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Liver System (liver + system)
Selected AbstractsIntrahepatic amino acid and glucose metabolism in a D -galactosamine,induced rat liver failure modelHEPATOLOGY, Issue 2 2001Kosuke Arai A better understanding of the hepatic metabolic pathways affected by fulminant hepatic failure (FHF) would help develop nutritional support and other nonsurgical medical therapies for FHF. We used an isolated perfused liver system in combination with a mass-balance model of hepatic intermediary metabolism to generate a comprehensive map of metabolic alterations in the liver in FHF. To induce FHF, rats were fasted for 36 hours, during which they received 2 D -galactosamine injections. The livers were then perfused for 60 minutes via the portal vein with amino acid,supplemented Eagle minimal essential medium containing 3% wt/vol bovine serum albumin and oxygenated with 95% O2/5% CO2. Control rats were fasted for 36 hours with no other treatment before perfusion. FHF rat livers exhibited reduced amino acid uptake, a switch from gluconeogenesis to glycolysis, and a decrease in urea synthesis, but no change in ammonia consumption compared with normal fasted rat livers. Mass-balance analysis showed that hepatic glucose synthesis was inhibited as a result of a reduction in amino acid entry into the tricarboxylic acid cycle by anaplerosis. Furthermore, FHF inhibited intrahepatic aspartate synthesis, which resulted in a 50% reduction in urea cycle flux. Urea synthesis by conversion of exogenous arginine to ornithine was unchanged. Ammonia removal was quantitatively maintained by glutamine synthesis from glutamate and a decrease in the conversion of glutamate to ,-ketoglutarate. Mass-balance analysis of hepatic metabolism will be useful in characterizing changes during FHF, and in elucidating the effects of nutritional supplements and other treatments on hepatic function. [source] Hepatocyte dynamics in a three-dimensional rotating bioreactorJOURNAL OF GASTROENTEROLOGY AND HEPATOLOGY, Issue 11 2007Mitsuo Miyazawa Abstract Background and Aims:, The use of an artificial liver system with extracorporeal circulation or a three-dimensional bioreactor perfused with liquid culture medium inevitably exposes hepatocytes to fluid mechanical stress (MS). The expression of liver-specific hepatocyte functions seems to be modulated by the magnitude of MS. Nonetheless, few studies have focused on the direct effects of MS on hepatocytes. We subjected hepatocytes to MS using an MS loading device and investigated the effects on the cytoskeleton and hepatocyte dynamics inside three-dimensional scaffolds by monitoring the changes in actin fiber, one of the components of the cytoskeleton. We also assessed the influence of MS on specific hepatocyte functions. Methods:, We subjected hepatocytes to MS by a rotating radial flow bioreactor (RRFB) and examined the effects by comparing the MS-loaded culture cells with cells cultured under stationary conditions without MS loading. The hepatocytes (1 × 106/cm3) were seeded on gauze without collagen coating and examined to determine morphological changes after 60 h incubation. Actin filaments in samples from the MS-loaded hepatocyte culture were stained by fluorescein isothiocyanate-labeled phalloidin. Results:, Hepatocyte aggregation was observed in the MS-loaded culture, but not in the unloaded stationary culture. Better albumin products were observed in the MS-loaded group than in the stationary culture group at all measurement points. Actin filaments extended toward the scaffold after the start of MS loading incubation and polymerized around the hepatocytes. The hepatocyte aggregation eventually advanced to the formation of spheroids. Conclusion:, These results suggest that MS-induced polymerization of actin filaments stimulate hepatocyte aggregation and thereby improve hepatocyte-specific function. [source] Hydrogel-Perfluorocarbon Composite Scaffold Promotes Oxygen Transport to Immobilized CellsBIOTECHNOLOGY PROGRESS, Issue 2 2008Kyuongsik Chin Cell encapsulation provides cells a three-dimensional structure to mimic physiological conditions and improve cell signaling, proliferation, and tissue organization as compared to monolayer culture. Encapsulation devices often encounter poor mass transport, especially for oxygen, where critical dissolved levels must be met to ensure both cell survival and functionality. To enhance oxygen transport, we utilized perfluorocarbon (PFC) oxygen