Adjacent Hepatocytes Research Articles

“Lipomatous” Lesions of Unknown Cellular Origin in the Liver of B6C3F1 Mice

The gross, microscopic, and ultrastructural features of lipomatous lesions in the liver of B6C3F1 mice are described. The cases were selected from a database of 45,406 male and 45,674 female mice used as treated, control, or vehicle-control animals in the National Cancer Institute's Bioassays or the National Toxicology Program's 2-year carcinogenicity studies. Thirteen hepatic lesions identified from cases within the database were re-evaluated microscopically and selected for further study. These lesions were present in ten males and three females that were between 85 and 113 weeks of age at the time of death. Grossly, the liver lesions were described as white to yellow or red to brown nodules/masses or foci that ranged from 2.0 to 25 mm in diameter. The lesions commonly involved the median and left lateral hepatic lobes. Microscopically, many of the lesions closely resembled lipomas described in the liver of human beings, and they consisted of nonencapsulated mature adipose-like tissue with irregular margins. The majority of the cells that comprised the lipomatous lesions were signet-ring shaped. These cells were positive for lipid as evidenced with oil red-O. The lipid droplets were also present within the hepatocytes that comprised the hepatic plates trapped within or surrounding many of the lipomatous lesions. At the margins of many of the lesions there were spindle-shaped cells that contained small intracytoplasmic lipid vacuoles. These cells were often within a stromal matrix that had focal areas of collagen and mucopolysaccharides, as evidenced by weak staining with Masson's trichrome and periodic acid-Schiff's stains, respectively. There was also disruption of the reticulum fibers in many of the lesions, as noted with a Gomori's reticulum stain. Ultrastructurally, cytoplasmic organelles, such as rough endoplasmic reticulum, free ribosomes and small lipid vacuoles, were present in the spindle-shaped cells, whereas signet-ring-shaped cells had few discernible organelles due to peripheral compression of the cytoplasm by single large vacuoles occupying the cytoplasmic space. The spindle-shaped cells were free of lysosomes. Thin collagen fibers were seen in contact with some of the spindle-shaped cells and were located between these cells and adjacent hepatocytes, or endothelial cells lining sinusoidal capillaries. A distinct basal lamina was not associated with spindle- or signet-ring-shaped cells. Similar lipomatous lesions were not found in other visceral organs. The exact cellular origin of the hepatic lesions described here is not known.

Isolation Culture, and Transplantation of Rat Hepatocytic Precursor (Stem-like) Cells

From a review of past studies and the report of new studies from our laboratory, this article provides strong evidence to show that WB-F344 (WB) rat liver epithelial cells are stem-like precursor cells for hepatocytes. WB cells are structurally and phenotypically simple epithelial cells that were isolated from the liver of an adult male Fischer 344 rat, under conditions that excluded their origin from hepatocytes in vivo. WB cells express a phenotypic repertory that overlaps, but is distinct from, that of both hepatocytes and bile duct epithelial cells. The complex phenotype of WB cells is compatible with their being embryonic or undifferentiated variants of either hepatocytes or bile duct epithelial cells. When WB cells are tagged genetically with genes for bacterial beta-galactosidase and neomycin resistance (BAG2-WB), they and their progeny can be distinguished from parental WB cells and hepatocytes by the expression of these gene products. Progeny of BAG2-WB cells that were transplanted into the liver parenchyma of syngeneic rats integrated into hepatic plates and acquired the morphological and functional attributes of adjacent host hepatocytes; the progeny of BAG2-WB cells in the liver express albumin, tyrosine aminotransferase, alpha-1-antitrypsin, and transferrin. We also demonstrate that progeny of BAG2-WB cells can be recovered from livers into which they have been transplanted, which may allow the elucidation of alterations in gene expression that accompany their differentiation.

Ultrastructural characteristics of intercellular contacts and bile canaliculi in neonatal rat hepatocytes in primary culture.

