👤 Sujith V W Weerasinghe

Carbamoyl phosphate synthetase 1 (CPS1) is a highly abundant mitochondrial urea cycle enzyme that is expressed primarily in hepatocytes. CPS1 is constitutively and physiologically secreted into bile but is released into the bloodstream upon acute liver injury (ALI). Given its abundance and known short half-life, we tested the hypothesis that it may serve as a prognostic serum biomarker in the setting of acute liver failure (ALF). CPS1 levels were determined using enzyme-linked immunosorbent assay and immunoblotting of sera collected by the ALF Study Group (ALFSG) from patients with ALI and ALF (103 patients with acetaminophen and 167 non-acetaminophen ALF etiologies). A total of 764 serum samples were examined. The inclusion of CPS1 was compared with the original ALFSG Prognostic Index by area under the receiver operating characteristic curve analysis. CPS1 values for acetaminophen-related patients were significantly higher than for non-acetaminophen patients (P < .0001). Acetaminophen-related patients who received a liver transplant or died within 21 days of hospitalization exhibited higher CPS1 levels than patients who spontaneously survived (P = .01). Logistic regression and area under the receiver operating characteristic analysis of CPS1 enzyme-linked immunosorbent assay values improved the accuracy of the ALFSG Prognostic Index, which performed better than the Model for End-Stage Liver Disease, in predicting 21-day transplant-free survival for acetaminophen- but not non-acetaminophen-related ALF. An increase of CPS1 but not alanine transaminase or aspartate transaminase, when comparing day 3 with day 1 levels was found in a higher percentage of acetaminophen transplanted/dead patients (P < .05). Serum CPS1 determination provides a new potential prognostic biomarker to assess patients with acetaminophen-induced ALF. Show less

Several serum markers are used to assess hepatocyte damage, but they have limitations related to etiology specificity and prognostication. Identification of novel hepatocyte-specific biomarkers could provide important prognostic information and better pathogenesis classification. We tested the hypothesis that hepatocyte-selective biomarkers are released after subjecting isolated mouse hepatocytes to Fas-ligand-mediated apoptosis. Proteomic analysis of hepatocyte culture medium identified the mitochondrial matrix protein carbamoyl phosphate synthetase-1 (CPS1) among the most readily detected proteins that are released by apoptotic hepatocytes. CPS1 was also detected in mouse serum upon acute challenge with Fas-ligand or acetaminophen and in hepatocytes upon hypoosmotic stress, independent of hepatocyte caspase activation. Furthermore, CPS1 was observed in sera of mice chronically fed the hepatotoxin 3,5-diethoxycarbonyl-1,4-dihydrocollidine. Mouse CPS1 detectability was similar in serum and plasma, and its half-life was 126 ± 9 min. Immune staining showed that CPS1 localized to mouse hepatocytes but not ductal cells. Analysis of a few serum samples from patients with acute liver failure (ALF) due to acetaminophen, Wilson disease, or ischemia showed readily detectable CPS1 that was not observed in several patients with chronic viral hepatitis or in control donors. Notably, CPS1 rapidly decreased to undetectable levels in sera of patients with acetaminophen-related ALF who ultimately recovered, while alanine aminotransferase levels remained elevated. Therefore, CPS1 becomes readily detectable upon hepatocyte apoptotic and necrotic death in culture or in vivo. Its abundance and short serum half-life, compared with alanine aminotransferase, suggest that it may be a useful prognostic biomarker in human and mouse liver injury. Show less