevulinic acid dehydratase ALAD-d porphyria), the characteristic severe neurovisceral involvement is mainly ascribed to a tissue accumulation of delta-aminolevulinic acid, a neurotoxic nonporphyrin precursor. Many different factors, both endogenous and exogenous, may favor the accumulation of this precursor in patients who are carriers of an enzymatic defect consistent with an acute porphyria, thus contributing to trigger the serious (and potentially fatal) clinical manifestations of the disease (acute porphyric attacks). To date, many different drugs are known to be able to precipitate an acute porphyric attack, so that the acute porphyrias are also considered as pharmacogenetic or toxygenetic diseases. This article reviews the different biochemical mechanisms underlying the capacity of many drugs to precipitate a porphyric acute attack (drug porphyrogenicity) in carriers of genetic mutations responsible for acute porphyrias, and addresses the issue of prescribing drugs for patients affected by these rare, but extremely complex, diseases.

KCHO-1, a Novel Antineuroinflammatory Agent, Inhibits Lipopolysaccharide-Induced Neuroinflammatory Responses through Nrf2-Mediated Heme Oxygenase-1 Expression in Mouse BV2 Microglia Cells

The brain is vulnerable to oxidative stress and inflammation that can occur as a result of aging or neurodegenerative diseases. Our work has sought to identify natural products that regulate heme oxygenase (HO)-1 and to determine their mechanism of action in neurodegenerative diseases. KCHO-1 is a novel herbal therapeutic containing 30% ethanol (EtOH) extracts from nine plants. In this study, we investigated the antineuroinflammatory effects of KCHO-1 in lipopolysaccharide- (LPS-) treated mouse BV2 microglia. KCHO-1 inhibited the protein expression of inducible nitric oxide synthase (iNOS), iNOS-derived nitric oxide (NO), cyclooxygenase- (COX-) 2, and COX-2-derived prostaglandin E2 (PGE2) in LPS-stimulated BV2 microglia. It also reduced tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and IL-6 production. This effect was correlated with the suppression of inhibitor of nuclear factor kappa B-α (IκB-α) phosphorylation and degradation and nuclear factor kappa B (NF-κB) translocation and DNA binding. Additionally, KCHO-1 upregulated HO-1 expression by promoting nuclear translocation of nuclear factor E2-related factor 2 (Nrf2) in mouse BV2 microglia. Tin protoporphyrin (SnPP), an HO activity inhibitor, was used to verify the inhibitory effects of KCHO-1 on proinflammatory mediators and proteins associated with HO-1 expression. Our data suggest that KCHO-1 has therapeutic potential in neurodegenerative diseases caused by neuroinflammation.

The cytoprotective effect of sulfuretin against tert-butyl hydroperoxide-induced hepatotoxicity through Nrf2/ARE and JNK/ERK MAPK-mediated heme oxygenase-1 expression

Sulfuretin is one of the major flavonoid components in Rhus verniciflua Stokes (Anacardiaceae) isolates. In this study, we investigated the protective effects of sulfuretin against tert-butyl hydroperoxide (t-BHP)-induced oxidative injury. The results indicated that the addition of sulfuretin before t-BHP treatment significantly inhibited cytotoxicity and reactive oxygen species (ROS) production in human liver-derived HepG2 cells. Sulfuretin up-regulated the activity of the antioxidant enzyme heme oxygenase (HO)-1 via nuclear factor E2-related factor 2 (Nrf2) translocation into the nucleus and increased the promoter activity of the antioxidant response element (ARE). Moreover, sulfuretin exposure enhanced the phosphorylation of c-Jun N-terminal kinase (JNK) and extracellular signal-regulated kinase 1/2 (ERK1/2), which are members of the mitogen-activated protein kinase (MAPK) family. Furthermore, cell treatment with a JNK inhibitor (SP600125) and ERK inhibitor (PD98059) reduced sulfuretin-induced HO-1 expression and decreased its protective effects. Taken together, these results suggest that the protective effect of sulfuretin against t-BHP-induced oxidative damage in human liver-derived HepG2 cells is attributable to its ability to scavenge ROS and up-regulate the activity of HO-1 through the Nrf2/ARE and JNK/ERK signaling pathways. Therefore, sulfuretin could be advantageous as a bioactive source for the prevention of oxidative injury.

