The effect of gamma-aminobutyric acid on hepatic regenerative activity following partial hepatectomy in rats

Immunological Tolerance in Liver Transplant Recipients: Putative Involvement of Neuroendocrine-Immune Interactions

The transplantation world changed significantly following the introduction of immunosuppressants, with millions of people saved. Several physicians have noted that liver recipients that do not take their medication for different reasons became tolerant regarding kidney, heart, and lung transplantations at higher frequencies. Most studies have attempted to explain this phenomenon through unique immunological mechanisms and the fact that the hepatic environment is continuously exposed to high levels of pathogen-associated molecular patterns (PAMPs) or non-pathogenic microorganism-associated molecular patterns (MAMPs) from commensal flora. These components are highly inflammatory in the periphery but tolerated in the liver as part of the normal components that arrive via the hepatic portal vein. These immunological mechanisms are discussed herein based on current evidence, although we hypothesize the participation of neuroendocrine-immune pathways, which have played a relevant role in autoimmune diseases. Cells found in the liver present receptors for several cytokines, hormones, peptides, and neurotransmitters that would allow for system crosstalk. Furthermore, the liver is innervated by the autonomic system and may, thus, be influenced by the parasympathetic and sympathetic systems. This review therefore seeks to discuss classical immunological hepatic tolerance mechanisms and hypothesizes the possible participation of the neuroendocrine-immune system based on the current literature.

Explorative study of serum biomarkers of liver failure after liver resection

Conventional biochemical markers have limited usefulness in the prediction of early liver dysfunction. We, therefore, tried to find more useful liver failure biomarkers after liver resection that are highly sensitive to internal and external challenges in the biological system with a focus on liver metabolites. Twenty pigs were divided into the following 3 groups: sham operation group (n = 6), 70% hepatectomy group (n = 7) as a safety margin of resection model, and 90% hepatectomy group (n = 7) as a liver failure model. Blood sampling was performed preoperatively and at 1, 6, 14, 30, 38, and 48 hours after surgery, and 129 primary metabolites were profiled. Orthogonal projection to latent structures-discriminant analysis revealed that, unlike in the 70% hepatectomy and sham operation groups, central carbon metabolism was the most significant factor in the 90% hepatectomy group. Binary logistic regression analysis was used to develop a predictive model for mortality risk following hepatectomy. The recommended variables were malic acid, methionine, tryptophan, glucose, and γ-aminobutyric acid. Area under the curve of the linear combination of five metabolites was 0.993 (95% confidence interval: 0.927–1.000, sensitivity: 100.0, specificity: 94.87). We proposed robust biomarker panels that can accurately predict mortality risk associated with hepatectomy.

GABA, γ-Aminobutyric Acid, Protects Against Severe Liver Injury

BACKGROUND

Acute liver failure (ALF) from severe acute liver injury is a critical condition associated with high mortality. The purpose of this study was to investigate the impact of preemptive administration of γ-aminobutyric acid (GABA) on hepatic injury and survival outcomes in mice with experimentally induced ALF.

MATERIALS AND METHODS

To induce ALF, C57BL/6NHsd mice were administered GABA, saline, or nothing for 7 d, followed by intraperitoneal administration of 500 μg of tumor necrosis factor α and 20 mg of D-galactosamine. The study mice were humanely euthanized 4-5 h after ALF was induced or observed for survival. Proteins present in the blood samples and liver tissue from the euthanized mice were analyzed using Western blot and immunohistochemical and histopathologic analyses. For inhibition studies, we administered the STAT3-specific inhibitor, NSC74859, 90 min before ALF induction.

RESULTS

We found that GABA-treated mice had substantial attenuation of terminal deoxynucleotidyl transferase dUTP nick end labeling-positive hepatocytes and hepatocellular necrosis, decreased caspase-3, H2AX, and p38 MAPK protein levels and increased expressions of Jak2, STAT3, Bcl-2, and Mn-SOD, with improved mitochondrial integrity. The reduced apoptotic proteins led to a significantly prolonged survival after ALF induction in GABA-treated mice. The STAT3-specific inhibitor NSC74859 eliminated the survival advantage in GABA-treated mice with ALF, indicating the involvement of the STAT3 pathway in GABA-induced reduction in apoptosis.

CONCLUSIONS

Our results showed that preemptive treatment with GABA protected against severe acute liver injury in mice via GABA-mediated STAT3 signaling. Preemptive administration of GABA may be a useful approach to optimize marginal donor livers before transplantation.

Assay to Detect Inhibitory Substances in Serum of Patients with Acute Liver Failure

Patients with acute liver failure accumulate toxic substances in the circulation which may impair recovery of hepatic function. The aim of this study was to test an in vitro assay to detect inhibitory substances in the serum of patients with acute liver failure. Human liver-derived HepG2 cells were incubated for 24h in 96 well plates (30,000 cells/well) with sera (10%) from 24 patients with acute liver failure due to paracetamol overdose or NANB hepatitis and 11 normal controls. DNA synthesis was determined from the incorporation of 3H-thymidine and cell viability by the metabolism of the tetrazolium dye MTS. HepG2 cells exposed to acute liver failure sera incorporated significantly less 3H-thymidine (median 30% of control, range 0.2–169%) than normal sera (100%, 76–133%, p=0.002). Cell viability was also reduced (75%, 33–112% vs 100%, 96–105%, p<0.00l). There was no correlation between these values and patient outcome or levels of plasma TNF-α or serum interferon-γ. The assay detected inhibitory substances in sera of patients with acute liver failure and could be used to monitor the use of liver support systems.

Protective roles of hepatic GABA signaling in acute liver injury of rats

γ-Aminobutyric acid (GABA) is produced by various cells through the catalytic activity of glutamic acid decarboxylase (GAD). Activation of type-A GABA receptor (GABA_AR) inhibits stem cell proliferation but protects differentiated cells from injures. The present study investigated hepatic GABA signaling system and the role of this system in liver physiology and pathophysiology. RT-PCR and immunoblot assays identified GAD and GABA_AR subunits in rat livers and in HepG2 and Clone 9 hepatocytes. Patch-clamp recording detected GABA-induced currents in Clone 9 hepatocytes and depolarization in WITT cholangiocytes. The function of hepatic GABA signaling system in rats was examined using models of d-galactosamine (GalN)-induced acute hepatocytic injury in vivo and in vitro. The expression of GAD increased whereas GABA_AR subunits decreased in the liver of GalN-treated rats. Remarkably, treating rats with GABA or the GABA_AR agonist muscimol, but not the GABA_BR agonist baclofen, protected hepatocytes against GalN toxicity and improved liver function. In addition, muscimol treatment decreased the formation of pseudobile ductules and the enlargement of hepatocytic canaliculi in GalN-treated rats. Our results revealed that a complex GABA signaling system exists in the rat liver. Activation of this intrahepatic GABAergic system protected the liver against toxic injury.NEW & NOTEWORTHY Auto- and paracrine GABAergic signaling systems exist in the rat hepatocytes and cholangiocytes. Activation of GABA signaling protects liver function from d-galactosamine injury by reducing toxic impairment of hepatocytes and by decreasing cholangiocyte proliferation.

