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PubMed2004

Methadone implants for methadone maintenance treatment. In vitro and in vivo animal studies.

Methadone implant formulations elaborated with polylactide-co-glycolide (PLGA) and polylactic acid (PLA) for 1 week and 1 month release duration, respectively, were evaluated in vitro and in vivo. One-week implants prepared with methadone clorhydrate, methadone clorhydrate/methadone base blend or methadone base were tested in vitro. Results showed that the methadone release rate decreased as the methadone base increased. The best release profile was achieve when the methadone base implants, made by compression of a 50:50 PLGA (12 kDa) and methadone base mix, were coated with PLA (30 kDa). For 1-month implants, the methadone base load was increased to 65% and PLA of 30 kDa was used as a matrix component. In this case the implants were coated with the same polymer. Deconvolution methods could not be used for in vivo release estimation because an increase in methadone clearance was observed with methadone clorhydrate solution multiple-dose treatment. Therefore the amount of drug remaining within the implants was evaluated and the deconvolution was only used to establish the release profile range. The upper limit was estimated applying the absorption-disposition function obtained after multiple-dose administrations while the lower curve was estimated using the single-dose function. Methadone serum levels were maintained around 200 ng/ml during 1 week and approximately 5 weeks with the optimised implants. In vivo-in vitro correlations were always very good with slopes near 1.

Animals↗
PubMed2004

Sampling distribution for microsatellites amplified by PCR: mean field approximation and its applications to genotyping.

Due to microsatellite mutations during PCR, stutter patterns may appear in the final PCR product, which hinder us from accurate genotyping microsatellite markers. The existing methods for microsatellite stutter pattern deconvolution required large amount of data. A mathematical model for microsatellite mutations during PCR and an estimation method based on mean field approximation for branching processes have recently been developed. In this paper, we study the asymptotic behaviors for mean field approximation when experiments are started from a large number of molecules, and we derive an upper bound for the approximation error when experiments are started from a finite number of molecules. Based on the theories of mean field approximation and Bayesian statistics, we develop a novel method for microsatellite stutter pattern deconvolution.

Gene Amplification↗
PubMed2004

Aspects on the accuracy of cerebral perfusion parameters obtained by dynamic susceptibility contrast MRI: a simulation study.

Several studies have indicated that deconvolution based on singular value decomposition (SVD) is a robust concept for retrieval of cerebral blood flow in dynamic susceptibility contrast (DSC) MRI. However, the behavior of the technique under typical experimental conditions has not been completely investigated. In the present study, cerebral perfusion was simulated using different temporal resolutions, different signal-to-noise ratios (S/Ns), different shapes of the arterial input function (AIF), different signal drops, and different cut-off levels in the SVD deconvolution. Using Zierler's area-to-height relationship in combination with the central volume theorem, calculations of regional cerebral blood volume (rCBV), regional cerebral blood flow (rCBF), and regional mean transit time (rMTT) were accomplished, based on simulated DSC-MRI signal curves corresponding to artery, gray matter (GM), white matter (WM), and ischemic tissue. Gaussian noise was added to the noise-free signal curves to generate different S/Ns. We studied image time intervals of 0.5, 1.0, 1.5, 2.0, 2.5, and 3.0 s, as well as different degrees of signal decrease. The singular-value threshold in the SVD procedure and the shape of the AIF were also varied. Increased rCBF was seen when noise was added, especially for rCBF in WM at the larger image time intervals. The rCBF showed large standard deviations using a low threshold value. A prolonged time interval led to a lower absolute value of rCBF both in GM and WM, and a low/broad AIF also underestimated the rCBF. When a larger maximal signal decrease was assumed, smaller standard deviations were observed. No systematic change of the average rCBV was observed with increasing noise or with increasing image time interval. At S/N = 40, a low cut-off value resulted in an rCBF that was closer to the true value. Furthermore, at low S/N it was difficult to differentiate ischemic tissue from WM.

Brain↗
PubMed2005

Comparative study of electrochemical degradation and ozonation of nonylphenol.

