Ischemia/reperfusion induces an increase in the hepatic portal vasoconstrictive response to endothelin-1

Human Atrial Natriuretic Peptide in Cold Storage of Donation After Circulatory Death Rat Livers: An Old but New Agent for Protecting Vascular Endothelia?

BACKGROUND

Current critical shortage of donor organs has increased the use of donation after circulatory death (DCD) livers for transplantation, despite higher risk for primary nonfunction or ischemic cholangiopathy. Human atrial natriuretic peptide (hANP) is a cardiovascular hormone that possesses protective action to vascular endothelia. We aimed to clarify the therapeutic potential of hANP in cold storage of DCD livers.

METHODS

Male Wistar rats were exposed to 30-minute warm ischemia in situ. Livers were then retrieved and cold-preserved for 6 hours with or without hANP supplementation. Functional and morphological integrity of the livers was evaluated by oxygenated ex vivo reperfusion at 37°C.

RESULTS

hANP supplementation resulted in significant reduction of portal venous pressure (12.2 ± 0.5 versus 22.5 ± 3.5 mm Hg, P < 0.001). As underlying mechanisms, hANP supplementation significantly increased tissue adenosine concentration (P = 0.008), resulting in significant upregulation of endothelial nitric oxide synthase and significant downregulation of endothelin-1 (P = 0.01 and P = 0.004 vs. the controls, respectively). Consequently, hANP significantly decreased transaminase release (P < 0.001) and increased bile production (96.2 ± 18.2 versus 36.2 ± 15.2 μL/g-liver/h, P < 0.001). Morphologically, hepatocytes and sinusoidal endothelia were both better maintained by hANP (P = 0.021). Electron microscopy also revealed that sinusoidal ultrastructures and microvilli formation in bile canaliculi were both better preserved by hANP supplementation. Silver staining also demonstrated that hANP significantly preserved reticulin fibers in Disse space (P = 0.017), representing significant protection of sinusoidal frameworks/architectures.

CONCLUSIONS

Supplementation of hANP during cold storage significantly attenuated cold ischemia/warm reperfusion injury of DCD livers.

Effects of warm ischemia and reperfusion on the liver microcirculatory phenotype of rats: underlying mechanisms and pharmacological therapy

Warm ischemia and reperfusion (WIR) causes hepatic damage and may lead to liver failure, however the mechanisms involved are largely unknown. Here we have characterized the microcirculatory status and endothelial phenotype of livers undergoing WIR, and evaluated the use of simvastatin in WIR injury prevention. Male Wistar rats received simvastatin, or vehicle, 30 min before undergoing 60 min of partial warm ischemia (70%) followed by 2 h or 24 h of reperfusion. Hepatic and systemic hemodynamics, liver injury (AST, ALT, LDH), endothelial function (vasodilatation in response to acetylcholine), KLF2 and nitric oxide pathways, oxidative stress, inflammation (neutrophil and macrophage infiltration) and cell death were evaluated. Profound microcirculatory dysfunction occurred rapidly following WIR. This was evidenced by down-regulation of the KLF2 vasoprotective pathway, impaired vasodilatory capability and endothelial activation, altogether leading to increased hepatic vascular resistance and liver inflammation, with significant leukocyte infiltration, oxidative stress and cell death. Simvastatin preserved the hepatic endothelial phenotype, and blunted the detrimental effects of WIR on liver hemodynamics and organ integrity. In conclusion, WIR-induced injury to liver sinusoidal endothelial cells is mitigated by pre-treatment with Simvastatin probably through a KLF2-dependent mechanism.

Perfusion computed tomography evaluation of partial hepatic ischemia reperfusion in a rabbit model

RATIONALE AND OBJECTIVES

An animal model of partial hepatic ischemia/reperfusion injury (I/R) has benefits for decision making and clinical management after liver transplantation or massive hepatic resection. The aim of this study was to evaluate the change in perfusion parameters after partial hepatic I/R in rabbits using multislice computed tomography perfusion imaging.

MATERIALS AND METHODS

Thirty rabbits underwent 60 minutes of left hepatic lobar ischemia followed by 0.5, 2, 6, 12, and 24 hours of reperfusion (six rabbits were used for each reperfusion interval). An additional six rabbits served as sham-operated controls. The perfusion indices of hepatic arterial perfusion, hepatic portal perfusion, total liver perfusion, and hepatic perfusion index were measured. Levels of serum aspartate transaminase and alanine transaminase and liver histopathology at different time points were also examined.

