Alpha-lipoic acid protects cardiomyocytes against hypoxia/reoxygenation injury by inhibiting autophagy

α-Lipoic acid alleviates myocardial injury and induces M2b macrophage polarization after myocardial infarction via HMGB1/NF-kB signaling pathway

BACKGROUND

Myocardial infarction (MI) is a serious cardiovascular disease with a poor prognosis. Macrophages are the predominant immune cells in patients with MI and macrophage regulation during the different phases of MI has important consequences for cardiac recovery. Alpha-lipoic acid (ALA) plays a critical role in MI by modulating the number of cardiomyocytes and macrophages.

METHODS

MI mice were generated by ligating the left anterior descending coronary artery. Macrophages were exposed to hypoxia to establish a hypoxia model and M1 polarization was induced by LPS and IFN-γ. Different groups of macrophages and MI mice were treated with ALA. The cardiomyocytes were treated with various macrophage supernatants and the cardiac function, cytokine levels, and pathology were also analyzed. Factors related to apoptosis, autophagy, reactive oxygen species (ROS), and the mitochondrial membrane potential (MMP) were assessed. Finally, the HMGB1/NF-κB pathway was identified.

RESULTS

ALA promoted M2b polarization in normal cells and suppressed inflammatory cytokines during hypoxia. ALA inhibited ROS and MMP production in vitro. Supernatants containing ALA inhibited apoptosis and autophagy in hypoxic cardiomyocytes. Moreover, ALA suppressed the HMGB1/NF-κB pathway in macrophages, which may be a potential mechanism for attenuating MI.

CONCLUSION

ALA alleviates MI and induces M2b polarization via the HMGB1/NF-κB pathway, impeding inflammation, oxidation, apoptosis, and autophagy, and might be a potential strategy for MI treatment.

Regulation of autophagy of the heart in ischemia and reperfusion

Ischemia/reperfusion (I/R) of the heart leads to increased autophagic flux. Preconditioning stimulates autophagic flux by AMPK and PI3-kinase activation and mTOR inhibition. The cardioprotective effect of postconditioning is associated with activation of autophagy and increased activity of NO-synthase and AMPK. Oxidative stress stimulates autophagy in the heart during I/R. Superoxide radicals generated by NADPH-oxidase acts as a trigger for autophagy, possibly due to AMPK activation. There is reason to believe that AMPK, GSK-3β, PINK1, JNK, hexokinase II, MEK, PKCα, and ERK kinases stimulate autophagy, while mTOR, PKCδ, Akt, and PI3-kinase can inhibit autophagy in the heart during I/R. However, there is evidence that PI3-kinase could stimulate autophagy in ischemic preconditioning of the heart. It was found that transcription factors FoxO1, FoxO3, NF-κB, HIF-1α, TFEB, and Nrf-2 enhance autophagy in the heart in I/R. Transcriptional factors STAT1, STAT3, and p53 inhibit autophagy in I/R. MicroRNAs could stimulate and inhibit autophagy in the heart in I/R. Long noncoding RNAs regulate the viability and autophagy of cardiomyocytes in hypoxia/reoxygenation (H/R). Nitric oxide (NO) donors and endogenous NO could activate autophagy of cardiomyocytes. Activation of heme oxygenase-1 promotes cardiomyocyte tolerance to H/R and enhances autophagy. Hydrogen sulfide increases cardiac tolerance to I/R and inhibits apoptosis and autophagy via mTOR and PI3-kinase activation.

Alpha-lipoic acid impedes myocardial ischemia-reperfusion injury, myocardial apoptosis, and oxidative stress by regulating HMGB1 expression

BACKGROUND

Inflammation, oxidative stress, and apoptosis contribute to myocardial ischemia/reperfusion injury (I/RI). Alpha-lipoic acid (ALA) plays a critical role in I/RI by impeding apoptosis and inflammation. Here, we aimed to explore the underlying mechanisms of ALA after I/RI.

METHODS

The left anterior descending coronary artery (LAD) was ligated, and H9c2 cells were exposed to hypoxia/reoxygenation (H/R) to establish an I/RI model. Prior to this, H9c2 cells and rats were treated using an appropriate amount of ALA. The cardiac function, inflammatory factors, and myocardial pathology were assessed in vitro. We detected cell viability, apoptosis, and oxidative stress-related factors in vivo. Moreover, proteins of the HMGB1/TLR4/NF-κB signaling pathway were detected both in vivo and in vitro.

RESULTS

We observed that ALA increased cell viability in vitro and decreased apoptosis in vitro and in vivo. ALA inhibited reactive oxygen species production, decreased malondialdehyde, and increased superoxide dismutase activity to resist oxidative stress in vitro. ALA also reduced the expression of inflammatory cytokines (IL-6, IL-1β, and TNF-α) in vivo. ALA also suppressed the levels of the apoptotic protein, Bax, and increased the expression of the anti-apoptotic protein Bcl-2, in vitro and in vivo. Moreover, we observed that ALA significantly inhibited the cytoplasmic localization of HMGB1, which might attenuate MI/RI or H/R via HMGB1/TLR4/NF-κB pathway.

CONCLUSION

ALA regulates HMGB1 translocation and attenuates I/R via the HMGB1/TLR4/NF-κB signaling pathway, thus impeding apoptosis, oxidation, and inflammation, and might be a potential target for myocardial ischemia/reperfusion injury.

Nutraceuticals as Modulators of Autophagy: Relevance in Parkinson’s Disease

Dietary supplements and nutraceuticals have entered the mainstream. Especially in the media, they are strongly advertised as safe and even recommended for certain diseases. Although they may support conventional therapy, sometimes these substances can have unexpected side effects. This review is particularly focused on the modulation of autophagy by selected vitamins and nutraceuticals, and their relevance in the treatment of neurodegenerative diseases, especially Parkinson’s disease (PD). Autophagy is crucial in PD; thus, the induction of autophagy may alleviate the course of the disease by reducing the so-called Lewy bodies. Hence, we believe that those substances could be used in prevention and support of conventional therapy of neurodegenerative diseases. This review will shed some light on their ability to modulate the autophagy.

