LA MODULAZIONE DEI LIVELLI DI GLUTATIONE COME STRATEGIA DI ATTACCO NELLE INTERAZIONI OSPITE-PARASSITA

Insect studies, dealing with parasitism of aphids, have shown that the disruption of host glutathione (GSH) pool and metabolisms significantly contributes to its physiological regulation and castration. The parasitic wasp Aphidius ervi injects into host aphids a venom containing large amounts of a gamma-glutamyltransferase (Ae-GGT) enzyme, which causes a depletion of GSH primarily involving ovarian tissue. Injected Ae-GGT in fact consumes substrate GSH, which ultimately triggers apoptosis. Studies on virulence factors of microrganisms have documented that the invasion strategies of selected pathogenic bacteria also target host GSH metabolism. Indeed, it has been shown that GGT activity of Helicobacter pylori and H. suis, the agents responsible of peptic ulcer, can exert antiproliferative and pro-apoptotic effects in gastric epithelial cells. By confocal microscopy, H. suis outer membrane vesicles (OMV) 12 submicroscopic structures 20-50 nm in diameter, budding from the cell surface 12 were identified as carriers of H. suis GGT, capable of delivering the enzyme to the deeper mucosal layers. In association with such membranous structures, active GGT from H. suis in fact translocates across the epithelial layers and can access lymphocytes residing in the gastric mucosa, resulting in the inhibition of lymphocyte proliferation, i.e., a perturbation of host immunity and a facilitation of bacterial infection. Cellular GSH appears, thus, to represent a conserved target for parasitic (micro)organisms which aim at altering host redox homeostasis to weaken its immune defenses, using GGT as a key-element of a virulence strategy. Taking into account the \u201cparasitic\u201d behavior exhibited by malignant cells spreading across tissues and organs of the patient (the \u201chost\u201d). GGT activity is in fact expressed in a number of malignant tumors, and expression levels often increase along with progression to more invasive phenotypes. Now, active GGT can be released from cells, including cancer cells, in association with submicroscopic vesicles resembling exosomes. The similarity of such structures with GGT-rich OMV particles of H. pylori and H. suis is indeed obvious. GGT activity of cancer cells can affect intracellular redox equilibrium, and produces in addition significant extracellular effects, e.g. on the redox status and ligand binding affinity of cell surface receptors related with cell survival/apoptosis balance. Thus, GGT-rich exosomes shed by cancer cells can produce in host\u2019s surrounding tissues effects comparable to those reported for Ae-GGT or Helicobacter GGT, possibly resulting in facilitation of malignant cells survival and diffusion

Antitumoral effects of pharmacological ascorbate on gastric cancer cells: GLUT1 expression may not tell the whole story

The recently reported results of Lu et al. (Theranostics. 2018; 8: 1312-26) – highlighting GLUT1 expression as a marker for sensitivity of gastric cancer cells to therapeutic doses of ascorbate – are discussed in the light of additional factors potentially affecting the underlying processes, such as the concomitant expression of membrane gamma-glutamyltransferase activity, the resistance of cancer cells to oxidative injury and other known biomarkers

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

BACKGROUND: The molecular mechanisms by which iron is physiologically transported trough the cellular membranes are still only partially understood. Several studies indicate that a reduction step of ferric iron to ferrous is necessary, both in the case of transferrin-mediated and transferrin-independent iron uptake. Recent studies from our laboratory described gamma-glutamyltransferase activity (GGT) as a factor capable to effect iron reduction in the cell microenvironment. GGT is located on the outer aspect of plasma membrane of most cell types, and is often expressed at high levels in malignant tumors and their metastases. The present study was aimed at verifying the possibility that GGT-mediated iron reduction may participate in the process of cellular iron uptake. RESULTS: Four distinct human tumor cell lines, exhibiting different levels of GGT activity, were studied. The uptake of transferrin-bound iron was investigated by using (55)Fe-loaded transferrin, as well as by monitoring fluorimetrically the intracellular iron levels in calcein-preloaded cells. Transferrin-independent iron uptake was investigated using (55)Fe complexed by nitrilotriacetic acid ((55)Fe-NTA complex). The stimulation of GGT activity, by administration to cells of the substrates glutathione and glycyl-glycine, was generally reflected in a facilitation of transferrin-bound iron uptake. The extent of such facilitation was correlated with the intrinsic levels of the enzyme present in each cell line. Accordingly, inhibition of GGT activity by means of two independent inhibitors, acivicin and serine/boric acid complex, resulted in a decreased uptake of transferrin-bound iron. With Fe-NTA complex, the inhibitory effect – but not the stimulatory one – was also observed. CONCLUSION: It is concluded that membrane GGT can represent a facilitating factor in iron uptake by GGT-expressing cancer cells, thus providing them with a selective growth advantage over clones that do not possess the enzyme

