Browsing by Subject "Glucose"
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Item Coherent anti-Stokes Raman scattering (CARS) optimized by exploiting optical interference(2012-07-16) Wang, XiThe purpose of this work is to study the interference between the coherent nonresonant four-wave-mixing (FWM) background and the Raman-resonant signal in the coherent anti-Stokes Raman spectroscopy (CARS). The nonresonant background is usually considered as a detriment to CARS. We prove that the background can be exploited in a controllable way, through the heterodyne detection due to the interference, to amplify the signal and optimize the spectral shape of the detected Raman signal, and hence enhance the measurement sensitivity. Our work is based on an optimized CARS technique which combines instantaneous coherent excitation of multiple characteristic molecular vibrations with subsequent probing of these vibrations by an optimally shaped, time-delayed, narrowband laser pulse. This pulse configuration mitigates the nonresonant background while maximizing the resonant signal, and allows rapid and highly specific detection even in the presence of multiple scattering. We investigate the possibility of applying this CARS technique to non-invasive monitoring of blood glucose levels. Under certain conditions we find that the measured signal is linearly proportional to the glucose concentration due to optical interference with the residual background light instead of a quadratic dependence, which allows reliable detection of spectral signatures down to medically-relevant glucose levels. With the goal of making the fullest use of the background, we study the interference between an external local oscillator (nonresonant FWM field) and the CARS signal field by controlling their relative phase and amplitude. Our experiment shows that this control allows direct observation of the real and imaginary components of the third-order nonlinear susceptibility (?(3)) of the Raman sample. In addition, this method can be used to amplify the signal significantly. Furthermore, we develop an approach by femtosecond laser pulse shaping to precisely control the interference between the Raman-resonant signal and its intrinsic nonresonant background generated within the same sample volume. This technique is similar to the heterodyne detection with the coherent background playing the role of the local oscillator field. By making fine adjustments to the probe field shape, we vary the relative phase between the resonant signal and the nonresonant background, and observe the varying spectral interference pattern. These controlled variations of the measured pattern reveal the phase information within the Raman spectrum, akin to holographic detection revealing the phase structure of a source.Item The development and application of glucose electrodes based on "wired" glucose oxidase(2001-12) Chen, Ting; Heller, AdamThe sensitivity of rapidly responding “wired” glucose sensing microelectrodes with a tailored outer membrane was examined in vivo. It is shown that these microsensors maintained in vivo sensitivities similar to those in buffer before the implantation and after the explantation when implanted intravenously or intraperitoneally for several hours in the rat. Maintenance of the sensitivity in vivo provides the basis for pre-calibrating the microsensors in vitro, lifting the requirement of in vivo calibration. The in vitro calibration results can be used by the patients as a reference in judging the reliability of sensor readings. The causes of much more rapid decaying current in the “wired” glucose oxidase-based microelectrodes in serum compared to their sensitivity in buffer were studied. Urate and transition metal ions were identified as two main causes for the loss in current. Urate is electrooxidized to dimeric or trimeric products, which precipitate in the electrocatalytic film, reducing the mobility of the redox sites of the polymer. Transition metal ions coordinatively crosslink pyridine or imidazole functions of the redox polymers and also inhibit glucose oxidase. Implantable “wired” glucose microsensors with novel polyionic membrane for mass transport-controlling were developed and tested in the jugular veins and in the intrascapular subcutaneous region of non-diabetic SpragueDawley rats. The micromembranes were assembled by sequentially chemisorbing polyanions and polycations on miniature enzyme electrodes. The sequential chemisorption process allowed the simultaneous tailoring of their sensitivity, dynamic range, drift and selectivity. The membranes also retained transition metal ions that bound to and damaged the redox polymer “wiring” the enzyme. All of the in vivo data points measured by the microsensors were clinically accurate after correcting the lag time of the glycemia in the subcutaneous fluid behind that of blood withdrawn from the vein. The “wired” glucose enzyme