Nonligated Lobes Research Articles

Two-Stage Portal Vein Ligation Facilitates Liver Regeneration Safely in Rats with Liver Cirrhosis

Background Portal vein (PV) embolization is performed prior to extended hepatectomy for the damaged liver to increase future remnant liver volume and prevent postoperative liver failure. This study examined whether two-stage PV ligation (PVL) increased regeneration and hypertrophy of the future remnant liver compared to conventional PVL, and whether two-stage PVL was safe for damaged liver. Method We produced a cirrhotic liver rat model with perioperatively maintained fibrosis. Rats were divided into: Group A (70%PVL), ligation of left branch of PV; Group B (90%PVL), ligation of right and left branches of PV; and Group C (two-stage 90%PVL), two-stage PVL with left branch ligation of PV followed by right branch ligation 7 days later. To evaluate liver regeneration, liver weight ratios, proliferating cell nuclear antigen (PCNA) labeling index (LI), mitotic index (MI), and TdT-mediated dUTP-biotin nick end labeling (TUNEL) LI in the non-ligated caudate lobe were measured. Results Fourteen-day survival rate was 20% in Group B but 100% in Group C. TUNEL LI differed significantly between Groups A and B at 2 and 7 days postoperatively. Weight ratios were significantly higher in Group C than in Groups A and B at 14 days postoperatively. PCNA LI and MI in the non-ligated caudate lobe decreased to preoperative levels by 7 days postoperatively in Groups A and B, but remained elevated until 14 days postoperatively in Group C. Conclusion In cirrhotic liver rats, two-stage PVL avoided the lethal liver failure seen with one-stage PVL, and significantly facilitated liver regeneration more than one-stage PVL.

Autophagy Contributes to Liver Regeneration After Portal Vein Ligation in Rats.

BackgroundThis study investigated the effect of 70% portal vein ligation (PVL), a widely used procedure for inducing rapid liver regeneration, on the expression of autophagy-related proteins in non-ligated liver lobes in rats.Material/MethodsRats were subjected to either sham (n=30, major portal vein branches were exposed but kept intact) or PVL (n=30, major portal vein branches were double-ligated) operations. Liver samples were collected 12, 24, 48, 72, and 168 h after the operation. Liver volume, liver color, non-ligated liver percentage, and the expressions of light chain (LC) 3, beclin 1, and cyclin D1 in the non-ligated liver lobes were determined.ResultsWhen compared to sham rats, increased (P<0.001) growth of the non-ligated liver lobes was observed in PVL rats as early as 12 h after surgery; an increased (P≤0.001) LC3 II/I ratio was observed in the non-ligated lobes of PVL rats as early as 24 h after surgery. Increased expressions of beclin 1 (P≤0.001) and cyclin D1 (P<0.001) were observed in the non-ligated lobes of PVL rats from 12 to 72 h after surgery and from 12 to 168 h after surgery, respectively, when compared to sham rats. In the non-ligated lobes, the expressions of beclin 1 and cyclin D1 were linearly and positively correlated with the LC3 II/I ratio.ConclusionsAutophagy is activated in the non-ligated liver after PVL. Both beclin 1 and cyclin D1 are linearly and positively correlated with autophagy activity in the PVL-induced rapid liver regeneration model.

Isoform-Dependent Changes in Cytochrome P450-Mediated Drug Metabolism after Portal Vein Ligation in the Rat

