Tumor necrosis factor alpha induces gamma-glutamyltransferase expression via nuclear factor-kappaB in cooperation with Sp1

The causal relationship between plasma protein-to-protein ratios and type 2 diabetes and its complications: Proteomics mendelian randomization study

AIM

In recent years, proteomics research has surged, with numerous observational studies identifying associations between plasma proteins and type 2 diabetes. However, research specifically focusing on the ratios of plasma proteins in type 2 diabetes remains relatively scarce.

METHODS

This study primarily employed a two-sample, two-step Mendelian randomization (MR) approach, leveraging genetic data from several large, publicly accessible genome-wide association studies, wherein single nucleotide polymorphisms served as proxies for exposures and diseases. Within this framework, we applied two-sample MR to assess the associations between the 2821 plasma protein-to-protein ratios and type 2 diabetes along with its complications and utilized reverse MR to confirm the unidirectionality of these causal relationships. In addition, we employed two-step MR to investigate the potential mediating role of body mass index in these associations. To augment the robustness of our findings, we systematically implemented a series of sensitivity analyses.

RESULTS

The results gleaned from the inverse-variance weighted method elucidated that a cumulative sum of 23 protein-to-protein ratios bore a causal nexus with type 2 diabetes across both sample cohorts. With each incremental elevation of 1 standard deviation in the genetically anticipated protein-to-protein ratio, the susceptibility to type 2 diabetes oscillated from 0.93 (95% confidence interval: 0.87, 1.00) for the CNTN3/NCSS1 protein level ratio to 1.13 (1.06, 1.22) for the DBNL/NCK2 protein level ratio. Moreover, a tally of eight protein-to-protein ratios correlated with a minimum of one complication linked to type 2 diabetes. Diverse sensitivity analyses corroborated the robustness of these observations.

CONCLUSIONS

The outcomes of our investigation unveiled correlations between 23 plasma protein-to-protein ratios and type 2 diabetes, with eight of these ratios entwined with complications of type 2 diabetes. These discoveries offer novel perspectives on the diagnosis and management of type 2 diabetes and its associated complications.

Gamma-glutamyl transferase to aspartate aminotransferase ratio (GSR) predicts prognoses in patients with colorectal cancer with liver metastasis after microwave ablation

BACKGROUND

Microwave ablation (MWA) is widely used to eliminate colorectal liver metastases (CRLM). However, the risk of tumor recurrence is difficult to predict due to lack of reliable clinical and biological markers. Elevation of gamma-glutamyl transferase (GGT) and aspartate transaminase (AST) provides signals for liver inflammation and cancer progression. The present study evaluated the association between pre-ablation GGT to AST ratio index (GSR) and hepatic recurrence in patients with CRLM after MWA.

METHODS

A retrospectively analyzed 192 CRLM patients who underwent MWA from January 2013 to December 2017. Pre-ablation GSR was classified into high (≤ 2.34) or low (> 2.34) using the upper quartile value. The prognostic value of GSR and other risk factors for liver progression-free survival (LPFS) and cancer-specific survival (CSS) were evaluated by univariate and multivariate analyses.

RESULTS

High GSR was significantly associated with males (P = 0.041), the presence of cholelithiasis (P = 0.012), but not pre-ablation chemotherapy (P = 0.355), which caused significantly increased levels of GGT (P = 0.015) and AST (P = 0.008). GSR showed a significant association with LPFS and CSS through univariate analysis (P = 0.002 and 0.006) and multivariate analysis (P = 0.043 and 0.037). The subgroup analysis demonstrated no interaction between GSR and all variables except for distribution in the sub-analysis of LPFS.

CONCLUSIONS

Our findings suggest that the pre-ablation GSR can be considered as a promising prognostic indicator for poor prognosis of patients with CRLM underwent MWA.

TRIAL REGISTRATION

Not applicable.

Glutathione‑degrading enzymes in the complex landscape of tumors (Review)

Glutathione (GSH)‑degrading enzymes are essential for starting the first stages of GSH degradation. These enzymes include extracellular γ‑glutamyl transpeptidase (GGT) and intracellular GSH‑specific γ‑glutamylcyclotransferase 1 (ChaC1) and 2. These enzymes are essential for cellular activities, such as immune response, differentiation, proliferation, homeostasis regulation and programmed cell death. Tumor tissue frequently exhibits abnormal expression of GSH‑degrading enzymes, which has a key impact on the development and spread of malignancies. The present review summarizes gene and protein structure, catalytic activity and regulation of GSH‑degrading enzymes, their vital roles in tumor development (including regulation of oxidative and endoplasmic reticulum stress, control of programmed cell death, promotion of inflammation and tumorigenesis and modulation of drug resistance in tumor cells) and potential role as diagnostic biomarkers and therapeutic targets.

