Glutathione S-transferases in normal and malignant human colon tissue

Biotransformation of xenobiotics in the human colon and rectum and its association with colorectal cancer

In humans, the liver is generally considered to be the major organ contributing to drug metabolism, but studies during the last years have suggested an important role of the extra-hepatic drug metabolism. The gastrointestinal tract (GI-tract) is the major path of entry for a wide variety of compounds including food, and orally administered drugs, but also compounds - with neither nutrient nor other functional value - such as carcinogens. These compounds are metabolized by a large number of enzymes, including the cytochrome P450 (CYP), the glutathione S-transferase (GST) family, the uridine 5'-diphospho- glucuronosyltransferase (UDP-glucuronosyltransferase - UGT) superfamily, alcohol-metabolizing enzymes, sulfotransferases, etc. These enzymes can either inactivate carcinogens or, in some cases, generate reactive species with higher reactivity compared to the original compound. Most data in this field of research originate from animal or in vitro studies, wherein human studies are limited. Here, we review the human studies, in particular the studies on the phenotypic expression of these enzymes in the colon and rectum to get an impression of the actual enzyme levels in this primary organ of exposure. The aim of this review is to give a summary of currently available data on the relation between the CYP, the GST and the UGT biotransformation system and colorectal cancer obtained from clinical and epidemiological studies in humans.

Identification of nitric oxide-releasing derivatives of oleanolic acid as potential anti-colon cancer agents

NO-releasing hybrid 6 regulates colon cancer-related signaling pathways, exhibiting potent anti-colon cancer activity in vitro and in vivo.

Binding of curcumin with glyoxalase I: Molecular docking, molecular dynamics simulations, and kinetics analysis

Glyoxalase I (GLOI) is a key metalloenzyme in glycolytic pathway by detoxifying reactive alpha-ketoaldehydes such as methylglyoxal. Recent studies demonstrate that the nature product curcumin is an efficient inhibitor of GLOI, but its binding mechanism towards GLOI is still unclear. In the present study, molecular docking and molecular dynamics (MD) simulations were performed to better understand the inhibitory mechanism of curcumin towards GLOI. The enol form of curcumin coordinates with the catalytic zinc ion of GLOI and forms a strong hydrogen bond with Glu 172, whereas its keto tautomer displays unfavorable electrostatic interactions with Glu 172 and Glu 99. The calculated binding free energies suggest that GLOI prefers the primary enol form (DeltaG=-30.38kcal/mol) to the keto tautomer (DeltaG=-24.16kcal/mol). The present work also reveals that bisdemethoxycurcumin binds to GLOI in a similar manner as curcumin and exhibits a slightly less negative predicted binding free energy, which is further validated by our comparative kinetics analysis (Ki=18.2 and 10.3muM for bisdemethoxycurcumin and curcumin, respectively). Results of the study can provide an insight into the development of novel and more effective GLOI inhibitors.

Glutathione S-transferase polymorphisms and survival in African-American and white colorectal cancer patients

BACKGROUND

Glutathione S-transferase (GST) enzymes are involved in electrophile detoxification. The authors investigated the association between GST genotype and survival in a racially diverse, population-based cohort of colorectal cancer (CRC) patients followed for a median of 9.6 years.

METHODS

Interviews were conducted with 315 African-American and White CRC patients in Connecticut, 1987-1991. Tumor tissue (n=197) was later retrieved from hospital of diagnosis and assayed using multiplex PCR (GSTM1 and GSTT1) and PCR and RFLP analysis (GSTP1). Cox proportional hazards models provided adjusted hazard ratios (HR) and 95% confidence intervals (CI).

RESULTS

Individuals with Ile/Val or Val/Val GSTP1 genotypes had a decreased risk of death (multivariate adjusted HR=0.72, 95% CI: 0.48, 1.09) relative to those with wild type (Ile/Ile). Among those who received chemotherapy, this benefit was more pronounced (HR=0.35, 95% CI: 0.16, 0.79); the interaction of reduced function GSTP1 genotype and chemotherapy was significant (P=0.05). GSTM1 and GSTT1 genotype were not associated with survival. GSTM1, GSTT1, and GSTP1 genotype did not vary by race and did not contribute significantly to the survival disadvantage observed in African-Americans.

