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PubMed2006

Sorption behavior of volatile phenols at the oak wood/wine interface in a model system.

The sorption in a model system of aroma compounds of enological interest (mixture of the eight derivatives from guaiacol, 4-ethylphenol, and whiskylactone) onto wood was investigated to assess the influence of wood on the concentration of these volatiles during the aging of wine. To evaluate the influence of the solubility of aroma compounds in sorption phenomena, this parameter was determined for each volatile compound in model wine at 10 and 25 degrees C. The solubility is significantly higher in the model wine than in water and remains constant in the range of temperatures studied, except for guaiacol and vanillin. Kinetic and equilibrium sorptions were investigated. Sorption kinetics showed that the sorption equilibrium for all aroma compounds was reached after 6-7 days. From the study of the individual sorption isotherms, two distinct kinds of sorption behavior were observed depending on the presence or not of an ethylenic para substituent conjugated to the phenyl ring. K(ww) partition coefficients between the wood and the model wine were determined, which exhibited an unusual positive variation with temperature.

Adsorption↗
PubMed2006

Linear and non-linear kinetics in the synthesis and degradation of acrylamide in foods and model systems.

Isothermal acrylamide formation in foods and asparagine-glucose model systems has ubiquitous features. On a time scale of about 60 min, at temperatures in the approximate range of 120-160 degrees C, the acrylamide concentration-time curve has a characteristic sigmoid shape whose asymptotic level and steepness increases with temperature while the time that corresponds to the inflection point decreases. In the approximate range of 160-200 degrees C, the curve has a clear peak, whose onset, height, width and degree of asymmetry depend on the system's composition and temperature. The synthesis-degradation of acrylamide in model systems has been recently described by traditional kinetic models. They account for the intermediate stages of the process and the fate of reactants involved at different levels of scrutiny. The resulting models have 2-6 rate constants, accounting for both the generation and elimination of the acrylamide. Their temperature dependence has been assumed to obey the Arrhenius equation, i.e., each step in the reaction was considered as having a fixed energy of activation. A proposed alternative is constructing the concentration curve by superimposing a Fermian decay term on a logistic growth function. The resulting model, which is not unique, has five parameters: a hypothetical uninterrupted generation-level, two steepness parameters; of the concentration climbs and fall and two time characteristics; of the acrylamide synthesis and elimination. According to this model, peak concentration is observed only when the two time constants are comparable. The peak's shape and height are determined by the gap between the two time constants and the relative magnitudes of the two "rate" parameters. The concept can be extended to create models of non-isothermal acrylamide formation. The basic assumption, which is yet to be verified experimentally, is that the momentary rate of the acrylamide synthesis or degradation is the isothermal rate at the momentary temperature, at a time that corresponds to its momentary concentration. The theoretical capabilities of a model of this kind are demonstrated with computer simulations. If the described model is correct, then by controlling temperature history, it is possible to reduce the acrylamide while still accomplishing much of the desirable effects of a heat process.

Acrylamide↗
PubMed2004

Optically active sum frequency generation from molecules with a chiral center: amino acids as model systems.

With amino acids as model systems, optically active sum frequency generation (OA-SFG) was used to probe the chirality of molecules with a chiral center and an intrinsically achiral chromophore in isotropic solution for the first time. Like that of circular dichroism (CD), the OA-SFG's near electronic resonance originates from the extrachromophoric chiral perturbation on the carboxyl chromophore. The difference in the relative strengths of OA-SFG and CD among different amino acids can be explained by the difference in the details of perturbations.

Amino Acids↗
PubMed1984

Study of the imprinting and overlap of insulin and concanavalin-A at the receptor level in a protozoan (Tetrahymena) model system.

In a protozoan (Tetrahymena) model system, insulin treatment produced a long-term imprinting which upon re-exposure to the hormone resulted in an enhanced binding of the hormone. Insulin pretreatment produced similar effect with regard to the binding of concanavalin-A. Concanavalin-A could only induce a short-term imprinting for itself and was not capable at all of inducing imprinting for insulin. Based on the results of this study it appears that the binding of the sugar component of the receptor, which can be achieved also by lectin, is not sufficient to induce imprinting but the whole (hormone) molecule is needed.