Induction of more aggressive tumoral phenotypes in LNCaP and PC3 cells by serum exosomes from prostate cancer patients

Prostate cancer (PCa) is the second most frequent and sixth most fatal cancer in men worldwide. Despite its high prevalence, our understanding of its etiology and the molecular mechanisms involved in the progression of the disease is substantially limited. In recent years, the potential participation of exosomes in this process has been suggested. Therefore, we aim to study the effect of exosomes isolated from the serum of patients with PCa on various cellular processes associated with increased tumor aggressiveness in two PCa cell lines: LNCaP-FGC and PC3. The exosomes were isolated by filtration wand ultracentrifugation. Their presence was confirmed by immunodetection of specific markers and their size distribution was analyzed by Dynamic Light Scattering (DLS). The results obtained demonstrated that serum exosomes from PCa patients increased migration of PC3 cells and neuroendocrine differentiation of LNCaP-FGC cells regardless of the grade of the tumor. PCa serum exosomes also enhanced the secretion of enzymes related to invasiveness and resistance to chemotherapeutics, such as extracellular matrix metalloproteases 2 and 9, and gamma-glutamyltransferase in both cell lines. Altogether, these findings support the pivotal participation of exosomes released by tumoral cells in the progression of PCa. Future studies on the molecular mechanisms involved in the observed changes could provide crucial information on this disease and help in the discovery of new therapeutic targets.

RNAseq analysis of treatment-dependent signaling changes during inflammation in a mouse cutaneous wound healing model

BACKGROUND

Despite proven therapeutic effects in inflammatory conditions, the specific mechanisms of phytochemical therapies are not well understood. The transcriptome effects of Traumeel (Tr14), a multicomponent natural product, and diclofenac, a non-selective cyclooxygenase (COX) inhibitor, were compared in a mouse cutaneous wound healing model to identify both known and novel pathways for the anti-inflammatory effect of plant-derived natural products.

METHODS

Skin samples from abraded mice were analyzed by single-molecule, amplification-free RNAseq transcript profiling at 7 points between 12 and 192 h after injury. Immediately after injury, the wounds were treated with either diclofenac, Tr14, or placebo control (n = 7 per group/time). RNAseq levels were compared between treatment and control at each time point using a systems biology approach.

RESULTS

At early time points (12-36 h), both control and Tr14-treated wounds showed marked increase in the inducible COX2 enzyme mRNA, while diclofenac-treated wounds did not. Tr14, in contrast, modulated lipoxygenase transcripts, especially ALOX12/15, and phospholipases involved in arachidonate metabolism. Notably, Tr14 modulated a group of cell-type specific markers, including the T cell receptor, that could be explained by an overarching effect on the type of cells that were recruited into the wound tissue.

CONCLUSIONS

Tr14 and diclofenac had very different effects on the COX/LOX synthetic pathway after cutaneous wounding. Tr14 allowed normal autoinduction of COX2 mRNA, but suppressed mRNA levels for key enzymes in the leukotriene synthetic pathway. Tr14 appeared to have a broad 'phytocellular' effect on the wound transcriptome by altering the balance of cell types present in the wound.

Impact of Serum γ-Glutamyltransferase on Overall Survival in Men with Metastatic Castration-Resistant Prostate Cancer Treated with Docetaxel

Simple Summary

γ-Glutamyltransferase (GGT) is a biomarker of oxidative stress and its elevation in the serum is linked to poor survival in various malignancies; however, reports on metastatic castration-resistant prostate cancer (mCRPC) are scarce. Moreover, the source of serum GGT in men with mCRPC is largely unknown. The aims of this study were to determine the impact of serum GGT on overall survival in men with mCRPC receiving docetaxel therapy, and to examine the association between systemic and local GGT levels using immunohistochemistry. Of note, high serum GGT was associated with adverse overall survival as were low hemoglobin and high prostate-specific antigen levels. Additionally, tissue GGT expression status in prostate specimens was moderately positively associated with serum GGT. We demonstrated that pre-therapeutic serum GGT was an independent prognosticator in men with mCRPC receiving docetaxel therapy, and that overexpression of GGT in cancer cells might be responsible for the elevation of serum GGT.