Background: Surgical removal of complicated liver tumors may be realized in two stages via selective portal vein ligation, inducing the atrophy of portally ligated lobes and the compensatory hypertrophy of nonligated liver lobes. Unlike morphological changes, functional aspects such as hepatic cytochrome P450 (CYP)-mediated drug metabolism remain vaguely understood, despite its critical role in both drug biotransformation and hepatic functional analysis. Our goal was the multilevel characterization of hepatic CYP-mediated drug metabolism after portal vein ligation in the rat. Methods: Male Wistar rats (n = 24, 210–230 g) were analyzed either untreated (controls; n = 4) or 24/48/72/168/336 h (n = 4 each) following portal vein ligation affecting approximately 80% of the liver parenchyma. Besides the weights of ligated and nonligated lobes, pentobarbital (30 mg/kg)-induced sleeping time, CYP1A(2), CYP 2B(1/2), CYP2C(6/11/13), CYP3A(1) enzyme activities, and corresponding isoform mRNA expressions, as well as CYP3A1 protein expression were determined by in vivo sleeping test, CYP isoform-selective assays, polymerase chain reaction, and immunohistochemistry, respectively. Results: Portal vein ligation triggered atrophy in ligated lobes and hypertrophy nonligated lobes. Sleeping time was transiently elevated (p = 0.0451). After an initial rise, CYP1A, CYP2B, and CYP3A enzyme activities dropped until 72 h, followed by a potent increase only in the nonligated lobes, paralleled by an early (24–48 h) transcriptional activation only in nonligated lobes. CYP2C enzyme activities and mRNA levels were bilaterally rapidly decreased, showing a late reconvergence only in nonligated lobes. CYP3A1 immunohistochemistry indicated substantial differences in positivity in the early period. Conclusions: Beyond the atrophy-hypertrophy complex, portal vein ligation generated a transient suppression of global and regional drug metabolism, re-established by an adaptive, CYP isoform-dependent transcriptional response of the nonligated lobes.

Functional shift with maintained regenerative potential following portal vein ligation

Selective portal vein ligation (PVL) allows the two-stage surgical resection of primarily unresectable liver tumours by generating the atrophy and hypertrophy of portally ligated (LL) and non-ligated lobes (NLL), respectively. To evaluate critically important underlying functional alterations, present study characterised in vitro and vivo liver function in male Wistar rats (n = 106; 210–250 g) before, and 24/48/72/168/336 h after PVL. Lobe weights and volumes by magnetic resonance imaging confirmed the atrophy-hypertrophy complex. Proper expression and localization of key liver transporters (Ntcp, Bsep) and tight junction protein ZO-1 in isolated hepatocytes demonstrated constantly present viable and well-polarised cells in both lobes. In vitro taurocholate and bilirubin transport, as well as in vivo immunohistochemical Ntcp and Mrp2 expressions were bilaterally temporarily diminished, whereas LL and NLL structural acinar changes were divergent. In vivo bile and bilirubin-glucuronide excretion mirrored macroscopic changes, whereas serum bilirubin levels remained unaffected. In vivo functional imaging (indocyanine-green clearance test; 99mTc-mebrofenin hepatobiliary scintigraphy; confocal laser endomicroscopy) indicated transitionally reduced global liver uptake and -excretion. While LL functional involution was permanent, NLL uptake and excretory functions recovered excessively. Following PVL, functioning cells remain even in LL. Despite extensive bilateral morpho-functional changes, NLL functional increment restores temporary declined transport functions, emphasising liver functional assessment.

Alterations in hepatic lobar function in regenerating rat liver

BackgroundLigation of a branch of the portal vein redirects portal blood to nonligated lobes resulting in lobar hypertrophy. Although the effect of portal vein ligation on liver volume is well documented, the parallel alterations in liver function are still the subject of controversy. Our aim was to assess the time-dependent reactions of regional hepatic function to portal vein ligation by selective biliary drainage. MethodsMale Wistar rats (n = 44) underwent 80% portal vein ligation. Before the operation as well as 1, 2, 3, 5, and 7 d after circulation, morphology and function (laboratory blood test; hepatic bile flow; plasma disappearance rate of indocyanine green; and biliary indocyanine green excretion) of the liver were examined. ResultsAlthough portal vein ligation affected liver circulation and morphology to a great extent, serum albumin levels, bilirubin levels, and total hepatic bile flow did not change significantly after the operation. Nevertheless, plasma disappearance rate and biliary indocyanine green excretion indicated a temporary impairment of total liver function with the lowest value on the second day and normalization by the fifth day. Bile production and biliary indocyanine green excretion of ligated lobes decreased rapidly after the operation and remained persistently suppressed, whereas the secretory function of nonligated lobes—after a temporary decline—showed a greater increase than the weight of the lobes. ConclusionsPortal vein ligation induced temporary impairment of total liver function, followed by rapid recovery mainly by reason of increase in the function of nonligated lobes. Functional increase in nonligated lobes was more pronounced than suggested by the degree of volume gain.

