Glutathione S-transferase activity in patients with cancer of the digestive tract

Spectrophotometric assay for serum glutathione transferase: a re-examination

OBJECTIVES

The aim of the present paper is a careful re-examination of an automated spectrophotometric procedure for glutathione transferase (GST) activity in human serum described previously and used in many laboratories.

DESIGN AND METHODS

GST activity in human serum has been assayed spectrophotometrically under various experimental conditions. Recombinant human GSTs and specific inhibitors were also used to check the possible occurrence of artifacts.

RESULTS

Basal level of the enzyme calculated using this method turns out to be much higher than that found using RIA and ELISA procedures. Relevant pH-dependent artifacts deeply affect this spectrophotometric assay. Notably, spectral changes previously interpreted as a measure of basal activity, are mainly due to an increase of the spontaneous reaction between the two substrates.

CONCLUSION

GST activity in normal serum cannot be correctly determined with the spectrophotometric assay described previously because of the very low enzyme concentration and the pH-dependent artifacts.

Sensitivity estimates of blood-based tests for colorectal cancer detection: impact of overrepresentation of advanced stage disease

A large number of blood-based markers have been proposed for early detection of colorectal cancer (CRC). Their sensitivity for detecting CRC has mostly been evaluated in clinical settings, and found to be higher in more advanced stages compared with earlier stages of the disease. The aim of this study is to estimate the overall sensitivity of blood-based markers expected in screening settings, where the proportion of advanced stages is typically lower than in clinical settings. A systematic literature review was performed on studies evaluating sensitivity and specificity of blood-based markers for early detection of CRC. For each study, overall sensitivity expected in screening settings was estimated by weighting stage-specific sensitivities according to the stage distribution of CRC expected in the screening setting. The latter was derived from 12,605 CRC cases diagnosed in the German screening colonoscopy program during 2003-2007. Overall, 73 studies evaluating 55 blood-based markers were identified. Adjusted sensitivity was lower than reported sensitivity in 120 (90%) evaluations of different markers. Median absolute reduction in sensitivity after adjustment was 9.0% (interquartile range: 4.0-13.0) units, whereas median relative reduction was 19.5% (interquartile range: 11.3-33.3%). Blood-based markers for CRC detection reported from clinical settings showed higher sensitivities than expected in the screening setting in most cases, mainly due to substantially higher proportions of advanced stage cancers. Adjustment of sensitivity to the stage distribution expected in the screening setting is crucial to obtain realistic and comparable estimates of sensitivities.

Blood markers for early detection of colorectal cancer: a systematic review

BACKGROUND

Despite different available methods for colorectal cancer (CRC) screening and their proven benefits, morbidity, and mortality of this malignancy are still high, partly due to low compliance with screening. Minimally invasive tests based on the analysis of blood specimens may overcome this problem. The purpose of this review was to give an overview of published studies on blood markers aimed at the early detection of CRC and to summarize their performance characteristics.

METHOD

The PUBMED database was searched for relevant studies published until June 2006. Only studies with more than 20 cases and more than 20 controls were included. Information on the markers under study, on the underlying study populations, and on performance characteristics was extracted. Special attention was given to performance characteristics by tumor stage.

RESULTS

Overall, 93 studies evaluating 70 different markers were included. Most studies were done on protein markers, but DNA markers and RNA markers were also investigated. Performance characteristics varied widely between different markers, but also between different studies using the same marker. Promising results were reported for some novel assays, e.g., assays based on SELDI-TOF MS or MALDI-TOF MS, for some proteins (e.g., soluble CD26 and bone sialoprotein) and also for some genetic assays (e.g., L6 mRNA), but evidence thus far is restricted to single studies with limited sample size and without further external validation.

CONCLUSIONS

Larger prospective studies using study populations representing a screening population are needed to verify promising results. In addition, future studies should pay increased attention to the potential of detecting precursor lesions.

