Two different gamma-glutamyltransferases during development of liver and small intestine: a fetal (sialo-) and an adult (asialo-) glycoprotein

Molecular characterization of tumor associated antigen in mice exposed to a hepatocarcinogen

The present investigation is aimed to identify and characterize tumor-associated antigen (TAA) in animals exposed to hepatocarcinogen. Swiss albino mice showed an enhanced expression of an approximately 58 kDa glycoprotein in liver cells upon exposure to a potential hepatocarcinogen N-nitrosodibutylamine (DBN). Carcinogenesis induction in mice was monitored by assays of y-glutamyl transpeptidase (GGT), acetylcholine esterase (AChE), glutathione-S-transferase (GST) activities and the level of glutathione (GSH) in liver. DBN treated animals showed cell distortion and extensive necrosis as observed by histological examination. The over-expressed TAA was purified by ion-exchange chromatography and further characterized by SDS-PAGE. The carbohydrate contents and glycan linkage to the polypeptide backbone was analyzed by using the DIG glycan differentiation and de-glycosylation kits. The glycoprotein has glycan chains that are N-linked via asparagines to the polypeptide backbone. It was also observed that the molecule is rich in sialic acid residues with a significantly high carbohydrate to protein ratio (> 2:1). The over-expressed high molecular weight glycoprotein TAA was found to be highly immunogenic and could eventually be used to induce immune response in order to counter tumor regression.

Is the expression of γ-glutamyl transpeptidase messenger RNA an indicator of biological behavior in recurrent hepatocellular carcinoma?

AIM: To investigate the correlation between gamma-glutamyl transpeptidase (γ-GTP) expression in the primary HCC and post-resection recurrence and its biological behaviors.

METHODS: Forty consecutive patients having curative resection for HCC were included in this study. The primers for reverse -transcription polymerase chain reaction (RT-PCR) were corresponding to the 5’-noncoding human γ-GTP mRNA of fetal liver (type A), HepG2 cells (type B), and placenta (type C). Both the cancer and non-cancerous tissues of the resected liver were analyzed. The correlations between the expression of γ-GTP and the clinicopathological variables and outcomes (recurrence and survival) were studied.

RESULTS: Those with type B γ-GTP mRNA in cancer had significant higher recurrence rate than those without it (63.6% vs 14.3%). Both those with type B in cancer and in non -cancer died significantly more than those without it (45.5% vs 0% and 53.6% vs 0%, respectively). By multivariate analysis, the significant predictors of recurrence included high serum AFP (P = 0.0108), vascular permeation (P = 0.0084), and type B γ-GTP mRNA in non-cancerous liver (P = 0.0107). The significant predictors of post-recurrence death included high serum AFP (P = 0.0141), vascular permeation ( P = 0.0130), and daughter nodules (P = 0.0053). As to the manifestations (recurrent number 2, recurrent extent 2 segments, extra-hepatic metastasis, and death) in recurrent patients, there were no statistical significant differences between those with type B in the primary tumor and those without it. The difference between those with type B in non-cancerous liver and those without it also was not significant.

CONCLUSION: Patients of HCC with type B γ-GTP mRNA both in cancer and in non-cancerous tissue had a worse outcome, earlier recurrence, and more post-recurrence death.

Evaluation of the albumin-gamma-glutamyltransferase isoenzyme as a diagnostic marker of hepatocellular carcinoma-complicating liver cirrhosis

AIM

The present study aimed to evaluate the usefulness of albumin-gamma-glutamyltransferase isoenzyme in the diagnosis of hepatocellular carcinoma.

METHODS

Electrophoretic assays of gamma-glutamyltransferase isoenzymes were performed on sera from 190 cirrhotics with (n = 131) or without (n = 59) hepatocellular carcinoma, 36 patients with chronic active hepatitis, 17 patients with liver metastases, and 16 control subjects. In the group of cirrhotic patients, the serum level of alpha-fetoprotein was also assessed.

RESULTS

Albumin-gamma-glutamyltransferase was found in 88 of 131 cirrhotics with hepatocellular carcinoma, 14 of 59 cirrhotics without hepatocellular carcinoma, nine of 17 patients with liver metastases, and in none of the chronic active hepatitis or control patients. Within the cirrhotic subgroup, albumin-gamma-glutamyltransferase was effective in detecting hepatocellular carcinoma in general (sensitivity: 67%; specificity: 76%; diagnostic accuracy: 70%), and small hepatocellular carcinoma (< 3 cm; corresponding figures: 58, 76, and 69%). The best alpha-fetoprotein value discriminating between hepatocellular carcinoma and non-hepatocellular carcinoma cirrhotics was 20 ng/mL (sensitivity: 54%; specificity 85%; accuracy: 64%). The combined use of albumin-gamma-glutamyltransferase and alpha-fetoprotein, > 20 ng/mL, was associated with greater sensitivity and accuracy (84 and 74%, respectively) than those observed with either of the two markers considered alone.

CONCLUSIONS

Albumin-gamma-glutamyltransferase appears to be a sensitive diagnostic marker of both advanced and small hepatocellular carcinoma-complicating liver cirrhosis.

The role of indigenous microflora in the development of murine intestinal fucosyl- and sialyltransferases

Most enteric bacteria use intestinal brushborder glycoconjugates as their target host cell receptors. It has been postulated that resident microbes regulate specific glycosyltransferases that are responsible for synthesizing brushborder glycoconjugates. To investigate this hypothesis, we measured glycosyltransferase enzyme activities in intestine from different regions of maturing conventional (CONV), germ-free (GF), and ex-germ-free (XGF) mice and compared them to general enzyme markers of gut development, for example, disaccharidases. High alpha2,3/6-Sialyltransferase (ST) activity and low alpha1,2-fucosyltransferase (FT) activities were detected from duodenum to colon in suckling CONV mice, but the relative levels of these activities reversed during the third postnatal wk, rapidly reaching adult levels by the fourth wk. These age-related enzyme changes were significantly attenuated in GF mice, maintaining an immature pattern well past 3 wk. Introduction of gut microflora in GF mice rapidly initiated maturation of glycosyltransferase activity but had no significant affect on developmental programming of dissacharidases. Therefore, in mice, intestinal glycosyltransferase activities are under tissue and developmental control and microflora play a major role in their specific ontogeny but not in overall development. These findings may help explain the regional specificity of commensal bacteria and of enteric pathogens and may also relate age-related changes in microflora to susceptibility to enteropathogens.