CONCLUSIONS

In summary, GSTP1 genotype may play a role in CRC survival in African-Americans and Whites, particularly among those who receive chemotherapy.

Glyoxalase I gene deletion mutants of Leishmania donovani exhibit reduced methylglyoxal detoxification

BACKGROUND

Glyoxalase I is a metalloenzyme of the glyoxalase pathway that plays a central role in eliminating the toxic metabolite methyglyoxal. The protozoan parasite Leishmania donovani possesses a unique trypanothione dependent glyoxalase system.

PRINCIPAL FINDINGS

Analysis of the L. donovani GLOI sequence predicted a mitochondrial targeting sequence, suggesting that the enzyme is likely to be targeted to the mitochondria. In order to determine definitively the intracellular localization of GLOI in L. donovani, a full-length GLOI gene was fused to green fluorescent protein (GFP) gene to generate a chimeric construct. Confocal microscopy of L. donovani promastigotes carrying this chimeric construct and immunofluorescence microscopy using anti-GLOI antibodies demonstrated that GLOI is localized in the kinetoplast of the parasite apart from the cytosol. To study the physiological role of GLOI in Leishmania, we first created promastigote mutants heterozygous for GLOI by targeted gene replacement using either hygromycin or neomycin phosphotransferases as selectable markers. Heterozygous mutants of L. donovani display a slower growth rate, have lower glyoxalase I activity and have reduced ability to detoxify methylglyoxal in comparison to the wild-type parasites. Complementation of the heterozygous mutant with an episomal GLOI construct showed the restoration of heterozygous mutant phenotype nearly fully to that of the wild-type. Null mutants were obtained only after GLOI was expressed from an episome in heterozygous mutants.

CONCLUSIONS

We for the first time report localization of GLOI in L. donovani in the kinetoplast. To study the physiological role of GLOI in Leishmania, we have generated GLOI attenuated strains by targeted gene replacement and report that GLOI is likely to be an important gene since GLOI mutants in L. donovani showed altered phenotype. The present data supports that the GLOI plays an essential role in the survival of this pathogenic organism and that inhibition of the enzyme potentiates the toxicity of methylglyoxal.

A New Class of Signal Transducer in His-Asp Phosphorelay Systems

Nitrate transport activity of the LtnT permease of the cyanobacterium Synechococcus elongatus is activated when LtnA, a response regulator without an effector domain, is phosphorylated by LtnB, a hybrid histidine kinase. We identified a protein (LtnC) that is required for activation of LtnT. LtnC consists of an N-terminal histidine-containing phosphoacceptor (HisKA) domain, a receiver domain, and a unique C-terminal domain found in some cyanobacterial proteins. Because LtnC lacks an ATP-binding kinase domain of a histidine kinase, it is incapable of autophosphorylation, but LtnC is phosphorylated by LtnA. The histidine residue in the HisKA domain but not the aspartate residue in the receiver domain is essential for phosphorylation of LtnC and activation of LtnT. LtnC phosphorylation leads to oligomerization of the protein. Fusion of the C-terminal domain of LtnC to glutathione S-transferase, which forms oligomers, also activates LtnT, suggesting that oligomerization of the LtnC C-terminal domain causes LtnT activation. These results indicate that the C-terminal domain of LtnC acts as an effector domain that directs the output of the signal from the phosphorelay system. The two-step (His-Asp-His) phosphorelay system, composed of the LtnB, LtnA, and LtnC proteins, is distinct from the known phosphorelay systems, namely, the typical two-component system (His-Asp) and the multistep phosphorelay system (His-Asp-His-Asp), because the HisKA domain of LtnC is the terminal phosphoacceptor that determines the signal output. LtnC is a new class of signal transducer in His-Asp phosphorelay systems that contains a HisKA domain and an effector domain.

