Electrophoretic fractionation of serum gamma-glutamyl transpeptidase in human hepatic cancer

Serum protein biomarkers relevant to hepatocellular carcinoma and their detection

Hepatocellular carcinoma (HCC) is one of the most recurrent and lethal cancers worldwide. The low survival rate of this particular strain of carcinoma is largely due to the late stages at which it is diagnosed. Tumorigenesis of hepatocellular carcinoma is most frequently detected through ultrasonography, magnetic resonance imaging and computerized tomography scans, however, these methods are poor for detection of early tumor development. This review presents alternative hepatocellular carcinoma detection techniques through the use of protein and enzyme/isozyme biomarkers. The detection methods used to determine the serum levels of α-fetoprotein (AFP), glypican-3 (GPC3), Golgi protein 73 (GP73), α-L-fucosidase (AFU), des-γ-carboxyprothrombin (DCP), γ-glutamyl transferase (GGT) and squamous cell carcinoma antigen (SCCA) are presented and each marker's respective validity in the diagnosis of hepatocellular carcinoma is evaluated.

Gamma-glutamyl transpeptidase: redox regulation and drug resistance

The expression of gamma-glutamyl transpeptidase (GGT) is essential to maintaining cysteine levels in the body. GGT is a cell surface enzyme that hydrolyzes the gamma-glutamyl bond of extracellular reduced and oxidized glutathione, initiating their cleavage into glutamate, cysteine (cystine), and glycine. GGT is normally expressed on the apical surface of ducts and glands, salvaging the amino acids from glutathione in the ductal fluids. GGT in tumors is expressed over the entire cell membrane and provides tumors with access to additional cysteine and cystine from reduced and oxidized glutathione in the blood and interstitial fluid. Cysteine is rate-limiting for glutathione synthesis in cells under oxidative stress. The induction of GGT is observed in tumors with elevated levels of intracellular glutathione. Studies in models of hepatocarcinogenesis show that GGT expression in foci of preneoplastic hepatocytes provides a selective advantage to the cells during tumor promotion with agents that deplete intracellular glutathione. Similarly, expression of GGT in tumors enables cells to maintain elevated levels of intracellular glutathione and to rapidly replenish glutathione during treatment with prooxidant anticancer therapy. In the clinic, the expression of GGT in tumors is correlated with drug resistance. The inhibitors of GGT block GGT-positive tumors from accessing the cysteine in extracellular glutathione. They also inhibit GGT activity in the kidney, which results in the excretion of GSH in the urine and a rapid decrease in blood cysteine levels, leading to depletion of intracellular GSH in both GGT-positive and GGT-negative tumors. GGT inhibitors are being developed for clinical use to sensitize tumors to chemotherapy.

Combined analysis of serum γ-glutamyl transferase isoenzyme II, α-L-fucosidase and α-fetoprotein detected using a commercial kit in the diagnosis of hepatocellular carcinoma

γ-glutamyl transferase isoenzyme II (GGT-II) is a sensitive biomarker of hepatocellular carcinoma (HCC). However, numerous disadvantages of the traditional manual method affected its application. The commercial kit provided a convenient and fast method for the determination of GGT-II levels. The purposes of the present study were to compare the reproducibility and sensitivity between the manual and commercial kit methods and to evaluate the diagnostic efficiency for HCC with the combined analysis of GGT-II, α-L-fucosidase (AFU) and α-fetoprotein (AFP). In patients with various liver diseases (HCC, liver cirrhosis and chronic hepatitis) and normal subjects, GGT-II was detected by manual and commercial polyacrylamide gel electrophoresis (PAGE). The levels of AFU and AFP were assayed by colorimetry and a chemiluminescence immunoassay, respectively. The commercial PAGE had equal diagnostic efficiency with traditional manual PAGE and no significant differences were observed in intra- and average-gel reproducibility and GGT-II sensitivities between the manual and commercial PAGE (P>0.05). The incidence of GGT-II detected by commercial PAGE in HCC patients was 84.1% and <8% in benign liver disease. The levels of AFU and AFP in the benign liver diseases and normal subjects were lower than those in HCC. According to the cut-off value obtained by receiver operating characteristic curves, a total of 56.6 and 59.3% of HCC patients (64 out of 113 and 67 out of 113) had AFU >636.5 μmol/l h and AFP >44.0 μg/l, respectively. There were no significant correlations between GGT-II and AFU or AFP. Combined detection of GGT-II with AFU or AFP increased the diagnostic sensitivity to 92.9 and 93.8%, respectively. These results suggest that commercial PAGE provides a simple and reproducible method for GGT-II detection. Combined determination of GGT-II with AFU or AFP exhibited superior sensitivity and specificity for the diagnosis of HCC.

