Gamma-glutamyltransferase, cardiovascular disease and mortality in individuals with diabetes mellitus

Gamma-glutamyl transferase and the risk of all-cause and disease-specific mortality in patients with diabetes: A nationwide cohort study

BACKGROUND

There exists a paucity of data regarding whether gamma-glutamyl transferase is associated with disease-specific mortality in patients with type 2 diabetes mellitus. This study aimed to investigate the association of serum gamma-glutamyl transferase levels with all-cause and disease-specific mortality in patients with diabetes mellitus using a Korean nationwide health-screening database.

METHODS

A total of 9 687 066 patients without viral hepatitis or liver cirrhosis who underwent health examination in 2009 were included. These patients were divided into four groups according to sex-specific quartiles of serum gamma-glutamyl transferase levels.

RESULTS

During a median follow-up period of 8.1 years, 222 242 deaths were identified. The all-cause mortality rate increased as the serum gamma-glutamyl transferase levels became higher (highest quartile vs lowest quartile: hazard ratio [HR], 1.57; 95% confidence interval [CI], 1.55-1.59; p for trend <.001). Similar trends were observed for cardiovascular disease (HR, 1.57; 95% CI, 1.53-1.62), ischemic heart disease (HR, 1.40; 95% CI, 1.33-1.48), and stroke (HR, 1.72; 95% CI, 1.60-1.85) in the highest quartile, as compared with the lowest quartile (p for trend <.001). As the gamma-glutamyl transferase quartiles became higher, mortality rates related to cancer (HR, 1.56; 95% CI, 1.52-1.60), liver disease (HR, 9.42; 95% CI, 8.81-10.07), respiratory disease (HR, 1.55; 95% CI, 1.49-1.62), and infectious disease (HR, 1.73; 95% CI, 1.59-1.87) also increased in the highest quartile, compared with the lowest quartile (p for trend <.001).

CONCLUSIONS

Serum gamma-glutamyl transferase levels may be useful for the risk assessment of all-cause and disease-specific mortality among patients with type 2 diabetes mellitus.

Serum/plasma biomarkers and the progression of cardiometabolic multimorbidity: a systematic review and meta-analysis

Background

The role of certain biomarkers in the development of single cardiometabolic disease (CMD) has been intensively investigated. Less is known about the association of biomarkers with multiple CMDs (cardiometabolic multimorbidity, CMM), which is essential for the exploration of molecular targets for the prevention and treatment of CMM. We aimed to systematically synthesize the current evidence on CMM-related biomarkers.

Methods

We searched PubMed, Embase, Web of Science, and Ebsco for relevant studies from inception until August 31st, 2022. Studies reported the association of serum/plasma biomarkers with CMM, and relevant effect sizes were included. The outcomes were five progression patterns of CMM: (1) no CMD to CMM; (2) type 2 diabetes mellitus (T2DM) followed by stroke; (3) T2DM followed by coronary heart disease (CHD); (4) T2DM followed by stroke or CHD; and (5) CHD followed by T2DM. Newcastle-Ottawa Quality Assessment Scale (NOS) was used to assess the quality of the included studies. A meta-analysis was conducted to quantify the association of biomarkers and CMM.

Results

A total of 68 biomarkers were identified from 42 studies, which could be categorized into five groups: lipid metabolism, glycometabolism, liver function, immunity, and others. Lipid metabolism biomarkers were most reported to associate with CMM, including TC, TGs, HDL-C, LDL-C, and Lp(a). Fasting plasma glucose was also reported by several studies, and it was particularly associated with coexisting T2DM with vascular diseases. According to the quantitative meta-analysis, HDL-C was negatively associated with CHD risk among patients with T2DM (pooled OR for per 1 mmol/L increase = 0.79, 95% CI = 0.77-0.82), whereas a higher TGs level (pooled OR for higher than 150 mg/dL = 1.39, 95% CI = 1.10-1.75) was positively associated with CHD risk among female patients with T2DM.

Conclusion

Certain serum/plasma biomarkers were associated with the progression of CMM, in particular for those related to lipid metabolism, but heterogeneity and inconsistent findings still existed among included studies. There is a need for future research to explore more relevant biomarkers associated with the occurrence and progression of CMM, targeted at which is important for the early identification and prevention of CMM.