Helicobacter, gamma-glutamyltransferase and cancer: further intriguing connections

Virulence of Helicobacter pylori , H. Suis and other bacteria appears to be partly mediated through a release of gamma-glutamyltransferase (GGT), an enzyme activity capable of promoting biochemical reactions ultimately resulting in damage to gastric epithelium and suppression of immune response. Recently published studies show that secretion of bacterial GGT occurs in the form of exosome-like vescicles. Very similar GGT-rich exosomes have been described to originate from human cancer cells, and the hypothesis is thus forwarded that in the resistant and invasive phenotype of malignant cells such vescicular/exosomal GGT may play roles akin to those described for Helicobacter infection, thus providing a significant contribution to the establishment of cancer metastases

The potential roles of gamma-glutamyltransferase activity in the progression of atherosclerosis and cardiovascular diseases.

The oxidation of low density lipoproteins (LDL) is regarded as a critical factor in the pathogenesis of atherosclerosis, especially the initial steps of the disease. In addition, other oxidative events have been shown to participate in the progression of atherosclerosis and precipitation of cardiovascular events, through modulation of important components of lesions of the vessel wall (smooth muscle cell proliferation, protease/antiprotease balance, endothelial functions). Our recent studies have provided evidence that the enzyme gamma-glutamyltransferase (GGT), normally found in serum, is often accumulated within the plaque environment in substantial amounts, and that this activity is a potential source of a variety of prooxidant species. Concurrently, epidemiological research has conclusively documented that the serum levels of GGT are an independent factor in prognosis of myocardial infarction and stroke in atherosclerotic patients. Several signs suggest that the GGT appearing in plaque tissue may originate from the serum enzyme, which in facts associates with the circulating lipoprotein fractions. Thus, data seem to point out that pathogenesis of atherosclerosis – and in particular of the events leading to progression of the disease and acute cardiovascular events – might include an as yet unexplored pathway, based on the prooxidant effects of gamma-glutamyltransferase accumulating as a result of LDL entry in the vessel wall

Plasma membrane gamma-glutamyltransferase activity facilitates the uptake of vitamin C in melanoma cells.

Adequate cellular transport of ascorbic acid (AA) and its oxidation product dehydroascorbate (DHA) is assured through specific carriers. It was shown that vitamin C is taken up as DHA by most cell types, including cancer cells, via the facilitative GLUT transporters. Thus, AA oxidation to DHA can be considered a mechanism favoring vitamin C uptake and intracellular accumulation. We have investigated whether such an AA-oxidizing action might be provided by plasma membrane g-glutamyltransferase (GGT), previously shown to function as an autocrine source of prooxidants. The process was studied using two distinct human metastatic melanoma clones. It was observed that the Me665/2/60 clone, expressing high levels of membrane GGT activity, was capable of effecting the oxidation of extracellular AA, accompanied by a marked increase of intracellular AA levels. The phenomenon was not observed with Me665/2/21 cells, possessing only traces of membrane GGT. On the other hand, AA oxidation and stimulation of cellular uptake were indeed observed after transfection of 2/21 cells with cDNA coding for GGT. The mechanism of GGTmediated AA oxidation was investigated in acellular systems, including GGT and its substrate glutathione. The process was observed in the presence of redox-active chelated iron(II) and of transferrin or ferritin, i.e., two physiological iron sources. Thus, membrane GGT activity—often expressed at high levels in human malignancies—can oxidize extracellular AA and promote its uptake efficiently

Photofunctionalization of titanium: an alternative explanation of its chemical-physical mechanism

Objectives To demonstrate that titanium implant surfaces as little as 4 weeks from production are contaminated by atmospheric hydrocarbons. This phenomenon, also known as biological ageing can be reversed by UVC irradiation technically known as photofunctionalization. To propose a new model from our experimental evidence to explain how the changes in chemical structure of the surface will affect the adsorption of amino acids on the titanium surface enhancing osteointegration. Methods In our study XPS and AES were used to analyze the effects of UVC irradiation (photofunctionalization) in reversing biological ageing of titanium. SEM was used to analyze any possible effects on the topography of the surface. Results UVC irradiation was able to reverse biological ageing of titanium by greatly reducing the amount of carbon contamination present on the implant surface by up to 4 times, while the topography of the surface was not affected. UVC photon energy reduces surface H2 O and increases TiOH with many -OH groups being produced. These groups explain the superhydrophilic effect from photofunctionalization when these groups come into contact with water. Significance Photofunctionalization has proven to be a valid method to reduce the amount of hydrocarbon contamination on titanium dental implants and improve biological results. The chemisorption mechanisms of amino acids, in our study, are dictated by the chemical structure and electric state present on the surface, but only in the presence of an also favourable geometrical composition at the atomical level

