Troubleshooting and improving the mouse and rat isolated perfused liver preparation

Hypothermic oxygenated perfusion inhibits CLIP1-mediated TIRAP ubiquitination via TFPI2 to reduce ischemia‒reperfusion injury of the fatty liver

The use of fatty livers in liver transplantation has emerged as a crucial strategy to expand the pool of donor livers; however, fatty livers are more sensitive to ischemia‒reperfusion injury (IRI). Excessive congenital inflammatory responses are crucial in IRI. Hypothermic oxygenated perfusion (HOPE) is a novel organ preservation technique that may improve marginal donor liver quality by reducing the inflammatory response. Tissue factor pathway inhibitor-2 (TFPI2) and CAP-Gly domain-containing linker protein 1 (CLIP1) exhibit modulatory effects on the inflammatory response. However, the underlying mechanisms of HOPE in fatty liver and the effects of TFPI2 and CLIP1 in fatty liver IRI remain unclear. Here, we aimed to explore the impact of HOPE on the inflammatory response in a rat model of fatty liver IRI and the mechanisms of action of TFPI2 and CLIP1. HOPE significantly reduces liver injury, especially the inflammatory response, and alleviates damage to hepatocytes and endothelial cells. Mechanistically, HOPE exerts its effects by inhibiting TFPI2, and CLIP1 can rescue the damaging effects of TFPI2. Moreover, HOPE promoted the ubiquitination and subsequent degradation of Toll/interleukin-1 receptor domain-containing adapter protein (TIRAP) by regulating the binding of R24 of the KD1 domain of TFPI2 with CLIP1, thereby negatively regulating the TLR4/NF-κB-mediated inflammatory response and reducing IRI. Furthermore, TFPI2 expression increased and CLIP1 expression decreased following cold ischemia in human fatty livers. Overall, our results suggest that targeting the inflammatory response by modulating the TFPI2/CLIP1/TIRAP signaling pathway via HOPE represents a potential therapeutic approach to ameliorate IRI during fatty liver transplantation.

Hepatic ischemia-reperfusion syndrome and its effect on the cardiovascular system: The role of treprostinil, a synthetic prostacyclin analog

Hepatic ischemia-reperfusion syndrome has been the subject of intensive study and experimentation in recent decades since it is responsible for the outcome of several clinical entities, such as major hepatic resections and liver transplantation. In addition to the organ's post reperfusion injury, this syndrome appears to play a central role in the dysfunction of distant tissues and systems. Thus, continuous research should be directed toward finding effective therapeutic options to improve the outcome and reduce the postoperative morbidity and mortality rates. Treprostinil is a synthetic analog of prostaglandin I2, and its experimental administration has shown encouraging results. It has already been approved by the Food and Drug Administration in the United States for pulmonary arterial hypertension and has been used in liver transplantation, where preliminary encouraging results showed its safety and feasibility by using continuous intravenous administration at a dose of 5 ng/kg/min. Treprostinil improves renal and hepatic function, diminishes hepatic oxidative stress and lipid peroxidation, reduces hepatictoll-like receptor 9 and inflammation, inhibits hepatic apoptosis and restores hepatic adenosine triphosphate (ATP) levels and ATP synthases, which is necessary for functional maintenance of mitochondria. Treprostinil exhibits vasodilatory properties and antiplatelet activity and regulates proinflammatory cytokines; therefore, it can potentially minimize ischemia-reperfusion injury. Additionally, it may have beneficial effects on cardiovascular parameters, and much current research interest is concentrated on this compound.

Treprostinil Supplementation Ameliorates Hepatic Ischemia Reperfusion Injury and Regulates Expression of Hepatic Drug Transporters: An Isolated Perfused Rat Liver (IPRL) Study

Purpose

IR injury is an unavoidable consequence in deceased donor liver transplantation. Cold preservation and warm reperfusion may change the expression and function of drug transporters in the liver due to vasoconstriction, infiltration of neutrophils and release of cytokines. We hypothesize that vasodilation, anti-platelet aggregation and proinflammatory downregulation activities of treprostinil will diminish the IR injury and its associated effects.

Methods

Livers obtained from male SD rats (n = 20) were divided into 1) Control, 2) IR, 3) Treprostinil-1 (preservation only), and 4) Treprostinil-2 (preservation and reperfusion) groups. Control livers were procured and immediately reperfused. Livers in the other groups underwent preservation for 24 h and were reperfused. All the livers were perfused using an Isolated Perfused Rat Liver (IPRL) system. Periodic perfusate, cumulative bile samples and liver tissue at the end of perfusion were collected. Liver injury markers, bile flow rates, m-RNA levels for uptake and efflux transporters (qRT-PCR) were measured.

