Impact of leukocytes and platelets in mediating hepatocyte apoptosis in a rat model of systemic endotoxemia

Apoptosis releases hydrogen sulfide to inhibit Th17 cell differentiation

Over 50 billion cells undergo apoptosis each day in an adult human to maintain immune homeostasis. Hydrogen sulfide (H2S) is also required to safeguard the function of immune response. However, it is unknown whether apoptosis regulates H2S production. Here, we show that apoptosis-deficient MRL/lpr (B6.MRL-Faslpr/J) and Bim-/- (B6.129S1-Bcl2l11tm1.1Ast/J) mice exhibit significantly reduced H2S levels along with aberrant differentiation of Th17 cells, which can be rescued by the additional H2S. Moreover, apoptotic cells and vesicles (apoVs) express key H2S-generating enzymes and generate a significant amount of H2S, indicating that apoptotic metabolism is an important source of H2S. Mechanistically, H2S sulfhydrates selenoprotein F (Sep15) to promote signal transducer and activator of transcription 1 (STAT1) phosphorylation and suppress STAT3 phosphorylation, leading to the inhibition of Th17 cell differentiation. Taken together, this study reveals a previously unknown role of apoptosis in maintaining H2S homeostasis and the unique role of H2S in regulating Th17 cell differentiation via sulfhydration of Sep15C38.

Toxic Effect of Combined Exposure of Microplastics and Copper on Goldfish (Carassius auratus): Insight from Oxidative Stress, Inflammation, Apoptosis and Autophagy in Hepatopancreas and Intestine

The enhancement of the toxic effect of microplastics (MPs) on heavy metals and its mechanism needs more in-depth and systematic research. In this study, the copper (Cu) accumulation, histological injury, and expression of genes involved in oxidative stress, inflammation, apoptosis, and autophagy of goldfish after single or combined exposure of MPs (1 mg/L) and Cu²⁺ (0.1 mg/L) for 7 days were determined. The results demonstrated that MPs enhanced the Cu accumulation in hepatopancreas and intestine of goldfish and induced more severe oxidative stress in the hepatopancreas and intestine of goldfish. Additionally, combined exposure of MPs and Cu induced inflammation, excessive apoptosis and insufficient autophagy in the hepatopancreas. Contrary, the inflammation and apoptosis were depressed in the intestine after combined exposure of MPs and Cu, which still requires further exploration. Hence, these findings provide further evidence for the threat of MPs and its adsorbed heavy metals.

Blocking of Caspases Exerts Anti-Inflammatory Effects on Periodontal Cells

Periodontitis is an inflammatory process that is associated with caspase activity. Caspases could thus become molecular targets for the modulation of the inflammatory response to harmful factors, such as lipopolysaccharides (LPS) and TNFα. Here, the impact of the pan-caspase inhibitor Z-VAD-FMK (carbobenzoxy-valyl-alanyl-aspartyl-[O-methyl]-fluoro-methyl ketone) on the modulation of the LPS-induced inflammatory response of murine RAW 264.7 cells and primary macrophages was examined. Moreover, the inflammatory responses of human gingival fibroblasts, HSC2 oral squamous carcinoma cells and murine ST2 mesenchymal fibroblasts when exposed to TNFα were studied. Data showed that Z-VAD-FMK significantly lowered the inflammatory response of RAW 264.7 cells and primary macrophages, as indicated by the expression of IL1 and IL6. In murine ST2 mesenchymal fibroblasts, the TNFα-induced expression of CCL2 and CCL5 was significantly reduced. In human gingival fibroblasts and HSC2 cells, Z-VAD-FMK considerably reduced the TNFα-induced expression of CXCL8 and CXCL10. These findings suggest that pharmacological blocking of caspases in an inflammatory environment lowers the expression of cytokines and chemokines in periodontal cells.

Platelets prevent the development of monocrotaline-induced liver injury in mice

Destruction of liver sinusoidal endothelial cells (LSECs) is an initial event in sinusoidal obstruction syndrome (SOS) that leads to accumulation of platelets in the liver. Herein, we explored the role of platelets during progression of experimental SOS induced by monocrotaline (MCT) in mice. Depletion of platelets using an anti-CD41 antibody or anti-thrombocyte serum exacerbated MCT-induced liver injury in C57BL/6 mice, as indicated by an increase in the alanine transaminase (ALT) level, which was associated with hemorrhagic necrosis. Thrombocytosis induced by thrombopoietin (TPO) or the TPO receptor agonist romiplostim (ROM) attenuated MCT-induced liver injury, as evidenced by lower levels of ALT and mRNA encoding matrix metalloproteinase (MMP) 9, and higher levels of mRNA encoding vascular endothelial growth factor receptor (VEGFR) 2 and VEGFR3. The level of activated hepatic platelets was higher in TPO- and ROM-treated mice than in saline-treated mice. Co-culture with a high number of platelets increased the viability of LSECs and their mRNA levels of CD31, VEGFR2, and VEGFR3, and decreased their mRNA level of MMP9. The level of VEGF-A was increased in the culture medium of LSECs co-cultured with platelets. These results indicate that platelets attenuate MCT-induced liver injury by minimizing damage to LSECs.

Sulfasalazine treatment can cause a positive effect on LPS-induced endotoxic rats

The aim of this study, was to determine the effect of sulfasalazine for different periods of time reduces disseminated intravascular coagulation, inflammation and organ damages by inhibiting the nuclear factor kappa beta pathway. The study was performed with 30 Wistar albino rats and the groups were established as Control group, LPS group; endotoxemia was induced with LPS, SL5 group: sulfasalazine (300 mg/kg, single dose daily) was administered for 5 days before the LPS-induced endotoxemia, and LS group: sulfasalazine (300 mg/kg, single dose) was administered similtenously with LPS. Hemogram, biochemical, cytokine (IL-1β, IL-6, IL-10, TNF-α) and acute phase proteins (HPT, SAA, PGE2) analyzes and oxidative status values were measured from blood samples at 3 and 6 h after the last applications in the all groups. The rats were euthanized at 6 h and mRNA levels of BCL2 and BAX genes were examined from liver and brain tissues. Sulfasalazine reduced the increased IL-1β, IL-6, TNF-α and PGE₂ levels and significantly increased anti-inflammatory cytokine IL-10 levels. In addition, decreasing of ATIII level was prevented in the SL5 group, and decreasing of fibrinogen levels were prevented in the LS and SL5 groups within first 3 h. In LPS group, leukocyte and thrombocyte levels were decreased, however sulfasalazine application inhibited decreases of leukocyte levels in LS and SL5 groups. In addition, sulfasalazine inhibited the decrease of total antioxidant capacity and unchanged apoptosis in brain and liver. In conclusion, the use of sulfasalazine in different durations reduce the excessive inflammation of endotoxemia cases.

Low-density lipoprotein (LDL)-dependent uptake of Gram-positive lipoteichoic acid and Gram-negative lipopolysaccharide occurs through LDL receptor

Lipoteichoic acid (LTA) and lipopolysaccharide (LPS) are bacterial lipids that stimulate pro-inflammatory cytokine production, thereby exacerbating sepsis pathophysiology. Proprotein convertase subtilisin/kexin type 9 (PCSK9) negatively regulates uptake of cholesterol by downregulating hepatic lipoprotein receptors, including low-density lipoprotein (LDL) receptor (LDLR) and possibly LDLR-related protein-1 (LRP1). PCSK9 also negatively regulates Gram-negative LPS uptake by hepatocytes, however this mechanism is not completely characterized and mechanisms of Gram-positive LTA uptake are unknown. Therefore, our objective was to elucidate the mechanisms through which PCSK9 regulates uptake of LTA and LPS by investigating the roles of lipoproteins and lipoprotein receptors. Here we show that plasma PCSK9 concentrations increase transiently over time in septic and non-septic critically ill patients, with highly similar profiles over 14 days. Using flow cytometry, we demonstrate that PCSK9 negatively regulates LDLR-mediated uptake of LTA and LPS by HepG2 hepatocytes through an LDL-dependent mechanism, whereas LRP1 and high-density lipoprotein do not contribute to this uptake pathway. Bacterial lipid uptake by hepatocytes was not associated with cytokine production or hepatocellular injury. In conclusion, our study characterizes an LDL-dependent and LDLR-mediated bacterial lipid uptake pathway regulated by PCSK9, and provides evidence in support of PCSK9 inhibition as a potential therapeutic strategy for sepsis.