NF-E2-related factor 2 promotes compensatory liver hypertrophy after portal vein branch ligation in mice

Hepatectomy is a standard therapy that allows liver cancer patients to achieve long-term survival. Preceding hepatectomy, portal vein embolization (PVE) is frequently performed to increase the remnant liver size and reduce complications. Although the clinical importance of PVE is widely accepted, molecular mechanisms by which PVE leads to compensatory hypertrophy of nonembolized lobes remain elusive. We hypothesized that NF-E2-related factor 2 (Nrf2), a master regulator of cytoprotection, promotes compensatory liver hypertrophy after PVE. To address this hypothesis, we utilized three mouse lines and the portal vein branch ligation (PVBL) technique, which primarily induces the redistribution of the portal bloodstream in liver in a manner similar to PVE. PVBL was conducted in Kelch-like ECH-associated protein 1 (Keap1) conditional knockout (Keap1-CKO) mice in which Nrf2 is constitutively activated, along with Nrf2-deficient (Nrf2-KO) mice. We found that hypertrophy of nonligated lobes after PVBL was enhanced and limited in Keap1-CKO and Nrf2-KO mice, respectively, compared to wild-type mice. In Keap1-CKO mice, Nrf2 activity was increased, consistent with transient activation of the phosphoinositide 3-kinase/protein kinase B (PI3K/Akt) pathway, and reactive hepatocyte proliferation was significantly prolonged after PVBL. Importantly, Nrf2 activation by a chemical inducer was also effective for enhancement of hypertrophy after PVBL. Nrf2 supports compensatory liver hypertrophy after PVBL. This finding is particularly intriguing, because the primary effect of PVBL is limited to the alteration of bloodstream; this effect is much milder than changes resulting from hepatectomy, in which intrahepatic bloodstream and bile production cease. Our results suggest that premedication with an Nrf2 inducer may be a promising strategy to improve the outcome of PVE; this approach expands the indication of hepatectomy to patients with poorer liver function.

Minimal portal vein stenosis is a promising preconditioning in living donor liver transplantation in porcine model

The main hindrance in promoting living donor liver transplantation remains the morbi-mortality risk for the donor. Considering the opposed remodeling influence of portal and hepatic artery flows, our working hypothesis was to identify a lobar portal vein stenosis capable of inducing a contralateral liver mass compensatory enlargement, without the downstream ipsilateral atrophic response. Twenty-four pigs entered this study. Six of them were used to establish hemodynamic changes following a progressive left portal vein (LPV) stenosis, in blood flow, pressure and vessel diameter of the LPV, main portal vein and hepatic artery. Sixteen pigs were divided into 4 groups: sham operated animals, 20% LPV stenosis, 50% LPV stenosis, and 100% LPV stenosis. Daily liver biopsies were collected until post-operative day 5 to investigate liver regeneration and atrophy (Ki67, STAT3, LC3, and activated caspase 3) according to the degree of LPV stenosis. Finally, changes in liver volumetry after 20% LPVS were investigated. A 20% LPV stenosis led to dilatation of the hepatic artery and a subsequent four-fold increase in hepatic arterial flow. Concomitantly, liver regeneration was triggered in the non-ligated lobe and the cell proliferation peak, 5 days after surgery, was comparable to that obtained after total LPV ligation. Moreover, 20% LPV stenosis preconditioning did not induce left liver atrophy contrary to 50 and 100% LPV stenosis. A 20% LPV stenosis seems to be the adequate preconditioning to get the remnant liver of living donor ready to take on graft harvesting without atrophy of the future graft.

