Prostanoid release of cultured liver sinusoidal endothelial cells in response to endotoxin and tumor necrosis factor. Comparison with umbilical vein endothelial cells

Tissue adaptation of CD4 T lymphocytes in homeostasis and cancer

The immune system is traditionally classified as a defense system that can discriminate between self and non-self or dangerous and non-dangerous situations, unleashing a tolerogenic reaction or immune response. These activities are mainly coordinated by the interaction between innate and adaptive cells that act together to eliminate harmful stimuli and keep tissue healthy. However, healthy tissue is not always the end point of an immune response. Much evidence has been accumulated over the years, showing that the immune system has complex, diversified, and integrated functions that converge to maintaining tissue homeostasis, even in the absence of aggression, interacting with the tissue cells and allowing the functional maintenance of that tissue. One of the main cells known for their function in helping the immune response through the production of cytokines is CD4+ T lymphocytes. The cytokines produced by the different subtypes act not only on immune cells but also on tissue cells. Considering that tissues have specific mediators in their architecture, it is plausible that the presence and frequency of CD4+ T lymphocytes of specific subtypes (Th1, Th2, Th17, and others) maintain tissue homeostasis. In situations where homeostasis is disrupted, such as infections, allergies, inflammatory processes, and cancer, local CD4+ T lymphocytes respond to this disruption and, as in the healthy tissue, towards the equilibrium of tissue dynamics. CD4+ T lymphocytes can be manipulated by tumor cells to promote tumor development and metastasis, making them a prognostic factor in various types of cancer. Therefore, understanding the function of tissue-specific CD4+ T lymphocytes is essential in developing new strategies for treating tissue-specific diseases, as occurs in cancer. In this context, this article reviews the evidence for this hypothesis regarding the phenotypes and functions of CD4+ T lymphocytes and compares their contribution to maintaining tissue homeostasis in different organs in a steady state and during tumor progression.

The role and mechanisms of macrophage polarization and hepatocyte pyroptosis in acute liver failure

Acute liver failure (ALF) is a severe liver disease caused by disruptions in the body's immune microenvironment. In the early stages of ALF, Kupffer cells (KCs) become depleted and recruit monocytes derived from the bone marrow or abdomen to replace the depleted macrophages entering the liver. These monocytes differentiate into mature macrophages, which are activated in the immune microenvironment of the liver and polarized to perform various functions. Macrophage polarization can occur in two directions: pro-inflammatory M1 macrophages and anti-inflammatory M2 macrophages. Controlling the ratio and direction of M1 and M2 in ALF can help reduce liver injury. However, the liver damage caused by pyroptosis should not be underestimated, as it is a caspase-dependent form of cell death. Inhibiting pyroptosis has been shown to effectively reduce liver damage induced by ALF. Furthermore, macrophage polarization and pyroptosis share common binding sites, signaling pathways, and outcomes. In the review, we describe the role of macrophage polarization and pyroptosis in the pathogenesis of ALF. Additionally, we preliminarily explore the relationship between macrophage polarization and pyroptosis, as well as their effects on ALF.

Drug-Induced Liver Injury: Cascade of Events Leading to Cell Death, Apoptosis or Necrosis

Drug-induced liver injury (DILI) can broadly be divided into predictable and dose dependent such as acetaminophen (APAP) and unpredictable or idiosyncratic DILI (IDILI). Liver injury from drug hepatotoxicity (whether idiosyncratic or predictable) results in hepatocyte cell death and inflammation. The cascade of events leading to DILI and the cell death subroutine (apoptosis or necrosis) of the cell depend largely on the culprit drug. Direct toxins to hepatocytes likely induce oxidative organelle stress (such as endoplasmic reticulum (ER) and mitochondrial stress) leading to necrosis or apoptosis, while cell death in idiosyncratic DILI (IDILI) is usually the result of engagement of the innate and adaptive immune system (likely apoptotic), involving death receptors (DR). Here, we review the hepatocyte cell death pathways both in direct hepatotoxicity such as in APAP DILI as well as in IDILI. We examine the known signaling pathways in APAP toxicity, a model of necrotic liver cell death. We also explore what is known about the genetic basis of IDILI and the molecular pathways leading to immune activation and how these events can trigger hepatotoxicity and cell death.

Mechanisms of adaptation and progression in idiosyncratic drug induced liver injury, clinical implications

In the past decade our understanding of idiosyncratic drug induced liver injury (IDILI) and the contribution of genetic susceptibility and the adaptive immune system to the pathogenesis of this disease process has grown tremendously. One of the characteristics of IDILI is that it occurs rarely and only in a subset of individuals with a presumed susceptibility to the drug. Despite a clear association between single nucleotide polymorphisms in human leukocyte antigen (HLA) genes and certain drugs that cause IDILI, not all individuals with susceptible HLA genotypes develop clinically significant liver injury when exposed to drugs. The adaptation hypothesis has been put forth as an explanation for why only a small percentage of susceptible individuals develop overt IDILI and severe injury, while the majority with susceptible genotypes develop only mild abnormalities that resolve spontaneously upon continuation of the drug. This spontaneous resolution is referred to as clinical adaptation. Failure to adapt or defective adaptation leads to clinically significant liver injury. In this review we explore the immuno-tolerant microenvironment of the liver and the mechanisms of clinical adaptation in IDILI with a focus on the role of immune-tolerance and cellular adaptive responses.

