The 1H NMR spectrum of urine exhibits a large number of detectable and quantifiable metabolites and hence urine metabolite profiling is potentially useful for the study of systems biology and the discovery of biomarkers for drug development or clinical applications. While a number of metabolites (50-100) are readily detectable in urine by NMR, a much larger number is potentially available if lower concentration species can be detected unambiguously. Lower concentration metabolites are thought to be more specific to certain disease states and thus it is important to detect these metabolites with certainty. We report the identification of 4-deoxythreonic acid, a relatively low concentration endogenous metabolite that has not been previously identified in the 1H NMR spectrum of human urine. The use of HPLC and NMR spectroscopy facilitated the unequivocal and non-invasive identification of the molecule in urine which is complicated by extensive peak overlap and multiple, similar resonances from other metabolites such as 3-hydroxybutanoic acid. High-resolution detection and good sensitivity were achieved by the combination of multiple chromatographic fraction collection, sample pre-concentration, and the use of a cryogenically cooled NMR probe.
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"The use of chromatographic methods to simplify sample matrices by isolating metabolites of interest prior to NMR analysis has high utility for a variety of biological investigations [24,25,26,27,28,29]. This approach has also benefited from the use of sample pre-concentration techniques such as solid phase extraction (SPE) and column trapping to extend NMR detection limits significantly and thus circumvent the issue of sample dilution attributed to solvent mixing in the chromatographic step . "
[Show abstract][Hide abstract] ABSTRACT: The complementary use of liquid chromatography (LC) and nuclear magnetic resonance (NMR) has shown high utility in a variety of fields. While the significant benefit of spectral simplification can be achieved for the analysis of complex samples, other limitations remain. For example, 1H LC-NMR suffers from pH dependent chemical shift variations, especially during urine analysis, owing to the high physiological variation of urine pH. Additionally, large solvent signals from the mobile phase in LC can obscure lower intensity signals and severely limit the number of metabolites detected. These limitations, along with sample dilution, hinder the ability to make reliable chemical shift assignments. Recently, stable isotopic labeling has been used to detect quantitatively specific classes of metabolites of interest in biofluids. Here we present a strategy that explores the combined use of two-dimensional hydrophilic interaction chromatography (HILIC) and isotope tagged NMR for the unambiguous identification of carboxyl containing metabolites present in human urine. The ability to separate structurally related compounds chromatographically, in off-line mode, followed by detection using 1H-15N 2D HSQC (two-dimensional heteronuclear single quantum coherence) spectroscopy, resulted in the assignment of low concentration carboxyl-containing metabolites from a library of isotope labeled compounds. The quantitative nature of this strategy is also demonstrated.
"A one-dimensional 1H selective TOCSY experiment (See additional file 1, Figure S1) observed three related 1H resonances in the same molecule. Further two-dimensional experiments [See additional file 1, Figure S2] allowed the full 1H and 13C characterization [See additional file 1, Table S1] of the two diastereoisomers of 2,3-dihydroxybutanoic acid [See additional file 1, Figure S3]: 4-deoxy-erythronic acid and 4-deoxy-threonic acid, both of which have previously been identified in human urine . "
[Show abstract][Hide abstract] ABSTRACT: The 'exposome' represents the accumulation of all environmental exposures across a lifetime. Top-down strategies are required to assess something this comprehensive, and could transform our understanding of how environmental factors affect human health. Metabolic profiling (metabonomics/metabolomics) defines an individual's metabolic phenotype, which is influenced by genotype, diet, lifestyle, health and xenobiotic exposure, and could also reveal intermediate biomarkers for disease risk that reflect adaptive response to exposure. We investigated changes in metabolism in volunteers living near a point source of environmental pollution: a closed zinc smelter with associated elevated levels of environmental cadmium.
High-resolution ¹H NMR spectroscopy (metabonomics) was used to acquire urinary metabolic profiles from 178 human volunteers. The spectral data were subjected to multivariate and univariate analysis to identify metabolites that were correlated with lifestyle or biological factors. Urinary levels of 8-oxo-deoxyguanosine were also measured, using mass spectrometry, as a marker of systemic oxidative stress.
Six urinary metabolites, either associated with mitochondrial metabolism (citrate, 3-hydroxyisovalerate, 4-deoxy-erythronic acid) or one-carbon metabolism (dimethylglycine, creatinine, creatine), were associated with cadmium exposure. In particular, citrate levels retained a significant correlation to urinary cadmium and smoking status after controlling for age and sex. Oxidative stress (as determined by urinary 8-oxo-deoxyguanosine levels) was elevated in individuals with high cadmium exposure, supporting the hypothesis that heavy metal accumulation was causing mitochondrial dysfunction.
This study shows evidence that an NMR-based metabolic profiling study in an uncontrolled human population is capable of identifying intermediate biomarkers of response to toxicants at true environmental concentrations, paving the way for exposome research.
BMC Medicine 06/2012; 10(1):61. DOI:10.1186/1741-7015-10-61 · 7.25 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Metabolomics was used to explore the mechanism of Rhizoma coptidis in treating type II diabetes mellitus. The rat model of type II diabetes mellitus was constructed by an injection of streptozocin (40 mg/kg), along with diets of fat emulsion. The rats were divided into four groups, the control group, the model group, the Rhizoma coptidis group (10 g/kg) and the metformin group (0.08 g/kg). After the treatment for 30 d, blood samples were collected to test biomedical indexes, and 24 h urine samples were collected for the metabolomics experiment. In the Rhizoma coptidis group, fasting blood glucose (FBG), total cholesterol (TC) and total plasma triglycerides (TG) were significantly decreased by 59.26%, 58.66% and 42.18%, respectively, compared with those in the model group. Based on gas chromatography-mass spectrometry, a urinary metabolomics method was used to study the mechanism of Rhizoma coptidis in treating diabetes mellitus. Based on the principal component analysis, it was found that the model group and control group were separated into two different clusters. The Rhizoma coptidis group was located between the model group and the control group, closer to the control group. Twelve significantly changed metabolites of diabetes mellitus were detected and identified, including 4-methyl phenol, benzoic acid, aminomalonic acid, and so on. After diabetic rats were administered with Rhizoma coptidis, 7 metabolites were significantly changed, and L-ascorbic acid and aminomalonic acid which related with the oxidative stress were significantly regulated to normal. The pharmacological results showed that Rhizoma coptidis could display anti-hyperglycemic and anti-hyperlipidemic effects. The Rhizoma coptidis had antioxidation function in preventing the occurrence of complications with diabetes mellitus to some extent. The work illustrates that the metabolomics method is a useful tool to study the treatment mechanism of traditional Chinese medicine.
Se pu = Chinese journal of chromatography / Zhongguo hua xue hui 06/2012; 30(1):8-13. DOI:10.3724/SP.J.1123.2011.08039