Microcirculation and red cell transfusion in patients with sepsis

Early identification of sepsis followed by diagnostic blood cultures and prompt administration of appropriate intravenous antibiotics covering all likely pathogen remains the corner stone in the initial management of sepsis. Source control, obtained by harvesting microbiological cultures and removal or drainage of the infected foci, is mandatory. However, optimization of hemodynamically unstable patients including volume support supplemented with vasopressor, inotropic and transfusion of red blood cells (RBCs) in case of persistent hypoperfusion have the potential to reduce morbidity and mortality. Given the imbalance between the ability of the cardiovascular system to deliver enough oxygen to meet the oxygen demand, transfusion of RBCs should theoretically provide the ideal solution to the challenge. However, both changes in the septic patients' RBCs induced by endogenous factors as well as the storage lesion affecting transfused RBCs have negative effects on the microcirculation. RBC morphology, distribution of fatty acids on the membrane surface, RBC deformability needed for capillary circulation and the nitrogen oxide (NO) signaling systems are involved. Although these deteriorating effects develop during storage, transfusion of fresh RBCs has not proven to be beneficial, possibly due to limitations of the studies performed. Until better evidence exists, transfusion guidelines recommend a restrictive strategy of RBC transfusion i.e. transfuse when hemoglobin (Hb)<7g/dL in septic patients.

THE ENDOTHELIUM IN SEPSIS

Sepsis affects practically all aspects of endothelial cell (EC) function and is thought to be the key factor in the progression from sepsis to organ failure. Endothelial functions affected by sepsis include vasoregulation, barrier function, inflammation, and hemostasis. These are among other mechanisms often mediated by glycocalyx shedding, such as abnormal nitric oxide metabolism, up-regulation of reactive oxygen species generation due to down-regulation of endothelial-associated antioxidant defenses, transcellular communication, proteases, exposure of adhesion molecules, and activation of tissue factor. This review covers current insight in EC-associated hemostatic responses to sepsis and the EC response to inflammation. The endothelial cell lining is highly heterogeneous between different organ systems and consequently also in its response to sepsis. In this context, we discuss the response of the endothelial cell lining to sepsis in the kidney, liver, and lung. Finally, we discuss evidence as to whether the EC response to sepsis is adaptive or maladaptive. This study is a result of an Acute Dialysis Quality Initiative XIV Sepsis Workgroup meeting held in Bogota, Columbia, between October 12 and 15, 2014.

Hemodynamic coherence in sepsis

Microvascular alterations are a hallmark of sepsis and play a crucial role in its pathophysiology. Such alterations are the result of overwhelming inflammation, which negatively affects all the components of the microcirculation. As the severity of microvascular alterations is associated with organ dysfunction and mortality, several strategies have been tested for improving microcirculation. Nevertheless, they are mainly based on the conventional manipulation of systemic hemodynamics to increase the total flow to the organs and tissues. Other therapeutic interventions are still being investigated. In this review, we discuss the pathophysiology of septic microcirculatory dysfunction and its implications for possible treatments.

Microcirculatory dysfunction in sepsis: pathophysiology, clinical monitoring, and potential therapies

Abnormal microvascular perfusion, including decreased functional capillary density and increased blood flow heterogeneity, is observed in early stages of the systemic inflammatory response to infection and appears to have prognostic significance in human sepsis. It is known that improvements in systemic hemodynamics are weakly correlated with the correction of microcirculatory parameters, despite an appropriate treatment of macrohemodynamic abnormalities. Furthermore, conventional hemodynamic monitoring systems available in clinical practice fail to detect microcirculatory parameter changes and responses to treatments, as they do not evaluate intrinsic events that occur in the microcirculation. Fortunately, some bedside diagnostic methods and therapeutic options are specifically directed to the assessment and treatment of microcirculatory changes. In the present review we discuss fundamental aspects of septic microcirculatory abnormalities, including pathophysiology, clinical monitoring, and potential therapies.

Role of cysteinyl-leukotrienes for portal pressure regulation and liver damage in cholestatic rat livers

Kupffer cells (KCs) have a major role in liver injury, and cysteinyl-leukotrienes (Cys-LTs) are known to be involved as well. The KC-mediated pathways for the production and secretion of Cys-LT in cholestatic liver injury have not yet been elucidated. Here, we hypothesized that KC activation by Toll-like receptor ligands results in Cys-LT-mediated microcirculatory alterations and liver injury in acute cholestasis. We hypothesized further that this situation is associated with changes in the secretion and production of Cys-LT. One week after bile duct ligation (BDL), livers showed typical histological signs of cholestatic liver injury. Associated microcirculatory disturbances caused increased basal and maximal portal pressure following KC activation. These differences were determined in BDL livers compared with sham-operated livers in vivo (KC activation by LPS 4 mg/kg b.w.) and in isolated perfused organs (KC activation by Zymosan A, 150 μg/ml). Treatment with the 5-lipoxygenase inhibitor MK-886 alone did not alter portal perfusion pressure, lactate dehydrogenase (LDH) efflux, or bile duct proliferation in BDL animals. Following KC activation, portal perfusion pressure increased. The degree of cell injury was attenuated by MK-886 (3 μM) treatment as estimated by LDH efflux. In normal rats, a large amount of Cys-LT efflux was found in the bile. Only a minor amount was found in the effluent perfusate. In BDL livers, the KC-mediated Cys-LT efflux into the sinusoidal system increased, although the absolute Cys-LT level was still grossly lower than the biliary excretion in sham-operated livers. In conclusion, our results indicate that treatment with Cys-LT inhibitors might be a relevant target for attenuating cholestatic liver damage.

Senescence-dependent impact of anti-RAGE antibody on endotoxemic liver failure

Aging often restricts the capacity of the immune system. Endotoxemia is characterized by an immune response initiated by a group of pattern recognition receptors including the receptor for advanced glycation end products (RAGE). The aim of this study was to clarify to which extent RAGE and its signaling pathways such as the so called mitogen-activated protein kinase (MAPK) pathways can contribute to the perpetuation of inflammation in the aging organism. We used senescence-accelerated-prone (SAMP8) and senescence-accelerated-resistant (SAMR1) mice and studied them at the age of 2 and 6 months. Livers of SAMP8 mice had significantly higher malondialdehyde concentrations and a modest reduction of glyoxalase-I expression. Consequently, the abundance of highly modified advanced glycation end products was increased in the liver and plasma of these mice. After galactosamine/lipopolysaccharide-induced acute liver injury, significant activation of the MAPK cascade was observed in both mouse strains. Administration of an anti-RAGE antibody diminished p42/44-phosphorylation as well as tissue injury in SAMP8 mice, whereas the identical treatment in SAMR1 mice leads to a significant increase in p42/44-phosphorylation and intensified liver injury. This observation suggests that dependent on the senescence of the organism, anti-RAGE antibody can have differential effects on the progression of endotoxemic liver failure.

Pathophysiology of microcirculatory dysfunction and the pathogenesis of septic shock

Multiple experimental and human trials have shown that microcirculatory alterations are frequent in sepsis. In this review, we discuss the various mechanisms that are potentially involved in their development and the implications of these alterations. Endothelial dysfunction, impaired inter-cell communication, altered glycocalyx, adhesion and rolling of white blood cells and platelets, and altered red blood cell deformability are the main mechanisms involved in the development of these alterations. Microcirculatory alterations increase the diffusion distance for oxygen and, due to the heterogeneity of microcirculatory perfusion in sepsis, may promote development of areas of tissue hypoxia in close vicinity to well-oxygenated zones. The severity of microvascular alterations is associated with organ dysfunction and mortality. At this stage, therapies to specifically target the microcirculation are still being investigated.

