Reversal of hepatorenal syndrome type 1 with terlipressin plus albumin vs. placebo plus albumin in a pooled analysis of the OT-0401 and REVERSE randomised clinical studies

BACKGROUND

The goal of hepatorenal syndrome type 1 (HRS-1) treatment is to improve renal function. Terlipressin, a synthetic vasopressin analogue, is a systemic vasoconstrictor used for the treatment of HRS-1, where it is available.

AIM

To compare the efficacy of terlipressin plus albumin vs. placebo plus albumin in patients with HRS-1.

METHODS

Pooled patient-level data from two large phase 3, randomised, placebo-controlled studies were analysed for HRS reversal [serum creatinine (SCr) value ≤133 μmol/L], 90-day survival, need for renal replacement therapy and predictors of HRS reversal. Patients received intravenous terlipressin 1-2 mg every 6 hours plus albumin or placebo plus albumin up to 14 days.

RESULTS

The pooled analysis comprised 308 patients (terlipressin: n = 153; placebo: n = 155). HRS reversal was significantly more frequent with terlipressin vs. placebo (27% vs. 14%; P = 0.004). Terlipressin was associated with a more significant improvement in renal function from baseline until end of treatment, with a mean between-group difference in SCr concentration of -53.0 μmol/L (P < 0.0001). Lower SCr, lower mean arterial pressure and lower total bilirubin and absence of known precipitating factors for HRS were independent predictors of HRS reversal and longer survival in terlipressin-treated patients.

CONCLUSIONS

Terlipressin plus albumin resulted in a significantly higher rate of HRS reversal vs. albumin alone in patients with HRS-1. Terlipressin treatment is associated with improved renal function. (ClinicalTrials.gov identifier: OT-0401, NCT00089570; REVERSE, NCT01143246).

Autoimmune hepatitis in African Americans: presenting features and response to therapy

OBJECTIVES

African Americans are at an increased risk for certain diseases and more frequently suffer complications of those diseases relative to their white counterparts. Most studies of autoimmune hepatitis consist of entirely white populations. The Emory University system of hospitals serves a large African American population, including a significant number of African Americans with autoimmune hepatitis. The goal of this study was to determine if the presentation and response to therapy in African Americans is, like other diseases, different than in whites.

METHODS

This is a retrospective study from a tertiary referral center that examines the initial presenting features and response to therapy of African Americans (n = 27) and whites (n = 24) with autoimmune hepatitis.

RESULTS

Eighty-five percent of African Americans had cirrhosis on the initial liver biopsy, as compared with 38% of whites. Although not statistically significant, the African Americans presented at an earlier age than white patients. The disease also appeared more advanced in African Americans, as bilibubin levels tended to be higher, but not significantly, and PTs were more prolonged. Both groups responded well to therapy, with significant falls in serum levels of AST, ALT, and bilirubin. Fifty percent of African Americans and 48% of whites entered a biochemical remission. The amount of prednisone required to maintain remission at follow-up was greater in African Americans.

CONCLUSION

In contrast to whites, the majority of African Americans present with cirrhosis. Despite the high prevalence of cirrhosis, the response to therapy is good. However, more immunosuppression is required to control the disease in African Americans.

Serum hyaluronic acid in patients with veno-occlusive disease following bone marrow transplantation

The development of hepatic veno-occlusive disease following bone marrow transplantation is associated with high-dose combination cytoreductive therapy. Experimental models have suggested that drug-induced injury to hepatic sinusoidal endothelial cells is involved in the pathogenesis of this syndrome. Hyaluronic acid is a polysaccharide that is metabolized, almost exclusively, by hepatic sinusoidal endothelial cells. The aim of the present study was to evaluate serum hyaluronic acid as a marker for endothelial cell injury in patients with veno-occlusive disease following bone marrow transplantation. Hyaluronic acid was measured in sera from patients with and without veno-occlusive disease using an enzyme-linked protein binding assay. Mean peak serum hyaluronic acid levels were significantly greater in patients who had a diagnosis of VOD compared to those transplant patients who did not, 1173.4 +/- 982.9 vs 444.9 +/- 735.6 ng/ml (P = 0.01). Serial serum samples obtained from a separate cohort of patients also demonstrated that serum hyaluronic acid levels were higher in patients with moderate or severe veno-occlusive disease compared to those with none or mild disease at days 7, 17 and 25 following transplantation (greatest difference at day 25: 366 +/- 327 vs 126 +/- 151, P = 0.01). Serum hyaluronic acid levels are increased in veno-occlusive disease and increase over time in patients with severe disease. Further studies are required to determine if elevated serum hyaluronic acid levels are due to decreased clearance by injured hepatic sinusoidal endothelial cells or increased production from early hepatic fibrogenesis associated with the acute liver injury.

Efficacy and safety of pegylated (40-kd) interferon alpha-2a compared with interferon alpha-2a in noncirrhotic patients with chronic hepatitis C

Administration of interferon (IFN) 3 times weekly in patients with chronic hepatitis C (CHC) is associated with low sustained responses, which may be, in part, related to this regimen's inability to maintain IFN concentrations sufficient to suppress viral replication. An enhanced IFN molecule produced by the covalent attachment of a branched 40-kd polyethylene glycol moiety to IFN alpha-2a (PEG[40kd] IFN alpha-2a) exhibits sustained absorption, a restricted volume of distribution, and reduced clearance compared with unmodified IFN alpha-2a. One hundred fifty-nine patients with CHC participated in a randomized, ascending-dose (45 or 90, 180, 270 microg) study comparing PEG(40kd) IFN alpha-2a administered once weekly with 3 MIU IFN alpha-2a administered 3 times weekly for 48 weeks to determine the most appropriate PEG(40kd) IFN alpha-2a dose for subsequent clinical trials. Efficacy was assessed by measuring hepatitis C virus (HCV) RNA following a 24-week treatment-free period. Sustained virological responses for PEG(40kd) IFN alpha-2a once weekly were 10% (45 microg; not significant), 30% (90 microg; P = .009), 36% (180 microg; P = .0006), and 29% (270 microg; P = .004), compared with 3% for the 3-times-weekly 3-MIU IFN alpha-2a regimen. The types and frequencies of adverse events and laboratory abnormalities were similar among all groups. In conclusion, once-weekly PEG(40kd) IFN alpha-2a was associated with a higher number of sustained virological responses compared with IFN alpha-2a 3 times weekly in patients with CHC, but had a similar safety profile. The 180-microg PEG(40kd) IFN alpha-2a dose appeared to be the optimal dose based on sustained virological response and its associated side-effect profile.

