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

Mechanisms of peroxisome proliferation by perfluorooctanoic acid and endogenous fatty acids

1. The effects of endogenous fatty acids and perfluorooctanoic acid (PFOA) and its analogs on peroxisomal acyl CoA oxidase (ACO) and microsomal laurate hydroxylase (LH) activities were evaluated in primary cultures of rat hepatocytes and activation of peroxisome proliferator-activated receptor alpha (PPARalpha) in CV-1 cells. The rank order for the stimulation of ACO activity in hepatocytes for selected compounds was PFOA >> octanoic acid>octanedioic acid, perfluorooctanol (inactive). Increases in ACO activity by PFOA, like those of ciprofibrate, were associated with a marked increase in peroxisome number and cytosolic occupancy volume. Maximal effects of ciprofibrate and PFOA on the stimulation of ACO activity were not additive, suggesting that these two compounds share a common pathway of peroxisome proliferation. 2. Saturated monocarboxylic acids of C4 to C18 chain length were inactive, and, among dicarboxylic acids, only small elevations (40-45%) in ACO activity were observed with the long-chain C12 and C16 dioic acids. Of the C18 fatty acids tested, only oleic and linoleic acids, at 1 mM, produced a two- to three-fold elevation in ACO and LH activities. In comparison with endogenous fatty acids, PFOA was more potent and exhibited a different time course and greater magnitude of stimulation of ACO and LH activities in cultured hepatocytes. 3. Addition of mitochondrial beta-oxidation inhibitors (3-mercaptopropionic and 2-bromooctanoic acids) did not alter ACO activity in the presence of octanoic acid or octanedioic acid; nor did they modify the stimulation of ACO activity by PFOA. The carnitine palmitoyltransferase I inhibitor 2-bromopalmitic acid produced a 2.5-fold increase in ACO stimulatory activity and reduced both ciprofibrate- and PFOA-mediated stimulations of ACO activity. 4. Cycloheximide treatment reduced PFOA- and ciprofibrate-induced ACO activities; however, the response to oleic acid was not blocked and increased slightly. 5. In rat and human PPARalpha transactivation assays, the rank order of activation was ciprofibrate > PFOA > oleic acid > or = octanoic acid > octanedioic acid or perfluorooctanol (inactive). PFOA, ciprofibrate and oleic acid were activators of rPPARalpha at concentrations that correlated favorably with the changes in ACO activity in cell culture. Octanoic acid did not increase ACO activity and was a weak activator of PPARalpha. 6. Our findings suggest that fatty acids such as oleic acid (endogenous fatty acids) and PFOA (a stable fatty acid) act through more than one pathway to increase ACO activity in rat hepatocytes. We conclude that the potent effects of PFOA are primarily mediated by a mechanism that includes the activation of liver PPARalpha.

Relation between spontaneous contraction and sarcoplasmic reticulum function in cultured neonatal rat cardiac myocytes

The relation between spontaneous contraction, Ca2+ oscillations, and sarcoplasmic reticulum (SR) function was studied in cultured neonatal rat cardiac myocytes. Spontaneous contraction and Ca2+ oscillations were irregular at day 2 of culture but became regular at day 6 of culture in neonatal rat cardiac myocytes. The rate of spontaneous contraction and the frequency of Ca2+ oscillations were decreased by verapamil and were abolished in the absence of extracellular Ca2+ at both day 2 and day 6 of culture. Ryanodine and thapsigargin increased the rate of contraction and the frequency of Ca2+ oscillations at day 2 of culture but did not affect contractions and Ca2+ oscillations at day 6 of culture. Ultrastructural observation showed that the structure of SR developed less at day 6 of culture. The present results suggest that spontaneous contraction and Ca2+ oscillations are due mainly to extracellular Ca2+ influx but not to Ca2+ release from SR in neonatal rat cardiac myocytes.

