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PubMed2006

Validated GC-MS analysis for the determination of residual fentanyl in applied Durogesic reservoir and Durogesic D-Trans matrix transdermal fentanyl patches.

The method development and validation characteristics are described of a simple gas chromatographic-mass spectrometric (GC-MS) analytical procedure to determine residual fentanyl in used Durogesic reservoir patches and Durogesic D-Trans matrix technology based systems to estimate the actual rate of transdermal fentanyl delivered in individual patients. The sample preparation protocol constituting a saline based extraction of sets of new patches of each nominal dose available, resulted in fentanyl extraction recoveries to increase steadily as a function of increasing extraction time. For the reservoir type transdermal therapeutic system (TTS), fentanyl extraction efficiencies at equilibrium (16 h) ranged from approximately 60% (100-microg/h TTS) to 95% (25-microg/h TTS), whereas for the matrix type system considerable lower recoveries were demonstrated for the highest nominal dose rates (35%-52%), while reaching 90% for the 25-microg/h system. For the latter type of fentanyl TTS, an optimized methanol based extraction protocol yielded virtually quantitative fentanyl recoveries for each matrix patch nominal dose level at substantially shorter extraction periods (15 min). The GC-MS analytical method using selected ion monitoring (SIM) and deuterated fentanyl as internal standard was shown to be adequately selective with regard to the presence of other compounds in the Durogesic patches. It was further demonstrated that the developed analytical protocols provided highly reproducible and accurate estimates of the initial fentanyl content of each patch type at all available nominal doses, with coefficients of variation and relative errors generally below 10%. These advantageous assay validation characteristics can be further transposed to the application of residual fentanyl level estimates in used patches, provided that with each batch of samples also a set of new TTSs with equal dose is assayed to perfectly mimic extraction phenomena. Finally, the presented GC-MS analytical protocol was successfully applied for the determination of residual fentanyl in a subset of 57 reservoir type patches obtained from four palliative patients.

Administration, Cutaneous↗
PubMed2006

Improvement of the inverse-gated-decoupling sequence for a faster quantitative analysis of various samples by 13C NMR spectroscopy.

The inverse-gated-decoupling sequence enables quantitative (1)H decoupled (13)C spectra to be obtained. We modified this sequence so as to obtain the same result in less time for molecules containing carbons with various relaxation properties. For that, we determined the optimal (13)C longitudinal-magnetization initial value for a faster relaxation while (1)H decoupler is stopped. This value can be calculated precisely via the nuclear Overhauser effects, the longitudinal relaxation times, together with the determination of the relaxation rate constants of carbons while (1)H are out of equilibrium. A supplementary delay of (1)H decoupling and/or a series of selective pulses applied at the beginning of the recovery delay allow an acceleration of (13)C longitudinal relaxation. We applied this method to the molecule of vanillin. The simultaneous quantification of all carbons was carried out with a recovery delay divided by two compared to the usual sequence.

Benzaldehydes↗
PubMed2001

Solubility and moisture sorption isotherms of whey-protein-based edible films as influenced by lipid and plasticizer incorporation.

Plasticized whey-protein and whey-protein emulsion films were produced using sorbitol and glycerol as plasticizers and butterfat and candelilla wax as lipids. Protein, plasticizer, and lipid ratios were optimized to obtain acceptable free-standing flexible films. Water solubility (20 degrees C, 24 h) and moisture sorption isotherms (0.18-0.90 a(w), 25 degrees C) of the films were determined. The experimental moisture sorption isotherm values were fitted using the Guggenheim-Anderson-DeBoer (GAB) model. Solubility and equilibrium moisture contents (EMC) of the films were influenced by plasticizer and lipid incorporation. EMCs of all films increased rapidly at a(w) > or = 0.65. Incorporation of lipids reduced solubilities and EMCs of sorbitol- and glycerol-plasticized films. The effects of plasticizer and lipid type on GAB constants were also determined.

Adsorption↗
PubMed2003

Stochastic annealing.

We show how to simulate a system in thermal equilibrium when the energy cannot be evaluated exactly: the error distribution needs to be symmetric, but it does not need to be known. We also solve the Ceperley-Dewing version of this problem, where the error distribution is taken to be fully known. These underlying ideas give an effective optimization strategy for problems where the evaluation of each design can be sampled only statistically, including an application to protein folding.

Models, Statistical↗
PubMed2002

Bioreactor studies of native and tissue engineered cartilage.

