In vitro replication models for the hepatitis C virus

Soon after the discovery of the hepatitis C virus (HCV), attention turned to the development of models whereby replication of the virus could be investigated. Among the HCV replication models developed, the HCV RNA replicon model and the newly discovered infectious cell culture systems have had an immediate impact on the study of HCV replication, and will continue to lead to important advances in our understanding of HCV replication. The aim of this study is to deal with developments in HCV replication models in a chronological order from the early 1990s to the recent infectious HCV cell culture systems.

Discharge−Flow Kinetics Measurements Using Intracavity Laser Absorption Spectroscopy

Intracavity laser absorption spectroscopy ("ICLAS") has been demonstrated as a feasible detection method for trace species in a discharge flow tube. This implementation has been used to measure the rate of the reaction between atomic hydrogen and NO to form HNO in helium carrier gas. A reaction rate constant of (4.3 +/- 0.4) x 10(-32) cm(6) molecule(-2) s(-1) at 295 K was measured for the reaction H + NO + M --> HNO + M (M = He). The pressure and concentration range enabled by ICLAS detection has allowed us to limit reactive pathways that would inhibit the formation of HNO. The sensitivity of ICLAS, coupled with the versatility of the discharge flow technique, suggests that intracavity absorption spectroscopy will be a useful technique for kinetics measurements on free radicals and other reactive species.

A strategy for obtaining near full-length HCV cDNA clones (assemblicons) by assembly PCR

Hepatitis C virus (HCV) genotype is a predictor of response, and guides the duration of antiviral therapy. However, with the exception of HCV genotype 1a, 1b and 2a, a limited number of clones from other genotypes exist. Here we report the optimization of long RT-PCR to generate three overlapping amplicons that span the near full length HCV genome from a panel of HCV genotypes (1a, 1b, 2a, 2b, 3a, 4a, 5a). Assembly-PCR (As-PCR) was used to construct near full-length cDNA clones (assemblicons) for each genotype. The optimization of the long RT-PCR on genotype 1a and 1b indicated that QIAamp Viral RNA kit (Qiagen, UK), Expand RT and Expand Long Template PCR system (Roche, UK), were the most efficient in producing the requisite three overlapping amplicons and assemblicons for each genotype. The genotype of each assemblicon was confirmed. Assemblicon generation was only possible when the overlapping amplicons were biotinylated. As-PCR obviated the need for time consuming ligations and cloning. The use of three overlapping amplicons in the construction of HCV assemblicons minimised the chimeric nature of the resultant clone. As-PCR may prove a methodological avenue through which a larger panel of consensus HCV clones could be made available for HCV in vitro investigation.

The role of radiotracer imaging in Parkinson disease

Radiotracer imaging (RTI) of the nigrostriatal dopaminergic system is a widely used but controversial biomarker in Parkinson disease (PD). Here the authors review the concepts of biomarker development and the evidence to support the use of four radiotracers as biomarkers in PD: [18F]fluorodopa PET, (+)-[11C]dihydrotetrabenazine PET, [123I]beta-CIT SPECT, and [18F]fluorodeoxyglucose PET. Biomarkers used to study disease biology and facilitate drug discovery and early human trials rely on evidence that they are measuring relevant biologic processes. The four tracers fulfill this criterion, although they do not measure the number or density of dopaminergic neurons. Biomarkers used as diagnostic tests, prognostic tools, or surrogate endpoints must not only have biologic relevance but also a strong linkage to the clinical outcome of interest. No radiotracers fulfill these criteria, and current evidence does not support the use of imaging as a diagnostic tool in clinical practice or as a surrogate endpoint in clinical trials. Mechanistic information added by RTI to clinical trials may be difficult to interpret because of uncertainty about the interaction between the interventions and the tracer.

Do Taq-generated RT-PCR products from RNA viruses accurately reflect viral genetic heterogeneity?

Since the first report of genetically heterogeneous, or quasispecies, populations of RNA viruses, the genetic heterogeneity of the RNA genomes of major viral pathogens has been extensively studied. These studies aim to provide insights into the evolutionary pressures that act upon viruses, in order to define windows where anti-viral therapies will be most effective, to take prognostic values from viral genetic distributions at a given time, and to aid the development of novel therapeutic compounds that may tilt viral replication towards information loss. Many methodologies are employed to analyse genetic distributions of a virus in a given sample, but all involve the generation, and subsequent analysis, of the sequence information contained in a reverse-transcription-polymerase chain reaction (RT-PCR) product. Despite the fact that the aim of these RT-PCRs is to obtain sequence information from viral genomes, their application to this task is approached without adequate consideration of this end-goal. The establishment of an RT-PCR for a specific viral target genome generally proceeds in the same fashion as one would apply to establishing a PCR to determine the presence or absence of a specific target sequence in a given sample. However, it is becoming increasingly apparent that RT-PCR products generated by amplification with the ubiquitous thermostable DNA polymerase Taq, coupled with standard cloning and sequencing methodologies, has the potential to yield inaccurate and misleading data as pertains to the information content of populations of RNA viral genomes. This review discusses varying approaches employed to analyse heterogeneous populations of hepatitis C virus RNA genomes.

An electromyographic study of vastus medialis oblique and vastus lateralis activity while ascending and descending steps

Imbalances in the firing pattern and contraction intensity of the vastus medialis oblique (VMO) and the vastus lateralis (VL) have been considered important factors contributing to patellofemoral joint dysfunction. Vastus medialis oblique and vastus lateralis electromyographic (EMG) activity were measured for 15 individuals without patellofemoral pain (asymptomatic group) and 13 subjects with patellofemoral pain (symptomatic group) while ascending and descending steps. The peak VMO/VL ratios of EMG activity and the difference in peak VMO and VL onset times were measured. Two-way mixed-model analyses of variance (ANOVA) were used to determine the main effects of group (asymptomatic and symptomatic), phase (concentric phase ascending and two eccentric phases descending stairs), and the interaction between group and phase. The ANOVAs indicated no difference between groups for the peak VMO/VL EMG ratio or for the onset timing between peak VMO and VL muscle activity. Combining groups, the peak VMO/VL EMG ratio was less for the eccentric weight acceptance phase of descent compared with the concentric phase of ascent. These findings suggest no differences between asymptomatic and symptomatic individuals, but differences may exist between concentric and eccentric VMO/VL ratios. Further research is needed to determine if VMO and VL muscle imbalances contribute to patellofemoral dysfunction.

Phase II clinical trial with high-dose methotrexate therapy and citrovorum factor rescue

One hundred and thirty-four patients with advanced malignant disease were treated with 496 infusions of high-dose methotrexate (HD-MTX) followed by citrovorum factor rescue. Most patients had failed to respond to previous combination chemotherapy. The overall response rate was 29% with 33 partial responses and six complete responses observed in patients with a variety of tumors. Plasma MTX levels were monitored in all patients during each course of therapy in order to identify those patients with delayed plasma MTX clearance. Patients with abnormally slow rates of plasma MTX decay received escalated doses of citrovorum factor rescue in order to prevent drug-induced toxicity. In general, during this study HD-MTX was well-tolerated. Because serious toxicity was neither frequent, severe, nor unpredictable, its use was not limited. HD-MTX should now be evaluated in well-designed controlled clinical trials to compare its antitumor activity to that of conventional- or standard-dose MTX regimens in diseases where HD therapy appears to have efficacy.