Reference materials for MS-based untargeted metabolomics and lipidomics: a review by the metabolomics quality assurance and quality control consortium (mQACC).

INTRODUCTION: The metabolomics quality assurance and quality control consortium (mQACC) is enabling the identification, development, prioritization, and promotion of suitable reference materials (RMs) to be used in quality assurance (QA) and quality control (QC) for untargeted metabolomics research. OBJECTIVES: This review aims to highlight current RMs, and methodologies used within untargeted metabolomics and lipidomics communities to ensure standardization of results obtained from data analysis, interpretation and cross-study, and cross-laboratory comparisons. The essence of the aims is also applicable to other 'omics areas that generate high dimensional data. RESULTS: The potential for game-changing biochemical discoveries through mass spectrometry-based (MS) untargeted metabolomics and lipidomics are predicated on the evolution of more confident qualitative (and eventually quantitative) results from research laboratories. RMs are thus critical QC tools to be able to assure standardization, comparability, repeatability and reproducibility for untargeted data analysis, interpretation, to compare data within and across studies and across multiple laboratories. Standard operating procedures (SOPs) that promote, describe and exemplify the use of RMs will also improve QC for the metabolomics and lipidomics communities. CONCLUSIONS: The application of RMs described in this review may significantly improve data quality to support metabolomics and lipidomics research. The continued development and deployment of new RMs, together with interlaboratory studies and educational outreach and training, will further promote sound QA practices in the community.

Phototransduction Influences Metabolic Flux and Nucleotide Metabolism in Mouse Retina.

Production of energy in a cell must keep pace with demand. Photoreceptors use ATP to maintain ion gradients in darkness, whereas in light they use it to support phototransduction. Matching production with consumption can be accomplished by coupling production directly to consumption. Alternatively, production can be set by a signal that anticipates demand. In this report we investigate the hypothesis that signaling through phototransduction controls production of energy in mouse retinas. We found that respiration in mouse retinas is not coupled tightly to ATP consumption. By analyzing metabolic flux in mouse retinas, we also found that phototransduction slows metabolic flux through glycolysis and through intermediates of the citric acid cycle. We also evaluated the relative contributions of regulation of the activities of α-ketoglutarate dehydrogenase and the aspartate-glutamate carrier 1. In addition, a comprehensive analysis of the retinal metabolome showed that phototransduction also influences steady-state concentrations of 5'-GMP, ribose-5-phosphate, ketone bodies, and purines.

Enzymatic synthesis of substituted epicatechins for bioactivity studies in neurological disorders.

Glucuronidated and/or methylated metabolites of the proanthocyanidin (PA) monomer (-)-epicatechin are detected in both blood and brain following feeding of rodents with a monomeric grape seed PA extract shown to reduce symptoms in a mouse model of Alzheimer's disease. To generate metabolites for future mechanistic studies, we investigated the ability of recombinant human glucuronosyl transferases of the UGT1A and UGT2B families to glucuronidate epicatechin or 3'-O-methyl epicatechin in vitro. Of twelve enzymes tested, UGT1A9 was the most efficient, producing epicatechin 3'-O-glucuronide as the major product. Incubation of UGT1A9 with 3'-O-methyl-epicatechin resulted in two major products, one of which was identified as 3'-O-methyl-epicatechin 5-O-glucuronide, a major metabolite found in blood plasma and brain tissue of the rodents following feeding with a grape seed extract. We also investigated in vitro methylation of epicatechin and epicatechin glucuronides by human catechol O-methyltransferase. Enzymatic production of 3'-O-methyl-epicatechin 5-O-glucuronide was optimized to 50% overall yield. These studies form a basis for generation of mg quantities of pure epicatechin (methyl) glucuronides of biological significance, and provide clarification of structure of previously identified epicatechin metabolites.