Liver Acinus Research Articles

Mimicry in primary rat hepatocyte cultures of the in vivo perivenous induction by phenobarbital of cytochrome P-450 2B1 mRNA: role of epidermal growth factor and perivenous oxygen tension.

Treatment of male rats with phenobarbital (PB) results in a perivenous and mid-zonal pattern of cytochrome P-450 (CYP)2B1 mRNA expression within the liver acinus. The mechanism of this zonated induction is still poorly understood. In this study sinusoidal gradients of oxygen and epidermal growth factor (EGF) besides those of the pituitary-dependent hormones growth hormone (GH), thyroxine (T4), and triiodothyronine (T3) were considered to be possible determinants for the zonated induction of the CYP2B1 gene in liver. Moreover, heme proteins seem to play a key role in oxygen sensing. Therefore, the influence of arterial (16% O2) and venous (8% O2) oxygen tension (pO2), and of the heme synthesis inhibitors CoCl2 and desferrioxamine (DSF) on PB-dependent CYP2B1 mRNA induction as well as the repression by EGF and, for comparison, by GH, T4, and T3, of the induction under arterial and venous pO2 were investigated in primary rat hepatocytes. Within 3 days, phenobarbital induced CYP2B1 mRNA to maximal levels under arterial pO2 and to about 40% of maximal levels under venous pO2. CoCl2 annihilated induction by PB under both oxygen tensions, whereas desferrioxamine and heme abolished the positive modulation by O2, suggesting that heme is a necessary component for O2 sensing. EGF suppressed CYP2B1 mRNA induction by PB only under arterial but not under venous pO2, whereas GH, T4, and T3 inhibited induction under both arterial and venous pO2. Thus, in hepatocyte cultures, an O2 gradient in conjunction with EGF mimicked the perivenous induction by PB of the CYP2B1 gene observed in the liver in vivo.

Spatial distribution of human liver aldehyde dehydrogenase isoenzymes.

To elucidate the pattern of lesions in the liver parenchyma after ethanol ingestion, the quantitative distribution profiles of both the cytosolic and the mitochondrial aldehyde dehydrogenase isoenzyme activities were determined by the use of ultrathin-layer electrophoresis. It was found that in human liver parenchyma, both isoforms of aldehyde dehydrogenase are almost homogeneously represented in the liver acinus. These quantitative data are supported by the results of an improved histochemical technique. Moreover, sex differences were not detected either in activity or in the distribution pattern. Consequently, it can be assumed that it is not the activity of total aldehyde dehydrogenase or its isoforms which is responsible for the higher susceptibility of the perivenous zone to alcohol-dependent damage.

Distribution of alcohol dehydrogenase isoenzymes in the human liver acinus.

By the use of a newly developed technique of ultrathin-layer electrophoresis, class I and class II alcohol dehydrogenase activity could be demonstrated in microdissected samples of the periportal, intermediate, and perivenous zones of the liver acinus in men and women. It could be demonstrated that both classes exhibit low activity in the periportal zone. From there, a rising gradient in the direction of the perivenous end was apparent. This increase, however, was found to be significant only in women. The analysis of class I alcohol dehydrogenase isoenzymes showed that the expression of alpha-, beta-, and gamma-containing isoforms did not differ in relation to the intraacinar position. The constant proportions of the isoenzymes to the maxima and minima of the total alcohol dehydrogenase activity support the view that the adult liver-specific isoenzyme pattern is determined during postnatal development.

Three-dimensional reconstruction of parenchymal units in the liver of the rat.

