Simvastatin-induced heme oxygenase-1 increases apoptosis of Neuro 2A cells in response to glucose deprivation

The different facets of heme-oxygenase 1 in innate and adaptive immunity

Heme oxygenase (HO) enzymes are responsible for the main oxidative step in heme degradation, generating equimolar amounts of free iron, biliverdin and carbon monoxide. HO-1 is induced as a crucial stress response protein, playing protective roles in physiologic and pathological conditions, due to its antioxidant, anti-apoptotic and anti-inflammatory effects. The mechanisms behind HO-1-mediated protection are being explored by different studies, affecting cell fate through multiple ways, such as reduction in intracellular levels of heme and ROS, transcriptional regulation, and through its byproducts generation. In this review we focus on the interplay between HO-1 and immune-related signaling pathways, which culminate in the activation of transcription factors important in immune responses and inflammation. We also discuss the dual interaction of HO-1 and inflammatory mediators that govern resolution and tissue damage. We highlight the dichotomy of HO-1 in innate and adaptive immune cells development and activation in different disease contexts. Finally, we address different known anti-inflammatory pharmaceuticals that are now being described to modulate HO-1, and the possible contribution of HO-1 in their anti-inflammatory effects.

Antioxidant Effects of Statins by Modulating Nrf2 and Nrf2/HO-1 Signaling in Different Diseases

Statins are competitive inhibitors of hydroxymethylglutaryl-CoA (HMG-CoA) reductase and have been used to treat elevated low-density lipoprotein cholesterol (LDL-C) for almost four decades. Antioxidant and anti-inflammatory properties which are independent of the lipid-lowering effects of statins, i.e., their pleiotropic effects, might be beneficial in the prevention or treatment of many diseases. This review discusses the antioxidant effects of statins achieved by modulating the nuclear factor erythroid 2 related factor 2/ heme oxygenase-1 (Nrf2/HO-1) pathway in different organs and diseases. Nrf2 and other proteins involved in the Nrf2/HO-1 signaling pathway have a crucial role in cellular responses to oxidative stress, which is a risk factor for ASCVD. Statins can significantly increase the DNA-binding activity of Nrf2 and induce the expression of its target genes, such as HO-1 and glutathione peroxidase) GPx, (thus protecting the cells against oxidative stress. Antioxidant and anti-inflammatory properties of statins, which are independent of their lipid-lowering effects, could be partly explained by the modulation of the Nrf2/HO-1 pathway.

Bisphenol a Induces Autophagy Defects and AIF-Dependent Apoptosis via HO-1 and AMPK to Degenerate N2a Neurons

Bisphenol A (BPA) is an environmental contaminant widely suspected to be a neurological toxicant. Epidemiological studies have demonstrated close links between BPA exposure, pathogenetic brain degeneration, and altered neurobehaviors, considering BPA a risk factor for cognitive dysfunction. However, the mechanisms of BPA resulting in neurodegeneration remain unclear. Herein, cultured N2a neurons were subjected to BPA treatment, and neurotoxicity was assessed using neuronal viability and differentiation assays. Signaling cascades related to cellular self-degradation were also evaluated. BPA decreased cell viability and axon outgrowth (e.g., by down-regulating MAP2 and GAP43), thus confirming its role as a neurotoxicant. BPA induced neurotoxicity by down-regulating Bcl-2 and initiating apoptosis and autophagy flux inhibition (featured by nuclear translocation of apoptosis-inducing factor (AIF), light chain 3B (LC3B) aggregation, and p62 accumulation). Both heme oxygenase (HO)-1 and AMP-activated protein kinase (AMPK) up-regulated/activated by BPA mediated the molecular signalings involved in apoptosis and autophagy. HO-1 inhibition or AIF silencing effectively reduced BPA-induced neuronal death. Although BPA elicited intracellular oxygen free radical production, ROS scavenger NAC exerted no effect against BPA insults. These results suggest that BPA induces N2a neurotoxicity characterized by AIF-dependent apoptosis and p62-related autophagy defects via HO-1 up-regulation and AMPK activation, thereby resulting in neuronal degeneration.

