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PubMed1998

Generation and the fate of C2, C3, and C4 reactive fragments formed in Maillard model systems of [13C]glucose and [13C]glycine or proline.

Model studies with pyrolysis/GC/MS using labeled [13C] glucoses with labeled [15N/13C]glycines and proline have indicated that the Maillard model systems consisting of glucose and glycine or proline generate similar C2, C3, C4 fragments such as acetic acid, and pyruvaldehyde. Furthermore, the labeling studies have enabled the identification of the origin of these reactive intermediates and their stable end-products such as N-acetylpyrrolidine, 1-(1'-pyrrolidinyl)-2-propanone amd 1-(1'-pyrrolidinyl)-2-butanone in proline model system and pyrazines and pyrazinones in glycine. In glycine model system, pyruvaldehyde and 2,3-butandione were found to be formed either from the degradation of the carbohydrate moiety (90 and 35%, respectively) or by an aldol-type interaction of glycine with alpha-ketoaldehydes. The same intermediates in proline system are formed exclusively from the carbohydrate degradation pathway.

Carbon Isotopes↗
PubMed1990

Immunotherapeutic approaches to leukemia: the use of the Friend virus-induced erythroleukemia model system.

We have developed a model system to study immunologically mediated regression of leukemia based on Friend virus-induced erythroleukemias. This system has been used to evaluate the immunotherapeutic activity of macrophages, specifically reactive T-cells (CTL/RFB), lymphokine-activated killer cells and interleukin 2, and tumor necrosis factor alpha and interferon-gamma. In the present studies, CTL/RFB were evaluated for their ability to prevent disease recurrence. Animals with the regressing strain of Friend virus at Day 39 post virus were treated with either one or two injections of 5 x 10(6) CTL/RFB. Animals given one or two injections of CTL/RFB had a significantly lower rate of recurrence than did untreated animals. The helper T-cell component of CTL/RFB was implicated in causing leukemia regression. Interleukin 1 alpha and tumor necrosis factor alpha, multifunctional cytokines with similar biological activities, were evaluated for their ability to suppress leukemic erythroid colony-forming cells and induce regression. Interleukin 1 alpha suppressed the conventional strain of, but not the polycythemia-inducing strain of, Friend virus-leukemic late erythroid colony-forming units and caused only a temporary regression of disease, while tumor necrosis factor alpha suppressed both forms of the disease and with multiple inoculations could cause permanent disease regressions. This system provides an excellent model for examining the efficacy of immunotherapy of leukemias with various mediators and effector mechanisms.

Animals↗
PubMed1991

Graduate and post-graduate medical education with the synchronous systems model.

Behavioral sciences have an important new role, particularly in medicine and prevention (Revans, 1990; Starr, 1982). A decade ago when the ideology of medical care shifted from a biomedical to a biopsychosocial model, behavioral and social factors ascended in importance in modern health concerns (see Engel, 1977). Now, a living systems model called Synchronous Systems (Jasnoski & Schwartz, 1985) incorporates environmental (including the social and physical) along with physiological and psychological factors into its structure. The environment has been gaining recognition as an important determinant in health, disease, and wellness (Daniel, 1990; Demick & Wapner, 1990; Lawton, 1990; Stokols, 1990). The phrase "Synchronous Systems" departs from the traditional linear thought patterns to depict contemporaneous occurrences. Synchrony refers to simultaneous experiences or events, with an emphasis on healthy, congruent process and function. Positive, beneficial process in human functioning emphasizes prevention as found in public health efforts but refers also to dysfunctional and recuperative foundation of medicine as a departure from the healthy norm. These process and functional dynamics in the Synchronous Systems Model derive conceptually from systems theory, specifically from control and cybernetic theories (Cannon, 1932; Weiner, 1948). The dynamic complexity of health in the whole human system, which also incorporates the environment, requires synthesis of knowledge from the biological, social, behavioral, and ecological sciences. This article provides the fundamentals of the structural and functional synthesis possible in the Synchronous Systems Model. Its direct application to multidisciplinary research is also presented along with its specific application to medical education, policy, research, and service delivery.

Curriculum↗
PubMed2006

Model systems in ecology: dissecting the endophyte-grass literature.