New insights into intracellular locations and functions of heme oxygenase-1

SIGNIFICANCE

Heme oxygenase-1 (HMOX1) plays a critical role in the protection of cells, and the inducible enzyme is implicated in a spectrum of human diseases. The increasing prevalence of cardiovascular and metabolic morbidities, for which current treatment approaches are not optimal, emphasizes the necessity to better understand key players such as HMOX1 that may be therapeutic targets.

RECENT ADVANCES

HMOX1 is a dynamic protein that can undergo post-translational and structural modifications which modulate HMOX1 function. Moreover, trafficking from the endoplasmic reticulum to other cellular compartments, including the nucleus, highlights that HMOX1 may play roles other than the catabolism of heme.

CRITICAL ISSUES

The ability of HMOX1 to be induced by a variety of stressors, in an equally wide variety of tissues and cell types, represents an obstacle for the therapeutic exploitation of the enzyme. Any capacity to modulate HMOX1 in cardiovascular and metabolic diseases should be tempered with an appreciation that HMOX1 may have an impact on cancer. Moreover, the potential for heme catabolism end products, such as carbon monoxide, to amplify the HMOX1 stress response should be considered.

FUTURE DIRECTIONS

A more complete understanding of HMOX1 modifications and the properties that they impart is necessary. Delineating these parameters will provide a clearer picture of the opportunities to modulate HMOX1 in human disease.

Decursin Isolated from Angelica gigas Nakai Rescues PC12 Cells from Amyloid β-Protein-Induced Neurotoxicity through Nrf2-Mediated Upregulation of Heme Oxygenase-1: Potential Roles of MAPK

Decursin (D), purified from Angelica gigas Nakai, has been proven to exert neuroprotective property. Previous study revealed that D reduced A β 25 ‒ 35-induced cytotoxicity in PC12 cells. Our study explored the underlying mechanisms by which D mediates its therapeutic effects in vitro. Pretreatment of cells with D diminished intracellular generation of ROS in response to A β 25 ‒ 35. Western blot revealed that D significantly increased the expression and activity of HO-1, which was correlated with its protection against A β 25 ‒ 35-induced injury. Addition of ZnPP, an HO-1 competitive inhibitor, significantly attenuated its protective effect in A β 25 ‒ 35-treated cells, indicating the vital role of HO-1 resistance to oxidative injury. Moreover, D induced Nrf2 nuclear translocation, the upstream of HO-1 expression. While investigating the signaling pathways responsible for HO-1 induction, D activated ERK and dephosphorylated p38 in PC12 cells. Addition of U0126, a selective inhibitor of ERK, blocked D-induced Nrf2 activation and HO-1 induction and meanwhile reversed the protection of D against A β 25 ‒ 35-induced cell death. These findings suggest D augments cellular antioxidant defense capacity through both intrinsic free radical scavenging activity and activation of MAPK signal pathways that leads to Nrf2 activation, and subsequently HO-1 induction, thereby protecting the PC12 cells from A β 25 ‒ 35-induced oxidative cytotoxicity.

Sensing endoplasmic reticulum stress by protein kinase RNA-like endoplasmic reticulum kinase promotes adaptive mitochondrial DNA biogenesis and cell survival via heme oxygenase-1/carbon monoxide activity

