Allyl alcohol toxicity in isolated renal epithelial cells: protective effects of low molecular weight thiols

The toxicity of allyl alcohol was studied in freshly isolated renal epithelial cells prepared from male and female rats. Cells from female rats demonstrated a greater susceptibility to allyl alcohol toxicity as assessed by glutathione depletion and loss of cell viability. The sensitivity of female rat renal cells appears to relate to the higher activity of alcohol dehydrogenase found in the female rat kidney, which metabolizes allyl alcohol to the highly reactive aldehyde, acrolein. Pyrazole, an inhibitor of alcohol dehydrogenase, abolished the cytotoxic effects of allyl alcohol whereas inhibition of aldehyde dehydrogenase by disulfiram treatment was found to increase the sensitivity of renal cells to the effects of allyl alcohol. The toxicity of allyl alcohol was decreased by a number of treatments which resulted in increased levels of glutathione or other low molecular weight thiols. These results indicate that acrolein is the toxic metabolite responsible for the renal cell injury following exposure to allyl alcohol, and unless immediately inactivated acrolein interacts with critical nucleophilic sites of the cell and initiates cell injury. These studies demonstrate that freshly isolated kidney cells represent a convenient model system for studies of thiol-mediated protective mechanisms against toxic renal cell injury.     

Acquisition of a beta-adrenergic response by adult rat hepatocytes during primary culture

In freshly isolated parenchymal hepatocytes of adult rats, the beta-adrenergic agonist isoproterenol (Ip) did not stimulate cAMP formation, protein kinase activity, or glycogenolysis, although glucagon markedly stimulated all these activities. However, the beta-adrenergic response appeared when rat hepatocytes were cultured as monolayers. This response had already appeared after 2-h culture and increased during further culture. The appearance of the beta-adrenergic response during culture was blocked by cycloheximide, actinomycin D, or alpha-amanitin. Thus adult rat hepatocytes acquired marked ability to respond to Ip during culture through the syntheses of mRNA and protein. Freshly isolated hepatocytes from postnatal rats showed a high beta-adrenergic response that did not increase further during culture. This response gradually decreased during development and had almost disappeared about 60 days after birth. In plasma membranes prepared from freshly isolated cells of adult rats the basal and NaF-stimulated activities of adenylate cyclase (EC 4.6.1.1) were similar to those of cultured cells and the enzyme activity was also stimulated by guanyl-5'-yl imidodiphosphate. However, in plasma membranes of freshly isolated cells Ip scarcely stimulated adenylate cyclase, but glucagon did. The intact cells, whether they were freshly isolated or cultured, accumulated cAMP when exposed to cholera toxin. Moreover, the two subunits of GTP-binding regulatory protein (also named G/F or Ns site) were detected by [32P]ADP ribosylation with cholera toxin and [32P]NAD+ in freshly isolated cells as well as in cultured cells. These results indicate that freshly isolated and cultured hepatocytes of adult rats contain sufficient levels of all the components of the postreceptor-adenylate cyclase system for activity. However, the number of beta-adrenergic receptors measured by binding of [125I]iodocyanopindolol, a potent beta-adrenergic antagonist, was very low in purified plasma membranes of freshly isolated cells (20 fmol/mg of protein), and the number increased about 6-fold without change in the dissociation constant (Kd = 132 pM) when the cells were cultured for 7 h. This increase in beta-adrenergic receptor sites was completely abolished by cycloheximide and alpha-amanitin. Thus it is concluded that the unresponsiveness of adult rat hepatocytes to Ip was due to a very low amount of beta-adrenergic receptor and that the appearance of a beta-adrenergic response during primary culture was due to new synthesis of beta-adrenergic receptor through synthesis of mRNA.     

