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At least 379 records · Page 21Linked to original sources
PubMed2003

[Nonlinear regression analysis of cardiac enzyme kinetic model with modified simplex method and DUD method using SAS software].

OBJECTIVE: To compare the efficacy of modified simplex method and DUD method using SAS software for nonlinear regression analysis of cardiac enzyme kinetic model. METHOD: By using cardiac enzyme kinetic one-compartment mathematical model, nonlinear regression results obtained from DUD methods using SAS software and modified simplex method were compared with the same starting values to fit the creatine kinase curves in 22 patients with acute myocardial infarction. RESULTS: The parameters calculated by DUD method and modified simplex method were the same in 4 cases, and smaller least square was resulted from DUD method in 4 cases. In the other 14 cases, modified simplex method yielded smaller least square. The mean value of the least square calculated by modified simplex method was less than that by DUD method (867 747 vs 6 712 989, P=0.013). CONCLUSION: Modified simplex method appears to be more adequate than DUD method in estimating circulatory parameters of the one-compartment model.

Humans↗
PubMed1985

Bactericidal effects of amoxycillin/clavulanic acid and ticarcillin/clavulanic acid in in-vitro kinetic models.

The bactericidal effects of amoxycillin and ticarcillin in the presence of clavulanic acid against beta-lactamase-producing bacteria were investigated in in-vitro kinetic models. Amoxycillin/clavulanic acid was rapidly bactericidal as a simulated intravenous 1.2 g bolus dose, against a strain of Klebsiella pneumoniae highly resistant to amoxycillin. Similarly, ticarcillin/clavulanic acid at concentrations similar to those achieved with a 30 min iv infusion of ticarcillin/clavulanic acid (5.0 g/200 mg) produced bactericidal effects against a ticarcillin-resistant strain of Pseudomonas aeruginosa. Addition of gentamicin to the system resulted in a further enhancement of activity.

Amoxicillin↗
PubMed2003

Kinetic model for the sonochemical degradation of monocyclic aromatic compounds in aqueous solution: new insights.

The kinetic model of De Visscher et al. [J. Phys. Chem. 100 (1996) 11636] for the sonochemical degradation of apolar monocyclic aromatic compounds in aqueous solution is based on a large number of assumptions, some of which have never been stated explicitly. An example is a homogeneous temperature of cavitation. The present study focuses on those "hidden assumptions", and reveals that some of them are not realistic. It is shown that an entirely different set of assumptions leads to essentially the same mathematical formulation of the kinetics. The old and new version of the model can be considered as limiting cases which envelope the real conditions of ultrasonic cavitation chemistry. However, the new model does not lead to the inconsistencies experienced with the old model.

Journal Article↗
PubMed1991

Kinetic modeling of in vivo--nuclear magnetic resonance spectroscopy data: 5-fluorouracil in liver and liver tumors.

Kinetic modeling has been applied to the time course of the nuclear magnetic resonance signal intensities of 5-fluorouracil and the sum of its catabolites, alpha-fluoro-beta-ureido propanoic acid and alpha-fluoro-beta-alanine, as monitored in liver tumors of seven patients with cancer after brief intraarterial infusion of 5-fluorouracil. Because these data represent only relative tissue concentrations, only ratios of clearance and volume parameters can be estimated (e.g., clearance/central volume of distribution or central volume of distribution/steady-state volume of distribution). On the other hand, parameters that do not refer to volumes, such as half-lives or maximal velocity of metabolic conversion of a nonlinear model, can be estimated in absolute terms. A nonlinear three-compartment model gave satisfactory fits with all of the individual data sets. Kinetics of 5-fluorouracil and catabolites were similar in five patients with metastases of colorectal adenocarcinomas but differed from those of two patients with cholangiocarcinoma and metastases of an anaplastic carcinoma of unknown origin, respectively.

Adult↗
PubMed1996

One-compartment urea kinetic modeling is not acceptable for quantifying the adequacy of hemodialysis: comparison of a one-compartment model with a two-compartment model.

We can quantify the adequacy of hemodialysis (HD) as the dialysis dose using urea kinetic modeling (UKM). Though the one-compartment model (1CM) has frequently been applied, there are some studies which have successfully applied the two-compartment model (2CM) including urea rebound. To clarify whether 1CM or 2CM is more acceptable, we analyzed 100 patients using UKM, applying each model. The dialysis dose was defined as the logarithm of pre-/post-HD urea volume in the body. In about half the patients analyzed, 1CM estimation of the dialysis dose exceeded 2CM estimation by more than 10%, and the 1CM was not considered to be acceptable.

