Putrescine decreases cytochrome P450 3A4 levels during liver regeneration in the rat

Transcriptomic Characterization of Key Factors and Signaling Pathways for the Regeneration of Partially Hepatectomized Liver in Zebrafish

Liver regeneration induced by partial hepatectomy (PHx) has attracted intensive research interests due to the great significance for liver resection and transplantation. The zebrafish (Danio rerio) is an excellent model to study liver regeneration. In the fish subjected to PHx (the tip of the ventral lobe was resected), the lost liver mass could be fully regenerated in seven days. However, the regulatory mechanisms underlying the liver regeneration remain largely unknown. In this study, gene expression profiles during the regeneration of PHx-treated liver were explored by RNA sequencing (RNA-seq). The genes responsive to the injury of PHx treatment were identified and classified into different clusters based on the expression profiles. Representative gene ontology (GO) enrichments for the early responsive genes included hormone activity, ribosome biogenesis and rRNA processing, etc., while the late responsive genes were enriched in biological processes such as glutathione metabolic process, antioxidant activity and cellular detoxification. The Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichments were also identified for the differentially expressed genes (DEGs) between the time-series samples and the sham controls. The proteasome was overrepresented by the up-regulated genes at all of the sampling time points. Inhibiting proteasome activity by the application of MG132 to the fish enhanced the expression of Pcna (proliferating cell nuclear antigen), an indicator of hepatocyte proliferation after PHx. Our data provide novel insights into the molecular mechanisms underlying the regeneration of PHx-treated liver.

British Society of Gastroenterology and UK-PSC guidelines for the diagnosis and management of primary sclerosing cholangitis

These guidelines on the management of primary sclerosing cholangitis (PSC) were commissioned by the British Society of Gastroenterology liver section. The guideline writing committee included medical representatives from hepatology and gastroenterology groups as well as patient representatives from PSC Support. The guidelines aim to support general physicians, gastroenterologists and surgeons in managing adults with PSC or those presenting with similar cholangiopathies which may mimic PSC, such as IgG4 sclerosing cholangitis. It also acts as a reference for patients with PSC to help them understand their own management. Quality of evidence is presented using the AGREE II format. Guidance is meant to be used as a reference rather than for rigid protocol-based care as we understand that management of patients often requires individual patient-centred considerations.

Mg2+/Mn2+-dependent phosphatase 1A is involved in regulating pregnane X receptor-mediated cytochrome p450 3A4 gene expression

Variations in the expression of human pregnane X receptor (hPXR)-mediated cytochrome p450 3A4 (CYP3A4) in liver can alter therapeutic response to a variety of drugs and may lead to potential adverse drug interactions. We sought to determine whether Mg(2+)/Mn(2+)-dependent phosphatase 1A (PPM1A) regulates hPXR-mediated CYP3A4 expression. PPM1A was found to be coimmunoprecipitated with hPXR. Genetic or pharmacologic activation of PPM1A led to a significant increase in hPXR transactivation of CYP3A4 promoter activity. In contrast, knockdown of endogenous PPM1A not only attenuated hPXR transactivation, but also increased proliferation of HepG2 human liver carcinoma cells, suggesting that PPM1A expression levels regulate hPXR, and that PPM1A expression is regulated in a proliferation-dependent manner. Indeed, PPM1A expression and hPXR transactivation were found to be significantly reduced in subconfluent HepG2 cells compared with confluent HepG2 cells, suggesting that both PPM1A expression and hPXR-mediated CYP3A4 expression may be downregulated in proliferating livers. Elevated PPM1A levels led to attenuation of hPXR inhibition by tumor necrosis factor-α and cyclin-dependent kinase-2, which are known to be upregulated and essential during liver regeneration. In mouse regenerating livers, similar to subconfluent HepG2 cells, expression of both PPM1A and the mouse PXR target gene cyp3a11 was found to be downregulated. Our results show that PPM1A can positively regulate PXR activity by counteracting PXR inhibitory signaling pathways that play a major role in liver regeneration. These results implicate a novel role for PPM1A in regulating hPXR-mediated CYP3A4 expression in hepatocytes and may explain a mechanism for CYP3A repression in regenerating livers.

