Analysis and Mathematical Modeling of Autonomously Oscillating Yeast Cultures.

The conditions that precede the onset of autonomous oscillations in continuous yeast cultures were studied in three different types of experiments. It was found that the final state of the culture depends on the protocol used to start-up the reactor. Reaching the desired operating point by slow dilution rate changes gave rise to different final states, two oscillatory states and one steady state, depending on the rate of change in dilution rate. The multiplicity of stable states at a single operating point is not explained by current distributed models and points towards a segregated mechanism of these oscillations. The ability of an age population balance model to capture experimentally observed oscillatory dynamics of continuous cultures of budding yeast was investigated. Consistent with experimental evidence, numerical simulations of the model revealed the existence of several, stable periodic solutions. However, each occurred over a different range of dilution rates. Experiments have shown that the steady state in continuous yeast cultures appears to be stable, even under conditions that allow oscillatory dynamics. The stability of the steady state of the age population balance model under conditions that allow oscillatory dynamics was not resolved. Another population balance model in terms of mass distribution of unbudded cells and age distribution of budded cells was also proposed. The model was based on a more detailed cell cycle than that used in the development of the age distribution model. Therefore, the hybrid mass-age model was superior to the age model in its ability to simulate situations in which the yeast culture is starved. In agreement with experimental evidence, the model predicts the auto-synchronization of batch yeast cultures during their batch growth with a final bimodal cell mass distribution. Furthermore, the oscillations occur spontaneously as the simulated batch culture is switched to continuous operation. The model also predicts multiple oscillatory states at separate regions of the dilution rate and predicts the existence of an oscillatory state and an extended unstable steady state at the same operating conditions

Retrospective Review of the Patient Cases at a Major Trauma Center in Nairobi, Kenya and Implications for Emergency Care Development

Introduction Low- and middle-income countries (LMICs) are continuing to experience a “triple burden” of disease - traumatic injury, non-communicable diseases (NCDs), and communicable disease with maternal and neonatal conditions (CD&Ms). The epidemiology of this triad is not well characterised and poses significant challenges to resource allocations, administration, and education of emergency care providers. The data collected in this study provide a comprehensive description of the emergency centre at Kenya\u27s largest public tertiary care hospital. Methods This study is a retrospective chart review conducted at Kenyatta National Hospital of all patient encounters over a four-month period. Data were collected from financial and emergency centre triage records along with admission and mortality logbooks. Chief complaints and discharge diagnoses collected by specially trained research assistants were manually converted to standardised diagnoses using International Classification of Disease 10 (ICD-10) codes. ICD-10 codes were categorised into groups based on the ICD-10 classification system for presentation. Results A total of 23,941 patients presented to the emergency centre during the study period for an estimated annual census of 71,823. The majority of patients were aged 18-64 years (58%) with 50% of patients being male and only 3% of unknown sex. The majority of patients (61%) were treated in the emergency centre, observed, and discharged home. Admission was the next most common disposition (33%) followed by death (6%). Head injury was the overall most common diagnosis (11%) associated with admission. Conclusions Trends toward NCDs and traumatic diseases have been described by this study and merit further investigation in both the urban and rural setting. Specifically, the significance of head injury on healthcare cost, utilisation, and patient death and disability points to the growing need of additional resources at Kenyatta National Hospital for acute care. It further demonstrates the mounting impact of trauma in Kenya and throughout the developing world

Differential effects of selenium and knock-down of glutathione peroxidases on TNFα and flagellin inflammatory responses in gut epithelial cells

