Ethanol effects in a rat hepatoma cell line: induction of gamma-glutamyltransferase

1α,25-Dihydroxyvitamin D3 enhances γ-glutamyl transpeptidase activity in LLC-PK1 porcine kidney epithelial cells

Mammalian γ-glutamyl transpeptidase (GGT) is expressed most highly in the kidney and serves to recover the constituent amino acids of glutathione in the proximal tubules. Serum GGT is used as a marker for obstructive jaundice and alcoholic liver disease and it has been reported that urinary GGT is a potential marker for bone resorption. The present study investigated the effect of derivatives of vitamin D3 on GGT activity in LLC-PK1 porcine renal tubular epithelial cells in order to analyze the biochemical basis of bone metabolism-associated alterations in GGT activity in the kidney. In the presence of 1α,25-dihydroxyvitamin D3 [1,25(OH)2VD3], GGT activity was observed to be significantly increased in LLC-PK1 cells, with an increase in GGT activity also found in the cell medium. While the stimulatory effect of 1-OH-VD3 was similar to that of 1,25(OH)2VD3, vitamin D3 and 25-OH-VD3 had no effect on GGT activity. The increased GGT activity caused by 1,25(OH)2VD3 in LLC-PK1 cells was the result of long-term stimulation of the cells, in contrast to the GGT-induced increase in alkaline phosphatase, which is more transient. Polymerase chain reaction analysis revealed that the 1,25(OH)2VD3‑induced increase in GGT activity was due to prolonged GGT turnover, rather than increased GGT expression, as no increase in GGT mRNA expression was observed. Thus, it is likely that the expression of GGT is not entirely constitutive in the kidney, but is altered under certain conditions, including under hormonal regulation.

The Serum Gamma Glutamyl Transpeptidase - A Non invasive Diagnostic Bio Marker of Chronic Anicteric Non Alcoholic Liver Diseases

BACKGROUND

The serum gamma glutamyl transpeptidase (GGT) levels rise and return to normal levels later in the chronic anicteric non alcoholic liver diseases than the transaminases levels. So, the estimation of GGT is of some value in monitoring the progress of acute to chronic hepatitis, when the values persist in high levels.

AIMS AND OBJECTIVES

To evaluate the serum GGT levels in patients with chronic anicteric non alcoholic liver diseases and to show that it can be used as a noninvasive diagnostic biomarker for the diagnosis of chronic anicteric non alcoholic liver disorders.

MATERIALS AND METHODS

This was a case control study, in which 50 cases and 50 controls were selected.The liver function tests with a special reference to the serum level of GGT were measured in the laboratory for both the cases and the controls and the serum GGT levels of the cases were compared with those of the controls. The Chi-square and the Fisher exact tests were used to find the significance of the proportions of the study parameters between the cases and the controls. The Student's t test (two tailed) was used to find the significance mean pattern of the study parameters between the cases and the controls.

RESULTS

The mean serum GGT level was 38.73±11 IU/L in the cases and in the controls, it was 20.42±9 IU/L(p<0.001).The mean value of serum ALT was 41.37±12.5 vs 16.3±8iu/l(p<0.001), that of AST was 28.14±8 vs 17.56±8.5iu/l(p<0.05), that of total bilirubin was 0.9±0.3 vs 0.5±0.2mg/dl and that of serum albumin was 4.17±0.6 vs 4.5±0.75gm/dl, as were seen in the cases and the controls respectively.

CONCLUSION

The serum gamma glutamyl transpeptidase level was elevated more consistently along with the alanine transaminase level in all types of anicteric nonalcoholic chronic liver diseases. The alanine transminase level has already been proved to be a marker in the diagnosis of chronic anicteric nonalcoholic liver diseases. So, in view of the persistent elevation, along with the high sensitivity, the elevated gamma glutamyl transpeptidase level can also be used as a noninvasive bio marker of chronic anicteric nonalcoholic liver diseases for both diagnostic and therapeutic purposes.