Reduced Activity of the Aortic Gamma-Glutamyltransferase Does Not Decrease S-Nitrosoglutathione Induced Vasorelaxation of Rat Aortic Rings

Aims: Gamma-glutamyl transferase (GGT), an enzyme present on the endothelium, is involved in the release of nitric oxide (NO) from S-nitrosoglutathione (GSNO) and in the GSNO-induced vasodilation. Endogenous GSNO is a physiological storage form of NO in tissues while exogenous GSNO is an interesting candidate for compensating for the decreased NO bioavailability occurring during cardiovascular diseases. We investigated in a rat model of human hypertension, the spontaneous hypertensive rat (SHR), submitted or not to high salt diet, whether a decreased vascular GGT activity modifies the vasorelaxant effect of GSNO. Methods: Thoracic aortic rings isolated from male SHR and Wistar Kyoto rats (WKY) aged 20–22 weeks—submitted or not for 8 weeks to a high salt diet (1% w/v NaCl in drinking water) were pre-constricted with phenylephrine then submitted to concentration-vasorelaxant response curves (maximal response: Emax; pD2) to carbachol or sodium nitroprusside to evaluate endothelial dependent or independent NO-induced vasodilation, or GSNO (exogenous NO vasodilation depending from the endothelial GGT activity). GGT activity was measured using a chromogenic substrate in aortic homogenates. Its role in GSNO-induced relaxation was assessed following inhibition of the enzyme activity (serine-borate complex). That of protein disulfide isomerase (PDI), another redox sensitive enzyme involved in GSNO metabolism, was assessed following inhibition with bacitracin. Results: Aortic GGT activity (18–23 μmol/min/mg of tissue in adult WKY) decreased by 33% in SHR and 45% in SHR with high salt diet. Emax and pD2 for sodium nitroprusside were similar in all groups. Emax for carbachol decreased by −14%, reflecting slight endothelial NO-dependent dysfunction. The GSNO curve was slightly shifted to the left in SHR and in SHR with high salt diet, showing a small enhanced sensitivity to GSNO. Involvements of GGT, as that of PDI, in the GSNO effects were similar in all groups (pD2 for GSNO −0.5 to −1.5 following enzymatic inhibition). Conclusion: Hypertension is associated with a decreased aortic GGT activity without decreasing the vasorelaxant effects of GSNO, whose bioactivity may be supplemented through the alternative enzymatic activity of PDI

Association between plasma gamma-glutamyltransferase fractions and metabolic syndrome among hypertensive patients

Among the risk factors associated to metabolic syndrome (MetS), hypertension shows the highest prevalence in Italy. We investigated the relationship between the newly identified serum γ-glutamyltransferase (GGT) fractions, b-s-m-f-GGT, and risk factors associated to MetS in hypertensive patients. A total of ninety-five consecutive hypertensive patients were enrolled. GGT fractions were analysed by gel-filtration chromatography, and hepatic steatosis was evaluated by ultrasound. MetS was diagnosed in 36% of patients. Considering the whole group, b-And f-GGT showed the highest positive correlation with BMI, glucose, triglycerides and insulin, and the highest negative correlation with HDL cholesterol. While both serum triglycerides and insulin were independently associated with b-GGT levels, only triglycerides were independently associated with f-GGT. The values of b-GGT activity increased with steatosis grade (g0 = 1.19; g2 = 3.29; ratio g2/g0 = 2.75, p < 0.0001 linear trend). Patients with MetS showed higher levels of b-GGT, m-GGT and f-GGT [median (25th-75th) U/L: 3.19 (1.50-6.59); 0.55 (0.26-0.81); 10.3 (9.1-13.6); respectively] as compared to subjects presenting with one or two MetS criteria [1.75 (0.95-2.85), p < 0.001; 0.33 (0.19-0.60), p < 0.05; 8.8 (7.0-10.6), p < 0.001]. Our data point to a potential role for b-And f-GGT fractions in identifying MetS patients among hypertensive subjects, thus providing a minimally invasive blood-based tool for MetS diagnosis