The endothelin/nitric oxide balance determines small-for-size liver injury after reduced-size rat liver transplantation

Molecular profiling of postreperfusion milieu determines acute kidney injury after liver transplantation: A prospective study

Acute kidney injury (AKI) after liver transplantation (LT) is a common event, but its pathogenesis remains unclear. The aim of this prospective study is to investigate the potential relationship between postreperfusion gene expression, serum mediators, and the onset of AKI after LT. Sixty-five consecutive patients undergoing LT were included in the study. Reverse transcription polymerase chain reaction (PCR) was performed on liver biopsies. Gene expression of 23 genes involved in ischemia/reperfusion injury (IRI) was evaluated. The serum concentrations of endothelin (ET)-1 and inflammatory cytokines were analyzed. AKI after LT developed in 21 (32%) recipients (AKI group). Reverse transcription PCR of reperfusion biopsy in the AKI group showed higher expression of several genes involved in IRI compared with the non-AKI group. Fold changes in the gene expression of ET-1, interleukin (IL) 18, and tumor necrosis factor α (TNF-α) were associated with creatinine peak value. AKI patients also had significantly higher ET-1, IL18, and TNF-α postoperative serum levels. Multivariate analysis showed that ET-1 (odds ratio [OR], 16.7; 95% confidence interval [CI], 3.34-83.42; P = 0.001) and IL18 (OR, 5.27; 95% CI, 0.99-27.82, P = 0.048) serum levels on postoperative day 1 were independently predictive of AKI. Receiver operating characteristic analysis demonstrated that the combination of biomarkers ET-1+IL18 was highly predictive of AKI (area under the receiver operating characteristic curve, 0.91; 95% CI, 0.83-0.99). Early allograft dysfunction and chronic kidney disease stage ≥ 2 occurred more frequently in AKI patients. These results suggest that the graft itself, rather than intraoperative hemodynamic instability, plays a main role in AKI after LT. These data may have mechanistic and diagnostic implications for AKI after LT. Liver Transplantation 24 922-931 2018 AASLD.

Effects of heme oxygenase-1-modified bone marrow mesenchymal stem cells on microcirculation and energy metabolism following liver transplantation

AIM

To investigate the effects of heme oxygenase-1 (HO-1)-modified bone marrow mesenchymal stem cells (BMMSCs) on the microcirculation and energy metabolism of hepatic sinusoids following reduced-size liver transplantation (RLT) in a rat model.

METHODS

BMMSCs were isolated and cultured in vitro using an adherent method, and then transduced with HO-1-bearing recombinant adenovirus to construct HO-1/BMMSCs. A rat acute rejection model following 50% RLT was established using a two-cuff technique. Recipients were divided into three groups based on the treatment received: normal saline (NS), BMMSCs and HO-1/BMMSCs. Liver function was examined at six time points. The levels of endothelin-1 (ET-1), endothelial nitric-oxide synthase (eNOS), inducible nitric-oxide synthase (iNOS), nitric oxide (NO), and hyaluronic acid (HA) were detected using an enzyme-linked immunosorbent assay. The portal vein pressure (PVP) was detected by Power Lab ML880. The expressions of ET-1, iNOS, eNOS, and von Willebrand factor (vWF) protein in the transplanted liver were detected using immunohistochemistry and Western blotting. ATPase in the transplanted liver was detected by chemical colorimetry, and the ultrastructural changes were observed under a transmission electron microscope.

RESULTS

HO-1/BMMSCs could alleviate the pathological changes and rejection activity index of the transplanted liver, and improve the liver function of rats following 50% RLT, with statistically significant differences compared with those of the NS group and BMMSCs group (P < 0.05). In term of the microcirculation of hepatic sinusoids: The PVP on POD7 decreased significantly in the HO-1/BMMSCs and BMMSCs groups compared with that of the NS group (P < 0.01); HO-1/BMMSCs could inhibit the expressions of ET-1 and iNOS, increase the expressions of eNOS and inhibit amounts of NO production, and maintain the equilibrium of ET-1/NO (P < 0.05); and HO-1/BMMSCs increased the expression of vWF in hepatic sinusoidal endothelial cells (SECs), and promoted the degradation of HA, compared with those of the NS group and BMMSCs group (P < 0.05). In term of the energy metabolism of the transplanted liver, HO-1/BMMSCs repaired the damaged mitochondria, and improved the activity of mitochondrial aspartate aminotransferase (ASTm) and ATPase, compared with the other two groups (P <0.05).

CONCLUSION

HO-1/BMMSCs can improve the microcirculation of hepatic sinusoids significantly, and recover the energy metabolism of damaged hepatocytes in rats following RLT, thus protecting the transplanted liver.

