Regional Hepatic Regeneration After Liver Resection Correlates Well with Preceding Changes in the Regional Portal Circulation in Humans

Background and Aims

While portal hemodynamics largely affects the liver regeneration after partial hepatectomy, whether the remnant liver homogeneously regenerates is unclear, especially in humans. We hypothesized that change in flow distribution varies in each remnant portal branch after liver resection in humans and the liver consequently regenerates heterogeneously.

Methods

Twenty-two patients who underwent anatomical hepatic resection preserving intact drainage veins were analyzed. Based on perioperative contrast-enhanced computed tomography, the regional hepatic regeneration in each segment was analyzed using a region growing software. The perioperative change in the distribution of blood flow in each portal branch was assessed using the computational flow dynamics technique. The correlation between the change in the portal flow distribution and the later regional hepatic regeneration was investigated.

Results

The distribution of portal blood flow in each remnant branch largely changed at 2 weeks (71–389 %). Each remnant segment also heterogeneously regenerated at 3 months (85–204 %). Meanwhile, a good correlation between the regional regeneration rate at 3 months and the relative change in the flow distribution in each circulating portal branch at 2 weeks was detected in each patient (r = 0.74–0.99).

Conclusions

After partial hepatectomy, the change in blood flow varies in each remnant portal branch and the liver heterogeneously regenerates in humans. The good correlation between the earlier change in the portal flow distribution and the later regional hepatic regeneration strongly suggests that the portal venous flow most likely regulates the non-uniform liver regeneration after hepatic resection in humans.     

Effect of remote ischemic preconditioning on hepatic microcirculation and function in a rat model of hepatic ischemia reperfusion injury

Background:

Liver transplantation involves a period of ischemia and reperfusion to the graft which leads to primary non-function and dysfunction of the liver in 5–10% of cases. Remote ischemic preconditioning (RIPC) has been shown to reduce ischemia reperfusion injury (IRI) injury to the liver and increase hepatic blood flow. We hypothesized that RIPC may directly modulate hepatic microcirculation and have investigated this using intravital microscopy.

Methods:

A rat model of liver IRI was used with 45 min of partial hepatic ischemia (70%) followed by 3 h of reperfusion. Four groups of animals (Sham, IRI, RIPC+IRI, RIPC+Sham) were studied (n= 6, each group). Intravital microscopy was used to measure red blood cell (RBC) velocity, sinusoidal perfusion, sinusoidal flow and sinusoidal diameter. Neutrophil adhesion was assessed by rhodamine labeling of neutrophils and cell death using propidium iodide.

Results:

RIPC reduced the effects of IRI by significantly increasing red blood cell velocity, sinusoidal flow and sinusoidal perfusion along with decreased neutrophil adhesion and cell death.

Conclusions:

Using intravital microscopy, this study demonstrates that RIPC modulates hepatic microcirculation to reduce the effects of IRI. HO-1 may have a key role in the modulation of hepatic microcirculation and endothelial function.     

Liver sinusoidal endothelial cell modulation upon resection and shear stress <Emphasis Type="Italic">in vitro</Emphasis>

Background  

Shear stress forces acting on liver sinusoidal endothelial cells following resection have been noted as a possible trigger in the early stages of hepatic regeneration. Thus, the morphology and gene expression of endothelial cells following partial hepatectomy or shear stress in vitro was studied.     

Insight on ALPPS – Associating Liver Partition and Portal Vein Ligation for Staged Hepatectomy – mechanisms: activation of mTOR pathway

Background

ALPPS procedure has been introduced to increase the volume of future liver remnant. The mechanisms underlying the accelerated regeneration observed with ALPPS are unknown. It was hypothesized that AMPK/mTOR is activated as an integrating pathway for metabolic signals leading to proliferation and cell growth. Our aim was to analyze increase in liver volume, proliferation parameters and expression of AMPK/mTOR pathway-related molecules in patients undergoing ALPPS.

Modulation of microcirculatory changes in the late phase of hepatic ischaemia-reperfusion injury by remote ischaemic preconditioning

Background

Remote ischaemic preconditioning (RIPC) is a novel method of protecting the liver from ischaemia–reperfusion (I–R) injury. Protective effects in the early phase (4–6 h) have been demonstrated, but no studies have focused on the late phase (24 h) of hepatic I–R. This study analysed events in the late phase of I–R following RIPC and focused on the microcirculation, inflammatory cascade and the role of cytokine-induced neutrophil chemoattractant-1 (CINC-1).

