Hypercholesterolemia aggravates myocardial ischemia reperfusion injury via activating endoplasmic reticulum stress-mediated apoptosis

Electrocontractile remodeling of isolated cardiomyocytes induced during early-stage hypercholesterolemia

Hypercholesterolemia is one of the most important risk factors for cardiovascular diseases. However, it is mostly associated with vascular dysfunction and atherosclerotic lesions, while evidence of direct effects of hypercholesterolemia on cardiomyocytes and heart function is still incomplete and controversial. In this study, we assessed the direct effects of hypercholesterolemia on heart function and the electro-contractile properties of isolated cardiomyocytes. After 5 weeks, male Swiss mice fed with AIN-93 diet added with 1.25% cholesterol (CHO), developed an increase in total serum cholesterol levels and cardiomyocytes cholesterol content. These changes led to altered electrocardiographic records, with a shortening of the QT interval. Isolated cardiomyocytes displayed a shortening of the action potential duration with increased rate of depolarization, which was explained by increased IK, reduced ICa.L and altered INa voltage-dependent inactivation. Also, reduced diastolic [Ca2+]i was found with preserved adrenergic response and cellular contraction function. However, contraction of isolated hearts is impaired in isolated CHO hearts, before and after ischemia/reperfusion, although CHO heart was less susceptible to arrhythmic contractions. Overall, our results demonstrate that early hypercholesterolemia-driven increase in cellular cholesterol content is associated with direct modulation of the heart and cardiomyocytes' excitability, Ca2+ handling, and contraction.

Chrysin reduces heart endoplasmic reticulum stress-induced apoptosis by inhibiting PERK and Caspase 3-7 in high-fat diet-fed rats

BACKGROUND

Chrysin (Chy) is a naturally occurring flavonoid found in fruits, vegetables, honey, propolis, and many plant extracts that has shown notable medicinal value. Chy exhibits diverse pharmacological properties, including anti-oxidative, anti-inflammatory, anti-apoptotic, anti-cholesteremic, and cardioprotective. However, the influence of Chy in mitigating high-fat diet (HFD)-induced ER stress of rat myocardium remains unknown.

PURPOSE

The current work intended to determine the therapeutic potential of Chy against HFD-induced endoplasmic stress-mediated apoptosis.

METHODS

To evaluate the therapeutic value of Chy in HFD-induced endoplasmic stress-mediated apoptosis in the myocardium; The male wistar rats were divided into different groups; control, HFD control, HFD fed followed by Chy-treated and HFD fed followed by atorvastatin (Atv) treated rats.

RESULTS

When compared to the control group, the HFD-fed rats had significantly higher levels of marker enzymes such as CK-NAC and ALP, as well as lipid peroxidation and lipid profile (TC, TG, LDL, and VLDL). Chy therapy greatly reversed these marker enzymes and the lipid profile. qRT-PCR Studies showed that Chy supplementation considerably improved Nrf2 and its target genes. In addition, Chy lowered the expression of PERK, CHOP, ATF6, GRP78, and Caspase-3 genes in the heart tissue of HFD-fed rats. Immunohistochemistry results demonstrated that Chy substantially enhanced the Nrf2 and reduced PERK and Caspase3-7 protein expression in HFD-fed rats.

CONCLUSION

The current study concluded that Chy may mediate the cardioprotective effect by activating Nrf2 and inhibiting PERK signaling pathway against ER stress-mediated apoptosis induced by HFD. Therefore, supplementation with Chy could serve as a promising therapeutic target against HFD-induced ER stress-mediated cardiac complication.

Natural Products Targeting PI3K/AKT in Myocardial Ischemic Reperfusion Injury: A Scoping Review

This scoping review aimed to summarize the effects of natural products targeting phosphoinositide-3-kinases/serine/threonine kinase (PI3K/AKT) in myocardial ischemia-reperfusion injury (MIRI). The review details various types of natural compounds such as gypenoside (GP), gypenoside XVII (GP-17), geniposide, berberine, dihydroquercetin (DHQ), and tilianin which identified to reduce MIRI in vitro and in vivo by regulating the PI3K/AKT signaling pathway. In this study, 14 research publications that met the inclusion criteria and exclusion criteria were shortlisted. Following the intervention, we discovered that natural products effectively improved cardiac functions through regulation of antioxidant status, down-regulation of Bax, and up-regulation of Bcl-2 and caspases cleavage. Furthermore, although comparing outcomes can be challenging due to the heterogeneity in the study model, the results we assembled here were consistent, giving us confidence in the intervention's efficacy. We also discussed if MIRI is associated with multiple pathological condition such as oxidative stress, ERS, mitochondrial injury, inflammation, and apoptosis. This brief review provides evidence to support the huge potential of natural products used in the treatment of MIRI due to their various biological activities and drug-like properties.