Endoplasmic reticulum (ER) stress activates the adaptive unfolded protein response, allowing cells to recover folding capacity in the organelle. However, the overwhelming response to severe damage results in apoptotic cell death. Because of the physical proximity between ER and mitochondria, a functional interrelationship between these two organelles, including mitochondrial ATP production and apoptosis, has been suggested. The adaptive response to ER stress includes the maintenance of cellular energetics, which eventually determines cell fate. We previously demonstrated that heme oxygenase-1 (HO-1) activity protects cells against ER stress in a protein kinase RNA-like endoplasmic reticulum kinase (PERK)-dependent pathway. Here, we provide evidence that PERK-mediated induction of HO-1 in murine macrophages, RAW264.7, relays ER stress to mitochondrial DNA (mtDNA) replication and function. ER stress induced by thapsigargin treatments (10-100 nM) resulted in a 2-fold increase in mtDNA contents compared with that in the untreated control. HO-1 activity on ER stress is proven to be critical for mitochondrial integrity because chemical inhibition (zinc protoporphyrin, 5-20 μM) and genetic depletion of HO-1 by small interference RNA transfection suppress the activation of transcription factors for mitochondrial biogenesis. Carbon monoxide (CO), an enzymatic by-product of HO-1 activity is responsible for the function of HO-1. Limited bioavailability of CO by hemoglobin treatment triggers cell death with a concomitant decline in ATP production. Approximately 78.1% of RAW264.7 cells were damaged in the presence of hemoglobin compared with the percentage of injured cells (26.9%) under ER stress alone. Mitochondrial generation of ATP levels significantly declined when CO availability was limited under prolonged ER stress. Taken together, these results suggest that the cellular HO-1/CO system conveys ER stress to cell survival signals from mitochondria via both the activation of transcriptional factors and functional integrity of mtDNA.

Integrative survival response evoked by heme oxygenase-1 and heme metabolites

Heme oxygenase (HO) catalyzes the rate-limiting step in heme degradation to produce carbon monoxide (CO), iron, and biliverdin. Biliverdin is subsequently converted to bilirubin by its reductase, and iron is recycled for heme synthesis. The inducible HO isoform, HO-1, is involved in the protection of multiple tissues and organs. The mechanism of protective actions of HO-1 has not been completely elucidated, but recent evidence suggests that one or more of heme metabolites can mediate the protective effects of HO-1. Particularly, CO mimics the antioxidant, anti-inflammatory, anti-apoptotic and antiproliferative actions of HO-1. Many of these effects of CO depend on the production of cyclic guanosine monophosphate (cGMP), and the modulation of mitogen-activated protein kinase (MAPK) pathways. The transcription factors, including nuclear factor E2-related factor-2 (Nrf2), and their upstream kinases, including MAPK pathway, play an important regulatory role in HO-1 expression by dietary antioxidants and drugs. This review attempts to concisely summarize the molecular and biochemical characteristics of HO-1, with a discussion on the mechanisms of signal transduction and gene regulation that mediate the induction of HO-1 by dietary antioxidants and drugs. In addition, the cytoprotective roles of HO-1 shall be discussed from the perspective of each of the metabolic by-products.

Protective role of heme oxygenase-1 against inflammation in atherosclerosis

Heme oxygenase-1 (HO-1) catalyzes the first and rate-limiting step in the metabolism of free heme into equimolar amounts of ferrous iron, carbon monoxide (CO), and biliverdin. Biliverdin is subsequently converted to bilirubin by biliverdin reductase. HO-1 has recently been identified as a promising therapeutic target in the treatment of vascular inflammatory disease, including atherosclerosis. HO-1 represses inflammation by removing the pro-inflammatory molecule heme and by generating CO and the bile pigments, biliverdin and bilirubin. These HO-1 reaction products are capable of blocking innate and adaptive immune responses by modifying the activation, differentiation, maturation, and/or polarization of numerous immune cells, including endothelial cells, monocytes/macrophages, dendritic cells, T lymphocytes, mast cells, and platelets. These cellular actions by CO and bile pigments result in diminished leukocyte recruitment and infiltration, and pro-inflammatory mediator production within atherosclerotic lesions. This review highlights the mechanisms by which HO-1 suppresses vascular inflammation in atherosclerosis, and explores possible therapeutic modalities by which HO-1 and its reaction products can be employed to ameliorate vascular inflammatory disease.