Differential lobular induction in rat liver of glutathione S-transferase A1/A2 by phenobarbital

Phenobarbital and other xenobiotics induce drug-metabolizing enzymes, including glutathione S-transferase A1/A2 (rGSTA1/A2). We examined the mechanism of induction of rGSTA1/A2 in rat livers after phenobarbital treatment. The induction of rGSTA1/A2 was not uniform across the hepatic lobule; steady-state transcript levels were threefold higher in perivenous hepatocytes relative to periportal hepatocytes when examined by in situ hybridization 12 h after a single dose of phenobarbital. Administration of a second dose of phenobarbital 12 or 24 h after the first dose did not equalize the induction of rGSTA1/A2 across the lobule. The transcriptional activity of the rGSTA1/A2 gene was increased 3.5- to 5.5-fold in whole liver by phenobarbital, but activities were the same in enriched periportal and perivenous subpopulations of hepatocytes from phenobarbital-treated animals. The half-life of rGSTA1/A2 mRNA in control animals was 3.6 h, whereas it was 10.2 h in phenobarbital-treated animals. We conclude that phenobarbital induces rGSTA1/A2 expression by increasing transcriptional activity across the lobule but induction of rGSTA1/A2 is greater in perivenous hepatocytes due to localized stabilization of mRNA transcripts.

Determinants of mortality in patients with advanced cirrhosis after transjugular intrahepatic portosystemic shunting

BACKGROUND & AIMS

Transjugular intrahepatic portosystemic shunt (TIPS) placement is effective in the treatment of complications of portal hypertension. This study evaluated the predictors of mortality in a group of cirrhotic patients with advanced liver disease after placement of TIPS.

METHODS

A retrospective analysis of all patients undergoing TIPS placement over a 21/2-year period was undertaken.

RESULTS

Fifty-six patients had TIPS placement for variceal hemorrhage, 49 for refractory ascites, and 24 for hepatic hydrothorax (total, 129). Of 21 variables available before TIPS placement, variceal hemorrhage requiring emergent TIPS placement (relative risk [RR], 37.5; 95% confidence interval [CI], 5.4-259) and bilirubin concentration > 3.0 mg/dL (RR, 5.4; 95% CI, 1.4-10.2) were independent predictors of 30-day mortality. Variceal hemorrhage requiring emergent TIPS placement (hazard ratio [HR], 5.1, 95% CI, 2. 2-9.1), alanine aminotransferase level > 100 IU/L (HR, 2.5; 95% CI, 1.2-5.5), bilirubin level > 3.0 mg/dL (HR, 2.6; 95% CI, 1.1-4.6), and pre-TIPS encephalopathy unrelated to bleeding (HR, 2.2; 95% CI, 1.2-4.8) independently predicted death during the follow-up period. A model was developed that separated the patients into 3 groups with significantly different survival rates.

CONCLUSIONS

A clinical index consisting of 4 pre-TIPS variables can reliably predict outcome after TIPS.

Predictors of large esophageal varices in patients with cirrhosis

OBJECTIVE

Recent guidelines recommend that all cirrhotics undergo screening upper endoscopy to identify those patients at risk for bleeding from varices. However, this practice may not be cost effective as large esophageal varices are seen only in 9-36% of these patients. The aim of this study was to determine whether clinical variables were predictive of the presence of large esophageal varices.

METHODS

This is a retrospective analysis of cirrhotics who had a screening upper endoscopy during an evaluation for liver transplantation at three different centers and who had not previously bled from varices. A multivariate model was derived on the combined cohort using logistic regression. Three hundred forty-six patients were eligible for the study.

RESULTS

The prevalence of large esophageal varices was 20%. On multivariate analysis, splenomegaly detected by computed tomographic scan (odds ratio: 4.3; 95% confidence interval: 1.6-11.5) or by physical examination (odds ratio: 2.0; 95% confidence interval: 1.1-3.8), and low platelet count were independent predictors of large esophageal varices. On the basis of these variables, cirrhotics were stratified into high- and low-risk groups for the presence of large esophageal varices. Patients with a platelet count of > or = 88,000/mm3 (median value) and no splenomegaly by physical examination had a risk of large esophageal varices of 7.2%. Those with splenomegaly or platelet count < 88,000/mm3 had a risk of large esophageal varices of 28% (p < 0.0001).

CONCLUSIONS

Our data show that clinical predictors could be used to stratify cirrhotic patients for the risk of large esophageal varices and such stratification could be used to improve the cost effectiveness of screening endoscopy.

Activation of rat hepatic stellate cells leads to loss of glutathione S-transferases and their enzymatic activity against products of oxidative stress

Oxidative stress, mediated partly by lipid peroxidation products, may lead to increased collagen synthesis by hepatic stellate cells (HSC). Stellate cells are protected from oxidative stress by enzymes of detoxication such as the glutathione S-transferases (GSTs), which form glutathione conjugates with lipid peroxidation products (e.g., 4-hydroxy-2-nonenal [HNE]). To better understand the role of GSTs in stellate cell biology, we examined the expression and enzymatic activity of GSTs in normal and activated (both culture- and in vivo-activated) stellate cells. Normal stellate cells contained numerous isoforms of GST including those that detoxify HNE. High levels of enzymatic activity toward 1-chloro-2,4-dinitrobenzene (CDNB) and HNE were present in normal stellate cells and were similar to levels present in whole liver. Following activation by growth in culture, the expression of several GSTs (rGSTA1/A2, A3, and M1) was lost. Also, enzymatic activities toward CDNB and HNE fell approximately 90%. However, expression of rGSTP1 was maintained. A similar loss of rGSTA1/A2, A3, and M1 with persistent expression of rGSTP1 was present after activation in vivo. Furthermore, we identified 2 subpopulations of activated stellate cells with different GST phenotypes from injured livers. In summary, activated stellate cells lose most forms of GST and associated enzymatic activities that are present in normal stellate cells. The findings raise the possibility that activated stellate cells have less ability to detoxify lipid peroxidation products and may be susceptible to oxidative stress. Additionally, we propose that the phenotypic change in GSTs is a sensitive marker of stellate cell activation.

Pharmacokinetics of fosphenytoin in patients with hepatic or renal disease

PURPOSE

The pharmacokinetic behavior of fosphenytoin (FOS), the water-soluble prodrug of phenytoin (PHT), has been characterized in normal subjects. This is the first study of the effect of hepatic or renal disease on the rate and extent of conversion of FOS to PHT.

METHODS

A single dose of fosphenytoin (250 mg over a period of 30 min) was administered to subjects with hepatic cirrhosis (n = 4), renal disease requiring maintenance hemodialysis (n = 4), and healthy controls (n = 4). Serial plasma concentrations were measured, and pharmacokinetic parameters were calculated.

RESULTS

The mean time to reach the peak plasma FOS concentration was similar for each of the three groups. However, the mean time to achieve peak plasma concentrations of PHT tended to occur earlier in the hepatic or renal disease groups than in healthy subjects. The half-life of FOS was 4.5, 9.2, and 9.5 min for the three groups, respectively. There was a trend toward increased FOS clearance and earlier peak PHT concentration in subjects with hepatic or renal disease. This finding is consistent with decreased binding of FOS to plasma proteins and increased fraction of unbound FOS resulting from decreased plasma protein concentrations associated with these disease states. The conversion of FOS to PHT was equally efficient in subjects with hepatic or renal disease and healthy subjects.

CONCLUSIONS

Although the differences in pharmacokinetic parameters between the three groups were not statistically significant, these data suggest the need for close clinical monitoring during FOS administration to patients with hepatic or renal disease. To minimize the incidence of adverse effects in this patient population, FOS may need to be administered at lower doses or infused more slowly.