Antioxidant, anti-diabetic and renal protective properties of Stevia rebaudiana

BACKGROUND

Stevia rebaudiana Bertoni has been used for the treatment of diabetes in, for example, Brazil, although a positive effect on antidiabetic and its complications has not been unequivocally demonstrated. This herb also has numerous therapeutic properties which have been proven safe and effective over hundreds of years. Streptozotocin is a potential source of oxidative stress that induces genotoxicity.

OBJECTIVE

We studied the effects of stevia leaves and its extracted polyphenols and fiber on streptozotocin induced diabetic rats. We hypothesize that supplementation of polyphenols extract from stevia to the diet causes a reduction in diabetes and its complications.

DESIGN/METHODS

Eighty Wistar rats were randomly divided into 8 groups; a standard control diet was supplemented with either stevia whole leaves powder (4.0%) or polyphenols or fiber extracted from stevia separately and fed for one month. Streptozotocin (60 mg/kg body weight, i.p) was injected to the diabetic groups on the 31st day. Several indices were analyzed to assess the modulation of the streptozotocin induced oxidative stress, toxicity and blood glucose levels by stevia.

RESULTS

The results showed a reduction of blood glucose, ALT and AST, and increment of insulin level in the stevia whole leaves powder and extracted polyphenols fed rats compared to control diabetic group. Its feeding also reduced the MDA concentration in liver and improved its antioxidant status through antioxidant enzymes. Glucose tolerance and insulin sensitivity were improved by their feeding. Streptozotocin was also found to induce kidney damage as evidenced by decreased glomerular filtration rate; this change was however alleviated in the stevia leaves and extracted polyphenol fed groups.

CONCLUSION

The results suggested that stevia leaves do have a significant role in alleviating liver and kidney damage in the STZ-diabetic rats besides its hypoglycemic effect. It might be adequate to conclude that stevia leaves could protect rats against streptozotocin induced diabetes, reduce the risk of oxidative stress and ameliorate liver and kidney damage.

High prevalence of metabolic syndrome in an elderly Croatian population - a multicentre study

OBJECTIVE

To investigate the prevalence and characteristics of metabolic syndrome (MetS) in a healthy elderly Croatian population.

DESIGN

Cross-sectional study consisting of a health check including anthropometric measures and food questionnaires as well as analysis of biochemical parameters related to MetS. The diagnostic criteria of the International Diabetes Federation (IDF) were used for diagnosis of MetS.

SETTING

Four centres in continental (Virovitica and Zagreb) and Adriatic coast (Split and Omiš) regions of Croatia.

SUBJECTS

Free-living elderly persons aged 70-90 years (n 320).

RESULTS

Significantly lower MetS prevalence was found among participants from small urban centres compared with those from large urban centres (59·1 % v. 69·6 %; P = 0·051). Participants without MetS consumed wine more frequently (P = 0·05) than those with MetS. Compared with their peers with HDL cholesterol (HDL-C) <1·03 mmol/l, more male participants with HDL-C ≥1·03 mmol/l consumed wine (P = 0·04) or pelagic fish (P = 0·03). The prevalence of participants with TAG ≥1·7 mmol/l was higher in wine non-consumers (P = 0·05) than in wine consumers. Multivariate analysis with age and gender as covariates showed a significant inverse association of wine consumption with total cholesterol (P < 0·001), a positive association with HDL-C (P < 0·001) and a marginally inverse association with TAG (P = 0·06). In the male population, alkaline phosphatase and γ-glutamyl transferase activities were higher in participants with MetS (P < 0·05).

CONCLUSIONS

High MetS prevalence was observed in an elderly Croatian population. Data showed that moderate consumption of wine and/or pelagic fish has a protective role against MetS in the population studied.

