gamma-Glutamyltransferase dependent generation of reactive oxygen species from a glutathione/transferrin system

Circulating angiopoietin-2 and soluble Tie-2 in type 2 diabetes mellitus: a cross-sectional study

BACKGROUND

Type 2 diabetes is associated with increased levels of Angiopoietin-2 (Ang-2) and soluble Tie-2 (sTie-2), but its impact on vascular disease is still unknown. This study aimed to further explore the associations of Ang-2 and sTie-2 with metabolic control and diabetic complications.

METHODS

In a cross-sectional designed study, levels of Ang-2 and sTie-2 as well as their relationships to cardiometabolic parameters were determined in 80 type 2 diabetic subjects (age 65 ± 7 years, female 47.4%).

RESULTS

After controlling for age and BMI, Ang-2 levels were associated with levels of sTie-2, diastolic blood pressure, plasma insulin, homeostasis model assessment of insulin resistance (HOMA-IR), creatinine, glomerular filtration rate (GFR), and gamma-glutamyl transferase (GGT) (all p < 0.02). Presence of diabetic macrovascular complications, polyneuropathy and insulin therapy were associated with higher Ang-2 levels (p < 0.05). Conversely, sTie-2 levels were associated with glycated hemoglobin (HbA1c), fasting plasma glucose and insulin, HOMA-IR, triglyceride, and liver function parameters (all p < 0.03). Multiple linear regression analysis showed that Ang-2 remained significantly associated only with levels of GGT (p < 0.04), whereas sTie-2 remained significantly associated with HbA(1c), insulin levels, and HOMA-IR (p < 0.03). No differences in Ang-2 and sTie-2 levels were observed with regard to gender of participants.

CONCLUSIONS

Ang-2 is independently associated with levels of GGT while sTie-2 is independently associated with levels of HbA(1c), plasma insulin and HOMA-IR in type 2 diabetic subjects. Therefore we suggest that the associations of Ang-2 and sTie-2 with type 2 diabetes are based on different patho-physiological mechanisms.

Antioxidant effects of fermented red ginseng extracts in streptozotocin- induced diabetic rats

The antioxidant activities of fermented red ginseng (FRG) were investigated in vitro and in vivo. The contents of total polyphenol and total flavonoid in FRG extracts were 17.01±2.00 μg/mg and 18.42±3.97 μg/mg, respectively. These extracts were capable of directly scavenging α, α-diphenyl-picrylhydrazyl free radicals. The antioxidative effects of the FRG extracts in streptozotocin (STZ)-induced diabetic rats were also investigated. The activities of plasma alanine transaminase, aspartate transaminase, and γ-glutamyltransferase were significantly decreased by extract administration as compared to an STZ control group. Hepatic glutathione content depleted by STZ treatment was significantly increased by treatment of the FRG extracts, but the elevation of lipid peroxide content induced by STZ was significantly decreased by the extracts. Activities of superoxide dismutase, catalase, glutathione peroxidase, and glutathione reductase decreased after STZ-treatment were recovered by the treatment of the FRG extracts. These results indicate that FRG extracts have antioxidative effets in STZ-induced diabetic rats.

Dynamic of oxidative and nitrosative stress markers during the convalescent period of stroke patients undergoing rehabilitation

Background

Stroke patients have a redox imbalance, a consequence of both the cerebrovascular event and the associated pathological conditions. Our study was aimed to investigate the dynamic of some oxidative and nitrosative markers during the convalescent phase of postacute stroke patients undergoing rehabilitation.

Methods

We assessed thiol, advanced oxidation protein product, protein carbonyl, 3-nitro-l-tyrosine, ceruloplasmin and oxidized LDL concentrations, as well as gamma-glutamyltranspeptidase (GGT) activity in 20 patients at the beginning of the hospitalization and at the discharge moment, respectively, and 24 apparently healthy controls.

Results

We found significantly increased values for GGT ( P = 0.04), ceruloplasmin ( P = 0.01) and protein carbonyl ( P = 0.04) in stroke patients at the hospitalization moment when compared with healthy controls, while total thiols were significantly decreased ( P = 0.002). Rehabilitation was associated with a significant decrease of protein carbonyl ( P = 0.03) and oxidized LDL particle concentrations ( P = 0.03), as well as GGT activity ( P = 0.02). At the hospitalization moment, both GGT and ceruloplasmin were significantly negatively correlated with non-proteic thiols ( r = −0.44, P = 0.049, and r = −0.53, P = 0.015, respectively) and significantly positively with protein carbonyls ( r = +0.80, P < 0.001, and r = +0.69, P < 0.001, respectively) suggesting putative roles of GGT and ceruloplasmin in the redox imbalance.

Conclusions

These results highlight the existence of a redox imbalance in postacute stroke patients, and the possible benefits of an antioxidant-based therapy for the recovery of these patients.

The Relationship between Serum Gamma-glutamyltransferase Level and Overweight in Korean Urban Children

BACKGROUND

Recently, it has been reported that gamma-glumyltransferase (GGT) is associated with various cardiovascular risk factors including overweight in adults. However, there are few studies on the relationship between GGT and cardiovascular risk factors in children. The aim of this study was to assess the relationship between serum GGT level and overweight in Korean urban children.

METHODS

This study was a cross-sectional study using data on 390 4th grade students of elementary schools in Gunpo, Korea. Children were divided into 4 groups according to gender-specific quartiles of serum GGT level. Body mass index, waist circumference and body fat percentage were quantified as adiposity indices.

RESULTS

All adiposity indices in children of the highest GGT level quartile were higher than those in children of the lowest quartile. Adjusted odd ratios on overweight of the highest quartile of GGT level compared to the lowest quartile were 14.40 (95% confidence interval [CI], 4.43 to 46.83) in boys and 2.94 (95% CI, 1.06 to 8.16) in girls.

CONCLUSION

This study shows that high serum GGT level is related with overweight in Korean urban children and this relationship is stronger in boys compared to girls.

The relationship of gamma-glutamyltransferase to aortic elastic properties in young patients with prehypertension

Some cross-sectional studies have demonstrated a positive association between serum gamma-glutamyltransferase (GGT) levels and blood pressure. Accordingly, we aimed to analyze serum GGT levels in patients with prehypertension and examine the relationship with aortic elasticity parameters. The study population consisted of 25 newly diagnosed prehypertensive individuals and 25 healthy control subjects. Aortic strain, distensibility index, and stiffness index beta were calculated from aortic diameters measured by echocardiography and blood pressures simultaneously measured by sphygmomanometry. Prehypertensive patients were detected to have significantly lower aortic distensibility and strain indexes compared to control subjects aortic distensibility. However, aortic stiffness index beta of the prehypertensive group was significantly higher compared to that of the control group (3.73 ± 1.41 vs. 2.97 ± 0.82, p = 0.02). The mean GGT levels were found to be higher in patients with prehypertension compared to those of controls (47.9 ± 15.9 U/L vs. 36.1 ± 9.4 U/L, p = 0.003). When multiple linear regression analysis was done to clarify the contributions of GGT to aortic elasticity adjusting for age, body mass index, uric acid, serum glucose, heart rate, low-density lipoprotein (LDL)-cholesterol, high-density lipoprotein (HDL)-cholesterol, and triglyceride, we observed that only serum GGT levels were significantly associated with aortic elasticity parameters (for aortic strain beta = -0.247, p < 0.001; for aortic distensibility beta = -0.108, p < 0.001; for stiffness index beta = 0.063, p < 0.001). Whatever the mechanism is, young patients with prehypertension have higher serum GGT levels compared to healthy control subjects. More importantly, increased GGT levels are independently associated with impaired aortic elasticity in patients with prehypertension.