Human glutathione S-transferases

Human glutathione S-transferases (GSTs) are a functionally diverse family of soluble enzymes of detoxification that use reduced glutathione (GSH) in conjugation and reduction reactions. Toxic electrophiles, including a variety of carcinogens, are substrates for the GSTs and after conjugation or reduction they are more easily excreted into bile or urine. Many of the GSTs have been cloned, and the three-dimensional structures of GSTs from several species, including humans, have been determined. These data have provided significant insight into how the GSTs function as enzymes. Many GST substrates are inducers of GST gene expression; nonsubstrate inducers include H2O2 and other reactive oxygen species. The regulatory elements of several human GST genes have been partially characterized, and the regulation of the GSTs in humans appears to be very different from that in rodents. Several polymorphisms of GST expression occur commonly in humans and have been associated with an increased susceptibility to certain cancers, particularly when combined with other genetic and environmental factors such as smoking. The role of GSTs in protecting cells from injury by toxic electrophiles continues to be developed.

Conversion of failed transjugular intrahepatic portosystemic shunt to distal splenorenal shunt in patients with Child A or B cirrhosis

OBJECTIVE

The authors demonstrate the feasibility of converting failed transjugular intrahepatic portosystemic shunt (TIPS) to distal splenorenal shunt (DSRS) in patients with good hepatic reserve for long-term control of variceal bleeding.

SUMMARY BACKGROUND DATA

TIPS is an effective method for decompressing the portal venous system and controlling bleeding from esophageal and gastric varices. TIPS insufficiency is, however, a common problem, and treatment alternatives in patients with an occluded TIPS are limited because most have already failed endoscopic therapy.

METHODS

The records of five patients who underwent conversion from TIPS to DSRS because of TIPS failure or complication in the past 36 months were reviewed.

RESULTS

Four patients had ethanol-induced cirrhosis and one patient had hepatitis C virus cirrhosis. Three patients were Child-Pugh class A and two were class B. All patients had excellent liver function, with galactose elimination capacities ranging from 388 to 540 mg/min (normal 500 +/- 100 mg/min). The patients had TIPS placed for acute (2) or sclerotherapy-resistant (3) variceal hemorrhage. All five TIPS stenosed 3 to 23 months after placement, with recurrent variceal hemorrhage and failed TIPS revision. One patient had stent migration to the superior mesenteric vein that was removed at the time of DSRS. All five patients underwent successful DSRS, and none have had recurrent hemorrhage 18 to 36 months after surgery.

CONCLUSIONS

TIPS provides inadequate long-term therapy for some Child-Pugh A or B patients with recurrent variceal hemorrhage. TIPS failure in patients with good liver function can be salvaged by DSRS in many cases.

Is vaccination against hepatitis B infection indicated in patients waiting for or after orthotopic liver transplantation?

It is a common practice to immunize patients against hepatitis B infection while they are waiting for liver transplantation, but the efficacy of this practice is unclear. This is a retrospective analysis of the antibody response to 20 microg of a recombinant hepatitis B vaccine in patients waiting for and after liver transplantation. The response to vaccination was measured 1-3 months after completion of the vaccination series. The risk of acquiring hepatitis B virus after liver transplant was determined by reviewing the results of tests for hepatitis B infection in 171 patients who underwent transplantation for non-hepatitis B diseases and who had not been vaccinated. Fifty-seven patients awaiting transplantation were eligible for the study, and a response to vaccination was observed in only 9 (16%). Patients with cholestatic liver disease had a significantly higher response (6 of 14; 43%) compared with noncholestatic liver disease (3 of 43; 7%; P = .004). Forty-five liver transplant recipients were immunized against hepatitis B after transplantation, and only 3 (6.7%) developed an antibody response. The frequency of posttransplant hepatitis B infection in the 171 patients who were not immunized and who lacked any evidence of hepatitis B infection pretransplantation was 4 of 171 (2.3%). The response rate to immunization with a recombinant hepatitis B vaccine in patients with chronic liver disease who are waiting for a liver transplant and after transplantation is poor. Given the poor response to vaccination and the low risk of acquiring hepatitis B virus after transplantation, centers need to reconsider the routine use of the hepatitis B virus vaccine in patients awaiting liver transplantation.

Ischaemia and reperfusion injury of rat liver increases expression of glutathione S-transferase A1/A2 in zone 3 of the hepatic lobule

Effects of ischaemia-reperfusion injury (I/R) of liver on expression of rat glutathione S-transferase (rGST) isoenzymes that metabolize products of oxidative stress were examined. Rats underwent lobar liver ischaemia for 30 min followed by reperfusion. In ischaemic lobes, rGSTA1/A2 transcript levels increased significantly 12 h after I/R (2.94-fold) and protein levels increased significantly at 24 h (1.45-fold); increased transcript levels were also observed in nonischaemic lobes (1.78-fold). Superoxide dismutase prevented I/R and the increases in transcript and protein levels in ischaemic and non-ischaemic lobes. By in-situ hybridization, increases in transcript levels at 6 h were present in zones 2 and 3 of the ischaemic lobes and peaked at 12 h (2.5-fold zone 2, 4.5-fold zone 3). Significant increases in transcript levels also were observed at 24 h in zones 2 (2.0-fold) and 3 (2.9-fold) of non-ischaemic lobes. Nuclear run-off assays showed a 1.8-fold increase in rGSTA1/A2 transcription rates in ischaemic lobes at 3 h. We conclude that I/R causes increased rGSTA1/A2 expression in the zone of the hepatic lobule most susceptible to oxidative injury and that this expression may be an important defence against injury.

Hepatic hydrothorax

Ascites is a common manifestation of portal hypertension in patients with cirrhosis. Approximately 5% of patients with cirrhosis may develop a pleural effusion. This is usually right sided. In the absence of cardiac or lung disease, the presence of a pleural effusion in a cirrhotic patient is known as hepatic hydrothorax. Small volumes of fluid within the pleura may be associated with significant respiratory symptoms which require the clinician to rapidly remove the fluid. The development of hepatic hydrothorax is secondary to passage of ascites from the abdomen to the pleural space via defects in the diaphragm. Once the diagnosis of hepatic hydrothorax is established with certainty, medical therapy with salt restriction and diuretics is initiated. When these measures are ineffective the patient has refractory hepatic hydrothorax. Based on current studies, transjugular intrahepatic portal systemic shunts appear to be the most effective form of treatment for these patients.