Region-specific ontogeny of alpha-2,6-sialyltransferase during normal and cortisone-induced maturation in mouse intestine

Regional differences in the ontogeny of mouse intestinal alpha-2,6-sialyltransferase activities (alpha-2,6-ST) and the influence of cortisone acetate (CA) on this expression were determined. High ST activity and alpha-2,6-ST mRNA levels were detected in immature small and large intestine, with activity increasing distally from the duodenum. As the mice matured, ST activity (predominantly alpha-2,6-ST) in the small intestine decreased rapidly to adult levels by the fourth postnatal week. CA precociously accelerated this region-specific ontogenic decline. A similar decline of ST mRNA levels reflected ST activity in the small, but not the large, intestine. Small intestinal sialyl alpha-2,6-linked glycoconjugates displayed similar developmental and CA induced-precocious declines when probed using Sambucus nigra agglutinin (SNA) lectin. SNA labeling demonstrated age-dependent diminished sialyl alpha2,6 glycoconjugate expression in goblet cells in the small (but not large) intestine, but no such regional specificity was apparent in microvillus membrane. This suggests differential regulation of sialyl alpha-2,6 glycoconjugates in absorptive vs. globlet cells. These age-dependent and region-specific differences in sialyl alpha-2,6 glycoconjugates may be mediated in part by altered alpha-2,6-ST gene expression regulated by trophic factors such as glucocorticoids.

Implication of insulin and nutritional factors in the regulation of intestinal galactosyltransferase activity during postnatal development

In the rat small intestine, galactosyltransferases are the enzymes implicated in the biosynthesis of glycoproteins of the brush-border membranes and mucins. During postnatal development, the circulating insulin level increased at weaning in parallel with the activities of intestinal galactosyltransferases on O-glycans and N-glycans. This study deals with the role of insulin in the regulation of galactosyltransferase activities during postnatal development. The treatment of immature suckling rats with insulin induced a precocious increase in the activities of the O-glycan and N-glycan galactosyltransferases, partly reproducing the increase in galactosyltransferase activity normally found at weaning, since the O-glycan galactosyltransferase activity increased more quickly than the N-glycan galactosyltransferase activity. The sensitivity of the two galactosyltransferase activities to insulin disappeared after weaning, a period when drastic diet changes occur. In 22-day-old rats submitted to prolonged nursing (high-fat diet), the activities of the O-glycan and N-glycan galactosyltransferases were lower than those found in age-matched normally weaned rats (high-carbohydrate diet), indicating a delay in the maturation of the intestine of prolonged-nursing rats. The circulating insulin level of these animals stayed lower than that of the age-matched weaned rats. When the prolonged-nursing animals were treated with insulin, the O-glycan and N-glycan galactosyltransferase activities reached levels similar to those of the weaned rats. These observations suggest that insulin is one of the maturation factors for intestinal glycoprotein galactosylation and may be partly responsible for the natural enhancement of intestinal galactosyltransferase activities observed during postnatal development in relation to the dietary changes at weaning.

Role of insulin and nutritional factors in intestinal glycoprotein fucosylation during postnatal development

This study deals with the role of insulin in the regulation of the intestinal glycoprotein fucosylation process during postnatal development in the rat. Circulating insulin level was found to increase at weaning time in parallel with alpha-1, 2-fucosyltransferase activity and with the appearance of alpha-1, 2-fucoproteins in brush-border membranes. Insulin treatment of young suckling rats induced a precocious increase in fucosyltransferase activity and in the biosynthesis of its substrate (GDP-fucose), but the sensitivity to insulin disappeared after weaning. The insulin level was lower in 22-day-old rats that received prolonged nursing (on a high-fat diet) compared with age-matched normally weaned rats (on a high-carbohydrate diet), whereas the appearance of alpha-1, 2-fucoproteins and the increase in activity of alpha-1, 2-fucosyltransferase were delayed, as was the decrease in the degradation of GDP-fucose. In 22-day-old animals that received prolonged nursing and insulin treatment, the alpha-1, 2-fucosyltransferase activity reached a level close to that observed in age-matched weaned rats, and several alpha-1,2-fucoproteins appeared in brush-border membranes with a molecular mass similar to that found in weaned rats. These results suggest that changes in insulin levels at weaning time (as caused, in the present case, by dietary modifications) may be responsible for the regulation of the glycoprotein fucosylation process, essentially by increasing fucosyltransferase activity.

Decreased expression of gamma-glutamyltranspeptidase in the intestinal cell line Caco-2 by inducers of cytochrome P450 1A1

Our purpose was to investigate whether inducers of cytochrome P450 1A1 (CYP1A1), which cause a decreased expression in Caco-2 cells, at both the mRNA and protein levels, of membrane proteins associated with the uptake and transport of hexoses, would also affect the expression of gamma-glutamyltranspeptidase (gammaGT) (EC 2.3.2.2). In Caco-2 clonal TC7 cells grown under standard conditions (25 mM glucose), exposure to beta-naphthoflavone (beta-NF), 2,3,7,8-tetrachlorodibenzo-p-dioxin, and 3-methylcholanthrene resulted in increased glucose consumption and decreased gammaGT activity in cells grown to confluence, i.e. when the differentiation is optimum. GammaGT activity was further analyzed during the time course of differentiation of TC7 cells treated or not with beta-naphthoflavone: while gammaGT activity in untreated cells showed a 10-fold increase from the exponential phase of growth until late postconfluence, gammaGT activity in beta-NF-treated cells, although increasing by 4-fold, remained at a much lower level (<25%). This decreased activity of gammaGT was associated with a decreased level of gammaGT mRNA. This inhibiting effect was not dependent on the CYP1A1 activity, as it also occurred in the presence of CYP1A1 inhibitors such as alpha-naphthoflavone, 8-methoxypsoralen or ellipticin. It was however dependent on glucose supply as it was not observed when the cells were cultured in low glucose (1 mM). These results raise the question of whether, in Caco-2 cells, CYP1A1 inducers or the signal transduction system which controls CYP1A1 are involved in the regulation of the expression of gammaGT through a mechanism involving glucose metabolism.

