Cytochrome P450IA2 and aromatic L-amino acid decarboxylase are hepatic autoantigens in autoimmune polyendocrine syndrome type I

Autoimmune chronic active hepatitis (AI-CAH) is a feared component of autoimmune polyendocrine syndrome type I (APS I). In this study, immunoreactivity was assessed in sera from eight APS I patients, of whom three had AI-CAH, in an attempt to identify hepatic autoantigens. We performed indirect immunofluorescence staining of human and rat liver sections, Western blots on subcellular fractions of human and rat liver, immunoprecipitations of labelled aromatic L-amino acid decarboxylase (AADC) and cytochrome P450IA2 (CYP IA2) expressed by an in vitro transcription and translation system and studies of enzymatic activity. Autoantibodies against AADC were present in sera from all eight APS I patients, while immunoreactivity against CYP IA2 was only found in sera from the three APS I patients with AI-CAH. Enzymatic activity of CYP IA2 was inhibited by sera from APS I patients with AI-CAH but not by control sera. Our results show that CYP IA2 and AADC constitute hepatic autoantigens in patients with APS I and that immunoreactivity against CYP IA2 is associated with the presence of AI-CAH.

Pharmacological aspects of pentoxifylline with emphasis on its inhibitory actions on hepatic fibrogenesis

1. Pentoxifylline (PTX), a derivative of the methylxanthine theobromine, has been used for many years in the treatment of peripheral vascular diseases. Increased red blood cell flexibility, reduction of blood viscosity, and decreased potential of platelet aggregation are the basic actions of PTX, resulting in therapeutic benefits due to improved microcirculation and tissue oxygenation. 2. PTX's generally accepted mechanism of action is the inhibition of phosphodiesterases, leading to increased intracellular levels of cyclic adenosine monophosphate (cAMP). 3. A number of studies have shown PTX's effects on the cytokine network. The most relevant clinical results are the therapeutic benefits of PTX in attenuating the effects of tumor necrosis factor-alpha (TNF-alpha) in conditions such as septic shock. 4. PTX also has been found to exert antifibrogenic actions, using cultured fibroblasts or animal models of fibrosis, including liver fibrosis. 5. In hepatic stellate cell culture PTX has been shown to inhibit the basic reactions of liver fibrogenesis, being effective on cytokines and growth factors relevant in fibrogenesis of the liver, too. 6. Therefore, PTX might be an effective drug with few side effects in the treatment of liver fibrosis. Further clinical studies have to be done to establish the real therapeutic benefits of PTX in liver fibrosis and cirrhosis.

Protective effect of fructose on survival and metabolic capacities of hepatocytes kept overnight under cold hypoxia before normothermic reoxygenation

The protective effect of fructose with regard to hypoxia-induced cell injury in overnight cold preserved hepatocytes (20 hr at 4 degrees C) was investigated. The addition of fructose (at 10 and 20 mM) resulted in an improved survival of hepatocytes during their normothermic (37 degrees C) reoxygenation, irrespective of the time of fructose addition before the onset of hypoxia (i.e. 10, 20 or 30 min). Such a protective effect was even higher than that observed when hepatocytes were incubated in the University of Wisconsin solution (UW). Moreover, neither Desferal (an iron chelator) nor adenosine (an ATP precursor), nor other carbohydrates (glucose, galactose and the antioxidant mannitol) were able to protect cells against such an hypoxia-mediated injury. The intracellular ATP content was lower in both adenosine- and fructose-treated hepatocytes than in control untreated cells. However, the cellular metabolic capacities such as protein synthesis and gluconeogenesis from lactate recovered faster during reoxygenation of previously hypoxic fructose-treated cells compared with both control and adenosine-treated cells.

The role of xenobiotic metabolizing enzymes in arylamine toxicity and carcinogenesis: functional and localization studies

In both animal models and humans, the first and obligatory step in the activation of arylamines is N-hydroxylation. This pathway is primarily mediated by the phase-I enzymes CYP1A1, CYP1A2 and CYP4B1. In the presence of flavonoids such as alpha-naphthoflavone and flavone, both CYP3A4 and CYP3A5 have also been shown to play a minor role in the activation of food-derived heterocyclic amines. The further activation of N-hydroxyarylamines by phase-II metabolism can involve both N, O-acetylation and N, O-sulfonation catalyzed by N-acetyltransferases (NAT1 and NAT2) and sulfotransferases, respectively. Using an array of techniques, we have been unable to detect constitutive CYP1A expression in any segments of the human gastrointestinal tract. This is in contrast to the rabbit where CYP1A1 protein was readily detectable on immunoblots in microsomes prepared from the small intestine. In humans, CYP3A3/3A4 expression was detectable in the esophagus and all segments of the small intestine. Northern blot analysis of eleven human colons showed considerable heterogeneity in CYP3A mRNA between individuals, with the presence of two mRNA species in some subjects. Employing the technique of hybridization histochemistry (also known as in situ hybridization), CYP4B1 expression was observed in some human colons but not in the liver or the small intestine. Hybridization histochemistry studies have also demonstrated variable NAT1 and NAT2 expression in the human gastrointestinal tract. NAT1 and NAT2 mRNA expression was detected in the human liver, small intestine, colon, esophagus, bladder, ureter, stomach and lung. Using a general aryl sulfotransferase riboprobe (HAST1), we have demonstrated marked sulfotransferase expression in the human colon, small intestine, lung, stomach and liver. These studies demonstrate that considerable variability exists in the expression of enzymes involved in the activation of aromatic amines in human tissues. The significance of these results in relation to a role for heterocyclic amines in colon cancer is discussed.

Evidence that "myofibroblast-like" cells are the cellular source of capsular collagen in hepatocellular carcinoma

BACKGROUND/AIMS

The prognosis for patients with hepatocellular carcinoma is poor although tumour encapsulation has been associated with improved survival and disease-free rates. While the source of the tumour capsule is unclear, the major role that activated hepatic stellate cells play in the deposition of liver matrix in normal and diseased states suggests the possible involvement of these cells in tumour encapsulation.

METHODS

Twenty-four liver tumours (seven encapsulated HCC, seven non-encapsulated HCC, 10 colorectal metastases) were studied. Activated hepatic stellate cells were identified by immunohistochemistry for alpha-smooth muscle actin (alpha-SMA) and in situ hybridization for pro-collagen alpha1 (I) mRNA. Collagen deposition was localized using Masson's trichrome stain.

RESULTS

Pro-collagen alpha1 (I) mRNA co-localized to alpha-SMA positive hepatic stellate cells within the region of increased collagen deposition in (i) the tumour capsule of encapsulated HCC, and (ii) the tumour junction of non-encapsulated HCC and colorectal metastasis. In addition, there was marked peritumour expression of alpha-SMA and procollagen alpha1 (I) mRNA, which diminished with distance away from the tumour in all tumour groups. The degree of expression was greatest with encapsulated HCC, less with non-encapsulated HCC and least with colorectal metastasis. This contrasted with the absence of alpha-SMA expression in normal liver from the same patients. Within the tumours, colorectal metastases differed from HCC by demonstrating marked alpha-SMA expression and collagen deposition in the septa.

CONCLUSIONS

Our findings demonstrate that activated hepatic stellate cells (i) are responsible for increased peritumour collagen production in non-encapsulated HCC and colorectal metastasis, and (ii) may be implicated in tumour capsule formation in HCC and metastasis stroma development. Thus, stellate cells may influence the local hepatic invasion by these tumours.

The hepatic stellate (Ito) cell: its role in human liver disease

The hepatic stellate (Ito) cell lies within the space of Disse and has a variety of functions. Stellate cells store vitamin A in characteristic lipid droplets. In the normal human liver, the cells can be identified by the presence of these lipid droplets; in addition, many stellate cells in the normal liver express alpha-smooth muscle actin. In acute liver injury, there is an expansion of the stellate cell population with increased alpha-smooth muscle actin expression; stellate cells appear to play a role in extracellular matrix remodelling after recovery from injury. In chronic liver injury, the stellate cell differentiates into a myofibroblast-like cell with marked expression of alpha-smooth muscle actin and occasional expression of desmin. Myofibroblast-like cells have a high fibrogenic capacity in the chronically diseased liver and are also involved in matrix degradation. In vitamin A intoxication, hypertrophy and proliferation of the stellate and myofibroblast-like cells may lead to non-cirrhotic portal hypertension, fibrosis and cirrhosis. In liver tumours, myofibroblast-like cells are involved in the capsule formation around the tumour and in the production of extracellular matrix within it. The transition of stellate cells into myofibroblast-like cells is regulated by an intricate network of intercellular communication between stellate cells and activated Kupffer cells, damaged hepatocytes, platelets, endothelial and inflammatory cells, involving cytokines and nonpeptide mediators such as reactive oxygen species, eicosanoids and acetaldehyde. The findings suggest that the stellate cell plays an active role in a number of human liver diseases, with a particular reactivity pattern in fibrotic liver disorders.