Demonstration of Metabolic and Cellular Effects of Portal Vein Ligation Using Multi-Modal PET/MRI Measurements in Healthy Rat Liver

ObjectivesIn the early recognition of portal vein ligation (PVL) induced tumor progression, positron emission tomography and magnetic resonance imaging (PET/MRI) could improve diagnostic accuracy of conventionally used methods. It is unknown how PVL affects metabolic patterns of tumor free hepatic tissues. The aim of this preliminary study is to evaluate the effect of PVL on glucose metabolism, using PET/MRI imaging in healthy rat liver.Materials and MethodsMale Wistar rats (n = 30) underwent PVL. 2-deoxy-2-(18F)fluoro-D-glucose (FDG) PET/MRI imaging (nanoScan PET/MRI) and morphological/histological examination were performed before (Day 0) and 1, 2, 3, and 7 days after PVL. Dynamic PET data were collected and the standardized uptake values (SUV) for ligated and non-ligated liver lobes were calculated in relation to cardiac left ventricle (SUVVOI/SUVCLV) and mean liver SUV (SUVVOI/SUVLiver).ResultsPVL induced atrophy of ligated lobes, while non-ligated liver tissue showed compensatory hypertrophy. Dynamic PET scan revealed altered FDG kinetics in both ligated and non-ligated liver lobes. SUVVOI/SUVCLV significantly increased in both groups of lobes, with a maximal value at the 2nd postoperative day and returned near to the baseline 7 days after the ligation. After PVL, ligated liver lobes showed significantly higher tracer uptake compared to the non-ligated lobes (significantly higher SUVVOI/SUVLiver values were observed at postoperative day 1, 2 and 3). The homogenous tracer biodistribution observed before PVL reappeared by 7th postoperative day.ConclusionThe observed alterations in FDG uptake dynamics should be taken into account during the assessment of PET data until the PVL induced atrophic and regenerative processes are completed.

Establishment of a rat model with selective portal vein ligation

Objective To establish a c1inical relevant rat selective portal vein ligation (sPVL) model under the microscopy for evaluating its effect on liver regeneration.Methods In the sPVL group,70％ of the portal veins (the left and median lobes) were ligated,while in the sham group,these branches were separated only but not ligated.The changes of the liver functions,weight ratio of ligated and non-ligated lobes to liver weight,and the regeneration rate of the non-ligated lobes in two groups were measured.Histopathological changes of the livers were observed.Results Thirty rats were subjected to sPVL successfully.Fourteen days post-operation,the weight ratio of the non-ligated lobes to liver weight was (90.36 ±0.21)％ in sPVL group and (34.39 ±2.50)％ in sham operation group (P＜0.01).Alanine transaminase (ALT) peaked at 48th h post-operation [(454.33 ± 116.00) U/L] and returned to the preoperative value [(59.67 ±9.00) U/L] on the day 7.Serum total bilirubin and albumin levels showed no significant changes.Hematoxylin and eosin (HE) staining revealed that the size of hepatocytes in the non-ligated lobes was enlarged,the hepatic sinusoid dilated and hepatocyte regeneration was observed.Masson staining showed that collagen deposited around the central veins and portal areas of the ligated lobes.Conclusion A rat sPVL model for inducing the regeneration of remnant liver was successfully established and it was proved to be stable,reproducible and similar to human portal vein ligation/embolization in clinical cases.It would be valuable for further use in clinical relevant researches. Key words: Selective portal vein ligation ; Liver regeneration ; Model,animal

Primary liver tumor growth rate in ligated and non-ligated hepatic lobe in animal mode after portal vein ligation

Objective To evaluate tumor growth in different lobes of the liver after portal vein ligation (PVL) in a rat model of hepatocellular carcinoma.Methods Twenty-seven male rats were equally divided into 3 groups.Nine non HCC rats served as a control (group A).Hepatocellular carcinoma was induced in 18 rats (group B,C).PVL was performed in group A and group C.Sham operations were performed in group B.The hepatic lobe and tumor volume changes were tested with positron emission tomography (PET) scans in different time after PVL.Results The volume of tumors in the ligated lobes of group C were significantly larger than that of the group B after PVL,[ (54.90 ±32.17) mm3 vs (28.41 ±11.04) mm3,P＜0.05].However,there was no significant difference in the non-ligated lobes (P＞0.05 ).Conclusion PVL can progress tumor growth in the ligated lobe in the HCC animal model,but not in the non-ligated lobe. Key words: Portal vein ligation; Hepatocellular carcinoma; Positron emission tomography