The altered expression of α1 and β3 subunits of the gamma-aminobutyric acid A receptor is related to the hepatitis C virus infection

The modulation of the gamma-aminobutyric acid type A (GABA A) receptors activity was observed in several chronic hepatitis failures, including hepatitis C. The expression of GABA A receptor subunits α1 and β3 was detected in peripheral blood mononuclear cells (PBMCs) originated from healthy donors. The aim of the study was to evaluate if GABA A α1 and β3 expression can also be observed in PBMCs from chronic hepatitis C (CHC) patients and to evaluate a possible association between their expression and the course of hepatitis C virus (HCV) infection. GABA A α1- and β3-specific mRNAs presence and a protein expression in PBMCs from healthy donors and CHC patients were screened by reverse transcription polymerase chain reaction (RT-PCR) and Western blot, respectively. In patients, HCV RNA was determined in sera and PBMCs. It was shown that GABA A α1 and β3 expression was significantly different in PBMCs from CHC patients and healthy donors. In comparison to healthy donors, CHC patients were found to present an increase in the expression of GABA A α1 subunit and a decrease in the expression of β3 subunit in their PBMCs. The modulation of α1 and β3 GABA A receptors subunits expression in PBMCs may be associated with ongoing or past HCV infection.

Daily ciprofloxacin treatment for patients with advanced liver disease awaiting liver transplantation reduces hospitalizations

BACKGROUND

Progressive deterioration in liver function is a common cause of hepatic decompensation and indication for liver transplantation in patients with advanced liver disease. Previous studies in animal models of acute and chronic liver disease revealed that daily ciprofloxacin improves biochemical parameters of hepatic function.

AIMS

The primary objective of this study was to determine whether hepatic function improves in patients with advanced liver disease after 1 month of daily ciprofloxacin therapy. A secondary objective was to determine whether ciprofloxacin treatment for 1 or 3 months results in fewer hospitalizations for decompensated liver disease.

METHODS

Forty-four patients with advanced liver disease awaiting liver transplantation received oral ciprofloxacin (250 or 500 mg twice daily) or placebo for 1 (n=22/group) or 3 (n=10 ciprofloxacin, 14 placebo) months.

RESULTS

Compared to placebo recipients, ciprofloxacin-treated patients had mild improvements in serum albumin levels (+1.5 versus -3.4%, p=0.026) while bilirubin and international normalized ratios (INR) of prothrombin times remained unchanged. Overall, fewer hospitalizations occurred in ciprofloxacin-treated patients (1/22, 5% versus 7/22, 32%, respectively, p=0.02) during the study period. Treatment was well tolerated and no resistant infections occurred in either cohort.

CONCLUSIONS

The results of this study suggest that daily ciprofloxacin may result in fewer hospitalizations for patients with advanced liver diseases awaiting liver transplantation but not by enhancing hepatic function.

Suppression of liver regeneration and hepatocyte proliferation in hepatocyte-targeted glypican 3 transgenic mice

Glypican 3 (GPC3) belongs to a family of glycosylphosphatidylinositol-anchored, cell-surface heparan sulfate proteoglycans. GPC3 is overexpressed in hepatocellular carcinoma. Loss-of-function mutations of GPC3 result in Simpson-Golabi-Behmel syndrome, an X-linked disorder characterized by overgrowth of multiple organs, including the liver. Our previous study showed that GPC3 plays a negative regulatory role in hepatocyte proliferation, and this effect may involve CD81, a cell membrane tetraspanin. To further investigate GPC3 in vivo, we engineered transgenic (TG) mice overexpressing GPC3 in the liver under the control of the albumin promoter. GPC3 TG mice with hepatocyte-targeted, overexpressed GPC3 developed normally in comparison with their nontransgenic littermates but had a suppressed rate of hepatocyte proliferation and liver regeneration after partial hepatectomy. Moreover, gene array analysis revealed a series of changes in the gene expression profiles in TG mice (both in normal mice and during liver regeneration). In unoperated GPC3 TG mice, there was overexpression of runt related transcription factor 3 (7.6-fold), CCAAT/enhancer binding protein alpha (2.5-fold), GABA A receptor (2.9-fold), and wingless-related MMTV integration site 7B (2.8-fold). There was down-regulation of insulin-like growth factor binding protein 1 (8.4-fold), Rab2 (5.6-fold), beta-catenin (1.7-fold), transforming growth factor beta type I (3.1-fold), nodal (1.8-fold), and yes-associated protein (1.4-fold). Changes after hepatectomy included decreased expression in several cell cycle-related genes.

CONCLUSION

Our results indicate that in GPC3 TG mice, hepatocyte overexpression of GPC3 suppresses hepatocyte proliferation and liver regeneration and alters gene expression profiles, and potential cell cycle-related proteins and multiple other pathways are involved and affected.

Liver regeneration after partial hepatectomy: critical analysis of mechanistic dilemmas

Liver regeneration after partial hepatectomy is one of the most studied models of cell, organ, and tissue regeneration. The complexity of the signaling pathways initiating and terminating this process have provided paradigms for regenerative medicine. Many aspects of the signaling mechanisms involved in hepatic regeneration are under active investigation. The purpose of this review is to focus on the areas still not well understood. The review also aims to provide insights into the ways by which current concepts of liver regeneration can provide understanding regarding malfunction of the regenerative process in liver diseases, such as acute liver failure.

GABA's control of stem and cancer cell proliferation in adult neural and peripheral niches

Aside from traditional neurotransmission and regulation of secretion, gamma-amino butyric acid (GABA) through GABA(A) receptors negatively regulates proliferation of pluripotent and neural stem cells in embryonic and adult tissue. There has also been evidence that GABAergic signaling and its control over proliferation is not only limited to the nervous system, but is widespread through peripheral organs containing adult stem cells. GABA has emerged as a tumor signaling molecule in the periphery that controls the proliferation of tumor cells and perhaps tumor stem cells. Here, we will discuss GABA's presence as a near-universal signal that may be altered in tumor cells resulting in modified mitotic activity.