Animals↗
PubMed2006

Assessing sexual conflict in the Drosophila melanogaster laboratory model system.

We describe a graphical model of interlocus coevolution used to distinguish between the interlocus sexual conflict that leads to sexually antagonistic coevolution, and the intrinsic conflict over mating rate that is an integral part of traditional models of sexual selection. We next distinguish the 'laboratory island' approach from the study of both inbred lines and laboratory populations that are newly derived from nature, discuss why we consider it to be one of the most fitting forms of laboratory analysis to study interlocus sexual conflict, and then describe four experiments using this approach with Drosophila melanogaster. The first experiment evaluates the efficacy of the laboratory model system to study interlocus sexual conflict by comparing remating rates of females when they are, or are not, provided with a spatial refuge from persistent male courtship. The second experiment tests for a lag-load in males that is due to adaptations that have accumulated in females, which diminish male-induced harm while simultaneously interfering with a male's ability to compete in the context of sexual selection. The third and fourth experiments test for a lag-load in females owing to direct costs from their interactions with males, and for the capacity for indirect benefits to compensate for these direct costs.

Animals↗
PubMed1976

Coordination of biogenic amines with synaptosomal and vesicular metal ions: equilibrium and spectral studies in model systems.

Thermodynamic equilibrium studies using model systems were carried out on the nature and extent of coordination of twelve different biogenic amines and adenosine-5'-triphosphate (ATP) with the bivalent metal ions, viz., Ca2+ and Zn2+, which occur in the subcellular fractions of the brain, at 25.0 +/- 0.1 degrees C and at an ionic strength of 1.0 (KNO3). In the combined presence of the individual monoamines and ATP the metal ions were predominantly coordinated by ATP in the pH range 3.0 to 6.5 with binding constants (log KML) of 2.84 +/- 0.06 and 3.19 +/- 0.39 for the Ca2+ and Zn2+ chelates, respectively. Each of the monoamines coordinated with the metal-ATP chelate above pH 6. The stabilities of the chelates of some of the amines with Ca2+ -ATP (1:1) system were NE, 2.33 +/- 0.33; AA, 2.24 +/- 0.19; OA, 1.94 +/- 0.29; NMeN, 1.60 +/- 0.22; DA, 2.14 +/- 0.09. Values for the Zn2+-ATP-amine systems were: NE, 8.35 +/- 0.26; OA, 4.53 +/- 0.07; DA, 10.05 +/- 0.39. Absorption spectral studies were carried out in order to examine the nature of coordination of NE, DA, TA, and AA with Cu2+, Fe2+, and Mg2+ ions in the combined presence of ATP. Results of the spectral studies taken together with the (thermodynamic) equilibrium data have indicated that in the pH range of biological interest, the catechol amines (NE and DA) and ATP are both coordinated to the "synaptosomal and vesicular" metal ions. The results further indicated that both the pyrocatechol and the ethanolamine groups of NE might be involved in the coordination of Cu2+. However, the interaction of the ethanolamine group of the NE molecule with the rest of the metal ions was not indicated.

Adenosine Triphosphate↗
PubMed2003

Gas chromatographic investigation of acrylamide formation in browning model systems.

Acrylamide formed in browning model systems was analyzed using a gas chromatograph with a nitrogen-phosphorus detector. Asparagine alone produced acrylamide via thermal degradation at the level of 0.99 microgram/g of asparagine. When asparagine was heated with triolein-which produced acrolein at the level of 1.82 +/- 0.31 (n = 5) mg/L of headspace by heat treatment-acrylamide was formed at the level of 88.6 microgram/g of asparagine. When acrolein gas was sprayed onto asparagine heated at 180 degrees C, a significant amount of acrylamide was formed (114 microgram/g of asparagine). On the other hand, when acrolein gas was sprayed onto glutamine under the same conditions, only a trace amount of acrylamide was formed (0.18 microgram/g of glutamine). Relatively high levels of acrylamide (753 microgram/g of ammonia) were formed from ammonia and acrolein heated at 180 degrees C in the vapor phase. The reaction of acrylic acid, which is an oxidation product of acrolein and ammonia, produced a high level of acrylamide (190 000 microgram/g of ammonia), suggesting that ammonia and acrolein play an important role in acrylamide formation in lipid-rich foods. Acrylamide can be formed from asparagine alone via thermal degradation, but carbonyl compounds, such as acrolein, promote its formation via a browning reaction.

