Unified Bayesian network for uncertainty quantification of physiological parameters in dynamic contrast enhanced (DCE) MRI of the liver

Objective. Physiological parameter estimation is affected by intrinsic ambiguity in the data such as noise and model inaccuracies. The aim of this work is to provide a deep learning framework for accurate parameter and uncertainty estimates for DCE-MRI in the liver.Approach. Concentration time curves are simulated to train a Bayesian neural network (BNN). Training of the BNN involves minimization of a loss function that jointly minimizes the aleatoric and epistemic uncertainties. Uncertainty estimation is evaluated for different noise levels and for different out of distribution (OD) cases, i.e. where the data during inference differs strongly to the data during training. The accuracy of parameter estimates are compared to a nonlinear least squares (NLLS) fitting in numerical simulations andin vivodata of a patient suffering from hepatic tumor lesions.Main results. BNN achieved lower root-mean-squared-errors (RMSE) than the NLLS for the simulated data. RMSE of BNN was on overage of all noise levels lower by 33% ± 1.9% forktrans, 22% ± 6% forveand 89% ± 5% forvpthan the NLLS. The aleatoric uncertainties of the parameters increased with increasing noise level, whereas the epistemic uncertainty increased when a BNN was evaluated with OD data. For thein vivodata, more robust parameter estimations were obtained by the BNN than the NLLS fit. In addition, the differences between estimated parameters for healthy and tumor regions-of-interest were significant (p< 0.0001).Significance. The proposed framework allowed for accurate parameter estimates for quantitative DCE-MRI. In addition, the BNN provided uncertainty estimates which highlighted cases of high noise and in which the training data did not match the data during inference. This is important for clinical application because it would indicate cases in which the trained model is inadequate and additional training with an adapted training data set is required.

Are slaughterhouse-obtained livers suitable for use in ex vivo perfusion research?

OBJECTIVES

The success of the ex vivo machine perfusion of pig livers used for preclinical research depends on organ quality and availability. In this study, we investigated whether livers obtained from slaughterhouses are suitable and equivalent to livers obtained from laboratory pigs.

METHODS

Livers were obtained from slaughterhouse pigs stunned by electrocution or CO2 inhalation and from laboratory pigs. For the latter group, 45 minutes of warm ischemia was mimicked for a subgroup, ensuring a valid comparison with slaughterhouse-derived livers.

RESULTS

Livers from CO2-stunned pigs showed lower indocyanine green clearance and bile production, higher blood lactate and potassium concentrations, and higher alanine aminotransferase activities than electrically stunned pigs. Furthermore, livers from electrically stunned pigs, and livers from laboratory pigs, subjected or not to warm ischemia, showed similar performance in terms of perfusion and metabolism.

CONCLUSION

For an ex vivo liver model generated using slaughterhouse pigs, electrical stunning is preferable to CO2 stunning. Livers from electrically stunned slaughterhouse pigs performed similarly to laboratory pig livers. These findings support the use of livers from electrically stunned slaughterhouse pigs, which may therefore provide an alternative to livers obtained from laboratory pigs, consistent with the principle of the 3Rs.

Interleukin 6 acutely increases gluconeogenesis and decreases the suppressive effect of insulin on cAMP-stimulated glycogenolysis in rat liver

Interleukin 6 (IL6) is an multifunctional cytokine that modulates several biological responses, including glucose metabolism. However, its acute effects on hepatic glucose release are still uncertain. The main purpose of this study was to investigate the effects of IL6 on gluconeogenesis from several glucose precursors (alanine, pyruvate and glutamine) and on the suppressive action of insulin on cAMP-stimulated glycogen catabolism in rat liver. IL6 effect on insulin peripheral sensitivity was also evaluated. IL6 was injected intravenously into rats and, 1 h later, gluconeogenesis and glycogenolysis were assessed in liver perfusion and peripheral insulin sensitivity by insulin tolerance test (ITT). IL6 intravenous injection increased hepatic glucose production from alanine, without changing pyruvate, lactate and urea production. IL6 injection also increased hepatic glucose production from pyruvate and glutamine. In addition, IL6 decreased the suppressive effect of insulin on cAMP-stimulated glucose and lactate production and glycogenolysis, without affecting pyruvate production. Furthermore, IL6 reduced the plasma glucose disappearance constant (kITT), an indicator of insulin resistance. In conclusion, IL6 acutely increased hepatic glucose release (gluconeogenesis and glycogenolysis) by a mechanism that likely involved the induction of insulin resistance in the liver, as evidenced by the reduced suppressive effect of insulin on cAMP-stimulated glycogen catabolism. In consistency, IL6 acutely induced peripheral insulin resistance.

Partial Hepatic Vein Occlusion and Venous Congestion in Liver Exploration Using a Hyperspectral Camera: A Proposal for Monitoring Intraoperative Liver Perfusion

INTRODUCTION

The changes occurring in the liver in cases of outflow deprivation have rarely been investigated, and no measurements of this phenomenon are available. This investigation explored outflow occlusion in a pig model using a hyperspectral camera.

METHODS

Six pigs were enrolled. The right hepatic vein was clamped for 30 min. The oxygen saturation (StO₂%), deoxygenated hemoglobin level (de-Hb), near-infrared perfusion (NIR), and total hemoglobin index (THI) were investigated at different time points in four perfused lobes using a hyperspectral camera measuring light absorbance between 500 nm and 995 nm. Differences among lobes at different time points were estimated by mixed-effect linear regression.

RESULTS

StO₂% decreased over time in the right lateral lobe (RLL, totally occluded) when compared to the left lateral (LLL, outflow preserved) and the right medial (RML, partially occluded) lobes (p < 0.05). De-Hb significantly increased after clamping in RLL when compared to RML and LLL (p < 0.05). RML was further analyzed considering the right portion (totally occluded) and the left portion of the lobe (with an autonomous draining vein). StO₂% decreased and de-Hb increased more smoothly when compared to the totally occluded RLL (p < 0.05).

