Effect Of Glucose Availability Research Articles

Integrated Proteomic and Metabolomic Analyses Show Differential Effects of Glucose Availability in Marine Synechococcus and Prochlorococcus.

We compared changes induced by the addition of 100 nM and 5 mM glucose on the proteome and metabolome complements in Synechococcus sp. strains WH8102, WH7803, and BL107 and Prochlorococcus sp. strains MED4, SS120, and MIT9313, grown either under standard light conditions or in darkness. Our results suggested that glucose is metabolized by these cyanobacteria, using primarily the oxidative pentoses and Calvin pathways, while no proof was found for the involvement of the Entner-Doudoroff pathway in this process. We observed differences in the effects of glucose availability, both between genera and between Prochlorococcus MED4 and SS120 strains, which might be related to their specific adaptations to the environment. We found evidence for fermentation in Prochlorococcus sp. strain SS120 and Synechococcus sp. strain WH8102 after 5 mM glucose addition. Our results additionally suggested that marine cyanobacteria can detect nanomolar glucose concentrations in the environment and that glucose might be used to sustain metabolism under darkness. Furthermore, the KaiB and KaiC proteins were also affected in Synechococcus sp. WH8102, pointing to a direct link between glucose assimilation and circadian rhythms in marine cyanobacteria. In conclusion, our study provides a wide overview on the metabolic effects induced by glucose availability in representative strains of the diverse marine picocyanobacteria, providing further evidence for the importance of mixotrophy in marine picocyanobacteria. IMPORTANCE Glucose uptake by marine picocyanobacteria has been previously described and strongly suggests they are mixotrophic organisms (capable of using energy from the sun to make organic matter, but also to directly use organic matter from the environment when available). However, a detailed analysis of the effects of glucose addition on the proteome and metabolome of these microorganisms had not been carried out. Here, we analyzed three Prochlorococcus sp. and three Synechococcus sp. strains which were representative of several marine picocyanobacterial clades. We observed differential features in the effects of glucose availability, depending on both the genus and strain; our study illuminated the strategies utilized by these organisms to metabolize glucose and showed unexpected links to other pathways, such as circadian regulation. Furthermore, we found glucose addition had profound effects in the microbiome, favoring the growth of coexisting heterotrophic bacteria.

The effect of glucose availability on cortisol stress reactivity in young healthy women with varying degrees of early life adversity

The effect of glucose availability on cortisol stress reactivity in young healthy women with varying degrees of early life adversity

Effects of glucose availability in Lactobacillus sakei; metabolic change and regulation of the proteome and transcriptome.

Effects of glucose availability were investigated in Lactobacillus sakei strains 23K and LS25 cultivated in anaerobic, glucose-limited chemostats set at high (D = 0.357 h-1) and low (D = 0.045 h-1) dilution rates. We observed for both strains a shift from homolactic towards more mixed acid fermentation when comparing high to low growth rates. However, this change was more pronounced for LS25 than for 23K, where dominating products were lactate>formate>acetate≥ethanol at both conditions. A multivariate approach was used for analyzing proteome and transcriptome data from the bacterial cultures, where the predictive power of the omics data was used for identifying features that can explain the differences in the end-product profiles. We show that the different degree of response to the same energy restriction revealed interesting strain specific regulation. An elevated formate production level during slow growth, more for LS25 than for 23K, was clearly reflected in correlating pyruvate formate lyase expression. With stronger effect for LS25, differential expression of the Rex transcriptional regulator and NADH oxidase, a target of Rex, indicated that maintainance of the cell redox balance, in terms of the NADH/NAD+ ratio, may be a key process during the metabolic change. The results provide a better understanding of different strategies that cells may deploy in response to changes in substrate availability.

