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

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".

Associations Between GGT/ALT Ratio and Carotid Plaque in Inpatients With Coronary Artery Disease: A RCSCD-TCM Study

This study investigated the relationship between gamma-glutamyltransferase/alanine aminotransferase (GGT/ALT) ratio and carotid plaques in patients with coronary artery disease (CAD). This multicenter retrospective study included 8,255 patients with CAD who were divided according to GGT/ALT quartiles: Q1 (GGT/ALT ≤ 1.00), Q2 (1.00 < GGT/ALT ≤ 1.41), Q3 (1.41 < GGT/ALT ≤ 2.05), and Q4 (GGT/ALT > 2.05). Logistic regression was used to analyze the relationship between GGT/ALT, carotid plaques, and carotid plaque echogenicity. GGT/ALT ratio (odds ratio [OR]: 1.16; 95% confidence interval [CI]: 1.11-1.21; P < .001) was significantly associated with carotid plaque risk. The degree of relevance was higher in men (OR: 1.71; 95% CI: 1.35-2.15; P < .001) than in women (OR: 1.56; 95% CI: 1.28-1.91; P < .001). The ORs value of carotid plaque risk was higher in middle-aged patients (OR: 2.23; 95% CI: 1.78-2.80; P < .001) than in older patients (OR: 1.77; 95% CI: 1.44-2.18; P < .001). The GGT/ALT ratio was significantly associated with different carotid plaque echogenicity, and the highest OR values were for isoechoic plaques (OR: 1.18; 95% CI: 1.12-1.24; P < .001). These findings suggest that the GGT/ALT ratio might be associated with a high risk of developing carotid plaques and different types of plaque echoes and was more significantly associated with isoechoic plaques.

Pathophysiology, cellular and molecular mechanisms of large and small vessel diseases

Cerebrovascular disease (CVD) is the second most common cause of cognitive impairment and dementia in aged population. CVD presents in a myriad number of clinical ways based on the functional location of pathology. While primary clinical emphasis has been placed on motor, speech and visual deficits, vascular cognitive decline is a vastly under recognized and devastating condition afflicting millions of Americans. CVD, a disease of the blood vessels that supply blood to brain involves an integration between small and large vessels. Cerebral large vessel diseases (LVD) are associated with atherosclerosis, artery-to-artery embolism, intracardiac embolism and a large vessel stroke leading to substantial functional disability. Cerebral small vessel disease (SVD) is critically involved in stroke, brain hemorrhages, cognitive decline and functional loss in elderly patients. An evolving understanding of cellular and molecular mechanisms emphasizes that inflammatory vascular changes contribute to systemic pathologic conditions of the central nervous systems (CNS), with specific clinical presentations including, cognitive decline. Advances in an understanding of pathophysiology of disease processes and therapeutic interventions may help improve outcomes. This review will focus on large and small vessels diseases and their relationship to vascular cognitive decline, atherosclerosis, stroke, and inflammatory neurodegeneration. We will also emphasize the molecular and cellular mechanisms, as well as genetic and epigenetic factors associated with LVD and SVD.

Binding of Gamma-Glutamyl Transferase to TLR4 Signalling Allows Tissue Factor Activation in Monocytes

Gamma-glutamyl transferase (GGT) is involved in the progression of atherosclerosis, since its enzymatic activity promotes the generation of reactive oxygen species (ROS). Besides, GGT may act as a prothrombotic factor by inducing tissue factor (TF) expression, independently of its enzymatic activity. The aim of this study was to assess whether GGT-induced TF stimulation was a consequence of binding to toll-like receptor 4 (TLR4) expressed on monocytes, the precursors of macrophages and foam cells which colocalize with GGT activity within atherosclerotic plaques. Experiments were performed in human peripheral blood mononuclear cells (PBMCs), THP-1 cells (a monocytic cellular model), and HEK293 cells, which were genetically modified to study the activation of TLR4. TF procoagulant activity was assessed by a one-stage clotting time test, and TF protein expression was estimated by western blot. Human recombinant (hr) GGT protein increased TF procoagulant activity and protein expression in both PBMCs and THP-1 cells. The GGT-induced TF stimulation was prevented by cellular pretreatment with TLR4/NF-κB inhibitors (LPS-Rs, CLI-095, and BAY-11-7082), and HEK293 cells lacking TLR4 confirmed that TLR4 is essential for GGT-induced activation of NF-κB. In conclusion, hrGGT induced TF expression in monocytes through a cytokine-like mechanism that involved the activation of TLR4/NF-κB signaling.

