Overexpression of Resistance-Nodulation-Division Efflux Pump Genes Contributes to Multidrug Resistance in Aeromonas hydrophila Clinical Isolates.

Aeromonas hydrophila is a Gram-negative bacterium that is a critical causative agent of infections in fish and is occasionally responsible for human infections following contact with contaminated water or food. Currently, the extensive use of antibiotics in clinical practice has led to increased number of isolates of multidrug-resistant (MDR) Aeromonas and has posed a serious public health challenge. The efflux pump system is a critical mechanism of antibiotic resistance in most Gram-negative bacteria. However, the role of resistance-nodulation-division (RND)-type efflux pumps in MDR A. hydrophila is not fully understood. We aimed to evaluate the contribution of the RND efflux pump system to MDR A. hydrophila clinical isolates. PCR results indicated a considerable variation in the presence of RND efflux pump genes in clinical isolates compared to that of the environmental reference strain ATCC7966T. Compared to non-MDR clinical isolates, the expression levels of three putative RND efflux pump genes, AHA0021, AHA1320, and AheB, were significantly elevated in MDR strains. The minimal inhibitory concentrations of piperacillin/tazobactam, imipenem, erythromycin, and polymyxin B were significantly reduced by phenylalanine-arginine ß-naphthylamide (PAßN), further supporting the contribution of the RND efflux system in MDR A. hydrophila. We provided evidence supporting the contribution of the RND efflux system to multidrug resistance in A. hydrophila clinical isolates. Further studies are warranted to elucidate the detailed mechanisms that confer intrinsic resistance to antimicrobials in A. hydrophila.

Synergistic Actions of Benzyl Isothiocyanate with Ethylenediaminetetraacetic Acid and Efflux Pump Inhibitor Phenylalanine-Arginine ß-Naphthylamide Against Multidrug-Resistant Escherichia coli.

The aim of this study was to assess the efficacy of benzyl isothiocyanate (BITC) in combination with efflux inhibitors and metal chelators against multidrug-resistant Escherichia coli. In vitro synergism between testing molecules was observed based on the minimal inhibitory concentration (MIC), minimal bactericidal concentration (MBC), fractional inhibitory concentration index (FICI), bactericidal kinetics, and growth inhibition assay. BITC alone exhibited moderate antibacterial activity against E. coli strains with MIC and MBC values of 0.625-1.25 µM and 1.25-2.5 µM, respectively. In contrast, double and triple combinations of BITC, ethylenediaminetetraacetic acid (EDTA), and phenylalanine-arginine ß-naphthylamide (PAßN) resulted in synergistic activities with FICI values between 0.18 and 0.5, whereas combination of BITC with carbonyl cyanide m-chlorophenyl hydrazone or 2, 2'-dipyridyl revealed additive or indifference effect with FICI values of 0.75-1.5 and 1-1.5, respectively. Results of bactericidal kinetics and growth inhibition assays also supported the synergistic effects of EDTA and PAßN with BITC against E. coli strains. Our data demonstrate the possible use of adjuvant agents, such as the chelating agent EDTA and the efflux inhibitor PAßN to improve the antibacterial potential of isothiocyanate and may help to develop an alternative strategy for reducing the occurrence of multidrug resistance.

Epigallocatechin-3-gallate downregulates PDHA1 interfering the metabolic pathways in human herpesvirus 8 harboring primary effusion lymphoma cells.

Primary effusion lymphoma (PEL) is an aggressive neoplasm correlated with human herpesvirus 8 (HHV8). Metabolic reprogramming is a hallmark of cancers. The alterations in cellular metabolism are important to the survival of HHV8 latently infected cells. Pyruvate dehydrogenase (PDH) controls the flux of metabolites between glycolysis and the tricarboxylic acid cycle (TCA cycle) and is a key enzyme in cancer metabolic reprogramming. Glutaminolysis is required for the survival of PEL cells. Glutamate dehydrogenase 1 (GDH1) converts glutamate into α-ketoglutarate supplying the TCA cycle with intermediates to support anaplerosis. Previously we have observed that epigallocatechin-3-gallate (EGCG) can induce PEL cell death and N-acetyl cysteine (NAC) attenuates EGCG induced PEL cell death. In this study, results showed that EGCG upregulated the expression of glucose transporter GLUT3, and reduced the expression of pyruvate dehydrogenase E1-alpha (PDHA1), the major regulator of PDH, and GDH1. NAC could partially reverse the effects of EGCG in PEL cells. Overexpression of PDHA1 in PEL cells or supplement of α-ketoglutarate attenuated EGCG induced cell death. EGCG also reduced the levels of oncometabolite D-2-hydroxyglutarate (D2HG). These results suggest that EGCG may modulate the metabolism of PEL cells leading to cell death.

