Effects of dexamethasone on albumin and collagen gene expression in primary cultures of adult rat hepatocytes

Comprehensive study of dexamethasone on albumin biogenesis during normal and pathological renal conditions

CONTEXT

Dexamethasone (DXM) has an anti-immunoinflammatory effect, and is often used in acute kidney injury (AKI). However, the effects of DXM on albumin (ALB) have not been fully studied.

OBJECTIVE

To investigate the effects of DXM on ALB production and renal function.

MATERIALS AND METHODS

Male Wistar rats were divided into normal and DXM groups (0.25, 0.5, 1 mg/kg for 5 days) (n = 15) for a dose-dependent study. Rats were divided into normal group and DXM groups (0.5 mg/kg for 3, 5, 7 days) (n = 9) for a time-dependent study. In AKI experiment, rats were divided into normal (saline), cisplatin (CP, 5 mg/kg, i.v.), CP + DXM groups (0.25, 0.5 and 1 mg/kg, i.m.) (n = 16). The blood and the organs were isolated for analysis.

RESULTS

In normal, serum ALB (sALB) and serum total protein (sTP) increased in DXM group with sALB increased 19.8-32.2% (from small to large dosages); and 30.2-32.5.6% (from 3 to 7 days of DXM); sTP 15.7-22.6% and 14.2-24.3%; urine ALB (uALB) 31.5-392.3%, and 1047.2-1390.8%; urine TP (uTP) 0.68-173.1% and 98.0-504.9%, compared with normal groups. DXM increased the mRNA expression of Cebp and Hnf, suppressing podocin. In AKI, DXM decreased serum BUN (53.7%), serum Cre (73.4%), sALB (30.0%), sTP (18.7%), uALB (74.5%), uTP (449.3%), rescuing the suppressed podocin in kidney.

CONCLUSIONS

DXM acts on Cebp and Hnf and promotes ALB production. This finding helps to evaluate the rationale of DXM for kidney injury.

Advances in the clinical use of collagen as biomarker of liver fibrosis

INTRODUCTION

Hepatic fibrosis is the excessive synthesis and deposition of extracellular matrix including collagen in the tissue. Chronic liver insult leads to progressive parenchymal damage, portal hypertension, and cirrhosis. Determination of hepatic collagen by invasive liver biopsy is the gold standard to estimate severity and stage of fibrosis. However, this procedure is associated with pain, carries the risk of infection and bleeding, and is afflicted with a high degree of sampling error. Therefore, there is urgent need for serological collagen-derived markers to assess collagen synthesis/turnover.

AREAS COVERED

Biochemical properties of collagens, cellular sources of hepatic collagen synthesis, and regulatory aspects in collagen expression. Markers are discussed suitable to estimate hepatic collagen synthesis and/or turnover. Discussed studies were identified through a PubMed search done in May 2020 and the authors' topic knowledge.

EXPERT OPINION

Hepatic fibrosis is mainly characterized by accumulation of collagen-rich scar tissue. Although traditionally performed liver biopsy is still standard in estimating hepatic fibrosis, there is evidence that noninvasive diagnostic scores and collagen-derived neo-epitopes provide clinical useful information. These noninvasive tests are less expensive than liver biopsy, better tolerated, safer, and more acceptable to patients. Therefore, these tests will lead to dramatic changes in diagnosis.

The association between serum albumin levels and metabolic syndrome in a rural population of Korea

OBJECTIVES

A positive association between serum albumin levels and metabolic syndrome has been reported in observation studies, but it has not been established in the Korean population. The purpose of this study was to evaluate the association between serum albumin levels and the presence of metabolic syndrome among a sample of apparently healthy Korean adults.

METHODS

This cross-sectional study analyzed data of 3189 community-dwelling people (1189 men and 2000 women) who were aged 40 to 87 years and were living in a rural area in Korea. Serum albumin levels were classified into quartile groups for each sex. Metabolic syndrome was defined according to the National Cholesterol Education Program Adult Treatment Panel III guidelines with an adjusted waist circumference cut-off value (≥90 cm for men and ≥85 cm for women). An independent association between serum albumin levels and metabolic syndrome was assessed by multiple logistic regression analysis.

RESULTS

Higher serum albumin levels were associated with increased prevalence of metabolic syndrome. The odds ratio (95% confidence interval) of the prevalence of metabolic syndrome for the highest versus the lowest serum albumin quartiles was 2.81 (1.91 to 4.14) in men and 1.96 (1.52 to 2.52) in women, after adjusting for age, smoking status, alcohol consumption, and physical activity. When each metabolic abnormality was analyzed separately, higher serum albumin levels were significantly associated with hypertriglyceridemia and hyperglycemia in both sexes, and with abdominal obesity in men.

CONCLUSIONS

These results suggest that higher serum albumin levels are positively associated with an increased risk of metabolic syndrome in Korean adults.

The differentiation of hepatocyte-like cells from monkey embryonic stem cells

Embryonic stem cells (ESC) hold great potential for the treatment of liver diseases. Here, we report the differentiation of rhesus macaque ESC along a hepatocyte lineage. The undifferentiated monkey ESC line, ORMES-6, was cultured in an optimal culture condition in an effort to differentiate them into hepatocyte-like cells in vitro. The functional efficacy of the differentiated hepatic cells was evaluated using RT-PCR for the expression of hepatocyte specific genes, and Western blot analysis and immunocytochemistry for hepatic proteins such as alpha-fetoprotein (AFP), albumin and alpha1-antitrypsin (alpha1-AT). Functional assays were performed using the periodic acid schiff (PAS) reaction and ELISA. The final yield of ESC-derived hepatocyte-like cells was measured by flow cytometry for cells that were transduced with a liver-specific lentivirus vector containing the alpha1-AT promoter driving the expression of green fluorescence protein (GFP). The treatment of monkey ESC with an optimal culture condition yielded hepatocyte-like cells that expressed albumin, alpha1-AT, AFP, hepatocyte nuclear factor 3beta, glucose-6-phophatase, and cytochrome P450 genes and proteins as determined by RT-PCR and Western blot analysis. Immunofluorescent staining showed the cells positive for albumin, AFP, and alpha1-AT. PAS staining demonstrated that the differentiated cells showed hepatocyte functional activity. Albumin could be detected in the medium after 20 days of differentiation. Flow cytometry data showed that 6.5 +/- 1.0% of the total differentiated cells were positive for GFP. These results suggest that by using a specific, empirically determined, culture condition, we were able to direct monkey ESC toward a hepatocyte lineage.

