Tumor cell proliferation requires rapid synthesis of macromolecules including lipids, proteins, and nucleotides. Many tumor cells exhibit rapid glucose consumption, with most of the glucose-derived carbon being secreted as lactate despite abundant oxygen availability (the Warburg effect). Here, we used 13 C NMR spectroscopy to examine the metabolism of glioblastoma cells exhibiting aerobic glycolysis. In these cells, the tricarboxylic acid (TCA) cycle was active but was characterized by an efflux of substrates for use in biosynthetic pathways, particularly fatty acid synthesis. The success of this synthetic activity depends on activation of pathways to generate reductive power (NADPH) and to restore oxaloacetate for continued TCA cycle function (anaplerosis). Surprisingly, both these needs were met by a high rate of glutamine metabolism. First, conversion of glutamine to lactate (glutaminolysis) was rapid enough to produce sufficient NADPH to support fatty acid synthesis. Second, despite substantial mitochondrial pyruvate metabolism, pyruvate carboxylation was suppressed, and anaplerotic oxaloacetate was derived from glutamine. Glutamine catabolism was accompanied by secretion of alanine and ammonia, such that most of the amino groups from glutamine were lost from the cell rather than incorporated into other molecules. These data demonstrate that transformed cells exhibit a high rate of glutamine consumption that cannot be explained by the nitrogen demand imposed by nucleotide synthesis or maintenance of nonessential amino acid pools. Rather, glutamine metabolism provides a carbon source that facilitates the cell's ability to use glucose-derived carbon and TCA cycle intermediates as biosynthetic precursors.cancer ͉ glioblastoma ͉ Warburg effect ͉ glutaminolysis ͉ anaplerosis I n mammals, cell proliferation is controlled by signal transduction pathways stimulated by lineage-specific growth factors or, in tumors, constitutive activation of these pathways through oncogenic mutations. A proximal effect of signaling pathways is a robust increase in nutrient uptake (1-3). Cells must also allocate these molecules into appropriate metabolic pathways to produce and maintain pools of intermediates needed to synthesize macromolecules. Therefore, a complete understanding of the biology of cell proliferation will require a comprehensive understanding of the regulation of metabolic fluxes.Glucose and glutamine are two of the most abundant nutrients in plasma, and together they account for most carbon and nitrogen metabolism in mammalian cells. Rapid cell proliferation has been associated with a robust but apparently wasteful metabolism of glucose. In the 1920s, Otto Warburg demonstrated that ascites tumor cells had high rates of glucose consumption and lactate production despite availability of sufficient oxygen to oxidize glucose completely (4). The ''Warburg effect'' is taken to be a metabolic hallmark of aggressive tumors; however, the phenotype is also observed in nontransformed cells during rapid proliferation (2, 5). Gl...

In recent years, a variety of low molecular weight antibiotics have been isolated from diverse animal species. These agents, which include peptides, lipids, and alkaloids, exhibit antibiotic activity against environmental microbes and are thought to play a role in innate immunity. We report here the discovery of a broad-spectrum steroidal antibiotic isolated from tissues of the dogfish shark Squalus acanthias. This water-soluble antibiotic, which we have named squalamine, exhibits potent bactericidal activity against both Gram-negative and Gram-positive bacteria. In addition, squalamine is fungicidal and induces osmotic lysis of protozoa. The chemical structure of the antibiotic 313-N-1-{N-[3-(4-aminobutyl)]-1,3-diaminopropane}-7a,24'-dihydroxy-Sacholestane 24-sulfate has been determined by fast atom bombardment mass spectroscopy and NMR. Squalamine is a cationic steroid characterized by a condensation of an anionic bile salt intermediate with spermidine. The discovery of squalamine in the shark implicates a steroid as a potential host-defense agent in vertebrates and provides insights into the chemical design of a family of broad-spectrum antibiotics.Animals must defend themselves against environmental microbes if they are to survive. Multiple mechanisms of host defense against microbes have been described such as the array of humoral and cellular responses of the classical vertebrate immune system and less-specific physical and chemical barriers. Over the past several years, an increasing number of low