Elevated Oxidative Stress Markers and its Relationship With Endothelial Dysfunction in Behçet Disease

Behçet’s disease (BD) is a multisystemic disorder characterized by endothelial dysfunction. However, the relationship between oxidative stress and endothelial function has not been clearly shown. We investigated the relationship between oxidative stress markers and endothelial function in patients with BD. Patients with BD (n = 40) having active disease and sex- and age-matched 40 controls were included. Endothelial function was assessed by flow-mediated dilatation (FMD) technique. Serum gamma-glutamyltransferase (GGT) and high-sensitive C-reactive protein levels (hsCRP) were measured in all participants. Brachial artery FMD was significantly lower in patients with BD than in controls. Gamma-glutamyltransferase and hsCRP levels were higher in patients with BD than in controls. Also, GGT and hsCRP levels were inversely correlated with endothelial function. Oxidative stress markers are elevated in patients with BD having active disease. This may be one of the reasons behind the vasculitis in active BD.

Hepatoprotective role of naringin on nickel-induced toxicity in male Wistar rats

Aim of the present study was planned to determine the protective role of naringin in attenuating the toxicity induced by nickel sulfate in rat liver. In this investigation nickel sulfate (20mg/kg body weight) was administered intraperitoneally for 20days to induce toxicity. Naringin was administered orally (20, 40 and 80mg/kg body weight) for 20days with intraperitoneal administration of nickel sulfate. Liver injury was measured by the increased activities of serum hepatic enzymes namely aspartate transaminase, alanine transaminase, alkaline phosphatase, gamma glutamyl transferase, lactate dehydrogenase and total bilirubin along with increased elevation of lipid peroxidation markers, thiobarbituric reactive acid substances, lipid hydroperoxides, protein carbonyl content and conjugated dienes. The toxic effect of nickel was also indicated by significantly decreased activities of enzymatic antioxidants like superoxide dismutase, catalase, glutathione peroxidase, glutathione-S-transferase, glutathione reductase and glucose-6-phosphate dehydrogenase and non-enzymatic antioxidants like reduced glutathione, total sulfhydryl groups, vitamin C and vitamin E levels were significantly decreased. Naringin administered at a dose of 80mg/kg body weight significantly reversed the activities of hepatic marker enzymes, decreasing lipid peroxidative markers, increasing the antioxidant cascade and decreasing the nickel concentration in the liver. The effect at a dose of 80mg/kg body weight was more pronounced than that of other two doses (20 and 40mg/kg body weight). All these changes were supported by histopathological observations. These results clearly demonstrate that naringin has the potential in alleviating the toxic effects of nickel in rat liver.

Serum gamma-glutamyl transferase and risk of heart failure in the community

OBJECTIVE

To examine the association of serum gamma-glutamyltransferase (GGT) with incident heart failure.

METHODS AND RESULTS

We related serum GGT to the incidence of heart failure in 3544 (mean age, 44.5 years; 1833 women and 1711 men) Framingham Study participants who were free of heart failure and myocardial infarction. On follow-up (mean, 23.6 years), 188 participants (77 women) developed new-onset heart failure. In multivariable Cox proportional hazards regression models adjusting for standard risk factors and alcohol consumption as time-varying covariates (updated every 4 years), each SD increase in log-GGT was associated with a 1.39-fold risk of heart failure (95% CI, 1.20 to 1.62). The linearity of the association was confirmed by multivariable-adjusted splines, and the relations remained robust on additional adjustment for hepatic aminotransferases and C-reactive protein. Participants with a serum GGT level at the median or greater had a 1.71-fold risk of heart failure (95% CI, 1.21 to 2.41) compared with individuals with GGT concentrations less than the median. GGT marginally increased the model C-statistic from 0.85 to 0.86 but improved the risk reclassification modestly (net reclassification index, 5.7%; P=0.01).

CONCLUSIONS

In this prospective study of a large community-based sample, higher serum GGT concentrations within the "normal" range were associated with greater risk of heart failure and incrementally improved prediction of heart failure risk.

Pooling-based genome-wide association study implicates gamma-glutamyltransferase 1 (GGT1) gene in pancreatic carcinogenesis

BACKGROUND/AIMS

Knowledge regarding genetic factors that influence pancreatic cancer risk is currently limited. To identify novel pancreatic cancer susceptibility loci, we conducted a two-stage genome-wide association study.

METHODS

The Affymetrix Genome-Wide Human SNP Array 6.0 and DNA pooling were used in the screening stage. Twenty-six single-nucleotide polymorphisms (SNPs) were selected for follow-up. These 26 lead SNPs and additionally selected tagSNPs for the regions around the lead SNPs were evaluated by individual genotyping of the pooling population and an independent validation population.

RESULTS

Of the lead SNPs, the strongest association was found with rs4820599 located in the gamma-glutamyltransferase 1 (GGT1) gene. This SNP was significantly associated with pancreatic cancer risk in the validation population and the combined dataset (p(allele-based) = 0.019 and p(allele-based) = 0.003, respectively). Statistically significant associations were also observed with two GGT1 tagSNPs: rs2017869 and rs8135987. Lead SNP rs4820599 is in high linkage disequilibrium (LD; pairwise r(2): 0.69) and tagSNP rs2017869 is in strong LD (pairwise r(2): 0.96) with SNP rs5751901, which has been reported to be associated with increased GGT1 serum levels. GGT is expressed in the pancreas and plays a key role in glutathione metabolism.

CONCLUSION

Our results suggest that common variation in the GGT1 gene may affect the risk of pancreatic cancer. .

The Association between Serum GGT Concentration and Diabetic Peripheral Polyneuropathy in Type 2 Diabetic Patients

BACKGROUND

Diabetic peripheral polyneuropathy (DPP) is one of the common complications of diabetes mellitus (DM) and can lead to foot ulcers or amputation. The pathophysiology of DPP includes several factors such as metabolic, vascular, autoimmune, oxidative stress and neurohormonal growth-factor deficiency and recent studies have suggested the use of serum gamma-glutamyl transferase (GGT) as an early marker of oxidative stress. Therefore, we investigated whether serum GGT may be useful in predicting DPP.