Liver function tests and their interpretation

Liver function tests (LFT) are a helpful screening tool, which are an effective modality to detect hepatic dysfunction. Since the liver performs a variety of functions so no single test is sufficient to provide complete estimate of function of liver. Often clinicians are faced with reports that do not tally with the clinical condition of the patient and they face difficulty in interpreting the LFT. An attempt is being made to study and understand the LFT and simplify their interpretation with algorithms.

Novel Method to Examine Hepatocyte-Specific Gene Expression in a Functional Coculture System

To mimic native tissue function, coculture systems are an extremely useful model. In many cases, differentiated functions can be maintained only through the interactions of various cell types. Therefore, methods for examining the interactions between cocultured cells are necessary. The assessment of cell-to-cell cross-talk at the level of gene expression is one such method to examine interactions between different cell types. However, it is generally difficult to determine the gene expression of specific cell types in coculture without first separating cell populations. To overcome these obstacles, we have established a novel method to determine gene expression levels of a targeted cell population in coculture, using species-specific primers. With this approach, we were able to determine hepatocyte-specific gene expression of Fao cells (a rat hepatocyte cell line) in culture with human umbilical vein endothelial cells (HUVECs). Expression of both albumin and apolipoprotein A-I (apoA-I) increased time dependently for 10 days and maintained significantly higher expression in the coculture system as compared with isolated Fao cells. This indicates that hepatocyte function increased gradually in our coculture system and could be maintained long-term, suggesting that the construction of mature cell-to-cell communication between the two cell lines required a considerable amount of time. The expression of HNF-4 and HNF-1alpha, which are liver-enriched transcription factors, did not differ between the monolayer and cocultured Fao cells, suggesting that expression of HNF-4 and HNF-1alpha was not responsible for the increased expression albumin and apoA-I. Our findings suggest that this novel method for the detection of gene expression of targeted cell populations can be a useful tool in determining the molecular mechanisms that regulate communication between different cell types.

Microstructured scaffolds for liver tissue cultures of high cell density: Morphological and biochemical characterization of tissue aggregates

Very high cell densities and optimal vascularization characterize among others organs and tissues in vivo. In order to study organ-specific functions in vitro or to make use of them in medical devices/treatments in the future, this natural architecture should be rebuilt. An important aspect in this context is the appropriate ratio of medium to cell volume being so far not optimally reestablished in most of the currently available in vitro systems. To improve such culture conditions, we constructed a microstructure to culture hepatocytes and (without any addition of extracellular matrix material) characterized liver tissue in the form of evenly sized aggregates. The liver-specific differentiation status of such aggregates was monitored by their ability to perform CYP450 dependent xenobiotic metabolism along with the measurement of albumin secretion. Freshly isolated adult rat hepatocytes show an initial loss of total CYP450 content and of associated activities (mixed function oxidases). However, in the aggregate system, this level did not decrease further but remained stable or even increased throughout the culture period of 10-13 days. The CYP450 dependent metabolism of the hepatocytes is able to respond to classic inducing agents. The described culture efficiently supports liver-specific functions of adult rat hepatocytes and seems to be suited not only for use in an extracorporeal liver device but also for the formation of evenly sized small aggregates to be of use in transplantation of differentiated liver tissue. Moreover, after design variations, the microstructure can be applied for functional analysis of metabolically active hepatocytes as well as for toxicological and pharmacological validation.

Steroid 5alpha reductase mRNA type 1 is differentially regulated by androgens and glucocorticoids in the rat liver

Testosterone and 5alpha-dihydrotestosterone (DHT) are the principal male hormones (androgens) in mammals. The enzyme, steroid 5alpha reductase catalyzes the conversion of testosterone (T) to its biologically potent steroid (DHT) in androgen dependent tissues. Two 5alpha reductase isoenzymes have been identified in rat tissues. The type I isoenzyme has been shown to be predominately expressed in the rat liver, whereas androgen target tissues of the genital tract express mainly isoenzyme II. The effects of androgens and glucocorticoids on the abundance of steroid 5alpha reductase type I (5alphaR1) messenger RNA in the rat liver were examined. Steady state levels of 5alphaR1 mRNA decreased dramatically to 1.5% of control levels 14 days following adrenalectomy (ADX), whereas dexamethasone (Dex) administered (0.5 mg/100 g) to ADX animals enhanced the expression of 5alphaR1 to twice its' normal values within 40 hours. Bilateral orchiectomy induced, within eight days, the expression of 5alphaR1 mRNA in the rat liver to 1.75 fold the normal value while testosterone injection failed to reduce this enhanced expression in castrated animals. Addition of Dex (1 microM) to primary cultures of rat hepatocyte resulted in a five- and three-fold reduction in the mRNA expression of 5alphaR1 after 24 and 48 hours, respectively. DHT (0.5 microM) however, induced the expression of 5alphaR1 mRNA by two- and seven-fold 24 and 48 hours post-treatment, respectively. In vitro nuclear run-on analysis of the 5alphaR1 gene showed no correlation between the rate of synthesis and steady state levels of this mRNA either in the intact liver or in cultured hepatocytes. These results appear to suggest that glucocorticoids and androgens differentially regulate 5alphaR1 mRNA in the rat liver. Moreover, our findings appear to indicate that regulation of 5alphaR1 gene is primarily at the post-transcriptional level.

Pathogenesis and management of alcoholic hepatitis

Alcoholic hepatitis is a potentially life-threatening complication of alcoholic abuse, typically presenting with symptoms and signs of hepatitis in the presence of an alcohol use disorder. The definitive diagnosis requires liver biopsy, but this is not generally required. The pathogenesis is uncertain, but relevant factors include metabolism of alcohol to toxic products, oxidant stress, acetaldehyde adducts, the action of endotoxin on Kupffer cells, and impaired hepatic regeneration. Mild alcoholic hepatitis recovers with abstinence and the long-term prognosis is determined by the underlying disorder of alcohol use. Severe alcoholic hepatitis is recognized by a Maddrey discriminant function >32 and is associated with a short-term mortality rate of almost 50%. Primary therapy is abstinence from alcohol and supportive care. Corticosteroids have been shown to be beneficial in a subset of severely ill patients with concomitant hepatic encephalopathy, but their use remains controversial. Pentoxifylline has been shown in one study to improve short-term survival rates. Other pharmacological interventions, including colchicine, propylthiouracil, calcium channel antagonists, and insulin with glucagon infusions, have not been proven to be beneficial. Nutritional supplementation with available high-calorie, high-protein diets is beneficial, but does not improve mortality. Orthotopic liver transplantation is not indicated for patients presenting with alcoholic hepatitis who have been drinking until the time of admission, but may be considered in those who achieve stable abstinence if liver function fails to recover.