Induced CYP3A4 expression in confluent Huh7 hepatoma cells as a result of decreased cell proliferation and subsequent pregnane X receptor activation

We have previously shown that confluent growth of the human hepatoma cell line Huh7 substantially induces the CYP3A4 mRNA, protein, and activity levels. Here, the mechanisms behind were investigated, and a transcriptome analysis revealed significant up-regulation of liver-specific functions, whereas pathways related to proliferation and cell cycle were down-regulated in the confluent cells. Reporter analysis revealed that the CYP3A4 gene was transcriptionally activated during confluence in a process involving pregnane X receptor (PXR). PXR expression was increased, and PXR protein accumulated in the nuclei during confluent growth. The PXR ligand rifampicin further increased the expression of CYP3A4, and siRNA-mediated knock-down of PXR in confluent cells resulted in decreased CYP3A4 expression. Cyclin-dependent kinase 2 (CDK2), a known modulator of the cell cycle and a negative regulator of PXR, was more highly expressed in proliferating control cells. Trypsinization of the confluent cells and replating them subconfluent resulted in a decrease in CYP3A4 and PXR expression back to levels observed in subconfluent control cells, whereas the CDK2 levels increased. Knock-down of CDK2 in proliferating control cells increased the CYP3A4 and PXR protein levels. Moreover, the CDK inhibitor roscovitine stimulated the expression of CYP3A4. A phosphorylation-deficient mutation (S350A) in the PXR protein significantly induced the CYP3A4 transcription. In conclusion, the data strongly suggest that the increased CYP3A4 expression in confluent Huh7 cells is caused by the endogenous induction of PXR as a result of cell-cell contact inhibited proliferation and subsequent decreased CDK2 activities, indicating an endogenous, non-ligand-dependent regulation of PXR and CYP3A4, possibly of physiologic and pharmacological significance.

Cyclin-dependent kinase 2 negatively regulates human pregnane X receptor-mediated CYP3A4 gene expression in HepG2 liver carcinoma cells

The human pregnane X receptor (hPXR) regulates the expression of critical drug metabolism enzymes. One of such enzymes, cytochrome P450 3A4 (CYP3A4), plays critical roles in drug metabolism in hepatocytes that are either quiescent or passing through the cell cycle. It has been well established that the expression of P450, such as CYP3A4, is markedly reduced during liver development or regeneration. Numerous studies have implicated cellular signaling pathways in modulating the functions of nuclear receptors, including hPXR. Here we report that inhibition of cyclin-dependent kinases (Cdks) by kenpaullone and roscovitine (two small molecule inhibitors of Cdks that we identified in a screen for compounds that activate hPXR) leads to activation of hPXR-mediated CYP3A4 gene expression in HepG2 human liver carcinoma cells. Consistent with this finding, activation of Cdk2 attenuates the activation of CYP3A4 gene expression. In vitro kinase assays revealed that Cdk2 directly phosphorylates hPXR. A phosphomimetic mutation of a putative Cdk phosphorylation site, Ser(350), significantly impairs the function of hPXR, whereas a phosphorylation-deficient mutation confers resistance to Cdk2. Using HepG2 that has been stably transfected with hPXR and the CYP3A4-luciferase reporter, enriched in different phases of the cell cycle, we found that hPXR-mediated CYP3A4 expression is greatly reduced in the S phase. Our results indicate for the first time that Cdk2 negatively regulates the activity of hPXR, and suggest an important role for Cdk2 in regulating hPXR activity and CYP3A4 expression in hepatocytes passing through the cell cycle, such as those in fetal or regenerating adult liver.

Usefulness of 18F-fluorodeoxyglucose positron emission tomography in differential diagnosis and staging of cholangiocarcinomas

BACKGROUND AND AIM

(18)F-Fluoro-2-deoxy-d-glucose positron emission tomography ((18)FDG-PET) is promising for diagnosis and treatment of various malignancies. The aim of this study was to evaluate the clinical usefulness of (18)FDG-PET in differential diagnosis and staging of cholangiocarcinomas according to the intrahepatic, perihilar and common bile duct lesions and to compare with computerized tomography (CT) scan.

METHODS

From January 2000 to September 2003, 54 patients with suspected cholangiocarcinoma underwent abdominal CT scan and (18)FDG-PET within a 2-week period. The PET images were analyzed visually and semiquantitatively.

