Involvement of multidrug resistance protein 4 in the hepatocyte efflux of lamivudine and entecavir.

Multidrug resistance protein 4 (MRP4) is capable of transporting acyclic nucleotide phosphonates, but little is known about its role in lamivudine (LAM) and entecavir (ETV) transport. In the present study, the involvement of MRP4 in the transport of LAM and ETV was investigated through in vitro experiments. The cytotoxicity of three antiviral drugs and their activities against HBV as characterized in HepG2.4D14 [wild­type hepatitis B virus (HBV)] and HepG2.A64 (ETV­resistant HBV) cells. LAM, ETV and tenofovir (TFV) demonstrated a 50% effective concentration against HBV of 4.14±0.03, 0.13±0.02 and 3.24±0.01 µM in HepG2.4D14 cells and of 5.94±0.20, 6.28±0.07 and 11.43±0.09 µM in HepG2.A64 cells, respectively. After administering 3-([(3-(2-[7-chloro-2-quinolinyl]ethyl)phenyl]-[(3-dimethylamino-3-oxoporphyl)-thio)-methyl]-thio) propanoic acid (MK571), the intracellular concentrations of all three drugs were much lower than the extracellular drug concentrations in these two cell types, whereas the intracellular drug concentrations in wild­type cells were higher than those in ETV­resistant cells. Furthermore, the intracellular levels of LAM, ETV and TFV were enhanced and the extracellular concentrations were reduced by addition of MK571. Thus, MRP4 is mainly responsible for the efflux of LAM and ETV in hepatocyte cultures. These results may contribute to enhancing antiviral efficacy.

Simple and rapid mercury ion selective electrode based on 1-undecanethiol assembled Au substrate and its recognition mechanism.

A simple and rapid mercury ion selective electrode based on 1-undecanethiol (1-UDT) assembled Au substrate (Au/1-UDT) has been well constructed. 1-UDT was for the purpose of generating self-assembled monolayer on gold surface to recognize Hg2+ in aqueous solution, which had a working concentration range of 1.0×10-8-1.0×10-4molL-1, with a Nernst response slope of 28.83±0.4mV/-pC, a detection limit of 4.5×10-9molL-1, and a good selectivity over the other tested cations. Also, the Au/1-UDT possessed good reproducibility, stability, and short response time. The recovery obtained for the determination of mercury ion in practical tremella samples was in the range of 99.8-103.4%. Combined electrochemical analysis and X-ray photoelectron spectroscopy (XPS) with quantum chemical computation, the probable recognition mechanism of the electrode for selective recognition of Hg2+ has been investigated. The covalent bond formed between mercury and sulfur is stronger than the one between gold and sulfur and thus prevents the adsorption of 1-UDT molecules on the gold surface. The quantum chemical computation with density functional theory further demonstrates that the strong interaction between the mercury atom and the sulfur atom on the gold surface leads to the gold sulfur bond ruptured and the gold mercury metallophilic interaction.

An outbreak of adult measles by nosocomial transmission in a high vaccination coverage community.

OBJECTIVES: The aims of this study were to determine the mechanism of an outbreak of measles in adults and to provide scientific measures for putting forward a measles elimination program. METHODS: We performed a cross-sectional investigation during the measles outbreak to identify a possible communication link. RESULTS: From November 1, 2011 to January 26, 2012, the town reported 11 cases of measles in total. The case study identified an obvious propagation chain, which showed ordered and intimate exposure between cases. CONCLUSIONS: Hospital exposure 1-2 weeks before infection with measles was the main cause of the measles outbreak. We must be fully aware of the possibility of nosocomial infection in an outbreak of measles; controlling nosocomial infections is a vital step in the prevention and control of the propagation of measles.

Cytotoxicity of 5-Aza-2'-deoxycytidine against gastric cancer involves DNA damage in an ATM-P53 dependent signaling pathway and demethylation of P16(INK4A).

The DNA methylation inhibitor 5-Aza-2'-deoxycytidine (5-Aza-CdR) has increasingly attracted worldwide attention for its antineoplastic potential. The cytotoxitic mechanisms, however, especially, the relative contribution of silenced genes reactivation by demethylation and enzyme-DNA adduct formation to the efficacy of 5-Aza-CdR is still a crucial unresolved question. In this investigation, we demonstrated that 5-Aza-CdR treatment resulted in growth suppression in a concentration and time-dependent manner and G2 phrase arrest - hallmarks of a DNA damage response in gastric cancer AGS cells. Formation of DNA double-strand breaks, as monitored by comet assay was examined in an ATM (ataxia-telangiectasia mutated)-dependent manner based on the fact that PI3K inhibitor Wortmannin abolished the action of cytotoxicity of 5-Aza-CdR. Upon treatment with 5-Aza-CdR, ATM activation was clearly associated with P53 phosphorylation at Ser(15), which was directly responsible for 5-Aza-CdR modified P21(Waf1/Cip1) expression. Further exploration revealed that demethylation of P16(INK4A) correlated with the strikingly down-regulated expressions of DNA methyltransferase 3A as well as 3B was, at least in part, attributed to the cytotoxicity of 5-Aza-CdR in AGS cells. Conclusively, these results greatly enhance our understanding of the mechanisms of cytotoxicity of 5-Aza-CdR and strongly provide the preclinical rationale for an assessment of 5-Aza-CdR to ameliorate patient outcome with gastric cancer.

5-Aza-2'-deoxycytidine induces cytotoxicity in BGC-823 cells via DNA methyltransferase 1 and 3a independent of p53 status.

The DNA methylation inhibitor 5-aza-2'-deoxycytidine (5-Aza-CdR) has therapeutic value for the treatment of cancer. However, the mechanism by which 5-Aza-CdR induces antineoplastic activity is not clear. The efficacy of 5-Aza-CdR on the contribution of gene reactivation by demethylation and enzyme-DNA adduct formation is an important unresolved question. The aim of this study was to explore the mechanism of the effect of 5-Aza-CdR on human gastric cancer growth. Human BGC-823 cells were treated with different concentrations of 5-Aza-CdR for different durations. Cell viability, DNA damage and gene expression were determined. The results showed that 5-Aza-CdR at low concentrations induced inhibition of gastric cancer BGC-823 cell proliferation as well as increased apoptosis caused by DNA damage. For the first time, we demonstrated that 5-Aza-CdR-induced cytotoxicity against BGC-823 cells was predominantly regulated via upregulation of DNA methyltransferase 1, 3a and partially via reactivation of RUNX3, which was independent of p53 status and its ability to activate p21Waf1/Cip1 expression. To our knowledge, this is the first demonstration of p53-independent 5-Aza-CdR action on DNA methyltransferases and demethylation. These results strongly provide the preclinical rationale for the clinical evaluation of 5-Aza-CdR to improve patient outcome in gastric cancer.