METHODS

We assessed 90 patients with type 2 DM who were evaluated for the presence of DPP using clnical neurologic examinations including nerve conduction velocity studies. We evaluated the association between serum GGT and the presence of DPP.

RESULTS

The prevalence of DPP was 40% (36 cases) according to clinical neurological examinations. The serum GGT concentration was significantly elevated in type 2 diabetic patients with DPP compared to patients without DPP (P < 0.01). There were other factors significantly associated with DPP including smoking (P = 0.019), retinopathy (P = 0.014), blood pressure (P < 0.05), aspartate aminotransferase (P = 0.022), C-reactive protein (P = 0.036) and urine microalbumin/creatinine ratio (P = 0.004). Serum GGT was independently related with DPP according to multiple logistic analysis (P < 0.01).

CONCLUSION

This study shows that increased levels of serum GGT may have important clinical implications in the presence of DPP in patients with type 2 diabetes.

Increased oxidative stress, decreased total antioxidant capacity, and iron overload in untreated patients with chronic hepatitis C

The aim of this study was to determine oxidative stress in patients with untreated chronic hepatitis C (CHC), relating the obtained results with iron status and disease activity markers. Two groups (CHC patients and controls) were studied. CHC patients presented significantly higher values than the control group in some parameters: ALT, AST, GGT, iron, ferritin, and transferrin saturation, and also in tert-butyl hydroperoxide initiate chemiluminescence and thiobarbituric acid-reactive substances (TBARS) as well as lower values in total radical-trapping antioxidant parameter (TRAP). TBARS showed a significant correlation with serum AST and with transferrin saturation, whereas TRAP correlated inversely with serum albumin. Serum ferritin correlated with ALT and GGT, whereas serum iron did so with GGT. In conclusion, lower antioxidant capacity, higher levels of pro-oxidants activity, and iron overload occur in untreated patients with CHC. This greater oxidative activity could play an important role in pathogenesis and evolution of hepatitis C and thus further investigations.

Serum gamma-glutamyltransferase within its normal range predicts a chronic elevation of alanine aminotransferase: A four year follow-up study

BACKGROUND

Previous epidemiological and experimental studies support the concept that serum gamma-glutamyltransferase (GGT) activity within its normal range is related to oxidative stress. Since oxidative stress plays a crucial role in the pathogenesis of various liver diseases, serum GGT may predict development of liver damage.

METHODS

A total of 6,523 healthy male workers with normal alanine aminotransferase (ALT, <35 U/l) in a steel manufacturing company were followed for four years. Liver damage was defined as a chronic elevation of serum ALT (both 2001 and 2002).

RESULTS

After adjusting for age, body mass index, alcohol consumption, cigarette smoking, exercise, and baseline value of ALT, in comparison with the group whose GGT level was <10 U/l, the adjusted relative risks for elevated ALT level among those with GGT levels 10-19, 20-29, 30-39, and over 40 U/l was 1.0, 2.5, 4.7, 7.4, and 12.0, respectively (P for trend <0.01). More importantly, this association was similarly observed even among non-drinkers; the corresponding relative risks were 1.0, 1.8, 3.8, 5.6, and 6.2 (P for trend <0.01). However baseline ALT did not predict abnormal GGT level four years later.

CONCLUSION

Serum GGT levels within normal range predict incidence of chronic elevation of ALT. Oxidative stress might explain this relationship.

Association of serum gamma-glutamyltransferase with C-reactive protein levels and white blood cell count in Korean adults

BACKGROUND

Elevated gamma-glutamyltransferase (GGT) has emerged as an independent predictor of cardiovascular disease (CVD) which is increasingly viewed as an inflammatory disease. Thus, the mechanism underlying the link between elevated GGT and CVD may be inflammation.

METHODS

We examined the relationship between GGT and C-reactive protein (CRP) levels and white blood cell (WBC) count in 4562 Korean adults (2104 men, 2458 women). The odds ratio (OR) and 95% confidence interval (CI) for high CRP and WBC count (> or = 75th percentile) for both men and women were calculated across each quartile of serum GGT.

RESULTS

Results for the OR (95% CI) for high CRP levels by GGT quartiles were 1.00, 1.67 (1.21-2.29), 2.10 (1.51-2.93) and 2.51 (1.81-3.60) in men, and 1.00, 1.05 (0.65-1.68), 1.45 (0.79-2.02) and 2.16 (1.37-3.41) in women after adjustment for age, smoking status, alcohol intake, exercise, body mass index, blood pressure, fasting plasma glucose, triglyceride, high-density lipoprotein-cholesterol, and uric acid. Similarly, positive associations between serum GGT and WBC count were also observed.

CONCLUSIONS

The present study demonstrates a positive correlation between GGT and two markers of inflammation, serum CRP and WBC count. Our findings suggest that serum GGT may be a surrogate inflammatory marker and a useful additional measure in assessing cardiovascular risk.

Gene expression and functional studies of the optic nerve head astrocyte transcriptome from normal African Americans and Caucasian Americans donors

PURPOSE

To determine whether optic nerve head (ONH) astrocytes, a key cellular component of glaucomatous neuropathy, exhibit differential gene expression in primary cultures of astrocytes from normal African American (AA) donors compared to astrocytes from normal Caucasian American (CA) donors.

METHODS

We used oligonucleotide Affymetrix microarray (HG U133A & HG U133A 2.0 chips) to compare gene expression levels in cultured ONH astrocytes from twelve CA and twelve AA normal age matched donor eyes. Chips were normalized with Robust Microarray Analysis (RMA) in R using Bioconductor. Significant differential gene expression levels were detected using mixed effects modeling and Statistical Analysis of Microarray (SAM). Functional analysis and Gene Ontology were used to classify differentially expressed genes. Differential gene expression was validated by quantitative real time RT-PCR. Protein levels were detected by Western blots and ELISA. Cell adhesion and migration assays tested physiological responses. Glutathione (GSH) assay detected levels of intracellular GSH.

RESULTS

Multiple analyses selected 87 genes differentially expressed between normal AA and CA (P<0.01). The most relevant genes expressed in AA were categorized by function, including: signal transduction, response to stress, ECM genes, migration and cell adhesion.

CONCLUSIONS

These data show that normal astrocytes from AA and CA normal donors display distinct expression profiles that impact astrocyte functions in the ONH. Our data suggests that differences in gene expression in ONH astrocytes may be specific to the development and/or progression of glaucoma in AA.

