Background and purpose:
Assessing the proarrhythmic potential of compounds during drug development is essential. However, reliable prediction of drug‐induced torsades de pointes arrhythmia (TdP) ...remains elusive. Along with QT interval prolongation, assessment of the short‐term variability of the QT interval (STV(QT)) may be a good predictor of TdP. We investigated the relative importance of IKs and IKr block in development of TdP together with correlations between QTc interval, QT interval variability and incidence of TdP.
Experimental approach:
ECGs were recorded from conscious dogs and from anaesthetized rabbits given the IKr blocker dofetilide (DOF), the IKs blocker HMR‐1556 (HMR) and their combination, intravenously. PQ, RR and QT intervals were measured and QTc and short‐term variability of RR and QT intervals calculated.
Key results:
DOF increased QTc interval by 20% in dogs and 8% in rabbits. HMR increased QTc in dogs by 12 and 1.9% in rabbits. Combination of DOF+HMR prolonged QTc by 33% in dogs, by 16% in rabbits. DOF or HMR given alone in dogs or HMR given alone in rabbits induced no TdP. Incidence of TdP increased after DOF+HMR combinations in dogs (63%) and following HMR+DOF (82%) and DOF+HMR combinations (71%) in rabbits. STV(QT) markedly increased only after administration of DOF+HMR combinations in both dogs and rabbits.
Conclusion and implications:
STV(QT) was markedly increased by combined pharmacological block of IKr and IKs and may be a better predictor of subsequent TdP development than the measurement of QTc interval prolongation.
British Journal of Pharmacology (2007) 151, 941–951; doi:10.1038/sj.bjp.0707297
Measles virus (MV) infection in brain tissue of a patient with measles inclusion body encephalitis was characterized by immunologic and biochemical techniques. Of the five major structural proteins ...of MV, only nucleocapsid (N) protein and phosphoprotein (P protein) were consistently detected in diseased brain areas. In contrast, hemagglutinin protein was seen only occasionally, and no membrane and fusion proteins were found in any of the sections studied. Messenger RNAs (mRNAs) specific for these five viral proteins were detected in all brain extracts examined; however, the mRNAs for the envelope proteins were clearly underrepresented in comparison with lytically infected cells. Only the mRNAs for N and P proteins appeared active in in vitro translations. These findings indicate quantitative differences in the pattern of mRNA expression in brain tissue and a restricted expression of MV envelope proteins in infected cells as observed in subacute sclerosing panencephalitis.
Persistent infection of the central nervous system (CNS) with measles virus (MV) is associated with characteristic restrictions of viral envelope gene expression as documented in subacute sclerosing ...panencephalitis (SSPE), measles inclusion body encephalitis (MIBE), or subacute measles encephalitis (SAME) in rats. To determine whether these restrictions are the result of a long lasting virus-host cell interaction or primarily based on intrinsic brain cell factors MV gene expression was analyzed in primary rat astroglial cultures. It could be shown that MV infection of these cells led to a defective replication cycle with a reduced synthesis of viral envelope proteins and a steep expression gradient of the monocistronic viral mRNAs similar to the findings in brain tissue of SSPE, MIBE, and SAME. This restriction of MV gene expression has not been observed in cells of nonneural origin. We suggest that this cell-type specific regulation of MV gene expression contributes to early events in the establishment of MV persistent infection in CNS tissue.
The nucleotide sequences of the large protein (L) gene derived from two wild-type measles viruses (MV) and two SSPE brain-derived viruses have been determined. All sequences have single large open ...reading frames encoding 2183 amino acid residues. The deduced L proteins are well conserved and the proposed functional domains which have been identified for rhabdo- and paramyxoviruses are completely conserved in all strains. The degree of variability of L proteins is the lowest of all structural proteins of MV, reflecting its role in virus reproduction and persistence. Biased hypermutation was not observed in the L genes derived from SSPE brain tissue. None of the nucleotide changes can be associated with the attenuated phenotype of the Edmonston vaccine viruses.
RNA was extracted from the diseased brain of a case of human subacute sclerosing panencephalitis (SSPE) and analysed for the expression of measles-specific RNA. Measles virus-specific mRNAs were ...present, but the amount of matrix (M) protein mRNA was greatly reduced in comparison to lytically infected cells and phospho- (P) protein mRNA was hardly detectable whereas the level of the corresponding intermediate-sized (is-) RNA was greatly increased. RNA obtained from the human brain was also translated in vitro and measles virus nucleocapsid and P protein was produced. However, in marked contrast to control reactions M protein was not detected in the products formed by translation in vitro. These results indicate an impaired measles virus M protein mRNA synthesis in infected brain tissue.
The elevation of culture temperatures from 35 degrees C to 39 degrees C led to the cessation of the synthesis of the fusion (F) protein of measles virus. This effect was caused by inhibition of the ...translation of the corresponding mRNA rather than by a decrease in the synthesis or stability of the mRNA or by increased degradation of the F protein at elevated temperatures. The haemagglutinin (H) and F mRNAs were distributed differently in gradients on which polysomes were fractionated. The H mRNA was present almost exclusively in the largest polysomes whereas the F mRNA was more evenly distributed over large and small polysomes. The distribution was not affected by a temperature shift. The inhibition of F protein synthesis thus appeared to be related to a cessation of elongation of the nascent polypeptide chain rather than to a defect in initiation of the translation of the F mRNA at 39 degrees C.
A purification procedure for genomic measles virus RNA, free of contaminating smaller RNA and of DNA, is described. Viral nucleocapsids were prepared from MA160 cells infected in spinner cultures ...with measles virus (Edmonston strain). Nucleic acid was extracted, treated with DNase and RNA sedimenting at about 50S in sucrose gradients was isolated. This method yielded 0.5 to 1.5 micrograms of genomic RNA per litre of culture. A molecular weight of 4.5 X 10(6) was determined by gel electrophoresis under fully denaturing conditions.
In KB cells productively infected with adenovirus type 2, alkali-stable >100S and 40-100S viral DNAs are synthesized starting 2-4 hr postinfection, i.e., before unit length (34 S) viral DNA is made. ...The amount of >100S and 40-100S viral DNA increases when 34S viral DNA synthesis begins, and at 16-18 hr postinfection, the 40-100S viral DNA represents 5-20% of the total intracellular viral DNA. The 40-100S viral DNA is synthesized throughout infection. Part of the 40-100S DNA synthesized 5-8 hr postinfection has a density in alkaline CsCl gradients intermediate between those of viral and cellular DNAs. This finding indicates that newly synthesized viral DNA is covalently linked to cellular DNA. Viral sequences can be excised from the cellular DNA of infected cells with the EcoRI restriction endonuclease. Fragments of viral DNA are detected in polyacrylamide-agarose gels by DNA· DNA hybridization, and these fragments correspond in size to most of the known EcoRI fragments of adenovirus 2 DNA. Viral DNA sequences in size-classes between the EcoRI-A and -C fragments are also found and probably represent viral DNA linked to cellular sequences.
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