A biochemical and stereological study of neonatal rat hepatocyte subpopulations. Effect of pre- and postnatal exposure to ethanol

Hepatocytes from 12-day-old rats, pre- and post-natally exposed to alcohol, together with those from pair-fed controls, were isolated and subfractionated in six cell subpopulations on Percoll density gradients. These cells were characterized using a combination of biochemical and stereological methods. The low density cells (F2) mainly showed biochemical and stereological features of perivenous hepatocytes, whereas the heavier cells (F6) were primarily periportal hepatocytes. The alcohol-metabolizing enzymes, alcohol dehydrogenase and aldehyde dehydrogenase (high and low Km) showed more activity in the F2 fraction. Alcohol-altered mitochondria and Golgi apparatus occurred mainly in F2 cells, whereas the endoplasmic reticulum and lysosomes appeared to be more altered in the F6 hepatocytes. Alcohol also induced the appearance of some small hepatocytes, with a well-developed rough endoplasmic reticulum and an increased number of mitochondria. Biochemical data indicated that glutamate dehydrogenase and alanine aminotransferase were more affected in F2 cells from alcohol-treated rats, and that the activity of the ethanol-metabolizing enzymes was alos reduced in these hepatocytes. Our results indicate that alcohol exposure during zonal development in the liver could have a selective effect on specific cell components depending on the acinar zone, and that the perivenous hepatocytes appear to be more damaged under these conditions.     

Loss of growth hormone-dependent characteristics of rat hepatocytes in culture

Summary The liver of rodents is sexually differentiated, i.e. the female liver differs from the male liver. This differentiation is largely controlled by the pattern of growth hormone (GH) secretion. We have attempted to maintain GH-dependent differentiation of cultured rat hepatocytes. We examined the level of alcohol dehydrogenase (ADH) activity, which responds to GH and is higher in female than in male liver, and the estrogen receptor, which is dependent on GH but is present in equal amounts in males and females. ADH activity was maintained in cells from male rats, but fell by 40% in cells from females in medium supplemented with insulin and dexamethasone. The estrogen receptor content of female cells fell dramatically to undetectable levels within 2 d of culture. Extensive supplementation of the medium failed to prevent the decrease in ADH activity in female cells; similarly, the addition of female sex steroids; rat serum; pituitary extracts; rat, human, or bovine GH; or ovine prolactin failed to maintain the enzyme activity. Insulin, dexamethasone, thyroid hormone plus GH or prolactin, or the combination of all five hormones also failed to prevent the loss of estrogen receptors. Short-term cultures of rat hepatocytes, although retaining the liver-specific expression of ADH at the male level, lose GH-dependent expression of the estrogen receptor and stimulation of ADH activity. Supported by grants AA 00081 and AA 06434 from the National Institute on Alcohol Abuse and Alcoholism, Bethesda, MD.     

Cysteine uptake and taurine biosynthesis in freshly isolated and primary cultured rat hepatocytes

Analysis of the uptake and metabolism of [14C]cysteine in rat liver was undertaken using freshly isolated hepatocytes and hepatocytes maintained in primary culture. The uptake of [14C]cysteine by freshly isolated hepatocytes was by means of both saturable and non-saturable transport systems and the former system was thought to involve facilitated diffusion. The uptake of [14C]cysteine by hepatocytes maintained in primary culture for 24 h also consisted of non-saturated and saturated transport mechanisms. The magnitude of the saturable transport system in cultured hepatocytes was, however, much greater than that found in freshly isolated hepatocytes, and was considered to be operated by active transport. Both freshly isolated and primary cultured hepatocytes had cysteine sulphinic acid decarboxylase activity, but this enzyme activity in the latter cells was noticeably reduced in comparison with that found in freshly isolated hepatocytes. Hepatocytes maintained in primary culture produced not only radiolabelled taurine, but also radiolabelled cysteine sulphinic acid, hypotaurine and alanine when incubated with [14C]cysteine. The present results indicate that cultured hepatocytes actively transport cysteine as well as metabolizing cysteine to taurine via cysteine sulphinic acid and hypotaurine.     