RAGE blockade and hepatic microcirculation in experimental endotoxaemic liver failure

BACKGROUND

Activation of the receptor for advanced glycation endproducts (RAGE) causes sustained activation of multiple inflammatory pathways. Therefore, RAGE has potential as a new therapeutic target in sepsis. The aim of this study was to analyse whether RAGE blockade in vivo prevents microcirculatory dysfunction and subsequent tissue injury in endotoxaemic liver failure.

METHODS

The hepatic microcirculation was analysed using intravital fluorescence microscopy in murine livers exposed to galactosamine/lipopolysaccharide (G/L) and treated with an anti-RAGE antibody (abRAGE) either 12 h before or h after exposure to G/L. Blood and liver tissue samples were harvested for analysis of leucocyte tissue infiltration, apoptotic and necrotic damage as well as RAGE downstream pathway signalling.

RESULTS

Sinusoidal perfusion failure in livers exposed to G/L was reduced significantly by both pretreatment and post-treatment with abRAGE. Hepatic inflammation induced by exposure to G/L was also attenuated by abRAGE administration, as shown by a 55 per cent reduction in sinusoidal leucocyte stasis, a 65 per cent decrease in venular leucocyte rolling and adhesion, and an 85 per cent reduction in leucocyte tissue infiltration. Treatment with abRAGE markedly reduced hepatocellular apoptosis and necrosis in livers exposed to G/L, and blunted the rise in plasma high-mobility group protein B1 levels. Finally, G/L-induced activation of the mitogen-activated protein kinase cascade was also reduced significantly by blockade of RAGE.

CONCLUSION

RAGE plays an important role in mediating endotoxaemic liver damage. RAGE blockade may have potential therapeutic value. SURGICAL RELEVANCE: The innate immune response to endoxaemia is initiated by a group of pattern recognition receptors, including the receptor for advanced glycation endproducts (RAGE). As RAGE is well known for perpetuation of inflammatory processes, blockade of this receptor might be of particular value in reducing or even halting endoxaemia-related organ disorders. Using intravital fluorescence microscopy this study demonstrated in vivo that pretreatment, but also post-treatment, with a RAGE-blocking antibody attenuated hepatic microcirculatory deterioration and leucocyte recruitment, and thus diminished liver injury in a murine model of endotoxaemic organ failure. These data underline the important role of RAGE in the innate immune response and support the potential therapeutic value of blocking this pattern recognition receptor.

A pan-caspase inhibitor reduces myocyte apoptosis and neuropathic pain in rats with chronic constriction injury of the sciatic nerve

BACKGROUND

Chronic constriction injury is a widely used model for neuropathic pain in rats. It presents with symptoms resembling human neuropathic pain, such as spontaneous pain, hyperalgesia, and allodynia. Recently, myocyte apoptosis was found in neuropathic rats as a possible promoter of pain and motor dysfunction. Our aim in this study was to demonstrate whether muscle cell apoptosis contributes to neuropathic pain in this animal model.

METHODS

To clarify this issue, we examined pain, nutritive perfusion, and inflammation in muscle tissue as well as myocyte apoptosis in rats with neuropathic pain established by chronic constriction injury of the sciatic nerve. Animals received either the pan-caspase inhibitor zVAD (OMe)-fmk (n = 5) or equivalent volumes of vehicle (n = 6). Sham-operated rats served as controls (n = 6).

RESULTS

At day 4 after nerve ligation, there were no signs of perfusion failure or muscle tissue inflammation in all experimental groups. However, animals treated with the vehicle had marked myocyte apoptosis, which was found almost completely blocked in zVA-Dtreated animals. The zVA-Dtreated animals presented with a significant reduction of pain upon heat, cold, and mechanical stimulation comparable with values found in sham controls.

CONCLUSIONS

Myocyte apoptosis possibly contributes to thermal and mechanical allodynia in this experimental model for neuropathic pain. The development of neuropathic pain symptoms did not depend on disturbances in microcirculation or muscle tissue inflammation.

Reactive oxygen and nitrogen species in sepsis-induced hepatic microvascular dysfunction

Objective and design

Hepatic microvascular dysfunction is a critical event in the development of liver failure during sepsis. Activated blood cells and reactive oxygen and nitrogen species (RONS) have been implicated in the pathogenesis of sepsis.

Methods

Intravital-videomicroscopy was used to determine whether RONS contribute to the recruitment of leukocytes/platelets in the hepatic microvasculature during sepsis. Six hours following cecal-ligation and puncture (CLP), disturbances of the hepatic microvasculature were assessed in WT-mice (C57Bl/6 J; n = 8), in mice lacking gp91^phox(n = 5), overexpressing superoxide-dismutase (SOD, n = 8), in WT-mice treated with a NOS-inhibitor (l-NAME, n = 5), lacking nNOS, eNOS or iNOS (n = 5 each), treated with the NO-donor DetaNO (n = 5), in WT-mice treated with gadolinium-chloride (GdCl₂, n = 5) and compared to a group of WT-mice following a sham operation (n = 8). Six hours post-CLP, the adhesion of leukocytes and platelets in terminal hepatic venules (THV) and sinusoids was quantified.

Results

In WT-mice, CLP elicited increases in the number of adherent leukocytes and platelets. Similar responses to CLP were noted in mice overexpressing SOD or lacking either eNOS or gp91^phox. The blood-cell recruitment was significantly blunted in septic iNOS-knockout mice and this response was reversed by pre-treatment with DetaNO.

Conclusion

These findings suggest that iNOS-derived NO is a determinant of the pro-inflammatory phenotype assumed by the hepatic microvasculature during sepsis.

Monitoring the microcirculation

One of the main goals of hemodynamic support is to preserve tissue perfusion. However issue perfusion is related more to microvascular perfusion than aortic blood flow. Monitoring the microcirculation has long been difficult. Recent technologic advances have made feasible monitoring of the microcirculation at bedside of critically ill patients. In this review, we will discuss the relevance of the various tools available to monitor the microcirculation. Videomicroscopic devices such as sidestream darkfield imaging are the most appropriate techniques to evaluate the microcirculation, taking into account the heterogeneous aspect of diseased microcirculation, as in sepsis. The microcirculation can also be indirectly assessed by measuring tissue PCO2. Transcutaneous PCO2 measurement at ear lobe is particularly promising. Finally, near infrared spectroscopy can also provide interesting information, especially using vascular occlusion tests which reactivity of the microcirculation to a transient hypoxic insult. These different devices have provided important data helping us to better understand the pathophysiology of sepsis and multiple organ failure.

Protective effect of melittin on inflammation and apoptosis in acute liver failure

Acute hepatic failure remains an extremely poor prognosis and still results in high mortality. Therefore, better treatment is urgently needed. Melittin, a major component of bee venom, is known to inhibit inflammatory reactions induced by lipopolysaccharide (LPS) or tumor necrosis factor (TNF)-α in various cell types. However, there is no evidence of the anti-inflammatory and anti-apoptotic effect of melittin on liver cells. In the present study, we investigated the effects of melittin on D: -galactosamine (GalN)/lipopolysaccharide (LPS)-induced acute hepatic failure. Acute liver injury was induced with GalN/LPS to determine in vivo efficacy of melittin. Mice were randomly divided into four groups: sterile saline treated group (NC), melittin only treated group (NM), GalN/LPS-treated group (GalN/LPS), and GalN/LPS treated with melittin group (M+GalN/LPS). Mice were given intraperitoneal GalN/LPS with or without melittin treatment. Liver injury was assessed biochemically and histologically. Inflammatory cytokines in the serum, apoptosis of hepatocytes, and cleavage of caspase-3 in the liver were determined. The expression of TNF-α and interleukin (IL)-1β were increased in the GalN/LPS group. However, treatment of melittin attenuated the increase of inflammatory cytokines. The M+GalN/LPS group showed significantly fewer apoptotic cells compared to the GalN/LPS group. Melittin significantly inhibited the expression of caspase and bax protein levels as well as cytochrome c release in vivo. In addition, melittin prevented the activation of the transcription factor nuclear factor-kappa B (NF-κB) induced by GalN/LPS. These results clearly indicate that melittin provided protection against GalN/LPS-induced acute hepatic failure through the inhibition of inflammatory cytokines and apoptosis.