Endoplasmic reticulum as a target in cardiovascular diseases: Is there a role for flavonoids?

Flavonoids are found in natural health products and plant-based foods. The flavonoid molecules contain a 15-carbon skeleton with the particular structural construction of subclasses. The most flavonoid's critical subclasses with improved health properties are the catechins or flavonols (e.g., epigallocatechin 3-gallate from green tea), the flavones (e.g., apigenin from celery), the flavanones (e.g., naringenin from citrus), the flavanols (e.g., quercetin glycosides from berries, onion, and apples), the isoflavones (e.g., genistein from soya beans) and the anthocyanins (e.g., cyanidin-3-O-glucoside from berries). Scientific data conclusively demonstrates that frequent intake of efficient amounts of dietary flavonoids decreases chronic inflammation and the chance of oxidative stress expressing the pathogenesis of human diseases like cardiovascular diseases (CVDs). The endoplasmic reticulum (ER) is a critical organelle that plays a role in protein folding, post-transcriptional conversion, and transportation, which plays a critical part in maintaining cell homeostasis. Various stimuli can lead to the creation of unfolded or misfolded proteins in the endoplasmic reticulum and then arise in endoplasmic reticulum stress. Constant endoplasmic reticulum stress triggers unfolded protein response (UPR), which ultimately causes apoptosis. Research has shown that endoplasmic reticulum stress plays a critical part in the pathogenesis of several cardiovascular diseases, including diabetic cardiomyopathy, ischemic heart disease, heart failure, aortic aneurysm, and hypertension. Endoplasmic reticulum stress could be one of the crucial points in treating multiple cardiovascular diseases. In this review, we summarized findings on flavonoids' effects on the endoplasmic reticulum and their role in the prevention and treatment of cardiovascular diseases.

Betulinic acid attenuates T-2 toxin-induced cytotoxicity in porcine kidney cells by blocking oxidative stress and endoplasmic reticulum stress

T-2 toxin is highly cytotoxic to animals, which causes damage to animal health and great economic losses to agriculture and livestock production. Betulinic acid (BA), a naturally occurring pentacyclic lupane-type triterpenoid, has various biological and medicinal activities in vivo and in vitro. The objective of the present study was to investigate the toxic effects of T-2 toxin and the reversal effect of BA on porcine kidney (PK-15) cells. We evaluated T-2 toxin-induced apoptotic responses via oxidative stress and endoplasmic reticulum stress pathways by assessing the repair effect of BA in PK-15 cells. The results proved that T-2 toxin (1 μM, treated for 24 h) is highly toxic to PK-15 cells. After pre-treatment with BA (0.25, 0.5, and 1 μM) for 24 h, the cell viabilities were significantly increased, and the lactate dehydrogenase (LDH) in the culture media was dramatically decreased compared to that in the T-2 toxin treatment group. BA also enhanced the activity of superoxide dismutase (SOD), glutathione peroxidase (GSH-PX), and catalase (CAT) and reduced the production of reactive oxygen species (ROS) and malondialdehyde (MDA) in cells. BA also dose-dependently increased the expression of glucose regulated protein (GRP78), reduced expression of activating transcription factor 4 (ATF4), C/EBP homologous protein (CHOP), the phosphorylation of protein kinase R-like endoplasmic reticulum kinase (PERK), eukaryotic initiation factor 2α (eIF2α), and intracellular Ca²⁺ concentration in a dose-dependent manner. In addition, BA significantly decreased the expression of cleaved-caspase-3 and caspase-12, consequently reducing T-2 toxin-induced PK-15 cell apoptosis in a dose-dependent manner. Collectively, we suggest that BA has a protective effect on T-2 toxin-induced cytotoxicity by ameliorating oxidative stress and endoplasmic reticulum stress in PK-15 cells.

