Methionine enkephalin concentration and enkephalin-degrading activity are elevated in blood in children with cholestasis

Abstract

Objective To examine the concentration and degradation of methionine enkephalin in children with cholestasis of differing aetiologies. Patients The study included 41 children aged from 3 months to 14 years, with Alagille syndrome, Byler's disease, extrahepatic biliary duct atresia, or idiopathic cholestasis. Methods Plasma methionine enkephalin was measured using a specific radioimmunoassay. Liver extracts were prepared from biopsy homogenates. Enkephalin-degrading activity was evaluated by an aluminium silicate binding assay for quantification of the degradation of ‘short’ radiolabelled peptide hormones, and with high-performance liquid chromatography. Results The patients showed statistically significant (P<0.005) elevation of blood enkephalin concentrations (mean ± SD): 190±195 versus 50±35 in healthy controls and 60±15pg/ml in disease controls. Serum enkephalin-degrading activity was also markedly elevated: 1149±269 (Alagille syndrome), 400±146 (Byler's disease), 1038±616 (extrahepatic biliary duct atresia), 549±180 (idiopathic cholestasis) versus 234±44 (disease controls), and 290±24 pg/min/ml (healthy controls; P<0.05). Enkephalin-degrading activity in the liver extracts was virtually the same in patients with extrahepatic biliary duct atresia and chronic active hepatitis: 42±18 versus 36±14pg/min/mg, respectively (P>0.05). Endogenous methionine enkephalin was stable in plasma extracted in EDTA but it was degraded in the serum samples. The inhibitory and substrate specificity data suggest that aminopeptidase-M is the major enkephalin-degrading enzyme in both the serum and liver extracts, and that its activity is elevated in children with cholestasis. Conclusion Children with cholestasis of differing aetiologies exhibit significant elevation of both circulating methionine enkephalin levels and activity of serum aminopeptidase-M. Hepatic enkephalin degradation was retained in patients with extrahepatic biliary duct atresia. The physiological and pathophysiological significance of these observations requires further study.