A critical appraisal of the hemodynamic signal driving liver regeneration

Exosomes Derived from Adipose Mesenchymal Stem Cells Promote Regeneration of Injured Liver in Minipigs

Hepatic ischemia/reperfusion injury (IRI) is an important factor affecting liver regeneration and functional recovery postoperatively. Many studies have suggested that mesenchymal stem cells (MSCs) contribute to hepatic tissue repair and functional recovery through paracrine mechanisms mediated by exosomes. Minipigs exhibit much more similar characteristics of the liver to those of humans than rodents. This study aimed to explore whether exosomes from adipose-derived MSCs (ADSCs-exo) could actively promote liver regeneration after hepatectomy combined with HIRI in minipigs and the role they play in the cell proliferation process. This study also compared the effects and differences in the role of ADSCs and ADSCs-exo in the inflammatory response and liver regeneration. The results showed that ADSCs-exo suppressed histopathological changes and reduced inflammatory infiltration in the liver; significantly decreased levels of ALT, TBIL, HA, and the pro-inflammatory cytokines TNF-α, IL-6, and CRP; increased levels of the anti-inflammatory cytokine IL-10 and the pro-regeneration factors Ki67, PCNA, CyclinD1, HGF, STAT3, VEGF, ANG1, ANG2; and decreased levels of the anti-regeneration factors SOCS3 and TGF-β. These indicators above showed similar changes with the ADSCs intervention group. Indicating that ADSCs-exo can exert the same role as ADSCs in regulating inflammatory responses and promoting liver regeneration. Our findings provide experimental evidence for the possibility that ADSCs-exo could be considered a safe and effective cell-free therapy to promote regeneration of injured livers.

Comparison of clinical efficacy between LAPS and ALPPS in the treatment of hepatitis B virus-related hepatocellular carcinoma

Background

Insufficient post-operative future liver remnant (FLR) limits the feasibility of hepatectomy for patients. Staged hepatectomy is an effective surgical approach that can improve the resection rate of hepatocellular carcinoma (HCC). This study aimed to compare the safety and efficacy of laparoscopic microwave ablation and portal vein ligation for staged hepatectomy (LAPS) and classical associating liver partition and portal vein ligation for staged hepatectomy (ALPPS) in the treatment of hepatitis B virus (HBV)-related HCC.

Methods

Clinical data of patients with HBV-related HCC who underwent LAPS or ALPPS in our institute between January 2017 and May 2022 were retrospectively analysed.

Results

A total of 18 patients with HBV-related HCC were retrospectively analysed and divided into the LAPS group (n = 9) and ALPPS group (n = 9). Eight patients in the LAPS group and eight patients in the ALPPS group proceeded to a similar resection rate (88.9% vs 88.9%, P = 1.000). The patients undergoing LAPS had a lower total comprehensive complication index than those undergoing ALPPS but there was not a significant different between the two groups (8.66 vs 35.87, P = 0.054). The hypertrophy rate of FLR induced by ALPPS tended to be more rapid than that induced by LAPS (24.29 vs 13.17 mL/d, P = 0.095). The 2-year recurrence-free survival (RFS) was 0% for ALPPS and 35.7% for LAPS (P = 0.009), whereas the 2-year overall survival for ALPPS and LAPS was 33.3% and 100.0% (P = 0.052), respectively.

Conclusions

LAPS tended to induce lower morbidity and FLR hypertrophy more slowly than ALPPS, with a comparable resection rate and better long-term RFS in HBV-related HCC patients.

In silico modeling for the hepatic circulation and transport: From the liver organ to lobules

The function of the liver depends critically on its blood supply. Numerous in silico models have been developed to study various aspects of the hepatic circulation, including not only the macro-hemodynamics at the organ level, but also the microcirculation at the lobular level. In addition, computational models of blood flow and bile flow have been used to study the transport, metabolism, and clearance of drugs in pharmacokinetic studies. These in silico models aim to provide insights into the liver organ function under both healthy and diseased states, and to assist quantitative analysis for surgical planning and postsurgery treatment. The purpose of this review is to provide an update on state-of-the-art in silico models of the hepatic circulation and transport processes. We introduce the numerical methods and the physiological background of these models. We also discuss multiscale frameworks that have been proposed for the liver, and their linkage with the large context of systems biology, systems pharmacology, and the Physiome project. This article is categorized under: Metabolic Diseases > Computational Models Metabolic Diseases > Biomedical Engineering Cardiovascular Diseases > Computational Models.

Application of associating liver partition and portal vein ligation for staged hepatectomy for initially unresectable hepatocellular carcinoma

OBJECTIVE

To evaluate the safety and efficacy of associating liver partition and portal vein ligation for staged hepatectomy (ALPPS) in the treatment of initially unresectable hepatitis B virus (HBV)-associated hepatocellular carcinoma (HCC) and to preliminarily explore the mechanism of rapid growth of the future liver remnant (FLR).

METHODS

Twenty-four patients with HBV-associated HCC who underwent ALPPS in our hospital from August 2014 to January 2021 were retrospectively studied. Propensity score matching was used to compare oncologic outcomes of patients treated with ALPPS and transarterial chemoembolization (TACE). The expression of YAP and JNK in liver tissue after two stages of ALPPS were detected.

RESULTS

The median standard liver volume (SLV) was 1471.4 ml. Before second stage of ALPPS, the median FLR increased by 74.4%, and the median FLR/SLV increased from 26.1 to 41.6%. Twenty-two patients (91.7%) received staged hepatectomy after a median interval of 15 (9-24) d. The total incidence of postoperative complications in ALPPS group was 54.5%, and of Clavien-Dindo ≥ IIIb postoperative complications (requiring surgical, endoscopic or radiological intervention under general anesthesia) was 9.1%. There was no significant difference in total complications between ALPPS group and TACE group, but there were lower rate of above grade III complications in the TACE group than that in the ALPPS group. The incidence of complications was lower in laparoscopic-ALPPS than that in open surgery. In ALPPS group, the 1-year, 2-year and 5-year overall survival rate were respectively 71.4%, 33.3% and 4.8%. Interval time was an independent risk factor associated with overall survival rate. There was no significant difference in overall survival rate between ALPPS group and TACE group. For advanced HCC (BCLC stage B and C), ALPPS group was not superior to TACE group in overall survival rate. The expression of YAP and p-JNK in the residual liver tissue after second stage procedure was higher than that after first stage procedure, and the co-expression of YAP and p-JNK was observed in the residual liver tissue.

CONCLUSION

ALPPS is a safe and effective treatment for initially unresectable HBV-associated HCC. Laparoscopic technique might improve the effect of ALPPS. YAP and JNK pathway might take a role in rapid FLR increase in ALPPS procedure.

Hepatic pseudolesions caused by alterations in intrahepatic hemodynamics

Hepatic pseudolesion may occur in contrast-enhanced computed tomography and magnetic resonance imaging due to the unique haemodynamic characteristics of the liver. The concept of hepatic arterial buffer response (HABR) has become mainstream for the understanding of the mechanism of the reciprocal effect between hepatic arterial and portal venous flow. And HABR is thought to be significantly related to the occurrence of the abnormal imaging findings on arterial phase of contrast enhanced images, such as hepatic arterial-portal vein shunt and transient hepatic attenuation difference, which mimic hypervascular tumor and may cause clinical problems. Third inflow to the liver also cause hepatic pseudolesion, and some of the cases may show histopathologic change such as focal hyperplasia, focal fatty liver, and focal sparing of fatty liver, and called pseudotumor. To understand these phenomena might be valuable for interpreting the liver imaging findings.