Simvastatin as a Potential Disease-Modifying Therapy for Patients with Parkinson's Disease: Rationale for Clinical Trial, and Current Progress

Many now believe the holy grail for the next stage of therapeutic advance surrounds the development of disease-modifying approaches aimed at intercepting the year-on-year neurodegenerative decline experienced by most patients with Parkinson’s disease (PD). Based on recommendations of an international committee of experts who are currently bringing multiple, potentially disease-modifying, PD therapeutics into long-term neuroprotective PD trials, a clinical trial involving 198 patients is underway to determine whether Simvastatin provides protection against chronic neurodegeneration. Statins are widely used to reduce cardiovascular risk, and act as competitive inhibitors of HMG-CoA reductase. It is also known that statins serve as ligands for PPARα, a known arbiter for mitochondrial size and number. Statins possess multiple cholesterol-independent biochemical mechanisms of action, many of which offer neuroprotective potential (suppression of proinflammatory molecules & microglial activation, stimulation of endothelial nitric oxide synthase, inhibition of oxidative stress, attenuation of α-synuclein aggregation, modulation of adaptive immunity, and increased expression of neurotrophic factors). We describe the biochemical, physiological and pharmaceutical credentials that continue to underpin the rationale for taking Simvastatin into a disease-modifying trial in PD patients. While unrelated to the Simvastatin trial (because this conducted in patients who already have PD), we discuss conflicting epidemiological studies which variously suggest that statin use for cardiovascular prophylaxis may increase or decrease risk of developing PD. Finally, since so few disease-modifying PD trials have ever been launched (compared to those of symptomatic therapies), we discuss the rationale of the trial structure we have adopted, decisions made, and lessons learnt so far.

Simvastatin induces heme oxygenase-1 via NF-E2-related factor 2 (Nrf2) activation through ERK and PI3K/Akt pathway in colon cancer

Statin has been known not only as their cholesterol-lowering action but also on their pleiotropic effects including anti-inflammatory and anti-oxidant as well as anti-cancer effect. Nrf2 (NF-E2-related factor 2) is a transcription factor to activate cellular antioxidant response to oxidative stress. There are little known whether statins affect activation of Nrf2 and Nrf2 signaling pathway in colon cancer cells. We investigated whether simvastatin stimulates the expression of Nrf2 and nuclear translocation of Nrf2 and which signal pathway is involved in the expression of Nrf2 and antioxidant enzymes. We investigated the effect of simvastatin on the expression of Nrf2 and nuclear translocation of Nrf2 in two human colon cancer cell lines, HT-29 and HCT 116 through cell proliferation assay, Western blotting and immunocytochemical analysis. We evaluated which signal pathway such as ERK or PI3K pathway affect Nrf2 activation and whether simvastatin induces antioxidant enzymes (heme oxygenase-1 (HO-1), NAD(P)H: quinine oxidoreductase 1 (NQO1), γ-glutamate-cysteine ligase catalytic subunit (GCLC)). We demonstrated simvastatin-induced dose-dependent up-regulation of Nrf2 expression and stimulated Nrf2 nuclear translocation in colon cancer cells. We also demonstrated that simvastatin-induced anti-oxidant enzymes (HO-1, NQO1, and GCLC) in HT-29 and HCT 116 cells. PI3K/Akt inhibitor (LY294002) and ERK inhibitor (PD98059) suppressed simvastatin-induced Nrf2 and HO-1 expression in both HT-29 and HCT 116 cells. This study shows that simvastatin induces the activation and nuclear translocation of Nrf2 and the expression of various anti-oxidant enzymes via ERK and PI3K/Akt pathway in colon cancer cells.

Red Yeast Rice Protects Circulating Bone Marrow-Derived Proangiogenic Cells against High-Glucose-Induced Senescence and Oxidative Stress: The Role of Heme Oxygenase-1

The inflammation and oxidative stress of bone marrow-derived proangiogenic cells (PACs), also named endothelial progenitor cells, triggered by hyperglycemia contributes significantly to vascular dysfunction. There is supporting evidence that the consumption of red yeast rice (RYR; Monascus purpureus-fermented rice) reduces the vascular complications of diabetes; however, the underlying mechanism remains unclear. This study aimed to elucidate the effects of RYR extract in PACs, focusing particularly on the role of a potent antioxidative enzyme, heme oxygenase-1 (HO-1). We found that treatment with RYR extract induced nuclear factor erythroid-2-related factor nuclear translocation and HO-1 mRNA and protein levels in PACs. RYR extract inhibited high-glucose-induced (30 mM) PAC senescence and the development of reactive oxygen species (ROS) in a dose-dependent manner. The HO-1 inducer cobalt protoporphyrin IX also decreased high-glucose-induced cell senescence and oxidative stress, whereas the HO-1 enzyme inhibitor zinc protoporphyrin IX and HO-1 small interfering RNA significantly reversed RYR extract-caused inhibition of senescence and reduction of oxidative stress in high-glucose-treated PACs. These results suggest that RYR extract serves as alternative and complementary medicine in the treatment of these diseases, by inducing HO-1, thereby decreasing the vascular complications of diabetes.