SIRT3 protects kidneys from ischemia-reperfusion injury by modulating the DRP1 pathway to induce mitochondrial autophagy

Renal ischemia-reperfusion injury (IRI) is a leading cause of acute kidney injury (AKI) and may influence renal graft survival. In this study, we investigate the involvement of SIRT3 and DRP1 in mitochondrial autophagy and AKI in a mouse model of IRI. Autophagy was detected in the absence of SIRT3, and hypoxic reoxygenation (H/R) experiments using renal tubular epithelial cells NRK52E were performed in vitro to validate these results. We found that autophagosomes increased following IRI and that the expression of autophagy-related genes was up-regulated. The inhibition of autophagy with 3-methyladenine exacerbated IRI, whereas the DRP1 inhibitor Mdivi-1 reversed this inhibition. Mdivi-1 did not reverse the inhibition of autophagy in the absence of SIRT3. During IRI, Mdivi-1 reduced autophagy and DRP1 expression, whereas SIRT3 overexpression attenuated this condition. Rescue experiment showed that autophagy was increased when both SIRT3 or DRP1 were over- or under-expressed or just DRP1 was under-expressed but expression was reduced when just SIRT3 was under-expressed. However, the expression of DRP1-related molecules was reduced when SIRT3 was overexpressed and when DRP1 was under-expressed. Taken together, these findings indicate that SIRT3 protects against kidney damage from IRI by modulating the DRP1 pathway to induce mitochondrial autophagy.

Effects of Lipoic Acid on Ischemia-Reperfusion Injury

Ischemia-reperfusion (I/R) injury often occurred in some pathologies and surgeries. I/R injury not only harmed to physiological functions of corresponding organ and tissue but also induced multiple tissue or organ dysfunctions (even these in distant locations). Although the reperfusion of blood attenuated I/R injury to a certain degree, the risk of secondary damages was difficult to be controlled and it even caused failures of these tissues and organs. Lipoic acid (LA), as an endogenous active substance and a functional agent in food, owns better safety and effects in our body (e.g., enhancing antioxidant activity, improving cognition and dementia, controlling weight, and preventing multiple sclerosis, diabetes complication, and cancer). The literature searching was conducted in PubMed, Embase, Cochrane Library, Web of Science, and SCOPUS from inception to 20 May 2021. It had showed that endogenous LA was exhausted in the process of I/R, which further aggravated I/R injury. Thus, supplements with LA timely (especially pretreatments) may be the prospective way to prevent I/R injury. Recently, studies had demonstrated that LA supplements significantly attenuated I/R injuries of many organs, though clinic investigations were short at present. Hence, it was urgent to summarize these progresses about the effects of LA on different I/R organs as well as the potential mechanisms, which would enlighten further investigations and prepare for clinic applications in the future.

Exosomes derived from MSC pre-treated with oridonin alleviates myocardial IR injury by suppressing apoptosis via regulating autophagy activation

This study aimed to investigate the molecular mechanisms underlying the role of bone marrow mesenchymal stem cells (BMMSCs)‐derived exosomes in ischaemia/reperfusion (IR)‐induced damage, and the role of oridonin in the treatment of IR. Exosomes were isolated from BMMSCs. Western blot analysis was done to examine the expression of proteins including CD63, CD8, apoptotic‐linked gene product 2 interacting protein X (AliX), Beclin‐1, ATG13, B‐cell lymphoma‐2 (Bcl‐2), apoptotic peptidase activating factor 1 (Apaf1) and Bcl2‐associated X (Bax) in different treatment groups. Accordingly, the expression of CD63, CD81 and AliX was higher in BMMSCs‐EXOs and IR + BMMSCs‐EXOs + ORI groups compared with that in the BMMSCs group. And BMMSCs‐derived exosomes inhibited the progression of IR‐induced myocardial damage, while this protective effect was boosted by the pre‐treatment with oridonin. Moreover, Beclin‐1, ATG13 and Bcl‐2 were significantly down‐regulated while Apaf1 and Bax were significantly up‐regulated in IR rats. And the presence of BMMSCs‐derived exosomes partly alleviated IR‐induced dysregulation of these proteins, while the oridonin pre‐treatment boosted the effect of these BMMSCs‐derived exosomes. The inhibited proliferation and promoted apoptosis of H9c2 cells induced by hypoxia/reperfusion (HR) were mitigated by the administration of BMMSCs‐derived exosomes. Meanwhile, HR also induced down‐regulation of Beclin‐1, ATG13 and Bcl‐2 expression and up‐regulation of Apaf1 and Bax, which were mitigated by the administration of BMMSCs‐derived exosomes. And oridonin pre‐treatment boosted the effect of BMMSCs‐derived exosomes. In conclusion, our results validated that BMMSCs‐derived exosomes suppressed the IR‐induced damages by participating in the autophagy process, while the pre‐treatment with oridonin could boost the protective effect of BMMSCs‐derived exosomes.

The effect of forskolin on membrane clock and calcium clock in the hypoxic/reoxygenation of sinoatrial node cells and its mechanism

BACKGROUND

In this study, we investigated the effect of forskolin (FSK, a selective adenylate cyclase agonist) on the automatic diastolic depolarization of sinus node cells (SNC) with hypoxia/reoxygenation (H/R) injury.

METHODS

The SNC of the newborn rat was randomly assigned into the control group, the H/R (H/R injury) group, or the H/R + FSK (H/R injury + FSK treatment) group. Patch-clamp was performed to record the action potential and electrophysiological changes. The cellular distribution of intracellular calcium concentration was analyzed by fluorescence staining.