Identification of hydrophobic proteins as biomarker candidates for colorectal cancer

Nowadays, colorectal cancer is one of the major causes of cancer death in Western countries. Due to the lack of biomarkers with clinical utility for this pathology, and considering that membrane and hydrophobic proteins have not been studied in depth, we performed a prefractionation of colorectal tissues prior to two-dimensional gel electrophoresis in order to identify hydrophobic proteins differentially expressed in colorectal cancer patients. Fractions enriched in hydrophobic proteins were obtained from healthy mucosa and tumor tissue by a specific extraction method based on temperature-dependent phase partitioning with Triton X-114. Proteins were separated by two-dimensional gel electrophoresis and gels were silver-stained, scanned and compared using the PDQuest software. Those spots presenting significantly different abundance were submitted to mass spectrometry for protein identification. Alterations in the expression of cytoskeletal proteins, including a decrease of vimentin and the absence of desmin, were found. We also detected alterations in antioxidant and transport proteins, chaperones, and in two isoforms of the calcium-binding protein S100A6. On the other hand, vimentin was chosen to corroborate the electrophoretic results by specific immunodetection. Most of the altered proteins have been related to cellular membranes, many of them to lipid rafts microdomains in the plasma membrane, and they have also been implicated in the control of cell proliferation, apoptosis, or metastasis. In conclusion, all the proteins found altered in colorectal tumor samples could be considered as candidates for future studies focused on their utility as markers for colorectal diagnosis and prognosis, or as targets for colorectal cancer therapy.

Glutathione S-transferase pi1 promotes tumorigenicity in HCT116 human colon cancer cells

GSTP1 is a member of the glutathione S-transferase enzyme superfamily, which catalyzes the conjugation of electrophiles with glutathione in the process of detoxification. GSTP1 is widely overexpressed in colorectal cancer, from aberrant crypt foci to advanced carcinomas. Increased expression of GSTP1 is associated with multidrug resistance and a worse clinical prognosis. However, GSTP1-null mice have an increased risk of tumor formation. Thus, the biological function of GSTP1 in colorectal cancer biology remains speculative. In an effort to gain further insights into the role of GSTP1 in tumorigenesis, we disrupted the GSTP1 gene in HCT116 human colorectal cancer cells using targeted homologous recombination. We find that loss of GSTP1 resulted in impaired clonogenic survival and proliferation. Specifically, under growth-limiting conditions, (a) GSTP1 protected HCT116 cells from oxidative stress and associated apoptosis and (b) promoted mitogen-activated protein kinase-extracellular signal-regulated kinase kinase/extracellular signal-regulated kinase-mediated G1-S cell cycle progression. In vivo, GSTP1 was critical for engraftment and growth of HCT116 tumor xenografts. These studies directly show that GSTP1 promotes clonogenic survival and proliferation in HCT116 human colon cancer cells.

Proteome analysis reveals novel proteins associated with proliferation and differentiation of the colorectal cancer cell line Caco-2