Hepatic stellate cells (Ito cells) but not collagen IV may partly be responsible for lower portal pressure after reversing secondary biliary cirrhosis in the rat

BACKGROUND/AIMS

Chronic bile duct obstruction in the rat leads to biliary cirrhosis and portal hypertension. Biliary decompression with Rouxen-Y choledocho-jejunostomy (RY) reverses most but not all of these changes. The aim of the present study was to determine whether hepatic stellate cells, as a main source of extracellular matrix proteins, participate in this process.

METHODS

Sprague-Dawley rats were allocated to one of three groups: Bile duct ligation (BDL) for 3 weeks, BDL followed by RY and sham-operated animals as controls (SHAM). At the end of the experimental period, portal pressure was measured, livers subjected to random sampling and hepatocytes, bile ducts/ductules, hepatic stellate cells and collagen IV determined stereologically. Hepatic stellate cells and collagen IV were characterized immunohistochemically with an antibody against desmin and collagen IV, respectively.

RESULTS

Volume fraction of hepatocytes decreased from 65.6 +/- 5.3 in sham-operated animals to 27.9 +/- 8.8% in bile duct ligated animals (p < 0.05). In contrast, volume fraction of bile ducts/ductules increased from 0.4 +/- 0.2 in sham-operated animals to 25.3 +/- 8.6% in bile duct ligated ones; similarly, hepatic stellate cells increased from 0.4 +/- 0.2 in sham-operated animals to 2.6 +/- 0.9% in bile duct ligated ones (p < 0.01) and collagen IV from 10.0 +/- 2.3 in sham-operated animals to 24.5 +/- 8.0% (p < 0.01) in bile duct ligated animals. These changes were partially reversed by Roux-en-Y choledocho-jejunostomy; hepatocytes, bile ducts/ductules, hepatic stellate cells and collagen IV averaging 54.8 +/- 13.1, 6.1 +/- 6.8, 1.6 +/- 0.6 and 14.5 +/- 3.6%, respectively (p < 0.05 RY vs. BDL). Portal pressure in sham-operated animals, bile duct ligated animals and those with a Roux-en-Y choledocho-jejunostomy averaged 13.4 +/- 0.7, 20.1 +/- 2.7 and 16.9 +/- 1.6 cm H2O, respectively, and correlated significantly with the volume fraction of hepatic stellate cells (rS = 0.96; p < 0.001) and less with collagen IV (rS = 0.61; p < 0.007). However, by stepwise regression, collagen IV did not significantly add to the ability of the equation to predict portal pressure.

CONCLUSIONS

These results lend further support to the notion that hepatic stellate cells are prominently involved in fibrogenesis and in the reversibility of these changes, but hepatic stellate cells do not completely revert to normal even 4 weeks after successful decompression. Furthermore, our data suggest that hepatic stellate cells may be related to maintenance of portal hypertension.

Cyclosporine therapy affects aminotransferase activity but not hepatitis C virus RNA levels in chronic hepatitis C

Interferon (IFN) therapy is of proven efficacy in chronic hepatitis C, but it is not universally effective and is often limited by side effects. Cyclosporine A (CsA) is a potent immunosuppressant widely used in organ transplantation. We conducted a pilot study to determine whether CsA therapy could affect aminotransferase activity and hepatitis C virus RNA levels in patients with chronic hepatitis C. Cyclosporine A was administered to 10 patients (mean age of 59 years; male:female = 9:1) who did not respond to IFN therapy previously and who had elevated serum alanine aminotransferase (ALT) values for at least 6 months. All patients were positive for HCV-RNA by RT-PCR with genotype 1b. Their mean duration of hepatitis was 15 years. Oral CsA was given for 3 months in a dose that was increased at 1 month intervals from 1.5-2.0 to 2.0-3.0 and 3.0-4.0 mg/kg per day. All patients completed the treatment schedule, although two patients developed mild non-symptomatic hypertension. Serum ALT levels gradually decreased in all but one patient. The mean percentage decrease was 59.5% at the end of therapy (from 153 +/- 82 to 62 +/- 48 IU/L; P < 0.02). The ALT levels fell to the normal range in five patients, although once therapy was discontinued the enzyme levels tended to return to pretreatment levels. Serum aspartate aminotransferase and g-glutamyl transpeptidase levels similarly decreased. The serum HCV-RNA titre, determined by competitive RT-PCR, did not change in any patient throughout the study period. There were no appreciable alterations in other laboratory tests, such as serum creatinine levels and lymphocyte subsets, except for an increase in serum alkaline phosphatase levels. These findings suggest that CsA, even in a relatively low dose, reduces serum aminotransferase levels without serious side effects in patients with chronic hepatitis C, although an antiviral effect was not noted.

Bromodeoxyuridine: a diagnostic tool in biology and medicine, Part III. Proliferation in normal, injured and diseased tissue, growth factors, differentiation, DNA replication sites and in situ hybridization

This paper is a continuation of parts I (history, methods and cell kinetics) and II (clinical applications and carcinogenesis) published previously (Dolbeare, 1995 Histochem. J. 27, 339, 923). Incorporation of bromodeoxyuridine (BrdUrd) into DNA is used to measure proliferation in normal, diseased and injured tissue and to follow the effect of growth factors. Immunochemical detection of BrdUrd can be used to determine proliferative characteristics of differentiating tissues and to obtain birth dates for actual differentiation events. Studies are also described in which BrdUrd is used to follow the order of DNA replication in specific chromosomes, DNA replication sites in the nucleus and to monitor DNA repair. BrdUrd incorporation has been used as a tool for in situ hybridization experiments.

Fast determination of low-level cytochrome P-450 1A1 activity by high-performance liquid chromatography with fluorescence or visible absorbance detection

A method to determine the activity of the cytochrome P-450 1A1 enzyme, by measuring 7-ethoxyresorufin-O-deethylase (EROD) activity using high-performance liquid chromatography (HPLC) with fluorescence or with visible absorbance detection of resorufin, is described. The lowest quantifiable activity (0.2 pmol/mg min) is obtained by incubation of 0.3 mg of human duodenal microsomal proteins using HPLC fluorescence detection. Using HPLC with visible absorbance detection, sensivity was ten times lower. However, the equipment for this last method is available in most laboratories. The use of both HPLC assays allows determination of the low EROD activity level in samples of small size, such as two or three human duodenal biopsies obtained by routine endoscopy. These methods will be a useful tool to study the role of drug intestinal metabolism by cytochrome P-450 1A1.

Transforming growth factor beta (TGF-beta) expression in isolated and cultured rat hepatocytes

It is still a subject of debate whether hepatocytes have the ability to express TGF-beta. Therefore, we investigated in freshly isolated and in monolayer cultures of rat hepatocytes the expression of TGF-beta isoform s at the RNA and protein level applying RT-PCR, immunocytochemistry, immunoblotting, and functional assays of TGF-beta. TFG-beta 1, -beta 2, and -beta 3 transcripts were detected in cultured cells, and the level of m RNA increased up to 48/72 h, but TGF-beta 1 transcripts were absent in freshly isolated cells. Using APAAP stainings the proteins of all three TGF-beta isoforms were observed in hepatocyte cultures from 5-96 h, but in hepatocytes in the liver in situ and in freshly isolated cell suspensions TGF-beta staining was negative. SDS-PAGE under reducing conditions followed by Western blotting detected in cell lysates the subunit of mature TGF-beta at about 13 kd. Analysis of TGF-beta bioactivity with the mink cell (Mv1Lu) proliferation inhibition assay and competitive radioligand assay confirmed in activated (i.e., acidified and subsequently neutralized) hepatocyte-conditioned media the presence of TGF-beta, which, however, is almost entirely in the latent form. It is concluded that TGF-beta can be expressed in cultured hepatocytes and that the level of expression is quickly upregulated under abnormal, not yet known, microenvironmental conditions.

Characterization of insulin-like growth factor (IGF)-I-receptor binding sites during in vitro transformation of rat hepatic stellate cells to myofibroblasts

Insulin-like growth factors are growth-promoting peptides structurally related to insulin which possess autocrine and paracrine activities. IGF-I is mainly synthesized in hepatocytes, but little is known about its paracrine action on hepatocyte-adjacent perisinusoidal hepatic stellate cells, the principal matrix producing precursor cell type in the liver. IGF-I might stimulate proliferation and phenotypical transformation of hepatic stellate cells into myofibroblasts, the cell type responsible for the excessive production of connective tissue elements during fibrogenesis. In this study we investigated the expression and function of the IGF-I receptor during transformation of isolated and cultured hepatic stellate cells. The respective stages of transformation of hepatic stellate cells were defined by determination of cellular smooth muscle iso-alpha-actin and retinyl-palmitate content, respectively. IGF-I receptor protein decreased stage-dependently down to 0.5 at the 4th day and about 0.17 at the 8th day. The number of IGF-I receptors was determined to be initially 1.3 x 10(5)/cell. Their quantity decreased to 0.8 x 10(5) sites/cell (4th day) down to 0.5 x 10(5) sites/cell at the 7th day and remained constant thereafter at 0.7 x 10(5) sites/cell. Dissociation constants (KD) for IGF-I range from 0.32-0.57 nmol/l showing constantly high receptor affinity. Northern blot analyses revealed distinct upregulation of IGF-I receptor mRNA level during culture. It is concluded that hepatocyte-generated IGF-I and/or IGF-I binding proteins are candidate mediators of hepatic stellate cell activation during the initial period of transformation to myofibroblasts. After completion of transformation the cell becomes relatively refractory to the action of IGF-I as judged from receptor density.

