Effects of carbon tetrachloride on isolated rat hepatocytes. Inhibition of protein and lipoprotein secretion.
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ABSTRACT:
SUBMITTER: Gravela E
PROVIDER: S-EPMC1186542 | biostudies-other | 1979 Feb
REPOSITORIES: biostudies-other
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Project description:1. Isolated parenchymal cells were prepared by collagenase perfusion of livers from fed rats that had been previously injected with [(3)H]leucine to label liver proteins. When these cells were incubated in a salts medium containing glucose, gelatin and EDTA, cellular integrity was maintained over a period of 6h. 2. Cells incubated in the presence of 2mm-leucine to minimize radioactive isotope reincorporation released [(3)H]leucine into the medium at a rate accounting for the degradation of 4.5% of the labelled cell protein per h. 3. Degradation of [(3)H]protein in these cells was inhibited by insulin and by certain amino acids, of which tryptophan and phenylalanine were the most effective. 4. Protein degradation was decreased by several proteinase inhibitors, particularly those that are known to inhibit lysosomal cathepsin B, and by inhibitors of cell-energy production. 5. Ammonia inhibited degradation, but only at concentrations above 1.8mm. Aliphatic analogues of ammonia were effective at lower concentrations than was ammonia. 6. High concentrations of ammonia inhibited degradation by 50%. The extent of this inhibition could not be increased further by the addition of the cathepsin B inhibitor leupeptin, which by itself inhibited degradation by approx. 30%. 7. The sensitivity of proteolysis in isolated hepatocytes to these various inhibitory agents is discussed in relation to their possible modes of action.
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Project description:The effect of adrenaline on triacylglycerol synthesis and secretion was examined in isolated rat hepatocytes. Cells were incubated with 0.5 mM-[1-14C]oleate, and the accumulation of triacylglycerol and [14C]triacylglycerol was measured in the incubation medium. Triacylglycerol appearing in the medium was present in a form with properties similar to very-low-density lipoproteins. Triacylglycerol, [14C]triacylglycerol and [14C]phospholipid contents of hepatocytes were also determined. Addition of 10 microM-(-)adrenaline decreased accumulation of glycerolipid in the incubation medium and also decreased cellular [14C]phospholipid content. Prazosin abolished these effects, whereas propranolol did not. The hormone did not affect cellular triacylglycerol content or rates of incorporation of [1-14C]oleate into cell triacylglycerol. The effect of adrenaline on the removal of newly secreted triacylglycerol and the secretion of synthesized glycerolipid was also examined. The catecholamine did not affect rates of removal of newly secreted triacylglycerol. Adrenaline did inhibit the secretion of pre-synthesized lipid by the cells, as assessed by the appearance of radiolabelled triacylglycerol from hepatocytes that had been preincubated with [1,2,3-3H]-glycerol. Adrenaline did not affect rates of fatty acid uptake by hepatocytes, but did stimulate oxidation of [1-14C]oleate, principally to 14CO2.
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Project description:Fibrogenesis is induced by repeated injury to the liver and reactive regeneration and leads eventually to liver cirrhosis. Pigment epithelium derived factor (PEDF) has been shown to prevent liver fibrosis induced by carbon tetrachloride (CCl4). A 44 amino acid domain of PEDF (44-mer) was found to have a protective effect against various insults to several cell types. In this study, we investigated the capability of synthetic 44-mer to protect against liver injury in mice and in primary cultured hepatocytes. Acute liver injury, induced by CCl4, was evident from histological changes, such as cell necrosis, inflammation and apoptosis, and a concomitant reduction of glutathione (GSH) and GSH redox enzyme activities in the liver. Intraperitoneal injection of the 44-mer into CCl4-treated mice abolished the induction of AST and ALT and markedly reduced histological signs of liver injury. The 44-mer treatment can reduce hepatic oxidative stress as evident from lower levels of lipid hydroperoxide, and higher levels of GSH. CCl4 caused a reduction of Bcl-xL, PEDF and PPAR?, which was markedly restored by the 44-mer treatment. Consequently, the 44-mer suppressed liver fibrosis induced by repeated CCl4 injury. Furthermore, our observations in primary culture of rat hepatocytes showed that PEDF and the 44-mer protected primary rat hepatocytes against apoptosis induced by serum deprivation and TGF-?1. PEDF/44-mer induced cell protective STAT3 phosphorylation. Pharmacological STAT3 inhibition prevented the antiapoptotic action of PEDF/44-mer. Among several PEDF receptor candidates that may be responsible for hepatocyte protection, we demonstrated that PNPLA2 was essential for PEDF/44-mer-mediated STAT3 phosphorylation and antiapoptotic activity by using siRNA to selectively knockdown PNPLA2. In conclusion, the PEDF 44-mer protects hepatocytes from single and repeated CCl4 injury. This protective effect may stem from strengthening the counter oxidative stress capacity and induction of hepatoprotective factors.
