Expression Of Gamma-glutamyl Transpeptidase Research Articles

Capecitabine enhances sensitivity to oxaliplatin in advanced gastric cancer and the effects on patients' FOXP1 and GGT levels

ObjectiveTo investigate the effect of capecitabine on the sensitivity of oxaliplatin and on the level of transcription factor forkhead box P1 (FOXP1) and gamma-glutamyl transpeptidase (GGT) in patients with intermediate and advanced gastric cancer. MethodsA total of 152 patients with intermediate and advanced gastric cancer diagnosed and treated in our hospital from April 2018 to May 2019 was selected as the research objects, and their clinical data were retrospectively analyzed. According to the different treatment methods, they were divided into the study group and the control group, with 76 cases in each group. The patients in the control group received with oxaliplatin, while the patients in the study group received with capecitabine on the basis of the control group. The therapeutic effect was evaluated according to the therapeutic effect evaluation criteria of solid tumors. The FOXP1 expression level in gastric cancer tissues was detected using immunohistochemistry. Serum levels of GGT were measured by chemiluminescence. The prognostic factors were analyzed by COX regression model, and the Kaplan-Meier survival curve was used to analyze the relationship between the influencing factors and the survival of gastric cancer. ResultsThe effective rate of capecitabine combined with oxaliplatin and oxaliplatin alone in the treatment of patients with intermediate and advanced gastric cancer were 94.74% and 76.32% respectively. Capecitabine enhanced the sensitivity of intermediate and advanced gastric cancer to oxaliplatin (P<0.05). Compared with adjacent normal tissues, the expression level of FOXP1 in gastric cancer tissues was lower (P<0.05). Before treatment, the expression of FOXP1 was low, and no significant difference was observed in the GGT level between the two groups (P>0.05). After treatment, the low expression rate of FOXP1 and serum GGT level were both significantly decreased, and those in the study group were lower than those in the control group (P<0.05). There was no difference in the incidence of adverse reactions between the two groups (P>0.05). The 1-year survival rates of the study group and the control group were 90.79% and 78.95%, while the 3-year survival rates of the study group and the control group were 75.00% and 51.32%, respectively. Both the 1-year and 3-year survival rate of the study group was higher than that in the control group (P<0.05). The 1-year survival rate of 152 patients with gastric cancer was 84.87% (129/152) and the 3-year survival rate was 63.17% (96/152). Age, tumor diameter, tumor-node-metastasis (TNM) stage, lymph node metastasis, chemotherapy regimen and the expression of FOXP1 and GGT had significant effects on the survival rate (P<0.05). Gastric cancer patients with age < 60 years, TNM stage of Ⅰ ∼ Ⅱ, lymph node metastasis N0 ∼ N1, high expression of FOXP1, GGT < 387.2, and combined with drug chemotherapy had higher survival rate. ConclusionCapecitabine effectively enhanced the sensitivity of intermediate and advanced gastric cancer to oxaliplatin, improved the therapeutic effect, reduced the proportion of patients with low FOXP1 expression rate and serum GGT level, decreased the recurrence rate and ameliorated the prognosis of patients.This is a retrospective study, all data were analyzed retrospectively. This research was approved by the Ethics Review Committees of Fuwai Central China Cardiovascular Hospital (approval number: 2023-EC-015).

Rapid visualization of mammary gland tumor lesions of dogs using the enzyme-activated fluorogenic probe; γ-glutamyl hydroxymethyl rhodamine green.

Since gamma-glutamyl transpeptidase (GGT) is highly and locally expressed in human breast cancer, a GGT-enzymatically activatable fluorescent probe, gamma-glutamyl hydroxymethyl rhodamine green (gGlu-HMRG), has been developed to detect the human breast cancer area with high performance. In this study, GGT expression and the efficacy of gGlu-HMRG on visualization were investigated in canine mammary gland tumors (MGT). Seventeen non-fixed fresh-frozen MGT specimens and each peritumoral control tissue were utilized. The GGT mRNA levels were highly observed in the tumor specimens compared with the control. GGT immunostaining was mostly observed on the cell membrane and cytosol of the alveolar and duct mammary epithelium of MGT tissues. These signals were strongly positive in several cases while they were mild to not observed in other cases. When gGlu-HMRG solution was dropped to the non-fixed tissue pieces of MGT or control tissues, the fluorescence intensities (FIs) were measured using Maestro in-vivo imaging device. FIs in MGT tissues were significantly higher than each control tissue 20 min after treatment. Based on Youden index method said that the maximum sensitivity and specificity of FI was 82.4% and 82.4%. These findings suggest that GGT is highly expressed in several MGTs in dogs and gGlu-HMRG could visualize at least a part of MGT tissues in dogs. Nevertheless, it should be needed to assess the false-negative areas more carefully in canine than human cases.