CONCLUSIONS

The variations of StO₂% and deoxy-Hb could be considered good markers of venous liver congestion.

A Narrative Review of the Applications of Ex-vivo Human Liver Perfusion

Ex-vivo perfusion describes the extra-corporeal delivery of fluid to an organ or tissue. Although it has been widely studied in the context of organ preservation and transplantation, it has also proven to be an invaluable tool in the development of novel models for translational pre-clinical research. Here, we review the literature reporting ex-vivo human liver perfusion experiments to further understand current perfusion techniques and protocols together with their applications. A computerised search was made of Ovid, MEDLINE, and Embase using the search words "ex-vivo liver or hepatic perfusion". All relevant studies in English describing experiments using ex-vivo perfusion of human livers between 2016 and 2021, inclusive, were included. Of 21 reviewed studies, 19 used ex-vivo human liver perfusion in the context of allogeneic liver transplantation. The quality and size of the studies varied considerably. Human liver perfusion was almost exclusively limited to whole organs and "split" livers, although one study did describe the successful perfusion of tissue sections following a partial hepatectomy. This review of recent literature involving ex-vivo human liver perfusion demonstrates that the technique is not limited to whole liver perfusion. Split-liver perfusion is extremely valuable allowing one lobe to act as a control and increasing the number available for research. This review also highlights the present lack of any reports of segmental liver perfusion. The discarded donor liver is a scarce resource, and the successful use of segmental perfusion has the potential to expand the available experimental models to facilitate pre-clinical experimentation.

Observations and findings during the development of a subnormothermic/normothermic long-term ex vivo liver perfusion machine

BACKGROUND

Ex situliver machine perfusion at subnormothermic/normothermic temperature isincreasingly applied in the field of transplantation to store and evaluateorgans on the machine prior transplantation. Currently, various perfusionconcepts are in clinical and preclinical applications. Over the last 6 years ina multidisciplinary team, a novel blood based perfusion technology wasdeveloped to keep a liver alive and metabolically active outside of the bodyfor at least one week.

METHODS

Within thismanuscript, we present and compare three scenarios (Group 1, 2 and 3) we werefacing during our research and development (R&D) process, mainly linked tothe measurement of free hemoglobin and lactate in the blood based perfusate. Apartfrom their proven value in liver viability assessment (ex situ), these twoparameters are also helpful in R&D of a long-term liver perfusion machine and moreover supportive in the biomedical engineering process.

RESULTS

Group 1 ("good" liver on the perfusion machine) represents the best liver clearance capacity for lactate and free hemoglobin wehave observed. In contrast to Group 2 ("poor" liver on the perfusion machine), that has shown the worst clearance capacity for free hemoglobin. Astonishingly,also for Group 2, lactate is cleared till the first day of perfusion andafterwards, rising lactate values are detected due to the poor quality of theliver. These two perfusate parametersclearly highlight the impact of the organ quality/viability on the perfusion process. Whereas Group 3 is a perfusion utilizing a blood loop only (without a liver).

CONCLUSION

Knowing the feasible ranges (upper- and lower bound) and the courseover time of free hemoglobin and lactate is helpful to evaluate the quality ofthe organ perfusion itself and the maturity of the developed perfusion device. Freehemoglobin in the perfusate is linked to the rate of hemolysis that indicates how optimizing (gentle blood handling, minimizing hemolysis) the perfusion machine actually is. Generally, a reduced lactate clearancecapacity can be an indication for technical problems linked to the blood supplyof the liver and therefore helps to monitor the perfusion experiments.Moreover, the possibility is given to compare, evaluate and optimize developed liverperfusion systems based on the given ranges for these two parameters. Otherresearch groups can compare/quantify their perfusate (blood) parameters withthe ones in this manuscript. The presented data, findings and recommendations willfinally support other researchers in developing their own perfusion machine ormodifying commercially availableperfusion devices according to their needs.

Pharmacological agents for defatting livers by normothermic machine perfusion

BACKGROUND

Ex-vivo normothermic machine perfusion (NMP) preserves the liver metabolism at 37°C and has rapidly developed as a promising approach for assessing the viability and improving the performance of organs from expanded criteria donors, including fatty liver grafts. NMP is an effective method for defatting fatty livers when combined with pharmaceutical therapies. Pharmacological agents have been shown to facilitate liver defatting by NMP.

OBSERVATIONS

This systematic review summarizes available pharmacological therapies for liver defatting, with a particular emphasis on defatting agents that can be employed clinically as defatting components during liver NMP as an ex vivo translational paradigm.

CONCLUSION

NMP provides an opportunity for organ treatment and can be used as a defatting platform in the future with defatting agents. Nagrath's cocktail is the most commonly used defatting cocktail in NMP; however, its carcinogenic components may limit its clinical application. Thus, the combination of a defatting cocktail with a new clinically applicable component, for example, a polyphenolic natural compound, may be a novel pharmacological option.

Hepatic perfusion as a new predictor of prognosis and mortality in critical care patients with acute-on-chronic liver failure

Background and aims

Liver diseases are frequent causes of morbidity and mortality worldwide. Liver diseases can lead to cirrhosis, with the risk of acute-on-chronic liver failure (ACLF). For the detection of changes in hepatic hemodynamics, Doppler ultrasonography is a well-established method. We investigated hepatic hemodynamics via serial Doppler ultrasonography to determine the predictive value of changes in hepatic perfusion for the outcome in patients with severe liver diseases compared to established prognostic models such as the MELD (Model for End-Stage Liver Disease) or CLIF-C (Chronic Liver Failure-Consortium) ACLF score.

