gamma-Glutamyl transpeptidase activity in liver disease: serum elevation is independent of hepatic GGTP activity

Advances and Perspectives of Responsive Probes for Measuring γ-Glutamyl Transpeptidase

Gamma-glutamyltransferase (GGT) is a plasma-membrane-bound enzyme that is involved in the γ-glutamyl cycle, like metabolism of glutathione (GSH). This enzyme plays an important role in protecting cells from oxidative stress, thus being tested as a key biomarker for several medical conditions, such as liver injury, carcinogenesis, and tumor progression. For measuring GGT activity, a number of bioanalytical methods have emerged, such as chromatography, colorimetric, electrochemical, and luminescence analyses. Among these approaches, probes that can specifically respond to GGT are contributing significantly to measuring its activity in vitro and in vivo. This review thus aims to highlight the recent advances in the development of responsive probes for GGT measurement and their practical applications. Responsive probes for fluorescence analysis, including "off-on", near-infrared (NIR), two-photon, and ratiometric fluorescence response probes, are initially summarized, followed by discussing the advances in the development of other probes, such as bioluminescence, chemiluminescence, photoacoustic, Raman, magnetic resonance imaging (MRI), and positron emission tomography (PET). The practical applications of the responsive probes in cancer diagnosis and treatment monitoring and GGT inhibitor screening are then highlighted. Based on this information, the advantages, challenges, and prospects of responsive probe technology for GGT measurement are analyzed.

Liver protection and hemostatic effects of medicinal plant Arnebia euchroma (Royle) I.M.Johnst extract in a rat model

ETHNOPHARMACOLOGICAL RELEVANCE

Arnebia euchroma (Royle) I.M.Johnst. (AE) is a Chinese medicinal herb that is traditionally used to treat various circulatory diseases. It exhibits certain effects, such as the promotion of blood circulation and cooling, rash clearance, and detoxification.

AIM OF THE STUDY

This study was designed to explore the hepatoprotective and hemostatic effects of the ethyl acetate extract of AE in rats with carbon tetrachloride (CCl4)-induced liver injury.

MATERIALS AND METHODS

Wistar rats were treated via oral gavage with different doses of the ethyl acetate extract of AE (3.5, 7, or 14 g kg^-1·day^-1) for 14 consecutive days, following which hemostatic and liver function tests were conducted. For the hemostatic tests, the platelet count, blood platelet aggregation, blood platelet adhesion to fibrinogen, platelet factor 4 (PF-4) secretion from blood platelets, prothrombin time (PT), activated partial thromboplastin time (aPTT), thrombin time (TT), and fibrinogen levels were measured at the end of the treatment period. For the liver function tests, 0.25 mL/200 g (1.25 mL kg^-1·day^-1) of olive oil was injected into the abdominal cavity of the control rats, whereas 15% CCl₄ plus olive oil (prescription: 7.5 mL CCl₄ + 42.5 olive oil) was injected into that of the treated rats at 1 h after extract administration on day 6, 13, and 20. Additionally, food and water were withheld from all the animals. On the following day, the rats were anesthetized and their albumin, aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP), serum glutamic oxaloacetic transaminase (SGOT), serum glutamic pyruvic transaminase (SGPT), gamma-glutamyl transpeptidase (GGT), lactate dehydrogenase (LDH), reactive oxygen species (ROS), methane dicarboxylic aldehyde (MDA), superoxide dismutase (SOD), catalase (CAT), and glutathione (GSH) levels were measured. Glutathione S-transferase (GST), glutathione reductase (GR), and glutathione peroxidase (GPx) levels among the groups were determined using a one-way analysis of variance.