To investigate the parenchymal units in the liver of the rat three-dimensionally, 15 micrometer cryosections were used for the demonstration of glucose-6-phosphatase (G6Pase) activity to visualize the borders of the individual units. Together with the supplying and draining vessels, they were traced through a sequence of 146 sections and reconstructed. A cone-shaped secondary unit with a height of 2.1 mm and a volume of 3.3 mm3 was reconstructed. It was "covered" by a continuous vascular surface, consisting of portal tracts and vascular septa, connecting the portal venular branches. The secondary unit was subdivided by portal tracts and vascular septa, and by branches of a draining central venular tree into 14 primary units. Most of them were tri- to heptahedral in shape. The height varied between 330 and 840 micrometer, and the volume varied between 0.094 and 0.621 mm3. The branches of the portal venular tree, with diameters from 28 +/- 5 micrometer to 61 +/- 14 micrometer, were oriented preferentially along the vertical axis of the units. Most of the primary units were drained by single branches of the central venular tree, located in the center and oriented along the vertical axis of the units. Vessel diameters ranged from 62 +/- 14 micrometer to 216 +/- 9 micrometer. The average length of the sinusoids was 355 +/- 3 micrometer. From the results of this reconstruction study, it was concluded that the concept of the liver acinus cannot be applied to the liver of the rat.

Murine hepatic microvascular adhesion molecule expression is inducible and has a zonal distribution.

The structural and functional heterogeneity of hepatocytes and non-parenchymal cells across the liver lobule or acinus has been well documented. The geographic distribution and potential for induced expression of adhesion molecules on murine hepatic microvascular cells has not been reported, although these molecules are able to influence the metastatic outcome of intravascular cancer cells. We have postulated that the expression of adhesion molecules on these cells is susceptible to regulation by environmental factors and that these molecules have a zonal distribution across the acinus. To test this hypothesis, we injected C57BL/6 mice with bacterial lipopolysaccharide, 1 microg/g body weight, i.p. At various time points (0-48 h) after stimulation, liver tissue sections were prepared for immunohistochemistry. Confocal microscopy was used to detect the expression of vascular cell adhesion molecule-1 (VCAM-1), E-selectin, intercellular adhesion molecule-1 (ICAM-1) and alpha v integrin. The expression patterns were quantitatively measured by histomorphometry. Under basal conditions, ICAM-1 was weakly expressed in terminal portal veins while minimal VCAM-1 and no E-selectin were detected. Following stimulation with lipopolysaccharide, VCAM-1 and E-selectin were expressed on the endothelium of terminal portal veins and on sinusoidal lining cells with significantly stronger expression in the periportal zone than midzone. VCAM-1 expression peaked at 4 h and decreased gradually by 48 h. E-selectin peaked at 2 h and disappeared by 12 h after stimulation. ICAM-1 expression showed a much stronger and more uniform expression across the acinus with the peak reached by 4 h and sustained for longer than 48 h after lipopolysaccharide administration. The alpha v integrin was not detected under basal conditions or after lipopolysaccharide stimulation. Expression of all these adhesion molecules (ICAM-1, VCAM-1, E-selectin and alpha v integrin) was induced by growth of B16F1 melanoma cells in the peritoneal cavity of the mouse. These results support the hypotheses that expression of microvascular adhesion molecules in the mouse liver is susceptible to regulation by environmental stimuli and has a zonal heterogeneity across the acinus.

Intravital microscopic investigation of xenogeneic microcirculation and impact of complement depletion by cobra venom factor.

Discordant xenografts are hyperacutely rejected within minutes. Disturbances in the microcirculation are considered to be the central mechanisms of hyperacute xenogeneic rejection (HXR). In this study intravital fluorescence microscopy was applied to investigate the dynamics of microcirculatory alterations in a setting in which HXR was inhibited by complement (C) depletion. Blood flow was measured as rat livers were perfused with isogeneic rat or xenogeneic human blood to assess the pattern of either physiological isogeneic hemoperfusion or in the course of HXR. Next, the complement system of the perfusate was inactivated by cobra venom factor (CVF) in order to inhibit HXR. Liver sinusoids of the isogeneic group were homogeneously perfused (sinusoidal perfusion rate 93.6+/-0.3%), whereas in the xenogeneic group the sinusoidal perfusion rate dropped to 67.1+/-3%. The perfusion in the periportal zone of an acinus was significantly lower ( 59.0+/-3.3%) than in the pericentral zone (76.2+/-3.1%). Treatment with CVF improved the sinusoidal perfusion to a value of 85.6+/-2.3%, physiological perfusion, however could not be reached. In contrast to the isogeneic group, massive white blood cell (WBC) and platelet accumulation was found in the xenogeneic group, especially in the terminal portal vessels and in the periportal zone of liver acini. WBC and platelet counts show that the adherence of these cells appears rapidly in the first 5 min after reperfusion as firm adherence. CVF was not able to inhibit WBC and platelet accumulation, indicating that WBC endothelial interactions do not require an intact complement system. Bile flow, a parameter of liver function, decreased only slightly during isogeneic perfusion. The addition of CVF to the rat blood reduced the bile flow to one half of the untreated isogeneic flow, indicating a hepatotoxic side-effect of CVF. In xenogeneic perfusion the bile flow dropped to 62.6% and with the addition of CVF to 37.5% in the first 15 min after reperfusion. The bile flow of the CVF treated groups recovered during the perfusion but could not reach isogeneic values.