Abstract

Background: Reports on the prognostic significance of serum γ-glutamyltransferase (GGT) in men with metastatic castration-resistant prostate cancer (mCRPC) are limited. In addition, GGT expression status in cancer tissues has not been well characterized regardless of cancer types. Methods: This retrospective study included 107 consecutive men with mCRPC receiving docetaxel therapy. The primary endpoints were associations of serum GGT with overall survival (OS) and prostate-specific antigen (PSA) response. The secondary endpoint was an association of serum GGT with progression-free survival (PFS). Additionally, GGT expression status was immunohistochemically semi-quantified using tissue microarrays. Results: A total of 67 (63%) men died during follow-up periods (median 22.5 months for survivors). On multivariable analysis, high Log GGT was independently associated with adverse OS (HR 1.49, p = 0.006) as were low hemoglobin (HR 0.79, p = 0.002) and high PSA (HR 1.40, p < 0.001). In contrast, serum GGT was not significantly associated with PSA response or PFS. Moreover, incorporation of serum GGT into established prognostic models (i.e., Halabi and Smaletz models) increased their C-indices for predicting OS from 0.772 to 0.787 (p = 0.066) and from 0.777 to 0.785 (p = 0.118), respectively. Furthermore, there was a positive correlation between serum and tissue GGT levels (ρ = 0.53, p = 0.003). Conclusions: Serum GGT may be a prognostic biomarker in men with mCRPC receiving docetaxel therapy. GGT overexpression by prostate cancer cells appears to be responsible for the elevation of GGT in the serum.

Altered microbiota-host metabolic cross talk preceding neutropenic fever in patients with acute leukemia

In 2 cohorts of patients with acute leukemia, Akkermansia expansion in the gut predicted a higher risk for neutropenic fever.

Metabolomics analysis suggested oxidative stress as the mediating pathway, thus offering potential targets for personalized prophylaxis.

Despite antibiotic prophylaxis, most patients with acute leukemia receiving mucotoxic chemotherapy develop neutropenic fever (NF), many cases of which remain without a documented etiology. Antibiotics disrupt the gut microbiota, with adverse clinical consequences, such as Clostridioides difficile infection. A better understanding of NF pathogenesis could inform the development of novel therapeutics without deleterious effects on the microbiota. We hypothesized that metabolites absorbed from the gut to the bloodstream modulate pyrogenic and inflammatory pathways. Longitudinal profiling of the gut microbiota in 2 cohorts of patients with acute leukemia showed that Akkermansia expansion in the gut was associated with an increased risk for NF. As a prototype mucolytic genus, Akkermansia may influence the absorption of luminal metabolites; thus, its association with NF supported our metabolomics hypothesis. Longitudinal profiling of the serum metabolome identified a signature associated with gut Akkermansia and 1 with NF. Importantly, these 2 signatures overlapped in metabolites in the γ-glutamyl cycle, suggesting oxidative stress as a mediator involved in Akkermansia-related NF. In addition, the level of gut microbial–derived indole compounds increased after Akkermansia expansion and decreased before NF, suggesting their role in mediating the anti-inflammatory effects of Akkermansia, as seen predominantly in healthy individuals. These results suggest that Akkermansia regulates microbiota-host metabolic cross talk by modulating the mucosal interface. The clinical context, including factors influencing microbiota composition, determines the type of metabolites absorbed through the gut barrier and their net effect on the host. Our findings identify novel aspects of NF pathogenesis that could be targets for precision therapeutics. This trial was registered at www.clinicaltrials.gov as #NCT03316456.

Association of PAF and its metabolic enzymes with GGT and the Fatty Liver Index in healthy volunteers

BACKGROUND

Platelet-activating factor (PAF) is a lipid inflammatory mediator implicated in liver disease. Its main biosynthetic enzymes are cytidine diphosphate (CDP)-choline:1-alkyl-2-acetyl-sn-glycerol-cholinephosphotransferase (PAF-CPT) and acetyl-coenzyme A: lyso-PAF-acetyltransferases (Lyso-PAF-AT), while PAF acetylhydrolase (PAF-AH) and lipoprotein-associated phospholipase A2 (Lp-PLA2) degrade PAF.

OBJECTIVE

To explore the relation of PAF metabolism with liver diseases and non-alcoholic fatty liver disease, as reflected by the fatty liver index (FLI).

METHODS

In 106 healthy volunteers, PAF concentration, the activity of its metabolic enzymes, and gamma-glutamyl transferase (GGT) were measured in whole blood, leukocytes, and serum, respectively, and the FLI was calculated. Partial correlations and linear regression models were used.