Metabolic flux analysis of hepatocyte function in hormone- and amino acid-supplemented plasma

Understanding the metabolic and regulatory pathways of hepatocytes is important for biotechnological applications involving liver cells. Previous attempts to culture hepatocytes in plasma yielded poor functional results. Recently we reported that hormone (insulin and hydrocortisone) and amino acid supplementation reduces intracellular lipid accumulation and restores liver-specific function in hepatocytes exposed to heparinized human plasma. In the current study, we performed metabolic flux analysis (MFA) using a simplified metabolic network model of cultured hepatocytes to quantitively estimate the changes in lipid metabolism and relevant intracellular pathways in response to hormone and amino acid supplementation. The model accounts for the majority of central carbon and nitrogen metabolism, and assumes pseudo-steady-state with no metabolic futile cycles. We found that beta-oxidation and tricarboxylic acid (TCA) cycle fluxes were upregulated by both hormone and amino acid supplementation, thus enhancing the rate of lipid oxidation. Concomitantly, hormone and amino acid supplementation increased gluconeogenic fluxes. This, together with an increased rate of glucose clearance, caused an increase in predicted glycogen synthesis. Urea synthesis was primarily derived from ammonia and aspartate generated through transamination reactions, while exogenous ammonia removal accounted for only 3-6% of the urea nitrogen. Amino acid supplementation increased the endogenous synthesis of oxaloacetate, and in turn that of aspartate, a necessary substrate for the urea cycle. These findings from MFA provide cues as to which genes/pathways relevant to fatty acid oxidation, urea production, and gluconeogenesis may be upregulated by plasma supplementation, and are consistent with current knowledge of hepatic amino acid metabolism, which provides further credence to this approach for evaluating the metabolic state of hepatocytes under various environmental conditions.

Alcohol-induced liver disease

Hepatic changes resulting from the regular ingestion of alcohol are many and include fat infiltration, alcoholic hepatitis, and cirrhosis. Only 10% to 15% of chronic alcoholics develop liver disease. Women are more susceptible. An area of considerable importance is the high prevalence of concomitant infection with hepatitis C virus in chronic alcoholics. Patients who have hepatitis C and alcohol-induced liver injury are much more likely to develop progressive liver disease and cirrhosis. Corticosteroid therapy has proven useful in the treatment of patients with severe acute alcoholic hepatitis.

Effects of insulin, dexamethasone and cytokines on alpha 1-acid glycoprotein gene expression in primary cultures of normal rat hepatocytes

While the effects of insulin, dexamethasone and cytokines on alpha 1-acid glycoprotein gene expression have been investigated in various hepatoma cell lines, the individual and combined effects of these components on the expression of this gene have been rarely studied in cultured normal rat hepatocytes. In this cell model, we have shown that mRNA levels of alpha 1-acid glycoprotein were not decreased at least during the first 24 h of culture under basal conditions. During these short-term cultures, the expression of alpha 1-acid glycoprotein in normal hepatocytes showed a high degree of responsiveness to dexamethasone alone (20-fold increase) and to dexamethasone associated with various cytokines (interleukin-1 beta, interleukin-6 and tumor necrosis factor alpha) with a 40 to 100-fold increase depending on the cytokine. Insulin alone did not modify alpha 1-acid glycoprotein mRNA; however, this hormone exerted a positive effect (about 50% increase) in the presence of dexamethasone or dexamethasone with cytokines. These results indicate that the regulation of alpha 1-acid glycoprotein in cultured normal rat hepatocytes presents major differences when compared to reported observations in rat hepatoma cell lines.

Hormonal regulation of albumin gene expression in primary cultures of rat hepatocytes

When primary cultures of rat hepatocytes were placed in a chemically defined serum-free medium containing a combination of insulin, glucagon, and dexamethasone, the synthesis of albumin and total protein and the cellular content of RNA and DNA were maintained at constant values for 8 days. Despite the constant rate of albumin synthesis, secretion of the protein increased more than twofold during the initial 4 days in culture and was then maintained at a value similar to that observed in vivo through day 8. This observation suggested an initial defect in albumin secretion that was corrected with time in culture. Deprivation of insulin between days 2 and 5 resulted in a decline in albumin secretion to approximately 40% of the control value. The decline in albumin secretion was accompanied by proportional decreases in albumin synthesis, albumin mRNA, and albumin gene transcription. Return of insulin-deprived cells to complete medium on day 5 restored albumin synthesis and secretion as well as albumin mRNA to control values by day 8. Deprivation of either glucagon or dexamethasone also resulted in reduced albumin synthesis and secretion accompanied by proportional decreases in albumin mRNA and gene transcription. However, the magnitude of the changes in these parameters was less with glucagon or dexamethasone deprivation compared with insulin deprivation. Return of glucagon- or dexamethasone-deprived cells to complete medium on day 5 restored albumin synthesis and secretion as well as albumin mRNA to control values by day 8.(ABSTRACT TRUNCATED AT 250 WORDS)

An improved long-term culture of rat hepatocytes to detect liver tumour-promoting agents: results with phenobarbital

Among various cocultures of hepatocytes with other cell types, we found that mouse embryonal cells (BALB/c 3T3) are more effective in maintaining rat hepatocytes in vitro. Because most human cancers are epithelial in origin, we thought that such a hepatocyte culture system could be used for the detection of tumour-promoting agents, most of which are inhibitors of gap-junctional intercellular communication. We, therefore, have examined the effect of the strong rat liver tumour promoter, phenobarbital, on the gap-junctional intercellular communication capacity of hepatocytes in long-term cultures. A single application of phenobarbital drastically inhibited the gap-junctional intercellular communication between hepatocytes in a coculture for only several hours, but treatment for 3 weeks provoked a constant decrease of gap-junctional intercellular communication (50%) throughout the treatment period. This type of long-term culture of rat hepatocytes may be usable in a rapid in vitro assay to detect tumour-promoting agents.

Lipogenic enzyme and apoprotein messenger RNAs in long-term primary culture of chicken hepatocytes

Hepatocytes isolated from 9-week-old chickens were cultured in a serum-free, hormonally defined medium. Relative amounts of mRNAs coding for lipogenic enzymes (acetyl-CoA carboxylase, fatty acid synthase, delta 9 desaturase, malic enzyme) and apoproteins (apoprotein A1 and apoprotein B) were determined until the 12th day. beta-actin and albumin mRNA, as well as albumin secretion, were also assessed. Cellular metabolic activity appeared to be very low for the first days of culture, but increased after the 7th day. All the mRNAs studied, except for that of malic enzyme, were present from this time throughout the culture lifespan. The biological significance of the observed results and the relevance of this chicken hepatocyte culture system for long-term metabolic and genetic studies are discussed.