Postreperfusion microcirculatory derangements after liver transplantation: Relationship to hemodynamics, serum mediators, and outcome

Despite the growing data supporting the role of microcirculation in regulating liver function, little of this knowledge has been translated into clinical practice. The aim of this study is to quantify hepatic microcirculation in vivo using sidestream dark field (SDF) imaging and correlate these findings with hepatic blood flow, hemodynamic parameters, and soluble mediators. Postreperfusion hepatic microcirculation was assessed using SDF imaging. Hepatic microcirculation measurements included functional sinusoidal density (cm/cm² ), sinusoidal diameter (μm), red blood cell velocity (μm/second), volumetric blood flow (pl/second), and flow heterogeneity (FH) index. The serum concentrations of endothelin 1 (ET-1) and other inflammatory markers were analyzed with Luminex technology. Portal venous and hepatic artery flows were measured using a flowmeter. Twenty-eight patients undergoing cadaveric liver transplantations have been included in this study. Early allograft dysfunction (EAD) occurred in 7 (25%) patients and was associated with microcirculatory dysfunction. Low arterial and portal flow, high dose of inotropes, cold ischemia time, steatosis, and high ET-1 levels were all associated with impaired microcirculation. The time interval between portal venous and hepatic arterial reperfusion significantly correlated with the changes of the liver grafts' microcirculation. EAD patients tended to have higher serum levels of ET-1 on postoperative days 1, 2, 5, and 7 (all P < 0.01). Serum levels of ET-1 correlated significantly with microcirculation parameters. In conclusion, postreperfusion hepatic microcirculation is a determinant of organ dysfunction after liver reperfusion and could be used to identify very early patients at risk of EAD. Liver Transplantation 23 527-536 2017 AASLD.

Reduced hepatic arterial perfusion impairs the recovery from focal hepatic venous outflow obstruction in liver-resected rats

BACKGROUND

Extended partial hepatectomy (PH) in patients is leading to portal hyperperfusion but reduced hepatic arterial perfusion (HAP), and is invariably causing focal hepatic venous outflow obstruction (FHVOO). We observed in a rat model that PH in combination with right median hepatic vein ligation (RMHV-L) caused confluent parenchymal necrosis interspersed with viable portal tracts in the obstructed territory and large sinusoidal vascular canals in the border zone. Lack of HAP impaired the spontaneous course of recovery in terms of enlarged parenchymal necrosis, delayed regeneration, and the absence of draining vascular canals. We aimed to investigate whether pharmacological intervention modulates the imbalance between portal venous and hepatic arterial inflow, aggravates the liver damage, and delays the recovery process after FHVOO in liver-resected rats.

METHODS

Male Lewis rats were subjected to 70% PH and RMHV-L. Molsidomine or NG-nitro-L-arginine methyl ester (L-NAME) or saline were applied daily. Hepatic damage, microcirculation, regeneration, and vascular remodeling were evaluated at postoperative days 1, 2, and 7. Animals subjected to RMHV-L only were used as "no HAP" control.

RESULTS

Significant increase of portal venous inflow with a concomitant decrease in HAP was observed in all groups after PH. Molsidomine treatment did neither affect hepatic hemodynamics nor the spontaneous recovery. In contrast, L-NAME treatment further decreased HAP which impaired hepatic microcirculation, aggravated parenchymal damage, decelerated recovery, and impaired the formation of sinusoidal canals.

CONCLUSIONS

Reduction of HAP through inhibition of nitric oxide production worsened the recovery from FHVOO. Drugs increasing HAP need to be evaluated to reverse the hyperperfusion-induced impairment of the spontaneous course after FHVOO.

Small-for-size syndrome in living-donor liver transplantation using a left lobe graft

In living-donor liver transplantation with a left lobe graft, which can reduce the burden on the donor compared to right lobe graft, the main problem is small-for-size (SFS) syndrome. SFS syndrome is a multifactorial disease that includes aspects related to the graft size, graft quality, recipient factors and even technical issues. The main pathophysiology of SFS syndrome is the sinusoidal microcirculatory disturbance induced by shear stress, which is caused by excessive portal inflow into the smaller graft. The donor age, the presence of steatosis of the graft and a poor recipient status are all risk factors for SFS syndrome. To resolve SFS syndrome, portal inflow modulation, splenectomy, splenic artery modulation and outflow modulation have been developed. It is important to establish strict criteria for managing SFS syndrome. Using pharmacological interventions and/or therapeutic approaches that promote liver regeneration could increase the adequate outcomes in SFS liver transplantation. Left lobe liver transplantation could be adopted in Western countries to help resolve the organ shortage.

