No abstract

A critical question facing the field of metabolomics is whether data obtained from different centers can be effectively compared and combined. An important aspect of this is the interlaboratory precision (reproducibility) of the analytical protocols used. We analyzed human samples in six laboratories using different instrumentation but a common protocol (the AbsoluteIDQ p180 kit) for the measurement of 189 metabolites via liquid chromatography (LC) or flow injection analysis (FIA) coupled to tandem mass spectrometry (MS/MS). In spiked quality control (QC) samples 82% of metabolite measurements had an interlaboratory precision of <20%, while 83% of averaged individual laboratory measurements were accurate to within 20%. For 20 typical biological samples (serum and plasma from healthy individuals) the median interlaboratory coefficient of variation (CV) was 7.6%, with 85% of metabolites exhibiting a median interlaboratory CV of <20%. Precision was largely independent of the type of sample (serum or plasma) or the anticoagulant used but was reduced in a sample from a patient with dyslipidaemia. The median interlaboratory accuracy and precision of the assay for standard reference plasma (NIST SRM 1950) were 107% and 6.7%, respectively. Likely sources of irreproducibility were the near limit of detection (LOD) typical abundance of some metabolites and the degree of manual review and optimization of peak integration in the LC-MS/MS data after acquisition. Normalization to a reference material was crucial for the semi-quantitative FIA measurements. This is the first interlaboratory assessment of a widely used, targeted metabolomics assay illustrating the reproducibility of the protocol and how data generated on different instruments could be directly integrated in large-scale epidemiological studies.

Inositol pyrophosphates belong to the diverse family of inositol polyphosphate species that have a range of signaling functions. Since the discovery of inositol pyrophosphates in the early 1990s, enormous progress has been achieved in characterising this class of molecules, linking their biological presence to a wide range of cellular functions, including vesicular trafficking, apoptosis, telomere maintenance and protein phosphorylation. The activity of inositol pyrophosphates appears to be related to their rapid turnover in cells and also to their pyrophosphate groups, which are considered to contain high-energy bonds. Together, these observations suggest that inositol pyrophosphates may represent a class of cellular messengers with basic and not yet fully characterised functions. This review aims at summarising the recent progress of our knowledge of this exciting class of molecules, from inositol pyrophosphate discovery to the description of their physiological functions.