Interaction between Kupffer cells and platelets in the early period of hepatic ischemia-reperfusion injury--an in vivo study

BACKGROUND

Hepatic ischemia-reperfusion (I/R) leads to activation of Kupffer cells (KCs). The activated KCs cause platelet and leukocyte adhesion to the sinusoidal endothelium. Previously, we reported that platelet-endothelium interactions occur earlier than leukocyte responses. The aim of this study was to evaluate the interaction between platelets and KCs in the hepatic microcirculation after I/R.

MATERIALS AND METHODS

Sprague-Dawley rats were divided into three groups: the no-ischemia group (control group; n = 6); the 20-min ischemia group (I/R group; n = 6); and the 20-min ischemia + anti-rat platelet serum group (APS group; n = 6). KCs were labeled using the liposome entrapment method. The number of adherent platelets was observed for up to 120 min after reperfusion by intravital microscopy. To investigate the effects of platelets on I/R injury, rats were injected intravenously with rabbit APS for platelet depletion.

RESULTS

In the I/R group, the number of adherent platelets increased significantly after I/R. More than 50% of the adherent platelets adhered to KCs. Electron microscopy indicated that the platelets attached to the KCs after hepatic ischemia. The histologic findings indicated liver damage and apoptosis of hepatocytes in zone 1. In the I/R group, but not in the control and APS groups, serum ALT increased immediately after reperfusion.

CONCLUSIONS

We succeeded in visualizing the dynamics of both KCs and platelets in the hepatic sinusoids. Liver ischemia induced the adhesion of platelets to KCs in the early period, which could play a key role in reperfusion injury of the liver.

The G-protein-coupled bile acid receptor, Gpbar1 (TGR5), negatively regulates hepatic inflammatory response through antagonizing nuclear factor κ light-chain enhancer of activated B cells (NF-κB) in mice

Gpbar1 (TGR5), a membrane-bound bile acid receptor, is well known for its roles in regulation of energy homeostasis and glucose metabolism. TGR5 also displays strong attenuation of macrophage reactivity in vitro, but the physiological roles of TGR5 in inflammatory response, and its mechanism, is unknown. Here, we demonstrate that TGR5 is a negative modulator of nuclear factor kappa light-chain enhancer of activated B cells (NF-κB)-mediated inflammation. TGR5 activation suppresses the phosphorylation of nuclear factor of kappa light polypeptide gene enhancer in B-cells inhibitor, alpha (IκBα), the translocation of p65, NF-κB DNA-binding activity, and its transcription activity. Furthermore, TGR5 activation enhances the interaction of IκBα and β-arrestin2. Suppression of NF-κB transcription activity and its target gene expression by TGR5 agonist are specifically abolished by the expression of anti-β-arrestin2 small interfering RNA. These results show that TGR5 suppresses the NF-κB pathway by mediation of the interaction between IκBα and β-arrestin2. In a lipopolysaccharide (LPS)-induced inflammation model, TGR5(-/-) mice show more severe liver necroses and inflammation, compared with wild-type (WT) mice. Activation of TGR5 by its agonist ligand inhibits the expression of inflammatory mediators in response to NF-κB activation induced by LPS in WT, but not TGR5(-/-), mouse liver.

CONCLUSION

These findings identify TGR5 as a negative mediator of inflammation that may serve as an attractive therapeutic tool for immune and inflammatory liver diseases.

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

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

Western diet enhances hepatic inflammation in mice exposed to cecal ligation and puncture

Background

Obese patients display an exaggerated morbidity during sepsis. Since consumption of a western-style diet (WD) is a major factor for obesity in the United States, the purpose of the present study was to examine the influence of chronic WD consumption on hepatic inflammation in mice made septic via cecal ligation and puncture (CLP). Feeding mice diets high in fat has been shown to enhance evidence of TLR signaling and this pathway also mediates the hepatic response to invading bacteria. Therefore, we hypothesized that the combined effects of sepsis and feeding WD on TRL-4 signaling would exacerbate hepatic inflammation. Male C57BL/6 mice were fed purified control diet (CD) or WD that was enriched in butter fat (34.4% of calories) for 3 weeks prior to CLP. Intravital microscopy was used to evaluate leukocyte adhesion in the hepatic microcirculation. To demonstrate the direct effect of saturated fatty acid on hepatocytes, C3A human hepatocytes were cultured in medium containing 100 μM palmitic acid (PA). Quantitative real-time PCR was used to assess mRNA expression of tumor necrosis factor-alpha (TNF-α, monocyte chemotactic protein-1 (MCP-1), intercellular adhesion molecule-1 (ICAM-1), toll-like receptor-4 (TLR-4) and interleukin-8 (IL-8).

Results

Feeding WD increased firm adhesion of leukocytes in the sinusoids and terminal hepatic venules by 8-fold six hours after CLP; the increase in platelet adhesion was similar to the response observed with leukocytes. Adhesion was accompanied by enhanced expression of TNF-α, MCP-1 and ICAM-1. Messenger RNA expression of TLR-4 was also exacerbated in the WD+CLP group. Exposure of C3A cells to PA up-regulated IL-8 and TLR-4 expression. In addition, PA stimulated the static adhesion of U937 monocytes to C3A cells, a phenomenon blocked by inclusion of an anti-TLR-4/MD2 antibody in the culture medium.

Conclusions

These findings indicate a link between obesity-enhanced susceptibility to sepsis and consumption of a western-style diet.

Effects of propionyl-L-carnitine on ischemia-reperfusion injury in hamster cheek pouch microcirculation

Background and purpose Propionyl-l-carnitine (pLc) exerts protective effects in different experimental models of ischemia–reperfusion (I/R). The aim of the present study was to assess the effects of intravenously and topically applied pLc on microvascular permeability increase induced by I/R in the hamster cheek pouch preparation. Methods The hamster cheek pouch microcirculation was visualized by fluorescence microscopy. Microvascular permeability, leukocyte adhesion to venular walls, perfused capillary length, and capillary red blood cell velocity (V_RBC) were evaluated by computer-assisted methods. E-selectin expression was assessed by in vitro analysis. Lipid peroxidation and reactive oxygen species (ROS) formation were determined by thiobarbituric acid-reactive substances (TBARS) and 2′-7′-dichlorofluorescein (DCF), respectively. Results In control animals, I/R caused a significant increase in permeability and in the leukocyte adhesion in venules. Capillary perfusion and V_RBC decreased. TBARS levels and DCF fluorescence significantly increased compared with baseline. Intravenously infused pLc dose-dependently prevented leakage and leukocyte adhesion, preserved capillary perfusion, and induced vasodilation at the end of reperfusion, while ROS concentration decreased. Inhibition of nitric oxide synthase prior to pLc caused vasoconstriction and partially blunted the pLc-induced protective effects; inhibition of the endothelium-derived hyperpolarizing factor (EDHF) abolished pLc effects. Topical application of pLc on cheek pouch membrane produced the same effects as observed with intravenous administration. pLc decreased the E-selectin expression. Conclusions pLc prevents microvascular changes induced by I/R injury. The reduction of permeability increase could be mainly due to EDHF release induce vasodilatation together with NO. The reduction of E-selectin expression prevents leukocyte adhesion and permeability increase.