Epigallocatechin-3-Gallate Suppresses Human Herpesvirus 8 Replication and Induces ROS Leading to Apoptosis and Autophagy in Primary Effusion Lymphoma Cells.

Epigallocatechin-3-gallate (EGCG), the major constituent of green tea, has been shown to induce cell death in cancer cells. Primary effusion lymphoma (PEL) is an aggressive neoplasm caused by human herpesvirus 8 (HHV8). In this study, we examined the role of EGCG on PEL cells in cell death and HHV8 replication. We performed trypan blue exclusion assay to assess the cell viability of PEL cells, flow cytometry analysis to examine the cell cycle distribution and reactive oxygen species (ROS) generation, caspase-3 activity to assay apoptosis, acridine orange staining to determine autophagy, and immunoblotting to detect the protein levels involved in apoptosis and autophagy as well as mitogen activated protein kinases (MAPKs) activation upon EGCG treatment. The expression of the HHV8 lytic gene was determined by luciferase reporter assay and reverse transcription-PCR, and viral progeny production was determined by PCR. Results revealed that EGCG induced cell death and ROS generation in PEL cells in a dose-dependent manner. N-acetylcysteine (NAC) inhibited the EGCG-induced ROS and rescued the cell from EGCG-induced cell death. Even though EGCG induced ROS generation in PEL cells, it reduced the production of progeny virus from PEL cells without causing HHV8 reactivation. These results suggest that EGCG may represent a novel strategy for the treatment of HHV8 infection and HHV8-associated lymphomas.

Resveratrol induces cell death and inhibits human herpesvirus 8 replication in primary effusion lymphoma cells.

Resveratrol (3,4',5-trihydroxy-trans-stilbene) has been reported to inhibit proliferation of various cancer cells. However, the effects of resveratrol on the human herpesvirus 8 (HHV8) harboring primary effusion lymphoma (PEL) cells remains unclear. The anti-proliferation effects and possible mechanisms of resveratrol in the HHV8 harboring PEL cells were examined in this study. Results showed that resveratrol induced caspase-3 activation and the formation of acidic vacuoles in the HHV8 harboring PEL cells, indicating resveratrol treatment could cause apoptosis and autophagy in PEL cells. In addition, resveratrol treatment increased ROS generation but did not lead to HHV8 reactivation. ROS scavenger (N-acetyl cysteine, NAC) could attenuate both the resveratrol induced caspase-3 activity and the formation of acidic vacuoles, but failed to attenuate resveratrol induced PEL cell death. Caspase inhibitor, autophagy inhibitors and necroptosis inhibitor could not block resveratrol induced PEL cell death. Moreover, resveratrol disrupted HHV8 latent infection, inhibited HHV8 lytic gene expression and decreased virus progeny production. Overexpression of HHV8-encoded viral FLICE inhibitory protein (vFLIP) could partially block resveratrol induced cell death in PEL cells. These data suggest that resveratrol-induced cell death in PEL cells may be mediated by disruption of HHV8 replication. Resveratrol may be a potential anti-HHV8 drug and an effective treatment for HHV8-related tumors.

Vibrio vulnificus RtxA1 modulated calcium flux contributes reduced internalization in phagocytes.

AIMS: Vibrio vulnificusis an opportunistic pathogen that causes primary septicemia and wound infection with high mortality rate. This pathogen produces an RTX toxin (RtxA1) which can cause host cell rounding, cell death and interference with internalization by host phagocytes. However, the mechanism of RtxA1-induced phagocyte paralysis is not clear. MAIN METHODS: Using the murine macrophage cell line RAW264.7, we measured cytotoxicity and phagocytosis of V. vulnificusin normal and calcium-depleted media. To deplete extracellular and cytosolic Ca(2+), cells were exposed to the calcium chelators ethylene glycol tetraacetic acid (EGTA) and 1,2-bis-(o-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid, tetraacetoxymethyl esteris (BAPTA-AM), respectively. The cytotoxicity was examined by measuring the activity of lactate dehydrogenase (LDH) released from the damaged cells. The gentamicin protection assay was conducted to determine the number of internalized bacteria, while acridine orange staining was applied to visualize the intracellular bacteria. The fluorescent indicator fura-2-acetoxymethyl ester (fura 2-AM) was used to measure the Ca(2+)signal post-infection. KEY FINDINGS: We revealed that extracellular Ca(2+)was essential for phagocytes to internalize V. vulnificus. Meanwhile, cytosolic Ca(2+)flux in RAW264.7 cells induced by an RtxA1 isogenic mutant was repressed by the parent strain. Furthermore, depletion of extracellular Ca(2+)level by EGTA significantly reduced the cytotoxicity but did not affect the antiphagocytic activity of RtxA1 toxin. SIGNIFICANCE: Our results indicated that RtxA1 may interfere with cytosolic Ca(2+)flux of phagocyte to promote bacteria colonization.

