UDP-glucuronosyltransferase in the regenerating rat liver

Oleanolic acid promotes liver regeneration after partial hepatectomy via regulating pregnane X receptor signaling pathway in mice

Liver regeneration after liver tumor resection or liver transplantation is crucial, the remaining liver frequently fails to regenerate in some patients. Oleanolic acid (OA), a pentacyclic triterpenoid compound which has been shown to protect against various liver diseases. However, the effect of OA on liver regeneration after partial hepatectomy (PHx) is still unclear. In this study, the results showed that OA (50 mg/kg, twice daily) treatment induced liver mass restoration and increased the liver-to-body weight ratio of mice following PHx. Meanwhile, OA promoted hepatocyte proliferation and increased the number of BrdU-, Ki67-and PCNA-positive cells. Furthermore, OA increased the nuclear accumulation of PXR and induced the expression of PXR downstream proteins such as CYP3A11, UGT1A1 and GSTM2 in mice, as well as in AML12 and HepRG cells. Luciferase reporter assay and nuclear localization of PXR further demonstrated the effect of OA on PXR activation in vitro. Molecular docking simulation showed that OA could interact with the PXR active sites. Moreover, OA inhibited the expression of FOXO1, RBL2 and CDKN1B, and increased the expression of PCNA, CCND1 and CCNE1 in vivo and in vitro. Silencing of Pxr further confirmed that OA-mediated upregulation of proliferation-related proteins depended on PXR. The current study illustrated that OA exhibited a significant promoting effect on liver regeneration following PHx, potentially through regulation of the PXR signaling pathway to accelerate liver recovery.

Coordinated cytochrome P450 expression in mouse liver and intestine under different dietary conditions during liver regeneration after partial hepatectomy

Liver resection is performed to remove tumors in patients with liver cancer, but the procedure's suitability depends on the regenerative ability of the liver. It is important to consider the effects of exogenous factors, such as diets, on liver regeneration for the recovery of function. The evaluation of drug metabolism during liver regeneration is also necessary because liver dysfunction is generally observed after the operation. Here, we investigated the influence of a purified diet (AIN-93G) on liver regeneration and changes in the mRNA expression of several cytochrome P450 (CYP) isoforms in the liver and small intestine using a two-thirds partial hepatectomy (PH) mouse model fed with a standard diet (MF) and a purified diet. Liver regeneration was significantly delayed in the purified diet group relative to that in the standard diet group. The liver Cyp2c55 and Cyp3a11 expression was increased at 3 day after PH especially in the purified diet group. Bile acid may partly cause the differences in liver regeneration and CYP expression between two types of diets. On the other hand, Cyp3a13 expression in the small intestine was transiently increased at day 1 after PH in both diet groups. The findings suggest that compensatory induction of the CYP expression occurred in the small intestine after attenuation of drug metabolism potential in the liver. The present results highlight the importance of the relationship between liver regeneration, drug metabolism, and exogenous factors for the effective treatment, including surgery and medication, in patients after liver resection or transplantation.

Pharmacokinetics of drugs in adult living donor liver transplant patients: regulatory factors and observations based on studies in animals and humans

INTRODUCTION

Limited information is available on the pharmacokinetics of drugs in the donors and recipients following adult living donor liver transplantation (LDLT). Given that both the donors and recipients receive multiple drug therapies, it is important to assess the pharmacokinetics of drugs used in these patients.

AREAS COVERED

Pathophysiological changes that occur post-surgery and regulatory factors that may influence pharmacokinetics of drugs, especially hepatic drug metabolism and transport in both LDLT donors and the recipients are discussed. Pharmacokinetic data in animals with partial hepatectomy are presented. Clinical pharmacokinetic data of certain drugs in LDLT recipients are further reviewed.

EXPERT OPINION

It takes up to six months for the liver volume to return to normal after LDLT surgery. In the LDLT recipients, drug exposure generally is higher with lower clearance during early period post-transplant; lower initial dosages of immunosuppressants are used than deceased donor liver transplant recipients during the first six months post-transplantation. In animals, the activities of hepatic drug metabolizing enzymes and transporters are known to be altered differentially during liver regeneration. Future studies on the actual hepatic function with reference to drug metabolism, drug transport, and biliary secretion in both LDLT donors and recipients are required.