Results

Cold preservation and warm reperfusion significantly increased the release of AST and ALT in untreated livers. Treprostinil supplementation substantially reduced liver injury. Bile flow rate was significantly improved in treprostinil-2 group. m-RNA levels of Slc10a1, Slc22a1, and Slc22a7 in liver were increased and m-RNA levels of Mdr1a were decreased by IR. Treprostinil treatment increased Abcb11 and Abcg2 m-RNA levels and maintained Slc22a1m-RNA similar to control livers.

Conclusions

Treprostinil treatment significantly reduced liver injury. IR injury changed expression of both uptake and efflux transporters in rat livers. Treprostinil significantly altered the IR injury mediated changes in m-RNA expression of transporters.

Glucagon, cyclic AMP, and hepatic glucose mobilization: A half‐century of uncertainty

For at least 50 years, the prevailing view has been that the adenylate cyclase (AC)/cyclic AMP (cAMP)/protein kinase A pathway is the predominant signal mediating the hepatic glucose‐mobilizing actions of glucagon. A wealth of evidence, however, supports the alternative, that the operative signal most of the time is the phospholipase C (PLC)/inositol‐phosphate (IP3)/calcium/calmodulin pathway. The evidence can be summarized as follows: (1) The consensus threshold glucagon concentration for activating AC ex vivo is 100 pM, but the statistical hepatic portal plasma glucagon concentration range, measured by RIA, is between 28 and 60 pM; (2) Within that physiological concentration range, glucagon stimulates the PLC/IP3 pathway and robustly increases glucose output without affecting the AC/cAMP pathway; (3) Activation of a latent, amplified AC/cAMP pathway at concentrations below 60 pM is very unlikely; and (4) Activation of the PLC/IP3 pathway at physiological concentrations produces intracellular effects that are similar to those produced by activation of the AC/cAMP pathway at concentrations above 100 pM, including elevated intracellular calcium and altered activities and expressions of key enzymes involved in glycogenolysis, gluconeogenesis, and glycogen synthesis. Under metabolically stressful conditions, as in the early neonate or exercising adult, plasma glucagon concentrations often exceed 100 pM, recruiting the AC/cAMP pathway and enhancing the activation of PLC/IP3 pathway to boost glucose output, adaptively meeting the elevated systemic glucose demand. Whether the AC/cAMP pathway is consistently activated in starvation or diabetes is not clear. Because the importance of glucagon in the pathogenesis of diabetes is becoming increasingly evident, it is even more urgent now to resolve lingering uncertainties and definitively establish glucagon’s true mechanism of glycemia regulation in health and disease.

Subnormothermic isolated organ perfusion with Nicorandil increased cold ischemic tolerance of liver in experimental model

BACKGROUND

The cold ischemia -reperfusion injury may lead to microcirculatory disturbances, hepatocellular swelling, inflammation, and organ dysfunction. Nicorandil is an anti-ischemic, ATP-sensitive potassium (KATP) channel opener drug and has proved its effectiveness against hepatic Ischemia/Reperfusion (I/R) injury.

OBJECTIVE

This study aimed to investigate the effect of Nicorandil on mitochondrial apoptosis, oxidative stress, inflammation, histopathological changes, and cold ischemic tolerance of the liver in an ex vivo experimental isolated-organ-perfusion model.

METHODS

We used an ex vivo isolated rat liver perfusion system for this study. The grafts were retrieved from male Wistar rats (n = 5 in each), preserved in cold storage (CS) for 2 or 4 hours (group 1, 2), or perfused for 2 or 4 hours (group 3, 4) immediately after removal with Krebs Henseleit Buffer (KHB) solution or Nicorandil containing KHB solution under subnormothermic (22-25°C) conditions (group 5, 6). After 15 minutes incubation at room temperature, the livers were reperfused with acellular, oxygenated solution under normothermic condition for 60 minutes.

RESULTS

In the Nicorandil perfused groups, significantly decreased liver enzymes, GLDH, TNF-alpha, and IL-1ß were measured from the perfusate. Antioxidant enzymactivity was higher in the perfused groups. Histopathological examination showed ameliorated tissue deterioration, preserved parenchymal structure, decreased apoptosis, and increased Bcl-2 activity in the Nicorandil perfused groups.

CONCLUSIONS

Perfusion with Nicorandil containing KHB solution may increase cold ischemic tolerance of the liver via mitochondrial protection which can be a potential therapeutic target to improve graft survival during transplantation.