Endothelin-1 receptor A blocker darusentan decreases hepatic changes and improves liver repopulation after cell transplantation in rats

Cell transplantation-induced hepatic ischemia and recruitment of vasoconstrictors (e.g., endothelin-1; Edn1) leads to clearance of transplanted cells and poses problems for liver repopulation. Therefore, we determined whether darusentan (DAR), which potently blocks Edn1 receptor type A, could benefit cell engraftment. We transplanted primary F344 rat hepatocytes with or without DAR in dipeptidyl peptidase IV-deficient rats. Analysis of microcirculatory events included hepatic ischemia, endothelial injury, including with gene expression arrays, and activations of Kupffer cells (KCs), neutrophils, or hepatic stellate cells (HSCs). The retrorsine-partial hepatectomy model was used for liver repopulation studies. Whether DAR was directly cytoprotective was examined in cultured rat hepatocytes or CFSC-8B rat HSCs. We found that DAR induced hepatic sinusoidal vasodilation, caused more transplanted cells to be deposited in liver parenchyma, and decreased hepatic ischemia and endothelial injury. This lessened perturbations in expression of endothelial biology genes, including regulators of vessel tone, inflammation, cell adhesion, or cell damage, versus drug-untreated controls. Moreover, in DAR-treated animals, cell transplantation-induced activation of KCs, albeit not of neutrophils, decreased, and fewer HSCs expressed desmin. In DAR-treated rats, improvements in cell engraftment led to greater extent of liver repopulation, compared to drug-untreated controls. In cell-culture assays, DAR did not stimulate release of cytoprotective factors, such as vascular endothelial growth factor, from HSCs. Moreover, DAR did not protect hepatocytes from tumor necrosis factor alpha- or oxidative stress-induced toxicity. Endothelin receptor A blockade in vitro did not improve engraftment of subsequently transplanted hepatocytes.

CONCLUSION

Systemic administration of DAR decreases hepatic ischemia-related events and thus indirectly improves cell engraftment and liver repopulation. This vascular mechanism may permit the development of combinatorial drug-based regimens to help optimize cell therapy.

A novel organ preservation for small partial liver transplantations in rats: venous systemic oxygen persufflation with nitric oxide gas

The prognosis for recipients of small liver grafts is poor. The aim of this study was to determine the impact of venous systemic oxygen persufflation (VSOP) with nitric oxide (NO) gas for 30% partial liver preservation and transplantation in rats. After we determined optimal NO concentration as 40 ppm in vitro with the isolated perfused rat liver model, we assessed liver injury and regeneration in vivo at 1, 3, 24 and 168 h after transplantation in the following three groups after 3 h-cold storage (n = 20 per group): control group = static storage; VSOP group = oxygen persufflation and VSOP+NO group = oxygen with NO persufflation. The liver graft persufflation was achieved with medical gas via the suprahepatic vena cava; In comparison with control group after transplantation, VSOP+NO preservation (1) increased portal circulation, (2) reduced AST and ALT release, (3) upregulated hepatic endothelial NO synthase, (4) reduced hepatocyte and bileductule damage and (5) improved liver regeneration. These results suggest that gaseous oxygen with NO persufflation is a novel and safe preservation method for small partial liver grafts, not only alleviating graft injury but also improve liver regeneration after transplantation.

Small-for-size syndrome in living donor liver transplantation

When the graft volume is too small to satisfy the recipient's metabolic demand, the recipient may thus experience small-for-size syndrome (SFSS). Because the occurrence of SFSS is determined by not only the liver graft volume but also a combination of multiple negative factors, the definitions of small-for-size graft (SFSG) and SFSS are different in each institute and at each time. In the clinical setting, surgical inflow modulation and maximizing the graft outflow are keys to overcoming SFSS. Accordingly, relatively smaller-sized grafts can be used with surgical modification and pharmacological manipulation targeting portal circulation and liver graft quality. Therefore, the focus of the SFSG issue is now shifting from how to obtain a larger graft from the living donor to how to manage the use of a smaller graft to save the recipient, considering donor safety to be a priority.

HTK-N, a modified HTK solution, decreases preservation injury in a model of microsteatotic rat liver transplantation

BACKGROUND

Ischemia/reperfusion injury is an obstacle especially in steatotic livers, including those with steatosis induced by acute toxic stress. Recently, a modified histidine-tryptophan-ketoglutarate (HTK) solution, HTK-N, has been developed. This solution contains N-acetylhistidine, amino acids, and iron chelators. This study was designed to test the effects of HTK-N on preservation injury to rat livers after acute toxic injury.

METHODS

Microvesicular steatosis was induced by a single dose of ethanol (8 g/kg BW). Livers were harvested and stored at 4 °C for 8 h with HTK or HTK-N before transplantation. Tissue and blood samples were taken at 1, 8, and 24 h after reperfusion to compare serum liver enzymes (aspartate aminotransferase, alanine aminotransferase, and lactate dehydrogenase), standard histology, and immunohistochemistry for myeloperoxidase (MPO), caspase-3, and inducible nitric oxide synthase. Survival was compared after 1 week. For statistics, Analysis of Variance and t test were used.

RESULTS

HTK-N improved survival from 12.5% in HTK to 87.5% (p < 0.05). Furthermore, liver enzymes were decreased to 2-75% of HTK values (p < 0.05). Necrosis and leukocyte infiltration and MPO, caspase-3, and iNOS expression after transplantation were decreased (p < 0.05).