Bacterial Gamma-Glutamyl Transpeptidase, an Emerging Biocatalyst: Insights Into Structure-Function Relationship and Its Biotechnological Applications.

Gamma-glutamyl transpeptidase (GGT) enzyme is ubiquitously present in all life forms and plays a variety of roles in diverse organisms. Higher eukaryotes mainly utilize GGT for glutathione degradation, and mammalian GGTs have implications in many physiological disorders also. GGTs from unicellular prokaryotes serve different physiological functions in Gram-positive and Gram-negative bacteria. In the present review, the physiological significance of bacterial GGTs has been discussed categorizing GGTs from Gram-negative bacteria like Escherichia coli as glutathione degraders and from pathogenic species like Helicobacter pylori as virulence factors. Gram-positive bacilli, however, are considered separately as poly-γ-glutamic acid (PGA) degraders. The structure–function relationship of the GGT is also discussed mainly focusing on the crystallization of bacterial GGTs along with functional characterization of conserved regions by site-directed mutagenesis that unravels molecular aspects of autoprocessing and catalysis. Only a few crystal structures have been deciphered so far. Further, different reports on heterologous expression of bacterial GGTs in E. coli and Bacillus subtilis as hosts have been presented in a table pointing toward the lack of fermentation studies for large-scale production. Physicochemical properties of bacterial GGTs have also been described, followed by a detailed discussion on various applications of bacterial GGTs in different biotechnological sectors. This review emphasizes the potential of bacterial GGTs as an industrial biocatalyst relevant to the current switch toward green chemistry.

Development and Validation of Nomograms Based on Gamma-Glutamyl Transpeptidase to Platelet Ratio for Hepatocellular Carcinoma Patients Reveal Novel Prognostic Value and the Ratio Is Negatively Correlated With P38MAPK Expression.

BackgroundEarly prediction of recurrence and death risks is significant to the treatment of hepatocellular carcinoma (HCC) patients. We aimed to develop and validate prognosis nomogram models based on the gamma-glutamyl transpeptidase (GGT)-to-platelet (PLT) ratio (GPR) for HCC and to explore the relationship between the GPR and inflammation-related signaling pathways.MethodsAll data were obtained from 2000 to 2012 in the Affiliated Hospital of Qingdao University. In the training cohort, factors included in the nomograms were determined by univariate and multivariate analyses. In the training and validation cohorts, the concordance index (C-index) and calibration curves were used to assess predictive accuracy, and receiver operating characteristic curves were used to assess discriminative ability. Clinical utility was evaluated using decision curve analysis. Moreover, improvement of the predictive accuracy of the nomograms was evaluated by calculating the decision curve analysis, the integrated discrimination improvement, and the net reclassification improvement. Finally, the relationship between the GPR and inflammation-related signaling pathways was evaluated using the independent-samples t-test.ResultsA larger tumor size and higher GPR were common independent risk factors for both disease-free survival (DFS) and overall survival (OS) in HCC (P < 0.05). Good agreement between our nomogram models’ predictions and actual observations was detected by the C-index and calibration curves. Our nomogram models showed significantly better performance in predicting the HCC prognosis compared to other models (P < 0.05). Online webserver and scoring system tables were built based on the proposed nomogram for convenient clinical use. Notably, including the GPR greatly improved the predictive ability of our nomogram models (P < 0.05). In the validation cohort, p38 mitogen-activated protein kinase (P38MAPK) expression was significantly negatively correlated with the GPR (P < 0.01) and GGT (P = 0.039), but was not correlated with PLT levels (P = 0.063). And we found that P38MAPK can regulate the expression of GGT by quantitative real-time PCR and Western blotting experiments.ConclusionsThe dynamic nomogram based on the GPR provides accurate and effective prognostic predictions for HCC, and P38MAPK-GGT may be a suitable therapeutic target to improve the prognosis of HCC patients.

Low expression of gamma-glutamyl transpeptidase 1 is an independent poor prognostic factor in ovarian clear cell carcinoma, in relation to up-regulation of immune suppressive genes and EMT-related genes.