Impact of portal branch ligation on tissue regeneration, microcirculatory response and microarchitecture in portal blood-deprived and undeprived liver tissue

Partial ligation of portal branches leads to atrophy of the deprived lobes and hypertrophy of the intact lobes. In this study we investigated the microcirculatory response and their consequences on tissue regeneration after left-sided portal branch ligation (PBL) in Sprague–Dawley rats. At day 1 and 3 after PBL the hepatic microcirculation was assessed by intravital microscopy (IVM). In addition histological, immunohistochemical and biochemical techniques were used to determine alterations of hepatic microarchitecture. IVM analysis of the microcirculation of the ligated hepatic lobes revealed significant alterations with a reduction in sinusoidal perfusion rate, a decrease of red blood cell velocity, an increase of sinusoidal diameter and a marked reduction in shear stress at days 1 and 3 after PBL. On the contrary, the non-ligated lobes presented with higher blood flow velocities, marked sinusoidal vasoconstriction and thus, shear stress elevation. In consequence, ligated liver lobes exhibited marked cell apoptosis and necrosis, being accompanied by massive intrahepatic leukocyte accumulation and a ~ 30% weight loss. The non-ligated liver tissue showed marked PCNA expression and thereby completely compensated weight loss. Beside full restoration of liver mass, sinusoidal blood flow was comparable in ligated and non-ligated lobes as well as in sham-treated controls. This study shows that the liver aims at constant tissue mass and blood flow, most probably for maintenance of adequate clearance function. In addition, it supports the hypothesis that shear stress plays a pivotal role in triggering liver hypertrophy in the non-ligated lobes.

Isolation and characterization of portal branch ligation-stimulated Hmga2-positive bipotent hepatic progenitor cells

Hepatic stem/progenitor cells are one of several cell sources that show promise for restoration of liver mass and function. Although hepatic progenitor cells (HPCs), including oval cells, are induced by administration of certain hepatotoxins in experimental animals, such a strategy would be inappropriate in a clinical setting. Here, we investigated the possibility of isolating HPCs in a portal branch-ligated liver model without administration of any chemical agents. A non-parenchymal cell fraction was prepared from the portal branch-ligated or non-ligated lobe, and seeded onto plates coated with laminin. Most of the cells died, but a small number were able to proliferate. These proliferating cells were cloned as portal branch ligation-stimulated hepatic cells (PBLHCs) by the limiting dilution method. The PBLHCs expressed cytokeratin19, albumin, and Hmga2. The PBLHCs exhibited metabolic functions such as detoxification of ammonium ions and synthesis of urea on Matrigel-coated plates in the presence of oncostatin M. In Matrigel mixed with type I collagen, the PBLHCs became rearranged into cystic and tubular structures. Immunohistochemical staining demonstrated the presence of Hmga2-positive cells around the interlobular bile ducts in the portal branch-ligated liver lobes. In conclusion, successful isolation of bipotent hepatic progenitor cell clones, PBLHCs, from the portal branch-ligated liver lobes of mice provides the possibility of future clinical application of portal vein ligation to induce hepatic progenitor cells.

