Dramatic Improvements to the Doubly Labeled Water Technique by Measurement of 17O

描述（由申请人提供）：美国肥胖症的高患病率是一个主要的公共卫生问题，因为超重和肥胖个体患许多慢性疾病的风险增加。肥胖源于总热量消耗和总能量消耗（TEE）之间的不平衡，因此TEE的准确测量在理解和最终扭转这种流行病方面起着关键作用。在自由生活的个体中测量TEE的金标准是双标记水（DLW）方法;该方法的主要局限性包括高成本和单个测量的精度仅为<$7%。在这个小企业创新研究（SBIR）项目中，洛斯加托斯研究（LGR）将开发、制造和测试一种新型的基于激光的分析仪，该分析仪基于LGR的基于激光的离轴集成腔输出光谱技术专利，通过测量17 O/16 O来校正18 O和2 H中的自然同位素波动，从而显著改善TEE的DLW测量。三同位素水分析仪（TIWA）将能够进行实时、同时、高通量的分析（45个样本/天）监测人体体液中的H2O中的2 H/1H、18 O/16 O和17 O/16 O，目标准确度和精度优于<$0.6%（2 H/1H）、<$0.15%（18 O/16 O）和<$天然同位素丰度下17 O/16 O为0.2%。对于已标记2 H和18 O的富集沃茨，准确度和精密度将与IRMS相当，2 H/1H优于<$1.0%，18 O/16 O优于<$0.2%。通过测量17 O/16 O，TIWA将允许在TEE的DLW测量期间量化18 O/16 O和2 H/1H的同位素背景波动，从而消除DLW实验期间所做的重要的“恒定背景”假设，从而提高测量精度并显著降低TEE实验的成本。基于在第一阶段测量的良好相关性，我们估计同位素背景波动的测量将导致TEE的DLW测试的精度增加40%，允许较小的研究规模，同时保持测量的统计功效，并将研究成本降低约72%！此外，提高的精度引入了将该技术从人群研究扩展到单个受试者的TEE的准确评估的可能性。在第二阶段，LGR将继续与Edward Melanson教授和John Speakman教授合作，展示和应用一种改进的仪器，使用最少准备的人类尿液样本进行同步同位素测量。将使用改进的三重同位素方法测量TEE，并将结果与代谢室中TEE的同时金标准测量、IRMS测量的标准DLW和使用基于激光的同位素分析测量的标准DLW进行比较。在本研究项目结束时，LGR将演示使用TIWA进行三同位素DLW测量，并根据经验确定TEE精度的提高和DLW方法成本的降低，这是由于使用17 O/16 O测量背景波动。

DESCRIPTION (provided by applicant): The high prevalence of obesity in the US is a major public health concern, as overweight and obese individuals are at increased risk for many chronic diseases. Obesity stems from an imbalance between total caloric consumption and total energy expenditure (TEE), therefore accurate measurements of TEE play a pivotal role in understanding and ultimately reversing this epidemic. The gold standard for measuring TEE in free-living individuals is the doubly labeled water (DLW) method; major limitations of the method include high cost and precision of only ¿ 7% for individual measurements. In this Small Business Innovative Research (SBIR) project, Los Gatos Research (LGR) will develop, fabricate, and test a novel, laser-based analyzer based on LGR's patented, laser-based Off-Axis Integrated Cavity Output Spectroscopy technology to dramatically improve DLW measurements of TEE by measuring 17O/16O to correct for natural isotopic fluctuations in 18O and 2H. The Triple Isotope Water Analyzer (TIWA) will be capable of real-time, simultaneous, high-throughput (45 samples/day) monitoring of 2H/1H, 18O/16O, and 17O/16O in H2O from human bodily fluids, with a target accuracy and precision of better than ¿0.6% for 2H/1H, ¿0.15% for 18O/16O, and ¿0.2% for 17O/16O at natural isotopic abundances. For enriched body waters that have been labeled with 2H and 18O, the accuracy and precision will be comparable to IRMS and better than ¿1.0% for 2H/1H and ¿0.2% for 18O/16O. By measuring 17O/16O, the TIWA will allow quantification of isotopic background fluctuation in 18O/16O and 2H/1H during DLW measurements of TEE, thus eliminating the significant "constant background" assumption made during DLW experiments, and thereby improving measurement precision and significantly reducing the cost of TEE experiments. Based on the excellent correlation measured during Phase I, we estimate that measurement of the isotopic background fluctuation will result in a 40% increase in the precision of DLW tests of TEE, allowing for smaller study sizes while maintaining the statistical power of the measurements and reducing study costs by an estimated 72%! Additionally, the improved precision introduces the possibility of extending this technique from population studies to the accurate assessment of the TEE of a single subject. During Phase II, LGR will continue to work with Prof. Edward Melanson and Prof. John Speakman to demonstrate and apply an improved instrument for simultaneous isotope measurements using minimally prepared, human urine samples. TEE will be measured using the improved, triple isotope method and the results compared with simultaneous, gold-standard measurement of TEE in a metabolic chamber, standard DLW as measured by IRMS, and standard DLW as measured using laser-based isotope analysis. At the conclusion of this research project, LGR will have demonstrated the use of the TIWA for triple-isotope DLW measurements and empirically determined the improvement in TEE accuracy and reduction in the DLW method cost due to the measurement of background fluctuation using 17O/16O.