RESPONSES OFF THE RAT'S LIVER AND SERUM GLUTAMATE AND ISOC1TRATE .DEHYDROGENASES AND ORNITHINE CARBOMYL- TRANSFERASE TO A HAEMAGGLUTININ FROM LIMA BEAN (Phaseolus lunatus Linn.)

The responses of liver and serum gluta­mate dehydrogenase (CDII; EC 1.4.1.2.), isocitrate dehydrogenase (ICDH; EC 1.1. 1.42) and the urea cycle enzyme, ornithine carbamoyltransferase (OCT; EC 2. 1.3.3) to dietary lima bean haemagglutinin (lectin) were assessed using a total of S4 growing rats. The GDH and ICDH activities in the liver were highly significantly (P < 0.001) eleva­ted by dietary haemagglutinin. The activi­ties correlated significantly (P < 0.01) with the haemagglutinin levels in a positive quadratic fashion as judged by their res­pective R2, coefficient of multiple deter­mination of 0.91 and 0.95. Liver OCT activity was significantly (P < 0.05) depresse­ed but correlated poorly with haemagglu­tinin levels. Activities of the serum dehydrogenases were significantly (P < 0.05) altered by dietary haemagglutinin. Although serum OCT activity tended to increase, such increases were however not significant. Serum GDH and ICDH values correlated significantly (P < 01.05) with haemagglutinin levels with respective R2 values of 0.71 and 0.67. The veterinary implication is highlighted and some remedies suggested.

Activity of the liver enzyme ornithine carbamoyltransferase (OTC) in blood: LC-MS/MS assay for non-invasive diagnosis of ornithine carbamoyltransferase deficiency

Background: Liver enzymes are released from hepatocytes into circulation and their activity can be measured in the blood. We examined whether the plasma activity of the liver enzyme ornithine carbamoyltransferase, determined by a novel liquid chromatography-mass spectrometry (LC-MS/MS) assay, could be utilized for the detection of OTC deficiency (OTCD), an X-linked inborn error of the urea cycle. Methods: The plasma ornithine carbamoyltransferase (OTC) activity was assayed in the reverse reaction using isotopically labeled citrulline-d4 as a substrate and by determination of the product, ornithine-d4, by LC-MS/MS analysis. Results: The plasma OTC activity in the controls was in the range of 111–658 pkat/L (n=49, median 272 pkat/L), and the activity increased linearly with serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activities in patients with hepatopathy. The OTC activity was subsequently determined in 32 individuals carrying mutations in the OTC gene, and OTC/ALT and OTC/AST ratios were calculated to account for the degree of hepatopathy, which is a common finding in OTCD. The OTC/ALT ratio enabled clear differentiation of OTCD hemizygotes (n=11, range 0–69×10−6) from controls (504–3440×10−6). This ratio also enabled the detection of 11 of 12 symptomatic heterozygotes (range 38–794×10−6), while this marker did not allow for reliable differentiation of asymptomatic heterozygotes (n=9) from controls. Conclusions: LC-MS/MS assay of plasma OTC activity enabled the detection of all hemizygous and the majority of symptomatic heterozygous OTCD patients in the tested cohort. This study demonstrates that non-invasive assay of enzymes expressed predominantly in the liver could be used as an alternative approach for diagnosing inborn errors of metabolism.