Role of preferential cyclooxygenase-2 inhibition by meloxicam in ischemia/reperfusion injury of the rat liver

BACKGROUND

Ischemia/reperfusion injury (IRI) is one of the major clinical problems in liver and transplant surgery. Livers subjected to warm ischemia in vivo often show a severe dysfunction and the release of numerous inflammatory cytokines and arachidonic acid metabolites. Cyclooxygenase (COX)-2 is the inducible isoform of an intracellular enzyme that converts arachidonic acid into prostaglandins. The aim of the study was to evaluate the effect of COX-2 inhibition and the role of Kupffer cells in IRI of the liver.

METHODS

Male Wistar rats [250- 280 g body weight (BW)] were anesthetized and subjected to 30-min warm ischemia of the liver (Pringle's maneuver) and 60-min reperfusion after median laparotomy. The I/R group received no additional treatment. In the COX-2 inhibitor (COX-2I) group, the animals received 1 mg/kg BW meloxicam prior to operation. Gadolinium chloride (GdCl3) (10 mg/kg BW) was given 24 h prior to operation in the GdCl3 and GdCl3 + COX-2I groups for the selective depletion of Kupffer cells. The GdCl3 + COX-2I group received both GdCl3 and meloxicam treatment prior to operation. Blood and liver samples were obtained at the end of the experiments for further investigations.

RESULTS

After 30 min of warm ischemia in vivo, severe hepatocellular damage was observed in the I/R group. These impairments could be significantly prevented by the selective COX-2 inhibition and the depletion of Kupffer cells. Alanine aminotransferase was significantly reduced upon meloxicam and GdCl3 treatment compared to the I/R group: I/R, 3,240 ± 1,262 U/l versus COX-2I, 973 ± 649 U/l, p < 0.001; I/R versus GdCl3, 1,611 ± 600 U/l, p < 0.05, and I/R versus GdCl3 + COX-2I, 1,511 ± 575 U/l, p < 0.01. Plasma levels of tumor necrosis factor alpha (TNF-α) were significantly reduced in the COX-2I treatment group compared to I/R (3.5 ± 1.5 vs. 16.3 ± 11.7 pg/ml, respectively; p < 0.05). Similarly, the amount of TxB2, a marker for COX-2 metabolism, was significantly reduced in the meloxicam treatment groups compared to the I/R group: I/R, 22,500 ± 5,210 pg/ml versus COX-2I, 1,822 ± 938 pg/ml, p < 0.001, and I/R versus GdCl3 + COX-2I, 1,530 ± 907 pg/ml, p < 0.001. All values are given as mean ± SD (n = 6).

CONCLUSION

These results suggest that the inhibition of COX-2 suppressed the initiation of an inflammatory cascade by attenuating the release of TNF-α, which is an initiator of the inflammatory reaction in hepatic IRI. Therefore, we conclude that preferential inhibition of COX-2 is a possible therapeutic approach against warm IRI of the liver.

The haematopoietic stem cell niche: new insights into the mechanisms regulating haematopoietic stem cell behaviour

The concept of the haematopoietic stem cell (HSC) niche was formulated by Schofield in the 1970s, as a region within the bone marrow containing functional cell types that can maintain HSC potency throughout life. Since then, ongoing research has identified numerous cell types and a plethora of signals that not only maintain HSCs, but also dictate their behaviour with respect to homeostatic requirements and exogenous stresses. It has been proposed that there are endosteal and vascular niches within the bone marrow, which are thought to regulate different HSC populations. However, recent data depicts a more complicated picture, with functional crosstalk between cells in these two regions. In this review, recent research into the endosteal/vascular cell types and signals regulating HSC behaviour are considered, together with the possibility of a single subcompartmentalised niche.

The importance of immune dysfunction in determining outcome in acute liver failure

Acute liver failure (ALF) shares striking similarities with septic shock with regard to the features of systemic inflammation, progression to multiple organ dysfunction and functional immunoparesis. While the existence of opposing systemic pro- and anti-inflammatory profiles resulting in organ failure and immune dysfunction are well recognised in septic shock, characterization of these processes in ALF has only recently been described. This review explores the evolution of the systemic inflammation in acute liver failure, its relation to disease progression, exacerbation of liver injury and development of innate immune dysfunction and extra-hepatic organ failure as sequelae. Defects in innate immunity are described in hepatic and extra-hepatic compartments. Clinical studies measuring levels of pro- and anti-inflammatory cytokines and expression of the antigen presentation molecule HLA-DR on monocytes, in combination with ex-vivo experiments, demonstrate that the persistence of a compensatory anti-inflammatory response syndrome, leading to functional monocyte deactivation, is a central event in the evolution of systemic immune dysfunction. Accurate immune profiling in ALF may permit the development of immunomodulatory strategies in order to improve outcome in this condition.