6042 Background: Ovarian clear cell carcinoma (OCCC) is a distinct entity from other epithelial ovarian cancers such as the most prevalent high-grade serous cancer (HGSC), and often exhibit less sensitivity to platinum-based chemotherapy. Several studies using cell lines have reported that glutathione (GSH) metabolism plays an important role in chemo-resistance of OCCC. Here, we aimed to correlate the prognosis of OCCC and the expression of gamma-glutamyltransferase 1 (GGT1), one of the key enzymes in GSH metabolism. Methods: We prepared a FFPE-tissue microarray, and analyzed 56 OCCC patients with the follow-up periods over 3 years. Expression level of GGT1 was evaluated by immunohistochemistry (IHC) using H-score (0-300), and was correlated with clinical outcomes. The prognostic significance was assessed by multivariate analysis using Cox regression model. To investigate the possible related pathways, we performed transcriptome analysis using Ion AmpliSeq Transcriptome Human Gene Expression Kit (Thermo Fisher Scientific) from the frozen tissue specimens collected from 33 ovarian cancer patients including 15 OCCC patients and 18 HGSC patients. Results: The OCCC patients were divided into two populations in the histogram of H-score in IHC staining, and the cut-off value was 90; 44 cases showed GGT1-high, and remaining 12 cases were GGT1-low. Follow-up periods, FIGO stage, and optimal surgery rate were not significantly different between two groups. However, platinum-resistant recurrent rate was significantly higher (42% vs. 14%, p=0.027), and overall survival (OS) was significantly shorter (5-year OS; 42% vs. 72%, p=0.0226) in GGT1-low OCCC. Multivariate analysis revealed that low expression of GGT1 was one of the independent poor prognostic factors as well as platinum-drug resistance. In enrichment analysis, the genes related to GSH metabolism, such as SLC3A1, GGT1, CSE, and GPX3 were up-regulated and positively correlated with HNF1B expression in OCCC. The expression level of GGT1 was inversely correlated with that of immune suppressive genes (TGF-b, IFNG, IL10, FOXP3, PD-L1, CTLA4) and epithelial-mesenchymal transition (EMT)-related genes (CDH2, VIM, TWIST1, ZEB1, ZEB2) in OCCC samples. Conclusions: Low expression of GGT1 is an independent poor prognostic factor probably in part due to suppression of tumor immunity and induction of EMT in OCCC.

Probing the Interactions of Sulfur-Containing Histidine Compounds with Human Gamma-Glutamyl Transpeptidase.

Gamma-glutamyl transpeptidase (GGT) is a cell surface enzyme involved in glutathione metabolism and maintenance of redox homeostasis. High expression of GGT on tumor cells is associated with an increase of cell proliferation and resistance against chemotherapy. GGT inhibitors that have been evaluated in clinical trials are too toxic for human use. We have previously identified ovothiols, 5(Nπ)-methyl-thiohistidines of marine origin, as non-competitive-like inhibitors of GGT that are more potent than the known GGT inhibitor, 6-diazo-5-oxo-l-norleucine (DON), and are not toxic for human embryonic cells. We extended these studies to the desmethylated form of ovothiol, 5-thiohistidine, and confirmed that this ovothiol derivative also acts as a non-competitive-like GGT inhibitor, with a potency comparable to ovothiol. We also found that both 5-thiohistidine derivatives act as reversible GGT inhibitors compared to the irreversible DON. Finally, we probed the interactions of 5-thiohistidines with GGT by docking analysis and compared them with the 2-thiohistidine ergothioneine, the physiological substrate glutathione, and the DON inhibitor. Overall, our results provide new insight for further development of 5-thiohistidine derivatives as therapeutics for GGT-positive tumors.

Abstract 4020: Correlation between the expression of glutathione metabolism-related genes and prognosis in ovarian clear cell carcinoma