Adult↗
PubMed1996

A kinetic model for cardiac PET with [1-carbon-11]-acetate.

UNLABELLED: Carbon-11-labeled acetate is a unique tracer for noninvasive assessment of myocardial oxidative metabolism with PET. Because adequate kinetic models have been missing, data evaluation in the past was performed mostly with phenomenological approaches such as mono- or biexponential fitting which cannot account for the influence of finite input duration and blood volume encountered in noninvasive PET investigations. METHODS: To investigate to what extent the current data evaluation schemes are justified, we developed a comprehensive model of [1-11C]-acetate kinetics in the myocardium which incorporates five tissue compartments: free acetate, activated acetate, CO2 precursors, amino acids and CO2. We derived the analytical solution of the model equations which is used for simulations and data fitting. RESULTS: The five-compartment model can reproduce in detail known experimental data. The resulting values of the eight model parameters compare favorably with existing biochemical facts. We have established the relation between parameters of the detailed model and one- and two-compartment models used for the evaluation of PET investigations. CONCLUSION: The kinetics of [1-11C]-acetate are adequately described by a five-compartment model. One- and two-compartment models are sufficient for simultaneous quantitative assessment of myocardial oxidative metabolism and perfusion with [1-11C]-acetate and PET.

Acetates↗
PubMed1977

[Influence of pH on the steady state kinetics of electron transfer through the cytochrome chain of submitochondrial particles. Kinetic model for regulating the activity of carriers by the local concentration of hydrogen ions in the membrane].

The kinetic parameters of the submitochondrial particles cytochrome chain obtained from steady-state kinetics were studied for pH dependence. The life-times of the activated states (tau) for cytochrome pairs b leads to c1 and a leads to a3 are shown to bear dissimilar dependence on pH of the medium, while for cytochrome pairs c1 leads to c and c leads to a they display practically no pH dependence at all. The rate constants of the non-activated state (alphai-kiCo) decreased for the pair b leads to c1 and increased for a leads to a3 with the increase of pH from 6.5 to 8.5. The apparent pK values obtained therefrom were 7.2 and 8.9, respectively. A kinetic model is proposed suggesting that local pH in the mitochondrial membrane, dependent on the rate of electron transfer, may be a controlling factor for the ratio of activated and non-activated carrier states. The model is in good consistence with the experimental dependences of k'i on V and the pH dependences of alpha2 for b leads to c1 and a leads to a3. It also gives a qualitative prediction for the pH dependences of the ordinate intercepts of the straight lines in l/(k'i--alphai) vs. l/V plots. The rate constants for the diffusion of hydrogen and hydroxyl ions in the membrane are estimated on the basis of our kinetic data to be 10(4)--10(5) s-1 and 10(2)--10(3) s-i, respectively.

Cytochromes↗
PubMed2001

Kinetic model and optimization of 2,4-D degradation by anodic Fenton treatment.

Anodic Fenton treatment (AFT) is a new technology derived from chemical Fenton treatment. It has several advantages as compared with classic Fenton treatment and electrochemical Fenton treatment. On the basis of assumptions about a second-order reaction between pesticides and hydroxyl radicals and about AFT technology, a new kinetic model was developed to accurately describe the degradation kinetics of 2,4-D and to quantitatively investigate the effect of operating conditions. 2,4-D (2,4-dichlorophenoxyacetic acid) was employed as a probe in this study to investigate the AFT system. It was found that an increased delivery rate of Fenton reagent increased the degradation rate of 2,4-D, but the efficiency was decreased. The effects of the H2O2:Fe2+ ratio, the temperature, the initial concentration of 2,4-D, and the presence of other organic compounds have also been investigated. Quantitative correlations have been established that allow the use of this technology as a controlled Fenton reaction to determine the reaction rate constants of other compounds with hydroxyl radicals easily and accurately.

2,4-Dichlorophenoxyacetic Acid↗
PubMed2002

Differential fraction-based kinetic model for simulating hydrodesulfurization process of petroleum fraction.

A differential fraction-based kinetic model (DFKM) was proposed to simulate the reaction process in view of the extremely large number of compounds in the petroleum fraction. The results of the simulation experiment on the hydrodesulfurization (HDS) process demonstrated that without considering the exact compounds, DFKM can depict the reaction processes not only of the whole petroleum fraction but of any narrow cut we are interested in. Apparently, this kind of ability, which can be considered as the 'zoom in/out' function, is very useful for the further study on the processing techniques of the petroleum fraction. In the meantime, different methods for obtaining the functions needed in DFKM were investigated and satisfactory results were presented.