Functional tissue engineering of cartilage involves the use of bioreactors designed to provide a controlled in vitro environment that embodies some of the biochemical and physical signals known to regulate chondrogenesis. Hydrodynamic conditions can affect in vitro tissue formation in at least two ways: by direct effects of hydrodynamic forces on cell morphology and function, and by indirect flow-induced changes in mass transfer of nutrients and metabolites. In the present work, we discuss the effects of three different in vitro environments: static flasks (tissues fixed in place, static medium), mixed flasks (tissues fixed in place, unidirectional turbulent flow) and rotating bioreactors (tissues dynamically suspended in laminar flow) on engineered cartilage constructs and native cartilage explants. As compared to static and mixed flasks, dynamic laminar flow in rotating bioreactors resulted in the most rapid tissue growth and the highest final fractions of glycosaminoglycans and total collagen in both tissues. Mechanical properties (equilibrium modulus, dynamic stiffness, hydraulic permeability) of engineered constructs and explanted cartilage correlated with the wet weight fractions of glycosaminoglycans and collagen. Current research needs in the area of cartilage tissue engineering include the utilization of additional physiologically relevant regulatory signals, and the development of predictive mathematical models that enable optimization of the conditions and duration of tissue culture.

Animals↗
PubMed1981

Fc gamma-receptor activity of isolated human placental syncytiotrophoblast plasma membrane.

Fc gamma-receptor activity of isolated human placental syncytiotrophoblast microvillous plasma membrane (StMPM) vesicle preparations has been determined in an immunoradiometric assay using Sepharose-immobilized protein A to separate free 125I-labelled human IgG from membrane-bound 125I-IgG. This receptor assay has been optimalized in terms of buffer pH and molarity, and used to demonstrate that prior 60 min washing of isolated membranes in 3 M KCl to remove extrinsic membrane-bound protein substantially increases the membrane-binding capacity for IgG. Inhibition studies have determined the syncytiotrophoblast Fc gamma-receptor equilibrium constant for association (Ka) as 4.0 x 10(7) M-1 at 37 degrees and the number of available Fc gamma-receptor sites as 1.5 x 10(14) per mg membrane protein.

Antibody Specificity↗
PubMed2001

[How and why does the metabolic equilibrium of the mother affect the embryo?].

Prevalence of congenital malformations in infants born to women with diabetes mellitus remains high (between 6 and 10%), which is between 3 and 5 times higher than in the general population. Major congenital anomalies are 7 to 10 times more frequent in infants born to diabetics. Normal pregnancy is a state of metabolic stress that requires a high degree of maternal physiological adaptation to help optimize fetal growth. Decreased insulin sensitivity throughout pregnancy with reactional hyperinsulinism helps metabolic efficiency. Changes are observed in glucose, lipid and protein metabolism during pregnancy with a rapid switch from anabolism to catabolism. Diabetic women have absolute or relative insulin deficiency and display abnormalities in carbohydrate, lipid and protein metabolism. These abnormalities can adversely affect embryo growth and explain the high prevalence of spontaneous abortions and congenital malformations. There is a multifactorial origin, of which hyperglycemia in early embryo development is the most important. Hyperglycemia-induced malformations are mediated by sorbital accumulation, arachidonic acid and myoinositol deficiencies and high concentrations of beta-hydroxybutyrate. Accumulation of free oxygen radicals by increased formation and decreased clearance may serve as metabolic common denominators for teratogenic processes. Other factors such as zinc deficiency, the presence of somatomedin inhibitors and released TNF alpha are candidates. Human clinical studies are not consistent with a genetic predisposition to diabetes-related malformations. Progress is needed in pre-conception care of diabetes and blood glucose must be strictly controlled during early pregnancy.

Congenital Abnormalities↗
PubMed2005

Influence of saline flushing on the optimal temporal window for CT of the liver using a time-density analysis.

PURPOSE: To evaluate the influence of saline flushing on the optimal temporal window for hepatic CT by analyzing time-density curves. MATERIALS AND METHODS: Eighty-eight patients were randomly assigned to three groups to receive 100 mL of contrast material alone (n=32; group A), 100 mL of contrast material with 30 mL of saline flush (n=26; group B), and 85 mL of contrast material with 30 mL of saline flush (n=30; group C). In each group, the time-density curves of the liver, portal vein, and aorta were obtained. The degree of mean peak enhancement (PE), mean time to peak (TTP), time to onset of the equilibrium phase (Teq), and time between aortic peak enhancemant and onset of equilibrium phase (Ta-eq) were analyzed. RESULTS: The PE of liver and portal vein for group B were significantly greater than those of group A (p<0.05). There was no significant difference in PE of liver, portal vein, and aorta, and TTP of liver and aorta between group A and group C. However, Teq and Ta-eq for group C were significantly shorter than those of group A and group B (p<0.0001). CONCLUSION: Using a saline flush was able to reduce iodine dose, however, when using the decreased contrast material with saline flush, the duration of the optimal temporal window for hepatic CT was shortened.