Big and Free Fractions of Gamma-Glutamyltransferase: New Diagnostic Biomarkers for Malignant Mesothelioma?

Malignant pleural mesothelioma (MPM) is a cancer mainly caused by asbestos fiber inhalation, characterized by an extremely long latency and poor prognosis. Recently, researchers have focused on testing the diagnostic ability of several biomarkers. Gamma-Glutamyltransferase (GGT) has been demonstrated to be the sum of several GGT sub-fractions activity, classified based on their molecular weight in big-GGT, medium-GGT, small-GGT, and free-GGT. This work aims to evaluate whether specific GGT fractional enzymatic activity patterns could be helpful in MPM diagnosis. We analyzed blood samples from 175 workers previously exposed to asbestos, 157 non-exposed healthy subjects, and 37 MPM patients through a molecular exclusion chromatographic method. We found a specific profile of GGT fractions activity, significantly associated with MPM, resulting in an increase in b-, m- activity, along with an evident, yet not significant, decrease in f-activity. Receiver-operating characteristic (ROC) analysis showed that the best Area Under Curve (AUC) value resulted from the combined index b/f (0.679, 95% CI: 0.582–0.777). Combining the b-/f-GGT activity with the levels of serum mesothelin-related protein (SMRP; another promising MPM biomarker) improved the diagnostic accuracy, increasing the AUC value to 0.875 (95% CI: 0.807–0.943, p = <0.0001). Since MPM has a specific pattern of GGT enzymatic activity, we could hypothesize that GGT fractions play different specific biochemical roles. The improvement in the diagnostic power given by the combination of these two biomarkers confirms that the strategy of biomarkers combination might be a better approach for MPM diagnosis.

Redefining residual inflammatory risk after acute coronary syndrome

Over the last decades, inflammation proved to play a pivotal role in atherosclerotic plaque formation, progression and destabilization. Several studies showed that the patients presenting with acute coronary syndrome are at increased risk of adverse cardiovascular events at both short- and long-term follow-up. Results from different clinical trials highlighted that a residual inflammatory risk exist and targeting inflammation is a successful strategy in selected cases associated to an increased inflammatory burden. Recently, the optimization of intracoronary and multimodality imaging allowed to also assess the entity of local inflammation, thus encouraging the individuation of plaque characteristics that portend a higher risk of future cardiovascular events. In this short review, we aim to highlight the role of systemic and local inflammation in acute coronary syndromes, to provide a summarized overview of the possible medical strategies applicable in selected cases and to underline the diagnostic and prognostic potential of multimodality imaging.

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.

Induction of Gamma-Glutamyltransferase Activity and Consequent Pro-oxidant Reactions in Human Macrophages Exposed to Crocidolite Asbestos