Plasma glutathione levels are independently associated with gamma-glutamyltransferase activity in subjects with cardiovascular risk factors

To investigate whether GGT (gamma-glutamyltransferase) is associated to specific redox patterns. GGT, total and reduced aminothiols and malondialdehyde, were measured in 150 subjects (83 males, 48 (39-56) years), with none, one or more risk factors. By univariable analysis GGT was positively associated with age (p =0.001), male gender (p <0.001), risk factor number (p <0.001), ACE-inhibitors (p =0.008), anti-platelet agents (p =0.029), atherothrombotic events (p =0.001), glucose (p =0.013), malondialdehyde (p =0.029), plasma total cysteine (p =0.046) and inversely associated with plasma total glutathione (p =0.001). By multivariable analysis only male gender (p <0.001), risk factor number (p <0.001) and glutathione (p <0.001) were independently associated with GGT activity. These findings suggest that an ongoing redox imbalance, in terms of decreased plasma glutathione, is associated with raised GGT activity in subjects with a greater risk factor burden.

Plasma gamma-glutamyl transferase activity predicts homocysteine concentration in a large cohort of unselected outpatients

OBJECTIVE

To evaluate the association between gamma-glutamyl transferase (GGT) and homocysteine in plasma.

METHODS

Combined results of GGT, total homocysteine, vitamin B12, folate and creatinine levels were analyzed in outpatients referred for laboratory testing over the past 5 years.

RESULTS

Cumulative results for homocysteine, GGT, B12, creatinine, folate could be retrieved for 449 outpatients > 35 years old over the study period. The concentration of homocysteine significantly increased among tertiles of GGT activity. In multivariable linear regression analysis, GGT activity was independently associated with homocysteine concentration, independent of age, gender, folate, vitamin B12 and serum creatinine levels.

DISCUSSION

Plasma GGT activity might be a useful means to predict homocysteine concentration in the general population.

Oxidative stress markers in oral lichen planus

Oral lichen planus (OLP) is a relatively common disorder whose cause is still unknown. Oral cancer is preceded in most cases by pre malignant lesions-leukoplasia, submucous fibrosis and lichen planus. Free radicals and reactive oxygen species play important roles in both pathogenesis of lichen planus and carcinogenesis. Thus monitoring systemic and saliva compounds important for the antioxidant defence (oxidative balance) could be important for the clinician's treatment strategy. Thorough medical management and early active treatment are necessary to improve symptoms and might also be a relevant prevention strategy from squamous cell carcinoma risk, although data to fully support this statement still need investigation. The principal aim of this study was to determine the systemic uric acid, GGT, and albumin levels as well as the levels of uric acid and albumin in 20 patients diagnosed with lichen planus and 20 controls. Extensive medline search failed to reveal any study of this type. Our results showed a significant decrease of saliva (p < 0.005) uric acid and an increase in serum gamma glutamyl transpherase (GGT) (p < 0.01) as well as in the total antioxidant capacity of saliva in patient group with respect to the control one. The preliminary conclusion of our study is that uric acid, the most important salivary antioxidant and GGT could be considered in the future as useful markers of oxidative stress for elaboration of treatment strategy and monitoring.

Serum gamma-glutamyl transferase activity: A new marker for stent restenosis?

Stent restenosis remains the main limitation of percutaneous coronary intervention. Elevated serum gamma-glutamyl transferase (GGT) level is associated with an inflammatory response. We aimed to determine the correlation of stent restenosis with the serums level of GGT. One hundred and twenty patients (age 58.56+/-10.46 years, 66% male) with a history of coronary stent implantation and had undergone control coronary angiography (60 with restenosis and 60 without) were included. All had baseline serum GGT activity and were free of systemic and hepatobiliary disease. Median baseline serum GGT activity was significantly higher in patients with restenosis (34.00 U/L (24.00-47.75)) than in those without restenosis (21.00 U/L (17.25-26.7500)) (P<0.0001). Stent restenosis was identified in 38% of the patients with a serum GGT value >40 U/L and in 5% of patients with a serum GGT value <or=40 U/L (P<0.001). Serum C-reactive protein (CRP) and total bilirubin levels were significantly higher (P=0.011 and 0.037, respectively) and alkaline phosphatase levels were significantly lower in patients with restenosis (P=0.029). Levels of GGT, CRP, and alkaline phosphatase were independent predictors of restenosis (P=0.001, 0.019 and 0.004, respectively). In conclusion, the serum level of GGT may be an independent marker for stent restenosis.

Gamma-glutamyltransferase, redox regulation and cancer drug resistance

Gamma-glutamyltransferase, a key enzyme of GSH metabolism, can modulate crucial redox-sensitive functions, such as antioxidant/antitoxic defences and cellular proliferative/apoptotic balance, with potential implications in tumour progression and drug resistance. Recent studies have elucidated the mechanisms of GGT involvement in various pathological processes suggesting its potential role as therapeutic target and diagnostic/prognostic marker.

Colorimetric coupled enzyme assay for γ-glutamyltransferase activity using glutathione as substrate

A colorimetric coupled enzyme assay for the determination of gamma-glutamyltransferase (GGT) activity using glutathione as substrate is described. The cysteine released from glutathione upon sequential action of GGT and leucine aminopeptidase is spectrophotometrically detected through its reaction with ninhydrin at 100 degrees C in acidic conditions. The method was applied to the determination of the activity of both bovine kidney and human serum GGT. In the described assay conditions with final GGT concentrations ranging from 0.18 to 4 mU/ml, a linear relationship between produced cysteine and incubation times up to 90 min was observed. When a standard chromogenic assay for GGT using L-gamma-glutamyl-3-carboxy-4-nitroanilide as substrate and the proposed assay were applied on the same serum sample a linear relationship between the two method was observed. Since the use of GSH as substrate, the proposed method can be usefully adopted for enzymological studies on GGT-related enzymes, a class of enzymes which is still waiting to be characterized.

Associations between gamma-glutamyl transferase, metabolic abnormalities and inflammation in healthy subjects from a population-based cohort: a possible implication for oxidative stress

AIM

To examine the relationships between gamma-glutamyl-transferase (GGT), alanine-aminotransferase (ALT), aspartate-aminotransferase (AST) and various metabolic parameters, C-reactive protein (CRP) and an oxidative stress marker (nitrotyrosine, NT) in subjects without any metabolic abnormalities from a population-based sample.

METHODS

Two hundred and five subjects with normal body mass index (BMI), glucose tolerance, and without any metabolic abnormality were studied out of 1 339 subjects, without known liver diseases, alcohol abuse or use of hepatotoxic drugs, who are representative of the 45-64 aged population of Asti (north-western Italy).

RESULTS

In all patients metabolic parameters and hs-CRP levels linearly increase from the lowest to the highest ALT and GGT tertiles, while in subjects without metabolic abnormalities, there is a significant association between fasting glucose, uric acid, waist circumference, hs-CRP, triglyceride values, and GGT levels. In these subjects, male sex, higher hs-CRP and glucose levels are associated with GGT levels in a multiple regression model, after adjustments for multiple confounders. In the same model, median NT levels are significantly associated with the increasing GGT tertile (beta = 1.06; 95%CI 0.67-1.45), but not with the AST and ALT tertiles. In a multiple regression model, after adjusting for age, sex, BMI, waist, smoking, and alcohol consumption, both NT (beta = 0.05; 95%CI 0.02-0.08) and hs-CRP levels (beta = 0.09; 95%CI 0.03-0.15) are significantly associated with fasting glycemia.