Journal Article↗
PubMed1996

Accurate kinetic modeling of alkaline phosphatase in the Escherichia coli periplasm: implications for enzyme properties and substrate diffusion.

Alkaline phosphatase in the periplasm of Escherichia coli presents many of the complex factors that may influence enzymes in vivo. These include an environment that contains a high enzyme concentration, is densely populated with other macromolecules, and is separated from other compartments by a partial diffusion barrier. A previous study provided a partial description of this situation and developed a model that utilized kinetic behavior to estimate the permeability of the outer membrane [Martinez, M. B., et al., (1992) Biochemistry 31, 11500]. This study extends that description to provide a complete model for the enzyme at all substrate levels. Some of the parameters needed for complete modeling include the following: outer membrane permeability to the substrate and product, catalytic efficiency of the enzyme, number of enzymes per cell, and effects of the reaction product (an inhibitor) on the enzyme. The theoretical model fit the data quite well over a wide range of values for each of these parameters. The best fit of theory with experimental data required that the rate constant for product escape from the periplasm was 4-fold greater than that for substrate entry. This correlated with the relative sizes of the substrate and product. The excellent fit of theory and results suggested that alkaline phosphatase and its substrate were unaffected by the solution conditions in the periplasm. That is, the catalytic parameters (kcat and KM), determined for the enzyme in dilute solution, appeared to be unchanged by the conditions in the periplasm. The major factor that altered the kinetic behavior was the combined effect of the permeability barrier and the dense population of enzyme molecules in the periplasm. Given the large impact of these parameters on reaction properties, the excellent fit of theory and results was striking. Overall, this study demonstrated that enzyme action in the complex biological environment can be accurately modeled, if all factors that influence enzyme behavior are known.

Alkaline Phosphatase↗
PubMed2007

A multi-step kinetic model for substrate assimilation and bacterial growth: application to benzene biodegradation.

A multi-step kinetic model based on the concept of synthesizing unit (SU) was developed for describing benzene biodegradation in Pseudomonas putida F1. The model herein presented considered substrate arrival rates to the SU rather than concentrations, and provided a reasonable good fit of the dynamics of both catechol and biomass concentrations experimentally determined. It was based on very general assumptions and could be applied to any process accumulating metabolic intermediates. Conventional growth models considering a single step can be regarded as a particular case of this multi-step model. Despite the merits of this model, its applicability strongly depends on the knowledge of the complex induction-repression and inhibition mechanisms governing the different catabolic steps of the degradation pathway, which in most cases are difficult to elucidate experimentally and/or to model mathematically. In this particular case repression of benzene oxidation by catechol and self-inhibition of catechol transformation were experimentally confirmed and considered in the simulation, resulting in a good fit (relative average error of 6%) of the experimental data.

Bacterial Proteins↗
PubMedDate not supplied

Assessment of efficiency using on-line urea kinetic modeling in hemodiafiltration.

Urea kinetics has recently been re-evaluated using an on-line urea monitoring system applied to hemodiafiltration. This system allows evaluation of different components possibly responsible for the gap between prescribed and delivered dose of dialysis, such as access and cardiopulmonary recirculation, and altered dialysis parameters, such as blood flow and dialysate flow rates. Furthermore, the system allows prediction of postdialysis rebound urea concentrations. The aim of the present study was to apply the on-line urea monitoring system to assess the dialytic efficiency of double chamber hemodiafiltration in different conditions of blood-dialysate flow rates, reinfusion volumes, and dialyzer configurations (high + low flux membranes or high + high flux membranes) in 10 patients (age, 60 +/- 9 years; dry weight, 65 +/- 5 kg). There was a significantly lower Kt/V (K, dialyzer clearance; t, dialysis time; V, urea distribution volume) at equilibrium with the high + high vs high + low flux configuration, possibly because of a higher tendency toward urea compartmentalization. This difference was evident when reinfusion was performed post dilution. These studies support the concept that small molecular weight uremic toxins may be more efficiently removed using low flux membranes in a modified form of hemodiafiltration.

Blood Flow Velocity↗
PubMedDate not supplied

Pharmacokinetics of urea: development of a kinetic model for correlating dietary nitrogen intake and urea metabolism in chronic renal failure.

