Blood platelets and inflammation: their relationship with liver and digestive diseases

An expansion of knowledge from basic and clinical research has highlighted the critical role of platelets in inflammation and tissue repair in addition to their established contribution to hemostasis. Activated platelets are a rich source of mediators participating to inflammation and tissue regeneration. Platelet-derived microparticles recapitulate essential platelet functions and their contribution to the pathogenesis of inflammatory diseases has been emphasized. Recent findings suggest that platelets are both friends and foes for the liver. Platelets are essential to liver regeneration, platelet-derived serotonin being critical. However platelets can also exacerbate liver damage, as in immune-mediated injury. The dual role of platelets has recently been exemplified in animal models of liver fibrosis. Platelets release profibrogenic mediators, such as CXC Chemokine Ligand 4, that is instrumental in the progression of liver fibrosis. On the other hand, thrombocytopenia aggravates liver fibrosis, an outcome linked to the downregulation of hepatic stellate cell collagen production by platelet derived hepatocyte growth factor. CD154, a key molecule in inflammation, is expressed by platelets and is a pathogenic mediator in inflammatory bowel disease. Here, we summarize some of the mechanisms linking platelets with inflammation and comment few recent articles indicating why platelets may prove to be important pathogenic mediators in liver and gastrointestinal diseases.     

Novel functions of platelets in the liver

Platelets contain not only proteins needed for hemostasis but also many growth factors that are required for organ development, tissue regeneration, and repair. Thrombocytopenia, which is frequently observed in patients with chronic liver disease (CLD) and cirrhosis, is due to various causes, such as decreased thrombopoietin production and accelerated platelet destruction caused by hypersplenism; however, the relationship between thrombocytopenia and hepatic pathogenesis and the role of platelets in CLD are poorly understood. Thus, in this paper, the experimental evidence for platelets improving liver fibrosis and accelerating liver regeneration is summarized and addressed based on studies conducted in our laboratory and current progress reports from other investigators. Platelets improve liver fibrosis by inactivating hepatic stellate cells to decrease collagen production. The level of intracellular cAMP is increased by adenosine through its receptors on hepatic stellate cells, thereby resulting in inactivation of these cells. Adenosine is produced by degradation of adenine nucleotides, which are stored in abundance within the dense granules of platelets. The regenerative effect of platelets in the liver consists of three mechanisms: a direct effect on hepatocytes, a cooperative effect with liver sinusoidal endothelial cells, and a collaborative effect with Kupffer cells. Based on these experiments, a clinical trial suggested that the increase in platelets induced by platelet transfusion improved liver function in patients with CLD in a clinical setting.We highlight the current knowledge concerning the role of platelets in CLD and expect to open a novel avenue for application of these clinical therapies to treat liver disease.     

Platelets in liver disease,cancer and regeneration

Although viral hepatitis treatments have evolved over the years, the resultant liver cirrhosis still does not completely heal. Platelets contain proteins required for hemostasis, as well as many growth factors required for organ development, tissue regeneration and repair. Thrombocytopenia, which is frequently observed in patients with chronic liver disease(CLD) and cirrhosis, can manifest from decreased thrombopoietin production and accelerated platelet destruction caused by hypersplenism; however, the relationship between thrombocytopenia and hepatic pathogenesis, as well as the role of platelets in CLD, is poorly understood. In this paper, experimental evidence of platelets improving liver fibrosis and accelerating liver regeneration is summarized and addressed based on studies conducted in our laboratory and current progress reports from other investigators. In addition, we describe our current perspective based on the results of these studies. Platelets improve liver fibrosis by inactivating hepatic stellate cells, which decreases collagen production. The regenerative effect of platelets in the liver involves a direct effect on hepatocytes, a cooperative effect with liver sinusoidal endothelial cells, and a collaborative effect with Kupffer cells. Based on these observations, we ascertained the direct effect of platelet transfusion on improving several indicators of liver function in patients with CLD and liver cirrhosis. However, unlike the results of our previous clinical study, the smaller incremental changes in liver function in patients with CLD who received eltrombopag for 6 mo were due to patient selection from a heterogeneous population. We highlight the current knowledge concerning the role of platelets in CLD and cancer and anticipate a novel application of platelet-based clinical therapies to treat liver disease.     

Plasma P-selectin levels are elevated in patients with chronic liver disease.