Present and future possibilities for early diagnosis of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) represents the fifth most common cancer in the world, and the third most frequent oncological cause of death. The incidence of HCC is on the increase. HCC typically develops in patients with chronic liver diseases, and cirrhosis, usually with viral etiology, is the strongest predisposing factor. Nowadays HCC diagnosis is a multistage process including clinical, laboratory, imaging and pathological examinations. The prognosis of HCC is mostly poor, because of detection at an advanced, non-resectable stage. Potentially curative treatment (surgery) is limited and really possible only for cases with small HCC malignancies. For this reason, more effective surveillance strategies should be used to screen for early occurrence of HCC targeted to the population at risk. So far, the generally accepted serological marker is α-fetoprotein (AFP). Its diagnostic accuracy is unsatisfactory and questionable because of low sensitivity, therefore there is a strong demand by clinicians for new HCC-specific biomarkers. In this review, we will focus on other biomarkers that seem to improve HCC diagnosis, such as AFP-L3, des-γ-carboxyprothrombin, α-l-fucosidase, γ-glutamyl transferase, glypican-3, squamous cell carcinoma antigen, a new generation of immunoglobulin M-immunocomplexes, and very promising gene-expression profiling.

Clinical application of an enzyme-linked immunosorbent assay detecting hepatoma-specific gamma-glutamyltransferase

AIM

To develop a sandwich enzyme-linked immunosorbent assay (ELISA) measuring hepatoma-specific datura stramonium agglutinin-tightly bounding gamma-glutamyltransferase (DSA-GGT) and evaluate its clinical application for hepatocellular carcinoma (HCC) diagnosis.

METHODS

Serum DSA-GGT concentrations were measured with the sandwich ELISA system in 96 patients with HCC, 240 patients with chronic liver diseases and 119 healthy subjects. The diagnostic performance of DSA-GGT for HCC was assessed using receiver operating characteristic (ROC) curves. The diagnostic accuracy of DSA-GGT was compared with serum alpha-fetoprotein (AFP).

RESULTS

The area under the ROC curve of DSA-GGT in discriminating patients with HCC from non-HCC was 0.865 (95% confidence interval: 0.818-0.915, P < 0.001). Serum DSA-GGT was positive in 67 out of 96 patients with HCC and 23 out of 240 patients with non-HCC diseases. The sensitivity and specificity of DSA-GGT and AFP for the diagnosis of HCC were 69.8% and 90.5%, and 72.9% and 89.1%, respectively. A higher sensitivity (93.8%) in the identification of HCC was observed by combining DSA-GGT and AFP.

CONCLUSION

The sandwich ELISA system showed good reliability and reproducibility, and using the measurement, we found that serum DSA-GGT was a valuable marker of HCC, as a usable complementary to AFP. The sensitivity for identifying HCC could be significantly improved by combining DSA-GGT and AFP, and the combination could be used in large-scale screening for HCC in susceptible individuals.

Diagnostic value of protein induced by vitamin K absence (PIVKAII) and hepatoma-specific band of serum gamma-glutamyl transferase (GGTII) as hepatocellular carcinoma markers complementary to alpha-fetoprotein

