Possible role of membrane gamma-glutamyltransferase activity in the facilitation of transferrin-dependent and -independent iron uptake by cancer cells

Hypothyroidism is a predictive factor of superior antitumour efficacy of programmed death 1 inhibitors in hepatocellular carcinoma

Programmed death 1 (PD-1) inhibitors are widely used for treatment of hepatocellular carcinoma (HCC). Hypothyroidism is commonly associated with this therapy, although the mechanism underlying this complication and effects on patient prognosis remain unclear. We retrospectively analysed the data of patients with HCC who received anti-PD-1 therapy at Tongji Hospital, Tongji Medical College of Huazhong University of Science and Technology between January 2018 and May 2020. Based on thyroid function evaluation, patients were categorised into hypothyroidism group and nonhypothyroidism group. Follow-up was completed on February 28, 2021. The primary endpoint of our study was progression free survival (PFS). The study included 74 patients, and the disease control rate was higher in hypothyroidism group (62.7%, 27/43) than in nonhypothyroidism group (36.4%, 11/31) (P = .020). The PFS was longer in hypothyroidism group (7.44 months) than in nonhypothyroidism group (5.68 months) (P = .006). Additionally, the PFS of patients with hypothyroidism before immunotherapy (6.27 months) was also longer than that in nonhypothyroidism group (5.68 months), although the difference was statistically nonsignificant (P = .527). Cox regression analysis showed that the hazard ratios of hypothyroidism, Child-Pugh grade B at initial admission and serum gamma-glutamyl transferase levels >71 U/L before immunotherapy were 0.404 (95% confidence interval [CI]: 0.207-0.791, P = .008), 2.753 (95%CI: 1.127-6.455, P = .026) and 2.469 (95%CI: 1.155-5.277, P = .020), respectively. Hypothyroidism was associated with prognosis in patients with HCC treated with PD-1 inhibitors, and prognosis was more favourable in patients with hypothyroidism than in those without hypothyroidism. Hypothyroidism and the Child-Pugh grade at initial admission were independently associated with patient prognosis.

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.

Correlation Between Gamma-Glutamyl Transferase Activity and Glutathione Levels in Molecular Subgroups of Breast Cancer

Objective

The gamma-glutamyl cycle catalyzed by gamma-glutamyl transferase (GGT) plays an important role in glutathione (GSH) homeostasis in the cell. In cells continuously exposed to the drug, the main phase of the enzymatic detoxification is the conjugation of the drug with GSH catalyzed by glutathione-S-transferase (GST). Conjugation of drugs with GSH is the first step in the development of chemotherapeutic drug resistance. In this study, we aimed to investigate the relationship between GGT and GSH in molecular subgroups of breast cancer patients.

Materials and Methods

Serum GGT activity and GSH levels for patients diagnosed with breast cancer (n=58) and healthy controls (n=8) were measured by a spectrophotometric method and a colorimetric kit, respectively.

Results

GGT activity was significantly higher in the total patient group and in the molecular subgroups than those in the control groups (p<0.05). Serum GSH levels were higher in the patient groups compared to controls without reaching statistical significance (p>0.05). GGT activity was positively correlated with GSH levels in the total patients and healthy controls (p<0.001 and p<0.05, respectively). There was also a positive correlation between GGT activity and GSH levels in Luminal A, HER2-positive (Human epidermal growth factor receptor 2), and Triple-negative groups (p<0.05).

Conclusion

This is the first study showing the relationship between GGT and GSH in molecular subgroups of breast cancer. An increase in GGT activity may affect intracellular GSH synthesis. Therefore, having a correlation between GGT and GSH in some molecular subgroups may affect the course of treatment in these patients.

Preoperative D-dimer and Gamma-Glutamyltranspeptidase Predict Major Complications and Survival in Colorectal Liver Metastases Patients After Resection

OBJECTIVES: To investigate the predictive value of the pre-operative D-dimer and gamma-glutamyltranspeptidase (GGT) for the prognosis in colorectal liver metastases (CRLM) patients after hepatic resection. METHODS: Two hundred and ninety-two patients between December 2008 and December 2016 and 101 patients at our center from January 2017 to December 2018 were selected as a training set and validation set, respectively. The combination of the pre-operative D-dimer and GGT status (CPDG score) was scored as follows: elevated D-dimer levels with elevated GGT levels was allocated a score of 2, decreased D-dimer levels with decreased GGT levels was allocated a score of 0, and all other combinations were allocated a score of 1. In the training set, a logistic regression was applied to explore potential predictors of major postoperative complications. A Cox proportional hazards analysis was used to analyze survival. We further verified our findings in the validation set. RESULTS: Major complications occurred in 43 (14.7%) and 25 (24.8%) patients in the training set and validation set, respectively. In the training set, multivariate analysis showed that elevated GGT levels and elevated D-dimer levels independently predicted major complications respectively. In the multivariate analyses, elevated pre-operative D-dimer levels remained independently associated with decreased overall survival (OS) (hazard ratio [HR] = 1.751, 95% confidence interval [CI]: 1.139-2.691, P = .01). The CPDG score was an independent prognostic factor for major complications and OS in the multivariate analyses. The predictive ability of the CPDG score was higher than either factor alone. A Kaplan-Meier survival analysis showed that compared with patients with CPDG score = 1 or CPDG score = 0, patients with a CPDG score = 2 had worsened OS. Furthermore, for OS comparisons, the differences between any two groups were significant. In the validation set, elevated GGT and D-dimer were also suggested to predict worse progression-free survival (PFS) and to be independently associated with major complications. CONCLUSIONS: The pre-operative D-dimer levels, GGT levels and CPDG score are reliable biomarkers to predict post-operative major complications or survival in CRLM patients after hepatic resection, which make it useful for CRLM patients in guiding surveillance approaches and prognosis assessments.