Model systems can facilitate and focus research efforts but ill-chosen or inapt ones can distract or impede scientific progress. In this Opinion article, we pose the question: how can the literature provide appropriate general conclusions if the model systems upon which the literature is based are unrepresentative of the relevant biological diversity? A good example of this problem is the endophyte-grass symbiosis, which is considered to be a classic example of mutualistic interactions. Meta-analysis of the primary literature demonstrates that the conceptual framework for endophyte-grass interactions has largely been based on endophyte-plant-herbivore studies of two agricultural grass species, tall fescue and perennial ryegrass. Consistent with conventional wisdom, the meta-analysis indicates that endophytes slightly increase grass resistance to herbivores. By contrast, endophytes appear not to affect plant performance or competitive ability. The positive effects of endophytes appear to be dependent on genetic variation in the host and endophyte, and on nutrient availability in soils. Thus, the agronomic grass model systems fail to capture the breadth of variability inherent in wild grass-endophyte populations and communities.

Animals↗
PubMed1987

A systems model approach to the ventilatory anaerobic threshold.

An analogue systems model of whole-body human bioenergetics predicts a change in kinetics of VO2 time series values as a result of exercise levels above an anaerobic threshold. Plotted VO2 results from exercising subjects appear to confirm this change. The purpose of this study is to describe the background to the systems model analogue of the anaerobic threshold and a test procedure devised to estimate this threshold. The estimate so obtained has the dual advantages of being based on model theory and of not being subject to the sort of ambient variations inherent in a single-test determination. A non-homogeneous group of eight subjects comprising a full replicate of a 2(3) factorial experimental design, with factors age, sex and training status, took part in the study. On one hand the results indicate acceptance of the systems model theory. On the other, the analogue threshold measure possesses corresponding properties to the conventional anaerobic threshold. It is higher for trained (155-214 W) than for untrained subjects (108-158 W), higher for males (149-214 W) than for females (108-170 W), and displays no evident interaction effects. Results for the VO2 time constant and for the work efficiency, display similar effects except for an interaction in the latter between age and training status. These experimental findings are regarded as confirmatory of the nature of the analogue threshold measure.

Adult↗
PubMed2004

Investigation of photoinduced electron transfer in model system of vitamin E-duroquinone by time-dependent density functional theory.

Photoinduced electron transfer of the model system composed of vitamin E and duroquinone has been investigated using time-dependent density functional theory. Calculations for the excited states tell that the photoexcitation of the model system can directly yield the charge transfer states in which the vitamin E moiety is positively charged but the duroquinone moiety is negatively charged. Our theoretical investigations indicate that the second charge transfer state of the model system can also be produced through the decay of higher locally excited state S(4). Since S(4) state in the model system corresponds to S(1) state of the isolated duroquinone used as a model for peroxyl radical, and S(2) state has the character of electron transfer from the tertiary amine group of the vitamin E moiety to the duroquinone moiety, the decay from S(4) to S(2) corresponds to the dynamic process following the photoexcitation of the duroquinone moiety of the model system, i.e., the initial stage of antioxidant reaction of vitamin E. Calculations of the kinetic parameters for the electron transfer have been carried out in the framework of the Marcus-Jortner-Levich formalism. Our calculations confirm that the electron transfer from S(4) to S(2) possesses the character of the inverted regime and the barrier is negligibly small.

Benzoquinones↗
PubMed2005

A systems model of training for patients in phase 2 cardiac rehabilitation.

BACKGROUND: The aim of this study was to apply a systems model of training for athletes in patients with coronary artery disease (CAD) undergoing phase 2 cardiac rehabilitation. METHODS: Data from six patients with CAD undergoing 20 conventional training sessions were used to test this model. The method required daily training quantification using heart rate, and regular assessment of real exercise tolerance using a constant-duration test. Convolution of training quantity with real exercise tolerance was provided for every patient model exercise tolerance, by minimizing the residual sum of squares. RESULTS: The results showed that application of the systems model of training to the six patients resulted in a strong fit between real and model exercise tolerances: r(2) = 0.77, 0.79, 0.83, 0.84, 0.85 and 0.92, respectively (P < 0.05). DISCUSSION: Moreover, the systems model admitted for all patients corresponded to one first-order transfer function, which was fitness. This result was in contrast with the systems models reported in athletes and in a patient with CAD undergoing phase 3 cardiac rehabilitation which were found to include two first-order transfer functions: fitness and fatigue, simultaneously. CONCLUSION: The systems model of training of patients with CAD undergoing phase 2 suggested two practical consequences: first, the improvement of exercise tolerance is directly related to training, and consequently second, patients who enter immediately phase 3 training may prevent a decrease in their exercise tolerance.

