Levels of vitamin K, immunoreactive prothrombin, des‐γ‐carboxy prothrombin and γ‐glutamyl carboxylase activity in hepatocellular carcinoma tissue

To clarify the mechanism of production of des-gamma-carboxy (abnormal) prothrombin (DCP) by hepatocellular carcinoma (HCC), we measured the levels of vitamin K, DCP, immunoreactive prothrombin and the activity of gamma-glutamyl carboxylase in liver tissues from HCC patients and in the medium of cultured human hepatoma cells. There was no significant difference in vitamin K (K1, MK-4) contents between HCC and non-HCC cirrhotic liver tissues. The activity of gamma-glutamyl carboxylase per unit amount of endogenous microsomal prothrombin precursor was decreased in HCC tissue compared with non-HCC liver tissue (positive plasma DCP: 335 +/- 72 vs 372 +/- 67, negative plasma DCP: 370 +/- 84 vs 393 +/- 56 nmol/min per mg prothrombin precursor, P > 0.05), although the total incorporation of 14COOH into microsomal precursor protein was higher in the former. By contrast, levels of DCP and immunoreactive prothrombin in HCC tissue were greater (P < 0.05) than those in non-HCC cirrhotic liver tissue. Furthermore, production of large amounts of immunoreactive prothrombin was observed in human hepatoma cells huH-1 and huH-2, which produced large amounts of DCP. These results suggest that there was excessive synthesis of prothrombin precursors by human HCC tissue and hepatoma cell lines huH-1 and huH-2. Thus, excessive synthesis of prothrombin precursors seems to be the main mechanism of DCP production by HCC.