Isolated Liver Perfusion System Research Articles

Cavitation enhances coagulated size during pulsed high-intensity focussed ultrasound ablation in an isolated liver perfusion system

Purpose: To investigate whether cavitation enhances the degree of coagulation during pulsed high-intensity focussed ultrasound (HIFU) in an isolated liver perfusion system.Methods: Isolated liver was treated by pulsed HIFU or continuous-wave HIFU with different portal vein flow rates. The cavitation emission during exposure was recorded, and real-time ultrasound images were used to observe changes in the grey scale. The coagulation size was measured and calculated.Results: HIFU treatment led to complete coagulation necrosis and total cell destruction in the target regions. Compared to exposure at a duty cycle (DC) of 100%, the mean volumes of lesions induced by 6 s exposure at DCs of 50% and 10% were significantly larger (P < .01) but were smaller at a DC of 5%. The necrosis volume was negatively related to the perfusion rate in the pulsed HIFU at a DC of 50% for exposure durations of 4 and 6 s, while the perfusion flow rate did not affect the necrosis volume for exposure durations of 1, 2 and 3 s. For increased perfusion flow rates, there was no significant decrease in the cavitation activity for the pulsed-HIFU (P > .05). For continuous-wave HIFU exposure, there was a significant decrease in the necrosis volume and cavitation activity for exposure times of 1, 2, 3, 4, and 6 s with increasing portal perfusion rates.Conclusion: Perfusion flow rates negatively influence cavitation activity and coagulation volume. Ablation is significantly enhanced during pulsed HIFU exposure compared with continuous-wave HIFU.

Thalidomide decreases intrahepatic resistance in cirrhotic rats

Increased intrahepatic resistance (IHR) within cirrhotic liver is caused by increased endotoxemia, cytokines tumor necrosis factor-α (TNF-α), vasoconstrictor thromboxane A 2 (TXA 2), and disrupted microvasculatures. We evaluated the effects of thalidomide-related inhibition of TNF-α upon the hepatic microcirculation of cirrhosis in rats. Portal venous pressure (PVP), hepatic TNF-α, expression of thromboxane synthase (TXS), and leukocyte common antigen (LCA) were measured in bile-duct-ligated (BDL) rats receiving 1 month of thalidomide (BDL-thalido rats). Portal perfusion pressure (PPP), IHR, and hepatic TXA 2 production were measured in the isolated liver perfusion system. Intravital microscopy was used to examine hepatic microvascular disruptions. In BDL-thalido rats, PVP, PPP, IHR, hepatic TXA 2 and TNF-α, hydroxyproline content, expression of TXS and LCA, and LPS-induced leukocyte recruitment were significantly decreased. Conversely, hepatic microvascular density and perfused sinusoids were significantly increased. Thalidomide decreased PVP and IHR by reducing hepatic TXA 2 and improving hepatic microvascular disruptions in rats with biliary cirrhosis.

Inhibition of TXA2 synthesis with OKY‐046 improves liver preservation by prolonged hypothermic machine perfusion in rats

We previously reported that hypothermic machine perfusion (HMP) for liver preservation is feasible, but hepatic microcirculatory dysfunction and significant liver damage remain major obstacles in its application when the preservation is extended to 24 h. The underlying injury mechanism is not well understood. The present study sought to investigate the role of thromboxane A(2) (TXA(2)) in the pathogenesis of liver injury after prolonged HMP. Livers isolated from Sprague-Dawley rats were subjected to continuous machine perfusion with University of Wisconsin (UW) solution at a flow rate of 0.4 mL/min/g liver at 4 degrees C for 24 h. A specific TXA(2) synthase inhibitor, OKY-046 (OKY), was added to UW solution during the preservation period and to the Krebs-Henseleit buffer during reperfusion. The performance of the livers after preservation was evaluated using an isolated liver perfusion system with Krebs-Henseleit buffer at a flow rate of 15 mL/min at 37 degrees C for 30 min. Prolonged HMP induced a significant release of TXA(2) into the portal circulation as indicated by markedly increased levels of TXB(2) in the perfusate during reperfusion (at 30 min, 1447.4 +/- 163.6 pg/mL vs 50.91 +/- 6.7 pg/mL for control). Inhibition of TXA(2) synthesis with OKY significantly decreased releases of TXA(2) (69.8 +/- 13.4 pg/mL) concomitant with reduced lactate dehydrogenase (LDH) releases (at 30 min, HMP + OKY: 144.9 +/- 27.9 U/L; HMP: 369.3 +/- 68.5 U/L; simple cold storage or SCS: 884.4 +/- 80.3 U/L), decreased liver wet/dry weight ratio (HMP + OKY vs SCS and HMP: 3.6 +/- 0.3 vs 4.4 +/- 0.1 and 3.9 +/- 0.2, respectively) and increased hyaluronic acid uptake (at 30 min, HMP + OKY vs SCS, HMP: 33.1 +/- 2.9% vs 13.9 +/- 3.6%, 18.6 +/- 2.4%, respectively). Liver histology also showed significant improvement in tissue edema and hepatocellular necrosis with OKY compared with HMP without OKY. The results demonstrate that TXA(2) is involved in the development of hepatocellular injury induced by HMP, and inhibition of TXA(2) synthesis during preservation and reperfusion protects liver hepatocytes and sinusoidal endothelial cells from injuries caused by prolonged HMP.