Kupffer cell depletion reduces hepatic inflammation and apoptosis but decreases survival in abdominal sepsis

OBJECTIVE

During abdominal sepsis, the activation of hepatic Kupffer cells (KC) and its consequences are of central interest. This study evaluates the impact of selective KC depletion on hepatic microcirculation, cytokine release, and systemic alterations in the colon ascendens stent peritonitis (CASP), a model of polymicrobial abdominal sepsis.

METHODS

For KC depletion clodronate liposomes were injected 24 h before CASP surgery in female C57BL/6N mice. Three and 12 h after CASP, in-vivo fluorescence microscopy of the liver was performed. Analysis of hepatocellular apoptosis was conducted by immunohistochemistry. In addition, levels of tumor necrosis factor (TNF), IL-6, and IL-10 in the liver, lungs, spleen, and plasma were determined, and bacteriology and survival analysis were performed.

RESULTS

CASP led to significant sinusoidal perfusion failure, increased leukocyte recruitment, hepatocellular apoptosis and increased levels of TNF, IL-6, and IL-10 in the liver and plasma. KC depletion before CASP significantly reduced leukocyte recruitment to the liver and hepatocellular apoptosis. IL-10 secretion decreased dramatically in the liver and plasma of KC-depleted septic mice. In contrast, TNF levels were clearly elevated after clodronate treatment. In the lung and spleen, a compensatory upregulation of IL-10 could be detected after KC depletion. Clodronate treatment resulted in a significant reduction in survival.

CONCLUSION

The results indicate that KC depletion is locally protective in polymicrobial abdominal sepsis, as it reduces hepatic inflammation and apoptosis. These effects could be observed in the presence of clearly elevated TNF levels. However, the lack of IL-10 in KC-depleted mice resulted in a detrimental systemic proinflammation.

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.

Urinary trypsin inhibitor protects against liver injury and coagulation pathway dysregulation induced by lipopolysaccharide/D-galactosamine in mice

Urinary trypsin inhibitor (UTI), a serine protease inhibitor, has been widely used for patients with inflammatory disorders including disseminated intravascular coagulation, shock, and pancreatitis in Japan. Our recent studies using UTI-null (-/-) mice have shown that UTI protects against systemic inflammatory responses and acute lung injury. However, the role of UTI in liver injury has not been elucidated. This study determined the contribution of UTI to liver injury and coagulatory disturbance induced by lipopolysaccharide and D-galactosamine (LPS/D-GalN) using UTI (-/-) and wild-type (WT) mice. LPS/D-GalN treatment caused severe liver injury characterized by neutrophilic inflammation, hemorrhagic change, necrosis, and apoptosis, which was more prominent in UTI (-/-) than in WT mice. In both genotypes of mice, LPS/D-GalN challenge caused elevations of aspartate amino-transferase and alanine amino-transferase, prolongation of the prothrombin and activated partial thromboplastin time, and decreases in fibrinogen and platelet counts, as compared with vehicle challenge. These changes, however, were significantly greater in UTI (-/-) than in WT mice. Circulatory levels of tumor necrosis factor (TNF)-alpha (P<0.05) and interferon (IFN)-gamma were also greater in UTI (-/-) than in WT mice after LPS/D-GalN challenge. These results suggest that UTI protects against severe liver injury and subsequent coagulatory disturbance induced by LPS/D-GalN, which was mediated, at least partly, through the suppression of TNF-alpha production along with its antiprotease activity.

Role of the perforin/granzyme cell death pathway in D-Gal/LPS-induced inflammatory liver injury

Cytotoxic T lymphocytes and their granule components, such as perforin and granzyme, play an important role in the defense of hepatic infections caused by different pathogens. Moreover, it has been shown in vitro that hepatocytes can initiate cell death via a perforin-dependent mechanism. Although it is well known that hepatocellular apoptosis in D-galactosamine/lipopolysaccharide (D-Gal/LPS)-associated liver failure is mediated by TNF-alpha-dependent Fas/FasL cytotoxicity, there is no information on the role of perforin-mediated mechanisms in vivo. Therefore, we studied whether the cytolytic perforin/granzyme pathway contributes to the D-Gal/LPS-associated hepatotoxicity. Perforin knockout (Pko) mice showed significantly higher hepatic TNF-alpha and IL-6 mRNA expression as well as plasma TNF-alpha and IL-6 concentrations within the first hour upon D-Gal/LPS challenge compared with perforin wild-type (Pwt) mice. At 6 h upon D-Gal/LPS challenge, Pko mice further presented with higher transaminase release and onconecrotic tissue damage, whereas hepatocellular apoptosis and caspase-3 cleavage remained unaffected by the perforin deficiency. Pretreatment with a recombinant human TNF-alpha receptor fusion protein attenuated necrotic and apoptotic tissue damage and reduced plasma transaminase activities as well as cytokine release, thereby preventing acute liver failure in Pko mice as effectively as in Pwt mice. These data do not only confirm the significance of TNF-alpha as distal mediator of hepatic injury in this model but simultaneously reveal a contribution of a perforin-dependent immunoregulation, limiting the D-Gal/LPS-induced overwhelming cytokine release and onconecrotic tissue injury.

Uncoupling protein-2 deficiency provides protection in a murine model of endotoxemic acute liver failure

OBJECTIVE

Liver injury and cell death are prominent features in the pathogenesis of acute liver failure. Mitochondrial uncoupling protein 2 plays a controversial role in liver cell death through its involvement in the production of reactive oxygen species and adenosine triphosphate.

DESIGN

This randomized controlled animal study was designed to investigate the exact role of uncoupling protein 2 in the pathogenesis of endotoxemic acute liver failure.

SETTING

Research laboratory of an academic institution. SUBJECTS, INTERVENTIONS, AND MEASUREMENTS: Uncoupling protein 2+/+ and uncoupling protein 2-/- mice were challenged with D-galactosamine (Gal, 720 mg/kg intraperitoneally) and Escherichia coli lipopolysaccharide (10 microg/kg intraperitoneally) and studied 6 hrs thereafter (n = 5 per group). Control mice received physiologic saline (n = 5 per group). Analysis included in vivo fluorescence microscopy of hepatic microcirculation and hepatocellular apoptosis as well as plasma malondialdehyde concentrations as reactive oxygen species-dependent lipid peroxidation product and hepatic adenosine triphosphate levels.

MAIN RESULTS

Administration of Gal-lipopolysaccharide in uncoupling protein 2+/+ mice caused systemic cytokine release and malondialdehyde production. Further, it provoked marked hepatic damage, characterized by intrahepatic leukocyte recruitment (10.5 +/- 1.3 n/mm2 vs. 3.3 +/- 0.5 n/mm2), microvascular perfusion failure (33.1% +/- 1.6% vs. 2.3% +/- 0.4%), and adenosine triphosphate depletion (3.4 +/- 0.9 micromol/g vs. 6.4 +/- 0.9 micromol/g). Furthermore, uncoupling protein +/+ mice revealed a huge rise in cell apoptosis, given by high numbers of hepatocytes exhibiting nuclear chromatin fragmentation (44.9 +/- 11.5 n/mm2 vs. 0.0 +/- 0.0 n/mm2) and cleaved caspase-3 expression (1.24 +/- 0.24 vs. 0.06 +/- 0.04). Liver injury was coexistent with enzyme release (alanine aminotransferase 442 +/- 126 U/L vs. 57 +/- 12 U/L) and necrotic cell death. Of interest, Gal-lipopolysaccharide-exposed uncoupling protein 2-/- mice exhibited higher rates of hepatocellular apoptosis (135.6 +/- 46.0 n/mm2) as well as cleaved caspase-3 expression (1.75 +/- 0.25), however, preserved hepatic adenosine triphosphate (6.4 +/- 1.7), milder perfusion failure (24.5 +/- 2.4) and decreased leukocyte recruitment (2.7 +/- 0.2), less necrotic injury, lower transaminase levels (340 +/- 91), and finally better survival rates.