CONCLUSIONS

This study demonstrates that HTK-N protects liver grafts with microvesicular steatosis caused by acute toxic injury from cold ischemic injury better than standard HTK most likely via inhibition of hypoxic injury and oxidative stress and amelioration of the inflammatory reaction occurring upon reperfusion.

Dual cytoprotective effects of splenectomy for small-for-size liver transplantation in rats

The problems associated with small-for-size liver grafts (ie, high mortality rates, postoperative complications, and acute rejection) remain critical issues in partial orthotopic liver transplantation (OLT). In association with partial OLT, splenectomy (SP) is a procedure used to reduce the portal pressure. However, the precise effects of SP on partial OLT have been unclear. In this study, using small-for-size liver grafts in rats, we examined the cytoprotective effects of SP on OLT. Liver grafts were assigned to 2 groups: a control group (OLT alone) and an SP group (OLT after SP). SP significantly increased animal survival and decreased liver damage. SP exerted the following cytoprotective effects: (1) it improved hepatic microcirculation and prevented increases in the portal pressure after OLT, (2) it suppressed the hepatic infiltration of neutrophils and macrophages through the direct elimination of splenic inflammatory cells before OLT, (3) it decreased the hepatic expression of tumor necrosis factor α and interleukin-6, (4) it attenuated sinusoidal endothelial injury, (5) it decreased plasma endothelin 1 levels and increased hepatic heme oxygenase 1 expression, (6) it suppressed hepatocellular apoptosis through the down-regulation of hepatic caspase-3 and caspase-8 activity, and (7) it increased hepatic regeneration. In conclusion, SP for small-for-size grafts exerts dual cytoprotective effects by preventing excessive portal vein hepatic inflow and eliminating splenic inflammatory cell recruitment into the liver; this in turn inhibits hepatocellular apoptosis and improves liver regeneration.

Classical and alternative activation of rat hepatic sinusoidal endothelial cells by inflammatory stimuli

The ability of rat hepatic sinusoidal endothelial cells (HSEC) to become activated in response to diverse inflammatory stimuli was analyzed. Whereas the classical macrophage activators, IFNγ and/or LPS upregulated expression of iNOS in HSEC, the alternative macrophage activators, IL-10 or IL-4+IL-13 upregulated arginase-1 and mannose receptor. Similar upregulation of iNOS and arginase-1 was observed in classically and alternatively activated Kupffer cells, respectively. Removal of inducing stimuli from the cells had no effect on expression of these markers, demonstrating that activation is persistent. Washing and incubation of IFNγ treated cells with IL-4+IL-13 resulted in decreased iNOS and increased arginase-1 expression, while washing and incubation of IL-4+IL-13 treated cells with IFNγ resulted in decreased arginase-1 and increased iNOS, indicating that classical and alternative activation of the cells is reversible. HSEC were more sensitive to phenotypic switching than Kupffer cells, suggesting greater functional plasticity. Hepatocyte viability and expression of PCNA, β-catenin and MMP-9 increased in the presence of alternatively activated HSEC. In contrast, the viability of hepatocytes pretreated for 2 h with 5 mM acetaminophen decreased in the presence of classically activated HSEC. These data demonstrate that activated HSEC can modulate hepatocyte responses following injury. The ability of hepatocytes to activate HSEC was also investigated. Co-culture of HSEC with acetaminophen-injured hepatocytes, but not control hepatocytes, increased the sensitivity of HSEC to classical and alternative activating stimuli. The capacity of HSEC to respond to phenotypic activators may represent an important mechanism by which they participate in inflammatory responses associated with hepatotoxicity.

[Small-for-size: experimental findings for liver surgery]

The characteristics of the hepatic macrocirculation, i.e., the parallel portal-venous and arterial blood supply, is of utmost relevance for liver surgery. With extended hepatectomy or transplantation of a reduced-size liver the remaining or transplanted liver tissue is overperfused because the liver fails to regulate the portal-venous inflow. This portal hyperperfusion is responsible for the initiation of liver cell proliferation but represents at the same time one of the substantial events in the pathogenesis of the small-for-size syndrome. Portal-venous hyperperfusion, the so-called hepatic arterial buffer response, which describes the semi-reciprocal relationship between the portal-venous and hepatic arterial blood flows, leads to an arterial hypoperfusion of the small-for-size liver. In this article experimental and clinical data are discussed which underline the high but so far overseen relevance of this arterial underperfusion in the development of a small-for-size syndrome.

