Nitrogen dioxide exposure activates gamma-glutamyl transferase gene expression in rat lung

Exposure to ambient air pollution and elevated blood levels of gamma-glutamyl transferase in a large Austrian cohort

Gamma glutamyl transferase (GGT) is related to oxidative stress and an indicator for liver damage. We investigated the association between air pollution and GGT in a large Austrian cohort (N = 116,109) to better understand how air pollution affects human health. Data come from voluntary prevention visits that were routinely collected within the Vorarlberg Health Monitoring and Prevention Program (VHM&PP). Recruitment was ongoing from 1985 to 2005. Blood was drawn and GGT measured centralized in two laboratories. Land use regression models were applied to estimate individuals' exposure at their home address for particulate matter (PM) with a diameter of <2.5 μm (PM2.5), <10 μm (PM10), fraction between 10 μm and 2.5 μm (PMcoarse), as well as PM2.5 absorbance (PM2.5abs), NO₂, NO_x and eight components of PM. Linear regression models, adjusting for relevant individual and community-level confounders were calculated. The study population was 56 % female with a mean age of 42 years and mean GGT was 19.0 units. Individual PM2.5 and NO₂ exposures were essentially below European limit values of 25 and 40 μg/m³, respectively, with means of 13.58 μg/m³ for PM2.5 and 19.93 μg/m³ for NO₂. Positive associations were observed for PM2.5, PM10, PM2.5abs, NO₂, NO_x, and Cu, K, S in PM2.5 and PM10 fractions and Zn mainly in PM2.5 fraction. The strongest association per interquartile range observed was an increase of serum GGT concentration by 1.40 % (95 %-CI: 0.85 %; 1.95 %) per 45.7 ng/m³ S in PM2.5. Associations were robust to adjustments for other biomarkers, in two-pollutant models and the subset with a stable residential history. We found that long-term exposure to air pollution (PM2.5, PM10, PM2.5abs, NO₂, NO_x) as well as certain elements, were positively associated with baseline GGT levels. The elements associated suggest a role of traffic emissions, long range transport and wood burning.

Association between empirically derived dietary patterns and liver function tests in adults: Shahedieh cohort study

OBJECTIVES

Limited data exist on the association between dietary patterns (DPs) and enzymes mainly produced by the liver. This study aimed to examine the relationship between empirically derived DPs and serum alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, and gamma glutamyl transferase (GGT) levels in addition to the alanine/aspartate aminotransferase ratio.

METHODS

This cross-sectional study was conducted on adults in the baseline phase of the Shahedieh cohort study in Yazd, Iran. Blood samples were taken from participants in a fasted state to provide data on dietary intake and other variables. Major DPs were derived using a principal component analysis.

RESULTS

In total, 4973 participants (age 46.33 ± 9.08 y) were included in the study. Three DPs were derived: Traditional diet (high in vegetables, fruits, tomatoes, dairy, dried fruits, fruit juice, yogurt, olive and olive oil, sweet desserts, and high-fat dairy products), western diet (high in pizza, refined grains, soft drinks, high-fat dairy products, processed meats, mayonnaise, and snack foods), and hydrogenated fat and sugar diet (high in hydrogenated fat, potatoes, sugars, and legumes). After adjustment for all confounders, the western DP had a significant linear association with serum GGT (P < 0.001). This diet was also associated with higher odds for developing abnormal levels of serum GGT (P_trend < 0.001). Although the other DPs had some linear associations with enzymes levels, they were not associated with the likelihood for developing abnormally high liver enzymes levels.

CONCLUSIONS

A higher consumption of a western DP might adversely affect serum GGT levels. Prospective studies are recommended to confirm our results.

Gamma Glutamyl Transpeptidase, Smokeless Tobacco, Chronic Periodontitis: Exploring the Link

INTRODUCTION

Oxidative Stress (OS) is implicated in the pathogenesis of many systemic and oral diseases such as periodontal disease. Smokeless tobacco extract produces apoptosis and causes an imbalance between reactive oxygen species and antioxidants, such as Gamma Glutamyl Transpeptidase (GGT). Epidemiological research implied serum GGT within its normal range to be an early sensitive enzyme related to OS.

AIM

To assess how GGT fares as a biomarker in periodontitis subjects with or without the usage of smokeless tobacco and correlate it with clinical parameters.

MATERIALS AND METHODS

Ninety subjects were divided into three groups of healthy, chronic periodontitis, and smokeless tobacco users with chronic periodontitis from the dental outpatient department of P.M. Nadagouda Memorial Dental College and Hospital. Serum samples of patients were collected after obtaining consent and analyzed for GGT. Statistical Analysis was performed using ANOVA, and Pearson's correlation coefficient.

RESULTS

GGT levels were found to be significantly higher in chronic periodontitis patients compared to smokeless tobacco users with chronic periodontitis and healthy subjects. Conclusion: GGT may be used as a quick, easy and precise marker for measuring OS in patients with chronic periodontitis and smokeless tobacco users.

Pulmonary epithelial cancer cells and their exosomes metabolize myeloid cell-derived leukotriene C4 to leukotriene D4

Leukotrienes (LTs) play major roles in lung immune responses, and LTD4 is the most potent agonist for cysteinyl LT1, leading to bronchoconstriction and tissue remodeling. Here, we studied LT crosstalk between myeloid cells and pulmonary epithelial cells. Monocytic cells (Mono Mac 6 cell line, primary dendritic cells) and eosinophils produced primarily LTC4 In coincubations of these myeloid cells and epithelial cells, LTD4 became a prominent product. LTC4 released from the myeloid cells was further transformed by the epithelial cells in a transcellular manner. Formation of LTD4 was rapid when catalyzed by γ-glutamyl transpeptidase (GGT)1 in the A549 epithelial lung cancer cell line, but considerably slower when catalyzed by GGT5 in primary bronchial epithelial cells. When A549 cells were cultured in the presence of IL-1β, GGT1 expression increased about 2-fold. Also exosomes from A549 cells contained GGT1 and augmented LTD4 formation. Serine-borate complex (SBC), an inhibitor of GGT, inhibited conversion of LTC4 to LTD4 Unexpectedly, SBC also upregulated translocation of 5-lipoxygenase (LO) to the nucleus in Mono Mac 6 cells, and 5-LO activity. Our results demonstrate an active role for epithelial cells in biosynthesis of LTD4, which may be of particular relevance in the lung.

Risks of borderline liver enzyme abnormalities to the incidence of impaired fasting glucose and diabetes mellitus: a 7 year follow up study of workers

Background

The aim of this study was to identify the relationships between borderline serum liver enzyme abnormalities and the incidence of impaired fasting glucose (IFG) and diabetes mellitus (DM) during a 7-year follow-up of workers, and to evaluate the quantitative level of risks.

Methods

A total of 749 workers in an electronics manufacturing company were divided into the normal fasting blood glucose (n = 633), IFG (n = 98), and DM (n = 18) groups, according to the results of their health checkup in 2006. Among 633 workers in the normal group, excluding 55 workers who were impossible to follow, incidence rate and relative risks of 578 workers to the IFG or DM in 2013 according to the levels of aspartate aminotransferase (AST), alanine aminotransferase (ALT), and gamma-glutamyltransferase (γ-GTP) were investigated. The liver enzyme levels were categorized as A (normal), B (borderline elevation), and R (definite elevation) following the standard of the National Health Insurance Service of Korea.

Results

The incidence rate of IFG or DM based on ALT level was 9.7 % for the A, 30.0 % for B, and 15.4 % for R. According to γ-GTP, the incidence rate was 9.8 % for A, 34.5 % for B, and 25.0 % for R. The relative risk(RR) to the incidence of IFG or DM depending on the level of ALT were 3.09 in B and 1.59 in R compared to A. According to γ-GTP, RR was 3.52 in B and 2.55 in R compared to A. AST level was not related to the incidence of IFG or DM. A multiple logistic regression analysis with the incidence of IFG or DM as a dependent variable resulted in an odds ratio of 2.664(1.214–5.849) for B level ALT, 3.685(1.405–9.667) for B level of γ-GTP even after adjustment for other variables such as age, sex, body mass index, AUDIT score, systolic blood pressure, and triglyceride.