Proliferative effects of gamma-aminobutyric acid on the gastric cancer cell line are associated with extracellular signal-regulated kinase 1/2 activation

BACKGROUND AND AIM

Gamma-aminobutyric acid (GABA) is the principal inhibitory neurotransmitter in the adult mammalian brain. However, GABA is found not only in peripheral neuronal tissue, but also in many peripheral non-neuronal tissues, and is thought to have important physiological functions in addition to neurotransmission. We previously reported that GABA participates in chondrocyte proliferation. In the present study, we investigated the effects of GABA on the proliferation of a gastric cancer cell line, KATO III.

METHODS

Reverse transcription polymerase chain reaction and immunohistochemical analyses were performed to examine the expression of the GABA synthesis enzyme, glutamate decarboxylase (GAD), and that of the GABA(A) and GABA(B) receptor subunits. The production of GABA was confirmed by immunohistochemistry. The proliferative effect of GABA on KATO III cells was analyzed by bromodeoxyuridine incorporation assay, and the activation status of mitogen-activated protein (MAP) kinases (extracellular signal-regulated kinase [ERK]-1/2, Jun-N-terminal kinase, and p38) and the expression of cyclin D1 were analyzed by western blotting.

RESULTS

KATO III cells expressed GAD and GABA. More than five GABA(A) receptor subunits, including the pi subunit, were expressed in KATO III cells; however, GABA(B) receptor subunits were not seen. The addition of GABA to the medium promoted KATO III proliferation, and maximum proliferative effects were observed in the presence of 10 or 1 microM GABA. The addition of 1 microM GABA predominantly activated ERK-1/2 among the three MAP kinases in addition to increasing cyclin D1 expression.

CONCLUSION

GABA is able to promote KATO III cell proliferation in an autocrine or a paracrine fashion through GABA(A) receptors followed by MAP kinase activation.

Decreased hepatocyte membrane potential differences and GABAA-beta3 expression in human hepatocellular carcinoma

To determine whether hepatocyte membrane potential differences (PDs) are depolarized in human HCC and whether depolarization is associated with changes in GABAA receptor expression, hepatocyte PDs and gamma-aminobutyric acid (GABA)A receptor messenger RNA (mRNA) and protein expression were documented in HCC tissues via microelectrode impalement, real-time reverse-transcriptase polymerase chain reaction, and Western blot analysis, respectively. HCC tissues were significantly depolarized (-19.8+/-1.3 versus -25.9+/-3.2 mV, respectively [P<0.05]), and GABAA-beta3 expression was down-regulated (GABAA-beta3 mRNA and protein expression in HCC; 5,693+/-1,385 and 0.29+/-0.11 versus 11,046+/-4,979 copies/100 mg RNA and 0.62+/-0.16 optical density in adjacent tumor tissues, respectively [P=0.002 and P<0.0001, respectively]) when compared with adjacent nontumor tissues. To determine the physiological relevance of the down-regulation, human malignant hepatocytes deficient in GABAA-beta3 receptor expression (Huh-7 cells) were transfected with GABAA-beta3 complementary DNA (cDNA) or vector alone and injected into nu/nu nude mice (n=16-17 group). Tumors developed after a mean (+/-SD) of 51+/-6 days (range: 41-60 days) in 7/16 (44%) mice injected with vector-transfected cells and 70+/-12 days (range: 59-86 days) in 4/17 (24%) mice injected with GABAA-beta3 cDNA-transfected cells (P<0.005).

CONCLUSION

The results of this study indicate that (1) human HCC tissues are depolarized compared with adjacent nontumor tissues, (2) hepatic GABAA-beta3 receptor expression is down-regulated in human HCC, and (3) restoration of GABAA-beta3 receptor expression results in attenuated in vivo tumor growth in nude mice.

The effects of colectomy on immediate-early proto-oncogene expression and hepatic regeneration in the rat

The intact liver exists in a state of replicative quiescence. The factor(s) responsible for maintaining this state and their tissue sources have yet to be identified. Because the colon synthesizes and/or absorbs numerous agents that inhibit hepatocyte proliferation, the principle purpose of this study was to determine whether total colectomy would result in the conversion of quiescent livers to a state of replicative competence. Thus, adult, male Sprague-Dawley rats (250-300 g) were randomized to undergo either total colectomy with ileostomy or sham surgery. Thereafter, rats were sacrificed (N=3-6/group) at times 15 and 30 min and 1, 2, 6, and 24 hr and the livers analyzed by Northern blot analyses for mRNA of the following immediate-early proto-oncogenes (IEP genes): c-fos, c-jun, and c-myc. Rats sacrificed at 24 hr also had hepatic regenerative activity documented by [3H]thymidine incorporation into hepatic DNA. The results of the study revealed that within 15 min, c-fos and c-jun mRNA expression increased in colectomized rats, with peak expression occurring at 30 and 60 min, respectively. c-myc mRNA expression was more delayed, with peak expression occurring at 6 hr post-colectomy. IEP gene expression also increased somewhat in sham-colectomy controls but the increases were not as prompt and, in general, were of lower magnitude than those in the colectomy group. Despite the differences in IEP gene expression between the two groups, [3H]thymidine incorporation at 24 hr was similar (mean+/-SE: colectomy group, 17.2+/-2.6 dpm/microg DNA; sham-colectomy controls, 14.8+/-1.4 dpm/microg DNA). To determine whether the increases in IEP gene expression expedite or augment the hepatic regenerative response to partial hepatectomy (PHx), rats that had undergone colectomy or sham colectomy 1 hr earlier and rats with no previous abdominal surgery then underwent a 70% PHx and were sacrificed at 8, 16, and 24 hr thereafter. At each time interval, [3H]thymidine incorporation was documented and found to be similar in the three groups. In conclusion, the results of this study indicate that total colectomy, and to a lesser extent abdominal surgery, induces the conversion of an intact, quiescent liver to a state of replicative competence. The results also suggest that, in addition to colectomy, the presence of mitogens and/or co-mitogens is required for further progression of hepatocytes through the cell cycle. Finally, a "primed" liver does not respond more promptly or vigorously to a regenerative stimulus than a "resting" liver.