RESULTS

Hepatic microvascular flow patterns showed heterogeneity in the 6-hour, 12-hour, and 24-hour groups. Computed tomographic perfusion parameters were significantly different between infarcted liver tissue and viable liver tissue. In poorly enhancing tissues in the 6-hour, 12-hour, and 24-hour groups, hepatic portal perfusion and total liver perfusion were lower compared to the sham group, but hepatic arterial perfusion of poorly enhancing tissues significantly increased in the 6-hour group and then decreased slightly from 12 to 24 hours after reperfusion. The hepatic perfusion index was always higher compared to that of the sham group. Hepatic arterial perfusion, hepatic portal perfusion, total liver perfusion, and hepatic perfusion index in the noninfarcted areas decreased slowly from 6 to 24 hours after reperfusion. The levels of alanine transaminase and aspartate transaminase in the I/R groups significantly increased after reperfusion and were correlated with the computed tomographic perfusion indices of infarcted liver tissue.

CONCLUSIONS

Computed tomographic perfusion can dynamically monitor the pathologic processes of liver I/R and reveal the underlying microvascular disorder, improving clinical management after liver surgery.

Development of a porcine model of post-hepatectomy liver failure

BACKGROUND

The aim of this study was to develop a porcine model of post-operative liver failure (POLF) that could accurately reproduce all the neurological and metabolic parameters of the corresponding clinical syndrome that may develop after extensive liver resections.

METHODS

In our model, we induced POLF by combining extended left hepatectomy and ischemia of the small liver remnant of 150 min duration. Subsequently, the remnant liver parenchyma was reperfused and the animals were closely monitored for 24 h.

MATERIALS

Twelve Landrace pigs (weight 25-30 kg) were randomly assigned in two groups; eight of them constituted the experimental group, in which POLF was induced (POLF group, n = 8), whereas the rest of them (n = 4) were included in the control group (sham laparotomy without establishment of POLF). RESULTS (MEANS ± SD): All POLF animals gradually developed neurological and biochemical signs of liver failure including, among many other parameters, elevated intracranial pressure (24.00 ± 4.69 versus 10.17 ± 0.75, P = 0.004) and ammonia levels (633.00 ± 252.21 versus 51.50 ± 9.49, P = 0.004) compared with controls. Histopathologic evaluation of the liver at the end of the experiment demonstrated diffuse coagulative necrosis and severe architectural distortion of the hepatic parenchyma in all POLF animals.

CONCLUSION

Our surgical technique creates a reproducible porcine model of POLF which can be used to study the pathophysiology and possible therapeutic interventions in this serious complication of extensive hepatectomies.

Innate immunity of the liver microcirculation

The liver is a complex organ with a unique microcirculation and both synthetic and immune functions. Innate immune responses have been studied in response to single inflammatory mediators and several clinically relevant models of infection and injury. While standard histological techniques have been used in many models, the liver microcirculation is also amenable to in vivo examination using epifluorescent, confocal and transillumination intravital microscopy. These techniques have begun to clarify not only the molecular mechanisms but also the specific cell populations involved in the liver inflammation. In this review, we discuss the cells and mediators involved in hepatic innate immunity in simple and complex models of injury and infection, and present the view that the liver microcirculation utilizes non-classical pathways for leukocyte recruitment.

Small-for-size liver graft injury--impact on tumor behavior

The success of liver transplantation has led to an ever-increasing demand for liver grafts. Since the first successful living donor liver transplantation, this surgical innovation has been well established in children and has significantly relieved the crisis of donor organ shortage for children. However, the extension of living donor liver transplantation to adult recipients is limited by the graft volume. The major concern of adult-to-adult living donor liver transplantation is the adequate graft that can be harvested from a living donor. Small-for-size graft injury is frequently observed. To develop novel effective treatments attenuating small-for-size liver graft injury during living donor liver transplantation, it is important to explore the precise mechanism of acute phase small-for-size graft damage. Recently, a number of clinical studies and animal experiments have been conducted to investigate the possible key issues on acute phase small-for-size liver graft injury, such as mechanical injury from shear stress, subsequent inflammatory responses, and imbalance of vasoregulatory factors. This review focuses on the mechanism of small-for-size liver graft injury based on the number of clinical and experimental studies. The latest research findings of the significance of acute phase liver graft injury on late phase tumor recurrence and metastasis are also addressed.

UP-REGULATED THROMBOXANE PRODUCTION IN THE RAT LIVER WITH BILIARY OBSTRUCTION DOES NOT CONTRIBUTE TO PROMOTE HEPATIC INJURY

This study sought to determine whether in vivo inhibition of thromboxane A2 (TXA2) action contribute to attenuate hepatic damage after bile duct ligation (BDL). Male Wistar rats were assigned to sham operation or BDL. At the time of operation, infusion pump with saline, ozagrel natrium (TXA2 synthase inhibitor), or SQ29548 (TXA2 receptor antagonists) was implanted in the abdominal cavity. Plasma alanine aminotransferase, aspartate aminotransferase, hyaluronic acid, and total bilirubin levels were measured at 4 days after the operation. The levels of plasma TXB2, a stable metabolite of TXA2, were significantly increased after BDL. Gene expression of TXA2 synthase was also significantly upregulated in the liver. Nonetheless, either an inhibition of TXA2 synthesis by ozagrel natrium or a blockade of TXA2 receptor by SQ29548 has no effect in every measured parameter related to hepatic function. These results indicated that despite a highly increased production in the liver, TXA2 is not directly related to the hepatic injury in BDL rats.