Liver sinusoidal endothelial cells veto CD8 T cell activation by antigen-presenting dendritic cells

The liver is known to induce tolerance rather than immunity through tolerogenic antigen presentation or elimination of effector T cells. In particular, hepatic dendritic cells (DC) are known to be little immunogenic for CD8 T cells. Here, we investigated whether this peculiar phenotype resulted from interaction with resident hepatic cell populations. Contact of DC with liver sinusoidal endothelial cells (LSEC) but not hepatocytes or B cells vetoed antigen-presenting DC to fully activate naive CD8 T cells. This MHC-independent regulatory effect of LSEC on DC function was not connected to soluble mediators but required physical contact. Because interaction with third-party LSEC still allowed antigen-presenting DC to stimulate expression of initial activation markers on naive CD8 T cells and to stimulate activated CD8 T cells, we hypothesize that LSEC controlled the DC costimulatory function. Indeed, contact with LSEC led to reduced DC expression levels of CD80/86 or IL-12, but supplementation of these signals failed to rescue the ability to prime naive CD8 T cells, indicating involvement of further molecules. Taken together, our results reveal a novel principle operative in hepatic tolerance induction, in which LSEC not only tolerize T cells themselves but also suppress neighboring APC normally capable of inducing T cell immunity.

Development and functional consequences of LPS tolerance in sinusoidal endothelial cells of the liver

Kupffer cells and liver sinusoidal endothelial cells (LSEC) clear portal venous blood from gut-derived bacterial degradation products such as lipopolysaccharide (LPS) without inducing a local inflammatory reaction. LPS tolerance was reported for Kupffer cells, but little is known whether sensitivity of LSEC toward LPS is dynamically regulated. Here, we demonstrate that LSEC react to LPS directly as a function of constitutive Toll-like receptor 4 (TLR4)/CD14 expression but gain a LPS-refractory state upon repetitive stimulation without loss of scavenger activity. LPS tolerance in LSEC is characterized by reduced nuclear localization of nuclear factor-kappaB upon LPS rechallenge. In contrast to monocytes, however, TLR4 surface expression of LSEC is not altered by LPS stimulation and thus does not account for LPS tolerance. Mechanistically, LPS tolerance in LSEC is linked to prostanoid production and may account for cross-tolerance of LPS-treated LSEC to interferon-gamma stimulation. Functionally, LPS tolerance in LSEC results in reduced leukocyte adhesion following LPS rechallenge as a consequence of decreased CD54 surface expression. Furthermore, LPS tolerance is operative in vivo, as we observed by intravital microscopy-reduced leukocyte adhesion to LSEC and improved sinusoidal microcirculation in the liver after repetitive LPS challenges. Our results support the notion that LPS tolerance in organ-resident scavenger LSEC contributes to local hepatic control of inflammation.

Role of thromboxane derived from COX-1 and -2 in hepatic microcirculatory dysfunction during endotoxemia in mice

Although thromboxanes (TXs), whose synthesis is regulated by cyclooxygenase (COX), have been suggested to promote inflammation in the liver, little is known about the role of TXA(2) in leukocyte endothelial interaction during endotoxemia. The present study was conducted to investigate the role of TXA(2) as well as that of COX in lipopolysaccharide (LPS)-induced hepatic microcirculatory dysfunction in male C57Bl/6 mice. We observed during in vivo fluorescence microscopic study that LPS caused significant accumulation of leukocytes adhering to the hepatic microvessels and non-perfused sinusoids. Levels of serum alanine transaminase (ALT) and tumor necrosis factor alpha (TNF alpha) also increased. LPS raised the TXB(2) level in the perfusate from isolated perfused liver. A TXA(2) synthase inhibitor, OKY-046, and a TXA(2) receptor antagonist, S-1452, reduced LPS-induced hepatic microcirculatory dysfunction by inhibiting TNF alpha production. OKY-046 suppressed the expression of an intercellular adhesion molecule (ICAM)-1 in an LPS-treated liver. In thromboxane prostanoid receptor-knockout mice, hepatic responses to LPS were minimized in comparison with those in their wild-type counterparts. In addition, a selective COX-1 inhibitor, SC-560, a selective COX-2 inhibitor, NS-398, and indomethacin significantly attenuated hepatic responses to LPS including microcirculatory dysfunction and release of ALT and TNF alpha. The effects of the COX inhibitors on hepatic responses to LPS exhibited results similar to those obtained with TXA(2) synthase inhibitor, and TXA(2) receptor antagonist. In conclusion, these results suggest that TXA(2) is involved in LPS-induced hepatic microcirculatory dysfunction partly through the release of TNF alpha, and that TXA(2) derived from COX-1 and COX-2 could be responsible for the microcirculatory dysfunction during endotoxemia.