Thioacetamide intoxication triggers transcriptional up-regulation but enzyme inactivation of UDP-glucuronosyltransferases

Thioacetamide (TAA) is a potent hepatotoxicant and has been widely used to develop experimental liver fibrosis/cirrhosis models. Although the liver toxicity of TAA has been extensively studied, little is known about its potential influence on UDP-glucuronosyltransferases (UGTs) associated with the development of liver fibrosis. The study presented here aimed to uncover the regulation patterns of UGTs in TAA-induced liver fibrosis of rats. Potential counteracting effects of hepatoprotective agents were also determined. TAA treatment for 8 weeks induced a significant transcriptional up-regulation of the major UGT isoforms, including UGT1A1, UGT1A6, and UGT2B1, accompanied with the dramatic elevations of most typical serum biomarkers of liver function and fibrosis scores. Upon TAA intoxication, the mRNA and protein levels of the major UGT isoforms were increased to 1.5- to 2.5-fold and 2.5- to 3.3-fold of that of the normal control, respectively. The hepatoprotective agents Schisandra spp. lignans extract and dimethyl diphenyl bicarboxylate could largely abolish TAA-induced up-regulation of all three UGT isoforms. However, enzyme activities of UGTs remained unchanged after TAA treatment. The dissociation of protein expression and enzyme activity could possibly be attributed to the inactivating effects of TAA, upon a NADPH-dependent bioactivation, on UGTs. This study suggests that the transcriptional up-regulation of UGTs may be an alternative mechanism of their preserved activities in liver fibrosis/cirrhosis.

Activity and expression of various isoforms of uridine diphosphate glucuronosyltransferase are differentially regulated during hepatic regeneration in rats

PURPOSE

Glucuronidation pathway is very important in the detoxification of endogenous and exogenous compounds. The objective of this study was to evaluate the activity and expression of various hepatic uridine diphosphate glucuronosyltransferases (UGTs) in rats at various time points after initiation of hepatic regeneration by partial hepatectomy (PHx).

METHODS

The mRNA expression of various UGTs was evaluated using real-time polymerase chain reaction (real-time PCR) with specific primers. The in vitro activity of UGTs was evaluated using different substrates such as estradiol (UGT1A1), acetaminophen (UGT1A6/7), morphine (UGT2B1), testosterone (UGT2B1/3/6), androsterone (UGT2B2), and (-)-borneol (UGT2B12).

RESULTS

Whereas the activity and mRNA expression of UGT1A1, UGT2B1, UGT2B1/3/6, UGT2B2, and UGT2B12 were lower, the activity and mRNA expression of UGT1A6/7 were preserved during hepatic regeneration. The mRNA expression of UGT2B8 was down-regulated, whereas the mRNA expression of UGT1A5 and UGT1A8 was not altered by PHx. The mRNA expression of UGT1A2 and UGT1A3 was increased during hepatic regeneration.

CONCLUSION

UGT-mediated drug-metabolizing ability of the liver was altered differentially in the regenerating rat liver. Individualized dosing regimen for different UGT substrates may be needed when using such substrates of these enzymes in patients with a regenerating liver, especially during the early postoperative period. However, the glucuronide conjugating capacity of the liver in the donor of a living donor liver transplantation is expected to completely return to normal with time after surgery.

Tacrolimus dosing requirements and concentrations in adult living donor liver transplant recipients

Living donor liver transplantation in adult recipients is becoming increasingly common. The liver metabolizes most drugs, including immunosuppressive agents. Right-lobe grafts used in adult living donor liver transplantation consist of only 50% to 60% of the total liver. The purpose of this study is to determine whether there is a difference between tacrolimus doses and concentrations in patients who received a partial liver transplant from a living donor (LRD) versus those who received a whole-liver transplant from a cadaveric donor (CAD). Thirteen LRD recipients and 13 CAD recipients who underwent transplantation between April 1998 and July 2000 were included in this analysis. A CAD control group matched for age, sex, and race was used for comparison. Tacrolimus doses and concentrations were analyzed weekly for the first 4 weeks, then monthly for 6 months posttransplantation. There was no difference in acute rejection rates, renal and liver function test results, or number of potentially interacting medications administered between groups. LRD recipients required significantly lower doses of tacrolimus compared with CAD recipients at 2 weeks (0.058 v 0.110 mg/kg/d; P <.01), 3 weeks (0.068 v 0.123 mg/kg/d; P <.02), 4 weeks (0.086 v 0.141 mg/kg/d; P <.02), 2 months (0.097 v 0.141 mg/kg/d; P <.03), and 3 months (0.099 v 0.138 mg/kg/d; P <.03). Tacrolimus 12-hour trough concentrations were similar between groups at all times except for 2 weeks posttransplantation, when LRD recipients' concentrations were significantly greater than those of CAD recipients (12.4 v 9.5 ng/mL; P <.03). In addition, in the first month posttransplantation, LRD recipients were more likely to have greater concentrations of tacrolimus (>15 ng/mL; 22.1% v 9.2%; P <.01). In conclusion, LRD recipients have significantly decreased tacrolimus dosing requirements compared with CAD recipients during the first 3 months posttransplantation despite having similar tacrolimus concentrations.