Differential mechanisms of hepatic vascular dysregulation with mild vs. moderate ischemia-reperfusion

Endotoxemia produces hepatic vascular dysregulation resulting from inhibition of endothelin (ET)-stimulated NO production. Mechanisms include overexpression of caveolin-1 (Cav-1) and altered phosphorylation of endothelial nitric oxide (NO) synthase (NOS; eNOS) in sinusoidal endothelial cells. Since ischemia-reperfusion (I/R) also causes vascular dysregulation, we tested whether the mechanisms are the same. Rats were exposed to either mild (30 min) or moderate (60 min) hepatic ischemia in vivo followed by reperfusion (6 h). Livers were harvested and prepared into precision-cut liver slices for in vitro analysis of NOS activity and regulation. Both I/R injuries significantly abrogated both the ET-1 (1 microM) and the ET(B) receptor agonist (IRL-1620, 0.5 microM)-mediated stimulation of NOS activity. 30 min I/R resulted in overexpression of Cav-1 and loss of ET-stimulated phosphorylation of Ser1177 on eNOS, consistent with an inflammatory response. Sixty-minute I/R also resulted in loss of ET-stimulated Ser1177 phosphorylation, but Cav-1 expression was not altered. Moreover, expression of ET(B) receptors was significantly decreased. This suggests that the failure of ET to activate eNOS following 60-min I/R is associated with decreased protein expression consistent with ischemic injury. Thus hepatic vascular dysregulation following I/R is mediated by inflammatory mechanisms with mild I/R whereas ischemic mechanisms dominate following more severe I/R stress.

Which Gender is Better Positioned in the Process of Liver Surgery? Male or Female?

Liver surgery is a process which induces various types of stress on the liver including the total occlusion of the blood inflow, hemorrhage, massive volume reduction, and postoperative infection. Animal studies have shown a gender dimorphic response of the liver for various stresses such as ischemia/reperfusion, hemorrhage/resuscitation, hepatectomy, portal branch ligation, and endotoxemia. Most of these studies demonstrated the female liver to be more tolerant under stressful conditions than the male liver. Estrogen, which is a representative female sex hormone, may be one of the responsible factors for this gender dimorphism. The mechanism of estrogen's salutary effect includes circulatory improvement, a reduced inflammatory response, a reduced oxygen radical production, and an improved hepatic regeneration. However, the clinical evidence that supports the results of these experimental studies is still insufficient. A well-controlled prospective clinical study is necessary to clarify the role of gender or sex hormone in the process of liver surgery. This may not only lead to a deeper understanding of the liver pathophysiology, but also to the possibility of hepatoprotective therapy using sex hormone modulators. This review summarizes the current understanding of gender dimorphism in the tolerance of the liver to various hepatic stresses, which occur during the process of major liver surgery.

Possible protection of sinusoidal endothelial cells by endothelin B receptor during hepatic warm ischemia-reperfusion

PURPOSE

Endothelins (ETs) are important regulators of the hepatic microcirculation. We investigated the pure biological roles of endothelin B receptors (ETB-Rs) on hepatic warm ischemia-reperfusion (I/R) injury using ETB-R deficient spotting lethal (sl) rats.

METHODS

Homozygous (sl/sl) and wild-type (+/+) rats were exposed to 60 min of 92% partial hepatic ischemia and then were killed at 2, 6, and 24 h, and 3 and 7 days after reperfusion. We measured the serum alanine aminotransferase (ALT) levels to assess hepatocyte injury, and the serum hyaluronic acid (HA) levels and factor VIII-related antigen (FVIIIRAg) staining to assess sinusoidal endothelial cell (SEC) injury. We also measured the concentrations of ET-1 and nitrite (NO2-) and nitrate (NO3-) of liver tissue samples.

RESULTS

Although no significant difference was observed in the ALT levels, the HA levels were significantly elevated at an early stage after reperfusion in the sl/sl rats. Regarding FVIIIRAg staining, positive SECs were enhanced in the sl/sl rats. The ET-1 levels were also significantly elevated at an early stage after reperfusion in the sl/sl rats. Regarding the NO2- and NO3- levels, no significant difference was observed.

CONCLUSION

Endothelin B receptor was shown to have a protective effect on SECs through the inhibition of ET-1 during hepatic warm I/R injury.

LPS exacerbates endothelin-1 induced activation of cytosolic phospholipase A2 and thromboxane A2 production from Kupffer cells of the prefibrotic rat liver

BACKGROUND/AIMS

Thromboxane A2 (TXA2) has been suggested to play a significant role in the development of portal hypertension in fibrosis, and Kupffer cell (KC) derived TXA2 has been shown to mediate the hyperresponsiveness of the portal circulation to the vasoconstrictive actions of endothelin-1 (ET-1) during endotoxemia. The aim of this study was to determine whether the double stresses of prefibrotic changes and endotoxemia additively activate KC to increase release of TXA2 in response to ET-1, resulting in elevated portal resistance.