The hepatic extracellular matrix. II. Ontogenesis, regeneration and cirrhosis

The unique nature of the hepatic extracellular matrix (ECM) is predicted by the special configuration of the space of Disse. Whereas other epithelial organs have two basement membranes (BM) and a substantial ECM interposed between endothelial and epithelial cells, the liver lobule has no BM and only an attenuated ECM, consisting mostly of fibronectin (FN), some collagen type I, and minor quantities of types III, IV, V, and VI. This configuration, together with the abundant fenestrations and gaps of the sinusoidal endothelial cells, seems ideally suited to facilitate the rapid bidirectional exchange of macromolecules normally taking place between plasma and hepatocytes. During organogenesis, the liver anlage is vascularized by continuous capillaries with BM, but by day 13.5 of development (in the rat) the vessels in the immediate proximity of hepatocytes become fenestrated, lacking specialized junctions and BM, suggesting that the hepatocytes produce signals capable of modulating the endothelial phenotype. In regeneration, hepatocyte proliferation precedes vascular proliferation resulting in the formation of hepatocyte clusters that, temporarily, lack sinusoids. Eventually, vascular proliferation follows and the normal hepatocyte-vascular relationships are restored. During this period laminin synthesis by Ito cells is prominent. As soon as hepatocytes become stable, secretion of the sinusoid phenotype-maintaining factors resumes and laminin synthesis and secretion terminates. The interplay between extracellular matrix and liver cells is essential for normal homeostasis and its modification results in deranged hepatic function.

A randomized trial of prednisolone in patients with severe alcoholic hepatitis

BACKGROUND

Controlled trials have yielded inconsistent results with regard to the efficacy of corticosteroids in the treatment of alcoholic hepatitis. Three meta-analyses suggest that they may be effective in patients with encephalopathy who have severe liver disease.

METHODS

We conducted a randomized, double-blind trial comparing 28 days of prednisolone treatment (40 mg per day) with placebo in 61 patients with biopsy-proved alcoholic hepatitis and either spontaneous hepatic encephalopathy (n = 19) or a discriminant-function value higher than 32. The discriminant function used was as follows: 4.6 (prothrombin time-control time [in seconds]) + serum bilirubin (in micromoles per liter)/17. Fifty-seven of the patients had evidence of cirrhosis on biopsy. The primary end point was death within two months.

RESULTS

One patient was lost to follow-up after 56 days. Treatment was discontinued in two patients because of drug toxicity. By the 66th day after randomization, 16 of 29 placebo recipients had died (mean [+/- SE] survival, 45 +/- 8 percent), as compared with 4 of 32 prednisolone recipients (survival, 88 +/- 5 percent) (log-rank test, 10.9; P = 0.001). The survival advantage for prednisolone persisted after stratification according to center and the presence of encephalopathy, and after adjustment for prognostic factors in a proportional-hazards model.

CONCLUSIONS

Treatment with prednisolone improves the short-term survival of patients with severe biopsy-proved alcoholic hepatitis.

Ito cell expression of a nuclear retinoic acid receptor

Although it has been suggested that retinoids regulate Ito cell proliferation and collagen synthesis, little is known about the ability of Ito cells to respond to retinoids in vivo. Because retinoids may mediate their molecular effects through nuclear receptors, Ito cells were examined for the presence of one of these receptors, nuclear retinoic acid receptor-beta. The modulation of nuclear retinoic acid receptor-beta expression was also studied during cell culture and hepatic fibrogenesis. Northern hybridization analysis revealed that Ito cells freshly isolated from normal rat liver contained nuclear retinoic acid receptor-beta messenger RNA at levels significantly higher than those found in other hepatic cell types. Ito cells also contained messenger RNA for two other nuclear retinoic acid receptors, nuclear retinoic acid receptor-alpha and nuclear retinoic acid receptor-gamma. Using an antibody to human nuclear retinoic acid receptor-beta, the nuclear presence of this receptor was demonstrated in normal Ito cells. In contrast, Ito cells cultured for at least 7 days had no detectable messenger RNA or nuclear staining for nuclear retinoic acid receptor-beta despite a 20 +/- 5-fold increase in the messenger RNA level of another retinoid binding protein, cellular retinol binding protein. Analysis of Ito cells isolated from rats with carbon tetrachloride-induced hepatic fibrosis revealed an 81% +/- 3% decrease in nuclear retinoic acid receptor-beta messenger RNA levels in these cells when compared with normal Ito cells. No difference in the messenger RNA levels of cellular retinol binding protein was found in Ito cells isolated from either normal or fibrotic liver.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of hepatic fibrosis on Ito cell gene expression

While Ito cells appear to be a major source of increased matrix synthesis during hepatic fibrogenesis, the cellular changes that occur in these cells during liver fibrosis have not been well delineated. In this study we examined Ito cell gene expression in isolated cells from normal rats, and rats with carbon tetrachloride-induced fibrosis, in order to better define the changes occurring in these cells during this pathologic process. Specifically, we addressed three questions: (1) which matrix genes are over expressed in Ito cells in fibrotic liver; (2) do these cells increase their expression of the fibrogenic cytokine transforming growth factor-beta 1 (TGF-beta 1); and (3) do Ito cells change their phenotype during hepatic fibrogenesis as reflected by alterations in the expression of their intermediate filament genes? Northern hybridization analysis revealed that Ito cells isolated from fibrotic livers had significant increases in mRNA levels of types I, III and IV procollagen compared to normal cells, while no increases were found in hepatocytes, and Kupffer/endothelial cells had only an increase in type I procollagen mRNA. Analysis of other matrix proteins which increase during hepatic fibrogenesis revealed elevations in laminin B and fibronectin mRNA levels only in Ito cells. Increased Ito cell matrix gene expression was also associated with a 4-fold increase in TGF-beta 1 levels in these cells. No increase in TGF-beta 1 mRNA was found in hepatocytes, and less than a 2-fold increase was found in Kupffer/endothelial cells isolated from fibrotic livers.(ABSTRACT TRUNCATED AT 250 WORDS)

Synthesis and degradation of eicosanoids in primary rat hepatocyte cultures

Arachidonic acid metabolites may play an important role in liver physiology, yet hepatocyte prostaglandin synthesis has not been characterized extensively. We used RIA to study production and clearance of several eicosanoids in confluent primary cultures of rat hepatocytes in serum-free, hormonally-defined medium. Under basal, unstimulated conditions 6-keto-PGF1 alpha (spontaneous breakdown product of prostacyclin) and 13,14-dihydro-15-keto-PGE (DHK-PGE, a metabolite of PGE) accumulated in the culture medium. Hepatocytes cleared 6-keto-PGF1 alpha, thromboxane B2, and DHK-PGE from the medium. Production of eicosanoids by primary cultures appeared resistant to indomethacin and several other cyclooxygenase inhibitors. This apparent resistance to indomethacin was not caused by rapid metabolism of indomethacin, by failure of the drug to enter hepatocytes, or by insensitivity of hepatocyte cyclooxygenase to the drug. Metabolism of PGE to DHK-PGE may be saturated under in vitro conditions. Hepatocytes can synthesize significant amounts of eicosanoids, although they are probably less active in this regard than are non-parenchymal cells.