Kernicterus in an adult who is heterozygous for Crigler-Najjar syndrome and homozygous for Gilbert-type genetic defect

Gilbert syndrome is a common genetic disorder associated with mild unconjugated hyperbilirubinemia and no clinical illness. In contrast, Crigler-Najjar syndrome types I and II are rare genetic disorders associated with severe unconjugated hyperbilirubinemia and a life-long risk of kernicterus. Patients with Gilbert syndrome have low levels of a normal form of uridinediphosphoglucuronate glucuronosyltransferase because of a defect in the promoter region of both alleles, whereas patients with Crigler-Najjar syndrome are homozygous for a defect that yields an abnormal form of the enzyme that has limited or no activity. This case report describes a young adult with Crigler-Najjar syndrome type II in whom kernicterus developed after a laparoscopic cholecystectomy. The development of kernicterus was the result of a largely preventable series of events that lead to an increase in the free fraction of his serum bilirubin. Analysis of his genetic defect showed that he was homozygous for the mutation associated with Gilbert syndrome and heterozygous for a second mutation in the open reading frame of one allele of the bilirubin uridinediphosphoglucuronate glucuronosyltransferase gene. The combined defect leads to severe hyperbilirubinemia and shows how seemingly benign genetic defects, when combined, can cause serious clinical disease.

Natural history of portal hypertension

A rise in pressure in the portal vein is a frequent occurrence in patients with cirrhosis. One common manifestation affecting at least 50% of cirrhosis patients is the development of gastroesophageal varices and portal hypertensive gastropathy. Bleeding from gastric or esophageal varices will occur in approximately 1/4 of cirrhotic patients with an associated high mortality. Large esophageal varices that have red color signs and isolated gastric varices in the fundus of the stomach are most likely to hemorrhage. The greatest risk of bleeding is during the first year following the index endoscopy. Once varices have bled they are almost certain to rebleed in the absence of therapy. Similarly, severe portal hypertensive gastropathy is likely to cause chronic blood loss. Knowledge of the natural history of gastroesophageal varices allows for the development of effective treatment strategies.

Hepatitis G virus co-infection in liver transplantation recipients with chronic hepatitis C and nonviral chronic liver disease

Hepatitis G virus (HGV) is a newly described RNA virus that is parenterally transmitted and has been found frequently in patients with chronic hepatitis C infection. To determine the impact of hepatitis G virus co-infection on morbidity and mortality following liver transplantation, we measured HGV RNA by polymerase chain reaction in pre and posttransplantation sera from a cohort of patients transplanted for chronic hepatitis C and a control group of patients transplanted for nonviral causes who were negative for hepatitis C virus (HCV) RNA in serum. The overall prevalence rate of HGV RNA in transplanted patients with chronic hepatitis C was 20.7%. HGV infection was present before transplantation in 13% while it appeared to have been acquired at the time of transplantation in 7.4%. Mean serum alanine aminotransferase activity, hepatic histological activity, and patient and graft survival were similar between HGV-positive and HGV-negative patients. The prevalence rate of HGV RNA in transplanted controls was 64% (P < .01) with a significantly higher rate of acquisition of HGV infection following transplantation (53%, P < .001) when compared with patients with chronic hepatitis C. Mean serum alanine aminotransferase activity was significantly lower in the control patients with HGV infection alone following transplantation than in patients co-infected with hepatitis C (37 +/- 9 vs. 70 +/- 33 U/L, P < .01). Thus, HGV is frequently found in transplantation patients co-infected with hepatitis C although it appears to have minimal clinical impact. In patients transplanted for nonviral causes of end-stage liver disease, a high rate of hepatitis G acquisition at the time of transplantation may occur but does not appear to predispose to chronic hepatitis.

Transjugular intrahepatic portosystemic shunt for the management of severe venoocclusive disease following bone marrow transplantation

Hepatic venoocclusive disease (VOD) is a common, life-threatening complication of bone marrow transplantation (BMT). Portal hypertension is usually present and accounts for many of the clinical manifestations of this syndrome. We describe the results of transjugular intrahepatic portosystemic shunt (TIPS) for the management of VOD after BMT TIPS was performed in six patients with histologically confirmed VOD who had progressive jaundice and ascites. Portal hypertension was improved by TIPS in all patients (mean portal pressure gradient before TIPS, 20.2 +/- 4.6 vs. 6.7 +/- 1.9 mm Hg post-TIPS, P < .004). Three patients who underwent TIPS late in the course of VOD did not demonstrate any clinical improvement after TIPS and expired within 2 weeks of the procedure. The remaining three patients had less advanced disease and demonstrated decreases in serum bilirubin, improvement in coagulopathy, and decreased ascites after TIPS. Two patients subsequently expired, one with persistent histological changes of VOD. The lone survivor continues to do well with resolution of ascites, jaundice, and coagulopathy as of her last outpatient visit. TIPS was an effective method for portal decompression in patients with VOD after BMT, and was associated with clinical improvement in some patients. However, these effects may be transient and may not improve overall survival.

Structural studies of a human pi class glutathione S-transferase. Photoaffinity labeling of the active site and target size analysis

The glutathione S-transferases (GSTs; EC 2.5.1.18) are a family of dimeric proteins that catalyze reactions between glutathione (GSH) and various electrophiles. A partial cDNA for human GST pi was obtained and the open reading frame completed. The completed cDNA was cloned, and GST pi protein was expressed in bacteria. Cloned enzyme was purified and had the same kinetic constants, molecular mass, pI value, and N-terminal sequence as placental GST pi except that some of the polypeptides had N-terminal methionines. A radiolabeled azido derivative of GSH, S-(p-azidophenacyl)-[3H]glutathione, was used to photoaffinity-label the active site of the cloned enzyme. Labeled enzyme did not bind to a GSH-agarose affinity column. Labeling was prevented in the presence of S-hexylglutathione, and noncovalently-bound azido affinity label was a competitive inhibitor towards 1-chloro-2,4-dinitrobenzene and GSH. These results suggest that the azido label was binding at the active site of the enzyme. Photoaffinity-labeled enzyme was trypsinized, and two labeled peptides were purified and sequenced. One peptide corresponded to residues 183-188, whereas the other corresponded to residues 183-186. These residues appear to form part of the hydrophobic (H-site) binding region of human GST pi that has not been shown previously. Cloned enzyme was subjected to radiation inactivation to assess the importance of subunit interactions in the maintenance of catalytic activity. The target size of enzymatic activity (23 kDa) was not significantly different from that of the protein monomer (24 kDa). Therefore, each subunit of human GST pi appears to be capable of independent catalytic activity.

Role of interleukin 6 and corticosteroids in the regulation of expression of glutathione S-transferases in primary cultures of rat hepatocytes

The effect of recombinant interleukin 6 (rIL-6) on the transcript levels of rat glutathione S-transferase (GST) genes rGSTA2, rGSTP1, rGSTM1 and rGSTM2 was examined in primary cultures of rat hepatocytes. rIL-6 had little effect on the increase in expression of rGSTP1 that occurs in cultured hepatocytes. Dexamethasone (DEX), in contrast, prevented the expression of rGSTP1 by hepatocytes, and rIL-6 in combination with DEX had no additional effect. Neither rIL-6 nor DEX alone had a significant effect on the transcript levels of rGSTA2, rGSTM1 and rGSTM2 in cultured hepatocytes. However, when both were present (15 ng/ml rIL-6 and 10(-7) M DEX) the transcript levels of rGSTA2, rGSTM1 and rGSTM2 decreased significantly (P < 0.05) after 48 h in culture. If the rIL-6 was removed from the cultures after 24 h, the levels of transcripts recovered and were the same at 48 h as cells cultured without rIL-6 for the entire period. Dose-response relationships of rIL-6 with 10(-7) M DEX were determined for transcripts of each GST isoenzyme and the IC50 values were between 1.5 and 7.5 ng/ml. Declines in transcript levels of rGSTA2 were observed with rIL-6 plus 10(-8) or 10(-7) M DEX but not with rIL-6 plus 10(-9), 10(-6), or 10(-5) M DEX. To determine if the cytokine and glucocorticoid effects were mediated by sequences in the 5'-flanking sequence of rGSTA2, a plasmid construct containing a 1.6 kb fragment of the 5'-flanking sequence of the rGSTA2 gene and the chloramphenicol acetyltransferase (CAT) reporter gene was used to transfect rat hepatocytes in primary culture. The addition of rIL-6 and DEX to the culture medium caused a significant (P < 0.05) decrease in CAT activity after 48 h in culture. If rIL-6 was removed after 24 h in culture, CAT activity after an additional 24 h in culture was greater than the CAT activity in cells cultured for 48 h without rIL-6. Therefore cytokines and glucocorticoids may be important physiological regulators of GST expression.