P-selectin is a leukocyte receptor and platelet activation marker that has been shown to be involved in thrombogenesis as well as bleeding disorders and may represent a possible link between inflammation and thrombosis. In animal models, high plasma levels correlated with a procoagulant tendency. In acute liver damage models such as hepatic ischaemia-reperfusion-injury, P-selectin was found to be a key mediator of liver injury. In order to investigate the clinical and pathogenetic role of P-selectin in chronic liver diseases, plasma P-selectin levels were measured in 111 patients with chronic liver diseases. P-Selectin was significantly elevated in patients (median 56 ng/ml, range 0-180) compared with controls (n = 38, median 20 ng/ml, range 3.3-42, P < 0.001). Current clinical bleeding symptoms were common, whereas thrombotic events occurred rarely. P-selectin levels were not associated with haemorrhagic or thromboembolic complications. P-selectin correlated with platelet and white-blood-cell counts, but not with endothelial injury markers thrombomodulin and tissue factor or coagulation factors. Interestingly, P-selectin levels were not associated with Child's stage of cirrhosis or disease aetiology, but were generally elevated in chronic liver diseases. Severe hepatic leukocyte infiltration in liver histology was associated with a tendency towards higher P-selectin levels. In line with its role in acute liver damage, P-selectin elevation in chronic liver disease may suggest a possible pathogenetic role in the course of liver cirrhosis.     

炎症小体与慢性肝脏疾病

多种慢性肝脏疾病都与组织的无菌性炎症有关。核苷酸结合寡聚化结构域样受体家族形成的多蛋白复合物——炎症小体,作为炎症反应的核心,能被多种外源或内源性刺激激活,引起下游炎症因子分泌,诱发炎症反应,其过度激活会造成组织损伤。现已证实炎症小体在酒精性和非酒精性脂肪性肝病、肝脏缺血再灌注损伤及药物性肝损伤等疾病中起关键作用,是肝脏发生纤维化和癌变的决定因素之一。本文就炎症小体的结构、活化信号及激活通路、调节机制及其与慢性肝脏疾病关系的研究进展作一综述,以期为慢性肝脏疾病的治疗提供新的方向和靶点。     

Steatosis: co-factor in other liver diseases

The prevalence of fatty liver is rising in association with the global increase in obesity and type 2 diabetes. In the past, simple steatosis was regarded as benign, but the presence of another liver disease may provide a synergistic combination of steatosis, cellular adaptation, and oxidative damage that aggravates liver injury. In this review, a major focus is on the role of steatosis as a co-factor in chronic hepatitis C (HCV), where the mechanisms promoting fibrosis and the effect of weight reduction in minimizing liver injury have been most widely studied. Steatosis, obesity, and associated metabolic factors may also modulate the response to alcohol- and drug-induced liver disease and may be risk factors for the development of hepatocellular cancer. The pathogenesis of injury in obesity-related fatty liver disease involves a number of pathways, which are currently under investigation. Enhanced oxidative stress, increased susceptibility to apoptosis, and a dysregulated response to cellular injury have been implicated, and other components of the metabolic syndrome such as hyperinsulinemia and hyperglycemia are likely to have a role. Fibrosis also may be increased as a by-product of altered hepatocyte regeneration and activation of bipotential hepatic progenitor cells. In conclusion, active management of obesity and a reduction in steatosis may improve liver injury and decrease the progression of fibrosis.     

Acute-on-chronic liver failure in patients with severe acute respiratory syndrome coronavirus 2 infection

The corona virus disease 2019(COVID-19) pandemic caused by the severe acute respiratory syndrome corona virus 2(SARS-CoV-2) has had a significant impact on the lives of millions of people,especially those with other concomitant diseases,such as chronic liver diseases.To date,seven corona viruses have been identified to infect humans.The main site of pathological action of these viruses is lung tissue.However,a substantial number of studies have proven that SARSCoV-2 shows affinity towards severa...     