The ultrastructure of the cellular contacts and bile canaliculi was examined in cultured neonatal (day 5) rat hepatocytes to elucidate the development of cellular polarity. A new scanning electron microscopic technique for cultured hepatocytes allowed a view of cell-cell attachment and the entire cell surface, including the underside on plastic dishes. At 3 h after plating, neonatal hepatocytes were shown to be round, with loss of the preferential localization of cell organelles. After 6 h of culture, the cells had become oblong; they were aggregated in groups of several cells and the cellular contacts were not as rigid or as straight as those in adult hepatocytes. Transmission electron microscopy showed the biliary functional polarity to be like that in vivo. On the undersurfaces of adjacent neonatal hepatocytes a hemicanalicular structure lined with microvilli was found, which probably corresponds to the ultrastructure of bile canaliculi in vivo. However, no canaliculi or orifices of bile channels were found in adult hepatocytes. These results suggest that in neonatal rat hepatocytes the formation of tight rigid cellular contacts was suppressed. Modulation of cell membranes appeared on the undersurfaces of neonatal hepatocytes in early culture stages. The differences in the development of cellular polarity could be caused by the proliferating activity of neonatal hepatocytes.

Tumor-suppressor p53 gene in hepatitis C and B virus-associated human hepatocellular carcinoma.

Abnormalities of the tumor-suppressor p53 gene have been discovered in human hepatocellular carcinoma (HCC). It is unclear, however, whether HCC related to chronic viral hepatitis is associated with p53 gene alterations. In this study, we have examined p53 abnormalities in HCC associated with hepatitis C and B virus (HCV and HBV) infections. Tissues from 18 HCC patients from several hospitals throughout the United States were collected (9 were HCV-infected, 5 were HBV-infected, 1 was HCV/HBV-infected, and 3 were non-virus-associated). Immunostaining with monoclonal pAb 1801 revealed expression of p53 protein in tumor-cell nuclei in one HCV-associated HCC, and in no case of HBV-associated HCC, while the nuclei of adjacent hepatocytes were negative. Using Hae III-digestion of chromosomal DNA, mutations at codon 249 were not found in any of 18 HCC tissues studied. Direct sequencing demonstrated a mutated codon 244 and a wild-type codon 249 in the conserved regions (exon 5-8) of p53 gene from the tumor tissue with nuclear p53 expression. By reverse-transcription-polymerase chain reaction (RT-PCR), the expression of p53 mRNA was demonstrated in tumor cells from 10 out of 16 HCC tissues. In conclusion, the specific mutation at codon 249 with G to T transversion was not observed in the HCCs associated with HCV or HBV infections. In HBV or non-virus-associated HCCs studied, no other p53 gene abnormalities were found. A point mutation at codon 244 with G to A transition of p53 gene was detected in only one of 10 HCV-associated HCCs, which suggests that p53 mutations may not play a significant role in HCV- or HBV-associated hepatocarcinogenesis.

Liver biopsy features of acute hepatitis C compared with hepatitis A, B, and non‐A, non‐B, non‐C

The diagnosis of acute hepatitis C (AHC) often can only be suspected because current serologic tests remain negative for over 3 months. Because histologic features might provide useful clues, we reviewed 85 liver biopsy specimens from 85 patients with acute viral hepatitis, comparing 22 cases of AHC with 23 cases of acute hepatitis A (AHA), 30 cases of acute hepatitis B (AHB), and 10 cases of acute hepatitis non-A, non-B, non-C (AHNC). AHC was characterized by dense portal lymphoid aggregates (7 cases) and Poulsen-Christoffersen-type cholangitis (8 cases); these lesions were not found in any other type of acute viral hepatitis, and thus appeared to be diagnostic. Sinusoidal inflammatory infiltrates also were common in AHC, particularly in biopsy specimens obtained during the early phase of the disease. These inflammatory infiltrates did not appear to affect adjacent hepatocytes. Necrosis in AHC usually was spotty and accompanied by mixed inflammatory cells. In AHNC, necrosis was also spotty but, as an added feature, pigmented macrophages predominated in them. In AHA, necrosis was predominantly periportal, whereas in AHB, severe zone-3 necrosis predominated. Fatty changes were predominantly microvesicular; they were common in AHC but were also found in other groups. Collectively, the described histologic features allowed diagnosis of AHC in biopsy specimens with reasonable confidence. However, histologic findings failed to predict the prognosis in individual cases.