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.

Hepatic Arterioportal Fistula Is Associated with Decreased Future Liver Remnant Regeneration after Stage-I ALPPS for Hepatocellular Carcinoma

BACKGROUND

Hepatocellular carcinoma (HCC) patients often developed hepatic arterioportal fistula (APF). The aim of this study is to evaluate the impact of APF on future liver remnant (FLR) regeneration and surgical outcomes after the first stage of associating liver partition and portal vein ligation for staged hepatectomy (stage-I ALPPS).

METHODS

Consecutive HCC patients who underwent ALPPS at our center between March 2017 and May 2019 were retrospectively studied. Data for the association between APF and clinicopathological details, liver volume, and surgical outcomes were analyzed.

RESULTS

The enrolled 35 HCC patients were divided into three groups: 15 patients with preoperative APF were classified as the APF I group, 10 patients developed APF after stage-I ALPPS as the APF II group, whereas the other 10 patients without APF before and after stage-I ALPPS as the control group. After stage-I ALPPS, patients in the APF I and APF II groups had lower kinetic growth rate (KGR) of FLR volume (6.1±3.2%, 11.4±8.4%, 25.0±8.8% per week, respectively, P<0.001) and took longer median time to reach the sufficient FLR volume for stage-II ALPPS (17.5 days, 12 days, 6 days, respectively, P<0.001) than those in the control group. Meanwhile, the incidence of posthepatectomy liver failure (PHLF) in the APF I and APF II groups was significantly higher than that of the control group (P=0.007). There are 27 (77.1%) patients who completed stage-II ALPPS. The overall survival (OS) rates at 1 and 3 years were 59.3% and 35.1%, whereas the disease-free survival (DFS) rates at 1 and 3 years were 44.4% and 22.9%, respectively.

CONCLUSIONS

Hepatic APF is significantly associated with decreased FLR regeneration and a higher risk of PHLF after stage-I ALPPS. HCC patients who are to undergo ALPPS may benefit from the timely perioperative intervention of APF.

Liver Resection Promotes (Regulates) Proinflammatory Cytokines in Patients with Hepatocellular Carcinoma

BACKGROUND

Several animal studies have shown the roles of cytokines in regulating liver regeneration following liver resection (LR), which is a type of surgery designed to remove cancerous tumors from the liver. This study investigated how the expressions and serum levels of some pro- and anti-inflammatory cytokines in patients with hepatocellular carcinoma (HCC) were changed during LR.

METHODS

Liver tissues from 15 patients with HCC were collected and the levels of interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-α), IL-1α, IL-1 β, IL-10, and transforming growth factor-beta1 (TGF-β1) were assessed using real-time PCR assay at different times before and after LR. The serum values of TNF-α and IL-6 were also measured by ELISA.

RESULTS

After 60 and 90 minutes of LR, IL-6 gene expression was significantly increased (P < 0.001 - 0.05). The same trend was also observed in TNF-α expression after 90 minutes of LR (P < 0.01). No significant changes were observed in the expressions of IL-1α, IL-1β, IL-10, and TGF-β1 before and after LR. In addition, LR had significant effects on TNF-α and IL-6 serum levels (P < 0.05 - 0.0001).

CONCLUSION

Our data provided further evidence to reveal that IL-6 and TNF-α cytokines are critical to improve liver regeneration.

Hypoxia maintains the fenestration of liver sinusoidal endothelial cells and promotes their proliferation through the SENP1/HIF-1α/VEGF signaling axis

Liver sinusoidal endothelial cells (LSECs), which play a very critical role in liver regeneration, function in hypoxic environments, but few studies have elucidated the specific mechanism. As a hypoxia-sensitive gene, Sentrin/SUMO-specific protease 1(SENP1) is upregulated in solid tumors due to hypoxia and promotes tumor proliferation. We speculate that LSECs may upregulate SENP1 in hypoxic environments and that SENP1 may act on downstream genes to allow the cells to adapt to the hypoxic environment. To elucidate the reasons for the survival of LSECs under hypoxia, we designed experiments to explore the possible mechanism. First, we cultured murine LSECs in hypoxic conditions for a certain time (24 h and 72 h), and then, we observed that the proliferation ability of the hypoxia group was higher than that of the normoxia group, and the number of unique fenestrae of the LSECs in the hypoxia group was more than that of the LSECs in the normoxia group. Then, we divided the LSECs into several groups for hypoxic culture for time points (6 h, 12 h, 24 h, 36 h, and 72 h), and we found that the expression of SENP1, HIF-1α and VEGF was significantly upregulated. Then, we silenced SENP1 and HIF-1α with si-SENP1 and si-HIF-1α, respectively. SENP1, HIF-1α and VEGF were significantly downregulated, as determined by RT-PCR, WB and ELISA. Unexpectedly, the proliferation activity of the LSECs decreased and the fenestrae disappeared more in the si-SENP1 and si-HIF-1α groups than in the control group. It is concluded that LSECs cultured under hypoxic conditions may maintain fenestrae and promote proliferation through the SENP1/HIF-1α/VEGF signaling axis, thereby adapting to the hypoxic environment.

Liver Regeneration after Hepatectomy and Partial Liver Transplantation

The liver is a unique organ with an abundant regenerative capacity. Therefore, partial hepatectomy (PHx) or partial liver transplantation (PLTx) can be safely performed. Liver regeneration involves a complex network of numerous hepatotropic factors, cytokines, pathways, and transcriptional factors. Compared with liver regeneration after a viral- or drug-induced liver injury, that of post-PHx or -PLTx has several distinct features, such as hemodynamic changes in portal venous flow or pressure, tissue ischemia/hypoxia, and hemostasis/platelet activation. Although some of these changes also occur during liver regeneration after a viral- or drug-induced liver injury, they are more abrupt and drastic following PHx or PLTx, and can thus be the main trigger and driving force of liver regeneration. In this review, we first provide an overview of the molecular biology of liver regeneration post-PHx and -PLTx. Subsequently, we summarize some clinical conditions that negatively, or sometimes positively, interfere with liver regeneration after PHx or PLTx, such as marginal livers including aged or fatty liver and the influence of immunosuppression.

Hemostasis and Liver Regeneration

The liver is unique in its remarkable regenerative capacity, which enables the use of liver resection as a treatment for specific liver diseases, including removal of neoplastic liver disease. After resection, the remaining liver tissue (i.e, liver remnant) regenerates to maintain normal hepatic function. In experimental settings as well as patients, removal of up to two-thirds of the liver mass stimulates a rapid and highly coordinated process resulting in the regeneration of the remaining liver. Mechanisms controlling the initiation and termination of regeneration continue to be discovered, and many of the fundamental signaling pathways controlling the proliferation of liver parenchymal cells (i.e., hepatocytes) have been uncovered. Interestingly, while hemostatic complications (i.e., bleeding and thrombosis) are primarily thought of as a complication of surgery itself, strong evidence suggests that components of the hemostatic system are, in fact, powerful drivers of liver regeneration. This review focuses on the clinical and translational evidence supporting a link between the hemostatic system and liver regeneration, and the mechanisms whereby the hemostatic system directs liver regeneration discovered using experimental settings.