Type of steatosis influences microcirculation and fibrogenesis in different rat strains

This study investigates the impact of rat strain on the development of nonalcoholic fatty liver disease (NAFLD) focusing on morphological features and microcirculation. Male rats of Lewis, Wistar, and Sprague Dawley (n = 6 per strain and group) were randomized into a high-fat group which was fed with a special high-fat nutrition for a 3-week period and a control group which received standard nutrition. Intravital microscopy was used for the evaluation of microcirculation and correlated to morphological changes using a fatty liver scoring system. All three strains receiving a high-fat diet developed a grade 3 steatosis (>66% liver cell steatosis). Whereas Lewis showed a solely microvesicular steatosis, Wistar developed a mixed form and Sprague Dawley showed a pure macrovesicular steatosis and the highest degree of fibrosis and hepatocyte damage. Microcirculatory results revealed that sinusoidal density was already affected by a microvesicular steatosis and decreased with increasing macrovesicular proportion (Lewis: 18%, Wistar: 31%, Sprague Dawley: 23%). The degree of steatosis correlates with reduced blood flow velocity in central veins as well as in sinusoids (Lewis: 28%, Wistar: 39%, Sprague Dawley 44%). The densities of hepatocytes and hepatic stellate cells were only impaired once macrovesicular cell steatosis (Wistar and Sprague Dawley) was present. The development of NAFLD in the rat revealed strain-specific morphological features correlating with microcirculatory changes that should be considered in further studies using these models.

Implanted adipose-derived stem cells attenuate small-for-size liver graft injury by secretion of VEGF in rats

Graft injury after small-for-size liver transplantation impairs graft function and threatens the survival of the recipients. The use of adipose-derived stem cells (ADSCs) for liver injury protection and repair is promising. Our aim was to investigate the role of vascular endothelial growth factor (VEGF) secreted by ADSCs in the treatment of small-for-size liver graft injury. Studies were performed using ADSCs with VEGF secretion blocked by RNA interference. In vitro, ADSCs prevented apoptosis of freshly isolated liver sinusoidal endothelial cells (LSECs) by secretion of VEGF. Syngeneic 35% orthotopic liver transplantation followed by implantation of syngeneic ADSCs through the portal vein system was performed using Wistar rats. We found VEGF secreted by implanted ADSCs improved graft microcirculatory disturbances, serum liver function parameters and survival. The improved microcirculatory status was also reflected by reduced hepatocellular damage, especially LSEC apoptosis and improved liver regeneration. These effects were accompanied by decreased expression of endothelin receptor type A, increased Bcl-2/Bax ratio, decreased expression of Bad and elevated proportion of phosphorylated Bad. In conclusion, implanted syngeneic ADSCs attenuated small-for-size liver graft injuries and subsequently enhanced liver regeneration in a rat 35% liver transplantation model. The VEGF secreted by implanted ADSCs played a crucial role in this process.

A critical appraisal of the hemodynamic signal driving liver regeneration

BACKGROUND

Many aspects of the signaling mechanisms involved in the initiation of hepatic regeneration are under current investigation. Nevertheless, the actual mechanisms switching liver regeneration on and off are still unknown. Hemodynamic changes in the liver following partial hepatectomy have been suggested to be a primary stimulus in triggering liver regeneration. Most of the new knowledge about the impact of hemodynamic changes on liver regeneration is both conceptually important and directly relevant to clinical problems.

PURPOSE

The purpose of this review is therefore to exclusively address the hemodynamic signal driving the liver regeneration process.

Hyperbaric oxygen therapy reduces the severity of ischaemia, preservation and reperfusion injury in a rat model of liver transplantation

BACKGROUND

  Approaches to increase organ availability for orthotopic liver transplantation (OLT) often result in the procurement of marginal livers that are more susceptible to ischaemia, preservation and reperfusion injury (IPRI).

METHODS

  The effects of post-OLT hyperbaric oxygen (HBO) therapy on IPRI in a syngeneic rat OLT model were examined at various time-points. The effects of IPRI and HBO on hepatocyte necrosis, apoptosis, proliferation, and sinusoidal morphology and ultrastructure were assessed.

RESULTS

  Post-OLT HBO therapy significantly reduced the severity of IPRI; both apoptosis [at 12 h: 6.4 ± 0.4% in controls vs. 1.6 ± 0.7% in the HBO treatment group (p < 0.001); at 48 h: 2.4 ± 0.2% in controls vs. 0.4 ± 0.1% in the HBO treatment group (p < 0.001)] and necrosis [at 12 h: 18.7 ± 1.8% in controls vs. 2.4 ± 0.4% in the HBO treatment group (p < 0.001); at 48 h: 8.5 ± 1.3% in controls vs. 3.4 ± 0.9% in the HBO treatment group (P= 0.019)] were decreased. Serum alanine transaminase was reduced [at 12 h: 1068 ± 920 IU/l in controls vs. 370 ± 63 IU/l in the HBO treatment group (P= 0.030); at 48 h: 573 ± 261 IU/l in controls vs. 160 ± 10 IU/l in the HBO treatment group (P= 0.029)]. Treatment with HBO also promoted liver regeneration [proliferation at 12 h: 4.5 ± 0.1% in controls vs. 1.0 ± 0.3% in the HBO treatment group (p < 0.001); at 48 h: 8.6 ± 0.7% in controls vs. 2.9 ± 0.2% in the HBO treatment group (p < 0.01)] and improved sinusoidal diameter and microvascular density index.

