Thermodynamic temperature assignment to the point of inflection of the melting curve of high-temperature fixed points.

The thermodynamic temperature of the point of inflection of the melting transition of Re-C, Pt-C and Co-C eutectics has been determined to be 2747.84 ± 0.35 K, 2011.43 ± 0.18 K and 1597.39 ± 0.13 K, respectively, and the thermodynamic temperature of the freezing transition of Cu has been determined to be 1357.80 ± 0.08 K, where the ± symbol represents 95% coverage. These results are the best consensus estimates obtained from measurements made using various spectroradiometric primary thermometry techniques by nine different national metrology institutes. The good agreement between the institutes suggests that spectroradiometric thermometry techniques are sufficiently mature (at least in those institutes) to allow the direct realization of thermodynamic temperature above 1234 K (rather than the use of a temperature scale) and that metal-carbon eutectics can be used as high-temperature fixed points for thermodynamic temperature dissemination. The results directly support the developing mise en pratique for the definition of the kelvin to include direct measurement of thermodynamic temperature.

Three-element trap filter radiometer based on large active area silicon photodiodes.

This paper shows the opto-mechanical design of a new filter radiometer built at the Physikalisch-Technische Bundesanstalt, Germany, for the accurate determination of the thermodynamic temperature of high-temperature blackbodies. The filter radiometer is based on a three-element reflection-type trap detector that uses three large active area silicon photodiodes. Its spectral coverage and field of view are defined by a detachable narrow-band filter and a diamond-turned precision aperture, respectively. The temperature of the filter radiometer is stabilized using a water-streamed housing and is measured using a thin-film platinum thermometer placed onto the first photodiode element. The trap "mount" has been made as compact as possible, which, together with the large active area of the chosen photodiodes, allows a wide field of view. This work presents the design of the filter radiometer and discusses the criteria that have been considered in order for the filter radiometer to suit the application.

Organic cation transporters OCT1 and OCT2 determine the accumulation of lamivudine in CD4 cells of HIV-infected patients.

PURPOSE: Identifying factors that determine concentrations of antiretroviral drugs in CD4 cells are important for improving therapeutic efficacy. Experimental models indicate that the nucleoside reverse transcriptase inhibitor lamivudine is transported by the organic cation transporters 1 and 2 (OCT1 and OCT2, respectively). Here, we tested whether OCT1 and OCT2 contribute to the uptake of lamivudine into native CD4 cells of human immunodeficiency virus (HIV)-infected individuals. METHODS: CD4 cells obtained by non-activated cell sorting from 35 individuals with HIV-1 infection were incubated with lamivudine (10 µM, 30 min), and intracellular concentrations of lamivudine and its active metabolite lamivudine triphosphate were determined by liquid chromatography tandem mass spectrometry. The expression of OCT1 and OCT2 mRNA was measured by quantitative real-time polymerase chain reaction (PCR). A model of OCT2-transfected CD4 cells was established for mechanistic investigations. RESULTS: Intracellular concentrations of lamivudine and its active metabolite lamivudine triphosphate showed strong linear correlations with each other and with the CD4 mRNA expression of OCT1 and OCT2 (r > 0.80). Coincubation with protease inhibitors (ritonavir, nelfinavir) that inhibit OCT1 and OCT2 yielded decreased intracellular concentrations of lamivudine and lamivudine triphosphate. Incubation of CD4 cells from healthy donors transfected with an OCT2 expression vector yielded increased concentrations of lamivudine and lamivudine triphosphate. CONCLUSION: Our studies indicate a role of OCT1 and OCT2 for the cellular accumulation of lamivudine in HIV-infected individuals.

Long-term beneficial effect of protease inhibitors on the intrinsic apoptosis of peripheral blood mononuclear cells in HIV-infected patients.