Acrolein↗
PubMed1985

Putative role of cholesteryl ester transfer protein in removal of cholesteryl ester from vascular interstitium, studied in a model system in cell culture.

A model system to study the putative role of cholesteryl ester transfer protein in the egress of interstitial cholesteryl ester is described. Confluent cultures of bovine aortic smooth muscle cells were labeled for 24 h with [3H]cholesteryl linoleyl ether and [14C]cholesteryl linoleate by incubation with bovine milk lipoprotein lipase. This method of labeling results in the transfer of cholesteryl linoleyl ether and cholesteryl ester to three compartments: a trypsin-releasable, trypsin-resistant and catabolic compartment (Stein, O., Halperin, G., Leitersdorf, E., Olivecrona, T. and Stein, Y. (1984) Biochim. Biophys. Acta 795, 47-59). The efflux of labeled cholesteryl linoleyl ether and cholesteryl ester from the extracellular and cell-surface related compartments into a serum-free culture medium containing 1% bovine serum albumin was studied during 24 h of postincubation. The efflux was expressed as a percentage of pulse value, i.e., radioactivity retained by the cell culture at the end of the labeling period. The efflux of [3H]cholesteryl linoleyl ether, [14C]cholesteryl ester and 14C-labeled free cholesterol (formed by cellular hydrolysis of cholesterol ester) into the culture medium with 1% bovine serum albumin was about 5% of the pulse value. Addition of human lipoprotein-deficient serum resulted in a 3-10-fold increase in the efflux of [3H]cholesteryl linoleyl ether and [14C]cholesteryl ester, but did not change markedly the efflux of 14C-labeled free cholesterol. Rat lipoprotein-deficient serum which does not contain cholesteryl ester transfer protein did not increase the efflux of [3H]cholesteryl linoleyl ether or [14C]cholesteryl ester. The rate of cholesteryl ester efflux in the presence of human lipoprotein-deficient serum was linear for about 6 h and increased further up to 24 h. Addition of Intralipid to medium containing human lipoprotein-deficient serum further enhanced the efflux of [3H]cholesteryl linoleyl ether and, to a lesser extent, that of cholesteryl ester. A similar effect was observed also by addition of rat VLDL to medium containing human lipoprotein-deficient serum. Inhibition of cholesteryl linoleyl ether and cholesteryl ester efflux and marked enhancement of free cholesterol efflux occurred when rat HDL was added to medium containing human lipoprotein-deficient serum, while human HDL was only slightly inhibitory. The results obtained with human lipoprotein-deficient serum were reproduced with partially purified cholesteryl ester transfer protein. Using the partially purified cholesteryl ester transfer protein, the efflux of cholesteryl linoleate was compared to that of cholesteryl oleate and was found to be the same.

Animals↗
PubMed1992

Development of a murine lymphoma model system for the characterization of natural killer:tumor cell interactions.