Production and secretion of endothelin by hepatocellular carcinoma.

To clarify whether hepatocellular carcinoma (HCC) may produce and secrete endothelin (ET), we measured plasma levels of ET-1 and big ET-1, a precursor form of ET-1, in 30 patients with HCC. When compared to normal subjects, a substantial number of patients had elevated plasma ET-1 and big ET-1 levels, determined by specific enzyme immunoassays. The mean (+/- SD) plasma concentrations of ET-1 (1.7 +/- 0.9 pmol/L) and big ET-1 (6.1 +/- 4.8 pmol/L) in patients' group were significantly (P < 0.01) higher than those (1.0 +/- 0.3 and 2.0 +/- 0.8 pmol/L, respectively) in control group. There was a significant positive correlation between plasma big ET-1 and alpha-fetoprotein (r = 0.77, P < 0.01). Some of the 29 patients with liver cirrhosis also had modestly elevated plasma big ET-1 levels. The mean (+/- SD) plasma big ET-1 concentration (3.1 +/- 0.9 pmol/L) in patients with liver cirrhosis was significantly (P < 0.01) higher than that in control group, although there was no significant difference between the mean plasma ET-1 levels of both groups. Raised plasma big ET-1 and, less markedly, ET-1 levels in patients with HCC decreased after successful transcatheter arterial embolization concomitantly with a reduction in tumor sizes and a decrease in plasma alpha-fetoprotein levels. In six patients, an arteriovenous difference in ET-1 and big ET-1 levels across the tumor bed with a higher concentration in the venous circulation was found. Reverse-phase high performance liquid chromatography revealed that major portions of immunoreactive ET-1 and big ET-1 in hepatic venous plasma coeluted with synthetic ET-1 and big ET-1, respectively. Immunohistochemistry of HCC tissues from two patients demonstrated HCC cells positive for ET-1 and big ET-1, whereas no ET immunoreactivity was found in adjacent nontumorous hepatocytes. We conclude from these results that ET is produced by and released from a substantial number of HCC, which may stimulate proliferation of carcinoma cells as an autocrine or paracrine growth factor.

Immunohistochemical Localization of Alkaline Phosphatase in Rat Liver.

Alkaline phosphatase (ALP) was purified from the rat kidney. The appropriate enzyme protein was injected subcutaneously into a rabbit as an antigen. The obtained antiserum showed a single precipitin line in the double diffusion test of Ouchterlony. The localization of ALP in the rat liver was examined by means of immunohistochemical techniques. At the light microscopic level, positive reactions were recognized along cell borders between adjacent hepatocytes. On examination with an electron microscope, gold particles were observed only on the surface of microvilli of bile canaliculi by immunogold staining. On the other hand, by the peroxidase-labeled antibody method, reaction products appeared not only on the bile canalicular membrane but also on the sinusoidal and lateral membranes.

Inhibition of intercellular communication in rat hepatocytes by phenobarbital, 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT) and gamma-hexachlorocyclohexane (lindane): modification by antioxidants and inhibitors of cyclo-oxygenase.