Properties of peroxisomes and their induction by clofibrate in normal adult rat hepatocytes in primary culture

Alterations in peroxisomes and catalase activity and their responsiveness to clofibrate in adult rat hepatocytes in primary culture were investigated. The numbers of peroxisomes with and without crystalloid nucleotids per unit cytoplasmic area were preserved in cultured hepatocytes for 2 d after seeding at a level comparable to that of freshly isolated hepatocytes. At Day 3 in culture, the number of anucleoid peroxisomes was reduced in untreated hepatocytes, accompanied by more significant reduction in the number of nucleoid-containing peroxisomes, which decreased until Day 5. Peroxisome diameters were reduced in untreated hepatocytes at Day 2 and this decrease in the diameter was continued until Day 7. Catalase activity in untreated hepatocytes decreased markedly with culture age. The number of anucleoid peroxisomes was significantly greater in hepatocytes treated with 2 mM clofibrate in culture than in freshly isolated hepatocytes for 2 d or in untreated hepatocytes of the same culture age through 7 d. The number of nucleoid-containing peroxisomes in the treated cells began to decrease in 3 d, but was greater than that of untreated cells at Days 3 and 5. Peroxisomes with well-developed nucleoids were observed frequently in the treated cells even at Day 7. Peroxisome diameters were greater in the treated cells than in untreated cells at Days 3, 5, and 7. Catalase activity was always higher in the treated cells than in untreated cells. These results suggest that clofibrate is effective in inducing peroxisome proliferation as well as in maintaining the organelles in cultured hepatocytes.     

Induction of glucose-6-phosphate dehydrogenase in primary cultures of adult rat hepatocytes. Requirement for insulin and dexamethasone

To determine the relative contributions of glucose, insulin, dexamethasone, and triiodothyronine to the induction of hepatic glucose-6-phosphate dehydrogenase, hepatocytes isolated from normal or adrenalectomized rats, either fasted or fed, were examined in culture. Addition of insulin (42 milliunits/ml, 0.9 microM) and dexamethasone (1 microM) to hepatocytes obtained from 3-day-fasted rats and cultured for 48 h in serum-free Dulbecco's medium resulted in a 7- to 11-fold increase in Glc-6-P dehydrogenase specific activity compared with a 2- to 3-fold increase in activity in control cultures incubated without added hormones. The effects of insulin and dexamethasone were independent of DNA synthesis, dose-dependent, and additive; each contributing about one-half of the total response. Medium glucose was neither sufficient nor necessary for the insulin- or dexamethasone-stimulated increase in Glc-6-P dehydrogenase specific activity. Addition of triiodothyronine (10 microM) preferentially blocked the dexamethasone-stimulated increase in Glc-6-P dehydrogenase specific activity. Insulin failed to stimulate the induction of Glc-6-P dehydrogenase in hepatocytes obtained from normal fed rats or from fasted and fed adrenalectomized rats. However, insulin caused a significant increase in the Glc-6-P dehydrogenase specific activity of these cells when dexamethasone was concurrently added to the culture medium.     

Properties of peroxisomes and their induction by clofibrate in normal adult rat hepatocytes in primary culture

Summary Alterations in peroxisomes and catalase activity and their responsiveness to clofibrate in adult rat hepatocytes in primary culture were investigated. The numbers of peroxisomes with and without crystalloid nucleoids per unit cytoplasmic area were preserved in cultured hepatocytes for 2 d after seeding at a level comparable to that of freshly isolated hepatocytes. At Day 3 in culture, the number of anucleoid peroxisomes was reduced in untreated hepatocytes, accompanied by more significant reduction in the number of nucleoid-containing peroxisomes, which decreased until Day 5. Peroxisome diameters were reduced in untreated hepatocytes at Day 2 and this decrease in the diameter was continued until Day 7. Catalase activity in untreated hepatocytes decreased markedly with culture age. The number of anucleoid peroxisomes was significantly greater in hepatocytes treated with 2mM clofibrate in culture than in freshly isolated hepatocytes for 2 d or in untreated hepatocytes of the same culture age through 7 d. The number of nucleoid-containing peroxisomes in the treated cells began to decrease in 3 d, but was greater than that of untreated cells at Days 3 and 5. Peroxisomes with well-developed nucleoids were observed frequently in the treated cells even at Day 7. Peroxisome diameters were greater in the treated cells than in untreated cells at Days 3, 5, and 7. Catalase activity was always higher in the treated cells than in untreated cells. These results suggest that clofibrate is effective in inducing peroxisome proliferation as well as in maintaining the organelles in cultured hepatocytes. This work was supported in part by Grants-in-Aid for Scientific Research from Ministry of Education, Science and Culture, Japan, 448143, 50168, 501069, and 577196, and by a Grant-in-Aid from Hokkaido Geriatrics Research Institute.     