CONCLUSION

The higher adenosine triphosphate availability in uncoupling protein 2-deficient mice might allow hepatocytes to undergo apoptosis as an energy-consuming mode of cell death, while at the same time cellular adenosine triphosphate levels seem to increase hepatic resistance against harmful effects upon Gal-lipopolysaccharide exposure. As net result, uncoupling protein 2 deficiency provided protection under endotoxemic stress conditions, underlining the significant role of the bioenergetic status in critical illness.

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.

Role of LPS in the hepatic microvascular dysfunction elicited by cecal ligation and puncture in mice

BACKGROUND/AIMS

Sepsis remains a leading cause of death in critically ill patients. Because endotoxemia is viewed as a key mediator of sepsis-induced inflammation, administration of bacterial endotoxin (LPS) is often used to simulate sepsis in experimental animals. This study tests the hypothesis that LPS is a critical determinant of the hepatic microvascular dysfunction in mice made septic by cecal ligation and puncture (CLP).

METHODS

Intravital videomicroscopy was used to quantify sinusoidal perfusion, and platelet and leukocyte adhesion in terminal hepatic venules (THV) and sinusoids in LPS-sensitive and LPS-insensitive mice subjected to CLP or LPS (i.p.). mRNA expression of TLR-2, TLR-4, MyD-88, and Ly-96 was also assessed.

RESULTS

While LPS-sensitive mice responded to both CLP and LPS challenges with elevated leukocyte and platelet adhesion in THV and sinusoids, and a reduced sinusoidal perfusion density, LPS-insensitive mice exhibited comparable blood cell adhesion and sinusoidal malperfusion following CLP, but not LPS. Hepatic mRNA of MyD-88 and TLR-2 was elevated in the CLP and LPS groups. Endotoxin was not detectable in the blood of LPS-sensitive mice after CLP, but was elevated after LPS administration.

CONCLUSIONS

These findings do not support a major role for LPS in the hepatic microvascular disturbances associated with polymicrobial sepsis.

Local interaction of apoptotic hepatocytes and Kupffer cells in a rat model of systemic endotoxemia

AIM

There is strong evidence that hepatocellular apoptosis is not only initiated by circulating blood cells which become adherent within the endotoxemic liver, but also contributes to further sustain the inflammatory cell-cell response.

METHODS

Because previous studies assumed the importance of the role of cellular cross-talk in mediating inflammatory liver injury, we herein examined the activation of Kupffer cells (KCs) and their spatial coincidence with intrahepatic leukocyte adherence and hepatocellular apoptosis at 6 h after intraperitoneal exposure of rats with lipopolysaccharide (10 mg/kg).

RESULTS

In vivo multifluorescence microscopy revealed liver injury including nutritive perfusion failure, tissue hypoxia, leukocyte accumulation, as well as KC activation and parenchymal apoptotic cell death. Detailed spatial analysis revealed frequent colocalization of activated KCs with apoptotic hepatocytes. Colocalization was absent in saline-treated controls.Colocalization was confirmed by histochemistry, which showed ED1-positive KCs neighboring and engulfing TUNEL-positive hepatocytes. Colocalization of KCs with leukocytes ranged between 4% and 5% and did not increase in endotoxemic animals. Taken together, the present results indicate that apoptotic cell death of hepatocytes may stimulate phagocytosis by neighboring KCs. Direct KC-leukocyte contact seems not to be mandatory for cellular communication in the process of hepatocellular apoptosis.

CONCLUSION

With respect to the fundamental importance of cell apoptosis, improved knowledge of these cell-cell interactions might allow the development of new therapeutic strategies through the regulation of apoptotic cell death.

Attenuation of inflammation and apoptosis by pre- and posttreatment of darbepoetin-alpha in acute liver failure of mice

In many liver disorders inflammation and apoptosis are important pathogenic components, finally leading to acute liver failure. Erythropoietin and its analogues are known to affect the interaction between apoptosis and inflammation in brain, kidney, and myocardium. The present study aimed to determine whether these pleiotropic actions also exert hepatoprotection in a model of acute liver injury. C57BL/6J mice were challenged with d-galactosamine (Gal) and Escherichia coli lipopolysaccharide (LPS) and studied 6 hours thereafter. Animals were either pretreated (24 hours before Gal-LPS exposure) or posttreated (30 minutes after Gal-LPS exposure) with darbepoetin-alpha (DPO, 10 mug/kg i.v.). Control mice received physiological saline. Administration of Gal-LPS caused systemic cytokine release and provoked marked hepatic damage, characterized by leukocyte recruitment and microvascular perfusion failure, caspase-3 activation, and hepatocellular apoptosis as well as enzyme release and necrotic cell death. DPO-pretreated and -posttreated mice showed diminished systemic cytokine concentrations, intrahepatic leukocyte accumulation, and hepatic perfusion failure. Hepatocellular apoptosis was significantly reduced by 50 to 75% after DPO pretreatment as well as posttreatment. In addition, treatment with DPO also significantly abrogated necrotic cell death and liver enzyme release. In conclusion, these observations may stimulate the evaluation of DPO as hepatoprotective therapy in patients with acute liver injury.

Antileukoproteinase protects against hepatic inflammation, but not apoptosis in the response of D-galactosamine-sensitized mice to lipopolysaccharide

BACKGROUND AND PURPOSE

There is major evidence for the strong bi-directional interrelation of parenchymal cell apoptosis and leukocyte accumulation and inflammation in acute liver injury. Therefore, the aim of this in vivo study was to investigate the anti-apoptotic and anti-inflammatory potential of antileukoproteinase (ALP) in a murine model of acute liver failure.

EXPERIMENTAL APPROACH

C57BL/6J mice were given galactosamine (D-GalN) and E. coli lipopolysaccharide (LPS) followed by administration of saline or ALP. Besides survival rate, hepatic tissue damage and inflammatory response were analyzed by intravital fluorescence microscopy 6 hours after treatment. In addition, immunohistochemical analysis of NFkappaB-p65 and hepatocellular apoptosis, plasma levels of AST/ALT, TNF-alpha and IL-10 were determined.

KEY RESULTS

Administration of D-GalN/LPS provoked hepatic damage, including marked leukocyte recruitment and microvascular perfusion failure, as well as hepatocellular apoptosis and enzyme release. NFkappaB-p65 became increasingly detectable in hepatocellular nuclei, accompanied by a rise of TNF-alpha and IL-10 plasma levels. ALP markedly reduced intrahepatic leukocyte accumulation, nuclear translocation of NFkappaB and plasma levels of TNF-alpha and IL-10. Moreover, liver enzyme levels indicated the absence of necrotic parenchymal cell death. In contrast, ALP failed to block both apoptosis and caspase-3 levels and the mortality rate of ALP-treated animals was comparable to that of saline-treated mice.

CONCLUSIONS AND IMPLICATIONS

ALP could effectively prevent D-GalN/LPS-associated intrahepatic inflammatory responses by inhibition of NFkappaB activity, but not apoptosis-driven mortality. Thus, a protease-inactivating approach such as application of ALP seems to be inadequate in damaged liver where apoptosis represents the predominant mode of cell death.

How microcirculation data have changed my clinical practice

PURPOSE OF REVIEW

The present review discusses how microcirculation assessment, which was recently made feasible, has altered clinical practice.

RECENT FINDINGS

Experimental data have provided important information on microcirculation alterations in disease states. Recent advances in imaging techniques have allowed microcirculation studies in critically ill patients. Derangements in microcirculation are variable and unpredictable, associated with organ dysfunction and outcome, and can be improved by therapeutic interventions. Recent studies not only confirm the beneficial effects of some drugs on the microcirculation, but also suggest new mechanisms of actions of these drugs. In particular, the interaction between the endothelial surface and circulating cells, and especially white blood cells, seems to be crucial. Although these imaging techniques provide important information, these remain difficult to implement at the bedside. Assessment of vasoreactivity using transient occlusion tests and indirect measurements of microvascular blood flow with laser Doppler or near infrared spectroscopy may be good alternatives.