CONCLUSION

GGT, an easy, universally standardized and available measurement, could represent an early marker of sub-clinical inflammation and oxidative stress in otherwise healthy individuals. Prospective studies are needed to establish if GGT could predict future diabetes in these subjects.

Serum gamma-glutamyltransferase is a predictor of incident coronary events in apparently healthy men from the general population

OBJECTIVE

To investigate whether serum gamma-glutamyltransferase (GGT) is an independent predictor for incident coronary events in initially healthy men from the general population.

METHODS AND RESULTS

The study was based on 1878 men (aged 25-64 years) who participated in the first MONICA Augsburg survey 1984/1985, and who were free of coronary heart disease at baseline. Up to 2002 a total of 150 incident acute coronary events occurred. Baseline levels of GGT were higher in men who experienced an event than in event-free men (28.4+/-2.0 units/l versus 22.4+/-2.1 units/l, p 0.0002). GGT was highly correlated with other cardiovascular risk factors. In a Cox proportional hazards model after age adjustment hazard ratios (HR) for incident myocardial infarction across GGT quartiles (<13, 13 to <20, 20 to <35, and >/=35 units/l) were 1.0, 1.84, 2.02, and 3.08 (p for trend 0.0001). Further adjustment for hypertension, TC/HDL ratio, diabetes, smoking, physical activity, alcohol intake, education years and BMI attenuated the association; comparing the highest versus lowest quartile of GGT the HR for a first-ever coronary event was then 2.34 (95% CI, 1.23-4.44).

CONCLUSIONS

Serum GGT is a strong predictor of acute coronary events in apparently healthy men from the general population, independent of other risk factors for cardiovascular disease.

Prooxidant reactions promoted by soluble and cell-bound gamma-glutamyltransferase activity

Recent studies have provided evidence for the prooxidant roles played by molecular species originating during the catabolism of glutathione (GSH) effected by gamma-glutamyltransferase (GGT), an enzyme normally present in serum and on the outer surface of numerous cell types. The reduction of metal ions by GSH catabolites is capable of inducing the redox cycling processes, leading to the production of reactive oxygen species and other free radicals. Through the action of these reactive compounds, cell membrane GGT activity can ultimately produce oxidative modifications on a variety of molecular targets, involving oxidation and/or S-thiolation of protein thiol groups in the first place. This chapter is a survey of the procedures most suitable to reveal GGT-dependent prooxidant reactions and their effects at the cellular and extracellular level, including methods in histochemistry, cytochemistry, and biochemistry, with special reference to methods for the evaluation of protein thiol redox status.

Expression of gamma-glutamyltransferase in cancer cells and its significance in drug resistance

The expression of gamma-glutamyltransferase (GGT), a cell surface enzyme involved in cellular glutathione homeostasis, is often significantly increased in human tumors, and its role in tumor progression, invasion and drug resistance has been repeatedly suggested. As GGT participates in the metabolism of cellular glutathione, its activity has been mostly regarded as a factor in reconsitution of cellular antioxidant/antitoxic defences. On this basis, an involvement of GGT expression in resistance of cancer cells to cytotoxic drugs (in particular, cisplatin and other electrophilic agents) has been envisaged. Mechanistic aspects of GGT involvement in antitumor pharmacology deserve however further investigations. Recent evidence points to a more complex role of GGT in modulation of redox equilibria, with effects acting both intracellularly and in the extracellular microenvironment. Indications exist that the protective effects of GGT may be independent of intracellular glutathione, and derive rather from processes taking place at extracellular level and involving reactions of electrophilic drugs with thiol metabolites originating from GGT-mediated cleavage of extracellular glutathione. Although expression of GGT cannot be regarded as a general mechanism of resistance, the involvement of this enzyme in modulation of redox metabolism is expected to have impact in cellular response to several cytotoxic agents. The present commentary is a survey of data concerning the role of GGT in tumor cell biology and the mechanisms of its potential involvement in tumor drug resistance.

Role of diallyl tetrasulfide in ameliorating the cadmium induced biochemical changes in rats

Cadmium (Cd) is an ubiquitous environmental and occupational toxic metal concerned with a variety of adverse effects. The present study was undertaken to evaluate the role of diallyl tetrasulfide (DTS), an organosulfur compound in alleviating the Cd induced biochemical changes in male Wistar rats. During the experiment, rats were injected with Cd (3mg/(kgday)) subcutaneously alone or with oral administration of DTS at different doses (10, 20 and 40mg/(kgday)) for 3 weeks. In Cd treated rats, the activities of aspartate transaminase (AST), alanine transaminase (ALT), alkaline phosphatase (ALP), lactate dehydrogenase (LDH) and gamma glutamyl transferase (GGT) were significantly increased in serum with elevated levels of bilirubin, urea and creatinine. The hemoglobin level and creatinine clearance were also significantly decreased in Cd treated rats. In addition, the levels of plasma lipid peroxidation markers: thiobarbituric acid reactive substances and lipid hydroperoxides were significantly increased while the levels of plasma reduced glutathione (GSH), Vitamins C and E were significantly decreased in Cd administered rats. Administration of DTS along with Cd significantly decreased the serum, liver and kidney markers towards near normal level in a dose dependent manner. DTS at a dose of 40mg/(kgday) was highly effective when compared to other doses (10 and 20mg/(kgday)). DTS also significantly reduced the accumulation of Cd in blood and tissues as well as decreased the level of lipid peroxidation markers with elevation of antioxidants in plasma. All these changes were accompanied by histological observations in liver. The obtained results demonstrated the beneficial effect of DTS in reducing the harmful effects of Cd.

1,2,3,4-Tetrahydroisoquinoline protects terminals of dopaminergic neurons in the striatum against the malonate-induced neurotoxicity

Malonate, a reversible inhibitor of the mitochondrial enzyme succinate dehydrogenase, is frequently used as a model neurotoxin to produce lesion of the nigrostriatal dopaminergic system in animals due to particular sensitivity of dopamine neurons to mild energy impairment. This model of neurotoxicity was applied in our study to explore neuroprotective potential of 1,2,3,4-tetrahydroisoquinoline (TIQ), an endo- and exogenous substance whose function in the mammalian brain, despite extensive studies, has not been elucidated so far. Injection of malonate at a dose of 3 mumol unilaterally into the rat left medial forebrain bundle resulted in the 54% decrease in dopamine (DA) concentration in the ipsilateral striatum and, depending on the examined striatum regions, caused 24-44% reduction in [3H]GBR12,935 binding to the dopamine transporter (DAT). TIQ (50 mg/kg i.p.) administered 4 h before malonate infusion and next once daily for successive 7 days prevented both these effects of malonate. Such TIQ treatment restored DA content and DAT binding almost to the control level. The results of the present study indicate that TIQ may act as a neuroprotective agent in the rat brain. An inhibition of the enzymatic activities of monoamine oxidase and gamma-glutamyl transpeptidase as well as an increase in the striatal levels of glutathione and nitric oxide found after TIQ administration and reported in our earlier studies are considered to be potential factors that may be involved in the TIQ-mediated protection of dopamine terminals from malonate toxicity.