RESULTS

In males, serum GGT activity was positively correlated with abdominal fat (as assessed by analysis of a manually defined region of interest in dual-energy X-ray absorptiometry), triacylglycerols, bound-PAF, and Lp-PLA2, while the FLI was positively correlated with Lp-PLA2 activity. In females, serum GGT activity was negatively associated with high-density lipoprotein cholesterol (HDL-C) (age-adjusted correlations, all p<0.05). Lp-PLA2 was a significant determinant of serum GGT activity in males after controlling for age, low-density lipoprotein cholesterol (LDL-C), and abdominal fat. The addition of bound-PAF in the model significantly increased the explained variance of serum GGT activity (total variance explanation 30%).

CONCLUSION

Bound-PAF and Lp-PLA2 activity predicted serum GGT activity, while Lp-PLA2 was also related to FLI. Our findings shed light on the metabolic pathways linking Lp-PLA2 to other atherosclerosis and/or oxidative markers, such as HDL-C, LDL-C, GGT, and FLI, and underline the important role of PAF.

Non-linear relationship between gamma-glutamyl transferase and type 2 diabetes mellitus risk: secondary analysis of a prospective cohort study

OBJECTIVE

To investigate the association between gamma-glutamyl transferase (GGT) and type 2 diabetes mellitus (T2DM) risk.

METHODS

This was a secondary analysis based on a publicly available DRYAD dataset that included 15 444 study participants that received medical examinations at a single centre in Japan between 2004 and 2015. Crude, minimally-adjusted and fully-adjusted regression models were used to evaluate the relationship between GGT levels and T2DM risk.

RESULTS

The study participants (mean ± SD age of 43.72 ± 8.90 years; 8415 of 15 444 [54.49%] were male) were followed-up for a median of 1968 days (5.39 years). After adjusting for potential covariates, a non-linear relationship between the baseline GGT level and T2DM incidence was observed. The inflection point for T2DM risk was 10 IU/l GGT; below this point, the T2DM incidence increased by 1.18-fold per unit change in GGT. Above this point, the association between GGT and the incidence rate of T2DM became nonsignificant.

CONCLUSION

Baseline GGT exhibited a non-linear association with T2DM incidence. Elevated GGT levels should be incorporated into routine screening for individuals at high risk of T2DM, allowing for early intervention targeting GGT to potentially reduce T2DM-related morbidity.

A Systematic Review of Serum γ-Glutamyltransferase as a Prognostic Biomarker in Patients with Genitourinary Cancer

γ-Glutamyltransferase (GGT), a membrane-bound enzyme, contributes to the metabolism of glutathione (GSH), which plays a critical physiological role in protecting cells against oxidative stress. GGT has been proposed as a biomarker of carcinogenesis and tumor progression given that GGT activity is important during both the promotion and invasion phases in cancer cells. Moreover, GGT expression is reportedly related to drug-resistance possibly because a wide range of drugs are conjugated with GSH, the availability of which is influenced by GGT activity. While serum GGT activity is commonly used as a quick, inexpensive, yet reliable means of assessing liver function, recent epidemiological studies have shown that it may also be an indicator of an increased risk of prostate cancer development. Moreover, elevated serum GGT is reportedly an adverse prognostic predictor in patients with urologic neoplasms, including renal cell carcinoma, prostate cancer, and urothelial carcinoma, although the background mechanisms have still not been well-characterized. The present review article summarizes the possible role of GGT in cancer cells and focuses on evidence evaluation through a systematic review of the latest literature on the prognostic role of serum GGT in patients with genitourinary cancer.

The dark side of gamma-glutamyltransferase (GGT): Pathogenic effects of an 'antioxidant' enzyme

Having long been regarded as just a member in the cellular antioxidant systems, as well as a clinical biomarker of hepatobiliary diseases and alcohol abuse, gamma-glutamyltransferase (GGT) enzyme activity has been highlighted by more recent research as a critical factor in modulation of redox equilibria within the cell and in its surroundings. Moreover, due to the prooxidant reactions which can originate during its metabolic function in selected conditions, experimental and clinical studies are increasingly involving GGT in the pathogenesis of several important disease conditions, such as atherosclerosis, cardiovascular diseases, cancer, lung inflammation, neuroinflammation and bone disorders. The present article is an overview of the laboratory findings that have prompted an evolution in interpretation of the significance of GGT in human pathophysiology.