Localization of cytochromes P450 in human tissues: implications for chemical toxicity

Cytochromes P450 comprise a remarkably diverse superfamily of heme-thiolate proteins critical in the metabolism of numerous endogenous ligands and xenobiotics. Among the myriad of P450 substrates are many compounds of toxicological and pharmacological significance. The precise complement of cytochrome P450 isoforms in any given tissue may therefore be an important determinant of susceptibility to chemical-mediated toxicity. We have used a histological approach to study the distribution of individual P450s in human and rabbit gastro-intestinal tissues. We have focused primarily on P450 enzymes of importance in the metabolism of carcinogens, namely CYP1A1, CYP1A2, CYP2E1, CYP3A4/3A5 and CYP4B1. Here we give an overview of the distribution of these enzymes in human and rabbit tissues and discuss the possible toxicological implications of the results. In addition we will discuss the value of archival human tissue specimens for histological analysis of P450 distribution.

Cytochromes P450, 1A2, and 2C9 are responsible for the human hepatic O-demethylation of R- and S-naproxen

A preliminary report implicated cytochrome P450 (CYP) 2C9 in the human liver microsomal O-demethylation of S-naproxen, suggesting that this pathway may be suitable for investigation of human hepatic CYP2C9 in vitro. Kinetic and inhibitor studies with human liver microsomes and confirmatory investigations with cDNA-expressed enzymes were undertaken here to define the role of CYP2C9 and other isoforms in the O-demethylation of R- and S-naproxen. All studies utilised a newly developed sensitive and specific HPLC assay that measured the respective O-desmethyl metabolites of R- and S-naproxen in incubations of human liver microsomes and in COS cell lysates. Microsomal R- and S-naproxen O-demethylation kinetics followed Michaelis-Menten kinetics, with respective mean apparent Km values of 123 microM and 143 microM. Sulfaphenazole, a specific inhibitor of CYP2C9, reduced the microsomal O-demethylation of R- and S-naproxen by 43% and 47%, respectively, and the CYP1A2 inhibitor furafylline decreased R- and S-naproxen O-demethylation by 38% and 28%, respectively. R,S-Mephenytoin was a weak inhibitor of R- and S-naproxen O-demethylation, but other CYP isoform specific inhibitors (e.g., coumarin, diethyldithiocarbamate, quinidine, troleandomycin) had little or no effect on these reactions. cDNA-expressed CYP2C9 and CYP1A2 were both shown to O-demethylate R- and S-naproxen. Apparent Km values (92-156 microM) for the reactions catalysed by the recombinant enzymes were similar to those observed for human liver microsomal R- and S-naproxen O-demethylation. The data demonstrate that CYP2C9 and CYP1A2 together account for the majority of human liver R- and S-naproxen O-demethylation, precluding the use of either R- or S-naproxen as a CYP isoform-specific substrate in vitro and in vivo.

Liver stellate cells in chronic viral hepatitis: the effect of interferon therapy

BACKGROUND/AIMS

Liver stellate cell proliferation and differentiation into myofibroblast-like cells is related to the development of liver fibrosis. Several cytokines, including interferons, regulate liver stellate cell proliferation and phenotypic modulation. Recent studies indicate that human liver stellate cells express the alpha-isotype of actin, specific to smooth muscle cell differentiation. We aimed to evaluate the expression of alpha-smooth muscle actin-positive liver stellate cells in patients with chronic viral hepatitis and to evaluate whether and how such expression can be modified by alpha-interferon treatment.

METHODS

Using immunohistochemistry, and a semi-quantitative scoring method, we evaluated alpha-smooth muscle actin expression in liver stellate cells before and after alpha-interferon therapy in a series of liver biopsies from 44 patients with chronic viral hepatitis.

RESULTS

Before therapy, a large number of liver stellate cells expressing alpha-smooth muscle actin were present throughout all acinar zones. A significant reduction in alpha-smooth muscle actin expression by liver stellate cells was demonstrated in biopsies performed after suspending the interferon treatment. The drop in the number of alpha-smooth muscle actin-labelled cells after therapy correlated closely with the improvement in the histological index of activity.

CONCLUSIONS

The results suggest a specific effect of interferon on liver stellate cells, possibly related to its anti-inflammatory action.

Immunohistochemical study of proteoglycans in D-galactosamine-induced acute liver injury in rats

In this study, we carried out an immunohistochemical investigation of time-dependent alterations in the distribution of proteoglycans, and the proliferation profiles of hepatocytes and fat-storing cells (FSCs) in the livers of rats intoxicated with D-galactosamine (GalN). The proliferative cells were analyzed by proliferative cell nuclear antigen (PCNA) staining. In untreated rats, heparan sulfate, dermatan sulfate, and chondroitin/chondroitin sulfate were detected within the portal spaces and the central veins, and, with the exception of chondroitin, also within the reticular fibers. After administration of GalN, the number of PCNA-positive cells (FSCs and hepatocytes) and FSCs increased, reaching maximal on the 2nd and 3rd days, respectively. Heparan sulfate showed complicated changes. Dermatan sulfate decreased in portal spaces from the 2nd to the 3rd day, and in reticular fibers from 12 h to the 6th day. Chondroitin/chondroitin sulfate staining was observed from 2 h to the 6th day in the sinusoidal endothelia, which suggests that the sinusoidal endothelia may produce chondroitin/chondroitin sulfate transiently during liver damage as part of the mechanism of regeneration. Heparan sulfate and chondroitin/chondroitin sulfate were detected in necrotic regions, but dermatan sulfate was not. These observations suggest that heparan sulfate and chondroitin/chondroitin sulfate are involved in cell proliferation or morphogenesis and that the dermatan sulfate plays a role in the differentiation or functional maintenance of cells in liver regeneration.

Enzymic and interindividual differences in the human metabolism of heterocyclic amines

Heterocyclic amines (HAs) present in cooked meat (PhIP and MeIQx) are activated only by CYP1A2 in the liver of most species, including man. This enzyme exhibits marked interindividual differences in its expression, due to induction and possibly also genetically. The absence of CYP1A2 appears to protect from HA-(PhIP and MeIQx) induced cancer, as exemplified by results in the cynomolgus monkey. Differences in the potency of these HAs are not due to differences in the kinetics of their activation. The catalytic efficiency of CYP1A2 towards HAs and their oxidative fate varies amongst species, in both cases increasing the susceptibility of humans compared to that of the rat. Interindividual and inter-organ differences in the further metabolism of N-hydroxy-HAs appear to be important determinants of cancer susceptibility, as does the glutathione S-transferase catalysed detoxication of esters of N-hydroxy-PhIP. There is a need for an effective means of quantifying the in vivo activation of HAs in man to enable the possible risk posed by these compounds to be assessed effectively.

Biotransformation of caffeine by cDNA-expressed human cytochromes P-450

OBJECTIVES

The biotransformation of caffeine has been studied in vitro using human cytochrome P-450 isoenzymes (CYPs) expressed in human B-lymphoblastoid cell lines, namely CYP1A1, 1A2, 2A6, 2B6, 2D6-Val, 2E1 and 3A4, and microsomal epoxide hydroxylase (EH). In addition, CYP2D6-Met was also studied, in which a valine in the wild type (CYP2D6-Val) has been replaced by a methionine due to a G to A mutation in position 112.

RESULTS

At caffeine 3 mmol center dot l-1, five CYPs (1A1, 1A2, 2D6-Met, 2E1 and 3A4) catalysed the biotransformation of caffeine. Among the enzymes studied, CYP1A2, which predominantly catalysed paraxanthine formation, had the highest intrinsic clearance (160 l center dot h-1 center dot mmol-1 CYP). Together with its high abundance in liver, it should be considered, therefore, to be the most important isoenzyme in caffeine metabolism. The affinity of caffeine for CYP1A1 was comparable to that of its homologue 1A2. CYP2D6-Met, which catalysed caffeine metabolism by demethylation and 8-hydroxylation, also had a relatively high intrinsic clearance (3.0 l center dot h-1 mmol-1 CYP), in particular for theophylline and paraxanthine formation, with kM values between 9-16 mmol center dot l-1. In contrast, the wild type, CYP2D6-Val, had no detectable activity. In comparison, CYP2E1 played a less important role in in vitro caffeine metabolism. CYP3A4 predominantly catalysed 8-hydroxylation with a kM value of 46 mmol center dot l-1 and an intrinsic clearance of 0.60 l center dot h-1 center dot mmol-1 CYP. Due to its high abundance in human liver, the latter CYP may contribute significantly to the in vivo formation of TMU.