RESULTS

Compared with the control cells, spontaneous pulsation frequency (SPF) and diastolic depolarization rate (DDR) of H/R cells were reduced from 244.3 ± 10.6 times/min and 108.7 ± 7.8 mV/s to 130.5 ± 7.6 times/min and 53.4 ± 6.5 mV/s, respectively. FSK significantly increased SPF and DDR of H/R cells to 208.3 ± 8.3 times/min and 93.2 ± 8.9 mV/s (n = 15, both p < 0.01), respectively. H/R reduced the current densities of I_f, I_Ca,T and inward I_NCX, which were significantly increased by 10 μM FSK treatment (n = 15, p < 0.01). Furthermore, reduced expression of HCN4 and NCX1.1 channel protein were significantly increased by FSK. Inhibitor studies showed that both SQ22536 (a selective adenylate cyclase inhibitor) and H89 (a selective protein kinases A [PKA] inhibitor) blocked the effects of FSK on SPF and DDR.

CONCLUSIONS

H/R causes pacemaker dysfunction in newborn rat sinoatrial node cells leading to divergence of the DD and the slow of spontaneous APs, which change can be dramatically reversed by FSK through increasing I_NCX and I_f current in H/R injury.

Long non-coding RNA ROR sponges miR-138 to aggravate hypoxia/reoxygenation-induced cardiomyocyte apoptosis via upregulating Mst1

BACKGROUND

Hypoxia/reoxygenation (H/R) injury of cardiomyocytes causes an irreversible damage to heart and largely results in acute myocardial infarction. Study has indicated lncRNA ROR aggravates myocardial ischemia/reperfusion (I/R) injury. Also, lncRNA ROR sponges miR-138 to promote osteogenesis. MiR-138 involves in hypoxic pulmonary vascular remodelling by targeting Mst1. However, the interaction between lncRNA ROR, miR-138 and Mst1 involved in myocardial H/R injury is still unknown.

METHODS

H9C2 cells were used to establish H/R injury model. The expression levels of lncRNA ROR and miR-138 were modified by transfection with the miR-138 mimics or lncRNA ROR overexpression plasmid. MTT and flow cytometry analysis were performed to detect cell proliferation and apoptosis. Dual luciferase reporter assay was used to determine interaction between lncRNA ROR and miR-138 or miR-138 and Mst1. Expression levels of lncRNA ROR, miR-138, Mst1 and apoptosis-related markers were determined by qRT-PCR or western blotting.

RESULTS

LncRNA ROR was significantly up-regulated, while miR-138 was obviously down-regulated in H/R-induced injury of H9C2 cells. Furthermore, miR-138 overexpression alleviated cardiac cell apoptosis induced by H/R injury. Mst1 was revealed to be a target of miR-138 and negatively regulated by miR-138. Mst1 overexpression reversed the protective effects of miR-138 on H/R injury of H9C2 cells. LncRNA ROR was identified as a sponge for miR-138. MiR-138 could protect H9C2 cells form H/R injury induced by lncRNA ROR overexpression.

CONCLUSION

Our study provides that lncRNA ROR sponges miR-138 to aggravate H/R-induced myocardial cell injury by upregulating the expression of Mst1.

α-Lipoic acid modulates liver fibrosis: A cross talk between TGF-β1, autophagy, and apoptosis

Autophagy and apoptosis are important players in the progression of hepatic fibrosis via activation of hepatic stellate cells (HSCs). Despite the recently depicted antifibrotic effects of alpha-lipoic acid (ALA), however, its modulatory effects on HSCs autophagy remain unverified. Our study aimed to elucidate the underlying antifibrotic mechanisms through which ALA mediates HSC autophagy and apoptosis. Liver fibrosis was induced via thioacetamide (TAA) intoxication in rats; TAA-intoxicated rats were treated with either silymarin or ALA. Effect of ALA on biochemical parameters and immunohistopathological examinations was measured and compared to silymarin. ALA restored normal hepatic architecture (S1 vs. S4), liver functions, hepatic glutathione, and transforming growth factor-β1 levels. ALA ameliorated hepatic levels of malondialdehyde, platelet-derived growth factor, tissue inhibitor metalloproteinases-1, hydroxyproline, and expression of alpha-smooth muscle actin. Moreover, ALA significantly reduced messenger RNA expression of LC3-II genes and triggered caspase-3 expression. Interestingly, ALA exhibited superior activities over silymarin regarding suppression of proliferation, activation and autophagy of HSCs, collagen deposition, and induction of HSCs apoptosis. In conclusion, treatment of TAA-intoxicated rats with ALA inhibited autophagy and induced apoptotic clearance of activated HSCs. Accordingly, this study provides mechanistic insights into the possible applicability of ALA in the treatment of hepatic fibrosis.

CD47 deficiency protects cardiomyocytes against hypoxia/reoxygenation injury by rescuing autophagic clearance

To assess the effect of cluster of differentiation (CD47) downregulation on autophagy in hypoxia/reoxygenation (H/R)‑treated H9c2 cardiomyocytes. H9c2 cells were maintained in normoxic conditions (95% air, 5% CO2, 37˚C) without CD47 antibodies, Si‑CD47 or chloroquine (CQ) treatment; H9c2 cells in the H/R group were subjected to 24 h of hypoxia (1% O2, 94% N2, 5% CO2, 37˚C) followed by 12 h of reoxygenation (95% air, 5% CO2, 37˚C). All assays were controlled, triplicated and repeated on three separately initiated cultures. The biochemical parameters in the medium supernatant were measured to evaluate the oxidative stress in cardiomyocytes. The Annexin V‑fluorescein isothiocyanate assay was used to detect the apoptotic rate in the H9c2 cells. Transmission electron microscope, immunofluorescent staining and western blot analysis were performed to detect the effect of the CD47 antibody on autophagic flux in H/R‑treated H9c2 cardiomyocytes. The cardiomyocytic oxidative stress and apoptotic rate decreased and autophagic clearance increased after CD47 downregulation. H/R triggered cell autophagy, autophagosome accumulation and apoptosis in H9c2 cell lines. However, these effects can be attenuated by CD47 downregulation. This study demonstrates its clinical implications in ischemia/reperfusion injury treatment.