Long-term cold storage preservation does not affect fatty livers from rats fed with a methionine and choline deficient diet

BACKGROUND

Waiting lists that continue to grow and the lack of organs available for transplantation necessitate the use of marginal livers, such as fatty livers. Since steatotic livers are more susceptible to damage from ischemia and reperfusion, it was investigated whether fatty livers with different lipidomic profiles show a different outcome when subjected to long-term cold storage preservation.

METHODS

Eight-week-old male Wistar rats fed for 2 weeks by a methionine-choline-deficient (MCD) diet or control diet were employed in this study. Livers were preserved in a University of Wisconsin (UW) solution at 4 °C for 6, 12 or 24 h and, after washout, reperfused for 2 h with a Krebs-Henseleit buffer at 37 °C. Hepatic enzyme release, bile production, O2-uptake, and portal venous pressure (PVP) were evaluated. The liver fatty acid profile was evaluated by a gas chromatography-mass spectrometry (GC/MS).

RESULTS

MCD rats showed higher LDH and AST levels with respect to the control group. When comparing MCD livers preserved for 6, 12 or 24 h, no differences in enzyme release were found during both the washout or the reperfusion period. The same trend occurred for O2-uptake, PVP, and bile flow. A general decrease in SFA and MUFA, except for oleic acid, and a decrease in PUFA, except for arachidonic, eicosadienoic, and docosahexanaeoic acids, were found in MCD rats when compared with control rats. Moreover, the ratio between SFA and the various types of unsaturated fatty acids (UFA) was significantly lower in MCD rats.

CONCLUSIONS

Although prolonged cold ischemia negatively affects the graft outcome, our data suggest that the quality of lipid constituents could influence liver injury during cold storage: the lack of an increased hepatic injury in MCD may be justified by low SFA, which likely reduces the deleterious tendency toward lipid crystallization occurring under cold ischemia.

Obeticholic acid reduces biliary and hepatic matrix metalloproteinases activity in rat hepatic ischemia/reperfusion injury

Background

We have previously shown that obeticholic acid (OCA) upregulates the biliary excretion of asymmetric dimethylarginine (ADMA), an inhibitor of iNOS regulating the activity of matrix metalloproteinases (MMPs). Here, the effects of OCA on MMP-2 and MMP-9 activity in liver, bile and serum were evaluated after hepatic ischemia/reperfusion (I/R) injury.

Material and methods

Male Wistar rats (n = 20) were orally administered 10 mg/kg/day of OCA (5 days) and subjected to a 60-min ischemia and 60-min reperfusion. Bile, serum and tissue were collected for MMP-2 and MMP-9 activity quantification. The MMP regulator tissue reversion-inducing cysteine rich protein with Kazal motifs (RECK), tissue inhibitor of metalloproteinases (TIMPs), iNOS and biliary levels of LDH, γGT, glucose and ADMA were quantified.

Results

In the I/R group, OCA administration reduced MMP-2 and MMP-9 in liver, bile and serum. A downregulation of tissue RECK and TIMPs, observed under I/R, were recovered by OCA. Immunohistochemical staining of hepatic tissue demonstrated that RECK expression is mainly localized in both cholangiocytes and hepatocytes. Hepatic iNOS positively correlated with tissue MMP-2 and MMP-9 activity. Biliary levels of LDH, γGT and glucose were lower in I/R rats treated with OCA; in bile, MMP levels positively correlated with LDH and γGT.

Conclusion

Thus, OCA administration confers protection to cholangiocytes via downregulation of biliary MMPs in livers submitted to I/R. This event is associated with hepatic RECK- and TIMP-mediated MMP decrease.

Isolation of rat hepatocytes for pharmacological studies on metabotropic glutamate receptor (mGluR) subtype 5: a comparison between collagenase I versus collagenase IV

Isolated hepatocytes can be obtained from the liver by collagenase infusion, a procedure that could affect cell isolation as well as the integrity of membrane receptors. In this respect we compared metabotropic glutamate subtype 5 receptor (mGluR5) protein expression and activity in rat hepatocytes isolated by two collagenases, type I and type IV. Hepatocytes were isolated from male Wistar rats (200-250 g) using collagenase I or collagenase IV and after isolation, viability and morphology of rat hepatocytes were assessed measuring mGluR5 protein expression by Western blot analyses. mGluR5 activation was evaluated by inositol-1-phosphate (IP-1) accumulation after treatment with the mGluR5 orthosteric agonist ACPD or the selective antagonist MPEP. No difference in cellular viability and morphology was observed using collagenase I when compared with collagenase IV. An increase in mGluR5 protein expression was observed in hepatocytes isolated using collagenase IV with respect to collagenase I. Moreover, hepatocytes treated with ACPD and with MPEP presented higher levels of IP-1 when isolated using collagenase IV compared to collagenase I. These results indicate that collagenase IV better preserves the activity of surface proteins such as mGluR5 in isolated rat hepatocytes, an in vitro model useful to reduce the use of experimental animals, in line with the 3R ethical framework.