CONCLUSION

The findings of this study indicate that i) microsomes from transfected human B-lymphoblastoid cell lines give results close to those obtained with microsomes isolated from human liver, ii) at least four CYP isoforms are involved in caffeine metabolism, iii) at a substrate concentration <0.1 mmol center dot l-1, CYP1A2 and 1A1 are the most important isoenzymes, iv) at higher concentrations the participation of other isoenzymes, in particular CYP3A4, 2E1 and possibly also CYP2D6-Met, are important in caffeine metabolism, and v) the nucleotide composition at position 1120 of CYP2D6 determines the activity of this isoenzyme in caffeine metabolism.

Modulating hypoxia-induced hepatocyte injury by affecting intracellular redox state

Hypoxia-induced hepatocyte injury results not only from ATP depletion but also from reductive stress and oxygen activation. Thus the NADH/NAD+ ratio was markedly increased in isolated hepatocytes maintained under 95% N2/5% CO2 in Krebs-Henseleit buffer well before plasma membrane disruption occurred. Glycolytic nutrients fructose, dihydroxyacetone or glyceraldehyde prevented cytotoxicity, restored the NADH/NAD+ ratio, and prevented complete ATP depletion. However, the NADH generating nutrients sorbitol, xylitol, glycerol and beta-hydroxybutyrate enhanced hypoxic cytotoxicity even though ATP depletion was not affected. On the other hand, NADH oxidising metabolic intermediates oxaloacetate or acetoacetate prevented hypoxic cytotoxicity but did not affect ATP depletion. Restoring the cellular NADH/NAD+ ratio with the artificial electron acceptors dichlorophenolindophenol and Methylene blue also prevented hypoxic injury and partly restored ATP levels. Ethanol which further increased the cellular NADH/NAD+ ratio increased by hypoxia also markedly increased toxicity whereas acetaldehyde which restored the normal cellular NADH/NAD+ ratio, prevented toxicity even though hypoxia induced ATP depletion was little affected by ethanol or acetaldehyde. The viability of hypoxic hepatocytes is therefore more dependent on the maintenance of normal redox homeostasis than ATP levels. GSH may buffer these redox changes as hypoxia caused cell injury much sooner with GSH depleted hepatocytes. Hypoxia also caused an intracellular release of free iron and cytotoxicity was prevented by desferoxamine. Furthermore, increasing the cellular NADH/NAD+ ratio markedly increased the intracellular release of iron. Hypoxia-induced hepatocyte injury was also prevented by oxypurinol, a xanthine oxidase inhibitor. Polyphenolic antioxidants or the superoxide dismutase mimic, TEMPO partly prevented cytotoxicity suggesting that reactive oxygen species contributed to the cytotoxicity. The above results suggests that hypoxia induced hepatocyte injury results from sustained reductive stress and oxygen activation.

Experimental biliary fibrosis correlates with increased numbers of fat-storing and Kupffer cells, and portal endotoxemia

In the present study, we have investigated the correlation between hepatic fibrosis in rats subjected to bile duct ligation, the numbers of Kupffer and fat-storing cells, and the level of endotoxin in both the portal and systemic circulation. The extent of hepatic fibrosis was measured by morphometry. Kupffer cells were identified by indirect immunoperoxidase staining using ED-2 anti-macrophage antibody. Fat-storing cells were stained with DE-B-5 anti-desmin antibody. Endotoxin levels were determined by the Limulus Lysate test. Following bile duct ligation, connective tissue septa rapidly developed in periportal areas. After 1 week, the volume density of connective tissue had increased from 0.6 +/- 0.1% in control animals to 3.8 +/- 1.1%. After 2 weeks, this volume increased to 19.9 +/- 1.3%, and after 3 weeks to 34.3% +/- 2.7%. The number of periportal fat-storing cells increased 2.8-fold during the first 2 weeks, whereas pericentral fat-storing cells increased only 1.7-fold. After 2 weeks, no further increase was observed. During the first week of bile duct ligation, the number of Kupffer cells increased nearly two-fold. Thereafter, no further increase was detected. In control rats, only two of ten rats showed low amounts of endotoxin in the portal blood. Portal endotoxemia increased with time after bile duct ligation. After 3 weeks, all rats were positive. The measured endotoxin levels were approximately 7 times higher than in control rats. We conclude that the development of fibrosis secondary to experimental bile duct ligation is accompanied by protal endotoxemia, and increases in the numbers of Kupffer and periportal fat-storing cells. We found a significant correlation between portal endotoxemia, the number of Kupffer and fat-storing cells, and the extent of fibrous septa, supporting the view that high endotoxemia levels coincide with Kupffer cell activation and fibrogenesis.

Novel insights into the biology and physiology of the Ito cell

Ito cells, perisinusoidal mesenchymal elements with possible pericytic functions within the liver, recently have been shown to play multiple physiological and pathophysiological roles. In particular, several in vivo and in vitro studies have clearly indicated that Ito cells play a relevant role in the progression of liver fibrogenesis. More recently, attention has been focussed on the mechanisms leading to Ito cell activation, proliferation and synthesis of extracellular matrix components. Among other soluble factors potentially involved in these processes, transforming growth factor-beta 1 and platelet-derived growth factor have been shown to act in a paracrine, and possibly autocrine, fashion on Ito cells, thus perpetuating their activated state. Finally, other studies have shown that Ito cells could play an active role in chronic liver tissue inflammation by promoting chemotaxis of infiltrating inflammatory cells.

Kupffer cell iron overload induces intercellular adhesion molecule-1 expression on hepatocytes in genetic hemochromatosis

The mechanisms underlying iron-induced liver fibrogenesis in patients with genetic hemochromatosis are poorly understood. We studied signs of Kupffer cell activation and inflammatory responses in liver biopsy specimens obtained from 15 patients with untreated and six patients with treated hemochromatosis. Immunohistochemistry was performed on 11 of the untreated and all treated patients. Three of the untreated patients (20%) had cirrhosis and eight (53%) had fibrosis. None had chronic active hepatitis (CAH). Immunohistochemistry indicated that 55% of the untreated patients had sparse intercellular adhesion molecule-1 (ICAM-1) expression by hepatocytes, and all of these had Kupffer cell iron overload. No ICAM-1 expression was seen by hepatocytes in treated patients or healthy controls. ICAM-1 was strongly expressed by hepatocytes from control patients with inflammatory liver disease. HLA-DR reactivity was seen on sinusoidal cells in all groups, but not on hepatocytes except for two of the control patients with CAH. Twenty-seven percent of the untreated hemochromatosis patients displayed moderate infiltration by CD3-positive lymphocytes. Electron microscopy of samples from untreated hemochromatosis patients showed hypertrophic Kupffer cells containing iron-rich remnants of phagocytosed hepatocytes. Fat-storing cells close to iron-laden hepatocytes contained multiple lipid droplets and adjacent collagen fibril bundles. Thus, in patients with untreated genetic hemochromatosis and Kupffer cell iron overload, hepatocytes occasionally express ICAM-1. In regions with heavy iron overload, Kupffer cell hypertrophy and transition of fat-storing cells are seen. Our findings indicate that release of factors from iron-loaded, activated Kupffer cells is of importance for the transformation of fat-storing cells and increased collagen deposition seen in genetic hemochromatosis.

Identification of human CYP isoforms involved in the metabolism of propranolol enantiomers--N-desisopropylation is mediated mainly by CYP1A2

1. Studies using human liver microsomes and six recombinant human CYP isoforms (i.e. CYP1A2, 2A6, 2B6, 2D6, 2E1 and 3A4) were performed to identify the cytochrome P450 (CYP) isoform(s) involved in the ring 4-hydroxylation and side-chain N-desisopropylation of propranolol enantiomers in humans. 2. alpha-Naphthoflavone and 7-ethoxyresorufin (selective inhibitors of CYP1A1/2) inhibited the N-desisopropylation of R- and S-propranolol by human liver microsomes by 20 and 40%, respectively, while quinidine (a selective inhibitor of CYP2D6) abolished the 4-hydroxylation of both propranolol enantiomers almost completely. In contrast, sulphaphenazole (CYP2C8/9 inhibitor), S-mephenytoin (CYP2C19 inhibitor), troleandomycin (CYP3A3/4 inhibitor) and diethyldithiocarbamate (CYP2E1 inhibitor) elicited only weak inhibitory effects on propranolol metabolism via the two measured metabolic pathways. 3. Significant (P < 0.01) correlations were observed between the microsomal N-desisopropylation of both propranolol enantiomers and that for the O-deethylation of phenacetin among the 11 different human liver microsome samples (r = 0.98 and 0.77 for R- and S-propranolol, respectively). A marginally significant (r = 0.60, P congruent to 0.05) correlation was also observed between N-desisopropylation of S-, but not of R-propranolol and the 4'-hydroxylation of S-mephenytoin. No significant correlations were observed between the N-desisopropylation of propranolol enantiomers and the 2-hydroxylation of desipramine, the hydroxylation of tolbutamide or the 6 beta-hydroxylation of testosterone. 4. Significant (P < 0.01) correlations were observed between the microsomal 4-hydroxylation of R- and S-propranolol and the 2-hydroxylation of desipramine (r = 0.85 and 0.98, respectively). A weak (r = 0.66), albeit significant (P < 0.05) correlation was observed between the 4-hydroxylation of R-, but not of S-propranolol and the hydroxylation of tolbutamide. No significant correlations were observed between the 4-hydroxylation of propranolol enantiomers and the oxidation of other substrates for CYP1A2, 2C19, and 3A3/4. 5. Recombinant human CYP1A2 and CYP2D6 exhibited comparable catalytic activity with respect to the N-desisopropylation of both propranolol enantiomers; only expressed CYP2D6 exhibited a marked catalytic activity with respect to the 4-hydroxylation of both propranolol enantiomers.(ABSTRACT TRUNCATED AT 400 WORDS)