Calreticulin expression in human cardiac myocytes induces ER stress-associated apoptosis

The global burden of heart failure following myocardial ischemia-reperfusion (IR) injury is a growing problem. One pathway that is key to understanding the progression of myocardial infarction and IR injury is the endoplasmic reticulum (ER) stress pathway, which contributes to apoptosis signaling and tissue death. The role of calreticulin in the progression of ER stress remains controversial. We hypothesized that calreticulin induction drives proapoptotic signaling in response to ER stress. We find here that calreticulin is upregulated in human ischemic heart failure cardiac tissue, as well as simulated hypoxia and reoxygenation (H/R) and thapsigargin-mediated ER stress. To test the impact of direct modulation of calreticulin expression on ER stress-induced apoptosis, human cardiac-derived AC16 cells with stable overexpression or silencing of calreticulin were subjected to thapsigargin treatment, and markers of apoptosis were evaluated. It was found that overexpression of calreticulin promotes apoptosis, while a partial knockdown protects against the expression of caspase 12, CHOP, and reduces thapsigargin-driven TUNEL staining. These data shed light on the role that calreticulin plays in apoptosis signaling during ER stress in cardiac cells.

Cholesterol enriched diet suppresses ATF6 and PERK and upregulates the IRE1 pathways of the unfolded protein response in spontaneously hypertensive rats: Relevance to pathophysiology of atherosclerosis in the setting of hypertension

Many studies have been dedicated to hypertension and hypercholesterolemia, as they are the primary conditions that influence the unfolded protein response (UPR). However, the concurrent effects of these two factors are unknown. Our research used spontaneously hypertensive rats (SHR) fed a cholesterol enriched diet (CED) as model of atherosclerosis formation to discover what effect the simultaneous actions of hypertension and hypercholesterolemia have on the UPR. The combination of hypertension and consumption of a CED (not the CED alone) caused the formation of early atherosclerotic features. Both increased expression of the CCAAT-enhancer-binding protein (CHOP) and the insulin induced gene 1 (INSIG1), which is the target gene of the sterol regulatory element-binding protein 1-c (SREBP1-c), and decreased expression of the spliced x-box binding protein1 (sXBP1) mRNA were observed in the SHR fed a CED. Cholesterol overload strongly suppressed glucose regulated protein 78 (GRP78), glucose regulated protein 94 (GRP 94), and the expression of CHOP and INSIG1 mRNA in both normotensive and hypertensive rats. Unlike other UPR factors, the sXBP1 mRNA expression was strongly downregulated in SHR fed a normal diet but upregulated in those fed a CED. The changes to UPR in the SHR fed a CED were associated with improvement of the initially impaired heart function of the rats.

Lycopene restores the effect of ischemic postconditioning on myocardial ischemia‑reperfusion injury in hypercholesterolemic rats

Ischemic postconditioning (IPoC) has been demonstrated to prevent myocardial ischemia-reperfusion injury (MIRI), but its cardioprotective effect is abrogated by hypercholesterolemia. The aim of the present study was to determine whether lycopene (LP), a type of carotenoid, can restore the cardioprotective effect of IPoC in hypercholesterolemic rats. Male Wistar rats were fed a cholesterol-enriched diet for 12 weeks to establish a hypercholesterolemic model. The rat hearts were isolated and subjected to 30 min ischemia and 60 min reperfusion using a Langendorff apparatus. LP was administered to the rats intraperitoneally for 5 consecutive days prior to ischemia and reperfusion. Myocardial pathological changes, infarct size and cell apoptosis were measured by hematoxylin and eosin, triphenyltetrazolium chloride and TUNEL staining, respectively. The changes in endoplasmic reticulum (ER) stress markers, the reperfusion injury salvage kinase (RISK) pathway and mitochondrial apoptosis-related proteins were detected by western blotting. Overall, the results demonstrated that low-dose LP in combination with IPoC ameliorated myocardial histopathological changes, reduced the infarct size and release of cardiac enzymes, and decreased cardiomyocyte apoptosis in hypercholesterolemic rats, but no beneficial effects were achieved by the same dose of LP or IPoC treatment were used alone. Furthermore, the combination of LP and IPoC inhibited the expression of glucose-regulated protein 78 and C/EBP homologous protein, increased the phosphorylation levels of AKT, ERK1/2 and glycogen synthase kinase-3β, repressed mitochondrial permeability transition pore opening, and reduced the expression of cytochrome c, cleaved caspase-9 and cleaved caspase-3. Collectively, these findings demonstrated that LP can restore the cardioprotective effects of IPoC on MIRI in hypercholesterolemic rats, and this restoration by LP was mediated by inhibition of ER stress and reactivation of the RISK pathway in hypercholesterolemic rat myocardium.