Treatment of solutions of nonylphenol (NP), Triton X-100 (TrX) and phenol in a flow-through undivided EC reactor equipped with a Co(2+)-promoted PbO(2) anode and a stainless steel cathode was accompanied by consistent changes of absorbance, fluorescence and mass spectra of the effluents, and formation of aldehydes ranging from formaldehyde to decyl aldehyde. Deconvolution of the absorbance spectra of EC-treated NP, TrX and phenol and examination of their fluorescence indicated that the compounds are rapidly degraded in the reactor. For NP, the degradation of the target proceeded via the generation (at current densities <25mA/cm(2)) of benzoquinone intermediates that yielded peaks with m/z ratios 223, 227, 235, and 241D in the mass spectra. Their breakdown at current densities >10mA/cm(2) was accompanied by the release of aldehydes that were predominated by acetaldehyde and formaldehyde. The total yield of aldehydes increased with the current density, but their speciation showed little sensitivity to it. Deconvolution of the absorbance spectra of NP solutions subjected to ozonation, and analysis for reaction by-products formed in these conditions showed the reaction pathway in the latter case was likely to be similar to that observed for the EC treatment.

Dose-Response Relationship, Drug↗
PubMed1995

Role of nuclear medicine in liver transplantation.

Orthotopic liver transplantation is now a very well-established technique for treating patients with end-stage liver disease. Since 1967, more than 26,000 liver transplants have been performed, including 15,000 in the United States. The overall 1-year survival rate is approximately 80% and 5-year survival is 70%. Nuclear imaging plays an important role in the management of liver transplant recipients before and after liver transplantation. The evaluation of candidates potentially includes liver-spleen scan for liver volume, multiple gated acquisition scan, adenosine or stress thallium study, bone scan, and quantitative ventilation perfusion scan for hepatopulmonary syndrome. In the post-transplant phase, the deconvolution analysis (which corrects for the problem of recirculation) is a promising tool for diagnosing rejection, although its role in the transplant population has to be established. A variety of nuclear medicine techniques are helpful in the postoperative diagnosis of biliary complications. By performing a semiquantitative analysis to discriminate hepatocyte dysfunction from biliary disease and measuring hepatocyte extraction fraction by deconvolution analysis and excretion, (T1/2 values measured by the nonlinear list squares technique) have been very promising.

Biliary Tract↗
PubMed2001

Trifluoperazine induces domain formation in zwitterionic phosphatidylcholine but not in charged phosphatidylglycerol bilayers.

The interaction of trifluoperazine with the zwitterionic lipids dipalmitoylphosphatidylcholine and dimyristoylphosphatidylcholine and with anionic dimyristoylphosphatidylglycerol was studied by means of microcalorimetry and fluorescence spectroscopy. Intercalation of drug molecules into the lipid bilayers was confirmed by the observed differential scanning calorimetry peak broadening and the decrease in chain-melting temperatures. For trifluoperazine:lipid mole ratios higher than 0.4 and 0.6 (for dipalmitoylphosphatidylcholine and dimyristoylphosphatidylcholine, respectively) the deconvolution of transition profiles into two Gaussian components was possible, which suggests phase separation in the studied mixtures. Deconvolution of the thermograms was not possible for any of the drug:dimyristoylphosphatidylglycerol mole ratios studied. To confirm the existence of phase separation in trifluoperazine-phosphatidylcholine mixtures fluorescence spectroscopy experiments were performed using Laurdan as a probe. From the generalised polarisation versus excitation wavelength dependences, recorded at different temperatures, we conclude that a phase separation occurs in the gel state of the studied trifluoperazine-phosphatidylcholine mixtures. We attribute the existence of domains in the bilayer to the dissimilar interactions of two protonation forms of trifluoperazine with phosphatidylcholine molecules. Structural defects present at domain boundaries could be related to the trifluoperazine induced increase of membrane permeability and fluidity. This may partially explain the mechanism of multidrug resistance modulation by trifluoperazine.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed2000

Analysis and implications of equivalent uniform approximations of nonuniform unitary synaptic systems.