Alpha-lipoic acid alleviated 6-OHDA-induced cell damage by inhibiting AMPK/mTOR mediated autophagy

Oxidative stress and autophagy are involved in the pathogenesis of Parkinson's disease. The relationship between oxidative stress and autophagy is a hot spot of scientific research. Alpha-lipoic acid (ALA) is a natural antioxidant. ALA has been reported to reduce oxidative stress and apoptosis in PD models, but its role in autophagy regulation of PD has been reported very little. In this study, we investigated the protective effects of ALA on 6-OHDA induced neurotoxicity, and explored the potential mechanisms associated with the crosstalk between oxidative stress and autophagy. Our results showed that 6-OHDA induced accumulation of ROS in SH-SY5Y cells, accompanied by excessive autophagy and apoptosis. ALA protected against 6-OHDA induced neuronal death through inhibition of oxidative stress and autophagy. Furthermore, we found that ALA inhibited AMPK phosphorylation while activated mTOR phosphorylation thereby blocking AMPK/mTOR signaling pathway involved autophagy. In conclusion, ALA alleviated 6-OHDA induced cell injury possibly by inhibiting autophagy mediated by AMPK/mTOR pathway.

Cardioprotective effects of constitutively active MEK1 against H2O2-induced apoptosis and autophagy in cardiomyocytes via the ERK1/2 signaling pathway

Oxidative stress injury is one of the main mechanisms of ischemia-reperfusion (I/R) injury. The extracellular signal-regulated kinase (ERK1/2) pathway plays an important role in cardioprotective during acute myocardial infarction. In this study, we used constitutively active MEK1 gene (CaMEK) transfection strategy to investigate whether CaMEK provides a protective effect against apoptosis and autophagy induced by Hydrogen peroxide (H₂O₂) in neonatal rat cardiac ventricular cardiomyocytes (NCMs) and the underlying mechanisms. As a result, CaMEK attenuated H₂O₂-induced apoptosis and cytotoxicity in NCMs, evidenced by decreased apoptotic cells and the ratio of Bax/Bcl-2, increased the mitochondrial membrane potential (Δψm) and cell vitality and reduced the level of lactate dehydrogenase (LDH). Further studies revealed that CaMEK attenuated H₂O₂-induced autophagy, evidenced by the decreased LC3-Ⅱ/LC3-Ⅰratio and SQSTM1/p62 (p62) degradation. Furthermore, we demonstrated that CaMEK phosphorylated the ERK1/2 pathway-related proteins, ERK1/2, p70S6K and GSK3β, in NCMs with H₂O₂ stimulation. In contrast, these effects could be reversed by co-treatment with the ERK1/2 inhibitor, PD98059. These results suggest that CaMEK plays an important role in protecting cardiomyocytes against H₂O₂-induced injury and autophagy in NCMs via ERK1/2 pathway. Therefore, transfection of CaMEK may provide a hopeful therapeutic strategy for I/R.

α‑lipoic acid protects against carbon tetrachloride‑induced liver cirrhosis through the suppression of the TGF‑β/Smad3 pathway and autophagy

α-lipoic acid (ALA) is a naturally occurring antioxidant with protective effects against various hepatic injuries. The aim of the present study was to investigate the mechanisms by which ALA protects the liver from carbon tetrachloride (CCl₄)-induced liver cirrhosis. The widely used liver cirrhosis rat model was established via an intraperitoneal injection of 2 mg/kg 50% CCl_4, three times/week for 8 weeks. Simultaneously, 50 or 100 mg/kg ALA was orally administrated to the rats every day for 8 weeks. The activity of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) was detected in the serum. The pathological liver injuries were analyzed using hematoxylin and eosin and Masson's trichrome staining. The principal factors involved in the transforming growth factor-β (TGF-β)/mothers against decapentaplegic homolog 9 (Smad3) and protein kinase B (AKT)/mammalian target of rapamycin (mTOR) pathways and in autophagy were examined using reverse transcription-quantitative polymerase chain reaction or western blot analysis. The results demonstrated that the administration of ALA alleviated CCl₄-induced liver injury, as demonstrated by decreased ALT and AST activity, improved pathological injuries and reduced collagen deposition. The CCl4-induced increase in TGF-β and phosphorylated-Smad3 expression levels was additionally inhibited by treatment with ALA. Furthermore, the administration of ALA reversed the CCl₄-induced upregulation of light chain 3II and Beclin-1, and downregulation of p62. The CCl₄-induced suppression of the AKT/mTOR pathway was additionally restored following treatment with ALA. In combination, the results of the present study demonstrated that ALA was able to protect CCl₄-induced liver cirrhosis, an effect that may be associated with inactivation of the TGF-β/Smad3 pathway and suppression of autophagy.