Inhibition of peroxisomal degradation by 3-methyladenine (3MA) in primary cultures of rat hepatocytes

BACKGROUND

A significant reduction in peroxisomes has been demonstrated in primary cultures of rat hepatocytes. This report demonstrates that 3-methyladenine (3MA), a potent inhibitor of autophagy, inhibits this effect.

METHODS

Hepatocytes from male Wistar rats were isolated by a two-step in situ perfusion technique using collagenase and were cultured in Williams E medium. After a 2-hr attachment period (day 0 of culture), the cells were treated with 200 microM bezafibrate (BF), a peroxisome proliferator, and 5 mM 3MA for 3 days. The cells in the culture dish were fixed in situ, stained for catalase, and embedded in Poly/Bed 812. The number and size of peroxisomes in electron micrographs were analyzed morphometrically.

RESULTS

After 3 days of culture, the number of peroxisomes had decreased to 30% of the day 0 level. However, the day 0 level was maintained by treatment with 3MA. In BF-treated cells, many autophagosomes were observed, and peroxisomes had proliferated significantly, although they did not exceed the day 0 level. In cells treated with a combination of 3MA and BF, the number and size of peroxisomes had increased remarkably.

CONCLUSIONS

These results suggest that 3MA is effective in maintaining both the number and size of peroxisomes in the course of primary cultures of rat hepatocytes. Suppression of peroxisome proliferation by treatment with BF may be regulated by autophagic/lysosomal degradation.

Subculture of proliferating adult rat hepatocytes in medium supplemented with nicotinamide and EGF

To establish parenchymal hepatocyte cell lines, we tried to subculture the primary hepatocytes isolated from adult rats. The hepatocytes were cultured in serum-free modified Dulbecco's modified Eagle's medium supplemented with 10 mM nicotinamide and 10 ng/ml epidermal growth factor. When 6 x 10(5) cells were plated on 35-mm dishes coated with rat tail collagen, the cells proliferated and reached confluence at Day 6 to Day 8. The first subculture was carried out at Day 8 using 0.005% collagenase and gentle pipettings. Most cells were recovered and plated on the new dishes coated with the collagen (first passage). The attached cells could proliferate and reached near confluence when the cells occupied more than two-thirds of the dish surface. About a week after the first subculture, the second one was conducted. Although the number of the recovered cells was smaller than at the first passage, the cells could attach and proliferate to a certain extent. Thereafter, they were maintained for more than 2 mo, but they never overgrew. Albumin secretion into the culture medium was confirmed in the subcultured cells. Ultrastructurally, these subcultured cells possessed hepatic characteristics such as peroxisomes with a crystalline nucleiod and bile-canaliculus structures. When 10% fetal bovine serum and ascorbic acid 2-phosphate were added to the cells of the second passage, they began to proliferate very slowly. These proliferating cells were mainly mononucleate and had a small cytoplasm. In addition, some of them could differentitate into typical mature hepatocytes by forming a three-dimensional structure interacting with nonparenchymal cells. In this experiment, we showed the successful subculturing of parenchymal hepatocytes isolated from adult rats and provided evidence that the subcultured cells still have the potential to proliferate and to differentiate.