Abstract Background: Ovarian clear cell carcinoma (OCCC) is more prevalent in Japan than western countries, exhibits chemoresistant phenotype and poor survival. Although the expression of the genes related to glutathione (GSH) metabolism had been reported as one of the possible chemoresistant mechanisms, correlation between the expressions of these genes and prognosis in OCCC patients remains unclear. In this study, we aim to investigate 1) enrichment pathway analysis in OCCC in comparison with high-grade serous carcinoma (HGSC), and 2) correlation between the expression of gamma-glutamyl transpeptidase 1 (GGT1), one of the enzymes in GSH metabolism and prognosis. Methods: We consecutively collected surgically resected tissue specimens from 33 ovarian cancer patients; 15 patients with OCCC and 18 patients with HGSC. The tissue specimens were collected in the vials containing RNA later® within 10 min. after resection of tumors. Total RNAs were extracted from the tumor tissues, and comprehensive gene expression analysis was performed using Ion AmpliSeq™ Transcriptome Human Gene Expression Kit (Thermo Fisher Scientific). For prognostic analysis, we used a tissue microarray (TMA) from 56 consecutive patients pathologically diagnosed with OCCC in our hospital, and assessed by immunohistochemistry (IHC) using H-score ranging from 0 to 300. Overall survival (OS) was estimated by Kaplan-Meier method, and analyzed by Cox-regression hazard model in multivariate analysis. Results: Gene expression profiles revealed that TCF1/2 target genes were up-regulated in OCCC samples in comparison with HGSC. In addition, genes related with amino-acid transporters, such as SLC3A1, a cystine transporter, and genes related to GSH metabolism, including GGT1, CSE, and GPX3 were also up-regulated. In the OCCC patients with high expression level of GSH-related genes, FOXP3 was down-regulated but the T-cell inflamed genes were not varied compared to the OCCC patients with low expression level. The expression level of GGT1 in gene expression analysis was strongly correlated with H-score of GGT1 in IHC (r = 0.7850, p = 0.0023). In prognostic analysis, there were no significant differences during follow up period (57.5 months vs. 53 months), FIGO stage (I: 50% vs 64%), optimal surgery (92% vs. 98%), or recurrent rate (42% vs. 30%) between GGT1 positive (n = 44) and negative (n = 12) OCCC in IHC. However, platinum-drug resistant recurrent rate was significantly higher in GGT1 negative OCCC than GGT1 positive OCCC (42% vs 14%, p = 0.027). OS in GGT1 negative OCCC was significantly worse than that of GGT1 positive OCCC (5-year OS was 42% vs 72%, p = 0.0226), and negative expression of GGT1 was one of the independent poor prognostic factors in OCCC. Conclusion: Negative expression of GGT1 in OCCC might be a poor prognostic maker via recruitment of regulatory T cells in tumor microenvironments. Citation Format: Hiroshi Asano, Ryosuke Matsuoka, Kanako C. Hatanaka, Yutaka Hatanaka, Tatsuya Kato, Yosuke Konno, Takashi Mitamura, Hirotoshi Akita, Yoshihiro Matsuno, Hidemichi Watari. Correlation between the expression of glutathione metabolism-related genes and prognosis in ovarian clear cell carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4020.

Mo1922 - Gamma-Glutamyltranspeptidase Expression by Helicobacter Saguini, a Novel Enterohepatic Helicobacter Species Isolated from Cotton Top Tamarins with Chronic Colitis

Mo1922 - Gamma-Glutamyltranspeptidase Expression by Helicobacter Saguini, a Novel Enterohepatic Helicobacter Species Isolated from Cotton Top Tamarins with Chronic Colitis

Tumor and serum gamma-glutamyl transpeptidase, new prognostic and molecular interpretation of an old biomarker in gastric cancer.

BackgroundGastric Cancer is one of the most lethal malignancies worldwide. Gamma-glutamyl transpeptidase (GGT) is an enzyme mainly involved in cellular glutathione homeostasis. We aim to explore the clinical value of GGT in gastric cancer.ResultsAmong 322 patients enrolled, 65/82 patients were determined as GGT positive in serum/tumor, respectively. High tumor GGT expression is significantly associated with lymph node metastasis, histological subtype, and Her2 expression. Kaplan-Meier curve shows that high tumor GGT patients have shorter overall survival (P log-rank=0.001) and progress-free survival (P log-rank =0.001). Patients with both high tumor and serum GGT have the poorest prognosis. The multivariable Cox analysis shows that the hazard ratio of overall survival for high tumor GGT is 1.69 (95% CI 1.19-2.37). High serum GGT is a poor prognostic factor in adjuvant chemotherapy hazard ratio=2.18, 95%CI (1.15-4.47). These findings were further validated in six online datasets. Gene Sets Enrichment Analysis showed that GGT promotes cancer progression through EMT, KRAS, SRC and PKCA pathways.MethodsTumor GGT and serum GGT levels were evaluated with immuno-histochemistry staining and enzymatic assay, respectively. Kaplan-Meier curve and Cox regression model were used to test the association between GGT and gastric cancer prognosis. Independent datasets from Gene Expression Omnibus and Gene Sets Enrichment Analysis were applied to validate the findings and explore the potential mechanisms.ConclusionBoth tumor GGT and serum GGT are poor prognostic factors in gastric cancer. Patients with high tumor and serum GGT levels require more intense treatment and follow-up.

Drinking Amount Associated with Abnormal Gamma-Glutamyl Transpeptidase Expression in Women.

