Metabolite profiling identifies pathways associated with metabolic risk in humans

Abstract

Background: Although metabolic risk factors are known to cluster in individuals who are prone to developing diabetes mellitus and cardiovascular disease, the underlying biological mechanisms remain poorly understood.

Methods and results: To identify pathways associated with cardiometabolic risk, we used liquid chromatography/mass spectrometry to determine the plasma concentrations of 45 distinct metabolites and to examine their relation to cardiometabolic risk in the Framingham Heart Study (FHS; n=1015) and the Malmö Diet and Cancer Study (MDC; n=746). We then interrogated significant findings in experimental models of cardiovascular and metabolic disease. We observed that metabolic risk factors (obesity, insulin resistance, high blood pressure, and dyslipidemia) were associated with multiple metabolites, including branched-chain amino acids, other hydrophobic amino acids, tryptophan breakdown products, and nucleotide metabolites. We observed strong associations of insulin resistance traits with glutamine (standardized regression coefficients, -0.04 to -0.22 per 1-SD change in log-glutamine; P<0.001), glutamate (0.05 to 0.14; P<0.001), and the glutamine-to-glutamate ratio (-0.05 to -0.20; P<0.001) in the discovery sample (FHS); similar associations were observed in the replication sample (MDC). High glutamine-to-glutamate ratio was associated with lower risk of incident diabetes mellitus in FHS (odds ratio, 0.79; adjusted P=0.03) but not in MDC. In experimental models, administration of glutamine in mice led to both increased glucose tolerance (P=0.01) and decreased blood pressure (P<0.05).

Conclusions: Biochemical profiling identified circulating metabolites not previously associated with metabolic traits. Experimentally interrogating one of these pathways demonstrated that excess glutamine relative to glutamate, resulting from exogenous administration, is associated with reduced metabolic risk in mice.

Figure 1

Beta coefficient and P values generated from age- and sex-adjusted regression analyses of the relation of each metabolite (standardized and log transformed) with insulin resistance phenotypes and metabolic traits (standardized) in the FHS sample.

Figure 2

Experimental results. (A) Mean (± standard error) area under the curve of serial glucose levels measured after intraperitoneal glucose tolerance test in mice treated for 8 weeks with dietary glutamine, glutamate, or standard chow alone (control). (B) Mean (± standard error) measures of glutamine and citrulline are shown in mice treated with dietary glutamine, glutamate, or standard chow alone (control). (C) Mean (± standard error) measures of systolic, diastolic, and mean blood pressure measurements are shown for mice following either intraperitoneal injection of glutamine plus saline (glutamine) or saline alone (control). (D) Mean (± standard error) measures of glutamine and citrulline are shown for mice following either intraperitoneal injection of glutamine plus saline (glutamine) or saline alone (control).