Conclusions

Even borderline elevations of ALT and γ-GTP, but not AST, increased the incidence and risk of IFG or DM after 7 years. Borderline elevation of ALT and γ-GTP was identified as an independent risk factor of IFG or DM.

Serum γ-Glutamyl Transferase Is Inversely Associated with Bone Mineral Density Independently of Alcohol Consumption

BACKGROUND

γ-Glutamyl transferase (GGT) is a well-known marker of chronic alcohol consumption or hepatobiliary diseases. A number of studies have demonstrated that serum levels of GGT are independently associated with cardiovascular and metabolic disorders. The purpose of this study was to test if serum GGT levels are associated with bone mineral density (BMD) in Korean adults.

METHODS

A total of 462 subjects (289 men and 173 women), who visited Severance Hospital for medical checkup, were included in this study. BMD was measured using dual energy X-ray absorptiometry. Cross-sectional association between serum GGT and BMD was evaluated.

RESULTS

As serum GGT levels increased from the lowest tertile (tertile 1) to the highest tertile (tertile 3), BMD decreased after adjusting for confounders such as age, body mass index, amount of alcohol consumed, smoking, regular exercise, postmenopausal state (in women), hypertension, diabetes mellitus, and hypercholesterolemia. A multiple linear regression analysis showed a negative association between log-transformed serum GGT levels and BMD. In a multiple logistic regression analysis, tertile 3 of serum GGT level was associated with an increased risk for low bone mass compared to tertile 1 (odds ratio, 2.271; 95% confidence interval, 1.340 to 3.850; P=0.002).

CONCLUSION

Serum GGT level was inversely associated with BMD in Korean adults. Further study is necessary to fully elucidate the mechanism of the inverse relationship.

Association of γ-glutamyl transferase with premature coronary artery disease

Accumulating evidence from epidemiological studies suggests that higher γ-glutamyl transferase (GGT) levels in the blood are associated with the incident of cardiovascular disease (CVD), including atherosclerosis, and have prognostic importance. However, to the best of our knowledge, the association of the GGT level with premature coronary artery disease (CAD) in an Asian Indian population has not been evaluated. In the present study, 240 (120 unaffected and 120 CAD affected) young subjects (males, ≤45 years and females, ≤50 years) were selected. The markers assayed were GGT, high-sensitivity C-reactive protein, lipids, secretory phospholipase A2, neopterin, myeloperoxidase, interleukin-6, cystatin-C, tumor necrosis factor-like weak inducer of apoptosis and lipoprotein (a). The plasma GGT levels in these subjects showed a positive correlation with quantitative variables, such as waist circumference, triglycerides, neopterin levels and cross-sectional correlation with qualitative variable smoking. The findings suggest that the subjects in the highest tertile of GGT had a 2.1-fold [odds ratio (OR), 2.104; 95% confidence interval (CI), 1.063-4.165; P=0.033] higher risk of developing premature CAD in comparison with the reference tertile. Furthermore, a 1 U/l increase of GGT (on a log scale) increased the OR by 5.2-fold (OR, 5.208; 95% CI, 1.018-24.624; P=0.048) and 7.4-fold (OR, 7.492; 95% CI, 1.221-45.979; P=0.030) on addition of associated risk factors. In conclusion, the elevated plasma GGT levels potentially indicate increased oxidative stress and the risk of developing premature CAD. Therefore, these findings could be potentially used in the risk stratification of premature CAD following further evaluation.

Gamma-glutamyl transpeptidase: redox regulation and drug resistance

The expression of gamma-glutamyl transpeptidase (GGT) is essential to maintaining cysteine levels in the body. GGT is a cell surface enzyme that hydrolyzes the gamma-glutamyl bond of extracellular reduced and oxidized glutathione, initiating their cleavage into glutamate, cysteine (cystine), and glycine. GGT is normally expressed on the apical surface of ducts and glands, salvaging the amino acids from glutathione in the ductal fluids. GGT in tumors is expressed over the entire cell membrane and provides tumors with access to additional cysteine and cystine from reduced and oxidized glutathione in the blood and interstitial fluid. Cysteine is rate-limiting for glutathione synthesis in cells under oxidative stress. The induction of GGT is observed in tumors with elevated levels of intracellular glutathione. Studies in models of hepatocarcinogenesis show that GGT expression in foci of preneoplastic hepatocytes provides a selective advantage to the cells during tumor promotion with agents that deplete intracellular glutathione. Similarly, expression of GGT in tumors enables cells to maintain elevated levels of intracellular glutathione and to rapidly replenish glutathione during treatment with prooxidant anticancer therapy. In the clinic, the expression of GGT in tumors is correlated with drug resistance. The inhibitors of GGT block GGT-positive tumors from accessing the cysteine in extracellular glutathione. They also inhibit GGT activity in the kidney, which results in the excretion of GSH in the urine and a rapid decrease in blood cysteine levels, leading to depletion of intracellular GSH in both GGT-positive and GGT-negative tumors. GGT inhibitors are being developed for clinical use to sensitize tumors to chemotherapy.

Inhibiting lung lining fluid glutathione metabolism with GGsTop as a novel treatment for asthma

Asthma is characterized by airway inflammation. Inflammation is associated with oxidant stress. Airway epithelial cells are shielded from this stress by a thin layer of lung lining fluid (LLF) which contains an abundance of the antioxidant glutathione. LLF glutathione metabolism is regulated by γ-glutamyl transferase (GGT). Loss of LLF GGT activity in the mutant GGT^enu1 mouse causes an increase in baseline LLF glutathione content which is magnified in an IL-13 model of allergic airway inflammation and protective against asthma. Normal mice are susceptible to asthma in this model but can be protected with acivicin, a GGT inhibitor. GGT is a target to treat asthma but acivicin toxicity limits clinical use. GGsTop is a novel GGT inhibitor. GGsTop inhibits LLF GGT activity only when delivered through the airway. In the IL-13 model, mice treated with IL-13 and GGsTop exhibit a lung inflammatory response similar to that of mice treated with IL-13 alone. But mice treated with IL-13 and GGsTop show attenuation of methacholine-stimulated airway hyper-reactivity, inhibition of Muc5ac and Muc5b gene induction, decreased airway epithelial cell mucous accumulation and a fourfold increase in LLF glutathione content compared to mice treated with IL-13 alone. Mice treated with GGsTop alone are no different from that of mice treated with saline alone, and show no signs of toxicity. GGsTop could represent a valuable pharmacological tool to inhibit LLF GGT activity in pulmonary disease models. The associated increase in LLF glutathione can protect lung airway epithelial cells against oxidant injury associated with inflammation in asthma.

Relationship of serum gamma-glutamyltransferase levels with pulmonary function and chronic obstructive pulmonary disease

BACKGROUND

Gamma-glutamyltransferase (GGT) levels within the normal reference range, possibly a biomarker of oxidative stress and/or exposure to various environmental chemicals, are associated with pulmonary function. However, it is unclear whether it is totally independent of cigarette smoking. Also, the potential interaction between serum GGT and cigarette smoking has not ever been evaluated. Therefore, this study investigated (1) whether serum GGT levels are associated with pulmonary function and chronic obstructive pulmonary disease (COPD), independent of cigarette smoking, and (2) whether there is any interaction between serum GGT and cigarette smoking status on pulmonary function.

METHODS

The study subjects were 4,583 participants aged ≥ 40 in the 2010-2011 Korean National Health and Nutrition Examination Survey. The outcomes were pulmonary function (forced expiratory volume in 1 second [FEV1] and forced vital capacity [FVC]) and spirometrically defined COPD.

