Aminopyrine--an effective modifier of liver and serum gamma glutamyl transpeptidase

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

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

Gamma glutamyl transferase

Serum gamma-glutamyl transferase (GGT) has been widely used as an index of liver dysfunction and marker of alcohol intake. The last few years have seen improvements in these areas and advances in understanding of its physiological role in counteracting oxidative stress by breaking down extracellular glutathione and making its component amino acids available to the cells. Conditions that increase serum GGT, such as obstructive liver disease, high alcohol consumption, and use of enzyme-inducing drugs, lead to increased free radical production and the threat of glutathione depletion. However, the products of the GGT reaction may themselves lead to increased free radical production, particularly in the presence of iron. There have also been important advances in the definition of the associations between serum GGT and risk of coronary heart disease, Type 2 diabetes, and stroke. People with high serum GGT have higher mortality, partly because of the association between GGT and other risk factors and partly because GGT is an independent predictor of risk. This review aims to summarize the knowledge about GGT's clinical applications, to present information on its physiological roles, consider the results of epidemiological studies, and assess how far these separate areas can be combined into an integrated view.

Transient hepatic dysfunction in an infant of an epileptic mother treated with carbamazepine during pregnancy and breastfeeding

OBJECTIVE

A case is reported of a carbamazepine (CBZ)-treated epileptic mother whose newborn presented with transient hepatic dysfunction characterized by direct hyperbilirubinemia and high concentrations of gamma-glutamyltransferase (GGT).

DATA SOURCES

Information was obtained from case reports, clinical trials, and relevant bibliographic laboratory studies.

DATA EXTRACTION

Data from case reports were evaluated and compared with those from our patient. The hepatotoxic reactions together with the microsomal enzymatic induction of CBZ were reviewed.

DATA SYNTHESIS

A female infant born to an epileptic mother treated with CBZ throughout pregnancy and breastfeeding presented with transient direct hyperbilirubinemia and high concentrations of GGT. The characteristics of her transient hepatic dysfunction were: early appearance (during the first day of life); discrepancy between the normal liver enzymes and high GGT concentrations; slow decrease of GGT, which nevertheless remained at above-normal concentrations even after the complete disappearance of direct hyperbilirubinemia; and spontaneous resolution in spite of only occasional breastfeeding. The possible explanations of this transient hepatic dysfunction (like enzymatic induction) are discussed.

CONCLUSIONS

CBZ-induced hepatic dysfunction in neonates appears to have different clinical expressions. Infants of epileptic mothers treated with CBZ throughout pregnancy and breastfeeding should be carefully monitored for possible adverse effects.

Gamma-glutamyl transpeptidase in synovial fluid, serum, and urine of patients with rheumatoid arthritis

The changes in the levels of GGT activity in various body fluids, ESR, SF-protein concentration, and SF-WBC count were determined in 59 RA patients and 18 control subjects. The SF-GGT and UGGT were markedly elevated in all RA patients investigated. The increase of SF-GGT is more pronounced than UGGT. The observation of comparable levels of SGGT in RA patients and control subjects indicates that SGGT does not gain entry into synovial fluid or urine. No differences were noticed in SF-protein concentration whereas ESR levels and SF-WBC counts were significantly higher in RA patients than in control subjects. Statistically significant correlations were observed between SF-GGT versus UGGT, SF-WBC, and ESR in females, and between SF-GGT and SF-protein and SGGT in male RA patients. The correlation coefficient values between UGGT versus SF-protein, SF-WBC, and ESR were found to be significant in male RA patients. UGGT levels correlated strongly with SGGT in all RA patients. These findings suggest that the measurement of SF-GGT and UGGT might be useful in understanding the pathogenesis of rheumatoid arthritis.

Relationship between inductions of monooxygenase activity and gamma-glutamyltranspeptidase in rat hepatocyte primary cultures

The proposition that changes in activity of gamma-glutamyltranspeptidase (GGT) in serum may provide a useful index of the extent of induction of liver drug-metabolizing enzymes by various drugs was examined by comparing control of GGT and monooxygenase activities in cultured hepatocytes. In rat hepatocyte monolayers maintained for up to 5 days the effects of xenobiotics and other factors on cellular GGT activity were compared with effects on a relatively broad measure of drug metabolism, the 7-ethoxycoumarin O-deethylase (ECD) activity of intact cells. A diverse group of drugs including phenobarbital and other barbiturates, diphenylhydantoin, glutethimide, aminopyrine and griseofulvin and the steroids dexamethasone and pregnenolone 16 alpha-carbonitrile were shown to induce both GGT and ECD under comparable culture conditions. Inductions of both activities were potentiated by glucocorticoids and depressed (where tested) by dibutyryl cyclic AMP. Some other hormones or nutrients modulated the activities differently. The magnitude of GGT induction by different drugs did not correlate with relative ECD induction and for several drugs the concentration-dependence of the two effects was different. Interpretation is complicated by the possible contribution of multiple forms of cytochrome P-450 to ECD activity but it seems unlikely that drugs which induce both GGT and drug metabolism do so via a common regulatory mechanism. For such drugs changes in serum GGT could provide only a crude guide to likely changes in drug metabolism. Some compounds including polycyclic hydrocarbons and warfarin induced ECD but had no associated effect on GGT in hepatocytes.