We have developed a model system which can be utilized for characterizing both the molecular basis of natural killer (NK):tumor interactions and the consequences of these interactions on tumor growth in vivo. This model system consists of several tumor lines which were derived from the murine lymphoma ASL1w under conditions which permitted the isolation of clonal lines that differ in their susceptibility to NK-mediated lysis. The NK-resistant clones used in this study (AW5J and AW5E) were susceptible to cytotoxic T-lymphocyte-mediated lysis and thus appear to be resistant to lytic processes utilized uniquely by NK cells. In competitive (cold target) inhibition assays, the AW5J clone did not inhibit NK recognition as well as the NK-sensitive clones. Thus AW5J may not be efficiently recognized by NK cells. The AW5E clone, on the other hand, competitively inhibited NK recognition as efficiently as the NK-sensitive clones; therefore, AW5E appears to evade a post-recognition event which is required for NK-mediated lysis. The susceptibility of these clones to killing by NK cells directly correlated with their lethality, suggesting that NK cells regulated the growth of these tumors in vivo. The level of host NK activity was also an important determinant of the level and site of tumor localization. Two-step immunofluorescence assays and flow cytometric analysis were used to quantitate the number of tumor cells in the bone marrow, spleen, and lymph nodes of mice with augmented or depleted NK activity. Increasing host NK activity decreased the number of tumor cells in each organ which could support the growth of the particular tumor tested. Furthermore, the extent of NK regulation was dependent, in part, upon the susceptibility of the particular tumor to NK-mediated lysis and the site of tumor growth. Thus, the data presented here demonstrate the utility of the ASL1w-derived clones as a model system which can be used to delineate the requirements and consequences of NK:tumor interactions.

Animals↗
PubMed2001

Interactions between artificial saliva and 20 aroma compounds in water and oil model systems.

The interactions between saliva components and 20 aroma compounds in water and oil model systems were systematically evaluated as a function of saliva composition and saliva/model system ratio. Air/liquid partition coefficients of dimethyl sulfide, 1-propanol, diacetyl, 2-butanone, ethyl acetate, 1-butanol, 2-pentanol, propyl acetate, 3-methyl-1-butanol, ethyl butyrate, hexanal, butyl acetate, 1-hexanol, 2-heptanone, heptanal, alpha-pinene, 2-octanone, octanal, 2-nonanol, and 2-decanone were determined by static headspace gas chromatography. Chain length of compounds within the homologous series determined the extent of interactions with the model system or saliva. Salts in the artificial saliva hardly interacted with aroma compounds. On the other hand, saliva proteins lowered retention of highly volatile compounds and increased retention of less volatile, hydrophobic compounds. Significant differences in volatility of compounds when artificial saliva or water was added indicated that saliva could not be sufficiently replaced by water. The model system/saliva ratio influenced air/liquid partitioning of the aroma compounds significantly for both model systems. Although saliva composition affected volatility of the aroma compounds, the saliva/model system ratio was of much greater influence.

Chromatography, Gas↗
PubMed2002

The agricultural dispersal-valley drift spray drift modeling system compared with pesticide drift data.

The coupling of the valley drift (VALDRIFT) atmospheric dispersion/deposition model with the agricultural dispersal (AGDISP) aircraft wake model generates a modeling system for predicting the off-target drift of pesticides sprayed in a mountain valley. The approach uses the AGDISP near-field spray model to estimate the mass fraction of pesticide remaining airborne after initial application, then the VALDRIFT complex terrain model to estimate the drift of pesticide from the target area. The modeling system inputs include detailed spray information, a measure (or estimate) of winds in the valley, and the valley topographic characteristics; the results are pesticide concentrations throughout the valley atmosphere and pesticide deposition to the valley surface. The AGDISP and VALDRIFT models are operated independently, with the results from AGDISP being used as input to VALDRIFT through user-created data files. The modeling system was evaluated using pesticide drift data from spray trials conducted in the Mill Creek Canyon of Utah's Wasatch Mountains, USA, during the late spring of 1993. The predicted deposition compared within a factor of three of the observations (70% of the time) at all sampling locations extending several kilometers down-valley from the spray treatment block. The overall average ratio of predicted-to-observed deposition was 0.9.

Agriculture↗
PubMed2005

Degradation of atrazine in a laboratory scale model system with Danube river sediment.