Differentiation-induced enhancement of the ability of cultured human keratinocytes to suppress oxidative stress

Human keratinocytes in culture were harvested at different stages of differentiation. Both the level of antioxidants and the response of cells to oxidative stress were measured as a function of growth and differentiation. As the keratinocyte cultures became confluent and began to differentiate, the cellular levels of glutathione, glutathione peroxidase, glutathione S transferase, and glucose-6-phosphate dehydrogenase increased. This higher level of antioxidants was maintained until the cells began to lose viability. Further, as the keratinocyte cultures began to differentiate, they became more resistant to the toxic effect of cumene hydroperoxide in terms of both of the rate of loss of cell mass and total glutathione and of the rate of decline in the activity of oxidation-sensitive enzymes. To determine how tightly the observed effects are linked to the calcium-dependent aspects of differentiation and to rule out effects related to time in culture, the cells were switched from 1.2 mM Ca++ to 0.03 mM Ca++ to suppress Ca(++)-dependent differentiation. After 4 d, these cells were then treated with 0.5 mM cumene hydroperoxide. The switch to 0.03 mM Ca++ blocked the normal increases in both glutathione peroxidase and glucose-6-phosphate dehydrogenase activities. Further, cells in 0.03 mM Ca++ had reduced resistance to cumene hydroperoxide relative to cells cultured for the same length of time in 1.2 mM Ca++. This indicates that there is a differentiation-associated, Ca(++)-specific increase in both the level of antioxidants and in tolerance to organic hydroperoxides.

Effect of distal splenorenal shunt on survival of patients with primary biliary cirrhosis

Distal splenorenal shunt is known to effectively control bleeding from esophageal and gastric varices; however, the effect of this selective shunt on liver function is less well understood. We examined retrospectively the effect of distal splenorenal shunt on the survival of 19 patients with primary biliary cirrhosis subjected to surgery for bleeding varices over a 20-yr period and had been followed for at least 1 yr. Actual Kaplan-Meier survival curve was compared with predicted survival curve based on the Mayo Clinic model using clinical data collected at the time of surgery. The patients median length of follow-up was 65.9 mo. Ten of the 19 patients died or underwent orthotopic liver transplantation during the period of observation. The actual Kaplan-Meier and predicted Mayo Clinic model survival curves were similar and did not differ significantly. Survival was best in patients with good liver function (i.e., low Mayo risk scores). Distal splenorenal shunt, therefore, did not appear to have an adverse effect on the survival of patients with primary biliary cirrhosis. We conclude that variceal bleeding in primary biliary cirrhosis patients with good liver function should not be considered an indication for liver transplantation. Instead, if treatment with sclerotherapy or beta-blockers fails then distal splenorenal shunt will prevent recurrent bleeding in 90% of patients and leave them with an excellent prognosis.

Transjugular intrahepatic portal systemic shunt for the management of symptomatic cirrhotic hydrothorax

OBJECTIVE

To investigate the safety and effectiveness of performing transjugular intrahepatic portal systemic shunt (TIPS) for the management of symptomatic cirrhotic hydrothorax in patients with advanced cirrhosis.

METHODS

TIPS was performed by standard technique after portal vein patency had been established by ultrasound. Portal-hepatic vein pressure gradient was determined before and after placement of the shunt. A portal-hepatic vein gradient of less than 12 mm Hg was the treatment goal.

RESULTS

Five patients underwent TIPS placement over an 11-month period. Despite use of diuretics, the patients had required a median of seven thoracenteses (range 2-11) for control of symptoms preceding placement of the shunt. A TIPS was placed without serious complications in all five patients. In two patients, insertion of the shunt was associated with no further need for thoracentesis. The other three patients had recurrent need for thoracentesis. These three patients were found to have occluded shunts which were rendered patent by angioplasty and/or urokinase. Subsequently, two required no further thoracentesis, whereas, in the other patient, the need for thoracentesis was decreased dramatically.

CONCLUSIONS

TIPS appears to be a safe and useful technique for the management of patients with symptomatic cirrhotic hydrothorax that is refractory to medical therapy. Recurrence of the pleural effusion after placement of TIPS may be an indication of shunt occlusion.

Liver hemorrhage: recurrent episodes during pregnancy complicated by preeclampsia

Intrahepatic hemorrhage with rupture is the most serious and potentially life-threatening liver complication of pregnancy. With improved management, more patients are surviving this complication, and therefore, a number of patients are at risk of a recurrence should they again become pregnant. This case describes a patient who suffered two episodes of intrahepatic hemorrhage in two different pregnancies. Each episode was associated with mild preeclampsia. The first hemorrhage was limited by the liver capsule and treated conservatively, whereas with the second hemorrhage, the subcapsular hematoma ruptured, requiring arterial embolization followed by surgery. An arteriogram performed during the second episode of hemorrhage showed numerous pseudoaneurysms in the area of bleeding, suggesting that a vasculopathy plays a primary role in the pathogenesis of the intrahepatic hemorrhage associated with pregnancy. This case shows that intrahepatic hemorrhage may recur with future pregnancies, and individuals who suffer this complication of pregnancy and again become pregnant should be carefully monitored for the development of preeclampsia.

Cellular sources of glutathione S-transferase P in primary cultured rat hepatocytes: localization by in situ hybridization

Hepatocytes in vivo express Alpha and Mu but not Pi forms of glutathione S-transferase (GST). GST P (a fetal Pi form) appears in rat hepatocytes after 2 days in primary culture, which suggests that hepatocytes may undergo dedifferentiation [Abramovitz, Ishigaki and Listowsky (1989) Hepatology 9, 235-239]. However, in this and other studies, primary rat hepatocyte cultures were shown by immunohistochemistry to contain significant numbers of lipocytes (Ito cells). Freshly isolated lipocytes contained GST activity when assayed with chlorodinitrobenzene (680 nmol/min per mg), and expression of Alpha, Mu and Pi forms of GST was detected by Western-blot analysis. Expression of GST P persisted during culture of the lipocytes. In situ hybridization of the cultured cells was performed to define whether hepatocytes, lipocytes or both expressed the enzyme. Lipocytes in culture contained abundant GST P transcripts. Hepatocytes contained no GST P transcripts after 12 h in culture, and after 24 h, only a few hepatocytes expressed this enzyme. After 48 h in culture all hepatocytes contained GST P transcripts, and the number of transcripts continued to increase up until 72 h. Therefore, in freshly isolated preparations of hepatocytes and early in hepatocyte culture, measurable levels of GST P protein or message appeared to reflect the presence of lipocytes. After 48 h in culture almost all of the GST P reflected expression by the hepatocytes. Lipocytes constitutively expressed Alpha-, Mu- and Pi-class GSTs and had significant intracellular levels of GSH (5.2 nmol/mg of protein). Lipocytes are capable therefore of detoxifying a number of injurious compounds.