Methods

A standard animal model was used. Remote preconditioning prior to I–R was induced by intermittent limb ischaemia. Ischaemia was induced in the left and median lobes of the liver (70%). The animals were recovered after 45 min of liver ischaemia. At 24 h, the animals were re-evaluated under anaesthesia. Hepatic microcirculation, sinusoidal leukocyte adherence and hepatocellular death were assessed by intravital microscopy, hepatocellular injury by standard biochemistry and serum CINC-1 by enzyme-linked immunosorbent assay (ELISA).

Results

At 24 h post I–R, RIPC was found to have improved sinusoidal flow by increasing the sinusoidal diameter. There was no effect of preconditioning on the velocity of red blood cells, by contrast with the early phase of hepatic I–R. Remote ischaemic preconditioning significantly reduced hepatocellular injury, neutrophil-induced endothelial injury and serum CINC-1 levels.

Conclusions

Remote ischaemic preconditioning is amenable to translation into clinical practice and may improve outcomes in liver resection surgery and transplantation.     

Extracorporeal continuous portal diversion plus temporal plasmapheresis for “small-for-size” syndrome

AIM:To investigate the effect of plasmapheresis via the portal vein for"small-for-size"syndrome(SFSS)aided by extracorporeal continuous portal diversion(ECPD).METHODS:Extensive or total hepatectomy in the pig is usually adopted as a postoperative liver failure(PLF)or SFSS model.In this study,animals which underwent85%-90%hepatectomy were randomized into either the Systemic group(n=7)or the Portal group(n=7).In the Systemic group,all pigs received temporal plasmapheresis(PP)via the extracorporeal catheter circuit(systemic to systemic circulation)from 24 to 30 h posthepatectomy(PH);in the Portal group,all pigs received ECPD to divert partial portal vein flow(PVF)to the systemic circulation after hepatectomy,then converted to temporal PP from 24 to 30 h PH,and subsequently converted to ECPD again until 48 h PH.In the Portal group,the PVF was preserved at 3.0-3.3 times that of the baseline value,similar to that following 70%hepatectomy,which was regarded as the optimal PVF to the hypertrophic liver remnant.At 48 h PH,all pigs were re-opened and the portal vein pressure(PVP),PVF,and HAF(hepatic artery flow)were measured,and then diversion of the portal venous flow was terminated.After1 h the PVP,PVF,and HAF were re-measured.The portal hemodynamic changes,liver injury,liver regeneration and bacterial/lipopolysaccharide(LPS)translocation were evaluated in the two groups.RESULTS:The PVP in the Portal group was significantly lower than that in the Systemic group during the time period from 2 to 49 h PH(P<0.05).Serum alanine aminotransferase(ALT),total bilirubin(TB)and ammonia were significantly reduced in the Portal group compared with the Systemic group from 24 to 48 h PH(P<0.05).The Portal group may have attenuated sinusoidal endothelial injury and decreased the level of HA compared with the Systemic group.In the Systemic group,there was significant sinusoidal dilation,hydropic changes in hepatocytes and hemorrhage into the hepatic parenchyma,and the sinusoidal endothelial lining was partially destroyed and detac     

Phosphodiesterase-5 inhibitors have distinct effects on the hemodynamics of the liver

Background  

The NO - cGMP system plays a key role in the regulation of sinusoidal tonus and liver blood flow with phosphodiesterase-5 (PDE-5) terminating the dilatory action of cGMP. We, therefore, investigated the effects of PDE-5 inhibitors on hepatic and systemic hemodynamics in rats.     

Role of the oestrogen receptor in liver regeneration in the male rat

Partial hepatectomy in male rats results in raised serum oestrogen levels, nuclear binding of oestrogen receptor (ER) and feminization of certain aspects of hepatic metabolism. It has been proposed that these changes may have an important role in liver regeneration. The present study was performed to ascertain the effects of the oestrogen agonist diethylstilbestrol (DES), 2 mg/kg, and the oestrogen antagonist tamoxifen (TAM), 2 mg/kg, on liver regeneration induced by partial hepatectomy in the male rat. Regenerative activity was determined by incorporation of [³H]-thymidine into hepatic DNA as well as by measurement of liver remnant weight. Following partial hepatectomy, there was a trend towards an increase in liver remnant weight at 24 h in rats treated with DES (DES, 5.95 ± 1.52 g; vehicle, 4.87 ± 0.66 g; P= 0.06) though by 48 h no effect was found. Tamoxifen treatment did not significantly affect liver weight at 24 h but by 48 h there was a highly significant reduction in liver remnant weight (TAM, 5.41 ± 0.85 g; vehicle, 7.31 ± 1.43 g; P < 0.001). Neither DES nor TAM treatment influenced liver regeneration as determined by [³H]-thymidine incorporation into hepatic DNA. We conclude that pharmacologic manipulation of oestrogens does not influence the initiation of the regenerative process but that oestrogen may facilitate later phases of hepatic growth.     