An in silico rat liver atlas

Numerous hepatic function, disease and pharmacological experiments are performed on rat livers. Many of these experiments rely on an accurate understanding of the rat liver anatomy. In this short paper, we present an in silico rat liver atlas which is constructed from the micro-CT images of explanted rat livers. The atlas consists of the parametric mesh for four liver lobes and a paracaval portion. 1D and 3D cubic Hermite mesh are used to represent the rat liver vessels and lobes, respectively. We discuss potential applications that can be performed from the in silico atlas.

Hypoxia sensing by hepatic stellate cells leads to VEGF-dependent angiogenesis and may contribute to accelerated liver regeneration

Portal vein ligation (PVL) induces liver growth prior to resection. Associating liver partition and portal vein ligation (PVL plus transection=ALPPS) or the addition of the prolyl-hydroxylase inhibitor dimethyloxalylglycine (DMOG) to PVL both accelerate growth via stabilization of HIF-α subunits. This study aims at clarifying the crosstalk of hepatocytes (HC), hepatic stellate cells (HSC) and liver sinusoidal endothelial cells (LSEC) in accelerated liver growth. In vivo, liver volume, HC proliferation, vascular density and HSC activation were assessed in PVL, ALPPS, PVL+DMOG and DMOG alone. Proliferation of HC, HSC and LSEC was determined under DMOG in vitro. Conditioned media experiments of DMOG-exposed cells were performed. ALPPS and PVL+DMOG accelerated liver growth and HC proliferation in comparison to PVL. DMOG alone did not induce HC proliferation, but led to increased vascular density, which was also observed in ALPPS and PVL+DMOG. Activated HSC were detected in ALPPS, PVL+DMOG and DMOG, again not in PVL. In vitro, DMOG had no proliferative effect on HC, but conditioned supernatant of DMOG-treated HSC induced VEGF-dependent proliferation of LSEC. Transcriptome analysis confirmed activation of proangiogenic factors in hypoxic HSC. Hypoxia signaling in HSC induces VEGF-dependent angiogenesis. HSC play a crucial role in the cellular crosstalk of rapid liver regeneration.

Whole Slide Imaging and Its Applications to Histopathological Studies of Liver Disorders

Histological analysis of hepatic tissue specimens is essential for evaluating the pathology of several liver disorders such as chronic liver diseases, hepatocellular carcinomas, liver steatosis, and infectious liver diseases. Manual examination of histological slides on the microscope is a classically used method to study these disorders. However, it is considered time-consuming, limited, and associated with intra- and inter-observer variability. Emerging technologies such as whole slide imaging (WSI), also termed virtual microscopy, have increasingly been used to improve the assessment of histological features with applications in both clinical and research laboratories. WSI enables the acquisition of the tissue morphology/pathology from glass slides and translates it into a digital form comparable to a conventional microscope, but with several advantages such as easy image accessibility and storage, portability, sharing, annotation, qualitative and quantitative image analysis, and use for educational purposes. WSI-generated images simultaneously provide high resolution and a wide field of observation that can cover the entire section, extending any single field of view. In this review, we summarize current knowledge on the application of WSI to histopathological analyses of liver disorders as well as to understand liver biology. We address how WSI may improve the assessment and quantification of multiple histological parameters in the liver, and help diagnose several hepatic conditions with important clinical implications. The WSI technical limitations are also discussed.

Transcriptional changes during hepatic ischemia-reperfusion in the rat

There are few effective targeted strategies to reduce hepatic ischemia-reperfusion (IR) injury, a contributor to poor outcomes in liver transplantation recipients. It has been proposed that IR injury is driven by the generation of reactive oxygen species (ROS). However, recent studies implicate other mediators of the injury response, including mitochondrial metabolic dysfunction. We examined changes in global gene expression after transient hepatic ischemia and at several early reperfusion times to identify potential targets that could be used to protect against IR injury. Male Wistar rats were subjected to 30 minutes of 70% partial warm ischemia followed by 0, 0.5, 2, or 6 hours of reperfusion. RNA was extracted from the reperfused and non-ischemic lobes at each time point for microarray analysis. Identification of differentially expressed genes and pathway analysis were used to characterize IR-induced changes in the hepatic transcriptome. Changes in the reperfused lobes were specific to the various reperfusion times. We made the unexpected observation that many of these changes were also present in tissue from the paired non-ischemic lobes. However, the earliest reperfusion time, 30 minutes, showed a marked increase in the expression of a set of immediate-early genes (c-Fos, c-Jun, Atf3, Egr1) that was exclusive to the reperfused lobe. We interpreted these results as indicating that this early response represented a tissue autonomous response to reperfusion. In contrast, the changes that occurred in both the reperfused and non-ischemic lobes were interpreted as indicating a non-autonomous response resulting from hemodynamic changes and/or circulating factors. These tissue autonomous and non-autonomous responses may serve as targets to ameliorate IR injury.

Hypoxia protects the liver from Small For Size Syndrome: A lesson learned from the associated liver partition and portal vein ligation for staged hepatectomy (ALPPS) procedure in rats

Portal hyperperfusion and "dearterialization" of the liver remnant are the main pathogenic mechanisms for Small For Size syndrome (SFSS). Associating liver partition and portal vein ligation for staged hepatectomy (ALPPS) induces rapid remnant hypertrophy. We hypothesized a similar increase in portal pressure/flow into the future liver remnant in ALPPS and SFSS-setting hepatectomies. In a rodent model, ALPPS was compared to SFSS-setting hepatectomy. We assessed mortality, remnant hypertrophy, hepatocyte proliferation, portal and hepatic artery flow, hypoxia-induced response, and liver sinusoidal morphology. SFSS-hepatectomy rats were subjected to local (hepatic artery ligation) or systemic (Dimethyloxalylglycine) hypoxia. ALLPS prevented mortality in SFSS-setting hepatectomies. Portal hyperperfusion per liver mass was similar in ALLPS and SFSS. Compared to SFSS, efficient arterial perfusion of the remnant was significantly lower in ALPPS causing pronounced hypoxia confirmed by pimonidazole immunostaining, activation of hypoxia sensors and upregulation of neo-angiogenic genes. Liver sinusoids, larger in ALPPS, collapsed in SFSS. Induction of hypoxia in SFSS reduced mortality. Hypoxia had no impact on hepatocyte proliferation but contributed to the integrity of sinusoidal morphology. ALPPS hemodynamically differ from SFSS by a much lower arterial flow in ALPPS's FLR. We show that the ensuing hypoxic response is essential for the function of the regenerating liver by preserving sinusoidal morphology.

Portal hyperperfusion after major liver resection and associated sinusoidal damage is a therapeutic target to protect the remnant liver

Extended liver resection results in loss of a large fraction of the hepatic vascular bed, thereby causing abrupt alterations in perfusion of the remnant liver. Mechanisms of hemodynamic adaptation and associated changes in oxygen metabolism after liver resection and the effect of mechanical portal blood flow reduction were assessed. A pig model (n = 16) of extended partial hepatectomy was established that included continuous observation for 24 h under general anesthesia. Pigs were randomly separated into two groups, one with a portal flow reduction of 70% compared with preoperative values, and the other as a control (n = 8, each). In controls, portal flow [mean (SD)] increased from 74 (8) mL·min^-1·100 g^-1 preoperatively to 240 (48) mL·min^-1·100 g^-1 at 6 h after resection (P < 0.001). Hepatic arterial buffer response was abolished after resection. Oxygen uptake per unit liver mass increased from 4.0 (1.1) mL·min^-1·100 g^-1 preoperatively to 7.7 (1.7) mL·min^-1·100 g^-1 8 h after resection (P = 0.004). Despite this increase in relative oxygen uptake, total hepatic oxygen consumption (V̇o₂) was not maintained, and markers of hypoxia and anaerobic metabolism were significantly increased in hepatocytes after resection. Reduced postoperative portal flow was associated with significantly decreased levels of aspartate aminotransferase and bilirubin and increased hepatic clearance of indocyanine green. In conclusion, major liver resection was associated with persistent portal hyperperfusion, loss of the hepatic arterial buffer response, decreased total hepatic V̇o₂ and with increased anaerobic metabolism. Portal flow modulation by partial portal vein occlusion attenuated liver injury after extended liver resection.NEW & NOTEWORTHY Because of continuous monitoring, the experiments allow precise observation of the influence of liver resection on systemic and local abdominal hemodynamic alterations and oxygen metabolism. Major liver resection is associated with significant and persistent portal hyperperfusion and loss of hepatic arterial buffer response. The correlation of portal hyperperfusion and parameters of liver injury and dysfunction offers a novel therapeutic option to attenuate liver injury after extended liver resection.