Malignant hepatic tumors: safety of high-dose percutaneous ethanol ablation therapy

The authors retrospectively analyzed clinical records to determine the safety and complication rate of percutaneous ethanol ablation therapy with more than 10 mL of ethanol administered per session for treatment of malignant hepatic tumors. Ten patients underwent a total of 35 sessions with 10 mL or more of ethanol, and four underwent 18 sessions with 10 mL or less. No serious complications occurred with any dose. Pain and fever were the most common complications at all doses, and the higher frequency of these at larger ethanol volumes may be related to the greater degree of tumor necrosis induced by the larger volume.

The effect of hepatic regeneration on the expression of the glutathione S-transferases

The effect of hepatic regeneration on expression of four glutathione S-transferase (GST) subunits (Ya, Yc, Yb1, Yb2) was examined in rats following partial hepatectomy (PH). mRNA levels of the Ya and Yc subunits (Alpha class) decreased and were 13% and 42% of levels in sham-operated animals respectively 12 h after surgery. mRNA levels for the Yb1 subunit (Mu class) also decreased but were not maximally reduced until 24 h after PH (22% of sham-treated level). mRNA levels of the Yb2 subunit were affected little by PH. Changes in levels of mRNA appeared to reflect a decrease in both transcriptional activity and mRNA stability. The decrease in mRNA levels was associated with a fall in enzymic activity and in protein levels of Alpha-class GSTs. Within 48 h of surgery, levels of mRNA, protein enzymic activity and transcriptional activity had all fully recovered. GSH levels also decreased in the first 6 h after PH. However, 24 h after surgery GSH levels in animals having undergone PH exceeded those in sham-treated animals by 2-fold and this difference persisted for 72 h. These findings suggest that during the early phases of hepatic regeneration, because of decreased GST and GSH levels, the liver may be unusually susceptible to injury by toxic compounds. However, by the first round of cell division (36-48 h post-surgery) the liver has fully recovered its ability to metabolize toxic electrophiles.

Nitroglycerin metabolism in vascular tissue: role of glutathione S-transferases and relationship between NO. and NO2- formation

Nitroglycerin is a commonly employed pharmacological agent which produces vasodilatation by release of nitric oxide (NO.). The mechanism by which nitroglycerin releases NO. remains undefined. Recently, glutathione S-transferases have been implicated as important contributors to this process. They are known to release NO2- from nitroglycerin, but have not been shown to release NO.. The present studies were designed to examine the role of endogenous glutathione S-transferases in this metabolic process. Homogenates of dog carotid artery were incubated anaerobically with nitroglycerin, and NO. and NO2- production was determined by chemiluminescence. The role of glutathione S-transferases was studied by incubating homogenates with nitroglycerin in the presence of 1 mM GSH or 1 mM S-hexyl-glutathione, a potent inhibitor of glutathione S-transferases. Homogenates released 163 pmol of NO./h per mg of protein from nitroglycerin, and 2370 pmol of NO2-/h per mg. Adding GSH decreased NO. production by 82% and increased NO2- production by 98%. S-Hexylglutathione inhibited glutathione S-transferase activity by 96% and decreased NO2- production by 78%, but had no effect on NO. release. A linear relationship between glutathione S-transferase activity and NO2- production was observed, whereas glutathione S-transferase activity and NO. release were unrelated. Western-blot analysis demonstrated that dog carotid vascular smooth muscle contained Pi and Mu forms of glutathione S-transferases, with a predominance of the former. Purified preparations of human Pi and rat Mu isoforms metabolized nitroglycerin only to NO2- and not to NO.. On the basis of these findings, we conclude that (1) glutathione S-transferases do not contribute to the bioconversion of nitroglycerin to NO., but instead act as a degradative pathway for nitroglycerin, and (2) the release of NO. from nitroglycerin is not dependent on the formation of NO2-.

The liver-spleen scan in systemic amyloidosis: a clue to the diagnosis

The clinical findings in cirrhosis and systemic amyloidosis may be similar, leading to difficulties in diagnosis. We studied three patients with systemic amyloidosis with a 99mTc sulfur colloid liver-spleen scan. In all three patients, uptake by the spleen was less than the liver, in contrast with the increased splenic uptake seen in patients with cirrhosis. The liver-spleen scan may be a useful tool in differentiating patients with cirrhosis from those with systemic amyloidosis when clinical findings fail to give the proper diagnosis.

Effect of inducers on the activity of glutathione S-transferase and other enzymes of the glutathione pathway in cultured human keratinocytes

Known inducers of the hepatic glutathione (GSH) S-transferases were tested at the limits of their solubility as inducers of the enzyme in cultured human keratinocytes. Neither phenobarbital, trans-stilbene oxide, propylthiouracil, nor butylated hydroxyanisole increased GSH S-transferase activity or led to the appearance of alpha- or mu-forms of the enzyme, as judged by Western blotting. Only the pi-form of the enzyme was found before and after all treatments. Thus, the enzyme is not inducible in keratinocytes. However, 4 mM propylthiouracil did lead to a 50% increase in GSH reductase activity, and phenobarbital at 4 mM completely abolished GSH peroxidase and GSH reductase activity and led to a significant loss of viability.

Effect of subunit interactions on enzymatic activity of glutathione S-transferases: a radiation inactivation study

The glutathione S-transferases are a family of dimeric enzymes. Three isozymes from the alpha family, termed YaYa, YaYc, and YcYc, and three from the mu family, termed Yb1Yb1, Yb1Yb2, and Yb2Yb2, were purified from rat liver. Binding studies were performed by equilibrium dialysis using a radiolabeled product, S(-)[14C](dinitrophenyl)glutathione. Each isozyme contained two independent binding sites which had equal affinity for the ligand. The presence of two independent active sites per enzyme dimer suggests that each subunit contains a complete active site. This conclusion was examined further using radiation inactivation which also allowed for assessment of the importance of subunit interactions in catalytic activity. The activity target size of YaYa (47 kDa) was significantly larger than the protein monomer target size (31 kDa); similarly the activity target size of YaYc was that of the dimer (54 kDa). In contrast, the activity target sizes of Yb1Yb1 and Yb2Yb2 were the same, being 35 and 29 kDa, respectively, and the protein monomer target size of Yb1Yb1 also was similar, being 32 kDa. These data indicate that interactions between subunits are critical for the maintenance of enzymatic activity of alpha class enzymes whereas each subunit of the two mu class proteins is capable of independent catalytic activity.