Caffeic acid phenethyl ester inhibits PDGF-induced proliferation of vascular smooth muscle cells via activation of p38 MAPK, HIF-1α, and heme oxygenase-1

Hyperproliferation of vascular smooth muscle cells (VSMCs) is critically involved in the onset of atherosclerosis and restenosis. Although caffeic acid phenethyl ester (CAPE, 1), one of the main constituents of honeybee propolis, has been shown to exert a beneficial effect in models of vascular injury in vivo, detailed mechanistic investigations in vascular cells are scarce. This study has examined the antiproliferative activity of 1 in platelet-derived growth factor (PDGF)-stimulated primary rat aortic VSMCs and aimed to shed light on underlying molecular mechanisms. Compound 1 inhibited the proliferation of VSMCs upon exposure to PDGF in a dose-dependent manner by interfering with cell cycle progression from the G0/1- to the S-phase. Enhanced phosphorylation of p38 mitogen-activated protein kinase (MAPK) as well as stabilization of hypoxia-inducible factor (HIF)-1α and subsequent induction of heme oxygenase-1 (HO-1) could be identified as molecular events contributing to the observed growth arrest in PDGF-activated VSMCs upon exposure to 1.

Targeting heme oxygenase-1 in vascular disease

Heme oxygenase-1 (HO-1) metabolizes heme to generate carbon monoxide (CO), biliverdin, and iron. Biliverdin is subsequently metabolized to bilirubin by biliverdin reductase. HO-1 has recently emerged as a promising therapeutic target in the treatment of vascular disease. Pharmacological induction or gene transfer of HO-1 ameliorates vascular dysfunction in animal models of atherosclerosis, post-angioplasty restenosis, vein graft stenosis, thrombosis, myocardial infarction, and hypertension, while inhibition of HO-1 activity or gene deletion exacerbates these disorders. The vasoprotection afforded by HO-1 is largely attributable to its end products: CO and the bile pigments, biliverdin and bilirubin. These end products exert potent anti-inflammatory, antioxidant, anti-apoptotic, and anti-thrombotic actions. In addition, CO and bile pigments act to preserve vascular homeostasis at sites of arterial injury by influencing the proliferation, migration, and adhesion of vascular smooth muscle cells, endothelial cells, endothelial progenitor cells, or leukocytes. Several strategies are currently being developed to target HO-1 in vascular disease. Pharmacological induction of HO-1 by heme derivatives, dietary antioxidants, or currently available drugs, is a promising near-term approach, while HO-1 gene delivery is a long-term therapeutic goal. Direct administration of CO via inhalation or through the use of CO-releasing molecules and/or CO-sensitizing agents provides an attractive alternative approach in targeting HO-1. Furthermore, delivery of bile pigments, either alone or in combination with CO, presents another avenue for protecting against vascular disease. Since HO-1 and its products are potentially toxic, a major challenge will be to devise clinically effective therapeutic modalities that target HO-1 without causing any adverse effects.

Effects of sappanchalcone on the cytoprotection and anti-inflammation via heme oxygenase-1 in human pulp and periodontal ligament cells

Sappanchalcone has been demonstrated to possess several biological effects. However, the molecular mechanism underlying these effects is not fully understood. In this study, we examined the effects of sappanchalcone on hydrogen peroxide (H(2)O(2))-induced cytotoxicity using human dental pulp (HDP) cells, and lipopolysaccharide (LPS)-induced inflammation using human periodontal ligament (HPDL) cells. Sappanchalone concentration proportionately increased heme oxygenase (HO)-1 protein expression and enzyme activity in both HDP and HPDL cells. It also protected HDP cells from H(2)O(2)-induced cytotoxicity and reactive oxygen species production. The cytoprotective effect of sappanchalcone was nullified by HO-1 inhibitor, Tin protoporphyrin (SnPP). Sappanchalcone is seen to inhibit LPS-stimulated nitric oxide (NO), prostaglandin E(2) (PGE(2)), interlukine-1beta (IL-1beta), tumor necrosis factor-alpha (TNF-alpha), interlukine-6 (IL-6) and interlukine-12 (IL-12) release in addition to inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) expression in HPDL cells. SnPP, a specific inhibitor of HO-1, partly blocked sappanchalcone mediated suppression of inflammatory mediator production, in LPS-stimulated HPDL cells. HDP and HPDL cells treated with sappanchalcone exhibited the transient activation of c-Jun NH2-terminal kinase (JNK) and NF-E2-related factor-2 (Nrf2). The expression of HO-1 protein by sappanchalcone was significantly reduced by pretreatment with JNK inhibitor. In conclusion, induction of HO-1 is an important cytoprotective mechanism by which sappanchalcone protects HDP cells from H(2)O(2) and in addition it also exhibits anti-inflammatory effects in LPS-stimulated HPDL cells. Thus, sappanchalcone could potentially be a therapeutic approach for periodontal, pulpal and periapical inflammatory lesion.

