3-nitro-tyrosine as a peripheral biomarker of minimal hepatic encephalopathy in patients with liver cirrhosis

Objectives: Between 30 and 50% of the cirrhotic patients who do not show symptoms of clinical hepatic encephalopathy (HE) present minimal hepatic encephalopathy (MHE), with mild cognitive impairment. MHE impairs the quality of life, increases the risk of suffering accidents, predicts the appearance of clinical HE, and is associated with shortened lifespan. Early detection of MHE would be very useful. The "gold standard" for MHE diagnosis is the psychometric hepatic encephalopathy score (PHES). However, it is time consuming and needs adjusting for age and educational level. It would be very useful to have some blood biomarker reflecting the presence of MHE in cirrhotic patients. The aim of this work was to identify serum molecules useful as biomarkers for MHE.

Methods: We measured in 63 controls, 43 cirrhotic patients without MHE, and 44 patients with MHE, from Hospital Clinico de Valencia, serum levels of different Amino acids, cyclic guanosine monophosphate (cGMP), nitrites+nitrates, and 3-nitrotyrosine. We analyzed for each parameter its diagnostic accuracy as an indicator of MHE, as assessed using the PHES.

Results: These studies supported that 3-nitro-tyrosine is a good marker for MHE. To validate its utility as a biomarker for MHE, we analyzed in a second cohort of 44 cirrhotic patients without MHE and 18 patients with MHE, from Hospital Arnau de Vilanova, serum levels of 3-nitro-tyrosine, methionine, and citrulline. Citrulline (173±17%), methionine (173±16%), and 3-nitro-tyrosine (857±92%) were increased in sera from patients with MHE when compared with those without MHE. The receiver operating characteristic (ROC) curve analysis of 3-nitro-tyrosine for the diagnosis of MHE in the first cohort showed an area under the curve (AUC) value of 0.96 (95% confidence interval 0.93-0.99). At the cutoff of 14 nM, the specificity was 93%, sensitivity 89%, and positive and negative predictive values were both 91%. When the same cutoff was applied to the second cohort, the specificity was 83% and sensitivity was 94%. The positive and negative predictive values were 70 and 97%, respectively.

Conclusions: This pilot study, to be validated in a larger cohort, shows that determination of 3-nitro-tyrosine in serum, which is easy and not time consuming, is useful to identify patients with MHE, with good sensitivity, specificity, and positive and negative predictive values.