Hepatic peroxisome proliferation in rodents and its significance for humans

Peroxisomes are subcellular organelles found in all eukaryotic cells. In the liver they are usually round and measure about 0.5-1.0 microns; in rodents they contain a prominent crystalloid core, but this may be absent in newly formed rodent peroxisomes as well as in human peroxisomes. A major role of the peroxisomes is the breakdown of long-chain fatty acids, thereby complementing mitochondrial fatty-acid metabolism. Many chemicals are known to increase the number of peroxisomes in rat and mouse hepatocytes. This peroxisome proliferation is accompanied by replicative DNA synthesis and liver growth. No clear structure-activity relationships are apparent. Many of these peroxisome proliferators contain acid functions that can modulate fatty acid metabolism. Two mechanisms have been proposed for the induction of peroxisome proliferation. One is based on the existence of one or several specific cytosolic receptors that bind the peroxisome proliferator, facilitating its translocation to the cell nucleus and the activation of the expression of specific genes. The second, perhaps more general, hypothesis involves chemically mediated perturbation of lipid metabolism. These two hypotheses are not mutually exclusive. Many peroxisome proliferators have been shown to induce hepatocellular tumours, despite being uniformly non-genotoxic, when administered at high dose levels to rats and mice for long periods. Three mechanisms have been proposed to explain the induction of tumours. One is based on increased production of active oxygen species due to imbalanced production of peroxisomal enzymes; it has been proposed that these reactive oxygen species cause indirect DNA damage with subsequent tumour formation. In rodents, an alternative mechanism is the promotion of endogenous lesions by sustained DNA synthesis and hyperplasia. Thirdly, it is conceivable that sustained growth stimulation may be sufficient for tumour formation. Marked species differences are apparent in response to peroxisome proliferations. Rats and mice are extremely sensitive, and hamsters show an intermediate response while guinea pigs, monkeys and humans appear to be relatively insensitive or non-responsive at dose levels that produce a marked response in rodents. These species differences may be reproduced in vitro using primary culture hepatocytes isolated from a variety of species including humans. The available experimental evidence suggests a strong association and a probable casual link between peroxisome-proliferator-elicited liver growth and the subsequent development of liver tumours in rats and mice. Since humans are insensitive or unresponsive, at therapeutic dose levels, to peroxisome-proliferator-induced hepatic effects, it is reasonable to conclude that the encountered levels of exposure to these non-genotoxic agents do not present a hepatocarcinogenic hazard to humans.(ABSTRACT TRUNCATED AT 400 WORDS)

Redifferentiation of proliferated rat hepatocytes cultured in L15 medium supplemented with EGF and DMSO

Primary adult rat hepatocytes were cultured in serum-free L15 medium supplemented with 20 mM NaHCO3 and 10 ng/ml epidermal growth factor in a 5% CO2:95% air incubator. The number of cells increased and reached about 180% of the initial value by Day 4, and after 2% dimethyl sulfoxide (DMSO) was added to the culture medium at Day 4, the cells continued to proliferate until Day 6. The number of cells reached about 210% at Day 6 and they were well maintained until Day 18. The cell number gradually decreased with time in culture, but many cells remained for more than 2 mo. On the other hand, without 2% DMSO, the cells proliferated until Day 5, but thereafter they rapidly decreased. After DMSO addition, albumin and transferrin were secreted into the medium and the production of both proteins continued for more than 2 mo. Immunocytochemically both proteins were strongly stained in the cells treated with 2% DMSO. Although the expression of G6Pase in the cells disappeared at Day 6 without DMSO, the cells treated with 2% DMSO recovered G6Pase activity at Day 16. In addition, induction of peroxisomes by 2 mM sodium clofibric acid was clearly shown in the hepatocytes at Day 14 and Day 25 using enzyme-cytochemistry. Ultrastructurally, DMSO-treated hepatocytes had many mitochondria and large peroxisomes with a crystalline nucleoid, and both gap junctions and desmosomes were well developed between the cells even at Day 40. Thus, the number of cells doubled, some differentiated functions of the primary hepatocytes were well restored by the use of 2% DMSO, and these functions were maintained for more than 2 mo.

Characteristics of small cell colonies developing in primary cultures of adult rat hepatocytes

