Compromise in uncertainty estimation by modelling and validation approaches for an HPLC-UV method for measurement of biochemical indicators of vitamins A and E.

It is common practice nowadays to associate the measurement uncertainty to the measurand, in order to judge the quality of a result related to the measurement process. However, the improvement of this parameter as well as the adaptation of its estimation modes always remain an analytical challenge, especially in chemical testing. In this paper, we outline a measurement uncertainty estimation mode based on the one-point linear calibration equation to fully establish a "bottom-up" approach for estimating the measurement uncertainty of a multi-point calibration-based HPLC-UV quantitative method. To demonstrate this estimation mode, we have followed as an example of interest the influences resulting from the simultaneous determination of two biochemical indicators, namely the human plasma vitamers retinol and α-tocopherol. Results from this estimation showed consistency when compared to those obtained from the validation-based alternative method, where the relative expanded uncertainties were found, at a 95% confidence level, to be less than 15% for the low concentration ranges of the two molecules. However, the modelling approach shows all the benefits of its use to identify and quantify all the uncertainty contributions arising from the different steps of the analytical process and seems to be quite achievable for comparative HPLC methods.

[Cerebral vasculopathy in children with sickle cell disease: Key issues and the latest data]. / Vasculopathie cérébrale de l'enfant drépanocytaire : points clés et nouveautés.

Cerebral vasculopathy is a common and severe complication of sickle cell disease in children. The pathophysiology consists of progressive damage to the basal intracranial arteries and cerebral microcirculation, while chronic anemia worsens exposure to cerebral hypoxia. It results in stroke and subclinical or poorly symptomatic ischemic lesions. Many clinical, biological, and radiological risk factors have been identified. The prevention strategy through systematic transcranial Doppler screening of large-vessel vasculopathy has revolutionized the management of this disease and has greatly decreased the risk of developing stroke. MRI-MRA is a complementary diagnostic tool for anatomical analysis of parenchymal and vascular lesions, which is used for chronic disease monitoring or in the context of an acute neurological event. New exploration opportunities are offered by submandibular Doppler sonography and indirect evaluation methods of cerebral oxygenation and perfusion. If chronic blood transfusion therapy is used to prevent the occurrence and recurrence of cerebral complications of sickle cell disease, only allogeneic hematopoietic stem cell transplantation can safely and definitively stop the transfusion program. It should therefore be proposed early, before irreversible cerebral or vascular lesions occur. Hydroxycarbamide treatment has recently emerged as a potential substitute for chronic transfusions for the maintenance of transcranial Doppler velocities, but only after an initial treatment by transfusions and provided there is close follow-up. In the long run, cerebral vascular damage can cause progressive cognitive impairment and disability, even in children without radiologically identified lesions, indicating the importance of systematic and repeated neuropsychological testing.

Synthesis and FTIR conformational studies of peptides from the basic region of c-Jun: a critical analysis on the basis of CD and NMR data.

The peptide (35 residues) corresponding to the basic subdomain (bSD) of c-Jun (residues 252-281) and its fragments NP (N-terminal peptide, 1-19) and CP (C-terminal peptide, 16-35) were synthesized in stepwise solid-phase using the tert-butyloxycarbonyl/benzyl strategy. In a previous paper, we have shown that during its binding to the DNA site CRE (cAMP-responsive element) the bSD structure was converted into alpha-helix from an initial random coil conformation [Krebs, D., Dahmani, B., El Antri, S., Monnot, M., Convert, O., Mauffret, O., Troalen, F. & Fermandjian, S. Eur. J. Biochem. 231, 370-380 (1995)]. Our results suggested both a high flexibility and a helical potential in bSD, these two properties seeming crucial for the accommodation of the basic subdomain of c-Jun to its specific DNA targets. In this work, we assessed the conformational variability of bSD through the study of the secondary structures of its NP and CP fragments in trifluoroethanol (TFE)/2H2O mixtures, using Fourier transform infrared (FTIR) spectroscopy. The IR results were critically analyzed in light of our previously reported circular dichroism (CD) and NMR data [Krebs, D., Dahmani, B., Monnot, M., Mauffret, O., Troalen, F. & Fermandjian, S. Eur. J. Biochem, 235, 699-712 (1996)]. Upon addition of TFE, the relative areas of the seven components of the amide I. band (1700-1620 cm-1) reflected the conversion of a large amount of random coil conformation into alpha-helix for the two fragments and bSD. This effect was accompanied by more subtle variations of the less populated structures, in agreement with the results of CD and NMR experiments. The IR results stipulated the conservation of the parent bSD secondary structures in both fragments; however, NP and CP peptides did not display similar random-to-alpha-helix stabilization pattern upon additions of TFE to aqueous solutions. The profile from CD signal at 222 nm was found sigmoidal for NP and almost linear for CP, while that corresponding to the parent peptide bSD was just in between those of its fragments. Thus, the present study confirms the high flexibility and helix propensity of the c-Jun basic subdomain and suggests that the N- and C-terminal parts of the peptide do not follow the same random-to-helix conversion profile during their complexation with DNA.

Dissection of the basic subdomain of the c-Jun oncoprotein: a structural analysis of two peptide fragments by CD, Fourier-transform infrared and NMR.

