The Aging Process: A Metabolomics Perspective

Abstract

Aging process is characterized by a progressive decline of several organic, physiological, and metabolic functions whose precise mechanism remains unclear. Metabolomics allows the identification of several metabolites and may contribute to clarifying the aging-regulated metabolic pathways. We aimed to investigate aging-related serum metabolic changes using a metabolomics approach. Fasting blood serum samples from 138 apparently healthy individuals (20−70 years old, 56% men) were analyzed by Proton Nuclear Magnetic Resonance spectroscopy (1H NMR) and Liquid Chromatography-High-Resolution Mass Spectrometry (LC-HRMS), and for clinical markers. Associations of the metabolic profile with age were explored via Correlations (r); Metabolite Set Enrichment Analysis; Multiple Linear Regression; and Aging Metabolism Breakpoint. The age increase was positively correlated (0.212 ≤ r ≤ 0.370, p < 0.05) with the clinical markers (total cholesterol, HDL, LDL, VLDL, triacylglyceride, and glucose levels); negatively correlated (−0.285 ≤ r ≤ −0.214, p < 0.05) with tryptophan, 3-hydroxyisobutyrate, asparagine, isoleucine, leucine, and valine levels, but positively (0.237 ≤ r ≤ 0.269, p < 0.05) with aspartate and ornithine levels. These metabolites resulted in three enriched pathways: valine, leucine, and isoleucine degradation, urea cycle, and ammonia recycling. Additionally, serum metabolic levels of 3-hydroxyisobutyrate, isoleucine, aspartate, and ornithine explained 27.3% of the age variation, with the aging metabolism breakpoint occurring after the third decade of life. These results indicate that the aging process is potentially associated with reduced serum branched-chain amino acid levels (especially after the third decade of life) and progressively increased levels of serum metabolites indicative of the urea cycle.

Keywords: liquid chromatography-high-resolution mass spectrometry; metabolism; metabolome; nuclear magnetic resonance.

Figure 1

Overall correlation heatmap between age, clinical markers, and metabolite levels. Blue and green colors represent positive and negative correlations (r), respectively. High-density lipoprotein (HDL); Low-density lipoprotein (LDL); Very low-density lipoprotein (VLDL).

Figure 2

Metabolite Set Enrichment Analysis. The size and color (varying from red to white) of each circle represent the pathway enrichment ratio (computed by Hits/Expected hits) and p-value, respectively. The most enriched pathways enjoying connections were labeled.

Figure 3

Score (A) and loading (C,D) plots of Principal Component Analysis (PCA) of main serum metabolites related to aging. Illustration of the metabolism breakpoint (B) from the intersection (dashed line) between the two straight lines (age vs. PC1 scores). Black and red circles represent Training and Test samples, respectively.