Tongda Xu

Targeting Cell Signaling and Apoptotic Pathways by Luteolin: Cardioprotective Role in Rat Cardiomyocytes Following Ischemia/Reperfusion

Myocardial ischemia often results in damaged heart structure and function, which can be restored through ischemia/reperfusion (I/R) in most cases. However, I/R can exacerbate myocardial ischemia reperfusion injury (IRI). Luteolin, a widely distributed flavonoid, a member of a group of naturally occurring polyphenolic compounds found in many fruits, vegetables and medicinal herbs, has been reported to exhibit anti-inflammatory, antioxidant and anti-carcinogenic activities. In recent years, luteolin has been shown to play an important role in the cardioprotection of IRI. However, its role and mechanism in cardioprotection against IRI has not been clearly elucidated with respect to the apoptosis pathway. The purpose of this paper is to review luteolin’s anti-apoptotic role and mechanism following I/R in rats, and indicate luteolin as a potential candidate for preventing and treating cardiovascular diseases.

ERK/PP1a/PLB/SERCA2a and JNK pathways are involved in luteolin-mediated protection of rat hearts and cardiomyocytes following ischemia/reperfusion.

Luteolin has long been used in traditional Chinese medicine for treatment of various diseases. Recent studies have suggested that administration of luteolin yields cardioprotective effects during ischemia/reperfusion (I/R) in rats. However, the precise mechanisms of this action remain unclear. The aim of this study is to confirm that luteolin-mediated extracellular signal regulated kinase (ERK1/2) and c-Jun N-terminal kinase (JNK) pathways are responsible for their cardioprotective effects during I/R. Wistar rats were divided into the following groups: (i) DMSO group (DMSO); (ii) I/R group (I/R); (iii) luteolin+I/R group (Lut+I/R); (iv) ERK1/2 inhibitor PD98059+I/R group (PD+I/R); (v) PD98059+luteolin+I/R group (PD+Lut+I/R); and (vi) JNK inhibitor SP600125+I/R group (SP+I/R). The following properties were measured: contractile function of isolated heart and cardiomyocytes; infarct size; the release of lactate dehydrogenase (LDH); the percentage of apoptotic cells; the expression levels of Bcl-2 and Bax; and phosphorylation status of ERK1/2, JNK, type 1 protein phosphatase (PP1a), phospholamban (PLB) and sarcoplasmic reticulum Ca2+-ATPase (SERCA2a). Our data showed that pretreatment with luteolin or SP600125 significantly improved the contraction of the isolated heart and cardiomyocytes, reduced infarct size and LDH activity, decreased the rate of apoptosis and increased the Bcl-2/Bax ratio. However, pretreatment with PD98059 alone before I/R had no effect on the above indexes. Further, these consequences of luteolin pretreatment were abrogated by co-administration of PD98059. We also found that pretreatment with PD98059 caused a significant increase in JNK expression, and SP600125 could cause ERK1/2 activation during I/R. In addition, we are the first to demonstrate that luteolin affects PP1a expression, which results in the up-regulation of the PLB, thereby relieving its inhibition of SERCA2a. These results showed that luteolin improves cardiomyocyte contractile function after I/R injury by an ERK1/2-PP1a-PLB-SERCA2a-mediated mechanism independent of JNK signaling pathway.

Salvianolic acid A demonstrates cardioprotective effects in rat hearts and cardiomyocytes after ischemia/reperfusion injury.