Serum protein induced by vitamin K absence or antagonist II (PIVKAII), hepatoma-specific band of serum gamma-glutamyl transferase (GGTII), and alpha-fetoprotein (AFP) levels were determined in 120 patients with hepatocellular carcinoma (HCC) and 90 patients with cirrhosis. The mean serum concentration of PIVKAII in HCC patients was higher than that in cirrhotic patients. A total of 53.3% of patients (64 out of 120) with HCC had PIVKAII levels above 40 mAU ml(-1). However, only 13 patients with cirrhosis had higher PIVKA II levels. Of 32 small HCC patients, 13 (40.6%) had PIVKAII values above 40 mAU ml(-1). An increased concentration of AFP (i.e. 20 ng ml(-1)) was observed in 70 out of 120 (58.3%) patients with HCC and in 33 out of 90 (36.7%) patients with cirrhosis. Positive GGTII was found in 74.0% (89 out of 120) cases of HCC (sensitivity), in 16 of 90 cases of cirrhosis, and 14 of 32 (43.8%) small HCC patients had GGTII positive. No significant correlation was found between serum levels of AFP and PIVKAII. Combining the information from PIVKAII, AFP, and GGTII significantly increases the sensitivity over AFP alone. PIVKAII and GGTII are useful tumour markers complementary to AFP for diagnosis of HCC.

Evaluation of the albumin-gamma-glutamyltransferase isoenzyme as a diagnostic marker of hepatocellular carcinoma-complicating liver cirrhosis

AIM

The present study aimed to evaluate the usefulness of albumin-gamma-glutamyltransferase isoenzyme in the diagnosis of hepatocellular carcinoma.

METHODS

Electrophoretic assays of gamma-glutamyltransferase isoenzymes were performed on sera from 190 cirrhotics with (n = 131) or without (n = 59) hepatocellular carcinoma, 36 patients with chronic active hepatitis, 17 patients with liver metastases, and 16 control subjects. In the group of cirrhotic patients, the serum level of alpha-fetoprotein was also assessed.

RESULTS

Albumin-gamma-glutamyltransferase was found in 88 of 131 cirrhotics with hepatocellular carcinoma, 14 of 59 cirrhotics without hepatocellular carcinoma, nine of 17 patients with liver metastases, and in none of the chronic active hepatitis or control patients. Within the cirrhotic subgroup, albumin-gamma-glutamyltransferase was effective in detecting hepatocellular carcinoma in general (sensitivity: 67%; specificity: 76%; diagnostic accuracy: 70%), and small hepatocellular carcinoma (< 3 cm; corresponding figures: 58, 76, and 69%). The best alpha-fetoprotein value discriminating between hepatocellular carcinoma and non-hepatocellular carcinoma cirrhotics was 20 ng/mL (sensitivity: 54%; specificity 85%; accuracy: 64%). The combined use of albumin-gamma-glutamyltransferase and alpha-fetoprotein, > 20 ng/mL, was associated with greater sensitivity and accuracy (84 and 74%, respectively) than those observed with either of the two markers considered alone.

CONCLUSIONS

Albumin-gamma-glutamyltransferase appears to be a sensitive diagnostic marker of both advanced and small hepatocellular carcinoma-complicating liver cirrhosis.

Clinical applications of lectin affinity electrophoresis

Principles and several modifications of lectin affinity electrophoresis are described. The results obtained using these newly developed techniques are reviewed for individual glycoproteins, the altered lectin reactivities of which have some clinical implications, showing different lectin reactivities, which occur not only on malignant transformation but also in association with inflammatory process and hormonal action.

Electrophoretic behavior and partial characterization of disease-associated serum forms of gamma-glutamyltransferase

We have recently devised an improved procedure for the rapid electrophoretic separation of multiple forms of serum gamma-glutamyltransferase (GGT). This procedure is based on the separation on cellulose acetate strips, usually employed for lipoprotein electrophoresis, followed by visualization with a fluorescent reagent. The method is highly sensitive and the fractions are more clearly resolved than with other procedures. Reference intervals have been evaluated in the sera from 142 healthy subjects and the patterns (two GGT forms comigrating with alpha 1 and alpha 2-globulin) are reproducible. In 150 sera from patients with various hepatobiliary diseases (including neoplasias), acute pancreatitis and non liver-involving neoplasias, we observed some disease-specific GGT forms: an albumin comigrating enzyme (Alb-GGT) specific of liver neoplasia; a gamma-globulin comigrating GGT (gamma-GGT) and a nonmigrating isoform (dep-GGT) both specifically associated to extrahepatic jaundice. Multiple lipoprotein fraction precipitation showed that beta-, gamma- and dep-GGT are complexes between GGT and low density lipoprotein and very low density lipoproteins (LDL + VLDL), and that some of the alpha 1-GGT from cirrhotic patients is a complex between GGT and high density lipoprotein (HDL). GGT fractions from normal subjects and Alb-GGT from patients with liver neoplasia do not appear to be complexed with lipoproteins.(ABSTRACT TRUNCATED AT 250 WORDS)