Overexpression of apelin receptor (APJ/AGTRL1) on hepatic stellate cells and sinusoidal angiogenesis in human cirrhotic liver

Background  

The apelin receptor (APJ) is related to angiotensin-like-receptor 1 (AGTRL1). This study was designed to elucidate the in vivo localization and changes of APJ in cirrhotic liver, and the in vitro changes of APJ expression in cultured hepatic stellate cells (HSCs) and capillarized sinusoidal endothelial cells (SECs) activated by growth factors.     

Bone Marrow Cells Enhance Liver Regeneration After Massive Hepatectomy in Mice

Background

Recent evidence indicates that transplanted autologous bone marrow cells (BMCs) can be converted into functional liver cells. BMC therapy can improve hepatic function and increase the potential for liver regeneration in patients with serious liver damage. We investigated whether BMC therapy influenced liver regeneration after massive hepatectomy in mice.

Methods

Male C57/BL6 mice underwent 70 % hepatectomy, followed by injection of BMCs via the portal vein (PV group), BMCs via the tail vein (IV group), or saline via the portal vein (control group). Analysis of serum enzyme levels and liver histology was performed on postoperative days (POD) 1, 3, and 5.

Results

Compared with the control group, the rate of liver regeneration on POD 3 and 5 was significantly higher in the PV group, but not in the IV group. Examination of the mitotic index and Ki-67 labeling index revealed that the increased liver regeneration resulted from stimulation of DNA synthesis. On POD 3, the serum levels of interleukin (IL)-6 and hepatocyte growth factor (HGF) were significantly higher and the expression of IL-6 and HGF mRNA in the remnant liver tended to be higher in the PV group than in the control group. Histological examination showed BMCs in the liver of the PV group, as well as conversion of BMCs into liver cells.

Conclusions

Our findings indicate that the injection of BMCs via the portal vein, but not the injection of BMCs via the tail, enhances liver regeneration after massive hepatectomy in mice.     

Response of sinusoidal mouse liver cells to choline-deficient ethionine-supplemented diet

Background  

Proliferation of oval cells, the bipotent precursor cells of the liver, requires impeded proliferation and loss of hepatocytes as well as a specific micro-environment, provided by adjacent sinusoidal cells of liver. Despite their immense importance for triggering the oval cell response, cells of hepatic sinusoids are rarely investigated. To elucidate the response of sinusoidal liver cells we have employed a choline-deficient, ethionine-supplemented (CDE) diet, a common method for inducing an oval cell response in rodent liver. We have utilised selected expression markers commonly used in the past for phenotypic discrimination of oval cells and sinusoidal cells: cytokeratin, E-cadherin and M2-pyruvate kinase for oval cells; and glial fibrillary acidic protein (GFAP) was used for hepatic stellate cells (HSCs).     

Role of angiotensin‐1 receptor blockade in cirrhotic liver resection

Background: The regeneration capacity of cirrhotic livers might be affected by angiotensin‐1 (AT1) receptors located on hepatic stellate cells (HSC). The effect of AT1 receptor blockade on microcirculation, fibrosis and liver regeneration was investigated. Materials and methods: In 112 Lewis rats, cirrhosis was induced by repetitive intraperitoneal injections of CCl₄. Six hours, 3, 7 and 14 days after partial hepatectomy or sham operation, rats were sacrificed for analysis. Animals were treated with either vehicle or 5 mg/kg body weight losartan pre‐operatively and once daily after surgery by gavage. Microcirculation and portal vein flow were investigated at 6 h. The degree of cirrhosis was assessed by Azan Heidenhein staining, activation of HSC by desmin staining, apoptosis by ssDNA detection and liver regeneration by Ki‐67 staining. Changes in expression of various genes important for liver regeneration and fibrosis were analysed at 6 h and 3 days. Haemodynamic parameters and liver enzymes were monitored. Results: Losartan treatment increased sinusoidal diameter, sinusoidal blood flow and portal vein flow after partial hepatectomy (P<0.05), but not after sham operation. AT1 receptor blockade resulted in increased apoptosis early after resection. HSC activation was reduced and after 7 days, a significantly lower degree of cirrhosis in resected animals was observed. Losartan increased the proliferation of hepatocytes at late time‐points and of non‐parenchymal cells early after partial hepatectomy (P<0.05). Tumour necrosis factor (TNF)‐α was significantly upregulated at 6 h and stem cell growth factor (SCF) was downregulated at 3 days (P<0.05). Conclusion: Losartan increased hepatic blood flow, reduced HSC activation and liver fibrosis, but interfered with hepatocyte proliferation after partial hepatectomy in cirrhotic livers.     