Several tumour promoting chemicals have been shown to inhibit intercellular communication (IC) through gap junctions in cell cultures. In the present investigation we studied the effect of the hepatic tumour promoters phenobarbital (PB), 1,1,1-trichloro-2,2-(p-chlorophenyl)ethane (DDT) and gamma-hexachlorocyclohexane (lindane) on IC in rat hepatocyte cultures. IC was evaluated by microinjection of fluorescent Lucifer Yellow CH dye and visualization of dye spread to adjacent hepatocytes. Incubation of hepatocytes with PB (2 mM), DDT (30 microM) and lindane (25 microM) decreased dye-coupling of the cells by about 30%, 42% and 35%, respectively; dye-coupling in untreated cultures was 88.1 +/- 0.7%. Inhibition of IC was reversible when the xenobiotics were removed from the medium. The antioxidant vitamin E (100 microM) prevented inhibition of dye-coupling by PB and lindane and partially that by DDT. Superoxide dismutase (100 units/microliters) counteracted the effect on dye-coupling by PB, but not that by the insecticides. Similarly, the cyclo-oxygenase inhibitors indomethacin and aspirin only reversed the effect of PB on IC, but not that of DDT or lindane. As indicated by further experiments, prevention by non-steroidal anti-inflammatory agents of PB-induced inhibition of IC is most likely not mediated by inhibition of cyclo-oxygenase. The results indicate significant differences in the action of PB, DDT and lindane on IC in hepatocyte cultures. This is suggested by the differential effects of superoxide dismutase and non-steroidal anti-inflammatory agents on the action of the three tumour promoting chemicals. Whereas superoxide radicals may be involved in the inhibition of dye-coupling by PB, radical intermediates of the insecticides may be responsible for the decrease in dye-coupling by DDT and lindane.

An in vitro model of rodent nongenotoxic hepatocarcinogenesis

An in vitro model of liver in which rat hepatocytes are maintained as cocultures with nonparenchymal epithelial cells (NPC) derived from liver has been developed and characterized with respect to maintenance of hepatocyte viability and differentiated function. The system was then evaluated as a model for studying peroxisome proliferator-induced rodent liver nongenotoxic carcinogenesis. Within the coculture model, hepatocyte viability and morphology were maintained for 1 month or more within a system that is both easily accessible for microscopic examination and is free of any additives that may lead to artifacts. Even after 1 month or more, hepatocyte cocultures retained expression of the constitutive liver marker albumin. In addition, they maintained the ability to show induction of the peroxisome proliferator-inducible enzymes peroxisomal bifunctional enzyme (PBE) and cytochrome P450IVA1 in response to the peroxisome proliferator nafenopin. After 4 weeks, NPC cocultures showed a six- and a fourfold induction of PBE and cytochrome P450IVA1 expression, respectively, which compared well with the three-and fivefold induction seen in freshly isolated cells. This was paralleled by an increase in the cytoplasmic volume fraction of peroxisomes averaging eightfold. Interestingly, great heterogeneity was exhibited between adjacent hepatocytes in terms of the degree of peroxisome proliferation, a finding reflected by immunocytochemical staining which indicated heterogeneity in the level of expression of the peroxisome proliferator-inducible enzymes. Other cell lines representing different tissue types, morphologies, and species were also examined for their ability to support hepatocyte survival but were found to be ineffective, with the exception of a bovine corneal endothelial cell line. This line supported hepatocyte survival and maintenance of differentiated function but to a lesser extent than that observed with NPC. Ultrastructural examination of NPC cocultures revealed extensive interhepatocyte junctional complexes and interdigitation of adjacent membranes together with the presence of bile canalicular structures. There were no junctional complexes between the hepatocytes and the supporting feeder cells with any contact being limited to a close association of the hepatocytes with the extracellular matrix presumably produced by the NPC. The data demonstrate that hepatocytes maintained in vitro within an NPC coculture system retain differentiated function and the ability to respond to the peroxisome proliferator class of nongenotoxic carcinogens. Cocultures will provide us with a model system for the study of changes in hepatocyte growth regulation during rodent liver nongenotoxic carcinogenesis.

Roles of Listeria monocytogenes virulence factors in survival: virulence factors distinct from listeriolysin are needed for the organism to survive an early neutrophil-mediated host defense mechanism.

