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Dipeptidyl peptidase-4 (DPP4) enzyme inhibition has been reported to increase plasma glucagon-like peptide-1 (GLP-1) level for controlling postprandial glucose concentration. Both DPP4 inhibitors and GLP-1 analog have been approved for antihyperglycemic agents. In addition to the insulinotropic effect, GLP-1 signaling was reported to modulate cardiac function. DPP4 inhibition was shown to improve survival rate after myocardial infarction in mice, but the precise mechanism remains unknown. We aimed to compare the cardiovascular responses of ischemia/reperfusion (I/R) between wild-type and DPP4-deficient rats and investigate the underlying mechanism. Rats were subjected to 45 min of coronary artery occlusion, followed by reperfusion for 2 h. Cardiac function was characterized by analyzing pressure-volume loops. As compared to wild-type rats, after I/R, DPP4-deficient rats had better cardiac performance in association with less infarct size and cardiac injury markers (LDH, ANP, and BNP), which could be attenuated by exendin-(9-39), a GLP-1 receptor antagonist. Exendin-(9-39) could diminish the increased phosphorylation levels of myocardial AKT and GSK-3β as well as the higher expression of GLUT4 in post-infarcted DPP4-deficient rats. However, exendin-(9-39) could not completely abrogate the less infarct size in DPP4-deficient rats as compared with that in wild-type rats, implicating the involvement of GLP-1 receptor-independent pathway. In summary, this study demonstrated that the benefit of cardiac protective action against I/R injury was demonstrated in DPP4-deficient rats, which is mediated through both GLP-1 receptor-dependent and receptor-independent mechanisms.

Thaliporphine was found to ameliorate endotoxin-induced circulatory failure and mortality in rodents. The aims of the present study were to assess whether thaliporphine could improve cardiac function in endotoxemic rats and to investigate the underlying mechanisms. Cardiac function was evaluated by pressure-volume loop analysis in pentobarbital-anesthetized rats 24 h after intravenous injection of lipopolysaccharide (LPS) (4 mg/kg) with or without thaliporphine (1 mg/kg, iv). The intracellular Ca(2+) transients, nitric oxide (NO), and reactive oxygen species (ROS) in enzymatically isolated ventricular cells were measured by fluorescent indicators. Western blotting was used to analyze the change of protein expression in response to LPS with or without thaliporphine in rat ventricle, H9C2 and Raw264.7 cells. Cardiac depression was found to coincide with the decreased intracellular Ca(2+) transients and the increased expression of nitrotyrosine on SERCA2 in rat ventricles after 24-h endotoxemia. Thaliporphine decreased intracellular NO and ROS level in ventricular cells and the nitrosylation of SERCA2, which resulted in recovering the functional properties of intracellular Ca(2+) handling and cardiac contraction. In H9C2 cells, LPS-induced nuclear translocation of nuclear factor kappa B (NF-κB) could be attenuated by thaliporphine. In Raw264.7 cells, thaliporphine attenuated LPS-induced TAK-1 phosphorylation and IκBα degradation in association with the inhibition of inducible nitric oxide synthase (iNOS) and tumor necrosis factor alpha (TNF-α) expression and the production of NO and ROS. In conclusion, thaliporphine ameliorates LPS-induced cardiac depression through attenuating TLR4 signaling in the downstream of TAK-1 phosphorylation and NF-κB signaling in both cardiomyocytes and macrophage to prevent cardiac SERCA2 from nitrosylation by peroxynitrite via decreasing iNOS and TNF-α expression.

Prazosin, a quinazoline-based α(1)-adrenoceptor antagonist, is known to induce cell death, and this effect is independent of its α-blockade activity. However, the detailed molecular mechanisms involved are still not fully understood. In this study, we found that prazosin, but not doxazosin, could induce patterns of autophagy in H9C2 cells, including intracellular vacuole formation, microtubule-associated protein 1 light chain 3 (LC3) conversion, and acidic vesicular organelle (AVO) augmentation. Western blot analysis of phosphorylated proteins showed that exposure to prazosin increased the levels of phospho-p53 and phospho-adenosine monophosphate-activated protein kinase (AMPK) but dramatically decreased the levels of phospho-mammalian target of rapamycin (mTOR), phospho-protein kinase B (Akt), and phospho-ribosomal protein S6 kinase (p70S6K). Furthermore, although pretreatments with the pharmacological autophagy inhibitor 3-methyladenine and the p53 inhibitor pifithrin-α suppressed prazosin-induced AVO formation, they did not reverse prazosin-induced decline in cell viability but enhanced prazosin-induced caspase-3 activation. From these results we suggest that prazosin induces autophagic cell death via a p53-mediated mechanism. When the autophagy pathway was inhibited, prazosin still induced programmed cell death, at least in part through apoptotic caspase-3 cascade enhancement. Thus, our results indicate a potential new target in prazosin-induced cell death.

