Plasma metabolomic profile in nonalcoholic fatty liver disease

Abstract

The plasma profile of subjects with non-alcoholic fatty liver disease (NAFLD), steatosis and steatohepatitis (NASH), was examined using an untargeted global metabolomic analysis in order to identify specific disease-related pattern/s and to identify potential non-invasive biomarkers. Plasma samples were obtained after an overnight fast from histologically confirmed non-diabetic subjects with hepatic steatosis (N=11) or NASH (N=24), and compared with healthy, age and sexmatched controls (n=25). Subjects with NAFLD were obese, were insulin resistant and had higher plasma concentration of homocysteine and total cysteine and lower plasma concentrations of total glutathione. Metabolomic analysis showed markedly higher levels of glycocholate, taurocholate and glycochenodeoxycholate in subjects with NAFLD. Plasma concentrations of long chain fatty acids were lower and concentrations of free carnitine, butyrylcarnitine and methylbutyryl carnitine were higher in NASH. Several glutamyl dipeptides were higher, while cysteine-glutathione levels were lower in NASH and steatosis. Other changes included higher branched chain amino acids, phosphocholine, carbohydrates (glucose, mannose), lactate, pyruvate, and several unknown metabolites. Random forest analysis and recursive partitioning of the metabolomic data could separate healthy subjects from NAFLD with an error rate of ~8%, and NASH from healthy controls with an error rate of 4%. Hepatic steatosis and steatohepatitis could not be separated using the metabolomic profile.Conclusion-Plasma metabolomic analysis revealed marked changes in bile salts and in biochemicals related to glutathione in subjects with non-alcoholic fatty liver disease. Statistical analysis identified a panel of biomarkers that could effectively separate healthy controls from NAFLD and healthy controls from NASH. These biomarkers can potentially be used to follow response to therapeutic interventions.

Genome-scale metabolic modelling of hepatocytes reveals serine deficiency in patients with non-alcoholic fatty liver disease

“…Three different enzymes constitute the SSP and it is earlier reported that PSPH is the rate-controlling enzyme for SSP in the liver 58 . Activation of the SSP through the amplification of PSPH may also decrease the flux through pyruvate and lactate formation in cytosol, as increased pyruvate and lactate levels were previously reported in NASH patients 50 . Recently, Frayling et al 59 performed a genome-wide association study using 1,004 non-diabetic individuals and identified 8 common genetic variants relevant to insulin sensitivity and type 2 diabetes that are strongly linked to NASH phenotype.…”

“…This could possibly result in an accumulation of intracellular glutamate, which would then be compensated for by reduced uptake from/increased export to the blood. Notably, a previous study detected a significantly higher level of glutamate (60% increase, P ¼ 9.808E À 09) in the plasma profiling of the amino acids in NASH patients 50 . At the same time, this may result in a higher demand for valine in hepatocytes, and given that valine is an essential amino acid this would arguably correlate with an increased uptake.…”

“…At the same time, this may result in a higher demand for valine in hepatocytes, and given that valine is an essential amino acid this would arguably correlate with an increased uptake. Indeed, the same study 50 reported that the plasma valine concentration displayed significant changes (10% increase, P-value ¼ 0.012).…”

“…To test this hypothesis, we checked the expression level of enzymes that catalyse the biosynthesis of serine in the liver of NASH patients, and it was observed that the expression levels of PHGDH, PSAT1, PSPH in serine synthesis pathway (SSP), and SHMT1 and SHMT2 enzymes were significantly downregulated (Supplementary Table 6). Decreased levels of serine in NASH patients was supported by plasma profiling of amino acids, where the serine level in the plasma is relatively decreased (15% decrease, P-value ¼ 0.0568) compared with healthy subjects 50 .…”

OCT1 is a high-capacity thiamine transporter that regulates hepatic steatosis and is a target of metformin

“…Twenty metabolites were overrepresented in the HEK293-OCT1 cells, including 2-methylbutyrylcarnitine, a metabolite that is elevated in patients with NAFLD ( Fig. 3A) (19). Notably, thiamine was among the most significantly elevated metabolites, ***P = 0.00016 (Fig.…”