Biochemical characteristics of gamma-glutamyl transpeptidase in capillaries from entorhinohippocampal complex of quinolinate-lesioned rat brain

Quinolinic acid (QUIN) is an endogenous excitotoxic agonist of the N-methyl-D-aspartate (NMDA) type of glutamate receptor, which causes slowly progressing degeneration of vulnerable neurons in some brain regions. Using changes in the activity of membrane-bound gamma-glutamyl transpeptidase (GGT) as a marker of cell damage, we found a significant decrease of this enzyme activity, which was preferentially located in the ipsilateral hippocampal formation and entorhinal cortex, 4 d after the unilateral intracerebroventricular (icv) injection of 0.5 mumol QUIN. The dose of QUIN divided into two half-doses injected bilaterally led to a symmetrical decline of GGT activity in hippocampal areas. The lesion was characterized by a suppression of GGT activity in hippocampal and entorhinal capillaries, corresponding to 60 and 81% of their initial value, respectively, but no significant changes were ascertained in synaptosomal membranes. The changes in the activity of capillary GGT were associated with the decrease of apparent maximal velocity Vmaxapp, whereas apparent Michaelis constant K(m)app (0.69-0.79 mM) remained unaffected. In the nonlesioned brain, concanavalin A (Con A) affinity chromatography revealed five glycoforms of synaptosomal GGT in contrast to only one found in hippocampal and entorhinal capillaries. The results document that neither the saccharide moiety of GGT nor the value of enzyme K(m)app is significantly affected by the QUIN-induced lesion of the rat brain. However, the suppression of GGT activity, which is accompanied by a decrease in the value of Vmaxapp in brain microvessels, may suggest dysfunction of the blood-brain barrier (BBB) in the QUIN-injured rat brain.

The hydrocortisone-induced transcriptional down-regulation of beta-galactoside alpha2,6-sialyltransferase in the small intestine of suckling rats is suppressed by mifepristone (RU-38.486)

The progressive loss of sialic acids of the brush-border membrane glycoproteins is one of the major biochemical changes which occur in the rat small intestine during the transition from suckling to weaning, and this process is speeded up by an injection of glucocorticoids to the suckling animals. We used the rat liver beta-galactoside alpha2,6-sialyltransferase (ST6(N), EC 2.4.99.1) cDNA as a probe to examine the mRNA level of this enzyme in the small intestine of both suckling (13-day-old) and weaned (25-day-old) rats. In the ileum of suckling rats, the ST6(N) mRNA level was about four times higher than in the jejunum, whereas the membrane-bound enzyme activity was less than two times higher. In comparison with the controls, hydrocortisone treatment significantly decreased the level of this transcript and of the corresponding enzyme activity in both segments of the small intestine of suckling rats. Additionally, the antiglucocorticoid mifepristone (RU-38.486) suppressed the effect of hydrocortisone. The expression of ST6(N) mRNA in the small intestine of weaned (25-day-old) rats was several times lower than that in suckling (13-day-old) rats, and was unresponsive to hydrocortisone as well as to mifepristone. These results indicate that the glucocorticoid-induced transcriptional down-regulation of ST6(N) expression in the small intestine of suckling rats is mediated via the glucocorticoid receptor pathway, and support the notion that alterations in sialylation of brush-border membrane glycoconjugates occurring upon weaning are the result of a lower expression of ST6(N).

Characterization of gamma-glutamyltranspeptidase in the liver of the frog: 1. Comparison to the rat liver enzyme

The characteristics of the enzyme gamma-glutamyltranspeptidase were determined in frog liver and compared to those of the rat. In Rana pipiens, tissue distribution studies indicated the order of activity to be: kidney >>> liver >> nerve > egg > lung > heart > skeletal muscle in homogenates. In the Rana pipiens relative to the Fischer 344 rat, the activity of the liver enzyme was somewhat greater (1.8-fold) and the kidney enzyme substantially less (25-fold). Frog liver gamma-glutamyltranspeptidase displayed strain-dependent differences in activity with Rana pipiens and Rana sylvatica exhibiting comparable activities and Xenopus laevis exhibiting 20-fold lower activities. No influence of sex was apparent in Rana pipiens in contrast to the sex dependent differences observed in the Fischer 344 rat: female:male = 7:1. In homogenates and plasma membrane fractions of Rana pipiens, Xenopus laevis and the Fischer 344 rat, high, and comparable relative specific activities, were observed, 8-11, coupled with protein yields of 2.2-2.5 per cent indicating the enzyme to be plasma membrane bound and associated with the sinusoidal surface of the liver cell.(ABSTRACT TRUNCATED AT 250 WORDS)

Microvillar enzyme activity in amniotic fluid, extraembryonic coelomic fluid and maternal serum in the first trimester of pregnancy

The activities of two microvillar enzymes, gamma-glutamyl transpeptidase and total alkaline phosphatase, have been measured in samples of amniotic fluid and extraembryonic coelomic fluid obtained by high-resolution transvaginal ultrasound-guided amniocentesis from 40 women between 7 and 12 weeks of gestation. There was a highly significant difference between gamma-glutamyl transpeptidase activity in amniotic fluid (median level 31 U/l; range 2-409 U/l) and extraembryonic coelomic fluid (median level 2 U/l; range less than 2-16 U/l) (P less than 0.001; Mann-Whitney U-test). Alkaline phosphatase activity was not detected in 84% of amniotic fluid samples and 97% of extraembryonic coelomic fluid samples. No difference was found between total alkaline phosphatase activity in these fluids (P = 0.14; Mann-Whitney U-test). Enzyme activities in amniotic fluid increased with gestational age. A significant linear correlation was found between amniotic fluid gamma-glutamyl transpeptidase activity and stage of gestation (r = 0.86; P less than 0.001) and total alkaline phosphatase activity in amniotic fluid and stage of gestation (r = 0.66; P less than 0.001).

