Serum epoxide hydrolase (preneoplastic antigen) in human and experimental liver injury.

Reports of an increase in a serum epoxide hydrolase (sEH), immunochemically related to microsomal EH in humans and rats with hepatocellular carcinoma (HCC), suggested its use as a serum marker for this disease. We have now measured sEH levels (as either immunochemically determined content or enzyme activity) in a number of human and experimental models of liver disease. sEH was elevated above the normal range in at least 50% of individuals with HCC, including: 3 of 6 northern Californians; 4 of 7 Koreans with hepatitis B-associated HCC; hepatitis B-associated HCC in woodchucks; and male rats receiving chronic treatment with aflatoxin B1 or ciprofibrate. sEH was rarely elevated in other forms of chronic liver disease. Only 2 of 9 Koreans with hepatitis B-associated cirrhosis, 1 of 8 carriers, but none with chronic active hepatitis or infection with no apparent liver disease had elevated sEH. In addition, no elevations were found in woodchucks with noncancerous viral hepatitis. In aflatoxin B1- and M1-treated rats sEH was not elevated in those with only hyperplastic foci or hepatocellular adenomas, and in two rat initiation-promotion protocols sEH was elevated only in those rats which received the entire set of treatments. sEH was also increased during acute hepatotoxicity in rats treated with CCl4 or 1,2-dibromo-3-chloropropane. The mechanism of increase in sEH during hepatocarcinogenesis appears to be different from that of other markers of HCC, for in the Korean patients, there was no correlation between sEH concentrations and those of alpha-fetoprotein or ferritin, nor was there a correlation with alpha-fetoprotein concentrations in the aflatoxin-treated rats. Furthermore, the increase in sEH does not correlate with induction of microsomal EH in the liver of experimental animals. Studies to date indicate that sEH is selective for HCC and severe hepatonecrotic injury, and may be of some use in the diagnosis of HCC, particularly as a complement to other serum markers.

Immunochemical comparison of human and rhesus monkey liver microsomal and the hepatocellular carcinoma-induced human serum epoxide hydrolases (preneoplastic antigens): basis for an enzyme-linked immunoabsorbent assay.

An antibody (anti-EH) specific for microsomal epoxide hydrolase (mEH) from rhesus monkey liver has been used to test the immunochemical relationship between human liver mEH and the serum EH levels in human patients with hepatocellular carcinoma (HCC). Immunoblots of separated rhesus monkey and human liver microsomal proteins revealed that anti-EH was selective for a single polypeptide band of similar mol. wt, approximately 49 kd, in both species. Anti-EH was also able to precipitate 100% of the activity for two substrates specific in the mouse for mEH, cis-stilbene oxide and benzo[a]-pyrene-4,5-oxide, in solubilized human liver microsomes. In contrast, only 20% of the microsomal trans-stilbene oxide hydrolase activity was precipitated under similar conditions, providing immunochemical evidence that a distinct EH, with substrate selectivity similar to the cytosolic EH, resides in human liver microsomes. Immunoprecipitation of serum from a patient with elevated EH activity resulted in total precipitation of cis-stilbene oxide hydrolase activity. An enzyme-linked immunoabsorbant assay (ELISA) was developed using anti-EH with detection limits of 1 ng/ml. A high correlation between the enzymatically and immunochemically determined levels of serum EH provided further evidence for the immunochemical similarity of human liver microsomal and serum EH. In addition, the ELISA was equally capable of identifying elevated serum EH in patients with HCC, and should prove invaluable in evaluating the effectiveness of serum EH levels as a marker for HCC.