Simvastatin protects ischemic spinal cord injury from cell death and cytotoxicity through decreasing oxidative stress: in vitro primary cultured rat spinal cord model under oxygen and glucose deprivation-reoxygenation conditions

Background

Ischemia and the following reperfusion damage are critical mechanisms of spinal cord injury. Statins have been reported to decrease ischemia–reperfusion injury in many organs including the spinal cord. Anti-oxidative effect is one of the main protective mechanisms of statin against neuronal death and cytotoxicity. We hypothesized that statins’ anti-oxidative property would yield neuroprotective effects on spinal cord ischemia–reperfusion injury

Methods

Primary cultured spinal cord motor neurons were isolated from Sprague–Dawley rat fetuses. Ischemia–reperfusion injury model was induced by 60 min of oxygen and glucose deprivation (OGD) and 24 h of reoxygenation. Healthy and OGD cells were treated with simvastatin at concentrations of 0.1, 1, and 10 μM for 24 h. Cell viability was assessed using water-soluble tetrazolium salt (WST)-8, cytotoxicity with LDH, and production of free radicals with DCFDA (2′,7′-dichlorofluorescein diacetate).

Results

OGD reduced neuronal viability compared to normoxic control by 35.3%; however, 0.1–10 μM of simvastatin treatment following OGD improved cell survival. OGD increased LDH release up to 214%; however, simvastatin treatment attenuated its cytotoxicity at concentrations of 0.1–10 μM (p < 0.001 and p = 0.001). Simvastatin also reduced deteriorated morphological changes of motor neurons following OGD. Oxidative stress was reduced by simvastatin (0.1–10 μM) compared to untreated cells exposed to OGD (p < 0.001).

Conclusions

Simvastatin effectively reduced spinal cord neuronal death and cytotoxicity against ischemia–reperfusion injury, probably via modification of oxidative stress.

Simvastatin Protects Human Melanocytes from H2O2-Induced Oxidative Stress by Activating Nrf2

The prevention of hydrogen peroxide (H₂O₂)-induced oxidative stress has proved to be beneficial to vitiligo patients. Simvastatin possesses antioxidative capacity and has shown protective effect in various oxidative stress-related diseases. However, whether simvastatin can protect human melanocytes against oxidative stress has not been investigated. In this study, we initially found that pretreatment with 0.1 μmol/L to 1.0 μmol/L simvastatin led to increased cell viability and decreased cell apoptosis of melanocytes in response to H₂O₂. In addition, simvastatin was able to potentiate the activity of antioxidant enzymes and lessen intracellular reactive oxygen species accumulation. Furthermore, we found that simvastatin promoted the activation of nuclear erythroid 2-related factor (Nrf2) and that knockdown of Nrf2 abolished the protective effect of simvastatin against H₂O₂-induced oxidative damage. More importantly, the mutual enhancement between mitogen-activated protein kinase pathways and p62 contributed to simvastatin-induced Nrf2 activation in melanocytes. Finally, simvastatin showed more antioxidative capacity and better protective effect than aspirin in H₂O₂-treated melanocytes. Taken together, our results show that simvastatin protects human melanocytes from H₂O₂-induced oxidative stress by activating Nrf2, thus supporting simvastatin as a potential therapeutic agent for vitiligo.

Amelioration of high fat diet-induced nephropathy by cilostazol and rosuvastatin

Multiple comorbidities of metabolic disorders are associated with facilitated chronic kidney disease progression. Anti-platelet cilostazol is used for the treatment of peripheral artery disease. In this study, we investigated the potential beneficial effects of cilostazol and rosuvastatin on metabolic disorder-induced renal dysfunctions. C57BL/6 mice that received high fat diet (HFD) for 22 weeks and a low dose of streptozotocin (STZ, 40 mg/kg) developed albuminuria and had increased urinary cystatin C excretion, and cilostazol treatment (13 weeks) improved these markers. Histopathological changes, including glomerular mesangial expansion, tubular vacuolization, apoptosis, and lipid accumulation were ameliorated by cilostazol treatment. Tubulointerstitial fibrosis that was indicated by the increases in collagen and transforming growth factor-β1 subsided by cilostazol. Renoprotective effects were also observed in rosuvastatin-treated mice, and combinatorial treatment with cilostazol and rosuvastatin demonstrated enhanced ameliorative effects in histopathological evaluations. Notably, repressed renal heme oxygenase-1 (Ho-1) level in HFD/STZ mice was restored in cilostazol group. Further, we demonstrated that cilostazol enhanced Nrf2/Ho-1 signaling in cultured proximal tubular epithelial cells. Collectively, these results suggest the potential advantageous use of cilostazol as an adjunctive therapy with statins for the amelioration of metabolic disorder-associated renal injury.