A simple urea pharmacokinetic model is developed to define the multiple correlations among dietary nitrogen intake, urea generation rate, and serum urea nitrogen. Model-based patient data are simulated during and between dialysis for serum urea nitrogen. Application of the kinetic model is demonstrated by retrospective fitting of serum urea nitrogen to the simultaneous equations which pertain to the model. The pharmacokinetic parameters obtained through the computer fitting can be integrated according to the mass balance equation to yield a quantitative solution to achieving the regulation of protein nitrogen intake. The kinetic approach is potentially advantageous over the conventional nitrogen balance method by virtue of its simplicity. Further validation of the pharmacokinetic model is required before its clinical application.

Blood Urea Nitrogen↗
PubMed2004

A tracer kinetic model for 18F-FHBG for quantitating herpes simplex virus type 1 thymidine kinase reporter gene expression in living animals using PET.

UNLABELLED: Reporter probe 9-(4-18F-fluoro-3-[hydroxymethyl]butyl)guanine (18F-FHBG) and reporter gene mutant herpes simplex virus type 1 thymidine kinase (HSV1-sr39tk) have been used for imaging reporter gene expression with PET. Current methods for quantitating the images using the percentage injected dose per gram of tissue do not distinguish between the effects of probe transport and subsequent phosphorylation. We therefore investigated tracer kinetic models for 18F-FHBG dynamic microPET data and noninvasive methods for determining blood time-activity curves in an adenoviral gene delivery model in mice. METHODS: 18F-FHBG (approximately 7.4 MBq [approximately 200 microCi]) was injected into 4 mice; 18F-FHBG concentrations in plasma and whole blood were measured from mouse heart left ventricle (LV) direct sampling. Replication-incompetent adenovirus (0-2 x 10(9) plaque-forming units) with the E1 region deleted (n = 8) or replaced by HSV1-sr39tk (n = 18) was tail-vein injected into mice. Mice were dynamically scanned using microPET (approximately 7.4 MBq [approximately 200 microCi] 18F-FHBG) over 1 h; regions of interest were drawn on images of the heart and liver. Serial whole blood 18F-FHBG concentrations were measured in 6 of the mice by LV sampling, and 1 least-squares ratio of the heart image to the LV time-activity curve was calculated for all 6 mice. For 2 control mice and 9 mice expressing HSV1-sr39tk, heart image (input function) and liver image time-activity curves (tissue curves) were fit to 2- and 3-compartment models using Levenberg-Marquardt nonlinear regression. The models were compared using an F statistic. HSV1-sr39TK enzyme activity was determined from liver samples and compared with model parameter estimates. For another 3 control mice and 6 HSV1-sr39TK-positive mice, the model-predicted relative percentage of metabolites was compared with high-performance liquid chromatography analysis. RESULTS: The ratio of 18F-FHBG in plasma to whole blood was 0.84 +/- 0.05 (mean +/- SE) by 30 s after injection. The least-squares ratio of the heart image time-activity curve to the LV time-activity curve was 0.83 +/- 0.02, consistent with the recovery coefficient for the partial-volume effect (0.81) based on independent measures of heart geometry. A 3-compartment model best described 18F-FHBG kinetics in mice expressing HSV1-sr39tk in the liver; a 2-compartment model best described the kinetics in control mice. The 3-compartment model parameter, k3, correlated well with the HSV1-sr39TK enzyme activity (r2 = 0.88). CONCLUSION: 18F-FHBG equilibrates rapidly between plasma and whole blood in mice. Heart image time-activity curves corrected for partial-volume effects well approximate LV time-activity curves and can be used as input functions for 2- and 3-compartment models. The model parameter k3 from the 3-compartment model can be used as a noninvasive estimate for HSV1-sr39TK reporter protein activity and can predict the relative percentage of metabolites.

Animals↗
PubMed2004

Kinetic modelling of continuous submerged fermentation of cheese whey for single cell protein production.