Rapid decrease of cytochrome P-450IIE1 in primary hepatocyte culture and its maintenance by added 4-methylpyrazole

Studies were conducted to evaluate the possible induction or the maintenance of cytochrome P-450IIE1 in primary hepatocyte cultures by the inducing agent 4-methylpyrazole. Hepatocytes were isolated from control (noninduced) rats and from rats treated in vivo with either pyrazole or 4-methylpyrazole to induce P-450IIE1. The content of P-450IIE1 was determined by Western blots with antipyrazole P-450 IgG, and catalytic activity was assessed by assays of dimethylnitrosamine demethylase activity. The treatment with 4-methylpyrazole in vivo increased the content of P-450IIE1 and dimethylnitrosamine demethylase activity sevenfold and fourfold, respectively. In cultures prepared from noninduced hepatocytes, P-450IIE1 levels fell to values of 76%, 65%, 31% and 1% of freshly isolated hepatocytes after 1, 3, 6 and 9 days in culture. A similar decrease in dimethylnitrosamine demethylase was observed during this time. In cultures prepared from induced hepatocytes, the decline in P-450IIE1 was more rapid as levels fell to 77%, 31%, 3% and 3% of initial values after 1, 3, 6 and 9 days in culture. Again, the fall in dimethylnitrosamine demethylase activity paralleled the decline in content of P-450IIE1 and was more rapid with the induced hepatocytes. With cultures prepared from noninduced or induced hepatocytes, the addition of 4-methylpyrazole in vitro did not increase the content of P-450IIE1 or the activity of dimethylnitrosamine demethylase over the initial values. However, 4-methylpyrazole appeared to stabilize the P-450IIE1 and to decrease its rate of decline in culture. In noninduced cultures, the percent remaining content of P-450IIE1 after 6 days was 31% in the absence of and 52% in the presence of 5 mol/L 4-methylpyrazole. In cultures from 4-methylpyrazole-induced hepatocytes, the percent remaining P-450IIE1 after 3 days was 31% in the absence of inducer and 59% with 4-methylpyrazole added in vitro. Similarly 4-methylpyrazole helped to prevent the rapid decline of dimethylnitrosamine demethylase activity in induced and noninduced cultures. Viability of the induced and noninduced cultures in the absence or presence of added 4-methylpyrazole was similar. Levels of mRNA for P-450IIE1 were similar for livers from control rats and from rats treated in vivo with 4-methylpyrazole. The mRNA levels rapidly declined in induced and noninduced cultures, and this decline, unlike the fall in P-450IIE1 or dimethylnitrosamine demethylase activity, could not be prevented by the addition of 4-methylpyrazole in vitro to the cultures.(ABSTRACT TRUNCATED AT 400 WORDS)

Large-scale production and cultivation of hepatocytes on Biosilon microcarriers

A method for large-scale production of hepatocytes on microcarriers have been developed for the purpose of bioartificial liver support system. Hepatocytes obtained by collagenase treatment of rat liver were efficiently attached and spread on a microcarrier surface in the presence of O2-saturated perfluorodecalin. In order to compare the metabolic activities of hepatocytes under long-term cultivation on microcarriers with those of cells under conventional monolayer culture, some liver-specific functions were investigated. Microcarrier-attached hepatocytes cultured in the absence of serum for 8 days synthesized and secreted albumin and fibronectin. Moreover, hepatocytes on microcarriers retained the ability to conjugate bilirubin for 4-5 days. With respect to these specific metabolic properties, microcarrier-attached hepatocytes were comparable to those from routine dish culture. These results suggest that this method developed for large-scale production of hepatocytes on microcarriers will allow one to obtain metabolically active cells suitable for extracorporeal liver support systems.

Alcoholic hepatitis: pathogenesis and approaches to treatment

Alcoholic hepatitis is a necrotizing, often inflammatory, process that is an important precursor to the development of cirrhosis. Acetaldehyde, which is derived from alcohol by the action of alcohol dehydrogenase, is apparently the most important factor leading to alcohol-induced liver injury. Other factors of importance in determining the appearance and rate of progression of liver diseases in patients who are chronic alcoholics include sex, nutritional status, and various immunologic reactions. In addition, there is an incompletely understood genetic predisposition to the development of alcoholic hepatitis. Several histologic features found in patients with alcoholic hepatitis have been evaluated in efforts to determine which are of prognostic value. The predominance of the alcohol-induced injury in zone III of the hepatic lobule; deposition of collagen, IgA, and fibronectin in the space of Disse; defenestration of endothelial cells; and transformation of lipocytes and myofibroblasts to fibroblasts have been investigated. Prolongation of the prothrombin time and marked elevation of serum bilirubin levels are indicators of a subgroup of patients with alcoholic hepatitis who have a poor prognosis, especially if there is also evidence of hepatic encephalopathy. Supportive care and abstinence from alcohol are the foundations of therapy. Corticosteroid therapy appears to decrease the number of early deaths in patients with severe alcoholic hepatitis. Other experimental approaches to therapy include the use of propylthiouracil, anabolic-androgenic steroids, and insulin and glucagon.

Ito-cell gene expression and collagen regulation

Ito cells are perisinusoidal cells thought to be a major source of collagen in normal and fibrotic livers. These cells appear to have features similar to several cell types but when cultured assume a fibroblast-like morphology. In this study we evaluated the phenotype of both freshly isolated and cultured Ito cells by examining their gene expression. To better define the modulators of Ito-cell collagen synthesis, we also examined the effect of transforming growth factor-beta 1, tumor necrosis factor-alpha and dexamethasone on collagen synthesis by these cells. Northern hybridization analysis revealed that cultured Ito cells expressed different types of procollagen mRNAs than did freshly isolated cells. Cultured cells contained large amounts of type I procollagen mRNA and lesser amounts of types III and IV, whereas freshly isolated cells contained more type IV procollagen mRNA than types I and III. Treatment of cultured cells with either transforming growth factor-beta 1 or tumor necrosis factor-alpha resulted in a greater than three-fold increase in total collagen content, and the effects of these cytokines on Ito-cell collagen synthesis involved different levels of gene regulation. Transforming growth factor-beta 1-treated cells had an approximately threefold increase in their type I procollagen mRNA levels, whereas no increase in this mRNA level was found in tumor necrosis factor-alpha-treated cells. Transforming growth factor-beta 1 treatment induced a twofold increase in transforming growth factor-beta 1 mRNA content in cultured cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of the effects of dexamethasone and 13-cis-retinoic acid on connective tissue biosynthesis in human skin fibroblasts

