Mechanisms of chloride in cardiomyocyte anoxia-reoxygenation injury: the involvement of oxidative stress and NF-kappaB activation

Sasanquasaponin induces increase of Cl‑/HCO3‑ exchange of anion exchanger 3 and promotes intracellular Cl‑ efflux in hypoxia/reoxygenation cardiomyocytes

Anion exchanger 3 (AE3) is known to serve crucial roles in maintaining intracellular chloride homeostasis by facilitating the reversible electroneutral exchange of Cl‑ for HCO3‑ across the plasma membrane. Our previous studies reported that sasanquasaponin (SQS) can inhibit hypoxia/reoxygenation (H/R)‑induced elevation of intracellular Cl‑ concentration ([Cl‑]i) and elicit cardioprotection by favoring Cl‑/HCO3‑ exchange of AE3. However, the molecular basis for SQS‑induced increase of Cl‑/HCO3‑ exchange of AE3 remains unclear. The present study demonstrated that SQS activates protein kinase Cε (PKCε) and stimulates the phosphorylation of AE3 in H9c2 cells. Notably, SQS‑induced AE3 phosphorylation was blocked by the PKCε selective inhibitor εV1‑2, and a S67A mutation of AE3, indicating that SQS could promote phosphorylation of Ser67 of AE3 via a PKCε‑dependent regulatory signaling pathway. Additionally, both inhibition of PKCε by εV1‑2 and S67A mutation of AE3 eradicated the SQS‑induced increase of AE3 activity, reversed the inhibitory effect of SQS on H/R‑induced elevation of [Cl‑]i, Ca2+ overload and generation of reactive oxygen species, and eliminated SQS‑induced cardioprotection. In conclusion, PKCε‑dependent phosphorylation of serine 67 on AE3 may be responsible for the increase of Cl‑/HCO3‑ exchange of AE3 and intracellular chloride efflux by SQS, and contributes to the cardioprotection of SQS against H/R in H9c2 cells.

Extracellular Cl--free-induced cardioprotection against hypoxia/reoxygenation is associated with attenuation of mitochondrial permeability transition pore

The isotonic substitution of extracellular chloride by gluconate (extracellular Cl^--free) has been demonstrated to elicit cardioprotection by attenuating ischaemia/reperfusion-induced elevation of intracellular chloride ion concentration ([Cl^-]_i). However, the downstream mechanism underlying the cardioprotective effect of extracellular Cl^--free is not fully established. Here, it was investigated whether extracellular Cl^--free attenuates mitochondrial dysfunction after hypoxia/reoxygenation (H/R) and whether mitochondrial permeability transition pore (mPTP) plays a key role in the extracellular Cl^--free cardioprotection. H9c2 cells were incubated with or without Cl^--free solution, in which Cl^- was replaced with equimolar gluconate, during H/R. The involvement of mPTP was determined with atractyloside (Atr), a specific mPTP opener. The results showed that extracellular Cl^--free attenuated H/R-induced the elevation of [Cl^-]_i, accompanied by increase of cell viability and reduction of lactate dehydrogenase release. Moreover, extracellular Cl^--free inhibited mPTP opening, and improved mitochondria function, as indicated by preserved mitochondrial membrane potential and respiratory chain complex activities, decreased mitochondrial reactive oxygen species generation, and increased ATP content. Intriguingly, pharmacologically opening of the mPTP with Atr attenuated all the protective effects caused by extracellular Cl^--free, including suppression of mPTP opening, maintenance of mitochondrial membrane potential, and subsequent improvement of mitochondrial function. These results indicated that extracellular Cl^--free protects mitochondria from H/R injury in H9c2 cells and inhibition of mPTP opening is a crucial step in mediating the cardioprotection of extracellular Cl^--free.

Sasanquasaponin-induced cardioprotection involves inhibition of mPTP opening via attenuating intracellular chloride accumulation

Sasanquasaponin (SQS) has been reported to elicit cardioprotection by suppressing hypoxia/reoxygenation (H/R)-induced elevation of intracellular chloride ion concentration ([Cl^-]_i). Given that the increased [Cl^-]_i is involved to modulate the mitochondrial permeability transition pore (mPTP), we herein sought to further investigate the role of mPTP in the cardioprotective effect of SQS on H/R injury. H9c2 cells were incubated for 24h with or without 10μM SQS followed by H/R. The involvement of mPTP was determined with a specific mPTP agonist atractyloside (ATR). The results showed that SQS attenuated H/R-induced the elevation of [Cl^-]_i, accompanied by reduction of lactate dehydrogenase release and increase of cell viability. Moreover, SQS suppressed mPTP opening, and protected mitochondria, as indicated by preserved mitochondrial membrane potential and respiratory chain complex activities, decreased mitochondrial reactive oxygen species generation, and increased ATP content. Interestingly, extracellular Cl^--free condition created by replacing Cl^- with equimolar gluconate resulted in a decrease in [Cl^-]_i and induced protective effects similar to SQS preconditioning, whereas pharmacologically opening of the mPTP with ATR abolished all the protective effects induced by SQS or Cl^--free, including suppression of mPTP opening, maintenance of mitochondrial membrane potential, and subsequent improvement of mitochondrial function. The above results allow us to conclude that SQS-induced cardioprotection may be mediated by preserving the mitochondrial function through preventing mPTP opening via inhibition of H/R-induced elevation of [Cl^-]_i.