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.

Developmental changes in the activity of membrane-bound gamma-glutamyl transpeptidase and in the sialylation of synaptosomal membranes from the chick embryonic brain

gamma-Glutamyl transpeptidase (GGT) is a membrane-bound sialoglycoprotein. The developmental changes in GGT activity and in sialic acid content were determined in a crude synaptosomal membrane fraction from the cerebral hemispheres of the chick embryo between days 11 and 19 of incubation. The GGT activity increased almost eightfold during the examined developmental period, while sialic acid content rose significantly only between days 11 and 15. Cortical administered on day 13 significantly increased GGT activity. On the other hand, the content of membrane bound sialic acid was not substantially affected. The value of the GGT apparent Michaelis constant (Kmapp) for gamma-glutamyl-p-nitroanilide in the presence of 20 mmol.l-1 glycylglycine was 1.5 mmol.l-1 and cortisol did not influence it. However, Vmax was increased by this hormone. The affinity of GGT to concanavalin A (ConA) did not change during development. Neither the administration of cortisol nor neuroaminidase treatment had any effect on the interaction of GGT with ConA. Desialylation of crude synaptosomal fraction did not change GGT activity. The results presented here suggest no developmental nor functional relationship between the activity of GGT and the level of sialylation in synaptosomal membranes from the cerebral hemispheres of the chick embryo.

Hormonal regulation of glycosylation process in rat small intestine: responsiveness of fucosyl-transferase activity to hydrocortisone during the suckling period, unresponsiveness after weaning

The aim of this study was to examine the possible role of certain hormones (especially hydrocortisone) in the developmental variations of intestinal fucosyl-transferase activity in rats. Thyroxine and insulin, injected into suckling rats, did not induce significant modifications of the fucosyl-transferase activity, under the conditions used, whereas this enzyme activity was highly enhanced after administration of glucocorticoids (cortisone and hydrocortisone). Hydrocortisone administration to suckling rats induced a precocious and progressive activation of the fucosyl-transferase activity up to adult level as a function of the duration of treatment. The responsiveness of suckling rats to hydrocortisone, as shown by increased fucosyl-transferase activity, disappeared at the end of the third week (corresponding to the weaning time). These physiological periods of responsiveness and unresponsiveness to hydrocortisone could be related to the binding of the hormones to receptors since the antiglucocorticoid RU 38486 counteracted the effect of hydrocortisone in suckling rats but did not prevent the developmental rise of the fucosyl-transferase activity, when administered in the third week of life. These results suggest that the normal developmental rise of the fucosyl-transferase activity is independent of glucocorticoids.

Participation of an endogenous inhibitor of fucosyltransferase activities in the developmental regulation of intestinal fucosylation processes

During the rat weaning period (about day 19 after birth) the intestinal maturation is accompanied by a drastic increase in the fucose content of mucosal glycoconjugates, concomitant with an increase in fucosyltransferase activities. The regulation of this fucosylation process appears to be a rather complex phenomenon, which involves several systems controlling fucosyltransferase activity or substrate availability. An endogenous protein inhibitor of the fucosyltransferase activities displays an opposite developmental pattern to that of fucosyltransferase activities, since its activity is high before weaning and is decreased 5-fold after weaning. Similarly, the GDP-fucose pyrophosphatase activity markedly decreases at weaning. The transformation of GDP-mannose into GDP-fucose increases early, at day 18, preceding the increase in fucosyltransferase activities. Before weaning, and especially at days 14 and 18, high levels of GDP-4-dehydro-6-deoxymannose, the product of the GDP-mannose 4,6-dehydratase activity, are produced during the transformation of GDP-mannose into GDP-fucose, even in excess of reduced coenzyme. This fact indicates that the second step of the transformation (epimerase-reductase reaction) could be a limiting factor for GDP-fucose availability before weaning, but not after weaning. The inverse relationship between the mucosal fucose content (or the fucosyltransferase activity) and the endogenous protein inhibitor during normal postnatal development supports the hypothesis of a physiological role for this inhibitor.

Glycosylation of lactase-phlorizin hydrolase in rat small intestine during development

Age-specific changes in glycosylation of rat intestinal lactase-phlorizin hydrolase were analyzed using enzyme immunoprecipitated from microvillus membranes of suckling, weaning, and adult rats, and carbohydrate moieties were examined by lectin affinity binding, metabolic labeling, and neuraminidase treatment. Lectin binding indicated the presence of N-linked and O-linked oligosaccharide chains containing mannose and galactose throughout development. An age-dependent shift in sialic acid and fucose was seen during the period of weaning; no fucose was detectable in lactase-phlorizin hydrolase until after the rats were 20 days of age, whereas sialic acid was reduced in adult lactase-phlorizin hydrolase. The presence of sialic acid in suckling intestines and fucose in adult was confirmed by metabolic labeling with appropriate radioactive precursors. Sodium dodecyl phosphate-polyacrylamide gel electrophoresis analysis of immunoprecipitated lactase-phlorizin hydrolase from the proximal and mid small intestine showed two bands of approximately 220 and 130 kilodaltons in all age groups. In the distal part of the adult small intestine, lactase-phlorizin hydrolase appeared as two bands of similar size to those found in the proximal and mid portions. In contrast, during the suckling and weaning periods, these distal bands were approximately 225 and 135 kilodaltons. [35S]-methionine labeling and fluorography of neonatal intestines confirmed these observations. The size difference between proximal and distal small intestines was virtually eliminated by neuraminidase treatment. These data indicate that the core structure of microvillus membrane lactase-phlorizin hydrolase, consisting of both N-linked and O-linked oligosaccharides, remains constant during development, although terminal sugars shift from predominantly sialic acid during the suckling period to fucose in adulthood. This alteration in glycosylation of the protein occurs in a different pattern from the postweaning decline in lactase specific activity. Consequently, age-dependent changes in glycosylation cannot account for the decrease in lactase-phlorizin hydrolase-specific activity observed during development.