Cisplatin disrupts the latency of human herpesvirus 8 and induces apoptosis in primary effusion lymphoma cells.

Human herpesvirus 8 (HHV8) is the etiologic agent for primary effusion lymphoma (PEL). The aim of this study is to investigate the effects of cisplatin on the PEL cells. Cisplatin treatment induced apoptosis and inhibited the growth of PEL cells, and the effect was more profound in the HHV8-positive lymphoma cells compared with the EBV-positive lymphoma cells. Cisplatin treatment decreased the expression of HHV8 latent genes and activated p53 at serine 15 in PEL cells. Our results indicate that cisplatin can disrupt HHV8 latency and induce reactivation of p53 and highly selective treatment modality for this virally induced lymphoma.

Nickel (II)-induced cytotoxicity and apoptosis in human proximal tubule cells through a ROS- and mitochondria-mediated pathway.

Nickel compounds are known to be toxic and carcinogenic in kidney and lung. In this present study, we investigated the roles of reactive oxygen species (ROS) and mitochondria in nickel (II) acetate-induced cytotoxicity and apoptosis in the HK-2 human renal cell line. The results showed that the cytotoxic effects of nickel (II) involved significant cell death and DNA damage. Nickel (II) increased the generation of ROS and induced a noticeable reduction of mitochondrial membrane potential (MMP). Analysis of the sub-G1 phase showed a significant increase in apoptosis in HK-2 cells after nickel (II) treatment. Pretreatment with N-acetylcysteine (NAC) not only inhibited nickel (II)-induced cell death and DNA damage, but also significantly prevented nickel (II)-induced loss of MMP and apoptosis. Cell apoptosis triggered by nickel (II) was characterized by the reduced protein expression of Bcl-2 and Bcl-xL and the induced the protein expression of Bad, Bcl-Xs, Bax, cytochrome c and caspases 9, 3 and 6. The regulation of the expression of Bcl-2-family proteins, the release of cytochrome c and the activation of caspases 9, 3 and 6 were inhibited in the presence of NAC. These results suggest that nickel (II) induces cytotoxicity and apoptosis in HK-2 cells via ROS generation and that the mitochondria-mediated apoptotic signaling pathway may be involved in the positive regulation of nickel (II)-induced renal cytotoxicity.

The dengue virus envelope protein induced PAI-1 gene expression via MEK/ERK pathways.

Dengue virus (DV) infections cause mild dengue fever or severe life-threatening dengue haemorrhagic fever (DHF)/ dengue shock syndrome (DSS). DV-infected patients have high plasma concentrations of plasminogen activator inhibitor type I (PAI-1). However, the mechanism to cause haemorrhage in DV infections remains poorly understood. In this study, investigation was carried out on the purified recombinant domain III of the envelope glycoprotein of DV serotypes 2 (EIII) and the signalling pathways of EIII leading to PAI-1 gene expression were measured by RT-PCR, Western blot, and immunofluorescence stain. Reporter gene constructs containing serially 5'-deleted sequences of the proximal human PAI-1 promoter region were constructed and then transfected to Huh7 cells, a human hepatoma cell line, prior to EIII treatment. EIII increased the PAI-1 mRNA and protein levels in a dose-dependent manner in Huh7 cells. Results showed that U0126, an inhibitor of extracellular signal-regulated kinase (ERK) kinase (MEK), almost completely suppressed EIII-induced PAI-1 expression. The results suggest that the MEK/ERK signalling pathways mediate the EIII-dependent induction of PAI-1 gene expression via the proximal promoter region.

Human herpesvirus 8 viral FLICE-inhibitory protein retards cell proliferation via downregulation of Id2 and Id3 expression.