Adult↗
PubMed2006

[Integrated model system for environmental policy analysis].

An integrated model system for environmental policy analysis is built up with a Computable General Equilibrium (CGE) model as a core model, which is linked with an environmental model, air dispersion model, and health effect model (exposure-response functions) in an explicit way, therefore the model system is capable of evaluating the effects of policies on environment, health and economy and their interactions comprehensively. This method is used to analyze the effects of Beijing presumptive (energy) taxes on air quality, health, welfare and economic growth, and the conclusion is that sole presumptive taxes may slow down the economic growth, but the presumptive taxes with green tax reform can promote Beijing sustainable development.

Environment↗
PubMed2000

Functional outcome for African Americans and Hispanics treated at a traumatic brain injury model systems centre.

OBJECTIVE: To describe the demographics, incidence and functional outcome for African Americans and Hispanics treated at a traumatic brain injury (TBI) model systems centre. DESIGN: Retrospective data analysis of patients admitted to an acute inpatient rehabilitation national TBI model systems centre. SETTING: A tertiary care university medical centre participating in the NIDRR Traumatic Brain Injury Model Systems project. SUBJECTS: Eighty-seven patients with TBI admitted to a Model Systems acute intensive interdisciplinary rehabilitation setting between 1989-1999. Information was extracted from the National TBI Model Systems data base for demographics such as age, race, education, gender, marital and employment status, sponsorship, injury aetiology and severity. OUTCOME MEASURES: Functional outcome was determined using the Functional Independence Measure (FIM), and the Disability Rating Scale (DRS) at the time of admission and discharge. RESULTS: Descriptive statistics were completed using SPSS. African American (94.3%) and Hispanic (5.7%) patients were injured most often as a result of motor vehicle accidents (48.8%). Males comprised 86.2% of this population, which had an average age of 34.5 years (SD = 13.1). On admission, average GCS score was 7.8 (SD = 3.6), average DRS was 13.5 (SD = 5.8), and average FIM total score was 49.8 (SD = 26.5). Average length of unconsciousness was 5.2 days (SD = 27.9), while average length of post-traumatic amnesia was 41.9 days (SD = 59.3). At the time of injury, 78.2% of the patients were not married. The majority of patients (97.7%) had private residences and 88.5% returned to their original home. Most patients had at least a high school education or passed a high school equivalent exam (49.4%) and were employed (70.1%) at the time of injury. Only 7% of the patients had a history of prior TBI. With regard to substance use, only 34.2% of patients reported pre-morbid illicit drug use. However, 50.5% met criteria for heavy or moderate alcohol use rates. Only 35.6% of patients reported a pre-morbid history of arrests, with the average number of arrests equal to 4.5 (SD = 10.2). Within this population, the number of drug or alcohol related arrests was 4.8 (SD = 13.5). CONCLUSIONS: Unmarried African American males, with an average age of 35 years, predominated at this institution. The primary mechanism of injury was motor vehicle accidents. The majority of patients had, at least, a high school education or passed an equivalency exam, were employed at the time of their injury and were discharged to their prior private residence. While half of the patients met criteria for moderate-to-heavy alcohol consumption, only one-third of the patients reported a history of pre-morbid illicit drug use. This descriptive analysis supports the need for further investigation of minority populations that sustain TBI and will enhance the accuracy of implications that minority status may have on functional outcome.

Activities of Daily Living↗
PubMed2001

Model-based administration of inhalation anaesthesia. 1. Developing a system model.

This paper is the first of a series of reports on a system model for the administration of inhalation anaesthesia. We present the development and basic testing of the model. It is a multiple-gas model; it covers fresh-gas flow rates from basal to more than total ventilation and includes an actual, not an idealized, circle-absorber breathing system featuring a standing bellows ventilator. Kinetics of nitrogen, oxygen, carbon dioxide, nitrous oxide, inhaled anaesthetic agents and helium are described. Their partial pressures sum to the total pressure. Ventilation and cardiac output are treated as continuous, not cyclical. The model of the breathing system was empirically matched to the chosen one (a GMS absorber and 7850 ventilator (Datex-Ohmeda)). Predictions for the wash-in of isoflurane and the uptake of desflurane and isoflurane agree well with observed data. The results obtained by continuously checking total gas pressures, calculating mass balances and simulating the measurement of alveolar space by the closed-circuit helium dilution method support the mathematical credibility of the model. It thus merits further exploration.

