Induction of Human UDP-glucuronosyltransferase 1A1 by Cortisol-GR

During the course of the study of UGT1A1 induction by bilirubin, we could not detect the induction of the reporter gene (−3174/+14) of human UGT1A1 in HepG2 by bilirubin (Mol. Biol. Rep. 31: 151–158 (2004)). In this report, we show the finding of the induction of the reporter gene of UGT1A1 by cortisol at 1 μM, a major natural cortico-steroid, with human glucocorticoid receptor (GR). RU486 of a typical GR antagonist at 10 μM inhibited the induction by cortisol from 5.9- to 1.8-fold. This result indicates that the induction by cortisol-GR is dependence on ligand-binding. This induction is caused by the UGT reporter gene itself, from the results of noinduction with control vector pGL2 (equal to pGV-C) in the presence of cortisol-GR. We confirmed that the induction of the reporter gene by cortisol is dependent on the position of proximal element (−97/−53) of UGT1A1. From this result, we concluded that the increase of corticosteroid in neonates must induce the elevation of UGT1A1 after birth and prevent jaundice. With the study of induction by corisol, we studied the influence of co-expression of PXR (pregnenolone xenobiotic receptor) with the UGT1A1 reporter gene and we could not find the induction of UGT1A1 expression in the presence of dexamethasone, rifampicin, or pregnenolone 16α-carbonitrile of the PXR ligands. These results suggest that the induction of UGT1A1 expression by GR is not mediated by PXR, unlike the induction of CYP3A4 through PXR.     

Effect of JBP485 on obstructive jaundice is related to regulation of renal Oat1, Oat3 and Mrp2 expression in ANIT-treated rats

The objective was to determine whether protective effects of JBP485 on biliary obstruction induced by alpha-naphthylisothiocyanate (ANIT) are mediated by the organic anion transporters Oat1, Oat3 and the multidrug resistance-associated protein Mrp2. The ANIT-induced increases in bilirubin (BIL), alanine aminotransferase (ALT) and aspartate transaminase (AST) in rat serum were inhibited significantly by oral administration of JBP485. The plasma concentration of JBP485 which is the substrate of Oat1 and Oat3 determined by LC–MS/MS was markedly increased after intravenous administration in ANIT-treated rats, whereas cumulative urinary excretion of JBP485 in vivo and the uptake of JBP485 in kidney slices were decreased remarkably. RT-PCR and Western blot showed the decreased expression of Oat1 and Oat3, increased expression of Mrp2 in ANIT-induced rats, meanwhile, the expression levels of Mrp2 and Oat1 were up-regulated after administration of JBP485. The up-regulation of Mrp2 and Oat1 was associated with a concomitant increase in urinary BIL after treatment with JBP485 in ANIT-treated rats. The mechanism for JBP485 to restore liver function might be related to improvement of the expression and function for Oat1 and Mrp2 as well as facilitation of urinary excretion for hepatoxic substance.     

The novel heme oxygenase-like protein from Plasmodiumfalciparum converts heme to bilirubin IXα in the apicoplast

The metabolic pathways in apicoplasts of human malaria parasites are promising drug targets. The apicomplexan parasites exhibit delayed cell death when their apicoplast is impaired, but the metabolic pathways within apicoplasts are poorly understood. A nuclear-encoded heme oxygenase (HO)-like protein with an apicoplast-targeted bipartite transit peptide was identified in the Plasmodiumfalciparum genome. Purified mature recombinant PfHO protein converted heme into bilirubin IXα as confirmed by high-performance liquid chromatography. In addition, PfHO required an iron chelator such as deferoxamine for complete activity. These observations lead to the conclusion that a novel enzymatic heme degradation system is present in human malaria parasites.     