Role of thromboxane A2 in early BDL-induced portal hypertension

Although the mechanisms of cirrhosis-induced portal hypertension have been studied extensively, the role of thromboxane A(2) (TXA(2)) in the development of portal hypertension has never been explicitly explored. In the present study, we sought to determine the role of TXA(2) in bile duct ligation (BDL)-induced portal hypertension in Sprague-Dawley rats. After 1 wk of BDL or sham operation, the liver was isolated and perfused with Krebs-Henseleit bicarbonate buffer at a constant flow rate. After 30 min of nonrecirculating perfusion, the buffer was recirculated in a total volume of 100 ml. The perfusate was sampled for the enzyme immunoassay of thromboxane B(2) (TXB(2)), the stable metabolite of TXA(2). Although recirculation of the buffer caused no significant change in sham-operated rats, it resulted in a marked increase in portal pressure in BDL rats. The increase in portal pressure was found concomitantly with a significant increase of TXB(2) in the perfusate (sham vs. BDL after 30 min of recirculating perfusion: 1,420 +/- 803 vs. 10,210 +/- 2,950 pg/ml; P < 0.05). Perfusion with a buffer containing indomethacin or gadolinium chloride for inhibition of cyclooxygenase (COX) or Kupffer cells, respectively, substantially blocked the recirculation-induced increases in both portal pressure and TXB(2) release in BDL group. Hepatic detection of COX gene expression by RT-PCR revealed that COX-2 but not COX-1 was upregulated following BDL, and this upregulation was confirmed at the protein level by Western blot analysis. In conclusion, these results clearly demonstrate that increased hepatic TXA(2) release into the portal circulation contributes to the increased portal resistance in BDL-induced liver injury, suggesting a role of TXA(2) in liver fibrosis-induced portal hypertension. Furthermore, the Kupffer cell is likely the source of increased TXA(2), which is associated with upregulation of the COX-2 enzyme.

Influences of a dietary fatty acid composition on the emergence of glutathione S-transferase-P (GST-P) positive foci in the liver of carcinogen-treated rats

The rats treated with a single i.p. injection of diethylnitrosoamine (DEN) and percial hepatectomy were fed for 11 weeks with a high fat diet mixed with 10% lard, eicosapentaenoic-acid-rich oil (EPA-oil) or arachidonic-acid-rich oil (AA-oil) and the emergence of glutathione S-transferase placental form (GST-P) in the liver was evaluated. There were no significant differences in the serum aminotransferase activities. The molar ratio of n-6 and n-3 fatty acid in the liver phospholipids was significantly low in the EPA-oil group compared with the other groups. In the EPA-oil group, the area percent and the unit area of GST-P positive foci were significantly smaller than the other groups. In the AA-oil group, no significant differences were recognized in the quantitative values for GST-P positive foci compared with the control and lard groups. In conclusion, a hepatic neoplasmic lesion induced by DEN was suppressed with EPA-rich fish oil, and arachidonic-acid-rich oil showed no effect of suppression or acceleration.

Biology and significance of T-cell apoptosis in the liver

The liver has emerged as an organ with distinct immunological properties. In this review, we summarize evidence that shows that the liver can remove apoptotic, or non-apoptotic but activated, CD8+ T cells from the circulation and induce apoptosis in these activated T cells by either active or passive mechanisms. Hepatitis viruses, particularly hepatitis C virus, often establish persistent infection. We review evidence that suggests that these viruses exploit intrahepatic tolerance mechanisms to protect themselves from immune attack.

Functions of anaphylatoxin C5a in rat liver: direct and indirect actions on nonparenchymal and parenchymal cells

Growing evidence obtained in recent years indicates that anaphylatoxin C5a receptors (C5aR) are not restricted to myeloid cells but are also expressed on nonmyeloid cells in different tissues such as brain, lung, skin and liver. In contrast to its well-defined systemic functions, the actions of anaphylatoxins in these organs are poorly characterized. The liver can be a primary target organ for the C5a anaphylatoxin since the liver is directly connected to the gut, via the mesenteric veins and portal vein which is a main source of complement activating lipopolysaccharides (LPS). In the normal rat liver, the C5aR is only expressed by nonparenchymal cells, i.e. strongly by Kupffer cells (KC) and hepatic stellate cells (HSC) and weakly by sinusoidal endothelial cells (SEC), but not expressed by the parenchymal hepatocytes (HC). Accordingly, direct effects of C5a were only found in the C5aR-expressing KC and HSC: C5a induced the release of prostanoids from KC and HSC and enhanced the LPS-dependent release of interleukin-6 from KC. These soluble mediators indirectly influenced effector functions of the C5aR-free HC. C5a enhanced the glycogen phosphorylase activity and thus the glucose output from HC indirectly via prostanoids released from KC and HSC. Glucose can serve as an energy substrate as well as an electron donor for the synthesis of reactive oxygen intermediates by KC. Moreover, C5a also enhanced transcription of the gene for the type-2 acute phase protein alpha 2-macroglobulin in HC indirectly by increasing LPS-dependent IL-6 release from KC. Under pathological conditions, C5aR was found to be upregulated in various organs including the liver. Simulation of inflammatory conditions by treatment of rats with IL-6, a main inflammatory mediator in the liver, caused a de novo expression of functional C5aR in HC. In livers of IL-6-treated rats, C5a initiated glucose output from HC and perhaps other HC-specific defense reactions directly without the intervention of soluble mediators from nonparenchymal cells.