METHODS

One week Bile duct ligation (BDL) rats and sham-operated controls were subjected to isolated liver perfusions following LPS or saline for 6h. In a separate experiment, KC were isolated from BDL or sham rats and incubated with LPS or saline for 6h before the ET-1 treatment.

RESULTS

The double stresses of early fibrosis and LPS resulted in a greater sustained increase in portal pressure in response to ET-1 in BDL rats, and this increase correlated well with the much enhanced release of TXA2 in the perfusate. Media from the cultured KC showed significantly greater TXA2 release in response to ET-1 in BDL group than those in sham group, and LPS exacerbated this effect. Protein levels of cytosolic phospholipase A2 (cPLA2), cyclooxygenase-2, and thromboxane synthase were also significantly elevated in KC from BDL rats. ET-1 produced a marked increase in cPLA2 activation as measured by the phosphorylation of cPLA2 in KC of both BDL and sham groups. LPS greatly exacerbated the activation of cPLA2.

CONCLUSIONS

The data suggest that the double stresses additively activate KC with an upregulation of the key enzymes in the TXA2 biosynthesis and release increased amount of TXA2 via the augmented activation of cPLA2 in response to ET-1, which leads to the increased portal resistance and ultimately hepatic microcirculatory dysfunction.

Prostacyclin in sepsis: A systematic review

According to current literature, infective processes greatly modify both vascular hemodynamics and anti-oxidant properties of affected tissues, causing a change in homeostasis that regulates the correct functioning of all cells responsible for the physiological and metabolic balance of various organs. As a consequence, the response to the infection that has caused the change is also likely to be weaker and, in the case of septic shock, ineffective. In this review, we will take into consideration these mechanisms and then focus on a group of vasodilator drugs (prostacyclin and its analogs) which, though have been used for over 20 years mainly to treat obstructive vascular diseases, have such hemodynamic and anti-inflammatory properties which prevent homeostatic changes. It is obvious that prostacyclin does not definitively have anti-infective characteristics; however, in association with anti-infective drugs (antibiotics, etc.), the effectiveness of the latter appears improved, at least in some circumstances. Similarly, the fact that prostacyclin and its analogs have a cytoprotective effect on the liver and reduce the ischemia-reperfusion damage following liver transplant is not a novelty and evidence that they improve hepatic hemodynamics suggests their use in those pathologies characterized by possible reduced perfusion or ascertained ischemia of the liver.

Current Understanding of Gender Dimorphism in Hepatic Pathophysiology1

Studies have shown gender dimorphic response of the liver for various hepatic stresses including ischemia/reperfusion, hemorrhagic shock-resuscitation, hepatectomy, liver cirrhosis, endotoxemia, and chronic alcoholic consumption. The mechanisms responsible for the gender dimorphic response include differences in pro-inflammatory cytokine release, production of reactive oxygen species, and alteration in hepatic vasoregulatory action. These effects were shown to be modulated by circulating sex steroid levels. In this regard, modulation of sex steroid levels by agents/drugs has been proposed as a therapeutic option for preventing hepatic damage in various hepatic stress models. Further elucidation of precise mechanisms responsible for the gender-related differences in the hepatic pathophysiology is essential for the potential clinical application of sex hormone modulation therapy. In this article, current progress in our understanding the gender difference in the hepatic pathophysiology under the condition of hepatic stress is reviewed and discussed.

Endothelial dysfunction and activation as an expression of disease: role of prostacyclin analogs

The endothelium is now considered a real endocrine-paracrine organ, important not only as a structural barrier between the circulation and surrounding tissue, but also because it plays an essential role for local hemodynamics, releasing substances that modulate the vascular calibre and blood cell activation. Here, after a brief but detailed analysis of the importance of the endothelium in vascular homeostasis, in the control of coagulation and in the relations with the different blood cells, we will explain the concept of endothelial dysfunction (altered NO release) and activation (amplified adhesion molecule expression) in inflammatory, connective tissue and post-trasplantation diseases. Furthermore, this review will focus on the activity of prostacyclin and synthetic analogs, especially their ability to interact with the vasodilatation system and their role in modulating cell interaction by surface adhesion molecule expression, cytokines and growth factors release as well as gene transcription factors. Finally, we will consider the therapeutic role of prostacyclin analogs in the prevention and treatment of connective tissue diseases.

Estradiol's effect on portal response to endothelin-1 after trauma-hemorrhage

BACKGROUND

The fine balance between vasoconstrictors and vasodilators maintains portal circulation. Studies have shown that portal response to endothelin-1 (ET-1), a potent vasoconstrictor, is enhanced following hemorrhagic-shock, which subsequently leads to the impaired hepatic circulation and hepatic damage. Although protective effects of 17beta-estradiol (E(2)) against hepatic damage following trauma-hemorrhage have been observed, it remains unknown whether E(2) directly improves hepatic circulation. We hypothesized that the salutary effects of E(2) are mediated, at least in part, by the attenuation of portal response to ET-1 following trauma-hemorrhage.