Real synaptic systems consist of a nonuniform population of synapses with a broad spectrum of probability and response distributions varying between synapses, and broad amplitude distributions of postsynaptic unitary responses within a given synapse. A common approach to such systems has been to assume identical synapses and recover apparent quantal parameters by deconvolution procedures from measured evoked (ePSC) and unitary evoked postsynaptic current (uePSC) distributions. Here we explicitly consider nonuniform synaptic systems with both intra (type I) and intersynaptic (type II) response variability and formally define an equivalent system of uniform synapses in which both uePSC and ePSC amplitude distributions best approximate those of the actual nonuniform synaptic system. This equivalent system has the advantage of being fully defined by just four quantal parameters: ñ, the number of equivalent synapses;p, the mean probability of quantal release; mu, mean; and sigma(2), variance of the uePSC distribution. We show that these equivalent parameters are weighted averages of intrinsic parameters and can be approximated by apparent quantal parameters, therefore establishing a useful analytical link between the apparent and intrinsic parameters. The present study extends previous work on compound binomial analysis of synaptic transmission by highlighting the importance of the product of p and mu, and the variance of that product. Conditions for a unique deconvolution of apparent uniform synaptic parameters have been derived and justified. Our approach does not require independence of synaptic parameters, such as p and mu from each other, therefore the approach will hold even if feedback (i.e., via retrograde transmission) exists between pre and postsynaptic signals. Using numerical simulations we demonstrate how equivalent parameters are meaningful even when there is considerable variation in intrinsic parameters, including systems where subpopulations of high- and low-release probability synapses are present, therefore even under such conditions the apparent parameters estimated from experiments would be informative.

Animals↗
PubMed1978

Structure determination of lipid bilayers.

A method of determining the phases of X-ray reflections from oriented model membrane systems at low resolution is described. The method involves deconvolution and requires that d less than or equal to 2v where v is the width of the head group region within the bilayer and d is the thickness of the bilayer. The method can be used with a single set of X-ray data and applies to lipid bilayers which have a relatively constant density in the hydrocarbon region. Phases for the first five or six orders of phosphatidylethanolamine and lecithin are derived. A refined analysis based upon deconvolution but using information inherent in the Fourier profile is also described.

Hydrocarbons↗
PubMed1990

Structure and dynamics of water in tendon from NMR relaxation measurements.

Nuclear magnetic relaxation times were measured in collagen tissue when varying the orientation of the fiber with respect to the static field. T1 was found to be only slightly dependent on theta, the fiber-to-field angle, but T2 was very sensitive to the orientation, with a maximum value at the magic angle. The transverse decay curves were multiexponential. Their deconvolution displayed four components; the ones that decayed most slowly were almost independent of theta, but the two fastest ones showed a strong angular dependence that was interpreted with a cross-relaxation model. Quadrupolar dips were visible in the 1/T1 dispersion curves. These dips were independent of theta, so that the magnetization transfer could also be assumed to be independent of the fiber orientation. Finally, each component was assigned to a fraction of protons localized in the macromolecular structure and characterized by particular dynamics. The model of Woessner was applied to the water molecules tightly bound into the macromolecules, which resulted in a dynamical description of this water fraction. This description is compatible with the two-sites model of Ramachandran based on x-ray diffraction and with the extensive studies of Berendsen. However, the important indications obtained from the deconvolution lead to a less static representation of the tissue.

Animals↗
PubMed1992

Effects of crystallization on the heme-carbon monoxide moiety of bovine heart cytochrome c oxidase carbonyl.

Cytochrome c oxidase isolated from bovine heart was crystallized in the fully reduced carbon monoxide (CO)-bound form. To evaluate the structure of the O2 reaction site in crystals and in solution, the bound C-O stretch infrared band in protein crystals was compared with the band for protein solution. In solution, the C-O stretch band could be deconvoluted into two extremely narrow bands, one at 1963.6 cm-1 with delta v1/2 = 3.4 cm-1 of 60% Gaussian/40% Lorentzian character represented 86% of the total band area and the other at 1960.3 cm-1 with delta v1/2 = 3.0 cm-1 of 47% Gaussian/53% Lorentzian character represented 14% of the total band area. The crystals exhibited two deconvoluted C-O infrared bands having very similar band parameters with those in solution. These findings support the presence of two structurally similar conformers in both crystals and solution. Thus crystallization of this enzyme does not affect the structure at the CO-binding site to as great extent as has been noted for myoglobin and hemoglobin carbonyls, indicating that the active (CO- or O2-binding) site of cytochrome c oxidase must be conformationally very stable and highly ordered compared to other hemoproteins such as hemoglobin.

Animals↗
PubMed1993

Multiwavelength analysis of the kinetics of reduction of cytochrome aa3 by cytochrome c.