Abstract Salvianolic acid A (Sal A), the water-soluble component from the root of the Salvia miltiorrhiza plant, possesses antioxidant, antiproliferative, and antiplatelet properties. However, whether it plays a role in the protection against ischemia–reperfusion (I/R) injury in rat hearts has yet to be elucidated. In the present study, we tested cell viability, shortening amplitude, necrosis, apoptosis, and the expression levels of Akt, phosphorylated Akt, Bcl-2, Bax, and caspase-3 after 3-hour simulated ischemia and 2- or 6-hour simulated reperfusion in cardiomyocytes. We further observed the contractile function and infarct size in isolated hearts after they were subjected to global 30-minute ischemia and 120-minute reperfusion. Pretreatment with Sal A markedly increased cell viability and shortening amplitude while reducing evidence of necrosis and apoptosis in the cells. In addition, the expression of Bcl-2 was upregulated and Bax was downregulated, thereby increasing the Bcl-2/Bax ratio. Sal A inhibited the activation of caspase-3 as well. The results also showed that Sal A significantly increased phosphorylation of Akt and that this phosphorylation can be partially inhibited by phosphoinositide 3-kinase/Akt inhibitor. Furthermore, Sal A improved I/R-induced myocardial contractile function and reduced infarct size. In summary, our results showed that Sal A prevents I/R-induced myocardial damage by reducing necrosis and apoptosis in isolated rat hearts and cardiomyocytes.

The anti-apoptotic and cardioprotective effects of salvianolic acid a on rat cardiomyocytes following ischemia/reperfusion by DUSP-mediated regulation of the ERK1/2/JNK pathway.

The purpose of this study was to observe the effects of salvianolic acid A (SAA) pretreatment on the myocardium during ischemia/reperfusion (I/R) and to illuminate the interrelationships among dual specificity protein phosphatase (DUSP) 2/4/16, ERK1/2 and JNK pathways during myocardial I/R, with the ultimate goal of elucidating how SAA exerts cardioprotection against I/R injury (IRI). Wistar rats were divided into the following six groups: control group (CON), I/R group, SAA+I/R group, ERK1/2 inhibitor PD098059+I/R group (PD+I/R), PD+SAA+I/R group, and JNK inhibitor SP600125+I/R group (SP+I/R). The cardioprotective effects of SAA on the myocardium during I/R were investigated with a Langendorff device. Heart rate (HR), left ventricular systolic pressure (LVSP), left ventricular end-diastolic pressure (LVEDP), maximum rate of ventricular pressure rise and fall (±dp/dtmax), myocardial infarction areas (MIA), lactate dehydrogenase (LDH), and cardiomyocytes apoptosis were monitored. To determine the crosstalk betwee JNK and ERK1/2 via DUSP2/4/16 with SAA pretreatment, siRNA-DUSP2/4/16 were performed. The expression levels of Bcl-2, Bax, caspase 3, p-JNK, p-ERK1/2 and DUSP2/4/16 in cardiomyocytes were assayed by Western blot. Our results showed that LDH, MIA and cell apoptosis were decreased, and various parameters of heart function were improved by SAA pretreatment and SP application. In the I/R group, the expression levels of p-ERK1/2 and DUSP4/16 were not significantly different compared with the CON group, however, the protein expression levels of p-ERK1/2, Bcl-2 and DUSP4/16 were higher, while p-JNK, Bax, caspase 3 and DUSP2 levels were reduced among the SAA+I/R, PD+SAA+I/R and SP+I/R groups. The above indices were not significantly different between the SAA+I/R and SP+I/R groups. Compared with the SAA+I/R group, p-ERK1/2 was increased and p-JNK was decreased in the SAA+si-DUSP2+I/R, however, p-ERK was downregulated and p-JNK was upregulated in SAA+si-DUSP4+I/R group. SAA exerts an anti-apoptotic role against myocardial IRI by inhibiting DUSP2-mediated JNK dephosphorylation and activating DUSP4/16-mediated ERK1/2 phosphorylation.

Luteolin inhibited hydrogen peroxide-induced vascular smooth muscle cells proliferation and migration by suppressing the Src and Akt signalling pathways

Objectives  Luteolin is a naturally occurring flavonoid found in many vegetables, fruits and medicinal plants. The migration and proliferation of vascular smooth muscle cells (VSMCs) are the critical pathological processes in various cardiovascular diseases, such as atherosclerosis. In this study, we investigated the effect of luteolin and its latent mechanism on the proliferation and migration of VSMCs stimulated by hydrogen peroxide (H2O2).