Transforming growth factor-beta1 elicits Nrf2-mediated antioxidant responses in aortic smooth muscle cells

The anti-inflammatory properties of transforming growth factor-beta(1) (TGF-beta(1)) account for its protection against atherosclerotic plaque rupture. This study investigates whether activation of the Nrf2 (nuclear factor erythroid 2 [NF-E2]-related factor 2) transcription pathway is involved in TGF-beta(1) mediated induction of the antioxidant enzyme heme oxygenase-1 (HO-1) in smooth muscle cells (SMC). Human aortic smooth muscle cells (HAoSMC) or wild-type and Nrf2-deficient mouse (MAoSMC) aortic SMC were treated with TGF-beta(1) (2.5-10 ng/ml, 0-24 hrs). We report the first evidence that TGF-beta(1) induces Nrf2 mediated HO-1 expression and antioxidant response element activity, which was paralleled by enhanced superoxide production and expression of the NAD(P)H oxidase subunit p22(phox). TGF-beta(1) failed to induce HO-1 expression in MAoSMC derived from Nrf2-deficient mice, and HO-1 induction by TGF-beta(1) in HAoSMC was attenuated by inhibition of extracellular signal regulated kinase or c-jun-N-terminal kinase but not p38 mitogen activated protein kinase. Inhibition of NAD(P)H oxidase or scavenging of superoxide diminished HO-1 induction in response to TGF-beta(1). The oxidative stress agents glucose oxidase (GOx) and diethylmaleate enhanced TGF-beta(1) generation and HO-1 expression in HAoSMC, while antagonism of TGF-beta(1) signalling by adenoviral Smad7 overexpression attenuated their induction of HO-1. Pre-treatment of HAoSMC with TGF-beta(1) reduced nuclear translocation of the pro-apoptotic mediator p53 elicited by GOx. Our findings demonstrate that Nrf2 is a new target of TGF-beta(1) signalling in the vasculature which may contribute to the atheroprotective properties attributed to this growth factor.

Copper chelator ATN-224 inhibits endothelial function by multiple mechanisms

Copper is required for the proliferation of endothelial cells and copper-lowering therapy reduces tumour growth in animal models. It has been reported that ATN-224, a novel copper chelator, potently inhibits the activity of the copper-dependent enzyme superoxide dismutase 1 (SOD1) in endothelial cells. We performed microarray analysis of gene expression in endothelial cells exposed to ATN-224 which revealed upregulation of stress response genes including heme-oxygenase 1 (HO-1) and differential regulation of several genes previously implicated in angiogenesis including CXCR4, ANGP2, PGES2, RHAMM, ITB4 and AQP1 (p<0.01). These changes were confirmed on qPCR. Treatment of HUVEC with ATN-224 caused increased superoxide levels, phospho-ERK signalling, nuclear NRF1 expression, HO-1 expression and induction of the anti-apoptotic proteins P21, BCL2 and BCLXL. There was also nuclear translocation of SOD1. SOD1 RNA interference replicated the effects of ATN-224 on endothelial cell function but did not cause upregulation of HO-1 or PGES2, suggesting additional mechanisms of action of ATN-224. Downregulation of AQP1, which has been shown to have a role in angiogenesis, was seen with both ATN-224 and SOD1 siRNA. AQP1 expression could be rescued after ATN-224 by added copper. RNA interference to AQP1 inhibited endothelial proliferation and migration, confirming the role of AQP1 in endothelial cell function. Therefore regulation of AQP1 may represent an important action of copper chelation therapy.

