DNA variation can be used as a systematic source of perturbation in segregating populations as a way to infer regulatory networks via the integration of large-scale, high-dimensional molecular profiling data.

Mutations in either the mitochondrial or nuclear genomes can give rise to respiratory chain disease (RCD), a large class of devastating metabolic disorders. Their clinical management is challenging, in part because we lack facile and accurate biomarkers to aid in diagnosis and in the monitoring of disease progression. Here we introduce a sequential strategy that combines biochemical analysis of spent media from cell culture with analysis of patient plasma to identify disease biomarkers. First, we applied global metabolic profiling to spotlight 32 metabolites whose uptake or secretion kinetics were altered by chemical inhibition of the respiratory chain in cultured muscle . These metabolites span a wide range of pathways and include lactate and alanine, which are used clinically as biomarkers of RCD. We next measured the cell culture-defined metabolites in human plasma to discover that creatine is reproducibly elevated in two independent cohorts of RCD patients, exceeding lactate and alanine in magnitude of elevation and statistical significance. In cell culture extracellular creatine was inversely related to the intracellular phosphocreatine:creatine ratio suggesting that the elevation of plasma creatine in RCD patients signals a low energetic state of tissues using the phosphocreatine shuttle. Our study identifies plasma creatine as a potential biomarker of human mitochondrial dysfunction that could be clinically useful. More generally, we illustrate how spent media from cellular models of disease may provide a window into the biochemical derangements in human plasma, an approach that could, in principle, be extended to a range of complex diseases.biochemical genetics | biomarker | metabolomics | mitochondria T he respiratory chain (RC) of mammalian cells comprises a series of five enzymatic complexes embedded in the inner mitochondrial membrane and serves as the machinery for oxidative phosphorylation. Changes in RC activity influence key parameters such as the cellular energy charge and the NADH/ NAD + ratio and can impact the numerous metabolic pathways coupled to the RC directly or indirectly. In humans, inherited defects in mitochondrial (mt) or nuclear genes that encode RC proteins or factors necessary for its maturation and assembly lead to respiratory chain disease (RCD) (1). It is estimated that RCD affects at least 18.4 in 100,000 people (2) and represents the most common group of inborn errors of metabolism (3).The clinical presentation of RCD is highly variable in severity, age of onset, and the combination of organ systems involved, and the factors contributing to this variability are poorly understood (1). Consequently, the diagnosis can be challenging, and there are very limited means of objectively monitoring disease progression. A number of diagnostic algorithms have been proposed (4-6) that integrate clinical, biochemical, histological, and molecular findings. Abnormal concentrations of several metabolites in biological fluids, including the elevation of lactate, alanine, pyruvate, and the lac...

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The quadruplex structure of the oligomer d(T2G4T) is more stable in the presence of K+ than in the presence of Na+. This enhanced stability correlates with the preferential binding of K+ to a small number of specific sites on the quadruplex. In contrast, Na+ and K+ compete on an equal footing for atmospheric binding. Both 39K+ and 23Na+ are, when specifically bound, significantly inhibited in their rotational mobility, so that the quadrupolar relaxation reflects the molecular tumbling of the oligomer, which occurs on the time scale of nanoseconds. This rotational immobilization is in distinct contrast to the high rotational mobility of atmospherically bound cations. On the other hand, all NMR-visible 39K+ in solution is in rapid exchange among all environments (free, specifically bound, and atmospherically bound) implying that the lifetime of specifically coordinated 39K+ must be significantly shorter than a millisecond. A similar conclusion holds for 23Na+. The oligomer d(T2G4T) forms two distinct Hoogsteen base-paired structures in NaCl solution, separated by a large kinetic barrier. Neither of these structures is as stable with respect to base pair opening as is the quadruplex structure formed in KCl solution. Only one of these two structures is associated with rotational immobilization of bound 23Na+.

The favorable bile acid binding characteristics of sevelamer provide a compelling explanation for its ability to lower LDL cholesterol in hemodialysis patients and in healthy volunteers.