Optimization of mass transfer for toxin removal and immunoprotection of hepatocytes in a bioartificial liver

This study was designed to determine optimal operating conditions of a bioartificial liver (BAL) based on mass transfer of representative hepatotoxins and mediators of immune damage. A microprocessor‐controlled BAL was used to study mass transfer between patient and cell compartments separated by a hollow fiber membrane. Membrane permeability (70, 150, or 400 kDa molecular weight cut‐off—MWCO), membrane convection (high: 50 mL/min; medium: 25 mL/min; low: 10 mL/min; diffusion: 0 mL/min), and albumin concentration in the cell compartment (0.5 or 5 g%) were considered for a total of 24 test conditions. Initially, the patient compartment contained pig plasma supplemented with ammonia (0.017 kDa), unconjugated bilirubin (0.585 kDa), conjugated bilirubin (0.760 kDa), TNF‐α (17 kDa), pig albumin (67 kDa), pig IgG (147 kDa), and pig IgM (900 kDa). Mass transfer of each substance was determined by its rate of appearance in the cell compartment. Membrane fouling was assessed by dextran polymer technique. Of the three tested variables (membrane pore size, convection, and albumin concentration), membrane permeability had the greatest impact on mass transfer (P < 0.001). Mass transfer of all toxins was greatest under high convection with a 400 kDa membrane. Transfer of IgG and IgM was insignificant under all conditions. Bilirubin transfer was increased under high albumin conditions (P = 0.055). Fouling of membranes ranged from 7% (400 kDa), 24% (150 kDa) to 62% (70 kDa) during a 2‐h test interval. In conclusion, optimal toxin removal was achieved under high convection with a 400‐kDa membrane, a condition which should provide adequate immunoprotection of hepatocytes in the BAL. Biotechnol. Bioeng. 2009; 104: 995–1003. © 2009 Wiley Periodicals, Inc.     

Effect of selenium-enriched malt on hepatocarcinogenesis, paraneoplastic syndrome and the hormones regulating blood glucose in rats treated by diethylnitrosamine

233 SD rats weighing 100 approximately 120 g were divided randomly into 6 groups. The animals in group I and group II received 0.1 mg/kg selenium in the form of sodium selenite only and served as the negative control and positive control, respectively. Animals in groups III, IV and V were fed with selenium as Se-enriched malt supplemented diets (0.3, 1 and 3 mg/kg), and group VI with selenium by using sodium selenite supplemented diets (3 mg/kg). Animals of groups II approximately VI were induced hepatoma by diethylnitrosamine (100 mg/l) for 16 weeks, then drunk with sterilized water for 2 more weeks. Subsequently, the effects of Se-enriched malt and sodium selenite on hepatoma nodules, relative liver weight, the liver function indices including alanine aminotransferase (ALT), alkaline phosphatase (ALP), albumin (ALB), total bilirubin (TBIL), and the tumor markers, named as gamma-glutamyltranspeptidase (GGT), alpha-fetoprotein (AFP), insulin-like growth factor-II (IGF-II) were recorded. The calcium concentration, glucose content in plasma and values of the hormones regulating blood glucose, such as insulin, glucagons and thyroid hormones (3,5,3'-tetraiodothyronine, T(3); 3,5,3'5'-tetraiodothyronine, T(4)) were observed as well. At the same time, the correlations between the concentration of plasma glucose and related hormones were also analyzed. The results indicated that Se-enriched malt showed a better chemopreventive efficiency in decreasing the number of hepatoma nodules, relative liver weight and the contents of AFP, GGT, IGF-II, ALT, ALP and TBIL in the plasma, and delaying the descent of hormones in the serum, names as insulin, glucagons, T(3) and T(4) than those feeding with sodium selenite. Effect of Se-enriched malt excelled sodium selenite in the aspects of deadening the descent of glucose concentration in the plasma and the rise of calcium concentration in the serum of the rats with hepatoma induced by diethylnitrosamine. The values of glucose and calcium were significantly related to those items fore-named. In conclusion, the function of Se-enriched malt in deadening the lesion and delaying the development of hepatoma of rats induced by diethylnitrosamine was better than that of sodium selenite. Hypoglycemia and hypercalcemia were significantly correlated with the multifactors mentioned above.     