SUMMARY

Microcirculation alterations are present in shock states, mainly septic shock, and can have a prognostic role and be the target of therapeutic interventions. To date, microcirculation analysis remains in the field of clinical investigation, but recently interesting clinical data have encouraged assessment of the microcirculation at the bedside.

Inhibition of Heme Oxygenase-1 Protects Against Tissue Injury in Carbon Tetrachloride Exposed Livers

BACKGROUND/AIMS

During the metabolism of the hepatotoxin carbon tetrachloride (CCl(4)) by cytochrome P450, heme, and free radicals are released. Heme oxygenase (HO-1) is an enzyme that is induced by heme as well as oxidative stress and has been reported to be involved in mediating protection against toxic liver injury. The purpose of the present study was to specify the role of HO-1 in CCl(4)-hepatotoxicity.

METHODS AND RESULTS

We could demonstrate an up-regulation of HO-1 protein in CCl(4)-exposed liver tissue that reaches its maximum after 6 to 12 h, along with intrahepatic leukocyte accumulation and tissue injury. When animals were pretreated with hemin for augmentation of HO-1 expression, CCl(4)-exposure was associated with a reduction of intrahepatic leukocyte accumulation, while inhibition of CCl(4)-induced HO-1 expression by tin protoporphyrin-IX (SnPP-IX) enhanced leukocytic response. Of interest, however, liver morphology, transaminases, and bile flow as parameters of hepatocellular integrity and excretory function did not concur with reduced leukocyte numbers in the hepatic microcirculation, and revealed best organ function and tissue preservation in case of HO-1 inhibition by SnPP-IX. In contrast, hemin-treated CCl(4)-exposed livers demonstrated pathologic enzyme release and cholestasis.

CONCLUSIONS

Taken together, inhibition of HO-1 in CCl(4)-hepatotoxicity protected the liver, while higher HO-1 activity harmed liver tissue, most probably due to interference of the HO-1 pathway with CCl(4)-dependent metabolism via cytochrome P450 and heme overload-associated toxicity.

Calpain inhibition attenuates iNOS production and midzonal hepatic necrosis in a repeat dose model of endotoxemia in rats

Systemic exposure to bacterial lipopolysaccharide (LPS, endotoxin) induces hypotension, disseminated intravascular coagulation and neutrophil infiltration in various organs including the lung, kidney and liver. A rat endotoxemic neutrophilic hepatitis model (repeat dose LPS, 10 mg/kg, i.v. 24 hours apart) was developed exhibiting hepatic neutrophil infiltration and mid-zonal hepatic necrosis. The goal of the study was to investigate the role of the intracellular enzyme calpain in the development of neutrophilic hepatitis with midzonal necrosis in this model. A second goal was to compare the observed protective effects of calpain inhibition with a relatively selective inducible nitric oxide synthase (iNOS) inhibitor aminoguanidine (AG) and an inhibitor of coagulation, heparin. When compared to rats administered LPS alone, administration of calpain 1 inhibitor prior to LPS significantly reduced hepatic iNOS expression, hepatic neutrophil infiltration and attenuated midzonal hepatic necrosis. Administration of AG or heparin prior to LPS also decreased liver iNOS expression, hepatic neutrophil infiltration and liver pathology comparable to calpain inhibition. Blood neutrophil activation, as measured by the neutrophil adhesion molecule CD11b integrin, was upregulated in all the LPS treated groups regardless of inhibitor administration. We conclude that amelioration of liver pathology via calpain inhibition is likely dependent on the down-regulation of iNOS expression in the rat model of LPS-mediated hepatitis.

Protective effects of PARP inhibition on liver microcirculation and function after haemorrhagic shock and resuscitation in male rats

OBJECTIVE

The aim of this study was to investigate the impact of the water-soluble poly-(ADP)-ribose-polymerase (PARP) inhibitor 5-aminoisoquinolinone (5-AIQ) on liver microcirculation and function after haemorrhagic shock and resuscitation.

DESIGN

Controlled, randomized animal study.

SETTING

University animal care facility and research laboratory.

SUBJECT

Male Sprague-Dawley rats were subjected to haemorrhagic shock for 1 h, followed by resuscitation with shed blood and crystalloid solution for a total of 5 h.

INTERVENTIONS

The PARP inhibitor 5-AIQ (3 mg/kg; n=7) or vehicle (n=7) was administered 5 min prior to resuscitation. Sham-operated animals without induction of shock served as controls (n=7).

MEASUREMENTS AND RESULTS

Using intravital fluorescence microscopy hepatic microcirculation was assessed at baseline, end of shock phase as well as 1 h and 5 h after resuscitation. Systemic arterial blood pressure and bile flow were continuously monitored. 5-AIQ treatment attenuated shock/resuscitation-induced increase of intrahepatic leukocyte-endothelial cell interaction with a marked reduction of both sinusoidal leukostasis and venular leukocyte adherence. Moreover, nutritive perfusion was found improved, guaranteeing sufficient oxygen supply to tissue, as indicated by low NADH autofluorescence, which was not different to that in controls. Most notably, excretory liver function reached baseline level over 5 h of reperfusion in 5-AIQ-treated animals.

CONCLUSIONS

In the present setting of shock/resuscitation in male rats the PARP inhibitor 5-AIQ proved to be very effective in ameliorating compromised liver microcirculation and function. Further research has to confirm that PARP inhibition is a suitable tool in the acute treatment of patients suffering from reduced circulating blood volume and thus microcirculatory organ dysfunction.

LPS/CD14 activation triggers SGLT-1-mediated glucose uptake and cell rescue in intestinal epithelial cells via early apoptotic signals upstream of caspase-3

Recent findings indicate that enhanced glucose uptake protects enterocytes from excessive apoptosis and barrier defects induced by LPS exposure. The aim of this study was to characterize the mechanisms responsible for increased sodium-dependent glucose cotransporter (SGLT)-1 activity in enterocytes challenged with LPS. SGLT-1-transfected Caco-2 cells were incubated with LPS in high glucose media. LPS increased SGLT-1 activity in dose- and time-dependent fashion, and is due to increased V(max) of the cotransporter. Elevated apical expression of SGLT-1 was also demonstrated. This LPS-induced effect was colchicine-inhibitable, suggesting microtubule-dependent translocation of SGLT-1 onto apical surface. Immunofluorescence staining showed expression of CD14 on the apical surface, but no TLR-4, on these cells. Neutralizing anti-CD14 decreased the LPS-induced upregulation of SGLT-1 activity, whereas anti-TLR-4 had no effect. Pharmacological studies indicated that signaling for LPS-mediated SGLT-1 glucose uptake depends on caspase-8 and -9 activation, but occurs independently of caspase-3. The findings describe a novel feedback mechanism within the apoptotic signaling pathway for SGLT-1-dependent cytoprotection. The observation suggests a new function for CD14 on enterocytes, involving the induction of the caspase-dependent SGLT-1 activity, which ultimately leads to cell rescue. The understanding of these signaling events may shed light on enterocytic cytoprotection and homeostasis mechanism upon pro-apoptotic challenges.

SGLT-1-mediated glucose uptake protects intestinal epithelial cells against LPS-induced apoptosis and barrier defects: a novel cellular rescue mechanism?