Evidence for the Pivotal Role of Endogenous Toll-Like Receptor 4 Ligands in Liver Ischemia and Reperfusion Injury

Although toll-like receptor 4 (TLR4) activation has been demonstrated to play a key role in the induction of intrahepatic inflammation, leading to hepatocellular damage in liver ischemia/reperfusion injury (IRI), the nature of TLR4 ligands generated during tissue injury remains to be elucidated. We hypothesized that endogenous TLR4 ligands, rather than endotoxin (lipopolysaccharide [LPS]), are instrumental in the activation of liver TLR4 leading to local inflammation response that culminates in ultimate organ IRI. By using the LPS-neutralizing agent, recombinant bactericidal/permeability-increasing protein, we showed that the endotoxin blockade failed to protect mouse livers from warm IRI, as assessed by serum alanine aminotransferase levels, intrahepatic inflammatory gene induction profile, and liver pathology. The recombinant bactericidal/permeability-increasing protein did not cause any hepatocytoxicity by itself if injected into normal naive mice. Furthermore, we demonstrated that liver perfusates, generated by isolated liver perfusion system, contained LPS-independent, heat-sensitive protein molecules that activated macrophages to produce tumor necrosis factor (TNF)-alpha through TLR4 but not TLR2 pathway. This study provides a definitive evidence that endogenous TLR4 ligands are critical in the pathogenesis of liver IRI.

The Isolated Perfused Liver Response to a ‘Second Hit’ of Portal Endotoxin during Severe Acute Pancreatitis

Background/Aim: During severe acute pancreatitis (AP), the liver may show an exaggerated response to the inflammatory products of gut injury transported in the portal vein. Our aim was to explore liver proinflammatory mediator production after a ‘second hit’ of portal lipopolysaccharide (LPS) during AP. Methods: Twenty-four rats underwent one of three ‘first-hit’ scenarios: (1) severe AP induced by intraductal glycodeoxycholic acid injection and intravenous caerulein infusion, (2) sham laparotomy, or (3) no first intervention. Eighteen hours later, all animals received a ‘second hit’ of portal LPS in an isolated liver perfusion system. Tumour necrosis factor-α (TNF-α), interleukin (IL)-1β, and IL-6 concentrations were measured in portal and systemic serum, and in the perfusate 30 and 90 min after the ‘second hit’. Neutrophil activation by the perfusate was assayed using dihydrorhodamine-123 fluorescence. Results: We observed a six-fold increase in IL-6 concentration across the liver during AP. All livers produced TNF-α after the portal LPS challenge, but this was not exaggerated by AP. No differential neutrophil activation by the perfusate was seen. Conclusion: TNF-α, IL-1β, IL-6 and neutrophil activator production by the isolated perfused liver, in response to a ‘second hit’ of portal LPS, does not appear to be enhanced during AP.

Improvement of rat liver graft quality by pifithrin-alpha-mediated inhibition of hepatocyte necrapoptosis.