Hemodynamic changes in ALPPS influence liver regeneration and function: results from a prospective study

BACKGROUND

Excessive increase of portal flow and pressure following extended hepatectomy have been associated to insufficient growth or function of the future liver remnant (FLR), with the risk of post-hepatectomy liver failure (PHLF). We prospectively assess the influence of liver hemodynamics on FLR regeneration and function in Associating Liver Partition and Portal vein ligation for Staged hepatectomy (ALPPS).

METHODS

Twenty-three patients underwent ALPPS; liver hemodynamics were assessed throughout the procedures. Volume and function of the FLR were evaluated by angio-CT and 99mTc-Mebrofenin-scintigraphy.

RESULTS

The portal vein flow at the end of stage-1 correlated with the increase of the FLR volume (p = 0.002). Patients with portal vein pressure (PVP) < 20 mmHg and hepatic to portal vein gradients (HVPG) < 15 mmHg at the end of ALPPS-1 showed higher FLR regeneration (76.7% vs. 30.6%, p = 0.04) and function (26.7% vs. -0.13%, p = 0.02). FLR regeneration was inversely correlated with baseline FLR/Total Liver Volume (p = 0.002) and FLR/Body Weight (p = 0.02). No correlation was found between volumes and function (p = 0.13).

CONCLUSION

Liver hemodynamic stress at the end of ALPPS-1 influences the increase of the FLR volume and function, which is higher with PVP < 20 and HVPG < 15 mmHg. Liver volume overestimates liver function and could be imprecise to set stage-2 timing.

The inhibitor of glycerol 3-phosphate acyltransferase FSG67 blunts liver regeneration after acetaminophen overdose by altering GSK3β and Wnt/β-catenin signaling

Repair mechanisms after acetaminophen (APAP) hepatotoxicity are poorly understood. We recently discovered that phosphatidic acid (PA) increases in mice and humans after APAP overdose, and is critical for liver regeneration. Here, we hypothesized that PA inhibits glycogen synthase kinase-3β (GSK3β), a component of canonical Wnt/β-catenin signaling, after APAP overdose. To test that, we treated mice with 300 mg/kg APAP at 0 h followed by vehicle or 20 mg/kg of the glycerol 3-phosphate acyltransferase inhibitor FSG67 at 3, 24 and 48 h. Some mice also received the GSK3 inhibitor L803-mts. Blood and liver were collected at multiple time points. Consistent with our earlier results, FSG67 did not affect toxicity (ALT, histology), APAP bioactivation (total glutathione), or oxidative stress (oxidized glutathione), but did reduce expression of proliferating cell nuclear antigen (PCNA) at 52 h. We then measured GSK3β phosphorylation and found it was dramatically decreased by FSG67 at 24 h, before PCNA dropped. Expression of cyclin D1, downstream of Wnt/β-catenin, was also reduced. To determine if the effect of FSG67 on GSK3β is important, we treated mice with FSG67 and L803-mts after APAP. Importantly, L803-mts rescued hepatocyte proliferation and survival. Our data indicate PA and lysoPA may support recovery after APAP overdose by inhibiting GSK3β.

Therapeutic implication of platelets in liver regeneration -hopes and hues

Mounting evidence highlights platelet involvement in liver regeneration via interaction with liver cells, growth factors release, and signaling contributions. Existing research suggests a compelling biological rationale for utilizing platelet biology, with the goal of improving liver function and accelerating its regenerative potential. Despite its expanding application in several clinical areas, the contribution of the platelet and its therapeutic implementation in liver regeneration so far has not yet fulfilled the initial high expectations. Areas covered: This review scrutinizes the progress, current updates, and discusses how recent understanding - particularly in the clinical implications of platelet-based therapy - may enable strategies to introduce and harness the therapeutic potential of the platelet during liver regeneration. Expert commentary: Several clinical and translational studies have facilitated a platform for the development of platelet-based therapy to enhance liver regeneration. While some of these therapies are effective to augment liver regeneration, the others have had some detrimental outcomes. The existing evidence represents a challenge for future projects that are focused on directly incorporating platelet-based therapies to induce liver regeneration.

Elevated ADAMTS13 Activity is Associated with Poor Postoperative Outcome in Patients Undergoing Liver Resection

Recently, von-Willebrand-Factor (vWF) has been shown to correlate with postoperative liver dysfunction (LD). Accordingly, “disintegrin-like metalloprotease with thrombospondin type1 motif” (ADAMTS13) is known to cleave vWF in less active fragments. Thus, we aimed to evaluate the diagnostic potential of ADAMTS13-activity (ADAMTS13-AC) to identify patients with postoperative LD after hepatectomy. Accordingly 37 patients undergoing hepatectomy for different neoplastic entities were included in this study. Plasma ADAMTS13-AC and vWF-Ag were measured 1 day prior to (preOP), 1 and 5 days (POD1/5) after hepatectomy. In accordance to the ISGLS-criteria LD was prospectively recorded. In this context, perioperative ADAMTS13-AC- and vWF-Ag/ADAMTS13-AC-ratio- levels revealed a significant increase after hepatectomy. Accordingly, elevated vWF-Ag/ADAMTS13-AC-ratio significantly predicted LD (preOP AUC: 0.75, p = 0.02; POD1 AUC: 0.80, p = 0.03). Patients who fulfilled our perioperative vWF-Ag/ADAMTS13-AC-ratio cut-off-levels (preOP: ≥116, POD1: ≥165) suffered from significantly higher incidences of LD (preOP: 70% vs. 30%, p = 0.01; POD1: 83% vs. 17%, p = 0.001). In conclusion, perioperative ADAMTS13-AC measurement may serve as a useful parameter to early detect high-risk patients developing postoperative LD prior to liver resection in patients suffering from hepatic malignancies. Indeed, further investigations have to be performed to consolidate its role as a predictive marker for LD.

Update on the Mechanisms of Liver Regeneration

Liver possesses many critical functions such as synthesis, detoxification, and metabolism. It continually receives nutrient-rich blood from gut, which incidentally is also toxin-rich. That may be why liver is uniquely bestowed with a capacity to regenerate. A commonly studied procedure to understand the cellular and molecular basis of liver regeneration is that of surgical resection. Removal of two-thirds of the liver in rodents or patients instigates alterations in hepatic homeostasis, which are sensed by the deficient organ to drive the restoration process. Although the exact mechanisms that initiate regeneration are unknown, alterations in hemodynamics and metabolism have been suspected as important effectors. Key signaling pathways are activated that drive cell proliferation in various hepatic cell types through autocrine and paracrine mechanisms. Once the prehepatectomy mass is regained, the process of regeneration is adequately terminated. This review highlights recent discoveries in the cellular and molecular basis of liver regeneration.