Simvastatin attenuates oleic acid-induced oxidative stress through CREB-dependent induction of heme oxygenase-1 in renal proximal tubule cells

BACKGROUND

Statins elicit antioxidant effects independently of their lipid-lowering properties. Heme oxygenase-1 (HO-1) induction may be a part of these pleiotropic effects, which are insufficiently described in the kidney. We hypothesize that simvastatin (SIM) transcriptionally activates HO-1 that protects renal proximal tubule cells from lipotoxic injury.

METHODS

Impact of SIM on 100 μmol/l oleic acid (OA)-mediated reactive oxygen species (ROS) production and consequent oxidative stress (4-hydroxynonenal (HNE) content) as well as cell injury/apoptosis (lactate dehydrogenase (LDH) release, caspase-3 activation) were determined in cultured renal proximal tubule (NRK52E) cells. Effect of SIM on the HO-1 promoter and its enhancer elements (antioxidant response element (ARE), CCAAT, AP1, and cAMP response element (CRE)) was also determined in reporter luciferase assays. Dominant-negative (dnMEK, M1CREB) and pharmacologic (H89) approaches were used to inhibit activation of extracellular signal regulated kinase (ERK), CREB, and protein kinase A (PKA), respectively.

RESULTS

SIM dose-dependently activated the HO-1 promoter that was essential for protection against OA-dependent ROS production/oxidative stress and LDH release/caspase-3 activation. We found that the HO-1 promoter was induced through ERK and PKA-dependent activation of the CRE by SIM.

CONCLUSION

SIM may protect the kidney from adverse effects of circulating fatty acids by upregulating the antioxidant HO-1, aside from its well-described lipid-lowering effects.

Statins more than cholesterol lowering agents in Alzheimer disease: their pleiotropic functions as potential therapeutic targets

Alzheimer disease (AD) is a progressive neurodegenerative disorder characterized by severe cognitive impairment, inability to perform activities of daily living and mood changes. Statins, long known to be beneficial in conditions where dyslipidemia occurs by lowering serum cholesterol levels, also have been proposed for use in neurodegenerative conditions, including AD. However, it is not clear that the purported effectiveness of statins in neurodegenerative disorders is directly related to cholesterol-lowering effects of these agents; rather, the pleiotropic functions of statins likely play critical roles. The aim of this review is to provide an overview on the new discoveries about the effects of statin therapy on the oxidative and nitrosative stress levels as well as on the modulation of the heme oxygenase/biliverdin reductase (HO/BVR) system in the brain. We propose a novel mechanism of action for atorvastatin which, through the activation of HO/BVR-A system, may contribute to the neuroprotective effects thus suggesting a potential therapeutic role in AD and potentially accounting for the observation of decreased AD incidence with persons on statin.

Atorvastatin treatment in a dog preclinical model of Alzheimer's disease leads to up-regulation of haem oxygenase-1 and is associated with reduced oxidative stress in brain

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by progressive cognitive impairment and neuropathology. Only acetylcholinesterase inhibitors and the NMDA antagonist memantine are approved for AD treatment. Recent preclinical and epidemiological studies proposed statins as novel therapeutics for AD, but the mechanisms of action are still unknown. Here, we demonstrate that atorvastatin (80 mg/d for 14.5 months) treatment resulted in an up-regulation of the inducible isoform of haem oxygenase (HO-1), an enzyme with significant neuroprotective activity. Atorvastatin selectively increased HO-1 in the parietal cortex but not cerebellum. In contrast, HO-2 was increased in cerebellum but not parietal cortex. No changes were observed in HO-1 or HO-2 in the liver. Significant negative correlations between HO-1 and oxidative stress indices and positive correlations with glutathione levels in parietal cortex were found. HO-1 up-regulation significantly correlated with lower discrimination learning error scores in aged beagles. Reference to therapeutic applications of atorvastatin in AD is discussed.