BACKGROUND: Viral suppression by antiretroviral therapy (ART) inhibits HIV-induced apoptosis and CD4 T-cell loss. It has been suggested that protease inhibitors (PIs) have nonviral antiapoptotic effects by maintaining mitochondrial integrity. Long-term clinical effects of PI-based ART on mitochondrial toxicity and lymphocyte apoptosis beyond viral suppression have not been exploited to date. METHODS: We conducted a 7-year study on HIV-1-infected patients from the Cologne HIV cohort with sufficient viral suppression under either a PI-based or nonnucleoside reverse transcriptase inhibitor (NNRTI)-based regimen. Eight patients on PI and eight on NNRTI were eligible for inclusion in the analysis. The primary outcome measure was defined as a change in the mitochondrial-to-nuclear DNA ratio in PBMCs. Further key molecules involved in extrinsic [tumour necrosis factor-related apoptosis-inducing ligand (TRAIL), Fas ligand (FasL) and caspase 8], intrinsic [B-cell lymphoma 2 (Bcl-2), Bcl-2-associated X protein (Bax), caspase 9 and lactate-to-pyruvate ratio] and overall apoptosis [Annexin+/7-aminoactinomycin D (7-AAD)- and caspase 3/7] and viral activity [negative regulatory factor (Nef), interferon-α (IFN-α) and myxovirus resistance protein A (MxA)] were measured. RESULTS: Demographic and baseline clinical parameters were similar in the two groups, except that patients in the PI group had a higher mean age. After 7 years of treatment, CD4 T-cell count increased and the expression of genes encoding the proapoptotic viral protein Nef and HIV-induced cytokine IFN-α and its downstream effector MxA decreased in both groups. Focusing on the different pathways of apoptosis, only in the PI group intrinsic apoptosis decreased significant and in the inter-group comparison the decrease was significantly higher than in the NNRTI group. CONCLUSIONS: Our study provides evidence that long-term therapy with a PI-based regimen may be superior to that with a NNRTI-based regimen with regard to its intrinsic antiapoptotic effect.

Phonon-mediated versus coulombic backaction in quantum dot circuits.

Quantum point contacts (QPCs) are commonly employed to detect capacitively the charge state of coupled quantum dots (QDs). An indirect backaction of a biased QPC onto a double QD laterally defined in a GaAs/AlGaAs heterostructure is observed. Energy is emitted by nonequilibrium charge carriers in the leads of the biased QPC. Part of this energy is absorbed by the double QD where it causes charge fluctuations that can be observed under certain conditions in its stability diagram. By investigating the spectrum of the absorbed energy, we find that both acoustic phonons and Coulomb interaction can be involved in the backaction, depending on the geometry and coupling constants.

Aspirin induces nitric oxide release from vascular endothelium: a novel mechanism of action.

1. The study was designed to test the hypothesis that aspirin may stimulate nitric oxide (NO) release from vascular endothelium, a pivotal factor for maintenance of vascular homeostasis. 2. Clinical evidence suggests that low-dose aspirin may improve vascular endothelial function. Since other cyclooxygenase (COX) inhibitors showed no beneficial vascular effects, aspirin may exhibit a vasculoprotective, COX-independent mechanism. 3. Luminal NO release was monitored in real time on dissected porcine coronary arteries (PCA) by an amperometric, NO-selective sensor. Additionally, endothelial NO synthase (eNOS) activity was measured in EA.hy 926 cell homogenates by an l-[(3)H]citrulline/l-[(3)H]arginine conversion assay. Superoxide scavenging capacity was assessed by lucigenin-enhanced luminescence. 4. Aspirin induced an immediate concentration-dependent NO release from PCA with an EC(50) of 50 nm and potentiated the NO stimulation by the receptor-dependent agonist substance P. These effects were independent of an increase in intracellular calcium and could be mimicked by stimulation with acetylating aspirin derivatives. The aspirin metabolite salicylic acid or the reversible cyclooxygenase inhibitor indomethacin failed to modulate NO release. Incubation of soluble eNOS for 15 min with 100 microm aspirin or acetylating aspirin analogues increased the l-[(3)H]citrulline yield by 40-80%, while salicylic acid had no effect. Aspirin and salicylic acid showed a similar, but only modest, magnitude and velocity of superoxide scavenging. 5. Our findings demonstrate that therapeutically relevant concentrations of aspirin elicit NO release from vascular endothelium. This effect appears to be due to a direct acetylation of the eNOS protein, but is independent of COX inhibition or inhibition of superoxide-mediated NO degradation.

