Depression of hepatic mixed-function oxidase activity by B. pertussis in splenectomized and athymic nude mice

miRNA-19b-3p Stimulates Cardiomyocyte Apoptosis Induced by Myocardial Ischemia Reperfusion via Downregulating PTEN

Objective

To clarify the function of miRNA-19b-3p in accelerating myocardial ischemia-reperfusion injury- (MIRI-) induced cardiomyocyte apoptosis by downregulating gene of phosphate and tension homology deleted on chromsome ten (PTEN), thus influencing the progression of acute myocardial infarction.

Materials and Methods

miRNA-19b-3p and PTEN levels in HCM cells undergoing hypoxia/reoxygenation (H/R) were determined. Meanwhile, activities of myocardium injury markers [lactate dehydrogenase (LDH), malondialdehyde; malonic dialdehyde (MDA), superoxide dismutase (SOD), and glutathione peroxidase (GSH-PX)] in H/R-induced HCM cells were tested. Through dual-luciferase reporter gene assay, the binding between miRNA-19b-3p and PTEN was verified. Regulatory effects of miRNA-19b-3p and PTEN on apoptotic rate and apoptosis-associated gene expressions (proapoptotic protein Bcl-2 associated X protein (Bax), antiapoptotic protein B-cell lymphoma-2 (Bcl-2), and cytochrome C) in H/R-induced human cardiac myocytes (HCM) cells were examined.

Results

miRNA-19b-3p was upregulated, while PTEN was downregulated in H/R-induced HCM cells. Knockdown of miRNA-19b-3p decreased activities of LDH, MDA, and GSH-PX, but increased SOD level in H/R-induced HCM cells. The binding between miRNA-19b-3p and PTEN was confirmed. More importantly, knockdown of miRNA-19b-3p reduced apoptotic rate, downregulated proapoptosis gene expressions (Bax and cytochrome C), and upregulated antiapoptosis gene expression (Bcl-2), which were reversed by silence of PTEN.

Conclusions

miRNA-19b-3p is upregulated in HCM cells undergoing hypoxia and reoxygenation, which accelerates MIRI-induced cardiomyocyte apoptosis through downregulating PTEN.

Neuroprotective effect of pharmacological postconditioning on cerebral ischaemia-reperfusion-induced injury in mice

OBJECTIVES

To investigate the mechanism of neuroprotection rendered via pharmacological postconditioning in cerebral ischaemia-reperfusion-induced injury in mice.

METHODS

Pharmacological postconditioning is strategy which either involves hindering deleterious pathway or inducing modest stress level which triggers intracellular defence pathway to sustain more vigorous insult leading to conditioning. Hence, in current research we explored the potentiality of CGS21680 (0.5 mg/kg; i.p), an adenosine A₂ A receptor agonist and PTEN inhibitor, SF1670 (3 mg/kg; i.p.) to trigger postconditioning after inducing cerebral global ischaemia (17 min) and reperfusion (24 h)-induced injury via occlusion of both carotid arteries. Mice were also given treatment with LY294002 (1.5 mg/kg; i.p.), a PI3K inhibitor and adenosine A₂ A receptor antagonist, Istradefylline (2 mg/kg; i.p.), to establish the precise mechanism of postconditioning. Various biochemical and behavioural parameters were assessed to examine the effect of pharmacological postconditioning.

KEY FINDINGS

Pharmacological postconditioning induced with CGS21680 and SF1670 attenuated the infarction along with improved behavioural and biochemical parameters in comparison with ischaemia-reperfusion control group. The outcome of postconditioning with CGS21680 and SF1670 was significantly reversed by LY294002 and Istradefylline, respectively.

CONCLUSIONS

The neuroprotective effects of CGS21680 and SF1670 postconditioning on cerebral ischaemia-reperfusion injury may be due to PI3K/Akt pathway activation.

MicroRNA-214 protects against hypoxia/reoxygenation induced cell damage and myocardial ischemia/reperfusion injury via suppression of PTEN and Bim1 expression

BACKGROUND

Myocardial apoptosis plays an important role in myocardial ischemia/reperfusion (I/R) injury. Activation of PI3K/Akt signaling protects the myocardium from I/R injury. This study investigated the role of miR-214 in hypoxia/reoxygenation (H/R)-induced cell damage in vitro and myocardial I/R injury in vivo.

METHODS AND RESULTS

H9C2 cardiomyoblasts were transfected with lentivirus expressing miR-214 (LmiR-214) or lentivirus expressing scrambled miR-control (LmiR-control) respectively, to establish cell lines of LmiR-214 and LmiR-control. The cells were subjected to hypoxia for 4 h followed by reoxygenation for 24 h. Transfection of LmiR-214 suppresses PTEN expression, significantly increases the levels of Akt phosphorylation, markedly attenuates LDH release, and enhances the viability of the cells subjected to H/R. In vivo transfection of mouse hearts with LmiR-214 significantly attenuates I/R induced cardiac dysfunction and reduces I/R-induced myocardial infarct size. LmiR-214 transfection significantly attenuates I/R-induced myocardial apoptosis and caspase-3/7 and caspase-8 activity. Increased expression of miR-214 by transfection of LmiR-214 suppresses PTEN expression, increases the levels of phosphorylated Akt, represses Bim1 expression and induces Bad phosphorylation in the myocardium. In addition, in vitro data shows transfection of miR-214 mimics to H9C2 cells suppresses the expression and translocation of Bim1 from cytosol to mitochondria and induces Bad phosphorylation.