Comparative morphofunctional study of liver acini in peritonitis of different origin

Structural and metabolic characteristics of liver acini are studied in the peritonitis patients. In peritonitis, changes in the activities of hepatocyte dehydrogenases in different acinus zones depend on its causes. The entry of gram-negative bacteria lipopolysaccharides into portal blood flow and liver is an important factor in the pathogenesis of progressing hepatic failure.

Differential expression of IGF-I and IGF-binding protein-1 and -2 in periportal and perivenous zones of rat liver.

IGF-I has important roles in regulating growth and metabolism. Circulating IGF-I is bound to specific binding proteins (IGFBP-1 to -6), with hepatocytes containing IGF-I, IGFBP-1 and -2 mRNA. Although many hepatic proteins are regionally expressed in the liver acinus, no studies have reported zonation of IGF protein expression. In this study we investigated the pattern of hepatic mRNA for the IGF proteins, vs the previously reported pepriportal gradient of phosphoenolpyruvate carboxykinase (PEPCK) expression. In situ hybridisation was used to analyse IGF-I, IGFBP-1, -2 and PEPCK mRNA in female Sprague-Dawley rats fed diets containing low (6%), normal (21%) or high (35%) protein. We report for the first time that IGFBP-1 and -2 and IGF-I are differentially expressed in the liver acinus. In the normal- and high-protein groups, levels of IGFBP-1 mRNA were higher in the perivenous region, i.e. the opposite gradient to PEPCK, with a higher gradient of IGFBP-1 expression in the high-protein group. In contrast, IGFBP-2 had a similar pattern to PEPCK, and a periportal gradient of IGF-I mRNA was also seen in the low-protein group. Using computerised image analysis, levels of IGFBP-1 and -2 mRNA were elevated 2- and 10-fold respectively, in the low- vs normal-protein groups. The level of IGF-I mRNA was reduced to 65% of normal, with circulating IGF-I levels at 30% and insulin levels 39% of normal. These results demonstrate that hepatocytes are a heterogeneous population with respect to regulation of IGF proteins, having specific expression patterns dependent on the position of the hepatocyte within the liver acinus.

Nonparenchymal cells in chronically hyperinsulinemic liver acini of diabetic rats, with special regard to hepatic stellate cells

Background/Aims: An increase in proliferative activity and other distinct hepatocellular alterations — resembling preneoplastic foci and progressing to hepatocellular tumors — have been shown to develop in liver acini draining the blood from islets of Langerhans, transplanted through the portal vein into the liver of streptozotocin-diabetic rats. Methods: Altered and unaltered liver acini were investigated for possible changes in hepatic stellate cells 4–76 days after islet transplantation. Results: Corresponding to a significant increase in the hepatocellular volume, the volume density of total non-parenchymal cells was significantly reduced in altered compared to unaltered liver acini. With regard to the total nonparenchymal cell volume, the hepatic stellate cell fraction was not different, whereas the fraction of Kupffer cells was significantly reduced and the fraction of sinusoidal endothelial cells was significantly increased in altered compared to unaltered liver acini, respectively. The volume density as well as the single volume of the hepatic stellate cell mitochondria increased significantly in altered compared to unaltered liver acini. Hepatic stellate cell lipid droplets did not show significant differences between altered and unaltered liver acini. In situ hybridization for hepatocyte growth factor mRNA showed no differences in intensity of the specific signals in hepatic stellate cells of altered versus unaltered liver acini. The transplanted islets were negative for hepatic growth factor mRNA. Conclusions: The results suggest that hepatic growth factor production by hepatic stellate cells or by islet cells is not relevant to hepatocellular proliferative activity in altered liver acini.