Gamma-glutamyltransferase, possible novel biomarker in colon diverticulosis: a case-control study

The gamma-glutamyltransferase (GGT) is recognized in medical practice as a useful indicator for the detection of liver lesions, especially those induced by the excessive consumption of alcoholic or cholesterol-associated drinks. The present study, although it includes a very small number of cases diagnosed with colon diverticulosis-diverticulitis associated with polyposis at the same intestinal level, identifies the presence of increased circulating concentrations of this enzyme in the serum. Its serum levels are tracked “dynamically” throughout a year after the diagnosis and start of the therapy. The study calls into question the release of the enzyme from the edge of the enterocytes’ brush-like edge, leading to the pathogenic disturbance of regional redox homeostasis. The hypothesis gives the circulating values of GGT predictive value for cellular oxidative stress, as well as for indirectly expressing the glutathione level in cytosol.

Metabolism of Glutathione S-Conjugates: Multiple Pathways

Many potentially toxic electrophilic xenobiotics and some endogenous compounds are detoxified by conversion to the corresponding glutathione S-conjugate, which is metabolized to the N-acetylcysteine S-conjugate (mercapturate) and excreted. Some mercapturate pathway components, however, are toxic. Bioactivation (toxification) may occur when the glutathione S-conjugate (or mercapturate) is converted to a cysteine S-conjugate that undergoes a β-lyase reaction. If the sulfhydryl-containing fragment produced in this reaction is reactive, toxicity may ensue. Some drugs and halogenated workplace/environmental contaminants are bioactivated by this mechanism. On the other hand, cysteine S-conjugate β-lyases occur in nature as a means of generating some biologically useful sulfhydryl-containing compounds.

Prognostic impact of pretherapeutic gamma-glutamyltransferase on patients with nasopharyngeal carcinoma

Background

Gamma-glutamyltransferase (GGT) is a membrane-bound enzyme involved in the metabolism of glutathione. Studies suggested that GGT played an important role in the tumor development, progression, invasion and drug resistance and prognosis. The association between GGT and prognosis of patients with nasopharyngeal carcinoma (NPC) was unknown. This study was conducted to investigate the association of pretherapeutic serum level of GGT with clinical-pathological parameters and survival in patients with NPC.

Methods

Two hundred and twenty-two patients with NPC were recruited in this study and were stratified into two GGT risk groups (≤ 34.5 U/L, > 34.5 U/L). The association of pretherapeutic serum GGT levels with clinical–pathological parameters was examined. Univariate and multivariate survival analyses were performed.

Findings

The pretherapeutic serum level of GGT was not associated with gender, age, pathology, T stage, N stage, TNM stage, chemotherapy or radiotherapy in patients with NPC. Patients in the high-risk GGT group had a poorer survival than the low-risk GGT group (3-year overall survival, 74.2% vs. 50.2%, P = 0.001; 3-year progression-free survival, 76.4% vs. 47.1%, P < 0.001; 3-year loco-regional relapse-free survival, 76.4% vs. 51.3%, P < 0.001; 3-year distant metastasis-free survival, 89.5% vs. 66.4%, P < 0.001). Multivariate analysis suggested that patients in the high-risk GGT group had 2.117 (95% confidence interval [CI], 1.225 ∼ 3.659, P = 0.007) times the risk of death, 2.836 (95% CI, 1.765 ∼ 4.557, P < 0.001) times the risk of progression, 2.551 (95% CI, 1.573 ∼ 4.138, P < 0.001) times the risk of relapse, and 3.331 (95% CI, 1.676 ∼ 6.622, P < 0.001) times the risk of metastasis compared with those in the low-risk GGT group.

Conclusion

The pretherapeutic serum level of GGT might serve as a novel independent prognostic factor for overall-survival, progression-free survival, loco-regional relapse-free survival and distant metastasis-free survival in patients with NPC.