Algorithms↗
PubMed2003

Volatile constituents of glutathione--ribose model system and its antioxidant activity.

Reaction between glutathione and ribose was carried out to study the volatiles formed via Maillard reaction and their antioxidant activity as well as their role in inhibition of LDL oxidation. The simultaneous distillation-extraction technique was used for trapping the volatile components followed by GC-MS analysis. Thirty six compounds were identified with the predominance of carbonyls and sulfur-containing compounds in the volatiles of this model system. Sensory evaluation was performed for the model system product according to the International Standard Methods (ISO). The results showed a high decrease in roasted and burnt attributes and remarkable increase in the like-boiled and roasted meat attributes. The sensory results of the model system product were confirmed by the presence of high concentrations of some volatile compounds having meat--like aroma such as 2-methyl-3-furanthiol and 2-furylmethanethiol. The radical scavenging activity of glutathione-ribose model system was quantified spectrophotometrically, using DPPH radical. The activity of the model system product was found to be slightly lower than that of gallic acid and BHA, but it was much higher than that of cinnamic acid (200 ppm. for each). A highly antioxidative activity was recorded by the model system product during the inhibition of LDL-oxidation in comparison with L-ascorbic acid as well as reduced glutathione (as a concentration of 0.5 micromol/L, for each) which may be due to the presence of some compounds such as 2-furylmethanethiol, 2-acetyl thiazole, 4-hydroxy-5-methyl-3(2H)-furanone.

Antioxidants↗
PubMed2005

Somatic transgenesis in the avian model system.

The chick embryo is a versatile model system, in which classical embryology can be combined with modern molecular approaches. In the last two decades, several efficient methods have been developed to introduce exogenous genes into the chick embryo. These techniques allow alteration of gene expression levels in a spatially and temporally restricted manner, thereby circumventing embryonic lethality and/or eliminating secondary effects in other tissues. Here, we present the current status of avian somatic transgenic techniques, focusing on electroporation and retrovirus-mediated gene transfer. Electroporation allows quick and efficient gain-of-function studies based on transient misexpression of genes. Retroviral vectors, which are capable of integrating exogenous genes into the host chromosome, permit analysis of long-term effects of gene misexpression. The variety of methods available for somatic transgenesis, along with the recent completion of the chicken genome, are transforming the chick embryo into one of the most attractive model systems to examine function of genes that are important for embryonic development.

Animals↗
PubMedDate not supplied

The femur-tibia control system of stick insects--a model system for the study of the neural basis of joint control.

In a form of top-down analysis, the femur-tibia control system of stick insects is investigated. Open-loop experiments show that it is mainly velocity-sensitive with an extremely low velocity-threshold, that it possesses a very high gain and that it has only a very small phase reserve and thus works close to instability. The closed-loop system generates catalepsy. The system consists of a single sense organ with approximately 80 sense cells with known characteristics, a small number of interneurones (mainly non-spiking ones) and a small number of motor neurones. The characteristics of the whole system can quantitatively be attributed to the characteristics of its elements. The gain of the loop is state-dependent and the system is 'switched off' during active movements and replaced by a control system with different attributes. It is discussed that most of the characteristics of this system are, at least qualitatively, similar to joint control systems in other animals. Because the described system can be more easily investigated than other systems (especially in vertebrates) it can serve as a model against which more complicated joint control loops may be compared.

Animals↗
PubMed1999

TBI model system grants

The Traumatic Brain Injury (TBI) Model Systems Program has been funded by the National Institute on Disability and Rehabilitation Research (NIDRR) since 1987. Until recently, this program has consisted of four centers that conducted priority-focused research on specific aspects of TBI and analyzed data on the basis of a uniform, comprehensive national database. In 1997, $5 million in additional funding was allocated for the expansion of this program. In October 1998, after a competitive renewal process, a total of 12 new centers were awarded, bringing the total TBI Model Systems to 17. In addition to the creation of new centers, funding was provided for specific collaborative research projects and increased resources for the TBI National Data Center. Below are the abstracts for both the newly funded systems and the existing systems.

