Radiation-induced upregulation of gamma-glutamyltransferase in colon carcinoma cells is mediated through the Ras signal transduction pathway

Radioprotective efficacy of GSH based peptidomimetic complex of manganese against radiation induced damage: DT(GS)2Mn(II)

The adverse effects of ionizing radiation (IR) on biological tissues are mediated via increased production of reactive oxygen species (ROS) often resulting in life-threatening injuries. The effects of ionizing radiation on cells include the formation of ROS, DNA single-strand breaks, double-strand breaks, and extensive base modifications inducing the complex DNA damage. The capacity to endure the radiation insult lies in the biochemical mechanisms and structural properties in many bacterial species such as Deinococcus radiodurans and Thermococcus radiotolerans. In addition, a mechanistic link has established between the presence and accumulation of short peptides and Mn²⁺ in the protection of bacteria (Deinococcus radiodurans) from the harmful ionizing radiation. This paradigm has opened up novel avenues of radioprotection in diverse settings and systems for human application. We hereby report a new bifunctional system that comprises of thiol groups in the form of Glutathione (GSH), and manganese to mimic the above system for radioprotection. The present study, therefore, adopts a novel approach to use GSH complexed Mn, and this conjugated system is complying with the prerequisite for radioprotection as seen in the above mechanism. This unique conjugate DT(GS)₂Mn(II) was evaluated for its efficacy invitro and invivo. Radioprotective efficacy of DT(GS)₂Mn(II) on NIH/3T3 cells revealed that compound could significantly protect cells against radiation-induced toxicity as compared to the standard compound N-acetyl cysteine. Pre-treatment of DT(GS)₂Mn(II) increased the survival of mice by 50% compared to radiation alone treatment group. A significant decrease in cytochrome c levels in the group pre-treated with test compound (0.50 ± 0.14) compared to radiation alone group (1.60 ± 0.07) was observed. DT(GS)₂Mn(II) attenuated radiation induced apoptosis by promoted expression of anti-apoptotic Bcl-2 along with suppression of cyt-c release and augmented cell survival following irradiation. A distinct improvement in villi length was observed in the group treated with DT(GS)₂Mn(II) with an average of 1546 ± 61 μm versus 763 ± 154 μm for radiation alone group. The present findings suggested DT(GS)₂Mn(II) is a promising radioprotective agent and exerts it protective effect both invitro and invivo systems by decreasing radiation induced cytotoxicity.

The prognostic significance of pretreatment serum γ-glutamyltranspeptidase in primary liver cancer: a meta-analysis and systematic review

Aim: To assess the prognostic value of the pretreatment serum γ-glutamyltranspeptidase (GGT) level in patients with primary liver cancer (PLC). Methods: Relevant studies were systematically searched online on Web of Science, PubMed, and Embase databases published until 9 October 2018. The end points were overall survival (OS), recurrence-free survival (RFS), and disease-free survival (DFS). Meta-analysis was conducted using hazard ratio (HR), and its 95% confidence interval (CI) as effect measure. Results: A total of 33 eligible studies with 9238 patients with PLC were included in this meta-analysis. The synthesized analysis showed that that higher serum GGT level was significantly related to poorer OS (HR: 1.79, 95% CI: 1.66–1.93, P<0.01), RFS (HR: 1.60, 95% CI: 1.46–1.77, P<0.01), and DFS (HR: 1.52, 95% CI: 1.33–1.73, P<0.01) of patients with PLC. Subgroup analyses demonstrated that the negative prognostic impact of higher serum GGT level on OS and RFS was still of significance regardless of ethnicity, pathological type, sample size, cut-off value, first-line treatment, and analysis type. Conclusion: The pretreatment serum GGT might be a predictive factor of poor prognosis for PLC patients.