Analysis of alloreactivity and intragraft cytokine profiles in living donor liver transplant recipients with graft acceptance

Although some previous studies have indicated the possibility of immunosuppression withdrawal in clinical liver transplantation, the mechanism of graft acceptance is not clear. The aim of this study is to elucidate the alloreactivity against the donor and intragraft cytokine profiles in living donor liver transplant (LDLT) recipients with graft acceptance. In October 1999, we had 23 patients who survived without immunosuppression after LDLT with a median drug-free period of 25 months (range: 3-69 months). They consisted of six patients who were electively weaned by an elective weaning protocol and 17 either forcibly or accidentally weaned patients due to various causes but mainly due to infection. We evaluated the alloreactivity against the donor in these patients by a mixed lymphocyte reaction and intragraft cytokine profiles by real-time reverse transcriptase-polymerase chain reaction. The development of donor-specific hyporeactivity was observed in the patients with graft acceptance. The cytokine pattern in the supernatant of the culture medium revealed a down regulation of T helper (Th) 1 cytokine INF gamma against the donor while no significant difference was seen in Th2 cytokine IL-10. Regarding the intragraft cytokine profiles, we could find no amplification of Thl cytokines (IL-2, INF y) and IL-4 while some of the patients revealed a gene expression of IL-10 with no significant difference from that of the normal, untransplanted liver specimen. In addition, no difference was observed in any other cytokines (IL-1beta, IL-8, IL-15, TNFalpha) compared with those of the normal controls. We propose that the down regulation of Th1 cytokine is one possible mechanism of graft acceptance in LDLT recipients.

Liver sinusoidal endothelial cells are not permissive for adenovirus type 5

Adenoviral vectors are known to transduce hepatocytes in normal liver tissue with high efficiency. The aim of this study was to investigate whether sinusoidal endothelial cells, which separate hepatocytes from the bloodstream in the sinusoidal lumen, are permissive for infection by adenoviruses. We show here that microvascular liver sinusoidal endothelial cells are not infected by adenovirus type 5 in vivo or in vitro unless high MOIs are used. In contrast, macrovascular endothelial cells from aorta are efficiently infected by adenovirus type 5. In addition, Kupffer cells, similar to sinusoidal endothelial cells, are not infected by adenovirus type 5. Liver sinusoidal endothelial cells do not express the integrin receptor alpha(v)beta3, which is required for efficient infection by adenoviruses. Our results demonstrate that hepatocytes are the main cell population of the liver that is infected by adenovirus type 5.

Increase by anaphylatoxin C5a of glucose output in perfused rat liver via prostanoids derived from nonparenchymal cells: direct action of prostaglandins and indirect action of thromboxane A(2) on hepatocytes

In the perfused rat liver the anaphylatoxin C5a enhanced glucose output, reduced flow, and elevated prostanoid overflow. Because hepatocytes (HCs) do not express C5a receptors, the metabolic C5a actions must be indirect, mediated by e.g. prostanoids from Kupffer cells (KCs) and hepatic stellate cells (HSCs), which possess C5a receptors. Surprisingly, the metabolic C5a effects were not only impaired by the prostanoid synthesis inhibitor, indomethacin, but also by the thromboxane A(2) (TXA(2)) receptor antagonist, daltroban, even though HCs do not express TXA(2) receptors. TXA(2) did not induce prostaglandin (PG) or an unknown factor release from KCs or sinusoidal endothelial cells (SECs), which express TXA(2) receptors, because (1) daltroban did neither influence the C5a-induced release of prostanoids from cultured KCs nor the C5a-dependent activation of glycogen phosphorylase in KC/HC cocultures and because (2) the TXA(2) analog, U46619, failed to stimulate prostanoid release from cultured KCs or SECs or to activate glycogen phosphorylase in KC/HC or SEC/HC cocultures. In the perfused liver, Ca(2+)-deprivation inhibited not only flow reduction but also glucose output elicited by C5a to similar extents as daltroban. Similarly, in the absence of extracellular Ca(2+), flow reduction and glucose output induced by U46619 were almost completely prevented, whereas glucose output induced by the directly acting PGF(2alpha) was only slightly lowered. Thus, in the perfused rat liver PGs released after C5a-stimulation from KCs and HSCs directly activated glycogen phosphorylase in HCs, and TXA(2) enhanced glucose output indirectly mainly by causing hypoxia as a result of flow reduction.