Journal Article↗
PubMed1999

TBI Model System Grants.

The Traumatic Brain Injury (TBI) Model Systems Program has been funded by the National Institute on Disability and Rehabilitation Research (NIDRR) since 1987. Until recently, this program has consisted of four center s that conducted priority-focused research on specific aspects of TBI and analyzed data on the basis of a uniform, comprehensive national database. In 1997, $5 million in additional funding was allocated for the expansion of this program. In October 1998, after a competitive renewal process, a total of 12 new centers were awarded, bringing the total TBI Model Systems to 17. In addition to the creation of new centers, funding was provided for specific collaborative research projects and increased resources for the TBI National Data Center. Below are the abstracts for both the newly funded systems and the existing systems.

Brain Injuries↗
PubMed2005

Yeast model systems for examining nitrogen oxide biochemistry/signaling.

The yeast Saccharomyces cerevisiae is an ideal model system for examining fundamental nitrogen oxide biochemistry. The utility of this model system lies in both the similarities and the differences between yeast and mammalian cells. The similarities between the two systems, with regards to many of the fundamental biochemical processes, allow studies in yeast to be extrapolated to mammalian systems. On the other hand, yeast has distinct differences that allow, for example, the facile examination of O2, pH, and genetic dependencies on a number of nitrogen oxide-mediated processes. Thus, the yeast system is amenable to experimentation that is otherwise problematic or impossible in mammalian systems. Herein, we present several examples of the utility of the yeast model system for studying the intimate details of basic nitrogen oxide biochemistry.

Antioxidants↗
PubMed2002

A model system study of the inhibition of heterocyclic aromatic amine formation by organosulfur compounds.

Organosulfur compounds and sodium bisulfite significantly inhibited (P < 0.05) heterocyclic aromatic amine (HAA) formation in model systems containing phenylalanine, creatinine, and glucose. There was, however, no inhibition by the same compounds in a model system containing only phenylalanine and creatinine. Diallyl disulfide (DAD) and dipropyl disulfide (DPD) concentrations in the model systems were significantly decreased (P < 0.05) after heating for 10 min at 180 degrees C. Only very low concentrations of sulfhydryl groups (4.19 and 4.00 micromol) were produced on heating DAD and DPD for 30 min. Reaction of glucose and DAD produced several sulfur-containing compounds. After 10 min of heating at 180 degrees C, HAA formation in the control model systems was increased significantly, and DAD was an effective inhibitor during this heating period. Tetrahydrothiophene-3-one (THT) and tetrahydrothiophene (THP); two products resulting from the interaction of glucose and DAD, had no direct influence on HAA formation in the model systems.

Allyl Compounds↗
PubMed1994

WI-38 cell long-term quiescence model system: a valuable tool to study molecular events that regulate growth.

A number of cell culture model systems have been used to study the regulation of cell cycle progression at the molecular level. In this paper we describe the WI-38 cell long-term quiescence model system. By modulating the length of time that WI-38 cells are density arrested, it is possible to proportionately alter the length of the prereplicative or G-1 phase which the cell traverses after growth factor stimulation in preparation for entry into DNA synthesis. Through studies aimed at understanding the cause and molecular nature of the prolongation of the prereplicative phase, we have determined that gene expression plays an important role in establishing growth factor "competence" and that once the cell becomes "competent" there is a defined order to the molecular events that follow during the remainder of G-1. More specifically, we have determined that the prolongation represents a delay in the ability of long term quiescent cells to become fully "competent" to respond to growth factors which regulate progression through G-1 into S. This prolongation appears to occur as a result of changes during long term quiescence in the ability of immediate early G-1 specific genes (such as c-myc) to activate the expression of early G-1 specific genes (such as ornithine decarboxylase). While ODC is the first and thus far only growth associated gene identified as a target of c-myc (and the Myc/Max protein complex), it is likely that further studies in this model system will reveal other early G-1 growth regulatory genes. We anticipate that future follow-up studies in this model system will provide additional valuable information about the function of growth-regulatory genes in controlling growth factor responsiveness and cell cycle progression.

Animals↗