Avirulent mutant strains of Listeria monocytogenes which fail to produce phosphatidylinositol-specific phospholipase C, or which produce reduced amounts of hemolytic listeriolysin O, are incapable of causing progressive infection in normal mice. However, both strains can grow progressively in mice that have been rendered incapable of focusing neutrophils at sites of infection as a result of being treated with monoclonal antibody 5C6, specific for the type 3 complement receptor of myelomonocytic cells. In 5C6-treated mice, phospholipase C-negative and listeriolysin-defective mutant strains of L. monocytogenes, like the wild-type strain, give rise in the liver to large numbers of discrete foci of infected hepatocytes that retain their morphological integrity during the first 24 h, despite their large bacterial burden. In normal mice, in contrast, sites of infection in the liver are indicated by discrete focal accumulations of neutrophils that occupy the space originally occupied by infected hepatocytes. It is apparent that in normal mice neutrophils function to lyse infected hepatocytes and thereby to release L. monocytogenes for ingestion and killing by neutrophils themselves and by macrophages. However, whereas a proportion of wild-type organisms survive this early mechanism of defense to give rise to progressive infection, the phospholipase C-negative organisms are totally eliminated. On the basis of these and other results, it is suggested that virulence factors other than listeriolysin are needed by L. monocytogenes to counteract the early neutrophil-mediated mechanism of defense. Listeriolysin, itself, is an intrinsic virulence factor that allows L. monocytogenes to survive and multiply in a proportion of the fixed phagocytes of the liver (permissive phagocytes) and which enables the organism to go on to infect and replicate in adjacent hepatocytes. It was found that a mutant strain of L. monocytogenes incapable of producing any listeriolysin was incapable of establishing progressive infection, even in 5C6-treated mice.

Kupffer cell-derived cytokines induce the synthesis of a leukocyte chemotactic peptide, interleukin-8, in human hepatoma and primary hepatocyte cultures

Communication circuits operating between activated monocytes/macrophages and adjacent hepatocytes in the liver effect important alterations in hepatocyte function. We demonstrate here that primary human hepatocytes and hepatoma cells are able to function as effector cells in the recruitment of inflammatory cells in hepatic disease and inflammatory states by synthesizing a neutrophil/lymphocyte chemotactic factor, interleukin-8. We have further investigated the possibility that endogenous factors elaborated by activated peripheral blood monocytes and Kupffer cells in the liver are mediators of hepatocyte-derived interleukin-8 expression. Twenty-four-hour conditioned medium from lipopolysaccharide-stimulated peripheral blood monocytes and nonparenchymal human liver cells enriched for Kupffer cells induced a time-dependent increase in interleukin-8 messenger RNA levels in SK-hepatoma cells over a 24-hr period, similar to that seen for tumor necrosis factor-alpha or interleukin-1 beta induction of interleukin-8 in primary hepatocytes. Exogenously added lipopolysaccharide or recombinant interleukin-6 had no effect. Cell-associated interleukin-8 antigen was present in SK-hepatoma and primary hepatocytes that had been incubated with macrophage-conditioned medium, tumor necrosis factor or interleukin-1 beta. Similarly, neutrophil chemotactic activity was secreted by SK-hepatoma cells, a significant proportion of which could be blocked with interleukin-8--specific antiserum. Preincubation of macrophage-conditioned medium with neutralizing antibodies to tumor necrosis factor-alpha or interleukin-1 beta reduced its interleukin-8 messenger RNA-inducing capacity. Exposure of SK-hepatoma to conditioned medium followed by removal of the stimulus resulted in a rapid down-regulation of interleukin-8 messenger RNA to 50% of the maximum level within the first hour. These data suggest that products derived from activated Kupffer cells can modulate hepatoma cells and primary hepatocyte interleukin-8 gene expression. In addition, macrophage/monocyte-derived tumor necrosis factor-alpha and interleukin-1 beta have major roles in the positive regulatory component of this modulation.

Hydrophobic ion transfer between membranes of adjacent hepatocytes: a possible probe of tight junction structure.