RESULTS

After adjusting for potential confounders, including cigarette smoking, serum GGT levels were inversely associated with FEV1 and FVC in both genders and positively associated with the risk of COPD in men (all P values < 0.01). In men, adjusted odds ratios of COPD were 1.0, 1.69, 1.97, and 2.02 across the quartiles of GGT level (P trend = 0.002). However, the associations between serum GGT and pulmonary function seemed to differ depending on the smoking status; inverse associations of GGT with FEV1 % and FVC % were clearly observed only among non-current smokers.

CONCLUSIONS

In conclusion, in non-smokers serum GGT levels can be used to detect individuals at high risk of decreased pulmonary function and/or COPD.

The association between liver enzymes and risk of type 2 diabetes: the Namwon study

BACKGROUND

We examined the association between liver enzymes and development of type 2 diabetes in a general Korean population.

METHODS

A total of 10,667 subjects (4,201 males and 6,466 females) aged 45 to 74 years participated in a baseline examination between 2004 and 2007. Among the subjects, 8,157 (3,231 males and 4,926 females) underwent follow-up examination from 2007 to 2011, for a median follow-up period of 4.2 years. Type 2 diabetes was defined as intake of anti-diabetic agents, insulin treatment, fasting glucose concentration of more than 126 mg/dl, or hemoglobin A1c of more than 6.5% at re-examination. Associations of liver enzymes with incidence of type 2 diabetes were analyzed using logistic regression models.

RESULTS

During the follow-up period, 548 subjects (235 males, 313 females) developed type 2 diabetes. After adjusting for comprehensive diabetes risk factor, the risk of type 2 diabetes was significantly higher in the highest alanine aminotransferase (ALT) quartile than in the lowest quartile (odds ratio (OR): 1.95, 95% confidence interval (CI): 1.18-3.21 in males; OR: 1.49, 95% CI: 1.03-2.16 in females). Similar results were observed for gamma-glutamyltransferase (GGT) quartiles, but in the fully adjusted analysis, the OR for the highest versus lowest quartiles was significant only for females (OR: 1.58, 95% CI: 0.95-2.63 in males; OR: 1.85, 95% CI: 1.23-2.79 in females).

CONCLUSIONS

Our results suggest that serum ALT concentrations were independently associated with type 2 diabetes in both sexes, and that GGT was also independently associated but only in females.

New evidence for an association between liver enzymes and pancreatic islet β-cell dysfunction in young obese patients

To explore the relationship between serum liver enzymes and both the glucose tolerance status and insulin secretion in young obese patients. A total of 734 young obese patients (BMI ≥ 25 kg m(-2)) and 231 lean healthy volunteers matched in age (BMI < 23 kg m(-2)) were enrolled in this cross-sectional observational study. The 734 obese patients were subdivided to three groups (OB-NGR, OB-IGR, and OB-DM) according to their glucose tolerance status. FSIVGTT was performed to assess the degree of insulin sensitivity (SI) and islet secretion function (AIRg). The disposition index (DI; product of SI and AIRg) was calculated as an integrated measurement of insulin secretion and insulin action after compensating for insulin resistance. The extent and distribution of hepatic fat infiltration was assessed using the liver/spleen ratio (L/S ratio) with CT scan. ALT and GGT levels in OB-NGR, OB-IGR, and OB-DM groups were significantly increased compared to the normal controls, and were incrementally increased in turn in the three groups, whereas DI decreased at the same time. One standard deviation increment in ALT and GGT increased the risk of β-cell dysfunction after controlling for potential confounders such as sex, age, BMI, waist-hip ratio, and blood pressure. Even after the adjustment of the serum lipid profile and L/S ratio, the odds ratio of ALT remained statistically significant (OR, 1.603; 95 % CI, 1.225-2.096). Serum levels of liver enzymes showed an independent close relationship with insulin secretion capacity. Excluding the impact of a fatty liver, increased ALT and GGT levels indicated a significant association with the attenuation of pancreatic β-cell function. This study provides the possibility that elevated liver enzymes might be treated as simple biomarkers of early insulin secretion deficit in type 2 diabetes, especially in young obese patients.

Oxidant-induced regulation of glutathione synthesis

This unit describes protocols for characterizing the expression of two glutathione biosynthesis enzymes: gamma-glutamylcysteine synthase (GCS) and gamma-glutamyl transpeptidase (GGT) in response to oxidants. GCS catalyzes the first and rate-limiting step of glutathione synthesis, while GGT degrades extracellular glutathione (GSH) to provide the amino acids required for intracellular synthesis of GSH. Northern blot hybridization is used to quantitatively assess the mRNAs for the two enzymes in response to oxidant. Nuclear run-on is used to determine the rate of transcription.

Induction of oxidative stress in liver and kidney of rats exposed to Nigerian bonny light crude oil

The local population of Niger-Delta in the Southern part of Nigeria have used bonny light crude oil (BLCO) as a remedy for various ailments and are exposed to some extent to this widespread environmental contaminant or its metabolites through the food chain. BLCO's hepatorenal toxicity was studied using oxidative stress indices to elucidate the precise nature and mechanism of action. BLCO was orally administered at concentrations of 0, 200, 400, and 800 mg kg⁻¹ to adult male rats for 7 days. After exposure, kidney weight was unaffected, but liver weight decreased significantly at 800 mg kg⁻¹ only compared with control. BLCO exposure resulted in dose-dependent elevation of serum aminotransferases, total bilirubin, urea, and creatinine. Activities of superoxide dismutase and catalase decreased significantly, whereas γ-glutamyltransferase activity and the level of glutathione increased significantly in BLCO-treated animals compared with control in both liver and kidney of rat. Renal activities of glucose-6-phosphatase and 5'-nucleotidase markedly decreased in a dose-dependent manner in BLCO-exposed rats. In addition, the levels of hydrogen peroxide and lipid peroxidation significantly increased, dose dependently, in liver and kidney of BLCO-treated rats compared with control. BLCO-treated rats showed marked degeneration of kidney evident in cortical hemorrhages, tubular necrosis, protein casts, and cellular infiltration. However, no treatment-related liver histopathology was observed. The results suggested that BLCO elicits disruption of antioxidant status and concomitant elevation of hydrogen peroxide and lipid peroxidation differentially in liver and kidney of rats. The hepatorenal toxicity of BLCO could be due to induction of oxidative stress in liver and kidney.

Inhibiting Glutathione Metabolism in Lung Lining Fluid as a Strategy to Augment Antioxidant Defense

Glutathione is abundant in the lining fluid that bathes the gas exchange surface of the lung. On the one hand glutathione in this extracellular pool functions in antioxidant defense to protect cells and proteins in the alveolar space from oxidant injury; on the other hand, it functions as a source of cysteine to maintain cellular glutathione and protein synthesis. These seemingly opposing functions are regulated through metabolism by gamma-glutamyl transferase (GGT, EC 2.3.2.2). Even under normal physiologic conditions, lung lining fluid (LLF) contains a concentrated pool of GGT activity exceeding that of whole lung by about 7-fold and indicating increased turnover of glutathione at the epithelial surface of the lung. With oxidant stress LLF GGT activity is amplified even further as glutathione turnover is accelerated to meet the increased demands of cells for cysteine. Mouse models of GGT deficiency confirmed this biological role of LLF GGT activity and revealed the robust expansiveness and antioxidant capacity of the LLF glutathione pool in the absence of metabolism. Acivicin, an irreversible inhibitor of GGT, can be utilized to augment LLF fluid glutathione content in normal mice and novel GGT inhibitors have now been defined that provide advantages over acivicin. Inhibiting LLF GGT activity is a novel strategy to selectively augment the extracellular LLF glutathione pool. The enhanced antioxidant capacity can maintain lung epithelial cell integrity and barrier function under oxidant stress.

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.