CONCLUSIONS

  Hyperbaric oxygen therapy has persistent positive effects post-OLT that may potentially transfer into clinical practice.

Role of hepatic stellate cells on graft injury after small-for-size liver transplantation

BACKGROUND AND AIM

Small-for-size grafts are prone to mechanical injury and a series of chemical injuries that are related to hemodynamic force. Hepatic stellate cells activate and trans-differentiate into contractile myofibroblast-like cells during liver injury. However, the role of hepatic stellate cells on sinusoidal microcirculation is unknown with small-for-size grafts.

METHODS

Thirty-five percent of small-for-size liver transplantation was performed with rats as donors and recipients. Endothelin-1 levels as well as hepatic stellate cells activation-related protein expression, endothelin-1 receptors, and ultrastructural changes were examined. The cellular localizations of two types of endothelin-1 receptors were detected. Furthermore, liver function and sinusoidal microcirculation were analyzed using two different selective antagonists of endothelin-1 receptor.

RESULTS

Intragraft expression of hepatic stellate cells activation-related protein such as desmin, crystallin-B and smooth muscle α-actin was upregulated as well as serum endothelin-1 levels and intragraft expression of the two endothelin receptors. The antagonist to endothelin-1 A receptor not to the endothelin-1 B receptor could attenuate microcirculatory disturbance and improve liver function.

CONCLUSIONS

Small-for-size liver transplantation displayed increased hepatic stellate cells activation and high level of endothelin-1 binding to upregulation of endothelin-1 A receptor on hepatic stellate cells, which contracted hepatic sinusoid inducing graft injury manifested as reduction of sinusoidal perfusion rate and elevation of sinusoidal blood flow.

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 CCl(4) . 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.

Regulation of hepatic blood flow: The hepatic arterial buffer response revisited

The interest in the liver dates back to ancient times when it was considered to be the seat of life processes. The liver is indeed essential to life, not only due to its complex functions in biosynthesis, metabolism and clearance, but also its dramatic role as the blood volume reservoir. Among parenchymal organs, blood flow to the liver is unique due to the dual supply from the portal vein and the hepatic artery. Knowledge of the mutual communication of both the hepatic artery and the portal vein is essential to understand hepatic physiology and pathophysiology. To distinguish the individual importance of each of these inflows in normal and abnormal states is still a challenging task and the subject of ongoing research. A central mechanism that controls and allows constancy of hepatic blood flow is the hepatic arterial buffer response. The current paper reviews the relevance of this intimate hepatic blood flow regulatory system in health and disease. We exclusively focus on the endogenous interrelationship between the hepatic arterial and portal venous inflow circuits in liver resection and transplantation, as well as inflammatory and chronic liver diseases. We do not consider the hepatic microvascular anatomy, as this has been the subject of another recent review.

Pharmacological strategies against cold ischemia reperfusion injury

IMPORTANCE OF THE FIELD

Good organ preservation is a determinant of graft outcome after revascularization. The necessity of increasing the quality of organ preservation, as well as of extending cold storage time, has made it necessary to consider the use of pharmacological additives.

AREAS COVERED IN THIS REVIEW

The complex physiopathology of cold-ischemia-reperfusion (I/R) injury--and in particular cell death, mitochondrial injury and endoplasmic reticulum stress--are reviewed. Basic principles of the formulation of the different preservation solutions are discussed.

WHAT THE READER WILL GAIN

Current strategies and new trends in static organ preservation using additives such as trimetazidine, polyethylene glycols, melatonin, trophic factors and endothelin antagonists in solution are presented and discussed. The benefits and mechanisms responsible for enhancing organ protection against I/R injury are also discussed. Graft preservation was substantially improved when additives were added to the preservation solutions.

TAKE HOME MESSAGE

Enrichment of preservation solutions by additives is clinically useful only for short periods. For longer periods of cold ischemia, the use of such additives becomes insufficient because graft function deteriorates as a result of ischemia. In such conditions, the preservation strategy should be changed by the use of machine perfusion in normothermic conditions.

Portal hyperperfusion: mechanism of injury and stimulus for regeneration in porcine small-for-size transplantation