In a previous paper, we reported on the structural properties of a 35-residue peptide corresponding to a modified basic subdomain (bSD) of the basic zipper protein c-Jun (residues 252-281) as determined by combined use of 1H-NMR, circular dichroism (CD) and Fourier transform infrared (FT-IR) spectroscopies [Krebs, D., Dahmani, B., El Antri, S., Monnot, M., Convert, O,. Mauffret, O., Troalen, F. & Fermandjian, S. (1995) Eur. J. Biochem. 231, 370-380]. The fragments NP and CP (the N-terminal residues 1-19 and C-terminal residues 16-35 of bSD, respectively) proved to be particularly useful for the assignment of the 1H-NMR spectra of the full-length bSD, which has been achieved completely in aqueous solution and partially in trifluoroethanol. Here, we report on the structural properties of NP and CP in aqueous solution and under varying H2O/trifluoroethanol conditions, again using 1H-NMR, CD and FT-IR experiments. Both CD and FT-IR results established that the fragments are weakly structured in aqueous solution. Addition of trifluoroethanol to aqueous solutions of the peptides produced their stabilization into helix, following a profile sigmoidal for NP and nearly linear for CP. Quantitative NOEs, secondary Halpha chemical shifts, NH temperature coefficients and 3JalphaN coupling constants for the peptides in aqueous solutions provided indications for weak helix features (nascent helices) manifested within two sites (continuous dNN NOEs) in both NP and CP. For each peptide, an excellent agreement was observed between experiments and predictions with the AGADIR program for the location of these nascent helices in the sequences. Trifluoroethanol provoked both the alpha-helix stabilization within these sites and the alpha-helix propagation to adjacent amino acid residues. Finally, our results reflected the high flexibility and helix potential of the NP and CP fragments, these two properties seeming crucial for the accommodation of c-Jun to its specific DNA targets. The results demonstrated also the fragmentation's benefits in dissecting a protein or a complex peptide into smaller fragments and analyzing their structure individually.

The basic subdomain of the c-Jun oncoprotein. A joint CD, Fourier-transform infrared and NMR study.

The structural properties of the basic subdomain of the basic zipper (bZIP) protein c-Jun were examined by joint means of 1H-NMR, CD and Fourier-transform infrared (FTIR) spectroscopies. The basic subdomain (residues 252-281 in c-Jun) is responsible for sequence-specific recognition of DNA. A modified basic subdomain bSD (residues 1-35) and its N-terminal part and C-terminal part fragments (NP, residues 1-19; and, CP, residues 16-35) were prepared by solid-phase synthesis and purified by HPLC. In aqueous solution, in the absence of DNA, bSD behaved mostly as an unstructured peptide characterized by only 5% alpha helix. However, upon mixing bSD and a specific DNA fragment, i.e. a CRE(cAMP-responsive element)-containing hexadecanucleotide, the alpha helix was stabilized to an extent of 20% at 20 degrees C or 35% at 2 degrees C. At the same time, no significant change could be detected in the DNA spectra. Addition of trifluoroethanol to an aqueous bSD sample resulted in an increase of the alpha-helix content so that about 60% of alpha helix was found at a ratio of 75% trifluoroethanol (20 degrees C). These effects were reflected in both CD and FTIR measurements. Changes shown by the CD spectra during the process suggested a mechanism dominated by a two-state helix/unordered transition. NMR data, namely alpha H chemical shifts, NOE cross-peaks and NH temperature coefficients provided indications for extended or nascent helix structures within four short stretches dispersed along the sequence for c-Jun bSD, contrasting with the unique and continuous stretch reported for Gcn4 (yeast general control protein 4) bSD in aqueous solution. Trifluoroethanol stabilized the alpha-helix structure mainly at these four sites. The malleability of the basic subdomain of c-Jun was emphasized in relation to its ability to fit the DNA helix in adopting an alpha-helix structure. The complex formation apparently requires substantial conformational change from the peptide and only little from the oligonucleotide.

[Health policy and financing in Tunisia]. / Politique de santé et financement en Tunisie.

Programmes for expanding preventive medicine were designed. They were considered part of the measures for promoting health cost containment. In practice, they were not given high priority. During the last decade, the budget of the Department of Health had a lower growth rate than the total budget of the State. Scarcity of resources, coupled with the demographic upward trend and growing per capita demand for health services were deteriorating the care provided to the population. To improve the situation, the National Sickness Insurance Fund created on its own 6 polyclinics. They were soon full of patients and the quality of the services they rendered were lowered. Moreover all the health system is facing two challenges: (i) the resistance to reorientating the system to better serve a larger segment of the population; (ii) the "clientelism" which leads resources to where they are not mostly needed. As a result, the country is divided into two parts: (a) the West, where there is an urgent need for beds and simple equipment; (b) the East, already well-equipped, where practitioners are applying for high-tech devices.

Frequency stabilization of semiconductor lasers by resonant optical feedback.

With simple optical geometries a separate resonant Fabry-Perot cavity can serve as an optical feedback element that forces a semiconductor laser automatically to lock its frequency optically to the cavity resonance. This method is used to stabilize laser frequencies and reduce linewidths by a factor of 1000 from 20 MHz to approximately 20 kHz.

[The demographic situation in a northwest region of Tunisia: Ain Draham (survey results)]. / Situation demographique d'une region du nord-ouest de la Tunisie: Ain Draham (resultats d'une enquete)

PIP: The author discusses the demographic situation and characteristics of the population in Ain Draham, the northwest region of Tunisia. Data are from a health survey of parents of children born between September 1982 and August 1983. Following a summary of the region's geography, health services, and local government, information is provided on spatial distribution, population density, education, fertility, contraceptive usage, infant mortality, maternal mortality, fetal death, and birth weight.^ieng