Modulation of liver injury by interleukin-10

Inflammation is commonly observed in liver diseases and is frequently complicated by fibrosis and cirrhosis in end-stage disease. The only curative treatment for cirrhotic patients is liver transplantation. However, organ shortage as well as an increasing organ demand call for early treatment of liver disease and prevention of fibrosis. Experimental data have shown the critical role of pro-inflammatory cytokines like tumor necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma) in the development of liver injury. Here, we review our work on the role of endogenously produced interleukin-10 (IL-10), a potent anti-inflammatory cytokine, in several experimental models of acute and chronic liver injury. First, in acute macrophage-mediated hepatitis induced by galactosamine/lipopolysaccharide administration, IL-10 neutralisation led to a more severe liver damage, whereas IL-10 injection, even delayed, was able to limit liver necrosis. A similar protective effect of IL-10 was observed in acute T cell-mediated hepatitis induced by concanavalin A (Con A) injection. The immunoregulatory role of IL-10 was then established after repeated exposition to Con A. In carbon tetrachloride liver injury, two other properties of IL-10 have been suggested: modulation of hepatocyte proliferation and modulation of liver fibrosis. Finally, the potential therapeutic applications in human liver disease as well as the potential side effects are discussed.     

Activation of blood platelets in chronic hepatitis and liver cirrhosis P-selectin expression on blood platelets and secretory activity of beta-thromboglobulin and platelet factor-4.

BACKGROUND/AIMS: Blood platelets are cells that quite often undergo damage in chronic liver diseases. Endotoxemia and hyperkinetic circulation influence platelets in an active manner. The role of platelets in the development of hepatitis and liver fibrosis is speculative. The aim of the study was to determine the influence of chronic liver diseases on platelets morphologic parameters, their secretory activity and P-selectin expression. METHODOLOGY: The examination was completed in the group of 29 patients with chronic hepatitis and 27 with liver cirrhosis of postinflammatory etiology (HBV, HCV). Liver biopsies were carried out in all patients. Thirty-two healthy individuals were the control group. Platelets morphological parameters (number, volume, platelet crit, micro- and macrothrombocyte fraction) were estimated. beta-thromboglobulin concentration and platelet factor 4 in blood serum as well as P-selectin expression on resting platelets and after thrombin activation were also examined. RESULTS: Number, volume, and platelet crit decreased with the advancement of a liver disease. Megathrombocyte fraction increased inversely with the severity of liver damage. The concentration of beta-thromboglobulin and platelet factor 4 alpha-granule contents in blood serum was higher 2- and 7-times, respectively than in healthy controls. P-selectin expression on resting platelets was considerably higher. After stimulation with thrombin, P-selectin expression was equal (chronic hepatitis) or higher (liver cirrhosis) than in the control. CONCLUSIONS: There are changes of platelet morphological parameters, with accompanying megathrombocyte fraction increase that occur in chronic liver diseases. Thrombocytes in chronic liver diseases and liver cirrhosis are more activated. Platelet sensitivity to stimuli in these ailments is higher (liver cirrhosis) than in the healthy controls.     

Acute kidney injury and post-reperfusion syndrome in liver transplantation

In the past decades liver transplantation(LT) has become the treatment of choice for patients with end stage liver disease(ESLD). The chronic shortage of cadaveric organs for transplantation led to the utilization of a greater number of marginal donors such as older donors or donors after circulatory death(DCD). The improved survival of transplanted patients has increased the frequency of long-term complications, in particular chronic kidney disease(CKD). Acute kidney injury(AKI) post-LT has been recently recognized as an important risk factor for the occurrence of denovo CKD in the long-term outcome. The onset of AKI post-LT is multifactorial, with pre-LT risk factors involved, including higher Model for End-stage Liver Disease score, more sever ESLD and pre-existing renal dysfunction, either with intra-operative conditions, in particular ischaemia reperfusion injury responsible for post-reperfusion syndrome(PRS) that can influence recipient's morbidity and mortality. Post-reperfusion syndrome-induced AKI is an important complication post-LT that characterizes kidney involvement caused by PRS with mechanisms not clearly understood and implication on graft and patient survival. Since preLT risk factors may influence intra-operative events responsible for PRS-induced AKI, we aim to consider all the relevant aspects involved in PRS-induced AKI in the setting of LT and to identify all studies that better clarified the specific mechanisms linking PRS and AKI. A Pub Med search was conducted using the terms liver transplantation AND acute kidney injury; liver transplantation AND post-reperfusion syndrome; acute kidney injury AND post-reperfusion syndrome; acute kidney injury AND DCD AND liver transplantation. Five hundred seventy four articles were retrieved on Pub Med search. Results were limited to title/abstract of English-language articles published between 2000 and 2015. Twenty-three studies were identified that specifically evaluated incidence, risk factors and outcome for patients developing PRS-induced AKI in liver transplantation. In order to identify intra-operative risk factors/mechanisms specifically involved in PRSinduced AKI, avoiding confounding factors, we have limited our study to "acute kidney injury AND DCD AND liver transplantation". Accordingly, three out of five studies were selected for our purpose.     