CONCLUSIONS

Our in vitro and in vivo data suggests that miR-214 protects cells from H/R induced damage and attenuates I/R induced myocardial injury. The mechanisms involve activation of PI3K/Akt signaling by targeting PTEN expression, induction of Bad phosphorylation, and suppression of Bim1 expression, resulting in decreases in I/R-induced myocardial apoptosis.

Protection against myocardial ischemia/reperfusion injury in TLR4-deficient mice is mediated through a phosphoinositide 3-kinase-dependent mechanism

TLRs play a critical role in the induction of innate and adaptive immunity. However, TLRs have also been reported to mediate the pathophysiology of organ damage following ischemia/reperfusion (I/R) injury. We have reported that TLR4(-/-) mice show decreased myocardial injury following I/R; however, the protective mechanisms have not been elucidated. We examined the role of the PI3K/Akt signaling pathway in TLR4(-/-) cardioprotection following I/R injury. TLR4(-/-) and age-matched wild-type (WT) mice were subjected to myocardial ischemia for 45 min, followed by reperfusion for 4 h. Pharmacologic inhibitors of PI3K (wortmannin or LY294002) were administered 1 h before myocardial I/R. Myocardial infarct size/area at risk was reduced by 51.2% in TLR4(-/-) vs WT mice. Cardiac myocyte apoptosis was also increased in WT vs TLR4(-/-) mice following I/R. Pharmacologic blockade of PI3K abrogated myocardial protection in TLR4(-/-) mice following I/R. Specifically, heart infarct size/area at risk was increased by 98% in wortmannin and 101% in LY294002-treated TLR4(-/-) mice, when compared with control TLR4(-/-) mice. These data indicate that protection against myocardial I/R injury in TLR4(-/-) mice is mediated through a PI3K/Akt-dependent mechanism. The mechanisms by which PI3K/Akt are increased in the TLR4(-/-) myocardium may involve increased phosphorylation/inactivation of myocardial phosphatase and tensin homolog deleted on chromosome 10 as well as increased phosphorylation/inactivation of myocardial glycogen synthase kinase-3beta. These data implicate innate immune signaling pathways in the pathology of acute myocardial I/R injury. These data also suggest that modulation of TLR4/PI3K/Akt-dependent signaling pathways may be a viable strategy for reducing myocardial I/R injury.

Factors involved in the down-regulation of cytochrome P450 during Listeria monocytogenes infection

The activation of host defense mechanisms has been shown to cause a depression in hepatic cytochrome P450-mediated metabolism in rodents and humans. In a previous study, it was demonstrated that the Gram-positive bacteria Listeria monocytogenes causes a down-regulation of hepatic cytochrome P450 and related substrate metabolism as a result of a pretranslational depression of apoprotein synthesis. The objectives of this study were to determine whether the effect of listeria on hepatocyte cytochrome P450 involves hepatic nonparenchymal cells and whether the hemolysin, secreted only by hemolytic forms of the bacteria, plays any part in mediating this effect. Total cytochrome P450 levels as well as ethoxyresorufin-O-dealkylase (EROD) and benzyloxyresorufin-O-dealkylase (BROD) activities were significantly reduced in hepatic microsomes isolated from mice infected in vivo for 48 h with 15U listeria, whereas the same dose of the avirulent non-hemolytic M3D strain had no effect. Listeria (15U) significantly depressed hepatocyte EROD and BROD activities after 24 h incubations with liver cell cultures containing hepatocytes and nonparenchymal cells, as the result of both a direct effect on the hepatocyte and an interaction of listeria with hepatic nonparenchymal cells. The M3D strain of listeria had no effect on cytochrome P-450-mediated metabolism in isolated cells, confirming that hemolysin is an essential component of the mechanism responsible for the down-regulation of cytochrome P450 during listeria infections.

Hepatic microsomal protein and cytochrome P-450 in BALB/c mice infected with Leishmania

The effects of infection of mice with Leishmania major on liver microsomal protein and cytochrome P-450 were examined. The levels of hepatic microsomal protein and cytochrome P-450 were monitored at 6, 7, 9 and 12 weeks post-infection. The results indicated that the amount of hepatic microsomal protein and cytochrome P-450 were unchanged throughout the course of infection with L. major, despite the high degree of parasite proliferation in Kupffer cells and marked reduction in phagocytosis. The current results clearly indicate that Leishmania-induced macrophage suppression has no inhibitory effect on hepatic microsomal protein and cytochrome P-450.

Influence of impairment of the immune system on hepatic biotransformation reactions, their postnatal development and inducibility

Neither destruction of thymus by N-methylnitrosourea or by X-rays nor thymectomy or splenectomy in rats of different ages affected hexobarbital sleeping time, ethylmorphine N-demethylation or ethoxycoumarin O-deethylation significantly and systematically. Thymectomy or thymus destruction by x-rays of newborn rats did not significantly influence postnatal development or inducibility by phenobarbital of the monooxygenase reactions.