Remethylation and transsulfuration of methionine in cirrhosis: Studies with L-[2H3-methyl-1-13C]methionine



Disturbances of the methionine cycle may result in liver injury. Patients with alcohol-induced liver disease often exhibit hypermethioninemia and a delayed clearance (CL) of methionine, but the extent to which transsulfuration and remethylation pathways of the cyclic methionine metabolism are affected is unknown. Methionine turnover was determined in 7 healthy volunteers and 6 patients with alcohol-induced cirrhosis after oral administration of 2 mg/kg [2H3-methyl-1-13C]methionine, which permitted us to follow transsulfuration by its decarboxylation to 13CO2 and remethylation by replacement of the labeled methyl group by an unlabeled one. Basal plasma concentrations of endogenous methionine (50 ± 5 vs. 25 ± 2 μmol/L, mean ± SEM, P < .001) were significantly higher in patients with cirrhosis and its CL was significantly decreased (774 ± 103 vs. 2,050 ± 141 mL/min, P < .001). Methionine turnover amounted to 42 ± 4 vs. 27 ± 3 μmol/kg/h (P < .05) in controls and patients with cirrhosis, respectively. The fraction of administered methionine undergoing remethylation was lower in patients with cirrhosis (7.6 ± 1.5 vs. 14.1 ± 1.1%, P < .005). However, because of the larger pool of circulating methionine, the total flux of methionine through the remethylation pathway was similar in both groups. A significantly lower fraction of the administered dose appeared in the form of 13CO2 in breath in patients with cirrhosis (2.2 ± 0.4 vs. 11.0 ± 0.8%, P < .001). In conclusion, the data indicate that the liver with cirrhosis compensates for a decreased activity of remethylating enzymes by operating at higher concentrations of methionine. In contrast, transsulfuration is impaired in patients with alcohol-induced cirrhosis such that an assessment of transsulfuration by a simple breath test may provide a clinically useful estimate of hepatic function.