BackgroundThis study investigated whether there is any difference in drinking amount associated with abnormal expression of gamma-glutamyl transpeptidase (GGT), one of the biological markers of excessive drinking, between flushing and non-flushing women after drinkingMethodsThe subjects were 797 women aged 20–59 years old who visited health promotion center of Chungnam National University Hospital between January, 2013 and July, 2014. Facial flushing status after drinking, amount of alcohol consumed per drinking episode, and the number of drinking days per week were assessed using a questionnaire. Age, abnormal GGT expression, smoking status, menopauase status, and body mass index (BMI) were obtained from the health screening data. The weekly drinking amount were categorized into <4 drinks; ≥4, <8 drinks; and ≥8 drinks. The association of abnormal GGT expression with weekly drinking amount was analyzed using multivariate logistic regression after controlling for confounding variables including age, smoking status, menopauase status, and BMI.ResultsCompared to nondrinkers, the abnormal GGT expression in the non-flushing group was significantly increased when the weekly drinking amount was ≥4 drinks (≥4, <8 drinks: adjusted odds ratio [aOR], 37.568; 95% confidence interval [CI], 9.793–144.116; ≥8 drinks: aOR, 20.350; 95% CI, 20.350–305.138). On the other hand, the abnormal GGT expression in the flushing group was significantly increased in every weekly drinking amount range (<4 drinks: aOR, 4.120; 95% CI, 1.603–10.585; ≥4, <8 drinks: aOR, 79.206; 95% CI, 24.034–261.031; ≥8 drinks: aOR, 111.342; 95% CI, 30.987–400.079). For each weekly drinking amount range, the flushing group showed significantly higher abnormal GGT expression than the non-flushing group (<4 drinks: aOR, 3.867; 95% CI, 1.786–8.374; ≥4, <8 drinks: aOR, 57.277; 95% CI, 24.430–134.285; ≥8 drinks: aOR, 104.871; 95% CI, 42.945–256.091).ConclusionThis study showed that abnormal GGT expression in the flushing female drinkers was induced by smaller amounts of alcohol than in the non-flushing female drinkers.

Abstract 683: Sensitizing tumors to pro-oxidant therapy by inhibiting gamma-glutamyl transpeptidase

Abstract We have reported that 73% of ovarian tumors express the cell surface enzyme gamma-glutamyl transpeptidase (GGT). Clinical studies have shown a poorer prognosis for ovarian tumors that are GGT-positive compared to GGT-negative tumors. GGT-positive tumors are able to use the glutathione in the interstitial fluid as an additional source of cysteine, the limiting component of intracellular glutathione synthesis in tumors. The concentration of cysteine/cystine in standard tissue culture media is more than 3 times the concentration in interstitial fluid. In this study we show that in studies of cultured cells, the high concentration of cysteine in tissue culture media obscured the role of GGT expression in drug resistance. However, culturing human ovarian tumor cells in tissue culture media containing physiological concentrations of cystine and glutathione demonstrated that the supply of cysteine/cystine regulates intracellular glutathione concentrations. In these studies, inhibition of GGT blocked the use of extracellular glutathione as a source of cysteine and sensitized the tumors to cisplatin, carboplatin and melphalan. Inhibiting GGT in patients would also inhibit GGT in the kidney resulting in the excretion of glutathione in the urine and depletion of cysteine from serum and interstitial fluid. As a result, inhibition of GGT in patients would sensitize both GGT-positive and GGT-negative tumors to pro-oxidant chemotherapy. Clinical application of this therapeutic strategy is limited by the fact that most inhibitors of GGT are glutamate analogs and too toxic for use in humans. We discovered a non-glutamate analog that is an uncompetitive inhibitor of GGT, and are developing more potent, non-toxic GGT inhibitors. We recently published the crystal structure of human GGT. We have now also solved the structure of the substrate-bound enzyme, the form of the enzyme to which our uncompetitive inhibitors bind. Using structure-based drug design and our physiologically relevant tissue culture system we are designing new GGT inhibitors and evaluating them for their ability to sensitize tumors to chemotherapy regimens used in the clinic. Supported by an Institutional Development Award (IDeA) from the National Institutes of Health under grant P20GM103640. Citation Format: Marie H. Hanigan, Nancy Wakeham, Stephanie Wickham, Simon S. Terzyan. Sensitizing tumors to pro-oxidant therapy by inhibiting gamma-glutamyl transpeptidase. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 683. doi:10.1158/1538-7445.AM2014-683

Efeito da tibolona na morfologia do músculo esquelético, nas enzimas hepáticas e no nível sérico de glicose em ratas castradas