The effects of glucocorticoids and retinoids on connective tissue biosynthesis were studied in cultured human skin fibroblasts (HSFs). More specifically attention was paid to the effects of dexamethasone and 13-cis-retinoic acid (RA) on total protein and collagen synthesis and on collagen and fibronectin mRNA levels. The results indicated that dexamethasone reduced the relative collagen synthesis and collagen mRNA levels in HSFs and increased the total incorporation of proline into proteins, the latter effect being due to increased activity in the intracellular proline pool. 13-cis-RA did not affect collagen synthesis at the concentration studied (10(-7) M) but it did reduce the corresponding mRNA levels. Simultaneous addition of both dexamethasone and 13-cis-RA or etretinate resulted in the largest decrease in type I and type III procollagen mRNA levels, indicating that retinoids do not oppose the effect of glucocorticoids on collagen synthesis in cultured HSFs. For comparison the effects of dexamethasone and 13-cis-RA on the mRNA levels of another extracellular matrix component, fibronectin, and of a constitutive enzyme, glyceraldehyde-3-phosphate dehydrogenase, were also studied. The results indicated, that dexamethasone treatment did not alter fibronectin mRNA levels in HSFs, while 13-cis-RA did so to a marked extent. Both dexamethasone and 13-cis-RA also reduced the mRNA level of glyceraldehyde-3-phosphate dehydrogenase, indicating that glucocorticoids and retinoids have both similar and different effects on gene expression in HSF.

Proliferation of fetal rat hepatocytes in response to growth factors and hormones in primary culture

Fetal rat hepatocytes (day 19 of gestation) multiply in primary culture in arginine-free, hydrocortisone-containing chemically defined medium MX-82 supplemented either with epidermal growth factor (EGF) or insulin or both. In contrast, hepatocytes did not multiply under similar culture conditions using Dulbecco's minimum essential medium (DMEM). Cells underwent two divisions within 10 days in cultures maintained in MX-82 medium without a medium change, and cells grew to increased final cell densities when the medium was renewed every third day. When the medium MX-82 was enriched by the addition of lipids, intermediary metabolites, and trace metals (medium MX-83), cells grew to higher densities. In the absence of the growth factors, cells became quiescent and subsequently could be induced to synthesize DNA in response to EGF. With the increasing numbers of cells per dish, the growth response of the hepatocytes diminished. Levels of hepatocyte-specific albumin and alpha-fetoprotein mRNAs at day 0 were similar to those observed at day 10 in primary fetal rat hepatocyte cultures and were maintained at higher levels in medium MX-83 than in medium MX-82.

Differential regulation of glutathione S-transferases in cultured hepatocytes

Specific cDNA probes were used to determine steady-state mRNA levels for the multiple glutathione S-transferases in primary hepatocyte cultures. In the first 24 hr of culture, gene transcripts for the Ya family decreased sharply, Yb3 disappeared completely, but changes in levels of mRNA for Yb1 and Yb2 were smaller. These results suggest that the isoenzymes are regulated independently. Yp mRNA, which is present at greatly elevated levels in hyperplastic nodules and hepatocellular carcinomas but not in normal adult livers, was hardly detectable in freshly isolated hepatocytes, but Yp transcripts rapidly accumulated in the first 24 hr in culture and continued to increase for 72 hr. Decreased levels in Ya and Yc and increases in Yp were detected by immunoblotting methods, indicating that translation products changed together with mRNA levels in the cultured cells. The appearance of Yp transcripts in hepatocytes was effectively blocked by addition of dexamethasone to the culture medium. Elevations of Yp levels are characteristic of the cell culture system and factors regulating Yp transcription in nodules and carcinomas may also be operative in cultured hepatocytes.

Reciprocal regulation of adult rat hepatocyte growth and functional activities in culture by dimethyl sulfoxide

Hepatocyte DNA synthesis, initiated by epidermal growth factor (EGF), is reversibly inhibited by 2% dimethyl sulfoxide (DMSO). At that concentration, both the survival of the cells in culture and the expression of differentiated functions are prolonged. DMSO does not affect thymidine uptake or EGF receptor binding. Moreover, EGF receptor binding is maintained at 84% of initial 12 hr binding when cells are cultured for several days in the presence of DMSO, whereas specific receptor binding declines to 49% of initial binding under standard culture conditions without DMSO. Studies of hepatocyte functional activity indicate that, during early culture, total cellular export protein synthesis, specific albumin synthesis, and glycogen synthesis are enhanced in the presence of DMSO. Dexamethasone is required for the effect of DMSO on survival, and although dexamethasone alone enhances hepatocyte DNA synthesis in the presence of EGF, it does not reverse the inhibitory effect of 2% DMSO on DNA replication. The correlation of prolonged survival with growth inhibition supports the hypothesis that hepatic growth and differentiated functional activity may be reciprocally regulated.

Cellular interactions promote tissue-specific function, biomatrix deposition and junctional communication of primary cultured hepatocytes

Hepatocytes, prepared from normal adult rat liver, were seeded onto a collagen substratum and cultured alone or in the presence of rat liver endothelial cells. When hepatocytes were cultured alone in a hormonally defined serum-free medium, decreased albumin production and rapid morphological deterioration of bile canaliculi structures and gap junctions occurred within 4 to 5 days. In contrast, hepatocytes cocultured with liver mesenchymal cells remained morphologically intact and biochemically functional for at least 4 weeks. They reorganized into small islands, continued to secrete high levels of albumin, did not express alpha-fetoprotein (a fetal marker), and remained strongly dye coupled. All of the hepatocytes synthesized albumin and retained their gap junctional channels. No junctional communication was observed between hepatocytes and endothelial cells. Long fibers containing fibronectin, Type I collagen and laminin distributed over the hepatocytes were induced in coculture but never appeared in hepatocytes cultured alone. Moreover, supplementation of the hormonally defined medium with phenobarbital and dimethyl sulfoxide, both of which improve the life span and functional activities of cultured hepatocytes, failed to induce reticulin fiber formation in pure culture of hepatocytes. The modulation of albumin secretion, biomatrix deposition and junctional communication observed in hepatocytes cultured with sinusoidal liver cells was also obtained when hepatocytes were in association with various epithelial or mesenchymal cells [rat liver epithelial cells (T51B), mouse embryonic fibroblasts (NIH 3T3), human or rat dermal fibroblasts and bovine aorta endothelial cells (AG 4762)].