Phenotypes of the cells developing into small colonies after days of primary culture of adult rat hepatocytes in serum-free modified Dulbecco Modified Eagles' medium containing 10 mM nicotinamide and 10 ng/ml epidermal growth factor were analyzed immunocytochemically, cytochemically and ultrastructurally. Albumin, cytokeratin 8 and 18 were seen by immunocytochemical techniques in the cells of the small colonies at Day 6. Transferrin, alpha 1-antitrypsin, ceruloplasmin, and haptoglobin, proteins secreted by mature hepatocytes, were faintly stained in these cells as was alpha-fetoprotein. These proteins were secreted into the culture medium as evidenced by immunoblot analysis. gamma-Glutamyltransferase, alkaline phosphatase and glucose 6-phosphatase were not present in the cells of the small colonies as well as the surrounding hepatocytes at Day 6 of culture. In addition, ultrastructural examinations of the cells in the small colonies indicated that these cells not only had many characteristic mitochondria and desmosomes, but also a few small peroxisomes. Such cells, even after 20 days in culture were proliferating, as evidenced by the intranuclear presence of the proliferating cell nuclear antigen. The potential relation of these cells to hepatocytes which may serve as the principal reserve for replicating hepatocytes is discussed.

Small cell colonies appear in the primary culture of adult rat hepatocytes in the presence of nicotinamide and epidermal growth factor

Colonies of small hepatocytes appeared after the culture of primary adult rat hepatocytes for 4 days in serum-free modified Dulbecco's modified Eagle's medium containing 10 mmol/L nicotinamide and 10 ng/ml epidermal growth factor. Each colony consisted of cells that had a single nucleus and a higher nucleus/cytoplasm ratio than surrounding hepatocytes, and immunocytochemically these cells were stained with albumin and transferrin. Ultrastructurally these cells had mitochondria, peroxisomes and desmosomes, indicating that they were derived from hepatocytes. When 6 x 10(5) cells were plated on 35-mm dishes, about 5.5 colonies/mm2 were observed. This result suggested that about 1.5% of adult rat hepatocytes has the potential for multiple replications and of forming a focal colony. These cell populations had higher proliferative activities than surrounding hepatocytes. DNA synthetic activity could not be inhibited by 2% dimethyl sulfoxide. Flow cytometric analysis showed that both 2N and 4N nuclei synthesized their DNA until day 4 but that the number of 2N nuclei rapidly increased at day 5. This result correlated with the observation of the appearance of small cell populations indicating that the cells of these focal colonies were predominantly diploid.

Identification of the proximate peroxisome proliferator(s) derived from di (2-ethylhexyl) adipate and species differences in response

Identification of the proximate peroxisome proliferator(s) derived from di (2-ethylhexyl) adipate (DEHA) has been achieved using primary hepatocyte cultures derived from different species and cyanide-insensitive fatty acyl CoA oxidase (PCO) as a marker enzyme for peroxisome proliferation. In rat and mouse hepatocytes, the parent compound (DEHA) had no effect on peroxisomal beta-oxidation, but primary metabolites of DEHA, mono (2-ethylhexyl) adipate (MEHA) and 2-ethylhexanol (EH), were approximately equipotent in PCO induction (5-fold at 0.5 mM final concentration). The secondary metabolite of DEHA, 2-ethylhexanoic acid (EHA), was in both species the most potent peroxisome proliferator (25- and 9-fold induction in mice and rats, respectively, at 1 mM final concentration). At 2 mM final concentration a tertiary metabolite of DEHA, 2-ethyl-5-hydroxyhexan-1-oic acid, was less effective in mouse and rat hepatocytes at inducing PCO (15- and 5-fold, respectively). 2-Ethyl-5-oxohexan-1-oic acid and 2-ethylhexan-1,6-dioic acid had little effect (2-3-fold in both rat and mouse hepatocytes). Thus, EHA was identified as the proximate peroxisome proliferator of DEHA and mouse hepatocytes were approximately twice as sensitive as rat hepatocytes to peroxisome proliferation due to MEHA, EH and EHA. We investigated further species differences in response to peroxisome proliferators by using guinea pig and marmoset primary hepatocyte culture. None of the chemicals studied stimulated peroxisomal beta-oxidation in these species up to a final concentration of 2 mM. Higher concentrations lead to cytotoxicity. This lack of sensitivity of guinea pig and marmoset hepatocytes is in agreement with previous studies with di (2-ethylhexyl) phthalate metabolites, suggesting the absence of a threat of hepatocarcinogenic damage to these species and confirming that primary hepatocytes cultures are useful models for investigating the phenomenon of peroxisome proliferation.