Serum γ-Glutamyltransferase Was Differently Associated with Microalbuminuria by Status of Hypertension or Diabetes: The Coronary Artery Risk Development in Young Adults (CARDIA) Study

Background: We hypothesized that serum γ-glutamyltransferase (GGT) would positively predict the risk of microalbuminuria, a frequent consequence of both diabetes and hypertension, because serum GGT predicted diabetes and hypertension in dose–response relationships.

Methods: In this prospective study, 2478 black and white men and women without microalbuminuria at year 10 provided urine samples 5 years later. Year 10 GGT cutpoints were 12, 18, and 29 U/L.

Results: The incidence of microalbuminuria across year 10 GGT categories was U-shaped. Adjusted odds ratios across quartiles of serum GGT were 1.0, 0.39, 0.54, and 0.94 (P &lt;0.01 for quadratic term), but the shape of association depended on the status of hypertension or diabetes (P &lt;0.01 for interaction). Among individuals who ever had hypertension or diabetes, year 10 serum GGT showed a clear positive dose–response association with incident microalbuminuria (P &lt;0.01 for trend), whereas among individuals with neither hypertension nor diabetes during the study, year 10 GGT showed a U-shaped association with it (P = 0.01 for quadratic term). When the long-term risk was evaluated in 3895 participants based on serum GGT at year 0 and prevalence of microalbuminuria at year 10 or year 15, the trends were similar but weaker than those of short-term incidence risk.

Conclusions: Serum GGT within the physiologic range predicted microalbuminuria among patients with hypertension or diabetes and may act as a predictor of microvascular and/or renal complications in these vulnerable groups. GGT showed a U-shaped association with microalbuminuria among persons who did not develop either hypertension or diabetes.

Treatment with 1,2,3,4-tetrahydroisoquinolone affects the levels of nitric oxide, S-nitrosothiols, glutathione and the enzymatic activity of γ-glutamyl transpeptidase in the dopaminergic structures of rat brain

Depletion of glutathione (GSH), nitrosative stress and chronic intoxication with some neurotoxins have been postulated to play a major role in the pathogenesis of Parkinson's disease. This study aimed to examine the effects of acute and chronic treatments with 1,2,3,4-tetrahydroisoquinoline (TIQ), an endo-/exogenous substance suspected of producing Parkinsonism in human, on the levels of nitric oxide (NO), S-nitrosothiols and glutathione (GSH) in the whole rat brain and in its dopaminergic structures. TIQ administered at a dose of 50 mg/kg i.p. significantly increased the tissue concentrations of NO and GSH in the substantia nigra (SN), striatum (STR) and cortex (CTX) of rats receiving this compound both acutely and chronically. Moreover, it decreased the level of oxidized glutathione (GSSG) and enhanced GSH:GSSG ratio affecting in this way the redox state of brain cells. TIQ also increased the level of S-nitrosothiols when measured in the whole rat brain and CTX, although it markedly decreased their level in the STR after both treatments. Inhibition of the constitutive NO synthase by l-NAME in the presence of TIQ caused decreases in GSH and S-nitrosothiol levels in the brain. The latter effect shows that the TIQ-mediated increases in GSH and S-nitrosothiol concentrations were dependent on the enhanced NO level. The above-described results suggest that TIQ can act as a modulator of GSH, NO and S-nitrosothiol levels but not as a parkinsonism-inducing agent in the rat brain.

Liver enzymes, the metabolic syndrome, and incident diabetes: the Mexico City diabetes study

OBJECTIVE

To test the hypothesis that enzymes conventionally associated with liver dysfunction (aspartate aminotransferase, alanine aminotransferase, gamma-glutamyltransferase [GGT], and alkaline phosphatase) may predict diabetes.

RESEARCH DESIGN AND METHODS

From a population-based diabetes survey, we selected 1,441 men and women in whom serum enzyme levels were < or =3 SDs of the mean population value, alcohol intake was <250 g/week, and hepatitis B and C virus testing was negative. At follow-up (7 years), 94 subjects developed diabetes and 93 impaired glucose tolerance (IGT).

RESULTS

At baseline, all four enzymes were related to most of the features of the metabolic syndrome. After controlling for sex, age, adiposity/fat distribution, alcohol intake, serum lipids, and blood pressure, higher alanine aminotransferase and GGT values were significantly (P < 0.01) associated with both IGT and diabetes, whereas alkaline phosphatase was associated with diabetes only (P = 0.0004) and aspartate aminotransferase with IGT only (P = 0.0001). Raised GGT alone was associated with all the features of the metabolic syndrome. Raised GGT was a significant predictor of either IGT or diabetes (odds ratio 1.62 [95% CI 1.08-2.42] top quartile vs. lower quartiles, P < 0.02) after controlling for sex, age, adiposity/fat distribution, alcohol consumption, fasting plasma insulin and proinsulin levels, and 2-h postglucose plasma glucose concentrations.

CONCLUSIONS

Although mild elevations in liver enzymes are associated with features of the metabolic syndrome, only raised GGT is an independent predictor of deterioration of glucose tolerance to IGT or diabetes. As GGT signals oxidative stress, the association with diabetes may reflect both hepatic steatosis and enhanced oxidative stress.

Association between serum gamma-glutamyltransferase and C-reactive protein

A series of epidemiological studies have suggested serum gamma glutamyltransferase (GGT) within its normal range might be an early marker of oxidative stress. Oxidative stress appears to be a key component of many reactions associated with chronic inflammation. Therefore, we examined the cross-sectional association between deciles of serum GGT and concentrations of serum C-reactive protein (CRP), a marker of chronic inflammation, among 12,110 adult participants in the third U.S. National Health and Nutrition Examination Survey. After adjustment for race, sex, age, cigarette smoking, alcohol intake, and body mass index (BMI), serum concentration of GGT across all deciles was positively associated with serum concentrations of CRP (P for trend<0.01). For example, adjusted relative risks of serum CRP> or =3.0mg/L by deciles of serum GGT were 1.0, 1.23, 1.40, 1.59, 1.62, 1.61, 2.17, 2.38, 2.45, and 3.41 (P for trend<0.01). This association was consistently observed among all subgroups; Non-Hispanic White, Non-Hispanic Black, Mexican American, men, women, non-drinkers, drinkers, non-smokers, ex-smokers, current smokers, BMI<25, BMI 25-29.9, and BMI> or =30. The strong association of serum GGT and CRP suggest that further studies on cellular and/or serum GGT might help to elucidate the association between oxidative stress and inflammation.