Asbestos is the main causative agent of malignant pleural mesothelioma. The variety known as crocidolite (blue asbestos) owns the highest pathogenic potential, due to the dimensions of its fibers as well as to its content of iron. The latter can in fact react with macrophage-derived hydrogen peroxide in the so called Fenton reaction, giving rise to highly reactive and mutagenic hydroxyl radical. On the other hand, hydroxyl radical can as well originate after thiol-dependent reduction of iron, a process capable of starting its redox cycling. Previous studies showed that glutathione (GSH) is one such thiol, and that cellular gamma-glutamyltransferase (GGT) can efficiently potentiate GSH-dependent iron redox cycling and consequent oxidative stress. As GGT is expressed in macrophages and is released upon their activation, the present study was aimed at verifying the hypothesis that GSH/GGT-dependent redox reactions may participate in the oxidative stress following the activation of macrophages induced by crocidolite asbestos. Experiments in acellular systems confirmed that GGT-mediated metabolism of GSH can potentiate crocidolite-dependent production of superoxide anion, through the production of highly reactive dipeptide thiol cysteinyl-glycine. Cultured THP-1 macrophagic cells, as well as isolated monocytes obtained from healthy donors and differentiated to macrophages in vitro, were investigated as to their expression of GGT and the effects of exposure to crocidolite. The results show that crocidolite asbestos at subtoxic concentrations (50-250 ng/1000 cells) can upregulate GGT expression, which raises the possibility that macrophage-initiated, GSH/GGT-dependent pro-oxidant reactions may participate in the pathogenesis of tissue damage and inflammation consequent to crocidolite intoxication.

Combination of the gamma-glutamyltransferase-to-prealbumin ratio and other indicators may be a novel marker for predicting the prognosis of patients with hepatocellular carcinoma undergoing locoregional ablative therapies

Objective

The aim of this study was to investigate the prognostic significance of the serum γ-glutamyltransferase (γ-GT)-to-prealbumin ratio (GPR) and whether combining this ratio with other parameters can lead to an improved prognostic value for patients with hepatocellular carcinoma (HCC) undergoing transcatheter arterial chemoembolization (TACE) combined with local ablation therapy.

Methods

A total of 235 HCC patients who were treated with combined therapies were retrospectively analyzed. The demographic data and clinicopathological data were collected. A fibrinogen (Fib)-GPR score of 2 was assigned to patients with elevated Fib and GPR values, and a score of 1 or 0 was assigned to patients with one or neither of these two markers, respectively. In addition, an N-score of 2 was assigned to patients with low neutrophil and high GPR values, and a score of 1 or 0 was assigned to patients with one or neither of these two markers, respectively. The optimal cutoff values and prognostic roles of GPR and other markers were identified according to the time-dependent receiver operating characteristic (ROC) curves and Youden’s index.

Results

Multiple tumors, high levels of α-fetoprotein (AFP) and Fib, as well as a high GPR, were found to be independent risk factors in recurrent patients, while multiple tumors, a low neutrophil count, and a high GPR were associated with reduced overall survival (OS) in patients with HCC who received combined therapies. Patients with a Fib-GPR score of 2 and N-GPR score of 2 had poor recurrence-free survival (RFS) and OS, respectively.

Conclusions

Fib-GPR and N-GPR scores may be helpful in predicting both recurrence and the prognosis of HCC patients, thereby assisting in the process to make a true clinical decision and optimize therapeutic options.

The combination of fatty liver and increased gamma-glutamyl transpeptidase levels as a risk factor for atherosclerotic plaque development in apparently healthy people

Background/aim

To elucidate how the combination of fatty liver and increased serum gamma-glutamyl transpeptidase (GGT) levels influences atherosclerotic plaque development in apparently healthy people.

Materials and methods

The study population included people who had received an annual health checkup for more than 7 years and had no evidence of carotid plaque at baseline. We investigated the risk factors for carotid plaque occurrence using the Cox proportional hazards model.

Results

A total of 107 people (76 men and 31 women; median age, 49 years) were enrolled. At baseline, fatty liver and a serum GGT level ≥50 U/L were observed in 13 and 38 people, respectively. During a median follow-up period of 13.3 years, carotid plaques appeared in 34 people. Multivariate analysis revealed that the combination of fatty liver and a serum GGT level ≥50 U/L was the only significant risk factor for carotid plaque occurrence (age- and sex-adjusted hazard ratio: 5.55; 95% confidence interval 1.70–18.14; P = 0.005).

Conclusion

The combination of fatty liver and increased serum GGT levels raises the risk for atherosclerotic plaque development in apparently healthy people.

