Detection of a few DNA copies by real-time electrochemical polymerase chain reaction.

In the current work, accurate quantification over 10 to 108 DNA copies has been successfully achieved for the first time by real-time electrochemical PCR. This has been made possible thanks to the combined use of a fully automated house-built electrochemical qPCR device, optimized for parallel heating and electrochemical monitoring of up to 48 PCR solutions, and the appropriate selection of a DNA intercalating redox probe retaining a strong affinity binding to ds-DNA at the PCR measurement temperature of 72 °C (corresponding to the PCR elongation step). This has also been achieved through the identification of the key parameters governing the onset electrochemical signal decrease and amplitude signal decrease as a function of the PCR cycle for a given DNA intercalating redox probe, thus allowing us to predict the electrochemical PCR kinetic plots from the values of the DNA affinity binding constant determined as a function of temperature. To the best of our knowledge, the analytical performances of the current electrochemical qPCR outperform all of those previously published, in terms of detection limit, dynamic range, reproducibility and melting curve analysis compared to that achieved on a commercialized bench-top fluorescence-based qPCR instrument.

GREFON recommendations for assessment of instrumental activities of daily living in memory clinics.

Following a review of the available assessment scales and current practices of evaluation of instrumental activities of daily living (IADL) in French memory centres by GREFON (Groupe de réflexion sur l'évaluation fonctionnelle; Working Group on Functional Assessment), the main aim of this position paper was to provide good clinical practice (GCP) guidelines for the assessment of IADL. Another aim was to highlight the need for innovative tools adapted to the present and future evolution of such activities in real life, including the use of new technologies, the need for earlier detection of IADL impairment during the diagnostic process of mild neurocognitive disorders, and greater sensitivity to IADL changes during follow-up to allow adaptation of clinical management and evaluation of the impact of therapeutic interventions.

Rate constants in two dimensions of electron transfer between pyruvate oxidase, a membrane enzyme, and ubiquinone (coenzyme Q8), its water-insoluble electron carrier.

The functionality of the membrane-bound, ubiquinone-dependent pyruvate oxidase from the respiratory chain of Escherichia coli was reconstituted with a supported lipidic structure. The artificial structure was especially designed to allow the electrochemical control of the quinone pool through the lateral mobility of the ubiquinone (Q(8)) molecules. The kinetic coupling of the enzyme bound to the lipid structure with the quinone pool was ensured by the regeneration of the oxidized form of ubiquinone at the electrochemical interface. Such an experimental approach enabled us to carry out an unprecedented determination of the kinetic parameters controlling the reaction between the enzyme bound and the electron carrier under conditions taking rigorously into account the fact that the freedom of motion is restricted to two dimensions. The kinetic constants we found show that the activated enzyme can be efficiently regulated by the oxidation level of the quinone pool in natural membranes.

Electrochemical measurement of lateral diffusion coefficients of ubiquinones and plastoquinones of various isoprenoid chain lengths incorporated in model bilayers.

The long-range diffusion coefficients of isoprenoid quinones in a model of lipid bilayer were determined by a method avoiding fluorescent probe labeling of the molecules. The quinone electron carriers were incorporated in supported dimyristoylphosphatidylcholine layers at physiological molar fractions (<3 mol%). The elaborate bilayer template contained a built-in gold electrode at which the redox molecules solubilized in the bilayer were reduced or oxidized. The lateral diffusion coefficient of a natural quinone like UQ10 or PQ9 was 2.0 +/- 0.4 x 10(-8) cm2 s(-1) at 30 degrees C, two to three times smaller than the diffusion coefficient of a lipid analog in the same artificial bilayer. The lateral mobilities of the oxidized or reduced forms could be determined separately and were found to be identical in the 4-13 pH range. For a series of isoprenoid quinones, UQ2 or PQ2 to UQ10, the diffusion coefficient exhibited a marked dependence on the length of the isoprenoid chain. The data fit very well the quantitative behavior predicted by a continuum fluid model in which the isoprenoid chains are taken as rigid particles moving in the less viscous part of the bilayer and rubbing against the more viscous layers of lipid heads. The present study supports the concept of a homogeneous pool of quinone located in the less viscous region of the bilayer.

An electrochemical approach of the redox behavior of water insoluble ubiquinones or plastoquinones incorporated in supported phospholipid layers.

Physiological mole fractions of long isoprenic chain ubiquinone (UQ[10]) and plastoquinone (PQ9) were incorporated inside a supported bilayer by vesicle fusion. The template of the bilayer was an especially designed microporous electrode that allows the direct electrochemistry of water insoluble molecules in a water environment. The artificial structure, made by self-assembly procedures, consisted of a bilayer laterally in contact with a built-in gold electrode at which direct electron transfers between the redox heads of the quinones molecules and the electrode can proceed. The mass balances of quinone and lipid in the structure were determined by radiolabeling and spectrophotometry. A dimyristoyl phosphatdylcholine stable surface concentration of 250 +/- 50 pmol x cm(-2), unaffected by the presence of the quinone, was measured in the fluid monolayer. The mole fraction of quinone was between 1 and 3 mol%, remaining unchanged when going from the vesicles to the supported layers. The lipid molecules and the quinone pool were both laterally mobile, and cyclic voltammetry was used to investigate the redox properties of UQ10 and PQ9 over a wide pH range. Below pH 12, the two electrons-two protons electrochemical process at the gold electrode appeared under kinetic control. Thus all thermodynamic deductions must be anchored in the observed reversibility of the quinone/hydroquinol anion transformation at pH > 13. Within the experimental uncertainty, the standard potentials and the pK(a)'s of the pertinent redox forms of UQ10 and PQ9 were found to be essentially identical. This differs slightly from the literature in which the constants were deduced from the studies of model quinones in mixed solvents or of isoprenic quinones without a lipidic environment.

Radiation injuries of the gastrointestinal tract in Hodgkin's disease: the role of exploratory laparotomy and fractionation. A study of 19 cases observed in a series of 134 patients treated at the Institut Gustave Roussy from 1972 to 1982.

Out of 134 patients irradiated below the diaphragm to a dose of 40 Gy for Hodgkin's disease at the Institut Gustave-Roussy, 19 (14%) were subsequently found to present with radiation injuries of the gastrointestinal tract. Since five patients presented with two different injuries, 24 radiolesions were observed. Most of them (17 out of 24) were gastric or duodenal. Twelve (out of 24) were ulcers. Nine patients required surgery. A complete cure of the radiation injuries was obtained in 15 out of 19 patients. Sex, age, stage, histology or initial chemotherapy were not found to play a role in the occurrence of radiation damage. On the contrary, the role of a previous exploratory laparotomy appeared important; for the patients who underwent laparotomy and irradiation, the complication rate was 23%. For the patients treated by irradiation alone, the complication rate was 7% (p less than 0.01). Fractionation was found to be another important parameter: for 52 patients treated using 3 weekly fractions of 3.3 Gy, the complication rate was 25%, compared to 8% (p less than 0.01) for 76 patients treated using 4 weekly fractions of 2.5 Gy. Combining these two factors, we found a 42% complication rate for the group of patients who underwent laparotomy and who were treated by means of 3 fractions of 3.3 Gy per week, whereas patients irradiated using 4 weekly fractions of 2.5 Gy, without any previous laparotomy, had only a 5% complication risk (p less than 0.001).