Inhibitors of the heme oxygenase - carbon monoxide system: on the doorstep of the clinic?

The past decade has seen substantial developments in our understanding of the physiology, pathology, and pharmacology of heme oxygenases (HO), to the point that investigators in the field are beginning to contemplate therapies based on administration of HO agonists or HO inhibitors. A significant amount of our current knowledge is based on the judicious application of metalloporphyrin inhibitors of HO, despite their limitations of selectivity. Recently, imidazole-based compounds have been identified as potent and more selective HO inhibitors. This 'next generation' of HO inhibitors offers a number of desirable characteristics, including isozyme selectivity, negligible effects on HO protein expression, and physicochemical properties favourable for in vivo distribution. Some of the applications of HO inhibitors that have been suggested are treatment of hyperbilirubinemia, neurodegenerative disorders, certain types of cancer, and bacterial and fungal infections. In this review, we address various approaches to altering HO activity with a focus on the potential applications of second-generation inhibitors of HO.

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.

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-releasing molecules (CO-RMs): vasodilatory, anti-ischaemic and anti-inflammatory activities

The well-known adverse effects of CO (carbon monoxide) intoxication are counterbalanced by its positive actions when small amounts are produced intracellularly by the cytoprotective enzyme HO-1 (haem oxygenase-1). As compelling scientific evidence accumulated to sustain that HO-1 plays a fundamental role in counteracting vascular and inflammatory disorders, we began to appreciate that a controlled delivery of CO to mammals may provide therapeutic benefits in a number of pathological states. This is the rationale for the recent development of CO-RMs (CO-releasing molecules), a group of compounds capable of carrying and liberating controlled quantities of CO in cellular systems, which offer a plausible tool for studying the pharmacological effects of this gas and identifying its mechanism(s) of action. The present review will highlight the encouraging results obtained so far on the vasodilatory, anti-ischaemic and anti-inflammatory effects elicited by CO-RMs in in vitro and in vivo models with an emphasis on the prospect of converting chemical CO carriers into CO-based pharmaceuticals.

Mitochondrial and cellular heme-dependent proteins as targets for the bioactive function of the heme oxygenase/carbon monoxide system

The toxic effect of high concentrations of CO gas in living organisms is coherently typified at biochemical levels by the high affinity of CO for hemoglobin and cytochromes, heme-dependent proteins that are indispensable for oxygen transport and mitochondrial respiration. However, the basal production of CO during heme degradation and the ability of heme oxygenase-1 (HO-1) to increase CO availability pose the question of how this gaseous molecule interacts with metal centers within the intracellular milieu to serve as one of the most unconventional signaling mediators. Emerging evidence indicates that the diverse and multifaceted beneficial effects exerted by "low concentrations" of CO cannot be explained solely by the activation of classic prototypic targets (i.e., guanylate cyclase/potassium channels) but entails the dynamic and concerted activation/inhibition of a group of CO-responsive proteins. As the complexity of the temporal and spatial action of CO is progressively being appreciated, this review aims to (a) highlight the current knowledge on certain metal-containing proteins that interact directly with CO; (b) analyze the latest notions on their functional role in response to CO; and finally (c) propose a rational view on the mode these CO targets may interrelate with and be regulated by the HO/CO pathway.

Pharmacologic induction of heme oxygenase-1

Heme oxygenase-1 (HO-1) is a cytoprotective protein whose expression is consistently associated with therapeutic benefits in a number of pathologic conditions such as atherosclerotic vascular disease and inflammation. Although the expression of HO-1 in most tissues is low, a large number of clinical and experimental pharmacologic compounds have been demonstrated to induce HO-1. This induction is suggested to be at least partially responsible for the perceived therapeutic efficacy of these compounds. The increase in HO-1 expression in response to these compounds is the result of a complex regulatory network involving many signaling pathways and transcription factors. Understanding both the pathways by which HO-1 is induced and the mechanism through which the enzyme exerts its beneficial effects may facilitate the development of novel drugs.