Urinary 20-hydroxyeicosatetraenoic acid excretion is associated with oxidative stress in hypertensive subjects

Oxidative stress has been implicated in the pathogenesis of hypertension. 20-Hydroxyeicosatetraenoic acid (20-HETE) is a cytochrome P450 product of arachidonic acid metabolism, thought to be involved in the regulation of blood pressure (BP). The metabolism of arachidonic acid by cytochrome P450 enzymes may be a significant source of oxidative stress. F2-isoprostanes are reliable markers of in vivo oxidative damage. gamma-Glutamyl transpeptidase (gamma-GT) has traditionally been associated with alcohol intake or liver dysfunction and may be an early marker of oxidative stress. The objective of the present study was to investigate relationships between 20-HETE excretion and markers of oxidative stress (F2-isoprostanes and gamma-GT). Sixty-nine treated hypertensive subjects underwent measurement of 24-h ambulatory BP, serum gamma-GT, and urinary F2-isoprostane and 20-HETE excretion. 20-HETE excretion was positively associated with 24-h diastolic BP (p = 0.005), alcohol intake (p = 0.008), gamma-GT (p = 0.007), and F2-isoprostanes (p = 0.005). F2-isoprostanes were positively associated with alcohol intake (p = 0.018) and gamma-GT (p = 0.01). In a multivariate regression, gamma-GT remained an independent predictor of 20-HETE excretion, after adjustment for age, gender, BMI, and alcohol intake. In conclusion, the study highlights the positive association observed between 20-HETE excretion and markers of oxidative damage. The study also provides evidence that gamma-GT may be a useful marker of oxidative stress.

Simultaneous analysis of host and pathogen interactions during an in vivo infection reveals local induction of host acute phase response proteins, a novel bacterial stress response, and evidence of a host-imposed metal ion limited environment

A fundamental goal in the study of infections is to understand the dynamic interplay between host and pathogen; however, direct in vivo interrogation of this disease process via transcriptional profiling has been lacking. Here we describe the development and application of novel bacterial RNA amplification technology to simultaneously identify key elements of both host and pathogen responses in a murine infection model. On the bacterial side, we found induction of an unusual pattern of stress response genes, a response to host-induced metal ion limitation, and a failure to achieve stationary phase in vivo. On the mammalian side, we observed the surprising induction of several genes encoding acute phase response proteins including hepcidin, haptoglobin, complement C3 and metallothionein 1 at the site of infection, as well as other mediators of innate immunity. Thus, our results reveal host-pathogen cross-talk not predicted by previous in vitro analyses and provide the framework to eavesdrop on a broad array of host-pathogen interactions in vivo. As described here, the comprehensive examination of host-pathogen interactions during an infection is critical to the discovery of novel approaches for intervention not predicted by current models.

Is serum gamma glutamyltransferase a marker of oxidative stress?

The primary role of cellular gamma glutamyltransferase (GGT) is to metabolize extracellular reduced glutathione (GSH), allowing for precursor amino acids to be assimilated and reutilized for intracellular GSH synthesis. Paradoxically, recent experimental studies indicate that cellular GGT may also be involved in the generation of reactive oxygen species in the presence of iron or other transition metals. Although the relationship between cellular GGT and serum GGT is not known and serum GGT activity has been commonly used as a marker for excessive alcohol consumption or liver diseases, our series of epidemiological studies consistently suggest that serum GGT within its normal range might be an early and sensitive enzyme related to oxidative stress. For example, serum and dietary antioxidant vitamins had inverse, dose-response relations to serum GGT level within its normal range, whereas dietary heme iron was positively related to serum GGT level. More importantly, serum GGT level within its normal range positively predicted F2-isoprostanes, an oxidative damage product of arachidonic acid, and fibrinogen and C-reactive protein, markers of inflammation, which were measured 5 or 15 years later, in dose-response manners. These findings suggest that strong associations of serum GGT with many cardiovascular risk factors and/or events might be explained by a mechanism related to oxidative stress. Even though studies on serum and/or cellular GGT is at a beginning stage, our epidemiological findings suggest that serum GGT might be useful in studying oxidative stress-related issues in both epidemiological and clinical settings.

Is serum gamma-glutamyltransferase inversely associated with serum antioxidants as a marker of oxidative stress?

A series of studies in black and white women and men have suggested that serum gamma-glutamyltransferase (GGT) within its normal range might be an early marker of oxidative stress. If serum GGT is a marker of oxidative stress, it might have important implications both clinically and epidemiologically because measurement of serum GGT is easy, reliable, and not expensive. We examined the cross-sectional association between deciles of serum GGT and concentrations of serum antioxidants among 9083 adult participants in the third U.S. National Health and Nutrition Examination Survey. After adjustment for race, sex, age, and total cholesterol, serum concentration of GGT across all deciles was inversely associated with serum concentrations of alpha-carotene, beta-carotene, beta-cryptoxanthin, zeaxanthin/lutein, lycopene, and vitamin C (p for trend <.01, respectively). Vitamin E was not associated with serum GGT. All these associations were not materially different after additional adjustment for total energy intake, body mass index, smoking status, smoking amount, alcohol intake, and exercise. These associations were similarly observed among most subgroups. In conclusion, the current and previous studies strongly suggest that serum GGT level within its normal range may be an early marker of oxidative stress.

Thiols, malonaldehyde and total antioxidant status in the Turkish patients with type 2 diabetes mellitus

Non-insulin dependent (Type 2) diabetes mellitus (NIDDM) is a risk factor for cardiovascular diseases (CVD). Oxidative stress mechanisms are often reported to be implied in type 2 diabetes mellitus. In order to determine their clinical relevance, we investigated several plasma indicators in the Turkish patients with NIDDM: (i) homocysteine (Hcy) and cysteine (Cys) which contribute to increase the risk of atherosclerosis during NIDDM, (ii) glutathione (GSH) and cysteinylglycine (CysGly) resulting from GSH degradation catalyzed by gamma-glutamylcysteine transferase (GGT), (iii) malonaldehyde (MDA) as a marker for lipid peroxidation, and (iv) total antioxidant status (TAS). Our main results were evaluated based on sex and diabetic status. In female patients, plasma concentrations of MDA and Hcy were significantly higher than in controls, while GSH levels were significantly lower. In males, a difference between control and diabetic groups was noticed only for Hcy, levels being also higher in patients. In the diabetic group, increase in serum glucose concentration was significantly correlated with increased GGT activity. In both controls and diabetic patients, GGT activity was correlated with a raised Cys concentration and a decreased GSH level. In both controls and diabetic patients, there were significant positive correlations between Cys and Hcy and between GSH and Hcy. We concluded that GSH and MDA levels are clinical indicators for an oxidative process linked to type 2 diabetes mellitus, especially in women.