MATERIALS AND METHODS

Male adult Sprague-Dawley rats were randomly assigned to sham operation or trauma-hemorrhage with or without in vivo E(2) treatment. Trauma-hemorrhage included midline laparotomy and approximately 90 min of hemorrhagic shock (35 mmHg), then resuscitation with four times the shed blood volume with Ringer's lactate solution over 60 min. For the E(2) treatment group, 1 mg/kg of E(2) was added to the Ringer's lactate solution. At 5 h after the end of resuscitation, the liver was isolated and perfused in vitro to measure portal pressure responses to exogenous ET-1 (60 pmol in 150 ml perfusate, bolus) with or without E(2) (1,500 pg/ml).

RESULTS

Peak portal pressure after the administration of ET-1 was significantly higher in vehicle-treated trauma-hemorrhage group compared with the sham group. This effect was significantly attenuated in the E(2) treatment group. Furthermore, E(2) treatment restored bile production and prevented hepatic damage following trauma-hemorrhage.

CONCLUSIONS

The beneficial effects of estradiol observed following trauma-hemorrhage, at least partly, are caused by the attenuation of portal pressure response to increased ET-1.

REMOTE TRAUMA SENSITIZES HEPATIC MICROCIRCULATION TO ENDOTHELIN VIA CAVEOLIN INHIBITION OF eNOS ACTIVITY

This study addresses the microvascular mechanisms by which a remote, mild stress such as blunt trauma sensitizes the liver to injury. Rats received closed femur fracture (FFx), and 24 h later livers were isolated and perfused at a similar starting flow rate for assessment of vascular response to endothelin-1 (ET-1). Sinusoidal volumetric flow (QS), red blood cell velocity (VRBC), and sinusoidal diameter (Ds) were determined by intravital microscopy. Baseline portal resistance in livers from FFx rats was not changed. The FFx group showed a lower baseline VRBC (322.9 +/- 26.4 and 207.3 +/- 17.2 microm/s in sham and FFx,) and QS (28.4 +/- 4.2 and 17.6 +/- 2.1 pL/s in sham and FFx, P < 0.05). ET-1 caused a decrease in the VRBC in sham but no change after FFx. In contrast, Ds was unchanged by ET-1 in sham but decreased in FFx (10.3 +/- 0.4 to 10.7 +/- 0.5 vs. 10.6 +/- 0.4 to 9.0 +/- 0.4 microm at 10 min in sham and FFx groups, P < 0.05). The overall result of these changes was a greater decrease in sinusoidal flow in FFx compared with sham. There was no significant change in mRNA for ET-1, endothelin A (ETA) receptor, or iNOS (inducible nitric oxide synthase) in FFx compared with sham. However, endothelin B (ETB) receptor mRNA and eNOS (endothelial nitric oxide synthase) mRNA were increased in the FFx group (ETB, 54.81 +/- 8.08 in sham vs. 83.28 +/- 8.19 in FFx; eNOS, 56.11 +/- 2.53 in sham vs. 83.31 +/- 5.51 in FFx; P < 0.05) while the levels of these proteins remained unchanged. Caveolin-1 (cav-1) protein levels were elevated in FFx, and coimmunoprecipitation with both ETB and eNOS showed increased associations with these proteins, suggesting a possible inactivation of eNOS. The eNOS activity was also blunted in FFx animals in the presence of increased cav-1 expression. Taken together, these results demonstrate that remote trauma sensitizes the liver to the sinusoidal constrictor effect of ET-1. We propose that this hyperresponsiveness occurs as a result of uncoupling of the ETB receptor from eNOS activity mediated by interaction of eNOS and possibly the ETB receptor with increased caveolin-1. This vascular sensitization that occurs after FFx may contribute to the exacerbation of injury during subsequent stresses.

Role of thromboxane in producing portal hypertension following trauma-hemorrhage

Thromboxane A2 (TXA2) and endothelin-1 (ET-1) have been proposed as the important vasoconstrictors that increase portal venous resistance in paracrine or autocrine fashion. We hypothesized that the hepatic damage following trauma-hemorrhage (T-H) is induced by the impaired hepatic circulation due to the increased production of vasoconstrictors such as ET-1 and TXA2 by the liver. To test this, male Sprague-Dawley rats (n = 6/group) were subjected to trauma (i.e., midline laparotomy) and hemorrhage (35-40 mmHg for 90 min followed by fluid resuscitation) or sham operation. At 2 or 5 h after the end of resuscitation, the liver was isolated and perfused and portal inflow pressure, bile flow, and release of ET-1 and thromboxane B2 (TXB2; a stable metabolite of TXA2) into the perfusate were measured. The level of portal pressure was higher at 5 h following T-H compared with 2 h after T-H and sham. The portal pressure was inversely correlated to the amount of bile production. Furthermore, the bile flow was significantly correlated to the hepatic damage as evidenced by release of lactate dehydrogenase into the perfusate. The level of ET-1 at 5 h following T-H in the perfusate after 30 min of recirculation did not show any difference from sham. However, the levels of TXB2 in the T-H group were significantly higher than those in sham at that interval. These results indicate that the increased release of TXA2 but not ET-1 following T-H might be responsible for producing the increased portal resistance, decreased bile production, and hepatic damage.