RESULTS

The platelet count and blood platelet aggregation, blood platelet adhesion to fibrinogen and PF-4 secretion levels were significantly increased in the (3.5 g kg^-1 day^-1) AE group as compared to those in the control group (all p < 0.001; for the 7 and 14 g kg^-1 day^-1 AE groups, all p > 0.05, respectively). Although the PT and aPTT were not affected by the AE extract (all p > 0.05), the TT was reduced and the FIB levels were significantly increased in all AE groups (p < 0.05). Liver function tests showed that CCl₄ caused significant liver damage, thereby decreasing the albumin, SOD, CAT, GSH, GST, GR, and GPx levels, while increasing the AST, ALT, ALP, SGOT, SGPT, GGT, LDH, ROS, and MDA levels (all p < 0.001). By contrast, treatment with the different doses of AE extract reversed the CCl₄ effects on all these parameters. Compared with the levels in the CCl₄ group, the GSH and GR levels in the three AE groups (3.5, 7, and 14 g kg^-1·day^-1) were significantly higher (p < 0.05, p < 0.01, and p < 0.001, respectively), whereas the differences in the other parameters for these three groups were all at the significance levels of p < 0.05, p < 0.05, and p < 0.01, respectively.

CONCLUSIONS

AE extracts administered orally exhibited hepatoprotective activity by affecting platelet production and blood coagulation and ameliorating liver function-damaging modifications. Specifically, a dosage of 3.5 g kg^-1·day^-1 resulted in the most optimal effects.

A Systematic Review of Serum γ-Glutamyltransferase as a Prognostic Biomarker in Patients with Genitourinary Cancer

γ-Glutamyltransferase (GGT), a membrane-bound enzyme, contributes to the metabolism of glutathione (GSH), which plays a critical physiological role in protecting cells against oxidative stress. GGT has been proposed as a biomarker of carcinogenesis and tumor progression given that GGT activity is important during both the promotion and invasion phases in cancer cells. Moreover, GGT expression is reportedly related to drug-resistance possibly because a wide range of drugs are conjugated with GSH, the availability of which is influenced by GGT activity. While serum GGT activity is commonly used as a quick, inexpensive, yet reliable means of assessing liver function, recent epidemiological studies have shown that it may also be an indicator of an increased risk of prostate cancer development. Moreover, elevated serum GGT is reportedly an adverse prognostic predictor in patients with urologic neoplasms, including renal cell carcinoma, prostate cancer, and urothelial carcinoma, although the background mechanisms have still not been well-characterized. The present review article summarizes the possible role of GGT in cancer cells and focuses on evidence evaluation through a systematic review of the latest literature on the prognostic role of serum GGT in patients with genitourinary cancer.

Associations between total serum GGT activity and metabolic risk: MESA

AIM

To evaluate associations between total serum GGT activity, metabolic risk factors and prevalent metabolic disease in MESA.

PATIENTS & METHODS

Continuous associations between GGT and fasting blood glucose (FBG), fasting insulin, HbA1c and Homeostasis Model Assessment Index of Insulin Resistance (HOMA-IR) were evaluated in the entire MESA cohort and in metabolic disease subgroups using linear regression models incrementally adjusted for age, gender, site, race, lifestyle, traditional risk factors and medications. Cross-sectional odds of prevalent impaired FBG, metabolic syndrome and Type 2 diabetes were calculated for GGT quintiles in the entire cohort and in subgroups defined by age (< or ≥65 years) and ethnicity.

RESULTS

In multivariable models, significant associations were present between GGT activity and FBG, fasting insulin, HbA1c and HOMA-IR, with the interaction between GGT and BMI affecting the association between GGT and HOMA-IR as well as the association between BMI and HOMA-IR (p < 0.0001). Adjusted odds ratios (95% CIs) of prevalent impaired FBG, metabolic syndrome and Type 2 diabetes for quintile 5 versus 1 in the entire cohort were 2.4 (1.7-3.5), 3.3 (2.5-4.5) and 2.8 (1.8-4.4), respectively (p < 0.0001). GGT associations weakened with age. The significance of linear trends for increased prevalent metabolic disease by increasing GGT quintile varied by ethnicity.

CONCLUSION

GGT is strongly associated with both cardiovascular and metabolic risk factors, including prevalent metabolic disease, in the MESA cohort.