Methods

In this prospective cohort study, hepatic perfusion was quantified at baseline before the initiation of treatment and every third day by means of serial measurements of the hepatic artery resistance index (HARI) and the maximum portal vein velocity (PVv) using Doppler ultrasonography in 50 consecutive patients with severe liver diseases admitted to a medical intensive care unit (MICU). The recorded hemodynamic parameters were compared to the MELD score, and the CLIF-C ACLF score to analyze their utility for the prediction of the outcome of patients with severe liver diseases, liver cirrhosis, and ACLF.

Results

The changes (delta) obtained by serial measurements of the MELD score, HARI, and PVv were analyzed through scatter plots. Bivariate correlation analysis yielded a new positive linear correlation between the delta-HARI and the delta-MELD score (r = 0.469; p < 0.001). In addition, our data revealed a new negative linear correlation between delta-PVv and the delta-MELD score (r = −0.279, p = 0.001). The leading cause of MICU mortality was acute-on-chronic liver failure (ACLF). A subgroup analysis of patients with liver cirrhosis revealed a positive linear correlation between the delta-HARI and the delta-CLIF-C-ACLF score (r = 0.252, p = 0.005). Of clinical relevance, non-survivors of ACLF exhibited a significantly higher mean value for the delta-HARI (0.010 vs. −0.005; p = 0.015) and a lower mean value for the delta-PVv (−0.7 vs. 1.9 cm/s; p = 0.037) in comparison to survivors of ACLF.

Conclusion

This study shows the prognostic value of the assessment of hepatic perfusion in critical care patients with severe liver diseases by bedside Doppler ultrasound examination and its utility as an accurate predictor of the outcome in patients with ACLF. Increasing HARI and a decreasing PVv are predictors of an adverse outcome. Delta-HARI and delta-PVv are new biomarkers of prognosis and ACLF-related mortality in patients with liver diseases. Delta-HARI and delta-PVv may be helpful in guiding clinical decision-making, especially in catecholamine and fluid management.

Enrichment Methods for Murine Liver Non-Parenchymal Cells Differentially Affect Their Immunophenotype and Responsiveness towards Stimulation

Hepatocytes comprise the majority of the liver and largely exert metabolic functions, whereas non-parenchymal cells (NPCs)—comprising Kupffer cells, dendritic cells and liver sinusoidal endothelial cells—control the immunological state within this organ. Here, we compared the suitability of two isolation methods for murine liver NPCs. Liver perfusion (LP) with collagenase/DNase I applied via the portal vein leads to efficient liver digestion, whereas the modified liver dissociation (LD) method combines mechanical dissociation of the retrieved organ with enzymatic degradation of the extracellular matrix. In cases of both LP and LD, NPCs were enriched by subsequent gradient density centrifugation. Our results indicate that LP and LD are largely comparable with regards to the yield, purity, and composition of liver NPCs. However, LD-enriched liver NPCs displayed a higher degree of activation after overnight cultivation, and accordingly were less responsive towards stimulation with toll-like receptor ligands that are frequently used as adjuvants, e.g., in nano-vaccines. We conclude that LP is more suitable for obtaining liver NPCs for subsequent in vitro studies, whereas LD as the less laborious method, is more convenient for parallel isolation of larger numbers of samples for ex vivo analysis.

Hepatectomy-Induced Alterations in Hepatic Perfusion and Function - Toward Multi-Scale Computational Modeling for a Better Prediction of Post-hepatectomy Liver Function

Liver resection causes marked perfusion alterations in the liver remnant both on the organ scale (vascular anatomy) and on the microscale (sinusoidal blood flow on tissue level). These changes in perfusion affect hepatic functions via direct alterations in blood supply and drainage, followed by indirect changes of biomechanical tissue properties and cellular function. Changes in blood flow impose compression, tension and shear forces on the liver tissue. These forces are perceived by mechanosensors on parenchymal and non-parenchymal cells of the liver and regulate cell-cell and cell-matrix interactions as well as cellular signaling and metabolism. These interactions are key players in tissue growth and remodeling, a prerequisite to restore tissue function after PHx. Their dysregulation is associated with metabolic impairment of the liver eventually leading to liver failure, a serious post-hepatectomy complication with high morbidity and mortality. Though certain links are known, the overall functional change after liver surgery is not understood due to complex feedback loops, non-linearities, spatial heterogeneities and different time-scales of events. Computational modeling is a unique approach to gain a better understanding of complex biomedical systems. This approach allows (i) integration of heterogeneous data and knowledge on multiple scales into a consistent view of how perfusion is related to hepatic function; (ii) testing and generating hypotheses based on predictive models, which must be validated experimentally and clinically. In the long term, computational modeling will (iii) support surgical planning by predicting surgery-induced perfusion perturbations and their functional (metabolic) consequences; and thereby (iv) allow minimizing surgical risks for the individual patient. Here, we review the alterations of hepatic perfusion, biomechanical properties and function associated with hepatectomy. Specifically, we provide an overview over the clinical problem, preoperative diagnostics, functional imaging approaches, experimental approaches in animal models, mechanoperception in the liver and impact on cellular metabolism, omics approaches with a focus on transcriptomics, data integration and uncertainty analysis, and computational modeling on multiple scales. Finally, we provide a perspective on how multi-scale computational models, which couple perfusion changes to hepatic function, could become part of clinical workflows to predict and optimize patient outcome after complex liver surgery.