The topology of the tight junction is probed by introducing dipicrylamine (dpa-), a lipid-soluble anion, into the membranes of hepatocyte pairs in culture. Once partitioned into the membrane, dpa- ions are free to move in the hydrophobic core of the membrane, where their mobile charges greatly increase membrane capacitance. If tight junctions are lines of membrane fusion, dpa- will cross the tight junction without traversing a polar headgroup layer. Furthermore, the electric potential across the tight junction will be equal to the difference in membrane potentials of the two cells. dpa- can therefore be expected to move electrophoretically from cell membrane to cell membrane across the junction in response to an intercellular voltage difference. Experiments performed under double whole-cell clamp show that this transfer occurs as follows: First, dpa- causes an intercellular current unrelated to gap junctions to flow in response to an intercellular voltage difference. Second, this electrophoretic removal or addition of dpa- from a cell's membrane through the tight junction must reduce or increase its dpa- content and thus its capacitance. Experiments confirm this prediction: We detect rapid, symmetric, and reversible changes in membrane capacitance in response to changes in the membrane potential of the neighboring cell. Finally, we find that hepatocyte membranes contain a negatively charged endogenous molecule that contain a negatively charged endogenous molecule that can move from cell to cell like dpa- under the influence of an intercellular potential difference. We conclude that membrane fusion occurs at tight junctions and that this hydrophobic intercellular pathway can play a role in intercellular communication.

The use of isolated rat hepatocyte couplets, microscopic optical planimetry and quantitative microfluorimetry in hepatobiliary physiology

Bile formation requires the vectorial transport of water and solutes into small canaliculi enclosed by two adjacent hepatocytes and further modifications by the biliary epithelium. Direct study of canalicular bile secretion has been hampered by the inacessibility of the tiny canalicular space to micropunture techniques and by the loss of polarity which rapidily occurs when hepatocytes are dissociated. For example, it is still debated whether the bile acid ursodeoxycholate (UDCA) stimulates hypercholeresis biliary HC03 secretion by activating hepatocellular +anq Na /H exchange or as a consequence of its reabsorption by the bile ducts. Part of the methodological limitations can be overcome with the use of isolated rat epatocyte couplets (IRHC). These isolated hepatocytes, which remain undissociated after liver collagenase digestion, retain their bile secretory polarity, and, after short term culture, reform a canalicular space, with competent tight junctions, and polariied expression of the canalicular marker Mg-ATPase. IRHC are also able to transport cholephilic flourescent anions and bile acids into the canalicular space, which rapidly expands following administration of choleretic bile acids. We have applied quantitative microfluorimetric techniques and microscopic opti;z$,;$animetry, to directly assess the effects of UDCA on exchange activity, luminal pH and canalicular expansion rates in these polarized hepatocytes.

Regulation on the Expression of Carcino-Embryonic Proteins in Newborn Rat Hepatocytes by Dexamethasone An Enzyme Histochemical and Immunohistochemical Study

Dexamethasone (DEX) was administrated intraperitoneally to newborn rats at a dose level of 2 micrograms/g body weight/day for four days, starting 4 days after birth. After administration of DEX, large quantities of glycogen granules accumulated in the cytoplasm of hepatocytes and the activity level of gamma-glutamyl transpeptidase (gamma-GTP) in liver homogenate increased significantly, whereas that of alkaline phosphatase (ALP) exhibited no significant difference in comparison with the control group. In the histochemical analysis, after administration of DEX, a high level of activity of gamma-GTP appeared along cell borders between adjacent hepatocytes in the peripheral portion of liver lobules. On the other hand, a low level of analysis, no hepatocyte showing positive reactions to Alpha-fetoprotein (AFP) could be recognized after administration of DEX, and in livers of newborn rats receiving DEX, the number of hepatocytes which incorporated bromodeoxyuridine (BUdR) decreased. The present study showed in newborn rat that DEX induced the differentiation of hepatocytes and regulated the expression of carcino-embryonic proteins.

Expression and compartmentalization of integral plasma membrane proteins by hepatocytes and their progenitors in the rat pancreas