Induction of peroxisomal fatty acyl-coenzyme A oxidase and total carnitine acetyl-coenzyme A transferase in primary cultures of rat hepatocytes by garlic extracts

Garlic has been proposed as a natural hypolipidemic substance. Most hypolipidemic compounds induce peroxisomal proliferation and increase enzyme activities associated with peroxisomal beta-oxidation in rat liver. Here we report that garlic methanol-extracts behave as hypolipidemic drugs, increasing the activity of peroxisomal fatty acyl-coenzyme A oxidase and of total carnitine acetyl-coenzyme A transferase in primary cultures of rat hepatocytes. Both enzymes are considered markers associated with increased peroxisomal beta-oxidation. As in the case of hypolipidemic peroxisome proliferators, garlic extracts partially prevented the decrease in fatty acyl-coenzyme A oxidase as the culture aged. No changes were observed in the activity of microsomal NADPH cytochrome c reductase or of mitochondrial glutamate dehydrogenase.

Induction of peroxisomal enzymes in cultured porcine endothelial cells by the hypolipidemic drug ciprofibrate

The purpose of this study was to determine if the hypolipidemic peroxisome proliferator ciprofibrate, which induces peroxisomes in the liver, can induce peroxisomes in cultured porcine pulmonary endothelial cells. Ciprofibrate was added at three concentrations to cell cultures for a 6-day period. The induction of peroxisomes in the cells was detected by determining total peroxisomal beta-oxidation and peroxisomal catalase activity. The addition of ciprofibrate was found to increase peroxisomal enzyme activities in a dose-dependent manner, with the highest activity being reached at 1000 microM ciprofibrate. Ciprofibrate also caused an increased transfer of albumin across endothelial cells cultured on micropore filters. This study shows that peroxisomal enzyme activities can be induced by ciprofibrate in endothelial cells, which may have implications in diseases mediated by vascular injury.

Morphometric and cytochemical evaluation of clofibrate-induced peroxisomal proliferation in adult rat hepatocytes cultured on floating collagen gels

The present ultrastructural morphometric and cytochemical studies demonstrate clofibrate induced changes in peroxisomes in adult rat hepatocytes maintained for 14 days in primary culture on floating collagen gels. Catalase activity and the number and diameter of peroxisomes were reduced in hepatocytes cultured for between 2/3 and 7 days. However, hepatocytes cultured for 7-14 days had well-developed peroxisomes containing crystalloid nucleoids. The number of anucleoid peroxisomes in hepatocytes treated with 2 mM Na clofibrate increased with culture age, and by day 14 the number was 2.9 times greater than in freshly isolated hepatocytes. Catalase activity, as well as the number of nucleoid-containing peroxisomes were much greater in treated hepatocytes than in untreated controls, but decreased slightly with culture age. The diameter of peroxisomes was not reduced in the treated cells. These results suggest that the treatment with Na clofibrate is effective both for proliferation and maintenance of peroxisomes and for enhancing catalase activity. In treated hepatocytes, matrical plates were formed in peroxisomes from days 5 to 14 and the number of plate-containing peroxisomes increased with culture age.

Active proliferation of mouse hepatocytes in primary culture under defined conditions as compared to rat hepatocytes

Mouse and rat hepatocytes were investigated for replicative potential in primary culture under defined conditions. Mouse hepatocytes replicated at least twice or three times by the 7th day of culture in response to EGF, while only a half of rat hepatocytes replicated once. Thus a far greater potential for proliferation was demonstrated by mouse than rat cells, although the mouse cells ceased dividing by the 10th day of culture. Immunocytochemical examination revealed that the cells produced both albumin and alpha-fetoprotein. Ultrastructural investigation revealed that these cells were immature hepatocytes in nature, based on the presence of microbodies with nucleoids. Thus, primary cultures of mouse hepatocytes seem to be a useful system for studying proliferation and transformation of hepatocytes in vitro.

