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May 1, 2013 (Vol. 33, No. 9)

Metabolomics Advances Reshape Dx Arena

  • Energy Pathways in Alzheimer’s

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    Nontargeted metabolomics approach using liquid chromatography time-of-flight mass spectrometry (LC-TOF-MS) demonstrated that metabolic changes in plasma (top) accurately mimic changes in cerebrospinal fluid (CSF, bottom). Analysis was done in plasma and CSF from the same 15 patients with Alzheimer’s Disease (AD) and age and gender matched cognitively normal (CNT) individuals. [Mayo Clinic]

    “Our research focuses on evaluation of the dynamic changes of mitochondrial functioning in relation to the progression of Alzheimer’s disease (AD),” noted Eugenia Trushina, Ph.D., associate consultant, Mayo Clinic.

    “Some assessments, such as mitochondrial trafficking and distribution in neurons, could only be done in animal models. However, metabolomic profiles of energy pathways could be developed by minimally invasive sampling of blood or cerebrospinal fluid. Moreover, these biochemical pathways are highly conserved between species, and therefore, easily translatable between mice and humans.”

    Results of FDG-PET scans of AD patients implicate early changes in energy metabolism. Dr. Trushina’s team analyzed multiple mitochondrial metabolic pathways, including Krebs cycle, amino-acid metabolism, and energy transfer, using transgenic animal models of familial AD.

    In comparison with nontransgenic mice, metabolic profiles of the three types of FAD mice revealed significant alterations. Distinction in metabolic profiles was observed early in AD development, before typical behavioral manifestations and prior to formation of amyloid plaques.

    “It is an exciting time in metabolomic analysis,” continued Dr. Trushina. “New statistical methods and quantitative algorithms now allow for analysis of thousands of metabolites. Even though the structure of some of them may not have been definitively identified, we can use the analysis to draw a map of correlative changes.”

    Using Mayo Clinic Alzheimer’s Disease Research Center and Mayo Clinic Study of Aging tissue repository, Dr. Trushina and colleagues demonstrated similar changes in mitochondrial pathways, along with alterations in pathways involved in lipid trafficking and homeostasis, in cerebrospinal fluid and plasma from patients with early AD.

    The team is planning to use targeted metabolomics to look at specific changes in mitochondrial metabolites in an attempt to identify predictive biomarkers of early AD, to compare the metabolic profiles of patients with various genetic backgrounds and of the patients transitioning from mild cognitive impairment to AD.

    “We hope that our research leads to the development of an in vivo drug testing model that would aid in the development of drugs targeting early pathways,” concluded Dr. Trushina. “Most current drugs attempt to combat the amyloid plaques. Our research indicates that by then it may be too late.”

  • Essential Lipid Pathways Uncovered

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    Waters reports that its SYNAPT® G2-S uses Triwave® ion mobility separations technology to provide greater analytical selectivity, specificity, and structural elucidation for applications ranging from proteins to small molecules. Ion mobility differentiates ions based on their size, shape and charge, and their mass.

    Lipids are a major constituent of food and are vitally important in our diet as an essential source of energy. Lipids play a key role in cell signaling, endocrine actions, and membrane functions.

    “Lipidomics is an emerging field in need of comprehensive analytical approaches,” commented Giorgis Isaac, Ph.D., senior research scientist, Waters. “Waters has developed state-of-the-art instrumentation that could accommodate both global profiling of intact molecules and determination of lipid structure.”

    Since the position of double bonds within lipid molecules impacts their signaling and other biological functions, localizing the bonds may be critical for understanding lipid metabolism. Waters has established itself as a player the lipidomics field with instruments equipped with ion mobility separation technology (IMS).

    IMS has the capability to separate ions by size, charge, and collisional cross sections. The latter roughly measures the “safe zones” around molecules before they collide, which helps to determine sizes of molecules in close proximity. Waters’ SYNAPT G2-S High Definition MS system performs fragmentation of a target molecule both before and after IMS, which helps determine the double bond position in the lipids. IMS is a very rapid method of lipid profiling, providing a greater degree of confidence for lipid identification, said Dr. Isaac.

    Scientists at Waters in collaboration with Jing X. Kang, M.D., Ph.D., at Harvard Medical School used SYNAPT G2-S to study lipid metabolism of a transgenic fat-1 mouse. This animal model is capable of what no other mammal can do—convert omega-6 into omega-3 fatty acids. The only difference between these two fatty acids is that for omega-3, double bonds start at the third carbon atom, and for omega-6, at the sixth carbon atom.

    TransOmics™, Waters’ data-processing tool, performed quantitative comparison and statistical analyses to find those lipids that significantly change between the samples and then identify the actual molecules from the MS data. “We completed detailed profiling of bioactive lipid species in plasma and liver samples from wild type and fat-1 mice,” said Dr. Isaac. “This research provides new clues to the pathways and mechanisms that can be associated with health benefits of omega-3 fatty acids.”

  • NMR for Epidemiological Screening

    “Mass spectrometry and nuclear magnetic resonance (NMR) play complementary roles in metabolomics analysis,” said Manfred Spraul, Ph.D., director of NMR applications, Bruker BioSpin. Bruker has expertise in analytical NMR applications for metabolomics profiling. The company has developed a suite of NMR-based products to support both food quality control and clinical applications.

    “NMR has several advantages that position this technology for analysis of biological fluids,” continued Dr. Spraul. “NMR needs minimal sample preparation, and it is extremely reproducible and fully quantitative over the full dynamic range of concentrations.”

    NMR reproducibility is what attracted the scientists to utilize it in large multinational phenome project studies. As long as the samples are collected under standard operating procedures and analyzed using the same magnetic field strength, the resulting data is readily comparable and exchangeable on a worldwide basis. Moreover, when a new pattern is found it can be compared with all previous data obtained under the same standards.

    Dr. Spraul’s team is the key partner in a project to establish NMR-based screening of newborn babies at 12 hospitals in Turkey. First, the team built an NMR profile of a “normal” newborn, using over 1,000 urine samples. The model captures all possible individual differences within normal range, claimed Dr. Spraul. In an untargeted approach, each new sample is compared with this spectral fingerprint.

    In targeted mode, 64 compounds indicative of inborn errors of metabolism are checked for deviations from the norm. Although rare, these deviations can be readily identified with high statistical probability even if previously unknown.

    “We are interested in creating models for each day of the newborn development,” said Dr. Spraul. By matching samples with the model reference spectrum, physicians will be able to detect the first signs of latent hereditary metabolic errors, he explained.

    Bruker also is a funding partner of the Imperial Clinical Phenome Centre, based at St. Mary’s Hospital in London. There, the NMR technology will be used to assist physicians by providing real-time data for the patients, especially in intensive care units.

    NMR spectra could predict whether or not a patient is recovering, experiencing organ rejection, or responding to the medication. “This technology has matured and is reaching the point when it can be a real partner in the clinical decision-making process,” concluded Dr. Spraul.

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