Expression of GABAA and GABAB receptors in rat growth plate chondrocytes: Activation of the GABA receptors promotes proliferation of mouse chondrogenic ATDC5 cells

Our previous study showed the local production of gamma-aminobutyrate (GABA) in hypertrophic-zone chondrocytes of the rat tibial growth plate, an important long bone growth site. The aim of this study was to identify the presence of GABA receptors in growth plate chondrocytes by reverse transcription-polymerase chain reaction (RT-PCR) and immunohistochemistry. Chondrocytes expressed both GABA(A) and GABA(B) receptor subunit mRNAs as well as the corresponding proteins necessary for the assembly of functional receptors. The GABA(A) receptor subunits detected included alpha1-alpha4, alpha6, beta1-beta3, and delta, and both R1 and R2 subunits of GABA(B) receptors were detected. All receptor subunits were expressed in chondrocytes of the proliferative and hypertrophic zones. These results suggest that GABA is an autocrine/paracrine factor that regulates the physiological state of the growth plate. Subsequent studies with the mouse chondrogenic cell line ATDC5 showed the presence of mRNAs and the corresponding proteins for GABA(A) receptor alpha1, beta2, and beta3 subunits and GABA(B) receptor R1 and R2 subunits. GABA, muscimol (a GABA(A) receptor agonist), and baclofen (a GABA(B) receptor agonist) increased 5-bromodeoxyuridine (BrdU) incorporation into ATDC5 cells. The effect of muscimol was blocked by bicuculline (a GABA(A) receptor antagonist), and the effect of baclofen was blocked by CGP 35348 (a GABA(B) receptor antagonist). These results suggest that GABA contributes to the ATDC5 cell proliferation via GABA(A) and GABA(B) receptors and these mechanisms may be involved in cartilaginous cell growth.

cDNA microarray analysis of lactoferrin expression in non-neoplastic human hepatocyte PH5CH8 cells

Lactoferrin (LF), a milk protein belonging to the iron transporter transferrin family, is known as a primary defense protein against pathogenic microorganisms. Previously, we found that bovine and human LFs prevented hepatitis C virus infection in cultured human hepatocytes by a direct interaction with the virus. Since LF is proposed to have transcriptional regulatory activity in addition to its antimicrobial function, we sought to identify the target genes that these two types of LF have in common. To this end, we were the first to perform microarray analysis (9970 genes) using human hepatocytes that expressed bovine or human LF by retrovirus-mediated gene transfer. In the results, LF could give a variety of expression profiles in the human hepatocytes, and showed that 9 and 19 genes were commonly up-regulated (more than 2.0-fold) and down-regulated (less than 0.50-fold), respectively, in both bovine and human LF-expressing cells compared with control cells. Among these genes, we found that gamma-aminobutyric acid (GABA)-B receptor 2 was transcriptionally down-regulated by bovine and human LFs, but not by human transferrin. Furthermore, we obtained the suggestive result that LF may modulate the level of intracellular cAMP. This modulation is one of the cellular responses that the GABA-B receptor modifies. This is the first report of microarray analysis applied to search inclusively for the target genes of LF.

Gamma-amino-butyric acid immunoreactivity in intramucosal colonic tumors

BACKGROUND AND AIM

The level of gamma-amino-butyric acid (GABA) is reported to be increased in colon cancer. Moreover, data suggests that GABA plays a role in the proliferation or maturation of some types of cells. We examined the expression of GABA in intramucosal colonic tumors to clarify the relation between GABA and the degree of atypia.

METHODS

Paraffin sections were prepared from 56 protruded-type colonic neoplasms, which were classified as intramucosal adenocarcinoma (AC), adenoma with severe atypia (ASA), or adenoma with mild to moderate atypia (AMA). Expression of GABA was investigated immunohistochemically, and GABA immunoreactivity was compared to the staining patterns of carcinoembryonic antigen (CEA) and cancer-associated antigen (CA19-9) which were classified into three categories.

RESULTS

Intense GABA immunoreactivity was observed in 73.7%, 54.6%, 13.3%, and 5.4% of AC, ASA, AMA, and normal mucosa specimens, respectively. Kendall's correlation coefficient between GABA immunoreactivity and the degree of atypia was 0.447. Strong, positive CEA staining (pattern 3) was observed in 57.9%, 36.3%, and 13.3% of AC, ASA, and AMA specimens, respectively. Strong, positive CA19-9 staining was observed: 26.3%, 9.1% and 0%, respectively. In AC and ASA, the proportion of glands with strong GABA immunoreactivity was greater than the proportion of glands that were strongly positive for CA19-9.

CONCLUSION

GABA may be useful as a tumor marker in combination with other tumor markers such as CEA and CA19-9.

Sequence and chromosomal assignment of a human novel cDNA: similarity to gamma-aminobutyric acid transporter

Gamma-aminobutyric acid (GABA) is the predominant inhibitory neurotransmitter in the mammalian brain. Although initially thought to be confined to the central nervous system, GABAergic activity has also been described in other tissues throughout the body. In the present study, we report the cloning and localization of human GABA transporter cDNA and document its expression in various human tissues. A human liver cDNA library was initially screened by a 32P-labeled murine brain GABA transporter 3 (GAT-3) cDNA probe, and full-length cDNA was cloned by employing Marathon-Ready(tm) human kidney cDNA. The human GABA transporter cDNA encoded a 569 amino acid hydrophobic protein with 12 transmembrane domains (TMs). Search of published sequences revealed high homology with rat GAT-2, murine GAT-3 cDNA, human solute carrier family 6 member 13 (SLC6A13), and a human peripheral betaine/GABA transporter. Northern blot analyses demonstrated that the human GABA transporter is expressed strongly in the kidney and to a lesser extent in the liver and brain. The sequence was well matched with human chromosome 12p13.3, suggesting the human GABA transporter contains 14 exons. The above findings confirm the existence of and further characterize a specific GABA transporter in human tissues.Key words: sequence, chromosome, GABA, GABA transporter.