Selenium (Se) is essential for human health. Despite evidence that Se intake affects inflammatory responses, the mechanisms by which Se and the selenoproteins modulate inflammatory signalling, especially in the gut, are not yet defined. The aim of this work was to assess effects of altered Se supply and knock-down of individual selenoproteins on NF-κB activation in gut epithelial cells. Caco-2 cells were stably transfected with gene constructs expressing luciferase linked either to three upstream NF-κB response elements and a TATA box or only a TATA box. TNFα and flagellin activated NF-κB-dependent luciferase activity and increased IL-8 expression. Se depletion decreased expression of glutathione peroxidase1 (GPX1) and selenoproteins H and W and increased TNFα-stimulated luciferase activity, endogenous IL-8 expression and reactive oxygen species (ROS) production. These effects were not mimicked by independent knock-down of either GPX1, selenoprotein H or W; indeed, GPX1 knock-down lowered TNFα-induced NF-κB activation and did not affect ROS levels. GPX4 knock-down decreased NF-κB activation by flagellin but not by TNFα. We hypothesise that Se depletion alters the pattern of expression of multiple selenoproteins that in turn increases ROS and modulates NF-κB activation in epithelial cells, but that the effect of GPX1 knock-down is ROS-independent

Selenium deficiency increases the expression of inducible nitric oxide synthase in RAW 264.7 macrophages: role of nuclear factor-kappaB in up-regulation.

The inducible isoform of nitric oxide synthase (iNOS) is implicated in atherosclerosis, malignancy, rheumatoid arthritis, tissue and reperfusion injuries. A key determinant of the pro-oxidant versus protective effects of NO is the underlying redox status of the tissue. Selenoproteins, such as glutathione peroxidases (GPxs) and thioredoxin reductases, are key components of cellular defence and promote optimal antioxidant/oxidant balance. In this study, we have investigated the relationship between Se status, iNOS expression and NO production in Se-deficient and Se-supplemented RAW 264.7 macrophage cell lines. The cellular GPx activity, a measure of Se status, was 17-fold lower in Se-deficient RAW 264.7 cells and the total cellular oxidative tone, as assessed by flow cytometry with 2',7'-dichlorodihydrofluorescein diacetate, was higher in the Se-deficient cells than the Se-supplemented cells. Upon lipopolysaccharide (LPS) stimulation of these cells in culture, we found significantly higher iNOS transcript and protein expression levels with an increase in NO production in Se-deficient RAW 264.7 cells than the Se-supplemented cells. Electrophoretic mobility-shift assays, nuclear factor-kappaB (NF-kappaB)-luciferase reporter assays and Western blot analyses indicate that the increased expression of iNOS in Se deficiency could be due to an increased activation and consequent nuclear localization of the redox-sensitive transcription factor NF-kappaB. These results suggest an inverse relationship between cellular Se status and iNOS expression in LPS-stimulated RAW 264.7 cells and provide evidence for the beneficial effects of dietary Se supplementation in the prevention and/or treatment of oxidative-stress-mediated inflammatory diseases

Autonomous oscillations in Saccharomyces cerevisiae during batch cultures on trehalose

International audienceWe report that autonomous oscillations, which usually happen in aerobic glucose-limited continuous cultures of yeast at low dilution rate, were also observed in trehalose discontinuous cultures of Saccharomyces cerevisiae. This unexpected oscillatory behaviour was therefore examined using fast Fourier transformation of online gas measurements. This robust mathematical analysis underlined the existence of two types of oscillation. The first was found to be linked to the cell cycle because (a) the periodicity corresponded to a fraction of the generation time and (b) the oscillations were accompanied by a transient increase in the budding index, mobilization of storage carbohydrates, and fermentative activity. Moreover, these oscillations occurred in a range of specific growth rates between 0.04 and 0.15 h)1. All these criteria were consistent with the cell-cycle-related metabolic oscillations observed in the same range of growth rates in glucoselimited continuous cultures. The second type were short-period respiratory oscillations, independent of the specific growth rate. Both types of oscillation were found to take place consecutively and ⁄ or simultaneously during batch culture on trehalose. In addition, mobilization of intracellular trehalose emerged as a key parameter for the sustainability of these autonomous oscillations as they were no longer observed in a mutant defective in neutral trehalase activity. We propose that batch culture on trehalose may be an excellent device for further investigation of the molecular mechanisms that underlie autonomous oscillations in yeast