Acute effects of diesel emission from the urea selective catalytic reduction engine system on male rats

Short-term inhalation experiments were performed using Fischer 344 rats exposed to emission from the urea selective catalytic reduction (SCR) diesel engine system to identify health effects and compare them to those of the conventional diesel engine system. Rats were exposed to high-, middle-, or low-concentration emission (dilution ratio 1:29, 1:290, or 1:580) or clean air (control) for 1, 3, or 7 days (6 h/day), under driving conditions at a speed of 1320 rpm and a torque of 840 Nm. For the high-concentration group, the major components of the urea SCR emission were 0.04 mg/m(3) particulate matter (PM) and 0.78 ppm nitrogen dioxide (NO(2)); those of the conventional emission were 0.95 mg/m(3) PM and 0.31 ppm NO(2). The authors evaluated the respiratory effects of each emission on rats. Lymphocytes for 3-day exposure of both emissions significantly increased in bronchoalveolar lavage fluid, but there were slight differences. With an increase in potential antioxidant (PAO), 8-hydroxy-2'-deoxyguanosine for the urea SCR emission was significantly decreased, but that of the conventional emission was highest among all groups and did not show a response to PAO. In lungs, heme oxygenase (HO)-1 and tumor necrosis factor (TNF)-alpha mRNA expressions for the urea SCR emission showed a tendency to increase compared to those of the conventional emission. Thus, gene analysis results suggested that NO(2) from the urea SCR emission affected the expressions of mRNAs in lungs. However, as a whole, the results suggested that the health effects of the urea SCR emission might be less than the conventional emission on rats.

Effects of atmospheric pollutants on the Nrf2 survival pathway

BACKGROUND, AIM, AND SCOPE

Atmospheric pollution is a worldwide problem. Exposure to atmospheric pollutants causes toxic cellular effects. One of the mechanisms of toxicity by these pollutants is the promotion of oxidative stress. Several signaling pathways control cellular redox homeostasis. In this respect, nuclear factor erythroid 2-related factor 2 (Nrf2) is a crucial transcription factor in the cell's response to oxidative stress.

MAIN FEATURES

In cellular animal models, exposure to atmospheric pollutants activates Nrf2, attenuating its toxic and even its carcinogenic effects. Therefore, we have reviewed the scientific literature in order to indicate that air pollutants, such as particulate matter, polycyclic aromatic hydrocarbons, and gaseous matter, are Nrf2 pathway inductors, triggering self-defense through the establishment of proinflammatory and antioxidant responses.

RESULTS AND DISCUSSION

Exposure to reactive molecules as atmospheric pollutants causes the activation of Nrf2 and the subsequent regulation of the expression of cytoprotective and detoxifying enzymes, as well as antioxidants. Moreover, induction of Nrf2 prior to exposure reduces the harmful effects of pollutants. The present article discusses the protective role of the Nrf2 pathway against different atmospheric pollutant insults.

CONCLUSIONS

Nrf2 regulates the expression of numerous cytoprotective genes that function to detoxify reactive species produced during atmospheric pollutant metabolic reactions. From the papers highlighted in this review, we conclude that Nrf2 has an important role in the defense against atmospheric pollutant-induced toxicity.

PERSPECTIVES

Further studies are needed to understand the signaling events that turn on the system in response to atmospheric pollutant stress. This could allow for the possibility of targeting the pathway for prevention benefits in the near future.

Redox regulation of gamma-glutamyl transpeptidase

gamma-Glutamyl transpeptidase (GGT) catalyzes the transfer of the glutamyl moiety from glutathione, and glutathione S-conjugates to acceptors to form another amide or to water to produce free glutamate. Functionally, GGT plays important roles in glutathione homeostasis and mercapturic acid metabolism. The expression of GGT is increased as an adaptive response upon the exposure of oxidative stress. The underlying mechanism of this, however, is nebulous, as GGT gene structure is complex and its transcription is usually controlled by multiple promoters that generate several subtypes of GGT mRNAs. Studies reveal that signaling pathways such as Ras, ERK, p38MAPK, and PI3K are involved in the induction of GGT gene expression in response to oxidative stress. Thus, not surprisingly, induction of GGT mRNA subtypes and the involvement of multiple signaling pathways vary depending on cell type and stimuli.

Differential pulmonary and cardiac effects of pulmonary exposure to a panel of particulate matter-associated metals

Biological mechanisms underlying the association between particulate matter (PM) exposure and increased cardiovascular health effects are under investigation. Water-soluble metals reaching systemic circulation following pulmonary exposure are likely exerting a direct effect. However, it is unclear whether specific PM-associated metals may be driving this. We hypothesized that exposure to equimolar amounts of five individual PM-associated metals would cause differential pulmonary and cardiac effects. We exposed male WKY rats (14 weeks old) via a single intratracheal instillation (IT) to saline or 1 micromol/kg body weight of zinc, nickel, vanadium, copper, or iron in sulfate form. Responses were analyzed 4, 24, 48, or 96 h after exposure. Pulmonary effects were assessed by bronchoalveolar lavage fluid levels of total cells, macrophages, neutrophils, protein, albumin, and activities of lactate dehydrogenase, gamma-glutamyl transferase, and n-acetyl glucosaminidase. Copper induced earlier pulmonary injury/inflammation, while zinc and nickel produced later effects. Vanadium or iron exposure induced minimal pulmonary injury/inflammation. Zinc, nickel, or copper increased serum cholesterol, red blood cells, and white blood cells at different time points. IT of nickel and copper increased expression of metallothionein-1 (MT-1) in the lung. Zinc, nickel, vanadium, and iron increased hepatic MT-1 expression. No significant changes in zinc transporter-1 (ZnT-1) expression were noted in the lung or liver; however, zinc increased cardiac ZnT-1 at 24 h, indicating a possible zinc-specific cardiac effect. Nickel exposure induced an increase in cardiac ferritin 96 h after IT. This data set demonstrating metal-specific cardiotoxicity is important in linking metal-enriched anthropogenic PM sources with adverse health effects.

Serum elevated gamma glutamyltransferase levels may be a marker for oxidative stress in Alzheimer's disease

BACKGROUND

Gamma glutamyltransferase (GGT) plays a role in cellular glutathione uptake, which is an important element of antioxidant mechanisms. An increase in serum GGT is thought to be an early and sensitive marker of oxidative stress. Oxidative stress has a role in the pathogenesis of Alzheimer's disease (AD). The aim of this study was to investigate the GGT levels in AD.

METHOD

In this cross-sectional study, 132 patients with AD (mean age: 74.1 +/- 7.4, female 62.9%) and 158 age- and gender-matched normal controls (mean age: 74.5 +/- 6.3, female 67.1%) were evaluated. For cognitive assessment, MMSE and clock drawing tests were performed; DSM-IV and NINCDS-ADRDA criteria were used. Serum GGT, aspartate aminotransferase, alanine aminotransferase and alkaline phosphatase concentrations were determined.

RESULTS

Median (min-max) GGT levels were 18 (9-70) in AD group and 17 (5-32) in normal controls. Mann-Whitney U test showed that GGT levels were significantly higher in AD patients (p = 0.012). Linear regression analysis revealed AD was an independent correlate of elevated GGT levels. Hypertension, diabetes mellitus, total cholesterol, and low density lipoprotein cholesterol were not associated with GGT levels.

CONCLUSION

GGT levels were increased significantly in AD patients. To evaluate the role of GGT as a marker of oxidative stress in AD, further studies are needed.

The relationship of gamma-glutamyltransferase to C-reactive protein and arterial stiffness

BACKGROUND AND AIMS

The relationships between gamma-glutamyltransferase (GGT), C-reactive protein (CRP), and arterial stiffness have not been fully investigated. The aim of this study was to clarify whether serum GGT is related to CRP and arterial stiffness estimated using brachial-ankle pulse wave velocity (baPWV).