Here, we describe a proteomics approach to study protein expression changes in differentiating Caco-2 cells. Caco-2 is a colorectal carcinoma cell line, which upon differentiation loses its tumorigenic phenotype and displays characteristics of mature enterocytes, including brush borders with microvilli. Cells were grown in culture flasks and harvested at different stages of differentiation (days post-confluence: -3, 0, 3, 7, 10, 14, and 18). Two-dimensional gel electrophoresis was used to analyse proteome changes. Approximately 1400 protein spots were detected within the Caco-2 proteome, within the pH 4-7 range. Two-dimensional gel electrophoresis allowed for the detection of 18 proteins from which the levels of expression were found to be associated with differentiation. Of these proteins, 11 were identified by means of MALDI-TOF or NANO-ESI-MS/MS mass spectrometry and include liver fatty acid binding protein (FABL), three forms of alpha-enolase (ENOA), nucleoside diphosphate kinase A (NDKA), cofilin-1 (COF1), translationally controlled tumour protein (TCTP), mitochondrial 60-kDa heat shock protein (CH60), probable protein disulfide isomerase (ER60), creatine kinase B (KCRB), and glutathione S-transferase alpha (GTA1). Thus, proteomics revealed that the differentiation-related change in phenotype of Caco-2 involves changes in a variety of distinct biochemical pathways. Some of these proteins have not been shown before to be associated with Caco-2 differentiation (ER60; COF1; CH60; NDKA; TCTP and ENOA). Therefore, processes related to protein folding and disulfide bridge formation, cytoskeleton formation and maintenance, nucleotide metabolism, glycolysis as well as tumorigenesis-associated proteins may be involved in Caco-2 differentiation. Changes in the expression of CH60, TCTP, GTA1, NDKA, and FABL have also been reported to be associated with in vivo colon carcinogenesis. These findings illustrate that a combination of proteomics and cell culture is a useful approach to find markers for Caco-2 differentiation, which could contribute to the comprehension of the process of colon carcinogenesis.

Loss of glutathione S-transferase (GST) mu phenotype in colorectal adenocarcinomas from patients with a GSTM1 positive genotype

Glutathione S-transferase (GST) mu phenotype was assessed in colon tissue from patients with ulcerative colitis and colorectal neoplasms that were positive for GSTM1 genotype. GST mu protein (enzyme linked immunosorbent assay) was absent in 2/9 unaffected colon tissue (22.3%), 4/13 tissues with chronic ulcerative colitis (CUC) (30.7%), 4/11 adenomas (36.4%) and 7/14 adenocarcinomas (50.0%; P<or=0.05). GST-3H-trans-stilbene oxide activity was detected in all tissues except 1/13 (7.6%) CUC tissues and 7/14 (50.0%, P<or=0.05) colorectal adenocarcinomas. Immunoreactive GST mu was observed in colonic epithelial cells but not in adjacent neoplastic cells by immunohistochemistry. Two-dimensional electrophoresis revealed several mu class isoforms in cytosol from unaffected colon that were absent in matched tumor cytosol. These results indicate that GSTM1 genotype may not necessarily reflect GST mu phenotype in colorectal tumors.

Cloning and characterization of glyoxalase I from soybean

Glyoxalase I and glutathione transferase (GST) are two glutathione-dependent enzymes which are enhanced in plants during cell division and in response to diverse stress treatments. In soybean, a further connection between these two enzymes has been suggested by a clone (Accession No. X68819) resembling a GST being described as a glyoxalase I. To characterize glyoxalase I in soybean, GmGlyox I resembling the dimeric enzyme from animals has been cloned from a cDNA library prepared from soybean suspension cultures. When expressed in Escherichia coli, GmGlyox I was found to be a 38-kDa dimer composed of 21-kDa subunits and unlike the enzyme from mammals showed activity in the absence of metal ions. GmGlyox I was active toward the hemithioacetal adducts formed by reacting methylglyoxal, or phenylglyoxal, with glutathione, homoglutathione, or gamma-glutamylcysteine, showing no preference for homoglutathione adducts over glutathione adducts, even though homoglutathione is the dominant thiol in soybean. When the clone X68819 was expressed in E. coli, the respective recombinant enzyme was active as a GST rather than a glyoxalase and was termed GmGST 3. GmGST 3 was active as a homodimer (45 kDa) composed of 26-kDa subunits and showed a preference for glutathione over homoglutathione when conjugating 1-chloro-2,4-dinitrobenzene. Both enzymes are associated with cell division in soybean cultures, but GmGST 3 (0.4% total protein) was 40 times more abundant than GmGlyox I (0.01%).

Nutrition and cancer: the herbal revolution

There is growing evidence that compounds of plant origin have the ability to prevent cancer. Populations with greater reliance on fruits and vegetables in the diet experience a reduced risk for the major cancers. Research has focused on specific micronutrients and nonnutrient compounds that may have health benefits. The term phytochemical means any compound of plant origin. This review focuses on the cancer-preventive aspects of phytochemicals and their mechanisms of action. The term phytomedicine applies to the health-maintaining aspects of these compounds and their implications for raising the standard of public health.