Alpha-lipoic acid regulates the autophagy of vascular smooth muscle cells in diabetes by elevating hydrogen sulfide level

Dysfunctional vascular smooth muscle (VSM) plays a vital role in the process of atherosclerosis in patients with type 2 diabetes mellitus (T2DM). Alpha-lipoic acid (ALA) can prevent the altered VSM induced by diabetes. However, the precise mechanism underlying the beneficial effect of ALA is not well understood. This study aimed to determine whether ALA ameliorates VSM function by elevating hydrogen sulfide (H₂S) level in diabetes and whether this effect is associated with regulation of autophagy of VSM cells (VSMCs). We found decreased serum H₂S levels in Chinese patients and rats with type 2 diabetes mellitus (T2DM). ALA treatment could increase H₂S level, which reduced the autophagy-related index and activation of the 5'-monophosphate-activated protein kinase (AMPK)/mammalian target of rapamycin (mTOR) pathway, thereby protecting vascular function in rats with T2DM. Propargylglycine (PPG), a cystathionine-γ-lyase inhibitor, could weaken the ALA effect. In cultured VSMCs, high glucose level also reduced H₂S level, upregulated the autophagy-related index and activated the AMPK/mTOR pathway, which were reversed by concomitant application of sodium hydrosulfide (NaHS, an H₂S donor) or ALA. The protective effect of NaHS or ALA was attenuated by rapamycin (an autophagy activator), 5-amino-1-β-d-ribofuranosyl-imidazole-4-carboxamide (an AMPK activator) or PPG. In contrast, Compound C (an AMPK inhibitor) enhanced the effect of ALA or NaHS. ALA may have a protective effect on VSMCs in T2DM by elevating H₂S level and downregulating autophagy via the AMPK/mTOR pathway. This study provides a new target for addressing diabetic macroangiopathy.

Inhibition of autophagy via activation of PI3K/Akt/mTOR pathway contributes to the protection of hesperidin against myocardial ischemia/reperfusion injury

Hesperidin has been reported to attenuate myocardial ischemia/reperfusion (I/R) injury; however, its effect on autophagy during myocardial I/R and the underlying mechanism remains unknown. The present study aimed to investigate whether hesperidin inhibited I/R-induced excessive myocardial autophagy through activating the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt)/mammalian target of rapamycin (mTOR) pathway. Male adult rats were pretreated with hesperidin for a total of 3 days prior to ischemia in the absence or presence of LY294002, a PI3K inhibitor, and then subjected to ischemia for 30 min followed by reperfusion for 4 h. Myocardial infarct size was measured by Evans blue/triphenyltetrazolium chloride staining. Hematoxylin and eosin staining was used for observing the histological changes in the heart, and the serum levels of creatine kinase-MB (CK-MB) and cardiac troponin I (cTnI) were measured by enzyme-linked immunosorbent assay. Additionally, the protein levels of light chain (LC) 3II, Beclin1, phosphorylated (p)-mTOR, p-Akt and p-PI3K were determined by western blot analysis. Hesperidin pretreatment significantly decreased the myocardial infarct size, myocardial damage and serum levels of CK-MB and cTnI. Furthermore, the expression levels of LC3II and Beclin1 were significantly downregulated and the expression levels of p-mTOR, p-Akt and p-PI3K were markedly upregulated by hesperidin. However, the aforementioned effects as a result of hesperidin were significantly reversed by the presence of LY294002. These results demonstrated that hesperidin reduced myocardial I/R injury by suppressing excessive autophagy. Activation of the PI3K/Akt/mTOR pathway contributed to the inhibitory effect of hesperidin on excessive autophagy.

Effect of Autophagy Inhibition on the Protection of Ischemia Preconditioning against Myocardial Ischemia/Reperfusion Injury in Diabetic Rats

BACKGROUND

Ischemia preconditioning (IPC) remains the most powerful intervention of protection against myocardial ischemia/reperfusion injury (IRI), but diabetes can weaken or eliminate its cardioprotective effect and detailed mechanisms remain unclear. In this study, we aimed to explore whether changes of autophagy in the diabetic condition are attributable to the decreased cardioprotective effect of IPC.

METHODS

Sixty diabetic male Sprague-Dawley rats were randomly divided into the control (C), IRI, rapamycin (R), wortmannin (W), rapamycin + IPC (R + IPC), and wortmannin + IPC (W + IPC) groups. The in vivo rat model of myocardial IRI was established by ligaturing and opening the left anterior descending coronary artery via the left thoracotomy. Durations of ischemia and reperfusion are 30 min and 120 min, respectively. Blood samples were taken at 120 min of reperfusion for measuring serum concentrations of troponin I (TnI) and creatine kinase isoenzyme MB (CK-MB) using the enzyme-linked immunosorbent assay. The infarct size was assessed by Evans blue and triphenyltetrazolium chloride staining. The expressions of LC3-II, beclin-1, phosphoinositide 3-kinase (PI3K), mammalian target of rapamycin (mTOR), and P-Akt/Akt ratio in the ischemic myocardium were assessed by Western blotting.

RESULTS

Compared to the IRI group, infarct size (56.1% ± 6.1% vs. 75.4 ± 7.1%, P < 0.05), serum cTnI (0.61 ± 0.21 vs. 0.95 ± 0.26 ng/ml, P < 0.05), and CK-MB levels (6.70 ± 1.25 vs. 11.51 ± 2.35 ng/ml, P < 0.05) obviously decreased in the W + IPC group. Compared with the C group, myocardial expressions of LC3-II (0.46 ± 0.04 and 0.56 ± 0.04 vs. 0.36 ± 0.04, P < 0.05) and beclin-1 (0.34 ± 0.08 and 0.38 ± 0.07 vs. 0.24 ± 0.03, P < 0.05) evidently increased, and myocardial expressions of mTOR (0.26 ± 0.08 and 0.25 ± 0.07 vs. 0.38 ± 0.06, P < 0.05), PI3K (0.29 ± 0.04 and 0.30 ± 0.03 vs. 0.38 ± 0.02, P < 0.05), and P-Akt/Akt ratio (0.49 ± 0.10 and 0.48 ± 0.06 vs. 0.72 ± 0.07, P < 0.05) markedly decreased in the IRI and R groups, indicating an increased autophagy. Compared with the IRI group, myocardial expression of beclin-1 (0.26 ± 0.03 vs. 0.34 ± 0.08, P < 0.05) significantly decreased, and myocardial expressions of mTOR (0.36 ± 0.04 vs. 0.26 ± 0.08, P < 0.05), PI3K (0.37 ± 0.03 vs. 0.29 ± 0.04, P < 0.05), and P-Akt/Akt ratio (0.68 ± 0.05 vs. 0.49 ± 0.10, P < 0.05) increased obviously in the W + IPC group, indicating a decreased autophagy.