A laboratory-scale model system of Danube river gravel bed was constructed. Evaluation of water chemical parameters and composition of bacterial communities confirmed the liability of the model. Degradation of atrazine, a frequent micropollutant of Danube water was examined in the model system. In case of an acute atrazine load, short-term retention of the compound was observed, accumulation and degradation were not significant. Long-term continuous dose of atrazine led to enhanced degradation of the pollutant. Principal metabolite was hydroxyatrazine. Atrazine utilizing strains isolated from the sediment belong to various, predominantly Gram positive genera and have diverse atrazine metabolism. Dominant metabolic reactions are dechlorination, dealkylation and deamination, with the sequential products ammeline and ammelide. The strain Delftia acidovorans D24 mineralizes atrazine as a sole source of carbon and nitrogen.

Atrazine↗
PubMedDate not supplied

Kinetics of the alkaline phosphatase catalyzed hydrolysis of disodium p-nitrophenyl phosphate in frozen model systems.

The alkaline phosphatase catalyzed hydrolysis of disodium-p-nitrophenyl phosphate was studied in four model systems comprising sucrose, maltodextrin, carboxymethylcellulose (CMC), and CMC-lactose in a temperature range of -28 to 20 degrees C. In the maltodextrin and CMC-lactose model systems, the reaction rate decreased to a very low value as the glass transition temperature was approached. In the CMC and CMC-lactose systems with low initial solute concentration, as a consequence of freeze-concentration, a rate maximum around the initial freezing temperature was observed. The Arrhenius equation described the temperature dependence of the reaction rate both in the liquid and the glassy states in all systems studied, while a slightly curved Arrhenius plot was observed in the "rubbery" state of the CMC and CMC-lactose systems. The WLF equation with system-dependent coefficients described the kinetics in the rubbery state of all the model systems except sucrose, excluding the short temperature range where reaction rate enhancement with decreasing temperature was observed.

Alkaline Phosphatase↗
PubMed2004

A novel ex vivo model system for evaluation of conditionally replicative adenoviruses therapeutic efficacy and toxicity.

PURPOSE: Current animal tumor models are inadequate for the evaluation of toxicity and efficacy of conditionally replicative adenoviruses. A novel model system is needed that will provide insight into the anticipated therapeutic index of conditionally replicative adenoviruses preclinically. We endeavored to show a novel model system, which involves ex vivo evaluation of conditionally replicative adenovirus toxicity and therapeutic efficacy in thin, precision-cut slices of human primary tumor and liver. EXPERIMENTAL DESIGN: The Krumdieck thin-slice tissue culture system was used to obtain and culture slices of tumor xenografts of ovarian cancer cell lines, human primary ovarian tumors, and human liver. We determined the viability of slices in culture over a period of 36 to 48 hours by ([3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxphenyl-2-(4-sulfophenyl)-2H-tetrazolium, inner salt)]) (MTS) assay. In vitro Hey cells, slices of Hey xenografts, and human ovarian tumor or human liver slices were infected with 500vp/cell of either replication competent wild-type adenovirus (Ad5/3wt), conditionally replicative adenovirus (Ad5/3cox-2), or the replication deficient adenovirus (Ad5/3luc1). At 12-, 24-, and 36-hour intervals, the replication of adenoviruses in these slices was determined by quantitative reverse transcription-PCR of adenoviral E4 copy number. RESULTS: Primary tumor slices were able to maintain viability for up to 48 hours after infection with nonreplicative virus (Ad5luc1). Infection of Hey xenografts with Ad5/3cox-2 showed replication consistent with that seen in Hey cells infected in an in vitro setting. Primary tumor slices showed replication of both Ad5/3wt and Ad5/3cox over a 36-hour time period. Human liver slices showed replication of Ad5/3wt but a relative reduction in replication of Ad5/3cox-2 indicative of conditional replication "liver off" phenotype, thus predicting lower toxicity. CONCLUSIONS: The thin-slice model system represents a stringent method of ex vivo evaluation of novel replicative adenoviral vectors and allows assessment of human liver replication relative to human tumor replication. This is the first study to incorporate this system for evaluation of therapeutic efficacy and replicative specificity of conditionally replicative adenoviruses. Also, the study is the first to provide a valid means for preclinical assay of potential conditionally replicative adenovirus-based hepatotoxicities, thus providing a powerful tool to determine therapeutic index for clinical translation of conditionally replicative adenoviruses.