| S-EPMC4934881 | biostudies-literature
Project description:The very-low-density-lipoprotein secretion rate of isolated hepatocytes obtained from rats fed a high-fat diet was half that of cells from control animals. In fat-fed rats, the initial cellular uptake of [l-14C]oleate in vitro was decreased by 25%, its esterification to triacylglycerols and phospholipids by 50% and its incorporation into very-low-density-lipoprotein triacylglycerols by 70%. Exogenous oleate was not the main precursor of very-low-density lipoproteins in these animals. Lipogenesis, a minor source of very-low-density lipoproteins with the control diet in our experimental conditions, was inhibited by 84% after fat-feeding. A short-term inhibition of lipogenesis in vitro did not result in a decrease in very-low-density-lipoprotein secretion rate. The results suggest that fat-feeding decreased availability of exogenous as well as endogenous fatty acids for synthesis of very-low-density lipoproteins.
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Project description:The effect of microcystin-LR, an inhibitor of protein phosphatases PP1 and PP2A, was studied on protein synthesis by measuring the incorporation of labelled amino acid into protein in isolated rat hepatocytes. Microcystin-LR inhibited protein synthesis in the first minutes of the incubation period, and half-maximum effect was obtained at about 60 nM. Such an inhibition was also observed in the presence of different protein phosphatase inhibitors, i.e. okadaic acid, calyculin A and microcystin-RR. This effect was observed in whole hepatocytes, in the supernatant of the post-mitochondrial fraction and in the microsomal fraction. It was independent of a substrate supply and of the labelled amino acid used. Furthermore, this inhibition preceded the previously reported glucose-6-phosphatase activation induced by microcystin-LR [Claeyssens, Chédeville and Lavoinne (1993) FEBS Lett. 315, 7-10].
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Project description:Carbonyl products were separated and identified in suspensions of rat liver microsomal fractions and in isolated hepatocytes, after stimulation of lipid peroxidation by incubation with the pro-oxidants CCl4 and ADP-iron. The carbonyl products were allowed to react with 2,4-dinitrophenylhydrazine, and the derivatives were extracted and separated by t.l.c. into three zones of non-polar materials, and one fraction of polar derivatives that remained at the origin. Separation of the individual non-polar hydrazones in each zone by h.p.l.c. demonstrated that zone I prepared from microsomal fraction or hepatocytes incubated with CCl4 or ADP-iron contained mainly 4-hydroxyhex-2-enal, 4-hydroxynon-2-enal and 4-hydroxynona-2,5-dienal. Zone III consisted mainly of the alkanals propanal, pentanal and hexanal, the 2-alkenals propenal, pent-2-enal, hex-2-enal, hept-2-enal, oct-2-enal and non-2-enal, the ketones butanone, pentan-2-one and pentan-3-one, and deca-2,4-dienal. Incubation of a microsomal fraction with ADP-iron was much more effective in producing malonaldehyde and other carbonyl products than an incubation with CCl4. Despite such quantitative differences, there were no obvious qualitative differences in the h.p.l.c. spectra obtained from zones I and III. However, the stoichiometric evaluation of fatty acid loss and the production of malonaldehyde and other carbonyls suggests that the pathways of lipid peroxidation triggered by CCl4 and ADP-iron are different. The accumulation of carbonyl products of lipid peroxidation in isolated hepatocytes is strongly affected by their metabolism; in particular, 4-hydroxyalkenals were found to be metabolized very rapidly. Nonetheless, both CCl4 and ADP-iron produced stimulation in the production of malonaldehyde and non-polar carbonyl production. After incubation of rat hepatocytes with CCl4 or ADP-iron it was found that approx. 50% of the total amount of non-polar carbonyls produced during incubation escaped into the external medium. This was not leakage from dead cells, as 90-95% of the hepatocytes had retained their integrity at the end of the incubation. Release of carbonyl products from cells stimulated to undergo lipid peroxidation may be a mechanism for spreading an initial intracellular disturbance to affect critical targets outside the parent cell.