Gene expression of gamma-glutamyltranspeptidase

gamma-Glutamyltranspeptidase is a heterodimeric glycoprotein that catalyzes the transpeptidation and hydrolysis of the gamma-glutamyl group of glutathione and related compounds. It is known that the enzyme plays a role in the metabolism of glutathione and in salvaging constituents of glutathione. In the adult animal, high levels of gamma-glutamyltranspeptidase are constitutively expressed in the kidney, intestine, and epididymis. On the other hand, although gamma-glutamyltranspeptidase is up-regulated in the liver during the perinatal stage, its expression is nearly undetectable in the adult. In addition, it has long been observed that the intake of certain xenobiotics, including carcinogens and drugs, induces the hepatic expression of the enzyme. This induction seems to be associated with both transcriptional regulation and the growth of certain types of cells in the injured liver. A number of studies have been carried out to explain the mechanism by which gamma-glutamyltranspeptidase expression is regulated. 5'-Untranslated regions of mRNAs of the enzyme differ in a tissue-specific manner but share a common protein coding region, and the tissue-specific and developmental stage-specific expression, as well as hepatic induction, are conferred by different promoters. As suggested by the capability of enzymatic activity-independent induction of osteoclasts, the expression of gamma-glutamyltranspeptidase may also be involved in various biological processes that are not directly associated with glutathione metabolism. This chapter briefly summarizes studies to date concerning the tissue-specific expression and induction of gamma-glutamyltranspeptidase and transcriptional regulation by the multiple promoter system is discussed.

Serum enzymes associated with cholestasis

Alkaline phosphatase, gamma-glutamyl transferase, and 5' nucleotidase are the most common enzymes used in the evaluation of cholestasis. The present knowledge of these enzymes including their function, activity measurement, biologic variables of enzyme activity in healthy persons and disease states, and clinical significance are reviewed. Usefulness of enzymes patterns for diagnosis of specific cholestatic disorders and future directions in evaluation of cholestasis are also discussed.

Gamma-glutamyltranspeptidase stimulates receptor activator of nuclear factor-kappaB ligand expression independent of its enzymatic activity and serves as a pathological bone-resorbing factor

A novel bone-resorbing factor was cloned using an expression cloning technique, which involved a Xenopus oocyte expression system and an assay for osteoclast formation. A candidate clone was isolated from a BW5147 mouse T-lymphoma cell cDNA library. Sequencing analysis identified the factor as gamma-glutamyltranspeptidase (GGT), which is an enzyme involved in glutathione metabolism. The addition of purified GGT protein to mouse bone marrow culture effectively induced formation of osteoclasts. An antibody against GGT inhibited osteoclast formation but not the enzymatic activity. We also demonstrated that an inactive form of GGT, the enzymatic activity of which had been blocked by chemical modification with a specific inhibitor, acivicin, supported osteoclast formation. These results indicate that GGT acts on osteoclast formation independent of its own enzymatic activity. Furthermore, both native GGT and inactive GGT stimulated the expression of the receptor activator of nuclear factor-kappaB ligand (RANKL) mRNA and protein from bone marrow stromal cells. This report is the first demonstration of a novel biological activity of GGT protein in a manner independent of its enzymatic activity.

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.

Primary active transport of organic anions on bile canalicular membrane in humans

Biliary excretion of several anionic compounds was examined by assessing their ATP-dependent uptake in bile canalicular membrane vesicles (CMV) prepared from six human liver samples. 2, 4-Dinitrophenyl-S-glutathione (DNP-SG), leukotriene C4 (LTC4), sulfobromophthalein glutathione (BSP-SG), E3040 glucuronide (E-glu), beta-estradiol 17-(beta-D-glucuronide) (E2-17G), grepafloxacin glucuronide (GPFXG), pravastatin, BQ-123, and methotrexate, which are known to be substrates for the rat canalicular multispecific organic anion transporter, and taurocholic acid (TCA), a substrate for the bile acid transporter, were used as substrates. ATP-dependent and saturable uptake of TCA, DNP-SG, LTC4, E-glu, E2-17G, and GPFXG was observed in all human CMV preparations examined, suggesting that these compounds are excreted in the bile via a primary active transport system in humans. Primary active transport of the other substrates was also seen in some of CMV preparations but was negligible in the others. The ATP-dependent uptake of all the compounds exhibited a large inter-CMV variation, and there was a significant correlation between the uptake of glutathione conjugates (DNP-SG, LTC4, and BSP-SG) and glucuronides (E-glu, E2-17G, and GPFXG). However, there was no significant correlation between TCA and the other organic anions, implying that the transporters for TCA and for organic anions are different also in humans. When the average value for the ATP-dependent uptake by each preparation of human CMVs was compared with that of rat CMVs, the uptake of glutathione conjugates and nonconjugated anions (pravastatin, BQ-123, and methotrexate) in humans was approximately 3- to 76-fold lower than that in rats, whereas the uptake of glucuronides was similar in the two species. Thus there is a species difference in the primary active transport of organic anions across the bile canalicular membrane that is less marked for glucuronides.