Piperine protects cisplatin-induced apoptosis via heme oxygenase-1 induction in auditory cells

Piperine is a major component of black pepper, Piper nigrum Linn, used widely in traditional medicine. In this study, we examined whether piperine could protect House Ear Institute-Organ of Corti 1 (HEI-OC1) cells against cisplatin-induced apoptosis through the induction of heme oxygenase (HO)-1 expression. Piperine (10-100 microM) induced the expression of HO-1 in dose- and time-dependent manners. Piperine also induced antioxidant response element-luciferase and translocated nuclear factor-E2-related factor-2 (Nrf2) to nucleus. Piperine activated the c-Jun N-terminal kinase (JNK), extracellular signal-regulated kinase and p38 mitogen-activated protein kinase (MAPK) pathways, and the JNK pathway played an important role in piperine-induced HO-1 expression. Piperine protected the cells against cisplatin-induced apoptosis. The protective effect of piperine was abrogated by zinc protoporphyrin IX, an HO inhibitor, and antisense oligodeoxynucleotides against HO-1 gene. These results demonstrate that the expression of HO-1 by piperine is mediated by both JNK pathway and Nrf2, and the expression inhibits cisplatin-induced apoptosis in HEI-OC1 cells.

Cataract: Window for systemic disorders

Cataract is the leading cause of visual handicap throughout the world, and almost all elderly individuals develop lens opacities. Epidemiological studies have shown that nuclear cataracts in young adults are associated with higher mortality. Many cataractogenic stressors induce endoplasmic reticulum (ER) stress, which in turn induces the unfolded protein response (UPR). The UPR can damage or kill a wide range of cell types and may be involved in many human diseases. We hypothesize that a cataract can be considered a window that can indicate the presence of systemic disorders. This is important because cataract is easily detected during a routine ocular examination. The slightest opacity in any region of the lenses, especially in younger patients, may be a sign of systemic disorders. Earlier detection of systemic disorders can save the lives of patients. If our hypothesis is correct, then elimination of known ER/cataractogenic stressors from individuals with cataracts should be the one of the first steps for treatments of the systemic disorders. We discuss the potential risk factors and beneficial effects of removal of such risk factors in patients with early cataracts. All patients with cataract should be referred for comprehensive medical examination.

2′,4′,6′-Tris(methoxymethoxy) chalcone attenuates hepatic stellate cell proliferation by a heme oxygenase-dependent pathway

Proliferation of hepatic stellate cells (HSCs) is central for the development of fibrosis during liver injury. We have shown previously that butein (3,4,2',4'-tetrahydroxychalcone) suppresses myofibroblastic differentiation of rat HSCs. Our aim in this study was to determine whether a new synthetic chalcone derivative, 2',4',6'-tris(methoxymethoxy) chalcone (TMMC) inhibits HSC proliferation induced by serum- or platelet-derived growth factor (PDGF). TMMC significantly inhibited growth factor-induced HSC proliferation. The inhibition of PDGF-induced proliferation by TMMC was associated with the phosphatidylinositol 3-kinase-Akt-p70(S6K) pathways. TMMC induced the expression of heme oxygenase 1 (HO-1) in HSCs. Using the chemical inhibitor tin protoporphyrin, we also found that the inhibitory action of TMMC on PDGF-induced proliferation is mediated by HO-1. Glutathione (GSH) depletion produced by TMMC activated extracellular signal-regulated kinase (ERK), which led to c-Fos expression and transactivation of activator protein 1 (AP-1) and HO-1 gene expression in the HSCs. These results demonstrate that TMMC preferentially activates ERK and that this activation leads to the transcriptional activation of AP-1 and consequently to HO-1 expression. HO-1 expression might be responsible for the antiproliferative effect of TMMC on HSCs.

The role of heme oxygenase-1 in pulmonary disease

Heme oxygenase (HO)-1, the inducible isoform of heme oxygenase, is a cytoprotective enzyme that plays a central role in the defense against oxidative and inflammatory insults in the lung. HO-1 catalyzes the degradation of heme, a potent oxidant, into biliverdin, iron, and carbon monoxide (CO). These downstream products of heme catabolism have recently been found to mediate the antioxidant, antiapoptotic, antiproliferative, vasodilatory, and anti-inflammatory properties of HO-1. Although absence of HO-1 is rare in humans, a number of HO-1 promoter polymorphisms have been identified that may influence HO-1 expression in vivo and lead to disease states. This review will summarize studies that implicate HO-1 and heme metabolites in the pathophysiology of pulmonary disease and discuss recent advances in the therapeutic applications of HO-1.