FABP4 silencing ameliorates hypoxia reoxygenation injury through the attenuation of endoplasmic reticulum stress-mediated apoptosis by activating PI3K/Akt pathway

Endoplasmic reticulum (ER) stress and subsequent apoptosis play a vital role in myocardial ischemia reperfusion (IR) injury. Fatty acid binding protein 4 (FABP4) may induce ER stress. The aim of this study was to investigate the mechanism and effect of FABP4 on IR injury in vitro. Rat H9c2 cells were exposed to hypoxia reoxygenation (HR) to create an IR model in vitro. FABP4 was overexpressed in HR-injured H9c2 cells. Transfection with FABP4 siRNA increased cell viability and decreased LDH upon HR stimulation. FABP4 cessation also suppressed apoptotic cells and caspase-3 activity after HR. Downregulation of FABP4 significantly inhibited ER stress by decreasing the protein expression of p-PERK, GRP78, and ATF6. FABP4 silencing also restrained the ER stress-mediated apoptotic pathway, as indicated by decreased pro-apoptotic proteins p-JNK, CHOP, Bax, and caspase-12, as well as upregulation of Bcl-2 during HR. Furthermore, FABP4 silencing activated the PI3K/Akt pathway. Blocking this pathway by the specific PI3K inhibitor-LY294002 restored HR-induced ER stress and subsequently reversed the protective effect of FABP4 silencing on HR injury. Taken together, our findings revealed that FABP4 silencing exerts protective effects against HR injury in H9c2 cells through inhibiting ER stress-induced cell apoptosis via activation of the PI3K/Akt pathway.

Glucagon-like peptide-1 attenuates endoplasmic reticulum stress-induced apoptosis in H9c2 cardiomyocytes during hypoxia/reoxygenation through the GLP-1R/PI3K/Akt pathways

Endoplasmic reticulum (ER) stress-induced apoptosis is a major cause of myocardial ischemia/reperfusion (I/R) injury. Emerging evidence indicates that glucagon-like peptide-1 (GLP-1) has potential cardioprotective effects. However, the precise mechanisms underlying the involvement of GLP-1 in I/R injury remain largely unknown. In the present study, we aimed to determine whether GLP-1 attenuates hypoxia/reoxygenation (H/R) injury in cardiomyocytes and to further elucidate the underlying signaling pathway. The results indicate that GLP-1 reversed the increased apoptotic ratio, the increased lactate dehydrogenase (LDH) levels, the reduced cell viability, the increased Caspase-3 activity, and the increased Bax/Bcl-2 ratio caused by H/R. Importantly, GLP-1 significantly decreased the expression of H/R-induced ER stress proteins (GRP78, CHOP) and Caspase-12. In addition, we found that GLP-1 increased the expression of p-Akt in H9c2 cells with H/R injuries, and that the protective action of GLP-1 against H/R-induced injury was blocked by the GLP-1 receptor (GLP-1R) inhibitor Exendin9-39 and the PI3K inhibitor LY294002. Exendin9-39 and LY294002 also blocked the downregulation of ER stress protein expression by GLP-1, after H/R injury. Therefore, we have shown that GLP-1 exerts its cardioprotective effects by alleviating ER stress-induced apoptosis due to H/R injury and that these effects are most likely associated with the activation of GLP-1R/PI3K/Akt signaling pathway.

Plasma LDL-Cholesterol Level at Admission is Independently Associated with Infarct Size in Patients with ST-Segment Elevation Myocardial Infarction Treated with Primary Percutaneous Coronary Intervention

Introduction

Hypercholesterolemia is a well-known risk factor for developing atherosclerosis and subsequently for the risk of a myocardial infarction (MI). Moreover, it might also be related to the extent of damaged myocardium in the event of a MI. The aim of this study was to evaluate the association of baseline low density lipoprotein-cholesterol (LDL-c) level with infarct size in patients with ST-segment elevation myocardial infarction (STEMI) after primary percutaneously coronary intervention (pPCI).