INTRODUÇÃO: O fígado é uma estrutura de elevada complexidade e é fundamental entender como determinadas substâncias podem afetar sua estrutura e suas funções. OBJETIVO: Analisar a influência da tibolona no metabolismo hepático por meio da avaliação de enzimas e metabólitos comumente utilizados em provas de função hepática. MÉTODOS: Foram utilizadas dez ratas Wistar, divididas em dois grupos: controle (n = 4) e tibolona (n = 6), em status de menopausa cirúrgica. A tibolona (1 mg) foi administrada diariamente por gavagem durante 20 semanas, com avaliação periódica do peso corporal. Após sedação, efetuou-se coleta de sangue para avaliação bioquímica de albumina (Alb) sérica, fosfatase alcalina (FA), transaminases (aspartato aminotransferase e alanina aminotransferase [AST/ALT]), gama-glutamiltranspeptidase (GGT) e glicose, mediante espectrofotometria. O músculo esquelético da coxa foi avaliado por histomorfometria em cortes histológicos corados com hematoxilina e eosina (HE). RESULTADOS: Os animais do grupo tibolona mostraram menor peso corporal, alterações musculares esqueléticas e discretas alterações bioquímicas. Além disso, AST e FA estavam diminuídas e GGT estava mais elevada, porém sem significância estatística. A histomorfometria do músculo revelou uma tendência de menor volume celular nesse grupo. CONCLUSÃO: A tibolona, administrada em alta dose e por tempo prolongado, não interfere de forma significativa nas funções metabólicas e de síntese hepáticas, bem como na permeabilidade da membrana celular, entretanto parece modular a expressão genômica da GGT. A tibolona apresenta influência sistêmica associada a menor peso e diminuição da massa muscular e aumento significativo no peso relativo do fígado, além de alteração da glicogenólise hepática e muscular, da gliconeogênese hepática e dos níveis de glicose circulante.

An Electrochemical Method to Detect Gamma Glutamyl Transpeptidase

Gamma glutamyl transpeptidase (GGT) is a transferase, which is of great importance in sustaining intracellular cysteine and glutathione levels. The abnormal expression of GGT is significantly associated with features of many metabolic syndromes (e.g., hepatocellular carcinoma). Therefore, it is essential to develop methods to detect GGT so as to monitor the physiological or pathological phenomena related to this species. In this work, by making use of a complex formed by Cu2+ and glutathione, which may exhibit excellent voltammetric response, we have proposed a novel potential electrochemical method for the detection of the enzyme. Results show that in the presence of GGT, the formation of Cu2+-glutathione complex on a working electrode will be disrupted, resulting in greatly depressed electrochemical signals. The primary method exhibits some advantages, such as it being fast, cost-efficient, and conveniently operated. It also has the potential to be further developed as an effective method in the quantitative detection of GGT in real samples.

Redox Regulation of γ-Glutamyl Transpeptidase

gamma-Glutamyl transpeptidase (GGT) catalyzes the transfer of the glutamyl moiety from glutathione, and glutathione S-conjugates to acceptors to form another amide or to water to produce free glutamate. Functionally, GGT plays important roles in glutathione homeostasis and mercapturic acid metabolism. The expression of GGT is increased as an adaptive response upon the exposure of oxidative stress. The underlying mechanism of this, however, is nebulous, as GGT gene structure is complex and its transcription is usually controlled by multiple promoters that generate several subtypes of GGT mRNAs. Studies reveal that signaling pathways such as Ras, ERK, p38MAPK, and PI3K are involved in the induction of GGT gene expression in response to oxidative stress. Thus, not surprisingly, induction of GGT mRNA subtypes and the involvement of multiple signaling pathways vary depending on cell type and stimuli.

A Novel, Species-specific Class of Uncompetitive Inhibitors of γ-Glutamyl Transpeptidase

Expression of gamma-glutamyl transpeptidase (GGT) in tumors contributes to resistance to radiation and chemotherapy. GGT is inhibited by glutamine analogues that compete with the substrate for the gamma-glutamyl binding site. However, the glutamine analogues that have been evaluated in clinical trials are too toxic for use in humans. We have used high throughput screening to evaluate small molecules for their ability to inhibit GGT and have identified a novel class of inhibitors that are not glutamine analogues. These compounds are uncompetitive inhibitors, binding the gamma-glutamyl enzyme complex. OU749, the lead compound, has an intrinsic K(i) of 17.6 microm. It is a competitive inhibitor of the acceptor glycyl-glycine, which indicates that OU749 occupies the acceptor site while binding to the gamma-glutamyl substrate complex. OU749 is more than 150-fold less toxic than the GGT inhibitor acivicin toward dividing cells. Inhibition of GGT by OU749 is species-specific, inhibiting GGT isolated from human kidney with 7-10-fold greater potency than GGT isolated from rat or mouse kidney. OU749 does not inhibit GGT from pig cells. Human GGT expressed in mouse fibroblasts is inhibited by OU749 similarly to GGT from human cells, which indicates that the species specificity is determined by differences in the primary structure of the protein rather than species-specific, post-translational modifications. These studies have identified a novel class of inhibitors of GGT, providing the basis for further development of a new group of therapeutics that inhibit GGT by a mechanism distinct from the toxic glutamine analogues.