Tumour markers in diagnosis and management

The 20-year period since the discovery of AFP by Abelev has seen the introduction of a wide range of new tumour markers and it is now clear that PLC is biologically heterogeneous. Hepatoblastomas, fibrolamellar carcinomas, hepatocellular carcinomas and cholangiocarcinomas may secrete a variety of distinctive markers which are predominantly glycoproteins, and may resemble those found in placenta or fetal liver. Diagnostically, AFP remains the best marker for HCC, both in sensitivity and specificity; it is known to consist of isoforms. In patients with elevated serum AFP and filling defects on liver scan, Con A reactive AFP may differentiate PLC from hepatic metastases, whilst fucosylated AFP may distinguish PLC from benign disorders when AFP is non-diagnostically elevated. With this recognition of tumour heterogeneity the value of a multiple-marker approach has become apparent. The measurement of vitamin B12 binding protein and neurotensin should lead to the detection of most patients with the fibrolamellar variant of HCC and many of these should be resectable. In patients with normal serum AFP levels, HCC-associated GGTP is of major value whilst in low-incidence areas for HCC, patients should also be screened for H-ALP; using a multiple marker approach in high-risk groups, 90% of clinically diagnosed hepatocellular carcinomas are serologically positive. The Chinese and Alaskan studies, in which small, potentially resectable tumours were detected, suggest that it is now possible to achieve 5-year survival figures of up to 60% in HCC patients detected by screening. The value of such a strategy in low-incidence countries is currently under study. In patient monitoring, as in diagnosis, AFP remains the outstanding marker. In AFP-negative patients, other markers including vitamin B12-binding protein, neurotensin, HCC-specific isoenzymes, des-gamma-carboxy-prothrombin and alpha-fucosidase, are of undoubted diagnostic value, but their value as indicants of disease progression remains to be established. In monitoring the response of hepatic metastases, CEA remains the least unsatisfactory marker but should always be used in conjunction with serial ultrasound scans. Tumour markers now play an important role in the diagnosis and monitoring of PLC but a role is also emerging in tumour imaging and drug targeting. The next 20 years should see the introduction of tumour markers of high sensitivity and specificity which make a fundamental contribution not only to detection and monitoring, but also to the effective treatment of liver cancer.

The diagnostic value of a hepatoma-specific band of serum gamma-glutamyl transferase

Using a vertical slab electrophoretic apparatus loaded with polyacrylamide stage gel plate, we observed a total of II bands of gamma-glutamyl transferase (EC 2.3.2.2,GGT) on a gel plate and designated these GGT I-XI by order of distance beginning at the positive pole. Positive GGT II was found in 81 (90%) of 90 cases of primary hepatic carcinoma (PHC), in 9(90%) of 10 cases of secondary hepatic carcinoma (SHC), and in only 4 (3.1%) of a total of 128 cases of acute and chronic liver disease. There was one case with positive GGT II among 45 cases of cancer of ampulla of Vater, but the possibility of hepatic metastasis could not be excluded. No GGT II was found in a total of 250 healthy persons and 21 pregnant women. PHC patients with negative alpha-fetoprotein (AFP) had a positive GGT II rate of 84.6%, whereas in those with negative GGT II the positive rate for AFP was only 44.4%.

Electrophoretic studies of serum gamma-glutamyl transferase from patients with hepatoma

Activities and isoenzyme patterns of gamma-glutamyl transferase (GGT) were studied in serum samples from fifteen Bantu males suffering from primary hepatoma; the results were compared with those obtained from normal samples. Enzyme activities were significantly higher in hepatoma patients than in controls. Results with Cellogel electrophoresis and the fluorescent substrate gamma-L-glutamine-7-amido-4-methylcoumarin were reproducible; two major bands of activity were observed in normal serum and three bands in hepatoma serum. The additional band seen in hepatoma serum was also detected in serum from patients with certain other disorders. With polyacrylamide gel electrophoresis using either gamma-L-glutamyl-alpha-naphthylamide or gamma-L-glutamyl-p-nitroanilide as substrates, results were inconsistent and difficult to interpret since there was a lack of specificity for GGT.