Pathways of interstitial fluid and lymph flow in the liver acinus of the sheep and mouse.

In the acinus of the sheep and mouse liver, lymphatic vessels are restricted to the portal tracts. Vessels less than about 25 microm across form a network around portal venules, and are closely associated with the limiting plate of hepatocytes. The perisinusoidal space of Disse is continuous with the interstitial space of the portal tracts at the origin of the sinusoids. It seems likely that excess interstitial fluid derived from the sinusoids flows along the perisinusoidal space of Disse to enter the portal tracts near the portal venules, and then enters the small lymphatics which lie adjacent to those venules. It then enters the larger vessels, which are adjacent to hepatic arterioles and bile ductules.

Experimental studies on the stem cell concept of liver regeneration. I

There are increasing references for the existence of a hepatic stem or progenitor cell system as well as its participation in the physiological as well as reparative regeneration of the liver and in carcinogenesis. For the physiological regeneration the existence of a dynamic "cell-renewal" system finds increasing consideration and in the "streaming liver concept" (Zajicek et al. 1985) its functional expression. This concept is still under discussion. The present paper tries to check this animal-experimentally (Wistar rats) under use of two different thymidine analogues (3H-thymidine and Bromodeoxyuridine). In different time intervals after labelling (1 h, 14, 30, 60, 90, 120 d) a shift of the labelling bias or a migration of the hepatocytes in the liver acinus (Rapaport) in portovenous direction could be shown. The average migration speed is 0.575 microm or 0.0315 cell positions per day, the cell production rate is one in 31.5 days. The present paper results support the inclusion of a stem or progenitor cell system into the physiological regeneration of the liver and allow the classification into the "streaming liver concept" (Zajicek et al. 1985).

The portal lobule in rat liver fibrosis: a re-evaluation of the liver unit.

We re-evaluated three schemes of liver organization: the classic lobule, the portal lobule, and Rappaport's liver acinus. The lobular angioarchitecture of normal rat liver and the three-dimensional structure of pseudolubules found in rat livers with fibrosis induced by swine serum were compared with the classic lobule of the pig. Normal and fibrotic rat livers and pig livers were perfused, injected with either India ink or 0.75% OsO4 through the portal and/or hepatic vein, and immersionfixed. Whole lobes and hand-cut thick sections were made transparent with a solution of benzyl benzoate and methyl salicylate. The angioarchitecture of normal rat liver differs from pig liver. In the former, terminal portal branches and central veins interdigitate, and in the latter, numerous terminal portal branches that arise from interlobular portal veins establish a vascular basket surrounding one central vein and forming classic lobule. The structure of liver acinus is never found in the pig liver. The terminal portal branch, together with the terminal hepatic artery and bile duct, are present inside each pseudolobule of fibrotic rat livers. Blood from the terminal portal branch flows through inlet venules into radiating sinusoids, and, at the periphery converges into newly formed septal and angular outlet venules; these venules terminate in fibrotic central veins located at each corner. Pseudolobules are not rugby ball-like as Rappaport's liver acini are but are polyhedron in shape. The rat pseudolobules are comparable with the portal lobule; its structure and microcirculation are the reverse of the pig classic lobule. Rat pseudolobules are different from liver acini, as shown by the following: 1) their three-dimensional shape is different; and 2) they have a reverse relationship to classic lobules while acini are defined to subdivide classic lobules. In normal and fibrotic rat livers, the liver unit is the portal lobule with a terminal portal branch as the axial branch and central veins at the periphery. The co-existence of liver acini and classic lobules is doubtful.