microelectrode was also used as the microanode in developing a compartmentless miniature biofuel cell intended to be an implanted mini power source for medical microdevice. The glucose-oxidizing anode was combined with a high current output “wired” laccase microcathode, which catalyzes the electro-reduction of O2 to water. The areas of the anode and the cathode of the cell are much smaller than any previously reported fuel cell. The power density of the cell exceeds by a factor of five that of the highest power density of earlier reported glucose-air biofuel cells. The effects of different buffers, oxygen concentration, pH and chloride on cell current were investigated.Item The effects of an amino acid mixture beverage on glucose tolerance, glycogen replenishment, muscle damage, and anaerobic exercise performance(2011-08) Wang, Bei, doctor of kinesiology; Ivy, John, 1945-; Farrar, Roger P.; Wilcox, Richard E.; Griffin, Lisa; Jolly, Christopher A.Recent research suggests that amino acids, such as leucine and isoleucine, can improve glucose tolerance in vivo and in vitro animal models by accelerating glucose uptake in peripheral tissues and stimulate glycogen synthesis in vitro in the absence of insulin. Our laboratory recently found that gavaging normal Sprague-Dawley rats with an amino acid mixture, composed of isoleucine, leucine, cystine, methionine, and valine, improved blood glucose response during an oral glucose challenge without an increase in the plasma insulin response. The blood glucose-lowering effect of the amino acid mixture was due to an increase in skeletal muscle glucose uptake. These results suggest that this amino acid supplement acutely improves muscle insulin sensitivity and blood glucose homeostasis. However, the effect of this amino acid mixture on glucose tolerance and muscle glycogen synthesis in humans has not been investigated. Some studies have also shown that daily supplementation or acute ingestion of amino acids may prevent muscle damage that occurs as a result of a prolonged, intense endurance exercise or strength training and therefore improves force production and exercise performance. However, the effects of the addition of an amino acid mixture to carbohydrate supplement on muscle damage after a prolonged endurance exercise, as well as on the subsequent anaerobic exercise performance, have not been characterized. Therefore, in this series of two studies, the effects of an amino acid mixture, composed of isoleucine, leucine, cyctine, methionine, and valine, on glucose tolerance, muscle glycogen resynthesis, muscle damage, and anaerobic exercise performance were investigated. Study 1 demonstrated that our amino acid mixture lowered the glucose response to an OGTT in healthy overweight/obese subjects in an insulin-independent manner. Study 2 demonstrated that both high and low dosages of amino acid mixture were effective in lowering blood glucose response to a carbohydrate bolus in athletes postexercise. High dosage of amino acid mixture was more potent in glucose regulation by providing a higher insulin response and amino acid effect. However, our amino acid mixture had no effects on post exercise muscle glycogen synthesis, exercise-induced muscle damage or subsequent anaerobic performance. Taken together, the results of this research series suggest that an amino acid mixture, composed of isoleucine and 4 additional amino acids, attenuates the glucose response to a glucose bolus in an insulin-independent manner, but does not enhance muscle glycogen restoration following exercise or prevent exercise-induced muscle damage.Item Glucose, insulin and lipase activity of rats fed chromium from beef and soy(Texas Tech University, 1983-08) Keim, Kathryn Sarah HochsprungNot availableItem Growth parameters for Saccharomyces cerevisiae in glucose containing media(Texas Tech University, 1985-08) Boyd, Glenn CraigNot availableItem Hydrolysis kinetics of gluconolactones(Texas Tech University, 1972-08) Parrott, Albert RossNot availableItem Insight into a unique carbon resource partitioning mechanism in Aggregatibacter actinomycetemcomitans(2010-08) Brown, Stacie Anne, 1979-; Whiteley, Marvin; Meyer, Richard; Walker, James; McLean, RobertAggregatibacter actinomycetemcomitans is a Gram negative bacterium found exclusively in the mammalian oral cavity where it resides in the gingival crevice, the space between the tooth and gum tissue. Though it has historically been considered a common commensal organism, it is now appreciated that A. actinomycetemcomitans is an opportunistic pathogen associated with the diseases periodontitis and endocarditis. To cause infection, A. actinomycetemcomitans must interact and compete with neighboring bacteria for space and nutrients, though little is known about the physiology it employs within the gingival crevice. Using A. actinomycetemcomitans grown in a chemically defined medium containing carbon sources found in