gamma-Glutamyl transpeptidase: catalytic mechanism and gene expression

The gamma-glutamyl transpeptidases are key enzymes in the so-called gamma-glutamyl cycle involving glutathione synthesis, the recovery of its constituents, and in the transport of amino acids. This membrane-bound ectoenzyme thus serves to regulate glutathione synthesis. This chapter deals with the active site chemistry of gamma-glutamyl transpeptidase, including the role of side-chain groups on the light subunit as well as several serine residues in the catalytic process. Also considered are genomic studies indicating (a) the presence of a single gene in mouse and rat; (b) the occurrence of multiple genes in humans; (c) the involvement of multiple promoters for gene expression; and (d) how these multiple promoters may play a role in the tissue-specific expression of gamma-glutamyl transpeptidases.

Effects of ethanol on hepatitis B virus Pre-S/S gene expression in the human hepatocellular carcinoma derived HEP G2 hepatitis B DNA positive cell line

BACKGROUND/AIMS

Among the reported interactions between ethanol and hepatitis B virus (HBV), studies of transgenic mice have suggested an effect of ethanol on the secretion of viral envelope proteins.

METHODS

We further investigated these interactions in vitro by determining HBs antigen levels and performing northern blots of viral mRNA in human cell culture (HepG2 HBV positive cells) exposed for 3 to 12 days to various concentrations of ethanol.

RESULTS

In cultures exposed to 200 mM ethanol, HBs antigen concentrations increased in the medium (p < 0.05) after 3 days as Pre-S1 and Pre-S2 protein concentrations. This increase was not specific, as albumin and ferritin increased in the same proportions. Ethanol also increased the HBs antigen concentration in the cells (p < 0.05), whereas levels of viral mRNA encoding surface proteins were unaffected.

CONCLUSIONS

These findings show that short-term ethanol exposure in vitro can induce HBs antigen overexpression via a post-transcriptional mechanism.

The effect of chronic and acute ethanol treatment on morphology, lipid peroxidation, enzyme activities and Na+ transport systems on WRL-68 cells

In this study we measured some parameters that are associated with ethanol damage to the liver. The method allowed us to determine the injury that chronic and acute ethanol treatments produce at the cellular level without interference from homeostatic or compensatory mechanisms. The system used is a hepatic fetal human cell line, WRL-68, which retains, in culture, many of the liver-specific functions. WRL-68 cells do not metabolise ethanol, and consequently we could evaluate the effect of ethanol alone. We explored two different conditions: 30 days with 0.1 M ethanol (chronic treatment) and 24 h in the presence of 0.5 M ethanol (acute treatment). 1. The transmission electron microscopy studies revealed, in both treatments, the presence of granules not usually present in the cytoplasm of control cells and morphological mitochondrial alterations in chronically treated cells. 2. Lipid peroxidation, measured as the rate of malondialdehyde production, increased three and a half times in acutely treated cells and about twofold in chronically treated cells. 3. The percentage of total activity (activity in the medium/(activity in the medium + activity of the cells). 100) and the enzymatic activity in the culture medium of gamma glutamyl transpeptidase (GGT), alanine amino transferase (ALAT), aspartate amino transferase (ASAT) and alkaline phosphatase (AI-P), increased. 4. We measured some parameters related to the transport of sodium across the membrane. Cells chronically treated with ethanol had higher rate constants and effluxes than control cells. There was no difference between the total and passive efflux. Ethanol treated cells apparently lacked the ouabain sensitive pathway. In acutely treated cells, the total sodium efflux and the rate constant were enhanced. Sodium pools in the acutely treated cells were diminished and active sodium pumping was seven times higher than in control cells. 5. We determined the number of high affinity ouabain binding sites per cell. Ethanol did not alter the number of pumps, rather it seems to induce a functional alteration. Our results indicate that ethanol per se induces lipid peroxidation, alters enzymatic activities, sodium transport systems, sodium pools and cellular morphology, and that all these changes may be partly responsible for ethanol-induced hepatotoxicity. The data compare favourably with those reported in the literature for many different systems. Therefore our model for studying the mechanism of alcohol effects appears to be valid, with the advantage of being able to compare experiments that can be done in the same system and under the same conditions.