Associations of Nutritional, Environmental, and Metabolic Biomarkers with Diabetes-Related Mortality in U.S. Adults: The Third National Health and Nutrition Examination Surveys between 1988-1994 and 2016

Background: Nutritional, environmental, and metabolic status may play a role in affecting the progression and prognosis of type 2 diabetes. However, results in identifying prognostic biomarkers among diabetic patients have been inconsistent and inconclusive. We aimed to evaluate the associations of nutritional, environmental, and metabolic status with disease progression and prognosis among diabetic patients. Methods: In a nationally representative sample in the NHANES III (The Third National Health and Nutrition Examination Survey, 1988−1994), we analyzed available data on 44 biomarkers among 2113 diabetic patients aged 20 to 90 years (mean age: 58.2 years) with mortality data followed up through 2016. A panel of 44 biomarkers from blood and urine specimens available from NHANES III were included in this study and the main outcomes as well as the measures are mortalities from all-causes. We performed weighted logistic regression analyses after controlling potential confounders. To assess incremental prognostic values of promising biomarkers beyond traditional risk factors, we compared c-statistics of the adjusted models with and without biomarkers, separately. Results: In total, 1387 (65.2%) deaths were documented between 1988 and 2016. We observed an increased risk of all-cause mortality associated with higher levels of serum C-reactive protein (p for trend = 0.0004), thyroid stimulating hormone (p for trend = 0.04), lactate dehydrogenase (p for trend = 0.02), gamma glutamyl transferase (p for trend = 0.02), and plasma fibrinogen (p for trend = 0.03), and urine albumin (p for trend < 0.0001). In contrast, higher levels of serum sodium (p for trend = 0.005), alpha carotene (p for trend = 0.006), and albumin (p for trend = 0.005) were associated with a decreased risk of all-cause mortality. In addition, these significant associations were not modified by age, sex, or race. Inclusion of thyroid stimulating hormone (p = 0.03), fibrinogen (p = 0.01), and urine albumin (p < 0.0001), separately, modestly improved the discriminatory ability for predicting all-cause mortality among diabetic patients. Conclusions: Our nationwide study findings provide strong evidence that some nutritional, environmental, and metabolic biomarkers were significant predictors of all-cause mortality among diabetic patients and may have potential clinical value for improving stratification of mortality risk.

Prognostic value of long-term gamma-glutamyl transferase variability in individuals with diabetes: a nationwide population-based study

We examined whether long-term gamma-glutamyl transferase (GGT) variability can predict cardiovascular disease (CVD) and mortality in individuals with diabetes. We included 698,937 Koreans diabetes patients older than 40 years without histories of CVD, chronic liver disease, or heavy alcoholics who received health exams supported by the Korean government more than once in 2009-2012 (baseline). We used Cox proportional analyses to estimate the risk of stroke, myocardial infarction (MI), and all-cause mortality until December 31, 2016, according to the quartiles of the average successive variability (ASV) of GGT measured during the five years before the baseline. A total 26,119, 15,103, and 39,982 cases of stroke, MI, and death, respectively, were found. GGT ASV quartile 4 had a significantly higher risk of stroke and all-cause mortality than quartile 1, with adjustment for risk factors, such as baseline glucose and GGT level, and comorbidities. Hazard ratios (95% confidence intervals) for GGT ASV quartile 4 were 1.06 (1.03-1.10) and 1.23 (1.20-1.27) for stroke and mortality, respectively. This significant association was shown consistently across the baseline GGT quartiles. GGT variability was related to the risk of stroke and all-cause mortality. The effect was most pronounced in all-cause mortality, irrespective of baseline GGT level.

Combined use of serum gamma glutamyl transferase level and ultrasonography improves prediction of perinatal outcomes associated with preeclamptic pregnancy

INTRODUCTION

Serum gamma glutamyl transferase (GGT), produced and released mostly from the liver and bile duct, is an enzyme involved in response to oxidative stress, and has been used as a maker for prediction of cardiovascular events. Umbilical artery blood flow resistance index, e.g., the systolic/diastolic ratio (S/D ratio) as determined by ultrasound, has been used to assess the fetal intrauterine conditions. While changes of GGT and S/D ratio in preeclampsia are found to be associated with the risk for adverse perinatal outcome, the potential value of combined use of the two measurements for the prediction of adverse perinatal outcome has not been determined.