Atorvastatin activates heme oxygenase-1 at the stress response elements

Statins are known to inhibit growth of a number of cancer cells, but their mechanism of action is not well established. In this study, human prostate adenocarcinoma PC-3 and breast adenocarcinoma MCF-7 cell lines were used as models to investigate the mechanism of action of atorvastatin, one of the statins. Atorvastatin was found to induce apoptosis in PC-3 cells at a concentration of 1 μM, and in MCF-7 cells at 50 μM. Initial survey of possible pathway using various pathway-specific luciferase reporter assays showed that atorvastatin-activated antioxidant response element (ARE), suggesting oxidative stress pathway may play a role in atorvastatin-induced apoptosis in both cell lines. Among the antioxidant response genes, heme oxygenase-1 (HO-1) was significantly up-regulated by atorvastatin. Pre-incubation of the cells with geranylgeranyl pyrophosphate blocked atorvastatin-induced apoptosis, but not up-regulation of HO-1, suggesting that atorvastatin-induced apoptosis is dependent on GTPase activity and up-regulation of HO-1 gene is not. Six ARE-like elements (designated StRE1 [stress response element] through StRE6) are present in the HO-1 promoter. Atorvastatin was able to activate all of the elements. Because these StRE sites are present in clusters in HO-1 promoter, up-regulation of HO-1 by atorvastatin may involve multiple StRE sites. The role of HO-1 in atorvastatin-induced apoptosis in PC-3 and MCF-7 remains to be studied.

Nrf2 represses FGF21 during long-term high-fat diet-induced obesity in mice

OBJECTIVE

Obesity is characterized by chronic oxidative stress. Fibroblast growth factor 21 (FGF21) has recently been identified as a novel hormone that regulates metabolism. NFE2-related factor 2 (Nrf2) is a transcription factor that orchestrates the expression of a battery of antioxidant and detoxification genes under both basal and stress conditions. The current study investigated the role of Nrf2 in a mouse model of long-term high-fat diet (HFD)-induced obesity and characterized its crosstalk to FGF21 in this process.

RESEARCH DESIGN AND METHODS

Wild-type (WT) and Nrf2 knockout (Nrf2-KO) mice were fed an HFD for 180 days. During this period, food consumption and body weights were measured. Glucose metabolism was assessed by an intraperitoneal glucose tolerance test and intraperitoneal insulin tolerance test. Total RNA was prepared from liver and adipose tissue and was used for quantitative real-time RT-PCR. Fasting plasma was collected and analyzed for blood chemistries. The ST-2 cell line was used for transfection studies.

RESULTS

Nrf2-KO mice were partially protected from HFD-induced obesity and developed a less insulin-resistant phenotype. Importantly, Nrf2-KO mice had higher plasma FGF21 levels and higher FGF21 mRNA levels in liver and white adipose tissue than WT mice. Thus, the altered metabolic phenotype of Nrf2-KO mice under HFD was associated with higher expression and abundance of FGF21. Consistently, the overexpression of Nrf2 in ST-2 cells resulted in decreased FGF21 mRNA levels as well as in suppressed activity of a FGF21 promoter luciferase reporter.

CONCLUSIONS

The identification of Nrf2 as a novel regulator of FGF21 expands our understanding of the crosstalk between metabolism and stress defense.

The role of the antioxidant and longevity-promoting Nrf2 pathway in metabolic regulation

PURPOSE OF REVIEW

The vertebrate cap'n'collar family transcription factor Nrf2 and its invertebrate homologues SKN-1 (in worms) and CncC (in flies) function as master mediators of antioxidant and detoxification responses and regulators of the cellular redox state. Nrf2 controls gene expression programs that defend various tissues against diverse electrophilic stressors and oxidative insults, thus protecting the organism from disorders that are caused or exacerbated by such stresses. Moreover, studies on model organisms implicate the Nrf2 pathway in the prevention of aging-related diseases and suggest that SKN-1-regulated and CncC-regulated gene expression can promote longevity. These facets of Nrf2 signaling have been thoroughly reviewed. This article discusses another aspect of the Nrf2 pathway's function that has not yet received the same degree of attention, but emerges as a topic of increasing interest and potential clinical impact: its role in metabolic regulation and its interaction with central signaling systems that respond to nutritional inputs.

RECENT FINDINGS

Recent evidence identifies Nrf2 signaling as a mediator of the salutary effects of caloric restriction. Nrf2 signaling also crosstalks with metabolic signaling systems such as the insulin/Akt pathway as well as with the metabolism of lipids. Moreover, Nrf2 has a protective role in models of diabetic nephropathy.

SUMMARY

The emerging role of Nrf2 as an effector of metabolic and longevity signals offers new therapeutic perspectives. The potential impact of pharmacological manipulation of Nrf2 signaling as a strategy for the prevention and treatment of metabolic disease can be envisioned.