剪切力对肝脏切除术后肝窦内皮细胞的作用

肝切除术是肝脏疾病尤其是肝脏肿瘤的重要治疗手段, 并且在肝切除术后会出现肝脏血流动力学的改变. 肝窦内皮细胞是肝窦毛细血管内一类特殊的内皮细胞, 对血流变化十分敏感. 本文就肝脏切除术后血流产生的剪切力作用于肝窦内皮细胞, 从而调节肝细胞再生和肝组织恢复的作用及机制作一综述.

Granulocyte colony-stimulating factor improves survival of patients with decompensated cirrhosis: a randomized-controlled trial

BACKGROUND

Liver transplantation is the only curative option for patients with decompensated cirrhosis; however, many patients die while awaiting transplantation. Granulocyte colony-stimulating factor (GCSF) has shown promising results in improving outcomes in patients with advanced liver disease. We evaluated the efficacy of GCSF in patients with decompensated cirrhosis in an open-labeled randomized-controlled trial.

METHODS

Consecutive patients with decompensated cirrhosis were randomized to receive either GCSF 300 μg twice daily for 5 days plus standard medical therapy (SMT) (GCSF+SMT group) or SMT alone (SMT alone group). Outcomes were assessed at 6 months from randomization.

RESULTS

A total of 126 patients [median age: 53 (range: 31-76) years, 85% men] received GCSF+SMT and 127 patients received SMT alone. Baseline characteristics were similar in both the groups. The 5-day GCSF therapy did not lead to any significant adverse effects. At 6 months, in the GCSF+SMT group, 17 patients had died and nine were lost to follow-up, whereas in the SMT-alone group, 30 patients had died and 11 were lost to follow-up. By intention-to-treat analysis, cumulative survival was significantly higher in the GCSF+SMT group (79 vs. 68%; P=0.025). Also, significantly more patients (66%) showed improvement or stability in the Child-Turcotte-Pugh score at 6 months in the GCSF+SMT group compared with the SMT-alone group (51%, P=0.021).

CONCLUSION

GCSF therapy improves survival and clinical outcome in patients with decompensated cirrhosis. It may be useful in patients awaiting transplantation to prevent worsening during the waiting period. Further studies are needed to explore whether repeated periodic GCSF courses can further increase the survival and decrease the need for liver transplantation.Clinical trial registered at https://clinicaltrials.gov vide NCT02642003.

Bile acids and their receptors during liver regeneration: "Dangerous protectors"

Tissue repair is orchestrated by a finely tuned interplay between processes of regeneration, inflammation and cell protection, allowing organisms to restore their integrity after partial loss of cells or organs. An important, although largely unexplored feature is that after injury and during liver repair, liver functions have to be maintained to fulfill the peripheral demand. This is particularly critical for bile secretion, which has to be finely modulated in order to preserve liver parenchyma from bile-induced injury. However, mechanisms allowing the liver to maintain biliary homeostasis during repair after injury are not completely understood. Besides cytokines and growth factors, bile acids (BA) and their receptors constitute an insufficiently explored signaling network during liver regeneration and repair. BA signal through both nuclear (mainly Farnesoid X Receptor, FXR) and membrane (mainly G Protein-coupled BA Receptor 1, GPBAR-1 or TGR5) receptors which distributions are large in the organism, and which activation elicits a wide array of biological responses. While a number of studies have been dedicated to FXR signaling in liver repair processes, TGR5 remains poorly explored in this context. Because of the massive and potentially harmful BA overload that faces the remnant liver after partial ablation or destruction, both BA-induced adaptive and proliferative responses may stand in a central position to contribute to the regenerative response. Based on the available literature, both BA receptors may act in synergy during the regeneration process, in order to protect the remnant liver and maintain biliary homeostasis, otherwise potentially toxic BA overload would result in parenchymal insult and compromise optimal restoration of a functional liver mass.

Hypoxia of the growing liver accelerates regeneration

BACKGROUND

After portal vein ligation of 1 side of the liver, the other side regenerates at a slow rate. This slow growth may be accelerated to rapid growth by adding a transection between the 2 sides, i.e., performing portal vein ligation and parenchymal transection. We found that in patients undergoing portal vein ligation and parenchymal transection, portal vein hyperflow in the regenerating liver causes a significant reduction of arterial flow due to the hepatic arterial buffer response. We postulated that the reduction of arterial flow induces hypoxia in the regenerating liver and used a rat model to assess hypoxia and its impact on kinetic growth.

METHODS

A rat model of rapid (portal vein ligation and parenchymal transection) and slow regeneration (portal vein ligation) was established. Portal vein flow and pressure data were collected. Liver regeneration was assessed in rats using computed tomography, proliferation with Ki-67, and hypoxia with pimonidazole and HIF-1α staining.

RESULTS

The rat model confirmed acceleration of regeneration in portal vein ligation and parenchymal transection as well as the portal vein hyperflow seen in patients. Additionally, tissue hypoxia was observed after portal vein ligation and parenchymal transection, while little hypoxia staining was detected after portal vein ligation. To determine if hypoxia is a consequence or an inciting stimulus of rapid liver regeneration, we used a prolyl-hydroxylase blocker to activate hypoxia signaling pathways in the slow model. This clearly accelerated slow to rapid liver regeneration. Inversely, abrogation of hypoxia led to a blunting of rapid growth to slow growth. The topical application of prolyl-hydroxylase inhibitors on livers in rats induced spontaneous areas of regeneration.

CONCLUSION

This study shows that pharmacologically induced hypoxic signaling accelerates liver regeneration similar to portal vein ligation and parenchymal transection. Hypoxia is likely an accelerator of liver regeneration. Also, prolyl-hydroxylase inhibitors may be used to enhance liver regeneration pharmaceutically.

Mechanistic insights of rapid liver regeneration after associating liver partition and portal vein ligation for stage hepatectomy

AIM

To highlight the potential mechanisms of regeneration in the Associating Liver Partition and Portal vein ligation for Stage hepatectomy models (clinical and experimental) that could unlock the myth behind the extraordinary capability of the liver for regeneration, which would help in designing new therapeutic options for the regenerative drive in difficult setup, such as chronic liver diseases. Associating Liver Partition and Portal vein ligation for Stage hepatectomy has been recently advocated to induce rapid future liver remnant hypertrophy that significantly shortens the time for the second stage hepatectomy. The introduction of Associating Liver Partition and Portal vein ligation for Stage hepatectomy in the surgical armamentarium of therapeutic tools for liver surgeons represented a real breakthrough in the history of liver surgery.

METHODS

A comprehensive literature review of Associating Liver Partition and Portal vein ligation for Stage hepatectomy and its utility in liver regeneration is performed.

RESULTS

Liver regeneration after Associating Liver Partition and Portal vein ligation for Stage hepatectomy is a combination of portal flow changes and parenchymal transection that generate a systematic response inducing hepatocyte proliferation and remodeling.

CONCLUSION

Associating Liver Partition and Portal vein ligation for Stage hepatectomy represents a real breakthrough in the history of liver surgery because it offers rapid liver regeneration potential that facilitate resection of liver tumors that were previously though unresectable. The jury is still out though in terms of safety, efficacy and oncological outcomes. As far as Associating Liver Partition and Portal vein ligation for Stage hepatectomy -induced liver regeneration is concerned, further research on the field should focus on the role of non-parenchymal cells in liver regeneration as well as on the effect of Associating Liver Partition and Portal vein ligation for Stage hepatectomy in liver regeneration in the setup of parenchymal liver disease.