Abstract 1180: Hexokinase II plays a pivotal role in colorectal cancer cell proliferation and survival

Abstract The Warburg Effect describes the widely observed metabolic phenotype of cancer cells and their heavy reliance on the glycolytic pathway for energy production regardless of oxygen tension. This is a result of alterations to metabolic signaling pathways leading to an upregulation in key glycolytic enzymes. Hexokinase II (HKII) catalyzes the first irreversible step of glycolysis and is often overexpressed in tumors. 3-bromopyruvate (3BP) has been shown to primarily target HKII, and is a promising anti-cancer compound capable of targeting critical metabolic pathways in cancer cells. Here we examine the importance of HKII to cell proliferation and survival and also whether its inhibition could provide a therapeutic strategy in human colorectal cancer (CRC). Initially, established human CRC cell lines (HCT116, Caco2, SW480, DLD-1) were screened for HKII mRNA and protein expression. Cell proliferation and survival following HKII inhibition via both siRNA and 3BP treatment was determined using crystal violet staining, flow cytometry and western blotting. Sensitivity to 3BP was correlated with HKII expression amongst the cell lines screened. We next examined the pro-survival AKT signaling pathway via western blotting and found that AKT phosphorylation was dependent on 3BP dose and was residue-specific. Immunofluorescence was then used to examine subcellular HKII localization. Following 3BP treatment, mitochondrial localization of HKII was lost. As a result of tumor vascular abnormalities, regions within a tumor are exposed to transient and/or chronic ischemia, resulting in altered oxygen and nutrient availablity. To examine the effects of glucose availability on 3BP sensitivity, media glucose was gradually reduced in a step-wise manner and HKII expression, cell proliferation and cell survival were evaluated in CRC cell lines. Cells grown under reduced or normal glucose conditions were less sensitive to 3BP exposure than cells grown under high glucose conditions, and responses correlated with changes in HKII expression. Using immunostaining, we examined the expression of HKII in both normoxic and ischemic regions in FFPE samples of human CRC. These results were correlated to tumor stage and grade, along with patient outcome. Results from this study further define the role of HKII in colorectal cancer progression and show that 3-bromopyruvate could be useful as an anti-cancer therapy against CRC tumors with high expression of HKII. Citation Format: Nelson Ho, Brenda L. Coomber. Hexokinase II plays a pivotal role in colorectal cancer cell proliferation and survival. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1180. doi:10.1158/1538-7445.AM2015-1180

Effects of glucose availability on expression of the key genes involved in synthesis of milk fat, lactose and glucose metabolism in bovine mammary epithelial cells.

As the main precursor for lactose synthesis, large amounts of glucose are required by lactating dairy cows. Milk yield greatly depends on mammary lactose synthesis due to its osmoregulatory property for mammary uptake of water. Thus, glucose availability to the mammary gland could be a potential regulator of milk production. In the present study, the effect of glucose availability on expression of the key genes involved in synthesis of milk fat, lactose and glucose metabolism in vitro was investigated. Bovine mammary epithelial cells (BMEC) were treated for 12 h with various concentrations of glucose (2.5, 5, 10 or 20 mmol/L). The higher concentrations of glucose (10–20 mmol/L) did not affect the mRNA expression of acetyl-CoA carboxylase, diacyl glycerol acyl transferase, glycerol-3 phosphate acyl transferase and α-lactalbumin, whereas fatty acid synthase, sterol regulatory element binding protein-1 and beta-1, 4-galactosyl transferase mRNA expression increased at 10 mmol/L and then decreased at 20 mmol/L. The content of lactose synthase increased with increasing concentration of glucose, with addition of highest value at 20 mmol/L of glucose. Moreover, the increased glucose concentration stimulated the activities of pyruvate kinase and glucose-6-phosphate dehydrogenase, and elevated the energy status of the BMEC. Therefore, it was deduced that after increasing glucose availability, the extra absorbed glucose was partitioned to entering the synthesis of milk fat and lactose by the regulation of the mRNA expression of key genes, promoting glucose metabolism by glycolysis and pentose phosphate pathway as well as energy status. These results indicated that the sufficient availability of glucose in BMEC may promote glucose metabolism, and affect the synthesis of milk composition.