Inhibition by interferon α-2b of rat liver regeneration: effect on ornithine decarboxylase and total protein synthesis ☆ ☆This work was presented, in part, at the 1999 Meeting of the Pan-American Association for Biochemistry and Molecular Biology (PABMB) and the American Society for Biochemistry and Molecular Biology (ASBMB). 1 1Abbreviations: IL, interleukin; TNFα, tumor necrosis factor-α; TGFβ, transforming growth factor-β; IFNα, interferon-α and ODC, ornithine decarboxylase

Polyamines are key factors in macromolecule synthesis during liver regeneration. It has been postulated that interferon-alpha (IFNalpha) decreases putrescine levels in regenerating liver by inhibiting ornithine decarboxylase (ODC) activity, the main enzyme in polyamine biosynthesis. In the present study, we analysed the effects of a pharmacological dose of IFNalpha on polyamine and ODC levels during the regenerative process following partial hepatectomy in rats. Synthesis of ODC by isolated hepatocytes from IFN-treated rats with regenerating livers was also assessed. Furthermore, we investigated the effect of IFNalpha-2b on DNA and total protein synthesis in 24-hr regenerating livers. No effect on DNA synthesis was observed at the dose of IFNalpha-2b used, but total protein synthesis decreased significantly in IFNalpha-2b-treated rats undergoing liver regeneration (7.0 +/- 2.0 and 12.1 +/- 1.7%. min(-1) in hepatectomized rats treated with IFNalpha-2b and saline, respectively). ODC levels were also reduced significantly (by 50%) in hepatectomized rats treated with IFNalpha-2b versus saline. In parallel with the ODC decrease, the concentrations of putrescine and spermidine (63 +/- 25 vs 101 +/- 15 nmol/g liver and 1.08 +/- 0.35 vs 2.14 +/- 0.22 micromol/g liver, respectively, in IFNalpha-2b- and saline-treated hepatectomized rats) showed similar, significant diminutions. Moreover, the incorporation of [35S]methionine into ODC was decreased dramatically in isolated hepatocytes from IFNalpha-2b-treated hepatectomized rats 12 hr after surgery. In conclusion, the protein synthesis rate in regenerating liver was impaired by therapeutic doses of IFNalpha-2b. In addition, the results presented in this study suggest that IFNalpha-2b negatively regulates ODC synthesis, causing a reduction in polyamine levels during liver regeneration.

Artificial liver support devices for fulminant liver failure

Artificial liver-support devices attempt to bridge patients with fulminant hepatic failure until either a suitable liver allograft is obtained for transplantation or the patient's own liver regenerates sufficiently to resume normal function. It is thought that toxins contribute to the clinical picture of fulminant hepatic failure. The earliest reports of successful toxin removal were blood- and plasma-exchange transfusions. Given these successful case reports, mechanical liver-support devices were designed to filter toxins. These mechanical devices used hemodialysis, charcoal hemoperfusion, hemoperfusion through cation-exchange resins, hemodiabsorption, and combinations of all of these techniques as in the MARS liver-support device. Despite promising case reports and small series, no controlled studies of mechanical devices have ever showed a long-term survival benefit. Thus, the removal of presumed toxins seems to be insufficient to support patients with fulminant hepatic failure, and the biologic function of the liver must also be replaced. Attempts at replacing the biologic function have included extracorporeal liver perfusion, cross-circulation, and hepatocyte transplantation. Current technologies have combined mechanical and biologic support systems in hybrid liver-support devices. The mechanical component of these hybrid devices serves both to remove toxins and to create a barrier between the patient's serum and the biologic component of the liver-support device. The biologic component of these hybrid liver support devices may consist of liver slices, granulated liver, or hepatocytes from low-grade tumor cells or porcine hepatocytes. These biologic components are housed within bioreactors. Currently the most clinically studied bioreactors are those that use capillary hollow-fiber systems. Both the bioartificial liver by Demetrious and the extracorporeal liver-assist device by Sussman and Kelly are in clinical trials. Although the trials seemed to have yielded good survival data when the devices are used as a bridge to transplantation, the type and degree of liver support provided by these devices remains uncertain. Thus, despite decades of great progress in the field of artificial liver support, no one technique alone yet provides sufficient liver support. A hybrid system seems to be the best option at present. Still to be determined is the best tissue to use, how much liver tissue should be used, and the optimal design of the bioreactor.

GABA in the Mammalian Enteric Nervous System

gamma-Aminobutyric acid (GABA) is a transmitter of enteric interneurons, targeting excitatory GABA(A) or inhibitory GABA(B) receptors that modulate motility and mucosal function. Enteric GABA may also subserve hormonal and paracrine signaling. Disruption in gastrointestinal function following perturbation of enteric GABA receptors presents potential new target sites for drug development.

Identification of gamma-aminobutyric acid receptor subunit types in human and rat liver

GABA is a potent inhibitory neurotransmitter that binds to heterooligomeric receptors in the mammalian brain. In a previous study, we documented specific GABA binding to isolated rat hepatocytes that resulted in inhibition of hepatocyte proliferation. The purpose of the present study was to define the nature of hepatic GABA(A) receptors and to document their expression during rapid liver growth (after partial hepatectomy). PCRs with gene-specific primers derived from published sequences were performed with Marathon-ready human and rat liver cDNA. Two GABA(A) receptor subunit types (beta3 and epsilon) were expressed in human liver and one subunit type (beta3) in rat liver. PCR amplification of the human GABA(A) receptorbeta3-subunit produced a single product (molecular mass 53-59 kDa). In the case of the epsilon-subunit, two PCR products were identified. After partial hepatectomy, GABA(A) receptorbeta3-subunit expression inversely correlated with regenerative activity (r = -0.527, P = 0.006). In conclusion, these results indicate that in the human liver GABA(A) receptors consist of the beta3- and epsilon-subunit types, whereas in the rat liver only the beta3-subunit type is expressed. The results also support the hypothesis that GABAergic activity serves to maintain hepatocytes in a quiescent state.

GABA and hepatocellular carcinoma

Data derived from models of hepatic regeneration indicate that transient, reciprocal changes in polyamines, potent growth promoters, and gamma aminobutyric acid (GABA), an amino acid neurotransmitter with growth inhibitory properties, play important roles in enhancing and inhibiting respectively regulated hepatocyte proliferation. Based on these findings and supportive data derived from studies of human carcinoma tissues and malignant cell lines we propose that permanent increases in polyamine and decreases in GABAergic activity act in concert to contribute to the pathogenesis of hepatocellular carcinoma.