CONCLUSIONS

Increased autophagy in the diabetic myocardium is attributable to decreased cardioprotection of IPC, and autophagy inhibited by activating the PI3K-Akt-mTOR signaling pathway can result in an improved protection of IPC against diabetic myocardial IRI.

The protective effect of alpha-lipoic acid against brain ischemia and reperfusion injury via mTOR signaling pathway in rats

Alpha-lipoic Acid(ALA), an endogenous short-chain fatty acid, has been found inducing a protective effect against ischemia and reperfusion(I/R) injury. Recently, mTOR signaling pathway has been proved to involve in the mechanism of I/R injury. In our previous study, we determined that ALA could protect cerebral endothelial cells against I/R injury via mTOR signaling pathway. However, whether ALA can protect against brain I/R injury in vivo and its mechanisms is uncertain. In this study, we try to explore if the ALA treatment can protect against brain I/R injury and confirm the relationship between ALA and mTOR signaling pathway. ALA was administrated to the animals after dMCAo and reperfusion model established with or without rapamycin pre-treatment. The results showed the infarct size was obviously reduced after ALA treatment in acute stage, neurological functions were also improved distinctly. The mTOR signaling pathway was remarkably blocked after brain I/R injury while it could be activated through ALA treatment. However, rapamycin, can abolish the protective effects induced by ALA treatment in both acute and long-term phase. In conclusion, we demonstrate the protective effects induced by ALA treatment against the brain I/R injury in rats and mTOR signaling pathway is required for the protective effects of ALA against brain I/R injury. The results might contribute to the potential clinical application of ALA and provide a potential therapeutic target on ischemic stroke.

Protective effect of sevoflurane on myocardial ischemia-reperfusion injury in rat hearts and its impact on HIF-1α and caspase-3 expression

This study was designed to investigate possible protective effects of sevoflurane on myocardial ischemia-reperfusion injury (MIRI) and its impact on expression of HIF-1α and caspase-3 in rats, so as to provide new insights for the treatment of MIRI. Forty SD rats were randomly divided into four groups (n=10) including Sham operation (Sham), ischemia-reperfusion (IR), sevoflurane preconditioning group (Sevo-Pre) and sevoflurane post-conditioning (Sevo-Post) groups. Perfusion was performed using ex vivo heart perfusion. The baseline values of cardiac function were recorded in each group at the end of balanced perfusion and after 60 min of reperfusion. Myocardial infarct size (MIS) was calculated at the end of perfusion using TTC staining. Levels of HIF-1α and caspase-3 protein and HIF-1α (western blotting) and Bcl-2 mRNA (RT-qPCR) were detected at the end of reperfusion. Our results showed no significant differences in cardiac function between the groups at the end of the balanced perfusion. After reperfusion for 60 min, however, the cardiac functions of the Sevo-Pre and Sevo-Post groups were significantly better than those in the IR group, and the MIS at the end of reperfusion was significantly decreased. Western blotting and RT-qPCR showed that expression of HIF-1α protein was significantly increased, expression of caspase-3 protein was significantly decreased and expression of HIF-1α and Bcl-2 mRNA were significantly increased in Sevo-Pre and Sevo-Post groups compared with the levels in the IR group at the end of reperfusion. There were no significant differences in experimental results between Sevo-Pre and Sevo-Post groups. Our data support the idea that sevoflurane can improve MIRI in rats by improving cardiac function and reducing MIS. This protective effect seems to be achieved by activation of HIF-1α and inhibition of caspase-3.

HMGB1 induces apoptosis and EMT in association with increased autophagy following H/R injury in cardiomyocytes

Hypoxia/reoxygenation (H/R) is a critical factor in the pathogenesis of tissue injury following myocardial infarction (MI) which can lead to tissue damage and pathological remodeling. Therefore, it is necessary to try and prevent myocardial H/R injury in order to optimize the treatment of MI. This study aimed to explore the functions and molecular mechanisms of action of high mobility group box 1 (HMGB1) and its role in H/R injury to H9c2 cells. The mRNA expression of levels genes were detected by RT-qPCR. The protein levels were examined by western blot analysis. The Beclin 1 expression level was further determined by immunocytochemistry (ICC). In addition, an HMGB1 overexpression vector and a shRNA lentiviral vector were constructed in order to induce the overexpression and silencing of HMGB1, respectively. The apoptotic rate of the H9c2 cells was determined by flow cytometry. The expression of miR-210 was markedly increased following the exposure of the cells to H/R, thus indicating that the cell model of H/R injury was successfully established. In addition, an in vivo model of MI was also created using rats. The mRNA and protein level of HMGB1 was found to be upregulated in the myocardial tissue of the rats with MI and in the H9c2 cells subjected to H/R injury. HMGB1 promoted apoptosis by increasing the expression of cleaved caspase-3 and the apoptotic rate of the cells, while decreasing the expression of Bcl-2 during H/R in the H9c2 cells. HMGB1 promoted epithelial-to-mesenchymal transition (EMT) by reducing the protein level of the epithelial marker, E-cadherin, while increasing the expression of the mesenchymal markers, vimentin and fibroblast-specific protein (FSP), during H/R in the H9c2 cells. HMGB1 induced the apoptosis of the H9c2 cells and EMT following H/R in association with the induction of autophagy. HMGB1 induced autophagy by upregulating the expression of discoidin domain receptor 1 (DDR1) and downregulating the phosphorylation levels of mammalian target of rapamycin (mTOR). In conclusion, the findings of our study suggest that HMGB1 promotes apoptosis and EMT in association with the induction of autophagy through the upregulation of the expression of DDR1 and the downregulation of the phosphorylation of mTOR following H/R injury in H9c2 cells.