Treatment With Anti-γ-Glutamyl Transpeptidase Antibody Attenuates Osteolysis in Collagen-Induced Arthritis Mice

The effectiveness of a new antibody treatment on arthritis-associated osteolysis was studied by using CIA mice. GGT, a newly identified bone-resorbing factor, was upregulated in arthritic joints. We generated monoclonal antibodies against GGT and injected them into CIA mice. Mice treated with antibodies showed a reduction in osteoclast number and bone erosion. Gamma-glutamyl transpeptidase (GGT) acts as a bone-resorbing factor that stimulates osteoclast formation. GGT expression has been detected in active lymphocytes that accumulate at inflammation sites, such as rheumatoid arthritis (RA). We hypothesize that GGT is an effective target for suppression of arthritis-related osteoclastogenesis and joint destruction. Here, we describe the therapeutic effect of neutralizing antibodies against GGT on joint destruction using a collagen-induced arthritis (CIA) mouse model. GGT expression in the synovium of RA patients and CIA mice was determined by immunohistochemistry and RT-PCR. Monoclonal antibodies were generated against recombinant human GGT (GGT-mAbs) using BALB/c mice. Antibody treatment was performed by intraperitoneal injections of GGT-mAbs into CIA mice. Effects of antibody treatment on arthritis and bone erosion were evaluated by incidence score, arthritis score, and histopathological observations. The role of GGT in osteoclast development was examined by using the established osteoclastogenic culture system. GGT expression was significantly upregulated in inflamed synovium. Immunohistochemistry revealed that GGT was present in lymphocytes, plasma cells, and macrophages, as well as capillaries. Injection of GGT-mAbs significantly decreased the number of osteoclasts and attenuated the severity of joint destruction in CIA mice. In vitro examination showed that GGT enhanced RANKL-dependent osteoclast formation. GGT stimulated the expression of RANKL in osteoblasts and its receptor RANK in osteoclast precursors, respectively. This study indicates that inflamed synovial tissue-derived GGT acts as a risk factor for joint destruction and that the antibody-mediated inhibition of GGT significantly decreases osteoclast number and bone erosion in CIA mice. GGT antagonists might be novel therapeutic agents for attenuating joint destruction in RA patients.

Differentiation potential of an immortalized non-tumorigenic human liver epithelial cell line as liver progenitor cells

We report the differentiation potential of an immortalized non-tumorigenic human liver epithelial cell line, THLE-5b. Under basic culture conditions THLE-5b showed undifferentiated phenotypes. When grown as cell aggregates, THLE-5b exhibited a hepatocyte-like ultrastructure, ammonia metabolic activity and several other indicators that suggest hepatocytic maturation, including up-regulation or induction of liver-specific genes such as albumin and tryptophane 2,3-dioxygenase, and down-regulation of biliary cell markers such as gamma-glutamyl transpeptidase (GGT). Under these conditions, transcriptional factors such as HNF-1 and HNF-4alpha were also up-regulated or induced. In Matrigel culture, expression of GGT was up-regulated. THLE-5b expressed both albumin and alpha 1-antitrypsin, but lost expression of CK19 in severe combined immunodeficient mice. Thus, THLE-5b can be aligned with progenitor cells, which are committed to the hepatocytic or biliary epithelial cell lineage. These results imply that bipotent progenitor cell populations similar to THLE-5b cells may exist in adult human liver.