Variations in sialic acid content of gamma-glutamyltransferase: a consequence for immunochemical determinations?

Using specific antibodies against the human kidney enzyme, gamma-glutamyltransferase (GGT, EC 2.3.2.2) was assayed from human kidney and serum by electroimmunodiffusion. Determination of the enzyme by such a method was highly influenced by the sialic acid content of the molecule. The peaks corresponding to the sialylated GGT were higher than those corresponding to the neuraminidase-treated enzyme. In contrast, sialylation of the protein had no influence on the results observed when measuring the enzyme by radial immunodiffusion. Moreover, immunoprecipitation curves of both sialylated and neuraminidase-treated samples were identical. The varying degrees of sialylation of GGT occurring under physiological or pathological conditions are known to be partly responsible for the heterogeneity of the enzyme in organs and biological fluids. Therefore, determination of the enzyme by electroimmunodiffusion may be hazardous.

Tumour-associated isoenzymes of gamma-glutamyl transferase in the serum of patients with hepatocellular carcinoma

Sera from 391 southern African Blacks with hepatocellular carcinoma, matched controls, patients with other malignant tumours, and with various forms of hepatobiliary disease were fractionated by polyacrylamide gradient gel electrophoresis to determine the prevalence of tumour-associated gamma-glutamyl transferase isoenzymes in Black patients with hepatocellular carcinoma. One or more tumour-associated isoenzymes (I', I'' or II') were present in 58.6% of the patients with hepatocellular carcinoma: I' in 54.5%, I'' in 27.1%, and II' in 34%. These isoenzymes were detected in one patient with prostatic cancer, occasionally in patients with acute viral hepatitis, but in no normal individuals. The presence of tumour-associated isoenzymes was not related to patient age, sex or hepatitis-B virus status or to the tumour burden. Isoenzymes were present in 42 percent of hepatocellular carcinoma patients with a normal serum alpha-foetoprotein concentration and in 50% of those with a non-diagnostic value. gamma-glutamyl transferase isoenzymes may be supplementary to alpha-foetoprotein in the diagnosis of hepatocellular carcinoma.

Clinical evaluation of specific gamma-GTP isoenzyme in patients with hepatocellular carcinoma

The authors evaluated specific gamma-GTP isoenzyme (specific gamma-GTP) found in sera of patients with hepatocellular carcinoma (HCC). In addition to band II and II' which had been reported in our previous publication, band I' also had a high specificity for HCC. One or more of these bands were detectable in 109 (55%) of 200 patients with HCC, but only in seven (3%) of 279 patients with other hepatobiliary diseases. Specific gamma-GTP was found in 38% of HCC patients with alpha-fetoprotein (AFP) levels below 400 ng/ml. The incidence of this isoenzyme was independent of the clinical stage as classified by liver scanning. Even in Stage I, where filling defects were not seen, the incidence was 52%. We conclude that the specific gamma-GTP is useful in diagnosis of HCC patients with low levels of AFP or at a relatively early stage.

Localization of gamma-glutamyl transferase on polyacrylamide gels using L-gamma-glutamyl-p-nitroanilide as substrate

A method has been developed for the localization of gamma-glutamyltransferase (gamma-GT) on polyacrylamide gels using L-gamma-glutamyl-p-nitroanilide as substrate. The optimum conditions for staining on polyacrylamide gels with this substrate were evaluated and compared with the staining method using N-gamma-L-glutamyl-alpha-naphthylamide as substrate. Using papain digested, purified gamma-GT from human fetal liver it was shown that the method could be used for quantitation of the enzyme on polyacrylamide gels. It was also shown that identical patterns of staining for serum gamma-GT could be obtained with L-gamma-glutamyl-p-nitroanilide and N-gamma-L-glutamyl-alpha-naphthylamide as substrate.