Adenoviridae↗
PubMed1989

Average values of a dissimilarity measure not requiring sequence alignment are twice the averages of conventional mismatch counts requiring sequence alignment for a computer-generated model system.

Three measures of sequence dissimilarity have been compared on a computer-generated model system in which substitutions in random sequences were made at randomly selected sites and the replacement character was chosen at random from the set of characters different from the original occupant of the site. The three measures were the conventional mismatch count between aligned sequences (AMC = m) and two measures not requiring prior sequence alignment. The latter two measures were the squared Euclidean distance between vectors of counts of t-tuples (t = 1-6) of characters in the two sequences (multiplet distribution distances or MDD = d) and counts of characters not covered by word structures of statistically significant length common to the two sequences (common long words or CLW = SIB, SIS, or SAB). Average MDD distances were found to be two times average mismatch counts in the simulated sequences for all values of t from 1 to 6 and all degrees of substitution from one per sequence to so many as to produce, effectively, random sequences. This simple relation held independently of sequence length and of sequence composition. The relation was confirmed by exact results on small model systems and by formal asymptotic results in the limit of so few substitutions that no double hits occur and in the limit of two random sequences. The coefficient of variation for MDD distances was greater than that for mismatch counts for singlets but both measures approached the same low value for sextets. Needleman-Wunsch alignment produced incorrect mismatch counts at higher degrees of substitution. The model satisfied the conditions for the derivation of the Jukes-Cantor asymptotic adjustment, but its application produced increasingly bad results with increasing degrees of substitution in accord with earlier results on model and natural sequences. This fact was a consequence of the increase with increasing degrees of substitution of the sensitivity of the adjustment to error in the observations. Average CLW distances for a variety of common word structures were more or less parallel to MDD distances for appropriately long t-tuples. These results on model systems supported the validity of the two dissimilarity measures not requiring sequence alignment that was found in earlier work on natural sequences (Blaisdell 1989).

Base Sequence↗
PubMed2006

The human PC346 xenograft and cell line panel: a model system for prostate cancer progression.

OBJECTIVE: Prostate cancer (PC) model systems that reflect the different disease stages are essential for studying the development and progression of PC and for testing new treatment modalities. This review summarizes the establishment and characterization of the PC346 progression model and compares it to other available human PC cell lines and xenografts. METHODS: The PC346 model was derived from the transurethral resection of a primary prostate tumor. Tumor samples were subcutaneously implanted into athymic mice, which resulted in the development of a series of xenografts from which in vitro cell cultures were established. RESULTS: The PC346 panel includes sublines with hormone-response characteristics that range from androgen-sensitive to androgen-independent (AI) growth. In vivo and in vitro selection of androgen-sensitive lines under androgen-depleted conditions replicated the clinically relevant relapse phenomenon, and resulted in a series of modifications in the androgen-receptor (AR) pathway: AR mutation, overexpression, and downregulation. CONCLUSIONS: The PC346 panel reproduces many biological characteristics of the different phases of clinical PC and the most common AR modifications observed in hormone-refractory tumors, being a valuable addition to the limited collection of available model systems.

Animals↗
PubMed1998

Alterations in transendothelial electrical resistance by vasoactive agonists and cyclic AMP in a blood-brain barrier model system.

We have previously reported that the co-culture of endothelial and glioma cell lines provides an in vitro model for investigating properties of the blood-brain barrier (BBB). To characterise the model system further we have investigated the effects of vasoactive substances implicated in increases in BBB permeability. Additionally, we have also examined whether activation of cyclic AMP signalling pathways, which elevate cerebral endothelial cell barrier function, similarly modulate our model system. ATP, histamine, bradykinin, and serotonin significantly decreased model BBB transendothelial electrical resistance and manipulations which elevate cyclic AMP enhanced culture resistance. These data indicate that our model BBB system responds in a manner characteristic of cerebral microvascular endothelial cells and the BBB in vivo. These data further emphasize the usefulness of our model system.

Blood-Brain Barrier↗