Diagnostic Applications of Nuclear Magnetic Resonance-Based Urinary Metabolomics

Abstract

Metabolomics is a rapidly growing field with potential applications in various disciplines. In particular, metabolomics has received special attention in the discovery of biomarkers and diagnostics. This is largely due to the fact that metabolomics provides critical information related to the downstream products of many cellular and metabolic processes which could provide a snapshot of the health/disease status of a particular tissue or organ. Many of these cellular products eventually find their way to urine; hence, analysis of urine via metabolomics has the potential to yield useful diagnostic and prognostic information. Although there are a number of analytical platforms that can be used for this purpose, this review article will focus on nuclear magnetic resonance-based metabolomics. Furthermore, although there have been many studies addressing different diseases and metabolic disorders, the focus of this review article will be in the following specific applications: urinary tract infection, kidney transplant rejection, diabetes, some types of cancer, and inborn errors of metabolism. A number of methodological considerations that need to be taken into account for the development of a clinically useful optimal test are discussed briefly.

Keywords: Diagnosis; NMR spectroscopy; metabolomics; urine.

Figure 1

Schematic diagram of metabolomics workflow in the urinalysis.,, 1D indicates 1-dimensional; 2D, 2-dimensional; ANOVA, analysis of variance; NMR, nuclear magnetic resonance; PCA, principal component analysis; PLS-DA, partial least squares discriminant analysis.

Figure 2

Nuclear magnetic resonance spectra of lactose metabolism in urine. Escherichia coli produces lactate, acetate, succinate, and ethanol through lactose metabolism. Lactate is the specific product in lactose metabolism by E coli; other bacilli (Pseudomonas aeruginosa, K pneumoniae, etc) do not produce lactate in urine.

Figure 3

Partial 500-MHz single-pulse hydrogen-1 nuclear magnetic resonance spectra of normal human urine (A) and urine collected from 4 patients on day 3 postrenal transplantation showing immediate functioning graft (B), urinary tract infection (C), renal tubular ischemia, (D) and nonfunctioning graft (E). DMA indicates dimethylamine; GLC glucose; TMAO, trimethylamine N-oxide.

Figure 4

Hydrogen-1 nuclear magnetic resonance spectrum (400 MHz) of a urine sample from a patient with type 2 diabetes showing the 2 input subregions and the 4 discriminatory regions identified by the optimal region selection algorithm.

Figure 5

The 500-MHz hydrogen-1 nuclear magnetic resonance spectra of urine from (A) a healthy (control) subject, and (B) a lung cancer patient. Signal assignment: 1, α-hydroxybutyrate; 2, valine; 3, isobutyrate; 4, β-aminoisobutyrate; 5, methyl-β-hydroxybutyrate; 6, β-hydroxyisovalerate; 7, lactic acid and threonine; 8, α-hydroxyisobutyrate; 9, alanine; 10, N-acetylglutamine; 11, pyruvate; 12, succinate; 13, α-ketoglutarate; 14, citrate; 15, dimethylamine; 16, creatinine; 17, trimethylamine N-oxide and betaine; 18, scyllo-inositol; 19, glycine; 20, hippurate; 21, trigonelline; 22, p-hydroxyphenylacetate; 23, phenylacetylglycine; 24, histidine; 25, 3-methylhisitidine; 26, formate; 27, trigonellinamide.