TGF β1 and PDGF AA override Collagen type I inhibition of proliferation in human liver connective tissue cells

Background  

A marked expansion of the connective tissue population and an abnormal deposition of extracellular matrix proteins are hallmarks of chronic and acute injuries to liver tissue. Liver connective tissue cells, also called stellate cells, derived from fibrotic liver have been thoroughly characterized and correspond phenotypically to myofibroblasts. They are thought to derive from fat-storing Ito cells in the perisinusoidal space and acquire a contractile phenotype when activated by tissue injury. In the last few years it has become evident that several peptide growth factors such as PDGF AA and TGF-β are involved in the development of fibrosis by modulating myofibroblast proliferation and collagen secretion. The fact that during the development of chronic fibrosis there is concomitant deposition of collagen, a known inhibitory factor, and sustained cell proliferation, raises the possibility that stellate cells from chronic liver fibrosis patients fail to respond to normal physiologic controls.     

The role of bone marrow stem cells in liver regeneration

Hepatic oval cells involved in some forms of liver regeneration express many markers also found on hematopoietic stem cells (HSCs). In addition, multiple independent reports have demonstrated that bone marrow cells can give rise to several hepatic epithelial cell types, including oval cells, hepatocytes, and duct epithelium. These observations have resulted in the hypothesis that bone marrow resident stem cells, specifically HSCs, are an important source for liver epithelial cell replacement, particularly during chronic injury. The function of such stem cells in hepatic injury responses is the topic of this article. Taken together, the published data on the role of bone marrow stem cells in liver damage suggest that they do not play a significant physiological role in the replacement of epithelial cells in any known form of hepatic injury. Fully functional bone marrow-derived hepatocytes exist but are extremely rare and are generated by cell fusion, not stem cell differentiation. Nonetheless, bone marrow-derived cells may play important indirect roles in liver regeneration. First, they may serve as a source for the replacement of endothelial cells. Second, hematopoietic cells, including lymphocytes, neutrophils, macrophages, and platelets, may provide crucial factors required for efficient healing of damaged liver.     

Platelets in regenerative medicine

Stem and progenitor cells have evolved as the central cell type in regenerative medicine. This focussed approach may, however, sometimes narrow the point of view. Recently, platelets have been shown to strongly influence progenitor cell biology and to serve as regenerative cells themselves. Platelets represent an important recruitment factor for circulating progenitor cells. Furthermore, they modulate progenitor cell chemotaxis, migration and differentiation. Platelets are crucial for the regeneration of parenchymatous organs such as the liver. Moreover, in the clinical setting, platelets are already applied for the restoration of connective and bone tissue. However, also adverse effects can be mediated by platelets and progenitor cells exposed to platelets, including the induction of pro-inflammatory processes. This review gives an update on platelets as regenerative cells and as modulators of progenitor cell biology in (patho-) physiological conditions. Abundant data obtained during the last decade have linked progenitor and stem cells to tissue repair. Very recent accumulating results from different groups revealed that platelets may have a strong influence on central functions of these progenitor cells. Only little is known about the impact of platelets themselves on tissue regeneration. Therefore, this review highlights the role of platelets themselves as a potential effector cell for tissue regeneration and their impact on progenitor cell biology.     

New insights into the coagulopathy of liver disease and liver transplantation

INTRODUCTION The liver plays several key roles in blood coagulation being involved in both primary and secondary hemostasis[1]. It is the site of synthesis of all coagulation factors and their inhibitors except for von Willebrand factor (vWf)[2]. Liver da…     

Dualistic role of platelets in living donor liver transplantation: Are they harmful?