Effect of 90 percentage portal branch ligation on liver regeneration and expression of metalloproteinase and tissue inhibitors of metalloproteinases in rats

To investigate the effect of 90% portal branch ligation on liver regeneration and expression of metalloproteinases and tissue inhibitors of metalloproteinases in rats. Ninety-six SD rats were randomly divided into Sham-PBL group and portal vein branches ligation group. The weight of both ligated and unligated lobes of liver were measured at post operation day (POD) 0.5, 1, 3, 5, 7, 14, 21 and 28. The morphological changes of the non-ligated liver lobes were observed by microscope. The expression of PCNA, MMP2, MMP9 and TIMP2 of the non-ligated liver lobes were studied by immunohistochemistry. 1) 95.8% rats survived from the ligation of 90% portal branch. Hepatic lobe at the ligated side diminished progressively after ligation, whereas the lobes of the unligated side underwent compensatory regeneration. The ratio of non-ligated lobes weight to the whole liver increased slowly within 1d, speeded up significantly during 1-5d period, increased slowly after POD5, and got the plateau stag at POD7; 2) PCNA index were markedly increased within POD 0.5-3 (P < 0.01). It reached the peak at POD5 and decreased slightly at POD7, but still higher than Sham-PBL group level, then gradually returned to normal. 3) The expression of MMP2,MMP9 and TIMP2 in the non-ligated liver lobes were markedly increased at 1d. It reached the peak at POD7 and gradually returned to normal within POD7-28. 4) The MMP2 and PCNA in liver had a positive correlation at POD 0.5, 1, 5, 7, 14. The expressions of MMP9 and PCNA had a positive correlation at POD 0.5, 1, 7, 21. The expressions of TIMP2 and PCNA had a positive correlation at POD1, 7, 14, 21. The expression of MMP2, MMP9 and TIMP2 of the non-ligated liver lobes is markedly increased at POD1. It reaches the peak at POD7, and dropped to normal level gradually. The expressions of MMP2, MMP9 and TIMP2 and PCNA were correlated in 90% portal branch Ligation rats. The expression of MMP2,MMP9 and TIMP2 may play a pivotal role in liver regeneration.

Portal vein ligation accelerates tumor growth in ligated, but not contralateral lobes

To investigate the mechanisms of liver growth and atrophy after portal vein ligation (PVL) and its effects on tumor growth. Mice were subjected to PVL, partial hepatectomy, or sham surgery. The morphological alterations, activation of transcription factors, and expression of cytokines and growth factors involved in liver regeneration were evaluated. In a separate set of experiments, murine colorectal carcinoma cells were injected via the portal vein and the effect of each operation on liver tumor growth was studied. Liver regeneration after PVL and partial hepatectomy were very similar. In ligated lobes, various cytokines, transcription factors and regulatory factors were significantly upregulated compared to non-ligated lobes after PVL. Atrophy in ligated lobes was a result of early necrosis followed by later apoptosis. Tumor growth was significantly accelerated in ligated compared to non-ligated lobes. Tumor growth was accelerated in ligated liver lobes and appeared to be a result of increased growth factor expression.

Role of Acid Sphingomyelinase of Kupffer Cells in Cholestatic Liver Injury in Mice

Kupffer cells, resident tissue macrophages of the liver, play a key role in the regulation of hepatic inflammation, hepatocyte death, and fibrosis that characterize liver diseases. However, it is controversial whether Kupffer cells promote or protect from liver injury. To explore this issue we examined the role of Kupffer cells in liver injury, cell death, regeneration, and fibrosis on cholestatic liver injury in C57BL/6 mice using a model of partial bile duct ligation (BDL), in which animals do not die and the effects of BDL can be compared between injured ligated lobes and nonligated lobes. In cholestatic liver injury, the remaining viable cells represented tolerance for tumor necrosis factor alpha (TNF-alpha)-induced hepatocyte apoptosis and regenerative features along with AKT activation. Inhibition of AKT by adenovirus expressing dominant-negative AKT abolished the survival and regenerative properties in hepatocytes. Moreover, Kupffer cell depletion by alendronate liposomes increased hepatocyte damage and the sensitivity of TNF-alpha-induced hepatocyte apoptosis in ligated lobes. Kupffer cell depletion decreased hepatocyte regeneration and liver fibrosis with reduced AKT activation. To investigate the impact of acid sphingomyelinase (ASMase) in Kupffer cells, we generated chimeric mice that contained ASMase-deficient Kupffer cells and -sufficient hepatocytes using a combination of Kupffer cell depletion, irradiation, and the transplantation of ASMase-deficient bone marrow cells. In these mice, AKT activation, the tolerance for TNF-alpha-induced apoptosis, and the regenerative responses were attenuated in hepatocytes after BDL. Kupffer cells have a protective role for hepatocyte damage and promote cell survival, liver regeneration, and fibrosis in cholestatic liver disease. Kupffer cell-derived ASMase is crucial for AKT activation of hepatocytes that is required for the survival and regenerative responses.