Nutrition and cancer: the herbal revolution

There is growing evidence that compounds of plant origin have the ability to prevent cancer. Populations with greater reliance on fruits and vegetables in the diet experience a reduced risk for the major cancers. Research has focused on specific micronutrients and nonnutrient compounds that may have health benefits. The term phytochemical means any compound of plant origin. This review focuses on the cancer-preventive aspects of phytochemicals and their mechanisms of action. The term phytomedicine applies to the health-maintaining aspects of these compounds and their implications for raising the standard of public health.

Experimental evidence for cancer preventive elements in foods

The last decade has witnessed an incredible advance in our understanding of how fruits and vegetables work to prevent cancer. Epidemiological studies have suggested that a diet rich in fruits and vegetables is associated with reduced risk for a number of common cancers. Food chemists and natural product scientists have identified hundreds of 'phytochemicals' that are being evaluated for the prevention of cancer. Food components can modify carcinogenesis in one of five different ways. They may: (1) modify carcinogen activation by inhibiting Phase 1 enzymes; (2) modify how carcinogens are detoxified through Phase 2 pathways; (3) scavenge DNA reactive agents; (4) suppress the abnormal proliferation of early, preneoplastic lesions; and (5) inhibit certain properties of the cancer cell.

Quantitative and qualitative characterization of 1H NMR spectra of colon tumors, normal mucosa and their perchloric acid extracts: decreased levels of myo-inositol in tumours can be detected in intact biopsies

Sixteen colonic tumours and 10 normal mucosa biopsies have been examined by 1H NMR spectroscopy at 9.4 T. A complete characterization and quantification of the aliphatic region of PCA extract spectra and the analysis of the two-dimensional COSY spectra of five pairs of intact biopsies (tumor and control mucosa) has been carried out. The analysis of the PCA extracts demonstrated a significant increase in the concentration of the endogenous compounds: lactate, glutamate, aspartate, taurine, spermine, glutathione and glycerophosphoethanolamine, and a significant decrease of myo- and scyllo-inositol, in tumours with respect to mucosae. Among these metabolites, the high myo-inositol and taurine levels and the reciprocal changes found between them in tumours and mucosae make their resonances interesting as possible malignancy markers if they are detectable in vivo. In contrast to the easy observation of taurine in one-dimensional spectra of intact biopsies, the difficulty of observing myo-inositol prompted us to use two-dimensional COSY spectra for the detection and quantification of both these metabolites. In the two-dimensional spectra, the use of a ratio between the cross-peak volumes of both metabolites permits an excellent differentiation between tumours and normal mucosa and suggests its potential to detect malignant changes in the healthy tissue, provided a two-dimensional approach is used.

Influence of ethacrynic acid on glutathione S-transferase pi transcript and protein half-lives in human colon cancer cells

Ethacrynic acid (EA) is a plant phenolic acid that is both an inhibitor and an inducer of glutathione S-transferase (GST) activity. To determine contributory factors in the increased GST activity caused by EA treatment, human colon carcinoma HT29 cells were compared with a cloned EA-resistant population (HT6-8) maintained in medium containing 72 microM EA. Several factors are involved in the increased expression of GST pi in HT6-8. For example, nuclear run-on experiments showed an approximately 2-fold increase in the rate of transcription of GST pi. In addition, the half-life of GST pi transcript was increased from 4.1 (wild type, HT29, HT4-1) to 8.4 hr. The half-life of GST pi protein was 1-2 hr in HT4-1 cells versus 8-9 hr in HT6-8 cells. When either human ovarian carcinoma cells (SKOV3) or human prostatic carcinoma cells (DU145) were treated with EA, the half-life of the GST pi transcript was also increased. The transcript half-lives of another thiol-metabolism enzyme, gamma-glutamylcysteine synthetase (gamma-GCS), and a phase II detoxification enzyme, dihydrodiol dehydrogenase (DDH), were also increased in HT6-8, SKOV3 and DU145 cells treated with EA. However, the half-lives of transcripts from "housekeeping genes," such as glyceraldehyde 3-phosphate dehydrogenase (G3PDH), beta-actin and beta-tubulin, were not changed in these cell lines following EA. Apparently, a number of coordinated factors are involved in EA-enhanced expression of GST pi and other detoxification enzymes.