Methods

Baseline blood samples were obtained from all patients admitted between 2004 and 2014 with STEMI who underwent pPCI. Patients were excluded in case of out of hospital cardiac arrest, treatment delay of at least 10 h or no complete reperfusion after pPCI in the culprit vessel. Peak creatine kinase (CK) level was used for infarct size estimation, defined as the maximal value during admission.

Results

A total of 2248 patients were included in this study (mean age 61.8 ± 12.2 years; 25.0% female). Mean LDL-c level was 3.6 ± 1.1 mmol/L and median peak CK level was 1275 U/L (IQR 564–2590 U/L). Baseline LDL-c level [β = 0.041; (95% CI 0.019–0.062); p < 0.001] was independently associated with peak CK level. Furthermore, left anterior descending artery as culprit vessel, initial TIMI 0–1 flow in the culprit vessel, male gender, and treatment delay were also correlated with high peak CK level (p < 0.05). Prior aspirin therapy was associated with lower peak CK level [β = − 0.073 (95% CI − 0.146 to 0.000), p = 0.050].

Conclusion

This study demonstrates that besides the more established predictors of infarct size, elevated LDL-c is associated with augmented infarct size in patients with STEMI treated with pPCI.

Electronic supplementary material

The online version of this article (10.1007/s40119-019-0126-5) contains supplementary material, which is available to authorized users.

Tyrosine 450 in the Voltage- and Calcium-Gated Potassium Channel of Large Conductance Channel Pore-Forming (slo1) Subunit Mediates Cholesterol Protection against Alcohol-Induced Constriction of Cerebral Arteries

Alcohol (ethanol) at physiologically relevant concentrations (<100 mM) constricts cerebral arteries via inhibition of voltage- and calcium-gated potassium channels of large conductance (BK) located in vascular smooth muscle (VSM). These channels consist of channel-forming slo1 (cbv1, KCNMA1) and accessory beta1 (KCNMB1) subunits. An increase in VSM cholesterol (CLR) via either dietary CLR intake or in vitro CLR enrichment was shown to protect against endothelium-independent, alcohol-induced constriction of cerebral arteries. The molecular mechanism(s) of this protection remains unknown. Here, we demonstrate that CLR enrichment of de-endothelialized middle cerebral arteries (MCAs) of rat increased CLR content in the VSM in a concentration-dependent manner. CLR enrichment blunted MCA constriction evoked by 18-75 mM but not by 100 mM alcohol. MCA enrichment with coprostanol (COPR) also blunted vasoconstriction by 50 mM alcohol, despite the fact that COPR and CLR differ in their ability to modify several major physical properties of the bilayer. CLR protection against 50 but not 100 mM alcohol was also observed in C57BL/6 and KCNMB1 knockout (KO) mice. Permeabilization of KCNMA1 KO MCAs with Y450Fcbv1 totally ablated CLR, but not COPR protection against vasoconstriction by 50 mM alcohol. Thus, CLR and alcohol interact at the level of the BK channel slo1 subunit, with Y450 being critical for CLR protection against alcohol-induced vasoconstriction. We document for the first time a functional competition between CLR and alcohol in regulating cerebral artery diameter and a critical role of a single amino acid within the BK channel pore-forming subunit in controlling CLR-alcohol interaction at the organ level.

Ameliorative effect of sevoflurane on endoplasmic reticulum stress mediates cardioprotection against ischemia-reperfusion injury 1