MATERIALS AND METHODS

This study included severe preeclampsia patients in late pregnancy and determined their serum GGT levels and ultrasonic flow resistance index of umbilical artery within a week before delivery. Demographic data and perinatal outcomes including perinatal death, five-minute Apgar score, admission to neonatal intensive care unit, respiratory distress syndrome, and intrauterine growth restriction, are documented and analyzed.

RESULTS

It was found that serum GGT combined with umbilical artery S/D ratio predicted perinatal adverse outcomes in severe preeclampsia patients with a sensitivity of 94.30% and a specificity of 80.00%. Moreover, absent or reversed UA diastolic blood flow was found to be an independent risk factor for intrauterine growth restriction.

CONCLUSION

GGT in combination with umbilical artery S/D ratio is a potentially useful marker for the prediction of adverse outcome in severe preeclampsia patients. Future studies in a larger cohort of patients should be performed to verify the efficacy of the strategy. Early and accurate prediction of adverse perinatal events can facilitate the efforts to improve the perinatal outcomes of neonates associated with preeclamptic pregnancies.

Gamma-glutamyl transferase and cardiovascular disease

Gamma-glutamyl transferase (GGT) is an enzyme located on the external surface of cellular membranes. GGT contributes in maintaining the physiological concentrations of cytoplasmic glutathione and cellular defense against oxidative stress via cleavage of extracellular glutathione and increased availability of amino acids for its intracellular synthesis. Increased GGT activity is a marker of antioxidant inadequacy and increased oxidative stress. Ample evidence suggests that elevated GGT activity is associated with increased risk of cardiovascular disease (CVD) such as coronary heart disease (CHD), stroke, arterial hypertension, heart failure, cardiac arrhythmias and all-cause and CVD-related mortality. The evidence is weaker for an association between elevated GGT activity and acute ischemic events and myocardial infarction. The risk for CVD or CVD-related mortality mediated by GGT may be explained by the close correlation of GGT with conventional CVD risk factors and various comorbidities, particularly non-alcoholic fatty liver disease, alcohol consumption, oxidative stress, metabolic syndrome, insulin resistance and systemic inflammation. The finding of GGT activity in atherosclerotic plaques and correlation of intra-plaque GGT activity with histological indexes of plaque instability may suggest a participation of GGT in the pathophysiology of CVD, particularly atherosclerosis. However, whether GGT has a direct role in the pathophysiology of CVD or it is an epiphenomenon of coexisting CVD risk factors or comorbidities remains unknown and Hill's criteria of causality relationship between GGT and CVD are not fulfilled. The exploration whether GGT provides prognostic information on top of the information provided by known cardiovascular risk factors regarding the CVD or CVD-related outcome and exploration of molecular mechanisms of GGT involvement in the pathophysiology of CVD and eventual use of interventions to reduce circulating GGT activity remain a duty of future studies.

Risk prediction of major complications in individuals with diabetes: the Atherosclerosis Risk in Communities Study

AIMS

To develop a prediction equation for 10-year risk of a combined endpoint (incident coronary heart disease, stroke, heart failure, chronic kidney disease, lower extremity hospitalizations) in people with diabetes, using demographic and clinical information, and a panel of traditional and non-traditional biomarkers.

METHODS

We included in the study 654 participants in the Atherosclerosis Risk in Communities (ARIC) study, a prospective cohort study, with diagnosed diabetes (visit 2; 1990-1992). Models included self-reported variables (Model 1), clinical measurements (Model 2), and glycated haemoglobin (Model 3). Model 4 tested the addition of 12 blood-based biomarkers. We compared models using prediction and discrimination statistics.

RESULTS

Successive stages of model development improved risk prediction. The C-statistics (95% confidence intervals) of models 1, 2, and 3 were 0.667 (0.64, 0.70), 0.683 (0.65, 0.71), and 0.694 (0.66, 0.72), respectively (p < 0.05 for differences). The addition of three traditional and non-traditional biomarkers [β-2 microglobulin, creatinine-based estimated glomerular filtration rate (eGFR), and cystatin C-based eGFR] to Model 3 significantly improved discrimination (C-statistic = 0.716; p = 0.003) and accuracy of 10-year risk prediction for major complications in people with diabetes (midpoint percentiles of lowest and highest deciles of predicted risk changed from 18-68% to 12-87%).

CONCLUSIONS

These biomarkers, particularly those of kidney filtration, may help distinguish between people at low versus high risk of long-term major complications.