A mathematical model describing the kinetics of continuous production of single cell protein from cheese whey using Kluyveromyces fragilis was developed from the basic principles of mass balance. The model takes into account the substrate utilization for growth and maintenance and the effect of substrate concentration and cell death rate on the net cell growth and substrate utilization during the fermentation process. A lactose concentration below 1.91 g/L limited growth of yeast cells whereas a lactose concentration above 75 g/L inhibited the growth of the yeast. The model was tested using experimental data obtained from a continuous system operated at various retention times (12, 18 and 24 h), mixing speeds (200, 400 and 600 rpm) and air flow rates (1 and 3 vvm). The model was capable of predicting the effluent cell and substrate concentrations with R2 ranging from 0.95 to 0.99. The viable cell mass and lactose consumption ranged from 1.3 to 34.3 g/L and from 74.31% to 99.02%, respectively. A cell yield of 0.74 g cell/g lactose (close to the stoichiometric value of 0.79 g cell/g lactose) was achieved at the 12 h retention time-3 vvm air flow rate-600 rpm mixing speed combination. The total biomass output (viable and dead cells) at this combination was 37 g/L.

Biomass↗
PubMed2026

Kinetic model of a determinate legume root nodule reveals plant metabolic characteristics for more efficient nitrogen fixation symbiosis.

While nitrogen fertilizers are widely used in agricultural production, their application incurs significant environmental and energetic costs. In contrast, some crops are less dependent on these fertilizers because they engage in symbioses with rhizobia, nitrogen-fixing bacteria that provide ammonium to the plant in exchange for carbon. However, the carbon cost associated with nitrogen fixation can negatively impact crop yields. Improving the efficiency of this metabolic process could alleviate this impact on crop productivity. Mathematical models can help us quantitatively explore metabolic behavior and identify potential targets for metabolic engineering. In this work, we developed a kinetic model of determinate root nodule metabolism, where this symbiotic exchange of carbon from the plant and nitrogen from the bacteria occurs. We used this model to evaluate how the predicted metabolic behavior differs between inefficient and efficient nodules, and to identify potential engineering targets for improving nitrogen fixation efficiency and rate. We show that the enzymes phosphoenolpyruvate carboxylase and pyruvate kinase have significant influence on the predicted rate and efficiency of nitrogen fixation, especially when their expression is varied in combination with oxidative Pentose Phosphate Pathway enzymes like glucose-6-phosphate dehydrogenase and 6-phosphogluconolactonase. The model predicts that pairing a 3-fold decrease in glucose-6-phosphate dehydrogenase activity along with either a 3-fold increase in phosphoenolpyruvate carboxylase activity or decrease in pyruvate kinase activity could increase nitrogen fixation rate by 8.82% while improving nitrogen fixation efficiency by 10.99%.

Enzyme kinetics↗
PubMed1990

A kinetic model for calcium distribution.

Models for the distribution of minerals in the body are of interest as they allow researchers to trace the effect of a dose on mineral levels in plasma, storage and other compartments. Limited models are available in the literature for tracing the distribution of a calcium dose through a short time period. We propose a more general kinetic model which includes both limited absorption through the gut and loss of calcium via excretion. This new method has the advantages of giving reasonable results over moderate time periods, and allowing the extrapolation of calcium levels in extracellular fluid and storage. We fit the model to published data in order to obtain typical parameter values. These values are then used to analyze the implications of the model regarding the effect of calcium dose on calcium levels in various compartments.

Animals↗
PubMed1994

[11C]tropanyl benzilate-binding to muscarinic cholinergic receptors: methodology and kinetic modeling alternatives.

Quantitative estimation of cerebral muscarinic receptors was investigated with the use of the antagonist [11C]tropanyl benzilate ([11C]TRB) and positron emission tomography (PET). Kinetic modeling alternatives were examined with the goal of identifying an analysis method providing stable receptor measures, yet avoiding biases from inappropriate reductions in model complexity. Dynamic PET scans were performed on six young normal volunteers. Several modeling approaches yielding relative receptor density measures were evaluated: (a) a single "late" scan using relative tracer concentration values; (b) a slope estimate from graphic analysis (Patlak plot); (c) a two-compartment, two-parameter model (transport and total ligand distribution volume); (d) a three-compartment, two-parameter model using the free+nonspecific distribution volume, DV', fixed to the cerebellar value; (e) an early scan for transport, a fixed value for DV', and a single late scan for the binding rate constant; and (f) a three-compartment, three-parameter model. Both computer simulations and PET scan results indicate all methods provide receptor density index measures with the same rank order as in vitro measures. Oversimplified approaches (methods 1 and 2) yield a more highly nonlinear relation between the estimated receptor density index and the known receptor density than do methods retaining greater model complexity (methods 3-6). However, noise propagation into the receptor measure is greater for the more complex methods. Reliable receptor density information can be obtained from kinetic [11C]TRB PET studies, with methods 3-5 providing the most appropriate levels of model complexity for estimates of relative muscarinic receptor density.

Adult↗