Understanding the pathogenesis of small-for-size (SFS) syndrome is critical to expanding the applicability of partial liver transplantation. We aimed to characterize its acute presentation and association with alterations in hepatic hemodynamics, microstructure, and regeneration in a porcine model. Eighteen SFS liver transplants were performed. Donors underwent 70% hepatectomy. Partial grafts were implanted into larger recipients. Whole liver transplants were also performed (n = 6). Recipients were followed until death or for 5 days. Hemodynamics were measured, and tissue was sampled intraoperatively and at the study end. Serum was sampled regularly during follow-up. Seventeen SFS transplants and 6 whole liver transplants were included. SFS grafts represented 23.2% (19.3%-25.3%) of the recipients' standard liver volume. The survival rate was 29% and 100% in the SFS and whole liver groups, respectively. The portal venous flow, pressure gradient, and resistance were significantly higher in recipients of SFS grafts versus whole livers after portal and arterial reperfusion. Arterial flow as a percentage of the total liver blood flow was significantly lower after reperfusion in SFS grafts and remained so when measured again after 5 days. Markers of endothelial cell injury increased soon after reperfusion, and those of hepatocellular injury increased later; both predicted the appearance of either graft failure or histological recovery. Proliferative activity peaked earlier and higher among nonsurvivors in the SFS group. Surviving grafts demonstrated a slower but maintained rise in regenerative activity, although metabolic activity failed to improve. In SFS transplantation in the acute setting, portal hyperperfusion is a stimulus for regeneration but may simultaneously cause irreparable endothelial injury. This porcine model not only helps to elucidate the inciting factors in SFS pathogenesis but also offers a clinically relevant means to study its prevention.

Sinusoidal microcirculatory changes after small-for-size liver transplantation in rats

Small-for-size graft injury is characterized by portal venous hypertension and loss of intracellular homeostasis early after transplant. The long-term alteration of sinusoidal microcirculatory hemodynamic state remains unknown. A syngeneic rat orthotopic liver transplantation model was developed using small-for-size grafts (35% of recipient liver weight) or whole grafts (100% of recipient liver weight). Graft survival, portal pressure, liver function, hepatocellular apoptosis as well as morphological changes (by light microscopy and electron microscopy) were assessed. Sinusoidal microcirculatory hemodynamics was examined by intravital fluorescence microscopy. Although portal hypertension lasted only for 1 h after performance of small-for-size liver transplantation, a sustained microcirculatory disturbance was accompanied by dramatic reduction of sinusoidal perfusion rate, elevation of sinusoidal diameter as well as increase in the number of apoptotic hepatocytes during the first 7 days. These resulted in lower survival rate (50% vs. 100%, P = 0.012), higher level of liver function, and more severe morphological changes, which could induce small-for-size syndrome. In conclusion, persistent microcirculatory hemodynamic derangement during the first 7 days after reperfusion as well as transient portal hypertension is significant manifestation after small-for-size liver transplantation. Long-term microcirculation disturbance displayed as decrease of sinusoidal reperfusion area and increase of spread in functional liver mass seems to be the key factor for graft injuries.

The cytoprotective effects of addition of activated protein C into preservation solution on small-for-size grafts in rats

Small-for-size liver grafts are a serious obstacle for partial orthotopic liver transplantation. Activated protein C (APC), a potent anticoagulant serine protease, is known to have cell-protective properties due to its anti-inflammatory and antiapoptotic activities. This study was designed to examine the cytoprotective effects of a preservation solution containing APC on small-for-size liver grafts, with special attention paid to ischemia-reperfusion injury and shear stress in rats. APC exerted cytoprotective effects, as evidenced by (1) increased 7-day graft survival; (2) decreased initial portal pressure and improved hepatic microcirculation; (3) decreased levels of aminotransferase and improved histological features of hepatic ischemia-reperfusion injury; (4) suppressed infiltration of neutrophils and monocytes/macrophages; (5) reduced hepatic expression of tumor necrosis factor alpha and interleukin 6; (6) decreased serum levels of hyaluronic acid, which indicated attenuation of sinusoidal endothelial cell injury; (7) increased hepatic levels of nitric oxide via up-regulated hepatic endothelial nitric oxide synthesis expression together with down-regulated hepatic inducible nitric oxide synthase expression; (8) decreased hepatic levels of endothelin 1; and (9) reduced hepatocellular apoptosis by down-regulated caspase-8 and caspase-3 activities. These results suggest that a preservation solution containing APC is a potential novel and safe product for small-for-size liver transplantation, alleviating graft injury via anti-inflammatory and antiapoptotic effects and vasorelaxing conditions.

The hepatic microcirculation: mechanistic contributions and therapeutic targets in liver injury and repair

The complex functions of the liver in biosynthesis, metabolism, clearance, and host defense are tightly dependent on an adequate microcirculation. To guarantee hepatic homeostasis, this requires not only a sufficient nutritive perfusion and oxygen supply, but also a balanced vasomotor control and an appropriate cell-cell communication. Deteriorations of the hepatic homeostasis, as observed in ischemia/reperfusion, cold preservation and transplantation, septic organ failure, and hepatic resection-induced hyperperfusion, are associated with a high morbidity and mortality. During the last two decades, experimental studies have demonstrated that microcirculatory disorders are determinants for organ failure in these disease states. Disorders include 1) a dysregulation of the vasomotor control with a deterioration of the endothelin-nitric oxide balance, an arterial and sinusoidal constriction, and a shutdown of the microcirculation as well as 2) an overwhelming inflammatory response with microvascular leukocyte accumulation, platelet adherence, and Kupffer cell activation. Within the sequelae of events, proinflammatory mediators, such as reactive oxygen species and tumor necrosis factor-alpha, are the key players, causing the microvascular dysfunction and perfusion failure. This review covers the morphological and functional characterization of the hepatic microcirculation, the mechanistic contributions in surgical disease states, and the therapeutic targets to attenuate tissue injury and organ dysfunction. It also indicates future directions to translate the knowledge achieved from experimental studies into clinical practice. By this, the use of the recently introduced techniques to monitor the hepatic microcirculation in humans, such as near-infrared spectroscopy or orthogonal polarized spectral imaging, may allow an early initiation of treatment, which should benefit the final outcome of these critically ill patients.