P-glycoprotein is not expressed in a majority of colorectal carcinomas and is not regulated by mutant p53 in vivo

Overexpression of the MDR1 product, P-glycoprotein (Pgp), has been shown to be one of the mechanisms underlying the development of multidrug resistance (MDR). Recently, one mutant p53 has been shown to stimulate the MDR1 gene promoter in vitro, whereas wild-type p53 repressed this activity. We measured Pgp and p53 expression by immunoblotting in 34 colorectal tumours, and performed mutation analyses on the p53-positive tumours to confirm the presence of mutant p53 protein. Tumour DNA indices (DIs) were also measured using flow cytometry. Pgp was detected in 44% (15/34) of the tumours and in 100% (13/13) of the normal mucosas (P = 0.0005), with highest levels of expression seen in normal mucosa, suggesting that initial drug resistance in colorectal tumours is not caused by Pgp. Highly DNA aneuploid tumours demonstrated the lowest levels of Pgp expression relative to moderately aneuploid and diploid colorectal tumours. p53 protein was detected in 53% (18/34) of the tumours, and 12 of 14 p53-positive tumours had p53 gene mutations, p53-negative tumours had approximately twice the level of Pgp expression of p53-positive tumours. Pgp expression was not associated with either p53 expression (P = 0.73) or incidence of p53 gene mutation (P = 0.70), suggesting that mutant p53 does not induce Pgp overexpression in colorectal carcinomas.

The role of the glutathione-dependent system in tumor sensitivity to cisplatin: a study of human tumor xenografts

BACKGROUND

Glutathione, the most important intracellular thiol, has been implicated in modulating tumor cell sensitivity to alkylating agents and cisplatin. However, the role of the glutathione-dependent detoxification system in mediating cisplatin resistance of human tumors remains unclear.

DESIGN

Glutathione content and related enzyme activities were assessed in a series of human tumor xenografts representative of responsive (i.e., small-cell lung cancer and ovarian carcinoma) and resistant tumor types (i.e., non-small-cell lung cancer and colorectal carcinoma), in an attempt to establish a correlation with response to cisplatin treatment.

RESULTS

The pattern of tumor response to cisplatin treatment for tumors selected in the two panels corresponded to the one expected from the clinical experience, since drug-induced tumor growth inhibition ranged from 70% to 100% in the group of sensitive tumors and from 20% to 60% in the group of resistant tumors. No correlation was observed between glutathione level and cisplatin response in the resistant tumor panel. An inverse correlation was found for glutathione-S-transferase activity level and tumor response only in the panel of chemoresponsive tumors. In the latter panel, the only unresponsive tumor (POCS) showed the highest glutathione level in the entire series investigated. No significant correlation was found between other enzymes investigated and tumor response to cisplatin treatment. In addition, a very low activity of gamma-glutamyltranspeptidase was found to be associated with sensitive tumors.

CONCLUSIONS

Although glutathione may have a role in modulating cisplatin cell sensitivity, it is unlikely that alteration in glutathione level and metabolism is a primary mechanism of cisplatin resistance in human tumors, since: a) no significant correlations were found between glutathione level and response to cisplatin treatment in a series of chemosensitive and chemoresistant human tumor xenografts; b) a marked increase in glutathione level might be responsible for cisplatin resistance but, in contrast to findings on cell systems selected in vitro for resistance, it is not a frequent event in human tumors.