Different gamma-glutamyl transpeptidase mRNAs are expressed in human liver and kidney

In human, the two subunits of gamma-glutamyl transpeptidase (GGT) arise from a common precursor encoded by a multigene family. Until now, a single specific coding sequence for this precursor (type I) has been identified in human placenta and liver. In the present study, we have isolated from a human kidney cDNA library, a GGT specific clone (0.8 Kb). The sequence of which (type II) i) covers the carboxy terminal part of the GGT precursor, ii) exhibits 22 point mutations and a 30 bp deletion as compared to the type I GGT sequence. The sequencing of a human genomic clone reveals that this type II GGT mRNA is encoded by a different gene than the type I GGT mRNA. Both type I and type II GGT mRNAs are expressed in human liver, while almost exclusively type II GGT mRNA is detected in human kidney.

The sugar-chain heterogeneity of human gamma-glutamyl transferases from the reproductive system and kidney

The sugar-chain heterogeneity of gamma-glutamyl transferase (gamma-GTP, EC 2.3.2.2) from the human reproductive system (seminal plasma, prostate and testis) and kidney was investigated using the serial lectin affinity technique and their properties were compared. According to the results of serial lectin affinity chromatography, a possible sugar chains of enzymes from reproductive system were mainly of the hybrid type without fucose linkages to the innermost GlcNAc and/or the biantennary complex type sugar chains and a few were of the multiantennary complex-type with branched GlcNAc (beta 1-4) Man and bisecting complex type sugar chains. On the contrary, the major sugar chains of kidney gamma-GTP were of the multiantennary complex type and/or bisecting complex type sugar chains. Results of isoelectric focusing showed the gamma-GTP bound multiantennary complex type sugar chains to be the most acidic glycoprotein. Moreover, the biantennary type sugar chains were slightly more acidic than the high mannose and/or hybrid type sugar chains, varying with the degree of sialylation.

Umbilical cord gamma-glutamyl transpeptidase and placental dysfunction

Placental dysfunction has been suspected if human placental lactogen level and/or cystine-aminopeptidase activity were lower than 10th centile. Significant rise in gamma-glutamyl transpeptidase (GGTP) has been found in samples of arterial cord blood of newborns born to mothers with placental insufficiency. We observed the relationship between GGTP activity and decrease in cord pH and lower Apgar score of corresponding infants. We suggest that chronic hypoxemia as a consequence of placental dysfunction may result in damage of fetal liver cells.

Functional properties of human thyroid follicles cultured within collagen gel

Cultures of human thyroid follicles embedded in collagen gel were performed to investigate certain functional properties under bovine thyrotropin (TSH) stimulation. Follicles obtained from normal glands responded to increasing concentrations of TSH administered on day 4 in culture and for 3 days by increased amounts of cyclic AMP (cAMP), thyroglobulin (Tg) and triiodothyronine (T3) and by decreased levels of thyroxine (T4). Effect was maximal at 2000 microU/ml TSH (cAMP) or 200 microU/ml (Tg, T3, T4). When methimazole or propylthiouracil (PTU) were added, the T3 levels decreased. Follicle lumens contained a periodic acid-Schiff substance which was identified by immunoreaction as Tg. Thyroid follicles obtained from Graves' disease glands gave modified results with an earlier and intensified T3 response and no increase in Tg. These data show that (1) Tg and T3 are secretory products of functional follicles giving a cAMP-mediated response to TSH. (2) The detected T3 also derives from T4 5'-deiodination inhibited by PTU. (3) Intensified T3 response in Graves' follicles is probably due to enhanced conversion of T4 to T3.

Characterization of gamma-glutamyltransferase from neoplastic and non-neoplastic liver tissues in man and during rat liver hepatocarcinogenesis

The activity and the affinity for concanavalin A-Sepharose (Con A) of liver gamma-glutamyltransferase (gamma GT) were investigated in man, under various clinical conditions and in rats during experimental hepatocarcinogenesis. In man, gamma GT activity was higher than normal in hepatomas and (except for 1 case of hemochromatosis) also higher in the surrounding cirrhotic liver. The proportion of gamma GT which did not bind to Con A (Con A- form) was also increased in the tumors and in the surrounding liver, yet (with the same exception as above) to a greater extent in the hepatomas. In rat, gamma GT activity was higher in fetal liver (15-fold) and in hepatocarcinomas (10-fold) than in normal adult liver; total liver gamma GT activity gradually increased during progression from foci of altered cells to neoplastic nodules and tumors. The proportion of the Con A- form of gamma GT in the early or late stage of the carcinogenic process did not significantly differ from that in normal adult or regenerating rat liver, i.e. about 20% of the total activity. By contrast, nearly all the gamma GT from fetal rat liver bound to Con A. This suggests that gamma GT expression in rat liver carcinoma does not correspond to so-called retrodifferentiation process.