Antioxidative effect of luteolin pretreatment on simulated ischemia/reperfusion injury in cardiomyocyte and perfused rat heart

OBJECTIVE

To investigate the antioxidative effect and mechanism of luteolin on rat cardiomyocytes and isolated hearts followed by simulated ischemia/reperfusion (SI/R) injury.

METHODS

The left ventricular cardiomyocytes and the isolated hearts from adult rats were subjected to SI/R injury. The experiment groups included control, SI/R, luteolin + SI/R (Lut + SI/R), vitamin E (Vit E) + SI/R, and LY294002 + luteolin + SI/R (LY + Lut + SI/R) groups. Cell viability, shortening amplitude, lactate dehydrogenase (LDH) release, superoxide dismutase (SOD) activity, the production of reactive oxygen species (ROS) and malondialdehyde (MDA), expression levels of Akt, phosphorylated Akt, NOX2 (gp91phox), NOX2 mRNA, mitogen-activated protein kinase (p38 MAPK) and phosphorylated p38MAPK were all measured after 3-h simulated ischemia and 2-h simulated reperfusion procedure in cardiomyocytes. Vit E was used as a standard control. The contractile function of isolated hearts was further observed after they were subjected to 30-min global ischemia and 120-min reperfusion.

RESULTS

Pretreatment with 8-μmol/L luteolin substantially increased cell viability and shortening amplitude, while reducing evidence of oxidative stress-induced damage in the cells. In addition, the expression of NOX2, NOX2 mRNA and phosphorylation of p38MAPK were all downregulated. Furthermore, pretreatment with 40-μmol/L luteolin improved the recovery of myocardial contractile function following SI/R-induced injury, and luteolin markedly increased phosphorylation of Akt. However, all of the above effects were partially inhibited by the phosphatidylinositol 3-kinase (PI3K) inhibitor, LY294002.

CONCLUSIONS

Luteolin prevents SI/R-induced myocardial damage by reducing oxidative stress-induced injury in isolated rat hearts and cardiomyocytes, and the cardioprotection induced by luteolin was partially mediated by the PI3K/Akt pathway.

Sasanquasaponin promotes cellular chloride efflux and elicits cardioprotection via the PKCε pathway

Sasanquasaponin (SQS) is an active component of Camellia oleifera Abel. A recent study by our group demonstrated that SQS was able to inhibit ischemia/reperfusion‑induced elevation of the intracellular chloride ion concentration ([Cl‑]i) and exerted cardioprotective effects; however, the underlying intracellular signal transduction mechanisms have yet to be elucidated. As protein kinase C ε (PKCε) is able to mediate Cl‑ homeostasis, the present study investigated its possible involvement in the effects of SQS on cardiomyocytes subjected to ischemia/reperfusion injury. Cardiomyocytes were pre‑treated with or without SQS or SQS plus εV1‑2, a selective PKCε inhibitor, followed by simulated ischemia/reperfusion (sI/R). The effects on cell viability, PKCε phosphorylation levels, [Cl‑]i, mitochondrial membrane potential and reactive oxygen species (ROS) production were assessed using an MTS assay, western blot analysis, colorimetric assays and flow cytometry. The results revealed that treatment with SQS prior to sI/R increased the viability of cardiomyocytes, and efficiently attenuated lactate dehydrogenase and creatine phosphokinase release induced by sI/R. In addition, SQS promoted PKCε phosphorylation and inhibited sI/R‑induced elevation of [Cl‑]i, paralleled by the attenuation of mitochondrial membrane potential loss and ROS generation. However, when the cardiomyocytes were treated with εV1‑2 prior to SQS pre‑conditioning, the cardioprotection induced by SQS was reduced and the inhibitory effects of SQS on sI/R‑induced elevation of [Cl‑]i, production of ROS and loss of mitochondrial membrane potential were also attenuated. These findings indicated that SQS may inhibit sI/R‑induced elevation of [Cl‑]i through the PKCε signaling pathway to elicit cardioprotection in cultured cardiomyocytes.

TMEM16A mediates the hypersecretion of mucus induced by Interleukin-13

Previous studies showed that the Ca(2+)-activated Cl(-) channel (CaCC) was involved in the pathogenesis of mucus hypersecretion induced by Interleukin-13 (IL-13). However, the mechanisms underlying the process were unknown. Recently, transmembrane protein 16A (TMEM16A) was identified as the channel underlying the CaCC current. The aim of the current study was to investigate whether the TMEM16A channel is part of the mechanism underlying IL-13-induced mucus hypersecretion. We observed that both TMEM16A mRNA and protein expression were significantly up-regulated after treatment with IL-13 in human bronchial epithelial 16 (HBE 16) cells, which correlated with an increase in mucus production. Additionally, mucus hypersecretion in rat airways was induced by intratracheal instillation of IL-13 and similar increases were observed in the expression of TMEM16A mRNA and protein in the bronchial epithelium. Niflumic acid (NA), a selective antagonist of CaCC, markedly blocked IL-13-induced mucin (MUC) 5AC mRNA and protein production in vivo and in vitro. Further investigation with HBE16 cells revealed that TMEM16A overexpression clearly promoted mucus production, IκBα phosphorylation, and p65 accumulation in the nucleus. The loss of TMEM16A resulted in inhibition of mucus production, and the TMEM16A-mediated production of MUC5AC was significantly blocked by a nuclear factor-kappa B (NF-κB) inhibitor. Therefore, the TMEM16A channel acts upstream of NF-κB in the regulation of mucus production. This is the first demonstration that the TMEM16A-NF-κB pathway is positively involved in IL-13-induced mucus production, which provides novel insight into the molecular mechanism of mucin overproduction.