The effects of acute ethanol exposure on inhibitors of hepatic regenerative activity in the rat

The purpose of this study was to identify the mechanism(s) whereby acute ethanol exposure inhibits hepatic regenerative activity in the rat. Adult, male, Sprague-Dawley rats (200-250 g) were randomized to receive either ethanol (1 g/kg i.p. q 4 h) or an equal volume of saline (controls) for 24 h beginning 1 h prior to a 70% partial hepatectomy (PHx). At 0, 3, 6, 12 and 24 h post-PHx, rats were sacrificed (N = 4-6/group), and the expression of the following genes associated with inhibition of hepatocyte proliferation were documented; p53, p21, transforming growth factor-beta1 (TGF-beta1) and gamma aminobutyric acid transport protein (GABA-TP). Inhibition of hepatic regenerative activity was confirmed by 3H-thymidine incorporation into hepatic DNA at 24 h post-PHx. The results of the study revealed that in ethanol-treated rats, DNA synthesis was inhibited by 37% when compared to saline-treated controls (p < 0.01). Regarding suppressor gene expression, both p21 and TGF-beta1 mRNA expression in ethanol-treated rats were similar to those obtained in saline-treated controls. Although p53 mRNA expression differed in the two groups, in the ethanol-treated group, p53 mRNA expression was decreased rather than increased (relative to controls) at 24 h post-PHx, a finding not in keeping with inhibition of DNA synthesis. GABA-TP mRNA was strongly expressed prior to PHx in both ethanol- and saline-treated rats. Following PHx, GABA-TP mRNA expression decreased in both groups but remained low in the saline-treated group while returning to pre-PHx values in ethanol-treated rats. In summary, the results of this study indicate that the inhibitory effects of ethanol on hepatic regeneration are not associated with significant or the appropriate changes in mRNA expression of the p53, p21 or TGF-beta1 suppressor genes. On the other hand, transcriptional changes in GABA-TP gene expression post-PHx are in keeping with an inhibitory effect of GABA on hepatic regeneration.

Effect of preoperative interventions on outcome following liver resection in a rat model of cirrhosis

BACKGROUND/AIMS

High morbidity and mortality rates in cirrhotic patients undergoing resections for hepatocellular malignancies underscore the need for identifying a therapy that will decrease fibrosis or enhance hepatic regenerative activity in the perioperative period. Thus, in the present study, 104 carbon tetrachloride-induced cirrhotic rats received either saline (untreated cirrhotic controls) or one of the following agents that have been reported to decrease hepatic fibrosis or increase hepatic regeneration; pentoxifylline, ciprofloxacin or a traditional Chinese herbal remedy (TCHR). Twelve additional rats served as healthy, non-cirrhotic controls.

METHODS

Treatments were administered daily by gavage for 4 weeks followed by a 70% partial hepatectomy. Hepatic fibrosis was documented at the time of surgery by computer-assisted quantitation of collagen content. Liver function and hepatic regenerative activity were documented 24 h post partial hepatectomy by serum bilirubin determinations and a combination of 3[H]-Thymidine incorporation into hepatic DNA and proliferating cell nuclear antigen (PCNA) quantitation, respectively.

RESULTS

Compared to untreated cirrhotic controls (8.1 +/- 0.7%), fibrosis was significantly reduced in the pentoxifylline- and ciprofloxacin-treated groups (4.6 +/- 0.2%, p<0.005 and 5.5 +/- 0.6%, p<0.05) but unchanged in the TCHR-treated group (6.6 +/- 11.0%). Post-operatively, total serum bilirubin levels were lower in the pentoxifylline (1.40 +/- 0.15 mg/dl,p<0.01) and ciprofloxacin (1.87 +/- 0.25 mg/dl, p<0.05)-treated groups, but unchanged in the TCHR group (2.20 +/- 0.45 mg/dl), when compared to untreated cirrhotic controls (3.00 +/- 0.37 mg/dl). Hepatic regenerative activity was also significantly improved in the pentoxifylline-treated group (17.8 +/- 2.2 versus 9.9 +/- 1.9 DPM/microg DNA in untreated cirrhotic controls, p<0.05), but unchanged in the ciprofloxacin (16.1 +/- 1.8 DPM/microg DNA) and TCHR (10.9 +/- 1.2 DPM/microg DNA)-treated groups. PCNA protein determinations were in keeping with the 3[H]-Thymidine results

CONCLUSIONS

Pre-operative pentoxifylline holds promise as a useful therapeutic intervention for patients with cirrhosis requiring hepatic resection.

Pantoprazole versus ranitidine in the treatment of duodenal ulcer: a multicenter study in Brazil

OBJECTIVE

The aim of this study was to compare the effectiveness and tolerance of pantoprazole versus ranitidine in the treatment of duodenal ulcers in the Brazilian population.

METHODS

A total of 222 patients with active duodenal ulcers (DU) were randomly allocated to a double dummy blind treatment, either with ranitidine (RAN) 300 mg (111, aged from 20-68 yr old, 56 female) or with pantoprazole (PANT) 40 mg (111 patients, 18-70 yr old, 45 female). After a 2-wk course of treatment, each patient was clinically and endoscopically assessed for ulcer healing. Failure to heal required a further 2-wk course of treatment and a new evaluation thereafter.

RESULTS

In all, 77 of the 103 patients in the PANT group (74.8%) and 42 of the 94 patients in the RAN group (44.7%) who completed the study had ulcer healing after one 2-wk treatment course, and an additional 23 in the PANT group (22.3%) and 28 in the RAN group (29.8%) after the second 2-wk treatment course, totaling 100 (97.1%) and 70 (74.5%), respectively. Therapeutic gain in favor of pantoprazole was significant both at the end of the first and the second 2-wk treatment course (p<0.001). At 2 wk, symptoms remission was significantly higher in the PANT group (97.6%) than with the RAN group (77.5%) (p<0.001). The Intention-to-treat analysis showed results statistically similar to those observed in the per-protocol analysis. Minor adverse events were reported by four patients in the PANT group and three in the RAN group. No relevant laboratory abnormalities were seen. No patient withdrew from the study due to adverse events.

CONCLUSIONS

Our results show that pantoprazole is more effective than ranitidine in the treatment of duodenal ulcer providing faster ulcer healing in most patients (97.1%), in 4 wk. Adverse events were rare and were similar in both groups, and had no influence on the therapeutic outcome.

Increased GABAergic activity inhibits alpha-fetoprotein mRNA expression and the proliferative activity of the HepG2 human hepatocellular carcinoma cell line

BACKGROUND/AIMS

Gamma aminobutyric acid (GABA) is a potent inhibitory neurotransmitter with growth regulatory properties. Recent data indicate that increased GABAergic activity inhibits hepatocyte proliferation in regenerating livers. In the present study, we aimed to investigate whether GABA inhibits the growth of malignant hepatocytes.