Metabolism of theophylline by cDNA-expressed human cytochromes P-450

1. Theophylline metabolism was studied using seven human cytochrome P-450 isoforms (CYPs), namely CYP1A1, 1A2, 2A6, 2B6, 2D6, 2E1 and 3A4, and microsomal epoxide hydroxylase (EH), expressed in human B-lymphoblastoid cell lines. 2. At a high theophylline concentration of 10 mM four CYPs (1A1, 1A2, 2D6, 2E1) catalyzed the metabolism of theophylline. 3. Theophylline had the highest affinity (apparent Km range 0.2-1.0 mM) for the CYP1A subfamily and the kinetics of metabolic formation mediated by CYP1A2 indicated substrate-inhibition (Ki range 9-16 mM). 4. CYP1A2 catalyzed the demethylation of theophylline as well as its hydroxylation, and was associated with the highest intrinsic clearance (1995 l h-1 per mol CYP) to 1,3-dimethyluric acid (DMU). Therefore, this isoform can be considered to be the most important enzyme involved in theophylline metabolism in vitro. 5. CYP2E1 was responsible for a relatively high intrinsic clearance by 8-hydroxylation (289 l h-1 per mol CYP). The apparent Km value of this reaction was about 15 mM, suggesting that CYP2E1 may be the low-affinity high-capacity isoform involved in theophylline metabolism. 6. The affinity of theophylline for CYP1A1 was comparable with that of its homologue 1A2. When induced, the participation of CYP1A1 in theophylline metabolism may be important. 7. CYP2D6 played only a minor role and CYP3A4 was not active in the in vitro metabolism of theophylline. 8. Our findings confirm the major role of CYP1A2 in theophylline metabolism and explain why in vivo the elimination kinetics of theophylline are non-linear and in vitro theophylline metabolism by human liver microsomes does not obey monophasic kinetics. 9. The data suggest also that not only tobacco smoking but also chronic alcohol intake may influence theophylline elimination in man as ethanol induces CYP2E1.

Immunostaining for membrane attack complex of complement is related to cell necrosis in fulminant and acute hepatitis

BACKGROUND/AIMS

Complement activation is one of the mechanisms involved in inflammatory lesions. Initiation of the complement terminal pathway at a cell surface leads to the formation of a cytolytic membrane attack complex. Our study assess whether a membrane attack complex-associated mechanism is involved in liver cell necrosis of fulminant and subfulminant hepatitis.

METHODS

Immunostaining for membrane attack complex was compared with immunostaining for cytokeratin and complement inhibitory proteins such as membrane cofactor protein, decay-accelerating factor, and homologous restriction factor in 15 patients with fulminant hepatitis and 5 patients with nonfulminant acute hepatitis.

RESULTS

In all patients, hepatocytes surrounding necrotic areas, but not those at a distance, were stained for membrane attack complex, whereas the opposite staining pattern for membrane cofactor protein was observed. In controls, no hepatocyte staining for membrane attack complex was observed, whereas membrane cofactor protein, but not decay-accelerating factor or homologous restriction factor, was detected on hepatocytes.

CONCLUSIONS

Complement activation by antibody-dependent or non-antibody-dependent mechanisms might be involved in the pathogenesis of either fulminant or acute hepatitis. Modulation of membrane cofactor protein expression on hepatocytes might contribute to the sensitivity of hepatocytes to membrane attack complex and subsequent cell lysis.

Characterisation of CYP3A gene subfamily expression in human gastrointestinal tissues

The human CYP3A subfamily is of interest due to its multiplicity, activity toward known carcinogens, and extrahepatic expression. In situ hybridisation analysis of formalin fixed, routinely processed biopsy specimens was used to localise CYP3A mRNA in human gastrointestinal tissues from several individuals. CYP3A mRNA is abundant in human liver and in mucosal epithelial cells of all segments of the human small intestine. RNA blot analyses showed that the mRNA species observed in most livers and in human small intestine represent CYP3A3/3A4 transcripts. This was confirmed at the protein level by immunoblot comparison of small intestine microsomes to in vitro expressed CYP3A4 and CYP3A5 proteins. In liver and small intestine, CYP3A mRNA is not uniformly distributed, with grain density highest in cells within the respective non-proliferative compartments. CYP3A mRNA was also observed in human oesophagus and colon. RNA blot analysis of multiple colons showed heterogeneity in the CYP3A mRNAs present. Two CYP3A mRNAs (CYP3A3/3A4 and CYP3A5) were detected in colon samples from several individuals. In addition to those localisation studies, the capacity of expressed CYP3A4 and CYP3A5 to activate the dietary heterocyclic amine MeIQ in the presence of alpha-naphthoflavone was shown. These results show that there is considerable heterogeneity in the expression of the CYP3A subfamily in human gastrointestinal tissues.

Weak immunogenicity of the preS2 sequence and lack of circumventing effect on the unresponsiveness to the hepatitis B virus vaccine

The preS2 sequence is known to circumvent immunological unresponsiveness to the S protein and to induce a 'carrier' effect on the anti-S antibody production, in mice. In humans, an anti-S response was found in 100% and 97% of healthy subjects vaccinated with the S and S + preS2 preparations, respectively, whereas less than 50% of drinkers responded whatever the vaccine used. Anti-preS2 were found in 44% of healthy recipients of the S + preS2 vaccine, whereas there were no anti-preS2 responders in drinkers. Anti-preS2 remained undetectable in 32% of the blood donors hyperimmunized with the S + preS2 vaccine, whereas anti-S antibody boosted in all cases. In humans, in contrast to mice, immunogenicity of the preS2 sequence appears weak and the preS sequence does not circumvent the anti-S unresponsiveness.

Induction of micronuclei and sister chromatid exchanges by polycyclic and N-heterocyclic aromatic hydrocarbons in cultured human lymphocytes

Many natural environments are contaminated with carcinogenic polycyclic aromatic hydrocarbons (PAHs) and N-heterocyclic aromatic hydrocarbons (NHAs) as complex mixtures of coal tar, petroleum, and shale oil. These potentially hazardous substances are prevalent at many former tar production and coal gasification sites. Three polycyclic [benzo(a)pyrene (BaP), benz(a)anthracene (BAA), and 7,12-dimethylbenz(a)anthracene (DMBA)] and two N-heterocyclic [7H-dibenzo(c,g)carbazole (DBC), and dibenz(a,j)acridine (DBA)] aromatic hydrocarbons were analyzed for cytotoxic and genotoxic effects on human lymphocytes. All of these polyaromatic compounds are normally present in the environment, except for DMBA. Lymphocytes from healthy donors were isolated from whole blood. The 5-ring polycyclic aromatic BaP consistently induced micronuclei in a linear dose-dependent manner with doses from 0.1-10.0 micrograms/ml, whereas the 4-ring compounds (BAA and DMBA) had no effect on the induction of micronuclei above controls except at 5 and 10 micrograms/ml. Of the two N-heterocyclic compounds, DBC produced a significant increase in micronuclei in lymphocytes, but the dose response tended to plateau above 0.1 microgram/ml. DBA showed an effect on the frequency of micronuclei above controls only at high doses of 5 and 10 micrograms/ml. The average background frequency of micronuclei for 7 lymphocyte donors averaged 3.1 per 1,000 stimulated cells, whereas the average frequency of micronuclei at 10 micrograms/ml BaP was 36.8 per 1,000 stimulated cells. The lowest effective dose in 2 donors for BaP occurred at 0.1 microgram/ml. At a challenge dose of 1 microgram/ml (4 microM) of BaP, considerable variation in micronuclei induction between 7 individuals was observed, ranging from 2-6-fold increases above spontaneous frequency. Over a dose range of 1-10.0 micrograms/ml (4-40 microM), BaP also induced sister chromatid exchanges (SCEs) in lymphocytes, whereas BAA had no effect above controls. Parallel studies of both cytogenetic endpoints showed that the micronucleus assay is a more sensitive indicator of BaP exposure at equivalent doses. Mitotic and replication indices of BaP-exposed lymphocytes showed that cell proliferation is only moderately inhibited even at the highest dose; this shows that bulky DNA-adducts are generally compatible with cell survival. The cytogenetic data are consistent, first-off, with reports that individuals in the population vary widely with respect to the inducibility of the CYP1A1 gene, which is known to be involved in polycyclic aromatic hydrocarbon metabolism, in particular, in BaP. Secondly, the data support the fact that polyaromatic compounds differ with regard to micronucleus induction within the same sample(s) of human lymphocytes, indicating selective metabolism of polyaromatic compounds that may reflect carcinogen sensitivity of the individual.(ABSTRACT TRUNCATED AT 400 WORDS)