Endotoxin Down-Regulates T Cell Activation by Antigen-Presenting Liver Sinusoidal Endothelial Cells

Endotoxin is physiologically present in portal venous blood at concentrations of 100 pg/ml to 1 ng/ml. Clearance of endotoxin from portal blood occurs through sinusoidal lining cells, i.e., Kupffer cells, and liver sinusoidal endothelial cells (LSEC). We have recently shown that LSEC are fully efficient APCs. Here, we studied the influence of endotoxin on the accessory function of LSEC. Incubation of Ag-presenting LSEC with physiological concentrations of endotoxin lead to ≥80% reduction of the accessory function, measured by release of IFN-γ from CD4+ T cells. In contrast, conventional APC populations rather showed an increase of the accessory function after endotoxin treatment. Inhibition of the accessory function in LSEC by endotoxin was not due to lack of soluble costimulatory signals, because neither supplemental IL-1β, IL-2, IFN-γ, or IL-12 could rescue the accessory function. Ag uptake was not influenced by endotoxin in LSEC. However, we found that endotoxin led to alkalinization of the endosomal/lysomal compartment specifically in LSEC but not in bone marrow macrophages, which indicated that Ag processing, i.e., proteolytic cleavage of protein Ags into peptide fragments, was affected by endotoxin. Furthermore, endotoxin treatment down-regulated surface expression of constitutively expressed MHC class II, CD80, and CD86. In conclusion, it is conceivable that endotoxin does not alter the clearance function of LSEC to remove gut-derived Ags from portal blood but specifically affects Ag processing and expression of the accessory molecules in these cells. Consequently, Ag-specific immune responses by CD4+ T cells are efficiently down-regulated in the hepatic microenvironment.

IL-10 down-regulates T cell activation by antigen-presenting liver sinusoidal endothelial cells through decreased antigen uptake via the mannose receptor and lowered surface expression of accessory molecules

Our study demonstrates that antigen-presenting liver sinusoidal endothelial cells (LSEC) induce production of interferon-gamma (IFN-gamma) from cloned Th1 CD4+ T cells. We show that LSEC used the mannose receptor for antigen uptake, which further strengthened the role of LSEC as antigen-presenting cell (APC) population in the liver. The ability of LSEC to activate cloned CD4+ T cells antigen-specifically was down-regulated by exogenous prostaglandin E2 (PGE2) and by IL-10. We identify two separate mechanisms by which IL-10 down-regulated T cell activation through LSEC. IL-10 decreased the constitutive surface expression of MHC class II as well as of the accessory molecules CD80 and CD86 on LSEC. Furthermore, IL-10 diminished mannose receptor activity in LSEC. Decreased antigen uptake via the mannose receptor and decreased expression of accessory molecules may explain the down-regulation of T cell activation through IL-10. Importantly, the expression of low numbers of antigen on MHC II in the absence of accessory signals on LSEC may lead to induction of anergy in T cells. Because PGE2 and IL-10 are released from LSEC or Kupffer cells (KC) in response to those concentrations of endotoxin found physiologically in portal venous blood, it is possible that the continuous presence of these mediators and their negative effect on the local APC may explain the inability of the liver to induce T cell activation and to clear chronic infections. Our results support the notion that antigen presentation by LSEC in the hepatic microenvironment contributes to the observed inability to mount an effective cell-mediated immune response in the liver.

Stimulation by anaphylatoxin C5a of glycogen phosphorylase in rat hepatocytes via prostanoid release from hepatic stellate cells but not sinusoidal endothelial cells

In the perfused rat liver, the anaphylatoxin C5a has been shown to enhance glucose output. Since hepatocytes lack C5a receptor mRNA, the metabolic effect of C5a must be elicited indirectly via C5a receptor expressing non-parenchymal liver cells. Kupffer cells were found to be able to mediate the C5a action via release of prostanoids. However, elimination of the Kupffer cells by pretreatment of the animals with gadolinium chloride reduced the metabolic effect of C5a to only about 40%. Therefore, it was investigated whether not only Kupffer cells but in addition also hepatic stellate cells or sinusoidal endothelial cells released prostanoids in response to C5a. In isolated hepatic stellate cells but not in sinusoidal endothelial cells, recombinant rat C5a induced a time- and dose-dependent release of thromboxane B2 and prostaglandins D2, E2 and F2alpha. The rate of prostanoid release was maximal within the first two minutes and then declined again. C5a-induced prostanoid release from hepatic stellate cells was smaller than that from Kupffer cells and it differed in the prostanoid ratios (PGE2/PGD2/PGF2alpha/TXB2 = 1:1:0.1:0.6 and 1:4:1:3, respectively). RrC5a activated hepatocellular glycogen phosphorylase via prostanoid release in cocultures of hepatocytes with hepatic stellate cells but not with sinusoidal endothelial cells. Thus, the part of the rrC5a-induced glucose output in the perfused rat liver, which was not abrogated by elimination of the Kupffer cells with gadolinium chloride, most likely was mediated by prostanoids released from hepatic stellate cells.