Alcohol induction of ferritin expression in a human hepatoblastoma cell line (HEP G2)

Hyperferritinemia, an unclear mechanism, is frequently observed in chronic alcoholics. The aim of this work was to study the effect of alcohol on ferritin expression in a human hepatoblastoma cell line, HepG2. This cell line proved to be sensitive to alcohol, since alcohol increased gamma-GT activity both in cells and media. The most striking result was the increase of ferritin in cells and media by alcohol. Moreover, this effect was specific, since it contrasted with a decrease in total protein synthesis and secretion, a decrease in transferrin excretion and a lack of effect on orosomucoid. In our model, alcohol was able to induce, in a specific manner, ferritin expression.

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)

Regulation of mouse mammary-gland gamma-glutamyltranspeptidase mRNA during pregnancy, lactation and weaning

The level of gamma-glutamyltranspeptidase (GGT) activity and of its mRNA were determined in the mouse mammary gland during pregnancy, lactation and weaning. The GGT activity, which is very low in the virgin-mouse mammary gland (5 munits/mg of protein), increases progressively during pregnancy (3-fold), reaches its maximum at the onset of lactation (8-fold) and returns rapidly to basal level at weaning. Although no GGT-specific mRNA is detected in the virgin-mouse mammary gland, a single faint band of 2.2 kb in size is found during pregnancy. During lactation, an additional mRNA of 2.4 kb in size appears, and the level of both mRNAs is higher. This high level of mRNA persists during weaning as well. Southern-blot analysis of mouse mammary-gland DNA provides convincing evidence that there is only one gene which codes for the two mRNAs. The present study provides the first evidence for a physiological regulation of the two GGT mRNAs in the same tissue.

Diagnostic value of serum gamma-glutamyl-transferase activity and mean corpuscular volume in alcoholic patients with or without cirrhosis

In an attempt to assess the diagnostic values of serum gamma-glutamyltransferase (GGT) and mean corpuscular volume (MCV) variations as markers of liver disease and of abstinence in alcoholic patients, we compared 174 patients with alcoholic cirrhosis, 175 with noncirrhotic alcoholic liver disease and 67 patients with nonalcoholic cirrhosis. GGT and MCV values were checked three times, the day of admission, 7 days later, and on the last sample available during follow-up (1 to 12 months), and were compared according to the liver disease and abstinence. A decrease of GGT activity during the 1st week of hospitalization was noted in alcoholics with (-9 IU/liter) or without (-13 IU/liter) cirrhosis and not in nonalcoholic cirrhosis (+8 IU/liter), without MCV variations. During follow-up, median GGT activity was strikingly different in abstinent patients with (27 IU/liter) or without (21 IU/liter) cirrhosis and in nonabstinent patients (99 IU/liter and 123 IU/liter, respectively) (p less than 0.001). MCV decrease was noted in alcoholics whatever their abstinence or not, contrasting with the absence of decrease in nonalcoholic patients. For the diagnosis of alcoholism in cirrhotic patients, the positive predictive value (PPV) of a GGT or a MCV decrease during the 1st week of hospitalization was 0.82 and 0.78, respectively, and the negative predictive value (NPV) was 0.33 and 0.70, respectively. For abstinence during follow-up, the PPV of a GGT activity less than 50 IU/liter was 0.92 and the NPV was 0.65.(ABSTRACT TRUNCATED AT 250 WORDS)