Serum gamma-glutamyltransferase is not associated with subclinical atherosclerosis in patients with type 2 diabetes

BACKGROUND

This study investigated the association between serum gamma-glutamyltransferase (GGT) level and subclinical atherosclerosis in patients with type 2 diabetes.

METHODS

This cross-sectional study involved 1024 patients with type 2 diabetes mellitus. Measurement of brachial-ankle pulse wave velocity (baPWV; as a marker of arterial stiffness) and an ultrasound assessment of carotid atherosclerosis were performed. Subclinical atherosclerosis was defined by the presence of a high baPWV (≥1720 cm/s), carotid atherosclerosis (intima-media thickness >0.8 mm or the presence of plaques), and carotid stenosis (≥50 % of luminal narrowing). The subjects were stratified into quartiles according to GGT level, and the relationship between GGT level and subclinical atherosclerosis was analysed.

RESULTS

Serum GGT levels were closely associated with obesity, atherogenic dyslipidemia, and metabolic syndrome. However, serum GGT levels did not show a linear association with baPWV, carotid intima-media thickness, or plaque grade. The prevalence of high baPWV, carotid atherosclerosis, and carotid stenosis did not differ between the quartiles in men and women. Multivariate logistic regression analyses revealed no association between GGT level and high baPWV, carotid atherosclerosis, and carotid stenosis, either as continuous variables or quartiles.

CONCLUSIONS

Serum GGT levels were significantly associated with obesity, atherogenic dyslipidaemia, and metabolic syndrome, but not with the early and late stages of atherosclerotic vascular changes, in patients with type 2 diabetes. Serum GGT level may not be a reliable marker of subclinical atherosclerosis in type 2 diabetes.

Prognostic value of gamma-glutamyl transferase in patients with diabetes mellitus and coronary artery disease

OBJECTIVES

The aim of the study was to investigate the association between gamma-glutamyl transferase (GGT) activity and mortality in patients with diabetes mellitus and coronary artery disease (CAD).

DESIGN AND METHODS

The study included 1448 patients with diabetes and angiography-proven CAD who underwent percutaneous coronary intervention (PCI). Baseline GGT measurements were available in all patients. The primary outcome was 3-year mortality.

RESULTS

Patients were divided into 3 groups: a group consisting of patients with a GGT activity in the 1st tertile (GGT≤29.4U/L; n=487), a group consisting of patients with a GGT activity in the 2nd tertile (GGT>29.4-52.5U/L; n=479) and a group consisting of patients with GGT in the 3rd tertile (GGT>52.5U/L; n=482). Overall, there were 179 deaths: 46 (11.9%), 49 (12.1%) and 84 deaths (21.4%) among patients of the 1st, 2nd and 3rd GGT tertiles, respectively (adjusted hazard ratio [HR]=1.25, 95% confidence interval [CI] 1.05-1.49, P=0.011). Cardiac death occurred in 101 patients: 22 (5.8%), 30 (7.2%) and 49 deaths (12.9%) among patients of the 1st, 2nd and 3rd GGT tertiles, respectively (adjusted HR=1.23 [0.96-1.58], P=0.104, with risk estimates calculated per standard deviation increase in the logarithmic scale of GGT). GGT improved the risk prediction of models of all-cause (P=0.020) but not cardiac (P=0.135) mortality (P values show the difference in C-statistics between the models without and with GGT).

CONCLUSION

In patients with diabetes and CAD treated with PCI, elevated GGT was independently associated with the risk of 3-year all-cause mortality.

Serum Gamma-Glutamyltransferase Levels Predict Clinical Outcomes in Hemodialysis Patients

BACKGROUND

Gamma-glutamyltransferase (GGT) is a biomarker of liver injury. GGT has also been reported to be a marker of oxidative stress and a predictor of mortality in the general population. Hemodialysis (HD) patients suffer from oxidative stress. The aim of our study was to investigate the relationship between serum GGT levels and clinical outcomes in HD patients.

METHODS

A total of 1,634 HD patients were enrolled from the Clinical Research Center registry for end-stage renal disease, a prospective cohort in Korea. Patients were categorized into three groups by tertiles of serum GGT levels. The primary outcome was all-cause, cardiovascular, or infection-related mortality and hospitalization.