Expression and characterization of the multiplied, recombinant preS1 antigen of hepatitis B virus

The amino acid sequence encoded by the preS1 region of hepatitis B virus genome is expressed on the surface of virions and subviral particles. The preS1 region is involved in the recognition of specific receptors responsible for the attachment of HBV to the host cell. The cell receptor binding site was assigned to the preS1 (20-47 aa) fragment. In order to obtain a large quantity of preS1 binding domains of HBV the expression vector pWX4 was constructed. It contains four tandemly joined DNA sequences, each coding for preS1 (20-49 aa), fused with the 3' end of a DNA fragment coding for 450 aa of beta-galactosidase. E. coli cells transformed with this vector produce fusion protein beta-gal-preSlx4 in the form of inclusion bodies. Owing to the specific trypsin digestion, the preSlx4 domain was cleaved from the fusion protein. The resulting product, a 16 kDa protein, was isolated and purified by anion exchange chromatography. The presence of four Asp-Pro bonds in this sequence and the primary structure of the first 28 N-terminal amino acids were determined. Following the confirmation of the antigenic properties, the recombinant preS1 protein was used for detection of the anti-preS1 response in sera from HBV infected patients.

Pretranslational induction of cytochrome P4501A enzymes by beta-naphthoflavone and 3-methylcholanthrene occurs in different liver zones

Most of the cytochrome P450 (CYP) genes are expressed in an uneven, zonated pattern in the liver. Factors regulating this regionally restricted expression are not well known. In this study we have analysed cell lysates obtained from opposite zones of rat liver by infusing digitonin to the perfused liver to study the zonation of CYP1A1 and CYP1A2 induction. 3-Methylcholanthrene induced CYP1A1 protein in perivenous cells, while a low dose of beta-naphthoflavone caused periportal induction. Analysis of CYP1A1 mRNA from cell lysates by reverse transcriptase-coupled polymerase chain reaction (RT-PCR) and in situ hybridization experiments both demonstrated that this inducer-specific differently localized effect occurred at the pretranslational level. A corresponding difference in the regional pattern of CYP1A2 induction was seen: induction by beta-naphthoflavone reversed the constitutive perivenous pattern into a periportal CYP1A2 mRNA pattern while induction after 3-methylcholanthrene treatment was more panacinar. Attempts to identify the regiospecific factors involved were made by comparing the in vitro induction of CYP1A1 by beta-naphthoflavone and 3-methylcholanthrene in hepatocytes isolated from the periportal and perivenous region. However, after isolation, induction seemed to be independent of the source of the cells. Our results demonstrate the existence in the liver of regionally acting factors that mediate the induction of CYP1A1 and 1A2 in a local and inducer-specific fashion. These factors could be Ah receptor associated binding proteins operating in vivo, but no longer in isolated cells.

Expression of xenobiotic-metabolizing cytochrome P450 forms in human adult and fetal liver

Expression of human cytochrome P450 (CYP) genes in human adult and fetal liver were studied using the reverse transcriptase-polymerase chain reaction (RT-PCR) method. In adult liver mRNA of CYPs 1A1, 1A2, 2A6/2A7, 2B6/2B7, 2C8-19, 2D6, 2E1, 3A3/3A4 and 3A7 were detected while CYPs 2F1 and 4B1 were absent. In fetal liver mRNA of CYPs 2C8, 2D6, 3A3/3A4 and 3A7 were found but all other forms studied were undetectable. The results provide a comprehensive qualitative picture of the expression of CYP genes in families CYP1 through CYP4 in human adult and fetal liver.

Diabetes-induction reduction in the hepatic accumulation of 70-kDA dextran: role of hyperglycemia and hypoinsulinemia

In vivo studies were conducted in rats to determine the role of hyperglycemia and hypoinsulinemia in the previously reported reduction in the hepatic accumulation and increase in the serum concentrations of 70-kDa fluorescein-dextran (FD-70) in diabetic (D) rats. The serum, urine, and hepatic concentrations of FD-70 were measured by size exclusion chromatography after i.v. administration of a single doses (5 mg/kg) of FD-70. Intravenous administration of a single 2 IU/kg dose of insulin to D rats at time zero or 4 h after the administration of FD-70 resulted in an increase in some and no change in other animals in their rate of elimination of FD-70 from serum. The presence or absence of a significant insulin effect on the disposition of FD-70 in these animals was, respectively, associated with the presence or absence of a significant insulin-induced hypoglycemic effect. Fasting D rats for 24 h caused normoglycemia, and subsequently, the disposition of FD-70 became similar to that in nondiabetic (ND) rats. Likewise, i.p. injections of glucose to ND rats rendered them hyperglycemic, and the disposition of FD-70 in these rats became similar to that in untreated D animals. However, i.v. injection of glucose, which did not result in sustained hyperglycemia, did not change the disposition of FD-70 in ND rats. Further, the disposition of FD-70 remained unaffected by an i.v. 2 IU/kg dose of insulin administered to ND rats at time zero. Considering all animals, there was a significant negative relationship between the 12-h hepatic recovery of FD-70 and the area under the serum concentration-time curves of glucose. It is concluded that the reduction in the hepatic accumulation of FD-70 in D rats is due to hyperglycemia and not

Caffeine metabolism by human hepatic cytochromes P450: contributions of 1A2, 2E1 and 3A isoforms

Caffeine (CA) N1-, N3- and N7-demethylase, CA 8-hydroxylase and phenacetin O-deethylase activities were measured in microsomes from 18 separate human livers which had been characterized previously for a range of cytochrome P450 (CYP) isoform-specific activities and immunoreactive CYP protein contents. Correlations between the high affinity components of the three separate CA N-demethylations were highly significant (r = 0.77-0.91, P < 0.001) and each of the three high affinity CA N-demethylations correlated significantly (r = 0.64-0.93, P < 0.05-0.001) with the high affinity phenacetin O-deethylase, 2-acetylaminofluorene N-hydroxylation and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) and 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) mutagenicity (all predominantly CYP1A2-mediated reactions). Consistent with these observations, cDNA-expressed human CYP1A2 catalyzed the N1-, N3- and N7-demethylation of CA and apparent Km values were similar (0.24-0.28 mM) for all three reactions and comparable to those observed previously with human liver microsomes. The low affinity components of CA N1- and N7-demethylation correlated significantly (r = 0.55-0.85, P < 0.05-0.001) with immunoreactive CYP2E1 content and the CYP2E1-specific activities 4-nitrophenol and chlorzoxazone hydroxylation. Diethyldithiocarbamate, a selective inhibitor of CYP2E1, inhibited the low affinity CA N1- and N7-demethylation, with IC50 values of 23 microM and 11 microM, respectively. The apparent Km values for CA N1- and N7-demethylation by cDNA-expressed CYP2E1 (namely 28 and 43 mM, respectively) were of a similar order to those calculated for the low affinity microsomal activities. Significant correlations (r = 0.87-0.97, P < 0.001) were observed between CA 8-hydroxylation and immunoreactive CYP3A content and the CYP3A-mediated reactions benzo(a)pyrene hydroxylation, omeprazole sulfoxidation and aflatoxin B1 mutagenesis. Effects of alpha-naphthoflavone, erythromycin, troleandomycin and nifedipine on microsomal CA 8-hydroxylation were generally consistent with CYP3A involvement. Taken together with previous data, the results indicate a major involvement of CYP1A2 in the high affinity component of all three human hepatic CA N-demethylations. In contrast, CYP2E1 appears to be the main enzyme involved in the low affinity components of CA N1- and N7-demethylation while CA 8-hydroxylation is catalysed predominantly by a CYP3A isoform(s).

Thiobarbiturate and fructosamine assays: significance and interest of the borohydride blank

The acute-phase reaction (APR) induces the production by the liver of short-lived glycoproteins. The carbohydrate moiety of these proteins is thought to interfere with the thiobarbiturate (TBA) and nitroblue tetrazolium colorimetric tests which are used for assaying non-enzymatic glycosylation (NEG) of serum proteins. The aim of the present study was to assess the effect of the APR on the specificity of the colorimetric tests in non-diabetic and diabetic subjects. A positive correlation was found between C-reactive protein (CRP), an APR glycoprotein, and non-specific TBA reactivity as determined after borohydride reduction (BH4-resistant TBA, BR-TBA), both in non-diabetics (r = 0.61; P < 0.01) and diabetics (r = 0.68; P < 0.01). The BH4-sensitive specific TBA (SP-TBA) was not influenced by glycoproteins, and its increase in diabetics was correlated with the nitroblue tetrazolium assay (r = 0.89; P < 0.01). An independent effect of diabetes and APR on non-specific TBA was also demonstrated, suggesting an effect of hyperglycaemia on both protein glycation and glycosylation. TBA with borohydride reduction is an attractive tool for the study of complex glycoproteins in diabetes.