Microglial Toll-like receptor 2 contributes to kainic acid-induced glial activation and hippocampal neuronal cell death

Recent studies indicate that Toll-like receptors (TLRs), originally identified as infectious agent receptors, also mediate sterile inflammatory responses during tissue damage. In this study, we investigated the role of TLR2 in excitotoxic hippocampal cell death using TLR2 knock-out (KO) mice. TLR2 expression was up-regulated in microglia in the ipsilateral hippocampus of kainic acid (KA)-injected mice. KA-mediated hippocampal cell death was significantly reduced in TLR2 KO mice compared with wild-type (WT) mice. Similarly, KA-induced glial activation and proinflammatory gene expression in the hippocampus were compromised in TLR2 KO mice. In addition, neurons in organotypic hippocampal slice cultures (OHSCs) from TLR2 KO mouse brains were less susceptible to KA excitotoxicity than WT OHSCs. This protection is partly attributed to decreased expression of proinflammatory genes, such as TNF-α and IL-1β in TLR2 KO mice OHSCs. These data demonstrate conclusively that TLR2 signaling in microglia contributes to KA-mediated innate immune responses and hippocampal excitotoxicity.

Ras inhibits endoplasmic reticulum stress in human cancer cells with amplified Myc

In neuroblastoma LAN-1 cells harboring an amplified MycN gene, disruption of cooperation between Ras and MycN proteins by the Ras inhibitor farnesylthiosalicylic acid (FTS, Salirasib) reportedly arrests cell growth. Our aim was to establish whether this is a general phenomenon. We examined the effects of FTS on gene-expression profiles, growth and death of NCIH929 myeloma cells and K562 leukemia cells, which-like LAN-1 cells-exhibit Myc gene amplification and harbor active Ras. Under specified conditions, FTS reduced Ras and Myc and induced cell growth arrest and death in all Myc-amplified cell lines but not in SHEP, a neuroblastoma cell line without Myc gene amplification. Gene-expression analysis revealed a common pattern of FTS-induced endoplasmic reticulum (ER) stress, known as the unfolded protein response (UPR), in Myc-amplified cells, but not in SHEP. Thus, Ras negatively regulates ER stress in cells with amplified Myc. ER stress was also inducible by dominant-negative (DN)-Ras or shRNA to Ras isoforms, all of which induced an increase in BIP (the master regulator of ER stress) and its downstream targets Nrf2 and eIF2alpha, both regulated by active p-PERK. FTS also induced an increase in p-PERK, while small interfering RNA to PERK reduced Nrf2 and ATF4 and rescued cells from FTS-induced death. BIP and its downstream targets were also increased by inhibitors of MAPK p38 and MEK. Ras, acting through MAPK p38 and MEK, negatively regulates the ER stress cascades BIP/PERK/Nrf2 and eIF2alpha/ATF4/ATF3. These findings can explain the Ras-dependent protection of Myc-amplified cells from ER stress-associated death.

Simvastatin induces heme oxygenase-1 expression but fails to reduce inflammation in the capsule surrounding a silicone shell implant in rats

BACKGROUND

Statins are lipid-lowering agents that are widely used in medical practice. Some studies have demonstrated that statins reduce proinflammatory signaling and have antioxidant and anti-inflammatory effects. The inducible heme oxygenase-1 (HO-1) catalyzes the stepwise degradation of heme to produce equimolar quantities of biliverdin, iron, and carbon monoxide; it has also been suggested to promote the important cholesterol-independent cytoprotective action of statins against oxidative insults. However, overexpression of HO-1 may have dual effects under oxidative stress, and the overaccumulation of ferric iron from heme may result in detrimental rather than cytoprotective effects. This study was designed to investigate the effect of a specific statin, simvastatin, and the role of HO-1 on the inflammatory status of the capsule surrounding a silicone shell implant in rats.

METHODS

Sprague-Dawley rats were randomly assigned to different groups according to the indicated implantation time (1 , 2 wk, 1 , 2 , and 3 mo postimplant) and the presence or absence of additional treatment (2 mg/kg oral simvastatin daily and/or 2 mg/kg HO inhibitor zinc protoporphyrin (ZnPP) by intraperitoneal injection daily). The formed de novo capsular tissue around the silicone implant was dissected away at the indicated time of sacrifice for experiments regarding the HO-1 expression and the inflammatory status.

RESULTS

We found a biphasic pattern of inflammation of the capsule with increased production of TNF-α, IL-1β, and COX-2, and activation of NF-κB at 1 wk and again at 1 mo postimplantation. Numerous CD68+monocytes or macrophages were diffusely distributed in the capsule in the early stage but not in the late stage postimplantation. In addition, the implantation procedure induced HO-1 expression, which was significantly up-regulated in the first 2 wk but decreased after 1 mo. Although daily feeding of the rats with simvastatin at 2 mg/kg induced HO-1 expression in the capsule throughout the experimental period, simvastatin treatment failed to reduce the production of TNF-α, IL-1β, and COX-2, or limit NF-κB activation in the early or late stages after implantation. Additionally, simvastatin treatment did not decrease the amount of CD68+cells distributed in the capsule at 1 wk postimplantation. HO-1 up-regulation by simvastatin treatment or down-regulation by additional injection of ZnPP did not demonstrate significant correlation with the inflammatory status of the capsule.