Associations between γ-glutamyltransferase (GGT) and biomarkers of atherosclerosis: the Multi-ethnic Study of Atherosclerosis (MESA)

OBJECTIVE

To evaluate associations between total serum γ-glutamyltransferase activity (GGT) and biomarkers of arteriosclerosis in the Multi-Ethnic Study of Atherosclerosis (MESA), including 6783 participants from four ethnic subgroups, i.e., White, Chinese, Black and Hispanic.

METHODS

Associations between fasting total serum GGT activity and oxidized low-density lipoproteins (oxLDL), interleukin-6 (IL-6), C-reactive protein (CRP), and soluble intercellular adhesion molecule-1 (sICAM-1) were assessed. Following evaluation of linear trends between GGT and biomarkers of interest, multivariable linear regression models were serially adjusted for age, gender, site, ethnicity (M1); M1+lifestyle variables (M2); M2+traditional cardiovascular risk factors plus medications (M3); and M3+metabolic status (M4). Interactions were evaluated between GGT and age and ethnicity in all models.

RESULTS

Linear trends were positive and significant between GGT and oxLDL, IL-6, CRP and sICAM-1 in crude models, and trends remained significant in all ethnic subgroups for CRP (p<0.0001) and sICAM-1 (p<0.001), and for IL-6 except in the Chinese. Trends between GGT and oxLDL were significant in the entire cohort and the White subgroup (p<0.0001), but not in other ethnic subgroups. Multivariable models demonstrated continuous strong, positive associations between GGT and CRP, IL-6 and sICAM-1. Associations between GGT and oxLDL were attenuated upon adjustment for LDL-C and other traditional risk factors. All models were attenuated with adjustment for metabolic status. No age interactions were evident.

CONCLUSIONS

Our findings support the hypothesis that total serum GGT activity represents the impact of metabolic disease on vascular injury and atherosclerosis.

Biochemical Evaluation of Patients of Alcoholic Liver Disease and Non-alcoholic Liver Disease

Alcoholic liver disease (ALD) is due to excessive alcohol intake for long duration. Distinguishing ALD from non-ALD (non-alcoholic steatohepatitis, hepatitis of viral origin) is difficult as patient may deny alcohol abuse. Clinical examination, histology and serology may not differentiate these conditions. Accurate diagnosis is important as management of ALD differs from non-ALD patients. The aim of our study was (1) To evaluate the patients of ALD and non-ALD by biochemical parameters compared to controls, (2) To assess whether these parameters can differentiate ALD from non-ALD. Study was carried out on 50 patients of ALD in group I and 35 patients of NASH (non-alcoholic steatohepatitis) and acute viral hepatitis each in group II. Age matched healthy controls n = 50. Selection criteria-history of alcohol intake (amount and duration), clinical examination, sonography of abdomen, serum alanine transaminase (ALT) and bilirubin levels. Blood samples were analyzed for bilirubin, aspartate transaminase (AST), ALT, alkaline phosphatase (ALP), gamma glutamyl transferase (GGT) by kinetic method. Statistical analysis was done by Student unpaired 't' test. Patients of ALD have raised AST/ALT ratio (De Ritis ratio) (>2), ALP and GGT compared to controls (P < 0.01).There is significant difference in AST/ALT ratio, serum GGT and ALP in ALD group compared to that in NASH and acute viral hepatitis (P < 0.05). This study suggests that De Ritis ratio >2 in ALD patients may be due to alcohol induced hepatic mitochondrial injury and pyridoxine deficiency. High GGT and ALP values may indicate enzyme induction by alcohol and mild cholestasis. Thus ALD patients have severe hepatic damage. De Ritis ratio <1 and normal to mild elevation in GGT level in NASH and acute viral hepatitis suggest mild hepatic injury of non-alcoholic origin. Our study concludes that ALD patients can be differentiated from NASH and acute viral hepatitis with certainty by measuring serum AST/ALT ratio, GGT and ALP. These biochemical parameters may help clinicians to support the diagnosis of ALD and non-ALD.