RESULTS

During the median follow-up period of 30 months, the highest tertile of serum GGT levels had a significantly higher risk for all-cause mortality (hazard ratio (HR) 2.39, 95% confidence interval (CI), 1.55-3.69, P<0.001), cardiovascular mortality (HR 2.14, 95% CI, 1.07-4.26, P = 0.031) and infection-related mortality (HR 3.07, 95% CI, 1.30-7.25, P = 0.011) using tertile 1 as the reference group after adjusting for clinical variables including liver diseases. The highest tertile also had a significantly higher risk for first hospitalization (HR 1.22, 95% CI, 1.00-1.48, P = 0.048) and cardiovascular hospitalization (HR 1.42, 95% CI, 1.06-1.92, P = 0.028).

CONCLUSIONS

Our data demonstrate that high serum GGT levels were an independent risk factor for all-cause, cardiovascular, and infection-related mortality, as well as cardiovascular hospitalization in HD patients. These findings suggest that serum GGT levels might be a useful biomarker to predict clinical outcomes in HD patients.

Serum Gamma-Glutamyltransferase Levels Predict Mortality in Patients With Peritoneal Dialysis

Serum gamma-glutamyltransferase (GGT) level has been considered marker of oxidative stress as well as liver function. Serum GGT level has been reported to be associated with the mortality in hemodialysis patients. However, it is not well established whether serum GGT level is associated with all-cause mortality in peritoneal dialysis (PD) patients. The aim of this study was to determine the association between serum GGT levels and all-cause mortality in PD patients.PD patients were included from the Clinical Research Center registry for end-stage renal disease cohort, a multicenter prospective observational cohort study in Korea. Patients were categorized into 3 groups by tertile of serum GGT levels as follows: tertile 1, GGT < 16 IU/L; tertile 2, GGT = 16 to 27 IU/L; and tertile 3, GGT > 27 IU/L. Primary outcome was all-cause mortality.A total of 820 PD patients were included. The median follow-up period was 34 months. Kaplan-Meier analysis showed that the all-cause mortality rate was significantly different according to tertiles of GGT (P = 0.001, log-rank). The multivariate Cox regression analysis showed that higher tertiles significantly associated with higher risk for all-cause mortality (tertile 2: hazard ratio [HR] 2.08, 95% confidence interval [CI], 1.17-3.72, P = 0.013; tertile 3: HR 1.83, 95% CI, 1.04-3.22, P = 0.035) in using tertile 1 as the reference group after adjusting for clinical variables.Our study demonstrated that high serum GGT levels were an independent risk factor for all-cause mortality in PD patients. Our findings suggest that serum GGT levels might be a useful biomarker to predict all-cause mortality in PD patients.

What does serum γ-glutamyltransferase tell us as a cardiometabolic risk marker?

γ-glutamyltransferase plays a key role in the synthesis and metabolism of extracellular glutathione, a major antioxidant in several defence mechanisms in the body. γ-glutamyltransferase is affected by environmental and genetic factors, and is raised when there is depletion of glutathione. Hence, it is a marker of oxidative stress. There is robust evidence that γ-glutamyltransferase even when values are within the reference interval is associated with increased cardiovascular and all-cause mortality in both sexes, in normal subjects and subjects with coronary artery disease, in the middle-aged and the elderly after adjusting for confounding factors. γ-glutamyltransferase even within the reference interval is associated with future presentation of type 2 diabetes, and the longitudinal increase in γ-glutamyltransferase activity is associated with increased risk of type 2 diabetes and cardiovascular mortality. γ-glutamyltransferase is associated with cardiovascular risk factors and metabolic syndrome. It has a prognostic value after a previous acute myocardial infarction and may be an indicator of adverse outcome in acute coronary syndromes and other chronic cardiac disorders. There is limited data about γ-glutamyltransferase and any association with peripheral arterial disease and also whether knowing γ-glutamyltransferase activity improves cardiovascular risk prediction beyond conventional risk factors. γ-glutamyltransferase is present in atherosclerotic lesions in the coronary and carotid arteries, and has a prooxidant role leading to the production of reactive oxygen species and atherosclerosis. Current reference intervals for γ-glutamyltransferase are inappropriate and need to be addressed. Some laboratories still use non- International Federation of Clinical Chemistry methods for estimation of γ-glutamyltransferase which are associated with lower results. Such laboratories should review their method and consider changing to the International Federation of Clinical Chemistry method.

Predictive models for all-cause and cardiovascular mortality in type 2 diabetic inpatients. A cohort study

BACKGROUND

Many authors have analysed premature mortality in cohorts of type 2 diabetic patients, but no analyses have assessed mortality in hospitalised diabetic patients.