Abstract 4833: Glucose restriction induces degradation of p53 mutants via a selective autophagy-mediated pathway

Abstract Introduction. More than 50% of human tumors harbor missense mutations of the p53 gene product. In its wild-type conformation p53 is degraded via the proteasome, mainly through the action of the MDM2 E3 ubiquitin ligase. Unlike the wild-type protein, mutant forms of p53 accumulate at high levels and elude proteolysis, in part due to an altered modality of interaction with MDM2. High levels of p53 mutants in tumors appear to correlate with resistance to radio- and chemo-therapy, and are proposed to promote tumor progression. Furthermore, therapeutic interventions aimed at reducing p53 mutant levels have shown anti-tumor activity in vitro and in vivo. The mechanisms that regulate the stability of wild-type p53 are well understood during the DNA damage response. However, p53 can also be stabilized during adaptive metabolic stress conditions, such as during glucose deprivation. The goal of this work was to determine the effects of glucose availability on the oncogenic activity of mutant p53. Methods. We investigated the effects of glucose availability in tumor cells expressing p53 mutants, in transgenic animals harboring p53 mutant alleles, and in xenograft models of breast cancer. The read-outs of these experiments were p53 stability, cellular proliferation and response to therapeutic agents. Results. We found that p53 mutant protein levels are exquisitely sensitive to glucose availability: high glucose levels stabilize p53 mutants, while glucose restriction (GR) leads to their MDM2- and proteasome-independent degradation. This degradation requires instead the participation of the autophagic machinery and of the autophagic protein Beclin-1, which forms a complex with p53 in GR-treated cells. Importantly, in breast cancer cell lines GR alone does not lead to a net increase in autophagic flux, thus differing from autophagy activated during serum- or amino acid- depletion. Rather, GR uses the autophagic machinery to degrade selective targets, such as mutant p53. We further show that tumor cells where p53 mutant levels are lower due to GR, have reduced proliferation potential compared to tumors expressing native p53, and can be easily chemo-sensitized, significantly reducing the IC50 of all drugs examined. We then asked whether dietary restriction of glucose affects p53 mutant stability in living organisms. Preliminary results indicate that p53 mutant levels are higher in tissues of animals fed with high glucose-diet, relative to animals fed with a low glucose diet. We are currently investigating whether this change in p53 levels affects proliferation rates. Conclusions. We propose that GR uses the autophagic machinery to induce degradation of oncogenic mutant p53, and thus interrupts their proliferative signals. Our findings further imply that dietary restriction of glucose would keep p53 mutant activity in check. Finally, GR overcomes the well-known chemo-resistance conveyed by p53 mutations. Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4833.

Effects of Non-protein Energy Intake on Whole Body Protein Synthesis, Nitrogen Retention and Glucose Turnover in Goats

The responses of whole body protein and glucose kinetics and of nitrogen (N) metabolism to non-protein energy intake (NPEI) were determined using an isotope dilution approach and measurement of N balance in three adult male goats. The diets containing 1.0, 1.5 and 2.0 times ME maintenance requirement, with fixed intake of CP (1.5 times maintenance) and percentage of hay (33%), were fed twice daily for each 21 d experimental period. After an adaptation period of 11 d, N balance was determined over 3 d. On day 17, whole body protein synthesis (WBPS) and glucose irreversible loss rate (ILR) were determined during the absorptive state by a primed-continuous infusion of []phenylalanine, []tyrosine, []tyrosine and []glucose, with simultaneous measurements of plasma concentrations of metabolites and insulin. Ruminal characteristics were also measured at 6 h after feeding over 3 d. Nitrogen retention tended to increase (p) that of tyrosine. Whole body protein synthesis increased (p). These results suggest that increasing NPEI may enhance WBPS and glucose turnover at the absorptive state and improve the efficiency of digestible N retention in goats, with possibly decreased ammonia and increased amino acid absorption. In addition, simultaneous increases in WBPS and glucose ILR suggest stimulatory effect of glucose availability on WBPS, especially when sufficient amino acid is supplied.