Serum Predictors of Percent Lean Mass in Young Adults

Lustgarten, MS, Price, LL, Phillips, EM, Kirn, DR, Mills, J, and Fielding, RA. Serum predictors of percent lean mass in young adults. J Strength Cond Res 30(8): 2194-2201, 2016-Elevated lean (skeletal muscle) mass is associated with increased muscle strength and anaerobic exercise performance, whereas low levels of lean mass are associated with insulin resistance and sarcopenia. Therefore, studies aimed at obtaining an improved understanding of mechanisms related to the quantity of lean mass are of interest. Percent lean mass (total lean mass/body weight × 100) in 77 young subjects (18-35 years) was measured with dual-energy x-ray absorptiometry. Twenty analytes and 296 metabolites were evaluated with the use of the standard chemistry screen and mass spectrometry-based metabolomic profiling, respectively. Sex-adjusted multivariable linear regression was used to determine serum analytes and metabolites significantly (p ≤ 0.05 and q ≤ 0.30) associated with the percent lean mass. Two enzymes (alkaline phosphatase and serum glutamate oxaloacetate aminotransferase) and 29 metabolites were found to be significantly associated with the percent lean mass, including metabolites related to microbial metabolism, uremia, inflammation, oxidative stress, branched-chain amino acid metabolism, insulin sensitivity, glycerolipid metabolism, and xenobiotics. Use of sex-adjusted stepwise regression to obtain a final covariate predictor model identified the combination of 5 analytes and metabolites as overall predictors of the percent lean mass (model R = 82.5%). Collectively, these data suggest that a complex interplay of various metabolic processes underlies the maintenance of lean mass in young healthy adults.

Non enzymatic upregulation of tissue factor expression by gamma-glutamyl transferase in human peripheral blood mononuclear cells

Background

Besides maintaining intracellular glutathione stores, gamma-glutamyltransferase(GGT) generates reactive oxygen species and activates NFkB, a redox-sensitive transcription factor key in the induction of Tissue Factor (TF) gene expression, the principal initiator of the clotting cascade. Thus, GGT might be involved in TF-mediated coagulation processes, an assumption untested insofar.

Methods

Experiments were run with either equine, enzymatically active GGT or human recombinant (hr) GGT, a wheat germ-derived protein enzymatically inert because of missing post-translational glycosylation. TF Procoagulant Activity (PCA, one-stage clotting assay), TF antigen(ELISA) and TFmRNA(real-time PCR) were assessed in unpooled human peripheral blood mononuclear cell(PBMC) suspensions obtained from healthy donors through discontinuous Ficoll/Hystopaque density gradient.

Results

Equine GGT increased PCA, an effect insensitive to GGT inhibition by acivicin suggesting mechanisms independent of its enzymatic activity, a possibility confirmed by the maintained stimulation in response to hrGGT, an enzymatically inactive molecule. Endotoxin(LPS) contamination of GGT preparations was excluded by heat inactivation studies and direct determination(LAL method) of LPS concentrations <0.1 ng/mL practically devoid of procoagulant effect. Inhibition by anti-GGT antibodies corroborated that conclusion. Upregulation by hrGGT of TF antigen and mRNA and its downregulation by BAY-11-7082, a NFkB inhibitor, and N-acetyl-L-cysteine, an antioxidant, was consistent with a NFkB-driven, redox-sensitive transcriptional site of action.

Conclusions

GGT upregulates TF expression independent of its enzymatic activity, a cytokine-like behaviour mediated by NFκB activation, a mechanism contributing to promote acute thrombotic events, a possibility in need, however, of further evaluation.

Serum gamma-glutamyl transferase and risk of type 2 diabetes in the general Korean population: a Mendelian randomization study

Elevated gamma-glutamyl transferase (GGT) levels are associated with higher risk of type 2 diabetes in observational studies, but the underlying causal relationship is still unclear. Here, we tested a hypothesis that GGT levels have a causal effect on type 2 diabetes risk using Mendelian randomization. Data were collected from 7640 participants in a South Korean population. In a single instrumental variable (IV) analysis using two stage least squares regression with the rs4820599 in the GGT1 gene region as an instrument, one unit of GGT levels (IU/L) was associated with 11% higher risk of type 2 diabetes (odds ratio (OR) = 1.11, 95% confidence interval (CI): 1.04 to 1.19). In a multiple IV analysis using seven genetic variants that have previously been demonstrated to be associated with GGT at a genome-wide level of significance, the corresponding estimate suggested a 2.6% increase in risk (OR = 1.026, 95% CI: 1.001 to 1.052). In a two-sample Mendelian randomization analysis using genetic associations with type 2 diabetes taken from a trans-ethnic GWAS study of 110 452 independent samples, the single IV analysis confirmed an association between the rs4820599 and type 2 diabetes risk (P-value = 0.04); however, the estimate from the multiple IV analysis was compatible with the null (OR = 1.007, 95% CI: 0.993 to 1.022) with considerable heterogeneity between the causal effects estimated using different genetic variants. Overall, there is weak genetic evidence that GGT levels may have a causal role in the development of type 2 diabetes.