Selective shunt in the management of variceal bleeding in the era of liver transplantation

This study reports the Emory experience with 147 distal splenorenal shunts (DSRS) and 110 orthotopic liver transplants (OLT) between January 1987 and December 1991. The purpose was to clarify which patients with variceal bleeding should be treated by DSRS versus OLT. Distal splenorenal shunts were selected for patients with adequate or good liver function. Orthotopic liver transplant was offered to patients with end-stage liver disease who fulfilled other selection criteria. The DSRS group comprised 71 Child's A, 70 Child's B, and 6 Child's C patients. The mean galactose elimination capacity for all DSRS patients was 330 +/- 98 mg/minute, which was significantly (p less than 0.01) above the galactose elimination capacity of 237 +/- 82 mg/minute in the OLT group. Survival analysis for the DSRS group showed 91% 1-year and 77% 3-year survival, which was better than the 74% 1-year and 60% 3-year survivals in the OLT group. Variceal bleeding as a major component of end-stage disease leading to OLT had significantly (p less than 0.05) poorer survival (50%) at 1 year compared with patients without variceal bleeding (80%). Hepatic function was maintained after DSRS, as measured by serum albumin and prothrombin time, but galactose elimination capacity decreased significantly (p less than 0.05) to 298 +/- 97 mg/minute. Quality of life, measured by a self-assessment questionnaire, was not significantly different in the DSRS and OLT groups. Hospital charges were significantly higher for OLT (median, $113,733) compared with DSRS ($32,674). These data support a role for selective shunt in the management of patients with variceal bleeding who require surgery and have good hepatic function. Transplantation should be reserved for patients with end-stage liver disease. A thorough evaluation, including tests of liver function, help in selection of the most appropriate therapeutic approach.

Characterization of glutathione S-transferase in cultured human keratinocytes

The glutathione S-transferase activity and isozymic composition of cultured human keratinocytes were characterized. Keratinocytes were grown in culture and harvested at different stages of differentiation. Glutathione S-transferase activity was found in the soluble cell fraction but not in the microsomal cell fraction. The glutathione S-transferase specific activity of the soluble cell fraction was found to increase as the keratinocytes differentiated in culture. All of the enzymatic activity was found to reside with a single isozymic form that was concluded to be the pi form of the enzyme based on substrate specificity, sensitivity to inhibitors, molecular weight, and reactivity towards antibodies raised to alpha, mu, and pi forms of the enzyme. It is concluded that all of the isozymic forms of glutathione S-transferase noted in whole skin, with the exception of pi, are of extra-keratinocyte origin.

Localization of a portion of the active site of two rat liver glutathione S-transferases using a photoaffinity label

The glutathione S-transferases are a family of dimeric enzymes that catalyze the reaction between GSH and a variety of electrophiles. Two closely related isozymes, referred to as YaYa and YcYc, were purified from rat liver. A radiolabeled azido derivative of glutathione (S-(p-azidophenacyl)[3H]glutathione) was prepared and used to label covalently the active site of the above two glutathione S-transferases. The noncovalently bound affinity label was a competitive inhibitor of glutathione S-transferase YaYa toward both 1-chloro-2,4-dinitrobenzene and GSH. The covalently labeled enzymes no longer bound to a GSH-affinity column, and covalent labeling was reduced in the presence of GSH and S-(dinitrophenyl)glutathione. These results suggest that the affinity label was binding at the active site. The covalently labeled enzymes were digested with trypsin, and the labeled peptides were purified by HPLC and then sequenced. A single-labeled peptide was identified in the tryptic digest of the YaYa isozyme, whereas two labeled peptides were present in the tryptic digest of YcYc. The Ya peptide sequence was identical with the published deduced sequence of amino acids between residues 212 and 218 and the sequences of the two peptides purified from Yc were identical with the deduced sequence of amino acids between 91 and 110 and 206 and 218. Hence, the Ya peptide and the smaller peptide purified from Yc came from the same region of the Ya and Yc subunits. This common region and a second region of the Yc subunit appear to form a portion of the active site of these two forms of glutathione S-transferase.

The glutathione S-transferases: an update

Over the last 15 years, we have passed through an initial period in which multiple forms of GST in various organs and different species were identified and characterized. The focus of current research is to define the role of the numerous isozymes in cell function, to ascertain the relationship between structure and function of different isozymes and to determine how the expression of GST is regulated in different tissues. During these studies, it is expected that new roles for the GST will be proposed, and this family of multifunctional proteins will continue to hold the interest of numerous investigators for many years.

Hepatic efflux of glutathione by the perfused rat liver: role of membrane potential difference

Glutathione (GSH) is released into hepatic sinusoids by a carrier-mediated process. The importance of transmembrane potential difference (PD) as a driving force for hepatic efflux of GSH from isolated perfused rat liver was investigated. The membrane PD was measured using intracellular microelectrodes as PD was altered over the physiological range by ion substitution in the perfusate. The effect of a change in membrane PD on the rate of efflux of GSH into the perfusate was determined. Because GSH carries a net negative charge at physiological values of pH, we predicted that hyperpolarization of cells would increase efflux, whereas depolarization would decrease efflux. Three different manipulations were used to depolarize the hepatocyte membrane to a similar degree, and variable effects on GSH efflux were observed. Substitution of Cl with gluconate in the perfusate depolarized the hepatocyte but had no effect on GSH efflux, whereas substitution of Na with choline in the perfusate increased GSH efflux to 110% of basal values. Perfusion with K+ inhibited GSH efflux by 21%. The latter two manipulations were associated with evidence of hepatic injury. Hyperpolarization of the hepatocyte also had variable effects on GSH efflux. Substitution of Cl with nitrate in the perfusate transiently increased the membrane PD and decreased GSH efflux, whereas perfusion with glucagon caused a sustained increase in membrane PD but did not alter GSH efflux rates. None of the latter manipulations was associated with hepatic injury and thus no consistent relationship between membrane PD and sinusoidal efflux of GSH was demonstrated. We conclude that in the isolated perfused rat liver, efflux of GSH is not driven directly by membrane PD.

Characterization of the activation of rat liver glutathione S-transferases by nonsubstrate ligands

In previous work (D.A. Vessey and T.D. Boyer, 1986, Biochem. Pharmacol., 35, 289-295) the activity of glutathione S-transferase form YcYc from rat liver was found to be stimulated by the herbicide 2,4,5-T. We have extended that work and examined the effect of over 40 structural analogs on the activity of YcYc. Over half of these compounds stimulated by 10 to 232% when added to assays at a concentration of 1 mM. The best activators all contained the "2,4,5-trichlorophenyl-" structure. While 2,4,5-T gave the greatest activation at 1 mM (2.3-fold), 2,4,5-trichlorobenzene sulfonate gave the greatest maximum activation (6.0-fold). Compounds that had no effect on activity did not affect activation by 2,4,5-T suggesting that they have a poor affinity for the enzyme. Two of the analogs tested (chloramine-T and 6-hydroxydopamine) proved to be good inhibitors and ethacrynic acid was an extremely potent inhibitor. Indomethacin activated at low concentrations but inhibited above 2 mM. Activations were greater at low temperature (5 degrees C) and decreased with increasing temperature. The extent of activation was largely unaffected by the concentration of either substrate. Examination of the organic peroxidase activity of the enzyme revealed inhibition by 2,4,5-T and 2,4-D rather than activation.

