Search Results (8)

Background: Insufficient treatment options are available for metabolic dysfunction-associated steatotic liver disease (MASLD). Flavonoids and topiramate have been studied for weight loss but need investigation into their effects on liver metabolism. This study’s aim was to examine the effects of flavonoids or topiramate on glucose metabolic carbon flux in a cell culture model of steatosis. Methods: Steatosis was induced in HepG2 cells through exposure to oleic acid (OA, 0.5 mml/L) conjugated to bovine serum albumin (2:1). Additionally, 50% U¹³C-glucose was supplied in the medium as a stable isotope tracer. Cells were treated with DMSO, 10 μM of naringenin, morin, silibinin, or topiramate (44 μM) for 72 h. A non-steatotic, untreated HepG2 cell control was included. Cell extracts were analyzed by gas chromatography/mass spectrometry and mass isotopomer distribution analysis for glycogen synthesis, de novo fatty acid synthesis, tricarboxylic acid (TCA) cycle activity, and ribose synthesis. Groups were compared by ANOVA with Tukey’s pair-wise testing. Results: Compared to untreated HepG2 controls, OA-exposed steatotic cells exhibited increased lipid accumulation by ORO staining (1.6-fold), enhanced palmitate de novo synthesis, reduced pyruvate carboxylase/pyruvate dehydrogenase (PC/PDH) ratio, and reduced ribose synthesis. Treatment with topiramate or silibinin ameliorated the lipid accumulation (1.3-fold) and mitigated enhancement of de novo synthesis. Morin-treated cells exhibited enhanced de novo synthesis but suppressed ribose synthesis. Conclusions: Potential mechanisms of reduced lipid accumulation by topiramate and silibinin may include suppression of palmitate de novo synthesis and a relative decrease in carbon flux through the PDH pathway. Further studies are needed on potential utility in MASLD based on their specific metabolic effects. Full article

The pentose phosphate pathway (PPP) plays a key role in the cellular regulation of immune function; however, little is known about the interplay of metabolic adjustments in granulocytes, especially regarding the non-oxidative PPP. For the determination of metabolic mechanisms within glucose metabolism, we propose a novel set of measures for ¹³C-metabolic flux analysis based on ex vivo parallel tracer experiments ([1,2-¹³C]glucose, [U-¹³C]glucose, [4,5,6-¹³C]glucose) and gas chromatography–mass spectrometry labeling measurements of intracellular metabolites, such as sugar phosphates and their fragments. A detailed constraint analysis showed that the permission range for net and irreversible fluxes was limited to a three-dimensional space. The overall workflow, including its Bayesian flux estimation, resulted in precise flux distributions and pairwise confidence intervals, some of which could be represented as a line due to the strength of their correlation. The principal component analysis that was enabled by these behaviors comprised three components that explained 99.6% of the data variance. It showed that phagocytic stimulation reversed the direction of non-oxidative PPP net fluxes from ribose-5-phosphate biosynthesis toward glycolytic pathways. This process was closely associated with the up-regulation of the oxidative PPP to promote the oxidative burst. Full article

Glycogen is a readily deployed intracellular energy storage macromolecule composed of branched chains of glucose anchored to the protein glycogenin. Although glycogen primarily occurs in the liver and muscle, it is found in most tissues, and its metabolism has been shown to be important in cancers and immune cells. Robust analysis of glycogen turnover requires stable isotope tracing plus a reliable means of quantifying total and labeled glycogen derived from precursors such as ¹³C₆-glucose. Current methods for analyzing glycogen are time- and sample-consuming, at best semi-quantitative, and unable to measure stable isotope enrichment. Here we describe a microscale method for quantifying both intact and acid-hydrolyzed glycogen by ultra-high-resolution Fourier transform mass spectrometric (UHR-FTMS) and/or NMR analysis in stable isotope resolved metabolomics (SIRM) studies. Polar metabolites, including intact glycogen and their ¹³C positional isotopomer distributions, are first measured in crude biological extracts by high resolution NMR, followed by rapid and efficient acid hydrolysis to glucose under N₂ in a focused beam microwave reactor, with subsequent analysis by UHR-FTMS and/or NMR. We optimized the microwave digestion time, temperature, and oxygen purging in terms of recovery versus degradation and found 10 min at 110–115 °C to give >90% recovery. The method was applied to track the fate of ¹³C₆-glucose in primary human lung BEAS-2B cells, human macrophages, murine liver and patient-derived tumor xenograft (PDTX) in vivo, and the fate of ²H₇-glucose in ex vivo lung organotypic tissue cultures of a lung cancer patient. We measured the incorporation of ¹³C₆-glucose into glycogen and its metabolic intermediates, UDP-Glucose and glucose-1-phosphate, to demonstrate the utility of the method in tracing glycogen turnover in cells and tissues. The method offers a quantitative, sensitive, and convenient means to analyze glycogen turnover in mg amounts of complex biological materials. Full article

