Panax quinquefolium saponin attenuates cardiomyocyte apoptosis induced by thapsigargin through inhibition of endoplasmic reticulum stress

Unfolded protein response during cardiovascular disorders: a tilt towards pro-survival and cellular homeostasis

The endoplasmic reticulum (ER) is an organelle that orchestrates the production and proper assembly of an extensive types of secretory and membrane proteins. Endoplasmic reticulum stress is conventionally related to prolonged disruption in the protein folding machinery resulting in the accumulation of unfolded proteins in the ER. This disruption is often manifested due to oxidative stress, Ca²⁺ leakage, iron imbalance, disease conditions which in turn hampers the cellular homeostasis and induces cellular apoptosis. A mild ER stress is often reverted back to normal. However, cells retaliate to acute ER stress by activating the unfolded protein response (UPR) which comprises three signaling pathways, Activating transcription factor 6 (ATF6), inositol requiring enzyme 1 alpha (IRE1α), and protein kinase RNA-activated-like ER kinase (PERK). The UPR response participates in both protective and pro-apoptotic responses and not much is known about the mechanistic aspects of the switch from pro-survival to pro-apoptosis. When ER stress outpaces UPR response then cell apoptosis prevails which often leads to the development of various diseases including cardiomyopathies. Therefore, it is important to identify molecules that modulate the UPR that may serve as promising tools towards effective treatment of cardiovascular diseases. In this review, we elucidated the latest advances in construing the contribution imparted by the three arms of UPR to combat the adverse environment in the ER to restore cellular homeostasis during cardiomyopathies. We also summarized the various therapeutic agents that plays crucial role in tilting the UPR response towards pro-survival.

Intermedin protects thapsigargin‑induced endoplasmic reticulum stress in cardiomyocytes by modulating protein kinase A and sarco/endoplasmic reticulum Ca2+‑ATPase

Intermedin (IMD) is a calcitonin/calcitonin-related peptide that elicits cardioprotective effects in a variety of heart diseases, such as cardiac hypertrophy and heart failure. However, the molecular mechanism of IMD remains unclear. The present study investigated the effects of IMD on neonatal rat ventricular myocytes treated with thapsigargin. The results of the present study demonstrated that thapsigargin induced apoptosis in cardiomyocytes in a dose- and time-dependent manner. Thapsigargin induced endoplasmic reticulum stress, as determined by increased expression levels of 78-kDa glucose-regulated protein, C/EBP-homologous protein and caspase-12, which were dose-dependently attenuated by pretreatment with IMD. In addition, IMD treatment counteracted the thapsigargin-induced suppression of sarco/endoplasmic reticulum Ca²⁺-ATPase (SERCA) activity and protein expression levels, and cytoplasmic Ca²⁺ overload. IMD treatment also augmented the phosphorylation of phospholamban, which is a crucial regulator of SERCA. Additionally, treatment with the protein kinase A antagonist H-89 inhibited the IMD-mediated cardioprotective effects, including SERCA activity restoration, anti-Ca²⁺ overload, endoplasmic reticulum stress inhibition and antiapoptosis effects. In conclusion, the results of the present study suggested that IMD may protect cardiomyocytes against thapsigargin-induced endoplasmic reticulum stress and the associated apoptosis at least partly by activating the protein kinase A/SERCA pathway.

Cardioprotection by ginseng: experimental and clinical evidence and underlying mechanisms

Protection of the ischemic and reperfused myocardium represents a major therapeutic challenge. Translating results from animal studies to the clinical setting has been disappointing, yet the need for effective intervention, particularly to limit heart damage following infarction or surgical procedures such as coronary artery bypass grafting, is substantial. Among the many compounds touted as cardioprotective agents is ginseng, a medicinal herb belonging to the genus Panax, which has been used as a medicinal agent for thousands of years, particularly in Asian societies. The biological actions of ginseng are very complex and reflect composition of many bioactive components, although many of the biological and therapeutic effects of ginseng have been attributed to the presence of steroid-like saponins termed ginsenosides. Both ginseng and many ginsenosides have been shown to exert cardioprotective properties in experimental models. There is also clinical evidence that traditional Chinese medications containing ginseng exert cardioprotective properties, although such clinical evidence is less robust primarily owing to the paucity of large-scale clinical trials. Here, we discuss the experimental and clinical evidence for ginseng, ginsenosides, and ginseng-containing formulations as cardioprotective agents against ischemic and reperfusion injury. We further discuss potential mechanisms, particularly as these relate to antioxidant properties.

5-Hydroxy-7-Methoxyflavone Triggers Mitochondrial-Associated Cell Death via Reactive Oxygen Species Signaling in Human Colon Carcinoma Cells

Plant-derived compounds are an important source of clinically useful anti-cancer agents. Chrysin, a biologically active flavone found in many plants, has limited usage for cancer chemotherapeutics due to its poor oral bioavailability. 5-Hydroxy-7-methoxyflavone (HMF), an active natural chrysin derivative found in various plant sources, is known to modulate several biological activities. However, the mechanism underlying HMF-induced apoptotic cell death in human colorectal carcinoma cells in vitro is still unknown. Herein, HMF was shown to be capable of inducing cytotoxicity in HCT-116 cells and induced cell death in a dose-dependent manner. Treatment of HCT-116 cells with HMF caused DNA damage and triggered mitochondrial membrane perturbation accompanied by Cyt c release, down-regulation of Bcl-2, activation of BID and Bax, and caspase-3-mediated apoptosis. These results show that ROS generation by HMF was the crucial mediator behind ER stress induction, resulting in intracellular Ca²⁺ release, JNK phosphorylation, and activation of the mitochondrial apoptosis pathway. Furthermore, time course study also reveals that HMF treatment leads to increase in mitochondrial and cytosolic ROS generation and decrease in antioxidant enzymes expression. Temporal upregulation of IRE1-α expression and JNK phosphorylation was noticed after HMF treatment. These results were further confirmed by pre-treatment with the ROS scavenger N-acetyl-l-cysteine (NAC), which completely reversed the effects of HMF treatment by preventing lipid peroxidation, followed by abolishment of JNK phosphorylation and attenuation of apoptogenic marker proteins. These results emphasize that ROS generation by HMF treatment regulates the mitochondrial-mediated apoptotic signaling pathway in HCT-116 cells, demonstrating HMF as a promising pro-oxidant therapeutic candidate for targeting colorectal cancer.