Plasma iPGE2 and i6-keto PGF1 alpha in the course of liver cirrhosis

Plasma iPGE2 and i6-keto PGF1 alpha were measured with an EIA assay in twenty patients with alcohol-related liver cirrhosis (ALC group) and 13 patients with hepatitis B virus as an etiologic factor of liver cirrhosis (HLC group). Significant increase of both prostanoids was observed irrespectively of the etiology of liver cirrhosis. Their levels increased depending on the degree of liver insufficiency with the highest values in patients classified as Child-Pugh C class. A significant, positive correlation with Child-Pugh score was found regarding PGE2 (r = 0.657; p < 0.001) as well as 6-keto PGF1 alpha (r = 0.736; p < 0.001). Correlation (r = 0.789; p < 0.001) was also observed between levels of both prostaglandins. In conclusion we have shown that plasma iPGE2 and i6-keto PGF1 alpha arise simultaneously with the degree of liver insufficiency, that can be a result of activation of non-parenchymal liver cells accompanying hepatic fibrosis.

Hepatic sinusoidal endothelial cell G1/S arrest correlates with severity of alcoholic liver injury in the rat

BACKGROUND/AIMS

Capillarization of the hepatic sinusoid occurs in alcoholic liver disease. Because endothelial cell proliferation is relevant to capillarization, we used the intragastric feeding rat model to evaluate the relationship between pathological liver injury and endothelial cell proliferation.

METHODS

Male Wistar rats (225-250 g) were fed liquid diets containing corn oil and ethanol for periods ranging between 1 week and 2 months. At the time the rats were killed, the severity of pathological injury and endothelial cell proliferation using anti-rat proliferating cell nuclear antigen/antibody was evaluated.

RESULTS

Two distinctly different populations of proliferating sinusoidal lining cells were identified; one population showed relatively weak granular staining consistent with cells arrested at the G1/S boundary. The other population of cells showed strong granular staining of the nucleoplasm and nucleoli (cells in mid to late S phase). A strong correlation (r = 0.85; P < 0.01) was obtained between pathological severity and G1/S-arrested endothelial cells. There was no correlation between cells in S phase.

CONCLUSIONS

The presence of an increased number of G1/S-arrested endothelial cells in animals with severe pathological change suggests that stimuli are present for both endothelial cell proliferation and G1/arrest. The identification of these stimuli could lead to a better understanding of the pathogenesis of alcoholic liver disease.

Acetaldehyde-protein adducts, but not lactate and pyruvate, stimulate gene transcription of collagen and fibronectin in hepatic fat-storing cells

Hepatic fibrosis is an important morphological feature of alcohol-induced liver injury. We previously reported that acetaldehyde, but not ethanol can stimulate type I collagen and fibronectin synthesis in cultures of rat fat-storing cells (FSC) by increasing transcription of the specific genes. The effect of lactate and pyruvate was studied on collagen I, III, fibronectin accumulation by cultured rat FSCs and it was investigated whether acetaldehyde could increase procollagen I and fibronectin gene transcription through the formation of protein adducts. Lactate and pyruvate (5, 15 and 25 mmol/l) did not significantly affect collagen I, III and fibronectin production by cultured FSCs. Pyridoxal-phosphate and p-hydroxymecuribenzoate (inhibitors of acetaldehyde-protein adduct formation) blocked the stimulatory effect of acetaldehyde on procollagen I and fibronectin gene transcription. These data suggest that ethanol may act as a liver fibrogenic factor through acetaldehyde, its immediate metabolite, whereas lactate does not seem to play a role. Acetaldehyde might stimulate gene transcription of extracellular matrix components by liver FSCs through the formation of adducts with proteins.

In vitro DNA synthesis of mouse hepatocytes stimulated by tumor necrosis factor is inhibited by glucocorticoids and prostaglandin D2 but enhanced by retinoic acid

We have recently shown that TNF is produced in liver rapidly after partial hepatectomy and that TNF can stimulate DNA synthesis of hepatocyte primary culture with its inhibition by interleukin 6 and transforming growth factor-beta, indicating a pivotal role of TNF and TNF-driven cytokine induction in liver regeneration. We here examined the effects of biological or inflammatory mediators of low molecular weight on the in vitro DNA synthesis of hepatocytes stimulated by TNF. Simultaneous addition of dexamethasone markedly suppressed the growth-stimulating action of TNF, maximally at 10(-7) M and effectively at about 10(-8) M. However, the growth-stimulating effect of EGF was not affected by dexamethasone at all. Physiological glucocorticoids, corticosterone, and hydrocortisone showed virtually the same effect, but other steroid hormones, beta-estradiol, or progesterone did not. Retinoic acid at 10(-7) M, however, enhanced TNF-stimulated hepatocyte DNA synthesis and even more effectively the growth response to EGF. PGD2 at 20 microM was markedly suppressive but PGE2 was not. The addition of indomethacin enhanced the hepatocyte in vitro growth by TNF and EGF at 2-20 microM. These results indicate that the growth of hepatocytes stimulated by TNF is up- and down-regulated by inflammatory mediators and hormones as well as cytokines and suggest the biological significance of TNF and TNF-driven inflammatory reactions in liver regeneration.