Synthesis of coagulation factors during long-term ex situ liver perfusion

Robust viability assessment of grafts during normothermic liver perfusion is a prerequisite for organ use. Coagulation parameters are used commonly for liver assessment in patients. However, they are not yet included in viability assessment during ex situ perfusion. In this study, we analysed coagulation parameters during one week ex situ perfusion at 34℃. Eight discarded human livers were perfused with blood-based, heparinised perfusate for one week; perfusions in a further four livers were terminated on day 4 due to massive ongoing cell death. Coagulation parameters were well below the physiologic range at perfusion start. Physiologic levels were achieved within the first two perfusion days for factor V (68.5 ± 35.5%), factor VII (83.5 ± 26.2%), fibrinogen (2.1 ± 0.4 g/L) and antithrombin (107 ± 26.5%) in the livers perfused for one week. Despite the increased production of coagulation factors, INR was detectable only at 24h of perfusion (2.1 ± 0.3) and prolonged thereafter (INR > 9). The prolongation of INR was related to the high heparin level in the perfusate (anti-FXa > 3 U/mL). Intriguingly, livers with ongoing massive cell death also disclosed synthesis of factor V and improved INR. In summary, perfused livers were able to produce coagulation factors at a physiological level ex situ. We propose that single coagulation factor analysis is more reliable for assessing the synthetic function of perfused livers as compared to INR when using a heparinised perfusate.

Ex-Vivo Pharmacological Defatting of the Liver: A Review

The ongoing organ shortage has forced transplant teams to develop alternate sources of liver grafts. In this setting, ex-situ machine perfusion has rapidly developed as a promising tool to assess viability and improve the function of organs from extended criteria donors, including fatty liver grafts. In particular, normothermic machine perfusion represents a powerful tool to test a liver in full 37 °C metabolism and add pharmacological corrections whenever needed. In this context, many pharmacological agents and therapeutics have been tested to induce liver defatting on normothermic machine perfusion with promising results even on human organs. This systematic review makes a comprehensive synthesis on existing pharmacological therapies for liver defatting, with special focus on normothermic liver machine perfusion as an experimental ex-vivo translational model.

Liver perfusion MRI in a rodent model of cirrhosis: Agreement with bulk-flow phase-contrast MRI and noninvasive evaluation of inflammation in chronic liver disease using flow-sensitive alternating inversion recovery arterial spin labelling and tissue T1

Noninvasive measurements of liver perfusion and fibrosis in cirrhotic small animals can help develop treatments for haemodynamic complications of liver disease. Here, we measure liver perfusion in cirrhotic rodents using flow-sensitive alternating inversion recovery arterial spin labelling (FAIR ASL), evaluating agreement with previously validated caval subtraction phase-contrast magnetic resonance imaging (PCMRI) total liver blood flow (TLBF). Baseline differences in cirrhotic rodents and the haemodynamic effects of acute inflammation were investigated using FAIR ASL and tissue T1. Sprague-Dawley rats (nine bile duct ligated [BDL] and ten sham surgery controls) underwent baseline hepatic FAIR ASL with T1 measurement and caval subtraction PCMRI (with two-dimensional infra-/supra-hepatic inferior vena caval studies), induction of inflammation with intravenous lipopolysaccharide (LPS) and repeat liver FAIR ASL with T1 measurement after ~90 minutes. The mean difference between FAIR ASL hepatic perfusion and caval subtraction PCMRI TLBF was -51 ± 30 ml/min/100 g (Bland-Altman 95% limits-of-agreement ±258 ml/min/100 g). The FAIR ASL coefficient of variation was smaller than for caval subtraction PCMRI (29.3% vs 50.1%; P = .03). At baseline, FAIR ASL liver perfusion was lower in BDL rats (199 ± 32 ml/min/100 g vs sham 316 ± 24 ml/min/100 g; P = .01) but liver T1 was higher (BDL 1533 ± 50 vs sham 1256 ± 18 ms; P = .0004). Post-LPS FAIR ASL liver perfusion response differences were observed between sham/BDL rats (P = .02), approaching significance in sham (+78 ± 33 ml/min/100 g; P = .06) but not BDL rats (-49 ± 40 ml/min/100 g; P = .47). Post-LPS differences in liver tissue T1 were nonsignificant (P = .35). FAIR ASL hepatic perfusion and caval subtraction PCMRI TLBF agreement was modest, with significant baseline FAIR ASL liver perfusion and tissue T1 differences in rodents with advanced cirrhosis compared with controls. Following inflammatory stress, differences in hepatic perfusion response were detected between cirrhotic/control animals, but liver T1 was unaffected. Findings underline the potential of FAIR ASL in the assessment of vasoactive treatments for patients with chronic liver disease and inflammation.

Predictive value of perfusion CT for blood loss in liver resection

Blood loss is associated with the degree of damage in liver stiffness. Severe liver steatosis is a matter of concern in liver surgery, but does not correlate with liver stiffness. This study aimed to assess the relationship between blood perfusion of the liver and blood loss in liver pathologies. Data from elective liver resection for liver cancer were analyzed. All patients underwent preoperative assessments including perfusion CT. Patients were divided into 4 groups in accordance with the pathological background of liver parenchyma. Relationships between portal flow as assessed by perfusion CT and perioperative variables were compared. Factors correlating with blood loss were analyzed. In 166 patients, portal flow from perfusion CT correlated positively with platelet count and negatively with indocyanine green retention rate at 15 min. Background liver pathology was normal liver (NL) in 43 cases, chronic hepatitis (CH) in 56, liver cirrhosis (LC) in 42, and liver steatosis (LS) in 25. Rates of hepatitis viral infection and pathological hepatocellular carcinoma were more frequent in LC and CH groups than in the other groups (p < 0.05). LC and LS showed significantly worse liver function than the NL and CH groups. Portal flow from perfusion CT correlated positively with damage to liver parenchyma and negatively with blood loss at liver transection. Low portal flow on perfusion CT predicts blood loss during liver transection.

