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Apr 1, 2009 (Vol. 29, No. 7)

Getting a Handle on Metabolic Disorders

Targets and Methods Vary, but the End-Goal Is the Same—More Effective Therapeutics

  • Biomarker Profiling

    Three researchers at Duke University, Svati Shah, M.D., department of medicine, division of cardiology and center for human genetics; Bill Kraus, M.D., department of medicine, division of cardiology; and Chris Newgard, Ph.D., at the Sarah W. Stedman Center for Nutrition and Metabolism are taking a targeted approach to metabolic and biomarker profiling to identify markers that segregate with metabolic disease states, obesity, and diabetes. 

    The group employs mass spectroscopy-based methods to investigate the relationship of over 70 targeted, quantitative metabolites derived from lipid, protein, and carbohydrate metabolism with human disease. 

    Dr. Shah outlined the potential role of profiling these small molecule metabolites, which are byproducts of cellular metabolism, in understanding disease mechanism and as biomarkers of disease risk. She detailed examples of her group’s work in using these quantitative metabolomic profiles, and showed how they have led to a deeper understanding of obesity and cardiovascular disease. She also described the team’s effort to link to other omics in their studies for a systems biology approach. 

    Dr. Shah shared data from two studies conducted by the group. In the Genecard study, they evaluated whether these metabolite profiles were heritable in families heavily burdened with early-onset coronary artery disease, with the eventual goal of identifying markers predictive of cardiovascular disease prior to overt clinical presentation. These investigations built upon prior reports in plants and mice that these small molecule metabolites are heritable.

    “Specifically, we are looking for blood markers that could report on risk,” Dr. Shah said. “The study uses samples taken from families where at least two siblings presented with cardiovascular disease before the age of 51 in men and before the age of 56 in women. Eight families sampled over three generations revealed that these small molecule metabolites were more similar within families than between families, even after adjusting for shared environmental effects, suggesting a strong genetic component to variability in these profiles.

    “The profiles themselves suggest that disturbances in mitochondrial function may be mediating cardiovascular disease in these families. We are continuing to expand these studies, to study different ethnicities and expand the study to other geographies.”

    Based on an unbiased statistical approach using principal components analysis the team found that metabolites in three pathways tended to track together: a signature reporting on urea cycle activity in mitochondria, one reporting on arginine metabolism, and one reporting on branched chain amino acid metabolism. 

    In a different study, Dr. Newgard’s group has shown that obese patients who also display insulin resistance show aberrant branched chain amino acid metabolism. Further, the team found that this aberrancy was associated with insulin resistance independent of the patient’s weight. 

    Having established the heritability of these metabolite profiles in families burdened with early-onset cardiovascular disease, the team then investigated whether they could serve as biomarkers of coronary artery disease status. Dr. Kraus initiated a study called Cathgen in the cardiac catheterization laboratory at Duke in 2001, where all consenting patients are enrolled in a biorepository of DNA, RNA, and plasma samples combined with carefully collected clinical data. 

    From this study of over 8,000 individuals, the team then conducted a case-control study in two independent subsets and found that metabolic profiles similar to ones in the Genecard study could differentiate patients with coronary artery disease from those without, and importantly, these profiles seem to add to what we already know about a person’s clinical risk of cardiovascular disease based on age, race, sex, and risk factors. 

    Finally the team discussed what they called “Retro-Translation,” which refers to their work to understand the underlying biology of metabolic signatures in human disease. These mechanisms can only be investigated by animal testing where it’s possible to be more invasive to look for cause and effect. In fact, Dr. Newgard’s group has done such studies of branched chain amino acid metabolism in obese rats.

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