ESTROGEN PROMOTES HEPATIC REGENERATION VIA ACTIVATING SEROTONIN SIGNAL

The aim of this study was to determine if estrogen plays any role in the process of hepatic regeneration of nonligated lobe after portal vein branch ligation (PBL). We also investigated whether estrogen has any association with serotonin action during liver regeneration. Ovariectomized female rats with (E group) or without (non-E group) estrogen pellet were subjected to PBL on the left and middle lobes. Thereafter, the rats were killed, and blood, liver, and small intestine were sampled and analyzed. Sham animals underwent only ovariectomy and laparotomy. The E group showed a significantly greater regeneration rate than the non-E group at days 1, 2, and 7 after PBL. The activation of hepatic regeneration-related genes (such as IL-6, TNF-alpha, hepatic growth factor, c-fos, and c-myc) was also significantly higher in the E group as compared with the non-E group. Gene expression of serotonin receptor (5-HT2A) in the liver and tryptophan hydroxylase 1 in the small intestine were also up-regulated in the E group, indicating an activation of serotonin system in the E group. Additionally, total intestinal flow, portal venous flow, and hepatic arterial flow determined by fluorescent microsphere were significantly higher in the E group compared with the non-E group. Moreover, serotonin receptor antagonist (ketanserin) significantly attenuated liver regeneration rate in the E group. These results indicated that estrogen plays an important role in the process of liver regeneration after PBL. Our results also indicated that estrogen is at least partly related to the activation of serotonin system, which is also important in the process of liver regeneration.

Mechanism of liver regeneration after liver resection and portal vein embolization (ligation) is different?

Whether or not liver regeneration after portal branch embolization (PE) (ligation, PVL) in the non-embolized (ligated) lobe is by the same mechanism as regeneration in the remnant lobe after liver resection has been reviewed. Portal vein branch embolization and heat shock protein are then discussed. Tumor growth accelerated in the remnant liver after hepatectomy. In contrast, PE or PVL resulted in marked contralateral hepatic hypertrophy and significant reduction of tumor growth in the non-embolized (non-ligated) lobes. Follistatin administration significantly increased liver regeneration after hepatectomy in rats. In contrast, regeneration of non-ligated lobes after PVL was not accelerated by exogenous follistatin. Tumor growth also was not accelerated. The liver regeneration rate peaked at 48-72 h in the nonligated lobe after PVL, a delay of 24 h compared with the remnant liver after hepatectomy. In the postoperative early stage, the expression of activin betaA, betaC, and betaE mRNAs was stronger in PVL than in hepatectomy. At 72 h the expression of activin receptor type IIA mRNA reached a peak in hepatectomy, but was significantly lower in PVL. Thus, regulation of activin signaling through receptors is one of the factors determining liver regeneration after hepatectomy and PVL. These serial experimental results imply that the mechanism of liver regeneration after portal branch ligation (embolization) is different from that after hepatectomy. Heat shock protein was induced in the liver experimentally by intermittent ischemic preconditioning and could play some beneficial role in the recovery of liver function after hepatectomy, even in cirrhotic patients. When heat shock protein following right portal vein embolization in both the embolized and non-embolized hepatic lobes was investigated in clinical cases, a two to fourfold increase in HSP70 was induced in the non-embolized lobe compared with the embolized lobe. Oral administration of geranylgeranylacetone (a non-toxic HSP inducer) suppressed inflammatory responses and improved survival after 95% hepatectomy by induction of HSP70 in rats.

Does estrogen contribute to the hepatic regeneration following portal branch ligation in rats?