Hypothermic Oxygenated Machine Perfusion Alleviates Donation After Circulatory Death Liver Injury Through Regulating P-selectin-dependent and -independent Pathways in Mice

BACKGROUND

Hypothermic oxygenated machine perfusion (HOPE) has been shown to improve the quality of liver donation after circulatory death (DCD) compared to cold storage (CS). However, the mechanism by which HOPE works is unclear. In this study, a mouse liver HOPE system was developed to characterize the role of P-selectin in the protective effect of HOPE on DCD livers.

METHODS

A warm ischemia model of the liver and an isolated perfused liver system were established to determine a suitable flow rate for HOPE. Perfusate and tissue samples from wild-type and P-selectin knockout (KO) mice were used to determine liver function, apoptosis and necrosis rates, deoxyribonucleic acid injury and oxidative stress levels, leukocyte and endothelial cell activation, and inflammatory reactions.

RESULTS

A mouse liver HOPE system was successfully established. HOPE at flow rates between 0.1 and 0.5 mL/min · g were shown to have a protective effect on the DCD liver. P-selectin KO improved the quality of the DCD liver in the CS group, and reduction of P-selectin expression in the wild-type HOPE group had similar protective effects. Moreover, there was a reduction in the degree of oxidative stress and deoxyribonucleic acid injury in the P-selectin KO HOPE group compared with the P-selectin KO CS group.

CONCLUSIONS

We established a mouse HOPE system and determined its suitable flow. We also proved that P-selectin deficiency alleviated DCD liver injury. HOPE protected the DCD liver through regulating P-selectin-dependent and -independent pathways.

Severe steatosis induces portal hypertension by systemic arterial hyporeactivity and hepatic vasoconstrictor hyperreactivity in rats

Non-alcoholic fatty liver disease (NAFLD) has become the most prevalent chronic liver disease. The presence of portal hypertension has been demonstrated in NAFLD prior to development of inflammation or fibrosis, and is a result of extrahepatic and intrahepatic factors, principally driven by vascular dysfunction. An increased intrahepatic vascular resistance potentially contributes to progression of NAFLD via intralobular hypoxia. However, the exact mechanisms underlying vascular dysfunction in NAFLD remain unknown. This study investigates systemic hemodynamics and both aortic and intrahepatic vascular reactivity in a rat model of severe steatosis. Wistar rats were fed a methionine-choline-deficient diet, inducing steatosis, or control diet for 4 weeks. In vivo hemodynamic measurements, aortic contractility studies, and in situ liver perfusion experiments were performed. The mean arterial blood pressure was lower and portal blood pressure was higher in steatosis compared to controls. The maximal contraction force in aortic rings from steatotic rats was markedly reduced compared to controls. While blockade of nitric oxide (NO) production did not reveal any differences, cyclooxygenase (COX) blockade reduced aortic reactivity in both controls and steatosis, whereas effects were more pronounced in controls. Effects could be attributed to COX-2 iso-enzyme activity. In in situ liver perfusion experiments, exogenous NO donation or endogenous NO stimulation reduced the transhepatic pressure gradient (THPG), whereas NO synthase blockade increased the THPG only in steatosis, but not in controls. Alpha-1-adrenergic stimulation and endothelin-1 induced a significantly more pronounced increase in THPG in steatosis compared to controls. Our results demonstrate that severe steatosis, without inflammation or fibrosis, induces portal hypertension and signs of a hyperdynamic circulation, accompanied by extrahepatic arterial hyporeactivity and intrahepatic vascular hyperreactivity. The arterial hyporeactivity seems to be NO-independent, but appears to be mediated by specific COX-2-related mechanisms. Besides, the increased intrahepatic vascular resistance in steatosis appears not to be NO-related but rather to vasoconstrictor hyperreactivity.

