During tumor growth-when nutrient and anabolic demands are high-autophagy supports tumor metabolism and growth through lysosomal organelle turnover and nutrient recycling. Ras-driven tumors additionally invoke non-autonomous autophagy in the microenvironment to support tumor growth, in part through transfer of amino acids. Here we uncover a third critical role of autophagy in mediating systemic organ wasting and nutrient mobilization for tumor growth using a well-characterized malignant tumor model in Drosophila melanogaster. Micro-computed Xray tomography and metabolic profiling reveal that Ras V12 ; scrib À/À tumors grow 10-fold in volume, while systemic organ wasting unfolds with progressive muscle atrophy, loss of body mass, -motility, -feeding, and eventually death. Tissue wasting is found to be mediated by autophagy and results in host mobilization of amino acids and sugars into circulation. Natural abundance Carbon 13 tracing demonstrates that tumor biomass is increasingly derived from host tissues as a nutrient source as wasting progresses. We conclude that host autophagy mediates organ wasting and nutrient mobilization that is utilized for tumor growth.

Although the advantages of online δ(18)O analysis of organic compounds make its broad application desirable, researchers have encountered NO(+) isobaric interference with CO(+) at m/z 30 (e.g. (14)N(16)O(+), (12)C(18)O(+)) when analyzing nitrogenous substrates. If the δ(18)O value of inter-laboratory standards for substrates with high N:O value could be confirmed offline, these materials could be analyzed periodically and used to evaluate δ(18)O data produced online for nitrogenous unknowns. To this end, we present an offline method based on modifications of the methods of Schimmelmann and Deniro (Anal. Chem. 1985; 57: 2644) and Sauer and Sternberg (Anal. Chem. 1994; 66: 2409), whereby all the N(2) from the gas products of a chlorinated pyrolysis was eliminated, resulting in purified CO(2) for analysis via a dual-inlet isotope ratio mass spectrometry system. We evaluated our method by comparing observed δ(18)O values with previously published or inter-laboratory calibrated δ(18)O values for five nitrogen-free working reference materials; finding isotopic agreement to within ±0.2‰ for SIGMA® cellulose, IAEA-CH3 cellulose (C(6)H(10)O(5)) and IAEA-CH6 sucrose (C(12)H(22)O(11)), and within ±1.8‰ for IAEA-601 and IAEA-602 benzoic acids (C(7)H(6)O(2)). We also compared the δ(18)O values of IAEA-CH3 cellulose and IAEA-CH6 sucrose that was nitrogen-'doped' with adenine (C(5)H(5)N(5)), imidazole (C(3)H(4)N(2)) and 2-aminopyrimidine (C(4)H(5)N(3)) with the undoped δ(18)O values for the same substrates; yielding isotopic agreement to within ±0.7‰. Finally, we provide an independent analysis of the δ(18)O value of IAEA-600 caffeine (C(8)H(10)N(4)O(2)), previously characterized using online systems exclusively, and discuss the reasons for an average 1.4‰ enrichment in δ(18)O observed offline relative to the consensus online δ(18)O value.

The measurement of the oxygen stable isotope content in organic compounds has applications in many fields, ranging from paleoclimate reconstruction to forensics. Conventional High-Temperature Conversion (HTC) techniques require >20 microg of O for a single delta(18)O measurement. Here we describe a system that converts the CO produced by HTC into CO(2) via reduction within a Ni-furnace. This CO(2) is then concentrated cryogenically, and 'focused' into the isotope ratio mass spectrometry (IRMS) source using a low-flow He carrier gas (6-8 mL/min). We report analyses of benzoic acid (C(7)H(6)O(2)) reference materials that yielded precise delta(18)O measurement down to 1.3 microg of O, suggesting that our system could be used to decrease sample requirement for delta(18)O by more than an order of magnitude.

Carbon stable isotope ratios in U.S. milk samples varied with macronutrient content and region of purchase, suggesting that SIA can provide insight into production processes within the U.S. dairy industry, with potential applications in national food adulteration and authentication efforts.

Background Radioactive or stable isotopic labeling of metabolites is a strategy that is routinely used to map the cellular fate of a selected labeled metabolite after it is added to cell culture or to the circulation of an animal. However, a labeled metabolite can be enzymatically changed in cellular metabolism, complicating the use of this experimental strategy to understand how a labeled metabolite moves between organs. These methods are also technically demanding, expensive and potentially toxic. To allow quantification of the bulk movement of metabolites between organs, we have developed a novel application of stable isotope ratio mass spectrometry (IRMS). Results We exploit natural differences in 13C/12C ratios of plant nutrients for a low-cost and non-toxic carbon labeling, allowing a measurement of bulk carbon transfer between organs in vivo. IRMS measurements were found to be sufficiently sensitive to measure organs from individual Drosophila melanogaster larvae, giving robust measurements down to 2.5 μg per sample. We apply the method to determine if carbon incorporated into a growing solid tumor is ultimately derived from food or host tissues. Conclusion Measuring tumor growth in a D. melanogaster larvae tumor model reveals that these tumors derive a majority of carbon from host sources. We believe the low cost and non-toxic nature of this methodology gives it broad applicability to study carbon flows between organs also in other animals and for a range of other biological questions.