Rapid Cancer Fluorescence Imaging Using A γ-Glutamyltranspeptidase-Specific Probe For Primary Lung Cancer

BACKGROUND: We set out to examine the activity of γ-glutamyltranspeptidase (GGT) in lung cancer and the validity of γ-glutamyl hydroxymethyl rhodamine green (gGlu-HMRG) for intraoperative imaging of primary lung cancer. METHODS: GGT activities and mRNA expression levels of GGT1 (one of the GGT subtypes) in five human lung cancer cell lines were examined by fluorescence imaging and quantitative reverse transcription polymerase chain reaction. In vivo imaging of an orthotopic A549 xenograft model in nude mice was performed to confirm its applicability to intraoperative imaging. Furthermore, ex vivo imaging of 73 specimens from lung cancer patients were performed and analyzed to calculate the sensitivity/specificity of gGlu-HMRG for lung cancer diagnosis. RESULTS: GGT activities and mRNA expression levels of GGT1 are diverse depending on cell type; A549, H441, and H460 showed relatively high GGT activities and expression levels, whereas H82 and H226 showed lower values. In the in vivo mouse model study, tiny pleural dissemination and hilar/mediastinal lymph node metastasis (less than 1 mm in diameter) were clearly detected 15 minutes after topical application of gGlu-HMRG. In the ex vivo study of specimens from patients, the sensitivity and specificity of gGlu-HMRG were calculated to be 43.8% (32/73) and 84.9% (62/73), respectively. When limited to female patients, never smokers, and adenocarcinomas, these values were 78.9% (15/19) and 73.7% (14/19), respectively. CONCLUSIONS: Although GGT activity of lung cancer cells vary, gGlu-HMRG can serve as an intraoperative imaging tool to detect small foci of lung cancer when such cells have sufficient GGT activity.

Prognostic value of preoperative serum gamma-glutamyltranspeptidase in patients with hepatocellular carcinoma after hepatectomy

Gamma-glutamyltranspeptidase (γ-GGT), an oxidative stress marker, is correlated with inflammation in the extracellular hepatic microenvironment. This study aimed to evaluate the prognostic value of serum γ-GGT levels in patients with hepatocellular carcinoma (HCC) after hepatectomy. Three hundred and eight patients who underwent hepatic resection for HCC were included in the study. Preoperative serum γ-GGT levels, as well as demographic, clinical, and pathologic data, were analyzed. The optimal cutoff value of γ-GGT was 88 U/L. All patients were divided into γ-GGT ≤ 88 U/L group (n = 146) and γ-GGT > 88 U/L group (n = 162). The disease-free survival (DFS) and overall survival (OS) rates of patients in the γ-GGT > 88 U/L group were poorer than those in γ-GGT ≤ 88 U/L group. Preoperative serum γ-GGT levels, associating with gender, HBsAg status, tumor size, capsulation, tumor number, and vascular invasion, was an independent prognostic predictor of disease-free survival [hazard ratio (HR) = 1.616; 95 % confidence interval (CI), 1.223-2.135; P = 0.001] and overall survival (HR = 2.043; 95 % CI, 1.509-2.766; P < 0.001). Furthermore, γ-GGT was also associated with DFS and OS in small HCC (tumor size ≤5 cm) and alpha-fetoprotein (AFP) ≤ 200 ng/mL subgroup. In conclusion, γ-GGT is a promising and reliable prognostic biomarker in HCC patients after hepatic resection, especially for patients with small HCC or AFP ≤ 200 ng/mL.

Prognostic significance of gamma-glutamyltransferase in patients with resectable esophageal squamous cell carcinoma

Gamma-glutamyltransferase (GGT) is a membrane-bound enzyme involved in the glutathione metabolism. Studies suggested that GGT was a marker of apoptotic balance and modulated tumor progression, invasion and drug resistance. Recently, GGT was shown to be associated with the progression of high-grade esophageal epithelial dysplasia to invasive carcinoma. This study was conducted to investigate the value of pre-therapeutic serum GGT levels as prognostic parameter in esophageal squamous cell carcinoma. Six hundred thirty-nine resectable esophageal squamous cell carcinoma patients were recruited in this study and were stratified into two GGT risk groups. The association of pre-therapeutic serum GGT levels and clinical-pathological parameters was examined. Univariate and multivariate survival analyses were performed. GGT serum levels were associated with gender, smoking status, TNM stage and lymph node involvement. Higher pre-therapeutic serum GGT was found in males, smoker, advanced TNM stage and lymph node positive patients. Patients assigned to the low-risk group had higher 5-year overall survival rate (53.1% vs. 33.0%, P < 0.01) and disease-free survival rate (45.2% vs. 23.4%, P < 0.01) than the high-risk group. Patients with high-risk group of GGT had 1.568 (95% confidence interval [CI], 1.259 ∼ 1.952) times the risk of death and 1.582 (95% CI, 1.286 ∼ 1.946) times the risk of disease recurrence contrast with those with low-risk group of GGT. The pre-therapeutic serum GGT is a novel independent prognostic parameter for disease-free survival and overall survival in resectable esophageal squamous cell carcinoma.