Effects of Hepatic Drug-metabolizing Enzyme Induction on Clinical Pathology Parameters in Animals and Man

Hepatic drug-metabolizing enzyme (DME) induction is an adaptive response associated with changes in preclinical species; this response can include increases in liver weight, hepatocellular hyperplasia and hypertrophy, and upregulated tissue expression of DMEs. Effects of DME induction on clinical pathology markers of hepatobiliary injury and function in animals as well as humans are not well established. This component of a multipart review of the comparative pathology of xenobiotically mediated induction of hepatic metabolizing enzymes reviews pertinent data from retrospective and prospective preclinical and clinical studies. Particular attention is given to studies with confirmation of DME induction and concurrent evaluation of liver and/or serum hepatobiliary marker enzyme activities and histopathology. These results collectively indicate that in the rat, when histologic findings are limited to hepatocellular hypertrophy, DME induction is not expected to be associated with consistent or substantive changes in serum or plasma activity of hepatobiliary marker enzymes such as alanine aminotransferase, alkaline phosphatase, and gamma glutamyltransferase. In the dog and the monkey, published studies also do not demonstrate a consistent relationship across DME-inducing agents and changes in these clinical pathology parameters. However, increased liver alkaline phosphatase or gamma glutamyltransferase activity in dogs treated with phenobarbital or corticosteroids suggests that direct or indirect induction of select hepatobiliary injury markers can occur both in the absence of liver injury and independently of induction of DME activity. Although correlations between tissue and serum levels of these hepatobiliary markers are limited and inconsistent, increases in serum/plasma activities that are substantial or involve changes in other markers generally reflect hepatobiliary insult rather than DME induction. Extrahepatic effects, including disruption of the hypothalamic-pituitary-thyroid axis, can also occur as a direct outcome of hepatic DME induction in humans and animals. Importantly, hepatic DME induction and associated changes in preclinical species are not necessarily predictive of the occurrence, magnitude, or enzyme induction profile in humans.

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.

Laboratory markers of ethanol intake and abuse: a critical appraisal

Laboratory markers for ethanol intake and abuse and chronic alcoholism currently in use have been critically reviewed. The merits and pitfalls of each test have been evaluated. The clinical use of the new test of carbohydrate-deficient transferrin has been particularly emphasized. Carbohydrate-deficient transferrin currently provides the highest specificity and sensitivity of all commonly used markers of alcoholism.

Gamma-glutamyl transferase ectoactivity in the intact rat liver: effect of chronic alcohol consumption

The localization of gamma-glutamyl transferase (GGT) in the intact rat liver was studied by a new approach in which the chromogenic gamma-glutamyl donor substrate of GGT gamma-glutamyl-p-nitroanilide is perfused through the portal vein to yield p-nitroaniline, which is monitored spectrophotometrically. GGT activity was markedly increased by the gamma-glutamyl acceptors glycyl-glycine, cystine and methionine, following Michaelis-Menten kinetics. Infusion of glutathione (GSH), the natural substrate of GGT, was shown to markedly reduce or to abolish the formation of p-nitroaniline without entering the liver cells, indicating the existence of a GGT ectoactivity accessible to the sinusoidal circulation. This ectoenzyme was shown to remove significant amounts of GSH from the circulation, amounting, in the naive rat, to 20-25% of the net rate at which GSH is contributed by the liver into the circulation. Chronic alcohol consumption is known to increase hepatic GGT activity, although the biological significance of such an effect remains unknown. Present studies show that chronic administration of alcohol to rats leads to a significant (40-75%) increase in hepatic GGT ectoactivity. GGT ectoactivity significantly correlates with total liver GGT, both in control and alcohol-treated animals (r = .76 and r = .90, respectively). Livers of alcohol-fed rats showed an increased (80-110%) capacity to remove circulating GSH which strongly correlated with total liver GGT (r = .96; p less than 0.0001).(ABSTRACT TRUNCATED AT 250 WORDS)

High hepatic gamma-glutamyltransferase (gamma-GT) activity with normal serum gamma-GT in children with progressive idiopathic cholestasis

gamma-Glutamyl transferase (gamma-GT) was assayed in the serum and liver biopsies of children affected with either progressive idiopathic cholestasis (PIC, Byler's disease), or other types of cholestatic (biliary atresia, cholestasis of various origins) and non-cholestatic diseases. The mean liver gamma-GT activity was increased significantly only in PIC and biliary atresia. In contrast, the serum gamma-GT activity, raised in children with evident damage to the main bile ducts or to the interlobular bile ducts, was normal in children with PIC. Although the mechanism for such a discrepancy between high liver and normal serum gamma-GT activities in PIC is still speculative, this peculiarity could prove to be of use in leading to a better understanding of the disease.