METHODS AND RESULTS

The subjects were 3412 males and 854 females. GGT, CRP, baPWV, and conventional risk factors were evaluated. On multiple regression analysis, after adjustment for the conventional risk factors, log GGT was significantly associated with log CRP in male and female subjects (male subjects: beta=0.168, p<0.0001; female subjects: beta=0.098, p<0.05). After adjustment for the conventional risk factors, log GGT was significantly associated with PWV in male subjects (beta=0.060, p<0.0001), but in female subjects, no significant relationships were found after adjustment (beta=0.007, p=0.82).

CONCLUSION

These results suggest that GGT is independently associated with an increased level of CRP in both males and females. In addition, in males, GGT is related to an increased level of arterial stiffness.

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.

Liver enzymes as a predictor for incident diabetes in a Japanese population: the Hisayama study

OBJECTIVE

We studied the relationship between liver enzymes and the development of diabetes in a general Japanese population.

RESEARCH METHODS AND PROCEDURES

A total of 1804 non-diabetic subjects 40 to 79 years of age were followed-up prospectively for a mean of 9.0 years.

RESULTS

During the follow-up, 135 subjects developed diabetes. In both sexes, the age-adjusted cumulative incidence of diabetes increased significantly with elevating quartiles of serum gamma-glutamyltransferase (GGT) and alanine aminotransferase (ALT) levels. This pattern was also observed in aspartate aminotransferase (AST) quartiles for men but not for women. In multivariate analyses after adjusting for comprehensive risk factors and other liver enzymes, the risk of developing diabetes was significantly higher in the highest GGT quartile than in the lowest quartile [odds ratio (OR), 2.54; 95% confidence interval (CI), 1.03 to 6.26 for men; OR, 5.73; 95% CI, 1.62 to 20.19 for women]. Similar results were observed in ALT quartiles (OR, 2.32; 95% CI, 0.91 to 5.92 for men; OR, 4.40; 95% CI, 1.38 to 14.06 for women) but not in AST quartiles in either sex. Significant positive associations of GGT and ALT with diabetes were seen within each stratified category of risk factors, namely fasting insulin, BMI, waist-to-hip ratio, high-sensitivity C-reactive protein, and alcohol consumption. In receiver operating characteristic analyses, the areas under the receiver operating characteristic curve of GGT and ALT were significantly larger than that of AST, fasting insulin, waist-to-hip ratio, or C-reactive protein.

DISCUSSION

Our findings suggest that serum GGT and ALT concentrations are strong predictors of diabetes in the general population, independent of known risk factors.

Intake of purple sweet potato beverage affects on serum hepatic biomarker levels of healthy adult men with borderline hepatitis

OBJECTIVE

To examine the effect of purple sweet potato (PSP) beverage rich in acylated anthocyanins on serum hepatic biomarkers in healthy Japanese men.

DESIGN

A randomized, double-blind, placebo-controlled, parallel study.

SETTING

Kumamoto in Japan.

SUBJECTS

Healthy adult men (30-60 years) with borderline hepatitis who had one or more of serum gamma-glutamyl transferase (GGT), aspertate aminotransferase (AST) and alanine aminotransferase (ALT) levels over normal ranges, and who were negative for hepatitis virus were openly recruited by an advertisement. Of the 48 persons enrolled, 38 (mean age 43.0 years (30-54 years)) completed the study.

METHODS

The subjects were randomly assigned to the PSP group and the placebo group. During the 8-week intervention, the subjects in the PSP group consumed two bottles of the PSP beverage with acylated anthocyanins (200.3 mg anthocyanins per 125 ml per bottle) per day, and the subjects in the placebo group, two bottles of a placebo beverage (1.7 mg anthocyanins per 125 ml per bottle). All of the data measured were analyzed by two-way repeated measures analysis of variance (ANOVA) with groups and times. The data of the hepatic markers were analyzed using the Dunnett multiple comparison among the time points and t-test between groups at the same time point. Two-sided P<0.05 were defined as the level of significance.

RESULTS

Serum GGT, AST and ALT levels showed interactions (P<0.05) between the beverage groups and time; the others were not affected. The PSP beverage group showed lower hepatic marker levels than the placebo group during the ingestion period, particularly the GGT level (-14.1 IU/l, 95% Confidence intervel (CI) -25.4 to -2.7, P=0.017 at 2 weeks; -16.8 IU/l, 95% CI -36.2 to 2.5, P=0.081 at 4 weeks; -26.7 IU/l, 95% CI -47.6 to -5.7, P=0.014 at 6 weeks and -27.9 IU/l, 95% CI -49.9 to -5.9; P=0.014 at 8 weeks). No correlation between alcohol consumption and each hepatic biomarker level before and after the ingestion was observed.

CONCLUSION

The intake of the PSP beverage significantly decreased the serum levels of hepatic biomarkers, particularly the GGT level, in healthy men with borderline hepatitis.

gamma-Glutamyl transpeptidase is induced by 4-hydroxynonenal via EpRE/Nrf2 signaling in rat epithelial type II cells

gamma-Glutamyl transpeptidase (GGT) plays key roles in glutathione homeostasis and metabolism of glutathione S-conjugates. Rat GGT is transcribed via five tandemly arranged promoters into seven transcripts. The transcription of mRNA V is controlled by promoter 5. Previously we found that GGT mRNA V-2 was responsible for the induction of GGT in rat alveolar epithelial cells by 4-hydroxynonenal (HNE). In the current study, the underlying mechanism was investigated. Reporter deletion and mutation analysis demonstrated that an electrophile-response element (EpRE) in the proximal region of GGT promoter 5 (GP5) was responsible for the basal- and HNE-induced promoter activity. Gel-shift assays showed an increased binding activity of GP5 EpRE after HNE exposure. The nuclear content of NF-E2-related factor 2 (Nrf2) was significantly increased by HNE. The recruitment of Nrf2 to GP5 EpRE after HNE treatment was demonstrated by supershift and chromatin immunoprecipitation assays. The tissue expression pattern of GGT mRNA V was previously unknown. Using polymerase chain reaction, we found that GGT mRNA V-2 was expressed in many tissues in rat. Taken together, GGT mRNA V-2 is widely expressed in rat tissues and its basal and HNE-induced expression is mediated through EpRE/Nrf2 signaling.

High serum carotenoids are inversely associated with serum gamma-glutamyltransferase in alcohol drinkers within normal liver function

BACKGROUND

Many studies have reported that the consumption of alcohol induces the generation of free radicals. Moreover, recent studies suggest that serum gamma-glutamyltransferase (gamma-GTP) within its normal range might be an early marker of oxidative stress. In this study, we tested the hypothesis that serum antioxidant carotenoids would be inversely associated with serum gamma-GTP in alcohol drinkers within normal liver function.

METHODS

A total of 266 Japanese men who had received health examination in 2003 participated in the study. The associations of serum gamma-GTP and serum-carotenoid concentrations stratified by alcohol intake levels were evaluated cross-sectionally. The participants were divided into three groups according to their ethanol intake level (non-drinker, less than 1 g/day; light drinker, 1-25 g/day; and moderate and heavy drinkers, 25+ g/day). The multivariate-adjusted geometric means of the serum gamma-GTP concentrations in each tertile of the serum-carotenoid concentrations were calculated after adjustment for ethanol intake, age, body mass index, total cholesterol, triacylglycerols, current tobacco use, and habitual exercise.

RESULTS

The serum gamma-GTP concentrations were significantly high in accordance with the ethanol intake level. In moderate and heavy drinkers, the multivariate-adjusted geometric means of serum gamma-GTP concentrations were significantly low in accordance with the tertiles of the serum lycopene, alpha-carotene, beta-carotene, and beta-cryptoxanthin concentrations.

CONCLUSIONS

The serum antioxidant carotenoids were inversely associated with alcohol-induced increases of serum gamma-GTP in moderate and heavy drinkers within normal liver function.