Isolated Perfused Rat Livers to Quantify the Pharmacokinetics and Concentrations of Gd-BOPTA

With recent advances in liver imaging, the estimation of liver concentrations is now possible following the injection of hepatobiliary contrast agents and radiotracers. However, how these images are generated remains partially unknown. Most experiments that would be helpful to increase this understanding cannot be performed in vivo. For these reasons, we investigated the liver distribution of the magnetic resonance (MR) contrast agent gadobenate dimeglumine (Gd-BOPTA, MultiHance®, Bracco Imaging) in isolated perfused rat livers (IPRLs). In IPRL, we developed a new set up that quantifies simultaneously the Gd-BOPTA compartment concentrations and the transfer rates between these compartments. Concentrations were measured either by MR signal intensity or by count rates when the contrast agent was labelled by [¹⁵³Gd]. With this experimental model, we show how the Gd-BOPTA hepatocyte concentrations are modified by temperature and liver flow rates. We define new pharmacokinetic parameters to quantify the canalicular transport of Gd-BOPTA. Finally, we present how transfer rates generate Gd-BOPTA concentrations in rat liver compartments. These findings better explain how liver imaging with hepatobiliary radiotracers and contrast agents is generated and improve the image interpretation by clinicians.

Selective Blockade of the Metabotropic Glutamate Receptor mGluR5 Protects Mouse Livers in In Vitro and Ex Vivo Models of Ischemia Reperfusion Injury

2-Methyl-6-(phenylethynyl)pyridine (MPEP), a negative allosteric modulator of the metabotropic glutamate receptor (mGluR) 5, protects hepatocytes from ischemic injury. In astrocytes and microglia, MPEP depletes ATP. These findings seem to be self-contradictory, since ATP depletion is a fundamental stressor in ischemia. This study attempted to reconstruct the mechanism of MPEP-mediated ATP depletion and the consequences of ATP depletion on protection against ischemic injury. We compared the effects of MPEP and other mGluR5 negative modulators on ATP concentration when measured in rat hepatocytes and acellular solutions. We also evaluated the effects of mGluR5 blockade on viability in rat hepatocytes exposed to hypoxia. Furthermore, we studied the effects of MPEP treatment on mouse livers subjected to cold ischemia and warm ischemia reperfusion. We found that MPEP and 3-[(2-methyl-1,3-thiazol-4-yl)ethynyl]pyridine (MTEP) deplete ATP in hepatocytes and acellular solutions, unlike fenobam. This finding suggests that mGluR5s may not be involved, contrary to previous reports. MPEP, as well as MTEP and fenobam, improved hypoxic hepatocyte viability, suggesting that protection against ischemic injury is independent of ATP depletion. Significantly, MPEP protected mouse livers in two different ex vivo models of ischemia reperfusion injury, suggesting its possible protective deployment in the treatment of hepatic inflammatory conditions.

Fatty liver oxidative events monitored by autofluorescence optical diagnosis: Comparison between subnormothermic machine perfusion and conventional cold storage preservation

AIMS

Livers with moderate steatosis are currently recruited as marginal organs to face donor shortage in transplantation, even though lipid excess and oxidative stress increase preservation injury risk. Sensitive, real-time detection of liver metabolism engagement could help donor selection and preservation procedures, ameliorating the graft outcome. Hence, we investigated endogenous biomolecules with autofluorescence (AF) properties as biomarkers supporting the detection of liver oxidative events and the assessment of metabolic responses to external stimuli.

METHODS

Livers from male Wistar rats fed a 12-day methionine/choline-deficient (MCD) diet were subjected to AF spectrofluorometric analysis (fiber-optic probe, 366-nm excitation) before and after organ isolation, and following preservation (cold storage or 20°C machine perfusion) and reperfusion.

RESULTS

Innovative dynamic AF results on lipid oxidation to lipofuscin-like lipopigments, correlating with biochemical oxidative damage (thiobarbituric acid reactive substances) and antioxidant defense (glutathione) parameters, suggested lipid engagement in MCD livers counteracting reactive oxidizing species. The maintained MCD liver functionality was supported by limited changes in bilirubin AF spectral profile, reflecting bile composition balance, despite their intrinsic mitochondrial weakness, confirmed by adenosine 5'-triphosphate levels, and regardless of different preservation effects on energy metabolism revealed by conventional reduced forms of nicotinamide adenine dinucleotide and nicotinamide adenine dinucleotide phosphate and flavin AF data.

CONCLUSION

Autofluorescence showed that, after a relatively short time on an MCD diet, livers are still able to face oxidizing events and maintain a functional balance. These results strengthen AF as a supportive diagnostic tool in experimental hepatology, to characterize marginal livers in real time, monitor their response to ischemia/reperfusion, and investigate protective therapeutic agents.