Prevention and Treatment of Hepatic Venocclusive Disease after High-Dose Cytoreductive Therapy

Venocclusive disease of the liver (VOD) is one of the most common and serious complications following stem cell transplantation. High-dose chemotherapy or chemoradiotherapy injures the structures of Zone 3 of the liver acinus and produces the clinical syndrome of hepatomegaly or right upper quadrant pain, jaundice, and fluid retention. VOD occurs in up to 54% of stem cell transplant recipients and is fatal in 25-50% of them. While the clinical signs of VOD usually manifest during the first post-transplant week, late presentation can occur. The purpose of this review is to discuss the manifestations and pathophysiology of VOD and the options for prevention and treatment.

Hepatic Foci in Rats after Diethylnitrosamine Initiation and 2,3,7,8-Tetrachlorodibenzo-p-dioxin Promotion: Evaluation of a Quantitative Two-Cell Model and of CYP 1A1/1A2 as a Dosimeter

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a potent hepatic tumor promoter in female rats. We used a quantitative, stochastic initiation-promotion model based on R. B. Conolly and J. S. Kimbell (Toxicol. Appl. Pharmacol.124,284–295, 1994) to analyze initiation–promotion results from a previously published study (H. C. Pitotet al., Carcinogenesis8,1491–1499, 1987) within the context of a negative selection model of tumor promotion. In this model, two types of initiated cells (called A and B cells) are produced by DEN initiation. Visually excellent correspondence between model predictions and data (i.e., foci/cm3liver and percentage of liver occupied by foci) are obtained when TCDD is described as having dose–responsive effects on division and death (apoptotic) rates of these two cell types. For A cells, both the division and the death rates increase while the difference between division and apoptotic rates decreases. For B cells, the difference between division and apoptotic rates increases, primarily due to a decrease in the apoptotic rate. We also linked these alterations in cell kinetics to a pharmacokinetic model for TCDD incorporating a five subcompartment model of the liver acinus with induction of CYP1A1 and 1A2 genes in the subcompartments. Alterations in A cell kinetics correlate with effects of TCDD in the region most sensitive to induction (subcompartment 5—centrilobular region); B cell dynamics correlate with induction in subcompartments 3–5 (centrilobular and mid-zonal regions). In summary, these modeling exercises show that (1) the two-cell model, without presuming effects of TCDD on the mutation rate of normal hepatocytes, reproduces the data of Pitotet al.(1987) and (2) induction of CYP1A1/1A2 in different regions of the hepatic acinus can be used as a general correlate of these presumed changes in cell growth kinetics.

Membrane transport in hepatic clearance of drugs. II: Zonal distribution patterns of concentration-dependent transport and elimination processes.

The objective of the present simulation study was to investigate the effects of hepatic zonal heterogeneity of membrane transporter proteins and intrinsic elimination activities on hepatic clearance (CL) and drug concentration gradient profiles in the sinusoidal blood and hepatocytes. The model used in the simulations assumes an apparent unidirectional carrier-mediated transport and a bidirectional diffusion of substrates in the hepatic sinusoidal membrane as well as a nonlinear intrinsic elimination. Three different distribution patterns of the transporter and the metabolizing enzyme along the sinusoidal flow path were used for the simulations. The effects of changes in the Michaelis-Menten parameters for those nonlinear processes, and in the unbound fractions of the drug in blood and tissue components were investigated. Significant differences in CL occurred when the distribution patterns of the transporter and/or the metabolizing enzyme activities were altered under nonlinear conditions. The highest CL values were observed when the transporter and the metabolizing enzyme had similar distribution patterns within the liver acinus, while opposite distribution patterns produced the lowest CL values. Tissue concentration profiles were significantly affected by the distribution patterns of the transporter, but the changes in blood concentration profiles were relatively small. Altering protein binding in blood produced significant changes in CL, and blood and tissue concentration gradients, while altering protein binding in tissue affected only drug accumulation patterns within hepatocytes, regardless of the distribution patterns of the transporter or the metabolizing enzyme. The present simulations demonstrate that hepatic zonal heterogeneities in the transporter and the metabolizing enzyme activities can significantly influence hepatic clearance and/or drug concentration gradient profiles in the sinusoidal blood and hepatocytes.