4-Hydroxynonenal induces rat gamma-glutamyl transpeptidase through mitogen-activated protein kinase-mediated electrophile response element/nuclear factor erythroid 2-related factor 2 signaling

Gamma-glutamyl transpeptidase (GGT) plays critical roles in glutathione homeostasis and metabolism. Rat GGT is a single-copy gene from which seven types of GGT mRNA with a common protein encoding sequence, but different 5'-untranslated regions, may be transcribed. We previously showed that type V-2 was the predominant form of GGT mRNA in rat L2 epithelial cells, and that it could be induced by 4-hydroxynonenal (HNE) through the electrophile response element (EpRE) located in GGT promoter 5 (GP5). Here, we report transcription factors binding to GP5 EpRE and the involved signaling pathways. Immunodepletion gel shift assays demonstrated that GP5 EpRE bound JunB, c-Jun, FosB, and Fra2 from unstimulated cells, and that after exposure to HNE, EpRE binding complexes contained nuclear factor erythroid 2-related factor (Nrf) 1, Nrf2, JunB, c-Jun, FosB, c-Fos, Fra1, and Fra2. HNE-induced binding of Nrf2 and c-Jun in GP5 EpRE was confirmed by chromatin immunoprecipitation assays. Using reporter assays and specific inhibitors, we found that HNE induction of rat GGT mRNA V-2 was dependent on activation of extracellular signal-regulated kinase (ERK) and p38 mitogen-activated protein kinase (MAPK), but not protein kinase C or phosphatidylinositol 3-kinase. Pretreatment with ERK and p38MAPK inhibitors also blocked HNE-increased EpRE binding. HNE-increased nuclear content of Nrf1, Nrf2, and c-Jun in L2 cells was partially blocked by inhibition of either ERK1/2 or p38MAPK and completely blocked by simultaneous inhibition of both MAPKs. In conclusion, HNE induces GGT mRNA V-2 through altered EpRE transcription factor binding mediated by both ERK and p38MAPK.

Serum gamma-glutamyltransferase within its normal concentration range is related to the presence of diabetes and cardiovascular risk factors

AIMS

Although many studies have reported an association between serum gamma-glutamyltransferase (GGT) and cardiovascular risk factors, the mechanism of this relationship has not been clarified.

METHODS

The medical records of 29,959 subjects (age, median 48, range 14-90 years; 16,706 men, 13,253 women) who visited the Center for Health Promotion at Samsung Medical Center for a medical check-up between January 2001 and December 2003, were investigated. Subjects with hepatic enzyme/GGT concentrations higher than three times the upper limit of the reference range, a positive test for hepatitis C virus antibody, a positive test for hepatitis B virus surface antigen, currently taking anti-diabetic/anti-hypertensive/anti-lipid medication, or a white blood cell (WBC) count higher than 10,000 cells/ml, were excluded. The subjects of each gender were classified into five groups according to their serum GGT concentrations, into quartiles of the normal range of GGT (groups 1, 2, 3 and 4) and into a group with elevated GGT (group 5).

RESULTS

As the group number increased (group 1 --> 5), the frequencies of all of the following increased: (i) diabetes and impaired fasting glucose (IFG); (ii) hypertension, obesity (body mass index > or = 27 kg/m2), dyslipidaemia (LDL-cholesterol > or = 4.1 mmol/l and/or triglyceride > or = 2.46 mmol/l, or HDL-cholesterol < 1.16 mmol/l); (iii) metabolic syndrome. Moreover, these significant relationships between GGT concentrations within its normal range and the presence of diabetes/IFG, hypertension, obesity, dyslipidaemia, and metabolic syndrome persisted after adjusting for several clinical and biochemical variables and for the presence of fatty liver based on ultrasonographic findings. Odds ratios (95% CI) for group 4 (highest quartile of normal range of GGT) vs. group 1 (lowest quartile of normal range of GGT); the referent group, were 3.16 (2.15-4.65) for diabetes, 2.24 (1.73-2.90) for IFG, 1.93 (1.59-2.33) for obesity, 1.38 (1.23-1.55) for dyslipidaemia and 2.88 (2.28-3.65) for metabolic syndrome in men. In women, the odds ratios were 2.72 (1.34-5.52), 3.67 (2.26-5.97), 2.10 (1.61-2.74), 1.80 (1.58-2.04) and 3.57 (2.52-5.07), respectively.

CONCLUSIONS

Our data show that, even within its normal range, serum GGT concentrations are closely associated with the presence of diabetes and cardiovascular risk factors, and that these associations are independent of a fatty liver by ultrasonography.

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.

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.

The significance of serum gamma-glutamyltransferase in cardiovascular diseases

Since early after the introduction of serum gamma-glutamyltransferase (GGT) in clinical practice as a reliable and widely employed laboratory test, epidemiological and prospective studies have repeatedly shown that this activity possesses a prognostic value for morbidity and mortality. The association is independent of possibly concomitant conditions of liver disease, and notably, a significant independent correlation of serum GGT exists with the occurrence of cardiovascular diseases (myocardial infarction, stroke). Experimental work has documented that active GGT is present in atherosclerotic plaques of coronary as well as in cerebral arteries. These findings, and the recently recognized functions of GGT in the generation of reactive oxygen species, indicate that serum GGT represents a true marker of cardiovascular diseases and underlying atherosclerosis. Further insights into potential therapeutic interest will probably be derived from studies investigating the origin of GGT activity in plaque tissue.

4-Hydroxynonenal increases gamma-glutamyl transpeptidase gene expression through mitogen-activated protein kinase pathways

gamma-Glutamyl transpeptidase (GGT) plays key roles in the metabolism of glutathione. Previous studies have shown that GGT expression was increased by oxidants, but the mechanism remains unclear. In the present study, the effects of 4-hydroxy-2-nonenal (HNE), an electrophilic end product of lipid peroxidation, on GGT expression were investigated in rat lung epithelial type II (L2) cells. We demonstrated that HNE increased GGT activity and mRNA content in both time- and dose-dependent manners. Actinomycin D, an RNA transcription inhibitor, blocked HNE-stimulated increase in GGT mRNA, suggesting transcriptional regulation of GGT mRNA by HNE. Of the seven GGT mRNA transcripts known to be produced from the single rat GGT gene, we found that types I, II, and V-2 were constitutively expressed in L2 cells, but only types I and V-2 were increased by HNE. PD98059 and SB203580, relatively specific inhibitors of the ERK and the p38MAPK kinase pathway, respectively, significantly attenuated HNE induction of both GGT activity and mRNA content. In contrast, studies with JNK inhibitor I, a cell-permeable peptide, indicated that JNK was not involved in the GGT induction by HNE. We also found that GGT induction by HNE could be completely blocked by a cocktail of PD98059 and SB203580, suggesting a combined effect of ERK and p38MAPK pathways in HNE-mediated GGT induction. In conclusion, our results demonstrate that HNE increased GGT expression in rat alveolar type II cells and that the induction of GGT by HNE was mediated through activation of the ERK and p38MAPK pathways.

Gamma-glutamyl transpeptidase in glutathione biosynthesis

Glutathione (GSH) is the most abundant nonprotein thiol in cells and has multiple biological functions. Glutathione biosynthesis by way of the gamma-glutamyl cycle is important for maintaining GSH homeostasis and normal redox status. As the only enzyme of the cycle located on the outer surface of plasma membrane, gamma-glutamyl transpeptidase (GGT) plays key roles in GSH homeostasis by breaking down extracellular GSH and providing cysteine, the rate-limiting substrate, for intracellular de novo synthesis of GSH. GGT also initiates the metabolism of glutathione S-conjugates to mercapturic acids by transferring the gamma-glutamyl moiety to an acceptor amino acid and releasing cysteinylglycine. GGT is expressed in a tissue-, developmental phase-, and cell-specific manner that may be related to its complex gene structure. In rodents, there is a single GGT gene, and several promoters that generate different mRNA subtypes and regulate its expression. In contrast, several GGT genes have been found in humans. During oxidative stress, GGT gene expression is increased, and this is believed to constitute an adaptation to stress. Interestingly, only certain mRNA subtypes are increased, suggesting a specific mode of regulation of GGT gene expression by oxidants. Here, protocols to measure GGT activity, relative levels of total and specific GGT mRNA subtypes, and GSH concentration are described.