Some new approaches to the kinetic study of the reduction of cytochrome aa3 by cytochrome c are presented. The primary innovations are the use of a spectrometer which can acquire multiwavelength data as fast as every 10 microseconds, and the application of a variety of analytical methods which can utilize simultaneously all of the time-resolved spectral data. These techniques include singular value decomposition (SVD), deconvolutions based on pure Gaussian models for absorption peaks, deconvolutions based on isolated absorption spectra for the pure components, and simulations of SVD-deduced and actual experimental difference spectra. The reduction characteristics of the anaerobic resting enzyme can be distinguished from those of pulsed forms. In the former case, only two electrons can be bound by cytochrome aa3, whereas in the latter case complete reduction of the enzyme is achieved.

Animals↗
PubMed1995

Fourier transform infrared spectroscopy indicates a major conformational rearrangement in the activation of rhodopsin.

The study of the structural differences between rhodopsin and its active form (metarhodopsin II) has been carried out by means of deconvolution analysis of infrared spectra. Deconvolution techniques allow the direct identification of the spectral changes that have occurred, which results in a significantly different view of the conformational changes occurring after activation of the receptor as compared with previous difference spectroscopy analysis. Thus, a number of changes in the bands assigned to solvent-exposed domains of the receptor are detected, indicating significant decreases in extended (beta) sequences and in reverse turns, and increases in irregular/aperiodic sequences and in helices with a non-alpha geometry, whereas there is no decrease in alpha-helices. In addition to secondary structure conversions, qualitative alterations within a given secondary structure type are detected. These are seen to occur in both reverse turns and helices. The nature of this spectral change is of great importance, since a clear alteration in the helices bundle core is detected. All these changes indicate that the rhodopsin --> metarhodopsin II transition involves not a minor but a major conformational rearrangement, reconciling the infrared data with the energetics of the activation process.

Analysis of Variance↗
PubMed1999

Cell membrane orientation visualized by polarized total internal reflection fluorescence.

In living cells, variations in membrane orientation occur both in easily imaged large-scale morphological features, and also in less visualizable submicroscopic regions of activity such as endocytosis, exocytosis, and cell surface ruffling. A fluorescence microscopic method is introduced here to visualize such regions. The method is based on fluorescence of an oriented membrane probe excited by a polarized evanescent field created by total internal reflection (TIR) illumination. The fluorescent carbocyanine dye diI-C(18)-(3) (diI) has previously been shown to embed in the lipid bilayer of cell membranes with its transition dipoles oriented nearly in the plane of the membrane. The membrane-embedded diI near the cell-substrate interface can be fluorescently excited by evanescent field light polarized either perpendicular or parallel to the plane of the substrate coverslip. The excitation efficiency from each polarization depends on the membrane orientation, and thus the ratio of the observed fluorescence excited by these two polarizations vividly shows regions of microscopic and submicroscopic curvature of the membrane, and also gives information regarding the fraction of unoriented diI in the membrane. Both a theoretical background and experimental verification of the technique is presented for samples of 1) oriented diI in model lipid bilayer membranes, erythrocytes, and macrophages; and 2) randomly oriented fluorophores in rhodamine-labeled serum albumin adsorbed to glass, in rhodamine dextran solution, and in rhodamine dextran-loaded macrophages. Sequential digital images of the polarized TIR fluorescence ratios show spatially-resolved time-course maps of membrane orientations on diI-labeled macrophages from which low visibility membrane structures can be identified and quantified. To sharpen and contrast-enhance the TIR images, we deconvoluted them with an experimentally measured point spread function. Image deconvolution is especially effective and fast in our application because fluorescence in TIR emanates from a single focal plane.

Adsorption↗
PubMed2001

Analysis of enantiomers giving partially overlapped peaks by using different treatments of the chromatographic ultraviolet signals: quantification of pseudoephedrine enantiomers.

Different strategies for the quantification of partially coeluting optical isomers have been investigated. The methods tested are based on the use of different features as the analytical UV signals: peak heights, perpendicular drop areas, first and second derivatives of the chromatograms, peak areas obtained by deconvolution of the overlapped peaks with data fitting optimization, and a multivariate model (principal component regression, PCR). The amphetamine-derivative drug pseudoephedrine was selected as a model compound. For chromatography, LiChrospher 100 RP18 and a mobile-phase consisting of methanol and a solution of carboxymethyl-beta-cyclodextrin (the chiral selector) were used. The UV detector was set at 215 nm. The accuracy obtained with the tested methods at different degrees of overlapping and at different concentration ratios between enantiomers was evaluated. The results of this study demonstrated that the best option for quantification of partially overlapped UV peaks of enantiomers and to obtain the enatiomeric excess is the use of a PCR model using peak heights, perpendicular drop peak areas and deconvoluted peak areas as the original variables. The predictive ability of the proposed calibration model is of about 2-8 times better (depending on the overlapping degree) than that achieved with the other models tested.