Interactions of inhibitors of carnitine palmitoyltransferase I and fibrates in cultured hepatocytes

Culture of rat hepatocytes with etomoxir, an inhibitor of carnitine palmitoyltransferase I (CPT I), for 48 h, resulted in increased carnitine acetyltransferase (CAT) activity (74%), a marked decrease in CPT activity (82%) measured in detergent extracts, and increased activities of glucose-6-phosphate dehydrogenase (227%) and fructose-1,6-bisphosphatase (65%). Changes in CAT and CPT activities were not observed after 4 h culture with etomoxir. When hepatocytes were cultured with etomoxir and benzafibrate (a hypolipidaemic analogue of clofibrate) for 48 h, etomoxir prevented the 5-fold increase in CAT activity caused by bezafibrate, whereas bezafibrate suppressed the increase in glucose-6-phosphate dehydrogenase and fructose-bisphosphatase caused by etomoxir. However, bezafibrate did not prevent the suppression of CPT activity by etomoxir. Etomoxir inhibited palmitate beta-oxidation and ketogenesis after short-term (0-4 h) and long-term (48 h) exposure, but it caused accumulation of triacylglycerol in hepatocytes only after short-term exposure (0-4 h). These effects of etomoxir on fatty acid metabolism and suppression of CPT (after 48 h) were similar in periportal and perivenous hepatocytes, but the increases in CAT and glucose-6-phosphate dehydrogenase activities were higher in periportal than in perivenous cells. The effects of CPT I inhibitors on CAT activity and long-term suppression of CPT activity are probably mediated by independent mechanisms.

Fatty acid metabolism in hepatocytes cultured with hypolipidaemic drugs. Role of carnitine

The direct effects of clofibrate analogues on carnitine acyltransferase activities and fatty acid metabolism were studied in cultured hepatocytes. Rat hepatocytes cultured with bezafibrate or ciprofibrate (0.1-10 micrograms/ml) for 48 h had increased activities of carnitine acetyltransferase (CAT; 4-6-fold) and carnitine palmitoyltransferase (CPT; 12-34%). The increase in CAT was higher in hepatocytes from the periportal zone (440%) of rat liver compared with cells from the perivenous zone (266%). In human hepatocytes, in contrast with rat, the fibrates did not cause a marked increase in CAT activity. The effects of fibrates on palmitate metabolism were dependent on the carnitine status. In the presence of exogenous carnitine (1 mM), rat hepatocytes cultured with bezafibrate had higher rates of total palmitate metabolism (29-34%) without increased partitioning of palmitate towards beta-oxidation, relative to control cultures. At low endogenous carnitine concentrations, cells cultured with bezafibrate had a greater increase in palmitate metabolism, esterification and cellular accumulation of triacylglycerol compared with the corresponding increases in the presence of carnitine. The changes in palmitate metabolism at either high or low carnitine concentrations were small in comparison with the changes in CAT activity. It is concluded that the increase in hepatic carnitine that occurs in vivo after fibrate feeding probably plays the major role in the changes in partitioning of fatty acid between beta-oxidation and esterification.

Prevention of peroxisomal proliferation by carnitine palmitoyltransferase inhibitors in cultured rat hepatocytes and in vivo

1. The induction of peroxisomal beta-oxidation activities by bezafibrate in cultured rat hepatocytes and in the rat in vivo was prevented by inhibitors of carnitine acyltransferase, e.g. 2-bromopalmitate, 2-[5-(4-chlorophenyl)pentyl]oxirane-2-carboxylate or 2-tetradecylglycidic acid. 2. The prevention of peroxisomal proliferation by carnitine palmitoyltransferase inhibitors could not be accounted for by inhibition of mitochondrial beta-oxidation, since 2-bromo-octanoate, acting as an inhibitor of beta-oxidation, did not prevent the induction of peroxisomal activities in cultured rat hepatocytes. 3. The putative role of the acylcarnitine derivative of bezafibrate was analysed by studying the formation of bezafibroylcarnitine with bezafibroyl-CoA as substrate. However, no bezafibroylcarnitine formation was demonstrated in the presence of rat liver preparations capable of catalysing transfer to carnitine of medium- or long-chain fatty acids. 4. The prevention of peroxisomal proliferation by carnitine acyltransferase inhibitors may help in dissecting the causal relationship between the multiple effects mediated by peroxisomal proliferators.