A combination of Western blotting, Northern blotting and immunofluorescence was used to examine the expression and compartmentalization of plasma membrane proteins by those hepatocyte-like cells that arise in the pancreases of rats subjected to sequential dietary copper depletion and repletion. The pancreatic hepatocytes were found to: (1) express several integral membrane proteins known to be concentrated within the apical, lateral or basolateral domains of the plasma membranes of hepatocytes in liver; and (2) compartmentalize the membrane proteins to equivalent plasma membrane domains, despite the organization of these cells into clusters instead of highly vascularized plates. The apical plasma membrane proteins dipeptidylpeptidase IV and HA 4 were found to line bile canaliculus-like openings between adjacent pancreatic hepatocytes; these openings were shown to be continuous with the pancreatic exocrine duct by India ink infusion. In contrast, the basolateral plasma membrane protein rat hepatic lectin-1 and lateral plasma membrane protein HA 321 were detected elsewhere about the surfaces of the pancreatic hepatocytes: by analogy to their respective localizations on hepatocytes in liver, rat hepatic lectin-1 was concentrated on those surfaces exposed to the pancreatic matrix at the periphery of the hepatocyte clusters (the basal surface equivalent), whereas HA 321 was concentrated on those surfaces exposed to adjacent hepatocytes within the clusters. The hepatocyte plasma membrane proteins were found to be expressed in the pancreas at different times during the copper depletion/repletion protocol: for example, rat hepatic lectin-1 and the bulk of the HA 4 were expressed relatively late in the protocol, only after large numbers of pancreatic hepatocytes had appeared; whereas dipeptidylpeptidase IV was induced greater than 10-fold early in the protocol and proved to be an apical-specific marker for those ductular epithelial cells that are believed to be the progenitors of the pancreatic hepatocytes.

Cadmium toxicity in perinatal rat hepatocytes: Electron microscopy, X-ray microanalysis, and morphometric analysis

Effects of cadmium on the fetal and postnatal rat hepatocytes were studied with an electron microscope and an X-ray microanalyzer. Pregnant and lactating Wistar rat dams at 15 and 21 days of pregnancy and at 3 days after delivery received intraperitoneal injections of cadmium sulfate (1 mg/kg body weight) for 3 days. On the day following the last injection, the livers were isolated from the fetal and suckling rats and provided for electron microscopy. The livers from the untreated fetal and newborn rats served as control. Large bile canaliculi, which were formed by five or more hepatocytes, were frequently observed in the cadmium-treated perinatal rat livers. The intercellular space between each adjacent hepatocyte was widened. By X-ray microanalysis, cadmium peaks were preferentially detected out from intramitochondrial granules of the cadmium-treated hepatocytes. By morphometric analysis, the increase both in the mitochondria volume and in the number of intramitochondrial granules was evident in the cadmium-treated hepatocytes when compared to those of control. These data suggest the preferential accumulation of cadmium in mitochondria of the hepatocytes interferes with the morphogenesis of the perinatal rat liver.

Isolated trout liver cells: Establishing short-term primary cultures exhibiting cell-to-cell interactions

Composition and interactions of cell types in rainbow trout (Oncorhynchus mykiss) liver digested with collagenase and cultured in serum-free media were investigated. Suspensions obtained after digesting trout liver with collagenase contained all the cell types present in the liver, including liver parenchymal cells (hepatocytes), biliary epithelial cells, sinusoidal endothelium, fat-storing cells of Ito, and macrophages. A major cell pellet, mainly hepatocytes but containing significant numbers of biliary epithelial cells, was obtained by centrifuging the cell suspension at 120 X g for 1 min. Cells present in this pellet quantitatively attached to culture plates coated with a trout skin extract and remain attached for 4 to 6 d with good retention of intracellular enzymes and DNA. When in culture, significant changes in and among the cells were observed. Initial preparations were rounded, single cells. Within several hours, however, cellular interactions leading to aggregation became evident and aggregates increased in size for 2 to 3 d. Scanning electron microscopy (EM) showed frequent shaftlike projections from margins of the aggregates. Transmission EM indicated that these projections represent biliary ductules forming in vitro. Adjacent hepatocytes also showed plasma membrane specializations forming junctional complexes and canaliculi characteristics of normal trout liver. After 5 to 6 d in culture, significant numbers of the cell aggregates dislodged from the plate. Analysis showed the dislodged cells were viable but vacuolated. The reestablishment in vitro of morphologic relationships resembling in situ tissue components suggest these culture preparations may have significant utility in cooperative metabolic studies of cell interactions in trout liver.

Apoptosis--the mechanism of cell death in dimethylnitrosamine-induced hepatotoxicity.