AIM

To construct predictive models to estimate the likelihood of all-cause mortality and cardiovascular mortality in type 2 diabetic inpatients.

DESIGN

Cohort study with follow-up from 2010 to 2014.

METHODS

We evaluated mortality in a randomly selected cohort of 112 type 2 diabetic inpatients at the Hospital of Elda (Spain) in 2010-2012.

OUTCOMES

all-cause mortality and cardiovascular mortality during the follow-up. Other variables: gender, age, depression, asthma/chronic obstructive pulmonary disease, hypertension, dyslipidemia, insulin, pills, smoking, walking, baseline blood glucose and creatinine. Predictive tables with risk groups were constructed to estimate the likelihood of all-cause mortality and cardiovascular mortality. Calculations were made of the area under the ROC curve (AUC).

RESULTS

During the follow-up, 52 inpatients died (46.4%, 95% CI, confidence interval: 37.2-55.7%), 22 because of cardiovascular causes (19.6%, 95% CI: 12.3-27.0%). The mean follow-up time was 2.7 ± 1.5 years. The AUC for the all-cause mortality model was 0.84 (95% CI: 0.77-0.92, p < 0.001). Associated parameters: pills, smoking, walking, gender, insulin and age. The AUC for the cardiovascular mortality model was 0.79 (95% CI: 0.67-0.91, p < 0.001). Associated parameters: age, pills, walking, smoking, depression and insulin.

CONCLUSIONS

This study provides tools to predict premature mortality in type 2 diabetic inpatients. However, before their general application they require joint validation by the internal medicine unit, emergency department, primary healthcare unit and endocrinology service to enable better prediction of the prognosis and more adequate decision-taking.

Serum Gamma-glutamyltransferase Levels Predict the Progression of Coronary Artery Calcification in Adults With Type 2 Diabetes Mellitus

Progression of coronary artery calcification (CAC) may be more predictive of future coronary heart disease events than a baseline CAC score. We determined whether serum gamma-glutamyltransferase (GGT) activity can independently predict the progression of CAC in adults with type 2 diabetes mellitus (T2DM). Patients (n = 326) without symptomatic cardiovascular (CV) disease were evaluated by CAC imaging. The CAC scores were assessed at baseline and after 20 ± 4 months. Serum GGT activities were significantly higher in progressors compared with nonprogressors (39 ± 16 vs 27 ± 11 U/L, P < .001). Multivariable analyses demonstrated that GGT activity retained a strong association with CAC progression after adjustment for CV risk factors. Additionally, there was a graded association between GGT activity quartile and annualized CAC progression. In asymptomatic patients with T2DM, we prospectively found that serum GGT activity may be an independent predictor of CAC progression but not a predictor of CAC incidence.

Gamma-glutamyltransferase predicts increased risk of mortality: a systematic review and meta-analysis of prospective observational studies

The aim of this study was to evaluate the association between gamma-glutamyltransferase (GGT) and mortality through a comprehensive analysis of existing evidence. PubMed, Embase, Chinese Biomedical Literature, and Science Citation Index databases were electronically searched. Studies were included if the study design was prospective and included reference and at-risk levels of GGT at baseline and mortality as a separate outcome. The quality of the studies included was assessed on the basis of Newcastle-Ottawa scale. Data from selected qualified studies were systematically reviewed, pooled, and analyzed according to the MOOSE guidelines and PRISMA statement. The results included the following: 1. 35 studies including 571,511 participants and 72,196 cases of mortality; 2. GGT, even at physiologic levels, was associated with increased all-cause mortality and cardiovascular mortality, and might also be associated with cancer-related mortality in the general population; and 3. GGT was very likely to be associated with all-cause mortality and cardiovascular mortality in patients with coronary artery disease and type 2 diabetes mellitus. Many of the studies included did not specifically exclude subjects with hepatic diseases or alcohol abuse, which may have obscured the results. Moderate heterogeneity was observed in the meta-analysis of GGT and all-cause mortality. Different compositions of cause-specific mortality might be the reason. However, subgroup analysis could only be performed on cardiovascular death because of insufficient information. GGT, even at physiologic high levels, predicted mortality, especially cardiovascular mortality and cancer mortality. The underlining mechanism and potential effects of GGT-targeted intervention on health warrant further investigation.