The proteasome inhibitor lactacystin enhances GSH synthesis capacity by increased expression of antioxidant components in an Nrf2-independent, but p38 MAPK-dependent manner in rat colorectal carcinoma cells

Proteasome inhibitors may induce ER stress and oxidative stress, disrupt signaling pathways, and trigger apoptosis in several cancer cells. However, they are also reported to increase glutathione (GSH) synthesis and protect cells from oxidative stress. In the present study, we showed that the proteasome inhibitor lactacystin increased reactive oxygen species (ROS) and GSH levels after the treatment of HT-29 colorectal cancer cells. The increased GSH depended upon the activity of glutamate cysteine ligase (GCL), uptake of cystine/cysteine via the cystine/glutamate transporter [Formula: see text], and the activity of γ-glutamyltransferase (GGT). Increased transcription levels of the catalytic subunit of glutamate cysteine ligase (GCLC), the catalytic subunit xCT of [Formula: see text], and GGT were induced by lactacystin, although with different kinetics and stoichiometry. Lactacystin treatment also augmented protein levels of GCLC, xCT, and GGT, but significant levels were not detected until 48 h after initiation of lactacystin treatment. These increases in protein levels were dependent on the p38 MAPK pathway. Studies in cells transfected with siRNA against the transcription factor Nrf2 demonstrated that the promoter activities of xCT and GCLC, but not of GGT, depended on Nrf2. However, depletion of Nrf2 had no effect on lactacystin-induced upregulation of the GGT, GCLC, and xCT mRNA levels. Taken together, our results suggest that oxidative stress provoked by proteasomal inhibition results in the elevation of cellular GSH levels due to increased synthesis of GSH and uptake of cystine/cysteine. Following treatment with lactacystin, enhanced expression of antioxidant components involved in GSH homeostasis is p38 MAPK-dependent, but Nrf2-independent, resulting in increased GSH synthesis capacity.

Monocytes/macrophages activation contributes to b-gamma-glutamyltransferase accumulation inside atherosclerotic plaques

Background

Gamma-glutamyltransferase (GGT) is a well-established independent risk factor for cardiovascular mortality related to atherosclerotic disease. Four GGT fractions have been identified in plasma, but only b-GGT fraction accumulates in atherosclerotic plaques, and correlates with other histological markers of vulnerability. The present study was aimed to evaluate whether macrophagic lineage cells may provide a source of b-GGT within the atherosclerotic plaque.

Methods

GGT expression and release were studied in human monocytes isolated from peripheral blood of healthy donors. The growth factors GM-CSF and M-CSF were used to induce differentiation into M1-like and M2-like macrophages, respectively. Plaque GGT was investigated in tissue samples obtained from patients undergoing carotid endoarterectomy.

Results

We found that M1-like macrophages express higher levels of GGT as compared to M2-like, and that both monocytes and M1-like macrophages—but not M2-like—are able to release the b-GGT fraction upon activation with pro-inflammatory stimuli. Western blot analysis of b-GGT extracted from plaques confirmed the presence of a GGT immunoreactive peptide coincident with that of macrophages.

Conclusions

Our data indicate that macrophages characterized by a pro-inflammatory phenotype may contribute to intra-plaque accumulation of b-GGT, which in turn may play a role in the progression of atherosclerosis by modulating inflammatory processes and favouring plaque instability.

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.

Celecoxib prevents curcumin-induced apoptosis in a hematopoietic cancer cell model

Molecules targeting pro-inflammatory pathways have demonstrated beneficial effects in cancer treatment. More recently, combination of natural and synthetic anti-inflammatory drugs was suggested as an appealing strategy to inhibit tumor growth. Herein, we show that curcumin, a polyphenol from Curcuma longa and celecoxib induce apoptosis in hematopoietic cancer cell lines (Hel, Jurkat, K562, Raji, and U937). Further investigations on the most sensitive cell line, U937, indicated that these effects were tightly associated with an accumulation of the cells in S and G2/M for curcumin and in G0/G1 phase of cell cycle for celecoxib, respectively. The effect of celecoxib on cell cycle is associated with an induction of p27 and the down-regulation of cyclin D1. However, in the case of combination experiments, the pretreatment of U937 cells with celecoxib at non-apoptogenic concentrations counteracted curcumin-induced apoptosis. We found that this effect correlated with the prevention of the accumulation in S and G2/M phase of cell cycle induced by curcumin. Similar results have been obtained when celecoxib and curcumin were co-administrated at the same time. Overall our data suggest that this natural and synthetic drug combination is detrimental for cell death induction.