Comparison of the short-term hepatic effects of orally administered citral in Long Evans hooded and Wistar albino rats

The short-term effects of citral on the liver have been studied in two strains of rat. Hepatomegaly was accompanied in citral-treated rats by an altered distribution of lipid and glycogen in the liver and peroxisome proliferation occurred in a manner reminiscent of that associated with some hypolipidaemic compounds. Specific biochemical markers supported the morphological changes in the peroxisomes. Cyanide-insensitive palmitoyl CoA oxidation showed, at the maximum, fourfold and threefold inductions in Wistar albino and Long Evans hooded rats, respectively. In addition, induction of cytochrome P-450 levels was greater in the Long Evans than in the Wistar rats, the maximal increases recorded being 81 and 27% respectively. A peroxisome-associated polypeptide of molecular weight 80,000 daltons (PPA-80) was induced, especially in Long Evans rats. No alterations in plasma triglycerides or total cholesterol were detected. The differential induction of the mixed-function oxidase system and the differential proliferation of peroxisomes in these two strains of rat suggest that citral may be metabolized differently in the two strains. The study indicates that peroxisomal and possibly also mitochondrial changes are involved in the action of citral on lipid metabolism.

Enrichment and characterization of clonogenic epithelial cells from adult rat liver and initiation of epithelial cell strains

A highly efficient method is described for obtaining proliferative epithelial cells from adult rat livers for the reproducible establishment of liver epithelial cell strains. When cells were isolated from livers of 10- to 15-wk-old male Fischer 344 rats by a collagenase-perfusion method, collected by centrifugation at 50 X g for 5 min, and cultured in Williams' medium E containing fetal bovine serum and dexamethasone, colonies of epithelial cells different in size and morphology from hepatocytes were obtained. Sequential perfusion with collagenase and dispase yielded numerous epithelial cell colonies. When isolated cells were fractionated by differential centrifugation, the great majority of hepatocytes were sedimented at 50 X g for 1 min, whereas many non-hepatocytic cells remained in the supernatant and could be sedimented by a second centrifugation at 50 X g for 5 min. Culture of the two fractions revealed that almost all the epithelial cell colonies were derived from cells in the non-hepatocytic cell fraction. The epithelial cells were cytochemically negative for gamma-glutamyl transpeptidase activity, whereas an increase in the activity was detected in hepatocytes with duration in culture. Ultrastructural characteristics of hepatocytes were not found in the cells of newly established cell strains. These results suggest that adult rat liver epithelial cells propagable in culture were derived from a cell type other than the hepatocyte.

Characterization of ciprofibrate and clofibric acid as peroxisomal proliferators in primary cultures of rat hepatocytes