CO as a cellular signaling molecule

Many biological functions of heme oxygenase (HO), such as cytoprotection against oxidative stress, vasodilation, neurotransmission in the central or peripheral nervous systems, and anti-inflammatory, anti-apoptotic, or anti-proliferative potential, have been attributed to its enzymatic byproduct carbon monoxide (CO), although roles for biliverdin/bilirubin and iron have also been proposed. In addition to these well-characterized effects, recent findings reveal that HO-derived CO may act as an oxygen sensor and circadian modulator of heme biosynthesis. In lymphocytes, CO may participate in regulatory T cell function. A number of the known signaling effects of CO depend on stimulation of soluble guanylate cyclase and/or activation of mitogen-activated protein kinases (MAPK). Furthermore, modulation of caveolin-1 status may serve as an essential component of certain aspects of CO action, such as growth control. In this review, we summarize recent findings of the beneficial or detrimental effects of endogenous CO with an emphasis on the signaling pathways and downstream targets that trigger the action of this gas.

Therapeutic applications of carbon monoxide-releasing molecules

Carbon monoxide (CO), which is formed in mammalian cells through the oxidation of haem by the enzyme haem oxygenase, actively participates in the regulation of key intracellular functions. Emerging evidence reveals that an increased generation of haem oxygenase-derived CO plays a critical role in the resolution of inflammatory processes and alleviation of cardiovascular disorders. The authors have identified a novel class of substances, CO-releasing molecules (CO-RMs), which are capable of exerting a variety of pharmacological activities via the liberation of controlled amounts of CO in biological systems. A wide range of CO carriers containing manganese (CORM-1), ruthenium (CORM-2 and -3), boron (CORM-A1) and iron (CORM-F3) are currently being investigated to tailor therapeutic approaches for the prevention of vascular dysfunction, inflammation, tissue ischaemia and organ rejection.

4-Hydroxynonenal induces adaptive response and enhances PC12 cell tolerance primarily through induction of thioredoxin reductase 1 via activation of Nrf2

4-Hydroxynonenal (4-HNE) is one of the major end products of lipid peroxidation. It has been widely accepted that 4-HNE can induce oxidative stress, implicating into extensive stress-related diseases. In the present study, however, 4-HNE was found to exert adaptive cytoprotective effect at low concentrations, which was primarily through induction of thioredoxin reductase 1 (TR1) via transcriptional activation of NF-E2-related factor 2 (Nrf2). Pretreatment with 4-HNE at sublethal concentrations significantly protected PC12 cells against the subsequent oxidative cell death induced by H2O2 and 6-hydroxydopamine. The cellular antioxidative glutathione system did not show any considerable changes, whereas the TR1 activity as well as the mRNA level was significantly elevated by the 4-HNE treatment. Cells treated with TR1 small interfering RNA exhibited less resistance to oxidative stress, and the adaptive response was completely abolished. The Nrf2 was transcriptionally activated by 4-HNE. Cells treated with Nrf2-small interfering RNA exerted lower constitutive levels of TR1 and exhibited less resistance to oxidative stress, and the 4-HNE-induced TR1 expression and subsequent adaptive response were again abolished in such cells. Treatment with 4-HNE at the adaptive concentration induced transient activation of extracellular signal-regulated protein kinase 1/2 and Akt/protein kinase B. Pharmacological inhibition of both these kinase pathways effectively attenuated 4-HNE-induced TR1 expression and subsequent adaptive protection. The above findings, taken together, suggest that stimulation with 4-HNE at sublethal concentrations induces adaptive response and enhances cell tolerance, primarily through induction of TR1 via transcriptional activation of Nrf2 signaling pathway, thereby protecting cells against the forthcoming oxidative stress.