RESULTS

The overall accuracy of (18)FDG-PET for discriminating malignant diseases of bile duct from benign conditions was slightly higher than that of CT scan (88.9% vs 81.5%). The sensitivity of (18)FDG-PET in perihilar cholangiocarcinoma was lower than the value of intrahepatic and common bile duct cancers (83.3% vs 91.3%, 90.9%); moreover, in cases of perihilar cancer, the sensitivity of (18)FDG-PET was lower than that of CT scans (83.3% vs 91.7%). (18)FDG-PET detected nine distant metastatic lesions not found by other imaging studies and excluded two patients who potentially had resectable condition in other imaging studies from unnecessary laparotomy.

CONCLUSION

The clinical usefulness of (18)FDG-PET in differential diagnosis of bile duct cancers is related to the site of primary disease. Although it is a helpful method for differential diagnosis especially in cases of intrahepatic and common bile duct cancers, (18)FDG-PET can not provide confirmative clues in perihilar cholangiocarcinoma. (18)FDG-PET may hold promise in the detection of hidden distant metastasis and can play an additional role in the evaluation of resectability. (18)FDG-PET can be complementary to CT scan in diagnosing and staging of cholangiocarcinoma.

Impact of dietary amino acids and polyamines on intestinal carcinogenesis and chemoprevention in mouse models

Colon cancer in humans is influenced by both genetic and dietary risk factors. The majority of colon cancers have somatic mutations in the APC (adenomatous polyposis coli) tumour-suppressor gene. Dietary arginine enhances the risk of APC-dependent colon carcinogenesis in mouse models by a mechanism involving NOS2 (nitric oxide synthase 2), as elimination of NOS2 alleles suppresses this phenotype. DFMO (difluoromethylornithine), a specific inhibitor of polyamine synthesis, also inhibits dietary arginine-induced colon carcinogenesis in C57BL/6J-Apc(Min)/J mice. The primary consequence of dietary arginine is to increase the adenoma grade in these mice. Either loss of NOS2 alleles or inhibition of polyamine synthesis suppresses the arginine-induced increase in adenoma grade. In addition to promoting intestinal carcinogenesis, polyamines can also reduce the efficacy of certain intestinal cancer chemopreventive agents. The NSAID (non-steroidal anti-inflammatory drug) sulindac is a potent inhibitor of intestinal carcinogenesis in the C57BL/6J-Apc(Min)/J mouse model and is used to treat humans with FAP (familial adenomatous polyposis). Dietary putrescine reduces the ability of sulindac to suppress intestinal tumorigenesis in the mouse model. These data suggest that reducing polyamine metabolism and dietary polyamine levels may enhance strategies for colon cancer chemoprevention.

Quantitative liver function tests in donors and recipients of living donor liver transplantation

The unique ability of the liver to regenerate quickly after resection makes living donor liver transplantation (LDLT) possible. This technique uses the unique ability of the liver to regenerate to full size after partial resection. However, the quality and course of this regeneration process in humans are still widely unexplored. In the present study we investigated the quantitative liver function tests galactose elimination capacity (GEC), indocyanine green half-life (ICG), and lidocaine half-life as markers for the quality of the liver regeneration in the first 3 months after LDLT. In this study, 22 consecutive living liver donors and their corresponding recipients were analyzed at baseline and at 10 and 90 days after LDLT. Six recipients lost their grafts during the study period. We compared donors and recipients at the different time points. After LDLT, GEC decreased (-42.6%) and ICG increased (+50.6%) significantly in donors. ICG and GEC remained significantly altered over 3 months in donors with an improvement between days 10 and 90 (GEC, +59.3%; ICG, -9.1%). ICG and GEC improved significantly in recipients between days 10 and 90 (ICG, -63.7%; GEC, +16.3%). The lidocaine half-life showed no significant changes. The donors had better test results and recovered faster than the recipients. In conclusion, after LDLT the parameters for liver capacity and flow remain altered in donors and recipients despite rapid volume growth.

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.

Effects of sildenafil citrate on hepatic function and regeneration in normal and alcohol-fed rats

Sildenafil citrate is a potent inhibitor of specific phosphodiesterase-5, which mediates metabolism of intracellular second message -- cGMP. Sildenafil citrate has been widely used for erectile dysfunction in men. Moreover, it is known that men with liver diseases have higher rate of erectile dysfunction. Furthermore, it has been demonstrated that nitric oxide plays an important role in liver function and regeneration. The present study evaluates effects of sildenafil citrate on hepatic function and regeneration in normal and alcohol-fed rats. In normal rats sildenafil citrate has a trend to improve hepatic function after partial hepatectomy (PHx). Moreover, sildenafil citrate significantly reduces hepatic regenerative activity at the concentration of 5 mg/kg body weight. However, sildenafil had no effects on hepatic function and regeneration of alcohol-fed rats. In general, sildenafil citrate did not induce significant changes in hepatic function and regenerative activity after PHx in normal and alcohol-fed rats, except at concentration of 5 mg/kg sildenafil citrate significantly inhibit hepatic regeneration in normal rats.