vivo, I use transcriptome analyses and growth studies to show that A. actinomycetemcomitans preferentially utilizes lactate over the phosphotransferase system (PTS) sugars glucose and fructose. Additionally, the presence of lactate or pyruvate inhibits the transport and metabolism of these sugars in a post-transcriptionally controlled process I have termed PTS substrate exclusion. Since lactate is an energetically inferior carbon source, PTS substrate exclusion appears to be a carbon resource partitioning mechanism that allows A. actinomycetemcomitans to avoid competition for energetically favorable sugars with other species, and I propose a model to describe this phenomenon. To begin to understand the mechanism of PTS substrate exclusion, I examine the first step of the proposed model by purifying and characterizing the L-lactate dehydrogenase (LctD) from A. actinomycetemcomitans. I demonstrate that, unlike other studied lactate dehydrogenases, the LctD from A. actinomycetemcomitans does not exhibit feedback inhibition in the presence of physiologically relevant concentrations of pyruvate, which supports my hypothesis that elevated intracellular pyruvate levels inhibit the PTS. The results of my studies provide insight into a new regulatory mechanism governing carbon utilization in this bacterium.Item MAPK Signaling Pathways in Pancreatic Beta Cells: The Regulation of RAF Activation by Nutrient Stimuli(2011-02-01T19:32:08Z) Duan, Lingling; Cobb, MelanieIn pancreatic β cells cells, ERK1 and ERK2 participate in nutrient sensing and their activities rise and fall as a function of glucose concentration over the physiologic range. Glucose metabolism triggers calcium influx and release of calcium from intracellular stores which are required for ERK1/2 activity. Calcium influx also activates the calcium-dependent phosphatase calcineurin, which is required for maximal ERK1/2 activation by glucose. Calcineurin controls insulin gene expression by ERK1/2-dependent and -independent mechanisms. This study showed that in β cells, glucose activates the ERK1/2 cascade primarily through B-Raf. Glucose also enhances dimerization of B-Raf with C-Raf. Furthermore, calcineurin up-regulates B-Raf activity and stabilizes C-Raf/B-Raf in response to glucose. Calcineurin binds to B-Raf in both unstimulated and stimulated cells. B-Raf phospho-T401 is one of the target sites that can be dephosphorylated by calcineurin. This study reveals that cross-talk between Raf and calcineurin is essential for the maximal activation of ERK1/2 in the glucose signaling pathways. [Keywords: TCF; POP-1; Wnt; embryogenesis; C. elegans]Item Study of pure and conjugated culture batch fermentation of Cephalosporium acremonium(Texas Tech University, 1986-12) Khang, Yong HoPenicillin N and cephalosporin C (CPC) were produced sequentially by ATCC 36225 (69). Cell-free extracts of its mutant, ATCC 52518, catalyzed the conversion of penicillin N into cephalosporin C (38). It was postulated that the yield of CPC production might be altered when these two cultures were grown together. Optimum experimental conditions were determined by examining the effect of aeration, agitation, and other parameters on growth. The effect of sample size on the analysis of cell dry weight was also examined to reduce experimental error. The proper air flow rate was found to be 50 ml/min in a 2-L glass fermenter when no antifoam agent was added. Microbial films were severely reduced when 60-70% of fermenter volume was used as working volume. The relationship between the two microorganisms was found to be neutralistic when the cellular growth of conjugated cultures (ATCC 36225 + ATCC 52518) was compared with that of each pure culture (Figure 4.14). The growth yield of ATCC 36225 was twice that of ATCC 52518 and the growth yield of conjugated cultures was the same as that of ATCC 36225 (Table 4.5). The CPC production yield of conjugated cultures, however, was less than that of the ATCC 36225 culture. On the basis of these results, it was concluded that precursor amino acids (L-(a)-aminoadipate, L-cysteine, and L-valine) produced by ATCC 52518 could not stimulate CPC synthesizing enzymes of ATCC 36225 to synthesize 3-lactam antibiotics in the conjugated cultures.Item The Effect of Glucose Utilization and Feed Efficiency on Beef Cattle Production(2012-02-14) Bradbury, BrookFeed efficiency and metabolism affect profitability of the various components of the beef industry by modulating distribution and use of nutrients within cattle. Separate studies were conducted to determine the 1) repeatability of feed efficiency measurements over time as beef heifers mature into cows, and 2) whether the production and regulation of glucose in heifers is affected by temperament. The influence of temperament on glucoregulatory hormones was studied in Angus crossbred heifers and Brahman heifers whose temperament was determined at weaning. The 6 most calm