Skewed ratios between CD3(+) T cells and monocytes are associated with poor prognosis in patients with HBV-related acute-on-chronic liver failure

Tempering of the innate immune response by T lymphocytes has been demonstrated to play a critical role in protecting animals from inflammation-induced death; however, its role in humans remains unknown. Patients with HBV-related acute-on-chronic liver failure (ACLF) share a striking similarity to the inflammatory response in septic shock where a hyperactive innate response is observed. The present study attempted to characterize the features of CD3⁺ T cells and monocytes and evaluate their clinical implications in 55 patients with HBV-related ACLF, 30 patients with chronic hepatitis B (CHB) and 30 healthy controls (HC). We found that the ratio between circulating CD3⁺ T cells and monocytes (T/M) was decreased in ACLF patients, due to decreased CD3 counts and increased monocyte counts compared with CHB and HC subjects. We also found that the T/M ratios were decreased from the early to the intermediate stage and reached the lowest value at the late stage in ACLF patients. Analyses with clinical parameters revealed that T/M ratios were negatively correlated with the Model for End-Stage Liver Disease Score and direct bilirubin, and positively correlated with prothrombin activity. Moreover, increased T/M ratios were observed in patients with good prognosis, but not in patients with a poor outcome; and ACLF patients who received liver transplantation exhibited an increased T/M ratio. Importantly, we found that programmed death-1 receptor (PD-1) was drastically upregulated on both CD4⁺ T and CD8⁺ T cells in ACLF, which at least in part contributed to the T-cell loss in these patients. Mechanically, the in vitro co-culture assay revealed that both CD4⁺ T and CD8⁺ T cells, as well as regulatory T cells, could inhibit TNF-α secretion by monocytes. In addition, the TNF-α levels in ACLF serum were negatively correlated with T/M ratios. In conclusion, our study identified the novel potential role of T/M ratio in predicting disease progression and provided novel evidences for further studies of the immunopathogenesis in ACLF.     

Direct electron transfer from graphite and functionalized gold electrodes to T1 and T2/T3 copper centers of bilirubin oxidase

Direct electron transfer (DET) from bare spectrographic graphite (SPGE) or 3-mercaptopropionic acid-modified gold (MPA-gold) electrodes to Trachyderma tsunodae bilirubin oxidase (BOD) was studied under anaerobic and aerobic conditions by cyclic voltammetry and chronoamperometry. On cyclic voltammograms nonturnover Faradaic signals with midpoint potentials of about 700 mV and 400 mV were clearly observed corresponding to redox transformations of the T1 site and the T2/T3 cluster of the enzyme, respectively. The immobilized BOD was differently oriented on the two electrodes and its catalysis of O₂-electroreduction was also massively different. On SPGE, where most of the enzyme was oriented with the T1 copper site proximal to the carbon with a quite slow ET process, well-pronounced DET-bioelectroreduction of O₂ was observed, starting already at > 700 mV vs. NHE. In contrast, on MPA-gold most of the enzyme was oriented with its T2/T3 copper cluster proximal to the metal. Indeed, there was little DET-based catalysis of O₂-electroreduction, even though the ET between the MPA-gold and the T2/T3 copper cluster of BOD was similar to that observed for the T1 site at SPGE. When BOD actively catalyzes the O₂-electroreduction, the redox potential of its T1 site is 690 mV vs. NHE and that of one of its T2/T3 copper centers is 390 mV vs. NHE. The redox potential of the T2/T3 copper cluster of a resting form of BOD is suggested to be about 360 mV vs. NHE. These values, combined with the observed biocatalytic behavior, strongly suggest an uphill intra-molecular electron transfer from the T1 site to the T2/T3 cluster during the catalytic turnover of the enzyme.     