Increased UDP-glucuronyltransferase and gamma-glutamyltranspeptidase in enzyme-altered rat liver lesions produced by low doses of aflatoxin B1

Preneoplastic liver lesions were produced in female Wistar rats by low doses of aflatoxin B1 (Model 1: administration of 37.5 micrograms/kg 12 and 24 h after partial hepatectomy; Model 2: continuous application of 3.5 micrograms/kg in tap water daily for 28 days with partial hepatectomy after 14 days. The animals then received sodium phenobarbital, 0.1% in tap water, for 180 to 400 days). In both models numerous altered hepatic foci (AHF) and hyperplastic nodules (HN) were detected enzyme histochemically by their negative ATPase and positive gamma-glutamyltranspeptidase reactions. Immunohistochemically these lesions were also UDP-glucuronyltransferase positive. Increased UDP-glucuronyltransferase adds to permanent alterations of a number of drug metabolizing enzymes observed in a variety of different tumor models. These alterations are responsible for the toxin-resistant phenotype (Faber 1984b). Increased gamma-glutamyltranspeptidase was detected both enzyme histochemically and immunohistochemically; whereas gamma-glutamyltranspeptidase activity was present in both AHF/HN and in periportal areas by enzyme histochemistry, the immunohistochemical method selectively stained gamma-glutamyltranspeptidase in AHF and HN. Immunohistochemically detectable UDP-glucuronyltransferase and gamma-glutamyltranspeptidase are markers of putative precancerous liver lesions which may be useful in the analysis of the prestages of liver carcinogenesis.

Developmental changes in the activities of sialyl- and fucosyltransferases in rat small intestine

To study an enzymatic basis for the postnatal changes in intestinal glycosylation, the activities of sialyl- and fucosyltransferases were determined in the particulate fraction of mucosal cells prepared from rat small intestine of various ages. The results show that sialyltransferase activity was present in increased levels compared to adults during the preweaning period (1-2 weeks) and subsequently declined 5-fold to adult levels after weaning, while fucosyltransferase activity was decreased compared to adults in the first 3 weeks of life, rapidly increased at 4 weeks, and reached adult levels (10-fold) by 5 weeks. The changes in both sialyl- and fucosyltransferase activities were reflected by the membranous content of glycosidic-bound sialic acid and fucose, respectively. Cortisone injection precociously induced a decreased sialyltransferase activity and an increased fucosyltransferase activity in 2-week-old suckling rats. This study indicates that the activities of sialyl- and fucosyltransferases were reciprocally related and modulated by cortisone action in the developing intestine. These enzyme changes may be responsible for the previously noted shift from sialylation to fucosylation of the intestinal mucosa during maturation.

Discrimination of gamma-glutamyltranspeptidase from normal and carcinomatous pancreas

Two types of gamma-glutamyltranspeptidase (gamma-GTP) were identified in normal human pancreas, but ductal cell carcinomas of the pancreas showed only one type on analysis with polyacrylamide gel electrophoresis, anion exchange column chromatography, concanavalin A affinity chromatography and isoelectric focusing. gamma-GTP from carcinoma tissue was almost identical to the sialic acid-rich type of normal pancreatic gamma-GTP, and our methods did not evidence a difference between the two. However, E-PHA lectin column chromatography demonstrated differences in their elution pattern. Compared with normal pancreatic gamma-GTPs, the elution pattern of the carcinoma gamma-GTP was slowly delayed by the E-PHA lectin column. This finding suggests the presence of a bisecting N-acetylglucosamine-rich sugar chain in pancreatic carcinoma gamma-GTP, as well as the possible presence of a different sugar structure in the carcinoma gamma-GTP.

Comparative structural and lectin-binding studies on gamma-glutamyltransferase from human adult liver, fetal liver and primary hepatoma

gamma-Glutamyltransferase was purified to apparent homogeneity from human adult liver, fetal liver and hepatoma by deoxycholate extraction, immunoaffinity chromatography, papain digestion, phenyl-Sepharose chromatography and preparative polyacrylamide gel electrophoresis. The purified enzyme from all three sources had an apparent Mr of 82 000 by Sephadex G-150 gel filtration and on dodecyl sulphate/polyacrylamide gel electrophoresis two nonidentical subunits of Mr 57 000 and 23 000 were obtained. The pI of all three forms was 3.85 and after neuraminidase treatment they each gave at least five bands with pI values ranging over 5.9-6.6. Sialic acid content was 188 (adult liver), 182 (fetal liver) and 188 (hepatoma) nmol/mg protein. Total neutral sugar content was 702 (adult and fetal liver) and 700 (hepatoma) nmol/mg protein. The hexosamine content of the enzyme from all the three sources was the same (354 nmol/mg protein) and galactosamine was absent. Partially purified hydrophobic and hydrophilic forms of gamma-glutamyltransferase from all the three sources were precipitated by Concanavalin A, Ricinus communis agglutinin and wheat germ agglutinin. These results show that gamma-glutamyltransferase from human adult liver, fetal liver and hepatoma are structurally similar and that the elevated levels found in fetuses and hepatoma are only a quantitative increase and are not due to a new isoenzyme.

Pre- and postnatal development of differentiated functions in rat intestinal epithelial cells

A panel of monoclonal antibodies to intestinal cell surface components has been used to compare the expression of differentiation-specific antigens in the epithelial cells of fetal, suckling, and adult rat small intestine. Indirect immunofluorescence staining, and immunopurification of detergent-solubilized membrane proteins, followed by single- and two-dimensional slab gel electrophoretic analysis, have demonstrated that fetal intestinal cells (at day 21 of gestation) express most differentiation-specific markers typical of adult absorptive villus cells. A marked heterogeneity in antigen expression was observed among different villus cell populations in suckling rat intestine, and three cell surface components were identified which are exclusively present during this period of intestinal development. Striking changes in the patterns of antigen expression in crypt and villus cells, and variations in the apparent isoelectric points for most luminal membrane components, were associated with the maturation of the intestinal mucosa at weaning. These changes could not be prematurely induced by cortisone injection in newborn rats, suggesting that factors other than glucocorticoids are responsible for the postnatal development of the intestinal epithelium. These results suggest that basic differences in biological properties and regulatory mechanisms exist among intestinal epithelial cells at different stages of pre- and postnatal maturation.