Graft injury in relation to graft size in right lobe live donor liver transplantation: a study of hepatic sinusoidal injury in correlation with portal hemodynamics and intragraft gene expression

OBJECTIVE

To investigate the degree and mechanism of hepatic sinusoidal injury in different graft sizes in right lobe live donor liver transplantation (LDLT).

SUMMARY BACKGROUND DATA

Liver grafts from living donors are likely to be small-for-size for adult recipients. Graft injury after reperfusion is common, but the mechanism and degree of injury remain unclear. The hepatic sinusoidal injury in different graft sizes and its relationship with portal hemodynamics and intragraft gene response at the early phase after reperfusion have not been studied in right lobe LDLT.

METHODS

From May 2000 to November 2001, 40 adults receiving right lobe LDLT had portal pressure measured continuously before and after reperfusion. Liver biopsies were taken before and after reperfusion for detection of vasoregulatory genes (endothelin-1 and endothelial nitric oxide synthase) and heat shock genes (heat shock protein 70 and heme oxygenase-1), and electron microscope examination. Blood samples from the portal vein and suprahepatic inferior vena cava were taken for the measurement of plasma nitric oxide level.

RESULTS

The recipients were grouped according to the ratio of graft weight to estimated standard liver weight: group 1 (n = 10), less than 40%; group 2 (n = 21), 40% to 60%; and group 3 (n = 9), more than 60%. The portal pressures recorded after reperfusion in group 1 were significantly higher within 30 minutes of reperfusion than those in groups 2 and 3. After reperfusion, the intragraft endothelin-1 mRNA level in group 1 increased by 161% of the basal level but decreased by 31.5% and 62% of the basal level in groups 2 and 3, respectively. The intragraft mRNA level of heme oxygenase-1 in groups 1 and 2 decreased by 75.5% and 25.3% of the basal level respectively but increased by 41% of basal level in group 3. The intragraft protein level of heat shock protein 70 decreased by 50 ng/mL after reperfusion in group 1 but increased by 12.4 ng/mL and 0.6 ng/mL in groups 2 and 3, respectively. The portal vein plasma nitric oxide level decreased more significantly after reperfusion in group 1 than in group 2. Electron microscope examination of liver biopsies in group 1 showed tremendous mitochondrial swelling as well as irregular large gaps between the sinusoidal lining cells. There were two hospital deaths in group 1 and none in the other two groups.

CONCLUSIONS

Patients implanted with grafts less than 40% of standard liver weight suffered from transient portal hypertension early after reperfusion. The phenomenon was accompanied by intragraft upregulation of endothelin-1 and ultrastructural evidence of sinusoidal damage. The transient portal hypertension after reperfusion, subsequent endothelin-1 overexpression, and plasma nitric oxide level reduction, together with downregulation of heme oxygenase-1 and heat shock protein 70, may account for the small-for-size graft injury.

Potentiated hepatic microcirculatory response to endothelin-1 during polymicrobial sepsis

We conducted this study to elucidate the role of endothelins (ET-1) in mediating the hepatic microcirculatory dysfunction observed in response to sepsis. Following 24 h of cecal ligation and puncture (CLP), we performed intravital microscopy both in vivo and on isolated perfused livers. Portal resistance increased in response to ET-1 in both sham and septic rats, with no significant difference between the two in either in vivo or in isolated livers. Sinusoidal volumetric flow (Qs) was evaluated using red blood cell velocity (V(RBC)) and sinusoidal diameter (Ds) to determine microvascular hemodynamic integrity. Qs decreased in response to ET-1 in livers from CLP rats compared with sham (P < 0.05, CLP vs. sham) in both in vivo and isolated livers. In vivo infusion of ET-1 resulted in greater constriction of sinusoids in the CLP group compared with sham (P < 0.05), resulting in higher sinusoidal resistance. Microvascular hyper-responsiveness was accompanied by hepatocellular injury in CLP rats, but not in sham rats. RT-PCR was performed to measure mRNA levels of ET-1, its receptors ET(A) and ET(B), inducible and constitutive nitric oxide (NO) synthase (iNOS and eNOS, respectively), and heme oxygenase 1 (HO-1). After CLP, both ET-1 and ET(B) mRNA increased, whereas ET(A) mRNA tended to decrease, although the change was not statistically significant. Livers from CLP rats showed no significant change in levels of eNOS mRNA, but showed a significant increase in iNOS expression (13.5-fold over sham). There was no change in the level of HO-1 mRNA between sham and CLP groups. Taken together, these results suggest that sepsis sensitizes the hepatic microcirculation to ET-1. More importantly, an impaired microcirculatory flow due to ET-1 in sepsis contributes to hepatic injury. Further, localized imbalances between endothelins and NO may mediate the altered microvascular response during sepsis.