Helicobacter pylori gamma-glutamyltranspeptidase upregulates COX-2 and EGF-related peptide expression in human gastric cells

Gastric mucosa responds to Helicobacter pylori-induced cell damage by increasing the expression of COX-2 and EGF-related peptides. We sought to investigate the bacterial virulence factor/s and the host cellular pathways involved in the upregulation of COX-2, HB-EGF and amphiregulin in MKN 28 and AGS gastric mucosal cells. H. pylori strain CCUG 17874 was grown in Brucella broth supplemented with 0.2% (2,6-dimethyl)-beta-cyclodextrins. The soluble proteins released in the culture medium by the bacterium were fractionated by exclusion size and anion exchange chromatography. A single peak retaining the ability to upregulate COX-2 and HB-EGF mRNA and protein expression was obtained. SDS-PAGE analysis of the peak showed two peptides with an apparent molecular weight of 38 and 22 kDa, which were identified by automated Edman degradation analysis as the N-terminal and C-terminal peptides of H. pylori gamma-glutamyltranspeptidase respectively. Acivicin, a selective gamma-glutamyltranspeptidase inhibitor, counteracted H. pylori-induced upregulation of COX-2 and EGF-related peptide mRNA expression. An H. pylori isogenic mutant gamma-glutamyltranspeptidase-deficient strain did not exert any effect on COX-2, HB-EGF and amphiregulin mRNA expression. Blockade of phosphatidylinositol-3 kinase and p38 kinase, but not MAP kinase kinase, inhibited H. pylori gamma-glutamyltranspeptidase-induced upregulation of COX-2 and EGF-related peptide mRNA expression.

Gamma-glutamyltransferase: an effect modifier in the association between age and hypertension in a 4-year follow-up study

We performed a prospective study to assess whether the relationship of age with hypertension was stronger in men with high normal serum gamma glutamyltransferase (GGT) than in those with lower GGT levels. The study population included 8170 healthy male workers in a steel manufacturing company who had undergone health examinations in both 1994 and 1998. The higher the baseline GGT level, the effect of age on the development of hypertension was stronger. The incidence of hypertension among those aged 25-34, 35-44 and 45-50 years was 0.9, 2.2, 3.8% in those with GGT<20 U/l; 1.0, 4.1, 12.5% in those with GGT between 20 and 39 U/l; and 1.9, 6.3, 17.2% in those with GGT> or =40 U/l, respectively. All relationships persisted after adjusting for baseline values of body mass index, alcohol intake, smoking, exercise, family history of hypertension, systolic and diastolic blood pressure, and changes of body mass index during 4 years (P for interaction=0.03). Our data supported the hypothesis that the effect of age on the development of hypertension differed by baseline GGT level, although the underlying mechanism for this interaction is unclear.

New role for leucyl aminopeptidase in glutathione turnover

A manganese-dependent cysteinyl-glycine hydrolysing activity has been purified to electrophoretic homogeneity from bovine lens. The characterization of the purified enzyme (molecular mass of the native protein, molecular mass of the subunit and extensive primary structure analysis) allowed the unequivocal attribution of the cysteinyl-glycine hydrolysing activity, which is usually associated with alanyl aminopeptidase (EC 3.4.11.2) or membrane-bound dipeptidase (EC 3.4.13.19), to LAP (leucyl aminopeptidase; EC 3.4.11.1). Analysis of the pH dependence of Cys-Gly hydrolysis catalysed by LAP, supported by a molecular modelling approach to the enzyme-substrate conformation, gave insights into the ability of the enzyme to recognize Cys-Gly as a substrate. Due to the effectiveness of LAP in hydrolysing Cys-Gly (K(m)=0.57 mM, kcat=6.0x10(3) min(-1) at pH 7.4 and 25 degrees C) with respect to other dipeptide substrates, a new role for this enzyme in glutathione turnover is proposed.

Gamma-glutamyltransferase is a predictor of incident diabetes and hypertension: the Coronary Artery Risk Development in Young Adults (CARDIA) Study

BACKGROUND

Gamma-glutamyltransferase (GGT), which maintains cellular concentrations of glutathione, may be a marker of oxidative stress, and GGT itself may produce oxidative stress. We performed a prospective study to examine whether serum GGT predicts diabetes and hypertension.

METHODS

Study participants were 4844 black and white men and women 18-30 years of age in 1985-1986; they were reexamined 2, 5, 7, 10, and 15 years later. Year 0 GGT cutpoints were 12, 17, 25, and 36 U/L (overall 25th, 50th, 75th, and 90th percentiles; the laboratory cutpoints for abnormal are 40 U/L in women and 50 U/L in men). We deleted 32 participants with prevalent diabetes and 140 participants with prevalent hypertension from the respective incidence analyses.

RESULTS

After adjustment for study center, race, sex, and age in proportional hazards regression, the hazard ratios across year 0 GGT categories were 1.0, 1.6, 1.7, 4.0 (95% confidence interval, 2.0-8.1), and 5.5 (2.7-11.1) for 15-year incident diabetes and 1.0, 1.2, 1.7 (1.2-2.2), 2.3 (1.7-3.2), and 2.3 (1.7-3.2) for hypertension. Additional adjustment for year 0 alcohol consumption, body mass index, cigarette smoking, and physical activity attenuated this relationship, but GGT remained a significant predictor.

CONCLUSIONS

Serum GGT within a range regarded as physiologically normal is associated with incident diabetes and hypertension. Considering known functionality of GGT, these associations are consistent with a role for oxidative stress in risk for diabetes and hypertension.

Gamma-glutamyltransferase and diabetes--a 4 year follow-up study

AIMS/HYPOTHESIS

Gamma-glutamyltransferase (GGT) is located on the external surface of most cells and mediates the uptake of gluthathione, an important component of intracellular antioxidant defenses. An increase in GGT concentration has been regarded as a marker of alcohol consumption or liver disease. However, more subtle gradations in GGT could be informative because its expression is enhanced by oxidative stress and it could be released by several conditions inducing cellular stress. Recently, serum GGT concentrations have been associated with many cardiovascular disease risk factors or components of the insulin resistance syndrome. We did a prospective study with the hypothesis that serum GGT is a predictor of incident diabetes.

METHODS

A total of 4,088 healthy men working in a steel manufacturing company were examined in 1994 and 1998. Diabetes was defined as a serum fasting glucose concentration of more than 126 mg/dl or the use of diabetes medication.

RESULTS

There was a strong dose-response relation between serum GGT concentrations at baseline and the incidence of diabetes. In contrast to the 31% of men with GGT concentrations under 9 U/l, adjusted relative risks for incidence of diabetes for GGT concentrations 10-19, 20-29, 30-39, 40-49, and over 50 U/l were 8.0, 13.3, 12.6, 19.6 and 25.8, respectively. The associations of age and BMI with incident diabetes became stronger the higher the value of baseline serum GGT concentration.

CONCLUSION/INTERPRETATION

This study suggests that an increase in GGT concentration within its physiological range is a sensitive and early biomarker for the development of diabetes.