Glutathione-linked detoxification pathway in normal and malignant human bladder tissue

This study compares the levels of glutathione (GSH) and GSH-dependent detoxification enzymes, which have been implicated in anti-cancer drug resistance, in paired normal and malignant human bladder tissues, a tumor with high incidence of inherent drug resistance. Although the mean GSH transferase (GST) activity did not differ significantly in normal and neoplastic bladder tissues, this enzyme activity was relatively higher in tumor tissues of five out of ten patients as compared with corresponding normal tissues. Similarly, the mean GSH content and GSH reductase activity did not differ significantly between normal and neoplastic bladder tissues. On the other hand, the mean GSH peroxidase activity towards cumene hydroperoxide and catalase activity in bladder tumors was higher by about 1.5 and 1.4 times, respectively (P < 0.05), compared with those of normal tissues. GST isoenzymes corresponding to the three major classes (alpha, mu and pi) were expressed in every normal bladder tissue examined in the present study. Overexpression of GST pi was observed in 60% of the bladder tumors, whereas alpha and mu type GST proteins in tumor tissues were lower at frequencies of 62.5% and 37.5%, respectively, compared with the corresponding normal tissues. These results suggest that (a) elevated levels of GSH peroxidase, catalase and GST pi in human bladder tumors may contribute, at least in part, to the intrinsic drug resistance of this neoplasm and (b) anti-oxidative enzymes GSH peroxidase and/or catalase may represent markers for this neoplasia, although a large number of tissue specimens must be analyzed to validate this hypothesis.

Analysis of glyoxalase-I from normal and tumor tissue from human colon

Glyoxalase-I (Gly-I) is part of the glyoxalase system which converts methylglyoxal to D-lactic acid via an S-D-lactoylglutathione intermediate. This glutathione (GSH)-binding protein was purified from human colon tumors and corresponding normal tissue. The GSH-affinity purified fraction from normal human colon tissue showed enzyme activity of 30.6 +/- 11.5 mumol/min per mg protein, with methylglyoxal as substrate. Corresponding fractions from carcinomas showed significantly elevated Gly-I activity of 54.5 +/- 15 mumol/min per mg protein. Polyclonal antibodies made against human Gly-I cross-reacted weakly with mouse liver Gly-I but not with yeast Gly-I. Isoelectric points of Gly-I from human, mouse and yeast were determined to be 4.6, 4.9 and 7.0, respectively, by horizontal IEF. Immunohistochemical analysis confirmed the increase of Gly-I in human colon carcinoma in 16 out of 21 samples when compared to corresponding normal tissue. The elevated levels of Gly-I in colon tumors may be an indicator of the enhanced proliferative status of the neoplastic condition.

Time course of glutathione S-transferase elevation in Walker mammary carcinoma cells following chlorambucil exposure

Resistance of Walker 256 rat mammary carcinoma cells to chlorambucil has been shown to be accompanied by a specific increase in the A2-2 subunit of glutathione S-transferase (GST) (Buller et al., Mol Pharmacol 31: 575-578, 1987). Analysis of the time course of GST activity following chlorambucil exposure revealed a 7.5- and 3-fold elevation on day 7 post-treatment in Walker-sensitive (WS) and Walker-resistant (WR) cells, respectively. Flow activated cell sorting (FACS) analyses using antibodies specific for rat liver cytosolic GST supported these results and demonstrated the heterogeneous response of WS cells to chlorambucil exposure. The range of GST levels in drug-treated cells was very broad as compared to that of untreated cells. Transcripts for each class of GST (alpha, mu and pi) were quantified for days 1-9 post-treatment from densitometric scans of RNA slot blots. Elevations in GST alpha RNA preceded increases in GST activity (day 7) in both WS and WR cells. Because fluctuations in GSTA1-1 transcripts were not observed, it was concluded that the increased expression of the alpha class must be attributed to increases in GSTA2-2 transcripts. Amplification of the GST genes in drug-treated cells was not present. These results support the role of GSTA2-2 in the detoxification of chlorambucil. The time course of the cellular response to chlorambucil suggests that the elevation of GSTA2-2 transcripts following alkylating agent exposure may represent only one component of a series of events which collectively confer protection and lead to the establishment of drug resistance.