Venocclusive disease of the liver after bone marrow transplantation: The role of hemostasis

Venocclusive disease of the liver is a relatively frequent early complication of bone marrow transplantation related to pre-transplant toxic injury to the liver. Events that lead to toxicity of the liver in the pre-transplant setting are infection, anti-neoplastic and anti-infectious drug administration and radiation. The histological correlates of venocclusive disease are lesions mainly localized to structures in zone 3 of the liver acinus and in the sublobular central venules. At some point in the pathogenesis of venocclusive disease, blood clotting and inflammation occur. The first is characterized by laboratory signs of coagulation activation, by an increase in several procoagulant proteins and by a decrease in naturally occuring anticoagulants, particularly protein C, the latter being a sensitive index of liver injury. Inflammation is mediated by cytokine production, which maintains procoagulant endothelial responses and liver injury. Severe venocclusive disease is associated with multi-organ failure and elevated mortality. Attempts at finding predictive markers of the disease have succeeded in identifying some coagulation and inflammatory proteins which can be useful in predicting the occurrence of VOD in selected patient groups. The role of hemostasis in venocclusive disease is under-scored also by the reports on the successful prophylaxis and management of the disease with heparin and thrombolytic agents.

Mechanistic considerations in benzene physiological model development.

Benzene, an important industrial solvent, is also present in unleaded gasoline and cigarette smoke. The hematotoxic effects of benzene in humans are well documented and include aplastic anemia, pancytopenia, and acute myelogenous leukemia. However, the risks of leukemia at low exposure concentrations have not been established. A combination of metabolites (hydroquinone and phenol, for example) may be necessary to duplicate the hematotoxic effect of benzene, perhaps due in part to the synergistic effect of phenol on myeloperoxidase-mediated oxidation of hydroquinone to the reactive metabolite benzoquinone. Because benzene and its hydroxylated metabolites (phenol, hydroquinone, and catechol) are substrates for the same cytochrome P450 enzymes, competitive interactions among the metabolites are possible. In vivo data on metabolite formation by mice exposed to various benzene concentrations are consistent with competitive inhibition of phenol oxidation by benzene. In vitro studies of the metabolic oxidation of benzene, phenol, and hydroquinone are consistent with the mechanism of competitive interaction among the metabolites. The dosimetry of benzene and its metabolites in the target tissue, bone marrow, depends on the balance of activation processes such as enzymatic oxidation and deactivation processes such as conjugation and excretion. Phenol, the primary benzene metabolite, can undergo both oxidation and conjugation. Thus the potential exists for competition among various enzymes for phenol. Zonal localization of phase I and phase II enzymes in various regions of the liver acinus also impacts this competition. Biologically based dosimetry models that incorporate the important determinants of benzene flux, including interactions with other chemicals, will enable prediction of target tissue doses of benzene and metabolites at low exposure concentrations relevant for humans.

The location of hepatocytes in the rat liver acinus determines their sensitivity to calcium-mobilizing hormones