Purification and characterization of hepatic glutathione S-transferases of rhesus monkeys. A family of enzymes similar to the human hepatic glutathione S-transferases

Thirteen forms of glutathione S-transferase were purified from the livers of female rhesus monkeys (Macaque mulatta). Most (74.7%) of the activity in the hepatic cytosol adhered well to the GSH affinity column and could be eluted only with the addition of GSH to the eluting buffer. The predominant isoenzymes (n = 5) in this 'high-affinity' fraction had alkaline pI values (greater than 9.0) and contained a subunit with an Mr value of 24,000. All of these isoenzymes had high organic peroxidase activity and, on the basis of amino acid analysis, substrate specificities and affinity for non-substrate ligands, appear to belong to the family of glutathione S-transferases that have been termed alpha [Mannervik, Alin, Guthenberg, Jensson, Tahir, Warholm & Jörnvall (1985) Proc. Natl. Acad. Sci. U.S.A. 82, 7202-7206]. Also within the high-affinity fraction was an isoenzyme with an acidic (5.8) pI value. This acidic isoenzyme was composed of a unique subunit (Mr 23,000). The N-terminal sequence (ten residues) of this acidic enzyme was identical with that of a human form that is referred to as pi. The predominant form of enzyme in the 'low-affinity' (eluted from the GSH affinity column with an increase in buffer pH) fraction was a homodimer of a 26,000-Mr subunit. It had an alkaline pI (greater than 9.0) but it lacked organic peroxidase activity. The N-terminal sequence (ten residues) of this enzyme was identical with that of a human enzyme referred to as mu. The substrate specificities and affinity for non-substrate ligands of this monkey enzyme also were similar to those of the human enzyme. In conclusion, the liver cytosol of rhesus monkeys contains a number of glutathione S-transferase isoenzymes that are very similar to the human hepatic enzymes.

Inhibition of human cationic glutathione S-transferase by nonsubstrate ligands

Inhibition of a major hepatic form of human cationic glutathione S-transferase by bilirubin, biliverdin, indocyanine green and chenodeoxycholic acid was investigated as a function of pH (range = 6.5 to 9.1). Changes in pH had little effect on the extent of inhibition by indocyanine green. However, inhibition by bilirubin, biliverdin and chenodeoxycholic acid was found to be pH-dependent, with markedly less inhibition at the high values of pH. The reduced inhibition at the high values of pH could not be ascribed to a failure of the enzyme to bind the nonsubstrate ligand. Instead, the complete inhibition observed at pH 6.5 became partial (hyperbolic) inhibition at pH 9.1. This behavior can be ascribed to the binding of the nonsubstrate ligands at a site other than the active site, i.e., at high values of pH there is formation of an enzyme-substrate-inhibitor complex which still retains considerable catalytic activity. At physiologic values of pH (7.0), the human transferase was completely inhibited by saturating concentrations of the tested nonsubstrate ligands. This is in contrast to our previous studies performed with the rat transferases where, although inhibition also was affected by buffer pH, some forms of the enzyme retained significant catalytic activity at pH 7.0 despite high concentrations of nonsubstrate ligands. We conclude that the ability of the human cationic glutathione S-transferases to serve as enzymes of detoxification in the presence of high intracellular concentrations of nonsubstrate ligands may be significantly reduced, and this may render the cholestatic liver unusually susceptible to injury by toxic electrophiles.

Excretion of glutathione conjugates by primary cultured rat hepatocytes

Conjugation of xenobiotics with glutathione occurs commonly within the liver, and these glutathione conjugates are then preferentially excreted into bile. We have characterized this excretory process using primary cultured hepatocytes (24 h). 1-Chloro-2,4-dinitrobenzene rapidly entered the cells and formed a glutathione conjugate, S-(dinitrophenyl)glutathione, irrespective of the temperature of incubation. In contrast, the efflux of the glutathione conjugate was essentially absent in the cold but recovered rapidly upon rewarming of the cells. Therefore, initial rates of efflux of the conjugate at 37 degrees C were measured from cells preloaded biosynthetically at 10 degrees C. Efflux was a saturable process with respect to intracellular S-(dinitrophenyl)glutathione with an apparent Km of 0.58 +/- 0.12 mM and Vmax of 0.15 +/- 0.05 nmol/min/mg of protein. The excretion of S-(dinitrophenyl)glutathione had an energy of activation of 15.3 kcal/mol. The glutathione conjugate of p-nitrobenzylchloride when formed within the hepatocytes acted as a competitive inhibitor of S-(dinitrophenyl)glutathione efflux. Cultured hepatocytes, therefore, appeared to have a specific transport process for the excretion of glutathione conjugates. The addition of S-(dinitrophenyl)glutathione, but not GSH, GSSG, or methionine, to the medium caused a decrease in the rate of efflux of radiolabeled S-(dinitrophenyl)glutathione. The hepatocytes were able, however, to excrete the glutathione conjugate against an excess of extracellular S-(dinitrophenyl)glutathione. This observation suggested that extracellular S-(dinitrophenyl)glutathione, although capable of binding to the carrier, entered the hepatocytes quite slowly relative to rates of efflux. This carrier may function in a manner that would minimize the reuptake by hepatocytes of conjugates that have been excreted into the bile.

Radiation inactivation of microsomal glutathione S-transferase

Radiation inactivation analysis was used to determine the target size of rat liver microsomal glutathione S-transferase both in situ and following purification. When Tris-HCl-washed microsomes were irradiated, there was a 1.5-2.0-fold increase in enzymatic activity over the first 3-6 megarads followed by a decrease in enzymatic activity. Above 48 megarads the radiation inactivation curve of the Tris-HCl-washed microsomes was described by a monoexponential function which gave a target size of 48 kDa. The enzymatic activity of the microsomal enzyme was selectively increased by treating the Tris-HCl-washed microsomes either with N-ethylmaleimide or washing the microsomes with small unilamellar vesicles made from phosphatidylcholine. The inactivation curves obtained with both types of treated microsomes were simple monoexponential decays in enzymatic activity with target sizes of 46 kDa (N-ethylmaleimide) and 44 kDa (unilamellar vesicles). The microsomal enzyme was detergent solubilized and purified. The Mr value of the purified protein was 15,500 (sodium dodecyl sulfate-polyacrylamide gel electrophoresis). These data suggest that the functional unit of the microsomal form of glutathione S-transferase in situ is a trimer. The target size of the purified enzyme solubilized in Triton X-100 was 85 kDa, and no increase in activity was observed at the lower radiation doses. The increase in the target size of the purified enzyme could not be ascribed solely to the presence of the detergent. This result suggests that the microsomal form of this enzyme can exist as catalytically active oligomers of different sizes depending on its environment.