Human GGT2 does not autocleave into a functional enzyme: A cautionary tale for interpretation of microarray data on redox signaling

AIMS

Human γ-glutamyltranspeptidase 1 (hGGT1) is a cell-surface enzyme that is a regulator of redox adaptation and drug resistance due to its glutathionase activity. The human GGT2 gene encodes a protein that is 94% identical to the amino-acid sequence of hGGT1. Transcriptional profiling analyses in a series of recent publications have implicated the hGGT2 enzyme as a modulator of disease processes. However, hGGT2 has never been shown to encode a protein with enzymatic activity. The aim of this study was to express the protein encoded by hGGT2 and each of its known variants and to assess their stability, cellular localization, and enzymatic activity.

RESULTS

We discovered that the proteins encoded by hGGT2 and its variants are inactive propeptides. We show that hGGT2 cDNAs are transcribed with a similar efficiency to hGGT1, and the expressed propeptides are N-glycosylated. However, they do not autocleave into heterodimers, fail to localize to the plasma membrane, and do not metabolize γ-glutamyl substrates. Substituting the coding sequence of hGGT1 to conform to alterations in a CX3C motif encoded by hGGT2 mRNAs disrupted autocleavage of the hGGT1 propeptide into a heterodimer, resulting in loss of plasma membrane localization and catalytic activity.

INNOVATION AND CONCLUSIONS

This is the first study to evaluate hGGT2 protein. The data show that hGGT2 does not encode a functional enzyme. Microarray data which have reported induction of hGGT2 mRNA should not be interpreted as induction of a protein that has a role in the metabolism of extracellular glutathione and in maintaining the redox status of the cell.

Gamma-glutamyltransferase is associated with cardiovascular and all-cause mortality: a meta-analysis of prospective cohort studies

OBJECTIVE

The purpose of the present study was to investigate whether gamma-glutamyltransferase (GGT) is an independent predictor for future cardiovascular (CV) and all-cause mortality with prospective observational studies by meta-analysis.

METHODS

Electronic literature databases (Cochrane Library, Medline, and Embase) were searched for relevant prospective observational studies on the association between baseline GGT and CV and all-cause mortality published prior to June 2012. Pooled adjust relative risk (RR) and corresponding 95% confidence intervals(CI) were calculated separately for categorical risk estimates(highest vs. lowest GGT quartile) and continuous risk estimates (per unit-log GGT increment).

RESULTS

Seven studies with 273,141 participants were identified and analyzed. The pooled RR of CV mortality for highest vs. lowest GGT quartile was 1.52 (95% CI 1.36-1.70). The pooled RR of CV mortality for per unit-log (GGT) increment was 1.76 (95% CI 1.60-1.94). The pooled RR for all-cause mortality for highest vs. low GGT quartile was 1.56 (95% CI 1.34-1.83). Subgroup analyses based on region, gender, follow-up duration, and sample size showed that the positive association between GGT and risk of CV mortality was consistently observed in each subgroup except for the Asia subgroup (RR=1.59, 95% CI 0.76-3.30).

CONCLUSIONS

GGT is an independent predictor for future CV mortality and all-cause mortality, and might be independent of alcohol intake.

Serum thiols and cardiovascular risk scores: a combined assessment of transsulfuration pathway components and substrate/product ratios

Background

Serum thiols have shown associations with surrogate markers of cardiovascular disease. However, little information is available on their combined association with validated cardiovascular risk scores for primary prevention at population level. We sought to determine whether individual serum thiol concentrations and substrate/product ratios within the transsulfuration pathway are independently associated with such scores.

Methods

Data on clinical and demographic characteristics, serum thiols (homocysteine, cysteine, taurine, glutamylcysteine, total glutathione and cysteinylglycine) and high-sensitivity C-reactive protein (CRP) were collected from a sample of the Hunter Community Study without previous cardiovascular events [n=350, median age (IQR) = 62 (59–66) years]. Five-year absolute cardiovascular risk score for each subject was calculated using the Framingham Risk Equation.

Results

Median risk score was 7% (IQR 4–10). After adjusting for body mass index, estimated glomerular filtration rate and physical activity regression analysis showed independent associations between cardiovascular risk scores and a) higher serum homocysteine (B 0.066, 95% CI 0.040 to 0.091, P<0.001) and lower cysteine (B −0.003, 95% CI −0.005 to −0.001, P=0.003) and glutathione (B −0.029, 95% CI −0.056 to −0.003, P=0.03) concentrations; and b) higher homocysteine/cysteine (B 0.114, 95% CI 0.066 to 0.161, P<0.001) and lower glutathione/cysteinylglycine (B −1.145, 95% CI −2.030 to −0.260, P=0.011) ratios. No significant associations were observed between cardiovascular risk scores, taurine and CRP.