Model Systems for Studying the Role of Canalicular Efflux Transporters in Drug-Induced Cholestatic Liver Disease

Bile formation is a key function of the liver. Disturbance of bile flow may lead to liver disease and is called cholestasis. Cholestasis may be inherited, for example, in progressive familial intrahepatic cholestasis or acquired, for example, by drug-mediated inhibition of bile salt export from hepatocytes into the canaliculi. The key transport system for exporting bile salts into the canaliculi is the bile salt export pump. Inhibition of the bile salt export pump by drugs is a well-established cause of drug-induced cholestasis. Investigation of the role of the multidrug resistance protein 3, essential for biliary phospholipid secretion, is emerging now. This overview summarizes current concepts and methods with an emphasis on in vitro model systems for the investigation of drug-induced cholestasis in the general context of drug-induced liver injury.

Predictions of bisphenol A hepatic clearance in the isolated perfused rat liver (IPRL): impact of albumin binding and of co-administration with naproxen

1. This study aimed (i) to characterise hepatic clearance (CL) of bisphenol A (BPA) and naproxen (NAP) administered alone or in binary mixtures to highlight the influence of a binding to albumin (ALB) using an isolated perfused rat liver (IPRL) system; and (ii) to compare results of prediction algorithms with measured clearance rates. 2. The IPRL system and liver microsomes were used to determine the metabolic constants of BPA and NAP either in the presence or absence of ALB. In this study, the IPRL was used as proxy for the in vivo situation. Accordingly, diverse in vitro-to-in vivo and in vivo-to-in vivo extrapolations (IVIVEs) were made to predict CL of BPA determined in situ/in vivo with ALB from metabolic data determined without ALB by using different binding correction methods (i.e., direct and conventional scaling as well as a novel scaling considering an ALB-facilitated uptake mechanism). 3. The addition of ALB significantly influenced the liver kinetics of BPA and NAP either administered alone or in binary mixtures, which was reflected in the Michaelis-Menten constants. Analysis of concomitant exposures of BPA and NAP gave a fully competitive inhibition. Furthermore, the IVIVE method based on the ALB-facilitated uptake mechanism provided the most accurate predictions of CL_{in vivo} as compared with the other IVIVE methods when the impact of ALB is considered. 4. Our findings support the notion that high binding to ALB reduces the biotransformation of BPA and NAP when administered alone or in mixtures in the IPRL system. However, the free drug concentration in liver in vivo is probably higher than expected since the IVIVE method based on a potential ALB-facilitated uptake mechanism is the most robust prediction method. Overall, this study should improve the physiologically-based pharmacokinetic (PBPK) modelling of chemical-drug interactions.

Autofluorescence Spectroscopy for Monitoring Metabolism in Animal Cells and Tissues

Excitation of biological substrates with light at a suitable wavelength can give rise to a light emission in the ultraviolet (UV)-visible, near-infrared (IR) spectral range, called autofluorescence (AF). This is a widespread phenomenon, ascribable to the general presence of biomolecules acting as endogenous fluorophores (EFs) in the organisms of the whole life kingdom. In cytochemistry and histochemistry, AF is often an unwanted signal enhancing the background and affecting in particular the detection of low signals or rare positive labeling spots of exogenous markers. Conversely, AF is increasingly considered as a powerful diagnostic tool because of its role as an intrinsic biomarker directly dependent on the nature, amount, and microenvironment of the EFs, in a strict relationship with metabolic processes and structural organization of cells and tissues. As a consequence, AF carries multiple information that can be decrypted by a proper analysis of the overall emission signal, allowing the characterization and monitoring of cell metabolism in situ, in real time and in the absence of perturbation from exogenous markers. In the animal kingdom, AF studies at the cellular level take advantage of the essential presence of NAD(P)H and flavins, primarily acting as coenzymes at multiple steps of common metabolic pathways for energy production, reductive biosynthesis and antioxidant defense. Additional EFs such as vitamin A, porphyrins, lipofuscins, proteins, and neuromediators can be detected in different kinds of cells and bulk tissues, and can be exploited as photophysical biomarkers of specific normal or altered morphofunctional properties, from the retinoid storage in the liver to aging processes, metabolic disorders or cell transformation processes. The AF phenomenon involves all living system, and literature reports numerous investigations and diagnostic applications of AF, taking advantage of continuously developing self-assembled or commercial instrumentation and measuring procedures, making almost impossible to provide their comprehensive description. Therefore a brief summary of the history of AF observations and of the development of measuring systems is provided, along with a description of the most common EFs and their metabolic significance. From our direct experience, examples of AF imaging and microspectrofluorometric procedures performed under a single excitation in the near-UV range for cell and tissue metabolism studies are then reported.