Liver cytoprotection by prostaglandins

During the last decade intensive work on the relationships between the liver and the arachidonic acid cascade has greatly expanded our knowledge of this area of research. The liver has emerged as the major organ participating in the degradation and elimination of arachidonate products of systemic origin. The synthesis in the liver of arachidonate products derived from the cyclooxygenase, lipoxygenase and cytochrome P450 system pathways has been demonstrated. The participation of leukotriene B4 and cysteinyl-leukotrienes as mediators of liver damage and the possible therapeutic usefulness of prostaglandins (PGs) in acute liver injury has attracted the interest of clinicians. This article reviews the essential features regarding the role of arachidonate metabolites in liver disease and specially focuses on the cytoprotective effects on the liver displayed by PGE2, PGE1, PGI2 and synthetic PG analogs in experimental models of liver damage induced by ischemia-reperfusion injury, carbon tetrachloride, bacterial lipopolysaccharide and viral hepatitis and on the possible mechanisms underlying liver cytoprotection in these experimental models. The therapeutic usefulness of PGs in clinical practice is critically analyzed on the basis of available evidence in patients with fulminant hepatic failure and primary graft nonfunction following liver transplantation.

Modulation of prostacyclin production by cytokines in vascular endothelial cells

The data presented in this review clearly show that many different cytokines regulate the synthesis of PGI2 in vascular EC (Tables 1 & 2). Since these agents are synthesized, stored, and/or released from platelets, leukocytes and cells present in the vascular wall (Fig.), they are to be found at sites of vascular injury and may, through their effect on the synthesis of PGI2 and other prostanoids, regulate thrombogenesis and atherogenesis. Despite the mass of detailed data, the picture is still fragmentary. Very little, for instance, is known about the 'orchestral effects' of different combinations of cytokines. In addition, it seems that the regulation of PGI2 synthesis by cytokines varies with the species and with the type of vasculature from which the cells originated. However, discrepancies may also be due to the use of different culture conditions. Moreover, we must remember that the present data are almost exclusively from in vitro studies, and the representativeness of these results in in vivo situations remains to be clarified.

Sinusoidal endothelial liver cells in vitro release endothelin--augmentation by transforming growth factor beta and Kupffer cell-conditioned media

Endothelin is the most potent vasoconstrictor peptide known today. Using a radioimmunoassay for endothelin, we measured immunoreactive endothelin in culture media of guinea pig sinusoidal endothelial liver cells and human umbilical vein endothelial cells. A time-dependent release of immunoreactive endothelin by confluent sinusoidal endothelial liver cells in culture was found. Sinusoidal endothelial liver cells produced similar amounts of immunoreactive endothelin as umbilical vein endothelial cells, about 900 pg/microgram DNA per 24 h. In the presence of transforming growth factor beta a dose-dependent increase of immunoreactive endothelin release was measured. The maximal increase of 50% was found at a concentration of 1 ng transforming growth factor per ml. To a similar extent Kupffer cell-conditioned media augmented the release of immunoreactive endothelin by sinusoidal endothelial liver cells, especially when Kupffer cells had been stimulated by endotoxin. Endotoxin itself did not alter the release of immunoreactive endothelin. Endothelin released by sinusoidal endothelial liver cells might influence the pericytes of the liver, i.e., the Ito-cells.

Diagnosis and recommended management of esophageal perforation and rupture

Over the past 47 years (1937 to 1984), a total of 127 patients with esophageal perforation or rupture were evaluated at Duke Medical Center or the Durham Veterans Administration Medical Center. In 13 patients, the diagnosis was established at the time of autopsy and in the remaining 114, the diagnosis was established clinically. The etiology, radiological findings, underlying esophageal disease, time interval between onset of symptoms and therapy, and eventual outcome were evaluated. Patients with anastomotic leaks and those in whom carcinoma resulted in perforation or fistula were excluded. Iatrogenic causes were responsible for 55% of perforations, followed by spontaneous rupture in 15%, foreign body perforation in 14%, and traumatic perforation in 10%. Of the 127 patients, 114 underwent treatment involving primary closure (43%), drainage alone (28%), resection (9%), or nonoperative therapy (20%). The overall mortality among these 114 patients was 21%. Fourteen patients sustained a major complication requiring additional operative intervention. The overall mortality among patients requiring reoperation was 57%. Survival was significantly influenced by a delay in treatment of greater than 24 hours. With the exception of nonoperative therapy, survival was improved for all forms of treatment instituted within 24 hours. Primary closure within 24 hours resulted in the most favorable outcome (92% survival). In addition to early treatment, other factors associated with a favorable outcome included traumatic perforation (100% survival), foreign-body perforations (94% survival), and iatrogenic causes (80% survival). Spontaneous rupture resulted in the lowest survival (37%). The incidence of esophageal perforation has increased dramatically since 1967.(ABSTRACT TRUNCATED AT 250 WORDS)