Perinatal nutrition affects future milk production. The number of mammary epithelial cells affect milk production capacity. Therefore, it was hypothesized that the level of colostrum intake affects the proliferation rate and the total number of mammary epithelial cells in the gland. The ratio of newly synthesized protein to newly synthesized DNA reflects the relative amount of cellular differentiation to cell division. The study objective was to determine the relationship between the level of colostrum intake and 24 h-level of circulating amino acid, glucose and insulin with mammary parenchyma histological features, cell division and protein synthesis over the first week postnatal. One of two standardized doses of a homogenate colostrum sample, 10% (n = 8) and 20% (n = 8) of birth bodyweight, was fed to gilts over the first 24 h postnatal. Gilts were administered deuterium oxide immediately after birth and daily to label newly synthesized DNA and proteins. Gilts were euthanized on postnatal day seven, and DNA and protein were isolated from mammary parenchyma. DNA and protein fractional synthesis (f) and fractional synthetic rate (FSR) were calculated using mass isotopomer distribution analysis. The ratio of protein f and FSR to DNA f and FSR were calculated and used to indicate the relative amounts of differentiation to cell division. Mammary morphological development was also analyzed by measuring the parenchymal epithelial area and the stromal and epithelial proliferation index on postnatal day seven. Colostrum dose was not related to any of the variables used to evaluate mammary development. However, plasma lysine levels at 24 h postnatal were positively related to average daily gain (ADG; r = 0.54, p = 0.05), DNA f (r = 0.57; p = 0.03) and DNA FSR (r = 0.57; p = 0.03) in mammary parenchyma. Plasma lysine was inversely related to the ratio of protein to DNA f and FSR (r = −0.56; p = 0.04). ADG was related to the parenchymal epithelial area and DNA and protein f and FSR (p < 0.05). These relationships support the idea that the nutritional environment affects early mammary development and that higher lysine levels in the perinatal period favored a greater degree of cell division versus differentiation in mammary of neonatal pigs and thus, warrant further investigations. Full article

Lipids comprise diverse classes of compounds that are important for the structure and properties of membranes, as high-energy fuel sources and as signaling molecules. Therefore, the turnover rates of these varied classes of lipids are fundamental to cellular function. However, their enormous chemical diversity and dynamic range in cells makes detailed analysis very complex. Furthermore, although stable isotope tracers enable the determination of synthesis and degradation of complex lipids, the numbers of distinguishable molecules increase enormously, which exacerbates the problem. Although LC-MS-MS (Liquid Chromatography-Tandem Mass Spectrometry) is the standard for lipidomics, NMR can add value in global lipid analysis and isotopomer distributions of intact lipids. Here, we describe new developments in NMR analysis for assessing global lipid content and isotopic enrichment of mixtures of complex lipids for two cell lines (PC3 and UMUC3) using both ¹³C₆ glucose and ¹³C₅ glutamine tracers. Full article

The goal of this study is to map the metabolic pathways of poorly understood bacterial phytopathogen, Xanthomonas oryzae (Xoo) BXO43 fed with plant mimicking media XOM2 containing glutamate, methionine and either 40% [¹³C₅] xylose or 40% [¹³C₆] glucose. The metabolic networks mapped using the KEGG mapper and the mass isotopomer fragments of proteinogenic amino acids derived from GC-MS provided insights into the activities of Xoo central metabolic pathways. The average ¹³C in histidine, aspartate and other amino acids confirmed the activities of PPP, the TCA cycle and amino acid biosynthetic routes, respectively. The similar labelling patterns of amino acids (His, Ala, Ser, Val and Gly) from glucose and xylose feeding experiments suggests that PPP would be the main metabolic route in Xoo. Owing to the lack of annotated gene phosphoglucoisomerase in BXO43, the ¹³C incorporation in alanine could not be attributed to the competing pathways and hence warrants additional positional labelling experiments. The negligible presence of ¹³C incorporation in methionine brings into question its potential role in metabolism and pathogenicity. The extent of the average ¹³C labelling in several amino acids highlighted the contribution of pre-existing pools that need to be accounted for in ¹³C-flux analysis studies. This study provided the first qualitative insights into central carbon metabolic pathway activities in Xoo. Full article