Clinical use of serum enzymes in liver disease

Some of the many enzymes found in hepatocytes can be measured in the serum and are used as tests of liver function. We now review the current knowledge of their physiology and pathophysiology and outline their clinical usefulness. We divide them into two categories: enzymes that primarily reflect cholestasis, such as the alkaline phosphatase, the 5'-nucleotidase, and the gamma-glutamyl transpeptidase, and those that primarily reflect hepatocellular necrosis, such as the aminotransferases. We also briefly discuss several enzymes of more limited usefulness.

Enhanced biliary gamma-glutamyltransferase excretion following prolonged alcohol consumption in rats

In order to study the question of whether chronic ethanol consumption may alter the biliary excretion of gamma-glutamyltransferase (gamma-GT), female rats were pair-fed nutritionally adequate liquid diets containing either ethanol (36% of total calories) or isocaloric carbohydrates for 24 days. Compared to pair-fed controls, the administration of the alcohol-containing diet resulted in an increased biliary excretion of gamma-GT (5.84 +/- 0.73 mU 6 h-1 100 g-1 b.w. vs. 8.82 +/- 0.79, P less than 0.001). This was associated with a corresponding enhanced biliary output of total bile acids. An apparent linear relation between the biliary output rates of gamma-GT and those of total bile acids was observed both in alcohol-fed animals (r = 0.83) and in their pair-fed controls (r = 0.95). In addition, there was a significant increase of gamma-glutamyltransferase activities in the liver homogenate and in liver plasma membranes, both in fractions rich in bile canalicular and basolateral membranes and in those rich in blood sinusoidal site. Serum gamma-glutamyltransferase activities as well as serum bile acid concentrations were also enhanced by 96.8% (P less than 0.001) and 233% (P less than 0.001), respectively. These data show that chronic alcohol consumption enhances hepatic gamma-GT activities, leading to an increased efflux of gamma-GT into the bile and possibly into the blood out of the liver cell. Furthermore, these data suggest the involvement of bile acids with their solubilizing properties for the biliary excretion of gamma-GT.

Duodenal gamma-glutamyltransferase activity in human biopsies: effect of chronic ethanol consumption and duodenal morphology

Gamma-glutamyltransferase activity was determined in duodenal biopsies, and in the sera of forty-six non-alcoholic and eighteen alcoholic patients with a daily alcohol consumption of more than 80 g. Additionally, duodenal morphology was examined in biopsy material obtained at the same time. In both alcoholics (P less than 0.05) and in non-alcoholics (P less than 0.001) the duodenal gamma-glutamyltransferase activity revealed a significant positive correlation with duodenal villus length. In addition, alcoholics exhibited a significant decrease in duodenal villus length (338 +/- 13 vs. 363 +/- 13 microns, P less than 0.01), and a significant increase in duodenal gamma-glutamyltransferase activity (13.0 +/- 1.4 vs. 8.4 +/- 0.6 mU mg-1 protein, P less than 0.01) when compared to controls. No significant correlation was found between duodenal and serum gamma-glutamyltransferase activity in alcoholics and non-alcoholics. During follow up of two patients, duodenal gamma-glutamyltransferase activity decreased and duodenal villus length increased after withdrawing alcohol. These data underline the damaging effect of alcohol on the duodenal mucosa and demonstrate that chronic alcohol intake reversibly effects duodenal gamma-glutamyltransferase. In addition, the small intestine appears of minor importance as an origin for the elevated serum gamma-glutamyltransferase activities seen in the alcoholic.