Effects of various interventions on the occurrence of macrovascular invasion of hepatocellular carcinoma after the baseline serum γ-glutamyltransferase stratification

Background

Elevated serum γ-glutamyltransferase (γ-GT) levels are related to an increased cancer risk and worse prognosis in many cancers. We evaluated the effects of γ-GT stratification on the occurrence of macrovascular invasion (MVI) in patients with hepatocellular carcinoma (HCC) who underwent hepatic resection (HR), transcatheter arterial chemoembolization (TACE), or TACE combined with radiofrequency ablation (TACE-RFA).

Patients and methods

A total of 903 patients with HCC in Barcelona Clinic Liver Cancer Stage A or B were included. Of these patients, 118 underwent HR, 445 underwent TACE-RFA, 256 underwent TACE, and 84 patients received conservative treatment only (control group). γ-GT, albumin, α-fetoprotein, and intervention were selected as significant predictive factors for MVI in 1 year by forward selection. The optimal cutoff value of γ-GT was 39 IU/L according to receiver operating characteristic analysis, with a sensitivity and specificity of 87.0% and 45.6%, respectively.

Results

The 1-year MVI incidence of patients with HCC in the group with γ-GT ≥39 IU/L was higher than that of the group with γ-GT <39 IU/L treated with HR, TACE-RFA, or TACE (P=0.0166, P=0.0041, and P<0.001, respectively). The MVI rates at 1 year were similar in the group with γ-GT ≥39 IU/L that underwent HR, TACE-RFA, or TACE and the control group (P=0.4402, P=0.2214, and P=0.4159, respectively). Different effects of various treatments with γ-GT <39 IU/L group on the occurrence of MVI are not significant (P=0.5167). However, the incidence of MVI after TACE was significantly higher than that after HR or TACE-RFA in γ-GT ≥39 IU/L group (P=0.0253).

Conclusion

Baseline serum γ-GT stratification may help select the appropriate treatment to reduce the MVI incidence.

Glutathione: Antioxidant Properties Dedicated to Nanotechnologies

Which scientist has never heard of glutathione (GSH)? This well-known low-molecular-weight tripeptide is perhaps the most famous natural antioxidant. However, the interest in GSH should not be restricted to its redox properties. This multidisciplinary review aims to bring out some lesser-known aspects of GSH, for example, as an emerging tool in nanotechnologies to achieve targeted drug delivery. After recalling the biochemistry of GSH, including its metabolism pathways and redox properties, its involvement in cellular redox homeostasis and signaling is described. Analytical methods for the dosage and localization of GSH or glutathiolated proteins are also covered. Finally, the various therapeutic strategies to replenish GSH stocks are discussed, in parallel with its use as an addressing molecule in drug delivery.

Elevated Preoperative Serum Gamma-glutamyltranspeptidase Predicts Poor Prognosis for Hepatocellular Carcinoma after Liver Transplantation

Gamma-glutamyltransferase (γ-GGT) is a membrane-bound enzyme that is involved in biotransformation, nucleic acid metabolism, and tumourigenesis. Elevated serum γ-GGT levels are related to an increased cancer risk and worse prognosis in many cancers. In the present study, we evaluated the prognostic value of preoperative serum γ-GGT in patients with hepatocellular carcinoma (HCC) who underwent liver transplantation (LT). A total of 130 HCC patients after LT were included in the study. The optimal cut-off value of γ-GGT was 128U/L by receiver operating characteristic analysis, with a sensitivity and specificity of 60.0% and 72.9%, respectively. Elevated preoperative serum γ-GGT was significantly associated with high alpha-fetoprotein (AFP), large tumor size, and macro- and micro-vascular invasion. The 1-, 3-, 5-year disease-free survival (DFS) and overall survival (OS) rates of HCC patients in the γ-GGT > 128U/L group were poorer than those in the γ-GGT ≤ 128U/L group. Stratification analysis revealed that γ-GGT exhibited a greater predictive value for DFS and OS in HCC patients beyond the Milan criteria and no macro-vascular invasion. In conclusion, elevated preoperative serum γ-GGT was significantly associated with advanced tumor stage and aggressive tumor behaviors, and serum γ-GGT can be considered as a prognostic factor for HCC patients after LT, especially for patients beyond the Milan criteria or without macro-vascular invasion.