Crystal structure of a biliverdin IXalpha reductase enzyme-cofactor complex

Biliverdin reductase (BVR) catalyzes the last step in heme degradation by reducing the gamma-methene bridge of the open tetrapyrrole, biliverdin IXalpha, to bilirubin with the concomitant oxidation of a beta-nicotinamide adenine dinucleotide (NADH) or beta-nicotinamide adenine dinucleotide phosphate (NADPH) cofactor. Bilirubin is the major bile pigment in mammals and has antioxidant and anticompliment activity. We have determined X-ray crystal structures of apo rat BVR and its complex with NADH at 1.2 A and 1.5 A resolution, respectively. In agreement with an independent structure determination of the apo-enzyme, BVR consists of an N-terminal dinucleotide-binding domain (Rossmann-fold) and a C-terminal domain that contains a six-stranded beta-sheet that is flanked on one face by several alpha-helices. The C-terminal and N-terminal domains interact extensively, forming the active site cleft at their interface. The cofactor complex structure reported here reveals that the cofactor nicotinamide ring extends into the active site cleft, where it is adjacent to conserved amino acid residues and, consistent with the known stereochemistry of the reaction catalyzed by BVR, the si face of the ring is accessible for hydride transfer. The only titratable side-chain that appears to be suitably positioned to function as a general acid in catalysis is Tyr97. This residue, however, is not essential for catalysis, since the Tyr97Phe mutant protein retains 50% activity. This finding suggests that the dominant role in catalysis may be performed by hydride transfer from the cofactor, a process that may be promoted by proximity of the invariant residues Glu96, Glu123, and Glu126, to the nicotinamide ring.     

Inhibition of secretory phospholipase A2 enzyme by bilirubin: A new role as endogenous anti-inflammatory molecule

Bilirubin is a powerful antioxidant that suppresses the inflammatory process. However its interaction with proinflammatory PLA₂ enzyme is not known. Inhibition of several secretory phospholipase A₂ (sPLA₂) enzyme activities by bilirubin was studied using ¹⁴C-oleate labeled Escherichia coli as substrate. Bilirubin inhibits purified sPLA₂ enzyme from Vipera russellii and Naja naja venom and partially purified sPLA₂ enzymes from human ascitic fluid, pleural fluid and normal serum in a dose dependent manner. IC₅₀ values calculated for these enzymes ranges from 1.75 to 10.5 μM. Inflammatory human sPLA₂ enzymes are more sensitive to inhibition by bilirubin than snake venom sPLA₂s. Inhibition of sPLA₂ activity by bilirubin is independent of calcium concentration. Increasing substrate concentration (upto 180 nmol) did not relieve the inhibition of sPLA₂ by bilirubin and it is irreversible. Bilirubin quenched the relative fluorescence intensity of sPLA₂ in a dose dependent manner in the same concentration range at which in vitro sPLA₂ inhibition was observed. In the presence of bilirubin, apparent shift in the far UV-CD spectra of sPLA₂ was observed, indicating a direct interaction with the enzyme. Inhibition of sPLA₂ induced mouse paw edema by bilirubin confirms its sPLA₂ inhibitory activity in vivo also. These findings indicate that inhibition of sPLA₂ by bilirubin is mediated by direct interaction with the enzyme and bilirubin may act as an endogenous regulator of sPLA₂ enzyme activity.     

Effects of some biologically active compounds on phagosome-lysosome fusion in peritoneal macrophages of mice.

Effects of biologically active compounds bilirubin (BR), farmorubicin (FR), and chelerythrine (CR) on phagosome-lysome (P-L) fusion in mouse peritoneal macrophages were studied using fluorescent dye acridine orange as lysosomal labelling and yeast cells as target. It was found that all three compounds tested enhanced P-L fusion. To investigate mechanisms of these effects, changes in fluidity of rat liver lysosomal membranes under influence of BR, FR and CR were studied by measuring fluorescence intensity, lifetime, and polarization of DPH or TMA-DPH incorporated in isolated rat liver lysosomes. In order to characterize the cytoskeleton changes under the action of these biologically active compounds F-actin content in peritoneal macrophages of mice was determined. Our results demonstrate that BR action induces a decrease in DPH and TMA-DPH polarization, FR increases DPH and TMA-DPH polarization, and CR causes only an increase in TMA-DPH polarization in lysosomal membranes. All three compounds tested increase F-actin content in peritoneal macrophages. Thus, the effect of BR on P-L fusion is connected with increasing fluidity of lysosomal membranes and the cytoskeleton changes. The enhancement of P-L fusion under the action of FR and CR can most likely be explained by changes of the cytoskeleton state.