BACKGROUND & AIMS: In multicellular systems of rat hepatocytes and in the intact liver, inositol 1,4,5-trisphosphate (IP3)-dependent agonists induce sequentially ordered calcium ion signals. The mechanisms by which sequential waves are oriented from one hepatocyte to another are unknown. The aim of this study was to investigate the relationship between hepatocyte location in the acinus and cellular sensitivity to noradrenaline, vasopressin, adenosine triphosphate, and angiotensin II. METHODS: Periportal (PP) and pericentral (PC) rat hepatocyte suspensions, isolated by the digitonin-collagenase technique, were loaded with quin2-acetoxymethyl ester, and hormonal responses were studied in a spectrofluorimeter. The function of the IP3 receptor was studied by measuring the IP3-mediated 45Ca2+ release from permeabilized PP and PC hepatocytes. RESULTS: Increases in noradrenaline and vasopressin-induced intracellular Ca2+ concentration were greater in PC than in PP hepatocytes. In contrast, PP cells were more responsive than PC cells to adenosine triphosphate, and angiotensin II induced similar intracellular Ca2+ concentration increases in both hepatocyte populations. In permeabilized PP and PC hepatocytes, internal Ca2+ stores showed the same loading kinetics, the responses to IP3 were similar, and the sizes of the IP3 sensitive compartment were not different. CONCLUSIONS: Hepatocyte location in the acinus determines cellular sensitivity to Ca(2+)-mobilizing agonists. Intercellular Ca2+ waves in the liver could be driven by sensitivity gradients along the hepatocyte plate. (Gastroenterology 1996 Nov;111(5):1343-52)

Overexpression of cytochrome P-450 isoforms involved in aflatoxin B1 bioactivation in human liver with cirrhosis and hepatitis.

Studies were carried out to test the hypothesis that inflammatory liver disease increases the expression of specific cytochrome P-450 isoenzymes involved in aflatoxin B1 (AFB) activation. The immunohistochemical expression and localization of various human cytochrome P-450 isoforms, including CYP2A6, CYP1A2, CYP3A4, and CYP2B1, were examined in normal human liver and liver with hepatitis and cirrhosis. The constitutive expression of CYP3A4 in normal liver showed a characteristic pattern of distribution in centrilobular hepatocytes, whereas CYP1A2, CYP2A6, and CYP2B1 were expressed uniformly throughout the liver acinus. In sections of liver infected with hepatitis B virus (HBV) or hepatitis C virus (HCV), the expression of CYP2A6 was markedly increased in hepatocytes immediately adjacent to areas of fibrosis and inflammation. CYP3A4 and CYP2B1 were induced to a lesser degree, and expression of CYP1A2 was unaffected. In HBV-infected liver, double immunostaining revealed that overexpression of CYP2A6 occurred in hepatocytes expressing the HBV core antigen. In HCV-infected liver, CYP2A6, CYP3A4, and CYP2B1 were overexpressed in hepatocytes with hemosiderin pigmentation. These results suggest that alterations in phenotypic expression of specific P-450 isoenzymes in hepatocytes associated with hepatic inflammation and cirrhosis might increase susceptibility to AFB genotoxicity.

In vivo infusion of growth factors enhances the mitogenic response of rat hepatic ductal (oval) cells after administration of 2-acetylaminofluorene

Expression of several growth factors is elevated in rat liver, after induction of oval cell proliferation by chemical carcinogens. However, the exact roles played by individual factors are not defined. We infused and examined the effects of epidermal growth factor (EGF) and hepatocyte growth factor (HGF) on the proliferation of ductal and periductal cells after their activation with 2-acetylaminofluorene (2- AAF). Furthermore, we included studies on urokinase-type plasminogen activator (uPA), because Northern blot analysis showed a strong coincidence of uPA expression with oval cell proliferation. Low doses of 2-AAF were used to activate ductal and periductal cells, whereafter growth factors were infused. Infusion of EGF, HGF, uPA, or any combination thereof for up to 7 days resulted in increased numbers of [3H]thymidine-labeled ductal and periductal cells expanding into the liver acinus. Although the growth factors all increased the number of labeled cells, they preferentially acted on different cell populations. Although exposure to 2-AAF alone or combined with infusion of HGF resulted in proliferation of almost equal numbers of ductal and Ito cells, infusion of EGF and any combination hereof resulted in 75% to 80% of labeled cells having a ductal phenotype. Also, infusion of EGF and HGF resulted in decreased numbers of cells undergoing apoptosis in response to 2-AAF. Our results demonstrate that, although 2-AAF acts as a mitogenic stimulus for ductal and periductal cells, growth factors are necessary for survival, motility, and expansion of these cells into the liver acini. (Hepatology 1996 Jan;23(1):71-9)