Effect of prior nutritional status on the activity of lipogenic enzymes in primary monolayer cultures of rat hepatocytes.

Effect of prior nutritional status of the animal on the activity of lipogenic enzymes and the fatty acid content of cultured hepatocytes was investigated. Hepatocytes were isolated from rats that were starved for 24 h ('starved') or continuously fed ('fed'), or starved for 48 h and then re-fed for 48 h ('re-fed') with a carbohydrate-rich fat-free diet, and maintained as monolayer cultures for 96 h in a serum-free glucose-rich medium (Waymouth's MB752/1) supplemented with insulin, dexamethasone and tri-iodothyronine. The fatty acid content and the activities of acetyl-CoA carboxylase, fatty acid synthase, glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase were determined initially at 3 h after plating and then every 24 h. Initially the activities of all the four enzymes were highest in hepatocytes isolated from the re-fed rats and lowest in those from the starved rats. With time in culture, the activity of all these enzymes increased severalfold (2-5, depending on the enzyme under consideration) in hepatocytes isolated from fed and starved rats, whereas there was a severalfold (2-5) decrease in the activity of these enzymes in hepatocytes isolated from re-fed rats. The initial fatty acid content of the hepatocytes from re-fed rats was 2-3 times that in the other two groups of hepatocytes. The fatty acid content seemed to increase in all three groups of hepatocytes during the 96 h in culture, but these apparent increases were not statistically significant.     

Regulation of the branched-chain 2-oxo acid dehydrogenase complex in hepatocytes isolated from rats fed on a low-protein diet.

Hepatocytes isolated from rats fed on a chow diet or a low-protein (8%) diet were used to study the effects of various factors on flux through the branched-chain 2-oxo acid dehydrogenase complex. The activity of this complex was also determined in cell-free extracts of the hepatocytes. Hepatocytes isolated from chow-fed rats had greater flux rates (decarboxylation rates of 3-methyl-2-oxobutanoate and 4-methyl-2-oxopentanoate) than did hepatocytes isolated from rats fed on the low-protein diet. Oxidizable substrates tended to inhibit flux through the branched-chain 2-oxo acid dehydrogenase, but inhibition was greater with hepatocytes isolated from rats fed on the low-protein diet. 2-Chloro-4-methylpentanoate (inhibitor of branched-chain 2-oxo acid dehydrogenase kinase), dichloroacetate (inhibitor of both pyruvate dehydrogenase kinase and branched-chain 2-oxo acid dehydrogenase kinase) and dibutyryl cyclic AMP (inhibitor of glycolysis) were effective stimulators of branched-chain oxo acid decarboxylation with hepatocytes from rats fed on a low-protein diet, but had little effect with hepatocytes from rats fed on chow diet. Activity measurements indicated that the branched-chain 2-oxo acid dehydrogenase complex was mainly (96%) in the active (dephosphorylated) state in hepatocytes from chow-fed rats, but only partially (50%) in the active state in hepatocytes from rats fed on a low-protein diet. Oxidizable substrates markedly decreased the activity state of the enzyme in hepatocytes from rats fed on a low-protein diet, but had much less effect in hepatocytes from chow-fed rats. 2-Chloro-4-methylpentanoate and dichloroacetate increased the activity state of the enzyme in hepatocytes from rats fed on a low-protein diet, but had no effect on the activity state of the enzyme in hepatocytes from chow-fed rats. The results indicate that protein starvation greatly increases the sensitivity of the hepatic branched-chain 2-oxo acid dehydrogenase complex to regulation by covalent modification.     