Conclusions

Serum homocysteine, cysteine and glutathione are independently associated with cardiovascular risk scores at population level. Enzymatic pathways involved in reduced bioconversion of homocysteine into cysteine and increased glutathione degradation might play an important role in such associations.

Serum γ-glutamyltranspeptidase predicts all-cause, cardiovascular and liver mortality in older adults

BACKGROUND

Serum γ-glutamyltranspeptidase (GGT), a marker of fatty liver disease (FLD), predicts mortality in young adults. However, the association between serum GGT and mortality in older adults is unclear.

OBJECTIVES

To examine if elevated serum GGT predicts all-cause, cardiovascular (CVD), and liver mortality in community-dwelling older adults.

DESIGN AND SETTING

A prospective cohort study including 2364 participants (mean-age 70 yr, BMI-24.5 kg/m², 54% women) from the Rancho Bernardo Study who attended a research visit in 1984-87 when multiple metabolic covariates were ascertained including serum GGT. They were followed for a mean (± standard deviation) of 13.7 (±6.2) years.

MEASUREMENT

Multivariable-adjusted Cox-proportional hazards analyses were conducted to examine the association between elevated serum GGT (>51 U/L in men and > 33 U/L in women) and all-cause, CVD, and liver mortality.

RESULTS

In these older men and women, cumulative mortality was 56.2% (n=1329) with CVD and liver mortality accounting for 49.4% and 2.3% of all deaths, respectively, over 32,387 person-years of follow-up. In multivariate analyses (adjusted for age, sex, alcohol use, body-mass-index, total cholesterol, HDL cholesterol, serum triglyceride, smoking status, systolic blood pressure, diabetes mellitus, serum interleukin-6, and c-reactive protein), serum GGT elevation was significantly associated with all-cause (HR, 1.55, 95% CI, 1.21-1.98), CVD (HR, 1.51, 95% CI, 1.04-2.17), and liver mortality (HR, 9.10, 95% CI, 3.42-24.26).

CONCLUSIONS

In community-dwelling older adults, serum GGT is an independent predictor of all-cause, CVD, and liver mortality.

Gamma-glutamyltransferase and risk of cardiovascular disease mortality in people with and without diabetes: pooling of three British Health Surveys

BACKGROUND & AIMS

The relation between gamma-glutamyltransferase (GGT) and mortality risk has been little explored in people with diabetes. We examined (a) the association of GGT with cardiovascular disease (CVD) and all-cause mortality in people with and without diabetes; and (b) the predictive validity observed when adding GGT to a CVD risk algorithm.

METHODS

Participants were 17,852 adults from three British cohorts representative of the general population in England (N=1) and Scotland (N=2). Follow-up was to December 2009 (Scottish cohorts) and February 2008 (English cohort). Cox models were used to compute the hazard ratio (HR) and 95% confidence interval (95% CI) for a standard deviation (SD) increase log(e)(GGT) in relation to mortality according to diabetes status. The value of adding GGT to a CVD risk engine was assessed through c-statistic and relative integrated discrimination improvement.

RESULTS

In an analytical sample of 17,852 participants, 583 (3.3%) had baseline diabetes. During 10.1 years of follow-up, there were 235 deaths from all causes (77 from CVD) in diabetics. Corresponding results for non-diabetics were 2859 and 719. The age- and sex-adjusted HR (95%CI) for a one SD increase in log(e)(GGT) in relation to CVD mortality risk in participants with diabetes was 1.43 (1.13-1.81) and in those without diabetes was 1.27 (1.18-1.37). Corresponding results for total mortality were 1.24 (1.08-1.44) and 1.30 (1.25-1.34). Thus, there was no evidence that diabetes status modified the strength of the GGT-mortality relationship (p value for interaction ≥0.16). Adding GGT to model with classical predictors only marginally enhanced the prediction of CVD in both people with and without diabetes.

CONCLUSIONS

Higher GGT levels are a risk factor for all-cause and cardiovascular disease death in people with and without diabetes. However, knowledge of GGT does not improve cardiovascular predictions beyond traditional risk factors.