Sevoflurane post-conditioning reduces rat myocardial ischemia reperfusion injury through an increase in NOS and a decrease in phopshorylated NHE1 levels

The protective effects of sevoflurane post-conditioning against myocardial ischemia/reperfusion (I/R) injury (MIRI) have been previously reported. However, the mechanisms responsible for these protective effects remain elusive. In this study, in order to investigate the molecular mechanisms responsible for the protective effects of sevoflurane post-conditioning on isolated rat hearts subjected to MIRI, Sprague-Dawley rat hearts were randomly divided into the following 6 groups: i) the sham-operated control; ii) 2.5% sevoflurane; iii) ischemia/reperfusion (I/R); iv) 2.5% sevoflurane post-conditioning plus I/R; v) 2.5% sevoflurane post-conditioning + NG-nitro-L-arginine methyl ester (L-NAME) plus I/R; and vi) L-NAME plus I/R. The infarct size was measured using 2,3,5-triphenyl tetrazolium chloride (TTC) staining. Additionally, the myocardial nitric oxide (NO), NO synthase (NOS) and nicotinamide adenine dinucleotide (NAD⁺) levels were determined. Autophagosomes and apoptosomes in the myocardium were detected by transmission electron microscopy. The levels of Bcl-2, cleaved caspase-3, Beclin-1, microtubule-associated protein light chain 3 (LC3)-I/II, Na⁺/H⁺ exchanger 1 (NHE1) and phosphorylated NHE1 protein were measured by western blot analysis. NHE1 mRNA levels were measured by reverse transcription-quantitative polymerase chain reaction. Compared with the I/R group, 15 min of exposure to 2.5% sevoflurane during early reperfusion significantly decreased the myocardial infarct size, the autophagic vacuole numbers, the NHE1 mRNA and protein expression of cleaved caspase-3, Beclin-1 and LC3-I/II. Post-conditioning with 2.5% sevoflurane also increased the NO and NOS levels and Bcl-2 protein expression (P<0.05 or P<0.01). Notably, the cardioprotective effects of sevoflurane were partly abolished by the NOS inhibitor, L-NAME. The findings of the present study suggest that sevoflurane post-conditioning protects the myocardium against I/R injury and reduces the myocardial infarct size. The underlying protective mechanisms are associated with the inhibition of mitochondrial permeability transition pore opening, and with the attenuation of cardiomyoctye apoptosis and excessive autophagy. These effects are mediated through an increase in NOS and a decrease in phopshorylated NHE1 levels.

Translational Implications of the Alcohol-Metabolizing Enzymes, Including Cytochrome P450-2E1, in Alcoholic and Nonalcoholic Liver Disease

Fat accumulation (hepatic steatosis) in alcoholic and nonalcoholic fatty liver disease is a potentially pathologic condition which can progress to steatohepatitis (inflammation), fibrosis, cirrhosis, and carcinogenesis. Many clinically used drugs or some alternative medicine compounds are also known to cause drug-induced liver injury, which can further lead to fulminant liver failure and acute deaths in extreme cases. During liver disease process, certain cytochromes P450 such as the ethanol-inducible cytochrome P450-2E1 (CYP2E1) and CYP4A isozymes can be induced and/or activated by alcohol and/or high-fat diets and pathophysiological conditions such as fasting, obesity, and diabetes. Activation of these P450 isozymes, involved in the metabolism of ethanol, fatty acids, and various drugs, can produce reactive oxygen/nitrogen species directly and/or indirectly, contributing to oxidative modifications of DNA/RNA, proteins and lipids. In addition, aldehyde dehydrogenases including the mitochondrial low Km aldehyde dehydrogenase-2 (ALDH2), responsible for the metabolism of acetaldehyde and lipid aldehydes, can be inactivated by various hepatotoxic agents. These highly reactive acetaldehyde and lipid peroxides, accumulated due to ALDH2 suppression, can interact with cellular macromolecules DNA/RNA, lipids, and proteins, leading to suppression of their normal function, contributing to DNA mutations, endoplasmic reticulum stress, mitochondrial dysfunction, steatosis, and cell death. In this chapter, we specifically review the roles of the alcohol-metabolizing enzymes including the alcohol dehydrogenase, ALDH2, CYP2E1, and other enzymes in promoting liver disease. We also discuss translational research opportunities with natural and/or synthetic antioxidants, which can prevent or delay the onset of inflammation and liver disease.

Pharmacological modulation of autophagy to protect cardiomyocytes according to the time windows of ischaemia/reperfusion

BACKGROUND AND PURPOSE

Targeted modulation of autophagy induced by myocardial ischaemia/reperfusion has been the subject of intensive investigation, but it is debatable whether autophagy is beneficial or harmful. Hence, we evaluated the effects of pharmacological manipulation of autophagy on the survival of cardiomyocytes in different time windows of ischaemia/reperfusion.

EXPERIMENTAL APPROACH

We examined the autophagy and apoptosis in cardiomyocytes subjected to different durations of anoxia/re-oxygenation or ischaemia/reperfusion, and evaluated the effects of the autophagic enhancer rapamycin and inhibitor wortmannin on cell survival.