METHODS

Increasing concentrations of muscimol (0.05-50 microM), a specific GABA(A) receptor agonist, were added to HepG2 human hepatocellular carcinoma cells and alpha-fetoprotein (AFP) and albumin mRNA expression were determined for varying periods of time (maximum 24 h) thereafter. Cell proliferation was also documented after 48 h of exposure to muscimol.

RESULTS

Muscimol significantly (p<0.0001) decreased AFP mRNA expression (maximum decrease: 65% below baseline values) without affecting albumin mRNA expression. However, the effect on AFP mRNA was transient (maximum duration: 3-6 h) and not associated with changes in cell proliferation. Because preliminary data indicate that GABA(A) receptor activity is markedly downregulated in malignant hepatocytes, transfection studies were performed wherein HepG2 cells were cotransfected with GABA(A) receptor beta2 and beta2 subunit genes in a pCDM8 expression vector or vector alone followed by re-exposure to either muscimol (5 betaM) or saline. In this series of experiments, in addition to AFP mRNA inhibition being as extensive and more prolonged (maximum duration: 6-12 h) in muscimol-treated, GABA(A) receptor-transfected cells, proliferative activity was also significantly inhibited when compared to saline-treated GABA(A) receptor-transfected controls (p<0.01) and muscimol-treated cells transfected with vector alone (p<0.005).

CONCLUSION

The results of this study indicate that increased GABAergic activity inhibits AFP mRNA expression and cell proliferation in this malignant hepatocyte cell line.

Effects of acute and chronic ethanol exposure on the hepatic gamma-aminobutyric acid transport system in rats

Ethanol-induced increases in gamma-aminobutyric (GABA)ergic activity contribute to the impairment in hepatic regeneration associated with alcohol-induced liver disease. To determine the mechanism(s) whereby ethanol increases GABAergic activity in the liver, we documented the effects of acute (5 g/kg x 1) and chronic (36% of total calories over 6 weeks) ethanol exposure as well as exogenous GABA (500 microg/g body weight) administration on GABA transport protein (GABA-TP) mRNA expression in the livers of adult male Sprague-Dawley rats at various times (0-72 h) post 70% partial hepatectomy (PHx). We also documented the in vitro effects of ethanol (30-90 microM) on [3H]-GABA uptake in isolated rat hepatocytes. The results of the study revealed that compared to saline-exposed controls, acute but not chronic ethanol exposure resulted in significant decreases in GABA-TP mRNA expression at 12, 24, and 48 h post PHx (saline exposed, 1.04 +/- 0.06, 1.19 +/- 0.21, and 1.15 +/- 0.05. vs. acute ethanol exposed, 0.80 +/- 0.16, 0.88 +/- 0.09, and 0.86 +/- 0.16 optical density units, p < 0.01, 0.05, and 0.05, respectively). An inhibitory effect was also observed following exogenous GABA administration (GABA-TP mRNA expression at 3 h was approximately 40% that of baseline, p < 0.05). [3H]-GABA uptake in isolated rat hepatocytes in vitro was unaffected by the presence of ethanol. In conclusion, the results of this study indicate that acute but not chronic ethanol exposure and exogenously administrated GABA inhibit hepatic GABA-TP mRNA expression following partial hepatectomy in the rat. These findings suggest that the increased GABAergic activity that occurs in the liver following acute ethanol exposure results from alterations in the hepatic GABA transport system at a transcriptional level.

Effects of acute ethanol exposure on polyamine and gamma-aminobutyric acid metabolism in the regenerating liver

Recently, it has been suggested that ethanol-induced inhibition of liver regeneration results from decreases in hepatic putrescine levels and/or increases in hepatic gamma-aminobutyric acid (GABA)ergic activity. Because putrescine can be metabolized by diamine (DAO) and monoamine (MAO) oxidases to GABA, we documented the effects of acute ethanol exposure on hepatic MAO or DAO activity following partial hepatectomy (PHx) in rats. We also documented the effects of ethanol on GABA transaminase (GABA-T), the enzyme responsible for GABA metabolism in the liver, and tissue putrescine and GABA levels. Adult, male Sprague-Dawley rats (200-250 g) were treated with either ethanol (3 g/kg) or equal volumes of saline by gastric gavage 1 h prior to a 70% PHx or sham surgery. Rats were then sacrificed (n = 5-7/group) at various times (0-72 h) post-PHx. Enzymatic activity and putrescine/GABA levels were determined by standard isotopic techniques and high-performance liquid chromatography respectively. Hepatic DAO activities in ethanol-treated rats were transiently higher than in saline-treated controls (30% increases at 6 h, p < 0.05). Hepatic MAO and GABA-T activities in acute ethanol-treated rats were essentially identical to saline-treated controls. Although hepatic putrescine levels were similar in ethanol- and saline-treated rats, hepatic GABA levels were approximately three times higher in ethanol-treated rats at 12 and 24 h post-PHx (p < 0.0001). In conclusion, the results of this study indicate that acute ethanol exposure has a limited effect on the enzymatic conversion of putrescine to GABA following partial hepatectomy in the liver. The results also indicate that increased GABAergic inhibition rather than decreased putrescine stimulation is more likely to play a role in ethanol-induced inhibition of hepatic regeneration.

The effects of ethanol and gamma aminobutyric acid alone and in combination on hepatic regenerative activity in the rat

BACKGROUND/AIMS

Both ethanol and gamma aminobutyric acid (GABA) have been reported to inhibit hepatic regenerative activity in the rat. Because alcoholic beverages contain appreciable amounts of GABA, we documented whether the inhibitory effects of alcohol on the liver are derived from ethanol alone or the combination of ethanol plus GABA.

METHODS

Adult male Sprague-Dawley rats (n=6/group) were treated with either ethanol (3 g/kg), GABA (500 mg/kg) or ethanol plus GABA (3 kg and 500 mg/kg, respectively), beginning 1 h prior to a 70% partial hepatectomy and continued every 4 h thereafter for a total of 24 h. Rats were then sacrificed and hepatic regenerative activity was documented by 3H-thymidine incorporation into hepatic DNA.

RESULTS

DNA synthesis was significantly inhibited by ethanol (-37%, p<0.005) and GABA (-19%, p<0.05). Maximum inhibition was achieved with the combination of ethanol plus GABA (-52%, p<0.001). To determine whether the additive effects of ethanol plus GABA were mediated by ethanol-induced enhancement of hepatic GABA(A) receptor activity, additional rats (n=6/group) receiving the combination of ethanol plus GABA were pre-treated with a single injection of either ciprofloxacin (50 mg/kg), a GABA(A) receptor antagonist, or an equal volume of saline. In these experiments, ciprofloxacin pre-treatment prevented the inhibitory effects of the ethanol plus GABA combination.