Liver regeneration investigated in a non-human primate model (Macaca mulatta)

BACKGROUND/AIMS: An adequate model to study liver regeneration in humans is presently unavailable. We explored the feasibility of studying liver regeneration in a genetically similar species to man, the non-human primate Rhesus macaque. METHODS: Five animals were studied; two underwent 60% hepatectomy, one underwent 30% hepatectomy, and cholecystectomy alone was performed on two animals. Laparoscopic-guided or open liver biopsies were performed on days 1, 2, 7, 14, 21, 30 and 60 following all surgeries. Liver regeneration was evaluated by measuring Ki-67, proliferating cell nuclear antigen expression and mitotic index, calculating changes in the surface area of the liver remnant and assessing intrahepatic production of cytokines. RESULTS: Significant liver regeneration was induced in the animals that underwent 60% hepatectomy, peaking between days 21-30 postoperatively. Regeneration was minimal in all other animals studied. Cytokine production followed a similar pattern. Maximal liver regeneration correlated with restoration of surface area in the liver remnant. CONCLUSIONS: Sixty percent hepatectomy in a non-human primate model induced significant liver regeneration, maximizing 21-30 days following partial hepatectomy, suggesting a significant interspecies difference when compared to a rodent hepatectomy model. A partial hepatectomy model in Rhesus macaques may allow further characterization of liver regeneration in a species closer to humans.     

Liver sinusoidal endothelial cells represents an important blood clearance system in pigs

Background  

Numerous studies in rats and a few other mammalian species, including man, have shown that the sinusoidal cells constitute an important part of liver function. In the pig, however, which is frequently used in studies on liver transplantation and liver failure models, our knowledge about the function of hepatic sinusoidal cells is scarce. We have explored the scavenger function of pig liver sinusoidal endothelial cells (LSEC), a cell type that in other mammals performs vital elimination of an array of waste macromolecules from the circulation.     

Acute liver failure after amanitin poisoning: a porcine model to detect prognostic markers for liver regeneration

Purpose

Over 90 % of fatal mushroom poisoning occurs after ingestion of amanitin-containing species. This study aimed to investigate markers indicating spontaneous liver regeneration in a porcine acute liver failure (ALF) model after α-amanitin intoxication.

Methods

German landrace pigs received either 0.15 mg/kg (n = 5) α-amanitin intravenously or 0.35 mg/kg (n = 5) intraportally. Pigs were invasively monitored and kept under general anesthesia throughout the experiment. Laboratory parameters were analyzed every 8 h.

Results

ALF occurred in all animals (10/10) 41 ± 3 h after intoxication. All pigs receiving 0.35 mg/kg α-amanitin and one pig receiving 0.15 mg/kg α-amanitin died 57 ± 16 h after the primary onset of ALF. Four pigs of the 0.15 mg/kg intoxication group recovered spontaneously from ALF after 56 ± 6 h. Starting at 32 h after intoxication, significantly higher values of albumin and total plasma protein could be measured in surviving animals (p < 0.05). A significant temporary increase in the tumor necrosis factor alpha (TNF-α) plasma concentration was detected 40–80 h after intoxication in recovering animals (p < 0.05).

Conclusions

This porcine model represents a novel tool to analyse multiple aspects of liver regeneration following α-amanitin poisoning to allow early discrimination between a fatal course and survivors. Decreased albumin and total plasma protein concentrations in the early intoxication phase indicated a lethal outcome, while an increase in the TNF-α plasma concentration was identified as the earliest prognostic plasma marker detecting liver regeneration a long time before liver function was biochemically and clinically impaired.     

Sorafenib inhibits liver regeneration in rats

Background

Sorafenib is a multikinase inhibitor with antiangiogenic and antiproliferative properties, approved for the treatment of hepatocellular carcinoma. The effect of Sorafenib on liver regeneration in healthy rats was investigated.

