A sensitive enzyme-linked immunosorbent assay of serum ornithine carbamoyltransferase

Investigation of ornithine carbamoyltransferase as a biomarker of liver cirrhosis

OBJECTIVE

Ornithine carbamoyltransferase (OCT) is a liver-specific mitochondrial matrix enzyme and potential biomarker of liver fibrosis. This study investigated the OCT levels in patients with chronic liver disease with or without cirrhosis in order to assess the usefulness of OCT as a biomarker of cirrhosis.

METHODS

The subjects included 440 Japanese patients with chronic liver disease and 80 control subjects. The patients were divided into two groups, those with and without cirrhosis, both of which were further stratified into high-OCT and low-OCT subgroups.

RESULTS

In the non-cirrhosis group, the patients with non-alcoholic steatohepatitis (NASH), alcoholic liver disease, primary biliary cirrhosis and primary sclerosing cholangitis (PSC) comprised the high-OCT subgroup, while the patients with hepatitis B, hepatitis C and autoimmune hepatitis formed the low-OCT subgroup. There were significant differences in the OCT levels, OCT/aspartate aminotransferase ratios and OCT/alanine transaminase (ALT) ratios between these two subgroups (p<0.001). The same findings were observed in the cirrhosis group. The OCT levels were markedly higher in the cirrhosis group than in the non-cirrhosis group, particularly among the patients with PSC (p<0.001). The most useful biomarker for predicting cirrhosis was the OCT/ALT ratio in the patients with hepatitis C and NASH and the OCT level in patients with PSC.

CONCLUSION

The OCT level differs among patients with different chronic liver diseases. The role of OCT should be further evaluated in order to improve our understanding of the pathogenesis of these diseases. The OCT level is a useful surrogate marker of cirrhosis, particularly in PSC patients.

Mechanism-based bioanalysis and biomarkers for hepatic chemical stress

Adverse drug reactions, in particular drug-induced hepatotoxicity, represent a major challenge for clinicians and an impediment to safe drug development. Novel blood or urinary biomarkers of chemically-induced hepatic stress also hold great potential to provide information about pathways leading to cell death within tissues. The earlier pre-clinical identification of potential hepatotoxins and non-invasive diagnosis of susceptible patients, prior to overt liver disease is an important goal. Moreover, the identification, validation and qualification of biomarkers that have in vitro, in vivo and clinical transferability can assist bridging studies and accelerate the pace of drug development. Drug-induced chemical stress is a multi-factorial process, the kinetics of the interaction between the hepatotoxin and the cellular macromolecules are crucially important as different biomarkers will appear over time. The sensitivity of the bioanalytical techniques used to detect biological and chemical biomarkers underpins the usefulness of the marker in question. An integrated analysis of the biochemical, molecular and cellular events provides an understanding of biological (host) factors which ultimately determine the balance between xenobiotic detoxification, adaptation and liver injury. The aim of this review is to summarise the potential of novel mechanism-based biomarkers of hepatic stress which provide information to connect the intracellular events (drug metabolism, organelle, cell and whole organ) ultimately leading to tissue damage (apoptosis, necrosis and inflammation). These biomarkers can provide both the means to inform the pharmacologist and chemist with respect to safe drug design, and provide clinicians with valuable tools for patient monitoring.

A sensitive ELISA for serum ornithine carbamoyltransferase utilizing the enhancement of immunoreactivity at alkaline pH

BACKGROUND

We developed a new enzyme-linked immunosorbent assay (ELISA) for ornithine carbamoyltransferase (OCT) and evaluated its usefulness.

METHODS

Recombinant human OCT expressed in E. coli was used as an antigen to obtain the monoclonal antibodies for this assay.

RESULTS

The reactivity of the antibodies to native OCT as well as recombinant OCT was enhanced at alkaline pH (8.5-10), and the assay's sensitivity was markedly improved. The antibodies react identically with native and recombinant OCT at pH 9.4. The dilution test showed a good linearity between dilution ratios and the concentrations. Different concentrations of OCT added were recovered on average at 90.4%. There was a good correlation between OCT protein levels in the ELISA and OCT enzyme activities (r=0.987, p<0.0001). A significant difference in the serum level of OCT was observed between chronic hepatitis patients (110.7+/-80 ng/ml) and healthy subjects (34.4+/-20.7 ng/ml) (p<0.0001). The serum levels of OCT between sexes differed significantly in the healthy subjects (p<0.0001).

CONCLUSIONS

Our newly established ELISA for OCT using monoclonal antibodies is sensitive enough for clinical application.