Gamma-glutamyl transpeptidase of rat seminal vesicles; effect of orchidectomy and hormone administration on the transpeptidase in relation to its possible role in secretory activity

Acute exposure to bis(2-ethylhexyl)phthalate disrupts calcium homeostasis, energy metabolism and induces oxidative stress in the testis of Danio rerio

Bis(2-ethylhexyl)phthalate (BEHP) negatively affects testicular functions in different animal species, disturbing reproductive physiology and male fertility. The present study investigated the in vitro acute effect of BEHP on the mechanism of action of ionic calcium (Ca²⁺) homeostasis and energy metabolism. In addition, the effect of BEHP on oxidative stress was studied in vitro and in vivo in the testis of Danio rerio (D. rerio). Testes were treated in vitro for 30 min with 1 μM BEHP for ⁴⁵Ca²⁺ influx measurements. Testes were also incubated with 1 μM BEHP for 1 h (in vitro) or 12 h (in vivo) for the measurements of lactate content, ¹⁴C-deoxy-d-glucose uptake, lactate dehydrogenase (LDH) and gamma-glutamyl transpeptidase (GGT) activity, total reactive oxygen species (ROS) production and lipid peroxidation. In addition, the effect of BEHP (1 μM) on GGT, glutamic oxaloacetic transferase (GOT) and glutamic pyruvic transferase (GPT) activity in the liver was evaluated after in vivo treatment for 12 h. BEHP disturbs the Ca²⁺ balance in the testis when given acutely in vitro. BEHP stimulated Ca²⁺ influx occurs through L-type voltage-dependent Ca²⁺ channels (L-VDCC), transitory receptor potential vaniloid (TRPV1) channels, reverse-mode Na⁺/Ca²⁺ exchanger (NCX) activation and inhibition of sarco/endoplasmic reticulum Ca²⁺-ATPase (SERCA). BEHP affected energy metabolism in the testis by decreasing the lactate content and LDH activity. In vitro and in vivo acute effects of BEHP promoted oxidative stress by increasing ROS production, lipid peroxidation and GGT activity in the testis. Additionally, BEHP caused liver damage by increasing GPT activity.

Non-monotonic dose-response effect of bisphenol A on rare minnow Gobiocypris rarus ovarian development

Bisphenol A (BPA) is widely spread in the environment, and can cause various reproductive disrupting effects on different organisms, including fish. Our previous published study showed that BPA has non-monotonic (inverted U-shaped) dose-response effect on rare minnow Gobiocypris rarus ovarian weight at different concentrations. To investigate the potential mechanism, we exposed female rare minnow to 1, 15 and 225 µg L(-1) BPA for 7 days in the present study. The levels of vitellogenin (Vtg), sex hormones, hydrogen peroxide (H2O2), glutathione (GSH) and triglyceride (TG) were measured. RNA-seq of ovary tissues was also performed. Result showed that Vtg, sex hormone and TG levels showed an inverted U-shaped increased response, while H2O2 and GSH levels showed a U-shaped inhibited response. RNA-seq data showed that many genes involved in lipid metabolism, oxidative stress, and proteolysis processes were altered. The change of Vtg, H2O2, GSH and TG levels was possibly related to the altered sex hormone levels. Sex hormone's direct effect, Vtg accumulation, TG accumulation and oxidative stress induced proteolysis may contribute to the change of ovary weight.

Functional Importance of 1α,25(OH)2-Vitamin D3 and the Identification of Its Nongenomic and Genomic Signaling Pathways in the Testis

The 1α,25(OH)2-vitamin D3 (1,25-D3) is known by its classic effects on Ca2+ metabolism and regulation of cellular proliferation and differentiation. The hormone 1,25-D3 acts in the testis through nongenomic and genomic events being implicated in the success of spermatogenesis in rats and in human being. The aim of this review was to highlight the effect and intracellular pathways of 1,25-D3 to modulate the spermatogenesis. The pivotal role of 1,25-D3 in male reproduction is reinforced by the presence of VDR and 1α-hydroxylase in reproductive tract. Also, the marked expression of VDR and the VD metabolizing enzymes in human testis, ejaculatory tract, and mature spermatozoa implicates the 1,25-D3 in spermatogenesis and maturation of human spermatozoa. Among genomic events, 1,25-D3 influences the expression of calcium binding protein and stimulates aromatase gene expression through a nongenomic activation of the membrane-bound VDR receptor involving the PKA pathway in the testis. Also, 1,25-D3 stimulates amino acid transport and exocytosis in testis by nongenomic events coupled to ionic currents triggered at plasma membrane. All together, the demonstration that 1,25-D3 regulates both Sertoli cell and sperm function may be useful for the study and development of new therapeutic strategies for the male reproductive disorders.