Glucagon-like peptide-1 (GLP-1) is rapidly cleaved by widely expressed dipeptidyl peptidase-4 (DPP4) enzyme. Both DPP4 inhibitors and GLP-1 analogue are being developed as a novel class of oral antihyperglycemic agent in the treatment of diabetes. However, the benefits of both agents on the cardiovascular function of endotoxemic animals remains poorly understood. In this study, the cardiac function of wild-type and DPP4-deficient rats was evaluated by pressure–volume loops in control and 4 h after lipopolysaccharide (LPS, 10 mg/kg, i.v.) treatment. LPS-induced suppression of cardiovascular function in wild-type rats was associated with a significant reduction in cardiac cAMP level, phosphorylation of phospholamban, and attenuation of aortic contractile response to phenylephrine. DPP4-deficient rats had better preservation of cardiovascular function than wild-type rats during endotoxemia, which was correlated with a more prominent elevation of GLP-1 signaling. These findings coincided with the pretreatment of GLP-1 analogue, exendin-4, where the deterioration of cardiovascular function during endotoxemia was significantly reversed in wild-type rats. Furthermore, the benefit of DPP4 deficiency or GLP-1 analogue not only preserved cardiovascular function but also alleviated multiple organ injury and improved survival rate during endotoxemia. In summary, this study demonstrated that the resistance to LPS in DPP4-deficient rats seems to be derived from the higher GLP-1 production, and exendin-4 prevents cardiac dysfunction in wild-type rats with endotoxemia. This study proves that GLP-1 agonists or DPP4 inhibitor may possibly be used as a preventive or even as a novel therapeutic agent in septic shock.

The mechanism of doxazosin-induced apoptosis through alpha(1)-adrenoceptor-independent pathway has been reported in various types of cell models. However, the molecular events involved in this effect are still not fully discovered. In present study, we proposed that the transforming growth factor-beta type I receptor (TbetaRI/ALK5) may contribute to the doxazosin-induced apoptosis in H9C2 cardiomyoblasts. Via the detection of cell viability, apoptotic nuclei, and caspase-3 activity, we found that doxazosin induced concentration- and time-dependent apoptosis in H9C2 cells. The cell apoptosis induced by 30 muM doxazosin was exacerbated by the addition of 10 ng/ml transforming growth factor-beta1 (TGF-beta1). Doxazosin or TGF-beta1 alone respectively elevated p38 mitogen-activated protein kinases (MAPK) and Smad3 protein phosphorylation in H9C2 cells. However, the cotreatment of doxazosin and TGF-beta1 attenuated the TGF-beta1-induced Smad3 protein phosphorylation and increased doxazosin-induced p38 MAPK protein phosphorylation. Furthermore, inhibitors of TbetaRI/ALK5 (SB431542) and p38 MAPK (SB202190) or TbetaRI/ALK5 knockdown all dramatically reduced the doxazosin-induced apoptosis in H9C2 cells. In conclusion, our results demonstrated that TbetaRI/ALK5-p38 MAPK phosphorylation signaling pathway could contribute to doxazosin-induced cell apoptosis, which could be further enhanced by TGF-beta1 in association with attenuating Smad3 phosphorylation in H9C2 cells.

Petasites formosanus, an indigenous species of Petasites, has been used to treat cardiovascular diseases such as hypertension for years. We have suggested recently that S-petasin, a major sesquiterpene from P. formosanus, inhibits vascular smooth muscle contraction through inhibition of voltage-dependent Ca(2+) channels, a phenomenon possibly responsible for the hypotensive effect of P. formosanus. This study was designed to examine the chronotropic and inotropic actions of S-petasin in the heart in vivo and in vitro. Administration of S-petasin (0.1-1.5 mg/kg i.v.) in anesthetized rats reduced heart rate dose-dependently. This response was consistent with significant suppression of both contractile amplitude and spontaneous firing rate of isolated atria, responses that were not antagonized by atropine (1 microM). Mechanical evaluation in isolated ventricular myocytes showed that S-petasin (0.1 to 100 microM) depressed peak myocyte contraction and intracellular Ca(2+) transients concentration-dependently. The duration of myocyte contraction was not affected. Whole-cell voltage clamp analysis revealed that S-petasin inhibited the L-type Ca(2+) current ( I(Ca,L)) concentration-dependently and shifted the steady-state inactivation curve of I(Ca,L) to more negative potentials. However, a receptor-binding assay failed to identify any significant interaction between S-petasin (0.1-300 microM) and the dihydropyridine binding sites of L-type voltage-dependent Ca(2+) channels. Taken together, these data show that the negative chronotropic and inotropic properties of S-petasin that can be ascribed mainly to I(Ca,L) inhibition, but not to blockade of dihydropyridine binding sites of L-type Ca(2+) channel or to muscarinic receptor activation.