and 6 most temperamental heifers of each breed were fitted with jugular cannulas. Blood was collected at cannulation and then via the cannula during a 90-min rest period. Following 90 min, dextrose was infused (0.5 mg/kg BW) and blood samples were collected at specific intervals for 3 h total. In the crossbred heifers cortisol (P = 0.0560) and glucose (P = 0.0485) concentrations during the challenge were higher in temperamental relative to calm crossbred heifers. Insulin concentrations tended (P = 0.0737) to be higher in temperamental crossbred heifers. Cortisol (P = 0.0282) and glucose (P = 0.0011) concentrations were significantly higher in temperamental Brahman heifers. Insulin concentrations tended (P = 0.0793) to be greater for calm Brahman heifers. Temperamental cattle had a greater HPA axis response, which led to greater concentrations of cortisol and glucose, possibly because the glucose was being utilized differently by the temperamental cattle. Mature Brahman cow feed efficiency data was collected over two years, on two different cohorts of cows that had previous residual feed intake data as post-weaning heifers. In 2009 and 2010, 37 and 41 cows, respectively, in their first trimester of gestation were evaluated for RFI via the Calan gate system. Cows were fed 2.6% BW for 70 d with BW recorded weekly. Cows were classified according to their RFI values as either efficient or inefficient. Heifer RFI was not correlated to mature cow RFI based on assessment of the Pearson?s correlation coefficient (r = -0.06, P = 0.57). This study indicates that establishment of RFI in heifers may not accurately predict their feed efficiency as mature cows.Item Understanding the Molecular Basis for FGF15/19 and FGF21 Actions on Energy Homeostasis(2012-07-09) Boney-Montoya, Jamie; Kliewer, Steven A.Insulin and glucagon have long been known to play essential roles in controlling energy balance during the fed and fasted states, respectively. Recently, additional metabolic hormones have been discovered within a subfamily of the fibroblast growth factor superfamily. The FGF15/19 subfamily is composed of atypical FGFs lacking the heparin-binding domain, which enables them to act in an endocrine fashion by diffusing away from their tissues of origin. They signal through cell-surface receptors complexed with beta-Klotho, a membrane-spanning protein, to mediate signaling cascades that lead to physiological responses. One member, FGF19, causes reduced glucose and insulin levels with enhanced insulin sensitivity when expressed in transgenic mice. Another member, FGF21, has been shown to act as an insulin sensitizer pharmacologically by improving glucose tolerance and reducing insulin. The prevalence of metabolic disorders (e.g. type 2 diabetes) in today’s society has led to the investigation of these two endocrine FGFs for use in a clinical setting. However, the mechanisms underlying these responses have not been characterized. // To elucidate the mechanisms utilized by FGF15/19, we used several animal models to show a role for FGF15/19 in regulating hepatic glucose production. Like insulin, FGF15/19 represses gluconeogenesis. Specifically, FGF15/19 inhibits expression of the transcriptional coactivator PGC1-alpha, a key regulator of gluconeogenic gene expression. The repressive effect of FGF15/19 on gluconeogenic gene expression is lost when PGC1-alpha is overexpressed. FGF15/19 causes the dephosphorylation and inactivation of the transcription factor CREB, thereby blunting its ability to bind and induce the PGC1-alpha promoter. The results demonstrated that FGF15/19 works subsequent to insulin as a postprandial regulator of gluconeogenesis through inhibition of the CREB/ PGC1-alpha pathway. // To fully understand the effects of FGF21, we began studying the downstream kinase signaling cascades and the protein substrates affected by this hormone. Utilizing stable isotope labeling of amino acids in cell culture (SILAC), an unbiased phosphoproteomic profile was obtained of potential FGF21 targets in rat H4IIE hepatoma cells. One of the most highly regulated targets was FetuinA, which was dephosphorylated by FGF21 treatment. FetuinA is an inhibitor of insulin receptor signaling and the FetuinA knockout mouse exhibits aberrant glucose homeostatsis. Our in vitro data suggested a relationship between FGF21 and FetuinA in regulating insulin sensitivity but further exploration lead to the conclusion that FGF21 was not directly regulating FetuinA in vivo. // Taken together, the important role of FGF15/19 and FGF21 in regulating carbohydrate metabolism as well as their pharmacological actions makes them attractive drug candidates for metabolic diseases. However, further study will be required to determine their molecular mechanisms more completely and their long-term efficacy in the clinic. [Keywords: FGF15/19, FGF21, gluconeogenesis, CREB, PGCI-alpha, Fetuin-A, phosphorylation, beta-klotho]