We aimed to investigate whether the cardioprotection of sevoflurane against ischemia-reperfusion (IR) injury is via inhibiting endoplasmic reticulum stress. The rat in vivo model of myocardial IR injury was induced by ligation of the left anterior descending coronary artery. Sevoflurane significantly ameliorated the reduced cardiac function, increased infarct size, and elevated troponin I level and lactate dehydrogenase activity in plasma induced by IR injury. Sevoflurane suppressed the IR-induced myocardial apoptosis. The increased protein levels of glucose-regulated protein 78 and C/EBP homologous protein (CHOP) after myocardial IR were significantly reduced by sevoflurane. The protein levels of phosphorylated protein kinase RNA-like endoplasmic reticulum kinase (PERK), phosphorylated eukaryotic initiation factor 2 (eIF2α), and activating transcription factor 4 (ATF4) were significantly increased in rats with IR and attenuated by sevoflurane treatment. The phosphorylation of Akt was further activated by sevoflurane. The cardioprotection of sevoflurane could be blocked by wortmannin, a PI3K/Akt inhibitor. Our results suggest that the cardioprotection of sevoflurane against IR injury might be mediated by suppressing PERK/eIF2a/ATF4/CHOP signaling via activating the Akt pathway, which helps in understanding the novel mechanism of the cardioprotection of sevoflurane.

Cardioprotection of tilianin ameliorates myocardial ischemia-reperfusion injury: Role of the apoptotic signaling pathway

Our previous research demonstrated that tilianin protects the myocardium in a myocardial ischemia reperfusion injury (MIRI) rat model and has prominent pharmacological potential as a cardiovascular drug. Our study aimed to investigate the molecular signaling implicated in the improvement of myocardial survival induced by tilianin, a flavonoid antioxidant. Tilianin (2.5, 5, and 10 mg/kg/d) or saline was orally administered to rats for 14 days. On the 15th day, ischemia was induced by ligating the left anterior descending artery for 45 min, followed by 4 h of reperfusion. The levels of MIRI-induced serum myocardial enzymes and cardiomyocyte apoptosis as well as infarct size were examined to assess the cardioprotective effects. Cardiac tissues were collected for western blot analyses to determine the protein expression of anti-apoptotic signaling molecules. In MIRI-treated rats, our results revealed that pre-administration of high dose-tilianin the reduced release of LDH, MDA, and CK-MB and increased the plasma SOD level, and significantly attenuated the infarct size. Western blot analysis showed that a remarkable rise in expression of Bcl-2 and XIAP, and decline in expression of Bax, Smac/Diablo, HtrA2/Omi, cleaved caspase-3, caspase-7 and caspase-9 was observed in the myocardium. The apoptosis index of cardiomyocytes further supports the cardioprotective effect of tilianin. Additionally, compared with the MIRI model group, pretreatment with high dose-tilianin group upregulated phosphorylated Akt and PI3K. In contrast, using the PI3K inhibitor LY294002 to block Akt activation effectively inhibited the protective effects of tilianin against MIRI. Tilianin pretreatment was beneficial for activating the PI3K/Akt signaling pathway and inhibiting myocardial apoptosis.

Effect of hypercholesterolaemia on myocardial function, ischaemia-reperfusion injury and cardioprotection by preconditioning, postconditioning and remote conditioning

Hypercholesterolaemia is considered to be a principle risk factor for cardiovascular disease, having direct negative effects on the myocardium itself, in addition to the development of atherosclerosis. Since hypercholesterolaemia affects the global cardiac gene expression profile, among many other factors, it results in increased myocardial oxidative stress, mitochondrial dysfunction and inflammation triggered apoptosis, all of which may account for myocardial dysfunction and increased susceptibility of the myocardium to infarction. In addition, numerous experimental and clinical studies have revealed that hyperlcholesterolaemia may interfere with the cardioprotective potential of conditioning mechanisms. Although not fully elucidated, the underlying mechanisms for the lost cardioprotection in hypercholesterolaemic animals have been reported to involve dysregulation of the endothelial NOS-cGMP, reperfusion injury salvage kinase, peroxynitrite-MMP2 signalling pathways, modulation of ATP-sensitive potassium channels and apoptotic pathways. In this review article, we summarize the current knowledge on the effect of hypercholesterolaemia on the non-ischaemic and ischaemic heart as well as on the cardioprotection induced by drugs or ischaemic preconditioning, postconditioning and remote conditioning. Future perspectives concerning the mechanisms and the design of preclinical and clinical trials are highlighted.

LINKED ARTICLES

This article is part of a themed section on Redox Biology and Oxidative Stress in Health and Disease. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.12/issuetoc.