| S-EPMC1144883 | biostudies-other
Project description:Phospholipid transfer protein (PLTP) plays an important role in atherogenesis, and its function goes well beyond that of transferring phospholipids between lipoprotein particles. Previous studies showed that genetic deficiency of PLTP in mice causes a substantially impaired hepatic secretion of apolipoprotein-B (apoB), the major protein of atherogenic lipoproteins. To understand whether the impaired apoB secretion is a direct result from lack of PLTP activity, in this study, we further investigated the function of PLTP in apoB secretion by using PLTP inhibitors. We identified a series of compounds containing a 3-benzazepine core structure that inhibit PLTP activity. Compound A, the most potent inhibitor, was characterized further and had little cross-reactivity with microsomal triglyceride transfer protein. Compound A reduced apoB secretion in human hepatoma cell lines and mouse primary hepatocytes. Furthermore, we confirmed that the reduction of apoB secretion mediated by compound A is PLTP-dependent, because the PLTP inhibitor had no effect on apoB secretion from PLTP-deficient hepatocytes. These studies provided evidence that PLTP activity regulates apoB secretion and pharmacologic inhibition of PLTP may be a new therapy for dyslipidemia by reducing apoB secretion.
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Project description:The metabolism of lysophosphatidylcholine was studied in cultured rat hepatocytes deficient in choline and methionine. Even though the cells were defective in phosphatidylcholine biosynthesis, the albumin-stimulated release of lysophosphatidylcholine (1.9 nmol/h per mg of cellular protein) was similar to that in hepatocytes supplemented with choline. Albumin also stimulated (1.4-fold) the release of phosphatidylcholine from the deficient cells. The extra phosphatidylcholine and lysophosphatidylcholine in the medium were largely recovered in the albumin fraction (density greater than 1.18 g/ml), suggesting that albumin released these lipids from hepatocytes because of binding to this protein. The secretion of glycerophosphocholine was decreased by about 40% by the addition of albumin. When choline-deficient hepatocytes were supplemented with lysophosphatidylcholine, it was transported into the cells and mainly acylated to form phosphatidylcholine, which increased in mass by 30-35% in the first 4 h of incubation. Lysophosphatidylcholine was shown to be as effective as choline in restoring the secretion of very-low-density lipoproteins to normal amounts, as judged by the secretion of triacylglycerol, phosphatidylcholine and the apolipoproteins associated with very-low-density lipoproteins. Thus phosphatidylcholine synthesis via reacylation of lysophosphatidylcholine, via the CDP-choline pathway or via methylation of phosphatidylethanolamine, will satisfy the requirements for secretion of very-low-density lipoprotein from hepatocytes.
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Project description:Carbon tetrachloride (CCl4)-induced liver injury is predominantly caused by free radicals, in which mitochondrial function of hepatocytes is impaired, accompanying with the production of ROS and decreased ATP energy supply in animals intoxicated with CCl4. Here we explored a novel therapeutic approach, mitochondrial transplantation therapy, for treating the liver injury. The results showed that mitochondria entered hepatocytes through macropinocytosis pathway, and thereby cell viability was recovered in a concentration-dependent manner. Mitochondrial therapy could increase ATP supply and reduce free radical damage. In liver injury model of mice, mitochondrial therapy significantly improved liver function and prevented tissue fibrogenesis. Transcriptomic data revealed that mitochondrial unfold protein response (UPRmt), a protective transcriptional response of mitochondria-to-nuclear retrograde signaling, would be triggered after mitochondrial administration. Then the anti-oxidant genes were up-regulated to scavenge free radicals. The mitochondrial function was rehabilitated through the transcriptional activation of respiratory chain enzyme and mitophage-associated genes. The protective response re-balanced the cellular homeostasis, and eventually enhanced stress resistance that is linked to cell survival. The efficacy of mitochondrial transplantation therapy in the animals would suggest a novel approach for treating liver injury caused by toxins.
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Project description:Acute hepatic failure (AHF) usually occurs due to the rapid necrosis of liver cells or serious liver injury induced by a variety of pathogenic factors. We used Rat Genome 230 2.0 microarray to further highlight the rat liver tissues after carbon tetrachloride treatment.
2015-09-29 | GSE73494 | GEO