Clinical Implications of Hepatic Hemodynamic Evaluation by Abdominal Ultrasonographic Imaging in Patients With Heart Failure

Background It has been reported that liver stiffness assessed by transient elastography are correlated with right atrial pressure, which is associated with worse outcome in patients with heart failure (HF). We aimed to clarify clinical implications of hepatic hemodynamic evaluation (liver congestion and hypoperfusion) by abdominal ultrasonography in patients with HF. Methods and Results We performed abdominal ultrasonography, right-heart catheterization, and echocardiography, then followed up for cardiac events such as cardiac death or worsening HF in patients with HF. Regarding liver congestion, liver stiffness assessed by shear wave elastography (SWE) of the liver was significantly correlated with right atrial pressure determined by right-heart catheterization (R=0.343; P<0.01), right atrial end-systolic area, and inferior vena cava diameter determined by echocardiography. Regarding liver hypoperfusion, peak systolic velocity (PSV) of the celiac artery was correlated with cardiac index determined by right-heart catheterization (R=0.291; P<0.001) and tricuspid annular plane systolic excursion determined by echocardiography. According to the Kaplan-Meier analysis, HF patients with high SWE and low PSV had the highest cardiac event rate (log-rank P=0.033). In the Cox proportional hazard analysis, high SWE and low PSV were associated with high cardiac event rate (high SWE: hazard ratio [HR], 2.039; 95% CI, 1.131-4.290; low PSV: HR, 2.211; 95% CI, 1.199-4.449), and the combination of high SWE and low PSV was a predictor of cardiac events (HR, 4.811; 95% CI, 1.562-14.818). Conclusions Intrahepatic congestion and hypoperfusion determined by abdominal ultrasonography (liver SWE and celiac PSV) are associated with adverse prognosis in patients with HF.

Split-Liver Ex Situ Machine Perfusion: A Novel Technique for Studying Organ Preservation and Therapeutic Interventions

Ex situ machine perfusion is a promising technology to help improve organ viability prior to transplantation. However, preclinical studies using discarded human livers to evaluate therapeutic interventions and optimize perfusion conditions are limited by significant graft heterogeneity. In order to improve the efficacy and reproducibility of future studies, a split-liver perfusion model was developed to allow simultaneous perfusion of left and right lobes, allowing one lobe to serve as a control for the other. Eleven discarded livers were surgically split, and both lobes perfused simultaneously on separate perfusion devices for 3 h at subnormothermic temperatures. Lobar perfusion parameters were also compared with whole livers undergoing perfusion. Similar to whole-liver perfusions, each lobe in the split-liver model exhibited a progressive decrease in arterial resistance and lactate levels throughout perfusion, which were not significantly different between right and left lobes. Split liver lobes also demonstrated comparable energy charge ratios. Ex situ split-liver perfusion is a novel experimental model that allows each graft to act as its own control. This model is particularly well suited for preclinical studies by avoiding the need for large numbers of enrolled livers necessary due to the heterogenous nature of discarded human liver research.

Intravoxel incoherent motion imaging has the possibility to detect liver abnormalities in young Fontan patients with good hemodynamics

INTRODUCTION

Liver fibrosis and cirrhosis are one of the critical complications in Fontan patients. However, there are no well-established non-invasive and quantitative techniques for evaluating liver abnormalities in Fontan patients. Intravoxel incoherent motion diffusion-weighted imaging with MRI is a non-invasive and quantitative method to evaluate capillary network perfusion and molecular diffusion. The objective of this study is to assess the feasibility of intravoxel incoherent motion imaging in evaluating liver abnormalities in Fontan children.

MATERIALS AND METHODS

Five consecutive Fontan patients and four age-matched healthy volunteers were included. Fontan patients were 12.8 ± 1.5 years old at the time of MRI scan. Intravoxel incoherent motion imaging parameters (D, D*, and f values) within the right hepatic lobe were compared. Laboratory test, ultrasonography, and cardiac MRI were also conducted in the Fontan patients. Results of cardiac catheterization conducted within one year of the intravoxel incoherent motion imaging were also examined.

RESULTS

In Fontan patients, laboratory test and liver ultrasonography showed almost normal liver condition. Cardiac catheter and MRI showed good Fontan circulation. Cardiac index was 2.61 ± 0.23 L/min/m2. Intravoxel incoherent motion imaging parameters D, D*, and f values were lower in Fontan patients compared with controls (D: 1.1 ± 0.0 versus 1.3 ± 0.2 × 10-3 mm2/second (p = 0.04), D*: 30.8 ± 24.8 versus 113.2 ± 25.6 × 10-3 mm2/second (p < 0.01), and f: 13.2 ± 3.1 versus 22.4 ± 2.4% (p < 0.01), respectively).

CONCLUSIONS

Intravoxel incoherent motion imaging is feasible for evaluating liver abnormalities in children with Fontan circulation.

Using MRI to study the alterations in liver blood flow, perfusion, and oxygenation in response to physiological stress challenges: Meal, hyperoxia, and hypercapnia

BACKGROUND

Noninvasive assessment of dynamic changes in liver blood flow, perfusion, and oxygenation using MRI may allow detection of subtle hemodynamic alterations in cirrhosis.

PURPOSE

To assess the feasibility of measuring dynamic liver blood flow, perfusion, and T₂ * alterations in response to meal, hypercapnia, and hyperoxia challenges.

STUDY TYPE

Prospective.

SUBJECTS

Ten healthy volunteers (HV) and 10 patients with compensated cirrhosis (CC).

FIELD STRENGTH/SEQUENCE

3T; phase contrast, arterial spin labeling, and T 2 * mapping.

ASSESSMENT

Dynamic changes in portal vein and hepatic artery blood flow (using phase contrast MRI), liver perfusion (using arterial spin labeling), and blood oxygenation ( T 2 * mapping) following a meal challenge (660 kcal), hyperoxia (target P_ET O₂ of 500 mmHg), and hypercapnia (target increase P_ET CO₂ of ∼6 mmHg).

STATISTICAL TESTS

Tests between baseline and each challenge were performed using a paired two-tailed t-test (parametric) or Wilcoxon-signed-ranks test (nonparametric). Repeatability and reproducibility were determined by the coefficient of variation (CoV).