Decarboxylation of branched-chain alpha-ketoacids in hepatocytes from alloxan-diabetic rats. The effect of insulin

The flux through branched-chain alpha-ketoacid dehydrogenase and the activity of the branched-chain alpha-ketoacid dehydrogenase complex were measured in hepatocytes isolated from fed, starved and alloxan diabetic rats. The highest rate of branched-chain alpha-ketoacid oxidation was found in hepatocytes isolated from starved rats, slightly lower in those from fed rats, and significantly lower in diabetic hepatocytes. The amount of the active form of branched-chain alpha-ketoacid dehydrogenase was only slightly diminished in diabetic hepatocytes, whereas the flux through the dehydrogenase was inversely correlated with the rate of endogenous ketogenesis. The same was observed in hepatocytes isolated from starved rats when branched-chain alpha-ketoacid oxidation was measured in the presence of added oleate. In both cases the diminished flux through the dehydrogenase, restored by a short preincubation of hepatocytes with insulin, was paralleled by a decrease of fatty acid-derived ketogenesis. The significance of these findings is discussed in relation to the role of insulin in branched-chain alpha-ketoacid oxidation in liver of diabetic rats.     

Localization of collagen prolyl hydroxylase to the hepatocyte : Studies in primary monolayer cultures of parenchymal cells from adult rat liver

Significant levels of prolyl hydroxylase activity (prolyl-glycyl-peptide, 2-oxoglutarate: oxygen oxidoreductase; EC 1.14.11.2) have been found in freshly isolated hepatocytes prepared from normal or regenerated adult rat liver and primary non-proliferating monolayer cultures of these cells. Four days after partial hepatectomy, the intact regenerated liver contained two times the normal level of prolyl hydroxylase activity. Freshly isolated hepatocytes contained 24% of the total prolyl hydroxylase activity in normal liver and 47% of that in regenerated liver. Upon incubation of hepatocytes for 24 h in a chemically defined culture medium containing insulin, prolyl hydroxylase activity rose 2- to 3-fold, and gradually declined during the next 48 h. The rise in prolyl hydroxylase activity was blocked by addition of cycloheximide to the culture medium. The presence of prolyl hydroxylase activity in hepatocyte cultures was not likely due to contamination with non-parenchymal liver cells. The latter cells contained less than 20% of the total enzyme activity recovered in all cells isolated from the liver. Furthermore, prolyl hydroxylase was localized by immunofluorescence uniformly to the hepatocytes in culture. Cultured hepatocytes converted [¹⁴C]proline to [¹⁴C]hydroxyproline at rates comparable to those reported for whole liver. However, only a small portion of the hydroxyproline containing product was present as collagen protein, suggesting its rapid degradation in culture. We conclude that the liver parenchymal cell may actively participate in collagen synthesis and possibly in collagen degradation.     

Differential increase of steroid sulfatase activity in XX and XY trophoblast cells from human term placenta with syncytia formation in vitro

Steroid sulfatase (STS, EC 3.1.6.2) catalyzes the hydrolysis of the sulfate ester bonds of a variety of sulfated steroids, such as cholesterol, dehydroepiandrosterone, and estrone sulfate, a reaction influencing fertility and breast cancer in mammals. The activity of the enzyme is substantially elevated in placental syncytiotrophoblasts and is lower in other somatic cells. The polypeptide sequence of the enzyme is encoded by a gene located on the distal short arm of the human X chromosome. Prior studies have shown that the STS gene escapes X-chromosome inactivation. We studied the expression of the STS gene in primary cultures of cytotrophoblasts from human term placentae and compared it with the expression of autosomally encoded placental alkaline phosphatase (PALP) and X-linked glucose-6-phosphate dehydrogenase (G6PD). During 90 h in culture, the mononucleated cytotrophoblast cells did not proliferate, but differentiated into multinucleated, syncytiotrophoblast-like cells. STS activity in freshly isolated cytotrophoblasts was low (about 17%), compared to placental tis- sue, and about 1.7-fold higher in female than in male cells. During cultivation, STS activity increased 2- to 3-fold in female, but not in male, cells. PALP activity was very low in freshly isolated cytotrophoblasts (about 5% of placental tissue), and no significant difference between female and male cells was detectable. Within 90 h in culture, PALP activity increased in all preparations about 2- to 4-fold. G6PD activity in freshly isolated cytotrophoblasts showed great variation among preparations, and no significant difference between female and male cells was detectable. In both male and female cells the activity declined to about 50% of initial activity during cultivation. We conclude that human cytotrophoblasts in primary culture show a sex-specific regulation of STS activity, perhaps as a unique feature of the STS gene. The cytotrophoblast system may offer a new possibility to study the regulation of STS gene expression.     