Expression of rat renal gamma-glutamyltransferase cDNA in Escherichia coli

To obtain the expression of rat kidney gamma-glutamyltransferase (GGT) cDNA in E. coli, plasmids containing the cDNA sequences coding for various parts of GGT were constructed. Transformation of E. coli cells by these hybrid vectors results in a production of unglycosylated recombinant proteins, immunologically recognized by specific antirat kidney GGT antibodies. Plasmid, expressing the complete coding sequence of GGT cDNA, allows the production of enzymatically active proteins localized in the periplasmic space, while the same sequence without the N-terminal hydrophobic region results in a production of cytoplasmic proteins. These recombinant proteins present a very basic isoelectric point (pI greater than 9). These results suggest that the presence of the N-terminal region seems to be necessary to direct the expressed proteins enzymatically active in the periplasmic space.

Glucocorticoid hormones prevent the induction of gamma-glutamyl transpeptidase by ethanol in a rat hepatoma cell line

The increase in serum gamma-glutamyl transpeptidase (GGT) is a well known marker of chronic alcoholism in man. We have previously shown that ethanol (180 mM) induces GGT activity 2-3-fold in the C2 rat hepatoma cell line. In this study, we have analyzed the interaction of ethanol with steroid hormones and drugs in this well defined cell culture system. Dexamethasone (100 nM), a synthetic glucocorticoid agonist, completely prevented the induction of GGT by ethanol, but had no effect when added alone. This inhibitory effect was also observed with other corticosteroids, but not with sex steroids; it was prevented by RU 486, a glucocorticoid antagonist. These observations suggest that dexamethasone acts through a high affinity glucocorticoid receptor. Conversely, ethanol did not interfere with the glucocorticoid induction of alanine aminotransferase in the same cell. We have analyzed the metabolism of ethanol in the C2 cells. These cells lack significant alcohol dehydrogenase activity as well as any cytochrome P-450 Alc immunoreactivity. Dexamethasone did not modify the disappearance of ethanol in the culture medium of those cells. We conclude that glucocorticoid hormones interact with ethanol at the cellular level, and that this interaction does not involve a modification of alcohol metabolism.

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.

Cloning and nucleotide sequence of human gamma-glutamyl transpeptidase

We have identified the gene for human gamma-glutamyl transpeptidase [GGT; glutamine:D-glutamyl-peptide 5-glutamyltransferase (also called gamma-glutamyltransferase), EC 2.3.2.2] in a BCR gene-related region located in band q11----qter of chromosome 22. Two cDNAs complementary to the GGT mRNA have been isolated from a human placental library constructed in phage lambda gt11. The largest cDNA has a size of 2535 base pairs (bp) and an open reading frame of 1707 nucleotides encoding 569 amino acids. By using a probe corresponding to this cDNA, a mRNA of approximately 2.4 kilobases was detected by RNA blot-hybridization analysis in mouse kidney RNA. The GGT precursor encoded by the coding sequence would have an estimated Mr of 61,400. We compared our nucleotide and deduced amino acid sequences with the published results of rat kidney cDNAs. The human and rat amino acid sequences are similar; however, a considerable discrepancy in nucleotide sequence was found within a 180-bp fragment of the heavy chain, resulting in a completely different amino acid sequence for this region. In addition, the 5' untranslated sequence of the human cDNA (669 bp) is substantially larger than that determined in the rat cDNA (227 bp). Our results may be valuable for further studies on the protein structure of human GGT as well as studies on the regulation of the enzyme.

Specific modulation by ethanol of the protein synthesis pattern in the C2 rat hepatoma cell line

The effect of ethanol on protein synthesis in the C2 rat hepatoma cell line was analyzed by two-dimensional gel electrophoresis after the labeling with [35S]methionine of cells that were untreated or had been treated with 180 mM ethanol. In this cell line, this concentration of ethanol is known to induce gamma-glutamyl transpeptidase, a marker of alcoholism in man (Barouki et al., Hepatology 1983; 3: 323-329). In the present work we demonstrate that ethanol, besides causing a slight decrease in overall protein synthesis (less than 25%), primarily regulates the expression of two unique proteins among 1500 labeled products that were analyzed: one of these was induced and did not correspond to gamma-glutamyl transpeptidase, and one was repressed after 20 h of ethanol treatment. We conclude that the set of hepatic proteins altered by ethanol is likely to be very limited in number, which reflects the specificity of alcohol action on protein synthesis in the C2 cell line.