Modulation of rat epididymal gamma-glutamyl transpeptidase by nonylphenols

1. gamma-Glutamyl-transpeptidase (gamma-GTP), present at low levels in the testis, seminal vesicle, prostate gland and epididymis in rat at 4 days of age, showed rapid developmental increases at the time of weaning. 2. Administration of nonylphenols (NP) to the neonatal male rat pup (from days 1 to 15) impaired the subsequent development of gamma-GTP in the epididymis but not in the testis, seminal vesicles or prostate gland. 3. Single injection of NP to weaned pups at approximately 22 days of age decreased gamma-GTP in the epididymis but not in other male accessory sex organs. This effect was transient, dose-dependent and blocked by the oestrogen receptor-specific antagonist ICI 182,780. 4. Single injection of oestradiol to weaned rat at approximately 22 days of age also decreased gamma-GTP in the epididymis but not in the testis, prostate gland or seminal vesicles. 5. In in vitro assays, NP did not inhibit epididymal gamma-GTP activity even at 100 microM final concentration. Under similar conditions, acivicin, a specific inhibitor for gamma-GTP, showed a dose-dependent inhibition of gamma-GTP activity. 6. It is suggested that NP impair gamma-GTP expression in the epididymis of developing male rat and act in part via the oestrogen receptor.

Cauda epididymal sperm interactions with seminal vesicle fluid

The interaction of rat cauda epididymal sperm cAMP-dependent protein kinase (PKA) with seminal vesicle fluid (SVF) proteins was examined. Specific proteins in SVF act as substrates for the sperm cell PKA. The apparent molecular weights of these proteins are 45.0, 31.5, 17.2, 14.7, and 13.3 kDa. The phosphorylation of one low-molecular-weight cauda sperm protein is blocked in the presence of SVF. There is no PKA enzyme activity in SVF. The presence of phosphate transfer activity between the sperm cell enzyme and the SVF proteins is species dependent. For example, mouse and rat SVF proteins are efficient phosphate acceptors, but there is no phosphorylation activity when hamster SVF is used as the enzyme substrate. The sperm cell samples were also assessed for membrane integrity. Specifically, cauda sperm cells used in these assays were judged to be intact when examined microscopically using the fluorescent vital dye carboxyfluorodiacetate. Although there was enzyme activity in the supernatants of the rat sperm cell samples, in the protein kinase assay it required three times as much supernatant volume (compared with intact cell sample volume) to measure the activity. Supernatant enzyme activity did not increase with washing, indicating that the cells were not damaged by this procedure. The enzyme itself does not adhere to the sperm cells, so the PKA enzyme activity is most likely oriented on the external surface of the sperm cell.

Purification and immunological characterization of a new form of gamma-glutamyltransferase of human semen

A new form of gamma-glutamyltransferase was purified from human seminal plasma. The purified enzyme was composed of two non-identical subunits with apparent molecular masses of 150 and 95 kDa on polyacrylamide gel electrophoresis (PAGE) in the presence of sodium dodecyl sulfate (SDS), and showed a molecular mass of 500 and 250 kDa on gel filtration in the absence and presence of 1% Triton X-100, respectively. This enzyme was different from human renal gamma-glutamyltransferase not only in apparent molecular masses, but also in amino acid compositions of both the subunits to each other. Experiments with the antisera raised against the purified enzyme revealed that the enzyme was different from the renal, hepatic and testicular enzymes in reactivity to the antibody though partially related to those enzymes. Ouchterlony double diffusion analysis indicated that both human seminal plasma and prostatic extract contained two types of gamma-glutamyltransferase, one is that we purified and the other the renal type. Hence, it is most likely that gamma-glutamyltransferase accounting for most of the enzyme activity in semen results from prostata followed by secretion to seminal plasma.