Methods

Sixty Wistar rats received either Sorafenib (group S; 15 mg/kg) or placebo for 14 days prior to resection and until sacrifice. After a 70% partial hepatectomy, the rats were euthanized on post-operative days (POD) 2, 4 or 8. Hepatocyte proliferation was estimated by immunohistochemistry for Ki-67 antigen using stereological methods on sections prepared by systematic uniform random sampling.

Results

Seven animals (12%) died after surgery. Death rates were similar in treated rats and controls. At hepatectomy, the body weight was significantly lower in group S rats. The liver weight and regeneration rates were lower in group S rats on PODs 2, 4 and 8. Hepatocyte proliferation was significantly lower in group S animals on PODs 2 and 4. Alanine aminotransferase ALAT was significantly higher in the Sorafenib-treated group on PODs 2, 4 and 8. Alkaline phosphatase ALP and bilirubin levels were similar in the two groups, although bilirubin was elevated in group S rats on POD 8.

Conclusion

In this rat model, Sorafenib did not increase post-hepatectomy mortality, but was associated with a significant impaired liver weight gain, regeneration rates and hepatocyte proliferation.     

Mouse model of carbon tetrachloride induced liver fibrosis: Histopathological changes and expression of CD133 and epidermal growth factor

Background  

In the setting of chronic liver injury in humans, epidermal growth factor (EGF) and EGF receptor (EGFR) are up-regulated and have been proposed to have vital roles in both liver regeneration and development of hepatocellular carcinoma (HCC). Chronic liver injury also leads to hepatic stellate cell (HSC) differentiation and a novel subpopulation of HSCs which express CD133 and exhibit properties of progenitor cells has been described in rats. The carbon tetrachloride (CCl₄)-induced mouse model has been historically relied upon to study liver injury and regeneration. We exposed mice to CCl₄ to assess whether EGF and CD133+ HSCs are up-regulated in chronically injured liver.     

Early increases in plasminogen activator activity following partial hepatectomy in humans

Background  

Increases in urokinase-like plasminogen activator (uPA) activity are reported to be amongst the earliest events occurring in remnant liver following partial hepatectomy in rats, and have been proposed as a key component of the regenerative response. Remodelling of the extracellular matrix, conversion of single chain hepatocyte growth factor to the active two-chain form and a possible activation of a mitogenic signalling pathway have all been ascribed to the increased uPA activity. The present study aimed to determine whether similar early increases in uPA activity could be detected in the remnant liver following resection of metastatic tumours in surgical patients.     

Early effect of a single intravenous injection of ethanol on hepatic sinusoidal endothelial fenestrae in rabbits

Background  

It has been postulated that ethanol affects hepatic sinusoidal and perisinusoidal cells. In the current experimental study, we investigated the early effect of a single intravenous dose of ethanol on the diameter of liver sinusoidal endothelial fenestrae in New Zealand White rabbits. The diameter of fenestrae in these rabbits is similar to the diameter found in humans with healthy livers. The effect of ethanol on the size of fenestrae was studied using transmission electron microscopy, because plastic embedding provides true measures for the diameter of fenestrae.     

A vascularized model of the human liver mimics regenerative responses

Liver regeneration is a well-orchestrated process that is typically studied in animal models. Although previous animal studies have offered many insights into liver regeneration, human biology is less well understood. To this end, we developed a three-dimensional (3D) platform called structurally vascularized hepatic ensembles for analyzing regeneration (SHEAR) to model multiple aspects of human liver regeneration. SHEAR enables control over hemodynamic alterations to mimic those that occur during liver injury and regeneration and supports the administration of biochemical inputs such as cytokines and paracrine interactions with endothelial cells. We found that exposing the endothelium-lined channel to fluid flow led to increased secretion of regeneration-associated factors. Stimulation with relevant cytokines not only amplified the secretory response, but also induced cell-cycle entry of primary human hepatocytes (PHHs) embedded within the device. Further, we identified endothelial-derived mediators that are sufficient to initiate proliferation of PHHs in this context. Collectively, the data presented here underscore the importance of multicellular models that can recapitulate high-level tissue functions and demonstrate that the SHEAR device can be used to discover and validate conditions that promote human liver regeneration.