Platelets are anucleate fragments mainly involved in hemostasis and thrombosis, and there is emerging evidence that platelets have other nonhemostatic potentials in inflammation, angiogenesis, regeneration and ischemia/reperfusion injury (I/R injury), which are involved in the physiological and pathological processes during living donor liver transplantation (LDLT). LDLT is sometimes associated with impaired regeneration and severe I/R injury, leading to postoperative complications and decreased patient survival. Recent studies have suggested that perioperative thrombocytopenia is associated with poor graft regeneration and postoperative morbidity in the short and long term after LDLT. Although it is not fully understood whether thrombocytopenia is the cause or result, increasing platelet counts are frequently suggested to improve posttransplant outcomes in clinical studies. Based on rodent experiments, previous studies have identified that platelets stimulate liver regeneration after partial hepatectomy. However, the role of platelets in LDLT is controversial, as platelets are supposed to aggravate I/R injury in the liver. Recently, a rat model of partial liver transplantation (LT) was used to demonstrate that thrombopoietin-induced thrombocytosis prior to surgery accelerated graft regeneration and improved the survival rate after transplantation. It was clarified that platelet-derived liver regeneration outweighed the associated risk of I/R injury after partial LT. Clinical strategies to increase perioperative platelet counts, such as thrombopoietin, thrombopoietin receptor agonist and platelet transfusion, may improve graft regeneration and survival after LDLT.     

Use of statins in patients with liver disease

Opinion statement  Cardiovascular disease is as common in individuals with chronic liver disease as in the general population. Moreover, recent data suggest that patients with nonalcoholic fatty liver disease (NAFLD) may have a cardiovascular risk greater than that conferred by the conventional risk factors. There is unequivocal evidence that cardiovascular disease is an important cause of morbidity and mortality in this patient population and thus requires consideration of aggressive therapy with lipid-lowering agents such as statins. Because all statins are hepatically cleared and can cause elevations in liver biochemistries, there is a concern that patients with underlying liver disease may be at increased risk for hepatotoxicity. However, recent data, along with an assessment of statin safety by the Liver Expert Panel, suggest that statins are generally well tolerated in patients with chronic liver disease such as NAFLD, primary biliary cirrhosis, and hepatitis C virus. These drugs also appear to be safe in patients with stable/compensated cirrhosis. However, decompensated cirrhosis and acute liver failure should be considered contraindications for lipid-lowering therapy as these patients are unlikely to benefit because of their generally grave prognosis. Although routine hepatic biochemical test monitoring is recommended, the cost-effectiveness of this approach has been questioned. The benefit of statins in patients with underlying liver disease who are otherwise important candidates for statin therapy far outweighs the risk of a very rare event of serious liver injury.     

Hepatic stellate cell behavior during resolution of liver injury

Acute self-limiting and chronic liver injury are both associated with activation and proliferation of hepatic stellate cells (HSCs). In chronic injury, activated stellate cells are the major source of the collagens that comprise fibrosis and cirrhosis, as well as of the tissue inhibitors of metalloproteinases (TIMPs) which inhibit collagen degradation. Recovery from acute and chronic injury is characterized by apoptosis of activated HSCs, which removes extracellular matrix-producing cells that are also expressing TIMPs, thereby relieving the inhibition of matrix degradation. HSC apoptosis is regulated in progressive injury and counterbalances cell proliferation. Apoptosis probably also represents a default pathway for the HSCs. The survival of activated HSCs in liver injury is dependent on soluble growth factors and cytokines, and on components of the fibrotic matrix. Additionally, stimulation of death receptors expressed on HSCs can precipitate their apoptosis. Our increasing understanding of the process of stellate cell behavior in recovery from injury is likely to be important to the design of antifibrotic therapies.     

Role of Platelets in Acute Lung Injury After Extracorporeal Circulation in Cardiac Surgery Patients: A Systemic Review

In vitro circulation (cardiopulmonary bypass, CPB) has been widely used in heart surgery. In the past, it was believed that the reduction of platelet count and impaired platelet function during cardiac surgery were the main causes of acute lung injury (ALI). ALI is a life-threatening clinical syndrome in critically ill patients due to an uncontrolled systemic inflammatory response resulting from direct injury to the lung or indirect injury in the setting of a systemic process. Platelets have an emerging and incompletely understood role in a myriad of ALI after extracorporeal circulation in cardiac surgery patients. An electronic literature search was performed using Pubmed, Scopus and Cinahl investigating ALI, pathogenesis, and role of platelets, treatment and management for ALI patients. Many studies have shown that in vitro circulation is a nonphysiological process that can lead to a decrease in the number of platelets and impaired platelet function, as well as varying degrees of lung damage. The relationship between the effects of in vitro circulation on platelets and acute lung injury is still controversial. This review article discusses the role of platelets in lung injury after cardiopulmonary bypass and resent development in the management of ALI.