Luteolin inhibits inflammatory responses via p38/MK2/TTP-mediated mRNA stability.

Luteolin (Lut) is a common dietary flavonoid present in Chinese herbal medicines that has been reported to have important anti-inflammatory properties. The purposes of this study were to observe the inhibition of lipopolysaccharide (LPS)-induced inflammatory responses in bone marrow macrophages (BMM) by Lut, and to examine whether this inhibition involves p38/MK2/TTP-mediated mRNA stability. Lut suppressed the production of tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) in a dose-dependent manner according to enzyme-linked immunosorbent assay (ELISA) analysis. Lut also shortened the half-lives of the TNF-α and IL-6 mRNAs according to real-time PCR analysis. Western blots were performed to assess the activation of p38 and MK2 as well as the expression of TTP. The results indicated that Lut inhibited p38 and MK2 phosphorylation while promoting TTP expression. These results suggest that the anti-inflammatory effects of Lut are partially mediated through p38/MK2/TTP-regulated mRNA stability.

Positive Feedback Regulation of Proliferation in Vascular Smooth Muscle Cells Stimulated by Lipopolysaccharide Is Mediated through the TLR 4/Rac1/Akt Pathway

Toll-like receptor 4 (TLR4) are important in inflammation and regulating vascular smooth muscle cells (VSMCs) proliferation, which are related to atherosclerosis and restenosis. We have investigated the mechanisms involved in Lipopolysaccharide (LPS)-induced proliferation of VSMCs. Stimulation of rat aortic VSMCs with LPS significantly increases the proliferation of VSMCs. This effect is regulated by Rac1 (Ras-related C3 botulinum toxin substrate l), which mediates the activation of phosphatidylinositol 3-kinase/Akt (PI3K/Akt) signaling pathways. Inhibition of Rac1 activity by NSC23766 is associated with inhibition of Akt activity. Treatment with NSC23766 or LY294002 significantly decreases LPS-induced TLR4 protein and mRNA expression. The data show that positive feedback regulation of proliferation in VSMCs is mediated through the TLR4/Rac1/Akt pathway.

Luteolin Attenuates Foam Cell Formation and Apoptosis in Ox-LDL-Stimulated Macrophages by Enhancing Autophagy

Background: Our previous studies demonstrated that luteolin, which is rich in flavones, has various biological properties and can exert anti-oxidant, anti-inflammatory and anti-apoptotic activities. However, its effect on ox-LDL-induced macrophage lipid accumulation and apoptosis has not been revealed. Aims: This study aimed to explore the role of luteolin in ox-LDL-induced macrophage-derived foam cell formation and apoptosis and to delineate the underlying mechanism. Methods: Murine RAW264.7 cells were stimulated with oxidized low-density lipoprotein (ox-LDL) (50 µg/ml) for 24 h and then pretreated with 25 µM luteolin for another 24 h. The effects of luteolin on lipid accumulation in RAW264.7 cells induced by ox-LDL were assayed using Oil red O staining and high performance liquid chromatography (HPLC). Apoptosis was confirmed by acridine orange/ethidium bromide (AO/EB) staining, flow cytometric analysis and the TUNEL assay. Immunofluorescence, Western blot and monodansylcadaverine (MDC) staining analyses were then used to further investigate the molecular mechanisms by which luteolin protects macrophages from ox-LDL-induced foam cell formation and apoptosis. 3-Methyladenine (3-MA), an autophagy inhibitor, was used as a positive control. Results: Treatment with 25 µM luteolin not only significantly attenuated ox-LDL-induced macrophage lipid accumulation but also decreased the apoptotic rate of RAW264.7 cells, the number of TUNEL-positive macrophages and the expression of Bax, Bak, cleaved caspase-9 and cleaved caspase-3. In addition, luteolin pretreatment significantly increased autophagosome formation and Beclin-1 activity, thus increasing the ratio of LC3-II/LC3-I. Moreover, these effects were abolished by 3-MA. Conclusions: Taken together, these results highlight that luteolin treatment attenuates foam cell formation and macrophage apoptosis by promoting autophagy and provide new insights into the molecular mechanism of luteolin and its therapeutic potential in the treatment of atherosclerosis.