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.

Molecular cloning and nucleotide sequence of rat kidney gamma-glutamyl transpeptidase cDNA

We have screened a cDNA library (20,000 clones) made from rat kidney poly(A)+ RNA, using an oligonucleotide probe that was a mixture of 14-base DNA oligomers containing all 32 possible sequences coding for residues 32-36 of the gamma-glutamyl transpeptidase (EC 2.3.2.2.) heavy chain. We isolated and sequenced two cDNAs corresponding to the mRNA coding for the entire length of the enzyme precursor. The nucleotide sequence that we obtained (2072 bases) reveals an open reading frame of 1707 nucleotides coding for the common precursor of both enzyme subunits. The amino acid sequence begins with the 21 residues located at the NH2-terminal hydrophobic region of the heavy subunit. We show that this sequence, which is not processed, is the only possible signal peptide in the sequence. Five potential N-glycosylation sites are present in the gamma-glutamyl transpeptidase sequence. Using one of the two cDNA clones as probe, a 2.2-kilobase sequence was detected by blot analysis in rat kidney and human fetal liver RNA.

Effects of chronic ethanol feeding on glutathione turnover in the rat

Glutathione (GSH) is important in protection of cells against electrophilic drug injury and against reactive oxygen species. Both steady-state concentrations and turnover of GSH are important determinants of susceptibility of the hepatocyte to injury. Chronic ethanol administration is known to enhance susceptibility to electrophilic drug injury. We have examined the effects of chronic ethanol feeding on GSH turnover and the hepatic activities of GSH peroxidase and enzymes of the gamma-glutamyl cycle in the rat. Turnover of GSH was measured in individual animals by measuring the decrease in specific activity of GSH in bile over time after i.v. administration of [35S]cysteine. Rats fed ethanol had significantly increased rates of GSH turnover, 0.287 +/- 0.050 hr-1 vs 0.131 +/- 0.041 hr-1 (P less than 0.001), as well as steady-state GSH levels, 6.59 +/- 1.55 vs 4.30 +/- 1.28 mumoles/g liver (P less than 0.01). The activities of gamma-glutamyltransferase (GGT) and GSH-synthesizing enzymes were correspondingly increased significantly. By contrast, GSH peroxidase activity was decreased in ethanol-fed rats, 194 +/- 20.8 vs 311 +/- 89.9 nmoles NADPH oxidized/min/mg protein (P less than 0.001). Biliary output and concentrations of GSH and GSSG were similar in both groups. The increase in turnover of GSH was not due to an increase in oxidation of GSH. There was, however, an association between GSH turnover and the activity of hepatic GGT in ethanol-fed but not in control rats.

Serum activity of mitochondrial aspartate aminotransferase: a sensitive marker of alcoholism with or without alcoholic hepatitis

Serum activity of the mitochondrial isoenzyme of aspartate aminotransferase (mAST) was measured with an immunological method in 74 subjects. Fourty-six were chronic alcoholics with (30) or without (16) obvious alcoholic liver disease; 28 were nonalcoholic controls among whom 14 had acute or chronic viral hepatitis, the remaining 14 being healthy individuals. Mean mAST activity was much higher in all the alcoholic subjects, with or without liver disease, 10.4 and 1.95 units per liter, respectively, than in the healthy controls (0.43, p less than 0.001). The mean mAST to total AST ratio was similar in the healthy controls and in the patients with viral hepatitis (2.98 and 3.19%, NS), whereas it was about 4 times higher in the alcoholics with a sensitivity which reached 93% in the patients with alcoholic liver disease and 100% in those without. Both gamma-glutamyl transpeptidase and glutamate dehydrogenase serum activities were far less sensitive and specific. As almost all chronic alcoholics had similar abnormal values of mAST/total AST ratio, this leads to question whether "normal" liver may really exist in any of such subjects.