Characterization of gamma-glutamyltranspeptidase from human exocrine pancreatic carcinomas

Two different types of gamma-glutamyltranspeptidase (gamma-GTP) have been found in normal human pancreas following bromelain treatment. On the other hand, three human pancreatic ductal cell carcinomas have only a single type of gamma-GTP upon analysis with polyacrylamide gel electrophoresis, anion-exchange column chromatography and isoelectric focusing. Carcinoma gamma-GTPs were almost identical to one of the two types of normal pancreatic gamma-GTPs. The gamma-GTP from pancreatic carcinomas bound to anion-exchange column and was eluted at the same NaCl fractions as normal pancreatic gamma-GTP. The properties of pancreatic carcinoma-gamma-GTP, as assessed by binding to concanavalin A and lentil lectin affinity columns, were also similar to one of the two enzymes of normal pancreas. No apparent difference in isoelectric points was found between the carcinoma gamma-GTPs and one of the two normal pancreatic gamma-GTPs.

Variations in sialic acid content of gamma-glutamyltransferase: a consequence for immunochemical determinations?

Using specific antibodies against the human kidney enzyme, gamma-glutamyltransferase (GGT, EC 2.3.2.2) was assayed from human kidney and serum by electroimmunodiffusion. Determination of the enzyme by such a method was highly influenced by the sialic acid content of the molecule. The peaks corresponding to the sialylated GGT were higher than those corresponding to the neuraminidase-treated enzyme. In contrast, sialylation of the protein had no influence on the results observed when measuring the enzyme by radial immunodiffusion. Moreover, immunoprecipitation curves of both sialylated and neuraminidase-treated samples were identical. The varying degrees of sialylation of GGT occurring under physiological or pathological conditions are known to be partly responsible for the heterogeneity of the enzyme in organs and biological fluids. Therefore, determination of the enzyme by electroimmunodiffusion may be hazardous.

Two types of human pancreatic gamma-glutamyl transpeptidase

Two different types of gamma-glutamyl transpeptidase (gamma-GTP) were extracted from human pancreas by protease treatments such as bromelain. Furthermore, human pancreatic gamma-GTP, extracted with trypsin, was separated into two different components by additional treatment with bromelain. One component displayed fast electrophoretic mobility during polyacrylamide gel electrophoresis and an apparent affinity for an anion-exchange column, while the other showed slow electrophoretic mobility and passed through the anion-exchange column with starting buffer. In addition, the percentage affinity to concanavalin A (Con A) of the former was 52.2% and of the latter only 7.2%. On heat stability, the former was more sensitive than the latter at 56 degrees C. These results indicate the existence of two types of gamma-GTP in human pancreas.

Tumour-associated isoenzymes of gamma-glutamyl transferase in the serum of patients with hepatocellular carcinoma

Sera from 391 southern African Blacks with hepatocellular carcinoma, matched controls, patients with other malignant tumours, and with various forms of hepatobiliary disease were fractionated by polyacrylamide gradient gel electrophoresis to determine the prevalence of tumour-associated gamma-glutamyl transferase isoenzymes in Black patients with hepatocellular carcinoma. One or more tumour-associated isoenzymes (I', I'' or II') were present in 58.6% of the patients with hepatocellular carcinoma: I' in 54.5%, I'' in 27.1%, and II' in 34%. These isoenzymes were detected in one patient with prostatic cancer, occasionally in patients with acute viral hepatitis, but in no normal individuals. The presence of tumour-associated isoenzymes was not related to patient age, sex or hepatitis-B virus status or to the tumour burden. Isoenzymes were present in 42 percent of hepatocellular carcinoma patients with a normal serum alpha-foetoprotein concentration and in 50% of those with a non-diagnostic value. gamma-glutamyl transferase isoenzymes may be supplementary to alpha-foetoprotein in the diagnosis of hepatocellular carcinoma.

Gamma-glutamyl transferase activity in fetal serum, maternal serum, and amniotic fluid during gestation

Gamma-glutamyl transferase activity was measured in fetal serum, maternal serum, and amniotic fluid in 173 pregnancies from 15 to 40 weeks' gestation. Fetal serum was obtained in the second trimester by fetoscopy and in the third trimester by umbilical cord puncture at caesarian section or vaginal delivery. Enzyme activities in maternal blood (10 IU/1, SD 2) and fetal blood (88 IU/1, SD 20) remained relatively constant throughout gestation, whereas in the amniotic fluid there was a significant decrease at term from the value in the second trimester (p less than 0.001). Electrophoretic separation of the enzyme showed one isoenzyme in the fetal blood and at least two in the amniotic fluid. The fetal isoenzyme had the same mobility as the major isoenzyme in the amniotic fluid.

Microvillar peptidase activity in amniotic fluid: possible use in the prenatal diagnosis of cystic fibrosis

The activities of two microvillar peptidases, gamma-glutamyl transpeptidase (GGTP) and aminopeptidase M (APM), have been measured in 132 samples of mid-trimester amniotic fluid. These included samples from 16 pregnancies at risk for cystic fibrosis. The activities of both peptidases were significantly below the normal range in amniotic fluids from the 6 affected pregnancies. This points to early pathological changes in fetal tissues in which microvilli are prominent. In contrast, 4-methylumbelliferylguanidinobenzoate-reactive protease activity in amniotic fluid from the 6 affected pregnancies was normal. Correlation of individual values between GGTP and APM was close in all cases examined, so that when a further 7 samples from cases at risk became available they were tested for GGTP alone. Of these, the 3 affected pregnancies had significantly reduced GGTP activity, particularly in the early weeks of gestation. It is suggested that early amniocentesis and examination of gamma-glutamyl-transpeptidase isoenzyme constitution might make possible the reliable early diagnosis of cystic fibrosis.

gamma-Glutamyl transpeptidase of human amniotic fluid

gamma-Glutamyl transpeptidase (GGTP) activity in normal amniotic fluids and corresponding maternal sera obtained at various gestational periods was measured. The ontogenic pattern of enzyme activity in amniotic fluid is very similar to alpha fetoprotein (AFP). However, the levels of these two proteins behaved differently in corresponding maternal sera. Also, in amniotic fluids obtained from pregnancies with neural tube defects (NTD), only AFP concentration was abnormally high whereas GGTP activity was normal.