Luteolin Inhibits Ischemia/Reperfusion-Induced Myocardial Injury in Rats via Downregulation of microRNA-208b-3p

Background Luteolin (LUT), a kind of flavonoid which is extracted from a variety of diets, has been reported to convey protective effects of various diseases. Recent researches have suggested that LUT can carry out cardioprotective effects during ischemia/reperfusion (I/R). However, there have no reports on whether LUT can exert protective effects against myocardial I/R injury through the actions of specific microRNAs (miRs). The purpose of this study was to determine which miRs and target genes LUT exerted such function through. Methods Expression of various miRs in perfused rat hearts was detected using a gene chip. Target genes were predicted with TargetScan, MiRDB and MiRanda. Anoxia/reoxygenation was used to simulate I/R. Cells were transfected by miR-208b-3p mimic, inhibitor and small interfering RNA of Ets1 (avian erythroblastosis virus E26 (v ets) oncogene homolog 1). MiR-208b-3p and Ets1 mRNA were quantified by real-time quantitative polymerase chain reaction. The percentage of apoptotic cells was detected by annexin V-fluorescein isothiocyanate/propidium iodide dyeing and flow cytometry. The protein expression levels of cleaved caspase-3, Bcl-2, Bax, and Ets1 were examined by western blot analysis. A luciferase reporter assay was used to verify the combination between miR-208b-3p and the 3’-untranslated region of Ets1. Results LUT pretreatment reduced miR-208b-3p expression in myocardial tissue, as compared to the I/R group. And LUT decreased miR-208b-3p expression and apoptosis caused by I/R. However, overexpression of miR-208b-3p further aggravated the changes caused by I/R and blocked all the effects of LUT. Knockdown of miR-208b-3p expression also attenuated apoptosis, while knockdown of Ets1 promoted apoptosis. Further, the luciferase reporter assay showed that miR-208b-3p could inhibit Ets1 expression. Conclusion LUT pretreatment conveys anti-apoptotic effects after myocardial I/R injury by decreasing miR-208b-3p and increasing Ets1 expression levels.

Luteolin Exerts Cardioprotective Effects through Improving Sarcoplasmic Reticulum Ca2+-ATPase Activity in Rats during Ischemia/Reperfusion In Vivo

The flavonoid luteolin exists in many types of fruits, vegetables, and medicinal herbs. Our previous studies have demonstrated that luteolin reduced ischemia/reperfusion (I/R) injury in vitro, which was related with sarcoplasmic reticulum Ca2+-ATPase (SERCA2a) activity. However, the effects of luteolin on SERCA2a activity during I/R in vivo remain unclear. To investigate whether luteolin exerts cardioprotective effects and to monitor changes in SERCA2a expression and activity levels in vivo during I/R, we created a myocardial I/R rat model by ligating the coronary artery. We demonstrated that luteolin could reduce the myocardial infarct size, lactate dehydrogenase release, and apoptosis during I/R injury in vivo. Furthermore, we found that luteolin inhibited the I/R-induced decrease in SERCA2a activity in vivo. However, neither I/R nor luteolin altered SERCA2a expression levels in myocardiocytes. Moreover, the PI3K/Akt signaling pathway played a vital role in this mechanism. In conclusion, the present study has confirmed for the first time that luteolin yields cardioprotective effects against I/R injury by inhibiting the I/R-induced decrease in SERCA2a activity partially via the PI3K/Akt signaling pathway in vivo, independent of SERCA2a protein level regulation. SERCA2a activity presents a novel biomarker to assess the progress of I/R injury in experimental research and clinical applications.