Determination of energy scales in few-electron double quantum dots.

The capacitive couplings between gate-defined quantum dots and their gates vary considerably as a function of applied gate voltages. The conversion between gate voltages and the relevant energy scales is usually performed in a regime of rather symmetric dot-lead tunnel couplings strong enough to allow direct transport measurements. Unfortunately, this standard procedure fails for weak and possibly asymmetric tunnel couplings, often the case in realistic devices. We have developed methods to determine the gate voltage to energy conversion accurately in the different regimes of dot-lead tunnel couplings and demonstrate strong variations of the conversion factors. Our concepts can easily be extended to triple quantum dots or even larger arrays.

Which platelet function test is suitable to monitor clopidogrel responsiveness? A pharmacokinetic analysis on the active metabolite of clopidogrel.

BACKGROUND: Multiple platelet function tests claim to be P2Y12-pathway specific and capable of capturing the biological activity of clopidogrel. OBJECTIVES: The aim of the present study was to determine which platelet function test provides the best reflection of the in vivo plasma levels of the active metabolite of clopidogrel (AMC). PATIENTS/METHODS: Clopidogrel-naive patients scheduled for elective percutaneous coronary intervention (PCI) received a 600 mg loading dose of clopidogrel and 100 mg of aspirin. For pharmacokinetic analysis, blood was drawn at 0, 20, 40, 60, 90, 120, 180, 240 and 360 min after clopidogrel loading and peak plasma concentrations (C(max)) of the AMC were quantified with liquid chromatography-tandem mass spectrometry (LC-MS/MS). Platelet function testing was performed at baseline and 360 min after the clopidogrel loading. RESULTS: The VASP-assay, the VerifyNow P2Y12-assay and 20 micromol L(-1) adenosine diphosphate (ADP)-induced light transmittance aggregometry (LTA) showed strong correlations with C(max) of the AMC (VASP: R(2) = 0.56, P < 0.001; VerifyNow platelet reactivity units (PRU): R(2) = 0.48, P < 0.001; VerifyNow %inhibition: R(2) = 0.59, P < 0.001; 20 micromol L(-1) ADP-induced LTA: R(2) = 0.47, P < 0.001). Agreement with C(max) of the AMC was less evident for 5 micromol L(-1) ADP-induced LTA or whole blood aggregometry (WBA), whereas the IMPACT-R ADP test did not show any correlation with plasma levels of the AMC. CONCLUSION: The flow cytometric VASP-assay, the VerifyNow P2Y12 assay and, although to a lesser extent, 20 micromol L(-1) ADP-induced LTA correlate best with the maximal plasma level of the AMC, suggesting these may be the preferred platelet function tests for monitoring the responsiveness to clopidogrel.

Preferential upregulation of interferon-alpha subtype 2 expression in HIV-1 patients.

Humans tailor virus-specific immune responses through modulated expression of 12 different interferon (IFN)-alpha subtypes. However, exacerbated expression of certain IFN-alpha subtypes causes immunopathology in the context of autoimmune conditions and chronic viral infections. We showed that progression to AIDS is associated with elevated expression of IFN-alpha in unstimulated peripheral blood mononuclear cells. Here, we sought to determine whether distinct IFN-alpha subtypes are involved in this phenomenon. We used quantitative RT-PCR to assess expression levels of 12 IFN-alpha subtypes in peripheral blood mononuclear cells from normal donors and HIV-1 patients at CDC stage A and stage C of the disease. Three patterns of IFN-alpha subtype expression emerged. First, IFN-alpha2 and IFN-alpha6 mRNA levels were elevated in both patient groups. Second, IFN-alpha1/13, IFN-alpha8, IFN-alpha14, IFN-alpha16, IFN-alpha17, and IFN-alpha21 were upregulated in stage C but not stage A patients. Third, expression levels of IFN-alpha4, IFN-alpha5, IFN-alpha7, and IFN-alpha10 did not change among the three groups of volunteers. Among all other subtypes, IFN-alpha2 was preferentially upregulated, showing >60-fold higher levels in stage A and >400-fold in stage C patients compared with controls, which correlated with declining CD4 counts. Our results demonstrate that distinct IFN-alpha subtypes are sequentially activated during HIV-1 infection, which may be predictive of disease progression.