Glucocorticoid hormones increase the activity of gamma-glutamyltransferase in a highly differentiated hepatoma cell line

Gamma-Glutamyltransferase activity was detected in the plasma membrane of the highly differentiated hepatoma cell line Fao, (0.93 mU/mg cell protein). Dexamethasone (1 microM) provoked a 2-3-fold increase in the activity of the enzyme in the presence of fetal calf serum. Maximal induction occurred 48-72 h after addition of the glucocorticoid to the cell culture medium. The hormonal specificity was demonstrated by the relative potencies of several glucocorticoids and sex steroids: hydrocortisone and corticosterone increased gamma-glutamyltransferase activity while tetrahydrocorticosterone and all sex steroids tested were ineffective. The effect of dexamethasone on gamma-glutamyltransferase activity wa specific since the activities of several other plasma membrane enzymes were not modified. The mechanism of the dexamethasone-induced increase in gamma-glutamyltransferase activity was neither by modification of the affinity of the enzyme for its substrates nor by alteration of the subcellular distribution of the enzyme. This increase was prevented by cycloheximide and actinomycin D. The data presented are consistent with a specific glucocorticoid receptor-mediated induction of gamma-glutamyltransferase activity in Fao cells. The kinetic parameters of the induction process by glucocorticoids are very similar to those found in adult rat liver. These results suggest that the Fao cell line is a very convenient system for the study of the molecular mechanisms of glucocorticoid effects on differentiated cells.

Properties of gamma-glutamyltranspeptidase, and glutathione levels in rat mammary gland

gamma-Glutamyltranspeptidase activity and glutathione levels were studied in rat mammary gland during the lactogenic cycle; both increased during mid-lactation. The enzyme's specific activity with several amino acids showed that glutamine and methionine were the best substrates. Maleate decreased the transpeptidation reaction and increased the hydrolytic activity. These results suggest that gamma-glutamyltranspeptidase from the mammary gland is similar to the enzyme described in other tissues in relation to these properties and the physiological role proposed in amino acids transport.

In vivo modulation of rat hepatic gamma-glutamyltransferase activity by glucocorticoids

The gamma-glutamyltransferase (gamma-GT) activity decreased by 50% following adrenalectomy of female rats, in homogenate as well as in a purified plasma membrane preparation from liver. In contrast, such a variation was not found in the kidney. None of 3 other enzyme activities of the plasma membrane, namely 5'-nucleotidase, alkaline phosphatase, and alkaline phosphodiesterase I, was decreased by adrenalectomy. Administration of hydrocortisone (5 mg/100 g body weight) resulted in a 2.6-fold increase in hepatic gamma-GT activity from adrenalectomized rats. The hydrocortisone-mediated stimulation of gamma-GT activity was dose- and time-dependent. The 5'-nucleotidase and leucine aminopeptidase activities were not modified by the hydrocortisone treatment. The activity of gamma-GT was mainly associated with nuclear fractions (nuclei and plasma membranes) obtained from liver homogenates of either control, adrenalectomized or adrenalectomized hydrocortisone-treated animals, and this activity was purified 18-fold in a plasma-membrane preparation as compared to homogenate. These data suggest that adrenalectomy and conversely hydrocortisone treatment modulate specifically the hepatic plasma-membrane gamma-GT activity. This represents one of the first demonstrations of a specific modulation by glucocorticoids of an enzyme activity typical of the plasma membrane.

Structural, functional, and clinical aspects of gamma-glutamyltransferase

GGT catalyses the transfer of gamma-glutamyl residues to amino acids or small peptides. A number of publications report the purification of GGT, the rat kidney enzyme being the best characterized. Bromelain treatment liberates an active form with a molecular weight of 68,000 separable into two nonidentical glycopeptides with molecular weights of 46,000 and 22,000; the latter contains the gamma-glutamyl binding site. GGT is intimately concerned in the synthesis and metabolism of glutathione through the gamma-glutamyl cycle. There is good evidence that this plays a role in the absorption of amino acids from the glomerular filtrate and from the intestinal lumen through a translocation mechanism. Many studies indicate that the GGT content of liver is increased by enzyme-inducing drugs and that this increase is reflected in elevated activity of the enzyme in blood serum. The serum assay has potential in monitoring drug compliance. Increased serum GGT activity encountered in chronic alcoholics seems to be partly due to microsomal enzyme induction. Utility of the assay in detecting alcoholism is controversial, but it is a useful index to compliance with therapy. Dramatic increases in activity are found in many chemically-induced animal tumors, and can be recognized in premalignant cells long before any morphological changes become evident. It has been used as a test for hepatic metastases, but its predictive value has shown a wide range in the hands of many authors. A similar controversy applies to its role in monitoring cancer therapy. Many synthetic substrates have been used to measure serum GGT activity. Currently, L-gamma-glutamyl-p-nitroanilide is the most popular. Males have higher values than females; activity is very high in the neonate and rather low in pregnancy. The most universal application of serum GGT assay is in diagnosis of liver and biliary tract disease. It is widely believed that higher values occur in biliary obstruction than in parenchymal disease. However, the percentage incidence of abnormalities and the overlap of values in individual cases in different disease categories are so great that the enzyme cannot be recommended for this purpose. Isoenzyme analyses have been performed in an attempt to improve the diagnostic specificity of the serum GGT assay. Tissue-specific patterns have not been described, and disease-specific patterns cannot be reproduced with confidence. Whereas exciting advances are being made in understanding the molecular structure, mechanism, and functions of the enzyme it has yet to find a genuinely useful diagnostic role substantiated by a convincing body of scientific data.

