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

Targeting gamma-glutamyl transpeptidase: A pleiotropic enzyme involved in glutathione metabolism and in the control of redox homeostasis

Gamma-glutamyl transpeptidase (GGT) is an enzyme located on the outer membrane of the cells where it regulates the metabolism of glutathione (GSH), the most abundant intracellular antioxidant thiol. GGT plays a key role in the control of redox homeostasis, by hydrolyzing extracellular GSH and providing the cell with the recovery of cysteine, which is necessary for de novo intracellular GSH and protein biosynthesis. Therefore, the upregulation of GGT confers to the cell greater resistance to oxidative stress and the advantage of growing fast. Indeed, GGT is upregulated in inflammatory conditions and in the progression of various human tumors and it is involved in many physiological disorders related to oxidative stress, such as cardiovascular disease and diabetes. Currently, increased GGT expression is considered a marker of liver damage, cancer, and low-grade chronic inflammation. This review addresses the current knowledge on the structure-function relationship of GGT, focusing on human GGT, and provides information on the pleiotropic biological role and relevance of the enzyme as a target of drugs aimed at alleviating oxidative stress-related diseases. The development of new GGT inhibitors is critically discussed, as are the advantages and disadvantages of their potential use in clinics. Considering its pleiotropic activities and evolved functions, GGT is a potential "moonlighting protein".

Blood Plasma's Protective Ability against the Degradation of S-Nitrosoglutathione under the Influence of Air-Pollution-Derived Metal Ions in Patients with Exacerbation of Heart Failure and Coronary Artery Disease

One of the consequences of long-term exposure to air pollutants is increased mortality and deterioration of life parameters, especially among people diagnosed with cardiovascular diseases (CVD) or impaired respiratory system. Aqueous soluble inorganic components of airborne particulate matter containing redox-active transition metal ions affect the stability of S-nitrosothiols and disrupt the balance in the homeostasis of nitric oxide. Blood plasma’s protective ability against the decomposition of S-nitrosoglutathione (GSNO) under the influence of aqueous PM extract among patients with exacerbation of heart failure and coronary artery disease was studied and compared with a group of healthy volunteers. In the environment of CVD patients’ plasma, NO release from GSNO was facilitated compared to the plasma of healthy controls, and the addition of ascorbic acid boosted this process. Model studies with albumin revealed that the amount of free thiol groups is one of the crucial factors in GSNO decomposition. The correlation between the concentration of NO released and -SH level in blood plasma supports this conclusion. Complementary studies on gamma-glutamyltranspeptidase activity and ICP-MS multielement analysis of CVD patients’ plasma samples in comparison to a healthy control group provide broader insights into the mechanism of cardiovascular risk development induced by air pollution.

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.

Flush with a flash: natural three-component antimicrobial combinations based on S-nitrosothiols, controlled superoxide formation and "domino" reactions leading to peroxynitrite

S-Nitrosothiols are ˙NO releasing agents renowned for vasodilatory and antioxidant properties. O2˙- promotes their decomposition, forming highly aggressive peroxynitrite ions (ONOO-). Since the production of O2˙- can be controlled by enzymes or by visible light, such otherwise harmless components can be turned into effective antimicrobial and nematicidal combinations with numerous potential applications in medicine.

Synthesis of novel mono and bis nitric oxide donors with high cytocompatibility and release activity

Four compounds bearing amidoxime functions were synthetized: (1) 2a,b bearing an aromatic amidoxime function, (2) 2c bearing an aliphatic amidoxime function, and (3) 2d bearing aromatic and aliphatic amidoximes functions. The ability of these compounds to release NO was evaluated in vitro using the oxidative metabolism of cytochrome P450 from rat liver microsomes. Results obtained demonstrate that all amidoximes were able to release NO with a highest amount of NO produced by the 2a aromatic amidoxime. Moreover, all amidoximes exhibit cytocompatibility with human aorta smooth muscle cells. Using intracellular S-nitrosothiol formation as a marker of NO bioavailability, compounds 2a-c were demonstrated to deliver a higher amount of NO in the intracellular environment than the reference. Considering that the concentration of the bis-amidoxime 2d was two times lower that than of 2a and 2b, we can assume that 2d is the most potent molecule among the tested compounds for NO release.