Effect of endotoxin on portal hemodynamic in rats

AIM: To study the effects of endotoxin on portal hemodynamic of normal and noncirrhotic portal hypertensive rats.

METHODS: Normal rats were intraperitonealy injected with 0.1, 0.25, 0.5, 1.0, 2.0, 4.0 mg·kg^-1 of lipopolysaccharide (LPS) respectively, portal vein ligation (PVL) and intrahepatic portal occlusion (IPO) rats as well as sham-operated rats were treated with an intraperitoneal injection of 1.0 mg·kg^-1 of LPS, the portal vein pressure (PVP), portal venous flow (PVF), inferior vena cava pressure (IVCP) and portal vein resistance (PVR) were detected 4 hours after injection.

RESULTS: PVF of the 5 groups of rats accepting intraperitoneal injection of LPS were increased from 14.0 to 18.0, 22.2, 26.2, 34.8, 39.6, 38.8 mL·min^-1 4 hours after injection of LPS (P < 0.01). PVP of the 4 groups of rats accepting more than 0.1 mg/kg·b.w of LPS was increased from 1.04 to1.25, 1.50, 1.80, 1.95, 2.05 kPa (P < 0.01). The increments of PVF and PVP were in a dose-dependent manner of LPS. PVR of the 5 groups of rats was decreased from 51 to 42, 44, 48, 45, 44, 47 kPa·min·L^-1 (P < 0.05) and no dose-dependent manner was observed. PVF of PVL, IPO and sham-operated rats increased from 22.6 to 32.8, 22.0 to 28.0, 14.0 to 34.8 mL·min^-1 (P < 0.01), and PVP increased from 1.86 to 2.24, 1.74 to 1.95, 1.04 to 1.80 kPa (P < 0.01), PVR decreased from 71 to 61, 67 to 61, 52 to 44 kPa·min·L^-1 after intraperitoneal injection of 1 mg·kg^-1 of LPS. The increments of PVF and PVP of PVL and IPO rats were significantly less than the sham-operated rats (P < 0.01), There was no significant difference between the amounts of PVR decreased in the two groups of PHT model rats and sham-operated rats (P > 0.05) after intraperitoneal injection 1 mg·kg^-1 of LPS.

CONCLUSION: Endotoxin could prompt portal hypertension of the normal and noncirrhotic portal hypertensive rats by increasing portal blood flow mainly.

Endothelin 1 impairs oxygen delivery in livers from LPS-primed animals

Endothelin 1 (ET-1) is a potent vasoactive peptide that acts at sinusoidal and extrasinusoidal sites in the liver. Sensitivity to ET-1 increases in LPS-primed animals and is associated with impaired liver microcirculation in these animals. We hypothesized that LPS priming leads to an exacerbation in the impaired oxygen delivery in response to intraportal infusion of ET-1. Rats were studied 24 h after LPS injection (1 mg/kg, i.p.). Surface PO2 was determined using a recently developed technology of O2 mapping. The baseline portal pressure was higher in LPS-primed animals (P < 0.05), and increased to'similar magnitude as sham animals after a 10-min infusion of ET-1. The resultant portal pressure remained elevated in LPS compared to sham animals. There was no significant difference in baseline mean arterial pressure, and no significant systemic response to ET-1 in either group. In contrast to the macrohemodynamic, the decrease in tissue surface PO2 in response to ET-1 infusion was potentiated by LPS treatment (increased from baseline levels 33.8+/-9 to 46.8+/-8.3 in sham; 42.3+/-9.1 to 69+/-6.5 gray scale units in LPS; P < 0.01, sham vs. LPS) at end of infusion of ET-1 for 10 min. This indicates tissue hypoxia in response to ET-1, which is exacerbated in livers from LPS-primed animals compared to sham. Frequency distribution analysis showed a shift in mode from lower intensity (higher PO2) to areas with higher fluorescent intensity ranges (lower PO2), indicating areas with shut down in perfusion in LPS-treated animals. In the whole liver, ET-1 suppressed oxygen consumption, and this response was potentiated by LPS pretreatment. We propose that ET-1 impairs oxygen delivery in the liver during endotoxemia, resulting in areas of focal hypoxia. This response is possibly due to potentiated action of ET-1 at both sinusoidal and extrasinusoidal sites in the liver during endotoxemia.