Responses of Listeria monocytogenes to acid stress and glucose availability monitored by measurements of intracellular pH and viable counts

Physiological aspects of the response of Listeria monocytogenes to acidic conditions and effect of glucose availability were studied by fluorescence ratio-imaging microscopy (FRIM) as compared with traditional viable counts. Three types of experiments were conducted: (i) static with measurements of intracellular pH (pH i) at extracellular pH (pH o) values ranging from pH 3.0 to 6.0 at 0.5 pH unit intervals; (ii) kinetic with monitoring of bacterial responses to changes in the pH o from the value of 6.0 to 4.0 or 3.0; (iii) survival experiments studying bacterial recovery in response to a shift to favourable conditions after a treatment at low pH. All the experiments were performed at three levels of glucose in the medium (0, 1, and 10 mM). Both survival and pH i were greatly affected by pH o and glucose availability with the highest values for CFU and pH i at highest glucose concentration and pH o values in the medium in all trials. A high correlation ( R 2=0.995) between pH i and CFU counts was observed. The pH gradient started to collapse at pH o 4 and below for trials with glucose in the medium and at pH o 5.5 and below without glucose. A recovery step was proposed after the apparently lethal treatment to assess cell viability by FRIM.

Effect of glucose availability on pulsatile luteinizing hormone release in rams before and after castration.

The hypothesis tested was that availability of glucose modulates the control of luteinizing hormone (LH) release. A second objective was to determine the role of testicular hormones in the control of pulsatile LH secretion during depressed blood glucose. Serial blood samples were collected at 15 min intervals for 8 h from intact pubertal Suffolk rams (n = 8; 7 months old) on consecutive days (Days 1, 2 and 3). Rams were castrated after sampling on Day 3 and samples were collected 3 weeks later on consecutive days (Days 4, 5 and 6). Insulin (120 units, iv) was given at Hour 4 of each of the six days to lower blood glucose. On Days 1 and 4, no other treatments were given (Control). On Days 2 and 5, LH releasing hormone (LHRH; 5 ng/kg, iv) was given at Hours 5, 6 and 7 to assess the ability of the pituitary to release LH. On Days 3 and 6, N-methyl-D,L-aspartate (NMA; 5 mg/kg, iv) was given at Hours 5, 6 and 7 to assess the ability of the hypothalamus to release LHRH. Insulin reduced plasma glucose by 52% for at least 3 h (P < 0.001). Insulin reduced the mean LH concentration (P < 0.05) and tended to reduce the LH response area (P < 0.10) in castrated animals during the control period. LHRH increased LH pulse number (P < 0.001) in intact rams and increased mean LH concentration (P < 0.01), LH pulse amplitude (P < 0.05) and LH response area (P < 0.01) in castrated animals compared to respective control periods. NMA increased mean LH concentration in intact rams (P < 0.0001) but did not affect mean LH in castrates. NMA increased LH pulse number in rams (P < 0.0001) but decreased number of pulses in castrates (P < 0.0001) compared to control periods. NMA increased LH pulse amplitude in both intact (P < 0.001) and castrated animals (P < 0.05). In conclusion, these results support the hypothesis that blood glucose concentrations influence the control of LH release in sheep. In addition, LH release in response to the LHRH secretagogue, NMA, is positively influenced by testicular hormones.