Intrahepatic Size Regulation in a Surgical Model: Liver Resection-Induced Liver Regeneration Counteracts the Local Atrophy following Simultaneous Portal Vein Ligation

BACKGROUND/AIM

Liver size regulation is based on the balance between hepatic regeneration and atrophy. To achieve a better understanding of intrahepatic size regulation, we explored the size regulation of a portally deprived liver lobe on a liver subjected to concurrent portal vein ligation (PVL) and partial hepatectomy (PHx).

MATERIALS AND METHODS

Using a surgical rat model consisting of right PVL (rPVL) plus 70% PHx, we evaluated the size regulation of liver lobes 1, 2, 3, and 7 days after the operation in terms of liver weight and hepatocyte proliferation. Portal hyperperfusion was confirmed by measuring portal flow. The portal vascular tree was visualized by injection of a contrast agent followed by CT imaging of explanted livers. Control groups consisted of 70% PHx, rPVL, and sham operation.

RESULTS

The size of the ligated right lobe increased to 1.4-fold on postoperative day 7 when subjected to rPVL + 70% PHx. The right lobe increased to 3-fold when subjected to 70% PHx alone and decreased to 0.3-fold when subjected to rPVL only. The small but significant increase in liver weight after the combined procedure was accompanied by a low proliferative response. In contrast, hepatocyte proliferation was undetectable in the right lobe undergoing atrophy after PVL only. The caudate lobe in the rPVL + 70% PHx group increased to 4.6-fold, which is significantly more than in the other groups. This increase in liver weight was paralleled by persisting portal hyperperfusion and a prolonged proliferative phase of 3 days.

CONCLUSIONS

A discontinued portal blood supply does not always result in atrophy of the ligated lobe. The concurrent regenerative stimulus induced by 70% PHx seemed to counteract the local atrophy after a simultaneously performed rPVL, leading to a low but prolonged regenerative response of the portally deprived liver lobe. This observation supports the conclusion that portal flow is not necessary for liver regeneration. The persisting portal hyperperfusion may be crucial for the specific kinetics of prolonged liver regeneration after rPVL + 70% PHx in the portally supplied caudate lobe. Both observations deserve more attention regarding the underlying mechanism in further studies.

An updated systematic review of the evolution of ALPPS and evaluation of its advantages and disadvantages in accordance with current evidence

The main obstacle to achieving an R0 resection after a major hepatectomy is inability to preserve an adequate future liver remnant (FLR) to avoid postoperative liver failure (PLF). Associating liver partition and portal vein ligation for staged hepatectomy (ALPPS) is a novel technique for resecting tumors that were previously considered unresectable, and this technique results in a vast increase in the volume of the FLR in a short period of time. However, this technique continues to provoke heated debate because of its high mortality and morbidity.The evolution of ALPPS and its advantages and disadvantages have been systematically reviewed and evaluated in accordance with current evidence. Electronic databases (PubMed and Medline) were searched for potentially relevant articles from January 2007 to January 2016.ALPPS has evolved into various modified forms. Some of these modified techniques have reduced the difficulty of the procedure and enhanced its safety. Current evidence indicates that the advantages of ALPPS are rapid hypertrophy of the FLR, the feasibility of the procedure, and a higher rate of R0 resection in comparison to other techniques. However, ALPPS is associated with worse major complications, more deaths, and early tumor recurrence.Hepatobiliary surgeons should carefully consider whether to perform ALPPS. Some modified forms of ALPPS have reduced the mortality and morbidity of the procedure, but they cannot be recommended over the original procedure currently. Portal vein embolization (PVE) is still the procedure of choice for patients with a tumor-free FLR, and ALPPS could be used as a salvage procedure when PVE fails. More persuasive evidence needs to be assembled to determine whether ALPPS or two-stage hepatectomy (TSH) is better for patients with a tumor involving the FLR. Evidence with regard to long-term oncological outcomes is still limited. More meticulous comparative studies and studies of the 5-year survival rate of ALPPS could ultimately help to determine the usefulness of ALPPS. Indications and patient selection for the procedure need to be determined.

Liver regeneration after different degrees of portal vein ligation

BACKGROUND

Selective portal vein ligation (PVL) is followed by ipsilateral atrophy and contralateral hypertrophy of the liver lobes. Although the atrophy-hypertrophy complex induced by PVL is a well-documented phenomenon, the effect of different degrees of extended portal vein occlusion on liver regeneration is not known. The aim of this study was to assess the effects of different degrees of portal occlusion on portal pressure and liver regeneration.

MATERIALS AND METHODS

Male Wistar rats (n = 96; 220-250 g) were randomized into three groups and underwent 70%, 80%, or 90% portal vein ligation, respectively. The portal pressure was measured immediately and 24, 48, 72, 120, and 168 h after PVL (n = 6/group/time point). The hepatic lobes and the spleen were weighed, and liver regeneration ratio was calculated. Changes in liver histology and the mitotic activity were assessed on hematoxylin-eosin stained slides.

RESULTS

Higher degree of portal occlusion triggered a stronger regenerative response (regeneration ratio of PVL 70%168h = 2.23 ± 0.13, PVL 80%168h = 3.11 ± 0.37, PVL 90%168h = 4.68 ± 0.48) PVL led to an immediate increase in portal pressure, the value of which changed proportionally to the mass of liver tissue deprived of portal perfusion (PVL 70%acute = 17 ± 2 mm Hg, PVL 80%acute = 19 ± 1 mm Hg, PVL 90%acute = 26 ± 4 mm Hg). Findings in histology showed necro-apoptotic lesions in the atrophic liver lobes and increased mitotic cell count in the hypertrophic lobes. The mitotic cell count of PVL 90% peaked earlier and at a significantly higher value than of PVL 70% and PVL 80% (PVL 9024h%: 96.0 ± 3.5 PVL 70%48h: 64.0 ± 2.1, PVL 80%48h: 56.3 ± 4.0). The mitotic index after 24 h showed a strong correlation with the acute portal hypertension.

CONCLUSIONS

A higher degree of portal vein occlusion leads to a greater regenerative response, presumably triggered by the proportional increase in portal pressure, which supports the role of the so-called "blood-flow" theory of PVL-triggered liver regeneration.

Biological Substrate of the Rapid Volumetric Changes Observed in the Human Liver During the Associating Liver Partition and Portal Vein Ligation for Staged Hepatectomy Approach

BACKGROUND

The associating liver partition and portal vein ligation for staged hepatectomy (ALPPS) strategy induces rapid future liver remnant (FLR) hypertrophy. Hepatocyte cellular and molecular changes associated with liver hypertrophy during ALPPS remain ill-defined in humans.

METHODS

Patients undergoing the ALPPS approach between June 2011 and October 2014 were extracted. Biopsies from the FLR were obtained during the first and second stages. Hematoxylin-eosin staining and immunohistochemical analysis for expression of the proliferating cell nuclear antigen (PCNA) and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) were performed. The proliferative index was defined as: PCNA-TUNEL ratio.