molecular weight antibiotic substances, believed to play a role in defense against environmental microbes, have been isolated from diverse species of animals. These molecules include peptides (1-3), lipids (4, 5), and alkaloids (6-8).In the course of our studies exploring the diversity of antibiotics from animal sources, we have surveyed tissues from a number of animal species (9, 10). We focused our search for antibiotic substances on the gastrointestinal tract of various animals after the recent discovery of peptide antibiotics in the gut of frogs (11), pigs (12, 13), mice (14), and humans (34). In the course of our survey, we discovered that stomach extracts of the shark Squalus acanthias exhibited potent antimicrobial activity, prompting efforts to purify and identify the responsible molecule.In this report we describe the isolation, structural determination, and characterization of a water-soluble cationic steroid from the shark that exhibits potent antimicrobial activity against fungi, protozoa, and both Gram-negative and Gram-positive bacteria. This molecule is shown to be an unusual adduct of spermidine with an anionic bile salt intermediate that, to our knowledge, is without precedent in vertebrates. We have named the aminosterol "squalamine," derived from the genus Squalus and its chemical structure as an amine. MATERIALS AND METHODSPurification of Squlamine. Squalus acanthias sharks were captured off the New England coast. The shark stomach tissue (400 g) was frozen immediately after dissectio...

Abstract-Recent evidence indicates that the type of atherosclerotic plaque, rather than the degree of obstruction to flow, is an important determinant of the risk of cardiovascular complications. In previous work, the feasibility of using MRI for the characterization of plaque components was shown. This study extends the previous work to all the plaque components and shows the accuracy of this method. Twenty-two human carotid endarterectomy specimens underwent ex vivo MRI and histopathological examination. Sixty-six cross sections were matched between MRI and histopathology. In each cross section, the presence or absence of plaque components were prospectively identified on the MRI images. The overall sensitivity and specificity for each tissue component were very high. Calcification and fibrocellular tissue were readily identified. Lipid core was also identifiable. However, thrombus was the plaque component for which MRI had the lowest sensitivity. A semiautomated algorithm was created to identify all major atherosclerotic plaque components. MRI can characterize carotid artery plaques with a high level of sensitivity and specificity. isruption of atherosclerotic plaques is the most frequent underlying cause of the unpredictable onset of acute thromboembolic vascular events including sudden death, myocardial infarction, unstable angina, stroke, transient cerebral ischemia, and peripheral thromboemboli. 1,2 Although clinical risk factors for atherosclerosis help predict risk of these events, identification of patients with plaques vulnerable to disruption is not possible by angiography that only visualizes the lumen. There is therefore a need for an in vivo noninvasive method for characterizing atherosclerotic plaques and identifying the "vulnerable" plaque.Previous work has shown that MRI can characterize both ex vivo 3-7 and in vivo 8 -11 the composition of human atherosclerotic plaques. However, the sensitivity and specificity of MRI have not been determined.This study reports the development of high-resolution MRI criteria for the ex vivo tissue characterization of human carotid atherosclerotic plaques and their sensitivity and specificity in comparison with histopathology. Using these criteria, a semiautomatic segmentation algorithm is developed for characterizing the constituents of an atherosclerotic plaque. Methods SpecimensHuman carotid endarterectomy specimens were studied. Specimens were obtained fresh and intact from the operating room, washed in phosphate buffered saline, grossly described, and samples taken for routine surgical pathology. The remaining 1-to 2-cm-long segments were flash frozen at Ϫ80°C until imaged. On the day of imaging, the specimens were placed in saline and slowly warmed to 37°C in a water bath. The artery was placed in either a 10-or 12-mm MR tube (Wilmad Glass) using the smallest possible tube for a given specimen. Care was taken to remove any air bubbles. Previous studies have shown no change in the T1 and T2 of atheromatous plaques under these conditions of freezing and rewa...