UDP glucuronosyltransferase mRNA levels in human liver disease

The UDP glucuronosyltransferases (UGT) are a family of enzymes in which substrates include drugs, xenobiotics, and products of endogenous catabolism. The main source of most UGT enzymes is the liver, a major organ in the detoxification and inactivation of compounds. Previous studies have indicated that glucuronidation, as measured by pharmacokinetic studies, is relatively spared in liver disease. Because UGT activity toward most substrates is the result of metabolism by different isoforms with overlapping specificities, these studies may not indicate the effect of disease on the levels of individual isoforms. We sought to extend these studies to the measurement of mRNA for individual isoforms in the liver of patients with various forms of liver disease. RNA was extracted from liver tissue samples of patients undergoing clinically necessary percutaneous liver biopsies. UGT mRNA levels for isoforms 1A1, 1A3, 1A4, 1A6, 1A9, 2B4, 2B7, 2B10, 2B11, 2B15, and 2B17 were determined by real-time reverse transcription-polymerase chain reaction. Biopsies were graded using the Metavir system. Results from patients with low fibrosis or inflammatory scores were compared with those with high scores. We found large interindividual variation in the levels of the various isoforms. This was greatest for UGT2B17. A consistent downward trend, reaching statistical significance for UGT1A4, UGT2B4, and UGT2B7, was observed in samples from patients with high inflammation scores. There was no such correlation with the degree of fibrosis. Our results indicate that hepatic UGT mRNA levels are reduced while the tissue is inflamed, but they are not affected in the noninflamed, chronically diseased liver.

Differential suppression of liver-specific genes in regenerating rat liver induced by extended hepatectomy

BACKGROUND/AIMS

The function of the remnant liver is critical to survival of patients following an extended hepatectomy. The aim of this study was to determine whether proliferating hepatocytes in the remnant liver preserve the expression of liver-specific genes.

METHODS

Using regenerating rat livers after 30, 70, and 90% partial hepatectomy (PHx), Northern blot analyses were performed with probes for seven liver-specific genes, six growth-related genes, two housekeeping genes and two acute phase reactant protein genes.

RESULTS

During the regeneration after 90% PHx, the transcription of liver-specific genes showed three chronological patterns: transcription of serum albumin and cytochrome P450 2B decreased rapidly and reached a nadir at 6 to 24 h after PHx; those of apolipoprotein A-1, phosphoenolpyruvate carboxykinase and ornithine transcarbamylase decreased gradually until 24 to 48 h; those of UDP-glucuronosyltransferase and hepatocyte nuclear factor 4 did not show any changes until 48 h after PHx. In contrast, expression levels of all the growth-related genes and of housekeeping genes increased rapidly after PHx. After 30 and 70% PHx, expression of these genes changed in a similar manner to the 90% PHx case but to a lower extent.

CONCLUSIONS

Based upon the fractions of Ki-67 positive hepatocytes in remnant livers, we could estimate the degree of expression of each liver-specific gene in the proliferating hepatocytes. The serum albumin gene was completely suppressed, while that encoding UDP-glucuronosyltransferase was not affected. These results correlated well with the patterns of albumin and bilirubin in rat serum after PHx. Other liver-specific genes were moderately suppressed in proliferating hepatocytes. Thus, expression of liver-specific gene is differentially suppressed when hepatocytes enter a proliferation cycle. Those that are unaffected may be indispensable for maintaining the homeostasis of the living organism.