Endothelin receptor remodeling induces the portal venous hyper-response to endothelin-1 following endotoxin pretreatment

The purpose of this study was to determine the changes in endothelin (ET) receptor subtype expression and their functional significance after endotoxin pretreatment. Rats were pretreated with lipopolysaccharide (LPS) or sterile saline (control). After 24 h, liver samples were homogenized and competitive receptor binding assays were performed. There was no significant difference in ET receptor binding affinity between the control and LPS groups. However, the receptor subtype density showed a significant increase in ET(B) receptors in LPS-treated rats, whereas the amount of ET(A) receptors was almost identical between the two groups. In control, almost all ET receptors (95%) were displaced by using combined ET(A) antagonist (BQ-610) and ET(B) agonist (IRL-1620) as competitors, whereas only 80% (P < 0.05 versus control) was displaced in LPS group, raising the possibility of novel type of ET receptor expression. An infusion of ET(B) agonist (Sarafotoxin 6c, S6c) through portal vein in isolated perfused livers produced the same pressure response in both LPS and control groups; however, the portal pressure increase in response to the ET-1, which binds all ET receptors, was significantly potentiated in LPS-treated rats compared to controls. We conclude that altered regulation of ET receptors, in particular, the appearance of ET binding capacity that is not displaced by ET(A) or ET(B) competitors, may explain the hyper-response of the portal venous system to ET-1 during endotoxemia.

Cerebral blood flow velocity and inflammatory response after severe traumatic brain injury

OBJECTIVES

The cerebral blood flow velocity (CBVF) was measured by transcranial Doppler sonography in patients with severe traumatic brain injury (TBI) in order to determine, whether it depends on the posttraumatic inflammatory response.

MATERIAL AND METHODS

CBVF in both middle cerebral arteries (MCA) was recorded in 25 comatous TBI patients (male 20; female five; mean age +/- standard deviation (S.D.), 41 +/- 20 years) and correlated to the levels of interleukine-(IL) 6, IL-8 and IL-10 in corresponding CSF/plasma samples, to PaCO2 and to intracranial (ICP), mean arterial (MAP) and cranial perfusion pressure (CPP).

RESULTS

CSF IL-6 and IL-8 were clearly higher than the corresponding plasma levels (mean CSF/plasma quotient for IL-6: 159 +/- 582; for IL-8: 143 +/- 311). CBVF did not show large side-to-side differences at each examination indicating that CBFV in both MCAs was determined mostly by systemic conditions and not by severe regional abnormalities. Since all other evaluated variables including interleukines represent also systemic conditions we used the mean value (MCBFV) of both CBFVs for analysis. By stepwise regression analysis between MCBVF (mean +/- S.D., 80 +/- 26 cm/s) and the variables PaCO2 (33 +/- 4 mmHg), MAP (86 +/- 12 mmHg), ICP (20 +/- 11 mmHg), CPP (70 +/- 14 mmHg) and CSF or plasma IL-6, IL-8 and IL-10, it turned out that MCBFV correlated significantly with PaCO2 (r = 0.478; P < 0.01) and CSF IL-8 (r = -0.361; P < 0.05).

CONCLUSIONS

When CPP is adequate for brain perfusion, CBFV in large brain supplying arteries depends predominantly on PaCO2 and shows only a slight association to intrathecal IL-8 levels. For clinical interpretation of CBFV data, the inflammatory response seems to be of minor relevance.

Strategies to modulate the deleterious effects of endothelin in hepatic ischemia-reperfusion

BACKGROUND

This study evaluates whether bosentan (endothelin [ET] receptor antagonist) or preconditioning (mechanism that inhibits the postischemic ET release) could reduce the microvascular disorders and the injurious effects of tumor necrosis factor (TNF) associated with hepatic ischemia-reperfusion (I/R).

METHODS

Hepatic I/R was induced in rats and the effects of bosentan or preconditioning on the deleterious effects of ET in hepatic I/R were evaluated. Transaminase and TNF levels in plasma; edema, vascular permeability, lactate, ET, and TNF levels in liver; and edema and myeloperoxidase activity levels in lung were measured after hepatic reperfusion.

RESULTS

The administration of bosentan or the induction of preconditioning previous to I/R attenuated the increase in vascular permeability, edema and lactate levels observed in liver after I/R. However, the addition of ET before preconditioning abolished its benefits. Preconditioning prevented both the increase in hepatic TNF and its release from the liver into the systemic circulation. This resulted in an attenuation of liver and lung damage. Addition of ET or TNF to the preconditioned group abolished the benefits of preconditioning, whereas the previous inhibition of TNF release with GdCl3 in the preconditioned group pretreated with ET did not modify the effects of preconditioning. The inhibition of ET with bosentan prevented the increase of both hepatic and plasma TNF, thus attenuating the liver and lung injury, whereas TNF addition abolished the benefits of bosentan.

CONCLUSIONS

These findings suggest that both bosentan and preconditioning, by inhibition of ET could attenuate the microvascular disorders and the deleterious effect of TNF on the liver and lung elicited by hepatic I/R.