Adult↗
PubMed1998

Modeling brewers' yeast flocculation

Flocculation of yeast cells occurs during the fermentation of beer. Partway through the fermentation the cells become flocculent and start to form flocs. If the environmental conditions, such as medium composition and fluid velocities in the tank, are optimal, the flocs will grow in size large enough to settle. After settling of the main part of the yeast the green beer is left, containing only a small amount of yeast necessary for rest conversions during the next process step, the lagering. The physical process of flocculation is a dynamic equilibrium of floc formation and floc breakup resulting in a bimodal size distribution containing single cells and flocs. The floc size distribution and the single cell amount were measured under the different conditions that occur during full scale fermentation. Influences on flocculation such as floc strength, specific power input, and total number of yeast cells in suspension were studied. A flocculation model was developed, and the measured data used for validation. Yeast floc formation can be described with the collision theory assuming a constant collision efficiency. The breakup of flocs appears to occur mainly via two mechanisms, the splitting of flocs and the erosion of yeast cells from the floc surface. The splitting rate determines the average floc size and the erosion rate determines the number of single cells. Regarding the size of the flocs with respect to the scale of turbulence, only the viscous subrange needs to be considered. With the model, the floc size distribution and the number of single cells can be predicted at a certain point during the fermentation. For this, the bond strength between the cells, the fractal dimension of the yeast, the specific power input in the tank and the number of yeast cells that are in suspension in the tank have to be known. Copyright 1998 John Wiley & Sons, Inc.

Journal Article↗
PubMed2003

Contribution of lateral substituents in symmetrical and non-symmetrical heptane-bisammonio compounds to the allosteric stabilization of N-methylscopolamine binding to muscarinic M2 receptors.

Allosteric modulators are able to enhance or decrease the equilibrium binding of orthosteric agonists or antagonists. The treatment of Alzheimer's disease and the organophosphorus poisoning can take advantage of the enhancement of the ligand binding. Prerequisite is the formation of ternary complexes consisting of the receptor protein, the orthosteric ligand, e. g. N-methylscopolamine (NMS), and the alloster optimized for the corresponding orthoster. In this study, heptane-bisammonio compounds were optimized with regard to the orthosteric antagonist NMS. Comparing pairs of compounds characterized by phthalimides, cyclohexanedicarbonic acid imide and succinimides at both ends or a phthalimide at one end and either of the three imides at the other end stressed the importance of an aromatic moiety at both ends of the heptane-bisammonio chain.

Animals↗
PubMed2000

Soft- and hard-modeling approaches for the determination of stability constants of metal-peptide systems by voltammetry.

The Zn(2+)-glutathione system is studied as a model for metal-peptide systems where some critical factors must be considered when using voltammetric techniques for the determination of stability constants. These factors are the presence of side reactions (in this case, both the protonation of glutathione and the hydrolysis of Zn(2+)), the association-dissociation rates of the complexes compared with the time scales of the measurements (which makes the complexes electrochemically labile or inert), and the electron transfer kinetics on the electrode surface (which makes the metal ion reduction reversible or irreversible). For the study of these factors, three data treatment approaches have been applied: (i) the electrochemical hard-modeling approach (modelization of both chemical equilibrium and electrochemical processes), (ii) a chemical hard-modeling approach (modelization of chemical equilibria only, based on the least-squares curve-fitting program SQUAD), and (iii) a previously developed model-free soft-modeling approach based on multivariate curve resolution with a constrained alternating least-squares optimization. By analyzing differential pulse polarographic data obtained under different experimental conditions, the influence of the mentioned factors on every approach is discussed and, if possible, the corresponding stability constants are computed. The results of this study showed the potential usefulness of voltammetry in combination with hard- and soft-modeling data analysis for the study of peptide complexation equilibria of metal ions such as Zn which have neither relevant spectroscopic properties nor proper isotopes for NMR measurements.

Drug Stability↗
PubMed1994

Capillary electrophoresis with chiral selectors: optimization of separation and determination of thermodynamic parameters for binding of tioconazole enantiomers to cyclodextrins.