RESULTS

Eleven of 34 patients treated were studied during both stages. Median FLR hypertrophy was 104 % in 6 days, with a mean difference between preoperative and postoperative volume of 361 ml (P < 0.001). The mean hepatocyte number increased from 52.7 cells/mm(2) in the first stage to 89.6 cells/mm(2) in the second stage (P = 0.001). PCNA expression increased by 190 % between stages with a linear correlation (r = 0.58) with macroscopic hypertrophy. The proliferative index increased from -3.78 cells/mm(2) in first stage to 2.32 cells/mm(2) in the second stage (P = 0.034).

CONCLUSIONS

The results of the present study indicate that the rapid FLR volumetric increase observed in ALPPS is accompanied by histological and molecular features of hepatocyte cell proliferation.

Fluid Flow Regulation of Revascularization and Cellular Organization in a Bioengineered Liver Platform

OBJECTIVE

Modeling of human liver development, especially cellular organization and the mechanisms underlying it, is fundamental for studying liver organogenesis and congenital diseases, yet there are no reliable models that mimic these processes ex vivo.

DESIGN

Using an organ engineering approach and relevant cell lines, we designed a perfusion system that delivers discrete mechanical forces inside an acellular liver extracellular matrix scaffold to study the effects of mechanical stimulation in hepatic tissue organization.

RESULTS

We observed a fluid flow rate-dependent response in cell distribution within the liver scaffold. Next, we determined the role of nitric oxide (NO) as a mediator of fluid flow effects on endothelial cells. We observed impairment of both neovascularization and liver tissue organization in the presence of selective inhibition of endothelial NO synthase. Similar results were observed in bioengineered livers grown under static conditions.

CONCLUSION

Overall, we were able to unveil the potential central role of discrete mechanical stimulation through the NO pathway in the revascularization and cellular organization of a bioengineered liver. Last, we propose that this organ bioengineering platform can contribute significantly to the identification of physiological mechanisms of liver organogenesis and regeneration and improve our ability to bioengineer livers for transplantation.

The Bile Acid Receptor TGR5 and Liver Regeneration

BACKGROUND

Most of the literature on the bile acid (BA) membrane receptor TGR5 is dedicated to its potential role in the metabolic syndrome, through its regulatory impact on energy expenditure, insulin and GLP-1 secretion, and inflammatory processes. While the receptor was cloned in 2002, very little data are available on TGR5 functions in the normal and diseased liver. However, TGR5 is highly expressed in Kupffer cells and liver endothelial cells, and is particularly enriched in the biliary tract [cholangiocytes and gallbladder (GB) smooth muscle cells]. We recently demonstrated that TGR5 has a crucial protective impact on the liver in case of BA overload, including after partial hepatectomy.

KEY MESSAGES

TGR5-KO mice after PH exhibited periportal bile infarcts, excessive hepatic inflammation and defective adaptation of biliary composition (bicarbonate and chloride). Most importantly, TGR5-KO mice had a more hydrophobic BA pool, with more secondary BA than WT animals, suggesting that TGR5-KO bile may be harmful for the liver, mainly in situations of BA overload. As GB is both the tissue displaying the highest level of TGR5 expression and a crucial physiological site for the regulation of BA pool hydrophobicity by reducing secondary BA, we investigated whether TGR5 may control BA pool composition through an impact on GB. Preliminary data suggest that in the absence of TGR5, reduced GB filling dampens the cholecystohepatic shunt, resulting in more secondary BA, more hydrophobic BA pool and extensive liver injury in case of BA overload.

CONCLUSIONS

In the setting of BA overload, TGR5 is protective of the liver through the regulation of not only secretory and inflammatory processes, but also through the control of BA pool composition, at least in part by targeting the GB. Thereby, TGR5 appears to be crucial for protecting the regenerating liver from BA overload.

Clinical implications of advances in liver regeneration

Remarkable advances have been made recently in the area of liver regeneration. Even though liver regeneration after liver resection has been widely researched, new clinical applications have provided a better understanding of the process. Hepatic damage induces a process of regeneration that rarely occurs in normal undamaged liver. Many studies have concentrated on the mechanism of hepatocyte regeneration following liver damage. High mortality is usual in patients with terminal liver failure. Patients die when the regenerative process is unable to balance loss due to liver damage. During disease progression, cellular adaptations take place and the organ microenvironment changes. Portal vein embolization and the associating liver partition and portal vein ligation for staged hepatectomy are relatively recent techniques exploiting the remarkable progress in understanding liver regeneration. Living donor liver transplantation is one of the most significant clinical outcomes of research on liver regeneration. Another major clinical field involving liver regeneration is cell therapy using adult stem cells. The aim of this article is to provide an outline of the clinical approaches being undertaken to examine regeneration in liver diseases.

Therapeutic inhibition of prolyl hydroxylase domain-containing enzymes in surgery: putative applications and challenges

Oxygen is essential for metazoans to generate energy. Upon oxygen deprivation adaptive and protective pathways are induced, mediated by hypoxia-inducible factors (HIFs) and prolyl hydroxylase domain-containing enzymes (PHDs). Both play a pivotal role in various conditions associated with prolonged ischemia and inflammation, and are promising targets for therapeutic intervention. This review focuses on aspects of therapeutic PHD modulation in surgically relevant disease conditions such as hepatic and intestinal disorders, wound healing, innate immune responses, and tumorigenesis, and discusses the therapeutic potential and challenges of PHD inhibition in surgical patients.

Triggered liver regeneration: from experimental model to clinical implications

BACKGROUND

Major liver resection is the only therapeutic option for patients with malignant liver tumors. However, extended hepatectomy often leads to postoperative liver failure, mainly due to insufficient amounts of the remnant liver. Recently, selective portal vein occlusion (PVO) has been introduced to increase the remnant liver volume. This novel surgical technique initiated a progressive development in liver surgery, resulting in a significant increment in potential candidates for curative liver resection.

SUMMARY

The theoretical basis for this great advancement is formed by an understanding of the mechanisms of PVO-induced liver regeneration, mainly obtained from animal studies. The aim of this review is to give a comprehensive overview of the relevant animal models of PVO and to discuss the main characteristics of triggered liver regeneration, including the induced hemodynamic, morphological and functional alterations as well as the underlying molecular mechanisms, which might be of interest in both the laboratory and the clinic. Key Messages: Although basic research revealed the main characteristics of PVO-triggered liver regeneration within the last decades, several important issues regarding the regenerative process remain uncertain. To answer these open questions, additional well-designed animal experiments are needed in the future, which allow further refinement of this surgical technique.

Portal vein thrombosis after hepatectomy

BACKGROUND

Although various complications after hepatectomy have been reported, there have been no large studies on postoperative portal vein thrombosis (PVT) as a complication. This study evaluated the incidence, risk factors, and clinical outcomes of PVT after hepatectomy.

METHODS

The preoperative and postoperative clinical characteristics of patients who underwent hepatectomy were retrospectively analyzed.

RESULTS

A total of 208 patients were reviewed. The incidence of PVT after hepatectomy was 9.1 % (n = 19), including main portal vein (MPV) thrombosis (n = 7) and peripheral portal vein (PPV) thrombosis (n = 12). Patients with MPV thrombosis had a significantly higher incidence of right hepatectomy (p < 0.001), larger resection volume (p = 0.003), and longer operation time (p = 0.021) than patients without PVT (n = 189). Multivariate analysis identified right hepatectomy as a significant independent risk factor for MPV thrombosis (odds ratio 108.9; p < 0.001). Patients with PPV thrombosis had a significantly longer duration of Pringle maneuver than patients without PVT (p = 0.002). Among patients who underwent right hepatectomy, those with PVT (n = 6) had a significantly lower early liver regeneration rate than those without PVT (n = 13; p = 0.040), and those with PVT had deterioration of liver function on postoperative day 7. In all patients with MPV thrombosis who received anticoagulation therapy, PVT subsequently resolved.