Collagen measured in primary cultures of normal rat hepatocytes derives from lipocytes within the monolayer

The cellular origin of hepatic collagen is under active investigation. Several recent studies using cells in primary culture suggest that hepatocytes are the source of much of the collagen in normal rat liver. In view of other data indicating that lipocytes produce substantial amounts of this protein, we have reexamined collagen biosynthesis in hepatocyte cultures that have been carefully characterized with respect to the presence of lipocytes. We find that routinely prepared hepatocyte isolates contain, by number, approximately 10% lipocytes. Lipocytes in early culture are difficult to visualize by phase-contrast microscopy but after 4 d proliferate and eventually replace the parenchymal cells. The size of the lipocyte subpopulation in these cultures correlates positively with collagen production. Similarly, removal of lipocytes by further processing of the initial hepatocyte isolate significantly reduces collagen production. Moreover, the only cells within hepatocyte cultures that display type I collagen by immunohistochemistry are lipocytes. We conclude that lipocytes are the principal source of collagen in primary hepatocyte cultures. The findings indicate also that these cells are the previously described "fibroblast" that appear in relatively long-term hepatocyte cultures.

Types I and IV procollagen gene expression in cultured rat hepatocytes

The molecular mechanism involved in the expression of collagens by hepatocytes were investigated in both pure and co-culture with another rat liver epithelial cell type (RLEC). We measured the steady-state levels of mRNAs coding for pro alpha 1(I) and pro alpha 1(IV) chains by Northern analysis and by dot blotting, using specific recombinant cDNA probes. In freshly isolated hepatocytes, only small amounts of pro alpha 1(I) and pro alpha 1(IV) mRNAs were detected by dot-blot analysis. After 3 days in culture, the pro alpha 1(I) and pro alpha 1(IV) mRNA levels increased 2 to 5 times. The amount of pro alpha 1(IV) mRNAs was identical in hepatocyte cultured with RLECs while the pro alpha 1(I) mRNA level was 5 times that in pure hepatocyte culture. Hydrocortisone reduced pro alpha 1(I) mRNA in hepatocyte cultures, but had no effect on co-cultured cells. In both culture systems, this glucocorticoid did not act on the steady-state pro alpha 1(IV) mRNA level. Whatever the age and the type of culture (pure or mixed) RLECs exhibited the highest levels of pro alpha 1(I) and pro alpha 1(IV) mRNAs, which were reduced by hydrocortisone. These results show that procollagen gene expression by hepatocytes is not directly correlated with their functional state and that corticosteroids differently affect the expression of different collagen genes and collagen deposition.

Hepatotoxicity and molecular aspects of hepatocyte function in primary culture

1. The application of primary cultures of hepatocytes in testing for hepatotoxicity of drugs is reviewed. 2. Hepatotoxicity results principally from the biotransformation of toxic agents. This process is very complex and specific and involves a powerful system of multigenic isozyme families for both phase I and phase II drug metabolizing reactions. Many of the isozymes are specifically expressed in the liver in relation to the maturation or differentiation state, and are specifically induced, possibly through a complex temporally programmed gene regulation. 3. This highly specific, coordinated, molecular regulation is difficult to maintain in vitro. Isolation of hepatocytes induces a prompt differential decline of liver-specific gene transcription, which leads to preferential loss of the most specific functions, including those of the drug metabolizing isozymes, whereas repair of cell damage remains active. 4. The use of serum-free, hormonally defined media stabilizes specific hepatic functions, but not transcriptional activity, for 4-5 days. Defined media retain active DNA replication but do not permit clonal growth of hepatocytes. Co-culturing hepatocytes with primitive biliary cells prolongs cell survival and their functional capacities for several weeks, including some of the transcriptional activity.

Serum albumin

The liver manufactures albumin at a massive rate and decreases production in times of environmental, nutritional, toxic and trauma stress. Osmotic pressure is a basic evolutionary regulatory factor, and hormonal control over albumin production has been demonstrated. Where and why new or old albumin is degraded are questions which have not been clarified, although the vascular endothelium may well be the degradative site. Albumin is important as a transport protein, as a measure of evolution and as a model to study secretion following synthesis without the intervening steps of glycosylation. Investigations as to how this protein enters the endoplasmic membrane may well answer some of the questions concerning signal peptide insertion (288). The role of the urea cycle intermediate ornithine and its participation in polyamine synthesis, which has a positive effect on albumin synthesis, is under study. Likewise, the inverse relation between acute-phase protein synthesis and albumin synthesis regulated by interleukin 1 and other cytokines will merit further study. These are a few of the concepts which will be tested in the future.

Albumin and alpha-fetoprotein gene expression and DNA methylation in rat hepatoma cell lines

To define systems for the study of gene control and differentiation in vitro, we analyzed albumin and alpha-fetoprotein (AFP) gene expression and gene methylation in a series of rat hepatoma-derived cell lines and controls. These cell lines had several specific phenotypes: adult (high albumin and low AFP mRNA), fetal (high albumin, high AFP), embryonic (low albumin, high AFP), or undifferentiated (no albumin or AFP). The adult hepatocyte phenotype is marked by a novel 2.2-kb AFP gene transcript and high DNA methylation. In general, tumor cell lines had higher albumin and AFP gene methylation than hepatocytes in vivo. Levels of total DNA methylation did not determine the methylation patterns of specific genes, except for one cell line with hypermethylated and one with hypomethylated DNA. 5'-Hypomethylation of the AFP gene correlated with gene activity in all cases; the albumin gene showed a similar relationship, but with some exceptions. Only adult hepatocytes, not cell lines, have a unique 3'-region of AFP gene demethylation.

Transcriptional and posttranscriptional effects of dexamethasone on albumin and procollagen messenger RNAs in murine schistosomiasis

We have previously shown that dexamethasone increases albumin mRNA and decreases procollagen steady-state mRNA levels in rat hepatocyte cultures. These studies were extended by evaluating an in vivo model of fibrogenesis (murine schistosomiasis) and by determining a more precise level of gene expression responsible for these changes. Control mice and litter mates infected with Schistosomiasis mansoni were evaluated at 8 weeks postinfection when the livers of the infected mice had become fibrotic and their serum albumin levels significantly decreased. The addition of 4 micrograms/mL dexamethasone to the drinking water of half of the infected mice led to a 75% decrease in the liver collagen content as determined by high-performance liquid chromatography. RNA was extracted from the livers of mice under three conditions: control and infected +/- dexamethasone. This RNA was then hybridized with cDNA probes to determine steady-state levels of specific mRNAs. In the infected mice, albumin mRNA levels were decreased compared to control; however, infected mice treated with dexamethasone increased their albumin mRNA content by 3-fold at 8 weeks. Types I and IV procollagen steady-state mRNA levels in infected mice were increased compared to control while dexamethasone suppressed the mRNA level of collagen in infected mice by 50%. The level of gene expression responsible for these steady-state changes was evaluated by nuclear run-on analysis. While the effect of schistosomiasis on these genes was primarily at a transcriptional level, dexamethasone exerted its effect on different genes in the injured liver by diverse mechanisms, i.e., decreasing collagen synthesis at a transcriptional level and increasing albumin by posttranscriptional mechanisms.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of albumin synthesis by hormones and amino acids in primary cultures of rat hepatocytes