We have determined the comparative activities of peroxisomal proliferators, ciprofibrate and clofibric acid on various hepatic parameters associated with endoplasmic reticulum, mitochondria and peroxisomes in primary cultures of rat hepatocytes. We have measured the activities of carnitine acetyltransferase and fatty acylCoA oxidase, and the amount of 60 and 80 kD polypeptides as biochemical markers of the peroxisomal function; laurate hydroxylase and cytochrome P-450 as markers of the endoplasmic reticulum; and carnitine palmitoyltransferase as a marker of mitochondria in primary cultures of hepatocytes. Ciprofibrate (0.01 to 0.3 mM) and clofibric acid (0.1 to 3 mM) produced similar changes in several components of cultured hepatocytes within 72 hr. Increases of protein (18 and 11%), carnitine palmitoyltransferase (23 and 97%), cytochrome P-450 (37 and 49%), carnitine acetyltransferase (484 and 614%), fatty acylCoA oxidase (529 and 931%) and laurate hydroxylase (624 and 671%) were obtained in hepatocytes after a 72-hr exposure to 0.1 mM ciprofibrate and 1.0 mM clofibric acid, respectively. In cultured hepatocytes, ciprofibrate was about 30-fold more active than clofibric acid for the stimulation of carnitine acetyltransferase, laurate hydroxylase and fatty acylCoA oxidase activities. Ciprofibrate was also more potent than clofibric acid as an inducer of the 60 and 80 kD proteins in hepatocytes. The maximal drug-induced increases in carnitine acetyltransferase activity were not additive, and the induction of carnitine acetyltransferase by ciprofibrate was blocked by addition (1 micrograms per ml) of cycloheximide or actinomycin D. Changes in protein and RNA synthesis preceded the drug-induced increases of carnitine acetyltransferase activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of extracellular matrix components on the growth and differentiation of cultured rat hepatocytes

Some effects of culturing adult rat hepatocytes on each of four different substrates--laminin (LN), collagen type I (C-I), collagen type IV (C-IV), and fibronectin (FN)--have been investigated under defined conditions. No differential effect on the attachment of the cells to the various substrates was noted; however, the spreading of hepatocytes shortly after initial plating was most strikingly enhanced by FN, whereas LN exhibited little or no such enhancement. The two collagen substrates enhanced the spreading of hepatocytes more than did LN, but less than FN. The different substrates had no differential effect on the induction of tyrosine aminotransferase by dexamethasone and glucagon for at least the first 10 d in culture. The longevity of the hepatocytes was not changed significantly by any of the substrates, at least through the 14th d of culture. During the culture periods the hepatocytes at high cell density were maintained as confluent monolayers, regardless of the substrate on which they had been cultured. After 14 d of culture, gamma-glutamyltranspeptidase activity was highest in cells cultured on C-IV, and lowest in those on FN. DNA synthesis in cultured hepatocytes at a low cell density was highest in cells cultured on FN, with decreasing levels of this parameter in cells cultured on C-IV, C-I, and LN, respectively. These results demonstrate that specific components of the extracellular matrix modulate both differentiated functions and the replication of hepatocytes cultured in serum-free medium.

Peroxisomes in human foetal kidney: variations in size and number during development

The kidneys of 15 human foetuses (10-18 weeks of age) were used for morphometric studies on peroxisomes during gestational development and in organ culture. The catalase positive organelles revealed by DAB were round to ovoid with a granular matrix delimited by a membrane occasionally deformed by marginal plates. Generally, the distribution was uniform in cells of proximal tubules. In the same cell, size and density varied. The number fluctuated from cell to cell. No significant difference in the mean diameter was observed from the 10th to 18th weeks of gestation, although the mean value (0.36 +/- 0.1 micron) was significantly less than the adult figure. These results indicate that size modifications might occur later on in gestation or after birth to reach the adult value. During the studied period, the mean number of peroxisomes per 100 micron2 of surface area did not differ significantly from that of the 10-12 week group (10.5 +/- 1.97). No important changes of peroxisome morphology in kidney explants cultured for 7 days were noticed on day 3-4. Thereafter, the shape of many peroxisomes became elongated or irregular; marginal plates were frequent. A decrease in the diameter of peroxisomes began at day 4, became significant on day 5 and more accentuated on day 7. In addition, as the culture matured, there was a progressive reduction in catalase activity, revealed by a diminished density of the peroxisomal matrix. The number of DAB positive organelles per surface area decreased steadily with culture age, and significantly on day 2 (p less than 0.01) to become drastically low on day 5 and negligible on day 7.(ABSTRACT TRUNCATED AT 250 WORDS)