Death receptor-mediated apoptosis is potently inhibited by viral FLIP (FLICE/caspase 8 inhibitory protein) through reduced activation of procaspase 8. In this study, we show that the human herpesvirus 8-encoded vFLIP retards cell proliferation. Overexpression of vFLIP caused cell cycle arrest, with an apparent decrease of cells in the S phase. The Id (inhibitor of DNA binding) proteins are considered as dominant negative regulators of differentiation pathways, but positive regulators of cellular proliferation. The mechanisms by which Id proteins promote the cell cycle are diverse, but appear to involve affecting the expression of cell cycle regulators. RT-PCR results demonstrated that the expression of vFLIP decreased the expression levels of Id2 and Id3 as well as cyclin E and cyclin A compared with the vFLIP-null cells. These indicate that vFLIP affects cell proliferation by decreasing the expression levels of cell cycle regulatory proteins.

The envelope glycoprotein domain III of Dengue virus type 2 induced the expression of anticoagulant molecules in endothelial cells.

Dengue virus (DV) causes a non-specific febrile illness known as Dengue fever (DF), and a severe life-threatening illness, Dengue hemorrhagic fever/Dengue shock syndrome (DHF/DSS). Hemostatic changes induced by this virus involve three main factors: thrombocytopenia, endothelial cell damage, and significant abnormalities of the coagulation and fibrinolysis systems. The pathogenesis of bleeding in DV infections remains unknown. In this article, we focused on the DV activating endothelial cells and altering the parameters of hemostasis system. The expression of hemostasis-related factors, Thrombomodulin, TF, TFPI, t-PA, and PAI-1, in DV-infected cells were determined by RT-PCR. Flow cytometry analysis and immunofluorescence staining confirmed that the expression levels of TM in the DV-infected HMEC-1 and THP-1 cells were increased. In addition, the purified recombinant domain III of the envelope glycoprotein of DV (EIII) could induce the expression of TM in the HMEC-1 cells and THP-1 cells. The TM expression induced by DV or EIII in the endothelial cells and monocytic cells suggests that the EIII of DV plays an important role in the pathogenesis of DHF/DSS.

Nickel(II)-induced oxidative stress, apoptosis, G2/M arrest, and genotoxicity in normal rat kidney cells.

In order to elucidate the effects of nickel (Ni) on oxidative stress, apoptosis, and genotoxicity in renal cells, the levels of intracellular oxidants, lipid peroxidation, apoptotic proteins, and DNA damage were measured in normal rat kidney (NRK) cells after nickel chloride (NiCl(2)) treatment. NiCl(2) appeared to increase the formation of the fluorescent oxidized compound (dichlorofluorescein, DCF) and levels of thiobarbituric acid-reactive substances (TBARS). In flow cytometric analysis, a rise in cell proportion in sub-G1 phase occurred in a concentration-dependent manner. After Ni treatment, there was reduced expression of Bcl-2 and Bcl-xL proteins, while induced Bad and Bax proteins expression was higher. Single-strand DNA breakage induced by Ni in NRK cells was determined by comet assay. Significant increase DNA damage score (arbitrary units) was noted in a concentration-related manner after treatment with Ni. Induction of intracellular oxidants by Ni was accompanied by an increasing frequency of DNA strand breakage. Our data indicate that Ni-induced oxidative stress and genotoxicity in NRK cells may involve reactive oxygen intermediates, and that Bcl family-mediated signaling pathway may be involved in positive regulation of Ni-induced renal cytotoxicity.

Staurosporine-induced G2/M arrest in primary effusion lymphoma BCBL-1 cells.

Staurosporine, an inhibitor of protein kinase C, is a potential antitumor drug and its derivatives are used as anticancer drugs in clinical trials. Human herpesvirus 8 (HHV-8) is implicated in all forms of Kaposi's sarcoma (KS), primary effusion lymphoma (PEL), and multicentric Castleman's disease (MCD), indicating it to be a DNA tumor virus. It is difficult to culture cell lines derived from KS patients; we therefore used a cell line derived from PEL (BCBL-1) to investigate whether staurosporine affects the HHV-8-related tumors. Our results show that staurosporine treatment reduces the cell viability of BCBL-1 cells and causes cell cycle arrest in the G2/M phase. The G2/M arrest was associated with the decrease in the expression of Cdc2 and cyclin B. Furthermore, the induction of the HHV-8 lytic cycle was not observed under the staurosporine treatment.