Non-parenchymal cell responses in paracetamol (acetaminophen)-induced liver injury

We have analysed Kupffer cell and 'activated' perisinusoidal cell populations in liver biopsies from patients with paracetamol (acetaminophen)-induced hepatic necrosis of varying degrees of severity. Kupffer cells were identified immunohistochemically using the monoclonal antibody KPJ and perisinusoidal cells by identification of alpha-smooth muscle actin expression. Material was available from four groups of individuals: (i) 11 cases with mild (grade I) injury; (ii) six cases with moderate (grade II) injury; (iii) six cases with severe (grade III) injury; and (iv) controls with normal liver histology (n = 23). Biopsies in groups (i)-(iii) were obtained within 5 days of drug ingestion. All patients in this study survived and follow-up biopsies were obtained at 4 months, by which time the histological abnormalities had fully resolved. Kupffer cells and perisinusoidal cell numbers were assessed in immunostained preparations of acute and recovery phase biopsies and in control specimens. In acute phase biopsies from patients with grade II and III injury there was expansion of the Kupffer cell and perisinusoidal cell populations within areas of injury. There was a strong correlation between the size of these two cell populations (r = 0.886). No significant difference in cell numbers was found between those with grade I injury and controls. In recovery phase biopsies from patients with paracetamol-induced injury, perisinusoidal cell numbers did not differ significantly from normal controls. Kupffer cells numbers also decreased in recovery phase biopsies compared with the acute phase, although there was persistent expansion of the Kupffer cells population in those who originally had grade III injury.(ABSTRACT TRUNCATED AT 250 WORDS)

PreS1 antigen/antibody patterns following interferon therapy in acute and chronic hepatitis B

The relation between preS1 antigen/antibody system and different phases of hepatitis B virus infection were studied in 425 serum samples from 50 hepatitis B patients before, during and after antiviral therapy using interferon alone or in combination with corticosteroid withdrawal. A typical profile of self-limited acute hepatitis B was characterized by hepatitis B virus-DNA clearance using polymerase chain reaction and preS antigens using monoclonal radioimmunoassays and by antibody responses to the middle and the large HBs proteins (gp33/gp36 and p39/gp42) using immunoblotting quantitative analysis. After interferon therapy in patients with protracted hepatitis B, complete eradication of the virus was observed in 70% of patients, and antibody response directed to middle HBs and large HBs proteins could be induced. Conversely, this antibody response was never detected in follow-up studies of chronic active hepatitis B patients who responded well to antiviral therapy and lost HBs, preS2 and preS1 antigens. Most interesting, in 50% of patients with HBeAg-positive chronic active hepatitis B who received combination therapy and in 67% of patients with anti-HBe-positive chronic active hepatitis B given interferon alone, the elevated serum preS1Ag/HBsAg ratio persisted after treatment was discontinued and even increased until the end of the follow-up when hepatitis B virus DNA was undetectable in serum by the conventional hybridization technique. This rebound of preS1 antigen expression following antiviral therapy in patients with chronic active hepatitis B may indicate virus persistence, suggesting the possibility of relapse through wild-type hepatitis B virus or the emergence of hepatitis B virus mutants.

Metabolic differences in colon mucosal cells

The colonic expression of cytochromes P450 from the CYP1A, CYP3A and CYP4B subfamilies has been characterized in rabbit and human tissues using RNA blotting, immunoblotting, immunohistochemistry and hybridization histochemistry. These studies demonstrate negligible expression of the CYP1A subfamily in either rabbit or human colon. The CYP3A6 gene is expressed in rabbit colon although at markedly reduced levels relative to liver and small intestine. Whilst at least two CYP3A genes are expressed at the mRNA level in human colon tissue from some individuals, no expression was demonstrated in others. Where expression was observed, this expression was continuous throughout the length of the colon. In rabbits, CYP4B1 represents a major colon P450 enzyme, expressed at levels in colon comparable to liver and small intestine. In contrast, the human CYP4B1 gene is expressed at low levels in some individuals. These studies highlight individual differences in the expression of cytochrome P450 enzymes of importance in procarcinogen metabolism.

Synergism between hepatocytes and Kupffer cells in the activation of fat storing cells (perisinusoidal lipocytes)

This study concerns the cooperation of hepatocytes (PC) and Kupffer cells (KC) in the activation of rat liver fat storing cells (FSC) in culture. Various dilutions of conditioned media collected from early, serum-free cultures of both cell types were added separately and in combination, either simultaneously or sequentially, to early, non-confluent, primary cultures of FSC maintained under serum-reduced (0.5% fetal calf serum) conditions to determine the effects on proliferation (incorporations of [3H]thymidine and bromodeoxyuridine [BrdUrd], DNA-content, cell number), transformation and morphology (phase contrast microscopy, immunostainings of desmin and smooth muscle-alpha-actin), on the deposition of fibronectin and laminin and on the formation of 35S sulfated medium proteoglycans. Media of both cell types stimulated cell proliferation in a dose-dependent manner but combined PC- and KC-conditioned media was most potent and increased the incorporation of [3H]thymidine to 4-times above control values. The multiplication stimulatory effects visualized by labeling cell nuclei with BrdUrd and the increase of cell number per culture well were additive. The sequential addition of KC-conditioned medium to FSC preexposed to PC-conditioned medium increased the multiplication of FSC further and in an additive manner. The mitogenic activity of the PC-medium and the enhancing effect of KC-induced FSC proliferation was measured also when PC were damaged by incubation under anoxic conditions during generation of the conditioned medium. This observation indicates the release of the mitogen by membrane damage presumably from a cytoplasmic pool. The PC-medium did not induce either significant morphological changes or transformation of FSC towards myofibroblast-like cells. KC, however, generated transformation of FSC as indicated by more elongated cells with spindle-like cellular extensions and a reduction of retinoid droplets. Both these morphological effects were visible when PC and KC media were added simultaneously. Both media act synergistically on the deposition of fibronectin and laminin in FSC cultures and these components were found to be elevated 2.3 and 2.8-fold, respectively, if the cells were exposed to the combined media. Proteoglycan synthesis was also maximally enhanced if FSC were exposed to PC- and KC-media simultaneously. These findings suggest the involvement of (damaged) hepatocytes in the process of FSC activation. A model of sequential, spatial and time-dependent activation of FSC is suggested where cells in the immediate proximity of hepatocytes are primed to proliferate by a mitogenic signal released by membrane damage presumably from a cytoplasmic pool of injured hepatocytes into the pericellular environment. This non-inflammatory stimulation is followed by secretions of activated Kupffer cells and other inflammatory cell types which further enhance the activation of FSC.(ABSTRACT TRUNCATED AT 400 WORDS)

Hepatitis B virus (HBV) binding factor in human serum: candidate for a soluble form of hepatocyte HBV receptor

A hepatitis B virus (HBV) binding factor (HBV-BF) was identified in normal human serum interacting with the pre-S1 and pre-S2 epitopes of the viral envelope located within the protein domains involved in recognition of hepatocyte receptor(s). This molecule was characterized as a 50-kDa glycoprotein showing an isoelectric point of 7.13 with a biological activity depending on its native molecular conformation and on intact sulfhydryl bonds. Monoclonal antibodies to HBV-BF recognized a membrane component of the normal human liver whereas they were unreactive with hepatocyte membranes of other species and with those of the HepG2 cell line. These results suggest that the HBV-BF represents a soluble fragment of the membrane component and can be related to the HBV receptor mediating attachment of HBV to human liver cells.

Expression of alpha-amylase isoenzymes and trypsin by the proliferating epithelium of large intrahepatic bile ducts and intrahepatic peribiliary glands in hepatolithiasis

The expression of alpha-amylase isoenzymes (pancreatic and salivary) and trypsin by the epithelium of large intrahepatic bile ducts and peribiliary glands was examined immunohistochemically in hepatolithiasis (n = 22), extrahepatic biliary obstruction (n = 20) and normal liver (n = 22). Hepatolithiasis was associated with marked proliferation of bile duct cells and peribiliary glands. Expression of pancreatic and salivary amylase was observed in the proliferating bile duct cells and peribiliary glands of all livers, and trypsin was found in 68% of the livers. In extrahepatic biliary obstruction, proliferation of the biliary epithelium was less marked, but expression of amylase isoenzymes was observed in all livers and trypsin was found in 50%. All normal livers showed expression of amylase isoenzymes in large intrahepatic bile ducts, septal bile ducts and peribiliary glands, and trypsin was found in 73%. The density of enzyme-containing acini was highest in hepatolithiasis, intermediate in extrahepatic biliary obstruction and lowest in normal liver. These results show that the proliferating biliary epithelium in hepatolithiasis contains amylase isoenzymes and trypsin and that biliary epithelium retains the ability to produce these enzymes after proliferation, suggesting that a large amount of amylase isoenzyme and trypsin may be secreted into the bile ducts in hepatolithiasis. These enzymes may play an important role in the pathophysiology of hepatolithiasis.