RESULTS

Portal vein velocity increased following the meal (70 ± 9%, P < 0.001) and hypercapnic (7 (5-11)%, P = 0.029) challenge, while hepatic artery flow decreased (-30 ± 18%, P = 0.005) following the meal challenge in HV. In CC patients, portal vein velocity increased (37 ± 13%, P = 0.012) without the decrease in hepatic artery flow following the meal. In both groups, the meal increased liver perfusion (HV: 82 ± 50%, P < 0.0001; CC: 27 (16-42)%, P = 0.011) with faster arrival time of blood (HV: -54 (-56-30)%, P = 0.074; CC: -42 ± 32%, P = 0.005). In HVs, T 2 * increased after the meal and in response to hyperoxia, with a decrease in hypercapnia (6 ± 8% P = 0.052; 3 ± 5%, P = 0.075; -5 ± 6%, P = 0.073, respectively), but no change in CC patients. Baseline between-session CoV <15% for blood flow and <10% for T 2 * measures.

DATA CONCLUSION

Dynamic changes in liver perfusion, blood flow, and oxygenation following a meal, hyperoxic, and hypercapnic challenges can be measured using noninvasive MRI and potentially be used to stratify patients with cirrhosis.

LEVEL OF EVIDENCE

2 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2019;49:1577-1586.

Impact of transjugular intrahepatic portosystemic shunt implantation on liver perfusion measured by volume perfusion CT

Background Implantation of a transjugular intrahepatic portosystemic shunt (TIPS) induces changes of liver perfusion. Purpose To determine the changes in arterial, portal venous, and total perfusion of the liver parenchyma induced by TIPS using the technique of volume perfusion computed tomography (VPCT) and compare results with invasively measured hepatic intravascular pressure values. Material and Methods VPCT quantification of liver perfusion was performed in 23 patients (mean age, 62.5 ± 8.8 years) with portal hypertension in the pre-TIPS and post-TIPS setting, respectively. A commercially available software package was used for post-processing, enabling separate calculation of the dual (arterial [ALP] and portal venous [PVP]) blood supply and additionally of the hepatic perfusion index (HPI) (HPI = ALP/(ALP + PVP)*100%). Invasive pressure measurements were performed during the intervention, before and after TIPS placement. Liver function tests performed before and after the procedure were compared. Results Mean decrease of pressure gradient through TIPS was 13.3 mmHg. Mean normal values for ALP, PVP, and total perfusion (ALP + PVP) before TIPS were 15.9, 37.7, and 53.5 mL/100 mL/min, respectively, mean HPI was 35.4%. After TIPS, ALP increased to a mean value of 37.7 mL/100 mL/min, PVP decreased (15.7 mL/100 mL/min, P < 0.05), whereas total perfusion remained unchanged (53.4 mL/100 mL/min, P = 0.97). HPI increased (71.9%; P < 0.05). No correlation between invasive pressure measurement and VPCT parameters was observed. After TIPS, liver function tests were found to worsen with a significant increase of bilirubin ( P < 0.05). Conclusion Following TIPS placement, ALP and HPI increased in all patients, whereas PVP markedly decreased. Interestingly, the magnitude of decrease in portosystemic pressure gradients was not found to correlate with VPCT parameters.

Helping prometheus: liver protection in acute hemorrhagic shock

Acute hemorrhagic hypovolemic shock is caused by a significant high blood loss and leads to hemodynamic instability. The decrease in intravascular volume results in cellular hypoxia and finally in damage to organs such as the liver and the kidney. The liver plays a decisive role in the development or prevention of multiple organ failure after hemorrhagic shock. Despite the large number of experimental studies, the knowledge of pathophysiological mechanisms in the liver after hemorrhagic shock is incomplete. The aim of this mini review was to provide an overview of the pathophysiological changes in liver function after acute hemorrhagic shock and to address treatment options to improve liver perfusion.

Glutamine dipeptide and cortisol change the liver glucose metabolism and reduce the severity of insulin-induced hypoglycaemia in untreated T1DM Swiss mice

CONTEXT

Glutamine is conditionally essential in type 1 diabetes mellitus, and might be useful to counteract hypoglycaemia.

OBJECTIVE

To investigate the systemic and hepatic effects of counter-regulatory hormones and glutamine dipeptide (GDP) during hypoglycemic episodes.

MATERIALS AND METHODS

Diabetic Swiss mice made hypoglycaemic by insulin injection (1 U/kg) were given counter-regulatory hormones and/or GDP. Sixty minutes later, liver histology, liver glucose metabolism and plasma were assessed.

RESULTS

Combined, cortisol and GDP improved the hypoglycemic profile. During liver perfusion, gluconeogenesis was possibly the major pathway leading to glucose release. Perfusion with gluconeogenic precursors after glycogen depletion by adrenaline increased liver glucose and urea release.

DISCUSSION

The less severe hypoglycaemia could result from cortisol stimulating periportal gluconeogenesis and GDP inhibiting pericentral glycogenolysis, both favouring liver glucose release.

CONCLUSIONS

At least some benefits of GDP and cortisol during hypoglycaemia came from their hepatic actions, and their use in diabetic patients should be explored.

Thyroid hormone treatment decreases hepatic glucose production and renal reabsorption of glucose in alloxan-induced diabetic Wistar rats

The thyroid hormone (TH) plays an important role in glucose metabolism. Recently, we showed that the TH improves glycemia control by decreasing cytokines expression in the adipose tissue and skeletal muscle of alloxan‐induced diabetic rats, which were also shown to present primary hypothyroidism. In this context, this study aims to investigate whether the chronic treatment of diabetic rats with T3 could affect other tissues that are involved in the control of glucose homeostasis, as the liver and kidney. Adult Male Wistar rats were divided into nondiabetic, diabetic, and diabetic treated with T3 (1.5 μg/100 g BW for 4 weeks). Diabetes was induced by alloxan monohydrate (150 mg/kg, BW, i.p.). Animals showing fasting blood glucose levels greater than 250 mg/dL were selected for the study. After treatment, we measured the blood glucose, serum T3, T4, TSH, and insulin concentration, hepatic glucose production by liver perfusion, liver PEPCK, GAPDH, and pAKT expression, as well as urine glucose concentration and renal expression of SGLT2 and GLUT2. T3 reduced blood glucose, hepatic glucose production, liver PEPCK, GAPDH, and pAKT content and the renal expression of SGLT2 and increased glycosuria. Results suggest that the decreased hepatic glucose output and increased glucose excretion induced by T3 treatment are important mechanisms that contribute to reduce serum concentration of glucose, accounting for the improvement of glucose homeostasis control in diabetic rats.