CONCLUSIONS

Postoperative PVT after hepatectomy is not rare. It is closely related to delayed recovery of liver function and delayed liver regeneration.

ALPPS: challenging the concept of unresectability--a systematic review

INTRODUCTION

Hepatic resection for malignancy is limited by the amount of liver parenchyma left behind. As a result, two-staged hepatectomy and portal vein occlusion (PVO) have become part of the treatment algorithm. Associating liver partition and portal vein ligation for staged hepatectomy (ALPPS) has been recently described as a method to stimulate rapid and profound hypertrophy.

MATERIALS AND METHODS

A systematic review of the literature pertaining to ALPPS was undertaken. Peer-reviewed articles relating to portal vein ligation (PVL) and in situ split (ISS) of the parenchyma were included.

RESULTS

To date, ALPPS has been employed for a variety of primary and metastatic liver tumors. In early case series, the perioperative morbidity and mortality was unacceptably high. However with careful patient selection and improved technique, many centers have reported a 0% 90-day mortality. The benefits of ALPPS include hypertrophy of 61-93% over a median 9-14 days, 95-100% completion of the second stage, and high likelihood of R0 resection (86-100%).

DISCUSSION

ALPPS is only indicated when a two-stage hepatectomy is necessary and the future liver remnant (FLR) is deemed inadequate (<30%). Use in patients with poor functional status, or advanced age (>70 years) is cautioned. Discretion should be used when considering this in patients with pathology other than colorectal liver metastases (CRLM), especially hilar tumors requiring biliary reconstruction. Biliary ligation during the first stage and routine lymphadenectomy of the hepatoduodenal ligament should be avoided.

CONCLUSIONS

A consensus on the indications and contraindications for ALPPS and a standardized operative protocol are needed.

P2Y2 purinergic receptor activation is essential for efficient hepatocyte proliferation in response to partial hepatectomy

Extracellular nucleotides via activation of P2 purinergic receptors influence hepatocyte proliferation and liver regeneration in response to 70% partial hepatectomy (PH). Adult hepatocytes express multiple P2Y (G protein-coupled) and P2X (ligand-gated ion channels) purinergic receptor subtypes. However, the identity of key receptor subtype(s) important for efficient hepatocyte proliferation in regenerating livers remains unknown. To evaluate the impact of P2Y2 purinergic receptor-mediated signaling on hepatocyte proliferation in regenerating livers, wild-type (WT) and P2Y2 purinergic receptor knockout (P2Y2-/-) mice were subjected to 70% PH. Liver tissues were analyzed for activation of early events critical for hepatocyte priming and subsequent cell cycle progression. Our findings suggest that early activation of p42/44 ERK MAPK (5 min), early growth response-1 (Egr-1) and activator protein-1 (AP-1) DNA-binding activity (30 min), and subsequent hepatocyte proliferation (24-72 h) in response to 70% PH were impaired in P2Y2-/- mice. Interestingly, early induction of cytokines (TNF-α, IL-6) and cytokine-mediated signaling (NF-κB, STAT-3) were intact in P2Y2-/- remnant livers, uncovering the importance of cytokine-independent and nucleotide-dependent early priming events critical for subsequent hepatocyte proliferation in regenerating livers. Hepatocytes isolated from the WT and P2Y2-/- mice were treated with ATP or ATPγS for 5-120 min and 12-24 h. Extracellular ATP alone, via activation of P2Y2 purinergic receptors, was sufficient to induce ERK phosphorylation, Egr-1 protein expression, and key cyclins and cell cycle progression of hepatocytes in vitro. Collectively, these findings highlight the functional significance of P2Y2 purinergic receptor activation for efficient hepatocyte priming and proliferation in response to PH.

How does a single cell know when the liver has reached its correct size?

The liver is a multi-functional organ that regulates major physiological processes and that possesses a remarkable regeneration capacity. After loss of functional liver mass the liver grows back to its original, individual size through hepatocyte proliferation and apoptosis. How does a single hepatocyte 'know' when the organ has grown to its final size? This work considers the initial growth phase of liver regeneration after partial hepatectomy in which the mass is restored. There are strong and valid arguments that the trigger of proliferation after partial hepatectomy is mediated through the portal blood flow. It remains unclear, if either or both the concentration of metabolites in the blood or the shear stress are crucial to hepatocyte proliferation and liver size control. A cell-based mathematical model is developed that helps discriminate the effects of these two potential triggers. Analysis of the mathematical model shows that a metabolic load and a hemodynamical hypothesis imply different feedback mechanisms at the cellular scale. The predictions of the developed mathematical model are compared to experimental data in rats. The assumption that hepatocytes are able to buffer the metabolic load leads to a robustness against short-term fluctuations of the trigger which can not be achieved with a purely hemodynamical trigger.

Musculoskeletal regeneration and its implications for the treatment of tendinopathy

Tendinopathies are common muskoloskeletal injuries that lead to pain and disability. Development and pathogenesis of tendinopathy is attributed to progressive pathological changes to the structure, function, and biology of tendon. The nature of this disease state, whether acquired by acute or chronic injury, is being actively investigated. Scarring, disorganized tissue, and loss of function characterize adult tendon healing. Recent work from animal models has begun to reveal the potential for adult mammalian tendon regeneration, the replacement of diseased with innate tissue. This review discusses what is known about musculoskeletal regeneration from a molecular perspective and how these findings can be applied to tendinopathy. Non-mammalian and mammalian models are discussed with emphasis on the potential of Murphy Roths Large mice to serve as a model of adult tendon regeneration. Comparison of regeneration in non-mammals, foetal mammals and adult mammals emphasizes distinctly different contributing factors to effective regeneration.

Deficiency of the oxygen sensor PHD1 augments liver regeneration after partial hepatectomy

PURPOSE

Liver regeneration after partial hepatectomy (PH) occurs in conditions of reduced oxygen supply. HIF prolyl hydroxylase enzymes (PHD1, PHD2, and PHD3) are oxygen sensors involved in adaptive response to hypoxia. Specific functions of these PHD enzymes in liver regeneration have, however, remained enigmatic. Here, we investigated the significance of PHD1 in liver regeneration following hepatectomy.

METHODS

Liver regeneration was studied in PHD1-deficient (PHD1(-/-)) and wild type (WT) mice subjected to 80% hepatectomy. For in vitro analyses, hepatocytes were isolated from PHD1(-/-) and WT livers. Cell cycle progression was studied via FACS-based analysis of nuclear DNA profile. Transcription factor binding assays, qRT-PCR, and immunoblotting were applied to study the relevance of PHD1 downstream effectors during liver regeneration.

RESULTS

Liver regeneration was significantly enhanced in PHD1(-/-) mice compared to WT littermates. This effect was due to enhanced proliferation rather than to hypertrophy of liver cells. Cell cycle progression was significantly enhanced, and transcriptional activity of the cell cycle regulator c-Myc was increased in PHD1-deficient hepatocytes. These changes coincided with increased expression of cyclin D2, a cell cycle-promoting c-Myc target, and decreased expression of the cell cycle-delaying c-Myc target p21.

CONCLUSIONS

Loss of PHD1 enhances liver regeneration by boosting hepatocyte proliferation in a c-Myc-dependent fashion. PHD1 might, therefore, represent a potential target to facilitate liver regeneration after surgical resection.