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

Glutathione S-transferase (GST) and carcinoembryonic antigen were measured in the plasma of 95 patients with neoplasm of digestive tract, in 40 patients suffering from non-neoplastic diseases and in 40 healthy subjects. The mean value of the GST activity was significantly (P < 0.001) elevated in patients with gastric, liver and colorectal cancer (10.4 U/l, 14.1 U/l and 12.3 U/l respectively) as compared with the reference population (3.2 U/l). GST elevations above normal were observed in 26 (90%) patients with gastric cancer, in 18 (100%) with liver cancer and in 25 (89%) with colorectal cancer. Carcinoembryonic antigen appeared less sensitive. In 15 patients the postoperative levels of serum GST were increased after surgery then gradually declined and after 1 month showed a normalization in 10 patients. Our data suggest that GST measurement may be useful as a tumour marker in gastric, liver and colorectal cancer. Moreover the combined determination of GST and other markers increase the sensitivity for cancer detection.

Gender related differences in the expression and characteristics of glutathione S-transferases of human colon

In the present study, the expression of glutathione S-transferase (GST) isozymes was compared in human male and female colon tissues. GST isozymes were purified and quantified in five male and five female colon tissue samples. Noticeable differences were observed in the isoelectric focusing profiles (IEF) of the GSTs, from male and female colon tissues. Both male and female colon tissues had three common GST peaks with pI values of 9.2, 6.7 and 4.8. An additional GST peak with a pI value of 6.2 found in all females was not found in males. Based on kinetic, immunological and structural properties, these isozymes were classified into alpha (pI 9.2), mu (pI 6.7 and 6.2) and pi (pI 4.8) classes. Activity of the alpha-class GST in male colon was approx. 2-fold higher than the corresponding isozyme in female colon. The pi-class GST 4.8 was the most predominant GST in both the sexes and its activity with CDNB as substrate was more abundant (about 1.6-fold) in female colon as compared to that in male colon. Significant differences were seen in substrate specificities between male and female colon GST 4.8. Sex related differences were also observed in the inhibition kinetics of GST pi from male and female colon in the presence of hematin. In addition, GST pi isolated from female colon was more thermostable as compared to the corresponding male isozyme. The thermostability of purified GST pi isozyme from males or females was not affected by incubation of the enzyme with either estrogen, testosterone or progesterone.

Glutathione S-transferases in human testicular germ cell tumors: changes of expression and activity

Glutathione S-transferases are involved in the detoxification of carcinogens and xenobiotics and are potentially associated with the development of drug-resistance. Forty-six testicular germ cell tumors and 33 adjacent normal testicular tissue specimens were analyzed at the RNA level for the expression of glutathione S-transferase alpha and pi. Glutathione S-transferase alpha was expressed in 31 of the 33 normal testicular tissues (94%) but in only three of the 46 germ cell tumors (7%). Glutathione S-transferase pi mRNA was detected in all normal and malignant testicular tissue samples. Thirteen testicular germ cell tumors and eight normal testicular tissue samples were analyzed at the protein level. The mean specific activity of total cytosolic glutathione S-transferase in tumor tissue was decreased by about 80% as compared to normal testicular tissue. Protein analysis of the glutathione S-transferase subunits of normal testicular tissue demonstrated the presence of the glutathione S-transferase classes alpha, mu and pi, with a predominance of the mu class. In testicular germ cell tumors the glutathione S-transferase subunit pattern showed a predominance of glutathione S-transferase pi representing 88% +/- 3% of total glutathione S-transferase. Since all three glutathione S-transferase isoenzyme classes contribute to the resistance to antineoplastic drugs, the altered glutathione S-transferase isoenzyme pattern and the decrease of glutathione S-transferase activity may play a role in the high inherent drug sensitivity of human testicular germ cell tumors.