Culture conditions necessary for optimizing albumin secretion were studied in rat hepatocytes maintained in a chemically defined, serum-free medium. Amino acid analysis of the culture medium, which was based on a 1:1 mixture of Ham's F12:Dulbecco's modified Eagle's medium (unsupplemented medium), revealed that certain essential amino acids were depleted from this medium over a 24-h incubation. Rates of albumin secretion were significantly higher and better maintained when the medium was supplemented with additional amino acids (supplemented medium). Moreover, selective removal of an essential amino acid resulted in an immediate decrease in total protein and albumin synthesis and after 48 h a further selective decrease in albumin synthesis. Linear rates of albumin secretion were observed over a wide variety of experimental conditions, but secretion was not strictly proportional to cell number. Maximal rates of secretion were obtained at plating densities of 2-3 X 10(6) cells/60 mm culture dish. Albumin secretion also increased with time in culture reaching a maximum on days 3 and 4. When added singly, either insulin or dexamethasone increased rates of albumin secretion in a dose-dependent manner, but both hormones and an adequate supply of amino acids were necessary for maximal rates of secretion as well as long-term maintenance of the hepatocytes (greater than 3-4 days). In the presence of dexamethasone the dose-response curve for insulin was shifted toward physiological insulin concentrations. Changes in rates of albumin secretion in response to added hormones in supplemented media were found to parallel changes in albumin synthesis and relative amounts of albumin mRNA. Changes in gene transcription were probably involved.

Glycosaminoglycans and proteoglycans induce gap junction expression and restore transcription of tissue-specific mRNAs in primary liver cultures

Normal rat hepatocytes maintained on tissue culture plastic and in serum-supplemented medium lose their gap junctions within 12 hr and expression of their tissue-specific functions within 24 to 72 hr. The gap junctions are lost via internalization and degradation, and the differentiated functions due to loss of synthesis and to rapid degradation of tissue-specific mRNAs. Near normal levels of tissue-specific mRNAs can be achieved by stabilization of the mRNAs but not by transcription (for most genes), if the cells are cultured in a serum-free, hormonally defined medium and on substrata of tissue culture plastic, fibronectin or laminin, or on various purified collagens. The hormonally defined medium also extends the life-span of the gap junctions to about 24 hr. Certain glycosaminoglycans, proteoglycans and anionic polysaccharides have proven to be potent inducers of gap junction expression and function, to increase abundance of tissue-specific mRNAs, and to lower abundance of common gene mRNAs, a level of gap junctions and a pattern of gene expression similar to that in vivo. Addition to the hormonally defined medium of 10 micrograms per ml of hyaluronates, dermatan sulfates, bovine lung heparan sulfate, chondroitin 4-sulfate or chondroitin 6-sulfate resulted in a weak response in induction of gap junctions (5 to 15% of the cells became dye and electrically coupled) and in gene expression. An intermediate response in gap junction expression (30 to 50% coupled cells) and in gene expression was observed with 50 to 100 micrograms per ml of heparins or hyaluronates.(ABSTRACT TRUNCATED AT 250 WORDS)

Studies on the metabolism of retinol-binding protein by primary hepatocytes from retinol-deficient rats

Studies were conducted to explore the regulation of retinol-binding protein (RBP) metabolism in cultured primary hepatocytes from retinol-deficient rats. Newly isolated hepatocytes from retinol-deficient rats contained elevated levels (3.4-fold) of RBP, compared to hepatocytes from normal (retinol-adequate) rats. Addition of retinol to retinol-depleted hepatocytes stimulated RBP secretion by the cells in a concentration-dependent manner. Maximal stimulation of RBP secretion was seen with a retinol level of 0.3 micrograms/ml. The effect of retinol was quite rapid, and was evident by 20 minutes after addition of retinol to the medium. Stimulation of RBP secretion was only seen during the first few hours after retinol addition. The effect of retinol was specific for RBP; thus, retinol had no effect on the secretion rates of transthyretin or albumin. Addition of retinoic acid also stimulated RBP secretion by retinol-deficient hepatocytes. Addition of dexamethasone to retinol-deficient cells did not maintain the initial rate of RBP secretion. Dexamethasone also had no effect on the secretion of transthyretin or albumin by these cells. The effects of retinol and of dexamethasone seen here with retinol-depleted cells differed dramatically from effects seen in other studies with normal (retinol-adequate) hepatocytes. Thus, with normal cells, dexamethasone maintains RBP, TTR, and albumin production and secretion rates close to initial rates. Also in normal hepatocytes, with ample retinol available within the cell, addition of exogenous retinol does not appear to influence RBP secretion. In contrast, and as shown previously in intact rats, in retinol deficiency the availability of retinol specifically regulates the secretion of RBP by hepatocytes.

Effects of nutritional and hormonal factors on the metabolism of retinol-binding protein by primary cultures of rat hepatocytes

Studies were conducted to explore hormonal and nutritional factors that might be involved in the regulation of retinol-binding protein (RBP) synthesis and secretion by the liver. The studies employed primary cultures of hepatocytes from normal rats. When cells were cultured in Dulbecco's modified Eagle's medium alone, a high rate of RBP secretion was observed initially, which declined and became quite low by 24 hr. Supplementing the medium with amino acids maintained RBP and albumin secretion at moderate (but less than initial) rates for at least 3 days. Further addition of dexamethasone maintained the production and secretion rates of RBP, transthyretin, and albumin close to the initial rates for up to 3-5 days in culture. The effects of dexamethasone were not rapid and were not specific for RBP; half-maximal effects were seen at 10(-9) to 10(-8) M levels. Hormonally treated hepatocytes produced and secreted RBP, transthyretin, and albumin at both absolute and relative rates similar to physiological values, as estimated from rates reported by others from studies in vivo (with both rats and humans) and with perfused livers. Glucagon addition partially maintained the secretion rates of these 3 proteins, but less effectively than did dexamethasone. A number of other hormones, added singly or in combination, did not affect RBP production or secretion. Addition of retinol to the cultured normal hepatocytes was without effect upon RBP secretion. These studies show that supplementing the culture medium of hepatocytes with amino acids and dexamethasone maintains RBP production and secretion for several days. In normal hepatocytes, with ample supply of retinol available within the cell, addition of exogenous retinol does not appear to influence RBP metabolism or secretion by the cells.