Ethanol increases cytochromes P450IIE, IIB1/2, and IIIA in cultured rat hepatocytes

In intact rats, ethanol treatment has been associated with increases in hepatic levels of both P450IIB1/2 and P450IIE. When rat hepatocytes were cultured on an extracellular tumor matrix (Matrigel), exposure to ethanol from 48 to 96 h in culture resulted in increases in cytochromes P450IIE, IIB1/2, and IIIA. Cytochrome P450IIE was detected immunologically and enzymatically, using two activities associated with cytochrome P450IIE, p-nitrophenol hydroxylation, and acetaminophen activation to a metabolite that binds to glutathione. The content of cytochrome P450IIE in freshly isolated cells decreased when the cells were placed in culture. Exposure of the cultured hepatocytes to ethanol from 48 to 96 h after inoculation resulted in an increase in cytochrome P450IIE compared to untreated cultured cells. In addition, in culture, the amount of enzymatically active protein after ethanol treatment was equal to that in hepatocytes freshly isolated from intact animals. Ethanol treatment resulted in increases in cytochrome P450IIB1/2 compared to untreated cells, as shown immunologically and by increased benzyloxyresorufin dealkylase activity. However, phenobarbital induced cytochrome P450IIB1/2 to higher levels, compared to ethanol. Ethanol and phenobarbital treatments both increased P450IIIA, as determined immunologically and by the amount of propoxycoumarin depropylase activity that is inhibited by triacetyloleandomycin. However, the amount of P450IIIA increased after ethanol treatment was less than that increased after treatment with dexamethasone in these cells. The ethanol-mediated increases in all four forms of cytochrome P450 in culture suggest that these increases in the intact animal result from direct effects of ethanol on the liver.     

Ploidy class-dependent variations during 24 h of glucose-6-phosphate and succinate dehydrogenase activity and single-stranded RNA content in isolated rat hepatocytes

The time-dependent variations over 24 h of glucose-6-phosphate dehydrogenase (G6PDH) activity, succinate dehydrogenase (SDH) activity and single-stranded RNA (ssRNA) content have been investigated by cytophotometric analysis of cytochemically stained isolated hepatocytes of different ploidy classes from adult male rats. A marked variation of 48 % over the day in G6PDH activity of the mononuclear diploid cells was revealed, but no significant variation in the binuclear tetraploid cells. The cells of the inbetween ploidy classes showed an amplitude of variation of 38 % (binuclear diploid cells) and 24% (mononuclear tetraploid cells), respectively. All cells showed a maximum activity of the enzyme at the middle of the day and a minimum during the night. The relative enzyme activity per mononuclear diploid cell was significantly higher than the relative activity in the other cells, especially at its maximum. The variation of the SDH activity in hepatocytes isolated from the same rats was similar in all cells, irrespective of their ploidy class. The activity was highest at the end of the activity phase of the animals. The SDH activity per cell was directly proportional to the quantity of genome copies. The ssRNA content of the hepatocytes showed a time-dependent variation with a maximum during the resting phase of the animals and a minimum during their activity phase. The variation was larger in the mononuclear diploid cells than in the cells of other ploidy classes and the ssRNA content was also significantly higher in these cells than in the hepatocytes of other ploidy classes when calculated on the basis of genome copies. It is concluded that the large amplitude of variation over the day and the high relative amount of G6PDH activity and ssRNA content in mononuclear diploid cells is related to the function of these cells as stem cells of the liver parenchyma.     

Central nervous system control of alcohol dehydrogenase activity in rats

The activity of alcohol dehydrogenase is higher in the livers of female rats than that in male rats. Stereotaxic lesions of the anterior periventricular hypothalamus of male rats increased the activity of alcohol dehydrogenase by about 50 percent; larger lesions which destroyed many of the major hypothalamic nuclei increased the enzyme activity 100 percent and abolished the sexual difference in alcohol dehydrogenase activity. The changes in enzyme activity were independent of changes in plasma thyroxine, testosterone and estradiol levels. Hypothalamic lesions in female rats had no effect on the enzyme activity. The sexual difference in alcohol dehydrogenase activity in rats is under hypothalamic control and does not appear to be mediated directly by the plasma level of androgens or estrogens.     