Review article: current management of primary sclerosing cholangitis

The management of primary sclerosing cholangitis (PSC) is hindered by incomplete understanding of the pathogenesis of the disease and the lack of good prognostic models. Few large randomized controlled trials of drug therapy have been published. Best practice in the management of PSC is currently based therefore on careful interpretation of the available evidence, close observation of individual patients and clinical experience of the disease. Drug therapy is useful for alleviating symptoms. Ursodeoxycholic acid may slow progression of the disease and reduce the frequency of complications. Consensus is emerging on the issues of screening for the malignant complications of PSC and the indications for liver transplantation are becoming broader and encompassing the earliest stages of cholangiocarcinoma. In view of the rarity of the disease in the general population, large international collaborations to study PSC are necessary to provide clearer answers in areas of uncertainty, and these are now beginning to emerge.

Pharmacokinetics of tacrolimus and mycophenolic acid are altered, but recover at different times during hepatic regeneration in rats

Hepatic regeneration is very critical to the success of living donor liver transplantation, which allows a reduced size liver to grow in size to accommodate the requirements of both the donor and the recipient. The objectives of this study were to evaluate 1) the hepatic metabolism of the two immunosuppressive drugs, tacrolimus and mycophenolic acid (MPA), and 2) the pharmacokinetics of tacrolimus and mycophenolic acid at various time points after initiation of hepatic regeneration by partial hepatectomy in rats. The hepatic intrinsic clearance of tacrolimus was decreased to 70% and 51% of the control level at the 24th h and the 6th day, respectively, but returned to normal level by day 14. The total body clearance of tacrolimus was reduced transiently but recovered completely by day 18. The hepatic intrinsic clearance of MPA was decreased to 52% and 51% of that in control rats at the 24th h and the 6th day, respectively, but recovered to normal level by day 14. The total body clearance of MPA was reduced at the 24th h but recovered by day 6. The magnitude of reduction in the clearance of tacrolimus and MPA was much smaller than what was predicted from in vitro data. The elimination clearance of MPA glucuronide was also impaired during hepatic regeneration but recovered to normal level with time. In conclusion, the pharmacokinetics of tacrolimus and mycophenolic acid were altered during hepatic regeneration but recovered completely at different rates over time. Caution must be exercised in extrapolating in vitro data to in vivo conditions during hepatic regeneration.

Role of nitric oxide increase on induced programmed cell death during early stages of rat liver regeneration

We analysed the possible cellular mechanism involved in the NO action in the balance between apoptosis and cell proliferation in liver regeneration process. We determined p53, proapoptotic protein Bax, antiapoptotic Bcl-xL, proliferating cell nuclear antigen (PCNA) and apoptotic index at the early stages of regenerative process after NO increase by lipopolysaccharide-induction (LPS) of inducible-type nitric oxide synthase (iNOS) and by direct NO donor (sodium nitroprusside, SNP). Male Wistar rats were randomised in four experimental groups: sham operated control (Sh), partial hepatectomised control (PH-C), partial hepatectomised pretreated with LPS (2 mg/kg body weight, i.p.) (PH-LPS), and partial hepatectomised pretreated with SNP (2.5 mg/kg body weight, i.v. at a rate of 1 ml/h) (PH-SNP). Animals were killed 5 h post-surgery. Hepatic cytosolic iNOS showed an increase of 34% in PH-C animals with respect to Sh, and LPS-treatment increased iNOS protein levels 30% compared with PH-C. Bax and p53 protein levels showed significant increases in LPS- and SNP-treated hepatectomised rats with respect to PH-C. The apoptotic indexes were increased 75% in both, PH-LPS and PH-SNP rats versus PH-C. The increase of NO did not show any change in the proliferation process. These results suggest that NO is involved in apoptosis via p53 and Bax proteins after PH, showing a tightly regulated growth process in liver regeneration.