Excessive apoptosis induced by enteric microbes leads to epithelial barrier defects. This mechanism has been implicated in the pathogenesis of inflammatory bowel diseases (IBD) and bacterial enteritis. The sodium-dependent glucose cotransporter (SGLT-1) is responsible for active glucose uptake in enterocytes. The aim was to investigate the effects of SGLT-1 glucose uptake on enterocyte apoptosis and barrier defects induced by bacterial lipopolysaccharide (LPS). SGLT-1-transfected Caco-2 cells were treated with LPS (50 mug/mL) in low (5 mM) or high (25 mM) glucose media. LPS in low glucose induced caspase-3 cleavage, DNA fragmentation, and increased paracellular permeability to dextran in epithelial cells. These phenomena were significantly attenuated in high glucose. LPS increased SGLT-1 activity in high, but not low glucose media. Addition of phloridzin, which competitively binds to SGLT-1, inhibited the cytoprotection mediated by high glucose. Western blot showed that LPS in high glucose increased the levels of anti-apoptotic Bcl-2 and Bcl-X(L,) and did not change proapoptotic Bax. Differential extraction of membranous vs. cytosolic cell components demonstrated that high glucose inhibits mitochondrial cytochrome c translocation to cytosol. Collectively, SGLT-1-mediated glucose uptake increases anti-apoptotic proteins, and protects enterocytes from LPS-induced apoptosis and barrier defects. The understanding of this novel glucose-mediated rescue mechanism may lead to therapeutic interventions for various enteric diseases.

Immunostimulatory CpG-oligodeoxynucleotides (CpG-ODN) induce early hepatic injury, but provide a late window for protection against endotoxin-mediated liver damage

BACKGROUND/AIMS

An impaired immunologic response to infection has been recognized as a major defect in the pathogenesis of sepsis and multi-organ failure. Sepsis-associated liver dysfunction and damage are main determinants for the course of the disease. CpG-motif-containing DNA-sequences (CpG-ODN) were previously shown to confer protection in models of infection by stimulating both innate and specific immune responses. Herein, we studied the effect of CpG-ODN in lipopolysaccharide (LPS)-associated hepatotoxicity.

METHODS

Sprague Dawley rats pre-treated at day 6 with either CpG-ODN or inert DNA were challenged with E. coli LPS and subsequently studied for liver injury at 6 and 16 h using in vivo fluorescence microscopy and immunohistochemistry. Western blot protein analysis served for assessment of expression of TLR4, TNF receptor-associated factor 6 (TRAF6), NFkappaB and caspase-3. To evaluate CpG-ODN effects during non-septic conditions, additional animals were solely exposed to CpG-ODN and studied after 1 and 6 days.

RESULTS

CpG-ODN application induced marked hepatic microcirculatory deterioration and liver dysfunction at day 1, however, with almost complete recovery to normal at day 6. Interestingly, CpG-ODN pre-treatment decreased LPS-induced leukocyte-endothelial cell interaction, sinusoidal perfusion failure and caspase-3-dependent apoptotic cell death. Although Kupffer cell phagocytic activity was not affected, CpG-ODN pre-treatment in LPS-challenged animals attenuated hepatic protein expression of TRAF6 and NFkappaB and increased TLR4 by almost 100%.

CONCLUSIONS

CpG-containing DNA-sequences induce early hepatic injury, but mediate long-term protection against LPS hepatotoxicity. The mechanism of protection is based on the induction of cross-tolerance, probably via inhibition of the downstream TRAF6-NFkappaB signaling pathway and upregulation of the TLR4 surface receptor.

Comprehensive analysis of the regenerating mouse liver: an in vivo fluorescence microscopic and immunohistological study

BACKGROUND

Regeneration of tissue is a fundamental parameter of the liver's response to injury and is essential for post-operative recovery from hepatic resection. An adequate microvascular supply of both remnant tissue and newly formed cell clusters is necessary for the accurate restoration of the organ. However, a comprehensive analysis of hepatic architecture and microcirculation during liver regeneration is missing.

METHODS

Using intravital high resolution multifluorescence microscopy and histological techniques we analyzed the regenerating liver of mice at days 3, 5, and 8 after 68% hepatectomy.

RESULTS

Within the 8-day course of regeneration, liver weight restored to approximately 90% of its original mass. During the 8-day period of observation density of hepatocytes and Ito cells was constantly found reduced from 4,200 and 800 cells/mm(2) in non-hepatectomized control livers to approximately 2,500 and approximately 500 cells/mm(2). A transient decline of sinusoidal density was partly compensated by recruiting all sinusoids for perfusion with a final perfusion index of 79, 89, and 98% at days 3, 5, and 8 after resection. Increase of sinusoidal diameters preserved functional vessel area after resection, guaranteeing an adequate tissue oxygenation, as verified by low parenchymal NADH autofluorescence. The number of PCNA expressing hepatocytes rose 11-, 4-, and 2-fold at days 3, 5, and 8 after resection, followed by a maximum proliferation of sinusoidal lining cells at day 5. Cell apoptosis slightly increased, most probably in response to the restoration and to eliminate redundant cells. Liver regeneration was not associated with enhanced leukocyte-endothelial cell interaction, disproving inflammation as a relevant trigger for the regeneration.

CONCLUSION

The present data contribute to a better understanding of the complex vascular and cellular mechanisms during liver regeneration to develop strategies fighting against impeded liver growth.

Platelet Recruitment in the Murine Hepatic Microvasculature During Experimental Sepsis: Role of Neutrophils

OBJECTIVES

Sepsis is a major clinical problem that often results in the dysfunction or failure of multiple organs, including the liver. While inflammatory cell activation has been implicated as an early critical event in sepsis-induced liver dysfunction, there is growing evidence for the involvement of activated platelets in this pathologic process.

METHODS

Intravital microscopy was used in this study to assess the magnitude and time course of platelet adhesion in the liver microcirculation during experimental sepsis and to determine whether the platelet accumulation is linked to leukocyte infiltration. The adhesion of platelets and leukocytes in terminal hepatic venules (THV) and sinusoids was quantified at 2, 4, and 6 h after abdominal sepsis induced by cecal ligation and puncture (CLP).

RESULTS

While the rolling and firm adhesion of platelets and leukocytes in THV were not altered in the first 2 h after CLP, platelet recruitment was observed at 4 h and further elevated at 6 h after CLP. Leukocyte adhesion in THV exhibited a similar time course. A similar accumulation of blood cells in sinusoids was noted after CLP. This was accompanied by an increased number of nonperfused sinusoids. CLP-induced leukocyte and platelet recruitment in THV and sinusoids was attenuated in mice rendered neutropenic with anti-neutrophil serum.

CONCLUSION

These findings indicate that sepsis is associated with a neutrophil-dependent recruitment of platelets in the liver microcirculation that impairs sinusoidal perfusion and may contribute to the liver dysfunction associated with sepsis.

Gene expression profile and synovial microcirculation at early stages of collagen-induced arthritis

A better understanding of the initial mechanisms that lead to arthritic disease could facilitate development of improved therapeutic strategies. We characterized the synovial microcirculation of knee joints in susceptible mouse strains undergoing intradermal immunization with bovine collagen II in complete Freund's adjuvant to induce arthritis (i.e. collagen-induced arthritis [CIA]). Susceptible DBA1/J and collagen II T-cell receptor transgenic mice were compared with CIA-resistant FVB/NJ mice. Before onset of clinical symptoms of arthritis, in vivo fluorescence microscopy of knee joints revealed marked leucocyte activation and interaction with the endothelial lining of synovial microvessels. This initial inflammatory cell response correlated with the gene expression profile at this disease stage. The majority of the 655 differentially expressed genes belonged to classes of genes that are involved in cell movement and structure, cell cycle and signal transduction, as well as transcription, protein synthesis and metabolism. However, 24 adhesion molecules and chemokine/cytokine genes were identified, some of which are known to contribute to arthritis (e.g. CD44 and neutrophil cytosolic factor 1) and some of which are novel in this respect (e.g. CC chemokine ligand-27 and IL-13 receptor α₁). Online in vivo data on synovial tissue microcirculation, together with gene expression profiling, emphasize the potential role played by early inflammatory events in the development of arthritis.