A systematic approach is outlined for optimization of enantiomeric separations in free solution capillary electrophoresis using chiral mobile-phase additives. Maximum electrophoretic mobility difference between the enantiomers occurs when the concentration of free selector is equal to the reciprocal of the average binding constant. General equations and data analysis methods are presented to relate mobilities to equilibrium constants in simple and competitive binding equilibria and used to determine thermodynamic parameters for host-guest complexation of tioconazole enantiomers with a range of cyclodextrin selectors. Selectivities are found to be in the reverse order of binding constants in the series dimethyl-beta-cyclodextrin (K1 = 6.9 x 10(3) M-1, alpha = 1.10) to hydroxypropyl-beta-cyclodextrin (K1 = 0.72 x 10(3) M-1, alpha = 1.29). For beta-cyclodextrin (K1 = 1.32 x 10(3)M-1, alpha = 1.20), delta H zero provides the dominant contribution to binding but delta delta H zero and T delta delta S zero terms give comparable contributions to the selectivity. Addition of alcohol does not affect the selectivity, but allows displacement of the optimum separation conditions to higher cyclodextrin concentration through either competitive binding (with cyclohexanol) or preferential solvation of reactants (with methanol).

Antifungal Agents↗
PubMed1993

Increase in left ventricular ejection rate during recovery from exercise in patients with myocardial infarction.

Changes in left ventricular (LV) ejection rate were evaluated during supine bicycle exercise and recovery in 12 patients with anterior myocardial infarction. Pulmonary artery wedge pressure (34 +/- 9 to 14 +/- 5 mm Hg) and plasma norepinephrine level decreased at 2 min recovery from peak exercise, whereas plasma lactate tended to increase. As a result, LV ejection rate reached the highest value at 2 min of recovery. Thus, both cardiac (optimal filling pressure) and peripheral factors (reduced vascular resistance) caused the increase in LV ejection rate at early recovery.

Acid-Base Equilibrium↗
PubMed1983

Automated rate-immunonephelometric determination of serum prealbumin (transthyretin).

We describe an automated determination of serum prealbumin (transthyretin), based on the maximum rate of light scatter of an antigen-antibody precipitate. Optimal dilutions of antibody reagent and of 100-microL serum samples are given. Within- and between-assay CVs are less than 5%. Results by this method are nearly identical with those obtained by a radial-immunodiffusion technique. Measuring the rate of light scatter provides a considerably faster test than equilibrium scatter, electrophoretic, or radial-immunodiffusion methods. Treatment before analysis to clear lipemic sera obviates falsely high results.

Aged↗
PubMed1994

[Acid-base equilibrium and the brain].

In physiological conditions, the regulation of acid-base balance in brain maintains a noteworthy stability of cerebral pH. During systemic metabolic acid-base imbalances cerebral pH is well controlled as the blood/brain barrier is slowly and poorly permeable to electrolytes (HCO3- and H+). Cerebral pH is regulated by a modulation of the respiratory drive, triggered by the early alterations of interstitial fluid pH, close to medullary chemoreceptors. As blood/brain barrier is highly permeable to Co2, CSF pH is corrected in a few hours, even in case of severe metabolic acidosis and alkalosis. Conversely, during ventilatory acidosis and alkalosis the cerebral pH varies in the same direction and in the same range than blood pH. Therefore, the brain is better protected against metabolic than ventilatory acid-base imbalances. Ventilatory acidosis and alkalosis are able to impair cerebral blood flow and brain activity through interstitial pH alterations. During respiratory acidosis, [HCO3-] increases in extracellular fluids to control cerebral pH by two main ways: a carbonic anhydrase activation at the blood/brain and blood/CSF barriers level and an increase in chloride shift in glial cells (HCO3- exchanged for Cl-). During respiratory alkalosis, [HCO3-] decreases in extracellular fluids by the opposite changes in HCO3- transport and by an increase in lactic acid synthesis by cerebral cells. The treatment of metabolic acidosis with bicarbonates may induce a cerebral acidosis and worsen a cerebral oedema during ketoacidosis. Moderate hypocapnia carried out to treat intracranial hypertension is mainly effective when cerebral blood flow is high and vascular CO2 reactivity maintained. Hypocapnia may restore an altered cerebral blood flow autoregulation. Instrumental hypocapnia requires a control of cerebral perfusion pressure and cerebral arteriovenous difference for oxygen, to select patients for whom this kind of treatment may be of benefit, to choose the optimal level of hypocapnia and to avoid any deleterious effect. If hypocapnia is maintained over several days, an adaptation of CSF pH may limit the therapeutic effect on the cerebral blood flow and the intracranial pressure.

Acid-Base Equilibrium↗
PubMed1986

Interleukin-2 monoclonal antibody affinity adsorption. The critical role of binding kinetics for optimal immunoadsorption.