The Therapeutic Potential of Nanoparticles to Reduce Inflammation in Atherosclerosis

Chronic inflammation is one of the main determinants of atherogenesis. The traditional medications for treatment of atherosclerosis are not very efficient in targeting atherosclerotic inflammation. Most of these drugs are non-selective, anti-inflammatory and immunosuppressive agents that have adverse effects and very limited anti-atherosclerotic effects, which limits their systemic administration. New approaches using nanoparticles have been investigated to specifically deliver therapeutic agents directly on atherosclerotic lesions. The use of drug delivery systems, such as polymeric nanoparticles, liposomes, and carbon nanotubes are attractive strategies, but some limitations exist. For instance, nanoparticles may alter the drug kinetics, based on the pathophysiological mechanisms of the diseases. In this review, we will update pathophysiological evidence for the use of nanoparticles to reduce inflammation and potentially prevent atherogenesis in different experimental models.

Rapid detection of metastatic lymph nodes of colorectal cancer with a gamma-glutamyl transpeptidase-activatable fluorescence probe

Rapid diagnosis of metastatic lymph nodes (mLNs) of colorectal cancer (CRC) is desirable either intraoperatively or in resected fresh specimens. We have developed a series of activatable fluorescence probes for peptidase activities that are specifically upregulated in various tumors. We aimed to discover a target enzyme for detecting mLNs of CRC. Among our probes, we found that gGlu-HMRG, a gamma-glutamyl transpeptidase (GGT)-activatable fluorescence probe, could detect mLNs. This was unexpected, because we have previously reported that gGlu-HMRG could not detect primary CRC. We confirmed that the GGT activity of mLNs was high, whereas that of non-metastatic lymph nodes and CRC cell lines was low. We investigated the reason why GGT activity was upregulated in mLNs, and found that GGT was induced under conditions of hypoxia or low nutritional status. We utilized this feature to achieve rapid detection of mLNs with gGlu-HMRG. GGT appears to be a promising candidate enzyme for fluorescence imaging of mLNs.

Targeting Inflammation With Nanosized Drug Delivery Platforms in Cardiovascular Diseases: Immune Cell Modulation in Atherosclerosis

Atherosclerosis (AS) is a disorder of large and medium-sized arteries; it consists in the formation of lipid-rich plaques in the intima and inner media, whose pathophysiology is mostly driven by inflammation. Currently available interventions and therapies for treating atherosclerosis are not always completely effective; side effects associated with treatments, mainly caused by immunodepression for anti-inflammatory molecules, limit the systemic administration of these and other drugs. Given the high degree of freedom in the design of nanoconstructs, in the last decades researchers have put high effort in the development of nanoparticles (NPs) formulations specifically designed for either drug delivery, visualization of atherosclerotic plaques, or possibly the combination of both these and other functionalities. Here we will present the state of the art of these subjects, the knowledge of which is necessary to rationally address the use of NPs for prevention, diagnosis, and/or treatment of AS. We will analyse the work that has been done on: (a) understanding the role of the immune system and inflammation in cardiovascular diseases, (b) the pathological and biochemical principles in atherosclerotic plaque formation, (c) the latest advances in the use of NPs for the recognition and treatment of cardiovascular diseases, (d) the cellular and animal models useful to study the interactions of NPs with the immune system cells.

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 (25^th-75^th) 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.

Gamma-glutamyltransferase and risk of cardiovascular mortality: A dose-response meta-analysis of prospective cohort studies

BACKGROUND

Serum gamma-glutamyltransferase (GGT) elevation likely contributes to cardiovascular (CV) mortality, however it has remained unknown whether a dose-response relationship exists between serum GGT and CV mortality.

METHODS

We searched the PubMed, EMBASE, and Cochrane library databases for prospective cohort studies published up to October 2, 2016. Summary hazard ratios (HRs) with their corresponding 95% confidence intervals (CIs) were calculated using a fixed effects model.