Proteome analysis and tissue microarray for profiling protein markers associated with lymph node metastasis in colorectal cancer

BACKGROUND

Understanding the proteins associated with lymph node metastasis (LNM) in colorectal cancer (CRC) will benefit us in the prediction of CRC prognosis and provide us new potential targets in the intervention of CRC. The aim of this study is to investigate the LNM-associated proteins and to evaluate the clinicopathological characteristics of these target proteins' expression in CRC.

METHODS

Fresh tumor and paired normal mucosa from five cases for each group of non-LNM CRC and LNM CRC were analyzed by two-dimensional electrophoresis coupled with MALDI-TOF-MS, followed by Western blotting confirmation. In 40 paraffin-embedded CRC samples, each for non-LNM CRC and LNM CRC, four differentially expressed proteins identified by proteomics analysis were detected by tissue microarray with immunohistochemistry staining to access the clinicopathological characteristics of these proteins in LNM of CRC.

RESULTS

Twenty-five proteins were found to be differentially expressed between normal mucosa and CRC tissue. Increased expression levels of heat shock protein-27 (HSP-27), glutathione S-transferase (GST), and Annexin II, but a decreased expression level of liver-fatty acid binding protein (L-FABP), existed in LNM CRC as compared with non-LNM CRC (p<0.01 or p<0.05, respectively).

CONCLUSION

The techniques of proteomic analysis combined with tissue microarray provide us a dramatic tool for screening of LNM-associated proteins in cancer research. The increased expression of HSP-27, GST, and Annexin II, but decreased expression of L-FABP, suggests a significantly elevated incidence of LNM in CRC.

In vivo optimizing of intracellular production of heterologous protein in Pichia pastoris by fluorescent scanning

Specific monitoring of recombinant protein titer in DNA recombinant biotechnology traditionally has relied on SDS-PAGE, Western blotting, or bioactivity-based assays, but these are labor-intensive, time-consuming, and destructive and are not a good choice for the optimization of recombinant protein production. We describe a study in which enhanced green fluorescence protein (EGFP) was fused to the C terminus of a model protein glutathione S-transferase (GST) to optimize the chimeric protein production in Pichia pastoris by measurements of fluorescence of living cells in a 96-well microtiter plate using simple fluorescent scanning. Several common factors (e.g., time course of expression, effect of methanol concentration, frequency of methanol addition, medium pH) were tested using this strategy. Western blotting assay showed that the correct full-length GST-EGFP chimeric protein was expressed intracellularly in P. pastoris. The fluorescence intensity and GST bioactivity of cell extract yielded a direct correlation. The results show that the reported method provides an attractive platform for the optimization of recombinant protein production in vivo in real time as well as handling at least 96 samples in parallel.

Relationship between genotype and enzyme activity of glutathione S-transferases M1 and P1 in Chinese

Glutathione S-transferases (GSTs) are the major detoxifying Phase II enzyme for eliminating electrophilic compounds. Mutations in GSTM1, GSTP1 and GSTT1 in Caucasian and GSTA1 in Chinese have been found to reduce enzyme activity. However, data on the impact of common genetic polymorphisms of GSTM1 and GSTP1 on enzyme activity in Chinese is lacking. This study aimed to investigate the effect of common GSTP1 and GSTM1 polymorphisms on erythrocyte GST activity in healthy Chinese (n = 196). GSTM1 null mutation (GSTM1*0) was analyzed by a PCR-Multiplex procedure, whereas GSTP1 313A-->G polymorphism (resulting in Ile105Val at codon 105) was analyzed by PCR-restriction fragment length polymorphism (RFLP) analysis. Erythrocyte GST activity was measured using 1-chloro-2,4-dinitro-bezene (CDNB) as the model substrate. The frequency of GSTM1 null genotype was 54.3% and the frequency of GSTP1-Ile/Ile, -Ile/Val, and -Val/Val genotype was 60.7%, 35.2% and 4.1%, respectively, with a frequency of 21.7% for the 105 valine allele. Age, gender and smoking did not significantly affect the erythrocyte GST activities. The mean erythrocyte GST enzyme activity for GSTP1*-Ile/Val genotype group (3.53 +/- 0.63U/gHb) was significantly lower than that for subjects with GSTP1-Ile/Ile genotype (4.25 +/- 1.07U/gHb, P = 0.004), while subjects with the GSTP1-Val/Val genotype had the lowest enzyme activity (2.44 +/- 0.67U/gHb). In addition, the GST activity in carriers of GSTM1*0/GSTP1-Ile/Ile was significantly higher than that of subjects inherited GSTM1*0/GSTP1-Ile/Val or GSTM1*0/GSTP1-Val/Val. However, there is no association between GSTM1 null mutation and reduced enzyme activity. GSTP1 codon 105 mutation led to reduced erythrocyte GST activity in Chinese. A combined GSTP1 and GSTM1 null mutations also resulted in significantly reduced GST activity. Further studies are needed to explore the clinical implications of GSTM1 and GSTP1 polymorphisms.