Dimethylinitrosamine (DMN) induces an acute haemorrhagic centrilobular necrosis when given as a single dose to rats. In this study, the progression of the lesion was studied at the ultrastructural level in order to elucidate the precise mechanisms of hepatic injury. Within 3 h of a single dose of DMN there was disruption of endothelial lining cells. In areas of endothelial cell loss, the exposed hepatocyte sinusoidal membranes became simplified and flattened. In the centrilobular area, hepatocytes became apoptotic and by 16 h apoptotic bodies, formed from degenerate hepatocytes, were engulfed by intact hepatocytes or by circulating macrophages. This progressive degeneration of hepatocytes and endothelial cells gave rise, by 24 h, to the classically recognized centrilobular haemorrhagic necrosis. The damage to the endothelial cells was concurrent with, or in some areas prior to, significant morphological changes in adjacent hepatocytes. This contrasts with other hepatotoxins such as carbon tetrachloride where the primary target is the hepatocyte, giving rise to hydropic degeneration and coagulative necrosis. DMN, however, results in apoptosis, a mechanism of cell death not normally associated with chemically induced injury.

An L-arginine-dependent mechanism mediates Kupffer cell inhibition of hepatocyte protein synthesis in vitro.

The hepatic failure associated with severe sepsis is characterized by specific, progressive, and often irreversible defects in hepatocellular metabolism (1). Although the etiologic microbe can often be identified, the direct causes and mechanisms of the hepatocellular dysfunction are poorly understood. We have hypothesized that Kupffer cells (KC), which interact with ambient septic stimuli, respond by providing signals to adjacent hepatocytes (HC) in sepsis . Furthermore, we have provided evidence (2, 3) that KC activated by LPS from Gram-negative bacteria can induce profound changes in the function of neighboring HC in coculture. In our model, coculture of either KC (2) or peritoneal macrophages (Mphi)(3) with HC normally promotes HC protein synthesis ([(3)H]leucine incorporation). The addition of LPS or killed Escherichia colt' to such cocultures induces a profound decrease in HC protein synthesis, as well as qualitative changes ([(35)S]methionine, SDS-gel electrophoresis) in protein synthesis without inducing HC death (2, 3) . In this report we show that the inhibition in protein synthesis is mediated via an L-arginine-dependent mechanism. The metabolism of L-arginine by activated Mphi to substances with cytostatic and even lethal effects on target cells is a relatively recent discovery. After the description by Stuehr and Marletta (4, 5) that LPS- triggered Mphi produced nitrite/nitrate (NO(2)(-)/NO(3)(-)), Hibbs et al. (6, 7) and Iyengar et al. (8) demonstrated that L-arginine was the substrate for the formation of both these nitrogen end products and citrulline. A role for the arginine-dependent mechanism in Mphi tumor cytotoxicity (6, 7) and microbiostatic activity (9) has been suggested. However, the in vivo functions of this novel Mphi mechanism have not yet been defined, but it is possible that there are both physiologic as well as pathologic roles. Our in vitro results raise the possibility that some metabolic responses to microbial invasion maybe partially mediated by the L-arginine-dependent mechanism. What other metabolic responses are affected and the possible pathologic consequences remain to be studied.

Changes in alkaline phosphatase and .GAMMA.-glutamyl transpeptidase during the process of rat hepatocyte proliferation.

D-galactosamine was injected i. p. into rats at a single dose level of 250mg/kg. Basophilic hepatocytes and their mitotic forms were observed 48hr and 72hr after the administration of the amino sugar. At these stages, the biochemical activities of alkaline phosphatase (ALPase) and γ-glutamyl transpeptidase (γ-GTP) in rat liver homogenate increased significantly in comparison to those in the control rats.In the histochemical analysis, 48hr and 72hr after administration of the amino sugar, a high level of activity of both ALPase and γ-GTP was seen along the cell borders between adjacent hepatocytes and along the entire hepatocyte surface. At the level of electron microscopy, the reaction products showing ALPase activity were observed in abundance along the complex interdigitation of the plasma membranes, which were present on the cell borders between adjacent hepatocytes.