FINDINGS

Nine prospective studies, including 527,589 participants and more than 7,011 cases, were included in this meta-analysis. For the moderate, high, and highest levels of GGT, the pooled HRs of CV mortality were 1.11 (95% CI = 1.04-1.19), 1.29 (95% CI = 1.21-1.38) and 1.59 (95% CI = 1.47-1.72), respectively (all p < 0.05 as compared to the lowest levels of GGT). Additionally, the HR per incremental increase of GGT by 10 U/L was 1.10 (95% CI = 1.08-1.11). Evidence of a positive relationship with nonlinear trend for GGT elevation with CV mortality in females was found (P = 0.04 for nonlinearity). However, a linear model was better fit to illustrate the GGT-CV mortality among males (P = 0.304 for nonlinearity).

CONCLUSIONS

These findings indicate that serum GGT activity within the reference interval is positively associated with increased risk of CV mortality in a dose-response manner.

Macrophages' Role in Tissue Disease and Regeneration

Inflammation is an essential component of the normal mammalian host tissue response and plays an important role during cardiovascular and musculoskeletal diseases. Given the important role of inflammation on the host tissue response after injury, understanding this process represents essential aspects of biomedical research, tissue engineering, and regenerative medicine. Macrophages are central players during the inflammatory response with an extensive role during wound healing. These cells exhibit a spectrum of activation states that span from pro-inflammatory to pro-healing phenotypes. The phenotype of the macrophages can have profound influences on the progression of disease or injury. As such, understanding and subsequent modulation of macrophage phenotype represents an exciting target area for regenerative medicine therapies. In this chapter, we describe the role of macrophages in specific cases of injury and disease. After myocardial infarction, a biphasic response of pro- and anti-inflammatory macrophages are involved in the remodeling process. In volumetric muscle loss, there is an intricate communication between inflammatory cells and progenitor cells affecting repair processes. Osteoarthritis is characterized by increased levels of pro-inflammatory macrophages over an extended period of time with significant impact on the progression of the disease. By harnessing the complex role of macrophages, enhanced therapeutic treatments can be developed that enhance the normal healing response as well as help the survival of therapeutic cells delivered to the site of injury.

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.

Soluble sortilin is released by activated platelets and its circulating levels are associated with cardiovascular risk factors

OBJECTIVE

Sortilin is involved multilaterally in the development of atherosclerosis. Here, we examine the release of soluble sortilin (sSortilin) from platelets and assess the association between circulating levels of sSoritlin and atherothrombosis such as coronary artery disease (CAD).

METHODS AND RESULTS

sSortilin levels measured in healthy subjects were higher in serum than in plasma (38.4 ± 8.7 vs. 15.8 ± 2.9 ng/mL; p < 0.0001). Platelets were shown to contain both membrane-bound sortilin and its soluble form lacking the cytoplasmic tail. Stimulation of platelet-rich plasma with collagen induced sSortilin release concomitantly with platelet aggregation, and the release was suppressed by aspirin. In clinical evaluation, plasma sSortilin was detected at significantly higher levels in cardiovascular risk patients with hypertension, dyslipidemia, and/or diabetes without CAD (non-CAD, 18.7 ± 3.3 ng/mL) than in patients with CAD under aspirin therapy (17.1 ± 3.6 ng/mL; p < 0.01) or in healthy controls (16.8 ± 2.9 ng/mL; p < 0.01). In these patients, plasma sSortilin levels were significantly correlated with platelet counts (rs = 0.33; p = 0.0085) and showed significant positive associations with cardiovascular risk factors: low-density lipoprotein cholesterol (rs = 0.37; p = 0.0023), triglycerides (rs = 0.28; p = 0.023), and serum uric acid (rs = 0.30; p = 0.017) in non-CAD, and γ-glutamyltransferase (rs = 0.43; p = 0.020) and high-sensitivity C-reactive protein (rs = 0.33, p = 0.0022) in CAD.

CONCLUSION

Elevated plasma sSortilin levels may be associated with in vivo platelet activation and could be a risk factor for atherothrombosis.