Significance of the O6-methylguanine-DNA methyltransferase and glutathione S-transferase activity in the sera of patients with malignant and benign ovarian tumors

OBJECTIVE

To demonstrate O6-methylguanine-DNA methyltransferase (MGMT) and glutathione S-transferase (GST) activities by analyzing the sera separately obtained from patients with malignant ovarian tumors, benign ovarian tumors, and healthy individuals.

STUDY DESIGN

Fourty-nine patients with ovarian cancer, nine patients with benign tumors, and 22 healthy women were included in this study. Blood samples were obtained from all the subjects in the malignant-tumor, benign-tumor, and control groups. Patients with malignant tumors underwent second and third phlebotomies one week following the surgery and after the chemotherapy regimen, respectively. MGMT, GST, and protein levels were measured for each serum sample. GST activity of the samples was measured by the method of Habig et al. using l-chloro-2-4 dinitrobenzene (CDNB) as substrate. MGMT activity was measured by the transfer of radio labelled methyl groups from a prepared MG-DNA substrate to the enzyme fraction of serum. Protein concentration was measured by biuret method.

RESULTS

Our work demonstrated that untreated patients with malignant ovarian tumors revealed significantly greater MGMT and GST activities in their sera than did both healthy individuals and patients with benign ovarian tumors, while no significant difference was found between the healthy group and the patients with benign ovarian tumors with respect to their sera MGMT and GST activities. GST activity following chemotherapy was significantly lower than the postoperative values preceding chemotherapy. A relationship between sera MGMT and GST activities, tumor histology and pathology was not found in this study.

CONCLUSION

Our work suggests the fact that detection of sera MGMT and GST activities is important in diagnostic and therapeutic approaches during the course of ovarian cancer.

Rapid spectrophotometric method for serum glutathione S-transferases activity

BACKGROUND

Glutathione S-transferases (GST) are a family of polymorphic enzymes responsible for the metabolism of a broad range of xenobiotics including carcinogens and endogenous compounds.

METHODS

The aim of this study was to develop a fully automated spectrophotometric method to determine serum GST activity.

RESULTS

The method had a detection limit of 7 U/l. The within- and between-run repeatability reached 2% and 3%, respectively. The reproducibility tested over a 6-month period was 7%. Serum GST activity is stable for at least 1 week at +37, +4 and -20 degrees C, 1 month at -20 degrees C and 6 months at -80 and -196 degrees C. The GST activities were determined on 374 supposedly healthy subjects coming to the Center of Preventive Medicine for a health screening. The sample population comprised 178 males and 196 females 4-80 years of age. The mean value of the serum GST activity calculated for this healthy population was 28.2+/-3.0 U/l without gender difference (range from 20.0 to 38.0 U/l). The global interindividual variability reached 11%.

CONCLUSIONS

This report describes a spectrophotometric assay for monitoring the serum GST activities in human. This method will be useful in examining the relationships between serum GST activities and the GST polymorphisms, especially pi-GST.