Endothelial γ-glutamyltransferase contributes to the vasorelaxant effect of S-nitrosoglutathione in rat aorta

S-nitrosoglutathione (GSNO) involved in storage and transport of nitric oxide (^•NO) plays an important role in vascular homeostasis. Breakdown of GSNO can be catalyzed by γ-glutamyltransferase (GGT). We investigated whether vascular GGT influences the vasorelaxant effect of GSNO in isolated rat aorta. Histochemical localization of GGT and measurement of its activity were performed by using chromogenic substrates in sections and in aorta homogenates, respectively. The role of GGT in GSNO metabolism was evaluated by measuring GSNO consumption rate (absorbance decay at 334 nm), ^•NO release was visualized and quantified with the fluorescent probe 4,5-diaminofluorescein diacetate. The vasorelaxant effect of GSNO was assayed using isolated rat aortic rings (in the presence or absence of endothelium). The role of GGT was assessed by stimulating enzyme activity with cosubstrate glycylglycine, as well as using two independent inhibitors, competitive serine borate complex and non-competitive acivicin. Specific GGT activity was histochemically localized in the endothelium. Consumption of GSNO and release of free ^•NO decreased and increased in presence of serine borate complex and glycylglycine, respectively. In vasorelaxation experiments with endothelium-intact aorta, the half maximal effective concentration of GSNO (EC50 = 3.2±0.5.10⁻⁷ M) increased in the presence of the two distinct GGT inhibitors, serine borate complex (1.6±0.2.10⁻⁶ M) and acivicin (8.3±0.6.10⁻⁷ M), while it decreased with glycylglycine (4.7±0.9.10⁻⁸ M). In endothelium-denuded aorta, EC₅₀ for GSNO alone increased to 2.3±0.3.10⁻⁶ M, with no change in the presence of serine borate complex. These data demonstrate the important role of endothelial GGT activity in mediating the vasorelaxant effect of GSNO in rat aorta under physiological conditions. Because therapeutic treatments based on GSNO are presently under development, this endothelium-dependent mechanism involved in the vascular effects of GSNO should be taken into account in a pharmacological perspective.

Endogenous oxidative stress induces distinct redox forms of tumor necrosis factor receptor-1 in melanoma cells

Receptors of the TNFR superfamily possess abundant thiols in their extracellular domains, which makes them susceptible to redox modulation by prooxidant agents and processes. Previous studies from our laboratory have documented that membrane gamma-glutamyltransferase (GGT) activity can originate reactive oxygen species in the extracellular milieu, during the GGT-mediated metabolism of extracellular glutathione. The present study was aimed thus to verify a possible redox-modulating effect of GGT activity on TNFR1 receptors. The thiol-specific probe maleimide-polyethylene glycol was used to selectively label the reduced thiol groups in proteins of cell lysates; fractions corresponding to TNFR1 were then identified by immunoblot. In human melanoma Me665/2 cells, expressing varying GGT levels, at least five distinct forms of TNFR1 have been thus identified. The more oxidized forms appear to be prevalent in the 2/60 clone, expressing higher GGT levels, as compared to clone 2/21. Stimulation of GGT activity in the latter induced an increase of the oxidized TNFR1 forms. It is conceivable that different redox states of TNFR1 may correspond to different binding affinity and/or changes in the transducing function of the receptor. As GGT is frequently expressed by malignant tumors, the described phenomena might concur to alter the sensitivity of cancer cells to agents targeted on activation of TNF-alpha-dependent signaling pathways.

Activity Determination, Kinetic Analyses and Isoenzyme Identification of Gamma Glutamyltransferase in Human Neutrophils

Gamma-glutamyltransferase (GGT, EC 2.3.2.2) which hydrolyzes glutathione (GSH), is required for the maintenance of normal intracellular GSH concentration. GGT is a membrane enzyme present in leukocytes and platelets. Its activity has also been observed in human neutrophils. In this study, GGT was purified from Triton X-100 solubilized neutrophils and its kinetic parameters were determined. For kinetic analyses of transpeptidation reaction, gamma-glutamyl p-nitroanilide was used as the substrate and glycylglycine as the acceptor. Apparent K(m) values were determined as 1.8 mM for gamma-glutamyl p-nitroanilide and 16.9 mM for glycylglycine. The optimum pH of GGT activity was 8.2 and the optimum temperature was 37 degrees C. It had thermal stability with 58 % relative activity at 56 degrees C for 30 min incubation. L-serine, in the presence of borate, was detected as the competitive inhibitor. Bromcresol green inhibited neutrophil GGT activity as a noncompetitive inhibitor. The neutrophils seem to contain only the isoenzyme that is present in platelets. We characterized the kinetic properties and compared the type of the isoenzyme of neutrophil GGT with platelet GGT via polyacrylamide gel electrophoresis (PAGE) under a standard set of conditions.