Targeted NMR-based serum metabolic profiling of serine, glycine and methionine in acute-on-chronic liver failure patients: Possible insights into mitochondrial dysfunction.

Background: A recent study based on blood metabolomics analysis revealed inflammation-associated mitochondrial dysfunction as a potential mechanism underlying acute-on-chronic liver failure (ACLF) in cirrhotic patients. Serine, glycine, and methionine serve to maintain a healthy immune system and adequately sustain mitochondrial functionality in hepatocytes for regulating redox homeostasis through the production of antioxidant glutathione (GSH). Based on this, we hypothesized that the circulatory levels of serine, glycine and methionine will be altered in ACLF patients due to acute worsening of hepatic function and may provide novel insights into the mitochondrial dysfunction as well.

Methods: The circulatory concentrations of serine, glycine, and methionine were estimated in the sera of 40 ACLF patients and 49 normal controls (NC) subject using 1D H-CPMG NMR spectra recorded at 800 MHz NMR spectrometer. The resulting metabolite concentrations were compared using unpaired Student -test and -value < 0.05 was considered as the criterion of statistical significance. The diagnostic potential and statistical correlations were established using receiver-operating-characteristic (ROC) curve analysis and Pearson-r method, respectively.

Results: Circulating levels of serine and glycine were significantly decreased in ACLF patients (Ser = 23.06 ± 1.67 µM and Gly = 83.11±7.52 µM) compared to NC subjects (Ser = 55.61 ± 2.28 µM and Gly = 156.9±7.16 µM) with -value < 0.0001, whereas those of methionine were significantly increased in ACLF (22.60 ± 2.49 µM) compared to NC subjects (=14.63 ± 0.85 µM) with -value < 0.0015. Further, the ROC analysis yielded satisfactory sensitivity and specificity for serine, glycine, and methionine-to-glycine ratio (MGR) with area under ROC (AUROC) curve values equal to: 0.95 [95%CI = 0.91-0.99] for Ser; 0.87 [95%CI = 0.79-0.95] for Gly; and 0.90 [95%CI = 0.83-0.97] for MGR.

Conclusion: Compared to NC subjects, the sera of ACLF patients were characterized by hypermethioninemia and aberrantly decreased levels of serine and glycine suggesting mitochondrial dysfunction as the possible mechanism for disturbed redox homeostasis and therefore depressed immune system in ACLF.