Anti-inflammatory and anticancer drugs from nature

Over the centuries, plant extracts have been used to treat various diseases. Until now, natural products have played an important role in anticancer therapy as there are more than 500 compounds from terrestrial and marine plants or microorganisms, which have antioxidant, antiproliferative, or antiangiogenic properties and are therefore able to reduce tumor growth. The recent discovery of new natural products has been accelerated by novel technologies (high throughput screening of natural products in plants, animals, marine organisms, and microorganisms). Vincristine, irinotecan, etoposide, and paclitaxel are examples of compounds derived from plants that are used in cancer treatment. Similarly, actinomycin D, mitomycin C, bleomycin, doxorubicin, and L-asparaginase are drugs derived from microorganisms. In this review, we describe the molecular mechanisms of natural compounds with anti-inflammatory and anticancer activities.

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.

Identification of differentially expressed proteins in curcumin-treated prostate cancer cell lines

Due to high prevalence and slow progression of prostate cancer, primary prevention appears to be attractive strategy for its eradication. During the last decade, curcumin (diferuloylmethane), a natural compound from the root of turmeric (Curcuma longa), was described as a potent chemopreventive agent. Curcumin exhibits anti-inflammatory, anticarcinogenic, antiproliferative, antiangiogenic, and antioxidant properties in various cancer cell models. This study was designed to identify proteins involved in the anticancer activity of curcumin in androgen-dependent (22Rv1) and -independent (PC-3) human prostate cancer cell lines using two-dimensional difference in gel electrophoresis (2D-DIGE). Out of 425 differentially expressed spots, we describe here the MALDI-TOF-MS analysis of 192 spots of interest, selected by their expression profile. This approach allowed the identification of 60 differentially expressed proteins (32 in 22Rv1 cells and 47 in PC-3 cells). Nineteen proteins are regulated in both cell lines. Further bioinformatic analysis shows that proteins modulated by curcumin are implicated in protein folding (such as heat-shock protein PPP2R1A; RNA splicing proteins RBM17, DDX39; cell death proteins HMGB1 and NPM1; proteins involved in androgen receptor signaling, NPM1 and FKBP4/FKBP52), and that this compound could have an impact on miR-141, miR-152, and miR-183 expression. Taken together, these data support the hypothesis that curcumin is an interesting chemopreventive agent as it modulates the expression of proteins that potentially contribute to prostate carcinogenesis.

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.

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.

Potential of the dietary antioxidants resveratrol and curcumin in prevention and treatment of hematologic malignancies

Despite considerable improvements in the tolerance and efficacy of novel chemotherapeutic agents, the mortality of hematological malignancies is still high due to therapy relapse, which is associated with bad prognosis. Dietary polyphenolic compounds are of growing interest as an alternative approach, especially in cancer treatment, as they have been proven to be safe and display strong antioxidant properties. Here, we provide evidence that both resveratrol and curcumin possess huge potential for application as both chemopreventive agents and anticancer drugs and might represent promising candidates for future treatment of leukemia. Both polyphenols are currently being tested in clinical trials. We describe the underlying mechanisms, but also focus on possible limitations and how they might be overcome in future clinical use – either by chemically synthesized derivatives or special formulations that improve bioavailability and pharmacokinetics.

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.

Redox regulation of gamma-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.

Membrane gamma-glutamyl transferase activity promotes iron-dependent oxidative DNA damage in melanoma cells

A number of recent observations have suggested a potential role for membrane-bound gamma-glutamyltransferase (GGT) in tumor progression and appearance of more aggressive and resistant phenotypes, through redox interactions leading to production of reactive oxygen species. The present study was aimed to evaluate whether such pro-oxidant activity of GGT can promote oxidative DNA damage, thus contributing to cancer genomic instability. Human GGT-transfected melanoma cells were studied, and DNA damage was measured by using the alkaline comet assay. Our results indicate that higher levels of GGT activity are associated with higher levels of background DNA damage and oxidized bases. This association cannot be explained by differences in cell cycle distribution or apoptotic rates. GGT-over-expressing cells also presented with a markedly higher glucose uptake, a phenomenon potentially leading to higher metabolic rate and oxidative DNA damage. Anyway, when GGT-over-expressing cells were incubated in the presence of GGT substrates and a source of catalytic iron, increased levels of DNA damage and oxidized bases were observed, an effect completely prevented in the presence of GGT inhibitors or various antioxidants.The findings reported indicate that GGT activity is able to promote iron-dependent DNA oxidative damage, thus potentially representing an important mechanism in initiation/progression of neoplastic transformation.