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.

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.

Association between serum gamma-glutamyltransferase and dietary factors: the Coronary Artery Risk Development in Young Adults (CARDIA) Study

BACKGROUND

Diet may be involved in the strong dose-response relation of gamma-glutamyltransferase (GGT) concentration with incident diabetes.

OBJECTIVE

We examined dietary correlates of serum GGT activity.

DESIGN

Study subjects were 3146 black and white men and women aged 17-35 y in 1985-1986. A diet history was taken at years 0 and 7. Food items were classified into alcohol; breaded, battered, or canned vegetables; fruit; fruit juice; refined grain; whole grain; dairy; legumes; meat; poultry; fish; fresh or frozen vegetables; nuts; and coffee.

RESULTS

After adjustment for nondietary factors and other food groups, GGT was positively associated with alcohol consumption and meat intake. Geometric means of year 10 GGT across categories of alcohol consumption (0, 1-9, 10-19, 20-29, and > or = 30 g/d) were 17.7, 18.8, 20.4, 21.8, and 24.8 U/L (P for trend < 0.01); corresponding means across quintiles of meat intake were 19.2, 20.2, 20.5, 21.8, and 21.2 times/wk (P for trend < 0.01). GGT was inversely associated with fruit intake. Among possible meat constituents, dietary heme iron, but not saturated fat, was associated with GGT. Dietary constituents typical of plant foods showed an inverse association. In contrast, vitamin supplements were positively associated with GGT.

CONCLUSIONS

Serum GGT activity increased in a dose-response manner as alcohol and meat consumption increased and fruit consumption decreased. Heme iron contained in meats and micronutrients contained in fruits may influence GGT metabolism. However, micronutrients taken as supplements had a positive association with GGT.

Association of serum carotenoids and tocopherols with gamma-glutamyltransferase: the Cardiovascular Risk Development in Young Adults (CARDIA) Study

BACKGROUND

Our previous studies suggest that serum gamma-glutamyltransferase (GGT) activity may be related to oxidative stress, supporting findings of experimental studies. To further examine the role of GGT in relation to oxidative stress, we investigated the association between serum carotenoids and tocopherols, which have antioxidant properties, and serum GGT.

METHODS

Study participants were 3128 black and white men and women 17-35 years of age in 1985-1986. Serum carotenoids and tocopherols were measured at years 0 and 7, and serum GGT was measured at years 0 and 10.

RESULTS

Circulating concentrations of alpha-carotene, beta-carotene, and beta-cryptoxanthin inversely predicted the serum GGT concentration measured 10 years later in a dose-response manner (P for trend <0.01). Year 0 zeaxanthin/lutein was weakly inversely associated with year 10 GGT (P for trend = 0.08), and year 0 lycopene was unrelated to year 10 GGT. Adjusted geometric means of serum GGT at year 10 according to quintile of the sum of four carotenoids at year 0 (alpha-carotene, beta-carotene, beta-cryptoxanthin, and zeaxanthin/lutein) were 19.9, 19.4, 18.9, 17.8, and 17.3 U/L (P for trend <0.01). Year 0 alpha-tocopherol was also a significant inverse predictor of year 10 serum GGT concentration (P for trend = 0.03), whereas gamma-tocopherol showed an inconsistent or possibly U-shaped association. However, year 0 serum GGT did not predict serum antioxidants measured 7 years later.

CONCLUSION

Our present findings support the contention that serum GGT concentration is a marker related with oxidative stress.

Characterization and regulation of the γ-glutamyl transpeptidase gene from the fission yeast Schizosaccharomyces pombe

The structural gene for the putative γ-glutamyl transpeptidase (GGT) was isolated from the chromosomal DNA of the fission yeast Schizosaccharomyces pombe. The determined sequence contained 3324 bp and encoded the predicted 630 amino acid sequence of GGT, which resembles counterparts in Homo sapiens, Rattus norvegicus, Saccharomyces cerevisiae, and Escherichia coli. The S. pombe cells harboring the cloned GGT gene showed about twofold higher GGT activity in the exponential phase than the cells harboring the vector only, indicating that the cloned GGT gene was functional. To monitor the expression of the S. pombe GGT gene, we fused the fragment 1085 bp upstream of the cloned GGT gene into the promoterless β-galactosidase gene of the shuttle vector YEp367R to generate the fusion plasmid pGT98. The synthesis of β-galactosidase from the fusion plasmid in S. pombe cells was enhanced by treatments with NO-generating sodium nitroprusside (SN), L-buthionine-(S,R)-sulfoximine (BSO), and glycerol. The GGT mRNA level in the S. pombe cells was increased by SN and BSO. Involvement of Pap1 in the induction of the GGT gene by SN and BSO was observed.Key words: fission yeast, genomic DNA, γ-glutamyl transpeptidase, Pap1, regulation, Schizosaccharomyces pombe.

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.

Bleomycin-induced pulmonary fibrosis is attenuated in gamma-glutamyl transpeptidase-deficient mice

To investigate repair mechanisms in bleomycin-induced pulmonary fibrosis, we used mice deficient in gamma-glutamyl transpeptidase (GGT-/-), a key enzyme in glutathione (GSH) and cysteine metabolism. Seventy-two hours after bleomycin (0.03 U/g), GGT-/- mice displayed a different inflammatory response to wild-type mice as judged by a near absence of neutrophils in lung tissue and bronchoalveolar lavage and a less pronounced rise in matrix metalloproteinase-9. Inflammation in GGT-/- mice consisted mainly of lymphocytes and macrophages. At 1 month, lungs from bleomycin-treated GGT-/- mice exhibited minimal areas of fibrosis compared with wild-type mice(light microscopy fibrosis index: 510 +/- 756 versus 1975 +/- 817, p < 0.01). Lung collagen content revealed a significant increase in bleomycin-treated wild-type (15.1 +/- 3.8 versus 8.5 +/- 0.7 microg hydroxy(OH)-proline/mg dry weight, p < 0.01) but not in GGT-/- (10.4 +/- 1.7 versus 8.8 +/- 0.8). Control lungs from GGT-/- showed a significant reduction of cysteine (0.03 +/- 0.005 versus 0.055 +/- 0.001, p < 0.02) and GSH levels (1.24 +/- 0.055 versus 1.79 +/- 0.065, p < 0.002). These values decreased after 72 hours of bleomycin in both GGT-/- and wild-type but reached their respective control values after 1 month. Supplementation with N-acetyl cysteine partially ameliorated the effects of GGT deficiency. These findings suggest that increased neutrophils and matrix metalloproteinase-9 during the early inflammatory response and adequate thiol reserves are key elements in the fibrotic response after bleomycin-induced pulmonary injury.

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.

Molecular mechanisms of nitrogen dioxide induced epithelial injury in the lung

The lung can be exposed to a variety of reactive nitrogen intermediates through the inhalation of environmental oxidants and those produced during inflammation. Reactive nitrogen species (RNS) include, nitrogen dioxide (.NO2) and peroxynitrite (ONOO-). Classically known as a major component of both indoor and outdoor air pollution, .NO2 is a toxic free radical gas. .NO2 can also be formed during inflammation by the decomposition of ONOO- or through peroxidase-catalyzed reactions. Due to their reactive nature, RNS may play an important role in disease pathology. Depending on the dose and the duration of administration, .NO, has been documented to cause pulmonary injury in both animal and human studies. Injury to the lung epithelial cells following exposure to .NO2 is characterized by airway denudation followed by compensatory proliferation. The persistent injury and repair process may contribute to airway remodeling, including the development of fibrosis. To better understand the signaling pathways involved in epithelial cell death by .NO2 or otherRNS, we routinely expose cells in culture to continuous gas-phase .NO2. Studies using the .NO2 exposure system revealed that lung epithelial cell death occurs in a density dependent manner. In wound healing experiments, .NO2 induced cell death is limited to cells localized in the leading edge of the wound. Importantly, .NO2-induced death does not appear to be dependent on oxidative stress per se. Potential cell signaling mechanisms will be discussed, which include the mitogen activated protein kinase, c-Jun N-terminal Kinase and the Fas/Fas ligand pathways. During periods of epithelial loss and regeneration that occur in diseases such as asthma or during lung development, epithelial cells in the lung may be uniquely susceptible to death. Understanding the molecular mechanisms of epithelial cell death associated with the exposure to .NO2 will be important in designing therapeutics aimed at protecting the lung from persistent injury and repair.