vectors, specifically perfluorooctyl bromide (PFOB) immobilized in an alginate matrix. Metabolic activity of HepG2 liver cells encapsulated in 1% alginate/10% PFOB composite system was 47,104% higher than alginate systems lacking PFOB. A cubic model was developed to understand the oxygen transport mechanism in the alginate/PFOB composite system. The theoretical flux enhancement in alginate systems containing 10% PFOB was 18% higher than in alginate-only systems. Oxygen uptake rates (OURs) of HepG2 cells were enhanced with 10% PFOB addition under both 20% and 5% O2 boundary conditions, by 8% and 15%, respectively. Model predictions were qualitatively and quantitatively verified with direct experimental OUR measurements using both a perfusion reactor and oxygen sensing plate, demonstrating a greater OUR enhancement under physiological O2 boundary conditions (i.e., 5% O2). Inclusion of PFCs in an encapsulation matrix is a useful strategy for overcoming oxygen limitations and ensuring cell viability and functionality both for large devices (>1 mm) and over extended time periods. Although our results specifically indicate positive enhancements in metabolic activity using the model HepG2 liver system encapsulated in alginate, PFCs could be useful for improving/stabilizing oxygen supply in a wide range of cell types and hydrogels. [source] Drug metabolic activity of cultured hepatocytes can synchronize with bile acid concentration in the mediumCELL BIOCHEMISTRY AND FUNCTION, Issue 1 2002Nobuhiro Sugihara Abstract The regulation of drug metabolic activity of cultured hepatocytes can be applied to the evaluation of pharmacokinetics, analysis of drug delivery and the bioartificial liver system. It is very difficult to maintain the drug metabolic activity mediated by cytochrome P-450 (CYP) 3A. Recently we found that the CYP3A aminopyrine N-demethylase (AMND) activity of hepatocytes cultured on collagen surface oscillated with culture time. This phenomenon was related to the concentration of bile acid in the culture medium. CYP3A, multidrug resistant gene 2 (MDR2) and heat shock protein 84 (HSP84) mRNA appeared in a manner corresponding to this oscillation. When a large quantity of bile acid was taken up into hepatocytes from the medium, low AMND activity was observed, and these proteins did not appear. When bile acid was secreted and the bile acid concentration inside the hepatocytes was low, high AMND activity was obtained, and these proteins appeared. In order to clarify the mechanism of oscillation between AMND activity and bile acid, 8,,M glycocholic acid was added to the culture medium 15,h before the measurement. No oscillation in AMND activity was observed in the presence of 8,,M glycocholic acid. Bile acid controls the AMND activity in the transcription of hepatocytes. Copyright © 2001 John Wiley & Sons, Ltd. [source] Disposition of isosteviol in the rat isolated perfused liverCLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY, Issue 5-6 2010Hongping Jin Summary 1. The aim of the present study was to investigate the mechanisms involved in the clearance of isosteviol using the rat isolated perfused liver. 2. Six livers from male Sprague-Dawley rats were perfused with 15.7 ,mol isosteviol in a recirculating system. Perfusate and bile samples were collected for 60 min and the liver was collected at the end of the perfusion. All samples collected were incubated with ,-glucuronidase. Isosteviol,glucuronide was determined as equivalent isosteviol. Isosteviol concentrations were determined using a previously developed liquid chromatography,tandem mass spectrometry method. The final isosteviol liver/perfusate (L/P), bile/liver (B/L) and isosteviol-glucuronide in bile/liver (BG/LG) ratios were determined. 3. Isosteviol has a high clearance (21.4 ± 4.8 mL/min) from the perfusate, with a short half-life (13 ± 4 min). ,-Glucuronidase incubation revealed that isosteviol is conjugated in the liver and excreted into the bile. There was no isosteviol-glucuronide detected in perfusate samples. The total recovery of the rat isolated perfused liver system is 74 ± 14% and glucuronidated isosteviol accounted for 23 ± 4% of the administered dose. 4. In conclusion, we are the first to characterize the metabolism of isosteviol using rat isolated liver perfusion. Our results strongly suggest that the liver is the main organ of isosteviol elimination and that isosteviol is glucuronidated in the liver before it is excreted into the bile. [source] | |||||||||||||