Quantification of liver perfusion using multidelay pseudocontinuous arterial spin labeling

PURPOSE

To develop a free-breathing multidelay pseudocontinuous arterial spin labeling (pCASL) technique for quantitative measurement of liver perfusion of the hepatic artery and portal vein, respectively.

MATERIALS AND METHODS

A navigator-gated pCASL sequence with balanced steady-state free precession (bSSFP) readout was developed and applied on five healthy young volunteers at 3T. Two labeling schemes were performed with the labeling plane applied on the descending aorta above the liver, and perpendicular to the portal vein before its entry to liver to label the hepatic artery and portal vein, respectively. For each labeling scheme, pCASL scans were performed at five or six postlabeling delays between 200 and 2000 msec or 2500 msec with an interval of 400 or 500 msec. Multidelay pCASL images were processed offline with nonrigid motion correction, outlier removal, and fitted for estimation of liver perfusion and transit time.

RESULTS

Estimated liver perfusion of the hepatic artery and hepatic portal vein were 21.8 ± 1.9 and 95.1 ± 8.9 mL/100g/min, with the corresponding transit time of 1227.3 ± 355.5 and 667.2 ± 85.0 msec, respectively. The estimated liver perfusion and transit time without motion correction were less reliable with greater residual variance compared to those processed with motion correction (P < 0.05).

CONCLUSION

The liver perfusion measurement using multidelay pCASL showed good correspondence with values noted in the literature. The capability to noninvasively and selectively label the hepatic artery and portal vein is a unique strength of pCASL as compared to other liver perfusion imaging techniques, such as computed tomography perfusion and dynamic contrast-enhanced MRI.

Instant coffee extract with high chlorogenic acids content inhibits hepatic G-6-Pase in vitro, but does not reduce the glycaemia

Coffee is the main source of chlorogenic acid in the human diet, and it contains several chlorogenic acid isomers, of which the 5-caffeoylquinic acid (5-CQA) is the predominant isomer. Because there are no available data about the action of chlorogenic acids from instant coffee on hepatic glucose-6-phosphatase (G-6-Pase) activity and blood glucose levels, these effects were investigated in rats. The changes on G-6-Pase activity and liver glucose output induced by 5-CQA were also investigated. Instant coffee extract with high chlorogenic acids content (37.8%) inhibited (p < 0.05) the G-6-Pase activity of the hepatocyte microsomal fraction in a dose-dependent way (up to 53), but IV administration of this extract did not change the glycaemia (p > 0.05). Similarly, 5-CQA (1 mM) reduced (p < 0.05) the activity of microsomal G-6-Pase by about 40%, but had no effect (p > 0.05) on glucose output arising from glycogenolysis in liver perfusion. It was concluded that instant coffee extract with high content of chlorogenic acids inhibited hepatic G-6-Pase in vitro, but failed to reduce the glycaemia probably because the coffee chlorogenic acids did not reach enough levels within the hepatocytes to inhibit the G-6-Pase and reduce the liver glucose output.

Stem cells with decellularized liver scaffolds in liver regeneration and their potential clinical applications

End-stage hepatic failure is a potentially life-threatening condition for which orthotopic liver transplantation (OLT) is the only effective treatment. However, a shortage of available donor organs for transplantation each year results in the death of many patients waiting for liver transplantation. Cell-based therapies and hepatic tissue engineering have been considered as alternatives to liver transplantation. However, primary hepatocyte transplantation has rarely produced therapeutic effects because mature hepatocytes cannot be effectively expanded in vitro, and the availability of hepatocytes is often limited by shortages of donor organs. Decellularization is an attractive technique for scaffold preparation in stem cell-based liver engineering, as the resulting material can potentially retain the liver architecture, native vessel network and specific extracellular matrix (ECM). Thus, the reconstruction of functional and practical liver tissue using decellularized scaffolds becomes possible. This review focuses on the current understanding of liver tissue engineering, whole-organ liver decellularization techniques, cell sources for recellularization and potential clinical applications and challenges.

Stem cells with decellularized liver scaffolds in liver regeneration and their potential clinical applications

End-stage hepatic failure is a potentially life-threatening condition for which orthotopic liver transplantation (OLT) is the only effective treatment. However, a shortage of available donor organs for transplantation each year results in the death of many patients waiting for liver transplantation. Cell-based therapies and hepatic tissue engineering have been considered as alternatives to liver transplantation. However, primary hepatocyte transplantation has rarely produced therapeutic effects because mature hepatocytes cannot be effectively expanded in vitro, and the availability of hepatocytes is often limited by shortages of donor organs. Decellularization is an attractive technique for scaffold preparation in stem cell-based liver engineering, as the resulting material can potentially retain the liver architecture, native vessel network and specific extracellular matrix (ECM). Thus, the reconstruction of functional and practical liver tissue using decellularized scaffolds becomes possible. This review focuses on the current understanding of liver tissue engineering, whole-organ liver decellularization techniques, cell sources for recellularization and potential clinical applications and challenges.