Prolonged hypoxia accelerates the posttranscriptional process of collagen synthesis in cultured fibroblasts

Molecular oxygen is essential for metazoan life. Hypoxia, a reduced oxygen condition, induces systemic and cellular responses for acclimation to the limited oxygen availability. Multicellularity of metazoans is maintained on extracellular matrices. Previously, we demonstrated that acute hypoxia up-regulated the prolyl 4-hydroxylase alpha(I) subunit, the rate-limiting subunit for the hydroxylation of proline residues of procollagens (Y. Takahashi, S. Takahashi, Y. Shiga, T. Yoshimi, and T Miura, 2000, J. Biol. Chem., 275, 14139-14146). The formation of hydroxyproline is an essential posttranscriptional process for stabilization of the helical trimer of procollagen polypeptides at physiological temperature. In this present study, we cultured fetal rat lung fibroblasts for up to 9 days and examined the effects of prolonged hypoxia on the level of procollagen mRNA in the cells and the posttranscriptional steps of collagen synthesis. Hypoxia accelerated the deposition of collagen molecules. These enhancements in hypoxic cultures were observed with or without ascorbic acid in the culture medium. The steady-state level of procollagen alpha1(I) mRNA was not affected by the prolonged hypoxia. In contrast, the mRNA and protein levels of the prolyl 4-hydroxylase alpha(I) subunit were increased by hypoxic culture under both ascorbic acid-sufficient and -deficient conditions. These results suggest that hypoxic enhancement of the posttranscriptional step of collagen synthesis contributed to the accelerated deposition of collagen fibrils.

Co-operation of the transcription factor hepatocyte nuclear factor-4 with Sp1 or Sp3 leads to transcriptional activation of the human haem oxygenase-1 gene promoter in a hepatoma cell line

We reported previously that the 5'-flanking region (nucleotides -1976 to -1655) of the human haem oxygenase-1 ( hHO-1 ) gene enhances hHO-1 promoter activity in human hepatoma HepG2 cells, but not in HeLa cells [Takahashi, Takahashi, Ito, Nagano, Shibahara and Miura (1999) Biochim. Biophys. Acta 1447, 231-235]. To define more precisely the regulatory elements involved, in the present study we have functionally dissected this region and localized the enhancer to a 50 bp fragment (-1793 to -1744). Site-direct mutagenesis analysis revealed that two regions were responsible for this enhancer activity, i.e. a hepatocyte nuclear factor-4 (HNF-4) homologous region and a GC box motif homologous region. Mutation in either region alone moderately decreased enhancer activity. However, mutations in both regions reduced promoter activity to the basal level. Electrophoretic mobility-shift assays demonstrated that the P5-2 fragment (-1793 to -1744) interacted with at least two nuclear factors, i.e. HNF-4 and Sp1/Sp3. Co-transfection experiments using Drosophila SL2 cells revealed that HNF-4 and Sp1/Sp3 synergistically stimulated the enhancer activity of the P5-2 fragment. These results indicate that co-operation of HNF-4 with Sp1 or Sp3 leads to the activation of hHO-1 gene expression in hepatoma cells.

Glutathione in defense and signaling: lessons from a small thiol

The mechanisms of thiol metabolism and chemistry have particular relevance to both cellular defenses against toxicant exposure and to redox signaling. Here, we will focus on glutathione (GSH), the major endogenous low- molecular-weight nonprotein thiol synthesized de novo in mammalian cells. The major pathways for GSH metabolism in defense of the cell are reduction of hydroperoxides by glutathione peroxidases (GSHPx) and some peroxiredoxins, which yield glutathione disulfide (GSSG), and conjugation reactions catalyzed by glutathione-S-transferases. GSSG can be reduced to GSH by glutathione reductase, but glutathione conjugates are excreted from cells. The exoenzyme gamma-glutamyltranspeptidase (GGT) removes the glutamate from extracellular GSH, producing cysteinyl-glycine from which a dipeptidase then generates cysteine, an amino acid often limiting for de novo GSH synthesis. Synthesis of GSH from the constituent amino acids occurs in two regulated, enzymatically catalyzed steps. The signaling pathways leading to activation of the transcription factors that regulate these genes are a current area of intense investigation. The elucidation of the signaling for GSH biosynthesis in human bronchial epithelial cells in response to 4-hydroxynonenal (4HNE), an end product of lipid peroxidation, will be used as an example. GSH also participates in redox signaling through the removal of H(2)O(2), which has the properties of a second messenger, and by reversing the formation of sulfenic acid, a moiety formed by reaction of critical cysteine residues in signaling proteins with H(2)O(2). Disruption of GSH metabolism will therefore have major a impact upon function of cells in terms of both defense and normal physiology.

Gamma-glutamyl transferase deficiency results in lung oxidant stress in normoxia

gamma-Glutamyl transferase (GGT) is critical to glutathione homeostasis by providing substrates for glutathione synthesis. We hypothesized that loss of GGT would cause oxidant stress in the lung. We compared the lungs of GGT(enu1) mice, a genetic model of GGT deficiency, with normal mice in normoxia to study this hypothesis. We found GGT promoter 3 (P3) alone expressed in normal lung but GGT P3 plus P1, an oxidant-inducible GGT promoter, in GGT(enu1) lung. Glutathione content was barely decreased in GGT(enu1) lung homogenate and elevated nearly twofold in epithelial lining fluid, but the fraction of oxidized glutathione was increased three- and fourfold, respectively. Glutathione content in GGT(enu1) alveolar macrophages was decreased nearly sixfold, and the oxidized glutathione fraction was increased sevenfold. Immunohistochemical studies showed glutathione deficiency together with an intense signal for 3-nitrotyrosine in nonciliated bronchiolar epithelial (Clara) cells and expression of heme oxygenase-1 in the vasculature only in GGT(enu1) lung. When GGT(enu1) mice were exposed to hyperoxia, survival was decreased by 25% from control because of accelerated formation of vascular pulmonary edema, widespread oxidant stress in the epithelium, diffuse depletion of glutathione, and severe bronchiolar cellular injury. These data indicate a critical role for GGT in lung glutathione homeostasis and antioxidant defense in normoxia and hyperoxia.

Gamma glutamyl transferase

Serum gamma-glutamyl transferase (GGT) has been widely used as an index of liver dysfunction and marker of alcohol intake. The last few years have seen improvements in these areas and advances in understanding of its physiological role in counteracting oxidative stress by breaking down extracellular glutathione and making its component amino acids available to the cells. Conditions that increase serum GGT, such as obstructive liver disease, high alcohol consumption, and use of enzyme-inducing drugs, lead to increased free radical production and the threat of glutathione depletion. However, the products of the GGT reaction may themselves lead to increased free radical production, particularly in the presence of iron. There have also been important advances in the definition of the associations between serum GGT and risk of coronary heart disease, Type 2 diabetes, and stroke. People with high serum GGT have higher mortality, partly because of the association between GGT and other risk factors and partly because GGT is an independent predictor of risk. This review aims to summarize the knowledge about GGT's clinical applications, to present information on its physiological roles, consider the results of epidemiological studies, and assess how far these separate areas can be combined into an integrated view.