The turnover of muscle protein is responsive to different (patho)-physiological conditions but little is known about the rate of synthesis at the level of individual proteins or whether this varies between different muscles. We investigated the synthesis rate of eight proteins (actin, albumin, ATP synthase alpha, beta enolase, creatine kinase, myosin essential light chain, myosin regulatory light chain and tropomyosin) in the extensor digitorum longus, diaphragm, heart and soleus of male Wistar rats (352 ± 30 g body weight). Animals were assigned to four groups (n = 3, in each), including a control and groups that received deuterium oxide (²H₂O) for 4 days, 7 days or 14 days. Deuterium labelling was initiated by an intraperitoneal injection of 10 μL/g body weight of 99.9% ²H₂O-saline, and was maintained by administration of 5% (v/v) ²H₂O in drinking water provided ad libitum. Homogenates of the isolated muscles were analysed by 2-dimensional gel electrophoresis and matrix-assisted laser desorption ionisation time of flight mass spectrometry. Proteins were identified against the SwissProt database using peptide mass fingerprinting. For each of the eight proteins investigated, the molar percent enrichment (MPE) of ²H and rate constant (k) of protein synthesis was calculated from the mass isotopomer distribution of peptides based on the amino acid sequence and predicted number of exchangeable C–H bonds. The average MPE (2.14% ± 0.2%) was as expected and was consistent across muscles harvested at different times (i.e., steady state enrichment was achieved). The synthesis rate of individual proteins differed markedly within each muscle and the rank-order of synthesis rates differed among the muscles studied. After 14 days the fraction of albumin synthesised (23% ± 5%) was significantly (p < 0.05) greater than for other muscle proteins. These data represent the first attempt to study the synthesis rates of individual proteins across a number of different striated muscles. Full article

The metabolism of 2-¹³C/¹⁵N-glycine and U-¹³C-glucose was determined in four tissue blocks (adductor muscle, stomach and digestive gland, mantle, and gills) of the Eastern oyster (Crassostrea virginica) using proton (¹H) and carbon-13 (¹³C) nuclear magnetic resonance (NMR) spectroscopy. The oysters were treated in aerated seawater with three treatments (5.5 mM U-¹³C-glucose, 2.7 mM 2-¹³C/¹⁵N-glycine, and 5.5 mM U-¹³C-glucose plus 2.7 mM 2-¹³C/¹⁵N-glycine) and the relative mass balance and ¹³C fractional enrichments were determined in the four tissue blocks. In all tissues, glycine was metabolized by the glycine cycle forming serine exclusively in the mitochondria by the glycine cleavage system forming 2,3-¹³C-serine. In muscle, a minor amount of serine-derived pyruvate entered the Krebs cycle as substantiated by detection of a trace of 2,3-¹³C-aspartate. In all tissues, U-¹³C-glucose formed glycogen by glycogen synthesis, alanine by glycolysis, and glutamate and aspartate through the Krebs cycle. Alanine was formed exclusively from glucose via alanine transaminase and not glycine via alanine-glyoxylate transaminase. Based on isotopomer analysis, pyruvate carboxylase and pyruvate dehydrogenase appeared to be equal points for pyruvate entry into the Krebs cycle. In the 5.5 mM U-¹³C-glucose plus 2.7 mM 2-¹³C/¹⁵N-glycine emergence treatment used to simulate 12 h of “low tide”, oysters accumulated more ¹³C-labeled metabolites, including both anaerobic glycolytic and aerobic Krebs cycle intermediates. The aerobic metabolites could be the biochemical result of the gaping behavior of mollusks during emergence. The change in tissue distribution and mass balance of ¹³C-labeled nutrients (U-¹³C-glucose and 2-¹³C/¹⁵N-glycine) provides the basis for a new quantitative fluxomic method for elucidating sub-lethal environmental effects in marine organisms called whole body mass balance phenotyping (WoMBaP). Full article