CONCLUSIONS

The results of this study indicate that the combination of ethanol plus GABA has a greater inhibitory effect on hepatic DNA synthesis following partial hepatectomy than ethanol alone. The clinical implication of this finding is that, when standardized for ethanol content, not all alcoholic beverages would be expected to have the same inhibitory effect on hepatic regeneration.

New approaches to supporting the failing liver

With the continued, growing disparity between the numbers of organ donations and patients waiting for liver transplantation, various efforts have been made to optimize the allocation of organs, as well as to devise means to support the failing liver. Over the years, the development of bioartificial liver-assist devices has aimed at replacing the three main functions of hepatocytes, which are synthetic, metabolic, and excretory. The application of porcine hepatocytes in humans to carry out biotransformation, as well as other metabolic functions and refinement of the membrane separator, have yielded some promising results in supporting patients with acute liver failure. Further advances will need to be made before these bioartificial devices can be considered for routine application in clinical settings.

The beneficial effects of ciprofloxacin on survival and hepatic regenerative activity in a rat model of fulminant hepatic failure

Recently, we reported that ciprofloxacin, an antimicrobial agent with gamma-aminobutyric acid (GABA(A)) receptor antagonist properties, significantly increases hepatic regenerative activity in animal models of alcohol-induced liver disease and cirrhosis. In the present study, we documented the effects of ciprofloxacin on survival and hepatic regeneration in a D-galactosamine (D-gal)-induced model of acute hepatic injury in rats. One hundred nineteen adult, male Sprague-Dawley rats (n = 19-20/group) were treated with intraperitoneal D-gal (total dose: 2.5 g/kg), followed by gastric gavage with either saline, ciprofloxacin (10, 50, or 100 mg/kg), norfloxacin (250 mg/kg), or intraperitoneal putrescine (300 micromol/kg), a potent hepatic growth promoter. Mortality rates were then documented over a 4-day period. An additional 45 rats (n = 15/group) received a sublethal dose of D-gal (1.0 g/kg), followed by gastric gavage with either saline or ciprofloxacin (100 mg/kg), or intraperitoneal putrescine (300 micromol/kg). In these rats, hepatic regenerative activity was documented at 12, 24, and 60 hours post-D-gal by 3H-thymidine incorporation into hepatic DNA and proliferating cell nuclear antigen (PCNA) staining. In the survival study, a dose-response effect of ciprofloxacin on survival was observed (ciprofloxacin: 10 mg/kg, 10%; 50 mg/kg, 26%; and 100 mg/kg, 35%) with the results in the 100-mg/kg-treated group being significant when compared with the 5% survival rate in saline-treated controls (P < .05). Survival figures in the norfloxacin- and putrescine-treated groups were not significantly improved (15% and 25%, respectively). In the regeneration study, compared with the D-gal + saline-treated control group, DNA synthesis rates at 60 hours were increased in the D-gal + ciprofloxacin and D-gal + putrescine groups (10.2 +/- 3.3 vs. 18.2 +/- 5.1 and 18.8 +/- 6.8 x 10(3) dpm/mg DNA respectively; P < .05). The results of PCNA staining also supported enhanced hepatic regeneration in the ciprofloxacin-treated group at 60 hours (saline, 13.4 +/- 3.7; ciprofloxacin, 47.4 +/- 7.3; and putrescine, 8.4% +/- 2.8% hepatocytes staining positive). Ciprofloxacin at a dose of 100 mg/kg significantly improves survival and hepatic regenerative activity in this animal model of acute hepatic injury.

Effect of quinolone antibiotics on hepatic growth and protein synthesis following partial hepatectomy in rats

Quinolone antibiotics inhibit eukaryotic as well as prokaryotic cell growth and protein synthesis. To determine whether these properties adversely affect hepatic growth and recovery following surgical resection, five groups of healthy, adult male rats (n = 7-8/group) were treated for 10 days with equal volumes of either ofloxacin (50 mg/kg), fleroxacin (25 mg/kg), ciprofloxacin (25 mg/kg), norfloxacin (15 mg/kg) or sterile saline (controls) prior to 70% partial hepatectomy (PH) and daily thereafter until death. Restituted liver mass, DNA and protein synthesis rates were determined at 24, 48 and 72 h PH. The results of the study revealed that all parameters of hepatic regeneration were similar in the five study groups at each time interval. To ensure that an effect on hepatic regeneration was not dose-dependent, additional experiments were performed where 1, 10 and 100 mg/kg ciprofloxacin was administered and DNA synthesis was measured 24 h post-PH. Once again, the results were similar to sterile saline-treated controls. These findings suggest that the quinolone antibiotics are unlikely to have an adverse effect on hepatic recovery following surgical resection of the liver and are safe to use in that setting.

Effect of exogenous gamma-aminobutyric acid (GABA) on hepatic insulin-like growth factor I (IGF-I) and IGF-I binding protein (IGFBP-I) mRNA abundance following partial hepatectomy in rats

Insulin-like growth factor I (IGF-I) and IGF-I binding protein (IGFBP-I) are highly expressed in the liver and may play an important role in enhancing hepatic regeneration following partial hepatectomy in rats. Since hepatic levels of these growth factors are influenced by pituitary growth hormone release, which in turn is regulated by systemic serum gamma-aminobutyric acid (GABA) concentrations, we chose to examine the effects of elevated serum GABA concentrations on hepatic IGF-I and IGFBP-I mRNA abundance following partial hepatectomy in the rat. The results of our experiments revealed that at serum GABA concentrations similar to those associated with liver failure, peak hepatic IGF-I and IGFBP-I mRNA levels were significantly lower in GABA-treated rats compared with saline-treated controls (p < 0.05 and 0.01, respectively). To exclude a direct effect of GABA on hepatocyte IGF-I and IGFBP-I mRNA expression, suspensions of isolated hepatocytes were incubated in the presence and absence of exogenous GABA. In these experiments GABA treatment did not lower either IGF-I or IGFBP-I mRNA or protein levels. These findings suggest that increased concentrations of GABA in the systemic circulation could contribute to the impairment in hepatic regenerative activity that occurs in animals and humans with advanced liver failure.