Ex vivo normothermic machine perfusion is safe, simple, and reliable: results from a large animal model

INTRODUCTION

Normothermic machine perfusion (NMP) is an emerging preservation modality that holds the potential to prevent the injury associated with low temperature and to promote organ repair that follows ischemic cell damage. While several animal studies have showed its superiority over cold storage (CS), minimal studies in the literature have focused on safety, feasibility, and reliability of this technology, which represent key factors in its implementation into clinical practice. The aim of the present study is to report safety and performance data on NMP of DCD porcine livers.

MATERIALS AND METHODS

After 60 minutes of warm ischemia time, 20 pig livers were preserved using either NMP (n = 15; physiologic perfusion temperature) or CS group (n = 5) for a preservation time of 10 hours. Livers were then tested on a transplant simulation model for 24 hours. Machine safety was assessed by measuring system failure events, the ability to monitor perfusion parameters, sterility, and vessel integrity. The ability of the machine to preserve injured organs was assessed by liver function tests, hemodynamic parameters, and histology.

RESULTS

No system failures were recorded. Target hemodynamic parameters were easily achieved and vascular complications were not encountered. Liver function parameters as well as histology showed significant differences between the 2 groups, with NMP livers showing preserved liver function and histological architecture, while CS livers presenting postreperfusion parameters consistent with unrecoverable cell injury.

CONCLUSION

Our study shows that NMP is safe, reliable, and provides superior graft preservation compared to CS in our DCD porcine model.

Robustness to noise of arterial blood flow estimation methods in CT perfusion

BACKGROUND

Perfusion CT is a technology which allows functional evaluation of tissue vascularity. Due to this potential, it is finding increasing utility in oncology. Although since its introduction continuous advances have interested CT technique, some issues have to be still defined, concerning both clinical and technical aspects. In this study, we dealt with the comparison of two widely employed mathematical models (dual input one compartment model - DOCM - and maximum slope - SM -) analyzing their robustness to the noise.

METHODS

We carried out a computer simulation process to quantify effect of noise on the evaluation of an important perfusion parameter (Arterial Blood Flow - BFa) in liver tumours. A total of 4500 liver TAC, corresponding to 3 fixed BFa values, were simulated using different arterial and portal TAC (computed from 5 real CT images) at 10 values of signal to noise ratio (SNR). BFa values were calculated by applying four different algorithms, specifically developed, to these noisy simulated curves. Three algorithms were developed to implement SM (one semiautomatic, one automatic and one automatic with filtering) and the last for the DOCM method.

RESULTS

In all the simulations, DOCM provided the best results, i.e., those with the lowest percentage error compared to the reference value of BFa. Concerning SM, the results are variable. Results obtained with the automatic algorithm with filtering are close to the reference value, but only if SNR is higher than 50. Vice versa, results obtained by means of the semiautomatic algorithm gave, in all simulations, the lowest results with the lowest standard deviation of the percentage error.

CONCLUSIONS

Since the use of DOCM is limited by the necessity that portal vein is visible in CT scans, significant restriction for patients' follow-up, we concluded that SM can be reliably employed. However, a proper software has to be used and an estimation of SNR would be carried out.

A distinct nitric oxide and adenosine A1 receptor dependent hepatic artery vasodilatatory response in the CCl-cirrhotic liver

Increase of portal venous vascular resistance is counteracted by decrease of hepatic arterial vascular resistance (hepatic arterial buffer response). This process is mediated by adenosine in normal livers. In cirrhosis, hepatic arterial vascular resistance is decreased but the involvement of adenosine in this process is unknown. The aim of our study was to identify the signalling pathway responsible for the decreased hepatic arterial resistance in cirrhotic livers.

METHODS

Cirrhosis was induced by CCl(4). Using a bivascular liver perfusion dose-response curves to adenosine of the HA were performed in the presence and the absence of pan-adenosine blocker (8-SPT), A1 blocker (caffeine) or nitric oxide synthase-blocker (l-NMMA) after preconstriction with an alpha1-agonist (methoxamine). Western blot of the HA were used to measure the density of the A1 and A2a receptors.

RESULTS

Adenosine caused a dose dependent relaxation of the hepatic artery of both cirrhotic and control animals that were blocked in both groups by 8-SPT (P<0.02). The response to adenosine was greater in cirrhotic rats (P=0.016). Both l-NMMA (P=0.003) and caffeine reduced the response to adenosine in cirrhotic but not in control animals. Western blot analysis showed a higher density of A1 and a lower density of A2a receptor in cirrhotic animals (P<0.05).

CONCLUSION

The adenosine-induced vasodilatation of the HA is increased in cirrhotic rats suggesting a role for adenosine-NO in the decreased hepatic arterial vascular resistance found in cirrhosis. This significantly greater response in cirrhosis by the A1 receptor follows the same pathway that is seen in hypoxic conditions in extra-hepatic tissues.

Removal of chylomicron remnants in transgenic mice overexpressing normal and membrane-anchored hepatic lipase

The LDL receptor and the LDL receptor-related protein (LRP) mediate the removal of chylomicron remnants. The LRP pathway involves sequestration of particles in the space of Disse. It has been proposed that either alone or in combination with other factors, such as apolipoprotein E and proteoglycans, hepatic lipase (HL) may contribute to the sequestration of chylomicron remnants. To test this hypothesis, we generated two lines of transgenic mice producing rat HL as a native or as a membrane-anchored form. These animals express HL at levels similar to normal rat. Chylomicron remnants were perfused in a single nonrecirculating pass into the livers of the rat HL transgenic, HL-deficient, and wild-type (WT) mice for 20 min, and the rate of chylomicron remnant removal was measured. Chylomicron remnants were removed at a rate of approximately 50% per pass in WT mice. It was slightly increased in both transgenic mice and reduced in HL-deficient mice compared with the WT mice. Confocal microscopy of liver sections showed that a modest amount of HL colocalized with chylomicron remnant clusters in the transgenic mice, suggesting that HL is a component of the LRP-proteoglycan clusters. These data suggest that HL helps to direct cholesterol to the tissues in which it is localized by a nonenzymatic mechanism.