KEY RESULTS

In neonatal rat cardiomyocytes (NRCs) or murine hearts, autophagy was increased in response to anoxia/reoxygenation or ischaemia/reperfusion in a time-dependent manner. Rapamycin-enhanced autophagy in NRCs led to higher cell viability and less apoptosis when anoxia was sustained for ≦ 6 h. When anoxia was prolonged to 12 h, rapamycin did not increase cell viability, induced less apoptosis and more autophagic cell death. When anoxia was prolonged to 24 h, rapamycin increased autophagic cell death, while wortmannin reduced autophagic cell death and apoptosis. Similar results were obtained in mice subjected to ischaemia/reperfusion. Rapamycin inhibited the opening of mitochondrial transition pore in NRCs exposed to 6 h anoxia/4 h re-oxygenation but did not exert any effect when anoxia was extended to 24 h. Similarly, rapamycin reduced the myocardial expression of Bax in mice subjected to short-time ischaemia, but this effect disappeared when ischaemia was extended to 24 h.

CONCLUSIONS AND IMPLICATIONS

The cardioprotection of autophagy is context-dependent and therapies involving the modification of autophagy should be determined according to the duration of ischaemia/reperfusion.

α-Lipoic acid protects against hypoxia/reoxygenation-induced injury in human umbilical vein endothelial cells through suppression of apoptosis and autophagy

α-lipoic acid (ALA) is known as a powerful antioxidant, which has been reported to have protective effects against various cardiovascular diseases. The present study aimed to determine whether ALA pre- or post-treatment induced protective effects against hypoxia/reoxygenation-induced injury via inhibition of apoptosis and autophagy in human umbilical vein endothelial cells (HUVECs). In order to simulate the conditions of hypoxia/reoxygenation, HUVECs were subjected to 4 h of oxygen-glucose deprivation (OGD) followed by 12 h of reoxygenation. For the pre-treatment, ALA was added to the buffer 12 h prior to OGD, whereas for the post-treatment, ALA was added at the initiation of reoxygenation. The results demonstrated that ALA pre- or post-treatment significantly reduced lactate dehydrogenase (LDH) release induced through hypoxia/reoxygenation in HUVECs in a dose-dependent manner; of note, 1 mM ALA pre- or post-treatment exhibited the most potent protective effects. In addition, ALA significantly reduced hypoxia/reoxygenation-induced loss of mitochondrial membrane potential, apoptosis and the expression of cleaved caspase-3 in HUVECs. In the presence of the specific autophagy inhibitor 3-methyladenine, hypoxia/reoxygenation-induced apoptosis was significantly reduced. Furthermore, the formation of autophagosomes, cytosolic microtubule-associated protein 1A/1B-light chain 3 ratio and beclin1 levels significantly increased following hypoxia/reoxygenation injury; however, all of these effects were ameliorated following pre- or post-treatment with ALA. The results of the present study suggested that ALA may provide beneficial protection against hypoxia/reoxygenation-induced injury via attenuation of apoptosis and autophagy in HUVECs.

H9c2 and HL-1 cells demonstrate distinct features of energy metabolism, mitochondrial function and sensitivity to hypoxia-reoxygenation

Dysfunction of cardiac energy metabolism plays a critical role in many cardiac diseases, including heart failure, myocardial infarction and ischemia-reperfusion injury and organ transplantation. The characteristics of these diseases can be elucidated in vivo, though animal-free in vitro experiments, with primary adult or neonatal cardiomyocytes, the rat ventricular H9c2 cell line or the mouse atrial HL-1 cells, providing intriguing experimental alternatives. Currently, it is not clear how H9c2 and HL-1 cells mimic the responses of primary cardiomyocytes to hypoxia and oxidative stress. In the present study, we show that H9c2 cells are more similar to primary cardiomyocytes than HL-1 cells with regard to energy metabolism patterns, such as cellular ATP levels, bioenergetics, metabolism, function and morphology of mitochondria. In contrast to HL-1, H9c2 cells possess beta-tubulin II, a mitochondrial isoform of tubulin that plays an important role in mitochondrial function and regulation. We demonstrate that H9c2 cells are significantly more sensitive to hypoxia-reoxygenation injury in terms of loss of cell viability and mitochondrial respiration, whereas HL-1 cells were more resistant to hypoxia as evidenced by their relative stability. In comparison to HL-1 cells, H9c2 cells exhibit a higher phosphorylation (activation) state of AMP-activated protein kinase, but lower peroxisome proliferator-activated receptor gamma coactivator 1-alpha levels, suggesting that each cell type is characterized by distinct regulation of mitochondrial biogenesis. Our results provide evidence that H9c2 cardiomyoblasts are more energetically similar to primary cardiomyocytes than are atrial HL-1 cells. H9c2 cells can be successfully used as an in vitro model to simulate cardiac ischemia-reperfusion injury.

Alpha-lipoic acid enhances DMSO-induced cardiomyogenic differentiation of P19 cells

Alpha-lipoic acid (α-LA) is a potent antioxidant that acts as an essential cofactor in mitochondrial dehydrogenase reactions. α-LA has been shown to possess anti-inflammatory and cytoprotective properties, and is used to improve symptoms of diabetic neuropathy. However, the role of α-LA in stem cell differentiation and the underlying molecular mechanisms remain unknown. In the present study, we showed that α-LA significantly promoted dimethyl sulfoxide (DMSO)-induced cardiomyogenic differentiation of mouse embryonic carcinoma P19 cells. α-LA dose dependently increased beating embryonic body (EB) percentages of DMSO-differentiated P19 cells. The expressions of cardiac specific genes TNNT2, Nkx2.5, GATA4, MEF2C, and MLC2V and cardiac isoform of troponin T (cTnT)-positively stained cell population were significantly up-regulated by the addition of α-LA. We also demonstrated that the differentiation time after EB formation was critical for α-LA to take effect. Interestingly, without DMSO treatment, α-LA did not stimulate the cardiomyogenic differentiation of P19 cells. Further investigation indicated that collagen synthesis-enhancing activity, instead of the antioxidative property, plays a significant role in the cardiomyogenic differentiation-promoting function of α-LA. These findings highlight the potential use of α-LA for regenerative therapies in heart diseases.