Pathogenesis of gallstones

Gallstones form as a result of many disorders. Unphysiologic supersaturation, generally from hypersecretion of cholesterol, is essential for the formation of cholesterol gallstones. The other common abnormalities of the hepatobiliary system in gallstone patients are accelerated nucleation, gallbladder hypomotility, and the accumulation of mucin gel. An attempt is made here to relate hypersecretion of cholesterol and biliary supersaturation to the molecular basis of the associated phenomena. Supersaturation of bile with calcium hydrogen bilirubinate, the acid calcium salt of unconjugated bilirubin, is essential for pigment gallstone formation, but its magnitude remains undefined in model systems. Nucleation and the precipitation of calcium hydrogen bilirubinate with the polymerization of the pigment in the gallbladder, together with the deposition of the inorganic salts, calcium carbonate and phosphate, result in black pigment gallstone formation. On the basis of ex vivo muscle studies, gallbladder hypomotility is unlikely in patients with black pigment stones but is invariably present in patients with cholesterol stones. Pigment supersaturation in the gallbladder is the result of hepatic hypersecretion of bilirubin conjugates in hemolytic disorders and possibly enterohepatic cycling of unconjugated bilirubin in nonhemolytic states. Less common is bile salt hyposecretion from impaired synthesis in constitutional disorders and cirrhosis, and uncompensated interruption of the enterohepatic circulation in ileal dysfunction syndromes. Bile salt deficiency causes incomplete solubilization of unconjugated bilirubin and impaired binding of calcium ions. Stasis and anaerobic bacterial infection are responsible for brown pigment stones, which usually form in the bile ducts. In addition to the precipitation of calcium hydrogen bilirubinate that remains unpolymerized, there is also the deposition of the calcium salts of saturated fatty acids and free bile acids, both of which are the result of bacterial enzymatic hydrolysis of biliary lipids.

Induction of cytochrome P-4502E1 in the human liver by ethanol is caused by a corresponding increase in encoding messenger RNA

The propensity of centrilobular liver damage to develop in alcohol abusers after exposure to various hepatotoxins, including ethanol itself, has been linked to the induction by ethanol of P-4502E1, a microsomal P-450 enzyme that bioactivates these agents to reactive metabolites. Whereas long-term ethanol consumption elicits a marked increase in hepatic P-4502E1 content, the molecular mechanism by which ethanol produces this effect is the subject of controversy in animals, and it has not been elucidated in human beings. Possible mechanisms include increased enzyme synthesis stemming from elevated 2E1 messenger RNA levels, enhanced translation of preexisting messenger RNA or stabilization of P-4502E1 protein. To determine which, if any, of these mechanisms underlies P-4502E1 induction in human beings, we examined the effects of ethanol intake on the hepatic intralobular distribution of P-4502E1 messenger RNA and the corresponding protein. Liver sections derived from needle biopsy specimens were obtained from five recently drinking alcoholics (last drink no more than 36 hr before) and eight control subjects (five abstaining alcoholics [last drink 96 hr or more before] and three nondrinkers). In situ hybridization of these liver sections with a human P-4502E1 complementary DNA probe was used to localize P-4502E1 messenger RNA transcripts. Quantitative image analysis of hybridized sections from control subjects revealed that P-4502E1 transcript content in perivenular (zone 3) hepatocytes was significantly higher (p < 0.05) than in midzonal (zone 2) and periportal (zone 1) cells (18.3 +/- 1, 9.5 +/- 2 and 3.1 +/- 2 arbitrary density units, respectively; mean +/- S.E.M.). In recent drinkers, acinar regions containing P-4502E1 transcripts were elevated 2.9-fold compared with those in controls (32.8% +/- 7% vs. 11.2% +/- 2%; p < 0.01), with this messenger RNA increase occurring mainly in perivenular cells (29.6 +/- 3 vs. 18.3 +/- 1 units; p < 0.01). P-4502E1 protein distribution, assessed by the immunohistochemical staining of liver sections with P-4502E1 antibodies, was found to be analogous to that of the messenger RNA in control subjects (the level in perivenular cells was greater than that in midzonal cells, which was greater than that in periportal cells), whereas recent drinkers exhibited marked elevations in enzyme content in both perivenular and midzonal hepatocytes. Moreover, cellular levels of P-4502E1 protein and messenger RNA were significantly correlated (rs = 0.79; p < 0.001) in all patients.(ABSTRACT TRUNCATED AT 400 WORDS)

Engineered yeast cells as model to study coupling between human xenobiotic metabolizing enzymes. Simulation of the two first steps of benzo[a]pyrene activation

Human microsomal epoxide hydrolase and cytochrome P450 (P450) 1A1 were coexpressed in Saccharomyces cerevisiae from expression cassettes integrated respectively into the host chromosomal DNA and on a multicopy plasmid in a strain already overexpressing yeast NADPH-cytochrome P450 reductase (P450 reductase). A styrene-oxide-hydrolase activity (2 nmol.min-1.mg microsomal protein-1) and a 7-ethoxyresorufin-O-deethylase activity (320 pmol.min-1.mg microsomal protein-1) characteristic respectively of microsomal epoxide hydrolase and P450 1A1 were detected. The conversion of benzo[a]pyrene (B[a]P) to B[a]P-7,8-dihydrodiol both in microsomal preparations and in growing yeast cells was observed, demonstrating an efficient coupling between the two human enzymes. Kinetic analysis indicated that the B[a]P-7,8-oxide produced by the P450-1A1-dependent reaction does not accumulate before hydrolysis by microsomal epoxide hydrolase. This system was also used as a control to evaluate the coupling efficiency of a mixture of microsomes or of yeast cells containing separately the individual enzymes (i.e., human P450 1A1 and microsomal epoxide hydrolase). B[a]P-7,8-oxide was well converted to the corresponding dihydrodiol with a mixture of microsomes. In contrast, when the same experiment was repeated with a mixture of cells expressing independently the two activities, dihydrodiol formation was not observed. Coexpression of human phase I and phase II enzymes in a single yeast cell and microsome mixture thus appear to be complementary tools for the simulation of human-drug-metabolism or carcinogen-metabolism pathways.

Changes in gallbladder bile composition following gallstone formation and weight reduction

Changes in gallbladder bile composition that occurred in patients who developed gallstones during weight reduction were evaluated. Bile was sampled directly from the gallbladder in 11 morbidly obese patients with no gallstones at the time of gastric bypass surgery and after gallstones had formed at cholecystectomy. Bile salt concentration ([BS]) increased significantly from a mean of 82.7-157.7 mmol/L (P less than 0.05). The concentration of cholesterol in gallbladder bile increased slightly and cholesterol saturation declined slightly with weight reduction and gallstone formation. Gallbladder mucin concentration increased 18-fold from a mean of 62 to 1110 micrograms/mL (P less than 0.001). Both free [Ca2+] and total calcium [Ca] increased 40% from mean values of 1.12 and 5.05 mmol/L at gastric bypass to 1.86 and 8.60 mmol/L after gallstone formation (P less than 0.05). The increase in [Ca2+] observed after gallstone formation was much greater than anticipated from changes in [BS] alone. This excess [Ca2+] in gallbladder bile increased curvilinearly with increasing mucin concentration. These results show that both gallbladder mucin and [Ca2+] increase with gallstone formation in humans and that mucin may modulate [Ca2+] in gallbladder bile.

Impaired hepatic apolipoprotein B and E translation in streptozotocin diabetic rats

Studies of streptozotocin-induced diabetes in rats have demonstrated that hepatic apo B and apo E production are reduced. To determine if reductions are related to decreases in hepatic mRNAs, we performed blotting analysis of total liver RNA with rat apo B, apo E, and albumin cDNA probes. The expected reduction in albumin mRNA levels to 48% of control livers occurred in diabetic rat liver, while apo B and apo E mRNA levels were unchanged. The proportion of translational stop codon (BSTOP) mRNA averaged 43% of total in diabetic rats similar to control levels. Long-term labeling experiments using [35S]methionine in primary cultures of rat hepatocytes and specific immunoprecipitations demonstrated production of apo B and apo E, and albumin by hepatocytes from diabetic rats was reduced to 37%, 53%, and 23% of controls. Pulse-chase studies, together with mRNA analyses, suggest that reduced hepatic secretion of apo B and apo E in diabetics is primarily a result of impaired translation and not intracellular degradation. Ribosome transit studies directly confirmed the prolonged elongation rates for apo B and apo E mRNAs in hepatocytes derived from diabetic rats. This effect was more pronounced on apo BH (higher molecular weight) than on apo BL (lower molecular weight). Treatment of diabetic rats with insulin for 7 d led to normalization of hepatic albumin mRNA levels with no substantial change in apo E mRNA levels. In contrast, insulin treatment resulted in significant increases in hepatic apo B mRNA over control levels. Results suggest hepatic albumin and apo B mRNA levels are responsive to insulin in the diabetic state.