Telegraph noise in coupled quantum dot circuits induced by a quantum point contact.

Charge detection utilizing a highly biased quantum point contact has become the most effective probe for studying few electron quantum dot circuits. Measurements on double and triple quantum dot circuits is performed to clarify a back action role of charge sensing on the confined electrons. The quantum point contact triggers inelastic transitions, which occur quite generally. Under specific device and measurement conditions these transitions manifest themselves as bounded regimes of telegraph noise within a stability diagram. A nonequilibrium transition from artificial atomic to molecular behavior is identified. Consequences for quantum information applications are discussed.

Traceability in fluorometry: Part II. Spectral fluorescence standards.

The need for the traceable characterization of fluorescence instruments is emphasized from a chemist's point of view, focusing on spectral fluorescence standards for the determination of the wavelength- and polarization-dependent relative spectral responsivity and relative spectral irradiance of fluorescence measuring systems, respectively. In a first step, major sources of error of fluorescence measurements and instrument calibration are revealed to underline the importance of this issue and to illustrate advantages and disadvantages of physical and chemical transfer standards for generation of spectral correction curves. Secondly, examples for sets of traceable chemical emission and excitation standards are shown that cover a broad spectral region and simple procedures for the determination of corrected emission spectra with acceptable uncertainties are presented. With proper consideration of the respective measurement principle and geometry, these dye-based characterization procedures can be not only applied to spectrofluorometers but also to other types of fluorescence measuring systems and even to Raman spectrometers.

Acute effects of glucose and insulin on vascular endothelium.

AIMS/HYPOTHESIS: Chronic exposure to high concentrations of glucose has consistently been demonstrated to impair endothelium-dependent, nitric oxide (NO)-mediated vasodilation. In contrast, several clinical investigations have reported that acute exposure to high glucose, alone or in combination with insulin, triggers vasodilation. The aim of this study was to examine whether elevated glucose itself stimulates endothelial NO formation or enhances insulin-mediated endothelial NO release. METHODS: We measured NO release and vessel tone ex vivo in porcine coronary conduit arteries (PCAs). Intracellular Ca(2+) was monitored in porcine aortic endothelial cells (PAECs) by fura-2 fluorescence. Expression of the Na(+)/glucose cotransporter-1 (SGLT-1) was assayed in PAECs and PCA endothelium by RT-PCR. RESULTS: Stimulation of PCAs with D: -glucose, but not the osmotic control L: -glucose, induced a transient increase in NO release (EC(50) approximately 10 mmol/l), mediated by a rise in intracellular Ca(2+) levels due to an influx from the extracellular space. This effect was abolished by inhibitors of the plasmalemmal Na(+)/Ca(2+) exchanger (dichlorobenzamil) and the SGLT-1 (phlorizin), which was found to be expressed in aortic and coronary endothelium. Alone, D: -glucose did not relax PCA, but did augment the effect of insulin on NO release and vasodilation. CONCLUSIONS/INTERPRETATION: An increased supply of extracellular D: -glucose appears to enhance the activity of the endothelial isoform of nitric oxide synthase by increasing intracellular Na(+) concentrations via SGLT-1, which in turn stimulates an extracellular Ca(2+) influx through the Na(+)/Ca(2+) exchanger. This mechanism may be responsible for glucose-enhanced, insulin-dependent increases in tissue perfusion (including coronary blood-flow), thus accelerating glucose extraction from the blood circulation to limit the adverse vascular effects of prolonged hyperglycaemia.