Early graft dysfunction due to ischemia reperfusion injury remains a major clinical challenge in liver transplantation. Because apoptosis may contribute to graft dysfunction, we studied whether transient inhibition of p53 is capable of improving graft quality by reducing apoptotic cell death. Rat livers were harvested and stored for 24 hours or 48 hours in a 4 degrees C solution containing either pifithrin-alpha (PFT-alpha), a specific p53-inhibitor, or the vehicle dimethyl-sulfoxide. Storage was followed by 2-hour reperfusion with 37 degrees C Krebs-Henseleit buffer in an isolated liver perfusion system. Besides caspase-3 activation, apoptosis was quantified using fluorescence microscopy and hematoxylin-eosin histology. Trypan blue allowed for assessment of cell membrane damage, indicating both secondary apoptosis and primary necrosis. Bile flow, oxygen consumption, K(+)-excretion and enzyme release served as indicators of overall graft quality. Upon 2-hour reperfusion, livers developed procaspase activation as well as a mixture of apoptotic and necrotic cell death, representing necrapoptosis. In livers that had been stored for 48 hours, necrapoptotic injury was more pronounced compared with that after 24-hour storage. PFT-alpha effectively attenuated caspase activation as well as hepatocellular apoptosis and necrosis. Attenuation of both modes of cell death by PFT-alpha was associated with improved liver function, metabolism, and integrity. Experiments with the caspase inhibitor z-VAD-fmk confirmed that apoptosis is one mode of cell death in cold ischemia reperfusion. In conclusion, inhibition of p53-dependent apoptosis by PFT-alpha reduces hepatic preservation-reperfusion injury and improves primary organ function and metabolism. Fortification of the preservation solution with PFT-alpha may represent a promising and easily applicable approach to mitigate reperfusion injury in liver transplants.

The hydroxyl radical scavenger MCI-186 protects the liver from experimental cold ischaemia–reperfusion injury

Oxidative stress contributes to hepatic ischaemia-reperfusion (IR) injury in a biphasic pattern. In addition to direct cytotoxic effects, oxidative stress also initiates the signal transduction processes that promote second-phase liver injury. The present study investigated the effects of the hydroxyl radical scavenger MCI-186 on the biphasic process of hepatic cold IR injury. After cold preservation for 16 h, rat livers were reperfused on an isolated liver perfusion system for 120 min with oxygenated Krebs-Henseleit bicarbonate buffer. Perfusate samples were obtained serially, and portal flow rates were also recorded. To determine whether MCI-186 affected cytokine levels that control the second-phase injury, levels of interleukin (IL) 10 and tumour necrosis factor (TNF) alpha were measured in the perfusate. Addition of MCI-186 1 mg/l into the perfusate significantly improved portal flow (P<0.050), hepatic enzyme release into the perfusate (P=0.038), total bile production (P=0.029) and malondialdehyde concentration (P=0.038). Furthermore, treatment with MCI-186 led to a substantial increase in IL-10 release (P=0.032). TNF-alpha levels were not affected. MCI-186, an agent ready for clinical use, appears to have direct and indirect protective effects against hepatic cold IR injury.

Hypovolemic stress-induced glycogenolysis. Isolated liver perfusion study.

Intrinsic hepatic glycogenolysis was examined after hypovolemic stress. Hemorrhagic hypotension of 70 (P70) and 40 mm Hg (P40) for 60 min was inflicted for two postprandial groups and of 70 mm Hg (S70) in a 24-h starved group. The results were compared with three control groups; one postprandial (Pc), one 24-h starved (Sc), and one starved for 9 h (Sc:9) to mimic the glycogen depletion produced by 70 mm Hg hemorrhagic hypotension. Glucose output was studied in vitro using av recirculating isolated liver perfusion system with a perfusate free of glucose and endocrine stimulation. Liver glycogen determination was made before perfusion start. Although the glycogen stores were decreased after hemorrhage glucose yield was increased (P70) and unchanged (P40) as compared to controls (Pc and Sc: 9). Both starved groups delivered small amounts of glucose, but the released fraction of the S70 group was more than twice that from the Sc group. These data suggest a liver enzyme activation with increased velocity of the enzyme-substrate reactions responsible for glycogen degradation, induced during in vivo hemorrhage and persisting for at least 30 min in vitro perfusion.

Ultrastructural demonstration of NADPH oxidase activity in Kupffer and endothelial cells using an isolated liver perfusion system - Comparison between ICR/d-strain and Jcl: Wistar-strain rats.

In order to cytochemically demonstrate the NADPH dependent H2O2 generation system in the sinusoidal lining cells of the liver, the authors applied the modified method of Briggs et al. (5) to an isolated liver perfusion system devised by Sugano et al. (21) . The rat liver was perfused with the reaction medium containing 40mg NADPH, 40mg CeCl3 7H2O and 2mg glucose in 100ml of 0.1M tris-maleate buffer solution (pH7.4), continuously supplied with a gas mixture (95%O2 and 5%CO2) . With respect to the specificity of the reaction, the in situ localization, and the amount of reaction products, adequate results were obtained with this system. Thus, the activity in the sinusoidal lining cells was compared between livers of the Jcl: Wistar-and the ICR/d-strain rats affected with spontaneously occurring cataracts and dermatitis.Both Kupffer and endothelial cells showed conspicuous reactivity. A specific and significant reaction product was observed, adherent to the plasma membrane, on the external cell surface, including that of invaginated portions or coated pits. Furthermore, it was also noted on the internal surface of phagocytic vacuoles or coated vesicles. Comparing the two strains of rat, a much higher reactivity was shown in the liver of ICR/d-rat, suggesting that a defensive activity may be enhanced in the sinusoidal area to compensate for constitutional defects such as immunological disorders inherent in the ICR/d-strain.