Subcellular localization and isolation of gamma-glutamyltransferase from rat hepatoma cells

Cultured rat hepatoma cells were homogenized and subjected to subcellular fractionation by analytical sucrose density centrifugation to determine the localization of gamma-glutamyltransferase ((5-glutamyl-)-peptide: amino acid 5-glutamyltransferase, EC 2.3.2.2). The activity was exclusively localized to the plasma membrane. Diazotized sulphanilic acid was used as a non-penetrant membrane reagent which inactivates ectoenzymes. With both intact and sonicated cells, only 70-75% inhibition of gamma-glutamyltransferase activity was observed. At least 12% of the total cell complement of gamma-glutamyltransferase activity is highly resistant to inactivation by diazotized sulphanilic acid even after Triton X-100 solubilization. The enzyme was purified from hepatoma cells and its properties compared with enzyme from normal liver. Apart from the striking increase in Vapp there were only minor differences between the enzymes from the two sources. In contrast to the complete abolition of transpeptidase activity of the purified hepatoma enzyme by diazotized sulphanilic acid, the hydrolytic activity of this preparation was only slightly inhibited.

Further investigations on a novel gamma-glutamyl transpeptidase in human renal carcinoma

The enzymic and immunological properties of a novel gamma-glutamyl transpeptidase found in human renal carcinoma tissues were investigated further in comparison with those of the normal kidney enzyme. On isoelectric focusing, the novel gamma-glutamyl transpeptidase separated into two main forms, having pI values below 3.6, while the normal kidney enzyme separated into multi-molecular forms with pI values of 4.0-5.0. Neuraminidase treatment diminished the difference between these two enzymes, the products of the novel enzyme and the normal kidney having pI values of 5.4 and 5.6, respectively. The percentages of the total activity of the novel gamma-glutamyl transpeptidase binding with Con A before and after neuraminidase treatment were about 40% and 80%, respectively, while the corresponding percentages of the activity of the normal kidney enzyme were less that 10% and about 25%, respectively. The novel gamma-glutamyl transpeptidase was immunologically identical with the normal kidney enzyme in the activity inhibition test and the double diffusion test. The present data suggest that the novel gamma-glutamyl transpeptidase has the same antigen site as the normal kidney enzyme, but differs from the latter at least in its sialic acid content and in some other carbohydrate moieties.

gamma-Glutamyltransferase from human hepatoma tissue in comparison with normal liver enzyme

gamma-Glutamyltransferase was solubilized from human hepatoma tissues by bromelain treatment, and some of its properties were compared with those of the normal adult liver enzyme. An electrophoretic study showed a slightly different mobility between the two enzymes before and after neuraminidase treatment. The hepatoma tissue enzyme was distinguished from the normal liver enzyme by decreased affinity to Con A. However, the enzymes from the two sources were found to be very similar or identical with respect to molecular weight, Michaelis constant, pH optimum, thermostability, effect of various L-amino acids as acceptors, behavior to divalent cations or ethylenediaminetetraacetate, inhibition by urea or sodium dodecyl sulfate, and immunological properties. These results suggest that the hepatoma tissue gamma-glutamyltransferase is largely due to altered glycosylation of this glycoprotein in hepatoma cells.

Purification and properties of gamma-glutamyl transferase from normal rat liver

gamma-Glutamyl transferase ((5-glutamyl)-peptide: amino-acid 5-glutamyltransferase, ED 2.3.2.2) has been partially purified from both whole rat liver (600-fold) and from isolated biliary tract (1200-fold). The most highly purified fraction gave two protein bands on polyacrylamide gel electrophoresis, the major band alone having enzyme activity. The enzyme purified from biliary tract appears identical to that from whole liver preparation according to molecular weight, kinetic parameters and the effects of various inhibitors. Three liver cell-types; parenchymal, Kupffer and biliary tract were isolated by perfusion of the rat liver in situ with collagenase, followed by selective cell isolation. Approx. 80-90% of the total recovered enzyme activity was found in the biliary tract. Nearly 50% of the apparent enzyme activity in the parenchymal cell was attributable to a nonspecific hydrolase.

Electrophoretic fractionation of serum gamma-glutamyl transpeptidase in human hepatic cancer

Serum gamma-glutamyl transpeptidase from patients with various hepatobiliary diseases was fractionated by polyacrylamide gradient gel slab electrophoresis to study the specific patterns of gamma-glutamyl transpeptidase fractions in hepatic cancer. On zymograms of normal serum gamma-glutamyl transpeptidase, a total of 10 fractions was observed. Additionally, fractions I', I" and II' were recognized in sera from hepatocellular carcinoma patients. Among these, fraction I', which migrated slightly, but significantly, slower than fraction I was the most specific; it was found in 55% of the hepatocellular carcinoma patients. Fractions I" and II' were also relatively specific, each was observed in about 29% of these patients. Fractions V to IX were observed in few hepatocellular carcinoma cases. Fraction I' is thought to be a hepatoma-related fraction, highly specific for the serum of hepatocellular carcinoma patients. Fractions I" and II' were also thought to be hepatoma-related fractions of gamma-glutamyl transpeptidase. We suggest that fractions I', I" and II' may be useful in the diagnosis of hepatocellular carcinoma.