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.

Glutathione S-conjugates as prodrugs to target drug-resistant tumors

Living organisms are continuously exposed to xenobiotics. The major phase of enzymatic detoxification in many species is the conjugation of activated xenobiotics to reduced glutathione (GSH) catalyzed by the glutathione-S-transferase (GST). It has been reported that some compounds, once transformed into glutathione S-conjugates, enter the mercapturic acid pathway whose end products are highly reactive and toxic for the cell responsible for their production. The cytotoxicity of these GSH conjugates depends essentially on GST and gamma-glutamyl transferases (γGT), the enzymes which initiate the mercapturic acid synthesis pathway. Numerous studies support the view that the expression of GST and γGT in cancer cells represents an important factor in the appearance of a more aggressive and resistant phenotype. High levels of tumor GST and γGT expression were employed to selectively target tumor with GST- or γGT-activated drugs. This strategy, explored over the last two decades, has recently been successful using GST-activated nitrogen mustard (TLK286) and γGT-activated arsenic-based (GSAO and Darinaparsin) prodrugs confirming the potential of GSH-conjugates as anticancer drugs.

Redox proteins and radiotherapy

Although conventional radiotherapy can directly damage DNA and other organic molecules within cells, most of the damage and the cytotoxicity of such ionising radiation, comes from the production of ions and free radicals produced via interactions with water. This 'indirect effect', a form of oxidative stress, can be modulated by a variety of systems within cells that are in place to, in normal situations, maintain homeostasis and redox balance. If cancer cells express high levels of antioxidant redox proteins, they may be more resistant to radiation and so targeting such systems may be a profitable strategy to increase therapeutic efficacy of conventional radiotherapy. An overview, with exemplars, of the main systems regulating redox homeostasis is supplied and discussed in relation to their use as prognostic and predictive biomarkers, and how targeting such proteins and systems may increase radiosensitivity and, potentially, improve the radiotherapeutic response.

Differential regulation of γ-glutamyltransferase and glutamate cysteine ligase expression after mitochondrial uncoupling: γ-glutamyltransferase is regulated in an Nrf2- and NFκB-independent manner

The enzymes γ-glutamyltransferase (GGT) and glutamate cysteine ligase (GCL) have important roles in glutathione (GSH) homeostasis, and both are frequently upregulated after acute oxidative stress. Mitochondria are major producers of ROS, and incubating the colorectal adenocarcinoma cell line HT-29 cells with mitochondrial uncouplers significantly increased endogenous ROS as well as mRNA for both GGT and GCLC (the catalytic subunit of GCL). However, no elevation in GGT protein or activity was detected, in contrast to the increased levels of GCLC protein found. The uncouplers initiated endoplasmic reticulum (ER) stress, as demonstrated by highly increased levels of CHOP and GRP78 mRNA. Using inhibitors of proteasomes and ER-associated degradation (ERAD) together with a mitochondrial uncoupler, increased GGT protein and activity levels were obtained indicating that GGT may be a substrate for ERAD. Uncoupling increased the mRNA levels of the two redox-regulated transcription factors Nrf2 and NFκB. Using siRNA to suppress Nrf2 and NFκB expression, downregulation of GCLC expression both at the basal level and after mitochondrial uncoupling was achieved. In contrast, the expression level of GGT was not affected by this treatment. These data strongly indicate a discrepancy between the regulation of GCLC and of GGT following the oxidative stress situation due to mitochondrial uncoupling. Both the enzymes are considered to be part of the cellular antioxidant system; however, the role of GGT as a consistent oxidative response parameter needs to be reevaluated.