Naringenin ameliorates hypoxia/reoxygenation-induced endoplasmic reticulum stress-mediated apoptosis in H9c2 myocardial cells: involvement in ATF6, IRE1α and PERK signaling activation

Naringenin, a flavanone mainly derived from grapes and citrus fruits, has been reported to exhibit cardioprotective effects. Accumulating evidence has confirmed that endoplasmic reticulum (ER) stress-mediated apoptosis participates in the process of myocardial ischemia/reperfusion injury and inhibiting ER stress is a potential therapeutic target/strategy in preventing cardiovascular diseases. Herein, the current study was designed to investigate whether naringenin protects H9c2 myocardial cells against hypoxia/reoxygenation (H/R) injury via attenuating ER stress or ER stress-mediated apoptosis. Our results showed that naringenin treatment resulted in obvious increases in the viability of H9c2 cells and the expression of Bcl-2 (anti-apoptotic protein), and decreases in the morphological changes of apoptotic cells, the activity of caspase-3 and the expression of Bax (pro-apoptotic protein) in H/R-treated H9c2 cells, implying the protective effects of naringenin against H/R-induced injury. In addition, naringenin also significantly reversed H/R-induced ER stress as evidenced by the up-regulation of Glucose-regulated protein 78, C/EBP homologous protein and Cleaved caspase-12 proteins. Meanwhile, naringenin remarkably reversed H/R-induced the increases in the expression of cleaved activating transcription factor 6 (ATF6) and phosphorylation levels of phospho-extracellular regulated protein kinases (PERK) and inositol-requiring enzyme-1α (IRE1α) in H9c2 cells. Finally, we found that ATF6 siRNA, PERK siRNA or IRE1α siRNA abolished H/R-induced cytotoxicity and apoptosis in H9c2 cells. In conclusion, these results confirmed that ER stress-mediated apoptosis contributes to the protection effects of naringenin against H/R injury, which is potentially involved in ATF6, IRE1α and PERK signaling activation.

Endoplasmic Reticulum Stress May Play a Pivotal Role in Lipid Metabolic Disorders in a Novel Mouse Model of Subclinical Hypothyroidism

Subclinical hypothyroidism (SCH) is becoming a global health problem due to its increasing prevalence and potential deleterious effects. However, the molecular mechanisms underlying the lipid metabolic disorders in SCH have not been fully clarified. Additionally, progress in elucidating the exact pathogenesis of SCH has been hampered by the lack of optimized mouse models. Methimazole (MMI) was applied to construct a noninvasive SCH mouse model. Eight-week-old C57BL/6 mice were administrated MMI through the drinking water. After 12 weeks, the MMI-treated mice showed the diagnostic criteria for SCH: increased serum thyrotropin (TSH) levels with constant thyroid hormone levels that persisted for approximately 8 weeks. Notably, SCH mice presented evident lipid metabolic disturbances, including dyslipidemia and hepatic lipid accumulation. Further analysis showed that hepatic endoplasmic reticulum stress (ER stress) was induced in the SCH mice or by the elevation of TSH in vitro, likely via the IRE1α/XBP-1 pathway. Interestingly, when we used 4-phenyl butyric acid to repress ER stress in SCH mice for 4 weeks, dyslipidemia and hepatic lipid accumulation were both significantly alleviated. Our findings indicate that an optimized SCH mouse model could be established using MMI, and ER stress may play a pivotal role in the lipid metabolic abnormalities in SCH.

Acute and Chronic Pretreatment With Atenolol Attenuates Intestinal Ischemia and Reperfusion Injury in Hypercholesterolemic Rats

OBJECTIVE

To evaluate the protective effects of preinjury atenolol (acute v chronic) on apoptosis, contractility, oxidative stress, and inflammatory markers in hypercholesterolemic rats undergoing intestinal ischemia-reperfusion (I/R) injury.

DESIGN

Prospective, experimental animal study.

SETTING

University laboratory.

PARTICIPANTS

Male Wistar rats (n = 32).

INTERVENTIONS

Rats were divided into the following 4 groups: 1 group was fed a normal diet (ND) (group ND+NoAT [no atenolol]), and the other 3 groups were fed a high-cholesterol diet (HCD)-group HCD+NoAT, group HCD+ChAT (chronic atenolol, 3 mg/kg/day for 8 weeks), and group HCD+AcAT (acute atenolol, 1.5 mg/kg, given 5 minutes before intestinal clamping). All rats underwent I/R injury. The superior mesenteric artery was clamped for 60 minutes, then opened for 120 minutes (reperfusion). Apoptotic cells and stimulated contractions of ileal segments were examined. Tissue markers of intestinal I/R injury were examined. Intestinal malondialdehyde, superoxide dismutase, and nitrate/nitrite levels were measured.