Collagen sandwich culture affects intracellular polyamine levels of human hepatocytes

Extracellular matrices, like collagen layers, play an important role in preventing dedifferentiation of hepatocytes in long-term culture experiments. It has also been shown that polyamines are crucial for cell growth and liver differentiation - regeneration. Primary cultured hepatocytes with their low mitotic activity might be a valuable tool in studying the role of polyamines in differentiation. Here, our goal was to investigate whether an extracellular cell culture matrix can influence intracellular polyamine levels in human hepatocytes during long-term culture. Primary human hepatocytes were isolated from surgical tissue resections and were maintained either in single collagen (SG) or double collagen gel (DG) layer (sandwich) culture systems. Cell viability and function were examined and intracellular polyamine levels were measured using a highly sensitive high performance liquid chromatography (HPLC) method. Hepatocytes showed high viability in both culture systems used, but albumin secretion was diminished in SG cultured hepatocytes after 14 days. In general, total intracellular polyamine levels of hepatocytes decreased markedly in both SG and DG within the first days of culture, but remained constant until day 21 with a SG/DG ratio of about 1.4. Individual polyamines levels were dependent on the culture time and system, where spermine decreased and putrescine increased in both SG and DG over time (day 14), but spermidine increased only in DG. Our results suggest that polyamine levels, in particular putrescine, might be important regulators of hepatocyte specific function in vitro and therefore serve as a marker of differentiation for cultivated human hepatocytes.

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.

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.

Nitric oxide release and enhancement of lipid peroxidation in regenerating rat liver

BACKGROUND/AIMS

Clarification of the role of lipid peroxidation in the onset of liver proliferation has been hampered by the fact that both higher and lower lipid peroxidation have been reported after two-thirds partial hepatectomy. Recently, it has been shown that nitric oxide might be involved in the control of early responses after partial hepatectomy. We analysed the possible involvement of nitric oxide production in lipid peroxidation levels during liver regeneration.

METHODS

Sham-operated, hepatectomised and sham and hepatectomised rats pretreated with two inhibitors of oxide nitric synthesis (aminoguanidine or N(G)-monomethyl-L-arginine) were used throughout. Animals were killed at 1, 3, 5 and 15 h after surgery. Cytosolic superoxide dismutase and microsomal-lysosomal catalase activities were measured. Lipid peroxidation levels were measured as thiobarbituric acid-reactive substances and conjugated dienes. Cytosolic nitrate (a stable metabolic product of nitric oxide) was enzymatically determined. Inducible-type nitric oxide synthase (iNOS) was analysed in hepatic cytosol by immunoblotting. DNA synthesis 24 and 48 h after surgery was assessed by [3H]thymidine incorporation.

RESULTS

Increased lipid peroxidation was found in total homogenate, cytosol and microsomes. The hepatic cytosolic content of nitrates increased, reaching the highest values at 5 h posthepatectomy. Aminoguanidine or N(G)-monomethyl-L-arginine pretreatment blocked the rise of nitric oxide production and lipid peroxidation levels and decreased the DNA synthesis. The increase in hepatic iNOS protein expression at 5 h after partial hepatectomy disappeared with aminoguanidine pretreatment.

CONCLUSIONS

Our experiments suggest that nitric oxide plays a role in the proliferation mechanism, although it is responsible, at least in part, for the enhanced lipid peroxidation.

Acute effects of griseofulvin on the pharmacokinetics and pharmacodynamics of warfarin in rats

It has been reported that prothrombin time (PT), which is prolonged by warfarin, is reduced when patients on warfarin also take griseofulvin repeatedly. We investigated the cause of the drug interaction and the initial effects of griseofulvin on warfarin pharmacokinetics. Total cytochrome P-450, and the activities of aminopyrine N-demethylase, aniline p-hydroxylase and 7-ethoxycoumarin O-deethylase, after repeated administration of griseofulvin (100 mg/kg orally daily for 5 days) were examined. Acute effects of single doses of griseofulvin (100 mg/kg) on coagulation activity (prothrombin time) and warfarin pharmacokinetics after administration of warfarin were also studied. Repeated administration of griseofulvin induced warfarin-metabolizing enzymes. In contrast, a single administration of griseofulvin increased prothrombin time and serum warfarin concentrations. The activity of a warfarin-metabolizing enzyme (7-ethoxycoumarin O-deethylase) was reduced when griseofulvin was added to rat liver microsomes. The results suggest that reduced warfarin action after repeated administration of griseofulvin may be due to induction of warfarin-metabolizing enzymes, but that there is also an initial increase in warfarin action.