Intestinal absorption of S-nitrosothiols: Permeability and transport mechanisms

S-Nitrosothiols, a class of NO donors, demonstrate potential benefits for cardiovascular diseases. Drugs for such chronic diseases require long term administration preferentially through the oral route. However, the absorption of S-nitrosothiols by the intestine, which is the first limiting barrier for their vascular bioavailability, is rarely evaluated. Using an in vitro model of intestinal barrier, based on human cells, the present work aimed at elucidating the mechanisms of intestinal transport (passive or active, paracellular or transcellular pathway) and at predicting the absorption site of three S-nitrosothiols: S-nitrosoglutathione (GSNO), S-nitroso-N-acetyl-l-cysteine (NACNO) and S-nitroso-N-acetyl-d-penicillamine (SNAP). These S-nitrosothiols include different skeletons carrying the nitroso group, which confer different physico-chemical characteristics and biological activities (antioxidant and anti-inflammatory). According to the values of apparent permeability coefficient, the three S-nitrosothiols belong to the medium class of permeability. The evaluation of the bidirectional apparent permeability demonstrated a passive diffusion of the three S-nitrosothiols. GSNO and NACNO preferentially cross the intestinal barrier though the transcellular pathway, while SNAP followed both the trans- and paracellular pathways. Finally, the permeability of NACNO was favoured at pH 6.4, which is close to the pH of the jejunal part of the intestine. Through this study, we determined the absorption mechanisms of S-nitrosothiols and postulated that they can be administrated through the oral route.

Regulation of protein function by S-nitrosation and S-glutathionylation: processes and targets in cardiovascular pathophysiology

Decades of chemical, biochemical and pathophysiological research have established the relevance of post-translational protein modifications induced by processes related to oxidative stress, with critical reflections on cellular signal transduction pathways. A great deal of the so-called ‘redox regulation’ of cell function is in fact mediated through reactions promoted by reactive oxygen and nitrogen species on more or less specific aminoacid residues in proteins, at various levels within the cell machinery. Modifications involving cysteine residues have received most attention, due to the critical roles they play in determining the structure/function correlates in proteins. The peculiar reactivity of these residues results in two major classes of modifications, with incorporation of NO moieties (S-nitrosation, leading to formation of proteinS-nitrosothiols) or binding of low molecular weight thiols (S-thionylation, i.e. in particularS-glutathionylation,S-cysteinylglycinylation andS-cysteinylation). A wide array of proteins have been thus analyzed in detail as far as their susceptibility to either modification or both, and the resulting functional changes have been described in a number of experimental settings. The present review aims to provide an update of available knowledge in the field, with a special focus on the respective (sometimes competing and antagonistic) roles played by proteinS-nitrosations andS-thionylations in biochemical and cellular processes specifically pertaining to pathogenesis of cardiovascular diseases.

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: E_max; 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. E_max and pD₂ for sodium nitroprusside were similar in all groups. E_max 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 of matrix metalloproteinase 3 and γ-glutamyltransferase 1 gene polymorphisms with the cardio-ankle vascular index in young Russians

Specific gene polymorphisms are known to be associated with a different arterial physiology in the younger generation. The present study found that young Russians with the matrix metalloproteinase 3 6A/6A and γ-glutamyltransferase 1AA genotypes have lower levels of the cardio-ankle vascular index - a recent measure of arterial stiffness. This observation may serve as an additional tool for cardiovascular disease prevention in the young population.