The aim of this study was to determine whether estrogen plays any role in the hepatic regeneration of nonligated lobe following portal branch ligation (PBL). Male rats were subjected to PBL on the left and middle lobes. Two and 7 days after PBL, the rats were killed and blood and liver samples were analyzed. Sham animals underwent only laparotomy. The serum estradiol levels were significantly elevated on day 2 following PBL and returned to normal levels on day 7. The expression of estrogen receptors (ER) in the liver evaluated by Western blotting did not show any change in the nonligated lobe compared with shams. Immunohistochemical study for ER showed a predominant ER expression in the hepatocyte nucleus in periportal area (zone 1), although there was no apparent difference in the amount and expression pattern between sham and PBL. However, chronic inhibition of ER by an ER antagonist (ICI 182,780) showed a significantly lower regeneration rate of the nonligated lobe compared with vehicle treatment. Liver regeneration-associated genes also were less activated in the ICI group. Moreover, portal venous flow, determined by fluorescent microsphere injection, was significantly lower in the ICI group compared with vehicle group. These changes correlated with the attenuated expression of endothelial nitric oxide synthase mRNA in both superior mesenteric arteries and veins. In conclusion, these results indicate that the estrogen's contribution on hepatic regeneration following PBL is at least partly mediated through maintaining mesenteric blood flow by mesenteric endothelial nitric oxide synthase upregulation rather than directly activating liver regeneration in the liver.

Systemic mediators induce fibrogenic effects in normal liver after partial bile duct ligation

Collagen production by activated hepatic stellate cells (HSCs) is a key event in liver fibrosis, and a number of factors have been characterized that trigger HSC activation and collagen production. However, it remains unclear if these factors act locally at the site of injury or also affect HSCs distant to the site of injury. A model of partial bile duct ligation (PBDL) in which fibrogenesis can be compared between the injured ligated lobe and the non-ligated lobe. After PBDL, HSCs showed an increased expression of procollagen type I alpha1 mRNA and collagen-reporter gene activity not only in the ligated lobe, but also in the non-ligated lobe, albeit at a lower level. In contrast, an increase in the number of desmin- and alpha-smooth muscle actin positive HSCs, and accumulation of inflammatory cells were observed only in the ligated lobe. Although transforming growth factor-beta (TGF-beta) mRNA was increased only in the ligated lobe, Smad2/3 were activated in the ligated and the non-ligated lobe. These data suggest that the systemic increase in profibrogenic mediators including TGF-beta induces collagen transcription in the uninjured liver. Systemic profibrogenic mediators from the injury site affect the residual non-injured liver.

Biphasic activation of liver regeneration-associated signals in an early stage after portal vein branch ligation

At an early stage in liver regeneration, a variety of factors including transcriptional factors, proinflammatory cytokines, and proto-oncogenes are activated or expressed. However, these responses are affected by surgical stress in the conventional portal vein branch ligation model (PVL). We sought to determine the net activation of early regeneration-associated signals after PVL using a newly developed non-surgical stress PVL model. Male Wistar rats were assigned into two groups, a stress-PVL (sPVL) model with laparotomy and portal vein branch ligation, and a non-stress-PVL (nsPVL) one subjected to portal vein branch ligation 1 week after laparotomy in which the effects of surgical stress were subsided. The activation of transcriptional factors and expression of immediate early genes were analyzed at an early time point (within 24h) by Western blotting and RT-PCR, respectively. A monophasic upregulation of nuclear factor-κB (NF-κB) and phosphorylated-signal transducer and activator of transcription 3 (p-STAT3) peaked at 3h after sPVL was observed. In contrast, the expression pattern of these factors was biphasic (first peak at 0.5–1h, second peak at 3–6h) in nsPVL group. The expression pattern of immediate early genes showed a similar trend between sPVL and nsPVL. cDNA array analysis for the non-ligated lobe at 2h after PVL revealed a much higher gene activation in sPVL than in nsPVL. These results indicate that previously observed activation pattern of regeneration-associated signals after PVL is significantly affected by the effect of laparotomy and our results using nsPVL model may more accurately represent liver regeneration-associated signal pattern.