The effect of dexamethasone, insulin and triiodothyronine on microsomal NADPH-cytochrome-c (P-450) reductase in primary cultures of isolated hepatocytes

NADPH-cytochrome-c (P-450) reductase, a flavoprotein, is a constituent of the hepatic microsomal polysubstrate monooxygenase and catalyzes the transfer of electrons from NADPH to cytochrome P-450. The hormonal regulation of NADPH-cytochrome-c reductase activity and protein has been examined in insolated hepatocytes cultured as monolayers for 48 h in Waymouth's MB752/1 medium fortified with insulin, dexamethasone and triiodothyronine. No similarity between the response of NADPH-cytochrome-c reductase and of tyrosine aminotransferase and malate dehydrogenase activity to dexamethasone and triiodothyronine treatment could be detected. In the absence of hormones about 65% of the original NADPH-cytochrome-c reductase activity and protein estimated by the immunochemical staining technique was retained. Culture of hepatocytes in insulin (10.0 mU/ml) or dexamethasone (100 nM) alone but not triiodothyronine improved the retention of reductase activity and protein. Only when hepatocytes were cultured in insulin, triiodothyronine and dexamethasone could NADPH-cytochrome-c reductase activity and protein be maintained at the original level. Dexamethasone alone was found to enhance consistently retention of reductase protein, but not reductase activity, to approximately the same level as in freshly isolated hepatocytes. The results suggest that microsomal NADPH-cytochrome-c reductase activity and protein can be maintained in isolated hepatocytes at the original level by culturing the cells in dexamethasone, insulin and triiodothyronine.     

Expression of microsomal and cytosolic epoxide hydrolases in cultured rat hepatocytes and hepatoma cell lines

Microsomal epoxide hydrolase activity, determined using benzpyrene 4,5-oxide and styrene 7,8-oxide, increased in cultured hepatocytes compared to freshly isolated cells. In contrast, cytosolic epoxide hydrolase activity, assayed using trans-stilbene oxide, had decreased 80% by 24 hr and was barely detectable after 96 hr in culture. There was no difference in enzyme activity between freshly isolated hepatocytes and the two rat hepatoma cell lines McA-RH 7777 and H4-II-E, when styrene 7,8-oxide was used as substrate. However, benzpyrene 4,5-oxide hydrolase activity of the McA-RH 7777 and H4-II-E cell lines were 55 and 10%, respectively, of freshly isolated hepatocytes. These results show that hepatoma cell lines provide a suitable system for studying the regulation of both the microsomal and cytosolic epoxide hydrolase enzymes.     

Ploidy class-dependent metabolic changes in rat hepatocytes after partial hepatectomy

Glucose-6-phosphate dehydrogenase (G6PDH), succinate dehydrogenase (SDH) activity and the single-stranded RNA (ssRNA) content of isolated hepatocytes of different ploidy classes from adult male rats have been studied after partial hepatectomy using quantitative cytochemical means. The SDH activity and ssRNA content in all classes of hepatocytes are decreased during the first hours after operation followed by an increase above control values. The increase of both SDH activity and ssRNA content is significant only in the mononuclear diploid (MD) cells but not in the hepatocytes of higher ploidy classes and is related with the mitotic wave at 32 h after hepatectomy. After the mitotic wave, the values quickly return to normal levels. The G6PDH activity does not show any significant change in hepatocytes other than MD cells. In MD cells the G6PDH activity is elevated on a highly significant level up to a maximum value of 3.5 times the control value at 48 h after operation. The G6PDH activity in MD cells is returned to normal values within 14 days after operation. It is concluded that: 1. The MD cells show a distinct metabolic behaviour due to their function as stem cells of liver parenchyma and retain at least some of their fetal characteristics. 2. G6PDH activity is not a transformation-linked discriminant for neoplastic metabolism.