CONCLUSION

Simvastatin failed to reduce inflammation of the capsule surrounding a silicone shell implant. Although simvastatin induced HO-1 expression throughout the experimental time, up-regulated HO-1 expression could not be attributed to the inflammatory status of the capsule.

Acute energy reduction induces caspase-dependent apoptosis and activates p53 in retinal ganglion cells (RGC-5)

The energy reduction-induced death of retinal ganglion cells is associated with many ophthalmic diseases. The present study was designed to investigate the apoptosis pathway of retinal ganglion cells (RGC-5) following acute ATP reduction by using glucose deprivation (GD). RGC-5 cells were cultured in glucose-free or normal DMEM for 3 days. The changes in intracellular ATP and cell viability were monitored by ATP assay and MTT assay. APOPercentage and in situ TUNEL assays were used to determine the cell death pattern. The involvement of oxidative stress was assessed by measuring intracellular ROS generation, the HO-1 expression, the effect of antioxidants, and the ratio of GSSG to total GSH. The activation of p53 and apoptosis markers was evaluated by Western blotting. We found that glucose deprivation caused an acute decline of intracellular ATP level, concomitantly decreasing cell viability. The cell death exhibited typical features indicative of apoptosis, including cell shrinkage, phosphatidylserine externalization and DNA fragmentation. Oxidative stress was involved in the cell death process; an antioxidant significantly protected the cells against glucose deprivation. p53 and apoptosis markers, caspase-3 and PARP-1 were activated after RGC-5 cells were cultured in glucose-free media for 32 h. Z-VAD-fmk, a pan-caspase inhibitor, was sufficient to prevent apoptosis. These results suggest that acute energy reduction induced by glucose deprivation triggers caspase-dependent apoptosis and activates p53. Blocking the critical steps in this cell death pathway may have therapeutic effects, rescuing the retinal ganglion cells from damages associated with acute energy reduction.

Mevastatin accelerates loss of synaptic proteins and neurite degeneration in aging cortical neurons in a heme-independent manner

The therapeutic use of statins in reducing cholesterol requires careful assessment of potential neuroprotective and/or neurotoxic mechanisms. Chronic treatment with mevastatin (MV) exerts effects on cortical neuron morphology, protein expression and synaptic function in primary culture. MV impaired expression of synaptic proteins, reduced N-methyl-d-aspartate receptor (NMDAR) currents and accelerated neurodegeneration associated with aging. The down-regulating effect of MV on neuronal protein expression was additive with aging-associated decline in culture. Induction of Heme oxygenase-1 (HMOX1) by MV was superimposed on age-related up-regulation. Comparison of MV-treated and heme-deficient neurons showed that inhibition of heme synthesis (by succinyl acetone) had similar damaging effect on neurite integrity and MNDAR expression and function but not on expression of the receptor for neuropeptide Y1 (NPY1R). Replacement of heme in heme-deficient cultures restored protein expression but had no effect in those cultures co-treated with MV. Despite the dramatic induction of HMOX1, intracellular heme remained sufficient in MV-treated cultures, consistent with a heme-independent mechanism of MV-induced neurotoxicity and this was confirmed by analysing neurons with lentiviral over-expression of HMOX1. We conclude that MV exerts a neurotoxic effect in cultured neurons in a heme-independent manner.

Heme oxygenase-1 and the vascular bed: from molecular mechanisms to therapeutic opportunities

Heme oxygenase-1, an enzyme degrading heme to carbon monoxide, iron, and biliverdin, has been recognized as playing a crucial role in cellular defense against stressful conditions, not only related to heme release. HO-1 protects endothelial cells from apoptosis, is involved in blood-vessel relaxation regulating vascular tone, attenuates inflammatory response in the vessel wall, and participates in blood-vessel formation by means of angiogenesis and vasculogenesis. The latter functions link HO-1 not only to cardiovascular ischemia but also to many other conditions that, like development, wound healing, or cancer, are dependent on neovascularization. The aim of this comprehensive review is to address the mechanisms of HO-1 regulation and function in cardiovascular physiology and pathology and to demonstrate some possible applications of the vast knowledge generated so far. Recent data provide powerful evidence for the involvement of HO-1 in the therapeutic effect of drugs used in cardiovascular diseases. Novel studies open the possibilities of application of HO-1 for gene and cell therapy. Therefore, research in forthcoming years should help to elucidate both the real role of HO-1 in the effect of drugs and the clinical feasibility of HO-1-based cell and gene therapy, creating the effective therapeutic avenues for this refined antioxidant system.