MEASUREMENTS AND MAIN RESULTS

The chronic atenolol group had fewer apoptotic cells and higher superoxide dismutase activity compared with the other groups. Intestinal contraction was higher in both atenolol pretreatment groups compared with the NoAT groups. Chronic and acute atenolol resulted in lower ileal levels of malondialdehyde and immunolabeling-positive cells (intestinal inducible nitric oxide synthase, endothelial nitric oxide synthase, interleukin-1, and interleukin-8) after I/R injury compared with the no atenolol groups.

CONCLUSIONS

Both chronic and acute pre-I/R injury treatment with atenolol attenuated I/R injury in this hypercholesterolemic rat model. These findings should encourage future studies of atenolol in hypercholesterolemic patients undergoing procedures with a high risk of intestinal ischemia.

Hypocholesterolemic effect of emodin by simultaneous determination of in vitro and in vivo bile salts binding

Emodin is an active anthraquinone derivative from Rheum palmatum and some other Chinese herbs and it is traditionally used for treating a variety of diseases. In this study, we investigated the hypocholesterolemic effects and mechanism of emodin on hypercholesterolemia rats. In vitro, capability of emodin binding to sodium deoxycholate which is one kind of bile salts (BAs) was evaluated by detection of surplus content of sodium deoxycholate. In vivo, hypocholesterolemic effects were assessed by determining total cholesterol (TC), triglyceride (TG), low density lipoprotein cholesterol (LDL-C) and high density lipoprotein cholesterol (HDL-C) level of serum and TC, TG level of the liver. Oil red O staining was employed to determine lipid droplet of the liver. The mechanism was explored by BAs in feces, the liver and small intestine. Furthermore, cholesterol 7α-hydroxylase (CYP7A1) activity was measured to evaluate cholesterol's transforming to BAs. The results indicated that TC level of emodin group apparently decreased comparing with model group (p<0.05). Emodin could bind to BAs both in vivo (p<0.05) and in vitro. CYP7A1 activity in emodin group apparently increased comparing with model group (p<0.05). Data suggested that emodin had the potential value for treatment of hypercholesterolemia. The underlying mechanism is probably associated with binding capability to BAs and subsequent increasing expression of CYP7A1.

Cardioprotective effects of Notoginsenoside R1 against ischemia/reperfusion injuries by regulating oxidative stress- and endoplasmic reticulum stress- related signaling pathways

Background: Recent reports suggested the involvement of oxidative stress- and endoplasmic reticulum stress (ERS)-associated pathways in the progression of ischemia/reperfusion (I/R) injury. Notoginsenoside R1 (NGR1) is a novel saponin isolated from P. notoginseng, which has a history of prevention and treatment of cardiovascular diseases. Objective: We aimed to examine the cardioprotective effects of NGR1 on I/R-induced heart dysfunction ex vivo and in vitro. Methods: H9c2 cadiomyocytes were incubated with NGR1 for 24 h and exposed to hypoxia/reoxygenation. Isolated rat hearts were perfused by NGR1 for 15 min and then subjected to global ischemia/reperfusion. Hemodynamic parameters were monitored as left ventricular systolic pressure (LVSP), heart rate, and maximal rate of increase and decrease of left ventricular pressure (±dP/dt max/min). Results: NGR1 pretreatment prevents cell apoptosis and delays the onset of ERS by decreasing the protein expression levels of ERS-responsive proteins GRP78, P-PERK, ATF6, IRE, and inhibiting the expression of pro-apoptosis proteins CHOP, Caspase-12, and P-JNK. Besides, NGR1 scavenges free radical, and increases the activity of antioxidase. NGR1 inhibits Tunicamycin-induced cell death and cardic dysfunction. Conclusion: We elucidated the significant cardioprotective effects of NGR1 against I/R injuries, and demonstrated the involvement of oxidative stress and ERS in the protective effects of NGR1.