Effects of dimethylnitrosamine on metabolism of N,N-dimethylaniline by rat liver microsomes. A comparative study of treatment in vivo, in isolated liver perfusion and in the microsomal system

The effect of dimethylnitrosamine (DMN) on rat liver microsomal detoxication was studied, using the non-carcinogenic aromatic amine N, N-dimethylaniline (dimethylaniline) as substrate. Prior to the preparation of microsomes, the rat liver was exposed to DMN either in vivo (by i.p. injection) or in the isolated liver perfusion system (by addition to the perfusion medium). DMN treatment in vivo (20 mg/kg body wt.) caused a 40% increase in dimethylaniline N-oxygenation and a 30% decrease in dimethylaniline C-oxygenation. When DMN was added to the perfusion medium to a final concentration of 5 or 25 mM, a similar effect was observed. With the 5 mM dose, C-oxygenation was decreased by 20% with a non-significant increase in N-oxygenation. The higher dose caused a 50% increase in N-oxygenation, whereas the decrease in C-oxygenation remained at 20%. When microsomes were incubated with both DMN (5 mM) and dimethylaniline (5 mM) in the system, a small but significant decrease in both N- and C-oxygenation of dimethylaniline was observed. The effect of DMN on the amino acid incorporation into liver and plasma proteins was also studied in the liver perfusion system. The synthesis of both liver and plasma proteins was reduced by DMN.

Neutropenia fails to prevent the acute phase stimulation of fibrinogen synthesis

This study evaluates the role of neutrophil granulocytes in mediating acute phase stimulation of fibrinogen synthesis. Turpentine was administered to neutropenic and non-neutropenic rats and fibrinogen synthetic rates measured in an isolated liver perfusion system. Using the ( 14C) carbonate technique for the measurement of the absolute synthetic rates of liver produced plasma proteins it was observed that the rates of fibrinogen synthesis of the neutropenic and non-neutropenic rats were significantly greater (p < 0.01) than those of normal control animals, but were not significantly different from each other. These results suggest that the neutrophil granulocyte may not be of major importance in mediating acute phase stimulation of fibrinogen synthesis.

Kinetics of uptake and biliary excretion of benzo(alpha)pyrene and mutagenic metabolites in isolated perfused rat liver.

An isolated liver perfusion system was used as a simplifying tool to study the metabolism and excretion of benzo(alpha)pyrene (BP) as a prototype carcinogen/mutagen. Phenobarbital (PB) was used to induce liver microsomal enzymes in Sprague-Dawley male rats prior to isolated liver perfusion. Control livers were run simultaneously using generally tritiated (G-3H)BP/BP as substrate in the perfusion medium. Both biliary excretion and liver weight were increased in the induced compared to control liver, but biliary flow when corrected for liver weight is statistically the same for both control and PB-induced livers. The excretion rat of radioactivity in the bile is always higher for PB-induced than for control liver (maximum radioactive excretion at 1 hr). There is a more rapid radioactivity removal in the liver perfusion medium for PB-induced than for control livers. Data are explained by increased metabolism of BP in induced liver leading to the presence of more polar metabolites undergoing preferential biliary excretion than in the control liver. Results support in vivo experimental data. Extracts from liver and bile were tested for microbial mutagenicity by the Ames test (TA 100) after TLC separation. The control liver shows virtually no mutagenicity in bile, only in TLC fractions from the liver. The PB-induced liver shows significant mutagenicity in several TLC fractions in both bile and liver. The net effect of induction is to produce more mutagenic metabolites of BP, excreted in the bile, and presenting a significant exposure of carcinogens/mutagens, and consequent hazard to man.