gamma-Glutamyltransferase in human and mouse breast tumours

A series of experimental mouse tumours were assayed for their gamma-glutamyltransferase activities. Significantly raised activities were found in a transplantable spontaneous mammary carcinoma compared to normal or lactating mouse breast. A study was therefore undertaken of human breast tumours. Carcinomas showed significantly elevated enzyme levels when compared with normal tissue or histologically uninvolved tissue from a breast containing a carcinoma. Fibroadenoma and chronic mastitis also showed significantly elevated levels when compared with normal tissue and did not differ significantly from carcinoma tissue. Benign breast cyst fluid showed very high levels of enzyme activity. Binding properties of the enzyme to Con A-Sepharose suggested that while normal tissue and fibroadenomas contained only asialated enzyme, carcinomas, chronic mastitis and cyst fluid contained a substantial proportion of sialated enzyme.

Purification and comparison of several catalytic parameters of the gamma-glutamyltranspeptidase of rat mammary adenocarcinoma (13762) and of normal rat mammary gland

A method for the purification of a membrane-bound glycoprotein, gamma-glutamyltranspeptidase ((gamma-glutamyl)-peptide:amino-acid gamma-glutamyltransferase, EC 2.3.2.2), from a transplantable rat mammary tumor (13762 MT) is described. The properties of the tumor enzyme were compared with those of gamma-glutamyltranspeptidase similarly isolated from mammary tissue of nonpregnant multiparous rats. Evidence has been presented elsewhere that the mammary and tumor enzymes exist as groups of species differing in isoelectric point and that the tumor enzyme contains more of the those species with lower isoelectric points. In this study the normal and tumor enzyme preparations are found to be identical or very similar in regards to the effect of papain on molecular size, the ratios of the enzymatic activities as measured with various amino acids, the Km for gamma-glutamyl-p-nitroanilide, and the Ki for inhibition by glutathione. Neuraminidase treatment had no effect on these catalytic properties. The properties observed were generally similar to those previously reported for highly purified rat kidney preparations.

GAMMA-Glutamyl transpeptidase of sheep-kidney cortex. Isolation, catalytic properties and dissociation into two polypeptide chains

Gamma-Glutamyl transpeptidase was isolated from sheep kidney cortex as an apparently homogeneous, highly active protein. At optimal pH and in the absence of acceptors, the enzyme catalyzes the release of about 510 mumol of p-nitroaniline per mg protein per min from the model substrate L-gamma-glutamyl-p-nitroanilide. Polyacrylamide gel electrophoresis in a sodium dodecylsulfate buffer system showed the presence of a large (Mr approximately 65000) and a small (Mr approximately 27000) polypeptide chain. Dissociation into two polypeptide chains was also achieved in 8 M urea. Amidination with dimethylsuberimidate produced a crosslinked protein of molecular weight approximately 90000. In the course of this work a convenient procedure was developed for the determination of gamma-glutamyl transpeptidase activity using L[glycine-2-3H]glutathione as the substrate. In this procedure the release of cysteinyl-[2-3H]glycine from glutathione is followed, after separation of the radioactive di-peptide from unreacted glutathione on a small Dowex-1 acetate column. The reactions with gamma-glutamyl-p-nitroanilide and glutathione are both strongly activated by several metal ions (Ca2+, Mg2+, Na+ and K+) and by a number of amino acids and peptide acceptors. The products of the reaction with glutathione were identified as cysteinylglycine, gamma-glutamylglutathione and glutamate. The formation of these products is consistent with the function of gamma-glutamyl transpeptidase in both the gamma-glutamyl transfer reaction and in the hydrolysis of the gamma-glutamyl bond. The activating effect of metal ions in the reaction with glutathione was shown to be dependent on the acceleration of the transfer reaction; the rate of hydrolysis of the gamma-glutamyl bond remaining unchanged.