Hepatic regenerative response in small-sized liver isografts in the rat

BACKGROUND

To investigate hepatic regenerative response and associated mechanisms in different-size liver grafts in the rat.

METHODS

Rat models of different-size-graft liver transplantation (whole, 50%-size, or 30%-size) were established, with a sham operation group serving as a control. Portal pressure, graft injury, interleukin 6 (IL-6), signal transducer and activator of transcription (Stat3), mitogen-activated protein kinase (MAPK), cyclin D1, and proliferating cell nuclear antigen (PCNA) were all assessed.

RESULTS

The portal pressure was significantly higher and hepatic injury more severe in the smaller sized groups than in the whole graft group, especially in the 30%-size grafts. Hepatic IL-6 and tumor necrosis factor-alpha (TNF-alpha) levels in the two smaller sized groups were significantly higher than in the whole graft group, while IL-6 levels appeared to be negatively associated with graft sizes. Downstream markers of IL-6, Stat3 and MAPK phosphorylation, cyclin D1, and PCNA expression were also markedly increased in the small-sized grafts compared with the whole grafts, and appeared to positively correlate with early measurements of portal pressure and subsequent hepatic injury.

CONCLUSION

Vigorous hepatic regeneration in small-for-size liver grafts may be associated with highly activated IL-6/Stat3 and MAPK signaling, which may in turn correlate with graft size, portal pressure, and hepatic injury.

Nitric oxide reduces organ injury and enhances regeneration of reduced-size livers by increasing hepatic arterial flow

Background

Reduced-size livers suffer from portal hyperperfusion, diminished arterial blood flow and the risk of postoperative liver injury. The aim of this experimental study was to unravel the role of nitric oxide in this setting.

Methods

Rats underwent 85 per cent partial hepatectomy and either substitution of nitric oxide with molsidomine or inhibition of nitric oxide synthase (NOS) with NG-nitro-l-arginine methyl ester. Untreated hepatectomized animals served as controls and unresected animals as the sham group.

Results

Ultrasonic flowmetry following partial hepatectomy revealed a marked increase in portal venous inflow with a concomitant decrease in hepatic arterial inflow. Nitric oxide substitution counteracted the decline in hepatic arterial inflow and caused a significantly greater increase in cell proliferation after partial hepatectomy compared with control or NOS-inhibited animals. Hepatectomized animals further profited from nitric oxide substitution, as indicated by reduced aminotransferase release and improved liver function.

Conclusion

Nitric oxide improves the postoperative course of rats with reduced-size livers by modulating hepatic macrohaemodynamics and mediating regeneration and cytoprotection, but not by reducing hepatic hyperperfusion and the accompanying sinusoidal shear stress.

Morphologic features in the regenerating liver—a comparative intravital, lightmicroscopical and ultrastructural analysis with focus on hepatic stellate cells

Different cell types play a role in the liver regeneration. The present study reveals morphological key steps of liver regeneration by correlating intravital, light, and electron microscopic with immunohistochemistry results focusing on hepatic stellate cells (HSCs). In Lewis rats, liver regeneration was induced by a 2/3-hepatectomy. Animals (n = 7 each) were killed after 0, 1, 2, 3, 4, 7, and 14 days. Morphological features were investigated by light microscopy, immunohistochemistry [alpha-smooth muscle actin (alpha-SMA), Desmin, vascular endothelial growth factor (VEGF)/VEGF receptor, Ki-67, ssDNA], intravital microscopy (sinusoid density, number of hepatocytes, and HSC), and electron microscopy focussed on cell-to-cell interactions. During liver regeneration, HSC were activated at day 3 showing a loss of autofluorescence and simultaneously an increased alpha-SMA expression and direct cell contact to hepatocytes. HSC activation was followed by increasing VEGF expression and sinusoid density. After 14 days, liver architecture and ultrastructure was restored and HSCs were deactivated showing decreased alpha-SMA expression as well as increased apoptosis and no more direct cell contact to hepatocytes. HSCs play a central role in the regenerating liver by governing angiogenesis and extracellular matrix remodeling. A direct cell contact to hepatocytes seems to be essential for HSC activation, whereas deactivation is accompanied by loosening of hepatocyte contact and increased apoptosis.