Chlorpyrifos inhibits cell proliferation through ERK1/2 phosphorylation in breast cancer cell lines

It is well known the participation of oxidative stress in the induction and development of different pathologies including cancer, diabetes, neurodegeneration and respiratory disorders among others. It has been reported that oxidative stress may be induced by pesticides and it could be the cause of health alteration mediated by pollutants exposure. Large number of registered products containing chlorpyrifos (CPF) is used to control pest worldwide. We have previously reported that 50 μM CPF induces ROS generation and produces cell cycle arrest followed by cell death. The present investigation was designed to identify the pathway involved in CPF-inhibited cell proliferation in MCF-7 and MDA-MB-231 breast cancer cell lines. In addition, we determined if CPF-induced oxidative stress is related to alterations in antioxidant defense system. Finally we studied the molecular mechanisms underlying in the cell proliferation inhibition produced by the pesticide. In this study we demonstrate that CPF (50 μM) induces redox imbalance altering the antioxidant defense system in breast cancer cells. Furthermore, we found that the main mechanism involved in the inhibition of cell proliferation induced by CPF is an increment of p-ERK1/2 levels mediated by H2O2 in breast cancer cells. As PD98059 could not abolish the increment of ROS induced by CPF, we concluded that ERK1/2 phosphorylation is subsequent to ROS production induced by CPF but not the inverse.

γ-Glutamyltransferase catabolism of S-nitrosoglutathione modulates IL-8 expression in cystic fibrosis bronchial epithelial cells

S-nitrosoglutathione (GSNO) is an endogenous nitrosothiol involved in several pathophysiological processes. A role for GSNO has been envisaged in the expression of inflammatory cytokines such as IL-8; however, conflicting results have been reported. γ-Glutamyltransferase (GGT) enzyme activity can hydrolyze the γ-glutamyl bond present in the GSNO molecule thus greatly accelerating the release of bioactive nitric oxide. Expression of GGT is induced by oxidative stress, and activated neutrophils contribute to GGT increase in cystic fibrosis (CF) lung exudates by releasing GGT-containing microvesicles. This study was aimed at evaluating the effect of GSNO catabolism mediated by GGT on production of IL-8 in CF transmembrane regulation protein-mutated IB3-1 bronchial cells. The rapid, GGT-catalyzed catabolism of GSNO caused a decrease in both basal and lipopolysaccharide-stimulated IL-8 production in IB3-1 cells, by modulating both NF-κB and ERK1/2 pathways, along with a decrease in cell proliferation. In contrast, a slow decomposition of GSNO produced a significant increase in both cell proliferation and expression of IL-8, the latter possibly through p38-mediated stabilization of IL-8 mRNA. Our data suggest that the differential GSNO catabolism mediated by GGT enzyme activity can downregulate the production of IL-8 in CF cells. Hence, the role of GGT activity should be considered when evaluating GSNO for both in vitro and in vivo studies, the more so in the case of GSNO-based therapies for cystic fibrosis.

Systems biology approach to the dissection of the complexity of regulatory networks in the S. scrofa cardiocirculatory system

Genome-wide experiments are routinely used to increase the understanding of the biological processes involved in the development and maintenance of a variety of pathologies. Although the technical feasibility of this type of experiment has improved in recent years, data analysis remains challenging. In this context, gene set analysis has emerged as a fundamental tool for the interpretation of the results. Here, we review strategies used in the gene set approach, and using datasets for the pig cardiocirculatory system as a case study, we demonstrate how the use of a combination of these strategies can enhance the interpretation of results. Gene set analyses are able to distinguish vessels from the heart and arteries from veins in a manner that is consistent with the different cellular composition of smooth muscle cells. By integrating microRNA elements in the regulatory circuits identified, we find that vessel specificity is maintained through specific miRNAs, such as miR-133a and miR-143, which show anti-correlated expression with their mRNA targets.

[Which future in cardiovascular therapy for nitric oxide and its derivatives?]

Nitric oxide (NO) is involved in the regulation of several physiological processes such as vascular homeostasis. Exogenous NO supply offers major therapeutic interest, especially in the treatment of coronary artery disease, ischemic syndromes and other cardiovascular pathologies. Nevertheless, the administration of NO itself is limited by its short half-life. NO prodrugs have been marketed for decades, e.g. organic nitrates for angina pectoris. These prodrugs display undeniable advantages such as angina crisis relief and preconditioning effect. Nevertheless, they suffer from several drawbacks: toxicity, tolerance, endothelial dysfunction exacerbation. These negative effects are related to massive production of reactive species derived from oxygen or nitrogen, which trigger oxidative and nitrosative stress. New NO donors are under development to overcome those disadvantages, among which the S-nitrosothiols family seems especially promising.