Key Points in Establishing a Model of Mouse Liver Transplantation

The explosion of interest in research into the mouse genome and immune system has meant that the mouse orthotopic liver transplantation (MOLT) model has become a popular means of studying transplantation immunity, organ preservation, ischemia-reperfusion injury, and surgical techniques, among others. Although numerous modifications and refinements of surgical techniques have simplified the operation, the relatively short duration of postoperative survival after MOLT remains an obstacle to longer-term follow-up studies. Here, we summarize the scientific basis of MOLT and our experience improving and refining the model in six key areas: anesthesia, operative technique, perfusion and preservation of the liver, cuff technique, anhepatic time, and the value of rearterialization for the liver graft. We also compare the characteristics of different surgical techniques, and give recommendations for the best means of tailoring technique to the objectives of a study. In doing so, we aim to assist other investigators in establishing and perfecting the MOLT model in their routine research practice.

Effect of Thiol-reducing Agents and Antioxidants on Sulfasalazine-induced Hepatic Injury in Normotermic Recirculating Isolated Perfused Rat Liver

Sulfasalzine is a widely administered drug against inflammatory-based disorders in human. However several cases of liver injury are associated with its administration. There is no stabilized safe protective agent against sulfasalazine-induced liver injury. Current investigation was designed to evaluate if N-acetylcysteine (NAC) and dithioteritol (DTT) as thiol reducing agents and/or vitamins C and E as antioxidants have any protective effects against sulfasalazine-induced hepatic injury in an ex vivo model of isolated rat liver. Rat liver was canulated and perfused via portal vein in a closed recirculating system. Different concentrations of sulfasalazine and/or thiol reductants and antioxidants were administered and markers of organ injury were monitored at different time intervals. It was found that 5 mM of sulfasalazine caused marked liver injury as judged by rise in liver perfusate level of alanine aminotransferase (ALT), aspartate aminotransferase (AST), and lactate dehydrogenase (LDH) (p < 0.05). A significant amount of lipid peroxidation and hepatic glutathione depletion were detected in drug-treated livers, accompanied with significant histopathological changes of the organ. Administration of NAC (500 μM), DTT (400 μM), Vitamin C (200 μM), or vitamin E (200 μM) significantly alleviated sulfasalazine-induced hepatic injury in isolated perfused rat liver. The data obtained from current investigation indicate potential therapeutic properties of thiol reductants and antioxidants against sulfasalazine-induced liver injury.

Metabolic shift in liver: Correlation between perfusion temperature and hypoxia inducible factor-1α

AIM: To study at what temperature the oxygen carried by the perfusate meets liver requirements in a model of organ perfusion.

METHODS: In this study, we correlated hypoxia inducible factor (HIF)-1α expression to the perfusion temperature and the hepatic oxygen uptake in a model of isolated perfused rat liver. Livers from Wistar rats were perfused for 6 h with an oxygenated medium at 10, 20, 30 and 37 °C. Oxygen uptake was measured by an oxygen probe; lactate dehydrogenase activity, lactate release and glycogen were measured spectrophotometrically; bile flow was gravitationally determined; pH of the perfusate was also evaluated; HIF-1α mRNA and protein expression were analyzed by real time-polymerase chain reaction and ELISA, respectively.

RESULTS: Livers perfused at 10 and 20 °C showed no difference in lactate dehydrogenase release after 6 h of perfusion (0.96 ± 0.23 vs 0.93 ± 0.09 mU/min per g) and had lower hepatic damage as compared to 30 and 37 °C (5.63 ± 0.76 vs 527.69 ± 45.27 mU/min per g, respectively, Ps < 0.01). After 6 h, tissue ATP was significantly higher in livers perfused at 10 and 20 °C than in livers perfused at 30 and 37 °C (0.89 ± 0.06 and 1.16 ± 0.05 vs 0.57 ± 0.09 and 0.33 ± 0.08 nmol/mg, respectively, Ps < 0.01). No sign of hypoxia was observed at 10 and 20 °C, as highlighted by low lactate release respect to livers perfused at 30 and 37 °C (121.4 ± 12.6 and 146.3 ± 7.3 vs 281.8 ± 45.3 and 1094.5 ± 71.7 nmol/mL, respectively, Ps < 0.02), and low relative HIF-1α mRNA (0.40 ± 0.08 and 0.20 ± 0.03 vs 0.60 ± 0.20 and 1.47 ± 0.30, respectively, Ps < 0.05) and protein (3.72 ± 0.16 and 3.65 ± 0.06 vs 4.43 ± 0.41 and 6.44 ± 0.82, respectively, Ps < 0.05) expression.

CONCLUSION: Livers perfused at 10 and 20 °C show no sign of liver injury or anaerobiosis, in contrast to livers perfused at 30 and 37 °C.