Involvement of Lactic Acidosis in Anoxia‐Induced Perturbations of Synaptosomal Function

L-Lactate (4-32 mM) added exogenously to resting or depolarised rat forebrain synaptosomes led to a significant decrease in intrasynaptosomal pH. Similarly depolarisation-induced increases in intrasynaptosomal calcium, calcium uptake, and acetylcholine release were all inhibited. These effects mimicked those previously observed in synaptosomes under anoxic conditions and suggest that lactate may be involved in limiting the damage due to calcium accumulation occurring during ischaemia. D-Lactate (added exogenously up to 32 mM) did not produce similar effects on these parameters even though the concentrations of intrasynaptosomal D-lactate reached levels comparable to those obtained with L-lactate (at 8-16 mM exogenous concentration). The results suggest that the mechanism of action of lactate on these parameters is stereospecific for the L-enantiomer. The effect of glucose availability on lactate production was assessed to explore the role of substrate availability on ischaemia/anoxic events. When exogenous glucose was increased (10-60 mM), there was no further increase in lactate production in normoxic synaptosomes, which suggests that glucose is not limiting under these conditions. When glucose was removed, as may occur in complete ischaemia, there was a significant decrease in lactate production after 60 min under anoxic or normoxic conditions. It would seem likely therefore that the mechanism underlying the changes observed in synaptosomes incubated under conditions reflecting complete ischaemia does not involve lactate.

An NMR study on the effect of glucose availability on carbohydrate metabolism in Dipetalonema viteae and Brugia pahangi

Adult Brugia pahangi and Dipetalonema viteae utilise a percentage of absorbed glucose (ca. 15%) in the formation of the disaccharide trehalose [8]. This paper reports an investigation, employing 13C-NMR techniques, of the utilisation of trehalose by these nematodes and also the effect of glucose availability on metabolic product composition. The metabolism of [1- 13C]trehalose in D. viteae differed dramatically from that of [1- 13C]glucose under normal experimental conditions. A succinate/lactate ratio of 0.73 was obtained from the metabolism of [1- 13C]trehalose compared with 0.05 from [1- 13C]glucose at an initial concentration of ca. 5 mM. Similar, but less consistent, results were obtained from B. pahangi adults. Macrofilariae of D. viteae were fed variable, low levels of glucose at hourly intervals for 8 h, and a significant relationship ( P < 0.001) between the glucose addition rate and the ratio of succinate to lactate production was obtained. The lower the amount of glucose added each hour, the higher was the observed succinate to lactate ratio. The percentage yield of succinate increased greatly as the amount of added glucose was diminished. Parallel experiments performed on B. pahangi macrofilariac indicated that B. pahangi did not increase their succinate output so greatly with reduced glucose availability. It is clear that in the absence of available external glucose, B. pahangi and D. viteae draw on their internal trehalose reserves as a source of carbohydrate for energy generation. It is further apparent, particularly in the case of D. viteae, that when glucose availability is reduced, there is a significant switch from homolactate fermentation of exogenous glucose, to the utilisation of a partial tricarboxylic acid cycle, either in the forward or the reverse direction.

The Effect of Glucose Availability and Utilization on Chylomicron Metabolism in the Rat

AbstractFollowing i.v. administration of H3 palmitate labelled chylomicrons a greater amount of radioactivity was recovered from adipose tissue of refed than fasted rats and from insulin treated than insulin deprived diabetic rats. Adipose tissue uptake of label appeared to be potentiated by insulin in normal as well as in diabetic rats. No definite differences in the rate of clearing chylomicrons from blood was noted in insulin treated and insulin deprived diabetic rats. Although the enhanced adipose tissue uptake of triglyceride fatty acid might be related to the availability of α glycerophosphate for esterification it is equally possible that adipose tissue lipoprotein lipase content may be a regulating factor. Heparin, as opposed to saline administration prior to chyle injection, produced marked acceleration in the rate of removal of chyle from the blood of treated and untreated diabetic animals. The accelerated removal was related to accelerated uptake of activity by the liver and could be attributed in part to intravascular lipolysis of chyle triglyceride. The effect of heparin on the degree and the nature of hepatic uptake was no different in treated and untreated diabetic animals.