Simvastatin activates Keap1/Nrf2 signaling in rat liver

Some of the statins' pleiotropic actions have been attributed to their antioxidant activity. The Nrf2 transcription factor controls the expression of a number of protective genes in response to oxidative stress. In the present study, wistar rats, primary hepatocytes as well as ST2 cells, were employed to explore the potential role of Nrf2 in mediating the reported antioxidant effects of statins. Simvastatin triggered nuclear translocation of Nrf2 in rat liver and in primary rat hepatocytes in a mevalonate-dependent and cholesterol-independent way. In liver, nuclear extracts from simvastatin-treated rats, the DNA-binding activity of Nrf2, was significantly increased and the mRNA of two known targets of Nrf2 (HO-1 and GPX2) was induced. In ST2 cells stably transfected with constructs bearing Nrf2-binding site (antioxidant responsive element), simvastatin enhanced Nrf2-mediated transcriptional activity in a mevalonate-dependent and cholesterol-independent fashion. In conclusion, activation of Keap1/Nrf2 signaling pathway by simvastatin might provide effective protection of the cell from the deleterious effects of oxidative stress.

Prevention of cold ischemia/rewarming-induced ERK 1/2, p38 kinase and HO-1 activation by trophic factor supplementation of UW solution

We have previously shown that trophic factor supplementation (TFS) of University of Wisconsin (UW) solution reduced early apoptotic changes in vascular endothelial cells. Here, we examine the effect of TFS on cell signaling pathways related to cell growth, differentiation, and apoptosis after cold ischemic storage. In this study, the effect of TFS on the phosphorylation of signaling molecules ERK (extracellular regulated-signaling kinase) 1/2 and p38 MAPK (mitogen activated protein kinases) and of HO-1 (hemeoxygenase-1), relative to changes seen in unmodified UW solution, were determined by Western blot in cells stored under cold ischemic conditions. Primary cultures of canine kidney proximal tubule cells (CKPTC) and human umbilical vein endothelial cells (HUVEC) were used in this study. There was a significant decrease, relative to UW solution, after 1 min rewarming in ERK 1 and 2 activity in CKPTCs. For p38 MAPK, a significant decrease after 5 min rewarming was seen in CKPTC (p<0.05) while significant reductions relative to UW solution were seen in HUVECs after both 1 and 5 min rewarming (p<0.05). Phosphorylated HO-1 was also decreased by 43% and 50% in HUVECs, relative to UW solution, after 1 and 5 min rewarming (p<0.05 at each time point). Collectively, TFS not only limits ERK 1/2 and p38 MAPK activity induced by cold ischemic injury and subsequent rewarming, but also substantially restricted increases in HO-1 phosphorylation.

Statin-induced heme oxygenase-1 increases NF-kappaB activation and oxygen radical production in cultured neuronal cells exposed to lipopolysaccharide

With potentially neuroprotective properties, heme oxygenase-1 (HO-1) has been suggested to be the main mediator of cholesterol-independent anti-inflammatory and antioxidant actions of statins. However, we had demonstrated that simvastatin-induced HO-1 increased apoptosis of Neuro 2A cells in glucose deprivation, and iron production from HO-1 activity may be responsible for the toxicity. This study was designed to explore the effect of simvastatin-induced HO-1 on cultured Neuro 2A and C6 cells exposed to lipopolysaccharide (LPS). We found that the HO-1 upregulation was significantly associated with increased nuclear factor kappa B (NF-kappaB) activation, manifested as IkappaBalpha phosphorylation and p65 nuclear translocation, as well as increased production of superoxides. Inhibition of the induced HO-1 by zinc protoporphyrin reduced the increased NF-kappaB activation and superoxides production. RNA interference with HO-1 siRNA reduced the expression of HO-1 transcripts and protein as well as oxygen radical production. Addition of the iron chelator desferrioxamine to reduce the accumulation of ferric iron from heme by HO-1 resulted in blockade of the aggravated oxygen radical production. There was no significant effect on production of oxygen radicals under these conditions in the presence of a CO donor (RuCO) or a CO scavenger (hemoglobin). In addition, the viable cells were significantly decreased in 48 h in those cells receiving simvastatin pretreatment plus LPS compared to those in control or exposed to simvastatin or LPS alone. This study revealed that simvastatin-induced HO-1 led to increased NF-kappaB activation and superoxides production in the neuronal cells when exposed to LPS, and iron production may play a role in such a response.