With the ready availability of monoclonal antibodies reactive with an extensive spectrum of antigens, immunoaffinity adsorption has become more widely applicable for protein purification. However, given several monoclonal antibodies reactive with the same antigen, most investigators have found that only a few antibodies are useful for solid-phase immunoaffinity antigen purification. Accordingly, in order to determine the parameters of monoclonal antibody-antigen binding most important for effective immunoaffinity adsorption, equilibrium and kinetic binding experiments were performed using radiolabeled interleukin-2 (IL-2) as antigen and four different IL-2-reactive monoclonal antibodies. The antibodies were found to differ primarily with respect to their kinetic binding characteristics; at 37 degrees C IL-2 bound to two of these antibodies very rapidly, while it bound to the other two more slowly. When binding was performed at 4 degrees C, the equilibrium dissociation constants for all of the antibodies decreased due to a more marked prolongation of the dissociation rate than the association rate. However, at 4 degrees C the association rates of the two slow-reactive antibodies became retarded so markedly that efficient affinity adsorption did not occur. By comparison, for both of these antibodies, efficient removal of IL-2 could be obtained if adsorption was performed at 37 degrees C, provided the column flow rate was adjusted according to the IL-2 association rate. Kinetic considerations also dictated IL-2 adsorption to mixtures of two or more monoclonal antibodies: IL-2 immunoadsorption correlated with the association rates of the individual antibodies, rather than the equilibrium binding constants. These results indicate that the most important parameter for efficient affinity adsorption is the association rate constant. In addition, the results obtained indicate that monoclonal antibodies may differ markedly as regards their kinetic binding characteristics, and that all antibodies can serve as effective immunoadsorbents, provided their antigen binding characteristics are known.

Antibodies, Monoclonal↗
PubMed1993

Interleukin-3/erythropoietin fusion proteins: in vitro effects on hematopoietic cells.

Erythropoietin (Epo) acts synergistically with interleukin-3 (IL-3) to induce proliferation and differentiation of erythroid progenitors. This synergy occurs at IL-3 concentrations that have little or no effect alone. To determine whether optimal expansion of erythroid cells results when they are targeted by a molecule with both IL-3 and Epo activities, fusion proteins were generated and analyzed. Expression vectors were constructed in which the coding regions of human IL-3 and Epo cDNAs were joined by either a short (2 to 3 amino acids) or long (23 amino acids) linker sequence and expressed in Chinese hamster ovary (CHO) cells. Analysis of equilibrium binding properties of the IL-3 and Epo moieties revealed that in all fusion proteins each retained the ability to bind receptor. When IL-3 was connected to Epo by a short linker, the binding affinity of the IL-3 moiety was lower. In vitro proliferative activity of each moiety was observed on cell lines responsive to IL-3, Epo or a combination of the two cytokines. Fusion of IL-3 to Epo through its amino terminus was found to result in partial loss of its function. All the fusion proteins were biologically active on human bone marrow. When IL-3 was located at the amino domain of the protein, induction of erythroid colonies was similar to that of a mixture of IL-3 and Epo. These results indicate that biological integrity of both IL-3 and Epo can be maintained when these cytokines are fused, but that enhancement of erythropoiesis over that observed with a mixture of the two cytokines cannot be achieved by their fusion alone. Other requirements such as the coexpression of the IL-3 and Epo receptors and the sharing of a receptor subunit are likely to be needed for an optimal cell response to the fusion growth factors.

Animals↗
PubMed1998

Discounting costs and effects: a reconsideration.

Using a simple societal utility function--giving equal weight to current and future generations-it is concluded that costs need to be discounted on the basis of the expected increase in income and the marginal utility of consumption, and that effects need to be discounted on the basis of the expected increase in health and the marginal utility of health. It is derived that both rates need to be equal when assuming a kind of perfect market, where growth rates are determined by the societal utility function. It is argued that this is an extremely heroic assumption and that different discount rates may be needed. Additionally, the traditional 'inconsistency arguments' of Weinstein and Stason and of Keeler and Cretin are reconsidered. Within the context presented earlier, the first inconsistency only emerges when a growth equilibrium is assumed, reinforcing the arguments put forward before. The Keeler and Cretin paradox is reconsidered by showing that absolutely no paradox emerges when programs are not supposed to stop after a year but are supposed to continue indefinitely. The conclusion is drawn that non-believers in market mechanisms assuring an optimal social policy, need to reconsider the use of their discount rates.

Cost-Benefit Analysis↗