Astrocyte control of fetal cortical neuron glutathione homeostasis: up‐regulation by ethanol

Ethanol increases apoptotic neuron death in the developing brain and at least part of this may be mediated by oxidative stress. In cultured fetal rat cortical neurons, Ethanol increases levels of reactive oxygen species (ROS) within minutes of exposure and reduces total cellular glutathione (GSH) shortly thereafter. This is followed by onset of apoptotic cell death. These responses to Ethanol can be blocked by elevating neuron GSH with N-acetylcysteine or by co-culturing neurons with neonatal cortical astrocytes. We describe here mechanisms by which the astrocyte-neuron gamma-glutamyl cycle is up-regulated by Ethanol, enhancing control of neuron GSH in response to the pro-oxidant, Ethanol. Up to 6 days of Ethanol exposure had no consistent effects on activities of gamma-glutamyl cysteine ligase or glutathione synthetase, and GSH content remained unchanged (p < 0.05). However, glutathione reductase was increased with 1 and 2 day Ethanol exposures, 25% and 39% for 2.5 and 4.0 mg/mL Ethanol by 1 day, and 11% and 16% for 2.5 and 4.0 mg/mL at 2 days, respectively (p < 0.05). A 24 h exposure to 4.0 mg/mL Ethanol increased GSH efflux from astrocyte up to 517% (p < 0.05). Ethanol increased both gamma-glutamyl transpeptidase expression and activity on astrocyte within 24 h of exposure (40%, p = 0.05 with 4.0 mg/mL) and this continued for at least 4 days of Ethanol treatment. Aminopeptidase N activity on neurons increased by 62% and 55% within 1 h of Ethanol for 2.5 and 4.0 mg/mL concentration, respectively (p < 0.05), remaining elevated for 24 h of treatment. Thus, there are at least three key points of the gamma-glutamyl cycle that are up-regulated by Ethanol, the net effect being to enhance neuron GSH homeostasis, thereby protecting neurons from Ethanol-mediated oxidative stress and apoptotic death.

Chemoprotective effect of caffeic acid phenethyl ester on promotion in a medium-term rat hepatocarcinogenesis assay.

Caffeic acid phenethyl ester (CAPE), a natural honeybee product exhibits a spectrum of biological activities including anti-microbial, anti-inflammatory, antioxidant and anti-tumoral actions. CAPE is also chemopreventive against intestinal, colon and skin cancer. Our aim was to extend the study of its chemoprotective features to the promotion of hepatocarcinogenesis. Male Wistar rats were subjected to a protocol under a modified promotion regimen of the resistant hepatocyte model. The altered hepatic foci (AHF) were quantitatively analyzed by histochemistry and image processing. When given during promotion, CAPE (20 mg/kg) decreased the expression of number and area gamma-glutamyl transpeptidase (GGT) positive AHF by 91% and 97%, respectively. When GGT expression was analyzed by RT-PCR, CAPE drastically decreased and prevented expression of almost all GGT transcripts at this stage of the carcinogenic process. Glutathione S-transferase placental form (GST-P), another protein marker for preneoplastic lesions was measured by Western blot and a decrease of 82% was observed. Additionally, we evaluated the effect of CAPE on the expression of nuclear factor NF-kappaB and found an 85% decrease in nuclear localization of the p65 subunit of NF-kappaB; however, their repressor, IkappaBalpha was not modified. Our results showed that CAPE given during promotion in hepatocarcinogenesis protects against induction of GGT-positive AHF, GST-P protein, GGT mRNA expression and translocation of p65. This phenomenon was independent of IkappaBalpha degradation.

Gamma-glutamyl transpeptidase activity alters the T cell response to oxidative stress and Fas-induced apoptosis.

The ectoenzyme gamma-glutamyl transpeptidase (GGT) is absent on resting naive peripheral blood T cells, highly expressed upon stimulation and intermediate on resting memory T cells. In other tissues, GGT is essential for the recapture of the antioxidant glutathione (GSH). T cells with different levels of GGT activity were examined for their ability to withstand oxidative stress. To create a model system that reflected the level of GGT seen on naive and memory T cells, Jurkat T cells were cloned by limiting dilution and their GGT expression analyzed. Jurkat expressing GGT at levels comparable to resting memory T cells have levels of intracellular reactive oxygen species (ROS) that are only 65% that seen in Jurkat that have low levels of GGT (similar to naive T cells). Treatment of the cells with H(2)O(2) increases ROS in both cells, although the level seen in the GGT(high) Jurkat is less than half that in the GGT(low) variant. Despite protection from oxidative stress, the GGT(high) Jurkat were found to be 2- to 3-fold more sensitive to Fas-induced apoptosis. The redox-regulated NF-kappaB pathway is activated in GGT(low) cells, resulting in higher levels of cIAP-1/2 proteins that limit caspase activity. The GGT(low) cells were found to have higher levels of NF-kappaB in the nucleus as well as lower levels of IkappaB-alpha. The GGT(low) cells also express higher levels of the caspase inhibitors cIAP-1/2 and have lower levels of caspase activity. These findings suggest that GGT expression regulates ROS in T lymphocytes and modulates Fas-induced killing by altering NF-kappaB activity.