Isolated liver perfusion — A tool in mutagenicity testing for the evaluation of carcinogens

An isolated liver perfusion system suitable for the combination with Chinese hamster V79 cells is described. With this system, it is possible to study, with the V79 cells as genetic targets, the mutagenic effect of a chemical after metabolic activation in the intact organ. Those substances commonly used in mutagenicity testing as inducers of drug metabolising enzymes, i.e. Arochlor 1254, Phenobarbital(PB) and 3-Methylcholantrene(3-MC), were studied for their effect in the isolated perfused liver. PB increased the bile flow, which was not significantly affected by the other inducers. Only Arochlor caused a significant increase in the amino acid incorporation into plasma proteins and total liver proteins (expressed per mg liver protein). None of the inducers had an effect on gluconeogenesis from lactate or urea synthesis. All three inducers caused an increase in the level of microsomal P-450 enzymes, the biggest increase being seen after Arochlor-induction (170%), followed by PB(90%) and 3-MC(50%). Arochlor- and PB-induction had a dramatic effect on N- and C-oxygenation of N, N-dimethylaniline: N-oxygenation was decreased by 35% and 40% respectively and C-oxygenation increased by 130% and 140% respectively. The advantages of the isolated perfused liver as an intact metabolising unit is discussed in relation to other mutagenicity assays, in which subcellular fractions are used as the metabolising system.

Chemical mutagenicity in Salmonella and Chinese hamster V79 cells after metabolic activation in an isolated liver perfusion system

Many toxic substances are excreted via the bile as chemically inert metabolites. In some cases, however, highly toxic, mutagenic and carcinogenic products can be derived from bile, either directly or after further metabolism by intestinal microflora or intestinal cells. Potential reactive substances may thus reach biliary tract and intestinal cells via this route and may undergo subsequent enterohepatic circulation. The possible role of biliary reactants in carcinogenesis of the biliary tract and intestine is discussed.

The isolated liver perfusion system as a tool in mutagenicity testing

The isolated liver perfusion system as a tool in mutagenicity testing

Regulation of rat liver glycogen synthesis and activities of glycogen cycle enzymes by glucose and galactose

Direct regulation of rat liver glycogen metabolism by glucose and galactose was studied using an isolated liver perfusion system. Activation of glycogen synthase and net glycogen synthesis increased linearly when perfusate glucose concentration was increased from 125 to 500 mg 100 ml . Galactose, rapidly taken up by isolated rat liver regardless of circulating glucose concentration, increased these responses to glucose. In the presence of galactose ( ≥ 75 mg 100 ml ), activation of synthase and glycogen synthesis were 1.5-fold higher at any given glucose concentration. The addition of insulin did not appreciably alter synthase activation by glucose and galactose. Phosphorylase activity, low at circulating glucose levels above 125 mg 100 ml , was further decreased as glucose was increased or when galactose was added to the perfusate. Release of glucose into the perfusate in response to aglycemia was increased in the presence of galactose.

Analysis of Regulatory Factors for Urea Synthesis by Isolated Perfused Rat Liver

Urea synthesis was studied using the isolated liver perfusion with ammonium cholride and glutamine as nitrogen sources. The rate of urea formation increases with ammonium cholorde concentration up to 5mM, and the rate remained constant in the range between 5 and 20mM of ammonium chloride as the substrate. The concentration of ammonia in the medium to support the half-maximum velocity of urea formation was 0.7mM. The rate of urea formation was stimulated by the addition of 2.5mM ornithine, and the greater part of the ornithine which was taken up into the liver was accumulated as citrulline in the presence of ammonia. A considerable accelerating effect of N-acetylglutamate on the synthetic rate was observed, but a rather high concentration of N-acetylglutamate was required in order to obtain the maximum effect possibly, because its permeability into liver cells may be limited. A marked additive effect on the rate of urea formation was observed with the combined addition of ornithine and N-acetylglutamate. The metabolic conversion of glutamine nitrogen to urea in the perfused rat liver and the effect of several compounds which stimulated urea synthesis with ammonia were further examined. The process of conversion of glutamine nitrogen to urea might be composed of the following three steps. In the first lag phase, a small amount of glutamine was removed from the medium. In the second stage, the glutamine level decreased rapidly and ammonia was accumulated in the perfusate. The third stage was a period in which glutamine concentration remained at a constant low level, and the accumulated ammonia was rapidly conversed to urea. The rate of urea formation in this third stage was found to be much higher than that with ammonia as the substrate. The maximum rate of glutamine removal was obtained at pH 7.7 of the perfusate and at a concentration of 10mM glutamine. Urea formation with glutamine was also stimulated by the addition of ornithine, malate, or N-acetylglutamate, which had accelerating effects on the urea synthesis with ammonia. This stimulation was due to an effective conversion of ammonia to urea, but no change in the rate of removal glutamine was obtained.