The liver possesses a unique capability to return to a constant size within a short time period after tissue loss (1–3). The most common model for studying liver regeneration is the two-thirds partial hepatectomy (PHx), which was first described in rats by Higgins in 1931 (4). During PHx, a large portion of the liver mass is resected, after which a coordinated regenerative response follows. The response involves cytokines, growth factors (5), increases in portal blood flow (6), and a dynamic interplay between hepatocytes (Heps) and nonparenchymal cells (7–9). Liver sinusoidal endothelial cells (LSECs) play a unique role by releasing paracrine-mediated growth factors (8, 10). Nonparenchymal cells are crucial for signal transduction as well as synthesis and secretion of cytokines and growth factors, which play complex regulatory roles in the process of liver regeneration. Various studies have elucidated that the IL-1R signaling pathway plays important roles in liver regeneration after acute liver failure and partial hepatectomy, although the exact mechanisms remain to be established (11). Despite the progress in elucidating which factors, pathways, and cell types participate in liver regeneration, the current model systems are largely based on observations made using rodent cells (12). While such models are plentiful, they often cannot isolate the contributions of the processes listed above, and the exact mechanisms and the interactions between the cellular identities in human liver are largely unknown. Beyond just anatomic differences, such as the presence or absence of lobation, there are also significant variations in ligand-dependent signaling pathways between rodent and human livers (13, 14). Thus, a three-dimensional (3D) model of liver regeneration that allows for paracrine interactions between human hepatocytes and human endothelial cells, and control over physiological inputs such as fluid flow would significantly improve our understanding of the process.Mechanisms mediating liver regeneration are well studied in rodent models. Using the PHx model in mice, Ding et al. showed that LSECs release angiocrine factors such as Wnt2 and hepatocyte growth factor (HGF), which augment hepatic proliferation (8, 15). Another secreted factor, prostaglandin E₂ (PGE₂), was shown to be a master regulator of liver regeneration in zebrafish (16). While these studies focused on soluble factors involved in regeneration, Lorenz et al. attempted to uncover a physiological trigger (17). They showed a correlation between increased blood flow in sinusoids and liver regeneration in mice, but were not in a position to report on how flow-dependent stimuli play a specific role in this process. Furthermore, little is known about how the regenerative process occurs in humans. Although precise media manipulations and coculture configurations have enabled the successful maintenance of human hepatocytes in vitro (18–30), these platforms do not incorporate physiological inputs such as shear stress or paracrine interactions between hepatocytes and endothelial cells that are necessary for modeling liver regeneration. Most microfluidic liver platforms that incorporate fluid flow either do not recapitulate multicellular paracrine interactions (31–33) or do not elicit human hepatocyte proliferation in response to proregenerative stimuli (34).Here we developed a microfluidic device called structurally vascularized hepatic ensembles for analyzing regeneration (SHEAR) by incorporating multiple design parameters to model the flow-dependent paracrine aspects of human liver regeneration. We first reviewed existing, published literature to identify critical aspects for liver regeneration: 1) hemodynamic alterations such as increased fluid flow, 2) biochemical inputs such as circulating cytokines that are necessary for promoting regeneration, and 3) paracrine interactions between parenchymal and nonparenchymal cells, specifically hepatocytes and endothelial cells. In order to synthesize these features into a bioinspired, functional platform, we fabricated organotypic microfluidic devices with perfusable endothelialized channels that can accommodate fluid flow changes. The lumen of the channel, which functionally represents the sinusoidal capillaries in a human liver, was embedded within an extracellular matrix (ECM) and lined with human endothelial cells. For the parenchymal component, we utilized 3D spheroids composed of primary human Heps (PHHs) and human dermal fibroblasts (HDFs), which our laboratory has previously shown to exhibit in vitro phenotypic hepatic stability in preaggregated constructs over a period of several weeks (35, 36). To mimic key aspects of regeneration, we exposed the multicellular SHEAR device to fluid flow and cytokines via perfusion of the central lumen. By quantifying secreted factors present in the flow through of the device, we delineate the effects of hemodynamic inputs such as shear stress and of biochemical inputs such as cytokines on endothelium- and hepatocyte-derived paracrine factors. Specifically, we show that stimulation by cytokines within fluid flow passing through the central channel promotes cell-cycle entry of human hepatocytes cultured within the device and leads to increased secretion of factors such as PGE₂. Using PGE₂ as a candidate regenerative factor, we show that PGE₂ is endothelium derived and also necessary for cytokine-dependent cell-cycle entry of primary human hepatocytes. Collectively, the data presented here depict the SHEAR device serving as a valuable model for gaining mechanistic insight into liver regeneration by enabling systematic deconstruction of the component inputs and can serve as a platform for discovery of factors that promote human liver regeneration.