Endogenous production of reactive oxygen species by the NADPH oxidase complexes is a determinant of γ-glutamyltransferase expression

γ-Glutamyltransferase (GGT) plays a significant role in antioxidant defence and participates in the metabolism of glutathione (GSH). The enzyme is up-regulated after acute oxidative stress and during pro-oxidant periods, but the underlying regulatory mechanisms are not well known. The present investigation studied whether the endogenous reactive oxygen species (ROS) level was a determinant for GGT expression. A substantial amount of ROS is produced through the NADPH oxidase (NOX) system and knockdown of p22phox, a sub-unit of NOX1-4, resulted not only in reduced ROS levels but also in reduced GGT expression in human endometrial carcinoma cells. Phorbol-12-myristate-13-acetate (PMA) is an activator of NOX and it was found that PMA treatment of human colon carcinoma cells both increased cellular ROS levels and subsequently up-regulated GGT expression. On the other hand, the NOX inhibitor apocynin reduced ROS levels as well as GGT expression. The GGT mRNA sub-type A was increased after PMA-induced NOX activation. These results demonstrate that ROS generated from NOX enzymes are a significant determinant for GGT expression and activity.

Extracellular/microenvironmental redox state

Extracellular redox (reduction-oxidation) state is a factor that serves as an important regulator of cell-microenvironmental interactions and is determined by several known variables; including redox-modulating proteins that are located on the plasma membrane or outside of cells, extracellular thiol/disulfide couples, and reactive oxygen species (ROS)/reactive nitrogen species (RNS) that are capable of traveling across plasma membranes into the extracellular space. The extracellular redox state works in concert with the intracellular redox state to control both the influx and efflux of ROS/RNS that may serve to modulate redox signaling or to perturb normal cellular processes or both. Under physiologic conditions, the extracellular space is known to have a relatively more-oxidized redox state than the interior of the cell. During pathologic conditions, such as cancer, the extracellular redox state may be altered, causing specific proteins such as proteases, soluble factors, or the extracellular matrix to have altered functions or activities. Recent studies have strongly supported an important relation between the extracellular redox state and cancer cell aggressiveness. The purpose of this review is to identify redox buffer networks in extracellular spaces and to emphasize the possible roles of the extracellular redox state in cancer, knowledge that may contribute to potential therapeutic interventions.

Pooling-based genome-wide association study implicates gamma-glutamyltransferase 1 (GGT1) gene in pancreatic carcinogenesis

BACKGROUND/AIMS

Knowledge regarding genetic factors that influence pancreatic cancer risk is currently limited. To identify novel pancreatic cancer susceptibility loci, we conducted a two-stage genome-wide association study.

METHODS

The Affymetrix Genome-Wide Human SNP Array 6.0 and DNA pooling were used in the screening stage. Twenty-six single-nucleotide polymorphisms (SNPs) were selected for follow-up. These 26 lead SNPs and additionally selected tagSNPs for the regions around the lead SNPs were evaluated by individual genotyping of the pooling population and an independent validation population.

RESULTS

Of the lead SNPs, the strongest association was found with rs4820599 located in the gamma-glutamyltransferase 1 (GGT1) gene. This SNP was significantly associated with pancreatic cancer risk in the validation population and the combined dataset (p(allele-based) = 0.019 and p(allele-based) = 0.003, respectively). Statistically significant associations were also observed with two GGT1 tagSNPs: rs2017869 and rs8135987. Lead SNP rs4820599 is in high linkage disequilibrium (LD; pairwise r(2): 0.69) and tagSNP rs2017869 is in strong LD (pairwise r(2): 0.96) with SNP rs5751901, which has been reported to be associated with increased GGT1 serum levels. GGT is expressed in the pancreas and plays a key role in glutathione metabolism.

CONCLUSION

Our results suggest that common variation in the GGT1 gene may affect the risk of pancreatic cancer. .

Gamma-glutamyltransferase, redox regulation and cancer drug resistance

Gamma-glutamyltransferase, a key enzyme of GSH metabolism, can modulate crucial redox-sensitive functions, such as antioxidant/antitoxic defences and cellular proliferative/apoptotic balance, with potential implications in tumour progression and drug resistance. Recent studies have elucidated the mechanisms of GGT involvement in various pathological processes suggesting its potential role as therapeutic target and diagnostic/prognostic marker.