Induction by butylated hydroxytoluene of rat liver gamma-glutamyl transpeptidase activity in comparison to expression in carcinogen-induced altered lesions

Butylated hydroxytoluene (BHT) at concentrations of 300-6000 ppm in the diet caused a dose-dependent increase in gamma-glutamyl transpeptidase (GGT) activity in normal F344 male rat liver at 18 weeks. However, the activities of glutathione S-transferases (GSTs) of rat liver cytosol were enhanced only at concentrations of 3000 or 6000 ppm BHT. Histochemically, the enhanced GGT activity was localized to hepatocytes surrounding the portal areas. Autoradiographic measurements of DNA synthesis showed that dietary BHT did not increase the level of cell proliferation and the GGT-positive hepatocytes did not exhibit different rates of DNA synthesis from those of GGT-negative cells. Feeding of the liver carcinogen N-2-fluorenylacetamide (FAA) induced foci and nodules of GGT-positive altered cells which exhibited higher rates of DNA synthesis than those of surrounding GGT-negative hepatocytes. Following iron loading, the periportal GGT-positive hepatocytes produced by BHT accumulated cellular iron, whereas the cells in FAA-induced lesions excluded iron. These results suggest that dietary BHT induces GGT activity in periportal hepatocytes without proliferation of the cells and that induction does not represent fetal expression or a preneoplastic alteration.

Perturbation of hepatic glutathione level and glutathione-related enzyme activities by repeated administration of aminopyrine in rats

The influence of repeated administration of aminopyrine on the tissue glutathione level and related enzyme activities was investigated in rats. Reduced glutathione level in the liver was not changed after 5 days of treatment but a significant increase was seen after 15 days of aminopyrine treatment. Oxidized glutathione level was unaltered throughout the experiment. Repeated administration of aminopyrine for 5 days caused a marked increase in gamma-glutamyl transpeptidase activities in liver whole homogenates as well as in the nuclear fraction, but not in liver microsomes. These results suggest that gamma-glutamyl transpeptidase located in plasma membrane may be induced by repeated administration of aminopyrine for 5 days. The activities of cytosolic glutathione peroxidase, which modulates glutathione level, were also significantly increased by aminopyrine treatment. Under the same conditions, glutathione peroxidase activity with H2O2 as a substrate was unaltered, while a time-dependent increase in the activity was found when cumene hydroperoxide was used as a substrate, even after a single administration of aminopyrine. The intracellular cysteine level was increased accompanying the increased gamma-glutamyl transpeptidase activities. Therefore, induced gamma-glutamyl transpeptidase may play a role in the reclamation of extracellular oxidized glutathione.

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.

Plasma gamma-glutamyl transpeptidase in heroin addicts

Plasma gamma-glutamyl transpeptidase was measured in 25 heroin addicts. The purpose was to find out if the long term administration of heroin would lead to a stimulation of GGTP due to the detoxication of this drug in the endoplasmatic reticulum of the liver. In 10 patients the elevation of GGTP could be attributed to liver damage, since other liver enzymes were also increased. 15 patients had normal GGTP activities, in 4 of them accompanied by minor elevations of single other hepatic enzymes. In 11 patients the GGTP activity as weel as that of the other enzymes was normal despite heavy chronic herioin abuse. It is therefore improbable that GGTP can be used to diagnose abuse of this drug and to evaluate the progress of drug detoxication treatments and drug abstention as has been proposed in chronic alcoholism.

Serum gamma-glutamyl transpeptidase activity and urinary D-glucaric acid excretion in newborns in the first week of life. Effects of phenobarbital and nicethamide combination

High serum gamma-glutamyl transpeptidase activity was found in cord blood of newborn boys. This activity decreased to lower values on the 4th and 7th days. In newborns treated for 3 days following the birth with a combination of phenobarbital and nicethamide an increase of gamma-glutamyl transpeptidase activity occurred from the 4th to the 7th days. The 7th day levels were significantly higher when compared with the controls. Simultaneous determination of urinary glucaric acid excretion confirmed the induction of hepatic microsomal enzymes in glucuronic acid pathway. This could also be demonstrated by a pronounced decrease of serum bilirubin levels in groups receiving the enzyme inducers whether phenobarbital was administered intramuscularly or orally as sodium salt solution.

The association between serum triglycerides and gamma glutamyl transpeptidase activity in diabetes mellitus

A study conducted on 228 diabetic patients has shown a significant positive association between serum gamma-glutamyl transpeptidase (GGT) and triglyceride levels. Both fall with treatment, the most marked reduction occurring in patients on insulin. We suggest that the association between serum GGT and triglyceride levels and also the higher incidence of raised GGT and triglyceride levels in new diabetics may reflect hepatic microsomal enzyme induction of the rate-limiting enzymes of triglyceride synthesis. Serum GGT does not seem to correlate with hepatomegaly in diabetes mellitus.