Ephedrine↗
PubMed2002

Unravelling the composition of very complex samples by comprehensive gas chromatography coupled to time-of-flight mass spectrometry. Cigarette smoke.

The potential and current limitations of comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (GC x GC-TOF-MS) for the analysis of very complex samples were studied with the separation of cigarette smoke as an example. Because of the large number of peaks in such a GC x GC chromatogram it was not possible to perform manual data processing. Instead, the GC-TOF-MS software was used to perform peak finding, deconvolution and library search in an automated fashion; this resulted in a peak table containing some 30000 peaks. Mass spectral match factors were used to evaluate the library search results. The additional use of retention indices and information from second-dimension retention times can substantially improve the identification. The combined separation power of the GC x GC-TOF-MS system and the deconvolution algorithm provide a system with a most impressive separation power.

Automation↗
PubMed2000

Application of orthogonal ultrasonic signals and binaural processing for imaging of the environment

Data acquisition rates in ultrasonic imaging systems are limited by the finite value of the speed of ultrasonic waves. In order to improve the imaging speed, it is proposed to perform simultaneous scanning of the environment in different directions. In order to avoid cross-talk between adjacent channels in different directions, different orthogonal signals are transmitted. Application of cross-correlation processing and non-linear iterative deconvolution enables the reliable separation of signals transmitted by different sources and reflected by multiple targets. The spatial positions of the targets are found using the data obtained after the non-linear deconvolution as the initial data for binaural or tri-aural processing. This approach has been exploited in ultrasonic sonar used for navigation of mobile robots.

Journal Article↗
PubMed1994

Testing pulse detection algorithms with simulations of episodically pulsatile substrate, metabolite, or hormone release.

Mathematical computer-assisted simulations of episodic hormone, substrate, or metabolite release can be accomplished using explicit algebra and high-speed microprocessors. Such simulations are useful to describe the behavior of single or multiple pulse generators, as well as the expected output of these systems. Simulated series are helpful in evaluating the sensitivity, specificity, positive accuracy, and negative accuracy of discrete peak detection methods, and in deconvolution analysis. Specifically, deconvolution analysis should recover the correct half-life, production rate, frequency, amplitude, mass, and duration of pulsatile hormone secretion, and it should accurately estimate concurrent basal secretion, if present. Finally, multiple pulse generators provide an interesting simulation model for testing random burst concordance, evaluating how the surgelike release of a hormone can be accomplished, and assessing the interactions among several control systems. Lastly, special problems remain in simulating neuroendocrine pulsatility, namely, the impact of multiple binding proteins (see Table 1, p. 392 in this volume), the effects of strong and/or correlated circadian variations in burst frequency or amplitude or basal secretion, the development of improved statements of error and experimental uncertainty in the data, and the description of various modes of basal secretion.

Activity Cycles↗
PubMed2001

In vivo-in vitro study of biodegradable methadone delivery systems.

Three one-week controlled-release methadone formulations: polylactic acid microspheres (F-PLA) and poly(lactide-co-glycolide) microspheres (F-PLGA) with 24 and 30% methadone content, respectively, and an implant of 50:50 poly(lactide-co-glycolide): methadone, were evaluated in vitro and in vivo. The implant released the total amount of methadone in vitro while microsphere formulations released the methadone incompletely, 63% from F-PLA and 85% from F-PLGA in a week. Methadone release in vivo was estimated by deconvolution, F-PLGA giving a bioavailability >99% (methadone was totally released in 48h), while the estimated bioavailability of F-PLA was lower than expected. The bioavailability of the implant by deconvolution was around 60%, but absence of methadone in the implant indicated its complete release. These differences are due to an increase in methadone clearance after 72 h of the in vivo experimental period had passed, disturbing a good in vivo-in vitro correlation. A linear correlation between in vitro methadone release and in vivo release calculated from the amount of drug remaining within the implant, was found until the drug was completely released.

Animals↗