Quantification of drug transport function across the multiple resistance-associated protein 2 (Mrp2) in rat livers

To understand the transport function of drugs across the canalicular membrane of hepatocytes, it would be important to measure concentrations in hepatocytes and bile. However, these concentration gradients are rarely provided. The aim of the study is then to measure these concentrations and define parameters to quantify the canalicular transport of drugs through the multiple resistance associated-protein 2 (Mrp2) in entire rat livers. Besides drug bile excretion rates, we measured additional parameters to better define transport function across Mrp2: (1) Concentration gradients between hepatocyte and bile concentrations over time; and (2) a unique parameter (canalicular concentration ratio) that represents the slope of the non-linear regression curve between hepatocyte and bile concentrations. This information was obtained in isolated rat livers perfused with gadobenate dimeglumine (BOPTA) and mebrofenin (MEB), two hepatobiliary drugs used in clinical liver imaging. Interestingly, despite different transport characteristics including excretion rates into bile and hepatocyte clearance into bile, BOPTA and MEB have a similar canalicular concentration ratio. In contrast, the ratio was null when BOPTA was not excreted in bile in hepatocytes lacking Mrp2. The canalicular concentration ratio is more informative than bile excretion rates because it is independent of time, bile flows, and concentrations perfused in portal veins. It would be interesting to apply such information in human liver imaging where hepatobiliary compounds are increasingly investigated.

Bilirubin: an autofluorescence bile biomarker for liver functionality monitoring

Excitation at 366-465 nm of bilirubin in aqueous solution with solubilizing agents results in emission spectra composed by two main bands. The variation of their relative contributions as shown by changes in the spectral shape are consistent with the bilirubin bichromophore nature. This latter accounts for an exciton-coupling phenomenon, intramolecular interchromophore energy transfer efficiency being affected by microenvironment. Excitation at 366 nm, despite the poor absorption of bilirubin, gives rise to appreciable emission signals from both pure compounds and bile - collected from functionally altered rat livers - favouring the spectral shape response to environment and molecular conformation changes. As compared to the merely bile flow estimation, real-time detection of fluorescence, revealing composition variations, improves near-UV optical-biopsy diagnostic potential in hepatology.

Current Concepts in Drug-Induced Bile Salt Export Pump (BSEP) Interference

Numerous drugs have been shown to inhibit the activity of the Bile Salt Export Pump (BSEP in humans, Bsep in animals), and this is now considered to be one of several mechanisms by which idiosyncratic drug-induced liver injury (DILI) may be initiated in susceptible patients. The potential importance of BSEP inhibition by drugs has been recognized by the European Medicines Agency and the International Transporter Consortium, who have recommended that it should be evaluated during drug development when evidence of cholestatic liver injury has been observed in nonclinical safety studies or in human clinical trials. In addition, some pharmaceutical companies have proposed evaluation and minimization of BSEP inhibition during drug discovery, when there is a chemical choice, to help reduce DILI risk. The methods that can be used to assess and quantify BSEP inhibition, and key gaps in our current understanding of the relationship between this process and DILI, are discussed.

Dipeptidylpeptidase-IV activity and expression reveal decreased damage to the intrahepatic biliary tree in fatty livers submitted to subnormothermic machine-perfusion respect to conventional cold storage

Graft steatosis is a risk factor for poor initial function after liver transplantation. Biliary complications are frequent even after normal liver transplantation. A subnormothermic machine perfusion (MP20) preservation procedure was developed by our group with high potential for reducing injury to hepatocytes and sinusoidal cells of lean and fatty livers respect to conventional cold storage (CS). We report the response of the biliary tree to CS or MP20, in lean and obese Zucker rat liver. Dipeptidylpeptidase-IV (DPP-IV), crucial for the inactivation of incretins and neuropeptides, was used as a marker. Liver morphology and canalicular network of lean livers were similar after CS/reperfusion or MP20/reperfusion. CS preservation of fatty livers induced serious damage to the parenchyma and to the canalicular activity/ expression of DPP-IV, whereas with MP20 the morphology and canalicular network were similar to those of untreated lean liver. CS and MP20 had similar effects on DPP-IV activity and expression in the upper segments of the intrahepatic biliary tree of fatty livers. DPP-IV expression was significantly increased after MP20 respect to CS or to the controls, both for lean and obese animals. Our data support the superiority of MP20 over CS for preserving fatty livers. Dipeptidylpeptidase-IV activity and expression reveal decreased damage to the intrahepatic biliary tree in fatty livers submitted to subnormothermic machine-perfusion respect to conventional cold storage.